extensive liquid meltwater storage in firn within the greenland ice sheet surface melt water from the greenland ice sheet can become trapped in firn delaying its journey to the sea radar and ice core observations provide direct evidence of a perennial aquifer in the firn layer in southern greenland that represents a potentially significant contribution to the greenland mass budget

a century of stability of avannarleq and kujalleq glaciers west greenland explained using high resolution airborne gravity and other data the evolution of greenland glaciers in a warming climate depends on their depth below sea level flow speed surface melt and ocean induced undercutting at the calving front we present an innovative mapping of bed topography in the frontal regions of sermeq avannarleq and kujalleq two major glaciers flowing into the ice choked torssukatak fjord central west greenland the mapping combines a mass conservation algorithm inland multibeam echo sounding data in the fjord and high resolution airborne gravity data at the ice ocean transition where other approaches have traditionally failed we obtain a reliable precision 40 m solution for bed topography across the ice ocean boundary the results reveal a 700 m deep fjord that abruptly ends on a 100 300 m deep sill along the calving fronts the shallow sills explain the presence of stranded icebergs the resilience of the glaciers to ocean induced undercutting by warm atlantic water and their remarkable stability over the past century

continuity of ice sheet mass loss in greenland and antarctica from the grace and grace follow on missions abstract we examine data continuity between the grace and grace fo missions over greenland and antarctica using independent data from the mass budget method mbm which calculates the difference between ice sheet surface mass balance and ice discharge at the periphery for both ice sheets we find consistent grace grace fo time series across the data gap at the continental and regional scales and the data gap is confidently filled with mbm data in greenland the grace fo data reveal an exceptional summer loss of 600 gigatonnes in 2019 following two cold summers in antarctica ongoing high mass losses in the amundsen sea embayment of west antarctica the antarctic peninsula and wilkes land in east antarctica cumulate to 2130 560 and 370 gigatonnes respectively since 2002 a cumulative mass gain of 980 gigatonnes in queen maud land since 2009 however led to a pause in the acceleration in mass loss from antarctica after 2016

an updated view on water masses on the pan west greenland continental shelf and their link to proglacial fjords the accelerated melt of the greenland ice sheet has been linked to a sudden increase in the presence of warm subsurface coastal water in west greenland yet pathways of warm coastal water along the entire west greenland coast have remained largely unstudied here we present the first near synoptic hydrographic observations at both the continental slope and fjord entrances of the west greenland coastal system from cape farewell 59 n to melville bay 75 n in summer 2016 we observed a distinct north south division in the water mass distribution in west greenland approximately partitioned by the northern part of davis strait and a division between the continental slope and fjord entrances waters from the regional southern freshwater source with origin in the east greenland current that rounds cape farewell are not observed to enter baffin bay the regional heat source transported by the west greenland current is blocked by southwest greenland coastal water in the south but the deep connections in the north allow warm deep subpolar mode water to enter fjords furthermore we observed cold and relative saline baffin bay polar water over the inner part of the banks periodically reaching as far south as 64 n suggesting the presence of an undescribed southward current at the southwest greenland continental shelf

influence of glacier runoff and near terminus subglacial hydrology on frontal ablation at a large greenlandic tidewater glacier charlie bunce is supported by a nerc dtp studentship ne l002558 1 ben davison is funded by the scottish alliance for geoscience environment and society sages and university of st andrews we acknowledge field and research grants from the rgs ibg postgraduate research fund and mackay weir greenland fund university of edinburgh awarded to charlie bunce and rgs ibg postgraduate research fund mackay weir greenland fund university of edinburgh and centenary funding university of edinburgh awarded to alexis moyer university of edinburgh

accumulation rates 2009 2017 in southeast greenland derived from airborne snow radar and comparison with regional climate models since the year 2000 greenland ice sheet mass loss has been dominated by a decrease in surface mass balance rather than an increase in solid ice discharge southeast greenland is an important region to understand how high accumulation rates can offset increasing greenland ice sheet meltwater runoff to that end we derive a new 9 year long dataset 2009 17 of accumulation rates in southeast greenland using nasa operation icebridge snow radar our accumulation dataset derived from internal layers focuses on high elevations 1500 3000 m because at lower elevations meltwater percolation obscured internal layer structure the uncertainty of the radar derived accumulation rates is 11 using firn densification model fdm density profiles and the average accumulation rate ranges from 0 5 to 1 2 m w e with our observations spanning almost a decade we find large inter annual variability but no significant trend accumulation rates are compared with output from two regional climate models rcms mar and racmo2 this comparison shows that the models are underestimating accumulation in southeast greenland and the models misrepresent spatial heterogeneity due to an orographically forced bias in snowfall near the coast our dataset is useful to fill in temporal and spatial data gaps and to evaluate rcms where few in situ measurements are available

a microscopic sedimentary succession of graded sand and microbial mats in modern siliciclastic tidal flats microscopic studies of thin sections from modern siliciclastic tidal flat sediments in the southern north sea demonstrate the significant role of microbial mats in the buildup of sedimentary sequences this is documented by a unit only a few millimetres thick it starts at the base with a fine to medium grained quartz sand often containing secondary pores fenestrae type merging gradually into finer sediments the lower siliciclastic part is superposed by an upper organically dominated layer built by microbial mats within the organic material single quartz grains without any contact to each other are oriented with their long axes parallel to the bedding planes each siliciclastic part in the lower section of the unit indicates the initial deposition of coarser grains in a stronger flow regime followed by gradually decreasing flow velocities each microbial mat in the upper part essentially represents a period of low sedimentation rate during its growth grains still settle down onto the mat and become bound in the organic matrix the orientation of these grains with their long axes parallel to the bedding plane points to an energetically suitable position to gravity achieved by the friction reduction of the soft organic matter repeated depositional events followed by low rate deposition cause the buildup of various units there is no visible reworking of the former surfaces since the microbial mats prevent erosion during periods of increased flow the buildup is characteristic of siliciclastic sediments repeatedly occupied stabilized and fixed by microbial films or mats

multifractal characterization of microbially induced magnesian calcite formation in recent tidal flat sediments abstract structures resulting from biogenic carbonate cementation of microbial mats in recent siliciclastic tidal flat sediments of the north sea are analyzed quantitatively by a novel combination of scanning electron microscopy and energy dispersive x ray spectrometry sem edx imaging and subsequent multifractal analysis evaluation of calcium distribution patterns and their links to sediment intrinsic mineralization processes show that the applied geometrical technique is an efficient tool for detecting microscopic variations in elemental distributions and related minerals within sedimentary matrices two main conclusions can be drawn i magnesian calcite is a rapidly formed product of the early diagenesis of organic matter in recent bioactive marine sediments and ii multifractal spectra are measures for the spatial inhomogeneity of authigenic calcification processes acting on the sedimentary structure this implies that elemental distribution patterns in a sedimentary system are scale independent phenomena processes causing such patterns have occurred over certain periods with varying rates and on different scales the detection of multifractal measures also opens a way towards a systematic survey of dynamic processes occurring in sedimentary structures

vulnerability of southeast greenland glaciers to warm atlantic water from operation icebridge and ocean melting greenland data we employ national aeronautics and space administration nasa s operation icebridge high resolution airborne gravity from 2016 nasa s ocean melting greenland bathymetry from 2015 ice thickness from operation icebridge from 2010 to 2015 and bedmachine v3 to analyze 20 major southeast greenland glaciers the results reveal glacial fjords several hundreds of meters deeper than previously thought the full extent of the marine based portions of the glaciers deep troughs enabling warm salty atlantic water aw to reach the glacier fronts and melt them from below and few shallow sills that limit the access of aw the new oceanographic and topographic data help to fully resolve the complex pattern of historical ice front positions from the 1930s to 2017 glaciers exposed to aw and resting on retrograde beds have retreated rapidly while glaciers perched on shallow sills or standing in colder waters or with major sills in the fjords have remained stable

fast retreat of zachariae isstrom northeast greenland after 8 years of decay of its ice shelf zachariae isstrom a major glacier of northeast greenland that holds a 0 5 meter sea level rise equivalent entered a phase of accelerated retreat in fall 2012 the acceleration rate of its ice velocity tripled melting of its residual ice shelf and thinning of its grounded portion doubled and calving is now occurring at its grounding line warmer air and ocean temperatures have caused the glacier to detach from a stabilizing sill and retreat rapidly along a downward sloping marine based bed its equal ice volume neighbor nioghalvfjerdsfjorden is also melting rapidly but retreating slowly along an upward sloping bed the destabilization of this marine based sector will increase sea level rise from the greenland ice sheet for decades to come

channelized bottom melting and stability of floating ice shelves 1 the floating ice shelf in front of petermann glacier in northwest greenland experiences massive bottom melting that removes 80 of its ice before calving into the arctic ocean detailed surveys of the ice shelf reveal the presence of 1 2 km wide 200 400 m deep sub ice shelf channels aligned with the flow direction and spaced by 5 km we attribute their formation to the bottom melting of ice from warm ocean waters underneath drilling at the center of one of channel only 8 m above sea level confirms the presence of ice shelf melt water in the channel these deep incisions in ice shelf thickness imply a vulnerability to mechanical break up and climate warming of ice shelves that has not been considered previously

growth of greenland ice sheet interpretation an observed 0 23 m year thickening of the greenland ice sheet indicates a 25 to 45 excess ice accumulation over the amount required to balance the outward ice flow the implied global sea level depletion is 0 2 to 0 4 mm year depending on whether the thickening is only recent 5 to 10 years or longer term 100 years if there is a similar imbalance in the northern 60 of the ice sheet area the depletion is 0 35 to 0 7 mm year increasing ice thickness suggests that the precipitation is higher than the long term average higher precipitation may be a characteristic of warmer climates in polar regions

the influence of microbial mats on the formation of sand volcanoes and mounds in the red sea coastal plain south jeddah saudi arabia abstract extensive areas covered by microbial mats have been found in the upper intertidal flats and supratidal pools in the red sea coastal plain of south jeddah saudi arabia numerous microbially controlled sediment surface morphologies are evident such as flat cohesive mats that commonly pass into mats with wrinkles reticulates and tufts together with erosion pockets and mat chips these microbial mats form cohesive surface layers that lead to biostabilization of the sediment surface fluidization of the underlying sediments is due to tidal influences and pressurized gas escape from decay and photosynthesis of microbial mats and causes deformation and rupture of the cohesive surface mat layer via vertical and sub vertical pipes extrusion of fluidized sediments and water through these pipes leads to redeposition of sediment grains above the surface mat layer to form sand volcanoes and mounds most of the sand volcanoes present in the intertidal flats and supratidal pools show a symmetrical morphology whereas in tidal channels asymmetrical forms are more common extrusion of underlying sediments through several adjacent vents leads to coalescence of sand volcanoes to form sand mounds in this study sand volcanoes are also compared with other cone like features from the red sea such as gas domes and crab mounds this comparison should help in differentiating similar cone like features associated with microbial mats in the rock record

microbial sand chips a non actualistic sedimentary structure abstract microbial mats show a marked decline with the transition from the precambrian to the phanerozoic most likely due to the advent of effective benthic grazing organisms hitherto most aquatic sediments up to sand grade were commonly coagulated by organic material allowing reworking to form intraclasts new term microbial sand chips presence of a microbial mat is indicated 1 by refractory remains of organic matter in the laminated parent sediment 2 by the concentration of early diagenetic pyrite associated with sandy intraclasts in quartzites indicating a concentration of organic matter in the clast and 3 by plastic deformation of the clasts during the erosive event as bioturbation spread into most aquatic depositional environments during the phanerozoic the formation of microbial sand chips became restricted to habitats where bioturbation and grazing are limited by environmental stress and where the preservation potential for microbial sand chips is very low therefore the widespread formation of microbial sand chips in precambrian sandy subaqueous sediments is non actualistic

topographic control on distribution of modern microbially induced sedimentary structures miss a case study from texas coast abstract modern back barrier tidal flats of galveston island follets island and matagorda peninsula of the texas coast are dominated by mud to fine sand sized siliciclastic sediments and prolific microbial mats these microbial mats modify sediment behavior and result in a variety of microbially induced sedimentary structures miss common structures include knobby surfaces reticulated surfaces gas domes mat cracks sieve like surfaces erosional pockets wrinkles and mat chips in general mat thicknesses increase from 1 mm in the upper supratidal to 3 cm maximum in the lower supratidal and then decrease to 2 mm in the lower intertidal areas this same wedge shaped pattern is displayed by detailed measurements of mat thicknesses from the rims into the deeper centers of depressions pools on the supratidal flats measurements of 175 mat cracks show that height of the curled edges of the mat crack polygons increases with increase in mat thickness similarly measurements of 150 gas domes reveal that the size of the gas domes also increases with increasing thickness of the associated mats because mat thickness varies with elevation on the tidal flat curl height of the mat cracks and size of the gas domes are also related to elevation six zones were identified based on the occurrence of miss within the supratidal zone i to upper subtidal zone vi areas at the highest elevation knobby surfaces characterize zone i whereas zone ii is defined by reticulated surfaces along with reticulated surfaces gas domes and mat cracks characterize zone iii and zone iv respectively association of sieve like surfaces with mat cracks typifies zone v whereas mat deformation structures and sieve like surfaces define zone vi boundaries between the miss zones in general are parallel and related to tidal zones the distribution patterns of the miss zones are strongly controlled by local topography of the sediment surface because the degree of inundation is the primary controlling factor for the mat growth and resultant miss therefore distribution of the microbially induced sedimentary structures in siliciclastics along with the dimension of the mat cracks and gas domes can be potentially helpful in interpretation of topography of paleodepositional surfaces

a case study of microbial mat related features in coastal epeiric sandstones from the paleoproterozoic pretoria group transvaal supergroup kaapvaal craton south africa the effect of preservation reflecting sequence stratigraphic models on the relationship between mat features and inferred paleoenvironment abstract the magaliesberg formation sandstones within the upper part of the pretoria group are interpreted as a second order highstand systems tract within an overall clastic epeiric marine setting where episodic braided fluvial systems fed sediment directly into a tidally dominated coastline setting mat related features are abundantly preserved within the inferred tidal flat and supratidal deposits the daspoort formation sandstones at a lower stratigraphic level are ascribed to a closely analogous paleoenvironmental setting yet have hardly any preserved mat features at all they are ascribed to a second order transgressive systems tract in a sequence stratigraphic framework during highstand the depositional systems are inferred to have aggraded thus preserving the mat related features formed in magaliesberg intertidal supratidal environments during second order transgression the formation of the wave tidal ravinement surface in the subtidal intertidal environments largely obliterated the features of the daspoort intertidal and supratidal environments leading to a paucity of mat related structures in the preserved daspoort succession this case study thus supports the application of mat related features to integrated paleoenvironmental and sequence stratigraphic analysis while emphasizing the role of preservation

acceleration of the contribution of the greenland and antarctic ice sheets to sea level rise 1 ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques over different time periods and at various levels of spatial detail considerable disparity remains between these estimates due to the inherent uncertainties of each method the lack of detailed comparison between independent estimates and the effect of temporal modulations in ice sheet surface mass balance here we present a consistent record of mass balance for the greenland and antarctic ice sheets over the past two decades validated by the comparison of two independent techniques over the last 8 years one differencing perimeter loss from net accumulation and one using a dense time series of time variable gravity we find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss in 2006 the greenland and antarctic ice sheets experienced a combined mass loss of 475 158 gt yr equivalent to 1 3 0 4 mm yr sea level rise notably the acceleration in ice sheet loss over the last 18 years was 21 9 1 gt yr2 for greenland and 14 5 2 gt yr2 for antarctica for a combined total of 36 3 2 gt yr2 this acceleration is 3 times larger than for mountain glaciers and ice caps 12 6 gt yr2 if this trend continues ice sheets will be the dominant contributor to sea level rise in the 21st century

drainage basin delineation for outlet glaciers of northeast greenland based on sentinel 1 ice velocities and tandem x elevations abstract the drainage divides of ice sheets separate the overall glaciated area into multiple sectors these drainage basins are essential for partitioning mass changes of the ice sheet as they specify the area over which basin specific measurements are integrated the delineation of drainage basins on ice sheets is challenging due to their gentle slopes accompanied by local terrain disturbances and complex patterns of ice movement until now in greenland the basins have been mostly delineated along the major ice divides which results in large drainage sectors containing multiple outlet glaciers however when focusing on measuring glaciological parameters of individual outlet glaciers more detailed drainage basin delineations are needed here we present for the first time a detailed and fully traceable approach that combines ice sheet wide velocity measurements by sentinel 1 and the high resolution tandem x global dem to derive individual glacier drainage basins we delineated catchments for the northeast greenland ice sheet with a modified watershed algorithm and present results for 31 drainage basins even though validation of drainage basins remains a difficult task we estimated basin probabilities from monte carlo experiments and applied the method to a variety of different ice velocity and dem datasets finding discrepancies of up to 16 in the extent of catchment areas the proposed approach has the potential to produce drainage areas for the entirety of the greenland and antarctic ice sheets

a high resolution record of greenland mass balance we map recent greenland ice sheet elevation change at high spatial 5 km and temporal monthly resolution using cryosat 2 altimetry after correcting for the impact of changing snowpack properties associated with unprecedented surface melting in 2012 we nd good agreement 3 cm yr bias with airborne measurements with the aid of regional climate and rn modeling we compute high spatial and temporal resolution records of greenland mass evolution which correlate r 0 96 with monthly satellite gravimetry and reveal glacier dynamic imbalance during 2011 2014 greenland mass loss averaged 269 51 gt yr atmospherically driven losses were widespread with surface melt variability driving large uctuations in the annual mass de cit terminus regions of ve dynamically thinning glaciers which constitute less than 1 of greenland s area contributed more than 12 of the net ice loss this high resolution record demonstrates that mass de cits extending over small spatial and temporal scales have made a relatively large contribution to recent ice sheet imbalance

coherent radar ice thickness measurements over the greenland ice sheet we developed two 150 mhz coherent radar depth sounders for ice thickness measurements over the greenland ice sheet we developed one of these using connectorized components and the other using radio frequency integrated circuits rfics both systems are designed to use pulse compression techniques and coherent integration to obtain the high sensitivity required to measure the thickness of more than 4 km of cold ice we used these systems to collect radar data over the interior and margins of the ice sheet and several outlet glaciers we operated both radar systems on the nasa p 3b aircraft equipped with gps receivers radar data are tagged with gps derived location information and are collected in conjunction with laser altimeter measurements we have reduced all data collected since 1993 and derived ice thickness along all flight lines flown in support of program for regional climate assessment parca investigations and the north greenland ice core project radar echograms and derived ice thickness data are placed on a server at the university of kansas http tornado rsl ukans edu greenlanddata htm for easy access by the scientific community we obtained good ice thickness information with an accuracy of 10 m over 90 of the flight lines flown as a part of the parca initiative in this paper we provide a brief description of the system along with samples of data over the interior along the 2000 m contour line in the south and from a few selected outlet glaciers

tidal modulation of buoyant flow and basal melt beneath petermann gletscher ice shelf greenland a set of collocated in situ oceanographic and glaciological measurements from petermann gletscher ice shelf greenland provides insights into the dynamics of under ice flow driving basal melting at a site 16 km seaward of the grounding line within a longitudinal basal channel two conductivity temperature ct sensors beneath the ice base and a phase sensitive radar on the ice surface were used to monitor the coupled ice shelf ocean system a 6 month time series spanning 23 august 2015 to 12 february 2016 exhibited two distinct periods of ice ocean interactions between august and december radar derived basal melt rates featured fortnightly peaks of 15 m yr 1 which preceded the arrival of cold and fresh pulses in the ocean that had high concentrations of subglacial runoff and glacial meltwater estimated current speeds reached 0 20 0 40 m s 1 during these pulses consistent with a strengthened meltwater plume from freshwater enrichment such signals did not occur between december and february when ice ocean interactions instead varied at principal diurnal and semidiurnal tidal frequencies and lower melt rates and current speeds prevailed a combination of estimated current speeds and meltwater concentrations from the two ct sensors yields estimates of subglacial runoff and glacial meltwater volume fluxes that vary between 10 and 80 m3 s 1 during the ocean pulses area average upstream ice shelf melt rates from these fluxes are up to 170 m yr 1 revealing that these strengthened plumes had already driven their most intense melting before arriving at the study site

bedmachine v3 complete bed topography and ocean bathymetry mapping of greenland from multibeam echo sounding combined with mass conservation greenland s bed topography is a primary control on ice flow grounding line migration calving dynamics and subglacial drainage moreover fjord bathymetry regulates the penetration of warm atlantic water aw that rapidly melts and undercuts greenland s marine terminating glaciers here we present a new compilation of greenland bed topography that assimilates seafloor bathymetry and ice thickness data through a mass conservation approach a new 150 m horizontal resolution bed topography bathymetric map of greenland is constructed with seamless transitions at the ice ocean interface yielding major improvements over previous data sets particularly in the marine terminating sectors of northwest and southeast greenland our map reveals that the total sea level potential of the greenland ice sheet is 7 42 0 05 m which is 7 cm greater than previous estimates furthermore it explains recent calving front response of numerous outlet glaciers and reveals new pathways by which aw can access glaciers with marine based basins thereby highlighting sectors of greenland that are most vulnerable to future oceanic forcing

facies and origin of shales from the mid proterozoic newland formation belt basin montana usa shales constitute more than 60 of the world s sediments yet while facies models for sandstones and carbonates are at a high level of sophistication the study of shales has clearly lagged behind in the mid proterozoic newland formation six major shale facies types deposited in nearshore to basinal environments are distinguished on the basis of bedding characteristics textural features and the proportions of silt clay and carbonate textural features of these shale types are related to sedimentary environments as deduced from associated lithologies the shales are undisturbed by bioturbation and their textural and sedimentary characteristics reflect subaqueous growth of microbial mats erosion and deposition by storms deposition of flocculated vs dispersed clays continuous slow background sedimentation winnowing by waves or currents and subaerial exposure

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

the response of petermann glacier greenland to large calving events and its future stability in the context of atmospheric and oceanic warming this study assesses the impact of a large 2010 calving event on the current and future stability of petermann glacier greenland and ascertains the glacier s interaction with different components of the climate and ocean system we use a numerical ice flow model that captures the major aspects of the glacier s mass budget the resistive forces controlling glacier flow and includes dynamic calving satellite observations and model results show that the recent break off of 25 of the floating tongue did not result in a significant glacier speed up due to the low lateral resistance of this relatively wide and thin ice tongue we demonstrate that seasonal speed up at petermann glacier is mainly driven by meltwater lubrication rather than freeze up conditions in the fjord results also show that sub shelf ocean melt may have a profound effect on the future stability of petermann glacier emphasizing the urgent need for more observations and a better understanding of fjord temperature variability and circulation

hagen brae a surging glacier in north greenland 35 years of observations we use remotely sensed ice velocities in combination with observations of surface elevation and glacier area change to investigate the dynamics of hagen brae north greenland in high detail over the last 35 years from our data we can establish for the first time that hagen brae is a surge type glacier with characteristics of both alaskan and svalbard type surging glaciers we argue that the observed surge was preconditioned by the glacier geometry and triggered by englacially stored meltwater at present the glacier is in a transitional state between active and quiescence phases and is not building up to its pre surge geometry we suggest that the glacier is adjusting to the loss of its floating section general thinning and changes in fjord conditions that occurred over the study period which are unrelated to the surge behavior the high temporal resolution of the ice velocity data gives insight to the sub annual glacier flow

early triassic environmental dynamics and microbial development during the smithian spathian transition lower weber canyon utah usa the early triassic biotic recovery following the end permian mass extinction is well documented in the smithian spathian thaynes group of the western usa basin this sedimentary succession is commonly interpreted as recording harsh conditions of various shallow marine environments where microbial structures flourished however recent studies questioned the relevance of the classical view of long lasting deleterious post crisis conditions and suggested a rapid diversification of some marine ecosystems during the early triassic using field and microfacies analyses we investigate a well preserved early triassic marine sedimentary succession in lower weber canyon utah usa the identification of microbial structures and their depositional settings provide insights on factors controlling their morphologies and distribution the lower weber canyon sediments record the vertical evolution of depositional environments from a middle smithian microbial and dolosiliciclastic peritidal system to a late smithian early spathian bioclastic muddy mid ramp the microbial deposits are interpreted as microbially induced sedimentary structures miss that developed either 1 in a subtidal mid ramp where microbial wrinkles and chips are associated with megaripples characterizing hydrodynamic conditions of lower flow regime or 2 in protected areas of inter to subtidal inner ramp where they formed laminae and domal structures integrated with other published data our investigations highlight that the distribution of these microbial structures was influenced by the combined effects of bathymetry hydrodynamic conditions lithology of the substrat physico chemical characteristics of the depositional environment and by the regional relative sea level fluctuations thus we suggest that local environmental factors and basin dynamics primarily controlled the modalities of microbial development and preservation during the early triassic in the western usa basin

pyritic shales and microbial mats significant factors in the genesis of stratiform pb zn deposits of the proterozoic extensive horizons of pyritic shale occur in mid proterozoic sediments of the eastern belt basin montana u s a these pyritic shales are of striped appearance laminated pyrite beds alternate with nonpyritic shale beds laminated pyrite beds have wavycrinkly internal laminae and are interpreted as mineralized microbial mats pyrite is essentially the only sulfide mineral in these shales pyritic shale horizons occur along the basin margins and it is feasible that colloidal iron was introduced by rivers into basin marginal lagoons and then incorporated into microbial mats and reduced to pyrite the pyritic shales in the newland formation show great similarity to those that host the pb zn deposits of mt isa and mcarthur river it is suggested that pyritic shales of this kind are relatively common in mid proterozoic shales and that the processes that led to the occasional formation of pb zn ore bodies in these shales are not related to those that formed the pyritic shales themselves

possible indicators of microbial mat deposits in shales and sandstones examples from the mid proterozoic belt supergroup montana u s a abstract it has been suspected for some time that microbial mats probably colonized sediment surfaces in many terrigenous clastic sedimentary environments during the proterozoic however domination of mat morphology by depositional processes post depositional compaction and poor potential for cellular preservation of mat building organisms make their positive identification a formidable challenge within terrigenous clastics of the mid proterozoic belt supergroup a variety of sedimentary structures and textural features have been observed that can be interpreted as the result of microbial colonization of sediment surfaces among these are a domal buildups resembling stromatolites in carbonates b cohesive behaviour of laminae during soft sediment deformation erosion and transport c wavy crinkly character of laminae d bed surfaces with pustular wrinkled appearance e rippled patches on otherwise smooth surfaces f laminae with mica enrichment and or randomly oriented micas g irregular curved wrinkled impressions on bedding planes h uparched laminae near mud cracks resembling growth ridges of polygonal stromatolites and i lamina specific distribution of certain early diagenetic minerals dolomite ferroan carbonates pyrite although in none of the described examples can it irrefutably be proven that they are microbial mat deposits the observed features are consistent with such an interpretation and should be considered indicators of possible microbial mat presence in other proterozoic sequences

an improved mass budget for the greenland ice sheet extensive ice thickness surveys by nasa s operation icebridge enable over a decade of ice discharge measurements at high precision for the majority of greenland s marine terminating outlet glaciers prompting a reassessment of the temporal and spatial distribution of glacier change annualmeasurements for 178 outlet glaciers reveal that despite widespread acceleration only 15 glaciers accounted for 77 of the 739 29 gt of ice lost due to acceleration since 2000 and four accounted for 50 among the top sources of loss are several glaciers that have received little scientific attention the relative contribution of ice discharge to total loss decreased from 58 before 2005 to 32 between 2009 and 2012 as such 84 of the increase in mass loss after 2009 was due to increased surface runoff these observations support recentmodel projections that surface mass balance rather than ice dynamics will dominate the ice sheet s contribution to 21st century sea level rise

meltwater penetration through temperate ice layers in the percolation zone at dye 2 greenland ice sheet meltwater retention in the firn layer of the greenland ice sheet is has the potential to buffer sea level rise due to ice sheet melt the capacity of the firn layer to store meltwater is unclear h

changes in the velocity structure of the greenland ice sheet using satellite radar interferometry observations of greenland we detected widespread glacier acceleration below 66 north between 1996 and 2000 which rapidly expanded to 70 north in 2005 accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year as more glaciers accelerate farther north the contribution of greenland to sea level rise will continue to increase

bed elevation of jakobshavn isbrae west greenland from high resolution airborne gravity and other data jakobshavn isbrae west greenland which holds a 0 6 m sea level volume equivalent has been speeding up and retreating since the late 1990s interpretation of its retreat has been hindered by difficulties in measuring its ice thickness with airborne radar depth sounders here we employ high resolution helicopter borne gravity data from 2012 to reconstruct its bed elevation within 50 km of the ocean margin using a three dimensional inversion constrained by fjord bathymetry data offshore and a mass conservation algorithm inland we find the glacier trough to be asymmetric and several 100 m deeper than estimated previously in the lower part from 1996 to 2016 the grounding line migrated at 0 6 km yr from 700 m to 1100 m depth upstream the bed drops to 1600 m over 10 km then slowly climbs to 1200 m depth in 40 km jakobshavn isbrae will continue to retreat along a retrograde slope for decades to come

surface meltwater runoff on the greenland ice sheet estimated from remotely sensed supraglacial lake infilling rate abstract surface runoff constitutes a large percentage of greenland ice sheet gris mass loss at present but is difficult to measure directly this study provides a novel method to estimate surface runoff through remote sensing of supraglacial lake volumes because terminal non draining consistently expanding during the melt season lakes impound runoff from their surrounding contributing catchments such changes reflect runoff produced within the catchment to estimate supraglacial lake volumes multi temporal lake maps derived from landsat 8 images are intersected with dry lake bed topographic depressions showing lake bathymetry identified for two supraglacial catchments 10 km2 in southwestern gris using high resolution 2 m arcticdems intersecting remotely sensed lake shorelines with their underlying ice surface topography yields multi temporal lake volume changes which are then compared with cumulative runoff as simulated by four surface mass balance smb models hirham5 mar3 6 racmo2 3 and merra 2 comparison of cumulative lake infilling with smb simulations for these two lakes over the period 8 31 july 2015 indicates that smb models overestimated surface runoff by 106 123 these large offsets improved after early july overestimating runoff by 40 55 the runoff delay function incorporated into the mar3 6 model improves simulation of early melt season runoff signifying the importance of integrating meltwater routing schemes into smb models for improved understanding of greenland supraglacial hydrology and surface mass balance

progressive increase in ice loss from greenland 1 laser altimeter measurements over greenland show increasing thickening rates above 2000 m reflecting increasing snowfall in a warming climate but near coastal thinning rates have increased substantially since the mid 1990s and net mass loss more than doubled from an average of 4 50 gt yr 1 between 1993 4 and 1998 9 to 57 105 gt yr 1 between 1998 9 and 2004 this increasing trend is very similar to findings from independent mass budget studies but differs widely from ers radar altimeter results this may result from limitations associated with the large ers footprint over sloping and undulating surfaces that typify fast narrow glaciers where thinning is most pronounced

elevation change of the southern greenland ice sheet from 1978 to 1988 interpretation the spatial pattern of elevation change estimates derived from satellite radar altimeter data for the period from 1978 to 1988 for the southern greenland ice sheet is examined as reported previously the results from 12 ice cores widely distributed in the study area indicate that much of the spatial variability in the elevation change estimates can be explained by temporal variations in accumulation most notably the areas of largest thickening and thinning east and west of the ice divide around 66 n recently experienced substantial decadal fluctuations in accumulation sufficient to explain the observed elevation change rates that span the range of 24 cm yr 1 elevation change estimates in the nw of the study area around the 2000 m elevation contour were found to be inconsistent with both short and long term changes in accumulation fluctuations examination of stratigraphy in several shallow ice cores in the nw indicates that significant melting took place in 1977 and 1978 and this was followed by many years of very little melt activity this likely resulted in a significant downward bias in the 1978 1988 elevation change estimates in the nw comparison of measured surface velocities with those calculated assuming steady state balance show very good agreement overall but there are many instances in the southeast where the steady state velocities are significantly smaller than measured surface velocities we cannot rule out the possibility that increased ice flow in lower elevation outlet glaciers has migrated farther upstream thereby causing negative long term mass imbalance in southeast greenland

ice flow in greenland for the international polar year 2008 2009 a digital representation of ice surface velocity is essential for a variety of glaciological geologic and geophysical analyses and modeling here we present a new reference comprehensive high resolution digital mosaic of ice motion in greenland assembled from satellite radar interferometry data acquired during the international polar year 2008 to 2009 by the envisat advanced synthetic aperture radar asar the advanced land observation system alos s phase array l band sar palsar and the radarsat 1 sar that covers 99 of the ice sheet in area the best mapping performance is obtained using alos palsar data due to higher levels of temporal coherence at the l band frequency but c band frequency sar data are less affected by the ionosphere the ice motion map reveals various flow regimes ranging from patterned enhanced flow into a few large glaciers in the cold low precipitation areas of north greenland to diffuse enhanced flow into numerous narrow fast moving glaciers in the warmer high precipitation sectors of northwest and southeast greenland we find that the 100 fastest glaciers v 800m yr drain 66 of the ice sheet in area marine terminating glaciers drain 88 of greenland and basal sliding motion dominates internal deformation over more than 50 of the ice sheet this view of ice sheet motion provides significant new constraints on ice flow modeling copyright 2012 by the american geophysical union

calcite formation in microbial mats modeling and quantification of inhomogeneous distribution patterns by a cellular automaton model and multifractal measures the evolution of early diagenetic calcite cements in microbial mats of recent supratidal sediments of the southern north sea is modeled in a two dimensional microscale approach by a cellular automaton model cam calcite is traced out in the model by virtual calcium distribution patterns obtained from runs under different assumptions concerning sediment intrinsic conditions for justification of the cam real calcium distribution patterns documented by scanning electron microscopy coupled with energy dispersive x ray spectrometry sem edx are quantitatively compared with the virtual patterns on the basis of multifractal analyses the formation of high magnesian calcite as a consequence of biogenic anaerobic decomposition of organic matter starts at certain initial calcite domains in this stage an inhomogeneous and multifractal calcium distribution is characteristic nearly complete remineralization of organic matter leads to monofractal behavior of generalized fractal dimensions db q 1 84 the cam results confirm that calcite formation is a self determining morphogenetical process and diffusive transport processes of reactants within the mat affect the biogenic calcite formation

history mass loss structure and dynamic behavior of the antarctic ice sheet antarctica contains most of earth s fresh water stored in two large ice sheets the more stable east antarctic ice sheet is larger and older rests on higher topography and hides entire mountain ranges and ancient lakes the less stable west antarctic ice sheet is smaller and younger and was formed on what was once a shallow sea recent observations made with several independent satellite measurements demonstrate that several regions of antarctica are losing mass flowing faster and retreating where ice is exposed to warm ocean waters the antarctic contribution to sea level rise has reached 8 millimeters since 1992 in the future if warming ocean waters and increased surface meltwater trigger faster ice flow sea level rise will accelerate

rapid changes in ice discharge from greenland outlet glaciers using satellite derived surface elevation and velocity data we found major short term variations in recent ice discharge and mass loss at two of greenland s largest outlet glaciers their combined rate of mass loss doubled in less than a year in 2004 and then decreased in 2006 to near the previous rates likely as a result of fast re equilibration of calving front geometry after retreat total mass loss is a fraction of concurrent gravity derived estimates pointing to an alternative source of loss and the need for high resolution observations of outlet dynamics and glacier geometry for sea level rise predictions

supraglacial forcing of subglacial drainage in the ablation zone of the greenland ice sheet 1 we measure hydrological parameters in meltwater draining from an outlet glacier in west greenland to investigate seasonal changes in the structure and behaviour of the hydrological system of a large catchment in the greenland ice sheet gris our data reveal seasonal upglacier expansion and increase in hydraulic efficiency of the subglacial drainage system across a catchment 600 km2 to distances 50 km from the ice sheet margin this expansion occurs episodically in response to the drainage of surface meltwaters into a hitherto inefficient subglacial drainage system as new input locations become active progressively further upglacier this system is similar to alpine glaciers these observations provide the first synopsis of seasonal hydrological behaviour in the ablation zone of the gris

greenland ice sheet mass balance distribution of increased mass loss with climate warming 2003 07 versus 1992 2002 we derive mass changes of the greenland ice sheet gis for 2003 07 from icesat laser altimetry and compare them with results for 1992 2002 from ers radar and airborne laser altimetry the gis continued to grow inland and thin at the margins during 2003 07 but surface melting and accelerated flow significantly increased the marginal thinning compared with the 1990s the net balance changed from a small loss of 7 3g t a 1 in the 1990s to 171 4g t a 1 for 2003 07 contributing 0 5 mm a 1 to recent global sea level rise we divide the derived mass changes into two components 1 from changes in melting and ice dynamics and 2 from changes in precipitation and accumulation rate we use our firn compaction model to calculate the elevation changes driven by changes in both temperature and accumulation rate and to calculate the appropriate density to convert the accumulation driven changes to mass changes increased losses from melting and ice dynamics 17 206 gt a 1 are over seven times larger than increased gains from precipitation 10 35 gt a 1 during a warming period of 2 k 10 a 1 over the gis above 2000 m elevation the rate of gain decreased from 44 to 28 gt a 1 while below 2000 m the rate of loss increased from 51 to 198 gt a 1 enhanced thinning below the equilibrium line on outlet glaciers indicates that increased melting has a significant impact on outlet glaciers as well as accelerating ice flow increased thinning at higher elevations appears to be induced by dynamic coupling to thinning at the margins on decadal timescales

regional acceleration in ice mass loss from greenland and antarctica using grace time variable gravity data we use gravity recovery and climate experiment grace monthly gravity fields to determine the regional acceleration in ice mass loss in greenland and antarctica for 2003 2013 we find that the total mass loss is controlled by only a few regions in greenland the southeast and northwest generate 70 of the loss 280 58 gt yr mostly from ice dynamics the southwest accounts for 54 of the total acceleration in loss 25 4 1 2 gt yr 2 from a decrease in surface mass balance smb followed by the northwest 34 and we find no significant acceleration in the northeast in antarctica the amundsen sea as sector and the antarctic peninsula account for 64 and 17 respectively of the total loss 180 10 gt yr mainly from ice dynamics the as sector contributes most of the acceleration in loss 11 4 gt yr 2 and queen maud land east antarctica is the only sector with a significant mass gain due to a local increase in smb 63 5 gt yr

mineralogical footprints of microbial life earth s geosphere is intimately tied to its biosphere a major link between the two lies in the microbial realm microorganisms grow in and upon rocks and minerals often relying on their substratum for critical compounds needed in order to produce cellular energy the presence of a metabolizing cell on a mineral substrate has a significant effect on the mineral texture and on the geochemistry of the surrounding microenvironment in nature microorganisms exist in microbial commu nities as mats or biofilms growing upon a solid substrate as such they cover a vast surface area both within and below the surface of earth s land and sea the following review will provide a glimpse into the latest findings in the field of geomicrobiology and is intended to convey a sense of the profound influence microorganisms can have upon the geological environment they inhabit

improving the estimate of the secular variation of greenland ice mass in the recent decades by incorporating a stochastic process abstract the irregular interannual variations observed in the greenland ice sheet gris mass balance can be interpreted as stochastic these variations often have large amplitudes and if not accounted for correctly in the mass change model parameterization could have profound impacts on the estimate of the secular trend and acceleration here we propose a new mass trajectory model that includes both the conventional deterministic components and a stochastic component this new model simultaneously estimates the secular rate and acceleration seasonal components and the stochastic component of mass changes simulations show that this new model improves estimates of model parameters especially accelerations over the conventional model without stochastic component using this new model we estimate an acceleration of 1 6 1 3 gt yr2 in mass change minus means mass loss for 2003 2017 using the gravity recovery and climate experiment grace data and an acceleration of 1 1 1 3 gt yr2 using the modeled surface mass balance plus observed ice discharge the corresponding rates are estimated to be 288 2 12 7 gt yr and 274 9 13 0 gt yr the greatest discrepancies between the new and the conventional model parameter determinations are found in the acceleration estimates 1 6 gt yr2 vs 7 5 gt yr2 from the grace data the estimated accelerations using the new method are apparently smaller than those estimated by other studies in terms of mass loss our quantitative analysis elucidates that the acceleration estimate using the conventional method is the lower bound i e 7 5 gt yr2 for 2003 2017 while the acceleration estimated by the new method lies in the middle of the possible ranges it is also found that these discrepancies between the new and the conventional methods diminish with sufficiently long 20 yr observation records

processes responsible for the development of soft sediment deformation structures ssds in the paleoproterozoic gordon lake formation huronian supergroup canada abstract an exposure of the paleoproterozoic gordon lake formation in the bruce mines area ontario canada contains abundant soft sediment deformation structures ssds including load casts convolute bedding pseudonodules ball and pillow structures flame structures and one dewatering pipe these features are developed in siltstone to fine grained sandstone beds and are between 1 and 120 cm in width and 3 78 cm high the primary trigger mechanism is interpreted to be storm or tsunami activity however seismic shock overloading brought about by density inversions or a combination of these processes may have influenced the formation of ssds to a lesser degree several beds also contain flat to wavy carbonaceous laminae locally with a botryoidal texture and concentrations of heavy minerals which are interpreted as relicts of microbial mats microbial mats may have played a minor role in the formation of ssds but do not appear to have been a prominent driving mechanism soft sediment deformation structures observed in the baie fine flack lake and cobalt plains regions of ontario are smaller and not as abundant as in the study area suggesting that the deposits in the study area were either affected by local events or different magnitudes of sedimentary processes in contrast to the tidal flat paleoenvironment interpreted for the gordon lake formation in the flack lake area the stratigraphically lower beds at the studied outcrop more closely resemble shallow shelf deposits

greenland ice sheet increased coastal thinning repeated laser altimeter surveys and modelled snowfall summer melt show average ice loss from greenland between 1997 and 2003 was 80 12 km3 yr 1 compared to about 60 km3 yr 1 for 1993 4 1998 9 half of the increase was from higher summer melting with the rest caused by velocities of some glaciers exceeding those needed to balance upstream snow accumulation velocities of one large glacier almost doubled between 1997 and 2003 resulting in net loss from its drainage basin by about 20 km3 of ice between 2002 and 2003 copyright 2004 by the american geophysical union

forty six years of greenland ice sheet mass balance from 1972 to 2018 we reconstruct the mass balance of the greenland ice sheet using a comprehensive survey of thickness surface elevation velocity and surface mass balance smb of 260 glaciers from 1972 to 2018 we calculate mass discharge d into the ocean directly for 107 glaciers 85 of d and indirectly for 110 glaciers 15 using velocity scaled reference fluxes the decadal mass balance switched from a mass gain of 47 21 gt y in 1972 1980 to a loss of 51 17 gt y in 1980 1990 the mass loss increased from 41 17 gt y in 1990 2000 to 187 17 gt y in 2000 2010 to 286 20 gt y in 2010 2018 or sixfold since the 1980s or 80 6 gt y per decade on average the acceleration in mass loss switched from positive in 2000 2010 to negative in 2010 2018 due to a series of cold summers which illustrates the difficulty of extrapolating short records into longer term trends cumulated since 1972 the largest contributions to global sea level rise are from northwest 4 4 0 2 mm southeast 3 0 0 3 mm and central west 2 0 0 2 mm greenland with a total 13 7 1 1 mm for the ice sheet the mass loss is controlled at 66 8 by glacier dynamics 9 1 mm and 34 8 by smb 4 6 mm even in years of high smb enhanced glacier discharge has remained sufficiently high above equilibrium to maintain an annual mass loss every year since 1998

large fluctuations in speed on greenland s jakobshavn isbrae glacier it is important to understand recent changes in the velocity of greenland glaciers because the mass balance of the greenland ice sheet is partly determined by the flow rates of these outlets jakobshavn isbrae is greenland s largest outlet glacier draining about 6 5 per cent of the ice sheet area and it has been surveyed repeatedly since 1991 ref 2 here we use remote sensing data to measure the velocity of jakobshavn isbrae between 1992 and 2003 we detect large variability of the velocity over time including a slowing down from 6 700 m yr 1 in 1985 to 5 700 m yr 1 in 1992 and a subsequent speeding up to 9 400 m yr 1 by 2000 and 12 600 m yr 1 in 2003 these changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter our observations indicate that fast flowing glaciers can significantly alter ice discharge at sub decadal timescales with at least a potential to respond rapidly to a changing climate

the depositional record of sandy versicolored tidal flats mellum island southern north sea abstract cyanobacteria fix and bind sediments and generate versicolored laminated patterns in quartz sand flats they are developed in the lower supratidal zone between mean high water and mean high water springs the cyanobacteria mats protect the sediments from erosion and desiccation and provide food for marine and terrestrial invertebrates burrowing and grazing polychaetes amphipods and gastropods are present as well as a diverse meiofauna the bioturbation structures are described at some places the population density of the macrofauna averages 20 000 individuals per m2 typical are smooth surfaces and erosional pockets with rippled sand the deposits consist of laminated sand in which organic rich mat generations are intercalated the sediment is medium to fine grained sand the development of versicolored systems by interaction of migrating cyanobacteria and episodic low rate sedimentation was studied in the laboratory the depositional record reveals characteristics from both the terrestrial and the marine surrounding there are bioturbation structures from marine and terrestrial burrowing animals hard skeletal parts from shelled marine organisms and plant roots of halophytes fenestrae produced by burrowing beetles are observed the described mats characterize the type of quartz sandy potential stromatolites

neap spring cycles in a subrecent tidal channel fill 3665 bp at schoorldam nw netherlands abstract neap spring tidal sequences are described from an intertidal channel fill the channel fill consists of a larger scale thinning up and fining up sequence of parallel laminations on a smaller scale more or less regular thickening up to thinning up sequences are formed separated from each other by more or thicker clay laminae peat detritus or echinocardium spicules deeper lying sequences contain about 28 laminae higher up the sequences become more irregular and contain gradually a lesser number of laminae these thickening up to thinning up sequences are interpreted as neap spring tidal sequences formed by semi diurnal flood tidal currents hence ca 28 laminae per 14 days three types have been found a cm thick sand clay alternations b ripple like sand mud alternations and c mm thick sand clay alternations these types show transitions to each other type a was deposited at higher current velocities and type c at lowest current velocities type b features are not linsen and flaser bedding but ripple like features which during flood only moved one cross lamina followed by one slackwater lamina clay peat or spicules they are called rippled tidal couplets the pattern of neap spring sequences is compared with recent hw water levels in the north sea and related to mean high water levels mhw and mean sea level msl

heat treated stone artifacts at shuidonggou northwest china and their archaeological implications artifacts from the shuidonggou sdg site complex in ningxia province provide extensive information and insights regarding the activities of early modern humans in china based on a series of experiments and physical analyses it appears that the stone artifacts from sdg locality 2 and locality 12 have undergone heat treatment that enhanced the utilization ratio and knapping properties of the lithic raw material from which they were made in order to investigate the mechanisms involved compression tests and xrd x ray diffraction examinations were conducted on lithic raw materials collected surround the sdg sites the results indicate that the heated stones present lower compression strength and better ductility and the raw material becomes more homogeneous as well the process of crack propagation also becomes easier to control thereby reducing knapping difficulties the application of heat treatment technology at sdg reflects the production capacities and risk management strategies of the sdg inhabitants and provides evidence for the level of understanding associated with early modern human behavior this discovery confirms the appearance of this technology in the east asia around 32 ka bp which lasts to 11 ka bp providing new evidence for the spread and distribution of heat treatment technology

mass balance of the greenland ice sheet from 1958 to 2007 we combine estimates of the surface mass balance smb of the greenland ice sheet for years 1958 to 2007 with measurements of the temporal variability in ice discharge d to deduce the total ice sheet mass balance during that time period we find a robust correlation r2 0 83 between anomalies in smb and in d which we use to reconstruct a continuous series of total ice sheet mass balance we find that the ice sheet was losing 110 70 gt yr in the 1960s 30 50 gt yr or near balance in the 1970s 1980s and 97 47 gt yr in 1996 increasing rapidly to 267 38 gt yr in 2007 multi year variations in ice discharge themselves related to variations in smb cause 60 20 more variation in total mass balance smb and therefore dominate the ice sheet mass budget copyright 2008 by the american geophysical union

early holocene collapse of marine based ice in northwest greenland triggered by atmospheric warming abstract knowledge about the future response of the greenland ice sheet to global climate change including ice sheet contributions to sea level rise is important for understanding the impact of climate change on society such studies rely in ice sheet model predictions and improved chronological constraints of past ice sheet extents and paleoclimatic trends many regions in greenland are well studied but northwest greenland and especially melville bay being one of the most important regions in terms of dynamical ice mass loss lack a firm chronology of holocene ice marginal fluctuations in this study we present the first comprehensive chronology for melville bay spanning 73 1 75 7 n based on 36 new 10be exposure ages of boulders and 39 new radiocarbon ages of marine molluscs in little ice age moraines from weighted mean 10be exposure ages excluding 6 outliers we find that the outer coast in melville bay was deglaciated 11 6 0 3 ka n 15 and the ice margin reached its present day position 40 km farther inland 11 5 0 3 ka n 15 our results suggest an interval of rapid ice marginal retreat i e collapse of the northwest gris in melville bay most likely triggered by rapidly rising atmospheric temperatures in early holocene additionally combining the comprehensive dataset of new radiocarbon ages with 26 radiocarbon ages from previous studies shows a restricted ice sheet extent from 9 1 0 2 to 0 4 0 1 cal ka bp which coincides with increased sea surface temperatures our results highlight past ice sheet sensitivity towards climate changes in one of the least explored and most vulnerable regions of greenland furthermore comparing our new results to already existing ice sheet models huy3 and huy3b emphasize the proximal relevance of the agassiz ice core temperature reconstruction for melville bay which indicates the possible sensitivity of the ice sheet to a warming climate and place improved constraints on ice sheet simulations

microbial structures in oolitic iron formations ferriferous ooids and microoncoids occur in many sedimentary iron formations these ferriferous coated grains are found in fine grained carbonate rich groundmasses iron mineral encrusted microbiota are observed in both the coated grains and the groundmass the branching nature and other morphological features of the microorganisms suggest fungal origins for the oolitic iron ores particularly of the lower jurassic lorraine minette the similarity of the microbial structures in coated grains and their groundmasses suggests that both had developed within microbial mats growing under calm environmental conditions the contribution of stromatolitic marine fungal mats to the fast extraction and immobilization of iron and thus to the genesis of iron ores is demonstrated observations on well preserved freshwater derived fungal stromatolites of the tertiary and laboratory experiments with organotrophic fungal mats confirm the findings on the jurassic and imply a general role of microorganisms in the formation of such deposits

the ichnogis method network science and geostatistics in ichnology theory and application grado lagoon italy abstract a new method is proposed for capturing managing analyzing and displaying geographically referenced ichnological data ichnogis this approach is based on the integration of spatial geostatistical techniques with network theory aiming to characterize the environmental significance of recent traces the efficiency of the ichnogis method is tested against a case study the grado lagoon italy the studied site located within the epeiric northern adriatic sea consists of a complex mosaic of peritidal environments in a barrier island context here a diverse ichnofauna includes the following incipient ichnotaxa arenicolites helminthoidichnites lockeia macanopsis monocraterion parmaichnus polykladichnus skolithos thalassinoides and squat burrows ichnofaunal distribution is described by the spatial and geostatistical tools proper of the ichnogis approach additionally the application of network theory documents the emergence of organized structures ichnoassociations from interactions driven by environmental factors our results elucidate the role that environmental processes play in producing the complex ichnological patterns of the grado site in particular emersion time hydrodynamics substrate firmness and microbial binding are the major control factors determining the structure and distribution of trace associations these structuring factors are used to define a predictive model of ichnoassociation composition providing an immediate tool for future palaeoenvironmental reconstitutions

the micromorphology of unconsolidated sediments this paper aims to describe the use of thin sections micromorphology in the sedimentology of unconsolidated sediments it provides examples of the use of thin sections in a variety of sedimentary environments from fault gouge through caves and volcanics to aeolian fluviatile marine periglacial and glacial it demonstrates that in the latter three fields the use of micromorphology is relatively widespread and that in glacial sedimentology it has revolutionised our way of thinking about subglacial sediments although micromorphology has been mainly descriptive so far methods of quantification observations are demonstrated some of the important aspects of micromorphology are its use for microstratigraphy and the possibility of relating observations to documented processes thereby allowing a more robust sedimentological interpretation of modern and ancient sediments

bathymetry of southeast greenland from oceans melting greenland omg data southeast greenland has been a major participant in the ice sheet mass loss over the last several decades interpreting the evolution of glacier fronts requires information about their depth below

stromatolites in the late ordovician eureka quartzite implications for microbial growth and preservation in siliciclastic settings well preserved siliciclastic domal stromatolites up to 2 m wide and 1ae 5m high are found in a 10 to 15 m thick interval within the late ordovician eureka quartzite of southern nevada and eastern california usa these stromatolites appear as either isolated features or patchy clusters that contain more than 70 by volume quartz grains their association with planar trough and herringbone cross bedding suggests that they were formed in an upper shoreface environment with high hydraulic energy in this environment sand bars or dunes may have provided localized shelter for initial microbial mat colonization biostabilization and early lithification of microbial mats effectively prevented erosion during tidal flushing and storm surges and the prevalence of translucent quartz sand grains permitted light penetration into the sediment leading to thick microbial mat accretion and the formation of domal stromatolites decimetre scale to metre scale stromatolite domes may have served as localized shelter and nucleation sites for further microbial mat colonization forming patchy stromatolite clusters enrichment of iron minerals including pyrite and hematite within dark internal laminae of the stromatolites indicates anaerobic mineralization of microbial mats the occurrence of stromatolites in the eureka quartzite provides an example of microbial growth in highly stressed siliciclastic sedimentary environments in which microbial communities may have been able to create microenvironments promoting early cementation lithification essential for the growth and preservation of siliciclastic stromatolites

mass changes of the greenland and antarctic ice sheets and shelves and contributions to sea level rise 1992 2002 changes in ice mass are estimated from elevation changes derived from 10 5 years greenland and 9 years antarctica of satellite radar altimetry data from the european remote sensing satellites ers 1 and 2 for the first time the dh dt values are adjusted for changes in surface elevation resulting from temperature driven variations in the rate of firn compaction the greenland ice sheet is thinning at the margins 42 2g t a 1 below the equilibrium line altitude ela and growing inland 53 2g t a 1 above the ela with a small overall mass gain 11 3g t a 1 0 03 mm a 1 sle sea level equivalent the ice sheet in west antarctica wa is losing mass 47 4g t a 1 and the ice sheet in east antarctica ea shows a small mass gain 16 11 gt a 1 for a combined net change of 31 12 gt a 1 0 08 mm a 1 sle the contribution of the three ice sheets to sea level is 0 05 0 03 mm a 1 t he antarctic ice shelves show corresponding mass changes of 95 11 gt a 1 in wa and 142 10 gt a 1 in ea thinning at the margins of the greenland ice sheet and growth at higher elevations is an expected response to increasing temperatures and precipitation in a warming climate the marked thinnings in the pine island and thwaites glacier basins of wa and the totten glacier basin in ea are probably ice dynamic responses to long term climate change and perhaps past removal of their adjacent ice shelves the ice growth in the southern antarctic peninsula and parts of ea may be due to increasing precipitation during the last century

an aerial view of 80 years of climate related glacier fluctuations in southeast greenland both marine and land terminating glaciers in southeast greenland have experienced dramatic recent retreat an 80 year record of historical aerial photographs and satellite imagery shows that many land terminating glaciers in this region retreated more rapidly in the 1930s than today whereas marine terminating glaciers have retreated faster in the 2000s