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In recent years, the Southern Ocean has experienced unprecedented surface warming and sea ice loss-a stark reversal of the sea ice expansion and surface cooling that prevailed over the preceding decades. Here, we examine the mechanisms that led to the abrupt circumpolar surface warming events that occurred in late 2016 and 2019 and assess the role of internal climate variability. A mixed layer heat budget analysis reveals that these recent circumpolar surface warming events were triggered by a weakening of the circumpolar westerlies, which decreased northward Ekman transport and accelerated the seasonal shoaling of the mixed layer. We emphasize the underappreciated effect of the latter mechanism, which played a dominant role and amplified the warming effect of air-sea heat fluxes during months of peak solar insolation. An examination of the CESM1 large ensemble demonstrates that these recent circumpolar warming events are consistent with the internal variability associated with the Southern Annular Mode (SAM), whereby negative SAM in austral spring favors shallower mixed layers and anomalously high summertime SST. A key insight from this analysis is that the seasonal phasing of springtime mixed layer depth shoaling is an important contributor to summertime SST variability in the Southern Ocean. Thus, future Southern Ocean summertime SST extremes will depend on the coevolution of mixed layer depth and surface wind variability. [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]

CCAMLR can use its management mandate to protect krill-dependent predators, including baleen whales, from adverse interactions with the krill fishery (Meyer et al., [11]). Within this multispecies aggregation of krill predators there were also four commercial krill vessels actively harvesting krill (Figure 1B). Prior to krill fishing, whales and phytoplankton blooms were often spatially separated perhaps due to local top-down control of phytoplankton by krill grazing (Hardy, [6]). Industrial krill harvesting in direct competition with foraging fin whales is concerning because the regional abundance of fin whales and krill remains far below the prewhaling baseline. [Extracted from the article]

Increasing melt of ice sheets at their floating or vertical interfaces with the ocean is a major driver of marine ice sheet retreat and sea level rise. However, the extent to which warm, salty seawater may drive melting under the grounded portions of ice sheets is still not well understood. Previous work has explored the possibility that dense seawater intrudes beneath relatively light subglacial freshwater discharge, similar to the "salt wedge" observed in many estuarine systems. In this study, we develop a generalized theory of layered seawater intrusion under grounded ice, including where subglacial hydrology occurs as a macroporous water sheet over impermeable beds or as microporous Darcy flow through permeable till. Using predictions from this theory, we show that seawater intrusion over flat or reverse-sloping impermeable beds may feasibly occur up to tens of kilometers upstream of a glacier terminus or grounding line. On the other hand, seawater is unlikely to intrude more than tens of meters through permeable till. Simulations using the Ice-sheet and Sea-level System Model (ISSM) show that even just a few hundred meters of basal melt caused by seawater intrusion upstream of marine ice sheet grounding lines can cause projections of marine ice sheet volume loss to be 10 %–50 % higher. Kilometers of intrusion-induced basal melt can cause projected ice sheet volume loss to more than double. These results suggest that further observational, experimental and numerical investigations are needed to determine the conditions under which seawater intrusion occurs and whether it will indeed drive rapid marine ice sheet retreat and sea level rise in the future. [ABSTRACT FROM AUTHOR]

The subpolar gyres of the Southern Ocean form an important dynamical link between the Antarctic Circumpolar Current (ACC) and the coastline of Antarctica. Despite their key involvement in the production and export of bottom water and the poleward transport of oceanic heat, these gyres are rarely acknowledged in conceptual models of the Southern Ocean circulation, which tend to focus on the zonally averaged overturning across the ACC. To isolate the effect of these gyres on the regional circulation, we carried out a set of numerical simulations with idealized representations of the Weddell Sea sector in the Southern Ocean. A key result is that the zonally oriented submarine ridge along the northern periphery of the subpolar gyre plays a fundamental role in setting the stratification and circulation across the entire region. In addition to sharpening and strengthening the horizontal circulation of the gyre, the zonal ridge establishes a strong meridional density front that separates the weakly stratified subpolar gyre from the more stratified circumpolar flow. Critically, the formation of this front shifts the latitudinal outcrop position of certain deep isopycnals such that they experience different buoyancy forcing at the surface. Additionally, the zonal ridge modifies the mechanisms by which heat is transported poleward by the ocean, favoring heat transport by transient eddies while suppressing that by stationary eddies. This study highlights the need to characterize how bathymetry at the subpolar gyre–ACC boundary may constrain the transient response of the regional circulation to changes in surface forcing. Significance Statement: This study explores the impact of seafloor bathymetry on the dynamics of subpolar gyres in the Southern Ocean. The subpolar gyres are major circulation features that connect the Antarctic Circumpolar Current (ACC) and the coastline of Antarctica. This work provides deeper insight for how the submarine ridges that exist along the northern periphery of these gyres shape the vertical distribution of tracers and overturning circulation in these regions. These findings highlight an underappreciated yet fundamentally important topographical constraint on the three-dimensional cycling of heat and carbon in the Southern Ocean—processes that have far-reaching implications for the global climate. Future work should explore how the presence of these ridges affect the time-evolving response of the Southern Ocean to changes in surface conditions. [ABSTRACT FROM AUTHOR]

Southern Ocean sea ice plays a central role in the oceanic meridional overturning circulation, transforming globally prevalent watermasses through surface buoyancy loss and gain. Buoyancy loss due to surface cooling and sea ice growth promotes the formation of bottom water that flows into the Atlantic, Indian, and Pacific basins, while buoyancy gain due to sea ice melt helps transform the returning deep flow into intermediate and mode waters. Because northward expansion of Southern Ocean sea ice during the Last Glacial Maximum (LGM; 19–23 kyr BP) may have enhanced deep ocean stratification and contributed to lower atmospheric CO2 levels, reconstructions of sea ice extent are critical to understanding the LGM climate state. Here, we present a new sea ice proxy based on the 18O/16O ratio of foraminifera (δ18Oc). In the seasonal sea ice zone, sea ice formation during austral winter creates a cold surface mixed layer that persists in the sub‐surface during spring and summer. The cold sub‐surface layer, known as winter water, sits above relatively warm deep water, creating an inverted temperature profile. The unique surface‐to‐deep temperature contrast is reflected in estimates of equilibrium δ18Oc, implying that paired analysis of planktonic and benthic foraminifera can be used to infer sea ice extent. To demonstrate the feasibility of the δ18Oc method, we present a compilation of N. pachyderma and Cibicidoides spp. results from the Atlantic sector that yields an estimate of winter sea ice extent consistent with modern observations. Plain Language Summary: Sea ice coverage in the Southern Ocean plays a critical role in Earth's climate system by influencing ocean‐atmosphere gas exchange and the global ocean circulation. While satellite observations provide detailed information on sea ice cover in the modern era, the satellite record is only a few decades in duration, limiting our long‐term perspective. An improved understanding of sea ice requires reconstructions in the geologic past under climate conditions different than today. Here, we propose a new technique for reconstructing sea ice extent in the Southern Ocean based on the 18O/16O ratio (δ18Oc) of foraminifera. The δ18Oc of foraminifera is sensitive to temperature and it can therefore be used to infer areas of surface cooling where sea ice tends to form and warmer areas where sea ice melts. We present an initial compilation of data showing that the δ18Oc method yields an estimate of modern sea ice extent consistent with satellite observations, highlighting the potential of the δ;18Oc method for paleoclimate studies. Key Points: Southern Ocean winter water and sea ice extent can be reconstructed using the oxygen isotopic composition of planktonic and benthic foraminiferaSummertime calcification of the planktonic foraminifer N. pachyderma likely occurs in sub‐surface winter waterPreliminary sea ice reconstruction for the late Holocene is consistent with satellite‐base estimates in the Atlantic sector of the Southern Ocean [ABSTRACT FROM AUTHOR]

In cold polar waters, temperatures sometimes drop below the freezing point, a process referred to as supercooling. However, observational challenges in polar regions limit our understanding of the spatial and temporal extent of this phenomenon. We here provide observational evidence that supercooled waters are much more widespread in the seasonally ice‐covered Southern Ocean than previously reported. In 5.8% of all analyzed hydrographic profiles south of 55°S, we find temperatures below the surface freezing point ("potential" supercooling), and half of these have temperatures below the local freezing point ("in situ" supercooling). Their occurrence doubles when neglecting measurement uncertainties. We attribute deep coastal‐ocean supercooling to melting of Antarctic ice shelves and surface‐induced supercooling in the seasonal sea‐ice region to wintertime sea‐ice formation. The latter supercooling type can extend down to the permanent pycnocline due to convective sinking plumes—an important mechanism for vertical tracer transport and water‐mass structure in the polar ocean. Plain Language Summary: Ocean water, which contains about 34 grams of salt per kilogram of seawater, generally freezes around −1.85°C. However, seawater can be cooled to even lower temperatures without turning into ice. This phenomenon is called supercooling. Supercooled water is found in the polar oceans, typically in regions where the ocean is in contact with ice, as is the case for the enormous seasonal sea‐ice region around Antarctica. But collecting measurements in this region under the thick ice cover during the dark and cold Antarctic winter is challenging. Here, we supplement rather sparse traditional ship‐based observations with data collected by autonomous floats and instrumented marine mammals to detect and analyze where, when, and how supercooled seawater forms in the Southern Ocean. We find widespread supercooling related to melting floating glaciers (ice shelves) along the Antarctic coast and sea‐ice formation. Our analysis enables us to detect sinking supercooled plumes from sea‐ice formation, which may be important for cooling the deep ocean and transporting constituents such as carbon, nutrients, or oxygen from the ocean's surface to deeper layers. Key Points: Potential and in situ supercooling occurs in large parts of the Southern Ocean seasonal sea‐ice zoneDeep coastal supercooling from below 100 m to the ocean bottom is associated with melting ice shelves and dense shelf water formationShallow supercooling is associated with sea‐ice formation and can penetrate as deep as the permanent pycnocline [ABSTRACT FROM AUTHOR]

Marine-terminating glaciers, such as those along the coastline of Greenland, often release meltwater into the ocean in the form of subglacial discharge plumes. Though these plumes can dramatically alter the mass loss along the front of a glacier, the conditions surrounding their genesis remain poorly constrained. In particular, little is known about the geometry of subglacial outlets and the extent to which seawater may intrude into them. Here, the latter is addressed by exploring the dynamics of an arrested salt wedge – a steady-state, two-layer flow system where salty water partially intrudes a channel carrying fresh water. Building on existing theory, we formulate a model that predicts the length of a non-entraining salt wedge as a function of the Froude number, the slope of the channel and coefficients for interfacial and wall drag. In conjunction, a series of laboratory experiments were conducted to observe a salt wedge within a rectangular channel. For experiments conducted with laminar flow (Reynolds number $Re), good agreement with theoretical predictions are obtained when the drag coefficients are modelled as being inversely proportional to $Re$. However, for fully turbulent flows on geophysical scales, these drag coefficients are expected to asymptote toward finite values. Adopting reasonable drag coefficient estimates for this flow regime, our theoretical model suggests that typical subglacial channels may permit seawater intrusions of the order of several kilometres. While crude, these results indicate that the ocean has a strong tendency to penetrate subglacial channels and potentially undercut the face of marine-terminating glaciers. [ABSTRACT FROM AUTHOR]

In this study, under-ice ocean data from profiling floats, instrumented seals, and shipboard casts are used to assess wintertime upper-ocean stability and heat availability in the sea ice–covered Southern Ocean. This analysis reveals that the southern Weddell Sea, which features a weak upper-ocean stratification and relatively strong thermocline, is preconditioned for exceptionally high rates of winter ventilation. This preconditioning also facilitates a strong negative feedback to winter ice growth. Idealized experiments with a 1D ice–ocean model show that the entrainment of heat into the mixed layer of this region can maintain a near-constant ice thickness over much of winter. However, this quasi-equilibrium is attained when the pycnocline is thin and supports a large temperature gradient. We find that the surface stress imparted by a powerful storm may upset this balance and lead to substantial ice melt. This response can be greatly amplified when coincident with anomalous thermocline shoaling. In more strongly stratified regions, such as near the sea ice edge of the major gyres, winter ice growth is weakly limited by the entrainment of heat into the mixed layer. Thus, the thermodynamic coupling between winter sea ice growth and ocean ventilation has significant regional variability. This regionality will influence the response of the Southern Ocean ice–ocean system to future changes in ocean stratification and surface forcing. [ABSTRACT FROM AUTHOR]

During each summer monsoon, the Bay of Bengal is inundated by a large amount of rain and river discharge. The effects of this freshening are gradually reversed over the course of the year, with near-surface salinities typically returning to their presummer monsoon levels before the start of the next rainy season. While the forcing responsible for the summertime freshening is clear, the processes that act to restore the bay's salinity are not well understood. To examine these processes, the authors construct a basin-integrated, near-surface, seasonal salinity budget using data-assimilated output from the Hybrid Coordinate Ocean Model (HYCOM). From this salinity budget, it is deduced that vertical salt fluxes are primarily responsible for counterbalancing the near-surface freshening caused by the summertime freshwater fluxes. These vertical salt fluxes are largest during the months that immediately follow the summer monsoon, when the near-surface halocline is strongest. These results must be tempered with the knowledge that HYCOM misrepresents some key features of the bay's salinity field. In particular, the model tends to overestimate salinity along the East Indian Coastal Current during its equatorward phase. Notwithstanding these biases, these results still suggest that vertical processes have a prominent role in the bay's near-surface salinity budget. [ABSTRACT FROM AUTHOR]

In this paper, reflection and the scholarship of integration are used to highlight, using a recent example of an internally-funded project, how the University of Technology, Jamaica is embracing a paradigm shift by capturing for commercial exploitation by industry the value that inheres in research results. The role of the university's research management office as a helpful intermediary, the lessons learnt, and the "pathway to impact" - where evidence of the translation of research into impacts is usually manifested - of the cited example are also discussed. It is concluded that taking the results of this research project from "lab to market" holds extremely important lessons for other researchers at UTech, Jamaica, students of the university, and the wider Jamaican society in that the actions taken together represent a "live" demonstration of the process of converting science into tangible value that has income-earning potential (i.e., "capitalization of science"). [ABSTRACT FROM AUTHOR]

This paper addresses a problem associated with Solar Powered Adsorption Cooling (SPAC) systems. The problem is the difficulty in knowing if the complete charcoal bed reaches desorption temperature during the isosteric heating process. In addressing the issue, the process is modeled and the results are compared with those from experiments. The temperature-profile modelling of the isosteric-heating-process establishes a time-related formulation that gives the temperature, at any radius, across a cylindrical shaped bed comprising of charcoal/methanol pair of adsorbent/adsorbate; and the results from modelling compare favorably with the measured temperature-profiles obtained from the experiments. [ABSTRACT FROM AUTHOR]