Collaborative Research: Grazing and Iron Controls of Diatom Blooms in the Arabian Sea

合作研究：阿拉伯海硅藻华的放牧和铁控制

• 批准号: 0826626
• 负责人: Michael Landry
• 金额: $ 51.67万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-01-01 至 2013-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0826626&HistoricalAwards=false
• 关键词: Collaborative; Research; Grazing; Iron; Controls

The Arabian Sea is important in global C and N budgets because of its high rates of annual primary production, its extensive zone of oxygen depletion and denitrification, and its expected strong response to global warming via ocean-atmosphere feedback to monsoon winds and upwelling intensity, especially the Oman Upwelling, driven by the SW Monsoon. The paradox of the Arabian Sea is that it produces a very weak and delayed phytoplankton response compared to other physically dynamic upwelling systems. Thick blooms of large diatoms are uniquely not evident in the Arabian Sea despite apparently abundant nutrients, seed stocks and favorable hydrographic conditions. The subdued response shifts carbon export offshore of the coastal upwelling area and delays major flux events until the latter stages of the SW Monsoon, with important implications for the western boundary of the oxygen minimum zone. This work will test the hypotheses that grazing interactions, iron limitation, or both, control diatoms and, more generally, phytoplankton biomass, production and the delayed flux characteristics of the Arabian Sea. Grazer control was a major, but as yet untested, conclusion of the US JGOFS program. In 2007, one of the investigators found that a large region of the central and southern Arabian Sea was Fe-limited during the SW Monsoon, consistent with recent modeling studies. Iron limitation may exacerbate grazing regulation, and integration of Fe and grazing experiments is a central part of the work plan. A cruise to the Oman upwelling region during the SW Monsoon in 2010 will include iron and nutrient biogeochemistry, plankton community structure and dynamics, taxon-specific estimates of phytoplankton growth and production, grazing contributions of micro- and mesozooplankton, with a focus on large copepods (Calanoides carinatus, Subeucalanus crassus, Paraeucalanus sewelli), whose life histories, abundance and size are consistent with a top-down regulatory role. The approach will involve assessment of net community rates of changes following a Lagrangian drift array and contemporaneous in situ studies of phytoplankton growth, production, micro- and mesozooplankton grazing. Shipboard experiments will address the response of phytoplankton to added Fe and Si and reproductive responses of dominant large grazers to food supply, their ability to modulate the grazing impacts of micro-herbivores and their direct and indirect effects on lower trophic levels. The sampling program will resolve the abundances, depth distribution and lipid contents of major grazers during a critical time of year (August-September) when there is little previous data and as the animals are preparing to leave surface waters for their seasonal diapause migration to mesopelagic depths. Grazing control in the Arabian Sea, if confirmed, will be a unique example of top-down regulation of a significant open-ocean ecosystem with important consequences for carbon and nitrogen cycling. Furthermore, understanding the potential limiting effects of Fe availability will allow us to better anticipate how the ocean ecology and biogeochemistry will respond to changes in climate and monsoon intensity that affect dust fluxes from the surrounding arid landmasses.The most recent IPCC report cites changes in monsoon intensity as a likely impact of the present trend in planetary warming. This project seeks to understand ecological, biological and geochemical constraints on production, carbon cycling and export in the upwelling system so that the effects of climate changes can be better anticipated and modeled. This project will also contribute to the oceanographic infrastructure of India and Oman, both critical US partners in the Indian Ocean, as well as continue ongoing activities in public outreach, K-12 education, broadening undergraduate educational opportunities, for example through the MATE program, and graduate training of diversity students in marine science.

阿拉伯海在全球C和N预算中具有重要意义，因为它的年初级生产量高，缺氧和反硝化区域广泛，并且通过海洋-大气对季风和上升流强度的反馈，特别是由西南季风驱动的阿曼上升流，对全球变暖做出了强烈的反应。阿拉伯海的矛盾之处在于，与其他物理动态上升流系统相比，它产生的浮游植物反应非常微弱和延迟。尽管阿拉伯海显然有丰富的营养、种子储备和有利的水文条件，但大型硅藻的密集繁殖却不明显。这种微弱的响应将碳输出转移到沿海上升流区近海，并将主要通量事件推迟到西南季风后期，这对氧最小带的西部边界具有重要意义。这项工作将测试放牧相互作用、铁限制或两者兼而有之的假设，控制硅藻，更一般地说，控制浮游植物生物量、产量和阿拉伯海的延迟通量特征。放牧控制是美国JGOFS计划的一个主要但尚未经过测试的结论。2007年，其中一名研究人员发现，在西南季风期间，阿拉伯海中部和南部的大片地区是铁有限的，这与最近的模型研究一致。铁的限制可能会加剧放牧调节，铁与放牧实验的整合是工作计划的核心部分。在2010年西南季风期间，对阿曼上升流地区的巡航将包括铁和营养生物地球化学，浮游生物群落结构和动态，浮游植物生长和生产的分类群特定估计，微型和中型浮游动物的放牧贡献，重点关注大型桡足类（Calanoides carinatus, subbeucalanus crassus, Paraeucalanus sewelli），其生活史，丰度和大小与自上而下的调节作用一致。该方法将包括评估拉格朗日漂移阵列后的净群落变化率，以及同时对浮游植物生长、生产、微型和中型浮游动物放牧进行现场研究。船载实验将探讨浮游植物对添加铁和硅的响应、优势大型食草动物对食物供应的生殖响应、它们调节微食草动物放牧影响的能力以及它们对低营养水平的直接和间接影响。采样计划将在一年中的关键时期（8 - 9月）解决主要食草动物的丰度，深度分布和脂质含量，因为之前的数据很少，并且动物正准备离开表层水进行季节性滞育迁移到中深海。阿拉伯海的放牧控制如果得到证实，将成为一个独特的例子，对一个重要的开放海洋生态系统进行自上而下的监管，对碳和氮循环产生重要影响。此外，了解铁可用性的潜在限制效应将使我们能够更好地预测海洋生态和生物地球化学将如何响应气候和季风强度的变化，这些变化会影响周围干旱陆地的沙尘通量。IPCC最近的报告指出，季风强度的变化可能是当前全球变暖趋势的一个影响。该项目旨在了解上升流系统中对生产、碳循环和输出的生态、生物和地球化学限制，以便更好地预测和模拟气候变化的影响。该项目还将为印度和阿曼（这两个国家都是美国在印度洋的重要合作伙伴）的海洋基础设施做出贡献，并继续开展公共宣传、K-12教育、扩大本科教育机会（例如通过MATE项目）以及海洋科学专业多元化学生的研究生培训等活动。