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）是与活的或死的物质有关的部分；由植物从二氧化碳中产生，由微生物和动物转化，并通过呼吸、降解等再矿化回二氧化碳。大陆边缘（近岸带和陆架）是有机碳循环的重要场所。它们从陆地和海洋中吸收有机碳，它的产生和破坏使它们成为与大气进行动态二氧化碳交换的场所。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）。世界上大约75%的人口生活在边缘地带，他们的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，包括海冰的减少、河流径流的改变和永久冻土的融化。因此，在更温暖、更新鲜、更无冰和可能更高产的沿海水域中，OC来源的变化和OC处理过程的改变将影响OC循环。食物网将受到这些变化的影响，二氧化碳交换也是如此。最大的未知数之一是，古老的陆源碳会对气候变化产生多大的影响。这种碳已经被锁在地下土壤和永久冻土中数千年了，但当永久冻土融化时，它就会被释放出来，并在边缘地区被再矿化成二氧化碳，特别是当高度可降解的海洋OC发挥“启动效应”时。由于存在大量的古陆源OC，其退化对气候变化具有重要的潜在反馈作用。这项发现计划的总体目标是提高我们对决定高纬度大陆边缘陆源OC命运的过程的理解。这些过程有些发生在水柱中，有些发生在地表沉积物中。由于边界在空间和时间上是可变的，我们将重点关注“热点”和“热点时刻”，沿着i)动态的，河流主导的开放陆架区域进行实地研究，我们知道旧的陆源OC正在释放；ii)受保护的海岸码头，野生动物和因纽特人广泛使用，但在OC循环方面几乎没有研究。我将与至少9个南方HQP和类似数量的北方HQP合作，研究水柱中OC的分布；比较冬季和夏季，并使用沉积物捕集器收集年度时间序列。我们将检查沉积物中的OC，以了解最近的变化。限制有机碳损失率的箱形模型将立即有助于为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善陆地-海洋界面在物理模型中的表现方式，制定可靠的未来预测，并更好地设计监测计划，以跟踪气候变化的影响。

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.