Abstract
Abstract. We present a 2700-year annually resolved chronology and snow accumulation history for the Roosevelt Island Climate Evolution (RICE) ice core, Ross Ice Shelf, West Antarctica. The core adds information on past accumulation changes in an otherwise poorly constrained sector of Antarctica. The timescale was constructed by identifying annual cycles in high-resolution impurity records, and it constitutes the top part of the Roosevelt Island Ice Core Chronology 2017 (RICE17). Validation by volcanic and methane matching to the WD2014 chronology from the WAIS Divide ice core shows that the two timescales are in excellent agreement. In a companion paper, gas matching to WAIS Divide is used to extend the timescale for the deeper part of the core in which annual layers cannot be identified. Based on the annually resolved timescale, we produced a record of past snow accumulation at Roosevelt Island. The accumulation history shows that Roosevelt Island experienced slightly increasing accumulation rates between 700 BCE and 1300 CE, with an average accumulation of 0.25±0.02 m water equivalent (w.e.) per year. Since 1300 CE, trends in the accumulation rate have been consistently negative, with an acceleration in the rate of decline after the mid-17th century. The current accumulation rate at Roosevelt 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 to 0.8 mm yr−2. The decline observed since the mid-1960s is 8 times faster than the long-term decreasing trend taking place over the previous centuries, with decadal mean accumulation rates consistently being below average. Previous research has shown a strong link between Roosevelt Island accumulation rates and the location and intensity of the Amundsen Sea Low, which has a significant impact on regional sea-ice extent. The decrease in accumulation rates at Roosevelt Island may therefore be explained in terms of a recent strengthening of the ASL and the expansion of sea ice in the eastern Ross Sea. The start of the rapid decrease in RICE accumulation rates observed in 1965 CE may thus mark the onset of significant increases in regional sea-ice extent.
Highlights
Accurate timescales are fundamental for reliable interpretation of paleoclimate archives, including ice cores
A highly dynamic synoptic-scale system brings this precipitation to Roosevelt Island: positive Roosevelt Island Climate Evolution (RICE) precipitation anomalies have been linked to the increased occurrence of eastern Ross Sea–Amundsen Sea blocking events associated with a weak state of the quasistationary Amundsen Sea Low (ASL) pressure system
The upper part of the RICE ice core from Roosevelt Island, Ross Ice Shelf, West Antarctica, was dated by annual-layer counting back to 700 BCE based on multiple high-resolution impurity records
Summary
Accurate timescales are fundamental for reliable interpretation of paleoclimate archives, including ice cores. Reconstructions of past accumulation rates are important for improving our understanding of the natural fluctuations in snow accumulation and their climate drivers Such knowledge is essential to accurately evaluate the current and future surface mass balance of glaciers and ice sheets, a critical and currently under-constrained factor in sea level assessments (Shepherd et al, 2012). ECMWF ERA-Interim (ERAi) reanalysis fields (Dee et al, 2011) indicate that precipitation at Roosevelt Island is strongly influenced by the Amundsen Sea Low (ASL) and associated ridging (Raphael et al, 2016), and it is anticorrelated with precipitation in Ellsworth Land and the Antarctic Peninsula (Hosking et al, 2013; Bertler et al, 2018; Emanuelsson et al, 2018) These differences emphasize the need for high spatial and temporal coverage when reconstructing regional mass balance patterns. With few other ice cores from the Ross Sea region, the RICE accumulation history adds information on past changes in mass balance from an otherwise poorly constrained sector of the Antarctic continent
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