absolute calibration of the greenland time scale implications for antarctic time scales and for δ14c abstract we propose a new age scale for the two ice cores grip and gisp2 that were drilled at greenland summit based on accelerator mass spectrometry 14c dating of foraminifera in core md95 2042 paleoceanography 15 2000 565 calibrated by means of recently obtained paired 14c and 230th measurements on pristine corals marine radiocarbon calibration curve spanning 10 500 to 50 000 years bp thousand years before present based on paired 230th 234u 238u and 14c dates on pristine corals geological society of america bulletin 2003 submitted for publication the record of core md95 2042 can be correlated very precisely to the greenland ice cores between 30 and 40 ka bp our scale is 1 4 ka older than the grip ss09sea time scale journal of quaternary science 16 2001 299 at the older end of marine isotope stage 3 we use published 230th dates from speleothems to calibrate the record using this scale we show a 14c record that is broadly consistent with the modelled record earth planet sci lett 200 2002 177 and with the data of hughen et al science 303 2004 202 but not consistent with the high values obtained by beck et al science 292 2001 2453 or by voelker et al radiocarbon 40 1998 517 we show how a set of age scales for the antarctic ice cores can be derived that are both fully consistent with the greenland scale and glaciologically reasonable

dansgaard oeschger and heinrich event imprints in alboran sea paleotemperatures past sea surface temperature sst evolution in the alboran sea western mediterranean during the last 50 000 years has been inferred from the study of c37 alkenones in international marine global change studies md952043 core this record has a time resolution of 200 years allowing the study of millennial scale and even shorter climatic changes the observed sst curve displays characteristic sequences of extremely rapid warming and cooling events along the glacial period comparison of this alboran record with 18o from greenland ice greenland ice sheet project 2 core shows a strong parallelism between these sst oscillations and the dansgaard oeschger events five prominent cooling episodes standing out in the sst profile are accompanied by an anomalous high abundance of neogloboquadrina pachyderma sinistral which is confined to the duration of these cold intervals these features and the isotopic record reflect drastic changes in the surface hydrography of the alboran sea in association with heinrich events hl 5

deglacial warming of the northeastern atlantic ocean correlation with the paleoclimatic evolution of the european continent abstract isotopic micropaleontologic and pollen analyses of deep sea cores from the bay of biscay and the northeastern atlantic ocean show that the deglacial warming of this oceanic area was closely correlated with the paleoclimatic evolution of the adjacent european continent temperatures were at least as warm as those of today in the bay of biscay between 13 300 and 11 000 b p coinciding with the combined bolling allerod warm continental events a major spread of polar water occurred between 11 000 and 10 000 b p during this event which coincides with the younger dryas continental cold event marine temperatures were almost as low as those of the last glacial maximum the final deglacial warming of the norteastern atlatntic ocean occurred during the following 3000 yr

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

a solar irradiance trigger for millennial scale abrupt changes in the southwest monsoon 1 marine sedimentary records of the last glacial from tropical monsoon latitudes indicate climate fluctuations comparable to rapid changes in 18o recorded in greenland synchronizing two high resolution sedimentary records from the oman and pakistan margins we resolve millennial scale reversals in sea surface temperature sst gradient sst across the arabian sea which directly correspond with the majority of dansgaard oeschger d o events for the last 65 kyr the relative amplitude of individual monsoon and d o events appears comparable suggesting coupled and at least hemispheric forcing to explore this quasi cyclic forcing we compare alkenone based geologic data with modern satellite derived sst estimates between sites interstadial conditions fall within the range of monsoons during the holocene but stadial conditions have no analogs following published associations between eurasian winter snow cover ewsc and monsoon rainfall and el nino southern oscillation enso events and anomalous ewsc we find a good correlation between the southern oscillation index soi and arabian sea sst throughout the modern data set an apparent 11 year cyclicity in the soi reveals an association between the monsoon soi and solar output variability the soi primarily tracks solar total irradiance but the soi monsoon linkage becomes nonlinear during excursions of the soi associated with el nino events strong el ninos coincide precisely with minimum solar irradiance during the solar cycle which we attribute to threshold behavior in tropical pacific ssts and associated trade wind strength we propose that both short term interannual decadal and long term centennial millennial changes in solar output are consistent with records of enso variability monsoon intensity and d o event timing

links between salinity variation in the caribbean and north atlantic thermohaline circulation variations in the strength of the north atlantic ocean thermohaline circulation have been linked to rapid climate changes1 during the last glacial cycle through oscillations in north atlantic deep water formation and northward oceanic heat flux2 3 4 the strength of the thermohaline circulation depends on the supply of warm salty water to the north atlantic which after losing heat to the atmosphere produces the dense water masses that sink to great depths and circulate back south2 here we analyse two caribbean sea sediment cores combining mg ca palaeothermometry with measurements of oxygen isotopes in foraminiferal calcite in order to reconstruct tropical atlantic surface salinity5 6 during the last glacial cycle we find that caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2 4 and 6 and lower salinities during the warm stages 3 and 5 covarying with the strength of north atlantic deep water formation7 at the initiation of the bolling allerod warm interval caribbean surface salinity decreased abruptly suggesting that the advection of salty tropical waters into the north atlantic amplified thermohaline circulation and contributed to high latitude warming

surface and deep ocean circulation in the subpolar north atlantic during the mid pleistocene revolution 1 we investigated surface and deep ocean variability in the subpolar north atlantic from 1000 to 500 thousand years ago ka based on two ocean drilling program odp sites feni drift site 980 55 29 n 14 42 w and bjorn drift site 984 61 25 n 24 04 w benthic foraminiferal stable isotope data planktic foraminiferal faunas ice rafted debris data and faunally based sea surface temperature estimates help test the hypothesis that oceanographic changes in the north atlantic region were associated with the onset of the 100 kyr world during the mid pleistocene revolution based on percentage of neogloboquadrina pachyderma s records from both sites surface waters during interglacials and glacials were cooler in the mid pleistocene than during marine isotope stages mis 5 and 6 in particular interglaciations at bjorn drift site 984 were significantly cooler faunal evidence suggests that the interglacial arctic front shifted from a position between the two sites to a position northwest of bjorn drift site 984 after ca 610 ka as during the late pleistocene we find faunal evidence for lagging surface warmth at most of the glacial initiations during the mid pleistocene each initiation is associated with high benthic 13c values that are maintained into the succeeding glaciation which we term lagging nadw production these findings indicate that lagging warmth and lagging nadw production are robust features of the regional climate system that persist in the middle to late pleistocene

correlated millennial scale changes in surface hydrography and terrigenous sediment yield inferred from last glacial marine deposits off northeastern brazil abstract the stable isotope composition of planktonic foraminifera correlates with evidence for pulses of terrigenous sediment in a sediment core from the upper continental slope off northeastern brazil stable oxygen isotope records of the planktonic foraminiferal speciesglobigerinoides sacculiferandglobigerinoides ruber pink reveal sub milankovitch changes in sea surface hydrography during the last 85 000 yr warming of the surface water coincided with terrigenous sedimentation pulses that are inferred from high xrf intensities of ti and fe and which suggest humid conditions in northeast brazil these tropical signals correlate with climatic oscillations recorded in greenland ice cores dansgaard oeschger cycles and in sediment cores from the north atlantic heinrich events trade winds may have caused changes in the north brazil current that altered heat and salt flux into the north atlantic thus affecting the growth and decay of the large glacial ice sheets

high frequency palaeoceanographic changes during the past 140 000 yr recorded by the organic matter in sediments of the iberian margin abstract biogenic records of the marine palaeoproductivity carbonates organic carbon and c 37 alkenones and the molecular stratigraphy of past sea surface temperatures ssts u 37 k were studied at high resolution in two cores of the iberian margin the comparison of these records indicates that the oceanographic conditions switched abruptly during the past 160 kyr between three kinds of regimes a first regime with high 17 22 c sst and low productivity typifies the interglacial periods marine isotopic stages mis 5 and 1 several periods during mis 6 2 and the terminations ii and i are characterised by about 4 5 c colder sst and a higher organic matter accumulation both of which define the second regime this anticorrelation between sst and marine productivity suggests that these variations are related to the intensity of the coastal upwelling by contrast with this upwelling behaviour extremely low biological productivity and very cold sst 6 12 c occurred during short phases of glacial mis 6 4 and 2 and as abrupt events 1 kyr or less during mis 3 the three oceanographic regimes are consistent with micropalaeontological changes in the same cores based on foraminifera and diatoms the general trend of these hydrologic changes follows the long term glacial interglacial cycle but the millennium scale variability is clearly related to heinrich events and dansgaard oeschger cycles strengthening of the upwelling corresponds probably to an intensification of the subtropical atmospheric circulation over the north atlantic which was influenced by the presence of continental ice sheets however extreme glacial conditions due to massive discharges of icebergs interrupted the upwelling interestingly both terminations ii and i coincided with strong but transient intensification of the upwelling

planktic foraminifers and hydrography of the eastern and northern caribbean sea the distribution of living planktic foraminifers and their relation to the hydrography of the caribbean sea was investigated in plankton net tows and surface sediment samples taken along the antilles island arc during april may 1996 the planktic foraminiferal community was strongly influenced by spatial variations in salinity that were largely due to the influx of orinoco river water into the southeastern caribbean sea and inflowing sargasso sea water in the north along the antilles island arc globigerinoides ruber was the dominant species in the surface waters throughout in the southeastern caribbean sea where orinoco river outflow influences the planktic community standing stocks of planktic foraminifers 100 m between 4 and 50 specimens m 3 were medium to low the southeastern faunas between tobago and guadeloupe were characterized by increased proportions of neogloboquadrina dutertrei highest standing stocks of 159 specimens m 3 in the upper 20 m of the water column were recorded in the northeastern caribbean sea and the assemblages were characterized by high proportions of globigerinita glutinata associated with cyclonic eddies in the anegada passage where sargasso sea water flows into the caribbean sea low standing stocks of 18 specimens m 3 indicate oligotrophic conditions together with the oligotrophic surface waters the subtropical underwater enters the caribbean sea through the anegada passage in water depths between 100 and 300 m these waters are characterized by higher concentrations of globorotalia truncatulinoides relative to the adjacent water masses comparison of the living planktic foraminiferal fauna with empty test assemblages from the water column and from surface sediments shows that differences in the faunal composition mostly correspond to the distribution of water masses and to the differential dissolution of species in the vicinity of islands globigerinoides ruber reaches higher relative frequencies than in the open ocean pointing towards a higher tolerance of this species towards neritic conditions than in other species

comparison of alkenone estimates with other paleotemperature proxies 1 to a certain degree all sea surface temperature sst proxies suffer from uncertainty due to signal preservation problems and to perturbations by other environmental variables however a multiproxy reconstruction is justified because most biases should in principle cancel out as they are specific to the biological groups and or to the analyzed chemical species such a multiproxy strategy has proven crucial for calibrating these proxies and is also useful in assessing downcore profiles until now there have been only a dozen deep sea cores where it is possible to compare directly alkenone based ssts with other paleotemperature records from this still limited data set the broad picture is of general agreement for the amplitude of changes at low and middle latitudes the few observed discrepancies suggest that alkenone based temperatures are more comparable to those based on mg ca ratios than those obtained through statistical analysis of the foraminiferal distribution more systematic differences are noted at higher latitudes where alkenones indicate warmer temperatures during the glacial period than transfer functions based on foraminifera or diatoms several reasons have been invoked to resolve the mismatch but more ground truthing work is needed before deciding which temperature changes are the most accurate

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

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

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

brief interstadial events in the santa barbara basin ne pacific during the past 60 kyr the instability of the northern hemisphere glacial climate over the past 100 kyr has been revealed by at least 20 brief warm interstadial episodes called dansgaard oeschger events recorded in greenland ice cores1 3 and in north atlantic sedimentary records4 5 a few of these events have been recognized elsewhere6 8 here we describe a record of ocean oxygenation and circulation from the santa barbara basin in the northeast pacific ocean which correlates well with the greenland ice core records we see 19 of the 20 dansgaard oeschger events in the form of laminated sediments deposited under anoxic conditions and we can correlate at least 16 of these with the 17 ice core interstadials of the past 60 kyr thus these short term events were not restricted to the north atlantic region the events had substantial ecological and oceanographic effects in the santa barbara basin including changes in benthic faunal populations and in the age and composition of bottom waters similar ventilation changes have been seen in the gulf of california9 10 suggesting that these changes may have been widespread and synchronous along the northeast pacific margin these results suggest sensitivity of broad areas of the ocean atmosphere cryosphere system to short term climate change

ecological thresholds and patterns of millennial scale climate variability the response of vegetation in greece during the last glacial period the regional expression of millennial scale climate variability during the last glacial is examined with particular reference to the vegetation response in greece inspection of three pollen records from contrasting bioclimatic areas suggests that differences in the magnitude of cold events as recognized in the north atlantic and western mediterranean are expressed in terms of tree population changes only in areas with a range of favorable habitats by contrast records from sites where populations approach their tolerance threshold do not appear to resolve differences in the amplitude of the climate oscillations understanding the importance of local factors in modulating the biological response to climate change is critical when attempting to establish the spatial pattern of millennial variability

synchroneity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the mediterranean region land sea climatic proxies have been obtained from the last glacial section of images core md95 2043 western mediterranean sea vegetation and alkenone derived sst curves indicate rapid 150 years and synchronous terrestrial and marine climatic changes paralleling the dansgaard oeschger d o climatic variability over greenland this frequency of climate change can be related to shifts between the two modes of operation of the north atlantic oscillation nao transfer functions applied to the pollen data indicate that there was an amplification of the climatic signal during heinrich events hes in comparison with other d o stadials the development and persistence of both scandinavian and atlantic mobile polar highs over southwestern europe may explain the extreme cooling 10 c and dryness 400 mm during heinrich events 5 and 4 in the mediterranean region comparison of the results of core md95 2043 with similar climatic data from images core md95 2042 located off portugal indicates that thermal and precipitation gradients occurred between the mediterranean and the atlantic sides of iberia within hes hes 4 and 5 are associated with more humid conditions in the atlantic by 200 mm than in the mediterranean site as is the case at the present time this comparison also illustrates the different behaviour of these areas during the d o stadials in contrast with the mediterranean site the atlantic site shows similar precipitation and temperature drops for all the d o stadials including those related to the hes here we propose the operation of different mobile polar highs mph as the driving mechanism for this difference in behaviour between the atlantic and mediterranean sides of iberia hes are related to a stronger influence of the scandinavian mph forcing a severe aridification and cooling of the full iberian peninsula the atlantic mph may have been dominant during the other stadials which would preferentially affect southwestern iberia

mechanisms and variations of the paleoproductivity off northern chile 24 s 33 s during the last 40 000 years 1 a multiparameter investigation including organic carbon carbonate opal and planktic foraminifera was carried out on five sediment cores from the coastal upwelling area between 24 s and 33 s along the peru chile current to reconstruct the history of the paleoproductivity and its driving mechanisms during the last 40 000 years inferred from our data we conclude that the antarctic circumpolar current as the main nutrient source in this region mainly drives the productivity by its latitudinal shifts associated with climate change simplified its northerly position during the last glacial led to enhanced productivities and its southerly position during the holocene caused lower productivities at 33 s the paleoproductivity was additionally affected by the southern westerlies and records highest levels during the last glacial maximum lgm north of 33 s several factors e g position and strength of the south pacific anticyclone wind stress continental runoff and el nino southern oscillation events supplementary influenced upwelling and paleoproductivity where maximum values occurred prior to the lgm and during the deglaciation

pleistocene climatic history reflected in planktonic foraminifera from odp site 1073 leg 174a new jersey margin nw atlantic ocean abstract abundance records of planktonic foraminifera 150 m from the upper 520 m of odp site 1073 hole 1073a leg 174a 639 m water depth have been integrated with specmap derived isotope stratigraphy percentage of calcium carbonate and coarse sediment fraction data in order to investigate the pleistocene climatic history of the new jersey margin six planktonic taxonomic groups dominate the foraminiferal assemblage at site 1073 neogloboquadrina pachyderma d mean 33 8 turborotalita quinqueloba 18 5 n pachyderma s 18 4 globigerina bulloides group 11 4 globorotalia inflata group 9 4 and globigerinita glutinata 4 1 based on the distributions of these six foraminiferal groups the pleistocene section can be divided into three paleoclimatic intervals interval i intermediate corresponds to the quaternary sediments from sequence boundary pp1 to the seafloor 79 5 0 mbsf emiliania huxleyi acme 85 ka at 72 mbsf interval ii warm occurs between sequence boundaries pp3 and pp1 325 79 5 mbsf last occurrence of pseudoemiliania lacunosa 460 ka at 330 mbsf and interval iii coldest occurs between sequence boundaries pp4 and pp3 520 325 mbsf calcareous nannofossils and dinocysts in proximity to pp4 indicate that the sedimentary record for 0 9 1 7 ma is either missing altogether or highly condensed within the basal few meters of the section neogloboquadrina pachyderma d displays eight peaks of abundance which correlate for the most part with depleted 18o values increases in calcium carbonate percentages low coarse fraction percentages increased planktonic fragmentation greater dissolution and low n pachyderma s abundances these intervals are interpreted as representing warmer interglacial conditions neogloboquadrina pachyderma s displays seven peaks of abundance which correlate for the most part with 18o increases decreases in calcium carbonate percentages increases in coarse fraction percentages and low n pachyderma d abundances these intervals are interpreted as representing cooler glacial conditions in interval iii a faunal response to relative changes in sea surface temperature is reflected by abundance peaks in neogloboquadrina pachyderma d followed by turborotalita quinqueloba and then n pachyderma s proceeding from warmest to coolest respectively this tripartite response is consistent with the oxygen isotope record and although not as clear also occurs in intervals i and ii six peaks peak intervals of globigerina bulloides abundance are closely matched by peaks in globigerinita glutinata and occur within oxygen isotope stage ois 2 latter part 3 4 5 8 9 13 14 and 15 we speculate that these intervals reflect increased upwelling and nutrient levels during both glacials and interglacials eight peak intervals of globorotalia inflata show a general inverse correlation with g bulloides and may reflect lowered nutrient and warmer surface waters

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

centennial scale surface hydrology off portugal during marine isotope stage 3 insights from planktonic foraminiferal fauna variability 1 the marine isotopic stage 3 mis3 at ocean drilling program odp site 1060 gulf stream shows both sharp onset and end of interstadials the existence of very short lived warm events during stadials and points to differences in detail between the sea surface temperature sst record from the western north atlantic and the atmospheric temperature record inferred from 18o in greenland ice investigating mis3 and obtaining comparable data from other locations appears crucial the eastern atlantic provides well documented records of climate changes we have selected a core from off portugal and use it to examine dansgaard oeschger events d o at centennial scale resolution 139 years on average between two data points we have obtained a faunal data set for core md01 2444 37 n 10 w 2600 m water depth and use a group of species globigerina bulloides globigerinita glutinata as a proxy of upwelling intensity driven by trade winds intensity changes we tentatively relate the variation of this group to a north atlantic oscillation like phenomenon nao off portugal we observe that it resembles the rainfall index in the caribbean as recorded at odp site 1002 cariaco basin which traces the intertropical convergence zone itcz location through changes of terrigenous inputs the driest intervals itzc to the south at site 1002 correspond to intervals of increased upwelling in md01 2444 as well as the driest periods identified during stadials on similar cores in the area because the itzc to the south is consistent with an el nino southern oscillation enso situation our study suggests a positive correlation between enso like conditions and nao like conditions at a millennial timescale during interstadial intervals when increased wetness over cariaco is recorded itcz to the north and the upwelling in md01 2444 is decreased we see from both ssts and faunal tropical indicators that md01 2444 site is warm in addition interstadials are equally warm through each so called bond cycle this contrasts with the greenland ice core project grip record where interstadial peaks are successively cooler through each bond cycle this record confirms a link between tropical climate linked to itcz position and the climate of southern europe at millennial timescales in spite of showing a very good correlation with polar latitudes grip through 18o on globigerina bulloides in addition because the warmest ssts and the 18o on g bulloides are so remarkably different our work points to changes in seasonality as a strong control over the climatic pattern of the north atlantic area and the marked influence of winter conditions

paleoceanographic reconstructions from planktonic foraminifera off the iberian margin temperature salinity and heinrich events a quantitative analysis of planktonic foraminifera in a core from the iberian margin allows a reconstruction of the evolution of oceanographic parameters during the last glacial cycle with a resolution of 1000 years a principal component analysis performed on 19 species allows the identification of 11 intervals characterized by increased abundances of the subpolar species the youngest six of these intervals are correlated with the last 6 heinrich events hes the five cold events older than stage 4 are dated at 81 90 110 129 and 140 ka respectively paleotemperatures reconstructed using the modern analog technique indicate 4 c decreases during all even numbered isotopic stages and stage 3 during the hes temperature decreases reach 10 c and seawater 18o anomalies reach 1 temperature and salinity reconstructions indicate that the environment of the iberian margin has been under the combined influence of global factors such as the migration of the polar front and iceberg discharge and of regional factors such as the precipitation evaporation regime on both oceanic and continental area

the oligocene ophiolite derived breccias and sandstones of the val marecchia nappe insights for paleogeography and evolution of northern apennines italy abstract ophiolite derived debrites microbreccias and olistoliths are interbedded in the monte morello and argille varicolori formations of the val marecchia nappe constituting the highest tectonic unit of the north eastern apennines and usually considered as having originated from the external ligurian domain the ophiolite derived clastic rocks were supplied exclusively by an oceanic sequence consisting of peridotite gabbro basalt radiolarite pelagic limestone and shale they are interbedded within a succession made up of fine grained carbonate and siliciclastic turbidites and of pelagic claystones petrographic and sedimentological features of the ophiolite derived breccia and sandstone units testify to an intrabasinal source area for these clastic rocks rather than an extrabasinal origin from subaerially exposed oceanic crust forming the inner flank of the basin as previously suggested due to their oligocene earliest miocene age the deposits in which debrites and olistoliths occur are related to early neo alpine tectonic events that caused reactivation and or inversion of old normal transform faults unstable fault escarpments provided a preferential path for submarine landslide and turbidite emplacement debrites microbreccias and olistoliths therefore were added to the basin fill of fine grained turbidite and pelagic deposits this study suggests that the val marecchia nappe succession was deposited on an oceanic substratum stratigraphy and age of the succession of this nappe can be well framed only in the evolution of the sub ligurian domain whereas they conflict with the interpretation of the val marecchia nappe as a nappe originated from the external ligurian domain as suggested previously by most authors this interpretation also requires an oceanic substratum for the sub ligurian domain i e the existence of an oceanic belt external to the ligurian domain which was deformed only in the early miocene the sub ligurian domain therefore would be an eastern branch of the central tethys and would represent the extension in the northern apennines of the maghrebian lucanian oceanic realm as recognized in the betic cordillera maghrebian chain and southern apennines

faunal and alkenone reconstructions of subtropical north atlantic surface hydrography and paleotemperature over the last 28 kyr two techniques for estimating past variations in sea surface temperature sst have been used to investigate climatic change in biogeochemical oceanic flux study bofs core 31k 19 n 20 w from the eastern subtropical atlantic high resolution sst records for the last 28 kyr have been produced using planktonic foraminiferal assemblages based on the imbrie kipp transfer function technique and the uk 37 index derived from abundances of c37 alkenones biosynthesized by prymnesiophyte algae modern observations suggest that these indices reflect particular hydrographic conditions in the upper ocean the uk 37 index corresponds to the temperature at the time of maximum coccolith productivity typically late spring early summer in the study area today whereas the faunal transfer function is calibrated for seasonal maximum and minimum temperatures in general the faunal and biomarker paleotemperature records display comparable sst variations during the last glacial and deglacial but although the overall trends are similar differences exist in the magnitude and timing of these temperature changes most notably the faunal twarm and uk 37 sst estimates diverge by 3 c between 8 ka and 6 ka and this offset persists through the late holocene this difference cannot be adequately explained by uncertainties associated with either the calibration data sets or fluctuating preservation levels we therefore propose that the deviation in sst estimates is linked to a switch in the seasonal timing of maximum coccolith production from the summer in the glacial ocean to the late spring early summer in the modern ocean our results suggest that a dual approach to sst estimation based on faunal and biomarker proxies can provide a valuable means of evaluating mixed layer and productivity changes associated with the movement of oceanographic frontal zones during the late quaternary

millennial scale variability of deep water temperature and δ18odw indicating deep water source variations in the northeast atlantic 0 34 cal ka bp 1 paired measurements of mg ca and 18occ calcite 18o in benthic foraminifera from a deep sea core recovered on the iberian margin md99 2334k 37 48 n 10 10 w 3 146 m have been performed in parallel with planktonic 18occ analyses and counts of ice rafted debris ird the synchrony of temperature changes recorded in the greenland ice cores and in north atlantic planktonic 18occ allows the proxy records from md99 2334k to be placed confidently on the gisp2 time scale this correlation is further corroborated by ams 14c dates benthic mg ca measurements in md99 2334k permit the reconstruction of past deep water temperature tdw changes since 34 cal ka bp calendar kiloyears before present using these tdw estimates and parallel benthic 18occ measurements a record of deep water 18o 18odw has been calculated results indicate greatly reduced tdw in the deep northeast atlantic during the last glaciation until 15 cal ka bp when tdw warmed abruptly to near modern values in parallel with the onset of the bolling allerod interstadial subsequently tdw reverted to cold glacial values between 13 4 and 11 4 cal ka bp in parallel with the younger dryas cold reversal and the h0 ice rafting event similar millennial scale tdw changes also occurred during the last glaciation indeed throughout the last 34 cal ka millennial 18odw and tdw changes have remained well coupled and are linked with ird pulses coincident with heinrich events 3 2 1 and the younger dryas when transitions to lower tdw and 18odw conditions occurred in general millennial tdw and 18odw variations recorded in md99 2334k describe an alternation between colder low 18odw and warmer high 18odw conditions which suggests the changing local dominance of northern sourced north atlantic deep water nadw versus southern sourced antarctic bottom water aabw the observed similarity of the tdw and gisp2 18oice records would therefore suggest a common component of variability resulting from the coupling of nadw formation and greenland climate a link between greenland stadials and the incursion of cold low 18odw aabw in the deep northeast atlantic is thus implied which contributes to the relationship between greenland climate and the millennial benthic 18occ signal since 34 cal ka bp

molecular stratigraphy of cores off northwest africa sea surface temperature history over the last 80 ka the molecular stratigraphy of biogeochemical oceanic flux study core 31k 19 n 20 10 w and ocean drilling program hole 658c 20 45 n 18 35 w has been studied for c37 alkenone abundances over the past 80 ka at high resolution circa 200 500 years the derived uk37 sea surface temperature record for both cores shows a range of temperatures from about 18 c during the last glacial to 21 5 c during the early holocene both records also reveal changes in sea surface temperature as much as 2 4 c over a few hundred years which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the ne atlantic associated with heinrich events our results indicate that meltwater produced by these ice rafting events was transmitted southward by the canary current where it had considerable impact on sea surface temperatures in the subtropical eastern atlantic

millennial scale sea surface temperature variability in the western tropical north atlantic from planktonic foraminiferal census counts planktonic foraminiferal census counts are used to construct high resolution sea surface temperature sst and subsurface thermocline temperature records at a core site in the tobago basin lesser antilles the record is used to document climatic variability at this tropical site in comparison to middle and high latitude sites and to test current concepts of cross equatorial heat transports as a major player in interhemispheric climate variability temperatures are estimated using transfer function and modern analog techniques glacial maximum cooling of 2 5 3 c is indicated maximum cooling by 4 c is inferred for isotope stage 3 the sst record displays millennial scale variability with temperature jumps of up to 3 c and closely tracks the structure of ice core dansgaard oeschger cycles sst variations in part of the record run opposite to the sst evolution at high northern latitude sites pointing to thermohaline circulation and marine heat transport as an important factor driving sst in the tropical and high latitude atlantic both on orbital and suborbital timescales

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

reconstructing the phytoplankton community of the cariaco basin during the younger dryas cold event using chlorin steryl esters 1 a record of the downcore distribution of chlorin steryl esters cses through the younger dryas was produced from cariaco basin sediments in order to assess the potential use of cses as recorders of the structure of phytoplankton communities through time using an improved high performance liquid chromatography method for the separation of cses we find significant changes in the distribution of cses during the younger dryas in the cariaco basin during the younger dryas enhanced upwelling in the cariaco basin caused an increase in the diatom population and therefore an increase in the relative abundance of cses derived from diatoms in contrast the dinoflagellate population and therefore cses derived from dinoflagellates decreased in response to the climate change during the younger dryas these community shifts agree well with the shifts observed in the present day on a seasonal basis that result from the north south migration of the intertropical convergence zone over the cariaco basin we also identify changes in the abundance of several cses that seem to reflect rapid warming and cooling events this study suggests that cses are useful proxies for reconstructing phytoplankton communities and paleoenvironments index terms 1055 geochemistry organic geochemistry 4267 oceanography general paleoceanography 4855 oceanography biological and chemical plankton keywords younger dryas cariaco basin chlorin steryl esters

combined marine proxy and pollen analyses reveal rapid iberian vegetation response to north atlantic millennial scale climate oscillations abstract a deep sea sediment core from the western portuguese margin has provided a continuous high resolution record of millennial scale climatic oscillations during the interval 9000 65 000 yr b p pollen analysis of the same sequence allows direct in situ assessment of the phase relationship between the north atlantic climate system and vegetation changes on the adjacent landmass this demonstrates for the first time that variability in nw iberian tree population size closely tracked millennial scale climate variability

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

changes in sea surface hydrology associated with heinrich event 4 in the north atlantic ocean between 40 and 60 n abstract the changes in distribution of sea surface temperature and salinity in the north atlantic between 40 and 60 n were reconstructed for the time interval between 40 and 30 kyr bp which includes the large iceberg discharge event associated with the deposition of heinrich layer 4 we found that the meltwater input during deposition of heinrich layer 4 resulted in a 1 2 kyr temperature decrease of about 2 c and a salinity decrease in the range of 1 5 3 5 between 40 and 50 n sites above 50 n did not experience significant salinity variations a much larger area was affected by the reduction in sea surface temperature the amplitude of the sea surface temperature shift was however much smaller than the atmospheric temperature changes over greenland at gisp and grip sites

evidence for an additional heinrich event between h5 and h6 in the labrador sea 1 an additional heinrich ice rafting event is identified between heinrich events 5 and 6 in eight cores from the labrador sea and the northwest atlantic ocean it is characterized by sediment rich in detrital carbonate 40 caco3 with high concentration of floating dropstones high coarse fraction 150 m content and has a sharp contact with the underlying but grades into the overlying hemipelagic sediment it also shows lighter 18onpl values indicating freshening due to iceberg rafting and or meltwater discharge this event is correlated with dansgaard oeschger event 14 and interpreted as an additional heinrich event h5a the thickness of h5a in the labrador sea reaches up to 220 cm this additional heinrich event has also been reported in cores ps2644 and so82 5 from the northern north atlantic with the recognition of h5a the temporal spacing between heinrich events 1 to 6 becomes more uniform 7 ka

the lanthanide tetrad effect in apatite from the altay no 3 pegmatite xingjiang china an intrinsic feature of the pegmatite magma abstract apatite and associated minerals such as spessartite tourmaline beryl and alkali feldspar from the altay no 3 granite pegmatite in xinjiang china have highly variable concentrations of rare earth elements rees and possess chondrite normalized ree patterns that show a clear convex tetrad effect the y ho and sr eu ratios of the apatite samples are extremely fractionated relative to the corresponding chondritic values based on the la lu sr eu and y ho ratios of these minerals the crystallization zones of the pegmatite can be divided into two groups that are interpreted to reflect two main stages of magma evolution namely a magmatic and a magmatic hydrothermal transition stage the degree of the lanthanide tetrad effect in ree patterns of the apatite expressed by the quantification factor te 1 3 ranges from 1 3 to 1 9 the size of the tetrads correlates with y ho eu eu and sr eu ratios in addition to the mineral samples from the pegmatite the ree patterns of the altered wall rocks also show a convex tetrad effect a mass balance calculation was carried out to constrain the ree partitioning between the aqueous fluid crystalline phases and the residual melt it was found that the ree patterns of these three phases are dominated by the concentration of the rees in the initial pegmatite forming melt accordingly it is proposed that the ree tetrad effect and the fractionation of the chemically coherent isovalent element pairs in the studied mineral separates represent intrinsic features of the granitic pegmatite forming melt it appears unlikely that these geochemical characteristics developed as a result of melt mineral fluid interactions taking place during magma crystallization after its intrusion interaction of an external fluid with pegmatite magma before emplacement or with parent materials of the highly evolved granitic rocks before melting would be favorable for producing the ree tetrad effect in highly evolved granitic rocks

sea level changes forced ice breakouts in the last glacial cycle new results from coral terraces abstract sea level cycles recorded by coral terraces at huon peninsula hp in papua new guinea match rapid climate changes that occurred between 30 000 and 65 000 years ago seen in greenland ice cores and marine sediments each cycle of 6000 7000 years ended with a sea level rise of 10 15 m lasting 1000 2000 years following a longer period of falling sea level precise dating shows that each rise corresponds to a heinrich episode of ice rafted detritus in north atlantic signalling massive ice outbreak from north america sea level may be the trigger that forced near synchronous breakouts of ice from north america and eastern greenland the hp sea level changes also correspond to similar cycles in benthic oxygen isotopes reported from the north atlantic which are too large to be explained entirely in terms of ice volumes jointly the sea level and isotope records suggest that the north atlantic deep ocean cooled as sea level fell and warmed as sea level rose in each 6000 year cycle

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

precise dating of dansgaard oeschger climate oscillations in western europe from stalagmite data the signature of dansgaard oeschger events millennial scale abrupt climate oscillations during the last glacial period is well established in ice cores and marine records but the effects of such events in continental settings are not as clear and their absolute chronology is uncertain beyond the limit of 14 c dating and annual layer counting for marine records and ice cores respectively here we present carbon and oxygen isotope records from a stalagmite collected in southwest france which have been precisely dated using 234u 230th ratios we find rapid climate oscillations coincident with the established dansgaard oeschger events between 83 000 and 32 000 years ago in both isotope records the oxygen isotope signature is similar to a record from soreq cave israel and deep sea records indicating the large spatial scale of the climate oscillations the signal in the carbon isotopes gives evidence of drastic and rapid vegetation changes in western europe an important site in human cultural evolution we also find evidence for a long phase of extremely cold climate in southwest france between 61 2 0 6 and 67 4 0 9 kyr ago