Enrichment index related to seamounts and islands in the South West Indian Ocean from chlorophyll-a satellite remote sensing data

This data set is the result of the calculation of an original “enrichment index” (EI) from chlorophyll-a (chl-a) remote sensing data (MODIS-Aqua sensor) and initially dedicated to highlight localized chl-a enrichments associated to isolated seamounts and islands in the South West Indian Ocean, in order to estimate their contribution in increasing the local primary productivity. Details and results are described in the DSR-II paper entitled “Satellite observations of phytoplankton enrichments around seamounts in the South West Indian Ocean with a special focus on the Walters Shoal” from Demarcq et al. 2020.
    1. Initial data used
We used daily L3 data chl-a and sea surface temperature (SST) collected by the MODIS (Moderate-resolution Imaging Spectroradiometer) sensor on board the Aqua platform (downloaded from https://oceancolor.gsfc.nasa.gov/) from January 2003 to December 2018. This has  a spatial resolution of 1/24° (ca. 4.5–5 km). The data covers the region  (45°S – 10°S / 25°W – 80°W).
    2. The calculation method
The calculations were done at the pixel level. The EI is the difference (expressed in %) between the value of each ‘candidate pixel’ and its medium range surrounding, defined as the average value of all chl-a values around the candidate pixel between a fix range of distance between 30 and 90 km, the R1 and R2 terms of the equation enclosed.
    3. Data sets
The data set contains two files:
  - the monthly climatology (12 frames) of the EI from January to December (2003 to 2018 average), in an internally compressed netCDF-4 format (NC-compliant or almost)
  - the yearly average of the EI (period 01/2003 - 12/2018)

Two images are joined with this data set:
  -  a "technical view" of the yearly average of the index for the full region sub-region (45°S – 10°S / 25°W – 80°W)
     (file: indsw4_modis_p100_4km_16y_20030101_20181231.R2018.0.enrichment-index.dist-30-90km.png).

  -  a slightly improved view of the yearly average of the index for the sub-region (40°S – 10°S / 30°W – 70°W).
     (file: Figure-enrichment-index.pdf)

An improved version of this index will be available in a near future.