Abstract

During the last deglaciation (ca. 19–6.5 ka), increased freshwater discharge to the North Atlantic likely caused reductions in Atlantic meridional overturning circulation (AMOC) strength. However, the locations and rates of freshwater discharge are not well constrained, particularly those during the centennial-scale climate oscillations of the Bølling-Allerød warm periods (ca. 14.6–12.9 ka). Here we reconstruct the salinity-dependent δ18Osw (sw, seawater) adjacent to the eastern outlets of North America, using paired Mg/Ca and δ18O records on planktonic foraminifera, to investigate whether increased discharge to the North Atlantic caused reductions in AMOC during the Bølling-Allerød and earlier periods of deglaciation. In general, δ18Osw decreased and inferred freshwater discharge increased during periods of reduced AMOC. During the Bølling-Allerød, δ18Osw decreases coincided with three reductions in AMOC strength ca. 14.1, 13.8, and 13.3 ka. Freshwater discharge modeling suggests that discharge increases of 0.03–0.05 Sverdrups (106 m3 s−1) would explain these δ18Osw decreases, which were sufficient to force reductions in AMOC strength. Concurrent changes in North Atlantic temperature, and subtropical and tropical atmospheric circulation and precipitation imply that small variations in the North Atlantic hydrologic system may have significant impacts on Northern Hemisphere climate.

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