Ocean Acidification

The ongoing oceanic uptake of anthropogenic carbon dioxide  (CO₂) is significantly altering the carbonate chemistry of  seawater, a phenomenon referred to as ocean  acidification. Experimental manipulations have been increasingly  used to gauge how continued ocean acidification will potentially  impact marine ecosystems and their associated biogeochemical cycles  in the future; however, results amongst studies, particularly when  performed on natural communities, are highly variable, which in part  likely reflects inconsistencies in experimental approach. To  investigate the potential for identification of more generic  responses and greater experimentally reproducibility, we devised and  implemented a series of highly replicated (n = 8), short term (2–4  days) multi-level (&geq; 4 conditions) carbonate chemistry/nutrient  manipulation experiments on a range of natural microbial communities  sampled in Northwest European shelf seas.  Carbonate chemistry  manipulations and resulting biological responses were found to be  highly reproducible within individual experiments and to a lesser  extent between geographically different experiments. Statistically  robust reproducible physiological responses of phytoplankton to  increasing pCO₂, characterized by a suppression of net  growth for small sized cells (< 10 μm), were observed  in the majority of the experiments, irrespective of nutrient  status. Remaining between-experiment variability was potentially  linked to initial community structure and/or other site-specific  environmental factors. Analysis of carbon cycling within the  experiments revealed the expected increased sensitivity of carbonate  chemistry to biological processes at higher pCO₂ and hence  lower buffer capacity. The results thus emphasize how  biological-chemical feedbacks may be altered in the future ocean.

Richier, S., Achterberg E. P., Dumousseaud C., Poulton A. J., Suggett D. J., Tyrrell T., Zubkov M. V. & Moore C. M., 2014. Carbon cycling and phytoplankton responses within highly-replicated shipboard carbonate chemistry manipulation experiments conducted around Northwest European Shelf Seas. Biogeosciences Discussions 11:3489-3534. Article.