Sea Glacier Research Articles

Characteristics and rarity of the strong 1940s westerly wind event over the Amundsen Sea, West Antarctica

Abstract. Glaciers in the Amundsen Sea Embayment of West Antarctica are rapidly retreating and contributing to sea level rise. Ice loss is occurring primarily via exposure to warm ocean water, which varies in response to local wind variability. There is evidence that retreat was initiated in the mid-20th century, but the perturbation that may have triggered retreat remains unknown. A leading hypothesis is that large pressure and wind anomalies in the 1940s drove exceptionally strong oceanic ice-shelf melting. However, the characteristics, drivers, and rarity of the atmospheric event remain poorly constrained. We investigate the 1940s atmospheric event using paleoclimate reconstructions and climate model simulations. The reconstructions show that large westerly wind anomalies occurred from ∼1938–1942, a combined response to the very large El Niño event from 1940–1942 and other variability beginning years earlier. Climate model simulations provide evidence that events of similar magnitude and duration may occur tens to hundreds of times per 10 kyr of internal climate variability (∼0.2 to 2.5 occurrences per century). Our results suggest that the 1940s westerly event is unlikely to have been exceptional enough to be the sole explanation for the initiation of Amundsen Sea glacier retreat. Additional factors are likely needed to explain the onset of retreat in West Antarctica, such as naturally arising variability in ocean conditions prior to the 1940s or anthropogenically driven trends since the 1940s.

The stability of present-day Antarctic grounding lines – Part 2: Onset of irreversible retreat of Amundsen Sea glaciers under current climate on centennial timescales cannot be excluded

Abstract. Observations of ocean-driven grounding-line retreat in the Amundsen Sea Embayment in Antarctica raise the question of an imminent collapse of the West Antarctic Ice Sheet. Here we analyse the committed evolution of Antarctic grounding lines under the present-day climate. To this aim, we first calibrate a sub-shelf melt parameterization, which is derived from an ocean box model, with observed and modelled melt sensitivities to ocean temperature changes, making it suitable for present-day simulations and future sea level projections. Using the new calibration, we run an ensemble of historical simulations from 1850 to 2015 with a state-of-the-art ice sheet model to create model instances of possible present-day ice sheet configurations. Then, we extend the simulations for another 10 000 years to investigate their evolution under constant present-day climate forcing and bathymetry. We test for reversibility of grounding-line movement in the case that large-scale retreat occurs. In the Amundsen Sea Embayment we find irreversible retreat of the Thwaites Glacier for all our parameter combinations and irreversible retreat of the Pine Island Glacier for some admissible parameter combinations. Importantly, an irreversible collapse in the Amundsen Sea Embayment sector is initiated at the earliest between 300 and 500 years in our simulations and is not inevitable yet – as also shown in our companion paper (Part 1, Hill et al., 2023). In other words, the region has not tipped yet. With the assumption of constant present-day climate, the collapse evolves on millennial timescales, with a maximum rate of 0.9 mm a−1 sea-level-equivalent ice volume loss. The contribution to sea level by 2300 is limited to 8 cm with a maximum rate of 0.4 mm a−1 sea-level-equivalent ice volume loss. Furthermore, when allowing ice shelves to regrow to their present geometry, we find that large-scale grounding-line retreat into marine basins upstream of the Filchner–Ronne Ice Shelf and the western Siple Coast is reversible. Other grounding lines remain close to their current positions in all configurations under present-day climate.

The potential for stabilizing Amundsen Sea glaciers via underwater curtains.

Rapid sea level rise due to an ice sheet collapse has the potential to be extremely damaging the coastal communities and infrastructure. Blocking deep warm water with thin flexible buoyant underwater curtains may reduce melting of buttressing ice shelves and thereby slow the rate of sea level rise. Here, we use new multibeam bathymetric datasets, combined with a cost-benefit model, to evaluate potential curtain routes in the Amundsen Sea. We organize potential curtain routes along a "difficulty ladder" representing an implementation pathway that might be followed as technological capabilities improve. The first curtain blocks a single narrow (5 km) submarine choke point that represents the primary warm water inflow route towards western Thwaites Glacier, the most vulnerable part of the most vulnerable glacier in Antarctica. Later curtains cross larger and deeper swaths of seabed, thus increasing their cost, while also protecting more of the ice sheet, increasing their benefit. In our simple cost-benefit analysis, all of the curtain routes achieve their peak value at target blocking depths between 500 and 550 m. The favorable cost-benefit ratios of these curtain routes, along with the trans-generational and societal equity of preserving the ice sheets near their present state, argue for increased research into buoyant curtains as a means of ice sheet preservation, including high-resolution fluid-structural and oceanographic modeling of deep water flow over and through the curtains, and coupled ice-ocean modeling of the dynamic response of the ice sheet.

Sea-glacier retreating rate and climate evolution during the marine deglaciation of a snowball Earth

During the Neoproterozoic snowball Earth events, the climate was cold and the oceans were covered by marine ice of ~1000 m thick (sea glacier). Extremely high CO 2 level was required in order to trigger the deglaciation these events. It is unclear how long it would take for the sea-ice cover to be completely ablated after the deglaciation started, and what the physical state of the ocean looked like. Here we use a fully coupled general circulation model, CCSM3, to evaluate the rate of poleward retreating of the marine ice and estimate an upper-bound timescale for the marine deglaciation. It is found that the deglaciation will take at most ~300 to 1500 years, depending on the surface albedo of ice; as the albedo decreases, the deglaciation will be prolonged due to the lower CO 2 level required to start the deglaciation. Such fast calving/melting of sea ice allows a fresh water lid of ~800 m to develop at the end of the deglaciation. • The sea-glacier retreating of snowball Earth is studied using a climate model • The complete ablation of the thick marine ice takes at most ~300 yr to 1500 yr • The elapsed time is longer if the sea-ice albedo is lowered, e.g., by dust • A fresh water lid of hundreds of meters thick would form upon completion

Maximum extent and readvance dynamics of the Irish Sea Ice Stream and Irish Sea Glacier since the Last Glacial Maximum

ABSTRACTThe BRITICE‐CHRONO Project has generated a suite of recently published radiocarbon ages from deglacial sequences offshore in the Celtic and Irish seas and terrestrial cosmogenic nuclide and optically stimulated luminescence ages from adjacent onshore sites. All published data are integrated here with new geochronological data from Wales in a revised Bayesian analysis that enables reconstruction of ice retreat dynamics across the basin. Patterns and changes in the pace of deglaciation are conditioned more by topographic constraints and internal ice dynamics than by external controls. The data indicate a major but rapid and very short‐lived extensive thin ice advance of the Irish Sea Ice Stream (ISIS) more than 300 km south of St George's Channel to a marine calving margin at the shelf break at 25.5 ka; this may have been preceded by extensive ice accumulation plugging the constriction of St George's Channel. The release event between 25 and 26 ka is interpreted to have stimulated fast ice streaming and diverted ice to the west in the northern Irish Sea into the main axis of the marine ISIS away from terrestrial ice terminating in the English Midlands, a process initiating ice stagnation and the formation of an extensive dead ice landscape in the Midlands.

How Should Snowball Earth Deglaciation Start

AbstractThe formation of melt ponds is pervasive on sea ice and ice shelves prior to their disintegration. Such process should be critical for the deglaciation of a snowball Earth but has never been considered in previous studies. Here we develop a module to explicitly track the initiation, growth and refreezing of melt ponds on ice. Incorporation of the module into a climate model indicates that it provides a strong positive feedback to the climate. Deglaciation of a snowball Earth will start when the annual mean equatorial surface temperature is only −7.7°C rather than 0°C. At this point, seasonal melt ponds start to appear in the mid‐latitude region. Its positive feedback induces the appearance of perennial melt ponds within the equatorial region and can increase the annual mean temperature there to 6.1°C in less than 10 years. Thus, our results indicate that the threshold CO2 required to deglaciate a snowball Earth will be greatly overestimated (by a factor of ∼4 for the model we use) if the annual mean surface temperature reaching 0°C is used as the criteria. The results also demonstrate unambiguously that the deglaciation of snowball Earth should start from the equator. We then speculate on what will happen to the tropical sea glacier after the surface melting starts.

Kinematics of global mean thermosteric sea level during 1993–2019

Abstract Because oceans cover 71% of Earth’s surface, ocean warming, consequential for thermal expansion of sea water, has been the largest contributor to the global mean sea level rise averaged over the 20 th and the early 21 st century. This study first generates quasi-observed monthly globally averaged thermosteric sea level time series by removing the contributions of global mean sea level budget components, namely, Glaciers, Greenland, Antarctica, and Terrestrial Water Storage from satellite altimetry measured global sea level changes during 1993–2019. A baseline kinematic model with global mean thermosteric sea level trend and a uniform acceleration is solved to evaluate the performance of a rigorous mixed kinematic model. The model also includes coefficients of monthly lagged 60 yearlong cumulative global mean sea surface temperature gradients and control variables of lunisolar origins and representations for first order autoregressive disturbances. The mixed kinematic model explains 94% (Adjusted R 2)1 of the total variability in quasi-observed monthly and globally averaged thermosteric time series compared to the 46% of the baseline kinematic model’s Adjusted R 2. The estimated trend, 1.19±0.03 mm/yr., is attributed to the long-term ocean warming. Whereas eleven statistically significant (α = 0.05) monthly lagged cumulative global mean sea surface temperature gradients each having a memory of 60 years explain the remainder transient global mean thermosteric sea level changes due to the episodic ocean surface warming and cooling during this period. The series also exhibit signatures of a statistically significant contingent uniform global sea level acceleration and periodic lunisolar forcings.

The evolution of the terrestrial‐terminating Irish Sea glacier during the last glaciation

ABSTRACTHere we reconstruct the last advance to maximum limits and retreat of the Irish Sea Glacier (ISG), the only land‐terminating ice lobe of the western British Irish Ice Sheet. A series of reverse bedrock slopes rendered proglacial lakes endemic, forming time‐transgressive moraine‐ and bedrock‐dammed basins that evolved with ice marginal retreat. Combining, for the first time on glacial sediments, optically stimulated luminescence (OSL) bleaching profiles for cobbles with single grain and small aliquot OSL measurements on sands, has produced a coherent chronology from these heterogeneously bleached samples. This chronology constrains what is globally an early build‐up of ice during late Marine Isotope Stage 3 and Greenland Stadial (GS) 5, with ice margins reaching south Lancashire by 30 ± 1.2 ka, followed by a 120‐km advance at 28.3 ± 1.4 ka reaching its 26.5 ± 1.1 ka maximum extent during GS‐3. Early retreat during GS‐3 reflects piracy of ice sources shared with the Irish‐Sea Ice Stream (ISIS), starving the ISG. With ISG retreat, an opportunistic readvance of Welsh ice during GS‐2 rode over the ISG moraines occupying the space vacated, with ice margins oscillating within a substantial glacial over‐deepening. Our geomorphological chronosequence shows a glacial system forced by climate but mediated by piracy of ice sources shared with the ISIS, changing flow regimes and fronting environments.

Interannual variability of summer surface mass balance and surface melting in the Amundsen sector, West Antarctica

Abstract. Understanding the interannual variability of surface mass balance (SMB) and surface melting in Antarctica is key to quantify the signal-to-noise ratio in climate trends, identify opportunities for multi-year climate predictions and assess the ability of climate models to respond to climate variability. Here we simulate summer SMB and surface melting from 1979 to 2017 using the Regional Atmosphere Model (MAR) at 10 km resolution over the drainage basins of the Amundsen Sea glaciers in West Antarctica. Our simulations reproduce the mean present-day climate in terms of near-surface temperature (mean overestimation of 0.10 ∘C), near-surface wind speed (mean underestimation of 0.42 m s−1), and SMB (relative bias <20 % over Thwaites glacier). The simulated interannual variability of SMB and melting is also close to observation-based estimates. For all the Amundsen glacial drainage basins, the interannual variability of summer SMB and surface melting is driven by two distinct mechanisms: high summer SMB tends to occur when the Amundsen Sea Low (ASL) is shifted southward and westward, while high summer melt rates tend to occur when ASL is shallower (i.e. anticyclonic anomaly). Both mechanisms create a northerly flow anomaly that increases moisture convergence and cloud cover over the Amundsen Sea and therefore favors snowfall and downward longwave radiation over the ice sheet. The part of interannual summer SMB variance explained by the ASL longitudinal migrations increases westward and reaches 40 % for Getz. Interannual variation in the ASL relative central pressure is the largest driver of melt rate variability, with 11 % to 21 % of explained variance (increasing westward). While high summer SMB and melt rates are both favored by positive phases of El Niño–Southern Oscillation (ENSO), the Southern Oscillation Index (SOI) only explains 5 % to 16 % of SMB or melt rate interannual variance in our simulations, with moderate statistical significance. However, the part explained by SOI in the previous austral winter is greater, suggesting that at least a part of the ENSO–SMB and ENSO–melt relationships in summer is inherited from the previous austral winter. Possible mechanisms involve sea ice advection from the Ross Sea and intrusions of circumpolar deep water combined with melt-induced ocean overturning circulation in ice shelf cavities. Finally, we do not find any correlation with the Southern Annular Mode (SAM) in summer.

Big Time

The Proterozoic Eon was once regarded as the neglected middle half of Earth history. The name refers to early animals, but they did not appear until the eon (2.5–0.54 Ga) was nearly over. Eukaryotic cells and sexual reproduction evolved much earlier in the eon, as did chloroplasts. Molecular dioxygen, the presence of which altered the geochemical behavior of nearly every element essential to life, rose from negligible to near-modern levels, and then plummeted before rising fitfully again. Plate tectonics took on a modern form, and two supercontinents, Nuna and Rodinia, successively congregated and later dispersed. Climate regulatory failures, i.e., Snowball Earth, appear to be a uniquely Proterozoic phenomenon, having occurred twice in rapid succession near the end of the eon (from 717 to 660 Ma and from 650 to 635 Ma) and arguably once near its beginning (ca. 2.43 Ga). Dynamic sea glaciers covered Snowball Earth oceans from pole to pole, and equatorial sublimation drove slow-moving ice sheets on land. Ultimately, the gradual accumulation of CO2 triggered rapid deglaciation and transient greenhouse aftermaths. Physically based and geologically tested, Neoproterozoic Snowball Earth appears to have molecular legacies in ancient bitumens and modern organisms. This is the story of my love affair with an eon that is now a little less neglected.

Estimating the mass change of mountain glacier using a novel method based on InSAR observations

Melting glaciers have a direct contribution to sea level rise, runoff and glacier lake outburst flood disasters. Therefore, accurate estimations of glacier mass balances with high spatial (large region) and temporal (annual, seasonal) resolutions are very important. However, the estimation of glacial mass balances in mountainous regions is usually hampered by remoteness and the lack of high-precision topographic data for most mountain ranges. This study presents a novel method for estimating mass changes in mountain glaciers using InSAR data. We utilised observations of glacier surface deformation to derive changes in thickness, and then calculated the mass change. This method can accurately estimate short-term mass changes. We apply this method to the Koxkar glacier in the Tien Shan Mountain Range in China and successfully estimate the seasonal mass change. Using theoretical error and statistical error analysis, we determined that the accuracy of this method is much better than other geodetic methods. We analyse the spatial characteristics of the mass changes in the ablation zone for the first time. The results show considerable spatial and seasonal variability, which were mainly from ablation in the summer, with the greatest amount of glacial ablation reaching up to − 3872 mm water equivalent (w.e.), and from accumulation in the winter.

Snowball Earth: Asynchronous coupling of sea‐glacier flow with a global climate model

AbstractDuring Snowball Earth episodes of the Neoproterozoic and Paleoproterozoic, limited amounts of tropical open ocean (Jormungand), or tropical ocean with thin ice cover, would help to explain (1) vigorous glacial activity in low latitudes, (2) survival of photosynthetic life, and (3) deglacial recovery without excessive buildup of atmospheric CO2. Some previous models have suggested that tropical open ocean or thin‐ice cover is possible; however, its viability in the presence of kilometer‐thick sea glaciers flowing from higher latitudes has not been demonstrated conclusively. Here we describe a new method of asynchronously coupling a zonal sea‐glacier model with a 3‐D global climate model and apply it to Snowball Earth. Equilibrium curves of ice line versus CO2 are mapped out, as well as their dependence on ocean heat transport efficiency, sea‐glacier flow, and other model parameters. No climate states with limited tropical open ocean or thin ice are found in any of our model runs, including those with sea glaciers. If this result is correct, then other refugia such as cryoconite pans would have been required for life to survive. However, the reasons for the differences between our results and others should first be resolved. It is suggested that small‐scale convective dynamics, affecting fractional snow cover in low latitudes, may be a critical factor accounting for these differences.

Could promontories have restricted sea-glacier penetration into marine embayments during Snowball Earth events?

Abstract. During the Neoproterozoic (∼ 1000–550 Ma), Earth experienced several climate excursions of extreme cold, often referred to as the Snowball Earth events. During these periods, thick flowing ice, referred to as sea glaciers, covered the entire planet's oceans. In addition, there is evidence that photosynthetic eukaryotic algae survived during these periods. With thick sea glaciers covering the oceans, it is uncertain where these organisms survived. One hypothesis is that these algae survived in marine embayments hydrologically connected to the global ocean, where the flow of sea glacier could be resisted. In order for an embayment to act as a refugium, the invading sea glacier must not completely penetrate the embayment. Recent studies have shown that straight-sided marine embayments could have prevented full sea-glacier penetration under a narrow range of climate conditions suitable for the Snowball Earth events. Here we test whether promontories, i.e., headlands emerging from a side shoreline, could further restrict sea-glacier flow. We use an ice-flow model, suitable for floating ice, to determine the flow of an invading sea glacier. We show that promontories can expand the range of climate conditions allowing refugia by resisting the flow of invading sea glaciers.

A conceptual model of oceanic heat transport in the Snowball Earth scenario

Abstract. Geologic evidence suggests that the Earth may have been completely covered in ice in the distant past, a state known as Snowball Earth. This is still the subject of controversy, and has been the focus of modeling work from low-dimensional models up to state-of-the-art general circulation models. In our present global climate, the ocean plays a large role in redistributing heat from the equatorial regions to high latitudes, and as an important part of the global heat budget, its role in the initiation a Snowball Earth, and the subsequent climate, is of great interest. To better understand the role of oceanic heat transport in the initiation of Snowball Earth, and the resulting global ice covered climate state, the goal of this inquiry is twofold: we wish to propose the least complex model that can capture the Snowball Earth scenario as well as the present-day climate with partial ice cover, and we want to determine the relative importance of oceanic heat transport. To do this, we develop a simple model, incorporating thermohaline dynamics from traditional box ocean models, a radiative balance from energy balance models, and the more contemporary "sea glacier" model to account for viscous flow effects of extremely thick sea ice. The resulting model, consisting of dynamic ocean and ice components, is able to reproduce both Snowball Earth and present-day conditions through reasonable changes in forcing parameters. We find that including or neglecting oceanic heat transport may lead to vastly different global climate states, and also that the parameterization of under-ice heat transfer in the ice–ocean coupling plays a key role in the resulting global climate state, demonstrating the regulatory effect of dynamic ocean heat transport.

Cryoconite pans on Snowball Earth: supraglacial oases for Cryogenian eukaryotes?

Geochemical, paleomagnetic, and geochronological data increasingly support the Snowball Earth hypothesis for Cryogenian glaciations. Yet, the fossil record reveals no clear-cut evolutionary bottleneck. Climate models and the modern cryobiosphere offer insights on this paradox. Recent modeling implies that Snowball continents never lacked ice-free areas. Wind-blown dust from these areas plus volcanic ash were trapped by snow on ice sheets and sea ice. At a Snowball onset, sea ice was too thin to flow and ablative ice was too cold for dust retention. After a few millenia, sea ice reached 100s of meters in thickness and began to flow as a 'sea glacier' toward an equatorial ablation zone. At first, dust advected to the ablative surface was recycled by winds, but as the surface warmed with rising CO2 , dust aka cryoconite began to accumulate. As a sea glacier has no terminus, cryoconite saturated the surface. It absorbed solar radiation, supported cyanobacterial growth, and sank to an equilibrium depth forming holes and decameter-scale pans of meltwater. As meltwater production rose, drainages developed, connecting pans to moulins, where meltwater was flushed into the subglacial ocean. Flushing cleansed the surface, creating a stabilizing feedback. If the dust flux rose, cryoconite was removed; if the dust flux waned, cryoconite accumulated. In addition to cyanobacteria, modern cryoconite holes are inhabited by green algae, fungi, protists, and certain metazoans. On Snowball Earth, cryoconite pans provided stable interconnected habitats for eukaryotes tolerant of fresh to brackish cold water on an ablation surface 60millionkm2 in area. Flushing and burial of organic matter was a potential source of atmospheric oxygen. Dominance of green algae among Ediacaran eukaryotic primary producers is a possible legacy of Cryogenian cryoconite pans, but a schizohaline ocean-supraglacial freshwater and subglacial brine-may have exerted selective stress on early metazoans, or impeded their evolution.

Effects of bubbles, cracks, and volcanic tephra on the spectral albedo of bare ice near the Transantarctic Mountains: Implications for sea glaciers on Snowball Earth

Spectral albedo was measured along a 6 km transect near the Allan Hills in East Antarctica. The transect traversed the sequence from new snow through old snow, firn, and white ice, to blue ice, showing a systematic progression of decreasing albedo at all wavelengths, as well as decreasing specific surface area (SSA) and increasing density. Broadband albedos under clear‐sky range from 0.80 for snow to 0.57 for blue ice, and from 0.87 to 0.65 under cloud. Both air bubbles and cracks scatter sunlight; their contributions to SSA were determined by microcomputed tomography on core samples of the ice. Although albedo is governed primarily by the SSA (and secondarily by the shape) of bubbles or snow grains, albedo also correlates highly with porosity, which, as a proxy variable, would be easier for ice sheet models to predict than bubble sizes. Albedo parameterizations are therefore developed as a function of density for three broad wavelength bands commonly used in general circulation models: visible, near‐infrared, and total solar. Relevance to Snowball Earth events derives from the likelihood that sublimation of equatorward‐flowing sea glaciers during those events progressively exposed the same sequence of surface materials that we measured at Allan Hills, with our short 6 km transect representing a transect across many degrees of latitude on the Snowball ocean. At the equator of Snowball Earth, climate models predict thick ice, or thin ice, or open water, depending largely on their albedo parameterizations; our measured albedos appear to be within the range that favors ice hundreds of meters thick.

Robust elements of Snowball Earth atmospheric circulation and oases for life

Atmospheric circulation in a Snowball Earth is critical for determining cloud behavior, heat export from the tropics, regions of bare ice, and sea glacier flow. These processes strongly affect Snowball Earth deglaciation and the ability of oases to support photosynthetic marine life throughout a Snowball Earth. Here we establish robust aspects of the Snowball Earth atmospheric circulation by running six general circulation models with consistent Snowball Earth boundary conditions. The models produce qualitatively similar patterns of atmospheric circulation and precipitation minus evaporation. The strength of the Snowball Hadley circulation is roughly double modern at low CO2 and greatly increases as CO2 is increased. We force a 1‒D axisymmetric sea glacier model with general circulation model (GCM) output and show that, neglecting zonal asymmetry, sea glaciers would limit ice thickness variations to (10%). Global mean ice thickness in the 1‒D sea glacier model is well‒approximated by a 0‒D ice thickness model with global mean surface temperature as the upper boundary condition. We then show that a thin‒ice Snowball solution is possible in the axysymmetric sea glacier model when forced by output from all the GCMs if we use ice optical properties that favor the thin‒ice solution. Finally, we examine Snowball oases for life using analytical models forced by the GCM output and find that conditions become more favorable for oases as the Snowball warms, so that the most critical time for the survival of life would be near the beginning of a Snowball Earth episode.

Oceanographic observations at the shelf break of the Amundsen Sea, Antarctica

The glaciers draining into the Amundsen Sea Embayment are rapidly losing mass, making a significant contribution to current sea level rise. Studies of Pine Island Glacier (PIG) in this region indicate that the mass loss is associated with rapid melting of its floating ice shelf driven by warm Circumpolar Deep Water (CDW) that is able to penetrate all the way to its grounding line, and that recent intensification of the mass loss is associated with higher melt rates and stronger subice‐shelf circulation. CDW is sourced from within the Antarctic Circumpolar Current (ACC) situated well north of the glacial ice fronts. To be able to access the Amundsen Sea glaciers, CDW must first cross the continental shelf break where the deep ocean meets the shallower waters of the continental shelf. Here, we present data that shows how CDW moves along the continental slope and across the shelf break into the Amundsen Sea. On‐shelf flow of CDW is enhanced where a subsea trough bisects the shelf edge. A previously unreported undercurrent is observed flowing eastward along the shelf edge and when this current encounters the trough mouth it circulates southward into the trough and toward the glaciers. Upwelling associated with this trough circulation appears to allow Lower CDW onto the shelf that would otherwise be blocked by the topography. These observations concur with the results of a theoretical modeling study of circulation in a similar topographic setting and also with the results of a regional ocean/ice modeling study of the Amundsen Sea specifically.

Refugium for surface life on Snowball Earth in a nearly-enclosed sea? A first simple model for sea-glacier invasion

[1] The existence of photosynthetic eukaryotic algae during the so-called Snowball Earth events presents a conundrum. If thick ice covered the oceans, where could such life persist? Here we explore the possibility that photosynthetic life persisted at the end of long narrow seas, analogous to the modern-day Red Sea. In this first analytical model, we test the ability of the global sea glacier to penetrate a Red Sea analogue under climatic conditions appropriate during a Snowball Earth event. We find the Red Sea is long enough to provide a refugium only if certain ranges of climatic conditions are met. These ranges would likely expand if the restrictive effect of a narrow entrance strait is also considered.

Sea glacier flow and dust transport on Snowball Earth

[1] Accumulation of dust on the surface of ice in the tropics has been proposed as a possible mechanism for the termination of Neoproterozoic Snowball Earth episodes. This Mudball hypothesis relies on the assumption that sea glacier flow transports dust to the tropical ablation zone, leading to the accumulation of a dust moraine there and consequent lowering of tropical albedo. Here, we use a 1-D sea-glacier flow model to simulate the ice thickness and flow on a globally glaciated Earth, and study the dust transport associated with the ice flow. Dust is entirely confined to a meteoric ice layer which does not exchange water with the ocean. Dust falling onto the surface of this layer is carried downward with the ice flow in extratropical regions, carried equatorward by the global ice flow, and re-emerges on the top of the ice in the tropical ablation zone. The ice flow acts as a dust conveyor belt which converges dust to tropics, resulting in an amplification of effective tropical dust flux by a factor of 2 to 20 over the global average. This lends support to the Mudball hypothesis.