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

Peer reviewe

An overview of Antarctic polynyas: sea ice production, forcing mechanisms, temporal variability and water mass formation

Polynyas are irregular open water bodies within the sea ice cover in polar regions under freezing weather conditions. In this study, we reviewed the progress of research work on dynamical forcing, sea ice production (SIP), and water mass formation for both coastal polynyas and open-ocean polynyas in the Southern Ocean, as well as the variability and controlling mechanisms of polynya processes on different time scales. Polynyas play an irreplaceable role in the regulation of global ocean circulation and biological processes in regional ocean ecosystems. The coastal polynyas (latent heat polynyas) are mainly located in the Weddell Sea, the Ross Sea and on the west side of protruding topographic features in East Antarctica. During the formation of coastal polynyas, which are mainly forced by offshore winds or ocean currents, brine rejection triggered by high SIP results in the formation of high salinity shelf water, which is the predecessor of the Antarctic bottom water — the lower limb of the global thermohaline circulation. The open-ocean polynyas (sensible heat polynyas) are mainly found in the Indian sector of the Southern Ocean, which are formed by ocean convection processes generated by topography and negative wind stress curl. The convection processes bring nutrients into the upper ocean, which supports biological production and makes the polynya regions an important sink for atmospheric carbon dioxide. The limitations and challenges in polynya research are also discussed

The Weddell Gyre, Southern Ocean: present knowledge and future challenges

The Weddell Gyre (WG) is one of the main oceanographic features of the Southern Ocean south of the Antarctic Circumpolar Current which plays an influential role in global ocean circulation as well as gas exchange with the atmosphere. We review the state‐of‐the art knowledge concerning the WG from an interdisciplinary perspective, uncovering critical aspects needed to understand this system's role in shaping the future evolution of oceanic heat and carbon uptake over the next decades. The main limitations in our knowledge are related to the conditions in this extreme and remote environment, where the polar night, very low air temperatures and presence of sea ice year‐round hamper field and remotely sensed measurements. We highlight the importance of winter and under‐ice conditions in the southern WG, the role that new technology will play to overcome present‐day sampling limitations, the importance of the WG connectivity to the low‐latitude oceans and atmosphere, and the expected intensification of the WG circulation as the westerly winds intensify. Greater international cooperation is needed to define key sampling locations that can be visited by any research vessel in the region. Existing transects sampled since the 1980s along the Prime Meridian and along an East‐West section at ~62°S should be maintained with regularity to provide answers to the relevant questions. This approach will provide long‐term data to determine trends and will improve representation of processes for regional, Antarctic‐wide and global modeling efforts – thereby enhancing predictions of the WG in global ocean circulation and climate

The Antarctic Slope Current in a Changing Climate

The Antarctic Slope Current (ASC) is a coherent circulation feature that rings the Antarctic continental shelf and regulates the flow of water towards the Antarctic coastline. The structure and variability of the ASC influences key processes near the Antarctic coastline that have global implications, such as the melting of Antarctic ice shelves and water mass formation that determines the strength of the global overturning circulation. Recent theoretical, modeling, and observational advances have revealed new dynamical properties of the ASC, making it timely to review. Earlier reviews of the ASC focused largely on local classifications of water properties of the ASC's primary front. Here, we instead provide a classification of the current's frontal structure based on the dynamical mechanisms that govern both the along‐slope and cross‐slope circulation; these two modes of circulation are strongly coupled, similar to the Antarctic Circumpolar Current. Highly variable motions, such as dense overflows, tides, and eddies are shown to be critical components of cross‐slope and cross‐shelf exchange, but understanding of how the distribution and intensity of these processes will evolve in a changing climate remains poor due to observational and modeling limitations. Results linking the ASC to larger modes of climate variability, such as El Niño, show that the ASC is an integral part of global climate. An improved dynamical understanding of the ASC is still needed to accurately model and predict future Antarctic sea ice extent, the stability of the Antarctic ice sheets, and the Southern Ocean's contribution to the global carbon cycle

The recent dynamics of Moscow University Glacier and Moscow University Ice Shelf, East Antarctica (1963 – 2022)

Mass loss from the Antarctic Ice Sheet is dominated by ice discharge through outlet glaciers, many of which are buttressed by peripheral ice shelves. In Wilkes Land, East Antarctica, an ocean-driven increase in ice flux from several large outlet glaciers has caused accelerated mass loss over recent decades. Wilkes Land overlies the Aurora Subglacial Basin (ASB), which contains an ice volume large enough to raise global sea level by 5 m and is potentially susceptible to pervasive retreat. However, ice dynamics within some areas of Wilkes Land remain largely unstudied. This includes Moscow University Glacier (MUG) and Moscow University Ice Shelf (MUIS), which regulate ice discharge from a catchment containing 128 cm of potential sea level rise within the ASB and are subject to intrusions of warm Circumpolar Deep Water. Employing optical satellite imagery and remote sensing datasets to record changes in terminus position, ice surface velocity, ice surface elevation, grounding line location and sea ice distribution, this thesis aims to investigate the ice dynamics of MUIS and MUG between 1963 and 2022. Migration of the MUIS ice front is limited to the unconfined ice shelf region. Both MUG and MUIS exhibited negligible change in flow velocity between 2000 and 2021, and the results suggest limited grounding line retreat of 1.4 km between 1996 and 2017 (~67 m yr). Ice surface elevation remained stable from 1993 to 2010, but MUG was recorded to thin at an accelerated rate (0.86 m yr) between 2011 and 2016, and regions of enhanced surface lowering were observed to correlate with areas of faster ice flow. Overall, these findings imply that MUG and MUIS have remained largely stable in recent decades, but may be starting to exhibit the early indicators of dynamic change. It is suggested that topography exerts critical stabilising stresses on MUIS, enhancing its capacity to buttress the flow of MUG. Continued monitoring of MUG and MUIS, as well as topographically-constrained ice flow modelling, will be important in understanding the response of the Moscow University catchment to future ocean forcing