@article {chu_earthquake-enhanced_2023,
	title = {Earthquake-enhanced dissolved carbon cycles in ultra-deep ocean sediments},
	journal = {Nature Communications},
	volume = {14},
	year = {2023},
	month = {09/2023},
	pages = {5427},
	abstract = {Hadal trenches are unique geological and ecological systems located along subduction zones. Earthquake-triggered turbidites act as efficient transport pathways of organic carbon (OC), yet remineralization and transformation of OC in these systems are not comprehensively understood. Here we measure concentrations and stable- and radiocarbon isotope signatures of dissolved organic and inorganic carbon (DOC, DIC) in the subsurface sediment interstitial water along the Japan Trench axis collected during the IODP Expedition 386. We find accumulation and aging of DOC and DIC in the subsurface sediments, which we interpret as enhanced production of labile dissolved carbon owing to earthquake-triggered turbidites, which supports intensive microbial methanogenesis in the trench sediments. The residual dissolved carbon accumulates in deep subsurface sediments and may continue to fuel the deep biosphere. Tectonic events can therefore enhance carbon accumulation and stimulate carbon transformation in plate convergent trench systems, which may accelerate carbon export into the subduction zones., Earthquakes enhance dissolved carbon production and fuel the microbial activities in hadal trench subsurface sediments, and ultimately strengthen carbon accumulation and transformation in the subduction zones.},
	issn = {2041-1723},
	doi = {10.1038/s41467-023-41116-w},
	url = {https://www.nature.com/articles/s41467-023-41116-w},
	author = {Chu, Mengfan and Bao, Rui and Strasser, Michael and Ikehara, Ken and Everest, Jez and Maeda, Lena and Hochmuth, Katharina and Xu, Li and McNichol, Ann and Bellanova, Piero and Rasbury, Troy and K{\"o}lling, Martin and Riedinger, Natascha and Johnson, Joel and Luo, Min and M{\"a}rz, Christian and Straub, Susanne and Jitsuno, Kana and Brunet, Morgane and Cai, Zhirong and Cattaneo, Antonio and Hsiung, Kanhsi and Ishizawa, Takashi and Itaki, Takuya and Kanamatsu, Toshiya and Keep, Myra and Kioka, Arata and McHugh, Cecilia and Micallef, Aaron and Pandey, Dhananjai and Proust, Jean No{\"e}l and Satoguchi, Yasufumi and Sawyer, Derek and Seibert, Chlo{\'e} and Silver, Maxwell and Virtasalo, Joonas and Wang, Yonghong and Wu, Ting-Wei and Zellers, Sarah}
}
@article {2948,
	title = {RADIOCARBON IN DISSOLVED CARBON BY UV OXIDATION: AN UPDATE OF PROCEDURES AND BLANK CHARACTERIZATION AT NOSAMSABSTRACT},
	journal = {Radiocarbon},
	volume = {64},
	year = {2022},
	month = {Jan-02-2022},
	pages = {195 - 199},
	abstract = {This note describes improvements of UV oxidation method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). The procedural blank is reduced to 2.6 +/- 0.6 mu g C, with Fm of 0.42 +/- 0.10 and delta C-13 of -28.43 +/- 1.19 parts per thousand. The throughput is improved from one sample per day to two samples per day.},
	issn = {0033-8222},
	doi = {10.1017/RDC.2022.4},
	url = {https://www.cambridge.org/core/product/identifier/S0033822222000042/type/journal_articlehttps://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033822222000042},
	author = {Xu, Li and Roberts, Mark L and Elder, Kathryn L and Hansman, Roberta L and Gagnon, Alan R and Kurz, Mark D}
}
@article {2924,
	title = {Compound-specific radiocarbon reveals sources and land{\textendash}sea transport of polycyclic aromatic hydrocarbons in an urban estuary},
	journal = {Water Research},
	volume = {198},
	year = {2021},
	month = {Jan-06-2021},
	pages = {117134},
	abstract = {As typical chemical indicators of the Anthropocene, polycyclic aromatic hydrocarbons (PAHs) and their environmental behavior in urban estuaries can reveal the influence of anthropogenic activities on coastal zones worldwide. In contrast to conventional approaches based on concentration datasets, we provide a compound-specific radiocarbon ( 14 C) perspective to quantitatively evaluate the sources and land{\textendash}sea transport of PAHs in an estuarine{\textendash}coastal surficial sedimentary system impacted by anthropogenic activities and coastal currents. Compound-specific 14 C of PAHs and their 14 C end-member mixing models showed that 67 -73\% of fluoranthene and pyrene and 76 -80\% of five- and six-ring PAHs in the Jiulong River Estuary (JRE, China) originated from fossil fuels (e.g., coal, oil spill, and petroleum-related emissions). In the adjacent Western Taiwan Strait (WTS), the contributions of fossil fuel to these PAH groups were higher at 74 -79\% and 84 -87\%, respectively. Furthermore, as a significant biomarker for source al- location of terrigenous organic matter, perylene, a typical five-ring PAH, and its land{\textendash}sea transport from the basin through the JRE and finally to the WTS was quantitatively evaluated based on the 14 C transport models. In the JRE, fluvial erosions and anthropogenic emissions affected the 14 C signature of perylene ( 14 C perylene , -535 {\textpm}5 {\textperthousand} ) with contributions of > 38\% and < 62\%, respectively. From the JRE to the WTS, the decreased 14 C perylene (-735 {\textpm}4 {\textperthousand} ) could be attributed to the long{\textendash}range transport of {\textquotedblleft}ocean current- driven{\textquotedblright} perylene (-919 {\textpm}53 {\textperthousand} ) with a contribution of 53 {\textpm}8\%. This compound-specific 14 C approach and PAH transport model help provide a valuable reference for accurately quantifying land{\textendash}sea transport and burial of organic pollutants in estuarine{\textendash}coastal sedimentary systems.},
	issn = {00431354},
	doi = {10.1016/j.watres.2021.117134},
	url = {https://www.sciencedirect.com/science/article/pii/S0043135421003328},
	author = {Ya, Miaolei and Wu, Yuling and Xu, Li and Li, Yongyu and Chen, Hanzhe and Wang, Xinhong}
}
@article {2922,
	title = {RADIOCARBON IN DISSOLVED ORGANIC CARBON BY UV OXIDATION: PROCEDURES AND BLANK CHARACTERIZATION AT NOSAMSABSTRACT},
	journal = {Radiocarbon},
	volume = {63},
	year = {2021},
	month = {Jan-02-2021},
	pages = {357 - 374},
	abstract = {This study describes a procedural blank assessment of the ultraviolet photochemical oxidation (UV oxidation) method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). A retrospective compilation of Fm and δ 13 C results for secondary standards (OX-II, glycine) between 2009 and 2018 indicated that a revised blank correction was required to bring results in line with accepted values. The application of a best-fit mass-balance correction yielded a procedural blank of 22.0 {\textpm} 6.0 μg C with Fm of 0.30 {\textpm} 0.20 and δ 13 C of-32.0 {\textpm} 3.0{\textperthousand} for this period, which was notably higher and more variable than previously reported. Changes to the procedure, specifically elimination of higher organic carbon reagents and improved sample and reactor handling, reduced the blank to 11.0 {\textpm} 2.75 μg C, with Fm of 0.14 {\textpm} 0.10 and δ 13 C of-31.0 {\textpm} 5.5{\textperthousand}. A thorough determination of the entire sample processing blank is required to ensure accurate isotopic compositions of seawater DOC using the UV oxidation method. Additional efforts are needed to further reduce the procedural blank so that smaller DOC samples can be analyzed, and to increase sample throughput.},
	keywords = {blank, dissolved organic carbon, radiocarbon, UV oxidation},
	issn = {0033-8222},
	doi = {10.1017/RDC.2020.102},
	url = {https://www.cambridge.org/core/journals/radiocarbon/article/abs/radiocarbon-in-dissolved-organic-carbon-by-uv-oxidation-procedures-and-blank-characterization-at-nosams/AA39A2C74772934B44D9BF81C2DF723C},
	author = {Xu, Li and Roberts, Mark L and Elder, Kathryn L and Kurz, Mark D and McNichol, Ann P and Reddy, Christopher M and Ward, Collin P and Hanke, Ulrich M}
}
@article {2871,
	title = {Dissolved organic carbon in basalt-hosted deep subseafloor fluids of the Juan de Fuca Ridge flank},
	journal = {Earth and Planetary Science Letters},
	volume = {513},
	year = {2019},
	month = {Jan-05-2019},
	pages = {156 - 165},
	abstract = {Marine dissolved organic carbon (DOC) is highly depleted in radiocarbon and thus inferred to be largely refractory to removal processes that operate on less than millennial timescales. However, a growing number of reports have shown that a large fraction of marine DOC can be effectively removed during circulation through submarine hydrothermal systems. What is not clear, however, is whether the DOC that remains in hydrothermal fluids is remnant non-reactive DOC from recharged seawater, or DOC that has been largely produced in the subsurface. We collected and characterized warm (\~{}65 {\textdegree}C) hydrothermal fluids from deep (18, 40, 73, 200 m) within the basalt-hosted basement of the Juan de Fuca Ridge flank in the Northeast Pacific Ocean. DOC concentrations in hydrothermal fluids were 9 to 18 μM, much lower than measured in local deep seawater (37.5 μM). DOC C values of -683{\textperthousand} to -856{\textperthousand} were much lower than the C-dissolved inorganic carbon (DIC) values of -880{\textperthousand} to -918{\textperthousand}, while DOC C values of -23.6{\textperthousand} to -27.0{\textperthousand} were much heavier than that of the particulate organic carbon (POC) pool ({\textperthousand}), suggesting that biological production in the subsurface is not a primary source of DOC. Rather, our data suggest that isotopically enriched DOC are selectively removed from recharged seawater, leaving DOC that is very isotopically depleted in the basaltic basement fluids. Despite the removal of 50{\textendash}75\% of DOC in the subsurface, nuclear magnetic resonance (NMR) functional group analyses indicate that aromatic compounds were added to basaltic basement fluids during passage through the deep subseafloor and may partly contribute to the depleted 14C DOC in the ridge-flank basement fluids.},
	keywords = {aromatic organic compound, basaltic basement fluid, carbon isotopes, dissolved organic carbon, Juan de Fuca, selective removal, subseafloor},
	issn = {0012821X},
	doi = {10.1016/j.epsl.2019.02.008},
	url = {https://linkinghub.elsevier.com/retrieve/pii/S0012821X19300998},
	author = {Lin, Huei-Ting and Repeta, Daniel J. and Xu, Li and Rapp{\'e}, Michael S.}
}
@article {2757,
	title = {Significance of Perylene for Source Allocation of Terrigenous Organic Matter in Aquatic SedimentsSignificance of Perylene for Source Allocation of Terrigenous Organic Matter in Aquatic Sediments},
	journal = {Environmental Science \& Technology},
	volume = {53},
	year = {2019},
	month = {Apr-07-2020},
	pages = {8244 - 8251},
	abstract = {Perylene is a frequently abundant, and sometimes the only polycyclic aromatic hydrocarbon (PAH) in aquatic sediments, but its origin has been subject of a longstanding debate in geochemical research and pollutant forensics because its historical record differs markedly from typical anthropogenic PAHs. Here we investigate whether perylene serves as a source-specific molecular marker of fungal activity in forest soils. We use a well-characterized sedimentary record (1735-1999) from the anoxic-bottom waters of the Pettaquamscutt River basin, RI to examine mass accumulation rates and isotope records of perylene, and compare them with total organic carbon and the anthropogenic PAH fluoranthene. We support our arguments with radiocarbon (14C) data of higher plant leaf-wax n-alkanoic acids. Isotope-mass balance-calculations of perylene and n-alkanoic acids indicate that \~{}40\% of sedimentary organic matter is of terrestrial origin. Further, both terrestrial markers are pre-aged on millennial time-scales prior to burial in sediments and are insensitive to elevated 14C concentrations following nuclear weapons testing in the mid-20th Century. Instead, changes coincide with enhanced erosional flux during urban sprawl. These findings suggest that perylene is definitely a product of soil-derived fungi, and a powerful chemical tracer to study the spatial and temporal connectivity between terrestrial and aquatic environments. },
	issn = {0013-936X},
	doi = {10.1021/acs.est.9b0234410.1021/acs.est.9b02344.s001},
	url = {https://pubs.acs.org/doi/10.1021/acs.est.9b02344},
	author = {Hanke, Ulrich M. and Lima-Braun, Ana L. and Eglinton, Timothy I. and Donnelly, Jeffrey P. and Galy, Valier and Poussart, Pascale and Hughen, Konrad and McNichol, Ann P. and Xu, Li and Reddy, Christopher M.}
}
@article {2613,
	title = {Dimensions of Radiocarbon Variability within Sedimentary Organic MatterABSTRACT},
	journal = {Radiocarbon},
	volume = {60},
	year = {2018},
	month = {Jan-06-2018},
	pages = {775 - 790},
	abstract = {Organic carbon (OC) radiocarbon (14C) signatures in marine surface sediments are highly variable and the
causes of this heterogeneity remain ambiguous. Here, we present results from a detailed 14C-based investigation of an Arabian Sea sediment, including measurements on organic matter (OM) in bulk sediment, specific grain size fractions, and OC decomposition products from ramped-pyrolysis-oxidation (RPO). Our results show that 14C ages of OM increase with increasing grain size, suggesting that grain size is an important factor controlling the 14C heterogeneity in marine sediments. Analysis of RPO decomposition products from different grain size fractions reveals an overall increase in age of corresponding thermal fractions from finer to coarser fractions. We suggest that hydrodynamic properties of sediment grains exert the important control on the 14C age distribution of OM among grain size fractions. We propose a conceptual model to account for this dimensionality in 14C variability that invokes two predominant modes of OM preservation within different grain size fractions of Arabian Sea sediment: finer (<63 μm) fractions are influenced by OM-mineral grain aggregation processes, giving rise to relatively uniform 14C ages, whereas OM preserved in coarser (>63 μm) fractions includes materials encapsulated within microfossils and/or entrained fossil (14C-depleted) OC hosted in detrital mineral grains. Our findings highlight the value of RPO for assessment of 14C age variability in sedimentary OC, and for assessing mechanisms of OM preservation in aquatic sediments.},
	keywords = {arabian sea, grain size, hydrodynamic processes, organicmatter, radiocarbon, ramped pyrolysis-oxidation},
	issn = {0033-8222},
	doi = {10.1017/RDC.2018.22},
	url = {https://www.cambridge.org/core/journals/radiocarbon/article/dimensions-of-radiocarbon-variability-within-sedimentary-organic-matter/A81022494F34D8C3B88D39A43112BB08},
	author = {Bao, Rui and McNichol, Ann P and McIntyre, Cameron P and Xu, Li and Eglinton, Timothy I}
}
@article {2891,
	title = {Fossil Fuel-Derived Polycyclic Aromatic Hydrocarbons in the Taiwan Strait, China, and Fluxes across the Air{\textendash}Water InterfaceFossil Fuel-Derived Polycyclic Aromatic Hydrocarbons in the Taiwan Strait, China, and Fluxes across the AirWater Interface},
	journal = {Environmental Science \& Technology},
	volume = {52},
	year = {2018},
	month = {Mar-07-2018},
	pages = {7307 - 7316},
	abstract = {On the basis of the application of compound-specific radiocarbon analysis (CSRA) and air{\textendash}water exchange models, the contributions of fossil fuel and biomass burning derived polycyclic aromatic hydrocarbons (PAHs) as well as their air{\textendash}water transport were elucidated. The results showed that fossil fuel-derived PAHs (an average contribution of 89\%) presented the net volatilization process at the air{\textendash}water interface of the Taiwan Strait in summer. Net volatile fluxes of the dominant fluorene and phenanthrene (>58\% of the total PAHs) were 27 {\textpm} 2.8 μg m{\textendash}2 day{\textendash}1, significantly higher than the dry deposition fluxes (average 0.43 μg m{\textendash}2 day{\textendash}1). The Δ14C contents of selected PAHs (fluorene, phenanthrene plus anthracene, fluoranthene, and pyrene) determined by CSRA in the dissolved seawater ranged from -997 {\textpm} 4{\textperthousand} to -873 {\textpm} 6{\textperthousand}, indicating that 89{\textendash}100\% (95 {\textpm} 4\%) of PAHs were supplied by fossil fuels. The South China Sea warm current originating from the southwest China in summer (98\%) and the Min-Zhe coastal current originating from the north China in winter (97\%) input more fossil fuel PAHs than the Jiulong River estuary (90\%) and Xiamen harbor water (93\%). The more radioactive decayed 14C of fluoranthene (a 4-ring PAH) than that of phenanthrene and anthracene (3-ring PAHs) represented a greater fossil fuel contribution to the former in dissolved seawater.},
	issn = {0013-936X},
	doi = {10.1021/acs.est.8b01331},
	url = {https://pubs.acs.org/doi/10.1021/acs.est.8b01331},
	author = {Ya, Miaolei and Xu, Li and Wu, Yuling and Li, Yongyu and Zhao, Songhe and Wang, Xinhong}
}
@article {1284,
	title = { Allochthonous sources and dynamic cycling of ocean dissolved organic carbon revealed by carbon isotopes},
	journal = {GEOPHYSICAL RESEARCH LETTERS},
	volume = {44},
	year = {2017},
	month = {03/2017},
	pages = {2407-2415},
	abstract = {We present concentration and isotopic profiles of total, size, and polarity fractionated dissolved organic carbon (DOC) from Station ALOHA (A Long-term Oligotrophic Habitat Assessment), an oligotrophic site in the North Pacific Ocean. The data show that, between the surface and 3500 m, low molecular weight (LMW) hydrophilic DOC, LMW hydrophobic DOC, and high molecular weight (HMW) DOC constitute 22-33\%, 45-52\%, and 23-35\% of DOC, respectively. LMW hydrophilic DOC is more isotopically depleted (delta C-13 of -23.9 parts per thousand to -31.5 parts per thousand and Delta C-14 of -304 parts per thousand to -795 parts per thousand; mean age of 2850 to 15000 years) than the LMW hydrophobic DOC (delta C-13 of -22 parts per thousand to -23 parts per thousand and Delta C-14 of -270 parts per thousand to -568 parts per thousand; 2470 to 6680 years) and HMW DOC (delta C-13 of similar to-21 parts per thousand and Delta C-14 of -24 parts per thousand to -294 parts per thousand; 135-2700 years). Our analyses suggest that a large fraction of DOC may be derived from allochthonous sources such as terrestrial and hydrothermal DOC and cycle on much longer time scales of > 10000 years or enter the ocean as preaged carbon.},
	keywords = {ATLANTIC BIGHT, BLACK CARBON, C-14, HUMIC SUBSTANCES, MATTER, NORTH PACIFIC-OCEAN, RADIOCARBON ANALYSIS, SARGASSO SEA, SEAWATER, SPECTROMETRY},
	doi = {10.1002/2016GL071348},
	author = {Zigah, Prosper K. and McNichol, Ann P. and Xu, Li and Johnson, Carl and Santinelli, Chiara and Karl, David M. and Repeta, Daniel J.}
}
@article {2805,
	title = {What on Earth Have We Been Burning? Deciphering Sedimentary Records of Pyrogenic CarbonWhat on Earth Have We Been Burning? Deciphering Sedimentary Records of Pyrogenic Carbon},
	journal = {Environmental Science \& Technology},
	volume = {51},
	year = {2017},
	month = {Jul-11-2017},
	pages = {12972 - 12980},
	abstract = {Humans have interacted with fire for thousands of years, yet the utilization of fossil fuels marked the beginning of a new era. Ubiquitous in the environment, pyrogenic carbon (PyC) arises from incomplete combustion of biomass and fossil fuels, forming a continuum of condensed aromatic structures. Here, we develop and evaluate 14C records for two complementary PyC molecular markers, benzene polycarboxylic acids (BPCAs) and polycyclic aromatic hydrocarbons (PAHs), preserved in aquatic sediments from a suburban and a remote catchment in the United States (U.S.) from the mid-1700s to 1998. Results show that the majority of PyC stems from local sources and is transferred to aquatic sedimentary archives on subdecadal to millennial time scales. Whereas a small portion stems from near-contemporaneous production and sedimentation, the majority of PyC (\~{}90\%) experiences delayed transmission due to {\textquotedblleft}preaging{\textquotedblright} on millennial time scales in catchment soils prior to its ultimate deposition. BPCAs (soot) and PAHs (precursors of soot) trace fossil fuel-derived PyC. Both markers parallel historical records of the consumption of fossil fuels in the U.S., yet never account for more than 19\% total PyC. This study demonstrates that isotopic characterization of multiple tracers is necessary to constrain histories and inventories of PyC and that sequestration of PyC can markedly lag its production.},
	issn = {0013-936X},
	doi = {10.1021/acs.est.7b03243},
	url = {https://pubs.acs.org/doi/10.1021/acs.est.7b03243},
	author = {Hanke, Ulrich M. and Reddy, Christopher M. and Braun, Ana L. L. and Coppola, Alysha I. and Haghipour, Negar and McIntyre, Cameron P. and Wacker, Lukas and Xu, Li and McNichol, Ann P. and Abiven, Samuel and Schmidt, Michael W. I. and Eglinton, Timothy I.}
}
@article {14,
	title = {Quantification of refractory organic material in Amazon mudbanks of the French Guiana Coast},
	journal = {Marine Geology},
	volume = {363},
	year = {2015},
	pages = {93-101},
	abstract = {Sub-oxic overturning mudbanks originating in the Amazon outlet and traveling northwestward along the coast of South America store 3.5 Tg organic carbon on the Amazon shelf, annually. The predominance of old soil carbon burial associated with the sediment has been supported by relatively old bulk radiocarbon ages (~ 2200{\textendash}3200 14C y) reported, but this amount has yet to be quantified for this dynamic setting. Here, we employ ramped pyrolysis radiocarbon dating to mudbank sediments from three cores to further constrain the amount of refractory sedimentary organic carbon present. Using radiocarbon age as a proxy for reactivity, we find that at least 36\% of this organic carbon is pre-aged refractory terrestrial organic carbon, likely sourced from terrestrial soils and averaging ages of 16,100 {\textpm} 300 14C y. This implies significant preservation of pre-aged terrestrial soil material in this marine environment despite the mobility and oxygen availability in the muds. Concurrently, an average of 77\% of this organic material is aged over 1000 14C y, consistent with previous estimates that the majority of organic carbon buried along the shelf is refractory. Analyses of extracted lignin phenols and terrestrial humic acids also support this preservation of refractory terrestrial material. These data indicate that sediment discharged from the Amazon River may preserve refractory terrestrial carbon in marine sediments at a minimum of 3.1 Tg C/y, which is more efficient than originally thought.},
	issn = {0025-3227},
	doi = {10.1016/j.margeo.2015.02.009},
	url = {http://www.sciencedirect.com/science/article/pii/S0025322715000456},
	author = {Williams, Elizabeth K. and Rosenheim, Brad E. and Allison, Mead and McNichol, Ann P. and Xu, Li}
}
@article {22,
	title = {Source-age dynamics of estuarine particulate organic matter using fatty acid delta C-13 and Delta C-14 composition},
	journal = {Limnology and Oceanography},
	volume = {60},
	year = {2015},
	note = {PT: J; TC: 0; UT: WOS:000351126500020},
	pages = {611-628},
	abstract = {This study used a multiproxy approach to elucidate the source and age composition of estuarine particulate organic matter (POM) using bulk stable isotopes (C-13(POC)), fatty acid (FA) biomarkers, and compound specific isotopic analyses in surface waters along the Delaware River and Bay (Delaware Estuary, hereafter). C-13 values of FA (C-13(FA)) ranged more widely (-30.9 parts per thousand to -21.8 parts per thousand) than C-13(POC) (-27.5 parts per thousand to -23.5 parts per thousand), providing greater insight about POM sources along the estuary. C-13 values of C-16:0 phospholipid FA (primarily, aquatic sources) increased along the salinity gradient (-29.8 parts per thousand to -23.4 parts per thousand), while C-13(FA) values of long-chain neutral fatty acid (terrestrial sources) decreased (-28.6 parts per thousand to -30.9 parts per thousand). C-13(FA) values for C-18{\textquoteright}s FA indicated the importance of marsh-derived organic matter within Delaware Estuary. Compound specific radiocarbon analysis showed the heterogeneous age structure of FA associated with POM (FA(POM)). C-14 ages of FA ranged from modern (postbomb) to 1790BP; aged FA (120BP to 1700BP) derived primarily from the watershed, whereas modern FA were produced within Delaware Estuary. C-14 ages of short-chain FA (aquatic sources) reflected differences in the age of dissolved inorganic carbon along the estuary and had older C-14 ages at the river end-member. C-14 ages of FA from terrigenous sources were older than water and sediment residence times indicating this source derived from the watershed. This study is the first to document the complex age distribution of FA(POM) along the estuarine salinity gradient and shows that inorganic carbon sources, watershed inputs and autochthonous production contribute to variation in the ages of POM.},
	issn = {0024-3590},
	doi = {10.1002/lno.10053},
	author = {McIntosh, Hadley A. and McNichol, Ann P. and Xu, Li and Canuel, Elizabeth A.}
}
@article {2638,
	title = {Hidden cycle of dissolved organic carbon in the deep ocean},
	journal = {Proceedings of the National Academy of Sciences},
	volume = {111},
	year = {2014},
	month = {Jan-11-2016},
	pages = {16706 - 16711},
	abstract = {Marine dissolved organic carbon (DOC) is a large (660 Pg C) reactive carbon reservoir that mediates the oceanic microbial food web and interacts with climate on both short and long timescales. Carbon isotopic content provides information on the DOC source via [Formula: see text]C and age via [Formula: see text]C. Bulk isotope measurements suggest a microbially sourced DOC reservoir with two distinct components of differing radiocarbon age. However, such measurements cannot determine internal dynamics and fluxes. Here we analyze serial oxidation experiments to quantify the isotopic diversity of DOC at an oligotrophic site in the central Pacific Ocean. Our results show diversity in both stable and radio isotopes at all depths, confirming DOC cycling hidden within bulk analyses. We confirm the presence of isotopically enriched, modern DOC cocycling with an isotopically depleted older fraction in the upper ocean. However, our results show that up to 30\% of the deep DOC reservoir is modern and supported by a 1 Pg/y carbon flux, which is 10 times higher than inferred from bulk isotope measurements. Isotopically depleted material turns over at an apparent time scale of 30,000 y, which is far slower than indicated by bulk isotope measurements. These results are consistent with global DOC measurements and explain both the fluctuations in deep DOC concentration and the anomalous radiocarbon values of DOC in the Southern Ocean. Collectively these results provide an unprecedented view of the ways in which DOC moves through the marine carbon cycle.},
	keywords = {Carbon cycle, carbon isotopes, dissolved organic carbon, Oceanography, radiocarbon},
	issn = {0027-8424},
	doi = {10.1073/pnas.1407445111},
	url = {http://www.pnas.org/lookup/doi/10.1073/pnas.1407445111https://syndication.highwire.org/content/doi/10.1073/pnas.1407445111},
	author = {Follett, Christopher L. and Repeta, Daniel J. and Rothman, Daniel H. and Xu, Li and Santinelli, Chiara}
}
@article {108,
	title = {14C and 13C characteristics of higher plant biomarkers in Washington margin surface sediments},
	journal = {Geochimica et Cosmochimica Acta},
	volume = {105},
	year = {2013},
	note = {id: 2267},
	pages = {14-30},
	abstract = {Plant wax lipids and lignin phenols are the two most common classes of molecular markers that are used to trace vascular plant-derived OM in the marine environment. However, their 13C and 14C compositions have not been directly compared, which can be used to constrain the flux and attenuation of terrestrial carbon in marine environment. In this study, we describe a revised method of isolating individual lignin phenols from complex sedimentary matrices for 14C analysis using high pressure liquid chromatography (HPLC) and compare this approach to a method utilizing preparative capillary gas chromatography (PCGC). We then examine in detail the 13C and 14C compositions of plant wax lipids and lignin phenols in sediments from the inner and mid shelf of the Washington margin that are influenced by discharge of the Columbia River. Plant wax lipids (including n-alkanes, n-alkanoic (fatty) acids, n-alkanols, and n-aldehydes) displayed significant variability in both δ13C (-28.3{\textperthousand} to -37.5{\textperthousand}) and Δ14C values (-204{\textperthousand} to +2{\textperthousand}), suggesting varied inputs and/or continental storage and transport histories. In contrast, lignin phenols exhibited similar δ13C values (between -30{\textperthousand} and -34{\textperthousand}) and a relatively narrow range of Δ14C values (-45{\textperthousand} to -150{\textperthousand}; HPLC-based measurement) that were similar to, or younger than, bulk OM (-195{\textperthousand} to -137{\textperthousand}). Moreover, lignin phenol 14C age correlated with the degradation characteristics of this terrestrial biopolymer in that vanillyl phenols were on average \~{}500 years older than syringyl and cinnamyl phenols that degrade faster in soils and sediments. The isotopic characteristics, abundance, and distribution of lignin phenols in sediments suggest that they serve as promising tracers of recently biosynthesized terrestrial OM during supply to, and dispersal within the marine environment. Lignin phenol 14C measurements may also provide useful constraints on the vascular plant end member in isotopic mixing models for carbon source apportionment, and for interpretation of sedimentary records of past vegetation dynamics.},
	issn = {0016-7037},
	doi = {10.1016/j.gca.2012.11.034},
	url = {http://www.sciencedirect.com/science/article/pii/S0016703712006874},
	author = {Feng, Xiaojuan and Benitez-Nelson, Bryan C. and Montlu{\c c}on, Daniel B. and Prahl, Fredrick G. and McNichol, Ann P. and Xu, Li and Repeta, Daniel J. and Eglinton, Timothy I.}
}
@article { ISI:000315194800002,
	title = {C-14 and C-13 characteristics of higher plant biomarkers in Washington margin surface sediments},
	journal = {GEOCHIMICA ET COSMOCHIMICA ACTA},
	volume = {105},
	year = {2013},
	month = {MAR 15},
	pages = {14-30},
	type = {Article},
	abstract = {Plant wax lipids and lignin phenols are the two most common classes of molecular markers that are used to trace vascular plant-derived OM in the marine environment. However, their C-13 and C-14 compositions have not been directly compared, which can be used to constrain the flux and attenuation of terrestrial carbon in marine environment. In this study, we describe a revised method of isolating individual lignin phenols from complex sedimentary matrices for C-14 analysis using high pressure liquid chromatography (HPLC) and compare this approach to a method utilizing preparative capillary gas chromatography (PCGC). We then examine in detail the C-13 and C-14 compositions of plant wax lipids and lignin phenols in sediments from the inner and mid shelf of the Washington margin that are influenced by discharge of the Columbia River. Plant wax lipids (including n-alkanes, n-alkanoic (fatty) acids, n-alkanols, and n-aldehydes) displayed significant variability in both delta C-13 (-28.3 parts per thousand to -37.5 parts per thousand) and Delta C-14 values (-204 parts per thousand to +2 parts per thousand), suggesting varied inputs and/or continental storage and transport histories. In contrast, lignin phenols exhibited similar delta C-13 values (between -30 parts per thousand and -34 parts per thousand) and a relatively narrow range of Delta C-14 values (-45 parts per thousand to -150 parts per thousand; HPLC-based measurement) that were similar to, or younger than, bulk OM (-195 parts per thousand to -137 parts per thousand). Moreover, lignin phenol C-14 age correlated with the degradation characteristics of this terrestrial biopolymer in that vanillyl phenols were on average similar to 500 years older than syringyl and cinnamyl phenols that degrade faster in soils and sediments. The isotopic characteristics, abundance, and distribution of lignin phenols in sediments suggest that they serve as promising tracers of recently biosynthesized terrestrial OM during supply to, and dispersal within the marine environment. Lignin phenol C-14 measurements may also provide useful constraints on the vascular plant end member in isotopic mixing models for carbon source apportionment, and for interpretation of sedimentary records of past vegetation dynamics. (C) 2012 Elsevier Ltd. All rights reserved.},
	issn = {0016-7037},
	doi = {10.1016/j.gca.2012.11.034},
	author = {Feng, Xiaojuan and Benitez-Nelson, Bryan C. and Montlu{\c c}on, Daniel B. and Prahl, Fredrick G. and McNichol, Ann P. and Xu, Li and Repeta, Daniel J. and Eglinton, Timothy I.}
}
@article {114,
	title = {Organic carbon export from the Greenland ice sheet},
	journal = {Geochimica et Cosmochimica Acta},
	volume = {109},
	year = {2013},
	note = {id: 2276},
	pages = {329-344},
	abstract = {Glacial meltwater exports a unique type of organic carbon to marine systems, distinct from non-glacially derived riverine export, potentially capable of stimulating downstream marine primary productivity. Here, we describe for the first time the bulk-level dissolved organic carbon (DOC) and particulate organic carbon (POC) isotopic composition of glacial meltwater draining the Greenland ice sheet (GrIS). These data, in conjunction with an earlier study that investigated the molecular-level composition of GrIS dissolved organic matter, collectively describe the concentration, radiocarbon content, and lability of organic carbon in subglacial discharge from a land-terminating outlet glacier during a melt season. By scaling up our measurements across the ice sheet, we estimate that the annual DOC flux from the GrIS (0.08 Tg/y) is equivalent to that from a small Arctic river (discharge (Q) 200 km3/y). The DOC flux is derived primarily from beneath the glacier (subglacial) (>75\%) in the early season, and from surface ice-melt (up to 100\%) transmitting through the subglacial environment at the peak of the meltseason. The POC flux is primarily derived from the subglacial environment throughout the meltseason. The early season (low flow) glacier discharge contains higher DOC concentrations (0.5{\textendash}4.1 mg L-1), and exports more enriched carbon (Δ14CDOC \~{} -250{\textperthousand}) compared to the peak season (high flow) discharge, when the concentrations are lower (0.1{\textendash}0.6 mg L-1) and the Δ14C is more depleted (Δ14CDOC \~{} -400{\textperthousand}). Conversely, the POC export (1.4{\textendash}13.2 mg L-1, Δ14CPOC \~{} -250{\textperthousand}) shows no temporal variation in either concentration or radiocarbon content throughout the meltseason. Dissolved ion loads in concomitant samples reflected the seasonal evolution of the subglacial drainage system, confirming the influence of subglacial hydrology on the composition of the bulk carbon pools. Based on this work, we conclude that (1) different mechanisms control the DOC and POC flux from glacial systems; (2) chemically-distinct DOC pools are accessed by seasonally-evolving hydrological flow-paths; and (3) the GrIS can deliver labile carbon, which may also be 14C-depleted, to downstream proglacial and marine environments.},
	issn = {0016-7037},
	doi = {10.1016/j.gca.2013.02.006},
	url = {http://www.sciencedirect.com/science/article/pii/S0016703713000835},
	author = {Bhatia, Maya P. and Das, Sarah B. and Xu, Li and Charette, Matthew A. and Wadham, Jemma L. and Kujawinski, Elizabeth B.}
}
@article {121,
	title = {Correction to" Isotopic characterization of aerosol organic carbon components over the eastern United States" (vol 117, D13303, 2012)},
	journal = {Journal of Geophysical Research-Atmospheres},
	volume = {117},
	year = {2012},
	note = {id: 2251; PT: J; TC: 0; UT: WOS:000307471700004},
	pages = {D15399-D15399},
	issn = {0148-0227},
	doi = {10.1029/2012JD018478},
	author = {Wozniak, Andrew S. and Bauer, James E. and Dickhut, Rebecca M. and Xu, Li and McNichol, Ann P.}
}
@article {122,
	title = {Isotopic characterization of aerosol organic carbon components over the eastern United States},
	journal = {Journal of Geophysical Research-Atmospheres},
	volume = {117},
	year = {2012},
	note = {id: 2252; PT: J; TC: 1; UT: WOS:000306237000001},
	pages = {D13303-D13303},
	abstract = {Carbon isotopic signatures (delta C-13, Delta C-14) 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) delta C-13 values (-27 to -24 parts per thousand) indicated predominantly terrestrial C-3 plant and fossil derived sources. Total solvent extracts (TSE) and their aliphatic, aromatic, and polar OC components were depleted in delta C-13 (-30 to -26 parts per thousand) relative to TOC and WSOC. Delta C-14 signatures of aerosol TOC and TSE (-476 to +25 parts per thousand) suggest variable fossil contributions (similar to 5-50\%) to these components. Aliphatic OC while comprising a small portion of the TOC (},
	issn = {0148-0227},
	doi = {10.1029/2011JD017153},
	author = {Wozniak, Andrew S. and Bauer, James E. and Dickhut, Rebecca M. and Xu, Li and McNichol, Ann P.}
}
@article { ISI:000299864400020,
	title = {Modern and Fossil Contributions to Polycyclic Aromatic Hydrocarbons in PM2.5 from North Birmingham, Alabama in the Southeastern U.S.},
	journal = {ENVIRONMENTAL SCIENCE \& TECHNOLOGY},
	volume = {46},
	number = {{3}},
	year = {2012},
	month = {FEB 7},
	pages = {1422-1429},
	type = {Article},
	abstract = {Analyzing the radiocarbon (C-14) content of polycyclic aromatic hydrocarbons (PAHs) in atmospheric particulate matter can provide estimates on the source contributions from biomass burning versus fossil fuel. The relative importance of these two sources to ambient PAHs varies considerably across regions and even countries, and hence there is a pressing need to apportion these sources. In this study, we advanced the radiocarbon analysis from bulk carbon to compound class specific radiocarbon analysis (CCSRA) to determine Delta C-14 and delta C-13 values of PAHs in PM2.5 samples for investigating biomass burning and fossil fuel source contributions to PAHs from one of the Southeastern Aerosol Research and Characterization (SEARCH) sites in North Birmingham (BHM), Alabama during winter (December 2004-February 2005) and summer (June-August 2005) by accelerator mass spectrometry. To compare our ambient samples to known sources, we collected and analyzed fenceline samples from the vicinity of a coke plant in BHM. As expected, PAHs from the coke plant fenceline samples had very low radiocarbon levels. Its Delta C-14 varied from -990 to -970 parts per thousand, indicating that 97 to 99\% were of fossil source. PAHs in the ambient PM2.5 had Delta C-14 from -968 to -911 parts per thousand, indicating that 92-97\% of PAHs were from fossil fuel combustion. These levels indicated the dominance of fossil sources of ambient PAHs. The radiocarbon level of ambient PAHs was higher in winter than in summer. Winter samples exhibited depleted delta C-13 value and enriched Delta C-14 value because of the increased contribution of PAHs from biomass burning source. However, biomass burning contributed more to heavier PAHs (modern source accounting for 6-8\%) than fighter ones with a modern contribution of 3\%.},
	issn = {0013-936X},
	doi = {10.1021/es2043189},
	author = {Xu, Li and Zheng, Mei and Ding, Xiang and Edgerton, Eric S. and Reddy, Christopher M.}
}
@article {164,
	title = {A two-dimensional, heart-cutting preparative gas chromatograph facilitates highly resolved single-compound isolations with utility towards compound-specific natural abundance radiocarbon (14C) analyses},
	journal = {Journal of Chromatography A},
	volume = {1220},
	year = {2012},
	note = {id: 2152},
	pages = {122-131},
	abstract = {Motivated by the need to develop clean, high purity preparative enrichments of individual compounds for micro-scale compound-specific natural abundance isotope and radiocarbon (14C) analyses, we describe a new, two-dimensional, heart-cutting, low-bleed, three-oven, single GC preparative system, demonstrate its resolving capabilities as applied to a typically complex environmental sample matrix, and investigate the robustness with which it preserves the authigenic 13C/12C and 14C/12C ratios of individual compounds it targets for preparative enrichment. The system is comprised of a programmable temperature vaporizing (PTV) inlet, a single GC oven, two modular, door-mounted, resistively heated low thermal mass (LTM) columns, a preparative fraction collector (PFC), and a Deans pneumatic switching device which facilitates heart-cutting between the system{\textquoteright}s 1{\textdegree} and 2{\textdegree} chromatographic dimensions. Further, the system{\textquoteright}s inlet and trapping parameters are optimized for the efficient preparative enrichment of the methyl ether and ester derivatives of the lignin phenol compound class. The lignin phenols include such compounds as the vanillyl and syringyl aldehydes, ethanones, and acids and are unrivaled biomarkers of terrestrial organic matter, some of which are also important components of fragrances and flavors. Using this suite of compounds, the suitability of this augmented preparative capillary GC (PCGC) system was investigated for micro-scale compound-specific (CS) stable isotope and natural abundance radiocarbon analyses (RA). Analysis of a >300 injection enrichment scheme reveals the instrument to fractionate 13C in predictable ways and to preserve the authigenic Δ14C of compounds it targets for preparative enrichment to within 6.7 {\textpm} 5.0{\textperthousand}, demonstrating the promising new utility of such systems towards micro-scale CSRA investigations for which clean and high resolution separation techniques are prerequisite.},
	issn = {0021-9673},
	doi = {10.1016/j.chroma.2011.11.021},
	url = {http://www.sciencedirect.com/science/article/pii/S0021967311017031},
	author = {Ball, Gregory Ian and Xu, Li and McNichol, Ann P. and Aluwihare, Lihini I.}
}
@article { ISI:000277965100004,
	title = {Coastal New England pilot study to determine fossil and biogenic formaldehyde source contributions using radiocarbon},
	journal = {JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES},
	volume = {115},
	year = {2010},
	month = {MAY 18},
	type = {Article},
	abstract = {Compound specific radiocarbon analyses of atmospheric formaldehyde are reported as fraction modern (Fm) for a limited number of winter and summer air samples collected in coastal southern New England in 2007. The 11 of 13 samples with Fm < 0.2 were collected under the influence of the semipermanent Bermuda high-pressure system with transport from the Washington, D. C., to New York City urban corridor. The two samples with Fm > 0.2 (max similar to 0.35) were collected on days with strong northwesterly flow and the least urban impact. The Fm data were combined with VOC observations from the Rhode Island Department of Environmental Management, estimates of oxygenated VOC (OVOC), and back trajectories to interpret the relative contributions of biogenic and fossil carbon sources. It is argued that CH2O sources were dominated by pollutant VOCs and OVOCs from upwind coastal cities as opposed to more local biogenic VOCs at the times of sample collection.},
	issn = {2169-897X},
	doi = {10.1029/2009JD012810},
	author = {Shen, Haiwei and Heikes, Brian G. and Merrill, John T. and McNichol, Ann P. and Xu, Li}
}
@article { ISI:000268455600046,
	title = {Radiocarbon Analysis of Atmospheric Formaldehyde Using Cystamine Derivatization},
	journal = {ANALYTICAL CHEMISTRY},
	volume = {81},
	number = {{15}},
	year = {2009},
	month = {AUG 1},
	pages = {6310-6316},
	type = {Article},
	abstract = {A compound specific radiocarbon analysis method was developed to evaluate the C-14 composition of atmospheric formaldehyde. In this method, gaseous formaldehyde was collected with a high-volume air sampler using glass-fiber filters pretreated with sodium bisulfite. Collected formaldehyde was then released into water and derivatized with cysteamine to thiazolidine. The thiazolidine was extracted into dichloromethane and concentrated by evaporation. Concentrated thiazolidine was separated from other compounds using preparative capillary gas chromatography and uniquely collected as a phosphate salt with a fraction collector. The C-14 composition of the salt was analyzed by accelerator mass spectrometry after combustion to CO2 and subsequent reduction to graphite. In a pilot study, ambient formaldehyde samples collected on the roof of the CACS building at Narragansett Bay Campus, Narragansett, RI, showed a significantly larger fraction of fossil carbon than modern carbon.},
	issn = {0003-2700},
	doi = {10.1021/ac9004666},
	author = {Shen, Haiwei and McNichol, Ann P. and Xu, Li and Gagnon, Alan and Heikes, Brian G.}
}
