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

这是一项联合研究计划（F. Azam和H. Ducklow, co- pi），作为美国JGOFS阿拉伯海过程研究的一个组成部分，对细菌在介导和调节阿拉伯海碳和氮的生物地球化学通量中的意义进行定量研究。我们提出了一个核心测量计划，以量化碳和氮库和通量，以及机制研究，以了解细菌介导的过程对许多初级生产的剧烈变化的响应，这些变化是由于阿拉伯海季风逆转而经常发生的。JGOFS核心测量将包括细菌丰度和生物量，细菌产量（通过3H胸腺嘧啶和3H亮氨酸掺入方法），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量和出口通量产生差异影响？2)下沉颗粒在缺氧区分解是否减慢，从而导致通过该层的垂直通量增强？我们假设，高富营养化和低富营养化生产力制度的顺序发生，在贫营养化期间以牺牲富营养化期间积累的缓慢降解的DOM为代价，创造了一个独特的强大的微生物循环。我们预测，微生物环的强大优势使贫营养期呈净异养状态，这对碳氧化和交换的时空格局具有重要意义。“储存”的DOC也可能支持高细菌碳需求（高于颗粒通量所支持的）。我们希望验证的第二个假设是，在地表水中下沉的颗粒被定植细菌的水解外酶迅速溶解，但酶的溶解作用在亚氧层中大大减少，导致POC的深度耗散慢得多。

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.