Stratigraphy and chronology of IODP Exp. 374 (Ross Sea West Antarctic Ice Sheet History) drill cores: implications for West Antarctic glaciations

Lead Research Organisation: University of Southampton
Department Name: School of Ocean and Earth Science

Abstract

Over the past 55 million years, Earth's climate changed from a greenhouse into an icehouse world. Antarctica has been (partially) glaciated since ~34 million years ago. Initially, the Antarctic ice sheet probably grew to a larger size than it is at present-day. At present-day, however, the Antarctic continent is 'full' and the ice sheet cannot grow much larger anymore. Therefore the capacity of the Antarctic continent to store ice must have changed in the past. This has most likely happened in West Antarctica, where the ice sheet is now (shallow-)marine based, but is reconstructed to have been predominantly continental-based at its formation. The date of this change is currently unknown, and that is one of the key questions of this proposal: when did this so-called overdeepening occur?

To address this question, this proposal will provide accurate age models for new cores, to be recovered from the Ross Sea (West Antarctica) in January-March 2018. These cores will also help with the evaluation of the instability of the West Antarctic ice sheet. A new climate model suggests that the West Antarctic ice sheet is not as stable as originally thought. This can result in global sea level of up to ~2 m by the end of this century, if we continue CO2 emissions under the business-as-usual scenario. The best way to evaluate this new model is by looking at its accuracy for past climates. Over the past millions of years, the size of the West Antarctic ice sheet has grown and shrunk due to climatic variations, which may be an analogy for future anthropogenic warming. In this proposal we will provide an accurate stratigraphy and age model for the recovered cores. We can then accurately reconstruct the size and position of the West Antarctic ice sheet and compare these to the predicted size and position from the model. Therefore, we can test the accuracy of the prediction that global sea levels will be up to ~2 m higher under business-as-usual CO2 emission scenarios.

Planned Impact

The results of this proposal will benefit a wide variety of users and communities, including 1) UK Earth Science community, and especially the International Ocean Discovery Program (IODP) and palaeoclimate community; 2) Global communities of scientists involved in IODP, palaeoclimate, and palaeomagnetism research; 3) UK government, most notably Department for Business, Energy & Industrial Strategy and the Committee on Climate Change; 4) International bodies, such as the Intergovernmental Panel on Climate Change (IPCC), that matches with UN goal no. 13: Take urgent action to combat climate change and its impacts, and 5) the general public.

The Fifth Assessment Report of the IPCC (IPCC 5AR) predicted severe impacts on society and ecology under the business-as-usual emission (RCP8.5) scenario. Substantial uncertainties, however, effected the predictions for Antarctic ice sheet behaviour under rising CO2 emissions and increasing global temperatures. New models of Antarctic ice sheet behaviour (e.g., DeConto & Pollard, 2016) address this uncertainty, for instance by including the collapse of marine-terminating ice-cliffs. These new models revise the original IPCC 5AR mean sea level rise predictions (suggesting up to 1 m under business-as-usual emission scenarios), and predict that Antarctica alone already has the potential to contribute to more than ~1 m to mean sea level rise. Most notably, the West Antarctic ice sheet (WAIS) appears to be most vulnerable to the collapse of marine-terminating ice-cliffs and may therefore contribute more significantly to potential future sea level rise than previously predicted. This will have especially big effects on the UK because melting of the WAIS will raise regional sea levels around the UK more than elsewhere on the globe (e.g., Larour et al., 2017).

This proposal also provides the opportunity to verify the accuracy of recently published models of Antarctic ice sheet behaviour (e.g., DeConto & Pollard, 2016). The combination of stratigraphy and chronology in this proposal provides the fundamental framework for WAIS reconstructions during periods with warmer-than-present climates. To ensure that this framework will be available to all users and communities as outlined above, all results of this proposal will be integrated with other results from IODP Expedition 374. These integrated results will be published in both widely read and high-impact journals in a timely and efficient manner. This encourages and enables further data-model integration and research of the WAIS stability that will be communicated to the media via relevant channels (e.g., the University of Southampton press team). These results will also open the opportunity to directly engage with the general public (e.g., during the Open Day at the National Oceanography Centre) to discuss topics as scientific drilling, Antarctic research, Earth's past climates, and how these topics may contribute to better understanding of future anthropogenic climate change.

References:
DeConto, R. M., & Pollard, D. (2016). Contribution of Antarctica to past and future sea-level rise. Nature, 531(7596), 591-597. https://doi.org/10.1038/nature17145
Larour, E., Ivins, E. R., & Adhikari, S. (2017). Should coastal planners have concern over where land ice is melting? Science Advances, 3(11), e1700537. https://doi.org/10.1126/sciadv.1700537

Publications

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Description Post-cruise palaeomagnetic analyses of u-channel and discrete cube samples show results that are generally consistent with shipboard magnetic stratigraphy. Detailed analyses on the u-channel and bulk samples from Site U1524 show intervals with magnetic phases that apparently have higher coercivity. Our working hypothesis is that these magnetic phases are dominated by maghemite, which could have formed during sea floor oxidation of detrital magnetite. The oxidation could have happened/enhanced during time with increased oxygen level at the sediment surface, possibly due to availability of highly oxygenated fresher water that relates to melting of West Antarctic Ice Sheet.
Exploitation Route We are currently analysing the rich set of data collected during this project and discussing with collaborators from the broader IODP Expedition 374 Science party to test our working hypothesis and explore its potential implication on chronology of the recovered sediments and the history of West Antarctic Ice Sheet.
Sectors Education,Environment