Did West Antarctic Ice Sheet collapse during the Last Interglacial?
Rising sea levels due to the melting of Earth's continental ice sheets under a warming climate pose a direct threat to our societies. A major source of uncertainty in projecting future sea level rises is the West Antarctic Ice Sheet (WAIS), which is grounded on bedrock that currently lies below sea level (Mercer, 1968; Hughes, 1973). Looking into past warm periods with higher sea levels, such as the Last Interglacial (LIG) between 130 ka and 115 ka, could help constrain ice sheet sensitivity to climate change. However, historical changes of individual ice sheets are notoriously difficult to constrain. First, past sea levels alone cannot diagnose the actual location of ice losses. Second, terrestrial records such as were erased by subsequent advancing ice sheets. Third, marine records often do not have the sufficient temporal resolution to allow past ice sheet reconstructions. In fact, whether WAIS collapsed in the LIG is not fully resolved.
My solution is utilizing records within the cryosphere. The underlying principle of this approach is straightforward: the position of the ice margin and sea ice extent impact atmospheric circulation and local climate, which should be in turn recorded by the ice (e.g. Steig et al, 2015; Holloway et al, 2016; Goursaud et al, 2020). Of course, a prerequisite is that some ice must survive to record those changes. An absence of ice core records dating back to the LIG in central West Antarctica (a telling observation itself) obscures a clear ice-core perspective on the WAIS, which is the motivation for drilling in Hercules Dome (Steig et al, 2020).
The East Antarctic Ice Sheet on the other hand is thought to remain largely stable in the LIG. If there is an East Antarctic ice record that borders on the WAIS, it may answer whether it collapsed in the LIG. S27, an ice core drilled in Allan Hills Blue Ice Areas (Figure 1), provides a continuous climate record of between ~110 ka and ~250 ka (Spaulding et al, 2013). Its proximity to the current north edge of the Ross Ice Shelf makes it a sentinel for past ice shelf and ice sheet behaviors.
Figure 1. Map of Antarctica, where the location of the S27 ice core is marked in star. (map source: Alexrk2, Wikimedia Commons; licensed under the Creative Commons Attribution-Share Alike 3.0 Unported License).
In a recent paper published on Climate of the Past (Yan et al, 2021), I calculated the snow accumulation rate recorded in the S27 ice core based on the age difference of the ice and the trapped air at the same depth. We observed an order-of-magnitude increase in accumulation rates across the penultimate deglaciation, peaking at 129 ka during the maximum LIG warming (Figure 2). In contrast, accumulation rates typically vary by a factor of two to three on glacial-interglacial timescales in other ice cores (Siegert, 2003). We attributed this drastic change to possible changes in local ice mass configurations, such as more open-water conditions in the Ross Sea and a southward retreat of Ross Ice Shelf, perhaps due to the collapse of West Antarctic Ice Sheet during the early LIG. Importantly, the hypothesized ice retreat in the Ross Sea makes a number of falsifiable predictions, such as a negative excursion in the deuterium excess (defined as δD – 8*δ18O) and changes to aerosol loadings, which will be explored in the future.
Figure 2. Paleoclimate records during Termination II and the Last Interglacial. A detailed description of each panel is presented in Yan et al (2021).
References
Goursaud, S., Holloway, M., Sime, L., Wolff, E., Valdes, P., Steig, E.J. and Pauling, A., 2021. Antarctic Ice Sheet elevation impacts on water isotope records during the Last Interglacial. Geophysical Research Letters, 48(6), p.e2020GL091412.
Holloway, M.D., Sime, L.C., Singarayer, J.S., Tindall, J.C., Bunch, P. and Valdes, P.J., 2016. Antarctic last interglacial isotope peak in response to sea ice retreat not ice-sheet collapse. Nature communications, 7(1), pp.1-9.
Hughes, T., 1973. Is the West Antarctic ice sheet disintegrating?. Journal of Geophysical Research, 78(33), pp.7884-7910.
Mercer, J., 1968. Antarctic Ice and Sangamon Sea Level, International Association of Scientific Hydrology Publication, 79, pp.217-225.
Siegert, M., 2003. Glacial-interglacial variations in central East Antarctic ice accumulation rates. Quaternary Science Reviews, 22, pp.741-750.
Spaulding, N.E., Higgins, J.A., Kurbatov, A.V., Bender, M.L., Arcone, S.A., Campbell, S., Dunbar, N.W., Chimiak, L.M., Introne, D.S. and Mayewski, P.A., 2013. Climate archives from 90 to 250 ka in horizontal and vertical ice cores from the Allan Hills Blue Ice Area, Antarctica. Quaternary Research, 80(3), pp.562-574.
Steig, E.J., Duetsch, M., Blossey, P.N., Pauling, A., Bitz, C.M., Aydin, M., Fudge, T.J., Roop, H.A., Souney Jr, J.M., Twickler, M. and Christianson, K.A., 2020, December. Hercules Dome ice core project: Prospects for obtaining Eemian records that constrain the size of the West Antarctic ice sheet through time. AGU Fall Meeting 2020 Abstracts.
Steig, E.J., Huybers, K., Singh, H.A., Steiger, N.J., Ding, Q., Frierson, D.M., Popp, T. and White, J.W., 2015. Influence of West Antarctic ice sheet collapse on Antarctic surface climate. Geophysical Research Letters, 42(12), pp.4862-4868.
Yan, Y., Spaulding, N.E., Bender, M.L., Brook, E.J., Higgins, J.A., Kurbatov, A.V. and Mayewski, P.A., 2021. Enhanced Moisture Delivery into Victoria Land, East Antarctica During the Early Last Interglacial: Implications for West Antarctic Ice Sheet Stability. Climate of the Past, 17, pp.1841-1855.