Lake Water Isotope Research Articles

Comparisons of observed and modelled lake δ18O variability

With the substantial number of lake sediment δ18O records published in recent decades, a quantitative, process-based understanding of these systems can increase our understanding of past climate change. We test mass balance models of lake water δ18O variability against five years of monthly monitoring data from lakes with different hydrological characteristics, in the East-Midlands region of the UK, and the local isotope composition of precipitation. These mass balance models can explain up to 74% of the measured lake water isotope variability. We investigate the sensitivity of the model to differing calculations of evaporation amount, the amount of groundwater, and to different climatic variables. We show there is only a small range of values for groundwater exchange flux that can produce suitable lake water isotope compositions and that variations in evaporation and precipitation are both required to produce recorded isotope variability in lakes with substantial evaporative water losses. We then discuss the potential for this model to be used in a long-term, palaeo-scenario. This study demonstrates how long term monitoring of a lake system can lead to the development of robust models of lake water isotope compositions. Such systematics-based explanations allow us to move from conceptual, to more quantified reconstructions of past climates and environments.

An isotopic study on water system of Lake Barkol and its implication for Holocene climate dynamics in arid central Asia

Mechanism of arid central Asia climate dynamics is still an open question even it has been studied for a long time. Interpreting climatic proxy data properly is crucial for better understanding the paleoclimate in such a sensitive area and its role in the earth system. According to the analysis of water stable isotope (δ18O and δD), Lake Barkol catchment obeys the typical isotopic model of a hydrologically closed lake: Lake input water inherits the feature of the weighted mean annual isotopes in precipitation, and lake water isotopes move along the local evaporation line from the start point of input water isotopes, modulated by the regional effective moisture. Based on the modern water isotopes and its relation to the climate, sediment carbonate oxygen isotope (δ18Ocarb) record re-interpretation suggests that the Asian monsoon incursion to arid central Asia area alone is unlikely the reason for the early Holocene δ18Ocarb negative, as the calculated extreme summer rainfall δ18O change to compensate the more negative δ18Ocarb in the early Holocene is far beyond our knowledge of precipitation isotopes in the real world. Besides, a 40 % of winter precipitation increase could explain the δ18O negative change in the early Holocene, which does, more importantly, reconcile the contradiction between the pollen Aretemisia/Chenopodiaceae effective moisture and δ18O records.

The influence of salinity on D/H fractionation in dinosterol and brassicasterol from globally distributed saline and hypersaline lakes

Salinity, growth rate, growth stage, nutrient limitation and temperature have all been shown to influence the magnitude of D/H fractionation in algal lipids through laboratory and field studies. Of these factors, salinity has been studied most extensively in the field, but to date all such investigations have focused on transect studies within specific and isolated environments. Here we test the relationship between salinity and the magnitude of D/H fractionation in algal lipids through paired analyses of sedimentary and particulate lipid and water hydrogen isotope values at a wide range of continental and coastal lake sites spanning salinities from 0 to 117ppt. Our results demonstrate broad consistency between D/H fractionations in dinosterol and brassicasterol with those obtained from previous work, with salinity changes of 1ppt resulting in lipid δD changes of 0.7–1‰. Although our results also show variability in D/H fractionation between sites that is not related to salinity, the fact that any relationship emerges above the influences of other factors suggests that the salinity effect is dominant for some lipids in the majority of saline to hypersaline environments. This improved understanding of D/H fractionation in dinosterol and brassicasterol synthesis supports the use of these compounds as paleohydrologic indicators. When combined with D/H measurements from a second lipid or oxygen isotope measurements from carbonate, quantitative reconstructions of salinity and lake water isotope changes are possible. Extending the number of algal lipids within which a consistent relationship between D/H fractionation and salinity has been identified also supports the notion that the relationship is widespread among unicellular photoautotrophs.

Hydrochemical characteristics and recharge sources of Lake Nuoertu in the Badain Jaran Desert

We present a case study of physical and chemical indicators and isotope characteristics of Lake Nuoertu, one of the largest and deepest lakes of the Badain Jaran Desert. We analyze the concentrations of eight ions, total dissolved solids, and stable isotope composition of the lake and groundwater, as well as radioactive isotope tritium concentration in groundwater. The results show that annual and seasonal variations of the physical and chemical characteristics of Lake Nuoertu water are significantly greater than those of groundwater. The lake is uniformly mixed in the horizontal and vertical directions, and the hydrochemical types of the lake at different depths are consistent for Na–Cl–CO3–(SO4). Stable isotope composition of the lake and groundwater at Nuoertu is distributed along the local evaporation line (EL) slope, which is less than the slope of the global meteoric water line. The comparatively small slope shows the characteristic strong evaporation in the study area. Lake water isotopes are mostly in the upper right corner of the EL, whereas groundwater is mostly in the lower left corner. The main recharge source of Nuoertu lake water is groundwater, in combination with lake water and groundwater level change. The age of tufa springs around Nuoertu is about 75–80 a, which shows that the initial recharge source of the lake is a mix between modern and 1952 or older; however, further research is required.

Vulnerability of shallow subarctic lakes to evaporate and desiccate when snowmelt runoff is low

AbstractSnowmelt is a crucial source of water for many shallow subarctic lakes, but climate models predict that snowfall will decrease in some regions, with profound ecological consequences. Here we use lake water isotope data across gradients of terrestrial vegetation cover (open tundra to closed forest) and topographic relief to identify lakes that are vulnerable to desiccation under conditions of low snowmelt runoff in two subarctic landscapes—Old Crow Flats, Yukon, and Hudson Bay Lowlands, Manitoba (Canada). Lakes located in low‐relief, open tundra catchments in both landscapes displayed a systematic, positive offset between directly measured lake water δ18O over multiple sampling campaigns and lake water δ18O inferred from cellulose in recently deposited surface sediments. We attribute this offset to a strong evaporative 18O‐enrichment response to lower‐than‐average snowmelt runoff in recent years. Notably, some lakes underwent near‐complete desiccation during midsummer 2010 following a winter of very low snowfall. Based on the paleolimnological record of one such lake, the extremely dry conditions in 2010 may be unprecedented in the past ~200 years. Findings fuel concerns that a decrease in snowmelt runoff will lead to widespread desiccation of shallow lakes in these landscapes.

Tracing contributions to hydro‐isotopic differences between two adjacent lakes in the southern Tibetan Plateau

AbstractHydrological processes of lakes in the Tibetan Plateau are an important indicator of climate change. Due to the high elevation, inaccessibility and limited availability of historical observations, water budget evaluation of typical lake basins has been inadequate. In this study, stable isotopes are used to trace the multiple water sources contributing to two adjacent lakes on the north slope of the Himalayas, Gongmo‐tso and Drem‐tso. The two lakes have nearly the same elevation, lake area and climatic condition. However, the isotopic composition of the two lakes presents significant differences. Qualitative observations attribute the differences to hydrological discrepancies: Gongmo‐tso is a through‐flow lake, whereas Drem‐tso is a terminal lake. Quantitative analyses, including water and isotope mass balance modelling, clarify the fluxes and isotopic compositions among the various hydrological elements. The isotopic composition of input water, calculated as the summation of rainfall and upstream runoff, is estimated using the local meteoric water line (LMWL) combined with the time series of lake water isotope values. The isotopic composition of evaporation is calculated with a linear resistance model using local meteorological data. The results show that Drem‐tso is a closed lake in a hydrological steady state with relatively more enriched lake water isotope values resulting mainly from evaporation. In contrast, through‐flow accounts for more than 88% of the water input into Gongmo‐tso. The large amount of upstream runoff with lower isotopic composition and enrichment due to evaporation are the major contributions to the observed lake water isotope values. Isotopic modelling of the two neighbouring lakes is effective for isotopic and hydrological research in this region with limited in situ observations. Copyright © 2013 John Wiley & Sons, Ltd.

A synthesis of hydrogen isotope variability and its hydrological significance at the Qinghai–Tibetan Plateau

Hydrogen isotope ratios of sedimentary biomarkers are known to record the climatic variability in terrestrial and marine environments. However, there is still a lack of calibration studies that can quantitatively retrace the driving forces, especially at the Tibetan Plateau. Here, we elaborate the actual influence of environmental parameters such as temperature, evapotranspiration, salinity and biosynthetic fractionation on δD values of n-alkanes.We measured hydrogen isotope values (δD) of n-alkanes in recent sediment and plant samples as well as δD values of different water sources (lake and inflow water, precipitation as well as leaf, root and soil water) from six Tibetan lakes along a 10°-spanning longitudinal transect covering an aridity gradient. As expected, the deuterium record can be used to distinguish two water pools at the Plateau: (I) precipitation water, which supplies water for the lake inflow and terrestrial plants, and (II) enriched lake water having a clear evaporative signal. Based on significant correlations of the source water and δD values of n-alkanes, δD of alkane n-C23 record the lake water isotope composition and track the evaporative enrichment of the lake system. In contrast, δD of alkane n-C29 can be used to retrace the isotope composition of the inflow displaying the integrated rainfall signal in the vegetation period modified by soil and leaf water evaporation. While temperature changes are less pronounced across the Tibetan transect, the isotopic difference between C23 and C29 could potentially be used as a proxy to reconstruct effective moisture (precipitation minus evaporation). Areas with lower precipitation amounts and higher evaporation rates are characterized by higher ΔδDC23–C29 values. This relationship is more pronounced in regions with mean annual precipitation below 350 mm. Even in contrasting environments, the application of the δD proxies is very promising. Combining other Tibetan studies, it is possible to present a comprehensive picture of the usage of compound-specific hydrogen isotopes of n-alkanes on the Tibetan Plateau.

Controls on recent Alaskan lake changes identified from water isotopes and remote sensing

High‐latitude lakes are important for terrestrial carbon dynamics and waterfowl habitat driving a need to better understand controls on lake area changes. To identify the existence and cause of recent lake area changes in the Yukon Flats, a region of discontinuous permafrost in north central Alaska, we evaluate remotely sensed imagery with lake water isotope compositions and hydroclimatic parameters. Isotope compositions indicate that mixtures of precipitation, river water, and groundwater source ~95% of the studied lakes. The remaining minority are more dominantly sourced by snowmelt and/or permafrost thaw. Isotope‐based water balance estimates indicate 58% of lakes lose more than half of inflow by evaporation. For 26% of the lakes studied, evaporative losses exceeded supply. Surface area trend analysis indicates that most lakes were near their maximum extent in the early 1980s during a relatively cool and wet period. Subsequent reductions can be explained by moisture deficits and greater evaporation.

Isotopic and hydrologic responses of small, closed lakes to climate variability: Hydroclimate reconstructions from lake sediment oxygen isotope records and mass balance models

Hydroclimate sensitivity simulations were conducted with a lake-catchment hydrologic and isotope mass balance model adapted to two small, closed lakes (Castor and Scanlon) located in the Pacific Northwest. Model simulations were designed to investigate the combined influences of persistent disequilibrium, reddening, and equifinality on lake water and sediment (i.e., biogenic and endogenic carbonate mineral) oxygen isotope (δ18O) values and to provide a basis for quantitative, probabilistic climate reconstructions using lake sediment δ18O records. Simulation results indicate that within closed-basin lakes changes in long-term (i.e., multi-decadal) precipitation amounts produce inconsistent responses in lake water and sediment δ18O values that are strongly influenced by lake basin outseepage and morphometry. Simulations of variable initial conditions in which randomly generated monthly climate data (i.e., precipitation, temperature, and relative humidity) were used to force the model during the equilibration period (which precedes the application of instrumental climate data) demonstrate that Castor Lake and Scanlon Lake have a somewhat limited isotopic ‘memory’ of ∼10years. Additional tests conducted using a Monte Carlo ensemble (in which random climate data were used to force the model) combined with δ18O analyses of water samples collected from 2003 to 2011 AD, indicate that within small, closed lakes in the Pacific Northwest November–February precipitation is the strongest seasonal, climatic control on sediment oxygen-isotope values. Further, a Monte Carlo based reconstruction of 20year average November–February precipitation amounts strongly correlates (R2=0.66) to instrumental values from the 20th century (with all observed values falling within modeled 95% prediction limits), indicating that probabilistic, quantitative paleoclimate interpretations of lake sediment δ18O records are attainable.

Modeling the Evaporation Line of Lake Water Isotopes in Golmud Drainage Basin, P.R. China

The δD-δ18O line features are very important properties of isotopic characteristics. The δD-δ18O line usually is estimated by regression analysis when samples are sufficient. In thisSuperscript textpaper, the isotopic characteristic of rain water, shallow groundwater and lake water in Golmud drainage area of Qaidam Basin were analyzed, and the isotopic evaporation line of lake water was calculated with Rayleigh fractionation function because the regression analysis method is insufficient in the condition that measured samples of lake water are short. The result shows that the groundwater is the main source of lakes; and the isotopic fractionation of hydrogen and oxygen in lake water controlled by kinetic effect in the process of evaporation. The calculated evaporation line of lake water is δD=3.26δ18O-21.00, which is matched with measured samples. The sensitivity analysis of the slop to the temperature, dissolved salt composition in lake water and relative humidity of air shows that the slop is negative related to the temperature and dissolved composition and is positive related to relative humidity. In typical environmental condition, the slop is increased by 0.0303, 0.1016 and 0.0205, respectively, when temperature decreased 1°C, dissolved NaCl decreased 1mol/L and relative humidity increased by 1%.

Late Holocene climate change in central Sweden inferred from lacustrine stable isotope data

AbstractStable isotopes (δ18O and δ13C) of lacustrine carbonates (Chara spp. algae and Pisidium spp. molluscs) from a lake sedimentary sequence in central Sweden were analysed to infer changes in lake hydrology and climate during the late Holocene. Results from analysis of lake water isotopes (δ18O and δ2H) show that Lake Blektjärnen water isotope composition is responsive to the balance between evaporation and input water (E/I ratio). A high E/I ratio results from a dry and probably warmer climate, decreasing the relative importance of precipitation input. Under such conditions evaporation and atmospheric equilibration probably enrich lake water in 18O and 13C, respectively, which is reflected in the isotopic composition of the carbonates in the lake. From the relatively positive Chara δ18O values we infer that conditions were dry and warm between 4400 and 4000 cal. a BP, whereas more negative values indicate that conditions were wetter and probably cooler between 4000 and 3000 cal. a BP. A drier climate is inferred from more positive values between 2500 and 1000 cal. a BP. However, a successive depletion after ca. 1750 cal. a BP, also detected in several other δ18O records (carbonate and diatom), suggest increasingly wetter conditions in Scandinavia after that time, which is probably related to increased strength of the zonal flow. Copyright © 2010 John Wiley & Sons, Ltd.

An oxygen-isotope record of Holocene climate change in the south-central Brooks Range, Alaska

Understanding the ecological and socio-economic impacts of climatic warming requires knowledge of associated changes in moisture balance. Reconstructions of Holocene moisture-balance variation offer indispensible baseline information against which recent changes can be evaluated. We analyzed Chara-stem encrustations in the sediments of Takahula Lake, located in the south-central Brooks Range of Alaska, for oxygen and carbon-isotope composition to infer climatic change over the past 8000 years. To help constrain climatic interpretations of the sediment δ 18O record, we also analyzed water samples from Takahula and other lakes in the region for oxygen and hydrogen isotope composition. Results show that winter precipitation dominates the water balance of these lakes and that post-input evaporation is a key control of lake-water isotope composition of Takahula Lake. Stratigraphic patterns in Chara-δ 18O, supplemented by those in δ 13C and sediment lithology, reveal distinct changes in effective moisture (precipitation minus evaporation) over the past 8000 years. Effective moisture was relatively high from 8000 to 5000 cal BP, with marked fluctuations between 6800 and 5000 cal BP. It then decreased to reach a minimum around 4000 cal BP and increased with fluctuations from 4000 to ∼2500 cal BP, followed by a decreasing trend toward the present that was interrupted by a wet Little Ice Age (centered at 400 cal BP). Aridity during the 20th century was among the highest of the entire 8000-year record. At the millennial timescale, the temporal patterns of moisture-balance shifts at Takahula Lake are broadly coherent with those inferred from previous paleoclimate records from the region. The Chara-δ 18O values around 5600 cal BP and during the Little Ice Age are up to 5‰ lower than at present and 3.6‰ lower than that of the modern input-water to the lake. These exceptionally low values suggest that factors other than effective moisture must have contributed to the pronounced variations in the Takahula Lake δ 18O record. Increased winter precipitation associated with a westerly Aleutian Low position may account for 1‰ of the δ 18O decrease. Other factors leading to the 18O-depletion during these periods probably include decreased temperatures, as well as increased lake-ice cover and associated reductions in evaporation.

Controlling factors on a paleo-lake oxygen isotope record (Yammoûneh, Lebanon) since the Last Glacial Maximum

Late Quaternary paleoclimatic changes in the Levant are difficult to extract from carbonate oxygen isotope records partly because the factors controlling the terrestrial δ 18O signals are not fully understood in this region characterized by sharp climatic gradients. Here, we address this purpose by presenting the first 14C-dated isotope record from the northern Levant. The record is based on oxygen isotopes from ostracod shells from lacustrine-palustrine deposits accumulated in a small karstic, hydrologically open basin (Yammoûneh), located on the eastern flank of Mount Lebanon. We have first constructed a composite isotopic record obtained from three different ostracod taxa. This yields an oxygen isotope record of ostracods (δ ost) related to the most widespread species ( Ilyocypris inermis), and converted to δ 18O values coeval with calcite precipitated in equilibrium (δ C) with the lake water (δ L). As with other records from the Mediterranean region, the Yammoûneh profile shows maximum and minimum δ C values during the LGM and the early Holocene, respectively, and a slight late Holocene increase. In order to discuss the potential causes of the observed δ 18O values fluctuations (e.g., changes in the isotopic composition of the moisture source, temperature, precipitation minus evaporation (P-E) balance, or atmospheric circulation), we tentatively reconstruct the lake water isotope composition by correcting the δ C values for lake water temperature using regional paleotemperature estimates. Inferred δ L values were then corrected for the isotopic composition of the Eastern Mediterranean sea surface water (the moisture source) derived from planktonic foraminifera δ 18O values corrected for alkenone-based sea surface temperature. Our study suggests that Holocene δ L fluctuations are primarily linked to changes in the sea surface water composition (source effect) amplified by enhanced inland rainfall during the early Holocene. During the LGM, low δ L values at Yammoûneh are likely due to the ground-temperature effect on the rainfall isotope composition, possibly associated with a steeper altitudinal thermal gradient inland, and with changes in air mass trajectories over the Mediterranean Sea.

Modeling Mediterranean lake isotope variability

Palaeorecords of lake oxygen isotope records across the Mediterranean basin show general regional trends but vary in the magnitude of variability and absolute isotope value. Theoretical models of lake isotope mass balance can help to understand and quantify these differences. Here, 5 sites from the WMO, 2004/WMO Global Network for Isotopes in Precipitation, in varying climatological settings across the Mediterranean basin, are used to model the response of lakes with varying hydrology to common climate forcings. The effects of geographical location, hydrological closure, residence time and climate on lake water isotope values are investigated.

Hydrogen and oxygen isotopic compositions of lake water in the western United States

Lake-water isotopes can be used to track moisture regimes and water sources at present and in the geologic record. However, the effects of seasonal drought and the seasonal distribution of precipitation on lake-water isotopes are not well documented. To improve our understanding of lake-water isotopes, we analyzed the δD and δ 18 O values of water from a hundred lakes in the western United States across a broad range of seasonal precipitation regimes. Our results show that the isotopic composition of lake-water inputs is correlated with the isotopic composition of annual precipitation. In areas associated with the summer monsoon in northern New Mexico and southern Colorado, lake-water inputs are skewed toward summer precipitation. These results contrast with published western U.S. river-water isotopic data, which are biased toward winter precipitation, and the paradigm that lakes represent the annual moisture surplus. From the lake-water input compositions, on plots of oxygen versus hydrogen isotopes, evaporative enrichment of individual lakes follows regionally coherent evaporation trends (0.96 2

North Atlantic region atmospheric circulation dynamics inferred from a late-Holocene lacustrine carbonate isotope record, northern Swedish Lapland

The first high-resolution record of climate variation based on the oxygen and carbon isotope composition of authigenic carbonate for northern Scandinavia is presented. Modern lake-water isotope data indicate that controls on its oxygen and hydrogen (δ18Ow and δDw) composition are unlikely to be evaporation or temperature, and its variations must therefore reflect changes in, or at the source of, precipitation. Substantial and persistent changes of the isotopic composition of the precipitation are required to change the mean annual isotope composition of lake surface water. For this reason we argue that the recorded changes were significant and that the recurrence of such changes would greatly affect future regional climate conditions in the North Atlantic region. Oxygen isotope (δ18O) minima occurring at ∼ 200, 500, 1300, 1600 and at 2900 cal. yr BP all coincide with major peaks in North Atlantic ice rafted debris deposition. We suggest that the depletion events in δ18O cycles recorded in several lakes in northern Swedish Lapland are caused by the same climatic shifts as those noted in the North Atlantic marine records. This is because changes of atmospheric circulation pattern and the lower ocean and atmospheric temperatures associated with the IRD events help to explain why 18O depletion of precipitation occurred during these events. Our findings indicate that the recorded changes in North Atlantic ice drift and surface hydrography are coupled to changes in atmospheric circulation.

Paleohydrological changes during the last deglaciation in Northern Brazil

We here report a reconstruction of hydrological balance variations in Northern Brazil for the last 20 ka deduced from the δD values of aquatic and land plant molecules extracted from the sediment infill of Lake Caçó. Our reconstructed precipitation, lake water isotope ratio and evaporation–evapotranspiration isotope effect allows us to obtain an estimate of moisture balance, and, to a lesser extent, precipitation amount and seasonality changes. During the end of the Last Glacial Maximum (LGM, between ca 20 and 17.3 ka), high δD values and smaller fractionation of leaf waxes indicate an arid to semi-arid climate with a long lasting dry season. An abrupt change towards much wetter conditions occurred within ca 500 years from 17.3 to 16.8 ka, as shown by a 50‰ decrease in D/H ratios and a marked increase in H isotopic fractionation of leaf waxes. This abrupt isotopic change coincides with a major transformation from savanna-dominated vegetation to humid rain forest around the lake, based on pollen data. Comparisons with other paleo-precipitation records from South American sites indicate that Lateglacial humid conditions were controlled by intensification of the ITCZ and/or a southward shift of its mean position across our study site. Our isotope data show only a small rise in aridity during Younger Dryas event (13–11.5 ka). Although the Holocene was not screened in details, D/H ratios of terrestrial and aquatic compounds show near constant offsets, suggesting stable and relatively humid climate conditions during this period.

Sulfur cycling in an acid mining lake and its vicinity in Lusatia, Germany

The sulfur cycle plays a key role in the hydrochemical development of lignite and coal mining districts, which are often characterized by acid mine drainage. Identification of sulfur sources and transformations is essential if we are to understand the current status of acid lakes and propose successful remediation strategies. We utilized stable isotope (δ34Ssulfate, δ18Osulfate, δ34Sdissolved sulfide, δ18Owater) and hydrochemical data of lake and groundwater samples as well as the concentrations and isotope ratios of various sedimentary sulfur compounds (acid-soluble sulfate [ASS], acid-volatile sulfur [AVS], chromium-reducible sulfur [CRS]) in aquifer and lake sediments for assessing the biogeochemical sulfur cycle in a Lusatian acidic mining lake (ML111) and the surrounding area.Pyrite oxidation is the dominant source of sulfate and iron in the two aquifers west and east of mining lake ML111. Concentration and isotope data for dissolved sulfate suggest that bacterial (dissimilatory) sulfate reduction became an increasingly important process in the flow direction of the western aquifer, thereby improving water quality. In contrast, bacterial sulfate reduction was only of local importance in the dump aquifer on the eastern side of the lake. Oxygen isotope ratios of the lake water sulfate, and mass and isotope balances demonstrate that ∼80% of the sulfate in mining lake ML111 is derived via groundwater influx from the dump aquifer, with the remainder contributed by the western aquifer. In-lake pyrite oxidation or bacterial sulfate reduction in the water column are insignificant. The latter process is restricted to the monimolimnion, which represents less than 1% of the lake volume. Hence, the potential for natural generation of alkalinity by bacterial (dissimilatory) sulfate reduction is presently low. For successful remediation of ML111, it is essential to reduce significantly the continuous input of sulfate and acidity from inflowing dump groundwater.

Oxygen isotope ratios of organic matter in arctic lakes as a paleoclimate proxy: field and laboratory investigations

Paleoclimate research based on the stable isotopic composition of lake sediments is often hampered by the lack of preservation of suitable material for isotopic analysis. We examined organic material as a proxy for past water isotopic composition in a series of experiments. First, we cultured aquatic moss under constant illumination, temperature, and water δ18O, and show that new cellulose records source water δ18O precisely (r2 = 0.9997). Second, we analyzed paired lakewater and vegetation samples collected from sites spanning strong climatic gradients. In field conditions, the relationship between organic δ18O and water δ18O is more variable, though it is still controlled by environmental water isotopic composition. However, terrestrial mosses in the arctic are often significantly enriched in δ18O relative to aquatic mosses in nearby lakes due to their use of different water sources. Third, we measured δ18O of cellulose extracted from disseminated sedimentary organic material. In the majority of the middle- to high-arctic lakes in this study, the δ18O of disseminated sediment cellulose is greatly enriched relative to the expected values based on lakewater δ18O, suggesting a significant component of terrestrial cellulose. This interpretation is supported by radiocarbon dates from a Holocene sediment core in which 14C ages of sediment cellulose are 700-5000 yrs older than the enclosing sediments. We conclude that aquatic cellulose can be used as a reliable tracer of lakewater isotope ratios, but terrestrial cellulose often dominates the sedimentary cellulose pool in places such as Baffin Island where sedimentation rates are low enough to allow the degradation of aquatic cellulose. Care must be taken when interpreting sediment cellulose δ18O records where diagenesis has played a role, because terrestrial cellulose is more resistant to degradation, and therefore can predominate in environments with low organic carbon burial.