Increase of PCO2 during blooms of Emiliania huxleyi: Theoretical considerations on the asymmetry between acquisition of HCO3‐ and respiration of free CO2

Abstract

The principal source of dissolved inorganic carbon (C,) of most marine phytoplankton is thought to be free CO,, but Emiliania huxleyi can utilize HCO,-ion both for calcification (C') and photosynthesis (P). We present a simple model that simulates continuous diurnal removal of C, as either free CO, or HCO,-across the range of C, typically encountered in seawater (2,100-1,800 pmol kg,,-'). Removal as free CO, forces a drawdown in partial pressure of dissolved carbon dioxide (Pco,), at given C,, of up to 170 patm greater than that forced by removal as HCO,-by E. huxleyi (assuming C,,,, : P,,, = 1.0). Diurnal C,,, : P,,, must exceed 1.5 for Pco, to increase during removal of HCO,-. When nocturnal respiration of free CO, (Z?) is incorporated into the model, the respective drawdowns in Pco, forced by diurnal removal of free CO, and HCO; are balanced by diel ratios R : P,,,, = 1 .O and R : (P+ C),, = 0.15. Therefore, with diel R : (P+C),,, > 0.15 but diurnal Cnct : P,,, = 1 .O, E. huxleyi can theoretically grow with net diel increase in Pco,; however, diel C,,, : P,,, > 1 .O is forced by nocturnal loss of particulate organic carbon but not particulate inorganic carbon. Published values for C : P do not necessarily represent diel C,,, : P,,, and caution is required when extrapolating these ratios to predict changes in C, and Pco, during natural blooms of E. huxleyi.

Biogenic controls on the air—water carbon dioxide exchange in the Sundarban mangrove environment, northeast coast of Bay of Bengal, India

“…Therefore, blooming of these diatom species could decrease f CO2 in water by HCO uptake. Crawford and Purdie (1997) …”

The hydrography and biology of a bloom of the coccolithophorid Emiliania huxleyi in the northern North Sea

“…Elevated pCO 2 values have been observed in E. huxleyi blooms in both oceanic waters (Holligan et al, 1993a;Robertson et al, 1994) and mesocosms (Purdie and Finch, 1994), but the relative importance of several potential mechanisms responsible for such an increase have not been clarified (Crawford and Purdie, 1997). It has been shown theoretically that growth of E. huxleyi can either decrease the air-sea gradient in pCO 2 driven by 'organic' production or depending on the relative rates of photosynthesis, calcification and respiration, could cause a direct elevation in pCO 2 levels (Crawford and Purdie, 1997;Nimer et al, 1992;Steemann Nielsen, 1966).…”

“…It has been shown theoretically that growth of E. huxleyi can either decrease the air-sea gradient in pCO 2 driven by 'organic' production or depending on the relative rates of photosynthesis, calcification and respiration, could cause a direct elevation in pCO 2 levels (Crawford and Purdie, 1997;Nimer et al, 1992;Steemann Nielsen, 1966). In addition to the possible production of CO 2 as a result of calcification (Robertson et al, 1994), a reduction in the air-sea pCO 2 gradient at the western end of the transect could also result from the lower rates of carbon fixation in comparison with values observed in the diatom-dominated assemblages to the east.…”

Biogeochemistry and carbon mass balance of a coccolithophore bloom in the northern Bay of Biscay (June 2006)

“…In coccolithophore blooms, CAL is an additional source of CO 2 to the surrounding seawater that modulates the net balance of community CO 2 fluxes (Purdie and Finch, 1994;Crawford and Purdie, 1997;Frankignoulle and Borges, 2001;Suykens et al, 2010a). The NCP, corresponding to the potential for C export from the photic layer to the aphotic zone, was compared to the integrated DCR aphotic in the aphotic layer (i.e., the aphotic C demand).…”

“…Both processes transfer C to depth and impact on the speciation of dissolved inorganic C (DIC) and CO 2 flux across the air-sea interface (Purdie and Finch, 1994;Buitenhuis et al, 1996Buitenhuis et al, , 2001Crawford and Purdie, 1997;Frankignoulle and Borges, 2001;Suykens et al, 2010a). Changes of C fluxes of pelagic calcifiers under ocean acidification (e.g., Orr et al, 2005), namely a decrease in calcification rates, could provide a negative feedback in response to increasing atmospheric CO 2 as suggested by controlled experiments either in cultures (e.g., Riebesell et al, 2000;Sciandra et al, 2003;De Bodt et al, 2008 or mesocosms (e.g., Delille et al, 2005;Riebesell et al, 2007).…”