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Ice shelf dynamics and morphology play an important role in the stability of floating bodies of ice by driving fracturing that can lead to calving, in turn impacting the ability of the ice shelf to buttress upstream grounded ice. Following a 2016 calving event at the Nansen Ice Shelf (NIS), East Antarctica, we collected airborne and ground-based radar data to map ice thickness across the shelf. We combine these data with published satellite-derived data to examine the spatial variations in ice shelf draft, the cause and effects of ice shelf strain rates, and the possibility that a suture zone may be channelizing ocean water and altering patterns of sub-ice-shelf melt and freeze-on. We also use our datasets to assess limitations that may arise from relying on hydrostatic-balance equations applied to ice surface elevation to determine ice draft morphology. We find that the Nansen Ice Shelf has a highly variable basal morphology driven primarily by the formation of basal fractures near the onset of the ice shelf suture zone. This morphology is reflected in the ice shelf strain rates but not in the calculated hydrostatic-balance thickness, which underestimates the scale of variability at the ice shelf base. Enhanced melt rates near the ice shelf terminus and in steep regions of the channelized suture zone, along with relatively thin ice in the suture zone, appear to represent vulnerable areas in the NIS. This morphology, combined with ice dynamics, induce strain that has led to the formation of transverse fractures within the suture zone, resulting in large-scale calving events. Similar transverse fractures at other Antarctic ice shelves may also be driven by highly variable morphology, and predicting their formation and evolution could aid projections of ice shelf stability. [ABSTRACT FROM AUTHOR]

Understanding the foraging behavior of marine animals is crucial for assessing their ecological significance and responses to environmental changes. In the context of Antarctica, marine animals face rapid and profound environmental changes related with global warming. However, our understanding of their responses remains limited owing to the formidable challenges inherent in conducting observations, particularly during the harsh austral winter months. In this study, we investigated the influence of changes in seawater properties and light conditions on the seasonal foraging behavior of Weddell seals (Leptonychotes weddellii) in the Ross Sea, Antarctica. We affixed 35 Weddell seals with CTD tags to record their locations and dive profiles, including depth, head acceleration, temperature, and salinity. We found that seals foraged more frequently in modified shelf water and ice shelf water compared to Antarctic surface water. This preference could be connected to greater food availability. Additionally, seals also dove to greater depths and displayed increased activity in capturing prey during daylight hours. This behavior may correspond to the diel vertical migration of pelagic prey in response to varying light conditions. Our findings suggest that Weddell seals have adjusted their foraging behaviors to adapt to spatial and temporal changes in oceanographic conditions. This highlights the importance of extrinsic factors in estimating their seasonal foraging behavior. [ABSTRACT FROM AUTHOR]

Understanding ice shelf water (ISW) structure is crucial for studying the basal melting of ice shelves. In this study, we performed large‐eddy simulation experiments to assess ISW structure and basal melt patterns under different current velocity scenarios observed in the Larsen C ice shelf, Antarctica. The LES results revealed that the thickness of ISW is primarily determined by the meridional velocity (perpendicular to the grounding line), while the zonal velocity influences the potential temperature and salinity of ISW. We found that a key parameter determining the basal melt rate was northward meltwater advection which originates from variances in meltwater generation. This advection, in turn, leads to the tilted isopycnals and the potential for thermohaline interleaving in a diffusive convection regime. The different slopes of isopycnals induce distinct heat fluxes, resulting in different basal melt rates far from and near the grounding line (∼0.44 and 1.59 m yr−1, respectively). Plain Language Summary: The loss of ice mass from the Antarctic ice sheet is accelerating, posing a threat to human lives through global sea level rise. Understanding ice shelf water (ISW), which refers to seawater below freezing temperature, is crucial as it directly or indirectly influences basal ice melting. However, direct observations are extremely challenging, leaving this understanding unclear. To tackle this issue, we utilized a numerical model to gain insight into the fundamental characteristics of ISW. We demonstrated that the direction and magnitude of ocean currents beneath the ice shelf play a significant role in determining the thickness and properties of ISW. Moreover, the key factor in basal melting was the northward movement of meltwater from intense ice melting regions near the grounding line. This movement determined the spatial distribution of ocean temperature and salinity. The horizontal gradient of ocean temperature and salinity induces mixing and horizontal intrusion. Interestingly, these mixing and intrusion phenomena occur in opposite directions, resulting in a wiggling pattern in the velocity profile. The main findings of our study will contribute to the formulation of a parameterization for basal melting, which can be incorporated into large‐scale ocean models or ice sheet dynamics models. Key Points: Direction and magnitude of ocean currents beneath an Larsen C ice shelf affect the ice shelf water thickness and propertiesNorthward meltwater advection causes 0.052°C difference of thermal drivings with different melt rates far from and near the grounding lineOcean heat intrusion to ice shelf base is induced by Ekman dynamics and thermohaline interleaving by tilted isopycnals [ABSTRACT FROM AUTHOR]

Ice melting beneath Antarctic ice shelves is caused by heat transfer through the ice-shelf–ocean boundary layer (IOBL). However, our understanding of the fluid dynamics and thermohaline physics of the IOBL flow is poor. In this study, we utilize a large-eddy simulation (LES) model to investigate ocean dynamics and the role of turbulence within the IOBL flow near the ice front. To simulate the varying turbulence intensities, we imposed different theoretical profiles of the velocity. Far-field ocean conditions for the melting at the ice-shelf base and freezing at the sea surface were derived based on in situ observations of temperature and salinity near the ice front of the Nansen Ice Shelf. In terms of overturning features near the ice front, we validated the LES simulation results by comparing them with the in situ observational data. In the comparison of the velocity profiles to shipborne lowered acoustic Doppler current profiler (LADCP) data, the LES-derived strength of the overturning cells is similar to that obtained from the observational data. Moreover, the vertical distribution of the simulated temperature and salinity, which were mainly determined by the positively buoyant meltwater and sea-ice formation, was also comparable to that of the observations. We conclude that the IOBL flow near the ice front and its contribution to the ocean dynamics can be realistically resolved using our proposed method. Based on validated 3D-LES results, we revealed that the main forces of ocean dynamics near the ice front are driven by positively buoyant meltwater, concentrated salinity at the sea surface, and outflowing momentum of the sub-ice-shelf plume. Moreover, in the strong-turbulence case, distinct features such as a higher basal melt rate (0.153 m yr -1), weak upwelling of the positively buoyant ice-shelf water, and a higher sea-ice formation were observed, suggesting a relatively high speed current within the IOBL because of highly turbulent mixing. The findings of this study will contribute toward a deeper understanding of the complex IOBL-flow physics and its impact on the ocean dynamics near the ice front. [ABSTRACT FROM AUTHOR]

Pine Island Ice Shelf (PIIS) buttresses the Pine Island Glacier, the key contributor to sea-level rise. PIIS has thinned owing to ocean-driven melting, and its calving front has retreated, leading to buttressing loss. PIIS melting depends primarily on the thermocline variability in its front. Furthermore, local ocean circulation shifts adjust heat transport within Pine Island Bay (PIB), yet oceanic processes underlying the ice front retreat remain unclear. Here, we report a PIB double-gyre that moves with the PIIS calving front and hypothesise that it controls ocean heat input towards PIIS. Glacial melt generates cyclonic and anticyclonic gyres near and off PIIS, and meltwater outflows converge into the anticyclonic gyre with a deep-convex-downward thermocline. The double-gyre migrated eastward as the calving front retreated, placing the anticyclonic gyre over a shallow seafloor ridge, reducing the ocean heat input towards PIIS. Reconfigurations of meltwater-driven gyres associated with moving ice boundaries might be crucial in modulating ocean heat delivery to glacial ice. Glacial melt can modify heat transport, and therefore ocean processes, associated with ice front retreat, as revealed by direct observations from the Pine Island Bay region of Antarctica. [ABSTRACT FROM AUTHOR]

Antarctica's Getz Ice Shelf has been rapidly thinning in recent years, producing more meltwater than any other ice shelf in the world. The influx of fresh water is known to substantially influence ocean circulation and biological productivity, but relatively little is known about the factors controlling basal melt rate or how basal melt is spatially distributed beneath the ice shelf. Also unknown is the relative importance of subglacial discharge from the grounded ice sheet in contributing to the export of fresh water from the ice shelf cavity. Here we compare the observed spatial distribution of basal melt rate to a new sub-ice-shelf bathymetry map inferred from airborne gravity surveys and to locations of subglacial discharge from the grounded ice sheet. We find that melt rates are high where bathymetric troughs provide a pathway for warm Circumpolar Deep Water to enter the ice shelf cavity and that melting is enhanced where subglacial discharge fresh water flows across the grounding line. This is the first study to address the relative importance of meltwater production of the Getz Ice Shelf from both ocean and subglacial sources. [ABSTRACT FROM AUTHOR]

Supra- and sub-glacial meltwater drainage becomes widespread in Antarctica, but its contribution to regional water masses has not been thoroughly quantified. For a better understanding of physical-chemical fractionations, we employ water isotopes (δ18O, δD) as practical tracers for hydrological researches. During the Antarctic summer expeditions (2014/15, 2015/16, 2016/17, and 2017/18) conducted by Korea Polar Research Institute, we sampled seawater performed with CTD casts in the Terra Nova Bay, Western Ross Sea. Picarro L2301-i CRDS is used for water isotope analysis, and preliminary results represent that sampled glacial meltwater contains both terrestrial meltwater and fresh water from ice shelf basal melting. The relationship of δ18O and δD shows the slope value around less than 7 (P1: δD=6.74×δ18O-0.02), however, the glacial meltwater shows the value around 8 (P1:δD=7.69×δ18 O+0.41). Water isotope differentiated presenting various values relative to given salinity. The various values of water isotopes imply other differentiation factors like evaporation and sea ice formation occurred. [ABSTRACT FROM AUTHOR]

We describe the first year-long hydrographic mooring timeseries from a location just to the south of the Drygalski Ice Tongue – the ice margin that forms the southern boundary of the Terra Nova Bay Polynya in the western Ross Sea. The region is where any northward flowing component of the Victoria Land Coastal Current encounters the ice tongue and supports an occasional polynya. The hydrographic mooring was deployed nearby Geikie Inlet from February 2017 through to March 2018, and was coupled with several contemporaneous oceanographic moorings to the north of the Drygalski Ice Tongue. This provides data with which to examine the water column dynamics in the context of local circulation and interaction with the ice tongue. The Terra Nova Bay region is subject to strong katabatic winds, however the polynya to the south of the Drygalski Ice Tongue operates at different times through the annual cycle when compared to the Terra Nova Bay Polynya to the north, as the sea ice in the south-side region is far more constrained in its motion yet, temperature and salinity are broadly consistent north and south of the ice tongue. Sub-surface Ice Shelf Water is observed south of the ice tongue. Transients in near-bed temperature and salinity are observed on both sides of the ice tongue, albeit with the northside leading by ∼8–9 days. Notably, the temperature transient precedes that of salinity by around 40 days. This suggests that, at this near-coastal position, the circulation beneath the ice tongue is primarily southward. [ABSTRACT FROM AUTHOR]

A part of the Southern Ocean, the Ross Sea, together with the Ross Ice Shelf and the atmosphere over the region represent a coupled system with respect to the low-frequency (with the periods longer than 1 hour) wave processes observed in the three media. We study interconnections between them using a unique combination of geophysical sensors: hydrophones measuring pressure variations on the bottom of the open ocean, seismographs measuring vertical displacements of the surface of the Ross Ice Shelf, and the Jang Bogo Dynasonde system measuring wave parameters at the altitudes of the lower thermosphere. Analysis of a year-long data sets from Ross Ice Shelf-based instruments reveals presence in their average power spectra of the peaks in the 2-11 hours period range that may be associated with the low-order resonance vibrations of the system. More harmonics of the 24 hour tide (seven) are detected by the RIS seismographs compared to the sea floor sensor (where only two are clearly visible). This may be a consequence of the RIS resonance-related broadband amplification effect predicted by our model. There are several peaks in the RIS vibration spectrum (T = 8.37, 8.23, 6.3 and 6.12 hours) that are not detected by the hydrophone and may be directly related to RIS resonances. The prominent T = 25.81 hour peak is a likely candidate for the sub-inertial RIS resonance. The periods of lower RIS resonance modes predicted by our simple model and the observed spectral peaks are in the same general band. This is the first direct observation of the resonance effects in vibrations of the Ross Ice Shelf. Our results demonstrate the key role of the resonances of the Ross Ice Shelf in maintaining the wave activity in the entire coupled system. We suggest that the ocean tide is a major source of excitation of the Ross Ice Shelf's resonances. The ice shelf vibrations may also be supported by the energy transfer from wind, swell, and infragravity wave energy that couples with the ice shelf. Overlapping 6-month-long data sets reveal a significant linear correlation between the spectra of the vertical shifts of the Ross Ice Shelf and of the thermospheric waves with the periods of about 2.1, 3.7, and 11.1 hours. This result corroborates earlier lidar observations of persistent atmospheric wave activity over McMurdo. We propose a theory that quantifies the nexus between the ocean tide and the resonance vibrations of the Ross Ice Shelf. It complements the theoretical model of the process of generating the atmospheric waves by the resonance vibrations of the Ross Ice Shelf published by us earlier. [ABSTRACT FROM AUTHOR]