30 years of sea ice for both Arctic and Antarctic Oceans

Sea ice response is an important key to monitoring the climate change and forecasting the sea ice evolution and its retroactions on the climate. 
Sea ice extent has been measured from space since as far as 1978 and now provides us with daily information on its evolution. However, this information is not sufficient to predict its future evolution: Thin ice does react in the same way as thick ice to climatic hazards such as strong winds, rough seas or heat waves.

Knowing the thickness of the ice allows forecasts to be extended from a few days to a few months. It also makes it possible to estimate variations in ice volume and in the seasonal flows of freshwater (during melting) and salts (during ice formation), parameters that are fundamental in understanding and assessing the vertical movements of the ocean, the transport of nutrients, the exchange of oxygen and the ocean currents induced by these circulations.

The most widely used method for measuring sea ice thickness is based on space altimetry, and more specifically on CryoSat-2's SAR altimeter, which has provided numerous results since its launch in 2010. However, this time series is still too short to infer major climate trends, and in particular the effects on ocean circulation.

However, altimetry satellites have covered the Polar Regions without interruption since the launch of ERS-1 in 1991, followed by ERS-2 in 1994, Envisat in 2002 and Cryosat-2 in 2010 providing a continuous series of radar measurements until now. But these pre-Cryosat-2 measurements are difficult to exploit because the altimetry technique of the time (aka “Low Resolution Mode”), does not offer sufficient spatial resolution.

Thanks to AI techniques and the overlapping flight periods of these missions, Legos was able to successively calibrate Envisat on Cryosat-2, ERS-2 on Envisat, and ERS-1 on ERS-2, thus reconstructing a homogeneous 30-year series (1994-2023) of sea ice thickness and volume variations over the two hemispheres.

These results confirm the decreasing trend over the whole Arctic Ocean, while the changes in Antarctic sea ice is more complex, with different regional variability but a with episodes of very significant overall decreases in volumes from 2016 onwards. The launch of the Cristal (Sentinel-9) satellite in 2027 will take over these observations of the polar areas, and enable to continue monitoring sea ice in particular.

See also:

• Image of the Month, September 2023: Sea ice variations around Antarctica
• Image of the Month, October 2021: Snow on ice
• Image of the Month, February 2010: Arctic sea ice shrinks and thins
• Missions: Cryosat-2
• Applications: Sea ice

Other web site on this topic:

• Data at CTOH

References:

• Bocquet, M., Fleury, S., Rémy, F., & Piras, F. (2024). Arctic and Antarctic sea ice thickness and volume changes from observations between 1994 and 2023. Journal of Geophysical Research: Oceans, 129, e2023JC020848. https://doi.org/10.1029/2023JC020848
• Fleury, S., 30 years of sea ice thickness and volume over Arctic and Antarctic from satellite altimetry, 30 Years of Progress in Radar Altimetry Symposium, Montpellier (France), 2-7 September 2024