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: 0825767
• 负责人: JOAQUIM GOES
• 金额: --
• 依托单位: Bigelow Laboratory for Ocean Sciences
• 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 2011-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0825767&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.

阿拉伯海在全球碳和氮预算中很重要，因为它的年初级生产率很高，其广泛的氧气消耗和反硝化区域，以及通过海洋大气对季风和上升流强度的反馈对全球变暖的强烈反应。特别是由西南季风驱动的阿曼上升流。阿拉伯海的悖论在于，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且延迟。尽管阿拉伯海的营养物质、种子储备和有利的水文条件明显丰富，但大型硅藻的密集繁殖在阿拉伯海并不明显。减弱的响应将碳输出转移到沿海上升流区域，并将主要通量事件推迟到西南季风后期，这对最低含氧区的西部边界具有重要影响。这项工作将检验以下假设：放牧相互作用、铁限制或两者兼而有之，控制硅藻，更广泛地说，控制阿拉伯海浮游植物的生物量、产量和延迟通量特征。格雷泽控制是美国 JGOFS 计划的一个主要但尚未经过检验的结论。 2007年，一名研究人员发现，西南季风期间，阿拉伯海中部和南部的大片区域铁含量有限，这与最近的模型研究一致。铁的限制可能会加剧放牧管制，铁和放牧实验的结合是工作计划的核心部分。 2010年西南季风期间前往阿曼上升流区域的航行将包括铁和营养物生物地球化学、浮游生物群落结构和动态、浮游植物生长和生产的分类单元特定估计、微型和中型浮游生物的放牧贡献，重点是大型桡足类（Calanoides carinatus、Subeucalanus crassus、Paraeucalanus sewelli），其生活史，丰度和规模与自上而下的监管作用相一致。该方法将涉及拉格朗日漂流阵列后群落净变化率的评估以及浮游植物生长、生产、微型和中型浮游生物放牧的同期现场研究。船上实验将研究浮游植物对添加的铁和硅的反应以及主要大型食草动物对食物供应的生殖反应，它们调节微型食草动物的放牧影响的能力以及它们对较低营养水平的直接和间接影响。采样计划将解决一年中关键时期（8月至9月）主要食草动物的丰度、深度分布和脂质含量，当时几乎没有先前的数据，而且动物正准备离开地表水域进行季节性滞育迁徙到中层。深处。如果阿拉伯海的放牧控制得到证实，这将成为对重要的开放海洋生态系统进行自上而下监管的独特例子，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应对气候和季风强度的变化，这些变化会影响周围干旱陆地的尘埃通量。最新的IPCC报告引用了季风的变化强度作为当前地球变暖趋势的可能影响。该项目旨在了解上升流系统中生产、碳循环和出口的生态、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美国在印度洋的重要合作伙伴的海洋学基础设施做出贡献，并继续开展公共宣传、K-12 教育、扩大本科生教育机会等活动，例如通过 MATE 计划，以及海洋科学多样性学生的研究生培训。