By late March, 2013, Arctic sea ice had passed its annual maximum extent, and was beginning its seasonal decline in the lengthening daylight of spring. According to the National Snow and Ice Data Center (NSIDC), the total extent of Arctic sea ice in 2013 was well below average through March, although it was not a record low.
On March 31, the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite captured this true-color image of the Gulf of Bothnia still carrying a thick mantle of white, especially in the far north. The Gulf of Bothnia is the northernmost arm of the Baltic Sea, and lies between Finland (to the east) and Sweden (west).
Freeze-up in the Gulf of Bothnia normally begins in the northernmost tip in November, and much of the ice has thawed by mid-April, although ice can persist into May, and sometimes as late as June in the northern reaches of the Gulf. Fast ice, which is thick and clings to the shorelines, blocks the ports for shipping, and commerce relies on icebreaking vessels to keep the waters passable. A broad band of bright white ice can be seen clinging to the northern shorelines in this image.
On April 13, the Baltic Sea Ice Services reported that the northern Bay of Bothnia (the northernmost part of the Gulf of Bothnia) still retained 50-75 cm thick fast ice in the archipelago, and further out there was 40-70 cm thick ridged consolidated ice, with cracks and leads in the ice field. Also, 35-60 cm thick fast ice remained in the archipelago of the southern Bay of Bothnia, with 30-60 cm thick rafted and ridged very close ice further out. Finland currently reports five icebreakers at work in the Bay of Bothnia, while it has two more working further south in the Gulf.