Millennial-scale tropical atmospheric and Atlantic Ocean circulation change from the Last Glacial Maximum and Marine Isotope Stage 3

Abstract

Abrupt, millennial-scale climate oscillations, known as Dansgaard-Oeschger (D-O) cycles, characterized the climate system of the last glacial period. Although proxy evidence shows that D-O cycles resulted in large-scale changes in atmospheric circulation patterns around the planet, an understanding of how Atlantic Meridional Overturning Circulation (AMOC) varied across these events remains unclear. Here, we take advantage of the fact that both tropical atmospheric circulation changes corresponding to northsouth shifts in the Intertropical Convergence Zone (ITCZ) and large-scale changes in ocean circulation associated with AMOC variability can be reconstructed in the same sediment core from the Florida Straits to examine the relationship between atmospheric and ocean circulation changes across D-O events. To reconstruct surface water conditions, Mg/Ca-paleothermometry and stable isotope measurements were combined on the planktonic foraminifera Globigerinoides ruber (white variety) from sediment core KNR166-2 JPC26 (24 • 19.61 N, 83 • 15.14 W; 546 m depth) to reconstruct a high-resolution record of sea surface temperature and δ 18 O seawater (a proxy for upper mixed layer salinity) during Marine Isotope Stages (MIS) 2 and 3 from 20-35 ka BP. As an additional proxy for upper water column salinity change, we also generate a faunal abundance record of the salinity-sensitive planktonic foraminifera Neogloboquadrina dutertrei. Our results suggest that rapid reductions in sea surface salinity occurred at the onset of D-O interstadials, while stadials are characterized by increased surface salinities. The most likely cause of these salinity changes was variation in the strength and position of the ITCZ across D-O events. Finally, we examine the relationship between millennial-scale atmospheric circulation changes recorded in the planktonic records and ocean circulation changes inferred from the benthic δ 18 O record from our core. Our results provide some of the first evidence that AMOC strength did vary across at least one of the millennial-scale D-O cycles of MIS 3.

Deglacial Heat Uptake by the Southern Ocean and Rapid Northward Redistribution Via Antarctic Intermediate Water

“…There is no evidence for sample contamination by clay minerals and/or diagenetic coatings assessed from Al/Ca, Mn/Ca, and Fe/Ca ratios, ruling out any falsifying effect on the reconstructed IWT Mg/Ca . A detailed discussion can be found in the supporting information (Figures S3 and S4; Barker et al, ; Poggemann et al, ; Roberts et al, ; Rühlemann et al, ; Them et al, ). A small number of single data points yielded unrealistically high/low values compared with neighboring data.…”

“…Paleoceanography and Paleoclimatology 2017; Roberts et al, 2016;Rühlemann et al, 2004;Them et al, 2015). A small number of single data points yielded unrealistically high/low values compared with neighboring data.…”

The Atlantic Meridional Overturning Circulation and Abrupt Climate Change

“…Density reconstructions from the Florida Straits extend only as far back as D-O interstadial 6. Although there is no evidence of circulation change over the very short events, there are δ 18 O excursions consistent with a strong upper branch of the AMOC for D-O interstadials 5 and 6 (Them et al 2015). Thornalley et al (2013) presented a thorough and convincing analysis of the flow speed of deep western boundary currents off North America over the transition between late marine isotope stage 5 and stage 4 based on the sortable silt grain size proxy.…”

Controls on the Tropical Response to Abrupt Climate Changes

“…During DO events, there is evidence that the ocean circulation evolved from being relatively slow and shallow during the stadials to deeper and more vigourous during the interstadials (e.g. Burckel et al, 2015;Henry et al, 2016); however, this evidence is not conclusive (e.g., Them et al, 2015;Thornalley et al, 2013). Furthermore, it is not obvious whether the ocean circulation is a unique driver of change or just part of an internal oscillation of the coupled ocean-atmosphere-sea ice system (Brown & Galbraith, 2016;Drijfhout et al, 2013;Kleppin et al, 2015;Martin et al, 2015;Sidorenko et al, 2014;Vettoretti & Peltier, 2018).…”