Coastal Zone Control of Interacting C-N-P Cycles Under Global Change

全球海岸带的面积约为海洋表面积的7%，其体积约为海洋表层体积（3 × 10公里）的9%。尽管其面积相对较小，但高达20%的海洋生物总产量发生在那里，至少80%到达海洋的陆源物质沉积在那里，海洋中30%至50%的碳酸盐和80%的有机碳积累发生在沿海地区。此外，由于生物地球化学动力学和碳（C）、氮（N）和磷（P）循环的改变，海岸带环境正受到严重影响，其影响程度远远超过更大面积的公海。碳、氮和磷是六种主要生命必需元素中的三种（其他三种是硫、氧和氢）。海岸带受其邻近的陆地、海洋、沉积物和大气环境地球化学变化的强烈影响。由于气候变化和人类对环境的强迫，这一海洋区域最容易受到人为物质通量以及水质、有机生产力和生物多样性变化的影响。直到最近，人们才注意到全球范围内的海岸带及其在全球碳-氮-磷地球化学循环中的作用，而碳-氮-磷地球化学循环对陆地和海洋中的生命都很重要。在气候变化和人类活动的影响下，海岸带C-N-P耦合地球化学循环的最近过去、现在和近期行为。我们研究的时间尺度是几十年到几个世纪，包括过去300年不断增加的人类扰动和大约一个世纪的未来，根据目前对扰动幅度的预测。为了实现我们的目标，我们采用了一种建模方法，我们开发的NSF支持下，分析全球系统的四个域的环境变化：土地，海洋，沉积物和大气。我们处理以下研究问题：（a）作为有机生产力和一般碳循环的驱动因素，从陆地和公海到沿海地区的营养盐N和P通量的变化作用;（B）沿岸带有机碳代谢的变化状态，以及沿岸沃茨释放或吸收大气中的二氧化碳，受沿海地区有机碳和无机碳（CaCO 3）的生产和储存控制;（c）大气CO_2浓度上升对海岸带有机和无机C-N-P循环的影响;以及（d）海洋温盐环流和沿海海洋环流可能发生变化的影响（上升流和上涌）对海岸边缘C-N-P循环的影响及其与陆地、大气、沉积物、我们希望我们的研究结果能显示，在何种程度上的耦合C-N-P循环和增加营养输入的变化，在陆地域已负责从最近的过去到现在的海岸带的生态地球化学动力学。我们还希望我们的研究结果表明，陆地环境变化的预测趋势，温盐环流和海岸上升流的幅度变化，以及全球气候可能会使海岸带成为一个更活跃和数量上重要的网站，在它与陆地，大气，沉积物和开放的海洋子域之间的物质转移在未来。这一初步结论对沿海地区相对于依赖于它的人口的生物地球化学状态具有重要意义。

AbstractThe area of the global coastal zone, approximated by the continental shelves, is about 7% of the surface area of the ocean, and its volume is about 9% of the volume of the surface ocean layer (3 x 10 km). Despite its relatively small size, up to 20% of total oceanic biological production occurs there, at least 80% of the mass of terrigenous materials reaching the ocean is deposited there, and 30 to 50% of total carbonate and 80% of total organic carbon accumulation in the ocean occur in the coastal zone. In addition, coastal zone environments are being heavily impacted, disproportionately more than the much larger area of the open ocean, by modifications of the biogeochemical dynamics and cycles of carbon (C), nitrogen (N), and phosphorus (P), three of six of the major life-essential elements (the other three being sulfur, oxygen, and hydrogen). The coastal zone is strongly affected by the environmental biogeochemical changes occurring in its neighboring domains of land, ocean, sediments, and atmosphere. Because of both climatic change and human-induced forcings on the environment, it is this region of the ocean that is most susceptible to anthropogenic fluxes of materials and changes in water quality, organic productivity, and biodiversity. Until very recently, little attention has been paid to the coastal zone on a global scale and its role in the global C-N-P biogeochemical cycles that are important to life on land and in the oceans.In this proposal we address a fundamental scientific problem that is also of substantial concern to the human society: the recent past, present, and near future behavior of the coupled C-N-P biogeochemical cycles in the coastal marine zone that are influenced by climatic change and human activities. The time scale of our research is decades to centuries, including the past 300 years of increasing human perturbations and about a century of the future, as based on current projections of the magnitudes of the perturbations. To accomplish our goals, we employ a modeling methodology developed by us under previous NSF support to analyze environmental change in the global system of four do-mains: land, ocean, sediments, and atmosphere. We deal with the following research issues: (a) the changing roles of nutrient N and P fluxes to the coastal zone from land and from the open ocean as drivers of organic productivity and the carbon cycle in general; (b) the changing state of organic carbon metabolism in the coastal zone, and the release or uptake of atmospheric carbon dioxide by coastal waters, as controlled by the production and storage of organic and inorganic carbon (CaCO3 ) in the coastal zone; (c) the effect of rising atmospheric CO2 concentrations on the organic and inor-ganic C-N-P cycles in the coastal zone, and (d) the effects of possible changes in the thermohaline circulation of the ocean and in coastal oceanic circulation (upwelling and onwelling) on the C-N-P cycles in the coastal margin and their linkages to the land, atmosphere, sediments, and open ocean.We expect our results to show to what extent the coupling between the C-N-P cycles and increased nutrient inputs from changes in the land domain have been responsible for the biogeochemical dynamics of the coastal zone from the recent past to the present. We also expect our results to show that the projected trends of environmental change on land, changes in the magnitude of thermohaline circulation and coastal upwelling, and global climate are likely to make the coastal zone a more active and quantitatively important site in the transfer of materials between it and the domains of land, atmosphere, and sediments and sub-domain of open ocean in the future. This tentative conclusion has important implications to the biogeochemical state of the coastal zone relative to the human population that depends on it.