Ocean processes over the southern Weddell Sea shelf using seal tags

南极底水（AABW）是世界深海冷却和通风的重要水团。AABW的主要来源之一是源于威德尔海西南部大陆架上冬季海冰产生的冷而稠密的水。但是，对于控制源水最初进入大陆架和稠密水从大陆架输出的过程，仍然存在很大的不确定性。这种不确定性来自威德尔海南部存在的极具挑战性的海冰条件，特别是在冬季。对于任何基于船只的工作来说，冬季感兴趣的地区的条件都异常困难，而在相对不那么困难的夏季部署在海洋中的仪器，以及在冬季期间监测水的性质，很容易被经过的冰山疏浚。我们将使用最近成熟的技术来解决这个问题。我们建议在威德尔海豹（Leptonychotes weddellii）上附加电导率-温度-深度（CTD）标签，小型化的海洋仪器。这些标签上有一个卫星发射器，可以传送海豹潜水时收集的海洋数据，以及潜水位置。该标签使用标准的海洋双组分环氧树脂无害地粘在动物的皮毛上，并在大约11个月后的年度换毛期间再次脱落。英国南极调查局进行了一项试点研究，对四只海豹进行了标记，其中三只海豹提供了冬季数据集。虽然只有三个标签的覆盖范围令人印象深刻，强调证实了该技术的实用性，但感兴趣的区域面积接近500,000 km^2，一个全面的数据集需要更多的标记动物。我们将在2010/2011年的南夏末，在费尔奇纳-罗纳冰架北部的冰架断裂东端标记20只威德尔海豹。这些动物在冬季潜水所得的数据集将提供迄今为止最全面的南威德尔海大陆架海洋状况的图像。通过绘制海底附近水的温度图，我们将确定密集水离开陆架的位置，以及所涉及的过程：要么在重力作用下直接流下斜坡，要么在陆架边缘与陆架外的水混合，然后下降到斜坡上。我们还将能够确定水源从哪里流入大陆架。威德尔海豹是非常熟练的潜水员，它们长时间反复潜水，经常到达大陆架海底的深度。在南极的海豹中，威德尔海豹也栖息在最南端的水域，冬天当浮冰向北扩张时，它们就呆在浮冰中。这些特性使威德尔密封件非常适合所提出的研究。虽然主要是一个海洋学项目，威德尔海豹的运动和潜水行为引起了海豹生物学家的极大兴趣，他们希望了解南极洲不同地区的不同行为。这些变化在试验期间被标记的动物异常多样的行为中得到了有力的证明，并与之前在南极其他地区追踪到的物种进行了比较。在初步研究中追踪到的一些海豹所表现出的长距离运动对该物种来说是不典型的，至少在南极的其他地方，可能与当地的海洋条件有关。人们普遍认为，这里提出的多学科研究将为我们提供更好地预测分布、行为和最终人口状况如何受到海洋和气候条件变化的影响的工具。

Antarctic Bottom Water (AABW) is an important water mass in the cooling and ventilation of the World's deep ocean. One of the principal sources of AABW has its roots in the production of cold, dense water that results from wintertime sea-ice production over the continental shelf of the southwestern Weddell Sea. However, there remains great uncertainty about the processes controlling the initial import of the source waters onto the continental shelf, and the export of the dense waters from the shelf regime. The uncertainty results from the extremely challenging sea ice conditions existing in the southern Weddell Sea, especially during winter. Conditions in the area of interest during winter are exceptionally difficult for any ship-based work, and instruments deployed in the ocean during the rather less difficult summer months, and which are left to monitor the water properties over the Winter period, are vulnerable to dredging by passing icebergs. We will tackle the problem using a technology that has recently come of age. We propose to attach conductivity-temperature-deph (CTD) tags, miniaturised oceanographic instruments, to Weddell seals (Leptonychotes weddellii). The tags have a satellite transmitter that relays the oceanographic data collected during the seals' dives, together with the dive location. The tag is glued harmlessly to the animal's fur using standard marine two-component epoxy and comes off again during the annual moult about eleven months later. A pilot study undertaken by the British Antarctic Survey involved the tagging of four seals, three of which supplied over-winter datasets. Although the coverage was impressive from only three tags, emphatically confirming the practicality of the technique, the region of interest is nearly 500,000 km^2 in area and a comprehensive dataset requires substantially more tagged animals. We will tag 20 Weddell seals at the eastern end of the shelfbreak north of the Filchner-Ronne Ice Shelf during the late Austral summer of 2010/2011. The resulting dataset resulting from the animals' dives during the winter will give the most comprehensive picture to date of the ocean conditions over the southern Weddell Sea continental shelf. By mapping the temperature of the water near the sea floor we will determine the locations where dense waters leave the shelf, and the processes involved: either a direct flow down the slope under gravity, or initially mixing at the shelf edge with waters from off the shelf before descending down the slope. We will also be able to determine where the source waters come on to the shelf. Weddell seals are very accomplished divers, diving repeatedly for long periods and to depths regularly reaching the on-shelf seafloor. Among Antarctic seals, Weddell seals also inhabit the southernmost waters, and remain within the pack-ice in winter when the ice expands northward. These characteristics make Weddell seals ideally suited for the proposed study. Although primarily an oceanographic project, the movements and diving behaviour of Weddell seals is of great interest to seal biologists who wish to understand differing behaviours in different parts of Antarctica. These variations were ably demonstrated by the extraordinarily diverse behaviour of the animals tagged during the pilot, and by comparisons with previous tracking of this species in other parts of the Antarctic. The long-ranging movements displayed by some of the seals tracked during the pilot study are untypical for the species, at least at other Antarctic locations, and may be related to the local oceanographic conditions. It is widely recognised that multidisciplinary studies such as proposed here will provide us with the tools to better predict how the distribution, behaviour and ultimately population status may be affected by changing ocean and climate conditions.