Changing Arctic: New insight on freeze-melt cycle of sea ice

Source: The post is based on the article “Changing Arctic: New insight on freeze-melt cycle of sea ice” published in Down To Earth on 8th December 2022

What is the News?

According to a study, the surface and bottom of the Arctic sea ice often do not melt and freeze simultaneously.

About Arctic Sea Ice

The Arctic sea ice is seasonal. It forms in the winter when seawater freezes into massive floating ice blocks and thaws during the summer. When sea ice is present, it insulates the ocean against heat loss.

The sea ice reflects sunlight into space, regulating ocean and air temperature and maintaining habitats above and below the water.

Understanding the timings of the thawing of sea ice and freeze onsets, as well as the lengths of the melt and freeze seasons is crucial. These play a vital role in the “heat budget” of the atmosphere-ice-ocean system. 

Note: A heat budget is a balance between incoming heat absorbed by the earth and outgoing heat escaping it. 

What did the study find on the Arctic Sea Ice?

Until now, most studies calculated the Arctic melt and freeze onsets using remote sensing observations from the surface, but rarely investigated the freeze-thaw process at the ice bottom.

The researchers have now analyzed data from 2001 to 2018 to explore how melting and freezing vary at the ice surface and bottom. 

They found that the surface and bottom of the Arctic sea ice often do not melt and freeze simultaneously. For instance, at the Beaufort Gyre — a major ocean current in the Arctic Ocean — the average ice melt at the bottom is approximately 17 days earlier than the surface melt onset.

This longer melt season under the ice is likely playing a key role in the enhanced thinning of the ice that is keeping the summer extents low.