Climate Change and Weather Extremes
Ocean currents in the SA-IMOS region appear to be influenced by ENSO/El Niño events in the Pacific, with evidence suggesting that the thermocline is raised by 170 m or so leading to enhanced upwelling off the Bonney Coast and Kangaroo Island. In addition, evidence suggests that such El Niño events also reduce the wintertime Leeuwin Current and eastward shelf currents along Australia’s southern shelves.
In addition, changes in the position of atmospheric high and low pressure systems driven by the Southern Annular Mode affect the influence and strength of westerly/easterly winds in the Southern Ocean. Changes of winds in the Southern Ocean (and, indeed, the Pacific and Indian Oceans) may be important to changes in wind stress curl and thus Sverdrup transport and strength of boundary currents that impact the SA-IMOS Node region.
The following high-level science questions will guide the South Australia IMOS observing strategy in this area:
a) What is the impact of ENSO events on upwelling, downwelling and alongshore shelf currents? What other factors drive upwelling variability in the region (e.g. variability in the SAM)? Data sets needed are the continuation of the SA-IMOS and WA-IMOS observing systems along with additional deep water (to 300 m) CTD/seaglider transects. These data (and shelf and slope moorings) will be collected for both the Kangaroo Island and Bonney Coast regions to be compared to hydrodynamic model output so as to determine the above.
b) How do long-term changes in wind stress curl affect the boundary currents important to the region? The data needed here will include the SA-IMOS moorings along with those off the southern tip of Tasmania and Perth. The required meteorological data/modelling is collected/available elsewhere. The effects of changes in the wind stress curl will be determined using the data collected and assimilating models that the node will build in the next decade.
c) What is the role of weather extremes in the shelf currents, cross-shelf exchange? Over the next 10 years, we expect that the individual oceanographic processes will become better documented and understood. However, SA-IMOS may need to adapt some of its sampling strategies to examine the effects of extreme events.