Alongflow variability of the Labrador Current during the Holocene

Abstract

The Labrador Current (LC) provides freshwater from the Arctic to the North Atlantic, modulating the Atlantic Meridional Overturning Circulation (AMOC), and therefore affecting the broader North Atlantic climate. The Holocene alongflow variability of the LC vigor, and the associated forcing mechanisms, are poorly understood due to the limited data near the southern limit of the LC. Here we present a new 9.4 ka record of distal LC vigor over the Scotian Shelf using the sortable-silt proxy, which allows for the first time an assessment of the alongflow changes in Holocene LC vigor and hence its forcing mechanisms. LC speed on the Scotian Shelf decreased slightly from 9.4 to 8.0 ka, during which the 8.1 ka meltwater event had a strong influence. The LC progressively intensified from 8.0 to 5.0 ka, weakened between 5.0 and 1.8 ka and gradually intensified from 1.8 to 0.5 ka. Our synthesis reveals that the Holocene flow history of the LC appears geographically variable due to the interaction of the inner and outer LC. The mean size of the sortable silt data on the Scotian Shelf involve inner or outer LC signals in different periods of the Holocene. The LC vigor on the Scotian Shelf between 9.4–8.0 ka and 1.8–0.5 ka represent the outer LC, which is consistent with the stronger West Greenland Current and increased influx of Atlantic-sourced water to the outer LC. We find a broad agreement between inner LC vigor and AMOC-related sea surface temperature (SST) of the subpolar North Atlantic and the North Atlantic Oscillation (NAO), which suggests that a strong (weak) inner LC is generally associated with regional warm (cold) climate and negative (positive) NAO. The outer LC vigor is dominated by the NAO during the Holocene and partly controlled by freshwater supply between 10.0 and 5.0 ka. We also demonstrate the negative/positive link between the inner/outer LC vigor and the NAO on a millennium time scale. This study improves our understanding of LC variability and sensitivity to anthropogenic warming, and suggest that inner (outer) LC vigor may experience not only a decreasing (increasing) trend in a future warmer climate, with additional effects resulting from enhanced melting of the Greenland ice sheet.