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Abstract
Abstract. Improving our knowledge of the temporal and spatial variability of the Antarctic Ice Sheet (AIS) surface mass balance (SMB) is crucial to reduce the uncertainties of past, present, and future Antarctic contributions to sea level rise. An examination of the surface air temperature–SMB relationship in model simulations demonstrates a strong link between the two. Reconstructions based on ice cores display a weaker relationship, indicating a model–data discrepancy that may be due to model biases or to the non-climatic noise present in the records. We find that, on the regional scale, the modeled relationship between surface air temperature and SMB is often stronger than between temperature and δ18O. This suggests that SMB data can be used to reconstruct past surface air temperature. Using this finding, we assimilate isotope-enabled SMB and δ18O model output with ice core observations to generate a new surface air temperature reconstruction. Although an independent evaluation of the skill is difficult because of the short observational time series, this new reconstruction outperforms the previous reconstructions for the continental-mean temperature that were based on δ18O alone. The improvement is most significant for the East Antarctic region, where the uncertainties are particularly large. Finally, using the same data assimilation method as for the surface air temperature reconstruction, we provide a spatial SMB reconstruction for the AIS over the last 2 centuries, showing large variability in SMB trends at a regional scale, with an increase (0.82 Gt yr−2) in West Antarctica over 1957–2000 and a decrease in East Antarctica during the same period (−0.13 Gt yr−2). As expected, this is consistent with the recent reconstruction used as a constraint in the data assimilation.
Highlights
The spatial coverage of climate observations in Antarctica and the Southern Ocean is sparse (e.g., Jones et al, 2016; Neukom et al, 2018)
The Antarctic Ice Sheet (AIS) surface mass balance (SMB) over the last millennium has been estimated for each general circulation models (GCMs) by computing the difference between precipitation and sublimation–evaporation
When analyzing the ensemble of simulations performed with CESM1–CAM5, the ensemble mean shows a relatively homogeneous increase, but some simulations display a contrast between East Antarctica and West Antarctica close to the one observed in the reconstruction (Fig. 3)
Summary
The spatial coverage of climate observations in Antarctica and the Southern Ocean is sparse (e.g., Jones et al, 2016; Neukom et al, 2018). Since around 1995, the contribution to the global sea level rise from the ice sheets – Greenland Ice Sheet (GrIS) and the Antarctic Ice Sheet (AIS) – has strongly increased and is slowly outpacing the contributions from mountain glaciers and ocean thermal expansion (Shepherd et al, 2018). The GrIS has been dominating the ice sheet contribution so far (Rignot et al, 2019), but AIS mass loss increased 5-fold in 2012–2017 relative to 1992– 1997, with current AIS mass loss values that approach those of the GrIS. Reliable estimates of AIS MB and its relationship with internal cli-
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