isotope geochemistry sr nd pb and petrogenesis of leucite bearing volcanic rocks from colli albani volcano roman magmatic province central italy inferences on volcano evolution and magma genesis the colli albani composite volcano is made up of strongly silica undersaturated leucite bearing rocks magmas were erupted during three main periods but a complex plumbing system dominated by regional tectonics channelled magmas into different reservoirs the most alkali rich magmas restricted to the caldera forming period pre caldera are extremely enriched in incompatible trace elements and display more radiogenic sr 87sr 86sr 0 71057 0 71067 with slightly less radiogenic pb with respect to those of the post caldera period post caldera volcanic activity was concentrated in three different volcanic environments external to the caldera along the caldera edge and within the caldera the post caldera magmas produced melilite to leucitite bearing plagioclase free leucitites in contrast to the pre caldera lavas they are characterised by lower incompatible trace element abundances and less radiogenic sr 87sr 86sr 0 71006 0 71039 magmas evolved through crystal fractionation plus minor crustal assimilation in a large magma chamber during the pre caldera period the multiple caldera collapses dissected and partially obliterated the early magma chamber during the post caldera stage magmas were channelled through several pathways and multiple shallow level magma reservoirs were established a lithospheric mantle wedge previously depleted in the basaltic component and subsequently enriched by metasomatic slab derived component is suggested as the mantle source of colli albani parental magmas two different parental magmas are recognised for the pre and post caldera stages the differences may be related to the interplay between smaller degrees of melting for the pre caldera magmas and more carbonate rich recycled subducted lithologies in the post caldera magmas

variations in high latitude oceanographic fronts in the southern indian ocean an estimation based on faunal changes a quantitative estimate of the magnitude of late pleistocene holocene variations in the migration of siliceous microfauna is calculated from fossil assemblages preserved in marine sediments from piston cores located in the southeast indian ocean sector of the subantarctic results of this modern analog technique indicate that fauna characteristic of colder waters today occupied surface and near surface waters overlying the core sites for much of the last half million years warm water fauna inhabited these waters for only brief time periods usually during the early portion of interglacial isotopic stages the estimated faunal migration pattern from the most southern sites is similar in most respects to that of atmospheric temperatures over antarctica recorded in the vostok ice core a model of changes in the positions of the subtropical convergence and the antarctic polar front constructed from time series of faunal variations indicates that although southward migrations of these oceanographic fronts in this region of the southern ocean were limited to approximately 4 of latitude northward displacements were of the order of 5 to 7 of latitude fauna at the antarctic polar front react earlier than either the fauna at the subtropical convergence or the global ice volume signal to major global warming terminations providing further documentation of the early response of the high latitude southern ocean relative to other components of the climate system to the various factors forcing pleistocene climate

the colli albani mafic caldera roma italy stratigraphy structure and petrology new results for the colli albani volcano roma italy surveyed for the geological map of italy at 1 50 000 scale carg project integrated with previous data provide insights on caldera evolution the colli albani a quiescent volcano became active at 600 ka eruptive compositions are consistently mafic 50 km 3 deposits forming the villa senni eruption unit ignimbrites at ca 355 ka two edifices were built within the caldera 1 the horseshoe shaped tuscolano artemisio ta composite edifice or lithosome consists of coalescing peri caldera fissure related scoriae cones interbedded with lava flows the fissure system forms two segments controlled by regional fractures 2 the steep sided faete stratovolcano 949 m a s l filled the caldera the ta and faete lithosomes partly interfinger and were emplaced at 350 260 ka their products indicate reduced eruption rates relative to the vl period and a change to effusive and mildly explosive eruptions the most recent and still active phase of phreatomagmatic activity formed overlapping maars and tuff cones along the western and northern slopes of the volcano collectively named via dei laghi composite lithosome the colli albani caldera is poly phase 1 a piecemeal caldera is associated with large volume ignimbrites of the vl edifice the present shape of the caldera is related to the villa senni eruption 2 the ta composite edifice erupted from peripheral caldera fissures is unrelated to explosive phases of caldera collapse the ta final products cover a morphologically stable caldera wall the peripheral fractures feeding the ta composite edifice are interpreted as volcano tectonic structures activated during the late stage downsag of the caldera reduced eruption rates during the ta and the faete stages 10 1 km 3 1 ka respect to 10 0 km 3 1 ka for the vl edifice suggest a reduced recharge of the magma chamber that may have induced prolonged deflation and downsagging of the caldera floor and the opening of outward dipping peripheral fractures by this interpretation the ta edifice represents the surface expression of ring dykes at depth the absence of similar fissure structures along the western caldera rim may relate to the deep geometry of the ring faults dipping inward in those areas and therefore not favourably oriented for magma intrusion during a period of general subsidence by contrast the following and still active phreatomagmatic phase that has emplaced the via dei laghi composite edifice is located right on the western side of the caldera and may therefore relate to resurgent conditions classical petrological and pers pearce elements ratios analyses indicate that lavas are co genetic and show a differentiation trend up through stratigraphy driven by

the geochemical evolution of clinopyroxene in the roman province a window on decarbonation from wall rocks to magma abstract we present results from magma carbonate interaction experiments designed to shed light on the geochemical evolution of clinopyroxene in the roman province central italy atmospheric pressure experiments were performed at 1140 1160 and 1180 c under nno mh and air oxygen buffering conditions the starting materials were a shoshonite and a phonotephrite doped with different amounts of cao and cao mgo whose stoichiometric proportions reproduced the assimilation by magmas of calcite and dolomite respectively the results show that clinopyroxenes spinels and residual glasses are ubiquitous phases in all run products calcite doped runs crystallize more clinopyroxene than dolomite doped runs at the same conditions this leads to the formation of strong desilicated cao rich melts showing compositions comparable to those of magmatic skarns during magma carbonate interaction the content of fe3 in clinopyroxene increases with increasing fo2 promoting the substitution of al for si in tetrahedral site local charge imbalances are also compensated by the incorporation of highly charged cations such as ti into the crystal lattice according to this cation substitution al ca fe3 ti rich clinopyroxenes of the skarn environment testify to continuous co2 fluxes produced by the thermal decomposition of carbonate wall rocks nevertheless the oxidative capacity of co2 progressively decreases from the skarn shells towards the interior of the magma chamber driving the crystallization of si fe2 mg rich clinopyroxenes

primary magmatic calcite reveals origin from crustal carbonate abstract we have investigated lava flows representative of the whole eruptive history of the colli albani ultrapotassic volcanic district central italy one of the most intriguing features concerning some of these lava flows is the occurrence of primary magmatic calcite in the groundmass the primary magmatic nature of calcite has been inferred by microtextural investigations showing that it typically occurs i interstitially associated with clinopyroxene nepheline and phlogopite ii in spherical ocelli associated with nepheline fluorite and tangentially arranged clinopyroxene and iii in corona like reaction zones around k feldspar xenocrysts these microtextural features distinctly indicate that calcite crystallized from a carbonate melt in a partially molten groundmass implying that the temperature of the system was above the solidus of the hosted lava flow 850 c geochemical features of calcite crystals i e stable isotope values and trace element patterns corroborate their primary nature and give insights into the origin of the parental carbonate melt the trace element patterns testify to a high temperature crystallization process not hydrothermal involving a carbonate melt coexisting with a silicate melt the high 18o around 27 smow and wide 13c 18 to 5 pdb values measured in the calcites preclude a mantle origin but are consistent with an origin in the crust in this framework the crystallization of calcite can be linked to the interaction between magmas and carbonate bearing wall rocks and in particular to the entrapment of solid and or molten carbonate in the silicate magma the stability of carbonate melt at low pressure and the consequent crystallization of calcite in the lava flow groundmass are ensured by the documented high activity of fluorine in the studied system and by the limited ability of silicate and carbonate melts to mix at syn eruptive time scales

climate records covering the last deglaciation the oxygen 18 oxygen 16 ratio of molecular oxygen trapped in ice cores provides a time stratigraphic marker for transferring the absolute chronology for the greenland ice sheet project gisp ii ice core to the vostok and byrd ice cores in antarctica comparison of the climate records from these cores suggests that near the beginning of the last deglaciation warming in antarctica began approximately 3000 years before the onset of the warm bolling period in greenland atmospheric carbon dioxide and methane concentrations began to rise 2000 to 3000 years before the warming began in greenland and must have contributed to deglaciation and warming of temperate and boreal regions in the northern hemisphere

post caldera activity in the alban hills volcanic district italy 40ar 39ar geochronology and insights into magma evolution we present 24 40ar 39ar ages for the youngest volcanic products from the alban hills volcanic district rome combined with petrological data on these products we have attempted to define the chronology of the most recent phase of activity and to investigate the magma evolution of this volcanic district the early mainly explosive activity of the alban hills spanned the interval from 561 1 to 351 3 ka after approximately 50 kyr of dormancy a mainly effusive phase of activity took place accompanied by the strombolian activity of a small central edifice monte delle faete this second phase of activity spanned the interval 308 2 to 250 1 ka after another dormancy period of approximately 50 kyr a new hydromagmatic phase of activity started at 200 ka at several centers located to the southwest of the monte delle faete edifice after an initial recurrence period of approximately 50 kyr which also characterized this new phase of activity the longest dormancy period approximately 80 kyr in the history of the volcanic district preceded the start of the activity of the albano and giuturna centers at 70 1 ka results of our study suggest a quasi continuous magmatic activity feeding hydromagmatic centers with a new acme of volcanism since around 70 ka based on data presented in this paper we argue that the alban hills should not be considered an extinct volcanic district and a detailed re assessment of the volcanic hazard for the area of rome is in order

the villa senni eruption alban hills central italy the role of h2o and co2 on the magma chamber evolution and on the eruptive scenario abstract the villa senni eruption unit vseu belongs to the tuscolano artemisio phase of volcanic activity in the alban hills volcanic district the closest to rome of the recent or active volcanoes of central italy the most important products of this eruption are represented by pyroclastic flow deposits named lower and upper flow unit lfu and ufu respectively three main rock types form vseu as follows 1 juvenile k foiditic scoria clasts of the lfu 2 juvenile phonotephritic scoria clasts of the ufu and 3 holocrystalline phonotephritic lithic inclusions italites in the ufu on the basis of the chemistry mineralogy and petrography of the three studied rock types their phase relations have been discussed other petrologic constraints from laboratory melting experiments are presented and used to investigate the role of volatiles on the evolution of the magma chamber system some broad implications on withdrawal pattern are also presented it has been verified the lfu rock type can be obtained from a parental melt of ufu composition by a co2 controlled crystal liquid fractionation of a solid assemblage close in composition to that of italites because it can be proved that the storage of magma occurred at shallow depth within the mesozoic carbonate country rocks it is proposed that co2 diffusion originating from thermal decomposition of wall rock carbonates controlled the evolution trend of the melt at the periphery of the magma chamber whereas the inner part of the magma body retained the volatile component essentially h2o of the original melt the corresponding eruption model is therefore comprehensive of an early eruptive phase lfu rock type involving the more differentiated central magma bulb whereas the late eruptive phase ufu rock type tapped the more mafic peripheral magma the italite xenoliths are believed to represent the chilled margins of the magma chamber

340 000 year centennial scale marine record of southern hemisphere climatic oscillation in order to investigate rapid climatic changes at mid southern latitudes we have developed centennial scale paleoceanographic records from the southwest pacific that enable detailed comparison with antarctic ice core records these records suggest close coupling of mid southern latitudes with antarctic climate during deglacial and interglacial periods glacial sections display higher variability than is seen in antarctic ice cores which implies climatic decoupling between mid and high southern latitudes due to enhanced circum antarctic circulation structural and temporal similarity with the greenland ice core record is evident in glacial sections and suggests a degree of interhemispheric synchroneity not predicted from bipolar ice core correlations

old radiocarbon ages in the southwest pacific ocean during the last glacial period and deglaciation marine radiocarbon 14c dates are widely used for dating oceanic events and as tracers of ocean circulation essential components for understanding ocean climate interactions past ocean ventilation rates have been determined by the difference between radiocarbon ages of deep water and surface water reservoirs but the apparent age of surface waters currently approximately 400 years in the tropics and approximately 1 200 years in antarctic waters might not be constant through time as has been assumed in radiocarbon chronologies and palaeoclimate studies here we present independent estimates of surface water and deep water reservoir ages in the new zealand region since the last glacial period using volcanic ejecta tephras deposited in both marine and terrestrial sediments as stratigraphic markers compared to present day values surface reservoir ages from 11 900 14c years ago were twice as large 800 years and during glacial times were five times as large 2 000 years contradicting the assumption of constant surface age furthermore the ages of glacial deep water reservoirs were much older 3 000 5 000 years the increase in surface to deep water age differences in the glacial southern ocean suggests that there was decreased ocean ventilation during this period

surface water temperature changes in the high latitudes of the southern hemisphere over the last glacial interglacial cycle a set of numerical equations is developed to estimate past sea surface temperatures sst from fossil antarctic diatoms these equations take into account both the biogeographic distribution and experimentally derived silica dissolution the data represent a revision and expansion of a floral data base used previously and includes samples resulting from progressive opal dissolution experiments factor analysis of 166 samples 124 holocene core top and 42 artificial samples resolved four factors three of these factors depend on the water mass distribution one subantarctic and two antarctic assemblages factor 4 corresponds to a dissolution assemblage inclusion of this factor in the data analysis minimizes the effect of opal dissolution on the assemblages and gives accurate estimates of sst over a wide range of biosiliceous dissolution a transfer function dtf 166 34 4 is derived from the distribution of these factors versus summer sst its standard error is 1 c in the 1 to 10 c summer temperature range this transfer function is used to estimate sst changes in two southern ocean cores 43 s and 55 s which cover the last climatic cycle the time scale is derived from the changes in foraminiferal oxygen and carbon isotopic ratios the reconstructed sst records present strong analogies with the air temperature record over antarctica at the vostok site derived from changes in the isotopic ratio of the ice this similarity may be used to compare the oceanic isotope stratigraphy and the vostok time scale derived from ice flow model the oceanic time scale if taken at face value would indicate that large changes in ice accumulation rates occurred between warm and cold periods

a new 27 ky high resolution east antarctic climate record the ice core recently drilled at the dome concordia site on the east antarctic plateau provides a new high resolution isotope record covering part of the last glacial the last transition and the holocene the two step shape of the deglaciation is remarkably similar for all the ice cores now available on the east antarctic plateau the first warming trend ends about 14000 years ago and is followed by the well marked antarctic cold reversal acr with a secondary peak common to all records during the deglaciation there are more similarities between the near coastal site of taylor dome and inland east antarctica than between taylor dome and central greenland however the results for epica do appear to confirm the taylor dome timescale after about 14 ka showing cooling into the acr roughly in phase between greenland and antarctica while the overall deglacial pattern is asynchronous this suggests that the now classical picture of a temperature seesaw between antarctica and greenland may be too simplistic

paleo sea surface temperature calculations in the equatorial east atlantic from mg ca ratios in planktic foraminifera a comparison to sea surface temperature estimates from u37k oxygen isotopes and foraminiferal transfer function we present two 270 kyr paleo sea surface temperature sst records from the equatorial divergence and the south equatorial current derived from mg ca ratios in the planktic foraminifer globigerinoides sacculifer the present study suggests that the magnesium signature of g sacculifer provides a seasonal sst estimate from the upper 50 m of the water column generated during upwelling in austral low latitude fall winter common to both down core records is a glacial interglacial amplitude of 3 3 5 c for the last climatic changes and lower holocene and glacial oxygen isotope stage 2 temperatures compared with interglacial stage 5 5 and glacial stage 6 temperatures respectively the comparison to published sst estimates from alkenones oxygen isotopes and foraminiferal transfer function from the same core material pinpoints discrepancies and conformities between methods

strong hemispheric coupling of glacial climate through freshwater discharge and ocean circulation the climate of the last glacial period was extremely variable characterized by abrupt warming events in the northern hemisphere accompanied by slower temperature changes in antarctica and variations of global sea level it is generally accepted that this millennial scale climate variability was caused by abrupt changes in the ocean thermohaline circulation here we use a coupled ocean atmosphere sea ice model to show that freshwater discharge into the north atlantic ocean in addition to a reduction of the thermohaline circulation has a direct effect on southern ocean temperature the related anomalous oceanic southward heat transport arises from a zonal density gradient in the subtropical north atlantic caused by a fast wave adjustment process we present an extended and quantitative bipolar seesaw concept that explains the timing and amplitude of greenland and antarctic temperature changes the slow changes in antarctic temperature and its similarity to sea level as well as a possible time lag of sea level with respect to antarctic temperature during marine isotope stage 3

high level triggers for explosive mafic volcanism albano maar italy abstract colli albani is a quiescent caldera complex located within the roman magmatic province rmp italy the recent via dei laghi phreatomagmatic eruptions led to the formation of nested maars albano maar is the largest and has erupted seven times between ca 69 33 ka the highly explosive nature of the albano maar eruptions is at odds with the predominant relatively mafic sio 2 48 52 wt foiditic k 2 o 9 wt composition of the magma the deposits have been previously interpreted as phreatomagmatic however they contain large amounts up to 30 vol of deep seated xenoliths skarns and all pre volcanic subsurface units all of the xenoliths have been excavated from depths of up to 6 km rather than being limited to the depth at which magma and water interaction is likely to have occurred suggesting an alternative trigger for eruption high precision geochemical glass and mineral data of fresh juvenile magmatic clasts from the small volume explosive deposits indicate that the magmas have evolved along one of two evolutionary paths towards foidite or phonolite the foiditic melts record ca 50 mixing between the most primitive magma and ca rich melt late stage prior to eruption a major result of our study is finding that the generation of ca rich melts via assimilation of limestone may provide storage for significant amounts of co 2 that can be released during a mixing event with silicate magma differences in melt evolution are inferred as having been controlled by variations in storage conditions residence time and magma volume

oxygen isotope geochemistry of pyroclastic clinopyroxene monitors carbonate contributions to roman type ultrapotassic magmas the oxygen isotope geochemistry and chemical composition of clinopyroxene crystals from alban hills pyroclastic deposits constrain the petrological evolution of ultrapotassic roman type rocks volcanic eruptions in the 560 35 ka time interval produced thick pyroclastic deposits bearing clinopyroxene phenocrysts with recurrent chemical characteristics clinopyroxenes vary from si mg rich to al fe rich with no compositional break indicating that they were derived from a continuous process of crystal fractionation based on the 18o and trace element data no primitive samples were recovered monomineralic clinopyroxene cumulates set the oxygen isotope composition of primary magmas in the range of uncontaminated mantle rocks 5 5 but their ree composition resulted from extensive crystal fractionation departing from these mantle like 18ocpx values the effects of crustal contamination of clinopyroxene o isotope composition were identified and used to monitor chemical variations in the parental magma 18o values in si mg rich clinopyroxene are slightly higher than typical mantle values 5 9 6 2 and the low ree contents are representative of early stages of magmatic differentiation 18o values as high as 8 2 are associated with al fe3 rich clinopyroxene showing high ree contents these 18o values are characteristic of crystals formed during the late magmatic stages of each main eruptive phase geochemical modelling of 18o values vs trace element contents indicates that these ultrapotassic magmas were derived from fractional crystallization plus assimilation of limited amounts of carbonate wall rocks starting from a primary melt and from interaction with co2 derived from country rocks during crystal fractionation

melts_excel a microsoft excel based melts interface for research and teaching of magma properties and evolution the thermodynamic modeling software melts is a powerful tool for investigating crystallization and melting in natural magmatic systems rhyolite melts is a recalibration of melts that better captures the evolution of silicic magmas in the upper crust the current interface of rhyolite melts while flexible can be somewhat cumbersome for the novice we present a new interface that uses web services consumed by a vba backend in microsoft excel the interface is contained within a macro enabled workbook where the user can insert the model input information and initiate computations that are executed on a central server at ofm research results of simple calculations are shown immediately within the interface itself it is also possible to combine a sequence of calculations into an evolutionary path the user can input starting and ending temperatures and pressures temperature and pressure steps and the prevailing oxidation conditions the program shows partial updates at every step of the computations at the conclusion of the calculations a series of data sheets and diagrams are created in a separate workbook which can be saved independently of the interface additionally the user can specify a grid of temperatures and pressures and calculate a phase diagram showing the conditions at which different phases are present the interface can be used to apply the rhyolite melts geobarometer we demonstrate applications of the interface using an example early erupted bishop tuff composition the interface is simple to use and flexible but it requires an internet connection the interface is distributed for free from http melts ofm research org

the two step shape and timing of the last deglaciation in antarctica the two step character of the last deglaciation is well recognized in western europe in greenland and in the north atlantic for example in greenland a gradual temperature decrease started at the bolling b around 14 5 ky bp spanned through the allerod a and was followed by the cold younger dryas yd event which terminated abruptly around 11 5 ky bp recent results suggest that this ba yd sequence may have extended throughout all the northern hemisphere but the evidence of a late transition cooling is still poor for the southern hemisphere here we present a detailed isotopic record analyzed in a new ice core drilled at dome b in east antarctica that fully demonstrates the existence of an antarctic cold reversal acr these results suggest that the two step shape of the last deglaciation has a worldwide character but they also point to noticeable interhemispheric differences thus the coldest part of the acr which shows a temperature drop about three times weaker than that recorded during the yd in greenland may have preceded the yd antarctica did not experienced abrupt changes and the two warming periods started there before they started in greenland the links between southern and northern hemisphere climates throughout this period are discussed in the light of additional information derived from the antarctic dust record

magma chambers emplaced in carbonate substrate petrogenesis of skarn and cumulate rocks and implications for co2 degassing in volcanic areas crystal rich lithic clasts occurring in volcanic deposits are key tools to understand processes of storage cooling and fractionation of magmas in pre eruptive volcanic systems these clasts represent snapshots of the magma chamber host rock interface before eruption and provide information on crystallization differentiation and degrees of interaction between magma and wall rock in this study we have focused on the petrology of clasts of cumulate and skarn rocks from the colli albani volcanic district with the aim of shedding light on magma carbonate interaction and co2 emission in volcanic areas by means of phase relations bulk rock chemistry mineral compositions and isotope data we have identified different types of cumulates and skarns cumulates containing either clinopyrox

cold climatic episode of younger dryas age in tierra del fuego pronounced climatic change during the last glacial maximum is recognized as global in extent and has been attributed to orbital forcing1 not readily explained in a global context because of the equivocal nature of the evidence are the late glacial climatic events of short 100 1 000 yr duration the cold climate of the younger dryas chron 11 000 10 000 yr bp for example is known to have been particularly pronounced over the north atlantic and parts of europe and north america2 3 whereas in the southern hemisphere cold conditions for that time are not well established here we present evidence for late glacial climatic cooling in southernmost south america from studies of radiocarbon dated glacial and pollen stratigraphy at sites along the beagle channel in tierra del fuego where a forest tundra tension zone in the region is especially sensitive to shifting climate we conclude that the cold episode corresponds with the time of the younger dryas in europe when a drop in temperature ascribed most recently to colder sea surface temperatures and production rate of deep water in the north atlantic4 5 apparently occurred worldwide

sea surface temperature of the western equatorial pacific ocean during the younger dryas high resolution 200 yr sample spacing records of sea surface temperature for the past 15 000 yr have been inferred from planktonic foraminiferal assemblages in a sediment core from the south china sea although the assemblages imply a large glacial to interglacial temperature change 7 c for winter temperatures they give no indication of a cooling during younger dryas time this suggests that the younger dryas increase in 18o observed in cores from the western equatorial pacific is not due to a climatic cooling but rather to a change in the isotopic composition of the oceans

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

the oxygen isotope composition of tropical ocean surface water during the last deglaciation evidence of abrupt climate change in each of the tropical oceans can be found in high deposition rate sediments from the continental margins new ams 14 c dated sediments from the arabian sea reveal a two step depletion of surface ocean 18 o 16 o during the last deglaciation with a return to more enriched values approximately 10 5 ka bp the two step depletion can be correlated among isotope records derived from foraminifer calcite in the arabian sea the gulf of mexico the sulu sea and gulf of california confirming the existence of the two step depletion and 18 o enriched event at 10 5 ka bp in at least three tropical sites outside the north atlantic to determine whether the isotopic enrichment at 10 5 ka bp was caused by local cooling of the surface ocean we estimated sea surface temperatures over this interval using quantitative paleo ecological techniques there is no evidence for cooling in the arabian sea sulu sea or gulf of mexico consistent with the hypothesis that the enrichment at 10 5 ka bp is related to a change in the isotopic composition of the tropical surface ocean and not change in the temperature of calcification we conclude that the cooling at higher latitudes that occurred at 10 5 ka bp did not extend southward to the tropical ocean more cores from high sedimentation rate sites in the tropics are needed to identify the cause and extent of the 18 o signal however these preliminary results are consistent with two meltwater pulses during the deglaciation that distributed isotopically depleted water into each of the tropical oceans with a slow down in meltwater flux at 10 5 ka bp the most likely transport route for the isotopically depleted water from the melting northern hemisphere ice sheets to these isolated tropical ocean basins is via the relatively fast circulation of the atmosphere although other pathways are possible

late glacial and early holocene glacier activity in the southern alps new zealand abstract in the southern alps of new zealand glaciers advanced to their last glacial maximum limits between 22 3 and 18 ka bp and there is evidence for at least four more advances between 18 and 8 ka bp a widespread glacier advance possibly with two maxima occurred between 16 and 14 ka bp during which glaciers reached positions close to those attained at the last glacial maximum after 14 ka bp there was a significant and sustained retreat of glaciers that marks the beginning of the post glacial interval in new zealand locally known as the aranui interglacial during the aranui there is evidence for a much smaller glacier advance around 11 ka bp that may have been coeval with the younger dryas stade but opinions on this are still controversial two younger ice advances may have occurred close to 10 25 and 8 6 ka bp although regional patterns of late glacial advances are reasonably well established the post glacial advances are known only from single sites and require closer investigation

co2 driven large mafic explosive eruptions the pozzolane rosse case study from the colli albani volcanic district italy generally the intensity and magnitude of explo sive volcanic activity increase in parallel with sio2 content pyroclastic flow forming eruptions in the colli albani ultrapotassic volcanic district italy represent the most striking exception on a global scale with volumes on the order of tens of cubic kilometres and k foiditic composi tions sio2 even 42 wt here we reconstruct the pre eruptive scenario and event dynamics of the 456 ka pozzolane rosse pr eruption the largest mafic explosive event of the colli albani district in particular we focus on the driving mechanisms for the unusually explosive eruption of a low viscosity mafic magma geologic petrographic and geochemical data with mass balance calculations supported by experimental data for colli albani magma compositions provide evidence for signif icant ingestion of carbonate wall rocks by the pozzolane rosse k foiditic magma moreover the scattered occurrence of cored bombs in pozzolane rosse pyroclastic flow deposits records carbonate entrainment even at the eruptive time scale as also tested quantitatively by thermal modelling of magma carbonate interaction and carbonate assimilation experiments we suggest that the addition of free co2 from decarbonation of country rocks was the major factor controlling magma explosivity high co2 activity in the volatile component coupled with magma depressurisation produced extensive leucite crystallisation at short time scales resulting in a dramatic increase in magma viscosity and volatile pressurisation which was manifested a change of eruptive dynamics from early effusion to the pozzolane rosse s highly explosive eruption climax

younger dryas in southernmost south america an update abstract high resolution pollen data from a peat section in southern tierra del fuego documents high paleoenvironmental variability between 11 ka and 9 ka detailed analysis of plant macro remains in the same section showed that the repeated high amplitude changes in pollen taxa were related to repeated fire disturbance burning at least once even the surface of the mire in many peat sections from southernmost patagonia and tierra del fuego charcoal particles have been found intermittently since about 13 ka and in great abundance especially after 11 ka this suggests that the environmental changes previously interpreted to imply a return to colder climates comparable to the north atlantic younger dryas event instead are in response to local and regional disturbances by fires

alkenone sea surface temperature in the southern ocean for the last two deglaciations a piston core taken from the tasman plateau in the southern ocean has been studied for organic compounds to reconstruct the late pleistocene marine environments here we report paleo sea surface temperature sst for the last two deglaciations using the unsaturation degree of alkenones u k 37 preserved in the marine sediments the u k 37 record indicates that the sst was at least 4 c lower than the present sst at the last glacial maximum lgm and the amplitude of paleo sst is at most 5 2 c from the penultimate glacial mis 6 to the last interglacial warm period the eemian our results also demonstrate that the eemian warm period in the southern ocean lasted only 3 000 years followed by a sharp cooling at around 120 kyr bp the sharp cooling in the southern ocean seemed to occur a few millennia 2 3 kyrs before the beginning of continental ice sheet growth

mineralogical and geochemical study of granular xenoliths from the alban hills volcano central italy bearing on evolutionary processes in potassic magma chambers granular xenoliths ejecta from pyroclastic deposits emplaced during the latest stages of activity of the alban hills volcano range from ultramafic to salic ultramafic types consist of various proportions of olivine spinel clinopyroxene and phlogopite they show low sio2 alkalies and incompatible element abundances and very high mgo however cr co and sc are anomalously low at a few ppm level olivine is highly magnesian up to fo 96 and has rather high cao 1 ca and very low ni around a few tens ppm contents these characteristics indicate a genesis of ultramafic ejecta by thermal metamorphism of a siliceous dolomitic limestone probably with input of chemical components from potassic magma the other xenoliths have textures and compositional characteristics which indicate that they represent either intrusive equivalents of lavas or cumulates crystallized from variably evolved ultrapotassic magmas one sample of the former group has major element composition resembling ultrapotassic rocks with kamafugitic affinity some cumulitic rocks have exceedingly high abundances of th 81 84 ppm and light rare earth elements lree la ce 421 498 ppm and extreme ree fractionation la yb 288 1393 not justified by their modal mineralogy which is dominated by sanidine leucite and nepheline finegrained phases are dispersed through the fractures and within the interstices of the main minerals semiquantitative eds analyses show that th and lree occur at concentration levels of several tens of percent in these phases indicating that their presence is responsible for the high concentration of incompatible trace elements in the whole rocks the interstitial position of these phases and their association with fluorite support a secondary origin by deposition from fluorine rich fluids separated from a highly evolved potassic liquid the nd isotopic ratios of the cjecta range from 0 51182 to 0 51217 87sr 86sr ratios range from 0 70900 to 0 71036 with the exception of one sample these values are lower than those of the outcropping lavas which cluster around 0 7105 3 this indicates either the occurrence of several isotopically distinct potassic magmas or a variable interaction between magmas and wall rocks however this latter hypothesis requires selective assimilation of host rocks in order to explain isotopic and geochemical characteristics of lavas and xenoliths the new data indicate that the evolutionary processes in the potassic magmas of the alban hills were much more complex than envisaged by previous studies interaction of magmas with wall rocks may be an important process during magmatic evolution element migration by gaseous transfer often invoked but rarely constrained by sound data is shown to have occurred during the latest stages of magmatic evolution such a process was able to produce selective enrichment of th u lree and to a minor degree ta and hf in the wall rocks of potassic magma chamber finally the occurrence of xenoliths with kamafugitic composition points to the existence of this type of ultrapotassic magma at the alban hills

glacial interglacial sea surface temperature changes across the subtropical front east of new zealand based on alkenone unsaturation ratios and foraminiferal assemblages 0 are compared to those derived from foraminiferal assemblages using the modern analog technique in two of these cores reconstructions of sst in core tops and holocene sediments agree well with modern average summer temperatures of 18 c in subtropical waters and 14 c in subpolar waters with a 4 5 c gradient across the front down core u37 k 0 sst estimates indicate that the regional summer sst was 4 5 c cooler during the last glaciation with an sst of 10 c in subpolar waters and an sst of 14 c in subtropical waters temperature reconstructions from foraminiferal assemblages agree with those derived from alkenones for the holocene in subtropical waters reconstructions also agree with a glacial cooling of 4 to 14 c in contrast reconstructions for subantarctic pre holocene waters indicate a cooling of 8 c with glacial age warm season water temperatures of 6 c thus the alkenones suggest the glacial temperature gradient across the front was the same or reduced slightly to 3 5 4 c whereas foraminiferal reconstructions suggest it doubled to 8 c our results support previous work indicating that the stf remained fixed over the chatham rise during the last glacial maximum however the differing results from the two techniques require additional explanation a change in euphotic zone temperature profiles seasonality of growth or preferred growth depth must have affected the temperatures recorded by these biologically based proxies regardless of the specific reason a differential response to the environmental changes between the two climate regimes by the organisms on which the estimates are based suggests increased upwelling associated with increased winds and or a shallowing of the thermocline associated with increased stratification of the surface layer in the last glaciation index terms 4267 oceanography general paleoceanography 4850 oceanography biological and chemical organic marine chemistry 1050 geochemistry marine geochemistry 4835 4850 1055 geochemistry organic geochemistry keywords paleoceanography sea surface temperature alkenones southern ocean last glacial maximum

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

a minimum thermodynamic model for the bipolar seesaw 1 the simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of antarctic ice cores the model results from the classic bipolar seesaw by coupling it to a heat reservoir in this thermal bipolar seesaw the heat reservoir convolves northern time signals with a characteristic timescale applying the model to the data of grip and byrd we demonstrate that maximum correlation can be obtained using a timescale of about 1000 1500 years higher correlations are obtained by first filtering out the long term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw the model resolves the apparent confusion whether northern and southern climate records are in or out of phase synchronous or time lagged

interaction between ultrapotassic magmas and carbonate rocks evidence from geochemical and isotopic sr nd o compositions of granular lithic clasts from the alban hills volcano central italy abstract magma carbonate rock interaction is investigated through a geochemical and sr nd o isotope study of granular lithic clasts ejecta from the alban hills ultrapotassic volcano central italy some samples group 1 basically represent intrusive equivalents of alban hills magmas a few samples group 2 are ultramafic have high mgo 30 to 40 wt and 18o and originated by accumulation of mafic phases that crystallised from ultrapotassic melts during assimilation of dolomitic rocks group 3 ejecta consist of dominant k feldspar and show major element compositions similar to phonolites which however are absent among the alban hills volcanics finally another group group 4 contains corroded k feldspars surrounded by a microgranular to porphyritic matrix made of igneous minerals k feldspar foids clinopyroxene phlogopite plus wollastonite garnet and some cuspidine group 4 ejecta are depleted in sio2 and enriched in cao with respect to group 3 the analysed ejecta have similar 143nd 144nd 0 51204 0 51217 as the alban hills lavas whereas 87sr 86sr 0 70900 0 71067 is similar to lower whole rocks 18o ranges from 7 0 to 13 2 reaching maximum values in ultramafic samples a positive correlation with cao is observed in single rock groups large ion lithophile element lile abundances and ree fractionation are generally high and extreme values of th u and lree are found in some group 3 and group 4 rocks mineralogical petrological and geochemical data reveal extensive interaction between magma and carbonate wall rocks involving both dolostones and limestones these processes had dramatic effects on magma compositions especially on phonolites which were transformed to foidites evidence of such a process is found in group 4 samples in which k feldspar is observed to react with a matrix that represents strongly undersaturated melts formed by interaction between silicate magma and carbonates trace element data also testify to a very important role for f co2 h2o s fluids during magma wall rock interaction fluid transfer was responsible for extreme enrichments in th u and lree especially observed in group 3 and group 4 rocks implications of these processes for potassic magma evolution in central italy are discussed

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

response of surface water masses and circulation to late quaternary climate change east of new zealand a series of cores from east of new zealand have been examined to determine the paleoceanographic history of the late quaternary in the sw pacific using planktonic foraminiferal data distinct shifts of species can be seen between glacial and interglacial times especially south of chatham rise east of south island foraminiferal fragmentation ratios and benthic planktonic foraminiferal ratios both show increased dissolution during glacials especially isotope stage 2 to the south of chatham rise the present day subtropical convergence appears to be tied to the chatham rise at 44 s but during glacial times this rise separated cold water to the south from much warmer water to the north with an associated strong thermal gradient across the rise we estimate that this gradient could have presented as much as an 8 c temperature change across 4 of latitude during the maximum of the last ice age there is only weak evidence of the younger dryas cool event but there is a clear climatic optimum between 8 and 6 4 ka with temperatures 1 2 c higher than the present day the marine changes compare well with vegetational changes on both south and north island

deglacial paleoceanographic history of the bay of plenty new zealand 1 we present sea surface temperature sst records with centennial scale resolution from the bay of plenty north of new zealand foraminiferal assemblage based paleo sst estimates provide a deglacial record of sst since 16 5 14c ka average holocene ssts are 15 6 c for winter and 20 3 c for summer whereas average glacial values were 14 2 c for winter and 19 5 c for summer compared to modern time cooling of ssts at the last glacial maximum lgm was 0 9 c in winter and 1 5 c in summer the shift from glacial to holocene temperatures began at 14 25 14c ka warming by 2 c until 12 85 14c ka when temperatures dipped back to glacial values at 11 65 14c ka the timing of this return to glacial like sst correlates well with the antarctic cold reversal acr rather than the younger dryas and documents that the influence of the acr extended into the subtropics of the southern hemisphere at least in this region of the southwest pacific by 10 55 14c ka an sst maximum in summer ssts of up to 3 c warmer than modern occurred 24 c after which sst dropped remaining at present day temperatures since 9 3 14c ka this early holocene climatic optimum has been widely noted in the southern ocean and this record indicates that this phenomenon also extended into the subtropics to the north of new zealand

relationships between ultrapotassic and carbonate rich volcanic rocks in central italy petrogenetic and geodynamic implications the pleistocene intra apennine volcanic iav centres occurring east of the potassium rich roman comagmatic province show variable petrological and geochemical composition some rocks have a strongly undersaturated ultrapotassic kamafugitic affinity with k2o na2o 8 20 whereas the rocks from the southern center of mt vulture are still strongly undersaturated in silica but are enriched in both na2o and k2o with k na around unity carbonate rich pyroclastic rocks believed to represent carbonatitic magmas are found in the iav centers kamafugites have high abundances of lile and high lile hfse ratios and their incompatible element patterns resemble closely those of ultrapotassic rocks from the adjoining roman province the vulture volcanics also display high contents of lile but their lile hfse ratios are intermediate between intraplate alkaline rocks and kamafugites the carbonate rich rocks exhibit an exotic mineralogy and high enrichments in lile which speaks for a carbonatitic affinity however they have similar incompatible element patterns but consistently lower abundances of almost all the elements than the associated silicate volcanics these data favour the hypothesis that the iav carbonate rocks may represent mixtures of silicate magmas and geochemically depleted carbonate material the sedimentary carbonates that crop out extensively along the apennine chain may be the source of barren carbonate material overall geochemical data of iav centres and of the rocks from the roman province display strong geochemical and isotopic evidence of being generated in an upper mantle that was modified by addition of upper crustal material brought down by subduction processes a possible exception is represented by mt vulture which however occurs east of the main axis of the apennines on the western margin of the foreland adria plate the occurrence of strongly undersaturated alkaline rocks requires magma generation at high pressures and xco2 this is in agreement with the hypothesis that subduction processes under the apennines occurred by consumption of poorly hydrated thinned or delaminated continental crust

late pleistocene environments of the central ukraine the vyazivok loess sequence from the dnieper plain ukraine documents regional environmental changes during the late pleistocene and holocene pedological and palynological analyses and low field magnetic susceptibility document changes from dense temperate forest during the last interglacial maximum to open harsh loess steppe during the latest pleistocene the vyazivok section overlies hillwash derived from a lower pleistocene terrace and consists of two stratified soil complexes kaydaky and pryluky marine isotope stage mis 5 equivalent separated by a layer of eolian dust tyasmyn silt the lower soils in both complexes formed within forest these soils are overlain by the uday mis4 and bug mis2 loess units which are separated by boreal soils of the vytachiv mis3 complex the coldest conditions within the record occurred in the youngest loess holocene soils cap the bug loess the vyazivok section shows remarkable similarities with other classical loess sequences in western europe the czech republic and austria the kaydaky pryluky and vytachiv deposits correlate with the pkiii pkii and pki soil complexes respectively of the czech republic the tyasmyn and prylyky silt layers correspond to marker horizons from central europe c 2001 university of washington

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

evidence for the presence of carbonate melt during the formation of cumulates in the colli albani volcanic district italy abstract fergusite and syenite xenoliths and mafic lapilli from two locations in the villa senni ignimbrite of the colli albani volcanic district show evidence for fractionation of a silicate magma that led to exsolution of an immiscible carbonate melt the fergusite xenoliths are divided into two groups on the basis of their clinopyroxene compositions group 1 clinopyroxene records the crystallisation of a silicate melt and enrichment of the melt in al ti and mn and depletion in si as well as enrichment in incompatible trace elements the second group of clinopyroxene compositions group 2 comes mainly from ba f phlogopite and ti andradite bearing fergusites they have significantly higher si and lower al and ti and like the coexisting phlogopite and garnet are strongly enriched in mn the minerals in the fergusites containing group 2 clinopyroxene are enriched in ba sr cs v and li all of which are expected to partition strongly into a carbonate melt phase relative to the coexisting silicate melt the compositional data suggest that the group 1 fergusites record sidewall crystallisation of co2 rich silicate melt and that once the melt reached a critical degree of fractionation carbonate melt exsolved the group 2 fergusites record continued crystallisation in this heterogeneous silicate carbonate melt system composite xenoliths of fergusite and thermometamorphic skarn record contact times of hundreds to a few thousand years indicating that fractionation and assimilation was relatively rapid

f phlogopites in the alban hills volcanic district central italy indications regarding the role of volatiles in magmatic crystallisation abstract a systematic analysis of micas contained in effusive pyroclastic and hypabyssal rocks of the alban hills volcanic district ahvd central italy was made in order to characterise minerals of pyroclastic units for tephrostratigraphy and to obtain as much information as possible on the activity of volatiles in this magmatic system the phlogopite shows a large range of f contents between 0 50 and 7 50 wt that make it possible to discriminate different ahvd lithologies in particular micas of lava groundmass are characterised by extremely high f up to 7 50 wt and ba up to 9 70 wt contents seldom or never found in other magmatic ultrapotassic rocks moreover the micas of pyroclastics ultramafic cumulates and holocrystalline inclusions made up of leucite clinopyroxene and phlogopite hereafter italites show mg mg fe values between 0 65 and 0 90 that are not correlated with f contents the variations in f contents observed in the ahvd micas do not appear to be due to a temperature effect or pressure changes but they may be due to variations in the h 2 o and co 2 activities in the magma chamber they make it possible to differentiate three crystallisation environments in the ahvd magmatic system the first one had elevated co 2 activity and formed the italites near the carbonate contact these rocks represent at least those enriched in clinopyroxene without skarn minerals the hypabyssal crystallisation of the ahvd magmas at the periphery of magma chamber the second one characterised by a higher water activity is represented by the micas of the ultramafic cumulates and pyroclastic scorias and is located in the inner part of magma chamber the third environment the groundmass of the lavas it is not related with the previous ones and is characterised by the absence of water and by a high f activity in general our results suggest that the compositional variations observed in the micas al si ti ba reflect different h 2 o activities inversely correlated with f activity in the magma chamber

lateglacial landscape and vegetation change and the younger dryas climatic oscillation in new zealand abstract lateglacial sequences in new zealand show progressive afforestation and landscape stabilization reflecting a warming climate between 14 500 bp and 11 500 bp afforestation and landscape stability was achieved throughout most of the north island and the northwest sector of the south island in the south island scrub and tree ferns were replacing previous grasslands in the east by 11 000 bp and broadleaved forest was spreading in the west no significant reversals of these trends occurred and afforestation was complete by 9500 bp glaciers of the high central part of the southern alps made a series of advances between 14 000 and 9000 bp most of these advances are poorly dated but two moraines are of younger dryas age glacial advances in the face of the general lateglacial warming trend may have been driven by stronger westerly winds increasing snowfall on high altitude neves and by reduced ablation as a consequence of moist cloudy low insolation summers the cause of the northern hemisphere younger dryas cooling is still uncertain and expected southern hemisphere responses may differ according to the mechanism proposed for the cooling poor chronological resolution and apparent conflict between the various types of evidence for climatic change make detection of an unambiguous younger dryas in new zealand problematical

time dependent geochemistry of clinopyroxene from the alban hills central italy clues to the source and evolution of ultrapotassic magmas abstract we investigated chemical and isotopic compositions of clinopyroxene crystals from well age constrained juvenile scoria clasts lava flows and hypoabyssal magmatic ejecta representative of the whole eruptive history of the alban hills volcanic district the alban hills is a quaternary ultra potassic district that was emplaced into thick limestone units along the tyrrhenian margin of italy alban hills volcanic products even the most differentiated are characterised by low sio2 content we suggest that the low silica activity in evolving magmas can be ultimately due to a decarbonation process occurring at the magma limestone interface according to the liquid line of descent we propose the differentiation process is driven by crystallisation of clinopyroxene leucite apatite magnetite coupled with assimilation of a small amount of calcite and or with interaction with crustal co2 by combining age chemical data strontium and oxygen isotopic compositions and ree content of clinopyroxene we give insights into the evolution of primitive ultrapotassic magmas of the alban hills volcanic district over an elapsed period of about 600 kyr geochemical features of clinopyroxene crystals consistent with data coming from other italian ultrapotassic magmas indicate that alban hills primary magmas were generated from a metasomatized lithospheric mantle source in addition our study shows that the 87sr 86sr and lree hree of alban hills magmas continuously diminished during the 600 35 ka time interval of the alban hills eruptive history possibly reflecting the progressive depletion of the metasomatized mantle source of magmas

el nino like pattern in ice age tropical pacific sea surface temperature sea surface temperatures ssts in the cold tongue of the eastern equatorial pacific exert powerful controls on global atmospheric circulation patterns we examined climate variability in this region from the last glacial maximum lgm to the present using a sst record reconstructed from magnesium calcium ratios in foraminifera from sea floor sediments near the galapagos islands cold tongue sst varied coherently with precession induced changes in seasonality during the past 30 000 years observed lgm cooling of just 1 2 c implies a relaxation of tropical temperature gradients weakened hadley and walker circulation southward shift of the intertropical convergence zone and a persistent el nino like pattern in the tropical pacific this is contrasted with mid holocene cooling suggestive of a la nina like pattern with enhanced sst gradients and strengthened trade winds our results support a potent role for altered tropical pacific sst gradients in global climate variations

global nature of the younger dryas cooling event inferred from oxygen isotope data from sulu sea cores the younger dryas an approximately 1 000 year long return to near glacial conditions interrupted the glacial holocene climate transition during which most of the northern hemisphere ice sheets melted evidence for the younger dryas event has been found mainly in sediments from the north atlantic ocean and northwest europe and this has led to the idea that the event was caused by an injection of meltwater into the north atlantic ocean1 3 this model however has been recently questioned in the light of coral reef data on the rate of sea level changes during this transition4 here we present high resolution oxygen isotope records from benthic and planktonic foraminifera from two radiocarbon dated cores in the sulu sea showing that the younger dry as occurred synchronously in the surface and deep waters of the sulu sea and the northern atlantic ocean by combining our results with other palaeoclimate data we suggest that the younger dry as event was a global phenomenon and we believe it to have been caused by low atmospheric co2concentrations

the younger dryas cool episode in the gulf of mexico data are presented from orca basin piston core en32 pc4 in the gulf of mexico that confirm the existence of surface water cooling during the younger dry as chronozone 11 10 ka late glacial planktonic foraminiferal species made a reappearance between 11 4 and 9 8 ka an episode also marked by distinctly higher oxygen isotopic values derived from the planktonic foraminifer globigerinoides ruber the presence of the younger dryas event in the gulf at 27 n demonstrates that surface water cooling extended to mid latitude regions in the north atlantic the cool surface water interval is bracketed by rapid shifts in 18o related to changes in the influx of meltwater to the gulf of mexico a chronology based upon seven accelerator radiocarbon dates indicates that cooling commenced over a 500 year period and ended in less than 200 years these results are among the first deep sea sediment data documenting the climatic transitions bracketing the younger dryas with a rapidity observed in ice core records a rapid decrease in 18o values measured in the white form of gs ruber at 10 2 ka is explained by significant meltwater influx into the gulf and rapid increase in sea surface temperatures surprisingly a similar decrease is not observed in the pink form of gs ruber a summer surface water dweller in the gulf this discrepancy may be explained by continued meltwater influx throughout the younger dryas during the summers only such that there was no change in the 18o of the pink form at the end of the episode an additional possibility is that warming at the end of the younger dryas raised year average temperatures and summer temperatures remained constant the coincidence of rapid shifts in 18o with the younger dryas strongly suggests a dynamic causal relationship and therefore supports a model for the cause of the younger dryas cooling based on changes in the routing of laurentide glacial meltwater

estimates of sea surface temperature in the coral sea at the last glacial maximum the climap 1981 reconstruction of the coral sea found relatively little cooling 2 c in the low latitudes 10 s but a warming off australia at about 25 s the small low latitude changes are of interest because terrestrial pollen and snowline data from the new guinea highlands imply that surface temperatures may have been 6 to 9 c colder at the last glacial maximum lgm the purpose of this paper is to evaluate these conclusions on the basis of additional core sites new oxygen isotope stratigraphy and new sea surface temperature sst estimates using the modern analog technique mat in the northern coral sea planktonic foraminifer assemblages consist of tropical subtropical species that show little change over the past 20 kyr quantitative estimates of sst using the modern analog technique mat confirm the climap 1981 conclusion that little or no temperature change occurred in this tropical region at the lgm thus reinforcing the conflict with terrestrial evidence in the southern region 25 s two cores indicate that foraminifer faunas became more subtropical at the lgm the mat estimates for the lgm are 3 to 4 c colder than modern producing a steeper thermal gradient in the southern coral sea these data remove the warm sst anomaly along the eastern coast of australia and indicate that during the lgm cool high latitude waters were displaced northward along the coast of australia into the southern coral sea

retreat velocity of the north atlantic polar front during the last deglaciation determined by 14 c accelerator mass spectrometry the glacial oscillations which dominate the quaternary global climate are closely related to changes in incoming solar radiation but the details of palaeoclimatic spectra suggest that other parameters usually referred to as feedback have significantly increased the climatic response to extraterrestrial forcing1 the last deglaciation appears to be one of the more characteristic examples of nonlinearity because its abruptness strongly contrasts with the smooth shape of the associated solar radiation maximum dated at 11 000 yr bp in addition the presence of the younger dryas cold event concomitant with the solar radiation maximum could be interpreted as a transitory phenomenon caused by the rapid meltwater influx linked to the first phase of the ice sheet s disintegration2 3 here using accelerator mass spectrometry we date precisely the movements of the polar front during the whole period of glacial retreat 15 000 8 000 yr bp our results show that the polar front has moved between 35 n and 55 n in 1 000 yr for the earliest retreat 12 500 12 000 bp and moved almost instantaneously that is 400 yr during the two abrupt climatic changes associated with the younger dry as cold event

genesis evolution and tectonic significance of k rich volcanics from the alban hills roman comagmatic region as inferred from trace element geochemistry trace element data are reported in 21 lava samples from the alban hills one of the most important volcanic complexes of the roman comagmatic region the samples consist mostly of tephritic leucitites with minor phonolitic tephrites and tephritic phonolites emplaced during two distinct phases of activity separated by a caldera collapse