In the far North Atlantic, scientists have uncovered new evidence that an unusual infusion of freshwater into the ocean may already be affecting the ocean’s circulation. Mostly likely sourced from melting glaciers in Greenland or Arctic sea ice, the freshwater remains on the surface of the ocean for longer than denser saltwater. This could affect the ocean’s natural process known as convection, in which northbound surface water becomes denser and colder, thus sinking then traveling south at great depths. “Until now, models have predicted something for the future … but it was something that seemed very distant,” study lead author Marilena Oltmanns told the Washington Post. “But now we saw with these observations that there is actually freshwater and that it is already affecting convection, and it delays convection quite a lot in some years.”
The research team gathered data on Irminger Sea to the southeast of Greenland, where they used ocean moorings to take measurements regarding the circulation of ocean water at key convection sites. While the study does not make any specific predictions regarding how convection may be affected, or how quickly it may change, the conclusion that freshwater from melting glaciers or sea ice may be already affecting convection is noteworthy. In 2010, 40 percent of melted freshwater remained on the surface through winter and into the next year. The staying power of the melted freshwater may suggest a positive feedback loop that could drive further mixing.
“It is possible that there is a threshold, that if there is a lot of freshwater that stays at the surface, and mixes with the new freshwater from the new summer, it suddenly doubles, or increases a lot, and the next winter, it’s a lot more difficult to break through,” said Oltmanns. It is already established that Atlantic circulation has been weaker than average since 2008, with scientists crediting climate change, cyclical patterns, or both. While the changes to convection may occur over time, the latest study indicates that change may occur more rapidly than expected. “There might be a threshold that is crossed, and it’s harder to get back to where we were before,” said Oltmanns. “It’s possible.”