Past ice ages sometimes cut the Arctic off from the Atlantic

Geochemical evidence suggests the Arctic Ocean and Nordic Seas had sharply reduced exchange with the North Atlantic during full glacial periods.

Editorial illustration — not from the study.

Researchers used the ratio of two forms of beryllium preserved in marine sediments to trace water exchange between the Arctic Mediterranean—the Arctic Ocean and Nordic Seas—and the North Atlantic across glacial and interglacial periods. During fully glacial conditions, the ratio in the Arctic Mediterranean was more than 10 times lower than in the North Atlantic at the same time.

The result is consistent with strongly reduced exchange across the Greenland-Scotland Ridge. The researchers describe a dynamic pattern in which the regions alternated between isolation during glacials and rapid reconnection during deglaciation, when ice-age conditions ended.

The Arctic’s lost connection

The authigenic 10Be/9Be ratio was uniformly low in the fully glacial Arctic Mediterranean, at more than one order of magnitude below the ratio in the coeval North Atlantic. Because this tracer is less affected by changes in how quickly sediment accumulates, the finding supports strongly reduced water exchange across the Greenland-Scotland Ridge during glacial periods. The researchers interpret the pattern as alternating between glacial isolation and rapid reconnection during deglaciation.

Why the connection matters

The findings suggest that the Arctic Ocean and Nordic Seas did not remain continuously connected to the North Atlantic during past ice ages. If this changing connection affected the movement of water between the regions, it could be relevant to understanding how the global ocean circulation system operated during glacial cycles. The study leaves open how important this link was for that circulation.

Evidence and limits

The study is based on geochemical measurements in marine sediments, using the authigenic 10Be/9Be ratio as a tracer of water masses. The researchers chose this ratio because it is less vulnerable to changes in sedimentation that can create misleading isotope minima. The results support reduced exchange, but the abstract does not establish the exact conditions in the Arctic Mediterranean, such as whether it was fully fresh or covered by a thick ice shelf. The broader role of the connection in global ocean circulation also remains an open question.

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