coastal and marine natural values of the kimberley - wwf - Australia

32. Coastal and Marine Natural Values of the Kimberley5.3 OCEANOGRAPHY ANDGEOMORPHOLOGY5.3.3 Meta-scale oceanographyThe Indonesian Throughflow (ITF)heavily influences oceanography andclimate in the Kimberley region, as it hasdistinct seasonal variation in strength.When active, it transports a 200-300mthick layer of warm low-density surfacewater from the Timor Sea into the IndianOcean and feeds the South EquatorialCurrent (Figure 9).The ITF is strongest during the southeastmonsoon (Austral winter, approx. Juneto September), and weakest during thenorthwest monsoon (Austral summer,approx. November to March). Duringthe winter dry season when southeasttrade winds blow from the Australianmainland, the ITF empties water from theeastern Indonesian archipelago. Surfacewaters in oceanic areas of northwestAustralia actually cool by several degrees(Hobday, 2001) and overall chlorophyll alevels throughout the region (includingthe Indonesian Archipelago) increasesubstantially 4 . Important mixing andalgal bloom events occur at locationssuch as the Strait of Ombai (Moore &Marra, 2002) and there is evidence oflarge scale upwelling in the EasternBanda Sea south of Java (Moore &Marra, 2000). The ITF also channelswater south along the entire NorthernKimberley and Dampierland coast, andfeeds the Leeuwin Current which mostlyruns south of the northwest Cape.During the summer wet season when thenorthwest monsoon occurs, this patternchanges abruptly. Strong northerlywinds force surface waters into theeastern Indonesian archipelago (Moore& Marra, 2000) and the ITF weakensand in some cases, may even ceasealtogether, especially under the influencesof the easterly flowing Indian OceanCountercurrent that occurs in winter justsouth of the equator.Figure 9: Simplified seasonal oceanography of northwest Australia showingmajor current systems (top) and productivity (bottom). During the southeasterlymonsoon (winter dry season), productivity is very high, fuelled by upwelling in theIndonesian archipelago and strong currents. During the northwest monsoon (wetseason), productivity falls and currents abate though productivity remains relativelyhigh at offshore islands due to upwelling, and near the coast as a consequence ofriver plumes.4DRAFT: SeaWiFS movie of surface Chlorophyll, 1997-2001 in the Australian Region.