Effect of increased pCO2 on the planktonic metabolic balance during a mesocosm experiment in an Arctic fjord

[摘要] The effect of ocean acidification on the balance between gross communityproduction (GCP) and community respiration (CR) (i.e., net communityproduction, NCP) of plankton communities was investigated in summer 2010 inKongsfjorden, west of Svalbard. Surface water, which was characterized by lowconcentrations of dissolved inorganic nutrients and chlorophyll a (a proxyof phytoplankton biomass), was enclosed in nine mesocosms and subjected toeight pCO₂ levels (two replicated controls and seven enhanced pCO₂treatments) for one month. Nutrients were added to all mesocosms on day 13 ofthe experiment, and thereafter increase of chlorophyll a was provoked inall mesocosms. No clear trend in response to increasing pCO₂ was foundin the daily values of NCP, CR, and GCP. For further analysis, theseparameters were cumulated for the following three periods: phase 1 – end ofCO₂ manipulation until nutrient addition (t4 to t13); phase 2 –nutrient addition until the second chlorophyll a minimum (t14 to t21);phase 3 – the second chlorophyll a minimum until the end of this study(t22 to t28). A significant response was detected as a decrease of NCPwith increasing pCO₂ during phase 3. CR was relatively stablethroughout the experiment in all mesocosms. As a result, the cumulative GCPsignificantly decreased with increasing pCO₂ during phase 3. After thenutrient addition, the ratios of cumulative NCP to cumulative consumption ofNO₃ and PO₄ showed a significant decrease during phase 3 withincreasing pCO₂. The results suggest that elevated pCO₂influenced cumulative NCP and stoichiometric C and nutrient coupling of theplankton community in a high-latitude fjord only for a limited period.However provided that there were some differences or weak correlationsbetween NCP data based on different methods in the same experiment, thisconclusion should be taken with caution.

[学科分类] 地球化学与岩石