Consistency between fluorometric and remotely sensed chlorophyll in the north west Atlantic

Abstract

Chlorophyll concentration in the marine environment is a critical parameter for understanding the state of the ocean, marine ecosystem modeling and monitoring coastal ecosystem health. Existing ocean observation infrastructure measures ocean chlorophyll on a variety of spatio-temporal scales, depending on if the sensor is based on satellite remote sensing remote or in situ fluorometry. In-situ fluorometric estimates of chlorophyll are plagued by daytime non-photochemical quenching, which reduces chlorophyll concentration estimates from the true value. Furthermore, these fluorometers are known to have broad regional oceanographic sensor biases that potentially inhibit consistency between remote sensing and fluorometric chlorophyll estimates. We used sixty-two calibrated Integrated Ocean Observing System (IOOS) and Ocean Observatories Initiative (OOI) AUV missions to test the hypothesis that correcting for NPQ and known sensor bias will improve the consistency between remotely sensed and fluorometric estimates of chlorophyll concentration. Surprisingly, we find that accounting for NPQ and sensor bias reduces agreement with satellite observations. The most agreement between satellite and AUV measured chlorophyll is by taking an exponentially weighted average of chlorophyll profiles determined by the diffuse attenuation coefficient, and not correcting for NPQ or known global biases on AUV fluorometers. NPQ corrections only improved agreement in coastal waters, where chlorophyll biomass is high and diffuse attenuation are high.