variations in mode of formation and temperature of oceanic deep waters over the past 125 000 years marked changes in the deep water temperature of the different oceanic basins during the past 125 kyr are revealed by a detailed comparison of the oxygen isotopic composition ofbenthicforaminiferafrom sediment cores taken from the norwegian sea and the pacific atlantic and southern oceans the last interglacial deep water temperatures were similar to the modern ones at the 5e 5d transition around 115 kyr bp the deep water temperatures dropped below approximately 0 c in the pacific and southern indian oceans in the atlantic ocean the deep water temperature dropped in 2 successive steps at 115 and 75ky bp the global ocean deep water temperatures were in the 0 to 1 c range for the whole of the last ice age isotope stages 4 2

eemian cooling in the norwegian sea and north atlantic ocean preceding continental ice sheet growth changing conditions in the north atlantic region may drive global climate changes1 2 according to previous reconstructions of the last interglacial the eemian north atlantic sea surface tempera tures ssts were similar to present day values3 in the norwegian sea even warmer conditions appeared as a single pulse of short duration4 5 whereas the greenland ice record suggests that the warm interglacial air temperatures were interrupted by several cold periods6 here we use faunal and stable isotope analyses of foraminifera in two sediment cores from the north atlantic ocean and norwegian sea to reconstruct high resolution records of sst and sea surface salinity sss during the eemian interglacial our results which differ significantly from the greenland record6 show a sharp decrease in sst and sss of the norwegian sea associated with a more moderate cooling and freshening of the north atlantic at the middle of isotope substage 5e several millennia before the beginning of continental ice sheet growth changes in the norweg ian sea surface conditions appear to have represented an important climate change affecting global atmospheric and thermohaline circulations

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

coupled deep water flow and climate variability in the middle pleistocene north atlantic abrupt changes in the strength of the atlantic meridional overturning circulation comprising northward flow of warm water and a cold southward return flow are implicated in abrupt climate changes in the late pleistocene a sensitive place to assess this circulation is in the cold return flow of deep western boundary currents here in records of flow speed and isotopic composition of surface and bottom waters from a deep western boundary current location near the northern source of north atlantic deep water we show both orbital and millennial scale coupling between deep ocean flow and climate in the middle pleistocene 0 75 0 87 ma when the boundary conditions in terms of the mean state and amplitude of climate change were different from more recent periods the coupling appears as a phased series of events initiated by reduced vertical density gradients and initial ventilation of deep waters the occurrence of these events in interglacials during the middle pleistocene suggests that the millennial scale climate variability in the north atlantic was more pronounced at that time than previously thought this demonstrates that given the right boundary conditions rapid climate shifts can also occur during relatively warm climate conditions

younger dryas style cooling events at glacial terminations i vi at odp site 658 associated benthic δ13c anomalies constrain meltwater hypothesis high resolution planktonic and epibenthic stable isotope records from ocean drilling program site 658 off northwest africa provide a basis for a detailed study of glacial terminations i vi during the last 650 000 years the duration of the terminations was about one half to one quarter of an orbital precession cycle 5800 10 700 years when its amplitude was high at low amplitudes the terminations lasted longer than half an obliquity cycle 29 000 years marked climatic rebounds similar to the younger dryas each with a duration of 1000 2500 years subdivided all six terminations into distinct steps a b and c important parts of the deglacial steps were as brief as 700 1000 years the speed of climatic change suggests that special associations existed between orbital forcing and inherent instability of the ice sheets in harmony with published models the more rapid pulses of glacial meltwater incursions to the northern north atlantic led to one or more brief short term shut downs of north atlantic deep water formation this process is reflected by pronounced benthic 13c minima that precisely coincide in most cases with the end of the 18o deglaciation steps and immediately terminate with succeeding younger dryas style cooling events thus we conclude that the rebounds resulted from a short term antecedent estuarine circulation regime in the north atlantic except for the younger dryas itself which succeeded the allerod with its well ventilated atlantic deepwater circulation and hence continues to be an enigma

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

termination ii interstadial stadial climate change recorded in two stalagmites from the north european alps abstract understanding the sequence of events that take place during glacial interglacial climate transitions is important for improving our knowledge of abrupt climate change here we present a new stacked high resolution precisely dated speleothem stable isotope record from the northern alps which provides an important record of temperature and moisture source changes between 134 and 111 ka for europe and the wider north atlantic realm the record encompasses the penultimate deglaciation termination ii tii which lies beyond the limit of radiocarbon dating thus providing an important new archive for a crucial period of rapid paleoclimate change warmer and wetter ice free conditions were achieved by 134 1 0 7 ka modelled ages as indicated by the presence of liquid water at the site temperatures warmed further at 133 7 0 5 ka and led into an interstadial synchronous with slightly elevated monsoon strength during the week monsoon interval the interstadial experienced an unstable climate with a trough in temperature associated with a slowdown in atlantic meridional overturning circulation amoc and a reduction in north atlantic deep water nadw formation the interstadial ended with a more extreme cold reversal lasting 500 years in which nadw formation remained active but the subpolar gyre weakened allowing cool polar waters to penetrate southwards the main warming associated with tii was very rapid taking place between 130 9 0 9 and 130 7 0 9 ka coeval with initial monsoon strengthening temperatures then plateaued before being interrupted by a 600 year cold event at 129 1 0 6 ka associated once again with penetration of polar waters southwards into the north atlantic and a slowdown in monsoon strengthening sub orbital climate oscillations were thus a feature of tii in the north atlantic realm which broadly resemble the bolling allerod younger dryas 8 2 ka event pattern of change observed in termination i despite monsoon records indicating strong differences between the last and penultimate deglaciation

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

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

evolution of the central nordic seas over the last 20 thousand years the deep and surface water paleoceanographic evolution of the central nordic seas over the last 20 thousand years was reconstructed using various micropaleontological isotopic and lithological proxy data these show a high spatial and temporal complexity of the oceanic circulation when compared with other records from the region during early deglaciation a collapse of ice sheets surrounding the nordic seas released large amounts of freshwater that affected both the surface and bottom water circulation and significantly contributed to heinrich stadial 1 during the younger dryas the central nordic seas were affected by a last major freshwater plume which probably originated from the arctic ocean when major ice rafting had ceased around 11ka subsurface temperatures started to rise however atlantic water advection and subsurface temperatures reached their maximum in the central nordic seas later than along the eastern continental margin that spatio temporal offset is explained by a gradual re routing and westward expansion of the atlantic water flow during times when the greenland sea gyre system became more steadily established in the greenland basin the holocene thermal maximum ended c 5 5ka and time coeveal with an increase in sea ice export from the arctic in the lofoten basin the cooling occurred later after 4ka and together with a weakening of the overturning processes the neoglacial cooling was reached c 3ka together with low solar irradiance expanding sea ice and a slight decrease in deep convection at c 2ka subsurface temperatures began to rise again due to an increasing influence of atlantic waters

development of glacial and interglacial conditions in the nordic seas between 1 5 and 0 35 ma sedimentological and geochemical proxy records of a deep sea sediment core from the southern central nordic seas were used to reconstruct the development of glacial and interglacial conditions during the early and middle pleistocene i e late matuyama to middle brunhes chron 1 5 0 35 ma an enhancement of both glacial and interglacial characteristics is observed during early brunhes oxygen isotope stages ois 16 and 15 respectively any intensification of the climatic conditions prior to this as was previously described for the eastern part of the nordic seas is not recognized at our study site it is further shown that the glacial interglacial environmental contrasts increased from the early to the middle bruhnes chron of all glacial periods investigated ois 12 is characterized by the most severe conditions showing both maximum input of iceberg rafted debris ird as well as planktic foraminiferal 18o values comparable to those of the last glacial maximum among the interglaciations ois 11 is by far the longest interval and the first to show fully developed interglacial conditions i e holocene like 18o values and a minimum of ird deposition hence our comparison supports bottom water 18o studies that have indicated the existence of a gradual intensification of glacial interglacial climate contrasts during the middle pleistocene

temporal and spatial structure of multi millennial temperature changes at high latitudes during the last interglacial the last interglacial lig 129e116 thousand of years bp ka represents a test bed for climate model feedbacks in warmer than present high latitude regions however mainly because aligning different palaeoclimatic archives and from different parts of the world is not trivial a spatio temporal picture of lig temperature changes is difficult to obtain here we have selected 47 polar ice core and sub polar marine sediment records and developed a strategy to align them onto the recent aicc2012 ice core chronology we provide the first compilation of high latitude temperature changes across the lig associated with a coherent temporal framework built between ice core and marine sediment records our new data synthesis highlights non synchronous maximum temperature changes between the two hemispheres with the southern ocean and antarctica records showing an early warming compared to north atlantic records we also observe warmer than present day conditions that occur for a longer time period in southern high latitudes than in northern high latitudes finally the amplitude of temperature changes at high northern latitudes is larger compared to high southern latitude temperature changes recorded at the onset and the demise of the lig we have also compiled four data based time slices with temperature anomalies compared to present day conditions at 115 ka 120 ka 125 ka and 130 ka and quantitatively estimated temperature uncertainties that include relative dating errors this provides an improved benchmark for performing more robust model data comparison the surface temperature simulated by two general circulation models ccsm3 and hadcm3 for 130 ka and 125 ka is compared to the corresponding time slice data synthesis this comparison shows that the models predict warmer than present conditions earlier than documented in the north atlantic while neither model is able to produce the reconstructed early southern ocean and antarctic warming our results highlight the importance of producing a sequence of time slices rather than one single time slice averaging the lig climate conditions

surface and deep water hydrography on gardar drift iceland basin during the last interglacial period changes in surface and deep water hydrography were inferred from variations in stable isotopes and sortable silt mean grain size respectively on the southern gardar drift in the subpolar north atlantic the bathymetric 13c gradient during the penultimate glaciation was similar to the last glaciation with high 13c glacial north atlantic intermediate water above 2000 m and low 13c water derived from the southern ocean below during termination ii low 13c water was present throughout the water column with minimum values at intermediate depths 1500 2000 m and below 3000 m this pattern continued well into the early part of the last interglacial lig period sortable silt mean size at 3275 m suggests that deep water circulation on gardar drift was relatively weak during the earliest part of the lig 128 to 124 5 ka when planktonic 18o was at a minimum reflecting warming and or reduced salinity we suggest that low 13c water and slow current speed on gardar drift during the early part of the lig was related to increased melt water fluxes to the nordic seas during peak boreal summer insolation which decreased the flux and or density of overflow to the north atlantic the resumption of the typical interglacial pattern of strong well ventilated iceland scotland overflow water was delayed until 124 ka these changes may have affected atlantic meridional overturning circulation

oxygen isotope composition of living neogloboquadrina pachyderma sin in the arctic ocean data from the nansen basin of the arctic ocean are used to investigate the habitat and conditions under which the polar planktic foraminifer neogloboquadrina pachyderma sin calcifies the vertical distribution of 18o values of net sampled speciments together with their abundances and proportion of calcification are compared with 18o values from both water samples and foraminiferal tests from core top sediments within the nansen basin the average depth of habitat of n pachyderma sin changes from about 150 m in the southern part to about 80 m in the northern the average depth of calcification however in both regimes varies between 100 and 200 m water depth 18o data from net sampled n pachyderma sin are directly reflected in the core top sediment data but compared to equilibrium calcite 18o values derived from measurements of the ambient water a consistent offset of about 1 over all depth intervals is observed while in the southern part of the nansen basin advection through fram strait of planktic foraminifers from further south may play a role the data from the northern part of the nansen basin give clear evidence that the observed offset in 18o values is caused by a vital effect of n pachyderma sin

late warming and early cooling of the sea surface in the nordic seas during mis 5e eemian interglacial abstract geochemical identification of a tephra layer found in two cores from the ne atlantic ocean and the se norwegian sea respectively and dated to 127 ka bp has enabled us to obtain a precise correlation across the iceland scotland ridge at the marine isotope stage mis 6 5 transition the direct distance between the two cores is only about 200 km south of the iceland scotland ridge sea surface temperatures rose abruptly at 130 ka bp at the onset of mis 5e and at least 2 3000 years earlier than north of the ridge maximum sea surface temperatures south of the ridge occurred during this initial phase of mis 5e when temperatures in the nordic seas were still low north of the ridge the sea surface warmed rapidly at 127 ka bp correlations between the north atlantic records and the eemian of northwest europe tentatively indicate that the initial phase of mis 5e correlates with the early part of the eemian characterised by a warm continental type of climate the period after the warming of the nordic seas corresponds to the slightly cooler and more oceanic middle eemian interval in europe the sea surface temperatures fell gradually north of the ridge during the later part of mis 5e and they were low during mis 5d 5a south of the ridge the temperatures remained relatively high the data shows that there was no outflow of deep water from the norwegian sea during the later part of mis 6 outflow began at the mis 6 5 transition simultaneous with the sea surface warming south of the ridge

glacial interglacial instabilities of the western boundary under current during the last 365 kyr from sm nd ratios of the sedimentary clay size fractions at odp site 646 labrador sea we present 40 sm nd isotope measurements of the clay size 2 m fractions of sediments from the sout hern greenland rise odp 646 that span the last 365 kyr these data track changes in the relative supply o f fine particles carried into the deep labrador sea by the western boundary under current wbuc back to the fourth glacial interglacial cycles earlier studies reveal ed three general sources of particles to the core s ite i precambrian crustal material from canada greenland and or scandinavia north american shield nas ii palaeozoic or younger crustal material from east gr eenland nw europe and or western scandinavia young crust yc and iii volcanic material from iceland and the mid atlantic ridge mar clay size fractions from glacial sediments have the lowest nd isotopic ratios supplies of young crustal particles were si milar during glacial oxygen isotope stages ois 2 6 and 10 i n contrast the mean volcanic contributions decrease d relative to old craton material from ois 10 to ois 6 and the n from ois 6 to ois 2 the glacial ois 8 interval d isplays a mean sm nd ratio similar to those of interglacials ois 1 5 and 9 compared with other interglacials ois 7 was marked by a higher yc contribution but a similar 3 0 mar supply the overall nas contribution dropped by a factor of 2 during each glacial interglacial tran sition with the mar contribution broadly replacing it during interglacials to decipher between higher supplies and or dilution particle fluxes from each end memb er were estimated glacial nas fluxes were systematically h igher than interglacial fluxes during the time int erval examined fine particle supplies to the labrador se a were strongly controlled by proximal ice margin e rosion and thus echoed the glacial stage intensity in con trast the wbuc carried mar supplies from the eastern basins did not change significantly throughout the last 36 5 kyr except for a marked increase in surface sedi ments that suggests unique modern conditions distal wbuc controlled inputs from the northern and ne north atlant ic seem to have been less variable than proximal suppl ies linked with glacial erosion rate

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

tidal asymmetry and velocity skew over tidal flats and shallow channels within a macrotidal river delta 1 it is often assumed that in short shallow estuaries at leading order velocity and elevation are exactly out of phase so that duration asymmetries in the rise and fall of the tide should be manifest as skewed velocities we observed alternating ebb and flood dominant velocity skew in response to the spring neap modulation of incident asymmetry generated by the mixed mainly semidiurnal astronomical tides within the macrotidal skagit river delta in puget sound washington we describe three factors that may contribute to local asymmetries 1 ebb dominance caused by phase lags between the surface gradient and local depth 2 ebb dominance due to fluvial discharge and 3 near bed flood dominance due to baroclinicity large spring tides led to greater frictionally generated phase lags and resulted in ebb dominant velocity skew this ebb dominance caused by tidal drainage was reinforced by fluvial discharge across the tidal flat at lower low water the baroclinic component of this discharge however produced flood dominant near bed velocity skew that countered the ebb dominance of the frictional effects the balance of these processes depends strongly on the spring neap cycle magnitude of river discharge and position within the tidal flat and channel system our observations are notable in the context of previous studies describing these processes because our analyses indicate that these mechanisms are relevant over very short spatial scales of just a few kilometers and in very shallow systems

high resolution climate records from the north atlantic during the last interglacial the two deep ice cores recovered by the grip1 and gisp22 projects at summit greenland agree in detail over the past 100 000 years3 and demonstrate dramatic climate variability in the north atlantic region during the last glacial before the current period of holocene stability this glacial climate instability has subsequently been documented in the marine sedimentary record of surface ocean conditions in the north atlantic4 before 100 kyr ago the two ice core records are discrepant however casting doubt on whether the oxygen isotope fluctuations during the last interglacial eemian seen in the grip core1 5 represent a true climate signal here we present high resolution records of foraminiferal assemblages and ice rafted detritus from two north atlantic cores for the interval 65 kyr to 135 kyr ago extending the surface ocean record back to the eemian the correlation between our records and the greenland ice core records is good throughout the period in which the two ice cores agree suggesting a regionally coherent climate response during the eemian our marine records show a more stable climate than that implied by the grip ice core suggesting that localized phenomena may be responsible for the variability in the latter record during the eemian

milankovitch forcing of the last interglacial sea level during the last interglacial sea level was as high as present 4000 to 6000 years before peak northern hemisphere insolation receipt 126 000 years ago the sea level results are shown to be consistent with climate models which simulate a 3 to 4 c july temperature increase from 140 000 to 130 000 years ago in high latitudes with all northern hemisphere land areas being warmer than present by 130 000 years ago the early warming occurs because obliquity peaked earlier than precession and because precession values were greater than present before peak precessional forcing occurred these results indicate that a fuller understanding of the milankovitch climate connection requires consideration of fields other than just insolation forcing at 65 n

the role of the north atlantic drift in the millennial timescale glacial climate fluctuations abstract the greenland ice core records show that the overall cold climate of the last glacial period was repeatedly interrupted by short rapid warmings the events known as dansgaard oeschger d o events are strongly imprinted in the north atlantic marine records suggesting that they were linked to north atlantic circulation changes however the causes of the d o events are poorly understood and they represent one of the most intriguing puzzles of the last glacial period in order to investigate a possible mechanism we have studied variations in the distribution of benthic and planktonic foraminifera oxygen isotopes and ice rafted debris during the last glacial period in eight cores from the north atlantic and the nordic seas taken at mid depth from 853 to 1760 m the parameters indicate in agreement with previous studies that the circulation system during the interstadials resembled the present system atlantic surface water flowed north into the nordic seas where most of it sank through convection and as cold deep water flowed back into the north atlantic during the stadials a halocline was established in the nordic seas and in the northernmost part of the north atlantic and the outflow from the nordic seas stopped however below the cold light surface layer the relatively warm water of the north atlantic drift continued to flow across the north atlantic and into the nordic seas here warming up the deep water masses we suggest that the warm water gradually made the water column unstable the pivotal abrupt climate warmings were caused by sudden upwelling of the deep warm water masses causing overturning of the entire water column and onset of convection

glacial interglacial variability in deep sea ostracod assemblage composition at iodp site u1314 in the subpolar north atlantic abstract we present a detailed study of glacial interglacial deep sea benthic ostracod assemblage variability at iodp site u1314 subpolar north atlantic in relation to the history of ice rafting events and changes in deep ocean circulation over the past 170 ky our records of ostracod diversity abundance and dissolution and sediment properties ird and caco 3 show an excellent correspondence to high amplitude orbital and millennial variability observed in the climate records 13 c and 18 o from neighboring deep water sites suggesting that the benthic meiofauna fluctuates synchronously with the prevailing oceanographic conditions surface ocean conditions deep ocean circulation and water temperature and food flux krithe dominant argilloecia and cytheropteron are the most abundant and diverse genera in association with rockallia enigmatica three ostracod assemblages are recognized the genera pennyella argilloecia pelecocythere ambocythere pseudobosquetina bradleya and nannocythere are associated with interglacials and interstadials and possibly reflect increased flux of food to the sediments and more vigorous nadw formation a transitional assemblage composed of species of cytheropteron xestoleberis and eucythere is restricted to climatic transitions and indicate moderate environmental conditions and seasonal productivity a glacial stadial assemblage is characterized by a temporal predominance of either intermediate depth and shallow water arctic subarctic species belonging to cytheropteron polycope pedicythere swainocythere cluthia heterocyprideis elofsonella and finmarchinella or abyssal north atlantic ostracods bythocythere dutoitella bathycythere and bythocypris the influx of high latitude taxa can be partially explained by ice rafting but may also represent a shift of the location of intermediate and deep water convection to the area south of iceland therefore the combination of species characteristic of different watermasses during glacials may reflect shifts in the influence of high nutrient southern source water e g aabw vs low nutrient gnaiw during glacials

magnetic properties of deep sea sediments off southwest greenland evidence for major differences between the last two deglaciations high resolution rock magnetic data atomic mass spectroscopy 14 c dates 18 o and grain size analyses from a piston core hu90 013 013 located off southwest greenland provide a record of the last two deglaciations during termination i a welldefined interval having high volumetric magnetic susceptibility k and a low ratio of anhysteretic susceptibility to volumetric magnetic susceptibility k arm k postdates the younger dryas and the 18 o change marking the stage 2 1 boundary and correlates with sedimentological and geomorphological evidence for greenland ice sheet retreat from the coastline to the continental interior during termination ii a very similar magnetic signal coincides with the 18 o shift marking the stage 6 5 glacial interglacial transition and continues throughout substage 5e we suggest that this magnetic signal during both termination i and termination ii marks continental meltwater carried detritus from greenland if so the synchronous changes in magnetic and oxygen isotopic records at termination ii indicate very early and rapid deglaciation of greenland in contrast to the relatively late deglaciation observed for termination i distinct fluctuations in k and k arm k occur below the onset of the 18 o change at termination i where they occur at 16 900 yr b p and at termination ii these fluctuations are interpreted as due to sudden influxes of detritus into the basin caused by unpinning of ice from the continental shelf at the inception of deglaciation

dinoflagellate cyst evidence for warm interglacial conditions at the northern barents sea margin during marine oxygen isotope stage 5 dinoflagellate cyst analysis has been conducted on a sediment core from the northern barents sea margin eastern arctic ocean to reconstruct sea surface conditions during marine oxygen isotope stage 5 cyst concentrations and composition of assemblages display a distinct variability reflecting deglacial warming and the onset of relatively warm interglacial conditions in early stage 5 dinoflagellate cyst assemblages of the last interglacial which corresponds broadly to substage 5e are comparable with those from recent sediments of the area but have lower abundances of cold water taxa such assemblages suggest that sea surface temperatures of the last interglacial were therefore at least as warm as today or even warmer after a distinct cooling relatively stable cold conditions with minor periods of surface water warming prevailed from mid substages 5d to 5b temperatures might have been similar in substages 5a and 5e but the different compositions of assemblages indicate a stronger stratification of surface waters probably owing to a larger meltwater supply in substage 5a these results are compared with previous studies on marine carbonate and calcareous microfossil records from the fram strait and yermak plateau area which show that the general view of a cold last interglacial in the eastern arctic ocean is untenable copyright 2001 john wiley sons ltd

the mechanism of postseismic deformation triggered by the 2006 2007 great kuril earthquakes received 21 january 2011 accepted 15 february 2011 published 24 march 2011 1 in 2006 2007 a doublet of great earthquakes mw 8 struck in the center of the kuril subduction zone a thrust event followed by an extensional event our observations of the kuril gps array in 2006 2009 outline a broad zone of postseismic deformation with initial horizontal velocities to 90 mm a and postseismic uplift we show that most of the postseismic signal after the great kuril doublet is caused by the viscoelastic relaxation of shear stresses in the weak asthenosphere with the best fitting maxwell viscosity in the range of 5 10 10 17 pa s an order of magnitude smaller than was estimated for several subduction zones we predict that the postseismic deformation will die out in about a decade after the earthquake doublet our results suggest large variations among subduction zones in the asthenospheric viscosity one of the most important rheological parameters citation kogan m g n f vasilenko d i frolov j t freymueller g m steblov b w levin and a s prytkov 2011 the mechanism of postseismic deformation triggered by the 2006 2007 great kuril earthquakes geophys res lett 38 l06304 doi 10 1029 2011gl046855

suborbital timescale variability of north atlantic deep water during the past 200 000 years we generated 200 kyr long proxy records of surface and deepwater variability from a subpolar north atlantic core v29 202 enabling us to assess the linkage between surface and deepwater changes on suborbital timescales in particular we used a benthic 13c record to evaluate the deep water response to dansgaard oeschger temperature oscillations and to heinrich events times of massive iceberg delivery to the north atlantic we found that the reduction of north atlantic deep water nadw production was generally associated with cold or dropping sea surface temperatures ssts as indicated by planktonic foraminiferal assemblages the nadw contribution to the site did not drop appreciably during heinrich events h4 through h2 probably because these events followed intervals of prolonged surface cooling already characterized by low rates of nadw production by contrast nadw reduction appears to have been synchronous with h5 sst rise associated with both dansgaard oeschger oscillations and heinrich events was usually accompanied by increasing nadw strength in a few cases the nadw recovery appeared to lag the sst rise however the apparent delay is most likely an artefact of the sedimentary record low concentrations of benthic foraminifera as a result of low benthic foraminiferal abundances during stage 6 the stage 6 benthic foraminiferal 13c record is of lower resolution than the younger part of the record the stage 6 proxy records for surface hydrography nevertheless reveal millennial scale oscillations similar to those seen in stage 3 the available 13c data suggest that nadw weakened in association with the cold portions of stage 6 sst oscillations we also sought to confirm a recent study which concluded that there was little nadw variability during the peak of the last interglaciation marine oxygen isotope substage 5e eemian isotope stage 5 was marked by a trend of increasing benthic 13c in v29 202 rising 13c through isotope stage 5 is also seen in tropical surface water records and at some deep atlantic sites and may reflect the common derivation of these water masses variations of 0 5 superimposed on this rising 13c trend within substage 5e in v29 202 are so far not evident in tropical feed waters and may therefore indicate that nadw production was weaker during the late than mid eemian an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type quit to leave the system paper 95pa02089 suborbital timescale variability of north atlantic deep water during the past 200 000 years by d w oppo and s j lehman diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

stable oxygen and carbon isotopes in planktic foraminifers from arctic ocean surface sediments reflection of the low salinity surface water layer planktic foraminifers neogloboquadrina pachyderma sin from 87 eastern and central arctic ocean surface sediment samples were analyzed for stable oxygen and carbon isotope composition additional results from 52 stations were taken from the literature the lateral distribution of 18o full size image 33 atlantic waters entering the arctic ocean through the fram strait 18o values decrease both to the barents shelf and to the north pole in accordance with the decreasing salinities of the halocline waters in the nansen basin a strong n s 18o gradient is in contrast with a relatively low salinity change and suggests contributions from different freshwater sources i e salinity reduction from sea ice meltwater in the south and from light isotope waters meteoric precipitation and river runoff in the northern part of the basin north of the gakkel ridge 18o and salinity gradients are in good accordance and suggest less influence of sea ice melting processes the 13c full size image 1 k values of n pachyderma sin from arctic ocean surface sediment samples are generally high 0 75 0 95 lower values in the southern eurasian basin appear to be related to the intrusion of atlantic waters the high 13c values are evidence for well ventilated surface waters because the perennial arctic sea ice cover largely prevents atmosphere ocean gas exchange ventilation on the seasonally open shelves must be of major importance lack of 13c gradients along the main routes of the ice drift from the siberian shelves to the fram strait suggests that primary production i e co2 consumption does probably not change the co2 budget of the arctic ocean significantly

the sequence of events surrounding termination ii and their implications for the cause of glacial interglacial co2 changes events surrounding termination ii as preserved in the vostok ice core provide a number of clues about the mechanisms controlling glacial to interglacial climate change antarctic temperature and the atmosphere s co2 content increased together over a period of 8000 years this increase is bounded by a drop in dust flux at its onset and by a drop in the 18o of trapped air at its finish a similar lag between dust flux and foraminiferal 18o is seen in a southern ocean marine record suggesting that the 18o in air trapped in vostok ice is a valid proxy for ice volume the synchronous change of atmospheric co2 and southern hemisphere temperature thus preceded the melting of the northern hemisphere ice sheets this observation coupled with the fact that nutrient reorganization in the north atlantic occurs with or after the sea level rise eliminates many scenarios proposed to explain the co2 rise including those which rely on sea level change conveyor related nutrient redistribution or north atlantic cooling southern ocean scenarios become the front runners but the most popular mechanism iron fertilization has two problems in explaining the co2 rise before termination ii first much of the dust demise occurs prior to the change in co2 so if iron is the villain a threshold value of its supply must be called upon above which productivity does not continue to increase second the co2 rise continues for some 4 5 kyr after the dust flux has fallen to close to zero these problems may be solved if the increased iron supply in dust caused higher rates of nitrogen fixation during the glacial periods in this case the residence time of oceanic nitrate of a few thousand years would enable decreasing productivity to be a global rather than a local phenomenon and would explain the slow rampup of atmospheric co2

persistent suborbital climate variability in marine isotope stage 5 and termination ii new surface water records from two high sedimentation rate sites located in the western subtropical north atlantic near the axis of the gulf stream provide clear evidence of suborbital climate variations through marine isotope stage mis 5 persisting even into the warm peak of the interglaciation substage 5e we found that the amplitude of suborbital climate oscillations did not vary significantly for the whole of mis 5 implying that ice volume has little or no influence on the amplitude of suborbital climate variability in this region although some records suggest that longer suborbital variations 4 10 kyr during mis 5 are linked to deepwater changes none of the existing records is of sufficient resolution to assess if a linkage occurred for oscillations shorter than 4 kyr however when examined in conjunction with published data from the norwegian sea new evidence from the subpolar north atlantic suggests that coupled surface deepwater oscillations occurred during the penultimate deglaciation this supports the hypothesis that during glacial and deglacial times ocean ice interactions and deepwater variability amplify suborbital climate change at higher latitudes we suggest that during the penultimate deglaciation the north atlantic deepwater source varied between nordic sea and open north atlantic locations in parallel with surface temperature oscillations

monitoring termination ii at high latitude anomalies in the planktic foraminiferal record microfaunal studies of planktic foraminifera carried out on 21 sediment cores from the norwegian greenland sea ngs reveal the spatial and lateral distribution as well as meltwater implication of today s non polar subpolar species beella megastoma earland previous findings are verified in that this foraminifera is characteristic only of the deglaciation phases of termination ii iii and vi and not the ensuing interglacial optima thus rendering this species a meltwater indicator its distribution is restricted to cores from the central i e more pelagic part of the ngs covering an area as far north as 77 latitude a detailed investigation of termination ii indicates that b megastoma first appeared in the southwest of the ngs at 131 ka and then about 6 kyr later in the eastern and northern parts of the ngs for the entire duration b megastoma always coincided with the deposition of distinct ice rafted detritus ird suggesting the presence of drifting icebergs during this period two different oceanographic models each with a two stepped evolution of the post saalian surface water circulation are proposed to account for this time transgressive character the mechanism of brine formation as possible oceanic phenomenon forcing atlantic water northwards is suggested for being responsible for the occurrence of b megastoma in the ngs during early termination ii the presence of b megastoma always ceased with the culmination of the interglacial optimum oxygen isotopic substage 5 51 eemian when the subpolar foraminiferal fauna reached highest abundances and a general lack of ird is observed

freshwater pulses in the eastern arctic ocean during saalian and early weichselian ice sheet collapse abstract improved multiparameter records from the northern barents sea margin show two prominent freshwater pulses into the arctic ocean during mis 5 that significantly disturbed the regional oceanic regime and probably affected global climate both pulses are associated with major iceberg rafted debris ird events revealing intensive iceberg sea ice melting the older meltwater pulse occurred near the mis 5 6 boundary 131 000 yr ago its 2000 year duration and high ird input accompanied by high illite content suggest a collapse of large scale saalian glaciation in the arctic ocean movement of this meltwater with the transpolar drift current into the fram strait probably promoted freshening of nordic seas surface water which may have increased sea ice formation and significantly reduced deep water formation a second pulse of freshwater occurred within mis 5a 77 000 yr ago its high smectite content and relatively short duration is possibly consistent with sudden discharge of early weichselian ice dammed lakes in northern siberia as suggested by terrestrial glacial geologic data the influence of this mis 5a meltwater pulse has been observed at a number of sites along the transpolar drift through fram strait and into the nordic seas it may well have been a trigger for the north atlantic cooling event c20

last interglacial surface water conditions in the eastern nordic seas inferred from dinocyst and foraminiferal assemblages marine sediments from the voring plateau norwegian sea have been studied for their dinoflagellate cyst dinocyst and foraminiferal content in order to reconstruct sea surface conditions in the eastern norwegian sea during marine isotope stage mis 5e in combination with stable oxygen isotope and ice rafted detritus ird data the variations in foraminiferal and dinocyst assemblage composition reflect a stepwise transition from the final phase of deglaciation termination ii into typical interglacial conditions this stepwise change is repeated subsequently during the cooling conditions of glacial inception towards mis 5d the interval studied is characterized by relatively high abundances of bitectatodinium tepikiense in comparison to present day values in the area indicating a larger seasonal temperature amplitude with enhanced surface water stratification during mis 5e the important occurrence of the warm temperate dinocyst spiniferites mirabilis s l concurrent with subpolar foraminifers turborotalita quinqueloba globigerina bulloides and globigerinita glutinata reveals that most pronounced interglacial marine conditions prevailed in the area just prior to the transition towards mis 5d the late stratigraphic position of this phase in the interglacial is verified by comparison with dinocyst data from south of iceland manifesting its over regional implication besides the good agreement in dinocyst and foraminiferal assemblage changes the variations in and between both fossil assemblages also point to the existence of some significant surface water variability in the eastern norwegian sea during mis 5e

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

distribution of planktic foraminifera at the ice margin in the arctic fram strait planktic foraminifera were collected in net tows 63 m along two east west transects at 78 and 80 n in the fram strait northern nordic seas at five concurrent depth intervals in the upper 200 m of the water column in the ice free zone absolute abundances in the upper 200 m of the water column up to 500 individuals m3 were obtained along the ice margin the absolute abundances reached up to 1250 ind m3 while in the ice covered areas not more than 50 ind m3 have been found surprisingly these strong variations in abundance are not accompanied by significant changes in faunal assemblages between the ice free and the ice covered regions neogloboquadrina pachyderma is the dominant species in most samples making up to 60 of the total faunal assemblage globigerina quinqueloba contributes 38 and all other species combined make up only 2 of the total fauna both absolute and relative abundances of the collected foraminifera are strongly dependent on the mesh size used using smaller mesh sizes provides a wider species spectrum which is of special interest for paleoceanographic reconstructions in the nordic seas where fossil assemblages 150 m often consist of only one species the specific hydrographic conditions in the fram strait with warm atlantic waters underlying cold polar surface waters result in a rather atypical depth distribution of the planktic foraminifera all species seem to prefer the temperate atlantic waters between 50 m and 200 m thus the species composition as well as geochemical tracers do not reflect the surface ocean conditions which again has potentially interesting implications for paleoceanographic reconstructions

deep sea records from the southeast labrador sea ocean circulation changes and ice rafting events during the last 160 000 years 1 results from two deep sea cores from northeast of newfoundland at 1251 and 2527 m water depth respectively indicate that during the time period from 160 000 to 10 000 years bp ice rafting events in the labrador sea were accompanied by rapid variations in deep and surface water circulation twelve ice rafting events occurred each coinciding with high concentrations of detrital carbonate and oxygen isotopic depletion of both surface and bottom waters eleven of these can be correlated with the north atlantic heinrich events h1 h11 the remaining very conspicuous ice rafting event took place early in mis substage 5e at a time when the planktic faunal assemblage suggests marked warming of the sea surface in the shallower core benthic delta 13 c values rise from a minimum during the deglaciation to peak substage 5e values following the last ice rafting event indicating that the ventilation of intermediate depths was renewed after the deglaciation was complete and continued throughout substage 5e the benthic foraminifera suggest that this well ventilated water mass was comparable to the modern labrador sea water lsw the benthic faunas suggest that a relatively warm intermediate water mass entered the se labrador sea during heinrich events generally low benthic delta 13 c values indicate that this water mass was poorly ventilated and rich in inorganic nutrients isotope data and benthic faunal distributions indicate that north atlantic deep water nadw formed in the norwegian greenland sea reached the se labrador sea between the heinrich events

late quaternary deep sea ostracodes in the polar and subpolar north atlantic paleoecological and paleoenvironmental implications two sediment cores from the northern north atlantic one from the iceland plateau and one from the rockall plateau were investigated in order to examine the response of deep sea benthic ostracodes to climate related environmental changes since marine isotope stage mis 7 ostracode fauna was divided into three factor assemblages by using q mode factor analyses and diversity was calculated using the shannon wiener index the iceland plateau revealed an interglacial assemblage dominated by henryhowella a transitional assemblage dominated by eucythere and a background assemblage that consists of the common taxa krithe and cytheropteron the presence of henryhowella is linked to conditions that prevailed during the peak interglacial periods mis 5e and 1 characterized by increased food supply well oxygenated bottom water and lateral advection the presence of eucythere mainly during the interstadial periods appears to be related to slightly increased food supply whereas the background assemblage is considered to be opportunistic and able to cope with decreased food supply as interpreted for glacial times on the rockall plateau the opportunistic background assemblage consisting mainly of krithe argilloecia and cytheropteron shows no obvious relation to climate changes the interglacial assemblage consists of several taxa dominated by pelecocythere but as on the iceland plateau it also contains henryhowella the third assemblage is the glacial assemblage that consists of a variety of taxa several of which are known from the modern arctic ocean and the greenland sea shelf thus this assemblage indicates glacial conditions on the rockall plateau that are comparable to those found in the present day arctic ocean diversity calculations revealed higher ostracode diversities in glacial than in interglacial episodes in both cores and particularly high diversities during periods of increased input of iceberg rafted debris ird in the rockall plateau core both cores reveal lower surface water productivity during the glacial compared to the interglacial periods and particularly low productivity during the ird events as inferred from carbonate contents we assume therefore that ostracode diversity in the study areas is negatively correlated with food flux

species composition and glacial interglacial variations in the ostracode fauna of the northeast atlantic during the past 200 000 years sediment core m23414 from the rockall plateau north atlantic covering the last two climatic cycles marine isotope stages mis 7 to 1 was investigated for glacial interglacial variations in the deep sea benthic ostracode fauna a highly diversified ostracode fauna including 98 species was found two climate related assemblages were identified associated with interglacial and peak glacial periods respectively the interglacial group occurs during the end of mis 7 5 and 1 and is composed of the genera henryhowella pelecocythere echinocythereis cytherella bradleya aversovalva and eucytherura the glacial group consists of the genera acetabulastoma which is known as sea ice indicator in the modern arctic ocean polycope bythoceratina rhombobythere and some species possibly belonging to the genus pseudocythere and is found during mis 6 4 and 2 these longer term variations within the ostracode fauna seem related to the particular glacial and interglacial climate conditions that affected both deep water production as well as primary production in the surface waters however a detailed comparison of ostracode abundances with the occurrence of events marked by increased ice rafted debris reveals also much shorter term climate related changes in the ostracode fauna thus the temporal fluctuations within ostracode assemblages reflect long and short term alterations of the deep sea environment that are clearly linked to climate changes

last interglacial mis5e hydrographic shifts linked to meltwater discharges from the east greenland margin abstract proximal evidence of the surface ocean response to size reduction of the greenland ice sheet gis during the last interglacial mis5e and preceding glacial termination t2 remains largely elusive using a new sediment record from the western iceland sea the behavior of the northeastern gis and its relation to the subpolar north atlantic surface hydrography is examined extremely light oxygen isotopic 18o values are found off central east greenland during early mis5e and point to enhanced meltwater release potentially from the northeastern sector of the gis data from downstream the cold east greenland current egc and its eastward branches suggest a far reaching effect of this meltwater not only in the nordic seas but also in the se labrador sea in particular whereas an early mis5e warming at 128 5 126 5 ka in the two regions coincided with the relative reduction of meltwater input into the egc the subsequent cooling noted at 126 5 ka followed a renewed major freshwater event off central east greenland our data further indicate persistent freshwater influence from the east greenland margin over the entire mis5e interval and in addition also reveal a late mis5e meltwater event the latter event occurred just prior to the last glacial inception and emphasizes the importance of greenland meltwater as forcing factor on interglacial climates

last interglacial arctic warmth confirms polar amplification of climate change the warmest millennia of at least the past 250 000 years occurred during the last interglaciation when global ice volumes were similar to or smaller than today and systematic variations in earth s orbital parameters aligned to produce a strong positive summer insolation anomaly throughout the northern hemisphere the average insolation during the key summer months m j j was ca 11 above present across the northern hemisphere between 130 000 and 127 000 years ago with a slightly greater anomaly 13 over the arctic greater summer insolation early penultimate deglaciation and intensification of the north atlantic drift combined to reduce arctic ocean sea ice allow expansion of boreal forest to the arctic ocean shore across vast regions reduce permafrost and melt almost all glaciers in the northern hemisphere insolation amplified by key boundary condition feedbacks collectively produced last interglacial summer temperature anomalies 4 5 c above present over most arctic lands significantly above the average northern hemisphere anomaly the last interglaciation demonstrates the strength of positive feedbacks on arctic warming and provides a potentially conservative analogue for anticipated future greenhouse warming

surface and deep water changes in the subpolar north atlantic during termination ii and the last interglaciation to reconstruct the history of water mass exchange between the ne atlantic and the nordic seas sediment cores from 2 km water depth were studied across termination ii tii and through the last interglaciation mis5e during early tii the sudden appearance of the low latitude planktonic foraminifera beella megastoma is noted in both regions along with a steep decrease in benthic foraminiferal 18o since other proxies indicate that surface waters were cold and stratified because of meltwater conditions which prevented near surface thermohaline circulation and vertical convection in the nordic seas water mass exchange between the two areas occurred at the subsurface during later tii surface conditions changed and this subsurface circulation style was eventually replaced by vertical convection in the nordic seas b megastoma vanished from the record together with ice rafted debris ird at the end of tii while subpolar foraminiferal abundance rose peak interglacial conditions with intensive vertical convection now fully developed generating a bottom water temperature gradient of 4 c between the two areas however surface water temperatures deteriorated in the nordic seas already notably before ird recurred and 18o increased at the end of mis5e

comparison of glacial and interglacial conditions between the polar and subpolar north atlantic region over the last five climatic cycles a multiparameter based interpretation of sediment records from the northeast atlantic and the western nordic seas suggests that during the last 500 000 years only in marine isotopes stage mis 11 5e and 1 were there somewhat comparable interglacial boundary conditions in both regions i e strongly reduced occurrence of iceberg rafted debris ird and high carbonate bioproductivity although the northeast atlantic experienced such conditions during all peak interglaciations with the exception of mis 7 planktic foraminiferal 18o from this region would still indicate that significantly colder sea surface temperatures sst prevailed during mis 11 than during mis 9 5e and 1 this assumption is corroborated by a continuous input of ird into the western nordic seas during mis 11 implying a much steeper sst gradient between the polar and subpolar region and an overall reduced thermohaline activity in the polar latitudes the iceberg proxy also reveals that maximum ird discharge always happened during the final phase of glaciation and into early deglaciation terminations as these ird records from the two regions are characterized by a high time coherency it is concluded that short term variability is a persistent feature of the glacial climate system

marine core evidence for reduced deep water production during termination ii followed by a relatively stable substage 5e eemian we present oxygen and carbon isotope records of benthic foraminifera from the glacial stage 6 through interglacial substage 5e eemian sections of several cores from the subpolar north atlantic the cores range in water depth from 1451 to 2658 m in one core we generated estimates of sea surface temperature sst and of ice rafted detritus ird delivery for all of stage 5 we reconstruct bathymeric profiles of 13c for stage 6 termination ii and three time slices of substage 5e the 13c profiles indicate that local deep water geometry during stage 6 was similar to that of the last glaciation with glacial north atlantic intermediate water gnaiw overlying deeper waters partially of southern origin an anomalously large peak in ird coupled with planktonic 18o evidence for iceberg melting immediately precedes termination ii and is otherwise similar to stage 2 and 3 heinrich events during the termination low 13c values are observed in cores near and above 2 km providing evidence of reduced gnaiw production in association with deglacial melting in the shallowest cores low 13c values persist into early substage 5e indicating that the southward retreat of southern source waters was not completed until well after the beginning of the substage in contrast to termination i ssts remained cold until the end of the deglaciation this may be why there is little evidence from marine and terrestrial sequences for a pronounced climate reversal on termination ii despite what is now clear evidence of a significant reduction in ocean ventilation the faunal data suggest that ssts during early 5e were about 7 c warmer than during the glaciation sst rose several degrees from early to middle substage 5e peaked in middle substage 5e at about 10 c above glacial values and then gradually declined by about 5 c these changes were linked to variations in water mass configuration as interpreted from benthic 13c evidence most of the evidence suggests that oscillations superimposed on the gradual sst trend were 1 2 c in contrast to the larger sst changes 3 4 c documented for substage 5d

evidence for a steeper eemian than holocene sea surface temperature gradient between arctic and sub arctic regions sediment proxy data from the norwegian greenland and iceland seas nordic seas are presented to evaluate surface water temperature sst differences between holocene and eemian times and to deduce from these data the particular mode of surface water circulation records from planktic foraminiferal assemblages caco3 content oxygen isotopes of foraminifera and iceberg rafted debris form the main basis of interpretation all results indicate for the eemian comparatively cooler northern nordic seas than for the holocene due to a reduction in the northwardly flow of atlantic surface water towards fram strait and the arctic ocean therefore the cold polar water flow from the arctic ocean was less influencial in the southwestern nordic seas during this time as can be further deduced from the eemian data slightly higher eemian ssts are interpreted for the western iceland sea compared to the norwegian sea ca south of 70 n this eemian situation is in contrast to the holocene when the main mass of warmest atlantic surface water flows along the norwegian continental margin northwards and into the arctic ocean thus a moderate northwardly decrease in sst is observed in the eastern nordic seas for this time causing a meridional transfer in ocean heat due to this distribution in ssts the holocene is dominated by a meridional circulation pattern the interpretation of the eemian data imply a dominantly zonal surface water circulation with a steep meridional gradient in ssts

sediment color record from the northeast atlantic reveals patterns of millennial scale climate variability during the past 500 000 years a 500 000 yr long deep sea sediment color record from the northeast atlantic was investigated to reconstruct the evolution of late pleistocene climate variability on millennial time scales variations of the red green color intensity are probably caused by climatically induced changes in the ice rafted input of red colored iron bearing terrigenous material to the core site the resolution of the age model impedes the detection of distinct spectral features at sub milankovitch periodicities hence millennial scale climate variability is quantified as time dependent variance of the high pass filtered color time series the course of the estimated variance shows distinct patterns which can be linked to continental ice mass during the past 500 000 yr large amplitude millennial scale climate variability occurs only if continental ice mass exceeds a threshold level equivalent to sea level at approximately 40 of the lowering during the last glacial maximum

last glacial benthic foraminiferal δ18o anomalies in the polar north atlantic a modern analogue evaluation modern processes are evaluated to understand the possible mechanisms behind last glacial benthic foraminiferal 18o anomalies that occurred concurrent with meltwater events in the polar north atlantic such anomalies in the nordic seas were recently interpreted to be caused by brine formation despite intensive sea ice production on circumarctic shelves modern data show that brines ejected from sea ice formation containing low 18o water do not significantly contribute to deep waters in the arctic ocean today assuming that this process was nevertheless responsible for 18o anomalies in nordic seas deep water during the last glaciation a broad shallow shelf area adjacent to the nordic seas such as the barents sea had to be seasonally free of sea ice in order to serve as an area for brine formation another process which may explain 18o depleted water at depth is found in the weddell sea today where a low 18o signal in deep waters originates from ice shelf interactions if temperature were considered the main mechanism for the low benthic 18o values an increase of 4 c must have occurred in the deep water an analogous situation with a reversed water temperature pattern due to a subsurface inflow of warm atlantic water is found today in the eastern arctic ocean and deep water warming is observed in the greenland gyre in the absence of deep convection because paleoproxy data also indicate an atlantic water inflow into the nordic seas during such benthic 18o anomalies temperature as a principal mechanism of changing 18o cannot be excluded

contrasting ocean changes between the subpolar and polar north atlantic during the past 135 ka variations in the poleward directed atlantic heat transfer was investigated over the past 135 ka with special emphasis on the last and present interglacial climate development eemian and holocene both interglacials exhibited very similar climatic oscillations during each preceding glacial terminations deglacial ti and tii like ti also tii has pronounced cold warm cold changes akin to events such as h1 bolling allerod and the younger dryas but unlike ti the cold events in tii were associated with intermittent southerly invasions of an atlantic faunal component which underscores quite a different water mass evolution in the nordic seas within the eemian interglaciation proper peak warming intervals were antiphased between the nordic seas and north atlantic moreover inferred temperatures for the nordic seas were generally colder in the eemian than in the holocene and vice versa for the north atlantic a reduced intensity of atlantic ocean heat transfer to the arctic therefore characterized the eemian requiring a reassessment of the actual role of the ocean atmosphere system behind interglacial but also glacial climate changes key points reduced amoc during the eemian ba yd type warming cooling in termination 1 and 2 comparison of glacial inceptions reveals present climate status

implications of stratigraphic and paleoclimatic records of the last interglaciation from the nordic seas climatic reconstruction of glacial to interglacial episodes from oxygen isotopes in sediment cores from the nordic seas is complicated by strong local meltwater contributions to the oxygen isotope changes combination of benthic and planktic foraminiferal isotope data with foraminiferal abundances and ice rafted debris ird allows separation of local and global effects and subdivision of the marine oxygen isotope events 6 2 5 4 which include the last interglaciation into 1 a meltwater phase after glacial stage 6 recorded by large amounts of ird and low foraminiferal abundance indicating surface water warming 2 an ird free period with high deposition rates of subpolar foraminifera and other caco3pelagic components recognized here as the full interglaciation and 3 a phase with the recurrence of ird and the demise of subpolar species comparison of ice core records and marine data implies that the global climate during the last full interglaciation and that during the postdeglacial holocene were similar the records show no significantly different variations in the proxy data in contrast the oxygen isotopes of planktic foraminifera and ice cores indicate significant differences during each of the deglacial transitions terminations i and ii that preceded these two interglaciations these suggest that during termination ii the climatic evolution in the nordic seas was less affected by abrupt changes in ocean atmosphere circulation than during the last glacial to interglacial transition

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

interglacial climates and the atlantic meridional overturning circulation is there an arctic controversy arctic palaeorecords are important to understand the natural range of forcing and feedback mechanisms within the context of past and present climate change in this temperature sensitive region a wide array of methods and archives now provide a robust understanding of the holocene climate evolution by comparison rather little is still known about older interglacials and in particular on the effects of the northward propagation of heat transfer via the atlantic meridional ocean circulation amoc into the arctic terrestrial records from this area often indicate a warmer and moister climate during past interglacials than in the holocene implying a more vigorous amoc activity this is in conflict with marine data although recognized as very prominent interglacials in antarctic ice cores cross latitudinal surface ocean temperature reconstructions show that little of the surface ocean warmth still identified in the northeast atlantic during older interglacial peaks e g mis5e 9 11 was further conveyed into the polar latitudes and that each interglacial developed its own specific palaeoclimate features interactive processes between water mass overturning and the hydrological system of the arctic and how both developed together out of a glacial period with its particular ice sheet configuration and relative sea level history determined the efficiency of an evolving interglacial amoc because of that glacial terminations developed some very specific water mass characteristics which also affected the climate evolution of the ensuing interglacial periods moreover the observed contrasts in the arctic directed meridional ocean heat flux between past interglacials have implications for the palaeoclimatic evaluation of this polar region crucial environmental factors of the arctic climate system such as the highly dynamical interactions between deep water mass flow surface ocean temperature salinity sea ice and atmosphere exert strong feedbacks on interglacial climate regionality that goes well beyond the arctic a sound interpretation of such processes from palaeoarchives requires a good understanding of the applied proxies fossils in particular are often key to the reconstruction of past conditions but the tremendously flexible adaptation strategies of biota sometimes hampers further in depth interpretations especially when considering their palaeoenvironmental meaning in the context of rapid palaeoclimatic changes and long term pleistocene evolution

eemian and early weichselian 140 60 ka paleoceanography and paleoclimate in the nordic seas with comparisons to holocene conditions paleoceanographic and paleoclimatic time series were extracted from norwegian iceland and greenland sea the nordic seas sediment sequences covering the time intervals 60 140 ka and 0 15 ka on the basis of stable isotope stratigraphy planktonic foraminiferal faunas and sedimentological methods the proxy temperature records from the norwegian iceland sea display a number of high frequency and high amplitude variations within the last interglacial the eemian indicating marked changes in heat flux at high northern latitudes eemian holocene comparisons document that the climate of the norwegian iceland sea in the last interglacial was less stable than that of the present interglacial and that the distribution of surface water masses in the eemian differed from that of the holocene within the greenland sea uniform cold conditions prevailed throughout both interglacials cooling of the nordic seas as well as the initial growth of the surrounding ice sheets began within the eemian interval before the main increase in global ice volume heat flux to the nordic seas was significantly higher during the interglacials than at any time during the early weichselian 60 113 ka and no marked stadial interstadial changes in sea surface temperature and deep water ventilation are documented in the early weichselian records contrary to the pattern found in north atlantic sediment records however fluctuations in planktonic foraminiferal content planktonic 13c and ice rafting on suborbital timescales mostly comparable in number and age to the stadial interstadial fluctuations in the greenland ice cores are demonstrated in our records the ice rafted detritus records provide a more detailed account of ice sheet variability than previously known for the early weichselian period and demonstrate that glaciers advanced to sea level somewhere around the nordic seas several times during this interval

benthic δ18o records in the north atlantic over the last glacial period 60 10 kyr evidence for brine formation four high resolution benthic isotope records from north atlantic and south norwegian sea cores are compared for the past 60 kyr the benthic records show light 18o peaks simultaneously to or following the heinrich events the amplitude of these light peaks varies between 1 for the most northern core enam93 21 and 0 35 for the deep north atlantic cores the high 18o gradient between the north atlantic cores and the pacific core v19 30 suggests a regional influence of 18o depleted meltwater to deeper depth during periods of iceberg discharges the most likely process for transferring 18o depleted meltwater to depth is sea ice formation induced by brine formation during heinrich events 4 and 3 this mecanism was of major importance compared to open ocean convection in the southern norwegian sea and at the northern boundaries of the atlantic leading to intermediate to deep water formation other 18o excursions appearing in all the records point to the contribution of both brine formation and global changes in the 18o of seawater associated with the heinrich event periods

paleoclimatic significance of subpolar foraminifera in high latitude marine sediments census data of subpolar planktonic foraminifera in high latitude sediment cores obtained using a 149 m mesh can be directly related to past surface water conditions in contrast analyses performed using material sieved with a 62 m mesh produce results that must be interpreted with regard to past dissolution conditions of the local deep or bottom waters this conclusion bears directly on the validity of several recent papers purporting to relate baffin bay and labrador sea paleo oceanography with wisconsinan glacial events in northeastern canada

stability of north atlantic water masses in face of pronounced climate variability during the pleistocene 1 geochemical profiles from the north atlantic ocean suggest that the vertical 13c structure of the water column at intermediate depths did not change significantly between glacial and interglacial time over much of the pleistocene despite large changes in ice volume and iceberg delivery from nearby landmasses the most anomalous 13c profiles are from the extreme interglaciations of the late pleistocene this compilation of data suggests that unlike today an extreme interglaciation the two primary sources of northern deep water norwegian greenland sea and labrador sea subpolar north atlantic had different characteristic 13c values over most of the pleistocene we speculate that the current open sea ice conditions in the norwegian greenland sea are a relatively rare occurrence and that the high 13c deep water that forms in this region today is geologically unusual if northern source deep waters can have highly variable 13c then this likelihood must be considered when inferring past circulation changes from benthic 13c records

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

were glacial iceberg surges in the north atlantic triggered by climatic warming high resolution physical mineralogical sedimentological and micropalaeontological studies were carried out on north atlantic cores from the reykjanes ridge at 59degreesn and from the region southwest of the faeroe islands all core sites are situated along the pathway of iceland scotland overflow water isow and the various parameters measured display similar features previously identified carbonate oscillations keigwin and jones 1994 j geophys res 99 12397 12410 in the time span back to the marine isotope stage 5 4 transition and late glacial lithic events bond and lotti 1995 science 267 1005 1010 such as the heinrich ice rafting events are all represented in the core records long term trends and higher frequency changes in isow intensity were reconstructed on the basis of various independent proxy records the long term trends in circulation match theoretical orbitally forced insolation changes our observed links between ice rafted detritus ird input variations in sea surface temperature sst and circulation at greater depth point to the need to re examine the origin of ird events we suggest that these events may have been triggered by enhanced partly sub surface heat transport to the north enhanced northward heat transport may have caused bottom melting of floating outlet glaciers and ice shelves leading to increased iceberg discharge and ice sheet destabilization this discharge resulted in lower sst s and a lower temperature over greenland thus as shown by our records this scenario implies a temporary de coupling of surface processes and circulation at greater depth a key feature is the occurrence of a saw tooth pattern in the marine data which is similar to the greenland ice core records moreover the warming theory of ird events would explain the observed out of phase relationship between the greenland and antarctic ice core records and also the rapid establishment of higher temperatures over greenland immediately after the cold phases stadials of the dansgaard oeschger cycles less

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

sedimentary record of rapid climatic variability in the north atlantic ocean during the last glacial cycle comparisons between a greenland ice core isotopic record and marine sediment grey level records of the north atlantic ocean show that rapid temperature variations witnessed by the ice core dansgaard oeschger events during the last glacial period can also be detected in marine sediments this shows that the resolution obtained in marine cores can be sufficiently high to record rapid climatic fluctuations several spectral analyses of those grey level marine records consistently indicate that significative fluctuations of the climatic response exist with periodicities of 5 to 1 kyr in addition to orbital forcing these high frequencies are close to those predicted by various dynamic ocean models

hydrological variability in florida straits during marine isotope stage 5 cold events modeling and proxy studies indicate that a reduction of atlantic meridional overturning circulation amoc strength profoundly impacts temperatures and salinities in the sub tropical atlantic especially on subsurface levels while previous studies focused on prominent periods of amoc reduction during the last deglaciation we aim to test whether similar reconfigurations of the subtropical hydrography occurred during the moderate climatic alterations punctuating the last interglacial marine isotope stage mis 5 here we present temperature and salinity records from a florida straits core by combining d18o and mg ca analyses on surface globigerinoides ruber white and deep dwelling globorotalia crassaformis foraminifera covering mis 5 in high resolution the data reveal increasing salinities at intermediate depths during interglacial cooling episodes decoupled from relatively stable surface conditions this probably indicates the spatial expansion of saline subtropical gyre waters due to enhanced ekman downwelling and might also point to a changed density structure and altered geostrophic balance in florida straits notably these oceanographic alterations are not consistently occurring during periods of amoc reduction the data suggest that the expansion of gyre waters into florida straits was impeded by the increasing influence of antarctic intermediate water aaiw from mis 5 5 to 107 kyr bp afterward increasingly positive benthic d13c values imply a recession of aaiw allowing the temporary expansion of gyre waters into florida straits we argue that the inferred transient subtropical salt accumulation and warm pool expansion might have played a pivotal role in reinvigorating meridional overturning and dampen the severity of interglacial cold phases

rapid changes in ocean circulation and heat flux in the nordic seas during the last interglacial period the apparent similarity of climate variability in the north atlantic region in the last interglacial period1 5 and the present interglacial holocene has recently been challenged by the rapid oscillations in climate conditions indicated by some marine6 7 and terrestrial climate records8 10 for the last interglacial ocean circulation in the northern north atlantic seems to be intimately coupled to the processes of climate change on various time scales11 12 so that climate variability and the associated mechanisms of change should be well recorded by sediments from these high latitudes previous studies in this region5 13 have indeed indicated an apparently less stable last interglacial climate than at middle latitudes of the north atlantic ocean4 here we present detailed records from marine sediments in the nordic seas of oceanographic conditions during the last interglacial the records show three large sea surface temperature fluctuations a weakening of the east west sea surface temperature gradient with time and changes in deep water properties in contrast similar analyses of a core from the same region indicate that sea surface temperature during the holocene has been relatively stable our data along with those from the labrador sea7 indicate rapid changes in ocean circulation and oceanic heat fluxes at high northern latitudes during the last interglacial which may have been associated with marked temperature changes on adjacent continents

the intensification of northern component deepwater formation during the mid pleistocene climate transition we reconstruct mid pleistocene marine isotope stages miss 13 18 deepwater hydrography at ocean drilling program site 1063 4583 m water depth subtropical north atlantic using benthic foraminiferal stable isotope records these new records complete an 900 kyr long stratigraphy spanning miss 8 29 250 1030 ka when combined with previously published records from site 1063 the results indicate a change in the circulation regime of the abyssal subtropical north atlantic during mis 17 prior to mis 17 no significant glacial or interglacial 13c gradients are evident between site 1063 and the deep south atlantic after mis 17 interglacial intervals at site 1063 are characterized by 13c values that consistently approach those recorded in the deep north atlantic comparing site 1063 13c values to 26 additional published records throughout the entire atlantic basin supports the idea that this 13c increase is unique to the deep north atlantic after mis 17 the basin wide influence of higher 13c values suggests an increased relative flux of northern sourced bottom waters during interglacial periods the timing of northern sourced water influence at site 1063 is consistent with the timing of a shift in the orientation of the arctic front thus this shift may signify a link between the northward penetration of relatively warm saline surface waters into the norwegian greenland seas stimulating deep convection our findings fit well with the model of imbrie et al 1993 for the importance of the nordic heat pump in establishing strong 100 kyr cyclicity in late pleistocene glacial cycles

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