Influences of glacier melt and permafrost thaw on the age of dissolved organic carbon in the Yukon...

Influences of glacier melt and permafrost thawon the age of dissolved organic carbonin the Yukon River basinGeorge R Aiken1 Robert G M Spencer2 Robert G Striegl1 Paul F Schuster1 and Peter A Raymond3

1US Geological Survey Boulder Colorado USA 2Department of Earth Ocean andAtmospheric Science Florida StateUniversityTallahassee Florida USA 3Yale School of Forestry and Environmental Studies Yale University New Haven Connecticut USA

Abstract Responses of near-surface permafrost and glacial ice to climate change are of particular significancefor understanding long-term effects on global carbon cycling and carbon export by high-latitude northernrivers Here we report Δ14C-dissolved organic carbon (DOC) values and dissolved organic matter optical datafor the Yukon River 15 tributaries of the Yukon River glacial meltwater and groundwater and soil waterend-member sources draining to the Yukon River with the goal of assessing mobilization of aged DOC withinthe watershed Ancient DOC was associated with glacial meltwater and groundwater sources In contrastDOC from watersheds dominated by peat soils and underlain by permafrost was typically enriched in Δ14Cindicating that degradation of ancient carbon stores is currently not occurring at large enough scales toquantitatively influence bulk DOC exports from those landscapes On an annual basis DOC exported waspredominantly modern during the spring period throughout the Yukon River basin and became olderthrough summer-fall and winter periods suggesting that contributions of older DOC from soils glacialmeltwaters and groundwater are significant during these months Our data indicate that rapidly recedingglaciers and increasing groundwater inputs will likely result in greater contributions of older DOC in theYukon River and its tributaries in coming decades

1 Introduction

An important question in global carbon cycling is how climate change will alter the flux chemical naturereactivity and fate of dissolved organic matter (DOM) released from northern high-latitude watersheds andtransported in rivers to estuaries and coastal margins [Dittmar and Kattner 2003 Benner et al 2004 Strieglet al 2005 Holmes et al 2012] Riverine DOM is known to play important roles in many ecological andgeochemical processes associated with aquatic systems [Aiken 2014] however its fate in coastal oceansespecially with regard to carbon cycling remains poorly understood [Fichot and Benner 2014] Arctic and sub-Arctic river basins yield disproportionately large amounts of water and terrigenous DOM to northern seas andthe Arctic Ocean [Opsahl et al 1999 Benner et al 2004 Raymond et al 2007] and as northern high latitudeswarm the amount and chemical nature of DOM exported from these basins is expected to change withimportant ramifications for ecosystem biogeochemistry [Guo et al 2007Walvoord and Striegl 2007 Frey andMcClelland 2009] It is commonly assumed that as peat and soil organic matter are increasingly degradedolder and compositionally different DOM will be transported in waters draining these soils [Neff et al 2006]While the production and release of DOM in northern high-latitude and temperate systems is sensitive toclimate variability [Freeman et al 2001 Frey and Smith 2005 Davidson and Janssens 2006] quantitativeunderstanding of these processes is limited and to date little evidence for mobilization of permafrost-derivedDOM has been observed in major rivers [Benner et al 2004 Raymond et al 2007 Striegl et al 2007]

The 3340 km long Yukon River drains 854700 km2 of northwest Canada and Alaska and discharges intothe Bering Sea ultimately contributing DOM to the Arctic Ocean It is the longest free-flowing river in the worldand having little development is relatively pristine [Nilsson et al 2005] The export of DOMby the Yukon River tothe Bering Sea is strongly seasonally dependent [Striegl et al 2007 Spencer et al 2009] As observed in otherhigh-latitude northern rivers the Yukon has maximum dissolved organic carbon (DOC) concentrations inconjunction with the period of maximum discharge during the spring flush resulting in a significant proportionof the annual DOC export occurring during this relatively short time period [Raymond et al 2007 Holmes et al2012 Spencer et al 2009] Also DOC radiocarbon age (Δ14C) and composition are seasonally dependent and tiedto discharge in high-latitude northern rivers The oldest DOC is transported under ice in the winter and the

AIKEN ET AL copy2014 American Geophysical Union All Rights Reserved 525

PUBLICATIONSGlobal Biogeochemical Cycles

RESEARCH ARTICLE1010022013GB004764

Key Pointsbull Oldest DOC found in glacial meltwaterand groundwater dominated systems

bull Streams draining peat soils underlain bypermafrost enriched in modern carbon

bull Old carbon from thawing permafrostsoils not apparent in DOC data atthis time

Correspondence toG R Aikengraikenusgsgov

CitationAiken G R R G M Spencer R G StrieglP F Schuster and P A Raymond (2014)Influences of glacier melt and permafrostthaw on the age of dissolved organiccarbon in the Yukon River basin GlobalBiogeochem Cycles 28 525ndash537doi1010022013GB004764

Received 7 NOV 2013Accepted 21 APR 2014Accepted article online 29 APR 2014Published online 22 MAY 2014

Table 1 DOC Concentration Specific Ultraviolet Absorbance (SUVA254) δ13C-DOC and Δ14C-DOC Measurements for Samples Collected in the Yukon River

and its Tributariesa

Sample Site With Site NumberDistance From Yukon

Source at Atlin Lake (km) Dateb DOC (mg C L1) SUVA254 (LmgC m) δ13C (permil) Δ14C (permil) Age (yBP)

Yukon River Main Stem6 Yukon River at Whitehorse 232 82704 11 15 258 203 17199 Yukon River above White River 772 9204 20 18 261 124 95912 Yukon River below Stewart River 800 9304 21 20 208 78 55014 Yukon River at Eagle 1057 9604 25 22 241 64 42615 Yukon River above Circle AK 1343 82405 27 25 222 294 269116 Yukon River above Ft Yukon AK 1475 52005 93 34 269 76 Modern

6305 68 32 265 53 Modern22 Yukon River near Stevenrsquos Village 1874 32406 20 19 258 38 20528 Yukon River at Pilot Station AK 3294 81804 31 28 261 34 169

92204 31 27 268 59 38351305 122 29 267 68 Modern51705 166 30 242 67 Modern6105 107 37 270 65 Modern61405 77 34 250 41 Modern71205 61 31 264 17 2781605 46 25 272 49 30092705 77 32 271 14 3

Glaciated Catchments4 Atlin River 0 82604 10 10 275 453 47435 Nares River 101 82504 12 18 259 223 192027 Tanana River at Nenana 2121 51505 53 30 ND 191 1599

52705 31 26 265 112 84932306 12 20 ND 254 2246

26 Tanana River at Delta Junction na 32306 10 ND ND 312 289825 Clearwater River na 32506 05 12 160 340 3235

Blackwaters13 Fortymile River 975 9504 157 33 275 3 Modern19 Porcupine River na 51505 280 32 273 109 Modern

52505 150 35 275 96 Modern82605 68 27 271 7 Modern

23 Hess Creek na 51305 261 37 271 20 Modern52105 32 38 244 92 Modern

18 Black River na 51405 234 35 274 101 Modern52605 109 34 273 67 Modern6206 123 36 275 80 Modern

Nonglaciated Clearwaters7 Big Salmon River 392 83004 18 18 260 101 7538 Pelly River 628 9104 26 21 263 101 74110 White River 778 9204 17 21 278 101 75311 Stewart River 795 9304 22 21 237 71 49120 Christian River na 82705 56 25 269 12 Modern21 Chandalar River na 82705 20 17 265 85 60217 Sheenjek River na 82605 16 16 269 129 1006

Glacial Waters24 Gulkana Glacier 22ndash24 cm na 42606 ND ND ND 650 831624Gulkana Glacier 45ndash70 cm ND ND ND 521 317424 Gulkana Glacier 80ndash90 cm ND ND ND 335 58061 Atlin Lake 2 0 7606 ND ND ND 681 90652 Atlin Lake 3 ND ND ND 677 89753 Atlin Lake 4 ND ND ND 718 10058

a(na = not applicable ND=not determined)bDates are formatted as monthdayyear

Global Biogeochemical Cycles 1010022013GB004764


youngest DOC is exported during the spring flush when discharge is greatest and there is a strong contributionof terrigenous organic matter [Neff et al 2006 Raymond et al 2007 Striegl et al 2007 Spencer et al 2008 2009]

In combination with DOM chemistry data information about Δ14C content is relevant for identifying sources ofDOM and understanding watershed processes [Butman et al 2012 Spencer et al 2012b] The majority of Δ14Cand DOM export data available for major rivers has been reported for samples collected at the mouths of therivers [eg Raymond and Bauer 2001 Raymond et al 2007 Butman et al 2012 Spencer et al 2012a Hosslerand Bauer 2013] However more detailed analyses of watersheds are required to resolve uncertainties inunderstanding the drivers responsible for this export and to anticipate future changes in DOM composition andflux Here we present Δ14C-DOC data obtained from the major tributaries and the main stem of the YukonRiver The Yukon River basin is diverse with respect to tributaries draining different source areas common tonorthern high latitudes (eg glaciers mountainous uplands forested lowlands and peatlands) As such it is wellsuited to address the variability of contributions from these sources on the age and composition of DOM Ourgoals therefore were to assess the age and chemical quality of current contributions of DOM from tributaries tothe main stem of the Yukon River to improve understanding of how future changes in climate might impactthe nature of DOM exported from these and other similar high-latitude watersheds draining to the ArcticOcean and to establish baseline data against which future changes may be assessed

2 Materials and Methods21 Sample Sites and Collection

The Yukon River and its tributaries have been the subject of intensive US Geological Survey (USGS) investigationssince 2001 [Schuster et al 2011] Water samples were collected between August 2004 and July 2006 for DOCconcentration DOC optical properties and DOC isotopic composition (δ13C and Δ14C) throughout the YukonRiver basin at different locations on themain stem of the Yukon River (from near the headwaters to just above thehead of tidal influence at Pilot Station) from a range of tributaries incorporating groundwater-dominatedclearwaters peat-dominated blackwaters and glacial meltwaters (Table 1 and Figure 1) Additional samples werecollected through September 2008 for DOC concentration and DOC optical property analyses Samples werefiltered in the field (045μm) and shipped on ice to the USGS laboratory in Boulder Colorado for DOC UV-visibleand fluorescence analyses and to Yale University for isotope analyses For a subset of samples particulate organiccarbon (POC) samples were obtained by filtering 300 mL of water through prebaked glass fiber filters (07 μm)Filters were frozen and shipped to Yale University

Figure 1 Map of the Yukon River basin showing measurement station locations and the watershed boundaries for thePorcupine River and Tanana River watersheds Site identification data for numbered sites can be found in Table 1



22 Dissolved Organic Matter Analyses

DOCmeasurements were performed on an OI Analytical Model 700 total organic carbon analyzer [Aiken 1992]UV-visible absorbance was measured at room temperature on a Hewlett-Packard photodiode arrayspectrophotometer (model 8453) between 200 and 800 nm Absorbance data are expressed as decadal (linear)absorption coefficients determined at λ=254 nm (a254) in units of cm1 and were determined by dividing theabsorbance (A(254)) by the cell path length (l) in centimeters [Braslavsky 2007] Specific UV absorbance(SUVA254) values a measure of DOC aromaticity were determined by dividing the UV absorbance measured atλ=254 nm by the DOC concentration [Weishaar et al 2003] Fluorescence data were obtained on whole watersamples diluted to an A(254) of lt 02 absorbance units (AU) using a Horiba-JY Fluoromax-3 spectrofluorometerwith DataMax software Fluorescence excitation emission matrices (EEMs) were measured at room temperatureon aqueous samples by measuring fluorescence intensity across excitation wavelengths ranging from 240 to450 nm (5 nm intervals) and emission wavelengths ranging from 300 to 600 nm (2 nm intervals) Excitation andemission slit widths were 5 nm and the instrument was configured to collect fluorescence scans in ratiomode Both fluorescence EEMs and absorbance scans were blank-corrected with Milli-Q water and EEMswere Raman normalized and corrected for any inner-filter effects [McKnight et al 2001 Murphy et al 2010]

23 Organic Carbon Isotopic Analyses

Carbon isotopic analyses were performed using methods described previously [Raymond and Bauer 2001]Briefly river water (120 mL) was placed into a clean quartz tube and acidified with 02 mL of ultrahigh purity(UHP) 40phosphoric acid The samples were then spargedwith UHP nitrogen to remove any inorganic carbonPure UHP O2 was subsequently sparged through the system to provide an oxidant for the UV oxidation of DOCThe sample was then oxidized with UV The resulting CO2 was transferred to a vacuum line and cryogenicallypurified For POC samples filters were acidified overnight with 1 concentrated sulfurous acid to removecarbonates thoroughly dried and the POC oxidized to CO2 by dry combustion with CuO and Ag metal at 850degCin 9 mm quartz tubes [Raymond and Bauer 2001] For both DOC and POC samples purified CO2 gas sampleswere converted to graphite targets by reducing CO2 with an iron catalyst under 1 atm H2 at 550degC and thetargets were subsequently analyzed for carbon isotopes (δ13C inpermil and 14C as fraction modern carbon) at theNational Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility at the Woods Hole OceanographicInstitution or the University of Arizonarsquos AMS facility Δ14C data (inpermil) were corrected for isotopic fraction usingmeasured δ13C values for those cases where a δ13C measurement was unavailable a value of25permilwas usedΔ14C and radiocarbon age were determined from percent modern carbon using the year of sample analysisaccording to Stuiver and Polach [1977] Ages are presented as Modern when the fraction modern exceeded 1

3 Results and Discussion31 Age and Composition of Dissolved Organic Matter in the Yukon River Basin

The most depleted Δ14C-DOC values (ie oldest DOC radiocarbon ages) in the Yukon River basin weremeasured in headwater streams and tributaries strongly influenced by glacial meltwater and groundwaterdischarge (Table 1) In the headwaters of the Yukon River old DOCwasmeasured in Atlin River (Δ14C=453permil)Nares River (Δ14C =223permil) and in the main stem of the Yukon River at Whitehorse (Δ14C =203permil)(Table 1) These rivers drain water predominantly from glaciers and ice fields in the Yukon Territory and BritishColumbia and also have a substantial amount of groundwater contribution to flow (31ndash38 of annualdischarge) [Walvoord and Striegl 2007] Ancient DOC (age range 850ndash3235 yBP) was also measured in riversreceiving groundwater that originates from glacial and snowpack meltwater in the Alaska Range includingthe Clearwater River (Δ14C =340permil) the largest spring-fed tributary of the Tanana River and the TananaRiver (Δ14C =112 to 312permil) DOC in meltwaters collected directly from Gulkana Glacier (Alaska Range(Δ14C =335 to650permil Table 1) which drains to the Yukon River via the Tanana River and Llewellyn Glacier(Juneau Icefield British Columbia) meltwaters in Atlin Lake (Δ14C =677 to718permil Table 1) were the oldestsamples found in our study ranging in age from about 3200ndash10000 yBP The Δ14C-DOC values for theseglacier-derived meltwaters are comparable to other reported values for a range of watersheds in southeastAlaska having varying contributions of glacier meltwater to downstream stream water [Hood et al 2009Stubbins et al 2012] In the most heavily glaciated watershed examined by Hood et al [2009] (Sheridan 64glacier cover) theΔ14C-DOC value was386permil which is similar to that observed in glaciated catchments andwaters in this study within the Yukon River basin (Table 1)



The concentrations of DOC in these glacially dominated sampleswere low (typically less than 12mg C L1) andDOM optical property data show little terrigenous signature as has been noted for other glacial systems [Sharpet al 1999 Hodson et al 2008 Hood and Scott 2008] Fluorescence EEMs (Figure 2) indicate the predominanceof a fluorophore (excitation270emission305) commonly associated with protein-like material (tyrosine) andsimple phenols and a marked absence of humic and fulvic-like fluorophores associated with vascular plant andupper soil horizon sources of DOM [Maie et al 2007 Hernes et al 2009 Fellman et al 2010a] (eg excitation λ260 nm emission λ 448ndash480 nm and excitation λ 320ndash360 nm emission λ 420ndash460 nm) This observation isfurther supported by low SUVA254 values (in general lt 20 L mg C1 m1) in the glacially dominated samples[Weishaar et al 2003] Our results are consistent with those reported for other glacial systems from a range oflocations [LaFreniere and Sharp 2004 Barker et al 2006Hood et al 2009 Stubbins et al 2012 Singer et al 2012]

a

b

d

e

fc

Figure 2 Fluorescence excitation emission spectra for (a) Atlin Lake (7606) (b) Clearwater River (32506) (c) Hess Creek (51706 (d) Yukon River at Pilot Station(11608) (e) Yukon River at Pilot Station (52808) and (f ) Yukon River at Pilot Station (92408)



Given that ice residence times for glaciers in the Juneau Icefield are estimated to be approximately 300 years(eg Mendenhall Glacier [Stubbins et al 2012]) it is unlikely that simple storage effects of DOC within theglaciers account for the age of the DOC (3200ndash10000 yBP) reported here DOM associated with precipitationhas been shown to be of sufficient concentrations and to contain a number of atmospherically transportedanthropogenic compounds depleted in 14C to strongly influence the signals we are observing in our glaciersamples [Raymond 2005 Jurado et al 2008 Yan and Kim 2012 Mead et al 2013] In particular glaciers areknown to accumulate anthropogenically derived compounds and act as sources of these compounds tosystems receiving glacial meltwaters [Blais et al 2001 Jenk et al 2006 Grannas et al 2006 Stubbins et al2012] Recent analyses of glacial DOM associated with the coastal maritime glaciers of the Juneau Icefieldand streams influenced directly by glacial meltwaters suggest that anthropogenic aerosols derived fromfossil fuel burning may be important sources of ancient DOM in our samples [Stubbins et al 2012]

Evidence that glacial meltwaters directly discharge into some rivers and streams in the Yukon River basin areto be found in the river discharge data Water discharge is highly seasonal throughout the Yukon River basinDischarge for rivers directly influenced by glacial meltwaters (eg Tanana River White River and Atlin River)typically peak during the summer (July) whereas discharges for nonglaciated rivers (eg Yukon River andPorcupine River) peak in MayndashJune [Striegl et al 2007] The situation for DOM delivered in ground water(eg Tanana River and Clearwater River winter samples) is more complicated since this pool of organicmatter can also be influenced by overlying soils and geologic materials such as formations containing shalesand coal which may also supply ancient carbon to the DOC pool Groundwater-bearing deposits in the TananaRiver basin however are primarily thick silt sand and gravel deposits [Pewe and Reger 1983] While theinfluence of geologic materials is not likely in this scenario they cannot be discounted at this time

In contrast blackwater rivers draining low-lying areas influenced by permafrost and containing organicmatter rich soils (eg Hess Creek Black River and Fortymile River Table 1) all contained modern DOCwith Δ14C ranging from 7 to 109permil (Table 1) DOC concentrations for these samples were much greater(68ndash320mg C L1) than those in rivers having large percentages of water fromglacial and groundwater sourcesand contained substantially more aromatic DOM as evidenced by high SUVA254 values (27ndash38 L mg C1 m1Table 1) and strong fluorescence signals associated with terrestrially derived organic matter (ie EEMsdominated by humic and fulvic-like fluorophores) (Figure 2) The fluorescence data and the high SUVA254

values associated with these samples indicate the presence of relatively unaltered organic matter derivedfrom leaf litter and upper soil horizons [Wickland et al 2007 Fellman et al 2010a] DOC associated with theserivers also contains elevated carbon-normalized yields of lignin phenols a biomarker for vascular plantsources [Spencer et al 2008]

Older DOC has been reported for rivers draining regions containing managed agricultural soils and degradedpeatlands supporting the hypothesis that the age of DOC can reflect the relative degree of oxidation of oldersoil organic matter [Evans et al 2007 Kalbitz and Geyer 2002 Moore et al 2013] Therefore our results indicatethat older DOM from peat or soils in permafrost-rich landscapes is not being mobilized and transported fromblackwater catchments within the Yukon River basin at this time in sufficient quantities to be reflected stronglyin the 14C-DOC signature This observation is perhaps surprising given that degradation of permafrost soils isknown to be occurring across northern latitudes For instance Vonk et al [2013] report very old (gt21000 years)highly biolabile DOC in thaw streams draining Siberian yedoma deposits although the influence of these smallstreams on the 14C-DOC signal in the Kolyma River a major river was not explored However as pointed out byVonk et al [2013] DOC from these small meltwater streams is subject to both high in-stream turnover anddilution by substantially greater flows in the Kolyma River which has an average discharge of 136 km3yearcompared to 208 km3year for the Yukon River [Holmes et al 2012] Each of these processes acts to mask thepresence of DOC from Yedoma sources when considering bulk 14C-DOC data

While our blackwater DOC samples were modern POC ages for the samples were relatively old Forty MileRiver (2213 yBP) Hess Creek (2861 yBP) Black River (1576 and 2585 yBP) and Porcupine River (1800 3849and 4728 yBP) These values are similar to those reported for deeper organic horizons and mineral soils in theactive layers of soil profiles obtained in the Hess Creek drainage [OrsquoDonnell et al 2011] suggesting thatdeeper soil horizons are being physically eroded however the link between these horizons and the exportof DOC from these soils is not apparent from the river samples Organic matter below the active layerreported by OrsquoDonnell et al [2011] was much older (Δ14C =800permil approximate age of 12500 years)



Samples from rivers draining nonglaciatedmountainous regions (eg Big Salmon Pelly andStewart) were younger in age than samples fromglaciated regions although older than modernwith Δ14C-DOC ranging from 12 to 129permil(Table 1) These samples which were collectedduring the late summer periods of 2004 and 2005typically had greater DOC concentrations andgreater SUVA254 values than the samples fromglaciated and groundwater dominated rivers butlower than those measured in blackwater rivers(Table 1) In the late summer period the influence oforganic matter derived from organic rich upper soilhorizons is much less than during the spring flushresulting in DOM that is less aromatic containsrelatively smaller amounts of high molecular weightaromatic moieties and exhibits lower lignin carbon-normalized yields than during the spring flush period[Striegl et al 2005 2007 Spencer et al 2008] The agesof these samples were similar to the age of a sampleof soil-ice meltwater collected below the organiclayer at a site near Fort Yukon (Δ14C-DOC=83permil593 yBP) This soil-ice meltwater sample also had aSUVA254 value (25 L mg C1 m1) similar to that inthe Yukon River at that time (26 L mg C1 m1) andis representative of OM leaching from deeper soilhorizons (ie different DOM source pools hydrologicflow paths and microbial mineralization rates oforganic matter) We previously showed that samplesin the Yukon River basin are depleted in ligninphenol concentrations and have lower lignin carbon-normalized yields under base flow conditions orwith increased contributions from glacial meltwateror groundwater [Spencer et al 2008 2009] Samplesare enriched during the spring flush period wheninputs from leached plant materials and upper soilhorizons dominate the DOM pool consistent withour findings here

32 Relationships Between Dissolved Organic Matter Composition and Age

For the samples in this study the relationship between DOC concentration and the absorption coefficientat λ=254 nm (a254) nmwas linear (R2 = 09927) similar to results published previously for a different subset ofsamples in this system [Spencer et al 2009] There is also a strong correlation between DOC concentrationand Δ14C-DOC (Figure 3a r= 086 plt 0001) and between a254 and Δ14C-DOC (Figure 3b r= 083 plt 0001These relationships are nonlinear because Δ14C is an intensive property with an upper limit imposed bythe modern carbon signal Almost all samples with a DOC concentrationgt 5 mg C L1 contain modern carbonwhereas those samples with DOC concentration lt 5 mg C L1 are depleted with respect to Δ14C-DOC(Figure 3a) DOC is predominantly modern above a threshold value for a254 of 02 cm1 (Figure 3b)

There is a broad relationship between SUVA254 and Δ14C-DOC (Figure 4) SUVA254 reflects the contributionof aromatic moieties to the optical signature of DOM [Butman et al 2012 Spencer et al 2012a Weishaaret al 2003] Figure 4 reinforces the aforementioned influence of organic matter derived from leaf litterand upper soil horizons on the age of DOC in these rivers The trend is similar to that observed in theKolyma River in Siberia [Neff et al 2006] for a much smaller range of SUVA254 (22 to 46 L mg C1 m1) and

DOC (mg L-1)

0 5 10 15 20 25 30 35

4 C-D

OC

(o oo

)

-500

-400

-300

-200

-100

0

100

200

a254 (cm-1)

00 02 04 06 08 10 12 14

4 C-D

OC

(o oo

)

-500

-400

-300

-200

-100

0

100

200

R = 086 p lt 0001

R = 083 p lt 0001

a)

b)

Figure 3 (a) Dissolved organic carbon and (b) the absorptioncoefficient a254 plotted against Δ14C-DOC for samples fromthe Yukon River basin Tributary samples are groupedaccording to source water type black circles = Yukon mainstem white squares = glacial waters light grey triangles =blackwaters and inverted dark grey triangles = clearwaters



Δ14C-DOC (88 to +150permil) values Foreach river modern high SUVA254 DOMwas associatedwith elevated flowperiodssuch as during the spring freshet DOMbecomes both less aromatic and olderwith declining discharge as the balancebetween different DOM sources shiftsto favor deeper soil horizons andgroundwater and for the Yukon Riversystem glacial meltwaters

The trend observed for samplesthroughout the Yukon River basin isalso generally similar to SUVA254 andΔ14C-DOC data obtained for samplescollected across the hydrograph at themouths of 15 large temperate NorthAmerican rivers (Figure 4) [Butmanet al 2012] These data are presentedhere to illustrate some commonpatterns regarding DOC age and opticalcharacteristics in riverine systemsNotably modern DOM and high-averageSUVA254 values are characteristic ofsystems with high productivity andprecipitation (eg Atchafalaya River)underscoring the importance of wetlands

plant litter and surface soils in the mobilization of modern aromatic DOM In contrast rivers influencedsubstantially by groundwater contained older DOM with low-average SUVA254 values (eg Colorado River) Itis important to note that within basin trends between SUVA254 and Δ14C-DOC for these rivers were highlyvariable owing to substantial differences in hydrology watershed dynamics sources of DOM and anthropogenicinfluences [Butman et al 2012] Therefore caution is warranted in generalizing the use of DOM optical data toinfer DOC age for systems that have not been adequately characterized For example the St Lawrence Riversampled approximately 115 km downriver of Lake Ontario consistently contained low SUVA254 modern DOCdue to the autochthonous production of DOM within the Great Lakes

We previously established strong relationships between UV-visible absorption coefficients and lignin phenolconcentrations and subsequently used these relationships to refine the export of DOC and lignin phenolsfrom the Yukon River basin [Spencer et al 2008 2009] Optical measurements such as absorbance thatrequire small sample volumes are comparatively inexpensive and data are relatively abundant [Spencer et al2012b] compared to Δ14C-DOC data Optical properties may also be measured in situ at high temporalresolution [Spencer et al 2007 Bass et al 2011] Relationships between DOC absorption coefficients andlignin phenols DOC concentration or Δ14C-DOC are system dependent [Spencer et al 2012a] and potentiallysubject to change as dynamics within river basins change Here we utilize the relationship between a254 andΔ14C-DOC to infer information about the 14C content of DOC in the present-day Yukon River and itstributaries from the easily obtained and inexpensive a254 data with clear potential for developing a hightemporal resolution proxy in the future

The relative influences of glacial versus blackwater tributaries on the age of DOC can be seen in a comparisonof a254 data for the Tanana and Porcupine Rivers These rivers are the two largest tributaries to the YukonRiver with similar drainage areas in terms of size but with different catchment and DOC export characteristics[Striegl et al 2007] DOC concentrations and absorption coefficients for both rivers are heavily influencedby hydrologic controls [Striegl et al 2007 Spencer et al 2009 Figure 5] however a254 data indicate that formost of the year much older DOC is transported by the glacially influenced Tanana River than by thenonglaciated blackwater influenced Porcupine River (Figure 5a) With the exception of the low-flow winter

SUVA254 (LmgC m)

00 05 10 15 20 25 30 35 40 45 50

4 C-D

OC

(o oo

)

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

50

100

150

R2 = 066 p lt 0001

Figure 4 Graph showing the relationship between specific ultravioletabsorption (SUVA254) and Δ14C for samples across the Yukon River basin(black dots) 15 temperate rivers (white triangles) and the St LawrenceRiver (grey squares) Data for the temperate rivers and the St LawrenceRiver were previously reported by Butman et al [2012] The regression linewith associated statistics is for the Yukon River basin samples



period (presumably ground water) a254 for thePorcupine River either exceeded or approximated02 cm1 suggesting the export of young DOCfor most of the hydrograph whereas a254 wasmuch less for the Tanana River for most of theyear (Figure 5a) After peaking during springsnowmelt a254 steadily declines during thesummer-fall period in the Porcupine River Thismay be due in part to the influence of older Cstocks from thawing permafrost soils or it mayrepresent the combination of decreased flowsdirectly off the surface landscape coupled withincreasing influence of groundwater DOM as thehydrograph falls

Absorption coefficient data also indicate thatDOC is more depleted in Δ14C-DOC in the mainstem of the Yukon River at upper river locationsnear glacial sources and becomes progressivelyenriched as tributaries draining blackwatercatchments contribute DOM to the main stem ofthe Yukon (Figure 4b) For example absorptioncoefficient data for the Yukon River at Carmackslocated 500 km downstream from the headwatersof the river are much lower throughout theyear compared to a254 data measured at Eagle(1057 km from source) (Figure 5b) The relativeinfluences of different water sources on DOCcharacteristics within this system are mostapparent when comparing Δ14C-DOC data anddistance from source for samples collectedduring the same time period in the upper Yukonregion (Figure 6) The most depleted samples(eg Atlin River and Nares River) stronglyinfluence the upper Yukon River (eg Yukon Riverat Whitehorse Canada Location 6 Figure 1) TheYukon main stem becomes more enriched withrespect to Δ14C-DOC due to DOC additions fromnonglaciated rivers (eg Pelly Big Salmon andespecially the Stewart River) moving downstreamfrom the headwaters The Fortymile River at

975 km is the first significant blackwater tributary in the Yukon River basin and has modern DOC Beyond thispoint blackwater tributaries exert a strong influence on DOM composition in the Yukon River

33 Export of 14C-DOC to the Ocean

The oldest DOC reported near the mouth of the Yukon River at Pilot Station was measured during the wintermonths when low flow is dominated by groundwater (Table 1) Compositional changes in the DOM associatedwith these time periods are apparent in SUVA254 and fluorescence EEM data (Table 1 and Figures 2dndash2f) Ofsignificance is the presence of fluorophores associated with vascular plants and soil organic matter in additionto fluorophores indicative ofmicrobial sources in the Yukon River at Pilot Stationwinter sample suggesting thatcontributions of waters from nonglaciated catchments influence the DOC in the Yukon River even in winterwhen there is no surface water runoff These results are consistent with those reported byOrsquoDonnell et al [2012]who observed considerable variability in DOM composition under base flow conditions across 60 rivers andstreamswithin the Yukon River basin Differences among systemswere attributable to the relative contributionsof suprapermafrost and subpermafrost aquifers to individual rivers

01-Jan-05 01-Apr-05 01-Jul-05 01-Oct-05 01-Jan-0600

02

04

06

08

10

12


254

(cm

-1)

254

(cm

-1)

00

02

04

06

08

10

Date

a)

b)

Figure 5 Graphs showing absorption coefficient (a254) versusdate (a) for samples collected in 2005 from the PorcupineRiver (light grey triangles dashed line) and Tanana River (whitesquares solid line) and (b) for samples collected in 2004 fromthe Yukon River at Eagle Alaska (black diamonds dashed line)and Carmacks Yukon Territories (white circles solid line) Thehorizontal black line represents the a254 threshold value abovewhich DOC is predominantly modern (Figure 3b)



Based on 5 year averages (2001ndash2005) ofDOC exported by the Yukon River at PilotStation 13 was estimated to occur inthe winter (31 October to 30 April) 52in spring (1 May to 30 June) and 35 inthe summer-fall (1 July to 31 October)[Striegl et al 2007] Average a254 data forthese periods based on 11 years of data(2001ndash2011) are 007 plusmn 002 cm1 (n= 37)in winter 040 plusmn 013 cm1 (n=132) inspring and 016 plusmn 0052 cm1 (n= 60) insummer-fall periods Applying therelationship between a254 and Δ14C-DOC(Figure 3b) for samples from only YukonRiver at Pilot Station to these averageabsorbance values permits a tighteningof estimates of seasonal Δ14C-DOC exportthat have previously been based on onlya few data points This approach yieldsestimated values for average Δ14C of89permil (winter) 55permil (spring) and 7permil(summer-fall) The export of older DOCespecially during the summer-fall period

may indicate increased metabolism of soil-derived organic matter increased inputs from permafrost thaw atthe time of year when active layers are deepest andor the influence of greater glacial contributions insummer when glacial melting is at its annual peak

34 Implications of DOC Export to the Ocean From Glacial-Dissolved Organic Matter

Whereas the seasonal DOC export trend is similar to those for other major Arctic rivers (eg Lena Ob YeniseyMackenzie and Kolyma) DOC transported by the Yukon River is on average more depleted in Δ14C thansamples from the other major Arctic rivers [Raymond et al 2007] A possible reason for this difference is thatthe Yukon River is more heavily influenced by glacial meltwater than the other major Arctic rivers Thewatershed of the Yukon River has an estimated glacial surface area of 10500 km2 which is substantiallygreater than that of the major Siberian Arctic Rivers (eg Lena River 188 km2 Obrsquo River 1750 km2 andYenisey River 507 km2) [Dyurgerov and Carter 2004] In recent decades a number of the glacial tributariesin the Yukon River basin have exhibited increases in annual discharge due to increased glacier melt [Brabetsand Walvoord 2009] In addition the Yukon River flows east to west through the discontinuous permafrostzone whereas the other major Arctic rivers flow predominantly south to north A consequence of theorientation of the Yukon River is that permafrost underlies much of the Yukon River basin [Striegl et al 2007]and it is particularly vulnerable to permafrost degradation The Yukon River and its tributaries thereforerepresent a major sentinel river system for observing the effects of climatic change and any associatedincreased glacier melt and permafrost degradation signature in North America

Our work identifies glacially derived organic matter as an important source of old DOC in those catchmentsoriginating in ice and snowfields in the south central and southeastern portions of the Yukon River basinGlobally DOC currently frozen in glacial ice is a pool of organic matter that represents a potential sourceof relict carbon if mobilized by rapid glacial melting Glacier-derived DOC has been shown to be highlybiolabile and to represent an important source of reduced carbon to downstream freshwater and marineecosystems [Hood et al 2009 Fellman et al 2010b] In addition Dyurgerov and Carter [2004] demonstratedthat freshwater contributions from pan-Arctic glaciers exceeded those of rivers flowing into the ArcticOcean including the Yukon for the 1961ndash1998 period Presently little is known about the chemistry or fluxof DOM associated with these glacially derived waters although the presence of compounds from bothmicrobial and fossil fuel sources have been reported for glacial waters associated with the Juneau Icefield[Stubbins et al 2012]

Figure 6 Δ14C-DOC versus distance from source in the upper YukonRiver basin Black circles represent values from the Yukon River mainstem and white squares represent tributaries



4 Conclusions

All catchments within the Yukon River basin are subject to changes in DOC export related to climate effectsPresently drainages such as the Tanana are experiencing melting of Alpine glaciers and perennial snow fields[Arendt et al 2002] whereas drainages dominated by permafrost and organic-rich soils are experiencingpermafrost degradation the formation of thermokarst features and drying of areas where thermokarst lakeshave drained [Yoshikawa and Hinzman 2003 Riordan et al 2006 Jorgenson et al 2001 2006] Continuedglacier melting and permafrost thaw within different catchments could profoundly influence DOM chemistryand DOC export within the Yukon River basin by changing regional hydrology soil productivity andmicrobial activity While Alaskarsquos glaciers continue to melt at a rapid rate there are uncertainties about long-term permafrost thaw and its influence on carbon cycling and DOC export [Arendt et al 2002 Froese et al2008 Grosse et al 2011] It is anticipated that as permafrost thaws the groundwater contribution to overallriver flow throughout the Yukon River basin will increase substantially [Walvoord et al 2012] This changein hydrology is projected to result in decreased DOC concentrations and decreased SUVA254 values[OrsquoDonnell et al 2010 OrsquoDonnell et al 2012] Our results suggest that these changes will also result in moreΔ14C-depleted DOC in the river

For large Arctic rivers such as the Yukon the ability to observe and quantify changes in DOC composition andexport resulting from climate change is complicated by the diversity of subwatersheds large disparity indischarge between the river main stem and impacted tributaries and differences in the rates of processesdriving carbon cycling within subwatersheds As a result it is difficult to link changes in soil dynamics to DOCexport when sampling only at the mouths of large rivers As our data indicate however drainages withinthe Yukon River basin exhibit different DOM characteristics due to different geologic hydrologic andpermafrost influences A fruitful strategy for assessing climate-based influences in the Yukon River basintherefore is the identification and monitoring of smaller sentinel tributaries especially sensitive to the meltingof glaciers changes in watershed hydrology resulting from permafrost thaw andor the mobilization oforganic matter in permafrost soils currently below the active layer

ReferencesAiken G R (1992) Chloride interference in the analysis of dissolved organic carbon by the wet oxidation method Environ Sci Technol 26

2435ndash2439Aiken G R (2014) Dissolved organic matter in aquatic systems in Comprehensive Water Quality and Purification vol 1 edited by S Ahuja

pp 205ndash220 Elsevier doi101016B978-0-12-382182-900014-1Arendt A A K A Echelmeyer W D Harrison C S Lingle and V B Valentine (2002) Rapid wastage of Alaska glaciers and their contribution

to rising sea level Science 297 382ndash386Barker J D M J Sharp S J Fitzsimmons and Turner (2006) Abundance and dynamics of dissolved organic carbon in glacier systems

Arc Antarc Alpine Res 38 163ndash172 doi1016571523-0430(2006)38[163AADODOJ]20CO2Bass A M M I Bird M J Liddell and P N Nelson (2011) Fluvial dynamics of dissolved and particulate organic carbon during periodic

discharge events in a steep tropical rainforest catchment Limnol Oceanogr 56 2282ndash2292 doi104319lo20115662282Benner R B Benitez-Nelson K Kaiser and RMW Amon (2004) Export of terrigenous dissolved organic carbon from rivers to the Arctic Ocean

Geophys Res Lett 31 L05305 doi1010292003GL019251Blais J M D W Schindler D C G Muir M Sharp D Donald M Lafreniere E Braekevelt and W M J Strachan (2001) Melting glaciers

A source of persistent organochlorines to subalpine Bow Lake in Banff National Park Canada Ambio 30 410ndash415Brabets T P and M A Walvoord (2009) Trends in streamflow in the Yukon River basin from 1944 to 2005 and the influence of the Pacific

Decadal Oscillation J Hydrol 371 108ndash119 doi101016jjhydrol200903018Braslavsky S E (2007) Glossary of terms used in photochemistry 3rd ed Pure Appl Chem 79 293ndash465 doi101351pac200779030293Butman D P A Raymond K Butler and G Aiken (2012) Relationships between Δ

14C and the molecular quality of dissolved organic carbon

in rivers draining to the coast from the conterminous United States Global Biogeochem Cycles 26 GB4014 doi1010292012GB004361Davidson E A and I Janssens (2006) Temperature sensitivity of soil carbon decomposition and feedbacks to climate change Nature 440

165ndash173 doi101038nature04514Dittmar T and G Kattner (2003) The biogeochemistry of the river and shelf ecosystem of the Arctic Ocean A reviewMar Chem 83 103ndash120Dyurgerov M B and C L Carter (2004) Observational evidence of increases in freshwater inflow to the Arctic Ocean Arc Antarct Alp Res

36 117ndash122Evans C D C Freeman L G Cork D N Thomas B Reynolds M F Billett M H Garnett and D Norris (2007) Evidence against recent

climate-induced destabilization of soil carbon from14C analysis of riverine dissolved organic matter Geophys Res Lett 34 L07407

doi1010292007GL029431Fellman J B E Hood and R G M Spencer (2010a) Fluorescence spectroscopy opens new windows into dissolved organic matter dynamics

in freshwater ecosystems A review Limnol Oceanogr 55 2452ndash2462 doi104319lo20105562452Fellman J B R G M Spencer P J Hernes R T Edwards D V DrsquoAmore and E Hood (2010b) The impact of glacier runoff on the biodegradability

and biogeochemical composition of terrigenous dissolved organic matter in near-shore marine ecosystems Mar Chem 121 112ndash122doi101016jmarchem201003009

Fichot C G and R Benner (2014) The fate of terrigenous dissolved organic carbon in a river-influenced coastal marginGlobal Biogeochem Cycles28 doi1010022013GB004670

AcknowledgmentsThis study was supported by the UnitedStates Geological Survey NationalStream Quality Accounting Network(httpwaterusgsgovnasqan) and theUSGS National Research Program(httpwaterusgsgovnrp) RGMSacknowledges support from NSFgrants DEB-1145932 OPP-1107774and ANT-1203885 We wish to thankKenna Butler (USGS-Boulder) for analyticalassistance We also thank JonathanOrsquoDonnell of the US National ParkService and two anonymous reviewersfor their critical reviews of the manu-script Any use of trade firm or productnames is for descriptive purposes onlyand does not imply endorsement by theUS Government



Freeman C C D Evans D T Monteith B Reynolds and N Fenner (2001) Export of organic carbon from peat soils Nature 412 785Frey K E and J W McClelland (2009) Impacts of permafrost degradation on arctic river biogeochemistry Hydrol Proc 23 169ndash182

doi101002hyp7196Frey K E and L C Smith (2005) Amplified carbon release from vast West Siberian peatlands by 2100 Geophys Res Lett 32 L09401

doi1010292004GL022025Froese D G J A Westgate A V Reyes R J Enkin and S J Preece (2008) Ancient permafrost and a future warmer Arctic Science 321 1648

doi101126science1157525Grannas A M W C Hockaday P G Hatcher L G Thompson and E Mosley-Thompson (2006) New revelations on the nature of organic

matter in ice cores J Geophys Res 111 D04304 doi1010292005JD006251Grosse G et al (2011) Vulnerability of high-latitude soil organic carbon in North America to disturbance J Geophys Res 116 G00K06

doi1010292010JG001507Guo L C L Ping and R W Macdonald (2007) Mobilization pathways of organic carbon from permafrost to Arctic rivers in a changing

climate Geophys Res Lett 34 L13603 doi1010292007GL030689Hernes P J B A Bergamaschi R S Eckard and R G M Spencer (2009) Fluorescence-based proxies for lignin in freshwater dissolved

organic matter J Geophys Res 114 G00F03 doi1010292009JG000938Hodson H A M Anesio M Tranter A Fountain M Osborn J Priscu J Laybourn-Parry and B Sattler (2008) Glacial ecosystems Ecol Monogr

78 41ndash67 doi10189007-01871Holmes R M et al (2012) Seasonal and annual fluxes of nutrients and organic matter from large rivers to the Arctic Ocean and surrounding

seas Estuaries Coasts 35 369ndash382 doi101007s12237-011-9386-6Hood E and D Scott (2008) Riverine organic matter and nutrients in southeast Alaska affected by glacial coverage Nat Geosci 1 583ndash587

doi101038ngeo280Hood E J Fellman R G M Spencer P J Hernes R Edwards D DrsquoAmore and D Scott (2009) Glaciers as a source of ancient and labile

organic matter to the marine environment Nature 462 1044ndash1047 doi101038nature08580Hossler K and J E Bauer (2013) Amounts isotopic character and ages of organic and inorganic carbon exported from rivers to ocean margins

1 Estimates of terrestrial losses and inputs to the Middle Atlantic Bight Global Biogeochem Cycles 27 331ndash346 doi101002gbc20033Jenk T M S Szidat M Schwikowski H W Gaggeler S Brutsch L Wacker H A Synal andM Saurer (2006) Radiocarbon analysis in an Alpine

ice core Record of anthropogenic and biogenic contributions to carbonaceous aerosols in the past Atmos Chem Phys 6 5381ndash5390Jurado E J Dachs C M Duarte and R Simo (2008) Atmospheric deposition of organic and black carbon to the global oceans Atmos Environ

42 7931ndash7939Jorgenson M T C H Racine J C Walters and T E Osterkamp (2001) Permafrost degradation and ecological changes associated with a

warming climate in central Alaska Clim Change 48 551ndash579Jorgenson M T Y L Shur and E R Pullman (2006) Abrupt increase in permafrost degradation in Arctic Alaska Geophys Res Lett 33 L02503

doi1010292005GL024960Kalbitz K and S Geyer (2002) Different effects of peat degradation on dissolved organic carbon and nitrogen Org Geochem 33 319ndash326LaFreniere M J and M J Sharp (2004) The concentration and fluorescence of dissolved organic carbon (DOC) in glacial and nonglacial

catchments Interpreting hydrological flow routing and DOC sources Arc Antarct Alpine Res 36 156ndash165Maie N N M Scully O Pisani and R Jaffe (2007) Composition of protein-like fluorophore of dissolved organic matter in coastal wetland

and estuarine systems Water Res 41 563ndash570 doi101016jwatres200611006McKnight D M E W Boyer P K Westerhoff P T Doran T Kulbe and D T Anderson (2001) Spectrofluorometric characterization of dissolved

organic matter for indication of precursor organic material and aromaticity Limnol Oceanogr 46 38ndash48Mead R N K M Mullaugh G B Avery R J Kieber J D Willey and D C Podgorski (2013) Insights into dissolved organic matter complexity

in rainwater from continental and coastal storms by ultrahigh resolution Fourier transform ion cyclotron resonance spectroscopyAtmos Chem Phys 13 4829ndash4838 doi105194acp-13-4829-2013

Moore S et al (2013) Deep instability of deforested tropical peatlands revealed by fluvial organic carbon fluxes Nature 493 660ndash664doi101038nature11818

Murphy K R K D Butler R G M Spencer C A Stedmon J R Boehme and G R Aiken (2010) Measurement of dissolved organic matterfluorescence in aquatic environments An interlaboratory comparison Environ Sci Technol 44 9405ndash9412 doi101021es102362t

Neff J C J C Finlay S A Zimov S P Davydov J J Carrasco E A G Schuur and A I Davydova (2006) Seasonal changes in the age andstructure of dissolved organic carbon in Siberian rivers and streams Geophys Res Lett 33 L23401 doi1010292006GL028222

Nilsson C C A Reidy M Dynesius and C Revenga (2005) Fragmentation and flow regulation of the worldrsquos largest river systems Science308 405ndash408 doi101126science1107887

OrsquoDonnell J A G R Aiken E S Kane and J B Jones (2010) Source water controls on the character and origin of dissolved organic matter instreams of the Yukon River basin Alaska J Geophys Res 115 G03025 doi1010292009JG001153

OrsquoDonnell J A G R Aiken M A Walvoord and K D Butler (2012) Dissolved organicmatter composition of winter flow in the Yukon River basinImplications of permafrost thaw and increased groundwater discharge Global Biogeochem Cycles 26 GB0E06 doi1010292012GB004341

OrsquoDonnell J A J W Harden A D McGuire M Z Kanevskiy M T Jorgenson and X Xu (2011) The effect of fire and permafrost interactions onsoil carbon accumulation in an upland black spruce ecosystem of interior Alaska Implications for post-thaw carbon loss Global Change Biol17 1461ndash1474 doi101111j1365-2486201002358x

Opsahl S R Benner and R W Amon (1999) Major flux of terrigenous dissolved organic matter through the Arctic Ocean Limnol Oceanogr44 2017ndash2023

Pewe T L and R D Reger (1983) Middle Tanana River valley in Guidebook to Permafrost and Quaternary Geology Alongside the Richardsonand Glenn Highways Between Fairbanks and Anchorage Alaska edited by T L Pewe and R D Reger pp 5ndash45 Alaska Div of Geol andGeophys Survs Fairbanks Alaska

Raymond P A and J E Bauer (2001) Riverine export of aged terrestrial organic matter to the North Atlantic Ocean Nature 409497ndash500

Raymond P A J W McClelland R M Holmes A V Zhulidov K Mull B J Peterson R G Striegl G R Aiken and T Y Gurtovaya (2007) Flux andage of dissolved organic carbon exported to the Arctic Ocean A carbon isotopic study of the five largest rivers Global Biogeochem Cycles21 GB4011 doi1010292007GB002934

Raymond P A (2005) The composition and transport of organic carbon in rainfall Insights from the natural (13C and

14C) isotopes of carbon

Geophys Res Lett 32 L14402 doi1010292005GL022879Riordan B D Verbyla and A D McGuire (2006) Shrinking ponds in subarctic Alaska based on 1950ndash2002 remotely sensed images J Geophys

Res 111 Go4022 doi1010292005JG000150



Schuster P F R G Striegl G R Aiken D P Krabbenhoft J F DeWild K Butler B Kamark and M Dornblaser (2011) Mercury export from theYukon River basin and potential response to a changing climate Environ Sci Technol 45 9262ndash9267 doi101021es202068b

Sharp M J Parkes B Cragg I J Fairchild H Lamb andM Tranter (1999) Widespread bacterial populations at glacial beds and their relationshipto rock weathering and carbon cycling Geology 27 107ndash110

Singer G A C Faschin L Wilhelm J Niggemann P Steier T Dittmar and T J Battin (2012) Biogeochemically diverse organic matter in Alpineglaciers and its downstream fate Nat Geosci 5 710ndash714 doi101038NGEO1581

Spencer R G M B A Pellerin B A Beramaschi B D Downing T E C Kraus D R Smart A Dahlgren and P J Hernes (2007) Diurnalvariability in riverine dissolved organic matter composition determined by in-situ optical measurement in the San Joaquin River(California USA) Hydrol Processes 21 3181ndash3189 doi101002hyp6887

Spencer R G M G R Aiken K P Wickland R G Striegl and P J Hernes (2008) Seasonal and spatial variability in dissolved organic matterquantity and composition from the Yukon River basin Alaska Global Biogeochem Cycles 22 GB4002 doi1010292008GB003231

Spencer R G M G R Aiken K D Butler M M Dornblaser R G Striegl and P J Hernes (2009) Utilizing chromophoric dissolved organicmatter measurements to derive export and reactivity of dissolved organic carbon exported to the Arctic Ocean A case study of the YukonRiver Alaska Geophys Res Lett 36 L06401 doi1010292008GL036831

Spencer R G M K D Butler and G R Aiken (2012a) Dissolved organic carbon and chromophoric dissolved organic matter properties ofrivers in the USA J Geophys Res 117 G03001 doi1010292011JG001928

Spencer R G M et al (2012b) An initial investigation into the organic matter biogeochemistry of the Congo River and estuary GeochimCosmochim Acta 84 614ndash627 doi101016jgca201201013

Striegl R G G R Aiken M M Dornblaser P A Raymond and K P Wickland (2005) A decrease in discharge-normalized DOC export by theYukon River during summer through autumn Geophys Res Lett 32 L21413 doi1010292005GL024413

Striegl R G M M Dornblaser G R Aiken K P Wickland and P A Raymond (2007) Carbon export and cycling by the Yukon Tanana andPorcupine Rivers Alaska 2001ndash2005 Water Resour Res 43 W02411 doi1010292006WR005201

Stubbins A et al (2012) Anthropogenic aerosols as a source of ancient dissolved organic matter in glaciers Nat Geosci 5 198ndash201doi101038ngeo1403

Stuiver M and H A Polach (1977) Reporting of C-14 data Discussion Radiocarbon 19 355ndash363Vonk J E et al (2013) High biolability of ancient permafrost carbon upon thaw Geophys Res Lett 40 doi101002grl50348Walvoord M A and R G Striegl (2007) Increased groundwater to stream discharge from permafrost thawing in the Yukon River basin

Potential impacts on lateral export of carbon and nitrogen Geophys Res Lett 34 L12402 doi1010292007GL030216Walvoord M A C I Voss and T P Wellman (2012) Influence of permafrost distribution on groundwater flow in the context of climate-

driven permafrost thaw Example from Yukon Flats basin United States Water Resour Res 48 W07524 doi1010292011WR011595Weishaar J L G R Aiken B A Bergamaschi M S Fram R Fuji and KMopper (2003) Evaluation of specific ultraviolet absorbance as an indicator

of the chemical composition and reactivity of dissolved organic carbon Environ Sci Technol 37 4702ndash4708 doi101021es030360xWickland K P J C Neff and G R Aiken (2007) Dissolved organic carbon in Alaskan boreal forest Sources chemical characteristics and

biodegradability Ecosystems 10 1323ndash1340 doi101007s10021-007-9101-4Yan G and G Kim (2012) Dissolved organic carbon in the precipitation of Seoul Korea Implications for global wet depositional flux of fossil-fuel

derived organic carbon Atmos Env 59 117ndash124Yoshikawa K and L D Hinzman (2003) Shrinking thermokarst ponds and groundwater dynamics in discontinuous permafrost near Council

Alaska Permafrost Periglac Process 14 151ndash160



Table 1 DOC Concentration Specific Ultraviolet Absorbance (SUVA254) δ13C-DOC and Δ14C-DOC Measurements for Samples Collected in the Yukon River

and its Tributariesa

Sample Site With Site NumberDistance From Yukon

Source at Atlin Lake (km) Dateb DOC (mg C L1) SUVA254 (LmgC m) δ13C (permil) Δ14C (permil) Age (yBP)

Yukon River Main Stem6 Yukon River at Whitehorse 232 82704 11 15 258 203 17199 Yukon River above White River 772 9204 20 18 261 124 95912 Yukon River below Stewart River 800 9304 21 20 208 78 55014 Yukon River at Eagle 1057 9604 25 22 241 64 42615 Yukon River above Circle AK 1343 82405 27 25 222 294 269116 Yukon River above Ft Yukon AK 1475 52005 93 34 269 76 Modern

6305 68 32 265 53 Modern22 Yukon River near Stevenrsquos Village 1874 32406 20 19 258 38 20528 Yukon River at Pilot Station AK 3294 81804 31 28 261 34 169

92204 31 27 268 59 38351305 122 29 267 68 Modern51705 166 30 242 67 Modern6105 107 37 270 65 Modern61405 77 34 250 41 Modern71205 61 31 264 17 2781605 46 25 272 49 30092705 77 32 271 14 3

Glaciated Catchments4 Atlin River 0 82604 10 10 275 453 47435 Nares River 101 82504 12 18 259 223 192027 Tanana River at Nenana 2121 51505 53 30 ND 191 1599

52705 31 26 265 112 84932306 12 20 ND 254 2246

26 Tanana River at Delta Junction na 32306 10 ND ND 312 289825 Clearwater River na 32506 05 12 160 340 3235

Blackwaters13 Fortymile River 975 9504 157 33 275 3 Modern19 Porcupine River na 51505 280 32 273 109 Modern

52505 150 35 275 96 Modern82605 68 27 271 7 Modern

23 Hess Creek na 51305 261 37 271 20 Modern52105 32 38 244 92 Modern

18 Black River na 51405 234 35 274 101 Modern52605 109 34 273 67 Modern6206 123 36 275 80 Modern

Nonglaciated Clearwaters7 Big Salmon River 392 83004 18 18 260 101 7538 Pelly River 628 9104 26 21 263 101 74110 White River 778 9204 17 21 278 101 75311 Stewart River 795 9304 22 21 237 71 49120 Christian River na 82705 56 25 269 12 Modern21 Chandalar River na 82705 20 17 265 85 60217 Sheenjek River na 82605 16 16 269 129 1006

Glacial Waters24 Gulkana Glacier 22ndash24 cm na 42606 ND ND ND 650 831624Gulkana Glacier 45ndash70 cm ND ND ND 521 317424 Gulkana Glacier 80ndash90 cm ND ND ND 335 58061 Atlin Lake 2 0 7606 ND ND ND 681 90652 Atlin Lake 3 ND ND ND 677 89753 Atlin Lake 4 ND ND ND 718 10058

a(na = not applicable ND=not determined)bDates are formatted as monthdayyear



















a

b

d

e

fc
















DOC (mg L-1)

0 5 10 15 20 25 30 35

4 C-D

OC

(o oo

)

-500

-400

-300

-200

-100

0

100

200

a254 (cm-1)

00 02 04 06 08 10 12 14

4 C-D

OC

(o oo

)

-500

-400

-300

-200

-100

0

100

200

R = 086 p lt 0001

R = 083 p lt 0001

a)

b)









SUVA254 (LmgC m)

00 05 10 15 20 25 30 35 40 45 50

4 C-D

OC

(o oo

)

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

50

100

150

R2 = 066 p lt 0001










02

04

06

08

10

12


254

(cm

-1)

254

(cm

-1)

00

02

04

06

08

10

Date

a)

b)












4 Conclusions



























































Res 111 Go4022 doi1010292005JG000150







































a

b

d

e

fc
















DOC (mg L-1)

0 5 10 15 20 25 30 35

4 C-D

OC

(o oo

)

-500

-400

-300

-200

-100

0

100

200

a254 (cm-1)

00 02 04 06 08 10 12 14

4 C-D

OC

(o oo

)

-500

-400

-300

-200

-100

0

100

200

R = 086 p lt 0001

R = 083 p lt 0001

a)

b)









SUVA254 (LmgC m)

00 05 10 15 20 25 30 35 40 45 50

4 C-D

OC

(o oo

)

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

50

100

150

R2 = 066 p lt 0001










02

04

06

08

10

12


254

(cm

-1)

254

(cm

-1)

00

02

04

06

08

10

Date

a)

b)












4 Conclusions



























































Res 111 Go4022 doi1010292005JG000150



































DOC (mg L-1)

0 5 10 15 20 25 30 35

4 C-D

OC

(o oo

)

-500

-400

-300

-200

-100

0

100

200

a254 (cm-1)

00 02 04 06 08 10 12 14

4 C-D

OC

(o oo

)

-500

-400

-300

-200

-100

0

100

200

R = 086 p lt 0001

R = 083 p lt 0001

a)

b)









SUVA254 (LmgC m)

00 05 10 15 20 25 30 35 40 45 50

4 C-D

OC

(o oo

)

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

50

100

150

R2 = 066 p lt 0001










02

04

06

08

10

12


254

(cm

-1)

254

(cm

-1)

00

02

04

06

08

10

Date

a)

b)












4 Conclusions



























































Res 111 Go4022 doi1010292005JG000150




























SUVA254 (LmgC m)

00 05 10 15 20 25 30 35 40 45 50

4 C-D

OC

(o oo

)

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

50

100

150

R2 = 066 p lt 0001










02

04

06

08

10

12


254

(cm

-1)

254

(cm

-1)

00

02

04

06

08

10

Date

a)

b)












4 Conclusions



























































Res 111 Go4022 doi1010292005JG000150





























02

04

06

08

10

12


254

(cm

-1)

254

(cm

-1)

00

02

04

06

08

10

Date

a)

b)












4 Conclusions



























































Res 111 Go4022 doi1010292005JG000150































4 Conclusions



























































Res 111 Go4022 doi1010292005JG000150


























































Res 111 Go4022 doi1010292005JG000150























Influences of glacier melt and permafrost thaw on the age of dissolved organic carbon in the Yukon...

Documents

Transcript of Influences of glacier melt and permafrost thaw on the age of dissolved organic carbon in the Yukon...