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AUXILIARY MATERIAL
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Results
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Construction of the Local Evaporation Line
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The hydrogen and oxygen isotope compositions of precipitation and surface waters typically
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plot along two trajectories in 18O-2H space [Edwards et al., 2004]. The isotopic composition
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of global precipitation plots close to the Global Meteoric Water Line (GMWL), described by 2H
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= 8 18O + 10 [Craig, 1961]. The position of amount-weighted precipitation along the GMWL is
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mainly dependent on the distillation history of atmospheric moisture contributing to precipitation
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and commonly leads to rain plotting along an isotopically-enriched portion of the GMWL
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relative to snow. In contrast, surface water isotopic compositions typically cluster along a Local
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Evaporation Line (LEL), which generally has a slope of 4-6 and intersects the GMWL at the
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average annual isotopic composition of precipitation (P) for that region. Thus, the LEL for a
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given watershed defines the expected isotopic evolution of a surface water body undergoing
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evaporation, fed by waters of composition P. Displacement of water compositions along the
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LEL from P reflects evaporative loss while deviation from the LEL is often indicative of mixing
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with source waters such as snowmelt or rainfall, which tend to plot on the GMWL. Key
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reference points along the LEL include the terminal (i.e., closed-drainage) basin steady-state
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isotopic composition (SSL), which represents the special case of a water body at hydrologic and
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isotopic steady-state in which evaporation exactly equals inflow, and the limiting non-steady-
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state isotopic composition (*), which indicates the maximum potential transient isotopic
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enrichment of a water body as it approaches complete desiccation.
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For the Churchill region, the LEL was predicted using the linear resistance model of Craig
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and Gordon [1965] following similar approaches presented in Brock et al. [2007]. Note that the
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following equations are expressed in decimal notation. The equilibrium liquid-vapour
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fractionation factors (α*) for oxygen and hydrogen are dependent on temperature, and have been
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determined empirically by Horita and Wesolowski [1994], where
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1000lnα* = -7.685 + 6.7123(103/T) - 1.6664(106/T2) + 0.35041(109/T3)
(S1)
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30
for 18O, and
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1000lnα* = 1158.8(T3/109) - 1620.1(T2/106) + 794.84(T/103) - 161.04 + 2.9992(109/T3)
(S2)
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34
for δ2H, where T represents the interface temperature in K. ε* is the temperature-dependent
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equilibrium separation between liquid and vapour water. ε* is given by
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ε* = α* - 1
(S3)
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and kinetic separation (εK) is expressed by
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εK = CK (1 - h)
(S4)
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where constant enrichment values (CK) for oxygen and hydrogen are 0.0142 and 0.0125,
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respectively, and h is relative humidity [Gonfiantini, 1986]. δAS is the isotopic composition of
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ambient atmospheric moisture, often assumed to be in isotopic equilibrium with evaporation-
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flux-weighted local precipitation such that
2
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δAS = (δPS - ε*) / α*
(S5)
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The limiting isotopic enrichment of a water body approaching desiccation (δ*) has been defined
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by Gonfiantini [1986] and can be determined from
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δ* = (hδAS + εK + ε*/α*) / (h - εK - ε*/α*)
(S6)
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δSSL represents the isotopic composition of a terminal basin in which evaporation is exactly
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compensated by inflow, as defined by Gonfiantini [1986]:
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SSL = *I (1 – h + K) + *hAS + *K + *
(S7)
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where the isotope composition of inflow, I, is assumed to be equal to P. Results from
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calculations of the isotope parameters described above are shown in Table S1.
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Sediment core chronologies
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Total 210Pb activity profiles generally declined with increasing sediment depth and were used
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to establish the sediment core chronologies (Figure S1). The presence of intact algal mats on the
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sediment surface of the ponds provides evidence that sediment mixing cannot be the factor
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producing near-constant total 210Pb concentrations in the upper few cm for all ponds. This
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feature in the 210Pb profiles may indicate recent increases in sedimentation rates. Despite recent
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observations of desiccation at Puddle Pond, there are no artifacts in the 210Pb profile that would
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suggest discontinuous sedimentation. The sediment core was collected at a location that
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contained a thin film of water and, as the water isotope data demonstrate, is replenished in the
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spring. Evidently, spring inflow is sufficient to support aquatic production and the preservation
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of a continuous sediment record. Sediment ages to ~1850 C.E. were calculated using the
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Constant Rate of Supply (CRS) model [Appleby, 2001] and then were extrapolated down core.
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Thus, there is greater uncertainty for the pre-1850 sediment core chronologies.
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Loss-on-ignition [LOI; Dean, 1974] profiles were generated to compare stratigraphic records
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from the paired sediment cores from each study pond (Figure S2). Similar records were
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produced for paired cores from Left and Erin ponds, and therefore the chronologies established
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for the 210Pb-dated cores were directly transferred to the cores analyzed for cellulose oxygen
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isotope composition. Establishing the chronology for the cores from Larch and Puddle ponds
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analyzed for cellulose oxygen isotope composition required incorporating a slight stratigraphic
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offset evident between the two LOI profiles (Figure S2). For Larch Pond, this was accomplished
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by transferring the dates for the 210Pb-dated core at 10.5 cm (1927) and at 9.5 cm (1943) to the
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corresponding depths for the non-210Pb-dated core (8.5 and 7.0 cm, respectively). Linear
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interpolation was used to re-calculate the sedimentation rates between the surface of the core
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(2009) and 7.0 cm depth (1943) and between 7.0 cm (1943) and 8.5 cm depth (1927). The latter
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sedimentation rate was used for the interval below 8.5 cm. For Puddle Pond, the chronology for
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the core analyzed for cellulose oxygen isotope composition was determined by transferring the
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dates for the 210Pb-dated core at 25.0 cm (1830) and at 19.5 cm (1897) to the corresponding
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depths for the non-210Pb-dated core (27.0 and 22.0 cm, respectively). Linear interpolation was
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used to re-calculate the sedimentation rates between the surface of the core (2009) and 22.0 cm
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depth (1897) and between 22.0 cm (1897) and 27.0 cm depth (1830). The latter sedimentation
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rate was used for the interval below 27.0 cm. Figure S1 displays the depth-age relations for both
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the Larch Pond and Puddle Pond cores directly dated using 210Pb and for the cores analyzed for
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cellulose oxygen isotope composition.
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Tables
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Table S1. All values used to calculate the Local Evaporation Line for Churchill, Manitoba.
Term
Definition
Value
Reference
9oC
T
Flux-weighted temperature
(climate normal, 1971-2000)
Flux-weighted relative humidity
(climate normal, 1971-2000)
77.1%
H
Equilibrium liquid-vapour
fractionation factor (18O, 2H)
Kinetic separation (18O, 2H)
Equilibrium separation (18O, 2H)
Limiting isotope enrichment of a
water body approaching complete
desiccation (δ18O, δ2H)
Steady-state isotope composition
of a terminal basin (δ18O, δ2H)
Isotope composition of ambient
atmospheric moisture (δ18O, δ2H)
Isotope composition of
precipitation (δ18O, δ2H)
1.0108, 1.0984
Environment Canada
(http://climate.weatheroffice.gc.ca/;
Churchill Airport station)
Environment Canada
(http://climate.weatheroffice.gc.ca/;
Churchill Airport station)
Equations (S1) and (S2)
3.3, 2.8
10.8, 98.4
-4.5‰, -54‰
Equation (S4)
Equation (S3)
Equation (S6)
-7.5‰, -73‰
Equation (S7)
-22.6‰, -168‰
Equation (S5) (fitted to pond water
isotope data; see Light [2011])
Churchill CNIP station

K
*
*
δSSL
δAS
δP
-17.2‰, -129‰
98
6
99
Figures
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101
Figure S1. Total and supported 210Pb (mean 214Bi and/or 214Pb) activity profiles, and depth-age
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relations for sediment cores obtained from Left, Larch, Erin and Puddle ponds.
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Figure S2. Loss-on-ignition profiles for sediment cores obtained from Left, Larch, Erin and
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Puddle ponds. Cores on the left of each pair were analyzed for 210Pb; cores on the right of each
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pair were analyzed for cellulose oxygen isotope composition.
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107
References
108
Appleby, P.G. (2001), Chronostratigraphic techniques in recent sediments, in Tracking
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Environmental Change Using Lake Sediments: Basin Analysis, Coring, and Chronological
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Techniques, Developments in Paleoenvironmental Research, vol. 1, edited by W.M. Last and J.P.
111
Smol, pp. 171-203, Kluwer Academic Publishers, Dordrecht.
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Brock B.E., B.B. Wolfe and T.W.D. Edwards (2007), Characterizing the hydrology of shallow
114
floodplain lakes in the Slave River Delta, NWT, using water isotope tracers, Arctic Ant. Alp.
115
Res., 39, 388-401.
116
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Craig, H. (1961), Isotopic variations in meteoric waters, Science, 133, 1702-1703.
118
119
Craig, H. and L.I. Gordon (1965), Deuterium and oxygen 18 variations in the ocean and the
120
marine atmosphere, in Stable Isotope in Oceanographic Studies and Paleotemperatures, edited
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by E. Tongiorgi, pp. 9-130, Laboratorio di Geologia Nucleare, Pisa, Italy.
122
123
Dean, W.E. (1974), Determination of carbonate and organic matter in calcareous sediments and
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sedimentary rocks by loss on ignition: comparison with other methods, J. Sed. Petrol., 44, 242-
125
248.
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Edwards, T.W.D., B.B. Wolfe, J.J. Gibson and D. Hammarlund (2004), Use of water isotope
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tracers in high-latitude hydrology and paleohydrology, in Long-Term Environmental Change in
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Arctic and Antarctic Lakes, Developments in Paleoenvironmental Research, vol. 7, edited by R.
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Pienitz, M. Douglas and J.P. Smol, pp. 187-207, Springer, Dordrecht.
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132
Gonfiantini, R. (1986), Environmental isotopes in lake studies, in Handbook of Environmental
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Isotope Geochemistry, The Terrestrial Environment, vol. 2, edited by P. Fritz and J.-C. Fontes,
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pp. 113-168, Elsevier, New York.
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Horita, J. and D. Wesolowski (1994), Liquid-vapour fractionation of oxygen and hydrogen
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isotopes of water from the freezing to the critical temperature, Geochim. Cosmochim. Acta, 58,
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3425-3437.
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Light, E. (2011), Characterizing the present and past hydrology of shallow ponds in the Churchill
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area using isotopic methods, MSc thesis, Wilfrid Laurier Univ., Waterloo, Ont., Canada.
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