Observing the Oceans

Observing the Oceans around Australia

Ocean profiling float being launched (photo: Institute Fuer Meereskunde Kiel Germany)

Only through the scientific design and development of ocean observing systems will Australia have the capacity to successfully monitor, predict, utilise and protect its vast marine environment.

Our Exclusive Economic Zone (EEZ) is the third largest in the world; but the influence of the Indian, Pacific and Southern Oceans on Australia extends thousands of miles beyond those artificial boundaries.

In the past two decades, Australian governments, business, industry and science have begun investing in ocean monitoring as part of research into climate and rainfall, fisheries, defence, coastal pollution, ocean engineering, shipping and transport and environmental protection.

Substantial gains have already come from that investment. The refinement of space and ocean technology, and recognition that ocean research offers significant returns, spawned many new projects and opportunities through the 1990s. Participation in international programs ensures wider benefits from a global ocean observing network, building a system Australia cannot possibly achieve alone.

Probing the deep

The ocean plays an extremely important role in the global climate system. In order to observe and understand that role it is necessary to carry out repeated measurements of the upper ocean to see how it varies.

Measurements must be taken routinely over a long period of time and over large areas of ocean. The results are then used to see how the temperature and salinity change from season to season and year to year.

A highly innovative and extremely cost-effective method of collecting this information has been established by linking up with volunteer merchant ships that are frequent carriers on particular routes, spanning regions known to affect Australia’s climate.

The CSIRO Ocean Observing Network using these commercial vessels began operation in 1983, initiated in part by the memorable drought, which affected much of eastern Australia in 1982-83. It is the major, routine subsurface ocean temperature observing network in the Indian and Southern Ocean, and an important contributor to the international networks in the Pacific Ocean.

The objective of the "Ship of Opportunity Program" is to collect a large number of measurements of ocean temperature, salinity, and velocity to a depth of 800 metres on a routine basis. This is done in two ways — as broadscale and widely dispersed sampling through volunteer observers to determine large-scale upper ocean heat and salt content or by frequently repeated high-density sampling along exactly-repeating sections to observe the transport of heat by ocean currents and eddies.

Shipping routes operated by Australia include;

• Brisbane — Fiji
• Sydney — Wellington
• Hobart — Australian and French Antarctic research facilities
• Perth — Singapore
• Perth — Red Sea
• Perth — Durban
• Singapore — Torres Strait

Centrepiece of the Network is the XBT (Expendable Bathythermograph), a probe which carries sensors whose electrical properties change with varying ocean temperature. Generally, the officer-of-the-watch deploys the probes from the bridge of the ship at preset intervals, but usually every 4-6 hours. The probes are in fact designed to be deployed from moving vessels, so as not to interrupt the ship’s normal operations.

The probe remains in contact with the ship by a fine copper-wire link while free-falling through the water column. The subsurface temperature is recorded every 60cm until the terminal depth of the probe is reached, usually 800 metres or deeper. Once the wire runs out, the probe drops to the seabed and is expended.

The data are stored on the microcomputer, and a condensed version is transmitted via satellite and distributed to scientists and climate prediction centres around the world. At the end of the voyage, all the information is sent to CSIRO and the Bureau for full processing and analysis.

CSIRO initially developed this Network under the auspices of the international Tropical Ocean Global Atmosphere (TOGA) program and the World Ocean Circulation Experiment (WOCE). The network continues to be a contribution to the international XBT network. Since 1997, it has been an operational Australian contribution to the Global Ocean Observing System (GOOS), jointly supported by the Bureau of Meteorology and CSIRO.

In 20 years of operation (1983-2003) around 50,000 XBT measurements have been taken and included in the observation database for the Australian region. CSIRO and the Bureau are deeply indebted to participating ship companies, their agents and ships personnel for their contribution to this valuable work.

Information from dedicated vessels

To be sure of the accuracy of key environmental information, to undertake intensive process studies, and to establish the extent of marine living resources, scientists also need access to sophisticated platforms at the surface from which to work and obtain ocean or coastal measurements.

CSIRO's mobile data-gathering platforms include the Southern Surveyor, a fully-equipped ocean-going vessel able to work in regions from the tropics to the sub-Antarctic. Its primary function is deep-ocean monitoring, mapping and biological sampling.

Other vessels utilised by Australia’s marine science effort include L’Astrolabe (French Institute of Polar Affairs), Aurora Australis (operated by the Australian Antarctic Division), Lady Basten (Australian Institute of Marine Science), Bluefin (Australian Maritime College, vessels operated by State fisheries management and research authorities, Royal Australian Navy ships, and commercial vessels participating in the "Ship of Opportunity Program".

Other Instrumentation

For many ocean observations, instrumentation has been developed and refined over many years of research into reliable off-the-shelf instruments. They include -

Conductivity Temperature Depth probe (CTD)

Used from research vessels such as Southern Surveyor, this electronic measuring system is a mainstay of ocean research, providing details of temperature, salinity and nutrients, dissolved oxygen and chlorofluorocarbons to depths of 6,000 metres.

Research vessels remain at a station or geographic location while the CTD is lowered to sample the water at different levels, a process that can take up to three hours. In deep ocean work, this information sheds light on climatically important deep-water masses and their circulation, so scientists can understand their links to climate change occurring over periods of years to decades.

Acoustic Doppler Current Profiler (ADCP)

Fixed to the hull of a research ship, the profiler sends a signal to a depth of 300 metres to measure current speeds at different depths.

Moored instruments: These can be kept on site in the open ocean for periods of a year or more to record variations in ocean currents, temperatures and salinities. The instruments are moored at carefully determined depths. They are retrieved by ship when released from their mooring by an acoustic signal. In the past 10 years, CSIRO has built and deployed hundreds of moored instrument arrays, with a 90 per cent recovery rate. In the World Ocean Circulation Experiment from1994-96, moored instruments were deployed in the Indian, Pacific and Southern oceans to obtain temperature and salinity data, which revealed the size of ocean currents, their speed and direction.

Ocean profilers

XBT tracks around Australia region.

While simple drifting cards were initially used to help scientists gather information on ocean behaviour, the first generation of torpedo-shaped, satellite-tracked surface drifter buoys began tracking pathways of the major ocean currents around Australia in the early 1970s via French and US satellites.

The latest generation of profilers can sink to pre-programmed depths of 2,000 metres to obtain temperature and salinity profiles. Periodically, they surface automatically and upload their data to a passing satellite, before once again descending to their park depth of 2,000 metres. An international program to deploy 3000 such profilers - 600 in the Australian region - is currently being planned. Once deployed, the profilers cannot be recovered. However, each profiler has a 'life' of up to four years. Their main application is in broad ocean and climate research in Australian and regional waters, and to help predict regional and worldwide climate trends.

Joint Australian Facility for Ocean Observing Systems

In 1998, CSIRO Marine and Atmospheric Research (CMAR) and the Bureau of Meteorology Research Centre (BMRC) created the Joint Australian Facility for Ocean Observing Systems (JAFOOS). This facility specialises in the scientific design of ocean observing systems relevant to Australia's needs, and is an effort to maximise available, although limited, resources to ensure the best regional outcomes from scientific research and environmental monitoring.

Much more needs to be done to expand our present ocean observing systems to adequately monitor our marine environment. In keeping with the Federal Government's Marine Science & Technology Plan and Ocean Policy requirements, JAFOOS builds on the extensive research and development capabilities of both CSIRO and BMRC to assist in the implementation of operational marine systems and baseline ocean monitoring networks. It will support and enhance Australia's overall marine monitoring capacity, and especially the operational marine observations program of the Bureau of Meteorology.

Dedicated to developing and improving the Australian Ocean Observing System (AOOS), JAFOOS also supports the design and development of other intimately related monitoring and prediction systems, including those of the: Global Ocean Observing System (GOOS), Global Climate Observing System (GCOS), Global Sea Level Observing System (GLOSS), World Climate Research Program (WCRP) and Global Ocean Data Assimilation Experiment (GODAE).

It is this coordinated effort of working with international partners that is giving Australia its best opportunity of developing an ocean observation and forecasting capability.