Volcanic CO2 seep geochemistry and use in understanding ocean acidification

Ocean acidification is one of the most dramatic effects of the massive atmospheric release of anthropogenic carbon dioxide (CO 2 ) that has occurred since the Industrial Revolution, although its effects on marine ecosystems are not well understood. Submarine volcanic hydrothermal fields have geochemical conditions that provide opportunities to characterise the effects of elevated levels of seawater CO 2 on marine life in the field. Here, we review the geochemical aspects of shallow marine CO 2 -rich seeps worldwide, focusing on both gas composition and water chemistry. We then describe the geochemical effects of volcanic CO 2 seepage on the overlying seawater column. We also present new geochemical data and the first synthesis of marine biological community changes from one of the best-studied marine CO 2 seep sites in the world (off Vulcano Island, Sicily). In areas of intense bubbling, extremely high levels of pCO 2 (> 10,000 μatm) result in low seawater pH (