The West Antarctic Ice Sheet is highly sensitive to ocean forcing and is currently experiencing grounding line retreat and ice shelf thinning. Since the response of the ice sheet to a warming world is unknown, it is important to analyze past warmer-than-present periods, e.g. the Pliocene, for comparison with possible future changes. Two drill sites, Site U1532 and Site U1533 of IODP Expedition 379, were linked to a large network of 2D high-resolution seismic reflection data to analyze changes of the West Antarctic Ice Sheet from the latest Miocene to the Pleistocene. During the Pliocene, between 4.2 to 3.2 Ma, a warm period was recognized with a highly dynamic West Antarctic Ice Sheet, correlating with reduced ocean bottom current activity. This period can be described as an overarching warm period with several advance and retreat phases of the West Antarctic Ice Sheet in the Amundsen Sea Sector.

Global sea-level rise contributed by Antarctic ice-mass loss could soon outpace all other sources. The ice-mass-loss signal of the Antarctic Ice Sheet is dominated by the Amundsen Sea Embayment (ASE) in West Antarctica. Ice shelves in the ASE influence the ice-mass-loss rates of the Antarctic Ice Sheet through their ability to buttress the grounded ice and modulate ice-flow speed. Ice shelves reduce ice flow and retreat by buttressing grounded ice. Previous studies show that sea ice can buttress ice shelves via mechanical bonding and provide protection from ocean swells. Whereas several studies have examined the trends in West Antarctic sea ice and dynamics of ice shelves in the ASE separately, the interaction between ice shelves and sea ice in the ASE is poorly understood. This study investigated the relationship between sea-ice-area (SIA) anomalies and ice-shelf velocities of three large ASE ice shelves, of Thwaites Eastern Ice Shelf (TEIS), Pine Island Glacier Ice Shelf (PIGIS) and Crosson Ice Shelf (CIS), on seasonal and monthly timescales from summer 2001-02 to 2021-22 and 2014 to 2022, respectively. SIA anomalies and ice-shelf velocities were derived from satellite remote sensing data. Sea ice in the ASE experienced four- to seven-year periods of relatively consistent positive or negative SIA anomalies. Time series of TEIS average velocity shows increased velocity in the early 2000's, followed by relative stability, then again an increase from the late-2010's onwards. Time series of the PIGIS average velocity shows increased velocities over the 20-year period, with consistent acceleration from the late-2010's onwards. Time series of the CIS average velocity shows relatively stable to slightly decreasing trends over the 20-year period. Correlation analysis of sea ice and ice shelves predominantly showed no significant relationship. Fewer than 15% of Spearman's correlation coefficients between the SIA anomalies and ice-shelf velocities were statistically significant. Therefore, results of this study indicate no apparent relationship between sea ice and ice-shelf velocity in the ASE, at least on seasonal and monthly time scales. The relationship may be more evident on an episodic basis than in a long-term record, as previous studies identified the influence of sea-ice events (i.e., sea-ice breakout or retreat) on Antarctic ice shelves on daily to weekly time scales.

Few scientists doubt the prediction that the antropogenic release of carbon dioxide in the atmosphere will lead to some warming of the earth's climate. So there is good reason to investigate the possible effects of such a warming, in dependence of geographical and social economic setting. Many bodies, governmental or not, have organized meetings and issued reports in which the carbon dioxide problem is defined, reviewed, and possible threats assessed. The rate at which such reports are produced still increases. However, while more and more people are getting involved in the 'carbon dioxide business', the number of investigators working on the basic problems grows, in our view, too slowly. Many fundamental questions are still not answered in a satisfactory way, and the carbon dioxide building rests on a few thin pillars. One such fundamental question concerns the change in sea level associated with a climatic warming of a few degrees. A number of processes can be listed that could all lead to changes of the order of tens of centimeters (e. g. thermal expansion, change in mass balance of glaciers and ice sheets). But the picture of the carbon dioxide problem has frequently be made more dramatic by suggesting that the West Antarctic Ice Sheet is unstable, implying a certain probability of a 5 m higher sea-level stand within a few centuries.

Recent work has documented dramatic changes in the West Antarctic Ice Sheet (WAIS) over the past 30 years (e.g., mass loss, glacier acceleration, surface warming) due largely to the influence of the marine environment. WAIS is particularly vulnerable to large-scale atmospheric dynamics that remotely influence the transport of marine aerosols to the ice sheet. Understanding seasonal- to decadal-scale changes in the marine influence on WAIS (particularly sea-ice concentration) is vital to our ability to predict future change. In this thesis, I develop tools that enable us to reconstruct the source and transport variability of marine aerosols to West Antarctica in the past. I validate new firn-core sea-ice proxies over the satellite era; results indicate that firn-core glaciochemical records from this dynamic region may provide a proxy for reconstructing Amundsen Sea and Pine Island Bay polynya variability prior to the satellite era. I next investigate the remote influence of tropical Pacific variability on marine aerosol transport to West Antarctica. Results illustrate that both source and transport of marine aerosols to West Antarctica are controlled by remote atmospheric forcing, linking local dynamics (e.g., katabatic winds) with large-scale teleconnections to the tropics (e.g., Rossby waves). Oxygen isotope records allow me to further investigate the relationship between West Antarctic firn-core records and temperature, precipitation origin, sea-ice variability, and large-scale atmospheric circulation. I show that the tropical Pacific remotely influences the source and transport of the isotopic signal to the coastal ice sheet. The regional firm-core array reveals a spatially varying response to remote tropical Pacific forcing. Finally, I investigate longer-term (-200 year) ocean and ice-sheet changes using the methods and results gleaned from the previous work. I utilize sea-ice proxies to reconstruct long-term changes in sea-ice and polynya variability in the Amundsen Sea, and show that the tropics remotely influence West Antarctica over decadal timescales. This thesis utilizes some of the highest-resolution, most coastal records in the region to date, and provides some of the first analyses of the seasonal- to decadal-scale controls on source and transport of marine aerosols to West Antarctica.

This thesis analyses satellite-based radar data to improve our understanding of the interactions between the Antarctic Ice Sheet and the ocean in the Amundsen Sea Sector of West Antarctica. Over the last two decades, the European Remote Sensing (ERS) Satellites have provided extensive observations of the marine and cryospheric environments of this region. Here I use this data record to develop new datasets and methods for studying the nature and drivers of ongoing change in this sector. Firstly, I develop a new bathymetric map of the Amundsen Sea, which serves to provide improved boundary conditions for models of (1) ocean heat transfer to the ice sheet margin, and (2) past ice sheet behaviour and extent. This new map augments sparse ship-based depth soundings with dense gravity data acquired from ERS altimetry and achieves an RMS depth accuracy of 120 meters. An evaluation of this technique indicates that the inclusion of gravity data improves the depth accuracy by up to 17 % and reveals glaciologically-important features in regions devoid of ship surveys. Secondly, I use ERS synthetic aperture radar observations of the tidal motion of ice shelves to assess the accuracy of tide models in the Amundsen Sea. Tide models contribute to simulations of ocean circulation and are used to remove unwanted signals from estimates of ice shelf flow velocities. The quality of tide models directly affects the accuracy of such estimates yet, due to a lack of in situ records, tide model accuracy in this region is poorly constrained. Here I use two methods to determine that tide model accuracy in the Amundsen Sea is of the order of 10 cm. Finally, I develop a method to map 2-d ice shelf flow velocity from stacked conventional and multiple aperture radar interferograms. Estimates of ice shelf flow provide detail of catchment stability, and the processes driving glaciological change in the Amundsen Sea. However, velocity estimates can be contaminated by ocean tide and atmospheric pressure signals. I minimise these signals by stacking interferograms, a process which synthesises a longer observation period, and enhances long-period (flow) displacement signals, relative to rapidly-varying (tide and atmospheric pressure) ones. This avoids the reliance upon model predictions of tide and atmospheric pressure, which can be uncertain in remote regions. Ice loss from Amundsen Sea glaciers forms the largest component of Antarctica's total contribution to sea level, yet because present models cannot adequately characterise the processes driving this system, future glacier evolution is uncertain. Observations and models implicate the ocean as the driver of glaciological change in this region and have focussed attention on improving our understanding of the nature of ice-ocean interactions in the Amundsen Sea. This thesis contributes datasets and methods that will aid historical reconstructions, current monitoring and future modelling of these processes.

Covering more than seven percent of the earth’s surface, sea ice is crucial to the functioning of the biosphere—and is a key component in our attempts to understand and combat climate change. With On Sea Ice, geophysicist W. F. Weeks delivers a natural history of sea ice, a fully comprehensive and up-to-date account of our knowledge of its creation, change, and function. The volume begins with the earliest recorded observations of sea ice, from 350 BC, but the majority of its information is drawn from the period after 1950, when detailed study of sea ice became widespread. Weeks delves into both micro-level characteristics—internal structure, component properties, and phase relations—and the macro-level nature of sea ice, such as salinity, growth, and decay. He also explains the mechanics of ice pack drift and the recently observed changes in ice extent and thickness. An unparalleled account of a natural phenomenon that will be of increasing importance as the earth’s temperature rises, On Sea Ice will unquestionably be the standard for years to come.

The Antarctic Slope Current (ASC) is a narrow and westward circulation feature that surrounds the Antarctic continental shelves. It regulates onshore ocean heat transport toward the Antarctic ice shelves and dense water outflow, playing an important role in global meridional overturning circulation, glacier melt, and sea level rise. Despite its significance to Earth's climate system, the circulation and heat transport around the Antarctic margins remain poorly understood due to the difficulties and expense in observation and modeling. In this work, the dynamics of the ASC and the ice-ocean interactions around the Antarctic margins are investigated using high-resolution process-oriented simulations. The key results are summarized as follows: (i) Due to topographic eddy suppression, almost no wind-input momentum is transferred vertically over the continental slope; as a result, sea ice horizontally redistributes the wind-input momentum away from the continental slope, playing a critical role in the momentum balance of the ASC. (ii) Melt-induced freshening of the coastal waters that are buoyant compared with the open ocean leads to increased eddy-driven shoreward heat flux, which implies a positive feedback in a warming climate that may cause further melt of ice shelves. (iii) The West Antarctic slope undercurrent originates from the cyclonic vorticity input by meltwater upwelling in the cavities of West Antarctic ice shelves, which drives warm Circumpolar Deep Water toward the glaciers; increased basal melt therefore strengthens the slope undercurrent and enhances onshore heat transport, which indicates another positive feedback that may accelerate future melt, potentially further destabilizing the West Antarctic Ice Sheet. The work in this dissertation advances the understanding of the ice-ocean system near the Antarctic margins and highlights previously unrecognized climate feedbacks that may be key to projecting future changes in Antarctic ice sheets and thus sea level rise. In addition, our results help guide future climate model development and future observations of near-Antarctic ocean heat flux and glacier melt.

Papers and abstracts from the Symposium on Ice-Ocean Dynamics, including sea-ice dynamics, sea-ice mechanics, ice-plate dynamics and mechanics, local ice-ocean interaction phenomena, relict flow stripes, and atmosphere-ice-ocean interactions in both the Arctic and Antarctic.