Deglacial temperature history of West Antarctica

Abstract

The most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how Earth's climate responds to various forcings, including a rise in atmospheric CO 2 . This transition has left a direct thermal remnant in the polar ice sheets, where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings. For Antarctica, the deglacial warming has previously been constrained only by the water isotopic composition in ice cores, without an absolute thermometric assessment of the isotopes' sensitivity to temperature. To overcome this limitation, we measured temperatures in a deep borehole and analyzed them together with ice-core data to reconstruct the surface temperature history of West Antarctica. The deglacial warming was 11.3 ± 1.8 • C, approximately two to three times the global average, in agreement with theoretical expectations for Antarctic amplification of planetary temperature changes. Consistent with evidence from glacier retreat in Southern Hemisphere mountain ranges, the Antarctic warming was mostly completed by 15 kyBP, several millennia earlier than in the Northern Hemisphere. These results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on Antarctic temperature. Although climate models perform well on average in this context, some recent syntheses of deglacial climate history have underestimated Antarctic warming and the models with lowest sensitivity can be discounted.climate | paleoclimate | Antarctica | glaciology | temperature F rom the Last Glacial Maximum (LGM) around 21 ka to the middle of the Holocene, increased greenhouse gas concentrations and reduced reflectivities of the surface and atmosphere directly increased the uptake of energy to Earth's climate system by about 7W·m −2 (1-3) and warmed the surface by 3-6 • C on average (4-7). Although contributing little to this global average because of the comparatively small area involved, the warming in polar regions holds particular interest. In addition to driving changes of ice sheets, permafrost, and hydrology and modulating oceanic and atmospheric circulations, polar warming partly controlled both the evolution of surface reflectivity and the transfer of carbon dioxide from ocean to atmosphere and hence the climate forcing itself. Further, reconstructions of polar warming during deglaciation permit quantification of one key prediction of climate theory-that feedback processes amplify temperature changes in polar regions relative to the global average (4, 8, 9), a phenomenon referred to as polar amplification. Arctic data reveal a warming three to four times the global average based on a wide variety of indicators (6), including combined analyses of ice-core data and borehole temperatures (10, 11). Limited available constraints suggest a smaller but still amplified Antarctic warming, roughly 1.5 to 2.5 times greater than the global average (6, 12). T...

Changes in Intermediate Circulation in the Bay of Bengal Since the Last Glacial Maximum as Inferred From Benthic Foraminifera Assemblages and Geochemical Proxies

“…The changes in the carbon isotope record and B-P age offsets obtained on the sedimentary section from MD77-176 at the 17-14 and 13-10.6 cal kyr BP intervals correspond to warming episodes in Antarctica and the Southern Hemisphere during the deglaciation (e.g., Cuffey et al, 2016;Epica, 2006). These time intervals also correspond to a decrease of the Antarctic sea-ice (Shemesh et al, 2002;Wais, 2013) and the reduction of stratification resulting in better ventilation in the South Ocean (e.g., Anderson et al, 2009;Skinner et al, 2010).…”

New methods for measuring atmospheric heavy noble gas isotope and elemental ratios in ice core samples

“…For our purposes here it is sufficient to correct the data only for gravitational firn fractionation, because the BCTZ alterations are fairly strong and because during the involved time windows (Holocene) surface temperatures/thermal fractionations were fairly constant/small . For the WAIS Divide data we use δ 40 Ar values for gravitational correction following Headly and Severinghaus while for the NEEM data we use δ 86 Kr values accordingly.…”

Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion

“…1). At the same time, Antarctic ice cores record a sharp decrease in SH continental dust (11), a widespread decline in sea salt deposition, a marked upturn in water isotopic ratios indicating warming (12,13), and a trend of increasing atmospheric methane (CH 4 ) (12) and carbon dioxide (CO 2 ) (14, 15) coincident with a drop in the stable carbon isotopic ratios in CO 2 (14) (Fig. 1).…”