Plankton [formula omitted] variations in Monterey Bay, California: evidence of non-diffusive inorganic carbon uptake by phytoplankton in an upwelling environment

Abstract

A test of the hypothesis that photosynthetic 13 C fractionation, ε p, is affected by variations in diffusive transport of CO 2aq into phytoplankton cells was conducted in Monterey Bay over a 4 yr period. Counter to predictions based on diffusive CO 2aq transport were observations of very weak to non-existent correlations between ε p and: (i) CO 2aq concentration, (ii) mean phytoplankton community growth rate, (iii) cell size, (iv) carbon demand, or (v) [CO 2aq]-normalized functions of ii–iv. The preceding decoupling between ε p and CO 2 supply/demand and the low 13 C fractionation associated with carboxylation ( ε f) implied in this study are consistent with several recent reports of active bicarbonate uptake and utilization in similar coastal environments. If the frequent low ε p seen here is indicative of such carbon acquisition, it suggests that active bicarbonate transport in situ (1) may not be restricted to diatoms, (2) can be present even in high-[CO 2aq] low-growth-rate waters, (3) may be a common feature of low-latitude upwelling environments, and (4) may help explain the common 13 C/ 12 C dichotomy between marine planktonic and terrestrial C 3 autotrophs.