Sub sea surface temperatures in the Polar North Atlantic during the Holocene: Planktic foraminiferal Mg/Ca temperature reconstructions

Abstract

Holocene sea surface temperatures in the eastern Fram Strait are reconstructed based on Mg/Ca ratios measured on the planktic foraminifer Neogloboquadrina pachyderma (sin). The reconstructed sub sea surface temperatures (sSSTMg/Ca) fluctuate markedly during the earliest Holocene at ~11.7 and 10.5 kyr BP. This is probably in response to the varying presence of sea-ice and deglacial meltwater. Between ~10.5–7.9 kyr BP, the sSSTMg/Ca values are relatively high (~4°C) and more stable reflecting high insolation and intensified poleward advection of Atlantic Water. After 7.9 kyr BP, the sSSTMg/Ca values decline to an average of ~3°C throughout the mid-Holocene. These changes can be attributed to a combined effect of reduced poleward oceanic heat advection and a decline in insolation as well as a gradually increased influence of eastward migrating Arctic Water. The sSSTMg/Ca values increase and vary between 2.1°C and 5.8°C from ~2.7 kyr BP to the present. This warming is in contrast to declining late-Holocene insolation and may instead be explained by factors including increased advection of oceanic heat to the Arctic region possibly insulated beneath a widening freshwater layer in the northern North Atlantic in conjunction with a shift in calcification season and/or depth habitat of N. pachyderma (sin).