Your access to IMOS Expendable Bathythermograph (XBT) data discovery and exploration is through the Australian Ocean Data Network (AODN) Portal.

Brisbane to Fiji

On each section up to 100 XBT casts are made which enables the fine temperature structure to be fully resolved down to 800m.  In the section below we see the East Australian Current (EAC) at the western (Brisbane) end of the section.  This is represented by the isotherms (contours of temperature) sharply rising towards the surface.

Sydney to Wellington

A typical example of a section along the Sydney to Wellington track is shown below.  The black dots show the locations of the XBT casts - they are more closely spaced at the Sydney end to capture the full structure of the EAC and eddies.  The upper panel shows the sea surface temperature (SST) and the middle panel shows the sea surface height – both obtained from satellite measurements.  The most notable features are the 2 eddies that the ship track cuts through.  The first one, near Sydney, forms part of the East Australian Current.  The lower panel gives the temperature as obtained from the XBT casts.  We are able to see the depth structure of the 2 eddies – they reach down to at least 800m, the maximum depth of the XBT profiles.

The 4 temperature sections collected along PX30 and PX34 in 1993.  The EAC and eddies are nearly always present at the western end of the sections.  An unusual occurrence was in May 1993 when the EAC was very weak.

Average Conditions

After collecting many measurements on each section we are able to calculate the average temperature pattern for each ocean region.  The figure below shows the mean (or average) temperature (the contour lines) and the variability (standard deviation) along each section of the Tasman Box.  The presence of the EAC is clearly shown by the high variability off Sydney.  These temperature patterns show that the current breaks up into large eddies by the time it reaches the Sydney region.

Fremantle to Indonesia

Another very important set of measurements are made between Fremantle and Indonesia.  Here we are able to estimate the flow of water coming from the Pacific Ocean into the Indian Ocean through the Indonesian Islands.  The strength of this flow has a major influence on the climate of Western Australia and is a central factor on the distribution of ocean properties around the global ocean.