To determine the impact of a CO2 leak on seafloor ecosystems and their function.
Laboratory experiments are widely used to find out how marine organisms, communities and their processes are likely to respond to elevated levels of CO2. These data have yet to be tested under more realistic field conditions and so the confidence with which we can predict the likely response of marine ecosystems to a CO2 leak is low. This work package aims to remedy this by carrying out the following tasks:
Task 4.1: Determine the impact of a controlled CO2 release on the structure and diversity of a seafloor community (Plymouth Marine Laboratory, British Geological Survey).
Over the course of the release experiment divers were used to collect a series of core samples from the seabed. These samples are now being analysed in the laboratory to determine the type and quantity of organisms (from microbes to large shellfish and worms) living in each of the 4 different exposure zones at each of the different time points during the 1 month exposure to CO2 as well as after the CO2 release had been stopped. By doing this we will be able to see any changes that have occurred in the structure, activity and diversity of seafloor communities in response to the CO2 release. Preliminary findings seem to indicate that the impact of the CO2 is largely restricted to the zone immediately above the release point and that the sediments further away remain unaffected. At the beginning of May this year (2013), divers will return to the site and will collect a final series of cores. By analysing these cores will see if the area immediately around the release point has been able to recover fully from any impacts caused by the CO2.
Task 4.2: Assess the physiological response of different organisms to varying levels of CO2 to identify which parts of the seafloor community are likely to be most vulnerable to high levels of CO2 (University of Southampton, Plymouth Marine Laboratory)
During the QICS field experiment cages (Figures 1 and 2) of mussels and scallops we deployed around the experimental site to establish the effects of any released CO2 plume on the physiology of bivalve shellfish. During the experiment samples were recovered from the sea bed at regular intervals by divers and brought to the surface. In addition, divers collected samples of burrowing urchins from around the release site and at distances away from the point of release. These samples have provided tissue samples that are currently being processed at the University of Southampton for analysis of changes in gene expression. Changes in expression of genes coding for proteins required for cellular acid/base balance (sodium potassium ATPases), cellular carbon dioxide regulation (carbonic anhydrases) and detoxification (metallothioneins) are being measured. The data from these samples will be available to the science team by the end of 2013.
Task 4.3: Determine the impact of a controlled CO2 release on key biological process rates in seafloor sediments (Scottish Association for Marine Sciences)
In this part of the project, we calculate the impact of exposure to elevated levels of CO2 on the rates of key biogeochemical processes which occur in seafloor sediments. We measured directly the exchange of oxygen, dissolved inorganic carbon, alkalinity, calcium and nutrients between the sediment and the overlying seawater. These data provide information about the extent to which total organic matter turnover rates and the rate that calcium carbonate dissolves within the sediment is affected by exposure to high CO2 conditions.
Using the observations and measurements collected during the controlled CO2 release we are calculating the impact of exposure to elevated levels of CO2 on the rates of key biogeochemical processes which occur in seafloor sediments. We used various techniques, from sediment chamber incubations (see Figure 3) to state-of-the-art micro-profiling to directly measure the exchange of oxygen, dissolved inorganic carbon, alkalinity and nutrients between the sediment and the overlying seawater as well as sediment distributions of pH and oxygen. We also measured the exchange rates of metals between the sediment and the water, as well as the mobility of metals within the water trapped in the sea-floor sediments (see Figure 4). These data are already providing important information about the extent to which total organic matter turnover rates and the rate of calcium carbonate dissolution within the sediment is affected by exposure to high CO2 conditions, as well as the rate at which fundamental changes in the sediment, such as pore water pH, occur and then recover after the exposure to high CO2 conditions.