Equipped with a variety of sensors, ocean gliders are designed to deliver ocean profile data. Their unique design enables them to move horizontally through the water while collecting vertical profiles.
Deployments in 2015 represented 606 glider days at sea, traversing a total of 11,829 kms, to collect valuable data on temperature, salinity, currents and other variables at a range of depths in Australian waters.
New glider deployment locations included the two ‘Greats’: Great Australian Bight (Seaglider) and Great Barrier Reef (Slocum gliders). Glider deployments in the Pilbara and Kimberley ceased in March.
In 2015, the introduction of rechargeable batteries in the Slocum gliders allowed for a longer mission duration. As a result of this innovation a new record was set with a deployment of 30 days duration off Two Rocks in September. The extended deployment period also had a benefit in November when the formation of a sub-surface chlorophyll maximum was captured towards the end of the deployment. With the older batteries, the glider would have been recovered and this event missed.
Numbers alone don't tell the whole story of the 2015 glider missions. The effort and drama that goes into keeping the glider program running includes numerous Friday afternoon and Sunday evening emergencies, shark bites that destroy instruments and long searches to locate wayward gliders.
Professor Charitha Pattiaratchi, who leads the IMOS Ocean glider facility, reflects on 2015, describing the challenge of conducting glider missions.
“It wasn’t unusual to find ourselves head scratching, trying to make sense of what's happening when gliders behave unexpectedly,” said Dr Pattiaratchi.
The Great Barrier Reef measurements extended from Port Douglas in the north to Townsville in the south. Regular cross shelf transects captured upwelling and verified the latest circulation models for the reef.
These missions provided a big challenge to glider piloting in an area with high shipping activity and shallow water reef systems. The gliders needed to be piloted to avoid both of these ‘obstructions’.
The team has been making measurements along the Two Rocks transect since January 2009 and has documented the formation of Dense Shelf Water Cascade (DSWC) along this this transect. This is where higher salinity water, formed in the coastal region, is transported offshore along the sea bed (downwelling).
In February 2015, they observed the opposite phenomenon, upwelling, where deeper, cooler offshore water was moved onto the shelf due to strong winds. This was was persistent over 3 weeks – the entire time the glider was taking measurements.
Dr Pattiaratchi praised the IMOS Ocean gliders team of Dennis Stanley, Alessandra Mantovanelli, Kah Kiat Hong and Paul Thomson for their efforts during the year. He also acknowledged the contribution of the glider team at CSIRO in Hobart and the various node personnel across Australia who helped with local logistics.
“We could not have done this without the cooperation of such great people around the country, including our charter operators who put up with our last minute changes in plans,” he said.