Collaborative Research: Mechanisms of nutrient input at the shelf margin supporting persistent winter phytoplankton blooms downstream of the Charleston Bump

智力优势：在多年卫星叶绿素图像中，观察到冬季长湾外南大西洋湾（SAB）大陆架沿着持续的浮游植物水华。这一部分大陆架位于“查尔斯顿隆起”（北纬32.5-33.5°之间）以北，墨西哥湾流经常在此处强烈转向离岸。由于这种离岸偏转，这不是一个与湾流锋面涡相关的上升流会增强营养物输入到陆架的区域，这是SAB陆架其他部分营养物输入的主要机制（Lee等人，1991年）。然而，先前的原位观测表明，从冬季到早春，从上斜坡到长湾外大陆架有营养物质的重复输入。本项目将调查外大陆架到上斜坡区域物理-生物耦合的一个基本方面。PI将检验以下假设：1）长湾外陆架冬季水华的持续性是由于营养物输入和混合的重复发生，从而在较长时间内维持营养物充足的条件; 2）涉及几种物理机制，包括沿上斜坡/陆架折带沿着这一部分的内潮增强的混合能量; 3）相对高营养盐、间歇性扰动的环境有利于较大的水华形成浮游植物。后者可能对更高的营养水平产生重要影响，包括冬季至早春沿着长湾陆架边缘产卵的鱼类的早期生活史策略。什么是频率和幅度上的货架运输的硝酸盐从上斜坡？2.在冬季遇到的水文和强迫条件范围内，从上斜坡到外大陆架区的营养输送机制是什么？3.什么是三维结构的外大陆架水文和相关的冬季水华的功能，以及如何通过多个营养输入/混合事件这些演变？4.与冬季水华相关的硝酸盐利用率和初级生产率是多少？5.冬季制度一贯有利于水华组合占主导地位的较大的硅藻形式？将利用两个自主滑翔机进行近乎连续的跨大陆架和上斜坡观测，利用一套系泊仪器（包括在大陆架断裂处的系泊剖面测量系统）进行外大陆架和斜坡的时间序列测量，并利用拖曳式波浪形成套设备进行跨大陆架和沿大陆架的船舶反复勘测。船站工作将包括利用微流控/成像系统测量初级生产量和船上分析浮游植物组合的关键功能特性（细胞形式、丰度、大小和生物量分布）。这些系统结合起来，将提供物理、营养和生物场的一定程度的空间和时间分辨率，这是以前以台站为基础的实地研究所无法达到的，并为更好地了解经常性营养物输入大陆架的物理机制以及冬季营养物、混合和循环状况如何构成浮游植物群落奠定基础。该项目将使人们更深入地了解大陆架/斜坡交换过程以及这些过程如何影响大陆架生态系统，从而产生有助于在该区域实施基于生态系统的管理的信息。海洋科学和电气与计算机工程的研究生将在这项研究中发挥重要作用。6-12年级的教育部分将建立在与COSEE SE计划活动的先前互动的基础上，并将强调：1）海洋学固有的跨学科性质，侧重于区域背景下的物理-生物耦合，以及2）科学和工程的接口，通过采用的观测技术说明。沿海博物学家将通过实地方案的海鸟调查组成部分参与，这将增加关于冬季远洋海鸟的现有信息，并确定它们与南大西洋中部海湾陆架和斜坡海洋学特征的关系。

Intellectual Merit: Sustained phytoplankton blooms along the outer South Atlantic Bight (SAB) continental shelf off Long Bay are observed in winter in multi-year satellite chlorophyll imagery. This section of the shelf lies north of the "Charleston Bump" (between 32.5-33.5°N), where the Gulf Stream is often strongly deflected offshore. Due to this offshore deflection, this is not an area where nutrient input to the shelf would be enhanced by upwelling associated with Gulf Stream frontal eddies, a major mechanism of nutrient input in other parts of the SAB shelf (Lee et al., 1991). Yet prior in situ observations suggest that there is recurring input of nutrients from the upper slope to the outer shelf off Long Bay from winter to early spring. This project will investigate a fundamental aspect of physical-biological coupling in the outer shelf to upper slope region. The PIs will test the hypotheses that: 1) the persistence of winter blooms on the outer shelf off Long Bay results from repeated episodes of nutrient input and mixing which maintains nutrient-sufficient conditions for extended periods; 2) several physical mechanisms are involved, including enhanced mixing energy from the internal tide along this section of the upper slope/shelf break; 3) the relatively high nutrient, intermittently turbulent environment will favor larger bloom-forming phytoplankton. The latter could have important implications for higher trophic levels, including early life history strategies of fish that spawn along the shelf margin off Long Bay in winter to early spring.This project will combine several maturing observational technologies to address the following:1. What is the frequency and magnitude on on-shelf transport of nitrate from the upper slope? 2. What are the mechanisms of nutrient delivery from the upper slope to the outer continental shelf zone that are operating off Long Bay under the range of hydrographic and forcing conditions encountered in winter? 3. What is the 3-D structure of outer shelf hydrography and associated winter bloom features and how do these evolve through multiple nutrient input/mixing events? 4. What are the rates of nitrate utilization and primary production associated with the winter blooms? 5. Does the winter regime consistently favor a bloom assemblage dominated by larger diatom forms? Near-continuous cross-shelf and upper slope observations will be obtained with two autonomous gliders, time-series measurements on the outer shelf and slope from a set of moored instruments (including a moored profiling system at the shelf break), and repeated cross- and along-shelf ship surveys using a towed, undulating package. Ship station work will include measurements of primary production and on-board analyses of key functional characteristics of the phytoplankton assemblage (cell forms, abundance, size and bio-volume distributions) using a microfluidics/imaging system. In combination, these systems will provide a level of spatial and temporal resolution of physical, nutrient and biological fields that could not be achieved in earlier, station-based field studies and the basis for improved understanding of physical mechanisms of recurring nutrient input to the shelf, and how the nutrient, mixing, and circulation regime in winter structures the phytoplankton community.Broader Impacts: This project will provide a deeper understanding of shelf/slope exchange processes and how these influence shelf ecosystems, generating information that will contribute to implementation of ecosystem-based management in the region. Graduate students in Marine Sciences and in Electrical and Computing Engineering will have important roles in the study. A grade 6-12 education component will build on prior interactions with the COSEE SE program activities and will emphasize: 1) the inherently interdisciplinary nature of oceanography, focusing on physical-biological coupling in a regional context, and 2) the interface of science and engineering, illustrated by observational technologies employed. Coastal naturalists will be engaged through a seabird survey component of the field program that will augment existing information on pelagic seabirds in winter and define their association with oceanographic features on the central South Atlantic Bight shelf and slope.