NSFGEO-NERC Paleoclimate signatures of the climate response to West Antarctic ice sheet collapse

A major unanswered question in paleoclimate and glaciological research is whether the West Antarctic ice sheet (WAIS) collapsed during the last interglacial period, Marine Isotope Stage (MIS) 5e, between ~130 and ~116 ka. There is solid evidence for WAIS collapse at some point within the last 700,000 years (Scherer et al., 1998), but the evidence for WAIS collapses at specific times is either indirect (and equivocal) or is insufficient to constrain the timing and magnitude (Joughin and Alley, 2011). Lack of knowledge of both the timing and rate of WAIS collapse in the past hampers our ability to validate models of potential WAIS collapse in the future. A recent report of the U.S. National Academy of Sciences identified this question - the rate and timing of previous WAIS collapses, and particularly whether collapse occurred during MIS 5e - as a top priority for strategic investments in polar research (Polar Research Board, 2015).

It may be possible to constrain both the rate and timing of WAIS collapse in the past through evidence of the response of the climate system to that collapse. This idea is distinct from that of looking for glacial-geological evidence of former ice configurations (e.g., Naish et al., 2009), or inferring ice sheet size from sea level records. Instead, the idea here is that significant changes in ice sheet size will cause changes in atmospheric and ocean circulation that are recorded in paleoclimate archives such as ice cores, speleothems, or marine and lake sediments. Recent modeling work shows that the climate responses to WAIS collapse likely include the following (Justino et al., 2015; Steig et al., 2015; Singh et al., in press; Holloway et al., in review):

- changes in AMOC (Atlantic meridional overturning circulation)
- a northward shift in the ITCZ (intertropical convergence zone)
- changes in temperature and 18O ratios in precipitation over Antarctica, including areas outside the region of collapse

These climate responses are not the consequences of meltwater forcing (though this may also be important), but instead are owing to changes in atmospheric circulation resulting from the significant changes in the morphology of the Antarctic ice sheet. That ice sheet morphology affects atmospheric circulation is not a new concept; there have been many studies demonstrating this for the Laurentide and Fennoscandian ice sheets (e.g., Kutzbach and Guetter, 1986; Roe and Lindzen, 2001). But the idea that the comparatively small changes in the Antarctic ice sheet that may have occurred during previous interglacial periods (and that may occur in the future in response to anthropogenic climate forcing) is novel, and deserves further exploration. This is the basis of the work proposed here.

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