Organic carbon cycling along high-latitude continental margins and implications of climate change

碳循环涉及大气、陆地和海洋，并影响全球气候。有机碳(OC)是与生物或死亡物质有关的部分；由植物从二氧化碳中产生，经微生物和动物转化，通过呼吸、降解等作用重新矿化成二氧化碳。大陆边缘(近岸地带和陆架)是有机碳循环的重要场所。它们同时接受陆地和海洋的有机碳，其产生和破坏使它们与大气进行动态的二氧化碳交换。大陆边缘也接受来自河流和海岸侵蚀的沉积物，这促进了有机碳的埋藏(封存)。世界上约75%的人口生活在边缘地带，其生态系统服务每年价值25万亿美元。*高纬度地区正在经历快速的气候变化，包括海冰消失、河流径流变化和永久冻土融化。因此，有机碳循环将受到来源变化和更温暖、更新鲜、更无冰、可能更具生产力的沿海水域有机碳加工变化的影响。食物网将受到这些变化的影响，二氧化碳交换也将受到影响。最大的未知数之一是陆源碳将在多大程度上促进变化。几千年来，这种碳一直被锁在地下土壤和永久冻土中，但在永久冻土融化时释放出来，在边缘地区可以被重新矿化为二氧化碳，特别是当高度可降解的海洋有机碳发挥启动作用时。由于有非常大量的古老陆源有机碳，其退化代表着对气候变化的一个重要的潜在反馈。*这项拟议的探索计划的总体目标是提高我们对决定高纬度大陆边缘陆源有机碳命运的过程的理解。其中一些过程发生在水柱中，另一些发生在表层沉积物中。由于边缘在空间和时间上是可变的，我们将重点放在“热点”和“热点时刻”上，沿着i)动态的、以河流为主的开阔陆架地区进行实地研究，我们知道那里正在释放古老的陆源OC；ii)受保护的沿海海湾，被野生动物和因纽特人广泛使用，但几乎没有人就其OC循环进行研究。与至少9个南方HQP和类似数量的北方人合作，我将研究水柱中有机碳的分布；比较冬季和夏季，并使用沉积物捕捉器收集年度时间序列。我们将检查沉积物中的有机碳，以告知我们最近的变化。限制有机碳损失率的盒子模型将立即帮助对与旧陆源有机碳相关的气候反馈提供更好的数字和时间表。最终，这些结果将有助于改进陆地-海洋界面在物理模型中的表示方式，制定可靠的未来预测，并更好地设计跟踪气候变化影响的监测计划。

The carbon cycle involves the atmosphere, land and ocean and influences global climate. Organic carbon (OC) is the portion associated with living or dead matter; produced by plants from CO2, transformed by microbes and animals, and remineralized back to CO2 by respiration, degradation etc. Continental margins (nearshore zones and shelves) are important sites of OC cycling. They receive OC from both the land and the ocean and its production and destruction makes them sites of dynamic CO2 exchange with the atmosphere. Continental margins also receive sediment from rivers and coastal erosion, which promotes burial (sequestration) of OC. About 75% of the world's population lives along margins and their ecosystem services are worth $25 trillion annually.***High-latitude areas are experiencing rapid climate change, including loss of sea ice, altered river runoff and thawing permafrost. The OC cycle will thus be affected by changes in sources and altered processing of OC in warmer, fresher, more ice-free, and possibly more productive coastal waters. Food webs will be impacted by these changes, as will CO2 exchange. One of the largest unknowns is how old terrigenous carbon will contribute to change. This carbon has been locked up in subsurface soils and permafrost for thousands of years, but is released when permafrost thaws and can be remineralized to CO2 in margin areas, particularly when highly-degradable marine OC exerts a priming effect'. Because there is a very large amount of old terrigenous OC, its degradation represents a significant potential feedback to climate change.***The overall objective of this proposed Discovery program is to improve our understanding of the processes that determine the fate of terrigenous OC along high-latitude continental margins. Some of these processes occur in the water column and some in surface sediments. Because the margin is variable in space and time, we will focus on “hot spots” and “hot moments”, conducting field studies along i) dynamic, river-dominated open shelf areas, where we know old terrigenous OC is being released; and ii) protected coastal embayments, used extensively by wildlife and Inuit, but virtually unstudied in terms of their OC cycling. Working with at least nine southern HQP and a similar number of Northerners, I will study the distributions of OC in the water column; compare winter and summer, and collect annual time series using sediment traps. We will examine the OC in sediments to inform us about recent change. Box models that constrain the rates of OC losses will immediately help put better numbers and timelines on the climate feedback associated with old terrigenous OC. Ultimately, the results will help improve how the land-ocean interface is represented in physical models, develop robust future projections, and better design monitoring plans for tracking impacts of climate change.**