N-alkanoic Acids Research Articles

Paleoclimate, paleoenvironment, and human impact over the last 400 years based on lipid biomarkers from Lake Höglwörth, Germany

Lipid biomarkers are valuable proxies for reconstructing paleoclimate and paleoenvironmental changes as well as human impact. However, little attention has been paid on evaluating how the combination of biomarkers can be used to reconstruct various aspects of local paleoenvironmental conditions. This study presents a suite of lipid biomarker records from a sediment core from Lake Höglwörth, southern Germany, covering the past 400 years. Compound-specific hydrogen isotopic compositions (δD) of terrestrial n-alkanes (n-C29-alkane) and n-alkanoic acids (n-C30-acid) indicate minor changes in isotopic composition of precipitation. The δD of n-C22-acid is interpreted to record the isotopic composition of the lake water and evaporative enrichment, which drops after 1700 CE, coinciding with the construction of a mill and the related rerouting of a creek into Lake Höglwörth. The δD of n-C25-alkane is also enriched but decoupled from the reconstructed isotopic composition of precipitation and lake water. Therefore, we suggest that δD of n-C25-alkane reflects the leaf water isotopic composition of Sphagnum, which is present in the catchment and undergoes transpirative enrichment. Both short-chain compounds have become more enriched over the last century, maybe related to increasing temperature associated with anthropogenic climate warming. The faecal biomarkers record the changes in human population, partly related to the history of the local Monastery, the World Wars I and II as well as the intensive farming after the mid-20th century. Polycyclic aromatic hydrocarbons (PAHs) reveal a significant change in combustion activities associated with human activities such as the industrial revolution, biomass burning, and environmental cleanup as well as the implementation of emission standards. Our study demonstrates that the combination of plant wax compounds, faecal biomarkers, and PAHs from lacustrine sediment serves as a valuable tool to reconstruct and distinguish various aspects of paleoclimate and paleoenvironmental changes including human impacts.

Plant type effect overweighs seasonal variation in n-alkanoic acid biomarker on regional Loess Plateau of China

Plant type effect overweighs seasonal variation in n-alkanoic acid biomarker on regional Loess Plateau of China

Characterization of natural organic matter in Wyoming-type bentonites irradiated at varied moisture levels

Wyoming-type bentonite clay (MX-80; Wyoming, USA) will be used in a deep geological repository (DGR) for the long-term storage of used nuclear fuel in Canada. The natural organic matter (NOM) found in bentonite may serve as a microbial nutrient source and potentially compromise the performance of the used fuel containers. Previous investigations indicate that NOM is present in low concentrations in MX-80 and has undergone extensive diagenetic alteration, though limited knowledge is available regarding NOM chemistry under simulated DGR conditions. Of particular concern is the possibility for gamma-radiation to alter NOM dissolution and reactivity due to the presence of reactive species generated by water radiolysis in Wyoming-type bentonites. In this study, NOM chemistry was investigated using complementary molecular-level techniques following exposure to a total gamma-radiation dose of 100 kGy (1.08 kGy/h for 93 h) at varied moisture levels (20%, 40%, 60% and 80%) and room temperature. Treated samples exhibited relatively low total organic carbon concentrations (0.074–0.232%), with no evidence of any major changes in total, organic, and inorganic carbon concentrations. Solid-state 13C NMR spectroscopy detected no changes in solid-phase NOM chemistry after irradiation. Solubilization of NOM increased significantly with radiation exposure at 80% moisture, suggesting higher levels of water saturation may enhance dissolved organic matter (DOM) production. Solution-state 1H nuclear magnetic resonance (NMR), and UV–Vis analyses did not identify any significant differences in DOM composition. More sensitive, targeted compound analysis revealed significant decreases in total n-alkanol concentration at lower moisture content levels (20% and 40%). Several individual compound concentrations also differed significantly at the nanogram-level, including n-octacosanol and several n-alkanoic acids at elevated moisture levels (60% and 80%). These findings suggest the majority of NOM in MX-80 remains chemically stable under the anticipated initial conditions of the proposed DGR.

Changes in Indo-Pacific Warm Pool hydroclimate and vegetation during the last deglaciation

Drying across much of the Indo-Pacific Warm Pool (IPWP) during the Last Glacial Maximum (LGM) has been widely recognized from interpretations of sedimentological, geochemical, and paleoecological records. Reconstructions of precipitation isotopic compositions have emerged as a powerful tool to reconstruct rainfall amount in many tropical regions, yet it has proven difficult to reconcile precipitation isotope records from the IPWP with records of widespread drying. To evaluate the signals preserved in precipitation isotope records, we produced new hydrogen and carbon isotope records from Lake Towuti and Lake Matano in Sulawesi, Indonesia using long-chain n-alkanes. We then compared these new records to existing n-alkanoic acid records from the same lakes and compiled available marine runoff, salinity, leaf wax hydrogen isotope (δ2Hwax), and leaf wax carbon isotope (δ13Cwax) records in the IPWP. During the last deglaciation, marine runoff and salinity proxies reveal that precipitation amount began to increase dramatically between ∼12.3 ka at the end of the Younger Dryas. A principal component analysis of precipitation isotope records indicates a shift from more 2H-enriched to 2H-depleted waxes at ∼12.3 ka as sea level rise inundates most of the Sunda and Sahul shelves, coincident with runoff and salinity proxies, suggesting precipitation isotopes respond strongly to rainfall amount in this region. Over 70% of IPWP δ13Cwax records show a transition from more to less 13C-enriched waxes beginning about 19.9 ka, prior to the reconstructed increases in precipitation. We suggest that vegetation shifted in response to the changing seasonality of precipitation. The dramatic changes in the IPWP during the last deglaciation highlight the capacity for the region to experience dynamic changes in precipitation, vegetation, and atmospheric circulation.

Evolution of winter precipitation in the Nile river watershed since the last glacial

Abstract. Between 14.5 and 5 ka, the Sahara was vegetated owing to a wet climate during the African humid period. However, the climatic factors sustaining the “green Sahara” are still a matter of debate. Particularly the role of winter precipitation is poorly understood. Using the stable hydrogen isotopic composition (δD, where D stands for deuterium) of high molecular weight (HMW) n-alkanoic acids in a marine sediment core from the eastern Mediterranean, we provide a continuous record for winter precipitation in the Nile river delta spanning the past 18 kyr. Pairing the data with δD records from HMW n-alkanes from the same core, we show that HMW n-alkanoic acids constantly derived from the delta, while the HMW n-alkanes also received significant contributions from the headwaters between ∼ 15–1 ka when fluvial runoff enhanced. This enables us to reconstruct the evolution of Mediterranean (winter) and monsoonal (summer) rainfall in the Nile river watershed in parallel. In the delta, the Heinrich stadial 1 (HS1) evolved in two phases, with a dry episode between ∼ 17.5–16.0 ka, followed by wet conditions between ∼ 16–14.5 ka. Winter rainfall enhanced substantially between 11–6 ka, lagging behind the intensification of the summer monsoon by ca. 3 kyr. Heavy winter rainfall resulted from a southern position of the Atlantic storm track combined with elevated sea surface temperatures in the eastern Mediterranean, reinforcing local cyclogenesis. We show that during the green Sahara, monsoon precipitation and Mediterranean winter rainfall were both enhanced and infer that the winter rainfall zone extended southwards, delivering moisture to the Sahara. Our findings corroborate recent hypotheses suggesting that winter rains that extended southward were a crucial addition to the northward displacement of the summer monsoon in helping to sustain a green Sahara.

Deglacial export of pre-aged terrigenous carbon to the Bay of Biscay

Abstract. The last deglaciation is the most recent relatively well-documented period of pronounced and fast climate warming, and, as such, it holds important information for our understanding of the climate system. Notably, while research into terrestrial organic carbon reservoirs has been instrumental in exploring the possible sources of atmospheric carbon dioxide during periods of rapid change, the underlying mechanisms are not fully understood. Here we investigate the mobilization of organic matter to the Bay of Biscay, located in the north-eastern Atlantic Ocean off the coasts of France and Spain. Specifically, we focus on the area that was the mouth of the Channel River during the last deglaciation, where an enhanced terrigenous input has been reported for the last glacial–interglacial transition. We conducted a comprehensive suite of biomarker analyses (e.g. n-alkanes, hopanes and n-alkanoic acids) and isotopic investigations (radiocarbon dating and δ13C measurements) on a high-resolution sedimentary archive. The present study provides the first direct evidence for the fluvial supply of immature and ancient terrestrial organic matter to the core location. Moreover, our results reveal the possibility of permafrost carbon export to the ocean, driven by processes such as deglacial warming and glacial erosion. These findings are consistent with observations from other regions characterized by present or past permafrost conditions on land, which have shown that permafrost thaw and glacial erosion can lead to carbon remobilization, potentially influencing atmospheric carbon dioxide levels.

Multi-molecular 14C evidence for mineral control on terrestrial carbon storage andexport.

Compound- and compound class-specific radiocarbon analysis of source-diagnostic 'biomarker' molecules has emerged as a powerful tool to gain insights into terrestrial carbon cycling. While most studies thus far have focused on higher plant biomarkers (i.e. plant leaf-wax n-alkanoic acids and n-alkanes, lignin-derived phenols), tracing paedogenic carbon is crucial given the pivotal role of soils in modulating ecosystem carbon turnover and organic carbon (OC) export. Here, we determine the radiocarbon (14C) ages of glycerol dialkyl glycerol tetraethers (GDGTs) in riverine sediments and compare them to those of higher plant biomarkers as well as markers of pyrogenic (fire-derived) carbon (benzene polycarboxylic acids, BPCAs) to assess their potential as tracers of soil turnover and export. GDGT Δ14C follows similar relationships with basin properties as vegetation-derived lignin phenols and leaf-wax n-alkanoic acids, suggesting that the radiocarbon ages of these compounds are significantly impacted by intermittent soil storage. Systematic radiocarbon age offsets are observable between the studied biomarkers, which are likely caused by different mobilization pathways and/or stabilization by mineral association. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.

Experimental evidence suggests dominance of species effect on the variability in hydrogen isotope fractionation between leaf wax compounds and source water

Quantifying the hydrogen isotope fractionation between leaf wax compounds and source water (εapp) is a prerequisite for hydrogen isotopic composition (δD) based paleo-hydrological studies. However, characterization of the εapp values, mostly done in field-based studies, are predominantly carried out in northern mid-latitude regions, as compared to that in the tropics. Further, the εapp values estimated in field-based studies are often associated with inherent uncertainties which could stem from (i) incorrect source water δD values, (ii) a species-effect, and (iii) varying climatic conditions (as in transect studies). Hence, to characterize the εapp values in tropics and to decouple the factors affecting the variability of εapp, we conducted an outdoor experiment wherein four evergreen and three deciduous angiosperm trees were grown under similar climatic conditions for 85 days with water of known δD value (−2‰). The εapp values in the studied species were −119 ± 23‰ (n = 14) for n-alkanes and −126 ± 27‰ (n = 12) for n-alkanoic acids of chain lengths C31 and C30, respectively. We observed inter-species variabilities in εapp values that are consistent with previous field and transect studies. As the plants were grown under similar climatic conditions and irrigated with water of the same δD value, the variability in εapp values observed here suggested that the species-specific hydrogen isotopic fractionation likely has a dominant control over the uncertainty in the community-averaged εapp values. Further, the εapp values of deciduous and evergreen species showed no systematic differences, suggesting that changes in the relative proportion of these taxa may not affect the community-averaged εapp and the reconstructed δD values of paleo-precipitation in angiosperm tree dominated catchments.

Comparing extraction methods for analyzing n-alkyl lipids in shelf sediments from the China Sea

n-Alkyl lipids including n-alkanes, n-alkanols, and n-alkanoic acids, are essential biomarkers in oceanic sediments and have been widely employed in both modern- and paleo-ecological and environmental studies. The selection of appropriate extraction methods for different research purposes, particularly for compounds with different polarities, remains a challenge. In this study, we compared the efficacy of Bligh-Dyer extraction (BDE), ultrasound-assisted extraction (UAE), accelerated solvent extraction (ASE), as well as a combination of Bligh-Dyer extraction and ultrasound-assisted extraction (BD + UAE) to extract n-alkanes, free n-alkanols, and free n-alkanoic acids from ocean sediments. Our findings indicate that BD + UAE is a suitable method for extracting n-alkanes, ASE is an optimal for extracting free n-alkanols, and BDE provides a suitable method for simultaneous extraction of free n-alkanoic acids with intact polar lipids (IPLs). Additionally, BDE exhibited a preference for compounds with an odd carbon number and short chains, whereas the UAE favored compounds with an even carbon number and long chains, particularly for n-alkanes. These results offer novel insights into the investigation of past paleoclimate and sediment chemistry and serve as a basis for future research on organic matter extraction from ocean sediments.

Holocene precipitation hydrogen isotopic values on Nilgiri Plateau (southern India) suggest a combined effect of precipitation amount and transport paths

Paleoclimate investigations of the peat deposits in the Nilgiri Plateau, an important paleoclimate archive of India, are mainly restricted to the carbon isotope composition ((δ13C) of plant-derived materials and pollen studies. However, it is unclear whether these proxies reflect past variability in temperature or hydrology. Here, we report the hydrogen and carbon isotopic variability of n-alkanoic acid of chain length 28 (δDC28and δ13CC28, respectively) and demonstrate that the peatland leaf wax hydrogen isotopes provide a sensitive record of past hydrology. The decoupling of δ13CC28and δD of vegetation-corrected rain during the Holocene indicate that δD of the leaf wax compounds mainly respond to past hydrological variability whereas δ13C variations might reflect the temperature-controlled variability of C3 and C4 vegetation. Conforming with the other paleoclimate records from the region, the δDC28variations showed a reducing precipitation trend since the early Holocene. However, a large amplitude of reconstructed δD of rain (~44‰) during the Holocene indicated changes in the moisture source and trajectory could be an additional factor contributing to the orbital-scale δD variability of proxies from the Indian region.

Hydroclimate variations over the last 17,000 years as estimated by leaf waxes in rodent middens from the south-central Atacama Desert, Chile

Leaf cuticular waxes are one of the most important environment-plant interaction structural systems that enable desert plants to withstand extreme climatic conditions. We present a long chain n-alkyl lipids study in fresh plant leaves and rodent palaeomiddens collected along an elevational gradient in the south-central Atacama Desert of Chile, covering six different vegetation belts: Steppe (4500-4000 m asl), Puna (4000-3300 m asl), pre-Puna (3300-2400 m asl), Absolute Desert (2400-1000 m asl) and Coastal Desert (1000-0 m asl). The 28 rodent palaeomiddens analyzed from Quebrada Incahuasi (25.6 °S, 3600 m asl) span the last 17,000 years. Modern-day distribution of long-chain n-alkanes and n-alkanoic acids varies among the dominant plant associations of the Atacama Desert. These plants show a species-specific chemotaxonomy linked to the climatic conditions. Furthermore, differences in average chain length (ACL) and carbon preference index (CPI) suggest that these plant communities are highly adapted to extreme environmental conditions. The sum of leaf wax n-alkanes was highest under wet conditions, while n-alkanoic acids (between n-C24 and n-C28) increased with hyperaridity. Similarly, analysis of n-alkane time series from palaeomiddens showed that the greatest changes in leaf wax n-alkane distributions (ACL and CPI) corresponded to the greatest increases in moisture during the Central Andean Pluvial Event (CAPE; between 18 and 9 ka cal BP) and the Late Holocene. The shift in the palaeomidden n-alkane distributions is corroborated by the relative abundance of rainfall-dependent extra-local taxa. This is the first study to report leaf wax content obtained from ancient rodent middens, and shows promising results as a robust hydroclimate proxy for the Atacama Desert region.

Chemical speciation of PM emissions from heavy-duty vehicles

Particulate matter (PM) is recognised as the deadliest form of air pollution, with vehicle emissions being one of its most important sources. Verification of compliance with the emission standards has been reported in numerous works. However, the detailed chemical speciation of PM is still very poorly understood. In this study, different heavy-duty vehicles (HDV) were tested on a chassis dynamometer under different driving cycles. Particulate matter (PM) emission factors for Euro V and Euro VI vehicles ranged from 24.9 to 51.2 mg kWh−1 and from 8.4 to 14.7 mg kWh−1, respectively. Major and trace elements, in their oxidised form, accounted for PM mass fractions between 6.3 and 58%. The lowest PM values were obtained for the Euro V vehicle fuelled with gas-to-liquids (GTL) under the world harmonised vehicle cycle (WHVC) with cold start, while the highest amounts were observed for the Euro VI vehicle fuelled with diesel over the hot start WHVC cycle. In general, Na and Sr were the most abundant elements, followed by Al and Ca. Several oxygenated organic compounds were detected, as far as we know, for the first time in exhaust particulates. Greater varieties (from C11 to C31 with no preference for odd versus even carbon numbers) and amounts of n-alkanes were detected in the emitted particulate matter (up to 7938 μg per g of PM) for the GTL fuelled vehicle (Euro V) tested by the WHVC driving cycle with cold start. The start-up phase mass fractions of ∑18PAHs were much higher (552 μg g−1) when the diesel-powered Euro V vehicle followed the VTT cycle than in the following tests (28.8–48.1 μg g−1). A homologous series of n-alkanoic acids, from C8 to C22, were found in the exhausts, accounting for particulate mass fractions ranging from 0.50 to 19.4 mg g−1, and peaking at C14, C16 and C18. Benzenedicarboxylic acids were observed at higher concentrations in emissions from Euro VI vehicles compared to Euro V. n-Alkanols from C8 to C30, with a clear dominance of C18 were detected in all PM samples. Ethylene glycol and other glycols were always present.

Synthesis, crystal structures, Hirshfeld surface analysis, and quantum chemistry calculations of two novel hydrous long-chain dibasic ammonium salts CnH2(n+4)N2O6 (n = 31 and 33)

The synthesis of long-chain single-crystal compounds is a gordian knot. Through the salification reaction of carboxylic acid, long-chain n-alkanoic acid was successfully connected at both ends of 1,3-propylene diamine, and the carbon chain of long-chain n-alkanoic acid was doubled. Hydrous 1, 3-propanediamine ditetradecanoate (abbreviated as 3C14) and 1, 3-propanediamine dipentadecanoate (abbreviated as 3C15) were successfully synthesized. The crystal structures of the two compounds were characterized by X-ray single-crystal diffraction. The molecular structure and crystal structure of the two compounds were analyzed, and their composition, spatial structure, and coordination mode were determined. Hirshfeld surface analysis revealed the intermolecular interaction of the two title compounds. The 3D energy framework enabled the intermolecular interaction to be presented more intuitively and digitally, in which dispersion energy can play a leading role. The energy values of HOMO and LUMO of the two title compounds were calculated, and their energy gaps were 0.2947 eV and 1.6286 eV, respectively. The charge distributions in the compounds were visualized using a molecular electrostatic potential (ESP) surface. ESP maps indicated that the electrophilic sites are localized around the oxygen atom. The crystallographic data and parameters of quantum chemical calculation in this paper will provide data and theoretical support for the development and application of such materials.

Analysis, distribution and evolution of individual carboxylic acids in crude oil during biodegradation

Carboxylic acids (CAs) are important molecular markers in the study of petroleum biodegradation. This work presents a vortex-assisted liquid–liquid microextraction (VALLME) method, followed by comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC–MS) analysis for the profiling of CAs in complex oils. The designed extractant containing CAs in VALLME can be silylated immediately and injected into GC × GC–MS without any post-treatment. More than 400 individual CAs, including alkanoic acids, cyclic aliphatic acids and aromatic acids, were putatively or positively identified. With good reproducibility and high sensitivity, VALLME combined with GC × GC–MS was applied to investigate the distribution and evolution of individual CAs in crude oil during laboratory biodegradation. It was found that acyclic acids and monocyclic aliphatic/aromatic acids could be detected at all stages of oil biodegradation, while polycyclic aliphatic/aromatic acids could only be identified in oils at a relatively higher degree of biodegradation. In addition, the contents of each type of CA changed regularly during biodegradation. Targeted analysis on the distributions of individual acyclic acids showed that the abundance ratio of short chain to long chain n-alkanoic acids kept increasing during biodegradation, which might reflect the multiple origins of short chain n-alkanoic acids. Moreover, based on the distributions of pristanic/phytanic acid and pristane/phytane in oils with different biodegradation degrees, pristanic and phytanic acid seemed to be more susceptible to degradation compared to their hydrocarbon analogues, and pristane might be more susceptible to degradation in comparison to phytane.

Molecular dynamics and thermo physical properties of solid catanionic surfactants composed of octadecyltrimethylammonium bromide and n-alkanoic acids

Two mixed surfactants comprising cationic octadecyltrimethylammonium bromide CH3(CH2)17N+(CH3)3Br− (C18TAB) modified with dodecanoic C12H24O2 (DDA) or hexadecanoic C16H32O2 (HDA) acids have been studied in the solid state in a wide temperature range (25–150 °C). The molecular dynamics and thermotropic properties of acid-modified asymmetric DDA-C18TAB and symmetric HDA-C18TAB surfactants were investigated using DSC measurements and temperature-variable FTIR spectroscopy complemented by room-temperature powder X-ray diffraction. XRD showed a formation of a new layered compound, the acid-modified C18TAB mixed surfactant comprising a hydrophobic moiety formed by two alkyl chains of different lengths. DSC measurements revealed the difference in thermal behavior between symmetric and asymmetric mixed surfactants showing successive phase transitions and several polymorphs in the solid state. With FT-IR spectroscopy, the phase transitions seen in DSC were identified as related to subtle lattice rearrangements in the low-temperature phases C1C2, the trans-gauche conformational disorder and rotational motions of methylene chains followed with lattice instabilities in the intermediate phases C3 and C4, and finally rotational disorder of the alkyl chains and the ionic layer in the high temperature phase H. For the first time, the stabilization effect of DDA acid on the bilayer structure of C18TAB was found.

Controllable construction of the underwater superoleophobic surface from superhydrophilicity to superhydrophobicity in oil

Superwetting that is being subdivided to multiple superlyphobic states exists unique superiority in a specific interfacial application. Fine controlling superwetting surface is lack of systematic research. Due to the harsh conditions on the creation of underoil superhydrophilicity and suerhydrophobicity in oil of underwater superoleophobic surface, so far controllable fabrication strategies of the underwater superoleophobic surfaces in oil still remain a challenge. Herein, underwater superoleophobic surfaces from superhydrophilicity to superhydrophobicity in oil are controllable constructed by mixing commercial titanium dioxide nanoparticles, aluminum phosphate, and n-Alkyl acids, where the surface heterogeneous chemistry is finely controlled by changing the chain length of n-alkanoic acids. Under the rational surface energy, underoil superhydrophilicity and underoil superhydrophobicity of the underwater superoleophobic surfaces can be efficiently regulated via simply adjusting the chain length of n-alkanoic acids. The under-liquid dual superlyophobic surface can be achieved when an appropriate parameter denoted chain length of n-Alkyl acids (n) is between 14 and 16. However, when the parameter (n) is to be within 4 and 6, the superhydrophilicity in oil of underwater superoleophobic surface can be realized. This finding can connect the molecular-level conformational transformation and the conversion of macroscopic surface alternative wettability, providing the molecular-level design principle of superwetting interfacial in under-liquid environments.

The role of earthquakes and storms in the fluvial export of terrestrial organic carbon along the eastern margin of the Tibetan plateau: A biomarker perspective

Driven by earthquakes and intense rainfall, steep tectonically active mountains are hotspots of terrestrial organic carbon mobilization from soils, rocks, and vegetation by landslides into rivers. Subsequent delivery and fluvial mobilization of organic carbon from different sources can impact atmospheric CO2 concentrations across a range of timescales. Extreme landslide triggering events can provide insight on processes and rates of carbon export. Here we used suspended sediment collected from 2005 to 2012 at the upper Min Jiang, a main tributary of the Yangtze River on the eastern margin of the Tibetan Plateau, to compare the erosion of terrestrial organic carbon before and after the 2008 Wenchuan earthquake and a storm-derived debris flow event in 2005. To constrain the source of riverine particulate organic carbon (POC), we quantified lignin phenols and n-alkanoic acids in the suspended sediments, catchment soils and landslide deposits. We found that riverine POC had higher inputs of less-degraded, discrete organic matter at high suspended sediment loads, while the source of POC seemed stochastic at low suspended sediment concentrations. The debris flow in 2005 mobilized a large amount of POC, resulting in an export of lignin within a single day equivalent to a normal year. In comparison, the 2008 Wenchuan earthquake increased the flux of POC and particulate lignin, albeit with limited impact on POC sources in comparison to seasonal variations. Our results highlight the important role of episodic events in the fluvial export of terrestrial carbon.

Biomarker evidence of the water mass structure and primary productivity changes in the Chukchi Sea over the past 70 years

The Chukchi Sea has experienced significant changes under global warming in the Common Era, including the shift of primary productivity. However, modern observations are too short to fully investigate the effects of environmental changes in this area. Here, we analyzed lipid biomarkers (e.g. long-chain n-alkanes, n-alkanols, n-alkanoic acids, diols, and sterols) from a sediment core (R07) collected from the Chukchi Sea shelf to determine phytoplankton primary productivity variations and factors influencing these changes over the past 70 years. Similar trends of the abundance of terrestrial ecosystem-derived compounds (e.g. long-chain n-alkanes, n-alkanols, n-alkanoic acids, and C32 1,15-diol) indicate that terrigenous input increased from ca. 1946 towards ca. 1983 and then decreased thereafter. In comparison, biomarkers with marine origin indicate that the ratio of diatoms to dinoflagellates increased after ca. 1983 towards the core-top (ca. 2011). Concurrent changes in terrigenous input and phytoplankton community indicated a shift in water mass structure at ca. 1983 (i.e. the Alaska Coastal Water decreased and the Bering Sea Water increased), which may be attributed to the phase shift of the Arctic Oscillation and/or unsynchronized flow changes in different water masses. Owing to the different water mass properties, the change of water mass structure caused intense water mixing and the resulting high turbidity in the study area, which led to light limitation for phytoplankton growth. These conditions probably account for the reduced phytoplankton primary productivity from ca. 1983 to ca. 2000 in the general trend of increasing. The results indicate that, in addition to global warming and sea ice retreat, other factors, such as change in regional water mass structure (i.e. different water masses), may also have a significant influence on the primary productivity and the phytoplankton community in the Chukchi Sea shelf.

Variation in organic matter across the Cretaceous-Paleogene boundary in New Zealand supports the “Living Ocean” model of biotic recovery

The Cretaceous-Paleogene (K-Pg) boundary represents the most recent mass extinction in Earth history. Although it is widely accepted that a bolide impact in North America caused the extinction, many questions persist about how this impact affected Earth's climate and environment. Here we explore changes in organic matter inputs across the K-Pg in an impact-distal section in New Zealand (mid-Waipara River section, North Canterbury, New Zealand). The section is 21.2 m thick, including 1.2 m of uppermost Cretaceous and 20 m of lower Paleocene sediment, the latter spanning ~1 Myr, albeit interrupted by at least one major unconformity. We examine the abundance and distribution of n-alkanes and n-alkanoic acids (mixed sources), acyclic isoprenoids (pristane and phytane), steranes (eukaryotes), hopanes and hopanoic acids (bacteria) and GDGTs (glycerol dialkyl glycerol tetraether lipids) to explore changes in the relative contribution of marine vs terrestrial sources. Minimal differences in the biomarker assemblages between sediments below and above the K-Pg boundary suggest a rapid recovery of the non-fossilizing phytoplankton community, similar to that observed in other distal settings. However, the organic matter source became variable immediately after the impact event. Variations in the concentrations and distribution of the high-molecular-weight n-alkanes and n-alkanoic acids, terrestrial-aquatic ratios, and GDGT branched to isoprenoidal tetraether indices indicate an increase in the absolute and proportional abundance of terrestrial soil- and plant-derived organic matter just after the impact event. This co-occurs with an apparently transient decline in marine productivity, indicated by a decrease in concentrations of low-molecular-weight n-alkanoic acids, concentrations of pristane + phytane (of putative algal chlorophyll origin), and sterane/hopane ratios. This suggests that the bolide did affect the mid-Waipara biomarker-producing bacterial and algal assemblages, distinct from what has been observed at other distal sites. However, it remains unclear if this was a direct consequence of the impact or the wider post-impact reorganisation of environment and oceanography as has been previously observed in this region.

Assessment of heat and radiation impacts on natural organic matter composition in bentonite for used nuclear fuel disposal

Bentonite clay (Wyoming, USA) is proposed as a buffer layer for the engineered barrier system for the deep geologic repository to store Canada's used nuclear fuels in the long-term. The presence of natural organic matter (NOM) in the mined bentonite may support microbial activity which may promote the corrosion of used fuel containers. The NOM found in Wyoming-type bentonite is diagenetically altered, however, there is limited knowledge about how NOM chemistry may change with heat and radiation when exposed to the proposed deep geologic repository conditions. To investigate this further, molecular-level techniques were used to analyze NOM compositional differences in bentonite with different heat (30–105 °C for 3 days, and 90 °C for 14, 28 and 42 days) and gamma-radiation exposure (100 kGy for 3 days). Elemental analysis results indicated that all bentonite samples exhibited low total organic carbon concentrations (0.15–0.27%) and 1.6–3.3% of these were in the form of extractable dissolved organic carbon. Solution-state 1H nuclear magnetic resonance (NMR) and solid-state 13C NMR analyses revealed that chemical signatures of dissolved organic matter and overall NOM composition did not vary between samples. Slightly increased concentrations of short-chain (C9-C19) n-alkanoic acids were observed with heat (14, 28 and 42 days at 90 °C), which is likely due to the oxidation of long-chain (≥C20) n-alkanes or n-alkanols. However, the broader assessment of NOM composition via principal component analysis of forty-four targeted NOM compounds indicated no significant differences after heat or radiation exposure. Collectively, the molecular-level analyses indicate that heat and radiation only imparted nanogram-level differences in some targeted compound concentrations, but the overall NOM chemistry was not altered. These results expand the understanding of NOM chemistry in bentonite clay and suggest that under the conditions tested, NOM composition in bentonite was largely insensitive to heat and radiation exposure. Further work is warranted to investigate longer exposure durations and the overall stability of NOM in a deep geologic repository setting.