A subsurface CF maximum could be biased by non-photochemical quenching (NPQ) [45 (link)], exhibiting as a subsurface peak, by quenching the signal close to the surface rather than representing the true distribution of chlorophyll a in the water column. We compared CF predictions from in situ AUV data and shipborne CF measurements with the in vitro concentrations of chlorophyll a from water samples. To validate the data retrieved from sensors, discrete water samples for measurement of in vitro chlorophyll a were collected using 10 L Niskin bottles [46 ] on board the work boat. Sample depths were selected based on layers of relatively high, medium and low chlorophyll a concentrations estimated by the model generated in the operator hub from data from the AUVs. Seawater was filtered (0.5 L) onto Whatman GF/F glass fiber filters [5 (link)]. In the laboratory, chlorophyll a was extracted in 100% methanol after 20 hours at −20°C in darkness. The chlorophyll a concentrations were determined using a Turner Designs Trilogy fluorometer (model: 7200–000) following the non-acidification method [47 (link)].
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