Early Interglacial Legacy of Deglacial Climate Instability

Abstract

Throughout the last glacial cycle millennial timescale variations in atmospheric CO2 occurred in parallel with perturbations in deep ocean circulation, which were themselves reflected by observable changes in surface conditions across the North Atlantic region. Here we use continuous proxy records to argue that an equivalent relationship has held throughout the last 800 kyr, that is, since before the first occurrence of Heinrich events (strictly defined). Our results highlight the importance of internal climate dynamics in amplifying external (insolation) forcing on the climate system to produce the large amplitude of glacial terminations (deglaciations) during the middle to late Pleistocene. We show that terminations are characterized by an interval of intense ice rafting followed by a subsequent and abrupt shift to anomalously warm surface conditions (with respect to the more gradually evolving background state), which we interpret to reflect an abrupt recovery of deep ocean circulation in the Atlantic. According to our synthesis, this is followed by a period of enhanced (or at least anomalous) overturning lasting thousands of years until equilibrium interglacial conditions are attained and during which atmospheric CO2 is likely to decrease. Our results therefore suggest that deglacial oscillations in ocean circulation can have a lasting influence on early interglacial climate and highlight the transient nature of atmospheric CO2 overshoots associated with the onset of some previous interglacials. Accordingly, we suggest that these intervals should be considered as a part of the deglacial process. This has implications for studies concerned with the evolution of atmospheric CO2 during interglacial periods including the Holocene.

Global ocean heat content in the Last Interglacial

“…These observations raise the question 31 of how much of the warmer-than-modern MOT in the early LIG was due to the weakened AMOC state, and how much can be attributed to the stable interglacial climate. In our record, MOT decreased and eventually stabilized by ~127 ka (at latest by ~124 ka) at a temperature that is comparable to Holocene/modern MOT (+0.2±0.3°C).…”

Strengthening Atlantic Inflow Across the Mid‐Pleistocene Transition

“…For this study we processed 2,783 samples along the splice of ODP 983 [Jansen et al, 1996] (extending previous work [Barker et al, 2015;Barker et al, 2019]) and 636 samples along the splice of ODP 981 [Jansen et al, 1996]. Sediment samples were spun overnight and washed…”

CO2‐Induced Decoupling of Tropical Surface and Thermocline Water Temperature at the Onset of Interglacials

“…Considering that atmospheric CO 2 has increased persistently since the mid‐Holocene, which is also unique among interglacials (Broecker et al, 2001) and likely caused by human activities (Ruddiman et al, 2016), the greenhouse effect on SST seems robust. Moreover, this so‐called CO 2 “overshoot” occurred during most of the early interglacial periods, except MIS11, and has been attributed to enhanced Atlantic meridional overturning circulation (AMOC) recovery (Barker et al, 2019). Such an enhanced overturning may last thousands of years until equilibrium interglacial conditions are attained and during which atmospheric CO 2 is likely to decrease (Barker et al, 2019), allowing the influence of the CO 2 “overshoot” on SST last for thousand years as well.…”

“…Moreover, this so‐called CO 2 “overshoot” occurred during most of the early interglacial periods, except MIS11, and has been attributed to enhanced Atlantic meridional overturning circulation (AMOC) recovery (Barker et al, 2019). Such an enhanced overturning may last thousands of years until equilibrium interglacial conditions are attained and during which atmospheric CO 2 is likely to decrease (Barker et al, 2019), allowing the influence of the CO 2 “overshoot” on SST last for thousand years as well. Conversely, the consistent interglacial decoupling process between SST and TWT during the past six deglacial‐interglacial cycles indicates enhanced air‐sea interaction during the beginning of interglacials, which is in agreement with modeling results and shows accelerated recovery of AMOC after a major shutdown (Krebs & Timmermann, 2007).…”