04 Apr 2022
04 Apr 2022
Status: this preprint is open for discussion.

Physiological flexibility of phytoplankton impacts modeled biomass and primary production across the North Pacific Ocean

Yoshikazu Sasai1, Sherwood Lan Smith1, Eko Siswanto2, Hideharu Sasaki3, and Masami Nonaka3 Yoshikazu Sasai et al.
  • 1Earth Surface System Research Center (ESS), Research Institute for Global Change (RIGC), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
  • 2ESS,RIGC,JAMSTEC,Yokohama, Japan
  • 3Application Laboratory (APL), Research Institute for Value - Added - Information Generation (VAiG), JAMSTEC, Yokohama, Japan

Abstract. Phytoplankton growth, and hence biomass responds to changing light and nutrient conditions in the near-surface ocean. Although a wide variety of physiological photoacclimation models have been developed and tested against laboratory results, their application and testing against oceanic observations remain limited. Hence the biogeochemical implications of photoacclimation in combination with ocean circulation have yet to be fully explored. We compare modeled phytoplankton biomass and primary production from a recently developed flexible phytoplankton functional type model (FlexPFT), which incorporates photoacclimation and variable carbon (C) : nitrogen (N) : chlorophyll (Chl) ratios, to that obtained with an inflexible control model (InFlexPFT), which assumes fixed C : N : Chl ratios. We couple each plankton model with a 3-D eddy-resolving ocean circulation model of the North Pacific and evaluate their respective performance versus observations of Chl, nutrients, and primary production. These two models yield different horizontal and vertical distributions of Chl and primary production. The FlexPFT reproduces observed subsurface Chl maxima, although it overestimates Chl concentrations. In the subtropical gyre, where light is sufficient, even at low nutrient concentrations, the FlexPFT yields faster growth rates, as well as high Chl concentration and primary production in the subsurface layer. Compared to the FlexPFT, the InFlexPFT yields slower growth rates, and lower Chl and primary production. In the subpolar gyre, the FlexPFT also predicts faster growth near the surface, where light and nutrient conditions are most favorable. Compared to the InFlexPFT, the key differences that allow the FlexPFT to better reproduce the observed patterns are its assumption of variable, rather than fixed, C : N : Chl ratios and inter-dependent, rather than strictly multiplicative, effects of light- and nutrient-limitation.

Yoshikazu Sasai et al.

Status: open (until 10 Jun 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-91', Anonymous Referee #1, 15 May 2022 reply

Yoshikazu Sasai et al.

Yoshikazu Sasai et al.


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Short summary
We have investigated the adaptive response of phytoplankton growth to changing light, nutrient, and temperature over the North Pacific using two physical-biological models. We compared modeled phytoplankton biomass and primary production from a recently developed phytoplankton model, FlexPFT, which incorporates photoacclimation and variable C : N : Chl ratios for changing light and nutrient conditions, and the InFlexPFT control, which lacks photoacclimation and assumes constant C : N : Chl ratios.