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 0:250:02m 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 0:2100:002m w.e. yr1 (average since 1965 CE), and it is rapidly declining with a trend corresponding to 0.8mmyr2. 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 seaice extent.
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Acknowledgements. This work is a contribution to the Roosevelt Island Climate Evolution (RICE) Program, funded by national contributions from New Zealand, Australia, Denmark, Germany, Italy, China, Sweden, UK, and USA. The main logistic support was provided by Antarctica New Zealand (K049) and the US Antarctic Program. We thank all the people involved in the RICE logistics, field-work, sampling, and analytical programs. The Danish contribution to RICE was funded by the Carlsberg Foundation’s North–South Climate Connections project grant. The research also received funding from the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013) ERC grant agreement 610055 as part of the Ice2Ice project. The RICE Program was supported by funding from NSF grants (PLR-1042883, ANT-0837883, ANT-0944021, ANT-0944307, and ANT-1643394) and New Zealand Ministry of Business, Innovation, and Employment grants issued through Victoria University of Wellington (RDF-VUW-1103, 15-VUW-131), GNS Science (540GCT32, 540GCT12), and Antarctica New Zealand (K049). Figure 1 was made using Quantarctica2 (Norwegian Polar Institute) base maps and QGIS software. We acknowledge the WAIS Divide ice-core project and thank Joe McConnell, Jihong Cole-Dai, and the students and staff of the ice-core labs at the Desert Research Institute and at South Dakota State University for providing the WAIS Divide sulfate data. We have presented here ice-core data collected and analyzed by Henrik Clausen, Willi Dansgaard, Sigfus Johnsen, Steffen Bo Hansen, and Jan Nielsen under the Ross Ice Shelf Project (RISP) carried out between 1973 and 1978. We acknowledge the pioneering work conducted by these researchers and the ongoing international collaborations they established.
© Author(s) 2019.