Eastern North American freshwater discharge during the Bølling-Allerød warm periods

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 Bolling-Allerod warm periods (ca. 14.6–12.9 ka). Here we reconstruct the salinity-dependent δ 18 O sw (sw, seawater) adjacent to the eastern outlets of North America, using paired Mg/Ca and δ 18 O records on planktonic foraminifera, to investigate whether increased discharge to the North Atlantic caused reductions in AMOC during the Bolling-Allerod and earlier periods of deglaciation. In general, δ 18 O sw decreased and inferred freshwater discharge increased during periods of reduced AMOC. During the Bolling-Allerod, δ 18 O sw 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 (10 6 m 3 s −1 ) would explain these δ 18 O sw 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.