Collaborative Research: The Influence of the Mendeleev Ridge and the Chukchi Borderland on the Large-scale Circulation of the Arctic Ocean

最重要的北冰洋地下运输系统是沿大陆斜坡和主要的跨北极山脊组织起来的气旋（这里是逆时针）边界流，它将来自大西洋（通过弗拉姆海峡和巴伦支海）和太平洋（通过白令海峡）的水、示踪剂和污染物分布到北极深盆地周围和内部。在绕北极的路径上，部分地形引导的洋流从大陆边缘转向，通常沿着地形山脊。边界洋流遇到的最复杂的障碍是门捷列夫脊/楚科奇边界，位于太平洋北极入口以北。这一地区是南部源自太平洋的水和西部由边界流携带的大西洋水的交汇处。曲折的水深测量为地形导向的水流提供了许多路径，而存在的稀疏数据的空间变异性清楚地表明了该地区的复杂性。这些数据还显示了显著的年际变化，与过去十年整个北极地区的主要变化一致，它们进一步表明该地区将大量的水转移到深盆地，表明该地区对陆架-盆地交换、深盆地通风以及环北极和跨北极环流的重要性（对世界海洋环流有反馈影响）。然而，由于缺乏足够集中的观察，这一领域的途径和交流在质量和数量上仍然不清楚。本研究将于2002年8 / 9月在楚科奇边境地区和门捷列夫海岭南端进行高空间分辨率的水文和示踪调查，以短期系泊流和CTD测量为支持。目标是：-划定携带大西洋水经过门捷列夫海岭和楚科奇边境的边界流的路径；-确定门捷列夫海脊和楚科奇边界附近的边界流和冰架对北冰洋深处的输入；-了解和量化太平洋水域流经该地区的路径和变化；-描述边界流的水平和垂直结构，并估计其输送；并通过将过去十年的空间稀疏数据与新的详细天气测量相结合，量化该地区最近的时间变化。在一次为期35天的破冰船考察中，将测量12个区域的温度、盐度、溶解氧、营养物质、氟氯化碳、钡和18-O，这些区域穿过边界流和太平洋输入，在地形连接点和假设的水流改道区域之前和之后。这套示踪套件将能够确定边界流和太平洋起源水的路径，并量化大西洋和太平洋的不同影响，以及来自冰融化和不同河流的淡水输入。此外，将部署三个系泊，在巡航期间跨越边界水流。电流计和系泊电导率和温度传感器将量化边界电流的垂直和水平范围，其结构和可变性，并将产生对传输的估计和对边界电流携带或越过边界电流的漩涡的描述。为了全面了解该系统，整个数据集将与过去十年的水文、示踪和系泊时间序列数据一起进行综合分析。由于信号通过该区域的传输时间为2-4年，旧数据为新的高空间分辨率数据提供了时间背景，而新数据将为理解旧调查的变动性提供必要的空间框架。这项工作将大大增加对该地区在北极环流中的作用的了解，包括确定途径、量化交换和评估时间变化。它的时间定在2002年，将填补加拿大盆地水文调查的空白，此时北极有史以来最剧烈的变化正在通过该地区传播。该项目将为潜在的SEARCH和北极-亚北极海洋通量项目提供必要的背景和机制信息，并为楚科奇海和波弗特海的SBI第二阶段实地项目提供必要的远场信息。此外，这些结果将对验证和改进北极的高分辨率计算机和概念模型至关重要，并将为物理机制问题提供见解，例如边界流的驱动机制和等效正压流与陡峭和尖锐地形的相互作用。

The most important subsurface Arctic Ocean transport system, a cyclonic (here anticlockwise) boundary current, organized along the continental slopes and major trans-Arctic ridges, distributes waters, tracers and contaminants from the Atlantic (via Fram Strait and the Barents Sea) and the Pacific (via Bering Strait) around and into the deep Arctic basins. On its circum-Arctic pathway, parts of the topographically steered current are diverted away from the continental margin, generally along topographic ridges. The most complex obstacle the boundary current encounters is the Mendeleev Ridge/Chukchi Borderland complex, north of the Pacific entrance to the Arctic. This region is the cross- roads for Pacific-origin waters from the south and Atlantic waters carried from the west with the boundary current. The tortuous bathymetry offers many routes for a topographically steered current, and the spatial variability of the sparse data that exist clearly indicates the complexity of the region. These data also show significant interannual variability, in line with the major changes seen in the last decade throughout the Arctic, and they further suggest that the region diverts significant amounts of water into the deep basins, indicating this region's importance to shelf-basin exchange, deep basin ventilation, and circum- and trans-Arctic circulation (with feedback implications to the World Ocean circulation). Yet, the pathways and exchanges in this area are still unclear, both qualitatively and quantitatively, due to the lack of sufficiently concentrated observations. This research will conduct a high spatial resolution hydrographic and tracer survey, supported by short-term moored current and CTD measurements, in the region of the Chukchi Borderland and the southern end of the Mendeleev Ridge during August/September 2002.The objectives are to:- delineate the pathways of the boundary current carrying the Atlantic water past the Mendeleev Ridge and through the Chukchi Borderland;- ascertain the input from the boundary current and the shelves to the deep Arctic Ocean in the vicinity of the Mendeleev Ridge and the Chukchi Borderland;- understand and quantify the pathways and transformations of the Pacific waters through this region;- describe the horizontal and vertical structure of the boundary current, and estimate its transport; and- quantify recent temporal changes in this region by combining the spatially sparse data extending through most of the past decade with new detailed synoptic measurements.On a 35-day expedition on an ice-breaking research vessel, measurements will be made of temperature, salinity, dissolved oxygen, nutrients, CFCs, Ba, and 18-O on 12 sections that cross both the boundary flow and the Pacific inputs to the region before and after topographic junctions and hypothesized regions of flow diversion. This tracer suite will enable identification of the pathways of the boundary current and the Pacific-origin waters, and quantification of the different Atlantic and Pacific influences, as well as freshwater input from ice melt and different rivers. In addition, three moorings will be deployed, spanning the boundary current for the duration of the cruise. Current meters and moored conductivity and temperature sensors will quantify the vertical and horizontal extent of the boundary current, its structure and variability, and will yield an estimate of the transport and a description of eddies carried with or across the boundary current. To give a comprehensive picture of the system, the entire data set will be analyzed collectively and in tandem with hydrographic, tracer, and moored time series data from the last decade. Since the transit time of signals through this region is 2-4 years, the older data provide a temporal background for the new high spatial resolution data, whilst the newer data will supply an essential spatialframework for understanding the variability of the older surveys.The work will yield a substantially increased understanding of the role of this region in the Arctic circulation, including a determination of pathways, a quantification of exchanges, and an assessment of temporal change. Its timing in 2002 will fill a pending hiatus in hydrographic surveys in the Canadian Basin at a time when the most dramatic changes ever observed in the Arctic are propagating through this region. The project will provide necessary background and mechanistic information to the potential SEARCH and Arctic-Subarctic Ocean Flux programs, and essential far-field information to the SBI Phase II field program in the Chukchi and Beaufort seas. In addition, the results will be pivotal to validating and improving high resolution computer and conceptual models of the Arctic, and will offer insights to physical mechanistic problems, such as the driving mechanism of the boundary current and the interaction of an equivalent barotropic current with steep and sharp topography.