Collaborative Research: GLOBEC-01: Tidal Front Mixing and Exchange on Georges Bank: Controls on the Production of Phytoplankton, Zooplankton, and Larval Fishes

乔治浅滩支持丰富的渔业，因为：（1）大部分浅滩足够浅，浮游植物的光限制通常不重要;（2）富含无机营养物的深水沃茨可用于混合到岸边;（3）浅滩的顺时针循环可以保留重要鱼类的浮游阶段。 潮汐混合锋（NEM）通过在北部注入营养物和在南侧保留幼虫的过程，对乔治银行的生产力至关重要。 这两个区域由一条沿锋面沿着的环流路径连接，在这条路径中，营养物质导致浮游植物和浮游动物生长，从而在波峰周围形成一个高产量的甜甜圈形区域。 这表明，该途径的生产力是北方边缘养分注入的结果，并容易受到气候影响，在该地区的养分供应。 该项目的总体目标是了解TMF内维持乔治浅滩生物生产力以及目标物种鳕鱼和黑线鳕成功的过程。 这就需要了解混合和循环内的蚯蚓提供新的营养物质，支持初级生产，并保留幼虫。 GLOBEC染料示踪实验首次直接测量了近底拉格朗日环流和混合。 结果表明，在前面的垂直混合，并通过底部的堤岸流，动态连接。 本研究正在根据这些测量来检查TMF的三维动力学。 模型将有助于评估跨等深线和沿等深线环流的强度如何确定与鳕鱼和黑线鳕幼鱼发育相适应的时间和空间尺度。 该项目包括数据分析和建模活动的混合。 首先，染料分散数据和简单的剪切分散模型被用来了解两岸流动和垂直混合之间的联系。 第二，将使用有限体积沿海海洋模式（FVCOM）来计算进入海洋的营养盐通量的时空结构。 对比北方和南方侧翼输入。 一个耦合的FVCOM-NPZ（营养盐-浮游植物-浮游动物）模型正被用来检验以下假设：㈠北部的营养盐注入是在岸顶周围平流输送的，导致浮游植物和浮游动物产量增加的羽流。 (ii)羽流丰富了南侧幼虫夹带的区域。 如果上述陈述是正确的，那么在羽的生产可以改变源沃茨的营养成分在东北海峡的缅因州，这些变化将影响幼鳕鱼和黑线鳕的喂养环境。 最后，模型将测量的3-D流和湍流场被用来检查幼虫保留的空间模式，并定义在此过程中，幼虫经历的环境过渡的种类。

Georges Bank supports a rich fishery because: (1) large portions of the bank are shallow enough that light-limitation of phytoplankton is usually not important; (2) deep waters rich in inorganic nutrients are available for mixing onto the bank; and (3) the Bank's clockwise circulation can retain the planktonic stages of important fish species. The tidally mixed front (TMF) is central to the productivity of Georges Bank through the processes of nutrient injection in the north and retention of larvae on the south flank. These two regions are connected by a circulation pathway along the front in which nutrients lead to phytoplankton and zooplankton growth, creating a donut-shaped region of high production surrounding the crest. It is suggested that the productivity of this pathway is the result of northern edge nutrient injections and is susceptible to climatic influences on nutrient supply in that region. The overall objective of this project is to understand the processes within the TMF that sustain the biological productivity of Georges Bank and the success of the target species, cod and haddock. This requires understanding how mixing and circulation within the TMF supplies new nutrients, supports primary production, and retain larvae. GLOBEC dye tracer experiments have, for the first time, measured directly the near-bottom Lagrangian circulation and mixing in the TMF. Results show that vertical mixing in the front, and the on-bank flow through the base of the TMF, are dynamically connected. This study is examining the 3-dimensional dynamics of the TMF based on these measurements. Models will help assess how the strength of the across- and along-isobath circulation sets time and space scales compatible with the development of cod and haddock larvae. This project consists of a mix of data analysis and modeling activities. First, dye dispersion data and simple shear dispersion models are being used to understand the link between cross-bank flow and vertical mixing. Second, a finite-volume coastal ocean model (FVCOM) will be used to calculate the temporal and spatial structure of nutrient flux into the TMF, contrasting northern and southern flank inputs. A coupled FVCOM- NPZ (nutrient-phytoplankton-zooplankton) model are being used to test the following hypotheses: (i) Nutrient injections in the north are advected around the crest of the bank and lead to a plume of elevated phytoplankton and zooplankton production. (ii) The plume enriches the area of larval entrainment on the south flank. If the above statements are true, then production in the plume can be altered by the nutrient content of source waters in the Northeast Channel of the Gulf of Maine, and these changes will affect the feeding environment of larval cod and haddock. Finally, models incorporating the measured 3-D flow and turbulence fields are being used to examine spatial patterns of larval retention and define the kinds of environmental transitions that larvae experience during this process.