DOI: 10.25921/59sb-ah75
title: NOAA/WDS Paleoclimatology - North Atlantic Deglacial Isotope Data and Reconstructions of Salinity and SST

description: Paired Mg/Ca–d18O 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–d18O data from these species monitor changes in the temperature and seawater d18O 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–d18O 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.
description: Data collected by David J.R. Thornalley (Univ. of Cambridge); Principal Investigator: I. Nick McCave (Univ. of Cambridge); cruise CD-159, funded by UK RAPID program. Stable isotope values relative to VPDB standard, run in Godwin Laboratory, Univ. of Cambridge. Temperature calculated using Mg/Ca = B exp (0.1 × T). B = 0.794, 0.76 and 0.52 for G. bulloides, G. inflata and N. pachy. (s) respectively. Core notes:
RAPiD-10-1P: N. pachy. (s) and Cib. spp. isotope data originally presented in Thornalley, Elderfield & McCave, 2010, DOI:10.1029/2009PA001833. 
RAPiD-12-1K: Please cite Thornalley, Elderfield & McCave, Nature, 2009. For % sand and G. inflata d13C data, please cite Thornalley, Elderfield & McCave, 2010, Paleoceanography, DOI:10.1029/2009PA001833. Vital effect of -0.24 applied to Melonis d18O data. Salinity calculated using Kim and O'Neil (1997) to obtain d18Osw, including a 0.6‰ offset for G. bulloides, and VPDB to SMOW conversion of 0.27‰; Converted to salinity using Schmidt and Legrande (2006) N. Atlantic d18Osw-S relationship; Also corrected for whole ocean d18O and salinity changes (1 per mil glacial-interglacial) scaled to Fairbanks (1989) sea-level curve. Core-top age assignment: The core-top was not lost; assume 0cm=2004AD, but account for top 2 cm well mixed by bioturbation.
RAPiD-15-4P: All data except N. pachy.(s) originally presented in Thornalley, McCave & Elderfield, 2010, Paleoceanography, DOI:10.1029/2009PA001772. N. pachy. (s) isotope data originally presented in Thornalley, Elderfield & McCave, 2010, Paleoceanography, DOI:10.1029/2009PA001833. d18Osw calculated using Kim and O'Neil (1997), including a -0.6‰ offset for G. bulloides.  Note - no offset used for N. pachy.(s) contrary to manuscript, and VPDB to SMOW conversion of 0.27‰ "Ice-volume corrected" for whole ocean changes using Fairbanks (1989) sea-level curve, assuming a LGM to late Holocene shift of 1‰. Salinity calculated based on North Atlantic relation of LeGrande and Schmidt (2006) and also for N. pachyderma for mixing with a freshwater endmember
RAPiD-17-5P: C. wuell. And IRD data originally presented in Thornalley, Elderfield & McCave, 2010, Paleoceanography, DOI:10.1029/2009PA001833. d18Osw calculated using Kim and O'Neil (1997), including a 0.6‰ offset for G. bulloides, and VPDB to SMOW conversion of 0.27‰. "Ice-volume corrected" for whole ocean changes using Fairbanks (1989) sea-level curve, assuming a LGM to late Holocene shift of 1‰.