In the Arctic, the loss of sea ice, particularly of multi-year ice (MYI), has accelerated since 2001 and even low emissions scenarios show ice-free summers by 2050. In contrast, sea ice around Antarctica has been comparatively stable over the past several decades of satellite observations, growing in some regions and decreasing in others. However, after record-high sea ice concentration in 2014, an unexpected and precipitous reduction has started that was equivalent to 30 years of sea ice loss in the Arctic (Eayrs et al. 2021). Regional changes during the recent decline were almost opposite to the long-term trend (Rackow et al. 2022) Thus, current climate model simulations are uncertain about sea-ice future in the Southern Ocean.
In both polar regions, glaciers and ice sheets have lost mass especially since 2000 (even in parts of the more stable East Antarctica), and further loss is predicted under all emissions scenarios. In the coastal Arctic and Antarctic Peninsula regions, many marine-terminating glaciers have retreated, and some of them became land-based in the last decades producing newly ice-free areas (Błaszczyk et al. 2013, Jerosch et al. 2018). In the Southern Ocean, over 30,000 km2 have been exposed since the second half of the last century, particularly in the Antarctic Peninsula region, due to the collapse of several ice shelves (Cook and Vaughan 2010). The East Antarctic Ice Sheet could also retreat substantially if temperatures rise +1.8°C compared to pre-industrial levels (currently at +1.1°C). In contrast to sea ice dynamics, once ice sheet melt accelerates due to higher temperatures, it cannot be stopped or reversed for many thousands of years, even once temperatures stabilise. Importantly, sea-ice loss increases both ice shelves and glaciers activity, and disturbance by drifting icebergs (Smale and Barnes 2008, Barnes and Souster 2011b).
As the polar regions warm, glacial meltwater plumes and riverine input will carry increased sediment and nutrient loads (Syvitski 2002), in particular across all coastal Arctic and the Antarctic Peninsula. Increased run-off from glaciers and ice shelves is also freshening the surface waters of the polar seas (Nummelin et al. 2015). This colder, fresher water prevents nutrients from deeper and saltier waters from reaching the surface, thus increasing stratification.