spatial and temporal variations of albedo on nine glaciers in western china from 2000 to 2011 this research demonstrates the spatiotemporal variations of albedo on nine glaciers in western china during 2000 2011 by the albedo derived from two types of datasets landsat tm etm images and mod10a1 product then the influence factors of glacier albedo and its relationship with glacier mass balance are also analyzed by the correlation approach which is frequently used in geostatistics the paper finds that there are different spatiotemporal variations over the glaciers in western china 1 for a single glacier the albedo varies gently with altitude on its tongue and increases fast in the middle part while in the accumulation zones the albedo value appears in the form of fluctuation this could provide a quantitative method to retrieve the snowline by determining the threshold albedo value of snowpack and bare ice 2 for the glaciers in western china the albedo decreases with distance to the center of tibetan plateau tp this may relate to the elevation of glacier for the speed of glacier retreat highly depends on air temperature 3 in the summer period albedo on most glaciers declines over the last 12years and it decreases much faster in southeastern tp than other regions for which air temperature overwhelms the black carbon concentration in addition the trend of glacier albedo in summer is greatly correlated with that of measured glacier mass balance which implies that the long term albedo datasets by remote sensing technology could be used to monitor and predict the change of glacier mass balance in the future 2013 john wiley sons ltd

changes in the parkland boreal forest boundary in northwestern ontario over the holocene abstract changes in vegetation were tracked from a well dated sediment core from a boreal lake lake 239 at 200 year resolution over the holocene this presently oligotrophic lake is located 100 km east from the present day parkland forest ecotone in northwestern ontario near shore sediment core transects from lake 239 have previously shown this lake was at least 8 m lower than present in the mid holocene or 58 less lake volume in comparison to today large shifts were expected in the terrestrial vegetation if the low lake levels were related to climate the core from lake 239 shows increases in the relative abundance and concentration of pollen such as cupressaceae and ambrosia indicating a more open boreal forest between 4500 8000 cal yr bp pollen based inferences of average summer and winter temperatures suggest that temperatures were on average up to 1 2 c warmer than today with winter temperatures up to 4 c warmer the pollen inferences also suggest enhanced precipitation likely in the summer but with an overall increase in evaporation and evapotranspiration resulting in reduced effective moisture to assess regional climate changes pollen based reconstructions of temperature and precipitation were developed and synthesized from sediment cores from eight previously published lakes from which pollen sites were available to both the west and east of lake 239 spanning present day prairie lakes to forested lakes up to 300 km east of the prairie boreal ecotone all sites show shifts in pollen assemblages that indicate a warm mid holocene period prairie sites west of the experimental lakes area ela show mid holocene decreases in precipitation relative to today whereas sites near or east of ela show consistent increases in precipitation but with increased temperatures and enhanced evaporation during the mid holocene

holocene water levels at rice lake ontario canada sediment pollen and plant macrofossil evidence four cores taken along a transect from the western basin and four cores from the middle basin of rice lake ontario provide evidence for shoreline transgression during the early holocene for low

uplift driven expansion delayed by middle holocene desiccation in lake winnipeg manitoba canada new findings of paleoenvironmental change in lake winnipeg southern manitoba reveal evidence of unexpectedly dry conditions from 7 5 to 4 ka 7500 to 4000 radiocarbon years before present with reduced lake area in the north and a desiccated lake basin in the south changes in extent of this large lake now 400 km long can be explained by a combination of 1 expansion due to postglacial differential uplift tilting and 2 lake area reduction due to drier climates associated with the former presence of dry grassland vegetation comparing lake areas sustainable by grassland climate with computed potential lake areas based on the assumption of open overflowing conditions we quantify the atmospheric moisture reduction represented by the middle holocene dry conditions this approach holds promise for calibrating regional models of climate change and exploring the effects of dry paleoclimates in other large lake basins such as the laurentian great lakes the ongoing postglacial tilting is of societal concern because it contributes to long term lakeshore erosion and to the decrease in discharge capacity of the inflowing flood prone red river in a populated region

upper ocean and subsurface variability in the bay of bengal during cyclone roanu a synergistic view using in situ and satellite observations in this study the upper ocean and subsurface variability during the different phases of the cyclonic storm roanu along the western bay of bengal bob in may 2016 are investigated by using the moored buoys argos hf radar and satellite datasets in the proximity of the cyclone track the moored buoy observations recorded a decrease of sea surface temperature sst by 1 c all over the track whereas increase in salinity by 1 5 psu was detected along with the highest wind speed of 16 m s 1 pressure drop of 14 hpa and air temperature drop of 4 c the cooling at the cyclone centers from the satellite data indicated higher lower sst drops when translation speed of the cyclone was low high and took more less time to recover to its pre cyclone state in southern northern bob mostly higher sst drop was observed along the right side of the cyclone track interestingly the opposite phenomenon occurred before landfall where sst drop was higher on the left due to upwelling in the head bay as observed both from wave rider buoy wrb at digha and satellite sst the wrb near vizag showed the maximum increase in significant wave heights by 2 4 m during the passage of cyclone argos also captured cyclone induced drop in temperature due to upwelling and entrainment reasonably well in the southwestern bay significant upwelling was observed from the argos with drop in temperature and increase in salinity in the upper layers however a strong stratification was observed from argos in the northwestern bob due to lesser salinity and higher precipitation the currents from in situ as well as hf radar datasets measured the increase in current magnitude during the passage of roanu rotary spectral analysis showed strong inertial currents with frequency 2 1 days at bd11 location with higher amplitudes of the clockwise component during the cyclone period

a reconstruction of moorhead and emerson phase environments along the eastern margin of glacial lake agassiz rainy river basin northwestern ontario mapping of quaternary geology in the rainy river lowland northwestern ontario resulted in discovery of several fossil bearing localities organic remains are associated with both the moorhead and

atmospheric storm triggered and intensified by geodynamics case studies from andaman sea and bay of bengal region in the indian ocean the study analyses the possible connection between the onset of cyclone and volcano tectonic seismicity in the andaman region the historical data of the major volcanic seismic and atmospheric events from the region show that several of the geodynamic activities were followed by severe atmospheric disturbances over the region in this study we consider the case of three recent cyclones phailin hudhud and nilam that either originated or were intensified over the andaman sea and bay of bengal and examine their correlation with the volcano tectonic seismic events during the cyclone occurrence the zenith total delay ztd time series derived from global positioning system data from the pbr2 station on andaman island overlapping with the period of the cyclone occurrence were examined to distinguish the onset and intensification of the atmospheric events the comparison of the sharp changes in ztd associated with the cyclone and the seismic events during the period indicates that the atmospheric changes almost coincide or follow the geodynamic activity our study illustrates that volcano tectonics of the region plays a role in the triggering of atmospheric disturbances

a method for monitoring glacier mass balance using satellite albedo measurements application to vatnajskull iceland we compare satellite albedo images of vatnajokull iceland with mass balance measurements for the years 1991 99 we find that the equilibrium line is mostly not visible when it is located above its position of the previous year s equilibrium line detection is further hindered by clouds and a gradual transition between ice and firn or snow consequently firn line elevation at the end of the melting season is not particularly useful for estimating the annual mass balance instead we propose to study the mean albedo of the entire ice cap throughout the melting season so that all available information about the surface albedo is taken into account the mean net potential global radiation which can be estimated from the mean surface albedo alone both depends on and influences summer melt it also depends on winter precipitation and integrated over the melting season is found to relate linearly to the specific mass balance b r 0 87 and 0 94 for different outlets of vatnajokull b can be estimated quantitatively when this relation is known and qualitatively when it is not the uncertainty in the satellite derived value of b is 0 5 0 8 m w e which for vatnajokull corresponds to about 27 of the interannual variability of b

upper ocean variability in the bay of bengal during the tropical cyclones nargis and laila upper ocean variability at different stages in the evolution of the tropical cyclones nargis and laila is evaluated over the bay of bengal bob during may 2008 and may 2010 respectively nargis initially developed on 24 april 2008 intensified twice on 27 28 april and 1 may and eventually made landfall at myanmar on 2 may 2008 laila developed over the western bob in may 2010 and moved westward towards the east coast of india data from the argo profiling floats the research moored array for african asian australian monsoon analysis and prediction rama and various satellite products are analyzed to evaluate upper ocean variability due to nargis and laila the analysis reveals pre conditioning of the central bob prior to nargis with warm 30 c sea surface temperature sst low 33 psu sea surface salinity sss and shallow 30 m mixed layer depths during march april 2008 enhanced ocean response to the right of the storm track due to nargis includes a large sst drop by 1 76 c sss increase up to 0 74 psu mixed layer deepening of 32 m shoaling of the 26 c isotherm by 36 m and high net heat loss at the sea surface during nargis strong inertial currents up to 0 9 ms 1 were generated to the right of storm track as measured at a rama buoy located at 15 n 90 e producing strong turbulent mixing that lead to the deepening of mixed layer this mixing facilitated entrainment of cold waters from as deep as 75 m and together with net heat loss at sea surface and cyclone induced subsurface upwelling contributed to the observed sst cooling in the wake of the storm a similar upper ocean response occurs during laila though it was a significantly weaker storm than nargis

a study of ablation variations on the tongue of hintereisferner austrian alps austria here we discuss the interpretation of detailed ablation measurements on the tongue two profiles are considered one along the glacier axis and one across the glacier tongue at the crossing an energybalance station was operated providing the necessary meteorological data at all stakes the albedo was measured several times with a simple light weight instrument described separately in the appendix the absorption of solar radiation was calculated for all stake positions taking into account local albedo slope aspect and shading effects it appears that the differences in ablation can be explained almost entirely by the differences in surface albedo both along and across the glacier tongue

modelling albedo and specific balance of the greenland ice sheet calculations for the sondre stromfjord transect glacio meteorological data obtained during the greenland ice margin experiment gimex investigations in west greenland the sondre stromfjord transect have been used to test and calibrate four energy balance mass balance models for the ice snow surface the region is characterised by the development of a wide zone of low surface albedo in the course of the melting season this zone was simulated in one of the energy balance models by including the effect of surficial meltwater on albedo observed mass balance and albedo data were used to constrain the models although all the models are capable of predicting the transect balance reasonably well only the model with the meltwater albedo coupling is able to reproduce the observed albedo pattern and mass balance profile along the transect by including the feedback between surficial meltwater and albedo in the model the sensitivity of the specific balance to changes in air temperature is found to be greatest just below the equilibrium line in contrast to what is generally found for valley glaciers a 1 k warming of the air temperature would increase the mean ablation along the transect by 0 5 m w e year 1

diatom inferred changes in effective moisture during the late holocene from nearshore cores in the southeastern region of the winnipeg river drainage basin canada the winnipeg river drainage basin wrdb within the boreal forest region of northwest ontario is a region that is expected to be negatively affected by climate warming inferences of droughts over the past two millennia from little raleigh lake were based on two nearshore sediment cores the core locations were from depths of 12 and 15 m and were based on sufficient nearshore sediment accumulation and distance from the modern benthic to planktonic diatom boundary where a distinct shift from dominance of benthic taxa changed to dominance of planktonic taxa in surficial sediments at 11 8 m diatom inferred depth was based on a model developed from 60 surficial sediments within the study lake depth inferences indicate that prolonged periods of aridity occurred from ad 950 to 1300 corresponds to medieval climate anomaly and from ad 1625 to 1750 aridity during little ice age we found that the core collected from a depth closer to the benthic to planktonic diatom boundary was more sensitive to changes in lake level than the deeper core where planktonic diatoms dominated the assemblage the inferred low water stands of the past two millennia are well outside of the range of the past 100 years suggesting that recent drought history may not be a good estimate of future extremes

regional aridity in north america during the middle holocene increased aridity throughout the great plains and rocky mountain region during the middle holo cene has been documented from pollen records aeolian proxy variables in lake cores and active sand dune migration varve calibration provided by a continuously varved record of the holocene from a core from elk lake northwestern minnesota shows that the influx of aeolian clastic material increased beginning about 8 ka and ended about 3 8 ka with peak aeolian activity at about 6 ka if aeolian influx to elk lake corresponds in time to aeolian influx in other lakes and to maximum dune activity in minnesota dune fields then the varve calibration in elk lake provides precise time calibration of periods of peak aeolian activity in minnesota palaeowind studies from the minnesota dune fields show that the dominant wind direction when the dunes were active was from the northwest the same as the dominant wind direction in dune fields throughout the great plains and rocky mountains if the mid holocene aeolian act

estimating the mass balance of vatnajokull iceland from noaa avhrr imagery we investigate the possibility of obtaining the mass balance of vatnajo kull iceland from us national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr albedo images for the years 1991 2002 de ruyter de wildt and others 2002 demonstrated that the mean potential absorbed radiation averaged over the melting season correlates well with the mean specific mass balance and that can be estimated from the evolution of the surface albedo here we improve the retrieval method of de ruyter dewildt and others 2002 by introducing the more realistic 6s atmospheric transfer model and by adding the latest narrowto broadband ntb albedo conversion equations bidirectional reflectance distribution functions for both ice and snow are used where appropriate we show that the choice of the ntb conversion equations greatly influences the calculated measured mass balance correlates well with if enough cloud free images can be found through the year and if the spatial variation in measured mass balances is high enough the correlation coefficient for all drainage basins combined is 0 92 with a residual standard deviation of 0 18mw e we present an estimated mass balance series for the whole of vatnajo kull based on our findings switching between different avhrr instruments over time may cause serious errors in the calculated mass balance

the ablation zone in northeast greenland ice types albedos and impurities ice types albedos and impurity content are characterized for the ablation zone of the greenland ice sheet in kronprinz christians land 80 n 24 w along this ice margin the width of the ablation zone is only about 8 km the emergence and melting of old ice in the ablation zone creates a surface layer of dust that was originally deposited with snowfall high on the ice sheet this debris cover is augmented by locally derived wind blown sediment subsequently the surface dust particles often aggregate together to form centimetre scale clumps that melt into the ice creating cryoconite holes the debris in the cryoconite holes becomes hidden from sunlight raising the area averaged albedo relative to surfaces with uniform debris cover spectral and broadband albedos were obtained for snow ice hummocks debris covered ice cryoconite studded ice and barren tundra surfaces broadband ice albedos varied from 0 2 for ice with heavy loading of uniform debris to 0 6 for ice hummocks with cryoconite holes the cryoconite material itself has albedo 0 1 when wet areal distribution of the major surface types was estimated visually from a transect video as a function of distance from the ice edge 330 m a s l ablation rates were measured along a transect from the ice margin to the slush zone 8 km from the margin 550 m a s l traversing both pleistocene and holocene ice ablation rates in early august averaged 2 cm d 1 impurity concentrations were typically 4 3 mg l 1 in the subsurface ice surface concentrations were about 16 g m 2 on surfaces with low impurity loading and heavily loaded surfaces had concentrations as high as 1 4 kg m 2 the mineralogical composition of the cryoconite material is comparable with that of the surrounding soils and with dust on a snowdrift in front of the ice margin implying that much of the material is derived from local sources a fine mode clay is present in the oldest ice but not in the nearby soil suggesting that its origin is from wind deposition during pleistocene glaciation

distributed mass balance modelling on two neighbouring glaciers in ortles cevedale italy from 2004 to 2009 a 6 year application of an enhanced temperature index mass balance model to careser and la mare glaciers eastern italian alps is presented the two glaciers exhibit very different characteristics and a comprehensive dataset of distributed mass balance measurements was used to test the model performance the model was run using meteorological data acquired outside the glaciers the work was focused on two main aspects 1 the development of a morphological redistribution procedure for snow and 2 the comparison of three different melt algorithms proposed in the literature the results show that the simple method proposed for snow redistribution can greatly improve simulation of winter balance and further improvements would be achievable by collecting data on inaccessible and high altitude areas all three melt formulations displayed a good skill level and very similar results in modelling the mass balance distribution over glacier areas with slightly better results from a multiplicative algorithm in capturing the vertical balance gradient the simulation errors are related to aspect and elevation and tend to be spatially aggregated some assumptions concerning the spatial and temporal distribution of air temperature and incoming solar radiation although reasonable and widely used in the literature may be responsible for this aggregation hence there is a need to further investigate the processes that regulate the distribution of melt energy and that appear to control the current deglaciation phase in this area

east antarctic sea ice albedo thickness distribution and snow cover characteristics of springtime sea ice off east antarctica were investigated during a cruise of the australian national antarctic research expedition in october through december 1988 the fractional coverage of the ocean surface the ice thickness and the snow cover thickness for each of several ice types were estimated hourly for the region near the ship these observations were carried out continuously during the 4 weeks the ship was in the ice thin and young ice types were prevalent throughout the region and the observations show a systematic increase in the total area weighted pack ice thickness including open water area from only 0 2 m within 50 km of the ice edge to 0 45 m close to the coast ice thickness averaged over the ice covered region only is also relatively thin ranging from 0 35 m near the ice edge to 0 65 m in the interior these values are probably typical of average winter thickness for the area the average snow cover thickness on the ice increased from 0 05 m near the ice edge to 0 15 m in the interior average ice concentration increased from less than 6 10 near the ice edge to 8 10 in the interior the ship observed concentrations were in good agreement with concentrations derived from passive microwave satellite imagery except in some regions of high concentration in these regions the satellite derived concentrations were consistently lower than those estimated from the ship possibly because of the inability of the satellite sensors to discriminate the appreciable percentage of very thin ice observed within the total area spectral albedo was measured for nilas young grey ice grey white ice snow covered ice and open water at wavelengths from 420 to 1000 nm allwave albedo was computed by using the spectral measurements together with estimates of near infrared albedo and modeled spectral solar flux area averaged albedos for the east antarctic sea ice zone in spring were derived from representative allwave albedos together with the hourly observations of ice types these area averaged surface albedos increased from about 0 35 at the ice edge to about 0 5 at 350 km from the edge remaining at 0 5 to the coast of antarctica the low average albedo is in part due to the large fraction of open water within the pack but extensive fractions of almost snow free thin ice also play an important role

cold climate during the closest stage 11 analog to recent millennia abstract the early part of marine isotopic stage 11 near 400 000 years ago provides the closest analog to holocene insolation levels of any interglaciation during the era of strong 100 000 year climatic cycles the ch 4 concentration measured in vostok ice fell to 450 ppb and co 2 values to 250 ppm these natural decreases contrast with the increases in recent millennia and support the early anthropogenic hypothesis of major gas emissions from late holocene farming during the same interval d values fell from typical interglacial to nearly glacial values indicating a major cooling in antarctica early in stage 11 other evidence suggests that new ice was accumulating during the closest insolation analog to the present day a major increase in 18 o atm at vostok a similar increase in marine 18 o values and re initiation of ice rafting in the nordic sea the evidence permits extended 20 000 year intervals of stage 11 interglacial warmth in the antarctic and north atlantic yet it also requires that this warmth ended and a new glacial era began when insolation was most similar to recent millennia the holocene co 2 anomaly was produced only in part by direct anthropogenic emissions over half of the anomaly resulted from the failure of co 2 values to fall as they had during previous interglaciations because of natural responses including a sea ice advance in the antarctic and ice sheet growth in the northern hemisphere

contact spectroscopy for determination of stratigraphy of snow optical grain size we present a technique for in situ measurement of the vertical and spatial stratigraphic distribution of snow optical grain size with a coupled contact illumination probe and field spectroradiometer accurate measurements of optical equivalent grain size are critical for modeling radiative properties of snow such as spectral albedo and microwave emission measurements of the spectral reflectance of the snow pit surface are made at 2 cm intervals in the vertical plane under constant illumination and view geometries we invert the integral of the continuum normalization of the ice absorption feature with maximum at 1 03 mm wavelength for optical equivalent grain size using the validated model of nolin and dozier 2000 that has accuracy of 10 50 mm across the grain size range 50 900 mm results are presented for an alpine site in southwest colorado usa across the ablation season and for a greenland ice sheet site at the onset of snowmelt these results suggest that traditional measurements of grain size using a hand lens are nearly accurate only for rounded grains r 2 0 41 rmse 160 mm for polycrystals and faceted grains the hand lens approach is very inaccurate r 2 0 03 and 0 24 rmse 1206 and 1010 mm respectively we demonstrate an order of magnitude improvement in modeling of shortwave spectral albedo and net shortwave flux with contact spectroscopy measurements of grain size stratigraphy over those from a hand lens

diatom inferred lateglacial and holocene climatic variability in the south carpathian mountains romania climatic and environmental changes were studied using siliceous algae diatoms and chrysophycean cysts analyses in a mountain lake in the south carpathian mountains for the lateglacial and holocene lake brazi 1740 a s l is a small shallow lake in the retezat mountains according to the basal radiocarbon dating of the core the lake was formed around 15 750 cal bp and sediment accumulation has been continuous ever since high resolution diatom analyses were carried out together with loss on ignition and biogenic silica measurements total epilimnetic phosphorus tp concentrations and ph were reconstructed quantitatively ten statistically significant zones were distinguished six of which appeared in the lateglacial and early holocene suggesting the instability of diatom assemblages after deglaciation the uppermost zone covered six thousand years which suggests that diatom assemblages remained quite stable during the second half of the holocene high lake level occurred between 9500 and 9000 cal bp after 6300 cal bp the lake level gradually increased again until 5800 cal bp a further increase was detected at 3000 cal bp while after 1500 cal bp water level decreased although there is limited knowledge regarding the environmental constraints of several diatom taxa present in the sequence e g aulacoseira laevissima which makes the precise environmental interpretation of the diatom record more difficult the available data provide an important new insight into the environmental history of lake brazi and the carpathian mountains the most remarkable changes in the aquatic ecosystem were observed at 6000 cal bp in the holocene and 12 800 cal bp at the onset of the younger dryas marked changes were also detected at 10 500 10 300 9800 9500 9000 8900 8800 8300 6300 5800 and 3100 3000 cal bp

middle holocene dry climate caused by change in atmospheric circulation patterns evidence from lake levels and stable isotopes sediment hiatuses detritus layers and inwashed terrestrial moss layers in five cores at crawford lake ontario canada show that the lake level was low between ca 4 8 and 2 ka 1 ka 1000 14 c yr b p this low level is attributed to a dry and warm climate which has also been documented at other sites in southern ontario southern michigan and southern wisconsin oxygen isotope 18 o values from authigenic marl show a negative shift of 2 4 from 9 to 11 4 vienna peedee belemnite between ca 5 and 2 ka enhanced evaporation under dry and likely closed basin conditions would lead to more enrichment in 18 o so we suggest that the trend to depleted 18 o indicates a significant change in the 18 o value of the source meteoric water the major moisture source for the great lakes region is the gulf of mexico from which the amount and seasonality of precipitation are affected by the interplay of air masses from the gulf of mexico and north pacific probably controlled by jet stream positions and storm tracks in the late middle holocene the isotopically heavy moisture from the gulf might have contributed less precipitation and or a higher proportion in winter months probably caused by more frequent eastward extension of dry pacific air depleted in 18 o this hypothesis implies that the 18 o values of paleoprecipitation in the middle holocene reflected moisture source history more strongly than paleotemperature

climate related eutrophication of a small boreal lake in northwestern ontario a palaeolimnological perspective a palaeolimnological investigation of changes in water quantity and quality in lake 239 experimental lakes area in northwestern ontario indicates marked changes in limnological conditions during the holocene water quantity changes are based on the analysis of diatoms and inferences of lake level changes from a nearshore sediment core changes in water quality are based on the analysis of diatom assemblages and associated quantitative inferences of total phosphorus tp from a deep central core as well as changes in diatom accumulation rates the proportion of chrysophyte scales to diatoms and changes to organic matter content lake levels at least 8 m lower than today were inferred from the nearshore core and were concurrent with an increase in nutrient rich diatom assemblages an increase in diatom accumulation and a decrease in the chrysophytes relative to diatoms in the central core fragilaria crotonensis and aulacoseira subarctica were two of the dominant nutrient rich taxa that contributed to an

scale dependent analysis of satellite imagery for characterization of glacier surfaces in the karakoram himalaya abstract information regarding process structure relationships and change in the karakoram himalaya is of great importance in studying glacier hydrollogy mass balance and dynamic environmental change such information is not readily available detailed spatio temporal assessment requires field investigation coupled with quantitative remote sensing studies we conducted an investigation of the large batura glacier in pakistan to determine if spectral variability can be quantified and used to characterize glacier surfaces specifically spot panchromatic satellite data were evaluated for differentiating features of glacier structure resulting from ice movement ablation and supraglacial fluvial action image semivariogram analysis was conducted for assessing spectral variability patterns and fractal analysis was used to examine scale dependent variation in the data results indicate that spectral variability from fields of ice seracs can exhibit fractal characteristics although most surface features on the glacier exhibit a change in the fractal dimension over different ranges in scale the fractal dimension was found to be useful for differentiating between glacier surfaces such as white ice and debris covered ice characteristics of the debris load and the scale dependent nature of calculating the fractal dimension ultimately determined the potential of class separability

spectral reflectances of snow and fresh water ice from 340 through 1100 nm interpretation des mesures effectuees au spectroradiometre a balayage determination des plages de reflectance de la neige fraiche ou peu transformee des inclusions de glace de la neige fondante regelee des crepes du brash et slush

patterns of early lake evolution in boreal landscapes a comparison of stratigraphic inferences with a modern chronosequence in glacier bay alaska the chronosequence approach which infers temporal patterns of environmental change from a spatial array of modem sites has been a major tool for studying successional processes a model of early lake ontogeny in boreal landscapes developed from a chronosequence of lakes in alaska suggests that long term soil development and related hydrological change produce a loss of alkalinity and base cations a decrease in ph an increase in doc and a transient increase followed by a decrease in lakewater nitrogen concentrations over time we compare this model of lake ontogeny with patterns of change reconstructed from diatom assemblages in 10 sediment cores from the same region lakewater ph declined in the majority of lakes but the pattern rate and magnitude of decline varied considerably among sites apparently related to local differences in hydrologic setting inferred trends in nitrogen concentration over time are not spatially uniform and appear to vary because of local differences in vegetation history

diurnal patterns of the bi directional reflectance of fresh water ice to improve the interpretation of surface cryospheric albedo from satellite sensor data diurnal measurements of the spectral bidirectional reflectance of a commonly found fresh water ice type were made from which hemispherical reflectance can be derived the purpose of this study is to document its clear sky bidirectional reflectance characteristics in the visible 650 670 nm and near infrared 810 840 nm region assess the diurnal nature of the reflectance and quantify the surface anisotropy bidirectional reflectances of the refrozen slush ice measured show a spectral dependence and change significantly with solar zenith angle considerable variation occurs at each view angle and among view angles throughout the day although diurnal reflectance patterns were similar in both bands magnitudes varied greatly being highest in the visible and lowest in the near infrared region with the exception of peak saturated specular values in the forward scatter direction bidirectional reflectance was generally highest in the morning when the surface and the illumination were most diffuse in character

spatial and temporal variations of the surface albedo and other factors influencing urumqi glacier no 1 in tien shan china glacier albedo controls the surface energy budget the variability of which affects the glacier surface melt rate and in turn impacts the mass balance of the glacier during 2013 and 2014 spatial and temporal variations of albedo were investigated using 18 landsat images of urumqi glacier no 1 factors influencing these spatiotemporal profiles were analyzed an established retrieval process including geolocation radiometric calibration atmospheric topographic and anisotropic correction and narrow to broadband conversion was applied for the first time to landsat 8 images differences between landsat image derived albedo values and albedo values measured using a handheld spectroradiometer ranged from 0 024 to 0 049 spatial and temporal variations of surface albedo were significant especially in the ablation area the variability of the values of ice albedo ranged from 0 06 to 0 44 due to topographic effects and light absorbing impurities the results suggest that this retrieval method can be used to investigate the spatial and temporal variability of surface albedo from landsat 8 images on mountain glaciers moreover as constant albedo values for ice and snow cannot be assumed the distribution of albedo was not completely dependent on altitude under conditions of more intense ablation and by reason of light absorbing impurities during the melt season

the interaction of supertyphoon maemi 2003 with a warm ocean eddy understanding the interaction of ocean eddies with tropical cyclones is critical for improving the understanding and prediction of the tropical cyclone intensity change here an investigation is presented of the interaction between supertyphoon maemi the most intense tropical cyclone in 2003 and a warm ocean eddy in the western north pacific in september 2003 maemi passed directly over a prominent 700 km 500 km warm ocean eddy when passing over the 22 n eddy rich zone in the northwest pacific ocean analyses of satellite altimetry and the best track data from the joint typhoon warning center show that during the 36 h of the maemi eddy encounter maemi s intensity in 1 min sustained wind shot up from 41 ms 1 to its peak of 77 m s 1 maemi subsequently devastated the southern korean peninsula based on results from the coupled hurricane intensity prediction system and satellite microwave sea surface temperature observations it is suggested that the warm eddies act as an effective insulator between typhoons and the deeper ocean cold water the typhoon s self induced sea surface temperature cooling is suppressed owing to the presence of the thicker upper ocean mixed layer in the warm eddy which prevents the deeper cold water from being entrained into the upper ocean mixed layer as simulated using the coupled hurricane intensity prediction system the incorporation of the eddy information yields an evident improvement on maemi s intensity evolution with its peak intensity increased by one category and maintained at category 5 strength for a longer period 36 h of time without the presence of the warm ocean eddy the intensification is less rapid this study can serve as a starting point in the largely speculative and unexplored field of typhoon warm ocean eddy interaction in the western north pacific given the abundance of ocean eddies and intense typhoons in the western north pacific these results highlight the importance of a systematic and in depth investigation of the interaction between typhoons and western north pacific eddies

postglacial water level changes of a small lake in southern quebec canada sediment stratigraphy and palaeobotanical data from five cores were used to reconstruct the postglacial water level changes of a small lake in southern quebec the cores were taken along two transects from the centre of the lake to the margins lake level was relatively high before 11 000 cal bp when sedimen tation was characterized by the deposition of silty gyttja 13 000 cal bp and marl 13 000 11 000 cal bp from 11 000 to 7000 cal bp a sediment hiatus was indicated by the lack of two regional pollen zones between the marl and the overlying gyttja suggesting either nondeposition or erosion of the previously deposited sedi ments due to a low lake level the lake level was approximately 2 m lower than present on the basis of macrofossil assemblages a rise in the water level of about 1 m occurred around 7000 cal bp which was interrupted by a second lowering between 6100 and 4400 cal bp as indicated by a hiatus in the pollen stratigra phy during this low period the water level was at leas

comparison of in situ and landsat derived reflectance of alaskan glaciers abstract calculation of snow and ice albedo is necessary for developing physically realistic simulations of the earth s climate using general circulation models and useful for analysis of glacier mass balance change using remote sensing reflectances calculated from tm data and corrected for atmospheric effects correspond with in situ measured reflectances in the nadir viewing mode and are shown to be related to a glacier s mass balance if measured over a period of years a reflectance of 0 895 for a test site in the wrangell mountains alaska was calculated from tm band 4 0 76 0 90 m data and corrected for atmospheric effects this value was comparable to the in situ reflectance of 0 90 measured in the same 0 76 0 90 m wavelength region for the same site a reflectance value of 0 79 derived from integrating over most 0 40 3 0 m of the reflective portion of the electromagnetic spectrum was quite different from the integrated reflectance of 0 95 calculated for the spectral range 0 40 1 0 m this demonstrates the importance of using the full reflective energy spectrum for calculating the albedo of snow and for obtaining a meaningful computation of a glacier s energy and mass balance change

the surface albedo of the greenland ice sheet satellite derived and in situ measurements in the sondre stromfjord area during the 1991 melt season the temporal and spatial variation in the surface albedo of the greenland ice sheet during the ablation season of 1991 is investigated the study focuses on an area east of sondre stromfjord measuring 200 km by 200 km and centred at 67 5 n 48 13 w the analysis is based on satellite radiance measurements carried out by the advanced very high resolution radiometer avhrr the broad band albedo is estimated from the albedos in channel 1 visible and channel 2 near infrared the results are calibrated with the surface albedo of sea and dry snow satellite derived albedos are compared with gimex ground measurements at three stations there is a high degree of consistency in temporal variation at two of the three stations large systematic differences are attributed to albedo variations on subpixel scale in the course of the ablation season four zones appear each parallel to the ice edge it is proposed that these are in order of increasing altitude i clean and dry ice ii ice with surface water iii superimposed ice and iv snow an extensive description of these zones is given on the basis of the situation on 25 july 1991 zones i iii and iv reveal fairly constant albedos 0 46 0 65 and 0 75 on average whereas zone ii is characterised by an albedo minimum 0 34 survey of the western margin of the greenland ice sheet up to 71 n shows that the zonation occurs between 66 and 70 n

combining satellite multispectral image data and a digital elevation model for mapping debris covered glaciers automated glacier mapping from satellite multispectral image data is hampered by debris cover on glacier surfaces supraglacial debris exhibits the same spectral properties as lateral and terminal moraines fluvioglacial deposits and bedrock outside the glacier margin and is thus not detectable by means of multispectral classification alone based on the observation of low slope angles for debris covered glacier tongues we developed a multisource method for mapping supraglacial debris the method combines the advantages of automated multispectral classification for clean glacier ice and vegetation with slope information derived from a digital elevation model dem neighbourhood analysis and change detection is applied for further improvement of the resulting glacier debris map a significant percentage of the processing can be done automatically in order to test the sensitivity of our method against different dem qualities it was also applied to a dem obtained from aster stereo data additionally we compared our multisource approach to an artificial neural network ann classification of debris using only multispectral data while the combination with an aster derived dem revealed promising results the ann classification without dem data does not

century scale paleoclimatic reconstruction from moon lake a closed basin lake in the northern great plains estimates of past lake water salinity from fossil diatom assemblages were used to infer past climatic conditions at moon lake a climatically sensitive site in the northern great plains a good correspondence between diatom inferred salinity and historical records of mean annual precipitation minus evapotranspiration p et strongly suggests that the sedimentary record from moon lake can be used to reconstruct past climatic conditions century scale analysis of the holocene diatom record indicates four major hydrological periods an early holocene transition from an open freshwater system to a closed saline system by 7300 b p which corresponds with a transition from spruce forest to deciduous parkland to prairie and indicates a major shift from wet to dry climate a mid holocene period of high salinity from 7300 to 4700 b p indicating low effective moisture p et a transitional period of high salinity from 4700 to 2200 b p characterized by poor diatom preservation and a late holocene period of variable lower salinity during the past 2 200 yr indicating fluctuations in effective moisture

spectral signature of alpine snow cover from the landsat thematic mapper mapping of snow and estimation of snow characteristics from satellite remote sensing data require that we distinguish snow from other surface cover and from clouds and compensate for the effects of the atmosphere and rugged terrain the spectral signature of the snowpack is calculated from a radiative transfer model accounting for scattering and absorption by the ice grains water inclusions and particulates in interpreting the spectral reflectance measured from the thematic mapper or from any other satellite we need to account for topographic effects without requiring that satellite data be precisely registered to digital elevation data because the poor quality of most digital elevation data introduces considerable noise into calculations of slope and azimuth for a range of snow types atmospheric profiles and topographic illumination conditions i estimate typical spectral signatures for the landsat thematic mapper tm images of the southern sierra nevada are analyzed to distinguish several classes of snow from other surface covers snow can be reliably distinguished from other surfaces and from clouds at all sun angles encountered in the mid latitudes in tm band 1 or 2 snow is brighter than other natural surfaces and in band 5 clouds are usually much more reflective than snow therefore the intersection of the following criteria maps the snow cover planetary reflectance rp in tm band 1 is greater than about 0 16 rp tm5 is less than about 0 2 the normalized band 2 5 difference rp tm2 rp tm5 rp tm2 rp tm5 is greater than about 0 4 large surface grain sizes can be distinguished from areas where the grain size is finer at the snow surface using tm bands 2 4 and 5 because of saturation in tm band 1 estimation of the degree of contamination by absorbing aerosols is not feasible rp tm2 rp tm5 rp tm2 rp tm5 is

hydrologic variation in the northern great plains during the last two millennia abstract reconstructions of lake water salinity at decadal resolution for the last 2000 yr are compared among three lakes in north dakota to infer regional patterns of drought the intersite comparisons are used to distinguish local variation in climate or hydrology from regional patterns of change at one lake diatom inferred salinity and lake water mg ca inferred from ostracode shell chemistry are coherent both in terms of direction and magnitude of change indicating that each is a robust technique for reconstructing lake water chemistry the data show that the last 2000 yr have been characterized by frequent shifts between high and low salinity suggesting shifts between dry and moist periods long intervals of high salinity suggest periods of multiple decades when droughts were intense and frequent thus indicating times when drought was more persistent than in the 20th century both the medieval period and little ice age were hydrologically complex and there is no clear evidence to suggest that either interval was coherent or unusual in effective moisture relative to long term patterns differences among the three sites may be attributed to variation in local hydrology and these differences emphasize the need for multiple sites in deriving regional climate interpretations from paleoecological data

reconstruction of holocene lake level from diatoms chrysophytes and organic matter in a drainage lake from the experimental lakes area northwestern ontario canada abstract a paleolimnological study of lake level changes in lake 239 rawson lake a headwater lake in the experimental lakes area in northwestern ontario indicates large fluctuations have occurred over the holocene analyses are based on diatoms the proportion of chrysophyte scales to diatoms and organic matter content from near shore sediment cores quantitative estimates of lake level are based on a diatom inferred depth model that was developed from surficial sediments collected along several transects in lake 239 declines of 1 3 m occurred during the late holocene whereas declines of at least 8 m occurred during the more arid mid holocene these results provide the first substantive evidence of large declines in lake level in northwestern ontario during the mid holocene conditions during the mid holocene may provide a partial view of future conditions under increasing global temperatures

submesoscale processes at shallow salinity fronts in the bay of bengal observations during the winter monsoon abstractlateral submesoscale processes and their influence on vertical stratification at shallow salinity fronts in the central bay of bengal during the winter monsoon are explored using high resol

temporal and spatial variation of the surface albedo of the morteratschgletscher switzerland as derived from 12 landsat images this investigation uses landsat images from 12 days in 1999 and 2000 to study the spatial and temporal variation in surface albedo of a glacier with a rugged topography morteratschgletscher switzerland our retrieval method considers all processes that substantially influence the relationship between the satellite signal and the surface albedo the correction for the anisotropy of the reflected radiation field of ice and snow ranges up to 0 10 depending on wavelength band solar zenith angle and surface type we analyzed the uncertainties in the retrieval method and mainly expect errors in satellite derived albedos for areas with large variation in topography and high albedos the latter is due to application of bidirectional reflectance distribution function brdf parameterizations for the anisotropic correction to albedos outside the parameterizations validity on average satellite derived albedos exceed the measured surface albedo by 0 03 the glacier tongue is characterized by bands of low and high albedo relating to ice with higher and lower concentrations of debris the ice albedo shows no dependence on altitude except at 2000 2200 m a s l it increases during summer which is likely associated with rainfall as concluded from a comparison between summer rainfall and measured albedos

effects of bubbles cracks and volcanic tephra on the spectral albedo of bare ice near the transantarctic mountains implications for sea glaciers on snowball earth 1 spectral albedo was measured along a 6 km transect near the allan hills in east antarctica the transect traversed the sequence from new snow through old snow firn and white ice to blue ice showing a systematic progression of decreasing albedo at all wavelengths as well as decreasing specific surface area ssa and increasing density broadband albedos under clear sky range from 0 80 for snow to 0 57 for blue ice and from 0 87 to 0 65 under cloud both air bubbles and cracks scatter sunlight their contributions to ssa were determined by microcomputed tomography on core samples of the ice although albedo is governed primarily by the ssa and secondarily by the shape of bubbles or snow grains albedo also correlates highly with porosity which as a proxy variable would be easier for ice sheet models to predict than bubble sizes albedo parameterizations are therefore developed as a function of density for three broad wavelength bands commonly used in general circulation models visible near infrared and total solar relevance to snowball earth events derives from the likelihood that sublimation of equatorward flowing sea glaciers during those events progressively exposed the same sequence of surface materials that we measured at allan hills with our short 6 km transect representing a transect across many degrees of latitude on the snowball ocean at the equator of snowball earth climate models predict thick ice or thin ice or open water depending largely on their albedo parameterizations our measured albedos appear to be within the range that favors ice hundreds of meters thick

late holocene climatic changes in west africa a high resolution diatom record from equatorial cameroon abstract holocene climatic changes in west africa are usually explained by increased decreased activity of the monsoon from the guinean gulf toward the continent according to a diatom record from lake ossa 3 50 n 9 36 e we suggest that in the near coastal areas of cameroon phases of intensification of the monsoon were marked by reduced precipitation and reduced evaporation conditions nowadays prevailing south of the equator 4 5 s during the austral winter lake ossa is a shallow lake located in one of the rainiest area of the african rain forest belt during the wet season march november it is fed by acid meteoric waters entailing low ph in the lacustrine waters during the dry season december february groundwater discharges allow the persistence of acid waters near the borders of the lake but in the inner parts the waters tend to be alkaline alkaliphilous diatoms are abundant in the surface sediment samples and are used as indicators of low precipitation at that time atmospheric dust containing reworked diatoms from saharan quaternary deposits is transported by the northern trade winds and reaches the ossa area wind blown diatoms are considered as a signature of the northern trade winds a diatom record from the western deep part of lake ossa has provided climatic data for the mid late holocene at a resolution of 50 60 years a major climatic change at 2700 cal yr bp was marked by the appearance of wind blown diatoms a millennial scale alternation between low and high precipitation episodes is recorded during the last 5500 years the low precipitation episodes before 2700 cal yr bp are interpreted as a consequence of a northward extension of the climatic conditions that nowadays characterize the southern congo during the austral winter when the monsoon extends into west africa and reaches the northern sub tropical latitudes the effects of low precipitation on the water balance and on the rain forest were obliterated by an extremely low evaporation between 2700 and 1300 cal yr bp precipitation was high and the rain forest intensively disturbed in response to convective storms a low precipitation episode between 1300 and 600 cal yr bp is explained contrarily to the previous similar episodes by tropical rainfalls located farther south than today during a larger part of the year the modern climate settles at about 600 cal yr bp the climatic oscillations on a millennial time scale were apparently coincident with temperature changes in the northern and southern atlantic suggesting that the monsoon over west africa was essentially driven by interactions between both hemispheres this interpretation is in agreement with available data from other equatorial and sub tropical regions of west africa

air sea coupling during the tropical cyclones in the indian ocean a case study using satellite observations in the years 1999 and 2001 three intense tropical cyclones formed over the northern indian ocean two over the bay of bengal during 15 19 and 25 29 october 1999 and one over the arabian sea during 21 28 may 2001 we examined the thermal salinity and circulation responses at the sea surface due to these severe cyclones in order to understand the air sea coupling using data from satellite measurements and model simulations it is found that the sea surface temperature sst cooled by about 0 5 0 8 c in the bay of bengal and 2 c in the arabian sea in the bay of bengal this cooling took place beneath the cyclone center whereas in the arabian sea the cooling occurred behind the cyclone only a few days later this contrasting oceanic response resulted mainly from the salinity stratification in the bay of bengal and thermal stratification in the arabian sea and the associated mixing processes in particular the cyclones moved over the region of low salinity and smaller mixed layer depth with a distinct mixed layer deepening to the left side of the cyclone track it is envisaged that daily satellite estimates of sst and sea surface salinity sss using outgoing longwave radiation olr and model simulated mixed layer depth would be useful for the study of tropical cyclones and prediction of their path over the northern indian ocean

elevational changes in meteorological variables along a midlatitude glacier during summer during the summer of 1994 a glaciometeorological experiment was carried out on the pasterze a glacier in austria this paper reports on the data from six energy balance stations ranging in altitude from 2075 to 3225 m above sea level asl the wind regime was dominated by the glacier wind on the tongue directional constancies ranged between 0 94 and 0 97 mean 2 m wind speed and specifie humidity were almost constant along the glacier the variation in the 2 m temperature along the glacier cannot be described by the usually assumed constant decrease with elevation on the tongue the 2 m temperature even increased with elevation a much better description of the temperature distribution is given by a linear relation between the potential temperature and the distance along the flow line this can be understood from a simple thermodynamic analysis of the glacier wind layer it is further shown that changes in clear sky global radiation with elevation are due mainly to changes in local albedo and relief and hardly at all to changes in absolute optical path length and atmospheric water vapor and aerosol content on the tongue the laterally averaged ice albedo is almost constant with elevation the flux of incoming long wave radiation during clear sky conditions at u2 2310 m asl was 48 w m2 higher than the flux at u5 3225 m asl on average more than half of the difference was due to systematic differences in the shape of the temperature profile probably the inversion depth is larger at u2 the rest can be ascribed to higher 2 m temperatures and larger amounts of upper hemisphere slopes at u2 the distributions of the meteorological variables and the parameterizations described in this paper might be incorporated in surface energy balance models designed to simulate the surface mass balance

a scale dependent model to represent changing aerodynamic roughness of ablating glacier ice based on repeat topographic surveys turbulent fluxes make a substantial and growing contribution to the energy balance of ice surfaces globally but are poorly constrained owing to challenges in estimating the aerodynamic roughness length z0 here we used structure from motion sfm photogrammetry and terrestrial laser scanning tls surveys to make plot scale 2 d and 3 d microtopographic estimations of z0 and upscale these to map z0 across an ablating mountain glacier at plot scales we found spatial variability in z0 estimates of over two orders of magnitude with unpredictable z0 trajectories even when classified into ice surface types tls derived surface roughness exhibited strong relationships with plot scale sfm z0 estimates at the glacier scale a consistent increase in z0 of 0 1 mm d 1 was observed space for time substitution based on time since surface ice was exposed by snow melt confirmed this gradual increase in z0 over 60 d these measurements permit us to propose a scale dependent temporal z0 evolution model where unpredictable variability at the plot scale gives way to more predictable changes of z0 at the glacier scale this model provides a critical step towards deriving spatially and temporally distributed representations of z0 that are currently lacking in the parameterisation of distributed glacier surface energy balance models less

spectral albedos of sea ice and incident solar irradiance in the southern beaufort sea spectral albedos and incident spectral irradiances have been measured over the wavelength range 400 to 2400 nm on the sea ice near the naval arctic research laboratory narl at pt barrow alaska the observation interval extended from mid may when the ice was still relatively cold until mid june when summer melting was fully established the temporal dependence of albedo for the available surface types was obtained over this time interval showing a general decrease from snow and snow covered ice to blue ice and melt ponds data were also obtained for glacier ice on the athabasca glacier for melting lake ice and for certain other nonice surfaces in the vicinity of narl snow and ice albedos are characteristically highest at visible wavelengths decreasing strongly in the infrared because of the increase in absorption by ice and water local maxima in the spectra correspond to minima in the ice and water absorption variations in albedo are due primarily to differences in the vapor bubble density crystal structure and free water content of the upper layers of the ice incident spectral shortwave radiation was measured as a function of cloudiness and the optical thickness of arctic clouds is significantly less than the thickest clouds at lower latitudes the decrease of the infrared component relatiave to the visible portion of the irradiance with increasing cloud cover is determined this can give rise to an increase in wavelength integrated albedos of as much as 15 using the present data a graphical method is outlined by which visible near infrared satellite imagery can be used to distinguish among melt ponds open leads and other spring and summer sea ice surface types

a statistical description of the microstructure of young sea ice in order to fully exploit microwave models of sea ice the standard ice characterization must be supplemented by a statistical description of the ice microstructure for the strong fluctuation theory this statistical description takes the form of the mean and variance of the permittivity plus correlation lengths we have computed these statistics for over 50 samples of young ice including both columnar congelation ice and desalinated bubbly ice samples were taken from different vertical depths and horizontal positions within the ice sheet and encompassed a comprehensive range of ice temperatures and brine volumes for each of these samples horizontal thin sections were photographed then digitized and analyzed on a personal computer based image processing system results indicate that correlation lengths correspond to the physical dimensions of the inclusions the brine pocket size typically tenths of a millimeter for saline ice and the air bubble size typically millimeters for desalinated ice for saline ice the shape of the correlation function was elliptical similar to the shape of the brine pockets in one case as the ice warmed from 20 to 1 c and the brine volume increased from 2 to 37 the correlation length increased from 0 14 to 0 22 mm

complex responses of phototrophic communities to climate warming during the holocene of northeastern ontario canada historical changes in holocene climate in northeastern ontario were quantified using analyses of sedimentary pollen diatoms and pigments in a small boreal lake modern analog reconstructions of a

role of mesoscale eddies on the variability of biogenic flux in the northern and central bay of bengal 1 mesoscale cyclonic eddies cold core are though known to enhance the phytoplankton biomass in the bay of bengal their contribution to the carbon export to the deep ocean are yet to be quantified using biogenic flux data obtained from the sediment traps located at 17 27 n 89 13 e northern bay of bengal trap nbbt and 13 07 n 84 24 e central bay of bengal trap cbbt we explored the variability of biogenic flux in response to cyclonic eddies temporal variation of the biogenic flux at nbbt 1994 1998 and cbbt 1993 1996 showed four distinct peaks with no well defined seasonal pattern the inverse relationship between the high flux events and sea surface height anomaly ssha along with the dominant periodicity of 10 15 weeks from the chi square analysis of ssha confirmed the role of eddies in the observed higher biogenic fluxes during the eddy events enhanced opal flux suggested eddy driven new production while lower carbonate to opal ratio along with high organic carbon indicated large export via diatoms finally we show that 42 of the total organic carbon collected at mid depth 1000 m in the bay of bengal is contributed by eddy driven processes via diatom bloom making it a regional sink for co2

deglaciation chronology and revegetation in northwestern ontario along a 420 km transect in northwestern ontario canada sediments from four lakes were analyzed with respect to lithology pollen and macrofossils radiocarbon dates show that the region was deglaciated between ca 11 500 and 8000 years bp and periods of both rapid ice retreat and readvance influenced the history of glacial lake agassiz in the south the ice sheet was succeeded by a lengthy interval of park tundra with stands of spruce ash and elm the ash and elm seem to have disappeared during a suggested cool period 11 100 10 200 years bp farther north the park tundra phase lasted not more than 50 100 years after ca 10 200 years bp before boreal trees dominated the climatic change around 10 200 years bp permitted the very rapid migration of spruce larch birch and jack or red pine into northwestern ontario from northern minnesota the migration routes for pinus strobus white pine alnus rugosa and a crispa were divided however one from the south south of lake superior and one from t

theory of the optical properties of lake ice a radiative transfer model is developed to illustrate the processes which determine the spectral albedo and transmission of lake ice the calculated spectral albedo is dominated by specular reflection from the ice surface in the near infrared whereas multiple scattering by bubbles below the surface dominates the visible albedo adding a snow cover to lake ice will normally increase the visible albedo but may reduce the albedo in some regions of the near infrared if the sun is low by reducing the specular reflection in a preliminary test of the model spectral albedo was measured on the natural ice cover of a frozen lake the measurements are explained using the radiative transfer model applied to the air bubble size distribution measured in the same ice the uncertainty in measurement of bubble size distribution leads to uncertainty in the theoretical albedo which is much larger than the error due to approximations used in derivation of the model