A marine record of Patagonian ice sheet changes over the past 140,000 years.

Terrestrial glacial records from the Patagonian Andes and New Zealand Alps document quasi-synchronous Southern Hemisphere-wide glacier advances during the late Quaternary. However, these records are inherently incomplete. Here, we provide a continuous marine record of western-central Patagonian ice sheet (PIS) extent over a complete glacial-interglacial cycle back into the penultimate glacial (~140 ka). Sediment core MR16-09 PC03, located at 46°S and ~150 km offshore Chile, received high terrestrial sediment and meltwater input when the central PIS extended westward. We use biomarkers, foraminiferal oxygen isotopes, and major elemental data to reconstruct terrestrial sediment and freshwater input related to PIS variations. Our sediment record documents three intervals of general PIS marginal fluctuations, during Marine Isotope Stage (MIS) 6 (140 to 135 ka), MIS 4 (~70 to 60 ka), and late MIS 3 to MIS 2 (~40 to 18 ka). These higher terrigenous input intervals occurred during sea-level low stands, when the western PIS covered most of the Chilean fjords, which today retain glaciofluvial sediments. During these intervals, high-amplitude phases of enhanced sediment supply occur at millennial timescales, reflecting increased ice discharge most likely due to a growing PIS. We assign the late MIS 3 to MIS 2 phases and, by inference, older advances to Antarctic cold stages. We conclude that the increased sediment/meltwater release during Southern Hemisphere millennial-scale cold phases was likely related to higher precipitation caused by enhanced westerly winds at the northwestern margin of the PIS. Our records complement terrestrial archives and provide evidence for PIS climate sensitivity.

Detection of Four Distinct Volatile Indicators of Colorectal Cancer using Functionalized Titania Nanotubular Arrays.

Screening of colorectal cancer is crucial for early stage diagnosis and treatment. Detection of volatile organic compounds (VOCs) of the metabolome present in exhaled breath is a promising approach to screen colorectal cancer (CRC). Various forms of volatile organic compounds (VOCs) that show the definitive signature for the different diseases including cancers are present in exhale breathe. Among all the reported CRC VOCs, cyclohexane, methylcyclohexane, 1,3-dimethyl- benzene and decanal are identified as the prominent ones that can be used as the signature for CRC screening. In the present investigation, detection of the four prominent VOCs related to CRC is explored using functionalized titania nanotubular arrays (TNAs)-based sensor. These signature biomarkers are shown to be detected using nickel-functionalized TNA as an electrochemical sensor. The sensing mechanism is based on the electrochemical interaction of nickel-functionalized nanotubes with signature biomarkers. A detailed mechanism of the sensor response is also presented.

Radiolytic Effects on Biological and Abiotic Amino Acids in Shallow Subsurface Ices on Europa and Enceladus.

Europa and Enceladus are key targets to search for evidence of life in our solar system. However, the surface and shallow subsurface of both airless icy moons are constantly bombarded by ionizing radiation that could degrade chemical biosignatures. Therefore, sampling of icy surfaces in future life detection missions to Europa and Enceladus requires a clear understanding of the necessary ice depth where unaltered organic biomolecules might be present. We conducted radiolysis experiments by exposing individual amino acids in ices and amino acids from dead microorganisms in ices to gamma radiation to simulate conditions on these icy worlds. In the pure amino acid samples, glycine did not show a detectable decrease in abundance, whereas the abundance of isovaline decreased by 40% after 4 MGy of exposure. Amino acids in dead Escherichia coli (E. coli) organic matter exhibited a gradual decline in abundances with the increase of exposure dosage, although at much slower rates than individual amino acids. The majority of amino acids in dead A. woodii samples demonstrated a step function decline as opposed to a gradual decline. After the initial drop in abundance with 1 MGy of exposure, those amino acids did not display further decreases in abundance after exposure up to 4 MGy. New radiolysis constants for isolated amino acids and amino acids in dead E. coli material for Europa/Enceladus-like conditions have been derived. Slow rates of amino acid destruction in biological samples under Europa and Enceladus-like surface conditions bolster the case for future life detection measurements by Europa and Enceladus lander missions. Based on our measurements, the "safe" sampling depth on Europa is ∼20 cm at high latitudes of the trailing hemisphere in the area of little impact gardening. Subsurface sampling is not required for the detection of amino acids on Enceladus-these molecules will survive radiolysis at any location on the Enceladus surface. If the stability of amino acids observed in A. woodii organic materials is confirmed in other microorganisms, then the survival of amino acids from a potential biosphere in Europa ice would be significantly increased.

Climate change and human impacts on aquatic communities at Etoliko Lagoon in western Greece.

The Etoliko Lagoon in western Greece has experienced extensive human modification since the 20th century, both on the surrounding land and in the aquatic environment. To examine human impacts and disentangle climatic from anthropogenic changes, we present a suite of biomarker records that span the past two centuries (∼1790-2011). Specifically, we use terrigenous (n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and phytosterols) and aquatic (dinosterol, brassicasterol, cholesterol, and stigmasterol) biomarkers to document changes in nutrient inputs, combustion, and algal productivity. During most of the 19th and 20th centuries, aquatic communities respond to temperature, forced mainly by solar irradiance and volcanic activity, and precipitation, controlled largely by summer and winter North Atlantic Oscillation (NAO) patterns that determine freshwater runoff. PAHs illustrate the acceleration of coal combustion during the 1800s, and declining concentrations since the 1950s correspond to the implementation of emission controls and reductions in rainfall that likely inhibited PAH transport. As human pressures increased in the late 1900s and water column anoxia grew, the absence of a clear human waste and eutrophication signal suggests that other factors also contributed to limited oxygen availability. Overall, environmental degradation of the late 20th and early 21st centuries is clear and can be attributed to a combination of especially arid conditions and human interferences that altered lagoon hydrography, trophic state, and aquatic community composition.

Responses of sediment n-alkanes to climate factors and anthropogenic disturbances from three lakes with different elevations, arid Central Asia.

Biomarkers n-alkanes and pertinent indices in lake sediments are frequently used to infer past changes in climate and environmental conditions in and around lakes. Interpretation of n-alkane records can be confounded by a lack of understanding of the multiple factors that control n-alkanes in sediments. Here, we studied n-alkanes in sediment cores from two alpine lakes, Lakes Son-Kul and Issyk-Kul, and from terminal Lake Balkhash, in arid Central Asia to identify natural and human-mediated influences on sediment n-alkane profiles. Altitudinal differences in climate, as well as in lake trophic status, proved to be important drivers of n-alkane compositional differences in the lake sediments. In the alpine lakes, the distribution of n-alkanes was biased toward long-chain components (n-C29, n-C31, and n-C33), and showed higher carbon preference index (CPIH) values, which come from dense terrestrial plant communities, promoted by greater precipitation. In contrast, n-alkanes in the core from the terminal lake displayed higher proportions of short-chain n-alkanes (n-C17, n-C19, and n-C21) because a greater proportion of the organic matter (OM) input to the sediments was derived from algae, a consequence of higher temperatures and trophic status. In recent decades, increasing nutrient inputs from human activities have caused greater accumulation of short-chain n-alkanes in sediments of alpine, oligotrophic Lake Issyk-Kul. In Lake Balkhash, n-C20 and n-C22 alkanes are exceptionally abundant, suggesting large contributions from microbial reworking of terrestrial OM. In all three study lakes, ∑(n-C29-n-C33) was elevated in sediments that correspond to periods of intense agricultural exploitation. Moreover, expansion of agriculture from low to high altitudes resulted in both synchronous and asynchronous peaks in ∑ (n-C29-n-C33) in the studied cores, suggesting the n-alkanes faithfully record the history of agricultural expansion. These findings provide insights into applications of n-alkane proxies and the response of the lake system to climate and anthropogenic impacts.

Late Holocene volcanic and anthropogenic mercury deposition in the western Central Andes (Lake Chungará, Chile).

Volcanism is one of the major natural processes emitting mercury (Hg) to the atmosphere, representing a significant component of the global Hg budget. The importance of volcanic eruptions for local-scale Hg deposition was investigated using analyses of Hg, inorganic elemental tracers, and organic biomarkers in a sediment sequence from Lake Chungará (4520 m a.s.l.). Environmental change and Hg deposition in the immediate vicinity of the Parinacota volcano were reconstructed over the last 2700 years, encompassing the pre-anthropogenic and anthropogenic periods. Twenty eruptions delivering large amounts of Hg (1 to 457 µg Hg m-2 yr-1 deposited at the timescale of the event) were locally recorded. Peaks of Hg concentration recorded after most of the eruptions were attributed to a decrease in sedimentation rate together with the rapid re-oxidation of gaseous elemental Hg and deposition with fine particles and incorporation into lake primary producers. Over the study period, the contribution of volcanic emissions has been estimated as 32% of the total Hg input to the lake. Sharp depletions in primary production occurred at each eruption, likely resulting from massive volcaniclastic inputs and changes in the lake-water physico-chemistry. Excluding the volcanic deposition periods, Hg accumulation rates rose from natural background values (1.9 ±â€¯0.5 µg m-2 yr-1) by a factor of 2.3 during the pre-colonial mining period (1400-900 yr cal. BP), and by a factor of 6 and 7.6, respectively, during the Hispanic colonial epoch (400-150 yr cal. BP) and the industrial era (~140 yr cal. BP to present). Altogether, the dataset indicates that lake primary production has been the main, but not limiting, carrier for Hg to the sediment. Volcanic activity and climate change are only secondary drivers of local Hg deposition relative to the magnitude of regional and global anthropogenic emissions.

Applications of chemical imaging techniques in paleontology.

Chemical imaging techniques, based on a combination of microscopy and spectroscopy, are designed to analyse the composition and spatial distribution of heterogeneous chemical complexes within a sample. Over the last few decades, it has become an increasingly popular tool for characterizing trace elements, isotopic information and organic biomarkers (molecular biosignatures) found in fossils. Here, we introduce the analytical principle of each technique and the interpretation of the chemical signals, followed by a review of the main applications of these techniques in paleontology. We also demonstrate that each technique is associated with pros and cons, and the current limitations and obstacles associated with the use of each specific technique should be taken into account before being applied to fossil samples. Finally, we propose that, due to the rapid advances in the available technology and overall trends towards more multi-disciplinary studies in paleontology, chemical imaging techniques can be expected to have broader applications in paleontology in the near future.

Tracing the fate of steroids through a hypersaline microbial mat (Kiritimati, Kiribati/Central Pacific).

Eukaryotic steranes are typically absent or occur in very low concentrations in Precambrian sedimentary rocks. However, it is as yet unclear whether this may reflect low source inputs or a preservational bias. For instance, it has been proposed that eukaryotic lipids were profoundly degraded in benthic microbial mats that were ubiquitous prior to the advent of vertical bioturbation in the Cambrian ("mat-seal effect"). It is therefore important to test the microbial turnover and degradation of eukaryotic steroids in real-world microbial mats. Here we assessed steroid inventories in different layers of a microbial mat from a hypersaline lake on Kiritimati (Central Pacific). Various eukaryote-derived C27 -C30 steroids were detected in all mat layers. These compounds most likely entered the mat system as unsaturated sterols from the water column or the topmost mat, and were progressively altered during burial in the deeper, anoxic mat layers over c. 103  years. This is reflected by increasing proportions of saturated sterols and sterenes, as well as the presence of thiosteranes in certain horizons. Sterol alteration can partly be assigned to microbial transformation but is also due to chemical reactions promoted by the reducing environment in the deeper mat layers. Notably, however, compounds with a sterane skeleton were similarly abundant in all mat layers and their absolute concentrations did not show any systematic decrease. The observed decrease of steroid/hopanoid ratios with depth may thus rather indicate a progressive "dilution" by lipids derived from heterotrophic bacteria. Further, pyrolysis revealed that steroids, in contrast to hopanoids, were not sequestered into non-extractable organic matter. This may lead to a preservational bias against steroids during later stages of burial. Taken together, steroid preservation in the microbial mat is not only controlled by heterotrophic degradation, but rather reflects a complex interplay of taphonomic processes.

Focused ultrasound solid-liquid extraction for the determination of organic biomarkers in beachrocks.

Beachrocks are consolidated coastal sedimentary formations resulting mainly from the relative rapid cementation of beach sediments by different calcium carbonate polymorphs. Although previous works have already studied the elemental composition and the mineral phases composing these cements, few of them have focused their attention on the organic matter present therein. This work describes an extraction methodology based on focused ultrasound solid-liquid extraction (FUSLE), followed by analysis using large volume injection (LVI) in a programmable temperature vaporizer (PTV) combined with gas chromatography-mass spectrometry (GC-MS) in order to determine organics such as polycyclic aromatic hydrocarbons (PAHs) and biomarkers (hopanes), which can increase and confirm the information obtained so far. This goal has been achieved after the optimization of the main parameters affecting the extraction procedure, such as, extraction solvent, FUSLE variables (amplitude, extraction time and pulse time) and also variables affecting the LVI-PTV (vent time, injection speed and cryo-focusing temperature). The developed method rendered results comparable to traditional extraction methods in terms of accuracy (77-109%) and repeatability (RSD<23%). Finally, the analyses performed over real beachrock samples from the Bay of Biscay (Northern Spain) revealed the presence of the 16 EPA priority PAHs, as well as some organic biomarkers which could increase the knowledge about such beachrock formation.