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 (δ18O) 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 δ18O). Lighter foraminiferal δ18O values are recorded during the early Holocene between 11000 and 7000 years ago. Part of these lighter foraminiferal δ18O values can be explained by increased calcification temperatures. Reconstructed seawater δ18O values were, however, still on average 0.5‰ 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.

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