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）的浓度部分取决于海洋中光合作用的速率，因为二氧化碳被海洋表面的微小植物（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，较少消耗由13C原子组成的二氧化碳分子。测量溶解在海水中的13CO2和12CO2的比例提供了一种估算光合作用速率的方法。在发生光合作用的表层（光层）以下，细菌通过呼吸作用（与光合作用反应相反）将下沉的浮游生物物质作为食物和能量。呼吸作用在海洋的深层产生二氧化碳。我们研究的目标是沿着一条从阿拉斯加苏厄德开始向南到塔希提岛的巡航路线，测量从太平洋表面到底部的海水中13CO2和12CO2的浓度。我们将利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。这种二氧化碳传输速率很重要，因为它影响大气中二氧化碳（一种温室气体）的浓度和海洋酸度的增加。其他更广泛的影响包括将这项研究的结果纳入研究人员所教授的课程。作为该项目的一部分，华盛顿大学的一名本科生将得到支持和培训。我们研究的具体目标是测量在北太平洋的GEOTRACES PMT巡航（苏沃德，AK到塔希提岛）期间溶解无机碳（DIC）的13C/12C的深度分布。本文拟对850个海水样品进行d13C-DIC的采集和测定。PMT部分将跨越广泛的生物生产体制，从塔希提岛和夏威夷附近的少营养环流到赤道和亚北极海洋中更富有生产力的HNLC区域。预期的经向生产力变化应提供机会，以确定有机物质（OM）输出和随后的深度降解对PMT剖面上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的经向变化和与露头水团的接近程度如何影响沿着PMT巡航轨道在整个温跃层和深海中的d13C， PO4， NO3和生物活性TEs（如镉）的分布。提高我们对控制现代海洋中d13C、TEs和养分分布的过程的理解，将提高我们利用沉积记录中的d13C和TEs测量作为海洋环流和碳循环过去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，并评估这些物种的来源、汇和内部循环，以更完整地表征调节其分布的物理、化学和生物过程。其次，了解控制地球化学物种浓度的过程，这些物种被用作海洋过去环境的代用物，这将有利于古海洋学界。

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.