Andrew Newton

Buried iceberg scours reveal reduced North Atlantic Current during the stage 12 deglacial.

Reconstructing past ocean-climate environments and heat transport requires proxies from which these conditions can be quantified. This is particularly important for the evaluation of numerical palaeoclimate models. Here we present new evidence for a reduced North Atlantic Current (NAC) at the termination of the third last glacial, for which palaeocurrent information was previously unavailable. This is based on an exquisitely preserved set of buried iceberg scours seen in three-dimensional seismic reflection images from the mid-Norwegian slope. The scours were formed ∼430 ka during the transition from glacial to interglacial conditions. The spiral geometry of the scours suggests that they were carved by grounded icebergs influenced by tidal and geostrophic ocean currents. Using the ratio between the estimated tidal and geostrophic current velocities and comparing them with velocities from the Last Glacial Maximum and the present, we show that the stage 12 NAC velocities may have been ∼50% slower than the present.

Extensive marine-terminating ice sheets in Europe from 2.5 million years ago

Ice sheets repeatedly advanced into the central North Sea, south of ~60°N, from 2.53 Ma ago onward moving over slippery beds with low slung profiles. Geometries of Early Pleistocene [2.58 to 0.78 million years (Ma) ago] ice sheets in northwest Europe are poorly constrained but are required to improve our understanding of past ocean-atmosphere-cryosphere coupling. Ice sheets are believed to have changed in their response to orbital forcing, becoming, from about 1.2 Ma ago, volumetrically larger and longer-lived. We present a multiproxy data set for the North Sea, extending to over a kilometer below the present-day seafloor, which demonstrates spatially extensive glaciation of the basin from the earliest Pleistocene. Ice sheets repeatedly entered the North Sea, south of 60°N, in water depths of up to ~250 m from 2.53 Ma ago and subsequently grounded in the center of the basin, in deeper water, from 1.87 Ma ago. Despite lower global ice volumes, these ice sheets were near comparable in spatial extent to those of the Middle and Late Pleistocene but possibly thinner and moving over slippery (low basal resistance) beds.

A persistent Norwegian Atlantic Current through the Pleistocene glacials

Changes in ocean-circulation regimes in the northern North Atlantic and the Nordic Seas may affect not only the Arctic but potentially hemispheric or even global climate. Therefore, unraveling the long-term evolution of the North Atlantic Current-Norwegian Atlantic Current system through the Pleistocene glaciations could yield useful information and climatological context for understanding contemporary changes. In this work, ~50,000 km of 3-D seismic reflection data are used to investigate the Pleistocene stratigraphy for evidence of paleo-oceanographic regimes on the mid-Norwegian margin since 2.58 Ma. Across 33 semicontinuous regional paleo-seafloor surfaces ~17,500 iceberg scours have been mapped. This mapping greatly expands our spatiotemporal understanding of currents and iceberg presence in the eastern Nordic Seas. The scours display a dominant southwest-northeast trend that complements previous sedimentological and numerical modeling studies that suggest northward-flowing currents in the Norwegian Sea during the Pleistocene. This paleo-oceanographic study suggests that through many of the Pleistocene glaciations, the location of surface ocean currents in the Norwegian Sea and, by extension, the eastern North Atlantic, were broadly similar to the present. Plain Language Summary The bridging location of the northern North Atlantic Ocean and the Nordic Seas between low and high latitudes means that environmental changes in one region can potentially be transmitted on a hemispheric or global scale. The Norwegian Atlantic Current crosses this region, and in the present-day setting, it helps to bring heat up from the tropics and toward the Arctic. This heat exchange helps to keep the climate of NW Europe relatively mild. Over a longer time scale (e.g., the last 2.58 million years) the history of this current is poorly known, not least of all how it behaved through different ice ages. In this work we use evidence of floating icebergs in the Norwegian Sea to reconstruct the ocean currents that controlled the drift directions of the icebergs. This has shown that through many of the glacial periods in the last 2.58 million years, there is evidence for the Norwegian Atlantic Current still reaching high latitudes. This has important implications for understanding the main controls and stability of ocean currents in the region and how they may impact regional and global climate.