Multi-decadal Ocean Change

The column inventory of anthropogenic CO2 for the oceans (Sabine et al., 2004)
The column inventory of anthropogenic CO2 for the oceans (Sabine et al., 2004)

The global oceans constitute the primary source of thermal inertia of the climate system and also contain the largest pool of active carbon in our planetary system. Thus, they are a key player in setting the rate at which anthropogenic greenhouse gases build up in the atmosphere and how fast the surface warms in response to the radiative forcing that results. Tracking and understanding the processes by which both carbon and heat are sequestered into the global oceans is therefore essential for monitoring rates of global change and for informing Earth System Models (ESMs) used to project future climate.

Tracking and understanding the processes by which heat and carbon are sequestered into the global oceans is essential for the detection, interpretation and projection of climate change. Knowledge of regional and global ocean circulation throughout the full ocean depth is also needed to determine where and for how long heat and carbon are sequestered in the ocean.

A major impediment to understanding and modelling of the Southern Ocean, for example, is the large uncertainty in present estimates of air-sea fluxes of heat, momentum and freshwater; direct high-quality measurements such as those provided by the Southern Ocean Flux Station (SOFS) are critical to identify biases in flux products derived from models and remote sensing.

IMOS uses a number of platforms to collect the observations needed to track multi-decadal change in Australia’s oceans, providing broad-scale observations of temperature, salinity, velocity (and increasingly oxygen and chlorophyll) from Argo floats (Argo facility) and sensors deployed on marine mammals (AATAMS); physical and biogeochemical sampling of the upper ocean along ship of opportunity lines (SOOP); and deepwater moorings deployed in key boundary currents and interbasin exchanges in the Indonesian Throughflow, the East Australian Current, and Antarctic polynyas.  

The time series of atmospheric, physical oceanographic and biogeochemical variables provided by the Southern Ocean Flux Station (SOFS) and Southern Ocean Time Series (SOTS) stations are uniquely valuable (ABOS) because they provide the only high-quality, continuous observations of these properties in the Southern Ocean.

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

Ocean Heat Content

  • How are the global energy balance and the broadscale ocean temperature patterns changing? What is the impact on regional sea level rise? 
  • How are open ocean temperature changes related to temperature changes on the shelf?
  • How does ocean heat content vary with time, location, and depth?  Do earth system models capture the evolution of ocean heat content, and if not, why not?

Global Ocean Circulation

  • How is the overturning circulation of the Southern Ocean changing with time?
  • How and why are the major current systems in Australian waters (including the East Australian Current, Indonesian Throughflow, Leeuwin Current and Antarctic Circumpolar Current) changing?

Global hydrological cycle

  • How is ocean salinity changing and what do changes in salinity tell us about the response of the global hydrological cycle to climate change? 
  • How is the salinity of the deep ocean changing and what do these changes say about ocean – ice shelf interaction and/or changes in high latitude precipitation?

Global carbon budget

  • What is the global ocean carbon inventory and how is it changing on decadal timescales?
  • What is the seasonal through interannual variability in air-sea CO2 fluxes for Australian shelves and regional seas and the Southern Ocean?
  • What are the key biological and physical processes driving air-sea CO2 exchange in the Southern Ocean and Australian region and how sensitive are they to climate change?