argopy.extensions.OpticalModeling.DCM

argopy.extensions.OpticalModeling.DCM#

OpticalModeling.DCM(axis: str = 'PRES', chla: str = 'CHLA', bbp: str = 'BBP700', max_depth: float = 300.0, resolution_threshold: float = 3.0, median_filter_size: int = 5, surface_layer: float = 15.0, inplace: bool = True, axis_bbp: str = 'PRES') → DataArray | Dataset[source]#

Search and qualify Deep Chlorophyll Maxima

This method return the main characteristics and drivers of Deep Chlorophyll Maxima (DCM). Different drivers are possible because DCMs result from photo-acclimation or biomass accumulation, depending on the availability of light and nitrate. See notes below.

Parameters:

  • axis (str, optional, default='PRES') – Name of the pressure axis to use for CHLA and BBP. If BBP is not on the same vertical axis as CHLA, you can specify which variable to use with the optional parameter axis_bbp.

  • chla (str, optional, default='CHLA') – Name of the Chl-a concentration variable to use.

  • bbp (str, optional, default='BBP700') – Name of the particulate backscattering coefficient variable to use.

  • inplace (bool, optional, default: True) – Should we return the new variable (False) or the dataset with the new variable added to it (True).

  • max_depth (float, optional, default: 300.) – Maximum depth allowed for a deep CHLA maximum to be found.

  • resolution_threshold (float, optional, default: 3.) – CHLA vertical axis resolution threshold below which a smoother is applied.

  • median_filter_size (int, optional, default: 5) – Size of the scipy.ndimage.median_filter() filter used with CHLA.

  • surface_layer (float, optional, default: 15.) – Depth value defining the surface layer above which twice the median CHLA value may qualify a DCM as such.

Returns:

DCM driver as a xarray.DataArray or, if the inplace argument is True, dataset is modified in-place with new variable DCM.

Return type:

xarray.DataArray or xarray.Dataset

See also

Dataset.argo.optic, argopy.utils.optical_modeling.DCM

Notes

Following [1] Section 2.4 “Identification and Classification of Deep Maxima Profiles”, a DCM is identified and then qualified along this procedure:

  • the depth of the Chla maximum is searched between the first vertical level and max_depth, 300m by default, assuming that no phytoplankton Chla can develop below 300 m.

  • A Chla profile is definitively qualified as a DCM if the maximum Chla value of the un-smoothed profile is greater than twice the median of the Chla values at depths above surface_layer (15. by default).

If the vertical resolution is less than 3 db or meters, the Chla profile is smoothed using a scipy.ndimage.median_filter() filter.

If the vertical resolution is less than 3 db or meters, the BBP profile is smoothed using a scipy.ndimage.median_filter() and a scipy.ndimage.uniform_filter1d() filters.

References

[1]

Cornec, M., Claustre, H., Mignot, A., Guidi, L., Lacour, L., Poteau, A., et al. (2021). Deep

chlorophyll maxima in the global ocean: Occurrences, drivers and characteristics. Global Biogeochemical Cycles, 35, e2020GB006759. https://doi.org/10.1029/2020GB006759

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