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

applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

allochthonous and autochthonous contributions to carbon accumulation and carbon store in southeastern australian coastal wetlands estimates of carbon store and carbon accumulation rate in mangrove and saltmarsh are beset by issues of scale and provenance estimates at a site do not allow scaling to regional estimates if the drivers of variability are not known also carbon accumulation within soils provides a net offset only if carbon is derived in situ or would not otherwise be sequestered we use a network of observation sites extending across 2000 km of southeastern australian coastline to determine the influence of geomorphic setting and coastal wetland vegetation type on rates of carbon accumulation carbon store and probable sources carbon accumulation above feldspar marker horizons over a 10 year period was driven primarily by tidal range and position in the tidal frame and was higher for mangrove and saltmarsh dominated by juncus kraussii than for other saltmarsh communities the rate of carbon loss with depth varied between geomorphic settings and was the primary determinant of carbon store a down core enrichment in d 13 c was consistent with an increased relative contribution of mangrove root material to soil carbon as mangrove roots were found to be consistently enriched compared to leaves we conclude that while surface carbon accumulation is driven primarily by tidal transport of allocthonous sediment in situ carbon sequestration is the dominant source of recalcitrant carbon and that mangrove and saltmarsh carbon accumulation and store is high in temperate settings particularly in mesotidal and fluvial geomorphic settings

improving sub salt imaging using 3d basin model derived velocities abstract the quality of depth imaging is directly related to the accuracy of the underlying velocity model in most sub salt settings lack of angular illumination severely degrades the resolution and accuracy of velocity information derived from the seismic data itself a standard approach for building a starting velocity model uses more reliable velocity information outboard of salt which is subsequently extrapolated to populate the sub salt regions the shortcoming of this method lies in the assumption that the effective stress observed outboard of salt can be extrapolated beneath salt solely as a function of depth below mudline velocities derived from basin model effective stress data show excellent large scale agreement to seismic velocities 3d basin modeling represents the most rigorous approach for determining sub salt effective stresses because it accounts for depositional history sand distribution and connectivity variable shale properties timing of salt emplacement all of which influence the magnitude and distribution of abnormal pore pressure in the presented study a calibrated present day effective stress cube from a 3d basin model was used to calculate sub salt velocities for an exploration well in the central gulf of mexico the comparison between basin modeling derived velocities and the original velocity field showed remarkable differences particularly in that the former indicated a far more complex sub salt velocity distribution than the latter utilizing basin model sediment velocities to re migrate the seismic data set resulted in a more detailed image as well as changed source rock geometries where the original image showed a deep de focus at the source rock level the new geometry would focus hydrocarbons into the identified trap based on the results of the subsequently drilled exploration well it has to be assumed that the re migrated data aided by basin modeling derived velocities provide a more accurate image of the sub salt geology

integrating basin modeling with seismic technology and rock physics we explore the link between basin modelling and seismic inversion by applying different rock physics models this study uses the e dragon ii data in the gulf of mexico to investigate the impact of different rock physics models on the link between basin modelling and seismic inversion we first model relationships between seismic velocities and both 1 porosity and 2 effective stress for well log data using published rock physics models then we build 1d basin models to predict seismic velocities derived from basin modelling with different rock physics models in a comparison with average sonic velocities measured in the wells finally we examine how basin modelling outputs can be used to aid seismic inversion by providing constraints for the background low frequency model for this we run different scenarios of inverting near angle partial stack seismic data into elastic impedances to test the impact of the background model on the quality of the inversion results the results of the study suggest that the link between basin modelling and seismic technology is a two way interaction in terms of potential applications and the key to refine it is establishing a rock physics models that properly describes changes in seismic signatures reflecting changes in rock properties

a case of post depositional aerobic degradation of terrestrial organic matter in turbidite deposits from the madeira abyssal plain abstract a set of oxidized and unoxidized sediment intervals from the f turbidite identified in two piston cores from the madeira abyssal plain map was analyzed for calcium carbonate total organic carbon toc total nitrogen tn stable carbon composition of toc 13c toc total hydrolyzable amino acids thaa total neutral sugars tsug lignin phenols lig two different lipid biomarkers of marine phytoplankton origin and vascular plantwax n alkanes and n acids comparison shows changes for all properties depicting the effect of post depositional aerobic oxidation the oxidation process re mineralized approximately 80 of the toc and approximately 60 of the tn in the original deposit and left the residual organic matter depleted in 13c by 1 7 2 9 thaa and tsug account for 10 or less of the toc in all samples leaving approximately 90 of the toc chemically unidentified thaa tsug lig marine phytoplankton biomarkers and plantwax n acids were lost from the oxidized deposit to an extent as great as that for toc two non protein amino acids alanine and aminobutyric acid and plant wax n alkanes displayed much less degradation 9 37 and concentrated 3 3 4 8 times relative to toc by the oxidation process these observations show that both marine and terrestrial components contribute to the re mineralized toc fraction a binary mixing approach was used to model quantitatively the change in 13c toc and plantwax n alkane concentration results suggest that terrestrial organic carbon contributes approximately 15 to the toc content of the original turbidite its abundance increases approximately 2 4 times as a consequence of the oxidation process and approximately 40 and 90 of the terrestrial and marine component of toc in the original turbidite respectively was destroyed by the oxidation process although selective preservation of terrestrial relative to marine organic carbon is a well documented phenomenon in sedimentary processes this study represents the first attempt to assess the sensitivity of terrestrial organic matter to oxidative degradation in a sedimentary environment

distribution and sources of bulk organic matter om on a tropical intertidal mud bank in french guiana from elemental and isotopic proxies the mobile french guiana coast is a shoreface region downdrift of the amazon river where enormous quantities of inorganic and organic materials are exchanged with the atlantic ocean the rapid accumulation of these materials forms highly unstable shore attached mud banks which can be temporally emerged and then rapidly colonized and stabilized by microphytobenthos and opportunistic mangroves i e avicennia germinans mud banks are preferential sites for the accumulation and significant remineralization of organic matter om due to intense erosion deposition cycles and potential biological colonization the distribution and sources of bulk sedimentary om were characterized by elemental and isotopic analyses of four sediment cores together with samples from three potential om sources mangrove plants suspended particulate matter spm and microphytobenthos all collected from the landward face of the macouria mud bank french guiana total organic carbon toc and nitrogen tn concentrations in the sediment cores showed that om sources were characterized by spatio temporal variations in this mud bank the relative contributions of mangrove plants spm and microphytobenthos were estimated using a three end member mixing model based on tn toc atomic ratios and 13c values sedimentary om is mostly controlled by spm associated with variable amounts of om derived from mangrove plants and microphytobenthos these variations could be explained by topography and bed elevation which decrease submersion time and increase desiccation higher contributions of microphytobenthos are associated with black om rich laminae identified in sedimentary cores and linked to temporal emersion phases of the mud bank which favor the growth of benthic microalgae this result is confirmed by the calculation of the average sediment accumulation rate around 36 7 14 8 cm yr 1 taking into account the emersion of the study site every spring tide a fortnightly cycle this value is within the range of the previous results from other mud banks in french guiana but is more than ten times greater than values generally obtained in other coastal contexts

subsalt pressure prediction from multicomponent seismics and more predrill pore pressure predictions are vitally important in deepwater arenas where extreme depth and drilling window conditions typical of current prospects and developments require expensive rigs and highly trained personnel to successfully plan and execute complex wellbores

nonlinear response of iceberg side melting to ocean currents icebergs calving into greenlandic fjords frequently experience strongly sheared flows over their draft but the impact of this flow past the iceberg is not fully captured by existing parameterizations we present a series of novel laboratory experiments to determine the dependence of submarine melting along iceberg sides on a background flow we show for the first time that two distinct regimes of melting exist depending on the flow magnitude and consequent behaviour of melt plumes side attached or side detached with correspondingly different meltwater spreading characteristics when this velocity dependence is included in melt parameterizations melt rates estimated for observed icebergs in the attached regime increase consistent with observed iceberg submarine melt rates we show that both attached and detached plume regimes are relevant to icebergs observed in a greenland fjord further depending on the regime iceberg meltwater may either be confined to a surface layer or distributed over the iceberg draft

role of the molecular sublayer in the melting or freezing of sea ice abstract in an earlier paper a second moment turbulence closure model was applied to the problem of the dynamic and thermodynamic interaction of sea ice and the ocean surface mixed layer an overly simplistic parameterization of the molecular sublayers of temperature and salinity within the mixed layer was used this paper investigates the use of a more recent parameterization by yaglom and kader which is supported by laboratory data a relatively low melt rate results in the case where ice overlays warm water this agrees with some recent observations in the interior of the marginal ice zone a surface heat sink drives the freezing case which due to the large difference in heat and salt molecular diffusivities produces a strong supercooling effect this is converted into an estimate of frazil ice production through a simple scheme the model results provide an explanation for high frazil ice concentrations observed in the arctic and antarctic

the response of ice shelf basal melting to variations in ocean temperature abstract a three dimensional ocean general circulation model is used to study the response of idealized ice shelves to a series of ocean warming scenarios the model predicts that the total ice shelf basal melt increases quadratically as the ocean offshore of the ice front warms this occurs because the melt rate is proportional to the product of ocean flow speed and temperature in the mixed layer directly beneath the ice shelf both of which are found to increase linearly with ocean warming the behavior of this complex primitive equation model can be described surprisingly well with recourse to an idealized reduced system of equations and it is shown that this system supports a melt rate response to warming that is generally quadratic in nature this study confirms and unifies several previous examinations of the relation between melt rate and ocean temperature but disagrees with other results particularly the claim that a single melt rate sensitivity to warming is universally valid the hypothesized

characterizing englacial drainage in the ablation zone of the greenland ice sheet rapid local drainage of surface meltwater to the base of the greenland ice sheet is thought to result in surface velocity variations as far inland as the equilibrium zone zwally and others 2002 ice penetrating radar surveys throughout this region allow us to characterize englacial drainage features that appear as vertically stacked diffraction hyperbolae in common offset profiles these data are used with a radar simulation model which allows for variations in geometry penetration depth and infill material to understand the characteristics of these hyperbolae and the likelihood that they are produced by moulins we find only a moderate correlation between the locations of these possible moulins and supraglacial lakes indicating that many lakes drain over the surface of the ice sheet or do not contain sufficient water to reach the bed through moulin formation we find a strong correlation between moulin location in the ablation region and elevated along flow tension due to flow over rough bedrock which generates surface crevassing and provides an entry point for meltwater although theory suggests that moulins may form anywhere on the ice sheet given sufficient meltwater input our data suggest that they are far more common in the ablation zone than near or inland from the equilibrium line

changes in organic carbon accumulation driven by mangrove expansion and deforestation in a new zealand estuary abstract mangroves are rapidly being lost to deforestation in many locations while expanding their areal extent in other subtropical and temperate regions currently there is a paucity of information on how these changes may alter the carbon accumulation capacity of coastal areas here sediment cores were collected from two areas and used to determine the influence of mangrove migration and deforestation on sediment carbon stocks and accumulation rates the deforested area contained lower sedimentary organic carbon stocks 2767 580 g m 2 compared to the preserved area 6949 84 g m 2 sediment accumulation rates derived from excess 210 pb and 239 240 pu depositional signatures ranged from 0 19 to 0 35 cm yr 1 the total sedimentary organic carbon toc accumulation rates for the period after mangrove deforestation 2005 2011 exhibited significant differences between preserved areas core c 43 9 6 9 g m 2 yr 1 core d 83 1 5 9 g m 2 yr 1 and the deforested area core b 25 8 6 0 g m 2 yr 1 suggesting a decline after deforestation for the preserved area the toc accumulation under mangrove dominance 65 5 16 3 g m 2 yr 1 after 1944 was higher than under saltmarsh dominance 23 5 15 9 g m 2 yr 1 before 1944 as revealed by carbon isotopic signatures 13 c the increase in the toc accumulation due to mangrove expansion in this new zealand estuary was conservatively estimated as three fold higher and two fold higher in stocks in comparison to the period when this ecosystem was dominated by non mangrove vegetation

identifying the causes of sea level change global mean sea level change has increased from a few centimetres per century over recent millennia to a few tens of centimetres per century in recent decades a review of the latest work shows that global mean sea level rise is unlikely to exceed one metre over the twenty first century but regional departures from this global mean could reach several decimetres

sediment plume response to surface melting and supraglacial lake drainages on the greenland ice sheet increased mass losses from the greenland ice sheet and inferred contributions to sea level rise have heightened the need for hydrologic observations of meltwater exiting the ice sheet we explore whether temporal variations in ice sheet surface hydrology can be linked to the development of a downstream sediment plume in kangerlussuaq fjord by comparing 1 plume area and suspended sediment concentration from moderate resolution imaging spectroradiometer modis imagery and field data 2 ice sheet melt extent from special sensor microwave imager ssm i passive microwave data and 3 supraglacial lake drainage events from modis results confirm that the origin of the sediment plume is meltwater release from the ice sheet interannual variations in plume area reflect interannual variations in surface melting plumes appear almost immediately with seasonal surface melt onset provided the estuary is free of landfast sea ice a seasonal hysteresis between melt extent and plume area suggests late season exhaustion in sediment supply analysis of plume sensitivity to supraglacial events is less conclusive with 69 of melt pulses and 38 of lake drainage events triggering an increase in plume area we conclude that remote sensing of sediment plume behavior offers a novel tool for detecting the presence timing and interannual variability of meltwater release from the ice sheet

a review of coastal palaeoclimate and relative sea level reconstructions using δ13c and c n ratios in organic material holocene reconstructions of relative sea level rsl and environmental change in the coastal zone have become progressively more numerous since the importance of assessing possible future sea level rises has become apparent traditionally this has been achieved using a combination of biological and physical indicators e g pollen diatoms foraminifera grain size etc in some circumstances microfossils can be rare or absent from holocene sediments and in these cases carbon isotope ratios 13c and organic carbon to total nitrogen ratios c n can be used because they have the potential to provide information as to the origin of organic material preserved in coastal environments the distinction in 13c and c n of the various sources of carbon to estuarine sediments has led to its wide use as a tracer of carbon pathways and storage in estuaries more recently these techniques have been applied to holocene sediments to decipher changes in palaeocoastal environments and thus position relative to sea level and or palaeoriver discharge which have direct relevance to palaeoclimate this paper reviews the studies that have utilised this technique and explores examples from a wide range of coastal environments saltmarshes estuaries lagoons isolation basins and fjords it also discusses the potential alteration of geochemical signatures as a result of decompositional processes organic matter decomposition has been shown to change sediment 13c and c n values and thus an understanding of the processes involved is necessary in order to have confidence in the palaeoenvironmental interpretation of holocene 13c and c n decompositional shifts in c n and particularly 13c can occur over a relatively short time period however it is the direction of change in 13c and c n rather than absolute values that is key for interpreting changes in relative sea level and thus such changes are commonly preserved

basin scale integrated earth model building using rock physics constraints earth modeling plays a decisive role in seismic imaging presently methods such as tomography and full waveform inversion fwi are widely used to generate 3d high resolution velocity models across sedimentary basins however given the nonunique nature of the solution the relative fidelity of these velocity models remains low moreover earth model building must incorporate a dual strategy in particular it must derive a velocity model for migration and yield a series of rock properties such as density temperature effective stress and pore pressure these large scale basin sized rock properties are used for drilling purposes and as an initial model for small scale reservoir property inversion hence one must inquire how can we improve an earth model built at basin scale using seismic data traditional workflows will simply convert seismic derived velocity into rock properties thereby propagating the uncertainty without addressing the issue to alleviate this problem and fully exploit the potential of seismic data an alternate workflow will be discussed the new workflow involves using rock physics to link rock properties with velocity and the physical range of the rock properties is used to constrain velocity when derived from surface seismic data this way we reinforce the reliability of the final earth model the application of this new workflow is demonstrated using gulf of mexico examples

distribution and sources of organic matter in surface sediments of bohai sea near the yellow river estuary china total organic carbon toc and total nitrogen tn concentrations and c and n stable isotope compositions in 64 surface sediment samples from the mouth of the yellow river yr and from the bohai sea bs outline the distribution and sources terrestrial and marine of sediment organic matter comparatively high toc 0 5 0 9 and tn 0 07 0 11 concentrations in the central bs correlate with fine grained sediments that contain high concentrations of algal derived organic carbon aoc and biogenic silica bsi together they indicate a dominant contribution of autochthonous organic matter from marine primary production low toc 0 2 and tn 0 03 contents characterize surface sediments in the bohai strait and are typically associated with coarse grained sediments of low aoc and bsi contents delta c 13 values 21 to 22 parts per thousand are characteristic of marine derived organic carbon in the central bs and the bohai strait whereas a significant terrigenous contribution of 40 50 is indicated by lower values 23 parts per thousand near the yr mouth the spatial pattern of rising delta c 13 from the yr mouth to offshore areas indicates rapid sedimentation of fluvial suspensions within the vicinity of the river mouth and in laizhou bay so that only approximately 10 20 of yr derived sediments are transported to and deposited in the central bs and or the bohai strait at most sites delta n 15 values are in the typical range of marine organic matter produced from assimilation of marine nitrate by phytoplankton 5 5 5 parts per thousand but some relatively high values 6 7 28 parts per thousand mark the southern area of the laizhou bay as a significant sink of anthropogenic nitrogen c 2015 elsevier ltd all rights reserved

velocity determination for pore pressure prediction overpressured formations exhibit several of the following properties when compared with a normally pressured section at the same depth dutta 2002 1 higher porosities 2 lower bulk densities 3 lower effective stresses 4 higher temperatures 5 lower interval velocities and 6 higher poisson s ratios

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

combining seismic reservoir characterization workflows with basin modeling in the deepwater gulf of mexico mississippi canyon area in this study we explore the value added by application of basin modeling to seismic reservoir characterization in a structurally complex area we focus on the thunder horse minibasin in the gulf of mexico first we build a two dimensional basin model along the strike direction of the main structure in the area to investigate differences in pressure and thermal histories the results suggest differences in both histories across the study area and these differences can be reasonably assessed by basin modeling even with a single well calibration we combine basin modeling results with rock physics models to build a training data set of seismic impedance derived lithofacies the training data set thus captures spatial trends in the desired property beyond available well data in addition we demonstrate how to improve the seismic inversion results by integrating the basin modeling insights with limited well data our new workflow combining basin modeling output with rock physics and impedance based lithofacies prediction significantly improves the predicted spatial distribution of reservoir lithofacies in the scenarios of spatially limited well control

impact of tide topography interactions on basal melting of larsen c ice shelf antarctica 1 basal melting of ice shelves around antarctica contributes to formation of antarctic bottom water and can affect global sea level by altering the offshore flow of grounded ice streams and glaciers tides influence ice shelf basal melt rate wb by contributing to ocean mixing and mean circulation as well as thermohaline exchanges with the ice shelf we use a three dimensional ocean model thermodynamically coupled to a nonevolving ice shelf to investigate the relationship between topography tides andwb for larsen c ice shelf lcis in the northwestern weddell sea antarctica using our best estimates of ice shelf thickness and seabed topography we find that the largest modeled lcis melt rates occur in the northeast where our model predicts strong diurnal tidal currents 0 4 m s 1 this distribution is significantly different from models with no tidal forcing which predict largest melt rates along the deep grounding lines we compare several model runs to explore melt rate sensitivity to geometry initial ocean potential temperature 0 thermodynamic parameterizations of heat and freshwater ice ocean exchange and tidal forcing the resulting range of lcis averagedwb is 0 11 0 44 m a 1 the spatial distribution of wb is very sensitive to model geometry and thermodynamic parameterization while the overall magnitude of wb is influenced by 0 these sensitivities in wbpredictions reinforce a need for high resolution maps of ice draft and sub ice shelf seabed topography together with ocean temperature measurements at the ice shelf front to improve representation of ice shelves in coupled climate system models

submarine melting of the 1985 jakobshavn isbrae floating tongue and the triggering of the current retreat 1 photogrammetric reanalysis of 1985 aerial photos has revealed substantial submarine melting of the floating ice tongue of jakobshavn isbrae west greenland the thickness of the floating tongue determined from hydrostatic equilibrium tapers from 940 m near the grounding zone to 600 m near the terminus feature tracking on orthophotos shows speeds on the july 1985 ice tongue to be nearly constant 18 5 m d 1 indicating negligible dynamic thinning the thinning of the ice tongue is mostly due to submarine melting with average rates of 228 49 m yr 1 0 62 0 13 m d 1 between the summers of 1984 and 1985 the cause of the high melt rate is the circulation of warm seawater thermal forcing of up to 4 2 c beneath the tongue with convection driven by the substantial discharge of subglacial freshwater from the grounding zone we believe that this buoyancy driven convection is responsible for a deep channel incised into the sole of the floating tongue a dramatic thinning retreat and speedup began in 1998 and continues today the timing of the change is coincident with a 1 1 c warming of deep ocean waters entering the fjord after 1997 assuming a linear relationship between thermal forcing and submarine melt rate average melt rates should have increased by 25 57 m yr 1 sufficient to destabilize the ice tongue and initiate the ice thinning and the retreat that followed

seasonal surface velocity variations on a sub polar glacier in west greenland huit balises implantees dans les zones d accumulation et d ablation d un glacier de groenland ont ete relevees tous les dix jours pendant les etes 1982 et 1983 l analyse des vitesses laisse penser qu un reseau sous glaciaire permet a l eau de fusion produite dans la zone d ablation de remonter vers l amont

the role of meltwater advection in the formulation of conservative boundary conditions at an ice ocean interface abstract upper boundary conditions for numerical models of the ocean are conventionally formulated under the premise that the boundary is a material surface in the presence of an ice cover such an assumption can lead to nonconservative equations for temperature salinity and other tracers the problem arises because conditions at the ice ocean interface differ from those in the water beneath advection of water with interfacial properties into the interior of the ocean therefore constitutes a tracer flux neglect of which induces a drift in concentration that is most rapid for those tracers having the lowest diffusivities if tracers are to be correctly conserved either the kinematic boundary condition must explicitly allow advection across the interface or the flux boundary condition must parameterize the effects of both vertical advection and diffusion in the boundary layer in practice the latter alternative is often implemented although this is rarely done for all tracers

temporal variability of carbon and nutrient burial sediment accretion and mass accumulation over the past century in a carbonate platform mangrove forest of the florida everglades the objective of this research was to measure temporal variability in accretion and mass sedimentation rates including organic carbon oc total nitrogen tn and total phosphorous tp from the past century in a mangrove forest on the shark river in everglades national park usa the 210pb constant rate of supply model was applied to six soil cores to calculate annual rates over the most recent 10 50 and 100 year time spans our results show that rates integrated over longer timeframes are lower than those for shorter recent periods of observation additionally the substantial spatial variability between cores over the 10 year period is diminished over the 100 year record raising two important implications first a multiple decade assessment of soil accretion and oc burial provides a more conservative estimate and is likely to be most relevant for forecasting these rates relative to long term processes of sea level rise and climate change mitigation second a small number of sampling locations are better able to account for spatial variability over the longer periods than for the shorter periods the site average 100 year oc burial rate 123 19 standard deviation g m 2 yr 1 is low compared with global mangrove values high tn and tp burial rates in recent decades may lead to increased soil carbon remineralization contributing to the low carbon burial rates finally the strong correlation between oc burial and accretion across this site signals the substantial contribution of oc to soil building in addition to the ecosystem service of co2 sequestration

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

stable carbon isotopes as potential sea level indicators in salt marshes north carolina usa we compared the use of 13c values and c n ratios from salt marsh sediments to reconstruct relative sea level rsl with an established approach using foraminifera analysis of bulk organic sediment and plant samples collected along transects at two sites in north carolina usa demonstrates that sediment 13c values can be used to distinguish between spartina alterniflora dominated low marsh c photosynthetic pathway 13c values from 17 6 to 16 1 and juncus roemerianus dominated high marsh c 3 photosynthetic pathway 13c values from 28 2 to 21 8 environments juncus roemerianus plants undergo little decompositional change in 13c average 0 8 although there is a clear difference between spartina alterniflora tissue and bulk organic sediments approximately 4 c n ratios on bulk organic sediment from freshwater upland and salt marsh environments converge during early diagenesis rendering them of little use in reconstructing rsl the utility of 13c values as a sea level indicator is limited by the elevational range of c4 plants making it difficult to recognize salt marsh subenvironments and improve the precision of rsl reconstructions furthermore juncus roemerianus dominated high marsh and freshwater upland sediments cannot be adequately distinguished with 13c values

carbon and nutrient accumulation in tropical mangrove creeks amazon region abstract the marapanim river estuary mre is part of the amazon estuarine system located in northern brazil which is characterized as having extensive mangrove forests given that previous studies reported co2 and ch4 fluxes from mangrove creeks in this region here we investigate the potential organic carbon sequestration of the creek mudflats to get a better understanding of the carbon cycling through these systems sediment accumulation rates derived from 210pb dating indicated that sampled cores represent the previous 24 4 yr the approximately 24 year total organic carbon toc total nitrogen tn and total phosphorus tp burial rates were estimated to be 192 5 43 5 15 3 4 1 and 3 2 0 8 g m 2 yr 1 respectively a binary source mixing model based on carbon stable isotopes 13c revealed that the sedimentary organic matter om is mainly influenced by marine phytoplankton input 49 to 95 furthermore the toc accumulation rates found here were slightly higher than the global averages estimated for within mangrove forests suggesting that these unaccounted carbon sinks along creek mudflat environments are relevant for carbon budgets in mangrove colonized coastal zones the highest contents stocks and accumulation rates were found in the tidal creek sediments that are most influenced by nearby mangroves and are more protected than sediments from major river margins our results indicate that the creek mudflats play a major role in carbon and nutrients sequestration directly related to grain size and om sources

hydrologic response of the greenland ice sheet the role of oceanographic warming the response of the greenland ice sheet to ongoing climate change remains an area of great uncertainty with most previous studies having concentrated on the contribution of the atmosphere to the ice mass balance signature here we systematically assess for the first time the influence of oceanographic changes on the ice sheet the first part of this assessment involves a statistical analysis and interpretation of the relative changes and variations in sea surface temperatures ssts and air temperatures around greenland for the period 1870 2007 this analysis is based on hadisst1 and reynolds oi v2 sst analyses in situ sst and deeper ocean temperature series surface air temperature records for key points located around the greenland coast and examination of atmospheric pressure and geopotential height from ncep ncar reanalysis second we carried out a novel sensitivity experiment in which ssts were perturbed as input to a regional climate model and document the resulting effects on simulated greenland climate and surface mass balance we conclude that sea surface ocean temperature forcing is not sufficient to strongly influence precipitation snow accumulation and melt runoff of the ice sheet additional evidence from meteorological reanalysis suggests that high greenland melt anomalies of summer 2007 are likely to have been primarily forced by anomalous advection of warm air masses over the ice sheet and to have therefore had a more remote atmospheric origin however there is a striking correspondence between ocean warming and dramatic accelerations and retreats of key greenland outlet glaciers in both southeast and southwest greenland during the late 1990s and early 2000s copyright 2008 john wiley sons ltd

a laboratory study of iceberg side melting in vertically sheared flows abstractan earlier study indicates that the side melting of icebergs subject to vertically homogeneous horizontal velocities is controlled by two distinct regimes which depend on the melt plume be

modeling ice shelf cavities in a z coordinate ocean general circulation model 1 processes at the ice shelf ocean interface and in particular in ice shelf cavities around antarctica have an observable effect on the solutions of basin scale to global coupled ice ocean models despite this these processes are not routinely represented in global ocean and climate models it is shown that a new ice shelf cavity model for z coordinate models can reproduce results from an intercomparison project of earlier approaches with vertical or isopycnic coordinates as a proof of concept ice shelves are incorporated in a 100 year global integration of a z coordinate model in this simulation glacial meltwater can be traced as far as north as 15 s the observed effects of processes in the ice shelf cavities agree with previous results from a coordinate model notably the increase in sea ice thickness however melt rates are overestimated probably because the parameterization of basal melting does not suit the low resolution of this configuration

spatial and temporal melt variability at helheim glacier east greenland and its effect on ice dynamics this is the publisher s version also available electronically from http onlinelibrary wiley com

sediment accretion and organic carbon burial relative to sea level rise and storm events in two mangrove forests in everglades national park abstract the goal of this investigation was to examine how sediment accretion and organic carbon oc burial rates in mangrove forests respond to climate change specifically will the accretion rates keep pace with sea level rise and what is the source and fate of oc in the system mass accumulation accretion and oc burial rates were determined via 210pb dating i e 100 year time scale on sediment cores collected from two mangrove forest sites within everglades national park florida usa enhanced mass accumulation accretion and oc burial rates were found in an upper layer that corresponded to a well documented storm surge deposit accretion rates were 5 9 and 6 5 mm yr 1 within the storm deposit compared to overall rates of 2 5 and 3 6 mm yr 1 these rates were found to be matching or exceeding average sea level rise reported for key west florida organic carbon burial rates were 260 and 393 g m 2 yr 1 within the storm deposit compared to 151 and 168 g m 2 yr 1 overall burial rates the overall rates are similar to global estimates for oc burial in marine wetlands with tropical storms being a frequent occurrence in this region the resulting storm surge deposits are an important mechanism for maintaining both overall accretion and oc burial rates enhanced oc burial rates within the storm deposit could be due to an increase in productivity created from higher concentrations of phosphorus within storm delivered sediments and or from the deposition of allochthonous oc climate change amplified storms and sea level rise could damage mangrove forests exposing previously buried oc to oxidation and contribute to increasing atmospheric co2 concentrations however the processes described here provide a mechanism whereby oxidation of oc would be limited and the overall oc reservoir maintained within the mangrove forest sediments

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

effect of a sheared flow on iceberg motion and melting icebergs account for approximately half the freshwater flux into the ocean from the greenland and antarctic ice sheets and play a major role in the distribution of meltwater into the ocean global climate models distribute this freshwater by parameterizing iceberg motion and melt but these parameterizations are presently informed by limited observations here we present a record of speed and draft for 90 icebergs from sermilik fjord southeastern greenland collected in conjunction with wind and ocean velocity data over an 8 month period it is shown that icebergs subject to strongly sheared flows predominantly move with the vertical average of the ocean currents if as typical in iceberg parameterizations only the surface ocean velocity is taken into account iceberg speed and basal melt may have errors in excess of 60 these results emphasize the need for parameterizations to consider ocean properties over the entire iceberg draft

an introduction to velocity based pore pressure estimation abnormal pore pressures are encountered worldwide often resulting in drilling problems such as kicks blow outs borehole instability stuck pipe and lost circulation because of this a quantitative predrill prediction of pore pressure is required for the safe and economic drilling of wells in overpressured formations in this paper the basic concepts used in pore pressure prediction are defined and the way in which pore pressure can be estimated using velocity measurements is explained a predrill estimate of pore pressure can be obtained from seismic velocities using a velocity to pore pressure transform calibrated with offset well data however velocities obtained from processing seismic reflection data often lack the spatial resolution needed for accurate pore pressure prediction due to assumptions such as layered media and hyperbolic moveout in the following paper in this section chopra and huffman review the available methods of velocity model building and discuss the advantages and disadva

ocean regulation hypothesis for glacier dynamics in southeast greenland and implications for ice sheet mass changes synchronous acceleration and thinning of southeast se greenland glaciers during the early 2000s was the main contributor that resulted in the doubling of annual discharge from the ice sheet we show that this acceleration was followed by a synchronized and widespread slowdown of the same glaciers in many cases associated with a decrease in thinning rates and we propose that ice sheet ocean interactions are the first order regional control on these recent mass changes sea surface temperature and mooring data show that the preceding dynamic thinning coincides with a brief decline in the cold east greenland coastal current egcc and east greenland current we suggest this decline was partly induced by a reduction in ice sheet runoff which allowed warm water from the irminger current to reach the se greenland coast a restrengthening of the cold waters coincides with the glaciers subsequent slowdown we argue that this warming and subsequent cooling of the coastal waters was the cause of the glaciers dynamic changes we further suggest that the restrengthening of the egcc resulted in part from cold water input by increased glacier calving during the speedup and increased ice sheet runoff we hypothesize that the main mechanism for ice sheet mass loss in se greenland is highly sensitive to ocean conditions and is likely subject to negative feedback mechanisms copyright 2010 by the american geophysical union

important role for ocean warming and increased ice shelf melt in antarctic sea ice expansion changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature in contrast to arctic sea ice sea ice surrounding antarctica has expanded1 with record extent2 in 2010 this ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling3 here we show that accelerated basal melting of antarctic ice shelves is likely to have contributed significantly to sea ice expansion specifically we present observations indicating that melt water from antarctica s ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves simulating these processes in a coupled climate model we find that cool and fresh surface water from ice shelf melt indeed leads to expanding sea ice in austral autumn and winter this powerful negative feedback counteracts southern hemispheric atmospheric warming although changes in atmospheric dynamics most likely govern regional sea ice trends4 our analyses indicate that the overall sea ice trend is dominated by increased ice shelf melt we suggest that cool sea surface temperatures around antarctica could offset projected snowfall increases in antarctica with implications for estimates of future sea level rise

seasonal variability of submarine melt rate and circulation in an east greenland fjord 1 the circulation in a glacial fjord driven by a large tidewater glacier is investigated using a nonhydrostatic ocean general circulation model with a melt rate parameterization at the vertical glacier front the model configuration and water properties are based on data collected in sermilik fjord near helheim glacier a major greenland outlet glacier the approximately two layer stratification of the fjord s ambient waters causes the meltwater plume at the glacier front to drive a double cell circulation with two distinct outflows one at the free surface and one at the layers interface in summer the discharge of surface runoff at the base of the glacier subglacial discharge causes the circulation to be much more vigorous and associated with a larger melt rate than in winter the simulated double cell circulation is consistent in both seasons with observations from sermilik fjord seasonal differences are also present in the vertical structure of the melt rate which is maximum at the base of the glacier in summer and at the layers interface in winter simulated submarine melt rates are strongly sensitive to the amount of subglacial discharge to changes in water temperature and to the height of the layers they are also consistent with those inferred from simplified one dimensional models based on the theory of buoyant plumes our results also indicate that to correctly represent the dynamics of the meltwater plume care must be taken in the choice of viscosity and diffusivity values in the model

calving fluxes and basal melt rates of antarctic ice shelves iceberg calving has been assumed to be the dominant cause of mass loss for the antarctic ice sheet with previous estimates of the calving flux exceeding 2 000 gigatonnes per year1 2 more recently the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front3 4 5 so far however no study has reliably quantified the calving flux and the basal mass balance the balance between accretion and ablation at the ice shelf base for the whole of antarctica the distribution of fresh water in the southern ocean and its partitioning between the liquid and solid phases is therefore poorly constrained here we estimate the mass balance components for all ice shelves in antarctica using satellite measurements of calving flux and grounding line flux modelled ice shelf snow accumulation rates6 and a regional scaling that accounts for unsurveyed areas we obtain a total calving flux of 1 321 144 gigatonnes per year and a total basal mass balance of 1 454 174 gigatonnes per year this means that about half of the ice sheet surface mass gain is lost through oceanic erosion before reaching the ice front and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking1 2 7 in addition the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves we find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering8 and enhanced discharge9 we suggest that basal mass loss is a valuable metric for predicting future ice shelf vulnerability to oceanic forcing

a one dimensional model of ice shelf ocean interaction large scale oceanic circulation beneath antarctic ice shelves is driven by the thenmohaline differences which result from mass and energy exchange at the ice ocean interface dense saline waters are drawn underneath the ice shelves and emerge cooled and diluted as plumes of ice shelf water a simple one dimensional model of this process has been developed in which the ice shelf water plume is treated as a turbulent gravity current initiated at the inland margin by a flow of fresh meltwater emerging from beneath the grounded ice subsequent evolution of the plume as it ascends along an ice shelf base of specified geometry can be simulated the model has been applied to a flow line on ronne ice shelf antarctica to explain the observed distribution and rate of basal melting and freezing calculations indicate that the present mean melt rate of 0 6 m yr 1 would increase to 2 6 m yr 1 if the underlying water were to warm by 0 6 c this would not only lead to significant thinning of the ice shelf but could also cause a profound change in ocean circulation on the open continental shelf

adjoint sensitivities of sub ice shelf melt rates to ocean circulation under the pine island ice shelf west antarctica we investigate the sensitivity of sub ice shelf melt rates under pine island ice shelf west antarctica to changes in the oceanic state using an adjoint ocean model that is capable of representing the flow in sub ice shelf cavities the adjoint code is based on algorithmic differentiation ad of the massachusetts institute of technology s ocean general circulation model mitgcm the adjoint model was extended by adding into the ad process the corresponding sub ice shelf cavity code which implements a three equation thermodynamic melt rate parameterization to infer heat and freshwater fluxes at the ice shelf ocean boundary the inferred sensitivities reveal dominant timescales of 30 60 days over which the shelf exit is connected to the deep interior via advective processes they exhibit rich three dimensional time evolving patterns that can be understood in terms of a combination of the buoyancy forcing by inflowing water masses the cavity geometry and the effect of rotation and topography in steering the flow in the presence of prominent features in the bedrock bathymetry dominant sensitivity pathways are found over a sill as well as shadow regions of very low sensitivities to the extent that these transient patterns are robust they carry important information for decision making in observation deployment and monitoring

surface area control of organic carbon accumulation in continental shelf sediments the relationship between organic carbon oc and grain size found in most continental shelf sediments is here reinterpreted in terms of the surface area of the sediments cores from many north american shelf environments show downcore decreases in oc to similar refractory background concentrations if expressed relative to the surface area of the sediments this consistent concentration is 0 86 mg oc m 2 which is equivalent in concentration to a monolayer of organic matter coating all mineral surfaces a more global collection of sediment water interface samples show that this relationship is even more extensive with exceptions occurring in areas of very high riverine sediment input organic pollution or low oxygen water columns density separations indicate that organic matter is largely adsorbed to mineral grains the microtopography of surfaces was examined with n2 sorption and most surface area was found to be inside pores of 10 nm width these data lead to a hypothesis that organic matter is protected by its location inside pores too small to allow functioning of the hydrolytic enzymes necessary for organic matter decay such protection would likely work in concert with other protection mechanisms such as humification this consistent surface area correlation with oc concentration may explain control of spatial and temporal variations in oc burial rates by sedimentation rates the pore protection hypothesis provides a causal mechanism for this observed control