Silicic acid leakage from the Southern Ocean as a possible mechanism for explaining glacial atmospheric pCO 2, Global Biogeochem

• Main Authors: Katsumi Matsumoto, Jorge L. Sarmiento, Mark A. Brzezinski
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Numerical modeling; 4267 Oceanography; Antarctic; Bruland; Southern Ocean; Antarc*
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.144.3413; http://www.gfdl.noaa.gov/reference/bibliography/2002/knm0201.pdf

[1] Using a simple box model, we investigate the effects of a reduced Si:N uptake ratio by Antarctic phytoplankton on the marine silica cycle and atmospheric pCO2. Recent incubation experiments demonstrate such a phenomenon in diatoms when iron is added [Hutchins and Bruland, 1998; Takeda, 1998; Franck et al., 2000]. The Southern Ocean may have supported diatoms with reduced Si:N uptake ratios compared to today during the dustier glacial times [Petit et al., 1999]. A similar reduction in the uptake ratio may be realized with an increased production of nondiatom phytoplankton such as Phaeocystis. Our model shows that reduced Si:N export ratios in the Southern Ocean create excess silicic acid, which may then be leaked out to lower latitudes. Any significant consumption of the excess silicic acid by diatoms that leads to an enhancement in their growth at the expense of coccolithophorids diminishes CaCO3 production and therefore diminishes the carbonate pump. In our box model the combination of a reduced carbonate pump and an open system carbonate compensation draw down steady state atmospheric CO2 from the interglacial 277 to 230–242 ppm, depending on where the excess silicic acid is consumed. By comparison, the atmospheric pCO2 sensitivity of general circulation