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

Lead Research Organisation: NERC British Antarctic Survey
Department Name: Science Programmes

Abstract

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.

Planned Impact

NA

Publications

10 25 50
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Boer A (2018) Interconnectivity Between Volume Transports Through Arctic Straits in Journal of Geophysical Research: Oceans

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Holloway M (2017) The Spatial Structure of the 128 ka Antarctic Sea Ice Minimum in Geophysical Research Letters

 
Description Several studies have suggested that sea-level rise during the last interglacial implies retreat of the West Antarctic Ice Sheet (WAIS). The prevalent hypothesis is that the retreat coincided with the peak Antarctic temperature and stable water isotope values from 128,000 years ago (128 ka); very early in the last interglacial. By by analysing climate model simulations of last interglacial WAIS loss featuring water isotopes, we show instead that the isotopic response to WAIS loss is in opposition to the isotopic evidence at 128 ka. Instead, a reduction in winter sea ice area of 65±7% explains the 128 ka ice core evidence. Our finding of a marked retreat of the sea ice at 128 ka demonstrates the sensitivity of Antarctic sea ice extent to climate warming.

Further we show that current climate models are capable of producing a realistic simulation of last interglacial warmth. This aids confidence in future climate projects from these models.
Exploitation Route The sea ice finding are of consdierable value to the climate community - particularly for testing sea ice models.
Sectors Other

 
Description EPSRC-PEN feasibility study
Amount £8,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 01/2017 
End 12/2017
 
Title Southern Hemisphere winter sea ice concentration simulated by HadCM3 to best explain the early last interglacial Antarctic isotope peak 
Description The file contains Southern Hemisphere winter (September) sea ice concentration (sic) from a simulation performed using the isotope-enabled HadCM3 climate model forced with early last interglacial boundary conditions, centred approximately 128,000 years ago. The resulting sic represents a reduction in winter sea ice area of approximately 54% relative to pre-industrial and is proposed as the best explanation for the Antarctic ice core data from 128,000 years ago. The spatial pattern of sea ice retreat was determined using a large ensemble of model experiments and a pattern search optimization approach to match the last interglacial ice core isotope peak. Further details can be found in the published manuscript (https://doi.org/10.1002/2017GL074594). 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
 
Title Surface elevation of 69 Greenland Ice Sheet morphologies and associated d18O anomalies (with respect to Pre-industrial) simulated by HadCM3 
Description The text file (.csv) contains d18O changes simulated at six Greenland deep ice cores (NEEM, NGRIP, GRIP, GISP2, Camp Century and DYE3) from 69 simulations performed using the isotope-enabled HadCM3 climate model forced with mid last interglacial boundary conditions, centred at 125,000 years ago. HadCM3 is used to reproduce the d18O response to 69 modified Last Interglacial (LIG) Greenland Ice Sheet (GIS) morphologies at the ice-core sites. To parameterise the set of 69 GIS morphologies, we undertake a Principal Component Analysis (PCA) approach. The text file also contains the 8PC coefficients for each of the 69 morphologies. The netcdf file (.nc) contains the 8PC shapes and the average shape. To obtain any of the 69 GIS morphologies: (1) store the 8 PC coefficients of a specific GIS morphology and, (2) take a linear combination of the PC shapes (according to those coefficients) and add the average shape. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
Impact Recovery of the past shape/volume of the Greenland ice sheet. 
URL https://doi.org/10.5285/35aed839-1634-4692-b6d6-4d6312953eb5
 
Description Eric J. Steig Professor, Earth & Space Sci. And IsbLab 
Organisation University of Washington
Department Department of Biostatistics
Country United States 
Sector Academic/University 
PI Contribution Provision of Climate Model isotopic output for location of possible US led Hercules Dome ice coring site.
Collaborator Contribution Provision of Climate Model isotopic output for location of possible US led Hercules Dome ice coring site.
Impact Papers in preparation.
Start Year 2016
 
Description The Past Earth Network (PEN) 
Organisation University of Leeds
Country United Kingdom 
Sector Academic/University 
PI Contribution Co-leader of the PEN Model-Data comparison group. Myself and my research group will be helping to organise PEN workshops in the coming years.
Collaborator Contribution Organising conference sessions and PhD studentships: earth sciences and statisticians
Impact Conference sessions and PhD studentships: earth sciences and statisticians
Start Year 2015
 
Description Maker workshops in London 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Free creative workshops using art, crafts and model making to share ideas about responding to the impacts of climate change.

2:30pm 24 January, 21 February, 20 March

The news is full of fires and floods and it is difficult to know how to help. These workshops will imagine and invent ways we can respond to the experience of
climate change in different ways around the world.
Year(s) Of Engagement Activity 2019,2020