Sedimentary trace element records over the last 200 kyr from within and below the northern Arabian Sea oxygen minimum zone
Sedimentary trace element records over the last 200 kyr from within and below the northern Arabian Sea oxygen minimum zone
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DOI：
10.1016/j.margeo.2006.05.013
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发表时间：
2006-09
期刊：
影响因子：
2.9
通讯作者：
C. H. Weijden;G. Reichart;B. Os
中科院分区：
文献类型：
--
作者：
C. H. Weijden;G. Reichart;B. Os
两个活塞芯（PC），包含两个完整的冰川周期，在默里岭检索。一个岩心（PC 463）含有沉积在920 mbsl处的沉积物，另一个岩心（PC 464）含有沉积在当前氧气最小区OMZ（O2：≤2 μM）以下1470 mbsl处的沉积物。有机碳（OC）含量的变化与两个核心之间的相关性很好;高OC含量对应于高日照时期，并伴随着一个稳定和密集的OMZ。成岩组分是相似的，并且具有相当恒定的组成。V，Mn，Co，Cu，Se，Zn和Sb在这些馏分中的含量与标准页岩（SS）中的值相当一致。成岩组分中Ni的含量高于SS，这是由于其在区域风成输入中的高含量; Mo、Re和U的含量高于SS，这是同生和（或）成岩叠加的结果。两个岩芯中Mn、Co与OC呈负相关，其它元素与OC呈正相关。可以设想四种有助于沉积物富集微量元素的过程：1）作为微量或痕量成分在含氢和生物颗粒中的释放，2）在水柱中的清除，3）在主相分解期间（部分）保留在沉积物中，4）通过沉积物-水界面扩散到沉积物中，随后由于还原或沉淀为硫化物而固定。钒、钼、铼、铀明显富集，镍、铜、锌、硒可能富集。富集或耗尽微量元素在PC 463相对于PC 464进行了测试，作为底层水氧（BWO）的条件下，在有机物的最大积累速率期间的代理。只有钼，Re和Re/Mo似乎是明确的代理站点463和464之间的沉积条件的差异。使用这些代理人，它被发现，OMZ扩展到至少深度的网站464从155到135 ka。
Two piston cores (PCs), containing two full glacial cycles, were retrieved at Murray Ridge. One core (PC463) contains sediment deposited at 920 mbsl within, the other (PC464) has sediment deposited at 1470 mbsl below the current oxygen minimum zone, OMZ (O2: ≤2 μM). Variations in the organic carbon (OC) content correlate well between the two cores; high OC contents correspond with periods of high insolation and are accompanied by a stable and intensive OMZ. The lithogenic fractions are similar and have a rather constant composition. The V, Mn, Co, Cu, Se, Zn and Sb contents in these fractions are in fair agreement with the values in standard shales (SS). The Ni content of the lithogenic fraction is higher than in SS due to its high content in the regional eolian input, and the Mo, Re and U contents are higher as a result of syngenetic and(or) diagenetic overprints. In both cores, Mn and Co have a negative, the other elements a positive correlation with OC. Four processes, contributing to sedimentary enrichment in trace elements, can be envisaged: 1) delivery, as minor or trace components, in hydrogenous and biogenic particles, 2) scavenging in the water column, 3) (partial) retention in the sediment during decomposition of host phases, 4) diffusion into the sediment across the sediment–water interface and subsequent immobilization in response to reduction or precipitation as sulfides. Vanadium, Mo, Re, and U were found to be clearly enriched, and Ni, Cu, Zn and Se to be possibly enriched as a result of these processes. Enrichment or depletion in trace elements in PC463 relative to PC464 was tested as a proxy for bottom-water oxygen (BWO) conditions during periods of maximum accumulation rates of organic matter. Only Mo, Re and Re/Mo appear to be unambiguous proxies for differences in depositional conditions between sites 463 and 464. Using these proxies, it was found that the OMZ expanded to at least the depth of site 464 from 155 to 135 ka.