Collaborative Research: Flux and Transformation of Organic Carbon across the Eroding Coastline of Northern Alaska

知识价值：陆地北极生态系统储存了世界上25.33%的土壤有机碳（OC），大量长期封存的OC通过阿拉斯加北部约2000公里海岸线的侵蚀而迅速释放出来。这种被侵蚀的OC可用于生物地球化学循环，并对海洋生态系统以及向大气排放二氧化碳和甲烷做出了巨大但鲜为人知的贡献。虽然已经对侵蚀海岸线上的OC通量进行了粗略估计，并且已知其受地冰稳定性的影响，但对陆地OC在穿过陆地/海洋界面时的转化知之甚少。该团队假设，一旦OC通过物理分散、淋溶和氧化从储存中释放出来，波浪冲刷的前海岸区域对OC的转化至关重要。有机碳的生物有效性如何受到有机质的年龄、大小和组成的控制，以及这些因素与影响过去土壤发育的地貌环境之间的关系，是量化有机碳转化的关键。这些有机碳中有多少成为海洋生态系统的生物可利用性，并在穿过这个狭窄的过渡带时释放到大气中，有多少在近岸沉积物中长期封存，对于了解北冰洋的碳预算和评估与气候和海冰变化相关的反馈至关重要。海岸带过程最值得关注的反馈是释放的OC有可能：改变生物地球化学循环，增加二氧化碳和甲烷排放，促进气候变暖，加速海冰退缩，增加裸露海岸的取水和波浪能；并最终进一步增加侵蚀速率和OC通量。因此，本研究有四个组成部分，旨在：(1)与地貌环境相关的土壤有机碳和地面冰的性质和丰度特征；(2)估算整个海岸的总有机碳通量，并建立经验模型来评估夏季海冰减少导致海岸侵蚀加剧的脆弱性；(3)通过实地研究和实验室实验，确定与陆地/海洋界面上各种溶解形式和颗粒形式相关的有机碳的生物地球化学转化和生物利用度；(4)通过国际合作将成果整合到泛北极范围。这项研究将包括在整个阿拉斯加波弗特海岸的50个地点进行广泛的采样，以精确估计侵蚀和OC通量。在主要海岸线类型的三个主要地点进行密集采样，以评估侵蚀OC的转变。将增加三个二级地点，以扩大监测范围至其他海岸线类型，并让当地社区参与评估海岸变化。更广泛的影响：该项目将为了解阿拉斯加北部沿海变化的生物地球化学后果提供关键信息，并可通过国际合作用于估计泛北极沿海OC和沉积物输入。研究结果可用于提高我们在处理碳循环和北极气候系统的相关模型中的预测能力。特别相关的将是在一系列土壤环境中对长期封存的有机碳的生物有效性进行表征，对评估气候变暖下阿拉斯加北部地形稳定性至关重要的地面冰的量化；以及对海岸侵蚀对向北冰洋输入碳和营养物质的作用的进一步了解。该项目将在巴罗、努克苏特和卡克托维克与当地村庄代表、石油工业和美国鱼类和野生动物管理局合作，将研究、专业人员和学生培训以及社区参与结合起来，传播研究结果，并向当地居民通报对海洋生态系统及其生存活动至关重要的沿海过程。

Intellectual Merit: Terrestrial arctic ecosystems store 25.33% of the world's soil organic carbon (OC), and large amounts of the long-sequestered OC is rapidly released by erosion along the ~2000 km coastline of northern Alaska. This eroded OC becomes available for biogeochemical cycling and makes a substantial, but poorly known, contribution to marine ecosystems and to CO2 and methane emissions to the atmosphere. While crude estimates of the flux of OC across the eroding coastline have been developed and are known to be affected by ground-ice stability, little is known about the transformation of terrestrial OC as it crosses the land/ocean interface. This team hypothesizes that the wave-washed foreshore zone is critical to the transformation of OC once it is released from storage through physical dispersion, leaching, and oxidation. How the bioavailability of OC is controlled by the age, size and composition of the organic matter, and how these factors relate to geomorphic environments that have influenced past soil development is critical to quantifying OC transformation. How much of this OC becomes bioavailable to marine ecosystems and is released to the atmosphere as it crosses this narrow, transient zone, and how much returns to long-term sequestration in nearshore sediments is critical to understanding carbon budgets of the Arctic Ocean and to assessing feedbacks associated with climate and sea-ice changes. The feedback of greatest concern to coastal processes is the potential for released OC to: alter biogeochemical cycling, increase CO2 and methane emissions, contribute to climate warming, accelerate sea ice retreat, increase fetch and wave energy to exposed coasts; and ultimately further increase erosion rates and OC flux. Accordingly, this research has four components designed to: (1) characterize the nature and abundance of soil OC and ground ice in relation to geomorphic environments, (2) estimate the total OC flux along the entire coast and develop empirical models to assess the vulnerability of the coast to increased erosion resulting from decreasing summer sea-ice, (3) determine the biogeochemical transformation and bioavailability of OC associated with various dissolved and particulate forms across the land/sea interface through field study and laboratory experimentation; and (4) integrate results to the pan-arctic scale through international collaboration. The study will involve extensive sampling at 50 sites along the entire Alaskan Beaufort Sea coast to develop precise estimates of erosion and OC flux. Intensive sampling at three primary sites along dominant coastline types will be conducted to evaluate the transformation of the eroded OC. Three secondary sites will be added to broaden the monitoring to other coastline types and to involve local communities in assessing coastal changes. Broader Impacts: This project will provide information critical to understanding the biogeochemical consequences of coastal changes in northern Alaska and can be used to estimate pan-arctic coastal OC and sediment inputs through international collaboration. Results can be used to increase our predictive capabilities in related models that address the carbon cycle and the arctic climate system. Of particular relevance will be the characterization of the bioavailability of long-sequestered OC across a range of soil environments, quantification of ground ice that is essential to assessing terrain stability in northern Alaska under a warming climate; and an improved understanding of the role of coastal erosion to the input of carbon and nutrients to the Arctic Ocean. This project will integrate research, professional and student training, and community involvement at Barrow, Nuiqsut, and Kaktovik, in partnership with local village representatives, the oil industry, and the U.S. Fish and Wildlife Service, to communicate study results and inform local residents about the coastal processes that are import to marine ecosystems and their subsistence activities.