Molecular fossils within bitumens and kerogens from the ~ 1 Ga Lakhanda Lagerstätte (Siberia, Russia) and their significance for understanding early eukaryote evolution

The emergence and diversification of eukaryotes during the Proterozoic is one of the most fundamental evolutionary developments in Earth’s history. The ca. 1-billion-year-old Lakhanda Lagerstätte (Siberia, Russia) contains a wealth of eukaryotic body fossils and offers an important glimpse into their ecosystem. Seeking to complement the paleontological record of this remarkable lagerstätte, we here explored information encoded within sedimentary organic matter (total organic carbon = 0.01–1.27 wt.%). Major emphasis was placed on sedimentary hydrocarbons preserved within bitumens and kerogens, including molecular fossils (or organic biomarkers) that are specific to bacteria and eukaryotes (i.e. hopanes and regular steranes, respectively). Programmed pyrolysis and molecular organic geochemistry suggest that the organic matter in the analyzed samples is about peak oil window maturity and thus sufficiently well preserved for detailed molecular fossil studies that include hopanes and steranes. Together with petrographic evidence as well as compositional similarities of the bitumens and corresponding kerogens, the consistency of different independent maturity parameters establishes that sedimentary hydrocarbons are indigenous and syngenetic to the host rock. The possible presence of trace amounts of hopanes and absence of steranes in samples that are sufficiently well preserved to retain both types of compounds evidences an environment dominated by anaerobic bacteria with no or very little inputs by eukaryotes. In concert with the paleontological record of the Lakhanda Lagerstätte, our study adds to the view that eukaryotes were present but not significant in Mesoproterozoic ecosystems.

Fungal biomarkers are detectable in Martian rock-analogues after space exposure: implications for the search of life on Mars

Mars is a primary target of astrobiological interest: its past environmental conditions may have been favourable to the emergence of a prebiotic chemistry and, potentially, biological activity. In situ exploration is currently underway at the Mars surface, and the subsurface (2 m depth) will be explored in the future ESA ExoMars mission. In this context, BIOlogy and Mars EXperiment was performed to evaluate the stability and detectability of organic biomarkers under space and Mars-like conditions. Our data suggested that some target molecules, namely melanin, azelaic acid and nucleic acids, can be detected even after 16 months exposure to Low Earth Orbit conditions by multidisciplinary approaches. We used the same techniques as onboard the ExoMars rover, as Raman and infrared spectroscopies and gas chromatograph-mass spectrometer, and polymerase chain reaction even if this is not planned for the imminent mission to Mars. These results should be taken into account for future Mars exploration.

Seasonal sea ice persisted through the Holocene Thermal Maximum at 80°N

The cryospheric response to climatic warming responsible for recent Arctic sea ice decline can be elucidated using marine geological archives which offer an important long-term perspective. The Holocene Thermal Maximum, between 10 and 6 thousand years ago, provides an opportunity to investigate sea ice during a warmer-than-present interval. Here we use organic biomarkers and benthic foraminiferal stable isotope data from two sediment cores in the northernmost Barents Sea (>80 °N) to reconstruct seasonal sea ice between 11.7 and 9.1 thousand years ago. We identify the continued persistence of sea-ice biomarkers which suggest spring sea ice concentrations as high as 55%. During the same period, high foraminiferal oxygen stable isotopes and elevated phytoplankton biomarker concentrations indicate the influence of warm Atlantic-derived bottom water and peak biological productivity, respectively. We conclude that seasonal sea ice persisted in the northern Barents Sea during the Holocene Thermal Maximum, despite warmer-than-present conditions and Atlantic Water inflow.

Application of Nitrogenated Holey Graphene for Detection of Volatile Organic Biomarkers in Exhaled Breath of Humans With Chronic Kidney Disease: A Density Functional Theory Study

The possibility of using nitrogenated holey graphene (NHG) sheet to detect volatile organic biomarkers in exhaled breath of humans with kidney disease is investigated. Heptanal, hexanal, pentanal, and isoperene are known as the prominent biomarkers of chronic kidney disease. Adsorption of these molecules on NHG sheet is studied using density functional theory. All the molecules are weakly physisorbed on NHG sheet, which predicts easy desorption and the possibility of using NHG sheet as a reusable sensor. The NHG sheet acts as a semiconductor with a direct band gap. Adsorption of the considered molecules causes n-type semiconducting properties in the sheet. Increasing the concentration of the adsorbed molecules decreased the energy band gaps and consequently increased the electric conductivity of NHG sheet. Hence, the electronic properties of NHG sheet are sensitive to the presence and concentration of heptanal, hexanal, pentanal, and isoperene molecules. Our results open a new opportunity to design a new sensor to diagnose chronic kidney disease using exhaled breath analysis.

Biomarkers in the rock outcrop of the Kazusa Group reveal palaeoenvironments of the Kuroshio region

Long-chain alkenones and n-alkanes preserved in marine and lake sediment cores are widely used to reconstruct palaeoenvironments. However, applying this technique to exposed sedimentary rock sequences is relatively challenging due to the potential for the diagenetic alteration of organic biomarkers. Here, we extract long-chain alkenones and n-alkanes from an exposed outcrop of the Kazusa Group in central Japan, one of the most continuous sedimentary successions in the world, covering almost the entire Pleistocene. We find that the alkenone unsaturation ratio and average chain length of n-alkanes appears to reflect the glacial-interglacial changes in sea surface temperature and terrestrial climate, respectively. Alkenone-based sea surface temperatures between 1.1 and 1.0 million years ago concur with foraminiferal Mg/Ca-based temperature estimates and may reflect an intrusion of the Kuroshio Current. We suggest that the preservation of these biomarkers in the Kazusa Group demonstrates its potential to provide a detailed palaeoenvironmental record.

A warmer Mediterranean region at the Miocene to Pliocene transition

<p>Between 5.97-5.33 Ma several kilometre-thick evaporite units were deposited in the Mediterranean Basin during the Messinian Salinity Crisis (MSC). The MSC reflects a period featured by a negative hydrological budget, with a net evaporative loss of water exceeding precipitation and riverine runoff. The contemporary changes in continental and marine circum-Mediterranean temperature are, however, poorly constrained. Here we reconstruct continental mean annual temperatures (MAT) using branched glycerol dialkyl glycerol tetraether (GDGT) biomarkers for the time period corresponding to MSC Stage 3 (5.55-5.33 Ma). Additionally, for the same time interval, we estimate sea surface temperatures (SSTs) of the Mediterranean Sea using isoprenoidal GDGTs based TEX<sub>86</sub> proxy. The excellently preserved organic biomarkers were extracted from outcrops and DSDP cores spread over a large part of the onland (Malaga, Sicily, Cyprus) and offshore (holes 124 and 134 from the Balearic abyssal plane and hole 374 from the Ionian Basin) Mediterranean Basin domain. The calculated MATs for the 5.55 to 5.33 Ma interval show values around 16 to 18 ºC for the Malaga, Sicily and Cyprus outcrops. The MAT values calculated for DSDP Leg 13 holes 124, 134 and Leg 42A hole 374 are lower, around 11 to 13 ºC.</p><p>For samples where the branched and isoprenoid tetraether (BIT) index was lower than the 0.4 we could calculate TEX<sub>86</sub> derived SSTs averaging around 27 ºC for all sampled locations. Where available (i.e. Sicily), we compared the TEX<sub>86</sub> derived SSTs with alkenone based, U<sup>k</sup><sub>37</sub> derived SST estimates from the same samples. The TEX<sub>86</sub> derived SST values are slightly higher than the U<sup>k</sup><sub>37</sub> derived SST of 20 to 28 ºC. For the Mediterranean region, values between 19 and 27 ºC of the U<sup>k</sup><sub>37</sub> derived SSTs were calculated for the interval between the 8.0 and 6.4 Ma (Tzanova et al., 2015), close to our calculations for Sicily section (20 to 28 ºC). Independent of common pitfalls that may arise in using molecular biomarkers as temperature proxies, both SST estimates independently hint towards much warmer Mediterranean Sea water during the latest phase (Stage 3) of the MSC. These elevated temperatures coincide with higher δD values measured on alkenones and long chain n-alkanes (both records indicating for more arid and/or warmer conditions than today between 5.55 and 5.33 Ma). We therefore conclude that the climate between 5.55 to 5.33 Ma was warmer than present-day conditions, recorded both in the Mediterranean Sea and the land surrounding it.</p>

Use of soil organic biomarkers for tracing the origin of eroded sediment: case study in Petzenkirchen (Austria)

<p>Compound-specific stable isotopes (CSSI) technique based on the measurement of δ<sup>13</sup>C signatures of organic biomarker compounds such as fatty acids (FAs) has been used since the end of the 2000s to reinforce the knowledge about sediment production and budget in various ecosystems.<br>The watershed of Petzenkirchen, located 100 km west from Vienna (Austria), was selected to establish the origin of the sediment produced at its outlet using δ<sup>13</sup>C-FAs analysis. The climatic conditions of the area are temperate with continental influences with a mean temperature of 9.5˚ C and yearly precipitation of 823 mm. The dominant soil types are Cambisols and Planosols. Based on existing land-use records, most of the agricultural fields are dominated by a rotation of winter wheat followed by maize cultivation.<br>Considering the specific geomorphology, the flow of the runoff, the significant interaction of roads, the distance and connection of the potential sources to the outlet, the contributing area of the site has been set to around 50 ha and 7 sources most likely to contribute to the sediment at the outlet were investigated. Using the mixing polygons approach, the δ<sup>13</sup>C of saturated long chain FAs (i.e. C24:0 and C26:0) allowed the best discrimination for establishing the contribution of sources to the sediment collected at the exit of the watershed (i.e. the mixture). The relative contribution to the soil mixture of the different source soils identified has been determined using the Stable Isotope Mixing Models in R (SIMMR) and the specific organic carbon content of each source. The simulated results derived with SIMMR highlights that more than half of the sediment reaching the outlet of the watershed originates from stream bank. <br>This Austrian study confirms that the information gained with δ<sup>13</sup>C-FAs analysis could provide unique support for allowing effective agroecosystems management.</p>