Estimation of CO2 Sources and Sinks

Ocean CO2 Sources and Sinks - An Estimate

Australia’s Exclusive Economic Zone (EEZ) extends 200 nautical miles (about 370 km) beyond its shoreline, and encompasses an area about twice its land area. An estimate of the amount of CO2 entering or being produced in the zone (CO2 flux) is important in understanding the role of these ocean waters in CO2 cycling.

The CO2 flux has been estimated by using Geographic Information Systems (GIS), mathematical models and data from the World Meteorological Organisation’s digital database, the World Weather Disk (WWD). The GIS was used to map the extent of the EEZ and to enable area calculations. Data for 1987, the latest year of records on sea-surface temperature and wind velocity, were extracted from the WWD and matched to their location within the EEZ.

Calculations of average CO2 fluxes in ‘cells’ of 50 x 50 kilometres suggest that Australia’s oceans represent a sink for about 87 million tonnes of CO2 per year, representing a moderate ‘sink’ for CO2. In comparison, Australia’s man-made CO2 emissions amounted to about 420 million tonnes in 1990.

The method used to determine total CO2 mass for the Australian EEZ has been extended to the WWD data for the World’s ocean areas. The inputs are sea-surface temperature, wind velocity and direction and a global average value for the flux of CO2in the atmosphere. A GIS was used to organise the data and to aid in the generation of a seasonal CO2 exchange surface for 48 years of data.

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