analysis of lake ice dynamics and morphology on lake el gygytgyn ne siberia using synthetic aperture radar sar and landsat 1 a time series of more than 450 combined ers 2 radarsat 1 and landsat 7 scenes acquired between 1998 and 2001 was analyzed to develop a fairly complete picture of lake ice dynamics on lake el gygytgyn ne siberia 67 5 n 172 e this 14 km3 lake partially fills a meteorite impact crater formed 3 6 million years ago and is home to a paleoenvironmental coring project the duration of lake ice cover and the onset of lake ice breakup are important both to interpretations of the archived sediment core record and to future drilling projects that will use the ice as a stable platform ice formation snowmelt and ice breakup likely occur in late october mid may and early july respectively these data were used to validate a one dimensional energy balance lake ice model which can now be used to hindcast paleoclimate based on core proxy information synthetic aperture radar sar backscatter from the lake ice also revealed unusual spatial variations in bubble content which were found to indicate the level of biological productivity in the sediments directly beneath the ice with the highest productivity located in the shallowest 0 10 m as well as the deepest 170 175 m regions of the lake seismic data indicates that the backscatter anomaly above the deepest water is collocated with the central peak of the impact crater 500 m below the surface several hypotheses are presented to explain this anomaly regardless of cause the fact that large spatial variations in biological productivity exist in the lake has important implications for selecting the locations of future sediment cores

a widespread and abundant chlorophyll transformation product in aquatic environments abstract an abundant chlorophyll a transformation product found previously in a lake sediment chlorophyllone a has been identified by lc ms in sediments from five aquatic environents both marine and lacustrine its previously unrecognized wide sedimentary occurrence and apparent post burial stability suggest it is an important preservational sink for the chlorophyll produced in the euphotic zone it contains a seven membered ring fused to a five membered ring and therefore provides further evidence for a transformation pathway linking chlorophyll a to a recently reported sedimentary bicycloalkanochlorin and a suite of sedimentary porphyrins of the bicycloalkanoporphyrin bi cap type

estimation of ice thickness on large northern lakes from amsr e brightness temperature measurements abstract an ice thickness retrieval algorithm utilizing data from the advanced microwave scanning radiometer earth observing system amsr e was developed and applied to great bear lake gbl and great slave lake gsl northwest territories canada for the period 2002 2009 the temporal evolution of vertically polarized amsr e brightness temperature t b at 18 7 ghz was explored to estimate ice thickness between the late freeze up ice on and early break up melt onset periods the sensitivity of amsr e t b at h and v polarizations to the seasonal evolution of ice thickness was examined statistically and with forward simulations of t b using the most recent version of the helsinki university of technology hut model which incorporates a freshwater ice layer the strong relation found between t b at 18 7 ghz v pol and ice thickness was exploited for the development of a regression based ice thickness retrieval algorithm simple linear regression equations allow for the estimation of ice thickness on a monthly basis from january to april one the global equation combines t b data for gbl and gsl and two others the regional equations use t b data for each lake alone estimated late winter ice thicknesses on gbl were determined to be on average 5 10 cm thicker than on gsl with the exception of ice season 2005 2006 when it was estimated to be 10 cm thicker on gsl for both lakes the 2004 2005 and 2008 2009 ice seasons experienced the thickest end of winter ice thicknesses ranging from 130 to 134 cm on gbl and gsl the thinnest end of winter ice thicknesses were on average 120 cm on gbl 2005 2006 and 123 cm on gsl 2007 2008 variability in air temperature snowfall and subsequent redistribution by wind and lake depth explain ice thickness variations within and between lakes over the seven winter seasons analyzed estimated ice thicknesses from amsr e compare well with coincident in situ measurements collected on gbl and gsl over a limited number of ice seasons and sites within the large passive microwave footprints mean bias error mbe 6 cm root mean square error rmse 19 cm

gravity field determination and characteristics retrospective and prospective gravimetry has had a long history using pendulums torsion balances and static spring gravimeters relative accuracy adequate for many geophysical problems was already attained by 1900 but it took another half century to build readily portable gravimeters calibration and datum definition remained problems until the 1970s when free fall absolute gravimeters were developed that now have a precision of 10 3 mgal the problems of geographic inaccessibility and field party costs notably in areas of greatest tectonic interest are now being overcome by airborne gravimetry that has already achieved accuracies of 1 3 mgal with resolutions of 10 to 20 km satellite techniques are the best way to determine the long wavelength variations of the gravity field the resolution of the models has steadily improved with the number of satellites and the precision of the observations the best current model includes tracking data from more than 30 satellites satellite altimetry and surface gravimetry and has a resolution of about 290 km harmonic degree 70 with the most recent improvements coming from doppler orbitography and radiopositioning integrated by satellite doris tracking of the spot 2 satellite and satellite laser ranging slr doris and global positioning system gps tracking of the topex poseidon satellite meanwhile radar altimetry has become the dominant technique to infer the marine geoid with a resolution of tens of kilometers or shorter similarly the gravity fields of the moon venus and mars have been determined to harmonic degrees 70 75 and 50 respectively although tracking limitations result in variations of spatial resolution modeling earth s gravity field from the abundance of precise data has become an increasingly complex task with which the development of computer capacity has kept pace contemporary solutions now entail about 10 000 parameters half of them for effects other than the fixed gravity field of earth temporal variations arising from tides have long been well modeled and nontidal changes are now being identified the improvement in gravitational models engendered corresponding advances in geophysical interpretation isostatic models were refined and expanded to account for regional thermal and tectonic histories interpretation of the long wavelength gravity field determined by satellite techniques has been mainly in terms of plate tectonics as a manifestation of mantle convection gravity has been significant in inferring that there must be a large increase in viscosity with depth most strongly from the apparent slow sinking of subducted slabs the prospects for increasing accuracy and resolution in the determination of earth s gravity field rest primarily with the development of new measurement systems airborne gravimetry is taking promising new steps using gps but significant global model improvement awaits a dedicated satellite gravimetry system and future satellite altimeter missions will do more for ocean dynamics studies than geoid improvement advances in interpretation will occur through the development of other data such as seismic tomography and larger scale computer modeling of tectonics and convection

snow distribution and melt modelling for glaciers in zackenberg river drainage basin north eastern greenland a physically based snow evolution modelling system snowmodel that includes four sub models micromet enbal snowpack and snowtran 3d was used to simulate eight full year evolutions of snow accumulation distribution sublimation and surface melt from glaciers in the zackenberg river drainage basin in north east greenland meteorological observations from two meteorological stations were used as model inputs and spatial snow depth observations snow melt depletion curves from photographic time lapse and a satellite image were used for model testing of snow and melt simulations which differ from previous snowmodel tests methods used on greenland glaciers modelled test period average end of winter snow water equivalent swe depth for the depletion area differs by a maximum of 14 mm w eq or 6 more than the observed and modelled test period average snow cover extent differs by a maximum of 5 or 0 8 km2 less than the observed furthermore comparison with a satellite image indicated a 7 discrepancy between observed and modelled snow cover extent for the entire drainage basin about 18 31 mm w eq of the solid precipitation was returned to the atmosphere by sublimation modelled mean annual snow melt and glacier ice melt for the glaciers in the zackenberg river drainage basin from 1997 through 2005 september august averaged 207 mm w eq year 1 and 1198 mm w eq year 1 respectively yielding a total averaging 1405 mm w eq year 1 total modelled mean annual surface melt varied from 960 mm w eq year 1 to 1989 mm w eq year 1 the surface melt period started between mid may and the beginning of june and lasted until mid september annual calculated runoff averaged 1487 mm w eq year 1 150 106 m3 1997 2005 with variations from 1031 mm w eq year 1 to 2051 mm w eq year 1 the model simulated a total glacier recession averaging 1347 mm w eq year 1 136 106 m3 1997 2005 which was almost equal to previous basin average hydrological water balance storage studies 244 mm w eq year 1 125 106 m3 1997 2003 copyright 2007 john wiley sons ltd

orbital forcing of organic carbon burial in the proto north atlantic during oceanic anoxic event 2 the cenomanian turonian c t intervals at dsdp sites 105 and 603b from the northern part of the proto north atlantic show high amplitude short term cyclic variations in total organic carbon toc content the more pronounced changes in toc are also reflected by changes in lithology from green claystones toc 1 although their depositional history was different the individual toc cycles at sites 105 and 603b can be correlated using stable carbon isotope stratigraphy sedimentation rates obtained from the isotope stratigraphy and spectral analyses indicate that these cycles were predominately precession controlled the coinciding variations in hi oi 13corg and the abundance of marine relative to terrestrial biomarkers as well as the low abundance of lignin pyrolysis products generated from the kerogen of the black claystones indicate that these cyclic variations reflect changes in the contribution of marine organic matter om the cooccurrence of lamination enrichment of redox sensitive trace metals and presence of molecular fossils of pigments from green sulfur bacteria indicate that the northern proto north atlantic ocean water column was periodically euxinic from the bottom to at least the base of the photic zone 150 m during the deposition of the black claystones in contrast the green claystones are bioturbated are enriched in mn do not show enrichments in redox sensitive trace metals and show biomarker distributions indicative of long oxygen exposure times indicating more oxic water conditions at the same time there is evidence e g abundance of biogenic silica and significant 13c enrichment for oc of phytoplanktic origin for enhanced primary productivity during the deposition of the black claystones we propose that increased primary productivity periodically overwhelmed the oxic om remineralisation potential of the bottom waters resulting in the deposition of om rich black claystones because the amount of oxygen used for om remineralisation exceeded the amount supplied by diffusion and deep water circulation the northern proto north atlantic became euxinic during these periods both sites 105 and 603b show trends of continually increasing toc contents and hi values of the black claystones up section which most likely resulted from both enhanced preservation due to increased anoxia and increased production of marine om during oceanic anoxic event 2 oae2

diazotrophic cyanobacteria as the major photoautotrophs during mid cretaceous oceanic anoxic events nitrogen and carbon isotopic evidence from sedimentary porphyrin abstract we determined both the nitrogen and carbon isotopic compositions of nickel chelated deoxophylloerythroetioporphyrin ni dpep a major sedimentary porphyrin extracted from the livello selli and livello bonarelli black shales deposited in the western tethys sea during mid cretaceous oceanic anoxic events oaes based on empirical isotopic relationships between the tetrapyrrole nuclei of chlorophylls and photoautotroph cells we estimate that the mean nitrogen isotopic composition of the entire photoautotrophic communities during these periods ranged from 2 to 1 this result strongly suggests that n2 fixation was an important primary process in photoautotrophic production during these oaes the estimated carbon isotopic composition of the photoautotrophs was elevated between 20 and 22 relative to typical cretaceous examples indicating as much as a 5 reduction in the magnitude of carbon isotopic fractionation associated with photosynthesis during oaes in the western tethys sea this anomaly can be well explained if cyanobacteria were the dominant producers because they commonly conduct carboxylation and or active transport of carbon substrates resulting in reduced carbon isotopic fractionation we therefore conclude that diazotrophic cyanobacteria were the dominant components of primary production during oae 1a and oae 2 in the western tethys sea

compound specific δ 15 n and chlorin preservation in surface sediments of the peru margin with implications for ancient bulk δ 15 n records abstract understanding the processes that control the preservation of paleoceanographic proxies is of clear importance surface sediments from the peru margin oxygen minimum zone are subject to lateral and downslope transport by bottom currents that decrease organic matter om quality indicators of bulk om quality pyrolysis hydrogen index pyrolysis s1 s2 and c n demonstrate significant degradation between 150 and 400 m water depth within the oxygen minimum zone concentrations of the three most abundant chlorins chlorophyllone pheophytin and pyropheophytin decrease from 750 to 150 nmol g toc 1 from 150 to 400 m water depth though the relative abundances of the chlorins in an individual sample do not change this suggests that the three chlorins have similar reactivity over the ambient conditions values for 15n of bulk sediments 15nbulk decrease by 3 from the inner shelf to the upper slope 1000 m but co occurring compound specific 15n values 15nchlorin do not decrease downslope the low variability of 15nchlorin values supports a single source for the chlorins and demonstrates the recalcitrance of 15nchlorin values despite degradation this set of observation raises questions about which type of om fraction best records primary signatures we assess two possible models to guide our interpretation of these disparate datasets 1 that decreasing 15nbulk values are the result of degradation of a 15n enriched fraction during downslope transport and that 15nchlorin values reflect primary values 2 that 15nbulk values are primary and that chlorins are derived from material transported from upslope these data reaffirm that in active sedimentary environments such as the eastern tropical pacific transport of om can significantly alter bulk geochemical parameters of om integrity but the impacts on the 15n record of bulk sediments and chlorins are less clear and require more study to be thoroughly understood

a novel sedimentary metallochlorin abstract the major chlorin in messel oil shale eocene lacustrine f r g has been isolated and assigned as the nickel complex of mesopyrophaephorbide a by spectral comparison with a synthesised standard the component whose structure clearly indicates a chlorophyll origin and which co occurs with its free base counterpart has the same carbon skeleton as the major nickel porphyrin acid assigned previously but is present in much lower abundance and still retains the c 131 carbonyl group found in all chlorophylls it appears that mesopyrophaeophorbide a represents the major part of the residual chlorin fraction which has survived aromatisation and carbonyl reduction and like the alkyl porphyrins and carboxylic acids has become metallated with nickel

effect of digital elevation model resolution on the simulation of the snow cover evolution in the high atlas the snow melt from the high atlas represents a crucial water resource for crop irrigation in the semiarid regions of morocco recent studies have used assimilation of snow cover area data from high resolution optical sensors to compute the snow water equivalent and snow melt in other mountain regions these techniques however require large model ensembles and therefore it is a challenge to determine the adequate model resolution that yields accurate results with reasonable computation time here we study the sensitivity of an energy balance model to the resolution of the model grid for a pilot catchment in the high atlas we used a time series of 8 m resolution snow cover area maps with an average revisit time of 7 5 days to evaluate the model results the digital elevation model was generated from pleiades stereo images and resampled from 8 to 30 90 250 500 and 1 000 m the results indicate that the model performs well from 8 to 250 m but the agreement with observations drops at 500 m this is because significant features of the topography were too smoothed out to properly characterize the spatial variability of meteorological forcing including solar radiation we conclude that a resolution of 250 m might be sufficient in this area this result is consistent with the shape of the semivariogram of the topographic slope suggesting that this semivariogram analysis could be used to transpose our conclusion to other study regions

porphyrin geochemistry of atlantic jurassic cretaceous black shales abstract late jurassic early cretaceous black shales and an overlying sequence of albian campanian zeolitic claystones from the falkland plateau dsdp ipod leg 71 site 511 were analyzed for tetrapyrrole pigment type and abundance the black shale sequence was found to be rich in dpep series dominated free base nickel ni and to a lesser extent vanadyl v 0 porphyrins a low level of organic maturity i e precatagenesis is indicated for these strata as nickel chelation by free base porphyrins is only 50 75 complete proceeding down hole to 627 meters sub bottom electronic and mass spectral data reveal that the proposed benzo dpep bd and tetrahydrobenzo dpep thbd series are present in the free base and ni species as well as the more usual occurrence in v 0 porphyrin arrays highly reducing conditions are suggested by an abundance of the pah perylene substantial amounts of the thbd bd series and a redox equilibrium between free base dpep and 7 8 dihydro dpep series which exist in a 7 1 molar ratio the albian campanian claystone strata were found to be tetrapyrrolepoor and those pigments present were typed as cu ni highly dealkylated c26 max etioporphyrins thought to be derived via redeposition and oxidation of terrestrial organic matter om results from the present study are correlated to our past analyses of jurassic cretaceous sediments from atlantic margins in an effort to relate tetrapyrrole quality and quantity to basin evolution and om sources in the proto atlantic

enhanced productivity led to increased organic carbon burial in the euxinic north atlantic basin during the late cenomanian oceanic anoxic event 1 three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in 13c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

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

simulation of ice phenology on great slave lake northwest territories canada a one dimensional thermodynamic lake ice model canadian lake ice model or climo is used to simulate ice phenology on great slave lake gsl in the mackenzie river basin northwest territories canada model simulations are validated against freeze up and break up dates as well as ice thickness and on ice snow depth measurements made in situ at three sites on gsl back bay near yellowknife 1960 91 hay river 1965 91 charlton bay near fort reliance 1977 90 freeze up and break up dates from the lake ice model are also compared with those derived from ssm i 85 ghz passive microwave imagery over the entire lake surface 1988 99 results show a very good agreement between observed and simulated ice thickness and freeze up break up dates over the 30 40 years of observations particularly for the back bay and hay river sites climo simulates the ice thickness and annual freeze up break dates with a mean error of 7 cm and 4 days respectively however some limitations have been identified regarding the rather simplistic approach used to characterize the temporal evolution of snow cover on ice future model improvements will therefore focus on this particular aspect through linkage or coupling to a snow model

a geological constraint on relative sea level in marine isotope stage 3 in the larsemann hills lambert glacier region east antarctica 31 366 33 228 cal yr bp abstract in this paper we present geological evidence from the larsemann hills lambert glacier amery ice shelf region east antarctica of marine sediments at an altitude of c 8 m a s l as revealed by diatom pigment and geochemical proxies in a lake sediment core the sediments yielded radiocarbon dates between c 26 650 and 28 750 14c yr bp 31 366 33 228 cal yr bp this information can be used to constrain relative sea level adjacent to the lambert glacier at the end of marine isotope stage 3 these data are compared with the age and altitude of marine isotope stage 3 marine deposits elsewhere in east antarctica and discussed with reference to late quaternary ice sheet history and eustatic sea level change

solid phase fluorescence determination of chlorins in marine sediments abstract chlorophyll degradation products are preserved in marine sediments over timescales of thousands of years the production of chlorophyll in the water column is related to biological productivity so chlorophyll degradation products chlorins preserved in marine sediments can be used as indicators of paleoproductivity a new rapid non destructive method of determining chlorin concentrations in marine sediments is presented potential interferences associated with the solid phase fluorescence spf method are explored using reference materials yet this method compares favorably with spectroscopic and high performance liquid chromatographic hplc methods of analysis using marine sediments from boston harbor and the continental shelf off northwest africa

diagenetic and catagenetic pathways for porphyrins in sediments abstract porphyrins from a range of sediments have been studied in order to deduce the diagenetic processes involved in the formation and alteration of porphyrins in sediments and oils porphyrins from e1 lajjun shale jordan have been studied in detail a c 33 di dpep vanadyl porphyrin has been isolated and characterised by mass spectrometry and nuclear magnetic resonance spectrometry the proposed structure explains the origin of di dpep and rhodoporphyrins etioporphyrins are thought to arise from oxidative cleavage of chlorophyll derivatives and not from thermal cleavage of dpep molecules a change in dpep to etioporphyrin ratio occurs because of generation of etioporphyrins from kerogen and also because of the higher thermal stability of etioporphyrins compared with dpep molecules

structural characterization of the major chlorins in a recent sediment the identities of the two major tetrapyrroles in the bottom sediment of a eutrophic lake assigned previously by spectral comparison with standards have been confirmed as phaeophytin a and pyrophaeophytin a through the use of 2d cosy and noe difference nmr techniques this provides the first unambiguous characterization of sedimentary chlorins the components being early products in the degradative pathway of chlorophyll a in the aquatic environment

the joint gravity model 3 an improved earth geopotential model complete to spherical harmonic degree and order 70 has been determined by combining the joint gravity model 1 jgm 1 geopotential coefficients and their associated error covariance with new information from slr doris and gps tracking of topex poseidon laser tracking of lageos 1 lageos 2 and stella and additional doris tracking of spot 2 the resulting field jgm 3 which has been adopted for the topex poseidon altimeter data rerelease yields improved orbit accuracies as demonstrated by better fits to withheld tracking data and substantially reduced geographically correlated orbit error methods for analyzing the performance of the gravity field using high precision tracking station positioning were applied geodetic results including station coordinates and earth orientation parameters are significantly improved with the jgm 3 model sea surface topography solutions from topex poseidon altimetry indicate that the ocean geoid has been improved subset solutions performed by withholding either the gps data or the slr doris data were computed to demonstrate the effect of these particular data sets on the gravity model used for topex poseidon orbit determination

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

sedimentary pigments as markers for environmental change in an antarctic lake abstract fossil pigments were identified in a sediment core from kirisjes pond a small lake in the larsemann hills east antarctica using reversed phase hplc and lc ms ms chlorophyll a and b derived components indicate the presence of oxygenic primary producers steryl chlorin esters provide evidence of grazing while shifts in their esterifying sterol composition record changes in the primary producer community bacteriochlorophyll c and d derived components indicative of photic zone anoxia were identified with structural variations including extensive alkylation in the macrocycle up to c 6 the pigment distribution reveals a change from oxygenated freshwater to a stratified water body with development of photic zone anoxia this coincides with a marine incursion identified from diatom records and is followed by re isolation and reversion to oxygenated freshwater conditions

freshwater flux and spatiotemporal simulated runoff variability into ilulissat icefjord west greenland linked to salinity and temperature observations near tidewater glacier margins obtained using instrumented ringed seals abstractthe distribution of terrestrial surface runoff to ilulissat icefjord west greenland is simulated for the period 2009 13 to better emphasize the spatiotemporal variability in freshwater flux and the link between runoff spikes and observed hydrographic conditions at the greenland ice sheet tidewater glacier margins runoff model simulations were forced with automatic weather station data and verified against snow water equivalent depth equilibrium line altitude and quasi continuous salinity and temperature observations obtained by ringed seals instrumented seals provide a novel platform to examine the otherwise inaccessible waters beneath the dense ice melange within the first 0 10 km of the calving front the estimated mean freshwater flux from land was 70 6 4 2 km3 yr 1 with an 85 contribution of ice discharge from jakobshavn isbrae also known as sermeq kujalleq 14 from runoff and the remaining 1 from precipitation on the fjord surface area subglacial geothermal melting and fricti

sedimentary purpurins oxidative transformation products of chlorophylls examination of sediments from three contemporary lakes priest pot loch ness and lake baikal reveals the presence of oxidative transformation products of chlorophyll a in two of the settings purpurin 18 phytyl ester not previously reported in sediments occurs in the two lakes that have deep water columns the free acid counterpart purpurin 18 occurs in only one of the samples that from loch ness although where present the abundance of purpurin 18 phytyl ester is similar to that of individual chlorin steryl esters there appears not to be a correlation between their abundances in the sediments suggesting that formation of the purpurins is not mediated by herbivory the presence of oxidative transformation products of chlorophyll in contemporary lake bottom sediments indicates their formation during the earliest stages in chlorophyll degradation their preservation in sediments demonstrates that oxidative transformation reactions in the aquatic environment lead not only to destruction of the chlorophyll macrocycle but also to structures modified in ring e this lends support to the view that sedimentary aetioporphyrins originate mainly though not exclusively from transformations of chlorophylls that involve oxidative cleavage of the five membered exocyclic ring

temporal changes in the phytoplankton community of the southern basin of lake baikal over the last 24 000 years recorded by photosynthetic pigments in a sediment core abstract photosynthetic pigments and other indicators of phytoplankton were analyzed in a dated undisturbed sediment core obtained from the southern basin of lake baikal to reveal temporal changes in the phytoplankton community in the lake through the last glacial post glacial transition the sedimentation age of the core spans the last 24 14c ka chlorophyll a its derivatives carotenoids and total organic carbon toc started to increase after 15 14c ka and the onset of biogenic silica occurred at 10 14c ka this indicated that the post glacial growth of diatoms was preceded by that of other phytoplankton groups in the record of the pigments and toc a temporary decrease was observed in the period 11 5 10 5 14c ka corresponding to the younger dryas cold period the similarity found between the depth profiles of pyropheophytin a and steryl chlorin esters formed through predation of phytoplankton by zooplankton and that of toc suggested the important contribution of fecal pellets to sedimentary organic matter in the lake

hydrogeomorphic processes of thermokarst lakes with grounded ice and floating ice regimes on the arctic coastal plain alaska thermokarst lakes cover 20 of the landscape throughout much of the alaskan arctic coastal plain acp with shallow lakes freezing solid grounded ice and deeper lakes maintaining perennial liquid water floating ice thus lake depth relative to maximum ice thickness 1 5 2 0 m represents an important threshold that impacts permafrost aquatic habitat and potentially geomorphic and hydrologic behaviour we studied coupled hydrogeomorphic processes of 13 lakes representing a depth gradient across this threshold of maximum ice thickness by analysing remotely sensed water quality and climatic data over a 35 year period shoreline erosion rates due to permafrost degradation ranged from 0 2 m year in very shallow lakes 0 4 m up to 1 8 m year in the deepest lakes 2 6 m this pattern of thermokarst expansion masked detection of lake hydrologic change using remotely sensed imagery except for the shallowest lakes with stable shorelines changes in the surface area of these shallow lakes tracked interannual variation in precipitation minus evaporation p el with periods of full and nearly dry basins shorter term 2004 2008 specific conductance data indicated a drying pattern across lakes of all depths consistent with the long term record for only shallow lakes our analysis suggests that grounded ice lakes are ice free on average 37 days longer than floating ice lakes resulting in a longer period of evaporative loss and more frequent negative p el these results suggest divergent hydrogeomorphic responses to a changing arctic climate depending on the threshold created by water depth relative to maximum ice thickness in acp lakes copyright 2011 john wiley sons ltd

a euxinic southern north atlantic ocean during the cenomanian turonian oceanic anoxic event abstract during mid cretaceous times large amounts of organic carbon corg became sequestered in black shales possibly due to oceanic anoxic events characterized by the development of an extended oxygen minimum zone omz here we provide the first direct evidence for an open ocean omz in the cenomanian turonian c t southern north atlantic and in fact show that the base of the photic zone was euxinic as revealed by molecular fossils from photosynthetic green sulfur bacteria in c t black shales this together with evidence for bottom water anoxia and accumulation of redox sensitive trace metals and hydrogen rich organic matter indicates a continuously euxinic water column concurrent with the high corg accumulation rates which are 15 150 times greater in the southern than in the northern north atlantic and the low biological productivity this suggests that preservation controlled the accumulation of corg in c t black shales

characterisation of fossil porphyrins of the di dpep type four basic structural types of alkyl porphyrins have been reported frequently to occur in sedimentary organic matter as metallocomplexes the purpose of this note is i to report the structural assignment of two representatives c32 c33 of the so called di dpep series isolated from el lajjun shale a bituminous limestone of central jordan upper cretaceous el lajjun basin ii to evaluate a previous suggestion that this type of compound and sedimentary monobenzoporphyrins are related in structure and origin

novel functionalised chlorins in sediments of the messinian vena del gesso evaporitic sequence evidence for a facile route to reduction for biomarkers fossil pigment distributions from sediments of the messinian vena del gesso italy include two novel sedimentary chlorins as revealed by high performance liquid chromatography and liquid chromatography multistage mass spectrometry the two novel chlorin components are meso derivatives of chlorophyllone a and represent early stage diagenetic intermediates in the formation of bicycloalkano chlorin and porphyrin structures that occur in these and other carbonaceous sediments their presence indicates the operation of a facile route to reduction during early diagenesis

a comparison of simulated and measured lake ice thickness using a shallow water ice profiler in northern regions where observational data is sparse lake ice models are ideal tools as they can provide valuable information on ice cover regimes the canadian lake ice model was used to simulate ice cover for a lake near churchill manitoba canada throughout the 2008 2009 and 2009 2010 ice covered seasons to validate and improve the model results in situ measurements of the ice cover through both seasons were obtained using an upward looking sonar device shallow water ice profiler swip installed on the bottom of the lake the swip identified the ice on off dates as well as collected ice thickness measurements in addition a digital camera was installed on shore to capture images of the ice cover through the seasons and field measurements were obtained of snow depth on the ice and both the thickness of snow ice if present and total ice cover altering the amounts of snow cover on the ice surface to represent potential snow redistribution affected simulated freeze up dates by a maximum of 22 days and break up dates by a maximum of 12 days highlighting the importance of accurately representing the snowpack for lake ice modelling the late season ice thickness tended to be under estimated by the simulations with break up occurring too early however the evolution of the ice cover was simulated to fall between the range of the full snow and no snow scenario with the thickness being dependant on the amount of snow cover on the ice surface copyright 2011 john wiley sons ltd

lake ice growth and decay in central alaska usa observations and computer simulations compared abstract the canadian lake ice model climo a one dimensional thermodynamic model withunsteady heat conduction and penetrating solar radiation is used to simulate ice growth and decay onshallow ponds in and near fairbanks central alaska usa simulations are compared with observationsof ice thickness and composition snow ice congelation ice freeze up break up and duration simulations run using us national weather service meteorological data as input variables do not agreewellwith ice thickness measurements the simulations improve significantly when the model is run withmore representative locally measured data forair temperature and depth of snowon the ice the causesof some discrepancies between simulations and observations are discussed and some suggestions formodel improvements are made 1 introduction lake ice growth and decay includes freeze up in theautumn a long period of growth and thickening in winter a short period of ice melting and thinning and finally break up and the complete disappearance of the ice cover inspring the sensitivity of lake ice growth and decay particularly freeze up break up and thus duration some times referred to as ice phenology to climate variabilityandchange has been demonstrated by observation on theground and from space e g palecki and barry 1986 robertson and others 1992 wynne and others 1998 magnuson and others 2000 the sensitivity of icephenology and thickness to climate variability and changehas also been investigated using computer models e g liston and hall 1995b vavrus and others 1996 stefan andfang 1997 zhang and jeffries 2000 an important aspectof computer modelling of lake ice indeed of any modellingexercise is the evaluation of model performance by com parison of simulated results with recent observations andmeasurements heron and woo 1994 liston and hall 1995a fang and others 1996 walsh and others 1998 me nard and others 2002 duguay and others 2003 using the canadian lake ice model climo me nard andothers 2002 duguay and others 2003 morris and others 2005 simulate the effects of the mid 1970s alaska climateshift on lake ice phenology thickness and composition congelation ice snow ice in central alaska usa and thesensitivity of those variables to possible future changes in themagnitude and timing of air temperature and precipitation inthe region prior to performing the climate sensitivity study we assessed the performance of climo by simulating icephenology thickness and composition in ice seasons 2001 02 and 2002 03 and comparing the results with observationsand measurements made at ponds in the vicinity of pokerflat research range pfrr and in fairbanks central alaska this paper describes the model performance assessment which is based on a more comprehensive dataset than wasavailable to duguay and others 2003 for pfrr ice season1999 2000 this assessment includes freeze up and break up data obtained every 1 2days at 11 ponds and weeklydata for ice thickness and the depth and density of the snowon the ice during the winter

absolute positioning using doris tracking of the spot 2 satellite the french doris doppler satellite tracking positioning system has been operational on the spot 2 satellite since 1990 we have analyzed 80 days of data from 42 ground beacons and determined three dimensional site coordinates which agree with a set of slr vlbi positions at the 20 30 millimeter level in each coordinate after removal of common rotations translations and a scale difference the accuracy of the vertical component is comparable to that of the horizontal components indicating that residual troposphere error is not a limiting factor the translation parameters indicate that the doris network realizes a geocentric frame to about 50 mm in each component the considerable amount of data provided by the nearly global all weather doris network allowed this complex parameterization required to reduce the unmodelled forces acting on the low earth satellite the positioning results obtained from tracking using essentially the same ground network and the higher altitude topex poseidon spacecraft should be superior to those obtained for spot 2

numerical simulation of permafrost thermal regime and talik development under shallow thaw lakes on the alaskan arctic coastal plain 1 thaw lakes are one of the most obvious manifestations of the hydrological system at work in the tundra regions of the alaskan arctic coastal plain but the extent of the role of thaw lakes in arctic land atmosphere interactions and feedback has yet to be fully understood this study uses a two dimensional heat transfer model with phase change under a cylindrical coordinate system to simulate the long term influence of shallow thaw lakes on the thermal regime of permafrost and talik development on the alaskan arctic coastal plain on the basis of previous studies of permafrost and thaw lakes at barrow alaska a series of simulation cases was conducted using different combinations of long term mean lake bottom temperature and lake depth the simulated results indicate that shallow thaw lakes are a significant heat source to permafrost and talik for a thaw lake with a long term mean lake bottom temperature of greater than 0 0 c a talik forms under the thaw lake the maximum talik thicknesses vertical distance from the ground surface to the permafrost surface are 28 0 43 0 and 53 2 m 3000 years after the formation of a shallow thaw lake with long term mean lake bottom temperatures of 1 0 2 0 and 3 0 c respectively talik development rate is very high in the first several years after a thaw lake formation and decreases gradually with time no talik forms below a thaw lake with a long term mean lake bottom temperature equal to or lower than 0 0 c but the temperature of permafrost below the thaw lake increases with time three thousand years after the formation of a thaw lake with a long term mean lake bottom temperature of greater than or equal to 2 0 c ground temperature increases of more than 0 5 c occur as far as 300 m from the lake shore and as deep as about 400 m below the ground surface it is concluded that variation of long term mean lake bottom temperature has a significant influence on permafrost thermal regime and talik development continued monitoring for thaw lake bottom temperature and ground temperature under shallow thaw lakes is needed to further improve the simulation

mapping snow distribution in the alaskan arctic using aerial photography and topographic relationships a method is presented for mapping the end of winter snow distribution in the arctic using vertical aerial photographs taken during the melt the photos show a limited number of distinctive snowmelt patterns that arise reliably year after year data and results from an energy balance melt model indicate that the patterns are not caused by differential melt but instead represent areas of distinctive end of winter snow depth a map of these snowmelt patterns is thus a map of the end of winter snow distribution because wind transport of snow is common the patterns are closely related to the topography rules based on this pattern topography relationship are developed and used to map the snow cover directly from topographic maps for three areas covering 220 km2 of the kuparuk basin in northern alaska analysis of the snow maps suggests that about 75 of the area was mapped correctly applicability reliability and limitations of this mapping approach are discussed

origin and significance of 13 2 hydroxychlorophyll derivatives in sediments abstract the authenticity of hydroxychlorophyll derivatives in sediments has been verified by subjecting pure chlorophyll preparations to the extraction method used for sediments model studies of chlorophyll autoxidation reveal hydroxychlorophyll as the major product formed in the presence of hydrogen peroxide its stability to further oxidation implies that hydroxychlorophyll derivatives are not precursors of aetioporphyrins and are more likely to produce cycloalkanoporphyrins via the processes of diagenesis the occurrence of 13 2 hydroxyphaeophytin a throughout a sediment core from loch ness confirms it to be a widespread chlorophyll oxidation product formed during early diagenesis profiles of hydroxychlorophyll derivatives in a sediment core from an antarctic lake demonstrate their potential for use as markers of oxidation processes in palaeoenvironmental assessment

an energy balance model of lake ice evolution a physically based mathematical model of the coupled lake lake ice snow and atmosphere system is developed for studying terrestrial atmospheric interactions in high elevation and high latitude regions the ability to model lake ice freeze up break up total ice thickness and ice type offers the potential to describe the effects of climate change in these regions model output is validated against lake ice observations made during the winter of 1992 93 in glacier national park montana u s a the model is driven with observed daily atmospheric forcing of precipitation wind speed and air temperature in addition to simulating complete energy balance components over the annual cycle model output includes ice freeze up and break up dates and the end of season clear ice snow ice and total ice depths for two nearby lakes in glacier national park each in a different topographic setting modeled ice features are found to agree closely with the lake ice observations model simulations illustrate the key role that the wind component of the local climatic regime plays on the growth and decay of lake ice the wind speed affects both the surface temperature and the accumulation of snow on the lake ice surface higher snow accumulations on the lake ice depress the ice surface below the water line causing the snow to become saturated and leading to the formation of snow ice deposits in regions having higher wind speeds significantly less snow accumulates on the lake ice surface thus limiting snow ice formation the ice produced by these two different mechanisms has distinctly different optical and radiative properties and affects the monitoring of frozen lakes using remote sensing techniques

lake ice formation processes and thickness evolution at lake abashiri hokkaido japan lake ice properties at lake abashiri hokkaido japan were examined using field observations and a 1 d thermodynamic model to clarify formation processes at mid latitudes subject to significant snowfall as well as moderate air temperature at all lake sites examined the ice comprised two distinct layers a snow ice si layer on top and a congelation ice ci layer below the si layer occupied as much as 29 73 of the total ice thickness a much greater fraction than that reported for lakes at arctic high latitudes in the model the ci growth rate was estimated using the traditional heat budget method while the si growth rate was calculated assuming the excessive snowfall from the isostatic balance is converted to si by a snow compression rate with the surface melting rate added when the surface heat budget becomes positive by tuning the value of to the observational results of si thickness the model outcome successfully reproduced the observational thicknesses of ci and si and the break up date of the lake essentially the model findings show how snow and its formation into si reduce by about half the seasonal variability of total ice thickness

the distribution of dissolved zinc in the atlantic sector of the southern ocean the distribution of dissolved zinc zn was investigated in the atlantic sector of the southern ocean in the austral autumn of 2008 as part of the ipy geotraces expedition zero drake research focused on transects across the major frontal systems along the zero meridian and across the drake passage there was a strong gradient in surface zinc concentrations observed across the antarctic polar front along both transects and high zinc levels were found in surface waters throughout the southern ocean vertical profiles for dissolved zinc showed the presence of local minima and maxima in the upper 200 m consistent with significant uptake by phytoplankton and release by zooplankton grazing respectively highest deep water zinc concentrations were found in the centre of the weddell gyre associated with central intermediate water ciw a water mass which is depleted in o2 elevated in co2 and is regionally a cfc minimum our data suggests that the remineralization of sinking particles is a key control on the distribution of zn in the southern ocean disappearance ratios of zinc to phosphate zn p in the upper water column increased southwards along both transects and based on laboratory studies they suggest slower growth rates of phytoplankton due to iron or light limitation zinc and silicate were strongly correlated throughout the study region but the disappearance ratio zn si was relatively uniform overall except for the region close to the ice edge on the zero meridian

chlorins in mid cretaceous black shales of the demerara rise the oldest known occurrence abstract liquid chromatography multi stage mass spectrometry lc ms n of acetone extracts confirms the presence of mesochlorophyllone in the mid cretaceous black shales of demerara rise this finding represents molecular confirmation of the oldest primary chlorins in the geologic record and is evidence for a chlorophyll a source for bicycloalkanoporphyrins in the demerara rise black shales

ice processes and surface ablation in a shallow thermokarst lake in the central qinghai tibetan plateau the qinghai tibetan plateau qtp is characterized by a cold climate and a large number of lakes the long ice season necessitates study of the widespread ice covers in the region an unprecedented multidisciplinary field campaign was conducted on lake ice processes in the central qtp during the period 2019 13 the study lake generally froze up in late october or early november and broke up in mid or late april with a maximum ice thickness of 50 70 cm the mass balances at both ice surface and bottom were measured continuously significant ice surface sublimation ablation was detected and accounted for up to 40 of the whole ice thickness over the ice season a simple heat transfer model was developed for the surface ice loss the calculated values were in good agreement with the observations they also indicated that atmospheric conditions including low air humidity and prevailing strong winds are the primary drivers of the ice surface sublimation

distributions of pigments in the organic matter of marls from the vena del gesso evaporitic sequence abstract the porphyrins and carotenoids of marl horizons within the messinian evaporitic cycles of the vena del gesso basin show variations in abundance and composition throughout a sequence of ten cycles significant variations are also apparent within individual marl horizons the differences in pigment distribution reflect significant changes in the environmental conditions during sediment deposition the presence of significant amounts of isorenieratene and co occurrence of an alkyl porphyrin with a c 34 skeleton provide evidence for anoxic conditions extending into the photic zone of the palaeo water column variations in the free pigment contents of the marls reflect a regressive trend both during deposition of an individual marl and over the entire sequence

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

meltwater flux and runoff modeling in the ablation area of jakobshavn isbrae west greenland the temporal variability in surface snow and glacier melt flux and runoff were investigated for the ablation area of lakobshavn isbrae west greenland high resolution meteorological observations both on and outside the greenland ice sheet gris were used as model input realistic descriptions of snow accumulation snow and glacier ice melt and runoff are essential to understand trends in ice sheet surface properties and processes snowmodel a physically based spatially distributed meteorological and snow evolution modeling system was used to simulate the temporal variability of lakobshavn isbrre accumulation and ablation processes for 2000 01 2006 07 winter snow depth observations and modis satellite derived summer melt observations were used for model validation of accumulation and ablation simulations agreed well with observed values simulated annual surface melt varied from as low as 3 83 x 10 sup 9 m sup 3 2001 02 to as high as 8 64 x 10 sup 9 m sup 3 2004 05 modeled surface melt occurred at elevations reaching 1 870 m a s l for 2004 05 while the equilibrium line altitude ela fluctuated from 990 to 1 210 m a s l during the simulation period the snowmodel meltwater retention and refreezing routines considerably reduce the amount of meltwater available as ice sheet runoff without these routines the lakobshavn surface runoff would be overestimated by anmore average of 80 from september october through may june no runoff events were simulated the modeled interannual runoff variability varied from 1 81 x 10 sup 9 m sup 3 2001 02 to 5 21 x 10 sup 9 m sup 3 2004 05 yielding a cumulative runoff at the jakobshavn glacier terminus of approx 2 25 m w eq to approx 4 5 m w eq respectively the average modeled lakobshavn runoff of approx 3 4 km sup 3 y sup 1 was merged with previous estimates of jakobshavn ice discharge to quantify the freshwater flux to illulissat icefiord for both runoff and ice discharge the average trends are similar indicating increasing insignificant influx of freshwater to the illulissat icefiord for the period 2000 01 2006 07 this study suggests that surface runoff forms a minor part of the overall jakobshavn freshwater flux to the fiord around 7 approx 3 4 km sup 3 y sup 1 of the average annual freshwater flux of approx 51 0 km sup 3 y sup 1 originates from the surface runoff less

instruments and methods simulating complex snow distributions in windy environments using snowtran 3d we present a generalized version of snowtran 3d version 2 0 that simulates wind related snow distributions over the range of topographic and climatic environments found globally this version includes three primary enhancements to the original liston and sturm 1998 model 1 an improved wind sub model 2 a two layer sub model describing the spatial and temporal evolution of friction velocity that must be exceeded to transport snow the threshold friction velocity and 3 implementation of a three dimensional equilibrium drift profile sub model that forces snowtran 3d snow accumulations to duplicate observed drift profiles these three sub models allow snowtran 3d to simulate snow transport processes in variable topography and different snow climates in addition snowtran 3d has been coupled to a high resolution spatially distributed meteorological model micromet to provide more realistic atmospheric forcing data micromet distributes data precipi tation wind speed and direction air temperature and relative humidity obtained from meteorological stations and or atmospheric models located within or near the simulation domain snowtran 3d has also been coupled to a spatially distributed energy and mass balance snow evolution modeling system snowmodel designed for application in any landscape and climate where snow is found snowtran 3d is typically run using temporal increments ranging from 1 hour to 1 day horizontal grid increments ranging from 1 to 100 m and time spans ranging from individual storms to entire snow seasons

nitrogen cycling during the cretaceous cenomanian turonian oceanic anoxic event ii low 15n values ranging from 1 2 to 3 9 and atomic carbon nitrogen c n ratios of 25 50 are characteristic of black shales deposited during the cenomanian turonian boundary interval and oceanic anoxic event ii oae ii an observed antithetic relationship between c n ratios and 15n could suggest a predominance of terrestrially derived organic matter or a diagenetic control on 15n variability shifting bulk 15n values lower however hydrogen indices hi generally 450 and a positive correlation of hi with c n mitigates against a significant terrestrial organic matter fraction high c n values are likely the result preferential degradation of labile n rich compounds during early diagenesis and loss of n as ammonium from sediments through time a hypothetical model that considers the degradation of a 15n enriched labile protein fraction yields only small 1 2 negative shifts in 15n however 15n depletion during diagenesis is contrary to normal isotope kinetics which should result in 15n enrichment of bulk organic matter therefore we conclude that the bulk 15n values in this study reflect primary changes in the nitrogen cycle the 15n data support the hypothesis of expanded nitrogen fixation driven by upwelling of nutrient nitrogen poor phosphorus replete waters during oae ii and from the mid cenomanian to santonian at demerara rise the low 15n values which are significantly lower than bulk 15n values in modern regions where nitrogen fixation is known to be important probably result from a more significant fraction of dissolved inorganic nitrogen being produced by nitrogen fixation during the peak of oae ii a marked shift to lower 15n values is observed this shift possibly reflects greater utilization of 15n depleted ammonium during a chemocline upward excursion cue dominance of low 15n values from other periods of more widespread marine anoxia is likely the result of similar processes

present day tectonic plate motions and crustal deformations from the doris space system doppler orbitography and radiopositioning integrated by satellite doris data acquired between january 1993 and december 1996 from the spot 2 spot 3 and topex poseidon satellites have been analyzed to determine velocities for 45 sites on eight major tectonic plates for 28 sites far from deformation zones the velocity estimates agree with plate model predictions least squares computation of poles of rotation which model the plate motions shows that for eurasia africa pacific and south america plates the agreement is better with nuvel 1 while for australia antarctica nazca and north america plates the doris euler vectors are closer to ntjvel 1a in general doris results do not differ significantly from other space geodetic techniques determinations but provide better estimates for plates poorly or inhomogeneously covered by global positioning system gps very long baseline interferometry vlbi and satellite laser ranging slr networks such as africa the doris coverage of this plate allows discussion of intraplate deformations due to the motion of the eastern africa part which constitues the somalia plate sites located in deformation zones such as western eurasia boundaries central asia southwestern america coast south east asia show motion with respect to their own plates comparisons with other geodetic measurements for colocated stations or with regional geodynamical models show the interest of doris in active zones where global plate models are not valid

further evidence for the development of photic zone euxinic conditions during mesozoic oceanic anoxic events periods in earth history characterized by extensive organic carbon deposition so called oceanic anoxic events oaes are the subject of considerable scrutiny insight into the extent of anoxic conditions in the water column has been provided by the reported occurrence of derivatives of isorenieratene a carotenoid found only in green sulphur bacteria and thus indicative of photic zone euxinia i e a water column containing free h 2 s in north atlantic deep sea sediments deposited during the cenomanian turonian boundary oae2 bonarelli event in this study we have used the distributions of chlorophyll and bacteriochlorophyll degradation products maleimides 1 h pyrrole 2 5 diones and high molecular weight porphyrins to examine further the cenomanian turonian boundary oae2 as well as other oaes of the early toarcian posidonienschiefer event and early aptian selli event in particular methyl isobutyl me i bu maleimide on structural grounds appears to be diagnostic of green sulphur bacteria this compound occurs in five of seven examined marls that record the early toarcian oae marche umbria italy further expanding the geographical range of toarcian sediments where evidence for photic zone euxinic conditions has been found me i bu maleimide occurs in three of six black shales spanning the livello selli marche umbria italy the type locality for the aptian oae1a providing the first evidence for photic zone euxinic conditions during this event with respect to the cenomanian turonian oae maleimide evidence for photic zone euxinic conditions was found in all the north atlantic sites investigated including those characterized by relatively organic lean sediments several tethyan sites and one site off western australia these data indicate that euxinic conditions were common in the water column during mesozoic oceanic anoxic events

terrestrial and planetary gravity fields the determination of the gravity field together with knowledge of the surface topography provides one of the primary means of inferring the density structure and dynamics of planetary interiors phillips and lambeck 1980 hager 1985 after removing the topographic gravity signal the distribution of internal density anomalies caused by thermal or compositional differences can be studied gravity field models can also be used to study the compensation of surface topography which can provide information on the mechanical properties and state of stress of the lithosphere the determination of these models has been accomplished using a wide variety of different measurement types and solution techniques the near earth measurement types can be divided into satellite tracking measurements surface gravity measurements and satellite altimeter measurements in both near earth and interplanetary contexts tracking data are used to measure gravitational perturbations affecting satellites with the accuracy and spatial temporal distribution of the data being the most important factors in the resulting field accuracy and resolution surface gravity data provide a more direct measurement of the gravity field but acquiring data uniformly over the earth has always been difficult satellite altimetry provides precise measurements of the marine gravity field provided that satellite orbit errors and non geoidal sea surface height variations can be adequately modeled comprehensive gravity field solutions must incorporate these disparate data types in order to estimate mathematical parameters describing the gravity field such as spherical harmonic coefficients the proper combination of these data along with the desire to acquire an accurate representation of the model errors require that complex procedures be developed for computing these solutions

nitrogen isotope and productivity variations along the northeast pacific margin over the last 120 kyr surface and subsurface paleoceanography 1 glacial interglacial changes in sedimentary 15n over the last 120 kyr display a remarkably similar pattern in timing and amplitude in core records extending from the denitrification zone in the eastern tropical north pacific etnp where subsurface denitrification is active to the oregon margin where no denitrification occurs today low 15n values 4 6 generally characterize glacial stages 2 and 4 and higher 15n values 7 10 are representative of the holocene millennial scale periods within stage 3 and stage 5 the inferred synchroneity of 15n variations along the entire margin implies that the nitrate isotopic signal produced in the oxygen poor subsurface waters in the etnp is rapidly advected northward and recorded at sites far beyond the boundaries of the modern denitrification zone similar to 15n primary production indicators percent corg ba al and percent opal show glacial interglacial as well as millennial scale variations along the ne pacific margin with higher primary production during warm periods however the relative phasing between 15n and paleoproduction tracers within individual records changes latitudinally whereas 15n and primary production vary approximately synchronously in the midlatitudes production lags 15n in the etnp by several kiloyears this lag calls for a new understanding of the processes driving denitrification in the etnp we suggest that oxygen input by the equatorial undercurrent as well as local organic matter flux controls denitrification rates in the etnp moreover the differences in relative timing point to a time transgressive development of upwelling favorable winds along the ne pacific margin after the last glaciation with those in the north developing several kiloyears earlier

unexpected occurrence and significance of zinc alkyl porphyrins in cenomanian turonian black shales of the demerara rise abstract we analyzed alkyl porphyrins in acetone extracts of cenomanian turonian black shales from the demerara rise using reverse phase high performance liquid chromatography and liquid chromatography tandem mass spectrometry the major alkyl porphyrins comprise mixtures of free base and metallo porphyrins of the c 33 bicycloalkanoporphyrin bicap structural type the most abundant porphyrins in the sediments are vanadyl complexes occurring with varying relative amounts of free base porphyrins nickel complexes and unexpectedly zinc complexed c 33 alkylporphyrins the geochemical conditions that favor production of vanadyl zinc nickel and free base porphyrins are very different although the geochemical conditions that controlled metal availability were highly variable spatially and temporally over the sample interval the dominant precursor chlorophyll s appears to have remained constant giving rise to limited structural variation with a dominance of bicap structures

a novel sedimentary chlorin structural evidence for a chlorophyll origin for aetioporphyrins a novel sedimentary transformation product of chlorophyll purpurin 7 phytyl ester has been identified by atmospheric pressure chemical ionisation liquid chromatography mass spectrometry in sediments from lake baikal russia loch ness and priest pot uk this product of oxidative transformation is an intermediate on the transformation pathway leading to sedimentary aetioporphyrins and its occurrence lends strong support to the view that aetioporphyrins derive mainly from precursor chlorophylls

aging of marine organic matter during cross shelf lateral transport in the benguela upwelling system revealed by compound specific radiocarbon dating organic matter accumulation and burial on the namibian shelf and upper slope are spatially heterogeneous and strongly controlled by lateral transport in subsurface nepheloid layers much of the material deposited in depo centers on the slope ultimately derives from the shelf supply of organic matter from the shelf involves selective transport of organic matter we studied these selective transport processes by analyzing the radiocarbon content of co occurring sediment fractions here we present radiocarbon data for total organic carbon as well as three tracers of surface ocean productivity phytoplankton derived alkenones membrane lipids of pelagic crenarchaeota crenarchaeol and calcareous microfossils of planktic foraminifera in core top and near surface sediment samples the samples were collected on the namibian margin along a shelf slope transect 85 to 1040 m at 24 s and from the upper slope depo center at 25 5 s in core top sediments alkenone ages gradually increased from modern to 3490 radiocarbon years with distance from shore and with water depth crenarchaeol while younger than alkenones also increased in age with distance offshore it was concluded that the observed ages were a consequence of cross shelf transport and associated aging of organic matter radiocarbon ages of preserved lipid biomarkers in sediments thus at least partially depend on the relative amount of laterally supplied pre aged material present in a sample highlighting the importance of nepheloid transport for the sedimentation of organic matter over the namibian margin

thermal simulation of a lake with winter ice cover1 a one dimensional thermodynamic model of a two component ice and snow cover is added to an existing one dimensional lake mixing model emphasis is placed on the thermodynamic coupling between the ice and mixing models absent in previous models the two dimensional effects of partial ice cover are incorporated into this one dimensional framework by using a minimum ice thickness the model is applied to lake laberge yukon territory and to babine lake british columbia for periods covering the formation and demise of full ice cover the results of the model are compared to snow and ice measurements in the first case and to water column data during the spring period in the second the comparisons are good implying that the ice and snow model is performing satisfactorily and emphasizing the importance of the coupling between the ice and the underlying water the successful simulation of the observed mixed layer under the ice driven by convective stirring caused by short wave heating below the temperature of maximum density is an example of the ability of the model to provide physical insight into processes occurring in lakes

positioning results with doris on spot2 after first year of mission a new space system named doris has been developed by the centre national d etudes spatiales in france with the collaboration of the institut geographique national for precise orbit determination and positioning it is a doppler based system with a worldwide ground network of transmitting beacons and an onboard receiver the spot2 satellite launched in january 1990 carries doris as an experimental instrument in this study we present positioning results obtained from the analysis of the first 10 months of doris data through a semi dynamical approach i e the satellite orbit is improved simultaneously with the beacon positions external calibration with satellite laser ranging slr and very long baseline interferometry vlbi positions indicates that doris accuracy from a few months of data is presently 15 20 cm rms in absolute and relative baseline length 1000 km positioning for very short baselines 1000 km positioning results is in the range 10 20 cm rms for the shortest baselines 100 km the month to month repeatability is better than 5 cm in cartesian coordinates this repeatability is only 2 cm in the north and east components whereas it is 12 cm in the vertical component suggesting that tropospheric errors are important it should be possible to improve these results in the future by reducing the residual orbit error especially the atmospheric drag perturbation which was particularly troublesome in 1990 a year having very large solar activity and by improving modeling of the tropospheric correction

phytoplankton assemblage in the plio pleistocene record of lake baikal as indicated by sedimentary steryl chlorin esters abstract past changes in phytoplankton assemblages in lake baikal over the last 4 5 ma both in population and composition are inferred from the downcore profiles of the relatively stable chlorophyll derivatives steryl esters of pyropheophorbides a and b steryl chlorine esters sces in the 0 200 m section of the bdp 98 drill core supplemented by the data on biogenic silica bsi and total organic carbon toc contents sces a and b dominate among sedimentary chlorophyll derivatives in the bdp 98 sediments except for the upper few meters indicating their high stability during diagenetic alteration of sediments the depth age profiles of sces a are consistent with bsi and toc profiles and are interpreted as reflecting primary productivity of the lake in the past baikal proxies reveal close correlation with marine oxygen isotope records mis stratigraphy these observations confirm that climate change in the northern hemisphere has been a primary factor controlling the total phytoplankton productivity in lake baikal during the last several million years among sces a c30 dinostanol sce a a marker of dinoflagellates was identified by gc ms analysis sce b a marker of green algae was identified by its uv vis spectrum the ratio of c30 sce a to total sces a tsces a was higher during 4 5 4 2 and 1 7 1 3 ma suggesting that dinoflagellates proliferated preferentially in those periods the early pleistocene maximum of this ratio corresponds to the broad minimum of diatom abundance previously suggested to have recorded a prolonged regional cooling an abrupt increase in the sce b tsces a ratio was observed at 2 5 2 6 ma indicating that green algae containing chlorophyll b have proliferated in lake baikal during this period this interval has also been suggested to contain evidence for a significant regional cooling based on minima of diatom abundance and bsi in sediments the depth profile of c27 5 cholesterol sce a relative to tsces a showed a trend similar to that of bsi suggesting that c27 5 sce a tsces a ratio is a potential marker of diatoms in lake baikal certain mismatches between the lake baikal profiles of biological indicators and the marine oxygen isotope records as well as the slight temporal offsets between different lake baikal biological marker signals suggest that the regional component of climatic and or lacustrine environmental changes also have played a role in determining the composition of the lake baikal plio pleistocene phytoplankton assemblage

nitrogen cycle dynamics in the late cretaceous greenhouse abstract great attention has been paid to the origin of anomalously low nitrogen isotope values during the late cretaceous nitrogen isotope values are often as low as 3 and are typically less than 2 even in relatively organic matter lean sediments here we evaluate nitrogen isotope variability during a relatively quiescent phase of the late cretaceous greenhouse between oceanic anoxic events 2 and 3 using the black shales of demerara rise dr selection of this site allows us to isolate some of the factors that control nitrogen cycle dynamics and contribute to low nitrogen isotope values new n isotope measurements from odp site 1259 reveal 15 n values that range from 0 2 to 3 5 and oscillate by 1 5 to 3 over 1 6 million years ma temporal calibration of our data using a new astronomical time scale reveals a strong 100 thousand year ka eccentricity cyclicity in 15 n we attribute this cyclicity to oscillations in the position of the intertropical convergence zone itcz over dr that modulate upwelling intensity chemocline depth and the degree of 15n depletion we also recognize a statistically significant correlation p 0 0022 between the tex86 indices and 15 n with the lowest 15 n corresponding to the highest tex86 indices this relationship suggests that the activity and ecology of ammonia oxidizing thaumarchaeota and the 15 n of dissolved inorganic nitrogen utilized by primary producers are linked we therefore interpret the observed variability in the 15 n data and tex86 indices as primarily reflecting fluctuation of upwelling intensity and chemocline depth and the significant inverse relationship between these data sets suggests that caution should be exercised when interpreting the tex86 in terms of temperature in similar paleoenvironmental settings

global geodesy using doris data on spot 2 the doris system developed for precise orbitography and precise positioning has been operational since the launch of the spot 2 satellite in january 1990 doppler doris data have been currently analysed since the beginning of the mission for geodetic objectives absolute positioning results based on a semi dynamical orbital analysis approach have been derived with the 2 years of doris data available cartesian coordinates of the global doris network 43 beacons derived on a monthly basis show a month to month repeatability of 5 7 cm rms comparison between doris station coordinates and those determined by vlbi or slr collocated with doris beacons indicates an accuracy of 5 7 cm rms in the 3 coordinates earth pole positions are determined at 5 day intervals with a standard deviation of 1 2 mas the comparison of the pole positions estimated from the doris data with a homogeneous series provided by the international earth rotation service shows differences with an amplitude of a few mas

the mulhouse basin evidence from porphyrin distributions for water column anoxia during deposition of marls abstract marls from the evaporitic mulhouse basin oligocene alsace france contain alkyl porphyrins dominated by nickel complexed species the presence in high relative abundance of a range of components with carbon numbers up to c 37 indicates that anaerobic photosynthetic bacteria made a significant contribution to the photosynthetic community in the palaeoenvironment and in turn that anoxic conditions extended into the photic zone of a stratified water column further evidence is given by the assignment by hplc coinjection with a standard of a c 34 component with the same carbon skeleton as one of the bacteriochlorophylls d of such bacteria significant differences in the nickel and vanadyl porphyrin distributions in one of the samples examined appear to result from changes in the depositional environment which are recorded with a stratigraphic resolution below that sampled or indicate derivation of these two porphyrin pools from different parts of the water column

origins of etioporphyrins in sediments evidence from stable carbon isotopes abstract in samples of the julia creek and condor oil shales australia albian and early tertiary respectively etioporphyrin iii is significantly depleted in 13 c 4 relative to porphyrins derived from chlorophylls this isotopic difference suggests a large contribution from some independent source the haem group found in cytochromes derived from microbial sources is the most likely candidate

changes in ocean denitrification during late carboniferous glacial interglacial cycles rates of denitrification below some oceanic upwelling zones reach a maximum during periods when sea level rise was fastest throughout the pleistocene glacial cycles nitrogen isotope data from north american shales deposited 300 million years ago during palaeozoic glaciations are indicative of a similar pattern

analysis of ers 1 synthetic aperture radar data of frozen lakes in northern montana and implications for climate studies lakes that freeze each winter are good indicators of regional climate change if key parameters such as freeze up and breakup date and maximum ice thickness are measured over a decade scale time frame synthetic aperture radar sar satellite data have proven to be especially useful for measurement of climatologically significant parameters characteristic of frozen lakes in this paper five lakes in glacier national park montana have been studied both in the field and using ers 1 sar data during the 1992 1993 winter the lakes are characterized by clear ice sometimes with tubular or rounded bubbles and often with a layer of snow ice on top of the clear ice they are also often snow covered freeze up is detected quite easily using ers 1 sar data as soon as a thin layer of ice forms the effect of snow ice on the backscatter is thought to be significant but is as yet undetermined on the five lakes studied relative backscatter was found to increase with ice thickness until a maximum was reached in february breakup an often ill defined occurrence is difficult to detect because surface water causes the sar signal to be absorbed thus masking the ice below comparison of the bubble structure of thaw lakes in northern alaska with lakes in northern montana has shown that the ice structure is quite different and this difference may contribute to differential sar signature evolution in the lakes of the two areas

large scale tectonic plate motions measured with the doris space geodesy system we have analysed approximately 3 years of doppler tracking measurements of the doris system on the spot2 and topex poseidon satellites absolute velocities of 19 stations of the doris network have been computed through a dynamic orbit computation method these stations are located on 9 major tectonic plates for 14 stations relative velocities across 28 plate boundaries involving 8 different plates agree quite well with the nuvel 1 geological estimates with a correlation coefficient of 0 982 and a slope of 1 00 0 02 this study provides the first space geodesy derived motion of the african plate which is based on data taken at 4 stations computed rotation vectors for the relative motions between the eurasian pacific and african plates show a good agreement with nuvel 1 vectors for the remaining sites which are typically located close to plate boundaries measured motions depart significantly from the ones predicted by nuvel 1 the site of fairbanks alaska appears to move anomalously compared to earlier vlbi results

enhanced productivity rather than enhanced preservation led to increased organic carbon burial in the euxinic southern proto north atlantic ocean during the cenomanian turonian oceanic anoxic event three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins