The geochemistry of redox sensitive trace metals in sediments
The geochemistry of redox sensitive trace metals in sediments
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DOI：
10.1016/s0016-7037(99)00126-x
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发表时间：
1999-06-01
影响因子：
5
通讯作者：
Emerson, S
中科院分区：
文献类型：
--
作者：
Morford, JL;Emerson, S
我们分析了西北非洲边缘、美国西北边缘和阿拉伯海表层沉积物中氧化还原敏感元素V、Mo、U、Re和Cd，以确定它们在一系列氧化还原条件下的响应。当氧气进入沉积物1厘米或更少时，Mo和V扩散到上覆的水中，因为Mn被还原和再活化。在这些氧化还原条件下，铀、稀土和镉的自生富集是明显的。随着硫酸盐还原作用的开始，所有金属均自积累，其中稀土的富集程度最高。通过计算3种主要氧化还原机制的自生通量来描述自生金属积累的一般趋势：氧、氧穿透小于或等于1厘米的还原和缺氧条件。利用简单的成岩作用模型和全球有机碳雨率和海底氧气浓度估计值，我们计算出在1000米水深以下，氧气穿透小于或等于1厘米的沉积物面积占洋底的4%。我们的结论是，在氧气渗透小于或等于1cm的沉积物中，使用本工作和其他文献中的自生金属浓度和积累速率，以各自河流通量的140%-260%、60%-150%和5%-10%的速率向海水释放Mn、V和Mo。这些沉积物是Re、Cd和U的汇，其埋藏通量分别为其溶解河流输入量的70% ~ 140%、30% ~ 80%和20% ~ 40%。我们模拟了海水Re、Cd和V浓度对氧渗透小于或等于1cm的还原性沉积物面积变化响应的敏感性。我们的分析表明，海水中Re浓度的变化可以忽略不计，而如果还原性沉积物的面积增加2倍，海水中Cd和V的浓度可能分别下降和增加5%-10%，如果面积增加3倍，海水中Cd和V的浓度可能分别下降10%-20%。在过去40kyr中，还原沉积物面积中Cd/Ca和V/Ca比值的浓度变化增加了2倍，与有孔虫壳中Cd/Ca和V/Ca比值的不确定性大致相同。这意味着，在最近的过去，深度超过1000米（4%）的海洋中减少沉积物的面积不超过当前值的两倍。版权所有爱思唯尔科学有限公司
We analyzed the redox sensitive elements V, Mo, U, Re and Cd in surface sediments from the Northwest African margin, the U.S. Northwest margin and the Arabian Sea to determine their response under a range of redox conditions. Where oxygen penetrates 1 cm or less into the sediments, Mo and V diffuse to the overlying water as Mn is reduced and remobilized. Authigenic enrichments of U, Re and Cd are evident under these redox conditions. With the onset of sulfate reduction, all of the metals accumulate authigenically with Re being by far the most enriched. General trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes: oxic, reducing where oxygen penetrates less than or equal to 1 cm, and anoxic conditions. Using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations, we calculate the area of sediments below 1000 m water depth in which oxygen penetration is less than or equal to 1 cm to be 4% of the ocean floor. We conclude that sediments where oxygen penetrates less than or equal to 1 cm release Mn, V and Mo to seawater at rates of 140%-260%, 60%-150% and 5%-10% of their respective riverine fluxes, using the authigenic metal concentrations and accumulation rates from this work and other literature. These sediments are sinks for Re, Cd and U, with burial fluxes of 70%-140%, 30%-80% and 20%-40%, respectively, of their dissolved riverine inputs. We modeled the sensitivity of the response of seawater Re, Cd and V concentrations to changes in the area of reducing sediments where oxygen penetrates less than or equal to 1 cm. Our analysis suggests a negligible change in seawater Re concentration, whereas seawater concentrations of Cd and V could have decreased and increased, respectively, by 5%-10% over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10%-20% if the area increased by a factor of 3. The concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of Cd/Ca and V/Ca ratios observed in foraminifera shells over the last 40 kyr. This implies that the area of reducing sediments in the ocean deeper than 1000 m (4%) has not been greater than twice the present value in the recent past. Copyright (C) 1999 Elsevier Science Ltd.