Reconciling the surface temperature–surface mass balance relationship in models and ice cores in Antarctica over the last 2 centuries

Abstract

Abstract. Ice cores are an important record of the past surface mass balance (SMB) of ice sheets, with SMB mitigating the ice sheets' sea level impact over the recent decades. For the Antarctic Ice Sheet (AIS), SMB is dominated by large-scale atmospheric circulation, which collects warm moist air from further north and releases it in the form of snow as widespread accumulation or focused atmospheric rivers on the continent. This suggests that the snow deposited at the surface of the AIS should record strongly coupled SMB and surface air temperature (SAT) variations. Ice cores use δ18O as a proxy for SAT as they do not record SAT directly. Here, using isotope-enabled global climate models and the RACMO2.3 regional climate model, we calculate positive SMB–SAT and SMB–δ18O annual correlations over ∼90 % of the AIS. The high spatial resolution of the RACMO2.3 model allows us to highlight a number of areas where SMB and SAT are not correlated, and we show that wind-driven processes acting locally, such as foehn and katabatic effects, can overwhelm the large-scale atmospheric contribution in SMB and SAT responsible for the positive SMB–SAT annual correlations. We focus in particular on Dronning Maud Land, East Antarctica, where the ice promontories clearly show these wind-induced effects. However, using the PAGES2k ice core compilations of SMB and δ18O of Thomas et al. (2017) and Stenni et al. (2017), we obtain a weak annual correlation, on the order of 0.1, between SMB and δ18O over the past ∼150 years. We obtain an equivalently weak annual correlation between ice core SMB and the SAT reconstruction of Nicolas and Bromwich (2014) over the past ∼50 years, although the ice core sites are not spatially co-located with the areas displaying a low SMB–SAT annual correlation in the models. To resolve the discrepancy between the measured and modeled signals, we show that averaging the ice core records in close spatial proximity increases their SMB–SAT annual correlation. This increase shows that the weak measured annual correlation partly results from random noise present in the ice core records, but the change is not large enough to match the annual correlation calculated in the models. Our results thus indicate a positive correlation between SAT and SMB in models and ice core reconstructions but with a weaker value in observations that may be due to missing processes in models or some systematic biases in ice core data that are not removed by a simple average.

West Antarctic Surface Climate Changes Since the Mid‐20th Century Driven by Anthropogenic Forcing

“…This results in surface warming in Eastern WAIS and the Antarctic Peninsula, and surface cooling in the Western WAIS (Marshall & Thompson, 2016). Over the Antarctic Peninsula and Eastern and Central WAIS, an overall positive correlation between atmospheric temperature and snow accumulation is noticed (Cavitte et al., 2020). In these regions, when warm, moist air from the ocean is brought to the continent by the ASL, air moisture content precipitates due to the orographic lifting, leading to more snow accumulation in these regions.…”

Age‐Depth Stratigraphy of Pine Island Glacier Inferred From Airborne Radar and Ice‐Core Chronology

“…Previous studies have successfully combined ice‐core records with modeled modern‐day accumulation rates to reconstruct Holocene accumulation (Cavitte et al., 2018; Fudge et al., 2016; Nielsen et al., 2018), although non‐climatic noise in the observations and model biases have resulted in small discrepancies between ice‐core and model reconstructions (Cavitte et al., 2020; Dalaiden et al., 2020). When assessing the ability of the 1‐D model to reproduce the ages for R2‐3 derived at the WD2014 Ice Core, we find that the best match (to within < 10%) is achieved using the modern accumulation rates provided by the MED14 and RACMO2 products.…”

Can we reconstruct the formation of large open-ocean polynyas in the Southern Ocean using ice core records?

“…In addition to those observations close to the region of polynya formation, another constraint on our reconstructions could come from a comparison to estimates of past largescale changes that are expected to favor open-ocean polynya formation or that would be a consequence of their occurrence. In particular, changes in surface winds influence the horizontal oceanic circulation, potentially inducing the upwelling of deep waters and, thus, a salt input in the surface layers, creating conditions more prone to deep convection (Cheon et al, 2015;Campbell et al, 2019;Kaufman et al, 2020). In this framework, it has been argued that a per-sistent negative phase of the Southern Annular Mode (which is the main mode of atmospheric variability in the Southern Hemisphere extra-tropics) in the preceding decade could have created favorable conditions for the formation of the Weddell polynya in the 1970s (Gordon et al, 2007;Kaufman et al, 2020).…”

“…Deep convection requires some preconditioning of the ocean, reducing the overall stability of the water column (Morales Maqueda et al, 2004;Dufour et al, 2017;Kurtakoti et al, 2018;Campbell et al, 2019). The opening of a polynya is then triggered by the winds and, specifically, by the passage of storms that export sea ice out of the region, enhance turbulent mixing in the ocean and may bring additional heat (Morales Maqueda et al, 2004;Cheon et al, 2015;Jena et al, 2019;Francis et al, 2019;Campbell et al, 2019). After the formation of the polynya by a particular event, the convection is self-sustained.…”