Increasing atmospheric CO2, ocean acidification and pelagic ecosystems

• Main Author: Gangstø, Reidun
• Other Authors: Joos, F., Gehlen, M.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2009
• Subjects: 530 Physics; Ocean acidification
• Online Access: https://boris.unibe.ch/192496/1/gangsto09phd.pdf; https://boris.unibe.ch/192496/

This thesis explores the impacts of rising atmospheric CO2 and the subsequent ocean acidification on pelagic calcifiers. The ocean plays a major role in the global carbon cycle and in regulating the atmospheric concentrations of CO2. About one third of the CO2 emitted to the atmosphere each year by human activities is taken up by the ocean. This leads to a reduction in pH (a measure of acidity) and a decrease in CaCO3 saturation state, which makes the ocean more corrosive to the mineral CaCO3. The pH of the oceans has already dropped by 0.1 units since pre-industrial times, and the current rate at which this process is occurring will likely have large biological consequences for ocean ecosystems within the near future. Plankton which build shells out of CaCO3 (mainly coccolithophores, foraminifers, and pteropods) might have difficulties producing and maintaining their shells. Two important forms of CaCO3 in the ocean are calcite and aragonite, the latter being 50% more soluble. Pteropods, which produce their shells of aragonite, might thus be especially vulnerable to increasing atmospheric CO2. These species are an important element of the food web in high-latitude surface waters and changes in their abundance will affect the whole food chain up to higher levels. A decrease in CaCO3 production would also provide a negative feedback on atmospheric CO2, with an additional CO2 uptake by the oceans. A prerequisite to address the impact of ocean acidification on pelagic ecosystems is a quantitative understanding of the evolution of the aragonite and calcite saturation states. In order to project this evolution, evaluate the global and regional impacts on the carbonate budget and determine the associated feedbacks, global biogeochemical models are essential. The studies performed in this thesis are all based on the biogeochemical model PISCES, which simulates the marine biological productivity and the biogeochemical cycles of carbon and main nutrients. This model is used in combination with two global dynamical models ...