Gases and seabed fluid fluxes at the Panarea shallow hydrothermal vents (Aeolian Islands)

CO2 leaking into the shallow sediments and overlying seawater is partitioned in different forms, each migrating at its own rate and having potentially different impacts. To begin with the CO2 gas will migrate through the shallow subsurface either alone as a free gas or together with associated deep fluids (e.g. brines), with the free-phase CO2 equilibrating with the surrounding pore waters/associated brines. Migrating upward these fluids will enter the base of the water column, with the release of gas bubbles (and possibly associated waters) from the sediments into the overlying seawater. The bubbles will rise in the water column creating what is known as a bubble “flare” with the CO2 in the bubbles dissolving in the surrounding surface water as they rise. Depending on the depth and the chemical/physical characteristics of the water column, these bubbles may or may not reach the water surface. Any co-migrating water/brine will also be released into the water column, creating a plume having a chemical composition that is distinct from the surrounding seawater, consisting of dissolved gases (mainly CO2), elements in the original brine, and elements liberated via CO2-induced water-rock interaction. The height that this dissolved plume will reach in the water column will depend on the original flow rate across the sediment-water interface and the density contrast between the plume and surrounding seawater. Both the gas-induced and water plumes will then migrate laterally and vertically as a result of the local currents, water column stratification, and density effects, meaning that there is the potential for impact both in the near and far field for pelagic organisms, both in terms of a lower pH and the possibility of elevated concentrations of toxic elements. This study was carried out in the framework of two EC funded projects, RISCS and ECO2 related to research on sub-seabed CO2 storage as climate change mitigation strategy, and potential impact on marine ecosystems. Here, we investigated how CO2-leakage, a risk associated with subseafloor CO2-storage, can affect physical and chemical characteristics of the surrounding ecosystem. We studied the Panarea natural laboratory site (Aeolian Islands), where natural CO2 is leaking from the seafloor into the overlying water column, as an analogue for a leakage scenario

Preliminary Experiments and Modelling of the Fate of CO2 Bubbles in the Water Column Near Panarea Island (Italy)

Although CO2 capture and storage in deep, offshore reservoirs is a proven technology, as illustrated by over 15 years of operation of the Sleipner site in the Norwegian North Sea, potential leakage from such sites into the overlying water column remains a concern for some stakeholders. Therefore, we are obliged to carefully assess our ability to predict and monitor the migration, fate, and potential ecosystem impact of any leaked CO2. The release of bubbles from the sea floor, their upward movement, and their dissolution into the surrounding water controls the initial boundary conditions, and thus an understanding of the behavior of CO2 bubbles is critical to address such issues related to monitoring and risk assessment. The present study describes results from an in situ experiment conducted in 12 m deep marine water near the extinct volcanic island of Panarea (Italy). Bubbles of a controlled size were created using natural CO2 released from the sea floor, and their evolution during ascent in the water column was monitored via both video and chemical measurements. The obtained results were modelled and a good fit was obtained, showing the potential of the model as a predictive tool. These preliminary results and an assessment of the difficulties encountered are examined and will be used to improve experimental design for the subsequent phase of this research

Developments since 2005 in understanding potential environmental impacts of CO2 leakage from geological storage

This paper reviews research into the potential environmental impacts of leakage from geological storage of CO2 since the publication of the IPCC Special Report on Carbon Dioxide Capture and Storage in 2005. Possible impacts are considered on onshore (including drinking water aquifers) and offshore ecosystems. The review does not consider direct impacts on man or other land animals from elevated atmospheric CO2 levels. Improvements in our understanding of the potential impacts have come directly from CO2 storage research but have also benefitted from studies of ocean acidification and other impacts on aquifers and onshore near surface ecosystems. Research has included observations at natural CO2 sites, laboratory and field experiments and modelling. Studies to date suggest that the impacts from many lower level fault- or well-related leakage scenarios are likely to be limited spatially and temporarily and recovery may be rapid. The effects are often ameliorated by mixing and dispersion of the leakage and by buffering and other reactions; potentially harmful elements have rarely breached drinking water guidelines. Larger releases, with potentially higher impact, would be possible from open wells or major pipeline leaks but these are of lower probability and should be easier and quicker to detect and remediate

Water column monitoring at CO2 leaking sites near Panarea Island

The fate and transport of geologically produced CO2 that leaks from the sea floor into the overlying water column has numerous important implications related to large scale carbon cycling and potential impact on marine organisms, and is of interest for the development of improved monitoring techniques and strategies for offshore Carbon Capture and Storage (CCS) sites. The CO2 leakage areas off the east coast of Panarea Island, Italy provides an excellent environment to study these processes given the wide range of different flux rates in relatively shallow water. The water column at this site was monitored using two completely different but complementary approaches, continuous monitoring along short 2D transects using GasPro pCO2 sensors and discrete seasonal sampling along a 700 m transect crossing multiple leakage areas. Results are discussed in terms of the movement of CO2, and associated tracers, in the water column

The Panarea natural CO2 seeps: fate and impact of the leaking gas (PaCO2) ; R/V URANIA, Cruise No. U10/2011, 27 July – 01 August 2011, Naples (Italy) – Naples (Italy)

Carbon capture and storage (CCS), both on- and offshore, is expected to be an important technique to mitigate anthropogenic effects on global climate by isolating man-made carbon dioxide (CO2) in deep geological formations. In marine environments, however, the potential impacts of CO2 leakage, appropriate detection methods, and risk and pathways of atmospheric emissions are poorly defined. The natural CO2 gas seeps that occur in the relatively shallow waters off the coast of Panarea Island (Aeolian Islands, Italy) can be studied as a large-scale, real-world analogue of what might occur at a leaking offshore CCS site and what tools can be used to study it. The oceanographic survey PaCO2 was performed aboard R/V Urania from 27 July – 01 August 2011 (Naples – Naples). The project’s ship-time was funded by Eurofleets, with work being performed as a sub-project of the Seventh Framework Programme projects “ECO2” and “RISCS”, which provided subsidiary funding. Large amounts of data and samples were collected during the cruise which will be interpreted in the coming months, with preliminary results detailed here. Of particular importance was the discovery of much larger areas showing gas seepage than previously reported. Interdisciplinary measurements were performed at the Panarea seepage site. The international team of scientists onboard R/V Urania performed complementary sampling and measurements for biological, chemical, and physical parameters throughout the area. Together with the dedication of R/V Urania’s Captain and crew, and the eagerness and cooperation of the scientific crew, we were able to obtain excellent scientific results during this six-day cruise