Assessment of Sub Sea Ecosystem Impacts

Publication Overview

This report looks at the potential impacts of leaks from a subsea CO₂ storage project.It addresses the use of natural analogues, and estimates the relevance of potential CO₂ storage leaks against the effects from natural analogues. It highlights knowledge gaps that exist, and also indicates any species that could be particularly vulnerable to CO₂ leaks from storage operations.

Publication Summary

The report has highlighted the areas of the world that are likely to be used for sub-seafloor geological storage in the near future, which are: West Africa, Western Europe, South East Asia and Oceania.

It is noted that there are sub seafloor leaks of CO₂ from natural sources which are several orders of magnitude lower than the ocean surface sequestration of CO₂, and further that leaks from sub seafloor geological storage of CO₂ are unlikely to equate to even 2% of this level of naturally occurring leakage. These natural analogues (such as volcanic arcs and hydrothermal vents) occur in many of the areas where subsea geological storage is likely to take place, and can therefore be used as analogies for leaks from geological storage reservoirs. This will allow operators to perform assessments on the likely implications of leakage events before storage commences. It also suggests that any leaks in these areas will have a relatively low significance, as the leaked CO₂ will represent a lower percentage change to the seawater chemistry in these areas.

It will be necessary to identify a range of key indicator species to act as target organisms for monitoring programmes. Such monitoring programmes will prove beneficial in early detection of leakage, should it occur, and detailed study of these organisms will facilitate greater understanding of the potential risks of longer term exposure. Associated with this study will be the determination of exposure limits and recovery rates of affected species. This will allow much more accurate quantification of risk during the initial risk assessment and site characterisation process.

It should be noted that the potential immediate impacts on ocean ecosystems of CO₂ currently released into the atmosphere is significantly higher than any potential impacts of leakage from storage reservoirs in the future. Predictions of potential impacts in the future cannot be quantified; site selection criteria will focus activities on reservoirs that are likely to perform to high standards, minimising the risks of leakage and ecosystem impacts.