Effect of increased &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; on the planktonic metabolic balance during a mesocosm experiment in an Arctic fjord

T Tanaka,S Alliouane,A De Kluijver,U Riebesell,J Czerny,K G Schulz,J.-P Gattuso,A Silyakova,R G B Bellerby

doi:10.5194/bg-10-315-2013

Abstract

Abstract. 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 pCO2 levels (two replicated controls and seven enhanced pCO2 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 pCO2 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 CO2 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 NCP with increasing pCO2 during phase 3. CR was relatively stable throughout the experiment in all mesocosms. As a result, the cumulative GCP significantly decreased with increasing pCO2 during phase 3. After the nutrient addition, the ratios of cumulative NCP to cumulative consumption of NO3 and PO4 showed a significant decrease during phase 3 with increasing pCO2. The results suggest that elevated pCO2 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.

Highlights

The balance between photosynthetic carbon production and consumption of organic carbon in the ocean’s surface layer is of importance in understanding the ocean’s role in the global carbon cycle
The results suggest that elevated pressure of CO2 (pCO2) influenced cumulative Net community production (NCP) and stoichiometric C and nutrient coupling of the plankton community in a high-latitude fjord only for a limited period
The water temperature was homogeneous in the water column of the mesocosms at the beginning, and increased gradually, especially in the upper 5 to 10 m, until the end of the experiment (∼ 2.7 to ∼ 5.5 ◦C), while it was always similar in all mesocosms

Summary

Introduction

The balance between photosynthetic carbon production and consumption of organic carbon in the ocean’s surface layer is of importance in understanding the ocean’s role in the global carbon cycle. Marine phytoplankton play an important role in the carbon cycle, being responsible for about half of the global primary production (Field et al, 1998). A large portion of organic carbon produced by photosynthesis is remineralized by respiration (del Giorgio and Duarte, 2002). Heterotrophic prokaryotes (hereafter “bacteria”) can consume a significant fraction of primary production in pelagic systems (Cole et al, 1988; Ducklow and Carlson, 1992). Mineral nutrients (e.g., N, P) can be a limiting factor of growth or organic carbon production by phytoplankton and bacteria

Objectives

Methods

Results

Conclusion