Mean Annual Accumulation Research Articles

Identification and Characterization of Life Zones at Satipo District in the Tropics of Central Peru

At present, the life zones have undergone great changes due to anthropic activities, so the present study was carried out with the aim of identifying and characterizing the life zones of the Satipo district. The applied methodology was the Holdridge life zone classification, the meteorological variables were analyzed, the vegetation cover was identified, also using the ArcGIS, QGIS, ENVI and Microsoft Excel software, the data analysis and field information were processed. In the investigation of bioclimatic factors they show that there are four important determinants: annual biotemperature, mean annual accumulation, humidity provinces and attitudinal levels. Noticing the decline of forests, overpopulation, among others, many companies are choosing to reduce products that lead to the loss of life zones. In the district of Satipo, three life zones were identified and two of a transitory nature of the one hundred and twenty-three existing ones.

A quantitative method of resolving annual precipitation for the past millennia from Tibetan ice cores

Abstract. Net accumulation records derived from alpine ice cores provide the most direct measurement of past precipitation. However, quantitative reconstruction of accumulation for past millennia remains challenging due to the difficulty in identifying annual layers in the deeper sections of ice cores. In this study, we propose a quantitative method to reconstruct annual accumulation from alpine ice cores for past millennia, using as an example an ice core drilled at the Chongce ice cap in the northwestern Tibetan Plateau (TP). First, we used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) technology to develop ultra-high-resolution trace element records in three sections of the ice core and identified annual layers in each section based on seasonality of these elements. Second, based on nine 14C ages determined for this ice core, we applied a two-parameter flow model to established the thinning parameter of this ice core. Finally, we converted the thickness of annual layers in the three sample sections to past accumulation rates based on the thinning parameter derived from the ice flow model. Our results show that the mean annual accumulation rates for the three sample sections are 109 mm yr−1 (2511–2541 years BP), 74 mm yr−1 (1682–1697 years BP), and 68 mm yr−1 (781–789 years BP), respectively. For comparison, the Holocene mean precipitation is 103 mm yr−1. This method has the potential to reconstruct continuous high-resolution precipitation records covering millennia or even longer time periods.

Aboveground Biomass and Carbon Accumulation 19 Years Post-Windthrow and Salvage Logging

Natural disturbances shape forest ecosystem characteristics, including carbon storage and structure. Often, natural disturbances are compounded with anthropogenic disturbances, which may alter the trajectory of forest carbon stock recovery. Heterogeneous levels of disturbance severity in compound disturbance events add an additional layer of complexity. This paper examines the effect of a moderate-severity wind disturbance and subsequent salvage logging on forest biomass and carbon stock recovery over 19 years. We investigate the recovery of aboveground tree biomass following a wind disturbance and salvage logging and examine the role of wind disturbance severity on biomass accumulation rates. We use pre-disturbance, 3 years post-wind disturbance and 19 years post-wind disturbance measurements of tree biomass across two adjacent sites at Natchez Trace State Forest for Site A and Site B in east central Tennessee. We found no significant difference in the carbon storage at Site A (pre = 92 MgC/ha; 19 years post-disturbance = 83 MgC/ha) or Site B (pre = 66 MgC/ha; 19 years post-disturbance = 67) when comparing the pre-disturbance level of aboveground tree carbon storage with the 19-years post-disturbance levels. Furthermore, we found no evidence that salvage logging reduced the rate of live tree carbon accumulation. The corresponding rates of mean annual carbon accumulation (MgC/ha) are as follows: Site A Unsalvaged (1.07), Site A Salvaged (1.25) and Site B Salvaged (2.02). Contrary to our prediction, greater wind damage severity was weakly associated with higher rates of biomass accumulation (R2 = 0.17). While we found no negative effect of salvage logging on the aboveground tree carbon accumulation rate, salvage logging alters other carbon pools, including coarse woody debris. Salvage logging did not reduce the rate of carbon stock recovery, and a higher wind disturbance severity was associated with a greater rate of carbon stock recovery.

On the retrieval of internal temperature of Antarctica Ice Sheet by using SMOS observations

Internal temperature is an essential parameter for understanding ice sheet dynamics. Glaciological models provide estimations of temperature profiles over Antarctica and few boreholes are also available, but, at present, no measurement exists at the scale of the whole continent. The analysis of passive L-band observations from the Soil Moisture and Ocean Salinity (SMOS) satellite shows that, thanks to the high penetration depth (i.e. up to 1500 m), it is possible to infer information on in depth glaciological properties of the ice sheet including temperature. In this study, the temperature profile is retrieved from SMOS observations using jointly glaciological and emission models. The developed methodology is valid in the inner part of Antarctica where the ice sheet is almost stable (i.e. its velocity is limited to 10 m yr−1). This analysis points out that in several cases, differences are observed between retrieved temperature profiles and those predicted by glaciological models. In particular, some geophysical parameters, namely the geothermal heat flux and the mean annual accumulation, need to be modified with respect to their prior values in order to simulate SMOS brightness temperatures. Results also clearly show that the reliability of the retrieved profile in depth decreases with increasing ice thickness due to the limited penetration of microwaves in the ice. The obtained results prove the capability of L band (1.4 GHz) passive microwave sensors for investigating the internal temperature of the ice-sheet.

Modeling Dry-Snow Densification without Abrupt Transition

An empirical model for the densification of dry snow has been calibrated using strain-rate data from Pine Island Glacier basin, Antarctica. The model provides for a smooth transition between Stage 1 and Stage 2 densification, and leads to an analytical expression for density as a function of depth. It introduces two new parameters with a simple physical basis: transition density ρ T and a scaling factor, M, which controls the extent of the transition zone. The standard (Herron and Langway) parameterization is used for strain rates away from the transition zone. Calibration, though tentative, produces best parameter values of ρ T = 580 kg m − 3 and M = 7 for the region. Using these values, the transition model produces better simulations of snow profiles from Pine Island Glacier basin than the well-established Herron and Langway and Ligtenberg models, both of which postulate abrupt transition. Simulation of density profiles from other sites using M = 7 produces the best values of ρ T = 550 kg m − 3 for a high accumulation site and 530 kg m − 3 for a low accumulation site, suggesting that transition density may vary with climatic conditions. The variation of bubble close-off depth and depth-integrated porosity with mean annual accumulation predicted by the transition model is similar to that predicted by the Simonsen model tuned for Greenland.

Snow Densification and Recent Accumulation Along the iSTAR Traverse, Pine Island Glacier, Antarctica

Neutron probe measurements of snow density from 22 sites in the Pine Island Glacier basin have been used to determine mean annual accumulation using an automatic annual layer identification routine. A mean density profile which can be used to convert radar two‐way travel times to depth has been derived, and the effect of annual fluctuations in density on estimates of the depth of radar reflectors is shown to be insignificant, except very near the surface. Vertical densification rates have been derived from the neutron probe density profiles and from deeper firn core density profiles available at 9 of the sites. These rates are consistent with the rates predicted by the Herron and Langway model for stage 1 densification (by grain‐boundary sliding, grain growth and intracrystalline deformation) and stage 2 densification (predominantly by sintering), except in a transition zone extending from ≈8 to ≈13 m from the surface in which 10–14% of the compaction occurs. Profiles of volumetric strain rate at each site show that in this transition zone the rates are consistent with the Arthern densification model. Comparison of the vertical densification rates and volumetric strain rates indicates that the expected relation to mean annual accumulation breaks down at high accumulation rates even when corrections are made for horizontal ice velocity divergence.

Revisión y comparación de escenarios de cambio climático para el Parque Nacional Isla del Coco, Costa Rica

Se revisaron y compararon escenarios de cambio climáticos utilizando distintas técnicas (MAGICC/SCENGEN, PRECIS and SDSM) con el objetivo de evaluar posibles cambios de temperatura y precipitación en el Parque Nacional Isla del Coco, Costa Rica, para el horizonte temporal del 2080 (2070-2099). Los resultados reflejan una dependencia importante con el Modelo de Circulación General, el método de ajuste de escala y con el escenario socio-económico usado. Los escenarios obtenidos reflejan un aumento en la media y la varianza del ciclo anual de la temperatura superficial del aire, siendo consistentes con un calentamiento global futuro. Los resultados para la precipitación difieren entre sí. Se observó que la mayoría de los escenarios analizados proyectan aumentos en al acumulado medio del ciclo anual, sin embargo, al considerar su variabilidad, no fue posible establecer una tendencia clara hacia un aumento o una disminución, debido principalmente a que casi todos los escenarios estudiados proyectan un incremento en la variabilidad del acumulado anual de la precipitación.

Trends in anthropogenic CO2 in water masses of the Subtropical North Atlantic Ocean

The variability in the storage of the oceanic anthropogenic CO2 (Cant) on decadal timescales is evaluated within the main water masses of the Subtropical North Atlantic along 24.5°N. Inorganic carbon measurements on five cruises of the A05 section are used to assess the changes in Cant between 1992 and 2011, using four methods (ΔC∗, TrOCA, φCT0, TTD). We find good agreement between the Cant distribution and storage obtained using chlorofluorocarbons and CO2 measurements in both the vertical and horizontal scales. Cant distribution shows higher concentrations and greater decadal storage rates in the upper layers with both values decreasing with depth. The greatest enrichment is obserbed in the central water masses, with their upper limb showing a mean annual accumulation of about 1μmolkg−1yr−1 and the lower limb showing, on average, half that value. We detect zonal gradients in the accumulation of Cant. This finding is less clear in the upper waters, where greater variability exists between methods. In accordance with data from time series stations, greater accumulation of Cant is observed in the upper waters of the western basin of the North Atlantic Subtropical Gyre. In intermediate and deep layers, the zonal gradient in the storage of Cant is more robust between methods. The much lower mean storage rates found along the section (<0.25μmolkg−1yr−1) become more obvious when longitudinal differences in the Cant accumulation are considered. In particular, west of 70°W the ventilation by the Labrador Sea Water creates a noticeable accumulation rate up to ∼0.5μmolkg−1yr−1 between 1000 and 2500dbar. If a Transient Stationary State of the Cant distributions is considered, significant bi-decadal trends in the Cant storage rates in the deepest North Atlantic waters are detected, in agreement with recent estimations.

Infection levels of plerocercoids of the tapeworm Triaenophorus crassus and feeding strategy in two fish species from the ultra-oligotrophic Lake Achensee, Austria.

Thus far, high burdens of Triaenophorus crassus plerocercoids have been reported only in old age groups of coregonid and salmonid fishes. Here we show heavy infection with T. crassus in young whitefish Coregonus lavaretus in the ultra-oligotrophic and regulated Achensee in Tyrol, Austria. Prevalence of T. crassus on C. lavaretus was 100% in all age groups and abundance significantly increased with fish age. The mean annual accumulation of T. crassus was 5.2 parasites in 0- to 7-year-old C. lavaretus, and 2-year-old specimens already harboured a mean of 19.4 plerocercoids. In Arctic charr Salvelinus umbla, however, the prevalence of T. crassus was less than 16% and the majority of infected fish contained only one or two plerocercoids. Triaenophorus nodulosus was present neither in C. lavaretus nor in S. umbla. We assume that the heavy T. crassus infection in C. lavaretus is largely related to their zooplankton-dominated diet and to the characteristics of Achensee, while habitat choice and feeding strategy of the S. umbla population are seen to be the main reasons for their low burdens of T. crassus.

Surface mass balance and stable oxygen isotope ratios from shallow firn cores on Fimbulisen, East Antarctica

AbstractThe mass balance of Antarctica is one of the crucial factors for determining sea-level change in a warming climate. The marginal zones of the continent, namely the ice shelves, are most sensitive to climate change. During the 2009/10 austral summer an extensive glaciological field campaign was carried out on Fimbulisen, an ice shelf in East Antarctica, to investigate its recent surface mass balance. Shallow (10–18 m) firn cores were drilled and accumulation rates and stable-isotope ratios determined. For firn-core dating, two different methods were compared: (1) seasonal variations of stable oxygen isotope ratios (δ18O), and (2) dielectric profiling, including using the volcanic eruptions of Pinatubo, Philippines (1991), and El Chichόn, Mexico (1982), as time markers. The mean annual accumulation for the period 1992–2009 ranges from 298 to 349 mmw.e. a–1. The interannual variability at the drilling sites is &gt;30%. Accumulation rates show a weak decreasing trend during the past 20–30 years, which is statistically significant only for one of the cores. Stable-isotope ratios were compared to the snowfall temperature of Neumayer station. Neither the temperatures nor the δ18O values show any trend for the investigated time period.

Time-elapsed evolution of aerosol size distributions by snow particles after the passage of blizzards over the Maitri (Antarctica)

Measurements of the aerosol size distribution in the diameter range 0.003–20 μm were made by a scanning mobility particle sizer (SMPS) and an aerodynamic particle sizer (APS) at Maitri (70° 45′ 52′′ S, 11° 44′ 03′′ E, Antarctica) during the 24th Indian Antarctic Expedition, which took place in January and February 2005. Time-elapsed evolutions of the aerosol size distributions on 30 January and 17 and 20 February 2005, after the passage of blizzards, were selected for estimation of the scavenging coefficient by considering the aerosol size distribution changes with snowfall over Antarctica. Scavenging efficiencies of snow particles and ice crystals collecting aerosols are obtained from the observed scavenging coefficients for 0.002–10μm aerosols. Also, theoretical snow scavenging efficiencies of snow particles and ice crystals in the diameter range 0.02–10 mm for 0.002–10 μm aerosols are determined and, thereupon, scavenging coefficients are calculated by assuming snowfall rates of 0.25 and 4 mm h−1 (in view of the reported decadal mean annual Antarctica snowfall accumulation rate of 180 mm yr−1). Snow scavenging efficiencies based on the scavenging coefficients found by considering the aerosol size distribution changes with snowfall after the occurrences of blizzards are higher than theoretical scavenging efficiencies and those of laboratory experiments for planar and columnar ice crystals. Also, the scavenging coefficients found are higher by two to three orders of magnitude than theoretical scavenging coefficients. Scavenging coefficients found from aerosol size distribution changes by snowfall after the passage of blizzards on 30 January and 17 and 20 February 2005 over Antarctica suggest that the orders of magnitude of their best estimation and the corresponding scavenging efficiencies can be viewed as being on a par with the natural snow scavenging of aerosols over this remote region.

Accumulation over the Greenland Ice Sheet as represented in reanalysis data

Annual precipitation, evaporation, and calculated accumulation from reanalysis model outputs have been investigated for the Greenland Ice Sheet (GrIS), based on the common period of 1989–2001. The ERA-40 and ERA-interim reanalysis data showed better agreement with observations than do NCEP-1 and NCEP-2 reanalyses. Further, ERA-interim showed the closest spatial distribution of accumulation to the observation. Concerning temporal variations, ERA-interim showed the best correlation with precipitation observations at five synoptic stations, and the best correlation with in situ measurements of accumulation at nine ice core sites. The mean annual precipitation averaged over the whole GrIS from ERA-interim (363 mm yr−1) and mean annual accumulation (319 mm yr−1) are very close to the observations. The validation of accumulation calculated from reanalysis data against ice-core measurements suggests that further improvements to reanalysis models are needed.

Spatial and temporal variability in snow accumulation at the West Antarctic Ice Sheet Divide over recent centuries

Ice cores collected in 2000 (ITASE 00‐1) and 2005 (WDC05A, WDC05Q) from the West Antarctic Ice Sheet Divide (WAIS Divide) project site were used to investigate the spatial and temporal variability in accumulation. The ice cores were dated based on annual layer counting of multiple glaciochemical measurements resulting in bottom depth ages for WDC05A, WDC05Q, and ITASE 00‐1 of 1775, 1521, and 1653 A.D., with mean annual accumulation rates of 0.200, 0.204, and 0.221 mweq a−1, respectively. Small‐scale spatial variability (SSV) was determined using an analysis of variance of accumulation in the ice core array, thereby quantifying the uncertainty in individual accumulation records. Results indicate that the spatial variability was 0.030 mweq a−1, or approximately 15% of the average annual accumulation. An accumulation record representative of the WAIS Divide local area over recent centuries was developed using a principal component analysis to identify the coherent accumulation signal. The WAIS Divide local record exhibited 14% interannual variability (1 standard deviation of the mean) with the SSV reduced to 0.017 mweq a−1. Correlations of the WAIS Divide local accumulation record with atmospheric indices (e.g., Antarctic Oscillation) exhibited periods when the records oscillate in and out of phase. Thus, reconstructing local and global atmospheric indices from WAIS Divide accumulation records over recent centuries may prove problematic.

Flux and fate of small mountainous rivers derived sediments into the Taiwan Strait

High-resolution CHIRP sonar profiles across the Taiwan Strait reveal a large silt–sand-dominated deltaic clinoform, up to 50-m thick, overlying the postglacial transgressive sea floor across the southeastern, central, and northern strait. Delta-like configuration and internal depositional sequences indicate a northwestward progradation from western Taiwan, primarily from the Choshui (Zhuoshui) River. Grain-size and mineral data confirm the sediment's Taiwanese derivation. The CHIRP profiles, together with existing radiocarbon and geomagnetic dates, suggest that the clinoform has formed over the past 10 kyr. The estimated volume of 375 km 3 of sediment (mainly sand and silt) suggests a mean annual accumulation of 60 × 10 6 t/yr. Presumably much of fine mud delivered by Taiwanese rivers has been washed away by the local currents, and escaped either northeastward into the Southern Okinawa Trough or southward into the South China Sea. Numerous shallow borings onshore over the central western Taiwan coastal plain reveal an additional 350 km 3 of fluvial sediment that has accumulated over the past 10 kyr. The combined onshore–offshore Holocene accumulation, together with an unknown amount of finer sediment that escapes the system, indicates that the long-term sediment flux from Western Taiwanese rivers exceeds 100 × 10 6 t/yr, which is not different from the present-day combined annual discharges from the Choshui, Tsengwen, Ehrjen and Wu rivers into the Taiwan Strait.

Snow accumulation rate on Qomolangma (Mount Everest), Himalaya: synchroneity with sites across the Tibetan Plateau on 50–100 year timescales

AbstractAnnual-layer thickness data, spanning AD 1534–2001, from an ice core from East Rongbuk Col on Qomolangma (Mount Everest, Himalaya) yield an age–depth profile that deviates systematically from a constant accumulation-rate analytical model. The profile clearly shows that the mean accumulation rate has changed every 50–100 years. A numerical model was developed to determine the magnitude of these multi-decadal-scale rates. The model was used to obtain a time series of annual accumulation. The mean annual accumulation rate decreased from ∼0.8 m ice equivalent in the 1500s to ∼0.3 m in the mid-1800s. From ∼1880 to ∼1970 the rate increased. However, it has decreased since ∼1970. Comparison with six other records from the Himalaya and the Tibetan Plateau shows that the changes in accumulation in East Rongbuk Col are broadly consistent with a regional pattern over much of the Plateau. This suggests that there may be an overarching mechanism controlling precipitation and mass balance over this area. However, a record from Dasuopu, only 125 km northwest of Qomolangma and 700 m higher than East Rongbuk Col, shows a maximum in accumulation during the 1800s, a time during which the East Rongbuk Col and Tibetan Plateau ice-core and tree-ring records show a minimum. This asynchroneity may be due to altitudinal or seasonal differences in monsoon versus westerly moisture sources or complex mountain meteorology.

Spatial mapping of multi-year superimposed ice on the glacier Kongsvegen, Svalbard

AbstractGround-penetrating radar (GPR) and satellite ERS-2 synthetic aperture radar (SAR) are used to map the thickness and extent of the superimposed ice (SI) zone on the surge-type glacier Kongsvegen, Svalbard. GPR imagery shows sub-horizontal SI layers lying unconformably above a discrete boundary. Below this boundary, the ice has a GPR signature similar to that of ice further down-glacier in the ablation zone. This boundary is posited to represent the closing of crevasses that were created during the last surge of Kongsvegen in ∼1948. Open crevasses would have interrupted the formation of sheet layers of SI due to efficient vertical drainage of the snowpack. Aerial photographs suggest that the crevasses closed sometime in the period 1956–66. A classified SAR image from 2003 is used to delineate the extent of the SI zone. The SI extent in the SAR image agrees well with the SI zone mapped by GPR. Using the SI spatial depth distribution, we estimate the mean annual accumulation of superimposed ice to be 0.16 ± 0.06 m w.e. a−1 (locally up to 0.43 m a−1 w.e.). This corresponds to ∼15–33% of the local winter balance and ∼5–10% of the total winter balance measured since 1987.

Carbon sequestration in European soils through straw incorporation: Limitations and alternatives

We compared alternate uses of cereal straw (4.25t dry matter ha(-1) containing 1.7t carbon (C)) for their effectiveness in relation to climate change mitigation. The scenarios were (1) incorporation into soil to increase soil organic carbon (SOC) content ("carbon sequestration") and (2) combustion to generate electricity. The Rothamsted Carbon Model was used to estimate SOC accumulation in a silty clay loam soil under the climatic conditions of north-west Europe. Using straw for electricity generation saved seven times more CO2 than from SOC accumulation. This comparison assumed that electricity from straw combustion displaced that generated from coal and used the mean annual accumulation of SOC over 100yr. SOC increased most rapidly in the early years, but then more slowly as a new equilibrium value was approached. We suggest that increased SOC from straw incorporation does not represent genuine climate change mitigation through carbon sequestration. In Europe, most straw not already incorporated in the field where it is grown is subsequently returned elsewhere, e.g., after use for animal bedding and production of manure. Only additional retention of C in soil compared to the alternative use represents sequestration. Maintenance of SOC for soil functioning is a more appropriate rationale for returning straw to soil than climate change mitigation. This analysis shows that considerably greater climate change mitigation is achieved through saved CO2 emissions by burning straw for electricity generation, replacing some use of fossil fuel.

Annual accumulation over recent centuries at four sites in central Greenland

Accurate accumulation records are fundamental to understanding mass balance of the Greenland ice sheet. Ice cores can provide multicentury, high‐resolution ground‐based point estimates of water accumulation. In 2003 and 2004, four new ice cores were collected in the central western (D4 and D5) and Summit (Sandy and Katie) regions of Greenland. Annual layer counting based on multiple glaciochemical parameters (primarily hydrogen peroxide, sea salt, and dust proxies) was used to date the ice cores, resulting in annual dating. The bottom depth ages for D4, D5, Sandy, and Katie were estimated at 1738, 1673, 1844, and 1934 A.D., with mean annual accumulation rates of 41.4, 35.2, 22.4, and 22.4 cmweq yr−1, respectively. These new records were in good agreement with previous accumulation maps and four previously published records from nearby multicentury ice cores. Spatial variability was quantified through an analysis of variance, thereby allowing for more meaningful comparisons to atmospheric processes. More regionally representative accumulation records were constructed for the central western and Summit regions spanning recent centuries using a principle component analysis of both the new and previously reported ice core measurements. These regional records exhibited 6–7% interannual variability (1 standard deviation of the mean) and had lower spatial variability uncertainties than individual accumulation records. Correlations indicate that ∼20% of the variance in the central western region was explained by the North Atlantic Oscillation (NAO), and suggests that an array of more northern ice cores may correlate more closely with NAO.

Periodic surface features in coastal East Antarctica

We found evidence for highly periodic dunes in a near‐coastal area of Dronning Maud Land, East Antarctica. Analysis of accumulation patterns, derived from ground‐penetrating radar (GPR) internal layering, and GPS‐based characteristics of surface topography, by means of auto‐ and cross‐covariance, indicate quasi‐harmonic oscillations of surface undulations, surface slope, and accumulation. The dunes occur at an elevation range of 1000–1350 m with the dominant wavelength of 5 km and undulations of ∼10 m. Accumulation and slope are anticorrelated at zero lag, with a mean annual accumulation of some 140 kg m−2 yr−1 and variations on the order of ±100 kg m−2 yr−1. Our findings have implications for studies aiming at the mass balance of coastal areas in Antarctica.

The geomorphic and paleoenvironmental record in the sediments of Atlin Lake, northern British Columbia

Atlin Lake in northern British Columbia and southern Yukon Territory is the largest natural lake in the North American Cordillera (791 km 2). Inflow from the Juneau Ice Field delivers large volumes of sediment to the proximal basins of Willison Bay and Llewellyn Inlet. Sediment is distributed by interflow and underflow through these basins. Based on acoustic data, each of these basins contain Holocene deposits about 120 m thick, representing mean annual accumulation since deglaciation of more than 1 cm/a. Cores confirm this, except that the formation of a small lake at the toe of Llewellyn Glacier during about the past 50 years is trapping sediment and has reduced accumulation in Llewellyn Inlet by an order of magnitude. Sills separate these basins from the main body of Atlin Lake and Torres Channel where accumulation is much less, averaging about 1–4 mm/a during the history of the lake. Late Pleistocene glacilacustrine sediment occurs as a thin, patchy deposit and is overlain by up to 10 m of Holocene lacustrine deposits. Unlike other large lakes in the Cordillera with thick late Pleistocene deposits indicating large volumes of sediment contributed by glaciers in the lakes and their basins, the pattern in Atlin Lake documents rapid retreat of glaciers from the lake and much of the drainage basin.