World conference on marine biodiversity 2011, session on life in a high CO2 world

26-30 September 2011
Aberdeen, Scotland

Themed session 8: Life in a high CO₂ world

Joint IPCC workshop of WGI and WGII on impacts of ocean acidification on marine biology and ecosystems

The oceans currently absorb about one-third of fossil fuel CO2 emitted to the atmosphere and have, as a consequence, been increasing in acidity. Ocean acidification is now recognized as a critical component of global change, potentially responsible for a wide range of impacts on ecosystems, with subsequent consequences on livelihoods and food security. Further, one important aspect is that more CO2 mitigation may be required to achieve particular stabilization targets, because acidification limits the ability of the oceans to continue to absorb CO2. Previous IPCC assessment reports considered biogeochemical and temperature effects of anthropogenic carbon on the oceans, but the direct impacts of ocean acidification, its combined effects with ocean warming on marine ecosystems and productivity, and potential feedbacks to the climate system have not been fully assessed.

La Méditerranée sous la menace du gaz carbonique ? (in French, videos)

L’augmentation du gaz carbonique (CO2) rejeté dans l’atmosphère par les diverses activités humaines (transport, chauffage, industrie, ..) influe non seulement sur le changement climatique mais aussi sur la chimie des océans. L’eau de mer devient progressivement plus acide. Des conséquences importantes sur les organismes marins pourraient en résulter : dégradation et fragilisation des coquilles et des carapaces calcaires, diminution de la biodiversité.

Phytoplankton-bacteria coupling under elevated CO2 levels: a stable isotope labelling study

The potential impact of rising carbon dioxide (CO₂) on carbon transfer from phytoplankton to bacteria was investigated during the 2005 PeECE III mesocosm study in Bergen, Norway. Sets of mesocosms, in which a phytoplankton bloom was induced by nutrient addition, were incubated under 1× (~350 μatm), 2× (~700 μatm), and 3× present day CO₂ (~1050 μatm) initial seawater and sustained atmospheric CO₂ levels for 3 weeks. ¹³C labelled bicarbonate was added to all mesocosms to follow the transfer of carbon from dissolved inorganic carbon (DIC) into phytoplankton and subsequently heterotrophic bacteria, and settling particles. Isotope ratios of polar-lipid-derived fatty acids (PLFA) were used to infer the biomass and production of phytoplankton and bacteria. Phytoplankton PLFA were enriched within one day after label addition, whilst it took another 3 days before bacteria showed substantial enrichment. Group-specific primary production measurements revealed that coccolithophores showed higher primary production than green algae and diatoms. Elevated CO₂ had a significant positive effect on post-bloom biomass of green algae, diatoms, and bacteria. A simple model based on measured isotope ratios of phytoplankton and bacteria revealed that CO₂ had no significant effect on the carbon transfer efficiency from phytoplankton to bacteria during the bloom. There was no indication of CO₂ effects on enhanced settling based on isotope mixing models during the phytoplankton bloom, but this could not be determined in the post-bloom phase. Our results suggest that CO₂ effects are most pronounced in the post-bloom phase, under nutrient limitation.