28 Jun 2022
28 Jun 2022
Status: this preprint is open for discussion.

FABM-NflexPD 2.0: Testing an Instantaneous Acclimation Approach for Modelling the Implications of Phytoplankton Eco-physiology for the Carbon and Nutrient cycles

Onur Kerimoglu1, Markus Pahlow2, Prima Anugerahanti3,a, and Sherwood Lan Smith3 Onur Kerimoglu et al.
  • 1Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Oldenburg, Germany
  • 2GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
  • 3Earth SURFACE Research Center, Research Institute for Global Change, JAMSTEC, Yokosuka, Japan
  • apresent address: Dept. of Earth, Ocean and Ecological Sciences, School of Environmental Sciences, University of Liverpool, Liverpool, United Kingdom

Abstract. The acclimative response of phytoplankton, which adjusts their nutrient and pigment content in response to changes in ambient light, nutrient levels, and temperature, is an important determinant of observed chlorophyll distributions and biogeochemistry. Acclimative models typically capture this response and its impact on the C : nutrient : Chl ratios of phytoplankton by explicitly resolving the dynamics of these constituents of phytoplankton biomass. The Instantaneous Acclimation (IA) approach only requires resolving the dynamics of a single tracer and calculates the elemental composition assuming instantaneous local equilibrium. IA can capture the acclimative response without substantial loss of accuracy in both 0D box models and spatially explicit 1D models. A major draw-back of IA so far has been its inability to maintain mass balance for the elements with unresolved dynamics. Here we extend the IA model to capture both C and N cycles in a 0D setup, which requires analytical derivation of additional flux terms to account for the temporal changes in cellular N quota, Q. We present extensive tests of this model, with regard to the conservation of total C an N, and its behavior in comparison to an otherwise equivalent, fully explicit Dynamic Acclimation (DA) variant, under idealized conditions with variable light and temperature. We also demonstrate a modular implementation of this model in the Framework for Aquatic Biogeochemical Modelling (FABM), which facilitates modelling competition between an arbitrary number of different acclimative phytoplankton types. In a 0D setup, we did not find evidence for computational advantages of the IA approch over the DA variant. In a spatially explicit setup, performance gains may be possible, but would require modifying the physical-flux calculations to account for spatial differences in Q between model grid cells.

Onur Kerimoglu et al.

Status: open (until 23 Aug 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-493', Hoa Nguyen, 12 Aug 2022 reply

Onur Kerimoglu et al.

Model code and software

OnurKerimoglu/fabm-nflexpd: FABM-NflexPD Version 2.0 release candidate 0 Onur Kerimoglu

Onur Kerimoglu et al.


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Short summary
In classical models that track the changes in the elemental composition of phytoplankton, additional state variables are required for each element resolved. In this study, we show how the behavior of such an explicit model can be approximated using an 'instantaneous acclimation' approach, in which the elemental composition of the phytoplankton is assumed to adjust to an optimal value instantaneously. Through rigorous tests, we evaluate the consistency of this scheme.