Export of nutrient rich Northern Component Water preceded early Oligocene Antarctic glaciation
Export of nutrient rich Northern Component Water preceded early Oligocene Antarctic glaciation
复制标题
DOI：
10.1038/s41561-018-0069-9
复制
发表时间：
2018-03-01
影响因子：
18.3
通讯作者：
Backman, Jan
中科院分区：
文献类型：
--
作者：
Coxall, Helen K.;Huck, Claire E.;Backman, Jan
北大西洋深水形成的开始被认为与大约3400万年前南极冰盖的增长相吻合(Ma)。然而，这一时间存在争议，部分原因是对形成于北大西洋深处的古代北方组分水(NCW)的地球化学特征存在疑问。在这里，我们提供了位于深水形成地点附近的北大西洋沉积物岩心的详细地球化学记录。我们发现，在36 Ma之前，大西洋西北部是分层的，营养丰富，底层低盐度。这个受限的盆地转变为NCW的管道，大约在最初的南极冰川形成前100万年，NCW开始向南流动。可能的导火索是亚北极海域的构造调整，使得格陵兰-苏格兰海脊之间的交流增加。表层盐度和密度的增加增强了NCW的产量。由于北冰洋化石碳的泄漏，始新世晚期深水团的碳同位素特征与现代值不同。这种富含营养的水的输出为地球系统提供了一个瞬时的二氧化碳脉冲，这可能导致了短期的变暖，而增强的NCW形成的长期影响是更大的向北输送的热量，使南极洲降温。
The onset of the North Atlantic Deep Water formation is thought to have coincided with Antarctic ice-sheet growth about 34 million years ago (Ma). However, this timing is debated, in part due to questions over the geochemical signature of the ancient Northern Component Water (NCW) formed in the deep North Atlantic. Here we present detailed geochemical records from North Atlantic sediment cores located close to sites of deep-water formation. We find that prior to 36 Ma, the northwestern Atlantic was stratified, with nutrient-rich, low-salinity bottom waters. This restricted basin transitioned into a conduit for NCW that began flowing southwards approximately one million years before the initial Antarctic glaciation. The probable trigger was tectonic adjustments in subarctic seas that enabled an increased exchange across the Greenland-Scotland Ridge. The increasing surface salinity and density strengthened the production of NCW. The late Eocene deep-water mass differed in its carbon isotopic signature from modern values as a result of the leakage of fossil carbon from the Arctic Ocean. Export of this nutrient-laden water provided a transient pulse of CO2 to the Earth system, which perhaps caused short-term warming, whereas the long-term effect of enhanced NCW formation was a greater northward heat transport that cooled Antarctica.