Holocene climate variability in the Labrador Sea

Formation of Labrador Sea Water proper commenced about 7000 years ago during the Holocene interglacial. To test whether fresher surface water conditions may have inhibited Labrador Sea Water convection during the early Holocene we measured planktonic foraminiferal (Globigerina bulloides) oxygen isotopes (delta O-18) and Mg/Ca ratios at Orphan Knoll (cores HU91-045-093 and MD95-2024, 3488 m) in the Labrador Sea to reconstruct shallow subsurface summer conditions (temperature and seawater delta O-18). Lighter foraminiferal delta O-18 values are recorded during the early Holocene between 11000 and 7000 years ago. Part of these lighter foraminiferal delta O-18 values can be explained by increased calcification temperatures. Reconstructed seawater delta O-18 values were, however, still on average 0.5 parts per thousand lighter compared with those of recent times, confirming that fresher surface waters in the Labrador Sea were probably a limiting factor in Labrador Sea Water formation during the early Holocene.