Tracking hydrothermal particles from the ridge axis to the sediment column along the Endeavour segment of the Juan de Fuca Ridge

IF 2.6 3区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY
Melissa Mills , Jay T. Cullen , Jody Spence , Patrick A. Rafter , Steve Mihaly , Laurence A. Coogan
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引用次数: 0

Abstract

Elemental fluxes associated with mid-ocean ridge hydrothermal systems are thought to be important in the ocean budgets of many elements but quantitative models of these fluxes, and how they vary in space and time due to different boundary conditions, are in their infancy. This is especially true for non-conservative elements that can be involved in multiple processes transforming them between the dissolved and particulate phases both in the water column and after sedimentation. To help develop a more robust database for parameterizing the processes operating, we undertook a coupled sediment trap and sediment core study of hydrothermal sediments on the west flank of the Endeavour segment of the Juan de Fuca Ridge. Sediment traps deployed in the Main Endeavour Field (MEF) and 3 and 9 km southwest of this field, along the mean flow direction of the hydrothermal plume, show that the rate of change of the concentration of sulfide-associated elements (Cu, Zn, Cd, Pb, Ag, As, Mo) in sediment settling from the plume differs between elements. We interpret this as indicating both different dissolution rates of phases containing these elements and different rates of scavenging of these elements from seawater. Scavenging is most readily tracked using elements for which the scavenged fraction is large relative to the hydrothermally derived fraction. For such elements, the relative efficiency of scavenging from seawater (REE > Cr > Ni > V > P > U) matches that previously reported from the TAG system on the Mid-Atlantic ridge despite different vent fluid and seawater chemistries that are expected to lead to both differing roles of Fe-sulfide and Fe-oxyhydroxides and different Fe oxidation rates. In the sediment trap samples collected 9 km off-axis, but not in those collected 3 km off-axis, the Mn and Ti concentrations correlate strongly despite these samples having much higher Mn concentrations than background sediment. Since Ti is sourced almost entirely from background terrigenous material such a correlation was not expected. The most reasonable explanation for this is that aggregation of hydrothermally derived particles with terrigenous material settling through the water column controls removal of hydrothermally derived particles from the water column. Changes in sediment composition with depth in the off-axis sediment core, along with differences between the composition of material from the sediment core and the off-axis sediment traps, are interpreted as indicating large post-deposition changes in sediment composition. For example, much or all of the Mn, P, As and Mo carried to the sediments with hydrothermally derived particles is released back into the water column during diagenesis. In contrast, V and REE concentrations in the sediment core are higher than those in the off-axis sediment trap samples, which may be due to continued scavenging in a benthic boundary layer post-deposition. Overall these data are interpreted as indicating that the net loss of many elements from the non-buoyant plume may not be a proxy for loss from the ocean, and a better understanding of post-depositional processes in hydrothermal settings may be important in understanding cycling of the aforementioned elements, and likely others, in seawater.
沿胡安德富卡海脊奋进者海段追踪从海脊轴到沉积柱的热液颗粒
与大洋中脊热液系统有关的元素通量被认为在许多元素的海洋预算中很重要,但这些通量的定量模型,以及它们如何因不同的边界条件而在空间和时间上变化,还处于起步阶段。这对于非守恒元素来说尤其如此,因为这些元素在水体中和沉积后会参与溶解相和颗粒相之间的多个转化过程。为了帮助开发一个更强大的数据库,对运行过程进行参数化,我们对胡安-德富卡海脊奋进段西侧的热液沉积物进行了沉积物捕集器和沉积岩芯耦合研究。沿热液羽流的平均流动方向,在主奋进区(MEF)和该区西南 3 公里和 9 公里处布设的沉积物捕集器显示,羽流沉积物中硫化物相关元素(铜、锌、镉、铅、银、砷、钼)的浓度变化率因元素而异。我们认为这既表明含有这些元素的相的溶解速率不同,也表明这些元素从海水中清除的速率不同。如果元素的清除部分相对于热液衍生部分较大,则最容易跟踪清除情况。对于这些元素,从海水中清除的相对效率(REE > Cr > Ni > V > P > U)与之前报告的大西洋中脊 TAG 系统相吻合,尽管喷口流体和海水的化学性质不同,预计会导致硫化铁和氧化铁的作用不同以及铁的氧化率不同。在离轴 9 千米处采集的沉积物捕集器样本中,锰和钛的浓度密切相关,但在离轴 3 千米处采集的样本中,锰和钛的浓度却不相关,尽管这些样本中的锰浓度远高于背景沉积物。由于钛几乎完全来自于背景陆相沉积物质,因此这种相关性是意料之外的。最合理的解释是,水热作用产生的颗粒与沉降在水体中的土著物质聚集在一起,控制了水热作用产生的颗粒从水体中的清除。轴外沉积岩芯中沉积物成分随深度的变化,以及沉积岩芯和轴外沉积物捕集器中物质成分的差异,被解释为表明沉积后沉积物成分发生了巨大变化。例如,在成岩过程中,随热液衍生颗粒带入沉积物的大部分或全部锰、钾、砷和钼被释放回水体。相比之下,沉积岩芯中的 V 和 REE 浓度高于离轴沉积物捕集器样本中的浓度,这可能是由于沉积后底栖边界层的持续清除作用造成的。总之,这些数据表明,非浮力羽流中许多元素的净损失量可能并不代表海洋中的损失量,更好地了解热液环境中的沉积后过程可能对了解海水中上述元素以及其他元素的循环情况非常重要。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Marine Geology
Marine Geology 地学-地球科学综合
CiteScore
6.10
自引率
6.90%
发文量
175
审稿时长
21.9 weeks
期刊介绍: Marine Geology is the premier international journal on marine geological processes in the broadest sense. We seek papers that are comprehensive, interdisciplinary and synthetic that will be lasting contributions to the field. Although most papers are based on regional studies, they must demonstrate new findings of international significance. We accept papers on subjects as diverse as seafloor hydrothermal systems, beach dynamics, early diagenesis, microbiological studies in sediments, palaeoclimate studies and geophysical studies of the seabed. We encourage papers that address emerging new fields, for example the influence of anthropogenic processes on coastal/marine geology and coastal/marine geoarchaeology. We insist that the papers are concerned with the marine realm and that they deal with geology: with rocks, sediments, and physical and chemical processes affecting them. Papers should address scientific hypotheses: highly descriptive data compilations or papers that deal only with marine management and risk assessment should be submitted to other journals. Papers on laboratory or modelling studies must demonstrate direct relevance to marine processes or deposits. The primary criteria for acceptance of papers is that the science is of high quality, novel, significant, and of broad international interest.
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