QUARTERLY FOCUS
June 2010

Understanding Australia's Oceans

Australia manages around 14 million km2 of ocean - an area roughly twice the size of the Australian continent. We have over 8,000 islands and nearly 60,000 kilometers of coastline.

We are a maritime nation.

Why are the oceans so important?
Since the beginnings of human society, the oceans have been a critical factor in our survival, development, interactions and general wellbeing.

Oceans cover more than 70% of the Earth’s surface. They are a major source of food, and contain a huge component of the earth’s biodiversity. Oceans provide us with minerals, energy, chemical and biological inputs and carry the vast shipping fleets that drive global trade and commerce.

The oceans also have an important role as key drivers of earth’s weather and climate, transporting huge quantities of heat around the planet. Heat, water and energy are transferred from the ocean to the atmosphere and vice versa, and the amount of heat and water in the atmosphere are primary factors in determining our weather and climate.

 

Early knowledge of the oceans
Modern technology has allowed us to learn a great deal about the ocean - currents, temperatures, and salinity, and we have the ability to monitor and forecast tsunamis, tides and waves. Early seafarers had no such knowledge and remained at the mercy of wind, waves and currents.

Early poets, philosophers and scientists speculated about the source of the oceans’ power, and the drivers of ocean processes. Greek poet Homer attributed Odysseus’s maritime problems to the Greek god of the sea, Poseidon, which was as good an explanation as any at the time:

Then Jove raised the North wind against us till it blew a hurricane, so that land and sky were hidden in thick clouds, and night sprang forth out of the heavens. We let the ships run before the gale, but the force of the wind tore our sails to tatters, so we took them down for fear of shipwreck, and rowed our hardest towards the land.

In 350BC, the philosopher and scientist Aristotle was the first to suggest that water cycles from ocean to air to land to ocean again, which is most fundamental to the living planet.

As traders and explorers voyaged over wider and wider sea areas, knowledge of the atmosphere and oceans increased. In the early 1500’s European ships began riding a powerful ocean current from the Caribbean to Spain. This current, now known as the Gulf Stream, was later studied and mapped by Benjamin Franklin.

In 1805, Sir Francis Beaufort, an admiral in the British Navy, developed a scale that ranked winds depending on their physical effects. For example, the number 0 is given when the sea is like a mirror, meaning there is no wind. The number 12 or above is given when the air is filled with sea spray and the sea is completely white with foam, which means the wind is very strong at 64 knots or more. Variations of the Beaufort scale are still used today.

Why do we monitor the oceans?

Forecasting the weather: The temperature (heat) of the ocean is a major factor in driving global atmospheric systems (lows, highs, fronts, etc), and thus influencing the weather we experience on a daily basis.

The Bureau takes measurements from the oceans and inputs the data to advanced computer models which generate forecasts. Meteorologists use the information from the computer models to prepare forecasts, and warnings about wind, waves, swell and severe ocean weather.

Climate forecasts and projections: The Bureau uses information about ocean conditions to help detect and forecast major climate signals like El Niño and La Niña.

Protection of life and property: Coastal protection and the safety of human life and property require risk analyses as well as forecasts and warnings of events such as extreme waves, storm surges and tsunamis.

Planning and operations for the public and marine industries: Many different marine industries use the Bureau’s information about ocean conditions (temperatures, salinity, currents, sea level and tides, waves) so they can work safely and efficiently:

1. The offshore oil and gas industry use information about wind, waves and currents to design and construct offshore rigs. They closely monitor the forecasts during daily operations.
2. Port and harbour operators, as well as shipping management, depend on accurate tide, current and wave information and predictions for safe and efficient operations.
3. Fisheries and aquaculture require information about the temperature and salinity of the ocean because it directly affects the growth rate, health and survival of marine life.
4. Coastal engineering and construction organisations use climatological information and information about winds, waves and currents for planning, design and operations.
5. Marine tourism and recreation require ocean and atmospheric climate information for design, planning and construction, as well as forecasts of weather, waves, tides, currents and sea temperatures for daily operations.
6. Maritime safety and rescue services are highly sensitive to extreme marine weather (winds and waves), as well as sea temperatures and currents.
7. Marine accident emergency response needs accurate analyses and forecasts of marine weather, waves and currents, for tracking and cleanup.
8. The shipping industry uses wind, wave and current information, for safety and to pick the best routes to save on fuel costs and reduce potential cargo damage.

What do we measure?

Sea surface temperature tells us how fast and how much heat and water moves between the atmosphere and the ocean. This information is used for short term weather prediction and predicting climate variability and change.

Temperature at depth gives us a measure of the total heat content of the upper ocean. The Bureau uses this information to forecast seasonal climate variability and climate variations over several years.

Surface currents can be measured by tracking the movement of sea surface drifting buoys, but more often they are derived from ocean models; they are used in many application areas, including maritime safety; marine accident response; maritime industry and commerce; recreation; and environmental management.

Salinity measurements help us work out how the ocean is circulating, and can be important to industries like fisheries and aquaculture..

Sea level and tide data are used by many coastal industries, including for port and harbour operations, as well as for climate studies and to help protect the coast from extreme events such as storm surges and tsunamis.

Ocean wave (sea and swell) measurements are of major concern in maritime safety, coastal management, tourism and recreation, marine operations and construction.

How do we measure it?

The Bureau monitors the oceans using satellites, wave buoys, drifting buoys, moored buoys, small upper ocean probes, profiling floats, as well as automated and manual observations from ships at sea.

Satellites are now a critical part of the Bureau’s observation, monitoring and forecasting systems. As well as visible and infrared cloud imagery, satellites measure air pressure profiles, upper air winds, sea surface waves and winds, sea surface temperature and salinity, sea surface heights (sea level), and ocean colour.

Australian and foreign ships volunteer to take routine weather observations whilst at sea. The data are transmitted to the Bureau and then put into computer models for weather and climate forecasting.

Drifting buoys take similar measurements but can float around between the shipping lanes. These extra measurements help fill in the gaps and give a better overall picture of the ocean conditions. The buoys are tracked by satellite, and their paths can be used to estimate surface currents.

Wave buoys measure wave height and wave period. The measurements are used in computer models to forecast wave heights.

Moored buoys are like weather stations in the ocean. They are anchored in water depths up to several kilometres and measure temperature, pressure, wind in the atmosphere as well as temperature, salinity and currents in the ocean. Some are also used to detect the passage of tsunami waves in deep water.

Profiling floats (Argo floats) sample the upper 2000m of the ocean measuring temperature and salinity. Every 10 days the floats will sink down to 2000m and then float back to the surface. As they move through the water column they record the temperature and salinity at different depths.

Small probes known as expendable bathythermographs (XBTs) are deployed from volunteer ships to record the temperature profile in the upper 800m of the ocean.

Tide gauges measure variations in local sea level.

Analysing and forecasting the oceans
From its establishment in 1908, the Bureau has been analysing and forecasting ocean wave conditions, traditionally using manual methods and nomograms. Today, the Bureau’s wave analyses, forecasts and climatologies are determined using sophisticated numerical models, and form a key component of our marine weather services.

Tidal predictions are made and issued by the Bureau’s National Tidal Centre in Adelaide, for over 100 ports and other locations around the Australian coastline, our island territories, as well as for several Pacific Island Countries. They are available on the web, in tide tables and from various other sources.

Tsunami warnings for Australia and its island territories are issued by the Joint Australian Tsunami Warning Centre, through the Bureau’s National Meteorological and Oceanographic Centre and its Regional Offices, as required and through a variety of media.

Resulting from the BLUElink project, the Bureau now issues, twice weekly, detailed analyses and forecasts of ocean conditions (temperatures, salinity, sea level anomaly and currents) forocean areas around our coastline and island territories, out to seven days in advance. These are available publicly in graphical form on the web, and as digital data sets via ftp.

- Peter Dexter 2010

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