Description: Within the last two decades several studies have focused on the conundrum of the bioavailability of ancient carbon. In high latitudes this is particularly important, as 40 to 50 % of organic matter (OM) in arctic sediments is estimated to be of petrogenic origin. Arctic Amplification will impact these regions severely in the coming decades. Arctic fjords act as hotspots of carbon burial on a global scale, especially for petrogenic carbon, which makes them an ideal location to study climatically induced changes in OM input to sediments and the related biodegradability of ancient petrogenic carbon. To assess these issues, sediment core HH14-897-MF-GC from Hornsund Fjord on Svalbard was analyzed for changes in OM input using biomarker abundances from 1961 to 2014. Further, the incorporation of ancient carbon by sedimentary bacterial communities was investigated using compound specific radiocarbon dating (CSRD) on intact polar lipid (ILP) derived fatty acids (FA), as indicators for viable microbiota in the sediments. Biomarker abundances indicate only minor changes in sedimentary OM, mainly related to tidewater glacier retreat and subsequent changes in the diagenetic setting caused by lower sedimentation rates. Further, petrogenic and marine OM appear to be the two primary OM sources, with predominantly ancient petrogenic material (〉90 %) resulting in bulk sediment ages ranging from 17,327 ± 48 years B.P. at the core top to ages consistently over 24,000 years B.P. below 50 cm sediment depth. Using a two-endmember model, radiocarbon signatures of analyzed IPL-FA suggest incorporation of substantial amounts of ancient petrogenic OM into viable sedimentary bacteria, ranging from 4 to 52 %. Increasing sediment depth and time of sedimentary storage seem to have the most impact on ancient carbon utilization, potentially due to priming.

Description: About 34% of global coast lines are underlain by permafrost. Rising temperatures cause an acceleration in erosion rates of up to 10s of meters annually, exporting increasing amounts of carbon and nutrients to the coastal ocean. The degradation of ancient organic carbon (OC) from permafrost is an important potential feedback mechanism in a warming climate. However, little is known about permafrost OC degradation after entering the ocean and its long term-fate after redeposition on the sea floor. Some recent studies have revealed CO2 release to occur when ancient permafrost materials are incubated with sea water. However, despite its importance for carbon feedback mechanisms, no study has directly assessed whether this CO2 release is indeed derived from respiration of ancient permafrost OC. We used a multi-disciplinary approach incubating Yedoma permafrost from the Lena Delta in natural coastal seawater from the south-eastern Kara Sea. By combining biogeochemical analyses, DNA-sequencing, ramped oxidation, pyrolysis and stable and radiocarbon isotope analysis we were able to: 1) quantify CO2 emissions from permafrost utilization; 2) for the first time demonstrate the amount of ancient OC contributing to CO2 emissions; 3) link the processes to specific microbial communities; and 4) characterize and assess lability of permafrost OC after redeposition on the sea floor. Our data clearly indicate high bioavailability of permafrost OC and rapid utilization after thawed material has entered the water column, while observing only minor changes in permafrost OC composition over time. Microbial communities are distinctly different in suspended Yedoma particles and water. Overall, our results suggest that under anthropogenic Arctic warming, enhanced coastal erosion will result in increased greenhouse gas emissions, as formerly freeze-locked ancient permafrost OC is remineralized by microbial communities when released to the coastal ocean.

Description: Rock-derived or petrogenic organic carbon has traditionally been regarded as being non-bioavailable and bypassing the active carbon cycle when eroded. However, it has become apparent that this organic carbon might not be so inert, especially in fjord systems where petrogenic organic carbon influxes can be high, making its degradation another potential source of greenhouse gas emissions. The extent to which subsurface micro-organisms use this organic carbon is not well constrained, despite its potential impacts on global carbon cycling. Here, we performed compound-specific radiocarbon analyses on intact polar lipid–fatty acids of live micro-organisms from marine sediments in Hornsund Fjord, Svalbard. By this means, we estimate that local bacterial communities utilize between 5 ± 2% and 55 ± 6% (average of 25 ± 16%) of petrogenic organic carbon for their biosynthesis, providing evidence for the important role of petrogenic organic carbon as a substrate after sediment redeposition. We hypothesize that the lack of sufficient recently synthesized organic carbon from primary production forces micro-organisms into utilization of petrogenic organic carbon as an alternative energy source. The input of petrogenic organic carbon to marine sediments and subsequent utilization by subsurface micro-organisms represents a natural source of fossil greenhouse gas emissions over geological timescales.

Description: Between 2019 and 2022 three sediment cores HH14-897-MF-GC (2014), He519_2-3 (2018), and He560_26-2 (2020) were analyzed using biogeochemical markers to assess organic carbon dynamics and its bio-availability in the Hornsund Fjord (Svalbard) sediments. Depositional history was assessed by 210Pb+137Cs data (obtained by γ-spectrometer) building the basis for associated sedimentary age models (Bruel & Sabatier, 2020), with bulk total organic carbon concentrations (using an element analyzer) and dual C-isotopes of δ13C (obtained by isotope ration mass spectrometer) and F14C (by accelerator mass spectrometry) (Werner & Brand, 2001, Brodie et al. 2011 and Mollenhauer et al., 2021). Additionally, lipid biomarker were extracted, separated, and quantified with wet chemical perpetrations of n-alkanes (Wei, 2020) (quantified with gas chromatography – flame ionization detector), fatty acids (quantified with gas chromatography – flame ionization detector) (Wei, 2020), and GDGTs (Hopmans, 2016) (quantified with gas chromatography – mass spectrometry). Included are datasets of associated biomarker indices of Carbon Preference Index (CPI) (Bray & Evans, 1961), Branched and Isoprenoid Tetraether (BIT) Index (Hopmann et al., 2004), and Terrestrial Aquatic Ratio (TAR) of fatty acids (Meyers, 1997). Further microbial utilization and bio-availability of petrogenic- and marine organic carbon was assed using Intact Polar Lipid (IPL) based compound specific radiocarbon analysis (CSRA) in combination with a DI14C age model of the local surface waters. IPLs were extracted form sediments with a modified Bligh and Dyer (1959) and subsequently separated with wet-chemical seperations (Slater, 2006). CSRA (Mollenhauer et al., 2021) of IPLs was performed on purified single compound fatty acid (FA) methyl esters of the IPL precursor lipids (Wei et al., 2021). The bio-availability of petrogenic organic carbon was based on CSRA data of IPL-FAs using an isotope mass balance with two endmembers of fossil petrogenic and modern marine primary production (DI14C age model of the local surface waters) (Ruben et al., 2022). For the DI14C age model of the local surface waters simulations were run using the Finite-volumE Sea ice-Ocean Model FESOM2 (Danilov et al., 2017) equipped with radiocarbon (Lohmann et al., 2020). Data validity was assessed by relative concentrations of IPLs in the radiocarbon analyzed PL-fraction (Wörmer et al., 2013). Detailed dataset interpretation can be found in Ruben et al. (2023).

Description: In July 2022 within the framework of an Alfred-Wegener-Institute-managed expedition and the Nunataryuk project, sediment cores were taken at three locations, off the coast of Herschel Island, Canada, using a hand corer: YC22_MR_6: 69°34'23.12N, 138°54'37.76W; 3 m water depth; July 6th 2022 YC22_MR_7: 69°34'23.53N, 138°56'37.66W, 6 m water depth; July 7th 2022 YC22_MR_8: 69°30'22.75''N, 138°53'21.69''W; 45 m water depth; July 24th 2022 Data sets were obtained to investigate carbon feedback from the sediments to the water column and atmosphere, using DIC concentrations and isotopic values. The local sediments are supplied primarily by organic carbon previously stored in adjacent permafrost soils (biomarker and bulk data), which erode and redeposit quickly (age model) on the ocean floor. The acquired data includes: 1) Sediment data: Bulk total organic carbon content (Lamping et al., 2021) and its isotopic values for 13C (Brodie et al., 2011; Werner & Brand, 2001) and 14C (Mollenhauer et al., 2021) and Biomarker data: Quantifying alkanes (CPI) , and fatty acids (TAR ratio) as described by Wei et al. (2020), Glycerol dialkyl glycerol tetraethers (GDGTs basis for BIT-Index) after Hopmans et al. (2016), Hopanes (fßß) following instructions by Meyer et al., (2019), and Sterols (Dinosterol) after Dauner et al. (2022). 2) Porewater was extracted from the cores using rhizomes and quantified as described in Oni et al., (2015). Dissolved inorganic carbon isotope signatures were determined as CO2 for 13C (Torres et al., 2005) and 14C (Mollenhauer et al., 2021). 3) Intact polar lipid fatty acids were extracted from the sediments, purified, and 14C analysis was performed as described in Ruben et al. (2023). The 13C isotopy was determined with GC-IRMS (Elvert et al., 2003). The respective precursor lipids of the polar fraction used for isotope analysis were quantified following the method described in Wörmer et al. (2013). Datasets are to be found at doi:10.1594/PANGAEA.966262 and doi:/10.1594/PANGAEA.966264. 4) Sedimentary age model of core YC22_MR_7 assuming constant rate of supply (CRS) model (Appleby, 2001), based on data obtained with a HPGe gamma detector.

Description: 85-day-long aerobic incubation of Yedoma permafrost soil from the Lena Delta into seawater from the eastern Kara Sea, at ~2°C in the dark. The setup is simulating the process of introduction of OC from eroding cost lines along the arctic cost and the resuspension in the shelf bottom waters via the later transport. Samples were incubated in a ratio of Yedoma 3mL to sea water 90 mL. Three treatments were set up 1) Yedoma+Sea water (untreated, 20 vials); 2) Yedoma+filtered Sea Water (0.2µm filter, 6 vials); 3) filtered Sea Water (0.2µm filter, 6 vials). Additionally, vials with pH and O₂ sensors were set up for each treatment: 1) 3 vials; 2) & 3) 2 vials each. Presented data include raw data of temperature, pH, oxygen concentrations, dissolved inorganic carbon concentrations (DIC) and radiocarbon signature (DI14), and sediment data (concentration and radiocarbon signature). Nutrients (NH₄, NO₂, NO₃, and PO₄), ions (Cl & SO₄), DIC, DI14C, total dissolved organic carbon (DOC), and total dissolved nitrogen (TDN) are reported normalized to the water volume in the vials. Further, parameters of the carbonate system were calculated, in order to access CO₂ release and its age signature over the cause of the experiment (carbon budget).

Description: The data was obtained by performing ramped pyrolysis and oxidation with 14C analysis of the emitted CO2 gases using the sedimentary residue of incubated permafrost soil (Yedoma) in seawater. The related data sets of the incubation experiment and experiment description can be found at doi:10.1594/PANGAEA.956711 and bacterial data at https://github.com/matthiaswietz/yedoma-bacteria. The ramped pyrolysis and oxidation setup is described in Hemingway et al. (2017a) and thermogram data conversion in E,p space is described in Hemingway et al. (2017b). Radiocarbon analysis was performed following Mollenhauer et al. (2021).

Description: In July 2022 within the framework of an Alfred-Wegener-Institute-managed expedition and the Nunataryuk project, sediment core YC22_MR_7 was taken off the coast of Herschel Island, Canada, using a hand corer. Data sets were obtained to investigate carbon feedback from the sediments to the water column and atmosphere, using DIC concentrations and isotopic values. The local sediments are supplied primarily by organic carbon previously stored in adjacent permafrost soils (biomarker and bulk data), which erode and redeposit quickly (age model) on the ocean floor. The acquired data includes: 1) Sediment data: Bulk total organic carbon content (Lamping et al., 2021) and its isotopic values for 13C (Brodie et al., 2011; Werner & Brand, 2001) and 14C (Mollenhauer et al., 2021). 2) Biomarker data: Quantifying alkanes (CPI) , and fatty acids (TAR ratio) as described by Wei et al. (2020), Glycerol dialkyl glycerol tetraethers (GDGTs basis for BIT-Index) after Hopmans et al. (2016), Hopanes (fßß) following instructions by Meyer et al., (2019), and Sterols (Dinosterol) after Dauner et al. (2022).

Description: In July 2022 within the framework of an Alfred-Wegener-Institute-managed expedition and the Nunataryuk project, sediment core YC22_MR_7 was taken off the coast of Herschel Island, Canada, using a hand corer. Data sets were obtained to investigate carbon feedback from the sediments to the water column and atmosphere, using DIC concentrations and isotopic values. The local sediments are supplied primarily by organic carbon previously stored in adjacent permafrost soils (biomarker and bulk data), which erode and redeposit quickly (age model) on the ocean floor. Porewater was extracted from the cores using rhizomes and quantified as described in Oni et al., (2015). Dissolved inorganic carbon isotope signatures were determined as CO2 for 13C (Torres et al., 2005) and 14C (Mollenhauer et al., 2021).

Description: In July 2022 within the framework of an Alfred-Wegener-Institute-managed expedition and the Nunataryuk project, sediment core YC22_MR_8 was taken off the coast of Herschel Island, Canada, using a hand corer. Data sets were obtained to investigate carbon feedback from the sediments to the water column and atmosphere, using DIC concentrations and isotopic values. The local sediments are supplied primarily by organic carbon previously stored in adjacent permafrost soils (biomarker and bulk data), which erode and redeposit quickly (age model) on the ocean floor. Porewater was extracted from the cores using rhizomes and quantified as described in Oni et al., (2015). Dissolved inorganic carbon isotope signatures were determined as CO2 for 13C (Torres et al., 2005) and 14C (Mollenhauer et al., 2021).