Introduction

The MATLAB functions in the biogeochem-phi repository evaluate the different equations presented by Humphreys et al. (2018).

Installation

Add all MATLAB functions from the biogeochem-phi repository to your MATLAB path.

Dependencies

To work correctly, the biogeochem-phi functions also require that you download the MATLAB functions from oceancarb-constants, and add them to your MATLAB path.

Functions

bgc_isocap

Evaluates the isocapnic quotient (Q) following Eq. (8) of Humphreys et al. (2018); its approximation, following their Eq. (6); and the "released CO₂:precipitated carbonate ratio" for calcification, of Frankignoulle et al. (1994).

Usage

[Q, Qx, Psi] = bgc_isocap(pco2, dic, temp, sal);

Inputs

Variable	Description	Unit	Type
`pco2`	Partial pressure of CO₂ in seawater	μatm	double
`dic`	Dissolved inorganic carbon	μmol/kg-sw	double
`temp`	Seawater temperature	°C	double
`sal`	Practical salinity	-	double

Outputs

Variable	Description	Unit	Type
`Q`	Isocap slope, i.e. ∂TA/∂DIC at constant seawater pCO₂	-	double
`Qx`	Approximation to the isocap slope	-	double
`Psi`	Special case of Φ for calcification (i.e. Ψ of Frankignoulle et al., 1994)	-	double

bgc_phi

Calculates Φ, the amount of CO₂ that must be released from or added to seawater after a change in TA and/or DIC in order to return back to the original seawater pCO₂, following Eq. (10) of Humphreys et al. (2018).

Usage

Phi = bgc_phi(Q,Aq_Cq);

Inputs

Variable	Description	Unit	Type
`Q`	Isocap slope, i.e. ∂TA/∂DIC at constant seawater pCO₂	-	double
`Aq_Cq`	1×2 vector of [ΔTA, ΔDIC]	μmol/kg-sw	double

Output

Variable	Description	Unit	Type
`Phi`	Φ, of Humphreys et al. (2018) Eq. (10)	μmol/kg-sw	double

bgc_normalise

Normalises an input vector to a magnitude of unity.

Usage

nCq_nAq = bgc_normalise(Aq_Cq);

Input

Variable	Description	Unit	Type
`Aq_Cq`	1×2 vector of [ΔTA, ΔDIC]	μmol/kg-sw	double

Output

Variable	Description	Unit	Type
`nAq_nCq`	Input vector normalised with a magnitude of unity	μmol/kg-sw	double