ABSTRACT: A predictive model of carbon isotope fractionation (sigma_p) and abundance (delta¹³C_phyto) is presented under circumstances where photosynthesis is strictly based on CO₂(aq) that passively diffuses into marine phytoplankton cells. Similar to other recent models, the one presented here is based on a formulation where the expression of intracellular enzymatic isotope fractionation relative to that imposed by CO₂(aq) transport is scaled by the ratio of intracellular to external [CO₂(aq)], c_i/c_e. Unlike previous models, an explicit calculation of c_i is made that is dependent on c_e as well as cell radius, cell growth rate, cell membrane permeability to CO₂(aq), temperature, and, to a limited extent, pH and salinity. This allows direct scaling of c_i/c_e to each of these factors, and thus a direct prediction of sigma_p and delta¹³C_phyto responses to changes in each of these variables. These responses are described, and, where possible, compared to recent experimental and previous modeling results.

KEY WORDS: delta¹³C . Photosynthesis . Isotope fractionation . Phytoplankton . CO₂ . Modeling

Published in MEPS Vol. 133 (1996) on March 28
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996