Abstract
Large amplitude variations in atmospheric CO2 were associated with glacial terminations of the Late Pleistocene. Here we provide multiple lines of evidence suggesting that the ∼20 p.p.m.v. overshoot in CO2 at the end of Termination 2 (T2) ∼129 ka was associated with an abrupt (≤400 year) deepening of Atlantic Meridional Overturning Circulation (AMOC). In contrast to Termination 1 (T1), which was interrupted by the Bølling-Allerød (B-A), AMOC recovery did not occur until the very end of T2, and was characterized by pronounced formation of deep waters in the NW Atlantic. Considering the variable influences of ocean circulation change on atmospheric CO2, we suggest that the net change in CO2 across the last 2 terminations was approximately equal if the transient effects of deglacial oscillations in ocean circulation are taken into account.
Highlights
The Late Pleistocene was characterized by large amplitude variations in atmospheric carbon dioxide (CO2) with corresponding changes in temperature and ice volume[1,2,3]
By analogy with similar conditions associated with Heinrich Stadial 1 (HS1, B18–14.6 ka) during the early part of Termination 1 (T1), evidence from North Atlantic marine sediments[16,17,18], Chinese speleothems[12] and Antarctic ice cores[1,13] has been used to infer that the Atlantic Meridional Overturning Circulation (AMOC) may have been in a weakened and or shallow mode throughout much of Termination 2 (T2) (refs 12,13; during a prolonged interval of North Atlantic cold identified as HS11, B135–129 ka) with resumption to a deep and warm mode of circulation occurring only later (B124–127 ka) within the penultimate interglacial period, Marine Isotope Stage (MIS) 5e
To further characterize environmental conditions across T2 and, crucially, to allow us to place our records within the chronostratigraphic framework of the ice-core records[23] (Methods section) we present new high resolution records of planktic foraminiferal d18O, planktic foraminiferal faunal abundance, ice rafted debris (IRD) counts, and additional carbonate preservation indices, all measured on the same samples from ODP Site 1063
Summary
The low values of benthic d13C and poor carbonate preservation (low % coarse fraction and high fragmentation) we observe during HS11 (Fig. 2b), in combination with less negative eNd values, suggest an enhanced influence of southern-sourced deep waters (glacial equivalent to modern Antarctic Bottom Water (AABW)) in the abyssal North Atlantic during HS11 relative to today. This is analogous to the millennial-scale cold events of the last glacial cycle[29]. We note that our new record of benthic d13C shows
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