Trends in the subpolar north atlantic carbon sink and ocean acidification: 1981-2008

Sergio Signorini, NASA GSFC, sergio.signorini@nasa.gov (Presenter)
Sirpa Häkkinen, NASA GSFC, sirpa.m.hakkinen@nasa.gov
Are Olsen, University of Bergen, are.olsen@gfi.uib.no
Nicolas Metzl, Université Pierre et Marie Curie, nicolas.metzl@upmc.fr
Kristinn Gudmundsson, MRI Iceland, kristinn@hafro.is
Abdiraham Omar, Bjerknes Institute, Bergen, abdirahman.omar@bjerknes.uib.no
Jón Olafsson, MRI Iceland, jon@hafro.is
Gilles Reverdin, Université Pierre et Marie Curie, gilles.reverdin@locean-ipsl.upmc.fr
Stephanie Henson, NOC, Southampton, UK, s.henson@noc.ac.uk
Charles McClain, NASA GSFC, charles.r.mcclain@nasa.gov

We use an ecosystem/biogeochemical model, which includes multiple phytoplankton functional groups and carbon cycle dynamics, to investigate physical-biological interactions in Icelandic waters. Satellite and in situ data were used to evaluate the model.

The seasonality of the coccolithophore and “other phytoplankton” (diatoms and dinoflagellates) blooms is in general agreement with satellite ocean color products. Nutrient supply, biomass and calcite concentrations are modulated by light and mixed layer depth seasonal cycles. Diatoms are the most abundant phytoplankton with a large bloom in early spring and a secondary bloom in fall. The diatom bloom is followed by blooms of dinoflagellates and coccolithophores. The effect of biological changes on the seasonal variability of the surface ocean pCO₂ is nearly twice the temperature effect.

During the peak of the bloom in summer, the net effect of the absence of the coccolithophores bloom is an increase in pCO₂ of more than 20 µatm and a reduction of atmospheric CO₂ uptake of more than 6 mmol m^-2 d^-1. Considering the areal extent of the bloom from satellite images within the Irminger and Icelandic basins, this reduction translates into an annual mean of nearly 1500 tonnes C yr^-1.

Winter pCO₂ trend is larger than summer: +2.9 µatm yr^-1 in winter compared to +1.6 µatm yr^-1 in summer. This is due to the different processes affecting the carbon variability in the two seasons, biological uptake and SST variations during spring-summer, and predominantly strong vertical mixing during winter bringing DIC rich waters to the surface. Both model and measurements show ocean pCO₂ growth rates higher than the mean atmospheric growth rate of +1.8 µatm yr^-1, which implies a decrease of the carbon sink. Trends in pH are related to pCO₂ trends. The winter pH trend is larger than summer, -0.003 yr^-1 in winter compared to -0.002 yr^-1 in summer.

Presentation Type:  Poster

Session:  Coupled Processes at Land-Atmosphere-Ocean Interfaces   (Mon 4:00 PM)

Associated Project(s): 

• McClain, Chuck: Assessment and Impact of Carbon Variability in the Nordic Seas ...details

Poster Location ID: 84