The role of cryptic nutrient cycling within sinking particles on trace element transport in oxygen minimum zones

控制海洋中生物活性微量金属内部循环的主要过程是通过下沉颗粒的吸收和再矿化。吸收可以通过活性生物吸收进入活细胞作为微量营养素，或化学吸附到下沉材料上而发生。后一个过程通常被称为清除。这些过程的相对重要性往往是不清楚的，特别是对于既有生物活性又有“粒子反应性”的元素。“后一个特征与海水中的溶解度以及与表面位点形成强络合物有关，例如铁。最近的证据表明，下沉颗粒作为金属络合的被动表面的简单观点可能需要一些修正。研究人员James Moffett和Seth John建议研究大型下沉颗粒中过渡金属的化学性质及其对金属地球化学循环的影响。他们将与华盛顿大学的一个小组合作，该小组最近获得资助，研究这些颗粒的微生物学和分子生物学。该项目的核心假设是，减少大颗粒内的微生物微环境支持氮和硫的高循环速率，大大增强了颗粒对金属化学的影响。研究人员将在东热带北太平洋氧气最低区（OMZ）研究这些过程。选择这一制度是因为在水柱中的氧化还原条件的范围很广，和强有力的初步证据表明，沉降颗粒内的微环境有重大的地球化学impactions.The主要目标是调查的相互作用的金属颗粒含有微环境，更高度还原比周围的沃茨。这种微环境出现时，占主导地位的终端电子受体（氧，或硝酸盐在氧最小区）变得耗尽和替代终端电子受体被利用。在还原性微环境中，金属氧化还原状态和配位化学不同于本体水柱，并且这些微环境可能主导金属颗粒相互作用。例如，硫酸盐还原为硫化物可以结合形成强硫化物络合物的金属，如镉和锌，以前认为这一过程仅限于硫化物环境。还原微环境可以解释还原物种如铁（II）的产生，即使它们的形成在本体水柱中是有害的。任务包括溶解和颗粒痕量金属和稳定同位素在研究区域的观测特性，采样和原位操纵粒子使用大尺寸沉积物陷阱，在一系列氧化还原条件下的船上实验孵化，和建模，提供从微观到全球尺度的洞察力。金属化学数据将在丰富的互补数据背景下进行解释，包括氮和硫循环速率，关键酶浓度的遗传学和蛋白质组学表征。更广泛的影响包括博士后科学家的培训，与墨西哥科学家的国际合作，以及本科生参与研究。

The major process controlling the internal cycling of biologically active trace metals in the oceans is through uptake onto and remineralization from sinking particles. Uptake can occur through active biological uptake into living cells as micronutrients, or chemical adsorption onto sinking materials. This latter process is often referred to as scavenging. The relative importance of these processes is often unclear, especially for elements that are both biologically active and also "particle reactive." The latter characteristic is associated with sparing solubility in seawater and the formation of strong complexes with surface sites, with examples such as iron. Recent evidence suggests that the simplistic view of a sinking particle as a passive surface for metal complexation may require some revision. Investigators James Moffett and Seth John propose to study the chemistry of transition metals within large sinking particles and the resultant effects on metal biogeochemical cycling. They will collaborate with a group at the University of Washington, recently funded to study the microbiology and molecular biology of these particles. The central hypothesis of this project is that reducing microbial microenvironments within large particles support high rates of nitrogen and sulfur cycling, greatly enhancing the particles' influence on metal chemistry. The investigators will study these processes in the Eastern Tropical North Pacific Oxygen Minimum Zone (OMZ). This regime was selected because of the wide range of redox conditions in the water column, and strong preliminary evidence that microenvironments within sinking particles have major biogeochemical impacts.The primary objective is to investigate the interactions of metals with particles containing microenvironments that are more highly reducing than the surrounding waters. Such microenvironments arise when the prevailing terminal electron acceptor (oxygen, or nitrate in oxygen minimum zones) becomes depleted and alternative terminal electron acceptors are utilized. Within reducing microenvironments metal redox state and coordination chemistry are different from the bulk water column, and these microenvironments may dominate metal particle interactions. For example, reduction of sulfate to sulfide could bind metals that form strong sulfide complexes, such as cadmium and zinc, processes previously thought to be confined to sulfidic environments. Reducing microenvironments may account for the production of reduced species such as iron(II), even when their formation is thermodynamically unfavorable in the bulk water column. Tasks include observational characterization of dissolved and particulate trace metals and stable isotopes in the study area, sampling and in situ manipulation of particles using large-dimension sediment traps, shipboard experimental incubations under a range of redox conditions, and modeling, providing insight from microscopic to global scales. The metal chemistry data will be interpreted within a rich context of complimentary data including rates of nitrogen and sulfur cycling, phylogenetics and proteomic characterization of the concentration of key enzymes. Broader impacts include training of a postdoctoral scientist, international collaborations with Mexican scientists, and involvement of undergraduate students in the research.