NOAA/WDS Paleoclimatology - WAIS Divide Ice Core 2,000 Year Hydrogen and Oxygen Isotope Data

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. Atmospheric circulation changes have also caused rapid warming over the West Antarctic Ice Sheet, and contributed to declining sea-ice cover in the adjacent Amundsen-Bellingshausen seas. It is unknown whether these changes are part of a longer-term trend. Here, we use water-isotope (d18O) 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 d18O 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, d18O 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 d18O 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.

过去五十年来，大气环流变化增强了风驱动的暖海水向南极大陆架的输入，使得暖水从下方侵蚀冰架。大气环流变化同时引发了西南极冰盖的快速增温，并导致邻近的阿蒙森-别林斯高晋海的海冰覆盖面积缩减。目前尚不清楚这些变化是否属于长期趋势的一部分。本研究利用多组冰芯记录获取的水同位素（δ¹⁸O）数据，将近期西南极的气候变化置于过去两千年的背景下开展分析。研究发现，过去50年间西南极降水的δ¹⁸O值随温度趋势同步显著升高，且在20世纪90年代可能达到了近200年来的最高水平。不过，在过去2000年中，与近数十年相当的δ¹⁸O异常约占总时长的1%。大气环流模式（General Circulation Model, GCM）模拟结果显示，西南极近期的δ¹⁸O与气候变化趋势，无法与起源于热带的年代际变率区分开来。我们由此得出结论：热带气候变率的不确定走向，是西南极气候与冰盖变化预测中不确定性的重要来源。