early diagenetic transformation of higher plant triterpenoids in deep sea sediments from baffin bay abstract a sediment sequence of early miocene to holocene from ocean drilling program site 645 in central baffin bay was found to contain abundant triterpenoids of higher plant origin including monodesmethyl derivatives and other oxidative degradation products 24 nor triterpenoids of the oleanene ursene and lupane series were found in the nonaromatic hydrocarbon and alcohol fractions of the sediment extracts other diagenetic transformation products included 24 28 dinor olean 17 ene and 24 nor urs 12 en 1 1 one as well as their tentatively identified des a counterparts the identification of these novel degradation products was confirmed by synthesis of a suite of reference compounds the simple reaction sequence applied to obtain 24 nor urs 12 ene from 3 acetoxyurs 12 en 24 oic acid is likely to happen in a similar manner during early diagenesis of organic matter in nature these results have implications for the understanding of the diagenetic reaction sequence leading to the formation of other demethylated triterpenoids of terrigenous origin e g 24 28 dinor lupanes 28 30 dinor 17 hopane is sometimes the dominant hydrocarbon in the most deeply buried samples its co occurrence with higher plant triterpenoids and the low abundance of other regular hopanoids is not considered an indication however that 28 30 dinor 17 hopane is derived from a higher plant precursor molecule it is suggested that two independent sedimentary processes are responsible for the presence of the two types of demethylated triterpenoids observed in baffin bay sediments

alkane terpene and polycyclic aromatic hydrocarbon geochemistry of the mackenzie river and mackenzie shelf riverine contributions to beaufort sea coastal sediment abstract to study the largest source of river sediment to the arctic ocean we have collected suspended particulates from the mackenzie river in all seasons and sediments from the mackenzie shelf between the river mouth and the shelf edge these samples have been analyzed for alkanes triterpenes and polycyclic aromatic hydrocarbons pahs we found that naturally occurring hydrocarbons predominate in the river and on the shelf these hydrocarbons include biogenic alkanes and triterpenes with a higher plant peat origin diagenetic pahs from peat and plant detritus petrogenic alkanes triterpenes and pahs from oil seeps and or bitumens and combustion pahs that are likely relict in peat deposits because these components vary independently the season is found to strongly influence the concentration and composition of hydrocarbons in the mackenzie river while essentially the same pattern of alkanes diagenetic hopanes and alkyl pahs is observed in all river and most shelf sediment samples alkane and triterpene concentration variations are strongly linked to the relative amount of higher plant peat material polycyclic aromatic hydrocarbon molecular mass profiles also appear to be tied primarily to varying proportions of peat with an additional petrogenic component which is most likely associated with lithic material mobilized by the mackenzie river at freshet consistent with the general lack of alkyl pahs in peat the higher pahs found in the river are probably derived from forest and tundra fires a few anthropogenic pyrogenic compounds are manifest only at the shelf edge probably due to a weakening of the river influence we take this observation of pyrogenic pahs and the pronounced source differences between two sediment samples collected at the shelf edge as evidence of a transition from dominance by the mackenzie river to the geochemistry prevalent in arctic regions far removed from major rivers

early diagenesis of terrigenous triterpenoids and its implications for petroleum geochemistry abstract the distribution of triterpanes in sediments and crude oils is commonly used for oil oil and oil source rock correlation in petroleum geochemistry while isomer ratios of such compounds are applied as maturity parameters the triterpane pattern in terrestrially influenced geological samples is however remarkably less diverse than the triterpenoid skeletons occurring in the extant higher plant biosphere natural observations laboratory experiments and molecular mechanics calculations have revealed that acid catalysed double bond isomerization and skeletal rearrangement reactions of terrigenous triterpenoids during early diagenesis are the key to understanding the triterpane patterns in more matured geological materials examples studied in detail are the double bond isomerization of oleanenes and the subsequent hydrogenation of the products into oleanane and 18 oleanane and the transformation of taraxer 14 ene and lup 20 29 ene into oleanenes although the reactions are likely to be kinetically controlled the main products formed and ultimately preserved are the thermodynamically most stable ones the experimental results and natural observations have significant implications for the use of terrigenous triterpenoid compounds in petroleum geochemistry

rise in frequency of surface melting at siple dome through the holocene evidence for increasing marine influence on the climate of west antarctica 1 a new melt layer history from siple dome west antarctica indicates notable late holocene summertime warming visual stratigraphic analyses of the 1004 m ice core identified 62 years with melt layers melting events began around 11 7 ka followed by a period of no melting from 8 8 6 6 ka melt layer frequency increased from 6 6 ka to the present with the 1000 year average melt layer frequency reaching a maximum of 2 at 0 8 ka we use our millennial scale archive of melt events as a unique seasonal paleothermometer to elucidate changes in west antarctic holocene summer climate our calibration suggests the change in melt frequency from 0 to 2 may represent a summer temperature increase of 2 c from the middle to late holocene this temperature change cannot be explained entirely by local change in ice elevation or summer insolation and is in contrast to east antarctic climate records which show peak warmth in the early holocene followed by stable or decreasing temperature we interpret the rise in melt frequency as evidence of an increasing marine influence on the ross sea sector of west antarctica although the surface elevation of siple dome has not changed greatly the continued lateral retreat of the west antarctic ice sheet from its last glacial maximum configuration across the outer continental shelf and the delayed drawdown in ice thickness from the adjacent coastal marie byrd land region in conjunction with periods of increased cyclogenesis perhaps related to variations in enso would allow a moderated maritime climate to more easily reach west antarctica

novel tricyclic and tetracyclic terpanes in tertiary deltaic oils structural identification origin and application to petroleum correlation abstract tricyclic terpanes of the cheilanthane series in crude oils and sediments are routinely used for geochemical correlation the cheilanthanes are particularly useful to identify crude oils derived from marine clastic or carbonate source rock as well as input to the source rocks from marine algal or terrigenous organic matter however they sometimes have limitations for the correlation of oils expelled from different source rocks that received similar organic matter e g oils from source rocks dominated by terrigenous organic matter novel non cheilanthane tricyclic terpanes consisting of c21 and c25 compounds and a c27 tetracyclic terpane were identified in oils from the assam india beaufort mackenzie canada and the niger nigeria deltas nmr data reveal that all three compounds have an oleanane type structure with rings c d and e intact while rings a and b have been degraded leaving a side chain attached to ring c in the case of the tricyclics and only a degraded a ring in the tetracyclic on the basis of occurrence nmr structure and co variance with oleanane abundance these new tricyclic and tetracyclic compounds are believed to form from a ring functionalised oleanoid precursors in angiosperm flowering plants the distribution of these compounds in representative oils from the niger delta accumulations permits separation of the oils into at least three distinct source rock organofacies

effect of surface roughness on bidirectional reflectance of antarctic snow the angular pattern of sunlight reflected by snow is altered by surface roughness which in the interior of antarctica is usually in the form of meter scale longitudinal erosional features sastrugi whose axes align with the direction of strong winds the bidirectional reflectance distribution function brdf changes over the course of a day as the solar azimuth changes relative to the sastrugi axis the normalized brdf or anisotropic reflectance factor r was measured at south pole station from a 22 m tower at 600 660 and 900 nm wavelengths the r pattern was similar at the three wavelengths it probably varies little from 300 to 900 nm measurements were made at solar zenith angles 0 from 67 to 90 over the full range of viewing zenith angle r azimuth angle between sun and view and azimuth angle between sun and sastrugi sas variation of r with sas was notable sastrugi oriented perpendicular to the solar beam cause a reduction of the forward peak and sastrugi at an oblique angle cause r to lose its symmetry about the solar azimuth however the effects of sastrugi are mostly restricted to large viewing zenith angles so remote sensing of albedo and atmospheric properties can be carried out accurately without knowledge of sastrugi height and orientation if only near nadir views are used this recommendation is opposite that for observations of broken clouds over dark surfaces for which large r is preferred a parameterization of r is developed valid for viewing angles r 50 sastrugi can cause a reduction of the snow albedo by altering the angle of incidence and by trapping of photons for the small sastrugi of the antarctic plateau the albedo is unaffected at visible wavelengths but can be reduced by a few percent at near infrared wavelengths when the sun is low

larsen ice shelf has progressively thinned the retreat and collapse of antarctic peninsula ice shelves in tandem with a regional atmospheric warming has fueled speculation as to how these events may be related satellite radar altimeter measurements show that between 1992 and 2001 the larsen ice shelf lowered by up to 0 27 0 11 meters per year the lowering is explained by increased summer meltwater and the loss of basal ice through melting enhanced ocean driven melting may provide a simple link between regional climate warming and the successive disintegration of sections of the larsen ice shelf

the diagenetic fate of taraxer 14 ene and oleanene isomers abstract the extractable organic matter in holocene to early miocene deep sea sediments from site 645 odp leg 105 in baffin bay contains almost exclusively biological markers of terrigenous origin pentacyclic triterpenoids of the ursene and amyrin oleanene type often occur as the most abundant compounds in the aliphatic hydrocarbon ketone and alcohol fractions of the sediment extract a specific diagenetic reaction involves the conversion of taraxer 14 ene into olean 12 ene in the upper 700 metres of the sedimentary sequence the taraxerene to oleanene conversion is complete before the onset of isomerisation of diasterenes at c 20 in the sediment as well as in laboratory simulation experiments olean 12 ene further isomerises to olean 13 18 ene and olean 18 ene the latter of which may be the direct precursor of 18 h and 18 h oleanane found in sediments containing more mature organic matter and in crude oils the subsurface interconversion of these triterpenoid skeletons indicate that oleanane does not necessarily start life as an oleanoid

climate response to increasing antarctic iceberg and ice shelf melt mass loss from the antarctic continent is increasing however climate models either assume a constant mass loss rate or return snowfall over land to the ocean to maintain equilibrium numerous studies have investigated sea ice and ocean sensitivity to this assumption and reached different conclusions possibly due to different representations of melt fluxes the coupled atmosphere land ocean sea ice model hadgem3 gc3 1 includes a realistic spatial distribution of coastal melt fluxes a new ice shelf cavity parameterization and explicit representation of icebergs this configuration makes it appropriate to revisit how increasing melt fluxes influence ocean and sea ice and to assess whether responses to melt from ice shelves and icebergs are distinguishable we present results from simulated scenarios of increasing meltwater fluxes and show that these drive sea ice increases and for increasing ice shelf melt a decline in antarctic bottom water formation in our experiments the mixed layer around the antarctic coast deepens in response to rising ice shelf meltwater and shallows in response to stratification driven by iceberg melt we find similar surface temperature and salinity responses to increasing meltwater fluxes from ice shelves and icebergs but midlayer waters warm to greater depths and farther north when ice shelf melt is present we show that as meltwater fluxes increase snowfall becomes more likely at lower latitudes and antarctic circumpolar current transport declines these insights are helpful for interpretation of climate simulations that assume constant mass loss rates and demonstrate the importance of representing increasing melt rates for both ice shelves and icebergs

melting runoff and the formation of frozen lakes in a mixed snow and blue ice field in dronning maud land antarctica large scale melting phenomena such as meltwater drainage channels and meltwater accumulation basins of frozen lakes were surveyed on the land ice mass in jutulgryta dronning maud land antarctica during the norwegian antarctic research expedition in 1989 90 nare 1989 90 the largest frozen lake that was observed was close to 1 km in width these melting features were also detected in a landsat thematic mapper image recorded on 12 february 1990 then during nare 1993 94 a 5year glaciological programme was started in this area in spite of negative air temperatures and the presence of a frozen ice surface sub surface melting and runoff were found within the uppermost metre in blue ice fields the sub surface melting is a consequence of solar radiative penetration and absorption within the ice i e the solid state greenhouse effect temperatures in blue ice were about 6 c higher than for snow internal melt and meltwater transport were observed throughout the 1 month of measurements the conditions for active melting in jutulgryta are probably marginal a slight increase of air temperatures can result in more classical surface melting whereas a cooling may disable sub surface melting studies of how the extent and characteristics of the melting features change with time can be particularly valuable as indicators of climate change this ongoing programme clearly identifies the importance of analyzing how these melting features originate of mapping their present areal distribution of determining how sensitive they are to climate change and of studying changes in the past and possible changes in the future

surface melting derived from microwave radiometers a climatic indicator in antarctica this paper aims at presenting a new dataset including the melt events derived from microwave remote sensing occurring in antarctica from summer 1979 80 to 2005 06 the method for detecting melt events and sources of error is presented and then trends in melt duration for every pixel are extracted from the dataset mapped and analyzed the analysis focuses on two particular cases and the main results show that 1 the trends over the period 1980 2006 in the antarctic peninsula match with lengthening of the melt season on the ice shelves and surprisingly shortening of the melt season in the mountainous area of the peninsula and 2 the trends over the period 1996 2006 on the entire continent show a dipolar pattern with the western regions experiencing decreasing melt duration whereas east antarctica and the ross ice shelf experience increasing melt duration this pattern closely mirrors the temperature pattern expected when the southern annular mode is in a decreasing trend as it is over the period 1996 2006 for further analysis and validation the dataset has been made available at http www lgge obs ujf grenoble fr picard melting

δ2 triterpenes early intermediates in the diagenesis of terrigenous triterpenoids a series of 2 triterpenoids oleana 2 12 diene oleana 2 13 18 diene oleana 2 18 diene ursa 2 12 diene and taraxera 2 14 diene has been identified in holocene buried mangrove sediments florida usa by comparison of the mass spectra of and by co injections with authentic standards in the oligocene brandon lignite vermont usa oleana 2 12 diene and oleana 2 13 18 diene were also identified along with two a ring contracted amyrin derivatives by comparison with the sedimentary occurrence of related analogues of oxyallobetulin and betulin and the demonstrated diagenetic formation of lup 2 ene from lupan 3 one these novel terrigenous biological markers are considered diagenetic products formed by dehydration of precursor molecules such as and amyrin and taraxerol the identification of these early intermediates brings us one step closer to the full understanding of the diagenetic fate of terrigenous triterpenoids

exceptional preservation of angiosperm markers in miocene and eocene ambers the traditional organic geochemical view suggests that polar triterpenoids are degraded easily during fossilization of organic matter for the first time we show that dammarane type tetracyclic polar triterpenoids are preserved in the geosphere hydroxydammarenone 20 hydroxy 24 dammaren 3 one a typical constituent of extant dipterocarpaceae an angiosperm tree family derived dammar resin is preserved in miocene amber the oxidative products of hydroxydammarenone i e 20 24 epoxy 25 hydroxydammaran 3 one and hexakisnor dammaran 3 20 dione are found in both miocene and eocene ambers the presence of hydroxydammarenone in miocene amber clearly depicts that natural biotriterpenoid markers can be preserved in the geosphere for tens of millions of years this result demonstrates that the dammarane type oxygenated compounds which are extensively used in archaeological studies can also be utilized as diagnostic markers for paleochemosystematics

aromatized arborane fernane hydrocarbons as molecular indicators of floral changes in upper carboniferous lower permian strata of the saar nahe basin southwestern germany abstract thirty seven coal samples of upper carboniferous and lower permian age from three boreholes in the saar nahe basin germany have been studied by organic geochemical and coal petrological methods the investigations were aimed at the recognition of floral changes in the upper carboniferous and lower permian strata the results show that compositional changes in the extracts are only partly caused by variations in coalification specific aromatic hydrocarbons appear in upper westphalian d coal seams and increase in concentration up to the rotliegendes the dominant compound has been identified by mass spectrometry and nmr spectroscopy as 5 methyl 10 4 methylpentyl des a 25 norarbora ferna 5 7 9 triene math and always occurs associated with 25 norarbora ferna 5 7 9 triene both compounds are thought to originate from isoarborinol fernene 3 ol or fernenes the strongly acidic conditions during deposition of the coals might have induced the 4 5 cleavage combined with a methyl shift in an arborane fernane type pentacyclic precursor yielding the math based on petrological investigations palynomorphs related to early gymnospermopsida such as pteridospermales and coniferophytes cordaitales and coniferales increased in abundance in the strata beginning with the upper westphalian d concomitant with the above mentioned biomarkers the results suggest the arborane fernane derivatives originate from the plant communities producing these palynomorphs

long melt seasons on ice shelves of the antarctic peninsula an analysis using satellite based microwave emission measurements we have examined the record of melt season duration on the antarctic peninsula using two techniques for detecting the presence of a melt signal in microwave emission time series covering the period 1978 2000 we have obtained similar estimates of melt season length using the cross polarized gradient ratio xpgr technique and calibrations previously applied in greenland and a technique which detects the jump in emission caused by melt without using a sensor and frequency dependent threshold value the close correspondence between results from the two techniques on peninsula ice shelves suggests that the xpgr analysis can be used over the length of the time series the results show that the long melt seasons of 1992 93 and several later years were exceptional occurrences on the northern parts of the larsen ice shelf these melt seasons were followed by disintegration events supporting a possible cause and effect relationship

snow and firn permeability at siple dome antarctica the nature of air snow exchange processes depends upon both the physical characteristics of the snow and forcing from the atmosphere an understanding of snow air transport processes and models of these processes are important for interpreting ice cores and for predicting remotely sensed snow surface characteristics accurate modeling requires knowledge of the physical characteristics of the snow and firn in this paper measurements of snow and firn permeability from the surface down to 12 m depth at siple dome antarctica are presented the permeability varies greatly as a function of layer and depth generally increasing to approximately 3 m and generally decreasing below that the maximum permeability 280 10 10 1 0 m2 occurs at approximately 3 m depth the lowest permeability in the top 12 m of snow and firn 10 10 10w m2 was measured in the surface wind pack the measurements show that layering and microstructure have large effects on permeability a mathematical expression for the overall variation of permeability with depth is presented it is shown that snow density is a poor indicator of permeability quantitative microscopy may be helpful in relating observed snow characteristics to permeability and useful in modeling firnification and chemical species transport

scale effect on geomorphologic and kinematic dispersion geomorphologic dispersion relates to the fraction of the variance of residence time distributions that can be directly linked to the heterogeneity of the paths available to hydrologic runoff of a river basin in response to suitable rainfall pulses it thus defines the dispersive characters of geomorphological origin hillslope transport processes and systematic variations of advective processes in the channel network define a kinematic component of dispersion here we suggest that channel borne kinematic effects are likely to be clouded by hillslope dispersion in a surprisingly wide spectrum of basin scales we find that the signatures of hillslope transport on travel time distributions do not fade away rapidly with the size of the catchment i e when the basin scale becomes much greater than the mean hillslope size in particular because of their major impact on the skewness of the travel time distribution we suggest that an appropriate description of hillslope channel transitions entails a combination of geomorphic and kinematic effects which plays a decisive role in shaping the main characters of the hydrologic response in cases of practical interest

radar sounding through the earth s ionosphere at 45 mhz radar sounding from aircraft or ground coupled radars has long provided scientists with a powerful technique to sound through ice layers to retrieve local depth and layering structure more recently it has been used to detect shallow aquifers in warm dry and desert regions at mars a long wavelength radar sounding from low orbit altitudes has produced global maps that reveal the presence of ice layering at all latitudes and glacial deposits on the flanks of volcanoes until now sounding from the earth orbit at wavelengths long enough to penetrate ice sheets and arid sand was thought to be infeasible because of the electromagnetic properties of the ionosphere in this paper we show that a radar sounding at frequencies as low as 45 mhz is in fact theoretically possible under viewing conditions that occur often enough to be practical this conclusion opens up a previously unutilized portion of the electromagnetic spectrum for large scale spaceborne remote sensing of subsurface features on the earth

seasonal evolution of supraglacial lakes on an east antarctic outlet glacier supraglacial lakes are known to influence ice melt and ice flow on the greenland ice sheet and potentially cause ice shelf disintegration on the antarctic peninsula in east antarctica however our understanding of their behavior and impact is more limited using 150 optical satellite images and meteorological records from 2000 to 2013 we provide the first multiyear analysis of lake evolution on langhovde glacier dronning maud land 69 11 s 39 32 e we mapped 7990 lakes and 855 surface channels up to 18 1 km inland 670 m above sea level from the grounding line and document three pathways of lake demise i refreezing ii drainage to the englacial subglacial environment on the floating ice and iii overflow into surface channels on both the floating and grounded ice the parallels between these mechanisms and those observed on greenland and the antarctic peninsula suggest that lakes may similarly affect rates and patterns of ice melt ice flow and ice shelf disintegration in east antarctica

molecular characterization of fossil and extant dammar resin extracts insights into diagenetic fate of sesqui and triterpenoids abstract the composition of sesquiterpenoids and triterpenoids in the solvent extract of extant miocene and eocene dammar i e class ii resins has been determined and compared to investigate the vulnerability of these biomarkers to diagenesis molecular evidence e g absence of bicadinanes and low rock eval maturity values tmax

a thermo hydrodynamic modelling study of an idealized low elevation blue ice area in antarctica low elevation blue ice areas in antarctica can contain significant amounts of subsurface liquid water during summer and may experience internal melt freeze cycles due to absorption of shortwave radiation an existing 2 d x z model has been used to study the phenomenon and this is improved by changing the lower boundary condition from a no flux condition to one that lets heat through and by changing the bulk optical properties to spectral values both changes made the model more realistic the optical and thermal boundary conditions together with the optical attenuation coefficient have a large effect on the amount of water produced in the ice our results show that if the lower boundary condition is changed from no flux to radiating subsurface melting is reduced dramatically using a spectral albedo produces less melting than using a corresponding bulk albedo the other variables left unchanged if optical properties are changed to spectral values the melting is different than using bulk values if the linear extent of the blue ice area is 0 7 and the subsurface ponds can persist over the winter if the albedo is 0 4

below surface ice melt on the coastal antarctic ice sheet in the jutulgryta area of dronning maud land antarctica subsurface melting of the ice sheet has been observed the melting takes place during the summer months in blue ice areas under conditions of below freezing air and surface temperatures adjacent snow covered regions having the same meteorological and climatic conditions experience little or no subsurface melting to help explain and understand the observed melt rate differences in the blue ice and snow covered areas a physically based numerical model of the coupled atmosphere radiation snow and blue ice system has been developed the model comprises a heat transfer equation which includes a spectrally dependent solar radiation source term the penetration of radiation into the snow and blue ice depends on the solar radiation spectrum the surface albedo and the snow and blue ice grain sizes and densities in addition the model uses a complete surface energy balance to define the surface boundary conditions it is run over the full annual cycle simulating temperature profiles and melting and freezing quantities throughout the summer and winter seasons the model is driven and validated using field observations collected during the norwegian antarctic research expedition nare 1996 97 the simulations suggest that the observed differences between subsurface snow and blue ice melting can be explained largely by radiative and heat transfer interactions resulting from differences in albedo grain size and density between the two mediums

climate variables along a traverse line in dronning maud land east antarctica temperature density and accumulation data were obtained from shallow firn cores drilled during an overland traverse through a previously unknown part of dronning maud land east antarctica the traverse area is characterised by high mountains that obstruct the ice flow resulting in a sudden transition from the polar plateau to the coastal region the spatial variations of potential temperature near surface firn density and accumulation suggest that katabatic winds are active in this region proxy wind data derived from firn density profiles confirm that annual mean wind speed is strongly related to the magnitude of the surface slope the high elevation of the ice sheet south of the mountains makes for a dry cold climate in which mass loss owing to sublimation is small and erosion of snow by the wind has a potentially large impact on the surface mass balance a simple katabatic wind model is used to explain the variations of accumulation along the traverse line in terms of divergence convergence of the local transport of drifting snow the resulting wind and snowdrift patterns are closely connected to the topography of the ice sheet ridges are especially sensitive to erosion while ice streams and other depressions act as collectors of drifting snow

surface melting on antarctic peninsula ice shelves detected by passive microwave sensors a 13 year time series of spaceborne passive microwave radiance measurements over the antarctic peninsula ice shelves reveals a systematic increase in the duration of the summer melt season combined with data from meteorological stations on the antarctic peninsula the annual motion and long term trends of the 0 c isotherm can be monitored

studies of snow surface characteristics by landsat tm in dronning maud land antarctica large scale melting phenomena like meltwater drainage channels and meltwater accumulation basins or frozen lakes have been surveyed on the land ice mass in dronning maud land antarctica these melting features were also detected in a landsat thematic mapper tm image recorded on 12 february 1990 image processing techniques such as principal component pc analysis band ratioing and histogram equalizing are carried out to emphasize the melting phenomena interestingly a histogram equalized single tm band 5 image appears to be a good discriminator leaving the melting phenomena as bright areas in the tm scene the largest frozen lake is close to 1km wide while some of the drainage channels stretch more than 5 km there is also a comparison of satellite derived and in situ reflectance and temperature the atmospheric corrected satellite data underestimate surface snow albedo by about 16 while tm measurements of surface temperature are 2 to 6 c lower than that measured on the ground

biomarker and micropetrographic investigations of coal from the krepoljin brown coal basin serbia abstract we investigated early diagenetic processes of the extractable organic matter from the miocene freshwater sequence which consists of coal fragments in clays sandstones and shales alternating with continuous brown coal layers we examined eight coals thirteen sediments and three non coaly underground layers the molecular assemblages of the identified aliphatic hydrocarbons in the krepoljin basin reflect the abundance of plant taxa as precursors or participants in the early diagenetic stage the data provide insight into the conditions prevailing in the lakes and bogs during early diagenesis the dominance of diterpanes indicates that the prevalent of the organic matter was of gymnosperous origin the hopanoid contents are considered to reflect microbial activity that the organic matter in the miocene krepoljin coal basin is immature was confirmed by the presence of biolipids such as hopanes c 27 17 h trisnorhopan saturated and aromatized abietanes pimaranes and phyllocladanes the most abundant compounds in all samples indicate a predominantly higher plant input related to the coniferous group but identification of the individual plant families was not possible amyrin and other triterpenoid derived triaromatic and triaromatic c ring cleaved hydrocarbons with triterpenoid structures are thought to be characteristic for angiosperms unsaturated compounds 2 triterpanes early intermediaries in the diagenetic transformation of angiosperms also indicate a low degree of sediment maturity

blue ice areas in antarctica derived from noaa avhrr satellite data we have mapped antarctic blue ice areas using the u s national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr antarctica cloud free image mosaic established by the united states geological survey the mosaic consists of 38 scenes acquired from 1980 to 1994 our results show that approximately 60 000 km2 of blue ice exist for each of the two main types of blue ice melt induced and wind induced normally the former type is located on slopes in coastal areas where climate conditions i e persistent winds and temperature together with favourable surface orientation sustain conditions for surface and near surface melt the latter blue ice category occurs near mountains or on outlet glaciers often at higher elevations where persistent winds erode snow away year round and combined with sublimation creates areas of net ablation furthermore we have identified an additional area of 121 000 km2 as having potential for blue ice however in these areas features such as mixed pixels glazed snow surfaces crevasses and or shadows make interpretation more uncertain in conclusion a conservative estimate of antarctic blue ice area coverage by this method is found to be 120 000 km2 0 8 of the antarctic continent with a potential maximum of 241 000 km2 1 6 of the antarctic continent

extent and duration of antarctic surface melting the extent and duration of surface melting on the antarctic ice shelves and margins of the antarctic ice sheet are derived from satellite passive microwave data for 1978 87 the occurrence of surface melting in daily maps of t b is indicated by a marked increase in microwave brightness temperature t b which is caused by moisture in the near surface firn t b increases of more than 30 deg above the annual mean t b are chosen to indicate melting most antarctic surface melting occurs during december and january the observed melting is correlated with regional air temperatures but some melt patterns also appear to be related to katabatic wind effects the correlations suggest that the surface melting in antarctica increases about 3 5 10 6 d km 2 per degree of summer temperature increase the surface melt index duration times area of melting calculated for antarctica is 24 10 6 d km 2 averaged over nine summers the observed inter annual and regional variability is large surface melting was most extensive during the 1982 83 summer 36 10 6 d km 2 and least extensive during the 1985 86 summer 15 10 6 d km 2 the data indicate a decline in surface melting over the 9 years but meaningful inferences regarding trends in surface melting are precluded by the large inter annual variability

temperatures heating rates and vapour pressures in near surface snow at the south pole a finite volume model is used to simulate 9 years 1995 2003 of snow temperatures at the south pole the upper boundary condition is skin surface temperature derived from routine upwelling longwave radiation measurements while the lower boundary condition is set to the seasonal temperature gradient at 6 5 m depth taken from prior measurements at the south pole we focus on statistics of temperature heat fluxes heating rates and vapour pressures in the top metre of snow but present results from the full depth of the model 6 5 m the monthly mean net heat flux into the snow agrees with results from previous studies performed at the south pole on shorter timescales the heating rates and vapour pressures show large variability the net heat flux into the snow which is between 5wm 2 in the monthly mean can be greater than 20 w m 2 on hourly timescales on sub daily timescales heating rates exceed 40 k d 1 in the top 10 cm of the snow subsurface temperatures and therefore heating rates are more variable during winter april september due to increased synoptic activity and the presence of a strong surface based atmospheric temperature inversion the largest vapour pressures 60 70 pa and vertical gradients of vapour pressure are found in the top metre of snow during the short summer december january in contrast during the long winter the low temperatures result in very small vapour pressures and insignificant vapour pressure gradients the high summertime vapour pressure gradients may be important in altering the isotopic composition of snow and ice on the antarctic plateau

the central myanmar burma oil family composition and implications for source abstract geochemical characteristics of 31 miocene through eocene oils seeps an eocene coal and an eocene resin from the central myanmar burma basin system are examined the oils seeps vary widely in api gravity 8 52 sulfur concentration 26 3550 ppm 13 c 27 6 to 23 4 and molecular composition this variability is caused by varying amounts of biodegradation superimposed upon a single genetic oil family and the difference between aliphatic and aromatic hydrocarbon carbon isotope ratios i e 13 c arom 13 c aliph provides a useful gauge of the extent of biodegradation the projected geochemical characteristics of unaltered central myanmar oils are as follows a api gravity 35 37 b s 0 05 0 10 c 13 c aliph 27 8 to 27 6 d 24 ethylcholestanes are the dominant steranes and e 20s 24 ethyldiacholestane various bicadinanes and oleanane are present the ratio of 18 h 22 29 30 trisnorneohopane to 17 h 22 29 30 trisnorhopane t s t m is postulated as a maturity parameter and on this basis relative bicadinane concentration increases and the trans trans trans cis cis trans bicadinane ratio decreases with increasing thermal maturity in this oil set geologic arguments suggest a deep paleogene source for these oils two geochemical arguments that support this inference are a the occurrence of saturated and unsaturated c 15 and c 30 cadinane monomers and dimers in pyrolyzates of an eocene resin and the kerogen from an eocene coal and b identical compound specific carbon isotope ratios for selected isoprenoids and n alkanes in a typical central myanmar oil and the hydrous pyrolyzate expelled from an eocene coal we propose an eocene resinous shale coal source for these oils with the oldest eocene reservoirs filling first and the youngest miocene reservoirs filling last consistent with the observation that the least mature oils are present in the oldest reservoirs according to this model surface seepage and near surface oil could result from subsurface traps that are filled to spillpoint

antarctic surface and subsurface snow and ice melt fluxes abstract this paper presents modeled surface and subsurface melt fluxes across near coastal antarctica simulations were performed using a physical based energy balance model developed in conjunction with detailed field measurements in a mixed snow and blue ice area of dronning maud land antarctica the model was combined with a satellite derived map of antarctic snow and blue ice areas 10 yr 1991 2000 of antarctic meteorological station data and a high resolution meteorological distribution model to provide daily simulated melt values on a 1 km grid covering antarctica model simulations showed that 11 8 and 21 6 of the antarctic continent experienced surface and subsurface melt respectively in addition the simulations produced 10 yr averaged subsurface meltwater production fluxes of 316 5 and 57 4 km3 yr 1 for snow covered and blue ice areas respectively the corresponding figures for surface melt were 46 0 and 2 0 km3 yr 1 respectively thus demonstrating the dominant role of subsurface ov

molecular and isotopic biogeochemistry of the miocene clarkia formation hydrocarbons and alcohols the miocene lacustrine deposit at clarkia northern idaho u s a is well known for its rich and exceptionally well preserved higher plant leaf fossils in the present study the distributions abundance and isotopic compositions of aliphatic hydrocarbons and alcohols isolated from two sediment samples and from two associated fossils magnolia latahensis and platanus dissecta are investigated the general similarity of these characteristics in the sediments suggests a relatively uniform depositional environment and consistent terrestrial input the sediment hydrocarbons are comprised mainly of compounds derived from higher plants and bacteria whereas the alcohols reflect contributions from both higher plants and algae a notable feature of the higher plant derived terpenoid hydrocarbons is the prevalence of des a triterpenes largely in the absence of their pentacyclic precursors indicating the dominance of a ring degradation for these pentacyclic triterpenoids the des a triterpenes include several novel compounds namely 19 h and 19 h 28 nor des a lup 17 ene and des a oleana 9 13 18 diene the sediment samples contain high abundances of c24 c32 long chain alkanediols consisting of a series of diols 1 diols 1 15 diols and an unusual series of 1 3 diols both fossil leaves show clear differences in their compound distributions and concentrations from the associated sediments which suggests that they retain a composition distinct from the sediment groundmass the 13c values of c25 c33 n alkanes and c24 c32 n alcohols in sediments and fossils are consistent with an origin from terrestrial c3 higher plants algal lipids in the two sediments are represented by dinostanol 24 6 and 25 9 inherited from dinoflagellates and long chain 1 15 alkanediols 26 4 to 29 7 derived from microalgae the long chain 1 and 1 3 alkanediols are more enriched in 13c 21 8 to 26 4 suggesting an origin from sources other than higher plants probably aquatic photoautotrophic organisms the 13c depletion of some hopanoids 35 9 to 61 0 attests to contributions from methanotrophic bacteria and suggests an active methane cycle at the time of deposition

sub surface melting in a seasonal snow cover the ability of solar radiation to penetrate into a snow cover combined with the low thermal conductivity of snow can lead to a sub surface temperature maximum this elevated sub surface temperature allows a layer of wet snow to form below the surface even on days when the air temperature remains subfreezing a high resolution frequency modulated continuous wave fmcw radar has been used to detect the onset of sub surface melting in a seasonal snow cover the experimental observation of sub surface melting is shown to be in good agreement with the predictions of a one dimensional mass and energy balance model the effects of varying snow characteristics and solar extinction parameters on the sub surface melt characteristics are investigated using model simulations

recent surface mass balance from syowa station to dome f east antarctica comparison of field observations atmospheric reanalyses and a regional atmospheric climate model stake measurements at 2 km intervals are used to determine the spatial and temporal surface mass balance smb in recent decades along the japanese antarctic research expedition traverse route from syowa station to dome f to determine smb variability at regional scales this traverse route is divided into four regions i e coastal lower katabatic upper katabatic and inland plateau we also perform a regional evaluation of large scale smb simulated by the regional atmospheric climate model versions 2 1 and 2 3 racmo2 1 and racmo2 3 and the four more recent global reanalyses large scale spatial variability in the multi year averaged smb reveals robust relationships with continentality and surface elevation in the katabatic regions smb variability is also highly associated with surface slope which in turn is affected by bedrock topography stake observation records show large inter annual variability in smb but did not indicate any significant trends over both the last 40 years for the coastal and lower katabatic regions and the last 20 years record for the upper katabatic and inland plateau regions the four reanalyses and the regional climate model reproduce the macro scale spatial pattern well for the multi year averaged smb but fail to capture the mesoscale smb increase at the distance interval 300 to 400 km from syowa station thanks to the updated scheme in the cloud microphysics racmo2 3 shows the best spatial agreement with stake measurements over the inland plateau region era interim jra 55 and merra exhibit high agreement with the inter annual variability of observed smb in the coastal upper katabatic and inland plateau regions and moderate agreement in the lower katabatic region while ncep2 and racmo2 1 inter annual variability shows no significant correlation with the observations for the inland plateau region

paleoceanographic significance of late paleocene dysaerobia at the shelf slope break around new zealand abstract a geochemical and micropaleontological study of the waipawa formation in new zealand was undertaken to investigate its depositional setting and possible relationship to major changes in the marine environment the organic rich formation was deposited in the late paleocene during a third order eustatic sea level rise precise age control is lacking but deposition can be placed between a climatic cooling at 59 1 ma and a thermal maximum at 55 5 ma during the transition from cold to warm saline deep water circulation in the south pacific deposition occurred around most of the land mass generally near the shelf break and microfaunal evidence suggests dysaerobic conditions there appears to have been no contemporaneous organic rich sedimentation on the shelf so the widespread high phytoplanktonic productivity which is reflected in positive excursions in kerogen 13c to 20 was probably caused by regional upwelling however the paleodistribution of the formation cannot be readily accounted for by wind driven upwelling alone there is strong positive correlation between organic content kerogen 13c values and unusually high abundance of 24 n propylcholestanes 20 55 of c27 c30 regular steranes surface water conditions favoured a particular group of phytoplankton that preferentially synthesised the precursor c30 sterols and there is microfaunal evidence for warming carbonate oxygen isotopic data are also consistent with warming but may be affected by diagenetic alteration the waipawa formation may result from regional upwelling of warm saline oxygen depleted nutrient rich deep water in what appears to be an earlier and longer term but geographically more restricted event than that responsible for the benthonic extinction event at 55 5 ma

snow crystal growth with varying surface temperatures and radiation penetration the temperature field is derived for a sinusoidally varying surface temperature with varying solar radiation penetration the growth rates of snow crystals are calculated to explain the rapidly growing layers of faceted crystals i e depth hoar that form just below the surface at high altitudes and in polar snow the solutions also show that a layer of wet snow can exist just below the surface even on days when the surface temperature remains sub freezing

recent changes in the microwave scattering properties of the antarctic ice sheet time series satellite microwave data are used to monitor and quantify changes in the scattering properties of the antarctic ice sheet daily ers scatterometer escat and special sensor microwave imager ssm i image data acquired since 1992 are analyzed to understand the seasonal and interannual changes over the ice sheet for regions of the ice sheet where azimuthal modulation is negligible seasonal cycles are observed in both the escat amplitude spl sim 0 5 db and ssm i data amplitude spl sim 10 k these cycles are attributed to seasonal changes in surface temperature interannual variability in the time series signatures appears to be associated with accumulation there is also evidence to suggest that shifts in the wind direction can alter the backscatter through azimuthal modulation over the period 1992 97 large trends are observed in the escat 1 k yr sup 1 signatures over several regions in antarctica these changes typically occur over ice shelves and at the margins of the ice sheet where previous melt events have occurred and where accumulation is relatively high 300 mm yr sup 1 it is likely the large changes result from the successive burial of an efficient scattering layer formed by refreezing after a melt event prior to 1992 there is also evidence to suggest that similarly large changes can be observed in the interior of the ice sheet due to the burial of depth hear layers in order to monitor long term change in the properties of the antarctic ice sheet it is necessary to remove the seasonal cycle from time series microwave data such anomaly data can then be used to understand the link between escat and ssm i with accumulation and wind shifts

a study of the surface mass balance in dronning maud land antarctica using automatic weather stations we use data from four automatic weather stations awss in dronning maud land east antarctica to study the surface mass balance and its components distinct differences were found between the moisture climates of the high plateau the katabatic wind zone and the coastal ice shelves significant undersaturation occurs year round in the katabatic wind zone while on the high plateau and on the coastal ice shelf the air is usually close to saturation in summer absorption of shortwave radiation at the snow surface enhances surface sublimation at all sites removing 3 9 of the annual solid precipitation significant summer melting is an equally important ablation term near the coast but vanishes inland vertically integrated column drifting snow sublimation was estimated using two different methods this process appears to be similar to or greater in magnitude than surface sublimation because intervals between significant precipitation events may last as long as several months sublimation and melt cause extended periods of surface ablation in summer in summer all ablation processes together remove 15 56 of the solid precipitation or 6 27 on an annual basis

organic geochemistry of the lower suban coal seam south sumatra basin indonesia palaeoecological and thermal metamorphism implications abstract hydrocarbons extracted from the tertiary age coals from the lower suban seam south sumatra basin indonesia have been investigated using gas chromatography gc and combined gas chromatography mass spectrometry gc ms low rank vitrinite huminite reflectance 0 41 0 45 coals from the tambang air laya mine represent different maceral assemblages of an ideal succession of ombrogenous palaeo peat development in a vertical section high rank coals vitrinite reflectance 1 42 5 18 from the suban mine have been thermally metamorphosed by an andesitic intrusion variations in the distributions of n alkanes isoprenoids and saturated and aromatic biomarkers in the low rank coals reflect variations in local source input and palaeomire conditions terpenoid biomarkers such as cadinane and eudesmane type sesquiterpenoids and oleanane and ursane type triterpenoids indicate the predominance of angiosperm plants in the palaeomire particularly dipterocarpaceae the distribution of hopanoids is affected by the organic facies of the coal and their maturity and correlates with the palaeomire evolution as derived from petrological studies close to the igneous intrusion rapid thermal stress has destroyed most of the biomarkers but variations in n alkane distributions attributable to palaeomire conditions remain reversals in the trends for molecular parameters based on aliphatic hydrocarbons n alkane distribution and pristane phytane ratio and aromatic hydrocarbons methyl phenanthrenes with coal rank are observed

molecular composition of a leaf and root bearing oligocene oxbow lake clay in the weisselster basin germany abstract a plant fossil bearing clay profile from the upper oligocene thierbach strata weisselster basin germany has been sectioned into horizons and the plant macrofossils of each section surface have been identified by morphological and anatomical studies in the upper half of the profile leaves from populus germanica and carpinus grandis and branchlets from the conifer taxodium balticum vel t dubium dominate the horizons while the lower part contains only root remains of unknown higher plants in the soxhlet extracted samples from each section n alkanes n alkanols n carboxylic acids and several terpenoids amyrin 24 25 dinoreleana 1 3 5 10 12 tetraene olean 12 en 3 one simonellite and hop 17 21 ene were identified by combined gas chromatography mass spectrometry the comparison of the extracted chemical compounds and the macrofossil record of the profile shows that simonellite occurs preferentially in the taxodium bearing horizons n alkanes n alkanols n carboxylic acids and amyrin were found in all sections but are enriched in the root containing part of the profile the distribution of hop 17 21 ene is independent of the input of higher plant remains

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

saturated and olefinic terrigenous triterpenoid hydrocarbons in a biodegraded tertiary oil of northeast alaska abstract dinorlupanes norlupanes olean 12 ene 18 olean 12 ene and urs 12 ene occur in a heavily biodegraded tertiary oil tested from the ocs y 0849 1 well drilled on the hammerhead prospect in the beaufort sea offshore northeast alaska these indicators and other source related characteristics of the hammerhead oil ring a degraded oleanoids ursanoids and lupanoids v and ni less than 2 0 ppm v v ni less than 0 5 indicate a land plant angiospermous character in the source facies the olefins in the hammerhead and canadian oils are considered to be contributed directly from the source rather than extracted from adjacent immature non source sediments during migration as indicated by a the accompanying presence in the oil of saturated angiosperm markers and b the absence of measurable amounts of other olefins characteristic of immature organic matter e g diasterenes and hopenes

role of channel and floodplain cross section geometry in the basin response 1 we investigate the role of cross section geometry in flow routing by developing an analytical framework based on the instantaneous response function irf and relationships of river basin geomorphology the cross section geometry is included explicitly within the framework by assuming a power law cross section that is in turn used to derive expressions for the at a site hydraulic geometry the analysis performed using the illinois river basin indicates that the cross section geometry takes on different roles depending on whether flows are in the channel or floodplain the cross section geometry where width dominates over depth width dominant i e the at a site width depth ratio increases with increasing depth tends to produce a larger network celerity and dispersion for the channel and the trend reverses for the high floodplain flows we found that the cross section geometry can influence the relative contribution of hydrodynamic and kinematic dispersion for the channel the depth dominant cross section produces a lower hydrodynamic dispersion than the width dominant cross section and vice versa for the floodplain we found that the nonlinear dependence of the irf on effective rainfall expressed in the irf time to peak and peak flow may vary depending on the cross section geometry with the nonlinearity decreasing for the width dominant cross sections additionally the effect of cross section geometry on the basin response can alter the relative contribution of the stream network and hillslopes to the basin dispersion the derived framework has potential as an a priori tool for incorporating channel and floodplain geometry into distributed rainfall runoff models

biogeochemistry of the miocene lacustrine deposit at clarkia northern idaho u s a abstract the lipid preservation observed in the sediments from clarkia reflects an extremely immature thermal history many biomarkers have still retained functionality even after 17 20 million years the soluble components are predominantly higher plant and algal derived lipids and the original sources for these compounds are still preserved in the sediment thus biogeochemical data are in agreement with the associated palaeontological evidence chemical changes noted in the lipids preserved in these sediments are similar to those observed in modern fresh water mesotropic or eutrophic lacustrine sediments therefore it can be inferred that the processes that operate in modern lacustrine sediments are similar to those that took place within the sediments at clarkia 17 20 million years ago

on the glaciological meteorological and climatological significance of antarctic blue ice areas this paper presents the current state of our knowledge about antarctic blue ice areas scattered widely over the antarctic continent yet covering only approximately 1 of its surface area blue ice areas have some peculiar characteristics that make them of particular interest for planetary geologists glaciologists meteorologists and climatologists for instance blue ice areas are subject to net ablation mainly by sublimation since any accumulation is easily swept off their smooth surfaces by winds moreover they are significantly warmer than their surroundings and the wind over them is generally more gusty an important feature of blue ice is its relatively low albedo 0 56 compared with that of snow 0 80 blue ice is probably considerably smoother than snow in the aerodynamic sense with roughness lengths as low as 3 10 6 m which indicates that blue ice is probably the only permanent natural surface over which the air flow is mainly in the aerodynamic smooth regime further since it is likely that very old ice is exposed at the surface of some blue ice areas this ice would be of great interest for paleoclimatic studies it has also been suggested that blue ice areas are sensitive to climate change this would make them useful as antarctic climate indicators because they can easily be monitored by satellite finally this paper addresses several gaps in our knowledge about blue ice areas and gives suggestions for future blue ice area research

investigation on the lignite deposits of surkha mine saurashtra basin gujarat western india their depositional history and hydrocarbon generation potential abstract an integrated approach is adopted to study the lignite deposits of surkha mine associated with the khadsaliya clays formation eocene of saurashtra basin western india the compilation of detailed investigation includes organic petrographical palynofacies and geochemical analyses the type and amount of organic matter and its relation to palaeoenvironmental conditions have been determined and discussed along with its significance as hydrocarbon source the macerals of huminite group show dominance av 61 over the liptinite and inertinite groups the petrographical indices gi tpi gwi vi indicate wood dominated precursors of peat were deposited in limno telmatic to telmatic regime under mesotrophic hydrological conditions in palynofacies analysis it is observed that the particulate organic matter is dominated by the phytoclasts group av 69 followed by the amorphous organic matter aom and palynomorphs the biomarker signatures show angiosperm and gymnosperm source vegetation the presence of sesquiterpenoids indicate the occurrence of dipterocarpaceae flora suggesting the existence of rain forest vegetation in the vicinity of depositional site the kaurane type of diterpenoids suggest the presence of conifers among the source flora the extrapolation of organic matter data on tyson s app diagram along with the pr n c 17 vs ph n c 18 plot indicate that the deposition took place in dysoxic suboxic conditions with intermittent shifting of the environment in proximal settings the huminite reflectance values av 0 31 r r show a good correlation with gross calorific values av 3917 cal g and average t max value 416 c of the lignites furthermore the abundance of thermally unstable hop 17 21 ene and hopane indicate immature stage of lignites these lignites contain high toc av 35 wt and low ash yields the volatile matter carbon and oxygen contents are relatively high whereas sulphur content is moderate and hydrogen and nitrogen contents are comparatively low in all the lignite samples the hydrogen index values vary between 53 and 538 mg hc g toc the atomic values of h c range from 0 47 to 1 04 and of o c from 0 20 to 0 29 overall the lignite bearing sequence is characterized by type ii iii admixed kerogens organic matters and has potential to generate hydrocarbons upon maturation

greenland freshwater runoff part i a runoff routing model for glaciated and nonglaciated landscapes hydroflow abstracta gridded linear reservoir runoff routing model hydroflow was developed to simulate the linkages between runoff production from land based snowmelt and icemelt processes and the associated freshwater fluxes to downstream areas and surrounding oceans hydroflow was specifically designed to account for glacier ice sheet and snow free and snow covered land applications its performance was verified for a test area in southeast greenland that contains the mittivakkat glacier the local glacier in greenland with the longest observed time series of mass balance and ice front fluctuations the time evolution of spatially distributed gridcell runoffs required by hydroflow were provided by the snowmodel snow evolution modeling system driven with observed atmospheric data for the years 2003 through 2010 the spatial and seasonal variations in hydroflow hydrographs show substantial correlations when compared with observed discharge coming from the mittivakkat glacier area and draining into the adjacent

glacier surge after ice shelf collapse the possibility that the west antarctic ice sheet will collapse as a consequence of ice shelf disintegration has been debated for many years this matter is of concern because such an event would imply a sudden increase in sea level evidence is presented here showing drastic dynamic perturbations on former tributary glaciers that fed sections of the larsen ice shelf on the antarctic peninsula before its collapse in 1995 satellite images and airborne surveys allowed unambiguous identification of active surging phases of boydell sjogren edgeworth bombardier and drygalski glaciers this discovery calls for a reconsideration of former hypotheses about the stabilizing role of ice shelves

an unusual aromatization process of higher plant triterpenes in sediments abstract the nmr structural elucidation of d b friedo 3 methyl 24 noroleana 1 3 5 10 triene 3 methyl 24 nor friedela 1 3 5 10 triene isolated from the messel shale germany highlights an unusual ring a aromatization process occurring during diagenesis of higher plant 3 oxygenated triterpenes this process which involves the shift of one of the gem dimethyl groups at c 4 to c 3 instead of its commonly observed elimination is probably induced by structural features of the precursors most likely the 5 or 5 10 gluten 3 ones an acid clay catalysed enone benzene transposition can indeed account for a direct abiotic ring a aromatization of such precursors

snow grain size measurements in antarctica grain size is an important but not well known characteristics of snow at the surface of antarctica in the past grain size has been reported using various methods the reliability reproducibility and inter comparability of which is not warranted in this paper we present and recommend depending on available logistical support 3 techniques of snow grain sampling and or imaging in the field as well as an ariginal digital image processing method which we have proved to provide reproducible and intercomparable measures of a snow grain size parameter the mean convex radius results from more than 500 samples and 3000 images of snow grains presented which yield a still spatially limited yet unprecendtedly wide picture of near surface snow grain size distribution from field work in antarctica in particular except at sites affected by a very particular meteorology surface grains in the interior of the ice sheet are uniformly small o 1 to 0 2 mm the climate related increase of grain size with depth through metamorphism is as expected not spatially uniform our antarctic snow grain size database will continue to grow as field investigators bring new samples images and measures of snow grain size

antarctic surface melting dynamics enhanced perspectives from radar scatterometer data 1 antarctic ice sheet surface melting can regionally influence ice shelf stability mass balance and glacier dynamics in addition to modulating near surface physical and chemical properties over wide areas here we investigate variability in surface melting from 1999 to 2009 using radar backscatter time series from the seawinds scatterometer aboard the quikscat satellite these daily continent wide observations are explored in concert with in situ meteorological records to validate a threshold based melt detection method radar backscatter decreases during melting are significantly correlated with in situ positive degree days as well as meltwater production determined from energy balance modeling at neumayer station east antarctica these results support the use of scatterometer data as a diagnostic indicator of melt intensity i e the relative liquid water production during melting greater spatial and temporal melting detected relative to previous passive microwave based studies is attributed to a higher sensitivity of the scatterometer instrument continental melt intensity variability can be explained in part by the dynamics of the southern annular mode and the southern oscillation index and extreme melting events across the ross ice shelf region may be associated with el nino conditions furthermore we find that the antarctic peninsula accounts for only 20 of antarctic melt extent but greater than 50 of the total antarctic melt intensity over most areas annual melt duration and intensity are proportional however regional and localized distinctions exist where the melt intensity metric provides greater insight into melting dynamics than previously obtainable with other remote sensing techniques

the response of the southern ocean and antarctic sea ice to freshwater from ice shelves in an earth system model abstractthe possibility that recent antarctic sea ice expansion resulted from an increase in freshwater reaching the southern ocean is investigated here the freshwater flux from ice sheet and ice shelf mass imbalance is largely missing in models that participated in phase 5 of the coupled model intercomparison project cmip5 however on average precipitation minus evaporation p e reaching the southern ocean has increased in cmip5 models to a present value that is about greater than preindustrial times and 5 22 times larger than estimates of the mass imbalance of antarctic ice sheets and shelves 119 544 two sets of experiments were conducted from 1980 to 2013 in cesm1 cam5 one of the cmip5 models artificially distributing freshwater either at the ocean surface to mimic iceberg melt or at the ice shelf fronts at depth an anomalous reduction in vertical advection of heat into the surface mixed layer resulted in sea surface cooling at high southern latitudes and an associated increase in sea i

saturated and aromatic diterpenoids and triterpenoids in eocene coals and mudstones from china several series of saturated diaromatic triaromatic c ring cleaved and triaromatic diterpenoids and triterpenoids have been detected in 4 immature coal and mudstone samples a number of these compounds appear to represent intermediates in a series of postulated pathways for progressive aromatization of biogenic diterpenoids and triterpenoids diagenetic pathways for the formation of tricyclic aromatic hydrocarbons from abietane and pimarane type diterpenoid precursors and for the formation of diaromatic triaromatic c cleaved and triaromatic hydrocarbons from amyrin and other triterpenoid precursors are proposed saturated and aromatized abietanes pimaranes and phyllocladanes which are the most abundant compounds in all 4 samples indicate a predominant higher plant input which can be related to the coniferales group but not to individual plant families amyrin and other triterpenoid derived triaromatic and triaromatic c ring cleaved hydrocarbons with triterpenoid structures are thought to be characteristic for angiosperms the relative concentrations of the triaromatic and triaromatic c ring cleaved hydrocarbons are higher in samples 9602 mudstone and 9603 coal than samples 9601 coal and 9604 mudstone indicating samples 9602 mudstone and 9603 coal contain relatively more angiosperm derived organic matter than samples 9601 coal and 9604 mudstone the distribution patterns and the relative concentrations of saturated and aromatic diterpenoids and triterpenoids thus are valuable markers for the determination of the relative contents of biological sources of organic material in geological samples

on river floodplain interaction and hydrograph skewness understanding hydrological processes occurring within a basin by looking at its outlet hydrograph can improve and foster comprehension of ungauged regions in this context we present an extensive examination of the roles that floodplains play on driving hydrograph shapes observations of many river hydrographs with large floodplain influence are carried out and indicate that a negative skewness of the hydrographs is present among many of them through a series of numerical experiments and analytical reasoning we show how the relationship between flood wave celerity and discharge in such systems is responsible for determining the hydrograph shapes the more water inundates the floodplains upstream of the observed point the more negatively skewed is the observed hydrograph a case study is performed in the amazon river basin where major rivers with large floodplain attenuation e g purus madeira and jurua are identified with higher negative skewness in the respective hydrographs finally different wetland types could be distinguished by using this feature e g wetlands maintained by endogenous processes from wetlands governed by overbank flow along river floodplains a metric of hydrograph skewness was developed to quantify this effect based on the time derivative of discharge together with the skewness concept it may be used in other studies concerning the relevance of floodplain attenuation in large ungauged rivers where remote sensing data e g satellite altimetry can be very useful

contrasted distributions of triterpene derivatives in the sediments of lake caco reflect paleoenvironmental changes during the last 20 000 yrs in ne brazil lipid fractions extracted from sediment layers deposited in a small brazilian lake during the last 20 000 yrs were investigated by gas chromatography mass spectrometry considerable differences in the distribution and the amount of triterpene derivatives in the aliphatic as well as in the aromatic fractions were observed all along the series although no precise identification of these compounds was undertaken our interpretation of mass spectral data allowed us to discriminate between des a triterpenes mono and triaromatic derivatives of pentacyclic triterpenes and a series of compounds tentatively identified as diaromatic derivatives of tetracyclic triterpenes the largest compound diversity was found in the lowest levels of the series dated back to the end of the last glacial maximum when good preservation of terrestrial plant debris was ensured by rapid burial in a semi arid climate then except for a period corresponding to the younger dryas only des a lupane was detected in significant amounts the high predominance of des a lupane is interpreted to result from the development of a belt of eleocharis sp spike rush that filtered most of organic inputs from the catchment and was the site of des a lupane production and exportation towards the lake centre during the younger dryas a strong influx of des a lupane is attributed to the destruction of the spike rush belt consecutive to the lowering of the lake level under drier conditions the temporary destruction of this barrier allowed other triterpene derivatives to reach the lake the distinct dynamics of des a and aromatic triterpene derivatives under variable medium conditions led us to hypothesis that these two families of compounds derive from distinct pools that contributed differently to the sediment depending on environmental and climatic conditions des a lupane was most probably produced in sub aquatic conditions within the belt of spike rush conversely aromatic derivatives of triterpenes could have resulted from the degradation of their biological precursors within reducing micro environments in the catchment

assessment and development of snowmelt retrieval algorithms over antarctica from k band spaceborne brightness temperature 1979 2008 abstract results from several previously published algorithms for wet snow detection in antarctica from k band spaceborne brightness temperature are compared and evaluated vs estimates of wet snow conditions from ground measurements in addition a new physically driven algorithm in which the detectable liquid water content is assumed constant is proposed and assessed all algorithms are also evaluated by analyzing their results during collapses of ice shelves two algorithms are selected for deriving updated trends of melting index mi the number of melting days times the area subject to melting between 1979 and 2008 over the whole antarctica and at sub continental scales in the first algorithm wet snow is identified when brightness temperature exceeds the mean of winter brightness temperature plus 30 k and the second is the new model based approach described here both negative and positive mi trends are obtained depending on the algorithm used a high number of melting days up to 100 days are detected over the wilkins ice shelf the peninsula and the george vi ice shelf over east antarctica the west and amery ice shelves are subject to melting for a maximum of approximately 50 days positive trends of number of melting days are detected over most of the west antarctica with peak values up to 1 2 days year over the larsen c ice shelf 1 8 days year over the george vi ice shelf and 0 55 days year over the wilkins ice shelf area the correlation between mi values and december january dj averaged air surface temperature over selected locations show values ranging between 0 8 and 0 4 results suggest that a 1 c increase in the monthly averaged dj air surface temperature corresponds to an average mi increase of approximately 2 106 km2 day

oleananes in oils and sediments evidence of marine influence during early diagenesis abstract the oleananes as markers for the angiosperms provide valuable source and age information when present in an oil nevertheless they are not quantitatively related to the land plant input and indeed their presence reflects only a small leak in diagenetic processes leading primarily to aromatic oleanoids because they are minor products the abundance of oleananes in terrigenous oils and sediments may be highly sensitive to changes in early diagenetic conditions here we present evidence that contact of plant matter with seawater during early diagenesis enhances the expression of oleananes in a mature sediment or oil oleananes are absent or present at very low concentrations in samples from the base of an eocene coal seam affected by postdepositional seawater intrusion however their abundance increases toward the top of the seam in correlation with organic sulphur dibenzothiophene phenanthrene and the homohopane index similarly in deltaic sediments from the south sumatra basin oleanane hopane is strongly correlated with indicators of marine influence such as c 27 c 29 steranes and the homohopane index in each case increasing oleanane abundance is accompanied by a reduction in the extent of aromatisation and for the south sumatra basin the proportion of a ring contracted oleananes an angiosperm derived miocene coal from the philippines deposited under freshwater conditions shows abundant aromatic oleanoids but no oleananes these results show that oleananes need to be used with caution as age and source markers in fluvio deltaic and lacustrine petroleum systems on the other hand their sensitivity to early diagenetic conditions may make them useful in locating effective source rocks in such systems

an energy and mass model of snow cover suitable for operational avalanche forecasting a numerical model has been developed to simulate energy and mass evolution of snow cover at a given location as a function of meteorological conditions precipitation air temperature humidity wind velocity and incoming short wave and long wave radiation this model named crocus was first tested on a well instrumented field during a whole winter showing its ability to simulate the important phenomena affecting the evolution of the snow layers high temperature gradients wetting compaction and melting freezing cycles a second test was conducted at two locations in the french network used for operational avalanche forecasting though the weather observations are made there only twice daily the snow profiles calculated by the model were very close to those obtained once a week by a pit observation crocus proved itself sufficient to be considered now as a useful objective tool for operational avalanche forecasting

early eocene equatorial vegetation and depositional environment biomarker and palynological evidences from a lignite bearing sequence of cambay basin western india abstract an investigation of palaeofloral distribution with depositional environment and palaeoclimatic condition of western indian subcontinent during early eocene period has been carried out from a lignite bearing succession of cambay basin western india the study of biomarkers palynological remains and petrography is taken as proxies for providing supportive evidence for our inference the petrographic results reveal that the sediments are thermally immature and coalification was extended up to the lignitic stage low rank b the palynological results show the dominance of angiosperms mainly members belonging to the arecaceae family throughout the studied section triterpenoids with oleanane ursane and lupane structure in extractable organic matter are derived from angiosperm wax pollen grains spinizonocolpites proxapertites dipterocarpuspollenites albertipollenites retipollenites arengapollenites lakiapollis and longapertites with pteridophyte spores and fungal fruiting bodies confirm the prevalence of tropical to subtropical climate during the deposition of the sediments sesquiterpenoids like longifolene 12 methanoazulene cadinane and selinene together with amyrin derivatives are the indicator of dipterocarpaceae family that grows in the extant tropical rain forests in se asia appearance of dinoflagellate cysts and the predominance of lower molecular weight part in n alkane series with the signature of submerged floating vegetation in the shale horizon indicate marine influence in the younger part of the mine section the presence of mangrove pollen such as spinizonocolpites proxapertites and acanthotricolpites further suggests that the lignite bearing sequence was deposited in marshy marginal marine environment

polythermal glacier hydrology a review 1 the manner by which meltwater drains through a glacier is critical to ice dynamics runoff characteristics and water quality however much of the contemporary knowledge relating to glacier hydrology has been based upon and conditioned by understanding gleaned from temperate valley glaciers globally a significant proportion of glaciers and ice sheets exhibit nontemperate thermal regimes the recent growing concern over the future response of polar glaciers and ice sheets to forecasts of a warming climate and lengthening summer melt season necessitates recognition of the hydrological processes in these nontemperate ice masses it is therefore timely to present an accessible review of the scientific progress in glacial hydrology where nontemperate conditions are dominant this review provides an appraisal of the glaciological literature from nontemperate glaciers examining supraglacial englacial and subglacial environments in sequence and their role in hydrological processes within glacierized catchments in particular the variability and complexity in glacier thermal regimes are discussed illustrating how a unified model of drainage architecture is likely to remain elusive due to structural controls on the presence of water cold ice near glacier surfaces may reduce meltwater flux into the glacier interior but observations suggest that the transient thermal layer of near surface ice holds a hydrological role as a depth limited aquifer englacial flowpaths may arise from the deep incision of supraglacial streams or the propagation of hydrofractures forms which are readily able to handle varied meltwater discharge or act as locations for water storage and result in spatially discrete delivery of water to the subglacial environment the influence of such drainage routes on seasonal meltwater release is explored with reference to summer season upwellings and winter icing formation moreover clear analogies emerge between nontemperate valley glacier and ice sheet hydrology the discussion of which indicates how persistent reassessment of our conceptualization of glacier drainage systems is required there is a clear emphasis that continued integrated endeavors focused on process glaciology at nontemperate glaciers are a scientific imperative to augmenting the existing body of research centered on ice mass hydrology

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

aliphatic and aromatic triterpenoid hydrocarbons in a tertiary angiospermous lignite abstract the hydrocarbon biomarker assemlage of a liptinite rich early tertiary angiospermous lignite has been characterized the biomarker fistribution for the lignite confirms the low maturity and previous paleobotanic interpretations the aliphatic hydrocarbon fraction consists predominantly of n alkanes showing a strong odd carbon predominance and numerous de a triterpenoids and triterpenoids derived from higher plants bacterially derived triterpenoids were represented primarily by homohopanes and hopenes the aromatic hydrocarbon fraction contains a series of mono di and triaromatic de a triterpenoids and mono tri and tetraaromatic triterpenoids derived from higher plants the concentration and abundance of monoaromatic triterpenoids containing one to three additonal degress of unsaturation have not seen previously observed in a single deposit as such a diagenetic scheme for angiosperm derived triterpenoids is presented which confirms and extends previous hypothesis

rapid degradation of permafrost underneath waterbodies in tundra landscapes toward a representation of thermokarst in land surface models waterbodies such as lakes and ponds are abundant in vast arctic landscapes and strongly affect the thermal state of the surrounding permafrost in order to gain a better understanding of the impact of small and medium sized waterbodies on permafrost and the formation of thermokarst a land surface model was developed that can represent the vertical and lateral thermal interactions between waterbodies and permafrost the model was validated using temperature measurements from two typical waterbodies located within the lena river delta in northern siberia impact simulations were performed under current climate conditions as well as under a moderate and a strong climate warming scenario the performed simulations demonstrate that small waterbodies can rise the sediment surface temperature by more than 10 c and accelerate permafrost thaw by a factor of between 4 and 5 up to 70 of this additional heat flux into the ground was found to be dissipated into the surrounding permafrost by lateral ground heat flux in the case of small shallow and isolated waterbodies under moderate climate warming the lateral heat flux was found to reduce permafrost degradation underneath waterbodies by a factor of 2 under stronger climatic warming however the lateral heat flux was too small to prevent rapid permafrost degradation the lateral heat flux was also found to strongly impede the formation of thermokarst despite this stabilizing effect our simulations have demonstrated that underneath shallow waterbodies 1 m thermokarst initiation happens 30 to 40 years earlier than in simulations without preexisting waterbody

identification of antarctic ablation areas using a regional atmospheric climate model the occurrence of antarctic ablation areas in dronning maud land the lambert glacier basin victoria land the transantarctic mountains and the antarctic peninsula is realistically predicted by the regional atmospheric climate model racmo2 ant with snowdrift related processes calculated offline antarctic ablation areas are characterized by a low solid precipitation flux in combination with strong sublimation snowdrift erosion and or melt the strong interaction between atmospheric circulation and topography plays a decisive role in the precipitation distribution and hence that of ablation areas three types of antarctic ablation areas can be distinguished all occurring in dry regions type 1 is the erosion driven ablation area caused by 1 d and or 2 d divergence in the katabatic wind field at high elevations 2000 3200 m asl type 2 is the sublimation driven ablation area this type occurs at lower elevations

a subgrid channel model for simulating river hydraulics and floodplain inundation over large and data sparse areas 1 this paper presents a new computationally efficient hydraulic model for simulating the spatially distributed dynamics of water surface elevation wave speed and inundation extent over large data sparse domains the numerical scheme is based on an extension of the hydraulic model lisflood fp to include a subgrid scale representation of channelized flows which allows river channels with any width below that of the grid resolution to be simulated the scheme is shown to be numerically stable and scalable before being applied to an 800 km reach of the river niger in mali the niger application focused on the performance of four different model structures a model without channels two dimensional 2 d model a model without a floodplain one dimensional 1 d model a model of the main channels and floodplain 1 d 2 d model and the subgrid approach developed here inclusion of both the channel network and the floodplain was shown to be essential meaning that large scale models of this region including routing models for land surface schemes will require a floodplain component including subgrid scale channels on the floodplain changed inundation dynamics over the delta significantly and increased simulation accuracy in terms of water level wave propagation speed and inundation extent furthermore only the subgrid model showed a consistent parameterization when calibrated against either gauge or icesat water level data suggesting that connectivity provided by small channels is a strong control on the hydraulics of the floodplain or at the very least that low resolution gridded hydraulic models require additional connectivity to represent the delta flow dynamics

spectral bi directional reflectance of snow and glacier ice measured in dronning maud land antarctica visible and near infrared spectral reflectances of snow and superimposed ice were measured in dronning maud land antarctica during the 1992 93 austral summer spectral reflectance curves of both snow and superimposed ice remain high 80 in the visible region a pronounced decrease in reflectance appears in the near infrared especially for superimposed ice superimposed ice with a 1 cm thick surface layer of ice bound snow crystals had a considerably higher reflectance than superimposed ice containing only a few snow crystals furthermore these data prove that snow and superimposed ice reflect solar radiation specularly and suggest that the anisotropy strengthens with increasing wavelengths integrated in situ reflectances corresponding to landsat tm bands 1 4 show that tm band 1 is least affected whereas tm band 4 is most affected by anisotropy furthermore the anisotropy increases with increasing off nadir viewing angles up to an angle corresponding to 90 s s solar elevation for a 15 off nadir sensor observation angle the average snow reflectance for tm bands 1 4 is about 10 higher than at nadir similarly the apparent reflectance can be more than 50 higher than the nadir reflectance for larger observation angles consequently if satellite derived reflectances are going to be considered as absolute values a topographic correction model is needed to correct for the effects of anisotropy

organic carbon as a palaeoenvironmental indicator in the marine realm recent developments in biogeochemistry have made accessible all information currently known to be present in sedimentary organic compounds i e the carbon skeleton structure the positions of functional groups and stable carbon isotope ratios this combined information has strengthened the applications of sedimentary organic compounds as biomarkers and palaeoenvironmental indicators this review summarizes the most important biomarkers and their applications in reconstructing marine palaeoenvironments and processes the marine environment is characterized by the combined presence of specific compounds such as organic sulphur compounds dinosteroids 24 n propylsteroids even in trace amounts high amounts of c hbi hydrocarbons and the absence of long chain n alkanes with odd over even predominance bicadinanes and specific higher plant triterpenoids e g oleanane furthermore palaeoenvironmental conditions such as photic zone anoxia hypersalinity microbial sulphate reducing activity algal blooming palaeo upwelling and palaeo surface seawater temperature are indicated by molecular and or isotopic characteristics biomarkers from terrestrial sources are included because land derived organic matter is an important contributor to coastal and shallow marine environments a short case study within a holocene terrestrial marine setting florida bay usa is also presented to illustrate the reconstruction of transgressive regressive trends using selected organic compounds

microwave emission from density stratified antarctic firn at 6 cm wavelength previous observations have shown spatial covariances between microwave emission from antarctic firn at 6cm wavelength physical firn temperature and firn density stratification such observations motivate us to understand the physics underlying such covariances and based on that understanding to develop estimation methods for firn temperature and layering parameters we present here a model for 6cm emission from firn in which density and therefore dielectric permittivity varies randomly in discrete layers with mean thicknesses on the order of centimeters the model accounts for depth profiles of the physical temperature mean density and variance of random density fluctuations from layer to layer we also present a procedure to estimate emission model input parameters objectively from in situ density profile observations as well as uncertainties in the input parameters and corresponding uncertainties in theoretical brightness temperature predictions we compare emission model predictions with ground based observations at four diverse sites in antarctica which span a range of accumulation rates and other parameters we use coincident characterization data to estimate model inputs at two sites layered medium emission model predictions based on the most probable input parameters i e with no model tuning agree with observations to within 3 5 for incidence angles 50 corresponding figures for the other two sites are 7 5 and 10 however uncertainties in the input parameters are substantial due to the limited length and depth resolution of the characterization data uncertainties in brightness temperature predictions are correspondingly substantial thus brightness temperature predictions for the last mentioned sites based on only slightly less probable input parameters are also in close agreement with observations the significance of agreements and discrepancies could be clarified using characterization measurements with finer depth resolution

a blue ice ecosystem on the margins of the east antarctic ice sheet freezing temperatures desiccation and high levels of solar radiation make the surface of the antarctic ice sheet one of earth s harshest habitats however our study in the vestfold hills area of east antarctica shows that favourable conditions for microbial production become established just beneath the surface of blue ice areas which collectively cover about 2 of the ice sheet periphery their translucent wind polished surface allows solar heating to create meltwater in a greenhouse type environment at depths of up to 1m melting is intensified around dark debris particles or cryoconite where we found microbiological activity to be greatest rates of photosynthesis average 2060 ngc g cryoconite 1 d 1 were adapted to low light intensities 10 of surface irradiance values and most likely dominated by cyanobacteria and chloroplastida a heterotrophic bacterial community was also found to be active within the cryoconite although average bacterial growth rates 5 7 ngc g cryoconite 1 d 1 were far lower than average community respiration 1870 ng c g cryoconite 1 d 1 the majority of the respired carbon was most likely associated with the autotrophs and several protists therefore blue ice areas constitute oases for microbial life around the periphery of earth s coldest ice sheet

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis