Boxhammer, Tim (2011) Impact of ocean acidification on export and composition of sedimenting material in an Arctic offshore mesocosm study. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 77 pp.

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Abstract

The anthropogenic release of the greenhouse gas carbon dioxide (CO2) is well known to cause global climate change. Additionally, oceanic uptake of CO2 leads to an acidification of the surface layers through the formation of carbonic acid. The observed drop in average ocean surface pH of 0.1 units since the Industrial Revolution is predicted to continue with almost unknown consequences for marine biota. As phytoplankton represents the basis of the marine food web and constitutes to 50% of global primary production, changes in abundance, taxonomic composition or elemental stoichiometry would have effects on all higher trophic levels, including humans. Changes in phytoplankton primary production would further influence composition of organic material and it's export from the euphotic zone to the deep ocean. This change could have the potential to alter global elemental cycling. The Arctic Ocean is one of the oceanic areas that will be primarily affected by ocean acidification, making changes in this region of particular global importance. The study presented here was part of the European Project on OCean Acidification (EPOCA) pelagic campaign 2010. The experiment for simulation of increasing CO2 partial pressure and corresponding ocean acidification was carried out with the Kiel OffShore Mesocosms for future Ocean Simulations (KOSMOS) in the Kongsfjord, Spitsbergen. The aim of the study was to close the gap between single species responses and those of plankton communities to increasing ocean acidification in the Arctic. This thesis focuses on the stoichiometry and export of sedimenting material under different CO2 partial pressures in the pelagic mesocosms. For the first time we examined the possibility to estimate export in a KOSMOS study, establishing new methods for sediment sample processing and analysis. By monitoring the daily export rates of the mesocosms, coupling of primary production in the water column and subsequent sedimentation was studied. As the experiment was terminated too early with respect to an on-going sedimentation event, just two thirds of the experimental time could be used for studying potential pCO2 effects. From the current point of view, it can be suggested that a pCO2 driven change of sedimenting particle elemental stoichiometry and potential export is unlikely in future Arctic coastal waters.

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