Organic Carbon Oxidation and Iron Remobilization by West Antarctic Shelf Sediments

一般声明：南极半岛以西的大陆架区域最近发生了巨大变化和生态系统转移，生活在海底沉积物中或以海底沉积物为食的生物群落正受到来自北方的物种入侵的影响。以前对这些沉积物的研究表明，这个社区可能消耗比以前估计的更多的区域生产力，这表明沉积物是这个生态系统的丰富和重要的组成部分，可能是一个成熟的戏剧性的变化。此外，在更丰富的沉积物条件下，铁被动员并释放回水柱。由于在这个生态系统的生产力被认为是有限的铁的可用性，增加铁从这些沉积物的释放率可以刺激生产力和促进更大的整体生态系统的变化。在这项研究中，将对整个大陆架区域的各种地点进行采样，以准确评估沉积物在消耗生态系统生产力方面的作用，并估计沉积物中铁释放的当前水平。该项目将提供一套基线沉积物结果，更全面地展示西南极大陆架生态系统的情况，并可与水柱测量结果进行比较，评价这一重要生态系统的基本运作情况。这一点特别重要，因为高纬度系统可能容易受到气候波动的影响。研究生和本科生都将接受培训。将在科学会议、其他大学和外联活动上作专题介绍。一个项目网站将向公众介绍主要成果，并解释这一新信息如何增进对南极生态系统的了解。项目技术说明：为了确定沉积物在西南极大陆架生态系统中的作用，该项目将确定帕尔默长期生态系统研究（LTER）研究区域各个地点的沉积物有机物氧化速率。为了估计铁和锰从沉积物中释放的速率，将对这些相同的地点进行采样，以获得这些金属在孔隙水和重要矿物相中的浓度的详细垂直分布。由于沉积物取样将在长距离接触试验地点进行，因此沉积物数据可与长距离接触试验的丰富生产力数据集相关联。具体而言，该项目：a）将确定南极半岛以西大陆架沉积物的耗氧率、有机碳氧化率、营养物释放率和铁活化率; B）将调查沉积物内成岩反应的垂直分布; c）将评估这些沉积率的区域重要性。将使用沉积物岩心来确定溶解氧、二氧化碳总量、营养物的沉积物-水通量、这些溶解化合物的垂直分布以及孔隙沃茨中的铁和锰。还将确定孔隙度、有机碳和氮含量、碳酸盐含量、生物硅含量以及多种固相铁、锰和硫物质的大量沉积物特性。这些测量将有助于确定总的有机碳氧化和反硝化速率，以及每个地点的好氧呼吸与厌氧呼吸的比例。沉积物成岩模拟将有机物氧化过程与金属活化联系起来。孔隙水和固相铁和锰的分布将被用来模拟这些沉积物中的铁成岩作用，并估计从沉积物到上覆沃茨的铁通量。最后，将把沉积过程的整个区域平均值和分布与季节平均叶绿素生物量和生产力的分布进行比较。

General Statement: The continental shelf region west of the Antarctic Peninsula has recently undergone dramatic changes and ecosystem shifts, and the community of organisms that live in, or feed off, the sea floor sediments is being impacted by species invasions from the north. Previous studies of these sediments indicate that this community may consume much more of the regional productivity than previously estimated, suggesting that sediments are a rich and important component of this ecosystem and one that may be ripe for dramatic change. Furthermore, under richer sediment conditions, iron is mobilized and released back to the water column. Since productivity in this ecosystem is thought to be limited by the availability of iron, increased rates of iron release from these sediments could stimulate productivity and promote greater overall ecosystem change. In this research, a variety of sites across the shelf region will be sampled to accurately evaluate the role of sediments in consuming ecosystem productivity and to estimate the current level of iron release from the sediments. This project will provide a baseline set of sediment results that will present a more complete picture of the west Antarctic shelf ecosystem, will allow for comparison with water column measurements and for evaluation of the fundamental workings of this important ecosystem. This is particularly important since high latitude systems may be vulnerable to the effects of climate fluctuations. Both graduate and undergraduate students will be trained. Presentations will be made at scientific meetings, at other universities, and at outreach events. A project web site will present key results to the public and explain how this new information improves understanding of Antarctic ecosystems. Technical Description of Project: In order to determine the role of sediments within the west Antarctic shelf ecosystem, this project will determine the rates of sediment organic matter oxidation at a variety of sites across the Palmer Long Term Ecosystem Research (LTER) study region. To estimate the rates of release of iron and manganese from the sediments, these same sites will be sampled for detailed vertical distributions of the concentrations of these metals both in the porewaters and in important mineral phases. Since sediment sampling will be done at LTER sites, the sediment data can be correlated with the rich productivity data set from the LTER. In detail, the project: a) will determine the rates of oxygen consumption, organic carbon oxidation, nutrient release, and iron mobilization by shelf sediments west of the Antarctic Peninsula; b) will investigate the vertical distribution of diagenetic reactions within the sediments; and c) will assess the regional importance of these sediment rates. Sediment cores will be used to determine sediment-water fluxes of dissolved oxygen, total carbon dioxide, nutrients, and the vertical distributions of these dissolved compounds, as well as iron and manganese in the pore waters. Bulk sediment properties of porosity, organic carbon and nitrogen content, carbonate content, biogenic silica content, and multiple species of solid-phase iron, manganese, and sulfur species will also be determined. These measurements will allow determination of total organic carbon oxidation and denitrification rates, and the proportion of aerobic versus anaerobic respiration at each site. Sediment diagenetic modeling will link the processes of organic matter oxidation to metal mobilization. Pore water and solid phase iron and manganese distributions will be used to model iron diagenesis in these sediments and to estimate the iron flux from the sediments to the overlying waters. Finally, the overall regional average and distribution of the sediment processes will be compared with the distributions of seasonally averaged chlorophyll biomass and productivity.