abrupt changes in antarctic intermediate water circulation over the past 25 000 years the formation and circulation of antarctic intermediate water has varied over glacial interglacial timescales a neodymium record from the atlantic ocean basin suggests that changes in circulation may have been driven by changes both in antarctic intermediate water formation in the southern ocean and in the strength of north atlantic meridional overturning

glacial to holocene changes in the surface and deep waters of the northeast indian ocean abstract stable carbon and oxygen isotopic investigations are carried out on planktonic and benthic foraminifera from an ams dated sediment core of the northeast indian ocean neio to infer glacial to holocene changes in surface and deep waters the chronology of this gravity core sk157 14 water depth 3306 m lat 5 11 n long 90 05 e was established using six ams radiocarbon ages and oxygen isotope stratigraphy variations in 18 o and 13 c values of planktonic globigerinoides ruber and benthic foraminifera cibicidoides spp are suggestive of large changes in the surface and deep water characteristics during the last 60 ka the 18 o pl values in core sk157 14 are significantly higher compared to the sediment cores in the northern bay of bengal and the andaman sea because of the diminished influence of riverine fresh water fluxes large variations in planktonic 18 o pl are noticed during the marine isotopic stage mis 3 1 and 3 3 glacial to holocene 18 o pl amplitude 1 8 is consistent with other published oxygen isotope records from the nearby locations maximum enrichment in 18 o pl occurs at 24 19 and the minimum during 7 6 ka bp spectral analysis of planktonic 18 o pl time series suggests a teleconnection between surface water 18 o and north atlantic climate oscillations benthic foraminiferal 18 o ben values indicate deep water cooling of 1 5 c during the last glacial maximum the 13 c ben values are generally higher for the holocene foraminifera suggesting greater contribution from the north atlantic deep water nadw however glacial benthic foraminifera are characterized by lower 13 c ben values highly depleted 13 c ben values during the 60 50 21 17 and 13 11 ka bp intervals suggest decrease contribution from the north atlantic deep water nadw and increase influx from the southern ocean deep water sodw in addition oxidation of organic matter and ageing of the deep water may have contributed in the pronounced decrease in 13 c ben during the glacial intervals

atlantic meridional overturning circulation during the last glacial maximum the circulation of the deep atlantic ocean during the height of the last ice age appears to have been quite different from today we review observations implying that atlantic meridional overturning circulation during the last glacial maximum was neither extremely sluggish nor an enhanced version of present day circulation the distribution of the decay products of uranium in sediments is consistent with a residence time for deep waters in the atlantic only slightly greater than today however evidence from multiple water mass tracers supports a different distribution of deep water properties including density which is dynamically linked to circulation

records of the nd isotope composition of seawater from the bay of bengal implications for the impact of northern hemisphere cooling on itcz movement abstract this study presents a record of planktonic foraminiferal neodymium isotopic gradients along a north south transect in the bay of bengal during time slices of late holocene and last glacial maximum lgm age together with a record of planktonic foraminiferal variation in the northern bay of bengal 15 n over the last 195 ky in late holocene core top planktonic foraminifera the north south end gradient rises from nonradiogenic values of 12 at 20 n to 10 at 5 n in parallel with the modern surface salinity gradient controlled by discharge of himalayan rivers in the northern bay during the lgm end increased throughout the bay the contrast between northernmost and southernmost sites decreased and maximum end values of 6 5 occurred between 12 and 15 n a small part of the shift to higher mean end throughout the bay during the glacial may arise from a uniform increase in deposition of far field dust from arabian and persian gulf regions however the spatial pattern of end variation between lgm and late holocene also suggests a shift from modern dominance of nonradiogenic nd sources from the ganges brahmaputra basin to lgm dominance of more radiogenic nd sources from arakan coastal rivers over the last 195 ky at 15 n the most radiogenic end values of 7 occur at glacial maxima and the most nonradiogenic values of 11 occur during interglacials end values are highly correlated with glacial interglacial variations in planktonic foraminiferal 18o in this record shifts in river sources from the more northerly ganges brahmaputra watershed to the more southerly arakan coastal river systems respond dominantly to inter tropical convergence zone itcz movement driven by northern hemisphere cooling during 100 ky glacial interglacial cycles with a small component of variation on precessional timescales the nonlinear correlation of end with ice volume suggests that itcz movement responds to aerial coverage of ice sheets and snow rather than to ice thickness and volume these data add support to recent general circulation models of itcz response to northern hemisphere ice sheets which simulate decreased glacial precipitation in the ganges brahmaputra basin and increased glacial precipitation in the southern arakan coastal basin

paleoceanographic record of the last glacial interglacial cycle in the red sea and gulf of aden abstract hydrographic conditions in the red sea are strongly controlled by regional climatic conditions and the restricted water exchange with the gulf of aden indian ocean in turn intermediate and deep water masses in the gulf of aden reflect the nature of red sea outflow planktonic and benthic foraminiferal faunas and the lithology and mineralogy of red sea and gulf of aden sediments were studied in order to evaluate changes in water mass conditions in the two basins during the last 18 000 years the results indicate that changes in the local climate and circulation regime during this period resulted in significant hydrographic changes in surface and bottom waters in the red sea and intermediate waters in the gulf of aden during the last glacial maximum high aridity and glacio eustatic sea level lowering resulted in surface and bottom water salinities in the red sea which were considerably higher than at present in the gulf of aden glacial surface salinities and temperatures remained similar to holocene values while surface water productivity may have been lower surface salinities in the red sea decreased after 18 000 years b p as the connection between the red sea and gulf of aden was reestablished however bottom water salinities remained high until at least 11 000 years b p pluvial conditions during deglaciation enhanced the density difference between surface and bottom waters in the red sea and resulted in a decrease in the oxygen content of the bottom waters hydrographic conditions in the western gulf of aden reflect a change in the properties of outflowing red sea water during deglaciation

a sequence of partial melting reactions at mt stafford central australia metasedimentary gneisses show a rapid change in grade in a 10 km wide low p high t regional aureole at mt stafford in the arunta block central australia migmatite occurs in all but the lowermost of five metamorphic zones which grade from greenschist zone 1 through amphibolite zones 2 3 to granulite facies zones 4 5 the sequence of partial melting reactions inferred for metapelitic rocks is dependant upon protolith temperature and fluid conditions the metapelite solidus in zone 2 reflects vapour present melting at p 3 kbar and t 640 c melting having initially been controlled by the congruent breakdown of the assemblage crd kfs bt qtz at slightly higher temperature andalusite in leucosome formed via the reaction kfs qtz bt h2oand melt and melt having been stabilized by the presence of boron sillimanite coaxially replaces andalusite in the high grade portion of zone 2 in zone 3 large aluminosilicate aggregates in leucosome are armoured by spl crd grt symplectites garnet partially pseudomorphs biotite cordierite or spinel in high grade portions of zone 3 zone 4 grt crd opx bearing metapsammite assemblages and garnet bearing leucosome reflect t 800 c and p 2 2 0 9 kbar in the model kfmash system the principal vapour absent melting step reflected significant modal changes related to the breakdown of the as bt tie line and the establishment of the spl crd tie line the bulk rock geochemistry of migmatite samples straddle the spl crd tie line the aluminous bulk rock composition of the common bedded migmatite restricted its potential to witness garnet forming and orthopyroxene forming reactions minor textural and modal changes in and above zone 3 reflecting biotite destablization in biotite poor assemblages

synchronous deglacial overturning and water mass source changes understanding changes in ocean circulation during the last deglaciation is crucial to unraveling the dynamics of glacial interglacial and millennial climate shifts we used neodymium isotope measurements on postdepositional iron manganese oxide coatings precipitated on planktonic foraminifera to reconstruct changes in the bottom water source of the deep western north atlantic at the bermuda rise comparison of our deep water source record with overturning strength proxies shows that both the deep water mass source and the overturning rate shifted rapidly and synchronously during the last deglacial transition in contrast any freshwater perturbation caused by heinrich event 1 could have only affected shallow overturning these findings show how changes in upper ocean overturning associated with millennial scale events differ from those associated with whole ocean deglacial climate events

no signature of abyssal carbon in intermediate waters off chile during deglaciation the rise in atmospheric carbon dioxide at the end of the last glacial maximum has been attributed to the release of carbon dioxide from the deep southern ocean however reconstructions of the radiocarbon signature of chilean margin intermediate waters during the glacial termination do not reflect the influence of such a release

13c record of benthic foraminifera in the last interglacial ocean implications for the carbon cycle and the global deep water circulation the 13c 12c ratios of upper holocene benthic foraminiferal tests genera cibicides and uvigerina of deep sea cores from the various world ocean basins have been compared with those of the modern total carbon dioxide tco2 measured during the geosecs program the 13c difference between benthic foraminifera and tco2 is 0 07 0 04 for cibicides and 0 83 0 07 for uvigerina at the 95 confidence level 13c analyses of the benthic foraminifera that lived during the last interglaciation isotopic substage 5e about 120 000 yr ago show that the bulk of the tco2 in the world ocean had a 13c value 0 15 0 12 lower than the modern one at the 95 confidence level reflecting a depletion compared to the present value of the global organic carbon reservoir regional differences in 13c between the various oceanic basins are explained by a pattern of deep water circulation different from the modern one the antarctic bottom water production was higher than today during the last interglaciation but the eastward transport in the circumpolar deep water was lower

rapid changes in ocean circulation and atmospheric radiocarbon a latitude depth coupled global ocean ice atmosphere model is extended to include a simple biosphere component a physically reasonable adjustment of runoff into the north atlantic is invoked to achieve a transient response to glacial meltwater perturbations which closely resembles the younger dryas climate event we then investigate the evolution of the isotopic ratio of atmospheric radiocarbon 14c due to the rapid changes of deep ocean circulation when the north atlantic branch of the conveyor belt circulation is interrupted the oceanic uptake of radiocarbon is reduced resulting in an increase of atmospheric 14c by about 35 the reduction of ventilation in the north atlantic is partly compensated by an increase of the 14c ratios of the biosphere the southern ocean and the upper ocean above 1000 m depth a plateau of the 14c year calendar year relation can be generated at the time of the rapid reinitiation of deep ocean ventilation which begins coincident with the major temperature increase and lasts for about 60 years it is hence significantly shorter than that found by analyzing tree rings during the termination of younger dryas longer than 400 years a sensitivity study reveals that the duration of the plateau depends strongly on the transient evolution of the gas exchange rate and can increase to 150 300 years if changes of pco2 or sea ice coverage are taken into account

the influence of air sea exchange on the isotopic composition of oceanic carbon observations and modeling although the carbon isotropic composition of ocean waters after they leave the surface ocean is determined by biological cycling air sea exchange affects the carbon isotopic composition of surface waters in two ways the equilibrium fractionation between oceanic and atmospheric carbon increases with decreasing temperature in southern ocean surface waters this isotopic equilibrium enriches delta sup 13 c relative to the delta sup 13 c expected from uptake and release of carbon by biological processes alone similarly surface waters in the subtropical gyres are depleted in delta sup 13 c due to extensive air sea exchange at warm temperatures countering the tendency toward isotopic equilibration with the atmosphere a relatively slow process are the effects of the equilibration of co sub 2 itself a much faster process in regions where there is a net transfer of isotopically light co sub 2 from the ocean to the atmosphere e g the equator surface waters become enriched in sup 13 c whereas in regions where isotopically light co sub 2 is entering the ocean e g the north atlantic surface waters become depleted in sup 13 c a compilation of high quality oceanic delta sup 13 c measurements along with experiments performed using a zonally averaged three basin dynamic ocean model are used to explore these processes 40 refs 14more figs 1 tab less

deglacial variability of antarctic intermediate water penetration into the north atlantic from authigenic neodymium isotope ratios 1 understanding intermediate water circulation across the last deglacial is critical in assessing the role of oceanic heat transport associated with atlantic meridional overturning circulation variability across abrupt climate events however the links between intermediate water circulation and abrupt climate events such as the younger dryas yd and heinrich event 1 h1 are still poorly constrained here we reconstruct changes in antarctic intermediate water aaiw circulation in the subtropical north atlantic over the past 25 kyr by measuring authigenic neodymium isotope ratios in sediments from two sites in the florida straits our authigenic nd isotope records suggest that there was little to no penetration of aaiw into the subtropical north atlantic during the yd and h1 variations in the northward penetration of aaiw into the florida straits documented in our authigenic nd isotope record are synchronous with multiple climatic archives including the greenland ice core 18o record the cariaco basin atmosphere 14c reconstruction the bermuda rise sedimentary pa th record and nutrient and stable isotope data from the tropical north atlantic the synchroneity of our nd records with multiple climatic archives suggests a tight connection between aaiw variability and high latitude north atlantic climate change

enhanced arabian sea intermediate water flow during glacial north atlantic cold phases abstract during the last glacial period polar ice cores indicate climate asynchrony between the poles at the millennial time scale yet surface ocean circulation in large parts of the globe varied in tune with greenland temperature fluctuations suggesting that any anti phase behavior to a substantial degree must lie in the deeper global ocean circulation which is poorly understood outside the atlantic ocean here we present data from the north western indian ocean which indicate that the timing of maxima in northward extensions of glacial antarctic intermediate water gaaiw coincides with dramatically reduced thermohaline overturn in the north atlantic associated with the heinrich ice surge events he the repeated expansion of the gaaiw during hes recorded far north of the equator in the arabian sea suggests that southern hemisphere driven intermediate water mass variability forms an integral part of the inter hemisphere asynchronous climate change behavior at the millennial time scale

radiocarbon reservoir age of high latitude north atlantic surface water during the last deglacial the radiocarbon reservoir age of high latitude north atlantic ocean surface water is essential for linking the continental and marine climate records and is expected to vary according to changes in north atlantic deep water nadw production measurements from this region also provide important input and or tests of oceanic radiocarbon using 3 d global ocean circulation models here we present a surface water radiocarbon reservoir age record of the high latitude western north atlantic for the deglacial period via the use of fossil cold water corals growing in waters that are rapidly exchanged with nearby surface waters the reservoir age of high latitude north atlantic surface waters was computed from the radiocarbon age difference between our radiocarbon calibration record http radiocarbon ldeo columbia edu and our marine radiocarbon data 230th 234u 238u dates provide the absolute coral ages our high latitude north atlantic ocean reservoir age data combined with recalculated reservoir ages based on published coexisting terrestrial and marine material and vedde ash radiocarbon dates from central and eastern north atlantic show modern values 380 140 year n 14 during the bolling and allerod warm period and a 200 year increase in reservoir age 590 130 year n 10 during the entire younger dryas yd cold episode the reservoir age then decreased to 270 20 year n 2 at the preboreal yd transition although the dates are too sparse for us to be confident in this estimate we are not able to resolve the timing of the transition to increased reservoir ages from the mid allerod to the yd due to the relatively small change and correspondingly large uncertainty in the estimates the atmospheric 14c record derived from our atmospheric radiocarbon record displays a 40 per mil increase from 12 900 to 12 650 cal years bp coincident with the shift to high reservoir ages in the early yd cold event intrusion of 14c depleted antarctic intermediate water aaiw to the high latitude north atlantic and reduction of nadw formation are possible causes for the coincident shift to high reservoir ages in the north atlantic surface ocean and increased atmospheric 14c during the beginning of the yd event

deep sea faunal provinces and their inferred environments in the indian ocean based on distribution of recent benthic foraminifera abstract multivariate analysis was performed on percentages of 46 species of unstained deep sea benthic foraminifera from 131 core top to near core top samples 322 5013 m from across the indian ocean faunal data are combined with geosecs geochemical data to investigate any relationship between benthic foraminifera assemblages and species and deep sea properties in general benthic foraminifera show a good correlation to surface productivity organic carbon flux to the sea floor deep sea oxygenation and to a lesser extent to bottom temperature without correlation with the water depths the foraminiferal census data combined with geochemical data has enabled the division of the indian ocean into two faunal provinces province a occupies the northwestern indian ocean arabian sea region where surface primary production has a major maximum during the summer monsoon season and a secondary maximum during winter monsoon season that leads to high organic flux to the seafloor making the deep sea one of the most oxygen deficient regions in the world ocean with a pronounced oxygen minimum zone omz this province is dominated by benthic foraminifera characteristic of low oxygen and high organic food flux including uvigerina peregrina robulus nicobarensis bolivinita pseudopunctata bolivinita sp bulimina aculeata bulimina alazanensis ehrenbergina carinata and cassidulina carinata province b covers southern southeastern and eastern parts of the indian ocean and is dominated by nuttallides umbonifera epistominella exigua globocassidulina subglobosa uvigerina proboscidea cibicides wuellerstorfi cassidulina laevigata pullenia bulloides pullenia osloensis pyrgo murrhina oridorsalis umbonatus gyroidinoides gyroidina soldanii and gyroidinoides cf gemma suggesting well oxygenated cold deep water with low oligotrophic and pulsed food supply

deglacial whole ocean δ13c change estimated from 480 benthic foraminiferal records terrestrial carbon storage is dramatically decreased during glacial periods due to cold temperatures increased aridity and the presence of large ice sheets on land most of the carbon released by the terrestrial biosphere is stored in the ocean where the light isotopic signature of terrestrial carbon is observed as a 0 32 0 7 depletion in benthic foraminiferal 13c the wide range in estimated 13c change results from the use of different subsets of benthic 13c data and different methods of weighting the mean 13c by volume we present a more precise estimate of glacial interglacial 13c change of marine dissolved inorganic carbon using benthic cibicidoides spp 13c records from 480 core sites more than 3 times as many sites as previous studies we divide the ocean into eight regions to generate linear regressions of regional 13c versus depth for the late holocene 0 6 ka and last glacial maximum 19 23 ka and estimate a mean 13c decrease of 0 38 0 08 2 for 0 5 5 km estimating large uncertainty ranges for 13c change in the top 0 5 km below 5 km and in the southern ocean we calculate a whole ocean change of 0 34 0 19 this implies a terrestrial carbon change that is consistent with recent vegetation model estimates of 330 694 gt c additionally we find that a well constrained surface ocean 13c change is essential for narrowing the uncertainty range of estimated whole ocean 13c change

textural analysis of magmatic enclaves from the kameni islands santorini greece abstract the kameni islands have been the focus of historic volcanic activity on santorini greece the islands comprise a series of dacite lavas the erupted compositions of which have remained approximately constant for the last 2200 years the dacite lava flows of nea kameni contain a variety of mafic enclaves distinguished by differences in texture composition and mechanical behaviour the mafic enclaves represent chilled fragments of mafic magma that crystallised rapidly on contact with the cooler more silicic host magma the absence of chilled margins on the enclaves suggests that the replenishing magma initially formed a dense layer at the base of the chamber groundmass textures are interpreted as an indication of the degree of undercooling between the enclaves and the host groundmass textural information obtained from the enclaves has been used to determine the relative volumes of replenishing magmas injected into the host magma before eruption which indicates that the volume of erupted magma is directly proportional to the volume of replenishing magma emplaced in the chamber prior to eruption which thus may act as a potential eruption trigger the variety of replenishing magmas implies the existence of a complex conduit and chamber system beneath santorini volcano andesitic enclaves with linear crystal size distributions are thought to have originated as an aphyric andesitic melt expelled from a crystal mush by filter pressing disequilibrium phenocryst assemblages in the lavas and phenocryst bearing enclaves provide evidence for the entrainment and recycling of older phenocryst populations

radiocarbon evidence for alternating northern and southern sources of ventilation of the deep atlantic carbon pool during the last deglaciation recent theories for glacial interglacial climate transitions call on millennial climate perturbations that purged the deep sea of sequestered carbon dioxide via a bipolar ventilation seesaw however the viability of this hypothesis has been contested and robust evidence in its support is lacking here we present a record of north atlantic deep water radiocarbon ventilation which we compare with similar data from the southern ocean a striking coherence in ventilation changes is found with extremely high ventilation ages prevailing across the deep atlantic during the last glacial period the data also reveal two reversals in the ventilation gradient between the deep north atlantic and southern ocean during heinrich stadial 1 and the younger dryas these coincided with periods of sustained atmospheric co2 rise and appear to have been driven by enhanced ocean atmosphere exchange primarily in the southern ocean these results confirm the operation of a bipolar ventilation seesaw during deglaciation and underline the contribution of abrupt regional climate anomalies to longer term global climate transitions

glacial interglacial variations in the neodymium isotope composition of seawater in the bay of bengal recorded by planktonic foraminifera this study presents neodymium isotope and elemental data for cleaned planktonic foraminifera from odp site 758 in the southernmost reaches of the bay of bengal in the north east indian ocean cleaning experiments using oxidative reductive techniques suggest that diagenetic fe mn oxyhydroxide coatings can be effectively removed and that the measured nd isotope composition reflects the composition of seawater from which the foraminiferal calcium carbonate was precipitated modern core top pulleniatina obliquiloculata and globorotalia menardii give end values of 10 12 0 16 and 10 28 0 16 respectively indistinguishable from recent direct measurements of surface seawater in this area a high resolution nd isotope record obtained from g menardii for the past 150 kyr shows systematic variations end 3 on glacial interglacial timescales the timing of those variations shows a remarkable correspondence with the global oxygen isotope record which suggests a process controlling the nd isotope composition that responds in phase with global climate cycles palaeoclimate reconstruction indicates that during the last glacial maximum changes in monsoon circulation resulted in a reduction in rainfall over the indian subcontinent and a decrease in the flux of river water delivered to the bay of bengal thus changes in the riverine input of nd a change in either flux or composition most likely caused the isotope variations although changes in dust source or local ocean circulation may have also played a role these results clearly establish a link between climate change and variations in radiogenic isotopes in the oceans and illustrate the potential of nd isotopes in foraminifera for high resolution palaeoceanographic reconstruction

carbon 13 in pacific deep and intermediate waters 0 370 ka implications for ocean circulation and pleistocene co2 stable isotopes in benthic foraminifera from pacific sediments are used to assess hypotheses of systematic shifts in the depth distribution of oceanic nutrients and carbon during the ice ages the carbon isotope differences between 1400 and 3200 m depth in the eastern pacific are consistently greater in glacial than interglacial maxima over the last 370 kyr this phenomenon of bottom heavy glacial nutrient distributions which boyle proposed as a cause of pleistocene co2 change occurs primarily in the 1 100 and 1 41 kyr 1 milankovitch orbital frequency bands but appears to lack a coherent 1 23 kyr 1 band related to orbital precession averaged over oxygen isotope stages glacial 13c gradients from 1400 to 3200 m depth are 0 1 greater than interglacial gradients the range of extreme shifts is somewhat larger 0 2 to 0 5 in both cases these changes in pacific 13c distributions are much smaller than observed in shorter records from the north atlantic this may be too small to be a dominant cause of atmospheric pco2 change unless current models underestimate the sensitivity of pco2 to nutrient redistributions this dampening of pacific relative to atlantic 13c depth gradient favors a north atlantic origin of the phenomenon although local variations of pacific intermediate water masses can not be excluded at present

the release of 14 c depleted carbon from the deep ocean during the last deglaciation evidence from the arabian sea article i nfo during the last deglaciation the concentration of co2 in the atmosphere increased and the radiocarbon activity 14 c of the atmosphere declined in two steps corresponding in timing to heinrich stadial 1 and the younger dryas these changes have been attributed to the redistribution of 14 c depleted carbon from the deep ocean into the upper ocean and atmosphere recently reconstructions of 14 c in intermediate waters of the eastern tropical pacific have revealed pulses of very old water during the deglaciation consistent with the release of 14 c depleted carbon from the deep ocean at this time here we present reconstructions of intermediate water 14 c from the northern arabian sea near the coast of oman these reconstructions record significant aging of intermediate waters in the arabian sea during heinrich stadial 1 and to a lesser extent during the younger dryas the timing and magnitude of 14 c depletion in the arabian sea during heinrich stadial 1 is very similar to that previously observed in the eastern north pacific near baja california indicating that similar mechanisms were involved in controlling 14 c at these two sites the most parsimonious explanation of the 14 c records from the arabian sea and baja california remains the release of 14 c depleted carbon from the deep ocean by renewal of upwelling and mixing in the southern ocean these

south atlantic intermediate water advances into the north east atlantic with reduced atlantic meridional overturning circulation during the last glacial period the nd isotopic composition end of seawater and cold water coral cwc samples from the gulf of cadiz and the alboran sea at a depth of 280 827 m were investigated in order to constrain middepth water mass dynamics within the gulf of cadiz over the past 40 ka end of glacial and holocene cwc from the alboran sea and the northern gulf of cadiz reveals relatively constant values 8 6 to 9 0 and 9 5 to 10 4 respectively such values are similar to those of the surrounding present day middepth waters from the mediterranean outflow water mow end 9 4 and mediterranean sea water msw end 9 9 in contrast glacial end values for cwc collected at thermocline depth 550 827 m in the southern gulf of cadiz display a higher average value 8 9 0 4 compared to the present day value 11 7 0 3 this implies a higher relative contribution of water masses of mediterranean msw or south atlantic origin east antarctic intermediate water eaaiw our study has produced the first evidence of significant radiogenic end values 8 at 19 23 24 and 27 ka which are coeval with increasing iceberg discharges and a weakening of atlantic meridional overturning circulation amoc since mow end values remained stable during the last glacial period it is suggested that these radiogenic end values most likely reflect an enhanced northward propagation of glacial eaaiw into the eastern atlantic basin

sulphide and oxide minerals from the ohmine granitic rocks in kii peninsula central japan and their primary paragenetic relations in the ohmine granitic rocks of kii peninsula central japan ilmenite rutile pyrrhotite pyrite and chalcopyrite commonly occur but no magnetite is present their primary paragenetic relations were confirmed by examining their mode of occurrences as inclusion species in major silicate minerals and the phase relations in the cu fe s system though their parageneses changed in cooling of the rocks this makes it possible to estimate the fugacities of oxygen and sulfur in the granitic rocks based upon their paragenetic relations and to discuss the nature of volatiles in the granitic rocks significant subsolidus reactions for sulfide minerals continued until the rocks cooled below 300 c and took place in two types of mineral grains in groundmass and as inclusions the removal of sulfur and copper through the silicate crystals was too easy to preserve the chemistry of sulfides included in silicates

sulfide and oxide minerals from s type and i type granitic rocks abstract in the ohmine i type and s type granitic rocks of miocene age kii peninsula central japan ilmenite rutile pyrrhotite pyrite and chalcopyrite are common but no magnetite is present the primary paragenetic relations of these minerals are determined by their modes of occurrence as inclusions within major plagioclase orthoclase quartz hornblende and biotite although their parageneses changed during cooling significant subsolidus reactions for sulfide minerals took place in both the groundmass and the inclusions until the rocks cooled below 300 c the loss of s and cu through silicate crystals was too easy to preserve the chemistry of sulfides included in silicates however the removal of ni through silicate crystals as well as along grain boundaries was restricted as indicated by the fact that the distribution frequency of ni bearing pyrrhotite is higher in inclusions than in the groundmass and significantly higher in i type cognate enclaves than in host i type rocks nickel bearing pyrrhotite is common in i type but rare in s type rocks sedimentary enclaves restates and country rocks this eliminates the possibility that the ohmine s type rocks were formed by interaction of i type magma and sedimentary rocks or by mixing between i type and an ideal s type magmas as interpreted from the chemistry of biotite and the chronology of these rocks on the basis of mineralogy and isotopic data for s o sr c and rare gases it was shown that i type granitic rocks were derived from partial melting of intermediate igneous rocks containing hornblende and plagioclase and s type from partial melting of sedimentary rocks containing biotite and orthoclase

investigating the sensitivity of glaciers to climate variability since the mis 2 in the upper ganga catchment saraswati valley central himalaya abstract moraines outwash gravel terraces fluvial drapes and lacustrine sequences are used to infer the pattern of glacial fluctuations in the saraswati valley upper ganga catchment located in transitional climatic zone between dry steppe of the tibetan plateau in the north and sub humid higher himalaya in the south the saraswati valley has preserved evidence of four glacier advances these are identified as the saraswati glacial stage sgs 1 oldest to sgs 4 youngest based on the relative dating and luminescence ages obtained on younger advances the sgs 1 is ascribed to pre marine isotopic stage mis 2 the sgs 2 is dated to the mis 2 24 5 2 8 21 2 2 0 ka the sgs 3 is speculatively ascribed to the younger dryas yd and the sgs 4 is suggested to be of the mid holocene 6 ka age the bifurcated moraine ridges of sgs 2 represent standstill conditions during the post last glacial maximum lgm period the deglaciation is represented by outwash gravel terraces impounded sedimentary lacustrine sequences and fluvial drapes overlying and abutting the moraines are dated to early mid 11 9 0 9 7 5 0 6 ka and late holocene 3 3 0 2 1 7 0 3 ka intensified moderate indian summer monsoon considering the timing of glacial advances and stand still condition it is proposed that across the orographic barrier rain shadow valleys glaciers responded sensitively to the intensified anticyclonic flow of the cooler mid latitude westerlies implying that in a monsoon dominated transient climatic zone even the rain shadow valleys responded sensitively to temperature changes

rapid deglacial injection of nutrients into the tropical atlantic via antarctic intermediate water highlights first high resolution cdw record from caribbean intermediate waters rapid nutrient enrichment during hs1 and yd tropical n atlantic aaiw nutrient content controlled by southern ocean enhanced aaiw nutrient content likely fed low to high latitude productivity dampening of the deglacial global co2 rise by aaiw nutrient enrichment as part of the return flow of the atlantic overturning circulation antarctic intermediate water aaiw redistributes heat salt co2and nutrients from the southern ocean to the tropical atlantic and thus plays a key role in ocean atmosphere exchange it feeds sub tropical upwelling linking high and low latitude ocean biogeochemistry but the dynamics of aaiw during the last deglaciation remain poorly constrained we present new multi decadal benthic foraminiferal cd ca and stable carbon isotope 13c records from tropical w atlantic sediment cores indicating abrupt deglacial nutrient enrichment of aaiw as a consequence of enhanced deglacial southern ocean upwelling intensity this is the first clear evidence from the intermediate depth tropical w atlantic that the deglacial reconnection of shallow and deep atlantic overturning cells effectively altered the aaiw nutrient budget and its geochemical signature the rapid nutrient injection via aaiw likely fed temporary low latitude productivity thereby dampening the deglacial rise of atmospheric co2

benthic foraminiferal δ13c and accumulation rates of organic carbon uvigerina peregrina group and cibicidoides wuellerstorfi the glacial to interglacial 13c records of the benthic foraminifera cibicidoides wuellerstorfi and the uvigerina peregrina group from deep sea cores cannot be adjusted by a generally valid constant the 13c values of the u peregrina group largely correlate with the accumulation rates of organic carbon suggesting a local habitat effect those of c wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the 13c of the ambient bottom water isotopic composition

onset of deglacial warming in west antarctica driven by local orbital forcing an annually resolved ice core record from west antarctica indicates that warming driven by local insolation resulting from sea ice decline began in that region about 2 000 years before warming in east antarctica reconciling two alternative explanations for deglacial warming in the southern hemisphere

surface and deep water changes in the northeast indian ocean during the last 60 ka inferred from carbon and oxygen isotopes of planktonic and benthic foraminifera abstract stable carbon and oxygen isotopic records of planktonic globigerinoides ruber and benthic foraminifera mostly cibicidoides wuellerstorfi from a deep sea core in the northeast indian ocean are used to infer surface and deep water characteristics for the last 60 kyr the gravity core sk 157 14 studied here was retrieved from the ninetyeast ridge 5 11 n 90 05 e at a water depth of 3306 m chronology of the core was established using nine radiocarbon dates and oxygen isotope stratigraphy significant variations in 18o during the last 2 60 kyr bp are suggestive of large changes in monsoonal precipitation over the indian sub continent the last glacial maximum lgm to holocene shift in planktonic foraminifera 18o 1 64 is less than documented earlier from the bay of bengal cores two prominent negative 18o excursions at 8 7 and 20 18 kyr bp are attributed to the sudden influx of freshwater as a result of intensified monsoonal precipitation large fluctuations in 18o of g ruber during the holocene suggest variability in riverine input planktonic 18o values show a combined effect of increased sea surface salinity and decreased sea surface temperature sst during the lgm in contrast the planktonic 13c values are not linked to the glacial to holocene transition comparison of the benthic 18o and 13c time series with those of a pacific core rc13 110 suggests a similar glacial deep water evolution the lgm to holocene 18o shift in benthic foraminifera mostly c wuellerstorfi exceeds the ice volume effect by 0 5 indicating a glacial deep water cooling of 2 c assuming no salinity change variations in the distribution of 13c in the glacial northeast indian ocean neio are most likely the result of deep ocean circulation changes the glacial deep neio 13c characteristics clearly point to reduced north atlantic deep water nadw input consequently the contribution from the southern ocean deep water may have increased resulting in low 13c a positive shift in 13c during the early deglaciation is consistent with other records from this region deglacial 13c fluctuations appear to have been caused by the switch on and off of nadw production

distant origin of circulation changes in the indian ocean during the last deglaciation abstract well dated benthic foraminifera isotopic records reveal that circulation changes repeatedly took place in the tropical indian ocean around 2000 m depth over the last deglaciation we show that the observed changes can be explained by large scale reorganization of intermediate water masses in the atlantic and indian oceans more specifically during heinrich event 1 and the younger dryas while the formation of north atlantic deep water was greatly reduced brine formation in the north atlantic and nordic seas led to the production of intermediate waters that extended far enough in the south atlantic to be deflected by the circumpolar currents into the indian ocean basin creating a circulation branch at intermediate depths that was more active than today in contrast during the last glacial maximum the bolling allerod and after the younger dryas there was no rapid transport of intermediate waters from the north atlantic to the south atlantic or indian ocean around 2000 m depth

sequence of events during the last deglaciation in southern ocean sediments and antarctic ice cores variation depends on the age model as 14 c determinations cannot be obtained for the time interval of 29 5 14 5 ka assuming a constant sedimentation rate for this interval our data suggest that sea ice and nutrient changes at about 19 ka b p lead the increase in atmospheric pco2 by approximately 2000 years our diatom based sea ice record is in phase with the sodium record of the vostok ice core which is related to sea ice cover and similarly leads the increase in atmospheric co2 if gas exchange played a major role in determining glacial to interglacial co2 variations then a delay mechanism of a few thousand years is needed to explain the observed sequence of events otherwise the main cause of atmospheric pco2 change must be sought elsewhere rather than in the southern ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4267 oceanography general paleoceanography 4845 oceanography biological and chemical nutrients and nutrient cycling 4870 oceanography biological and chemical stable isotopes 9325 information related to geographic region atlantic ocean keywords biogenic opal stable isotopes diatoms ird last glacial southern ocean

changes in intermediate circulation in the bay of bengal since the last glacial maximum as inferred from benthic foraminifera assemblages and geochemical proxies benthic foraminiferal assemblages and geochemical tracers delta o 18 delta c 13 and c 14 have been analyzed on benthic and planktonic foraminifera from core md77 176 located in the northern bay of bengal in order to reconstruct the evolution of intermediate circulation in the northern indian ocean since the last glaciation results indicate that during the last glacial maximum lgm southern sourced water masses were dominant at the core site a high relative abundance of intermediate and deep infaunal species during the lgm reflects low oxygen concentration and or mesotropic to eutrophic deep water conditions associated with depleted benthic delta c 13 values during the holocene benthic foraminiferal assemblages indicate an oligotropic to mesotrophic environment with well ventilated bottom water conditions compared with lgm higher values for benthic foraminifera delta c 13 and b p c 14 age offsets suggest an increased contribution of north atlantic deep water to the northern bay of bengal during the late holocene compared to the lgm millennial scale events punctuated the last deglaciation with a shift in the delta c 13 and the epsilon nd values coincident with low b p c 14 age offsets providing strong evidence for an increased contribution of antarctic intermediate water at the studied site this was associated with enhanced upwelling in the southern ocean reflecting a strong sea atmospheric co2 exchange through southern ocean ventilation during the last deglaciation

crystal size distributions csd in three dimensions insights from the 3d reconstruction of a highly porphyritic rhyolite growth histories and residence times of crystals in magmatic systems can be revealed by studying crystal sizes size distributions and shapes in this contribution serial sectioning has been employed on a sample of porphyritic rhyolite from a permo carboniferous laccolith from the halle volcanic complex germany to reconstruct the distribution of felsic phenocrysts in three dimensions in order to determine their true shapes sizes and three dimensional size distributions a model of all three phenocryst phases quartz plagioclase k feldspar with 217 crystals and a larger model containing 1599 k feldspar crystals was reconstructed in three dimensions the first model revealed a non touching framework of crystals in three dimensions suggesting that individual crystals grew freely in the melt prior to quenching of the texture however crystal shapes are complex and show large variation on a zingg diagram intermediate over long axis plotted against short over intermediate axis they often do not resemble the crystallographic shapes expected for phenocrysts growing unhindered from a melt indicating complex growth histories in contrast the three dimensional size distribution is a simple straight line with a negative slope stereologically corrected size distributions from individual sections compare well with stereologically corrected size distributions obtained previously from the same sample however crystal size distribution csd data from individual sections scatter considerably it is shown that csds can be robustly reproduced with a sampling size of greater than 200 crystals the kind of shape assumed in stereological correction of csds however has a large influence on the calculation and estimation of crystal residence times

strong and deep atlantic meridional overturning circulation during the last glacial cycle extreme abrupt northern hemisphere climate oscillations during the last glacial cycle 140 000 years ago to present were modulated by changes in ocean circulation and atmospheric forcing1 however the variability of the atlantic meridional overturning circulation amoc which has a role in controlling heat transport from low to high latitudes and in ocean co2 storage is still poorly constrained beyond the last glacial maximum2 3 4 here we show that a deep and vigorous overturning circulation mode has persisted for most of the last glacial cycle dominating ocean circulation in the atlantic whereas a shallower glacial mode with southern sourced waters filling the deep western north atlantic prevailed during glacial maxima3 5 our results are based on a reconstruction of both the strength and the direction of the amoc during the last glacial cycle from a highly resolved marine sedimentary record in the deep western north atlantic parallel measurements of two independent chemical water tracers the isotope ratios of 231pa 230th and 143nd 144nd 6 7 8 which are not directly affected by changes in the global cycle reveal consistent responses of the amoc during the last two glacial terminations any significant deviations from this configuration resulting in slowdowns of the amoc were restricted to centennial scale excursions during catastrophic iceberg discharges of the heinrich stadials severe and multicentennial weakening of north atlantic deep water formation occurred only during heinrich stadials close to glacial maxima with increased ice coverage probably as a result of increased fresh water input in contrast the amoc was relatively insensitive to submillennial meltwater pulses during warmer climate states and an active amoc prevailed during dansgaard oeschger interstadials greenland warm periods

structural study of two quartzite varieties from the utrillas facies formation olmos de atapuerca burgos spain from a petrographic characterisation to a functional analysis design abstract this overall research initiative was undertaken to evaluate the role of lithic raw material variability in use wear formation processes focusing specifically on two lithological varieties of quartzite present in the lower and middle pleistocene lithic assemblages of the gran dolina galeria and sima del elefante sites sierra de atapuerca burgos two arenas de utrillas facies varieties from a sand quarry located in olmos de atapuerca were studied using petrographic and sem analyses they were both identified as metaquartzites revealing differences in their granular structure and metamorphic grade sequential experiments employing the same quartzite varieties were then conducted involving different activities and several worked materials which made it possible to determine use wear formation on these two quartzite varieties the results helped to clarify the role of intra raw material variability in the process of use wear formation on quartzite and contributed to ongoing studies of the lithic materials from these archaeological sites

distribution of recent benthic foraminifera along continental slope of the sunda shelf south china sea the distribution of live rose bengal stained and dead benthic foraminiferal distribution 150 mu m was investigated in sediment surface samples 0 1 cm from the winter upwelling region off borneo on the continental slope of the sunda shelf and from the continental slope of southern vietnam shelf the benthic foraminiferal faunas of both areas are highly diverse h s 2 91 4 25 for living and 4 01 4 38 for dead a canonical correspondence analysis proved that bathyal assemblages are most strongly influenced by the decreasing rates of organic carbon flux with increasing water depth resulting in a pronounced depth related succession of assemblages correlation between estimated c org flux and factor 1 loadings of the cca for modem dead foraminiferal assemblages is very good r 2 0 96 thus a local transfer function y 5 0289x 6 8142 for estimating paleo c org flux rates from the down core samples has been successfully developed for the continental slope of the sunda shelf four benthic foraminiferal biofacies were recognised within the studied depth ranges upper bathyal biofacies siphotextularia foliosa cibicidoides robertsonianus well supplied and well oxygenated middle bathyal biofacies uvigerina auberiana nuttallides rugosus located within the oxygen minimum zone uppermost lower bathyal biofacies lagenammina difflugiformis uvigerina peregrina and lower bathyal biofacies paratrochammina challengeri parrelloides bradyi from the relatively well oxygenated but food limited environment c 2009 elsevier b v all rights reserved

carbon and oxygen isotopic records of benthic foraminifera from the northeast indian ocean implications on glacial interglacial atmospheric co2 changes abstract we present here continuous records of 18o and 13c in benthic foraminifera extending well into the last ice age in two piston cores from the andaman sea sill depth 1 3 km and the bay of bengal 3 km these show that contrary to the previous reports the glacial to interglacial shift in 13c at mid depths in the northeast indian ocean was indistinguishable from the mean oceanic 13c change negating a more vigorous renewal of intermediate waters globally during the glacial time the corresponding 13c shift in deep waters is estimated to be about 50 larger than that reported previously jointly with some recent data from the pacific our results indicate a modest glacial holocene shift in the intermediate to deep water chemical gradients in the indo pacific as a whole implying that it was perhaps not the dominant mechanism for the glacial interglacial atmospheric co2 variations also in conflict with previous work our measurements suggest significant cooling of both the intermediate and deep waters during the glacial time the high resolution records from the andaman sea help reconstruct paleoenvironmental changes at intermediate depths during the last deglaciation rapid increases in 13c occurring in two stages during the early deglaciation appear to have been caused by the fluctuations in the north atlantic deep water production a negative excursion in 13c during the mid deglaciation is ascribed to enhanced nutrient regeneration at mid depths associated with the greatly intensified summer monsoon around the pleistocene holocene boundary

variability in the deep and intermediate water circulation of the atlantic ocean during the past 25 000 years northern hemisphere modulation of the southern ocean the relative flux of north atlantic deep water nadw out of the atlantic can be monitored in the southern ocean where high 13c nadw mixes rapidly with low 13c recirculated pacific water before forming antarctic bottom water aabw by using 13c measured in benthic foraminifera as a water mass tracer it is shown that the southern ocean was dominated by pacific water with little nadw contribution during the last glaciation these tracer results document the direct physical connection between insolation controlled northern hemisphere oscillations and changes in the chemical and physical properties of southern ocean water the 13c records from the deep tropical atlantic document the transition from an atlantic dominated by southern ocean water during the last glaciation to an atlantic dominated by nadw during the holocene with more southern ocean water in the deep atlantic during the last glaciation the boundary between nadw and southern ocean water was north of its modern position allowing more southern ocean water to enter the eastern atlantic through the romanche fracture zone carbon isotope records from the caribbean and mediterranean seas suggest that the influence of mediterranean overflow water mow extended to the caribbean during the last glaciation and therefore was a volumetrically much more important water mass in the intermediate depth atlantic than it is today

changes in the distribution of δ13c of deep water σco2 between the last glaciation and the holocene carbon isotopic measurements on the benthic foraminiferal genus cibicidoides document that mean deep ocean 13c values were 0 46 lower during the last glacial maximum than during the late holocene the geographic distribution of 13c was altered by changes in the production rate of nutrient depleted deep water in the north atlantic during the late holocene north atlantic deep water with high 13c values and low nutrient values can be found throughout the atlantic ocean and its effects can be traced into the southern ocean where it mixes with recirculated pacific deep water during the glaciation decreased production of north atlantic deep water allowed southern ocean deep water to penetrate farther into the north atlantic and across low latitude fracture zones into the eastern atlantic mean southern ocean 13c values during the glaciation are lower than both north atlantic and pacific 13c values suggesting that production of nutrient depleted water occurred in both oceans during the glaciation enriched 13c values in shallow cores within the atlantic ocean indicate the existence of a nutrient depleted water mass above 2000 m in this ocean

coherent response of antarctic intermediate water and atlantic meridional overturning circulation during the last deglaciation reconciling contrasting neodymium isotope reconstructions from the tropical atlantic antarctic intermediate water aaiw plays important roles in the global climate system and the global ocean nutrient and carbon cycles however it is unclear how aaiw responds to global climate changes in particular neodymium isotopic composition end reconstructions from different locations from the tropical atlantic have led to a debate on the relationship between northward penetration of aaiw into the tropical atlantic and the atlantic meridional overturning circulation amoc variability during the last deglaciation we resolve this controversy by studying the transient oceanic evolution during the last deglaciation using a neodymium enabled ocean model our results suggest a coherent response of aaiw and amoc when amoc weakens the northward penetration and transport of aaiw decreases while its depth and thickness increase our study highlights that as part of the return flow of the north atlantic deep water nadw the northward penetration of aaiw in the atlantic is determined predominately by amoc intensity moreover the inconsistency among different tropical atlantic end reconstructions is reconciled by considering their corresponding core locations and depths which were influenced by different water masses in the past the very radiogenic water from the bottom of the gulf of mexico and the caribbean sea which was previously overlooked in the interpretations of deglacial end variability can be transported to shallow layers during active amoc and modulates end in the tropical atlantic changes in the aaiw core depth must also be considered thus interpretation of end reconstructions from the tropical atlantic is more complicated than suggested in previous studies

ominelite fe mg al3bsio9 fe2 analogue of grandidierite a new mineral from porphyritic granite in japan ominelite fe mg al3bsio9 is the fe2 analog of grandidierite the mineral occurs as elongated and euhedral to equant and anhedral grains in close association with sekaninaite fe dominant analogue of cordierite garnet biotite andalusite topaz alkali feldspar plagioclase muscovite quartz dumortierite schorl zircon ilmenite apatite monazite and pyrite in a porphyritic granite of miocene age exposed along the misen river in tenkawa yoshino nara prefecture japan 34 12 40 n 135 53 40 e temperatures r major lines in the powder pattern d in a i hkl are 5 57 m 020 5 21 vs 200 3 73 m 121 3 51 m 130 2 97 s 101 2 79 s 040 2 18 s 150 421 312 space group is pbnm lattice parameters are a 10 343 2 b 11 095 1 c 5 7601 8 a and v 661 0 2 a3 z 4 d calc 3 169 g cm3 refinement of the structure confirms that ominelite is isostructural with grandidierite with no detectable substitution of al by fe3

the δ13c in benthic foraminiferal tests of fontbotia wuellerstorfi schwager relative to the δ13c of dissolved inorganic carbon in southern ocean deep water implications for glacial ocean circulation models on a transect between 20 and 70 s in the eastern atlantic ocean and weddell sea water samples from 19 hydrographic stations and bottom water from 55 surface sediment samples taken with a multiple corer were investigated for the stable carbon isotopic composition of the total dissolved inorganic carbon 13c co2 these measurements were compared to 13c values determined on live specimens of the benthic foraminifer fontbotia wuellerstorfi and closely related genera from the same stations in addition at 16 stations the stable carbon isotope composition of sedimentary organic carbon was measured general deepwater and bottom water mass circulation patterns as inferred from the 13c co2 are in close agreement with those known from other nonconservative tracers very low 13c values of upper circumpolar deep water 0 3 pee dee belemnite pdb in the polar front region and the eastern limb of the weddell gyre coincide with nutrient maxima however a significant decoupling of the dissolved phosphate signal from the 13c co2 signal is indicated in the abyssal weddell sea we attribute this to temperature dependent fractionation processes during gas exchange of surface waters with the atmosphere at sites of bottom water formation multiple corer water from the sediment water interface is slightly 13c depleted relative to deepwater and bottom water 13 co2 the surface sediment organic carbon 13c is 3 to 4 lower south of the polar front than north of it and the 13corg in freshly accumulated phytodetritus is 3 to 4 lower than surface sediment organic carbon 13c comparison of live f wuellerstorfi 13c and related genera with bottom water 13c co2 exhibits at most stations between the subtropical front 41 s and the southern boundary of the antarctic circumpolar current 55 s a significant lowering of foraminiferal 13c values compilation of a mean last glacial interglacial 13c amplitude 13c from six published southern ocean cores results in a shift of 0 99 0 13 pdb this shift is greater than that in all other regions however all of these cores are from positions close to recent oceanic fronts thus for these peripheral areas of the southern ocean we suggest about half of the glacial interglacial shift can be explained by varying frontal zone positions and widths accompanied by a change in mode and height of export production

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

antarctic intermediate water penetration into the northern indian ocean during the last deglaciation abstract the two stage increase in atmospheric carbon dioxide co2 and the associated decrease in radiocarbon 14c during the last deglaciation are thought to have been linked to enhanced southern ocean upwelling and the rapid release of sequestered 14c depleted co2 antarctic intermediate water aaiw originating from the southern ocean reflects variations in the southern ocean and crucially mirrors the chemical signature of upwelling deep water however the penetration of aaiw into the northern indian ocean and its relationship with deglacial climate changes have not been thoroughly elucidated to date here we present the neodymium isotopic composition e nd of mixed planktonic foraminifera from core md77 176 from an intermediate depth in the northern indian ocean to reconstruct the past evolution of intermediate water during deglaciation the e nd record in the northern indian ocean displays two pulse like shifts towards more radiogenic southern ocean values during the deglaciation and these shifts coincide with excursions in 14 c and e nd records in the pacific and atlantic oceans these results suggest invasion of aaiw into the northern hemisphere oceans associated with enhanced southern ocean ventilation during deglaciation our new e nd record strongly supports the close linkage of aaiw propagation and atmospheric co2 rise through southern ocean ventilation during deglaciation

nd and sr isotopic variations in acidic rocks formed under a peculiar tectonic environment in miocene southwest japan initial nd and sr isotopic ratios were obtained for middle miocene igneous rocks as well as for related rocks from the outer zone of southwest japan to investigate the petrogenesis of acidic magmas and their relation to a peculiar tectonic environment bearing on the back arc spreading of the japan sea on the nd sr diagram data points for the acidic rocks fall in the nd sr quadrant occupying different positions from those for sedimentary and old crustal rocks and seem to define several subparallel lines which extend towards the lower righthand sedimentary field the s type acidic rocks occupy an intermediate position between i type rocks and sedimentary ones a fact suggesting mixing of an igneous component and a sedimentary one the linear mixing trend observed on the nd sr diagram can be attained in the restricted case that the igneous component has similar sr nd concentration ratios to that of the sedimentary one which implies an intermediate to acidic composition for the igneous component inconsistency between the elemental and isotopic variations observed may be reconciled by considering that mixing probably in the relatively deep part of the crust might have occured prior to chemical differentiation processes the episodic igneous activity and the high heat energy required to melt such materials involving sedimentary rocks may be explained by a model in which a hot mantle region probably corresponding to the rising part of the mantle convection supplied the heating energy to the outer zone of southwest japan when passing beneath southwest japan in the course of movement of the hot rising part from the shikoku basin areas to the japan sea area

phosphorus in s type magmas the p2o5 content of feldspars from peraluminous granites pegmatites and rhyolites

flowage differentiation in an andesitic dyke of the motru dyke swarm southern carpathians romania inferred from ams csd and geochemistry abstract two dykes of different thickness 5 5 m for tj31 and 23 m for tj34 from the late pan african calc alkaline motru dyke swarm s carpathians romania have been studied by electron microprobe mineral chemistry crystal size distribution csd anisotropy of magnetic susceptibility ams and whole rock geochemistry all the physical and chemical variations observed across the dyke s width point to concordant results and show that the variations of both modal abundance and size of the amphibole and biotite microphenocrysts inside the dykes deduced from the classical csd measurements are the result of a mechanical segregation of suspended crystals during magmatic transport despite a pene contemporaneous regional tectonic the flow induced differentiation in the thicker dyke is characterized by the concentration of pre existing ti rich pargasite tschermakite clinopyroxene and plagioclase crystals in the core of the dyke and of the extracted differentiated liquid near the walls this mechanical differentiation induces a chemical differentiation with a basaltic andesite composition for the core of the dyke whereas the margins are andesitic thus the chilled margins appear as a slightly more evolved liquid with a newtonian behaviour when compared to the average composition of the dyke the localization of the liquid on both sides of the dyke has certainly facilitated the ascent of the central part of the dyke that behaved as a binghamian mush

hydrographic changes in the southern bay of bengal during the last 65 000 y inferred from carbon and oxygen isotopes of foraminiferal fossil shells abstract we present 13 c and 18 o records of planktonic globigerinoides ruber and benthic foraminifera cibicidoides spp from two deep sea sediment cores sk157 15 and sk157 16 from the southern bay of bengal the chronology of these gravity cores was established using eleven ams radiocarbon ages from mixed species of planktonic foraminifera globigerinoides ruber and globigerinoides sacculifer and oxygen isotope stratigraphy large variations in 13 c and 18 o of planktonic and benthic foraminifera in these cores are suggestive of significant changes in surface and deep water masses for the 65 ka bp the 18 o values in planktonic foraminifera in both these cores are significantly higher relative to sediment cores from the western bay of bengal and the andaman sea because of the reduced influence of riverine fresh water fluxes benthic 13 c values in cores sk157 15 and sk157 16 exhibit significant variations in source water characteristics during the holocene and the last glaciation large decrease in 13 c values of bottom dwelling benthic foraminifera cibicidoides spp during the last glacial maximum lgm and 50 65 ka bp suggest drastic reduction in north atlantic deep water nadw fluxes into the southern bay of bengal and concurrent increase of deep water formed in the southern ocean sodw with significantly low 13 c values

deglacial temperature history of west antarctica the most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how earth s climate responds to various forcings including a rise in atmospheric co2 this transition has left a direct thermal remnant in the polar ice sheets where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings for antarctica the deglacial warming has previously been constrained only by the water isotopic composition in ice cores without an absolute thermometric assessment of the isotopes sensitivity to temperature to overcome this limitation we measured temperatures in a deep borehole and analyzed them together with ice core data to reconstruct the surface temperature history of west antarctica the deglacial warming was formula see text c approximately two to three times the global average in agreement with theoretical expectations for antarctic amplification of planetary temperature changes consistent with evidence from glacier retreat in southern hemisphere mountain ranges the antarctic warming was mostly completed by 15 kybp several millennia earlier than in the northern hemisphere these results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on antarctic temperature although climate models perform well on average in this context some recent syntheses of deglacial climate history have underestimated antarctic warming and the models with lowest sensitivity can be discounted

deglacial variability in the surface return flow of the atlantic meridional overturning circulation 1 benthic foraminiferal cd ca from a florida current sediment core documents the history of the northward penetration of southern source waters within the surface return flow of the atlantic meridional overturning circulation amoc cd seawater estimates cdw indicate that intermediate depth southern source waters crossed the equator and contributed to the florida current during the bolling allerod warm period of the last deglaciation consistent with evidence of only a modest amoc reduction compared to today the cdwestimates also provide the first paleoceanographic evidence of a reduction in the influence of intermediate depth southern source waters within the florida current during the younger dryas a deglacial cold event characterized by a weak north atlantic amoc our results reveal a close correspondence between the northward penetration of intermediate depth southern source waters and the influence of north atlantic deep water suggesting a possible link between intermediate depth southern source waters and the strength of the atlantic amoc

ventilation of the deep southern ocean and deglacial co2 rise past glacial interglacial increases in the concentration of atmospheric carbon dioxide co2 are thought to arise from the rapid release of co2 sequestered in the deep sea primarily via the southern ocean here we present radiocarbon evidence from the atlantic sector of the southern ocean that strongly supports this hypothesis we show that during the last glacial period deep water circulating around antarctica was more than two times older than today relative to the atmosphere during deglaciation the dissipation of this old and presumably co2 enriched deep water played an important role in the pulsed rise of atmospheric co2 through its variable influence on the upwelling branch of the antarctic overturning circulation

antarctic intermediate water circulation in the south atlantic over the past 25 000 years antarctic intermediate water is an essential limb of the atlantic meridional overturning circulation that redistributes heat and nutrients within the atlantic ocean existing reconstructions have yielded conflicting results on the history of antarctic intermediate water penetration into the atlantic across the most recent glacial termination in this study we present leachate foraminiferal and detrital neodymium isotope data from three intermediate depth cores collected from the southern brazil margin in the south atlantic covering the past 25 kyr these results reveal that strong chemical leaching following decarbonation does not extract past seawater neodymium composition in this location the new foraminiferal records reveal no changes in seawater nd isotopes during abrupt northern hemisphere cold events at these sites we therefore conclude that there is no evidence for greater incursion of antarctic intermediate water into the south atlantic during either the younger dryas or heinrich stadial 1 we do however observe more radiogenic nd isotope values in the intermediate depth south atlantic during the mid holocene this radiogenic excursion coincides with evidence for a southward shift in the southern hemisphere westerlies that may have resulted in a greater entrainment of radiogenic pacific sourced water during intermediate water production in the atlantic sector of the southern ocean our intermediate depth records show similar values to a deglacial foraminiferal nd isotope record from the deep south atlantic during the younger dryas but are clearly distinct during the last glacial maximum and heinrich stadial 1 demonstrating that the south atlantic remained chemically stratified during heinrich stadial 1