Upper ocean variability off NE Greenland (79°N) since the last glacial maximum reconstructed from stable isotopes in planktic foraminifer morphotypes
Upper ocean variability off NE Greenland (79°N) since the last glacial maximum reconstructed from stable isotopes in planktic foraminifer morphotypes
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自末次盛冰期以来格陵兰岛东北部（北纬79°）的上层海洋变化根据浮游有孔虫形态类型的稳定同位素重建
DOI：
10.1016/j.quascirev.2021.107070
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发表时间：
2021
影响因子：
4
通讯作者：
Mackensen
中科院分区：
文献类型：
--
作者：
Spielhagen;Mackensen
本文报道了两种不同形态的极地浮游有孔虫（即完全包壳和少量包壳的neogloboquadrina pachyderma）的稳定氧碳同位素数据，这些数据来自东北格陵兰大陆边缘的沉积物岩心。这些形态应该生活在该地区上层水柱的不同水深，该地区今天分层强烈，表面有一个低盐，冷水层。配对的同位素数据集提供了在所研究的形态类型的首选水深范围内过去水的盐度和温度的时间变化，并允许对上层水柱的分层作出结论。放射性碳定年的沉积物岩心覆盖了21 ~ 4 cal-ka的时间间隔，但由于受到底流的强烈侵蚀，未显示出去冰期早期（18.5 ~ 12.7 cal-ka）的特征。末次盛冰期晚期沉积物中薄壳与厚壳氧同位素差异。厚皮动物较低，指向较弱的分层，地表附近的淡水比现在少。碳同位素显示了一个密集的，常年的海冰覆盖，非常有限的生物生产，以及大西洋地下水层的存在。在冰川消退晚期至~ 10.3 cal-ka，两种形态型的稳定同位素值都明显较低，薄壳标本记录的振幅明显强于之后的记录。高振幅记录源于层状沉积物序列，其较老的部分是在短短几十年内沉积的。这些数据证明，研究区可能在12.7 ka之前开始发生强烈的淡水事件，并可能使海面盐度降低了4-5个实际盐度单位。作为淡水来源，我们讨论了东北格陵兰冰架冰的解体和从北冰洋内部的出口。这一事件可能导致了新仙女木时期大西洋经向翻转环流的减弱。在全新世早期和中期（10-4 cal-ka），同位素数据表明上层水柱结构与今天相似，具有发育良好的盐斜将低盐的近地表水与下伏的大西洋水层分开。季节性崩解的海冰使大量浮游生物得以生存。
We report on stable oxygen and carbon isotope data obtained on two different morphotypes of polar planktic foraminifers, i.e., fully encrusted and minor encrustedNeogloboquadrina pachyderma, from a sediment core taken on the NE Greenland continental margin. These morphotypes are supposed to live at different water depths of the upper water column in the area which today is strongly stratified, with a low-saline, cold-water layer at the surface. The paired isotopic data sets inform on temporal variations of past water salinity and temperature in the preferred water depth ranges of the investigated morphotypes and allow conclusions on the stratification of the upper water column. The radiocarbon-dated sediment core covers the time interval from 21 to 4 cal-ka, but the early part of the deglacial interval (18.5–12.7 cal-ka) is not represented, probably due to intense erosion by bottom currents. In sediments from the late last glacial maximum, oxygen isotope differences between thin-shelled and thick-shelledN. pachydermaare low and point at a weaker stratification with less freshwater than today near the surface. The carbon isotopes indicate a dense, perennial sea ice cover, very limited bioproduction, and the presence of a subsurface Atlantic Water layer. In the late deglaciation until ∼10.3 cal-ka, the stable isotope values of both analyzed morphotypes are considerably lower, with significantly stronger amplitudes in the record of thin-shelled specimens than later on. The high-amplitude record stems from a laminated sediment sequence whose older part was deposited within just a few decades. The data are evidence of a strong freshwater event in the research area that probably started before 12.7 ka and may have reduced sea surface salinities by 4–5 practical salinity units. As freshwater sources we discuss both the disintegration of NE Greenland shelf ice and export from the Arctic Ocean interior. The event may have contributed to the weakening of the Atlantic meridional overturning circulation during the Younger Dryas cold event. For the early and mid-Holocene (10-4 cal-ka), the isotope data suggest a structure of the upper water column similar to today, with a well-developed halocline separating low-saline near-surface waters from the underlying Atlantic Water layer. A seasonally disintegrated sea ice cover allowed for a considerable planktic bioproduction.
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--
发表时间：
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