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Snow is the most reflective, and also the most insulative, natural material on Earth. Consequently, it is an integral part of the sea-ice and climate systems. However, the spatial and temporal heterogeneities of snow pose challenges for observing, understanding and modelling those systems under anthropogenic warming. Here, we survey the snow–ice system, then provide recommendations for overcoming present challenges. These include: collecting process-oriented observations for model diagnostics and understanding snow–ice feedbacks, and improving our remote sensing capabilities of snow for monitoring large-scale changes in snow on sea ice. These efforts could be achieved through stronger coordination between the observational, remote sensing and modelling communities, and would pay dividends through distinct improvements in predictions of polar environments.

Understanding the causes of recent catastrophic ice shelf disintegrations is a crucial step towards improving coupled models of the Antarctic Ice Sheet and predicting its future state and contribution to sea-level rise. An overlooked climate-related causal factor is regional sea ice loss. Here we show that for the disintegration events observed (the collapse of the Larsen A and B and Wilkins ice shelves), the increased seasonal absence of a protective sea ice buffer enabled increased flexure of vulnerable outer ice shelf margins by ocean swells that probably weakened them to the point of calving. This outer-margin calving triggered wider-scale disintegration of ice shelves compromised by multiple factors in preceding years, with key prerequisites being extensive flooding and outer-margin fracturing. Wave-induced flexure is particularly effective in outermost ice shelf regions thinned by bottom crevassing. Our analysis of satellite and ocean-wave data and modelling of combined ice shelf, sea ice and wave properties highlights the need for ice sheet models to account for sea ice and ocean waves. Less sea ice allowed ocean swells to flex weakened ice shelves in Antarctica, contributing to their collapse.

The spreading of dense shelf water (DSW) from Antarctic coastal margins to lower latitudes plays a vital role in the ocean thermohaline circulation and the global climate system. Through enhanced localized sea ice production in Antarctic coastal polynyas, cold and saline DSW is formed over the continental shelf regions as a precursor to Antarctic Bottom Water (AABW). However, the detailed fate of coastal DSW over the Southern Ocean is still unclear. Here we conduct extensive passive tracer experiments using a circumpolar ocean‐sea ice‐ice shelf model to investigate pathways of the regional polynya‐based DSW from the Antarctic margins to the deep Southern Ocean basins. In the numerical experiments, the Antarctic coastal margin is divided into nine regions, and a passive tracer is released from each region at the same rate as the local sea ice production. The modeled spatial distribution of the total concentration of the nine tracers is consistent with the observed AABW distribution and clearly demonstrates nine routes of the DSW over the Southern Ocean along its bottom topography. Furthermore, the model shows that while ∼50% of the total tracer is distributed northward from the continental shelf to the deep ocean, ∼7% is transported poleward beneath ice shelf cavities. The comprehensive tracer experiments allow us to estimate the contribution of local DSW to the total concentration along each of the pathways. Passive tracer experiments detail the export of DSW formed in Antarctic coastal polynyas to the offshore basins of the Southern OceanNine key pathways of DSW over the Southern Ocean are describedThe contributions of regional DSW formation and distributions are estimated

In the marginal ice zone (MIZ), where ocean waves and sea ice interact, waves can produce flows of water across ice floe surfaces in a process known as wave overwash. Overwash potentially influences wave propagation characteristics, floe thermodynamics, and floe surface biological and chemical processes. However, the extent of the MIZ affected by overwash and its dependence on prevailing wave and ice conditions is unknown. In this paper, we propose a model of overwash extent caused by irregular incoming waves into a MIZ consisting of a random floe field. We validate the overwash extent model against laboratory experiments. We use the model to study mild to extreme incoming waves to floe field characteristics of the spring–summer ice retreat and autumn–winter ice advance and with compact ice edges. Overwash is typically predicted to extend a few kilometers and is generally greater for the autumn–winter advance than the spring–summer retreat. The model predictions provide a basis for improved understanding of the impacts of ocean waves on the ice cover. We also apply the model to incoming waves and a floe field with a diffuse ice edge representative of conditions during a field experiment, predicting overwash extents up to 16 km. During the field experiment, the wave and ice floe properties were intermittently monitored by a camera system, demonstrating how the sparse field data available on overwash can be advanced. Wave overwash is the flow of water across the surface of a thin floating body due to passing waves. It is an important process in the marginal ice zone (MIZ) where sea ice floes and ocean waves interact. Overwash reduces the energy of ocean waves, removes snow from, and wets the sea ice surface, which can drive growth or melting. Water left on the sea ice surface can host organisms and affects chemical processes taking place there. Overwash is pervasive in laboratory experiments where it has been measured and studied. In contrast, there are few reports of overwash in the field and the extent of its occurrence has not been measured. We propose a model to predict the region of the MIZ in which overwash occurs. We use the model to compare overwash extents for MIZs associated with the spring–summer ice retreat and autumn–winter ice advance for calm to energetic wave conditions, including the conditions observed during a winter Antarctic icebreaker voyage. For field conditions, the model predicts that overwash typically extends at least several kilometers into the MIZ, indicating that it likely contributes to the ice edge evolution. A mathematical model is proposed for the extent of wave overwash of ice floes in the marginal ice zone (MIZ) based on coupled floe–wave motionsFrequent overwash is predicted up to 16 km from the ice edge during a voyage into Antarctic MIZ composed of pancake iceWave overwash is predicted to be a persistent feature of the outermost MIZ, likely contributing to the evolution of the ice edge A mathematical model is proposed for the extent of wave overwash of ice floes in the marginal ice zone (MIZ) based on coupled floe–wave motions Frequent overwash is predicted up to 16 km from the ice edge during a voyage into Antarctic MIZ composed of pancake ice Wave overwash is predicted to be a persistent feature of the outermost MIZ, likely contributing to the evolution of the ice edge

The Mertz Glacier tongue (MGT), East Antarctica, has a large area of multi‐year fast sea ice (MYFI) attached to its eastern edge. We use various satellite data sets to study the extent, age, and thickness of the MYFI and how it interacts with the MGT. We estimate its age to be at least 25 years and its thickness to be 10–55 m; this is an order of magnitude thicker than the average regional sea‐ice thickness and too thick to be formed through sea‐ice growth alone. We speculate that the most plausible process for its growth after initial formation is marine (frazil) ice accretion. The satellite data provide two types of evidence for strong mechanical coupling between the two types of ice: The MYFI moves with the MGT, and persistent rifts that originate in the MGT continue to propagate for large distances into the MYFI. The area of MYFI decreased by 50% following the departure of two large tabular icebergs that acted as pinning points and protective barriers. Future MYFI extent will be affected by subsequent icebergs from the Ninnis Glacier and the imminent calving of the MGT. Fast ice is vulnerable to changing atmospheric and oceanic conditions, and its disappearance may have an influence on ice tongue/ice shelf stability. Understanding the influence of thick MYFI on floating ice tongues/ice shelves may be significant to understanding the processes that control their evolution and how these respond to climate change, and thus to predicting the future of the Antarctic Ice Sheet.