There are nine Seagliders and seven Slocum gliders currently in the IMOS fleet. Both weight 52kg which makes it easy to deploy from a small boat.
Slocum gliders are deployed in targeted regions around Australia with repeat transects on an annual basis. Some of these transects have been measured for over seven years (eg. Two Rocks, Marion Bay/Spencer Gulf). The Slocum gliders are currently deployed in Western Australia, New South Wales, South Australia, Tasmania and Queensland.
Every year (since 2009) there has been a number of Slocum glider deployments in Western Australia that complete a circuit from Two Rocks (north of Perth) to the edge of the Leeuwin Current and then returns through the axis of the Perth Canyon at Two Rocks. The frequency of these deployments has changed over time - currently (since 2013) there are four deployments a year. Slocum gliders were also deployed in the northern Western Australia as part of a WA Government funded project in the Kimberly and Pilbara between the end of 2011 and May 2015. Glider deployments in the North West of WA have been discontinued.
Slocum gliders are also deployed along the New South Wales coast to examine the dynamics and variability of the East Australian Current. Slocum gliders are used in this area to make cross-shelf transects of the adjacent shelf, investigating the challenging environment of the continental shelf off Stockton Bight, Jervis Bay and Eden. Slocum gliders sample recurrent features during three week deployments, such as tracking the maturation of phytoplankton after a cold core eddy brings nutrients into the photic zone. The inshore monitoring by Slocum gliders also tracks the effects of estuarine discharge and southern extensions of the isotherms off Eden. Gliders are usually deployed from either Port Stephens or Crowdy Head in winter-spring to coincide with the occurrence of East Coast Lows and the spring bloom phenomena.
There are two Slocum deployments in South Australian from Marion Bay and Spencer Gulf, with deployments lasting ~20 days. The Spencer Gulf is an inverse estuary located on the south coast of Australia. High evaporation in the Gulf leads to a strong salinity gradient which decreases toward the open boundary. During winter, cooling in the upper reaches of the gulf results the water becoming denser than the adjacent shelf waters which causes the high salinity water to exit the Gulf as a gravity current. Due to the effects of Coriolis this outflow is concentrated to the eastern side of the gulf and shelf waters flow in to replace it along the western boundary. The outflow is modulated by the spring-neap tidal cycle. Glider deployments in this region aim to monitor seasonal and long term variability in continental shelf – Spencer Gulf exchange.
There had been six deployments in Tasmania traverses a route from Storm Bay to the edge of the continental shelf since 2009, now reduced to 5 missions. It is expected that the Storm Bay missions will be reduced to 4, to allow the relocation of a glider mission into Bass Strait during the summer months. The continuous glider observations are helpful in the characterisation of regions with complex water mass dynamics which would be difficult to resolve by discrete sampling arrays. The glider data from Storm Bay will be used to assist in the validation of a 3-dimensional hydrodynamic, sediment and biogeochemical numerical model of the region and for the calibration of remote sensing observations. The summer trans-Bass Strait Slocum glider deployment will allow the observation of sub-surface waters of Bass Strait, when Bass Strait is stratified.
In Queensland, the Australian Institute of Marine Science recently deployed a Slocum glider “Amy” off Townsville, in collaboration with CSIRO and the IMOS glider facility. The glider was released on the 21 of October 2015 at mid-shelf northeast of Magnetic Island and will cruise for approximately 2-3 weeks to the outer shelf and back. Amy’s deployment is one of a series of planned glider releases over the next few months to support more comprehensive and cost-effective oceanographic observations of both the surface and sub surface conditions. As the glider moves through the water column it collects a range of information including temperature and salinity. This data then becomes available through satellite communication to improve operational modelling as part of the eReefs project.
Seagliders are also deployed on repeat transects. There are three deployments a year in each Western Australia to investigate the Leeuwin Current and in the Coral Sea.
Seagliders are deployed in order to aid ongoing research efforts to understand the role of the Leeuwin current system in controlling not only the marine life but also the climate of south-western Australia. Originating in the tropics, the Leeuwin current is a shallow, narrow band of warm, low salinity water, which flows poleward from Exmouth to Cape Leeuwin and into the Great Australian Bight. A Seaglider is deployed off Dampier every three months and traverses back and forth across the Leeuwin Current, completing its deployment in Freemantle. As Seagliders have a six month battery life, they can complete many cross-shore transects, dependant on the strength of the Leeuwin Current and the presence of eddies.
In the Coral Sea region off northern Queensland, two Seagliders undertake permanent transects along the coast collecting observations of temperature, salinity and oxygen in top 1000 m, as well as chlorophyll and backscatter from the mixed layer. The observations collected by these gliders will be incorporated into the nested hydrodynamic models being developed for Queensland to track changes in the coastal flows near the continental margin and on the shelf.
In addition to these Seaglider deployments, IMOS in collaboration with SARDI/CSIRO have deployed one Seaglider mission in 2014 and one in 2015 in the Great Australian Bight. Seaglider observations from these missions will help ground truth the hydrodynamic models developed for this region.
Other Seagliders deployments include off the NSW coast with the aim of increasing our understanding of the dynamics and variability of the East Australian Current (EAC), the Tasman Front, and eddies shed by the EAC. In 2010 and 2011, Seagliders were also deployed at the Southern Ocean Time Series site in the Southern Ocean southwest of Tasmania and traverse towards Tasmania. The measurements taken by gliders on this route provided a spatial context for the larger set of biogeochemical observations obtained from the moored observations at the site, to allow assessment of how representative they are of the region. Furthermore, transects across the Tasman Outflow and Zeehan Current between Hobart and the Southern Ocean Time Series site help in characterising the boundary currents that influence climate and marine ecosystems of the area.