Primary production, determined using an algorithm that incorporates in situ chlorophyll, ammonium, and photosynthetically active radiation, tuned to CCE C-14 NPP data, 2017 - (ongoing).

We investigated the processes driving variability in primary productivity in the California Current Ecosystem (CCE) in order to develop an algorithm for predicting primary productivity from in situ irradiance, nutrient, and chlorophyll (chl) measurements. Primary productivity data from seven process cruises of the CCE Long-Term Ecological Research (CCE LTER) program were used to parameterize the algorithm. An initial algorithm was developed using only irradiance to predict chl-specific productivity was found to have model-data misfit that was correlated with NH4+ concentrations. We thus found that the best estimates of primary productivity were obtained using an equation including NH4+ and irradiance: PP/Chl = V0m×(1-exp(-α×PAR/V0m)×NH4/(NH4+KS), where PP/Chl is chlorophyll-specific primary production in units of mg C d-1 / mg Chl, PAR is photosynthetically active radiation (units of µEi m-2 s-1) , NH4+ is in units of μmol L-1, V0m = 66.5 mg C d-1 / mg Chl , α = 1.5, and KS = 0.025 μmol L-1. We then used this algorithm to compute primary productivity rates for the CCE-P1706 cruise on which in situ primary productivity samples were not available. We compared these estimates to independent productivity estimates derived from protistan grazing dilution experiments and found excellent agreement. For additional details, see Stukel et al. 2019 (doi: 10.1101/590240).