ze_from_chla: Compute the lower limit of the euphotic zone from integrated...
In jiho/castr: Process CTD casts

Description Usage Arguments Details Value References See Also Examples

Compute the lower limit of the euphotic zone from integrated chlorophyll content

1	ze_from_chla(chla, depth, fit = c("piecewise-linear", "polynomial"))

`chla`	vector of chlorophyll concentration, in mg m-3.
`depth`	vector of depths at which `chla` is measured.
`fit`	method use to represent the relationship between `Ze` and integrated chlorophyll.

The lower limit of the euphotic zone (Ze) is normally computed from downwelling PAR irradiance (see ze_from_par()). But Morel (1988) modelled a strong correlation between integrated chlorophyll content and Ze. Morel and Berthon (1989) defined an approximation of this relationship (equations 1a and 1b). Morel and Maritorena (2001) provided an improved parameteriazation of the relationship, using either a piece-wise linear model or a polynomial one. This later parameterization is used here.

The piecewise linear relationship is valid for Ze in [10, 180] while the polynomial one is valid for Ze in [5, 180]. The function returns NA outside those ranges.

The depth of the lower limit of the euphotic zone.

Morel (1988). Optical modeling of the upper ocean in relation to its biogenous matter content (case I waters). Journal of Geophysical Research: Oceans, 93(C9), 10749-10768.

Morel and Berthon (1989). Surface pigments, algal biomass profiles, and potential production of the euphotic layer: Relationships reinvestigated in view of remote‐sensing applications. Limnology and Oceanography, 34(8), 1545-1562.

Morel and Maritorena (2001). Bio-optical properties of oceanic waters: A reappraisal. Journal of Geophysical Research: Oceans, 106(C4), 7163-7180. https://doi.org/10.1029/2000JC000319

interpolate() to interpolate chla vertically to a greater precision (as advised by Morel and Maritorena, 2001), smooth() for smoothing.

Other functions computing remarkable depths: clined, maxd, mld, ze_from_par, ze_from_surface_chla

plot(-depth ~ chla, data=d, type="l")
Ze <- ze_from_chla(d$chla, d$depth)
abline(h=-Ze, col="chartreuse4")

Ze <- ze_from_chla(d$chla, d$depth, fit="poly")
# same result