A model for uranium, rhenium, and molybdenum diagenesis in marine sediments based on results from coastal locations
A model for uranium, rhenium, and molybdenum diagenesis in marine sediments based on results from coastal locations
复制标题
DOI：
10.1016/j.gca.2009.02.029
复制
发表时间：
2009-05
影响因子：
5
通讯作者：
J. Morford;W. Martin;R. Francois;C. M. Carney
中科院分区：
文献类型：
--
作者：
J. Morford;W. Martin;R. Francois;C. M. Carney
这项研究的目的是描述控制海洋沉积物中铀(U)、Re(Re)和钼(Mo)自生积累的动员和固定过程。我们在美国马萨诸塞州巴扎德湾的一个底水氧浓度(2 30-300cm2μ/L)和高有机质氧化速率(390cmmolC/μ/y)的地点分析了底栖室、孔隙水和固相样品中的这些氧化还原敏感金属(RSM)。氧渗透深度在沉积物-水界面下2~9 mm范围内变化，但孔隙水硫化物低于检测范围(<；2μM)。RSM孔隙水剖面用包括灌溉的稳态成岩模型模拟，灌溉延伸到沉积物-水界面以下10-20 cm。为了提供对海洋沉积物中微量金属成岩作用的一致描述，对Buzzards Bay沉积物的RSM结果与以前对硫化物沉积物的研究进行了比较(Morford等人，GCA 71)。RSM在固相再矿化过程中释放到孔隙水中，发生在自生RSM形成带以上深度的沉积物-水界面附近。在两个地点，钼的释放是一致的，但只有在冬季，秃鹰湾的Re和U才会间歇性地释放。在秃鹰湾的地点，Re向固相的迁移延伸到剖面的底部，而U和Mo的迁移区域被限制在∼2-9 cm。自生再矿化与缺氧再矿化速率无关，符合非生物去除机制。自生铀的生成速率及其模拟的去除速率常数随缺氧再矿化速率的增加而增加，与微生物介导的铀还原一致。自生钼的形成与硫化物微环境的形成有关。孔隙水中钼的去除深度和程度与铁和硫酸盐还原的平衡以及形成硫化铁消耗孔隙水中的硫化物密切相关。在硫化物沉积物中，孔隙水RSM达到恒定的渐近浓度，而在Buzzards Bay，只有孔隙水Re在深度上是恒定的。Buzzards Bay站点的孔隙水U的增加与通过灌溉增加和随后向上扩散到去除区是一致的。深层孔隙水中的Mo浓度超过了底层水浓度，这是由于灌溉引起的氧化和固相的再活化。在硫化物沉积物中，由于没有灌溉和/或存在更稳定的自生RSM相，没有证据表明深层孔隙水U或Mo含量较高。硫化物沉积物中U、Mo的自生累积速率与底栖通量有很好的相关性。然而，Buzzards Bay的结果表明，灌溉最终会导致固相中U和Mo的部分损失，累积速率为模拟通量的20%-30%。灌溉可以增加(Re，可能是U)或降低(U，Mo)在沉积物中的自生积累，在确定大陆边缘沉积物的埋藏率时很重要。
The purpose of this research is to characterize the mobilization and immobilization processes that control the authigenic accumulation of uranium (U), rhenium (Re), and molybdenum (Mo) in marine sediments. We analyzed these redox-sensitive metals (RSM) in benthic chamber, pore water, and solid phase samples at a site in Buzzards Bay, Massachusetts (USA) that has high bottom water oxygen concentrations (230–300μmol/L) and high organic matter oxidation rates (390μmol C/cm2/y). The oxygen penetration depth varies from 2 to 9mm below the sediment-water interface, but pore water sulfide is below detection (<2μM). The RSM pore water profiles are modeled with a steady-state diagenetic model that includes irrigation, which extends 10–20cm below the sediment-water interface. To present a consistent description of trace metal diagenesis in marine sediments, RSM results from sediments in Buzzards Bay are compared with previous research from sulfidic sediments (Morford et al., GCA 71). Release of RSM to pore waters during the remineralization of solid phases occurs near the sediment-water interface at depths above the zone of authigenic RSM formation. This release occurs consistently for Mo at both sites, but only in the winter for Re in Buzzards Bay and intermittently for U. At the Buzzards Bay site, Re removal to the solid phase extends to the bottom of the profile, while the zone of removal is restricted to ∼2–9cm for U and Mo. Authigenic Re formation is independent of the anoxic remineralization rate, which is consistent with an abiotic removal mechanism. The rate of authigenic U formation and its modeled removal rate constant increase with increasing anoxic remineralization rates and is consistent with U reduction being microbially mediated. Authigenic Mo formation is related to the formation of sulfidic microenvironments. The depth and extent of Mo removal from pore water is closely associated with the balance between iron and sulfate reduction and the consumption of pore water sulfide via iron sulfide formation. Pore water RSM reach constant asymptotic concentrations in sulfidic sediments, but only pore water Re is constant at depth in Buzzards Bay. The increases in pore water U at the Buzzards Bay site are consistent with addition via irrigation and subsequent upward diffusion to the removal zone. Deep pore water Mo concentrations exceed its bottom water concentration due to irrigation-induced oxidation and remobilization from the solid phase. In sulfidic sediments, there is no evidence for higher pore water U or Mo concentrations at depth due to the absence of irrigation and/or the presence of more stable authigenic RSM phases. There are good correlations between benthic fluxes and authigenic accumulation rates for U and Mo in sulfidic sediments. However, results from Buzzards Bay suggest irrigation ultimately results in the partial loss of U and Mo from the solid phase, with accumulation rates that are 20–30% of the modeled flux. Irrigation can augment (Re, possibly U) or compromise (U, Mo) authigenic accumulation in sediments and is important when determining burial rates in continental margin sediments.