Holocene changes in eastern equatorial Atlantic salinity as estimated by water isotopologues
Holocene changes in eastern equatorial Atlantic salinity as estimated by water isotopologues
复制标题
DOI：
10.1016/j.epsl.2012.12.003
复制
发表时间：
2011-12
影响因子：
5.3
通讯作者：
G. Leduc;J. Sachs;O. Kawka;R. Schneider
中科院分区：
文献类型：
--
作者：
G. Leduc;J. Sachs;O. Kawka;R. Schneider
表层海水的同位素组成被广泛用于利用海洋沉积物中成对有孔虫Mg/Ca和δ 18 O来推断海水表层盐度的过去变化。在低纬度地区，使用这种方法重建古盐度主要用于记录水文循环的变化。这种方法通常假设现代海水δ 18 O（δ 18 Osw）/盐度关系随时间保持不变。模拟研究表明，这种假设可能是不正确的，因为与全球气候变化有关的大尺度大气环流模式可以局部改变海水δ 18 Osw/盐度关系。由于目前还没有办法重建海水δ 18 Osw/盐度关系的过去变化，因此迄今为止，这些过程还没有得到古数据的证实。我们已经解决了这个问题，应用多代理盐度重建从海洋沉积物中收集的核心几内亚湾。我们测量了C37：2烯酮的氢同位素（δDa），以估计海水中δD的变化。我们发现，在10 - 3 kyr BP之间，δ Dabe有一个平稳的、长期的增加，增加了1.10 ‰，随后在3 kyr BP和岩心顶部之间，δ Dabe迅速下降了1.10 ‰，其值略低于全新世早期。这些特征与已发表的基于δ 18 Oswand有孔虫Ba/Ca的盐度估计以及来自花粉分析的附近大陆降雨历史不一致。我们结合δ Da和δ 18 OSW值重建了全新世盐度记录，并将其与来自同一沉积序列的Ba/Ca盐度记录进行了比较。这种结合的方法提供了盐度的趋势，更好地与Ba/Ca衍生的盐度和区域降水量的变化推断从花粉记录。我们的研究结果表明，大气环流的变化可以触发降水同位素的变化，以一种反直觉的方式，最终影响基于海水同位素值的表面盐度估计。我们的数据表明，全新世降雨同位素值在低纬度地区的趋势可能不是唯一的结果，在当地降水量的变化与量的影响。
The isotopic composition of surface seawater is widely used to infer past changes in sea surface salinity using paired foraminiferal Mg/Ca and δ18O from marine sediments. At low latitudes, paleosalinity reconstructions using this method have largely been used to document changes in the hydrological cycle. This method usually assumes that the modern seawater δ18O (δ18Osw)/salinity relationship remained constant through time. Modelling studies have shown that such assumptions may not be valid because large-scale atmospheric circulation patterns linked to global climate changes can alter the seawater δ18Osw/salinity relationship locally. Such processes have not been evidenced by paleo-data so far because there is presently no way to reconstruct past changes in the seawater δ18Osw/salinity relationship. We have addressed this issue by applying a multi-proxy salinity reconstruction from a marine sediment core collected in the Gulf of Guinea. We measured hydrogen isotopes in C37:2alkenones (δDa) to estimate changes in seawater δD. We find a smooth, long-term increase of ∼10‰ in δDabetween 10 and 3kyr BP, followed by a rapid decrease of ∼10‰ in δDabetween 3kyr BP and core top to values slightly lighter than during the early Holocene. Those features are inconsistent with published salinity estimations based on δ18Oswand foraminiferal Ba/Ca, as well as nearby continental rainfall history derived from pollen analysis. We combined δDaand δ18Oswvalues to reconstruct a Holocene record of salinity and compared it to a Ba/Ca-derived salinity record from the same sedimentary sequence. This combined method provides salinity trends that are in better agreement with both the Ba/Ca-derived salinity and the regional precipitation changes as inferred from pollen records. Our results illustrate that changes in atmospheric circulation can trigger changes in precipitation isotopes in a counter-intuitive manner that ultimately impacts surface salinity estimates based on seawater isotopic values. Our data suggest that the trends in Holocene rainfall isotopic values at low latitudes may not uniquely result from changes in local precipitation associated with the amount effect.