Isotope and microbiome analysis indicates variety of N-cycle processes controlling N2O fluxes in a drained peatland forest soil : EGU21-10809

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Constraining the conditions of phosphogenesis : stable isotope and trace element systematics of Recent Namibian phosphatic sediments

This study was supported by the Estonian Science Agency project PRG447 and the Estonian Centre of Analytical Chemistry. K. Paiste was supported by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 894831. We would also like to thank the organizers and participants of the Regional Graduate Network in Oceanography Discovery Camp 2015, funded by the Agouron Institute and the Scientific Committee for Oceanographic Research (SCOR), as well as the Namibian Ministry of Fisheries and Marine Resources and the captain and crew of R/V Mirabilis for access to the coring site.Modern phosphogenesis occurs on continental margins influenced by upwelling and high primary productivity. The formation of phosphatic sediments is coupled to global climate fluctuations, biological cycling of phosphorus and local redox conditions. Although the processes involved in phosphogenesis are well described, high-resolution data on the redox and stable isotope systematics in Recent in-situ phosphorites are scarce. In this contribution, we investigate the trace element and sulfur, nitrogen and organic carbon stable isotope composition of Recent in-situ phosphatic sediments off the coast of Namibia. Also, we examine the reliability of different widely used geochemical proxies in phosphatic sediments. Our results suggest a shift from sulfidic to suboxic conditions, coinciding with the maximum in solid calcium phosphate mineral concentration. This shift is accompanied by unidirectional changes in Mo and Re enrichments and TOC abundance. Relatively low pyrite δ34S values (ca -20‰) of phosphatic sediments indicate open system fractionation during phosphogenesis. The initiation of phosphogenesis is also accompanied by negative shifts in sedimentary δ13Corg and δ15N values. Phosphate associated sulfate (PAS) δ34S values are lower than modern seawater sulfate values, suggesting the involvement of chemolithotrophic sulfur oxidation. Our results show a shift in redox conditions from sulfidic to (sub)oxic, coupled with active sulfur cycling are prerequisites for phosphogenesis. Phosphatic sediments show substantial enrichments in U and V highlighting the complexity of using these elements, as well as V/(V+Ni) and V/Cr, as redox proxies particularly in phosphorites and phosphatic sediments.PostprintPostprintPeer reviewe

Natural Nitrogen Isotope Ratios as a Potential Indicator of N2O Production Pathways in a Floodplain Fen

Nitrous oxide (N2O), a major greenhouse gas and ozone depleter, is emitted from drained organic soils typically developed in floodplains. We investigated the effect of the water table depth and soil oxygen (O2) content on N2O fluxes and their nitrogen isotope composition in a drained floodplain fen in Estonia. Measurements were done at natural water table depth, and we created a temporary anoxic environment by experimental flooding. From the suboxic peat (0.5–6 mg O2/L) N2O emissions peaked at 6 mg O2/L and afterwards decreased with decreasing O2. From the anoxic and oxic peat (0 and >6 mg O2/L, respectively) N2O emissions were low. Under anoxic conditions the δ15N/δ14N ratio of the top 10 cm peat layer was low, gradually decreasing to 30 cm. In the suboxic peat, δ15N/δ14N ratios increased with depth. In samples of peat fluctuating between suboxic and anoxic, the elevated 15N/14N ratios (δ15N = 7–9‰ ambient N2) indicated intensive microbial processing of nitrogen. Low values of site preference (SP; difference between the central and peripheral 15N atoms) and δ18O-N2O in the captured gas samples indicate nitrifier denitrification in the floodplain fen

Children of the grave: Investigating non-adult feeding practices in medieval and early modern Estonia through stable isotope analysis /

Studying infant diet and feeding practices through stable isotope analysis provides direct insight into the life and health of vulnerable population groups in the past. Although the gen- eral diet in medieval and early modern Livonia has been reconstructed from written sources, little is known about childhood diet during this tumultuous period of Eastern European his- tory. This study presents a comparative investigation of the staple non-adult diet in urban/ rural communities during the 13th-17th centuries AD, with a special focus on feeding prac- tices. We aim to reveal the impact of socio-economic circumstances on early childhood nutrition, which affects the physical development and overall survival of this susceptible pop- ulation group. Bone collagen samples from 176 individuals between the fetal and the 7–15 age categories from four urban/rural South-Estonian cemeteries were cross-sectionally analyzed via EA-IRMS (Elemental Analysis with Isotope Ratio Mass Spectroscopy) for δ13C and δ15N. Results suggest that South-Estonian children had a staple terrestrial C3 diet inte- grated with animal proteins. Significant divergences were observed between urban and rural sites and slight variation occurred among rural subgroups, possibly resulting from a wider food choice available in towns, different consumption of C4 foods, and/or secular changes. This study provides the first data regarding infant feeding practices in medieval and early modern Livonia. These practices were similar among the different contexts, indi- cating comparable cultural traditions in child rearing. Breastfeeding was likely practiced for 1–2 years, with supplementary foods introduced around 1 year of age. The weaning process was probably concluded around the age of 3. The δ13C and δ15N values of older children are comparable to those of the adults from the same sites, indicating their diets became sim- ilar after weaning, when they started working and obtained a more mature social status

Summary statistics of non-adult isotopic values for each subcategory.

Summary statistics of non-adult isotopic values for each subcategory.</p