Atmospheric carbon dioxide (CO2 ) has risen 31% since pre-industrial times, with 30% being absorbed by the surface ocean (Sabine et al., 2004; Raven et al., 2005), resulting in a reduction of pH 0.1 in surface seawater (Haugan & Drange, 1996). If CO2 emissions continue to rise in an IS92a “business as usual” scenario, models predicted a further decrease of 0.3-0.5 in pH by 2100 (Caldeira & Wickett, 2003). Thus far, little is known about the potential effect of ocean acidification on the nutrient biogeochemistry in coastal sediments. In our work we use a mesocosm approach to investigate whether there are changes in nutrient cycling in sediment columns which are fed with seawater at different pH’s. We aim to focus on whether processes of organic mineralization and nitrogen cycling (denitrification, nitrification, anammox etc) are affected and if so, use the experimental data to model whether ocean acidification may be responsible for changes in marine N budgets.

Traditionally biogeochemical cycling of N within shelf sediments has been assumed to account for 50 – 70% of oceanic N loss (Codispoti et al., 2001). This estimate neglects the contribution to N loss from permeable sediments, which are characterized by advective rather than diffusive transport. Recent research suggests that permeable sediments may play a more important role in biogeochemical cycling than previously expected. While working with permeable sediments to investigate the effects of ocean acidification I hope to further determine the role these sediments play in nitrogen cycling processes. This will involve comparing different types of permeable sediments (for example carbonate vs silicate sediments) as well as investigating whether some sediments are more sensitive to changes in seawater pH and carbonate chemistry.