A Conceptual Approach to Partitioning a Vertical Profile of Phytoplankton Biomass Into Contributions from Two Communities

Robert J. W. Brewin, Giorgio Dall'Olmo, John Gittings, Xuerong Sun, Priscila K. Lange, Dionysios E. Raitsos, Heather A. Bouman, Ibrahim Hoteit, Jim Aiken, Shubha Sathyendranath

Research output: Contribution to journalArticlepeer-review

Abstract

We describe an approach to partition a vertical profile of chlorophyll-a concentration into contributions from two communities of phytoplankton: one (community 1) that resides principally in the turbulent mixed-layer of the upper ocean and is observable through satellite visible radiometry; the other (community 2) residing below the mixed-layer, in a stably stratified environment, hidden from the eyes of the satellite. The approach is tuned to a time-series of profiles from a Biogeochemical-Argo float in the northern Red Sea, selected as its location transitions from a deep mixed layer in winter (characteristic of vertically well-mixed systems) to a shallow mixed layer in the summer with a deep chlorophyll-a maximum (characteristic of vertically stratified systems). The approach is extended to reproduce profiles of particle backscattering, by deriving the chlorophyll-specific backscattering coefficients of the two communities and a background coefficient assumed to be dominated by non-algal particles in the region. Analysis of the float data reveals contrasting phenology of the two communities, with community 1 blooming in winter and 2 in summer, community 1 negatively correlated with epipelagic stratification, and 2 positively correlated. We observe a dynamic chlorophyll-specific backscattering coefficient for community 1 (stable for community 2), positively correlated with light in the mixed-layer, suggesting seasonal changes in photoacclimation and/or taxonomic composition within community 1. The approach has the potential for monitoring vertical changes in epipelagic biogeography and for combining satellite and ocean robotic data to yield a three-dimensional view of phytoplankton distribution
Original languageEnglish (US)
JournalJournal of Geophysical Research: Oceans
Volume127
Issue number4
DOIs
StatePublished - Mar 18 2022

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