Gridded monthly chlorophyll climatology of the northern Indian Ocean utilizing BGC-Argo vertical profiles and remote sensing data.

A gridded chlorophyll climatology for the northern Indian Ocean is generated using the remote sensing data from MODIS-Aqua for surface and available in-situ biogeochemical (BGC)-Argo measured chlorophyll profiles for the sub-surface. In total, 6790 in-situ profiles from 40 BGC-Argo floats obtained from 2012 to 2020 have been used to generate the BGC-Argo-based chlorophyll product pertaining to the northern Indian Ocean. The gridded product is validated with a set of random profiles that are not used in its generation, and a correlation of 0.97 is observed. Other statistical parameters, viz., standard deviation and number of observations, are generated to check the uncertainty of the product. Surface chlorophyll data is used to amend the in-situ profiles to bring parity between the two observations. All the well-known signatures of chlorophyll variability on a monthly scale at surface and at different depths, viz., upwelling-induced productivity, convective mixing, are well captured by this three-dimensional gridded product, thereby authenticating its utility. The depth and concentration of deep chlorophyll maxima (DCM) have captured their temporal dynamics in terms of both depth and chlorophyll abundance on a spatial scale for the first time in this region. Depth-time sections along meridional and zonal axes captured the variability of chlorophyll distribution across the Arabian Sea (AS) and Bay of Bengal (BoB), reinforcing established patterns and shedding light on the underlying spatial and temporal variability. This initial product can be updated regularly with the availability of new profiles to increase its reliability and reduce uncertainties. Research Highlights: A three-dimensional gridded chlorophyll product using BGC-Argo chlorophyll profiles for the north Indian Ocean is generated for the first time. BGC-Argo chlorophyll profiles are collocated with Satellite-based chlorophyll to calibrate the factory coefficients of the BGC-Argo float to bring parity among all the observations. The variability of sub-surface chlorophyll distribution at different depths is observed The monthly variability of the depth of deep chlorophyll maximum and its concentration is mapped. [ABSTRACT FROM AUTHOR]