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  • Radiocarbon  (12)
  • Climate change  (10)
  • American Geophysical Union  (22)
  • 2010-2014  (22)
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  • 1
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    Minimum distribution of subsea ice-bearing permafrost on the U.S. Beaufort Sea continental shelf (2012)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Geophysical Research Letters 39 (2012): L15501, doi:10.1029/2012GL052222.
    Description: Starting in Late Pleistocene time (~19 ka), sea level rise inundated coastal zones worldwide. On some parts of the present-day circum-Arctic continental shelf, this led to flooding and thawing of formerly subaerial permafrost and probable dissociation of associated gas hydrates. Relict permafrost has never been systematically mapped along the 700-km-long U.S. Beaufort Sea continental shelf and is often assumed to extend to ~120 m water depth, the approximate amount of sea level rise since the Late Pleistocene. Here, 5,000 km of multichannel seismic (MCS) data acquired between 1977 and 1992 were examined for high-velocity (〉2.3 km s−1) refractions consistent with ice-bearing, coarse-grained sediments. Permafrost refractions were identified along 〈5% of the tracklines at depths of ~5 to 470 m below the seafloor. The resulting map reveals the minimum extent of subsea ice-bearing permafrost, which does not extend seaward of 30 km offshore or beyond the 20 m isobath.
    Description: This research was sponsored by DOE-USGS Interagency Agreement DE-FE0002911. L.B. was supported by a DOE NETL/NRC Methane Hydrate Fellowship under DE-FC26-05NT42248.
    Keywords: Beaufort Sea ; Climate change ; Methane hydrates ; Refraction ; Sea level ; Subsea permafrost
    Repository Name: Woods Hole Open Access Server
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  • 2
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    Direct measurement of riverine particulate organic carbon age structure (2012)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 39 (2012): L19703, doi:10.1029/2012GL052883.
    Description: Carbon cycling studies focusing on transport and transformation of terrigenous carbon sources toward marine sedimentary sinks necessitate separation of particulate organic carbon (OC) derived from many different sources and integrated by river systems. Much progress has been made on isolating and characterizing young biologically-formed OC that is still chemically intact, however quantification and characterization of old, refractory rock-bound OC has remained troublesome. Quantification of both endmembers of riverine OC is important to constrain exchanges linking biologic and geologic carbon cycles and regulating atmospheric CO2 and O2. Here, we constrain petrogenic OC proportions in suspended sediment from the headwaters of the Ganges River in Nepal through direct measurement using ramped pyrolysis radiocarbon analysis. The unique results apportion the biospheric and petrogenic fractions of bulk particulate OC and characterize biospheric OC residence time. Compared to the same treatment of POC from the lower Mississippi-Atchafalaya River system, contrast in age spectra of the Ganges tributary samples illustrates the difference between small mountainous river systems and large integrative ones in terms of the global carbon cycle.
    Description: This work was partially supported by U.S. National Science Foundation (NSF) Cooperative Agreement OCE-228996 to NOSAMS and NSF grants OCE-0851015 & OCE-0928582 to VG.
    Description: 2013-04-03
    Keywords: Ganges ; Himalaya ; Mississippi ; POC ; Carbon cycle ; Radiocarbon
    Repository Name: Woods Hole Open Access Server
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  • 3
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    Isotopic characterization of aerosol organic carbon components over the eastern United States (2012)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): D13303, doi:10.1029/2011JD017153.
    Description: Carbon isotopic signatures (δ13C, Δ14C) of aerosol particulate matter total organic carbon (TOC) and operationally defined organic carbon (OC) components were measured in samples from two background sites in the eastern U.S. TOC and water-soluble OC (WSOC) δ13C values (−27 to −24‰) indicated predominantly terrestrial C3 plant and fossil derived sources. Total solvent extracts (TSE) and their aliphatic, aromatic, and polar OC components were depleted in δ13C (−30 to −26‰) relative to TOC and WSOC. Δ14C signatures of aerosol TOC and TSE (−476 to +25‰) suggest variable fossil contributions (~5–50%) to these components. Aliphatic OC while comprising a small portion of the TOC (〈1%), was dominated by fossil-derived carbon (86 ± 3%), indicating its potential utility as a tracer for fossil aerosol OC inputs. In contrast, aromatic OC contributions (〈1.5%) contained approximately equal portions contemporary (52 ± 8%) and fossil (48 ± 8%) OC. The quantitatively significant polar OC fraction (6–25% of TOC) had fossil contributions (30 ± 12%) similar to TOC (26 ± 7%) and TSE (28 ± 9%). Thus, much of both of the fossil and contemporary OC is deduced to be oxidized, polar material. Aerosol WSOC consistently showed low fossil content (〈8%) relative to the TOC (5–50%) indicating that the majority of fossil OC in aerosol particulates is insoluble. Therefore, on the basis of solubility and polarity, aerosols are predicted to partition differently once deposited to watersheds, and these chemically distinct components are predicted to contribute in quantitatively and qualitatively different ways to watershed carbon biogeochemistry and cycling.
    Description: ASW was partially supported by a Graduate Fellowship from the Hudson River Foundation during the course of this study. Additional funding for this work came from a NOSAMS student internship award, a fellowship award from Sun Trust Bank administered through the VIMS Foundation, a student research grant from VIMS, and the following NSF awards: DEB Ecosystems grant DEB-0234533, Chemical Oceanography grant OCE-0327423, and Integrated Carbon Cycle Research Program grant EAR-0403949 to JEB; and Chemical Oceanography grant OCE-0727575 to RMD and JEB.
    Description: 2013-01-04
    Keywords: Aerosols ; Isotopes ; Organic carbon ; Particulate matter ; Radiocarbon ; Water soluble organic carbon
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Photochemical reactivity of ancient marine dissolved organic carbon (2012)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 39 (2012): L18602, doi:10.1029/2012GL052974.
    Description: Marine dissolved organic carbon (DOC) is the largest reservoir of reduced carbon in seawater and persists up to 4,000–6,000 conventional radiocarbon (14C) years on average. Photochemical degradation has been suggested as a geochemical sink for these long-lived molecules, yet there have been no studies relating photochemical lability to the 14C-ages of surface DOC. We observed apparent second order (2°) kinetics with respect to DOC and a strong trend from Δ14C-enriched to depleted values during exhaustive photomineralization of surface marine DOC with high energy UV light. Geochemically, these results suggest that surface DOC is an isotopically-heterogeneous mixture of molecules for which photochemical lability and 14C ages are correlated. Photochemical mineralization may therefore be an important control on the persistence of 14C-depleted DOC in the ocean.
    Description: This study was supported under NSF grant OCE-0961980 to E. R. M. Druffel.
    Description: 2013-03-20
    Keywords: DOC ; Kinetics ; Photochemistry ; Radiocarbon
    Repository Name: Woods Hole Open Access Server
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  • 5
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    The impact of the North Atlantic Oscillation on the uptake and accumulation of anthropogenic CO2 by North Atlantic Ocean mode waters (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 25 (2011): GB3022, doi:10.1029/2010GB003892.
    Description: The North Atlantic Ocean accounts for about 25% of the global oceanic anthropogenic carbon sink. This basin experiences significant interannual variability primarily driven by the North Atlantic Oscillation (NAO). A suite of biogeochemical model simulations is used to analyze the impact of interannual variability on the uptake and storage of contemporary and anthropogenic carbon (Canthro) in the North Atlantic Ocean. Greater winter mixing during positive NAO years results in increased mode water formation and subsequent increases in subtropical and subpolar Canthro inventories. Our analysis suggests that changes in mode water Canthro inventories are primarily due to changes in water mass volumes driven by variations in water mass transformation rates rather than local air-sea CO2 exchange. This suggests that a significant portion of anthropogenic carbon found in the ocean interior may be derived from surface waters advected into water formation regions rather than from local gas exchange. Therefore, changes in climate modes, such as the NAO, may alter the residence time of anthropogenic carbon in the ocean by altering the rate of water mass transformation. In addition, interannual variability in Canthro storage increases the difficulty of Canthro detection and attribution through hydrographic observations, which are limited by sparse sampling of subsurface waters in time and space.
    Description: We would like to acknowledge funding from the NOAA Climate Program under the Office of Climate Observations and Global Carbon Cycle Program (NOAA‐NA07OAR4310098), NSF (OCE‐0623034), NCAR, the WHOI Ocean Climate Institute, a National Defense Science and Engineering Graduate Fellowship and an Environmental Protection Agency STAR graduate fellowship. NCAR is sponsored by the National Science Foundation.
    Keywords: North Atlantic Oscillation ; Anthropogenic carbon ; Carbon cycle ; Climate change ; Global climate model ; Mode waters
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  • 6
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    Glacial flour dust storms in the Gulf of Alaska : hydrologic and meteorological controls and their importance as a source of bioavailable iron (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L06602, doi:10.1029/2010GL046573.
    Description: Iron is an essential micronutrient that limits primary productivity in much of the ocean, including the Gulf of Alaska (GoA). However, the processes that transport iron to the ocean surface are poorly quantified. We combine satellite and meteorological data to provide the first description of widespread dust transport from coastal Alaska into the GoA. Dust is frequently transported from glacially-derived sediment at the mouths of several rivers, the most prominent of which is the Copper River. These dust events occur most frequently in autumn, when coastal river levels are low and riverbed sediments are exposed. The dust plumes are transported several hundred kilometers beyond the continental shelf into iron-limited waters. We estimate the mass of dust transported from the Copper River valley during one 2006 dust event to be between 25–80 ktons. Based on conservative estimates, this equates to a soluble iron loading of 30–200 tons. We suggest the soluble Fe flux from dust originating in glaciofluvial sediment deposits from the entire GoA coastline is two to three times larger, and is comparable to the annual Fe flux to GoA surface waters from eddies of coastal origin. Given that glaciers are retreating in the coastal GoA region and in other locations, it is important to examine whether fluxes of dust are increasing from glacierized landscapes to the ocean, and to assess the impact of associated Fe on marine ecosystems.
    Description: We appreciate support from the USGS CMGP, NCCWSC, the Mendenhall postdoc program, the Woods Hole PEP intern program, and from NASA‐IDS.
    Keywords: Dust ; Glacier ; Iron ; Aerosol ; Climate change ; Micronutrient
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  • 7
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    Response and impact of equatorial ocean dynamics and tropical instability waves in the tropical Atlantic under global warming : a regional coupled downscaling study (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C03026, doi:10.1029/2010JC006670.
    Description: A regional coupled model is used for a dynamic downscaling over the tropical Atlantic based on a global warming simulation carried out with the Geophysical Fluid Dynamics Laboratory CM2.1. The regional coupled model features a realistic representation of equatorial ocean dynamical processes such as the tropical instability waves (TIWs) that are not adequately simulated in many global coupled climate models. The coupled downscaling hence provides a unique opportunity to assess their response and impact in a changing climate. Under global warming, both global and regional models exhibit an increased (decreased) rainfall in the tropical northeast (South) Atlantic. Given this asymmetric change in mean state, the regional model produces the intensified near-surface cross-equatorial southerly wind and zonal currents. The equatorial cold tongue exhibits a reduced surface warming due to the enhanced upwelling. It is mainly associated with the increased vertical velocities driven by cross-equatorial wind, in contrast to the equatorial Pacific, where thermal stratification is suggested to be more important under global warming. The strengthened upwelling and zonal currents in turn amplify the dynamic instability of the equatorial ocean, thereby intensifying TIWs. The increased eddy heat flux significantly warms the equator and counters the effect of enhanced upwelling. Zonal eddy heat flux makes the largest contribution, suggesting a need for sustained monitoring of TIWs with spatially denser observational arrays in the equatorial oceans. Overall, results suggest that eddy heat flux is an important factor that may impact the mean state warming of equatorial oceans, as it does in the current climate.
    Description: H.S. acknowledges the support from the NOAA Climate and Global Change Postdoctoral Fellowship Program and the Penzance Endowed Fund in Support of Assistant Scientists at WHOI. H.S. and S.‐P.X. are thankful for support from NOAA, NSF, and the Japan Agency for Marine‐Earth Science and Technology.
    Keywords: Climate change ; Ocean mesoscale eddy ; Equatorial Atlantic
    Repository Name: Woods Hole Open Access Server
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  • 8
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    Rapid radiocarbon (14C) analysis of coral and carbonate samples using a continuous-flow accelerator mass spectrometry (CFAMS) system (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 26 (2011): PA4212, doi:10.1029/2011PA002174.
    Description: 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.
    Description: This work was performed under NSF Cooperative Agreement OCE‐0753487, and also NSF‐OPP awards 0636787 and 0944474.
    Keywords: 14C ; CFAMS ; Carbonate ; Coral ; Paleoceanography ; Radiocarbon
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  • 9
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    Impact of ocean carbon system variability on the detection of temporal increases in anthropogenic CO2 (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 113 (2008): C03019, doi:10.1029/2007JC004153.
    Description: Estimates of temporal trends in oceanic anthropogenic carbon dioxide (CO2) rely on the ability of empirical methods to remove the large natural variability of the ocean carbon system. A coupled carbon-climate model is used to evaluate these empirical methods. Both the ΔC* and multiple linear regression (MLR) techniques reproduce the predicted increase in dissolved inorganic carbon for the majority of the ocean and have similar average percent errors for decadal differences (24.1% and 25.5%, respectively). However, this study identifies several regions where these methods may introduce errors. Of particular note are mode and deep water formation regions, where changes in air-sea disequilibrium and structure in the MLR residuals introduce errors. These results have significant implications for decadal repeat hydrography programs, indicating the need for subannual sampling in certain regions of the oceans in order to better constrain the natural variability in the system and to robustly estimate the intrusion of anthropogenic CO2.
    Description: We would like to acknowledge funding from NSF (OCE02-23869), NCAR, the WHOI Ocean Climate Institute, a Linden Earth Systems Graduate Fellowship (MIT), and a National Defense Science and Engineering Graduate Fellowship. NCAR is sponsored by the National Science Foundation. R.W. is supported by the Office of Oceanic and Atmospheric Research at NOAA.
    Keywords: Carbon dioxide ; Ocean carbon sink ; Climate change
    Repository Name: Woods Hole Open Access Server
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  • 10
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    Mineralization of ancient carbon in the subsurface of riparian forests (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 113 (2008): G02021, doi:10.1029/2007JG000482.
    Description: Microbial activity in saturated, subsurface sediments in riparian forests may be supported by recent photosynthate or ancient (〉500 ybp) soil organic carbon (SOC) in buried horizons. Metabolism of ancient SOC may be particularly important in riparian zones, considered denitrification hot spots, because denitrification in the riparian subsurface is often C-limited, because buried horizons intersect deep flow paths, and because low C mineralization rates can support ecosystem-relevant rates of denitrification. Buried horizons are common where alluvial processes (stream migration, overbank flow) have dominated riparian evolution. Our objectives were to determine: (1) the extent to which ancient SOC directly supports subsurface microbial activity; (2) whether different C sources support microbial activity in alluvial versus glaciofluvial riparian zones; and (3) how microbial use of ancient SOC varies with depth. In situ groundwater incubations and 14C dating of dissolved inorganic carbon revealed that ancient SOC mineralization was common, and that it constituted 31–100% of C mineralization 2.6 m deep at one site, at rates sufficient to influence landscape N budgets. Our data failed to reveal consistent spatial patterns of microbially available ancient C. Although mineralized C age increased with depth at one alluvial site, we observed ancient C metabolism 150 cm deep at a glaciofluvial site, suggesting that subsurface microbial activity in riparian zones does not vary systematically between alluvial and glaciofluvial hydrogeologic settings. These findings underscore the relevance of ancient C to contemporary ecosystem processes and the challenge of using mappable surface features to identify subsurface ecosystem characteristics or riparian zone N-sink strength.
    Description: We are grateful to the Cornell Program in Biogeochemistry for graduate research grants and to the U.S. EPA for a STAR Graduate Fellowship to Noel Gurwick. Support for radiocarbon analyses also came from USDANRICGP grant 99–35102– 8266, NSF cooperative agreement OCE-9807266, and an Andrew W. Mellon Foundation grant to the Institute of Ecosystem Studies. A graduate research grant to N. Gurwick from the Theresa Heinz Scholars for Environmental Research provided salary for Pete Seitz-Rundlett.
    Keywords: Riparian zone ; Alluvium ; Groundwater ; Denitrification ; Radiocarbon
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