The South Pole Ice Core (SPICEcore) chronology and supporting data

Abstract: The South Pole Ice Core (SPICEcore) was drilled in 2014-2016 to provide a detailed multi-proxy archive of paleoclimate conditions in East Antarctica during the Holocene and late Pleistocene. Interpretation of these records requires an accurate depth-age relationship. Here, we present the SP19 timescale for the age of the ice of SPICEcore. SP19 is synchronized to the WD2014 chronology from the West Antarctic Ice Sheet Divide (WAIS Divide) ice core using stratigraphic matching of 251 volcanic events. These events indicate an age of 54,302 +/- 519 years BP (before the year 1950) at the bottom of SPICEcore. Annual layers identified in sodium and magnesium ions to 11,341 BP were used to interpolate between stratigraphic volcanic tie points, yielding an annually-resolved chronology through the Holocene. Estimated timescale uncertainty during the Holocene is less than 18 years relative to WD2014, with the exception of the interval between 1800 to 3100 BP when uncertainty estimates reach +/- 25 years due to widely spaced volcanic tie points. Prior to the Holocene, uncertainties remain within 124 years relative to WD2014. Results show an average Holocene accumulation rate of 7.4 cm/yr (water equivalent). The time variability of accumulation rate is consistent with expectations for steady-state ice flow through the modern spatial pattern of accumulation rate. Time variations in nitrate concentration, nitrate seasonal amplitude, and δ15N of N2 in turn are as expected for the accumulation-rate variations. The highly variable yet well-constrained Holocene accumulation history at the site can help improve scientific understanding of deposition-sensitive climate proxies such as δ15N of N2 and photolyzed chemical compounds.摘要：南极冰芯（South Pole Ice Core, SPICEcore）于2014-2016年钻取，旨在获取东南极洲全新世与晚更新世时期高精度多代用指标古气候记录档案。对这些记录的解译需要精准的深度-年代关系。本文提供了SPICEcore冰体年龄的SP19年代标尺。SP19通过251次火山事件的地层匹配，与西南极冰盖分水岭（West Antarctic Ice Sheet Divide, WAIS Divide）冰芯的WD2014年表实现同步。这些火山事件显示，SPICEcore底部的年龄为54302±519年BP（即相对于1950年的距今年代）。研究利用钠、镁离子识别出的11341年BP以内的年层，在地层火山锚点之间进行插值，最终得到贯穿全新世的年分辨率年代序列。相对于WD2014年表，全新世期间的年代标尺不确定性小于18年，仅在1800~3100 BP时段例外——该时段因火山锚点间距过大，不确定性达到±25年。全新世之前，相对于WD2014年表的不确定性仍控制在124年以内。结果显示，该站点全新世平均冰积累速率为7.4 cm/yr（水当量）。冰积累速率的时间变率与现代空间分布格局下的稳态冰流预期相符。硝酸盐浓度、硝酸盐季节振幅以及氮气的δ¹⁵N的时间变化，也与冰积累速率变化的预期一致。该站点高度可变但约束良好的全新世冰积累历史，有助于提升学界对沉积敏感型气候代用指标的科学认知，例如氮气的δ¹⁵N以及光解化合物。