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This paper presents the results of an acoustic survey carried out from the fast ice in the shallow waters of the East Siberian Arctic Shelf (ESAS) using a single beam echosounder. The aim of this paper is to demonstrate an improved approach to study seafloor seepages in the Arctic coastal zone with an echosounder calibrated on site. During wintertime field observations of natural rising gas bubbles, we recorded three periods of their increased activity with a total of 63 short-term ejections of bubbles from the seabed. This study presents quantitative estimates of the methane (CH4) flux obtained in wintertime at two levels of the water column: (1) at the bottom/water interface and (2) at the water/sea ice interface. In winter, the flux of CH4 transported by rising bubbles to the bottom water in the shallow part of the ESAS was estimated at ~19 g·m−2 per day, while the flux reaching the water/sea ice interface was calculated as ~15 g·m−2 per day taking into account the diffusion of CH4 in the surrounding water and the enrichment of rising bubbles with nitrogen and oxygen. We suggest that this bubble-transported CH4 flux reaching the water /sea ice interface can be emitted into the atmosphere through numerous ice trenches, leads, and polynyas. This CH4 ebullition value detected at the water/sea ice interface is in the mid high range of CH4 ebullition value estimated for the entire ESAS, and two orders higher than the upper range of CH4 ebullition from the northern thermocarst lakes, which are considered as a significant source to the atmospheric methane budget. [ABSTRACT FROM AUTHOR]

Antarctic landfast sea ice (fast ice) is stationary sea ice that is attached to the coast, grounded icebergs, ice shelves, or other protrusions on the continental shelf. Fast ice forms in narrow (generally up to 200 km wide) bands, and ranges in thickness from centimeters to tens of meters. In most regions, it forms in autumn, persists through the winter and melts in spring/summer, but can remain throughout the summer in particular locations, becoming multi‐year ice. Despite its relatively limited extent (comprising between about 4% and 13% of overall sea ice), its presence, variability and seasonality are drivers of a wide range of physical, biological and biogeochemical processes, with both local and far‐ranging ramifications for the Earth system. Antarctic fast ice has, until quite recently, been overlooked in studies, likely due to insufficient knowledge of its distribution, leading to its reputation as a “missing piece of the Antarctic puzzle.” This review presents a synthesis of current knowledge of the physical, biogeochemical and biological aspects of fast ice, based on the sub‐domains of: fast ice growth, properties and seasonality; remote‐sensing and distribution; interactions with the atmosphere and the ocean; biogeochemical interactions; its role in primary production; and fast ice as a habitat for grazers. Finally, we consider the potential state of Antarctic fast ice at the end of the 21st Century, underpinned by Coupled Model Intercomparison Project model projections. This review also gives recommendations for targeted future work to increase our understanding of this critically‐important element of the global cryosphere.Plain Language Summary: Landfast ice (known more simply as fast ice) is sea ice that doesn't move horizontally, unlike pack ice. It can cover extensive regions of the Southern Ocean, and ranges in thickness up to several tens of meters. In many regions it melts or breaks out each summer, but can survive the melt season in others regions. Antarctic fast ice is critically important for a wide variety of coastal processes, and has far‐reaching consequences for the Earth system, however our knowledge of it is limited. This first review of Antarctic fast ice provides a synthesis of the current state of knowledge, including its baseline properties and its major roles in key glaciological, oceanographic, atmospheric, biogeochemical and biological interactions and processes, highlighting its crucial and far‐reaching importance. Antarctic fast ice is likely to reduce by the end of the 21st Century, in terms of its season length, thickness and possibly extent, but projections are highly uncertain due to a current lack of inclusion of fast ice in climate models. Observations of fast ice, including both ground‐ and satellite‐based, should be coordinated and expanded to allow deeper understanding of this important part of the global cryosphere and Antarctic coastal environment.Key Points: Antarctic landfast ice is a crucial but often overlooked part of the Antarctic coastal environmentOur review draws together the body of work which is wide‐ranging but tends to lack coordinationObservation programs need to be expanded and coordinated, and models need to incorporate realistic landfast ice [ABSTRACT FROM AUTHOR]

We present a 700 km airborne electromagnetic survey of late‐spring fast ice and sub‐ice platelet layer (SIPL) thickness distributions from McMurdo Sound to Cape Adare, providing a first‐time inventory of fast ice thickness close to its annual maximum. The overall mode of the consolidated ice (including snow) thickness was 1.9 m, less than its mean of 2.6 ± 1.0 m. Our survey was partitioned into level and rough ice, and SIPL thickness was estimated under level ice. Although level ice, with a mode of 2.0 m and mean of 2.0 ± 0.6 m, was prevalent, rough ice occupied 41% of the transect by length, 50% by volume, and had a mode of 3.3 m and mean of 3.2 ± 1.2 m. The thickest 10% of rough ice was almost 6 m on average, inclusive of a 2 km segment thicker than 8 m in Moubray Bay. The thickest ice occurred predominantly along the northwestern Ross Sea, due to compaction against the coast. The adjacent pack ice was thinner (by ∼1 m) than the first‐year fast ice. In Silverfish Bay, offshore Hells Gate Ice Shelf, New Harbor, and Granite Harbor, the SIPL transect volume was a significant fraction (0.30) of the consolidated ice volume. The thickest 10% of SIPLs averaged nearly 3 m thick, and near Hells Gate Ice Shelf the SIPL was almost 10 m thick, implying vigorous heat loss to the ocean (∼90 W m−2). We conclude that polynya‐induced ice deformation and interaction with continental ice influence fast ice thickness in the western Ross Sea. Plain Language Summary: Sea ice held stationary by the coast is named fast ice. Around Antarctica, it is often observed near floating land ice and grounded icebergs. Fast ice is a critical habitat for marine life and known to be a sensitive indicator to changing weather and oceanic processes. Despite its importance, satellite measurements of its area are recent, and little is known about its thickness. Using a specialized instrument on a fixed wing aircraft, we measured the 2017 November fast ice thickness in the western Ross Sea. Most of the fast ice surveyed was 2 m thick on average and had formed in sheltered embayments. Where floating glaciers are in contact with fast ice, a 3–10 m thick layer of loose ice crystals was sometimes observed beneath, which contributed to its thickness. However, most of the thicker ice was rough ice, formed when ferocious offshore winds pushed ice from the coast. It then drifted with the prevailing ocean currents until eventually becoming frozen in place against coastal topography. This rough ice, 3.3 m thick on average and comprising half the surveyed volume, was significantly thicker than adjacent freely moving pack ice. Our survey provides a baseline from which future change can be measured. Key Points: Annual maximum fast ice and sub‐ice platelet layer thickness distributions are surveyed by airborne electromagnetics over 700 km of Ross SeaDeformed against the coast, 50% of transect volume was rough first‐year fast ice (mode 3.3 m thick), that was thicker than nearby pack iceSub‐ice platelet layers over 0.5 m thick underlay level ice over large parts of four embayments, revealing land ice‐fast ice interaction [ABSTRACT FROM AUTHOR]

The Svalbard Archipelago has experienced some of the most severe temperature increases in the Arctic in the last three decades. This temperature rise has accelerated sea-ice melting along the coast of the archipelago, thus bringing changes to the local environment. In view of the importance of the near-future distribution of land-fast sea ice along the Svalbard coast, the available observation data on the ice extent between 1973 and 2018 are used herein to create a random forest (RF) model for predicting the daily ice extent and its spatial distribution according to the cumulative number of freezing and thawing degree days and the duration of the ice season. Two RF models are constructed by using either regression or classification algorithms. The regression model makes it possible to estimate the extent of land-fast ice with a root mean square error (RMSE) of 800 km2, while the classification model creates a cluster of submodels in order to forecast the spatial distribution of land-fast ice with less than 10% error. The models also enable the reconstruction of the past ice extent, and the prediction of the near-future extent, from standard meteorological data, and can even analyze the real-time spatial variability of land-fast ice. On average, the minimum two-monthly extent of land-fast sea ice along the Svalbard coast was about 12,000 km2 between 1973 and 2000. In 2005–2019, however, the ice extent declined to about 6,000 km2. A further increase in mean winter air temperatures by two degrees, which is forecast in 10 to 20 years, will result in a minimum two-monthly land-fast ice extent of about 1,500 km2, thus indicating a trend of declining land-fast ice extent in this area.

Sea-ice concentrations retrieved from satellite microwave radiometry data are influenced by many natural factors. In the work we consider sea-ice contamination. The values of sea-ice concentration derived with the use of the ASI, TUD, OSI-401-b, BT, NT, and CDR algorithms are analyzed on the example of fast ice in the East Siberian Sea. These algorithms are chosen because they are available for open access and are commonly used in scientific research. All of the algorithms return lower ice concentrations in contaminated ice as compared to clean ice during the active ice-melt period, from late May to early July. The ASI and TUD are the two most sensitive to sea-ice contamination, which is due to the high-frequency channels, 85–91 GHz, used in them. [ABSTRACT FROM AUTHOR]

We elucidated the effects of snow and remineralization processes on nutrient distributions in multi‐year landfast sea ice (fast ice) in Lützow‐Holm Bay, East Antarctica. Based on sea‐ice salinity, oxygen isotopic ratios, and thin section analyses, we found that the multi‐year fast ice grew upward due to the year‐by‐year accumulation of snow. Compared to ice of seawater origin, nutrient concentrations in shallow fast ice were low due to replacement by clean and fresh snow. In deeper ice of seawater origin (the lower half of the multi‐year fast ice column), remineralization was dominated by the degradation of organic matter. By comparison between first‐ and muti‐year ice, the biological uptake and the remineralization were dominated in relatively young ice and older ice, respectively, under the physical process of brine drainage. Plain Language Summary: Multi‐year landfast sea ice (fast ice) is abundant around the coast of Antarctica. Fast ice is an important component of Antarctic coastal marine ecosystems, providing a prolific habitat for ice algal communities. Although nutrients are essential for biological productivity within sea ice, the status of nutrients and processes affecting nutrient concentrations were previously not known for multi‐year fast ice. Here, we collected sea‐ice cores from multi‐year fast ice in Lützow‐Holm Bay, East Antarctica, and we analyzed nutrient concentrations using physical and biogeochemical parameters. Nutrient concentrations in the upper parts of the sea ice decreased due to the accumulation of clean (nutrient‐free) snow through melting and refreezing processes, contributing to upward ice growth. In deeper parts of the sea ice, nutrient concentrations were greatly affected by biological processes such as remineralization during the degradation of organic matter within sea ice. Key Points: Antarctic multi‐year landfast ice grew upward due to the year‐by‐year accumulation of snowNutrient concentrations decreased in the upper sea ice due to the replacement by clean snowIn deeper sea ice, remineralization by degradation of organic matter drove nutrient concentrations [ABSTRACT FROM AUTHOR]

The series of data on the fast ice thickness and the surface air temperature at the Roshydromet land-based polar stations in the Laptev Sea are analyzed. Observations for the last 15-year period (2005-2020) are compared to observations prior to 2004, and the changes corresponding to the new climatic conditions are revealed. Over the past 15 years ice thicknesses during the period of maximum ice growth (maximum ice thickness) have decreased by 6% on average. The ice growth process has become much slower, transition between the sequentional stages of ice development is observed 1-2 ten-days periods later. The surface air temperature at the considered stations was on average 3°C higher than for the previous period. The most significant changes are observed in the autumn months (October, November) and in April. The cumulative sum of the degree-day of frost averaged for the Laptev Sea stations, decreased by 15%; all 15 recent winter seasons can be classified as mild. It was revealed that the decrease of the cumulative sum of degree-day of frost is in a good agreement with the decrease of the mean-seasonal ice thickness (averaged for November-May) at the stations. This indicator seems to be more informative than the maximum ice thickness for estimation of the changes. Averaging over all stations revealed a 10% decrease of the mean-seasonal ice thickness during the past 15 years.

Over the past decades, sea ice in the polar regions has been significantly affecting local and even hemispheric climate through a positive ice albedo feedback mechanism. The role of fast ice, as opposed to drift ice, has not been well-studied due to its relatively small coverage over the earth. In this paper, the optical properties and surface energy balance of land fast ice in spring are studied using in situ observations in Barrow, Alaska. The results show that the albedo of the fast ice varied between 0.57 and 0.85 while the transmittance increased from 1.3×10−3 to 4.1×10−3 during the observation period. Snowfall and air temperature affected the albedo and absorbance of sea ice, but the transmittance had no obvious relationship with precipitation or snow cover. Net solar shortwave radiation contributes to the surface energy balance with a positive 99.2% of the incident flux, with sensible heat flux for the remaining 0.8%. Meanwhile, the ice surface loses energy through the net longwave radiation by 18.7% of the total emission, while the latent heat flux accounts for only 0.1%. Heat conduction is also an important factor in the overall energy budget of sea ice, contributing 81.2% of the energy loss. Results of the radiative transfer model reveal that the spectral transmittance of the fast ice is determined by the thickness of snow and sea ice as well as the amount of inclusions. As major inclusions, the ice biota and particulates have a significant influence on the magnitude and distribution of the spectral transmittance. Based on the radiative transfer model, concentrations of chlorophyll and particulate in the fast ice are estimated at 5.51 mg/m2 and 95.79 g/m2, which are typical values in the spring in Barrow. [ABSTRACT FROM AUTHOR]

This study provides the first documentation of polar bear (Ursus maritimus) maternity denning in snowdrifts around icebergs frozen into the fast ice or grounded on the seafloor. Based on six den observations in north and northeast Greenland during spring surveys in 2018 and 2019 (109 flight hours), together with observations of 20 adult females with 35 cubs of the year (COYs) in adjacent sea ice, we hypothesize that the use of snowdrifts around icebergs for maternity denning is an established behavior in the region and not a random event. Factors influencing maternity denning in snowdrifts around icebergs may include limited suitable drifts on the nearby terrestrial polar desert due to low precipitation, the presence of suitable wind-blown snow banks regardless of the direction of autumn storm winds, cold and stable habitat throughout the winter denning period, and access to ringed seal (Pusa hispida) pupping habitat in the nearby Northeast Water polynya. This type of maternity denning habitat is only available in glaciated regions of the Arctic where marine-terminating glaciers deposit mélange large enough to become grounded offshore and remain in place for months or years. This habitat may become less stable or disappear with long-term climate warming. [ABSTRACT FROM AUTHOR]

Field investigations of coastal fast ice near the research station Ice Base on the «Cape Baranova», carried out in 2013–2014, made possible to reveal a number of characteristics of the sea ice cover formation. It has been shown that during winter and early spring the sea ice thickness, being formed due to intensive snow drift and caused by that flooding of the ice cover just near the coast of the Bolshevik Island, substantially grows at its upper boundary, that is typical for the Antarctic seas. At the same time, similar process of the ice growth at a relatively short distance from the coast shows all features characteristic for the ice cover in the Arctic seas, and that is well reproduced by the conceptual numerical sea ice model. Thus, the region of the Ice Base «Cape Baranova» represents a natural laboratory for studying the processes of the sea ice formation in both, the Arctic and Antarctic seas under condition of the same atmospheric forcing. Transformation of the fast ice structure during the summer time is described. Results of the investigations has demonstrated that despite the radical changes in the structure thicknesses of the fast ice remained almost unchanged due to the ice growth on the bottom boundary of the ice cover until a destruction of it in August.

Sea ice algae are an important contributor of primary production in the Arctic ecosystem. Within the bottom-ice environment, access to nutrients from the underlying ocean is a major factor controlling production, phenology, and taxonomic composition of ice algae. Previous studies have demonstrated that tides and currents play an important role in driving the flux of nutrients to bottom-ice algal communities when biological demand during the spring bloom is high. In this study we investigate how surface currents under landfast first-year ice influence nutrient supply based on stoichiometric composition, algal chlorophyll a biomass and species composition during spring 2016, in Dease Strait, Nunavut. Stronger water dynamics over a shoaled and constricted strait dominated by tidal currents (tidal strait) supported turbulent flow more than 85% of the deployment duration in comparison to outside the tidal strait in an embayment where turbulent flow was only evidenced a small percentage (

The emperor penguin, an iconic species threatened by projected sea ice loss in Antarctica, has long been considered to forage at the fast ice edge, presumably relying on large/yearly persistent polynyas as their main foraging habitat during the breeding season. Using newly developed fine‐scale sea icescape data and historical penguin tracking data, this study for the first time suggests the importance of less recognized small openings, including cracks, flaw leads and ephemeral short‐term polynyas, as foraging habitats for emperor penguins. The tracking data retrieved from 47 emperor penguins in two different colonies in East Antarctica suggest that those penguins spent 23% of their time in ephemeral polynyas and did not use the large/yearly persistent, well‐studied polynyas, even if they occur much more regularly with predictable locations. These findings challenge our previous understanding of emperor penguin breeding habitats, highlighting the need for incorporating fine‐scale seascape features when assessing the population persistence in a rapidly changing polar environment. Plain Language Summary: Polar ecosystems are threatened by future loss of sea ice. The availability of satellite sea ice products has facilitated a better assessment of the impact of sea ice on polar species. Yet most studies have focused on coarse spatial scale sea ice products hampering an understanding of the mechanisms by which sea ice affects species. The development of fine‐scale sea ice products now provides an unprecedented opportunity to better understand the responses of sea ice obligate species to climate change. The emperor penguin is an iconic species threatened by projected sea ice loss in Antarctica. Here we used fine‐scale satellite sea ice observations to understand the emperor penguin's sea ice habitat during the entire breeding and Antarctic winter season. Sea ice characteristics affect both the foraging routes and effort of polar species, with consequences for their reproduction and survival, ultimately affecting population dynamics and species persistence. Emperor penguins dived at the edge of the landfast sea ice in cracks, flaw leads and open water areas called polynyas, formed by winds on both long and short time scales. By using daily passive microwave observations, we identified that emperor penguins did not venture into the large/persistent polynyas but dived instead in the ephemeral polynyas associated with daily changes in wind direction. Key Points: Dynamic fine‐scale sea icescape in East Antarctica affects the foraging routes and effort of emperor penguins during the breeding seasonEmperor penguins used short‐term ephemeral polynya openings to forage during the breeding season instead of using the persistent onesThe breeding foraging habitat was consistent among months, years, sexes, and sites despite the highly dynamic sea ice environment [ABSTRACT FROM AUTHOR]

Historical sea ice core chlorophyll‐a (Chla) data are used to describe the seasonal, regional, and vertical distribution of ice algal biomass in Antarctic landfast sea ice. The analyses are based on the Antarctic Fast Ice Algae Chlorophyll‐a data set, a compilation of currently available sea ice Chla data from landfast sea ice cores collected at circum‐Antarctic nearshore locations between 1970 and 2015. Ice cores were typically sampled from thermodynamically grown first‐year ice and have thin snow depths (mean = 0.052 ± 0.097 m). The data set comprises 888 ice cores, including 404 full vertical profile cores. Integrated ice algal Chla biomass (range: <0.1–219.9 mg/m2, median = 4.4 mg/m2, interquartile range = 9.9 mg/m2) peaks in late spring and shows elevated levels in autumn. The seasonal Chla development is consistent with the current understanding of physical drivers of ice algal biomass, including the seasonal cycle of irradiance and surface temperatures driving landfast sea ice growth and melt. Landfast ice regions with reported platelet ice formation show maximum ice algal biomass. Ice algal communities in the lowermost third of the ice cores dominate integrated Chla concentrations during most of the year, but internal and surface communities are important, particularly in winter. Through comparison of biomass estimates based on different sea ice sampling strategies, that is, analysis of full cores versus bottom‐ice section sampling, we identify biases in common sampling approaches and provide recommendations for future survey programs: for example, the need to sample fast ice over its entire thickness and to measure auxiliary physicochemical parameters. Plain Language Summary: Antarctic sea ice is a key driver of physical, chemical, and biological processes in the Southern Ocean. Importantly, sea ice serves as a substrate for microscopic algae which grow in the bottom, interior, and surface layers of the ice. These algae are considered an important food source for Antarctic marine food webs. Using a newly collated database of historical sea ice core chlorophyll‐a data (a proxy for ice algal biomass) from coastal sites, we describe the seasonal and vertical variability of algal biomass in Antarctic landfast sea ice. The seasonal chlorophyll‐a development is consistent with the current understanding of physical drivers of ice algal biomass, including the seasonal cycle of irradiance and surface temperatures driving landfast sea ice growth and melt. Our analyses show that algae in the lowermost third of ice cores drive the annual cycle of integrated biomass, but internal and surface communities are also important. Through comparison of biomass estimates based on different sea ice sampling strategies, that is, analysis of full cores versus bottom‐ice section sampling, we identify biases in common sampling approaches and provide recommendations for future survey programs: for example, the need to sample fast ice over its entire thickness and to measure auxiliary physical parameters, in particular snow‐thickness data. Key Points: First comprehensive collation of Antarctic landfast sea‐ice core chlorophyll‐a data establishedAlgae in lowermost third of ice cores drive annual cycle of integrated biomass, but internal and surface communities are also importantFull‐profile ice‐core sampling and systematic collection of auxiliary physico‐chemical parameters is recommended for future studies [ABSTRACT FROM AUTHOR]

Detailed mapping of landfast ice deformation can be used to characterize the rheological behavior of landfast ice effectively and to improve sea ice modeling subsequently. In order to analyze the characteristics, trends and causes of deformation comprehensively and accurately, the Sentinel-1A ascending and descending orbits data were used to detect the horizontal and vertical deformation of the fast ice in the Baltic Sea. Firstly, the fast ice edge lines were acquired through feature extraction with interferometric coherence images and SAR amplitude images. Then, the deformation transformed model was constructed according to the geometric relationship of multi-orbits deformation measurements. Finally, the landfast ice deformations were resolved and the horizontal and vertical deformations were obtained. The results showed that the maximum deformation was—44 cm in horizontal direction and 16 cm in vertical direction within the fast ice region of 960 km2 during the time from 2 to 16 February 2018. The southwest wind was the principal reason for the deformation, which made the deformation mainly occur in the horizontal direction from east to west. Moreover, the inner fast ice kept stable due to the protection of outer consolidated ice. The results showed that the deformation trend and characteristics can be better understood by using InSAR technology that was combined with multi-orbits SAR data to resolve and analyze the landfast ice deformation.

The study presents inter-annual variations in the backscatter response of fast ice (sea ice attached to the coast) to C band Advanced Scatterometer (ASCAT) (2012–2016). It also analyses the Ground Penetrating Radar (GPR) observations collected during the 35th Indian Scientific Expedition to Antarctica (ISEA, 2015–16) for identification of different fast ice features and to measure fast ice depth in the Larsemann Hills area, East Antarctica. Apart from clear demarcation of features like melt water channels, frozen icebergs within fast ice and underlying topography near island, GPR provided fast ice depth information, which was used to understand backscatter response. The seasonal variations of C band backscatter were caused due to changes in snow thickness, time of freezing and sporadic melt/freeze events apart from summer melt. The backscatter response to NOAA high resolution blended daily sea surface temperature (SST) variations indicate that sudden rise/fall in backscatter during winter is probably due to sporadic melt/freeze events caused by rise/fall in SST. The results show volumetric contribution from sheet ice and domination of snow metamorphism towards increase in backscatter over fast ice. This study highlights the importance of monitoring backscatter response of fast ice to determine its state and condition. Depending on the characteristics of backscatter inter-annual curve, information about time of freeze up, melt season, ice build-up, and sporadic freeze/ thaw events can be inferred which play an important role in the energy budget of Antarctica. [ABSTRACT FROM AUTHOR]

The dynamics of landfast sea ice, also called fast ice for short, has a large influence on the variability of polynyas and marine ecosystems, and the logistics for research stations near the Antarctic coast. Therefore, it is important to accurately measure the strain of fast ice and its seasonal variations, and to identify the cause of stresses on the ice. In this paper, we separate the strains from glacial stress and tidal stress of fast ice near the Campbell Glacier Tongue (CGT) in Terra Nova Bay, East Antarctica. This was done using observations from a series of one-day tandem COSMO-SkyMed Interferometric Synthetic Aperture Radar (InSAR) images obtained from December 2010 to January 2012. Firstly, we discriminated fast ice from pack ice and open water by analyzing the interferometric coherence values. We then identified the characteristics of the strains by investigating the equi-displacement lines of fringes in weekly InSAR and double-differential InSAR (DDInSAR) images. The weekly InSAR images predominantly showed glacial shear strain of the fast ice with fringes parallel to the sides of the CGT. This was due to the cumulative flow of the CGT for a week, while oscillating tidal signals were relatively small. The DDInSAR images, which cancelled glacial strain rates in two one-day InSAR images, showed a deformation of the fast ice by tidal sea surface tilt, with the fringes parallel to the coastline. Based on the unique characteristics of these strains, we separated them from the one-day InSAR images by decomposing the fringe patterns into glacial and tidal strain. Glacial shear strain rates of fast ice attached to the east of the CGT decreased from May to August owing to ice thickening and then stabilized until December. Those to the west of the CGT increased from May to July. This was possibly due to bottom melting of the ice by the increased ocean circulation during the expansion period of the nearby polynya. The glacial strain then decreased until December because of reduced polynya activity. The fast ice near the Jang Bogo Station (JBS) only showed tidal strain as it was isolated from the CGT by cracks and leads. Tidal strain rates of the fast ice were strongly correlated with the magnitude of tidal variations in all these regions, which represents shows that the tidal strain represents tidal sea surface tilt. The tidal response of fast ice to the west of the CGT and near the JBS was stronger than that to the east of the CGT, probably owing to thinner ice thickness there. [ABSTRACT FROM AUTHOR]

Fjords around Greenland connect the Greenland Ice Sheet to the ocean and their hydrography and circulation are determined by the interplay between atmospheric forcing, runoff, topography, fjord-shelf exchange, tides, waves, and seasonal growth and melt of sea ice. Limited knowledge exists on circulation in high-Arctic fjords, particularly those not impacted by tidewater glaciers, and especially during winter, when they are covered with sea-ice and freshwater input is low. Here, we present and analyze seasonal observations of circulation, hydrography and cross-sill exchange of the Young Sound-Tyrolerfjord system (74°N) in Northeast Greenland. Distinct seasonal circulation phases are identified and related to polynya activity, meltwater and inflow of coastal water masses. Renewal of basin water in the fjord is a relatively slow process that modifies the fjord water masses on a seasonal timescale. By the end of winter, there is two-layer circulation, with outflow in the upper 45 m and inflow extending down to approximately 150 m. Tidal analysis showed that tidal currents above the sill were almost barotropic and dominated by the M2 tidal constituent (0.26 m s −1 ), and that residual currents (∼0.02 m s −1 ) were relatively small during the ice-covered period. Tidal pumping, a tidally driven fjord-shelf exchange mechanism, drives a salt flux that is estimated to range between 145 kg s −1 and 603 kg s −1 . Extrapolation of these values over the ice-covered period indicates that tidal pumping is likely a major source of dense water and driver of fjord circulation during the ice-covered period. [ABSTRACT FROM AUTHOR]

A correct representation of the ice movement in an Arctic sea-ice–ocean coupled model is essential for a realistic sea-ice and ocean simulation. The aim of this study is to validate the observational and simulated sea-ice drift for the Laptev Sea Shelf region with in situ measurements from the winter of 2007/08. Several satellite remote-sensing data sets are first compared to mooring measurements and afterwards to the sea-ice drift simulated by the coupled sea-ice–ocean model. The different satellite products have a correlation to the in situ data ranging from 0.56 to 0.86. The correlations of sea-ice direction or individual drift vector components between the in situ data and the observations are high, about 0.8. Similar correlations are achieved by the model simulations. The sea-ice drift speed derived from the model and from some satellite products have only moderate correlations of about 0.6 to the in situ record. The standard errors for the satellite products and model simulations drift components are similar to the errors of the satellite products in the central Arctic and are about 0.03 m/s. The fast-ice parameterization implementation in the model was also successfully tested for its influence on the sea-ice drift. In contrast to the satellite products, the model drift simulations have a full temporal and spatial coverage and results are reliable enough to use as sea-ice drift estimates on the Laptev Sea Shelf.

Tidal cracks are linear features that appear parallel to coastlines in fast ice regions due to the actions of periodic and non-periodic sea level oscillations. They can influence energy and heat exchange between the ocean, ice, and atmosphere, as well as human activities. In this paper, the LINE module of Geomatics 2015 software was used to automatically extract tidal cracks in fast ice regions near the Chinese Zhongshan Station in East Antarctica from Landsat-8 Operational Land Imager (OLI) data with resolutions of 15 m (panchromatic band 8) and 30 m (multispectral bands 1-7). The detected tidal cracks were determined based on matching between the output from the LINE module and manually-interpreted tidal cracks in OLI images. The ratio of the length of detected tidal cracks to the total length of interpreted cracks was used to evaluate the automated detection method. Results show that the vertical direction gradient is a better input to the LINE module than the top-of-atmosphere (TOA) reflectance input for estimating the presence of cracks, regardless of the examined resolution. Data with a resolution of 15 m also gives better results in crack detection than data with a resolution of 30 m. The statistics also show that, in the results from the 15-m-resolution data, the ratios in Band 8 performed best with values of the above-mentioned ratio of 50.92 and 31.38 percent using the vertical gradient and the TOA reflectance methods, respectively. On the other hand, in the results from the 30-m-resolution data, the ratios in Band 5 performed best with ratios of 47.43 and 17.8 percent using the same methods, respectively. This implies that Band 8 was better for tidal crack detection than the multispectral fusion data (Bands 1-7), and Band 5 with a resolution of 30 m was best among the multispectral data. The semi-automatic mapping of tidal cracks will improve the safety of vehicles travel in fast ice regimes. [ABSTRACT FROM AUTHOR]

Fast ice affects many coastlines in high- and mid-latitude regions, shaping the coastal morphology by acting as both a protective barrier from winter storms and as an erosive agent through sediment entrainment and transport. It has been hypothesized that when sediment-rich ice is dislodged and transported beyond the depth of closure by storm waves, sediment is permanently removed from the nearshore, starving the littoral system and facilitating future erosion. However, despite this large potential impact on coastal sediment budgets, the rates and mechanisms of sediment-rich ice transport are poorly constrained. This study investigates the sediment entrainment process by fast ice, the mechanisms needed for ice mobilization, and the force needed to breakup and transport sediment-rich ice. We find that the Coulomb frictional strength of the sediment regulates the fast ice system and that the viscous rheology of the ice has no direct mechanical effect. Importantly, these results show that only the frictional coefficient of the beach sediment needs to be measured to estimate the resistive strength of the fast ice, significantly simplifying the requirements for evaluating the potential for fast ice mobilization and associated sediment transport. • Investigations on sediment entrainment and mobilization processes for fast ice. • Experiments reveal the force needed to breakup and transport sediment-rich ice. • The frictional strength of the sediment, not ice, regulates the fast ice system. • Blocks of ice with adhered sediment can be treated as a Coulomb material. [ABSTRACT FROM AUTHOR]

Ground counts during 1959-1968 compared with counts using high resolution (0.6 m2) satellite imagery during 2008-2012 indicated many fewer Weddell seals ( Leptonychotes weddellii) at two major molting areas in the western Ross Sea: Edisto Inlet-Moubray Bay, northern Victoria Land, and McMurdo Sound, southern Victoria Land. Breeding seals have largely disappeared from Edisto-Moubray, though the breeding population in McMurdo Sound appears to have recovered from harvest in the 1960s. The timing of decline, or perhaps spreading (lower numbers of seals in more places), is unknown but appears unrelated to changes in sea ice conditions. We analyzed both historic and satellite-derived ice data confirming a large expansion of pack ice mostly offshore of the Ross Sea, and not over the continental shelf (main Weddell seal habitat), and a thinning of fast ice along Victoria Land (conceivably beneficial to seals). Timing of fast ice presence and extent in coves and bays along Victoria Land, remains the same. The reduction in numbers is consistent with an altered food web, the reasons for which are complex. In the context of a recent industrial fishery targeting a seal prey species, a large-scale seal monitoring program is required to increase understanding of seal population changes. [ABSTRACT FROM AUTHOR]

Polynyas are an important yet poorly understood phenomena of high latitude oceans. A storm event during late December 2013 with down-fjord winds of up to 25 m/s forced the collapse of the landfast ice over the Young Sound (YS) fjord outlet in northeast Greenland. This storm created a coastal polynya that was further maintained by several consecutive wind events until early March 2014. During the polynya period, three landfast ice-tethered oceanographic moorings recorded an enhanced surface layer (∼0–40 m) transport towards the mouth of YS and a layer below (∼40–140 m) flowing into the fjord and supplying the interior with cool and saline water from the polynya. Subsequent CTD transects in May 2014 reveal that this lower layer contained polynya originated cool, saline and oxygen enriched water with oxygen concentrations significantly exceeding values from the previous summer. Salt balance bulk estimates show that the polynya generated a sufficient amount of brine to ventilate the fjord interior. [ABSTRACT FROM AUTHOR]

One hundred mega-boulders were tagged to survey their movements (RFID) for five winters (2012–2017) in Sainte-Luce, St. Lawrence Maritime Estuary, where the foreshore is frozen for two to four months per year. In addition, four boulders were fitted with accelerometers to determine the exact periods of motion. It was found that 81% of the boulders moved during at least one of the winters studied. The maximum transport recorded in one winter was 151.87 m for a 3.1 t boulder, but most boulders moved shorter distances (2012–2017 average transport: 9.74 m, standard deviation 23.71). The relationships between length/direction of boulder movements and fast-ice activity as well as weather and oceanic conditions were analyzed. 61% of mobility events took place at the end of the ice period during ice-foot break-up by storm waves or melting, but 37% took place at the beginning of the fast-ice phase during storms and/or high tide, which was unexpected. The length and direction of transport was found to depend on conditions during ice break-up (wind, waves, currents, ice thickness), which have large interannual variabilities. However, a greater proportion of boulders moved landward between 2012 and 2017. Two transport modes occurred: short pushing by ice floes and ice-rafting over longer distances. The first is much more common (70 to 90%) while the second seems to be more frequent during cold winters, when ice is thicker. Moreover, we demonstrated that the geomorphological setting exerts a strong control on boulder transport distance. The longest movements took place near mean sea level, where the ice foot is thicker and the rock platform smooth while cobble and boulder pavements inhibit movements. • Ice pushing and ice rafting are effective at moving boulders on cold coasts. • Roughness of the shore platform (pavement, isolated boulders) can inhibit movements. • Transport occurs during short periods of winter thaw or at the end of the ice period. • Waves, tide and winds during fast-ice break-up can explain interannual variability. • Winter harshness would control the length of transport via ice thickness. [ABSTRACT FROM AUTHOR]

Navigation in polar sea regions requires special attention to the sea ice condition because it is a major barrier for an icebreaker to break the drift ice or fast ice, allowing the vessel to keep moving forward. The advancement of remote sensing imagery pro-vides an effective means to classify and identify various features, including different types of sea ice. Hence, it permits fuel and time saving for the entire voyage, especially when drift ice or fast ice becomes a barrier for the icebreaker. In this study, we exploit the potential usage of high-resolution synthetic aperture radar (SAR) imageries from Radarsat-2 to identify sea ice conditions for precise navigation of China's icebreaker vessel (Xuelong) during the 29th Chinese Antarctic Research Expedition in December 2012. Different features on the fast ice were identified from horizontal-transmit and horizontal-receive polarized imagery. The potential usage of SAR imagery for precise navigation was confirmed by an expert witness on the Xuelong vessel at that time. The final voyage route has validated our analysis of fast ice and navigation of the Xuelong ssel. The predicted regions for unloading locations were also found to be matching well with the actual vessel unloading locations after the final voyage route. [ABSTRACT FROM AUTHOR]

Abstract: This study presents concentrations of dimethylsulphide (DMS) and its precursor compound dimethylsulphoniopropionate (DMSP), and chlorophyll a in a variety of sea ice and seawater habitats from pack and fast ice in the Antarctic sea ice zone (ASIZ) of eastern Antarctica. Estimated “hot spot” seawater DMS concentrations released during sea ice melting in October and derived from a total DMSP (DMSPt)-sea ice depth relationship and application of a DMSPt:DMS conversion ratio, predict that sea ice derived DMS of the order of 20–50nM is associated with DMSPt released from melting sea ice of 0.4m thickness. In November and December, melting of large areas of ice less than 0.6m thick could release larger amounts of DMS around 50–80nM and 150–270nM, respectively. In addition, DMSPt released from 1.0 to 1.2m thick ice in December could result in “hot spot” concentrations of DMS of around 100nM. DMS flux in November and mid to late December was highest in pack ice>fast ice>ice edge (pack ice=54μmolm−2 d−1; (range 1–325); fast ice=16μmolm−2 d−1; (range 10–50); ice edge=12 (range 1.2–26) and 23μmolm−2 d−1). In ice-free seawater in the Davis area from January to February, although dissolved DMS concentrations were low, DMS fluxes were high due to high wind speeds (DMS=3nM; DMS flux=27μmolm−2 d−1 (range 1–101)). DMS concentrations and flux from a fast ice tide crack (DMS=12nM; DMS flux 6–81μmolm−2 d−1), and two days following fast ice breakout from the Davis region DMS concentrations (12nM) and DMS flux (45–84μmolm−2 d−1) also indicated that fast ice was a significant source of DMS to the atmosphere of this region. In contrast DMS flux from a fast ice melt-pool was low (DMS flux 0.5–7μmolm−2 d−1). These measurements support the suggestion that during sea ice melting during late spring to early summer (November–December), the ASIZ is an area of high DMS (P) production from various sources, leading to very high and variable fluxes of DMS to the atmosphere of this region. As sea ice melts in late November voids in sea ice become larger enabling sea ice to vent DMS directly to the atmosphere, as well as being released from sea ice melting. At most sea ice sites DMS often displayed non-detectable to elevated concentrations of DMS (mean 11nM) in the surface 0–0.1m. Using average DMS concentrations from a range of studies we estimate that DMS flux from ASIZ in November is about 23μmolm−2 d−1, much lower than what we have estimated from pack ice using a DMSPt:DMS conversion ratio technique (54μmolm−2 d−1). The difference (31μmolm−2 d−1) could reflect venting or degassing of DMS directly from pack ice to the Antarctic atmosphere. Depth-integrated sea ice DMS concentrations varied with time of day, with elevated DMS concentrations (18–30nM) in the cores during the later part of the day (i.e. 16.00–20.00h), whilst close to mid-day (11.00–12.00h) concentrations were much lower (2–9nM). The lower depth-integrated DMS concentrations found in pack ice in November could suggest that large amounts of DMS are vented from pack ice close to mid-day when temperatures and wind speeds often increase. Varying DMSPt–chlorophyll a correlations in the sea ice highlight how varying biological activity affects DMSP concentrations, and suggest that variations in biological activity in sea ice also influence DMS flux. [Copyright &y& Elsevier]

Abstract: While feature tracking of sea ice using cross-correlation methods on pairs of satellite Synthetic Aperture Radar (SAR) images has been extensively carried out in the Arctic, this is not the case in the Antarctic. This is due to the dynamic nature of Antarctic pack ice, its microwave signature, the tendency for SAR swath paths to be poorly aligned with the often narrow sea ice zone around the continent and inadequate satellite sampling. A semi-automated system, known as IPADS (IMCORR [IMageCORRelation] Processing, Analysis and Display System), has been developed to map fast ice and pack ice in Antarctica using multiple pairs of SAR images. The software processing pipeline uses overlapping image pairs which are geocoded and roughly registered using only data contained in the image headers. Next, fast ice maps are rapidly generated using zero motion features located within ocean regions. This also provides precise image registration. Finally, the same image pairs are re-examined for pack ice motion in a slower off-line batch process. The pack and fast ice are identified using a cluster-based search method which compares both location and motion information. Each image pair generates a NetCDF file which adds to a growing database of Antarctic sea ice motion and ice roughness. Five image-pair examples are presented to illustrate the methods used as well as their strengths and limitations. Substantial pack ice motion can often be detected in the marginal ice zone on SAR images only a few days apart. [Copyright &y& Elsevier]

Abstract: Iron is a fundamental nutrient limiting phytoplankton growth in vast regions of the Southern Ocean. Sea ice, which covers ∼80% of the Southern Ocean (south of 60°S) during maximum extent, can concentrate iron up to two orders of magnitude higher than in the underlying sea water. The fractionation of iron between the particulate and dissolved fractions depends on the location and type of sea-ice formation and can impact on the bioavailability of this important trace element. This study is the first to document iron fractionation and concentration in both pack and fast ice during a single research study. Sampling was from within the 110–130°E sector of Antarctica. We observed markedly higher concentrations of particulate iron at our fast-ice site (0.96–214nM) relative to several pack-ice sites (0.87–77.7nM). A high particulate-to-dissolved iron ratio was observed at the fast-ice site (285:1) relative to the highest observed in pack ice (23:1). This suggests a decoupling between the sources and/or sinks of the dissolved and particulate fractions. Preferential release of dissolved iron (and not particulate iron) into brines at all sites sampled with the sack hole method (and therefore indicative of brine drainage) indicates the diffuse nature of the dissolved fraction. Furthermore, this indicates that there may be a temporal decoupling between the release of the dissolved and the particulate fractions into the water column as sea ice becomes more permeable during the seasonal melt. Implications for phytoplankton production in Antarctic sea ice are discussed. [Copyright &y& Elsevier]

A correct representation of the ice movement in an Arctic sea-ice-ocean coupled model is essential for a realistic sea-ice and ocean simulation. The aim of this study is to validate the observational and simulated sea-ice drift for the Laptev Sea Shelf region with in situ measurements from the winter of 2007/08. Several satellite remote-sensing data sets are first compared to mooring measurements and afterwards to the sea-ice drift simulated by the coupled sea-ice-ocean model. The different satellite products have a correlation to the in situ data ranging from 0.56 to 0.86. The correlations of sea-ice direction or individual drift vector components between the in situ data and the observations are high, about 0.8. Similar correlations are achieved by the model simulations. The sea-ice drift speed derived from the model and from some satellite products have only moderate correlations of about 0.6 to the in situ record. The standard errors for the satellite products and model simulations drift components are similar to the errors of the satellite products in the central Arctic and are about 0.03 m/s. The fast-ice parameterization implementation in the model was also successfully tested for its influence on the sea-ice drift. In contrast to the satellite products, the model drift simulations have a full temporal and spatial coverage and results are reliable enough to use as sea-ice drift estimates on the Laptev Sea Shelf. [ABSTRACT FROM AUTHOR]

Abstract: A method to generate high spatio-temporal resolution maps of landfast sea ice from cloud-free MODIS composite imagery is presented. Visible (summertime) and thermal infrared (wintertime) cloud-free 20-day MODIS composite images are used as the basis for these maps, augmented by AMSR-E ASI sea-ice concentration composite images (when MODIS composite image quality is insufficient). The success of this technique is dependent upon efficient cloud removal during the compositing process. Example wintertime maximum (~374,000km2) and summertime minimum (~112,000km2) fast-ice maps for the entire East Antarctic coast are presented. The summertime minimum map provides the first high-resolution indication of multi-year fast-ice extent, which may be used to help assess changes in Antarctic sea-ice volume. The 2σ errors in fast-ice extent are estimated to be ±2.98% when ≥90% of the fast-ice pixels in a 20-day period are classified using the MODIS composite, or ±8.76 otherwise (when augmenting AMSR-E or the previous/next MODIS composite image is used to classify >10% of the fast ice). Imperfect composite image quality, caused by persistent cloud, inaccurate cloud masking or a highly dynamic fast-ice edge, was the biggest impediment to automating the fast-ice detection procedure. [ABSTRACT FROM AUTHOR]

Abstract: The hydrography of the Laptev Sea is significantly influenced by river water and sea-ice processes, which are highly variable over the annual cycle. Despite of an estuarine structure the inner and outer shelf regions are decoupled at times as documented by the stability of a warm intermediate layer formed during summer below the Lena River plume. We demonstrate that a remnant of this warm layer is preserved below the fast ice until the end of winter, while only slightly farther to the north, offshore of the landfast ice in the polynya region, the pycnocline is eroded and no signature of this layer is found. The warm intermediate layer (WIL) formed during summer can be used as tracer for Laptev Sea shelf waters throughout the winter. Thereby, residence times of southern Laptev Sea waters can be estimated to be at least from summer to the end of winter/spring of the following year. [Copyright &y& Elsevier]

The article examines the significant function of heterotrophic dinoflagellates (HD) on the adundance and the sinking loss of ice algal diatoms from the ice in Syowa, Antarctica. It investigates the grazing impact of the diatoms and its major consumers. Furthermore, it explores the growth of HD and its function of prey abundance. It provides information on the environmental conditions and species compositions of the diatoms in the water column. Moreover, methods and materialas for the sampling and results of the study are discussed.

The aim of the study was to investigate the capacity of microalgae from the extremely low light habitat of bottom ice to acclimate to different light conditions. During austral spring 1997 the bottom layer of land-fast ice in Terra Nova Bay displayed high values of microalgal biomass up to 2,400 μg Chl a L−1 concentrated in a few centimetres ice layer. The algal assemblage was dominated by benthic pennate diatoms. Photoacclimation of the microalgae was addressed in terms of pigment spectra and photosynthetic parameters. Immediate and long term (minutes to days) changes in the photoprotective pigments (DD-cycle) were analysed. Severe photodamage occurred in microalgal assemblages exposed to high light. However, part of the bottom ice algal community showed a notable ability to acclimate to high irradiance levels. Changes in photosynthetic parameters preceded the sudden abrupt changes in pigment synthesis and the rapid increase in biomass and growth rates. [ABSTRACT FROM AUTHOR]

Abstract: Variation in macrofaunal composition in relation to sediment and water variables was analysed in nine regions of the western Canadian Arctic on the Beaufort Shelf and in Amundsen Gulf. We hypothesized that benthic community composition was distinctive (1) in a recurrent polynya in Amundsen Gulf and (2) in upwelling regions (Cape Bathurst and Mackenzie Canyon) and (3) changed in a linear gradient across the Beaufort Shelf. Analysis was based on 497 taxa >0.4 mm from 134 samples at 52 stations sampled over 2002–4 in 11–1000 m water depth. Abundance ranged from 490.7 m−2 in eastern Amundsen Gulf to 17,950 m−2 off Cape Bathurst. (1) Community composition in Amundsen Gulf was not significantly different from the Beaufort Shelf at similar depth, indicating a lack of benthic effect of the polynya in Amundsen Gulf. (2) The Mackenzie Canyon macrofauna, although abundant and diverse, were similarly indistinct from the shelf community at similar depth. However, there was a 10-fold increase in inshore abundance in the upwelling region of Cape Bathurst due to large numbers of the amphipod Ampelisca macrocephala and the polychaete Barantolla americana, species that were not abundant elsewhere. (3) In the inshore fast ice and flaw lead regions of the Beaufort Shelf, under the influence of ice scour, storm effects, coastal erosion and the Mackenzie River, the macrofauna were dominated by the bivalve Portlandia arctica and the polychaete Micronephthys minuta. Offshore, where these influences were less and upwelling of deep Atlantic water occurred, the polychaete Maldane sarsi dominated. Faunal distribution across the Beaufort Shelf correlated with depth, water and sediment changes but was not significantly linear. [Copyright &y& Elsevier]

Abstract: To investigate the fate of ice algae released from sea ice, we investigated the abundance, species composition, and sinking flux of diatoms in the water column under fast ice near Syowa Station, Antarctica during the summer of 2005/2006. The diatom assemblage in the water column consisted of chain-forming planktonic species, in contrast to the under-ice assemblage dominated by pennate species reported from this site in the past; this dissimilarity suggests the presence of an unconsolidated platelet ice layer under the congelation ice, within which planktonic species can bloom. Among the dominant diatoms, Porosira pseudodenticulata and Pseudo-nitzschia cf. turgiduloides were dominant in the water column, and their water column stocks were higher than their mass sedimentation. These species apparently maintain their populations in the surface layer, as their production remains in the water column. In contrast, Fragilariopsis kerguelensis and Thalassiosira australis were scarce in the water column but rich in the flux, indicating active sinking and export of their production to the benthic ecosystem. This distinction in buoyancy control and sinking characteristics of the dominant diatoms on release from the fast ice influences the diatom species composition and carbon flow under the ice. [Copyright &y& Elsevier]

Temporal variations in the microbial community structure of plankton, which is composed of autotrophic and heterotrophic pico-, nano- and microplankton, were investigated during the austral summer of 2005/2006 under fast ice near Syowa Station, eastern Antarctica. Autotrophic algal populations were composed almost entirely of diatoms followed by phytoflagellates such as autotrophic dinoflagellates and cryptophytes. Among the microbial community, heterotrophic biomass was dominated by heterotrophic dinoflagellates and naked ciliates and finally exceeded autotrophic biomass. Qualitative microscopic analysis revealed that heterotrophic dinoflagellates were ingesting large number of diatoms. Synchronizing fluctuation of naked ciliates with phytoflagellates suggested a predator–prey relationship between them. Our results suggest that the pelagic food webs under the extensive ice-covered areas in coastal Antarctic regions are not short but complex. [ABSTRACT FROM AUTHOR]

Abstract: Observations are presented of currents, hydrography and turbulence in a jet-type tidally forced fjord in Svalbard. The fjord was ice covered at the time of the experiment in early spring 2004. Turbulence measurements were conducted by both moored instruments within the uppermost 5m below the ice and a microstructure profiler covering 3–60m at 75m depth. Tidal choking at the mouth of the fjord induces a tidal jet advecting relatively warmer water past the measurement site and dominating the variability in hydrography. While there was no strong correlation with the observed hydrography or mixing and the phase of the semidiurnal tidal cycle, the mean structure in dissipation of turbulent kinetic energy, work done under the ice and the mixing in the water column correlated with the current when conditionally sampled for tidal jet events. Observed levels of dissipation of turbulent kinetic energy per unit mass, 1.1×10−7 Wkg−1, and eddy diffusivity, 7.3×10−4 m2 s−1, were comparable to direct measurements at other coastal sites and shelves with rough topography and strong forcing. During spring tides, an average upward heat flux of 5Wm−2 in the under-ice boundary layer was observed. Instantaneous (1h averaged) large heat flux events were correlated with periods of large inflow, hence elevated heat fluxes were associated with the tidal jet and its heat content. Vertical heat fluxes are derived from shear-probe measurements by employing a novel model for eddy diffusivity [Shih et al., 2005. Parameterization of turbulent fluxes and scales using homogeneous sheared stably stratified turbulence simulations. Journal of Fluid Mechanics 525, 193–214]. When compared to the direct heat flux measurements using the eddy correlation method at 5m below the ice, the upper 4–6m averaged heat flux estimates from the microstructure profiler agreed with the direct measurements to within 10%. During the experiment water column was stably, but weakly, stratified. Destabilizing buoyancy fluxes recorded close to the ice were absent at 5m below the ice, and overall, turbulence production was dominated by shear. A scaling for dissipation employing production by both stress and buoyancy [Lombardo and Gregg, 1989. Similarity scaling of viscous and thermal dissipation in a convecting boundary layer. Journal of Geophysical Research 94, 6273–6284] was found to be appropriate for the under-ice boundary layer. [Copyright &y& Elsevier]

Underwater vocalization monitoring and surveys, both on ice and underwater, were used to determine if Weddell seals ( Leptonychotes weddellii) near Mawson Station, Antarctica, remain under the fast ice during winter within close range of breeding sites. Daytime and nighttime underwater calling rates were examined at seven breeding sites during austral winter and spring to identify seasonal and diel patterns. Seals rarely hauled out at any of the sites during winter, although all cohorts (adult males, females, and juveniles) were observed underwater and surfacing at breathing holes throughout winter (June–September) and spring (October–December). Seal vocalizations were recorded during each sampling session throughout the study ( n= 102 daytime at seven sites collectively, and n= 5 24-h samples at each of two sites). Mean daytime calling rate was low in mid-winter (July) (mean = 18.9 ± 7.1 calls/min) but increased monthly, reaching a peak during the breeding season (November) (mean = 62.6 ± 15.7 calls/min). Mean nighttime calling rate was high throughout the winter and early spring (July–October) with mean nocturnal calling rate in July (mean = 61.8 ± 35.1 calls/min) nearly equal to mean daytime calling rate in November (during 24-h daylight). Reduced vocal behavior during winter daylight periods may result from animals utilizing the limited daylight hours for nonvocal activities, possibly feeding. [ABSTRACT FROM AUTHOR]

Abstract: The present study of temporal and spatial variations of shore-fast ice in the Kara Sea includes utilization of aircraft observations by the Arctic and Antarctic Research Institute (AARI) from 1953 to 1990, and surface brightness temperature from SSM/I from 1987 to 2001. Analyses of a time series of spatially distributed SSM/I brightness temperatures provide estimates of the shore-fast ice extent. The present work shows spatial distributions of frequencies of shore-fast ice coverage in the Kara Sea for each month, and it gives a time series of its area. The fast ice extent in early spring typically reaches a stable configuration, which falls into one of two different categories (modes) with significantly different area. The smaller of these two modes tends to appear with increased frequency since 1980. This gives, for this period, a negative trend in fast ice area during spring. There is a correlation above 0.5 between the average winter temperature and maximum ice thickness anomalies and fast ice area. Analysis of surface wind data and sea level pressure indicates that wind during winter controls much of the shore-fast ice development. Specially strong westerly and southwesterly winds tend to give a smaller fast ice extent than otherwise. Variations in river discharge tend only to have an observable effect on the ice at the river mouths. [Copyright &y& Elsevier]

Samples of the bottom layer (4 cm) of fast ice and under-ice water were collected in May 1997 from the Adventfjorden (Spitsbergen). Concentrations of particulate organic matter (POM) in the bottom layer of the fast ice and under-ice water were similar (about 5.5 mg l -1 ). However, the content of POM in total particulate matter (TPM) was significantly higher (p < 0.001) in ice (25%) than in water (16%). Algal biomass expressed as chlorophyll a within ice was 2.97 μg l -1 melt ice in comparison with 1.33 μg l -1 in under-ice water. Based on algal pigment determination we found that algal communities in the bottom of the fast ice were composed of the following taxonomic groups: diatoms (68.1%), chlorophytes (20.1%), prasinophytes (10.4%) and cryptophytes (1.4%), whereas under-ice water was dominated by diatoms (56.6%), chlorophytes (31.1%) and prasinophytes (12.3%). The ratio of diatoms and chlorophytes to chlorophyll a signal differed significantly between the two environments. Chlorophyllide a was the most abundant degradation product of chlorophyll a . [ABSTRACT FROM AUTHOR]

Detailed mapping of landfast ice deformation can be used to characterize the rheological behavior of landfast ice effectively and to improve sea ice modeling subsequently. In order to analyze the characteristics, trends and causes of deformation comprehensively and accurately, the Sentinel-1A ascending and descending orbits data were used to detect the horizontal and vertical deformation of the fast ice in the Baltic Sea. Firstly, the fast ice edge lines were acquired through feature extraction with interferometric coherence images and SAR amplitude images. Then, the deformation transformed model was constructed according to the geometric relationship of multi-orbits deformation measurements. Finally, the landfast ice deformations were resolved and the horizontal and vertical deformations were obtained. The results showed that the maximum deformation was—44 cm in horizontal direction and 16 cm in vertical direction within the fast ice region of 960 km2 during the time from 2 to 16 February 2018. The southwest wind was the principal reason for the deformation, which made the deformation mainly occur in the horizontal direction from east to west. Moreover, the inner fast ice kept stable due to the protection of outer consolidated ice. The results showed that the deformation trend and characteristics can be better understood by using InSAR technology that was combined with multi-orbits SAR data to resolve and analyze the landfast ice deformation. [ABSTRACT FROM AUTHOR]

Time-series analyses of satellite images reveal that sea ice extent in the Ross Sea has experienced significant changes over the last 40 years, likely triggered by large-scale atmospheric anomalies. However, resolving how sea ice in the Ross Sea has changed over longer timeframes has until now remained more elusive. Here we used a laminated sediment piston core (14.6 m) collected from the Edisto inlet (Western Ross Sea) to reconstruct fast ice dynamics over the last 2.6 ka. Our goal was to first understand the climate expression of selected well-defined sediment laminae and then use these characteristics for reconstructing past sea ice behaviour across the whole sedimentary sequence. We used the recently established sea ice diatom biomarker proxy IPSO 25 in combination with diatom census counts and bulk analyses. Analyses performed on a suite of discrete laminae revealed statistically significant differences between dark and light laminae reflecting different depositional conditions. Based on their respective biogeochemical fingerprints, we infer that dark laminae accumulated during sea ice thaws in early summer. Under these conditions, laminae contain relatively high concentrations of IPSO 25 and display an enriched δ13C composition for the bulk organic matter (OM). While diatom assemblages in dark laminae are relatively homogenous, as the thaw continues later in the summer, Corethron pennatum becomes the dominant diatom species, resulting in the formation of light laminae characterized by low IPSO 25 concentrations. Since C. pennatum can migrate vertically through the water column to uptake nutrients and avoid competition in oligotrophic waters, its high concentration likely reflects stratified and ice-free surface waters typical of late summer. Down-core trends show that the correlation between sediment brightness and geochemical fingerprint (i.e., IPSO 25 and δ13C) holds throughout the record. Based on the knowledge gained at lamina level, our down-core high-resolution reconstruction shows that the summer fast ice coverage changed dramatically during the late Holocene. Specifically, we conclude that the Edisto inlet experienced regular early summer opening between 2.6 ka, and ca. 0.7 ka, after which, coastal fast ice persisted during summer months and ice-free conditions became less frequent. Comparison with previous regional ice core data suggests that the sudden cooling recorded over the Victoria Land Coast region since 0.7 ka might potentially explain our observation of persistent summer fast ice in the Western Ross Sea. Our study has shown that multi-proxy data derived from laminated sediments can provide hitherto unknown detail regarding past summer sea ice dynamics in coastal Antarctic regions. • Dark and light sediment laminae exhibit different chemical and ecological features. • Dark and light sediment laminae reflect different fast ice coverage during summer. • Enriched δ13C and high IPSO 25 (dark laminae) track early thawing of fast ice. • High concentration of C. pennatum (light laminae) identifies protracted ice-free conditions. • Summer ice-free conditions became less frequent since 0.7 ka BP along the north-western Ross Sea. [ABSTRACT FROM AUTHOR]

Antarctic coastal polynyas serve as crucially-important sea-ice "factories" and are (in certain cases) of global significance as sites of Antarctic Bottom Water (AABW) formation e.g., the Cape Darnley Polynya (CDP) in East Antarctica. As such, understanding change and variability in their behaviour, and the factors responsible, is a high priority in climate (change) science. One such important factor that is both poorly understood and quantified is their linkage with adjacent landfast sea ice (fast ice). Here, we present a first detailed analysis that identifies and quantifies key linkages between the dynamics/behaviour of the CDP and fast ice. By forming a barrier to the incursion of pack ice at the eastern boundary, fast ice immediately upstream of the CDP (associated with the distribution of grounded icebergs) plays a crucially-important role in the polynya formation, maintenance and variability. This satellite data-based study builds upon earlier conceptual work on polynya-fast ice feedback mechanisms in the Mertz Glacier region by showing that statistical estimation of the rates of sea ice production (and hence AABW formation) in the CDP is significantly improved through inclusion of two key fast-ice metrics, compared to use of atmospheric covariates alone. These two metrics are the meridional extent of fast ice upstream of the polynya and total fast ice area within the region of high sea ice production. The work highlights the importance of accurate representation of the coupled Antarctic coastal polynya-fast ice system in global climate models. • Studies the Cape Darnley Polynya, a globally-important producer of bottom water • Details links between Antarctic landfast sea ice and coastal polynya ice production • Defines fast ice metrics which describe variability in polynya size and production • Fast ice metrics are as important as atmospheric quantities for this polynya. • Provides an inter-comparison between passive microwave and MODIS fast ice maps [ABSTRACT FROM AUTHOR]

Oxygen microelectrodes were used to measure the photosynthetic ratesof Antarctic fast ice algal mats. Using the oxygen flux across the diffusive boundary layer below the fast ice at Davis, a productivity range of 0--1.78 mg C m -2 h -1 was measured. This is at the lower end of fast ice productivity estimates and suggests that conventional 14C techniques may overestimate sea ice algal mat productivity. Photosynthetic capacity (P max ) approached 0.05 mg C. (mg chl a) - 1 h -1. Onset of photosynthesis saturation, E k , was found at c. 14 mu mol photons m - 1 s -1. The irradiance of photoinhibition onset, E inh , was c. 20 mu mol photons m - 2 s -1 and the irradiance at the compensationpoint, E c , was 4 mu mol photons m -2 s -1. [ABSTRACT FROM AUTHOR]