Collaborative Research: A Modeling Comparison of the Alaskan and Mackenzie Shelves

北极正在经历重大变化。北极地表气温的上升速度比地球上大多数其他地方都要快。覆盖北冰洋中部的多年冰层已从1960年S时代的3.1m减至1990年S时代的1.8m。在此期间，海冰的长期面积范围减少了14%。尽管这些变化可能是自然周期的一个组成部分，但这一趋势也可能是北极因人为气候变暖而“融化”的先兆。无论是人为的还是自然的，观测到的海冰面积的波动都极大地影响了独特而脆弱的北极海洋生态。评估目前海冰覆盖和水文地理的变化对北极海洋生态系统和区域气候的影响(尤其是北极海冰因气候变化而可能净减少的影响)，需要我们对淡水和海冰、海冰和气候以及海冰和生物地球化学通量之间的联系有实质性的了解。广阔的北极大陆架(占全球大陆架面积的25%)在任何北极变化情景中都是至关重要的。货架本身受到截然不同的物理和环境过程的强烈影响。一些大陆架的水域受北极外输入海水的影响，例如阿拉斯加大陆架受北太平洋水域通过白令海峡运输的影响，而另一些大陆架主要受河流输入的影响，如麦肯齐大陆架受麦肯齐河季节性流入的影响很大。不同的大陆架之间的海冰覆盖也可能有很大的不同，每个大陆架的陆上冰盖、铅波尼亚和Stamukhi区域的数量都不同。个别大陆架上的海冰覆盖的特点反过来又决定了大陆架上的海气热量和水分交换，并限制了生物生产力的强烈脉冲年度循环。冰盖性质的差异也影响到碳向远洋和海底食物网以及最终被固定的北极深海盆地的出口。鉴于大陆架的重要性，对于这些浅海沿海地区(北极盆地的30%)来说，对观测数据的需求尤其强烈，在这些地区，海冰的范围、厚度和持续时间的变化最为明显，北极海洋食物网最容易发生变化。近年来，已经启动了两个主要的观测计划，并在特定的北极大陆架上收集了大量的物理、地球化学和生物数据。阿拉斯加大陆架上的陆架-盆地相互作用项目和麦肯齐大陆架上的加拿大北极大陆架交换研究项目是在观测数据的质量和数量方面向前迈出的重要一步，可以在此基础上建立北冰洋大陆架系统目前和未来行为的模型。该项目将根据履行机构和CASES项目的观测数据集，建立阿拉斯加和麦肯齐大陆架生态系统及其与北极盆地相互作用的强大、耦合的物理和生物模型。将对这两个物理、化学和生物海洋学数据集进行彻底的分析和相互比较，以便更好地了解极地大陆架生态系统的普遍性和非普遍性。对两个具体的北极大陆架进行物理、化学和生物模型的耦合，并将它们嵌套在泛北极计算机模型中，将使我们能够更好地了解这些大陆架的当前功能，以及它们在更大的变化的北极环境中的未来行为。

The Arctic is now undergoing significant change. Arctic surface air temperatures are increasing at a faster rate than most anywhere else on Earth. The multi-year ice pack that covers the central Arctic Ocean has thinned from 3.1 m in the 1960's to 1.8 m in the 1990's. Over this time period, the long-term areal extent of sea ice has decreased by 14%. Although these changes could represent a component in a natural cycle, this trend could also be a harbinger of the "meltdown" of the Arctic in response to anthropogenic climate warming. Whether man-made or natural, the observed fluctuations in sea-ice extent dramatically affect the unique and fragile arctic marine ecology. Assessing the effects of present variability in sea-ice cover and hydrography on arctic marine ecosystems and regional climate (and a fortiori that of a potential net reduction of arctic sea ice in response to climate change) requires a substantial improvement in our understanding of the links between, among other components, freshwater and sea ice, sea ice and climate, and sea ice and biogeochemical fluxes.The extensive arctic shelves (25% of global shelf area) are of central importance in any arctic change scenario. The shelves themselves are strongly influenced by widely differing physical and environmental processes. The waters on some shelves are influenced by extra-Arctic import of ocean waters, for example, the Alaskan shelf is influenced by the North Pacific Ocean waters via transport through the Bering Strait, while other shelves are principally influenced by riverine input, such as the Mackenzie shelf which is greatly affected by the seasonal inflow of the Mackenzie River. The sea-ice cover can also vary greatly between shelves, with individual shelves having differing amounts of landfast ice cover, lead polynya, and stamukhi zones. The peculiarities of sea-ice cover over individual shelves, in turn, determines the air-sea exchange of heat and moisture over the shelf and constrains the strongly pulsed annual cycle of biological productivity. The differences in ice-cover character also affect the export of carbon to the pelagic and benthic food webs, and to the deep Arctic basins where it is ultimately sequestered.Given the importance of the shelves, the need for observational data has been particularly strong for these shallow, coastal regions (30% of the Arctic basin) where variability in the extent, thickness and duration of sea ice has been most pronounced and where Arctic marine food webs are most vulnerable to change. In recent years, two major observational programs have been launched and have garnished significant physical, geochemical, and biological data over specific Arctic shelves. The successful Shelf-Basin Interaction (SBI) project over the Alaskan Shelf and Canadian Arctic Shelf Exchange Study (CASES) over the Mackenzie shelf represents a major step forward in quality and quantity of observational data upon which a model of the present and future behavior of the Arctic shelf systems can be constructed. This project will construct a robust, coupled physical and biological model of the Alaskan and Mackenzie shelf ecosystems and their interaction with the Arctic basin, based on the observational data sets of the SBI and CASES programs. A thorough analysis and intercomparison of these two physical, chemical, and biological oceanographic data sets will be performed, allowing for an improved understanding of the universal and non-universal properties of polar shelf ecosystems. A coupled physical, chemical, and biological model of the two specific Arctic shelves and their nesting inside a pan-Arctic computer model will allow us to better understand the present function of these shelves, as well as their future behavior in the larger changing Arctic environment.