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RELATED INFORMATION:ARTICLES
OBSERVING THE OCEANS AROUND AUSTRALIA
(Images required: , cutaway of an xbt)
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 to Torres Strait
Sometimes scientists or oceanographic technicians on board
make extra measurements to determine the velocity of current,
in particular the narrow currents near the coasts.
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:
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.
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