The Arctic Ocean was filled with freshwater at least twice in the last 150,000 years, according to a new study from the Alfred Wegener Institute. The experts report that the Arctic Ocean, as well as the Nordic Seas, did not contain salt during two separate glacial periods.
The researchers determined that these oceans were filled with large amounts of freshwater under shelf ice that was up to 900 meters thick. The water could be released into the North Atlantic in very short periods of time.
The study has revealed that the floating parts of the northern ice sheets covered large parts of the Arctic Ocean in the past 150,000 years. During two time periods, freshwater accumulated under the ice, which transformed the Arctic Ocean for thousands of years.
“These results mean a real change to our understanding of the Arctic Ocean in glacial climates,” said study first author Dr. Walter Geibert. “To our knowledge, this is the first time that a complete freshening of the Arctic Ocean and the Nordic Seas has been considered – happening not just once, but twice.”
According to Dr. Geibert, the decay of naturally occurring uranium always results in the production of the isotope thorium-230 when water is salty. “This substance accumulates at the sea floor, where it remains detectable for a very long time due to its half-life of 75,000 years.”
“Here, its repeated and widespread absence is the giveaway that reveals to us what happened. According to our knowledge, the only reasonable explanation for this pattern is that the Arctic Ocean was filled with freshwater twice in its younger history – in frozen and liquid form,”explained Dr. Jutta Wollenburg.
A range of past climate fluctuations could be explained by the existence of enormous amounts of freshwater stored in the Arctic Ocean that were available for rapid release.
“The remains of coral reefs have pointed to a somewhat higher sea level in certain cold periods than reconstructions from Antarctic ice cores, or reconstructions from the calcareous shells of small marine organisms, would suggest,” said Dr. Geibert.
“If we now accept that freshwater may not only have been stored in solid form on land, but some of it also in liquid form in the ocean, the different sea level reconstructions agree better and we can reconcile the location of the coral reefs with calculations of the freshwater budget.”
Freshwater release from the Arctic may also be responsible for certain climate change events during the last glacial period, when temperatures in Greenland would abruptly rise by 8-10 degree centigrade within a few years.
“We see an example here of a past Arctic climate tipping point of the Earth system,” said Dr. Geibert. “Now we need to investigate in more detail how these processes were interconnected, and evaluate how this new concept of the Arctic Ocean helps in closing further gaps in our knowledge, in particular in view of the risks of manmade climate change.”
The study is published in the journal Nature.