Aerial view of sea ice (credits: Federico Scoto)

Sea ice responds synchronously to abrupt climate changes, study finds

A study conducted by two research institutes of the National Research Council-the Institute of Atmospheric and Climate Sciences (Isac) and the Institute of Polar Sciences (Isp)-in collaboration with Ca' Foscari University of Venice, the University of Padua, and several international partners (AWI, CIC, CSIC, PSI), has reconstructed, at high temporal resolution, the evolution of sea ice cover in the sub-polar region between Baffin Bay and the Labrador Sea, examining a series of abrupt climate  oscillations that occurred between 36 and 44 thousand years ago. The research paper, Sea ice fluctuations in the Baffin Bay and the Labrador Sea during glacial abrupt climate changes, is published in Proceedings of the National Academy of Science (PNAS). 

"The work combines two sea ice records, one based on the analysis of marine salts (bromine and sodium) from an ice core drilled in northwest Greenland and the other based on the association of biomarkers in a marine sediment core extracted in the Labrador Sea," explains Federico Scoto (CNR Isac), who led the study. "The results show that, in the sub-polar regions between the Baffin Bay and  the Labrador Sea, the sea ice response to the repeated abrupt atmospheric warmings imprinted in the Greenland ice, was nearly synchronous, or occurred conservatively within a decade, shifting from a thick persistent multi-year ice cover to open ocean and seasonal ice conditions," Scoto adds. This evidence provides further evidence of the close relationship between climate warming and Arctic  sea ice reduction.

"Climate cycles known as Dansgaard-Oeschger (D-O) events are characterized by an increase of up to +15 °C in atmospheric temperatures in Greenland in few decades, followed by a  progressive cooling that can last up to 1-2 thousand years," continues Carlo Barbante, director of CNR-Isp, professor at Ca' Foscari University of Venice and co-author of the study. "Although some hypotheses link such abrupt oscillations to changing sea ice cover in the Arctic, dynamics and temporal linkage of the two processes were not entirely clear. This study sheds light on these issues and confirms the importance of studying past climate variations to better understand the present and develop models for the future."  

Sea ice forms during winter in the polar regions and is one of the key climate variables. Arctic sea ice thickness can vary from a few tens of centimeters up to 5 meters, depending on the age of the ice: newly formed or first-year sea ice rarely exceeds one meter and is more fragile and prone to summer melting than older or multi-year sea ice, up to several meters thick and thus also more resistant. "In recent decades, due to the ongoing anthropogenic warming, Arctic sea ice extent at the end of summer  decreased of 13% per decade, compared to 1981-2010, with a global volume loss of more than 60 %  compared to 1982, largely due to the gradual disappearance of multi-year ice. At this rate, according to future climate scenarios, the Arctic Ocean will be ice-free in summer as early as 2050," warns  Barbante.  

"The new data confirm a previous study that aimed to reconstruct the Canadian Arctic sea ice evolution over the last glacial period which, however, did not have the temporal resolution to resolve in detail the transitions from cold stadial periods, to warm interstadial periods," concludes Andrea Spolaor, researcher at CNR-Isp. "Thanks to the temporal higher resolution, we found that multi-year sea ice reestablished itself during colder climate conditions, suggesting a feedback loop in which the gradual build-up of multi-year sea ice west and south of Greenland could have contributed to the transition of the climate system back to stadial conditions."