@article {white_refractory_2023,
	title = {Refractory Dissolved Organic Matter has Similar Chemical Characteristics but Different Radiocarbon Signatures With Depth in the Marine Water Column},
	journal = {Global Biogeochemical Cycles},
	volume = {37},
	number = {4},
	year = {2023},
	note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2022GB007603},
	month = {04/2023},
	pages = {e2022GB007603},
	abstract = {The >5,000-year radiocarbon age (14C-age) of much of the 630 {\textpm} 30 Pg C oceanic dissolved organic carbon (DOC) reservoir remains an enigma in the marine carbon cycle. The fact that DOC is significantly older than dissolved inorganic carbon at every depth in the ocean forms the basis of our current framing of the marine DOC cycle, where some component persists over multiple cycles of ocean mixing. As a result, 14C-depleted, aged DOC is hypothesized to be present as a uniform reservoir with a constant 14C signature and concentration throughout the water column. However, key requirements of this model, including direct observations of DOC with similar 14C signatures in the surface and deep ocean, have never been met. Despite decades of research, the distribution of Δ14C values in marine DOC remains a mystery. Here, we applied a thermal fractionation method to compare operationally defined refractory DOC (RDOC) from different depths in the North Pacific Ocean. We found that RDOC shares chemical characteristics (as recorded by OC bond strength) throughout the water column but does not share the same 14C signature. Our results support one part of the current paradigm{\textemdash}that RDOC is comprised of structurally related components throughout the ocean that form a {\textquotedblleft}background{\textquotedblright} reservoir. However, in contrast to the current paradigm, our results are consistent with a vertical concentration gradient and a vertical and inter-ocean Δ14C gradient for RDOC. The observed Δ14C gradient is compatible with the potential addition of pre-aged DOC to the upper ocean.},
	keywords = {marine dissolved organic matter, radiocarbon, ramped pyrolysis oxidation},
	issn = {1944-9224},
	doi = {10.1029/2022GB007603},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2022GB007603},
	author = {White, Margot E. and Nguyen, Tran B. and Koester, Irina and Lardie Gaylord, Mary C. and Beman, J. Michael and Smith, Kenneth L. and McNichol, Ann P. and Beaupr{\'e}, Steven R. and Aluwihare, Lihini I.}
}
@article {2664,
	title = {Illuminating microbial species-specific effects on organic matter remineralization in marine sediments},
	journal = {Environmental Microbiology},
	year = {2019},
	month = {Oct-12-2019},
	issn = {1462-2912},
	doi = {10.1111/1462-2920.14871},
	url = {https://apps.webofknowledge.com/InboundService.do?product=WOS\&Func=Frame\&DestFail=http\%3A\%2F\%2Fwww.webofknowledge.com\&SrcApp=search\&SrcAuth=Alerting\&SID=7Bytr67Z6qAbafBcvVL\&customersID=Alerting\&mode=FullRecord\&IsProductCode=Yes\&AlertId=ab9062f8-b111-4f95-},
	author = {Mahmoudi, Nagissa and Enke, Tim N. and Beaupr{\'e}, Steven R. and Teske, Andreas P. and Cordero, Otto X. and Pearson, Ann}
}
@article { ISI:000386966700005,
	title = {IsoCaRB: A novel bioreactor system to characterize the lability and natural carbon isotopic (C-14, C-13) signatures of microbially respired organic matter},
	journal = {LIMNOLOGY AND OCEANOGRAPHY-METHODS},
	volume = {14},
	number = {{10}},
	year = {2016},
	month = {OCT},
	pages = {668-681},
	type = {Article},
	abstract = {Organic matter is the dominant pool of reduced carbon in marine and freshwater systems. Mineralization of organic matter is largely attributed to complex and diverse microbial communities that mediate degradation and ultimately yield the terminal respiratory product, carbon dioxide (CO2). The factors that constrain the lability and degradation of organic matter remain unclear, but they involve a complex interplay between structural and chemical properties of the compounds, physical properties of the matrices, and the functional potential of the microorganisms that are present. To investigate these relationships, we developed a novel bioreactor system-called Isotopic Carbon Respirometer-Bioreactor (IsoCaRB)-that permits real-time monitoring of microbial CO2 production rates and collects sequential samples of this CO2 for off-line isotopic analyses (C-13, C-14). Application of this system to organic-rich sediments from Salt Pond, MA reveals that organic matter is oxidized both abiotically and microbially, and that the pattern of microbial respiration by the native sediment community is complex, accessing different carbon substrates over the course of incubation. Isotopic measurements show modern organic matter of progressively older ages (<= ca. 50 yr) is consumed, and this material has variable origins (salt marsh grasses, terrestrial, and marine organic matter). Collectively, the IsoCaRB system provides coupled insights into the sources, ages, and inherent biological and abiotic reactivity of natural organic matter.},
	issn = {1541-5856},
	doi = {10.1002/lom3.10121},
	author = {Beaupr{\'e}, Steven R. and Mahmoudi, Nagissa and Pearson, Ann}
}
@article { ISI:000372829700018,
	title = {A Note on Reporting of Reservoir C-14 Disequilibria and Age Offsets},
	journal = {RADIOCARBON},
	volume = {58},
	number = {{1}},
	year = {2016},
	month = {MAR},
	pages = {205-211},
	type = {Article},
	abstract = {Reservoir age offsets are widely used to correct marine and speleothem radiocarbon age measurements for various calibration purposes. They also serve as a powerful tracer for carbon cycle dynamics. However, a clear terminology regarding reservoir age offsets is lacking, sometimes leading to miscalculations. This note seeks to provide consistent conventions for reporting reservoir C-14 disequilibria useful to a broad range of environmental sciences. This contribution introduces the (FR)-R-14 and R-14 metrics to express the relative C-14 disequilibrium between two contemporaneous reservoirs and the R metric as the associated reservoir age offset.},
	keywords = {freshwater effect, hardwater effect, radiocarbon, Reservoir age, Reservoir effect, ventilation age},
	issn = {0033-8222},
	doi = {10.1017/RDC.2015.22},
	author = {Soulet, Guillaume and Skinner, Luke C. and Beaupr{\'e}, Steven R. and Galy, Valier}
}
@article { ISI:000354878700008,
	title = {Rapid, high-resolution C-14 chronology of ooids},
	journal = {GEOCHIMICA ET COSMOCHIMICA ACTA},
	volume = {159},
	year = {2015},
	month = {JUN 15},
	pages = {126-138},
	type = {Article},
	abstract = {Ooids are small, spherical to ellipsoidal grains composed of concentric layers of CaCO3 that could potentially serve as biogeochemical records of the environments in which they grew. Such records, however, must be placed in the proper temporal context. Therefore, we developed a novel acidification system and employed an accelerator mass spectrometer (AMS) with a gas accepting ion source to obtain radiocarbon (C-14) chronologies extending radially through ooids within one 8-h workday. The method was applied to ooids from Highborne Cay, Bahamas and Shark Bay, Australia, yielding reproducible C-14 chronologies, as well as constraints on the rates and durations of ooid growth and independent estimates of local C-14 reservoir ages. (C) 2015 Elsevier Ltd. All rights reserved.},
	issn = {0016-7037},
	doi = {10.1016/j.gca.2015.03.009},
	author = {Beaupr{\'e}, Steven R. and Roberts, Mark L. and Burton, Joshua R. and Summons, Roger E.}
}
@article {93,
	title = {Carbonate as sputter target material for rapid C-14 AMS},
	journal = {Nuclear Instruments \& Methods in Physics Research Section B-Beam Interactions with Materials and Atoms},
	volume = {294},
	year = {2013},
	note = {id: 2244; PT: J; CT: 12th International Conference on Accelerator Mass Spectrometry (AMS); CY: MAR 20-25, 2011; CL: Wellington, NEW ZEALAND; TC: 0; UT: WOS:000313234300064},
	pages = {328-334},
	abstract = {This paper describes a technique for measuring the C-14 content of carbonate samples by producing C- ions directly in the negative ion sputter source of an accelerator mass spectrometer CAMS) system. This direct analysis of carbonate material eliminates the time and expense of graphite preparation. Powdered carbonate is mixed with titanium powder, loaded into a target cartridge, and compressed. Beam currents for optimally-sized carbonate targets (0.09-0.15 mg C) are typically 10-20\% of those produced by optimally-sized graphite targets (0.5-1 mg C). Modern (>0.8 Fm) samples run by this method have standard deviations of 0.009 Fm or less, and near-modern samples run as unknowns agree with values from traditional hydrolysis/graphite to better than 2\%. Targets with as little as 0.06 mg carbonate produce useable ion currents and results, albeit with increased error and larger blank. In its current state, direct sputtering is best applied to problems where a large number of analyses with lower precision are required. These applications could include age surveys of deep-sea corals for determination of historic population dynamics, to identify samples that would benefit from high precision analysis, and for growth rate studies of organisms forming carbonate skeletons. (C) 2012 Elsevier B.V. All rights reserved.},
	issn = {0168-583X},
	doi = {10.1016/j.nimb.2012.05.014},
	author = {Longworth, Brett E. and Robinson, Laura F. and Roberts, Mark L. and Beaupr{\'e}, Steven R. and Burke, Andrea and W. J. Jenkins}
}
@article {84,
	title = {Distribution of Radiocarbon Ages in Soil Organic Matter by Thermal Fractionation},
	journal = {Radiocarbon},
	volume = {55},
	year = {2013},
	note = {id: 2346; PT: J; TC: 0; UT: WOS:000325752100093},
	pages = {1077-1083},
	issn = {0033-8222},
	doi = {10.2458/azu_js_rc.55.16310},
	author = {Plante, Alain F. and Beaupr{\'e}, Steven R. and Roberts, Mark L. and Baisden, Troy}
}
@article {81,
	title = {A High-Throughput, Low-Cost Method for Analysis of Carbonate Samples for C-14},
	journal = {Radiocarbon},
	volume = {55},
	year = {2013},
	note = {id: 2345; PT: J; TC: 0; UT: WOS:000325752100044},
	pages = {585-592},
	issn = {0033-8222},
	doi = {10.2458/azu_js_rc.55.16190},
	author = {Roberts, Mark L. and Beaupr{\'e}, Steven R. and Burton, Joshua R.}
}
@article {162,
	title = {Photochemical reactivity of ancient marine dissolved organic carbon},
	journal = {Geophysical Research Letters},
	volume = {39},
	year = {2012},
	note = {id: 2249; PT: J; TC: 0; UT: WOS:000309136800001},
	pages = {L18602-L18602},
	abstract = {Marine dissolved organic carbon (DOC) is the largest reservoir of reduced carbon in seawater and persists up to 4,000-6,000 conventional radiocarbon (C-14) 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 C-14-ages of surface DOC. We observed apparent second order (2 degrees) kinetics with respect to DOC and a strong trend from Delta C-14-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 C-14 ages are correlated. Photochemical mineralization may therefore be an important control on the persistence of C-14-depleted DOC in the ocean. Citation: Beaupre, S. R., and E. R. M. Druffel (2012), Photochemical reactivity of ancient marine dissolved organic carbon, Geophys. Res. Lett., 39, L18602, doi:10.1029/2012GL052974.},
	issn = {0094-8276},
	doi = {10.1029/2012GL052974},
	author = {Beaupr{\'e}, Steven R. and Druffel, Ellen R. M.}
}
