rapid circulation of warm subtropical waters in a major glacial fjord in east greenland the recent rapid increase in mass loss from the greenland ice sheet is primarily attributed to an acceleration of outlet glaciers oceanographic data obtained in summer 2008 show that subtropical waters that reside year round in the shelf ocean off greenland continuously enter a large glacial fjord in east greenland and contribute to melting at the glacier terminus the recent rapid increase in mass loss from the greenland ice sheet1 2 is primarily attributed to an acceleration of outlet glaciers3 4 5 one possible cause of this acceleration is increased melting at the ice ocean interface6 7 driven by the synchronous warming8 9 10 of subtropical waters offshore of greenland however because of the lack of observations from greenland s glacial fjords and our limited understanding of their dynamics this hypothesis is largely untested here we present oceanographic data collected in sermilik fjord east greenland by ship in summer 2008 and from moorings our data reveal the presence of subtropical waters throughout the fjord these waters are continuously replenished through a wind driven exchange with the shelf where they are present all year the temperature and renewal of these waters indicate that they currently cause enhanced submarine melting at the glacier terminus key controls on the melting rate are the volume and properties of the subtropical waters on the shelf and the patterns of along shore winds suggesting that the glaciers acceleration has been triggered by a combination of atmospheric and oceanic changes our measurements provide evidence for a rapid advective pathway for the transmission of oceanic variability to the ice sheet margins

ice flux divergence anomalies on 79north glacier greenland 1 the ice flux divergence of a glacier is an important quantity to examine because it determines the rate of temporal change of its thickness here we combine high resolution ice surface velocity observations of nioghalvfjerdsfjorden 79north glacier a major outlet glacier in north greenland with a dense grid of ice thickness data collected with an airborne radar sounder in 1998 to examine its ice flux divergence we detect large variations up to 100 m yr in flux divergence on grounded ice that are incompatible with what we know of the glacier surface mass balance basal mass balance and thinning rate we examine the hypothesis that these anomalies are due to the three dimensional flow of ice around and atop bumps and hollows in basal topography by comparing the flux divergence of three dimensional numerical models with its surface equivalent we find that three dimensional effects have only a small contribution to the observed anomalies on the other hand if we degrade the spatial resolution of the data to 10 km the anomalies disappear further analysis shows that the source of the anomalies is not the ice velocity data but the interpolation of multiple tracks of ice thickness data onto a regular grid using a scheme here block kriging that does not conserve mass or ice flux this problem is not unique to 79north glacier but is common to all conventional ice thickness surveys of glaciers and ice sheets and fundamentally limits the application of ice thickness grids to high resolution numerical modeling of glacier flow

distinct patterns of seasonal greenland glacier velocity predicting greenland ice sheet mass loss due to ice dynamics requires a complete understanding of spatiotemporal velocity fluctuations and related control mechanisms we present a 5 year record of seasonal velocity measurements for 55 marine terminating glaciers distributed around the ice sheet margin along with ice front position and runoff data sets for each glacier among glaciers with substantial speed variations we find three distinct seasonal velocity patterns one pattern indicates relatively high glacier sensitivity to ice front position the other two patterns are more prevalent and appear to be meltwater controlled these patterns reveal differences in which some subglacial systems likely transition seasonally from inefficient distributed hydrologic networks to efficient channelized drainage while others do not the difference may be determined by meltwater availability which in some regions may be influenced by perennial firn aquifers our results highlight the need to understand subglacial meltwater availability on an ice sheet wide scale to predict future dynamic changes

sensitivity analysis of pine island glacier ice flow using issm and dakota assessing output errors of ice flow models is a major challenge that needs to be addressed if we are to increase our confidence level in projections of mass balance in antarctica and greenland major inputs to ice flow models include geometry ice thickness and surface elevation constitutive laws and boundary conditions geothermal flux basal drag coefficient surface temperature these inputs can be either measured in which case they carry errors due to instruments or inferred using inverse methods such as basal drag which is inverted using insar surface velocities in which case they carry additional errors generated by the inversion process itself in both cases these input errors will result in uncertainties that propagate throughout a forward model and that influence output diagnostics in order to estimate the resulting error margins on diagnostics such as mass flux we develop a new framework based on the design analysis kit for optimization and terascale applications dakota which we interface to the ice sheet system model issm we present results on the pine island glacier west antarctica for which we evaluate error margins of mass flux across the whole glacier given currently known error margins on ice thickness basal friction and ice hardness our results suggest errors in these inputs propagate linearly through the ice flow model providing a way to 1 calibrate measurement requirements for field campaigns collecting data such as bedrock or surface topography 2 quantify uncertainties in projections of mass balance and 3 assess the sensitivity of model outputs to input parameters this new error propagation model should help quantify confidence levels that we assign to model projections for the mass balance of antarctica and greenland which will ultimately improve our projections of future sea level rise in a warming climate copyright 2012 by the american geophysical union

greenland ice sheet mass balance reconstruction part i net snow accumulation 1600 2009 ice core data are combined with regional atmospheric climate model version 2 racmo2 output 1958 2010 to develop a reconstruction of greenland ice sheet net snow accumulation rate at g spanning the years 1600 2009 regression parameters from regional climate model rcm output regressed on 86 ice cores are used with available cores in a given year resulting in the reconstructed values each core site s residual variance is used to inversely weight the cores respective contributions the interannual amplitude of the reconstructed accumulation rate is damped by the regressions and is thus calibrated to match that of the rcm data uncertainty and significance of changes is measured using statistical models a 12 or 86 gt yr 21 increase in ice sheet accumulation rate is found from the end of the little ice age in 1840 to the last decade of the reconstruction this 1840 1996 trend is 30 higher than that of 1600 2009 suggesting an accelerating accumulation rate the correlation of at g with the average surface air temperature in the northern hemisphere satnht remains positive through time while the correlation of at g with local near surface air temperatures or north atlantic sea surface temperatures is inconsistent suggestinga hemispheric scale climateconnection an annualsensitivityof at g to satnhtof 6 8 k 21 or 51 gt k 21 is found the reconstuction at g correlates consistently highly with the north atlantic oscillation index however at the 11 yr time scale the sign of this correlation flips four times in the 1870 2005 period

decadal scale sensitivity of northeast greenland ice flow to errors in surface mass balance using issm the behavior of the greenland ice sheet which is considered a major contributor to sea level changes is best understood on century and longer time scales however on decadal time scales its response is less predictable due to the difficulty of modeling surface climate as well as incomplete understanding of the dynamic processes responsible for ice flow therefore it is imperative to understand how modeling advancements such as increased spatial resolution or more comprehensive ice flow equations might improve projections of ice sheet response to climatic trends here we examine how a finely resolved climate forcing influences a high resolution ice stream model that considers longitudinal stresses we simulate ice flow using a two dimensional shelfy stream approximation implemented within the ice sheet system model issm and use uncertainty quantification tools embedded within the model to calculate the sensitivity of ice flow within the northeast greenland ice stream to errors in surface mass balance smb forcing our results suggest that the model tends to smooth ice velocities even when forced with extreme errors in smb indeed errors propagate linearly through the model resulting in discharge uncertainty of 16 or 1 9 gt yr we find that mass flux is most sensitive to local errors but is also affected by errors hundreds of kilometers away thus an accurate smb map of the entire basin is critical for realistic simulation furthermore sensitivity analyses indicate that smb forcing needs to be provided at a resolution of at least 40 km

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

can the equatorial ocean quickly respond to antarctic sea ice salinity anomalies 1 el nino southern oscillation enso plays a critical role in many of the extremes or anomalies of climate causing floods droughts and the collapse of fisheries recent studies have revealed a statistically significant link between equatorial processes and sea ice anomalies in the southern ocean the generally accepted view is that the primary interaction of the equatorial and polar oceans takes place via the atmosphere indeed the lag in these processes is usually of the order of a few months and is much too quick to be connected with ocean currents the question is can climate anomaly signals effectively and rapidly propagate by another oceanic mechanism it is demonstrated that signals generated by anomalies in the antarctic sea ice cover salinity distribution can propagate in a wave like manner in the form of fast moving barotropic rossby waves such waves propagates from the drake passage to the western pacific in only few days this signal is reflected at the western boundary of the pacific and generates an coastally trapped kelvin wave moving equatorwards the resulting temperature anomaly propagates northwards along the western coastline to the vicinity of the equator and increases in amplitude in time the anomaly in the western edge of the equatorial pacific then begins to move eastward along the equator as a trapped equatorial wave after about 2 3 months this wave reaches the eastern coast this process is suggested as one possible direct mechanism by which the extra tropical ocean can induce anomalies in the equatorial ocean

identifying the roles of the ocean and atmosphere in creating a rapid equatorial response to a southern ocean anomaly recent research has identified a rapid ocean response mechanism to salinity anomalies in the southern ocean using an idealised ocean model here we examine the relative importance of the ocean and atmosphere in creating an equatorial response to a southern ocean anomaly using a coupled climate model with realistic bottom topography and land relief two rapid teleconnections are produced from a high latitude anomaly an equatorial ocean response can be seen after 30 days the mechanism producing this response is shown to rely on barotropic and baroclinic oceanic wave propagation a second atmospheric response is seen in the northern hemisphere nh high latitudes driven by atmospheric rossby waves the ocean quickly responds to the atmospheric signal above it resulting in sea surface temperature anomalies at nh high latitudes

deformation warming and softening of greenland s ice by refreezing meltwater when basal meltwater refreezes the resulting warm ice can influence the flow dynamics of the ice sheet above an analysis of airborne gravity and radar data identifies extensive basal ice units across the northern greenland ice sheet that coincide with areas of deformed ice and fast ice flow

ice flow sensitivity to geothermal heat flux of pine island glacier antarctica model projections of ice flow in a changing climate are dependent on model inputs such as surface elevation bedrock position or surface temperatures among others of all these inputs geothermal heat flux is the one for which uncertainty is greatest in the area of pine island glacier antarctica available data sets differ by up to a factor of 2 5 here we evaluate the impact of such uncertainty on ice flow using sampling analyses based on the latin hypercube method first we quantify the impact of geothermal heat flux errors on ice hardness a thermal parameter that critically controls the magnitude of ice flow second we quantify the impact of the same errors on mass balance specifically on the mass flux advecting through thirteen fluxgates distributed across pine island glacier we contrast our results with similar uncertainties generated by errors in the specification of ice thickness model outputs indicate that geothermal heat flux errors yield uncertainties on ice hardness on the order of 5 7 with maximum uncertainty reaching 15 resulting uncertainties in mass balance remain however below 1 we discuss the uncertainty distribution and its relationship to the amount of heat available at the base of the ice sheet from friction viscous and geothermal heating we also show that comparatively errors in ice thickness contribute more to model uncertainty than errors in geothermal heat flux especially for fast flowing ice streams 2012 american geophysical union all rights reserved

a full stokes flow thermo mechanical model for firn and ice applied to the gorshkov crater glacier kamchatka the gorshkov crater glacier at ushkovsky volcano kamchatka is characterized by a large aspect ratio and special thermodynamic conditions at the bedrock caused by a locally enhanced and spatially varying geothermal heat flux furthermore large parts of this glacier consist of firn rather than pure ice which alters the rheological properties such as viscosity and compressibility of the glacier we present a newly developed thermo mechanically coupled three dimensional flow model based on the finite element fe modeling software elmer and apply it to the gorshkov crater glacier by assuming steady state conditions the present day velocity field temperature field basal melting rate and age distribution are simulated we find that flow velocities are generally small 10 s of centimeters per year horizontal and vertical velocities are of comparable magnitude which shows that the shallow ice approximation is not applicable owing to the spatially variable volcanic heat flux the thermal regime at the ice base is cold in the deeper parts of the glacier and temperate in the shallower parts the measured temperature profile and age horizons at the k2 borehole are reproduced quite well and remaining discrepancies may be attributed to transient non steady state conditions firn compressibility is identified as a crucial element for the modeling approach

rapid ocean wave teleconnections linking antarctic salinity anomalies to the equatorial ocean atmosphere system the coupled climate model forte is used to investigate rapid ocean teleconnections between the southern ocean and equatorial pacific ocean salinity anomalies located throughout the southern ocean generate barotropic signals that propagate along submerged topographic features and result in the growth of baroclinic energy anomalies around indonesia and the tropical pacific anomalies in the ross bellingshausen and amundsen seas exchange the most barotropic kinetic energy between high and low latitudes in the equatorial pacific baroclinic kelvin waves are excited which propagate eastwards along the thermocline resulting in sst anomalies in the central and eastern pacific sst anomalies are subsequently amplified to magnitudes of 1 25 c by air sea interaction which could potentially influence other coupled pacific phenomena

a quick response of the equatorial ocean to antarctic sea ice salinity anomalies the potential mechanisms for a quick response of the equatorial ocean to processes occurring in the high latitude southern ocean have been investigated in the southern ocean at the drake passage latitudes there is an zonally unbounded channel the antarctic circumpolar current belt accb it is demonstrated that in a multiconnected domain such as the accb signals generated by anomalies in the southern ocean sea ice cover salinity distribution can propagate in a wave like manner in the form of fast moving barotropic rossby waves a disturbance induced near the drake passage is demonstrated to generate a rossby wave that propagates across the pacific in only a few days this signal is reflected at the western boundary of the pacific and generates an equatorward propagating coastally trapped kelvin wave the resulting temperature anomaly moves northward along the western coastline up to the vicinity of the equator and increases in amplitude over time the anomaly in the western edge of equatorial pacific then begins to propagate eastward along the equator as a trapped equatorial wave after about 2 3 months this wave reaches the eastern coast reflects and generates the coastal trapped wave which propagates north and south along the coastline in both hemispheres this process is suggested as one possible direct mechanism by which the extratropical ocean can induce anomalies in the equatorial ocean

correlation of different maturity parameters in the ahmedabad mehsana block of the cambay basin abstract the potential use of organic matter maturation parameters in assessing the diagenetic catagenetic transition zone with the help of various known molecular parameters has been investigated in the ahmedabad mehsana block of the cambay basin a set of 24 conventional cores from the eocene shales covering a depth regime of 922 2500 m has been studied the oil generation threshold i e the boundary between the diagenetic and catagenetic maturation regimes is assessed to be at 1800 m based on a combination of parameters including percent hydrocarbons in eom saturate aromatic hydrocarbon ratio in eom and the rock eval production index the pr n c17 ratio rock eval hi and oi were not suitable for reliable maturation profiling nor for independently indexing the stages of maturation the extent of the catagenetic regime is distinguished by ph n c18 ratios

global teleconnections of meridional overturning circulation anomalies there is a wide range of evidence from both models and palaeoclimatic data that indicates the possibility of abrupt changes in the oceanic meridional overturning circulation moc however much of our dynamical understanding of the moc comes from steady state models that rely upon the assumption of thermodynamic equilibrium and are therefore only valid on millennial time scales here a dynamical model for the global teleconnections of moc anomalies on annual to multidecadal time scales is developed it is based on a linear theory for the propagation of zonally integrated meridional transport anomalies in a reduced gravity ocean and allows for multiple ocean basins connected by a circumpolar channel to the south the theory demonstrates that the equator acts as a low pass filter to moc anomalies as a consequence moc anomalies on decadal and shorter time scales are confined to the hemispheric basin in which they are generated and have little impact on the remainder of the global ocean the linear theory is compared with the results of a global nonlinear numerical integration which it reproduces to a good approximation

a mathematical representation of rock eval hydrogen index vs tmax profiles abstract different types of kerogens have different maturation paths on rock eval hydrogen index hi vs t max plots an equation hi 1 a exp b t max 435 c where a b and c are constants can be used to define hi t max profiles of particular source rock units the constants a b and c characterise the particular kerogen and also allow expression of its transformation ratio tr as a function of the t max by an equation tr hi 0 a exp b t max 435 hi 0 a exp b t max 435 1 where hi 0 1 c the hi t max equation constants were determined by nonlinear curve fitting for three standard type i ii and iii kerogens and for two geological sections second white speckled 2ws formation alberta basin and a source rock unit of cambay basin india high correlation coefficients for the fitted equations for four hi t max data sets of four groups of the 2ws samples segregated using oxygen index oi vs t max cross plot and for one data set of the cambay basin source rock unit show the validity of the proposed hi t max equation comparison of the calculated tr and measured production index pi values for the 2ws samples allow identification of samples that have expelled generated hydrocarbons and samples that contain unexpelled generated hydrocarbons for the cambay basin example where rock eval data of silty and sandy samples were screened out a reasonable match exists between the calculated trs and measured production index values up to a t max value of 445 c indicating onset of oil expulsion the proposed hi t max equation can thus characterise organic matter in a source rock unit with respect to its original generation potential and hydrocarbon generation threshold and rate it may also help to identify the effective source sections that have expelled generated hydrocarbons from several potential source rocks if present in a basin

high resolution ice thickness mapping in south greenland airborne radar sounding is difficult in south greenland because of the presence of englacial water which prevents the signal from reaching the bed data coverage remains suboptimal for traditional methods of ice thickness and bed mapping that rely on geostatistical techniques such as kriging because important features are missing here we apply two alternative approaches of high resolution 300 m ice thickness mapping that are based on the conservation of mass to two regions of south greenland 1 qooqqup sermia and kiattuut sermiat and 2 ikertivaq these two algorithms solve optimization problems for which the conservation of mass is either enforced as a hard constraint or as a soft constraint for the first region very few measurements are available but there is no gap in ice motion data whereas for ikertivaq more ice thickness measurements are available but there are gaps in ice motion data we show that mass conservation algorithms can be used as validation tools for radar sounding we also show that it is preferable to apply mass conservation as a hard constraint rather than a soft constraint as it better preserves elongated features such as glacial valleys and ridges

greenland ice sheet mass balance reconstruction part ii surface mass balance 1840 2010 abstractmeteorological station records ice cores and regional climate model output are combined to develop a continuous 171 yr 1840 2010 reconstruction of greenland ice sheet climatic surface mass balance bclim and its subcomponents including near surface air temperature sat since the end of the little ice age independent observations are used to assess and compensate errors melt water production is computed using separate degree day factors for snow and bare ice surfaces a simple meltwater retention scheme yields the time variation of internal accumulation runoff and bare ice area at decadal time scales over the 1840 2010 time span summer june august sat increased by 1 6 c driving a 59 surface meltwater production increase winter warming was 2 0 c substantial interdecadal variability linked with episodic volcanism and atmospheric circulation anomalies is also evident increasing accumulation and melt rates bare ice area and meltwater retention are driven by increasing sat as a con