ice moraine and landslide dams in mountainous terrain we review recent work on ice moraine and landslide dams in mountainous terrain thus complementing several comprehensive summaries on glacier dams in intracontinental and arctic areas of low relief we discuss the roles of tectonic and climatic forcing on ice moraine and landslide dam formation and sudden drainage and focus on similarities and differences between their geomorphic impacts on confined valleys drained by steep bedrock and gravel bed rivers despite numerous reported failures of natural dams in mountain belts throughout the world their relevance to long term dynamics of mountain rivers remains poorly quantified all types of dams exert local base level controls thus trapping incoming sediment and inhibiting fluvial bedrock incision pervasive geomorphic and sedimentary evidence of outburst events is preserved even in areas of high erosion rates suggesting that sudden dam failures are characterized by processes of catastrophic valley floor aggradation active channel widening and downstream dispersion of sediment during which little bedrock erosion seems to be achieved we find that in the absence of direct evidence of former dams a number of similarities among the geomorphic and sedimentologic characteristics of catastrophic outburst flows may give rise to ambiguous inferences on the dam forming process this is especially the case for tectonically active mountain belts where there is ample and comparable potential for the formation and failure of ice moraine landslide and polygenetic dams concomitant with climatic oscillations or earthquake disturbance hence the palaeoclimatic implications of erroneously inferring the cause of dam formation may be significant we recommend that future research on natural dams in mountainous terrain addresses a climate and earthquake controlled systematics in the pattern of formation and failure b quantification of response of mountain rivers to catastrophic outburst events and their concomitant process sequences c elaboration of a comprehensive classification of natural dams in mountainous terrain with special attention to polygenetic dams d physical based modelling of dam formation failure and routing of water and sediment outbursts and e quantitative controls on the contribution of natural dams to sediment budgets in mountainous terrain

changes in palaeoceanography and palaeoecology during marine isotope stage mis 5 in the eastern north atlantic odp site 980 deduced from calcareous nannoplankton observations abstract calcareous nannoplankton analyses on late quaternary sediments from the eastern north atlantic odp site 980 55 29 n 14 42 w provide detailed insight into palaeoceanographic and palaeoclimatic changes that occurred throughout the termination ii and the adjacent interglacial of the marine isotope stage mis 5 this study presents the development of the coccolith assemblage throughout the interglacial mis 5 towards the beginning of the glacial mis 4 in the vicinity of the rockall plateau and investigates and characterises the impact of climatic and environmental variations on the coccolith assemblage distribution between 135 and 65 ky in general the coccolith assemblage is dominated by gephyrocapsa muellerae and emiliania huxleyi whilst significant changes in palaeoceanographic and palaeoclimatic conditions are mainly shown by variations of subordinate species a drastic increase in coccolith accumulation rates and a change from a less to a higher diverse species assemblage indicate a rapid increase in surface water temperatures during the onset of mis 5 from c 127 5 ky on highest coccolith numbers high numbers of taxa and a large diversity indicate highest coccolithophore primary productivity and peak interglacial conditions during mis 5 5 which are due to the high influence of relatively warm surface water to this region coccolith numbers peak again around 120 ky and decline afterwards but stay above glacial levels the two cooling events of mis 5 4 and 5 2 interrupt the generally warm conditions and are indicated by lowered coccolith numbers a drop of thermophile species and a reduction of the species diversity decreasing coccolith numbers and a slightly reduced diversity indicate that environmental conditions deteriorated towards the onset of mis 4 the analysis of the coccolith assemblage reveals that not only the stadial events mis 5 4 and 5 2 are characterised by colder conditions but furthermore confirms the upcoming notion that mis 5 5 was terminated by a slight short term cooling of the surface water which occurred around 124 ky

a review of catastrophic drainage of moraine dammed lakes in british columbia abstract moraine dammed lakes are common in the high mountains of british columbia most of these lakes formed when valley and cirque glaciers retreated from advanced positions achieved during the little ice age many moraine dams in british columbia are susceptible to failure because they are steep sided have relatively low width to height ratios comprise loose poorly sorted sediment and may contain ice cores or interstitial ice in addition the lakes commonly are bordered by steep slopes that are prone to snow and ice avalanches and rockfalls moraine dams generally fail by overtopping and incision the triggering event may be a heavy rainstorm or an avalanche or rockfall that generates waves that overtop the dam the dam can also be overtopped by an influx of water caused by sudden drainage of an upstream ice dammed lake jokulhlaup melting of moraine ice cores and piping are other possible failure mechanisms failures of moraine dams in british columbia produce destructive floods orders of magnitude larger than normal streamflows most outburst floods are characterized by an exponential increase in discharge followed by an abrupt drop to background levels when the water supply is exhausted peak discharges are controlled by dam characteristics the volume of water in the reservoir failure mechanisms and downstream topography and sediment availability for the same potential energy at the dam site floods from moraine dammed lakes have higher peak discharges than floods from glacier dammed lakes the floodwaters may mobilize large amounts of sediment as they travel down steep valleys producing highly mobile debris flows such flows have larger discharges and greater destructive impact than the floods from which they form moraine dam failures in british columbia and elsewhere are most frequent following extended periods of cool climate when large lateral and end moraines are built a period of protracted warming is required to trap lakes behind moraines and create conditions that lead to dam failure this sequence of events occurred only a few times during the holocene epoch most notably during the last several centuries glaciers built large moraines during the little ice age mainly during the 1700s and 1800s and lakes formed behind these moraines when climate warmed in the 1900s twentieth century climate warming is also responsible for recent moraine dam failures in mountains throughout the world warming from the late 1800s until about 1940 and again from 1965 to today destabilized moraine dams with interstitial or core ice the warming also forced glaciers to retreat prompting ice avalanches landslides and jokulhlaups that have destroyed some moraine dams

living coccolithophore communities in the norwegian greenland sea and their record in sediments abstract investigation of epipelagic coccolithophore communities along a transect from the voring plateau off norway to scoresbysund east greenland and comparison with coccolith assemblages in underlying surface sediments reveal that sedimentation of coccoliths is dependent on the following factors 1 composition of the coccolithophore communities and their bloom phases 2 grazing and selective destruction by zooplanktonic organisms 3 type of vertical flux in fecal pellets and 4 varying carbonate dissolution in different water masses dissolution increases towards the boundaries of carbonate sedimentation as a result the original composition of the living communities becomes increasingly obscured in the impoverished taphocoenoses however differential resistance to dissolution of the two primary calcareous nannoplankton species emiliana huxleyi and coccolithus pelagicus is such that occurrence and ratio of the two species in surface sediments reflect the various water masses in the norwegian greenland sea

glacial to interglacial primary production and el nino southern oscillation dynamics inferred from coccolithophores of the santa barbara basin 1 we investigate the long term stability of el nino southern oscillation and pacific decadal oscillation based on the examination of coccolithophore assemblages in a largely laminated 35 ka sedimentary record retrieved in the santa barbara basin core md02 2503 at a centennial scale coccolith assemblages indicate low primary production in the basin from 35 to 11 5 ka b p whereas the holocene is characterized by high productivity conditions this pattern demonstrates the influence of the glacial interglacial cycles on productivity and by inference on the nutrient supply by the upwelling cell off point of conception on a shorter scale laminations associated with dansgaard oeschger events appear to be due to an injection of poorly oxygenated waters in the deepest part of the basin rather than anoxia due to high primary production a seasonal sampling in seven laminated sections spanning from 20 to 220 years extracted from holocene bolling allerod and dansgaard oeschger event 3 indicates el nino probably existed continuously during the last 28 ka the frequency of el nino varied through time between 1 2 5 and 1 5 event a 1 and appearing to follow the precession cycle el nino exhibits higher lower frequencies when the precession values are lower higher finally the holocene is characterized by a decrease in el nino s frequencies due to the reinforcement of el nino through this period

moisture supply for northern ice sheet growth during the last glacial maximum during the last ice age the barents sea ice sheet began to grow 22 kyr ago1 only 8 kyr before it began to disintegrate2 this implies that the ice must have grown very rapidly from the coast to the edge of the continental shelf such rapid growth of a large ice sheet requires significant amounts of moisture3 but the origin of this moisture has been unclear particularly as the climap climate reconstruction suggests4 5 that the greenland iceland norwegian gin seas were perennially ice covered during this period here we present data from deep sea sediment cores from the fram strait which suggest that relatively warm water from the north atlantic ocean was advected into the gin seas in two short term events 27 22 5 and 19 5 14 5 kyr ago we suggest that the resulting seasonally ice free waters were an important regional moisture source for the barents sea ice sheet and that the gin seas played a much more active role in climate during the last glaciation than has previously been supposed

multi proxy records showing significant holocene environmental variability the inner n iceland shelf hunafloi abstract over the last 50 yr the n iceland margin has seen dramatic changes in temperature and salinity associated with the relative dominance of warm atlantic water versus cold arctic or polar waters we report a study of holocene environmental changes to assess the sensitivity of this area on a longer timescale we present sedimentologic isotopic and biotic coccolith proxies from a 5 5 m piston core b997 330pc that was retrieved from a small basin on the inner n iceland shelf seven ams dates indicate a relatively constant rate of sediment accumulation which averaged 55 cm kyr sampling resolution of our proxies varied between 16 and 90 yr sample our data indicate substantial variability in environmental conditions over the last 10 000 cal yr total carbonate content and coccolith concentrations track each other and indicate that the early holocene was a time of low net carbonate accumulation net accumulation of carbonate reached maximum values in the mid to late holocene 4 2 cal ka but there has since been a substantial decrease with a minima during the little ice age north atlantic drift coccolith species show peaks in accumulation rates at 2 and 8 cal ka and low influx between 3 5 and 6 cal ka reworked neogene coccoliths occur also 8 ka and coincide with light 18 o values in the epifaunal foraminifera cibicides lobatulus principal component analysis indicates considerable covariance between biotic isotopic and sedimentological parameters three axes explain 84 of the variance in the data set and define three groups of interrelated variables a major change occurs ca 5 cal ka after which conditions become more variable with a 1 5 kyr cyclicity

dynamics of atlantic water advection to the norwegian greenland sea a time slice record of carbonate distribution in the last 300 ky abstract short term variability in volume and configuration of atlantic water advection to the norwegian greenland sea ngs has recently been identified as a new and significant element for northern hemisphere glacial interglacial climatic fluctuations the amount of salt heat and moisture transferred by atlantic waters to the high arctic effectively influences northern hemisphere climates and is critical for the overall oceanic turnover rate in particular determining the extent and duration of atlantic water intrusions in the ngs is essential because of 1 its effect on the climate of the nordic continents and 2 its trigger function on the stability of the ice sheets with a weak inflows of atlantic water during glacials promoting an increase in ice volume by moisture supply to polar areas and b positive feed back mechanisms of atlantic water intrusions during ice sheet decay in this study the dynamics of surface water mass regimes in the ngs have been reconstructed for the past 300 ky by means of time slice compilations of calcium carbonate distribution and micropaleontologic proxies in addition carbonate preservation records are used to quantify deep water ventilation and production rates in contrast to the climap scenario but in accordance with many recent publications results of this study indicate that atlantic water advection was also a common feature during most glacial periods but varied strongly in volume and configuration significant modes recognized are 1 the full interglacial mode with a wide inflow of warm atlantic waters covering a broad area in the eastern sector of the ngs and extending far north combined with excellent carbonate preservation and very efficient deep water formation stages 1 and 5 5 1 2 the moderate interglacial mode with a rather small extension of atlantic waters along a narrow corridor in the southeastern sector of the ngs but still very efficient deep water exchange stages 9 isotopic events 7 5 7 3 7 1 5 3 and 5 1 3 pronounced cool phases during interglacials with only a very narrow inflow of atlantic waters into the southeastern ngs while the coastal areas off norway were still affected by iceberg drift substages 7 4 and 5 2 carbonate preservation records indicate ongoing deep water formation in the ngs 4 the normal glacial mode characterized by a variable but persistent inflow of cool temperate atlantic water lower stage 8 repetitively during stages 6 4 3 1 and 2 carbonate preservation records indicate ongoing deep water formation in the ngs 5 short glacial and deglacial periods characterized by episodic high inputs of ird evidenced by a wide coverage of diamicton deposition and strong carbonate dissolution e g episodically within stages 10 6 and 2 the 6 5 4 3 and 2 1 transitions some of these ngs diamicton layers correlate with heinrich layers in the north atlantic but generally ngs diamicton layers occur more frequently than heinrich layers the role of atlantic water influence during these events remains enigmatic but atlantic water influence is frequently found just above and below these sections a scenario with rapid ice sheet disintegration induced by atlantic water advection via increase of the thermal regime along the ice margin possibly triggered by small scale sea level rise might be envisaged more obviously the short term cessation of deep water formation in the ngs as evidenced by the dissolution spikes may be correlated with contemporaneous ventilation minima in the north atlantic

living coccolithophores during the northeast monsoon from the equatorial indian ocean implications on hydrography abstract water samples collected at five stations along 93 e section 1 n 4 s during the northeast monsoon 12 15 february 2000 at five depths surface 50 100 150 and 200 m in the eastern equatorial indian ocean eeio were studied for coccolithophores this study has yielded 30 species of coccospheres showing more diversity compared to coccoliths represented by only 18 taxa high diversity and abundance of coccospheres were observed at the equator and at 2 s high concentrations of coccoliths were observed at shallow depths

timing and mechanisms of surface and intermediate water circulation changes in the nordic seas over the last 10 000 cal years a view from the north iceland shelf abstract the north iceland shelf bears essential components of the present surface and intermediate circulation of the northern north atlantic instrumental and historical data give evidence of the sensitivity of this domain to broad regional scale oceanic and atmospheric anomalies our investigation of the paleohydrological variability off northern iceland throughout the last 10 000 cal yr suggests that atmospheric forcing alone through combined changes in strength of the wind stress curl and sea level atmospheric pressure pattern over the nordic seas is sufficient to explain the recorded changes in origins and dynamics of surface and intermediate water masses our biotic proxies coccoliths and benthic foraminifera were extracted from a giant piston core md99 2269 collected in a shelf trough where sediment accumulated at an excess rate of 2 m kyr the mid holocene from 6 5 to 3 5 cal kyr bp was a time of peaked carbonate production and subsequent sedimentation and strong water column stratification with a thick layer of cold fresh arctic surface water overlapping an enhanced flow of irminger atlantic intermediate water applying conditions triggering present time carbonate plankton blooms in the studied area we infer that a lowered cyclonic activity associated with decreased winter storms and reduced production of arctic intermediate water in the iceland sea were conductive of the recorded mid holocene water column structure the opposite situation warm atlantic surface water low vertically integrated inflow of irminger water abutment of arctic intermediate water in deep shelf troughs characterized the early holocene as well as a shorter late holocene period centred at 2 cal kyr bp the little ice age ca 0 2 0 6 cal kyr bp and a short event at around 3 cal kyr bp stand as times of extreme advection of polar waters and extended sea ice development a comparison of the recorded long term holocene evolution of water column structure off northern iceland with climate and hydrological changes in the north eastern atlantic suggests that the strength of atlantic inflow into the nordic seas was subjected to a balance between the irminger and the norwegian branches this balance is thought to be mostly related to changes in the intensity and location of westerly winds and associated atmospheric pressure gradients in the north atlantic

water mass exchange between the north atlantic and the norwegian sea during the past 28 000 years the greenland iceland and norwegian gin seas are important regulators of heat transport in the northern hemisphere and of ocean atmosphere co2exchange1 5 rapid changes in the circulation of surface and deep waters in this region may induce nonlinear climatic effects and climate instabilities2 3 here we present carbon and oxygen isotope data that provide a record of circulation changes in the gin seas during and at the termination of the last glacial maximum lgm inflow of nutrient depleted waters from the gin seas to form intermediate waters of the north atlantic resulted in nutrient enrichment of north atlantic deep water and consequent enhanced drawdown of atmospheric co2 contributing to the lower atmospheric during the lgm the onset of deglaciation occurred at a time of low salinity in the gin seas and thus of reduced thermohaline circulation although strong thermohaline circulation was later reinitiated in the north atlantic as deglaciation proceeded it cannot therefore have caused the onset of warming similarly we find that rapid changes in thermohaline circulation cannot account for the transient return to a cooler climate during the younger dryas episode

distribution of coccoliths in surface sediments in the norwegian greenland sea abstract the distribution of coccoliths has been examined in 20 surface sediment samples along an east west transect in the norwegian sea based on the abundance and species richness of coccoliths three biogeographic zones have been established along this transect the distribution of coccolith assemblages in the surface sediments appears to match closely with the locations of the different surface water masses in the norwegian greenland sea

svalbard ice sheet decay after the last glacial maximum new insights from micropalaeontological and organic biomarker paleoceanographical reconstructions abstract a marine sediment core retrieved from the middle continental slope of the northwestern barents sea was analyzed for its geochemical alkenones and micropalaeontological diatoms coccolithophores and dinocyst content in order to reconstruct the evolution of upper ocean conditions and ice sheet dynamics during the last 25 kyr additionally quantitative reconstructions of sea surface conditions temperature salinity and sea ice cover extent were conducted based on the best analogue technique applied to dinocyst assemblages and on the alkenone unsaturation index the sediment core contains a post last glacial maximum depositional sequence unaffected by stratigraphic discontinuities low salinity and laminated sediments after 20 cal kyr bp indicate a massive settling of meltwater sediment laden plumes from the initial melting of the svalbard barents sea ice sheet on western svalbard first record of measurable alkenones together with a drop of the number of months of sea ice cover and increase in ssts suggests an intensification of the influx of atlantic waters into the study area at 15 cal kyr bp representing the termination of the last glacial period and onset of the bolling interstadial the first occurrence of diatoms and increase in the abundance of all microfossils marked the onset of the holocene at 11 2 cal kyr bp when modern type sea surface conditions were rapidly established in western svalbard reconstructions based on dinocyst data and alkenone unsaturation index suggest relatively warm and stable temperatures between 9 9 and 8 9 kyr bp and a decrease of ssts from 4 2 cal kyr bp to present coinciding with the holocene thermal maximum and the decrease of summer insolation in the high latitude northern hemisphere respectively

distribution of large emiliania huxleyi in the central and northeast atlantic as a tracer of surface ocean dynamics during the last 25 000 years the coccolithophore species emiliania huxleyi is characterized by a wide range of sizes which can be easily distinguished in the light microscope in this study we have quantified the abundance of

high resolution temperature and evaporation changes during the late holocene in the northeastern arabian sea in order to reconstruct the monsoonal variability during the late holocene we investigated a complete annually laminated sediment record from the oxygen minimum zone omz off pakistan for oxygen isotopes of planktic foraminifera and alkenone derived sea surface temperatures sst significant sst changes of up to 3 c which cannot be explained by changes in the alkenone producing coccolithophorid species inferred from the gephyrocapsa oceanica emiliania huxleyi ratio suggest that sst changes are driven by changes in the monsoon strength our high decadal resolution data indicate that the late holocene in the northeastern arabian sea was not characterized by a stable uniform climate as inferred from the greenland ice cores but by variations in the dominance of the sw monsoon conditions with significant effects on temperatures highest sst fluctuations of up to 3 0 c and 2 5 c were observed for the time interval from 4600 to 3300 years b p and during the past 500 years the significant short term sst changes during the past 500 years might be related to climatic instabilities known from the northern latitudes little ice age and confirm global effects surface salinity values reconstructed from 18o records after correction for temperature related oxygen isotope fractionation suggest that in general the past 5000 years were characterized by higher than recent evaporation and more intense sw monsoon conditions however between 4600 and 3700 years b p evaporation dropped sw monsoon weakened and ne monsoon conditions were comparatively enhanced for the past 1500 years we infer strongly fluctuating monsoon conditions comparisons of reconstructed salinity records with ice accumulation data from published tibetan ice core and tibetan tree ring width data reveal that during the past 2000 years enhanced evaporation in the northeastern arabian sea correlates with periods of increased ice accumulation in tibet and vice versa this suggests a strong climatic relationship between both monsoon controlled areas

ocean circulation in the norwegian sea during the last deglaciation isotopic evidence abstract three cores from different depths in the southeastern norwegian sea have been investigated for benthic and planktonic foraminiferal stable isotope records the cores confirm that the last deglaciation occurred in two distinct steps the first step termination ia may have occurred at about 13 000 yr b p while the second step took place shortly after 10 000 yr b p the benthic oxygen isotopes reveal strong influence of deglacial intermediate waters possibly flowing in from the north atlantic with a maximum influence at about 12 000 yr b p both carbon and oxygen isotopic records show that bottom water formation in the norwegian sea was reinitiated after 12 000 yr b p during the first part of the deglaciation the deep water circulation pattern may have been opposite to that of the present the oxygen content in the norwegian sea deep water was low during the last glacial maximum and remained low during the first part of the deglaciation due to low vertical circulation rates the large variations in deep water circulation in the norwegian sea during the last deglaciation may have had important consequences for the interchange of co 2 between ocean and atmosphere

variations in surface water mass conditions in the norwegian sea evidence from holocene coccolith and dinoflagellate cyst assemblages coccolith and dinoflagellate cyst assemblages have been investigated in five sediment cores from the norwegian sea and fram strait both fossil groups are characterized by similar patterns of composition the assemblages contain high proportions of single species the coccolith flora is of low diversity and consists almost entirely of coccolithus pelagicus and emiliania huxleyi the dinoflagellate cysts are generally dominated by operculodinium centrocarpum and nematosphaeropsis labyrinthus other species especially bitectatodinium tepikiense peridinium faeroense and impagidinium pallidum sometimes contribute considerably to the assemblages based on the abundance of the assemblages and the ratio change between the dominating species it has been possible to establish three intervals of distinct major changes in surface water mass conditions sparse occurrences of coccoliths and dinoflagellate cysts have been observed before 10 000 yrs b p indicating harsh environmental conditions with a distinct influence of meltwater and temporarily very slight inflow of atlantic water the modern surface water circulation pattern was reinitiated during termination ib the assemblages suggest slightly cooler and probably less saline surface water conditions than are present today until 7500 yrs b p solar insolation may have caused a first temperature peak which is responsible for the early holocene productivity maximum a considerable change in the composition of dinocyst and coccolith assemblages occurs corresponding approximately to the onset of the holocene climatic optimum this change was most probably linked to an almost synchronous reorganization of the hydrographic properties in the entire north atlantic realm after the ice sheets had vanished since 6000 yrs b p the norwegian current with its modern oceanographic and ecological properties has been fully established

new faunal and isotopic evidence on the late weichselian holocene oceanographic changes in the norwegian sea downcore studies of planktonic and benthonic foraminifera and 18o and 13c in the planktonic foraminifer neogloboquadrina pachyderma sin in two piston cores from the southern part of the norwegian sea suggest large changes in the oceanic circulation pattern at the end of oxygenisotope stage 2 and in the early part of stage 1 prior to oxygen isotope termination ia 16 000 13 000 yr b p an isolated watermass with lower oxygen content and temperature warmer than today existed below a low salinity ice covered surface layer in the norwegian sea close to termination ia well oxygenated deep water probably with positive temperatures was introduced this deep water which must have had physical and or chemical parameters different from those of present deep water in the norwegian sea could have been introduced from the north atlantic or been formed within the basin by another mechanism than that which forms the present deep water of the norwegian sea a seasonal ice cover in the southern part of the norwegian sea is proposed for the period between termination ia and the beginning of ib close to 10 000 yr b p the present situation with strong influx of warm atlantic surface water and deep water formation by surface cooling was established at termination ib

a stratigraphic study of late quaternary sediments on the voring plateau eastern norwegian sea abstract four gravity cores from the voring plateau west of the nordland coast in northern norway have been studied about 250 000 yrs of continuous hemipelagic sedimentation is represented in the cores this period has been divided into seven lithostratigraphic units and four planktonic foraminiferal assemblage zones to improve the reliability and precision of the isotopic stratigraphy a graphic comparison with several isotopic records previously described in the literature has been performed a taxonomy of 36 isotopic events is established following prell s technique the majority of these events seem to be recognizable in the isotopic records from the norwegian sea during the glacial stages however several local events are caused by influxes of isotopically light meltwater comparisons between the records indicate a general trend toward decreasing sedimentation rates with increasing distance from the continental margins for isotope stages 2 3 4 and 6 only small variations in sedimentation rates are observed during stages 5 and 7 comparisons with the land based stratigraphy of northwest europe indicate that the main glacials and interglacials as well as the fana and the torvaldstad interstadials are recognizable in the marine sequences correlations to the bolling and allerod interstadials and the younger dryas stadial is obscured by a period of rapid influx of meltwater at about 15 14 ka followed by a period of high influx of clastic material

structure and timing of the last deglaciation oxygen isotope evidence foraminiferal oxygen isotope data from 24 tropical atlantic sediment cores constrained by 77 14c dates are stacked to form a composite record of isotopic termination 1 this record indicates that most of the isotopic transition at the end of the last ice age occurred between 14 ka bp and 6 ka bp minor isotopic expression of deglaciation is permitted as early as 16 ka bp but the most rapid rate of change occurred between 14 ka bp and 12 ka bp three steps of maximum change are present although they are close to the statistical limits of detection in the composite record the clear presence of the steps in individual records suggests that they are real we estimate their timing at 14 12 ka bp termination 1 a 10 9 ka bp termination 1 b and 8 6 ka bp termination 1 c centering of the termination near 11 ka bp is consistent with the milankovitch hypothesis that high summer insolation caused deglaciation in detail however maximum rates of change prior to the 11 ka bp insolation extreme and the inferred steps require additional mechanisms controlling the tempo of glacial interglacial climate change steps equivalent to those in 18o have not been detected in ice margin retreat data steps in the isotopic transition if real may record thinning of the ice sheets not accompanied by loss of area alternation between near equilibrium and near stagnant ice sheet profiles during deglaciation is hypothesized perhaps due to calving and unstable down draw of the ice sheets followed by partial re equilibration significant problems remain the effects of temperature on the isotope record are only partially constrained presently available data allow only semi quantitative intercalibration of ice volume sea level and isotopic estimates of glaciation

the continental tree ring record absolute chronology 14c calibration and climatic change at 11 ka abstract tree ring chronologies are unique archives for various parameters indicating climatic change the wood structure of trees deposited in river gravel below the water table is well preserved even after several millennia and it provides information on a time scale of solar years during the past 25 years in the hohenheim tree ring laboratory long tree ring chronologies have been constructed now reaching back to 11 400 yr dendro b p in this contribution we demonstrate the evidence for climatic change in the early holocene which can be obtained both from botanical properties e g parameters of ring growth and from the isotopic information recorded in tree rings

status of the java upwelling area indian ocean during the oligotrophic northern hemisphere winter monsoon season as revealed by coccolithophores abstract coccolithophores were used as sensitive indicators for the present day functioning of the java upwelling area to better understand the key role of this region in the tropical indian ocean dipole mode sampling was conducted during the oligotrophic phase of the monsoonal cycle at all sites low abundance coccolithophore communities were found with surface assemblages either dominated by gephyrocapsa oceanica or umbellosphaera irregularis or a diverse mixture including the two named species plus palusphaera vandelii ophiaster hydroideus syracosphaera spp and calciosolenia spp with no clear dominance of a single species below a well defined thermocline a deep photic community was dominated by florisphaera profunda but also with high abundances of algirosphaera robusta gladiolithus flabellatus and oolithotus antillarum in the sediments only 19 taxa were found with the three species f profunda g oceanica and e huxleyi making up more than 90 of the assemblages the observed living communities were part of the recurrent seasonal cycle and corresponded to the environmental conditions the sediment assemblages distinctly differ from the living communities alteration effects appeared to be strong but were probably not the only cause for the biases between the living communities and the sediment assemblages the communities during ongoing upwelling also significantly contributed to and determined the sedimentary assemblage

sea surface conditions in the southern nordic seas during the holocene based on dinoflagellate cyst assemblages dinoflagellate cyst dinocyst records from the southern nordic seas were compiled in order to evaluate the evolution of upper ocean conditions on a millennial timescale and supported by a highly resolved record from the voring plateau after the transitional phase from the last deglaciation three main phases define the holocene the early holocene 7 5 ka bp features important numbers of cool temperate species dominated by nematosphaeropsis labyrinthus and impagidinium pallidum in the west the assemblage composition changes drastically at the transition from the early to the mid holocene from when on operculodinium centrocarpum dominates the changeover is dated between 6 1 and 7 5 ka bp perhaps earlier closer to the iceland scotland ridge and appears to be linked to the onset of a modern type of surface circulation warmest assemblages occur at the voring plateau shortly after the transition when atlantic waters also appear to have spread farthest westward the recurrence of colder elements can be linked to cooling from 2 4 ka bp at the voring plateau and presumably earlier in the west but is difficult to date there because of the low sedimentation rates this is a general issue in many areas of the nordic seas and appears to have an important effect on cyst concentrations and assemblage composition with the possible loss of oxygenation sensitive cysts in the older parts of the cores comparing dinocyst based quantitative reconstructions with those retrieved from other plankton reveals a significantly different trend between proxies linked to a differing autecological response to seasonal changes at their respective depth habitats

dissolution affected coccolithophore fluxes in the central greenland sea 1994 1995 coccolithophore fluxes were investigated by sediment trap studies in the central greenland sea from 1994 to 1995 the trap mooring comprised traps at 300 900 and 2100 m water depths with 19 trapping intervals 10 28 days this site was characterised by a very strong seasonality in coccolithophore fluxes the seasonal flux signal was most pronounced in the shallow trap with high fluxes only during two trapping intervals in september and early october 1994 max coccolithophore flux 12 x 10 6 ind m 2 d 1 no or only very low fluxes were recorded during most of the investigated time interval in the deeper traps high fluxes occurred over a longer time interval than in the upper traps from late august to november 1994 the dominant species 90 was coccolithus pelagicus f pelagicus only very few other species including emiliania huxleyi 7 occasionally occurred the coccolithophore settling assemblages of the investigated traps were strongly influenced by dissolution the dissolution impact probably diminished diversity and sharpened seasonality in fluxes dissolution was prominent in near surface waters of the east greenland current but not in bottom waters however maximum fluxes were of the same magnitude as previously reported fluxes from the nearby norwegian sea and higher than in the southern greenland sea in contrast to the other sites resuspension seemed to be of minor importance total annual coccolithophore fluxes differed significantly in the norwegian greenland seas reflecting the local oceanographic signature of coccolithophore production

late quaternary calcium carbonate sedimentation and terrigenous input along the east greenland continental margin nine large box cores collected in the western greenland iceland norwegian gin sea were analyzed for calcium carbonate content and coarse fraction components stratigraphic control is based on oxygen isotope records performed on four of the cores all cores were correlated using oxygen and carbon isotope data fluctuations in calcium carbonate content coarse terrigenous particle content and volcanic ash beds glacial and interglacial cycles are documented by a number of terrigenous particle events and differentiated calcium carbonate production which can be correlated to major paleoceanographic and paleoclimatic shifts in the older core sections extensive deposition of ice rafted detritus ird persisted until about oxygen isotope stage 9 and document a relatively stable environment in this area strongly influenced by cold surface water masses the following interval was characterized by variations in the general surface water circulation pattern although high amounts of ird are still present in iceland sea sediments pronounced shifts in terrigenous input and pelagic carbonate records were identified close to the oxygen isotope stage full size image 1 k and full size image 1 k boundaries indicating massive melting of icebergs in the western gin sea these enormous inputs of debris were followed by an increase in calcium carbonate production caused by maximum intrusion of warm atlantic surface waters relatively high calcium carbonate contents also show that only little dilution by fine grained material and a minimum of ice melting occurred during these warm phases during oxygen isotope stage 5 conditions were more uniform indicating a less pronounced westward penetration of atlantic waters as compared to the holocene the last glacial stages 4 2 is characterized by the occurrence of heinrich like events although high ird contents were present throughout this interval a distinct contrast between the northernmost cores and the cores in the south is indicative of a rather strong westward penetration of atlantic water in the north and of an area dominated by cold water east of the kolbeinsey ridge during the holocene however conditions west of jan mayen seem to have remained constantly dominated by cold surface waters throughout the whole time investigated

coccoliths in sediment traps from the norwegian sea abstract the fine fraction of surface sediment samples in the norwegian sea shows an unexpectedly high amount of calcareous nannoplankton investigations using time series sediment traps in the lofoten basin 69 n 1983 84 near bear island 75 n 1984 85 and in the fram strait 78 n 1984 85 provided information about the accumulation of this material in relation to the strong seasonality of biological production coccolith identification and counting by means of a scanning electron microscope indicated that the coccolith assemblages in the traps consist almost entirely of the two speciesemiliania huxleyi andcoccolithus pelagicus these species dominated the flux rate of the nannoplankton carbonate a further eight species only made minor contributions to the flux in the lofoten basin a distinct seasonality could be recognized in both standing crop and carbonate flux also the relationship between the two main species and the proportion of intact coccospheres showed an annual cycle in the sample series of the two northerly traps the seasonality was less distinct in general the coccolith flux decreases towards the north this was particularly evident for the smaller speciese huxleyi while the number of massivec pelagicus coccoliths and so the coccolith carbonate flux diminished only slightly additional investigations on water samples from the norwegian sea revealed species compositions that differed greatly from those in the sediment traps this suggests that selective processes change the relative species proportions during sedimentation

coccolithophore fluxes in the norwegian greenland sea seasonality and assemblage alterations abstract coccolithophore fluxes were investigated by sediment trap studies at two well separated oceanographic sites in the norwegian and greenland seas from 1990 to 1992 each trap mooring comprised traps at 500 and 1000 m water depth and 300 m above the seafloor both sites were characterized by a strong seasonality in coccolithophore fluxes in the norwegian sea fluxes were about 10 to 20 times higher than in the greenland sea maximum fluxes 13 106 ind m 2d 1 for the norwegian sea and 2 4 106 ind m 2d 1 for the greenland sea were reached during high sedimentation phases in late summer and autumn the settling assemblages represented already highly altered remnants of the former living communities dominant species were emiliania huxleyi in the norwegian sea and coccolithus pelagicus in the greenland sea despite severe alterations the coccolithophore assemblages of each site were characterized by a distinct signature reflecting the local oceanography the settling assemblages underwent only minor alterations during sinking from 500 to 1000 m water depth by contrast resuspension and lateral advection within an extensive bottom nepheloid layer strongly influenced the assemblages of the deep sediment traps 300 m above the seafloor wiping out the distinct seasonality in coccolithophore fluxes and diminishing the differences in assemblage compositions between the two sites

surface water dynamics in the reykjanes ridge area during the holocene as revealed by coccolith assemblages abstract the calcareous nannofossil assemblages from sediment core ds97 2p from the reykjanes ridge have been investigated to document oceanographic changes in surface water during the holocene the recorded variations in coccolithophore species assemblages and accumulation rates indicate that the region was subjected to rapid changes of surface water masses throughout the entire holocene coccolithophore assemblages generally are of low species diversity and consist mainly of emiliania huxleyi and coccolithus pelagicus ssp pelagicus two major events occurred at 8 5 7 ka and at 4 5 3 5 ka showing higher coccolith accumulation rates suggesting that the influence of relatively warm atlantic waters via the irminger current was strong in the investigated area the coccolithophore assemblages have been compared with diatom foraminifer and sedimentological records within the same core these data supported by a comparison with previously published proxy records add credit to the hypothesis that holocene changes did not occur uniformly across the north atlantic the results have highlighted the holocene pattern in the north atlantic as a period influenced by strong regionalism with discrepancies in the hydrographical trends and in the distribution of the planktonic proxies

glacier recession and glacial lake outburst flood studies in zanskar basin western himalaya abstract glacier recession and formation of glacial lakes along with outburst flood hazards are increasing in response to changing climate in the himalayan region this study describes evolution of dalung and padam glaciers and their associated lakes employing multi temporal datasets of landsat mss tm etm indian remote sensing liss iii google earthtm aster gdem and survey of india topographic maps the dalung glacier dg and lake dl are present in suru river catchment whereas the padam glacier pg and lake pl are present in tsarap river catchment of zanskar basin western himalaya from 1962 to 2015 the dg and pg have shrunk at different rates the dg has shrunk by 2 6 0 56 km2 19 2 4 1 at a rate of 0 05 0 01 km2 a 1 whereas the pg has shrunk by 3 4 0 65 km2 12 7 2 4 at a rate of 0 06 0 01 km2 a 1 the frontal recession was recorded as 1 240 0 02 km 15 7 2 0 at a rate of 20 0 4 m a 1 for dg and 2 690 0 5 m 21 3 2 1 at a rate of 50 7 0 1 m a 1 for pg consequently the proglacial glacial lakes have formed indicating an expansion of 20 3 4 dl and 58 4 5 pl during 1990 2015 using integrated criteria of standard indices for the identification of potentially dangerous glacial lakes pdgls the lakes were found to be vulnerable and have a potential to cause breaching in the coming years in order to provide inputs for the emergency action plan one dimensional mike 11 model was used to generate the peak flood hydrographs at the lake and other vulnerable sites downstream highest peak discharge of 3361 7 m3 s 1 dl and 4210 3 m3 s 1 pl were estimated at the lake sites which has reduced to 1520 9 m3 s 1 and 1722 4 m3 s 1 respectively at the outlet sites the reduced discharge at downstream sites still bears the potential to create dangerous flood hazards

rapid expansion of glacial lakes caused by climate and glacier retreat in the central himalayas glacial lake outburst floods are among the most serious natural hazards in the himalayas such floods are of high scientific and political importance because they exert trans boundary impacts on bordering countries the preparation of an updated inventory of glacial lakes and the analysis of their evolution are an important first step in assessment of hazards from glacial lake outbursts here we report the spatiotemporal developments of the glacial lakes in the poiqu river basin a trans boundary basin in the central himalayas from 1976 to 2010 based on multi temporal landsat images studied glacial lakes are classified as glacier fed lakes and non glacier fed lakes according to their hydrologic connection to glacial watersheds a total of 119 glacial lakes larger than 0 01km 2 with an overall surface area of 20 22km 2 10 8 were mapped in 2010 with glacier fed lakes being predominant in both number 69 58 0 and area 16 22km 2 80 2 we found that lakes connected to glacial watersheds glacier fed lakes significantly expanded 122 1 from 1976 to 2010 whereas lakes not connected to glacial watersheds non glacier fed lakes remained stable 2 8 during the same period this contrast can be attributed to the impact of glaciers retreating glaciers not only supply meltwater to lakes but also leave space for them to expand compared with other regions of the hindu kush himalayas hkh the lake area per glacier area in the poiqu river basin was the highest this observation might be attributed to the different climate regimes and glacier status along the hkh the results presented in this study confirm the significant role of glacier retreat on the evolution of glacial lakes copyright c 2014 john wiley sons ltd

late quaternary calcareous nannofossil biozonation chronology and palaeo oceanography in areas north of the faeroe iceland ridge abstract the stratigraphic distribution of late quaternary calcareous nannofossils from the european arctic ocean the fram strait and the norwegian and greenland seas are summarised in a biozonation scheme the nannofossil events are directly correlated to oxygen isotope stratigraphy leading to an absolute chronology comprising approximately the last 500 ka the zones are defined by the qualitative and quantitative content of calcareous nannofossils zones n g 2 4 6 8 and 10 comprise intervals mainly barren of nannofossils zone n g 1 is characterised by high abundances of coccolithus pelagicus and emiliania huxleyi zone n g 3 is recognised by dominant gephyrocapsa muellerae and common e huxleyi zone n g 5 is characterised by dominant g aperta n g 7 by dominant g muellerae n g 9 by common g muellerae g aperta and g caribbeanica and zone n g 11 is recognised by dominant g caribbeanica and rare pseudoemiliania lacunosa intervals in which nannofossils occur in high abundances reflect comparatively warmer periods and influences of north atlantic surface water strong inflows of north atlantic water have occurred several times during the last 500 ka in oxygen isotope stage 1 the last 8 ka and in oxygen isotope stages 5 11 12 and 13 north atlantic surface water penetrated into the central parts of the norwegian and greenland seas also during oxygen isotope stage 9 nannofossil barren intervals are mainly formed during time periods with a year round ice cover

coccolithophores in surface sediments of the arabian sea in relation to environmental gradients in surface waters abstract one hundred surface sediment samples of the arabian sea indian ocean were investigated and relative abundances of coccoliths were compared to mean annual gradients of temperature salinity chlorophyll po4 and mixed layer depth total coccolith concentrations ranged from 42 106 g sediment in coastal areas to more than 19 000 106 g sediment in oceanic regions the general distribution does not seem to be dependent on coccolithophore productivity in surface waters alone but also on the diluting input of terrigenous material a total of 27 taxa were identified the main species dominating the assemblages were gephyrocapsa oceanica emiliania huxleyi and florisphaera profunda with a combined average abundance of more than 70 several species and species groups reflect with their distribution the environmental parameters of the overlying water masses and may be successfully used to improve palaeoclimatic reconstructions e g a f profunda exhibits a high similarity or even positive correlation to the mean annual mixed layer depth b calciosolenids can be described as coastal or shelf species while temperature and salinity gradients do not seem to be crucial for coccolithophores in this region the mean mixed layer depth as well as the po4 concentration representative for total nutrient availability may control in part the coccolithophore assemblages according to the results of a cluster analysis and the distribution pattern of all species it was possible to differentiate three main coccolithophore assemblages a g oceanica dominated assemblage mainly occurs in the northern part of the study area and can be described as high nutrient assemblage the second assemblage dominated by f profunda may be typical for oligotrophic and stable conditions in open ocean waters a third assemblage with high amounts of coastal species characterises coastal conditions on the shelves

coupled response of the late glacial climatic shifts of northwest europe reflected in greenland ice cores evidence from the northern north sea the climatic regimes of the land areas adjacent to the north sea are controlled by the influx of atlantic water north of the british isles and into the north sea a high resolution record from the norwegian channel off western norway covering the past 15 ka 14 c shows that prior to the younger dryas there were three periods of sea surface conditions there similar to those of the present interspersed with arctic conditions these changes corresponding to an increase of approx 5 c in summer sea surface temperatures took place on the scale of

movement of oceanic fronts south of australia during the last 10 ka interpretation of calcareous nannoplankton in surface sediments from the southern ocean abstract preservation of calcareous nannoplankton in surface sediment samples from the southern ocean south of australia and adjacent to new zealand record a single assemblage the dominant species are emiliania huxleyi gephyrocapsa muellerae calcidiscus leptoporus helicosphaera carteri and coccolithus pelagicus the assemblage varies little in abundance and diversity with minor correlation to present day overlying surface water masses and oceanic fronts increase in abundance of h carteri and c pelagicus in the region of the subtropical front may reflect higher nutrients associated with this front the assemblage although altered by dissolution represents a warmer climatic interval than present day with the presence of preferentially dissolved warm water species preserved as far south as the polar front the presence of warm water species under sub antarctic waters at the polar front is interpreted as a relic population from the holocene climatic optimum of 10 8 ka the absence of coccoliths in sediments poleward of the polar front suggests an equatorward shift of this front following the climatic optimum resulting in increased productivity of siliceous phytoplankton associated with the colder waters and increased dissolution of coccoliths movement of the subtropical front for the same interval is not recorded in the preserved coccoliths the more heavily calcified form of e huxleyi which dominates the living assemblage north of the subtropical front is subject to dissolution in this region and is poorly preserved in the sediment assemblage

the faroe shetland gateway late quaternary water mass exchange between the nordic seas and the northeastern atlantic abstract thirteen piston and gravity cores from the faroe shetland area were investigated for their planktic and benthic foraminiferal and oxygen isotopic distributions eight time slices between 18 ka bp and the present were reconstructed to study variations in surface and deep water exchange between the se norwegian sea and the northeast atlantic ocean today a relatively strong northward flow of warm north atlantic surface water is counterbalanced by a southward outflow of newly convected cold bottom water the norwegian sea overflow water during the last glacial maximum at 18 ka bp both the surface and bottom flows were slow and the climate conditions were arctic the convection north of the faroe area was weak and unstable the first indication of the deglaciation is a decrease in the planktic oxygen isotope values discernible southwest of the faroe islands at 15 5 ka bp the deglaciation proceeded northeast and eastward synchronous with a gradual intensification of northward flowing warmer atlantic intermediate water along the sea bottom meltwater fluxes increased between 14 and 13 ka bp producing cold surface waters and the climatic cooling was extreme there was no southward overflow of cold bottom water during this time period and the exchange of water masses between the nordic seas and the north atlantic ocean was essentially reversed i e estuarine during the bolling interstadial at 12 5 ka bp northward flowing warm surface water was present to the east of the faroe shetland channel wedged below a tongue of polar water spreading from the northwest and reaching into the faroe shetland channel convection in the nordic seas and overflow of cold deep water started during the bolling interstadial the polar water spread more eastward and southward during the following cold spell the younger dryas around 10 3 ka bp the polar water was overlying the warmer but more saline atlantic water which flowed northward below the cold surface water the overflow of cold bottom water was supposedly only slightly weaker than during the bolling interstadial strong inflow of warm surface water took place during the early holocene at 9 5 ka bp and relatively dense cold water flowed southward along the bottom the rate of water mass exchange reached a maximum at 6 5 ka bp when both the inflow of warm atlantic surface water and the outflow of cold dense bottom water appear to have been stronger than today

basin scale motion in stratified upper lake constance this paper describes experimental and modeled wind induced oscillations in upper lake constance with an emphasis on a coherent understanding of the basin scale internal dynamics in this example of a large and stratified lake data were collected with eight lake diagnostic systems ldss consisting of thermistor chains and wind anemometers the isotherm displacements as measured by the ldss were interpreted using the three dimensional hydrodynamic estuary and lake computer model elcom three types of basin scale waves were found to dominate the wave motion the vertical mode one kelvin wave that had an observed period around 90 h two vertical mode one poincare waves that had periods near 8 h and 12 h and a vertical mode two poincare wave that had a period near 14 h after strong westerly winds upwelling of cold bottom water was observed east of the sill of mainau where the lake s two subbasins connect the width and length ratios of the subbasins spatial variations of the wind field and rotational effects over the lake are shown to play critical roles in the details of the upwelling structure a sudden fall of the isotherms in lake uberlingen formed a surge the reflection of the surge from the northwestern boundary induced a vertical mode two response leading to an intrusion in the metalimnion that caused a three layer velocity structure in the smaller subbasin

coccolithophore fluxes from sediment traps in the northeastern arabian sea off pakistan abstract we investigated coccolithophore fluxes from four sediment traps located in the northeastern arabian sea at the continental slope of pakistan two moorings wpt and ept western isastern pakomin trap consisting of one and two sediment traps were deployed at water depths of about 500 m and 1500 m they collected settling particles from october 1993 to february 1994 and from may 1995 to february 1996 at intervals of 22 and 24 days respectively a longer sampling was prevented probably due to high sedimentation events which occluded the trap cones both areas were characterised by a strong seasonality in coccolith fluxes high fluxes were recorded with up to 2000 10 6 coccoliths m 2 d 1 in the early sw summer monsoon and up to 5400 10 6 coccoliths m 2 d 1 in the early ne winter monsoon generally coccosphere fluxes exhibited a similar trend but were some orders of magnitude lower than coccolith fluxes twenty seven taxa were identified in this study all well to moderately well preserved and with a small range of diversity the species composition was dominated by gephyrocapsa oceanica florisphaera profunda and emiliania huxleyi making up about 70 of the assemblages during the sw summer monsoon high productivity in the surface waters of the eastern arabian sea may be linked to the upwelling system off oman apparently nutrient rich surface water derived from the southwestern upwelling areas off oman with high standing stocks were carried into this area by northeast flowing currents in contrast during the ne winter monsoon the locally observed high coccolithophore production is hypothesised to respond to local injections of nutrient rich deep water into the surface water due to sea surface cooling leading to convection consequently fluxes during the winter monsoon were in the same range as during the summer monsoon

response of the high latitude northern hemisphere to orbital climate forcing evidence from the nordic seas sediment cores from the nordic greenland iceland and norwegian seas provide evidence that this area acts as an initial responder to the forcing effect of orbitally driven changes in insolation on the climate system as postulated by j imbrie et al the 18 o record of the cores documents a widespread initial deglacial signal in the area between 15 and 13 ka 1000 yr before other deglacial signals from other parts of the northern hemisphere an even earlier meltwater event has been dated to 16 090 185 yr b p north of iceland at the initial rise of northern hemisphere insolation after the last glacial maximum during the period with lowered surface salinities the nordic seas were still cold reconstructions of the surface water conditions of the area show that as the summer insolation values of the northern hemisphere reached half of maximum values a sea ice free corridor opened along norway at 13 4 ka nearly contemporaneous fluctuations of the polar front and the sea surface temperatures with the insolation changes indicate that the nordic seas are very sensitive to insolation forcing especially in regions close to the sea ice margin a decrease in sea surface temperature and an increase in the areal extent of sea ice cover since 7 ka indicate that the area is currently on the way to glacial conditions supporting the predictions made earlier by j imbrie et al

millennial scale variability in atlantic water advection to the nordic seas derived from holocene coccolith concentration records abstract abundance patterns of coccolith species in two holocene marine cores retrieved off norway and northern iceland are indicative of millennial scale modulations in the flow of the main norwegian atlantic current and secondary north iceland irminger current branches of the north atlantic drift to the nordic seas long term trends in coccolith abundance changes reflect major holocene steps in atlantic water transfer to the nordic seas at orbital scale with important constraints on the convective activity of the nordic seas that leads to the formation of the precursor water mass of north atlantic deep water millennial scale holocene episodes of increased advection of atlantic waters off norway are associated with enhanced winter precipitation over scandinavia increased sea salt fluxes over greenland and strengthened wind over iceland thereby suggesting a common atmospheric forcing the location and intensity of the westerlies and the associated changes in mid to high latitude pressure gradients our biotic data indicate an opposite pattern of atlantic water inflow at suborbital scale between the western denmark and eastern iceland scotland straits of the northern atlantic throughout the holocene this as supported by present observational and simulated data further highlights the role of atmospheric oscillations in the recent history of the north atlantic nordic seas water mass exchanges across the greenland scotland ridge such atmospheric processes are thought to explain the observed coupling between periods of excess export of arctic sea ice to the nordic seas and intervals of maximum inflow of atlantic water to the norwegian sea throughout the last 11 000 years

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

multiproxy fossil comparison reveals contrasting surface ocean conditions in the western iceland sea for the last two interglacials abstract dinoflagellate cyst dinocyst coccolith and planktic foraminiferal assemblages from a core in the western iceland sea were used to reconstruct and compare the surface ocean developments of the holocene and the last interglacial marine isotopic stage or mis 5e while increasing subpolar planktic foraminifers from 10 ka indicate subsurface warming peaking around 7 5 ka the dinocyst data suggest that the uppermost ocean remained dominated by cold waters until 6 5 ka a reduced advection of cold polar waters through the east greenland east icelandic current thereafter entailed warmest and most saline holocene conditions between 6 5 and 5 ka in turn followed by a general cooling trend by contrast both planktic foraminifers and dinocysts show an increased presence of atlantic type waters from 122 ka onward resulting in a mis 5e thermal optimum around 120 5 ka nonetheless occasional freshwater input from melting drift ice created stratified but also seasonally variable conditions during this first half of mis 5e this stratification signature disappeared at 120 ka when a marked repositioning of the oceanographic fronts occurred slightly colder conditions are indicated by both phyto and zooplankton from there on until the end of mis 5e around 117 ka a late mis 5e cooling at the iceland plateau is opposite to a late mis 5e optimum observed in the eastern nordic seas this regional difference is likely explained by various feedback mechanisms following the major reorganisation of the oceanic fronts at 120 ka the holocene and mis 5e interglacial variability is not reflected in the quasi monospecific coccolith assemblages and illustrates the low sensitivity of living coccolithophore communities to subtle temperature changes in the low temperature regions of the nordic seas overall quite different surface water properties appear to have characterised both interglacial intervals with a higher share of warm atlantic elements in the planktic communities during mis 5e this suggests a higher contribution of atlantic waters in the southwestern nordic seas probably due to a more northward expansion of the irminger current under weakened polar east greenland east icelandic currents such a reduced influence of polar waters in the southwestern nordic seas may thus explain other evidence for relatively warm conditions in mis 5e all around southern greenland

late quaternary changes in surface water and deep water masses of the nordic seas and north eastern north atlantic a review quantitative and semiquantitative proxy data based on more than 200 core top samples and 100 deep sea cores lead to important new insights about late quaternary changes in paleo oceanography climate and microfaunal habitats in the north eastern north atlantic and nordic seas insights resulting from a detailed investigation by the kiel research project sfb 313 132 summarized in this paper planktonic foraminifera species provide reliable tracers of past sea surface temperatures and currents the genus beella in particular was found to trace subtropical water masses up to the far north benthic foraminifera species served as sensors of bottom currents and local flux rates of organic matter new orders of time resolution are reached via stable isotope stratigraphy and accelerator mass spectrometry carbon 14 dating allowing the identification of meltwater events lasting a few hundred years and shorter a time range where however the yet unquantified role of bioturbation presents a growing problem based on this high resolution stratigraphy a number of time slices synoptic time intervals are defined to reconstruct the incursion of atlantic water masses to map paleocurrent patterns within the nordic seas and the north eastern north atlantic and to test alternative circulation models for example for the last glacial maximum lgm and various meltwater episodes these are clearly coeval with dansgaard oeschger events found in greenland ice cores with the actual cause of the flickering climate as yet unknown likewise there is ongoing controversy about the extent of past sea ice cover and about possible changes from the present anti estuarine to estuarine mode of deep water exchange between the north atlantic and the nordic seas during the lgm south of iceland however the history of deep water renewal over the last glacial cycle covering the last 30000 years was largely deciphered

history of the last deglaciation and holocene in the nordic seas as revealed by coccolithophore assemblages abstract coccolithophore assemblages were investigated in 15 sediment cores from the nordic seas norwegian greenland iceland seas cores were selected which have a well constrained absolute chronology for the last 15 000 to 18 000 years enabling us to study in detail the development of the coccolithophore assemblages during the last deglaciation and the holocene the data have been used to reconstruct the paleoceanographic conditions of the surface waters the coccolithophore assemblages are of low diversity and consist almost entirely of coccolithus pelagicus and emiliania huxleyi other species such as gephyrocapsa muellerae calcidiscus leptoporus and syracosphaera pulchra in some cases contribute considerably to the assemblages sparse occurrences of coccolithophores together with a high number of reworked pre quaternary species are observed in the southeastern norwegian sea before about 11 500 cal yr b p indicating harsh environmental conditions with dominant influence of meltwater and very small inflow of atlantic surface water from 11 500 to about 8000 cal yr b p a stepwise increase towards a first maximum in absolute numbers of coccolithophores in the whole nordic seas coincides with maximum northern hemisphere summer insolation the assemblages from the greenland and iceland sea generally have lower concentrations than those of the norwegian sea and are characterised by a more abrupt onset in coccolithophore abundance this suggests that ice free surface water circulation was reinitiated after about 9500 cal yr b p although the influence of the warm atlantic inflow decreased towards the northwest of the study area a considerable change in the composition of coccolithophore assemblages occurred corresponding approximately to the establishment of modern conditions at about 7 500 cal yr b p since about 6 000 cal yr b p coccolithophore assemblages have been relatively stable suggesting that the current system in the nordic seas with its modern oceanographic and ecological properties has been fully established

surface water changes in the norwegian sea during last deglacial and holocene times stable carbon and oxygen isotopes of the polar planktic foraminifera neogloboquadrina pachyderma sinistral from sediment cores of the norwegian sea reveal several anomalous 13c and 18o depletions in the surface water during the last glacial to interglacial transition and during the later holocene the depletions that are observed between the last glacial maximum lgm and the end of the main deglacial phase were caused by massive releases of freshwater from thawing icebergs which consequently resulted in a stratification of the uppermost surface water layer and a non equilibrium between the water below and the atmosphere at 8 5 ka 14c bp this strong iceberg melting activity ceased as defined by the cessation of the deposition of ice rafted detritus after this time the dominant polar and subpolar planktic foraminiferal species rapidly increased in numbers however this post deglacial evolution towards a modern type oceanographic environment was interupted by a hitherto undescribed isotopic event 7 8 ka which on a regional scale is only identified in eastern norwegian sea surface water this event may be associated with the final pulse of glacier meltwater release from fennoscandia which affected the onset of intensified coastal surface water circulation off norway during a time of regional sea level rise all these data indicate that surface water changes are an integral part of deglacial processes in general yet the youngest observed change noted around 3 ka gives evidence that such events with similar effects occur even during the later holocene when from a climatic point of view relativelystable conditions prevailed

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes

palaeoproductivity of the eastern arabian sea during the past 200 ka a multi proxy investigation abstract two sediment cores from the eastern arabian sea were investigated for reconstructing the late quaternary palaeoproductivity using a variety of proxies the relative abundance of florisphaera profunda in the total coccolithophore flora fp organic carbon c org and calcium carbonate contents the low abundance of fp during glacial periods suggests a significantly enhanced primary productivity during those periods the high fp abundance during terminations ii and i implies that the productivity was low during deglaciation the reduced productivity was probably a result of the intensification of the sw monsoon during the two terminations the high c org content documented for glacial periods marine isotopic stages 2 4 and 6 also suggests that productivity was high during glacial periods the consistent results obtained from two independent proxies fp and c org for palaeoproductivity confirm that productivity was indeed high during glacial periods and hence the high c org content is not just an artifact of better preservation of organic matter due to high sedimentation rate down core variations in the caco 3 content and 18 o show coherent fluctuations and typical glacial interglacial cyclicity glacial periods were characterised by low caco 3 and interglacials by high caco 3 content interestingly the low caco 3 content during glacials is in contrast to the high productivity suggested by the low relative abundance of fp and the high c org content therefore the low carbonate content during glacial periods was probably due to dilution by terrigenous material and or increased biogenic opal production spectral analysis of data on palaeoproductivity proxies shows a 23 ka periodicity indicating that the earth s precessional cycle exerts a significant control on the palaeoproductivity of the eastern arabian sea

plankton in the norwegian greenland sea from living communities to sediment assemblages an actualistic approach a synoptic study is carried out to reconstruct the development of the plankton community in the late quaternary in the norwegian greenland sea it comprises quantitative analyses of coccolithophores dinoflagellate cysts diatoms and radiolarians an actualistic approach is applied to evaluate the different fossil records of these plankton groups the preliminary results of the current investigation are reported here

evidence from fram strait 78 n for early deglaciation recent syntheses of the history of the last northern hemisphere glaciation and deglaciation illustrate that understanding of the mechanisms and timing of deglaciation before approximately 12 000 years bp1 5 is limited after 12 000 yr bp however there is sufficient evidence from radiocarbon dated moraines raised beaches varved lake sediments and pollen records to provide a reasonable temporal and geographic picture of the decay of the ice sheets here we report on the first oxygen isotope record from the norwegian greenland sea that is radiocarbon dated directly by accelerator mass spectrometry a significant light oxygen isotope event is recorded at approximately 15 000 years bp which suggests that the marine based barents shelf ice sheet disintegrated rapidly at this time recent studies6 7 have estimated that the decay of this ice sheet could have contributed as much as 15 metres to eustatic sea level rise the decay of the barents shelf ice sheet is the earliest major deglacial event yet dated and may have triggered subsequent deglacial events through eustatic sea level effects

late quaternary sea surface conditions in the laurentian fan evidence from coccolith and dinocyst assemblages abstract the analyses of coccoliths and dinocysts from the images core md95 2033 collected on the laurentian fan 44 39 87n 55 37 21w water depth 1412 m in the northwest north atlantic provide a new dataset to assess the magnitude of climatic changes during the holocene with a millennial time resolution coccolith and dinocyst data were combined to reconstruct changes in past sea surface conditions in addition the dinocyst assemblages were used to reconstruct the sea surface temperature sst and salinity sss based on the modern analog technique the distribution of the coccolith and dinocyst assemblages suggests a succession of climatic events during the late quaternary and early holocene linked to change in the influence of the labrador current and or the st lawrence river discharge the dinocyst assemblages recorded a thermal optimum during the mid holocene in the late holocene coccolith concentrations show two peaks at 2 3 and 1 1 ky which coincide with the presence of species with different ecological properties likely due to the localized influence of the slope water jet swj current the presence of this current has played a role in the development of the coccolith and dinocyst assemblages and sst fluctuations especially in the last 2 ky overall the interaction between the st lawrence river the swj the lc and the nac has all controlled the sss ssts and the development of the coccolith and dinocyst assemblages confirming a significant regionalism of the entire area

palaeoclimatic changes in kveithola svalbard during the late pleistocene deglaciation and holocene evidences from microfossil and sedimentary records abstract climate changes are reflected in the arctic ecosystem history over different timescales we use a multi proxy based approach for palaeoenvironmental and palaeoclimatic reconstructions conducted on sediment cores compared with summer insolation and greenland ice core 18o data in order to establish a framework for climate changes from late pleistocene to late holocene our dataset includes the results compiled from a sediment core collected on the middle slope of the kveithola trough mouth fan south of svalbard during the coribar cruise 2013 the studied core presents remarkable lithological and magnetic susceptibility similarities with cores recovered in the same area during the svais 2007 and the ogs eglacom cruise 2008 allowing the construction of the age model the results indicate that during the last 14 5 cal ky bp advances and retreats of the svalbard barents sea ice sheet were strictly linked to the interplay of atlantic and arctic water inflows to the study area during the deglaciation from the last glacial maximum to the onset of the holocene the climate underwent a series of abrupt changes including the bolling allerod warm interstadial and the younger dryas cold event during the early holocene the investigated area was dominated by enhanced warm atlantic water inflow which was concomitant with summer insolation increase characterizing the holocene thermal maximum conversely the late holocene was governed by deteriorating climatic conditions with predominant arctic polar water inflow on the surface water masses off western svalbard possibly associated with summer insolation decline due to orbital forcing

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr