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Creators/Authors contains: "Eglinton, Timothy I."

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  1. Free, publicly-accessible full text available January 1, 2023
  2. Terrestrial vegetation and soils hold three times more carbon than the atmosphere. Much debate concerns how anthropogenic activity will perturb these surface reservoirs, potentially exacerbating ongoing changes to the climate system. Uncertainties specifically persist in extrapolating point-source observations to ecosystem-scale budgets and fluxes, which require consideration of vertical and lateral processes on multiple temporal and spatial scales. To explore controls on organic carbon (OC) turnover at the river basin scale, we present radiocarbon ( 14 C) ages on two groups of molecular tracers of plant-derived carbon—leaf-wax lipids and lignin phenols—from a globally distributed suite of rivers. We find significant negativemore »relationships between the 14 C age of these biomarkers and mean annual temperature and precipitation. Moreover, riverine biospheric-carbon ages scale proportionally with basin-wide soil carbon turnover times and soil 14 C ages, implicating OC cycling within soils as a primary control on exported biomarker ages and revealing a broad distribution of soil OC reactivities. The ubiquitous occurrence of a long-lived soil OC pool suggests soil OC is globally vulnerable to perturbations by future temperature and precipitation increase. Scaling of riverine biospheric-carbon ages with soil OC turnover shows the former can constrain the sensitivity of carbon dynamics to environmental controls on broad spatial scales. Extracting this information from fluvially dominated sedimentary sequences may inform past variations in soil OC turnover in response to anthropogenic and/or climate perturbations. In turn, monitoring riverine OC composition may help detect future climate-change–induced perturbations of soil OC turnover and stocks.« less
  3. ABSTRACT The radiocarbon ( 14 C) content of simultaneously deposited substrates in lacustrine archives may differ due to reservoir and detrital effects, complicating the development of age models and interpretation of proxy records. Multi-substrate 14 C studies quantifying these effects remain rare, however, particularly for large, terminal lake systems, which are excellent recorders of regional hydroclimate change. We report 14 C ages of carbonates, brine shrimp cysts, algal mat biomass, total organic carbon (TOC), terrestrial macrofossils, and n -alkane biomarkers from Holocene sediments of the Great Salt Lake (GSL), Utah. 14 C ages for co-deposited aquatic organic substrates are generallymore »consistent, with small offsets that may reflect variable terrestrial organic matter inputs to the system. Carbonates and long-chain n -alkanes derived from vascular plants, however, are ∼1000–4000 14 C years older than other substrates, reflecting deposition of pre-aged detrital materials. All lacustrine substrates are 14 C-depleted compared to terrestrial macrofossils, suggesting that the reservoir age of the GSL was > 1200 years throughout most of the Holocene, far greater than the modern reservoir age of the lake (∼300 years). These results suggest good potential for multi-substrate paleoenvironmental reconstruction from Holocene GSL sediments but point to limitations including reservoir-induced uncertainty in 14 C chronologies and attenuation and time-shifting of some proxy signals due to detrital effects.« less
  4. Abstract. Biogeochemical cycling in the semi-enclosed Arctic Ocean is stronglyinfluenced by land–ocean transport of carbon and other elements and isvulnerable to environmental and climate changes. Sediments of the ArcticOcean are an important part of biogeochemical cycling in the Arctic andprovide the opportunity to study present and historical input and the fate oforganic matter (e.g., through permafrost thawing). Comprehensive sedimentary records are required to compare differencesbetween the Arctic regions and to study Arctic biogeochemical budgets. Tothis end, the Circum-Arctic Sediment CArbon DatabasE (CASCADE) wasestablished to curate data primarily on concentrations of organic carbon(OC) and OC isotopes (δ13C, Δ14C) yet also ontotalmore »N (TN) as well as terrigenous biomarkers and other sedimentgeochemical and physical properties. This new database builds on thepublished literature and earlier unpublished records through an extensiveinternational community collaboration. This paper describes the establishment, structure and current status ofCASCADE. The first public version includes OC concentrations in surfacesediments at 4244 oceanographic stations including 2317 with TNconcentrations, 1555 with δ13C-OC values and 268 with Δ14C-OC values and 653 records with quantified terrigenous biomarkers(high-molecular-weight n-alkanes, n-alkanoic acids and lignin phenols).CASCADE also includes data from 326 sediment cores, retrieved by shallowbox or multi-coring, deep gravity/piston coring, or sea-bottom drilling.The comprehensive dataset reveals large-scale features of both OC contentand OC sources between the shelf sea recipients. This offers insight intorelease of pre-aged terrigenous OC to the East Siberian Arctic shelf andyounger terrigenous OC to the Kara Sea. Circum-Arctic sediments therebyreveal patterns of terrestrial OC remobilization and provide clues about thawing of permafrost. CASCADE enables synoptic analysis of OC in Arctic Ocean sediments andfacilitates a wide array of future empirical and modeling studies of theArctic carbon cycle. The database is openly and freely available online(https://doi.org/10.17043/cascade; Martens et al., 2021), is provided in variousmachine-readable data formats (data tables, GIS shapefile, GIS raster), andalso provides ways for contributing data for future CASCADE versions. Wewill continuously update CASCADE with newly published and contributed dataover the foreseeable future as part of the database management of the BolinCentre for Climate Research at Stockholm University.« less
  5. ABSTRACT In practice, obtaining radiocarbon ( 14 C) composition of organic matter (OM) in sediments requires first removing inorganic carbon (IC) by acid-treatment. Two common treatments are acid rinsing and fumigation. Resulting 14 C content obtained by different methods can differ, but underlying causes of these differences remain elusive. To assess the influence of different acid-treatments on 14 C content of sedimentary OM, we examine the variability in 14 C content for a range of marine and river sediments. By comparing results for unacidified and acidified sediments [HCl rinsing (Rinse HCl ) and HCl fumigation (Fume HCl )], we demonstratemore »that the two acid-treatments can affect 14 C content differentially. Our findings suggest that, for low-carbonate samples, Rinse HCl affects the Fm values due to loss of young labile organic carbon (OC). Fume HCl makes the Fm values for labile OC decrease, leaving the residual OC older. High-carbonate samples can lose relatively old organic components during Rinse HCl , causing the Fm values of remaining OC to increase. Fume HCl can remove thermally labile, usually young, OC and reduce the Fm values. We suggest three factors should be taken into account when using acid to remove carbonate from sediments: IC abundance, proportions of labile and refractory OC, and environmental matrix.« less