Underway discrete chlorophyll and post-calibrated underway fluorometer data during NES-LTER Transect cruises, ongoing since 2019

The continuous underway fluorescence, induced by in vivo chlorophyll-a (Chl-a), of surface waters of the Northeast U.S. shelf is compared to discrete Chl-a samples for post-calibration, collected ship-board as part of the Northeast U.S. Shelf Long-Term Ecological Research (NES LTER). Chl-a values derived from the manufacturer-calibrated sensors (hereafter, “continuous fluorescence”) and collected continuously are often different from the precise Chl-a concentrations obtained from discrete, extracted samples. Moreover, underway fluorometers and manufacturer calibrations differ per cruise. Thus, post-calibration of the continuous fluorescence signals using discrete Chl-a measurements is essential to standardize and compare the high-resolution underway Chl-a data along cruise tracks. For six cruises aboard the R/V Endeavor between summer 2019 and summer 2021, 12 to 22 discrete samples were collected from the underway system to measure Chl-a concentrations. These discrete Chl-a concentrations were then compared, using simple linear regressions (Model I least square fit), to corresponding continuous fluorescence values recorded by the two independent fluorometers installed with the underway system. For each cruise a preferred fluorometer was identified based on the best fit of the linear regression between discrete Chl-a concentrations and continuous fluorescence values. The slope and the intercept of the linear regression were used to post-calibrate continuous fluorescence values into standardized and intercomparable Chl-a concentration. This data package includes a table for the underway discrete Chl-a values and a table for the 1-min post-calibrated continuous fluorescence values for the preferred underway fluorometer per cruise.