Ecosystem Responses

Changes in the saturation state of aragonite for surface waters from the preindustrial era, represented by the year 1765, until year 2100. Values below one are undersaturated. The saturation states were modelled using the CSIRO carbon cycle model. Changes after the year 2000 based on the IS92a emission scenario have now been exceeded (Canadell et al., 2007), indicating a more rapid approach to undersaturation. Note the lowered saturation near Antarctic and the declines in saturation state further north. (Figure generated from CSIRO BGC model using the model simulations of Orr et al., 2005.)
Changes in the saturation state of aragonite for surface waters

Ecosystem change is anticipated via climate change impacts on temperature, the hydrologic cycle, and ocean circulation, and the influences of these changes on biogeochemical properties such as nutrient delivery and oxygen levels.  Direct forcing is also expected from the ocean acidification accompanying anthropogenic CO2 emissions.  Attention to the role of boundary currents and the overturning circulation provides a unifying approach for the assessment of what are likely to be diverse and complex impacts.

Australia’s two major poleward flowing boundary currents around, the East Australian Current and the Leeuwin Current, play a vital role in regulating the productivity of pelagic and benthic ecosystems. The warm boundary currents are generally nutrient poor with only patchy upwelling, leading to marine systems of low productivity.

Tropical and subtropical species can exist in relatively high latitudes, especially as the East Australian Current has increased in strength over the past 60 years. However, nutrient enrichment processes including cold-core eddies, shelf-edge upwelling, atmospheric dust inputs and topographic upwelling near capes, cause localised peaks in productivity. These productivity hotspots are critical to supporting diverse fisheries, seabirds, marine mammals and sea turtles.

Key knowledge gaps include understanding how lower trophic levels will respond to climate change, how this will influence the higher trophic levels, and the direct impacts of climate change on the distribution and abundance of higher trophic levels. 

The following high-level science questions will guide the Bluewater and Climate IMOS observing strategy in this area:

Circulation and nutrient fluxes

  • How does the large scale circulation control the links between the physical, chemical and biological environment?
  • What controls the temporal variation in biogeochemical fluxes of the ocean and how will they respond to climate variability?

Productivity

  • What is the relationship between rapid mixed-layer dynamics in the Southern Ocean, plankton production and carbon transports?
  • How do the changes in boundary currents (EAC and LC) and associated eddy fields influence ecosystem productivity?
  • How do cross-shelf exchange processes (boundary currents and shelf regions) influence coastal productivity and ecosystem connectivity?
  • How do changes in ocean acidification influence key vulnerable ecosystem components such as Southern Ocean calcifiers?

 Trophic connections

  • How do the different trophic levels respond to climate variability?
  • How are trophic levels connected and how might these connections be altered under a changing climate?
  • What are the most vulnerable regions and species (either particularly sensitive or unable to adapt) to changing environmental factors?