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The mixed layer of polynyas is vital for local climate as it determines the exchange of properties and energy between ocean, sea ice, and atmosphere. However, its evolution is poorly understood, as it is controlled by complex interactions among these components, yet highly undersampled, especially outside summer. Here, we present a 2-month, high vertical-resolution, full-depth hydrographic dataset from the southeastern Amundsen Sea polynya in austral autumn (from mid-February to mid-April 2014) collected by a recovered seal tag. This novel dataset quantifies the changes in upper-ocean temperature and salinity stratification in this previously unobserved season. Our seal-tag measurements reveal that the mixed layer experiences deepening, salinification, and intense heat loss through surface fluxes. Heat and salt budgets suggest a sea ice formation rate of ∼3 cm per day. We use a one-dimensional model to reproduce the mixed layer evolution and further identify key controls on its characteristics. Our experiments with a range of reduced or amplified air–sea fluxes show that heat loss to the atmosphere and related sea ice formation are the principal determinants of stratification evolution. Additionally, our modeling demonstrates that horizontal advection is required to fully explain the mixed layer evolution, underlining the importance of the ice-covered neighboring region for determining sea ice formation rates in the Amundsen Sea polynya. Our findings suggest that the potential overestimation of sea ice production by satellite-based methods, due to the absence of oceanic heat flux, could be offset by horizontal advection inhibiting mixed layer deepening and sustaining sea ice formation. [ABSTRACT FROM AUTHOR]

The detection of thin-ice thickness using satellite microwave radiometers is a strong tool for estimating sea-ice production in coastal polynyas, which leads to dense water formation driving ocean thermohaline circulation. Thin-ice areas are classified into two ice types: active frazil, comprising frazil ice and open water, and thin solid ice, areas of relatively uniform thin ice. A thin-ice algorithm for AMSR-E has been developed to classify these two ice types and estimate ice thickness of <20 cm. In this study, we validate the applicability of the algorithm to the successor, AMSR2, using validation data of ice types identified from Sentinel-1 and ice thickness derived from MODIS. The validation results show an ice-type misclassification rate of ~3% and mean absolute errors in ice thickness of 2.0 cm and 5.0 cm for active frazil and thin solid ice, respectively. These values are similar to those for AMSR-E, indicating that the thin-ice algorithm can be applied to AMSR2. Further validations with the moored ADCP backscattering data capturing underwater frazil ice signals demonstrate that the algorithm can accurately distinguish between two ice types and effectively detect deep-penetrating frazil ice. The AMSR2 thin-ice thickness data has been released as a JAXA research product. [ABSTRACT FROM AUTHOR]

Considering the physical characteristics of wind turbine wing icing, icing synthesis rate, and icing type, we selected the icing type and surface roughness of ice-coated blades as sensitive parameters. The focus of our research was on the equivalent particle roughness height correction model, and we numerically analyzed the two icing processes (frost ice and clear ice) on wind turbine blade surfaces by combining FENSAP-ICE and FLUENT analysis tools. We predicted the ice type on blade surfaces using a multi-time step method and analyzed how variations in icing shape and ice surface roughness affect the aerodynamic performance of blades during frost ice formation or clear ice formation. Our results indicate that differences in blade surface roughness and heat flux lead to disparities in both ice formation rate and shape between frost ice and clear ice. Clear ice has a greater impact on aerodynamics compared to frost ice, while frost ice is significantly influenced by the roughness of its icy surface. These findings can serve as valuable references for wind power operators and manufacturers seeking solutions to issues related to blade surface icing under extremely cold conditions. [ABSTRACT FROM AUTHOR]

The diel vertical migration (DVM) of zooplankton is one of the largest species migrations to occur globally and is a key driver of regional ecosystems and the marine carbon pump. Previously thought to be hampered by the extreme light regime prevailing in the Arctic Ocean, observations have revealed that DVM does occur in ice-covered Arctic waters and suggest the decline in Arctic sea ice may thereby impact DVM and its role in the Arctic ecosystem. However, coastal polynyas present a unique environment where open water or thin, nearly translucent, ice prevail when offshore winds advect the ice pack away from the coast, allowing light into the surface waters and potentially disrupting DVM. Here, four yearlong time series of acoustic backscatter collected by moored acoustic Doppler current profilers at two opposite sides of the circumpolar polynya system at the Laptev Sea shelf (2007–2008) and the Beaufort Sea shelf (2005–2006) were used to examine the annual cycle of acoustic scattering and therefore the annual cycle of DVM in these areas. The acoustic time series were used along with atmospheric and oceanic reanalysis and satellite data to interpret the results. Our observations show that DVM started to occur once the ice-free surface or under-ice layer irradiance exceeds a certain threshold (from ∼0.3 to 3.3 lx), which is about 2 to 10 times lower in the Beaufort Sea compared to the Laptev Sea. In the Laptev Sea, based on our data and methodology, DVM could not be detected during polar night. In contrast, civil twilight in the Beaufort Sea is sufficient to trigger DVM through polar night. This difference in DVM between the Laptev and Beaufort seas is not entirely assigned to the 3° difference in latitude between the mooring positions as it is also due to the different light threshold required to trigger DVM, different zooplankton communities' composition, and potentially different depths and predation pressures. We find examples in both the Laptev and Beaufort seas where the formation of polynyas and large leads caused DVM to abruptly cease or be disrupted, which we attribute to predator avoidance by the zooplankton in response to higher polar cod (Boreogadus saida) abundance near the open water. Finally, light attenuation by sea ice in the Beaufort Sea caused DVM to extend onto the polar day until the summer solstice. Overall, our results highlight the role of sea ice in disrupting synchronized DVM, the spatial variability in the relationship between sea ice and DVM, and the potential ecological impact of significant trends toward a more extensive circumpolar Arctic coastal polynya as part of changing ice conditions in the Arctic Ocean. [ABSTRACT FROM AUTHOR]

Atmospheric circulation has significant impacts on sea ice drifting patterns and mass balance, as wind drag induces pressure ridges and leads on the sea ice surface. In this study, the spatiotemporal distributions of these dynamic sea ice deformation features in the Ross Sea are examined using ICESat‐2 (IS2) ATL10 freeboard data (2019–2022). The temporal variation of the modal sea ice thickness (SIT), caused by thermodynamic ice growth and sea ice advection, varies from 0.7–1.0 m in April to 1.0–1.6 m in July–September and decreases thereafter in the northwest (NW) and northeast (NE) sectors. This temporal variation of modal SIT agrees with the air temperature (correlation coefficients >0.5). The southwest (SW) sector shows a consistently low modal SIT (<1.0 m) because of the production of new ice in polynyas and continuous northward sea ice drift. Meanwhile, the southeast (SE) sector shows the thickest ice in Octobers 2019 and 2020 because of the advection of thick ice from the Amundsen Sea, which was reduced in 2021 and 2022. In terms of dynamic sea ice deformation, the SE sector shows the largest deformation because of the wind‐driven convergence of sea ice movement. However, such intense deformation in the SE sector diminished in 2021 and 2022 due to the dominance of strong southerly wind associated with the Amundsen Sea Low (ASL). This study emphasizes the potential of IS2 sea ice products to assess the role of atmospheric driving forces on thermodynamic and dynamic sea ice changes. Plain Language Summary: The movement of sea ice is primarily driven by wind speed and direction. Furthermore, wind changes sea ice surface topography by forming sea ice deformation features. When sea ice floes collide with each other, the piled‐up sea ice fragments form thicker ice, namely, pressure ridges. Observation of such pressure ridges in the Southern Ocean has been limited to specific seasons or regions because of the lack of high‐resolution remote sensing data. However, high‐resolution observation of pressure ridges is now available regularly through NASA's satellite altimeter ICESat‐2. We investigate the spatiotemporal variations of sea ice topography in the Ross Sea, especially the distribution of pressure ridges, by using ICESat‐2 data. The observation from ICESat‐2 shows that the areal fraction of pressure ridges in the Ross Sea decreased in 2021 and 2022, particularly in the southeast Ross Sea. The comparison with weather data indicates that this decrease might be caused by strong southerly winds associated with the deep Amundsen Sea Low in these 2 years. This study demonstrates that ICESat‐2 can play an important role in understanding the influence of wind on sea ice drift and the formation of pressure ridges. Key Points: Variation of modal ice thickness is characterized by thermodynamic ice growth in the north Ross Sea and ice advection in the south Ross SeaSea ice in the southeast Ross Sea was significantly deformed in 2019–2020 due to the inflow of thick ice and convergent ice driftStrong southerly wind associated with the Amundsen Sea Low decreased sea ice deformation in the southeast Ross Sea in 2021 and 2022 [ABSTRACT FROM AUTHOR]

The formation of dense Brine‐enriched Shelf Water (BSW) in Storfjorden is analyzed during Winter 2016–2017 from mooring observations, a polynya model nudged to satellite observations, and an original BSW production model. The ice season was two months shorter than average, yet 44.2 km3 ${\text{km}}^{3}$ of sea ice were formed, in line with estimates for the period preceding the atlantification of the Barents Sea in the mid‐2000s: A thinner, more fragile ice may favor polynya openings and frazil ice production. A saline specimen of BSW was produced in large volumes, corresponding to an annual mean transport of 0.042 Sv, larger than previous estimates. The important production is due to the preconditioning of the polynya with a more saline source water, exceeding the pre‐2005 values by 0.37. The BSW overflow was observed on the West Spitsbergen shelf slope from hydrographic sections down to 750 m, thus entering the Norwegian Sea Deep Water layer. Its core temperature was about 1° $1{}^{\circ}$C warmer than the pre‐2005 values owing to the entrainment of a warmer water in Storfjordrenna, suggesting that a part of the excess surface heat of the Barents Sea could be exported into the deep ocean. Overall our results suggest that dense water formation in the Storfjorden polynya may not, at least for now, be hampered by the atlantification of the Barents Sea, and perhaps even temporarily favored by the more saline source water. Anomalous atmospheric warming during the Winter‐Spring may however disrupt the production, as was observed 1 year before. Plain Language Summary: Sea‐ice extent has strongly declined in the Barents Sea since the mid‐2000s. The sea has also become warmer and saltier, a phenomenon referred to as atlantification. This raises concerns regarding the future of dense water production in coastal polynyas, an essential cog in the climate machine. Polynyas work as ice factories, releasing large quantities of salt in the ocean, which can lead surface waters to cascade into the deep ocean when dense enough. We analyze dense water production in Winter 2016–2017 in the Storfjorden polynya (Svalbard) from a time series of hydrographic observations and an ice production model. Despite a shorter freezing season, the ice production and salt release remained average, while preconditioning with a more saline source water permitted the production of a particularly saline dense water in large volumes. The dense bottom plume was observed to sink into the deep ocean. It was warmer than in the past, suggesting that part of the excess surface heat could be stored at depth. Overall our results suggest that dense water production may not, at least for now, be hampered by the atlantification of the Barents Sea, unless strongly anomalous winter atmospheric warming disrupts ice production, as observed 1 year before. Key Points: A simple model to estimate the production of dense water from hydrographic time series and salt forcing is developedPreconditioning of the polynya with saltier source water promoted the production of dense Brine‐enriched Shelf Water (BSW) in 2017 despite an average ice productionThe BSW overflow was observed to sink down to the Deep Water layer: It was warmer than in observations prior to the atlantification [ABSTRACT FROM AUTHOR]

Polynyas play a critical role in the formation of Antarctic Bottom Water and the enhancement of polar primary productivity. Accurate and exhaustive identification of Antarctic polynyas is fundamental to advancing in-depth research. However, due to methodological limitations, previous studies paid more attention to frequent polynyas and infrequent polynyas have not been investigated much despite that they could be vulnerable to climate change. Inspired by a cyclone tracking algorithm, we develop a novel method to overcome challenges identifying all types of polynyas satisfying spatiotemporal criteria and tracing their daily evolution, extracting from an extensive amount of sea ice concentration data. Based on it, we establish a dataset called "Daily Edge of Each Polynya in Antarctica" (DEEP-AA). Validation against remote sensing and ship-based observations confirms DEEP-AA's reliability. Compared to existing maps, the DEEP-AA identifies a threefold number of polynyas and reveals the seasonal area recovery of infrequent polynyas is earlier than frequent ones. [ABSTRACT FROM AUTHOR]

Antarctic Bottom Water (AABW), which supplies the lower limb of the thermohaline circulation, originates from dense shelf water (DSW) forming in Antarctic polynyas. Here, combining a long mooring record of DSW measurements with numerical simulations and satellite data, we show that significant correlation exists between interannual variability of DSW production in the Ross Sea polynyas, where DSW contributes between 20–40% of the global AABW production, and the Southern Annular Mode (SAM). The correlation is largest when the Amundsen Sea Low (ASL) is weakened and shifted east of the Ross Sea. During positive SAM phases, enhanced offshore winds and lower air temperatures over the western Ross Sea increase sea ice production and promote DSW formation, with the opposite response during negative SAM phases. These processes ultimately modulate AABW thickness in the open ocean. A projected positive shift of the SAM and eastward displacement of the ASL thus has implications for the future of DSW and AABW formation. This study shows that the formation of bottom water and the related sea ice processes in the Ross Sea are significantly affected by major climate patterns in the southern hemisphere's extratropical regions. [ABSTRACT FROM AUTHOR]

The Amundsen Sea in West Antarctica features rapidly thinning ice shelves, large polynyas, and sizable spring phytoplankton blooms. Although considerable effort has gone into characterizing heat fluxes between the Amundsen Sea, its associated ice shelves, and the overlying atmosphere, the effect of the phytoplankton blooms on the distribution of heat remains poorly understood. In this modeling study, we implement a feedback from biogeochemistry onto physics into MITgcm‐BLING and use it to show that high levels of chlorophyll—concentrated in the Amundsen Sea Polynya and the Pine Island Polynya—have the potential to increase springtime surface warming in polynyas by steepening the attenuation profile of solar radiation with depth. The chlorophyll‐associated warm anomaly (on average between +0.2° ${}^{\circ}$C and +0.3° ${}^{\circ}$C) at the surface is quickly dissipated to the atmosphere, by increases in longwave, latent and sensible heat loss from open water areas. Outside of the coastal polynyas, the summertime warm anomaly leads to an average sea ice thinning of 1.7 cm across the region, and stimulates up to 20% additional seasonal melting near the fronts of ice shelves. The accompanying cold anomaly, caused by shading of deeper waters, persists year‐round and affects a decrease in the volume of Circumpolar Deep Water on the continental shelf. This cooling ultimately leads to an average sea ice thickening of 3.5 cm and, together with associated changes to circulation, reduces basal melting of Amundsen Sea ice shelves by approximately 7% relative to the model scenario with no phytoplankton bloom. Plain Language Summary: Near the Antarctic coastline the sea ice cover is broken by patches of open water, called polynyas, which often undergo a visible change in color from blue to green as spring progresses. This is due to the chlorophyll produced in blooms of microscopic algae. Here we use computer simulations to investigate the impact of this change in color on the delicate system of ice and ocean in the Amundsen Sea region of west Antarctica. We find that the "greening" of polynyas helps to trap more of the sun's energy close to the sea surface, but that this excess heat is then released back to the atmosphere over the course of the summer. Meanwhile, the deeper waters of the polynya are exposed to less energy from the sun and therefore are cooler than they would be if there were no algae bloom. Ultimately, the cooling of deep waters across the Amundsen Sea weakens the transport of heat toward the continent. Our computer simulations show that, as a result, ice shelves melt around 7% slower when large algae blooms are present compared to when the surface waters are clear. Key Points: We implement a feedback from biogeochemistry onto physics in MITgcm‐BLING in a model of Amundsen Sea phytoplankton bloomsChlorophyll induced warming of up to 0.3 ° ${}^{\circ}$C at the surface is short‐lived, with excess heat rapidly lost to the atmosphereSub‐surface cooling is persistent and leads to approximately 7% $\%$ reduced melting from ice shelves [ABSTRACT FROM AUTHOR]

The Ross Sea in the Southern Ocean is a key region for the formation of the Antarctic Bottom Water (AABW) that supplies the lower limb of the global overturning circulation, and contributes to 20–40 % of the total AABW production. AABW primarily originates from polynyas characterized by strong sea ice production and ocean convection that lead to the formation of Dense Shelf Water (DSW), the precursor of the AABW. The production and characteristics of DSW in the Ross Sea and AABW in the surrounding ocean are significantly affected by ice shelf meltwater transported from the nearby Amundsen Sea. The scarcity of long-term observations in the Ross Sea hinders the understanding of DSW and AABW variability, and numerical models are needed to explore the multi-scale variations of these water masses and the forcing mechanisms. In this work, a coupled high-resolution ocean-sea ice-ice shelf model is developed for the Ross Sea and Amundsen Sea, named RAISE (R oss- A mundsen Sea I ce- Se a Model). Detailed descriptions of the model configurations are provided. This study represents a first attempt to thoroughly evaluate the DSW properties and associated ocean-sea ice-ice shelf coupling processes among modelling studies in the Southern Ocean, using multiple datasets including satellite-based observations and hydrographic measurements from the World Ocean Database, Argo profilers and seal-tag sensors. In particular, the modelled temporal variations of DSW in polynyas and its key export passages are compared with long-term mooring observations, which are not seen in DSW studies before. RAISE demonstrates high skills in simulating the observed sea ice production rates in the Ross Sea polynyas, and the modelled spatial and temporal variability of DSW are significantly and strongly correlated with observations. RAISE can also effectively capture the observed long-term freshening trend of DSW prior to 2014 and the rebounding of DSW salinity after 2014. RAISE shows an overestimate of DSW density in the Ross Sea, which is associated with underestimate of ice shelf melting rates in the Amundsen Sea, missing ice shelf calving processes and subglacial discharge in the model. A sensitivity experiment simulating increased freshwater discharge from these processes can significantly improve the simulation of DSW properties. [ABSTRACT FROM AUTHOR]

Using two case studies, we analyze the effects of explicitly resolving polar lows in a global climate model (ICON‐Sapphire) with a high resolution of 2.5 km on the upper ocean and sea ice. We aim to understand the mechanism of how polar lows form in a global coupled model and how they interact with the upper ocean and sea ice. When polar lows form at the sea ice edge, they induce marine cold air outbreaks that lead to large heat loss from the ocean. This heat loss contributes to dense water formation in the Iceland and Greenland Seas, which replenishes the climatically important Denmark Strait Overflow Water (DSOW). The high wind speeds of polar lows open leads and polynyas in the sea ice cover, such as the Sirius Water Polynya in northeastern Greenland. Heat loss in polynyas is compensated for by the formation of new ice, and the rejected brine densifies the water on the Greenland shelf. In the Labrador Sea, polar lows intensify cold air outbreaks from the sea ice and rapidly deepen the ocean mixed layer. Resolving polar lows and kinematic features in the sea ice improves the realism of climate models, in particular the surface heat loss and the dense water formation in (sub)polar oceans. Plain Language Summary: We show for the first time that resolving polar lows (strong storms over polar oceans) in a global climate model, which has a high resolution of 2.5 km, leads to strong heat loss from the ocean near the sea ice edge and from leads and polynyas, which are open water areas in an otherwise closed ice cover. Heat loss and salt rejection during ice formation contributes to dense water formation along the sea ice margin and in polynyas above the Greenland shelf. Resolving polar lows and kinematic features in the sea ice improves the realism of climate models, in particular the surface heat loss and the dense water formation in (sub)polar oceans. Key Points: First explicit simulation of polar lows in a globally coupled climate simulation with kilometer‐scale (2.5 km) resolution in all componentsPolar lows lead to considerable heat loss from the ocean near the sea ice edge and from leads and polynyas in the sea ice coverPolar lows are important for water mass transformation in the western Iceland and Greenland Seas, in the Labrador Sea, and within polynyas [ABSTRACT FROM AUTHOR]

Open-ocean polynyas formed over the Maud Rise, in the Weddell Sea, during the winters of 2016-2017. Such polynyas are rare events in the Southern Ocean and are associated with deep convection, affecting regional carbon and heat budgets. Using an ocean state estimate, we found that during 2017, early sea ice melting occurred in response to enhanced vertical mixing of heat, which was accompanied by mixing of salt. The melting sea ice compensated for the vertically mixed salt, resulting in a net buoyancy gain. An additional salt input was then necessary to destabilize the upper ocean. This came from a hitherto unexplored polynya-formation mechanism: an Ekman transport of salt across a jet girdling the northern flank of the Maud Rise. Such transport was driven by intensified eastward surface stresses during 2015-2018. Our results illustrate how highly localized interactions between wind, ocean flow and topography can trigger polynya formation in the open Southern Ocean. [ABSTRACT FROM AUTHOR]

We tracked adult emperor penguins from Rothschild Island, west Antarctic Peninsula in 2015/2016 during a summer with extensive sea ice of long duration, contrasting with past years of reduced sea ice extent associated with the recent, rapid, warming trend across the region. We fitted ARGOS PTT devices to penguins of unknown breeding status. Of 33 penguins tracked, nine returned to the colony, presumably to provision offspring. Their foraging trips lasted 9.6 ± 3.7 days, with maximum distances of 75 ± 45 km from the colony within coastal waters. Also, 18 instruments transmitted until the initiation of the annual moult. Penguins travelled at ~ 2.3 km h−1 before slowing for moult. Post-moult, some devices continued to transmit, with speeds of ~ 0.8 km h−1, plausibly due to ice drift, which is rapid in this region. Penguins remained within the seasonal sea ice throughout, staying within 100 km of land, and generally within 5 to 10 km of features (open water, polynyas, leads, icebergs) that offered potential access to the ocean. Penguins were unlikely to have been constrained by the extensive sea ice habitat in 2015/2016. Similar habitats would also have been available in most years of the satellite record (since 1979); however, the moult locations in 2015/2016 would not have been available in many years, and penguins would have needed to find alternative moult locations during some years. Despite uncertainties, the moult period is a critical time for emperor penguins, particularly as sea ice declines, potentially affecting adult survival. [ABSTRACT FROM AUTHOR]

The correct representation of the Maud Rise open‐ocean polynya in the Weddell Sea remains a challenge for ocean models. Here we reproduce the most recent polynya openings in 2016–2017 using a regional configuration, and assess their dependencies on vertical convective mixing schemes and freshwater forcing, both separately and in combination. We test three vertical convective mixing schemes: the enhanced vertical diffusion (EVD), the Eddy‐Diffusivity Mass‐Flux (EDMF) parameterization, and a modified version of EDMF accounting for thermobaric effects. Using simulations for the period 2007–2017, we find that the modified EDMF reproduces the observed climatological evolution of the mixed layer depth better than the original EDMF and the EVD, but a polynya fails to open due to excessive freshwater forcing. We thus use the modified EDMF to perform sensitivity experiments with reduced precipitation during 2012–2017. The imposed freshwater forcing strongly affects the number of years with polynyas. The simulation with the best representation of the 2016–2017 polynyas is analyzed to evaluate the triggering mechanisms. The 2016 polynya was induced by the action of thermobaric instabilities on a weak ambient stratification. This opening preconditioned the water column for 2017, which produced a stronger polynya. By examining the impacts of the different convective mixing schemes, we show that the modified EDMF generates more realistic patterns of deep convection. Our results highlight the importance of surface freshwater forcing and thermobaricity in governing deep convection around Maud Rise, and the need to represent thermobaric instabilities to realistically model Maud Rise polynyas. Plain Language Summary: We investigate the impacts of representing numerical vertical mixing and surface freshwater forcing in a regional ocean model on polynyas (large openings in the pack ice) at Maud Rise, Southern Ocean. Maud Rise is prone to hosting polynyas, often associated with deep convection, which is a local vertical mixing process homogenizing the water column between surface and depths of several hundred meters. Numerical models often use simplistic strategies to represent this process, but improved parameterizations have recently become available. In this work, we test the impact of the representation of convective mixing in a particularly sensitive region. The last Maud Rise polynyas were observed in 2016 and 2017. Our regional simulation is capable of reproducing these polynyas, which has long been a challenge for ocean‐sea ice models. We show that the 2016 polynya resulted from the action of a vertical instability at depth acting on weak ambient stratification. This event preconditioned the stronger 2017 polynya and deep convection. We conclude that representing convective plumes as a sub‐grid scale process in models leads to a more realistic representation of open‐ocean polynyas and associated convection events. Key Points: The Eddy‐Diffusivity Mass‐Flux (EDMF) parameterization is tested in a regional simulation of the ocean around Maud RiseThermobaric effects on convective plumes are enabled by modifying the EDMF parameterizationSimulations of Maud Rise polynyas are highly sensitive to freshwater forcing and mixing schemes [ABSTRACT FROM AUTHOR]

Landfast ice is near-motionless sea ice attached to the coast. Despite its potential for modifying sea ice and ocean properties, most state-of-the-art sea ice models poorly represent landfast ice. Here, we examine two crucial processes responsible for the formation and stabilization of landfast ice, namely sea ice tensile strength and seabed–ice keel interactions. We investigate the impact of these processes on the Arctic sea ice cover and halocline layer using the global coupled ocean–sea ice model NEMO-LIM3. We show that including seabed–ice keel stress improves the seasonality and spatial distribution of the landfast ice cover in the Laptev and East Siberian Seas. This improved landfast ice representation sets the position of flaw polynyas to new locations approximately above the continental shelf break. The impact of sea ice tensile strength on the stability of the Arctic halocline layer is far more effective. Incorporating this process in the model yields a thicker, more consolidated, and less mobile Arctic sea ice pack that further decouples the ocean and atmosphere. As a result, the available potential energy of the Arctic halocline is decreased (increased) by ∼ 30kJ/m 2 (∼ 30kJ/m 2 ) in the Amerasian (Eurasian) compared to the reference simulation excluding sea ice tensile strength and seabed–ice keel stress. Our findings highlight the need to better understand landfast ice physical processes conjointly with the subsequent influences on the ocean and sea ice states. [ABSTRACT FROM AUTHOR]

Sea ice–wave interactions have been widely studied in the marginal ice zone, at relatively low wind speeds and wave frequencies. Here, we focus on very different conditions typical of coastal polynyas: extremely high wind speeds and locally generated, short, steep waves. We overview available parameterizations of relevant physical processes (nonlinear wave–wave interactions, energy input by wind, whitecapping and ice‐ related dissipation) and discuss modifications necessary to adjust them to polynya conditions. We use satellite‐ derived data and spectral modeling to analyze waves in 10 polynya events in the Terra Nova Bay, Antarctica. We estimate the wind‐input reduction factor over frazil/grease ice in the wave‐energy balance equation at 0.56. By calibrating the model to satellite observations we show that exact treatment of quadruplet wave–wave interactions (as opposed to the default Discrete Interaction Approximation) is necessary to fit the model to data, and that the power n > 4 in the sea‐ice source term Sice ∼ fn (where f denotes wave frequency) is required to reproduce the strong attenuation of high‐frequency waves observed for frazil streaks. We use a very‐high resolution satellite image of a fragment of one of the polynyas to determine whitecap fraction. We show that there are more than twofold differences in whitecap fraction over ice‐free and ice‐covered regions, and that the model produces realistic whitecap fractions without any tuning of the whitecapping source term. Finally, we estimate the polynya‐area‐integrated wind input, energy dissipation due to whitecapping, and whitecap fraction to be on average below 25%, 10% and 30%, respectively, of the corresponding open‐water values. [ABSTRACT FROM AUTHOR]

Polynyas, areas of open water embedded within sea ice, are a key component of ocean--atmosphere interactions that act as hotspots of sea-ice production, bottom-water formation, and primary productivity. The specific drivers of polynya dynamics remain, however, elusive and coupled climate models struggle to replicate Antarctic polynya activity. Here, we leverage a 44-y time series of Antarctic sea ice to elucidate long-term trends. We identify Antarctic-wide linear increases and a hitherto undescribed cyclical pattern of polynya activity across the Ross Sea region that potentially arises from interactions between the Amundsen Sea Low and Southern Annular Mode. While their specific drivers remain unknown, identifying these emerging patterns augments our capacity to understand the processes that influence sea ice. As we enter a potentially new age of Antarctic sea ice, this advance in understanding will, in turn, lead to more accurate predictions of environmental change, and its implications for Antarctic ecosystems. [ABSTRACT FROM AUTHOR]

The features of the spatial distribution of the long-term average ice-free period (IFP) characteristics and their trends in the Laptev Sea are calculated and described quantitatively based on the microwave remote sensing data for 1979–2021. The spatial distribution of the long-term average duration of the IFP mainly follows the spatial distribution of the long-term average IFP start dates. The highest value of the long-term average duration of the IFP is observed in the areas where the Anabar–Lena and Western New Siberian stationary flaw polynyas are formed. It is shown that south of 78° N, the duration of the IFP increased statistically significantly by +17 ± 7 days/10 year on average. The areas of the Laptev Sea north of 80° N are characterized by statistically insignificant changes in IFP characteristics. The duration of the IFP extends due to both the shift of the IFP start dates to the earlier time (an average rate of changes is –10 ± 4 days/10 year) and the shift of the IFP end dates to a later time (an average rate of changes is +8 ± 4 days/10 year). [ABSTRACT FROM AUTHOR]

Antarctic coastal polynyas are hotspots of biological production with intensive springtime phytoplankton blooms that strongly depend on meltwater‐induced restratification in the upper part of the water column. However, the fundamental physics that determine spatial inhomogeneity of the spring restratification remain unclear. Here, we investigate how different meltwaters affect springtime restratification and thus phytoplankton bloom in Antarctic coastal polynyas. A high‐resolution coupled ice‐shelf/sea‐ice/ocean model is used to simulate an idealized coastal polynya similar to the Terra Nova Bay Polynya, Ross Sea, Antarctica. To evaluate the contribution of various meltwater sources, we conduct sensitivity simulations altering physical factors such as alongshore winds, ice shelf basal melt, and surface freshwater runoff. Our findings indicate that sea ice meltwater from offshore is the primary buoyancy source of polynya near‐surface restratification, particularly in the outer‐polynya region where chlorophyll concentration tends to be high. Downwelling‐favorable alongshore winds can direct offshore sea ice away and prevent sea ice meltwater from entering the polynya region. Although the ice shelf basal meltwater can ascend to the polynya surface, much of it is mixed vertically over the water column and confined horizontally to a narrow coastal region, and thus does not contribute significantly to the polynya near‐surface restratification. Surface runoff from ice shelf surface melt could contribute greatly to the polynya near‐surface restratification. Nearby ice tongues and headlands strongly influence the restratification through modifying polynya circulation and meltwater transport pathways. Results of this study can help explain observed spatiotemporal variability in restratification and associated biological productivity in Antarctic coastal polynyas. Plain Language Summary: Antarctic coastal polynyas are key habitats of regional marine ecosystems. During spring, the upper part of the polynya water column restratifies and forms a near‐surface layer of low‐salinity water. This process is important for springtime phytoplankton blooms, as the stable surface layer keeps phytoplankton in the well‐lit region and enhances phytoplankton growth. Employing high‐resolution models of idealized coastal polynyas, this work unravels the spatial variation of restratification processes in a polynya and investigates the physical factors that affect them. It shows that sea ice meltwater from offshore regions is the foremost contributor to the near‐surface restratification in a polynya. Meanwhile, low‐salinity water from basal melt of a neighboring floating ice shelf contributes little to the near‐surface restratification in a polynya because much of the meltwater mixes vertically with ambient waters as it rises. This is in contrast to the sea ice meltwater being directly injected into the ocean surface. Freshwater runoff from the surface melt of an ice shelf is also directly injected into the polynya surface. However, due to earth rotation, it is often confined in a narrow coastal region next to the ice shelf and thus does not contribute to restratification in most of the polynya area. Key Points: Biologically‐important springtime near‐surface restratification in Antarctic coastal polynyas varies spatially within a polynyaSea ice meltwater from regions offshore of the polynya is the primary buoyancy source of polynya near‐surface restratificationIce shelf basal meltwater mixes over the water column during its ascent and contributes little to polynya near‐surface restratification [ABSTRACT FROM AUTHOR]

This study investigates winter polynyas in the southern Ross Sea, Antarctica where several polynyas are known to form. Coastal polynyas are areas of lower sea ice concentration and/or thickness along the coast that are otherwise surrounded by more extensive, thicker sea ice pack. Polynyas are also locations where organisms can exploit both the ice substrate and pelagic resources. Using a self organizing map algorithm, we identify polynya events in the Community Earth System Model Version 2 Large Ensemble (CESM2-LE). The neural network algorithm is able to identify polynya events without imposing an ice concentration or thickness threshold, as is often done when identifying polynyas. The CESM2-LE produces a wintertime polynya feature comparable in size and location to the Ross Sea polynya, and during polynya events there are large turbulent heat fluxes and export of sea ice from the Ross Sea. In the CESM2-LE polynya event frequency is projected to decrease sharply in the later twentyfirst century, leading to increasing sea ice concentrations and thicknesses in the region. The drivers of the polynya frequency decline are likely both large scale circulation changes and local atmosphere and ocean feedbacks. If declines in wintertime polynya frequency over the twentyfirst century do occur they may impact Antarctic Bottom Water formation and local net primary productivity. Thus, better understanding potential local and unexpected sea ice changes in the Ross Sea is important for both assessing climate system impacts and ecological impacts on the Ross Sea ecosystem, which is currently protected by an internationally recognized marine protected area. [ABSTRACT FROM AUTHOR]

Material transport by sea ice plays an important role in the biological production of spring blooms. We conducted backward-tracking simulations to estimate the origins of the sea ice in the southern part of the Sea of Okhotsk and examine the relationship between the origin of sea ice and biological production, the concentration of iron, and the frazil ice fraction. The simulation of the sea ice melted in areas, where the net community production (NCP) was estimated shows that the sea ice that melted in areas with high NCP tended to originate in coastal areas, mostly the Terpenia Bay and Sakhalin polynyas, where ice production is high and sea ice can incorporate the seafloor sediments. This result supports the hypothesis that the incorporation of sedimentary particles into sea ice and their release during ice melt are key factors in high biological production. The simulation of the sea ice floes sampled by the icebreaker Soya off Hokkaido coast suggests that the samples collected over the shelf with depths of less than 500 m or so were formed over the shelf around the southern tip of Sakhalin Island, whereas the samples, including that with high iron concentration, collected over the shelf slope at greater depths were likely transported from the northern area up to Terpenia Bay but not further north. The simulation also suggests that the sea ice floes with a high fraction of frazil ice could be formed anywhere in the southern part of the Sea of Okhotsk. [ABSTRACT FROM AUTHOR]

Seasonal phytoplankton blooms in the Antarctic Amundsen Sea Polynyas are thought to be supported by an external supply of iron (Fe) from circumpolar deep waters, benthic sediments, and/or ice shelf meltwaters. However, largely due to the limited amount of Fe data reported for the Amundsen Sea Polynyas, understanding of the sources and processes that affect the biogeochemistry of Fe in this region (notably within the ice shelf system) remains limited. Here, we present the first investigation of dissolved Fe isotope distributions (δ56Fe) along the conveyer belt of waters into and through the Amundsen Sea, via the Dotson Ice Shelf, from samples collected during austral summer (2017–2018). Our dataset allows us to characterize and compare the dissolved δ56Fe signatures of incoming modified Circumpolar Deep Water (mCDW) and of sedimentary sources on the continental shelf. The range in dissolved δ56Fe (–1 to +0.1 ‰) observed in the Amundsen Sea close to the seafloor, coupled with elevated dissolved Fe concentrations (up to 1.6 nmol/L), suggests that Fe is released from shelf sediments via a combination of reductive and non-reductive processes, with non-reductive dissolution input being relatively more important (20–56 %) than reductive dissolution (4–12 %). Near the Dotson Ice Shelf, the δ56Fe in the mCDW inflow (–0.70 ‰) was lower than the mCDW outflow (–0.23 ‰), whereas any change in dissolved Fe concentrations was negligible. We speculate that this shift in dissolved δ56Fe underneath the ice shelf is driven by a combination of enhanced preservation (and addition) of lithogenic colloidal Fe(III) and/or complexation with Fe-binding ligands, together with a differential loss of Fe2+. We also found distinct δ56Fe signatures in surface waters of the polynya, with apparent preferential uptake of isotopically light Fe in a bloom dominated by diatoms leading to a relatively heavy remnant dissolved δ56Fe signature of +1.06 ‰, compared to a bloom dominated by haptophytes where more modest and variable isotope fractionation was observed. The different isotopic composition between the two regions could be related to the dominance of different species, but this remains speculative. Despite prominent biological uptake, we suggest that other factors such as rapid recycling (e.g., adsorption and regeneration), bacterial regeneration, and complexation with organic ligands, together with the supply of lithogenic particles also play important roles in setting surface dissolved δ56Fe in the Amundsen Sea Polynyas. Overall, this study provides a further understanding of the external Fe sources and the biogeochemical processes in the Amundsen Sea and thus a baseline on how changing conditions in Antarctica can affect Fe cycling in the Southern Ocean and beyond. [ABSTRACT FROM AUTHOR]

Polynyas, or ice-free regions within the sea ice pack, are a common occurrence around Antarctica. A recurrent and often large polynya is the Terra Nova Bay Polynya (TNBP), located on the western side of the Ross Sea just off Victoria Land. In this study, we investigate the atmospheric conditions leading to the occurrence of the TNBP and its spatial variability, as estimated using satellite-derived ice surface temperature and sea ice concentration data. A cluster analysis revealed that katabatic winds descending the Transantarctic Mountains, account for about 45% of the days when the TNBP exceeded its 2010–2017 mean extent plus one standard deviation. Warmer and more moist air intrusions from lower-latitudes from the Pacific Ocean, which are favoured in the negative phase of the Southern Annular Mode, play a role in its expansion in the remaining days. This is more frequent in the transition seasons, when such events are more likely to reach Antarctica and contribute to the occurrence and the widening of the polynya. In-situ weather data confirmed the effects of the mid-latitude air intrusions, while sea ice drifts of up to 25 km day−1 cleared the ice offshore and promoted the widening of the polynya starting from the coastal areas. Knowing the atmospheric factors involved in the occurrence of coastal polynyas around Antarctica is essential as it helps in improving their representation and predictability in climate models and hence advance the models' capabilities in projecting Antarctic sea ice variability. [ABSTRACT FROM AUTHOR]

The features of the spatial distribution of the long-term average ice-free period (IFP) characteristics and their trends in the Laptev Sea are calculated and described quantitatively based on the microwave remote sensing data for 1979–2021. The spatial distribution of the long-term average duration of the IFP mainly follows the spatial distribution of the long-term average IFP start dates. The highest value of the long-term average duration of the IFP is observed in the areas where the Anabar–Lena and Western New Siberian stationary flaw polynyas are formed. It is shown that south of 78° N, the duration of the IFP increased statistically significantly by +17 ± 7 days/10 year on average. The areas of the Laptev Sea north of 80° N are characterized by statistically insignificant changes in IFP characteristics. The duration of the IFP extends due to both the shift of the IFP start dates to the earlier time (an average rate of changes is –10 ± 4 days/10 year) and the shift of the IFP end dates to a later time (an average rate of changes is +8 ± 4 days/10 year). [ABSTRACT FROM AUTHOR]

Open ocean areas surrounded by sea ice and maintained by ocean heat, or sensible‐heat polynyas, are linked to key ice‐sheet processes, such as ice‐shelf basal melt and ice‐shelf fracture, when they occur near ice‐shelf fronts. However, the lack of detailed multi‐year records of polynya variability prevent assessing coupling between polynya and frontal dynamics. Here, we present the first multi‐decadal polynya area record (2000–2022) at Pine Island Glacier (PIG), West Antarctica, from thermal and optical satellite imagery. We found substantial interannual variability in polynya area, with consistencies in the timing of polynya opening, maximal extent, and closing. Furthermore, the largest polynya in our record (269 km2) occurred at PIG's western margin just 68 days before iceberg B‐27 calved, suggesting that polynya size and position may influence rifting dynamics. Our new data set provides a pathway to assess coevolving polynya and frontal dynamics, demonstrating the importance of building long‐term, year‐round polynya variability records. Plain Language Summary: Persistent sensible‐heat polynyas are areas of open ocean surrounded by sea ice maintained by ocean heat. These surface features occur near ice‐shelf fronts at the coastal margins of Antarctica and therefore have the potential to impact ice‐shelf stability through heat transfer processes. However, our understanding of long‐term polynya variability remains limited due to the lack of multi‐year records documenting polynya evolution. Here, we use satellite imagery to measure polynya area near Pine Island Glacier (PIG) and build the first multi‐decadal record in Antarctica. We observed a large amount of year‐to‐year area variability from 2000 to 2022, with the largest polynya in our record (269 km2) occurring at the western edge of PIG just 68 days before a large iceberg calved from PIG. This correspondence suggests that polynya size and position may influence iceberg calving. Our new data set provides a pathway to assess potentially coupled ice and ocean processes, demonstrating the importance of building long‐term, year‐round polynya variability records. Key Points: We generated a 22 years record of polynya area at Pine Island Glacier from satellite thermal and optical imageryOur data set shows high variability in sensible‐heat polynya area (0–322 km2) from 2000 to 2022Large, marginal, and persistent sensible‐heat polynyas may reduce ice‐shelf buttressing and contribute to rift initiation and propagation [ABSTRACT FROM AUTHOR]

The long‐held view that the East Antarctic margin is isolated from warm offshore waters has been challenged by recent observations showing incursions of warm modified Circumpolar Deep Water (mCDW) reaching several East Antarctic ice shelves. However, large areas of the East Antarctic continental shelf remain poorly observed, making it challenging to determine if the supply of oceanic heat to the ice shelves is changing. Here, we use temperature and salinity profiles to the west of the Shackleton Ice Shelf (SIS; ≈100°E) spanning 60 years to assess the variability of the water masses in the context of a changing climate. We document warming and freshening of shelf waters. Prior to 1996, cold mCDW water (θ < −1.6°C) was found below the surface mixed layer and cold Dense Shelf Water (DSW) with a salinity of >34.5 dominated the water column. After 2010, warm mCDW (≥−1.0°C) was widespread over the continental shelf and DSW with salinity over 34.5 was no longer present. The mixing ratio of glacial meltwater indicates that warm mCDW observed in 2011 caused basal melting of the SIS, possibly reducing the salinity of DSW. Increased access of warm waters to the continental shelf may have also occurred on the eastern side of the ice shelf, where glaciological evidence shows the grounding line has retreated. These observations suggest a shift occurred prior to 2011 that has increased the ocean heat supply to the continental shelf and to the SIS, increasing basal melt and reducing DSW formation. Plain Language Summary: Recently, relatively warm waters that are normally found offshore are coming onto the Antarctic continental shelves, threatening the stability of East Antarctic ice shelves. The process, known as an "intrusion," is mostly reported in West Antarctica. Yet, recent studies have documented similar warm water intrusions in East Antarctica. East Antarctica contains more ice mass than West Antarctica and thus, its potential contributions to sea level rise are also higher. It is not known if these intrusions have always happened, or if they started at a particular point in time. Much less is known about what mechanisms make them happen. This study shows warm water intrusions reach the Shackleton Ice Shelf from 2011 onwards. The intrusions melt the ice shelf from below and the freshwater resulting from this melt goes into the ocean and freshens it. It also increases the stratification of the water column, making it harder for polynyas, massive open ocean areas that form next to the Antarctic margins during the Austral winter, to produce an important dense water variety that supplies the bottom layer of the world ocean's circulation. Key Points: Ocean observations spanning 60 years document a shift in shelf water properties west of the Shackleton Ice Shelf (SIS)Pre‐1996, modified Circumpolar Deep Water (mCDW) warmer than −1.6°C was not observed; post‐2010, warm mCDW (≥−1°C) was widespread to the west of the SISThe observed mCDW intrusions cause basal melt of the SIS, freshening Dense Shelf Water and hindering its production [ABSTRACT FROM AUTHOR]

Sea ice formation dominates surface salt forcing in the southern Weddell Sea. Brine rejected in the process of sea ice production results in the production of High Salinity Shelf Water (HSSW) that feeds the global overturning circulation and fuels the basal melt of the adjacent ice shelf. The strongest sea ice production rates are found in coastal polynyas, where steady offshore winds promote divergent ice movement during the freezing season. We used the Finite Element Sea ice–ice shelf–Ocean Model (FESOM) forced by output from the regional atmospheric model COSMO-CLM (CCLM) with 14 km horizontal resolution to investigate the role of polynyas for the surface freshwater flux of the southern Weddell Sea (2002–2017). The presence of stationary icescape features (i.e., fast-ice areas and grounded icebergs) can influence the formation of polynyas and, therefore, impact sea ice production. The representation of the icescape in our model is included by prescribing the position, shape and temporal evolution of a largely immobile ice mélange formed between the Filchner–Ronne Ice Shelf (FRIS) and a major grounded iceberg based on satellite data. We find that 70 % of the ice produced on the continental shelf of the southern Weddell Sea is exported from the region. While coastal polynyas cover 2 % of the continental shelf area, sea ice production within the coastal polynyas accounts for 17 % of the overall annual sea ice production (1509 km3). The largest contributions come from the Ronne Ice Shelf and Brunt Ice Shelf polynyas and polynyas associated with the ice mélange. Furthermore, we investigate the sensitivity of the polynya-based ice production to the (i) representation of the icescape and (ii) regional atmospheric forcing. Although large-scale atmospheric fields determine the sea ice production outside polynyas, both the treatment of the icescape and the regional atmospheric forcing are important for the regional patterns of sea ice production in polynyas. The representation of the ice mélange is crucial for the simulation of polynyas westward/eastward of it, which are otherwise suppressed/overestimated. Compared to using ERA-Interim reanalysis as an atmospheric forcing data set, using CCLM output reduces polynya-based ice production over the eastern continental shelf due to weaker offshore winds, yielding a more realistic polynya representation. Our results show that the location and not just the strength of the sea ice production in polynyas is a relevant parameter in setting the properties of the HSSW produced on the continental shelf, which in turn affects the basal melting of the Filchner–Ronne Ice Shelf. [ABSTRACT FROM AUTHOR]

This is Part II of a study examining wintertime destratification in Antarctic coastal polynyas, focusing on providing a qualitative description of the influence of ice tongues and headlands, both common geometric features neighboring the polynyas. The model of a coastal polynya used in Part I is modified to include an ice tongue and a headland to investigate their impacts on the dispersal of water formed at the polynya surface, which is referred to as Polynya Source Water (PSW) here. The model configuration qualitatively represents the settings of some coastal polynyas, such as the Terra Nova Bay Polynya. The simulations highlight that an ice tongue next to a polynya tends to break the alongshore symmetry in the lateral return flows toward the polynya, creating a stagnant region in the corner between the ice tongue and polynya where outflow of the PSW in the water column is suppressed. This enhances sinking of the PSW and accelerates destratification of the polynya water column. Adding a headland to the other side of the polynya tends to restore the alongshore symmetry in the lateral return flows, which increases the offshore PSW transport and slows down destratification in the polynya. This work stresses the importance of resolving small-scale geometric features in simulating vertical mixing in the polynya. It provides a framework to explain spatial and temporal variability in rates of destratification and Dense Shelf Water formation across Antarctic coastal polynyas, and helps understand why some polynyas are sources of Antarctic Bottom Water while others are not. [ABSTRACT FROM AUTHOR]

This study examines the process of water-column stratification breakdown in Antarctic coastal polynyas adjacent to an ice shelf with a cavity underneath. This first part of a two-part sequence seeks to quantify the influence of offshore katabatic winds, alongshore winds, air temperature, and initial ambient stratification on the time scales of polynya destratification through combining process-oriented numerical simulations and analytical scaling. In particular, the often-neglected influence of wind-driven circulation on the lateral transport of the water formed at the polynya surface—which we call Polynya Source Water (PSW)—is systematically examined here. First, an ice shelf–sea ice–ocean coupled numerical model is adapted to simulate the process of PSW formation in polynyas of various configurations. The simulations highlight that (i) before reaching the bottom, majority of the PSW is actually carried away from the polynya by katabatic wind–induced offshore outflow, diminishing water-column mixing in the polynya and intrusion of the PSW into the neighboring ice shelf cavity, and (ii) alongshore coastal easterly winds, through inducing onshore Ekman transport, reduce offshore loss of the PSW and enhance polynya mixing and PSW intrusion into the cavity. Second, an analytical scaling of the destratification time scale is derived based on fundamental physical principles to quantitatively synthesize the influence of the physical factors, which is then verified by independent numerical sensitivity simulations. This work provides insights into the mechanisms that drive temporal and cross-polynya variations in stratification and PSW formation in Antarctic coastal polynyas, and establishes a framework for studying differences among the polynyas in the ocean. [ABSTRACT FROM AUTHOR]

The interaction of air‐ice‐ocean‐biology plays a key role in the global environment and sea‐level changes. The basal channel at the bottom of the Amery Ice Shelf (AIS) and the Mackenzie polynya are the intense sites for the interaction of air‐ice‐ocean‐biology in the Prydz Bay. In this study, the spatio‐temporal distribution characteristics of the complex basal channel system from the 1990s to 2019 are discovered and analyzed. The shapes of the channels are inverted‐V in the deep parts, gradually becoming inverted‐U as it develops in accordance with the direction of erosion. The deepest part of the basal channel system is over 800 m resulting from the meltwater plumes at the southernmost grounding zone. The linear and thinner channel region is the weakest and most sensitive part under ocean forcing leading to instability of the AIS (e.g., longitudinal fractures and calving). Conductivity‐temperature‐depth data are used to confirm the paths and shapes of the warm and cold water in the interaction. Channels can be divided into warm and cold‐water channels based on filled water masses. Cold water channels collect the fresh melting water and drain it out. Paths of cold‐water columns from different channels extend to the Mackenzie polynya area, which prevents warm water from entering the west AIS. Meltwater from the channels, warm water, brine produced by the Mackenzie polynya, and marine mammals in the polynya together constitute a complex regional environment system of dynamical air‐ice‐ocean‐biology interactions. Plain Language Summary: The Amery Ice Shelf (AIS), ocean, and Mackenzie polynya compose a regional air‐ice‐ocean‐biology environment system, which is connected by basal channels. Basal channels are deep upward grooves at the base of ice shelves. Polynyas are open water surrounded by sea ice and release brine while producing sea ice. Remote sensing data are used to study the distribution and characteristics of basal channels and the threat on the AIS stability. The deepest channel is over 800 m, which is the deepest among any reported ice shelf basal channels. The shapes of channels are inverted‐V in the deep parts, and gradually become inverted‐U as the channels develop; these shapes are related to the type of ocean erosion. Supercooled meltwater carrying ions is discharged through the channels on the western AIS, which blocks the invasion of warm water and provides materials for primary productivity of the Mackenzie polynya. The brine released in Mackenzie polynya has considerable impacts on the basal melting of the AIS and circulation in the Prydz Bay. Basal channels and the Mackenzie polynya affect the local environment by weakening the stability of the AIS and altering the characters and paths of water masses. Key Points: The complex basal channel system beneath Amery Ice Shelf (AIS) is a sensitive area for the ocean forcing on ice shelf stabilityThe variations of channels' shape and size in different areas related to the erosion pattern of seawaterBasal channels collect the fresh melting water and drain it out the ice shelf, which prevents warm water entering the west AIS [ABSTRACT FROM AUTHOR]

Melt rates of West Antarctic ice shelves in the Amundsen Sea track large decadal variations in the volume of warm water at their outlets. This variability is generally attributed to wind‐driven variations in warm water transport toward ice shelves. Inspired by conceptual representations of the global overturning circulation, we introduce a simple model for the evolution of the thermocline, which caps the warm water layer at the ice‐shelf front. This model demonstrates that interannual variations in coastal polynya buoyancy forcing can generate large decadal‐scale thermocline depth variations, even when the supply of warm water from the shelf‐break is fixed. The modeled variability involves transitions between bistable high and low melt regimes, enabled by feedbacks between basal melt rates and ice front stratification strength. Our simple model captures observed variations in near‐coast thermocline depth and stratification strength, and poses an alternative mechanism for warm water volume changes to wind‐driven theories. Plain Language Summary: Ice loss from the West Antarctic Ice Sheet contributes significantly to current and projected rates of global sea‐level rise. The ice sheet is primarily losing mass via glaciers that flow from the Antarctic continent into the Amundsen Sea, where floating ice shelves are exposed to much warmer ocean waters than elsewhere around Antarctica. In this work we present a simplified mathematical model for the volume of warm water at Amundsen Sea ice shelf fronts that reproduces observed patterns of warm water variability. The modeled variability relies on interactions between ice shelf melt and coastal polynyas, regions where enhanced wintertime sea‐ice production can trigger mixing that diverts heat carried by warm waters away from the ice shelf and into the atmosphere. Higher melt rates inhibit polynya convection, allowing more warm water into the ice shelf cavity and reinforcing a high melt state, whilst lower melt rates facilitate polynya convection, diverting heat away from the ice shelf and reinforcing a low melt state. Interannual variations in polynya sea‐ice production trigger shifts between these reinforcing states. Our results promote the importance of coastal processes in explaining observed variations in Amundsen Sea ice shelf melt, which have previously been attributed to remote wind patterns. Key Points: Rates of ocean‐driven Amundsen Sea ice shelf melt respond to variations in warm water transport to the coast and modification at the coastA simple Amundsen Sea continental shelf overturning model, based on water mass transformation, reveals bistable high and low melt regimesFeedbacks between glacial melt and polynya convection are central to the bistability and produce variability consistent with observations [ABSTRACT FROM AUTHOR]

Seasonal formation of Dense Shelf Water (DSW) in the Ross Sea is a direct precursor to Antarctic Bottom Water, which fills the deep ocean with atmospheric gases in what composes the southern limb of the solubility pump. Measurements of seawater noble gas concentrations during katabatic wind events in two Ross Sea polynyas reveal the physical processes that determine the boundary value properties for DSW. This decomposition reveals 5–6 g kg−1 of glacial meltwater in DSW and sea‐ice production rates of up to 14 m yr−1 within the Terra Nova Bay polynya. Despite winds upwards of 35 m s−1 during the observations, air bubble injection had a minimal contribution to gas exchange, accounting for less than 0.01 μmols kg−1 of argon in seawater. This suggests the slurry of frazil ice and seawater at the polynya surface inhibits air‐sea exchange. Most noteworthy is the revelation that sea‐ice formation and glacial melt contribute significantly to the ventilation of DSW, restoring 10% of the gas deficit for krypton, 24% for argon, and 131% for neon, while diffusive gas exchange contributes the remainder. These measurements reveal a cryogenic component to the solubility pump and demonstrate that while sea ice blocks air‐sea exchange, sea ice formation and glacial melt partially offset this effect via addition of gases. While polynyas are a small surface area, they represent an important ventilation site within the southern‐overturning cell, suggesting that ice processes both enhance and hinder the solubility pump. Plain Language Summary: Previous scientific studies have demonstrated that the water which fills the deep sea is created in isolated regions of the surface ocean where wind, evaporation, heat loss, and sea ice formation can work in concert to make very cold salty seawater at the ocean surface. As this water leaves the surface it can carry oxygen and carbon dioxide, as well as heat away from the atmosphere for nearly a millennium, suggesting the sequestration mechanism may impact earth's climate and human climate change. This study sought to reveal how different types of sea ice and glacier ice might influence the gases that are dissolved in seawater and sequestered in the ocean. We made measurements of the noble gases (helium, neon, argon, krypton, and xenon) in the Ross Sea in late fall of 2017, when the conditions are cold and windy, leading to lots of dense water production. The results reveal that sea ice interrupts the process of air‐sea exchange of gases, which can slow down the uptake of human‐generated carbon dioxide by dense water. But our results also revealed that sea ice formation and glacial ice melt can both add gas to dense water during its creation. Key Points: Noble gas tracers can infer the rate of sea ice production in polynyasFrazil ice in polynyas appears to block air‐sea gas exchange mechanismsThe solubility pump is influenced by glacial ice melt and sea ice formation [ABSTRACT FROM AUTHOR]

We present the results of a ship-based field study about the sea-air transfer of marine combined carbohydrates (CCHO) from concerted measurements of the bulk seawater, the sea surface microlayer (SML), aerosol particles and fog. In seawater, CCHO ranged between 22–1070 µg L-1 with large differences among the different sea-ice related sea surface compartments: ice-free ocean, marginal ice zone (MIZ), open leads/polynyas within the pack ice and melt ponds. Enrichment factors in the SML relative to the bulk water were very variable in the dissolved (EFSML, d CCHO: 0.4–16) and particulate (EFSML,pCCHO: 0.4–49) phases with highest values in the MIZ and aged melt ponds. In the atmosphere, CCHO appeared in super- and submicron aerosol particles (CCHOaer,super: 0.07–2.1 ng m-3; CCHOaer,sub: 0.26–4.4 ng m-3) and fog water (CCHOfog,liquid: 18–22000 µg L-1; CCHOfog, atmos: 3–4300 ng m-3). The enrichment factors for the sea-air transfer were calculated for super- and submicron aerosol particles and fog, however strongly varied depending on which of the sea-ice related sea surface compartments was assumed as the oceanic emission source. Finally, we observed a quick atmospheric aging of CCHO after their emission with indications for both biological/enzymatic processes (based on very selective changes within the monosaccharide compositions of CCHO) and abiotic degradation (based on the depolymerization of long-chained CCHO to short free monosaccharides). All in all, the present study highlights the diversity of marine emission sources in the Arctic Ocean and atmospheric processes influencing the chemical composition of aerosol particles and fog. [ABSTRACT FROM AUTHOR]

Antarctic coastal polynyas produce dense shelf water, a primary source of Antarctic Bottom Water that contributes to the global overturning circulation. This paper investigates Antarctic dense water formation in the high-resolution version of the Energy Exascale Earth System Model (E3SM-HR). The model is able to reproduce the main Antarctic coastal polynyas, although the polynyas are smaller in area compared to observations. E3SM-HR also simulates several occurrences of open-ocean polynyas (OOPs) in the Weddell Sea at a higher rate than what the last 50 years of the satellite sea ice observational record suggests, but similarly to other high-resolution Earth system model simulations. Furthermore, the densest water masses in the model are formed within the OOPs rather than on the continental shelf as is typically observed. Biases related to the lack of dense water formation on the continental shelf are associated with overly strong atmospheric polar easterlies, which lead to a strong Antarctic Slope Front and too little exchange between on- and off-continental shelf water masses. Strong polar easterlies also produce excessive southward Ekman transport, causing a build-up of sea ice over the continental shelf and enhanced ice melting in the summer season. This, in turn, produces water masses on the continental shelf that are overly fresh and less dense relative to observations. Our results indicate that high resolution alone is insufficient for models to properly reproduce Antarctic dense water; the large-scale polar atmospheric circulation around Antarctica must also be accurately simulated. [ABSTRACT FROM AUTHOR]

The Chaudière River in Quebec, Canada, is well known for its frequent ice jam flooding events. As part of a larger watershed research program, an extensive field campaign has been carried out during the 2018-2019 and 2019-2020 winter seasons to quantify the spatiotemporal characteristics of the break-up processes along the Chaudière River. The results showed that mid-winter ice jams have formed in the Intermediate Chaudière and persisted until spring break-up. Spring break-ups were initiated in the Upper Chaudière, and then, almost simultaneously, in the Intermediate and Lower Chaudière reaches. The break-up in the Intermediate Chaudière usually lasts longer than the rest of the river since the slope is much milder, and the occurrence of mid-winter ice jams has been seen to delay the ice clearing. A reach-by-reach characterization of the cumulative degree day of thawing and discharge thresholds for the onset of break-up has been identified. During the field campaign, 51 ice jams were documented together with their location, length, date of formation, and the morphological feature triggering jam formation. Break-up patterns, hydrometeorological thresholds of ice mobilization, and ice jam sites identified in this study can serve as a basis for the implementation of an early warning system. [ABSTRACT FROM AUTHOR]

The region of Maud Rise, a seamount in the Weddell Sea, is known for the occurrence of irregular polynya openings during the winter months. Hydrographic observations have shown the presence of a warmer water mass below the mixed layer along the seamount's flanks, commonly termed the warm‐water Halo, surrounding a colder region above the rise, the Taylor Cap. Here we use two observational data sets, an eddy‐permitting reanalysis product and regional high‐resolution simulations, to investigate the interannual variability of the Halo and Taylor Cap for the period 2007–2022. Observations include novel hydrographic profiles obtained in the Maud Rise area in January 2022, during the first SO‐CHIC cruise. It is demonstrated that the temperature of deep waters around Maud Rise exhibits strong interannual variability within the Halo and Taylor Cap, occasionally to such an extent that the two features become indistinguishable. A warming of deep waters by as much as 0.8°C is observed in the Taylor Cap during the years preceding the opening of a polynya in 2016 and 2017, starting in 2011. By analyzing regional simulations, we show that most of the observed variability in the Halo is forced remotely by advection of deep waters from the Weddell Gyre into the region surrounding Maud Rise. Our highest‐resolution simulation indicates that mesoscale eddies subsequently transfer the properties of the Halo's deep waters onto the Taylor Cap. The eddies responsible for such transfer originate in an abrupt retroflection along the inner flank of the Halo. Plain Language Summary: A polynya is an opening within the sea ice cover during winter. In the Weddell Sea, polynyas occur irregularly and often emerge close to a seamount, Maud Rise. This topographic obstacle disturbs the local circulation of the Weddell Gyre and leads to the formation of two local permanent features: a Taylor Cap on top of the seamount, which is mainly an isolated water mass; and surrounding this, a warm‐water Halo, located along the flanks of Maud Rise. In this study, we use observational and model analyses to show the changes in the temperature of regional water masses on a timescale of years, and to identify the drivers of these changes. The properties of the warm‐water Halo are controlled by the advection of deep waters along the south‐eastern rim of the Weddell Gyre. These waters are partly mixed into the Taylor Cap by eddies, thereby preconditioning the water column for deep convection. In the years preceding the opening of a polynya in 2016–2017, we document a warming trend in the Taylor Cap, starting in 2011. Key Points: Interannual variability of the subsurface temperature maximum at Maud Rise is documented with observationsAdvection of anomalously cold and fresh deep waters from the Weddell Gyre into the Halo leads to a near‐vanishing of the Taylor Cap in 2014Observed warming of the subsurface layer in the Taylor Cap due to eddy transport preceded the polynya opening in 2016–2017 [ABSTRACT FROM AUTHOR]

Ocean–atmosphere–sea ice interactions are key to understanding the future of the Southern Ocean and the Antarctic continent. Regional coupled climate–sea ice–ocean models have been developed for several polar regions; however the conservation of heat and mass fluxes between coupled models is often overlooked due to computational difficulties. At regional scale, the non-conservation of water and energy can lead to model drift over multi-year model simulations. Here we present P-SKRIPS version 1, a new version of the SKRIPS coupled model setup for the Ross Sea region. Our development includes a full conservation of heat and mass fluxes transferred between the climate (PWRF) and sea ice–ocean (MITgcm) models. We examine open water, sea ice cover, and ice sheet interfaces. We show the evidence of the flux conservation in the results of a 1-month-long summer and 1-month-long winter test experiment. P-SKRIPS v.1 shows the implications of conserving heat flux over the Terra Nova Bay and Ross Sea polynyas in August 2016, eliminating the mismatch between total flux calculation in PWRF and MITgcm up to 922 W m -2. [ABSTRACT FROM AUTHOR]

Experiments were carried out on intravital otolith-tagging of juveniles of ocellated blenny after transition to benthic life mode with Alizarin Red S. Tagging at a dye concentration of 200 mg/L for 16–18 h at night, yielded 100% formation of fluorescent tags with zero mortality of experimental individuals. Alizarin tags on the otoliths correspond to "stress" tags in the form of darker microincrements, visible in transmitted light. Calculation of the microincrements in the zone between two consecutive taggings at an interval of 9 days confirmed the daily periodicity of their formation at this stage of development of ocellated blenny. This made it possible to determine the hatching period of juveniles in natural conditions in Zhitkov Bay (Russky Island, Peter the Great Bay, Sea of Japan). Larvae in 2017 for this species hatched, according to our estimates, from the last ten days of March to the end of the second ten days of April, with a peak in the first ten days of April. Hatching begins even under the ice at a slightly negative water temperature of –1 to 0°C, but it proceeds mainly already at a temperature of 1–3°C, after the bay is clear of ice. Taking into account the known timing of spawning of ocellated blenny in Peter the Great Bay (November–early December), it can be stated that development of their eggs in this area is greatly slowed at water temperatures below zero in December–March and can span 4–5 months, which is almost three times longer than the development time in the milder conditions of southern Hokkaido. [ABSTRACT FROM AUTHOR]

The Amundsen Polynya (AP) on the inner and middle continental shelf of the western Amundsen Sea Embayment is the fourth largest coastal polynya around Antarctica. The AP is highly productive when it opens in austral summer, with ∼20 times greater organic carbon accumulation rates over the last few thousand years compared to those at nearby shelf sites with more persistent seasonal sea‐ice cover. We examined sedimentary records at a site from the AP and another site from the outer shelf to investigate temporal variations in the depositional environment with a special focus on the timing of the AP opening since the deglaciation following the Last Glacial Maximum (LGM; ca. 23–19 cal. ka BP). In the AP region, sedimentological and biogeochemical proxy data reveal a transition from a sub‐glacial to a sub‐ice shelf and then seasonally open marine conditions comparable to those at present. Total organic carbon contents and diatom valve abundances during the seasonally open marine period imply that the polynya environments was reached at ca. 9.2 cal. ka BP. Since the post‐LGM deglaciation, diatom productivity and assemblages in the AP region appear to have varied in association with the variation in the physical environment. Compared to the AP site, only small amounts of organic carbon accumulated on the outer shelf. Differences in the depositional environments and productivity modes between the inner and outer shelf sites have persisted since ca. 10.5 cal. ka BP. Plain Language Summary: The Amundsen Polynya (AP) on the Amundsen Sea shelf is the fourth largest and the most productive coastal polynya around Antarctica. For the last few thousand years, the AP has maintained higher organic carbon accumulation rates compared to nearby sites outside of the polynya. We examined two sediment core records (one from the AP and one from a region with more persistent seasonal sea‐ice cover) to track temporal variations in biological production and organic carbon accumulation. A comparison of the sediment records reveals that the differences in the depositional environments and productivity modes between the inner and outer shelf sites have persisted since the grounded ice retreat from the shelf following the Last Glacial Maximum. This finding stresses the importance of polynyas with regard to organic carbon production and the accumulation of seabed sediments around Antarctica. Understanding variability in the past will provide useful information for predicting future environmental and ecological changes in Antarctic polynyas in response to global warming and the resulting sea‐ice and glacial ice melting. Key Points: Polynya‐like conditions similar to current conditions were established ∼9.2 cal. ka BP in the inner shelfHigher rates of deposition of organic carbon on the inner than outer shelf has persisted throughout the HoloceneBiogeochemical proxies in sediment cores reflect climate oscillations during the early, middle, and late Holocene [ABSTRACT FROM AUTHOR]

Ever since the abrupt drop in Antarctic sea ice extent (SIE) began in spring of 2016, as opposed to its consistent growth (1.95% decade–1 from 1979 to 2015), the SIE in the satellite era has reached record lows in 2017 and 2022. From spring 2016, the satellite-based SIE remained consistently lower than the long-term mean, with the trend dropping to 0.11% decade–1 from 1979 to 2022. The top record lowest SIE years were observed from 2016 to 2022, corresponding to the warmest years dating back to 1979. With this background, the rare features of Antarctic polynyas reoccurred frequently and the west Antarctic Peninsula remained ice-free throughout 2022. Recently, the SIE dropped to a record low in June 2022, July 2022, August 2022, January 2023, and February 2023, which were 13.67%, 9.91%, 6.79%, 39.29%, 39.56% below the long-term mean value, respectively for months described above. We find that the observed decline in SIE during 2016–2022 occurred due to the combined influences from the intensification of atmospheric zonal waves with enhanced poleward transport of warm-moist air and anomalous warming in the Southern Ocean mixed layer (>1°C). Although the sudden sea ice decline in spring of 2016 occurred corresponding to the transitional climate shift from IPO– (Interdecadal Pacific Oscillation, 2000–2014) to IPO+ (2014–2016), the recent decline after 2016 occurred in a dominant IPO– and Southern Annular Mode (SAM+). CMIP6 models showed a consistent decrease in ensemble-mean SIE from 1979 to 2022. The model trend exhibits similarities to the recent declining trend in SIE from satellite observations since 2016, suggesting a possible shift towards a warmer climatic regime.

A polynya is an area of open water or reduced concentration of sea ice surrounded by either concentrated sea ice or land ice. They are often seen as sites of intense ocean–atmosphere heat exchange and as ice production factories. Given their importance, it is crucial to quantify the accuracy of satellite-derived polynya information. Polynyas in their early evolution phase are generally narrow and occur at scales likely too fine to be detected by widely used passive microwave (PMW) radiometric sensors. We derived 40 m scale polynya information over the western Ross Sea from high-resolution Synthetic Aperture Radar (SAR) Sentinel-1 C-band data and examined discrepancies with larger-scale estimates. We utilized two automated algorithms, supervised (a rule-based approach) and unsupervised (a combination of texture analysis with k-means clustering), to accurately identify the polynya areas. We generated data for validation using Sentinel-1 data at instances where polynyas can be visually delineated. Results from PMW sensors (NSIDC and AMSR2) and SAR-based algorithms (rule-based and texture-based) are compared with manually delineated polynya areas obtained through Sentinel-1. Analysis using PMW sensors revealed that NSIDC overestimates larger polynyas and underestimates smaller polynyas compared to AMSR2. We were more accurately able to identify polynya presence and area using Sentinel-1 SAR observations, especially in clear cases and cases when PMW data miscalculates the polynya's presence. Of our SAR-based algorithms, the rule-based approach was more accurate than the texture-based approach at identifying clear polynyas when validated against manually delineated regions. Altogether, we emphasize the need for finer spatio-temporal resolution data for polynya studies. [ABSTRACT FROM AUTHOR]

Coastal polynyas around the Antarctic continent are regions of very strong ocean–atmosphere heat and moisture exchange that are important for local and regional weather, sea ice production, and water mass formation. Due to extreme atmospheric conditions (very strong offshore winds, low air temperature, as well as humidity) the surface ocean layer in polynyas is highly turbulent, with mixing due to combined Langmuir, wind-induced, and buoyancy-driven turbulence. One of the visible signs of complex interactions between the mixed-layer dynamics and the forming sea ice are frazil streaks, elongated patches of high ice concentration separated by areas of open water. In spite of their ubiquity, observational and modelling analyses of frazil streaks have been very limited largely due to the fact that their significance for heat flux and ice production is only just becoming apparent. In this study, the first comprehensive analysis of the spatial variability of surface frazil concentration is performed for the Terra Nova Bay Polynya (TNBP). Frazil streaks are identified in high-resolution (pixel size 10–15 m) visible satellite imagery, and their properties (surface area, width, spacing, and orientation) are linked to the meteorological forcing (wind speed and air temperature). This provides a simple statistical tool for estimating the extent and ice coverage of the region of high ice production under given meteorological conditions. It is also shown that the orientation of narrow streaks tends to agree with the wind direction, suggesting the dominating role of the local wind forcing in their formation. Very wide streaks, in turn, deviate from that pattern, as they are presumably influenced by several additional factors, including local water circulation and the associated convergence zones. An analysis of peak wavelengths and directions determined from the images, compared to analogous open-water wavelengths computed with a spectral wave model, demonstrates a significant slow-down in the observed wave growth in TNBP. This suggests an important role of frazil streaks in modifying wind-wave growth and/or dissipation in polynyas. [ABSTRACT FROM AUTHOR]

In the southwestern Sea of Okhotsk, a large spring phytoplankton bloom occurs after the sea ice melts. A suggested scenario is that sea ice with materials such as iron-containing sediment or ice algae is transported from the north and melted with release of them, inducing a prominent bloom. We hypothesize that sea ice containing materials that could enhance spring bloom originates from active coastal polynyas in the upstream region. To verify this hypothesis and identify which coastal areas generate sea ice that is further transported to the bloom area, we simulated the transport of sea ice produced in the coastal polynyas by a particle-tracking method. Sea ice production and drift velocity were derived from satellite microwave data. For regions near the coast, where ice drift data derived from the satellite are inaccurate, we combined ice drift data derived from the wind using the wind factor and the turning angle obtained from mooring data. Further, we used the apparent wind factor that expresses enhancement of the alongshore component of ice drift by the ocean current. The simulations suggest that most of the sea ice that melts in the western Kuril Basin originates from the Terpenia Bay and Sakhalin polynyas. The area where high net community production occurs after the sea ice melts corresponds well to the area where sea ice originating from these polynyas melts. The simulation of frazil ice suggests the importance of melt ice originating from the Terpenia Bay polynya with a higher rate of frazil ice production. [ABSTRACT FROM AUTHOR]

Toward understanding the trend and variability in the bottom water salinity in the Ross Sea, this study focuses on the seasonality of the salinity budget over the Ross Sea continental shelf, using a new coupled regional ocean‐sea ice‐ice shelf model. Owing to the sea ice production, the upstream advection, and the glacial melting, the Ross Sea continental shelf is characterized by the relatively saltier water on the western shelf than on the eastern shelf, with the saltiest water in the Terra Nova Bay Polynya. During the early freezing season (March–April), there is remarkable sea ice production over the broad continental shelf, which makes a significant contribution to the production of High Salinity Shelf Water (HSSW). The brine rejection in the polynyas leads to the salinification and deepening of the mixed layer, yet the upstream advection acts to decrease the salinity below the mixed layer until the deep convection is fully developed throughout the water column. The seasonal cycle of the salinity budget in the Ross Sea continental shelf is largely determined by the formation/melting of sea ice, the intrusion of modified Circumpolar Deep Water, and the outflow of HSSW, while the contribution of the Ross Ice Shelf melting is relatively small. Plain Language Summary: The large variability in the bottom water salinity in the Ross Sea has attracted great research interests. However, it's not clear what has driven the salinity variability since the contributions of the relevant processes haven't been fully quantified. Toward a quantitative understanding of the variability in the bottom water salinity in the Ross Sea, we did a salinity budget analysis for the Ross Sea continental shelf for the first time using the results from a new ocean‐sea ice‐ice shelf model. We quantified the seasonal cycles of the processes that control the seasonal salinity variations in the polynyas and over the shelf region. We found that the horizontal transport of the upstream salty water is also important for generating the saltiest water in the Terra Nova Bay polynya on the western shelf, in addition to the local sea ice formation. In the Ross Sea polynya and Terra Nova Bay polynya, when the surface salinity increases due to sea ice formation, the salinity below the mixed layer decreases owing to the fresher water inflow. During the sea ice growing phase, the sea ice production is also large over the broad shelf region, particularly during the initial sea ice growing phase (March–April). Key Points: The salt advection is important for the production of High Salinity Shelf Water in the polynyas of the Ross Sea continental shelfWithin the polynyas, brine rejection increases the salinity in the mixed layer, yet the advection freshens the underlying waterOver the continental shelf, there is remarkable sea ice production outside the polynyas, particularly during March–April [ABSTRACT FROM AUTHOR]

The Ross Sea has been the site of extensive investigations since the earliest days of polar exploration. The International Geophysical Year of 1957-58 enhanced research activities with the establishment of scientific stations and the collection of oceanographic observations in the area. While many features of its oceanography, ecology, physics, glaciology, geology, and biogeochemistry are known, recent advances provide new insights into its structure and function, as well as into its relationship to global climate. We present a comprehensive review of the advances of understanding the main processes occurring in the area, such as the formation of dense shelf water and the production of Antarctic Bottom Water (AABW), as well as the main drivers (at both large and local scales) of local dynamics and water mass variability. We also summarize the main modeling applications, which are still limited and need to be improved using high-resolution models and, locally, limited-area models to explain processes driven mainly by thermodynamics and water-mass transformations. The Ross Sea forms the most saline AABW due to the activity of two polynyas in the western sector. A salinity gradient occurs on the shelf, with fresh Low Salinity Shelf Waters concentrated in the eastern Ross Sea, which is influenced by the inflow of fresh water from the Amundsen and Bellingshausen Seas. This freshwater inflow was thought to be the cause of a multi-decadal freshening of the High Salinity Shelf Water, precursor to the AABW, although a rebound in salinity in the Ross Sea has been observed since 2014. The increase in salinity has also affected the production of AABW, with the respective rebound occurring almost simultaneously. [ABSTRACT FROM AUTHOR]

• Bubble ice cube with uniform bubble volume fraction is prepared. • Four typical mechanical properties have been chosen to be measured. • Bubbles have different effect on different mechanical properties of ice cube. • The effect of bubbles on the mechanical properties is related to loading rate. Icing is a common liquid–solid phase change process that usually has negative effects. Bubbles will form in ice since air is significantly less soluble in ice than it is in water and these bubbles will affect the mechanical properties of ice cubes. To quantitatively investigate the effect of air bubbles on the mechanical strength of ice cubes, an experimental setup is built to explore the mechanical strength and modulus of clear and bubble ice cubes at different loading rates. The results show that even a low volume fraction of air bubbles in the ice cubes as low as 1.98% can have a significant effect on their mechanical properties. The weakening of tensile, compressive and bending strengths by air bubbles is almost less than 20%, while the weakening of shear strength by air bubbles reaches almost 60%. The effect of air bubbles on the four typical mechanical moduli does not exceed 20%. This research helps to optimize the de-icing technique and also provides methods and ideas for preparing ice. [ABSTRACT FROM AUTHOR]