Sea ice alters ocean currents in warm climate

Bjerknes researchers Andreas Born and Kerim H. Nisancioglu show in a paper presented in Climate Dynamics that changes in sea ice induces drastic changes in ocean currents. They have studied past climate changes in a similar but warmer climate than present.

Looking into the geological past

While future projections of climate continuously improve, an independent estimate can be achieved by looking into the geological past. The Eemian interglacial 126,000 years ago, thus predating the last ice age, has often been used as an example for the warmer climate expected for the end of this century.

Output from a comprehensive climate model shows that as Arctic climate cooled towards the end of the Eemian interglacial, more sea ice was exported along the east coast of Greenland and into the North Atlantic. Since salt is rejected during the freezing process, this event also enhanced the southward transport of freshwater and resulted in a drastic weakening of the surface ocean current system called the subpolar gyre. Among the consequences of a weaker gyre is the northward displacement of the North Atlantic Current bringing warm subtropical waters to the European shores and increased heat transport into the Nordic Seas, counteracting the general high latitude cooling.
 

Implications of a warmer Arctic

With a warming Arctic in the next decades a similar - albeit reverse - change can be expected. Less freshwater transport by a shrinking sea ice cover might result in a stronger subpolar gyre circulation, eventually decreasing the amount of Atlantic water entering the Nordic Seas. Exploiting the usefulness of paleo climate analogues, this study highlights that the loss of Arctic sea ice not only affects local communities and ecosystems, but also has dynamical implications that go beyond the Arctic realm. It introduces a new mechanism to explain climate changes found in geological archives, emphasizing the surface circulation changes as opposed to the deep overturning circulation.
 

Changes of sea surface salinity (colors) and sea ice transport (arrows) after the Eemian interglacial. Increased export of Arctic sea ice along the east coast of Greenland reduces salinities in the North Atlantic. One consequence is a major reorganization of the surface current system.

Referance