Northward oceanic heat transport in the main branch of the Norwegian Atlantic Current over the late Holocene

Abstract

The Norwegian Atlantic Current represents the northernmost reaches of the (sub)surface limb of the Atlantic Meridional Overturning Circulation. Its shelf-edge branch, the Norwegian Atlantic Slope Current (NwASC), is of particular interest as it seems to be the main conduit for advected heat towards the Arctic. The objective of this study was to investigate northward oceanic heat transport in the NwASC on longer, geologically meaningful time scales. To this end, we reconstructed variations in the strength of the NwASC over the late Holocene using the sortable-silt method. We then analysed the statistical relationship between our palaeo-flow reconstructions and published upper-ocean hydrography proxy records from the same location on the mid-Norwegian Margin. Our sortable-silt time series show prominent multi-decadal to multi-centennial variability, but no clear long-term trend over the past 4200 years. These records we thus interpret to represent perturbations in a relatively stable late-Holocene mean flow. Our in-depth statistical analysis indicates that upper-ocean temperatures at the mid-Norwegian Margin may have varied independently from the strength of the NwASC on multi-decadal to multi-centennial time scales over the past few millennia.