Effect of increased p CO 2 on the planktonic metabolic balance during a mesocosm experiment in an Arctic fjord

• Published in: Biogeosciences
• Main Authors: J.-P. Gattuso, K. G. Schulz, A. Silyakova, A. de Kluijver, U. Riebesell, J. Czerny, R. G. B. Bellerby, S. Alliouane, T. Tanaka
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2013
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Arctic; Svalbard; Kongsfjord*; Kongsfjorden; Ocean acidification; Phytoplankton
• Online Access: https://doi.org/10.5194/bg-10-315-2013; https://doaj.org/article/4afa456406f647929d5ccbd1e473de2d

The effect of ocean acidification on the balance between gross community production (GCP) and community respiration (CR) (i.e., net community production, NCP) of plankton communities was investigated in summer 2010 in Kongsfjorden, west of Svalbard. Surface water, which was characterized by low concentrations of dissolved inorganic nutrients and chlorophyll a (a proxy of phytoplankton biomass), was enclosed in nine mesocosms and subjected to eight p CO 2 levels (two replicated controls and seven enhanced p CO 2 treatments) for one month. Nutrients were added to all mesocosms on day 13 of the experiment, and thereafter increase of chlorophyll a was provoked in all mesocosms. No clear trend in response to increasing p CO 2 was found in the daily values of NCP, CR, and GCP. For further analysis, these parameters were cumulated for the following three periods: phase 1 – end of CO 2 manipulation until nutrient addition ( t 4 to t 13); phase 2 – nutrient addition until the second chlorophyll a minimum ( t 14 to t 21); phase 3 – the second chlorophyll a minimum until the end of this study ( t 22 to t 28). A significant response was detected as a decrease of NCP with increasing p CO 2 during phase 3. CR was relatively stable throughout the experiment in all mesocosms. As a result, the cumulative GCP significantly decreased with increasing p CO 2 during phase 3. After the nutrient addition, the ratios of cumulative NCP to cumulative consumption of NO 3 and PO 4 showed a significant decrease during phase 3 with increasing p CO 2 . The results suggest that elevated p CO 2 influenced cumulative NCP and stoichiometric C and nutrient coupling of the plankton community in a high-latitude fjord only for a limited period. However provided that there were some differences or weak correlations between NCP data based on different methods in the same experiment, this conclusion should be taken with caution.