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

Date 2021-11
Author(s) Roquet FabienORCID1, Guinet Christophe2, Charrassin Jean-Benoit3, Costa Daniel P.4, Kovacs Kit M5, Lydersen Christian5, Bornemann Horst6, Bester Marthan N.7, Muelbert Monica C.8, Hindell Mark A.9, McMahon Clive R.ORCID9, Harcourt RobORCID10, Boehme LarsORCID10, Fedak Mike A.ORCID11
Affiliation(s) 1 : Department of Meteorology, Stockholm University, Stockholm, Sweden
2 : Centre d’Etudes Biologiques de Chizé, Centre National de la Recherche Scientifique, Villiers en Bois, France
3 : Laboratoire d’Océanographie et du Climat: Expérimentation et Approches Numériques, Paris, France
4 : Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, California, USA
5 : Norwegian Polar Institute, Tromsø, Norway
6 : Alfred-Wegener-Institut, Helmholtz Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany
7 : Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
8 : Instituto de Oceanografia, Universidade Federal do Rio Grande, Porto Alegre, Brazil
9 : Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
10 : Marine Predator Research Group, Department of Biological Sciences, Macquarie University, Sydney, New South Wales, Australia
11 : Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, St Andrews, UK
DOI 10.17882/45461
Publisher SEANOE
Keyword(s) Marine biology, physical oceanography, in-situ marine data, sea-mammals, CTD sensors, operational oceanography, Installations de suivi environnemental

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).

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Roquet Fabien, Guinet Christophe, Charrassin Jean-Benoit, Costa Daniel P., Kovacs Kit M, Lydersen Christian, Bornemann Horst, Bester Marthan N., Muelbert Monica C., Hindell Mark A., McMahon Clive R., Harcourt Rob, Boehme Lars, Fedak Mike A. (2021). MEOP-CTD in-situ data collection: a Southern ocean Marine-mammals calibrated sea water temperatures and salinities observations. SEANOE.