Multi-decadal Ocean Change
How will the key science questions be addressed?
How are the global energy balance and the large-scale temperature changing? What is the impact on regional sea level rise?
The Argo array provides the only available means of tracking changes in the large-scale subsurface ocean temperature and contribution to sea level changes. Re-processed historical satellite Sea Surface Temperature (SST) data are able to produce a long, accurate climate record of the ocean surface temperature. High precision altimetry captures the multidecadal changes in sea level and heat content. The calibration of satellite measurements is an essential requirement of the collection of climate quality data.
How is the Global Overturning Circulation (GOC) changing?
The changes in the basin-scale components of the GOC are monitored by frequently-repeated and high density XBT lines. Combined with satellite altimetry, repeat XBT lines can be used to build up long time series of major heat and volume transports. Monitoring important boundary flows at strategic locations is an efficient and cost-effective method of capturing aspects of the GOC.
What are the roles of the Antarctic Circumpolar Current (ACC) and the Indonesian Throughflow (ITF) in these changes? What are the causes?
We monitor the ACC using the Argo array, which provides a large scale description of the system, and the L’Astrolabe XBT section – one of only 3 sustained measurements across the ACC. The polyna array is able to monitor the production of Antarctic Bottom Water production in a major formation region. The Timor Strait mooring array (with the shelf section) forms part of a combined ITF monitoring array, and allows the full temporal changes in the ITF to be determined.
Sustained, global, high accuracy temperature and salinity measurements of the large-scale ocean structure from the Argo array are required to track changes in ocean the global hydrological cycle.
What is the response of the global ocean carbon cycle to climate change?
The Southern Ocean Time Series Site (SOTS) monitors the key processes controlling the Southern Ocean carbon sink. This remains the first and only attempt to collect these data in the Southern Ocean.
Can we quantify air-sea carbon fluxes and their variability?
The underway pCO2 measurements on the RV Southern Surveyor, L'Astrolabe and RSV Aurora Australis fill gaps in the global seasonal climatology of surface carbon fluxes. The L'Astrolabe and Aurora monitor seasonal and interannual changes of CO2 fluxes in the Southern Ocean.
How is the CO2 uptake on the Australian shelves and regional seas evolving?
The seasonal and interannual changes in coastal oceans and links to shelf and offshore variability in the CO2 system is documented by extending CO2 measurements in the coastal zone at selected National References Stations with the deployment of acidification moorings, building on the existing instrumentation at Yongala (Great Barrier Reef), Maria Island and Heron Island.
What are the key biological and physical processes involved in air-sea CO2 exchange in the Southern Ocean and Australian region? How sensitive are they to climate change?
Well-calibrated satellite ocean colour data sets are used extensively to determine drivers of carbon cycling and link the variability in CO2 and related parameters (nutrients, oxygen) observed on SOOP and moorings to regional and global scales. IMOS facilities collect a mixture of optical and biogeochemical parameters which can be used to improve global products.
How do changes in ocean acidification influence key vulnerable ecosystems such as the Southern Ocean, coral reefs and the continental shelves?
Measurements of CO2 fluxes from the underway systems on the research vessels (particularly the Auroa Australis and L’Astrolabe) and the coastal stations will provide inputs to understand the acidification influence in these regions. The SOTS mooring provides an integrated set of observations to resolve ecosystem responses that affect carbon cycling, and marine responses to ocean acidification in the Southern Ocean.