Last Sunday July 15th was Arctic Sea Ice Day, which is why we would like to tell you today a little bit about the importance of sea ice.
Isn’t sea ice just frozen seawater? Sure, that’s totally true, but it is frozen water with a global significance. Sea ice is one major component in our climate system. Depending on the season about three to seven percent of the earth’s surface are covered in sea ice.
Thereby it is not only restricting heat, momentum and gas exchange between the ocean and the atmosphere, but it also contributes to the earth’s albedo. Simply spoken, the albedo is the amount of sunlight reflected by the earth’s surface. White or lighter grounds (especially sea ice and ice sheets) reflect sunlight instead of absorbing it, which means that it prevents the earth from heating up further. So sea ice actually acts somehow as an air conditioning for the earth. This effect is highly dependent on the amount of sea ice. The sea ice extent (the area which is covered by sea ice to at least 15%) is seasonally changing, due to melting in summer in some areas (first year sea ice), while in some other areas it persists throughout the melting season (perennial or multi year sea ice).
Sea ice is not only important for our climate but also home to a variety of marine wild life, such as algae and other microorganisms, fish and of course as you all know, polar bears.
A lot of us are working with sea ice by modelling it, observing it from space or reconstructing its past development. The reason for that are the two really important roles of sea ice mentioned above and the fact that there has been a visible decline in multiyear sea ice within the last decades. Sea ice is not only diminishing in extent but also in volume. It is well shown in Kevin Pluck’s animation that sea ice volume is decreasing faster than the sea ice extent, caused by the decline of thicker multiyear ice.
The Arctic Sea Ice Day has been established to raise awareness to the lately observed sea ice loss. The day July 15th has been chosen by Polar Bears International because it is the historical date of Western Hudson Bay sea ice break up in mid-July. Sadly, the break-up happens now three weeks earlier than in the 1980s.
When the sea ice breaks in summer, polar bears (in Western Hudson Bay and elsewhere) are forced to migrate to shore, where hunting for food is harder than on the sea ice. The extension of this “ice free” period is challenging the polar bear’s hunt for survival.
That’s why it is so essentially important to monitor sea ice and find out more about its behavior and development. To learn from the past to predict the future.
Look forward to a different sea ice and polar bear story next week!