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Sonderforschungsbereich Transregio 172 (SFB TRR): Arktische Verstärkung: Klimarelevante Atmosphären- und Oberflächenprozesse und Rückkopplungsmechanismen (AC)3, Teilprojekt C03: Atmosphärische Zusammensetzung und Ozeanfarbe der Arktis abgeleitet von Satellitenmessungen

Die Änderungen und Verbindungen zwischen Halogenen und Phytoplankton sowie deren Reaktion auf veränderliche physikalische Eigenschaften (Meereisbedeckung und Dicke, welche abhängig vom Alter, Temperatur, Schichtung, Strahlung, usw. der Ozeanoberfläche und ABL ist) ist der wissenschaftliche Fokus dieses Teilprojekts. Um die Zielsetzungen zu erreichen werden konsistente und gemeinsame Datenprodukte, abgeleitet von Fernerkundungsinstrumenten auf Satelliten, generiert und analysiert um einen genaueren Einblick in die Änderungen der Bestandteile und Phytoplanktonarten sowie CDOM Absorption der letzten Jahrzehnte zu erhalten.

Absorption coefficients by coloured dissolved organic matter at 443 nm from a global in-situ collection of open ocean, coastal and inland surface waters matched to Ocean Land Colour Instrument

This in situ data set of absorption coefficients by coloured dissolved organic matter at band centred at 442.5 nm (aCDOM(443)), note: for brevity the band is named 443) consists of different data sets gathered together from measurements collected in open, coastal, and inland surface waters spread around the globe and covering the time from first data delivery by Ocean Land Colour Imager (OLCI) on Sentinel-3A (S3A) in May 2016 until November 2022 which were matched to OLCI on S3A and S3B and used in the paper by Bracher et al. (2025). We only used the absorption coefficient data derived from measurements on discrete water samples to ensure a similar method procedure followed and a similar uncertainty. It includes publicly available data and newly collected, measured and analysed data sets from the Phytooptics group at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI, PI: Astrid Bracher) and Hellenic Centre for Marine Research (HCMR, PI: Andrew C. Banks). This collection was matched that in situ data points had to fall within the 3x3 OLCI FR pixel box and a time window of + 12 hours which followed established community protocols (IOCCG 2018, IOCCG 2019) and particularly EUMETSAT's OLCI matchup protocol (EUMETSAT 2022). Firstly, a pre-processing for quality control and a conversion of the considered in situ data to a common format following Valente et al. (2022) was performed. We flagged and disregarded the following data from the final quality-controlled data set which had (1) unrealistic or missing date or geographic coordinate fields, (2) poor quality (e.g., original flags) or method of observation that did not meet the criteria for the dataset (e.g., not defined in the community protocols (IOCCG 2018, 2019a), and (3) spuriously high or low data. For the last item, the following limits were imposed: [0.0001–10] m−1 for aCDOM(443). OLCI pixels were discarded when flagged with the recommended flags in (EUMETSAT 2022), and the remaining matchups were only considered valid if more than 50% of satellite pixels were available at remote sensing reflectance centred at band 560 nm (Rrs(560), e.g., 5 out of 9 for the 3x3 criterion) per an in situ data point, and a coefficient of variation <0.2. Dedicated matchup software developed by EUMETSAT was used to ensure that the validation process followed the established guidelines, ThoMaS (the Tool to generate Matchups of OC products with S3 OLCI https://gitlab.eumetsat.int/eumetlab/oceans/ocean-science-studies/ThoMaS). In situ data from AODN-2 and Lehmann22 (see description of specific datasets below) were already provided at the nominal OLCI band 443 nm. All other aCDOM(λ) data were provided in hyperspectral resolution (1nm, 2nm or around 3.3 nm resolution). Following Zibordi et al. (2023), these hyperspectral absorption coefficients were transformed to the nominal OLCI bands by averaging over the specific bandwidth. The OLCI matchup data, based on their associated RRS data at the first eight OLCI bands, were assigned to the specific optical water classes (OWCs) according to the Mélin & Vantrepotte (2015) classification. This contains 17 OWCs which range from very turbid to (OWC 1) oligotrophic to very clear waters (OWC 17). The OWC is also delivered for each matchup point (if the assignment fails the field contains "NaN". We provide also for OLCI the standard deviation of the OLCI matchup data to a in situ data point within the 3x3 pixels. For the in situ data we provide the estimate of the uncertainty for each matchup point further described in Bracher et al. (2025).

Absorption coefficients by coloured detrital and dissolved organic matter from a global surface water in-situ collection at the first eight bands of and matched to the Ocean Land Colour Imager (OLCI)

This data set of absorption coefficients by coloured detrital and dissolved organic matter at the first eight Ocean Land Colour Imager (OLCI) bands (centred at 400 nm 412.5 nm, 442.5 nm, 490 nm, 510 nm, 560 nm, 620 nm, 665 nm, abbreviated as aCDM(400), aCDM(412), aCDM(443), aCDM(490), aCDM(510), aCDM(560), aCDM(620), and aCDM(665)) consists of different data sets gathered together in situ from measurements collected in open, coastal, and inland szrface waters spread around the globe and covering the time from first data delivery by OLCI on S3A in May 2016 until November 2022 which were matched to Ocean Land Colour Imager on Sentinel-3A and -3B and used in the paper by Bracher et al. (2025). We only used coincident hyperspectral absorption coefficients by non-algal particulates and coloured dissolved organic matter derived from measurements on discrete water samples to ensure a similar method procedure followed and a similar uncertainty. These coincident measurements were summed up to calculate aCDM(λ). The collection includes the matched OLCI aCDOM products and the publicly available data and newly collected, measured and analysed data sets from the Phytooptics group at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI, PI: Astrid Bracher) and Hellenic Centre for Marine Research (HCMR, PI: Andrew C. Banks). The data collection was matched that in situ data points had to fall within the 3x3 OLCI FR pixel box and a time window of + 12 hours which followed established community protocols (IOCCG 2018) and particularly EUMETSAT's OLCI matchup protocol (EUMETSAT 2022). Firstly, a pre-processing for quality control and a conversion of the considered in situ data to a common format following Valente et al. (2022) was performed. We flagged and disregarded the following data from the final quality-controlled data set which had (1) unrealistic or missing date or geographic coordinate fields, (2) poor quality (e.g., original flags) or method of observation that did not meet the criteria for the dataset (e.g., not defined in the community protocols (IOCCG 2018, 2019a, 2019b), and (3) spuriously high or low data. For the last item, the following limits were imposed: [0.0001–10] m−1 for aCDM(443). OLCI pixels were discarded when flagged with the recommended flags in (EUMETSAT 2022), and the remaining matchups were only considered valid if more than 50% of satellite pixels were available at remote sensing reflectance centred at band 560 nm (Rrs(560), e.g., 5 out of 9 for the 3x3 criterion) per an in situ data point, and a coefficient of variation <0.2. Dedicated matchup software developed by EUMETSAT was used to ensure that the validation process followed the established guidelines, ThoMaS (the Tool to generate Matchups of OC products with S3 OLCI https://gitlab.eumetsat.int/eumetlab/oceans/ocean-science-studies/ThoMaS). The aCDM(λ) data provided in hyperspectral resolution (1nm, 2nm or around 3.3 nm resolution) were transformed to the nominal OLCI bands by averaging over the specific bandwidth, following Zibordi et al. (2023). The OLCI matchup data, based on their associated RRS data at the first eight OLCI bands, were assigned to the specific optical water classes (OWCs) according to the Mélin & Vantrepotte (2015) classification. This contains 17 OWCs which range from very turbid to (OWC 1) oligotrophic to very clear waters (OWC 17). The OWC is also delivered for each matchup point (if the assignment fails the field contains "NaN". We provide also for OLCI the standard deviation of the OLCI matchup data to a in situ data point within the 3x3 pixels. For the in situ data we provide the estimate of the uncertainty for each matchup point further described in Bracher et al. (2025).

Colored dissolved organic matter (CDOM) absorption coefficients in the sea-surface microlayer and the underlying water during a mesocosm phytoplankton bloom in 2023

The effects of a phytoplankton bloom and photobleaching on colored dissolved organic matter (CDOM) in the sea-surface microlayer (SML) and the underlying water (ULW) were studied in a month-long mesocosm study, in May and June of 2023, at the Institute for Chemistry and Biology of the Marine Environment (ICBM) in Wilhelmshaven, Germany. The mesocosm study was conducted by the DFG research group BASS (Biogeochemical processes and Air–sea exchange in the Sea-Surface microlayer, Bibi et al., 2025) in the Sea Surface Facility (SURF) of the ICBM. The facility contains an 8 m × 1.5 m × 0.8 m large outdoor basin with a retractable roof, which was closed at night and during rain events. The basin was filled with North Sea water from the adjacent Jade Bay. Homogeneity of the ULW in the basin was achieved by constant mixing of the water column. The daily SML and ULW samples were collected alternating in the morning, about 1 h after sunrise, and in the afternoon, about 10 h after sunrise. The alternation of sampling times intended to capture a potential effect of sun-exposure duration on DOM transformations and elucidated the day and night variability of the layers. The SML was collected via glass plate sampling (Cunliffe and Wurl, 2014). The ULW was sampled via a submerged tube and a connected syringe suction system in 0.4 m depth. The removed sample volume was refilled with Jade Bay water every day. SML and ULW samples were filtered through pre-flushed 0.7 µm Whatman GF/F and 0.2 nucleopore filters into brown bottles and were stored dark and at 4 °C until measurement within weeks of the study. The brown bottles were previously combusted at 500 °C. CDOM was measured with three liquid waveguide capillary cells (LWCC, WPI, USA) of different pathlengths (10 cm, 50 cm, 250 cm) to increase the measurement sensitivity following the protocols of Röttgers et al. (2024) using a spectral detector (Avantes, Netherlands) for a total spectral range from 230 to 750 nm. A sodium chloride (NaCl) solution was used for the salinity correction. The blank-corrected absorbance spectra were then converted into Napierian absorption coefficients (Bricaud et al., 1981).

Absorption coefficients by coloured dissolved organic matter (CDOM) from North Sea to Fram Strait measured underway with a Liquid Waveguide Capillary Cell system during POLARSTERN cruise PS121

Water samples were taken during North Sea to Fram Strait expedition PS121 with RV Polarstern from 11 Aug to 10 Sep 2019. Water samples were collected from the ship's seawater supply pumped through teflon tubing from about 11m depth during underway as described in Liu et al (2018). The same water samples were measured as in Bracher et al. (2021). Water samples for CDOM absorption analysis are filtered through 0.2 µm filters and analysed onboard with a 2.5-m path length liquid waveguide capillary cell system (LWCC, WPI) following Levering et al. (2017). Details on method adaptation to our instrumentation set-up are provided in Alvarez et al. (2022). Salinity data were extracted from https://doi.pangaea.de/10.1594/PANGAEA.930022.

Absorption coefficients by coloured dissolved organic matter obtained underway with a Liquid Waveguide Capillary Cell system during HEINCKE cruise HE462 in the North Sea and Sogne Fjord

Water samples were taken during the spring (29 April to 7 May 2016) expedition HE462 with RV Heincke in the North Sea and Sogne Fjord. Water samples were collected from the ship's seawater supply pumped through teflon tubing from about 5 m depth during underway. These are the same samples as sampled in Bracher and Wiegmann (2019). Water samples for CDOM absorption analysis are filtered through 0.2 µm filters and analysed onboard with a 2.5-m path length liquid waveguide capillary cell system (LWCC, WPI) following Levering et al. (2017). Details on method adaptation to our instrumentation set-up are provided in Alvarez et al. (2022). Salinity data were extracted from https://doi.pangaea.de/10.1594/PANGAEA.873226.

Absorption coefficients by coloured dissolved organic matter obtained at fixed stations with a Liquid Waveguide Capillary Cell system during HEINCKE cruise HE462 in the North Sea and Sogne Fjord

Water samples were taken during the spring (29 April to 7 May 2016) expedition HE462 with RV Heincke in the North Sea and Sogne Fjord. Water samples were collected from CTD Niskin bottles at six different depths from the upper 100 m at 17 Stations. These are the same stations as sampled in Bracher and Wiegmann (2019). Water samples for CDOM absorption analysis are filtered through 0.2 µm filters and analysed onboard with a 2.5-m path length liquid waveguide capillary cell system (LWCC, WPI) following Levering et al. (2017). Details on method adaptation to our instrumentation set-up are provided in Alvarez et al. (2022). Salinity data were extracted from https://doi.pangaea.de/10.1594/PANGAEA.863445.

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