GLOBAL BIOGEOCHEMICAL CYCLES, Vol. 17, No. 3, 1079, doi: 10:1029/2002GBOO2021

On using pigment-normalized, light-saturated carbon uptake with satellite-derived pigment for estimating column photosynthesis

K. Banse and J. R. Postel

School of Oceanography, University of Washington, Seattle, Washington, USA

Using five Pacific open-sea data sets with five subsets, we linearly correlated observed column photosynthesis (P_t, mg C m^-2 d^-1, from ¹⁴C-uptake) with "satellite pigment" (C_sat, mg m^-3), simulated from in situ data at the same stations, and modeled P_t by a depth-integrated approach. The correlation (r²) of P_t with C_sat and its accuracy improved after combining C_sat with an in situ-based proxy for the light-saturated rate of photosynthesis, P^b_opt (mg C (mg chl d)^-1), for the particular stations. Incorporating station P^b_opt, always led to high r² and accuracy of the regression of modeled on observed P_t. However, P^b_opt cannot yet be determined from space, so that in practice, geographic or seasonal means of P^b_opt have to be used. For our 10 sets, such means lead to more imprecise (lower r² in 9 of 10 cases) and less accurate (for all) results, because P^b_opt and P_t are often correlated. We expect this error source to be widespread and to afflict all modeling of P_t using a term for light-saturated photosynthesis, but we cannot offer a solution to the quandary. On the basis of combining of data sets, we do not favor the use of a single algorithm employing light-saturated photosynthesis for calculating global P_t by a depth-integrated approach.