Seasonal temperatures in West Antarctica during the Holocene

Abstract

The recovery of long-term climate proxy records with seasonal resolution is rare because of natural smoothing processes, discontinuities and limitations in measurement resolution. Yet insolation forcing, a primary driver of multimillennial-scale climate change, acts through seasonal variations with direct impacts on seasonal climate1. Whether the sensitivity of seasonal climate to insolation matches theoretical predictions has not been assessed over long timescales. Here, we analyse a continuous record of water-isotope ratios from the West Antarctic Ice Sheet Divide ice core to reveal summer and winter temperature changes through the last 11,000 years. Summer temperatures in West Antarctica increased through the early-to-mid-Holocene, reached a peak 4,100 years ago and then decreased to the present. Climate model simulations show that these variations primarily reflect changes in maximum summer insolation, confirming the general connection between seasonal insolation and warming and demonstrating the importance of insolation intensity rather than seasonally integrated insolation or season duration2,3. Winter temperatures varied less overall, consistent with predictions from insolation forcing, but also fluctuated in the early Holocene, probably owing to changes in meridional heat transport. The magnitudes of summer and winter temperature changes constrain the lowering of the West Antarctic Ice Sheet surface since the early Holocene to less than 162 m and probably less than 58 m, consistent with geological constraints elsewhere in West Antarctica4–7.

Post-depositional modication on seasonal and 1 interannual timescales resets the deuterium excess 2 signals in summer snow layers in Greenland

“…Deeper in the rn and ice column (>2 m) and over longer time periods, diusion along isotopic gradients become a dominant smoothing process (Johnsen, 1977;Johnsen et al, 2000;Gkinis et al, 2014;Jones et al, 2017). Proper inversion of this process is necessary for accurate reconstruction of timing and magnitude of isotopic signals (e.g., Johnsen et al, 2000;Vinther et al, 2010;Jones et al, 2018Jones et al, , 2023, although we show here that additional isotopic corrections for surface and near-snow processes may still be needed.…”

“…A more nuanced interpretation of the δ 18 O, or δD, proxy is particularly important to studies like Jones et al (2023), who interpret summer-only δD changes in West Antarctica as changes in summer temperature due to changes in insolation. Interpreting changes in δD as both changes in temperature and latent heat ux could help explain why the manuscript submitted to JGR: Atmospheres West Antarctic summer δD pattern is correlated with Milankovitch insolation patterns even though annually coincident winter correlation in δD is not clearly evident.…”

“…Recent climate reconstruction eorts are not as dependent on temperatures inferred from water isotopes in polar snow, rather using an array of globally distributed proxies (e.g., Rohling et al, 2012;Dahl-Jensen et al, 2013;Buizert et al, 2021). However, simulation of past polar ice sheet mass balance and climate still require accurate knowledge of ice sheet temperatures often derived from empirical isotope-temperature sensitivities (e.g., Cuey et al, 2016;Jones et al, 2023). Past circulation and weather patterns are also possible to derive from combinations of isotope and other chemistry measurements from polar snow and ice (e.g., Mayewski et al, 1994;Steensen et al, 2008;Guillevic et al, 2013;Jones et al, 2018).…”

Holocene Palaeoenvironmental and Palaeoproductivity Changes in the Western Amundsen Sea Embayment of Antarctica

“…The onset of the TOC increase and diatom production marking the base of Subunit III‐1 coincided with the end of a phase of rapid increases at ∼10.5 cal. ka BP in the Antarctic air temperature recorded in the West Antarctic Ice Sheet (WAIS) Divide ice core (WDC) (Figure 4 and Figure S3 in Supporting Information ; Cuffey et al., 2016; Jones et al., 2023; Ólafur et al., 2003; data obtained from http://www.usap-dc.org/view/dataset/600377). The TOC contents (%) increased gradually from <0.3% to ∼1% (Figure 4).…”

Snow‐Atmosphere Humidity Exchange at the Ice Sheet Surface Alters Annual Mean Climate Signals in Ice Core Records

“…Implementing vapor exchange into simulations improves the representation of the seasonal amplitude in δ 18 O from 65% to 100.2% of the observed seasonal cycle. This may explain a known conundrum in the interpretation of the water isotopes, that the diffusion‐corrected seasonal amplitude is often substantially reduced compared to expectations of isotope‐temperature scaling based on the seasonal temperature cycle (Jones et al., 2023). Our results thus suggest that additional isotopic corrections are needed to convert a high‐frequency, seasonally resolved water‐isotope signal in a deep ice core back to a climate signal.…”