Variability in optical particle backscattering in contrasting bio-optical oceanic regimes
Résumé
Variability in the optical particle backscattering coefficient (b(bp)) is investigated in oceanic waters from two sites, namely the BOUee pour l'acquiSition d'une Serie Optique a Long termE site in the northwestern Mediterranean Sea and the Plumes and Blooms stations in the Santa Barbara Channel off Southern California. Data from these two sites span two orders of magnitude in b(bp) and likely cover typical open ocean values. A significant relationship is found between b(bp) at wavelengths of 442 and 555 nm and chlorophyll concentration. However the large spread in this relationship makes chlorophyll a poor predictor of b(bp). The relationship between b(bp) and the particulate beam attenuation coefficient at 660 nm is tighter for both sites, indicating covariability of the particle size ranges that determine both coefficients. A detailed study of the seasonal changes of the b(bp) vs. chlorophyll relationship reveals that this bio-optical relationship might be best described as a succession of distinct regimes with rapid transitions from one to another. The backscattering ratio ((b) over tilde (bp); the ratio of b(bp) to total particulate scattering, b(p)) ranges from about 0.2% to 1.5%, which is similar to previously reported values. The relationship between (b) over tilde (bp) and chlorophyll was not significant, while values of the backscattering ratio varied spectrally.