Millennial climate oscillations controlled the structure and evolution of Termination II

Abstract

The controls that affect the structure and timing of terminations are still poorly understood. We studied a tufa deposit from the Iberian Peninsula that covers Termination II (T-II) and whose chronology was synchronized to speleothem records. We used the same chronology to synchronize ocean sediments from the North Atlantic to correlate major climate events in a common timescale. We identify two stages within T-II. The first stage started with the increase of boreal summer integrated solar insolation, and during this stage three millennial climate oscillations were recorded. These oscillations resulted from complex ocean–atmosphere interactions in the Nordic seas, caused by the progressive decay of Northern Hemisphere ice-sheets. The second stage commenced after a glacial outburst that caused the collapse of the Thermohaline Circulation, a massive Heinrich event, and the onset of the Bipolar Seesaw Mechanism (BSM) that eventually permitted the completion of T-II. The pace of the millennial oscillations during the first stage of T-II controlled the onset of the second stage, when the termination became a non-reversible and global phenomenon that accelerated the deglaciation. During the last the two terminations, the BSM was triggered by different detailed climate interactions, which suggests the occurrence of different modes of terminations.

Abrupt climate changes in the last two deglaciations simulated with different Northern ice sheet discharge and insolation

“…In addition, based on the climate model results, a sustained weak AMOC during the middle and later stages was more critical to the peak Antarctic temperature during deglaciation. Even if the AMOC experienced strong modes in the early stage of the deglaciation, possibly corresponding to the observed climate fluctuations 54 , 55 , Antarctic temperature reached a similar thermal maximum in the late stage of the deglaciation (Supplementary Fig. S6 g).…”

“…S6 f). In particular, the AMOC oscillated twice during the early stage of T2 (135–133 ka), possibly corresponding to the abrupt climate changes recorded by dust concentrations in an Antarctic ice core from Dome Fuji 34 or the abrupt changes in the methane record and SSTs in the North Atlantic before 133 ka 4 , 54 , 55 . The stronger AMOC in the early stage of the deglaciation was likely because of the orbital parameters and atmospheric CO 2 forcing, which tend to warm temperatures over the North Atlantic and the Antarctic region.…”

Thermal impact of Heinrich stadials in cave temperature and speleothem oxygen isotope records

“…The magnitude and duration of the modeled HS considered data from the North Atlantic off the Iberian Peninsula and the Mediterranean during the Late Pleistocene (Cacho et al, 1999;Pérez-Folgado, et al, 2003;Essallami et al, 2007;Martrat et al, 2007;Castaneda et al, 2010;Voelker and de Abreu, 2011). The hypothetical HS that we reproduce does not consider HSs that occurred during terminations, as their duration, evolution, and climate conditions often differ from HSs that occur during full-glacial climate conditions (e.g., Denton et al, 2006;Domínguez-Villar et al, 2020). We assume that the continents and sea surface recorded similar thermal anomalies.…”

Heinrich Events

“…Domínguez-Villar et al (2021) follow by suggesting a modeling approach on speleothem records. They show that with increasing cave depth, the HE surface temperature anomaly is attenuated, and the lag time to build up a corresponding signal increases.…”