the 8 2 ka event from greenland ice cores we present a collection of high resolution chemistry and stable isotope records from the plateau of the greenland ice cap during the cold event 8200 yr ago using a composite of four records the cold event is observed as a 160 5 yr period during which decadal mean isotopic values were below average within which there is a central event of 69 yr during which values were consistently more than one standard deviation below the average for the preceding period four cores in north south and central greenland show differences at decadal and shorter timescales it is not yet clear if this represents significant spatial differences in response the results show clear evidence for colder temperatures and a decrease in snow accumulation rate however the changes in chemical concentrations for the ions looked at here are small suggesting only minor changes in atmospheric circulation for this event apart from the decrease in methane concentration greenland ice cores give only weak evidence for effects outside the north atlantic region

the influence of troughs and crests of ripple marks on the structure of subtidal benthic assemblages around rocky reefs this study tested the hypothesis that the small scale topography caused by ripples in sediment would affect benthic macrofaunal assemblages ripple marks were measured and macrofauna and sediments were sampled near to and far from subtidal rocky reefs at two sites ripples were significantly wider and taller close to than far from reefs sediment grain size was significantly different between crests and troughs microtopography clearly influenced the structure of the benthic macrofaunal assemblages in three of the four locations and 8 of the 12 sites examined numbers of taxa of the benthic macrofaunal assemblages and almost all individual taxa analysed showed significant greater abundances in troughs than in crests the results strongly support the model that benthic macrofauna are affected by locally varying hydrodynamic environments produced by ripple beds these in turn were influenced by their proximity to a reef models about passive transport of the macrofauna by water movement and active movements of the fauna are discussed furthermore it appeared that there was a relationship between spatial variability of the macrofaunal assemblages and size of ripples it is suggested that microtopography should be considered in experimental designs when patterns of distribution of benthic organisms are being evaluated

the impact of scour processes on a smothered reef system in the irish sea the irish sea like many marine areas is threatened by anthropogenic activities in particular the pisces reef system a series of smothered rocky reefs are subject to fishing pressures as a result of their position within a nephrops norvegicus fishery in an area of sediment deposition and retention the reefs modify the environment by increasing the energy of near bottom currents which results in localised scouring this is the first study to attempt to characterise and investigate the ecological functioning of the pisces reef system a multidisciplinary approach was essential for accurate investigation of the area to facilitate more effective management of the benthic habitats of the reef system this study integrates acoustic seismic grab sampling and video ground truthing methods for benthic habitat discrimination orientation of the scour hollows also suggest that seabed features could be used to infer dominant flow regimes such as the irish sea gyre the data revealed significant geology benthos relationships a unique biotope was described for the reef habitat and it was demonstrated that scouring may influence community composition through disturbance mechanisms this study provides preliminary information required for management of a unique habitat within a uniform region

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

a new late weichselian and holocene marine chronology for the western svalbard slope 30 000 0 cal years bp abstract data have been compiled from eleven sediment cores from 76 to 80 n on the western svalbard slope the cores are from water depths between 630 and 1880 m and show clear similarities in lithology and magnetic susceptibility all cores penetrated into mass transported sediments from glacigenic debris flow events and turbidity flow events the mass transport probably occurred when the ice reached the shelf edge the deposits date between 24 080 150 and 23 550 185 calibrated cal years bp the records also include laminated fine grained sediments interpreted as deposits from sediment laden meltwater plumes dated between 14 780 220 and 14 300 260 cal years bp in holocene sediments a diatom rich fine grained layer dates 10 100 150 to 9840 200 cal years bp the eleven cores have been stacked into one record with absolute age control from 35 ams14c dates together with oxygen isotope stratigraphy and contents of ice rafted detritus the stacked record provides a useful chronology tool for cores on the western svalbard slope our study improves the age control of earlier well documented glacial events and shows that the maximum glacial state and the onset of the deglaciation both occurred 2500 3000 years earlier than previously reconstructed for the western svalbard margin the results indicate that during the last 30 000 years advance and retreat of the svalbard barents sea ice sheet was closely linked to the flow of atlantic water and polar water over the margin

holocene glacial and climatic variations on spitsbergen svalbard holocene glacial and climatic variations have been inferred from investigations of sediment cores from the proglacial lake linnevatnet western spitsbergen a low content of glacially derived coal absence of regular laminations and a slow sedimentation rate in the lower part of the lacustrine sediments indicate that the former glaciers that existed within the catchment area during the last ice age melted quickly away as a result of the younger dryas holocene warming and during the next 6000 years there were no glaciers in the valley increasing coal content incipient laminations and rising sedimentation rates indicate that the glacier linnebreen started to form 4000 5000 years ago probably as a response to the late holocene cooling the holocene maximum extent of the glacier occurred during the little ice age starting with a pronounced ice advance in the thirteenth or fourteenth century a well dated core from billefjorden which is assumed to reflect glacial fluctuations in the inner part of the i

no reef associated gradient in the infaunal communities of rapa nui easter island are oceanic waves more important than reef predators abstract reef associated predators are thought to influence the distribution of invertebrates of surrounding sediment habitats in this study we analyzed the predation pressure and the distributional patterns of macro and meiofaunal assemblages in soft sediments surrounding two coral reef sites at rapa nui easter island in the central south pacific we tested the hypothesis that reef associated predators negatively affect sediment dwelling invertebrates causing macro and meiofauna to be less abundant and diverse in soft sediments near the reefs as expected predation intensity was greater nearer the reef than farther away but macro and meiofaunal assemblages did not differ significantly with distance from the reef taxon richness of macro and meiofaunal assemblages were similar irrespective of distance from the reef only meiofauna showed significant variation in total abundance with distance from the reef but this trend was not consistent between the two study sites no gradient in sediment texture was observed with distance from the reef underwater video recordings at one study site also revealed that local hydrodynamics cause frequent disturbance and resuspension of the upper sediment layers our results suggest that soft sediment assemblages are constantly reshuffled by oceanic waves thereby blurring the potential effects of predation on invertebrate assemblages closer to the reef

eemian interglacial reconstructed from a greenland folded ice core efforts to extract a greenland ice core with a complete record of the eemian interglacial 130 000 to 115 000 years ago have until now been unsuccessful the response of the greenland ice sheet to the warmer than present climate of the eemian has thus remained unclear here we present the new north greenland eemian ice drilling neem ice core and show only a modest ice sheet response to the strong warming in the early eemian we reconstructed the eemian record from folded ice using globally homogeneous parameters known from dated greenland and antarctic ice core records on the basis of water stable isotopes neem surface temperatures after the onset of the eemian 126 000 years ago peaked at 8 4 degrees celsius above the mean of the past millennium followed by a gradual cooling that was probably driven by the decreasing summer insolation between 128 000 and 122 000 years ago the thickness of the northwest greenland ice sheet decreased by 400 250 metres reaching surface elevations 122 000 years ago of 130 300 metres lower than the present extensive surface melt occurred at the neem site during the eemian a phenomenon witnessed when melt layers formed again at neem during the exceptional heat of july 2012 with additional warming surface melt might become more common in the future

holocene thinning of the greenland ice sheet the nature of the response of the greenland ice sheet gis to climate change is a fundamental question in climate science but the details remain unclear during the holocene climate optimum 6 000 to 9 000 years ago for example many locations in the northern hemisphere showed unusual warmth yet changes in greenland appeared inconsistent vinther et al now standardize the previously disparate seeming ice core records of climate history on the gis during the holocene and find consistent evidence for a stronger climate optimum than was previously recognized together with elevation reduction and marginal ice sheet thinning the response of the greenland ice sheet gis to changes in climate remains uncertain during the holocene climatic optimum an unusually warm period from about 9 000 to 6 000 years ago changes in greenland appear inconsistent with the rest of the northern hemisphere here the greenland holocene temperature history and the evolution of gis surface elevation are extracted from four gis locations the results may resolve this disparity on entering an era of global warming the stability of the greenland ice sheet gis is an important concern1 especially in the light of new evidence of rapidly changing flow and melt conditions at the gis margins2 studying the response of the gis to past climatic change may help to advance our understanding of gis dynamics the previous interpretation of evidence from stable isotopes 18o in water from gis ice cores was that holocene climate variability on the gis differed spatially3 and that a consistent holocene climate optimum the unusually warm period from about 9 000 to 6 000 years ago found in many northern latitude palaeoclimate records4 did not exist here we extract both the greenland holocene temperature history and the evolution of gis surface elevation at four gis locations we achieve this by comparing 18o from gis ice cores3 5 with 18o from ice cores from small marginal icecaps contrary to the earlier interpretation of 18o evidence from ice cores3 6 our new temperature history reveals a pronounced holocene climatic optimum in greenland coinciding with maximum thinning near the gis margins our 18o based results are corroborated by the air content of ice cores a proxy for surface elevation7 state of the art ice sheet models are generally found to be underestimating the extent and changes in gis elevation and area our findings may help to improve the ability of models to reproduce the gis response to holocene climate

hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability abstract hydrogen isotope ratios were measured on n alkanes n c12 to n c31 extracted from recent lake surface sediments along a n s european transect to test if modern climate variability is recorded in these biomarkers d values of the n alkanes are compared to d values of meteoric water from the iaea gnip database spanning a range from 119 in northern sweden to 41 in southern italy to lake water d values and to mean annual temperatures varying between 2 0 c in the north and 13 7 c in the south d values of the short chained n alkanes n c12 to n c20 excluding algal derived n c17 and n c19 are higher in the north and lower in the south the isotopic fractionation e for hydrogen between meteoric water and the short chained n alkanes is increasing from n to s by more than 100 and is significantly correlated to mean annual temperature for n c16 and n c18 this suggests that these n alkanes may originate from a different source in the northern lakes possibly due to petroleum contamination or are synthesized using a different biochemical pathway the n c17 and n c19 alkanes of algal origin the n c21 and n c23 alkanes originating from water plants and the long chain n alkanes n c25 n c27 n c29 and n c31 of terrestrial origin clearly correlate with d values of meteoric water lake water and mean annual temperature indicating that they excellently record the d value of meteoric water the mean hydrogen isotope fractionation ec17 w of 157 sd 13 between n c17 and meteoric water is fairly constant over the wide range of different climates and lake environments suggesting only minor influence of environmental factors on this biochemical fractionation this suggests that d values of n c17 are suitable to reconstruct the isotopic composition of source water the mean fractionation between the long chain n alkanes and water is 128 sd 12 the mean difference of 31 between both e values is likely due to evaporative enrichment of deuterium in the leaf water if this is the only influence on the enrichment the difference between the d values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

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

a complete record of holocene glacier variability at austre okstindbreen northern norway an integrated approach arctic glaciers are currently undergoing major changes but accurate knowledge about how they varied during the entire holocene is still scarce here we present a new complete glacier record from austre okstindbreen in nordland northern norway this reconstruction is based on a number of short and long cores retrieved from several downstream basins which have been analyzed by a suite of methods including geochemical elements xrf rock magnetic properties dry bulk density dbd and loss on ignition loi lake sediment distribution was surveyed and mapped prior to coring by the use of ground penetrating radar gpr independently lichen dated marginal moraines and historical information about the glacier frontal positions from old photographs and maps have made it possible to link the moraine sequence to the 210pb dated lake sediment chronology this integrated approach reveals that austre okstindbreen is the first known glacier in scandinavia to possibly have survived the holocene thermal optimum it also brackets the four largest glacier advances to c 7400 7000 1400 1200 900 700 and 300 150 years before ad 2000 b2k in contrast to most reconstructed glaciers in scandinavia the largest glacier advance was not associated with the little ice age but rather to an earlier period centred at 1300 b2k both the moraine chronology and the lacustrine records document this neoglacial advance compared to other glacier reconstructions from the northern hemisphere we identify near synchronous glacier advances occurring roughly at 4000 b2k 2700 b2k 1300 b2k and during the little ice age these correlative advances across the northern hemisphere suggest that these observed centennial scale events are a shared feature regardless of the large geographical distances separating them some minor discrepancies between different geographical areas may be caused by lack of precise dating but local climatic conditions may play a role as well

a review of molecular organic proxies for examining modern and ancient lacustrine environments molecular organic geochemical proxies are increasingly being utilized to reconstruct past environmental conditions as new tools continue to be discovered and developed to date organic geochemical proxies have been developed mainly for use in marine systems and are widely used in paleoceanography in contrast organic proxies have been less commonly used on lacustrine sedimentary records one reason for this is that the wide range in the physical and chemical properties of lakes complicates application of some organic geochemical proxies in lacustrine settings furthermore in comparison to marine studies presently only a small number of studies have conducted or are currently conducting fundamental research aimed at developing organic geochemical proxies for use in lacustrine settings despite this an increasing number of paleo limnological studies are currently applying organic geochemical techniques to examine present and past environmental conditions in this manuscript we review the use of a number of commonly utilized organic geochemical and isotopic proxies and discuss their potential for environmental reconstruction in quaternary lacustrine deposits

oceanic and atmospheric variations during the last deglaciation in the fram strait arctic ocean a coupled high resolution organic geochemical and sedimentological study abstract from a high sedimentation rate core obtained from the yermak slope arctic ocean we deduced short term climatic fluctuations of the last deglaciation lasting from 17 000 to 9000 years bp by using a coupled organic geochemical and sedimentological approach we reconstructed near bottom current conditions and assessed their significance in relation with comparable global thermohaline circulation patterns and surface water conditions highest concentrations and fluctuations of specific marine phytoplankton biomarkers were obtained in the bolling allerod when the major deglaciation of the svalbard barents sea ice sheet sbis occurred the marine biomarker record and the sedimentological record are consistent with climate reconstructions obtained from greenland ice cores and thermohaline circulation variations however beginning with the younger dryas yd episode bottom currents decreased during this time period but surface waters remained very productive the atmospheric conditions of the western fram strait reconstructed from biomarker data and thermohaline circulation signals reconstructed from sedimentological data were decoupled in the yd maximum insolation values of solar radiation and fohn like winds enabled open water conditions and increased productivity values in the northern fram strait at least in summer

north atlantic holocene climate evolution recorded by high resolution terrestrial and marine biomarker records abstract holocene climatic change is driven by a plethora of forcing mechanisms acting on different time scales including insolation internal ocean e g atlantic meridional overturning circulation amoc and atmospheric e g north atlantic oscillation nao variability however it is unclear how these driving mechanisms interact with each other here we present five biomarker based paleoclimate records air sea surface temperature and precipitation from a fjordic sediment core revealing north atlantic terrestrial and marine climate in unprecedented detail the early holocene 10 7 7 8 kyrs bp is characterised by relatively high air temperatures while ssts are dampened by melt water events and relatively low precipitation the middle holocene 7 8 3 2 kyrs bp is characterised by peak ssts declining air temperatures and high precipitation a pronounced marine thermal maximum occurs between 7 5 5 kyrs bp 3000 years after the terrestrial thermal maximum driven by melt water cessation and an accelerating amoc the neoglacial cooling between 5 8 and 3 2 kyrs bp leads into the late holocene we demonstrate that an observed modern link between icelandic precipitation variability during different nao phases may have existed from 7 5 kyrs bp a simultaneous decoupling of both air and sea surface temperature records from declining insolation at 3 2 kyrs bp may indicate a threshold after which internal feedback mechanisms namely the nao evolved to be the primary drivers of icelandic climate on centennial time scales

hydroclimate variability of high arctic svalbard during the holocene inferred from hydrogen isotopes of leaf waxes abstract the response of the arctic hydrologic cycle to global warming includes changes in precipitation patterns and moisture availability associated with variable sea ice extent and modes of atmospheric circulation reconstructions of past hydroclimate changes help constrain the natural range of these systems identify the manners in which they respond to different forcing mechanisms and reveal their connections to other components of the climate system all of which lead to a better understanding of present and future changes here we examine hydroclimate changes during the holocene in the high arctic archipelago of svalbard by reconstructing the isotopic composition of precipitation we measured the hydrogen isotopic composition d values of leaf wax compounds n alkanes c 25 c 31 in a sediment core from lake hakluytvatnet on the island of amsterdamoya northwest spitsbergen we interpret d values of mid chain c 25 and long chain c 29 c 31 length n alkanes to represent changes in the isotopic composition of lake water and precipitation over the last 12 9 ka after deglaciation of the catchment water supply became restricted and the lake experienced significant evaporative isotopic enrichment indicating warmer conditions from 12 8 to 7 5 ka the isotope values suggest an increase in the delivery of moisture from warmer sub polar air masses between 12 8 and 9 5 ka followed by generally warm but unstable conditions between 9 5 and 7 5 ka possibly indicating a response to meltwater forcing sedimentary evidence indicates a hiatus in deposition c 7 5 5 0 ka likely as a result of desiccation of the lake at c 5 0 ka lacustrine sedimentation resumed and over the last 5 ka there was a progressive increase in the influence of polar air masses and colder conditions which culminated in an abrupt shift to colder conditions at c 1 8 ka this late holocene cooling ended c 0 18 ka when isotopic data indicate warmer conditions and greater influence of moisture derived from lower latitudes

variability of sea ice conditions in the fram strait over the past 30 000 years sea ice is a critical component of the climate and oceanographic system in the north atlantic ocean a biomarker record reveals millennial scale and glacial interglacial fluctuations in sea ice coverage in the northernmost atlantic ocean over the past 30 000 years

postglacial climate reconstruction based on compound specific d h ratios of fatty acids from blood pond new england we determined hydrogen isotope ratios of individual fatty acids in a sediment core from blood pond massachusetts usa in order to reconstruct climate changes during the past 15 kyr in addition to palmitic acid c16n acid which has been shown to record lake water d h ratios our surface sediments and down core data indicate that behenic acid c22n acid produced mainly by aquatic macrophytes is also effective for capturing past environmental change calibration using surface sediments from two transects across eastern north america indicates that behenic acid records d variation of lake water down core variations in d values of behenic acid and pollen taxa are consistent with the known climate change history of new england by evaluating the hypothesis that d h fractionations of long chain even numbered fatty acids c24 c32n acids relative to lake water provide independent estimates of relative humidity during the growing season we find that differences between lake level records and isotopically inferred humidity estimates may provide useful insight into seasonal aspects of the hydrologic cycle combined analyses of d h of short and long chain fatty acids from lake sediment cores thus allow reconstructions of both past temperature and growing season relative humidity comparison of d records from two lakes in new england provides critical information on regional climate variation and abrupt climate change such as the 8 2 ka event

atlantic water advection versus sea ice advances in the eastern fram strait during the last 9 ka multiproxy evidence for a two phase holocene a sediment core from the west spitsbergen continental margin was studied to reconstruct climate and paleoceanographic variability during the last 9 ka in the eastern fram strait our multiproxy evidence suggests that the establishment of the modern oceanographic configuration in the eastern fram strait occurred stepwise in response to the postglacial sea level rise and the related onset of modern sea ice production on the shallow siberian shelves the late early and mid holocene interval 9 to 5 ka was generally characterized by relatively unstable conditions high abundance of the subpolar planktic foraminifer species turborotalita quinqueloba implies strong intensity of atlantic water aw inflow with high productivity and or high aw temperatures resulting in a strong heat flux to the arctic a series of short lived cooling events 8 2 6 9 and 6 1 ka occurred superimposed on the warm late early and mid holocene conditions our proxy data imply that simultaneous to the complete postglacial flooding of arctic shallow shelves and the initiation of modern sea ice production strong advance of polar waters initiated modern oceanographic conditions in the eastern fram strait at 5 2 ka the late holocene was marked by the dominance of the polar planktic foraminifer species neogloboquadrina pachyderma a significant expansion of sea ice icebergs and strong stratification of the water column although planktic foraminiferal assemblages as well as sea surface and subsurface temperatures suggest a return of slightly strengthened advection of subsurface atlantic water after 3 ka a relatively stable cold water layer prevailed at the sea surface and the study site was probably located within the seasonally fluctuating marginal ice zone during the neoglacial period

reconstruction of glacier variability from lake sediments reveals dynamic holocene climate in svalbard abstract the arctic is warming faster than anywhere else on earth holocene proxy time series are increasingly used to put this amplified response in perspective by understanding arctic climate processes beyond the instrumental period however available datasets are scarce unevenly distributed and often of coarse resolution glaciers are sensitive recorders of climate shifts and variations in rock flour production transfer this signal to the lacustrine sediment archives of downstream lakes here we present the first full holocene record of continuous glacier variability on svalbard from glacier fed lake hajeren this reconstruction is based on an undisturbed lake sediment core that covers the entire holocene and resolves variability on centennial scales owing to 26 dating points a toolbox of physical geochemical xrf and magnetic proxies in combination with multivariate statistics has allowed us to fingerprint glacier activity in addition to other processes affecting the sediment record evidence from variations in sediment density validated by changes in ti concentrations reveal glaciers remained present in the catchment following deglaciation prior to 11 300 cal bp culminating in a holocene maximum between 9 6 and 9 5 ka cal bp correspondence with freshwater pulses from hudson strait suggests that early holocene glacier advances were driven by the melting laurentide ice sheet lis we find that glaciers disappeared from the catchment between 7 4 and 6 7 ka cal bp following a late hypsithermal glacier reformation around 4250 cal bp marks the onset of the neoglacial supporting previous findings between 3380 and 3230 cal bp we find evidence for a previously unreported centennial scale glacier advance both events are concurrent with well documented episodes of north atlantic cooling we argue that this brief forcing created suitable conditions for glaciers to reform in the catchment against a background of gradual orbital cooling these findings highlight the climate sensitivity of the small glaciers studied which rapidly responded to climate shifts the start of prolonged neoglacial glacier activity commenced during the little ice age lia around 700 cal bp in agreement with reported advances from other glaciers on svalbard in conclusion this study proposes a three stage holocene climate history of svalbard successively driven by lis meltwater pulses episodic atlantic cooling and declining summer insolation

huascaran δ18o as an indicator of tropical climate during the last glacial maximum the interpretation of the isotopic composition of andes tropical mountain glaciers is reconsidered using a simple rayleigh distillation model it is shown that andes snowline depression and huascaran ice core 18o are consistent with a 3 c drop in sea surface temperature during the last glacial maximum accompanied by an increase from 40 at present to 60 during the lgm in the annual mean proportion of atmospheric water lost to continental runoff broecker s interpretation of huascaran 18o as a paleo hygrometer is discussed

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

delayed hydrological response to greenland cooling at the onset of the younger dryas in western europe during the younger dryas cold event about 12 800 years ago environmental change in western europe seems to occur 170 years after cooling over greenland lake sediment analyses confirm this delay and suggest european hydrological and vegetation change occurred only after the build up of sea ice in the north atlantic pushed the westerly wind system south

lipids of aquatic organisms as potential contributors to lacustrine sediments ii abstract the relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments previously examined for n alkanols and steroids is now reported for hydrocarbons ketones and carboxylic acids the n c7 alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment bacterial biomarkers including hopenes and i ai branched fatty acids were detected in the photosynthetic bacterial layer occurring just above the sediment water interface within the sediment the apparent conversion of free n alkanes alkan 2 ones and hydroxy acids to the corresponding bound form is noted microbiological oxidation of n alkanes to alkan 2 ones is supported by the detection of the intermediate alkan 2 ols with a distribution similar to that of the ketones the geochemistry of sediment deposited c 1900 prior to biological study of the site was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition a qualitative difference in algal input to the older sediment is inferred from the low 7 sterol content and presence of 2 6 10 trimethyl 7 3 methylbutyl dodecane however there was still significant dinoflagellate input as indicated by the presence of 4 methylsterols a difference in higher plant input to the older sediment indicated from the n alkane alkene and triterpenoid ketone distributions is consistent with the recent development of tree cover

holocene moraine chronology spitsbergen svalbard lichenometric evidence for multiple neoglacial advances in the arctic late holocene neoglacial moraines occurring within 1 or 2 km of present glacier margins are prominent features in the forefields of spitsbergen glaciers little ice age moraines are typically the most extensive and best preserved moraines of older holocene advances are much less common where observed older moraines occur as moraine remnants and provide irrefutable evidence of earlier neoglacial advances the fragmentary moraine record indicates two little ice age advances and two older neoglacial advances lichenometry provides calibrated ages for periods of moraine stabilization the oldest moraines stabilized by ca 1500 years ago and a second group of moraines stabilized by ca 1000 years ago little ice age moraines were deposited during two periods an early group of moraines stabilized ca 650 years ago and a later group during the last several centuries the proposed moraine chronology compares well with other proxy climate records on spitsbergen and with moraine records from areas borde

the noble gas systematics of late orogenic h2o co2 fluids mt isa australia abstract the noble gases he ne ar kr and xe are powerful geochemical tracers because they have distinctive isotopic compositions in the atmosphere crust and mantle this study illustrates how noble gases can be used to trace fluid origins in high temperature metamorphic and mineralising environments and at the same time provides new information on the composition of noble gases in deeper parts of the crust than have been sampled previously we report data for h2o and co2 fluid inclusions trapped at greenschist to amphibolite facies metamorphic conditions associated with three different styles of mineralisation and alteration in the proterozoic mt isa inlier of australia sulphide fluid inclusions are dominated by crustal 4he however co variations in fluid inclusion 20ne 22ne 21ne 22ne 40ar 36ar and 136xe 130xe indicate noble gases were derived from three or more reservoirs in most cases the fluid inclusions elemental noble gas ratios e g ne xe are close to the ranges expected in sedimentary and crystalline rocks however the elemental ratios have been modified in some of the samples providing evidence for independent pulses of co2 and interaction of co2 with high salinity aqueous fluids compositional variation is attributed to mixing of i magmatic fluids or deeply sourced metamorphic fluids characterised by basement derived noble gases with 20ne 22ne 8 4 21ne 22ne 0 4 40ar 36ar 40 000 and 136xe 130xe 8 ii basinal metamorphic fluids with a narrow range of compositions including near atmospheric values and iii noble gases derived from the meta sedimentary host rocks with 20ne 22ne 8 9 8 21ne 22ne these data provide the strongest geochemical evidence available for the involvement of fluids from two distinct geochemical reservoirs in mt isa s largest ore deposits in addition the data show how noble gases in fluid inclusions can provide information on fluid origins the composition of the crust s major lithologies fluid rock interactions and fluid fluid mixing or immiscibility processes

biogeochemical evidence for hydrologic changes during the holocene in a lake sediment record from southeast greenland holocene paleoclimate records from greenland help us understand the response of the greenland ice sheet and regional oceanic and atmospheric circulation systems to natural climate variability in or

10be surface exposure ages on the late pleistocene and holocene history of linnebreen on svalbard abstract arctic glaciers were sensitive to past changes in high latitude winter precipitation and summer temperature here we develop a late pleistocene to holocene history for linnebreen linne glacier in western svalbard using 10 be surface exposure ages on isolated erratic and moraine boulders we show that linnebreen had separated from the larger ice sheet over svalbard and was retreating up valley around the start of the younger dryas cold period we attribute this retreat during a cold period on svalbard to moisture starvation of linnebreen from advanced sea ice and or elevated shortwave boreal summer insolation that overwhelmed any reduction in sensible heat after an ice free period during the early to middle holocene linnebreen reformed sometime after 4 6 0 2 ka and was at a position roughly equivalent to its little ice age lia maximum extent before it began to retreat at 1 6 0 2 ka comparison with calibrated 14 c dates from three other glaciers could suggest that this period of ice retreat at 1 6 ka could be regional in extent linnebreen occupied the pre lia moraine when there was an increased ratio of cold arctic sourced relative to warm atlantic sourced waters around svalbard and advanced sea ice the retreat of linnebreen at 1 6 ka was concurrent with the increased presence of warm atlantic waters around svalbard and attendant sea ice retreat these coincident changes in ocean temperatures sea ice extent and linnebreen moraine age could imply a climatic forcing of the pre lia advance and retreat of linnebreen summer temperatures rather than changes in precipitation would then be dominant in driving ice retreat although the possibility of stochastic glacier margin variability cannot be excluded our data therefore suggest that linnebreen may have responded differently to past changes in sea ice extent that could depend on the background climate state deglacial climate vs late holocene climate which highlights the complexity in climatic controls on arctic glaciers

the influence of rocky reefs on structure of benthic macrofauna in nearby soft sediments abstract influences of rocky reefs on composition and abundances of species in assemblages of macrofauna in nearby subtidal soft sediments were examined by sampling at three distances from four rocky reefs three natural and one man made in botany bay nsw australia there was significant spatial variation in structure of assemblages between transects and among reefs the proportion of coarse material in sediments was generally larger close to than far from reefs assemblages sampled close to reefs were generally different in structure from those sampled away from rocky reefs in multivariate analyses assemblages close to reefs were spatially more variable than were those far from reefs analyses demonstrated that there were more species close to than far from the reefs polychaetes of the family syllidae were more abundant far from than near to rocky reefs artificial and natural rocky reefs influenced nearby benthic assemblages in sediments and various models are discussed to explain the patterns detected especially those concerning predation and characteristics of the sediments

holocene fluctuations of bregne ice cap scoresby sund east greenland a proxy for climate along the greenland ice sheet margin abstract the greenland ice sheet is a major component of the arctic cryosphere and the magnitude of its response to future climate changes remains uncertain longer term records of climate near the ice sheet margin provide information about natural climate variability and can be used to understand the causes of past changes in the greenland ice sheet as a proxy for holocene climate near the ice sheet margin we reconstruct the fluctuations of bregne ice cap in the scoresby sund region of central east greenland bregne is a small ice cap 2 5 km 2 in area and responds sensitively to summer temperatures we employ a multi proxy approach to reconstruct the ice cap fluctuations using geomorphic mapping 10 be ages of boulders and bedrock and lake sediment records past extents of bregne ice cap are marked by moraines and registered by sediments in downvalley lakes 10 be ages of bedrock and boulders outboard of the moraines indicate that bregne ice cap was within 250 m of its present day limit by at least 10 7 ka multi proxy data from sediments in two move lake located downvalley from bregne ice cap indicate that the ice cap likely completely disappeared during early and middle holocene time increasing magnetic susceptibility and percent clastic material from 6 5 to 1 9 cal ka bp in two move lake sediments suggest progressively colder conditions and increased snow accumulation on the highlands west of the lake laminated silt deposited at 2 6 cal ka bp and 1 9 cal ka bp to present registers the onset and persistence of bregne ice cap during the late holocene 10 be ages of boulders on an unweathered unvegetated moraine in the bregne ice cap forefield range from 0 74 to 9 60 ka the youngest 10 be age 0 74 ka likely represents the age of the moraine whereas older ages may be due to 10 be inherited from prior periods of exposure this late holocene moraine marks the second largest advance of the ice cap since deglaciation of the region at the end of the last ice age the oldest moraine in the forefield dates to 2 6 cal ka bp the fluctuations of bregne ice cap were likely influenced by northern hemisphere summer insolation throughout the holocene and abrupt late holocene cold events

holocene vegetational history and climatic change in west spitsbergen plant macrofossils from skardtjorna an arctic lake macrofossil analyses of a 335 cm long core from skardtjorna a small lake on the west coast of spitsbergen svalbard are presented the known processes of deposition of plant remains to arctic lake sediments are summarised and used in the interpretation of the vegetation history at skardtjorna the basal sediment is ams dated to 8110 110 bp the rest of the profile is dated by palaeomagnetic correlation the lowest sediments have the greatest macrofossil concentration and numbers of taxa per sample the occurrences of cassiope hypnoides and salix cf glauca before 4000 bp indicate a mean july temperature for the early holocene about 2 c higher than today comparable to the cassiope tetragona vegetation zone of the mid arctic region of the inner fjords increasing climatic severity resulted in the threshold from the cassiope to the dryas vegetation zone being passed at about 2500 bp the inferred climatic history at skardtjorna is compatible with other evidence from svalbard and elsewhere in the arctic