Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

Abstract

Abstract. The geometry of Antarctic ice sheets during warm periods of the geological past is difficult to determine from geological evidence, but is important to know because such reconstructions enable a more complete understanding of how the ice-sheet system responds to changes in climate. Here we investigate how Antarctica evolved under orbital and greenhouse gas conditions representative of an interglacial in the early Pliocene at 4.23 Ma, when Southern Hemisphere insolation reached a maximum. Using offlinecoupled climate and ice-sheet models, together with a new synthesis of high-latitude palaeoenvironmental proxy data to define a likely climate envelope, we simulate a range of icesheet geometries and calculate their likely contribution to sea level. In addition, we use these simulations to investigate the processes by which the West and East Antarctic ice sheets respond to environmental forcings and the timescales over which these behaviours manifest. We conclude that the Antarctic ice sheet contributed 8.6 ± 2.8 m to global sea level at this time, under an atmospheric CO 2 concentration identical to present (400 ppm). Warmer-than-present ocean temperatures led to the collapse of West Antarctica over centuries, whereas higher air temperatures initiated surface melting in parts of East Antarctica that over one to two millennia led to lowering of the ice-sheet surface, flotation of grounded margins in some areas, and retreat of the ice sheet into the Wilkes Subglacial Basin. The results show that regional variations in climate, ice-sheet geometry, and topography produce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points.

Back to the Future: Using Long-Term Observational and Paleo-Proxy Reconstructions to Improve Model Projections of Antarctic Climate

“…Recent studies have used Antarctic ice sheet contributions to mPWP and LIG global mean sea levels as tuning targets for ice sheet models to reduce the uncertainties on sea level projections [82,83]. Further investigations of Antarctic ice sheet sensitivity to past warm climate conditions (e.g., MMCO, [51]; mPWP, [28,84]; LIG, [85], and the last deglaciation, [86]) are needed to better constrain its tipping points under different level of atmospheric CO 2 concentration ( Figure 1).…”

West Antarctic sites for subglacial drilling to test for past ice-sheet collapse

“…1 and 2). This is not unique to our simulation; rather it is a robust feature of icesheet models forced with interglacial climates (e.g., Bamber et al, 2009;de Boer et al, 2015;Feldmann and Levermann, 2015;DeConto and Pollard, 2016;Golledge et al, 2017). The model demonstrates that in areas that remain glaciated, thinning occurs as the grounding line approaches, but then stops once the grounding line stabilizes, even if deglaciation continues in other sectors of the WAIS.…”

“…For example, cosmogenic 3 He, 21 Ne, and 36 Cl could be measured in basaltic pyroxene, or in a combination of quartz and sanidine from more felsic volcanic rocks. However, the relative abundance of useful minerals such as these is also important because of the small amount of rock that can be retrieved by subglacial drilling (Goodge and Severinghaus, 2016).…”

“…Because we were unable to image deeper portions of the ridge crest, we sited the second borehole northeast of the crest, above the gently dipping ridge flank. We used the Agile Sub-Ice Geological (ASIG) Drill, a modified wireline mineral exploration drill, which is similar in design to the much larger Rapid Access Ice Drill (RAID) (Goodge and Severinghaus, 2016). The ASIG Drill is designed to be able to drill 15 m of rock core beneath 700 m of ice.…”

“…In the 2016-2017 austral summer, the first cores of subglacial bedrock from West Antarctica were recovered from the Pirrit Hills and the Ohio Range (Fig. 1), which was made possible by recent advances in sub-ice drilling technology (e.g., Goodge and Severinghaus, 2016). For these as well as future drilling efforts to provide meaningful information about past WAIS configurations, the measurements made on the recovered bedrock must be representative of the past ice thickness at the drill site, which in turn must be linked to the extent of the broader ice sheet.…”