Abstract
Coccolithophores (calcifying phytoplankton) form extensive blooms in temperate and subpolar oceans as evidenced from ocean‐color satellites. This study examines the potential to detect coccolithophore blooms with BioGeoChemical‐Argo (BGC‐Argo) floats, autonomous ocean profilers equipped with bio‐optical and physicochemical sensors. We first matched float data to ocean‐color satellite data of calcite concentration to select floats that sampled coccolithophore blooms. We identified two floats in the Southern Ocean, which measured the particulate beam attenuation coefficient (c p) in addition to two core BGC‐Argo variables, Chlorophyll‐a concentration ([Chl‐a]) and the particle backscattering coefficient (b bp). We show that coccolithophore blooms can be identified from floats by distinctively high values of (1) the b bp/c p ratio, a proxy for the refractive index of suspended particles, and (2) the b bp/[Chl‐a] ratio, measurable by any BGC‐Argo float. The latter thus paves the way to global investigations of environmental control of coccolithophore blooms and their role in carbon export.
Highlights
Detecting major phytoplankton groups is essential to improve our understanding of the global biogeochemical cycles
The coccolithophore bloom detection method proposed in this study from time series analyses of satellite [PIC] showed that both floats operated throughout a coccolithophore bloom (Figures 2a and 2d)
Ocean‐color satellite observations of coccolithophore blooms were matched with bio‐optical measurements from BGC‐Argo floats to test the feasibility of developing a float‐based detection method for coccolithophore blooms
Summary
Detecting major phytoplankton groups is essential to improve our understanding of the global biogeochemical cycles One such group is the coccolithophores, calcifying phytoplankton which form calcite platelets called coccoliths. The coccolithophore species Emiliania huxleyi forms extensive blooms in the temperate and subpolar surface ocean, characterized by detachment and overproduction of coccoliths in the bloom decline phase (Balch et al, 1991, 1996). The accumulation of these high‐refractive‐index calcite particles increases the light backscattered from the ocean surface and colors the water milky‐turquoise (Holligan et al, 1983). Ship missions cover limited spatiotemporal scales and satellites are limited to surface waters and clear‐sky conditions, creating observational gaps, in high‐latitude regions
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