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

ABSTRACTOCE-0241310 / OCE-0241399 / OCE-0241023 / OCE-0241340 / OCE-0241011组成海洋中尺度的洋流、锋面和涡流，有时被称为“海洋内部天气”，是海洋环流的高能量和普遍特征。 这些现象的动力学后果包括化学和生物环境的扰动，这可能会极大地影响海洋中的生物地球化学循环。调节这种反应的过程非常复杂，挑战我们理解物理、生物和化学过程如何在功能上相关。最近的证据表明，中尺度涡流是主要副热带环流贫营养水域中的重要营养物输送机制。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新产量的地球化学估计，这远远超过了传统养分供应机制所能维持的产量。由于驱动该过程的事件在空间和时间上具有间歇性，因此对该过程的直接观察相对较少。现有数据表明，与某些类型的涡流相关的等密度位移可以将营养物质输送到透光区，导致上覆水域中叶绿素的积累。然而，生物反应的性质及其对生物地球化学循环和输出的影响尚未阐明。此外，涡流引起的上升流与混合层内外的二重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流驱动效应不可逆的程度，从而影响净生物地球化学通量。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、输出以及马尾藻海涡流引起的上升和混合的生物地球化学后果。在现场部署之前将通过遥感确定目标特征。 将使用包括快速重复率荧光计的波动拖曳仪器包进行高分辨率测量。这套仪器将有助于同时评估光合参数以及浮游植物和浮游动物的物种组合。这些测量将伴随着沿所选地物横截面的多组站中生物地球化学特性的离散水采样。输出将在中尺度结构内的选定位置进行测量。表面混合层与透光区底部水体之间的混合速率将从氦通量计推断出来，并直接使用六氟化硫示踪剂释放进行测量。总而言之，这些观测结果将足以检验涡流引起的上升流增加光合作用速率、改变群落结构并增加真光带出口的假设，从而在亚热带海洋的生物地球化学循环中发挥重要作用。这项研究将由来自伍兹霍尔海洋研究所、百慕大生物研究站、罗格斯大学、加利福尼亚大学圣塔芭芭拉分校和百慕大大学的十名主要研究人员合作进行。迈阿密。该工作计划包括两年的实地观察和最后一年的综合。

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.