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p4zint

Overview

The p4zint module computes auxiliary biogeochemical fields used throughout PISCES. These fields include temperature-dependent metabolic rates, nutrient limitation factors, photoperiod calculations, and redox condition diagnostics.

Module Name: p4zint
Model: PISCES (version NEMO 5.0)
Subroutine: p4z_int

p4z_int

Auxiliary Fields

1. Phytoplankton and Zooplankton Metabolic Rates

  • Generic temperature function for phytoplankton: tgfunc

Generic function of phytoplankton growth rate dependence on temperature (Eppley, 19721) applied for various biological rates.

  • Generic temperature function for zooplankton: tgfunc2

Specific temperature dependence of mesozooplankton metabolic processes (Buitenhuis et al., 20062) applied to grazing and metabolism of mesozooplankton and microzooplankton.

2. Silicon Limitation

Computes the silicon-dependent half-saturation constant (xksi, xksimax) for silica uptake by diatoms (Pondaven et al., 19983), only for p4z or p5z versions. The value is updated to 0 once per year at the last day.

Parameter:

  • xksilim = 16.5×10⁻⁶ mol/L: Half-saturation constant for Si computation

3. Day Length

Computes photoperiod (day length in hours, strn) based on latitude and day of year. Uses Earth's axial tilt of 23.5°.

Variables:

  • nday_year: Current day of the year
  • nyear_len(1): Length of the year in days
  • zcodel: Solar declination (radians)
  • φ = gphit(i,j): Latitude (degrees)
  • rad = π/180: Degree to radian conversion factor

4. Denitrification Factor

Diagnostic factor indicating the intensity of denitrification processes (nitrfac). Becomes active when oxygen levels fall below threshold. Value is bounded between 0 and 1. Used to modulate denitrification rates in low-oxygen zones.

Parameters:

  • Threshold: 6×10⁻⁶ mol/L
  • oxymin: Minimum oxygen concentration parameter

5. Redox Reactions Factor

Diagnostic factor for additional redox reactions occurring under very low nitrate concentrations (nitrfac2). Value is bounded between 0 and 1. Used to activate alternative electron acceptor pathways when nitrate is depleted.

Parameter:

  • Threshold: 1×10⁻⁶ mol/L

Input parameters

Parameter Type Intent Description
kt INTEGER IN Current time step index
Kbb INTEGER IN Time level index (before)
Kmm INTEGER IN Time level index (now/middle)

Variables

Inputs

Variable Source Description
ts(:,:,:,jp_tem,:) oce_trc Temperature field (°C)
tr(:,:,:,jpsil,:) trc Dissolved silica (mol/L)
tr(:,:,:,jpoxy,:) trc Dissolved oxygen (mol/L)
tr(:,:,:,jpno3,:) trc Nitrate concentration (mol/L)
gphit(:,:) Grid Latitude (degrees)
nday_year Time Current day of year
nyear_len(1) Time Days in year

Outputs

Variable Description Units
tgfunc(:,:,:) Generic temperature function Dimensionless
tgfunc2(:,:,:) Mesozooplankton temperature function Dimensionless
xksi(:,:) Silicon half-saturation constant mol/L
xksimax(:,:) Maximum Si half-saturation mol/L
strn(:,:) Day length Hours
nitrfac(:,:,:) Denitrification factor Dimensionless [0-1]
nitrfac2(:,:,:) Redox reactions factor Dimensionless [0-1]

Document Version: 1.0
Last Updated: October 2025
Source code: NEMO 5.0

  1. R. W. Eppley. Temperature and phytoplankton growth in the sea. Fish. Bull., U. S., 70 (4): 1063, 1972. ↩

  2. Erik Buitenhuis, Corinne Le Quéré, Olivier Aumont, Grégory Beaugrand, Adrian Bunker, Andrew Hirst, Tsutomu Ikeda, Todd O'Brien, Sergey Piontkovski, and Dietmar Straile. Biogeochemical fluxes through mesozooplankton. Global biogeochemical cycles, 2006. ↩

  3. P Pondaven, C Fravalo, D Ruiz-Pino, P Tréguer, B Quéguiner, and C Jeandel. Modelling the silica pump in the permanently open ocean zone of the southern ocean. Journal of Marine Systems, 17(1-4):587–619, 1998. ↩