Relative potential impacts of local and global CO2 release: comparison of natural variability and trends to Carbon Capture and Storage (CCS) risk for Bass Strait, Australia

Chair: Zoë Hilton

Nick Hardman-Mountford(1), Jim Greenwood(1), Bronte Tilbrook(
2)

1 CSIRO Oceans & Atmosphere, Floreat, WA 6913, Australia
2 CSIRO Oceans & Atmosphere, Hobart, TAS 7001, Australia

Background
The rise in atmospheric CO2 levels since the preindustrial era has increased the concentration of carbon dioxide and pH of surface ocean waters beyond the envelope of documented changes over 10s of millions of years. Coastal regions are home to many calcifying organisms, including those with significant commercial importance. Their carbonate chemistry and resident populations experience wider ranges of variability than are typical for open ocean environments. Quantifying this range of variability is vital for assessing potential impacts of such ocean acidification on these populations.
Subsea geological storage of CO2 is a proposed mitigation strategy for industrial CO2 emissions. Geological containment structures are recognised as being highly secure gas stores. Nonetheless, assessments of possible leak scenarios are required to provide public and regulatory confidence in the approach.

Methods
Here we describe seasonal and interannual variability in the carbonate system of Bass Strait using a time series of carbonate-system variables collected by a ship-of-opportunity. This variability is contrasted with modelling results describing putative leak scenarios from stored CO2 reservoirs or pipelines into Bass Strait waters.

Findings
The range of seasonal variability in pH is of the order of changes in ocean pH over the past 200 years. Hence, organisms are now likely to be experiencing CO2 conditions that remain outside their pre-industrial seasonal range for most of the year. This could have severe implications for the highly biodiverse marine ecosystem of Bass Strait and particularly for the high-value shellfish industry in this region. In contrast, potential changes in pH from CCS-related CO2 leakage would be highly localised and, in most cases, unlikely to exceed the range of natural seasonal variability.

Conclusions
We conclude that subsea geological storage of CO2 may be an effective method of mitigating industrial CO2 emissions and the global impacts of ocean acidification on coastal ecosystems.