Collaborative research: US GEOTRACES PMT: Measuring the d13C-DIC distribution and estimating organic matter export rates

海洋中二氧化碳气体(CO2)的浓度在一定程度上取决于海洋中的光合作用速率，因为二氧化碳被表层海洋中的微型植物(浮游植物)消耗。光合作用反应可以写成CO2-H2O光能-CH2O(糖)O2。在光合作用过程中，浮游生物优先消耗由12C原子组成的二氧化碳分子，而由13C原子组成的二氧化碳分子消耗较少。测量溶解在海水中的13CO2与12CO2的比率为估计光合作用速率提供了一种手段。在发生光合作用的表层(光层)下，细菌通过一种称为呼吸的过程(光合作用反应的相反过程)将下沉的浮游生物物质用作食物和能源。呼吸作用会在海洋的更深层产生二氧化碳。我们的研究目标是沿着一条从阿拉斯加苏厄德出发，向南到达塔希提岛的邮轮路径，测量从太平洋表面到海底海水中13CO2和12CO2的浓度。我们将使用这些测量来了解光合作用、呼吸作用和海洋中的混合如何控制13CO2和12CO2的分布。我们研究的更广泛的影响是确定光合作用、呼吸作用和海洋中的混合如何影响二氧化碳从大气到海洋的转移速率。二氧化碳的转移率很重要，因为它会影响大气中二氧化碳的浓度，以及海洋中不断增加的酸度。其他更广泛的影响包括将这项研究的结果纳入研究人员的课堂。华盛顿大学的一名本科生将作为该项目的一部分得到支持和培训。我们研究的具体目标是测量北太平洋GEOTRACES PMT邮轮(AK，Seward到Tahiti)期间溶解无机碳(DIC)的13C/12C的深度分布。我们打算收集和测量约850个海水样品中的d13C-DIC。PMT部分将跨越从塔希提岛和夏威夷附近的少营养环流到赤道和亚北冰洋生产力较高的HNLC区域等广泛的生物生产制度。生产力的预期经向变化应提供机会，以确定有机质(OM)输出和随后的深度退化对沿PMT剖面的上层海洋d13C-IC、微量元素(TES)和营养物质分布的影响。我们打算确定生产力和露头水团附近的经向变化如何影响d13C、PO4、NO3和生物活性TES(如镉)在整个温跃层和深海中沿PMT巡航轨迹的分布。提高我们对现代海洋中控制d13C、TES和营养物质分布的过程的理解，将提高我们使用沉积记录中的D13C和TES测量作为过去海洋环流和碳循环变化的示踪剂的能力。从更广泛的影响角度来看，我们的地址研究解决了GEOTRACES计划的两个基本目标。首先，确定选定微量元素和同位素的全球海洋分布，并评估这些物种的源、汇和内部循环，以更全面地描述调节其分布的物理、化学和生物过程。第二，了解控制用于替代海洋过去环境的地球化学物种浓度的过程，这将使古海洋学社区受益。

The concentration of carbon dioxide gas (CO2) in the ocean depends in part on the rate of photosynthesis in the ocean because CO2 is consumed by microscopic plants in surface ocean (phytoplankton). The photosynthesis reaction can be written as CO2 + H2O + light energy - CH2O (sugar) + O2. During photosynthesis, the plankton preferentially consume CO2 molecules comprised of 12C atoms and less so CO2 molecules comprised of 13C atoms. Measuring the ratio of 13CO2 to 12CO2 dissolved in seawater provides a means to estimate the photosynthesis rate. Below the surface layer where photosynthesis occurs (the photic layer), bacteria use sinking plankton material for food and energy via a process called respiration (which is the reverse of the photosynthesis reaction). Respiration produces CO2 in the deeper layers of the ocean. The goal of our research is to measure the concentration of 13CO2 and 12CO2 in seawater from the surface to the bottom of the Pacific Ocean along a cruise path that starts in Seward, Alaska and goes southward to Tahiti. We will use these measurements to understand how photosynthesis, respiration and mixing in the ocean control the distributions of 13CO2 and 12CO2. The broader impact of our research is to determine how photosynthesis, respiration and mixing in the ocean affect the transfer rate of CO2 from the atmosphere to the ocean. This CO2 transfer rate is important because it affects the concentration of CO2, a greenhouse gas, in the atmosphere and the increasing acidity of the ocean. Other broader impacts include incorporating results from this study into classes taught by the researcher. One undergraduate student from the University of Washington would be supported and trained as part of this project.The specific goal of our research is to measure the depth distribution of the 13C/12C of the dissolved inorganic carbon (DIC) during the GEOTRACES PMT cruise (Seward, AK to Tahiti) in the N. Pacific Ocean. We intend to collect and measure d13C-DIC on ~850 seawater samples. The PMT section will cross a wide range of biological productive regimes from the oligotrophic gyres near Tahiti and Hawaii to the more productive HNLC regions in the equatorial and subarctic oceans. The expected meridional variations in productivity should provide the opportunity to determine the impact of organic matter (OM) export and subsequent degradation at depth on upper ocean distribution of d13C-IC, trace elements (TEs), and nutrients along the PMT section. We intend to determine how the meridional variations in productivity and proximity to outcropping water masses affect the distributions of d13C, PO4, NO3 and bioactive TEs (like Cadmium) throughout the thermocline and deep sea along the PMT cruise track. Improving our understanding of the processes that control d13C, TEs and nutrient distributions in the modern ocean will improve our ability to use d13C and TEs measurements in the sedimentary record as tracers of past changes in the ocean circulation and carbon cycling. From a broader impact perspective, our address research addresses two basic goals of the GEOTRACES program. First, to determine global ocean distributions of selected trace elements and isotopes and evaluate the sources, sinks, and internal cycling of these species to characterize more completely the physical, chemical and biological processes regulating their distributions. Second, to understand the processes that control the concentrations of geochemical species used for proxies of the ocean's past environment which will benefit the paleoceanography community.