Estimating Primary Production of Picophytoplankton Using the Carbon-Based Ocean Productivity Model: A Preliminary...

Picophytoplankton are acknowledged to contribute significantly to primary production (PP) in the ocean while now the method to measure PP of picophytoplankton (PP_Pico) at large scales is not yet well established. Although the traditional ¹⁴C method and new technologies based on the use of stable isotopes (e.g., ¹³C) can be employed to accurately measure in situ PP_Pico, the time-consuming and labor-intensive shortage of these methods constrain their application in a survey on large spatiotemporal scales. To overcome this shortage, a modified carbon-based ocean productivity model (CbPM) is proposed for estimating the PP_Pico whose principle is based on the group-specific abundance, cellular carbon conversion factor (CCF), and temperature-derived growth rate of picophytoplankton. Comparative analysis showed that the estimated PP_Pico using CbPM method is significantly and positively related (r² = 0.53, P < 0.001, n = 171) to the measured ¹⁴C uptake. This significant relationship suggests that CbPM has the potential to estimate the PP_Pico over large spatial and temporal scales. Currently this model application may be limited by the use of invariant cellular CCF and the relatively small data sets to validate the model which may introduce some uncertainties and biases. Model performance will be improved by the use of variable conversion factors and the larger data sets representing diverse growth conditions. Finally, we apply the CbPM-based model on the collected data during four cruises in the Bohai Sea in 2005. Model-estimated PP_Pico ranged from 0.1 to 11.9, 29.9 to 432.8, 5.5 to 214.9, and 2.4 to 65.8 mg C m^-2 d^-1 during March, June, September, and December, respectively. This study shed light on the estimation of global PP_Pico using carbon-based production model.