@article {2869,
	title = {Radiocarbon age of different photoreactive fractions of freshwater dissolved organic matter},
	journal = {Organic Geochemistry},
	volume = {135},
	year = {2019},
	month = {Jan-09-2019},
	pages = {11 - 15},
	abstract = {Dissolved organic carbon (DOC) plays a major role in aquatic carbon cycling. In order to determine if DOC photolability was related to DOC age, we tested the effect of oxidation time using UV irradiation on natural radiocarbon concentrations (Δ14C) of DOC in six US rivers. The most photo-labile DOC was 14C youngest. After a 100 min UV irradiation, most DOC (>93\%) was oxidized in two out of the six rivers studied. On the other hand, the other four rivers still had a considerable amount (>20\%) of DOC resistant to UV oxidation, which showed lower Δ14C values than those of bulk DOC. We also found that the concentration and Δ14C value of bulk DOC are controlled by the photochemically intermediate fraction. The results suggest that 14C age of organic matter is not homogeneous within DOC, the degree of which may depend on the characteristics unique to rivers.},
	keywords = {dissolved organic carbon, Mixing model, Oxidation time, UV irradiation, Δ14C},
	issn = {01466380},
	doi = {10.1016/j.orggeochem.2019.06.006},
	url = {https://linkinghub.elsevier.com/retrieve/pii/S014663801930107X},
	author = {Ishikawa, Naoto F. and Butman, David and Raymond, Peter A.}
}
@article {2841,
	title = {Fossil Fuel Combustion Emission From South Asia Influences Precipitation Dissolved Organic Carbon Reaching the Remote Tibetan Plateau: Isotopic and Molecular Evidence},
	journal = {Journal of Geophysical Research: Atmospheres},
	volume = {123},
	year = {2018},
	month = {Apr-06-2019},
	pages = {6248 - 6258},
	abstract = {The dissolved organic carbon in precipitation (water-soluble organic carbon, WSOC) can provide a carbon subsidy to receiving ecosystems. The concentrations, isotopic signatures (δ13C/Δ14C), and molecular signatures (transform ion cyclotron mass spectrometry) of WSOC being delivered to Nam Co{\textemdash}a remote site on the inland Tibetan Plateau (TP){\textemdash}were compared to those of WSOC in the snowpack, and in wet deposition from urban cities fringing the TP. The average WSOC concentration at Nam Co (1.0 {\textpm} 0.9 mg C L-1) was lower than for the large cities (1.6 to 2.3 mg C L-1) but higher than in the snowpack samples (0.26 {\textpm} 0.09 mg C L-1). Based upon radiocarbon data, it is estimated that 15 {\textpm} 6\% of Nam Co WSOC was fossil derived, increasing to 20 {\textpm} 8\% for snowpack WSOC, 29 {\textpm} 4\% for Lhasa WSOC, and 34 {\textpm} 8\% for the three cities. Transform ion cyclotron mass spectrometry results revealed that the abundance of dissolved black carbon and sulfur-containing molecules of WSOC increased in the order Nam Co < snow pack < urban. The enrichment in 14C and depletion in dissolved black carbon and sulfurous organic molecules of Nam Co WSOC was suggestive of low, but still detectable inputs of fossil-derived organics to WSOC on the remote TP. Backward air mass trajectories for the precipitation events at Nam Co suggested that the fossil fuel contributions to WSOC in Nam Co region originated mainly from South Asia. This study provides novel radiocarbon age, chemistry, and source evidence that anthropogenic WSOC is delivered to the remote TP, one of the most remote regions on Earth.},
	doi = {10.1029/2017JD028181},
	url = {http://doi.wiley.com/10.1029/2017JD028181},
	author = {Li, Chaoliu and Chen, Pengfei and Kang, Shichang and Yan, Fangping and Tripathee, Lekhendra and Wu, Guangjian and Qu, Bin and Sillanp{\"a}{\"a}, Mika and Yang, Di and Dittmar, Thorsten and Stubbins, Aron and Raymond, Peter A.}
}
@article {2718,
	title = {Riverine Export of Aged Carbon Driven by Flow Path Depth and Residence Time},
	journal = {Environmental Science \& Technology},
	volume = {52},
	year = {2018},
	month = {Jun-02-2018},
	pages = {1028 - 1035},
	abstract = {The flux of terrestrial C to rivers has increased relative to preindustrial levels, a fraction of which is aged dissolved organic C (DOC). In rivers, C is stored in sediments, exported to the ocean, or (bio)chemically processed and released as CO2. Disturbance changes land cover and hydrology, shifting potential sources and processing of DOC. To investigate the likely sources of aged DOC, we analyzed radiocarbon ages, chemical, and spectral properties of DOC and major ions from 19 rivers draining the coterminous U.S. and Arctic. DOC optics indicated that the majority is exported as aromatic, high molecular weight, modern molecules while aged DOC tended to consist of smaller, microbial degradation products. Aged DOC exports, observed regularly in arid basins and during base flow in arctic rivers, are associated with higher proportion of mineral weathering products, suggesting deeper flows paths. These patterns also indicate potential for production of microbial byproducts as DOC ages in soil and water with longer periods of time between production and transport. Thus, changes in hydrology associated with landscape alteration (e.g., tilling or shifting climates) that can result in deeper flow paths or longer residence times will likely lead to a greater proportion of aged carbon in riverine exports.},
	issn = {0013-936X},
	doi = {10.1021/acs.est.7b0471710.1021/acs.est.7b04717.s00110.1021/acs.est.7b04717.s002},
	url = {https://pubs.acs.org/doi/10.1021/acs.est.7b04717},
	author = {Barnes, Rebecca T. and Butman, David E. and Wilson, Henry F. and Raymond, Peter A.}
}
@article {2840,
	title = {Aged dissolved organic carbon exported from rivers of the Tibetan Plateau},
	journal = {PLOS ONE},
	volume = {12},
	year = {2017},
	month = {Feb-05-2019},
	pages = {e0178166},
	abstract = {The role played by river networks in regional and global carbon cycle is receiving increasing attention. Despite the potential of radiocarbon measurements (14C) to elucidate sources and cycling of different riverine carbon pools, there remain large regions such as the climate-sensitive Tibetan Plateau for which no data are available. Here we provide new 14C data on dissolved organic carbon (DOC) from three large Asian rivers (the Yellow, Yangtze and Yarlung Tsangpo Rivers) running on the Tibetan Plateau and present the carbon transportation pattern in rivers of the plateau versus other river system in the world. Despite higher discharge rates during the high flow season, the DOC yield of Tibetan Plateau rivers (0.41 gC m-2 yr-1) was lower than most other rivers due to lower concentrations. Radiocarbon ages of the DOC were older/more depleted (511{\textpm}294 years before present, yr BP) in the Tibetan rivers than those in Arctic and tropical rivers. A positive correlation between radiocarbon age and permafrost watershed coverage was observed, indicating that 14C-deplted/old carbon is exported from permafrost regions of the Tibetan Plateau during periods of high flow. This is in sharp contrast to permafrost regions of the Arctic which export 14C-enriched carbon during high discharge periods.},
	keywords = {Carbon cycle, Carbon dioxide, Climate change, Rain, Rivers, Surface water, Tibetan people, TIBETAN PLATEAU},
	doi = {10.1371/journal.pone.0178166},
	url = {https://dx.plos.org/10.1371/journal.pone.0178166},
	author = {Qu, Bin and Sillanp{\"a}{\"a}, Mika and Li, Chaoliu and Kang, Shichang and Stubbins, Aron and Yan, Fangping and Aho, Kelly Sue and Zhou, Feng and Raymond, Peter A.},
	editor = {Lin, Senjie}
}
@article {2697,
	title = {The experimental flow to the Colorado River delta: Effects on carbon mobilization in a dry watercourse},
	journal = {Journal of Geophysical Research: Biogeosciences},
	volume = {122},
	year = {2017},
	month = {Jan-03-2017},
	pages = {607 - 627},
	abstract = {Here we report on the effects of an experimental flood on the carbon cycling dynamics in the dry watercourse of the Colorado River in Mexico. We observed post-flood differences in the degree of decay, age, and concentration of dissolved organic carbon (DOC), as well as dissolved CH4 and CO2 concentrations throughout the study site. Our results indicate that this flooded waterway was a limited source of CH4 and CO2 to the atmosphere during the event and that DOC age increased with time of flooding. Based on our findings, we suggest that the interplay between storage and mobilization of carbon and greenhouse gases in arid and semiarid regions is potentially sensitive to changing climate conditions, particularly hydrologic variability. Changes in the radiocarbon age of DOC throughout the flooding event suggest that organic matter (OM) that had been stored for long periods (e.g., millennial) was mobilized by the flooding event along with CO2. The OM residing in the dry riverbed that was mobilized into floodwaters had a signature reflective of degraded vascular plant OM and microbial biomass. Whether this microbial OM was living or dead, our findings support previous work in soils and natural waters showing that microbial OM can remain stable and stored in ecosystems for long time periods. As human appropriation of water resources continues to increase, the episodic drying and rewetting of once natural riverbeds and deltas may fundamentally alter the processing and storage of carbon in such systems.},
	keywords = {carbon cycling, Colorado River, dry watercourse, flooding, greenhouse gases, mobilization},
	doi = {10.1002/2016JG003555},
	url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2016JG003555},
	author = {Bianchi, Thomas S. and Butman, David and Raymond, Peter A. and Ward, Nicholas D. and Kates, Rory J. S. and Flessa, Karl W. and Zamora, Hector and Arellano, Ana R. and Ramirez, Jorge and Rodriguez, Eliana}
}
@article {2461,
	title = {Spatial Variation in the Origin of Dissolved Organic Carbon in Snow on the Juneau Icefield, Southeast Alaska},
	journal = {Environmental Science \& Technology},
	volume = {49},
	year = {2015},
	month = {Jun-10-2015},
	pages = {11492 - 11499},
	abstract = {Dissolved organic carbon (DOC) plays a fundamental role in the biogeochemistry of glacier ecosystems. However, the specific sources of glacier DOC remain unresolved. To assess the origin and nature of glacier DOC, we collected snow from 10 locations along a transect across the Juneau Icefield, Alaska extending from the coast toward the interior. The Δ14C-DOC of snow varied from -743 to -420{\textperthousand} showing progressive depletion across the Icefield as δ18O of water became more depleted (R2 = 0.56). Older DOC corresponded to lower DOC concentrations in snow (R2 = 0.31) and a decrease in percent humic-like fluorescence (R2 = 0.36), indicating an overall decrease in modern DOC across the Icefield. Carbon isotopic signatures (13C and 14C) combined with a three-source mixing model showed that DOC deposited in snow across the Icefield reflects fossil fuel combustion products (43{\textendash}73\%) and to a lesser extent marine (21{\textendash}41\%) and terrestrial sources (1{\textendash}26\%). Our finding that combustion aerosols are a large source of DOC to the glacier ecosystem during the early spring (April{\textendash}May) together with the pronounced rates of glacier melting in the region suggests that the delivery of relic DOC to the ocean may be increasing and consequently impacting the biogeochemistry of glacial and proglacial ecosystems in unanticipated ways.},
	issn = {0013-936X},
	doi = {10.1021/acs.est.5b02685},
	url = {http://pubs.acs.org/doi/10.1021/acs.est.5b02685http://pubs.acs.org/doi/pdf/10.1021/acs.est.5b02685},
	author = {Fellman, Jason B. and Hood, Eran and Raymond, Peter A. and Stubbins, Aron and Spencer, Robert G.M.}
}
@article {2459,
	title = {Source and biolability of ancient dissolved organic matter in glacier and lake ecosystems on the Tibetan Plateau},
	journal = {Geochimica et Cosmochimica Acta},
	volume = {142},
	year = {2014},
	month = {Jan-10-2014},
	pages = {64 - 74},
	abstract = {The Tibetan Plateau is the world{\textquoteright}s largest and highest plateau and holds the largest mass of ice on Earth outside the ice-sheets of Greenland and Antarctica, as well as abundant lakes. This study examined the molecular and isotopic signatures of dissolved organic matter (DOM) along with its biolability in glacier ice, glacier-fed streams, and alpine lakes on the Tibetan Plateau. The aim was to assess the sources of DOM and the potential of DOM to provide a carbon subsidy to downstream ecosystems. Tibetan glaciers and glacier streams exhibited low dissolved organic carbon (DOC) concentrations (17.7{\textendash}27.9 μM) and ancient DOC radiocarbon ages (749{\textendash}2350 ybp). The optical properties, stable carbon isotope ratios (δ13C-DOC) and the molecular composition (Fourier transform ion cyclotron resonance mass spectrometry) of Tibetan glacier DOM are consistent with data from other glacier systems around the world. The geochemical signatures and the ancient apparent ages of Tibetan glacier DOM suggest a significant fraction is derived from the atmospheric deposition of pre-aged, possibly fossil fuel derived organics. Within the Tibetan alpine lakes, DOC was also ancient (525{\textendash}675 ybp), due to either inputs of pre-aged organics from glacier runoff, direct deposition, or due to the aging of organics in situ (i.e. a radiocarbon reservoir effect). The glacier ice and glacier stream sites exhibited high biolability of DOC and so provide a carbon subsidy to downstream environments that will change as glaciers on the Tibetan Plateau recede.},
	issn = {00167037},
	doi = {10.1016/j.gca.2014.08.006},
	url = {http://linkinghub.elsevier.com/retrieve/pii/S0016703714005018http://api.elsevier.com/content/article/PII:S0016703714005018?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0016703714005018?httpAccept=text/plain},
	author = {Spencer, Robert G.M. and Guo, Weidong and Raymond, Peter A. and Dittmar, Thorsten and Hood, Eran and Fellman, Jason and Stubbins, Aron}
}
@article {2458,
	title = {Anthropogenic aerosols as a source of ancient dissolved organic matter in glaciers},
	journal = {Nature Geoscience},
	volume = {5},
	year = {2012},
	month = {Jul-02-2013},
	pages = {198 - 201},
	abstract = {Glacier-derived dissolved organic matter represents a quantitatively significant source of ancient, yet highly bioavailable carbon to downstream ecosystems1. This finding runs counter to logical perceptions of age{\textendash}reactivity relationships, in which the least reactive material withstands degradation the longest and is therefore the oldest2. The remnants of ancient peatlands and forests overrun by glaciers have been invoked as the source of this organic matter1, 3, 4. Here, we examine the radiocarbon age and chemical composition of dissolved organic matter in snow, glacier surface water, ice and glacier outflow samples from Alaska to determine the origin of the organic matter. Low levels of compounds derived from vascular plants indicate that the organic matter does not originate from forests or peatlands. Instead, we show that the organic matter on the surface of the glaciers is radiocarbon depleted, consistent with an anthropogenic aerosol source. Fluorescence spectrophotometry measurements reveal the presence of protein-like compounds of microbial or aerosol origin. In addition, ultrahigh-resolution mass spectrometry measurements document the presence of combustion products found in anthropogenic aerosols. Based on the presence of these compounds, we suggest that aerosols derived from fossil fuel burning are a source of pre-aged organic matter to glacier surfaces. Furthermore, we show that the molecular signature of the organic matter is conserved in snow, glacier water and outflow, suggesting that the anthropogenic carbon is exported relatively unchanged in glacier outflows.},
	keywords = {Atmospheric chemistry, Biogeochemistry, Cryospheric science},
	issn = {1752-0894},
	doi = {10.1038/ngeo1403},
	url = {http://www.nature.com/doifinder/10.1038/ngeo1403},
	author = {Stubbins, Aron and Hood, Eran and Raymond, Peter A. and Aiken, George R. and Sleighter, Rachel L. and Hernes, Peter J. and Butman, David and Hatcher, Patrick G. and Striegl, Robert G. and Schuster, Paul and Abdulla, Hussain A. N. and Vermilyea, Andrew W. and Scott, Durelle T. and Spencer, Robert G. M.}
}
@article { ISI:000290199000003,
	title = {Multiple-source heterotrophy fueled by aged organic carbon in an urbanized estuary},
	journal = {MARINE CHEMISTRY},
	volume = {124},
	number = {{1-4}},
	year = {2011},
	month = {MAR 20},
	pages = {14-22},
	type = {Article},
	abstract = {The lower Hudson River is a highly urbanized estuary that receives large inputs of treated wastewater. To determine how organic matter from wastewater influences carbon cycling in this type of system, we measured chlorophyll a, pCO(2). dissolved organic carbon (DOC), delta(13)C-DOC, and Delta(14)C-DOC along the salinity gradient and at wastewater treatment plants. Isotopic mixing curves indicate a net removal of DOC that is (13)C enriched and (14)C depleted. The amount of DOC removed was consistent with CO(2) evasion from the estuary. During two transects at average to low flow, the lower Hudson River Estuary was a heterotrophic system with CO(2) evasion balanced by the utilization of aged DOC derived from wastewater and marine phytoplankton that enter the estuary at the seaward end-member. DOC removals were largest during a period of high river flow, when isotopic mixing curves also suggest large contributions from labile terrestrial OC sources. Overall, our results suggest that net heterotrophy in the lower Hudson River Estuary is fueled by aged labile DOC derived from a combination of sources, which are influenced by seasonal phytoplankton blooms, hydrological conditions, and the nature of wastewater inputs. (C) 2010 Elsevier B.V. All rights reserved.},
	keywords = {(13)C, (14)C, Carbon cycle, Carbon dioxide, Chlorophyll, dissolved organic carbon, Heterotrophy, Hudson River Estuary, Isotope mixing curves, Sewage, USA, Wastewater},
	issn = {0304-4203},
	doi = {10.1016/j.marchem.2010.11.003},
	author = {Griffith, David R. and Raymond, Peter A.}
}
@article {390,
	title = {Flux and age of dissolved organic carbon exported to the Arctic Ocean: A carbon isotopic study of the five largest arctic rivers RID C-4087-2009 RID C-5396-2008},
	journal = {Global Biogeochemical Cycles},
	volume = {21},
	year = {2007},
	note = {id: 2033; PT: J; UT: WOS:000250704000002},
	pages = {GB4011-GB4011},
	abstract = {The export and Delta C-14-age of dissolved organic carbon (DOC) was determined for the Yenisey, Lena, Ob{\textquoteright}, Mackenzie, and Yukon rivers for 2004 - 2005. Concentrations of DOC elevate significantly with increasing discharge in these rivers, causing approximately 60\% of the annual export to occur during a 2-month period following spring ice breakup. We present a total annual flux from the five rivers of similar to 16 teragrams (Tg), and conservatively estimate that the total input of DOC to the Arctic Ocean is 25 - 36 Tg, which is similar to 5-20\% greater than previous fluxes. These fluxes are also similar to 2.5 x greater than temperate rivers with similar watershed sizes and water discharge. Delta C-14-DOC shows a clear relationship with hydrology. A small pool of DOC slightly depleted in Delta C-14 is exported with base flow. The large pool exported with spring thaw is enriched in D14C with respect to current-day atmospheric Delta C-14-CO2 values. A simple model predicts that similar to 50\% of DOC exported during the arctic spring thaw is 1 - 5 years old, similar to 25\% is 6 - 10 years in age, and 15\% is 11 - 20 years old. The dominant spring melt period, a historically undersampled period, exports a large amount of young and presumably semilabile DOC to the Arctic Ocean.},
	issn = {0886-6236},
	doi = {10.1029/2007GB002934},
	author = {Raymond, Peter A. and McClelland, J. W. and Holmes, R. M. and Zhulidov, A. V. and Mull, K. and Peterson, B. J. and Striegl, R. G. and Aiken, G. R. and Gurtovaya, T. Y.}
}
