Warm Atlantic water heats the Arctic

New findings show that the water coming from the Atlantic through the Fram Strait into the Arctic is warmer than it ever was in the last 2000 years. DR. ROBERT SPIELHAGEN from Leibniz Insittute of Marine Science (IFM-GEOMAR), Kiel, Germany and his colleagues have done research on drilled marine sediments off Western Svalbard, dating back 2000 years.

Bathymetric map of the Norwegian-Greenland Sea and Arctic Ocean (base map: www.ibcao.org) Yellow spot marks coring site. © R. Spielhagen, AoSHL/IFM-GEOMAR

The scientists have focused on certain one-celled organisms called foraminifera, whose shells are preserved for long periods of time in the sediment.

Dr. Robert Spielhagen, first author of the Science study samples the sediment core. © J. Steffen, IFM-GEOMAR

Some species are sub-polar species and grow in slightly warmer water than the truly polarspecies. The ratio between them is an indicator of the temperature they have experienced during their lifetimes. Another indicator of the temperature is the composition of the shells  themselves. Taking all this into account, Spielhagen and his colleagues conclude that the mean temperature during the last 120 years exceeds every maximum value for the previous 2,000 years and is about 2°C higher..

Scanning electron microscope image of polar planktic foraminifer Neogloboquadrina pachyderma (sinistral coiling). © T. Struve, IFM-GEOMAR

What seems to be just a modest increase is in fact a huge one. Through a positive feedback loop, the effect multiplies. The warmer water melts the ice, which normally would reflect the sunlight back into space. Less ice leads to increased absorption of solar heat into the ocean water and even more ice melts. In the fall, the warmer water can delay the ice formation for the season, thus leading to thinner ice cover the next summer. Scientists think this could lead to an ice-free summer in the Arctic.

This study is published in Science. Have a look at the abstract or read more on IFM-GEOMAR’s webpage.