Multi-decadal Ocean Change

Due to the high climate-sensitivity of the ocean boundary current systems off the north and west coasts of Australia, a better understanding of the multi-decadal climate change in the Indo-Pacific Ocean is crucial for understanding regional marine impacts off the coast of Northern Territory and Western Australia.

The Indonesian Throughflow transport is known to vary with regime shifts of the Indo-Pacific climate system; and the changes induce heat content anomalies that propagate to the Southwest Indian Ocean, and contributes to mighty decadal changes in sea level near the coast of Australia, such as the multi-decadal weakening of the Leeuwin Current between 1960s and 1990s, and its rebound of the 1990s.

The rebound of the Leeuwin Current strength since the 1990s appears to be highly related to the more frequent occurrences of the marine heat waves (Ningaloo Niño) over the last decade. In Australia the National Reference Station at Rottnest is one of only three national multidecadal observing points around our coast, and it has captured temperature and salinity change over the past 6 decades.

The data has been used to validate oceanographic models and provide valuable long term data sets to assess ecological change on shorter scales. Other multidecadal observing networks include the XBT network in the Indian Ocean over the past three decades and the state govt agencies such as the tide gauge sea level data have been proved to be crucial to our understanding of multidecadal variations of boundary current systems.

An objective of WA-IMOS is to create an ocean observing platform for understanding the links in the physics in the system and the biological responses. The node’s science is also well connected to the broader Indian Ocean, through national and international collaborations.

The following high-level science questions will guide the Western Australia IMOS observing strategy in this area:

  • What are the vertical structures of the long-term trend in ocean temperatures in the south-east Indian Ocean?
  • How do the multi-decadal changes in Indo-Pacific climate affect the Leeuwin Current and regional air sea coupling?
  • Do the long term changes of the Indonesian Throughflow, the Leeuwin Current and the wind regimes affect eddy energetics, coastal upwelling, ocean production, and marine ecosystem?