Collaborative Research: Impacts of Eddies and Mixing on Plankton Community Structure and Biogeochemical Cycling in the Sargasso Sea

海洋中尺度的海流、锋面和涡旋，有时也被称为“海洋内部天气”，是海洋环流中能量很高且无处不在的特征。 这些现象的动力学后果包括化学和生物环境的扰动，可对海洋中的生物地球化学循环产生巨大影响。调节这种反应的过程异常复杂，挑战我们理解物理、生物和化学过程在功能上是如何相关的。最近的证据表明，中尺度涡旋是主副热带环流贫营养沃茨中重要的营养盐输送机制。数值模拟和基于卫星的统计估计表明，涡流驱动的养分通量的大小可能足以平衡对新生产的地球化学估计，这远远超过了传统养分供应机制所能维持的产量。由于驱动这一过程的事件在空间和时间上的不连续性，对这一过程的直接观测相对较少，现有数据表明，与某些类型的涡旋有关的等密度线位移可以将营养物质输送到真光层，导致上覆沃茨中叶绿素的积累。然而，生物反应的性质及其对耦合地球化学循环和输出的影响尚待阐明。此外，涡动引起的上升流与混合层内和混合层下的底辟混合之间的关系仍然不清楚;这种相互作用的强度决定了涡旋驱动效应的不可逆程度，从而影响净海洋地球化学通量。在这个项目中，一组海洋学研究人员将记录浮游植物的生理反应，群落结构的变化，出口和涡旋引起的上升流和混合在马尾藻海的地球化学后果。在实地部署之前，将通过遥感确定目标特征。 高分辨率勘测将使用包括快速重复率荧光计在内的波浪形拖曳仪器包进行。这套仪器将有助于同时评估光合参数和浮游植物和浮游动物的物种组合。在进行这些测量的同时，还将在所选地物的沿着各站对水的地球化学性质进行不连续的水取样。将在中尺度结构内的选定位置测量输出。表面混合层和真光层底部沃茨之间的混合速率将从氦通量计推断，并直接用六氟化硫示踪剂释放进行测量。这些观测结果将足以验证一个假设，即涡旋引起的上升流增加了光合速率，改变了群落结构，增加了真光层的输出，从而在亚热带海洋的地球化学循环中发挥了重要作用。这项研究将在伍兹霍尔海洋研究所的10名主要研究人员的合作下进行，百慕大生物研究站、罗格斯大学、加州大学、圣巴巴拉和迈阿密大学。工作计划包括两年的实地观察，然后是最后一年的综合。

ABSTRACTOCE-0241310 / OCE-0241399 / OCE-0241023 / OCE-0241340 / OCE-0241011The currents, fronts and eddies that comprise the oceanic mesoscale, sometimes referred to as the "internal weather of the sea," are highly energetic and ubiquitous features of ocean circulation. Dynamical consequences of these phenomena include perturbation of the chemical and biological environment that can dramatically impact biogeochemical cycling in the ocean. The processes that regulate this response are extraordinarily complex, challenging us to understand how the physical, biological and chemical processes are functionally related.Recent evidence suggests that mesoscale eddies are an important nutrient transport mechanism in the oligotrophic waters of the main subtropical gyres. Numerical simulations and satellite-based statistical estimates indicate that the magnitude of the eddy-driven nutrient flux could be sufficient to balance geochemical estimates of new production, which far exceed that which can be sustained by traditional mechanisms of nutrient supply. Relatively few direct observations of this process are available, owing to the spatial and temporal intermittency of the events that drive it. Available data demonstrate that isopycnal displacements associated with certain types of eddies can transport nutrients into the euphotic zone, resulting in the accumulation of chlorophyll in the overlying waters. However, the nature of the biological response and its impact on coupled biogeochemical cycles and export has yet to be elucidated. Furthermore, the relationship between eddy-induced upwelling and diapycnal mixing in and below the mixed layer remains obscure; the strength of this interaction determines the degree to which the eddy-driven effects are irreversible and thereby effect a net biogeochemical flux.In this project, a team of oceanographic researchers will document phytoplankton physiological response, changes in community structure, export and the biogeochemical ramifications of eddy-induced upwelling and mixing in the Sargasso Sea. Target features will be identified prior to field deployment via remote sensing. High-resolution surveys will be undertaken with an undulating towed instrument package that includes a Fast Repetition Rate Fluorometer. This suite of instruments will facilitate simultaneous assessment of photosynthetic parameters and the species assemblage of phytoplankton and zooplankton. These measurements will be accompanied by discrete water sampling of biogeochemical properties in sets of stations along cross sections of the chosen features. Export will be measured at selected locations within the mesoscale structure. Rates of mixing between the surface mixed layer and waters at the base of the euphotic zone will be inferred from the Helium flux gauge and measured directly with a sulfur hexafluoride tracer release. Taken together, these observations will be sufficient to test the hypothesis that eddy-induced upwelling increases photosynthetic rates, changes community structure and increases export from the euphotic zone, thereby playing an important role in biogeochemical cycling of the subtropical oceans.The research will be carried out in a collaborative effort among ten principal investigators from the Woods Hole Oceanographic Institution, the Bermuda Biological Station for Research, Rutgers University, University of California, Santa Barbara, and the University of Miami. The work plan consists of two years of field observations followed by a final year of synthesis.