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

sediment fluxes along the northeastern european margin inferring hydrological changes between 20 and 8 kyr abstract in an attempt to delineate past hydrographic conditions on the northeastern atlantic ocean margin along a latitudinal transect 37 63 n and link the eastern north atlantic ocean with the norwegian sea we have investigated planktonic and benthic stable oxygen isotopes as well as abundances and fluxes of planktonic and benthic foraminifera calcium carbonate organic carbon and detrital grains in six sediment cores studied by the enam project in our joint approach we focused on the major climatic events of the last 20 kyr that is the last glacial maximum lgm the heinrich event 1 h1 the younger dryas yd and the holocene climatic optimum hco simmax temperature estimates suggest glacial ssts off portugal similar to holocene values contradicting the proposed polar front position of climap project members 1976 besides increased planktonic and benthic foraminiferal fluxes in the norwegian sea and the faeroe islands cores point to nordic seas partially ice free with seasonally productive polynas multiple ird spikes observed at the faeroe islands and norwegian sea sites coeval with h1 suggest multiple pulses of the fenno scandian ice sheet at the same time the presence of ird on the portuguese margin cores confirms the southward influence of icebergs the increase in foraminiferal abundances and fluxes that parallel ird spikes at all sites suggests that times of increased productivity either succeed or occur simultaneously with the iceberg surges in the open north atlantic productivity conditions similar to those observed during h1 are also registered during the yd even though planktonic foraminiferal assemblages suggest less cold conditions

sr and nd isotopes as tracers of north atlantic lithic particles paleoclimatic implications sr and nd isotopic compositions have been measured on the lithic fraction of last climatic cycle sediments from the north atlantic 40 n 60 n in order to identify the origins of the particles from the reconstruction of their transport pathways we deduce the mechanisms that explain their distributions the main source regions are the canadian shield mostly the area of baffin bay and western greenland the scandinavian shield the european region british isles and bay of biscay and iceland we observe a significant glacial interglacial contrast characterized by a dominant icelandic input via near bottom transport by north atlantic deep water nadw during the interglacials and a largely continent derived contribution of surface transported ice rafted detritus ird during the glacial period during the last glacial period the heinrich events abrupt massive discharges of ird originated not only from the laurentide ice sheet as heretofore envisioned but also from other sources three other major north atlantic ice sheets fennoscandian british isles and icelandic probably surged simultaneously discharging ice and ird into the north atlantic as opposed to theories implying a unique laurentide origin gwiazda et al 1995 driven by an internal mechanism mcayeal 1993 we confirm that the icelandic and the fennoscandian ice sheets also surged as recently proposed by other authors and we here also distinguish a possible detrital contribution from the british isles ice sheet this pan north atlantic phenomenon thus requires a common regional external forcing

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

controls on the provenance of late eocene to quaternary mozambique channel shales dsdp 25 site 242 abstract provenance determination of late eocene to quaternary sediments deposited at the dsdp 25 site 242 may help to evaluate the mechanisms that have controlled the sediment deposition in the mozambique channel to determine the provenance of the clay fraction we measure major and trace element concentrations as well as strontium 87sr 86sr and neodymium isotopic compositions expressed as nd 0 of thirty six sedimentary samples from dsdp 25 site 242 on the eastern flank of the davie fracture zone light rare earth element lree enrichment and heavy ree hree depletions against post archean australian shales paas associated with ce anomalies higher than or equal to 0 90 for all the analyzed samples suggest very little influence of authigenic smectite incorporation the absence of correlation of al si and cia with ree content eu eu cr th th sc and 87sr 86sr and nd 0 suggests that chemical weathering has not modified these provenance proxies slight increase of eu eu cr th ratios nd 0 values associated with slight decrease in 87sr 86sr and th sc ratios from the late eocene to the quaternary point to input of less differentiated and younger detritus to the dsdp 25 site 242 with age based on variations in nd 0 and nd concentrations we estimate an overall decrease of the southeast african rivers congo zambezi contribution from 65 7 standard deviation s d 13 2 in the late eocene to 28 5 s d 10 0 in the early pliocene the causes for the low nd 0 values and high southeast african contribution between the late eocene and the early oligocene remain to be determined it could record the onset of modern sedimentation in the zambezi delta or the discharge of the paleo congo river in the indian ocean the decrease of zambezi contribution between the late oligocene and early pliocene is attributed to the cumulative effect of increasing tectonic activity of the davie fracture zone and intensification of the mozambique current the late pliocene to quaternary glacial interglacial cycles promoted higher zambezi contribution during glacial sea level lowstands and in turn lower nd 0 detrital values whereas low zambezi contributions are favored during interglacial highstand causing higher nd 0 values hence the modern dispersal pattern of fine grained sediments within the mozambique channel is no younger than late pliocene

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

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

rare earth elements and nd and pb isotopes as source indicators for labrador sea clay size sediments during heinrich event 2 elemental abundances and nd and pb isotope ratios were determined on samples from the carbonate free clay size fractions of sediments from intervals above within and below heinrich event 2 h 2 in core hu87 9 from the northwest labrador sea slope in hu87 9 rare earth element ree distributions and elemental concentrations within the h 2 event are distinct from those outside this event end 0 and 206 pb 204 pbdata also indicate different values for sediments deposited within and outside the h 2 event comparisons of ree patterns from the h 2 interval with those from bedrock units in baffin island northern quebec and labrador indicate that the lake harbour group lhg which crops out on the north side of the hudson strait is the most probable bedrock source of the clay size fraction found within the h 2 interval in hu87 9 the tasiuyak gneiss tg and lac lomier complex llc have ree patterns including a negative eu anomaly similar to those found in h 2 sediments however the la ybratios of these units are smaller than those associated with h 2 sediments the nd and pbisotope data support and complement ree based interpretations of provenance i e the nd pb signatures of sediments deposited at the hu87 9 site during the h 2 event are similar to nd pbsignatures ob tained on diamicts from the western end of hudson strait published by elsevier science ltd

late quaternary sedimentation patterns on the meriadzek terrace bay of biscay esscamp 02 core 47 n 9 w abstract foraminiferal assemblage changes size and mineralogy of lithic grains oxygen isotopes caco 3 and dolomite content were studied along a 9 m long core from the meriadzek terrace to gain insight into climate productivity and sediment source changes at this part of the northeast atlantic margin during the late quaternary an age model has been generated on the basis of radiocarbon dating downcore foraminiferal assemblages and 18 o values high sedimentation rates at this site allow very detailed records for the last glacial period down to late isotopic stage 3 sea surface temperature sst inferred from the foraminiferal assemblages 18 o curve and the temperature estimation by the simmax analog technique reveal three distinctive periods during isotopic stage 2 with late stage 2 15 3 13 4 ka being the coldest period of the last 26 ka a northward retreat of the polar front at 13 4 ka based on the sst record coincides with the strongest peak of primary productivity as indicated by the foraminiferal fluxes levels rich in large lithic grains llg interpreted as ice rafted debris ird correspond to periods of low sst and are coeval with heinrich layers 1 2 and 3 however the hematite stained quartz found in the detrital fraction and the scarce dolomite and detrital carbonate content in our core point to an iceland and or fenno scandian rather than a laurentian or greenland origin of this material

late quaternary sediment flux on sedimentary drifts in the northeast atlantic abstract comparison between the last glacial and holocene periods of the terrigenous and carbonate sediment flux distributions in the whole northeastern atlantic basin points out the role of deep circulation relative to other processes during the holocene the global terrigenous flux is similar to that during the glacial period 4 compared with 4 7 g cm 2 ky 1 despite a general decrease of terrigenous supplies the flux distribution however is different high values are located in areas of bottom current sedimentation contourite drifts instead of along continental margins where downslope processes are dominant and areas with major ice rafting the global carbonate flux is higher during the holocene 3 compared with 1 5 g cm 2 ky 1 but the carbonate flux distribution matches that of the terrigenous flux both flux patterns are strongly controlled by reworking and redeposition of sediments by bottom currents flux variation in three cores collected on the feni gardar and faro drifts compared to areas of little or no bottom current activity highlights the deep water circulation fluctuations since the last glacial maximum in areas dominated by downslope processes bay of biscay or by ice rafted sediment deposition mid atlantic ridge around 45 n the sediment fluxes are maximum during the deglacial warming and minimum during the holocene period areas dominated by bottom current sedimentation are all characterized by highest sedimentation during the holocene but the flux variations reveal that the norwegian sea water overflow nswo and the mediterranean outflow mo fluctuated differently according to the regional climatic context and the latitudinal transgression of climatic warming on the feni and gardar drifts higher holocene fluxes coincide with the re initiation of nswo at about 10 000 yrs bp the highest flux on the gardar drift results from a stronger outflow across the iceland faeroe ridge than across the faeroe scotland ridge this flow is responsible for high sediment fluxes all along the eastern side of the mid atlantic ridge as far south as 45 n on the faro drift the reactivation of the mediterranean outflow mo took place earlier as three episodes of greater bottom current activity occurred since about 15 000 yrs bp fluxes are maximum during the deglacial warming and remain high during the holocene

a 50 000 year record of climate oscillations from florida and its temporal correlation with the heinrich events oscillations of pinus pine pollen in a 50 000 year sequence from lake tulane florida indicate that there were major vegetation shifts during the last glacial cycle episodes of abundant pinus populations indicate a climate that was more wet than intervening phases dominated by quercus oak and ambrosia type ragweed and marsh elder the pinus episodes seem to be temporally correlated with the north atlantic heinrich events which were massive periodic advances of ice streams from the eastern margin of the laurentide ice sheet possible links between the tulane pinus and heinrich events include hemispheric cooling the influences of mississippi meltwater on sea surface temperatures in the gulf of mexico and the effects of north atlantic thermohaline circulation on currents in the gulf

european contribution of ice rafted sand to heinrich layers h3 and h4 abstract this paper reports the sr nd isotopic composition of the carbonate free sand 63 m 1 mm fraction of heinrich layers 3 and 4 from about 17 cores from the northern atlantic ocean 38 n to 68 n the results indicate that the transporting icebergs were calved from many ice sheets from around the north atlantic at least the fennoscandian icelandic and laurentide our isotopic data show a more distinctly european origin for ice rafted debris ird deposited during the atypical heinrich event h3 than for background ird in contrast heinrich layer h4 a representative of typical heinrich events h1 h2 h4 and h5 presents a clear dominant laurentide signal this result confirms that these typical heinrich events are associated with a massive discharge of icebergs from the laurentide ice sheet however the theory that the laurentide ice sheet set the events into motion alley r b macayeal d r 1993 ice rafted debris associated with binge purge oscillations of the laurentide ice sheet paleoceanography 9 4 503 511 cannot explain the fact that a european signal of an early h4 sample has been observed prior to the laurentide signature of a late h4 sample in the same core along the european margin this observation indicates that the european ice sheets may have surged before the north american ones and suggests that the laurentide ice sheet was not the sole motor behind the heinrich events moreover in the norwegian sea ird has a scandinavian origin in both h3 and h4

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

salinity history of the northern atlantic during the last deglaciation the claim has been made see broecker et al 1988 that production of north atlantic deep water terminated during younger dryas time and that the onset of this termination occurred about 11 000 years ago when the flow of meltwater from a large segment of the southern margin of the laurentide ice sheet was diverted from the mississippi to the st lawrence drainage fairbanks 1989 points out a serious weakness in this argument based on a sea level curve derived from radiocarbon dates on coral obtained from borings made off the barbados coast he suggests that a lull in the melting of the ice caps during younger dryas time may have more than compensated for the impact of the diversion the purpose of this paper is to reassess the situation regarding the origin of the younger dryas in light of this new evidence currently the salinity of surface waters in the northern atlantic is influenced by three fluxes water vapor transport from the atlantic drainage basin to the pacific indian basin tends to raise the salinity of the entire atlantic the excess over evaporation of precipitation and runoff poleward of 40 n tends to reduce the salinity of waters in this region relative to the atlantic average the conveyor circulation of the atlantic trades more salty waters of the atlantic with less salty waters outside the atlantic tending to drive down the atlantic s salinity the conveyor circulation also flushes the northern atlantic pushing its salinity toward the mean for the atlantic during the period of deglaciation meltwater emanating from the laurentide and scandinavian ice sheets was also important this flux tended to lower not only the salinity of the entire atlantic but also the salinity of surface waters in the northern atlantic relative to the atlantic s mean as deepwater formation in the northern atlantic depends critically on the salinity of surface waters the interactions among these fluxes can change the strength of the conveyor

lateglacial and holocene environmental changes in portuguese coastal lagoons 1 the sedimentological and geochemical records of the santo andre coastal area the sedimentological and geochemical study of a core corresponding to sedimentation in the santo andre lowland since 14 000 bp allowed the reconstruction of environmental changes of this area and discussion of the relative importance of local versus global forcing factors responsible for its evolution the pre holocene section of the core represents terrestrial sedimentation in a fluviatile environment contemporaneous of a low sea level and a distal shoreline sediment inputs were terrestrial and resulting from intensive weathering and high erosion rate in the adjacent watershed during the early holocene c 10 020 to 5380 bp the sea invaded this lowland and defined an open marine shallow environment corresponding to a wide gulf which has been disturbed by multiple terrestrial inputs that might have been induced by massive episodes of fluvial discharge the first symptoms of confinement were noticed close to 5400 bp and c 5380 bp a major environmental threshold occurred possibly reflecting the marke

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

40ar 39ar ages and 40ar concentrations of fine grained sediment fractions from north atlantic heinrich layers abstract new k ar ages based on 40 ar 39 ar incremental heating of 40 ar 39 ar based k ar age of 970 4 from orphan knoll in the southern labrador sea within the range found in eastern north atlantic heinrich layers thus the k ar data are robust in their indication of a dominant labrador sea ice rafted source to even the finest sediment fraction in the eastern north atlantic during the massive detrital carbonate bearing heinrich events of the last glacial cycle h1 h2 h4 h5 close correspondence of the radiogenic argon concentration 40 ar from the de carbonated a 40 ar 39 ar based k ar age of 433 5 million years for h11 in v28 82 is within the range of published data from background sediments in the eastern north atlantic and is consistent with published results across this interval in the driezack seamounts in contrast the 40 ar 39 ar based k ar age of h11 in the western atlantic core ew9303 jpc37 is 614 5 million years a brick red sample from approximately the interval of h3 of core ew9303 ggc40 yielded a 40 ar 39 ar based k ar age of 567 1 million years comparable to the published range of 523 543 ma from the 2 16 m fractions from that interval on the dreizack seamounts both jpc37 and ggc40 are located in the path of the north atlantic drift the older ages from western samples of h3 and h11 may result from dilution of a hudson strait source or an elevated age from southeastern laurentide sources

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

upper ocean currents around taiwan abstract current velocity measured by shipboard acoustic doppler current profiler sb adcp during 1991 2000 was used to study the upper ocean the composite and moored currents revealed a branch of the kuroshio that intruded steadily and persistently into the south china sea part of the intruded kuroshio flowed out of the south china sea through the northern luzon strait and re united with the main stream kuroshio the kuroshio had two velocity maximum cores southeast of taiwan but gradually combined into one as the kuroshio flowed north the kuroshio was deflected by the i lan ridge east of taiwan and the zonal running shelf break northeast of taiwan at the shelf break the kuroshio split with one branch intruding onto the shelf west of the luzon strait the kuroshio intruded into the south china sea some water flowed northward into the taiwan strait and re joined the kuroshio currents in the taiwan strait flowed primarily in a northward direction except for the southward current near the coast of mainland china north of the taiwan strait a branch of the northward flow followed the northern coast of taiwan to join the kuroshio the composite current varied consistently from season to season there was generally poor correlation between currents and local winds especially in the deep water regime remote forces were important in the currents around taiwan

benthic foraminiferal δ18o in the ocean s temperature salinity density field constraints on ice age thermohaline circulation benthic 18o data from 95 core sites are used to infer possible temperature salinity t s fields of the atlantic and pacific oceans at the last glacial maximum lgm a constraint of stable density stratification yields logically consistent scenarios for both t and s the solutions are not unique but are useful as a thinking tool using geosecs data we solve for the modem relationship between 18owater w and salinity in the deep sea w smow 1 529 s 53 18 as a starting point we assume that the slope of this equation applies to lgm conditions and predict 18ocalcite c gradients in equilibrium with probable t s fields of lgm deep and bottom waters benthic foraminiferal 18o data from the deep pacific 2 4 km depth and the bottom atlantic 4 km depth are 0 1 0 2 lower than from the deep atlantic 2 4 km depth at the lgm if the modern w s slope applies atlantic deep and bottom waters were more dense than pacific deep waters this assumption would imply bottom waters both fresher s 0 5 and colder t 3 c than overlying deep waters in conflict with other data suggesting ice age deep water much colder than at present it is also possible that the observed c gradients are an artifact of laboratory intercalibration if atlantic deep and bottom water c values were similar to deep pacific values this would be consistent with the hypothesis of a stronger southern ocean versus north atlantic source for deep ocean ventilation at the lgm taking the observed gradients at face value however a solution could be that the lgm w s slope in deep and bottom waters was higher than at present conceivably because of a stronger contribution of salt to the deep ocean via more intense sea ice freezing this would allow pacific deep waters and atlantic bottom waters to have a common source again in the antarctic both would be more dense than atlantic deep waters even though the deep waters were much colder than at present to better constrain these inferences drawn from the spatial distribution of benthic 18o we must reduce scatter in the 18o data with more high quality measurements in high sedimentation rate cores this is especially true at bottom water sites also we must intercalibrate mass spectrometers at different isotope laboratories more accurately to insure our isotope data are compatible

geochemical characteristics of the eolian deposits in the zoige basin and their implications for provenance and weathering intensity abstract eolian deposits in the zoige basin at the northeastern region of the tibetan plateau tp were analyzed for their major trace elements and sm nd isotopic compositions to explore the provenance and weathering intensity the results are compared with the data from the lingtai section lt in the chinese loess plateau clp eolian deposits from different sections in the zoige basin have resembling geochemical compositions reflecting similar provenance their major element compositions are close to those of the ucc and their ucc normalized major trace element abundances and chondrite normalized rare earth element ree abundances are similar to the lt samples however the sio2 al2o3 tio2 zr hf sc co v ni concentrations and sio2 tio2 tio2 al2o3 co th la sc th sc end 0 147sm 144nd ratios of the zoige sections are quite different from those of the lt section which suggests different provenances for the eolian deposits in these two regions the relatively high abundances of sio2 zr hf and low abundances of trace elements indicate that local sediments on the tp are the major contributors to the eolian deposits in the zoige basin eolian deposits from the zoige basin have experienced the early na and ca removal stage and chemical weathering parameters suggest a moderate weathering condition in the source and deposition regions

latitudinal control of astronomical forcing parameters on the high resolution clay mineral distribution in the 45 60 n range in the north atlantic ocean during the past 300 000 years the clay mineralogy of four 5 5 to 13 5 m long cores sampled between 45 and 60 n in the north atlantic ocean has been investigated at high latitudes within a well constrained chronostratigraphic scale cross correlation spectral analyses have been performed on both clay mineral and 18o planktonic records detrital clay minerals display strong signals which are coherent with the 18o record within the three main milankovitch frequency bands eccentricity obliquity and precession the climatic control on clay mineral sedimentation largely depends on the latitudinal location of the sediment cores the 100 000 year signal occurs as a uniformly acting factor whereas the 41 000 year signal dominates clay sedimentation at high latitudes and the 23 000 year signal dominates at midlatitudes we suggest that the latitudinal variations of the orbital forcing on the detrital clay mineral distribution in the north atlantic ocean not only result from climatic control of the intensity of physical and chemical weathering but also from latitudinal control on the detrital clay supply linked to influences of the high latitude wind driven and midlatitude ocean driven transportation processes respectively

the holocene sedimentary regime in the northern mid atlantic ridge region the holocene 10 000 yr b p mid atlantic ridge sedimentary regime between 45 n and 65 n has been investigated by examination of sediments from 70 cores smectite chlorite and quartz 87sr 86sr isotopes and ree have been used as conservative tracers to provide source identification and to calculate accumulation rates the entire holocene sedimentary regime in this part of the atlantic can be attributed to particle fluxes from two sources the icelandic and north american systems two main transport mechanisms are identified 1 particles derived from the icelandic system have been transported southwards as far as 45 n by bottom currents 2 material coming from north america is mainly transported by the aeolian regime at 45 n the windborn accumulation rate is estimated to be 0 5 g cm 2 kyr 1 which is identical to the accumulation rate of bottom advected material from iceland finally a diagnostic model for the north atlantic sedimentary regime is proposed

provinciality of ice rafting in the north atlantic application of 40ar 39ar dating of individual ice rafted hornblende grains the history of the northern hemisphere ice sheets is an important aspect of the paleoclimate system the layered record of ice rafted detritus ird and other climate indicators preserved in deep sea sediment cores provides the potential to unravel the sequences of events surrounding important intervals during the last glacial cycle the work presented here is a first step in the goal to characterize the composition of glacially derived detritus in proximal locations near the laurentide greenland and scandinavian ice sheets the intent of this paper is to highlight the potential for using provenance studies of ird in marine sediments in particular 40 ar 39 ar ages of hornblende grains in this case to trace the history of ice sheets in the past published work on land and at the glacial marine margins has mapped the margins of important ice sheets including the locations where glacial ice extended to the shelf slope break at these shelf slope break locations large glacial marine fans termed trough mouth fans tmf are known to occur in about 25 locations around the north atlantic nordic arctic oceans by characterizing the sediment sources in these tmfs the major ird components for deposition in deep sea sediment cores are documented although there is substantial overlapin the geological histories of the continental sources around the north atlantic there are also some systematic variations that will allow distinction of different sources realization of the full potential awaits characterizing the sources with multiple tracers as well as sedimentological studies and documenting the geographic pattern of dispersal in marine sediments within small time windows r 2002 published by elsevier science ltd

100 000 years of african monsoon variability recorded in sediments of the nile margin abstract multiproxy analyses were performed on core ms27pt recovered in hemipelagic sediments deposited on the nile margin in order to reconstruct nile river palaeohydrological fluctuations during the last 100 000 years the strontium and neodymium isotope composition of the terrigenous fraction and the major element distribution reveal large and abrupt changes in source oscillating between a dominant aeolian saharan contribution during arid periods and a dominant nile river contribution during pluvial periods iron content shows a strong correlation with strontium and neodymium isotopes this allows the use of a high resolution continuous fe record as a proxy of blue nile sediment input over the last 100 000 years the detailed fe record with approximately 10 years resolution during pluvial periods is consistent with subtropical african records of well dated lake level fluctuations and thus constitutes a first continuous high resolution record of the east african monsoon regime intensity over ethiopia the detailed fe record shows the two main known pluvial periods attributed to strengthening of the african monsoon over ethiopia the nabtian period from 14 to 8 ka cal bp and the saharan period from 98 to 72 ka bp for the first time the last glacial period marine isotope stage mis 2 3 and 4 is documented with a continuous record showing large oscillations between high and low east african palaeo monsoon regimes the end of the nabtian period occurred at 8 ka in core ms27pt i e much earlier than on the east equatorial african region where it ended around 5 5 ka we interpret this as evidence that the southward shift of the rain belt occurred 3000 years earlier over the eastern ethiopian highland and propose that the gradual southward migration of the rain belt was associated with highly variable intensity and longer rainy seasons from 8 to 5 ka during the last glacial period two wet periods are present around 60 50 ka bp and 38 30 ka bp these two humid periods are in phase with the rise of atmospheric ch4 concentrations suggesting that wetland tropical african area was one of the sources of the atmospheric ch4 during the mis 3 during the last glacial maximum and mis 4 high saharan aeolian influxes in phase with records of aeolian dust deposited in east antarctica are documented this study highlights the importance of reconstructions of monsoon rainfall fluctuation at high temporal resolution to better understand the link between low and high latitude climate variability at millennial timescales

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

clay minerals and sr nd isotopes of the sediments along the western margin of india and their implication for sediment provenance mineralogy and sr nd isotopic composition of the 2 m fraction of the holocene and late pleistocene sediments from 12 gravity cores collected along the western margin of india were used to delineate the provenance and understand the response of isotopes with respect to the source rock composition holocene sediments show distinct clay mineral associations representing three major sources illite chlorite rich sediments from the indus smectite dominated sediments from the deccan traps and kaolinite and smectite enriched sediments from gneissic rocks the mixing of indus derived sediment with the deccan traps derived sediment or the deccan traps derived sediment with gneissic rock derived sediment occurs in the deeper water cores sr isotopes are very sensitive to weathering and laterization weathering does not influence nd isotopes the 87sr 86sr ratios of the holocene sediments in shallow water cores are higher and fluctuated widely than those in deeper water cores nd correlates well with the clay mineral associations indicating source rock composition or mixing of source sediments kaolinite enriched sediments coupled with high sr ratios and low nd on the sw margin of india suggest intense chemical weathering in the hinterland the influence of the sediment from the ganges brahmaputra transported by the bay of bengal waters during the ne monsoon surface current or sw monsoon underwater current on the composition of the sediments of the sw indian margin is insignificant the late pleistocene sediments reflect a decrease of hydrolytic processes resulting in decrease of smectite and sr isotopic ratio clay minerals and nd values suggest that the provenance and transport pathways of the late pleistocene sediments are the same as those of the holocene for each region

late glacial and holocene palaeocurrents around rockall bank ne atlantic ocean core samples and hydrographic data from 50 to 60 n and 15 to 25 w in the northeast atlantic ocean are used to study changes in current activity from the last glacial to present we establish a new method to distinguish between the effects of changing bottom current speed and varying size input by drawing upon sediment flux data and detailed grain size analysis changes in current speed are recorded by the mean size of the sortable coarse noncarbonate silt component which increases with current vigor by winnowing away of fines our method involves the definition of an ideal sortable silt input function recorded at a site accumulating unmodified pelagic flux only the ideal profile is then compared with records from other sites to determine the history of current speed at a range of water depths the upper surface of southern source water ssw probably shoaled during the glacial as indicated by the covariation of sortable silt records from sites presently covered by ssw and lower north atlantic deep water lnadw the data suggest that production of lnadw was suppressed during the glacial increased following the last glacial maximum and declined at the start of termination 1a a second pulse of production occurred immediately before the younger dryas event intermediate waters were generally faster flowing during the glacial and may have expanded their depth domain such that a single glacial intermediate water mass covered depths from 1100 to more than 2000 m

upper crustal recycling in southern britain evidence from nd and sr isotopes analyses of representative rocks from southern britain are used to examine in detail the evolution of this segment of continental crust the vast majority of late precambrian basement rocks have unradiogenic 87sr 86sr ratios and model tdmnd ages of 1 3 ga although locally the rosslare complex and rushton schists have model tdmnd ages 1 7 ga identifying for the first time an old component in the basement of southern britain following the closure of the iapetus ocean sediments exhibit a progressive increase in model tdmnd ages 1 35 ga in the lower palaeozoic to 1 75 ga in the jurassic this variation demonstrates the southerly transport of detritus tdmnd 2 0 ga from the mixed archaean proterozoic terrains of northern europe and america the granitoids have significantly higher end than those of contemporaneous sediments and thus yield a different nd isotope evolution curve when considered in isolation the majority of rocks analysed have model tdmsr ages in the range 1 2 to 0 46 ga with youngest sediments generally recording the lowest model ages therefore with time the sediments record a striking increase in the ratio of model nd to model sr age the data suggest that the rb sr ratios of the crustal rocks is increased by a factor of approximately 2 every 900 ma implying that on average the british upper crust was reworked by erosion and sedimentation every 600 ma

oceanic evidence for coherent fluctuations in fennoscandian and laurentide ice sheets on millennium timescales proxy temperature records from greenland ice cores1 2 and north atlantic sediment cores3 have provided evidence for a high degree of climate instability during the last glacial period much of this variability seems to be linked with the dynamics of the laurentide ice sheet that covered north america at this time3 which dis charged iceberg flotillas into the north atlantic that are now recorded in sediment cores as heinrich events4 how if at all this variability was manifested on the other side of the atlantic in the nordic seas and the ice sheets of northwest europe and scandinavia has been unclear here we present sediment micro fossil and oxygen isotope data from a sediment core in the norweg ian sea which reveal cooling events and iceberg discharges analogous to heinrich events we show that these climate fluctua tions in the norwegian sea were in phase or were phase locked with air temperatures over greenland suggesting that the rapid changes in heat fluxes in the north atlantic recorded in previous records3 were felt in this high latitude region the iceberg dis charges in our record seem to have come from the fennoscandian ice sheet implying that this and the laurentide ice sheets fluctu ated coherently on timescales shorter than those of milankovitch orbital cycles

neodymium isotopes as tracers in marine sediments and aerosols north atlantic nd and sm concentrations and nd isotopic compositions were measured on the detrital fraction of deep sea surface sediments and on aerosols sampled over the north atlantic and mediterranean sea the data expressed asend 0 and as model ages ranged from 14 5 end 0 4 9 and from 0 01 to 2 21 ga respectively two areas where the sediments contain relatively less radiogenic nd are to the west off north africa and eastward of the canadian shield this distribution is consistent with other tracers in suggesting that a significant fraction of the sediments are derived from aeolian material transported by major wind systems saharan dust transported in the equatorial trade winds belt and north american soil material transported in the latitudes of the westerlies between these aeolian dominated belts along an axis from the azores to gibraltar and the mediterranean lies a zone of more radiogenicend 0 values in sediments and aerosols influenced by the recent volcanism of this region previously reported distributions of nd isotopes in bottom formed iron manganese crusts and coatings are similar to distributions of nd isotope values in detrital sediments and aerosols this suggests that the detrital fraction has undergone partial dissolution and desorption in the water column and or in the pore waters of near surface sediments and that a significant proportion of nd in the authigenic ferromanganese phases is derived from this source and may therefore not represent strictly dissolved seawater nd isotope ratios useful as watermass tracers

simulated planetary wave tide interactions in the atmosphere of mars 1 this study is a first attempt to simulate the nonlinear interactions between planetary waves and tides in the atmosphere of mars and to examine the consequences of the secondary waves that result from these interactions recent analysis of aerobraking densities show clear signatures of secondary waves produced by the modulation of tides by planetary waves the vertically propagating secondary waves serve to modulate longitudinal density structures due to nonmigrating tides at planetary wave periods even in the local absence of planetary waves in this parametric study using a general circulation model of mars we determine the most important waves produced by these interactions and quantify their induced variability at aerobraking altitudes

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

a salt oscillator in the glacial atlantic 1 the concept as shown by the work of dansgaard and his colleagues climate oscillations of one or so millennia duration punctuate much of glacial section of the greenland ice cores these oscillations are characterized by 5 c air temperature changes severalfold dust content changes and 50 ppm co2 changes both the temperature and co2 change are best explained by changes in the mode of operation of the ocean in this paper we provide evidence which suggests that oscillations in surface water conditions of similar duration are present in the record from a deep sea core at 50 n based on this finding we suggest that the greenland climate changes are driven by oscillations in the salinity of the atlantic ocean which modulate the strength of the atlantic s conveyor circulation

biomarker evidence for heinrich events the so called heinrich layers found in north atlantic sediments have been attributed to quasi periodic discharges of armadas of icebergs originating from the laurentide ice sheet using the distribution of biomarkers in a sediment core bofs 5k we have attempted to provide more information about their origin and the effect of the heinrich events on oceanic circulation and the climatic system estimates of sea surface temperature changes via u3k7 measurements show that the surface ocean underwent significant cooling during the events probably as a result of incoming iceberg meltwater the low sea temperatures and the rapid variation in the accumulation of chlorophyll derived pigments suggest that the events provoked a major change in oceanographic conditions which may have affected the thermohaline circulation in the atlantic ocean within the most recent layers we have also found vanadyl alkyl porphyrins and aryl isoprenoid hydrocarbons diagenetic products of photosynthetic pig ments chlorophylls and carotenoids respectively these components are not expected to occur in late quaternary sediments so their presence demonstrates a contribution to the layers of ancient organic rich sedimentary material of continental origin the presence of vanadyl porphyrins and absence of their nickel counterparts and the distributional features of the aryl isoprenoids e g presence of the c40 reduced carotenoid isorenieratane of green sulphur bacterial origin indicate the existence of anoxic conditions in the photic zone of a marine water column in the original depositional setting of the contributed ancient sediment these results suggest that it should be possible using a biomarker correla tion approach to determine the source area of the ancient sediment eroded by the icebergs copyright 1997 elsevier science ltd

patterns of ice rafted detritus in the glacial north atlantic 40 55 n the observation by heinrich 1988 that during the last glacial period much of the input of ice rafted detritus to the north atlantic sediments may have occurred as a succession of catastrophic events rekindled interest on the history of the northern ice sheets over the last glacial period in this paper we present a rapid method to study the distribution of these events both in space and time using whole core low field magnetic susceptibility we report on approximately 20 cores covering the last 150 to 250 kyr well defined patterns of ice rafted detritus appear during periods of large continental ice sheet extent although these are not always associated within their maxima most of the events may be traced across the north atlantic ocean for the six most recent heinrich layers hl two distinct patterns exist hl1 hl2 hl4 hl5 are distributed along the northern boundary of the glacial polar front over most of the north atlantic between 40 and 50 n hl3 is more restricted to the central and eastern part of the northern atlantic the nd sr isotopic composition of the material constituting different heinrich events indicates the different provenance of the two patterns hl3 has a typical scandinavia arctic icelandic young crust signature and the others have a large component of northern quebec and northern west greenland old crust material these isotopic results obtained on core su 9008 from the north american basin are in agreement with the study by jantschik and huon 1992 who used k ar dating of silt and clay size fractions of an eastern basin core me 68 89 these data confirm the large spatial scale of these events and the enormous amount of ice rafted detritus they represent

deep circulation changes in the labrador sea since the last glacial maximum new constraints from sm nd data on sediments sm nd concentrations and nd isotopes were investigated in the fine fraction of two labrador sea cores to reconstruct the deep circulation patterns through changes in sedimentary supply since the last glacial stage three sources are involved the north american shield palaeozoic rocks from northeastern greenland and mid atlantic volcanism the variable input of these sources provides constraints on the relative sedimentary supply in conjunction with inception of deep currents during the last glacial stage a persistent but sluggish current occurred inside the labrador basin an increasing discharge of volcanic material driven by the north east atlantic deep water is documented since 14 3 kyr signaling the setup of a modern like deep circulation pattern throughout the labrador irminger and iceland basins during the last deglacial stage the isotopic record was punctually influenced by erosion processes related mainly to ice sheet instabilities especially 11 4 10 2 and 9 2 kyr ago

sr nd isotopic evidence of terrigenous flux variations in the bay of bengal implications of monsoons during the last 34 000 years 1 sr and nd isotopic compositions of a sediment core from the bay of bengal are used to constrain the provenance and transport pathways of their terrigenous component during the 3 to 34 14c kyr bp the results clearly demonstrate a distinctly different source for detrital fluxes on the ninetyeast ridge from that of distal and western fan sediments there is a systematic pattern of climate related variability in 87sr 86sr and nd o values at the studied location pulses of low 87sr 86sr higher radiogenic nd and high silt content occurring at 5 7 kyr intervals suggest significant changes in the detrital source increased supply of irrawaddy derived sediments appears to be the dominant source for these pulses our results support the hypothesis that rapid cold events of north atlantic heinrich events are characterized by the intensified northeast monsoon

sources of labrador sea sediments since the last glacial maximum inferred from nd pb isotopes pb isotopes have been measured in the clay size fraction of late glacial and holocene deep sea sediments recovered from two labrador sea piston cores that have been previously analyzed for nd isotopes the newly acquired pb isotopic data allow us to better constrain the different source areas that supplied clay size material during the last deglaciation until 8 6 kyr calendar ages nd pb data can be modeled mainly as a mixture between a precambrian crust and lower paleozoic material originating from the denudation of the pan african orogen the old material originates mainly from the archean lower proterozoic or both terranes of greenland and also probably corresponding terranes of labrador although minor input of other precambrian material is recorded in some detrital carbonate rich deglacial samples from orphan knoll the phanerozoic crustal end member consists of sediment material mainly originating from northwestern europe this source area is found to be the only significant source of young crustal material in early holocene sediments from the greenland rise no significant input from the mid atlantic volcanism is apparent this study puts further constraints on the deep circulation pattern during the last deglaciation it is concluded that at that time european phanerozoic material was carried from the norwegian sea through the wyville thompson ridge into the iceland basin by the north east atlantic deep water no evidence for an overflow is found either south of the iceland iceland scotland ridge or through the denmark strait

crustal residence ages of clastic sediments orogeny and continental evolution abstract the relationships between additions to the continental crust and periods of orogenesis have been investigated by means of sm 1bnd isotopic analyses of fine grained clastic sediments from the western canadian and baltic shields the crustal residence ages of these sediments indicate that proterozoic crustal additions occurred in both regions but in canada preceded the main magmatic stage of the wopmay orogeny demonstrating that proterozoic orogenic events are not always accompanied by identifiable crustal addition a review of sm 1bnd data for clastic sediments world wide suggests that the major sediment sources have undergone broadly similar evolutionary histories in quite separate continental areas and together yield a mean age estimate for the entire sedimentary mass of 2 0 0 2 ga a minimum crustal growth curve can be derived from these data which requires that 90 or more of the continental crust existed at the end of the proterozoic

thermohaline instability in the north atlantic during meltwater events stable isotope and ice rafted detritus records from core so75 26kl portuguese margin a benthic isotope record has been measured for core so75 26kl from the upper portuguese margin 1099 m water depth to monitor the response of thermohaline overturn in the north atlantic during heinrich events evaluating benthic 18o in ts diagrams in conjunction with equilibrium c fractionation implies that advection of mediterranean outflow water mow to the upper portuguese margin was significantly reduced during the last glacial 15 compared to 30 today the benthic isotope record along core so75 26kl therefore primarily monitors variability of glacial north atlantic conveyor circulation the 14c accelerator mass spectrometry ages of 13 54 07 and 20 46 12 ka for two ice rafted detritus ird layers in the upper core section and an interpolated age of 36 1 ka for a third ird layer deeper in the core are in the range of published 14c ages for heinrich events h1 h2 and h4 marked depletion of benthic 13c by 0 7 1 1 during the heinrich events suggests reduced thermohaline overturn in the north atlantic during these events close similarity between meltwater patterns inferred from planktonic 18o at site 609 and ventilation patterns inferred from benthic 13c in core so75 26kl implies coupling between thermohaline overturn and surface forcing as is also suggested by ocean circulation models benthic 13c starts to decrease 1 5 2 5 kyr before heinrich events hl and h4 fully increased values are reached 1 5 3 kyr after the events indicating a successive slowdown of thermohaline circulation well before the events and resumption of the conveyor s full strength well after the events benthic 13c changes in the course of the heinrich events show subtle maxima and minima suggesting oscillatory behavior of thermohaline circulation a distinct feature of thermohaline instability in numerical models inferrred gradual spin up of thermohaline circulation after hl and h4 is in contrast to abrupt wanning in the north atlantic region that is indicated by sudden increases in greenland ice core 18o and in marine faunal records from the northern north atlantic from this we infer that thermohaline circulation can explain only in part the rapid climatic oscillations seen in glacial sections of the greenland ice core record

organo and lithofacies of glacial interglacial deposits in the norwegian greenland sea responses to paleoceanographic and paleoclimatic changes abstract based on a multiparameter approach a combined litho and organofacies concept was developed for glacial and interglacial sediment sections along an e w transect through the central part of the norwegian greenland sea ngs modern and past surface water regimes are clearly displayed by specific litho and organofacies patterns interglacial conditions reveal specific atlantic water associated lithofacies a and b3 in the eastern and central sector of the norwegian greenland sea ngs corresponding interglacial organofacies in general are not well correlated to lithofacies due to strong diagenetic degradation of labile e g autochthonous organic matter om while in near surface sediments a marine dominated organofacies i 1 is preserved under atlantic water masses this correlation is not evident for lower holocene and isotope stage 5 deposits however during isotopic event 5 5 1 increased proportions of marine om are recorded in a high accumulating core on the voring plateau glaciomarine background lithofacies b and c indicate minor input of ice rafted debris ird and seasonal variable sea ice cover corresponding organofacies ii 1 non oxidized and ii 2 oxidized are dominated by allochthonous om most spectacular are glacial diamictons lithofacies e and f evidencing short term sediment pulses due to a sudden disintegration of far advanced tide water ice margins on the outer shelves these diamictons bear specific organofacies iii 1 and iii 2 with a clear predominance of terrigenous and reworked om some of the diamictons seem to occur contemporaneous with the so called heinrich layers h1 and h2 suggesting a common trigger mechanism for the almost simultaneous disintegration of huge continental ice masses along the shelves of north america and the eastern margin of the ngs application of a combined organo and lithofacies concept provides essential information on spatial and temporal variations of water mass characteristics the oceanic effects of ice sheet dynamics and circulation models

grain size separation and sediment mixing in arctic ocean sediments evidence from the strontium isotope systematic the 87 rb 86 sr and 87 sr 86 sr ratios of laptev sea sediments of arctic ocean sediments and of suspended particulate matter spm from siberian rivers lena and khatanga form pseudo isochrons due to grain size separation processes which are referred to as lena mixing envelope lme and as flood basalt envelope fbe at the land ocean transition the reduction of the particle velocity causes a deposition of coarser grained material and the contact with saline water enhances a precipitation of finer grained material the coarse grained material is enriched in sr showing less radiogenic 87 sr 86 sr ratios whereas fine grained material is depleted in sr relative to rb showing more radiogenic 87 sr 86 sr ratios the experimentally determined spread of the 87 rb 86 sr and 87 sr 86 sr ratios as a function of grain size in one sediment sample is on the same order as the natural spread of the 87 sr 86 sr ratios observed in all samples from the arctic ocean chemical index of alteration cia for the lena river spm tend to confirm previous observations that chemical alteration is negligible in the arctic environment thus these pseudo isochrons reflect an average age and the average isotope composition in the river drainage area calculated apparent ages from the fbe reflect the age of the siberian flood basalt of about 220 ma and the initial ratio of 0 707 1 reflects their mantle origin the age calculated from the lme of about 125 ma reflects accidentally the jurassic and cretaceous age of the sediments drained by the lena river and the initial ratio of 0 714 1 reflects the crustal origin of their source rocks comparison of geographical locations reveals that all samples from the eastern laptev sea east of 120 degrees e fall along the lme whereas all samples from the western laptev sea west of 120 degrees e fall between lme and fbe mixing calculations based on 143 nd 144 nd measurements not influenced by grain size show that about 75 of the western laptev sea sediments originate from the lena drainage area whereas about 25 of the sediments are delivered from the siberian flood basalt province sediments from the central arctic ocean are isotopically related to the lena drainage area and the siberian flood basalt province however sediments from the arctic ocean margins close to novaya semlya greenland the fram strait and svalbard originate from sources not yet identified c 1999 elsevier science b v all rights reserved

a high resolution study of ne atlantic sediments at station bengal geochemistry and early diagenesis of heinrich layers abstract high resolution geochemical analysis of a piston core from the deep ne atlantic revealed large differences in the major and trace element signature within the sedimentary record at station bengal 48 58 n 16 28 w water depth 4804 m a prominent heinrich layer h4 containing large amounts of ice rafted detritus ird and two less pronounced layers h1 and h2 were identified from mg al si al zr al and porosity profiles h3 and h5 were much less developed therefore not all identification criteria are applicable elevated si al and zr al ratios were probably caused by enhanced eolian loess input element al ratios of other elements cr rb fe v and zn not shown point to a change in the provenance of the terrigenous material of upper continental crust material delivered during the most intense heinrich event h4 the use of ba al toc al and carbonate content as paleoproductivity tracers revealed enhanced carbon input to the seafloor before and during he as well as for the period between h2 and h4 this results in redox boundary compressions in the sediments which has likely resulted in fe cycling at the sediment seawater interface as revealed by fe al and p al ratios a loss of mn by diffusion out of the sediments is probably also caused by this migration of the redox boundary to the sediment seawater interface a combination of low detrital al ratios in the upper part of h4 and redox enrichments at the base of this hl produced ambiguous signals of the redox metals fe ni and v

orbital forcing of bottom current enhanced sedimentation on feni drift ne atlantic during the mid pleistocene feni ridge is a plastered sediment drift deposited along the northwestern flank of rockall trough ne atlantic under the influence of deep geostrophic currents formed by intermittent overflows of arctic intermediate water from the norwegian sea across the iceland scotland ridge nsow lower deep water ldw a derivative of antarctic bottom water from the south atlantic mixed with old north atlantic deep water nadw also bathes the lower flanks of the drift below 2500 m deep sea drilling project site 610 was drilled in a sediment wave field on the surface of feni drift 2417 m though the sediments recovered proved to be typically pelagic preserving a high resolution 5 cm kyr 1 quaternary record of orbitally modulated ice rafting and biogenic productivity cycles but showing little evidence of current affected deposition from particle size and compositional analyses of the biogenic and lithogenic 10 m silt which we then compared with records of the percentage and flux of ice rafted detrital ird sand foraminifera and coccoliths for the same interval cross spectral comparisons were then made between these records and variations in a model of northern hemisphere ice volume ice sheet growth and decay in response to orbitally forced insolation changes at 65 n variations in the relative proportions and fluxes of ird sand foraminifera and coccoliths all covary closely with orbitally forced ice volume fluctuations but with differing amplitude coherency and phase relationships at each milankovitch frequency however there is a significant component of variance in pelagic and ice rafted sedimentation which is controlled by bottom currents and this shows excellent phase and coherency agreement with the ice volume model at all orbital frequencies the relative enrichment coarseness and flux of the contourite silt fraction of feni drift sediments all increase during glacial or cold stages of the mid pleistocene relative to warm stages suggesting that currents were stronger during these periods possible explanations for such changes in current activity include 1 an increased flux of nsow via the wyville thompson ridge into the rockall trough during glacials but not due to increased production of nsow 2 ldw presently lying below 2500 m rises during glacials by at least 50 60 m thereby flooding over the surface of feni ridge at site 610 3 the path of a major recirculation gyre in the lower nadw ldw system presently situated marginally south of site 610 encroaches upon the southern tip of feni ridge during glacials and 4 the rockall trough itself is a site of deep water formation during glacials analogous to labrador sea deep water formation today

sources of fine sized organic matter in north atlantic heinrich layers δ13c and δ15n tracers organic carbon oc and total nitrogen tn concentrations and stable isotope ratios d13c d15n of fine 50 m size fractions of deep sea sediments from the central north atlantic were employed to identify changes in sources of organic matter over the past 50 ka bp ambient glacial sediments are characterised by values that reflect mixtures of marine and terrestrial inputs averages 1s oc tn 7 6 0 8 d13c 22 8 1 0 d15n 5 5 0 6 d13c oc and tn concentrations shift to higher values during the holocene indicating a gradual decrease of fine terrigenous supply to the north atlantic the unchanged d15n record between last glacial and holocene stages indicates that the central north atlantic region remained oligotrophic at least during the past 50 ka bp but additional studies are required to support this result in terms of nitrogen oceanic budget during the phases of enhanced ice rafted detrital supply corresponding to prominent heinrich events hl1 hl2 hl4 and hl5 fine sized sedimentary organic matter has lower oc and tn concentrations contrasting sharply with those of ambient glacial sediments lower d13c down to 28 and d15n down to 1 6 values and high oc tn ratios up to 14 7 1 1 are found for hl1 hl2 and with lesser extent for hl4 these values reflect enhanced detrital supply originating from poorly differentiated soil horizons that characterise periglacial climate conditions and from organic matter bearing rock sources of the underlying geological basement during hl5 only the d13c offset records the input of fine size ice rafted organic matter gradually changing soil development conditions during the time interval covering hl5 to hl1 marine isotope stages 5 to 2 as well as varying erosion levels have been hypothesized on the basis of constant d13c increasing oc tn and decreasing d15n values

antarctic dome c ice core dust at 18 k y b p isotopic constraints on origins we have determined the source area from which dusts from the last glacial maximum lgm section of the dome c ice core were derived by comparing their strontium and neodymium isotopic ratios with those of samples from potential source areas the87sr 86sr and143nd 144nd isotope ratios of the dusts deposited 18 k y b p at the east antarctic dome c site were compared with potential antarctic australian southern african and south american sources the isotope ratios clearly define the patagonian provenance of the dust with the other potential source areas being at most minor contributors contributions by volcanic ash and tephra to the dust sample were also determined to be minimal based on the patterns of rare earth elements knowing the source of the dusts places constraints on the aeolian trajectory by which it was transported to antarctica and this serves as a test of the simulation of southern hemispheric circulation by atmospheric global circulation models during the lgm

plate tectonics radiogenic isotopic tracers and paleoceanography the case of the manganese crusts in the pacific abstract hydrogenous ferromanganese crust deposits on seafloor and volcanic seamounts are archives of past isotopic compositions of the ocean isotopic compositions of long life radiogenic isotopes that are dissolved in the ocean such as nd and pb are mixtures of different erosion products continents volcanics arcs ridges etc transported by oceanic currents or winds isotopic studies on mn crusts are thus potential paleogeographic and paleoceanographic tracers however global paleogeography can drastically evolve over the period of growth of crust as well as the latitude longitude and water depth of the mn crust thus each crust sampled a succession of geographic sites related to its spatial evolution through time for this reason valid information about the past ocean isotopic composition can only be extracted from mn crust under the condition that the successive paleogeographic and paleodepth positions can be reconstructed for each mn crust we followed this approach for six hydrogenous mn crusts from the pacific ocean that have recorded pb and nd isotopic signals for the past 80 myr the evolution of the isotopic data was considered within a proper geodynamical framework that takes into account the paleopositions of the pacific plate and surrounding continents of the hot spots and ridges as well as the paths of the six crusts the differences and similarities between the pb and nd revealed by our analysis emphasize their complementarity as paleoceanographic tracers the nd isotopes are strongly influenced by the exchange between indian and pacific waters specifically by the progressive closure of the indonesian gateway the closed central pacific characteristics are defined from the extrapolation of the isotopic trend this highlights the important role played by erosion of volcanic arcs in the nd isotopic value of seawater our approach also stresses the influence of local volcanic activity ridges or active hot spot for lead isotopes

magnetic susceptibility variations in upper pleistocene deep sea sediments of the ne atlantic implications for ice rafting and paleocirculation at the last glacial maximum magnetic susceptibility ms variations are used to intercorrelate 17 upper pleistocene sediment cores taken from the ne atlantic between 40 degrees and 60 degrees n the ms based correlation depends on regionally consistent patterns of variation in the deposition of ice rafted detritus ird in response to pleistocene glaciations and especially to high frequency ice rafting episodes referred to in recent studies as heinrich events the sedimentological and rock magnetic basis for the apparent relationship between the ms signal and ird content of ne atlantic sediments is examined by 1 comparing the ms profiles of selected cores with their records of coarse fraction 150 mu m lithic fragment abundance and neogloboquadrina pachyderma sin percentages and 2 normalizing ms by expressing it both on a carbonate free basis and as a quotient with anhysteretic remanent magnetization a parameter sensitive to magnetic mineral grain size variations these comparisons show that variations in bulk sediment ms are only partly driven by simple carbonate dilution productivity and dissolution effects changes in both the concentration and grain size of magnetic minerals within the lithogenic noncarbonate fraction also impose a significant influence on bulk ms values in particular horizons rich in ird are associated with significant increases in the relative proportion of coarse grained multidomain ferrimagnetic particles in the sediment this is because ice rafting in contrast to most other mechanisms capable of transporting detrital magnetic minerals to pelagic environments has a high potential for delivering large ferrimagnetic grains as components of sand sized polycrystalline lithic fragments this fundamental linkage between the ird content and ms signal of ne atlantic sediments is used to reconstruct the patterns of variation in ird deposition and by inference surface currents of the last glacial maximum lgm similar to 18 19 ka relative to the present day ne atlantic using the time slice mapping approach developed by the climap project group our lgm holocene ms ratio map based on sample pairs from over 80 deep sea cores confirms that there was a weak cyclonic gyre north of the polar front in the lgm north atlantic the gyre comprised a sluggish warm current in the ne atlantic flowing north between latitudes 47 degrees and 62 degrees n partly fed by subtropical waters from south of the polar front and carrying large numbers of icebergs derived from several sources most of which melted between latitudes 45 degrees and 52 degrees n the warm current probably continued its flow into the iceland basin where it fed into a south flowing current which transported melting icebergs from iceland and scandinavia along the western flank of the reykjanes ridge

preboreal onset of cold water coral growth beyond the arctic circle revealed by coupled radiocarbon and u series dating and neodymium isotopes cold water coral mounds of lophelia pertusa are widespread across the scandinavian shelf which was completely ice covered during the last glacial maximum between 22 to 18 ka bp rapid deglacial meltdown of the fennoscandian inland ice and the retreat of its ice streams freed most of the shelf of ice by 15 ka bp however cold water coral growth commenced only after the pleistocene holocene transition at 11 65 ka bp when modern like climatic patterns and oceanographic conditions were established a tight climatic coupling has been constrained with u series ages coupled 14c ages provide local reservoir ages from various gravity cores in a fjord setting in stjernsund at 70 n and on the open shelf in traenadjupet at 66 n reinvestigation of earlier 14c coral chronologies suggests that coral ecosystems widely established themselves across the entire 3000 km long scandinavian shelf prior to 10 ka bp the earliest occurrence of madrepora oculata at 2 4 ka bp suggests a late holocene colonization of the norwegian shelf which is linked to a prominent mound growth hiatus in traenadjupet 64 n mound growth rates near the northern biogeographic boundary of l pertusa with up to 614 cm ka 1 during certain growth periods are much higher than the previously reported fastest rates of 220 cm ka 1 from the irish margin contemporaneous rapid fjordbasin sedimentation is slower with 63 cm ka 1 matrix 14c ages overlap with coral 14c ages from the same horizon this indicates rapid framework construction and efficient trapping of background sediment hiatuses are frequent in on mound sediments and only short periods of coral growth are recorded coupled 14c and end values indicate a persistent holocene inflow of the north atlantic current in stjernsund but also deglacial meltwater mixing during the early holocene prior to 9 5 ka bp reservoir ages are overall close to the surface marine reservoir age but r is highly localized

ocean circulation at the last glacial maximum a combined modeling and magnetic proxy based study 1 formation of north atlantic deep water nadw is an important component of the ocean thermohaline circulation but debate exists over the ocean circulation state during glacial stages some geological and modeling studies suggest decreased nadw and increased formation of southern ocean deep water during the last glacial maximum lgm others indicate similar or higher rates of nadw advection here we test three different potential lgm ocean states by comparing the modeled iceberg trajectories each produces with magnetically mapped patterns and sources of lgm ice rafted debris ird the three lgm states are characterized by vigorous nadw formation deepwater production in the southern ocean and a third intermediate state with southern ocean deepwater formation but also some north atlantic intermediate water formation cluster analysis of sediment magnetic properties was used to characterize north atlantic ird patterns and sources which match most closely iceberg trajectories arising from some combination of the southern sinking and intermediate ocean circulation states the magnetic data indicate two major ird sources fennoscandia and greenland iceland and one minor source the st lawrence region the model and magnetic data suggest that the lgm north atlantic circulation was dominated by a cyclonic central north atlantic gyre separated from the north atlantic current which was displaced south of 42 n

abrupt changes heinrich events in late quaternary north atlantic marine environments a history and review of data and concepts in the last several years evidence has mounted that a series of abrupt changes in sediment delivery and palaeoceanography effected the north atlantic they are recorded in a variety of proxy records but most dramatically in changes of grain size and mineralogy associated with postulated iceberg rafting events specifically heinrich h events this review paper examines the evidence for such evidence prior to the development of the heinrich event concept 1988 1992 and then examines the explosion of data and correlations that stemmed from the acceptance and use of this paradigm specific attention is focused on ideas pertaining to the cause s of glaciological mechanisms sediment delivery and sediment source and major gaps in our understanding of the underlying glaciological glacial geological and glacial marine processes are stressed abrupt changes across boundaries associated with h 2 in the labrador sea are illustrated from core hu87033 009lcf the case is made that correlations between records need to be more rigorous especially within the range of radiocarbon dating but it appears that abrupt changes in the delivery of iceberg rafted debris which characterize these intervals are multisourced it is unclear how global climate can simultaneously influence the abrupt behaviour of ice margins in different parts of the world for marine based margins changes in relative sea level are one possibility a qualitative model is presented for triggering h events which includes global changes in mass balance changes in relative sea level at ice margins due to glacial isostasy and changes in the basal thermal regime of tidewater ice streams 1998 john wiley sons ltd

provenance of icebergs during heinrich event 3 and the contrast to their sources during other heinrich episodes the sources of ice rafted debris ird from heinrich layer 3 h 3 in the north atlantic were studied by means of pb isotopic analyses of single and multiple grain samples of ice rafted feldspars from core v28 82 49 27 n 22 16 w pb ratios of h 3 grains point to multiple continental sources and are similar to the isotopic composition of the background sediment this similarity as well as previous observations about the age and the sr and nd isotopic composition of the fine fraction of h 3 in cores of the same area are all consistent with the hypothesis that in the eastern north atlantic along the latitude band of maximum ird deposition 40 50 n h 3 is a product of foraminifera dissolution and or low productivity in contrast analyses of composite samples of h 1 h 2 h 4 and h 5 plot in 206pb 204pb versus 206pb 204pb coordinates along the churchill province line supporting the premise that the hudson strait was the major pathway of iceberg drainage during these four events since an advance of the laurentide ice sheet during h 3 is demonstrated by increases in detrital carbonate at the level of h 3 in cores from the western north atlantic the results obtained here suggest that if indeed that advance took place the iceberg discharge melted mostly in the western basin

a theory of ice sheet surges a simplified model of a two dimensional ice sheet is described it includes basal ice sliding dependent on the basal water pressure which itself is described by a simple theory of basal drainage we show that this simple but sophisticated model predicts surges of the ice mass in realistic circumstances and we describe these surges by solving the problem numerically we also are able to describe some parts of the surge analytically the numerical solution of the model is a delicate matter and highlights pitfalls to be avoided if more complicated models are to be solved successfully

the sr and nd isotopic variations of the chinese loess plateau during the past 7 ma implications for the east asian winter monsoon and source areas of loess abstract 143 nd 144 nd and 87 sr 86 sr ratios of the acid insoluble residues of the red clay and overlying loess paleosols from the lingtai profile of the loess plateau china were investigated the results show that variations of the 87 sr 86 sr ratios of the lingtai profile can be divided into two stages from 7 ma b p to 2 5 ma b p the acid insoluble residues in the red clay rc formation are characterized by higher 87 sr 86 sr ratios with an average of 0 7230 from 2 5 ma b p to the present the acid insoluble residues in the wuchen loess wl4 ws1 lishi loess l15 s1 malan loess l1 and holocene loess s0 have relatively lower 87 sr 86 sr ratios and display an overall descending trend from 0 7223 at 2 5 ma b p to 0 7182 at the present among three possible interpretations for the variations of 87 sr 86 sr ratios of acid insoluble residues of the loess provenance change chemical weathering change or grain size distribution change only grain size distribution change provides a satisfactory interpretation this implies that the east asian winter monsoon strength was weak and relatively stable from 7 ma b p to 2 5 ma b p but became continuously enhanced from 2 5 ma b p to the present all the red clay and the overlying loess paleosols in the lingtai profile have generally identical e nd 0 implying that the source regions of these eolian deposits of the chinese loess plateau may be relatively stable and has not changed since 7 ma b p

millennial scale iceberg discharges in the irminger basin during the last glacial period relationship with the heinrich events and environmental settings high resolution records of coarse lithic content and oxygen isotope have been obtained in a piston core from the irminger basin the last glacial period is characterized by numerous periods of increased iceberg discharges originating partly from iceland and corresponding to millennial scale instabilities of the coastal ice sheets and ice shelves in the nordic area a comparison with midlatitude sediment cores shows that ice rafted material corresponding to the heinrich events was deposited synchronously from 40 to 60 n there are thus two oscillating systems every 5 10 kyr massive iceberg armadas are released from large continental ice caps whereas more frequent instabilities of the coastal ice sheets in the high latitude regions occur every 1 2 3 8 kyr at the time of the heinrich events the synchroneity of the response from all the northern hemisphere ice sheets attests the existence of strong interactions between the two systems

climatic instability ice sheets and ocean dynamics at high northern latitudes during the last glacial period 58 10 ka bp abstract oxygen isotope magnetic susceptibility and foraminiferal distribution data are presented for a high resolution core enam93 21 located at the northeast faeroe margin this core recorded a rapid succession of faunistic sedimentologic and isotopic variations which paralleled the greenland ice core isotopic records with their typical succession of abrupt temperature rises and gradual coolings the dansgaard oeschger cycles the most notable feature was the contemporaneous changes in surface and bottom water conditions and circulation that appeared tightly coupled with the rapid climate fluctuations warm episodes interstadials were appeared with higher sea surface temperatures and thermohaline convection in the norwegian greenland sea the polar front was located north of the enam93 21 site cold episodes stadials were associated with an increase in the input of melting fennoscandian icebergs low sea surface temperature and salinity and no thermohaline convection in the norwegian greenland sea intermediate waters changed to an estuarine mode at the faeroe margin with a reversed flow pattern through the faeroe shetland channel the polar front was located south of the enam93 21 site

sediment transport time measured with u series isotopes results from odp north atlantic drift site 984 abstract high precision uranium isotope measurements of marine clastic sediments are used to measure the transport and storage time of sediment from source to site of deposition the approach is demonstrated on fine grained late pleistocene deep sea sediments from ocean drilling program site 984a on the bjorn drift in the north atlantic the sediments are siliciclastic with up to 30 carbonate and dated by 18o of benthic foraminifera nd and sr isotopes indicate that provenance has oscillated between a proximal source during the last three interglacial periods volcanic rocks from iceland and a distal continental source during glacial periods an unexpected finding is that the 234u 238u ratios of the silicate portion of the sediment isolated by leaching with hydrochloric acid are significantly less than the secular equilibrium value and show large and systematic variations that are correlated with glacial cycles and sediment provenance the 234u depletions are inferred to be due to recoil loss of 234th and are used to calculate comminution ages of the sediment the time elapsed between the generation of the small 50 m sediment grains in the source areas by comminution of bedrock and the time of deposition on the seafloor transport times the difference between comminution ages and depositional ages vary from less than 10 ky to about 300 to 400 ky for the site 984a sediments long transport times may reflect prior storage in soils on continental shelves or elsewhere on the seafloor transport time may also be a measure of bottom current strength during the most recent interglacial periods the detritus from distal continental sources is diluted with sediment from iceland that is rapidly transported to the site of deposition the comminution age approach could be used to date quaternary non marine sediments soils and atmospheric dust and may be enhanced by concomitant measurement of 226ra 230th 230th 234u and cosmogenic nuclides

the provenance and crustal residence ages of british sediments in relation to palaeogeographic reconstructions 24 smnd isotope analyses of fine grained phanerozoic and modern clastic sediments from britain and quebec are presented in combination with published data they have been used to calculate crustal residence ages tcr and to assess the provenance of the british sedimentary mass sediments now preserved on either side of the suture formed by the closure of the iapetus ocean ca 400 ma ago were derived from isotopically distinct source regions sediments north of the suture are characterised by1 7 tcr 2 8 ga whereas those to the south exhibit a smaller range and an average value of 1 6 ga the northern and southern source regions were most probably laurentia and gondwana respectively it seems likely that a third source perhaps baltica provided the lower palaeozoic southern uplands succession sediments deposited in southern britain after the closure of iapetus were derived mainly from the recycling of older sediments the tectonic rearrangements which occurred during the phanerozoic are not reflected in the smnd isotopic structure of the southern british sedimentary mass suggesting that the caledonian and hercynian orogenies and even the grenville orogeny involved minimal accretion of new mantle derived material into the british and adjacent continental crust smnd analyses of fine grained clastic sediments provide a powerful sedimentological tool for elucidating palaeogeography clastic source areas sediment recycling and maturity and some aspects of sediment transport

rock magnetic detection of distal ice rafted debries clue for the identification of heinrich layers on the portuguese margin abstract high resolution measurements of concentration and grain size dependent magnetic parameters along a sedimentary sequence deposited on the portuguese margin 38 n during the last 120 ka allowed the detection of multiple thin layers slightly enriched by a coarse lithogenic fraction sizes mineralogy shapes and mode of deposition identify the material as ice rafted detritus ird the four most recent events dated by calibrated radiocarbon ages are contemporaneous with heinrich events he1 he4 older events can be identified as he5 he6 or with minor ird that occurred during stage 5 the resolution and sensitivity obtained with rock magnetic methods enable the detection of multiple secondary events showing that iceberg delivery was a frequent phenomenon directly linked to temperature variations over ice caps heinrich events representing the extreme cases

calcareous nannofloral response to termination ii at 45 n 25 w northeast atlantic abstract termination ii glacial to interglacial transition from oxygen isotope stage 6 to stage 5 is considered to be one of the most rapid and abrupt climatic changes during the late quaternary our high resolution geochemical and nannofloral study of the interval from 140 to 100 ka in the northeast atlantic core t90 9p 45 17 5 n 25 41 3 w shows that termination ii 135 125 ka occurred in two steps of drastic changes interrupted by a short period of stability and followed by at least 25 ka of relatively stable interglacial conditions traditionally referred to as the eemian age substage 5 5 a primary productivity proxy based on coccolith accumulation rate number cm 2 ka 1 shows higher values during the eemian than during glacial stage 6 and interglacial substage 5 4 with the maximum values 70 10 9 coccoliths cm 2 ka 1 at 123 122 ka the coccolith assemblage was dominated by two morphotypes of gephyrocapsa alternating in dominance under different climatic conditions gephyrocapsa muellerae was more abundant in colder periods whereas small gephyrocapsa dominated in the eemian emiliania huxleyi syracosphaera pulchra and florisphaera profunda increased in the eemian whereas coccolithus pelagicus and helicosphaera carteri decreased small gephyrocapsa together with emiliania huxleyi are associated with periods of higher primary productivity the pelagic sedimentary record of termination ii in core t90 9p includes a 5 cm thick layer enriched in ice rafted material a heinrich layer in contrast to termination i where such a heinrich layer h1 is associated with the first meltwater pulse of the deglaciation the record of core t90 9p suggests that the heinrich event of termination ii h11 occurred during the second stage of deglaciation 129 4 127 1 ka it is characterised by accumulation of ice rafted debris and low coccolithophore diversity the coincident apparent drop in coccolith accumulation rate could be explained either by changes in primary productivity due to reduction in salinity and light or by dilution by ice rafted material five models are applied for the deposition of the heinrich layer with changing thickness 3 cm and duration 1000 500 and 250 yr these scenarios result in a lowered constant or even slightly increased primary productivity during this event

sediment flux patterns in the northeastern atlantic variability since the last interglacial abstract the distribution of terrigenous and carbonate absolute accumulation rates in the northeastern atlantic during the last climatic cycle shows that climate and sediment accumulation are closely coupled either directly or through oceanic circulation and eustatic variation the strong contrast between the glacial and holocene flux distribution is related to oceanic circulation changes either surface circulation which governs both the ice rafting supply and the planktonic biogenic production or more particularly deep circulations via the reinitiation of the iceland scotland overflow glacial erosion and the low sea level stand enhance the terrigenous supply but the holocene deep circulation reinforcement leads to important material reworking as a consequence an almost constant average sediment flux is obtained 4g 2 ky 1 during the holocene compared to 4 7 g cm 2 ky 1 during the glacial period during the holocene period the notable increase in mean carbonate flux from 1 5 to 3 g cm 2 ky 1 is associated with carbonate biogenic production but the carbonate flux distribution shows the influence of redistributive agents on margins fluxes do not simply decrease from continental sources to the oceanic basin eustatic drops leads to a shift in the areas of preferential accumulation from the upper to the lower slope during the deglacial warming period the fluxes are respectively an average of two and three times higher than during the holocene and the glacial periods their importance highlights the major impact of rapid climatic changes finally local conditions the location of terrigenous sources and the presence of contour currents are among the many factors which will modify the trends observed on a global scale

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

late quaternary high resolution biomarker and other sedimentary climate proxies in a northeast atlantic core we studied variations in terrigenous input and sea surface temperature over the last 208 ka using a multiproxy approach involving direct comparison of terrigenous and marine molecular biomarker foraminiferal abundance and other sedimentological data for the same horizons in a single northeast atlantic core core t88 9p 48 23 n 25 05 w 3193 m water depth 790 cm core length with a well resolved 18o stratigraphy the abundances of three land derived long chain compound classes the n alkanes c27 c29 and c31 the n alkanoic acids c24 c26 and c28 and the n alkanols c24 c26 and c28 show glacial interglacial related changes in the past 208 ka which generally parallel the weight percent noncarbonate the abundances of these three compound classes are higher in glacial than in interglacial sediments such changes are consistent with the expected higher dust inputs during glaciations as well as enhanced advection of particulate matter in current systems ice rafted debris heinrich events may also contribute to the terrigenous biomarker record the sea surface temperature sst signals derived from the alkenone unsaturation index uk 37 give an average sst during interglacial periods of 13 c which is about 3 4 c higher than the average glacial sst estimate the uk 37 derived sst values dropped markedly in some heinrich layers while sometimes leading the onset of the layer the percent neogloboquadrina pachyderma s which is another frequently used qualitative temperature proxy generally shows maxima coinciding with the layers our results show that most heinrich layers were produced during times of intensely cold waters in the eastern north atlantic they demonstrate that sufficient alkenones are present in the sediments for alkenone stratigraphy to be used as a tool for the assessment of short term variations in sea surface temperatures even in these oligotrophic north atlantic waters

sedimentary facies of glacial interglacial cycles in the norwegian sea during the last 350 ka sediment fluxes were highest in the norwegian sea during late glacial early deglacial periods i e at oxygen isotope transition 43 below transition 65 at various levels within stage 6 and below stage 9 dark diamictons deposited at these times reflect intense iceberg rafting in surface waters fed by surges along the front of the marine based parts of the continental ice sheets in the southeastern sector of the norwegian sea the high organic carbon content 0 5 1 3 in these layers reflects input from erosion of terrigenious matter rich sediments outcropping on the shelves partial oxidation of organic matter and decreased deep water renewal may explain the strong carbonate dissolution observed during these periods interglacial environments were strongly variable throughout the last 350 ka circulation patterns of stage 5e best resemble modern conditions while stage 7 and 9 sediments record a much weaker norwegian current

the importance of the terrigenous fraction within a cold water coral mound a case study in the nineties cold water coral mounds were discovered in the porcupine seabight ne atlantic west of ireland a decade later this discovery led to the drilling of the entire challenger cold water coral mound eastern slope porcupine seabight during iodp expedition 307 as more than 50 of the sediment within challenger mound consists of terrigenous material the terrigenous component is equally important for the build up of the mound as the framework building corals moreover the terrigenous fraction contains important information on the dynamics and the conditions of the depositional environment during mound development in this study the first in depth investigation of the terrigenous sediment fraction of a cold water coral mound is performed combining clay mineralogy sedimentology petrography and sr nd isotopic analysis on a gravity core md01 2451g collected at the top of challenger mound sr and nd isotopic fingerprinting identifies ireland as the main contributor of terrigenous material in challenger mound besides this a variable input of volcanic material from the northern volcanic provinces iceland and or the nw british isles is recognized in most of the samples this volcanic material was most likely transported to challenger mound during cold climatic stages in three samples the isotopic ratios indicate a minor contribution of sediment deriving from the old cratons on greenland scandinavia or canada the grain size distributions of glacial sediments demonstrate that ice rafted debris was deposited with little or no sorting indicating a slow bottom current regime in contrast interglacial intervals contain strongly current sorted sediments including reworked glacio marine grains the micro textures of the quartz sand grains confirm the presence of grains transported by icebergs in interglacial intervals these observations highlight the role of ice rafting as an important transport mechanism of terrigenous material towards the mound during the late quaternary furthermore elevated smectite content in the siliciclastic glaciomarine sediment intervals is linked to the deglaciation history of the british irish ice sheet biis the increase of smectite is attributed to the initial stage of chemical weathering processes which became activated following glacial retreat and the onset of warmer climatic conditions during these deglaciations a significant change in the signature of the detrital fraction and a lack of coral growth is observed therefore we postulate that the deglaciation of the biis has an important effect on mound growth it can seriously alter the hydrography nutrient supply and sedimentation processes thereby affecting both sediment input and coral growth and hence coral mound development

the origin of heinrich layers evidence from h2 for european precursor events recent well dated isotopic sr nd fingerprinting of heinrich layer ice rafted detritus ird on the european margin indicates supply from european ice sheets as precursors to laurentide ice sheet lis supply f e grousset et al geology 28 2000 123 126 h snoeckx et al mar geol 158 1999 197 208 these precursorevents lead lis input by up to 1 5 ka f e grousset et al geology 28 2000 123 126 and have been interpreted to indicate lis collapse during heinrichevents stimulated by events originating on the european side of the atlantic f e grousset et al geology 28 2000 123 126 such phasing of ird supply from different sources within heinrich layers therefore has implications for the origin and mechanics of heinrichevents we present evidence here that the ird comprising heinrich layer 2 h2 20 21 14c ka bp on the european continental margin contains detrital campanian upper chalk deriving from bedrock sources eroded on the celtic shelf by the british ice sheet bis in addition to lithic material sourced from the lis high resolution radiocarbon chronology indicates chalk grain deposition as discrete pulses both before and coincident with supply of lis sourced detritus the specificity of the chalk fingerprint to the bis enables a 700 1000 yr lag between the bis and lis events to be identified this phasing indicates a more rapid response of the outlet lobes draining the smaller bis than those draining the lis and implicates external climatic forcing of heinrichevents it is unlikely that this precursorevent represents ird event 18 the recently identified 1 2 ka ird cycle event which immediately precedes h2 because the lag between precursor and main event is here less than 1 5 ka and because such pervasive periodicity is not apparent in european continental margin ird records the later synchroneity between the bis and lis input in h2 identifies glacio eustatic sea level rise associated with lis discharges as a possible feedback mechanism causing destabilisation of ice streams elsewhere during heinrichevents

european climatic response to millennial scale changes in the atmosphere ocean system during the last glacial period abstract pollen foraminifer dinocyst and coarse lithic high resolution analyses and 18 o measurements have been carried out for the last glacial section of marine core md95 2042 located near the southwestern margin of the iberian peninsula the pollen data indicate a high frequency of vegetational changes on the adjacent continent during this period suggesting a climatic variability very similar to that of the dansgaard oeschger cycles recorded by the greenland ice cores the detailed direct correlation of the terrestrial and marine proxy data from core md95 2042 indicates a three phase pattern of heinrich events in land and ocean environments the first and last phases of the h5 and h4 events are characterized by a mild and humid climate in southwestern europe probably associated with the european origin of the ice rafted detritus the middle phase exhibits a cold and dry climate in iberia linked with the maximum input of ice rafted detritus this phase seems to correspond with the laurentide ice sheet surges between the heinrich events several cold and dry periods on land are correlated with stades of the dansgaard oeschger cycles the impact of the dansgaard oeschger stades in southwestern europe seems to be preferentially connected to the cold winter air masses reaching this mid latitude region

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

zooming in on heinrich layers theories explaining the origin of the abrupt massive discharges of ice rafted detritus ird into the glacial north atlantic the heinrich layers hls generally point to the laurentide ice sheet as the sole source of these events until it was found that the irds also originated from icelandic and european ice sheets bond and lotti 1995 snoeckx et al 1999 grousset et al 2000 this apparent contradiction must be reconciled as it raises fundamental questions about the mechanism s of hl origin we have analyzed two 12 cm thick hls in an ultrahigh resolution mode 1 2 century intervals in a mid atlantic ridge piston core the 18o record n pachyderma left coiling reveals strong excursions induced by the melting of the icebergs these excursions are associated with a strong decrease in the amount of planktic foraminafersand with a 3 c cooling of the surface waters counts of coarse detrital grains reveal that ird are deposited according to a typical sequence 1 volcanic glass 2 quartz and feldspars 3 detrital carbonate that implies a chronology in the melting of the differentpan atlantic ice sheets sr and nd isotopic composition confirm that in both heinrich layers h1 and h2 precursor ird came from first europe iceland followed then by laurentide derived ird an internal cyclicity can be identified during h1 and h2 about four to six major abrupt discharges occurred roughly on a century timescale the 13c and 15n records reveal that dominant inputs of continent derived organic matter are associated with ird within the hls hiding the plankton productivity signal