sedimentary record of recent climate impacts on an insular coastal lagoon in the gulf of california abstract sedimentary records are useful to evaluate environmental changes either from natural or anthropogenic causes such as global and climate change the recent changes in accumulation rates and geochemical characteristics grain size distribution elemental composition organic carbon and carbonate concentrations recorded in a sediment core from san jose island lagoon sjil gulf of california were evaluated to determine its relationship with anthropogenic impacts and climatic variability the 210 pb derived chronology was corroborated with 239 240 pu and 137 cs stratigraphic markers the mass accumulation rate increased up to 3 times during the past 100 years 0 16 0 03 to 0 51 0 06 g cm 2 yr 1 the contents of terrigenous and marine salinity indicator elements as well as fine grained sediments also increased considerably although no anthropization evidences were observed indeed the enrichment factor of trace elements indicated that the ecosystem is still a pristine environment by using multivariate statistical techniques we inferred that the larger input of fine grained terrigenous sediments could be related to the enhancement of soil erosion from the catchment under the influence of higher rainfall rates especially during the last 20 years in addition the higher concentrations of salinity indicator elements most likely resulted from higher evaporation rates in the lagoon caused by higher minimum atmospheric temperatures we concluded that recent climate variability has become the main driver for sedimentary geochemical changes in san jose island lagoon these observations confirmed the usefulness of 210 pb dated geochemical sediment records to study the impacts of recent climate variability where long term environmental data is scarce or non existent

impact processes permafrost dynamics and climate and environmental variability in the terrestrial arctic as inferred from the unique 3 6 myr record of lake el gygytgyn far east russia a review lake el gygytgyn in far east russia is a 3 6 myr old impact crater lake located in an area that has never been affected by cenozoic glaciations nor desiccation the unique sediment record of the l

glacial interglacial ice stream stability in the weddell sea embayment antarctica the resilience of the antarctic ice sheet and its effect on global sea level depends on the dynamics of ice streams antarctic ice streams are known to be responsive to changes at the ocean interface and as expected most have thinned in response to ocean warming and sea level rise since the last glacial maximum lgm here we provide direct and unexpected evidence that points toward the glacial interglacial stability of the slessor and recovery glaciers ice streams of the east antarctic ice sheet eais which merge with the west antarctic ice sheet wais to form the filchner ice shelf in the weddell sea embayment cosmogenic nuclide measurements in the shackleton range suggest that the slessor and recovery ice streams were not significantly thicker than today during the lgm we hypothesise that the glaciers did not thicken because the grounding line was not able to migrate seaward beyond the deep thiel crary trough beneath the filchner ice shelf immediately offshore this discovery reveals how a topographic threshold can affect the dynamics of ice streams it also reduces uncertainties on the thickness extent and volume of the antarctic ice sheet in a large but unknown sector of the antarctic ice sheet it constrains the potential sea level rise from antarctica it helps explain observed anomalies in glacio isostatic adjustment above all it suggests that the behaviour of the atlantic facing weddell sea sector of the wais contrasts with that of the pacific facing ross and amundsen sea sectors

past and future grounding line retreat of the west antarctic ice sheet the history of deglaciation of the west antarctic ice sheet wais gives clues about its future southward grounding line migration was dated past three locations in the ross sea embayment results indicate that most recession occurred during the middle to late holocene in the absence of substantial sea level or climate forcing current grounding line retreat may reflect ongoing ice recession that has been under way since the early holocene if so the wais could continue to retreat even in the absence of further external forcing

ross sea paleo ice sheet drainage and deglacial history during and since the lgm onshore and offshore studies show that an expanded grounded ice sheet occupied the ross sea embayment during the last glacial maximum lgm results from studies of till provenance and the orienta

late quaternary vegetation and lake system dynamics in north eastern siberia implications for seasonal climate variability although the climate development over the holocene in the northern hemisphere is well known palaeolimnological climate reconstructions reveal spatiotemporal variability in northern eurasia here we present a multi proxy study from north eastern siberia combining sediment geochemistry and diatom and pollen data from lake sediment cores covering the last 38 000 cal years our results show major changes in pyrite content and fragilarioid diatom species distributions indicating prolonged seasonal lake ice cover between 13 500 and 8900 cal years bp and possibly during the 8200 cal years bp cold event a pollen based climate reconstruction generated a mean july temperature of 17 8 c during the holocene thermal maximum htm between 8900 and 4500 cal years bp naviculoid diatoms appear in the late holocene indicating a shortening of the seasonal ice cover that continues today our results reveal a strong correlation between the applied terrestrial and aquatic indicators and natural seasonal climate dynamics in the holocene planktonic diatoms show a strong response to changes in the lake ecosystem due to recent climate warming in the anthropocene we assess other palaeolimnological studies to infer the spatiotemporal pattern of the htm and affirm that the timing of its onset a difference of up to 3000 years from north to south can be well explained by climatic teleconnections the westerlies brought cold air to this part of siberia until the laurentide ice sheet vanished 7000 years ago the apparent delayed ending of the htm in the central siberian record can be ascribed to the exceedance of ecological thresholds trailing behind increases in winter temperatures and decreases in contrast in insolation between seasons during the mid to late holocene as well as lacking differentiation between summer and winter trends in paleolimnological reconstructions

pleistocene variability of antarctic ice sheet extent in the ross embayment cores acquired by the andrill mcmurdo ice shelf project and 1b provide the basis for a new sedimentation model for glacimarine depositional sequences that reflect cyclic glacial interglacial fluctuations of a marine based ice sheet in the western ross embayment over the past 2 0 ma notwithstanding periodic erosion during advances of the ice sheet uncertainties inherent to the sedimentological interpretation and a limited number of chronological datums it is clear that subglacial to grounding zone sedimentation was dominant at the and 1b site during the late pleistocene with interglacials being represented only by thin intervals of ice shelf sediment each sequence is characterised by subglacial massive diamictite that pass upwards into glacimarine diamictites and mudstones this provides the first direct evidence that the marine based antarctic ice sheet has oscillated between a grounded and floating state at least 7 times in the ross embayment over the last 780ka implying a milankovitch orbital influence an unconformity in and 1b that spans most 200 kyr of the mid pleistocene transition is inferred to represent widespread expansion of a marine based ice sheet in the ross embayment at 0 8 ma prior to 1 0 ma interglacial periods are characterised by open water conditions at the drill site with high abundances of volcanoclastic deposits and occasional diatomaceous sediments these may have responded to precession 20 kyr or obliquity 40 kyr orbital control the occurrence of 6 7 m of phonolitic glass reworked from mt erebus in interglacial deposits beneath last glacial maximum till requires open ocean or ice shelf conditions in the western ross sea around the drill site within the past 250 ka and implies a ross ice shelf similar to or less extensive than today during marine isotope stage 7 or 5

ice complex permafrost of mis5 age in the dmitry laptev strait coastal region east siberian arctic ice complex deposits locally known as the buchchagy ice complex are exposed at both coasts of the east siberian dmitry laptev strait and preserved below the yedoma ice complex that formed during mis3 and mis2 marine isotope stage and lateglacial holocene thermokarst deposits mis1 radioisotope disequilibria 230th u of peaty horizons date the buchchagy ice complex deposition to 126 16 13 kyr and 117 19 14 kyr until 98 5 kyr and 89 5 kyr the deposit is characterised by poorlysorted medium to coarse silts with cryogenic structures of horizontal ice bands lens like and lenslike reticulated segregation ice two peaty horizons within the buchchagy ice complex and syngenetic ice wedges 2e4 m wide up to 10 m high are striking the isotopic composition d18o dd of buchchagy ice wedge ice indicates winter conditions colder than during the mis3 interstadial and warmer than during mis2 stadial and similar atmospheric winter moisture sources as during the mis2 stadial buchchagy ice complex pollen spectra reveal tundra steppe vegetation and harsher summer conditions than during the mis3 interstadial and rather similar vegetation as during the mis2 stadial short term climatic variability during mis5 is reflected in the record even though the regional chronostratigraphic relationship of the buchchagy ice complex to the last interglacial remains unclear because numerical dating is widely lacking the present study indicates permafrost ice complex formation during mis5 sensu lato and its preservation afterwards palaeoenvironmental insights into past climate and the periglacial landscape dynamics of arctic lowlands in eastern siberia are deduced from the record

shallow ice approximation second order shallow ice approximation and full stokes models a discussion of their roles in palaeo ice sheet modelling and development full stokes ice sheet models provide the most accurate description of ice sheet flow and can therefore be used to reduce existing uncertainties in predicting the contribution of ice sheets to futu

garwood valley antarctica a new record of last glacial maximum to holocene glaciofluvial processes in the mcmurdo dry valleys we document the age and extent of late quaternary glaciofluvial processes in garwood valley mcmurdo dry valleys antarctica using mapping stratigraphy geochronology and geochemical analysis of sedimentary and ice deposits geomorphic and stratigraphic evidence indicates damming of the valley at its ross sea outlet by the expanded ross sea ice sheet during the last glacial maximum damming resulted in development of a proglacial lake in garwood valley that persisted from late pleistocene to mid holocene time and in the formation of a multilevel delta complex that overlies intact supraglacial till and buried glacier ice detached from the ross sea ice sheet radiocarbon dating of delta deposits and inferred relationships between paleolake level and ross sea ice sheet grounding line positions indicate that the ross sea ice sheet advanced north of garwood valley at ca 21 5 ka and retreated south of the valley between 7 3 and 5 5 ka buried ice remaining in garwood valley has a similar geochemical fingerprint to grounded ross sea ice sheet material elsewhere in the southern dry valleys the sedimentary sequence in garwood valley preserves evidence of glaciofluvial interactions and climate driven hydrological activity from the end of the pleistocene through the mid holocene making it an unusually complete record of climate activity and paleoenvironmental conditions from the terrestrial antarctic

postglacial environmental succession of nettilling lake baffin island canadian arctic inferred from biogeochemical and microfossil proxies abstract nettilling lake baffin island nunavut is currently the largest lake in the canadian arctic archipelago despite its enormous size this freshwater system remains little studied until the present day existing records from southern baffin island indicate that in the early postglacial period the region was submerged by the postglacial tyrell sea due to isostatic depression previously exerted by the laurentide ice sheet however these records are temporally and spatially discontinuous relying on qualitative extrapolation this paper presents the first quantitative reconstruction of the postglacial environmental succession of the nettilling lake basin based on a 8300 yr long high resolution sedimentary record our multi proxy investigation of the glacio isostatic uplift and subsequent changes in paleosalinity and sediment sources is based on analyses of sediment fabric elemental geochemistry xrf diatom assemblage composition as well as on the first diatom based oxygen isotope record from the eastern canadian arctic results indicate that the nettilling lake basin experienced a relatively rapid and uniform marine invasion in the early holocene followed by progressive freshening until about 6000 yr bp when limnological conditions similar to those of today were established our findings present evidence for deglacial processes in the foxe basin that were initiated at least 400yrs earlier than previously thought

biophysical controls on accretion and elevation change in caribbean mangrove ecosystems abstract habitat stability of coastal ecosystems such as marshes and mangroves depends on maintenance of soil elevations relative to sea level many such systems are characterized by limited mineral sedimentation and or rapid subsidence and are consequently dependent upon accumulation of organic matter to maintain elevations however little field information exists regarding the contribution of specific biological processes to vertical accretion and elevation change this study used biogenic mangrove systems in carbonate settings in belize bz and southwest florida fl to examine biophysical controls on elevation change rates of elevation change vertical accretion benthic mat formation and belowground root accumulation were measured in fringe basin scrub and dwarf forest types plus a restored forest elevation change rates mm yr 1 measured with surface elevation tables varied widely bz dwarf 3 7 bz scrub 1 1 fl fringe 0 6 fl basin 2 1 bz fringe 4 1 and fl restored 9 9 root mass accumulation varied across sites 82 739 g m 2 yr 1 and was positively correlated with elevation change root volumetric contribution to vertical change mm yr 1 was lowest in bz dwarf 1 2 and fl fringe 2 4 intermediate in fl basin 4 1 and bz scrub 4 3 and highest in bz fringe 8 8 and fl restored 11 8 sites surface growth of turf forming algae microbial mats or accumulation of leaf litter and detritus also made significant contributions to vertical accretion turf algal mats in fringe and scrub forests accreted faster 2 7 mm yr 1 than leaf litter mats in basin forests 1 9 mm yr 1 but similarly to microbial mats in dwarf forests 2 1 mm yr 1 surface accretion of mineral material accounted for only 0 2 3 3 of total vertical change those sites with high root contributions and or rapid growth of living mats exhibited an elevation surplus 2 to 8 mm yr 1 whereas those with low root inputs and low or non living mat accumulation showed an elevation deficit 1 to 5 7 mm yr 1 this study indicates that biotic processes of root production and benthic mat formation are important controls on accretion and elevation change in mangrove ecosystems common to the caribbean region quantification of specific biological controls on elevation provides better insight into how sustainability of such systems might be influenced by global e g climate atmospheric co2 and local e g nutrients disturbance factors affecting organic matter accumulation in addition to relative sea level rise

controls on interior west antarctic ice sheet elevations inferences from geologic constraints and ice sheet modeling abstract knowledge of the west antarctic ice sheet wais response to past sea level and climate forcing is necessary to predict its response to warmer temperatures in the future the timing and extent of past interior wais elevation changes provides insight to wais behavior and constraints for ice sheet models constraints prior to the last glacial maximum lgm however are rare surface exposure ages of glacial erratics near the wais divide at mt waesche in marie byrd land and at the ohio range in the transantarctic mountains range from 10 ka to 500 ka without a dependence on elevation the probability distribution functions pdf of the exposure ages at both locations are remarkably similar during the last glaciation maximum interior ice elevations as recorded by moraines and erratics were reached between 10 ka and 12 ka however most exposure ages are older than the lgm and cluster around 40 ka and 80 ka the peak in the exposure age distributions at 40 ka includes ages of alpine moraine boulders at mercer ridge in the ohio range comparison of the pdf of exposures ages from the ohio range and mt waesche with the temperature record from the fuji dome ice core indicates that the youngest peak in the exposure age distributions corresponds to the abrupt warming during the last glacial termination a prominent peak in the ohio range pdf corresponds to the penultimate termination stage 5e during the intervening glacial period there is not a consistent relationship between the peaks in the pdf at each location and temperature a combined ice sheet ice shelf model with forcing scaled to marine 18 o predicts that interior wais elevations near the ice divide have varied 300 m over the last glacial cycle peaks in the pdf correspond to model highstands over the last 200 ka in the simulated elevation history maximum ice elevations at ohio range 100 m and mt waesche 60 m occur at 10 ka in agreement with observations from these sites during collapse of the marine portion of the wais ice elevations at ohio range and mt waesche are drawn down at least 200 m below the present ice elevation the good correspondence between the model results and observations at both the ohio range and mt waesche supports the conclusion that interior wais highstands do not occur during glacial maximums rather the highstands are controlled primarily by increased accumulation during temperature maximums that occur early in the interglacials interior down draw events follow highstands resulting from the arrival of a wave of thinning triggered by retreat of the wais grounding line coupled with decreasing accumulation rates

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

holocene sea subsurface and surface water masses in the fram strait comparisons of temperature and sea ice reconstructions highlights holocene sea subsurface temperatures after husum hald 2012 estimated from planktic foraminifer fauna in e fram strait biomarkers and ip25 derived indices including dip25 indicate surface water variability delayed onset of early holocene conditions in subsurface 10 6 ka compared to surface 11 7 ka water conditions warm atlantic layer likely occupied uppermost 200 m in eastern fram strait between 10 and 9 ka diverging late holocene trends in surface and subsurface conditions linked to presence of strong pycnocline stratification abstract two high resolution sediment cores from eastern fram strait have been investigated for sea subsurface and surface temperature variability during the holocene the past ca 12 000 years the transfer function developed by husum and hald 2012 has been applied to sediment cores in order to reconstruct fluctuations of sea subsurface temperatures throughout the period additional biomarker and foraminiferal proxy data are used to elucidate variability between surface and subsurface water mass conditions and to conclude on the holocene climate and oceanographic variability on the west spitsbergen continental margin results consistently reveal warm sea surface to subsurface temperatures of up to 6 c until ca 5 cal ka bp with maximum seawater temperatures around 10 cal ka bp likely related to maximum july insolation occurring at that time maximum atlantic water aw advection occurred at surface and subsurface between 10 6 and 8 5 cal ka bp based on both foraminiferal and dinocyst temperature reconstructions probably a less stratified ice free nutrient rich surface ocean with strong aw advection prevailed in the eastern fram strait between 10 and 9 cal ka bp weakened aw contribution is found after ca 5 cal ka bp when subsurface temperatures strongly decrease with minimum values between ca 4 and 3 cal ka bp cold late holocene conditions are furthermore supported by high planktic foraminifer shell fragmentation and high 18o values of the subpolar planktic foraminifer species turborotalita quinqueloba while ip25 associated indices as well as dinocyst data suggest a sustained cooling due to a decrease in early summer insolation and consequently sea ice increase since about 7 cal ka bp in surface waters planktic foraminiferal data including stable isotopes indicate a slight return of stronger subsurface aw influx since ca 3 cal ka bp the observed decoupling of surface and subsurface waters during the later holocene is most likely attributed to a strong pycnocline layer separating cold sea ice fed surface waters from enhanced subsurface aw advection this may be related to changes in north atlantic subpolar versus subtropical gyre activity

retreat history of the ross ice sheet shelf since the last glacial maximum from deep basin sediment cores around ross island abstract radiocarbon dated sediment cores from deep basins beneath the mcmurdo ice shelf and seasonally open water north of ross island mcmurdo sound display a characteristic succession of sedimentary facies that document the retreat of the ross ice sheet at the last glacial maximum to its present ice shelf configuration the facies succession records a transition from a nearly grounded ice sheet to open marine environments north of ross island that comprises in ascending stratigraphic order 1 slightly consolidated clast rich muddy diamict dominated by basement clasts from the transantarctic mountains and interpreted as melt out from the basal layer debris proximal to a retreating grounding zone 2 sparsely fossiliferous reworked diatom frustules and non bioturbated mud lacking lonestones interpreted as a sub ice shelf facies and 3 diatom mud and diatom ooze indicative of open marine conditions with evidence of iceberg rafting the succession in the open marine lewis basin north of ross island is similar though the diamict is much sandier and sedimentation rates 1 2 orders of magnitude higher we present a radiocarbon chronology from total organic carbon which implies that lift off of grounded ice in the 900 m deep marine basins surrounding ross island occurred by 10 100 14c years bp following lift off an ice shelf was maintained to the north of ross island until 8900 14c years bp we identify a phase of accelerated retreat at that time between the drygalski trough and ross island immediately preceding the timing of meltwater pulse 1b at 8900 14c years bp the calving line became pinned to ross island significantly decoupling from the grounding line and marking the transition from a retreating ice sheet to the development of the present ice shelf

deglaciation of fennoscandia abstract to provide a new reconstruction of the deglaciation of the fennoscandian ice sheet in the form of calendar year time slices which are particularly useful for ice sheet modelling we have compiled and synthesized published geomorphological data for eskers ice marginal formations lineations marginal meltwater channels striae ice dammed lakes and geochronological data from radiocarbon varve optically stimulated luminescence and cosmogenic nuclide dating this is summarized as a deglaciation map of the fennoscandian ice sheet with isochrons marking every 1000 years between 22 and 13 cal kyr bp and every hundred years between 11 6 and final ice decay after 9 7 cal kyr bp deglaciation patterns vary across the fennoscandian ice sheet domain reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins for example the ice sheet margin in the high precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice marginal deposits in many fjords and coastal valleys retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern sweden and rapid retreat of the calving ice margin in the baltic basin our reconstruction is consistent with much of the published research however the synthesis of a large amount of existing and new data support refined reconstructions in some areas for example the lgm extent of the ice sheet in northwestern russia was located far east and it occurred at a later time than the rest of the ice sheet at around 17 15 cal kyr bp we also propose a slightly different chronology of moraine formation over southern sweden based on improved correlations of moraine segments using new lidar data and tying the timing of moraine formation to greenland ice core cold stages retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet with the lowest rates on the high elevation and maritime norwegian margin retreat rates compared to the climatic information provided by the greenland ice core record show a general correspondence between retreat rate and climatic forcing although a close match between retreat rate and climate is unlikely because of other controls such as topography and marine versus terrestrial margins overall the time slice reconstructions of fennoscandian ice sheet deglaciation from 22 to 9 7 cal kyr bp provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the fennoscandian ice sheet and are an important resource for testing and refining ice sheet models

an east siberian ice shelf during the late pleistocene glaciations numerical reconstructions abstract a recent data campaign in the east siberian sea has revealed evidence of grounded and floating ice dynamics in regions of up to 1000 m water depth and which are attributed to glaciations older than the last glacial maximum 21 kyrs bp the main hypothesis based on this evidence is that a small ice cap developed over beringia and expanded over the east siberian continental margin during some of the late pleistocene glaciations other similar evidence of ice dynamics that have been previously collected on the shallow continental shelves of the arctic ocean have been attributed to the penultimate glaciation i e marine isotopes stage 6 140 kyrs bp we use an ice sheet model forced by two previously simulated mis 6 glacial maximum climates to carry out a series of sensitivity experiments testing the impact of dynamics and mass balance related parameters on the geometry of the east siberian ice cap and ice shelf results show that the ice cap developing over beringia connects to the eurasian ice sheet in all simulations and that its volume ranges between 6 and 14 m sle depending on the climate forcing this ice cap generates an ice shelf of dimensions comparable with or larger than the present day ross ice shelf in west antarctica although the ice shelf extent strongly depends on the ice flux through the grounding line it is particularly sensitive to the choice of the calving and basal melting parameters finally inhibiting a merging of the beringia ice cap with the eurasian ice sheet affects the expansion of the ice shelf only in the simulations where the ice cap fluxes are not large enough to compensate for the fluxes coming from the eurasian ice sheet

vegetation climate and lake changes over the last 7000 years at the boreal treeline in north central siberia abstract palaeoecological investigations in the larch forest tundra ecotone in northern siberia have the potential to reveal holocene environmental variations which likely have consequences for global climate change because of the strong high latitude feedback mechanisms a sediment core collected from a small lake radius 100 m was used to reconstruct the development of the lake and its catchment as well as vegetation and summer temperatures over the last 7100 calibrated years a multi proxy approach was taken including pollen and sedimentological analyses our data indicate a gradual replacement of open larch forests by tundra with scattered single trees as found today in the vicinity of the lake an overall trend of cooling summer temperature from a 2 c warmer than present mid holocene summer temperatures until the establishment of modern conditions around 3000 years ago is reconstructed based on a regional pollen climate transfer function the inference of regional vegetation changes was compared to local changes in the lake s catchment an initial small water depression occurred from 7100 to 6500 cal years bp afterwards a small lake formed and deepened probably due to thermokarst processes although the general trends of local and regional environmental change match the lake catchment changes show higher variability furthermore changes in the lake catchment slightly precede those in the regional vegetation both proxies highlight that marked environmental changes occurred in the siberian forest tundra ecotone over the course of the holocene

acceleration of jakobshavn isbrae triggered by warm subsurface ocean waters observations over past decades show a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning in 1997 this switch is associated with a doubling in glacier velocity hydrographic data show a concurrent sudden increase in subsurface ocean temperatures along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were triggered by the arrival of relatively warm water originating from the irminger sea observations over the past decades show a rapid acceleration of several outlet glaciers in greenland and antarctica1 one of the largest changes is a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning2 in 1997 associated with a doubling in glacier velocity3 suggested explanations for the speed up of jakobshavn isbrae include increased lubrication of the ice bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers4 and weakening and break up of the floating ice tongue that buttressed the glacier5 here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were instead triggered by the arrival of relatively warm water originating from the irminger sea near iceland we trace these oceanic changes back to changes in the atmospheric circulation in the north atlantic region we conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets

changes in ice front position on greenland s outlet glaciers from 1992 to 2007 1 previous studies in greenland show that retreat of tidewater glaciers may be linked to recent increases in ice loss raising greenland s contribution to sea level rise we examined ice front changes of 203 tidewater glaciers land terminating glaciers and glaciers terminating with ice shelves to understand greenland glacier behavior over three periods 1992 2000 2000 2006 and 2006 2007 we observed synchronous ice sheet wide increases in tidewater retreat during 2000 2006 relative to 1992 2000 coinciding with a 1 1 c increase in mean summer temperature at coastal weather stations rates of retreat for the southeast and east slowed during 2006 2007 when temperatures were slightly cooler than the 2000 2006 average our work suggests that regional greenland tidewater retreat responds strongly to climate change with higher temperatures corresponding to increasing retreat and helps confirm a link between ice thickness velocity and ice front position

sea level rise sedimentary record and organic carbon fluxes in a low lying tropical coastal ecosystem abstract sea level rise one of the most evident effects of recent climate change is already impacting coastal ecosystems because of its low relief population increase and economic development during the last century the celestun lagoon is highly vulnerable to global change including sea level rise here we study a sediment core from a tropical saltmarsh to evaluate the impact of sea level rise on sediment accretion and carbon fluxes some geochemical indicators in a 210pb dated sediment core showed clear signals of marine influence this was reflected on increased accretion rates from 0 3 0 1 mm yr 1 in 1941 to 2 9 1 2 mm yr 1 in 2012 these accretion rates were similar to eustatic sea level rise and mean acceleration ranged from 0 037 0 22 mm yr 2 implying a slr by 2100 ranging from 14 to 86 cm the one century 1917 2013 organic carbon stock in sediments was calculated to be 10 1 0 2 mg c ha 1 during the same period the organic carbon flux corrected for organic carbon degradation increased from 7 3 g c m 2 yr 1 to 73 26 g c m 2 yr 1 attributed to the impact of sea level rise in this ecosystem this work shows that tropical saltmarshes may provide useful information on sea level rise and the presented methodology may be used where instrumental records do not exist or they are too short

landscape evolution of the dry valleys transantarctic mountains tectonic implications there are different views about the amount and timing of surface uplift in the transantarctic mountains and the geophysical mechanisms involved our new interpretation of the landscape evolution and tectonic history of the dry valleys area of the transantarctic mountains is based on geomorphic mapping of an area of 10 000 km2 the landforms are dated mainly by their association with volcanic ashes and glaciomarine deposits and this permits a reconstruction of the stages and timing of landscape evolution following a lowering of base level about 55 m y ago there was a phase of rapid denudation associated with planation and escarpment retreat probably under semiarid conditions eventually downcutting by rivers aided in places by glaciers graded valleys to near present sea level the main valleys were flooded by the sea in the miocene during a phase of subsidence before experiencing a final stage of modest upwarping near the coast there has been remarkably little landform change under the stable cold polar conditions of the last 15 m y it is difficult to explain the sirius group deposits which occur at high elevations in the area if they are pliocene in age overall denudation may have removed a wedge of rock with a thickness of over 4 km at the coast declining to 1 km at a point 75 km inland which is in good agreement with the results of existing apatite fission track analyses it is suggested that denudation reflects the differences in base level caused by high elevation at the time of extension due to underplating and the subsequent role of thermal uplift and flexural isostasy most crustal uplift 2 4 km is inferred to have occurred in the early cenozoic with 400 m of subsidence in the miocene followed by 300 m of uplift in the pliocene

scaling factors for production rates of in situ produced cosmogenic nuclides a critical reevaluation abstract new scaling factors are presented describing the altitude and latitudinal dependence of production rates for in situ produced cosmogenic nuclides the new factors incorporate the influence of the non dipole contributions to the geomagnetic field on the cosmic ray flux the currently used scaling factors of lal earth planet sci lett 104 1991 424 439 are based on the assumption of a dipole field the overall strategy used in deriving the new scaling factors is however very similar to that of lal and relies on the same and or similar nuclear data in this reevaluation data are only used if the effective geomagnetic parameters inclination horizontal field strength can be reconstructed for the time of measurement the absorption free pathlengths for cosmic rays selected for this study are based on observational data at altitudes relevant for exposure age dating sea level to 7000 m at sea level and latitudes between 20 and 40 the new factors are up to 18 lower and at high altitudes more than 30 higher than those of lal in addition to accounting for the influence of the effective geomagnetic field and providing more applicable estimates of the new factors also allow for correction for the significant deviations from the standard pressure altitude relationship that exist in the atmosphere 10

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

accretion of a new england u s a salt marsh in response to inlet migration storms and sea level rise sediment accumulation rates were determined at several sites throughout nauset marsh massachusetts u s a a back barrier lagoonal system using feldspar marker horizons to evaluate short term rates 1 to 2 year scales and radiometric techniques to estimate rates over longer time scales 137cs 210pb 14c the barrier spit fronting thespartina dominated study site has a complex geomorphic history of inlet migration and overwash events this study evaluates sediment accumulation rates in relation to inlet migration storm events and sea level rise the marker horizon technique displayed strong temporal and spatial variability in response to storm events and proximity to the inlet sediment accumulation rates of up to 24 mm year 1were recorded in the immediate vicinity of the inlet during a period that included several major coastal storms while feldspar sites remote from the inlet had substantially lower rates trace accumulation to 2 2 mm year 1 during storm free periods accumulation rates did not exceed 6 7 mm year 1 but remained quite variable among sites based on137cs 3 8 to 4 5 mm year 1 and210pb 2 6 to 4 2 mm year 1 radiometric techniques integrating sediment accumulation over decadal time scales the marsh appeared to be keeping pace with the relative rate of sea level rise from 1921 to 1993 of 2 4 mm year 1 at one site the210pb based sedimentation rate and rate of relative sea level rise were nearly similar and peat rhizome analysis revealed thatdistichlis spicatarecently replaced this onces patenssite suggesting that this portion of nauset marsh may be getting wetter thus representing an initial response to wetland submergence horizon markers are useful in evaluating the role of short term events such as storms or inlet migration influencing marsh sedimentation processes however sampling methods that integrate marsh sedimentation over decadal time scales are preferable when evaluating a systems response to sea level rise

degradation of glacial deposits quantified with cosmogenic nuclides quartermain mountains antarctica many glacial deposits in the quartermain mountains antarctica present two apparent contradictions regarding the degradation of unconsolidated deposits the glacial deposits are up to millions of years old yet they have maintained their meter scale morphology despite the fact that bedrock and regolith erosion rates in the quartermain mountains have been measured at 0 1 4 0 m ma 1 additionally ground ice persists in some miocene aged soils in the quartermain mountains even though modeled and measured sublimation rates of ice in antarctic soils suggest that without any recharge mechanisms ground ice should sublimate in the upper few meters of soil on the order of 103 to 105 years this paper presents results from using the concentration of cosmogenic nuclides beryllium 10 10be and aluminum 26 26al in bulk sediment samples from depth profiles of three glacial deposits in the quartermain mountains the measured nuclide concentrations are lower than expected for the known ages of the deposits erosion alone does not always explain these concentrations and deflation of the tills by the sublimation of ice coupled with erosion of the overlying till can explain some of the nuclide concentration profiles the degradation rates that best match the data range 0 7 12 m ma 1 for sublimation of ice with initial debris concentrations ranging 12 45 and erosion of the overlying till at rates of 0 4 1 2 m ma 1 overturning of the tills by cryoturbation vertical mixing or soil creep is not indicated by the cosmogenic nuclide profiles and degradation appears to be limited to within a few centimeters of the surface erosion of these tills without vertical mixing may partially explain how some glacial deposits in the quartermain mountains maintain their morphology and contain ground ice close to the surface for millions of years copyright 2010 john wiley sons ltd

the application of radiocarbon age estimates to the dating of glacial sequences an example from the miami sublobe ohio u s a abstract despite the importance of dating glacial sequences little evidence has been available to highlight the stratigraphic issues associated with the interpretation of age analysis a compilation of radiocarbon data from the miami sublobe of the laurentide ice sheet provides a large enough data set more than 133 dates to identify at least two sources of error sample and unit variability and transportation problems analysis of different samples from the same stratigraphic level commonly differ by more than the reported one sigma error and 2 000 year differences do occur glacial entrainment and transportation emplace older organic material over younger in situ materials and this effect may also give age errors in the data set of up to 2 000 years at a minimum multiple radiocarbon ages from a sequence of units are necessary to assign a reliable age to events within a glacial sequence however representing multiple ages poses its own problems a graphical representation that combines the probability of each sample appears to be one solution

pleistocene dynamics of the interior east antarctic ice sheet current models describing past configurations of the east antarctic ice sheet are poorly constrained by observations exposure dating of bedrock surfaces using in situ produced cosmogenic nuclides provides an ideal tool for directly constraining former changes in ice sheet elevation we present cosmogenic radionuclide 10 be and 26 al measurements in bedrock surfaces and glacially transported cobbles in the grove mountains a group of nunataks within the slow flowing interior ice sheet dome hundreds of kilometers from the coastal ice margin and from ice streams samples were collected in vertical transects over 500 m of relief minimum bedrock and erratic exposure ages show a trend of increasing age with height above the ice sheet spanning a period from 0 3 to 4 0 ma and 50 900 ka respectively no evidence was found for thicker ice at the last glacial maximum compared to modern ice thickness the older bedrock exposure ages of 2 5 4 0 ma require steady state erosion rates of 1 the measured two isotope bedrock exposure ages are successfully modeled when changes in surface elevation of the ice sheet are described by a combination of linear long term ice surface lowering and shorter term high frequency glacial interglacial oscillations the best fit model requires a long term thinning rate of 50 m m y 1 and an elevation change of 100 m over a 100 k y glacial cycle

early to middle holocene valley glaciations on northernmost greenland abstract this paper presents the glacial stratigraphy and palaeoenvironmental evolution around constable bugt johannes v jensen land located on the north coast of greenland this is a land of extreme climate polar desert conditions and a coast bound by a permanent sea ice cover our data covers the period from the last glacial maximum lgm 18 22 cal ka bp into the holocene it records the history of a shelf based glaciation with ice flowing eastward along the coast as well as two local valley glacier advances from the south during the holocene with ice on the coastal plain during the lgm glaciolacustrine basins formed in marginal positions and in ice dammed valleys to the south into the mountainous area of peary land with the break up of shelf based ice there was a gradual marine inundation at which the marine limit formed at 45 m a s l this initial early holocene ice advance from the south formed prominent valley mouth moraines especially in sifs valley here both glaciolacustrine and marine sediments were remoulded and or dislocated as thrust blocks into a moraine ridge spanning more than 1 km in width and 60 m in height radiocarbon ages of sediments incorporated in this moraine as well as from on lapping sediments suggest that the moraine formed between 9 6 and 6 3 cal ka bp based on 14 c dating results the youngest ice advance phase can be narrowed down to 14 c ages between 5 5 5 0 cal ka bp the recorded ice advances took place during the holocene thermal maximum htm for north greenland the last one close to the beginning of the neoglacial cooling during the htm we have recorded a period of 2500 years during which the north coast of greenland as opposed to today experienced an absence to very restricted occurrence of land fast or multi year sea ice this observation can be explained by the altitudinal and temporal distribution of beach ridge complexes that must have formed by wave action and thus requiring at least partial open water conditions with a moisture source at hand we propose that this lead to enhanced precipitation in the near coastal areas which coupled to documented htm cold reversals caused a lowered glaciation limit and led to a positive mass balance and subsequent ice advance

millennial scale vegetation changes in the north eastern russian arctic during the pliocene pleistocene transition 2 7 2 5 ma inferred from the pollen record of lake el gygytgyn abstract the sediment record of lake el gygytgyn 67 30 n 172 05 e spans the past 3 6 ma and provides unique opportunities for qualitative and quantitative reconstructions of the regional paleoenvironmental history of the terrestrial arctic millennial scale pollen studies of the sediments that accumulated during the late pliocene and early pleistocene ca 2 7 to 2 5 ma demonstrate orbitally driven vegetation and climate changes during this transitional interval pollen spectra show a significant vegetation shift at the pliocene pleistocene boundary that is however delayed by a few thousand years compared to lacustrine response about 2 70 2 68 ma the vegetation at lake el gygytgyn currently a tundra area was mostly dominated by larch forests with some shrub pine shrub alder and dwarf birch in understory during the marine isotope stages g3 and g1 ca 2 665 2 647 and 2 625 2 617 ma some spruce trees grew in the local larch pine forests pointing to relatively warm climate conditions at the beginning of the pleistocene around 2 588 ma a prominent climatic deterioration led to a change from larch dominated forests to predominantly treeless steppe and tundra like habitats between ca 2 56 2 53 ma some climate amelioration is reflected by the higher presence of coniferous taxa mostly pine and larch but probably also spruce in the area after 2 53 ma a relatively cold and dry climate became dominant again leading to open steppe like and shrubby environments followed by climate amelioration between ca 2 510 and 2 495 ma when pollen assemblages show that larch forests with dwarf birch and shrub alder still grew in the lake s vicinity increased contents of green algae colonies botryococcus remains and zygnema cysts around 2 691 2 689 2 679 2 677 2 601 2 594 2 564 2 545 and 2 532 2 510 ma suggest a spread of shallow water environments most likely due to a lake level lowering these events occurred simultaneously with dry climate conditions inferred from broad distribution of steppe habitats with artemisia and other herbs

examination of surface exposure ages of antarctic moraines using in situ produced 10be and 26al concentrations of 10be t12 1 5 106 y and 26a1 t12 0 72 106 y have been determined by accelerator mass spectrometry ams in a suite of quartz samples taken from sandstone boulders in several moraines in arena valley a dry valley adjacent to the taylor glacier in the quatermain mountains southern victoria land east antarctica these isotopes are produced in surficial quartz by cosmic ray spallation of o and si the concentrations in these samples ranged from 6 1 105 to 3 0 107 at g 1 for 10be and from 9 4 106 to 1 2 108 at g 1 for 26a1 depending upon the extent of exposure at the surface analyses of 10be in several samples from a single moraine at altitudes ranging from 1300 to 1650 m permitted an estimation of the air attenuation pathlength of cosmic ray neutrons the value of 142 96 41 g cm 2 is consistent with other published values production rates of 17 6 4 at g 1 y 1 for 10be and 113 54 16 at g 1 y 1 for 26a1 at 1300 m and 87 s and a 26al 10be production ratio of 6 5 1 3 1 3 were calculated from the data these values correspond to sea level production rates at high geomagnetic latitude of 6 4 at g 1 y 1 and 41 7 at g 1 y 1 for 10be and 26a1 respectively consistent with determinations based on 11 ky glacially polished surfaces in the sierra nevada in california these production rates imply exposure ages for the various moraines ranging from 50 ky to 2 5 my in accordance with other geological evidence the 10be and 26al ages of these rocks compare favorably with those found using a similar dating method based on in situ production of 3he examination of the 3he concentrations in conjunction with the present data set yields an estimate of 3he production of 230 8540 at g 1 y 1 corresponding to 85 31 15 at g 1 y 1 at sea level this is lower than previously reported values of 240 60 at g 1 y 1 and 190 at g 1 y 1 scaled to sea level and high geomagnetic latitude based respectively on volcanic flows less than 2000 years old at low latitude and samples collected from 14 400 year old volcanic flows this discrepancy is likely due to diffusive losses which may become significant up to 50 for surface exposure ages on the order of 2 0 my nevertheless the general correlations among the three isotopes suggest that 3he does not suffer gross losses through diffusion

contributions and unrealized potential contributions of cosmogenic nuclide exposure dating to glacier chronology 1990 2010 abstract this paper reviews the application of cosmogenic nuclide exposure dating to glacier chronology exposure dating of glacial landforms has made an outsize impact on this field because the technique filled an obvious need that had already been recognized by glacial geologists by now hundreds of studies have used cosmogenic nuclide exposure dating to date glacial deposits and in fact it is rare to find a study of glacial geology or glacier chronology or any paleoclimate synthesis that makes use of such studies that does not involve exposure dating these developments have resulted in major contributions to glacier chronology and paleoclimate in particular i reconstructing antarctic ice sheet change ii establishing the chronology of late pleistocene and holocene glacier change in mountain regions where it was previously unknown iii establishing the broad chronological outlines of mountain glaciations prior to the last glacial maximum and iv gaining insight into subglacial erosional processes through the observation that many glaciated surfaces preserve cosmogenic nuclide inventories from long past ice free periods as well as the present one an important potential future contribution will be the application of the large data set of exposure dated glacier chronologies to better understand global and regional climate dynamics during lateglacial and holocene millennial scale climate changes however this contribution cannot be realized without significant progress in two areas i understanding and accounting for geologic processes that cause apparent exposure ages on glacial landforms to differ from the true age of the landform and ii minimizing systematic uncertainties in exposure ages that stem from cosmogenic nuclide production rate estimates and scaling schemes at present there exists an enormous data set of exposure ages on glacial deposits but these data cannot be used to their full potential in paleoclimate syntheses due to an inadequate understanding of geologic scatter and production rate uncertainties the intent of this paper is to highlight this situation and suggest some strategies for realizing this potential

deglaciation of a major palaeo ice stream in disko trough west greenland recent work has confirmed that grounded ice reached the shelf break in central west greenland during the last glacial maximum lgm here we use a combination of marine sediment core data including glacimarine lithofacies and ird proxy records and geomorphological and acoustic facies evidence to examine the nature of and controls on the retreat of a major outlet of the western sector of the greenland ice sheet gris across the shelf retreat of this outlet which contained the ancestral jakobshavns isbrae ice stream from the outer shelf in disko trough was rapid and progressed predominantly through iceberg calving however minor pauses in retreat tens of years occurred on the middle shelf at a trough narrowing forming subtle grounding zone wedges by 12 1 cal kyr bp ice had retreated to a basalt escarpment and shallow banks on the inner continental shelf where it was pinned and stabilised for at least 100 years during this time the ice margin appears to have formed a calving bay over the trough and melting became an important mechanism of ice mass loss fine grained sediments muds were deposited alternately with ird rich sediments diamictons forming a characteristic deglacial lithofacies that may be related to seasonal climatic cycles high influxes of subglacial meltwater emanating from the nearby ice margins deposited muddy sediments during the warmer summer months whereas winters were dominated by iceberg calving leading to the deposition of the diamictons this is the first example of this glacimarine lithofacies from a continental shelf setting and we suggest that the calving bay configuration of the ice margin plus the switching between calving and melting as ablation mechanisms facilitated its deposition by channelling meltwater and icebergs through the inner trough the occurrence of a major stillstand on the inner shelf in disko trough demonstrates that the ice dynamical response to local topography was a crucial control on the behaviour of a major outlet in this sector of the gris during retreat

simultaneous estimation of global present day water transport and glacial isostatic adjustment global water transport between oceans and continents during the transition from glacial to interglacial times has been enormous the viscoelastic solid earth has been responding to this unloading of large ice masses with a rise of the land masses in a process termed glacial isostatic adjustment in addition significant changes in the land ocean water distribution occur at present as both present day changes in the ice water thickness and glacial isostatic adjustment affect space geodetic measurements it is difficult to untangle the relative contributions of these two processes here we combine gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure to simultaneously estimate present day water transport and glacial isostatic adjustment we determine their separate contributions to movements in the geocentre which occur in response to changes in the earth s mass distribution with uncertainties below 0 1 mm yr 1 according to our estimates mass losses between 2002 and 2008 in greenland alaska yukon and west antarctica are 104 23 101 23 and 64 32 gt yr 1 respectively our estimates of glacial isostatic adjustment indicate a large geocentre velocity of 0 72 0 06 mm yr 1 in the polar direction we conclude that a significant revision of the present estimates of glacial isostatic adjustments and land ocean water exchange is required present day changes in the thickness of ice sheets and glacial isostatic adjustment both affect space geodetic measurements a combination of gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure allows the simultaneous estimation of present day water transport and glacial isostatic adjustment

history of the grounded ice sheet in the ross sea sector of antarctica during the last glacial maximum and the last termination knowledge of variations in the extent and thickness of the antarctic ice sheet is key for understanding the behaviour of southern hemisphere glaciers during the last ice age and for addressing issues involving global sea level ocean circulation and climate change insight into past ice sheet behaviour also will aid predictions of future ice sheet stability here we review ter restrial evidence for changes in ice geometry that occurred in the ross sea sector of antarctica at the last glacial maximum lgm and during subsequent deglaciation during the lgm a thick grounded ice sheet extended close to the continental shelf edge in the ross embayment this ice reached surface elevations of more than 1000 m along the coast of the central and southern trans antarctic mountains and marie byrd land the local lgm occurred by 18 ka on the coast but as late as 7 10 ka inland the first significant thinning took place at roughly 13 ka with most ice loss happening in the holocene this history makes it unlikely that the ross sea sector was a major contributor to meltwater pulse 1a mwp 1a resolution of a possible antarctic origin for mwp 1a awaits detailed reconstructions from all sectors of the ice sheet the antarctic ice sheet contains the world s larg est reservoir of fresh water and is a major control on southern hemisphere climate a history of changes in ice sheet extent and thickness is vital for answering questions involving the initiation of southern hemisphere glaciation and deglaciation

accretion rates in coastal wetlands of the southeastern gulf of california and their relationship with sea level rise sea level rise slr is one of the most conspicuous examples of the environmental impact of recent climate change since slr rates are not uniform around the planet local and regional data are needed for proper adaptation plans 210pb dated sediment cores were analyzed to determine the trends of sediment accretion rates sars at three tropical saltmarshes in the estero de urias lagoon gulf of california mexico in order to estimate the slr trends during the past 100 years under the assumption that these ecosystems accrete at a similar rate to slr a chemometric approach including multivariate statistical analysis factor analysis of geochemical data including 13c 15n c n ratios and br na and cl as proxies for marine transgression was used to identify the marine transgression in the sediment records based on core geochemistry only one of the three cores provided a long term record attributable to marine transgression slr trends estimated from sars showed increasing values from a min

past gateways palaeo arctic spatial and temporal gateways introduction and overview this special issue relates to the second international conference of the past gateways palaeo arctic spatial and temporal gateways network which was held in trieste italy in 2014 twenty five papers are included and they address topics under four main themes 1 the growth and decay of arctic ice sheets 2 arctic sea ice and palaeoceanography 3 terrestrial arctic environments and permafrost change and 4 holocene arctic environmental change geographically the focus is circum arctic the special issue includes detailed regional studies from greenland scandinavia russia and arctic north america and the adjoining seas as well as a series of synthesis type review papers on fennoscandian ice sheet deglaciation and holocene arctic palaeo climate change the methodologies employed are diverse and include marine sediment core and geophysical investigations terrestrial glacial geology and geomorphology isotopic analysis of ground ice palaeo ecological analysis of lacustrine and terrestrial sedimentary archives geochronology and numerical ice sheet modeling

retreat history of the east antarctic ice sheet since the last glacial maximum the east antarctic ice sheet eais is the largest continental ice mass on earth and documenting its evolution since the last glacial maximum lgm is important for understanding its present day and future behaviour as part of a community effort we review geological evidence from east antarctica that constrains the ice sheet history throughout this period 30 000 years ago to present this includes terrestrial cosmogenic nuclide dates from previously glaciated regions 14c chronologies from glacial and post glacial deposits onshore and on the continental shelf and ice sheet thickness changes inferred from ice cores and continental scale ice sheet models we also include new 14c dates from the george v land terre adelie coast shelf we show that the eais advanced to the continental shelf margin in some parts of east antarctica and that the ice sheet characteristically thickened by 300 400 m near the present day coastline at these sites this advance was associated with the formation of low gradient ice streams that grounded at depths of 1 km below sea level on the inner continental shelf the lambert amery system thickened by a greater amount 800 m near its present day grounding zone but did not advance beyond the inner continental shelf at other sites in coastal east antarctica e g bunger hills larsemann hills very little change in the ice sheet margin occurred at the lgm perhaps because ice streams accommodated any excess ice build up leaving adjacent ice free areas relatively unaffected evidence from nunataks indicates that the amount of ice sheet thickening diminished inland at the lgm an observation supported by ice cores which suggest that interior ice sheet domes were 100 m lower than present at this time ice sheet recession may have started 18 000 years ago in the lambert amery glacial system and by 14 000 years ago in mac robertson land these early pulses of deglaciation may have been responses to abrupt sea level rise events such as meltwater pulse 1a destabilising the margins of the ice sheet it is unlikely however that east antarctica contributed more than 1 m of eustatic sea level equivalent to post glacial meltwater pulses the majority of ice sheet recession occurred after meltwater pulse 1a between 12 000 and 6000 years ago during a period when the adjacent ocean warmed significantly large tracts of east antarctica remain poorly studied and further work is required to develop a robust understanding of the lgm ice sheet expansion and its subsequent contraction further work will also allow the contribution of the eais to post glacial sea level rise and present day estimates of glacio isostatic adjustment to be refined

groundwater geochemistry of the yucatan peninsula mexico constraints on stratigraphy and hydrogeology summary we report 87sr 86sr and ion concentrations of sulfate chloride and strontium in the groundwater of the northern and central yucatan peninsula mexico correlation between these data indicates that ejecta from the 65 95 m y old chicxulub impact crater have an important effect on hydrogeology geomorphology and soil development of the region ejecta are present at relatively shallow subsurface depths in north central yucatan and at the surface along the rio hondo escarpment in southeast quintana roo where they are referred to as the albion formation anhydrite gypsum and by inference celestite are common in impact ejecta clasts and in beds and cements of overlying paleocene and lower eocene rocks cored around the margin of the crater the sulfate rich minerals that are found in rocks immediately overlying the impact ejecta blanket may either be partially mobilized from the ejecta layer itself or may have been deposited after the k t impact event in an extensive pre oligocene shallow sea these deposits form a distinctive sedimentary package that can be easily traced by the eocene cretaceous 87sr 86sr signal a distinct sr isotopic signature and high so4 cl ratios are observed in groundwater of northwestern and north central yucatan that interacts with these rocks moreover the distribution of the gypsum rich stratigraphic unit provides a solution enhanced subsurface drainage pathway for a broad region characterized by dissolution features poljes extending from chetumal quintana roo to campeche campeche the presence of gypsum quarries in the area is also consistent with a sulfate rich stratigraphic package that includes ejecta the distinctive chemistry of groundwater that has been in contact with evaporite ejecta can be used to trace flow directions and confirms a groundwater divide in the northern peninsula information about groundwater flow directions and about deep subsurface zones of high permeability is useful for groundwater and liquid waste management in the area where it discharges at the coast the unique chemistry of the groundwater that has interacted with the evaporite ejecta strata may also have significant geomorphologic implications while groundwater seawater mixing at the coast has been shown to dissolve and erode limestone phreeqc modeling shows that mixing of water nearly saturated in caso4 with seawater has a less vigorous dissolution effect due to its high ca content

the physiography of high arctic cross shelf troughs abstract a comprehensive inventory of high arctic cross shelf troughs is compiled from international bathymetric chart of the arctic ocean ibcao bathymetric data v 3 0 the location of 75 cross shelf troughs is presented alongside a synthesis of their key physiographic characteristics and available glacial geological evidence the troughs are interpreted to have been occupied intermittently and eroded by marine terminating ice streams that traversed the shelf during at least one and often many quaternary full glacial periods considerable variation in cross shelf trough physiography exists in the high arctic trough lengths range between 35 and 1400 km widths from 12 to 260 km and maximum depths from 200 to 1000 m the longest cross shelf troughs extend through inter island channels on the beaufort sea queen elizabeth islands and barents kara sea margins the gradient of the upper slope beyond high arctic glacial troughs which ranges between 0 3 and 13 is shown to have a negative relationship with palaeo ice stream drainage basin area and trough length glacial sedimentary depocentres or trough mouth fans tmfs are inferred on the basis of bathymetric and where available seismic evidence to exist beyond the majority of high arctic cross shelf troughs evidence of shelf progradation or tmf development is absent from the slope beyond several high arctic troughs probably as a result of limited sediment supply to the margin and or sediment by passing of the upper slope on the south greenland continental margin it is likely that steep slopes prevented the development of significant glacial sedimentary depocentres beyond cross shelf troughs or that glacigenic debris has been removed from the upper slope by submarine slope failure

ice stream retreat following the lgm and onset of the west greenland current in uummannaq trough west greenland the deglacial history and oceanography of uummannaq trough central west greenland continental shelf was investigated using foraminiferal sedimentological and bathymetric records together with a radiocarbon chronology providing a timeline for the retreat of glacial ice after the last glacial maximum lgm to map ice stream retreat data were collected from cores from the outer jr175 vc45 and jr175 vc43 and inner jr175 vc42 uummannaq trough a large ice stream fed by confluent glaciers draining the interior of the greenland ice sheet extended across the outer shelf during the lgm and was in retreat by 15 0 cal kyr bp foraminiferal data indicate that the warm west greenland current wgc was established prior to 14 0 cal kyr bp which is the hitherto earliest record of atlantic water found on the west greenland shelf for each of the cores foraminifera indicate that ice sheet retreat was followed quickly by incursion of the wgc suggesting that the warm water may have enhanced ice retreat prior to the younger dryas cold event the radiocarbon chronology indicates that the ice sheet retreated to the mid shelf where it subsequently stabilised and formed a large grounding zone wedge gzw after the younger dryas around 11 5 cal kyr bp the ice retreated rapidly from the gzw and into the fjords

evolution of a high latitude sediment drift inside a glacially carved trough based on high resolution seismic stratigraphy kveithola nw barents sea abstract kveithola is a glacially carved e w trending trough located in the nw barents sea an epicontinental shelf sea of the arctic ocean located off northern norway and russia a set of confined sediment drifts the kveithola drift is located in the inner part of the trough in general drift deposits are commonly characterized by high lateral continuity restricted occurrence of hiatuses and relatively high accumulation rates and thus represent excellent repositories of paleo environmental information we provide for the first time a detailed morphological and seismostratigraphic insight into this sediment drift which is further supported by some preliminary lithological and sedimentological analyses the complex morphology of the drift imaged by combining all available multibeam data includes a main and a minor drift body two drift lenses in the outer part of the trough more or less connected drift patches in the innermost part and small perched sediment patches in a structurally controlled channel to the north the seismic parasound data show that the main and minor drift bodies are mainly well stratified characterized by sub parallel reflections of moderate to high amplitude and good lateral continuity the reflectors show an abrupt pinch out on the northern edge where a distinct moat is present and a gradual tapering to the south internally we identify the base of the drift and four internal horizons which we correlate throughout the drift two units display high amplitude reflectors marked lensoidal character and restricted lateral extent suggesting the occurrence of more energetic sedimentary conditions facies typical for contourite deposition are found in the sediment cores with strongly bioturbated sediments and abundant silty sandy mottles that contain shell fragments these characteristics along with the morphological and seismic information suggest a strong control by a bottom current flowing along the moat on the northern edge of the drift though both atlantic and arctic waters are known to enter the trough from the west and the north respectively brine enriched shelf water bsw produced during winter and flowing westward in the moat is suggested to be responsible for the genesis of the kveithola drift the formation of bsw is inferred to have started around 13 cal ka bp the onset of drift deposition suggesting that conditions leading to atmospheric cooling of the surface waters and or the presence of coastal polynyas and wind or floating ice shelves have persisted on the western barents shelf since that time the units inferred to have been deposited under more energetic sedimentary conditions tentatively dated to the younger dryas and to 8 9 8 2 cal ka bp are suggestive of stronger bsw formation in general we infer that variations in the bottom current regime were mainly related to bsw formation due to atmospheric changes they could also have been a response to successive episodes of grounded and sea ice retreat that allowed for a first limited later open shelf current which progressively established on the western barents sea shelf

a younger dryas re advance of local glaciers in north greenland abstract the younger dryas yd is a well constrained cold event from 12 900 to 11 700 years ago but it remains unclear how the cooling and subsequent abrupt warming recorded in ice cores was translated into ice margin fluctuations in greenland here we present 10be surface exposure ages from three moraines in front of local glaciers on a 50 km stretch along the north coast of greenland facing the arctic ocean ten ages range from 11 6 0 5 to 27 2 0 9 ka with a mean age of 12 5 0 7 ka after exclusion of two outliers we consider this to be a minimum age for the abandonment of the moraines the ages of the moraines are furthermore constrained using optically stimulated luminescence osl dating of epishelf sediments which were deposited prior to the ice advance that formed the moraines yielding a maximum age of 12 4 0 6 ka and bracketing the formation and subsequent abandonment of the moraines to within the interval 11 8 13 0 ka ago this is the first time a synchronous yd glacier advance and subsequent retreat has been recorded for several independent glaciers in greenland in most other areas there is no evidence for re advance and glaciers were retreating during yd we explain the different behaviour of the glaciers in northernmost greenland as a function of their remoteness from the atlantic meridional overturning circulation amoc which in other areas has been held responsible for modifying the yd drop in temperatures

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

a 2 million year glacial chronology of the hatherton glacier antarctica and implications for the size of the east antarctic ice sheet at the last glacial maximum abstract a series of distinct glacial deposits flanking the margins of the upper hatherton glacier an outlet glacier in the central transantarctic mountains are used to constrain the behaviour of the antarctic ice sheets cosmogenic exposure ages of 18 erratics from four glacial drifts covering the ice free dubris and bibra valleys range in age from 5 to 1997 ka our results document four glacial advance and retreat events superimposed on an overall long term ice thickness reduction of about 500 m since the mid pleistocene the lack of field evidence and absence of lgm exposure ages in the glacial deposits of the hatherton glacier supports our conclusion that at the lgm the east antarctic ice sheet was of similar size or may have been slightly smaller than present minimum exposure ages from the oldest two glacial events represented by the isca and danum drifts are 1 2 ma and 0 5 ma respectively the britannia ii drift previously assumed to mark the maximum extent of the last glacial maximum advance has a mean 10 be age of 126 3 2 ka n 5 ages from the younger britannia i drift suggest that since the mid holocene 6 5 1 2 ka n 5 approximately 200 m of additional ice has been lost

the last deglacial history of lutzow holm bay east antarctica past fluctuations of the antarctic ice sheet are poorly understood because of a lack of datable materials radiocarbon reservoir ages and severe environments direct evidence of the timing of ice retreat is important in order to understand the antarctic contribution to global sea level rise since the last glacial maximum here we report the first exposure ages constraining the timing of the last deglaciation from lutzow holm bay east antarctica our data suggest that the final retreat of the ice sheet in the region occurred rapidly in the early holocene and the reduction of the ice thickness in the region was at least 350 m this occurred after the major northern hemisphere deglaciation copyright 2011 john wiley sons ltd

geomorphological evidence of cold based glacier activity in south victoria land antarctica cold based glaciers have long been recognized as capable of covering and protecting landscapes however recent studies of modern cold based glaciers in antarctica show that in some situations erosion deformation and deposition can occur recognizing the dual ability of cold based glaciers to protect and preserve surfaces on the one hand and erode and modify on the other is important for correctly interpreting the often subtle imprint of cold based glaciers on landscapes a range of geomorphological features related to cold based glacier activity has now been documented along with an improved understanding of cold based glacier structure processes and interaction with various substrates collectively this provides an enhanced ability to understand the impact of cold based glaciers on landscapes and reappraise the geomorphological record such insight allows recognition of previously unknown glacial events and better interpretations of the landscape exposure record this is particularly important at the margins of the antarctic ice sheets where past fluctuations in ice sheet volume and its contributions to post glacial sea level rise are poorly constrained this paper reviews the known geomorphological evidence associated with cold based glaciers in the south victoria land region of the transantarctic mountains it aims to provide progress towards a set of criteria for recognizing cold based glacier activity in other regions and to highlight the implications of cold based glacial activity for surface exposure studies and interpreting glacial history cold based glaciers are below pressure melting point throughout and are therefore frozen to the substrate and move primarily by internal deformation drewry 1986 this led to the long standing view that cold based glaciers cannot slide and are thus incapable of erosion and deposition and therefore protect the underlying surface while numerous studies have shown this to be true in many situations recent investigations of modern cold based glaciers have revealed that in some circumstances complex processes operate at subfreezing temperatures in the basal zone and that cold based glaciers can generate a variety of geomorphological features these studies have forced a reappraisal of the geomorphic effectiveness of cold based glaciers and have confirmed that they can both protect and modify landscapes e g fitzsimons 1996 atkins et al 2002 fitzsimons 2003 waller et al 2012 thus the debate has moved on and the challenge now is to understand the full range of processes and products associated with cold based glaciers and the implications for landscape development hambrey fitzsimons 2010 waller et al 2012 recognizing the often subtle features indicative of cold based glacial activity offers the potential to delineate and date previously unknown or poorly constrained glacial events this is particularly relevant for interpreting glacial history and modelling ice sheet reconstructions for example numerous surface exposure dating studies have been carried out on ice marginal landforms with the aim of constraining past variations in the ice sheet volume however many of these studies have produced inconsistent contradictory results including evidence of complex exposure histories suggesting episodes of burial and reworking by cold based ice e g strasky et al 2008 di nicola et al 2009 compared with warm based glaciers there are still relatively few studies of cold based glaciers and significant gaps in our understanding of the processes and products remains in addition lingering misconceptions regarding the geomorphic effectiveness of cold based glaciers and historic use of ambiguous terminology to describe cold based sediments and landforms mean that the evidence and implications of past cold based glacial events have yet to be fully appreciated by the wider geomorphological community this review provides a summary of known geomorphological features associated with cold based glaciers in the south victoria land region of antarctica it aims to provide a basis for recognizing similar features elsewhere and attempts to draw attention to the implications of cold based glacial geomorphology for the correct application of surface exposure dating studies and interpretation of cold based glacial history

lake ice conveyor deposits geomorphology sedimentology and importance in reconstructing the glacial history of the dry valleys during the last glacial maximum lgm lake ice conveyors transported glacial debris across the surface of large proglacial lakes in the dry valleys region of antarctica the resulting sediments and landform assemblages are keys to interpreting the glacial history of the dry valleys and potentially other areas of antarctica paleoconveyor deposits occur in taylor miers wright and victoria valleys as well as in many other parts of the region sediments typically consist of stratified to massive sand and or silt grading upward into poorly sorted gravel cobbles and boulders these sediments make up a variety of landforms including mounds and moat line cross valley and longitudinal ridges the classic landform assemblage also displays an associated moraine bank as well as deltas and shorelines

repeated pleistocene glaciation of the east siberian continental margin during glacial periods ice sheets covered continental margins through much of arctic north america greenland and western eurasia marine structures suggest that an ice sheet up to a kilometre in depth periodically covered the east siberian continental shelf as well

late quaternary paleoenvironmental records from the chatanika river valley near fairbanks alaska abstract perennially frozen deposits are considered as excellent paleoenvironmental archives similar to lacustrine deep marine and glacier records because of the long term and good preservation of fossil records under stable permafrost conditions a permafrost tunnel in the vault creek valley chatanika river valley near fairbanks exposes a sequence of frozen deposits and ground ice that provides a comprehensive set of proxies to reconstruct the late quaternary environmental history of interior alaska the multi proxy approach includes different dating techniques radiocarbon accelerator mass spectrometry ams 14 c optically stimulated luminescence osl thorium uranium radioisotope disequilibria 230 th u as well as methods of sedimentology paleoecology hydrochemistry and stable isotope geochemistry of ground ice the studied sequence consists of 36 m thick late quaternary deposits above schistose bedrock main portions of the sequence accumulated during the early and middle wisconsin periods the lowermost unit a consists of about 9 m thick ice bonded fluvial gravels with sand and peat lenses a late sangamon mis 5a age of unit a is assumed spruce forest with birch larch and some shrubby alder dominated the vegetation high presence of sphagnum spores and cyperaceae pollen points to mires in the vault creek valley the overlying unit b consists of 10 m thick alternating fluvial gravels loess like silt and sand layers penetrated by small ice wedges osl dates support a stadial early wisconsin mis 4 age of unit b pollen and plant macrofossil data point to spruce forests with some birch interspersed with wetlands around the site the following unit c is composed of 15 m thick ice rich loess like and organic rich silt with fossil bones and large ice wedges unit c formed during the interstadial mid wisconsin mis 3 and stadial late wisconsin mis 2 as indicated by radiocarbon ages post depositional slope processes significantly deformed both ground ice and sediments of unit c pollen data show that spruce forests and wetlands dominated the area the macrofossil remains of picea larix and alnus incana ssp tenuifolia also prove the existence of boreal coniferous forests during the mid wisconsin interstadial which were replaced by treeless tundra steppe vegetation during the late wisconsin stadial unit c is discordantly overlain by the 2 m thick late holocene deposits of unit d the pollen record of unit d indicates boreal forest vegetation similar to the modern one the permafrost record from the vault creek tunnel reflects more than 90 ka of periglacial landscape dynamics triggered by fluvial and eolian accumulation and formation of ice wedge polygons and post depositional deformation by slope processes the record represents a typical wisconsin valley bottom facies in central alaska

landscape evolution degrades the geologic signature of past glaciations glaciers on land leave behind characteristic landforms and bedrock topography the spatial extent of this signature and dating of the erosional and depositional features has led to a good understanding of temporal and spatial shifts of past glaciers and climate at best the landscape contains considerable information on past glacial processes in the form of moraines and other depositional landforms however evidence suggests that all unconsolidated landforms degrade manifested in the general degradation and smoothing of the topography over time to determine the relative amount and pattern of degradation on glacial moraines we use a well documented moraine degradation model that uses both local slope and a proportionality constant to determine the diamicton transport rate this formulation results in diffusion type topographic smearing and smoothing of the initially angular topographic features more specifically diamicton is eroded at the crest of a moraine transported downhill and deposited on the gentler lower flank collectively this produces moraine cross profiles that closely resemble observations in the field by assuming an initial constant boulder frequency per unit volume of the diamicton the model tracks the surface lowering and the related exhumation of boulders to the moraine surface this produces a tightly constrained set of testable predictions 1 modelled moraine cross profile 2 modelled spatial pattern of surface boulders no boulders on the lower flank and 3 relative frequency of surface boulders smallest frequency of surface boulders at the inflection point highest frequency at the crest these characteristics were measured in the field of alpine tropical and antarctic moraines the correspondence between model predictions and field data is remarkably good and strongly supports our understanding of the time dependent evolution of glacial landscapes these results highlight the evolving nature of glacial landforms and indicate the complete removal of original moraine surfaces and postglacial emergence of spatial pattern in boulder frequency

holocene climate changes in eastern beringia nw north america a systematic review of multi proxy evidence abstract reconstructing climates of the past relies on a variety of evidence from a large number of sites to capture the varied features of climate and the spatial heterogeneity of climate change this review summarizes available information from diverse holocene paleoenvironmental records across eastern beringia alaska westernmost canada and adjacent seas and it quantifies the primary trends of temperature and moisture sensitive records based in part on midges pollen and biogeochemical indicators compiled in the recently published arctic holocene database and updated here to v2 1 the composite time series from these proxy records are compared with new summaries of mountain glacier and lake level fluctuations terrestrial water isotope records sea ice and sea surface temperature analyses and peatland and thaw lake initiation frequencies to clarify multi centennial to millennial scale trends in holocene climate change to focus the synthesis the paleo data are used to frame specific questions that can be addressed with simulations by earth system models to investigate the causes and dynamics of past and future climate change this systematic review shows that during the early holocene 11 7 8 2 ka 1 ka 1000 cal yr bp rather than a prominent thermal maximum as suggested previously temperatures were highly variable at times both higher and lower than present approximate mid 20th century average with no clear spatial pattern composited pollen midge and other proxy records average out the variability and show the overall lowest summer and mean annual temperatures across the study region during the earliest holocene followed by warming over the early holocene the sparse data available on early holocene glaciation show that glaciers in southern alaska were as extensive then as they were during the late holocene early holocene lake levels were low in interior alaska but moisture indicators show pronounced differences across the region the highest frequency of both peatland and thaw lake initiation ages also occurred during the early holocene during the middle holocene 8 2 4 2 ka glaciers retreated as the regional average temperature increased to a maximum between 7 and 5 ka as reflected in most proxy types following the middle holocene thermal maximum temperatures decreased starting between 4 and 3 ka signaling the onset of neoglacial cooling glaciers in the brooks and alaska ranges advanced to their maximum holocene extent as lakes generally rose to modern levels temperature differences for averaged 500 year time steps typically ranged by 1 2 c for individual records in the arctic holocene database with a transition to a cooler late holocene that was neither abrupt nor spatially coherent the longest and highest resolution terrestrial water isotope records previously interpreted to represent changes in the aleutian low pressure system around this time are here shown to be largely contradictory furthermore there are too few records with sufficient resolution to identify sub centennial scale climate anomalies such as the 8 2 ka event the review concludes by suggesting some priorities for future paleoclimate research in the region

tephra analysis in ombrotrophic peatlands a geochemical comparison of acid digestion and density separation techniques ombrotrophic peatlands often lack any substantial local mineral component and therefore present exceptional opportunities for the extraction and identification of tephra horizons following concerns of shard geochemistry alteration during isolation using acid digestion an alternative methodology using heavy liquids has been proposed however harsh basic and acidic digestions are rarely required in organic rich ombrotrophic peatlands consequently this study tested for geochemical differences between tephra shards from a known rhyolitic eruption isolated from the same stratigraphic depth of a peat sequence using density separation and an acid digestion methodology typically applied to ombrotrophic peat samples and analysed using electron probe microanalysis findings suggest that the two samples could not be geochemically distinguished using visual and statistical methods and that in the context of rhyolitic tephras in ombrotrophic peats acid digestion can be used without significant effects on the interpretation of results density separation may still be required in peatlands with high mineral input and further work is required to examine the effect of the acid digestion technique on tephra of non rhyolitic compositions copyright 2015 john wiley sons ltd

provenance analysis of central arctic ocean sediments implications for circum arctic ice sheet dynamics and ocean circulation during late pleistocene abstract mineralogical and geochemical data generated from the well referred shallow core 96 12 1pc on the lomonosov ridge central arctic ocean was used to evaluate ice transport from the circum arctic sources and variability in sediment drainage and provenance changes in this study heavy minerals in central arctic sediments were used to determine those most prominent provenance areas and their changes related to the late pleistocene history of glaciations in the arctic provenance changes were then used to infer variations in the paleoceanographic environment of the central arctic ocean such as variations in the distribution of sea ice icebergs controlled by the arctic ocean circulation four critical end members including victoria and banks islands the putorana plateau the anabar shield and the verkhoyansk fold belt were identified from the amerasian and eurasian source areas and their proportional contributions were estimated in relation to late pleistocene ice sheet dynamics and ocean circulation the results show changes in transport pathways and source areas within two examined transitions mis6 5 and mis4 3 the main source for material during mis6 5 transition was amerasian margin due to the high dolomite content in the studied section of sediments inferring strong beaufort gyre bg and transpolar drift tpd transport for this material ird material during late the mis6 to 5 deglacial event was from terrigenous input through from the mackenzie route banks victoria islands then transported as far as the lomonosov ridge area the transition mis4 3 in comparison with mis6 5 shows a clear shift in source areas reflected in a different mineralogical composition of sediments supplied from the eurasian margin such as the anabar shield the putorana plateau and the verkhoyansk fold belt during active decay of the barents kara ice sheet presumable associated with an ice dammed lake outburst then triggered by a strong tpd over the central arctic these two studied deglaciations suggest that contributions of different circum arctic sediment sources are related to interaction between ice sheet decay sea ice production and circulation

glacial lake victoria a high level antarctic lake inferred from lacustrine deposits in victoria valley we present evidence of a large lake glacial lake victoria that existed in victoria valley in the dry valleys region of antarctica between at least 20 000 and 8600 14c yr bp at its highstands glacial lake victoria covered 100 km2 and was ca 200 m deep the chronology for lake level changes comes from 87 ams radiocarbon dates of lacustrine algae preserved in deltas and glaciolacustrine deposits that extend up to 185 m above present day lakes on the valley floor the existence of glacial lake victoria as well as other large lakes in the dry valleys indicates a climate regime significantly different from that of today at the last glacial maximum and in the early holocene copyright 2002 john wiley sons ltd

glacial isostatic adjustment associated with the barents sea ice sheet a modelling inter comparison the 3d geometrical evolution of the barents sea ice sheet bsis particularly during its late glacial retreat phase remains largely ambiguous due to the paucity of direct marine and terrestrial based evidence constraining its horizontal and vertical extent and chronology one way of validating the numerous bsis reconstructions previously proposed is to collate and apply them under a wide range of earth models and to compare prognostic isostatic output through time with known relative sea level rsl data here we compare six contrasting bsis load scenarios via a spherical earth system model and derive a best fit 2 parameter using rsl data from the four main terrestrial regions within the domain svalbard franz josef land novaya zemlya and northern norway poor 2 values allow two load scenarios to be dismissed leaving four that agree well with rsl observations the remaining four scenarios optimally fit the rsl data when combined with earth models that have an upper mantle viscosity of 0 2 2 1021 pa s while there is less sensitivity to the lithosphere thickness ranging from 71 to 120 km and lower mantle viscosity spanning 1 50 1021 pa s gps observations are also compared with predictions of present day uplift across the barents sea key locations where relative sea level and gps data would prove critical in constraining future ice sheet modelling efforts are also identified

rapid sediment accumulation and microbial mineralization in forests of the mangrove kandelia candel in the jiulongjiang estuary china abstract rates of sediment accumulation and microbial mineralization were examined at three kandelia candel forests spanning the intertidal zone along the south coastline of the heavily urbanized jiulongljiang estuary fujian province china mass sediment accumulation rates were rapid range 10 62 kg m 2 y 1 but decreased from the low to the high intertidal zone high levels of radionuclides suggest that these sediments originate from erosion of agricultural soils within the catchment mineralization of sediment carbon and nitrogen was correspondingly rapid with total rate of mineralization ranging from 135 to 191 mol c m 2 y 1 and 9 to 11 mol n m 2 y 1 rates were faster in summer than in autumn winter rates of mineralization efficiency 70 93 for c 69 92 for n increased as burial efficiency 7 30 for c 8 31 for n decreased from the low to the high intertidal mangroves sulphate reduction was the dominant metabolic pathway to a depth of 1 m with rates 19 281 mmol s m 2 d 1 exceeding those measured in other intertidal deposits there is some evidence that fe and mn reduction oxidation cycles are coupled to the activities of live roots within the 0 40 cm depth horizon oxic respiration accounted for 5 12 of total carbon mineralization methane flux was slow and highly variable when detectable range 5 66 mol ch 4 m 2 d 1 nitrous oxide flux was also highly variable but within the range 1 6 106 5 mol n 2 o m 2 d 1 measured in other intertidal sediments rates of denitrification were rapid ranging from 1106 to 3780 mol n 2 m 2 d 1 and equating to 11 20 of total sediment nitrogen inputs denitrification was supported by rapid nh 4 release within surface deposits range 3 6 6 1 mmol m 2 d 1 our results support the notion that mangrove forests are net accumulation sites for sediment and associated elements within estuaries especially kandelia candel forests receiving significant inputs as a direct result of intense human activity along the south china coast

chronology of taylor glacier advances in arena valley antarctica using in situ cosmogenic 3he and 10be abstract in situ produced cosmogenic nuclides provide a new technique for constraining exposure ages of glacial deposits in situ3he and 10be in quartz sandstone boulders from arena valley southern victoria land antarctica provide chronological constraints for a sequence of moraines taylor ii ivb moraines related to expansions of taylor glacier and the east antarctic ice sheet mean 3he ages are 113 000 45 000 yr 208 000 67 000 yr 335 000 187 000 yr and 1 2 0 2 myr for taylor ii iii iva and ivb moraines respectively mean 1 corresponding mean 10be ages for taylor ii and ivb moraines are 117 000 51 000 yr and 2 1 0 1 myr for the older deposits the 3he ages are probably lower limits due to diffusive loss although the exposure ages appear consistent with the few previous age estimates particularly with an isotope stage 5 age for taylor ii each moraine exhibits a broad age distribution the distribution probably results from a variety of factors which may include prior exposure to cosmic rays 3he loss erosion postdepositional boulder movement and radiogenic production of 3he nonetheless the exposure ages provide direct chronological constraints for the moraine sequence and suggest a maximum thickening of taylor glacier relative to the present ice surface of 500 m since the late pliocene early pleistocene

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

scaling time integrated in situ cosmogenic nuclide production rates using a continuous geomagnetic model abstract spatial and temporal variations in earth s magnetic field affect the corresponding time integrated distribution of in situ cosmogenic nuclide cn production rates these effects can be quantified by the effective vertical cutoff rigidity r c a measure of the energy required for primary cosmic rays to penetrate the geomagnetic field and interact with the atmosphere at a given location recent cn production rate scaling models are based on atmospheric cosmic ray measurements parameterized using r c estimates derived from detailed modern geomagnetic field representations which include both dipole and non dipole field contributions however published methods for quantifying time integrated geomagnetic effects on cn production rate scaling rely on various geocentric dipolar approximations to r c driven by separate records of paleomagnetic pole position and paleointensity therefore applying dipolar paleomagnetic records spanning millennial time scales which explicitly ignore past non dipole effects to scaling models derived using modern geomagnetic field representations may lead to systematic errors in any calculated results a recently published continuous geomagnetic model covering the last 7 kyr cals7k 2 m korte and c g constable continuous geomagnetic field models for the past 7 millennia 2 cals7k 2005 geochem geophys geosyst 6 q02h16 doi 10 1029 2004gc000801 may allow reduction of such errors by bridging the gap between detailed modern geomagnetic and simplified paleomagnetic models we have developed a new model framework describing temporal and spatial variation in r c for 0 7 ka and earlier based on cals7k 2 which explicitly accounts for non dipole field effects while attempting to mitigate systematic scaling biases scaling factors derived using the new r c framework predict significant longitudinal variability in time integrated cn production while predictions using dipolar geomagnetic approximations do not one can test these predictions using in situ cosmogenic 14 c in situ 14 c in quartz due to its short half life 5 73 kyr 14 c attains secular equilibrium between production and decay after approximately 25 kyr of exposure at which point its measured concentration is only a function of its integrated average production rate initial in situ 14 c results from samples at secular equilibrium from 38 n and 3 5 km in tibet and eastern california are consistent with the longitudinal variability predicted by the new framework

210pb sediment radiochronology an integrated formulation and classification of dating models abstract environmental archives such as sediments banded corals and tree rings are widely used to reconstruct past environmental conditions of ecosystems in particular 210 pb has been used during more than 4 decades through dating of undisturbed sediment cores to study ecosystem changes during the last 100 yr since its inception diverse dating models have been proposed developed used and validated in numerous environments but their nomenclature and formulation is not homogenous in this work we emphasize that conceptual models used to date undisturbed sediment cores can be deduced from a single fundamental equation which relates excess 210 pb concentration in sediment its flux to the sediment surface and mass accumulation rate from this equation models were consistently named based on the main hypothesis used and using a unified and logical nomenclature dating equations were derived in detail we applied in detail most of the described models to a sediment core from mexico and uncertainty expressions were also included finally some recommendations to use the models are proposed we believe that this work can facilitate the use of 210 pb as a tool to date sediment cores in a more homogeneous way

cosmogenic evidence for limited local lgm glacial expansion denton hills antarctica abstract the geomorphology of the denton hills provides insight into the timing and magnitude of glacial retreats in a region of antarctica isolated from the influence of the east antarctic ice sheet we present 26 beryllium 10 surface exposure ages from a variety of glacial and lacustrine features in the garwood and miers valleys to document the glacial history of the area from 10 to 286 ka our data show that the cold based miers joyce and garwood glaciers retreated little since their maximum positions at 37 2 6 9 1 n 4 35 1 1 5 1 n 3 and 35 6 10 1 1 n 6 ka respectively the similar timing of advance of all three glaciers and the lack of a significant glacial expansion during the global lgm suggests a local lgm for the denton hills between ca 26 and 51 ka with a mean age of 36 0 7 5 1 n 13 ka a second cohort of exposure ages provides constraints to the behaviour of glacial lake trowbridge that formerly occupied miers valley in the late pleistocene these data show active modification of the landscape from 20 ka until the withdrawal of ice from the valley mouths and deposition of ross sea drift at 10 14 ka

paleo environmental gateways in the eastern canadian arctic recent isotope hydrology and diatom oxygen isotopes from nettilling lake baffin island canada abstract nettilling lake is located on baffin island nunavut canada between the areas of past warming canadian high arctic to the north and climatic stability northern quebec and labrador region to the south despite being the largest lake in the nunavut region with a postglacial marine to lacustrine transition history only a few paleo environmental investigations were completed in this area the oxygen isotope composition of diatoms 18odiatom can provide valuable insights into paleo environmental conditions here the recent isotope hydrology and hydrochemical data from the lake are presented to facilitate the interpretation of a 18odiatom record from an 82 cm sediment core ni 2b the well mixed lake 18owater 17 4 is influenced by a heavier less negative isotope composition 18 80 from amadjuak river draining amadjuak lake to the south and water of lighter more negative isotopic composition 16 4 from the isurtuq river originating from penny ice cap in the north east from the 18owater and 18odiatom of the topmost sample of core ni 2b a 18osilica water of 1000 ln silica water 40 2 for sub recent diatoms of nettilling lake was calculated matching the known water silica fractionation for fossil sediments well and thereby showing the general applicability of this proxy for paleo reconstructions in this region extremely large 18odiatom variations in the core of more than 13 are mainly induced by changes in the isotopic composition of the lake water due to a shift from glaciomarine 18odiatom 34 6 through brackish 23 4 to 27 2 towards lacustrine 21 5 conditions transition zones glaciomarine to brackish at 69 cm 7300 yr cal bp and brackish to lacustrine at 35 cm 6000 yr cal bp associated with a shift in the degree of salinity our study provides the first evidence that paleo salinity can be reconstructed by 18odiatom additionally for the lacustrine section it could be demonstrated that 18odiatom may serve as a proxy for past air temperature within the same core recording a late holocene cooling of about 4 c being consistent with other published values for the greater baffin region

constraints on age erosion and uplift of neogene glacial deposits in the transantarctic mountains determined from in situ cosmogenic 10be and 26al 10 be and 26 al data from sandstone boulders in three neogene glacial deposits in the mcmurdo sound dry valleys region of southern victoria land antarctica indicate minimum exposure ages of approx 3 ma and maximum long term erosion rates of approx 5 12 cm m y supporting the suggestion that polar desert conditions have persisted in the dry valleys since at least late pliocene time variation of cosmogenic nuclide production rate with altitude also allows constraints on past uplift rates model calculations employing 10 be data indicate little or no uplift in the dry valleys region in the past 3 m y precluding rapid 1 km m y late pliocene uplift previously suggested for some parts of the transantarctic mountains

cosmogenic nuclide exposure ages and glacial history of late quaternary ross sea drift in mcmurdo sound antarctica 3he 10be and26al surface exposure ages were determined for rock samples from late quaternary drift sheets deposited on the coast of mcmurdo sound antarctica by the ross sea ice sheet the youngest drift previously believed to be late wisconsin in age has exposure ages of 8 106 kyr 19 samples these results suggest that the apparent late wisconsin ice margin may represent a number of ice sheet advances during the last glacial period 3he exposure ages from analogous stratigraphically older drift range from 104 to 567 kyr seven samples and clearly distinguish the youngest drift from older deposits comparison of10be and3he concentrations in ross sea drift quartz samples indicates significant3he loss in only one sample suggesting that cosmogenic3he is generally retained in young antarctic quartz samples exposure age 100 kyr of appropriate grain size in two of the five quartz samples analyzed significant excesses of26al relative to10be preclude meaningful26al exposure age calculations these excesses may be due to nucleogenic26al produced as a byproduct of uranium and thorium decay

east antarctic deglaciation and the link to global cooling during the quaternary evidence from glacial geomorphology and 10be surface exposure dating of the sor rondane mountains dronning maud land abstract reconstructing past variability of the antarctic ice sheets is essential to understand their stability and to anticipate their contribution to sea level change as a result of future climate change recent studies have reported a significant decrease in thickness of the east antarctic ice sheet eais during the last several million years however the geographical extent of this decrease and subsequent isostatic rebound remain uncertain in this study we reconstruct the magnitude and timing of ice sheet retreat at the sor rondane mountains in dronning maud land east antarctica based on detailed geomorphological survey cosmogenic exposure dating and glacial isostatic adjustment modeling three distinct deglaciation phases are identified for this sector during the quaternary based on rock weathering and 10 be surface exposure data we estimate that the ice sheet thinned by at least 500 m during the pleistocene this thinning is attributed to the reorganization of southern ocean circulation associated with global cooling into the pleistocene which reduced the transport of moisture from the southern ocean to the interior of eais the data also show that since the last glacial maximum the ice surface has lowered less than ca 50 m and that this lowering probably started after ca 14 ka this suggests that the eais in dronning maud land is unlikely to have been a major contributor to postglacial sea level rise and meltwater pulse 1a

seismic architecture and evolution of the disko bay trough mouth fan central west greenland margin abstract the present study is the first to document the large scale glacigenic evolution of a west greenland trough mouth fan tmf system i e the disko bay tmf from onset of shelf based glaciation to present we have constrained the paleo ice sheet configuration in the disko bay region and determine the controlling factors of ice stream development using 2d and 3d seismic reflection data seabed bathymetry and stratigraphic information from two exploration wells this has revealed three stages of the disko bay tmf development the early stage probably of pliocene early pleistocene age marks the onset of a central depocentre located below the modern mid shelf and constructed by sediment progradation delivered through at least two erosive pathways related to fast flowing grounded ice at that time ice stream routing in the disko bay shelf region was strongly controlled by the pre glacial topography and structural boundaries associated with fracture zones and deep seated faults during the middle evolutionary stage the focus of deposition shifted from the mid shelf to two elongate areas fringing the outer margin the marginal depocentres were not only related to glacial processes but also alongslope deposition by contour currents which may have developed as a consequence of basin subsidence surrounding the davis strait high and the kangerluk structure the late stage of tmf development presumably representing the late pleistocene to holocene is characterized by the marginal depocentres becoming less significant and sediment aggradation occurring over wide parts of the mid outer shelf while features of subglacial erosion are generally absent in contrast to the inferred fast flowing ice streams of the early middle evolutionary stages this points to the existence of a rather thin and lightly grounded ice sheet i e at the threshold of floatation the lightly grounded ice sheet scenario applying to the late pleistocene interval of the disko bay tmf was possibly associated with floating ice shelves during periods of maximum cooling while intermittent and short lived advances of grounded ice streams may have occurred during interstadial stadial climate transitions a controlling factor for the development of the aggradational stage may relate to the prominent basement ridge that separates the disko trough from the egedesminde dyb depression we suggest that a neotectonic emergence of the ridge gradually restricted the flow of ice through the central disko trough forcing glaciers to diverge along the entire length of the ridge and find complementary drainage routes

holocene climate change in arctic canada and greenland abstract this synthesis paper summarizes published proxy climate evidence showing the spatial and temporal pattern of climate change through the holocene in arctic canada and greenland our synthesis includes 47 records from a recently published database of highly resolved holocene paleoclimate time series from the arctic sundqvist et al 2014 we analyze the temperature histories represented by the database and compare them with paleoclimate and environmental information from 54 additional published records mostly from datasets that did not fit the selection criteria for the arctic holocene database combined we review evidence from a variety of proxy archives including glaciers ice cores and glacial geomorphology lake sediments peat sequences and coastal and deep marine sediments the temperature sensitive records indicate more consistent and earlier holocene warmth in the north and east and a more diffuse and later holocene thermal maximum in the south and west principal components analysis reveals two dominant holocene trends one with early holocene warmth followed by cooling in the middle holocene the other with a broader period of warmth in the middle holocene followed by cooling in the late holocene the temperature decrease from the warmest to the coolest portions of the holocene is 3 0 1 0 c on average n 11 sites the greenland ice sheet retracted to its minimum extent between 5 and 3 ka consistent with many sites from around greenland depicting a switch from warm to cool conditions around that time the spatial pattern of temperature change through the holocene was likely driven by the decrease in northern latitude summer insolation through the holocene the varied influence of waning ice sheets in the early holocene and the variable influx of atlantic water into the study region

holocene ice wedge polygon development in northern yukon permafrost peatlands canada ice wedge polygon iwp peatlands in the arctic and subarctic are extremely vulnerable to climatic and environmental change we present the results of a multidisciplinary paleoenvironmental study on iwps in the northern yukon canada high resolution laboratory analyses were carried out on a permafrost core and the overlying seasonally thawed active layer from an iwp located in a drained lake basin on herschel island in relation to 14 accelerator mass spectrometry ams radiocarbon dates spanning the last 5000 years we report sedimentary data including grain size distribution and biogeochemical parameters organic carbon nitrogen c n ratio d13c stable water isotopes d18o dd as well as fossil pollen plant macrofossil and diatom assemblages three sediment units sus correspond to the main stages of deposition 1 in a thermokarst lake su1 4950 to 3950 cal yrs bp 2 during transition from lacustrine to palustrine conditions after lake drainage su2 3950 to 3120 cal yrs bp and 3 in palustrine conditions of the iwp field that developed after drainage su3 3120 cal yrs bp to 2012 ce the lacustrine phase pre 3950 cal yrs bp is characterized by planktonic benthic and pioneer diatom species indicating circumneutral waters and very few plant macrofossils the pollen record has captured a regional signal of relatively stable vegetation composition and climate for the lacustrine stage of the record until 3950 cal yrs bp palustrine conditions with benthic and acidophilic diatom species characterize the peaty shallow water environments of the low centered iwp the transition from lacustrine to palustrine conditions was accompanied by acidification and rapid revegetation of the lake bottom within about 100 years since the palustrine phase we consider the pollen record as a local vegetation proxy dominated by the plant communities growing in the iwp ice wedge cracking in water saturated sediments started immediately after lake drainage at about 3950 cal yrs bp and led to the formation of an iwp mire permafrost aggradation through downward closed system freezing of the lake talik is indicated by the stable water isotope record the originally submerged iwp center underwent gradual drying during the past 2000 years this study highlights the sensitivity of permafrost landscapes to climate and environmental change throughout the holocene

holocene deglaciation of marie byrd land west antarctica surface exposure ages of glacial deposits in the ford ranges of western marie byrd land indicate continuous thinning of the west antarctic ice sheet by more than 700 meters near the coast throughout the past 10 000 years deglaciation lagged the disappearance of ice sheets in the northern hemisphere by thousands of years and may still be under way these results provide further evidence that parts of the west antarctic ice sheet are on a long term trajectory of decline west antarctic melting contributed water to the oceans in the late holocene and may continue to do so in the future

10be dating reveals early middle holocene age of the drygalski moraines in central west greenland abstract we reconstruct the history of the greenland ice sheet margin on the nuussuaq peninsula in central west greenland through the holocene using lake sediment analysis and cosmogenic 10 be exposure dating of the prominent drygalski moraines erratics perched on bedrock outboard of the drygalski moraines constrain local deglaciation to 9 9 0 6 ka n 2 three drygalski moraine crests yield mean 10 be ages of 8 6 0 4 ka n 2 8 5 0 2 ka n 3 and 7 6 0 1 ka n 2 from outer to inner perched erratics between the inner two moraines average 7 8 0 1 ka n 2 and are consistent with the moraine ages sediments from a proglacial lake with a catchment area extending an estimated 2 km beneath inland of the present ice sheet terminus constrain an ice sheet minimum extent from 5 4 ka to 0 6 ka the moraine chronology paired with the lake sediment stratigraphy reveals that the ice margin likely remained within 2 km of its present position from 9 9 to 5 4 ka this unexpected early holocene stability preceded by rapid ice retreat and followed by minimum ice extent between 5 4 and 0 6 ka contrasts with many records of early holocene warmth and the northern hemisphere summer insolation maximum we suggest ice margin stability may instead be tied to adjacent ocean temperatures which reached an optimum in the middle holocene

north atlantic fennoscandian holocene climate trends and mechanisms abstract to investigate the mechanisms behind holocene regional climate trends from north of 58 n in the north atlantic fennoscandian region principal component analysis pca was performed and a temperature anomaly stack produced from 81 proxy derived summer temperature time series from 74 sites the pc results show distinctly different trends for near surface versus surface temperatures demonstrating the importance of handling these separately the first pc of weighted sea surface summer temperature time series and continental time series explains 45 8 of the variance where the uncertainty is the standard deviation of the distribution of variance explained across the 1000 age uncertain ensemble members pc1 has a relatively uniform expression over the whole region closely following the summer insolation at 65 n the second pc explains 22 4 of the variance and shows a non uniform expression with loadings in opposite directions in the northern and southeastern parts of the region comparing the pc time series with model runs and with the timing of the demise of the laurentide ice sheet lis suggest that this pattern reflects both topographic and albedo effects of the lis as well as release of meltwater into the north atlantic and arctic oceans comparing the stack of gridded records with published global stacks reveals an unusual holocene temperature development in the north atlantic fennoscandian region most likely resulting from the location relative to the decaying lis

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

ice elevation near the west antarctic ice sheet divide during the last glaciation 1 interior ice elevations of the west antarctic ice sheet wais during the last glaciation which can serve as benchmarks for ice sheet models are largely unconstrained here we report past ice elevation data from the ohio range located near the wais divide and the onset region of the mercer ice stream cosmogenic exposure ages of glacial erratics that record a wais highstand 125 m above the present surface date to 11 5 ka the deglacial chronology prohibits an interior wais contribution to meltwater pulse 1a our observational data of ice elevation changes compare well with predictions of a thermomechanical icesheet model that incorporates very low basal shear stress downstream of the present day grounding line we conclude that ice streams in the ross sea embayment had thin lowslope profiles during the last glaciation and interior wais ice elevations during this period were several hundred meters lower than previous reconstructions citation ackert r p jr s mukhopadhyay b r parizek and h w borns 2007 ice elevation near the west antarctic ice sheet divide during the last glaciation geophys res lett 34 l21506 doi 10 1029 2007gl031412

ice flow switching and east west antarctic ice sheet roles in glaciation of the western ross sea the long term behavior of the east and west antarctic ice sheets and their respective responses to forcing provide essential context for assessment of modern dynamic changes in ice flow regimes and ice sheet and shelf margins the western ross sea discharges ice from both the east and west antarctic ice sheets and the paleoglacial record from this region is therefore valuable in unraveling their long term behavior new high resolution multibeam bathymetric data reveal snapshots of well preserved glacial landforms on the seafloor around ross island and mcmurdo sound glacial lineations grounding zone wedges draped recessional moraines and meltwater channels record a series of different ice flow events in the region contradictions between which require major phases of ice flow reorganization from the glacial geomorphology we reconstruct a four stage model of ice flow evolution for the last glacial cycle consisting of 1 northeastward flow into the ross sea from mcmurdo sound 2 westward flow from the ross sea around ross island and onto the victoria land coast and coastal seafloor trough 3 a deglacial phase of ice sheet thinning minor shifts in flow and grounding line retreat into mcmurdo sound and 4 grounding line pinning on ross island during regional retreat uncoupling of a remnant ross island ice cap and local oscillation of victoria land outlet glaciers we find that east antarctic ice sheet ice discharge had a strong influence on ice flow geometry in this part of the ross sea during the last glacial stage but that it was not necessarily in phase with the behavior of the west antarctic ice sheet it is similarly evident that the ice streams that drained the ross sea over the continental shelf at the last glacial maximum did not all operate synchronously and exerted different drawdown power at different times finally we conclude that ross island acts as an important pinning point in the ross sea ice sheet shelf system stabilizing grounding line retreat and encouraging lasting ice shelf development

exposure ages from mountain dipsticks in mac robertson land east antarctica indicate little change in ice sheet thickness since the last glacial maximum past changes in east antarctic ice sheet eais volume are poorly known and diffi cult to measure yet are critical for predicting the response of the ice sheet to modern climate change in particular it is important to identify the sources of sea level rise since the last glacial maximum lgm and ascertain the present day stability of the world s largest ice sheet we present altitudinal transects of 10 be and 26 al exposure ages across the framnes mountains in mac robertson land that allow the magnitude and timing of eais retreat to be quantifi ed our data show that the coastal eais thinned by at most 350 m in this region during the past 13 k y this reduction in ice sheet volume occurred over a 5 k y period and the present icesheet profi le was attained ca 7 ka in contrast to the west antarctic ice sheet which continues to retreat today combined with regional offshore and terrestrial geologic evidence our data suggest that the reduction in eais volume since the lgm was smaller than that indicated by contemporary ice sheet models and added little meltwater to the global oceans stability of the ice margin since the middle holocene provides support for the hypothesis that eais volume changes are controlled by growth and decay of northern hemisphere ice sheets and associated global sea level changes

reconstruction of ice sheet changes in the antarctic peninsula since the last glacial maximum this paper compiles and reviews marine and terrestrial data constraining the dimensions and configuration of the antarctic peninsula ice sheet apis from the last glacial maximum lgm through deglaciation to the present day these data are used to reconstruct grounding line retreat in 5 ka time steps from 25 ka bp to present glacial landforms and subglacial tills on the eastern and western antarctic peninsula ap shelf indicate that the apis was grounded to the outer shelf shelf edge at the lgm and contained a series of fast flowing ice streams that drained along cross shelf bathymetric troughs the ice sheet was grounded at the shelf edge until 20 cal ka bp chronological control on retreat is provided by radiocarbon dates on glacimarine sediments from the shelf troughs and on lacustrine and terrestrial organic remains as well as cosmogenic nuclide dates on erratics and ice moulded bedrock retreat in the east was underway by about 18 cal ka bp the earliest dates on recession in the west are from bransfield basin where recession was underway by 17 5 cal ka bp ice streams were active during deglaciation at least until the ice sheet had pulled back to the mid shelf the timing of initial retreat decreased progressively southwards along the western ap shelf the large ice stream in marguerite trough may have remained grounded at the shelf edge until about 14 cal ka bp although terrestrial cosmogenic nuclide ages indicate that thinning had commenced by 18 ka bp between 15 and 10 cal ka bp the apis underwent significant recession along the western ap margin although retreat between individual troughs was asynchronous ice in marguerite trough may have still been grounded on the mid shelf at 10 cal ka bp in the larsen a region the transition from grounded to floating ice was established by 10 7 10 6 cal ka bp the apis had retreated towards its present configuration in the western ap by the mid holocene but on the eastern peninsula may have approached its present configuration several thousand years earlier by the start of the holocene mid to late holocene retreat was diachronous with stillstands re advances and changes in ice shelf configuration being recorded in most places subglacial topography exerted a major control on grounding line retreat with grounding zone wedges and thus by inference slow downs or stillstands in the retreat of the grounding line occurring in some cases on reverse bed slopes