JGOFS: Bacterial Cycling Of Dissolved And Particulate Organic Carbon In Oligotrophic And Eutrophic Production Regimes Of The Arabian Sea

9312695阿扎姆这是一项联合研究建议(F.Azam和H.Ducklow，共同-PI)，作为美国联合全球海洋研究中心阿拉伯海过程研究的组成部分，对细菌在调节和调节阿拉伯海碳和氮的生物地球化学通量方面的重要性进行定量研究。我们提出了一个岩心测量计划，以量化碳和氮池和通量，以及机制研究，以了解细菌介导的过程对由于阿拉伯海季风逆转而定期发生的许多初级生产的戏剧性变化的反应。JGOFS的核心测量将包括细菌丰度和生物量、细菌产量(通过3 H胸腺嘧啶核苷和3 H亮氨酸掺入法)、DOC、POC和Pn。我们的研究旨在进一步解决美国JGOFS确定的关于微生物异养过程的两个关键问题：1)在贫营养和富营养时期发生的群落结构如何对碳储存和输出通量产生不同影响？2)下沉颗粒的分解是否在亚缺氧区减缓并导致通过这一层的垂直通量增加？我们假设，高营养和低营养生产力的连续出现在低营养时期创造了一个独特的强大的微生物循环，代价是在富营养时期积累的缓慢降解的DOM。我们预测，微生物环的强大优势使寡养期呈现净异质性，这对碳氧化和交换的空间和时间模式有影响。“储存的”DOC也可能支持混合层以下的高细菌碳需求(高于颗粒通量所能支持的水平)。我们想要测试的第二个吸水作用是，定植细菌的水解胞外酶能迅速溶解表层下沉的颗粒，但亚氧层的酶促溶解作用大大减弱，导致POC的深度消散速度慢得多。

9312695 Azam This is a joint research proposal (F. Azam and H. Ducklow, co-PIs) to perform quantitative studies on the significance of bacteria in mediating and regulating biogeochemical fluxes of carbon and nitrogen in the Arabian Sea, as a component of the US JGOFS Arabian Sea Process Study. We propose a program of core measurements to quantify carbon and nitrogen pools and fluxes as well as mechanistic studies to understand the response of the bacteria-mediated processes to dramatic changes in many primary production that occur regularly due to monsoonal reversals in the Arabian Sea. The JGOFS core measurements will include bacterial abundance and biomass, bacterial production (by both 3H thymidine and 3H leucine incorporation methods), DOC, POC and PN. Our research is design, further, to address two key questions concerning microbial heterotrophic processes identified by US JGOFS: 1) How do the community structures which occur during the oligotrophic vs eutrophic periods differentially impact carbon storage and export fluxes? 2) Does the decomposition of sinking particles slow down in the suboxic zone and result in enhanced vertical flux though this layer? We hypothesize that sequential occurrence of highly eutrophic and oligotrophic productivity regimes creates a uniquely robust microbial loop during the oligotrophic period at the expense of slow-to-degrade DOM which accumulates during the eutrophic period. We predict that the strong dominance of the microbial loop renders the oligotrophic period net- heterotrphic and this has implications for spatial and temporal patterns of carbon oxidation and exchange. The 'stored' DOC may also support high bacterial carbon demand (higher than would be supported by particle flux) below the mixed layer following shoaling of the pycnocline. A second hyothesis we wish to test is that sinking particles in the surface waters are rapidly solubilized by hydrolytic ectoenzymes of colonizing bacteria but t he enzymatic solubilization is greatly reduced in the suboxic layer resulting in much slower depth-dissipation of POC.