Zooming in on Heinrich layers
Zooming in on Heinrich layers
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DOI：
10.1029/2000pa000559
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发表时间：
2001-06-01
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影响因子：
--
通讯作者：
Weber, O
中科院分区：
文献类型：
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作者：
Grousset, FE;Cortijo, E;Weber, O
解释冰筏碎屑（IRD）突然大量排放到冰川北大西洋（海因里希层（HLs））起源的理论通常指向劳伦泰德冰盖作为这些事件的唯一来源，直到发现IRD也起源于冰岛和欧洲冰盖[Bond和Lotti, 1995；Snoeckx等人，1999；Grousset et al., 2000]。这种明显的矛盾必须得到调和，因为它提出了关于HL起源机制的基本问题。我们以超高分辨率模式（1-2世纪间隔）分析了大西洋中脊活塞核心的两个相似的12厘米厚的高压。δ O-18记录（N. pachyderma左卷）显示由冰山融化引起的强烈漂移；这些活动与浮游有孔虫数量的急剧减少和地表水温度下降30度有关。粗粒碎屑颗粒计数表明，IRD的沉积顺序为(1)火山玻璃，(2)石英和长石，(3)碎屑碳酸盐，这暗示了不同泛大西洋冰盖融化的年代。Sr和Nd同位素组成证实，在H1和H2海因里希层中，“前体”IRD首先来自欧洲/冰岛，其次是laurentide衍生的IRD。内部循环性可以确定：在H1和H2期间，大约在一个世纪的时间尺度上发生了大约4到6次主要的突然放电。δ C-13和δ N-15记录显示，陆源有机质的主要输入与HLs内的IRD有关，掩盖了浮游生物生产力信号。
Theories explaining the origin of the abrupt, massive discharges of ice-rafted detritus (IRD) into the glacial North Atlantic (the Heinrich layers (HLs)) generally point to the Laurentide ice sheet as the sole source of these events, until it was found that the IRDs also originated from Icelandic and European ice sheets [Bond and Lotti, 1995; Snoeckx er al., 1999; Grousset et al., 2000]. This apparent contradiction must be reconciled as it raises fundamental questions about the mechanism(s) of HL origin. We have analyzed two similar to 12 cm thick HLs in an ultrahigh-resolution mode (1-2 century intervals) in a mid-Atlantic ridge piston core. The delta O-18 record (N. pachyderma left coiling) reveals strong excursions induced by the melting of the icebergs; these excursions are associated with a strong decrease in the amount of planktic foraminifers and with a 30 degreesC cooling of the surface waters. Counts of coarse detrital grains reveal that IRD are deposited according to a typical sequence (I) volcanic glass, (2) quartz and feldspars, (3) detrital carbonate, that implies a chronology in the melting of the differentpan-Atlantic ice sheets. Sr and Nd isotopic composition confirm that in both Heinrich layers H1 and H2, "precursor" IRD came from first Europe/Iceland, followed then by Laurentide-derived IRD. An internal cyclicity can be identified: during H1 and H2, about four to six major, abrupt discharges occurred roughly on a century timescale. The delta C-13 and delta N-15 records reveal that dominant inputs of continent-derived organic matter are associated with IRD within the HLs, hiding the plankton productivity signal.