Distinguishing current effects in sediments delivered to the ocean by ice. II. Glacial to Holocene changes in high latitude North Atlantic upper ocean flows

Shallow ocean flows in the northern North Atlantic are of key importance in the regulation of Earth's climate. In the northern North Atlantic nutrient-rich cold Arctic Ocean outflow (of modified Atlantic water) plus Pacific and ice-melt waters flow in the East Greenland Current (EGC) and in the Baffin Island Current which feeds into the Labrador Current. The outflows east of Greenland carry a substantial amount of warm salty North Atlantic water that flows into the Nordic Seas, mixes, recirculates - much of it via the Arctic Ocean - and contributes to both shallow and deep overflows. A key to understanding oceanic control of Earth's climate therefore resides in establishing the changes in these high-latitude currents. We have analysed 28 cores comprising similar to 2900 measured samples in the high-latitude N. Atlantic and Arctic Oceans of which >80% pass the reliability test of a correlation coefficient between sortable silt mean and percentage r > 0.5 (McCave and Andrews, 2019, Quat. Sci. Rev. 212, 92-107). There is a close similarity between the pattern of Holocene decrease in the strength of the Irminger Current inflow to the Nordic Seas and outflow recorded in the EGC and in deep overflow east of Reykjanes Ridge. This suggests that the flow of the EGC is strongly influenced by the influx of North Atlantic water, rather than supply of fresher water from ice sheet melt or Pacific origin. In contrast to the flows east of Greenland, those west of Greenland show a slow Holocene increase in flow. The freshest/coldest deep Denmark Strait overflow recorded at Orphan Knoll, as well as Labrador Sea water flow on the slope north of the Grand Banks, also show this gradual increase. This points to control on deep water overflows by the flux of cold fresh water from Greenland and the Arctic, some of which may have come from the Pacific via the Bering Strait. Models also show a Holocene east-west difference in deep-water formation with increase in the Labrador Sea and decrease in the Nordic seas. In almost all cases Holocene flow speed maxima lag the local Holocene Thermal Maxima by between 0 and 1000 years. It is therefore highly unlikely that the local Holocene thermal maxima are responses to increased flow of shallow currents in the adjacent ocean areas. Decelerations in flow speed accompany Holocene coolings, while accelerations accompany warmings. The LGM was a period of slow flow, and meltwater events usually show slowdowns as well. However, Heinrich events show slowdowns in some regions and faster flow in others. (C) 2019 Elsevier Ltd. All rights reserved.