As part of the global oceanic circulation system, the near-surface North Atlantic Current transports heat and salinity northward into the Nordic seas. As this water cools off, it sinks to the ocean bottom and moves southward in a conveyor belt–like system that continuously redistributes heat. Because changes in the circulation of the northernmost Atlantic Ocean have the potential to affect Arctic and global climate, resolving the history of these currents can provide crucial context for interpreting modern changes occurring within this system.
To understand the currents’ evolution during the Pleistocene, Newton et al. analyzed an extensive database of three-dimensional offshore seismic data collected west of central Norway’s rugged coast. The data span 50,000 square kilometers of the Naust Formation, a late Pliocene–Pleistocene sedimentary shelf deposit that records multiple glacial-interglacial cycles beginning about 2.8 million years ago.
On the 33 stratigraphic surfaces found within this record, the researchers identified more than 17,000 V- and U-shaped grooves up to about 500 meters wide and extending 10–30 meters below the paleoseafloor surface. The team interprets these structures as scours made by icebergs that became grounded as they floated above the shallow continental shelf during the Pleistocene.
Because the grooves on all of the surfaces are predominantly oriented southwest–northeast, the authors argue that they represent the direction of the surface paleocurrent at the time each horizon was deposited. In combination with numerical modeling studies and other geologic evidence, these data indicate that surface currents in this region consistently flowed northward throughout numerous Pleistocene glacial-interglacial cycles.
This study expands our knowledge of the currents and the behavior of icebergs in the Norwegian Sea during the last 2.8 million years. It also suggests that the position and direction of surface currents in the eastern North Atlantic during the Pleistocene were similar to those observed today. The results will help place modern observations within a long-term perspective and improve the calibration of Earth system models. (Geophysical Research Letters, https://doi.org/10.1029/2018GL077819, 2018)
—Terri Cook, Freelance Writer