The Aurora Australis has arrived at its first marine science station in the Southern Ocean, marked by the successful deployment of the first of five Argo floats which will provide close to real-time observations on the current station of the ocean to scientists around the world.
The first official science site is located between the Shackleton and West ice shelves, a region identified as important due to its high biodiversity and biological production which makes it a popular region for whales, seals, penguins and seabirds.
The ship will spend two days here, and along with the deployment of the Argo, a range of science will be undertaken and compared with observations from the last survey in this area which took place in 1996. Scientists will be taking measurements of Antarctic Bottom Water, recording the abundance of Antarctic krill, and investigating the amount of food for krill in this area.
Argo floats are a worldwide initiative that have revolutionised the monitoring of the ocean, with close to universal coverage over open oceans.
Argos sink to around 1000m below sea level and drift with the deep ocean currents. Ten days after deployment they descend to 2000m and then begin rising to the surface, measuring temperature and salinity on the way up. Once they reach the surface they transmit the data via satellite back to scientists around the world, before returning to 1000m and starting the cycle again.
To date, Australia has deployed roughly 500 Argo floats in the past 16 years, part of global deployment of 8000 floats. This international effort has given scientists unprecedented, near real-time observations of how the current state of the ocean and how it is slowly changing.
Following the departure of the Aurora Australis from Hobart last week, the team were able to test a range of equipment, including a sophisticated mid-water trawl system designed to catch small fish at different depths. The system includes a series of nets and each one remains open as it is gradually retrieved from 1000m. One net closes and another opens every 200m — all while the net is slowly being dragged behind the Aurora Australis at an approximate speed of 4 km/hour.
The deployment was a success, with a total catch of 3.4 kilograms including fish, krill and some salps — a small, clear gelatinous sack (the size of a squash ball) that filters phytoplankton.
The mid-water trawl net will be used over 30 times during the voyage to estimate the abundance of small fish across the region, and to monitor how the types of fish may change as the ship moves north from Antarctica towards Heard Island. These fish are important food for elephant seals, toothed whales and bigger fish yet the ecology and overall importance of these fish in Southern Ocean food webs remains poorly known.
The Continuous Plankton Recorder (CPR) is also operating. Designed in 1931, the CPR travels behind the ship at a depth of 7 metres, where it remains for up to 36 hours — covering more than 450 nautical miles at a time. It has ventured into the Southern Ocean in this region on many occasions and while we have many records, the work being done on this voyage will help understand how the routine collection of CPR data on ships-of-opportunity may be used to signal changes in the foodwebs.
The furious fifties, which lived up to the name, have given way to Antarctic waters and sea ice is beckoning in the next 24 hours. The marine science team are very excited that the Aurora Australis has reached the ice cold waters, icebergs, short nights and the science activity will begin to occur around the clock before the weekend begins.
