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

合作研究：陆架边缘养分输入机制支持查尔斯顿凸起下游冬季浮游植物持续大量繁殖

• 批准号: 1032276
• 负责人: Harvey Seim
• 金额: $ 68.84万
• 依托单位: University of North Carolina at Chapel Hill
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-10-01 至 2015-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1032276&HistoricalAwards=false
• 关键词: Collaborative; Research; Mechanisms; nutrient; input

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.

学术价值：在多年卫星叶绿素图像中，冬季观察到长湾外南大西洋湾 (SAB) 大陆架上浮游植物持续大量繁殖。大陆架的这一部分位于“查尔斯顿隆起”（北纬 32.5-33.5°之间）以北，湾流经常在此处强烈转向近海。由于这种近海偏转，该地区的陆架养分输入不会因与墨西哥湾流锋面涡旋相关的上升流而增强，而上升流是 SAB 陆架其他部分养分输入的主要机制（Lee 等，1991）。然而之前的现场观察表明，从冬季到早春，养分不断从上坡到长湾外陆架输入。该项目将研究外陆架到上斜坡区域的物理-生物耦合的基本方面。 PI 将测试以下假设： 1） 长湾外陆架冬季开花的持续存在是由于养分输入和混合的反复发生，从而长期维持养分充足的条件； 2) 涉及多种物理机制，包括沿着上坡/陆架折断部分的内潮汐增强的混合能量； 3）相对较高的营养、间歇性的湍流环境有利于较大的水华形成浮游植物的生长。后者可能对更高的营养水平产生重要影响，包括冬季到早春在长湾沿岸陆架边缘产卵的鱼类的早期生活史策略。该项目将结合几种成熟的观测技术来解决以下问题：1。上坡硝酸盐在货架上运输的频率和强度是多少？ 2. 在冬季遇到的水文和强迫条件下，长湾附近从上斜坡到外大陆架区域的养分输送机制是什么？ 3. 外陆架水文学和相关冬季水华特征的 3-D 结构是什么？这些特征如何通过多个养分输入/混合事件演变？ 4. 与冬季开花相关的硝酸盐利用率和初级生产力是多少？ 5. 冬季气候是否始终有利于以较大硅藻形式为主的水华组合？近乎连续的跨大陆架和上坡观测将通过两个自主滑翔机获得，通过一组系泊仪器（包括陆架断裂处的系泊剖面系统）对外架和坡度进行时间序列测量，并使用拖曳式波动包进行重复的跨陆架和沿陆架船舶测量。船舶站工作将包括使用微流体/成像系统对初级生产进行测量，并对浮游植物组合的关键功能特征（细胞形式、丰度、大小和生物体积分布）进行船上分析。结合起来，这些系统将提供物理、营养和生物场的一定水平的空间和时间分辨率，这是早期基于站的实地研究无法实现的，并为更好地理解陆架反复输入养分的物理机制，以及冬季的养分、混合和循环机制如何构建浮游植物群落奠定了基础。更广泛的影响：该项目将提供对陆架/斜坡的更深入的了解 交流过程以及这些过程如何影响陆架生态系统，产生有助于在该区域实施基于生态系统的管理的信息。海洋科学以及电气和计算工程专业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，重点关注区域背景下的物理-生物耦合，以及 2）科学与工程的界面，通过所采用的观测技术来说明。沿海博物学家将参与该实地计划的海鸟调查部分，该部分将扩大有关冬季远洋海鸟的现有信息，并确定它们与南大西洋中部湾陆架和斜坡海洋学特征的关联。