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.

过去一个世纪以来，格陵兰东南部海岸的海冰减少已严重影响该区域的冰筏沉积（ice-rafting）。为重建丹麦海峡区域过去约150年间的冰筏沉积与海洋学条件，我们对来自外坎格尔卢斯夸克海槽（水深约300米）的三根短沉积物岩心（20厘米）开展了多指标研究（multiproxy study）。所得的基于指标的数据已与历史及仪器观测数据进行对比，以深化对该区域冰盖-海洋相互作用（ice sheet-ocean interactions）的理解。基于对PO175GKC#9岩心（约66.2°N，32°W）的铅-210（210Pb）和铯-137（137Cs）测量结果，我们建立了可靠的年代序列，并通过方解石重量百分比记录的相关性将其扩展至相邻的两根岩心。我们的指标记录包括海冰及浮游植物生物标志物，以及基于<2毫米沉积物组分的多种矿物学测定结果——包括定量X射线衍射鉴定、63-150微米砂组分中的冰筏碎屑计数，以及基于45-250微米组分中氧化铁（Fe oxides）组成的物源识别。多变量统计分析表明，我们的指标记录与历史数据之间存在显著相关性，尤其与冰岛斯蒂基斯霍尔米（Stykkishólmur）的年平均温度数据及斯托里斯指数（storis index，即通过东格陵兰洋流输出海冰的历史观测数据）相关。特别是生物指标（方解石重量百分比、IP25、总有机碳百分比）与斯托里斯指数存在显著关联。我们的记录揭示了格陵兰东南部海岸近代历史中的两个明显阶段：第一阶段（公元1850-1910年）该区域以多年海冰环境为主，而第二阶段（公元1910-1990年）则呈现更多季节性开阔水域环境。