Over the past two decades, the Arctic has lost about one-third of its winter sea ice volume, mostly due to a decline in sea ice that persists over several decades, called multiyear ice, according to a new study. The study also revealed that sea ice is likely thinner than previous estimates.
Seasonal sea ice, which melts completely each summer rather than accumulating over years, is replacing thicker, multiyear ice and driving sea ice thinning trends, according to the study.
Arctic sea ice snow depth is estimated from a combination of lidar (ICESat-2) and radar (CryoSat-2) data. Using these estimates of snow depth and height of sea ice exposed above water, the study found multiyear Arctic sea ice has lost 16% of its winter volume, or roughly half a meter of thickness, in the three years since the launch of ICESat-2.
Scientists make satellite estimates of sea-ice thickness using snow depth and the height of the floating ice above the ocean surface. Snow can weigh ice down, changing how ice floats in the ocean. The new study compared ice thickness using snow depths from satellite lidar and radar to previous ice thickness and snow depth estimates from climate records. The researchers found that using climatology-based estimates of snow depth can result in overestimating sea-ice thickness by up to 20%, or up to 0.2 meters.
The study used an 18-year record of sea-ice observations from ICESat and the new ICESat-2 and CryoSat-2 satellites to capture monthly changes in Arctic sea-ice volume and thickness, to provide context for sea ice thickness estimates from 2018 to 2021. The 18 year record shows a loss of about 6,000 cubic kilometers of the volume of winter ice.
Older, multiyear ice tends to be thicker and more resistant to melting. As that “reservoir” of old Arctic sea ice is depleted and seasonal ice becomes the norm, the overall volume and thickness of Arctic sea ice is expected to decline.
https://phys.org/news/2022-03-icesat-remarkable-arctic-sea-ice.html