A helping hand for oceanographers

Whilst exploring Google Scholar, I came across an interesting article that used a rather different approach to oceanographic observation: elephant seals.

Screen Shot 2016-03-06 at 21.08.10Living in herds in the Southern Ocean, these three tonne tanks seem a strange choice when it comes to measuring various oceanic properties, but are surprisingly efficient. By attaching conductivity-temperature-depth sensors (or CTDs) onto the heads of elephant seals, these mammals act as a biological platform from which measurements can be made. In fact, elephant seals are well suited to this job: they dive very deep and are able to swim long distances, likely visiting a wide proportion of the Southern Ocean. In a study by Xing et al (2012), 15 elephant seals were tagged in the region surrounding the Kerguelen Islands – an archipelgelo that lies on the boundary of the Antarctic tectonic plate. This equated to 1894 profiles being collected in just over a year, and emphasises the potential of utilising animals in this way.  As it happens, the use of animals in scientific research is a growing field, and is known as biologging.

Biologging has only become possible relatively recently and is used primarily to monitor animal behaviour e.g. foraging, migration and even environmental assessment – such as the impact of offshore wind farms on seabirds. However, over the last 15 years, the development of Satellite Relay Loggers (that is, the combination of satellite relay – essentially fancy GPS) and CTD sensors has allowed a collaboration between biologists and physical oceanographers, expanding our observational capabilities of the ocean.

One of the main problems with observational oceanography is the sampling resolution: there are enormous parts of the ocean that remain a sampling mystery. This is due primarily to the fact that the sensors we use are very small and the ocean is very big, so only a limited proportion of the ocean can be measured at any one time. Combined with the fact that research ships are expensive to run, this leads to some parts of the global ocean that are very well-known to us (such as the easily accessible coastal regions) and areas that haven’t seen any CTD sensor in over ten years, if ever!

One of the ways to combat this problem is through the introduction of autonomous underwater vehicles (AUVs) – essentially robotic sensors. These robots are quite happy to go up, down, backwards and forwards, measuring the water column as they go for however long their lithium batteries last, and have drastically increased both the spatial and temporal resolution of observational oceanography.

However, they aren’t perfect, and there are still vast regions of the ocean where these robots can’t reach. Outside of 60°N-60°S latitudinal range, the presence of sea ice is a problem. When I was an undergraduate, we were told a story of a multimillion pound AUV that became lost beneath the Arctic sea ice. I have yet to know if it was ever recovered, but global warming might lead to some interesting robotic discoveries if the ice caps continue to melt.

New technological advances with AUVs are being made constantly, so it is highly possible that these type of limitations may not be permanent. In the meantime, however, biologging may be a useful and reliable alternative, particularly as elephant seals don’t need batteries and their thick skin is not prone to water leakage.

That being said, biologging does come with its own unique difficulties, the animal must be sedated for the sensor to be attached, and once again for its removal – a dangerous and sometimes laborious task. It also has to be noted that the animal’s welfare is a top priority for these researchers, and every effort is taken to ensure the animal is by no means distressed throughout the biologging process.

Nevertheless, biologging provides a useful tool to measure those hard to reach places where humans and robots dare not tread.

Post By: Jenny Jardine

References:

Charrassin, J B., and others, (2010), Bio-optical profiling floats as new observational tools for biogeochemical and ecosystem studies: potential synergies with ocean color remote sensing, IN J. Hall, D. E. Harrison and D. Stammer (Eds.), Proceedings of OceanObs 09: Sustained ocean observations and information for society (Vol. 2), Venice Italy, September 2009. ESA Publication WPP-306

Roquet, F., and others, (2011), Validation of hydrographic data obtained from animal-bourne satellite-relay data loggers, Journal of Atmospheric and Oceanic Technology, 28, 787-801

Xing, X., and others, (2012) Quenching correction for in vivo chlorophyll fluorescence acquired by autonomous platforms: A case study with instrumented elephant seals in the Kerguelen region (Southern Ocean), Limnology and Oceanography: Methods, 10, 483-495

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