Reconstruction of Temperature, Accumulation Rate, and Layer Thinning From an Ice Core at South Pole, Using a Statistical Inverse Method

Abstract

Data from the South Pole ice core (SPC14) are used to constrain climate conditions and ice‐flow‐induced layer thinning for the last 54,000 years. Empirical constraints are obtained from the SPC14 ice and gas timescales, used to calculate annual‐layer thickness and the gas‐ice age difference (Δage), and from high‐resolution measurements of water isotopes, used to calculate the water‐isotope diffusion length. Both Δage and diffusion length depend on firn properties and therefore contain information about past temperature and snow‐accumulation rate. A statistical inverse approach is used to obtain an ensemble of reconstructions of temperature, accumulation‐rate, and thinning of annual layers in the ice sheet at the SPC14 site. The traditional water‐isotope/temperature relationship is not used as a constraint; the results therefore provide an independent calibration of that relationship. The temperature reconstruction yields a glacial‐interglacial temperature change of 6.7 ± 1.0°C at the South Pole. The sensitivity of δ18O to temperature is 0.99 ± 0.03 ‰°C−1, significantly greater than the spatial slope of 0.8‰°C−1 that has been used previously to determine temperature changes from East Antarctic ice core records. The reconstructions of accumulation rate and ice thinning show millennial‐scale variations in the thinning function as well as decreased thinning at depth compared to the results of a 1‐D ice flow model, suggesting influence of bedrock topography on ice flow.

Subglacial precipitates record Antarctic ice sheet response to late Pleistocene millennial climate cycles

“…Changes in ice surface accumulation can drive ice thickening and basal melting during millennial warm phases, and ice thinning and basal freezing during millennial cold phases. However, ice cores proximal to our sample collection sites show a minimal change in accumulation rate above their noise floor of ~0.01 m/yr during AIM cycles [53][54][55][56] , and detailed records from ice proximal to EM show no change in accumulation during AIM events at the end of the last glacial period 57 . The only millennial-scale variations in accumulation rates clearly resolved in ice core records occur in WDC 58 , which is influenced by maritime climate and is not representative of our two sample collection sites located at the edge of the EAIS polar plateau.…”

The Ice Core Gas Age‐Ice Age Difference as a Proxy for Surface Temperature

“…Previous firn densification studies have reported difficulty in fitting the relatively small glacial firn column thickness indicated by δ 15 N in East Antarctic sites (Bréant et al., 2017; Capron et al., 2013; Landais et al., 2006). Here, I follow recent studies that suggest that using realistic forcings for LGM T and A , densification models can successfully fit LGM δ 15 N in East Antarctica (Buizert et al., 2021; Kahle et al., 2021). This section briefly explores the δ 15 N model‐data mismatch.…”

“…The spatial pattern of LGM cooling in Antarctica is attributed to the pattern of LGM‐preindustrial elevation changes (Buizert et al., 2021; Werner et al., 2018). For comparison, Figure 3a further shows independent LGM surface cooling estimates based on water isotope diffusion lengths in the South Pole ice core (Kahle et al., 2021), paleo data‐assimilation (Tierney et al., 2020), PMIP4 climate model simulations (Paleoclimate Model Intercomparison Project Phase 4; Kageyama et al., 2021), and traditional interpretation of water isotopes calibrated via the spatially calibrated slope (Werner et al., 2018). The smaller magnitude of LGM cooling in East Antarctica as found by B21 agrees well with the independent estimates from PMIP4 and Tierney et al.…”

Geophysics and Thermodynamics at South Pole Lake Indicate Stability and a Regionally Thawed Bed

“…Together, our temperature modeling and geophysical data interpretation suggest that for the present-day ice sheet: (a) sliding dominates over shear velocity; (b) the bed is currently thawed; and (c) the bed has been thawed for most of the past 800,000 years. The few times when modeled temperatures are close to or below freezing were (Kahle et al, 2021) and scaled from EPICA Dome C (gray) (Jouzel et al, 2007). (b) Surface accumulation rate reconstructed from ice cores as in (a).…”