Fig. 8
Fluorometric Chl a correction for calibrations. Standard methods of determining Fluorometric Chl a at Station ALOHA do not account for the contribution of Chl b and may therefore underestimate Chl a concentrations. The ratio of Chl a to Chl b decreases with depth (left). Chl a concentrations derived from HPLC measurements significantly correlate with fluorometrically determined Chl a (p-value < 0.0001), but are typically higher (center), especially at increasing depths where the relative contribution of Chl b to total Chl is higher. To account for this disagreement, we adjusted all Fluorometric Chl a concentrations using the linear regression between HPLC and Fluorometric Chl a concentrations derived from HOT observations. Only measurements deeper than 85 m (black dashed reference line in left, right panels) were used for the regression and adjusted. The adjusted Fluorometric Chl a concentrations are in good agreement with HPLC Chl a measurements (right). For the 2023 Seaglider missions, the adjusted Fluorometric Chl a observations were used for calibration.
