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（Southern Ocean）在调控全球气候中发挥着基础性作用。该海域同时拥有丰富且生产力极高的生态系统，且潜在易受气候变化的影响。当前各国及国际社会投入了大量资源，对物理海洋过程进行建模，以预测南大洋对全球气候变化的响应，以及大型海洋气候过程所扮演的角色。然而，这类建模工作因缺乏原位测量数据而受到极大限制，尤其是在高纬度海域以及冬季时段。

研究海洋环流所需的标准数据为温度与盐度的垂直剖面，借此可推算海水密度。这类数据通过CTD（Conductivity-Temperature-Depth，电导率-温度-深度）传感器采集，这类传感器通常部署于科研船只上，近年来也被应用于自主式Argo剖面浮标（Argo profilers）。使用传统科研船只采集这类数据成本极高，且无法保障在冬季海面存在海冰的区域开展作业。近期的替代方案是使用自主式Argo浮标，但该技术在冰川覆盖区域难以部署。

在此背景下，依托附着于海洋哺乳动物的CTD传感器采集水文剖面便具备极大优势。可通过选择物种、性别或年龄，有针对性地在海冰下方或大陆架等采样严重不足的区域获取数据。在海洋哺乳动物中，象海豹极具研究价值。实际上，它们具备持续深潜的特性：平均潜深为590±200米，最大潜深可达约2000米，单次潜泳时长平均为25±15分钟，最长可达80分钟。

21世纪初，科研人员开发了CTD-SRDL（Conductivity-Temperature-Depth Satellite Relay Data Logger，电导率-温度-深度卫星中继数据记录仪），可在海洋哺乳动物潜泳期间采集温度与盐度的垂直剖面数据（Boehme等，2009；Fedak，2013）。CTD-SRDL在陆地阶段被安装至海豹身上，随后在其觅食巡游期间记录水文剖面数据，当海豹返回海面时，会通过ARGOS卫星传输采集到的数据。

尽管为海豹加装传感器的最初目的是加深对海豹觅食策略的理解（Biuw等，2007），但该技术也附带产生了一种可行且经济高效的采样方法，可在南大洋诸多海域采集水文属性数据（Charrassin等，2008；Roquet等，2013）。