Constraining instantaneous fluxes and integrated compositions of fluvially discharged organic matter

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Freymond, C. V., Lupker, M., Peterse, F., Haghipour, N., Wacker, L., Filip, F., et al. (2018). Constraining instantaneous fluxes and integrated compositions of fluvially discharged organic matter. Geochemistry, Geophysics, Geosystems, 19, 2453 2462. doi: 10.1029/2018GC007539.Fluvial export of organic carbon (OC) and burial in ocean sediments comprises an important carbon sink, but fluxes remain poorly constrained, particularly for specific organic components. Here OC and lipid biomarker contents and isotopic characteristics of suspended matter determined in depth profiles across an active channel close to the terminus of the Danube River are used to constrain instantaneous OC and biomarker fluxes and integrated compositions during high to moderate discharges. During high (moderate) discharge, the total Danube exports 8 (7) kg/s OC, 7 (3) g/s higher plant‐derived long‐chain fatty acids (LCFA), 34 (21) g/s short‐chain fatty acids (SCFA), and 0.5 (0.2) g/s soil bacterial membrane lipids (brGDGTs). Integrated stable carbon isotopic compositions were TOC: −28.0 (−27.6)‰, LCFA: −33.5 (−32.8)‰ and Δ14C TOC: −129 (−38)‰, LCFA: −134 (−143)‰, respectively. Such estimates will aid in establishing quantitative links between production, export, and burial of OC from the terrestrial biosphere.This project was funded by the Swiss National Science Foundation SNF. Grant Number: 200021_140850. F.P. acknowledges funding from NWO‐VENI grant 863.13.016. We thank the sampling crews from both field campaigns (Björn Buggle, James Saenz, Alissa Zuijdgeest, Marilu Tavagna, Stefan Eugen Filip, Silvia Lavinia Filip, Mihai, Clayton Magill, Thomas Blattmann, and Michael Albani), Daniel Montluçon for lab support and Hannah Gies for PCGC work. Figures, tables, and equations can be found in supporting information

Kiezen voor dierenwelzijn

Om de consument beter te kunnen informeren over de diervriendelijkheid van vleesproducten heeft de Stichting Varkens in Nood (VIN) aan de voormalige Wetenschapswinkel Biologie (nu: Kennispunt Bètawetenschappen) in Utrecht gevraagd een “vleeswijzer” te ontwikkelen die uitgedeeld kan worden aan consumenten en waarop consumenten op een eenvoudige manier kunnen zien welke producten méér of juist minder diervriendelijk geproduceerd worden. Om deze vleeswijzer te ontwikkelen is in dit onderzoek een aantal dierenwelzijnsdeskundigen benaderd met de vraag de diervriendelijkheid van verschillende vleesproducten te beoordelen. In deze rapportage wordt dit onderzoek beschreven

Lipid biomarker temperature proxy responds to abrupt shift in the bacterial community composition in geothermally heated soils

Specific soil bacterial membrane lipids, branched glycerol dialkyl glycerol tetraethers (brGDGTs), are used as an empirical proxy for past continental temperatures. Their response to temperature change is assumed to be linear, caused by physiological plasticity of their, still unknown, source organisms. A well-studied set of geothermally warmed soils (Iceland) shows that the brGDGT fingerprint only changes when the soil mean annual temperature is warmer than 14 °C. This sudden change in brGDGT distribution coincides with an abrupt shift in the bacterial community composition in the same soils. Determining which bacterial OTUs are indicative for each soil cluster shows that Acidobacteria are possible brGDGT producers, together with representatives from the Actinobacteria, Chloroflexi, Gemmationadetes and Proteobacteria. Projecting the lipid fingerprint of the cold and warm bacterial communities onto the global soil calibration dataset creates two distinct soil clusters, in which brGDGTs respond differently to temperature and, especially, soil pH. We show that, on a local scale, a community effect rather than physiological plasticity can be the primary driver of the brGDGT-based paleothermometer along large temperature gradients. This threshold response needs to be taken into account when interpreting brGDGT-based paleo-records

Lipid biomarker temperature proxy responds to abrupt shift in the bacterial community composition in geothermally heated soils

Specific soil bacterial membrane lipids, branched glycerol dialkyl glycerol tetraethers (brGDGTs), are used as an empirical proxy for past continental temperatures. Their response to temperature change is assumed to be linear, caused by physiological plasticity of their, still unknown, source organisms. A well-studied set of geothermally warmed soils (Iceland) shows that the brGDGT fingerprint only changes when the soil mean annual temperature is warmer than 14 °C. This sudden change in brGDGT distribution coincides with an abrupt shift in the bacterial community composition in the same soils. Determining which bacterial OTUs are indicative for each soil cluster shows that Acidobacteria are possible brGDGT producers, together with representatives from the Actinobacteria, Chloroflexi, Gemmationadetes and Proteobacteria. Projecting the lipid fingerprint of the cold and warm bacterial communities onto the global soil calibration dataset creates two distinct soil clusters, in which brGDGTs respond differently to temperature and, especially, soil pH. We show that, on a local scale, a community effect rather than physiological plasticity can be the primary driver of the brGDGT-based paleothermometer along large temperature gradients. This threshold response needs to be taken into account when interpreting brGDGT-based paleo-records

Lipid biomarker temperature proxy responds to abrupt shift in the bacterial community composition in geothermally heated soils

Specific soil bacterial membrane lipids, branched glycerol dialkyl glycerol tetraethers (brGDGTs), are used as an empirical proxy for past continental temperatures. Their response to temperature change is assumed to be linear, caused by physiological plasticity of their, still unknown, source organisms. A well-studied set of geothermally warmed soils (Iceland) shows that the brGDGT fingerprint only changes when the soil mean annual temperature is warmer than 14 °C. This sudden change in brGDGT distribution coincides with an abrupt shift in the bacterial community composition in the same soils. Determining which bacterial OTUs are indicative for each soil cluster shows that Acidobacteria are possible brGDGT producers, together with representatives from the Actinobacteria, Chloroflexi, Gemmationadetes and Proteobacteria. Projecting the lipid fingerprint of the cold and warm bacterial communities onto the global soil calibration dataset creates two distinct soil clusters, in which brGDGTs respond differently to temperature and, especially, soil pH. We show that, on a local scale, a community effect rather than physiological plasticity can be the primary driver of the brGDGT-based paleothermometer along large temperature gradients. This threshold response needs to be taken into account when interpreting brGDGT-based paleo-records

The influence of soil chemistry on branched tetraether lipids in mid- and high latitude soils: Implications for brGDGT- based paleothermometry

Branched glycerol dialkyl glycerol tetraethers (BrGDGTs) are a suite of orphan bacterial membrane lipids commonly used as paleo-environmental proxies for mean annual air temperature (MAT) and pH. Recent calibrations between the Methylation of Branched Tetraethers index (MBT′5ME) and MAT, based on modern surface soils (including peats), show a considerable amount of scatter, especially in mid- and high latitude soils, suggesting that brGDGT signals are influenced by additional environmental and/or biological controls at these sites. Here we test the impact of soil chemical gradients and bacterial community changes (16S rDNA sequence-based) on brGDGT distributions at two grasslands sites (Ossenkampen [NL], ForHot [IS]), and one agricultural site (Craibstone [UK]). In addition to the variation in soil chemistry, the ForHot site experiences belowground warming. Of the studied edaphic parameters, soil pH is the primary factor that explains simultaneous changes in both the bacterial community composition and the brGDGT distribution. Variations in the MBT′5ME at two sites without soil warming indeed correlate strongly to soil pH (r = 0.9–1.0, pH = 4.5–7.3), whereas pH explains part of the variation in the MBT′5ME at the site with soil warming (mean soil temperature ranging between 5 and 14 °C). At all sites, soil pH is positively related with the same brGDGTs (Ib, IIb, IIIb, IIIc, IIa′, IIb′, IIc′, IIIa′, IIb′, IIIc′) and influences the ratio between main brGDGT compounds Ia, IIa and IIIa, impacting the MBT′5ME values. This change in brGDGT distributions coincides with a change in the composition of the bacterial community at all sites. The bacterial clades that vary at the three experimental sites (specifically Acidobacteria subgroups 1, 2, 3, 6, 22) have previously been shown to also respond to soil pH on a global scale. As soil pH changes on geological timescales, the impact of changing pH on the MBT′5ME paleothermometer should be considered when performing paleoclimate studies.ISSN:0016-7037ISSN:1872-953