Doctors Clive McMahon, Esther Tarszisz and Louise McMahon, all from the Sydney Institute of Marine Science, are teaming up to build on ten years of ocean sampling by Australian and French Antarctic Programs. They will continue the time-series of high-resolution oceanographic data that looks at annual variation in ocean structure and the formation of the globally important Antarctic Bottom Water.
Antarctic Bottom Water is known to drive the Southern Ocean component of the ‘global ocean conveyor belt’, a constantly moving system of deep-ocean circulation driven by temperature and salinity. This motion is caused by a combination of currents in the deep ocean and wind-driven currents on the surface. Cold, salty water is dense and sinks to the bottom of the ocean while warm water is less dense and remains on the surface.
The formation of Antarctic Bottom Water was, until recently, only observed when associated with the presence of an ice shelf or a large storage volume. We now know that bottom water production can also be driven primarily by the salt released by sea-ice formation.*
As seals dive very deep to feed, often to the sea floor under the ice, using seals to carry instrumentation allows data to be collected from parts of the ocean which are otherwise inaccessible because of sea-ice cover.
“Seals can go where we can’t go to collect information on variables such as water temperature and salinity,” says Clive McMahon.
“Their data collection is invaluable in projects like ours where we are trying to identify where bottom water forms,” he said.
Instrumentation developed by the University of St Andrews in Scotland is attached to seals which carry the device for about a year until they drop off during their annual moulting cycle. Occasionally devices are found and returned to researchers. This is a bonus as the device stores vast amounts of high-resolution information which is collected every four seconds. Whether the devices are recovered or not there will be a data stream collected from each instrument via the Argos satellite system each time the seals come to the surface.
Clive McMahon is excited by the potential of the project this summer. He believes the research is unique in that it integrates biological information with data on physical oceanography.
“Not only will we collect data to help us understand ocean systems and ultimately climate processes, we’ll also be learning about the seals themselves.
“We’ll be able to study seal movements while gathering data on and in their chosen habitats.
“This means we can make links between habitat structure and indicators of seal health such as growth rate and pup production,” he said.
With many years of experience working with seals the team, which includes a vet, have the utmost respect for the animals and have developed techniques and operating standards to attach these devices without compromising the wellbeing of the seals.
The team will return to Hobart in March 2016.
* Kay I. Ohshima, et al. (2013) ‘Antarctic Bottom Water production by intense sea-ice formation in the Cape Darnley polynya.’ Nature Geoscience , 24 February.