MEOP-CTD in-situ data collection: a Southern ocean Marine-mammals calibrated sea water temperatures and salinities observations

the southern ocean plays a fundamental role in regulating the global climate. this ocean also contains a rich and highly productive ecosystem, potentially vulnerable to climate change. very large national and international efforts are directed towards the modeling of physical oceanographic processes to predict the response of the southern ocean to global climate change and the role played by the large-scale ocean climate processes. however, these modeling efforts are greatly limited by the lack of in situ measurements, especially at high latitudes and during winter months. the standard data that are needed to study ocean circulation are vertical profiles of temperature and salinity, from which we can deduce the density of seawater. these are collected with ctd (conductivity-temperature-depth) sensors that are usually deployed on research vessels or, more recently, on autonomous argo profilers. the use of conventional research vessels to collect these data is very expensive, and does not guarantee access to areas where sea ice is found at the surface of the ocean during the winter months. a recent alternative is the use of autonomous argo floats. however, this technology is not easy to use in glaciated areas.in this context, the collection of hydrographic profiles from ctds mounted on marine mammals is very advantageous. the choice of species, gender or age can be done to selectively obtain data in particularly under-sampled areas such as under the sea ice or on continental shelves. among marine mammals, elephant seals are particularly interesting. indeed, they have the particularity to continuously dive to great depths (590 ± 200 m, with maxima around 2000 m) for long durations (average length of a dive 25 ± 15 min, maximum 80 min). a conductivity-temperature-depth satellite relay data logger (ctd-srdls) has been developed in the early 2000s to sample temperature and salinity vertical profiles during marine mammal dives (boehme et al. 2009, fedak 2013). the ctd-srdl is attached to the seal on land, then it records hydrographic profiles during its foraging trips, sending the data by satellite argos whenever the seal goes back to the surface.while the principle intent of seal instrumentation was to improve understanding of seal foraging strategies (biuw et al., 2007), it has also provided as a by-product a viable and cost-effective method of sampling hydrographic properties in many regions of the southern ocean (charrassin et al., 2008; roquet et al., 2013).

南大洋在全球气候调节中扮演着根本性的角色。该海洋亦拥有丰富且高度繁盛的生态系统，其可能受到气候变化的潜在威胁。国内外投入了巨大的努力，旨在模拟物理海洋学过程，以预测南大洋对全球气候变化的响应，以及大规模海洋气候过程所扮演的角色。然而，这些模拟努力受到实地测量数据的严重限制，尤其是在高纬度和冬季月份。研究海洋环流所需的标准数据包括温度和盐度的垂直剖面，通过这些数据，我们可以推算出海水的密度。这些数据通常使用CTD（电导率-温度-深度）传感器收集，这些传感器通常部署在研究舰船上，或近期，部署在自主型Argo探测器上。使用传统研究舰船收集这些数据成本高昂，且无法保证在冬季月份能够到达海冰覆盖的海洋区域。近期的一种替代方案是使用自主型Argo浮标。然而，这种技术在冰川地区并不易于使用。在此背景下，从海洋哺乳动物身上安装的CTD收集水文剖面数据具有极大的优势。物种选择、性别或年龄的选择可以用来有选择性地获取数据，尤其是在采样不足的区域，如海冰下或大陆架上。在海洋哺乳动物中，象海豹尤为引人注目。事实上，它们具有持续下潜至极深深度（590 ± 200米，最大值约为2000米）且持续时间长的特性（平均下潜时长为25 ± 15分钟，最大80分钟）。一种电导率-温度-深度卫星中继数据记录器（CTD-SRDL）在21世纪初被开发出来，用于在海洋哺乳动物下潜期间采样温度和盐度的垂直剖面（Boehme等，2009年，Fedak，2013年）。CTD-SRDL在陆地上附着在海豹身上，然后在其觅食旅途中记录水文剖面，当海豹回到水面时，通过卫星Argos发送数据。虽然海豹仪器化的初衷是为了提高对海豹觅食策略的理解（Biuw等，2007年），但它同时也意外地提供了一种可行且成本效益高的方法，用于在许多南大洋区域采样水文特性（Charrassin等，2008年；Roquet等，2013年）。