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

北极正在发生重大变化。北极地表气温的上升速度比地球上大多数地方都要快。覆盖北冰洋中部的多年冰原已经从60年代的3.1米减薄到90年代的1.8米。在此期间，海冰的长期面积减少了14%。尽管这些变化可能代表了自然循环的一个组成部分，但这种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，观测到的海冰范围波动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变化对北极海洋生态系统和区域气候的影响（尤其是对北极海冰因气候变化而可能出现的净减少的影响），需要我们大幅度提高对淡水和海冰、海冰与气候、海冰与生物地球化学通量等各组成部分之间联系的理解。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至关重要。冰架本身受到各种不同的物理和环境过程的强烈影响。一些大陆架上的水受到北极外海水输入的影响，例如，阿拉斯加大陆架受到通过白令海峡运输的北太平洋海水的影响，而其他大陆架主要受到河流输入的影响，例如麦肯齐大陆架受到麦肯齐河季节性流入的极大影响。在不同的冰架之间，海冰覆盖也会有很大的差异，单个冰架有不同数量的陆地冰覆盖、铅多冰带和stamukhi带。个别冰架上海冰覆盖的特性反过来又决定了冰架上的海气热湿交换，并限制了生物生产力的强烈脉冲年循环。冰盖特征的差异也影响到碳向远洋和底栖食物网的输出，以及最终被封存的北极深盆地。鉴于冰架的重要性，对这些浅海沿岸地区（占北极海盆的30%）的观测数据的需求尤为强烈，因为这些地区海冰的范围、厚度和持续时间的变化最为明显，而且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项目，并在特定的北极大陆架上收集了重要的物理、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（SBI）项目和麦肯齐大陆架上的加拿大北极大陆架交换研究（CASES）的成功，代表着在观测数据的质量和数量方面向前迈出了重要的一步，在这些观测数据的基础上，可以构建北极大陆架系统现在和未来行为的模型。该项目将基于SBI和case项目的观测数据集，构建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。将对这两种物理、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和非普遍特性。两个特定的北极冰架的物理、化学和生物耦合模型及其在泛北极计算机模型中的嵌套将使我们更好地了解这些冰架的当前功能，以及它们在更大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.