Tracking Antarctica’s Ice Fluctuations

What DEFIANT did

DEFIANT stands for ‘drivers and effects of fluctuations in sea ice in the Antarctic’.

Extreme changes in sea ice extent highlighted major challenges in prediction and understanding. The project addressed the need to:

• improve understanding of processes driving Antarctic sea ice variability
• assess drivers and climate impacts of sea ice loss across timescales from weeks to decades

Meeting these aims required a large research programme. This included year-round observations and improved climate model processes.

Why this matters

Climate models suggested that Antarctic sea ice extent should decrease as atmospheric CO₂ concentrations rise. Satellite observations showed a different pattern. Between 1979 and 2015, Antarctic sea ice extent increased by around 1.5% per decade.

In 2016, this trend was abruptly interrupted by an unprecedented reduction in sea ice extent. Sea ice later returned close to pre-2016 levels. This highlighted strong year-to-year variability in Antarctic sea ice conditions.

These fluctuations are important for the global climate system. Sea ice affects Antarctic Ice Sheet melting and the uptake of heat and CO₂ by the Southern Ocean.

How the project worked

DEFIANT delivered a major observational campaign focused on Antarctic sea ice variability. The project combined data from research ships, stations, aircraft, satellites, and robotic technologies.

Measurements were collected from RV Polarstern, RSS Sir David Attenborough, and BAS’s Rothera Research Station. These were supported by aircraft, satellites, Boaty McBoatface, and on-ice buoys. Together, these observations provided year-round measurements of the atmosphere, sea ice, and ocean.

RRS Sir David Attenborough during a sea ice science cruise

Science objectives

The project aimed to:

• support the development of improved ocean and climate models
• help identify drivers of sea ice decline
• assess its impacts on global ocean circulation, heat transport, and CO₂ movement

Who was involved

DEFIANT was funded by the Natural Environment Research Council (NERC), part of UK Research and Innovation (UKRI). 

With BAS as its lead institute, the project was co-designed and co-produced by eight UK institutes:

• National Oceanography Centre
• The Alan Turing Institute 
• University College London
• University of Leeds
• University of Reading
• University of Southampton
• UK Met Office

International collaborators included partners from Australia, Canada, Germany, the European Space Agency, India, Norway, Spain, and the USA.

The Specific Objectives (SOs) of DEFIANT are as follows:

SO1: Identify the atmospheric and oceanic processes that caused the 2016 rapid decline in Antarctic sea ice.

SO2: Improve the physical representation of the processes responsible for historical changes in Antarctic ice, ocean, and atmosphere models, including the decadal growth and recent collapse.

SO3: Identify the short-term (<10 years) effect of the sudden decrease in Antarctic sea ice on global oceanic circulation patterns using model simulations with improved physics.

SO4: Combine historical observations and model predictions to assess whether enhanced variability and loss of sea ice constitute a new normal and examine the implications for exchange and redistribution of heat and CO2 over decadal timescales.

SO5: Synthesise advances from above SOs, disseminate knowledge gained and deliver new climate modelling tools.

Delivery plan

Achieving our SOs requires a substantial, multi-disciplinary delivery plan, and extensive international cooperation. The DEFIANT team will (i) perform observations of governing processes to develop an enhanced process-level understanding of sea ice variability, especially in relation to the 2016 extreme event; (ii) deliver better representation of the underlying physics of these governing processes into models; (iii) provide more accurate predictions, through model enhancement, calibration and validation, of short-term (<10 years) impacts of sudden sea ice loss on global oceanic circulation patterns, and long-term (>10 years) implications for exchange and redistribution of heat and CO₂; and (iv) spread our new knowledge and modelling tools to the widest possible audience.

The SOs are achieved through four interlinked Work Packages (WPs). Within WPs1-3 we address the key research questions and each WP’s closing task is a synthesis of the knowledge gained. This information feeds into WP4, which focuses on synthesis, dissemination, and training and education. A significant WP4 output is the delivery of a White Paper that summarises the state of knowledge on Antarctic sea ice, including the impacts of sudden reductions in ice extent. This will provide a comprehensive follow-up to the US NAS workshop on Antarctic sea ice.

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