McIntyre Cameron P.

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McIntyre
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Cameron P.
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  • Article
    A continuous-flow gas chromatography 14C accelerator mass spectrometry system
    (Dept. of Geosciences, University of Arizona, 2010-08) McIntyre, Cameron P. ; Galutschek, Ernst ; Roberts, Mark L. ; von Reden, Karl F. ; McNichol, Ann P. ; Jenkins, William J.
    Gas-accepting ion sources for radiocarbon accelerator mass spectrometry (AMS) have permitted the direct analysis of CO2 gas, eliminating the need to graphitize samples. As a result, a variety of analytical instruments can be interfaced to an AMS system, processing time is decreased, and smaller samples can be analyzed (albeit with lower precision). We have coupled a gas chromatograph to a compact 14C AMS system fitted with a microwave ion source for real-time compoundspecific 14C analysis. As an initial test of the system, we have analyzed a sample of fatty acid methyl esters and biodiesel. Peak shape and memory was better then existing systems fitted with a hybrid ion source while precision was comparable. 14C/12C ratios of individual components at natural abundance levels were consistent with those determined by conventional methods. Continuing refinements to the ion source are expected to improve the performance and scope of the instrument.
  • Article
    Short communication : Massive erosion in monsoonal central India linked to late Holocene land cover degradation
    (Copernicus Publications on behalf of the European Geosciences Union, 2017-12-01) Giosan, Liviu ; Ponton, Camilo ; Usman, Muhammed ; Blusztajn, Jerzy S. ; Fuller, Dorian Q. ; Galy, Valier ; Haghipour, Negar ; Johnson, Joel E. ; McIntyre, Cameron P. ; Wacker, Lukas ; Eglinton, Timothy I.
    Soil erosion plays a crucial role in transferring sediment and carbon from land to sea, yet little is known about the rhythm and rates of soil erosion prior to the most recent few centuries. Here we reconstruct a Holocene erosional history from central India, as integrated by the Godavari River in a sediment core from the Bay of Bengal. We quantify terrigenous fluxes, fingerprint sources for the lithogenic fraction and assess the age of the exported terrigenous carbon. Taken together, our data show that the monsoon decline in the late Holocene significantly increased soil erosion and the age of exported organic carbon. This acceleration of natural erosion was later exacerbated by the Neolithic adoption and Iron Age extensification of agriculture on the Deccan Plateau. Despite a constantly elevated sea level since the middle Holocene, this erosion acceleration led to a rapid growth of the continental margin. We conclude that in monsoon conditions aridity boosts rather than suppresses sediment and carbon export, acting as a monsoon erosional pump modulated by land cover conditions.
  • Article
    A high-performance 14C accelerator mass spectrometry system
    (Dept. of Geosciences, University of Arizona, 2010-08) Roberts, Mark L. ; Burton, Joshua R. ; Elder, Kathryn L. ; Longworth, Brett E. ; McIntyre, Cameron P. ; von Reden, Karl F. ; Han, Baoxi ; Rosenheim, Brad E. ; Jenkins, William J. ; Galutschek, Ernst ; McNichol, Ann P.
    A new and unique radiocarbon accelerator mass spectrometry (AMS) facility has been constructed at the Woods Hole Oceanographic Institution. The defining characteristic of the new system is its large-gap optical elements that provide a larger-than-standard beam acceptance. Such a system is ideally suited for high-throughput, high-precision measurements of 14C. Details and performance of the new system are presented.
  • Article
    Trophic regions of a hydrothermal plume dispersing away from an ultramafic-hosted vent-system : Von Damm vent-site, Mid-Cayman Rise
    (John Wiley & Sons, 2013-02-22) Bennett, Sarah A. ; Coleman, Max ; Huber, Julie A. ; Reddington, Emily ; Kinsey, James C. ; McIntyre, Cameron P. ; Seewald, Jeffrey S. ; German, Christopher R.
    Deep-sea ultramafic-hosted vent systems have the potential to provide large amounts of metabolic energy to both autotrophic and heterotrophic microorganisms in their dispersing hydrothermal plumes. Such vent-systems release large quantities of hydrogen and methane to the water column, both of which can be exploited by autotrophic microorganisms. Carbon cycling in these hydrothermal plumes may, therefore, have an important influence on open-ocean biogeochemistry. In this study, we investigated an ultramafic-hosted system on the Mid-Cayman Rise, emitting metal-poor and hydrogen sulfide-, methane-, and hydrogen-rich hydrothermal fluids. Total organic carbon concentrations in the plume ranged between 42.1 and 51.1 μM (background = 43.2 ± 0.7 μM (n = 5)) and near-field plume samples with elevated methane concentrations imply the presence of chemoautotrophic primary production and in particular methanotrophy. In parts of the plume characterized by persistent potential temperature anomalies but lacking elevated methane concentrations, we found elevated organic carbon concentrations of up to 51.1 μM, most likely resulting from the presence of heterotrophic communities, their extracellular products and vent larvae. Elevated carbon concentrations up to 47.4 μM were detected even in far-field plume samples. Within the Von Damm hydrothermal plume, we have used our data to hypothesize a microbial food web in which chemoautotrophy supports a heterotrophic community of microorganisms. Such an active microbial food web would provide a source of labile organic carbon to the deep ocean that should be considered in any future studies evaluating sources and sinks of carbon from hydrothermal venting to the deep ocean.
  • Article
    Climate control on terrestrial biospheric carbon turnover
    (National Academy of Sciences, 2021-02-23) Eglinton, Timothy I. ; Galy, Valier ; Hemingway, Jordon D. ; Feng, Xiaojuan ; Bao, Hongyan ; Blattmann, Thomas M. ; Dickens, Angela F. ; Gies, Hannah ; Giosan, Liviu ; Haghipour, Negar ; Hou, Pengfei ; Lupker, Maarten ; McIntyre, Cameron P. ; Montlucon, Daniel B. ; Peucker-Ehrenbrink, Bernhard ; Ponton, Camilo ; Schefuß, Enno ; Schwab, Melissa S. ; Voss, Britta M. ; Wacker, Lukas ; Wu, Ying ; Zhao, Meixun
    Terrestrial vegetation and soils hold three times more carbon than the atmosphere. Much debate concerns how anthropogenic activity will perturb these surface reservoirs, potentially exacerbating ongoing changes to the climate system. Uncertainties specifically persist in extrapolating point-source observations to ecosystem-scale budgets and fluxes, which require consideration of vertical and lateral processes on multiple temporal and spatial scales. To explore controls on organic carbon (OC) turnover at the river basin scale, we present radiocarbon (14C) ages on two groups of molecular tracers of plant-derived carbon—leaf-wax lipids and lignin phenols—from a globally distributed suite of rivers. We find significant negative relationships between the 14C age of these biomarkers and mean annual temperature and precipitation. Moreover, riverine biospheric-carbon ages scale proportionally with basin-wide soil carbon turnover times and soil 14C ages, implicating OC cycling within soils as a primary control on exported biomarker ages and revealing a broad distribution of soil OC reactivities. The ubiquitous occurrence of a long-lived soil OC pool suggests soil OC is globally vulnerable to perturbations by future temperature and precipitation increase. Scaling of riverine biospheric-carbon ages with soil OC turnover shows the former can constrain the sensitivity of carbon dynamics to environmental controls on broad spatial scales. Extracting this information from fluvially dominated sedimentary sequences may inform past variations in soil OC turnover in response to anthropogenic and/or climate perturbations. In turn, monitoring riverine OC composition may help detect future climate-change–induced perturbations of soil OC turnover and stocks.
  • Article
    Rapid radiocarbon (14C) analysis of coral and carbonate samples using a continuous-flow accelerator mass spectrometry (CFAMS) system
    (American Geophysical Union, 2011-11-05) McIntyre, Cameron P. ; Roberts, Mark L. ; Burton, Joshua R. ; McNichol, Ann P. ; Burke, Andrea ; Robinson, Laura F. ; von Reden, Karl F. ; Jenkins, William J.
    Radiocarbon analyses of carbonate materials provide critical information for understanding the last glacial cycle, recent climate history and paleoceanography. Methods that reduce the time and cost of radiocarbon (14C) analysis are highly desirable for large sample sets and reconnaissance type studies. We have developed a method for rapid radiocarbon analysis of carbonates using a novel continuous-flow accelerator mass spectrometry (CFAMS) system. We analyzed a suite of deep-sea coral samples and compared the results with those obtained using a conventional AMS system. Measurement uncertainty is <0.02 Fm or 160 Ryr for a modern sample and the mean background was 37,800 Ryr. Radiocarbon values were repeatable and in good agreement with those from the conventional AMS system. Sample handling and preparation is relatively simple and the method offered a significant increase in speed and cost effectiveness. We applied the method to coral samples from the Eastern Pacific Ocean to obtain an age distribution and identify samples for further analysis. This paper is intended to update the paleoceanographic community on the status of this new method and demonstrate its feasibility as a choice for rapid and affordable radiocarbon analysis.
  • Article
    Isotopic evidence for sources of dissolved carbon and the role of organic matter respiration in the Fraser River basin, Canada
    (Springer, 2022-07-10) Voss, Britta M. ; Eglinton, Timothy I. ; Peucker-Ehrenbrink, Bernhard ; Galy, Valier ; Lang, Susan Q. ; McIntyre, Cameron P. ; Spencer, Robert G. M. ; Bulygina, Ekaterina ; Wang, Zhaohui Aleck ; Guay, Katherine A.
    Sources of dissolved and particulate carbon to the Fraser River system vary significantly in space and time. Tributaries in the northern interior of the basin consistently deliver higher concentrations of dissolved organic carbon (DOC) to the main stem than other tributaries. Based on samples collected near the Fraser River mouth throughout 2013, the radiocarbon age of DOC exported from the Fraser River does not change significantly across seasons despite a spike in DOC concentration during the freshet, suggesting modulation of heterogeneous upstream chemical and isotopic signals during transit through the river basin. Dissolved inorganic carbon (DIC) concentrations are highest in the Rocky Mountain headwater region where carbonate weathering is evident, but also in tributaries with high DOC concentrations, suggesting that DOC respiration may be responsible for a significant portion of DIC in this basin. Using an isotope and major ion mass balance approach to constrain the contributions of carbonate and silicate weathering and DOC respiration, we estimate that up to 33 ± 11% of DIC is derived from DOC respiration in some parts of the Fraser River basin. Overall, these results indicate close coupling between the cycling of DOC and DIC, and that carbon is actively processed and transformed during transport through the river network.
  • Article
    Temporal and spatial variability of particle transport in the deep Arctic Canada Basin
    (John Wiley & Sons, 2015-04-11) Hwang, Jeomshik ; Kim, Minkyoung ; Manganini, Steven J. ; McIntyre, Cameron P. ; Haghipour, Negar ; Park, Jong Jin ; Krishfield, Richard A. ; Macdonald, Robie W. ; McLaughlin, Fiona A. ; Eglinton, Timothy I.
    To better understand the current carbon cycle and potentially detect its change in the rapidly changing Arctic Ocean, we examined sinking particles collected quasi-continuously over a period of 7 years (2004–2011) by bottom-tethered sediment trap moorings in the central Canada Basin. Total mass flux was very low (<100 mg m−2 d−1) at all sites and was temporally decoupled from the cycle of primary production in surface waters. Extremely low radiocarbon contents of particulate organic carbon and high aluminum contents in sinking particles reveal high contributions of resuspended sediment to total sinking particle flux in the deep Canada Basin. Station A (75°N, 150°W) in the southwest quadrant of the Canada Basin is most strongly influenced while Station C (77°N, 140°W) in the northeast quadrant is least influenced by lateral particle supply based on radiocarbon content and Al concentration. The results at Station A, where three sediment traps were deployed at different depths, imply that the most likely mode of lateral particle transport was as thick clouds of enhanced particle concentration extending well above the seafloor. At present, only 1%–2% of the low levels of new production in Canada Basin surface waters reaches the interior basin. Lateral POC supply therefore appears to be the major source of organic matter to the interior basin. However, ongoing changes to surface ocean boundary conditions may influence both lateral and vertical supply of particulate material to the deep Canada Basin.
  • Article
    Reconciling drainage and receiving basin signatures of the Godavari River system
    (Copernicus Publications on behalf of the European Geosciences Union, 2018-06-07) Usman, Muhammed ; Kirkels, Frédérique M. S. A. ; Zwart, Huub M. ; Basu, Sayak ; Ponton, Camilo ; Blattmann, Thomas M. ; Ploetze, Michael ; Haghipour, Negar ; McIntyre, Cameron P. ; Peterse, Francien ; Lupker, Maarten ; Giosan, Liviu ; Eglinton, Timothy I.
    The modern-day Godavari River transports large amounts of sediment (170 Tg per year) and terrestrial organic carbon (OCterr; 1.5 Tg per year) from peninsular India to the Bay of Bengal. The flux and nature of OCterr is considered to have varied in response to past climate and human forcing. In order to delineate the provenance and nature of organic matter (OM) exported by the fluvial system and establish links to sedimentary records accumulating on its adjacent continental margin, the stable and radiogenic isotopic composition of bulk OC, abundance and distribution of long-chain fatty acids (LCFAs), sedimentological properties (e.g. grain size, mineral surface area, etc.) of fluvial (riverbed and riverbank) sediments and soils from the Godavari basin were analysed and these characteristics were compared to those of a sediment core retrieved from the continental slope depocenter. Results show that river sediments from the upper catchment exhibit higher total organic carbon (TOC) contents than those from the lower part of the basin. The general relationship between TOC and sedimentological parameters (i.e. mineral surface area and grain size) of the sediments suggests that sediment mineralogy, largely driven by provenance, plays an important role in the stabilization of OM during transport along the river axis, and in the preservation of OM exported by the Godavari to the Bay of Bengal. The stable carbon isotopic (δ13C) characteristics of river sediments and soils indicate that the upper mainstream and its tributaries drain catchments exhibiting more 13C enriched carbon than the lower stream, resulting from the regional vegetation gradient and/or net balance between the upper (C4-dominated plants) and lower (C3-dominated plants) catchments. The radiocarbon contents of organic carbon (Δ14COC) in deep soils and eroding riverbanks suggests these are likely sources of "old" or pre-aged carbon to the Godavari River that increasingly dominates the late Holocene portion of the offshore sedimentary record. While changes in water flow and sediment transport resulting from recent dam construction have drastically impacted the flux, loci, and composition of OC exported from the modern Godavari basin, complicating reconciliation of modern-day river basin geochemistry with that recorded in continental margin sediments, such investigations provide important insights into climatic and anthropogenic controls on OC cycling and burial.
  • Article
    Tectonically-triggered sediment and carbon export to the Hadal zone
    (Nature Publishing Group, 2018-01-09) Bao, Rui ; Strasser, Michael ; McNichol, Ann P. ; Haghipour, Negar ; McIntyre, Cameron P. ; Wefer, Gerold ; Eglinton, Timothy I.
    Sediments in deep ocean trenches may contain crucial information on past earthquake history and constitute important sites of carbon burial. Here we present 14C data on bulk organic carbon (OC) and its thermal decomposition fractions produced by ramped pyrolysis/oxidation for a core retrieved from the >7.5 km-deep Japan Trench. High-resolution 14C measurements, coupled with distinctive thermogram characteristics of OC, reveal hemipelagic sedimentation interrupted by episodic deposition of pre-aged OC in the trench. Low δ13C values and diverse 14C ages of thermal fractions imply that the latter material originates from the adjacent margin, and the co-occurrence of pre-aged OC with intervals corresponding to known earthquake events implies tectonically triggered, gravity-flow-driven supply. We show that 14C ages of thermal fractions can yield valuable chronological constraints on sedimentary sequences. Our findings shed new light on links between tectonically driven sedimentological processes and marine carbon cycling, with implications for carbon dynamics in hadal environments.