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.
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.
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.