Ice Conditions in the Fram Strait over the Last 30,000 Years Reconstructed
06.11.2009 - Water & Oceans, Ice & Snow, Other, Arctic
A new study, entitled "Variability of sea-ice conditions in the Fram Strait over the past 30,000 years" published in the online edition of Nature Geoscience on October 25th succeeded in reconstructing the ice conditions in the Fram Strait during the past 30,000 years. The study was a collaboration between researchers from the Alfred Wegener Institute (AWI) for Polar and Marine Research in the Helmholtz Association and from the University of Plymouth in Great Britain.
To reconstruct the ice conditions in this narrow passage between eastern Greenland and Spitsbergen, the scientists used fossilized algal remains in sediment cores to work out a uniform picture of the expansion of sea ice in the area. Using fossil organic molecular remains - also known as biomarkers - embedded in the layers of the sediment cores, the researchers were able to find out when the Fram Strait was covered by ice and when it was ice-free.
The biomarker IP25, a complex molecule produced by algae living in the sea ice, was found in varying concentrations in the sediment and was used as an indicator for the ice cover. A second biomarker, brassicasterol, which is produced by algae living in open water, was used as a counterpart in the analyses, indicating ice-free periods. It was the combination of these two biomarkers that enabled the researchers to reconstruct different ice conditions over the past 30,000 years.
During the last glacial maximum of about 20,000 years ago, the absence of these two biomarkers indicated there was permanent ice cover in the northern Fram Strait. For the short warming of the climate that occurred about 15,000 years ago, the early Bølling, the content of brassicasterol was much greater, indicating that the Fram Strait to have been ice-free during the winter months. The simultaneous occurrence of both biomarkers in sediments from the late Holocene (the past 5,000 years) shows that the strait was only ice-covered during the winter and spring months.
The drop in sea ice cover in the central Arctic with a dramatic minimum in the year 2007 alarmed many scientists and provoked research on natural changes in sea ice before humans had any impact on the climate. Arctic sea ice plays an important role in the thermal balance of the oceans as the ice influences the mechanisms of global ocean currents, which are propelled by differences in temperature and salt concentration. This circulation in particular is responsible for the mild climate in Europe in the form of the Gulf Stream, and one power source for this "heat pump" is located in the Fram Strait, which makes its history of ice cover so interesting to scientists.
