Surface sediment were extracted 4 times by ultrasonication with dichloromethane: methanol (9:1, v/v) for 15 min for FAs and alkanes. For quantification of FAs and alkanes, known amounts of 19-methylarachidic acid and squalane were added as internal standards prior to extraction. Supernatants from each extraction were obtained by centrifugation and combined. The total lipid extracts were concentrated and evaporated under a nitrogen stream. The total lipid extracts were saponified for 2 h at 80 °C with 1 mL of KOH (0.1 M) in methanol: H2O (9:1, v/v). After saponification, the neutral fractions were liquid-liquid extracted with n-hexane and alkanes were eluted from the neutral fractions by silica gel column chromatography with n-hexane. The remaining KOH solution was acidified to pH 1, from which FA were liquid-liquid extracted into dichloromethane. The extracted and dried FAs were converted to methyl ester derivatives (FAMEs) in methanol: HCl (95:5, v/v) at 60 °C for 12 h. After methylation, the FAME fraction was further purified by silica gel column chromatography using dichloromethane: hexane (2:1, v/v) to remove residual polar compounds. FAMEs and alkanes were analyzed on a 7890A gas chromatograph (GC) equipped with a DB-5MS fused silica capillary column (60 m, 250 µm, 0.25 µm) and a flame ionization detector (FID). Peak areas were determined by integrating the respective peaks and concentrations were calculated against the internal standards. FAME contents were subsequently corrected for the derivative methyl carbon to determine FA contents. FAs and alkanes were normalized to OC content.
Surface sediment were extracted 4 times by ultrasonication with dichloromethane: methanol (9:1, v/v) for 15 min for FAs and alkanes. For quantification of FAs and alkanes, known amounts of 19-methylarachidic acid and squalane were added as internal standards prior to extraction. Supernatants from each extraction were obtained by centrifugation and combined. The total lipid extracts were concentrated and evaporated under a nitrogen stream. The total lipid extracts were saponified for 2 h at 80 °C with 1 mL of KOH (0.1 M) in methanol: H2O (9:1, v/v). After saponification, the neutral fractions were liquid-liquid extracted with n-hexane and alkanes were eluted from the neutral fractions by silica gel column chromatography with n-hexane. The remaining KOH solution was acidified to pH 1, from which FA were liquid-liquid extracted into dichloromethane. The extracted and dried FAs were converted to methyl ester derivatives (FAMEs) in methanol: HCl (95:5, v/v) at 60 °C for 12 h. After methylation, the FAME fraction was further purified by silica gel column chromatography using dichloromethane: hexane (2:1, v/v) to remove residual polar compounds. FAMEs and alkanes were analyzed on a 7890A gas chromatograph (GC) equipped with a DB-5MS fused silica capillary column (60 m, 250 µm, 0.25 µm) and a flame ionization detector (FID). Peak areas were determined by integrating the respective peaks and concentrations were calculated against the internal standards. FAME contents were subsequently corrected for the derivative methyl carbon to determine FA contents. FAs and alkanes were normalized to OC content.
The grain size of sediments was determined with a Cilas 1180 laser-diffraction particle analyzer (range 0.04–2500 μm) and the mean grain size was calculated. The surface area (SA) was calculated from the grain size distribution of the sediments. The OC content of surface sediments was determined using a carbon-sulfur analyzer (CS-125, Leco) after decarbonization with HCl. The total carbon (TC) and nitrogen (TN) contents of the samples were analyzed using a carbon-nitrogen-sulfur analyzer (Elemental III, Vario) and used to calculate carbonate contents (CaCO3= (TC − OC) × 8.333) and the mass ratio of OC to TON content ((C/N)OC), which was corrected for mineral-associated inorganic N. The stable carbon isotope composition of OC in surface sediments (δ13COC) was measured using a Thermo Delta isotope ratio mass spectrometer coupled to a Carlo Erba elemental analyzer. δ13COC values are given in per mil notation relative to the Vienna Pee Dee Belemnite standard. The standard deviation of duplicate analyses ranged from 0.01‰ to 0.18‰, with an average of 0.10‰. See details in related publication (Wei et al., 2025).
In March 2022, 56 surface sediments were collected from the Helgoland Mud Area and surrounding sandy areas in the North Sea. These surface sediments were analyzed for grain size, organic carbon (OC) content, total nitrogen content (TN), stable carbon isotope of OC, and abundances of source-specific alkanes and fatty acids, in aim to determine and quantify composition and sources of OC, to understand the degradation and sequestration of marine and terrestrial OC in sediments, and to estimate the burial fluxes and burial efficiencies of marine and terrestrial OC in the Helgoland Mud Area. Detailed dataset interpretation can be found in Wei et al. (2024, in preparation).
Radiographs of gravity core HE443/10-3 that was collected in the Helgoland mud area. The radiographs were produced about 8 months after coring and sampling. The white spots derive from previous sediment sampling that was performed onboard through windows that were cut into the core liner. The core shows intervals with intact sedimentary structures, but also intervals that are strongly mixed by bioturbation.
Solid-phase samples were collected onboard (RV Heincke expedition HE443) using cut-off syringes. The MUC was sliced and sampled. For sampling the GC, small windows were drilled into the liner through which the syringes were introduced. All samples were stored anoxically and frozen at -20°C until processing. The processing involved freeze-drying and grinding before splitting the samples for the different kinds of analyses.
Solid-phase samples were collected onboard (RV Heincke expedition HE443) using cut-off syringes. The MUC was sliced and sampled. For sampling the GC, small windows were drilled into the liner through which the syringes were introduced. All samples were stored anoxically and frozen at -20°C until processing. The processing involved freeze-drying and grinding. Extracts deriving from the sequential extraction of Fe phases were processed for stable Fe isotope analysis after Henkel et al. (2016).
Pore water was collected onboard (RV Heincke expedition HE443) by use of rhizons that were inserted into the cores through drilled holes in the core liners. Samples were preserved and analyses were performed onshore (at AWI) shortly after the expedition.
Pore water for iron isotope analysis was collected by use of rhizons, acidified and stored at 4°C until processing onshore. Processing of pore water (purification and matching) was performed at the University of Cologne, and measurements were performed on a MC-ICPMS at the Steinmann Institute in Bonn.
This is a compilation of pore-water and solid-phase data for station HE443/10 in the Helgoland mud area (German Bight, North Sea). The data derive from a multicorer core (HE443/10-2) and a gravity core (HE443/10-3) which were collected during a RV HEINCKE Expedition in 2015 in order to study iron reduction processes that are linked to methane formation and oxidation. Solid-phase geochemical data includes the bulk elemental composition or the sediment as well as sequential extraction data including reactive iron oxides and sulfides. Furthermore, the stable iron isotope composition of dissolved iron and in sequentially extracted Fe pools has been determined.
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