Understanding the role of Antarctic sea ice in dense water formation and heat and carbon sequestration: from satellite altimetry to 'big data' analysi

The ocean is the largest carbon reservoir in the Earth system and it stores over 90% of the excess heat produced by anthropogenic activities. The rate at which both heat and carbon are absorbed by the ocean varies strongly, both in space and time, and the Southern Ocean is a key region for the uptake of both. However, we have limited skills in predicting how this will change in the future. Ice-ocean-atmosphere interactions are key in determining the rates of carbon and heat uptake by the ocean. Antarctic sea ice formation/export and circumpolar westerly winds are the dominant surface forcings in the Southern Ocean, driving the upwelling and ventilation of the dense waters that fill most of the ocean's interior and the formation of Antarctic Bottom Water, a key component of the global abyssal circulation. Polynyas - seasonal openings in the sea ice - are the other main contributors to the formation of deep and dense shelf waters around the Antarctic margins. However, Southern Ocean dynamics and circulation are poorly simulated in coupled climate models. Even state-of-the-art simulations fail to represent both ice-ocean-atmosphere interactions and biogeochemical processes adequately, and observations in these regions are scarce and patchy.

Methods

Satellite along-track altimetry data in Antarctic sea ice leads will be used to analyse the ocean's sea level inside polynyas, to identify the fingerprints of dense water formation and circulation. To this end, Sea Surface Height and Sea Height Anomaly products will be processed and analysed from both the CryoSat-2 (European Space Agency) and ICESat-2 (NASA) Polar satellite missions.

The representation of processes driving deep water formation and circulation in the Southern Ocean (such as winds and sea ice dynamics) will be assessed in state-of-the-art simulations from the 6th Coupled Model Intercomparison Project (CMIP6). This will be achieved by setting up advanced cloud-based computing capabilities (e.g. Pangeo) and using statistical tools and machine learning techniques to identify and explore the key relationships between ice-ocean-atmosphere processes and interactions.

These combined results will be used to determine the effect of Antarctic sea ice on ocean circulation and heat/carbon uptake, improve our understanding of present and past trends, and more skillfully predict how these may change in the future.

Training

The orbits of CryoSat-2 and ICESat-2 were partially aligned in 2020, to provide a unique dataset of coincident measurements from the satellites and increase the accuracy of sea ice measurements around Antarctica. Project work will include a hosted international visit at NASA, where ICESat-2 sea ice data are being developed. In addition, the CMIP6 archive of simulations has recently become available and will contribute to the 6th assessment report of the Intergovernmental Panel for Climate Change (IPCC).

These recent advances in both numerical modelling and satellite remote sensing make such a project especially timely, while the ability to process and interpret these types of data products is among the most in-demand skills in international environmental research. This PhD will enable the student to develop proficiency in these techniques, including computer programming and handling 'big data' archives, with the support of an international team with a diverse range of expertise.

The student will be based at the National Oceanography Centre in Southampton and work closely with supervisors based at the University of Leeds, where the student will be registered, the University of Southampton and the British Antarctic Survey. There will be opportunities to participate in Antarctic research cruises.