Recent climate and ice-sheet changes in West Antarctica compared with the past 2,000 years

Abstract

Changes in atmospheric circulation over the past five decades have enhanced the wind-driven inflow of warm ocean water onto the Antarctic continental shelf, where it melts ice shelves from below 1-3 . Atmospheric circulation changes have also caused rapid warming 4 over the West Antarctic Ice Sheet, and contributed to declining sea-ice cover in the adjacent Amundsen-Bellingshausen seas 5 . It is unknown whether these changes are part of a longer-term trend. Here, we use waterisotope (δ 18 O) data from an array of ice-core records to place recent West Antarctic climate changes in the context of the past two millennia. We find that the δ 18 O of West Antarctic precipitation has increased significantly in the past 50 years, in parallel with the trend in temperature, and was probably more elevated during the 1990s than at any other time during the past 200 years. However, δ 18 O anomalies comparable to those of recent decades occur about 1% of the time over the past 2,000 years. General circulation model simulations suggest that recent trends in δ 18 O and climate in West Antarctica cannot be distinguished from decadal variability that originates in the tropics. We conclude that the uncertain trajectory of tropical climate variability represents a significant source of uncertainty in projections of West Antarctic climate and ice-sheet change.The West Antarctic Ice Sheet (WAIS), which is grounded largely below sea level, is potentially unstable. Mass loss from the WAIS is contributing to present sea-level rise, owing to the widespread thinning of ice shelves and the acceleration of the large outlet glaciers that drain the ice sheet into the ocean 1 . Contemporaneous with the loss of mass from the WAIS, air temperatures over the WAIS have increased significantly in the past 50 years 4,6,7 .Climate and ice-sheet changes in West Antarctica are closely linked with one another by changes in regional atmospheric circulation 8 . Observations beneath the floating ice shelf of Pine Island Glacier, a major drainage system for the flow of the WAIS into the Amundsen Sea, show that the primary cause of ice-shelf thinning is the presence of warm Circumpolar Deep Water on

Mapping and assessing variability in the Antarctic marginal ice zone, pack ice and coastal polynyas in two sea ice algorithms with implications on breeding success of snow petrels

“…Earlier satellite data from the 1960s and 1970s and data from ship observations suggest periods of high and low sea ice extent and thus high natural variability (Meier et al, 2013b;Gallaher et al, 2014). Further evidence comes from ice core climate records, which suggest that the climate variability observed in the Antarctic during the last 50 years remains within the range of natural variability seen over the last several hundred to thousand years (Thomas et al, 2013;Steig et al, 2013). Thus, we may require much longer records to properly assess Antarctic sea ice trends in contrast to the Arctic, where negative trends are outside the range of natural variability and are consistent with those simulated from climate models.…”

Deglacial temperature history of West Antarctica

“…2B) indicates that the surface in central West Antarctica was colder during the LGM (average from 20 ka to 23 ka) than in the late Holocene by 11.3 ± 1.8 • C (2σ) (Table S3), whereas the net warming from the LGM to the middle Holocene thermal maximum (3-6 ka at this site) was perhaps as large as 13.7 (6,12,26). It is possible that there exists a real regional difference from West Antarctica, where the climate is more strongly influenced by the proximal ocean (24,27), but these values all derive from assumptions about the sensitivity of ice isotopes to climatic temperature, a method known to be inaccurate in Greenland (10,28).…”

“…Estimates of γ from studies of temporal and spatial covariation of δ and T in Antarctica range from γ 18 ≈ 0.4‰ to 1.0‰ • C −1 (22,23), corresponding to approximately ±5.5 • C of uncertainty in the LGM temperature at West Antarctic Ice Sheet Divide, three times the uncertainty of our reconstruction. Estimates of γ from temporal covariations, presumably the most relevant for climate reconstruction, average γ18 ≈ 0.55‰ • C −1 (24), whereas the continent-wide spatial covariation gives γ 18 ≈ 0.8 ‰ • C −1 (22,25). Fig.…”

Improved methodologies for continuous-flow analysis of stable water isotopes in ice cores

“…9). The lowresolution data were measured at the University of Washington (UW) using a Picarro 2120i at ∼ 50 cm increments (Steig et al, 2013). To determine inter-lab reproducibility, we averaged the high-resolution CRDS-CFA data to the exact low-resolution discrete CRDS increments; we refer to this as "down-sampling".…”