Seasonality of Glacial Snow and Ice Microbial Communities

Blooms of microalgae on glaciers and ice sheets are amplifying surface ice melting rates, which are already affected by climate change. Most studies on glacial microorganisms (including snow and glacier ice algae) have so far focused on the spring and summer melt season, leading to a temporal bias, and a knowledge gap in our understanding of the variations in microbial diversity, productivity, and physiology on glacier surfaces year-round. Here, we investigated the microbial communities from Icelandic glacier surface snow and bare ice habitats, with sampling spanning two consecutive years and carried out in both winter and two summer seasons. We evaluated the seasonal differences in microbial community composition using Illumina sequencing of the 16S rRNA, 18S rRNA, and ITS marker genes and correlating them with geochemical signals in the snow and ice. During summer, Chloromonas, Chlainomonas, Raphidonema, and Hydrurus dominated surface snow algal communities, while Ancylonema and Mesotaenium dominated the surface bare ice habitats. In winter, algae could not be detected, and the community composition was dominated by bacteria and fungi. The dominant bacterial taxa found in both winter and summer samples were Bacteriodetes, Actinobacteria, Alphaproteobacteria, and Gammaproteobacteria. The winter bacterial communities showed high similarities to airborne and fresh snow bacteria reported in other studies. This points toward the importance of dry and wet deposition as a wintertime source of microorganisms to the glacier surface. Winter samples were also richer in nutrients than summer samples, except for dissolved organic carbon—which was highest in summer snow and ice samples with blooming microalgae, suggesting that nutrients are accumulated during winter but primarily used by the microbial communities in the summer. Overall, our study shows that glacial snow and ice microbial communities are highly variable on a seasonal basis

Mobilisation of organic compounds from reservoir rocks through the injection of CO₂ - comparison of baseline characterization and laboratory experiments

In the framework of CO₂ storage activities, the aim of our investigations is mainly to evaluate the effects of supercritical CO₂ (scCO₂) on the quantitative and qualitative extraction of organic compounds from reservoir rocks. Within the scope of the CO₂ storage project CO₂SINK the major task was to identify key mechanisms occurring in the reservoir as a result of the injection of CO₂ into a saline aquifer. Here, it is of special interest what types and amounts of organic matter will be extracted and mobilized from the reservoir rocks in conjunction with the injection of scCO₂. Thus, our investigations may help to evaluate the efficiency and reliability of the long-term storage of CO₂ in such a geological system. Here, we present compound-specific results from laboratory scCO₂-extraction experiments on reservoir rock samples from the CO₂ storage site in Ketzin, Germany. Low molecular weight organic acids (LMWOA) as well as polar lipid fatty acids (PLFA) extracted by scCO2 were analysed using ion chromatography and gas chromatography-mass spectrometry, respectively. Through the exposure to scCO₂ mainly formate and acetate, but also other LMWOA were released from the rock samples in varying amounts. PLFA profiles of scCO₂ extracts were dominated by saturated and unsaturated fatty acids with 16 and 18 carbon atoms of bacterial origin. The results of scCO₂ extraction are compared with the characterization of the organic inventory of pristine rock samples and fluid samples from observation wells of the Ketzin site to obtain information on quantitative and qualitative significance of the solvent potential of scCO₂

Bulk organic carbon and n-alkane composition data for leaf litter, soil, and floodplain sediment from the Rio Bermejo (Argentina) collected in 2015 - 2018

Endmember samples were collected and analyzed to determine the sources of organic material in the river suspended sediment. Endmembers include soil, leaf litter, and floodplain sediment. Soil and leaf litter samples were collected using an ethanol-cleaned hand trowel. Floodplain sediment samples were collected using an Edelman-type hand auger drilled down to a maximum of ~5 m. Samples were stored in paper bags, and then oven-dried at 40°C. n-alkanes were identified and quantified using an Agilent gas chromatograph (GC 7890-A) with flame ionization detection (FID) coupled to a single quadrupole mass spectrometer (MS 5975-C). We quantified n-alkane concentrations relative to the peak response of the internal standard, and then normalized the abundance to the sediment mass. We measured n-alkane d13C via GC-C-IRMS (gas chromatography/combustion/isotope-ratio mass spectrometry) with helium as a carrier gas (Agilent 7890N, ThermoFisher Delta V Plus). All compounds were measured in triplicate with a standard deviation of =0.5‰. Measurement quality was checked regularly by measuring n-alkane standards (nC15, nC20, nC25) with known isotopic composition (provided by Campro Scientific, Germany). d13C values were normalized to the Vienna Pee Dee Belemnite (VPDB) standard. We measured n-alkane d2H via GC-IRMS using a ThermoFisher Scientific Trace GC 1310 coupled to a Delta-V isotope ratio mass spectrometer. All d2H measurements were made in duplicate, and measurement quality was checked with d2H values were normalized to the Vienna Standard Mean Ocean Water (VSMOW) standard using an n-alkane standard mix with known d2H values (nC16 - nC30, from A. Schimmelman/Indiana University)

Bulk organic carbon and n-alkane composition data for time-series samples from the Rio Bermejo (Argentina) at river km 865 collected in 2017 - 2018

Additionally, we employed a local resident to collect surface water suspended sediment samples at river km 865 throughout the 2017-2018 water year. These samples were collected in a bucket, the sediment was allowed to settle, and then the water was decanted off the top. Recovered sediment was stored in sterile Whirlpak bags, and then dried in an oven at 40°C. We homogenized and disaggregated the dry sediment using a mortar and pestle, and removed coarse plant material >1 mm. For each sample, we weighed an aliquot of sediment and loaded the material into aluminum cells for lipid extraction. Total lipid extracts (TLE) were recovered using an accelerated solvent extraction system (Dionex ASE) with 9:1 v/v dichloromethane: methanol. We added exactly 10 µg of internal standard (5-a-Androstane) to the TLE for unknown compound quantification. We then separated the TLE into three fractions using silica gel column chromatography with hexane (alkanes), 1:1 v/v hexane: dichloromethane (ketones), and 1:1 v/v dichloromethane: methanol (alcohols + acids) (Rach et al., 2020; doi:10.1016/j.orggeochem.2020.103995). Unsaturated compounds were removed from the alkane fraction using AgNO3-silica gel column chromatography with n-hexane (saturated n-alkanes) and DCM (unsaturated n-alkanes). n-alkanes were identified and quantified using an Agilent gas chromatograph (GC 7890-A) with flame ionization detection (FID) coupled to a single quadrupole mass spectrometer (MS 5975-C). We quantified n-alkane concentrations relative to the peak response of the internal standard, and then normalized the abundance to the sediment mass. We measured n-alkane d13C via GC-C-IRMS (gas chromatography/combustion/isotope-ratio mass spectrometry) with helium as a carrier gas (Agilent 7890N, ThermoFisher Delta V Plus). All compounds were measured in triplicate with a standard deviation of =0.5‰. Measurement quality was checked regularly by measuring n-alkane standards (nC15, nC20, nC25) with known isotopic composition (provided by Campro Scientific, Germany). d13C values were normalized to the Vienna Pee Dee Belemnite (VPDB) standard. We measured n-alkane d2H via GC-IRMS using a ThermoFisher Scientific Trace GC 1310 coupled to a Delta-V isotope ratio mass spectrometer. All d2H measurements were made in duplicate, and measurement quality was checked with d2H values were normalized to the Vienna Standard Mean Ocean Water (VSMOW) standard using an n-alkane standard mix with known d2H values (nC16 - nC30, from A. Schimmelman/Indiana University)

Bulk organic carbon and n-alkane composition data for river sediment depth profile samples from the Rio Bermejo (Argentina) collected in March 2017

We extracted and analyzed n-alkane compounds from river suspended sediment collected from the Rio Bermejo in Argentina. We collected 24 river depth profile samples collected during March 2017. We collected suspended particulate matter from water depth profiles at four locations along the mainstem Rio Bermejo (river km 135, 420, 865, 1220), one location on the Rio San Francisco (RSF) (river km -15), and one location on the Rio Bermejo upstream from the RSF confluence (river km -10) (Fig. 1a). We homogenized and disaggregated the dry sediment using a mortar and pestle, and removed coarse plant material >1 mm. For each sample, we weighed an aliquot of sediment and loaded the material into aluminum cells for lipid extraction. Total lipid extracts (TLE) were recovered using an accelerated solvent extraction system (Dionex ASE) with 9:1 v/v dichloromethane: methanol. We added exactly 10 µg of internal standard (5-a-Androstane) to the TLE for unknown compound quantification. We then separated the TLE into three fractions using silica gel column chromatography with hexane (alkanes), 1:1 v/v hexane: dichloromethane (ketones), and 1:1 v/v dichloromethane: methanol (alcohols + acids) (Rach et al., 2020; doi:10.1016/j.orggeochem.2020.103995). Unsaturated compounds were removed from the alkane fraction using AgNO3-silica gel column chromatography with n-hexane (saturated n-alkanes) and DCM (unsaturated n-alkanes). n-alkanes were identified and quantified using an Agilent gas chromatograph (GC 7890-A) with flame ionization detection (FID) coupled to a single quadrupole mass spectrometer (MS 5975-C). We quantified n-alkane concentrations relative to the peak response of the internal standard, and then normalized the abundance to the sediment mass. We measured n-alkane d13C via GC-C-IRMS (gas chromatography/combustion/isotope-ratio mass spectrometry) with helium as a carrier gas (Agilent 7890N, ThermoFisher Delta V Plus). All compounds were measured in triplicate with a standard deviation of =0.5‰. Measurement quality was checked regularly by measuring n-alkane standards (nC15, nC20, nC25) with known isotopic composition (provided by Campro Scientific, Germany). d13C values were normalized to the Vienna Pee Dee Belemnite (VPDB) standard. We measured n-alkane d2H via GC-IRMS using a ThermoFisher Scientific Trace GC 1310 coupled to a Delta-V isotope ratio mass spectrometer. All d2H measurements were made in duplicate, and measurement quality was checked with d2H values were normalized to the Vienna Standard Mean Ocean Water (VSMOW) standard using an n-alkane standard mix with known d2H values (nC16 - nC30, from A. Schimmelman/Indiana University)

Comprehensive geochemical correlation between surface and subsurface hydrocarbon occurrences in the Batman-Mardin-Sirnak area (SE Turkey)

Southeast Turkey is the main oil-producing region of the country, located at the northwestern part of the Zagros Basin. In this study, we investigated the geochemical characteristics of both surface and subsurface hydrocarbon occurrences in the Batman-Mardin-Sirnak area in southeast Turkey to determine whether a genetic relationship exists between the two. For this, thirty solid bitumens from twenty-two different veins along with ten heavy oils and thirteen oil seepage samples from nearby oilfields and seeps were studied using diverse geochemical tools. Firstly each of the different hydrocarbon types was considered individually with respect to source organofacies, level of thermal maturity and degree of biodegradation. The results obtained from the source-related parameters demonstrate a marine algal source for all investigated samples. Also, lithology determination based on various diasterane, tricyclic terpane, hopane and homohopane parameters, suggests a carbonate source for all samples, except for the Dadas and Iskar seeps (clastic). Thereafter, considering the influences caused by thermal and biological alteration processes, all heavy oils, less mature solid bitumens as well as the less biodegraded seep oils were selected to be correlated using selected additional parameters. Homohopane distributions reveal that solid bitumens, compared to heavy oils and seeps, are highly enriched in C-31. and depleted in higher homologues possibly due to cracking of high molecular weight homologues to lower ones during and/or after solidification processes. Furthermore, the similarities observed for the relative abundances of six series of aromatic hydrocarbons and their alkylated counterparts substantiate strong genetic affinities within the sample set. Finally, compound-specific stable carbon isotopes of individual components show that solid bitumens are more enriched in C-13 than the heavy oils which is mainly attributed to the preferential removal of light isotopes (C-12) during solidification. Our results strongly confirm that Turkish solid bitumens are genetically related to the nearby heavy oils, thereby providing new information on the petroleum system in this part of the southeast Anatolia

Vegetation state changes in the course of shrub encroachment in an African savanna since about 1850 CE and their potential drivers

Abstract Shrub encroachment has far‐reaching ecological and economic consequences in many ecosystems worldwide. Yet, compositional changes associated with shrub encroachment are often overlooked despite having important effects on ecosystem functioning. We document the compositional change and potential drivers for a northern Namibian Combretum woodland transitioning into a Terminalia shrubland. We use a multiproxy record (pollen, sedimentary ancient DNA, biomarkers, compound‐specific carbon (δ13C) and deuterium (δD) isotopes, bulk carbon isotopes (δ13Corg), grain size, geochemical properties) from Lake Otjikoto at high taxonomical and temporal resolution. We provide evidence that state changes in semiarid environments may occur on a scale of one century and that transitions between stable states can span around 80 years and are characterized by a unique vegetation composition. We demonstrate that the current grass/woody ratio is exceptional for the last 170 years, as supported by n‐alkane distributions and the δ13C and δ13Corg records. Comparing vegetation records to environmental proxy data and census data, we infer a complex network of global and local drivers of vegetation change. While our δD record suggests physiological adaptations of woody species to higher atmospheric pCO2 concentration and drought, our vegetation records reflect the impact of broad‐scale logging for the mining industry, and the macrocharcoal record suggests a decrease in fire activity associated with the intensification of farming. Impact of selective grazing is reflected by changes in abundance and taxonomical composition of grasses and by an increase of nonpalatable and trampling‐resistant taxa. In addition, grain‐size and spore records suggest changes in the erodibility of soils because of reduced grass cover. Synthesis. We conclude that transitions to an encroached savanna state are supported by gradual environmental changes induced by management strategies, which affected the resilience of savanna ecosystems. In addition, feedback mechanisms that reflect the interplay between management legacies and climate change maintain the encroached state