Investigation of the Rate of Shelf-Basin Interaction in the Western Arctic Using Radium Isotopes: SBI Phase II

大部分被陆地包围的北冰洋接收来自太平洋和大西洋以及流经周围大陆的河流的输入。这些流入是中部盆地盐、热、养分、沉积物和生物的重要来源。除了大西洋的一部分贡献外，这些输入必须跨越大陆架，在那里它们受到底栖生物、水柱和空气-冰-海洋相互作用的显著改变。由于跨陆架运输，陆架与中央盆地之间存在着显著的生物地球化学交换。然而，我们目前缺乏量化这些交流的信息。为了解决这一不足，本项目建议作为北极西部大陆架-盆地相互作用（SBI）第二阶段计划的一部分，应用同位素水团示踪技术来评估北极西部大陆架和北冰洋内部盆地之间的交换途径和速率。拟议的技术使用了水柱中两种天然存在的放射性同位素228Ra和226Ra的测量浓度。由于228Ra的半衰期为5.77年，仅来自陆架沉积物，因此它提供了陆架水存在的明确证据。因此，它在陆架和盆地水域的相对浓度可以提供陆架-盆地水运输的定量信息。该技术较为成熟，已在其他地区的陆架盆地交换调查中得到应用。在SBI第一阶段项目中进行的一个试点研究项目的结果已经证明了这种示踪技术在北冰洋西部的实用性。在拟议的研究中，将在近岸和海上油田的背景下分析从研究区域的横断面上收集的示踪剂数据，并进行建模研究，重点是了解跨大陆架运输。重点将放在中尺度涡旋在这种输送中的作用。在适当的情况下，寿命较短的224Ra（半衰期为3.64天）将在海上进行测量，以补充数据集。只要有可能，还将从其他平台收集镭示踪剂数据，例如由其他SBI调查人员提供的系泊阵列。

The largely landlocked Arctic Ocean receives input from the Pacific and Atlantic Ocean and from rivers draining the surrounding continents. These inflows are important sources of salt, heat, nutrients, sediment and organisms for the central basin. With the exception of a portion of the Atlantic Ocean contribution, these inputs must cross continental shelves where they are modified significantly by benthic, water column, and air-ice-ocean interactions. As a consequence of the cross-shelf transports, there are significant biogeochemical exchanges between the shelves and the central basin. However, we currently lack the information to quantify these exchanges. In order to address this lack, this project proposes as part of the western Arctic Shelf-Basin Interaction (SBI) Phase II program to apply an isotopic water mass tracer technique to assess the pathways and rates of exchange between the western Arctic shelves and the interior Arctic Ocean basin. The proposed technique uses the measured concentrations in the water column of the two naturally occurring radioisotopes 228Ra and 226Ra. Because 228Ra, which has a half life of 5.77 years, is derived solely from shelf sediments, it provides unambiguous evidence of the presence of shelf water. Its relative concentration in shelf and basin waters can therefore provide quantitative information on shelf-basin water transports. This technique is mature and has been used in shelf-basin exchange investigations in other regions. Results of a pilot research project carried out during the SBI Phase I program have demonstrated utility of this tracer technique in the western Arctic Ocean. For the proposed research, tracer data collected from vessels along transects through the study region will be analyzed within the context of nearshore and offshore field and modeling studies that focus on understanding cross-shelf transport. An emphasis will be placed on the role of mesoscale eddies in this transport. Where appropriate, the shorter-lived 224Ra with its 3.64-day half life will be measured at sea to supplement the dataset. Radium tracer data will also be collected whenever possible from other platforms such as moored arrays provided by other SBI investigators.