Porewater geochemistry of pockmark and reference stations in the southeastern Baltic Sea
Description
This database contains porewater geochemical data collected in the southeastern Baltic Sea from three areas containing pockmarks (MET1, MET3, and MET4). Sampling was conducted during a research cruise aboard the RV Oceanograf, owned by the University of Gdańsk, in October 2019. At each study area, samples were collected from two types of stations: the central parts of pockmarks (MET1-BH-p, MET1-MP-p, MET3-p, and MET4-p) and reference stations located on the surrounding seafloor, 100–150 m from the edges of the pockmarks (MET1-BH-s, MET1-MP-s, MET3-s, and MET4-s). Detailed characteristics of the sampling stations are provided in Łukawska-Matuszewska et al. (2026). The database includes concentrations of the major ions - chloride (Cl⁻), sulfate (SO₄²⁻), sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), and magnesium (Mg²⁺) - as well as dissolved iron (Fe) and manganese (Mn), dissolved inorganic carbon (DIC), and methane (CH₄). Measurements were performed in sediment porewater collected from the 0–85 cm sediment depth interval. References: Łukawska-Matuszewska, K., Brodecka-Goluch, A., Borkowski, A., 2026, Unique geochemical conditions and microbial composition of pockmark sediments in a brackish-water eutrophic continental shelf sea. Biogeochemistry, https://doi.org/10.1007/s10533-026-01361-9.
Files
Steps to reproduce
Sediment cores were collected using a Rumohr Lot gravity corer (Kopenhagen, Denmark) equipped with liners measuring 7.5 cm in diameter and 150 cm in length. Porewater was extracted from intact, tightly sealed sediment cores using Rhizon® samplers (Rhizosphere Research Products B.V., Wageningen, the Netherlands) equipped with porous membranes with a mean pore size of 0.15 μm. For methane analysis, 2 cm³ sediment samples were collected within 30 minutes of core recovery through pre-drilled holes in the core liners using 3 cm³ syringes with the Luer tips removed. The samples were transferred into 20 cm³ vials containing 6 cm³ of 2.5% sodium hydroxide. The vials were immediately sealed with butyl rubber stoppers and aluminium crimp seals, following the procedure described by Jørgensen et al. (2001). Methane concentrations were determined using the standard headspace technique with a gas chromatograph (PerkinElmer, Shelton, CT, USA) equipped with a flame ionization detector (FID) and an HP-5 column (30 m × 0.32 mm, 0.25 μm), using helium as the carrier gas. The limit of detection was 0.2 μmol dm⁻³. The concentrations of the major cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺) and dissolved Fe and Mn were determined using inductively coupled plasma optical emission spectrometry (ICP-OES; PerkinElmer OPTIMA 8300, Shelton, CT, USA), whereas chloride (Cl⁻) and sulfate (SO₄²⁻) concentrations were measured using ion chromatography. The analytical precision, expressed as relative standard deviation (RSD), was better than 3% for the major ions and 2% for Fe and Mn. Dissolved inorganic carbon (DIC) concentrations were determined in triplicate using a VarioTOC Cube TOC analyzer (Elementar GmbH, Langenselbold, Germany) equipped with a nondispersive infrared (NDIR) detector. Samples were acidified inside the instrument with 1% phosphoric acid, after which the released DIC was purged in the sparger and measured by the detector. The measurement accuracy, expressed as the recovery of certified reference material, was 98%, while the analytical precision was ≤2% RSD. The concentrations of hydrogen sulfide species (H₂S, HS⁻, and S²⁻; reported as total H₂S), dissolved silicate (dSi), and ammonium (NH₄⁺) were determined spectrophotometrically following Grasshoff et al. (1999). These analyses were performed immediately after sampling using a DR3600 spectrophotometer (HACH LANGE GmbH, Düsseldorf, Germany). The analytical precision was 3% RSD for total H₂S, 3% RSD for dSi, and 5% RSD for NH₄⁺. References: Jørgensen, B.B., Weber, A., Zopfi, J., 2001. Sulfate reduction and anaerobic oxidation in Black Sea sediments. Deep-Sea Res. Part I. 48, 2097–2120.
Institutions
- University of GdańskPomerania, Gdansk