Ice Shelf Basal Melt Research Articles

Subglacial discharge accelerates future retreat of Denman and Scott Glaciers, East Antarctica.

Ice shelf basal melting is the primary mechanism driving mass loss from the Antarctic Ice Sheet, yet it is unknown how the localized melt enhancement from subglacial discharge will affect future Antarctic glacial retreat. We develop a parameterization of ice shelf basal melt that accounts for both ocean and subglacial discharge forcing and apply it in future projections of Denman and Scott Glaciers, East Antarctica, through 2300. In forward simulations, subglacial discharge accelerates the onset of retreat of these systems into the deepest continental trench on Earth by 25 years. During this retreat, Denman Glacier alone contributes 0.33 millimeters per year to global sea level rise, comparable to half of the contemporary sea level contribution of the entire Antarctic Ice Sheet. Our results stress the importance of resolving complex interactions between the ice, ocean, and subglacial environments in future Antarctic Ice Sheet projections.

Ice Shelf Water Structure Beneath the Larsen C Ice Shelf in Antarctica

AbstractUnderstanding 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).

High‐Resolution Simulations of the Plume Dynamics in an Idealized 79°N Glacier Cavity Using Adaptive Vertical Coordinates

AbstractFor better projections of sea level rise, two things are needed: an improved understanding of the contributing processes and their accurate representation in climate models. A major process is basal melting of ice shelves and glacier tongues by the ocean, which reduces ice sheet stability and increases ice discharge into the ocean. We study marine melting of Greenland's largest floating ice tongue, the 79° North Glacier, using a high‐resolution, 2D‐vertical ocean model. While our fjord model is idealized, the results agree with observations of melt rate and overturning strength. Our setup is the first application of adaptive vertical coordinates to an ice cavity. Their stratification‐zooming allows a vertical resolution finer than 1 m in the entrainment layer of the meltwater plume, which is important for the plume development. We find that the plume development is dominated by entrainment only initially. In the stratified upper part of the cavity, the subglacial plume shows continuous detrainment. It reaches neutral buoyancy near 100 m depth, detaches from the ice, and transports meltwater out of the fjord. Melting almost stops there. In a sensitivity study, we show that the detachment depth depends primarily on stratification. Our results contribute to the understanding of ice–ocean interactions in glacier cavities. Furthermore, we suggest that our modeling approach with stratification‐zooming coordinates will improve the representation of these interactions in global ocean models. Finally, our idealized model topography and forcing are close to a real fjord and completely defined analytically, making the setup an interesting reference case for future model developments.

A Regime Shift on Weddell Sea Continental Shelves with Local and Remote Physical and Biogeochemical Implications is Avoidable in a 2°C Scenario

Abstract Tipping points in the Earth system describe critical thresholds beyond which a single component, part of the system, or the system as a whole changes from one stable state to another. In the present-day Southern Ocean, the Weddell Sea constitutes an important dense-water formation site, associated with efficient deep-ocean carbon and oxygen transfer and low ice-shelf basal melt rates. Here, a regime shift will occur when continental shelves are continuously flushed with warm, oxygen-poor offshore waters from intermediate depth, leading to less efficient deep-ocean carbon and oxygen transfer and higher ice-shelf basal melt rates. We use a global ocean–biogeochemistry model including ice-shelf cavities and an eddy-permitting grid in the southern Weddell Sea to address the susceptibility of this region to such a system change for four twenty-first-century emission scenarios. Assessing the projected changes in shelf–open-ocean density gradients, bottom-water properties, and on-shelf heat transport, our results indicate that the Weddell Sea undergoes a regime shift by 2100 in the highest-emission scenario, SSP5–8.5, but not yet in the lower-emission scenarios. The regime shift is imminent by 2100 in the scenarios SSP3–7.0 and SSP2–4.5, but avoidable under the lowest-emission scenario SSP1–2.6. While shelf-bottom waters freshen and acidify everywhere, bottom waters in the Filchner Trough undergo accelerated warming and deoxygenation following the system change, with implications for local ecosystems and ice-shelf basal melt. Additionally, deep-ocean carbon and oxygen transfer decline, implying that the local changes ultimately affect ocean circulation, climate, and ecosystems globally.

Future Response of Antarctic Continental Shelf Temperatures to Ice Shelf Basal Melting and Calving

AbstractWe investigate feedbacks between subsurface continental shelf ocean temperatures and Antarctic glacial melt using a coupled climate model. The model was forced with SSP5‐8.5 and an uncoupled projection of basal melt and calving fluxes. SSP5‐8.5 forcing with fixed pre‐industrial glacial melt warms all continental shelves, such that historically “cool” and “fresh” shelves transition to “warm.” Additional glacial melt, added at depth, cools the Eastern Ross, Amundsen, and Bellingshausen seas, suggesting a negative feedback on basal melt—a novel result for a coarse resolution coupled model. From the Weddell Sea, along East Antarctica, and into the western Ross Sea—where continental shelves transition to a “warm” state—additional glacial melt increases temperatures at the continental shelf sea floor, suggesting a positive feedback. The sign of the glacial melt–subsurface temperature feedback is critically dependent on continental shelf properties, climate state, and the vertical distribution of glacial melt inputs.

Unveiling spatial variability within the Dotson Melt Channel through high-resolution basal melt rates from the Reference Elevation Model of Antarctica

Abstract. The intrusion of Circumpolar Deep Water in the Amundsen and Bellingshausen Sea embayments of Antarctica causes ice shelves in the region to melt from below, potentially putting their stability at risk. Earlier studies have shown how digital elevation models can be used to obtain ice shelf basal melt rates at a high spatial resolution. However, there has been limited availability of high-resolution elevation data, a gap the Reference Elevation Model of Antarctica (REMA) has filled. In this study we use a novel combination of REMA and CryoSat-2 elevation data to obtain high-resolution basal melt rates of the Dotson Ice Shelf in a Lagrangian framework, at a 50 m spatial posting on a 3-yearly temporal resolution. We present a novel method: Basal melt rates Using REMA and Google Earth Engine (BURGEE). The high resolution of BURGEE is supported through a sensitivity study of the Lagrangian displacement. The high-resolution basal melt rates show a good agreement with an earlier basal melt product based on CryoSat-2. Both products show a wide melt channel extending from the grounding line to the ice front, but our high-resolution product indicates that the pathway and spatial variability of this channel is influenced by a pinning point on the ice shelf. This result emphasizes the importance of high-resolution basal melt rates to expand our understanding of channel formation and melt patterns. BURGEE can be expanded to a pan-Antarctic study of high-resolution basal melt rates. This will provide a better picture of the (in)stability of Antarctic ice shelves.

Modelling Antarctic ice shelf basal melt patterns using the one-layer Antarctic model for dynamical downscaling of ice–ocean exchanges (LADDIE v1.0)

Abstract. A major source of uncertainty in future sea level projections is the ocean-driven basal melt of Antarctic ice shelves. While ice sheet models require a kilometre-scale resolution to realistically resolve ice shelf stability and grounding line migration, global or regional 3D ocean models are computationally too expensive to produce basal melt forcing fields at this resolution on long timescales. To bridge this resolution gap, we introduce the 2D numerical model LADDIE (one-layer Antarctic model for dynamical downscaling of ice–ocean exchanges), which allows for the computationally efficient modelling of detailed basal melt fields. The model is open source and can be applied easily to different geometries or different ocean forcings. The aim of this study is threefold: to introduce the model to the community, to demonstrate its application and performance in two use cases, and to describe and interpret new basal melt patterns simulated by this model. The two use cases are the small Crosson–Dotson Ice Shelf in the warm Amundsen Sea region and the large Filchner–Ronne Ice Shelf in the cold Weddell Sea. At ice-shelf-wide scales, LADDIE reproduces observed patterns of basal melting and freezing in warm and cold environments without the need to re-tune parameters for individual ice shelves. At scales of 0.5–5 km, which are typically unresolved by 3D ocean models and poorly constrained by observations, LADDIE produces plausible basal melt patterns. Most significantly, the simulated basal melt patterns are physically consistent with the applied ice shelf topography. These patterns are governed by the topographic steering and Coriolis deflection of meltwater flows, two processes that are poorly represented in basal melt parameterisations. The kilometre-scale melt patterns simulated by LADDIE include enhanced melt rates in grounding zones and basal channels and enhanced melt or freezing in shear margins. As these regions are critical for ice shelf stability, we conclude that LADDIE can provide detailed basal melt patterns at the essential resolution that ice sheet models require. The physical consistency between the applied geometry and the simulated basal melt fields indicates that LADDIE can play a valuable role in the development of coupled ice–ocean modelling.

Subglacial Freshwater Drainage Increases Simulated Basal Melt of the Totten Ice Shelf

AbstractSubglacial freshwater discharge from beneath Antarctic glaciers likely has a strong impact on ice shelf basal melting. However, the difficulty in directly observing subglacial flow highlights the importance of modeling these processes. We use an ocean model of the Totten Ice Shelf cavity into which we inject subglacial discharge derived from a hydrology model applied to Aurora Subglacial Basin. Our results show (a) discharge increases melting in the vicinity of the outflow region, which correlates with features observed in surface elevation maps and satellite‐derived melt maps, with implications for ice shelf stability; (b) the change in melting is driven by the formation of a buoyant plume rather than the addition of heat; and (c) the buoyant plume originating from subglacial discharge‐driven melting is far‐reaching. Basal melting induced by subglacial hydrology is thus important for ice shelf stability, but is absent from almost all ice‐ocean models.

Influence of Shelf Break Processes on the Transport of Warm Waters Onto the Eastern Amundsen Sea Continental Shelf

AbstractThe heat transported onto the continental shelf by Circumpolar Deep Water (CDW) is the main driver of ice shelf basal melting in the Amundsen Sea. Here, we investigate the slope current system and the variability of the heat transported through the Pine Island‐Thwaites central and eastern troughs using data from five moorings deployed in the region between 5 March 2012 and 7 February 2016. Substantial variability on intermonthly time scales (3–4 months) is observed in the onshore heat flux, driven primarily by zonal wind stress north of the shelf break. Heat content, onshore flow, and heat flux are highly correlated between central and eastern troughs, which are most likely dynamically linked by the zonal wind stress forcing. This is the first time this dynamic link between troughs is observed. In the eastern the Amundsen Sea, during the El Niño of 2015/2016, strong eastward winds led to lower temperatures over the continental shelf while the onshore heat flux is intensified. We hypothesize that this anti‐correlation between heat content and heat flux results from a strengthened eastward undercurrent leading to upwelling of a colder and deeper CDW variety. These results highlight the complex and heterogeneous response of this region to environmental and the importance of velocity data for understanding the dynamics in this region. It also suggests that the hypothesized link between large‐scale atmospheric forcing (e.g., El Niño‐Southern Oscillation) and ice‐shelf melt is not produced via changes in heat content, but instead via changes in onshore heat flux.

Sensitivity of simulated water mass transformation on the Antarctic shelf to tides, topography and model resolution

Water mass transformation (WMT) around the Antarctic margin controls Antarctica Bottom Water formation and the abyssal limb of the global meridional overturning circulation, besides mediating ocean-ice shelf exchange, ice sheet stability and its contribution to sea level rise. However, the mechanisms controlling the rate of WMT in the Antarctic shelf are poorly understood due to the lack of observations and the inability of climate models to simulate those mechanisms, in particular beneath the floating ice shelves. We used a circum-Antarctic ocean-ice shelf model to assess the contribution of surface fluxes, mixing, and ocean-ice shelf interaction to the WMT on the continental shelf. The salt budget dominates the WMT rates, with only a secondary contribution from the heat budget. Basal melt of ice shelves drives buoyancy gain at lighter density classes (27.2<σθ< 27.6 kg m-3), while salt input associated with sea-ice growth in coastal polynyas drives buoyancy loss at heavier densities (σθ> 27.6). We found a large sensitivity of the WMT rates to model horizontal resolution, tides and topography within the Filchner-Ronne, East and West Antarctica ice shelf cavities. In the Filchner-Ronne Ice Shelf, an anticyclonic circulation in front of the Ronne Depression regulates the rates of basal melting/refreezing and WMT and is substantially affected by tides and model resolution. Model resolution is also found to affect the Antarctic Slope Current in both East and West Antarctica, impacting the on-shelf heat delivery, basal melt and WMT. Moreover, the representation of the ice shelf draft associated with model resolution impacts the freezing temperature and thus basal melt and WMT rates in the East Antarctica. These results highlight the importance of resolving small-scale features of the flow and topography, and to include the effects of tidal forcing, to adequately represent water mass transformations on the shelf that directly influence the abyssal global overturning circulation.

Ice Shelf Basal Melt Sensitivity to Tide‐Induced Mixing Based on the Theory of Subglacial Plumes

AbstractTidal currents are known to influence basal melting of Antarctic ice shelves through two types of mechanisms: local processes taking place within the boundary current adjacent to the ice shelf‐ocean interface and far‐field processes influencing the properties of water masses within the cavity. The separate effects of these processes are poorly understood, limiting our ability to parameterize tide‐driven ice shelf‐ocean interactions. Here we focus on the small‐scale processes within the boundary current. We apply a one‐dimensional plume model to a range of ice base geometries characteristic of Antarctic ice shelves to study the sensitivity of basal melt rates to different representations of tide‐driven turbulent mixing processes. Our simulations demonstrate that tides can either increase or decrease melt rates depending on the approach chosen to parameterize entrainment of ambient water into the turbulent plume layer, a process not yet well constrained by observations. A theoretical assessment based on an analogy with tidal bottom boundary layers suggests that tide‐driven shear at the ice shelf‐ocean interface enhances mixing through the pycnocline. Under this assumption our simulations predict a tide‐induced increase in melt and freeze rates along the base of the ice shelf, with the strongest plume path‐integrated effects for cold cavities (up to +400% in the realistic set up). An approximation is provided to account for this response in basal melt rate parameterizations that neglect the effect of tide‐induced turbulent mixing.

Ocean–Ice Sheet Coupling in the Totten Glacier Area, East Antarctica: Analysis of the Feedbacks and Their Response to a Sudden Ocean Warming

We coupled together high-resolution versions of the ocean–sea ice model NEMO and the ice sheet model BISICLES configured to the Totten Glacier area and ran a series of simulations over the recent past (1995–2014) and under warming conditions (2081–2100; SSP4-4.5) with NEMO in stand-alone mode and with the coupled model to assess the effects of the coupling. During the recent past, the ocean–ice sheet coupling has increased the time-averaged value of the basal melt rate in both the Totten and Moscow University ice shelf cavities by 6.7% and 14.2%, respectively. The relationship between the changes in ice shelf thickness and ice shelf basal melt rate suggests that the effect of the coupling is not a linear response to the melt rate but rather a more complex response, driven partly by the dynamical component of the ice sheet model. The response of the ice sheet–ocean coupling due to the ocean warming is a 10% and 3% basal melt rate decrease in the Totten and Moscow University ice shelf cavities, respectively. This indicates that the ocean–ice sheet coupling under climate warming conditions dampens the basal melt rates. Our study highlights the importance of incorporating ocean–ice sheet coupling in climate simulations, even over short time periods.

Range of 21st century ice mass changes in the Filchner-Ronne region of Antarctica

AbstractIncreases in ocean temperatures in the Filchner Ronne region of Antarctica are likely to result in increased ice mass loss and sea level rise. We constrain projections of the 21st century sea level contribution of this region using process-based ice-sheet modeling, with model parameters controlling ice dynamics calibrated using observed surface speeds and Markov-chain Monte Carlo sampling. We use climate forcing from Representative Concentration Pathway (RCP) scenarios as well as a set of hypothetical scenarios of deep ocean warming to evaluate the sensitivity of this region to ocean temperatures. Projected changes in regional ice mass correspond to a decrease in global mean sea level of 24±7 mm over 2015–2100 under RCP 2.6 and 28±9 mm under RCP 8.5. Increased regional inland surface accumulation related to higher warming levels in RCP 8.5 leads to more ice above flotation, offsetting increased ice shelf basal melt. The tests involving step changes in ocean temperatures with constant surface forcing show that one degree of ocean warming from present results in an additional +11 mm contribution to sea level by 2100 and 1% of the ice-covered area in the domain becomes ungrounded (23 200 km2). The rate of mass loss with temperature increases at higher temperatures.

Seasonal variations in Circumpolar Deep Water intrusions into the Ross Sea continental shelf

Intrusions of the warm and nutrient-rich Circumpolar Deep Water (CDW) across the Ross Sea shelf break play an important role in providing heat for ice shelf basal melting and setting the physical environment for biochemical processes. Several mechanisms driving CDW intrusions into the Ross Sea were proposed such as mesoscale eddies, tidal rectification, and interactions between the Antarctic Slope Current (ASC) and topographic features. The seasonal variations in the poleward transport of CDW are investigated using ERA-Interim wind data and a Ross Sea circulation model based on the Regional Ocean Modeling System (ROMS) between September 1999 and September 2014. The analyses focus on the currents along the shelf break and deep troughs on the Ross Sea shelf and discuss the wind-driven Ekman pumping in both shelf and adjacent open ocean regions. The results reveal that the poleward intrusions generally move up onto the continental shelf along the eastern flanks of deep troughs. Seasonal variations of the ocean surface stress torque exerted by wind and sea ice in the off-shelf area are correlated with CDW intrusions. The maxima of CDW intrusions usually occur in austral summer. There is a significant temporal correlation on the seasonal time scale between the on-shelf intrusions in deep troughs in the western Ross Sea shelf and poleward Sverdrup transports in the adjacent off-shelf open ocean driven by the Ekman pumping. The analysis of ocean surface stress fields also indicates that the vorticity fluxes through the Ekman pumping are in favor of southward and northward transports in the eastern and western parts of the Ross Sea, respectively. The relationships between currents, CDW intrusions, and ocean surface stress fields imply the importance of air–sea interactions and potential climate change to the environment in the Ross Sea.

Suppressed basal melting in the eastern Thwaites Glacier grounding zone

Thwaites Glacier is one of the fastest-changing ice–ocean systems in Antarctica1–3. Much of the ice sheet within the catchment of Thwaites Glacier is grounded below sea level on bedrock that deepens inland4, making it susceptible to rapid and irreversible ice loss that could raise the global sea level by more than half a metre2,3,5. The rate and extent of ice loss, and whether it proceeds irreversibly, are set by the ocean conditions and basal melting within the grounding-zone region where Thwaites Glacier first goes afloat3,6, both of which are largely unknown. Here we show—using observations from a hot-water-drilled access hole—that the grounding zone of Thwaites Eastern Ice Shelf (TEIS) is characterized by a warm and highly stable water column with temperatures substantially higher than the in situ freezing point. Despite these warm conditions, low current speeds and strong density stratification in the ice–ocean boundary layer actively restrict the vertical mixing of heat towards the ice base7,8, resulting in strongly suppressed basal melting. Our results demonstrate that the canonical model of ice-shelf basal melting used to generate sea-level projections cannot reproduce observed melt rates beneath this critically important glacier, and that rapid and possibly unstable grounding-line retreat may be associated with relatively modest basal melt rates.

Antarctic Sea Ice Holds the Fate of Antarctic Ice-Shelf Basal Melting in a Warming Climate

Abstract Changes in the Antarctic ice sheet play a critical role in the Southern Ocean and global climates. Although many studies have pointed out that enhanced ocean heat delivery onto the Antarctic continental shelf regions can cause significant changes in Antarctic ice-shelf basal melting, the associated physical mechanisms require further research. Here, we perform numerical experiments using an ocean–sea ice model with an ice-shelf component to simulate future projections in Antarctic ice-shelf basal melting in a warming climate, focusing on the driving mechanism and the physical linkages with the seasonal Antarctic sea ice fields and coastal water masses. The model projects a distinct superlinear response of ice-shelf basal melting to future atmospheric warming, demonstrating that future projections of the Antarctic and Southern Ocean climate bifurcate with the level of global warming. Detailed examinations of sea ice and water masses show that in an extreme warming scenario, a combination of enhanced intrusions of warm deep water and warm summertime surface water can cause the nonlinear response of Antarctic ice-shelf basal melting. A large reduction in Antarctic coastal sea ice and the associated ocean freshening by decreasing coastal sea ice production in winter provide favorable conditions for summertime warm surface water formation and warm deep water intrusions onto some continental shelves. The model results demonstrate that disappearing summertime sea ice along the Antarctic coastal margins in a warming climate heralds the nonlinear increase in Antarctic ice-shelf basal melting, presumably contributing to the negative mass balance of the Antarctic ice sheet and the sea level rise.

Sensitivity of the Relationship Between Antarctic Ice Shelves and Iron Supply to Projected Changes in the Atmospheric Forcing

AbstractUpward advection or mixing of iron‐rich deep waters due to circulation changes driven by the rate of basal ice shelf melt was shown to be a primary control on chlorophyll a production in coastal polynyas over the Antarctic continental shelf. Here, the effects of atmospheric changes projected in 2100 on this relationship were examined with a 5‐km resolution ocean/sea ice/ice shelf model of the Southern Ocean with different simulated dissolved iron sources and idealized biological uptake. The atmospheric changes are added as idealized increments to the forcing. Inclusion of a poleward shift and strengthening of the winds, increased precipitation, and warmer atmospheric temperatures resulted in doubling of the heat advected onto the continental shelf and an 83% increase in the total Antarctic ice shelf basal melt. The total dissolved iron supply to the surface waters over the continental shelf increased by 62%, while the surface iron supply due just to basal melt driven overturning increased by 48%. However, even though the ice shelf driven contribution becomes less important to the total iron supply on average (29% of total), the ice shelf involvement becomes relatively even more important in some locations, such as the Amundsen and Bellingshausen Seas. The modified atmospheric conditions also produced a reduction in summer sea ice extent and a shoaling of the summer mixed layers. These simulated responses to projected changes suggest relief of light and nutrient limitation for phytoplankton blooms over the Antarctic continental shelf and perhaps an increase in annual production in years to come.

Antarctic contribution to future sea level from ice shelf basal melt as constrained by ice discharge observations

Abstract. Antarctic mass loss is the largest contributor to uncertainties in sea level projections on centennial time scales. In this study we aim to constrain future projections of the contribution of Antarctic dynamics by using ice discharge observations. The contribution of Antarctica's ice discharge is computed with ocean thermal forcing from 14 Earth system models (ESMs) and linear response functions (RFs) from 16 ice sheet models for 3 shared socioeconomic pathway (SSP) scenarios. New compared to previous studies, basal melt sensitivities to ocean temperature changes were calibrated on four decades of observed ice discharge changes rather than using observation-based basal melt sensitivities. Calibration improved historical performance but did not reduce the uncertainty in the projections. The results show that even with calibration the acceleration during the observational period is underestimated for the Amundsen Region, indicating that ice and/or ocean processes are not well represented. Also the relative contribution of the Amundsen Region is underestimated. The Amundsen Region contribution and sea level acceleration are improved by choosing an Amundsen Region-specific calibration (rather than Antarctic-wide), quadratic basal melt parameterisation (rather than linear) and thermal forcing near the ice shelf base (rather than the deepest layer above the continental shelf). With these methodological choices we arrive at a median dynamic sea level contribution of 0.12 m for SSP1-2.6, 0.14 m for SSP2-4.5 and 0.17 m for SSP5-8.5 in 2100 relative to 1995–2014, sitting in between projections of previous multimodel studies (ISMIP6 emulator and LARMIP-2). Our results show that constraining the basal melt parameterisation on Amundsen Region ice discharge rather than applying the median basal melt sensitivities used in LARMIP-2 and the mean Antarctic distribution of ISMIP6 leads to higher sea level contributions. However, differences in basal melt sensitivities alone cannot explain the differences in our projections compared to the emulated ISMIP6 and LARMIP-2. We conclude that uncertainties associated with ESMs and ice sheet models affect the projected sea level contribution more than our methodological choices in the calibration and basal melt computation.

On the Multiscale Oceanic Heat Transports Toward the Bases of the Antarctic Ice Shelves

The mass balance of the Antarctic Ice Sheet (AIS) is important to global sea-level change. The AIS loses mass mainly through basal melting and subsequent calving of the Antarctic ice shelves. However, the simulated basal melting rates are very uncertain in ice sheet models, partially resulting from the poor understanding of oceanic heat transports. In this article, we review the recent progress in understanding and simulating such heat transports. Regulated by major circulation features, Circumpolar Deep Water (CDW) is much closer to the Bellingshausen–Amundsen Seas and the Cooperation Sea (60°E to 90°E) and the sector further east to 160°E. The ice shelves within these sectors are experiencing enhanced basal melting resulting from tropical forcing and intensified westerlies. Around West Antarctica, the isopycnal structure favors the delivery of CDW across slopes and shelves, while around East Antarctica, the persistent and strong westward Antarctic Slope Current (Front) acts to prevent warm-water intrusion. Both eddies and troughs favor heat transport to the fronts of the ice shelves and even into the cavities. The sharp contrast between the water column thicknesses on both sides of ice shelf fronts blocks the barotropic inflows and can excite topographic Rossby waves. Inside the cavities, the heat fluxes to the bases of the ice shelves are controlled by the cavity geometry, the circulations in the cavities, and the properties of the water masses beneath the ice shelves. Limited direct observations of cavities have promoted the development of various models. To improve basal melting simulations, meltwater plume models have been developed to study meltwater-laden mixed layer dynamics by increasing the vertical resolution, with recent advanced studies considering the vertical structures of frazil ice concentration and velocity. To reduce the uncertainties in the simulated and projected basal mass loss of the Antarctic ice shelves, future efforts should be devoted to improving the bathymetry and cavity geometry, investigating small-scale processes and parameterizing these processes in coupled climate–ice sheet models, and quantifying the feedback from the mass loss of the AIS.

Observed Tidal Currents in Prydz Bay and Their Contribution to the Amery Ice Shelf Basal Melting

Tides play a key role in regulating the circulation and water properties around Antarctica, yet tidal currents and the corresponding influences in Prydz Bay have not been quantified with observational datasets. This study focuses on the observed characteristics of tidal currents and quantifies the tidal contribution to the basal melting of the Amery Ice Shelf (AIS). Long-term hydrography observations are provided by 10 moorings over the continental shelf and 6 borehole sites drilled through the AIS. Based on the mooring observations, we analyze the observed tidal currents, and evident seasonality in the mixed diurnal–semidiurnal tidal currents is identified. Barotropic tides dominate the tidal currents at the AIS front, except at the western corner where the seabed is abruptly deeper. The spatially and temporally averaged magnitude of tidal currents for all the current meter records is only ~3 cm s −1 . However, an observed maximum tidal velocity of ~11 cm s −1 occurs at the AIS front, and the maximal time-averaged tidal kinetic energy reaches ~31% of the total kinetic energy over the outer continental shelf. Based on the borehole observations, tide-like pulsing is identified in the ocean layer adjacent to the AIS basal surface. The maximal tidal contribution of the AIS basal melting is estimated at 69% based on a simple model. Due to the paucity of long-term velocity observations in the sub-ice-shelf cavity, the uncertainties of the estimated tide-induced melting in this study could be attributed to the simulated velocity.