Description: Short sediment cores were taken at six stations in Wismar Bay, southern Baltic Sea (Germany) in May 2019 using a Rumohr-Lot device. Our aim in this study was to investigate the role of diagenetic element fluxes and different fresh water sources, including submarine groundwater discharge, on the water column in the bay. Porewaters were extracted from the sediment cores by applying the rhizon technique at a resolution between 2 and 5 cm. The porewaters were analyzed for major and trace metals and selected nutrients using a ICP-OES (iCAP, 7400, Duo Thermo Fischer Scientific), total sulphide by a Specord 40 spectrophotometer (Analytik Jena), dissolved inorganic carbon (DIC) and δ13CDIC using an isotope gas mass spectrometre (MAT 253) coupled to a Gasbench II, and δ18OH2O, and δ2HH2O using a CRDS system (laser cavity-ring-down-spectroscopy, Picarro L2140- I). Sediment cores were further sliced at 2 to 4 cm resolution and each freeze-dried solid subsample was analyzed for contents of total carbon, nitrogen, and sulphur using an Elemental Analyzer (Euro Vector EuroEA 3, 052), inorganic carbon using an Elemental Analyzer multi EA (Analytik Jena), total mercury by a DMA-80 analyzer, and HCl-extractable Pb, Mn and Fe using an ICP-OES (iCAP, 7400, Duo Thermo Fischer Scientific).

Description: This investigation was carried out in order to evaluate diagenetic element fluxes and different fresh water sources, including submarine groundwater discharge, on the water column of the Wismar Bay (Germany), southern Baltic Sea. Surface and bottom water samples were collected on board of the RV Littorina (L19-06) and a rubber boat by using a submersible pump in May 2019. The water was pumped through a filter cartridge (1 µM pore size) into barrels. Water samples from the barrels were pumped through manganese-coated acrylic fibers to extract radium (Ra) isotopes (223Ra, 224Ra). The Ra isotopes were measured within 3 and 10 days using radium-delayed coincidence counters (RaDeCC). Subsamples were taken via syringe and filtered (0.45 µM, cellulose acetate disposable filters) for analysis of dissolved concentrations of major and trace elements and selected nutrients using ICP-OES (iCAP, 7400, Duo Thermo Fischer Scientific), dissolved inorganic carbon (DIC) and δ13CDIC using isotope gas mass spectrometry (MAT 253 coupled to a Gasbench II), and δ18OH2O, δ2HH2O using a CRDS system (laser cavity-ring-down-spectroscopy, PICARRO L2140- I).

Description: The dataset compiles total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN) and total sulfur (TS) contents and stable isotope signatures (δ13C of TOC, δ15N, δ34S) of fine-grained deposits (clay, loam) over sandy subsoils of the saltmarsh of the barrier island Spiekeroog at the southern North Sea coast. Sampling was performed in September 2016 along three transects spanning from the high saltmarsh to the pioneer zone. At each sample point, soil samples were taken from the first 5 cm of the upper part (top samples) and from the deepest 5 cm of the lower part (bottom samples) of the fine-grained deposit. If the fine-grained deposit layer had a thickness 〈 10 cm, only one bulk soil sample (single samples) was taken for the depth range equal to the deposit thickness. Samples were ground to fine powder. TIC was measured on oven-dried samples coulometrically with an Analytik Jena multi EA 4000 analyzer. The total carbon (TC), TN, and TS were analyzed using a Thermo Scientific Flash EA Isolink Elemental Analyzer. The TOC contents were calculated as the difference between TC and TIC. TOC, TN, and TS contents are reported based on the original dry mass. For isotope analysis, dried and homogenized samples were weighed in tin cups and combusted in a Thermo Scientific Flash EA Isolink Elemental Analyzer, connected to a Thermo Finnigan MAT 253 gas mass spectrometer via a Thermo Conflo IV split interface. The δ13C values of TOC were measured after decalcification of the ground powders with p. a. grade HCl. The TN and δ34S analysis were carried out on a separate aliquot of sample powder. The isotope results are given in the conventional δ-notation.

Description: This dataset contains the concentrations of 34 elements, chloride, methane, ammonium, and dissolved inorganic carbon, as well as δ2H, δ18O, δ7Li, δ34S, 87Sr/86Sr and δ13C-DIC in groundwater and seawater samples as well as in sediment porewater samples from pockmarks associated with submarine groundwater discharge (SGD) at the Hanko cape in Finland, northern Baltic Sea. The groundwater samples were collected onshore from an observation well using a suction pump and from a water intake well. The seawater and pockmark porewater samples were collected from the research vessel Geomari of the Geological Survey of Finland (GTK). The seawater samples were collected onboard from 2 m, 6 m, and 10 m below sea surface at the pockmark locations using a Limnos water sampler. The porewater samples were extracted using Rhizons at 1-2 cm vertical intervals from sediment cores that were collected from the pockmarks at 11 m water depth. Multielement composition of the seawater, groundwater and porewater samples were analyzed using inductively coupled plasma optical emission and mass spectrometry (ICP-OES and ICP-MS). Ca, Fe, K, Mg, Mn, Na, and S were analysed by ICP-OES, whereas Ag, Al, As, B, Ba, Be, Bi, Cd, Co, Cr, Cu, I, Li, Mn, Mo, Ni, P, Pb, Rb, Sb, Se, Sr, Th, Tl, U, V, and Zn were analysed by ICP-MS. Major anions (Br, Cl, F, NO3 and SO4) were analyzed using ion chromatography. Alkalinity (as HCO3-), electrical conductivity, pH and KMnO4 consumption of the unfiltered and unpreserved groundwater samples were measured immediately upon arrival at the laboratory. Methane concentrations in the seawater, groundwater and porewater samples were determined by gas chromatography with flame ionization detector. Headspace CH4 concentrations were converted to total dissolved phase concentrations in the original porewater sample using Henry's Law. δ13CDIC values were determined by means of continuous-flow isotope-ratio-monitoring mass spectrometry (CF-irmMS). The concentrations of NH4+ and PO4 were analyzed spectrophotometrically. Hydrogen and oxygen isotope ratios of the groundwater, seawater and porewater samples were analyzed by cavity ring down spectroscopy (CRDS). The isotope ratios are reported as deviation from the international VSMOW-standard. The uncertainty (2σ) of measurement is 〈0.1‰ for oxygen analysis and 〈0.3‰ for hydrogen analysis. For the determination of δ7Li, δ34S and 87Sr/86Sr, the elements were eluted from the groundwater, seawater and porewater samples by liquid column chromatography. The isotope ratios in the eluted samples were analyzed by multi-collector ICP-MS. The Li, S and Sr isotope ratios are reported against the LSVEC, NBS987 and CDT reference materials, respectively. The standard mean deviations of Li and S isotope determinations are +/- 0.32 and +/- 0.52 ‰, respectively. The mean 2SE of Sr isotope determinations is +/- 0.000015. In the dataset, The given ‰ values are equivalent to mUr (milli Urey)

Description: The rewetting of peatlands is a promising measure to mitigate greenhouse gas (GHG) emissions by preventing the further mineralization of the peat soil through aeration. In coastal peatland, the rewetting with brackish water can increase the GHG mitigation potential by the introduction of sulfate, a terminal electron acceptor (TEA). Sulfate is known to lower the CH4 production and thus, its emission by favoring the growth of sulfate-reducers, which outcompete methanogens for substrate. The data contain porewater variables such as pH, electrical conductivity (EC) and sulfate, chloride, dissolved CO2 and CH4 concentrations, as well as absolute abundances of methane- and sulfate-cycling microbial communities. The data were collected in spring and autumn 2019 after a storm surge with brackish water inflow in January 2019. Field sampling was conducted in the nature reserve Heiligensee and Hütelmoor in North-East Germany, close to the Southern Baltic Sea coast. We took peat cores using a Russian peat corer in addition to pore water diffusion samplers and plastic liners (length: 60cm; inner diameter 10 cm) at four locations along a transect from further inland towards the Baltic Sea. We wanted to compare the soil and pore water geochemistry as well as the microbial communities after the brackish water inflow to the common freshwater rewetting state. Pore water was extracted using pore water suction samplers in the lab and environmental variables were quantified with an ICP. Microbial samples were sampled from the peat core using sterile equipment. We used quantitative polymerase chain reaction (qPCR) to characterize pools of DNA and cDNA targeting total and putatively active bacteria and archaea. qPCR was performed on key functional genes of methane production (mcrA), aerobic methane oxidation (pmoA) and sulfate reduction (dsrB) in addition to the 16S rRNA gene for the absolute abundance of total prokaryotes. Furthermore, we retrieved soil plugs to determine the concentrations and isotopic signatures of dissolved trace gases (CO2/DIC and CH4) in the pore water.

Description: Deoxygenation affects many continental shelf seas across the world today and results in increasing areas of hypoxia (dissolved oxygen concentration ([O2]) 〈1.4 ml/L). The Baltic Sea is increasingly affected by deoxygenation. Deoxygenation correlates with other environmental variables such as changing water temperature and salinity and is directly linked to ongoing global climate change. To place the ongoing environmental changes into a larger context and to further understand the complex Baltic Sea history and its impact on North Atlantic climate, we investigated a high accumulation‐rate brackish‐marine sediment core from the Little Belt (Site M0059), Danish Straits, NW Europe, retrieved during the Integrated Ocean Drilling Program (IODP) Expedition 347. We combined benthic foraminiferal geochemistry, faunal assemblages, and pore water stable isotopes to reconstruct seawater conditions (e.g., oxygenation, temperature, and salinity) over the past 7.7 thousand years (ka). Bottom water salinity in the Little Belt reconstructed from modeled pore water oxygen isotope data increased between 7.7 and 7.5 ka BP as a consequence of the transition from freshwater to brackish‐marine conditions. Salinity decreased gradually (from 30 to 24) from 4.1 to ~2.5 ka BP. By using the trace elemental composition (Mg/Ca, Mn/Ca, and Ba/Ca) and stable carbon and oxygen isotopes of foraminiferal species Elphidium selseyensis and E. clavatum, we identified that generally warming and hypoxia occurred between about 7.5 and 3.3 ka BP, approximately coinciding in time with the Holocene Thermal Maximum (HTM). These changes of bottom water conditions were coupled to the North Atlantic Oscillation (NAO) and relative sea level change.

Description: The dataset includes foraminiferal geochemistry and assemblage data, and pore water oxygen isotopes. The samples were collected during IODP Expedition 347 from Site M0059, located in the southern section of the Little Belt in the Baltic Sea. We have measured trace element concentrations (by LA-ICP-MS), oxygen and carbon isotopes of foraminiferal calcite, and fauna assemblage, for reconstruction of past environmental conditions over the past ~7.5 thousand years. We have also measured pore water oxygen isotopes from the same site. In the dataset we also present the trace element concentrations of foraminiferal calcite from IODP347 Site M0059 measured by solution-based ICP-OES. In addition, we include the measurement of water column salinity and oxygen isotopes data from cruise MSM 50 between the Skagerrak and the southern Baltic Sea.