Holocene climate variability reflected in diatom-derived sea surface temperature records from the subpolar North Atlantic

A detailed investigation of two deep-sea sediment cores from the Gardar Drift in the subpolar North Atlantic, cores MD99-2251 and MD99-2252, has been undertaken to determine the extent of Holocene climate variability reflected by changes in diatom floral abundances. Core MD99-2251 extends through the Holocene, while core MD99-2252 spans the last 7200 years. A new regional-based sea surface temperature (SST) calibration is derived using the weighted averaging partial least squares (WA-PLS) method based on 28 taxonomic categories within 53 coretops. WA-PLS-derived SST estimates indicate relatively small long-term SST changes of only 1–2°C during the Holocene. Notably, a well-defined thermal maximum is absent in the early Holocene record and the 8200-year event is not recognized as a discrete temperature minimum. However, lower SSTs between 8800 and 7800 years ago associated with the presence of sea ice and cold water species indicate an increased incursion of the subarctic water mass. A significant warming of ~2°C around 7000 years ago is the most unambiguous change in the SST records and is replicated in both cores. A brief interval of warmer sea surface conditions ~6000 years ago, associated with a Holocene maximum in North Atlantic Current indicator species, ended by 5300 years ago. Relatively muted SST variability is evident through the remainder of the Holocene.