Reconstructing North Atlantic deglacial surface hydrography and its link to the Atlantic overturning circulation

Thornalley, David J.R. and Elderfield, Harry and McCave, I. Nick (2011) Reconstructing North Atlantic deglacial surface hydrography and its link to the Atlantic overturning circulation. Global and Planetary Change, 79 (3-4). pp. 163-175. DOI

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Paired Mg/Ca-[delta]18O measurements on multiple species of planktic foraminifera are combined with published benthic isotope records from south of Iceland in order to assess the role North Atlantic freshwater input played in determining the evolution of hydrography and climate during the last deglaciation. We demonstrate that Globigerina bulloides and Globorotalia inflata are restricted to intervals when warm Atlantic waters reached the area south of Iceland, and therefore Mg/Ca-[delta]18O data from these species monitor changes in the temperature and seawater [delta]18O signature of the northward inflow of Atlantic water to the area. In contrast, Neogloboquadrina pachyderma (sinistral) calcifies within local subpolar/polar waters and new Mg/Ca-[delta]18O analyses on this species document changes in this water mass. We observe two major surface ocean events during Heinrich Stadial 1 (~ 17-14.7 ka): an early freshening of the Atlantic Inflow (~ 17-16 ka), and a later interval (16-14.7 ka) of local surface freshening, sea-ice formation and brine rejection that was associated with a further reduction in deep ocean ventilation. Centennial-scale cold intervals during the Bølling-Allerød (BA, 14.7-12.9 ka) were likely triggered by the rerouting of North American continental run-off during ice-sheet retreat. However, the relative effects of these freshwater events on deep ventilation and climate south of Iceland appear to have been modulated by the background climate deterioration. Two freshwater events occurred during the Younger Dryas cold interval (YD, 12.9-11.7 ka), both accompanied by a reduction in deep ventilation south of Iceland: an early YD freshening of the Atlantic Inflow and local subpolar/polar waters, and a late YD ice-rafted detritus event that was possibly related to brine formation south of Iceland. Based on our reconstructions, the strengthening of the Atlantic Meridional Overturning Circulation at the onset of BA and Holocene may have been promoted by the subsurface warming of subpolar/polar water, brine formation that drew warm saline Atlantic water northwards, and the high background salinity of the Atlantic Inflow.

Item Type: Article
Uncontrolled Keywords: 2011AREP; IA63;
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Global and Planetary Change
Volume: 79
Page Range: pp. 163-175
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 28 Jul 2011 09:52
Last Modified: 23 Jul 2013 10:02

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