@article {272,
	title = {Chemical and isotopic characterization of size-fractionated organic matter from cryoturbated tundra soils, northern Alaska},
	journal = {Journal of Geophysical Research-Biogeosciences},
	volume = {114},
	year = {2009},
	note = {id: 1828; 475IS Times Cited:0 Cited References Count:61Y},
	abstract = {Recent studies indicate a second layer of organic matter often accumulates in the lower active layer and upper permafrost in arctic tundra soils as a result of cryoturbation. In this study, cryoturbated organic matter was characterized using a combination of physical size fractionation and modern analytical techniques for elemental composition (C and N), stable isotopes (delta(13) C and delta N-15), radiocarbon content (Delta C-14), and molecular fingerprinting (pyrolysis-gas chromatography/mass spectrometry, Py-GC/MS). The results indicated that cryoturbated organic matter could be highly bioavailable. Soil organic matter (SOM) associated with fine sand particles was considered to be the organic carbon pool most sensitive to the changing climate. More organic matter is stabilized on clay minerals in arctic tundra soils compared to those in temperate and tropical soils. The bioavailable soluble organic matter extracted from cryoturbated soil was found to have significant long-term effects on carbon cycling. The similar molecular composition between cryoturbated and surface soil organic matter suggests that the vegetation cover has not significantly changed since the early Holocene. Furthermore, the SOM quality in moist acidic tundra was found to be higher than that of wet nonacidic tundra. With thawing permafrost and a deepening of the active layer, cryotrubated organic matter could reenter the biogeochemical cycles in the Arctic, resulting in a positive feedback to climate change.},
	issn = {0148-0227},
	doi = {10.1029/2008jg000846},
	author = {Xu, C. H. and Guo, L. D. and Ping, C. L. and White, D. M.}
}
@article {479,
	title = {Chemical and isotopic composition of high-molecular-weight dissolved organic matter from the Mississippi River plume},
	journal = {Marine Chemistry},
	volume = {114},
	year = {2009},
	note = {id: 1827; 465CM Times Cited:1 Cited References Count:51Y},
	pages = {63-71},
	abstract = {In order to examine the source and transformation of high-molecular-weight dissolved organic matter (HMW-DOM) in the mixing zone of the Mississippi River plume, HMW-DOM with sizes between 1 kDa and 0.2 mu m was collected along a salinity gradient using cross-flow ultrafiltration. Isolated OM samples were desalted, freeze-dried and characterized for elemental (C and N) and biochemical composition (proteins, carbohydrates and uronic acids), stable isotopic (delta C-13 and delta N-15) and radiocarbon (Delta C-14) signatures, and relative molecular composition using pyrolysis-gas chromatography/mass spectrometry. The organic carbon content of HMW-DOM samples ranged from 31 to 36 wt.\%, indicating that isolated colloids are mostly organic in nature. Contents of N ranged from 1.9\% to 3.3\%, resulting in a C/N ratio of 19-20 at lower salinity stations with a strong influence by terrestrial DOM and 12-15 at higher salinity stations with more freshly photosynthesized marine DOM. While OC-normalized protein contents decreased with increasing salinity, both carbohydrate and uronic acid contents increased with increasing salinity. Variations of pyrograms demonstrated that the proportion of furfural (an indicator of polysaccharides) in HMW-DOM also increased with increasing salinity, while the proportion of phenols decreased with increasing salinity. Changes in carbohydrate, (acid) polysaccharide and phenol contents of HMW-DOM samples reflect the variation in DOM sources along the salinity gradient, with higher phenol and low polysaccharide contents in lower salinity areas but higher polysaccharide and low phenol contents in coastal waters. Values of delta C-13 increased from -25.24 parts per thousand at the Mississippi River fresh water end-member station to -21.86 parts per thousand at an offshore station in the Gulf of Mexico. Changes in stable isotope composition resemble the changes in molecular composition from freshwater to coastal waters. Values of delta N-15, on the other hand, varied little, from 3.5 parts per thousand to 4.9 parts per thousand without a consistent trend, indicating that delta N-15 is a less sensitive source tracer. Measured radiocarbon signatures (Delta C-14) expressed as apparent C-14 ages ranged from > modern at lower salinity stations to 400-800 y BP at coastal stations. Results of isotopic mass balance revealed that, in addition to end-member organic matter from river and marine sources, at least 10-25\% of the HMW-DOM could derive from reworked or regenerated DOM in the Mississippi River plume, most likely through sediment-water interactions and lateral transport. Thus, reworking processes are important in governing the chemical and isotopic composition of DOM in the estuarine mixing zone. (C) 2009 Elsevier B.V. All rights reserved.},
	issn = {0304-4203},
	doi = {10.1016/j.marchem.2009.04.002},
	author = {Guo, L. D. and White, D. M. and Xu, C. and Santschi, P. H.}
}
@article {270,
	title = {Pan-Arctic patterns in black carbon sources and fluvial discharges deduced from radiocarbon and PAH source apportionment markers in estuarine surface sediments},
	journal = {Global Biogeochemical Cycles},
	volume = {22},
	year = {2008},
	note = {id: 820; 307ZP Times Cited:3 Cited References Count:89Y},
	abstract = {A pan-arctic geospatial picture of black carbon (BC) characteristics was obtained from the seven largest arctic rivers by combining with molecular combustion markers (polycyclic aromatic hydrocarbons) and radiocarbon (C-14) analysis. The results suggested that the contribution from modern biomass burning to BC ranged from low in the Yukon (8\%) and Lena (5\%) Rivers to high in the Yenisey River (88\%). The Mackenzie River contributed almost half of the total arctic fluvial BC export of 202 kton a(-1) (kton = 10(9) g), with the five Russian-Arctic rivers contributing 10-36 kton a(-1) each. The C-14-based source estimate of fluvially exported BC to the Arctic Ocean, weighted by the riverine BC fluxes, amount to about 20\% from vegetation/biofuel burning and 80\% from C-14-extinct sources such as fossil fuel combustion and relict BC in uplifted source rocks. Combining these pan-arctic data with available estimates of BC export from other rivers gave a revised estimate of global riverine BC export flux of 26 x 10(3) kton a(-1). This is twice higher than a single previous estimate and confirms that river export of BC is a more important pathway of BC to the oceans than direct atmospheric deposition.},
	issn = {0886-6236},
	doi = {10.1029/2007gb002994},
	author = {Elmquist, M. and Semiletov, I. and Guo, L. D. and Gustafsson, O.}
}
@article {267,
	title = {Mobilization pathways of organic carbon from permafrost to arctic rivers in a changing climate},
	journal = {Geophysical Research Letters},
	volume = {34},
	year = {2007},
	note = {id: 773; 187WS Times Cited:23 Cited References Count:29Y},
	abstract = {[1] Arctic warming may cause the release of vast amounts of soil organic carbon (SOC) from permafrost, which will manifest itself in the fluxes and composition of organic carbon in northern rivers and Arctic coastal regions. To elucidate the transport pathways of SOC, radiocarbon composition was measured for dissolved organic carbon (DOC), particulate organic carbon (POC), sediments and SOC from the Mackenzie, Sagavanirktok, and Yukon river basins, and soil leaching experiments were conducted. The radiocarbon ages of riverine suspended POC and sediments ranged from 4430 to similar to 7970 yr BP, while DOC was much younger (390-1440 yr BP) except samples from the Sag River. Soil leaching experiments released},
	issn = {0094-8276},
	doi = {10.1029/2007gl030689},
	author = {Guo, L. D. and Ping, C. L. and Macdonald, R. W.}
}
@article {2049,
	title = {Characterization of Siberian Arctic coastal sediments: Implications for terrestrial organic carbon export},
	journal = {Global Biogeochemical Cycles},
	volume = {18},
	year = {2004},
	note = {806knTimes Cited:99
Cited References Count:51
},
	month = {Mar 10},
	abstract = {Surface sediments were collected during the 2000 TransArctic Expedition along the Siberian Arctic coastline, including the Ob, Yenisey, Khatanga, Lena, and Indigirka estuaries. Sediments were characterized for elemental composition (total organic carbon, TOC, black carbon, BC, and total N, as well as major and trace elements), isotopic signature (delta(13)C, delta(15)N, Delta(14)C, epsilon(Nd), Sr-87/Sr-86), and organic molecular composition to better understand river export variations over the large spatial scale of the Siberian Arctic. On average, 79 +/- 9\% of the total C in sediments was organic while 21 +/- 9\% was inorganic. BC made up 9 +/- 4\% of the TOC pool, with a general increasing trend from west to east along the Siberian coast. The combined Nd- and Sr-isotopes (epsilon(Nd) and Sr-87/Sr-86) were used to define two distinct sediment sources between east and west Siberian regions with the Khatanga River as a boundary. Data from pyrolysis-GC/MS of the sedimentary organic carbon (SOC) indicated an increase in the freshness of the organic matter from west to east on the Siberian Arctic coast, with increasing relative abundance of furfurals (polysaccharides) with respect to nitriles. Values for the delta(13)C of SOC ranged from -27.1\% (mostly terrigenous) to -23.8\%, while delta(15)N increased from east to west (3.1 to 5.2\%) with a significant correlation with C/N ratio. Values for the Delta(14)C of SOC ranged from -805 to -279\%, with a consistent trend increasing from the east (Indigirka River) to the west (Ob River). These D 14 C values corresponded to a 14 C age of 2570 +/- 30 yBP in the Ob estuary and 13,050 +/- 50 yBP in the Indigirka estuary. Most importantly, D 14 C values were significantly correlated with the ratio of BC/TOC (R-2 = 0.91, n = 6), consistent with the distribution pattern of increasing permafrost zone from the west to the east along the Siberian coast. Together, our results suggest that older OC was derived from the release of recalcitrant BC during permafrost thawing and riverbank and coastal erosion, likely enhanced by ongoing environmental changes in the northern ecosystem.},
	keywords = {arctic ocean, BLACK CARBON, climate, CO2, continental-shelf, flux, isotopic composition, lena river, MATTER, ocean, organic carbon, quantification, Sediment},
	isbn = {0886-6236},
	doi = {10.1029/2003GB002087},
	url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2\&amp;SrcAuth=Alerting\&amp;SrcApp=Alerting\&amp;DestApp=WOS\&amp;DestLinkType=FullRecord;UT=WOS:000220432900001},
	author = {Guo, L. D. and Semiletov, I. and Gustafsson, O. and Ingri, J. and Andersson, P. and Dudarev, O. and White, D.}
}
