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The most extensive site of oceanographic investigation in the Timor Sea is the area around the BHP Jabiru Oil Field, located southwest of this area, and much of the regional data presented below are from these studies. BHP also commissioned studies of the currents at the Elang Field, located to the southeast (BHPP, unpublished data), and these findings are also summarised below. Water temperature Seawater temperature profiles have been measured over the Continental Shelf at South Bank, Elang and Jabiru Oil Field. The surface waters at South Bank are similar to those at Elang with well mixed surface waters with temperatures of 30oC and bottom waters of between 27oC and 30oC. Bottom temperatures are slightly lower at Elang (between 26oC and 27oC). This reflects the shallower depth at South Bank and also the mixing due to the interaction between the thermocline and the slope of the bank. The temperature profile at Elang is similar to that at Jabiru. During summer there is a weak thermocline with a decrease in temperatures of 3o to 4oC from the warmer surface waters to the cooler mid-depth to bottom waters. In winter, the upper 70 metres of water are isothermal, with no significant variation in the vertical temperature profile. Earlier studies, undertaken by the Commonwealth Scientific Industrial Research Organisation's (CSIRO) oceanographic studies (see Cresswell et al., 1993), found a similar vertical pattern, suggesting that this is characteristic of shelf waters. The waters over Big Bank are also well-mixed with surface temperatures of about 30oC. The temperatures were found to be variable and oscillate between 27oC and 31oC. Bottom-water temperatures were also found to oscillate between 23oC and 29oC. Temperature profiles taken in deeper waters off the Shelf, at the Laminaria field and south of Big Bank, suggest similar surface temperatures (27oC to 31oC) and cooler bottom temperatures (22oC to 25oC, and down to about 10oC ). This reflects the greater depths (>150 metres) at these sites. Waves and tides Total waves are composed of sea-waves, locally generated in response to wind conditions, and swell-waves that result predominantly from storms in the Southern Ocean or southern portion of the Indian Ocean. High sea-wave conditions will normally occur within 250 km of tropical cyclones and swell-waves may occur at further distances. Tides in the Echo Shoals area, the northeast region of the Sahul Shelf, are semidiurnal, with a typical tidal range of 4 metres at springs and 1.8 metres at neaps (Australian National Tide Tables - Echo Shoals). Tidal transformations for the Laminaria location indicate a 10 percent increase in amplitude, and a phase-lead of 40 minutes (Woodside, 1995). Tidal currents are expected to flow east-northeast, and ebb west-southwest, in the upper 100 metres of the water column, while flooding southeast, and ebbing west-northwest in the lower portion of the water column (Pinceratto and Oliver, 1996). Tidal current speeds in the order of 0.6 ms-1 (springs), and 0.2 ms-1 (neaps), are anticipated for the region. Currents Surface currents are expected to reflect seasonal wind regimes, with easterly to northeasterly currents in summer, and in winter westerly to southwesterly currents. Local wind driven surface currents may attain speeds of 0.6 ms-1 during monsoonal or Trade Wind surges. More typical speeds would be in the range of 0.2-0.3 ms-1. The Timor Sea region is influenced by the Pacific-Indian Ocean Throughflow, which contributes to the westward flowing South Equatorial Current (between 8o and 15o S latitude), and floods the North-West Shelf with relatively warm, low-salinity water. This current may introduce a small (0.1 ms-1) southwesterly component to the current regime in the Karmt Shoal area. The Through-flow appears to be subject to the pronounced inter-annual variations of the El Niño-Southern Oscillation (ENSO) events.
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