A day on board the Antarctic research vessel Aurora Australis
The video below was filmed by Antarctic researcher Dr Frederique Olivier onboard the recent voyage of the Australian Antarctic Division’s icebreaker the Research Supply Vessel Aurora Australis.
It encapsulates some of the incredible amount of work undertaken by researchers working in shifts continuously throughout the voyage to learn more about the Antarctic Ocean and its relationship to the rest of Earth’s environment.
The stop-motion clip focuses on the sampling of the ocean and the deployment of instrument packages attached to moorings at various stations, as the ship steams from Tasmania across the Southern Ocean towards the edge of Antarctica.
This research aims to characterise water masses which, as they become colder and thus denser than surrounding water, sink turning into major bottom ocean currents.
Samples of seawater are taken at various depths, as far down as ~5 km, which when processed will provide valuable data helping scientists understand processes at play in the Southern Ocean and its role in the global climate system.
In the video, researchers come and go from a metal instrument frame known as a CDT (conductivity, depth, temperature) rosette which holds long cylindrical containers known as “Niskin” sampling bottles. This rosette is used to capture water samples from specific depths, and to log water properties as the rosette is lowered and raised through the water. This rosette was dropped 149 times during the 32-day voyage – at almost five different locations each day.
Once it is brought back on board, scientists draw water samples from the “Niskin” bottles. They test the samples for a range of properties, including levels of salt, oxygen, pH, nitrate and phosphate.
Importantly, they also analyse the samples to detect how much carbon dioxide is found in the water at various depths. Although dissolved carbon is always present in sea water, studies[i] have established that levels of carbon in the ocean have been increasing significantly over the past century.
Researchers are interested in documenting the rate at which ocean carbon is increasing, which will help contribute to more accurate climate change predictions.
By testing other properties, such as salinity, temperature and chlorophyll, scientists can also learn how climate change and other environmental impacts will affect plankton, fish, coral and other marine organisms.
By characterising these properties of water at different depths we can designate ‘location tags’ that enable scientists to identify where the ocean water originated – whether it has travelled along a current from the North Atlantic ocean, or whether it originates from melting Antarctic ice bergs.
A recent article published by Dr Rintoul is based on data gathered on AAD expeditions and shows that the deepest water in the Antarctic Ocean is getting fresher, possibly due to increasing icemelt[ii]. One objective of the voyage is to test this idea.
In the second half of the film, staff set about assembling an Accoustic Doppler Current Profiler (ADCP) mooring. The mooring is dropped in a carefully selected site allowing for the ADCP to be in close proximity to the sea floor where it can measure the strength of deep ocean currents to help us understand the origin of waters moving from the Antarctic continental shelf into the deepest parts of the ocean, not only by measuring their properties but also their speeds.
Over the course of a year, it will continuously collect data by sending out soundwaves to measure water speed using the Doppler effect, in the same way police speed radars operate.
The ADCP will be collected during a future research voyage through the activation of a release command which will release the mooring and see it float to the surface to be collected by the research vessel.
The recent expedition was one of many, with results tabulated against data collected on similar AAD voyages from 1991 onwards.
For more information on the AAD or the research vessel Aurora Australis visit the AAD website.
[i] Sabine, C. L., R. A. Feely, N. Gruber, R. M. Key, K. Lee, J. L. Bullister, R. Wanninkhof, C. S. Wong, D. Wallace, B. Tilbrook, F. J. Millero, T. H. Peng, A. Kozyr, T. Ono, and A. F. Rios (2004), The oceanic sink for anthropogenic CO2, Science, 305, 367-371, doi:10.1126/science.1097403.
[ii] Rintoul, S. R. (2007), Rapid freshening of Antarctic Bottom Water formed in the Indian and Pacific oceans, Geophys. Res. Lett., 34, L06606, doi:10.1029/2006GL028550.