Warming in Greenland Sea Outpaces Global Ocean Warming

The Greenland Sea is warming nearly 10 times faster than warming rates estimated for the rest of the global ocean, according to research from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in Germany.

To investigate climate change in the region, the scientists compiled temperature and salinity measurements taken in the Greenland Sea since 1993 and coupled the data with historical observations dating back to the 1950s.

Writing in the journal Geophysical Research Letters, the scientists report that in the past three decades the water temperatures in the Greenland Sea at depths of 2,000 meters down to the sea floor have risen by 0.3 degrees Celsius.

"This sounds like a small number, but we need to see this in relation to the large mass of water that has been warmed," AWI scientist and lead study author Raquel Somavilla Cabrillo said in a statement. "The amount of heat accumulated within the lowest 1.5 kilometers in the abyssal Greenland Sea would warm the atmosphere above Europe by 4 degrees centigrade. The Greenland Sea is just a small part of the global ocean. However, the observed increase of 0.3 degrees in the deep Greenland Sea is ten times higher than the temperature increase in the global ocean on average. For this reason, this area and the remaining less studied polar oceans need to be taken into consideration."

Somavilla Cabrillo and her colleagues suggest the warming is the result of the cooling by deep sea convection of very cold surface waters during winter paired with warming brought on by comparatively warm deep water from the Arctic Ocean.

"Until the early 1980s, the central Greenland Sea has been mixed from the top to the bottom by winter cooling at the surface making waters dense enough to reach the sea floor," Somavilla explained. "This transfer of cold water from the top to the bottom has not occurred in the last 30 years. However, relatively warm water continues to flow from the deep Arctic Ocean into the Greenland Sea. Cooling from above and warming through inflow are no longer balanced, and thus the Greenland Sea is progressively becoming warmer and warmer," she said.

Ursula Schauer, head of the Observational Oceanography Department at the Alfred Wegener Institute, said the modified ocean conditions allowed for unique research opportunities.

"We use these changes as a natural experiment. The warming allows us to calculate how much water flows from the deep central Arctic into the Greenland Sea," Schauer said. "We observe here a distinct restructuring of the Arctic Ocean. This is a very slow process, and its documentation requires long term observations."

Schauer added that the large volume the deep thermal inertia present there creates a powerful heat buffer for climate warming.

"If we want to understand the role of the deep ocean in the climate system, we need to expand the measurements to remote regions like the Arctic," Schauer said.