Sea Ice Loss is Weakening Ocean’s Ability to Mop Up Atmospheric Carbon

New research suggests that melting sea ice is weakening the Arctic Ocean’s ability to capture and store atmospheric carbon. The study, carried out at the Catlin Arctic Survey’s Ice Base in March and April 2010 by a team at the Department of Fisheries and Oceans, Canada, focuses on the efficiency of an important biological ‘pump’ that captures atmospheric carbon near the sea surface and then draws it down and stores it on the sea floor.

Phytoplankton (plant plankton), near the sea surface, capture atmospheric carbon and store it as non-sinking microscopic particles. Although these particles do not themselves sink, their sticky nature means they can capture heavier organic debris and become sufficiently dense that they fall to the ocean floor as ‘marine snow’, effectively removing significant amounts of atmospheric CO2 to the deep ocean for thousands of years.

The findings also show that carbon-rich gel-like particles (so-called transparent exopolymer particles or TEPs) are stored in the sea ice during winter and are released into the water column during early spring. TEPs are an important feature in the carbon cycle as they both capture carbon and also give ‘marine snow’ its stickiness, enabling it to attract organic debris and therefore sink.

Future increases in surface freshwater from melting sea-ice will likely further strengthen water layering and could change carbon draw-down in the Arctic Ocean. Coupled with the continuing retreat of sea-ice, this has implications for the capacity of the Arctic Ocean to mitigate increasing atmospheric CO2 emissions via carbon capture.

The oceans represent the largest active carbon sink on earth, absorbing more than a quarter of the carbon dioxide that humans put into the air. According to a recent estimate, the Arctic is responsible for 5% to 14% of the world’s CO2 uptake, although it accounts for only 3% of its ocean surface area.

The Catlin Arctic Survey, sponsored by global specialty insurer and reinsurer Catlin Group, involves an ‘Ice Base’ and an ‘Explorer Team’.

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