Sequential measurement of 13 C, 15 N, and 34 S isotopic composition on nanomolar quantities of carbon, nitrogen, and sulfur using nano-elemental analysis/isotope ratio mass spectrometry.

RATIONALE: We report modifications to a commercial elemental analyzer-isotope ratio mass spectrometer that permit high-precision isotopic analysis of nanomoles of carbon (C), nitrogen (N), and sulfur (S) on a single sample without chemical or cryogenic trapping of gases. The sample size required for measurement by our system is about two orders of magnitude less than that for conventional analyses. METHODS: Our system builds on the analytical advancements offered by the EA IsoLink IRMS System and employs simple modifications to reduce the diameter of the flow path (reactors, water trap, and transfer lines), enhance peak separation (gas chromatography capillary column), and improve sample transfer to the ion source of the mass spectrometer (reduced flow rates). RESULTS: Conventional precision (<0.2‰) can be achieved down to c. 500 nmol C, N, and S for samples analyzed without modification of the commercial system. Further reduction in sample size (<50 nmol C, N, and S) was achieved with minor modifications. There is a significant carbon blank and a small nitrogen blank that can be measured directly and a sulfur blank that can be calculated using regression. Only 30 nmol of N, 22 nmol of C, and 12 nmol of S are needed to achieve better than 1‰ precision (1σ) from a single measurement. Larger samples and more replicate measurements provide better precision. CONCLUSIONS: The nano-EA method described here reduces sample size requirements by two orders of magnitude compared to traditional approaches and improves the accuracy and precision of isotope measurements on sample sizes less than 1 µmol. These advancements simplify the analytical technique and broaden the range and type of samples amenable to EA analysis.

Organic matter from the Chicxulub crater exacerbated the K-Pg impact winter.

An asteroid impact in the Yucatán Peninsula set off a sequence of events that led to the Cretaceous-Paleogene (K-Pg) mass extinction of 76% species, including the nonavian dinosaurs. The impact hit a carbonate platform and released sulfate aerosols and dust into Earth's upper atmosphere, which cooled and darkened the planet-a scenario known as an impact winter. Organic burn markers are observed in K-Pg boundary records globally, but their source is debated. If some were derived from sedimentary carbon, and not solely wildfires, it implies soot from the target rock also contributed to the impact winter. Characteristics of polycyclic aromatic hydrocarbons (PAHs) in the Chicxulub crater sediments and at two deep ocean sites indicate a fossil carbon source that experienced rapid heating, consistent with organic matter ejected during the formation of the crater. Furthermore, PAH size distributions proximal and distal to the crater indicate the ejected carbon was dispersed globally by atmospheric processes. Molecular and charcoal evidence indicates wildfires were also present but more delayed and protracted and likely played a less acute role in biotic extinctions than previously suggested. Based on stratigraphy near the crater, between 7.5 × 1014 and 2.5 × 1015 g of black carbon was released from the target and ejected into the atmosphere, where it circulated the globe within a few hours. This carbon, together with sulfate aerosols and dust, initiated an impact winter and global darkening that curtailed photosynthesis and is widely considered to have caused the K-Pg mass extinction.

Microbial biomarkers reveal a hydrothermally active landscape at Olduvai Gorge at the dawn of the Acheulean, 1.7 Ma.

Landscape-scale reconstructions of ancient environments within the cradle of humanity may reveal insights into the relationship between early hominins and the changing resources around them. Many studies of Olduvai Gorge during Pliocene-Pleistocene times have revealed the presence of precession-driven wet-dry cycles atop a general aridification trend, though may underestimate the impact of local-scale conditions on early hominins, who likely experienced a varied and more dynamic landscape. Fossil lipid biomarkers from ancient plants and microbes encode information about their surroundings via their molecular structures and composition, and thus can shed light on past environments. Here, we employ fossil lipid biomarkers to study the paleolandscape at Olduvai Gorge at the emergence of the Acheulean technology, 1.7 Ma, through the Lower Augitic Sandstones layer. In the context of the expansion of savanna grasslands, our results represent a resource-rich mosaic ecosystem populated by groundwater-fed rivers, aquatic plants, angiosperm shrublands, and edible plants. Evidence of a geothermally active landscape is reported via an unusual biomarker distribution consistent with the presence of hydrothermal features seen today at Yellowstone National Park. The study of hydrothermalism in ancient settings and its impact on hominin evolution has not been addressed before, although the association of thermal springs in the proximity of archaeological sites documented here can also be found at other localities. The hydrothermal features and resources present at Olduvai Gorge may have allowed early hominins to thermally process edible plants and meat, supporting the possibility of a prefire stage of human evolution.

The first day of the Cenozoic.

Highly expanded Cretaceous-Paleogene (K-Pg) boundary section from the Chicxulub peak ring, recovered by International Ocean Discovery Program (IODP)-International Continental Scientific Drilling Program (ICDP) Expedition 364, provides an unprecedented window into the immediate aftermath of the impact. Site M0077 includes ∼130 m of impact melt rock and suevite deposited the first day of the Cenozoic covered by <1 m of micrite-rich carbonate deposited over subsequent weeks to years. We present an interpreted series of events based on analyses of these drill cores. Within minutes of the impact, centrally uplifted basement rock collapsed outward to form a peak ring capped in melt rock. Within tens of minutes, the peak ring was covered in ∼40 m of brecciated impact melt rock and coarse-grained suevite, including clasts possibly generated by melt-water interactions during ocean resurge. Within an hour, resurge crested the peak ring, depositing a 10-m-thick layer of suevite with increased particle roundness and sorting. Within hours, the full resurge deposit formed through settling and seiches, resulting in an 80-m-thick fining-upward, sorted suevite in the flooded crater. Within a day, the reflected rim-wave tsunami reached the crater, depositing a cross-bedded sand-to-fine gravel layer enriched in polycyclic aromatic hydrocarbons overlain by charcoal fragments. Generation of a deep crater open to the ocean allowed rapid flooding and sediment accumulation rates among the highest known in the geologic record. The high-resolution section provides insight into the impact environmental effects, including charcoal as evidence for impact-induced wildfires and a paucity of sulfur-rich evaporites from the target supporting rapid global cooling and darkness as extinction mechanisms.

Structural brain abnormalities associated with cognitive impairments in bipolar disorder.

OBJECTIVE: Cognitive impairment has been highlighted as a core feature of bipolar disorder (BD) that often persists during remission. The specific brain correlates of cognitive impairment in BD remain unclear which impedes efficient therapeutic approaches. In a large sample of remitted BD patients, we investigated whether morphological brain abnormalities within dorsal prefrontal cortex (PFC) and hippocampus were related to cognitive deficits. METHODS: Remitted BD patients (n = 153) and healthy controls (n = 52) underwent neuropsychological assessment and structural MRI. Based on hierarchical cluster analysis of neuropsychological test performance, patients were classified as either cognitively impaired (n = 91) or cognitively normal (n = 62). The neurocognitive subgroups were compared amongst each other and with healthy controls in terms of dorsal PFC cortical thickness and volume, hippocampus shape and volume, and total cerebral grey and white matter volumes. RESULTS: Cognitively impaired patients displayed greater left dorsomedial prefrontal thickness compared to cognitively normal patients and healthy controls. Hippocampal grey matter volume and shape were similar across patient subgroups and healthy controls. At a whole-brain level, cognitively impaired patients had lower cerebral white matter volume compared to the other groups. Across all participants, lower white matter volume correlated with more impaired neuropsychological test performance. CONCLUSIONS: Our findings associate cognitive impairment in bipolar disorder with cerebral white matter deficits, factors which may relate to the observed morphological changes in dorsomedial PFC possibly due to increased neurocognitive effort to maintain symptom stability in these remitted patients.

Grassland fire ecology has roots in the late Miocene.

That fire facilitated the late Miocene C4 grassland expansion is widely suspected but poorly documented. Fire potentially tied global climate to this profound biosphere transition by serving as a regional-to-local driver of vegetation change. In modern environments, seasonal extremes in moisture amplify the occurrence of fire, disturbing forest ecosystems to create niche space for flammable grasses, which in turn provide fuel for frequent fires. On the Indian subcontinent, C4 expansion was accompanied by increased seasonal extremes in rainfall (evidenced by δ18Ocarbonate), which set the stage for fuel accumulation and fire-linked clearance during wet-to-dry seasonal transitions. Here, we test the role of fire directly by examining the abundance and distribution patterns of fire-derived polycyclic aromatic hydrocarbons (PAHs) and terrestrial vegetation signatures in n-alkane carbon isotopes from paleosol samples of the Siwalik Group (Pakistan). Two million years before the C4 grassland transition, fire-derived PAH concentrations increased as conifer vegetation declined, as indicated by a decrease in retene. This early increase in molecular fire signatures suggests a transition to more fire-prone vegetation such as a C3 grassland and/or dry deciduous woodland. Between 8.0 and 6.0 million years ago, fire, precipitation seasonality, and C4-grass dominance increased simultaneously (within resolution) as marked by sharp increases in fire-derived PAHs, δ18Ocarbonate, and 13C enrichment in n-alkanes diagnostic of C4 grasses. The strong association of evidence for fire occurrence, vegetation change, and landscape opening indicates that a dynamic fire-grassland feedback system was both a necessary precondition and a driver for grassland ecology during the first emergence of C4 grasslands.

Viable cyanobacteria in the deep continental subsurface.

Cyanobacteria are ecologically versatile microorganisms inhabiting most environments, ranging from marine systems to arid deserts. Although they possess several pathways for light-independent energy generation, until now their ecological range appeared to be restricted to environments with at least occasional exposure to sunlight. Here we present molecular, microscopic, and metagenomic evidence that cyanobacteria predominate in deep subsurface rock samples from the Iberian Pyrite Belt Mars analog (southwestern Spain). Metagenomics showed the potential for a hydrogen-based lithoautotrophic cyanobacterial metabolism. Collectively, our results suggest that they may play an important role as primary producers within the deep-Earth biosphere. Our description of this previously unknown ecological niche for cyanobacteria paves the way for models on their origin and evolution, as well as on their potential presence in current or primitive biospheres in other planetary bodies, and on the extant, primitive, and putative extraterrestrial biospheres.

Perceptions of Racially and Ethnically Diverse Women at High Risk of Breast Cancer Regarding the Use of a Web-Based Decision Aid for Chemoprevention: Qualitative Study Nested Within a Randomized Controlled Trial.

BACKGROUND: Chemopreventive agents such as selective estrogen receptor modulators and aromatase inhibitors have proven efficacy in reducing breast cancer risk by 41% to 79% in high-risk women. Women at high risk of developing breast cancer face the complex decision of whether to take selective estrogen receptor modulators or aromatase inhibitors for breast cancer chemoprevention. RealRisks is a patient-centered, web-based decision aid (DA) designed to promote the understanding of breast cancer risk and to engage diverse women in planning a preference-sensitive course of decision making about taking chemoprevention. OBJECTIVE: This study aims to understand the perceptions of women at high risk of developing breast cancer regarding their experience with using RealRisks-a DA designed to promote the uptake of breast cancer chemoprevention-and to understand their information needs. METHODS: We completed enrollment to a randomized controlled trial among 300 racially and ethnically diverse women at high risk of breast cancer who were assigned to standard educational materials alone or such materials in combination with RealRisks. We conducted semistructured interviews with a subset of 21 high-risk women enrolled in the intervention arm of the randomized controlled trial who initially accessed the tool (on average, 1 year earlier) to understand how they interacted with the tool. All interviews were audio recorded, transcribed verbatim, and compared with digital audio recordings to ensure the accuracy of the content. We used content analysis to generate themes. RESULTS: The mean age of the 21 participants was 58.5 (SD 10.1) years. The participants were 5% (1/21) Asian, 24% (5/21) Black or African American, and 71% (15/21) White; 10% (2/21) of participants were Hispanic or Latina. All participants reported using RealRisks after being granted access to the DA. In total, 4 overarching themes emerged from the qualitative analyses: the acceptability of the intervention, specifically endorsed elements of the DA, recommendations for improvements, and information needs. All women found RealRisks to be acceptable and considered it to be helpful (21/21, 100%). Most women (13/21, 62%) reported that RealRisks was easy to navigate, user-friendly, and easily accessible on the web. The majority of women (18/21, 86%) felt that RealRisks improved their knowledge about breast cancer risk and chemoprevention options and that RealRisks informed their (17/21, 81%) decision about whether or not to take chemoprevention. Some women (9/21, 43%) shared recommendations for improvements, as they wanted more tailoring based on user characteristics, felt that the DA was targeting a narrow population of Hispanic or Latina by using graphic novel-style narratives, wanted more understandable terminology, and felt that the tool placed a strong emphasis on chemoprevention drugs. CONCLUSIONS: This qualitative study demonstrated the acceptability of the RealRisks web-based DA among a diverse group of high-risk women, who provided some recommendations for improvement.

Doxorubicin-Induced Fetal Mesangial Cell Death Occurs Independently of TRPC6 Channel Upregulation but Involves Mitochondrial Generation of Reactive Oxygen Species.

Doxorubicin (DOX), a category D pregnancy drug, is a chemotherapeutic agent that has been shown in animal studies to induce fetal toxicity, including renal abnormalities. Upregulation of the transient receptor potential cation (TRPC) 6 channel is involved in DOX-induced podocyte apoptosis. We have previously reported that TRPC6-mediated Ca2+ signaling promotes neonatal glomerular mesangial cell (GMC) death. However, it is unknown whether DOX alters mesangial TRPC expression or viability in the fetus. In this study, cell growth was tracked in control and DOX-treated primary GMCs derived from fetal pigs. Live-cell imaging demonstrated that exposure to DOX inhibited the proliferation of fetal pig GMCs and induced cell death. DOX did not alter the TRPC3 expression levels. By contrast, TRPC6 protein expression in the cells was markedly reduced by DOX. DOX treatment also attenuated the TRPC6-mediated intracellular Ca2+ elevation. DOX stimulated mitochondrial reactive oxygen species (mtROS) generation and mitophagy by the GMCs. The DOX-induced mtROS generation and apoptosis were reversed by the mitochondria-targeted antioxidant mitoquinone. These data suggest that DOX-induced fetal pig GMC apoptosis is independent of TRPC6 channel upregulation but requires mtROS production. The mtROS-dependent GMC death may contribute to DOX-induced fetal nephrotoxicity when administered prenatally.

Occupational Therapist Treatment of Patients in the Neurological Critical Care Unit: Utilization and Patient Characteristics.

IMPORTANCE: Occupational therapy use in the neurological critical care unit (NCCU) may relate to patient factors, but data about these relationships remain unpublished. OBJECTIVE: To examine how patient factors predict NCCU occupational therapy use and intervention types. DESIGN: Retrospective cohort study of electronic health records data from adults admitted to the NCCU between May 2013 and September 2015. SETTING: NCCU in a large, urban academic hospital. PARTICIPANTS: Adults (age ≥18 yr; N = 1,134) admitted to the NCCU. MEASURES: Using length of stay (LOS), number of comorbidities, Glasgow Coma Scale (GCS) score, gender, age, and racial-ethnic minority status as independent variables, separate regression models identified predictors for each dependent variable: receipt of NCCU occupational therapy, occupational therapy onset (days after admission), and receipt of self-care or home management (ADL-Home); functional activities or cognitive training (Func-Cog); and therapeutic exercise (Ther-Ex). RESULTS: Four hundred twenty patients (37.0%) received occupational therapy in the NCCU. Receipt of occupational therapy was positively associated with LOS, number of comorbidities, GCS score, and age. Earlier occupational therapy onset was associated with higher GCS score and shorter LOS. Receipt of ADL-Home or Func-Cog interventions was significantly predicted by number of occupational therapy sessions, but patients with longer LOS were less likely to receive ADL-Home interventions. Receipt of Ther-Ex interventions became less likely as GCS score increased. CONCLUSIONS AND RELEVANCE: Patients are more likely to receive occupational therapy services if they are older and have a longer NCCU LOS, more comorbidities, and a higher level of consciousness. What This Article Adds: A patient's level of consciousness is clearly associated with occupational therapy utilization and hospital outcomes, but it should not be the only factor considered when prioritizing patients for NCCU occupational therapy services. Compared with patients who were more awake and alert, patients with a lower level of consciousness had a later onset of occupational therapy, which suggests an opportunity for NCCU occupational therapists to collaborate with physicians in the modification of sedation protocols to enable early rehabilitation.

Dexmedetomidine Provides Fewer Respiratory Events Compared With Propofol and Fentanyl During Third Molar Surgery: A Randomized Clinical Trial.

PURPOSE: Propofol and fentanyl can cause airway obstruction and respiratory depression when used together for intravenous sedation. This study investigated whether dexmedetomidine and midazolam would decrease respiratory events requiring intervention during deep sedation compared with propofol, fentanyl, and midazolam. PATIENTS AND METHODS: A prospective, randomized, double-blinded, controlled trial was designed to assess 2 intravenous treatment groups during third molar surgery. Patients were randomized into 2 groups. The control group (group P) received 0.8 µg/kg of fentanyl followed by propofol infusion at 125 µg/kg per minute over a 10-minute period with intraoperative boluses of 0.1 µg/kg. The study group (group D) received dexmedetomidine bolus infusion of 1 µg/kg over a 10-minute period followed by maintenance infusion at 0.5 µg/kg per hour. Both groups were given 0.03 mg/kg of midazolam before infusion. Scorers, masked to group, viewed the procedure remotely and evaluated the primary outcome variable of respiratory events requiring intervention. Secondary outcome variables evaluated by the scorers included the Behavioral Pain Scale for non-intubated patients at initial injection, cooperation score at 5 and 15 minutes, and time to ambulation and discharge. Patient satisfaction and hemodynamic stability were measured. The difference between groups regarding the occurrence of respiratory events was tested using the Fisher exact test, and mixed-effects models were used to compare repeated vital signs. RESULTS: The sample was composed of 141 patients randomly assigned to either group P (n = 67) or group D (n = 74). No statistically significant differences in the distribution of study variables were found between groups at baseline. A statistically significant difference in respiratory events requiring deliberate intervention existed between group P (25.4%) and group D (2.7%) (P < .0001). No statistically significant difference was found between groups for Behavioral Pain Scale score, cooperation score, time to ambulation or discharge, and patient satisfaction. CONCLUSIONS: Using dexmedetomidine and midazolam for outpatient surgery resulted in fewer respiratory events requiring deliberate intervention compared with propofol, fentanyl, and midazolam. Ambulation and discharge times were not prolonged using dexmedetomidine.

Soil organic carbon stability in forests: Distinct effects of tree species identity and traits.

Rising atmospheric CO2 concentrations have increased interest in the potential for forest ecosystems and soils to act as carbon (C) sinks. While soil organic C contents often vary with tree species identity, little is known about if, and how, tree species influence the stability of C in soil. Using a 40 year old common garden experiment with replicated plots of eleven temperate tree species, we investigated relationships between soil organic matter (SOM) stability in mineral soils and 17 ecological factors (including tree tissue chemistry, magnitude of organic matter inputs to the soil and their turnover, microbial community descriptors, and soil physicochemical properties). We measured five SOM stability indices, including heterotrophic respiration, C in aggregate occluded particulate organic matter (POM) and mineral associated SOM, and bulk SOM δ15 N and ∆14 C. The stability of SOM varied substantially among tree species, and this variability was independent of the amount of organic C in soils. Thus, when considering forest soils as C sinks, the stability of C stocks must be considered in addition to their size. Further, our results suggest tree species regulate soil C stability via the composition of their tissues, especially roots. Stability of SOM appeared to be greater (as indicated by higher δ15 N and reduced respiration) beneath species with higher concentrations of nitrogen and lower amounts of acid insoluble compounds in their roots, while SOM stability appeared to be lower (as indicated by higher respiration and lower proportions of C in aggregate occluded POM) beneath species with higher tissue calcium contents. The proportion of C in mineral associated SOM and bulk soil ∆14 C, though, were negligibly dependent on tree species traits, likely reflecting an insensitivity of some SOM pools to decadal scale shifts in ecological factors. Strategies aiming to increase soil C stocks may thus focus on particulate C pools, which can more easily be manipulated and are most sensitive to climate change.

Dietary options and behavior suggested by plant biomarker evidence in an early human habitat.

The availability of plants and freshwater shapes the diets and social behavior of chimpanzees, our closest living relative. However, limited evidence about the spatial relationships shared between ancestral human (hominin) remains, edible resources, refuge, and freshwater leaves the influence of local resources on our species' evolution open to debate. Exceptionally well-preserved organic geochemical fossils--biomarkers--preserved in a soil horizon resolve different plant communities at meter scales across a contiguous 25,000 m(2) archaeological land surface at Olduvai Gorge from about 2 Ma. Biomarkers reveal hominins had access to aquatic plants and protective woods in a patchwork landscape, which included a spring-fed wetland near a woodland that both were surrounded by open grassland. Numerous cut-marked animal bones are located within the wooded area, and within meters of wetland vegetation delineated by biomarkers for ferns and sedges. Taken together, plant biomarkers, clustered bone debris, and hominin remains define a clear spatial pattern that places animal butchery amid the refuge of an isolated forest patch and near freshwater with diverse edible resources.

U.S. Survey of Shared Decision Making Use for Treating Pregnant Women Presenting with Opioid Use Disorder.

Background: The incidence of pregnant women with an opioid use disorder (PWOUD) at delivery has quadrupled since 1999. State-specific statutes regarding PWOUD often pose punitive measures to the mother-infant dyad, involving the child welfare and criminal justice systems. Shared decision making (SDM) assists individuals through complex health and recovery processes. Objectives: To determine use of SDM in treating PWOUD and associated factors and to quantify physicians' review and discussion of child welfare statutes. Methods: The American College of Obstetricians and Gynecologists (ACOG) e-mailed the survey to a random sample of members, with 568 responding. Bivariate analyses to identify factors associated with each outcome were performed using Wilcoxon Rank Sum tests or Fisher's Exact tests. Variables yielding p values < .20 were included in initial logistic regression models; the final model included only significant (<.05) variables. Results: Sixty-one percent used SDM most of the time. Logistic regression indicated that those using SDM were more likely to have had training in substance use disorder and felt prepared for caring for PWOUD; 39% reviewed statutes, and 54% discussed them with PWOUDs. Conclusion: Survey results provide evidence for patient-centered care approaches that support PWOUD involvement in treatment decision making. The SDM model provides an empowerment framework for women to be involved in the process during their pregnancies and opioid use disorder treatments. Future studies might assess the effectiveness of SDM dialogs with PWOUD and evaluate CME training and medical curricula regarding the SDM model.

Speech treatment in Parkinson's disease: Randomized controlled trial (RCT).

BACKGROUND: As many as 89% of people with Parkinson's disease (PD) develop speech disorders. OBJECTIVES: This randomized controlled trial evaluated two speech treatments for PD matched in intensive dosage and high-effort mode of delivery, differing in subsystem target: voice (respiratory-laryngeal) versus articulation (orofacial-articulatory). METHODS: PD participants were randomized to 1-month LSVT LOUD (voice), LSVT ARTIC (articulation), or UNTXPD (untreated) groups. Speech clinicians specializing in PD delivered treatment. Primary outcome was sound pressure level (SPL) in reading and spontaneous speech, and secondary outcome was participant-reported Modified Communication Effectiveness Index (CETI-M), evaluated at baseline, 1, and 7 months. Healthy controls were matched by age and sex. RESULTS: At baseline, the combined PD group (n = 64) was significantly worse than healthy controls (n = 20) for SPL (P < 0.05) and CETI-M (P = 0.0001). At 1 and 7 months, SPL between-group comparisons showed greater improvements for LSVT LOUD (n = 22) than LSVT ARTIC (n = 20; P < 0.05) and UNTXPD (n = 22; P < 0.05). Sound pressure level differences between LSVT ARTIC and UNTXPD at 1 and 7 months were not significant (P > 0.05). For CETI-M, between-group comparisons showed greater improvements for LSVT LOUD and LSVT ARTIC than UNTXPD at 1 month (P = 0.02; P = 0.02). At 7 months, CETI-M between-group differences were not significant (P = 0.08). Within-group CETI-M improvements for LSVT LOUD were maintained through 7 months (P = 0.0011). CONCLUSIONS: LSVT LOUD showed greater improvements than both LSVT ARTIC and UNTXPD for SPL at 1 and 7 months. For CETI-M, both LSVT LOUD and LSVT ARTIC improved at 1 month relative to UNTXPD. Only LSVT LOUD maintained CETI-M improvements at 7 months. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Picomolar-scale compound-specific isotope analyses.

RATIONALE: We report modifications to compound-specific isotope analyses (CSIA) to enable high-precision isotopic analyses of picomoles of carbon for intact organic molecules. This sample size is two orders of magnitude below the amounts required for commercial systems. The greatly enhanced sensitivity of this system expands molecular isotope studies and applications previously prohibited by low concentrations and small samples. METHODS: We utilize the resolving power and low volumetric flow rates of narrow-bore capillary gas chromatography to improve sample transfer efficiency while maintaining narrow peak widths. Post-column peak broadening is minimized using a micro-fluidic valve for solvent diversion, capillary combustion reactor, narrow-bore capillary transfer lines, and cryogenic water trap. The mass spectrometer was fitted with collector amplifiers configured to 25 ms response times and a data logger board with firmware capable of rapid data acquisition. Carbon dioxide gas was introduced directly into the ion source to evaluate the dynamic range of the system and accuracy and precision of carbon isotope ratio (δ13 C value) measurements. The accuracy and precision for combusted compounds were evaluated using a suite of n-alkanes. RESULTS: For ≥30 pmol carbon introduced directly into the ion source, the mean difference between the measured and expected δ13 C values is 0.03‰ (1σ, n = 57) and the standard deviation of replicate measurements is 0.11‰ (1σ). The CO2 peak widths generated by the exponential dilution flask were 250 ms and the peak widths produced by combusting n-alkanes were ca 500 ms, less than 25% the width of conventional gas chromatography peaks. For a mixture of 15 n-alkanes (n-C16 to n-C30 ), the accuracy is 0.3‰ (1σ) and precision is 0.9‰ (1σ) for replicate δ13 C measurements with 100 pmol carbon per compound on column. CONCLUSIONS: The pico-CSIA method described here offers improved chromatographic resolution and reduces sample size requirements by two orders of magnitude. These advances significantly broaden the available analytical window for CSIA in research areas frequently hindered by sample size limitations, such as forensics, paleoclimate, astrobiology, and biochemistry.

Ecosystem variability and early human habitats in eastern Africa.

The role of savannas during the course of early human evolution has been debated for nearly a century, in part because of difficulties in characterizing local ecosystems from fossil and sediment records. Here, we present high-resolution lipid biomarker and isotopic signatures for organic matter preserved in lake sediments at Olduvai Gorge during a key juncture in human evolution about 2.0 Ma--the emergence and dispersal of Homo erectus (sensu lato). Using published data for modern plants and soils, we construct a framework for ecological interpretations of stable carbon-isotope compositions (expressed as δ(13)C values) of lipid biomarkers from ancient plants. Within this framework, δ(13)C values for sedimentary leaf lipids and total organic carbon from Olduvai Gorge indicate recurrent ecosystem variations, where open C(4) grasslands abruptly transitioned to closed C(3) forests within several hundreds to thousands of years. Carbon-isotopic signatures correlate most strongly with Earth's orbital geometry (precession), and tropical sea-surface temperatures are significant secondary predictors in partial regression analyses. The scale and pace of repeated ecosystem variations at Olduvai Gorge contrast with long-held views of directional or stepwise aridification and grassland expansion in eastern Africa during the early Pleistocene and provide a local perspective on environmental hypotheses of human evolution.

Water, plants, and early human habitats in eastern Africa.

Water and its influence on plants likely exerted strong adaptive pressures in human evolution. Understanding relationships among water, plants, and early humans is limited both by incomplete terrestrial records of environmental change and by indirect proxy data for water availability. Here we present a continuous record of stable hydrogen-isotope compositions (expressed as δD values) for lipid biomarkers preserved in lake sediments from an early Pleistocene archaeological site in eastern Africa--Olduvai Gorge. We convert sedimentary leaf- and algal-lipid δD values into estimates for ancient source-water δD values by accounting for biochemical, physiological, and environmental influences on isotopic fractionation via published water-lipid enrichment factors for living plants, algae, and recent sediments. Reconstructed precipitation and lake-water δD values, respectively, are consistent with modern isotopic hydrology and reveal that dramatic fluctuations in water availability accompanied ecosystem changes. Drier conditions, indicated by less negative δD values, occur in association with stable carbon-isotopic evidence for open, C(4)-dominated grassland ecosystems. Wetter conditions, indicated by lower δD values, are associated with expanded woody cover across the ancient landscape. Estimates for ancient precipitation amounts, based on reconstructed precipitation δD values, range between approximately 250 and 700 mm · y(-1) and are consistent with modern precipitation data for eastern Africa. We conclude that freshwater availability exerted a substantial influence on eastern African ecosystems and, by extension, was central to early human proliferation during periods of rapid climate change.

Export of submicron particulate organic matter to mesopelagic depth in an oligotrophic gyre.

Sixty percent of the world ocean by area is contained in oligotrophic gyres [Longhurst A (1995) Prog Oceanog 36:77-16], the biomass of which is dominated by picophytoplankton, including cyanobacteria and picoeukaryotic algae, as well as picoheterotrophs. Despite their recognized importance in carbon cycling in the surface ocean, the role of small cells and their detrital remains in the transfer of particulate organic matter (POM) to the deep ocean remains disputed. Because oligotrophic marine conditions are projected to expand under current climate trends, a better understanding of the role of small particles in the global carbon cycle is a timely goal. Here we use the lipid profiles, radiocarbon, and stable carbon isotopic signatures of lipids from the North Pacific Subtropical Gyre to show that in the surface ocean, lipids from submicron POM (here called extra-small POM) are distinct from larger classes of suspended POM. Remarkably, this distinct extra-small POM signature dominates the total lipids collected at mesopelagic depth, suggesting that the lipid component of mesopelagic POM primarily contains the exported remains of small particles. Transfer of submicron material to mesopelagic depths in this location is consistent with model results that claim the biological origin of exported carbon should be proportional to the distribution of cell types in the surface community, irrespective of cell size [Richardson TL, Jackson GA (2007) Science 315:838-840]. Our data suggest that the submicron component of exported POM is an important contributor to the global biological pump, especially in oligotrophic waters.