Painting a picture with integrated observations
THE changes happening in our oceans are invisible to the naked eye. But often, so too are the efforts that go into collating the data that helps us interpret what those changes are.
Hauling almost a tonne of tech at a time in and out of waters is not an easy task. Neither is meticulously cleaning months of algae and barnacle growth off valuable sensors. Yet, this is just some of the work that goes into maintaining one of the most valuable and integrated datasets in the world.
Researchers can follow the changes of our coasts and oceans thanks to a unique partnership between the Integrated Marine Observing System (IMOS), CSIRO and other institutions. Long-term trends and future impacts are now more easily identified, and significant marine events are tracked and better understood.
In 2011 a series of observations sites along the Western Australia coast captured and documented a destructive marine heatwave that led to coral bleaching, a loss of kelp forest, and a range shift of many fish species.
“Without this partnership we simply wouldn’t understand the impacts of that marine heatwave anywhere near as well as we do now,” says IMOS Director Mr Tim Moltmann.
A network of tech
Moorings are lines anchored to the seafloor and held upright in the water column by fixed floats. Instruments are mounted along the length of the line, measuring chemical and physical properties of the waters flowing past it. This includes carbon dioxide levels, oxygen levels, pH, salinity, chlorophyll levels, carbon fluxes, and flow velocity, as well as temperature. The mooring designs and configurations are carefully engineered for the range of wave and ocean current conditions expected at each individual site.
IMOS has funded an extensive network of moorings around Australia since 2006. CSIRO is the largest partner.
“The data collected from the moorings are a national research infrastructure, available for all Australian marine, climate and Antarctic scientists to use,” says Moltmann.
The network provides key insights into the state of the oceans and is a valuable resource for those managing our coasts, fisheries, tourism and communities.
“Moorings provide a high temporal resolution like nothing else can,” says Moltmann. “They are at a single point in the water all the time recording the daily, seasonal, annual, and eventually decadal trends of the region.”
Consistent 24/7 measurements
IMOS operates a broad range of moorings across the country’s coasts and oceans: there are deep moorings in the Southern Ocean, down to 5.5km; there are six that monitor the East Australia Current, ranging from 500m to 4.8km in depth; some moorings transmit sensor data via satellite; and, there are National Reference Stations, a network of seven locally managed mooring sites around the Australian coastline. These collectively represent the various Australian marine environments.
Some of the National Reference Stations were already functioning as part of the CSIRO Coastal Monitoring program long before 2006. The Maria Island site in Tasmania recorded temperature and salinity measurements by boat every month from 1944. The Rottnest Island site just off Perth in Western Australia commenced operations in 1951. It was the data from this array that attributed the climate drivers and dynamics of the 2011 marine heatwave.
“The unseasonable surge of the Leeuwin Current, an anomalous eastern boundary current off the west coast of Australia, and its heat transport, were factors,” says CSIRO physical oceanographer Dr Ming Feng.
The reference stations have some of the longest time series sites in the world. The historical data is valuable in showing just how and when conditions change.
“CSIRO were quite forward thinking in collecting long term observations and looking after the data,” says Moltmann. “When IMOS was established in 2006 we were able to build on the strength of operations that were already there for more than 70 years.”
IMOS made the program sustainable, introducing new technology and methods that weren’t in Australia at the time. The sites that CSIRO manage today are Rottnest Island, Maria Island and Stradbroke Island in QLD. All are coupled with a monthly bio-geochemical water-sampling regime.
The instruments on the moorings now record measurements around the clock. IMOS makes all of the data publicly available via the Australian Ocean Data Network, and feeds into international ocean monitoring programs.
How are moorings deployed?
Dr Bronte Tilbrook is a researcher with CSIRO and the Antarctic Climate and Ecosystems Co-operative Research Centre (ACE CRC). He leads the mooring project on Maria Island in southeast Tasmania, at the southern end of the East Australian Current.
His team from CSIRO uses fishing boats to deploy the moorings.
“The moorings and anchors weigh about 800 kg each,” says Tilbrook. “The moorings are placed in the water using the ship crane and the anchor. This is connected to the mooring buoy using chain and large multiple bungies that act as wave shock cords.”
One of CSIRO’s leading technical officers, Ryan Crossing, is part of a four-person team managing the Rottnest Island station. He adds that the moorings and instruments are deployed for up to six months at a time, depending on the amount of bio-fouling and battery life. Then they are swapped out with a spare set to allow maintenance.
The Rottnest Island team completes servicing trips aboard the CSIRO Research Vessel Linnaeus.
“We trigger the releases using an acoustic transponder. The floats surface with the mooring lines and instruments, which we then recover onto the boat and start disconnecting all the parts,” says Crossing.
He and his team then connect all the new gear together and redeploy the mooring, ensuring a seamless data set. Back at the workshop they clean the sensors, and download the data from the instruments.
During the monthly biogeochemical water sampling trips, the teams at each site collect zooplankton samples, a water column profile using highly accurate instruments lowered slowly to the bottom and then retrieved, and samples of water from discrete depths that correspond with the instruments on the mooring.
Data for the challenges ahead
Maria Island is a busy site, with multiple observations and monitoring projects in operation. In addition to his roles at CSIRO and ACE CRC, Tilbrook is also co-chair of the Global Ocean Acidification Observing Network, which reports to the United Nations Sustainable Development Goals. Tilbrook integrates this role into the IMOS Maria Island operations, and also at other National Reference Stations: on the Great Barrier Reef, and also Kangaroo Island, just off the coast of South Australia.
Looking at the oceans of the future, Tilbrook says warming and ocean acidification are major stressors for marine ecosystems.
“The level of ocean acidification is already outside the preindustrial range across the much of the world’s oceans,” he says. “And the increasing incursion of warmer and saltier subtropical waters along the east coast of Tasmania is bringing profound changes to local ecosystems.”
“In fact, the surface waters of the South Tasman Sea are some of the most rapidly warming surface waters on the planet,” he explains. “Subtropical fish are displacing temperate water species. How this is impacting the carbon uptake and ocean acidification are unknowns and need to be understood.”
Moltmann adds the ‘tropicalisation’ of the area has allowed a species of invasive sea urchin to thrive. The urchins graze on local kelp forests, which were already under stress from the warming waters to the point of decimation. Kelp forests are a habitat for lobster, and so the flow on effect has devastated Tasmania’s lobster industry.
Feng says both the Rottnest and Maria Island data have revealed warming of one to two degrees in the past several decades. “Both sites are within two of the world’s ocean hotspots for greenhouse gas induced global warming,” he says.
“Monitoring the long term physical and biological changes in the coastal environment using mooring technology and regular sampling will help the future mitigation of climate change impacts.”
Moltmann adds: “Our state-of-the-art integrated observations network is key in not only understanding the current state and rate of change of our oceans, but in securing their future.”