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Molecular and elemental composition of dissolved organic matter in anoxic basins (Mariager Fjord, Denmark; Gotland Basin, Baltic Sea; Black Sea)

The sampling campaigns were conducted in the Black Sea (POS539), Baltic Sea/Gotland Basin (EMB324), and on a boat in Denmark/Mariager Fjord. All three study sites are differently influenced by ocean deoxygenation and anoxia. While Mariager Fjord waters are seasonally anoxic, the deep waters of Gotland Basin and Black Sea can remain anoxic for decades and millennia, respectively. Furthermore, to target potential abiotic reactions, we incubated filtered Gotland Basin waters at low (<1.5µM O2) and high (>200µM O2) oxygen concentrations. All samples were filtered to 0.2 µm pore size and acidified with hydrochloric acid to pH2. DOM was extracted and desalted prior to molecular analysis with ultrahigh resolution mass spectrometry (FT-ICR-MS) following an established method using cartridges filled with a styrene-divinylbenzene copolymer (Agilent Bond Elut PPL, 1 g). This data set contains two files: (1) environmental data, including oxygen concentrations, salinity, temperature, dissolved and solid-phase extractable dissolved carbon (DOC, SPE-DOC), nitrogen (TDN, SPE-DON), sulfur (SPE-DOS), and phosphorus (SPE-DOP), and (2) processed FT-ICR-MS data for all samples.

Environmental data from anoxic basins in the Mariager Fjord in Denmark, the Gotland Basin in the Baltic Sea, and the Black Sea

We studied dissolved organic matter (DOM) dynamics in the anoxic basin Mariager Fjord, Gotland Basin, and Black Sea. In this data set we provide environmental data (oxygen, salinity, temperature), dissolved and solid-phase extracted carbon (DOC, SPE-DOC), nitrogen (TDN, SPE-DON), sulfur (SPE-DOS), and phosphorus (SPE-DOP) concentrations. Elemental analysis of carbon and nitrogen were carried out with a High-temperature catalytic combustion, Shimadzu, Shimadzu TOC-VCPH equipped with TDN unit, analysis of extractable sulfur and phosphorus with Inductively coupled plasma optical emission spectroscopy, Thermo Fisher Scientific GmbH, iCAP PRO.

Molecular DOM composition (relative peak intensities) obtained through ultra-high resolution mass spectrometry (FT-ICR-MS)

Here we present the dissolved organic matter (DOM) data of the sea surface microlayer (SML) and underlying water (ULW) during a multidisciplinary mesocosm study at the Sea sURface Facility (SURF) of the Institute for Chemistry and Biology of the Marine Environment (ICBM) in Wilhelmshaven, Germany (53.5148 °N, 8.1463 °E). The study was conducted from 18 May to 16 June 2023. Water samples were collected using a glass plate for the SML and a tube at a depth of 40 cm. DOM was extracted and desalinated by solid-phase extraction as described by Dittmar et al. (2008). The extracts were stored frozen in methanol until analysis. Aliquots were mixed with 50% ultrapure water (50:50 v/v) and diluted to a final carbon concentration of 2.5 ppm. DOM composition was analysed using a SolariX XR FT-ICR-MS (Bruker Daltonik GmbH, Bremen, Germany) with a 15 Tesla superconducting magnet and an electrospray ionisation source (ESI; Bruker Apollo II ion source) in negative ion mode. Data processing and molecular formula assignment were performed in ICBM-OCEAN, as described by Merder et al. (2020).

Environmental parameters, including dissolved organic carbon and molecular indices derived from ultra-high-resolution mass spectrometry (FT-ICR-MS) and infrared spectroscopy (ATR-FTIR)

We studied dissolved organic matter (DOM) dynamics in the sea surface microlayer (SML) during a multidisciplinary mesocosm study at the Sea sURface Facility (SURF) of the Institute for Chemistry and Biology of the Marine Environment (ICBM) in Wilhelmshaven, Germany (53.5148 °N, 8.1463 °E). The study was conducted from 18 May to 16 June 2023 as part of the BASS research unit (Biogeochemical processes and Air-sea exchange in the Sea-Surface microlayer). This dataset contains environmental data, including dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and DOM molecular indices (MLBwL, Ibio, Iphoto, IDEG) calculated from ultrahigh-resolution mass spectrometry data (Fourier-transform ion cyclotron resonance mass spectrometer, FT-ICR-MS). Furthermore, we present attenuated total reflectance Fourier Transform Infrared (ATR-FTIR) data from representative samples for each bloom phase. General metadata from the multidisciplinary mesocosm study, including temperature, salinity and chlorophyll a, are provided in Bibi et al. on PANGAEA at the following link: doi:10.1594/PANGAEA.984101.

Dissolved organic matter (DOM) dynamics obtained through ultra-high resolution mass spectrometry (FT-ICR-MS) in the anoxic basin Mariager Fjord, Gotland Basin, and Black Sea

We studied dissolved organic matter (DOM) dynamics in the anoxic basin Mariager Fjord, Gotland Basin, and Black Sea. Therefore, we performed a mass spectrometric analysis of DOM extracts via FT-ICR MS on a 15 Tesla solariX XR Fourier-transform ion cyclotron resonance mass spectrometer (Bruker Daltonik GmbH, Bremen, Germany). The system was equipped with an electrospray ionization source (ESI, Bruker Apollo II) applied in negative ionization mode. Methanol extracts were mixed with ultrapure water (50:50 v/v) for FT-ICR MS analysis and diluted to a final DOC concentration of 2.5 mg C/L. 200 single scans with an ion accumulation time of 0.1 s were recorded over a mass range of m/z 100 to 1,000 Da and added to one spectrum. Data processing, molecular formula assignments, and compound category classifications were done with the software pipeline ICBM-OCEAN. All sample data was normalized to the intensity sum of 1. FT-ICR-MS data from Mariager Fjord (Denmark), Gotland Basin (Baltic Sea), Black Sea, and an abiotic (de)oxygenation experiment are provided. The data consists of the molecular formula with corresponding m/z measured at an FT-ICR-MS and relative intensities for each sample of these molecular formulas. Additionally, we included common molecular parameters, including H/C, O/C and S/C ratios for each molecular formula.

Dissolved organic matter composition in the sea surface microlayer during a Mesocosm study in Wilhelmshaven, Germany (FT-ICR-MS and ATR-FTIR), spring 2023

We studied dissolved organic matter (DOM) dynamics in the sea surface microlayer (SML) during a mesocosm study at the Sea sURface Facility (SURF) of the Institute for Chemistry and Biology of the Marine Environment (ICBM) in Wilhelmshaven, Germany (53.5148 °N, 8.1463 °E). The study was conducted from 18 May to 16 June 2023 as part of the multidisciplinary BASS research unit (Biogeochemical processes and Air-sea exchange in the Sea-Surface microlayer). SURF was filled with pretreated natural seawater from the nearby Jade Bay (53° 28' 42'' N, 8° 12' 15'' E) to replicate natural conditions. We selected this approach to examine the regrowth of surviving phytoplankton cells after the initial water treatments, simulating a native microbial community starting with almost no bioproduction or pre-existing bioproduction products. To induce and maintain the phytoplankton bloom, inorganic nitrogen, phosphorus, and silicate were added on May 26, May 31, and June 01, 2023. By that, we induced an algal bloom of Emiliania huxleyi and Cylindrotheca closterium. Water samples were collected using a glass plate for the SML and a tube at 40 cm depth for the underlying water (ULW). This dataset contains DOM molecular data from ultrahigh-resolution mass spectrometry (Fourier-transform ion cyclotron resonance mass spectrometer, FT-ICR-MS), molecular indices calculated from FT-ICR-MS data (Ibio, Iphoto, IDEG) and environmental data, including dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). Furthermore, it contains attenuated total reflectance Fourier Transform Infrared (ATR-FTIR) data from representative samples for each bloom phase. By combining molecular analyses with nutrient and bloom-phase data, we highlight the in situ production of carbohydrate-like and laminarin-derived DOM as a significant contributor to SML composition. General metadata from the multidisciplinary mesocosm study, including temperature, salinity and chlorophyll a, are provided in Bibi et al. on PANGAEA at the following link: doi:10.1594/PANGAEA.984101.

Dissolved organic matter composition from a large scale enclosure experiment

During the summer of 2015, we reproduced three levels of browning and seven levels of nutrients using water from lake Stechlin (North-East Germany). We applied ultra-high-resolution mass-spectrometry and dissolved organic matter optical properties to retrieve the composition of the DOM at different levels of resolutions. Using a network analysis approach, we found that molecular formulas clustering together share a common origin.

Stable carbon isotopes of sediment core MFM09-A5-UR

Terrestrial aquatic ratios (based on C28, C26, C24, C16 and C14 (TAR(C24+C26+C28)/(C24+C26+C28+C14+C16)) fatty acids) of sediment core MFM09-A5-UR

Terrestrial aquatic ratios (based on C26 and C16 (TAR=C26/(C26+C16) fatty acids) of sediment core MFM09-A5-UR

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