A new study led by Walter Geibert at the Alfred Wegener Institute suggests that during certain ice age periods, the Arctic Ocean and the Nordic Seas were filled with fresh water and covered in ice, Ars Technica reports.
The study analyzed a pair of sediment cores taken from the bottom of the Arctic Ocean. These showed two separate time intervals during which thorium-230 — an isotope that exists in seawater proportionally to its salinity — fell to zero.
The intervals — one about 60,000 to 70,000 years ago and the other about 130,000 to 150,000 years ago — occurred during cold glacial periods during which great ice sheets covered large parts of the Northern Hemisphere.
By looking at eight other previously analyzed cores from across the Arctic and down into the seas off Greenland and Antarctica, the researchers found that their discovery was not a one-off as they contained the same periods of low or absent thorium.
Closing gaps in our knowledge related to 'manmade climate change'
The researchers believe that the Bering Land Bridge between Asia and North America at the time cut off the Arctic Ocean from the Pacific due to lower sea levels, leading to the drop in salinity.
Furthermore, the presence of floating ice shelves connected to glaciers on land could have restricted water flow from the Atlantic into the Arctic. Melting glacial ice might then have contributed enough freshwater into the Arctic that the remaining water flow would mostly go out towards the Atlantic, flushing out Arctic saltwater and preventing Atlantic saltwater from replacing it.
"These results mean a real change to our understanding of the Arctic Ocean in glacial climates. 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," Dr. Walter Geibert explains in a press release.
Dr. Geibert says the findings might help to explain sudden climate change events during the last glacial period and can help to close the gaps in our knowledge, "in particular in view of the risks of manmade climate change."