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Abstract. The S27 ice core, drilled in the Allan Hills Blue IceArea of East Antarctica, is located in southern Victoria Land, ∼80 km away from the present-day northern edge of the RossIce Shelf. Here, we utilize the reconstructed accumulation rate of S27covering the Last Interglacial (LIG) period between 129 ka and 116 ka (where ka indicates thousands of years before present) to infer moisture transport into the region. Theaccumulation rate is based on the ice-age–gas-age differences calculatedfrom the ice chronology, which is constrained by the stable water isotopesof the ice, and an improved gas chronology based on measurements of oxygenisotopes of O2 in the trapped gases. The peak accumulation rate in S27occurred at 128.2 ka, near the peak LIG warming in Antarctica. Even the mostconservative estimate yields an order-of-magnitude increase in theaccumulation rate during the LIG maximum, whereas other Antarctic ice coresare typically characterized by a glacial–interglacial difference of a factorof 2 to 3. While part of the increase in S27 accumulation rates mustoriginate from changes in the large-scale atmospheric circulation,additional mechanisms are needed to explain the large changes. Wehypothesize that the exceptionally high snow accumulation recorded in S27reflects open-ocean conditions in the Ross Sea, created by reduced sea iceextent and increased polynya size and perhaps by a southward retreat of theRoss Ice Shelf relative to its present-day position near the onset of the LIG.The proposed ice shelf retreat would also be compatible with a sea-levelhigh stand around 129 ka significantly sourced from West Antarctica. Thepeak in S27 accumulation rates is transient, suggesting that if the Ross IceShelf had indeed retreated during the early LIG, it would have re-advancedby 125 ka. 

Abstract. We present a 2700-year annually resolved chronology and snow accumulationhistory for the Roosevelt Island Climate Evolution (RICE) ice core, Ross IceShelf, West Antarctica. The core adds information on past accumulationchanges in an otherwise poorly constrained sector of Antarctica. The timescale was constructed by identifying annual cycles inhigh-resolution impurity records, and it constitutes the top part of theRoosevelt Island Ice Core Chronology 2017 (RICE17). Validation by volcanicand methane matching to the WD2014 chronology from the WAIS Divide ice coreshows that the two timescales are in excellent agreement. In a companionpaper, gas matching to WAIS Divide is used to extend the timescale for thedeeper part of the core in which annual layers cannot be identified. Based on the annually resolved timescale, we produced a record of past snowaccumulation at Roosevelt Island. The accumulation history shows thatRoosevelt Island experienced slightly increasing accumulation rates between700 BCE and 1300 CE, with an average accumulation of 0.25±0.02 mwater equivalent (w.e.) per year. Since 1300 CE, trends in the accumulationrate have been consistently negative, with an acceleration in the rate ofdecline after the mid-17th century. The current accumulation rate atRoosevelt Island is 0.210±0.002 m w.e. yr−1 (average since 1965 CE, ±2σ), and it is rapidly declining with a trend corresponding to0.8 mm yr−2. The decline observed since the mid-1960s is 8 times fasterthan the long-term decreasing trend taking place over the previouscenturies, with decadal mean accumulation rates consistently being belowaverage. Previous research has shown a strong link between Roosevelt Islandaccumulation rates and the location and intensity of the Amundsen Sea Low,which has a significant impact on regional sea-ice extent. The decrease inaccumulation rates at Roosevelt Island may therefore be explained in termsof a recent strengthening of the ASL and the expansion of sea ice in the easternRoss Sea. The start of the rapid decrease in RICE accumulation ratesobserved in 1965 CE may thus mark the onset of significant increases inregional sea-ice extent. 

The tropical Andes of southern Peru and northern Bolivia have several major mountain summits suitable for ice core paleoclimatic investigations. However, incomplete understanding of the controls on the isotopic ( δD, δ¹⁸O) composition of precipitation and a paucity of field observations in this region continue to limit ice-core-based paleoclimate reconstructions. This study examines four years of daily observations of δD and δ¹⁸O in precipitation from a citizen scientist network on the northeastern margin of the Altiplano, to identify controls on the subseasonal spatiotemporal variability in δ¹⁸O during the wet season (November–April). These data provide new insights into modern δ¹⁸O variability at high spatial and temporal scales. We identify a regionally coherent subseasonal signal in precipitation δ¹⁸O featuring alternating periods of high and low δ¹⁸O of 9–27-day duration. This signal reflects variability in precipitation delivery driven by synoptic conditions and closely relates to variations in the strength of the South American low-level jet and moisture availability over the study area. The annual layer of snowpack on the Quelccaya Ice Cap observed in the subsequent dry season retains this subseasonal signal, allowing the development of a snow-pit age model based on precipitation δ¹⁸O measurements, and demonstrating how synoptic variability is transmitted from the atmosphere to mountaintop snowpacks along the Altiplano’s eastern margin. This result improves our understanding of the hydrometeorological processes governing δ¹⁸O and δD in tropical Andean precipitation and has implications for improving paleoclimate reconstructions from tropical Andean ice cores and other paleoclimate records.