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Geochemistry of sediments from Fehmarn Belt area, southern Baltic Sea during cruise EMB238

The geochemical composition of surface sediments and pore waters from the Fehmarn Belt area, southern Baltic Sea, was analyzed in the context of the establishment of exclusion areas for bottom trawling activity. Samples were taken on cruise EMB238 in May/June 2020 using a multi corer or benthic lander device. Besides on-site measurements, further dissolved major and trace elements, dissolved inorganic carbon, nutrients were analyzed in home laboratory. Results are complemented by the analysis of potential microbial gross sulfate reduction rates and the geochemical composition of CNS and extractable sulfur (AVS, CrS(II), and acid-extractable Fe, Zn, Pb, Fe, Mn contents.

Soil physicochemical properties of the PhytOakmeter plot DGRL_14 (Greifenhagen, Germany) in 2016, 2020 and 2022

As part of PhytOakmeter platform (www.phytoakmeter.de), soil chemical parameters were determined in 2016, 2020 and 2022. Soil pH was measured using a glass electrode in a 1:2.5 soil-to-0.01 M CaCl2 suspension after one hour of equilibration. Gravimetric soil moisture was assessed with a fully automated moisture analyzer (DBS60-3, KERN & SOHN GmbH, Balingen, Germany), here defined as soil moisture (MOI). Total nitrogen (TN) and total carbon (TC) contents in the soil were analyzed in triplicate through dry combustion using a Vario elemental analyzer (EL III, Elementar, Hanau, Germany), and the carbon-to-nitrogen ratio (TC/TN) was subsequently calculated from these values. To evaluate the potentially bioavailable soil organic carbon and nitrogen for microbial activity, hot water-extractable carbon and nitrogen (HWC and HWN, respectively) were determined following the methods of Ghani et al. (2003) and Schulz et al. (2011). Additionally, the labile organic carbon and nitrogen easily decomposable by soil microorganisms were measured as cold water-extractable carbon (CWC) and nitrogen (CWN) based on procedures described by Zsolnay (1996), Zakharova et al. (2015), and Schmidt et al. (2017). Ammonium and nitrate (NH4±N and NO3—N, respectively) were quantified, with their sum representing the total mineral nitrogen content (Nmin).

Reproductive parameters and oocyte fatty acid compositions in European sprat Sprattus sprattus sampled in the Baltic Sea

Fecundity of marine fish species is highly variable, but trade-offs between fecundity and egg quality have rarely been observed at the individual level. We investigated spatial differences in reproductive investment of individual European sprat Sprattus sprattus (Linnaeus 1758) females by determining batch fecundity, condition indices (somatic condition index and gonadosomatic index) as well as oocyte dry weight, protein content, lipid content, spawning batch energy content, and fatty acid composition. Sampling was conducted in five different spawning areas within the Baltic Sea between March and May 2012. Sampling was conducted in the Baltic Sea during three cruises of the German RV “Alkor” in March (https://www2.bsh.de/aktdat/dod/fahrtergebnis/2012/20120331.htm), April (http://dx.doi.org/10.3289/CR_AL390), and May (http://dx.doi.org/10.3289/CR_AL392) 2012. Five different areas were sampled: KB, AB, Bornholm Basin (BB), Gdansk Deep (GD), and Gotland Basin (GB). Fish were caught with a pelagic trawl. Trawling time was in general 30 minutes per haul. The total lengths (TL, ±0.1 cm) of at least 200 sprat per haul were measured for length frequency analysis. Only female sprat with ovaries containing fully hydrated oocytes were sampled, running ripe females were rejected to avoid possible loss of oocytes, as this would lead to an underestimation of batch fecundity. Sprat were sampled immediately after the haul was on deck and stored on crushed ice. The sampled fish were weighed (wet mass WM, ±0.1 g) and measured (TL, ±0.1 cm), and their ovaries were dissected carefully. Oocytes were extracted from a single ovary lobe, rinsed with deionized water, and counted under a stereo microscope (Leica MZ 8). A counted number of oocytes (around 50 oocytes per fish) were transferred to pre-weighed tin-caps (8 x 8 x 15 mm). These samples were used to determine the oocyte dry weight, lipid content, and fatty acid composition. In addition, a counted number of oocytes (around 10 oocytes per fish) were sampled in Eppendorf caps for determination of protein content. Oocyte samples were stored at -80 °C for subsequent fatty acid and protein analysis in the laboratory. Finally, both ovary lobes were stored in 4% buffered formaldehyde solution for further fecundity analysis. Ovary free body mass (OFBM, ±0.1 g) of sampled frozen fish and fixed ovary mass (OM, ±0.1 g) were measured (Sartorius, 0.01 g) in the laboratory on land, to avoid imprecise measurements due to the ship's motion at sea. Absolute batch fecundity (ABF) was determined gravimetrically using the hydrated oocyte method suggested by Hunter et al. (1985) for indeterminate batch spawners. For ascertainment of the relative batch fecundity per unit body weight (RBF), ABF was divided by OFBM. Further, a condition index (CI) was determined: CI = (OFBM/〖TL〗^3 )× 100. A gonadosomatic index (GSI) was calculated with the following formula: GSI = (OM/OFBM)× 100. Oocyte dry weight was determined to the nearest 0.1 µg (Sartorius SC 2 micro-scale), using the samples stored in pre-weighed tin caps, after freeze-drying (Christ Alpha 1-4) for at least 24 hours. After subtracting the weight of the empty tin cap, the average oocyte dry mass (ODM) was then calculated by dividing the total weight by the number of oocytes contained in the tin cap. The fatty acid signature of oocytes was determined by gas chromatography (GC). Lipid extraction of the dried oocytes was performed using a 1:1:1 solvent mix of dichloromethane:methanol:chloroform. A five component fatty acid methyl ester Mix (13:0 - 21:0, Restek, Bad Homburg, Germany; c = 8.5 ng component µl-1) was added as an internal standard and a 23:0 fatty acid standard (Restek, Bad Homburg, Germany, c = 25.1 ng µl-1) was added as an esterification efficiency control. Esterification was performed over night at 50 °C in 200 µl 1% H2SO4 and 100 µl toluene. The solvent phase was transferred to 100 µl n-hexane and a 1 µl aliquot measured in a Thermo Fisher Trace GC Ultra with a Thermo Fisher TRACETM TR-FAME column (10 m*0.1 mm*0.2 µm). For more details on sample preparation and GC settings, see Hauss et al. (2012). The total lipid content per oocyte was determined by adding up the weights of all detected fatty acids. To ensure comparability with past studies, results for FA are given as a percentage of the combined weights of all detected FA. An average of 10 oocytes were transferred to 5*9 mm tin cups (Hekatech) and dried at 50 °C for >24 h. Total organic carbon (C) and nitrogen (N) content was measured using a Thermo Fisher Scientific Elemental Analyzer Flash 2000. From the total amount of N in the sample, the oocyte protein content was calculated according to Kjeldahl (Bradstreet, 1954), using a factor of 6.25. The oocyte gross energy content was calculated on the basis of measured protein and lipid content, which were multiplied with corresponding energy values from literature. The measured amount of proteins per given oocyte (P, mg) was multiplied by a factor of 23.66 J mg-1 and was added to the total amount of lipids per oocyte (L, mg) multiplied by 39.57 J mg-1 (Henken et al. 1986). Consequently, the oocyte energy content of each individual female sprat was multiplied by its relative batch fecundity in order to obtain a standardized estimate of the total amount of energy invested into a single spawning batch (SBEC, J g-1 OFBM): SBEC = [(P × 23.66 (J )/mg)+(L × 39.57 (J )/mg)]× RBF

Seawater carbonate chemistry and growth of calcifying tubeworm shells (Spirorbis spirorbis)

The calcareous tubeworm Spirorbis spirorbis is a widespread serpulid species in the Baltic Sea, where it commonly grows as an epibiont on brown macroalgae (genus Fucus). It lives within a Mg-calcite shell and could be affected by ocean acidification and temperature rise induced by the predicted future atmospheric CO2 increase. However, Spirorbis tubes grow in a chemically modified boundary layer around the algae, which may mitigate acidification. In order to investigate how increasing temperature and rising pCO2 may influence S. spirorbisshell growth we carried out four seasonal experiments in the Kiel Outdoor Benthocosms at elevated pCO2 and temperature conditions. Compared to laboratory batch culture experiments the benthocosm approach provides a better representation of natural conditions for physical and biological ecosystem parameters, including seasonal variations. We find that growth rates of S. spirorbis are significantly controlled by ontogenetic and seasonal effects. The length of the newly grown tube is inversely related to the initial diameter of the shell. Our study showed no significant difference of the growth rates between ambient atmospheric and elevated (1100 ppm) pCO2 conditions. No influence of daily average CaCO3 saturation state on the growth rates of S. spirorbis was observed. We found, however, net growth of the shells even in temporarily undersaturated bulk solutions, under conditions that concurrently favoured selective shell surface dissolution. The results suggest an overall resistance of S. spirorbis growth to acidification levels predicted for the year 2100 in the Baltic Sea. In contrast, S. spirorbis did not survive at mean seasonal temperatures exceeding 24 °C during the summer experiments. In the autumn experiments at ambient pCO2, the growth rates of juvenile S. spirorbis were higher under elevated temperature conditions. The results reveal that S. spirorbis may prefer moderately warmer conditions during their early life stages but will suffer from an excessive temperature increase and from increasing shell corrosion as a consequence of progressing ocean acidification.

TOC, TIC, TN and TS contents and stable isotope signatures (δ13C of TOC, δ15N, δ34S) of fine-grained saltmarsh deposits of the barrier island Spiekeroog at the southern North Sea Coast

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.

Seawater carbonate chemistry and in situ and laboratory measurements of calcification

Ocean acidification (OA) is generally assumed to negatively impact calcification rates of marine organisms. At a local scale however, biological activity of macrophytes may generate pH fluctuations with rates of change that are orders of magnitude larger than the long-term trend predicted for the open ocean. These fluctuations may in turn impact benthic calcifiers in the vicinity. Combining laboratory, mesocosm and field studies, such interactions between OA, the brown alga Fucus vesiculosus, the sea grass Zostera marina and the blue mussel Mytilus edulis were investigated at spatial scales from decimetres to 100s of meters in the western Baltic. Macrophytes increased the overall mean pH of the habitat by up to 0.3 units relative to macrophyte- free, but otherwise similar, habitats and imposed diurnal pH fluctuations with amplitudes ranging from 0.3 to more than 1 pH unit. These amplitudes and their impact on mussel calcification tended to increase with increasing macrophyte biomass to bulk water ratio. At the laboratory and mesocosm scales, biogenic pH fluc- tuations allowed mussels to maintain calcification even under acidified conditions by shifting most of their calcification activity into the daytime when biogenic fluctuations caused by macrophyte activity offered temporal refuge from OA stress. In natural habitats with a low biomass to water body ratio, the impact of biogenic pH fluctuations on mean calcification rates of M. edulis was less pronounced. Thus, in dense algae or seagrass habitats, macrophytes may mitigate OA impact on mussel calcification by raising mean pH and providing temporal refuge from acidification stress.

Seawater carbonate chemistry and biological processes during experiments with four strains of Emiliania huxleyi

Four strains of the coccolithophore E. huxleyi (RCC1212, RCC1216, RCC1238, RCC1256) were grown in dilute batch culture at four CO2 levels ranging from ~200 µatm to ~1200 µatm. Growth rate, particulate organic carbon content, and particulate inorganic carbon content were measured, and organic and inorganic carbon production calculated. The four strains did not show a uniform response to carbonate chemistry changes in any of the analysed parameters and none of the four strains displayed a response pattern previously described for this species. We conclude that the sensitivity of different strains of E. huxleyi to acidification differs substantially and that this likely has a genetic basis. We propose that this can explain apparently contradictory results reported in the literature.

The morphological response of Emiliania huxleyi to seawater carbonate chemistry changes: an inter-strain comparison

Four strains of the coccolithophore Emiliania huxleyi (RCC1212, RCC1216, RCC1238, RCC1256) were grown in dilute batch culture at four CO2 levels ranging from ~200 µatm to ~1200 µatm. Coccolith morphology was analyzed based on scanning electron micrographs. Three of the four strains did not exhibit a change in morphology over the CO2 range tested. One strain (RCC1256) displayed an increase in the percentage of malformed coccoliths with increasing CO2 concentration. We conclude that the sensitivity of the coccolith-shaping machinery to carbonate chemistry changes is strain-specific. Although it has been shown before that carbonate chemistry related changes in growth- and calcification rate are strain-specific, there seems to be no consistent correlation between coccolith morphology and growth or calcification rate. We did not observe an increase in the percentage of incomplete coccoliths in RCC1256, indicating that the coccolith-shaping machinery per se is affected by acidification and not the signalling pathway that produces the stop-signal for coccolith growth.

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