Abstract
Abstract. In the frame of the European Project on Ocean Acidification (EPOCA), the response of an Arctic pelagic community (<3 mm) to a gradient of seawater pCO2 was investigated. For this purpose 9 large-scale in situ mesocosms were deployed in Kongsfjorden, Svalbard (78°56.2´ N, 11°53.6´ E), in 2010. The present study investigates effects on the communities of particle-attached (PA; >3 μm) and free-living (FL; < 3 μm > 0.2 μm) bacteria by Automated Ribosomal Intergenic Spacer Analysis (ARISA) in 6 of the mesocosms, ranging from 185 to 1050 μatm initial pCO2, and the surrounding fjord. ARISA was able to resolve, on average, 27 bacterial band classes per sample and allowed for a detailed investigation of the explicit richness and diversity. Both, the PA and the FL bacterioplankton community exhibited a strong temporal development, which was driven mainly by temperature and phytoplankton development. In response to the breakdown of a picophytoplankton bloom, numbers of ARISA band classes in the PA community were reduced at low and medium CO2 (~ 185–685 μatm) by about 25%, while they were more or less stable at high CO2 (~ 820–1050 μatm). We hypothesise that enhanced viral lysis and enhanced availability of organic substrates at high CO2 resulted in a more diverse PA bacterial community in the post-bloom phase. Despite lower cell numbers and extracellular enzyme activities in the post-bloom phase, bacterial protein production was enhanced in high CO2 mesocosms, suggesting a positive effect of community richness on this function and on carbon cycling by bacteria.
Highlights
The increase in anthropogenic carbon dioxide (CO2) in the atmosphere causes an enhanced uptake of CO2 by the oceans (Raven et al, 2005), and, if CO2 emissions continue at current rates, this is expected to lead to the fastest drop in ocean pH in the last 300 million years (Caldera and Wickett, 2003)
The gradients predominantly explaining the development of the FL community over the course of the experiment were more evenly split between chlorophyll a (Chl a) and temperature (Fig. 1b) than for the PA community
Our study investigates the response of a pelagic bacterial community in an Arctic glacial fjord to a gradient of pCO2 values by Automated Ribosomal Intergenic Spacer Analysis (ARISA)
Summary
The increase in anthropogenic carbon dioxide (CO2) in the atmosphere causes an enhanced uptake of CO2 by the oceans (Raven et al, 2005), and, if CO2 emissions continue at current rates, this is expected to lead to the fastest drop in ocean pH in the last 300 million years (Caldera and Wickett, 2003). The cold water has a high solubility for CO2 and increased melting of sea ice will expand the area of surface water directly exposed to atmospheric influences within the current century. The related freshwater input will reduce the buffering capacity of the seawater. The sum of these processes is projected by the NCAR global coupled carbon cycle–climate model to result in an acceleration of ocean acidification by 20 % and a drop of 0.45 pH units at the end of the present century, turning the Arctic Ocean from a region of, compared to global average, high pH into a relatively low pH region (Steinacher et al, 2009). Potential consequences for Arctic marine ecosystems and their biogeochemical feedbacks are largely unknown to date
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