A comparison between multi-proxy and historical data of drift-ice conditions on the East Greenland shelf

The reduction in sea ice along the SE Greenland coast during the last century has severely impacted ice-rafting to this area. In order to reconstruct ice-rafting and oceanographic conditions in the area of Denmark Strait during the last ~150 years, we conducted a multiproxy study on three short (20 cm) sediment cores from outer Kangerdlugssuaq Trough (~300 m water depth). The proxy-based data obtained have been compared with historical and instrumental data to gain a better understanding of the ice sheet-ocean interactions in the area. A robust chronology has been developed based on 210Pb and 137Cs measurements on core PO175GKC#9 (~66.2°N, 32°W) and expanded to the two adjacent cores based on correlations between calcite weight percent records. Our proxy records include sea-ice and phytoplankton biomarkers, and a variety of mineralogical determinations based on the <2 mm sediment fraction, including identification with quantitative x-ray diffraction, ice-rafted debris counts on the 63-150 µm sand fraction, and source identifications based on the composition of Fe oxides in the 45-250 µm fraction. A multivariate statistical analysis indicated significant correlations between our proxy records and historical data, especially with the mean annual temperature data from Stykkishólmur (Iceland) and the storis index (historical observations of sea-ice export via the East Greenland Current). In particular, the biological proxies (calcite weight percent, IP25, and total organic carbon %) showed significant linkage with the storis index. Our records show two distinct intervals in the recent history of the SE Greenland coast. The first of these (ad 1850-1910) shows predominantly perennial sea-ice conditions in the area, while the second (ad 1910-1990) shows more seasonally open water conditions.

近一个世纪以来，格陵兰岛东南沿岸的海冰缩减已对该区域的冰筏沉积（ice-rafting）过程造成严重影响。为重建过去约150年间丹麦海峡区域的冰筏沉积与海洋环境状况，我们对取自康厄尔苏阿槽外区（水深约300米）的3根长20厘米的短沉积物岩芯（sediment cores）开展了多代用指标研究（multiproxy study）。
我们将获取的代用指标数据与历史及实测数据进行对比，以更好地理解该区域冰盖与海洋的相互作用。基于对岩芯PO175GKC#9（北纬66.2°，西经32°）的铅210（210Pb）与铯137（137Cs）测量结果，我们建立了可靠的年代序列（chronology），并通过方解石重量百分比（calcite weight percent）记录的相关性，将该年代序列拓展至另外两根相邻岩芯。
本次研究的代用指标记录涵盖海冰与浮游植物生物标志物（phytoplankton biomarkers），以及基于<2 mm沉积物组分的多种矿物学分析，包括定量X射线衍射（x-ray diffraction）物相鉴定、针对63~150 µm砂级组分的冰筏碎屑计数，以及基于45~250 µm组分中铁氧化物（Fe oxides）组成的物源识别。
多变量统计分析（multivariate statistical analysis）结果显示，我们的代用指标记录与历史数据存在显著相关性，尤其是与冰岛斯蒂克霍卢穆尔（Stykkishólmur）的年平均气温数据，以及通过东格陵兰洋流（East Greenland Current）输出海冰的史托里斯指数（Storris Index）。其中，生物代用指标（方解石重量百分比、IP25与总有机碳占比（total organic carbon %））与史托里斯指数表现出显著关联。
我们的记录揭示了格陵兰岛东南沿岸近期历史中的两个鲜明阶段：第一阶段（公元1850年至1910年）区域以多年期海冰环境为主，第二阶段（公元1910年至1990年）则呈现出更多季节性开阔水域的环境特征。