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

合作研究：GLOBEC-01：乔治滩潮汐锋混合和交换：对浮游植物、浮游动物和幼鱼生产的控制

• 批准号: 0228943
• 负责人: David Townsend
• 金额: $ 15万
• 依托单位: University of Maine
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-09-01 至 2006-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0228943&HistoricalAwards=false
• 关键词: Collaborative; Research; GLOBEC; 01; Tidal

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.

乔治浅滩拥有丰富的渔业资源，因为：(1) 浅滩的大部分区域足够浅，浮游植物的光照限制通常并不重要； (2)富含无机营养物质的深水可混入岸边； （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（TMF）是乔治滩生产力的核心，通过在北部注入养分和在南翼保留幼虫的过程。 这两个区域通过沿着前端的循环路径连接，其中营养物质导致浮游植物和浮游动物生长，在波峰周围形成一个高产的甜甜圈形区域。 有人认为，该途径的生产力是北缘养分注入的结果，并且容易受到该地区养分供应的气候影响。 该项目的总体目标是了解 TMF 内维持乔治银行生物生产力的流程以及目标物种鳕鱼和黑线鳕的成功。 这需要了解 TMF 内的混合和循环如何提供新的营养物质、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 TMF 中近底部的拉格朗日循环和混合。 结果表明，前端的垂直混合和通过 TMF 底部的岸流是动态连接的。 本研究正在根据这些测量结果检查 TMF 的 3 维动力学。 模型将有助于评估跨等深线环流和沿等深线环流的强度如何设定与鳕鱼和黑线鳕幼虫发育相适应的时间和空间尺度。 该项目由数据分析和建模活动组成。 首先，染料分散数据和简单的剪切分散模型被用来理解跨岸流动和垂直混合之间的联系。 其次，有限体积沿海海洋模型（FVCOM）将用于计算进入 TMF 的营养物通量的时间和空间结构，对比北侧和南侧的输入。 耦合的 FVCOM-NPZ（营养物-浮游植物-浮游动物）模型用于检验以下假设： (i) 北部的营养物注入在堤顶周围平流流动，导致浮游植物和浮游动物产量大量增加。 (ii) 羽流丰富了南侧幼虫夹带的区域。 如果上述陈述属实，那么缅因湾东北航道源水的营养成分含量可能会改变羽流的产量，而这些变化将影响鳕鱼和黑线鳕幼体的摄食环境。 最后，结合测量的 3D 流动和湍流场的模型被用来检查幼虫滞留的空间模式，并定义幼虫在此过程中经历的环境转变类型。