response to comment on mixed layer deepening during heinrich events a multi planktonic foraminiferal δ18o approach hillaire marcel and de vernal question our hypothesis of the homogenization of the upper water masses of the north atlantic during heinrich events 0 1 and 4 here we respond to their specific points and synthesize data from the southern labrador sea cores the basic tenet of hillaire marcel and de vernal s arguments

seasonal stratification shell flux and oxygen isotope dynamics of left coiling n pachyderma and t quinqueloba in the western subpolar north atlantic blooms this annual population overturning is marked by a 0 7 increase in d 18 o in both species the shell flux of n pachyderma peaks during the spring bloom and in late summer when stratification is close to its minimum and maximum respectively both export periods contribute about equally and account for 95 of the total annual flux shell fluxes of t quinqueloba show only a single broad pulse in summer thus following the seasonal stratification cycle the d 18 oo fn pachyderma reflects temperatures just below the base of the seasonal sml without offset from isotopic equilibrium the d 18 op attern oft quinqueloba shows a nearly identical amplitude and correlates highly with the d 18 oo fn pachyderma therefore t quinqueloba also reflects temperature near the base of the sml but with a positive offset from isotopic equilibrium these offsets contrast with observations elsewhere and suggest a variable offset from equilibrium calcification for both species in the irminger sea the species consistently show a contrast in their flux timings their flux weighted dd 18 o will thus dominantly be determined by seasonal temperature differences at the base of the sml rather than by differences in their depth habitat consequently their sedimentary dd 18 o may be used to infer the seasonal contrast in temperature at the base of the sml citation jonkers l g j a brummer f j c peeters h m van aken and m f de jong 2010 seasonal stratification shell flux and oxygen isotope dynamics of left coiling n pachyderma and t quinqueloba in the western subpolar north atlantic paleoceanography 25 pa2204 doi 10 1029 2009pa001849

origin of unusually thick heinrich layers in ice proximal regions of the northwest labrador sea ten piston cores and a 25 m long giant piston core from the ice proximal region off hudson strait contain heinrich layers 1 and 2 identified by their sedimentary structure and high detrital carbonate content both layers are unusually thick on the upper labrador slope 3 8 2 1 m and on the lower slope and rise 1 5 1 0 m heinrich layers 1 and 2 can be subdivided into three units unit a is restricted to the upper slope and overlies hemipelagic sediment with a gradational boundary it is 6 1 m thick dark black to dark gray in color and made up of coarse ice rafted sand and granules dispersed in hemipelagic mud with a few faint laminations towards the top the overlying unit b is up to 3 35 m thick and consists of two facies i centimeter thick graded carbonate rich mud layers containing dispersed coarser grains in the mud interpreted as nepheloid flow deposits with coarse ice rafted debris and ii carbonate rich finely laminated mud layers which alternate with millimeter thick laminae of ice rafted debris unit c up to 0 90 m thick is devoid of sedimentary structures and consists of hemipelagic sediment with dispersed dropstones that increase in abundance towards the top of the unit data suggest the following sequence of processes could have occurred during the deposition of heinrich layers in ice proximal sites as the laurentide ice sheet grew it extended through the hudson strait ice stream outlet to a floating ice margin near the shelf edge and perhaps beyond to the upper slope and deposited unit a by releasing dropstones from the basal debris rich layer unit b is interpreted to be the deposits of the combined processes of nepheloid layer flow low density turbidity currents and massive ice rafting maximum carbonate content s 50 the lightest n 18 o values in very sparse planktonic foraminifera and low magnetic susceptibility are characteristic of unit b unit c is inferred to represent the time of waning supply of fines as nepheloid flow deposition ceased while the relative concentration of dropstones increased as a result of continuing intense ice rafting due to the reduction of fine grained sediment supply the carbonate concentration decreased to the labrador sea background level this finding was further supported by the appearance of darker colored sediments and heavier n 18 o values in neogloboquadrina pachyderma s which indicates the reduction of meltwater discharge

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

isotope calibrated greenland temperature record over marine isotope stage 3 and its relation to ch4 large temperature variations on millennial time scales in greenland characterised the last ice age abrupt warmings known as dansgaard oeschger do events can be traced in the 18oice record of greenland ice cores however it has been shown that 18oice is not a direct temperature proxy measurements of the isotopic composition of gases trapped in the ice can be used to calibrate the paleothermometer here we present a continuous temperature record based on high resolution 15n measurements and firn model studies it covers a sequence of 9 do events 9 17 during the time period from 38 to 64 kyr bp for which temperature changes of 8 to 15 c were estimated the difference between the modern and the glacial 18oice t relationship can be explained by a combination of source temperature changes and changes in the annual distribution of precipitation a detailed comparison of the temperature evolution with reconstructions of the atmospheric methane ch4 concentration shows that ch4 rises lag temperature increases at the onset of do events by 25 to 70 yr within data resolution the strong correlation between greenland temperature and ch4 on millennial and submillennial time scales suggests that variations on these time scales were probably of hemispheric extent

climatic evolution of the central equatorial pacific since the last glacial maximum this paper investigates paleoceanographic changes at a central equatorial pacific site 6 40 n 177 28 w since the last glacial maximum using planktic foraminifera assemblages together with the oxygen isotope 18o and mg ca compositions of three species globigerinoides sacculifer pulleniatina obliquiloculata and globorotalia tumida that dwell in the mixed layer upper thermocline and lower thermocline respectively while the mg ca derived temperatures of the mixed layer and lower thermocline varied within a narrow range from 18 ka onward the upper thermocline temperature increased by as much as 3 c during the last deglaciation 18 12 ka with a simultaneous decrease of 18o these changes are best explained by an enhanced mixing of the upper ocean and a reduced habitat depth separation between p obliquiloculata and g sacculifer during the 18 12 ka interval the planktic foraminifera assemblage during the same period resembles modern composition at subtropical central pacific sites that are strongly influenced by the northeasterly trades and north equatorial current nec we suggest that the study site presently under the control of the intertropical convergence zone itcz north equatorial countercurrent had been influenced by the northeasterly trades and nec during the 18 12 ka interval this interpretation is consistent with previous documentation of a more southerly location of the itcz during two northern hemisphere cooling events the heinrich stadial 1 and the younger dryas and implies that the mean annual position of the itcz was located south of the study site by at least 2 of latitude

bias in foraminiferal multispecies reconstructions of paleohydrographic conditions caused by foraminiferal abundance variations and bioturbational mixing a model approach abstract a simple box model was applied to study the combined effect of bioturbation and foraminiferal abundance variations using synthetic isotope records constructed from the greenland oxygen isotope record gisp2 apart from the well known general smoothing of the signal the attenuation of peak heights and the up or downwards shift of the proxy records at intervals of changing abundance the modeling results draw attention to two effects of special importance to climatic reconstructions based on the comparison of proxy signals from two or more planktonic foraminifer species first the bioturbational mixing of tests out of abundance maxima and into over and underlying sediment can lead to the introduction of stratigraphic shifts between different species when species with opposing abundance patterns are used this shifting of the signals can easily result in apparent increases or decreases in the isotopic gradients between different species especially at intervals of rapidly changing climate conditions second in intervals with rapidly changing environmental conditions such as dansgaard oeschger cycles where species with different preferences often show opposing abundance patterns the mixing of foraminifer tests out of their respective abundance maxima can result in a general but artificial offset between the two species this offset then may disappear during intervals of slower variability these artifacts have the potential of seriously biasing any paleoceanographic and paleoclimatic reconstructions based on multispecies analysis where the studied species show opposing abundance patterns it is therefore highly recommended that species with as low abundance variations as possible or at least with similar abundance variations are used whenever multispecies reconstructions are attempted

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

nutrient conditions in the subpolar north atlantic during the last glacial period reconstructed from foraminifera bound nitrogen isotopes 1 surface nitrate concentration is a potentially useful diagnostic in reconstructing the past circulation of high latitude north atlantic waters moreover nutrient consumption in the north atlantic surface impacts the atmospheric concentration of carbon dioxide to reconstruct nutrient conditions in the subpolar north atlantic region during the last ice age a record of foraminifera bound 15n was measured in neogloboquadrina pachyderma sin from core v28 73 south of iceland 57 2 n 20 9 w foraminifera bound 15n is up to 2 lower during the last ice age than during the holocene suggesting as much as 25 less complete nitrate consumption during the former this is consistent with stronger light limitation associated with a deeper summer surface mixed layer perhaps related to the formation of glacial north atlantic intermediate water previously suggested to have occurred near the core site however three single point maxima in 15n in the glacial section and the sharp deglacial 15n rise coincide with heinrich event layers this suggests that increased water column stratification during heinrich events presumably due to surface freshening reduced the nutrient supply from below and led to nearly complete nitrate consumption in the summertime mixed layer the heinrich layers in v28 73 are not accompanied by 18o minima in either n pachyderma sin or globigerinoides bulloides which we tentatively attribute to extreme mixed layer shoaling the reconstructed subpolar north atlantic upper water column changes both glacial interglacial and millennial are inverse to those inferred for the antarctic

ice rafted debris associated with binge purge oscillations of the laurentide ice sheet the north atlantic sediment record suggests quasi periodic 7000 to 12 000 year period ice rafted debris ird depositions during at least the last glacial period the cause of these heinrich events as they are commonly known is not fully understood however they may point to surges of the ice stream that drained the hudson bay hudson strait region of the laurentide ice sheet we investigate a simple conceptual model of ice stream instability the binge purge model to suggest ways in which the ice stream could have entrained sufficient debris to account for the estimated mass of ird associated with a typical heinrich ird layer in the north atlantic 1 0 0 3 1015 kg we find that freezing of debris laden ice at the bed of the ice stream during the brief 750 years surge phase of the ice stream s hypothesized binge purge cycle can incorporate up to 5 1 1015 kg this amount is sufficient to meet the constraints of the north atlantic sediment record but by no means verifies the binge purge model as the cause of heinrich events

deep circulation change linked to heinrich event 1 and younger dryas in a middepth north atlantic core a core from the mid atlantic ridge at 43 5 n and 3 km water depth shows distinct evidence of the deglacial events known as heinrich event 1 probably the marine equivalent of oldest dryas cooling in europe and the younger dryas the heinrich event dated at three levels to between 14 3 and 15 0 ka is marked by a minimum in foraminifera per gram by maxima in rates of sedimentation ice rafted debris per gram and relative abundance of n pachyderma s and by a 18o minimum in planktonic foraminifera the younger dryas event is marked by peak abundance of n pachyderma s and a planktonic 18o maximum benthic foraminiferal 13c reaches minimum values during both the heinrich event and the younger dryas our data indicate pronounced changes in surface water properties were coupled with reduced production of north atlantic deep water at each of these times

glass production in late antiquity and the early islamic period a geochemical perspective first millennium ad glass production was divided between a relatively small number of workshops that made raw glass and a large number of secondary workshops that fabricated vessels glass compositions reflect the primary glassmaking source for most of the period egyptian mineral soda was fused with lime bearing siliceous sand to produce soda lime silica glass the location of the belus glassmaking sand which is known from the classical literature is located on that part of the levantine coast where iron contents are lowest sr 87 sr 86 of primary glass from workshops in the levantine region is close to that of modern seawater and confirms the use of beach sand which contained shell heavy mineral assemblages of levantine beach sands are dominated by hornblende hence the primary glasses are characterized by very similar trace element signatures glasses believed on archaeological grounds to have been made in other regions for example in inland egypt may have higher sr 87 sr 86 reflecting terrigenous sources of lime and have different trace element signatures compositional data for glasses from as far away as britain suggest origins of the glass material in the eastern mediterranean recycling of old glass may be recognized by the presence of elevated transition metals the use of plant ash as a flux became dominant practice in the ninth century and preliminary data for plant ash glasses from the early islamic world indicate that primary production centres may be separated using strontium and oxygen isotopes as well as by major and trace elements

condor seamount azores ne atlantic a morpho tectonic interpretation abstract high resolution datasets collected by multibeam and acoustic backscatter surveys were used to produce fine scale seafloor nature and morpho tectonic interpretations of the condor seamount condor constitutes an elongated volcanic ridge that extends for 39 km and rises more than 1800 m from the surrounding seafloor constructive morphologies include i linear eruptive centres ii volcanic cones with or without summit depressions iii lava flows and iv hummocky sectors eruptive type is interpreted to vary with depth on the deeper seamount extremities the predominance of highly acoustically backscattering volcanic cones and hummocky terrain is interpreted to result from effusive eruptions not yet covered by sediment deposits in contrast the smoother relief of the central seamount flanks is interpreted as draping and infilling of the underlying effusive relief by i primary volcaniclastic deposits produced by explosive eruptions on the shallowest parts of the ridge together with ii secondary volcanigenic sediments resulting from truncation of the seamount top by swell erosion and iii sediments resulting from biogenic production a set of wnw ese to nw se trending volcano tectonic structures are shown to control most of the fissural volcanism that formed the ridge a network of nnw sse trending faults is identified on the sea floor around condor but they show little relation with the distribution of volcanic edifices or with post emplacement dismantling of the seamount these fault sets are related to the transtensional regime acting on the azorean segment of the eurasia nubia plate boundary erosional features include i palaeo wave cut platforms on the seamount summit ii landslide scars produced by lateral collapses of the ne and sw facing flanks iii gullies and turbidity current channels and iv mass wasting deposits iceberg drag and bump marks are also identified on the seamount upper flanks representing the first reference to such features in the azores and an additional low latitude record given the lack of major erosional and tectonic dismantling condor is suggested to be a relatively young seamount a revised factoring of eustatic erosional and isostatic processes does not exclude that the summit may have been eroded as late as the last glacial maximum

stable isotope clue to episodic sea ice formation in the glacial north atlantic sea ice is a determinant parameter of the climate system which acts as amplifier through positive ice albedo feedbacks and induces deep water formation through brine production it is also one of the most elusive parameters in the paleoclimate record most proxies of sea ice provide information on its presence and extent of e g diatoms or dinocysts but do not permit assessment on its rate of formation however seemingly off equilibrium low 18o values in mesopelagic planktic foraminifer species as observed today in the arctic ocean are thought to relate to the production of isotopically light brines during sea ice formation and might thus provide a clue on the rate of sea ice growth with reference to the isotopic properties of modern planktic foraminifers in the arctic ocean and using multi proxy data sets from the last glacial stage in the northwest north atlantic we re examined some of the current interpretations of planktic isotope records in the glacial nw north atlantic the large amplitude light isotopic excursions recorded in neogloboquadrina pachyderma left coiling during heinrich events 1 for example correspond to extensive sea ice cover as reconstructed from dinocysts and do not seem unequivocally linked to low salinity pulses such light isotopic excursion more likely responded to enhanced rates of sea ice formation resulting in the production and sinking of isotopically light brines on the contrary the isotopically heavy planktic foraminifers of the last glacial maximum lgm interval stricto sensu would rather suggest relatively low rates of brine production thus low sea ice growth rates in the area this would imply that the lgm distribution of sea ice in the north atlantic was primarily linked to spreading and drifting from marginal and nordic source areas and not from enhanced in situ production at the scale of glacial interglacial cycles isotopic distillation processes relating to sea ice production at high latitudes could be one of the factors controlling the 18o salinity relationship in deep ocean water masses that might deserve closer examination as it would be independent of continental ice volume changes

simulation of abrupt climate change induced by freshwater input to the north atlantic ocean temperature records from greenland ice cores1 2 suggest that large and abrupt changes of north atlantic climate occurred frequently during both glacial and postglacial periods one example is the younger dryas cold event broecker3 speculated that these changes result from rapid changes in the thermohaline circulation of the atlantic ocean which were caused by the release of large amounts of melt water from continental ice sheets here we describe an attempt to explore this intriguing phenomenon using a coupled ocean atmosphere model in response to a massive surface flux of fresh water to the northern north atlantic of the model the thermohaline circulation weakens abruptly intensifies and weakens again followed by a gradual recovery generating episodes that resemble the abrupt changes of the ocean atmosphere system recorded in ice and deep sea cores4 the associated change of surface air temperature is particularly large in the northern north atlantic ocean and its neighbourhood but is relatively small in the rest of the world

sedimentology and history of sediment sources to the nw labrador sea during the past glacial cycle abstract the paleoceanography and sediment dynamics of the northernmost labrador sea provides critical records of glacial history glacially dominated sedimentation and paleocirculation a reference core at 938 m on the se baffin slope was investigated with new oxygen isotope stratigraphy x ray fluorescence geochemistry and 18 14c ams dates and correlated to 14 regional deep water cores the reference core provides a paleoceanographic and sediment source record over the last 40 ka overlying a 3 m thick blocky mass transport deposit over mis 5 autochthonous sediment detrital carbonate rich sediment layers h0 h4 based on bulk geochemistry were derived principally from hudson strait shortly after h2 and h3 the shelf crossing cumberland sound ice stream supplied dark brown ice proximal stratified sediments minor supply of carbonate rich sediment from baffin bay allows chronologic integration of the baffin bay and labrador sea detrital carbonate records and implies an open seaway through davis strait the counterparts of h3 h4 and h5 events in the deep labrador basin are 4 10 m thick units of thin bedded carbonate rich mud turbidites from glacigenic debris flows on the hudson strait slope the behavior of the hudson strait ice stream changed through the last glacial cycle in h1 and h2 the ice stream retreated back across the shelf but did not deglaciate hudson bay in h3 h5 it remained at the shelf break long enough to supply thick turbidites and subsequent retreat after h4 and h5 deglaciated hudson bay the maximum extent of ice streams in hudson strait cumberland sound and lancaster sound was not synchronous

centennial to millennial scale ice ocean interactions in the subpolar northeast atlantic 18 41 kyr ago in order to monitor the evolution of the british irish ice sheet biis and its influence in surface ocean structure during marine isotopic stages mis 2 and 3 we have analyzed the sediments recovered in core md04 2829cq rosemary bank north rockall trough northeast atlantic dated between 41 and 18 ka b p ice rafted debris flux and composition 40ar 39ar ages of individual hornblende grains multispecies planktonic stable isotope records planktonic foraminifera assemblage data and faunal based sea surface temperatures ssts demonstrate a close interaction between biis dynamics and surface ocean structure and water properties in this region the core location lies beneath the north atlantic current nac and is ideal for monitoring the shifts in the position of its associated oceanic fronts as recorded by faunal changes these data reveal a succession of biis sourced iceberg calving events related to low sst usually synchronous with dramatic changes in the composition of the planktonic foraminifera assemblage and with variations in the stable isotope records of the taxa neogloboquadrina pachyderma sinistral coiling and globigerina bulloides the pacing of the calving events from typically dansgaard oeschger millennial timescales during late mis 3 to multicentennial cyclicity from 28 ka b p represents the build up of the biis and its growing instability toward heinrich event he 2 and the last glacial maximum our data confirm the strong coupling between biis instabilities and the temperature and salinity of surface waters in the adjacent northeast atlantic and demonstrate the biis s ability to modify the nac on its flow toward the nordic seas in contrast subsurface water masses were less affected except during the greenland stadials that contain hes when most intense water column reorganizations occurred simultaneously with the deposition of cream colored carbonate sourced from the laurentide ice sheet

boron isotopic composition as a provenance indicator for the flux raw material in roman natron glass abstract boron is a trace element present in natron glass which largely enters the glass via the flux therefore the b isotope ratio is targeted as a means of provenancing this flux in this work 33 greco roman natron glasses and 18 natron samples were analysed for their b isotopic composition expressed as 11b all glasses except one of mixed flux origin show a 11b value close to the average value of 29 11 natron samples from the wadi natrun show an average 11b of 29 8 while the sample from al barnuj shows a 11b of 28 5 the average for 4 fezzan samples from libya is 25 3 and that for the 2 samples from lake pikrolimni in greece 10 5 there is an influence of the sand on the 11b of natron glass complicating the picture but in general the silica source will slightly lower the 11b of the glass compared to that of the natron source the high melting temperature has no significant effect on the b isotope ratio it can be concluded that greco roman natron glasses show a rather homogenous 11b the wadi natrun salts analysed fit a model in which the 11b of the glasses is somewhat lower than that of the natron source due to the input of low 11b sand the samples from lake pikrolimni in greece analysed in this study show too low 11b values to be used in glass making according to this model

a new concept for the paleoceanographic evolution of heinrich event 1 in the north atlantic new records of planktonic foraminiferal 18o and lithic and foraminiferal counts from eirik drift are combined with published data from the nordic seas and the ice rafted debris ird belt to portray a sequence of events through heinrich event 1 h1 these events progressed from an onset of meltwater release at not vert similar19 ka bp through the conventional h1 ird deposition phase in the ird belt starting from not vert similar17 5 ka bp to a final phase between 16 5 and not vert similar15 ka bp that was characterised by a pooling of freshwater in the nordic seas which we suggest was hyperpycnally injected into that basin after not vert similar15 ka bp this freshwater was purged from the nordic seas into the north atlantic which preconditioned the nordic seas for convective deep water formation this allowed an abrupt re start of north atlantic deep water nadw formation in the nordic seas at the bolling warming 14 6 ka bp in contrast to previous estimates for the duration of h1 i e 1000 years to only a century or two the total combined composite h1 signal presented here had a duration of over 4000 yrs not vert similar19 14 6 ka bp which spanned the entire period of nadw collapse it appears that deep water formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead the location of meltwater injections may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

hydrographic conditions along the western iberian margin during marine isotope stage 2 the surface water hydrography along the western iberian margin as part of the north atlantic s eastern boundary upwelling system consists of a complex seasonally variable system of equatorward and poleward surface and subsurface currents and seasonal upwelling not much information exists to ascertain if the modern current and productivity patterns subsisted under glacial climate conditions such as during marine isotope stage mis 2 and how north atlantic meltwater events especially heinrich events affected them to help answer these questions we are combining stable isotope records of surface to subsurface dwelling planktonic foraminifer species with sea surface temperature and export productivity data for four cores distributed along the western and southwestern iberian margin md95 2040 md95 2041 md99 2336 and md99 2339 the records reveals that with the exception of the heinrich events and greenland stadial gs 4 hydrographic conditions along the western iberian margin were not much different from the present during the last glacial maximum lgm subtropical surface and subsurface waters penetrated poleward to at least 40 6 n site md95 2040 export productivity was in general high on the western margin during the lgm and low in the central gulf of cadiz in agreement with the modern situation during the heinrich events and gs 4 on the other hand productivity was high in the gulf of cadiz and suppressed in the upwelling regions along the western margin where a strong halocline inhibited upwelling heinrich event 1 had the strongest impact on the hydrography and productivity off iberia and was the only period when subarctic surface waters were recorded in the central gulf of cadiz south of lisbon 39 n the impact of the other heinrich events was diminished and not all of them led to a significant cooling in the surface waters thus climatic impacts of heinrich events highly varied with latitude and the prevailing hydrographic conditions in this region

boron isotopic composition of marine and nonmarine evaporite borates abstract here we present the results of the boron isotopic analysis of borates from some well known marine and nonmarine evaporite deposits combining new analyses with analyses from the literature yields a mean 11 b value for nine marine evaporite borate analyses of 25 4 permil 11 b 10 b 4 15 0 02 and a mean for twenty five nonmarine evaporite borates of 7 10 permil 11 b 10 b 4 02 0 04 previous studies have shown that the boron isotopic composition of seawater 11 b 40 permil 11 b 10 b 4 20 is about four percent heavier than the boron isotopic composition of most crustal rocks and minerals we suggest that our results for marine and nonmarine evaporite borates reflect this difference thus it should be possible to use boron isotopic composition as a tracer for boron of marine evaporitic origin applications include borate bearing evaporite deposits and perhaps borate and or borosilicate bearing metamorphic rocks

the isotopic signature of planktonic foraminifera from ne atlantic surface sediments implications for the reconstruction of past oceanic conditions the stable isotope compositions of the planktonic foraminifera globigerina bulloides globigerinoides ruber white and pink varieties globigerinoides trilobus globorotalia inflata and globorotalia truncatulinoides right and left coiling types were examined as recorders of north atlantic surface water properties based on 40 box core surface sediments between 60 and 30 n while g ruber white and pink varieties and g trilobus mainly reflect summer surface water conditions in their oxygen isotope composition g bulloides reflects temperatures of the northward migrating spring bloom february march in the south to may june in the north our data show that g bulloides cannot be regarded as an indicator for summer temperatures as deduced from duplessy et al s data gt inflata and gt truncatulinoides right and left coiling build their shells in the coldest waters compared with the other species and reflect temperatures between 100 and 400 m water depth the difference in oxygen isotope composition between g bulloides and g inflata serves as a proxy for water mass stratification g bulloides is the only species that gives a distinct pattern in its carbon isotopic composition showing a high correlation with the surface water phosphate values along the transect and may serve as a proxy for palaeonutrients and or productivity

planktonic foraminifera as recorders of past surface water stratification the 18 o difference between shallow and deep living planktonic foraminifera is a proxy for the stratification of surface waters in holocene sediments from the atlantic this difference increases from about 0 in subpolar regions to 3 in the tropics the 18 o values of the shallow dwellers globigerinoides sacculifer and neogloboquadrina pachyderma mainly reflect surface water conditions the calcification depth of the deep living species globorotalia truncatulinoides right coiling is affected by the stratification of the water column in the subtropics shell formation of g truncatulinoides right coiling begins in weakly stratified surface waters in the tropics the initial shell is secreted below the mixed layer this hydrographically induced difference in calcification depth allows the use of the isotopic difference between g truncatulinoides and the shallow species as a proxy for the stratification of surface waters the 18 o between g truncatulinoides and g sacculifer from tropical gravity core geob 1523 1 was significantly lower during isotope stage 2 this suggests that the glacial temperature stratification of western equatorial atlantic surface waters was significantly reduced relative to the holocene

seasonal variations in planktonic foraminiferal flux and oxygen isotopic composition in the western north pacific implications for paleoceanographic reconstruction abstract the oxygen isotopic composition 18o of planktonic foraminiferal shells in seafloor sediment provides information on past surface oceanography knowledge of seasonal and depth habitat as well as the 18o disequilibrium vital effect is essential to constrain the interpretation of sedimentary 18o here we present a 1 year time series of planktonic foraminiferal shell fluxes and 18o from a sediment trap moored in the northwestern margin of the north pacific the vital effect and calcification depth for four species were estimated by comparing shell 18o and the predicted values of equilibrium calcite calculated from temperature and estimated 18o in seawater six major species neogloboquadrina incompta neogloboquadrina dutertrei neogloboquadrina pachyderma globigerina quinqueloba globigerina bulloides and globorotalia scitula constituted 97 of the total foraminiferal flux most major species showed large fluxes in june and december corresponding to periods of the development and disruption of the seasonal thermocline implying the importance of nutrient injection and or circulation for foraminiferal fluxes additional peaks in n dutertrei and n pachyderma were observed in august the seasonal successions of foraminiferal fluxes corresponded to surface ocean stratification conditions and food availability which are closely related to circulation of local currents vital effect estimations suggest that shells calcified in equilibrium for g bulloides and n pachyderma sinistral s and with a 0 7 offset for n dutertrei dextral d a 1 0 offset for n incompta d and a 0 3 offset for n pachyderma d the calculation of flux weighted 18o values reveals that the sedimentary 18o values of g bulloides n dutertrei d and n incompta d reflect surface temperature in winter season and those of n pachyderma s and n pachyderma d reflect summer and annual mean subsurface temperature respectively the shallow calcification depths for the four species suggest that 18o between different species 18o in the western north pacific does not work for reconstructing past stratification conditions unlike in other regions rather the 18o between n pachyderma s and g bulloides n dutertrei d or n incompta d may be a more suitable proxy for past seasonality

boron isotopic composition of tourmaline from massive sulfide deposits and tourmalinites boron isotope ratios 11b 10b have been measured on 60 tourmaline separates from over 40 massive sulfide deposits and tourmalinites from a variety of geologic and tectonic settings the coverage of these localities is global 5 continents and includes the giant ore bodies at kidd creek and sullivan canada broken hill australia and ducktown usa overall the tourmalines display a wide range in 11b values from 22 8 to 18 3 possible controls over the boron isotopic composition of the tourmalines include 1 composition of the boron source 2 regional metamorphism 3 water rock ratios 4 seawater entrainment 5 temperature of formation and 6 secular variations in seawater 11b the most significant control appears to be the composition of the boron source particularly the nature of footwall lithologies variations in water rock ratios and seawater entrainment are of secondary importance the boron isotope values seem especially sensitive to the presence of evaporites marine and non marine and carbonates in source rocks to the massive sulfide deposits and tourmalinites

western mediterranean sand deposits as a raw material for roman glass production abstract during the late roman and byzantine period natron glass was made from its raw materials in a limited number of primary production centres in egypt and syro palestine for the earlier hellenistic and roman period no primary furnaces have been found and the location of primary production during this era remains unclear ancient authors such as strabo and pliny the elder suggest that glassmaking sands were found near the river belus israel in egypt near the mouth of the volturno river italy and also in spain and france however primary production in the western part of the mediterranean is not supported by any direct archaeological evidence and possible sand raw materials from these regions have never been evaluated for their suitability to produce glass in this study 178 modern beach sands from spain france and italy were analysed for their major and minor elemental compositions by calculating the composition of the glasses that can be produced with these sediments after the addition of pure natron and comparison with the composition of typical roman natron glass we were able to judge whether or not these sands are suitable for roman glass production the results indicate that good glassmaking sands are rather rare only a very limited number of the 178 analysed beach sands would produce a glass with major and minor elemental compositions within the ranges of roman imperial natron glass the rest of the analysed sands are unsuitable for glass production in their present form due to their insufficient sio 2 high al 2 o 3 and fe 2 o 3 and either too low or too high cao contents if the sand raw material was too low in cao extra lime could be added to the glass batch in the form of shell or limestone this was taken into account in a second calculation overall we were able to define six limited areas where suitable sand raw materials would have been available to the roman glassmaker good glassmaking sands occur in the basilicata and puglia regions se italy and tuscany w italy after the addition of an extra source of lime also sands from the huelva province sw spain the murcia region se spain and from the provence se france would produce glasses with a typical roman composition

migration of the kuroshio extension in the northwest pacific since the last glacial maximum abstract the 18o values of planktic and benthic foraminifera and faunal assemblage of planktic foraminifera were investigated at a northwest pacific site 32 16 n 158 13 e 2514 m water depth to understand the oceanographic changes in the kuroshio extension ke region over the past 23 kyr the 18o differences between species and the relative abundances of the dominant planktic foraminiferal species have not changed greatly over the study period suggesting that the subarctic boundary and the subarctic subtropical transition zone have remained north of study site while the study site itself has been under the influence of ke nevertheless increased abundances of foraminiferal taxa that populated the subarctic subtropical transition zone during the last glacial maximum lgm indicate the input of transition zone water through the ke manifest as meandering cold core ring eddies generated along the ke since this unstable surface environment is most pronounced along the main axis of the ke it could have been induced by the southward displacement of the ke main axis to the vicinity of the study site in tandem with the overall southward displacement of the kuroshio oyashio extension system during the lgm the input of transition zone water mass has also increased during the deglacial northern hemisphere cold intervals i e heinrich stadial 1 and the younger dryas suggesting that the strengthened surface wind system regulated the surface ocean condition this demonstrates that the northern high latitudes are the dominant control on post glacial oceanographic changes in the northwest pacific ke region

sea ice switches and abrupt climate change we propose that past abrupt climate changes were probably a result of rapid and extensive variations in sea ice cover we explain why this seems a perhaps more likely explanation than a purely thermohaline circulation mechanism we emphasize that because of the significant influence of sea ice on the climate system it seems that high priority should be given to developing ways for reconstructing high resolution in space and time sea ice extent for past climate change events if proxy data can confirm that sea ice was indeed the major player in past abrupt climate change events it seems less likely that such dramatic abrupt changes will occur due to global warming when extensive sea ice cover will not be present

high resolution evidence for linkages between nw european ice sheet instability and atlantic meridional overturning circulation published studies show that ice rafted debris ird deposition preceding heinrich h events h1 and h2 in the ne atlantic was derived from the nw european ice sheets nweis possibly offering clues about ice sheet sensitivity and stability and the mechanisms that caused periodic collapse of the laurentide ice sheet lis we present detailed lithological and geochemical records including radiogenic isotope fingerprinting of ird deposits from core md01 2461 proximal to the last glacial british ice sheet bis demonstrating persistent instability of the bis with significant destabilisation occurring 1 5 1 9 kyr prior to both h1 and h2 dated at 16 9 and 24 1 kyr bp respectively in the ne atlantic paired mg ca and 18o data from the surface dwelling globigerina bulloides and subsurface dwelling neogloboquadrina pachyderma sinistral are used to determine late glacial variability of temperature salinity and stratification of the upper water column a picture emerges that the bis was in a continuing state of readjustment and never fully reached steady state increased sea surface temperatures appear to have triggered the episode of nweis instability preceding h1 it seems most probable that the so called precursor events were not linked to the h events however if response to a common thermal forcing is considered an increased response time of the lis up to 2 kyr longer than the nweis may be inferred negative salinity excursions of up to 2 6 indicate significant incursions of melt water associated with peaks in nweis instability decreased surface density led to a more stable stratification of the upper water column and is associated with reduced ventilation of intermediate waters recorded in depleted epibenthic 13c cibicidoides wuellerstorfi we suggest that instability and meltwater forcing of the nweis temporarily weakened atlantic meridional overturning circulation allowing transient advance of southern sourced waters to this site prior to h events 1 and 2

effects of glacial meltwater in the giss coupled atmosphereocean model 1 north atlantic deep water response varying magnitudes of freshwater input through the st lawrence are added to different versions of the giss coupled atmosphere ocean model the results show a generally linear response in percentage north atlantic deep water nadw reduction to the volume of water added without any obvious threshold effects when the estimated best guess freshwater input for the allerod younger dryas interval is added only small reductions in nadw production occur in less than a century with complete cessation requiring more than 300 years if the ocean circulation was weaker in the allerod preceding the younger dryas somewhat larger percentage reductions occur and it would take 150 200 years for a complete shutdown the freshening is aided by a positive feedback associated with the reduction in evaporation relative to precipitation in the north atlantic amounting to some 20 30 of the added freshwater runoff when the freshwater input is stopped after complete nadw shutdown nadw production does not resume with complete nadw cessation cooling eventually occurs throughout the northern hemisphere including regions where it is not thought to have arisen during the younger dryas and the globe cools by 1 c due primarily to the sea ice albedo feedback while in many regions the observed cooling is reproduced the cooling in greenland is much less than is estimated with only 50 nadw cessation cooling is primarily around the north atlantic no rapid warming is seen in response to freshwater cessation the sensitivity displayed here for nadw reduction due to freshwater input from the st lawrence is roughly similar to that associated with increased precipitation accompanying global warming in the next century so a similar sensitivity may arise with younger dryas freshwater inputs from other suspected locations greenland europe

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

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

pliny the elder and sr nd isotopes tracing the provenance of raw materials for roman glass production in roman and byzantine times natron glass was traded throughout the known world in the form of chunks production centers of such raw glass active from the 4th to 8th century ad were identified in egypt and syro palestine however early roman primary glass units remain unknown from excavation or scientific analysis the ancient author pliny described in 70 ad that besides egyptian and levantine resources also raw materials from italy and the gallic and spanish provinces were used in glass making in this study the primary provenance of 1st 3rd century ad natron vessel glass is investigated the use of combined sr and nd isotopic analysis allows the distinguishing and characterizing of different sand raw materials used for primary glass production the isotope data obtained from the glass samples are compared to the signatures of primary glass from known production centers in the eastern mediterranean and a number of sand samples from the regions described by pliny the elder as possible sources of primary glass eastern mediterranean primary glass has a nile dominated mediterranean nd signature higher than 6 0 nd while glass with a primary production location in the western mediterranean or north western europe should have a different nd signature lower than 7 0 nd most roman glass has a homogeneous 87sr 86sr signature close to the modern sea water composition likely caused by the intentional use of shell as glass raw material in this way strontium and neodymium isotopes now prove that pliny s writings were correct primary glass production was not exclusive to the levant or egypt in early roman days and factories of raw glass in the western roman empire will have been at play

mixed layer deepening during heinrich events a multi planktonic foraminiferal δ18o approach proxies from greenland ice cores and north atlantic marine sediment cores document repeated extreme climate swings of a few decades to millennia during the last glacial cycle including periods of intense ice rafting called heinrich events hes we have found similar oxygen isotope variations recorded in mixed layer and thermocline dwelling planktonic foraminifera during hes 0 1 and 4 suggesting that three foraminiferal taxa calcified their shells at similar temperatures in a homogenized upperwater column this implies that the surface mixed layer was deeper during hes similar deepening occurred on the northern margin of the ice rafted debris belt implying that these deep mixed layers during hes were widespread in the region we suggest that an increase in storminess during hes intensified the vertical mixing of meltwater from ice rafting in the upper ocean

changes in atmospheric circulation and ocean ice cover over the north atlantic during the last 41 000 years high resolution continuous multivariate chemical records from a central greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41 000 years these chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to greenland defined here as the polar circulation index pci and in the extent of ocean ice cover massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in pci during stadials without discharge events ocean ice cover appears to reach some common maximum level the massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling

adakite like signature of late miocene intrusions at the los pelambres giant porphyry copper deposit in the andes of central chile metallogenic implications adakite like features are recognized in the late miocene 10 ma porphyritic intrusions of the los pelambres giant porphyry copper deposit central chile 32 s located within the southern portion of the flat slab segment 28 33 s of the chilean andes the al and na rich porphyries of los pelambres display distinctly higher sr y 100 300 and lan ybn 25 60 ratios than contemporaneous and barren magmatic units e g la gloria pluton cerro aconcagua volcanic rocks of the same andean magmatic belt strong fractionation of heavy rare earth elements hree absence of eu anomalies high sr y and zr sm and low nb ta ratios suggest melt extraction from a garnet amphibolite source the late miocene adakite like porphyritic intrusions at los pelambres formed closely related in time and space to the subduction of the juan fernandez ridge jfr hotspot chain along the chilean margin current tectonic reconstructions reveal that at the time of formation of the los pelambres rocks a w e segment of the jfr started to subduct beneath them producing a slow down of a previously rapid southward migration of a ne ridge trench collision these particular tectonic conditions are favorable for the origin of the los pelambres porphyry suite by melting of subducting young hotspot rocks under flat slab conditions the incorporation of crustal components into the oceanic lithopheric magma source by subduction erosion is evidenced by the sr nd isotope composition of the los pelambres rocks different from the morb signatures of true adakites a close relationship apparently exists between the origin of this adakite like magmatism and the source of the mineralization in the los pelambres porphyry copper deposit