global upper ordovician correlation by means of δ13c chemostratigraphy implications of the discovery of the guttenberg δ13c excursion gice in malaysia apart from a single study of the early katian 13 c chemostratigraphy in two regions in china no investigations of the sandbian and katian chemostratigraphy have been published from anywhere in asia a recent study of the conodont biostratigraphy of the classical ordovician succession on langkawi islands peninsular malaysia showed the presence there of strata coeval with those having the guttenberg carbon excursion gice on the yangtze platform in an effort to establish for the first time the presence of this widespread 13 c excursion in southern asia a series of samples from the upper part of the kaki bukit formation was isotopically analysed this resulted in the discovery of a conspicuous 13 c excursion with peak values of 2 above the baseline values the excursion is located just above the baltoniodus alobatus subzone and near the level of the first appearance of hamarodus europaeus hence the same stratigraphic position as the gice on the yangtze platform using the gice the malaysian study interval is closely correlated with the gice intervals at three localities representing an approximately 23 000 km long transect from malaysia across baltoscandia to central north america this shows the usefulness of 13 c chemostratigraphy to clarify previously obscure stratigraphic relationships between geographically very widely separated localities

cryosphere applications of nscat data though designed to measure vector winds over the ocean new imaging techniques facilitate the use of nasa scatterometer data nscat in cryosphere studies nscat provides data of unprecedented coverage resolution and quality which when coupled with the scatterometer image reconstruction with filtering sirf algorithm enables images of spl sigma sup o at resolutions approaching 8 km over stationary targets such images are useful in ice mapping and classification and multidecadal studies are possible by comparison with seasat scatterometer sass data the utility of nscat data in polar ice studies is illustrated through a review of two cryosphere applications of nscat data 1 sea ice mapping and tracking and 2 ice sheet change in greenland and antarctica the wide swath and frequent revisit coupled with incidence and azimuth angle diversity makes nscat data very effective in mapping the extent of sea ice in greenland snow and ice facies are clearly delineated on the basis of the seasonally dependent radar backscattering cross section due to sensitivity of radar backscatter to diagenetic changes occurring at and beneath the surface comparison of nscat and sass data enables study of change in greenland between 1978 and 1996

detection of snowmelt regions on the greenland ice sheet using diurnal backscatter change snowmelt regions on greenland ice are mapped daily with the seawinds wideswath ku band 13 4 ghz scatterometer on the quikscat satellite the approach exploits the high temporal resolution of seawinds quikscat data for the melt mapping using diurnal backscatter change independent of the absolute calibration the results reveal several pronounced melting and refreezing events and effects of topography are evident in the melt patterns the spatial resolution is sufficient to identify melt features on the sukker toppen iskappe west of the main ice sheet an anomalous warming event caused by downward mixing of warm air is detected in late september 1999 over the west flank of the southern greenland ice sheet time series images of melt regions are presented over the period from summer to the fall freeze up the satellite observations are verified with in situ measurements from the greenland climate network stations

an alternative model for positive shifts in shallow marine carbonate 13c and 18o positive shifts in global seawater d 13 cdic are related to changes in the ratio of organic relative to inorganic carbon burial in oceanic basins whereas factors such as climatic cooling and the accumulation of polar ice are known to cause positive shifts in d 18 o here an alternative model is proposed for the formation of local positive isotope shifts in shallow marine settings the model involves geochemically altered platform top water masses and the effects of early meteoric diagenesis on carbonate isotopic composition both mechanisms are active on modern sub tropical carbonate platforms and result in low carbonate d 13 ca ndd 18 o relative to typical oceanic values during high amplitude transgressive events the impact of isotopically light meteoric fluids on the carbonate geochemistry is much reduced and 13 c depleted platform top water mixes with open oceanic water masses having higher isotope values both factors are recorded as a transient increase in carbonate 13 c and 18 o relative to low background values these processes must be taken into consideration when interpreting the geochemical record of ancient epeiric seas

δ13c stratigraphy of a turinian chatfieldian upper ordovician foreland succession ottawa embayment central canada resolving local and inter regional isotope excursions in a tectonically active basin abstract positive 13ccarb excursions are correlated through an upper turinian to lower chatfieldian carbonate platform succession along the axis of the ottawa embayment and into outliers of the northern ottawa bonnechere graben in central canada successive turinian excursions e1 and e2 are lithostratigraphically constrained by erosional surfaces and hosted within the watertown and overlying l orignal formations respectively the latter coeval with the selby formation in the adjacent northern appalachian basin the excursions coincide with periods of regional transgression but geographic patterns of 13c depletion versus enrichment coincide with structurally defined areas of stratigraphically condensed and preferentially thickened formation successions respectively differential subsidence is interpreted to have created bathymetric variation resulting in intrabasinal restriction of seawater exchange between these areas with preferential corg recycling with stratigraphic condensation by early chatfieldian time segmentation of the once regional carbonate platform l orignal formation produced a regional mosaic of low energy muddy carbonate banks rockland formation and a deeper water platform lower hull formation settings subject to fluctuating high to low energy current flow excursion e3 occurs in both successions but 13c enrichment is associated only with the bank top muddy facies this may identify preferential photosynthetic drawdown of 12c across the bank tops due to limited seawater exchange across the bank deeper platform boundaries excursions e1 to e3 and a younger excursion e4 in the hull formation are correlated with varying confidence with excursions across southern laurentia excursion e3 being the local expression of the guttenberg 13c excursion our study supports local modulation of regional if not global 13c excursions arising from structurally controlled changes in oceanography and productivity

seasonal acceleration of inland ice via longitudinal coupling to marginal ice we use an ice flow model to demonstrate how flow variations initiated in the marginal zone of an ice sheet affect flow farther inland through longitudinal along flow coupling our findings allow for an alternate interpretation of seasonal accelerations observed near the equilibrium line of the greenland ice sheet zwally and others 2002 we demonstrate that these observations can be explained by accelerations initiated up to 12 km closer to the margin where the ice is 40 thinner is heavily crevassed experiences a seasonal doubling of velocity and where the ablation rate surface meltwater flux and ice temperature are likely higher our modeling and observations suggest that conditions and processes normally found near ice sheet margins are adequate for explaining the observations of zwally and others 2002 this and considerations of the likely subglacial hydrology in the marginal zone lead us to suggest that seasonal accelerations may have limited impact on ice sheet mass balance even in the face of climate warming

development of the benethic nepheloid layer on the south texas continental shelf western gulf of mexico abstract a monitoring study of suspended sediment on the south texas continental shelf indicates that a turbid benthic nepheloid layer is regionally persistent a sequence of quasi synoptic measurements of the water column obtained during six cruises in an 18 month period indicates substantial spatial and temporal variability in nepheloidlayer characteristics regionally the thickness of the shelf nepheloid layer increases both seaward and in a convergent alongshelf direction greatest thicknesses occur over a muddy substrate indicating a causal relationship maximum observed local thickness is 35 m which occurs along the southern shelf break analyses of suspended particulate matter in shelf bottom waters indicate mean concentrations ranging from 49 10 4 to 111 10 4 particle counts cc concentrations persistently increase shoreward throughout the region bottom particulate matter is predominantly composed of inorganic detritus admixtures of organic skeletal particles primarily diatoms are generally present but average less than 10 of the total particulate composition texturally the particulate matter in bottom waters is predominantly poorly sorted sediment composed of very fine silt 3 9 7 8 m the variability in nepheloid layer characteristics indicates a highly dynamic shelf feature the relationship of nepheloid layer characteristics to hydrographic and substrate conditions suggests a conceptual model whereby nepheloid layer development and maintenance are the results of the resuspension of sea floor sediment bottom turbulence is attributed primarily to vertical shear and shoaling progressive internal waves generated by migrating shelf water masses especially oceanic frontal systems and secondarily to shoaling surface gravity waves

late ordovician sand wave complexes on anticosti island quebec a marine tidal embayment laterally discontinuous mixed carbonate siliciclastic sandstones in the upper vaureal and lower ellis bay formations of anticosti island were deposited on an equatorial carbonate ramp with a slope of less than 1 the 10 18 m thick sandstones are interpreted as subaqueous sand wave complexes analogous to detached parts of modern shoreface connected sand ridges these record storm enhanced tidal modification of a northerly derived shoal retreat massif that may have formed in response to recovery from global sea level lowstands in the late ordovician ashgill late rawtheyan hirnantian the sand wave complexes formed within a tidal embayment that was confined by the precambrian shield to the north and northwest by rising tectonic highlands of the humber zone in newfoundland to the east and by active tectonic highlands in the quebec appalachians gaspesie to the south paleocurrent distributions parallel to the western margins of the strait of belle isle suggest that the north end of the embayment w

greenland ice sheet surface properties and ice dynamics from ers 1 sar imagery c band synthetic aperture radar sar imagery from the european space agency s ers 1 satellite reveals the basic zonation of the surface of the greenland ice sheet the zones have backscatter signatures related to the structure of the snowpack which varies with the balance of accumulation and melt at various elevations the boundaries of zones can be accurately located with the use of this high resolution imagery the images also reveal a large flow feature in northeast greenland that is similar to ice streams in antarctica and may play a major role in the discharge of ice from the ice sheet

glacier surface temperatures in the canadian high arctic 2000 15 canada s queen elizabeth islands qei contain 14 of the world s glacier and ice cap area sparse in situ measurements indicate that interannual variability in glacier surface mass balance in this region is driven primarily by variations in summer melt and that the annual surface mass balance of four index glaciers has become increasingly negative since 2007 here we use a 16 a record of satellite derived mean summer june august land surface temperatures lst from nasa s moderate resolution imaging spectroradiometer to investigate large scale spatial and temporal variability in the duration and intensity of summer melt across glaciated surfaces in the qei from 2000 to 2015 during this period qei mean summer glacier surface temperatures increased at an average rate of 0 06 0 04 c a 1 for a total of nearly 1 c most of this increase occurred between 2005 and 2012 when mean summer near surface 2 m and upper air 700 hpa temperatures were 1 0 1 2 c higher than the 1948 2015 mean there is a strong correlation between the glacier lst and 700 hpa air temperature records r 0 8 the period 2005 12 when mean summer lsts were anomalously high was likely the warmest period in the region since at least 1948

an edge detection technique to estimate melt duration season and melt extent on the greenland ice sheet using passive microwave data the melt extent duration and melt season on the greenland ice sheet were estimated using an edge detection technique on passive microwave data from the ssm i and smmr instruments 18 19v ghz channel for the period 1979 to 1997 the annual brightness temperature tb time series at a pixel location that experiences summer melt has a steep rise and drop in tb with the onset and end of melt respectively a derivative of gaussian edge detector is used to detect edges corresponding to the onset and end of melt the time lapsed between the first upward and last downward edge on the annual tb time series gives an estimate of the melt season and the time lapsed between successive upward and downward edges gives the duration of melt while the maximum melt extent increased by 18 the total duration of melt increased by 3 7 and the total melt season decreased by 3 8 during the period 1979 1997

greenland ice sheet surface temperature melt and mass loss 2000 06 author posting international glaciological society 2008 this article is posted here by permission of international glaciological society for personal use not for redistribution the definitive version was published in journal of glaciology 54 2008 81 93 doi 10 3189 002214308784409170

satellite derived melt season surface temperature of the greenland ice sheet 2000 2005 and its relationship to mass balance 1 mean clear sky surface temperature of the greenland ice sheet was measured for each melt season from 2000 to 2005 using moderate resolution imaging spectroradiometer modis derived land surface temperature lst data product maps during the period of most active melt the mean clear sky surface temperature of the ice sheet was highest in 2002 8 29 5 29 c and 2005 8 29 5 43 c compared to a 6 year mean of 9 04 5 59 c in agreement with recent work by other investigators showing unusually extensive melt in 2002 and 2005 surface temperature variability shows a correspondence with the dry snow facies of the ice sheet a reduction in area of the dry snow facies would indicate a more negative mass balance surface temperature variability generally increased during the study period and is most pronounced in the 2005 melt season this is consistent with surface instability caused by air temperature fluctuations

transport of mud on continental shelves evidence from the texas shelf abstract transmissivity and suspended sediment data from three cruises on the east texas continental shelf confirm that a bottom nepheloid layer bnl exists across the shelf this layer is most turbid in the nearshore and outer shelf regions in addition surface nepheloid layers exist close to shore due to river and bay outflows and on the outer shelf intermediate nepheloid layers are present as a result of quasi horizontal advection from the bnl the character of the bnl is not directly linked to local hydrography or substrate being instead a function of the shelf dynamics in the nearshore regime high energy coastal processes and high sediment input from bays and rivers maintain the bnl at the shelf edge the bnl is formed by near inertial internal waves and shelf waves which resuspend and transport fine sediment present day sediment deposition on the east texas shelf can be directly related to the above processes mud is accumulating in the nearshore environment due to river input and on the inner and midshelf regions as a result of deposition from bnls and snls on the outer shelf bnls and inls transport fine sediment further offshore so that in effect suspended sediment bypasses the outer shelf

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

satellite derived surface type and melt area of the greenland ice sheet using modis data from 2000 to 2005 a new surface classification algorithm for monitoring snow and ice masses based on data from the moderate resolution imaging spectroradiometer modis is presented the algorithm is applied to the greenland ice sheet for the period 2000 05 and exploits the spectral variability of ice and snow reflectance to determine the surface classes dry snow wet snow and glacier ice the result is a monthly glacier surface type gst product on a 1 km resolution grid the gst product is based on a grouped criteria technique with spectral thresholds and normalized indices for the classification on a pixel by pixel basis the gst shows the changing surface classes revealing the impact of climate variations on the greenland ice sheet over time the area of wet snow and glacier ice is combined into the glacier melt area gma product the gma is analyzed in relation to the different surface classes in the gst product the results are validated with data from weather stations and similar types of satellite derived products the validation shows that the automated algorithm successfully distinguishes between the different surface types implying that the product is a promising indicator of climate change impact on the greenland ice sheet

greenland ice sheet melt extent 1979 1999 analysis of melt extent on the greenland ice sheet is updated to span the time period 1979 1999 and examined along with its spatial and temporal variability using passive microwave satellite data to acquire the full record the issue of continuity between the previous passive microwave sensors smmr ssm i f 8 and ssm i f 11 and the most recent ssm i f 13 sensor is addressed the f 13 cross polarized gradient ratio melt classification threshold is determined to be 0 0154 results show that for the 21 year record a positive melt trend of nearly 1 yr is observed but this trend falls just below the 90 significance level the observed melt increase does appear to be driven by conditions in the western portion of the ice sheet rather than the east where melt appears to have decreased slightly moreover the eruption of mount pinatubo in 1991 is likely to have had some impact on the melt but not so much as previously suspected the 1992 melt anomaly is 1 7 standard deviations from the mean finally the relationship between coastal temperatures and melt extent suggests an increase in surface runoff contribution to sea level of 0 31 mm yr for a 1 c temperature rise

particle dynamics of the surface intermediate and benthic nepheloid layers under contrasting conditions of summer monsoon and typhoon winds on the boundary between the taiwan strait and east china sea abstract two shipboard surveys of hydrographics and sediment dynamics were conducted off the mouth of minjiang the min river in july 2012 under contrasting summer monsoon and typhoon wind conditions observations included profiles of conductivity temperature depth fluorescence and suspended particle volume concentration and current velocity in addition water samples were taken for the analyses of mass concentration poc and chlorophyll of suspended sediment seafloor sediment samples were also taken for grain size analysis nepheloid layers nls were observed at surface intermediate and benthic depths snl inl bnl respectively the nl dynamics under the two wind conditions were mainly controlled by 1 the presence of the minjiang river plume and terrigenous material it carries 2 water column stability affected by wind current and waves 3 current induced resuspension of seafloor sediment and 4 physically coupled biological activities the wind field was the major forcing controlling the observed flow field and the upper water column stability in the typical summer condition southerly winds induced offshore directed currents enhancing the seaward dispersal of the minjiang river plume facilitating water column stratification thereby forming 3 nls in the water column phytoplankton growth was enhanced by terrigenous material and sunlight the suspension of the seafloor sediment was the one of the major sources for suspended particles in these nls furthermore the c n ratio of poc in the three nls is 5 72 almost identical to the redfield ratio indicating their predominant marine origin conversely under typhoon related northerly winds the offshore spread of the river plume was restricted the reduced riverine input and enhanced mixing resulted in the disappearance of the snl elevated turbidity in the inl was largely due to the presence of phytoplankton while the bnl was comprised of sediment resuspended off the seafloor and from horizontal advection our results suggest that the presence of the river plume from the minjiang at the study site sets the condition for the snl dynamics the dynamics of inl and bnl were dominated by the wind field and to a lesser degree the wave field and tidal current

avhrr surface temperature and narrow band albedo comparison with ground measurements for the greenland ice sheet an ice surface temperature retrieval algorithm for the greenland ice sheet was developed using noaa 11 thermal radiances from channels 4 and 5 temperature pressure and humidity profiles cloud observations and skin temperatures from the swiss federal institute of technology eth camp located at the equilibrium line altitude at 49 deg17 min w 69 deg 34 min n were used in the lowtran 7 model through a statistical analysis of daily clear sky profiles the coefficients that correct for the atmospheric effects were determined for the eth camp field season may to august surface temperatures retrieved by this method were then compared against the in situ observations with a maximum difference of 0 6 k the noaa 11 narrow band planetary albedo values for channels 1 and 2 were calculated using pre launch calibration coefficients scattering and absorption by the atmosphere were modelled with lowtran 7 then narrow band albedo values for the avhrr visible and near infrared channels were compared with in situ high resolution spectral reflectance measurements in the visible band 580 680 nm avhrr derived narrow band albedo and the in situ measurements corrected with radiative transfer model lowtran 7 showed a difference of less than 2 for the near infrared channel 725 1100 nm the difference between the measured and modelled narrow band albedo was 14 these discrepancies could be either the result of inaccurate aerosol scattering modelling lack of the in situ observation or the result of sensor drift due to degradation

surface melt induced acceleration of greenland ice sheet flow ice flow at a location in the equilibrium zone of the west central greenland ice sheet accelerates above the midwinter average rate during periods of summer melting the near coincidence of the ice acceleration with the duration of surface melting followed by deceleration after the melting ceases indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice bedrock interface interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting with larger increases accompanying higher amounts of summer melting the indicated coupling between surface melting and ice sheet flow provides a mechanism for rapid large scale dynamic responses of ice sheets to climate warming

relationship between hydrology and seasonal distribution of suspended sediments on the continental shelf of the bay of biscay abstract numerous oceanographic cruises with hydrology water sampling drift current measurements carried out since 1980 on the continental shelf of the bay of biscay together with available noaa avhrr infra red images form the basis of a proposed explanation for the processes responsible for the distribution of suspended sediments on the shelf the seasonal hydrographic structure of continental shelf waters is of paramount importance in sediment distribution in summer there is an horizontal stratification of water masses and suspended sediment distribution is closely related to the thermo haline structure a fresher water mass with less suspended material lies on a thicker and more turbid homogeneous layer during winter when sediment discharge from the rivers often reaches its annual maximum an oceanic thermo haline wedge occurs on the shelf at around 100 m as a result winter turbidity values on the outer continental shelf are low comparable to summer values and a permanent nepheloid layer is never observed the wedge which lasts for several months may act as a filter preventing transport to the slope high turbidities on the external shelf and the continental slope are only measured in spring when the thermo haline wedge disappears it seems possible that during winter time suspended materials brought by rivers are deposited in the grande vasiere the large mud patch it is postulated that the position of this mud patch is linked to the long term stable location of the thermo haline front that separates oceanic waters from the colder and less salty coastal waters

paleogeography of the matapedia basin in the gaspe appalachians initiation of the gaspe belt successor basin the matapedia basin consists of the uppermost ordovician lowermost silurian deep water fine grained carbonate siliciclastic rocks of the honorat garin formation and matapedia groups pabos and white head formations the lower rock assemblage of the gaspe belt in the gaspe appalachians paleogeographic maps of eight time slices from the caradocian to the llandoverian are presented to better understand the tectonosedimentary evolution of the matapedia basin deposition evolved from siliciclastic garin fm to argillaceous limestones pabos fm to limestones white head fm the overall change from terrigenous garin fm to limestone facies white head fm reflects a change in the source area paleocurrent directions and composition of sandstones indicate an orogenic source area to the south for the garin formation which is believed to be the inliers of the humber and dunnage zones in the southern gaspe and new brunswick appalachians lime muds deposited by turbidity currents coming from the nor

greenland ice sheet high elevation balance and peripheral thinning aircraft laser altimeter surveys over northern greenland in 1994 and 1999 have been coupled with previously reported data from southern greenland to analyze the recent mass balance of the greenland ice sheet above 2000 meters elevation the ice sheet is in balance on average but has some regions of local thickening or thinning thinning predominates at lower elevations with rates exceeding 1 meter per year close to the coast interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet sufficient to raise sea level by 0 13 millimeter per year approximately 7 of the observed rise

the influence of molluscan taxon on taphofacies development over a broad range of environments of preservation the sseti experience abstract we utilize information from a suite of molluscan species deployed in a variety of caribbean and gulf of mexico environments of preservation eop by sseti shelf and slope experimental taphonomy initiative to examine to what degree interpretation of the taphofacies is influenced by the mix of species presented to the observer the environment of preservation was the overwhelming determinant of taphonomic state at sseti sites species mix played a subsidiary role a few consistent trends were observed for example arctica islandica strombus luhuanus mytilus edulis and mercenaria mercenaria tended to be more highly dissolved than others mytilus edulis consistently was fragmented more than other species otherwise most species behaved uniquely over a range of eops significant species by eop interactions were the norm a taphofacies model is developed to examine further the role of species on the degradational state of the assemblage two metrics are described a taphonomic degradation score describes the overall degradational state of the assemblage from pristine to highly degraded and a taphonomic signature describes the relative importance of a suite of taphonomic processes model simulations show that the impact of species on degradational state is low initially because all shells are in relatively pristine condition shortly after death the impact is high at intermediate degradational states because factors inherent to the species modulate the time course of taphonomic decay the impact is low again at highly degraded assemblages as the taphonomic process brings shell condition to a common denominator of relatively intense degradation regardless of species fossil assemblages almost certainly express this continuum in some degree the consequence is that better preserved assemblages are ones in which species can affect taphofacies character and so similar eops may be judged distinctive due to differential dominance by one species or another teasing out characteristics that might forewarn the observer in this instance is an important goal simulations show that low evenness is an important warning sign

a five year record of summer melt on eurasian arctic ice caps abstract climatologies and annual anomaly patterns 2000 04 of melt season duration and dates of melt onset freeze up on eurasian arctic ice masses were derived from quick scatterometer quikscat backscatter data severnaya zemlya russia has later melt onset earlier freeze up and shorter melt seasons than svalbard norway novaya zemlya russia in all three archipelagos 2001 was the longest melt season and 2000 was the shortest anomalously long short melt seasons on svalbard were associated with negative positive sea ice concentration anomalies along the north coast in june and august annual mean melt duration was strongly correlated with the mean june august ncep ncar reanalysis 850 hpa air temperature allowing reconstruction of melt durations for the period of 1948 2005 the 2000 04 pentad had the second or third longest mean melt duration of all pentads in the 1950 2004 epoch while the 1950 54 pentad probably had the longest integration of these results with previous results from gre

daily air temperature estimation on glacier surfaces in the tibetan plateau using modis lst data the moderate resolution imaging spectroradiometer modis land surface temperature lst data have been widely used for air temperature estimation in mountainous regions where station observations are sparse however the performance of modis lst in high elevation glacierized areas remains unclear this study investigates air temperature estimation in glacierized areas based on ground observations at four glaciers across the tibetan plateau before being used to estimate the air temperature modis lst data are evaluated at two of the glaciers which indicates that modis night time lst is more reliable than modis daytime lst data then linear models based on each of the individual modis lst products from two platforms terra and aqua and two overpasses night time and daytime are built to estimate daily mean minimum and maximum air temperatures in glacierized areas regional glacier surface rgs models mean mean square differences 3 3 3 0 and 4 8 c for daily mean minimum and maximum air temperatures respectively show higher accuracy than local non glacier surface models mean root mean square differences 4 2 4 7 and 5 7 c in addition the rgs models based on modis night time lst perform better to estimate daily mean minimum and maximum air temperatures than using temperature lapse rate derived from local stations

stratigraphic variation in marine carbonate carbon isotope ratios stratigraphic variation in the carbon isotopic 13c value of marine carbonate and organic matter preserved within it has become a popular tool for supporting paleoclimatic hypotheses and refining stratigraphic correlation virtually every important biostratigraphic and sequence stratigraphic event of the last 800 million years has had a 13c dataset collected to aid in interpreting the causal environmental factors that contributed to the event the stratigraphic resolution obtainable using 13c has yielded critical temporal constraints on the interplay between carbon cycle variation and environmental events such as mass extinction and eustasy although the non uniqueness of the carbon isotopic response to different environmental stimuli has frustrated the identification of a unified mechanism linking marine 13c variation with distinct environmental forcing functions the interpretation of 13c variation can nonetheless provide important insights into processes that influence major global climatic and surficial systems early studies of marine carbonate minerals suggested that the 13c value of ancient oceans was essentially 0 versus the peedee belemnite standard pdb clayton and degens 1959 schidlowski et al 1975 see also keith and weber 1964 it was later recognized however that departures from the pdb standard represented secular variation in the 13c values of the marine environment rather than analytical noise that the record was potentially rich with stratigraphic and paleoenvironmental information scholle and arthur 1980 veizer et al 1980 wadleigh and veizer 1982 arthur et al 1985 holser et al 1986 zachos and arthur 1986 and that variation was intimately linked to the global carbon oxygen and sulfur cycles kump and garrels 1986 holser et al 1988 it is now well established that carbonate 13c values vary within 3 from the pdb standard for

evidence of recent flood deposits within a distal shelf depocenter and implications for terrestrial carbon preservation in non deltaic shelf settings abstract extreme episodic events have the capacity to transport large amounts of terrestrial material to the coastal ocean while estuaries and deltas are typically thought to trap most of this material some escapes these coastal features and is transported to distal depocenters along the continental shelf distal shelf depocenters can act as the ultimate sink for event deposits yet event sedimentation and the impact of terrestrial carbon burial within these shelf deposits remains understudied therefore this study investigated event sedimentation within the texas mud blanket tmb a distal shelf depocenter of the brazos river located in the northwestern gulf of mexico using a core that was collected from the tmb during a months long elevated discharge event in late 2015 to early 2016 we applied a multi proxy approach to delineate the event deposit we utilized physical sediment properties fabric texture and bulk density radioisotopes 7be and 210pb and organic geochemical properties 13c c n and lignin phenols to identify a 10 cm event layer at the surface of the core within this 10 cm layer we also distinguished two sub layers associated with separate extreme discharge periods in the winter and spring respectively using these event layer characteristics we identified three other earlier potential event deposits in the core that we have attributed to events in 2010 2007 and 2000 2001 from these results this study has demonstrated that the tmb may be an archive for event deposits over multi decadal time periods in particular the transition from periods of prolonged drought to extreme wetness associated with the brazos river this event dominated sedimentation regime can enhance long term carbon burial potentially increasing current estimates of carbon burial significantly in the tmb and other similar distal shelf depocenters ultimately this study highlights the potential for distal shelf depocenters as organic carbon burial hotspots and postulates that this role may expand in the future as climate change increases the intensity and frequency of extreme events

sources and dispersal of coarse silt on the south texas continental shelf abstract grain shape and mineralogical analyses of the coarse silt fraction of the surficial sediment of the south texas continental shelf were conducted to determine the sources of this sediment two quartz grain shape types are present in the coarse silt fraction one shape type is associated with coarse silt which is relatively mature in mineralogy and is considered to be derived from mature sedimentary rock sources the second shape type is associated with coarse silt which is relatively immature in mineralogy and is considered to be derived from both crystalline and sedimentary source rocks the distribution pattern of these two coarse silt types on the shelf is shown to reflect to varying degrees the late pleistocene paleogeography of the south texas continental shelf the compositions of rocks found in the drainage basins of the various rivers which drain onto this shelf and the redistributive effects of modern shelf currents it is concluded that grain shape analysis complemented by mineralogical analysis is a useful tool in determining the source and dispersal pattern of fine grained sediment

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

rapid mud accumulation on the central texas shelf linked to climate change and sea level rise abstract the holocene texas mud blanket tmb is a large 300 km3 containing 5 1011 t of sediment depocenter on the central texas shelf and represents a stratigraphic anomaly in that it is the only significant transgressive highstand depocenter in the northern gulf of mexico other than the mississippi river delta given its size and remoteness from large rivers the origin of the tmb has remained problematic our results demonstrate that the tmb accumulated mainly in the late holocene as a result of increased sediment supply from rivers and an increase in delivery of mississippi river sediments to the region by marine currents approximately 3000 km of high resolution 2d seismic data was used to construct detailed isopach maps of the tmb a robust radiocarbon age model derived from long sediment cores is used to measure its accumulation through time mineralogical xrd results provide information about temporal variability in the source of sediments to the tmb and indicate that sediments came mainly from the colorado brazos and mississippi rivers with the rio grande and smaller rivers of texas having been minor contributors the second largest source is from transgressive erosion of the shelf the tmb accumulated in a shelf depression that exists between the falling stage colorado and brazos deltas to the north and the rio grande delta to the south initial inundation of the outer shelf occurred 17 ka when terrestrial and lagoonal sediments filled the deepest parts of the depocenter between 17 and 9 ka was a time of rapid eustatic rise and low sedimentation var volumetric accumulation rate 0 4 km3 ka mar mass accumulation rate 0 7 106 t y at 9 ka sediment accumulation dramatically increased to 41 km3 ka 69 106 t y this sediment was mainly generated by ravinement of shelf strata including the ancestral brazos and colorado deltas between 7 5 and 4 ka texas was experiencing maximum temperature and minimum precipitation for the holocene the climatic optimum this was a time of minimum sedimentation in the tmb this was followed by a period of remarkable growth during the late holocene 3 5 ka to present when the tmb accumulated 172 km3 total volume or 2 86 1011 t of sediment accounting for 57 of its volume mineralogical results plus the sheer volume of sediment deposited during this time calls for a corresponding increase in sediment delivery to shelf from the brazos and colorado rivers and an increase in the delivery of sediment from the mississippi river by the late holocene the brazos and colorado rivers had filled their lower valleys with sediment thus eliminating onshore accommodation and increasing sediment delivery to the gulf the dramatic increase in sediment delivery from the mississippi river to the tmb during the late holocene is best explained by an increase in southeasterly winds which drive westward flowing marine currents in the northwestern gulf

remote sensing of greenland ice sheet using multispectral near infrared and visible radiances 1 we present the physical basis of and validate a new remote sensing algorithm that utilizes reflected visible and near infrared radiation to discriminate between dry and wet snow when applied to the moderate resolution imaging spectroradiometer modis satellite data our discrimination algorithm has the potential to retrieve melting regions of the ice sheet at a spatial resolution of 0 25 km 2 over three orders of magnitude higher than the resolution of current microwave methods the method should be useful for long term monitoring of the melt area of the greenland ice sheet especially regions close to ice sheet margins and of the outflow glaciers our analysis of modis retrievals of the western portion of the greenland ice sheet over the period 2000 to 2006 indicates significant interannual variability with a maximum melt extent in 2005 collocated in situ meteorological data reveal a high correlation 0 80 between the modis melt day area and the average summer temperature our analysis suggests that it is the magnitude of the summer temperature that dominates the melting not the variability of the length of the melting season furthermore we find that the melt day area increases by about 3 8 for each 0 1 k increase in the average surface air summer temperature we combine this empirical relationship with historic temperature data to infer that the melt day area of the western part of the ice sheet doubled between the mid 1990s and mid 2000s and that the largest ice sheet surface melting probably occurred between 1920s and 1930s concurrent with the warming in that period

the melt anomaly of 2002 on the greenland ice sheet from active and passive microwave satellite observations 1 active and passive microwave satellite data are used to map snowmelt extent and duration on the greenland ice sheet the passive microwave pm data reveal the extreme melt extent of 690 000 km2 in 2002 as compared with an average extent of 455 000 km2 from 1979 2003 a statistical analysis of the melt time series affirms an increased melt extent earlier in the melt season the quikscat qscat or am analysis for 1999 to 2004 confirms the extreme melt situation in 2002 qscat data show a significant increase in melt season length over several areas in 2003 ssm i and qscat melt data reveal that the later detects melt earlier and is more sensitive to surface melt qscat detects an earlier stage of melt and ssm i detects a later stage of melt the ssm i xgpr melt extent is approximately confined to the qscat melt areas experiencing 2 weeks or more of melting time

glacially streamlined hard and soft beds of the paleo ontario ice stream in southern ontario and new york state abstract an extensive tract of glacially streamlined terrain across a large part of southern ontario canada is recognized as the footprint of the paleo ontario ice stream ois within the easternmost great lakes sector of the last laurentide ice sheet the upstream part is a drumlinized and megagrooved hard bed underlain by cambro ordovician carbonates and sandstones subglacial plucking of jointed limestone on the lateral margins of drumlinized escarpment interfluves and rock drumlins generated a large flux of coarse debris within the ice base recorded by sporadic spreads of hummocky rubble moraine downstream the hard bed passes underneath a streamlined soft bed of till cored drift drumlins and megaridges of the classic peterborough and new york state drumlin fields the boundary between the two bed types is a 10 km wide mixed bed of isolated drift drumlins resting on drumlinized rock suggesting a common erosional origin spatial variation in the geomorphology of 2500 drift drumlins indicates that megaridges are clones resulting from the erosion and dissection of larger parent drumlins a large moraine system may mark the final collapse and melt of the ice stream accompanying abrupt flow switching of its margin

ice sheet mass balance assessment attribution and prognosis contrary to prior expectations that warming would cause mass addition averaged over the greenland and antarctic ice sheets and over the next century the ice sheets appear to be losing mass at least partly in response to recent warming with warming projected for the future additional mass loss appears more likely than not

comparison of satellite thermochron and air temperatures at summit greenland during the winter of 2008 09 current trends show a rise in arctic surface and air temperatures including over the greenland ice sheet where rising temperatures will contribute to increased sea level rise through increased melt we aim to establish the uncertainties in using satellite derived surface temperature for measuring arctic surface temperature as satellite data are increasingly being used to assess temperature trends to accomplish this satellite derived surface temperature or land surface temperature lst must be validated and limitations of the satellite data must be assessed quantitatively during the 2008 09 boreal winter at summit greenland we employed data from standard us national oceanic and atmospheric administration noaa air temperature instruments button sized temperature sensors called thermochrons and the moderate resolution imaging spectroradiometer modis satellite instrument to 1 assess the accuracy and utility of thermochrons in an ice sheet environment and 2 compare modis derived lsts with thermochron derived surface and air temperatures the thermochron derived air temperatures were very accurate within 0 1 0 3 c of the noaa derived air temperature but thermochron derived surface temperatures were 3 c higher than modis derived lsts though surface temperature is largely determined by air temperature these variables can differ significantly furthermore we show that the winter time mean air temperature adjusted to surface temperature was 11 c higher than the winter time mean modis derived lst this marked difference occurs largely because satellite derived lsts cannot be measured through cloud cover so caution must be exercised in using time series of satellite lst data to study seasonal temperature trends

recycling sediments between source and sink during a eustatic cycle systems of late quaternary northwestern gulf of mexico basin abstract the northwestern gulf of mexico basin is an ideal natural laboratory to study and understand source to sink systems an extensive grid of high resolution seismic data hundreds of sediment cores and borings and a robust chronostratigraphic framework were used to examine the evolution of late quaternary depositional systems of the northwestern gulf of mexico throughout the last eustatic cycle 125 ka to present the study area includes fluvial systems with a wide range of drainage basin sizes climate settings and water and sediment discharges detailed paleogeographic reconstructions are used to derive volumetric estimates of sediment fluxes volume accumulation rates the results show that the response of rivers to sea level rise and fall varied across the region larger rivers including the former mississippi western louisiana presumably the ancestral red river brazos colorado and rio grande rivers constructed deltas that advanced across the shelf in step wise fashion during marine isotope stages mis 5 2 sediment delivery to these deltas increased during the overall sea level fall due to increases in drainage basin area and erosion of sediment on the inner shelf where subsidence is minimal and transport of that sediment to the more rapidly subsiding outer shelf the sediment supply from the brazos river to its delta increased at least 3 fold and the supply of the colorado river increased at least 6 fold by the late stages of sea level fall through the lowstand repeated filling and purging of fluvial valleys from 119 22 ka contributed to the episodic growth of falling stage deltas during the mis 2 lowstand 22 17 ka the mississippi river abandoned its falling stage fluvial deltaic complex on the western louisiana shelf and drained to the mississippi canyon likewise the western louisiana delta was abandoned presumably due to merger of the red river with the mississippi river terminating growth of the western louisiana delta the brazos river abandoned its mis 3 shelf margin delta to merge with the trinity sabine and calcasieu rivers and together these rivers nourished a lowstand delta and slope fan complex the colorado and rio grande rivers behaved more as point sources of sediment to thick lowstand delta fan complexes lowstand incised valleys exhibit variable morphologies that mainly reflect differences in onshore and offshore relief and the time intervals these valleys were occupied they are deeper and wider than falling stage channel belts and are associated with a shelf wide surface of erosion sequence boundary during the early mis 1 17 ka to 10 ka sea level rise the offshore incised valleys of the calcasieu sabine trinity brazos colorado and rio grande rivers were filled with sediment the offshore valleys of smaller rivers of central texas would not be filled until the late holocene mainly by highstand mud the lower onshore portions of east texas incised valleys were filled with sediment mainly during the holocene with rates of aggradation in the larger brazos and colorado valleys being in step with sea level rise smaller rivers filled their valleys with back stepping fluvial estuarine and tidal delta deposits that were offset by flooding surfaces in general the sediment trapping capacity of bays increased as evolving barrier islands and peninsulas slowly restricted tidal exchange with the gulf and valley filling led to more shallow wider bays a widespread period of increased riverine sediment flux and delta growth is attributed to climate change during mis 1 between 11 5 and 8 0 ka and occurred mainly under cool wet climate conditions relatively small sea level oscillations during the mis 1 transgression 17 ka to 4 0 ka profoundly influenced coastal evolution as manifested by landward stepping shorelines on the order of tens of kilometers within a few thousand years the current barriers strand plains and chenier plains of the study area formed at different times over the past 8 ka due mainly to differences in sand supply and the highly variable relief on the mis 2 surface on which these systems formed modern highstand deposition on the continental shelf formed the texas mud blanket which occurs on the central texas shelf and records a remarkable increase in fine grained sediment supply this increase is attributed to greater delivery of sediments from the colorado and brazos rivers which had filled their lower valleys and abandoned their transgressive deltas by late holocene time and to an increase in westward directed winds and surface currents that delivered suspended sediments from the mississippi river to the texas shelf collectively our results demonstrate that source to sink analyses in low gradient basin settings requires a long term perspective ideally a complete eustatic cycle because most of the sediment that was delivered to the basin by rivers underwent more than one cycle of erosion transport and sedimentation that was regulated by sea level rise and fall climate was a secondary control the export of sediments from the hinterland to the continental shelf was not directly in step with temperature change but rather varied between different fluvial deltaic systems

melt season duration and ice layer formation on the greenland ice sheet 2000 2004 1 time series of enhanced resolution quikscat images were used to map the extent and duration of surface melt and the distribution of ice layer formation on the greenland ice sheet in the period 2000 2004 apart from the bare ice and the mixed pixels 10 along the ice sheet margin where melt cannot be determined reliably annual melt duration and melt anomaly maps were produced across the ice sheet 90 for each summer over the 5 year period the mean melt duration for the ice sheet ranged from 14 3 to 20 5 d the proportion of the ice sheet that experienced melting in a given year ranged from 44 2 to 79 2 extensive melt in 2002 was caused by a single melt event of a few days duration this event was associated with the intrusion of a ridge of high pressure from the north atlantic ocean that brought warm air onto the ice sheet the change in biweekly averaged backscatter between the freeze up periods in the current and previous falls was used to identify changes in the distribution of ice layers in snow between successive melt seasons the year 2002 had the maximum melt extent and duration and ice layer formation extended to higher elevations than in other years interannual changes in the distribution of ice layer formation may be associated with changes in surface height that are not necessarily indicative of mass balance changes mapping of ice layer formation is thus potentially useful for interpreting both real and apparent height changes measured by altimetry

sources and dispersal of late quaternary silt on the northern gulf of mexico continental shelf abstract the surficial sediments of the northern gulf of mexico continental shelf consist of large volumes of silt and clay and lesser amounts of sand of late quaternary age a study of the roundness and surface textures of quartz silt grains in these surficial sediments was conducted to determine the sources and dispersal patterns of this size fraction and to gain a better understanding of late quaternary sedimentation on this shelf the results indicate that there are six distinct silt provinces within the study area that can be distinguished on the basis of grain roundness and surface textures three of the provinces are characterized by relatively angular quartz silt grains on the average and an abundance of first cycle crystalline quartz grains the remaining three provinces are characterized by relatively rounded quartz silt grains and an abundance of multicyclic sedimentary rounded grains the dispersal patterns of these six provinces are partly controlled by the late wisconsinian paleogeography thus a comparison of the dispersal patterns with the locations of the modern and ancient fluviodeltaic depocenters allows the identification of these six provinces as deposits of the rio grande the coastal plain streams of south texas the brazos and colorado river the mississippi the mobile river and the rivers of the southeastern united states however the dispersal patterns have also been modified by the prevailing shelf and longshore currents and there is up to 400 km of downcurrent displacement of silt from its late wisconsinian sites of deposition on some parts of the shelf

comparison of foreland basin sequences trenton group in southern quebec and central new york abstract numerous high angle faults are recognizable within the autochthonous middle ordovician trenton group shelf sequence in southern quebec these faults were active during deposition of the trenton limestones as evidenced by rapid thickness changes over short distances on the shelf abrupt facies changes between fault blocks and associated slump fold zones syndepositional block faults have been described recently from the trenton group of central new york the times of movement were documented by use of the numerous interbedded bentonite beds bentonites although present in the trenton group in southern quebec are not abundant enough to correlate fault blocks instead the syndepositional nature of the fault blocks can be seen by examining the facies distribution of th deschambault limestone the deschambault limestone represents a skeletal buildup on the trenton shelf similar to those described from the southern appalachians the core facies of the buildups is exposed in the pont rouge region flank facies are present to the west near joliette the buildup facies are absent both downshelf and upshelf using the buildup facies as marker beds at least one period of movement can be recognized fault blocks were primarily active after the deschambault deposition the trenton in southern quebec can be compared to that in new york and southern ontario the facies changes among these areas can be shown to be controlled by proximity to or position within the taconic foreland basin end of article last page 1924

barrier island aggradation via inlet migration mustang island texas abstract after establishing its present location around 9 5 ka mustang island aggraded stacking over 20 m of barrier island sand in the same location throughout mustang island s history tidal inlets shifted within nearly the same location from 7 5 ka to the present leaving 10 15 m thick deposits of clean well sorted quartz sand deposited within only a few centuries these deposits lack some of the sedimentary features normally associated with tidal inlets such as tidal couplets and shell hash the lack of such features is attributed to the uniform nature of the deposits cut by the inlets during the island s relatively long period of aggradation mustang island was able to maintain an aggradation character throughout most of the holocene due to the sediment eroded from three sources pleistocene headlands the transgressive colorado river delta of texas and the ois 3 shoreline of the central texas shelf each of these sources was exposed to waves and accompanying longshore drift during the island s early history when sea level rose quickly but was flooded or capped by transgressive muds by the time sea level rise slowed during the middle holocene