Abstract
Abstract. The last deglaciation, which occurred from 18 000 to 11 000 years ago, is the most recent large natural climatic variation of global extent. With accurately dated paleoclimate records, we can investigate the timings of related variables in the climate system during this major transition. Here, we use an accurate relative chronology to compare temperature proxy data and global atmospheric CO2 as recorded in Antarctic ice cores. In addition to five regional records, we compare a δ18O stack, representing Antarctic climate variations with the high-resolution robustly dated WAIS Divide CO2 record (West Antarctic Ice Sheet). We assess the CO2 and Antarctic temperature phase relationship using a stochastic method to accurately identify the probable timings of changes in their trends. Four coherent changes are identified for the two series, and synchrony between CO2 and temperature is within the 95 % uncertainty range for all of the changes except the end of glacial termination 1 (T1). During the onset of the last deglaciation at 18 ka and the deglaciation end at 11.5 ka, Antarctic temperature most likely led CO2 by several centuries (by 570 years, within a range of 127 to 751 years, 68 % probability, at the T1 onset; and by 532 years, within a range of 337 to 629 years, 68 % probability, at the deglaciation end). At 14.4 ka, the onset of the Antarctic Cold Reversal (ACR) period, our results do not show a clear lead or lag (Antarctic temperature leads by 50 years, within a range of −137 to 376 years, 68 % probability). The same is true at the end of the ACR (CO2 leads by 65 years, within a range of 211 to 117 years, 68 % probability). However, the timings of changes in trends for the individual proxy records show variations from the stack, indicating regional differences in the pattern of temperature change, particularly in the WAIS Divide record at the onset of the deglaciation; the Dome Fuji record at the deglaciation end; and the EDML record after 16 ka (EPICA Dronning Maud Land, where EPICA is the European Project for Ice Coring in Antarctica). In addition, two changes – one at 16 ka in the CO2 record and one after the ACR onset in three of the isotopic temperature records – do not have high-probability counterparts in the other record. The likely-variable phasing we identify testify to the complex nature of the mechanisms driving the carbon cycle and Antarctic temperature during the deglaciation.
Highlights
Glacial–interglacial transitions, or deglaciations, mark the paleorecord approximately every 100 000 years over the past million years or so (Williams et al, 1997; Lisiecki and Raymo, 2005; Jouzel et al, 2007)
Volcanic ties between WAIS Divide (WD) and EPICA Dome C (EDC), WD and Talos Dome (TD), and WD and EPICA Dronning Maud Land (EDML) are developed in Buizert et al (2018); previously published volcanic ties were used between EDC and Dome Fuji (DF) (Fujita et al, 2015), placing all of the records on the WD2014 chronology (Buizert et al, 2015)
We focus on four major changes in trends which are common to both series: the onset of the deglaciation from 18.2 to 17.2 ka, the onset of the Antarctic Cold Reversal (ACR) at around 14.5 ka, the ACR end between 12.9 and 12.65 and the end of the deglaciation at approximately 11.5 ka
Summary
Glacial–interglacial transitions, or deglaciations, mark the paleorecord approximately every 100 000 years over the past million years or so (Williams et al, 1997; Lisiecki and Raymo, 2005; Jouzel et al, 2007). The last deglaciation, often referred to as glacial termination 1 (T1), offers a case study for a large global climatic change, very likely in the 3–8 ◦C range on the regional scale (Masson-Delmotte et al, 2013), and thought to be initiated by an orbitally driven insolation forcing (Hays et al, 1976; Berger, 1978; Kawamura et al, 2007). The canonical interpretation of this apparent puzzle is that insolation acts as a pacemaker of climatic cycles and the amplitude of glacial–interglacial transitions is mainly driven by two strong climatic feedbacks: atmospheric CO2 and continental-ice-surface–albedo changes. Reconstructing the phase relationship (leads and lags) between climate variables and CO2 during the last termination has become important, and has a substantial history in ice core research (Barnola et al, 1991; Raynaud and Siegenthaler, 1993; Caillon et al, 2003; Pedro et al, 2012; Parrenin et al, 2013)
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