Publications by authors named "Stewart Fallon"

22 Publications

  • Page 1 of 1

Assessing multiproxy approaches (Sr/Ca, U/Ca, Li/Mg, and B/Mg) to reconstruct sea surface temperature from coral skeletons throughout the Great Barrier Reef.

Sci Total Environ 2021 Sep 29;786:147393. Epub 2021 Apr 29.

Australian Institute of Marine Science, PMB No 3, Townsville MC, Qld 4810, Australia.

Due to the increasing concerns of global warming and short instrumental records of sea surface temperature (SST), coral-based proxies, such as δO, Sr/Ca, U/Ca, and Li/Mg have been developed and applied to reconstruct SST in paleoclimate studies. However, these proxies are not universally applicable in different environments, because they are affected by coral physiology and various environmental factors. In this study, seven long-lived Porites corals were collected from the southern sector of the Great Barrier Reef (GBR) off the coast of Gladstone and the central sector of the GBR within the Whitsunday Islands in 2017 and 2018. Coral sites were selected to cover a wide latitudinal range with different annual temperature ranges. Century-long geochemical records (Li/Ca, B/Ca, Mg/Ca, Sr/Ca, and U/Ca) were generated using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at weekly resolution. This study has tested the robustness of two traditional temperature proxies (Sr/Ca and U/Ca), a recently developed temperature proxy (Li/Mg), and an additional potential temperature proxy (B/Mg). U/Ca was found to be the most robust and stable temperature proxy for corals from the GBR over long-term timescales. Sr/Ca is a close second, however due to the lower response of Sr fractionation per 1 °C, it is more sensitive to analytical methods and less sensitive to annual SST changes than U/Ca. Li/Mg and B/Mg have clearer periodicity compared to Li/Ca and B/Ca. Both Li/Mg and B/Mg are strongly correlated with SST, which is due to the cancellation of temperature-independent commonality. Empirical calibrations established from this multi-proxy approach increase the certainty of temperature reconstruction when a single proxy does not perform well. These site- and colony-specific SST calibrations also provide an opportunity to revisit the universal multi-trace element calibration of sea surface temperatures (UMTECS) model, which does not require the knowledge of local SST for calibration.
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http://dx.doi.org/10.1016/j.scitotenv.2021.147393DOI Listing
September 2021

Phasing of millennial-scale climate variability in the Pacific and Atlantic Oceans.

Science 2020 11 1;370(6517):716-720. Epub 2020 Oct 1.

University of Central Missouri, Warrensburg, MO, USA.

New radiocarbon and sedimentological results from the Gulf of Alaska document recurrent millennial-scale episodes of reorganized Pacific Ocean ventilation synchronous with rapid Cordilleran Ice Sheet discharge, indicating close coupling of ice-ocean dynamics spanning the past 42,000 years. Ventilation of the intermediate-depth North Pacific tracks strength of the Asian monsoon, supporting a role for moisture and heat transport from low latitudes in North Pacific paleoclimate. Changes in carbon-14 age of intermediate waters are in phase with peaks in Cordilleran ice-rafted debris delivery, and both consistently precede ice discharge events from the Laurentide Ice Sheet, known as Heinrich events. This timing precludes an Atlantic trigger for Cordilleran Ice Sheet retreat and instead implicates the Pacific as an early part of a cascade of dynamic climate events with global impact.
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http://dx.doi.org/10.1126/science.aba7096DOI Listing
November 2020

Sediment controls dynamic behavior of a Cordilleran Ice Stream at the Last Glacial Maximum.

Nat Commun 2020 04 14;11(1):1826. Epub 2020 Apr 14.

Research School of Earth Science, The Australian National University, Canberra, ACT, 2601, Australia.

The uncertain response of marine terminating outlet glaciers to climate change at time scales beyond short-term observation limits models of future sea level rise. At temperate tidewater margins, abundant subglacial meltwater forms morainal banks (marine shoals) or ice-contact deltas that reduce water depth, stabilizing grounding lines and slowing or reversing glacial retreat. Here we present a radiocarbon-dated record from Integrated Ocean Drilling Program (IODP) Site U1421 that tracks the terminus of the largest Alaskan Cordilleran Ice Sheet outlet glacier during Last Glacial Maximum climate transitions. Sedimentation rates, ice-rafted debris, and microfossil and biogeochemical proxies, show repeated abrupt collapses and slow advances typical of the tidewater glacier cycle observed in modern systems. When global sea level rise exceeded the local rate of bank building, the cycle of readvances stopped leading to irreversible retreat. These results support theory that suggests sediment dynamics can control tidewater terminus position on an open shelf under temperate conditions delaying climate-driven retreat.
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http://dx.doi.org/10.1038/s41467-020-15579-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7156478PMC
April 2020

Early tropical crop production in marginal subtropical and temperate Polynesia.

Proc Natl Acad Sci U S A 2019 04 8;116(18):8824-8833. Epub 2019 Apr 8.

Centre for Integrated Ecology, School of Life and Environmental Sciences, Deakin University, Geelong, VIC 3216, Australia.

Polynesians introduced the tropical crop taro () to temperate New Zealand after 1280 CE, but evidence for its cultivation is limited. This contrasts with the abundant evidence for big game hunting, raising longstanding questions of the initial economic and ecological importance of crop production. Here we compare fossil data from wetland sedimentary deposits indicative of taro and leaf vegetable (including and spp.) cultivation from Ahuahu, a northern New Zealand offshore island, with Raivavae and Rapa, both subtropical islands in French Polynesia. Preservation of taro pollen on all islands between 1300 CE and 1550 CE indicates perennial cultivation over multiple growing seasons, as plants rarely flower when frequently harvested. The pollen cooccurs with previously undetected fossil remains of extinct trees, as well as many weeds and commensal invertebrates common to tropical Polynesian gardens. Sedimentary charcoal and charred plant remains show that fire use rapidly reduced forest cover, particularly on Ahuahu. Fires were less frequent by 1500 CE on all islands as forest cover diminished, and short-lived plants increased, indicating higher-intensity production. The northern offshore islands of New Zealand were likely preferred sites for early gardens where taro production was briefly attempted, before being supplanted by sweet potato (), a more temperate climate-adapted crop, which was later established in large-scale cultivation systems on the mainland after 1500 CE.
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http://dx.doi.org/10.1073/pnas.1821732116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6500154PMC
April 2019

Age structure of the Australian lungfish (Neoceratodus forsteri).

PLoS One 2019 23;14(1):e0210168. Epub 2019 Jan 23.

Griffith University, Brisbane, QLD, Australia.

The Australian lungfish has been studied for more than a century without any knowledge of the longevity of the species. Traditional methods for ageing fish, such as analysis of otolith (ear stone) rings is complicated in that lungfish otoliths differ from teleost fish in composition. As otolith sampling is also lethal, this is not appropriate for a protected species listed under Australian legislation. Lungfish scales were removed from 500 fish from the Brisbane, Burnett and Mary rivers. A sub-sample of scales (85) were aged using bomb radiocarbon techniques and validated using scales marked previously with oxytetracycline. Lungfish ages ranged from 2.5-77 years of age. Estimated population age structures derived using an Age Length Key revealed different recruitment patterns between river systems. There were statistically significant von Bertalanffy growth model parameters estimated for each of the three rivers based on limited sample sizes. In addition, length frequency distributions between river systems were also significantly different. Further studies will be conducted to review drivers that may explain these inter-river differences.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0210168PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6343868PMC
September 2019

Elevated CO Has Little Influence on the Bacterial Communities Associated With the pH-Tolerant Coral, Massive spp.

Front Microbiol 2018 1;9:2621. Epub 2018 Nov 1.

Department of Environmental Science and Policy, George Mason University, Fairfax, VA, United States.

Ocean acidification (OA) as a result of increased anthropogenic CO input into the atmosphere carries consequences for all ocean life. Low pH can cause a shift in coral-associated microbial communities of CO-sensitive corals, however, it remains unknown whether the microbial community is also influenced in corals known to be more tolerant to high CO/low pH. This study profiles the bacterial communities associated with the tissues of the CO-tolerant coral, massive spp., from two natural CO seep sites in Papua New Guinea. Amplicon sequencing of the hypervariable V3-V4 regions of the 16S rRNA gene revealed that microbial communities remained stable across CO seep sites (pH = 7.44-7.85) and adjacent control sites (ambient pH = 8.0-8.1). Microbial communities were more significantly influenced by reef location than pH, with the relative abundance of dominant microbial taxa differing between reefs. These results directly contrast with previous findings that increased CO has a strong effect on structuring microbial communities. The stable structure of microbial communities associated with the tissues of massive spp. under high CO/low pH conditions confirms a high degree of tolerance by the whole holobiont to OA, and suggest that pH tolerant corals such as may dominate reef assemblages in an increasingly acidic ocean.
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http://dx.doi.org/10.3389/fmicb.2018.02621DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6221987PMC
November 2018

Wintertime stress, nursing, and lead exposure in Neanderthal children.

Sci Adv 2018 10 31;4(10):eaau9483. Epub 2018 Oct 31.

The Senator Frank R. Lautenberg Environmental Health Sciences Laboratory, Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA.

Scholars endeavor to understand the relationship between human evolution and climate change. This is particularly germane for Neanderthals, who survived extreme Eurasian environmental variation and glaciations, mysteriously going extinct during a cool interglacial stage. Here, we integrate weekly records of climate, tooth growth, and metal exposure in two Neanderthals and one modern human from southeastern France. The Neanderthals inhabited cooler and more seasonal periods than the modern human, evincing childhood developmental stress during wintertime. In one instance, this stress may have included skeletal mobilization of elemental stores and weight loss; this individual was born in the spring and appears to have weaned 2.5 years later. Both Neanderthals were exposed to lead at least twice during the deep winter and/or early spring. This multidisciplinary approach elucidates direct relationships between ancient environments and hominin paleobiology.
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http://dx.doi.org/10.1126/sciadv.aau9483DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6209393PMC
October 2018

Rapid glaciation and a two-step sea level plunge into the Last Glacial Maximum.

Nature 2018 07 25;559(7715):603-607. Epub 2018 Jul 25.

Kyushu University, Fukuoka, Japan.

The approximately 10,000-year-long Last Glacial Maximum, before the termination of the last ice age, was the coldest period in Earth's recent climate history. Relative to the Holocene epoch, atmospheric carbon dioxide was about 100 parts per million lower and tropical sea surface temperatures were about 3 to 5 degrees Celsius lower. The Last Glacial Maximum began when global mean sea level (GMSL) abruptly dropped by about 40 metres around 31,000 years ago and was followed by about 10,000 years of rapid deglaciation into the Holocene. The masses of the melting polar ice sheets and the change in ocean volume, and hence in GMSL, are primary constraints for climate models constructed to describe the transition between the Last Glacial Maximum and the Holocene, and future changes; but the rate, timing and magnitude of this transition remain uncertain. Here we show that sea level at the shelf edge of the Great Barrier Reef dropped by around 20 metres between 21,900 and 20,500 years ago, to -118 metres relative to the modern level. Our findings are based on recovered and radiometrically dated fossil corals and coralline algae assemblages, and represent relative sea level at the Great Barrier Reef, rather than GMSL. Subsequently, relative sea level rose at a rate of about 3.5 millimetres per year for around 4,000 years. The rise is consistent with the warming previously observed at 19,000 years ago, but we now show that it occurred just after the 20-metre drop in relative sea level and the related increase in global ice volumes. The detailed structure of our record is robust because the Great Barrier Reef is remote from former ice sheets and tectonic activity. Relative sea level can be influenced by Earth's response to regional changes in ice and water loadings and may differ greatly from GMSL. Consequently, we used glacio-isostatic models to derive GMSL, and find that the Last Glacial Maximum culminated 20,500 years ago in a GMSL low of about -125 to -130 metres.
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http://dx.doi.org/10.1038/s41586-018-0335-4DOI Listing
July 2018

New dates on dingo bones from Madura Cave provide oldest firm evidence for arrival of the species in Australia.

Sci Rep 2018 07 19;8(1):9933. Epub 2018 Jul 19.

Research School of Earth Sciences, College of Science, Australian National University, Canberra, ACT, 0200, Australia.

The dingo is the only placental land mammal aside from murids and bats to have made the water crossings to reach Australia prior to European arrival. It is thought that they arrived as a commensal animal with people, some time in the mid Holocene. However, the timing of their arrival is still a subject of major debate with published age estimates varying widely. This is largely because the age estimates for dingo arrival are based on archaeological deposit dates and genetic divergence estimates, rather than on the dingo bones themselves. Currently, estimates vary from between 5000-4000 years ago, for finds from archaeological contexts, and as much as 18,000 based on DNA age estimates. The timing of dingo arrival is important as post arrival they transformed Indigenous societies across mainland Australia and have been implicated in the extinction of a number of animals including the Tasmanian tiger. Here we present the results of direct dating of dingo bones from their oldest known archaeological context, Madura Cave on the Nullarbor Plain. These dates demonstrate that dingoes were in southern Australia by between 3348 and 3081 years ago. We suggest that following their introduction the dingo may have spread extremely rapidly throughout mainland Australia.
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http://dx.doi.org/10.1038/s41598-018-28324-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6053400PMC
July 2018

Monitoring age-related trends in genomic diversity of Australian lungfish.

Mol Ecol 2018 Jul 10. Epub 2018 Jul 10.

Australian Rivers Institute, Griffith University, Nathan, Qld, Australia.

An important challenge for conservation science is to detect declines in intraspecific diversity so that management action can be guided towards populations or species at risk. The lifespan of Australian lungfish (Neoceratodus forsteri) exceeds 80 years, and human impacts on breeding habitat over the last half century may have impeded recruitment, leaving populations dominated by old postreproductive individuals, potentially resulting in a small and declining breeding population. Here, we conduct a "single-sample" evaluation of genetic erosion within contemporary populations of the Australian lungfish. Genetic erosion is a temporal decline in intraspecific diversity due to factors such as reduced population size and inbreeding. We examined whether young individuals showed signs of reduced genetic diversity and/or inbreeding using a novel bomb radiocarbon dating method to age lungfish nonlethally, based on C ratios of scales. A total of 15,201 single nucleotide polymorphic (SNP) loci were genotyped in 92 individuals ranging in age from 2 to 77 years old. Standardized individual heterozygosity and individual inbreeding coefficients varied widely within and between riverine populations, but neither was associated with age, so perceived problems with recruitment have not translated into genetic erosion that could be considered a proximate threat to lungfish populations. Conservation concern has surrounded Australian lungfish for over a century. However, our results suggest that long-lived threatened species can maintain stable levels of intraspecific variability when sufficient reproductive opportunities exist over the course of a long lifespan.
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http://dx.doi.org/10.1111/mec.14791DOI Listing
July 2018

Radiocarbon evidence for alternating northern and southern sources of ventilation of the deep Atlantic carbon pool during the last deglaciation.

Proc Natl Acad Sci U S A 2014 Apr 31;111(15):5480-4. Epub 2014 Mar 31.

Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, United Kingdom.

Recent theories for glacial-interglacial climate transitions call on millennial climate perturbations that purged the deep sea of sequestered carbon dioxide via a "bipolar ventilation seesaw." However, the viability of this hypothesis has been contested, and robust evidence in its support is lacking. Here we present a record of North Atlantic deep-water radiocarbon ventilation, which we compare with similar data from the Southern Ocean. A striking coherence in ventilation changes is found, with extremely high ventilation ages prevailing across the deep Atlantic during the last glacial period. The data also reveal two reversals in the ventilation gradient between the deep North Atlantic and Southern Ocean during Heinrich Stadial 1 and the Younger Dryas. These coincided with periods of sustained atmospheric CO2 rise and appear to have been driven by enhanced ocean-atmosphere exchange, primarily in the Southern Ocean. These results confirm the operation of a bipolar ventilation seesaw during deglaciation and underline the contribution of abrupt regional climate anomalies to longer-term global climate transitions.
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http://dx.doi.org/10.1073/pnas.1400668111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3992695PMC
April 2014

Subarctic weathering of mineral wastes provides a sink for atmospheric CO(2).

Environ Sci Technol 2011 Sep 29;45(18):7727-36. Epub 2011 Aug 29.

Mineral Deposit Research Unit, Department of Earth and Ocean Sciences, The University of British Columbia, 6339 Stores Road, Vancouver, British Columbia V6T 1Z4, Canada.

The mineral waste from some mines has the capacity to trap and store CO(2) within secondary carbonate minerals via the process of silicate weathering. Nesquehonite [MgCO(3)·3H(2)O] forms by weathering of Mg-silicate minerals in kimberlitic mine tailings at the Diavik Diamond Mine, Northwest Territories, Canada. Less abundant Na- and Ca-carbonate minerals precipitate from sewage treatment effluent deposited in the tailings storage facility. Radiocarbon and stable carbon and oxygen isotopes are used to assess the ability of mine tailings to trap and store modern CO(2) within these minerals in the arid, subarctic climate at Diavik. Stable isotopic data cannot always uniquely identify the source of carbon stored within minerals in this setting; however, radiocarbon isotopic data provide a reliable quantitative estimate for sequestration of modern carbon. At least 89% of the carbon trapped within secondary carbonate minerals at Diavik is derived from a modern source, either by direct uptake of atmospheric CO(2) or indirect uptake though the biosphere. Silicate weathering at Diavik is trapping 102-114 g C/m(2)/y within nesquehonite, which corresponds to a 2 orders of magnitude increase over the background rate of CO(2) uptake predicted from arctic and subarctic river catchment data.
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http://dx.doi.org/10.1021/es202112yDOI Listing
September 2011

Fixation and fate of C and N in the cyanobacterium Trichodesmium using nanometer-scale secondary ion mass spectrometry.

Proc Natl Acad Sci U S A 2009 Apr 30;106(15):6345-50. Epub 2009 Mar 30.

Wrigley Institute for Environmental Studies and Department of Biological Sciences, University of Southern California, 3616 Trousdale Parkway, Los Angeles, CA 90089-0373, USA.

The marine cyanobacterium Trichodesmium is ubiquitous in tropical and subtropical seas and is an important contributor to global N and C cycling. We sought to characterize metabolic uptake patterns in individual Trichodesmium IMS-101 cells by quantitatively imaging (13)C and (15)N uptake with high-resolution secondary ion mass spectrometry (NanoSIMS). Trichodesmium fix both CO(2) and N(2) concurrently during the day and are, thus, faced with a balancing act: the O(2) evolved during photosynthesis inhibits nitrogenase, the key enzyme in N(2) fixation. After performing correlated transmission electron microscopy (TEM) and NanoSIMS analysis on trichome thin-sections, we observed transient inclusion of (15)N and (13)C into discrete subcellular bodies identified as cyanophycin granules. We speculate that Trichodesmium uses these dynamic storage bodies to uncouple CO(2) and N(2) fixation from overall growth dynamics. We also directly quantified both CO(2) and N(2) fixation at the single cell level using NanoSIMS imaging of whole cells in multiple trichomes. Our results indicate maximal CO(2) fixation rates in the morning, compared with maximal N(2) fixation rates in the afternoon, bolstering the argument that segregation of CO(2) and N(2) fixation in Trichodesmium is regulated in part by temporal factors. Spatial separation of N(2) and CO(2) fixation may also have a role in metabolic segregation in Trichodesmium. Our approach in combining stable isotope labeling with NanoSIMS and TEM imaging can be extended to other physiologically relevant elements and processes in other important microbial systems.
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http://dx.doi.org/10.1073/pnas.0810547106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2669351PMC
April 2009

Extreme longevity in proteinaceous deep-sea corals.

Proc Natl Acad Sci U S A 2009 Mar 23;106(13):5204-8. Epub 2009 Mar 23.

Environmental Earth Systems Science, Stanford University, Stanford, CA 94305, USA.

Deep-sea corals are found on hard substrates on seamounts and continental margins worldwide at depths of 300 to approximately 3,000 m. Deep-sea coral communities are hotspots of deep ocean biomass and biodiversity, providing critical habitat for fish and invertebrates. Newly applied radiocarbon age dates from the deep water proteinaceous corals Gerardia sp. and Leiopathes sp. show that radial growth rates are as low as 4 to 35 mum year(-1) and that individual colony longevities are on the order of thousands of years. The longest-lived Gerardia sp. and Leiopathes sp. specimens were 2,742 years and 4,265 years, respectively. The management and conservation of deep-sea coral communities is challenged by their commercial harvest for the jewelry trade and damage caused by deep-water fishing practices. In light of their unusual longevity, a better understanding of deep-sea coral ecology and their interrelationships with associated benthic communities is needed to inform coherent international conservation strategies for these important deep-sea habitat-forming species.
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http://dx.doi.org/10.1073/pnas.0810875106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663997PMC
March 2009

Imaging and 3D elemental characterization of intact bacterial spores by high-resolution secondary ion mass spectrometry.

Anal Chem 2008 Aug 26;80(15):5986-92. Epub 2008 Jun 26.

Lawrence Livermore National Laboratory, Livermore, California 94551, USA.

We present a quantitative, imaging technique based on nanometer-scale secondary ion mass spectrometry for mapping the 3D elemental distribution present in an individual micrometer-sized Bacillus spore. We use depth profile analysis to access the 3D compositional information of an intact spore without the additional sample preparation steps (fixation, embedding, and sectioning) typically used to access substructural information in biological samples. The method is designed to ensure sample integrity for forensic characterization of Bacillus spores. The minimal sample preparation/alteration required in this methodology helps to preserve sample integrity. Furthermore, the technique affords elemental distribution information at the individual spore level with nanometer-scale spatial resolution and high (microg/g) analytical sensitivity. We use the technique to map the 3D elemental distribution present within Bacillus thuringiensis israelensis spores.
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http://dx.doi.org/10.1021/ac8006279DOI Listing
August 2008

Carbon and nitrogen fixation and metabolite exchange in and between individual cells of Anabaena oscillarioides.

ISME J 2007 Aug 5;1(4):354-60. Epub 2007 Jul 5.

Department of Biology, Portland State University, Portland, OR, USA.

Filamentous nitrogen fixing cyanobacteria are key players in global nutrient cycling, but the relationship between CO2- and N2-fixation and intercellular exchange of these elements remains poorly understood in many genera. Using high-resolution nanometer-scale secondary ion mass spectrometry (NanoSIMS) in conjunction with enriched H13CO3- and 15N2 incubations of Anabaena oscillarioides, we imaged the cellular distributions of C, N and P and 13C and 15N enrichments at multiple time points during a diurnal cycle as proxies for C and N assimilation. The temporal and spatial distributions of the newly fixed C and N were highly heterogeneous at both the intra- and inter-cellular scale, and indicative of regions performing active assimilation and biosynthesis. Subcellular components such as the neck region of heterocycts, cell division septae and putative cyanophycin granules were clearly identifiable by their elemental composition. Newly fixed nitrogen was rapidly exported from heterocysts and was evenly allocated among vegetative cells, with the exception of the most remote vegetative cells between heterocysts, which were N limited based on lower 15N enrichment. Preexisting functional heterocysts had the lowest levels of 13C and 15N enrichment, while heterocysts that were inferred to have differentiated during the experiment had higher levels of enrichment. This innovative approach, combining stable isotope labeling and NanoSIMS elemental and isotopic imaging, allows characterization of cellular development (division, heterocyst differentiation), changes in individual cell composition and cellular roles in metabolite exchange.
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http://dx.doi.org/10.1038/ismej.2007.44DOI Listing
August 2007

A driving dilemma.

Authors:
Fallon Stewart

J Pediatr Health Care 2007 Nov-Dec;21(6):401-2

University of Pennsylvania's Pediatric Nurse Program, Philadelphia, PA, USA.

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http://dx.doi.org/10.1016/j.pedhc.2007.08.014DOI Listing
January 2008

Mineralogy and petrology of comet 81P/Wild 2 nucleus samples.

Science 2006 Dec;314(5806):1735-9

Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA.

The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk.
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http://dx.doi.org/10.1126/science.1135842DOI Listing
December 2006

Isotopic compositions of cometary matter returned by Stardust.

Science 2006 Dec;314(5806):1724-8

Department of Earth and Space Sciences, University of California Los Angeles, Los Angeles, CA 90095-1567, USA.

Hydrogen, carbon, nitrogen, and oxygen isotopic compositions are heterogeneous among comet 81P/Wild 2 particle fragments; however, extreme isotopic anomalies are rare, indicating that the comet is not a pristine aggregate of presolar materials. Nonterrestrial nitrogen and neon isotope ratios suggest that indigenous organic matter and highly volatile materials were successfully collected. Except for a single (17)O-enriched circumstellar stardust grain, silicate and oxide minerals have oxygen isotopic compositions consistent with solar system origin. One refractory grain is (16)O-enriched, like refractory inclusions in meteorites, suggesting that Wild 2 contains material formed at high temperature in the inner solar system and transported to the Kuiper belt before comet accretion.
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http://dx.doi.org/10.1126/science.1135992DOI Listing
December 2006

Comet 81P/Wild 2 under a microscope.

Science 2006 Dec;314(5806):1711-6

Department of Astronomy, University of Washington, Seattle, WA 98195, USA.

The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.
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http://dx.doi.org/10.1126/science.1135840DOI Listing
December 2006

Coral record of increased sediment flux to the inner Great Barrier Reef since European settlement.

Nature 2003 Feb;421(6924):727-30

Research School of Earth Sciences, Australian National University, Canberra 0200, Australia.

The effect of European settlement on water quality in the Great Barrier Reef of Australia is a long-standing and controversial issue. Erosion and sediment transport in river catchments in this region have increased substantially since European settlement, but the magnitude of these changes remains uncertain. Here we report analyses of Ba/Ca ratios in long-lived Porites coral from Havannah Reef--a site on the inner Great Barrier Reef that is influenced by flood plumes from the Burdekin river--to establish a record of sediment fluxes from about 1750 to 1998. We find that, in the early part of the record, suspended sediment from river floods reached the inner reef area only occasionally, whereas after about 1870--following the beginning of European settlement--a five- to tenfold increase in the delivery of sediments is recorded with the highest fluxes occurring during the drought-breaking floods. We conclude that, since European settlement, land-use practices such as clearing and overstocking have led to major degradation of the semi-arid river catchments, resulting in substantially increased sediment loads entering the inner Great Barrier Reef.
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http://dx.doi.org/10.1038/nature01361DOI Listing
February 2003
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