Circulation in the Freshwater Switchyard of the Arctic Ocean: University of Washington CTD Profile Data

The Freshwater Switchyard of the Arctic Ocean (FSAO) project is a program to study freshwater circulation (sea ice and upper ocean) in the "freshwater switchyard" between Alert (Ellesmere Island) and the North Pole, through a series of annual springtime hydrographic surveys. An aircraft based at Alert on northern Ellesmere Island carries out the oceanographic surveys northward across the shelf break in late spring. These surveys are intended to measure the eastward-flowing boundary current and determine water property changes that occur in the transition from the deep Arctic Ocean basin to the shallow continental shelf. Measurements were made to 500m in late April and May of 2003-2009 using a Seabird Sea-Bird Electronics (SBE) 19plus SeaCAT internally recording CTD instrument with an Sea-Bird Electronics (SBE) 43 dissolved oxygen sensor. Data include depth, pressure, temperature in situ, potential temperature, conductivity, salinity, density and, if available, dissolved oxygen. In recent years, we have begun offering dissolved oxygen profiles in a separate archive to allow a different processing pathway. The basic CTD archives are preferred for all purposes that do not require oxygen. Through 2007, the aircraft was a Bell 206 helicopter. In April-May 2007, the worst Arctic flying weather in many years was encountered, negatively impacting many investigations. At Alert, a very wide shore lead evaporating ice fog never relented long enough to allow the helicopter to safely reach the study areas, so no data is included for 2007. In 2008, we used a Twin Otter skiplane to obtain many stations, at a cost of not being able to reach precise station positions from previous years. The 2009 data used primary Sea-Bird Electronics (SBE)-19 plus CTD (s/n 4344) was an Sea-Bird Electronics (SBE)-43 Dissolved Oxygen Sensor (s/n 408). Beginning with Cast 8, backup Sea-Bird Electronics (SBE)-19 (s/n 2373) with Sea-Bird Electronics (SBE)-43 (s/n 1406) was substituted, and that station recorded an excellent profile of oxygen as well as temperature and conductivity. The backup CTD itself failed completely at the first station the following day, for reasons under investigation by the manufacturer. At that point it was felt the safest course was to complete the survey removing the Sea-Bird Electronics (SBE)-43 from the primary CTD, to optimize our chances of collecting good CTD data. The result is 18 stations of quality CTD profiles, but only one (Cast 8) with oxygen. In 2010, Airborne Expendable CTD Probes were dropped into open leads from the Twin to record an ocean section across the north end of Nares Strait.

北冰洋淡水枢纽（Freshwater Switchyard of the Arctic Ocean, FSAO）项目是一项通过一系列年度春季水文调查，研究阿尔特（Alert，埃尔斯米尔岛）与北极点之间“淡水枢纽”区域内的淡水循环（海冰与上层海洋）的科研计划。驻扎在埃尔斯米尔岛北部阿尔特基地的航空器会在晚春时节向北穿越陆架坡折带开展海洋学调查。本调查旨在测量向东流动的边界流，并明确从北冰洋深海盆向浅海大陆架过渡过程中发生的水团属性变化。2003-2009年的4月末至5月间，研究团队使用内置记录式温盐深（CTD）仪——赛霸电子（Sea-Bird Electronics, SBE）19plus SeaCAT，搭配赛霸电子（SBE）43溶解氧传感器，完成了最大深度达500米的观测。数据集包含水深、压力、原位温度、位温、电导率、盐度、密度，以及可获取的溶解氧数据。近年来，团队已将溶解氧剖面数据单独归档，以支持差异化的数据处理流程。对于无需溶解氧数据的所有应用场景，优先推荐使用基础CTD归档数据。2007年之前，本次调查使用的航空器为贝尔206直升机。2007年4-5月，团队遭遇了多年来最为恶劣的北极飞行气象条件，对多项调查工作造成了显著负面影响。在阿尔特基地，一处宽阔的沿岸冰间湖持续蒸发形成冰雾，长时间未消散，导致直升机无法安全抵达研究区域，因此2007年无有效观测数据收录。2008年，团队采用双水獭（Twin Otter）滑雪式飞机完成了多个测站的观测，但受限于机型，无法抵达往年的精确测站位置。2009年的观测数据采集工作，主用设备为赛霸电子（SBE）-19plus CTD仪（序列号4344），搭配赛霸电子（SBE）-43溶解氧传感器（序列号408）。自第8次投站（Cast 8）起，团队更换为备用赛霸电子（SBE）-19 CTD仪（序列号2373），搭配赛霸电子（SBE）-43传感器（序列号1406），该测站成功获取了高质量的溶解氧、温度与电导率剖面数据。次日首个测站时，备用CTD设备完全失效，具体故障原因正由制造商调查。经评估，此时最稳妥的方案是移除主用CTD上的SBE-43溶解氧传感器，以尽可能获取优质的CTD观测数据。最终本次调查共获得18个测站的高质量CTD剖面数据，但仅第8次投站附带溶解氧观测数据。2010年，团队从双水獭飞机上向开放冰间湖投放机载投弃式CTD探头，以获取跨越内尔斯（Nares）海峡北端的海洋断面观测数据。