Assessing proxy signatures of temperature, salinity, and hypoxia in the Baltic Sea through foraminifera-based geochemistry and faunal assemblages
Assessing proxy signatures of temperature, salinity, and hypoxia in the Baltic Sea through foraminifera-based geochemistry and faunal assemblages
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DOI：
10.5194/jm-37-403-2018
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发表时间：
2018-09-07
影响因子：
2
通讯作者：
Schweizer, Magali
中科院分区：
文献类型：
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作者：
Groeneveld, Jeroen;Filipsson, Helena L.;Schweizer, Magali
当前的气候和环境变化强烈地影响着浅海和波罗的海等沿海地区。这就需要一个上下文来理解这些变化的严重性和潜在结果。背景可以从过去发生类似事件时期的古环境记录中得出。在本研究中，我们探讨了波罗的海大水文梯度下不同的底水条件如何影响底栖有孔虫动物群组合及其方解石测试的地球化学组成。我们对这些动物进行了形态学和分子分析，并对几种底栖有孔虫进行了测试，评估了海底水的化学特征是如何被记录的。我们专注于两个地点，一个在卡特加特（波罗的海西部），一个在哈诺湾（波罗的海南部）。结果表明，海水Mn/Ca、Mg/Ca和Ba/Ca （Mn/Ca-sw、Mg/Ca-sw和Ba/Ca-sw）的变化主要受溶解氧浓度和盐度的控制。它们各自在有孔虫方解石上的印记表明，Mn/Ca可能代表缺氧条件，Ba/Ca可能代表波罗的海等封闭盆地的盐度。不建议在该地区使用Mg- ca作为替代指标来重建过去的海水温度，因为它可能被盐度（特别是Bulimina marginata）、Mg/Ca-sw以及可能的碳酸盐体系的巨大变化所覆盖。盐度是控制动物组合的主要因素：高盐度（类似于32）卡特加特湾的动物比低盐度（类似于15）哈诺湾的动物更多样化。分子鉴定表明，只有Elphidium clavatum出现在这两个位置，而Elphidium和氨属的其他遗传类型则局限于低盐或高盐位置。有孔虫地球化学和环境参数的结合表明，在波罗的海这样一个高度变化的环境中，有孔虫组合的不同环境影响是可以分离出来的，因此可以使用Mn/Ca、Mg/Ca和Ba/Ca来重建过去具体条件的变化。
Current climate and environmental changes strongly affect shallow marine and coastal areas like the Baltic Sea. This has created a need for a context to understand the severity and potential outcomes of such changes. The context can be derived from paleoenvironmental records during periods when comparable events happened in the past. In this study, we explore how varying bottom water conditions across a large hydrographic gradient in the Baltic Sea affect benthic foraminiferal faunal assemblages and the geochemical composition of their calcite tests. We have conducted both morphological and molecular analyses of the faunas and we evaluate how the chemical signatures of the bottom waters are recorded in the tests of several species of benthic foraminifera. We focus on two locations, one in the Kattegat (western Baltic Sea) and one in Hano Bay (southern Baltic Sea). We show that seawater Mn/Ca, Mg/Ca, and Ba/Ca (Mn/Ca-sw, Mg/Ca-sw, and Ba/Ca-sw) variations are mainly controlled by dissolved oxygen concentration and salinity. Their respective imprints on the foraminiferal calcite demonstrate the potential of Mn/Ca as a proxy for hypoxic conditions, and Ba/Ca as a proxy for salinity in enclosed basins such as the Baltic Sea. The traditional use of Mg-Ca as a proxy to reconstruct past seawater temperatures is not recommended in the region, as it may be overprinted by the large variations in salinity (specifically on Bulimina marginata), Mg/Ca-sw, and possibly also the carbonate system. Salinity is the main factor controlling the faunal assemblages: a much more diverse fauna occurs in the higher-salinity (similar to 32) Kattegat than in the low-salinity (similar to 15) Hano Bay. Molecular identification shows that only Elphidium clavatum occurs at both locations, but other genetic types of both genera Elphidium and Ammonia are restricted to either low-or high-salinity locations. The combination of foraminiferal geochemistry and environmental parameters demonstrates that in a highly variable setting like the Baltic Sea, it is possible to separate different environmental impacts on the foraminiferal assemblages and therefore use Mn/Ca, Mg/Ca, and Ba/Ca to reconstruct how specific conditions may have varied in the past.