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Model Versions

The PISCES model offers the possibility of using different versions of its numerical code, varying in complexity. Thus, three versions of PISCES can be activated optionally, as well as a sedimentary diagenesis module and some optional features.

PISCES-Operational

PISCES-Operational is the standard version of the model and the one most widely used by the community. Its modelling formalism is based on a mixed Monod-quota approach in which constant Redfield ratios are imposed for C/N/P along varying ratios for Fe, Si, and CaCO\(_{3}\) (Aumont et al., 20151).

PISCES-Operational includes 24/25 prognostic tracers, i.e. explicitly computed by the model (Figure 1).

PISCES_Operational.png
Figure 1. Schematic diagram of PISCES-Operational describing the nutrients, carbon and oxygen cycles, as well as the processes represented in the model.

PISCES-Research

PISCES-Research includes a quota-based description of phytoplankton growth with fully variable C:N:P:Si:Fe:Chl ratios (Kwiatkowski et al., 20182). In addition, the basic structure of the model is modified with the addition of a third phytoplankton group, namely picophytoplankton.

PISCES-Research includes 39/40 prognostic tracers (Figure 2). The significant increase in the number of tracers makes this version more expensive than PISCES-Operational in terms of computational cost, representing an increase of approximately a factor of 2.

PISCES_Operational.png
Figure 2. Schematic diagram of PISCES-Research, the full quota version of PISCES.

Shared components Operational vs. Research

Large parts of the code are shared between PISCES-Operational and PISCES-Research. As a result, most configurable parameters are common, and most optional features of PISCES can be used in both versions.

PISCES-Simple

PISCES-Simple is the simplified NPZD version of PISCES-Operational. It simulates marine biogeochemical cycles using nine prognostic tracers and includes one single generic group for phytoplankton and for zooplankton. The model also incorporates the iron (Fe) cycle to enhance the representation of primary production in Fe-limited regions (Figure 3), such as in the Southern Ocean.

As the simplest and most computationally efficient version of PISCES, it runs approximately 2.5 times faster than PISCES-Operational.

PISCES_Simple
Figure 3. Schematic diagram of PISCES-Simple.

Use with caution

Note that PISCES-Simple is recent and does not have the same level of maturity in terms of tuning and evaluation as PISCES-Operational and PISCES-Research.

Sediment module

A fully prognostic diagenetic module can also be activated.

This module is a one-dimensional, time-dependent model that simulates early diagenetic reactions in surface seafloor sediments. It explicitly represents the cycling of organic matter, calcium carbonate, and biogenic silica, along with the dynamics of key terminal electron acceptors (O\(_2\), NO\(_3\), FeO\(_2\)H, and SO\(_4\)). The module accounts for both transport and biogeochemical processes in sediments, including advection, solute diffusion (with tortuosity), bioirrigation, bioturbation, and reactions involving dissolved and solid species.

A schematic of the sediment biogeochemical processes and exchanges with the overlying water column is shown in Figure 4.

PISCES_Sediment
Figure 4. Schematic diagram of the PISCES Sediment module.

Restriction on use of the sediment module

The sediment module can only be activated with PISCES-Operational. Indeed, the approach to modelling biogeochemical processes in sediment was developed specifically for PISCES-Operational, so this module is not functional with PISCES-Research and PISCES-Simple by design.

Optional features

Furthermore, several optional features of PISCES can be activated. These features are only available in PISCES-Operational and PISCES-Research:

  1. Prognostic ligands: An additional prognostic tracer is modeled to represent Fe complexing ligands. The formulation is described in Voelker and Tagliabue (20153).
  2. Diurnal Vertical Migration of mesozooplankton: A significant fraction of large marine organisms undertake diurnal vertical migrations—feeding at night in the surface ocean and descending to the mesopelagic zone during the day to avoid visual predators. A simplified parameterization of the impact of these migrations on the carbon cycle can be activated in PISCES, following Gorgues et al. (20194).
  3. One or two-way coupling between PISCES and the sediment module: By default, the sediment module does not influence water column biogeochemistry. However, two-way coupling can be enabled, allowing fluxes at the sediment–water interface to modify PISCES ocean prognostic variables.

  1. Olivier Aumont, Christian Ethé, Alessandro Tagliabue, Laurent Bopp, and Marion Gehlen. PISCES-v2: an ocean biogeochemical model for carbon and ecosystem studies. Geoscientific Model Development, 8:2465–2513, 2015. doi:10.5194/gmd-8-2465-2015. ↩

  2. Lester Kwiatkowski, Olivier Aumont, Laurent Bopp, and Philippe Ciais. The Impact of Variable Phytoplankton Stoichiometry on Projections of Primary Production, Food Quality, and Carbon Uptake in the Global Ocean. Global Biogeochemical Cycles, 32(4):516–528, 2018. doi:10.1002/2017GB005799. ↩

  3. Christoph Völker and Alessandro Tagliabue. Modeling organic iron-binding ligands in a three-dimensional biogeochemical ocean model. Marine Chemistry, 173:67–77, 2015. doi:10.1016/j.marchem.2014.11.008. ↩

  4. Thomas Gorgues, Olivier Aumont, and Laurent Memery. Simulated Changes in the Particulate Carbon Export Efficiency due to Diel Vertical Migration of Zooplankton in the North Atlantic. Geophysical Research Letters, 46(10):5387–5395, 2019. doi:10.1029/2018GL081748. ↩