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Continuous bio-optical measurements of chloropyll a and turbidity along RV MARIA S. MERIAN cruise MSM97/2

Underway bio-optical sensor measurements of chlorophyll a and turbidity were acquired along the cruise track of RV MARIA S. MERIAN cruise MSM97/2. Measurements were collected with two autonomous measurement systems (RSWS), which are located at 6.5 m below the sea surface. Usually, the RWS-System with measuring container 1 and 2 (MC1 and MC2) interchanged after 6 hours. Only en route data was collected and quality controlled. No data from stationary measurements (in situ) were included. Quality Control specifically for biogeochemical measurements had been applied. For details to all processing steps see Data Processing Report.

Continuous optical measurements of absorbance via UV-process spectrophotometer OPUS along RV MARIA S. MERIAN cruise MSM97/2

During R/V Maria S. Merian cruise MSM97/2 a sensor box (AddOn Box) was attached to a PocketFerryBox (4H Jena, Germany) in-line obtaining waters from the ships two autonomous measurement systems (RSWS). For the measurement of underway absorption spectra to calculate optical nitrate, the AddOn Box was equipped with two UV-process spectrophotometer (ProPS and OPUS, TriOS Mess- und Datentechnik GmbH, Germany). Data were recorded continuously in a ten-minute interval along the cruise track with an optical path length of 10 mm. The integration time was 256 ms. The ProPS photometer is equipped with a Deuterium lamp as light source whereas the OPUS photometer is equipped with a Xenon flash lamp. Baseline calibrations were done for both UV-photometer using ultrapure water. For the ProPS, the calibration was done in the laboratory before the cruise whereas the calibration for the OPUS was done by the manufacturer. The water inlet of the RSWS is allocated at approx. 6.5 m below the sea surface. While one box is measuring, the other box is being cleaned. The boxes switch after a user-defined measuring and cleaning interval. On MSM97/2, the boxes were alternating every 12 hours, including one short cleaning procedure during measurements after 4 hours. Absorption spectra obtained by the AddOn Box during the alternation process of the two RSWS, as well as during the internal cleaning procedure are not included. Spectra from station work are included. Within this dataset, absorption spectra were cut to a relevant wavelength range (from 189-360 nm (ProPS) and 199-360 nm (OPUS) to 210-260 nm). No further correction was done for the absorbance spectra in this processing step.

Continuous optical measurements of absorbance via UV-process spectrophotometer ProPS along RV MARIA S. MERIAN cruise MSM97/2

During R/V Maria S. Merian cruise MSM97/2 a sensor box (AddOn Box) was attached to a PocketFerryBox (4H Jena, Germany) in-line obtaining waters from the ships two autonomous measurement systems (RSWS). For the measurement of underway absorption spectra to calculate optical nitrate, the AddOn Box was equipped with two UV-process spectrophotometer (ProPS and OPUS, TriOS Mess- und Datentechnik GmbH, Germany). Data were recorded continuously in a ten-minute interval along the cruise track with an optical path length of 10 mm. The integration time was 256 ms. The ProPS photometer is equipped with a Deuterium lamp as light source whereas the OPUS photometer is equipped with a Xenon flash lamp. Baseline calibrations were done for both UV-photometer using ultrapure water. For the ProPS, the calibration was done in the laboratory before the cruise whereas the calibration for the OPUS was done by the manufacturer. The water inlet of the RSWS is allocated at approx. 6.5 m below the sea surface. While one box is measuring, the other box is being cleaned. The boxes switch after a user-defined measuring and cleaning interval. On MSM97/2, the boxes were alternating every 12 hours, including one short cleaning procedure during measurements after 4 hours. Absorption spectra obtained by the AddOn Box during the alternation process of the two RSWS, as well as during the internal cleaning procedure are not included. Spectra from station work are included. Within this dataset, absorption spectra were cut to a relevant wavelength range (from 189-360 nm (ProPS) and 199-360 nm (OPUS) to 210-260 nm). No further correction was done for the absorbance spectra in this processing step.

Calculated optical Nitrate along RV MARIA S. MERIAN cruise MSM97/2

During R/V Maria S. Merian cruise MSM97/2 a sensor box (AddOn Box) was attached to a PocketFerryBox (4H Jena, Germany) in-line obtaining waters from the ships two autonomous measurement systems (RSWS). For the measurement of underway absorption spectra to calculate optical nitrate, the AddOn Box was equipped with two UV-process spectrophotometer (ProPS and OPUS, TriOS Mess- und Datentechnik GmbH, Germany). Data were recorded continuously in a ten-minute interval along the cruise track with an optical path length of 10 mm. The integration time was 256 ms. The ProPS photometer is equipped with a Deuterium lamp as light source whereas the OPUS photometer is equipped with a Xenon flash lamp. Baseline calibrations were done for both UV-photometer using ultrapure water. For the ProPS, the calibration was done in the laboratory before the cruise whereas the calibration for the OPUS was done by the manufacturer. The water inlet of the RSWS is allocated at approx. 6.5 m below the sea surface. While one box is measuring, the other box is being cleaned. The boxes switch after a user-defined measuring and cleaning interval. On MSM97/2, the boxes were alternating every 12 hours, including one short cleaning procedure during measurements after 4 hours. Absorption spectra obtained by the AddOn Box during the alternation process of the two RSWS, as well as during the internal cleaning procedure are not included. Spectra from station work are included. Within this dataset, absorption spectra were cut to a relevant wavelength range (from 189-360 nm (ProPS) and 199-360 nm (OPUS) to 210-260 nm). No further correction was done for the absorbance spectra in this processing step. After the cruise, gathered absorption spectra were used to improve current processing algorithms of optical nitrate detection for coastal and open ocean waters. Processing was performed according to Zielinski et al. (2011) and Frank et al. (2014) using MATLAB (R2018a). Detailed processing steps for the calculation of optical nitrate can be found on Zenodo (doi 10.5281/zenodo.4091420 ). Temperature and salinity data are necessary to compute nitrate values from derived UV-spectra and were taken from the attached PocketFerryBox using a SBE45 probe (Sea Bird Scientific, USA). A linear CDOM-offset correction was carried out. Nitrate reference spectra and salinity reference spectra were measured in the laboratory before the cruise. Corresponding nitrate reference samples using wet chemical analysis will be published separately.

Reference measurements of surface waters during the RV MARIA S. MERIAN cruise MSM97/2

Reference measurements of surface waters were collected during the RV MARIA S Merian cruise MSM97/2 (12.12.2020 - 23.12.2020, Emden, Germany - Emden Germany). Accompanying the underway measurements of the DAM transit cruise water samples were taken from the CTD and the onboard measurement containers (RSWS) for later validation of bio-optical water properties. Turbidity and fluorescent dissolved organic matter (fDOM) were measured directly onboard via handheld instruments (see methods/device) whereas suspended particular matter (SPM) and chlorophyll a (Chl a) were filtered onboard on glas fibre filters (GFF, 47mm, 0,7 µm) and frozen at -25°C and -80°C immediately after sampling. Values were determined in the lab after the cruise within 2 months, for SPM via gravimetric analysis and for Chl a according to EPA Method 445. Water samples for nitrate analysis were taken and frozen at -25°immediately after sampling for later lab analysis according to Grasshoff et al. (1999).

Continuous optical measurements of absorbance for the calculation of optical Nitrate along RV MARIA S. MERIAN cruise MSM97/2

During R/V Maria S. Merian cruise MSM97/2 a sensor box (AddOn Box) was attached to a PocketFerryBox (4H Jena, Germany) in-line obtaining waters from the ships two autonomous measurement systems (RSWS). For the measurement of underway absorption spectra to calculate optical nitrate, the AddOn Box was equipped with two UV-process spectrophotometer (ProPS and OPUS, TriOS Mess- und Datentechnik GmbH, Germany). Data were recorded continuously in a ten-minute interval along the cruise track with an optical path length of 10 mm. The integration time was 256 ms. The ProPS photometer is equipped with a Deuterium lamp as light source whereas the OPUS photometer is equipped with a Xenon flash lamp. Baseline calibrations were done for both UV-photometer using ultrapure water. For the ProPS, the calibration was done in the laboratory before the cruise whereas the calibration for the OPUS was done by the manufacturer. The water inlet of the RSWS is allocated at approx. 6.5 m below the sea surface. While one box is measuring, the other box is being cleaned. The boxes switch after a user-defined measuring and cleaning interval. On MSM97/2, the boxes were alternating every 12 hours, including one short cleaning procedure during measurements after 4 hours. Absorption spectra obtained by the AddOn Box during the alternation process of the two RSWS, as well as during the internal cleaning procedure are not included. Spectra from station work are included. Within this dataset, absorption spectra were cut to a relevant wavelength range (from 189-360 nm (ProPS) and 199-360 nm (OPUS) to 210-260 nm). No further correction was done for the absorbance spectra in this processing step. After the cruise, gathered absorption spectra were used to improve current processing algorithms of optical nitrate detection for coastal and open ocean waters. Processing was performed according to Zielinski et al. (2011) and Frank et al. (2014) using MATLAB (R2018a). Detailed processing steps for the calculation of optical nitrate can be found on Zenodo (doi 10.5281/zenodo.4091420 ). Temperature and salinity data are necessary to compute nitrate values from derived UV-spectra and were taken from the attached PocketFerryBox using a SBE45 probe (Sea Bird Scientific, USA). A linear CDOM-offset correction was carried out. Nitrate reference spectra and salinity reference spectra were measured in the laboratory before the cruise. Corresponding nitrate reference samples using wet chemical analysis will be published separately.

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