geochemistry of the holocene sediments of lake chenghai sw china and its implications for paleoenvironmental reconstruction abstract analysis of lake sediment geochemistry is valuable for understanding past hydroclimatic changes via the reconstruction of changes in catchment erosion chemical weathering redox processes and the intensity of evaporation in this study we analyzed the geochemical composition magnetic susceptibility and carbonate content of the holocene sediments of lake chenghai in the jinsha river valley southwest china our aims were to determine the influence of holocene hydroclimate evolution and geo hazards on lacustrine sedimentation the results show that the hydroclimate was generally humid during 7 57 4 65 cal ka bp and that subsequently it became relatively dry during 4 65 1 37 cal ka bp our results also reveal that the centennial scale variability of the lake level during the holocene is forced by changes in solar activity and oceanic atmospheric feedback in addition the interval of 3 31 1 95 cal ka bp was the driest due to highly variable and intense el nino events and the southward migration of the intertropical convergence zone furthermore three large landslide events occurred at 7 30 6 36 and 0 76 cal ka bp around lake chenghai which are correlated with unusually large floods during the period of weakened monsoon activity and or with earthquake events

geomorphological evidence of holocene climatic change from northwest ellesmere island canadian high arctic proxy data from the northern coast of ellesmere island are used to reconstruct holocene palaeoclimate and appear to corroborate the ice core record from the canadian and greenland high arctic despite some regional variation geomorphological evidence indicates that deglaciation was associated with a marked climatic amelioration in the late pleistocene early holocene 10 ka bp this contrasts with glaciers on the south side of grant land mountains which started to retreat at 7 5 ka bp perhaps due to significant differences in glacioclimatic regime and the influence of the arctic ocean indicators of sea ice conditions on northern ellesmere island suggest that the early holocene was a period of considerable open water radiocarbon dates on driftwood collected from behind the north coast ice shelves suggest that the ice shelves formed during a mid holocene climatic deterioration geomorphic evidence shows that the ice shelves are presently breaking up and melting in response to recent warming glaciers hav

spatial and temporal distribution of holocene temperature maxima in the northern nordic seas interplay of atlantic arctic and polar water masses abstract subsurface and bottom water temperatures on the western shelf of svalbard at 79 n are reconstructed in order to investigate the relative influence of warm atlantic water cold arctic polar water and meltwater during the holocene the study is based on sediment core np05 21gc which has been investigated for the distribution of planktic foraminiferal species oxygen and carbon isotopes measured in benthic and planktic foraminifera and subsurface and bottom water temperatures calculated from transfer functions the data are compared to several other records from the western margin of svalbard the results indicate that until 9600 years bp the water column west of svalbard was stratified by a pycnocline situated at a water depth of c 100 m on the shelf and at c 30 m on the slope the water mass above the pycnocline consisted of cold arctic polar water and meltwater whereas the water mass below the pycnocline consisted of warm atlantic water after 9600 the supply of arctic polar water and meltwater diminished weakening the pycnocline and from 9000 to 6000 years bp warm atlantic water occupied the entire water column the upper and deeper water masses experienced different holocene temperature maxima in the atlantic water the temperature maximum occurred during the early holocene 11 500 8200 years bp only interrupted by the cold pre boreal oscillation c 11 300 10 800 years bp the maximum was followed by a gradual temperature decrease until c 5000 years bp in the upper water masses the temperature maximum occurred from c 9000 6000 years bp the timing of the maximum here is influenced by the decreasing supply of cold arctic polar water versus the increasing dominance of atlantic water the temperatures of both the surface and bottom water decreased to a minimum from c 5000 2000 years bp during the last 2000 years conditions have been increasingly unstable although with slightly increasing subsurface temperatures

a constraint to the wisconsinan glacial history canadian arctic archipelago thick ice bearing permafrost is not observed today beneath the deeper channels of the central queen elizabeth islands canadian arctic archipelago analysis of a precision temperature log recently obtained at an offshore well near ellef ringnes island indicates that the thermal regime beneath the seabed is in equilibrium with today s marine environment if thick permafrost similar to that observed on land today had existed in the pleistocene in areas that are presently offshore then such permafrost must have started melting no later than 25000 years ago in order to allow the present thermal regime to evolve this suggests that the inter island channels must have been water filled at least by that date

the isotopic and hydrologic response of small closed basin lakes to climate forcing from predictive models application to paleoclimate studies in the upper columbia river basin simulations conducted using a coupled lake catchment hydrologic and isotope mass balance model indicate that small closed basin lakes in north central washington are isotopically sensitive to changes in precipitation relative humidity and temperature most notably model simulations predicted inconsistent lake responses to precipitation changes due to differences in lake outseepage rates and surface area to volume sa v ratios greater outseepage within model experiments resulted in increased sensitivity to changes in mean precipitation moreover simulations suggest that in lakes with appreciable outseepage sa v ratio changes resulting from lake level variations control the direction of changes in lake water oxygen isotope composition 18o specifically in lakes with a sa v ratio that increases at higher lake levels steady state 18o values will increase in response to greater long term average precipitation these results suggest that closed basin lakes with low outseepage rates will exhibit a transient isotopic response to stochastic variability in hydrologic forcing but will not strongly respond at steady state to variation in mean hydrologic conditions conversely closed basin lakes with appreciable outseepage will exhibit strong isotopic responses to both stochastic variability and variation in mean hydrologic conditions i e mean precipitation relative humidity and temperature control of catchment hydrologic inputs to the lake these relationships provide a mechanism for explaining inconsistencies in the isotopic responses of lakes within a given region to hydrologic forcing and demonstrate that semiquantitative models for describing the relationship between lake hydrologic and isotopic responses to climate variability are not appropriate for all closed basin lakes

climatic forcing of carbon oxygen isotopic covariance in temperate region marl lakes carbon and oxygen stable isotopic compositions of lacustrine carbonate from a southeastern michigan marl lake display linear covariance over a range of 4 0 peedee belemnite pdb in oxygen and 3 9 pdb in carbon mechanisms of delta 13 c delta 18 o coupling conventionally attributed to lake closure in arid region basins are inapplicable to hydrologically open lake systems thus an alternative explanation of isotopic covariance in temperate region dimictic marl lakes is required we propose that isotopic covariance is a direct record of change in regional climate in short residence time temperate region lake basins summer meteoric precipitation is enriched in 18o relative to winter values and summer organic productivity enriches epilimnic dissolved inorganic carbon in 13c thus climate change toward longer summers and or shorter winters could result in greater proportions of warm month meteoric precipitation longer durations of warm month productivity and net long term enrichment in carbonate 18o and 13c isotopic covariance observed in the michigan marl lake cores is interpreted to reflect postglacial warming from 10 to 3 ka followed by cooler mean annual temperature a shift toward greater proportions of seasonal summer precipitation a shortening of the winter season or some combination of these three factors

nonuniform response of the major surface currents in the nordic seas to insolation forcing implications for the holocene climate variability 1 high resolution sediment cores from the voring plateau the north iceland shelf and the east greenland shelf have been studied to investigate the stability of major surface currents in the nordic seas during the holocene results from diatom assemblages and reconstructed sea surface temperatures ssts indicate a division of the holocene into three periods the holocene climate optimum 9500 6500 calendar cal years bp the holocene transition period 6500 3000 cal years bp and the cool late holocene period 3000 0 cal years bp the overall climate development is in step with the decreasing insolation on the northern hemisphere but regional differences occur regarding both timing and magnitude of sst changes sites under the direct influence of the norwegian atlantic current and the irminger current indicate sst cooling of 4 5 c from early holocene to present compared to 2 c recorded under the east greenland current superimposed on the general holocene cooling trend there is a high frequency sst variability which is in the order of 1 1 5 c for the voring plateau and the east greenland shelf and 2 5 3 c on the north iceland shelf

last glacial maximum and deglaciation of devon island arctic canada support for an innuitian ice sheet abstract the extent and origin of quarternary glaciers in the queen elizabeth islands of arctic canada especially during the last glacial maximum lgm has been debated for well over a century no consensus has yet emerged and the spectrum of interpretations within the last decade is the broadest ever the glacial geology of devon island strongly supports the late wisconsinan innuitian ice sheet hypothesis during lgm the southeastern part of the queen elizabeth islands was covered by an ice sheet flowing from a centre or a divide centrally located in the archipelago another ice divide extended from the centre across devon island flow from the innuitian centre and convergent flow from devon island and probably also from cornwallis and bathurst islands sustained an ice stream in wellington channel ice was locally advancing to its lgm limit about 23 ka bp recession in the vicinity of the present coastline was underway by 10 ka bp and final ice remnants west of the present devon ice cap vanished about 8 ka bp the island bears the same two part landscape zonation as do other islands and peninsulas in the region these reflect a cold based core and warm based periphery at lgm

variations in sediment wave dimensions across the tidally dominated irish sea nw europe abstract new high resolution multibeam echosounder data have been collected in the irish sea in the last decade sediment waves oriented transverse to tidal flow dominate many parts of the irish sea and exhibit an almost continuous spectrum of heights and spacings sediment wave growth remains poorly quantified and from the irish sea swath bathymetry data many bedform dimensions have been measured and examined statistically a strong positive power correlation between sediment wave height and spacing was observed s 0 0692 0 8020 n 935 r 0 853 while height and spacing only weakly vary with water depth to assess the main factors influencing sediment wave height and spacing deviations from the typical hydrodynamically analogue sediment wave geometry in equilibrium are qualitatively and semi quantitatively investigated in the irish sea in conjunction with seabed characteristics coarser sediment generally forms larger sediment waves while suppressed sediment growth is found likely due to the limitations in mobile sediment supply and inefficiency of very coarse bedload transport

coupling between 210pbex and organic matter in sediments of a nutrient enriched lake an example from lake chenghai china abstract sediment cores were collected from deep water areas of lake chenghai china in june 1997 the vertical profile of 137cs activity gives reliable geochronological results the results also indicate that sediment accumulation rates in deep water areas of lake chenghai were relatively constant in recent decades averaging 0 43 g cm 2 y 1 despite a variable organic carbon influx 210pbeq 226ra activity was relatively constant also with an average value of 54 3 3 2 bq kg 1 vertical profiles of 210pbex 210pbtotal 226ra decreased exponentially resulting in somewhat lower sediment accumulation rates 0 3 g cm 2 y 1 these lower rates are likely less reliable as the relatively large fluctuations in 210pbex activities correlate closely to the organic carbon corg content of the sediments for example the vertical profile of 210pbex activity displays peaks at mass depths of 3 7 4 7 g cm 2 10 12 cm and 10 11 g cm 2 25 28 cm similar to the maxima in the vertical profile of corg this phenomenon must be related to the delivery of particulate organic matter pom from the water to the sediments or to watershed soil erosion since the mean atomic ratios of horg corg and corg norg in lake chenghai sediments are 5 5 and 7 0 respectively indicating that pom was predominantly derived from the remains of authigenic algae this eliminates watershed erosion rates as a primary control on lake sedimentation rates as resolved by 210pbex sedimentation fluxes f corg of particulate organic carbon since 1970 varied between 60 to 160 g m 2 y 1 and appeared to closely influence variations in 210pbex concentrations for example sedimentation fluxes of 210pbex f 210pbex showed maxima in the years 1972 1974 and 1986 1989 likely reflecting historical variations of lake biological productivity or carbon preservation

constraining landscape history and glacial erosivity using paired cosmogenic nuclides in upernavik northwest greenland high latitude landscape evolution processes have the potential to preserve old relict surfaces through burial by cold based nonerosive glacial ice to investigate landscape history and age in the high arctic we analyzed in situ cosmogenic 10 be and 26 al in 33 rocks from upernavik northwest greenland we sampled adjacent bedrock boulder pairs along a 100 km transect at elevations up to 1000 m above sea level bedrock samples gave significantly older apparent exposure ages than corresponding boulder samples and minimum limiting ages increased with elevation two isotope calculations 26 al 10 be on 20 of the 33 samples yielded minimum limiting exposure durations up to 112 k y minimum limiting burial durations up to 900 k y and minimum limiting total histories up to 990 k y the prevalence of 10 be and 26 al inherited from previous periods of exposure especially in bedrock samples at high elevation indicates that these areas record long and complex surface exposure histories including significant periods of burial with little subglacial erosion the long total histories suggest that these high elevation surfaces were largely preserved beneath cold based nonerosive ice or snowfields for at least the latter half of the quaternary because of high concentrations of inherited nuclides only the six youngest boulder samples appear to record the timing of ice retreat these six samples suggest deglaciation of the upernavik coast at 11 3 0 5 ka average 1 standard deviation there is no difference in deglaciation age along the 100 km sample transect indicating that the ice marginal position retreated rapidly at rates of 120 m yr 1

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

climate and anthropogenic controls on the carbon cycle of xingyun lake china abstract the organic and inorganic carbon cycles in lakes are responsive to both natural climate variability and human induced environmental changes here we present an 8600 year sediment record from xingyun lake in yunnan china that provides insight into carbon cycling and lake primary productivity using stable isotope measurements of organic carbon and nitrogen carbon to nitrogen ratio inorganic carbon isotopes and mass accumulation rates of carbon nitrogen and calcite the early to middle holocene is characterized by relative stability in most proxies although some variation in organic carbon isotopes reflects fluctuating terrestrial organic matter inputs the middle to late holocene from 5300 to 3300 years bp is marked by amplified variability in nearly all proxies and suggests either increased c4 vegetation or increased primary productivity these changes are coincident with declining lake levels and increased aridity throughout the indian summer monsoon region after 3300 years bp the greatest variability is in nitrogen isotopes and coincides closely with human settlement in the region these changes are accompanied by further indications of increased primary productivity suggesting eutrophic lake conditions while we cannot definitively link human activity to these changes the balance of evidence suggests that other mechanisms are unlikely this study supports previous work that anthropogenic activities began measurably impacting the landscape in southwestern china within the last few millennia

time slice reconstructions of ocean circulation changes on the continental shelf in the nordic and barents seas during the last 16 000 cal yr b p abstract ocean circulation changes along the continental shelf of the nordic and barents seas have been investigated in order to reconstruct regional changes in the inflow of atlantic water aw through the last 16 000 calibrated cal years yr b p we have selected five time slices representing the late glacial 16 000 15 000 cal yr b p the bolling allerod warm interstadials 14 500 13 500 cal yr b p the younger dryas cold stadial 12 500 11 500 cal yr b p the early holocene 9500 7500 cal yr b p and the late holocene 4000 2000 cal yr b p twelve previously published records of the distribution of benthic foraminifera faunas and ice rafted debris have been compiled the earliest sign of atlantic water inflow was recorded at the northern iceland shelf at 16 000 15 000 cal yr b p the inflow of warm aw to the nordic seas shelf has been persistent since but with variable strength and geographic pattern an apparent zonal seesaw pattern in the strength of the norwegian atlantic current nwac and the irminger current ic during the late glacial bolling allerod and younger dryas periods was found during the holocene no zonal differences in the inflows of nwac and ic were found a strong meridional gradient with warmer conditions at lower latitudes and relatively cold conditions at high northern latitudes existed

potential gain and loss of sand by some sand banks in the southern bight of the north sea abstract a detailed echo sounding and side scan sonar survey has shown that sand banks in the southern bight of the north sea have rounded heads in the approximate upstream direction and tapered tails in the approximate downstream direction of net regional sand transport thus the plan view of sand banks can be used as an indicator of the approximate direction of net sand transport sand wave aprons occur in front of the heads and downstream of the tails of the sand banks the asymmetry of the sand waves implies that sand is being added to sand wave aprons at the heads and to the upstream flanks of these sand banks but is shed from the downstream sand wave aprons there is no evidence for a closed sand circulation on the banks

transgressions rethinking beringian glaciation abstract the purpose of this investigation is to encourage a fresh look at pleistocene beringia heretofore flooding of bering strait has been cited as the only barrier to migration with marine sea transgressions being a sea gate that closed off migration during glacial interstadials and interglaciations however the possibility exists that glacial advances were also barriers with marine ice transgressions being an ice gate that closed off migration during glacial stadials and glacial maxima this possibility proceeds from the marine ice transgression hypothesis mith which states that marine ice sheets form on the broad arctic continental shelf of northern hemisphere continents when sea ice thickens grounds and domes in shallow water and then transgresses landward as continental ice sheets and seaward as floating ice shelves hughes 1987 landward transgression is onto coastal lowlands during pleistocene glaciations a marine ice sheeet extending from spitsbergen to greenland may have transgressed the circumpolar continental landmass at its lowest and narrowest gap central beringia and calved into the pacific ocean four models of beringian glaciation are presented based on the distinction between marine glaciation and highland glaciation central beringia was glaciated only in highlands in the traditional model hopkins et al 1982 was also glaciated by a self sustaining ice shelf floating over the deep ocean basins of the bering sea in the model by grosswald and vozovik 1984 was glaciated by a marine ice sheet that covered highlands the continental shelf and supplied the ice shelf in a model for maximum pleistocene glaciation and was glaciated by a marine ice sheet in the chukchi sea that merged with highland glaciers transgressed the continental shelf of the western bering sea and calved into the southern bering sea along the edge of the continental shelf in a model for the last glaciation field tests are suggested to assess the viability of these four models the first model is already established for highland glaciation in alaska but less established in siberia the last model should be the easiest to evaluate for marine glaciation the last model limits human migration across the beringian land bridge to brief intervals between stadials and interstadials of the last glaciation cycle when both the ice gate and the sea gate were opened to human migration this model can influence the sea change now underway among quaternary scientists studying peopling of the americas based on the archaeological linguistic and ethnic diversity among native american populations

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

revision of the nw laurentide ice sheet implications for paleoclimate the northeast extremity of beringia and arctic ocean sedimentation abstract for the past half century reconstructions of north american ice cover during the last glacial maximum have shown ice free land distal to the laurentide ice sheet primarily on melville and banks islands in the western canadian arctic archipelago both islands reputedly preserve at the surface multiple laurentide till sheets together with associated marine and lacustrine deposits recording as many as three pre late wisconsinan glaciations the northwest corner of banks island was purportedly never glaciated and is trimmed by the oldest and most extensive glaciation banks glaciation considered to be of matuyama age 780 ka bp inside the limit of banks glaciation younger till sheets are ascribed to the thomsen glaciation pre sangamonian and the amundsen glaciation early wisconsinan stade the view that the western canadian arctic archipelago remained largely ice free during the late wisconsinan is reinforced by a recent report of two woolly mammoth fragments collected on banks and melville islands both dated to 22 ka bp these dates imply that these islands constitute the northeast extremity of beringia a fundamental revision of this model is now warranted based on widespread fieldwork across the adjacent coastlines of banks and melville islands including new dating of glacial and marine landforms and sediments on dundas peninsula southern melville island ams 14 c dates on ice transported marine molluscs within the most extensive laurentide till yield ages of 25 49 ka bp these dates require that late wisconsinan ice advanced northwestward from visount melville sound excavating fauna spanning marine isotope stage 3 laurentide ice that crossed dundas peninsula 300 m asl coalesced with melville island ice occupying liddon gulf coalescent laurentide and melville ice continued to advance westward through m clure strait depositing granite erratics at 235 m asl that require grounded ice in m clure strait as do streamlined bedforms on the channel floor deglaciation is recorded by widespread meltwater channels that show both the initial separation of laurentide and melvile ice and the successive retreat of laurentide ice southward across dundas peninsula into viscount melville sound sedimentation from these channels deposited deltas marking deglacial marine limit forty dates on shells collected from associated glaciomarine rhythmites record near synchronous ice retreat from m clure strait and dundas peninsula to north central victoria island 11 5 ka bp along the adjacent coast of banks island deglacial shorelines also record the retreat of laurentide ice both eastward through m clure strait and southward into the island s interior the elevation and age 11 5 ka bp of deglacial marine limit there is fully compatible with the record of ice retreat on melville island the last retreat of ice from mercy bay northern banks island previously assigned to northward retreat into m clure strait during the early wisconsinan is contradicted by geomorphic evidence for southward retreat into the island s interior during the late wisconsinan this revision of the pattern and age of ice retreat across northern banks island results in a significant simplification of the previous quaternary model our observations support the amalgamation of multiple till sheets previously assigned to at least three pre late wisconsinan glaciations into the late wisconsinan this revision also removes their formally named marine transgressions and proglacial lakes for which evidence is lacking erratics were also widely observed armouring meltwater channels originating on the previously proposed never glaciated landscape an extensive late wisconsinan laurentide ice sheet across the western canadian arctic is compatible with similar evidence for extensive laurentide ice entering the richardson mountains yukon farther south and with the innuitian ice sheet to the north widespread late wisconsinan ice in a region previously thought to be too arid to sustain it has important implications for paleoclimate ice sheet modelling arctic ocean ice and sediment delivery and clarifying the northeast limit of beringia

late wisconsinan glaciation of southern eureka sound evidence for extensive innuitian ice in the canadian high arctic during the last glacial maximum abstract southern eureka sound was originally proposed as the centre of an innuitian ice sheet in the canadian high arctic at the last glacial maximum lgm based largely on the pattern of holocene emergence this paper focuses on the glacial geological evidence for such an ice sheet in the region granite dispersal trains and ice moulded bedrock record regional westward flow of warm based ice into eureka sound from se ellesmere island regional ice was coalescent with local ice domes on inter fiord peninsulas marine limit in the form of raised deltas beaches and washing limits formed during deglaciation of the regional ice throughout southern eureka sound marine limit dates 9 2 ka bp indicating that ice commenced retreat during the early holocene ice divides were located along the highlands of central ellesmere and axel heiberg islands from which ice inundated eureka sound flowing north and south along the channel regional radiocarbon dates on marine limit show that deglaciation occurred in two steps initial break up and radial retreat of ice from eureka sound to the inner fiords was rapid and preceded stabilisation along adjacent coastlines and at fiord heads two step deglaciation is also reflected in differences in glacial geomorphology between the inner and outer parts of many fiords a prominent belt of fiord head glaciogenic landforms long proposed to mark the last glacial limit is re interpreted to record initial stabilisation of ice margins due predominantly to bathymetric control

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

glacier dynamics and paleoclimatic change during the last glaciation of eastern ellesmere island canada a 300 km transect along the east coast of ellesmere island fills a major gap in the late quaternary data base of the canadian high arctic the last glacial maximum lgm is marked by prominent moraines and meltwater channels that terminate within 30 km of modern ice margins shells in glaciomarine deposits collected beyond the lgm indicate deglaciation by more extensive ice prior to 35 ka bp more than 60 14c dates from glaciomarine sediments provide a chronology for past ice dynamics during the lgm to the north while many areas remained ice free due to severe aridity several glaciers remained in contact with the sea until 7 1 ka bp farther south most glaciers reached the coast and significantly infilled several fiords this southward increase in glacier extent is due to larger glacial catchment basins and increased precipitation towards storm tracks in northern baffin bay the earliest dates on deglaciation along the transect range from 8 1 to 7 7 ka bp initial retreat was controlled by the exten

more on deep glacial erosion by continental ice sheets and their tongues of distributary ice high latitude intracontinental seaways occupy great troughs carved by broad tongues of inland ice as it debouched to deep marine water such troughs occur in glaciated coasts but not in stable nonglaciated ones where ice flowed along the walls of troughs whose adjacent uplands held local glaciers the walls simulate alpine troughs with faceted spurs and submarine hanging tributary valleys where uplands were not glaciated trough walls are unbreached where ice flowed across them coasts are digitate in low relief in the northeastern sector of the laurentide ice sheet large glacial grooves converge toward the gulf of boothia prince regent inlet lancaster sound avenue of egress to open sea suggesting that it was an exit for inland ice which shaped it to its present form the subduction pacific coast of the americas is mostly harborless in nonglaciated latitudes but in southern chile and british columbia it is dissected a circular gravity high 2800 km across is concentric with the area covered by the laurentide ice sheet abyssal glacial silts are voluminous enough to account for an average of 100 150 m of erosion over the area covered by the laurentide ice sheet

the innuitian ice sheet configuration dynamics and chronology abstract portrayal of north american ice cover during the last glacial maximum is dominated by the laurentide ice sheet leaving little detail for the adjacent innuitian ice sheet iis four decades of geological fieldwork across the queen elizabeth islands now warrant specific treatment of the iis including its chronology configuration dynamics and retreat this reconstruction is relevant to the sedimentary history of the arctic ocean and to high latitude climate forcing the iis was composed of both an alpine and lowland sector the advance of the alpine sector occurred as recently as 19 14 c ka bp geological evidence configures outflow from alpine and lowland divides that produced several palaeo ice streams one extending northwestward across the canadian arctic archipelago to the polar continental shelf retreat of the iis commenced along its southwest margin 11 6 14 c ka bp however most of the ice sheet remained on the continental shelf during the younger dryas by 10 14 c ka bp marine based ice experienced widespread calving through the western and central archipelago in response to holocene warming and ongoing eustatic sea level rise the sea penetrated the eastern archipelago by 8 5 14 c ka bp gutting the alpine sector of the iis regional isobases record the glacioisostatic signature of the ice sheet and are congruent with the primary geological evidence the delayed buildup of the iis was out of phase with the growth of the laurentide ice sheet that occasioned climatic and glacio eustatic forcing in the innuitian region recent modelling experiments reinforce the hypothesis that growth of the laurentide ice sheet culminated in a split jet stream that temporarily favoured augmented precipitation and growth of the iis

comment holocene palaeoceanographic changes in barrow strait canadian arctic foraminiferal evidence t r gregory c w smart m b hart g masse l l vare and s t belt 2010 journal of quaternary science 25 903 910

glaciomarine sedimentation in disraeli fiord high arctic canada abstract disraeli fiord represents a glaciomarine environment unique to the north coast of ellesmere island featuring floating glacier tongues multi year landfast sea ice and a strongly stratified water body which results from enclosure of the fiord by ward hunt ice shelf it is a very low energy depositional environment even at sites proximal to glaciers sediment enters the fiord by interflow and is deposited through suspension settling ice rafting is precluded by the year round sea ice cover sedimentation rates in the inner fiord since about 7000 yrs b p are estimated to be 5 10 cm ka a reflection of the limited sediment influx from the cold based glaciers which contact the fiord changes in sediment structure through the holocene reflect changes in the rate and process of sediment input as well as changes in fiord circulation all of which relate to regional climate during deglaciation early holocene sedimentation rates were orders of magnitude greater than at present subglacial meltwater was the dominant source of inflow with sediment transported in turbid plumes as over or interflow and deposited through suspension settling this is supportive of other studies indicating that a pronounced climatic amelioration led to warm based glaciers at this time

quaternary glacial and marine environmental history of northwest greenland a review and reappraisal new information on middle and late quaternary deposits of the thule region northwest greenland necessitates the revision of the chronostratigraphy of the area and allows fuller understanding of the marine environmental changes in ba n bay the stratigraphic record is interpreted as the product of three marine events saunders qarmat and nuna in decreasing age during which marine sedimentation occurred on coastal areas now land and three or four glacial events of decreasing age and ice cover agpat narsaarsuk and kap abernathy wolstenholme fjord to which the marine events were glacio isostatically related subarctic atlantic water reached this northern part of ba n bay during all three marine events but the warmest conditions warmer than the present occurred in the qarmat event correlated with the deep sea oxygen isotope stage 5e the question of late stage 5 events is considered the nuna event dates to latest stage 2 and the holocene whilst the saunders event is of uncertain age but at least stage 6 a number of glacial events with advances confined to the fjords are dated to stage 2 wolstenholme fjord and late stage 6 narsaarsuk and an intermediate advance kap abernathy is undated in the range of stage 2 5 extension of glaciation to the shelf edge is dated to stage 6 agpat event 1999 elsevier science ltd all rights reserved

late holocene environmental conditions in coronation gulf southwestern canadian arctic archipelago evidence from dinoflagellate cysts other non pollen palynomorphs and pollen boxcore 99lssl 001 68 0958 n 114 1868 w 211 m water depth from coronation gulf represents the first decadal scale marine palynology and late holocene sediment record for the southwestern part of the northwest passage the record was studied for organic walled microfossils dinoflagellate cysts non pollen palynomorphs pollen terrestrial spores and sediment characteristics 210 pb 137 cs and three accelerator mass spectrometry 14 c dates constrain the chronology three prominent palaeoenvironmental zones were identified during the interval ad 1470 1680 zone i the climate was warmer and wetter than at present and environmental conditions were more favourable to biological activity and northward boreal forest migration with reduced sea ice and a longer open water growing season the interval ad 1680 1940 zone ii records sea ice increase and generally cool polar conditions during the little ice age during ad 1940 2000 zone iii organic microfossils indicate an extended open water season and decreased sea ice with suggested amelioration surpassing that of zone i although more marine studies are needed to place this record into an appropriate context the succession from ameliorated zone i to cooler sea ice influenced conditions zone ii and finally to 20th century warming zone iii corresponds well with several terrestrial climatic records from the neighbouring mainland and victoria island and with lower resolution marine records to the west copyright 2011 john wiley sons ltd

seafloor features delineate late wisconsinan ice stream configurations in eastern parry channel canadian arctic archipelago abstract multibeam imagery and 3 5 khz sub bottom profiles acquired from ccgs amundsen between 2003 and 2013 by arcticnet and the ocean mapping group at the university of new brunswick provide information on seafloor features geology bathymetry and morphology in eastern parry channel and the adjoining large channels in the canadian arctic archipelago together these include peel sound barrow strait lancaster sound wellington channel prince regent inlet admiralty inlet and navy board inlet those data are in part complemented by high resolution single channel seismic reflection profiles acquired by the geological survey of canada in the 1970s and 1980s and by sediment cores that provide chronological and depositional information the occurrence and pattern of streamlined mega scale ridge and groove lineations msgls indicate that these waterways were occupied by glacial ice streams in the past chronological information from marine and adjoining terrestrial areas suggests a long history of glacial events ranging in time from early pleistocene to late wisconsinan seafloor morphology and msgl trends together with terrestrial ice flow patterns indicate that ice streams flowed into barrow strait from peel sound and wellington channel and ice streams in prince regent admiralty and navy board inlets flowed northward into and eastward along lancaster sound recession of the ice stream westward along parry channel occurred 16 cal ka bp to 10 8 cal ka bp thick ice contact sediments deposited by a late ice advance from prince regent inlet constitute the seabed across a large area of western lancaster sound timing for that late ice advance appears to be bracketed between the 11 5 cal ka bp lift off of the eastern parry ice stream north of prince leopold island and the 10 0 cal ka bp deglaciation of prince regent inlet seafloor morphology and lineation trends suggest that ice delivered by the ice stream in peel sound was the westernmost tributary to the ice stream occupying lancaster sound during the late wisconsinan glaciation bathymetric data and msgls indicate that the ice stream emanating from m clintock channel flowed westward

juxtaposition of western pacific subtropical high on asian summer monsoon shapes subtropical east asian precipitation increasing lines of evidence question the homogenous response of asian summer monsoon asm precipitation patterns requiring rethinking of the forcing mechanisms here we show a 15 000 year quantitative precipitation history based on well dated lake levels at lake chenghai subtropical china lake levels and the inferred precipitation were high during the bolling allerod early and late holocene but low during the middle holocene the orbital scale precipitation trend is out of phase with boreal summer insolation the later has been widely suggested as the driver of asm precipitation lake chenghai long term lake levels are synchronous with trends in tropical pacific sea surface temperatures the related zonal sea surface temperature gradients and interhemispheric temperature gradients we propose that changes in either the interhemispheric or zonal pacific temperature gradients modulate the intensity and location of the western pacific subtropical high which is juxtaposed on the asm leading to heterogeneous hydroclimatic conditions over subtropical east asia

abrupt changes in indian summer monsoon strength during the last deglaciation and early holocene based on stable isotope evidence from lake chenghai southwest china identifying variability and the mechanisms driving variability in the indian summer monsoon ism since the last deglaciation is critical for understanding past hydroclimatic change in this study we present an accelerator mass spectrometry radiocarbon dated record of delta o 18 variations in authigenic carbonates derived from lake chenghai in southwest china a region that receives moisture mainly from the indian ocean the delta o 18 values vary from 11 9 to 0 1 parts per thousand providing a detailed record of variations in ism precipitation delta o 18 values and lake hydrological balance the record shows that the ism generally strengthened in the post glacial between 15 6 and 8 8 cal ka bp but that three centennial to millennial scale drought events were superimposed on the long term trend drought events as indicated by substantial positive shifts in 8 18 0 value occurred from 15 6 0 2 to 14 4 0 2 12 5 0 2 to 11 7 0 2 and 10 1 0 1 to 10 0 0 1 cal ka bp corresponding to the heinrich 1 younger dryas and bond 7 cold events in the north atlantic region respectively the timings of these droughts are suggested to be related to meltwater discharge into the north atlantic the weakened atlantic meridional overturning circulation which leads in turn to the southward migration of the intertropical convergence zone and cooling in the tropical indian ocean

δ13c δ18c covariance as a paleohydrological indicator for closed basin lakes the relationship between 18o and 13c in a closed basin lake is a function of hydrological change vapor exchange lake productivity and total co2 or carbonate alkalinity concentration covariance of 18o and 13c usually occurs in lake sediments under the condition of hydrological closure for time periods of the order of 5000 yr or longer on shorter time scales however certain subtleties in the use of the 13c 18o covariance as a hydrology history indicator must be recognized the covariant trend may not be found in hyper alkaline lakes because of the insensitivity of 13c to lake volume changes for less alkaline closed basin lakes covariance of 13c 18o will result from relatively rapid increase or decrease of lake volume with the rapid decrease condition giving rise to heavy and narrow ranged isotopic values for both 13c and 18o due to the coupled evaporation productivity effect when the lake volume remains stable as is the case for an over flowing open lake poor 13c 18o covariance will ensue due to the effect of vapor exchange with the atmosphere we have used the measured 13c 18o covariance in carbonate sediments of mono lake california to deduce paleo hydrological and lake water alkalinity and salinity variations and found the results in consonance with holocene lake level history derived from the 18o and other information

support for the innuitian ice sheet in the canadian high arctic during the last glacial maximum the extent of glacier ice in the canadian high arctic during the last glacial maximum lgm has been debated for decades one school proposed a regional innuitian ice sheet whereas another proposed a smaller non contiguous franklin ice complex research throughout western nares strait supports coalescent innuitian and greenland ice during the lgm based on widespread glacial and marine deposits dated by 14c and amino acid analyses this coalescence likely promoted a vigorous regional ice flow westward across ellesmere island to eureka sound post glacial emergence in eureka sound suggests a former ice thickness at least as great as that in nares strait 1 km recently independent field studies elsewhere in the high arctic also support an innuitian ice sheet during the lgm collectively these studies resolve a long standing debate and initiate new opportunities concerning the reconstruction of high latitude palaeoenvironmental and palaeoclimatic change 1998 john wiley sons ltd

cosmogenic 10be and 26al ages for the last glacial maximum eastern baffin island arctic canada a chronology for the last glacial maximum based on cosmogenic exposure dating in the pangnirtung fjord area eastern baffin island arctic canada is at odds with many decades of land based glacial stratigraphic research most previous chronologies focused primarily on relative weathering criteria and suggested that ice extent was restricted during the late wisconsinan ca 24 8 ka in contrast by directly dating glacial features we conclude that late wisconsinan ice was far more extensive than previously believed there are 36 gneissic boulders and 8 samples of ice molded gneissic bedrock that yield late wisconsinan 10 be and 26 al exposure ages for the last glaciation of pangnirtung fjord the prominent duval moraines which were previously interpreted to represent a significant early wisconsinan 100 60 ka ice advance on southern cumberland peninsula were actually deposited between 24 and 9 ka two boulders from a raised glaciomarine delta stratigraphically related to the duval moraines date to about 10 ka two recessional moraines and striated bedrock along pangnirtung fjord as well as erratics on the floor of the kolik river valley a tributary to pangnirtung fjord indicate that deglaciation began between 12 and 9 ka in situ produced 10 be and 26 al abundances indicate that ice filled pangnirtung fjord for about 15 k y either continuously or intermittently prior to 10 ka which is compatible with 14 c chronologies for adjacent cumberland sound thus our data support other recent studies that suggest the northern and southern margins of the laurentide ice sheet were generally in phase during the latest wisconsinan contrary to earlier interpretations

giant sandwaves in the hola glacial trough off vesteralen north norway abstract seabed data acquired from the hola glacial trough off vesteralen north norway reveal the morphology of spectacular sandwave fields and large sandwaves in great detail the sandwave fields are among the deepest known occurring in water depths of 200 260 m multibeam bathymetry and backscatter shallow seismic sediment samples and video data collected by the mareano programme and bottom current modelling results have been used to interpret morphology transport and distribution of the seabed sediments sand supply to the hola trough was initially from wave and current reworking of glacial and glaciomarine deposits during the eustatic sea level lowstand and sea level rise after the last glaciation more recently deposited bioclastic sand dominates the upper part of the sand unit which locally reaches 10 m thickness sand predominantly accumulates behind ridges where current strength decreases and in topographic lows straight crested and barchan type sandwaves up to 3 km long and 7 m high are interpreted to form by tidal and geostrophic currents with bottom current speeds reaching 0 7 0 8 m s 1 a large cluster of coral reefs occur immediately east of the barchan type sandwaves where modelling shows bottom current velocities up to c 1 m s 1 sandwaves occur in four major sandwave fields strong variation in the nature of sandwaves over short distances e g migration direction between neighbouring sandwave fields point to important local variations in current regime and sedimentary processes the present work demonstrates how local topography and interaction of several current systems may produce complex depositional patterns on a local scale detailed multibeam mapping and video inspection of open shelf troughs in other narrow shelf settings worldwide may reveal similar sandwave fields

isotopic and hydrologic responses of small closed lakes to climate variability comparison of measured and modeled lake level and sediment core oxygen isotope records abstract simulations conducted using a coupled lake catchment isotope mass balance model forced with continuous precipitation temperature and relative humidity data successfully reproduce within uncertainty limits long term i e multidecadal trends in reconstructed lake surface elevations and sediment core oxygen isotope 18 o values at castor lake and scanlon lake north central washington error inherent in sediment core dating methods and uncertainty in climate data contribute to differences in model reconstructed and measured short term i e sub decadal sediment i e endogenic and or biogenic carbonate 18 o values suggesting that model isotopic performance over sub decadal time periods cannot be successfully investigated without better constrained climate data and sediment core chronologies model reconstructions of past lake surface elevations are consistent with estimates obtained from aerial photography simulation results suggest that precipitation is the strongest control on lake isotopic and hydrologic dynamics with secondary influence by temperature and relative humidity this model validation exercise demonstrates that lake catchment oxygen isotope mass balance models forced with instrumental climate data can reproduce lake hydrologic and isotopic variability over multidecadal or longer timescales and therefore that such models could potentially be used for quantitative investigations of paleo lake responses to hydroclimatic change

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

the late quaternary environmental evolution of marine arctic canada barrow strait to lancaster sound abstract a marine sediment core from the east central canadian arctic archipelago core 86027 154 74 22 01 n 89 51 26 w 329 m water depth studied by a multiproxy approach lithostratigraphy biogeochemistry micropalaeontology dinoflagellate cysts other non pollen palynomorphs benthic and planktonic foraminifera ostracods and encompassing 14 ams 14 c dates provides valuable insights into regional deglacial to holocene palaeoenvironments six palaeoenvironmental zones are recognized based on prominent changes in the litho and biostratigraphy the waterlain diamicton of zone i records immediate deglaciation being derived from lift off and calving of previously grounded glacial ice though deglacial timing is complicated by the sparsity of dating materials and the portlandia effect age depth model extrapolation places deglaciation at 11 54 cal ka bp zone ii 11 5 11 0 cal ka bp represents a distinct progression from initially ice proximal to increasingly ice distal conditions interrupted by an interval of pervasive sea ice 11 4 11 2 cal ka bp noteworthy biological activity commences in zone iii 11 0 9 7 cal ka bp with a prominent signal of planktonic foraminifera neogloboquadrina pachyderma this likely signifies penetration of deeper atlantic derived water through the central canadian arctic archipelago upon deglaciation facilitated by the greater glacioisostatically induced water depths 80 m and implies separation of laurentide and innuitian ice sheets by 11 0 cal ka bp zone iv 9 7 7 2 cal ka bp records ameliorated biologically favourable conditions with reduced seasonal sea ice accompanied by high microfossil species diversity and the presence of subpolar taxa zone v 7 2 6 5 cal ka bp signals the exclusion of atlantic derived water concomitant with increasing sea ice simultaneously representing the termination of the dynamic deglacial to early holocene environments zones i iv conditions similar to modern typified by uniform sediment characteristics present day microfossil assemblage structures and sparse benthic foraminifera were established by 5 6 cal ka bp zone vi

eddy driven recirculation of atlantic water in fram strait eddy resolving regional ocean model results in conjunction with synthetic float trajectories and observations provide new insights into the recirculation of the atlantic water aw in fram strait that significantly impacts the redistribution of oceanic heat between the nordic seas and the arctic ocean the simulations confirm the existence of a cyclonic gyre around the molloy hole near 80 n suggesting that most of the aw within the west spitsbergen current recirculates there while colder aw recirculates in a westward mean flow south of 79 n that primarily relates to the eastern rim of the greenland sea gyre the fraction of waters recirculating in the northern branch roughly doubles during winter coinciding with a seasonal increase of eddy activity along the yermak plateau slope that also facilitates subduction of aw beneath the ice edge in this area

a synthesis of abrupt changes in the asian summer monsoon since the last deglaciation we have compiled 36 previously published palaeoclimate records to determine the timing and spatial pattern of century scale abrupt changes in asian monsoon precipitation since the last deglaciation we identify abrupt events from 1 the interpretations of the authors of these records and 2 the more objective moving t test calculation our results indicate that abrupt climatic changes occurred at 11 5 cal ka 4 5 5 0 cal ka and ad 1300 at the start of the holocene 11 5 cal ka asian monsoon precipitation increased dramatically this climatic change is synchronous with an abrupt warming in the north atlantic during the middle holocene there was a time of preferred and widespread weakening in monsoon strength 4 5 5 0 cal ka this result contradicts previous notions of either a gradual trend towards drier conditions or a series of abrupt events that occurred in an unorganized fashion across space and time the middle holocene abrupt event could have been synchronous with an abrupt cooling event in the north atlantic as well as a warming and intensie cation of internannual variability in the tropical pacie c in contrast to previous periods precipitation changes at ad 1300 have a heterogeneous spatial pattern we e nd no conclusive evidence for a change in the asian monsoon at 8 2 cal ka as suggested by several previous studies more high resolution data may be needed to observe this short lived event overall our results attest to the potential for rapid and major shifts in asian monsoon precipitation that may be triggered by variations in other components of the climatic system

sandbanks sandwaves and megaripples on spitsbergenbanken barents sea abstract recently acquired multibeam echosounder data from the shallowest part 26 53 m depth of spitsbergenbanken in the western barents sea reveal a variety of bedforms including megaripples sandwaves and sandbanks the bedforms exhibit varying degrees of superimposition and differ in their age of formation and present depositional regime being either active or moribund these are the first observations of co occurring current induced bedforms in the western barents sea and provide evidence of a high energy environment in the study area the bedforms indicate both sediment erosion and transport and confirm that there is enough sand available in this area to maintain them such conditions are not known to be common in the western barents sea and reflect the unique oceanographic and benthic environment of spitsbergenbanken

stratigraphy and palaeoecology of a possible interglacial site northernmost ellesmere island canada an extensive stratigraphic section at cape alfred ernest on the wootton peninsula northwest ellesmere island contains six lithofacies which appear to record two glacial phases separated by an organic layer 1 a lower massive gravel records a pre ice advance outwash phase 2 massive fine grained sediments record a period of non glacial marine deposition when sea level was higher than present 3 a massive diamicton records the advance of ice across the site 4 intermediate stratified beds record supraglacial and proglacial outwash and include an organic layer 5 massive diamicton grading down valley to stratified diamicton and then massive sheared diamicton overlain by laminated fine grained sediments with dropstones recording the last late wisconsinan glaciation 6 upward coarsening sands and gravels record proglacial outwash and grade to raised marine deltas radiocarbon dates of 39270 640 and 51000 yr bp were obtained on samples from the organic layer by accelerator mass spectrometry and conventional radiocarbon dating respectively palaeoecological data suggest that the organics accumulated in a wet sedge meadow environment when the climate was warmer than present stratigraphic considerations suggest that the organic layer represents an interglacial interval which if valid indicates that the site constitutes the northernmost interglacial stratigraphy in the canadian arctic alternatively the organic layer may date to plio pleistocene times

bedrock morphology reveals drainage network in northeast baffin bay a subglacial drainage network underneath the paleo ice sheet off west greenland is revealed by a new compilation of high resolution bathymetry data from melville bay northeast baffin bay this drainage network is an indicator for ice streaming and subglacial meltwater flow toward the outer shelf repeated ice sheet advances and retreats across the crystalline basement together with subglacial meltwater drainage had their impact in eroding overdeepened troughs along ice stream pathways these overdeepenings indicate the location of a former ice sheet margin the troughs inherit characteristics of glacial and subglacial meltwater erosion most of the troughs follow tectonic weakness zones such as faults and fractures in the crystalline bedrock many of these tectonic features correspond with the orientations of major fault axes in the baffin bay region the troughs extend from the present sub glacial fjord systems at the greenland coast and parallel modern outlet glacier pathways the fast flowing paleo ice streams were likely accelerated from the meltwater flow as indicated by glacial landforms within and along the troughs the ice streams flowed along narrow tributary troughs and merged to form large paleo ice streams bedded in the major cross shelf troughs of melville bay apart from the troughs a rough seabed topography characterises the bedrock and we see a sharp geomorphic transition where ice flowed onto sedimentary rock and deposits

glacial advances and stratigraphy in otto fiord and adjacent areas ellesmere island northwest territories hvitland and svartfjeld peninsulas have been glaciated at least two or three times since the late pliocene the earliest recognized glaciation is constrained by amino acid ratios on in situ pelecypods from marine sediments stratigraphically overlying till in otto fiord high amino acid ratios suggest that the shells may be pliocene and related to recently discovered late pliocene hvitland beds at white point the same samples yielded finite radiocarbon ages in the 30 2 34 8 ka bp range which cautions against their acceptance a second mid quaternary glaciation is suggested by intermediate amino acid ratios from in situ pelecypods and shell bearing till covering coastal uplands along nansen sound during the last glaciation the peninsula was covered by coalesced ice caps with glacial tongues descending tributary valleys and extending into the fiords deglaciation of a tributary valley in outer otto fiord proceeded before 11 6 ka bp and before 9 1 ka bp in mid otto fiord but major ice margins remained a

unblocking of the nares strait by greenland and ellesmere ice sheet retreat 10 000 years ago the extent of glaciation at the northern margin of the canadian greenland high latitude arctic region over the past 30 000 years is uncertain geological arguments have been made for greenland and ellesmere island ice sheets that coalesced to block the nares strait1 and for restricted ice sheets on the two islands2 leaving the strait open as it is today3 distinguishing between these two possibilities would provide significant constraints on present understanding of the past circulation between the arctic and atlantic oceans4 5 on estimates of past ice volume6 and on the response of the greenland ice sheet to climate change7 radiocarbon analyses provide dates for the deglaciation of the islands coasts but do not yield information on whether ice filled the strait here we present measurements of cosmogenic 36cl that has accumulated in situ in erratics and glacially polished bedrock on islands within the nares strait these data allow us to determine the time for which the rocks have been recently exposed to the atmosphere and thus the age of the final deglaciation of the strait we show that greenland and ellesmere ice sheets retreated from the nares strait about 10 000 years ago the strait was filled with ice during the last glaciation blocking this connection between the arctic and atlantic oceans and supporting the model of extensive and long lasting ice on land and sea in this region8 9 10 11

contour current driven continental slope situated sandwaves with effects from secondary current processes on the barents sea margin offshore norway abstract seabed data acquired from the southern barents sea continental margin offshore norway reveal detailed morphology of large sandwave fields multibeam echosounder bathymetry and backscatter shallow seismic sediment samples and seabed video data collected by the mareano program have been used to describe and interpret the morphology distribution and transport of the sandwaves the bedforms lie on a slope dominated by relict glacial forms and muddy sandy gravelly sediments sandwave migration across small gravity mass failures of the glacial mud constrains the field initiation as early post glacial or later the contour parallel nature of the fields and crestlines normal to the bathymetry contours and the geostrophic norwegian atlantic current nwac demonstrate that the nnw flowing oceanographic circulation is the primary driving current the fields coincide with the depth range at which a transition between warm saline and underlying cooler less saline waters fluctuate across the seabed statistically rigorous measurements of height width and various parameters of slope and symmetry confirm a tendency to downstream nnw sandwave migration but with significant exceptions anomalous bedform symmetry domains within the fields are tuned to meso scale topography along relict glacial debris flow chutes indicating current focusing upstream and upper slope derived winnowed sand transport eroded from the glacial sediments is the supposed source sandwave flank slope values are comparable to the regional slope such that the gravitational vector would have a cumulative downslope migration affect unless balanced by upslope drivers perpendicular cross cutting of stoss face 3 d ripples by linear 2 d ripples in the sandwave troughs and lee faces is evidence for non synchronous episodic current variations though deep ekman transport and internal wave action are unproven here these could explain chute related tuning of bedform symmetry through funneling in the debris flow chutes and favor sand recycling thus contributing to long term maintenance of the sandwave field

the isotopic response of lake chenghai sw china to hydrologic modification from human activity the human modification of lake hydrology is widespread in the industrial era however anthropogenic impacts have occurred for thousands of years in regions of the world with long histories of human occupation here we use geochemical analyses of lake sediment to document the isotopic and geochemical response of cheng lake chenghai in southwestern china to catchment modification including the construction of a downstream dam the chenghai record indicates that land use changes affected the lake catchment by at least ad 1150 as evidenced by an increased flux of terrestrial organic matter sediment with high concentrations of sorbed metals and variations in stable isotopes of oxygen in precipitated aragonite decreases in magnetic susceptibility and metal concentrations after ad 1360 indicate a change in sediment basin dynamics the construction of a downstream dam between ad 1573 and 1620 caused positive shifts in the isotopic composition of aragonite indicative of increased evaporative loss and a lo

early holocene temperature variability in the nordic seas the role of oceanic heat advection versus changes in orbital forcing received 7 january 2011 revised 15 july 2011 accepted 21 july 2011 published 22 october 2011 1 the separate roles of oceanic heat advection and orbital forcing on influencing early holocene temperature variability in the eastern nordic seas is investigated the effect of changing orbital forcing on the ocean temperatures is tested using the 1dice model and the 1dice results are compared with new and previously published temperature reconstructions from a transect of five cores located underneath the pathway of atlantic water from the faroe shetland channel in the south to the barents sea in the north the stronger early holocene summer insolation at high northern latitudes increased the summer mixed layer temperatures however ocean temperatures underneath the summer mixed layer did not increase significantly the absolute maximum in summer mixed layer temperatures occurred between 9 and 6 ka bp representing the holocene thermal maximum in the eastern nordic seas in contrast maximum in northward oceanic heat transport through the norwegian atlantic current occurred approximately 10 ka bp the maximum in oceanic heat transport at 10 ka bp occurred due to a major reorganization of the atlantic ocean circulation entailing strong and deep rejuvenation of the atlantic meridional overturning circulation combined with changes in the north atlantic gyre dynamic causing enhanced transport of heat and salt into the nordic seas

sedimentology and stratigraphy of a tidal sand bank in the southern north sea abstract a set of 125 vibrocores collected on the basis of a dense grid of high and very high resolution seismic coverage over a tidal sand bank the middelkerke bank provides a unique opportunity to reconstruct the stratigraphy and sedimentary facies succession of such a large tidal sand body five sedimentary facies are distinguished they range from clay to pebble and display various types of bedding and lithologies corresponding to different depositional environments a succession of four late quaternary units are defined on the basis of the stratigraphic framework given by the seismic grid the first unit represents the infill of a palaeovalley system by tidally influenced sedimentary facies it is followed by extensive and thick lagoonal or sub tidal deposits the third unit reveals the development of a landward prograding storm dominated sand bar this unit is dominated by clean fine sand the last unit corresponds to the present day tidal sand bank it shows the typical offshore tidal sand bank facies cross bedded sand prograding in an offshore direction like other banks located in a more offshore position the middelkerke bank is a composite bank incorporating facies which do not occur in classic tidal sand banks

contrasting the indian and east asian monsoons implications on geologic timescales the surface winds over the arabian sea and south china sea are meaningful indicators for the strength of the indian monsoon and east asian monsoon respectively paleo monsoon variability has been studied through analysis of sediment records from these two monsoon regions to facilitate interpretation of these records we focus on the impacts of internal and external forcing of the monsoon system by contrasting the annual cycle and interannual variability of two subsystems the monsoon over the indian sector 40 105 e and over the east asian sector 105 160 e differences in the annual cycle within these subsystems arise primarily from the different land ocean configurations that determines atmospheric response to the solar forcing thus factors that drive intensities of the monsoonal annual cycle share common features with the external geographic and orbital forcing that controls paleomonsoon variability we show that the differences in interannual variations between the two monsoon subsystems are primarily due to internal factors of the coupled atmosphere ocean land system such as remote impacts of el nin o la nin a and local monsoon ocean interactions the mechanisms that operate on interannual to interdecadal timescales may differ fundamentally from that on geologic orbital timescales the low level flows over the east asia and australia are essentially established by geographic forcing the amplification of the australia summer monsoon during increased solar precession is likely caused by an enhanced east asian winter monsoon rather than following an enhanced indian summer monsoon as on the interannual timescale it is also found that el nin o influences the low level flow moderately over the arabian sea but to a greater extent over the south china sea as such large changes in the pacific thermal conditions may significantly alter the intensity of the east asian monsoon but not the indian monsoon

buried iceberg keel scouring on the southern spitsbergenbanken nw barents sea abstract parasound 3 5 khz subbottom echosounder profiles acquired on the southern spitsbergenbanken nw barents sea show iceberg keel scouring features which are buried by sediment that accumulated during the post last glacial maximum lgm sea level rise four acoustic units units 1 to 4 in stratigraphic order were differentiated based on the characterization of their acoustic facies and reflection surfaces unit 1 shows a chaotic internal structure and is interpreted as a glacial till whereas the laminated units 2 to 4 accumulated by sediment settling from suspension clouds and bottom currents during the last deglaciation phase the top of unit 2 was frequently incised by iceberg keels resulting in up to 12 m deep ploughmarks which were later filled and buried by unit 3 and 4 sediments three main paleo evironmental changes controlled the evolution of the facies succession 1 the major shift from till formation unit 1 below grounded ice to the accumulation of laminated sediments unit 2 which are inferred to reflect ice lifting and meltwater release 2 iceberg keel scouring after sedimentation of unit 2 3 the probable abrupt termination of iceberg keel scouring related to the glacio eustatic sea level rise a linkage between these episodes of changes and short lasting phases of rapid post lgm sea level rise such as meltwater pulses is inferred although further studies are needed to better understand the temporal and genetic relationships between the sedimentary events recognized in the barents sea and climate changes

variations in temperature and extent of atlantic water in the northern north atlantic during the holocene we compare six high resolution holocene sediment cores along a s n transect on the norwegian svalbard continental margin from ca 601n to 77 41n northern north atlantic planktonic foraminifera in the cores were investigated to show the changes in upper surface and subsurface water mass distribution and properties including summer sea surface temperatures sst the cores are located below the axis of the norwegian current and the west spitsbergen current which today transport warm atlantic water to the arctic sediment accumulation rates are generally high at all the core sites allowing for a temporal resolution of 10 10 2 years sst is reconstructed using different types of transfer functions resulting in very similar sst trends with deviations of no more than 71 0 1 51c a transfer function based on the maximum likelihood statistical approach is found to be most relevant the reconstruction documents an abrupt change in planktonic foraminiferal faunal composition and an associated warming at the younger dryas preboreal transition the earliest part of the holocene was characterized by large temperature variability including the preboreal oscillations and the 8 2 k event in general the early holocene was characterized by ssts similar to those of today in the south and warmer than today in the north and a smaller s n temperature gradient 0 231c 1n compared to the present temperature gradient 0 461c 1n the southern proxy records 60 691n were more strongly influenced by slightly cooler subsurface water probably due to the seasonality of the orbital forcing and increased stratification due to freshening the northern records 72 77 41n display a millennial scale change associated with reduced insolation and a gradual weakening of the north atlantic thermohaline circulation thc the observed northwards amplification of the early holocene warming is comparable to the pattern of recent global warming and future climate modelling which predicts greater warming at higher latitudes the overall trend during mid and late holocene was a cooling in the north stable or weak warming in the south and a maximum s n sst gradient of ca 0 71c 1n at 5000 cal years bp superimposed on this trend were several abrupt temperature shifts four of these shifts dated to 9000 8000 5500 3000 and 1000 and 400 cal years bp appear to be global as they correlate with periods of global climate change in general there is a good correlation between the northern north atlantic temperature records and climate records from norway and svalbard r 2007 elsevier ltd all rights reserved

deglacial to holocene history of ice sheet retreat and bottom current strength on the western barents sea shelf abstract high resolution sediment echosounder data combined with radiocarbon dated sediment cores allowed us to reconstruct the late quaternary stratigraphic architecture of the kveithola trough and surrounding spitsbergenbanken the deposits display the successive deglacial retreat of the svalbard barents sea ice sheet basal subglacial till indicates that the grounded ice sheet covered both bank and trough during the late weichselian a glaciomarine blanket inside the trough coinciding with laminated plumites on the bank formed during the initial ice melting phase from at least 16 1 to 13 5 cal ka bp in close proximity to the ice margin after the establishment of open marine conditions at around 13 5 cal ka bp a sediment drift developed in the confined setting of the kveithola trough contemporary with crudely laminated mud an overlying lag deposit and modern bioclastic rich sand on spitsbergenbanken the kveithola drift shows a remarkable grain size coarsening from the moat towards the southern flank of the trough this trend contradicts the concept of a separated drift which would imply coarser grain sizes in proximity of the moat and indicates that the southern bank is the main sediment source for the coarse material building up the kveithola drift this depocenter represents therefore a yet undescribed combination of off bank wedge and confined drift although the deposits inside kveithola trough and on spitsbergenbanken display different depocenter geometries time equivalent grain size changes imply a region wide sediment dynamic connection we thus relate a phase of coarsest sediment supply 8 8 6 3 cal ka bp to an increase in bottom current strength which might be related to a stronger atlantic water inflow from the southeast across the bank leading to winnowing and off bank export of sandy sediments

ice keel seabed features in marine channels of the central canadian arctic archipelago evidence for former ice streams and iceberg scouring abstract the study area lies within the central part of the canadian arctic archipelago a region that was covered by the laurentide ice sheet during the late wisconsinan glaciation and earlier multibeam imagery from widely spaced transects indicates the presence of linear groove and ridge features on the seabed at several localities in peel sound franklin strait northern larsen sound and within m clintock channel these lineations resemble features in antarctica and in several formerly glaciated regions that have been interpreted to be sole marks emplaced beneath fast flowing ice streams based on these analogies a similar origin is inferred for the lineations on the channel floors within the study area the lineations are oriented parallel to the channel axes and margins they occur on all transects within the bathymetrically deeper area at the junction of franklin strait and peel sound northward in peel sound they occur extensively on the western and central transects and more locally on the eastern transect their north south orientation is normal to that of glacial flow features on somerset island and most of eastern prince of wales island which border peel sound to the east and west respectively the trend of the lineations is northeasterly parallel to the channel axis in franklin strait and mainly northerly in larsen sound and m clintock channel elsewhere the seabed imagery commonly displays scours of various sizes and orientations created by the keels of icebergs seabed sediments revealed by 3 5 khz sub bottom profiles are interpreted to consist primarily of ice contact sediments that in part are thinly mantled by draped water lain sediments the age of the lineations has not been established possibly their formation was coincident with an ice stream in the m clintock channel eastern victoria island region which formed an ice shelf in viscount melville sound that grounded on southern melville and byam martin islands at ca 10 4 9 6 14 c ka bp alternatively they could result from later glacial events

glacial dynamics and deglacial retreat pattern in fingerdjupet trough western barents sea abstract new high resolution multibeam bathymetry and sub bottom profile datasets from fingerdjupet are used for the first detailed geomorphological mapping of the seafloor in this area the mapped landforms provide evidence for a palaeo ice stream flowing in a southeasterly direction from spitsbergenbanken into fingerdjupet merging with bjornoyrenna ice stream and confirm a theorised palaeo ice divide located along the bank the combined landform records and acoustic stratigraphy allow a detailed reconstruction of the glacial dynamics during the last deglaciation the withdrawal of the fingerdjupet ice stream from bjornoyrenna was characterised by rapid retreat punctuated by periods of stable ice marginal conditions five to six major ice margin stillstands and or readvances associated with the last deglaciation are identified in the seafloor record and acoustic stratigraphy during these events large grounding zone wedges were deposited at the ice stream margin the seabed geomorphology indicates that ice stream dynamics changed as the ice stream retreated from the trough onto the shallower bank here numerous retreat moraines indicate that a grounded ice margin retreated slowly with several minor stillstands towards north northwest several controls and or drivers on the style of ice flow and retreat have been suggested including catchment size reduction sea level rise bedrock topography drawdown of bank ice and or migration of the main ice divide over the bank

stable isotope response to lake eutrophication calibration of a high resolution lacustrine sequence from baldeggersee switzerland stable isotope analyses of discrete seasonal layers from a 108 yr annually laminated freeze core from baldeg gersee a small eutrophic lake in central switzerland provide information on the climatological and environmental factors including lake eutrophication that control oxygen and carbon isotopic composition of epilimnic biologically induced calcite precipitate during the last 100 yr baldeggersee has undergone major increases in productivity and eutrophication in response to nutrient loading from agriculture and industrialization in the lake s watershed calibration of the isotopic signal in baldeggersee to historical limnological data quantitatively links evidence of isotopic depletion in the sedimented calcite to trophic state of the lake 18o values from the spring summer light sediment layers steadily diverged to more depleted values in response to historical eutrophication measured 18o values were up to 21 5 more negative than calculated equilibrium 18o values evidence for 13c depletion in the calcite relative to equilibrium values is more difficult to ascertain because of an overall dominance of isotopic enrichment in the dissolved inorganic pool as productivity in baldeggersee increases a positive association exists between the degree of oxygen 18 depletion and the calcite crystal size thus large amorphous calcite grains can be used as a proxy for recognizing apparent isotopic nonequilibrium in sediment sequences from highly productive lacustrine environments from all geologic time scales in contrast to the light layers the oxygen isotopic composition of the calcite in the late summer fall dark sediment layers is unaffected by the apparent isotope nonequilibrium oxygen and carbon isotope values from the dark laminae in the baldeggersee sediment therefore provide environmental and climatological proxies that can be calibrated with known environmental and regional climate data for the last century

deglaciation of the eurasian ice sheet complex the eurasian ice sheet complex eisc was the third largest ice mass during the last glacial maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea level lowering whilst recent terrestrial and marine empirical insights have improved understanding of the chronology pattern and rates of retreat of this vast ice sheet a concerted attempt to model the deglaciation of the eisc honouring these new constraints is conspicuously lacking here we apply a first order thermomechanical ice sheet model validated against a diverse suite of empirical data to investigate the retreat of the eisc after 23 ka bp directly extending the work of patton et al 2016 who modelled the build up to its maximum extent retreat of the ice sheet complex was highly asynchronous reflecting contrasting regional sensitivities to climate forcing oceanic influence and internal dynamics most rapid retreat was experienced across the barents sea sector after 17 8 ka bp when this marine based ice sheet disintegrated at a rate of 670 gigatonnes per year gt a 1 through enhanced calving and interior dynamic thinning driven by oceanic atmospheric warming and exacerbated by eustatic sea level rise from 14 9 to 12 9 ka bp the eisc lost on average 750 gt a 1 peaking at rates 3000 gt a 1 roughly equally partitioned between surface melt and dynamic losses and potentially contributing up to 2 5 m to global sea level rise during meltwater pulse 1a independent glacio isostatic modelling constrained by an extensive inventory of relative sea level change corroborates our ice sheet loading history of the barents sea sector subglacial conditions were predominately temperate during deglaciation with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network moreover the maximum eisc and its isostatic footprint had a profound impact on the proglacial hydrological network forming the fleuve manche mega catchment which had an area of 2 5 106 km2 and drained the present day vistula elbe rhine and thames rivers through the seine estuary during the bolling allerod oscillation after c 14 6 ka bp two major proglacial lakes formed in the baltic and white seas buffering meltwater pulses from eastern fennoscandia through to the younger dryas when these massive proglacial freshwater lakes flooded into the north atlantic ocean deglaciation temporarily abated during the younger dryas stadial at 12 9 ka bp when remnant ice across svalbard franz josef land novaya zemlya fennoscandia and scotland experienced a short lived but dynamic re advance the final stage of deglaciation converged on present day ice cover around the scandes mountains and the barents sea by 8 7 ka bp although the phase lagged isostatic recovery still continues today

radiocarbon geochemistry of modern and ancient arctic lake systems baffin island canada the accuracy of arctic lake chronologies has been assessed by measuring the14c activities of modern carbon sources and applying these isotopic mass balances to dating fossil lake materials small 1 km2 shallow 25 m arctic lakes with watersheds 12 km2have soil and peat stratigraphic sections with14c activities ranging from 98 to 51 modern the14c activity of particulate organic carbon dissolved organic carbon and dissolved inorganic carbon from lake and stream waters ranges from 121 to 95 modern the sediment water interface of the studied lakes shows consistent14c ages of 100014c yr although the14c activity of living aquatic vegetation is 115 modern radiocarbon measurements of components of the lacustrine carbon pool imply that the 100014c yr age of the sediment water interface results from deposition of14c depleted organic matter derived from the watershed

pliocene warmth polar amplification and stepped pleistocene cooling recorded in ne arctic russia understanding the evolution of arctic polar climate from the protracted warmth of the middle pliocene into the earliest glacial cycles in the northern hemisphere has been hindered by the lack of co

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

isotopic record of lead pollution in lake sediments from the northeastern united states abstract although it is common knowledge that pb concentrations have increased in lake sediments in the northeastern united states over the last 150 years the processes responsible have been the subject of debate in this study differences in lead isotopic compositions and concentrations in sediment from large lakes lake erie ontario and michigan and small ones deep lake and lake andrus are used to infer temporal changes in the source s of anthropogenic pb in the great lakes region a natural background component of pb is present in sediment deposited prior to 1860 in lake erie and the other lakes as indicated from low pb concentrations and uniform lead isotopic compositions changes in isotopic ratios of lake sediment reflect differing sources of anthropogenic pb superimposed on the natural component such as regional deforestation from 1860 1890 followed by coal combustion and ore smelting through 1930 combustion of leaded gasoline was the dominant anthropogenic pb source to the atmosphere and by inference to lake sediment from 1930 1980 temporal changes in lead isotopic compositions in lake sediment suggest that the source of the pb used in gasoline additives gradually changed from 1930 to present the best example is a distinct shift in lead isotopic ratios in lake sediment deposited after 1970 which corresponds to increased pb production from the viburnum trend deposits in missouri present in all lakes except ontario however the changes in lead isotopic compositions are much less variable than and do not parallel those calculated on the basis of annual united states mine production and imports rather anthropogenic recycling of pb as well as natural mixing processes during emission transport and deposition of pb in lake sediment control most of the variation in lead isotope ratios differences in lead isotopic ratios in lake michigan erie and deep lake sediment preserve regional differences in lead isotopic ratios from u s and canadian sources first noted in aerosols by sturges and barrie 1987 more localized sources of pb such as point discharges are needed to explain the results from lake ontario and andrus

marine transgression shoreline emergence evidence in seabed and terrestrial ground temperatures of changing relative sea levels arctic canada precise temperatures to depths of several hundred meters have been measured in abandoned petroleum exploration wells in coastal and offshore areas of the canadian arctic in these regions changes in relative sea level during the quaternary have left a strong thermal signature on deep ground temperatures surface temperature changes of the order of 10 20 k accompanied shoreline emergence due to uplift in some regions and marine transgression due to eustatic changes in sea levels in others classical analytic techniques are used to demonstrate that these anomalous features are a direct consequence of recent changes in sea level in coastal areas of the queen elizabeth islands modelling of the large near surface temperature depth gradients and the distinct curvature in the measured profiles yield emergence times in general agreement with dates taken from emergence curves the analysis suggests that surface temperatures of these coastal areas were 16 19 k higher than at present from the late wisconsinan until emergence in the holocene suggesting either marine conditions for this period or glacial ice cover with basal temperatures near the pressure melting point in contrast at two offshore wells on the beaufort shelf analyses of the negative temperature depth gradients below the seabed and profile curvature yield times of marine transgression generally consistent with the published sea level curve for the area the analyses suggest that surface temperatures of some present offshore areas were 10 16 k lower than today s sea bottom temperatures from the late wisconsinan until marine transgression in the holocene the characteristic ground temperature profiles measured in such arctic areas provide independent evidence for the relative changes in sea level indicated by proxy data it is especially valuable for these areas where there is little historical record and from which datable material such as shells driftwood and pumice fragments may be scarce or ambiguous these effects may not be observable in temperate areas because of the smaller contrast in sea bottom and terrestrial temperatures

model simulations of the tides in the barents sea a large scale numerical model covering the nordic seas and the arctic ocean with 25 12 5 km grid resolution has been applied to study the tides in the barents sea tidal charts for elevation and phase are presented for the four tidal constituents m2 s2 n2 and k1 computed harmonic constants for elevation and current have been compared with observations from 46 coastal and pelagic tidal stations the agreement between model and field data is good for most stations with an overall standard deviation of 2 5 cm for amplitude 18 30 for phase and 1 3 cm s for current speed calculated tidal residual currents show anticyclonic eddy circulation over the svalbard bank and around bear island and hopen particle trajectories and streaklines due to the tidal flow over svalbardbanken have been calculated and the computed streaklines are found to agree well with observed rifts in the ice cover due to stranded icebergs

long term evolution and internal architecture of a high energy banner ridge from seismic survey of banc du four western brittany france the recent completion of a coupled seismic and swath bathymetric survey conducted across the sand ridge system of the banc du four located on the atlantic continental shelf of brittany mer d iroise france provided new data for the study of the long term evolution of deep tidal sand ridges five seismic units are distinguished within the ridge separated by pronounced major bounding surfaces the basal unit is interpreted to be shoreface deposits forming the core of the ridge it is overlaid by a succession of marine sand dunes fields forming the upper units sandwave climbing which combines progradation and accretion is the major process controlling the growth of the ridge the elevation of the preserved dune foresets reaches values of about 20 30 m within the ridge the foresets indicate a combination of giant dunes characterized by numerous steep up to 20 clinoforms corresponding to a high energy depositional environment moreover the presence of scour pits linked to the 3d geometries of giant dunes allow the growth of bedforms migrating oblique to the orientation of giant dune crest lines all of the radiocarbon ages of the biogenic surficial deposits of the banc du four range from 10 036 to 2748 cal years b p and suggest the banc du four has grown during the last sea level rise the apparent absence of recent surface deposits could be caused by a change in benthic biogenic productivity or the non conservation of recent deposits in contrast the presence of relatively old sands at the top of the ridge could be explained by the reworking and leakage of the lower units that outcrop locally at the seabed across the ridge moreover the long term evolution of the ridge appears strongly controlled by the morphology of the igneous basement the multiphase accretion of the ridge is closely linked to the presence of a residual tidal current eddy consecutive with the progressive flooding of the coastal promontories and straits that structured the igneous basement therefore the banc du four should be thought of as a representative example of a large scale high energy banner bank

quaternary shelf sea palaeoceanography recent developments in europe abstract high quality palaeoceanographic reconstructions based on sequences preserved in shallow marine environments demonstrate that these constitute significant archives of climatic and oceanographic change such sequences are important first because their often very high resolution sometimes laminated nature enables high frequency cycles to be resolved and provides the basis for establishing spatial and temporal variability in the marine radiocarbon reservoir effect second sea level index points from shelves are important for the validation of glacio hydro isostatic geophysical models and for understanding sea level change during early deglaciation third shallow marine sequences contain excellent records of land ocean interaction often preserving paired terrestrial marine proxies in the same stratigraphic sequence a new development in shelf sea palaeoceanography is documenting the long term dynamics of shelf sea stratification this is the dominant hydrodynamic phenomenon of tide dominated shelf seas in the middle and high latitudes and has a profound influence on productivity and therefore global change through the carbon cycle detailing the evolution of seasonal stratification during eustatic highstands is therefore of relevance to the climate system

unusual rates and patterns of holocene emergence ellesmere island arctic canada substantial postglacial emergence up to 150 m characterizes the canadian high arctic following the last glacial maximum across northern ellesmere island rapid emergence is not observed during the early stages of deglaciation as it is in other parts of arctic canada rather the curves show an interval of slow emergence c 1 m per century during initial ice retreat this is attributed to a slow rate of glacial rebound that was countered by a similar rate of eustatic sea level rise normally isobases drawn on postglacial shorelines define broad cells of uplift that mimic centres of former maximum ice thickness however isobases on the 8 ka bp shoreline surveyed throughout northern ellesmere island indicate more complex patterns of crustal uplift that seem in congruent with reported ice thicknesses on west central ellesmere island the isobases 110 150 m asl trace a plunging ridge aligned with geological structure across an area considered to have had minimal ice cover during the last glacial maximum the ridge may record an important structural influence associated with the geologically youthful sverdrup basin collectively this evidence cautions against the view that postglacial emergence has a universally predictable signature solely portraying former ice loads

sandwaves and sand transport on the barents sea continental slope offshore northern norway we integrate morphological geological and geophysical observations with oceanographic measurements and modelling results to interpret the processes behind the origin and evolution of sandwaves on the upper continental slope of the southwestern barents sea seven sandwave fields covering c 130 km2 and with a volume of c 72 106 m3 occur in water depths of c 475 800 m individual sandwaves reach heights up to 6 m the sandwaves are sinusoidal with asymmetric stoss lee side relationships and time lapse multibeam bathymetry analysis indicates that some sandwaves have migrated up to 10 m towards the nnw over a 4 year time period this contour current parallel migration is counteracted by currents in several other directions and the sand unit is thus not a simple contourite measurements show prominent diurnal period oscillations and clear spring neap variations of current direction and speed with along slope and cross slope current velocities up to 75 cm s 1 and 65 cm s 1 respectively numerical ocean modelling results produce eddies travelling along the slope positionally stable daily recurring vortices and bottom current velocity up to 100 cm s 1 in the sandwave fields sandwave migration towards the se is also observed and the cross slope currents are capable of transporting sand up and down the slope as evidenced by ripples migrating normal to the sandwaves eroded sand accumulates in the sandwave fields along the boundary between north atlantic water and norwegian sea arctic intermediate water this is a consequence of the combined effect of the nnw directed along slope norwegian atlantic current and tidally induced topographic waves the sandwave fields started to form 11 000 13 000 14c yrs bp or possibly later by current erosion of glacial sediments on the continental shelf and slope

water quality and sediment geochemistry in lakes of yunnan province southern china yungui plateau lakes in southwestern china are economically important although few have been studied previously water and sediments of 24 lakes throughout yunnan province were sampled in october 1994 we describe the chemical and physical characteristics of yunnan lakes and address effects of regional geology and human influences on water quality and sediment type water quality differs between deep yunnan lakes of tectonic origin and shallow solution basins shallow lakes generally have higher nutrient concentrations and appear to be more susceptible to riparian disturbance than deeper lakes shallow lakes with high macrophyte standing crops nevertheless exhibit nutrient poor waters principal ions ca2 mg2 and hco3 reflect regional carbonate geology except in cheng hai which is a sodium bicarbonate lake specific conductance and 18o are positively correlated indicating that evaporation concentrates both solutes and 18o large shallow lakes in southeastern yunnan exhibit 18o enriched waters because of substantial evaporation whereas small deep lakes are 18o depleted lake waters are 18o depleted in small shallow basins that receive substantial rainwater input relative to their small volumes 18o enrichment in cheng hai suggests that a recent 5 m water level decline in this lake was caused by increased evaporation or diversion of freshwater inflow yunnan watersheds have undergone substantial deforestation agricultural cultivation soil erosion and industrialization limnetic nutrient concentrations indicate that human activities have affected water quality organic matter content is low in sediments because of increased non carbonate clastic sediment yield from watersheds environmental policies are needed to balance ecological contraints with economic activities that impact water quality

water and sediment movement in the vicinity of linear sandbanks the norfolk banks southern north sea geophysical surveys current meter measurements and fluorescent sand tracer experiments were undertaken in the vicinity of the broken bank the data are used to establish localised and regional patterns of water and sediment movement the results obtained confirm mechanisms proposed previously for sandbank growth with particular reference to the north sea these include the clockwise circulation of water and sand with convergence at the crestline secondary helical water circulations do not appear to be a dominant process influencing sandbank maintenance however such circulation may still be important in the initial formation of linear sandbanks and or at some stages in the bank development on a regional basis residual currents bedform asymmetries and tracer dispersion indicate an offshore sediment transport component this observation supports the hypothesis of other investigators formed on the basis of geomorphological observations and numerical model predictions concerning the movement of sand under extreme conditions moreover these transport pathways may persist under low wave and tidally dominated conditions as opposed to being restricted to storm activity

quaternary history of axel heiberg island bordering nansen sound northwest territories emphasizing the last glacial maximum the landscape of northeastern axel heiberg island records an erosional history since the neogene whereas the glacial and sea level history relate to late wisconsinan glaciation during the last glacial maximum northeastern axel heiberg island was covered by glaciers emanating from local and regional sources local ice caps expanded from highlands on axel heiberg island across the coastal slope a trunk glacier flowed northward out of eureka and flat sounds into nansen sound and reached northernmost axel heiberg island radiocarbon ages on marine shells suggest that the last glacial maximum was attained along the coast after 29 ka bp and extensive deglaciation was taking place by 10 3 ka bp the postglacial marine limit rises continuously from 78 m above sea level near the entrance to nansen sound to 158 m above sea level at the mouth of eureka sound showing greatest glacioisostatic loading to the south

glaciation and the evolution of the canadian high arctic landscape the canadian arctic islands represent a tertiary fluvial landscape developed on a contiguous landmass subsequently fractured by block faulting nonetheless some theoretical models invoke pervasive high latitude ice sheets and continue to misattribute the faulted landscape to glacially scoured river valleys quaternary fieldwork on northern ellesmere island suggests that these models are inappropriate for high latitude ice sheets and should be abandoned if there was ever a regional ice sheet over arctic canada it likely occurred on a prefaulted contiguous landmass that had a more temperate climate than at present possibly during the late tertiary after block faulting the marine channels permanently prevented the ice from inundating the landscape it once crossed tectonics and not climate have led to a fundamental change in glacial style this block faulting also may have played a role in terminating the late tertiary boreal forest to 80 n by establishing cold marine channels that diminished the continentality of the once contiguous landmass for a thorough understanding of the canadian arctic landscape future research should determine the continuity between the tertiary and quaternary paleoenvironments the unknown ages of the fiords and interisland channels are of primary importance

an inter ice stream glaciated margin submarine landforms and a geomorphic model based on marine geophysical data from svalbard well preserved submarine landforms from the continental shelf and fjords of northwest ernmost svalbard provide an example of ice sheet deposition in an inter ice stream setting em1002 swath bathymetric imagery covering 1280 km 2 was examined at the shelf edge a distinctive and continuous belt of hum mocky topography represents the grounding zone of a slow moving late weichselian ice sheet active ice on the outer shelf is inferred from subtle lineations orientated parallel to fl ow low amplitude transverse moraines crosscut the lineations suggesting ice retreat across the outer shelf with brief stillstands on the middle and inner shelf large moraine ridges indicate multiple stillstands during de glaciation there are arcuate moraine ridges at fjord mouths streamlined crag and tail landforms are preserved from when ac tive full glacial ice fl owed out of the fjords clusters of smaller transverse ridges indi cate slow retreat of grounded ice through the fjords holocene sedimentation is by rainout from sediment rich meltwater producing smooth basin fi ll small slides from the fjord walls are common little ice age glacier readvance produced another set of terminal moraines and smaller retreat moraines in the innermost fjords a schematic model of this inter ice stream glacial landform assem blage summarizes the geomorphic record it is compared with a model derived from sev eral svalbard cross shelf troughs occupied by fast fl owing late weichselian ice streams in general the seafl oor morphology of continen tal margins affected by ice streams is domi nated by streamlined subglacially produced landforms oriented in the former ice fl ow direction interrupted by major grounding zone wedges formed during temporary halts in ice retreat by contrast between ice streams shelf and fjord morphology records submarine landforms of various dimensions oriented mainly transverse to ice fl ow pro duced at slowly retreating grounded ice sheet margins there is little evidence for channeled subglacial water fl ow in the form of eskers and ice contact fans on the sval bard margin implying that basal water is drained or advected mainly within soft sub glacial sediments

oscillations in the indian summer monsoon during the holocene inferred from a stable isotope record from pyrogenic carbon from lake chenghai southwest china abstract a robust well dated record of centennial scale abrupt changes in the asian summer monsoon is crucial for understanding the potential forcing factors and their environmental effects in this study we analyzed the stable carbon isotopes of pyrogenic carbon 13cpc in a 556 cm long sediment core retrieved from lake chenghai in the yunnan plateau china the results provide a continuous 7660 year precipitation record of the indian summer monsoon ism they indicate that from 7600 cal yr bp precipitation in the lake chenghai catchment gradually increased until 5030 cal yr bp and then subsequently decreased in the second half of the holocene in addition at least six centennial scale droughts occurred at about 7300 6300 5500 3400 2500 and 500 cal yr bp our findings suggest that ism intensity is primary controlled by variations in solar irradiance on a centennial time scale this external forcing may be amplified by north atlantic cooling events and el nino southern oscillation activity in the eastern tropical pacific which shift the intertropical convergence zone further southwards