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

北冰洋最重要的次表层运输系统是沿大陆斜坡和主要的跨北极海脊组织的气旋式(这里是逆时针)边界流，将水、示踪剂和污染物从大西洋(通过弗拉姆海峡和巴伦支海)和太平洋(通过白令海峡)分配到北极深处盆地。在其环绕北极的路径上，部分地形引导的洋流被分流离开大陆边缘，通常是沿着地形脊线。边界流遇到的最复杂的障碍是北冰洋太平洋入口处以北的门捷列夫海岭/楚科奇边界综合体。这一地区是南起太平洋水域和西来带边界流的大西洋水域的交汇处。曲折的水深测量为地形控制的洋流提供了许多路线，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。这些数据还显示出显著的年际变化，与过去十年整个北极出现的重大变化相一致，它们进一步表明，该区域将大量水转移到深水盆地，表明该区域对陆架盆地交换、深水盆地通风、环北极环流和跨北极环流的重要性(对世界海洋环流具有反馈影响)。然而，由于缺乏足够集中的观测，这一领域的路径和交流在质量和数量上仍然不清楚。这项研究将在2002年8月/9月期间在楚科奇边界区域和门捷列夫海脊南端进行高空间分辨率水文和示踪调查，并辅之以短期系泊海流和CTD测量。其目的是：-划定边界流携带大西洋水通过门捷列夫海脊和通过楚科奇边界区域的路径；-确定边界流和大陆架对门捷列夫海脊和楚科奇边界附近北冰洋深海的输入；-了解和量化太平洋水域通过该区域的路径和变化；-描述边界流的水平和垂直结构，并估计其输送；以及-通过将过去十年大部分时间的空间稀疏数据与新的详细天气测量相结合，量化该区域最近的时间变化。在一艘破冰考察船上进行的一次为期35天的考察中，将在12个断面上测量温度、盐度、溶解氧、营养物质、CFCs、BA和18-O，这些断面跨越边界流和太平洋输入到该区域的地形交汇点和假想的分流区域。这套示踪剂将能够识别边界流和源自太平洋的水域的路径，并量化大西洋和太平洋的不同影响，以及来自冰川融化和不同河流的淡水输入。此外，在邮轮航行期间，将部署三个跨越边界洋流的系泊设施。海流计和系泊的电导率和温度传感器将量化边界流的垂直和水平范围、其结构和可变性，并将产生对边界流所携带或穿过边界流的涡流的估计和描述。为了全面了解该系统，将对整个数据集进行集体分析，并结合过去十年的水文、示踪和系泊时间序列数据进行分析。由于信号通过该地区的时间为2-4年，较旧的数据为新的高空间分辨率数据提供了时间背景，而较新的数据将为理解较旧调查的可变性提供基本的空间框架。这项工作将大大增加对该地区在北极环流中的作用的理解，包括确定路径、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测量中的一个悬而未决的空白，而此时北极有史以来观察到的最戏剧性的变化正在该地区蔓延。该项目将为潜在的搜索和北极-次北冰洋流动方案提供必要的背景和机械信息，并为印度国家石油公司在楚科奇和波弗特海的第二阶段实地方案提供必要的远场信息。此外，这些结果将对验证和改进高分辨率计算机和北极概念模式至关重要，并将为物理机制问题提供见解，如边界流的驱动机制和等效正压流与陡峭地形的相互作用。

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.