Fluorescence measurements of dissolved matter during RV METEOR cruise M148/2 in the Benguela Upwelling System and Angola Gyre

Water samples were taken from surface, deep chlorophyll maximum (DCM), oxygen depleted zone underneath the DCM and at depth layers aboard the RV Meteor during the cruise M148-2 in July 2018. The cruise was conducted in the Atlantic Ocean covering the Angola Gyre as well as the Benguela Upwelling System off the coast of Namibia. Here we report the measurements of fluorescent dissolved organic matter (FDOM) and chlorophyll-a fluorescence properties that were completed immediately after sample collection from the CTD rosette on board RV Meteor. 250 ml of water sample was poured into Schott glasses covered in aluminum foil to create a dark container and was left to reach room temperature for about 30 to 60 minutes. Filtration for the FDOM samples was completed using a 25 mm Nuclepore with pore size of 0.2 µm filter syringe and the filtrate was poured directly into a 1 cm quartz cuvette that had been pre-rinsed with Milli-Q water. This cuvette was again pre-rinsed three times with the filtrate water before measurement as recommended (Garaba et al., 2014). For the chlorophyll measurements the unfiltered sample was filled directly into the 1 cm quartz cuvette, again pre-rinsing was done three times with the unfiltered sample water. Here, we used Milli-Q as a reference blank sample. Fluorescence was determined using a Perkin Elmer LS55 fluorometer. During the FDOM measurements, the excitation spectrum was set from 220 nm to 450 nm at a 5 nm resolution whilst the emission wavelength range was from 240 nm to 560 nm at 0.5 nm resolutions. As for the chlorophyll-a observations, the excitation wavelengths ranged from 440 nm to 480 nm at 5 nm intervals and the emission spectrum ranged from 460 nm to 800 nm in 0.5 nm steps. The provided dataset contains the raw intensity units for each measurement.