oxygen isotope analyses and pleistocene ice volumes abstract the oxygen isotope record from fossil foraminifera in deep sea sediments is commonly used as a proxy for global ice volume the linkage between 18 o and ice volume however is probably nonlinear we have developed a simple numerical model of the isotopic response of the oceans to ice volume change the major features it simulates are 1 the changing mean isotopic composition of snow as a function of ice volume colder snow temperatures forced by climate change and higher elevation accumulation areas imply more negative mean 18 o 2 the nonequilibrium isotopic composition of ice sheets the past history of an ice sheet is integrated into its mean isotopic composition which introduces a lag of isotopic ice volume i e the measured 18 o record scaled to ice volume units behind true ice volume 3 selective preservation of isotopically more negative colder higher latitude ice this geographic effect can selectively amplify or dampen the isotopic response to the ice volume signal we illustrate the response of our model to simple hypothetical ice volume transitions of ice growth and ice decay sensitivity tests are illustrated for all model parameters the results suggest that oxygen isotope records reproduce the general patterns of ice volume change fairly accurately the foraminiferal isotope record however may misrepresent the true amplitude of the ice volume signal and lag true ice volume by 1000 to 3000 yr

variations in mode of formation and temperature of oceanic deep waters over the past 125 000 years marked changes in the deep water temperature of the different oceanic basins during the past 125 kyr are revealed by a detailed comparison of the oxygen isotopic composition ofbenthicforaminiferafrom sediment cores taken from the norwegian sea and the pacific atlantic and southern oceans the last interglacial deep water temperatures were similar to the modern ones at the 5e 5d transition around 115 kyr bp the deep water temperatures dropped below approximately 0 c in the pacific and southern indian oceans in the atlantic ocean the deep water temperature dropped in 2 successive steps at 115 and 75ky bp the global ocean deep water temperatures were in the 0 to 1 c range for the whole of the last ice age isotope stages 4 2

a multi proxy record of holocene climatic change in southwestern spain the laguna de medina cadiz palaeolimnological data diatoms ostracods foraminifera molluscs aquatic pollen and lithology from a radiocarbon dated sediment core from a saline lake the laguna de medina provide the first complete record of holocene lake level change for southwest spain for the last c 9000 cal years the lake has always been relatively shallow but has exhibited marked fluctuations in salinity and water depth especially in the earlier record when oscillations culminate in maximum lake levels from c 6960 6680 cal bp c 6070 5830 bp indicating enhanced early to mid holocene humidity and a mid holocene humidity maximum prolonged shallowing thereafter reflects in part increased aridity in the later holocene lake desiccation followed by a c 800 yr phase zone 2 of major limnological change commencing at c 8000 cal bp c 7200 bp and a number of other abrupt desiccation events are also noteworthy the mid holocene maximum is consistent with widespread evidence for high lake levels around 6000 bp but t

a decade of exploring a submarine intraplate volcano hydrothermal manganese and iron at lō ihi volcano hawai i 1 decadal time series observations of hydrothermal fluid emissions from l ihi volcano were initiated in 1992 using a combination of submersible and shipboard sampling strategies magmatic tectonic processes associated with a spectacular seismic event in july august 1996 led to the collapse of pele s vents 31 c near the volcano summit into a new pit crater pele s pit inundated by high temperature tmax 198 c focused and lower temperature 30 to 200 fold 1 5 months postcollapse and during the following year decreased a further twofold to threefold at pele s pit and 30 fold at east pit while a steady concentration of 400 nmol l tdfe prevailed throughout the remaining years of this study at pele s pit a gradual and threefold decrease in the concentration of dmn to about 15 nmol l was observed high temperature fluids 128 198 c 1997 1999 90 c 2001 venting simultaneously from different orifices within pele s pit had distinguishable fe mn ratios that can be attributed to different subseafloor origins fe mn ratios characteristic of fluids moderated by high temperature water rock reaction had low values in 1997 1998 1 6 0 7 increasing to about 7 in 1999 fluids moderated by magmatic degassing of co2 had much higher fe mn ratios increasing from 24 15 in 1997 1998 to 50 in 1999 and 63 87 in 2001 fe mn values of dispersing plumes at l ihi reflect an admixture of these sources and a relative fe abundance that is consistently high compared to mid ocean ridge systems the pulsed injection of mn and fe into the surrounding ocean associated with the 1996 tectonic magmatic event at l ihi was massive our decadal observations confirm that mn and fe are useful markers of the magnitude and evolution of the effects of magmatic perturbation on hydrothermal systems influenced by chronic magmatic degassing

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

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

conference on the last deglaciation timing and mechanism abstract for years paleoclimatologists have held the general view that the last deglaciation began around 17 000 to 15 000 yr ago that the shape of the globally integrated deglacial curve was smoothly sigmoidal with the fastest rate of change centered around 11 000 yr ago and that the deglaciation ended around 7000 to 5000 yr ago recent studies have challenged several aspects of this consensus and have suggested that the mechanisms responsible for the deglaciation are significantly different from those previously proposed as a result an international workshop was held at airlie house in virginia during may 2 6 of 1983 to evaluate a wide range of evidence relevant to this controversy the conference results suggested that 1 the decrease in global ice volume occurred in two steps with the dating of the earlier step still in doubt but the later step occurring at about 10 000 7000 yr ago and 2 the most likely feedback mechanisms for accelerating the initial forcing by orbital variations are delayed bedrock rebound marine downdraw calving and co 2 heating

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

land sea correlations for the last glaciation inferred from a pollen and dinocyst record from the portuguese margin pollen and dinoflagellate cyst assemblages from core su 81 18 recovered off portugal 37 46 n 10 11 w 3135 m water depth have been used to document the short term environmental changes that occurred in southwest europe since 25 000 yr b p the relationship between the oceanic and continental environments has been further examined by the use of other marine proxies coarse sedimentary fraction foraminifera and by comparison with proximal land pollen records heinrich 2 h2 and heinrich 1 h1 events were the most extreme parts of the highly variable last glacial period with the maximum extension of dry steppe on land and the occurrence of cool and dilute waters at the core site our study shows that h1 and h2 are divided in two distinct phases one with neogloboquadrina pachyderma left coiling associated with the maximum input of ice rafted debris reflecting the in situ release of icebergs and the occurrence of cool and dilute seawater at the core site the other with dinoflagellate cysts of subpolar affinity bitectatodinium tepikiense reflecting a seasonal control marked by warm summer sst and cold winter sst

sulphur eruptions at volcan poas costa rica since the recent desiccation of the crater lake at volcan poas costa rica vigorous fumarolic activity on the exposed lake bed has been associated with the manifestation of miniature sulphur volcanoes sulphur flows and sulphur pools in this paper observations of 2 3 m high active sulphur volcanoes are reported and mechanisms for their formation proposed and discussed their ejecta composed of milled particles crystals and accretionary lapilli of sulphur are unlike previously described pyroclastic sulphur deposits and probably form from a spray of crystallised sulphur forced to the surface by fumarolic gases passing upwards through shallow bodies of liquid sulphur while much of the erupted material is recycled the reservoir of molten sulphur can also be replenished by influxing magmatic hydrothermal fluids 34s isotope ratios of several samples of native sulphur collected at poas range between 9 4 and 12 3 cdt these are among the isotopically lightest volcanic deposits of elemental sulphur reported although this pronounced depletion is readily explained by the likely formation of the sulphur under the acidic conditions of the aqueous lake and hydrothermal system the total amount of native sulphur deposits contained within lake sediments at poas and perhaps at other active volcanoes with crater lakes is potentially substantial a large explosive eruption could by volatilisation and oxidation of this sulphur inject large volumes of sulphur dioxide into the atmosphere the greenish colouration of the sulphur reminiscent of other documented terrestrial sulphur eruptions is probably due to impurities this emphasises the point that interpretation of spectral reflectances of the jovian moon io regarding the possible contribution of sulphur cannot rely on extrapolation of laboratory data for pure materials

salinity changes in the north west pacific ocean during the late pliocene early quaternary from 2 73 ma to 2 52 ma recent research has increasingly advocated a role for the north pacific ocean in modulating global climatic changes over both the last glacial cycle and further back into the geological record here a diatom 18o record is presented from ocean drilling program site 882 over the pliocene quaternary boundary from 2 73 ma to 2 52 ma mis g6 mis 99 large changes in 18odiatom of c 4 from 2 73 ma onwards are documented to occur on a timeframe broadly coinciding with glacial interglacial cycles these changes are primarily attributed to large scale inputs of meltwater from glacials surrounding the north pacific basin and the bering sea despite these inputs and associated change in surface water salinity on the basis of existing opal and uk37 temperature data and new modelled water column densities no evidence exists to suggests a removal of the halocline stratification or a resumption of the high productivity system similar to that which prevailed prior to 2 73 ma the permanence of the halocline suggests that the region played a key role in driving global climatic changes over the early glacial interglacial cycles that followed the onset of major northern hemisphere glaciation by inhibiting deep water upwelling and ventilation of co2 to the atmosphere

satellite limb scanning thermal infrared observations of the el chichon stratospheric aerosol first results the infrared radiometer experiment on the solar mesosphere explorer satellite has been continuously measuring the 6 8 m thermal emission from the stratospheric aerosol from the el chichon volcano since the time of eruption in early april 1982 inversion results for the zonally averaged infrared extinction coefficient in height latitude and time show that the aerosol increased in mass to a maximum of 8 tg 8 1012gm about 15 weeks after the april 4 eruption it descended in height with an average speed consistent with the gravitational settling time of particles with a diameter of about 1 4 m

alkenones and multiproxy strategies in paleoceanographic studies 1 we assess multiproxy strategies involving alkenone based and other paleoceanographic indicators in an effort to define uncertainties and to advance understanding of past oceanic and climatic changes looking to the future we recommend a parallel strategy of applying proxies to the geologic record while continuously seeking refinements in methods and understanding of mechanisms that control each proxy a multiproxy strategy increases confidence in results and provides oceanographic context for more effective interpretation of processes a combination of proxies allows derivation of additional properties such as upper ocean paleosalinity or paleo pco2 for a more complete view of the oceanographic and climate mechanisms involved in changing earth s environment

the late quaternary coastal forests of western iberia a study of their macroremains plant remains collected from the portuguese coast some of them in situ were examined to provide local information on the vegetation of the iberian atlantic area over the last 35 000 years pinus gr sylvestris nigra from the wurm period was identified in sandy soils along with quercus gr robur petraea and fraxinus sp the presence of in situ remains of this pinus group on the northern portuguese coast indicates the local temperature and precipitation conditions that must have reigned at this time thirty two in situ pinus pinaster remains close to the mouth of the river tagus show the importance of this taxon in this area during the first half of the holocene other holocene macroremains indicate the presence of non riparian taxa quercus gr robur petraea and castanea sp hygrophilous plants fraxinus sp populus sp alnus sp and sambucus sp and shade intolerant taxa erica cinerea vagans

glacial holocene environment of the southeastern okhotsk sea evidence from geochemical and palaeontological data abstract environmental conditions and productivity changes in the southeastern okhotsk sea have been reconstructed for the last 20 ka using planktonic and benthic foraminiferal oxygen isotope records and calcium carbonate organic carbon and opal content data from two sediment cores species variability in benthic foraminiferal and diatom assemblages provides additional palaeoceanographic evidence ams radiocarbon dating of the sediments and oxygen isotope stratigraphy serve as the basis for the age models of the cores for the last 20 14 c kyr and for correlation between environmental variations in the okhotsk sea and regional and global climate changes benthic foraminiferal assemblages in the two cores depth 1590 and 1175 m varied with time so that we could recognise seven zones with different species composition changes in the benthic foraminiferal assemblages parallel major environmental and productivity variations during the last glaciation fluxes of organic matter to the sea floor showed strong seasonal variations indicated by the presence of abundant a weddellensis and infaunal uvigerina spp benthic foraminiferal assemblages changed with warming at 12 5 11 and 10 8 14 c kyr bp when productivity blooms and high organic fluxes were coeval with global meltwater pulses 1a and 1b younger dryas cooling caused a decline in productivity 11 10 kyr bp affecting the benthic faunal community subsequent warming triggered intensive diatom production opal accumulation and a strong oxygen deficiency causing significant changes in benthic fauna assemblages from 5 26 4 4 kyr bp to present time

correlations between eruption magnitude so2 yield and surface cooling about the book humans have long marvelled at and feared the odorous and colourful manifestations of volcanic emissions and in some cases have harnessed them for their economic value the degassing process responsible for these phenomena is now understood to be one of the key factors influencing the timing and nature of volcanic eruptions moreover the surface emissions of these volatiles can have profound effects on the atmospheric and terrestrial environment and climate even more fundamental are the relationships between the history of planetary outgassing differentiation of the earth s interior chemistry of the atmosphere and hydrosphere and the origin and evolution of life this book provides a compilation of 23 papers that investigate the behaviour of volatiles in magma the feedbacks between degassing and magma dynamics and the composition flux and environmental atmospheric and climatic impacts of volcanic gas emissions

forward modeling of carbonate proxy data from planktonic foraminifera using oxygen isotope tracers in a global ocean model the distribution and variation of oxygen isotopes in seawater are calculated using the goddard institute for space studies global ocean model simple ecological models are used to estimate the planktonic foraminiferal abundance as a function of depth column temperature season light intensity and density stratification these models are combined to forward model isotopic signals recorded in calcareous ocean sediment the sensitivity of the results to the changes in foraminiferal ecology secondary calcification and dissolution are also examined simulated present day isotopic values for ecology relevant for multiple species compare well with core top data hindcasts of sea surface temperature and salinity are made from time series of the modeled carbonate isotope values as the model climate changes paleoclimatic inferences from these carbonate isotope records are strongly affected by erroneous assumptions concerning the covariations of temperature salinity and 18ow habitat imposed biases are less important although errors due to temperature dependent abundances can be significant

deglacial surface circulation changes in the northeastern atlantic temperature and salinity records off nw scotland on a century scale sea surface temperature and salinity estimates reconstructed from a core collected on the barra fan northwest scotland 56 43 n 09 19 w water depth 1320 m show a series of rapid oscillations during the last deglacial period that are very similar to those observed in the 18o records from greenland ice cores these records indicate that the transport of heat and salt toward the nordic seas was highest during the bolling period this superconveyor weakened after the bolling probably as a consequence of increased meltwater flux reducing the oceanic salt content as suggested by the barbados sea level record evidence for a phase of ice rafting during the allerod is presented for the first time from this latitude in the northeast atlantic the younger dryas stadial resolved here at a century decadal scale is characterized by very rapid oscillations in temperature and salinity indicating that warm relatively saline waters repeatedly displaced cool polar waters at this latitude these observations attest to the inherent instability of the deglacial climate system

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

direct dating of the oxygen isotope record of the last deglaciation by 14c accelerator mass spectrometry major trends of quaternary global climate are reflected in the continental ice volume changes which have been reconstructed by oxygen isotope analysis1 2 18o records from deep sea sediments show that the net glacial build up occurs relatively slowly3 but that the end of an ice age occurs quickly in less than 10 000 yr implying a nonlinear response4 5 to simple milankovitch theory6 the latter observation suggests that the cause of the most recent deglaciation was the maximum in summer calorific radiation at the upper latitudes of the northern hemisphere centred around 11 000 yr ago a view supported by early studies7 later work has produced conflicting dates the main source of confusion being problems with obtaining accurate and reliable dates here by using accelerator mass spectrometry we have measured 14c for various species of foraminifera to produce a reliable timescale for the oxygen isotope record our results show that at the end of the last ice age continental ice sheets began to melt more than 4 000 yr before the northern hemisphere maximum of summer calorific radiation

century to millennial scale sedimentological geochemical records of glacial holocene sediment variations from the barra fan ne atlantic the barra fan located at the continental margin of nw scotland offers a unique possibility to retrieve records of exceptional high resolution to obtain climate records on a century millennial timescale we used a sedimentological geochemical approach to examine the sediment variations that reflect the palaeoceanography and climate history of the area inorganic chemistry combined with micropalaeontology reveals trends and changes in ne atlantic palaeoceanography and northwest european climate at the sub milankovitch frequency this study builds on results from two british geological survey cores and one giant piston core core 57 11 59 core 56 10 36 and images core md95 2006 that were obtained during the neapacc ne atlantic palaeoceanography special topic nerc phase geochemical records of lithogenic input fluctuate rapidly and their patterns parallel sea surface temperature and particle size records the cold periods are characterized by increased clay input compared to the warm periods the younger dryas period and other prominent periods such as the equivalent of heinrich event 1 show extremely expanded sections up to several metres in thickness enhancement of accumulation rates in the glacial section is due to the influence of downslope sedimentation meltwater deposition and large scale currents redistributing the sediment along the upper slope the radiochemical tracer excess 230 th shows that major shifts in terrigenous sediment supply were extremely rapid over the last 15 ka the shifts in terrigenous supply occurred over time spans of less than a century century scale events of lithogenic input can be visually correlated to other north atlantic climate records such as the gisp2 greenland ice core 18 o record for the last 15 ka although the resolution of radiocarbon dating of these events in the sediments is not sufficiently precise to verify that the visual correlations are correct the particle flux and biogenic records show sawtooth shaped cycles opposite to the dansgaard oeschger cycles

present day and past last 25000 years marine pollen signal off western iberia abstract the comparison between modern terrestrial and marine pollen signals in and off western iberia shows that marine pollen assemblages give an integrated image of the regional vegetation colonising the adjacent continent present day mediterranean and atlantic forest communities of iberia are well discriminated by south and north marine pollen spectra respectively results from total pollen concentration together with recognized conceptual models of fine particle dynamics in the iberian margin have allowed us to establish the present day pattern of pollen dispersion in this region the 25 000 year long record of continental pollen and marine 18 o of globigerina bulloides ice rafted detritus ird and neogloboquadrina pachyderma s proxies from the galician margin composite core md99 2331 and md03 2697 show that vegetation cover in north western iberia has responded contemporaneously to the climate variability of the north atlantic the vegetation response to the well known north atlantic heinrich events 2 and 1 h2 and h1 is however complex and characterised by two vegetation phases at low and mid altitudes of north western iberia the beginning of each heinrich event is marked on land by an important pine forest reduction and the expansion of heathers which are synchronous with the heaviest planktic 18 o values and the maxima of n pachyderma s suggesting that these first phases were cold and wet pinus forest expansion characterising the second phase of each heinrich event indicates a less cold episode associated during h1 with an increase of dryness as suggested by the development of semi desert associations the comparison of our galician margin multi proxy record with several pollen sequences from in and off iberia allows us to demonstrate that h1 event is the marine equivalent of the oldest dryas on the continent the occurrence of temperate trees during the last glacial maximum lgm and the rapid expansion of deciduous quercus during the bolling allerod period in our galician margin composite sequence show that not only the southern but also north western iberia was a refugium zone for deciduous trees during the last glacial period especially at low and mid altitude zones furthermore the comparison between southern and northern marine and terrestrial sequences allows us to confirm that vegetation responded to the bolling allerod warming the younger dryas cold event and the holocene more quickly in low and mid altitudes of north western iberia and in the south than in the high altitude northern region most likely as the result of the higher density of refugia for temperate trees in these zones during the lgm

aridity of the mediterranean sea at the last glacial maximum a reinterpretation of the δ18o record paleoclimate data show conflicting evidence for aridity in the mediterranean basin at the last glacial maximum lgm two recent modeling studies of the lgm mediterranean using water balance biome and ocean general circulation models respectively suggest that evaporation over the basin was reduced at the lgm compared with today in apparent conflict with these results is the strongly enhanced 18o signature of the lgm mediterranean surface waters particularly in the eastern basin which has been ascribed to a much higher salinity in an alternative interpretation presented here a box model of the balance between paleoclimate model evaporation and rainfall and paleoceanographic model advective terms shows that the observed lgm 18o signature can be reproduced without the need for an enhanced salinity with advection playing the dominant role in the 18o budget the box model also shows that the 18o data alone are insufficient to determine the type of exchange between the eastern and western basins the results emphasize that regional paleoceanographic water balances should consider all relevant processes and not just the evaporative flux

high resolution al and fe data from the atlantic ocean clivar co2 repeat hydrography a16n transect extensive linkages between atmospheric dust and upper ocean geochemistry 1 trace element sampling and shipboard flow injection analysis during the june august 2003 climate variability and predictability clivar co2 repeat hydrography a16n transect has produced a high resolution section of dissolved fe and al in the upper 1000 m of the atlantic ocean between 62 n and 5 s using the surface water dissolved al and the model of aluminum for dust calculation in oceanic waters madcow model we have calculated the deposition of mineral dust to the surface ocean along this transect and compare that to dissolved fe concentrations the lowest mean mineral dust depositions of 0 2 g m 2 a 1 are found to the north of 51 n a region which also exhibits characteristics of biological fe limitation through its low dissolved surface water fe 0 1 nm and residual macronutrients e g nitrate 2 m to the south of this region mean dust deposition increases by an order of magnitude reaching 3 g m 2 a 1 at 10 n underneath the saharan dust outflow surface water fe values also increase along this section to 1 nm distinct minima in fe concentrations at the depth of the chlorophyll maximum in the vertical profiles between 18 and 4 n illuminate the role that active biological uptake plays in fe cycling an extensive subsurface zone of enhanced dissolved fe concentrations 1 5 nm underlying this region is a result of the biological vertical transport and remineralization of the surface water fe and is coincident with the intermediate nutrient maximum and oxygen minimum of this region elevated concentrations of dissolved al in subsurface waters seen between 30 and 20 n coincide with the domain of the subtropical mode waters stmw which result from the sinking of surface waters in late winter in regions imprinted by dust deposition the magnitude of the al enrichment observed in this water mass implies that the predominant source to the stmw is from the more dust impacted western atlantic with only limited contributions from the stmw formation region near madeira a deeper subsurface al enrichment 30 45 n is associated with the outflow from the mediterranean another heavily dust impacted basin these two regions of al enrichment show the widespread geochemical connection between atmospheric transport processes and the north atlantic and underscore its susceptibility to imprinting by atmospherically borne materials natural as well as anthropogenic

paleo sea surface salinities in the low latitude atlantic the δ18o record of globigerinoides ruber white on the basis of the comparison of 18o values of globigerinoides ruber white 18og ruber from modern sediments and measured sea surface temperatures sst and salinity sss 18og ruber values most clearly record summer sst and sss of the uppermost 50 m of water in the low latitude atlantic a new transfer equation is presented for estimating local summer paleo sss at 0 50 m depth using 18og ruber paleo sst and the global 18o ice effect of sea water with the standard error reaching 0 72 0 77 sss the equation was applied to a 35 kyr long 18og ruber record and paleo sst estimates based on planktonic foraminiferal assemblages to reconstruct the paleo sss changes along the east atlantic margin off the northwest sahara the resulting local sss show a general increase by 0 3 1 4 during the last glacial maximum lgm and large parts of glacial termination i suggesting a general increase in the upwelling of the highly saline north atlantic central water and or a reduced lateral advection of less saline canary current water two short salinity lows up to 0 35 less than today during and after the lgm are coeval with the heinrich meltwater events 1 and 2 in the north atlantic indicating the breakdown of coastal upwelling and meltwater advection from the north both events are followed by an extreme sss maximum 38 15 along with the restoration of the salinity conveyor belt at 9 0 5 5 ka the salinity minimum up to 0 65 less than today reflects the continental runoff linked to the phase of strong north saharan humidity during the early holocene climatic optimum

routing of meltwater from the laurentide ice sheet during the younger dryas cold episode rooth1 proposed that the younger dryas cold episode which chilled the north atlantic region from 11 000 to 10 000 yr bp was initiated by a diversion of meltwater from the mississippi drainage to the st lawrence drainage system the link between these events is postulated to be a turnoff during the younger dryas cold episode of the north atlantic s conveyor belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the north atlantic region2 this turnoff is attributed to a reduction in surface water salinity and hence also in density of the waters in the region where north atlantic deep water nadw now forms here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from orca basin core en32 pc4 which reveal a significant reduction in meltwater flow through the mississippi river to the gulf of mexico from about 11 200 to 10 000 radiocarbon years ago this finding is consistent with the record for lake agassiz which indicates that the meltwater from the southwestern margin of the laurentide ice sheet was diverted to the northern atlantic ocean through the st lawrence valley during the interval from 11 000 to 10 000 years before present yr bp

α high resolution late holocene speleothem record from kaite cave northern spain δ18o variability and possible causes a high resolution calcite oxygen stable isotopic 18o record covering the past 4000 years was obtained from kaite cave northern spain the record has a mean 18o value of 6 25 vpdb and a range of 2 spectral analysis of the d18o data shows significant periodicities of 2400 1900 600 150 27 and 22 years the amplitudes during these periods range from 0 2 to 2 factors controlling the isotopic ratio in the speleothem were evaluated the calcite is most likely precipitated under equilibrium conditions with the cave calcite 18o interpreted as a proxy of oxygen isotopic composition in local rainwater other factors such as temperature or fractionation in the karst system prior to calcite precipitation are considered of negligible or of minor importance mechanisms affecting rainfall isotopic composition were also investigated on different time scales precipitation amount is the primary factor controlling the high frequency d18o oscillations other climate parameters such as changes of storm tracks may have significant contributions on centennial and millennial time scales

structure and timing of the last deglaciation oxygen isotope evidence foraminiferal oxygen isotope data from 24 tropical atlantic sediment cores constrained by 77 14c dates are stacked to form a composite record of isotopic termination 1 this record indicates that most of the isotopic transition at the end of the last ice age occurred between 14 ka bp and 6 ka bp minor isotopic expression of deglaciation is permitted as early as 16 ka bp but the most rapid rate of change occurred between 14 ka bp and 12 ka bp three steps of maximum change are present although they are close to the statistical limits of detection in the composite record the clear presence of the steps in individual records suggests that they are real we estimate their timing at 14 12 ka bp termination 1 a 10 9 ka bp termination 1 b and 8 6 ka bp termination 1 c centering of the termination near 11 ka bp is consistent with the milankovitch hypothesis that high summer insolation caused deglaciation in detail however maximum rates of change prior to the 11 ka bp insolation extreme and the inferred steps require additional mechanisms controlling the tempo of glacial interglacial climate change steps equivalent to those in 18o have not been detected in ice margin retreat data steps in the isotopic transition if real may record thinning of the ice sheets not accompanied by loss of area alternation between near equilibrium and near stagnant ice sheet profiles during deglaciation is hypothesized perhaps due to calving and unstable down draw of the ice sheets followed by partial re equilibration significant problems remain the effects of temperature on the isotope record are only partially constrained presently available data allow only semi quantitative intercalibration of ice volume sea level and isotopic estimates of glaciation

termination of the last glaciation in the iberian peninsula inferred from the pollen sequence of quintanar de la sierra abstract a 4 5 m thick late glacial pollen sequence supported by 17 ams14c dates has been investigated at the quintanar de la sierra marshland iberian cordillera north central spain pollen zones were defined that correspond to successive phases in vegetation history during the end of the late wurm late glacial interstade and younger dryas periods a transfer function approach has been adopted to derive quantitative climate estimates from the pollen assemblage data a first expansion ofjuniperusandhippophae about 13 50014c yr b p indicates the beginning of the late glacial interstade which is characterized by ajuniperus betula pinussuccession that suggests higher temperatures and moisture than during full glacial time the younger dryas interval is recorded by a 120 cm thick sediment unit that is dominated by herbaceous pollen transfer function estimates suggest that the climate during this period was cold with low precipitation during most of the year although not in summer the holocene arboreal recolonization in the area started about 10 00014c yr b p with a renewedjuniperus betula pinussuccession related to a strong increase in annual temperature and precipitation the start of this process was synchronous with mean sea surface temperature changes as recorded from the nearby su 81 18 marine core the strong affinity with other european late glacial pollen sequences demonstrates that the pattern of climatic changes during the last glacial interglacial transition was similar in both northwestern and southwestern europe

petrology and geochemistry of ordovician k bentonites in new york state constraints on the nature of a volcanic arc altered volcanic ashes k bentonites in the late ordovician caradocian utica shale of new york state are the product of explosive arc volcanism most of the 30 k bentonites examined in this investigation contain fragmental crystals and rock fragments microliths up to 600 mu m in diameter that generally are neither detrital contamination from the surrounding black shale nor igneous phenocrysts the dominant phases are garnet two groups gr sub 15 20 alm sub 45 75 py sub 35 0 sp sub 2 5 gr sub 2 5 alm sub 55 85 py sub 10 40 sp sub 1 plagioclase feldspar an sub 80 10 alkali feldspar or sub 99 0 clinopyroxene wo sub 50 40 en sub 50 30 fs sub 0 30 and orthopyroxene wo sub 1 2 en sub 77 32 fs sub 32 66 accompanied by lesser quantities of hornblende aluminosilicate quartz sphene fe ti oxides apatite and zircon most of the fragmental crystals appear to be derived from the same source as the metamorphic microliths which possess minerals with similar compositions both crystals and microliths are interpreted as xenocrysts and xenoliths from the ancient continental crust on which the ordovician arc was constructed they became entrained in the volcanic plume during explosive eruptions a precambrian age acquired on k feldspars from one k bentonite using the sup 40 ar sub 39 ar method shows that these xenocrysts were derived from depths of less than 5 10 km in the microcontinent at the time of late ordovicianmore volcanism the occurrence of xenocrysts and xenoliths in these k bentonites underscores the importance of performing detailed petrology on ash layers prior to the onset of more sophisticated tasks e g isotopic age determinations regional stratigraphic correlations of k bentonites based upon chemical compositions less

degassing at anatahan volcano during the may 2003 eruption implications from petrology ash leachates and so2 emissions abstract on 10 may 2003 anatahan volcano located at 16 21 n 145 40 e on the mariana arc entered its first historical eruptive episode sending ash to 12 km into the atmosphere abundant accretionary lapilli quenched pumice textures and hydrothermal minerals in the earliest eruptive deposits indicate hydromagmatic interaction and active mining of the pre eruptive hydrothermal system whole rock compositions of the products erupted within the first week are chemically homogenous with sio 2 61 mgo 2 1 k 2 o 1 4 na 2 o 4 1 and fe 2 o 3 9 1 the products are classified as medium k andesites with tholeiitic affinity slightly more silicic matrix glass compositions up to 63 sio 2 in microlite rich matrices overlap with whole rock suggesting limited crystal fractionation with microlite crystallization responsible for the more evolved residual melt decreasing corrected loi values 2 3 1 4 wt upsection are consistent with waning hydrothermal mineral contributions as the eruption progressed oxygen fugacity calculations based on the ferric to ferrous iron ratio of bulk samples indicate an oxidized magma with nno 1 two pyroxene equilibrium thermometry suggests magmatic temperatures of 1050 1100 c matrix glass volatile contents show a degassed residual melt with 2 o 1000 2000 ppm cl 480 780 ppm f 50 150 ppm s and 2 a magmatic so 2 flux of 3 4 5 kt day was measured by cospec on 21 may ash leachate data indicate a decreasing s cl ratio 3 3 0 7 in the eruptive plume between 10 and 21 may with a relatively constant cl concentration assuming a constant cl flux an so 2 flux of 14 22 kt day is calculated for 10 may the average s concentration from ash leachates 1230 mg kg suggests that at least 25 of the so 2 60 kt erupted from anatahan between 10 and 21 may was removed from the plume by the precipitation of sulphate salts in the eruption column adsorbtion onto ash particles and subsequent deposition molar ratios in ash leachates elucidate caso 4 and nacl as the most likely soluble salts formed in the plume total element abundances molar s ca 1 and ca mg na and k ratios in the leachates suggest a hydrothermal fluid contribution to elements present as water soluble salts adsorbed onto ash sulfur budget calculations based on estimates of pre eruptive magmatic and residual melt s contents mass of erupted magma and total so 2 output fluxes require an additional source of s other than the erupted magma multiple lines of evidence including high so 2 emissions early in the eruption the presence of accretionary lapilli and hydrothermal minerals in the early eruptive deposits quenched pumice textures and cation and anion ratios and abundances in ash leachates suggest that a s rich free volatile phase exsolved from a large magma body magmatic volatiles were stored as components of the hydrothermal system pressurized gases hydrothermal fluids and or hydrothermal minerals to be remobilized early in the eruption to contribute to the total so 2 output

the salinity contrast between the atlantic and pacific oceans during glacial time in today s ocean the salinity of low latitude surface waters in the pacific is on the average 1 per mil lower than in the atlantic oxygen isotope records for planktonic foraminifera suggest that an even larger salinity deficit may have existed for pacific surface water during glacial time if so the transport of water vapor from the atlantic to the pacific must have been as strong as or even stronger to balance the tendency toward salt buildup the atlantic would have had to export during glacial time waters saltier than it received from the other oceans

cd in planktonic and benthic foraminiferal shells determined by thermal ionisation mass spectrometry a highly sensitive method for cd determination in foraminiferal shells by isotope dilution tims has been developed and applied to 1 a more detailed reconstruction of seawater cd depth profiles for the north atlantic in the holocene and at the last glacial maximum lgm 2 the analysis of cd ca in individual benthic foraminifera shells and 3 determination of cd ca in holocene and glacial planktonic foraminifera although ca has a high first ionization potential through chemical separation of cd from the ca and optimization of the loading technique it is possible to analyze routine sized samples 10 benthics with a reproducibility in cd ca of 0 0025 micro mol mol between replicate picks from a single sample the blank of the method is 1 1 pg permitting analysis of individual benthics and of planktonic foraminifera the seawater cd reconstruction for the lgm is consistent with previous work but also suggests that depths 2 500 m were ventilated by a northern source of nutrient depleted deep water on the western side of the mid atlantic ridge individual benthic cd ca ratios show interspecimen variability which is averaged in routine analysis of multiple specimens planktonic cd ca from n atlantic cores shows interspecific differences between globigerina bulloides and neogloboquadrina pachyderma and holocene lgmmore contrasts which offers potential for use of planktonic cd ca as a palaeochemical tracer less

northeastern atlantic benthic foraminifera during the last 45 000 years changes in productivity seen from the bottom up we studied benthic foraminifera from the last 45 kyr in the 63 mu m size fraction in biogeochemical ocean flux studies bofs cores 5k 50 degrees 41 3 n 21 degrees 51 9 w depth 3547 m and 14k 58 degrees 37 2 n 19 degrees 26 2 w depth 1756 m at a time resolution of several hundreds to a thousand years the deepest site showed the largest fluctuations in faunal composition species richness and benthic foraminiferal accumulation rates the fluctuations resulted from changes in abundance of epistominella exigua and alabaminella weddellensis in the present oceans these species bloom opportunistically when a spring plankton bloom results in seasonal deposition of phytodetritus on the seafloor the phytodetritus species had very low relative abundances and accumulation rates during the last glacial maximum a strong increase in absolute and relative abundance of e exigua and a weddellensis during deglaciation paralleled the decrease in abundance of the polar planktonic foraminifer neogloboquadrina pachyderma s and the increase in abundance of warmer water planktonic species such as globigerina bulloides this strong increase in relative abundance of the phytodetritus species and the coeval increase in benthic foraminiferal accumulation rate were thus probably caused by an increase in the deposition of phytodetritus to the seafloor and thus probably of surface productivity when the polar front retreated to higher latitudes the abundance of phytodetritus species decreased during the younger dryas but not to the low levels of fully glacial conditions during heinrich events periods of excessive melt water formation and ice rafting benthic accumulation rates were very low as were the absolute and relative abundances of the phytodetritus species supporting suggestions that surface productivity was very low during these events in both cores pullenia and cassidulina species were common during isotope stages 2 3 and 4 as were bolivinid buliminid and uvigerinid species high relative abundances of these species have been interpreted as indicative either of sluggish deep water circulation or of high organic carbon fluxes to the seafloor in our cores relative abundances of these species are negatively correlated with benthic foraminiferal accumulation rates and we can thus not interpret them as indicative of increased productivity during glacials the percentage of these low oxygen species calculated on a phytodetritus species free basis decreased slightly at deglaciation at 5k but not at 14k this suggests that decreased production of north atlantic deep water during the last glacial might have slightly affected benthic foraminiferal faunas in the eastern north atlantic at 3547 m depth but not at 1756 m in conclusion major changes in deep sea benthic foraminiferal faunas over the last 45 000 years in our cores from the northeastern atlantic were the result of changes in surface water productivity not of changes in deep water circulation productivity was lower during the glacial probably because of extensive ice cover

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

modeling the paleocirculation of the mediterranean the last glacial maximum and the holocene with emphasis on the formation of sapropel s 1 an ocean general circulation model is used to simulate the thermohaline circulation in the mediterranean sea during the last glacial maximum and the holocene when the sapropel s1 was deposited the model is forced by prescribed surface temperatures and salinities where present day values lead to very realistic surface buoyancy fluxes different paleoreconstructions for the surface salinity and temperature distributions during these periods are tested in both periods under all reconstructions antiestuarine flow is maintained at gibraltar and sicily the holocene circulation has fresh intermediate water produced in the adriatic and an upward salt flux from the old waters below help maintain its outflow at sicily the depth of ventilation around the basin is broadly consistent with the shallowest sapropel layers observed shoaling of the eastern pycnocline occurs in all experiments in both periods possibly indicating enhanced productivity although the reasons for this are different in each case

explosive volcanic eruptions v observations of plume dynamics during the 1979 soufriere eruption st vincent summary during the 1979 eruption of the soufritre of st vincent west indies a 14min period of explosive activity occurred on april 22 the first three minutes of this activity were filmed five individual explosions formed distinct plumes which fed an eruption column which eventually ascended to a height of over 18 km the ascent velocities of the fronts of these plumes ranged from 8 5 to 61 7m s the half angle of spreading of the plume fronts ranged from 21 5 to 24 one of the plumes was observed to 8 km height and decelerated steadily from 5 1 5 to 23 m s l the main column fed by individual explosions was however observed to accelerate from 8 5 to 58 m s l in the same height interval a theoretical treatment of volcanic plume motion is presented measurements of dimensions velocities and spreading rates from the film are used to estimate plume parameters such as temperature particle content and volume discharge rate of magma from the theoretical relationships these calculations show that the individual plumes became hotter and richer in juvenile ash with time the acceleration of the main eruption column was the result of being fed by increasingly hotter and more ash rich explosions an average volume discharge rate of 12600m3s is estimated from the analysis of the plume motions this value agrees closely with an estimate of discharge rate based on the heat flux required to form an 18 km high column this agreement suggests that theories of convective motions in plumes can be successfully adapted to the volcanic case as long as the effect of hot entrained ash particles is considered

generation and dispersal of fine ash and dust by volcanic eruptions abstract the volcanic eruptions which generate the greatest quantities of fine ash and dust are those of ignimbrite forming plinian vulcanian and phreatomagmatic types these are also the eruptions which produce the widest dispersal of this material attributed to the superior height attained by their eruptive columns however much of the fine ash and dust may be rapidly flushed out of the eruptive plume by water particularly in phreatomagmatic eruptions recent studies made on the dispersal and grain size of pyroclastic deposits produced by examples of plinian and phreatomagmatic types have yielded estimates of the quantities of material generated in each grain size class besides the extent of their dispersal not all of the fine volcanic particles are produced by fragmentation at the eruptive vent in ignimbrite eruptions there is good evidence for their large scale generation in and loss from the moving ash flows

temperature and salinity records of the tyrrhenian sea during the last 18 000 years abstract we have used the modern analogue technique to derive sea surface temperature sst records of the last 18 000 years from two well dated deep sea cores recovered in the tyrrhenian sea results show two major cooling events synchronous with the european and north atlantic oldest and younger dryas events a later cooling of lower amplitude is observed between about 8000 and 4500 yr bp tyrrhenian ssts were similar to those of the upper holocene only during the bolling allerod event and at the beginning of the holocene we compared the sst and the planktonic foraminiferal oxygen isotope records to estimate the surface salinity variations our reconstruction shows that salinity decreased in the tyrrhenian sea during the three cold events whereas high ssts correlate with high salinities during most of the last 18 000 years tyrrhenian sea salinity variations were similar to those of the north atlantic ocean near the entrance of the mediterranean sea the salinity gradient between the two basins was thus constant indicating that the western mediterranean circulation pattern and the freshwater budget were not significantly different from the modern one the case was however different during the middle holocene when the strong salinity decrease associated with the sapropel deposit in the eastern mediterranean basin had no equivalent in the north atlantic ocean this peculiar event can only be explained by a local climatic change and an increase of precipitation

the deglacial history of the western tropical atlantic as inferred from high resolution stable isotope records off northeastern brazil abstract the western south atlantic boundary currents represent a sensitive system within the global thermohaline circulation thc we investigated the impact of deglacial thc changes on the western tropical atlantic studied in six high resolution sediment cores from the upper continental slope of brazil the stratigraphy of the cores is mainly based on 14c ams dating of monospecific foraminiferal samples changes in the upper layer tropical ocean during the deglaciation are inferred from stable oxygen isotope measurements on planktic and benthic foraminifera variations in the 18o residuals are assumed to be mainly temperature related during the oldest and younger dryas cooling periods two major deglacial thc disturbances are reported from north atlantic sediment cores concomitant to the repeated thc slowdown we observe an upper layer warming in the tropical ocean a reduced northward heat export from the tropical areas during these periods weak north brazil current is additionally reflected by low meridional gradients in the stable oxygen records this generally agrees with results from coupled ocean atmosphere models

oxygen isotope records and salinity changes in the northeastern atlantic ocean during the last 18 000 years a comparison of the deglaciation 18o record of northeastern atlantic core su 81 18 with that calculated by adding the 18o changes due to sea surface temperature and ice volume variations shows that planktonic foraminifera have also recorded seawater 18o changes due to salinity local advection and evaporation precipitation e p changes using a simple ocean box model of meltwater dilution during the deglaciation we show that sea surface salinity covaried with temperature despite the injection of meltwater associated with the climate warming sea surface salinity was high when sea surface water was warm and low during cold events this implies that the combined effect of local e p changes and northward advection of saline subtropical water were the main factor responsible for the surface water salinity variations in the northeastern atlantic ocean during the last 18 000 years

the continental margin is a key source of iron to the hnlc north pacific ocean here we show that labile particulate iron and manganese concentrations in the upper 500m of the western subarctic pacific an iron limited high nutrient low chlorophyll hnlc region have prominent subsurface maxima between 100 200 m reaching 3 nm and 600 pm respectively the subsurface concentration maxima in particulate fe are characterized by a more reduced oxidation state suggesting a source from primary volcagenic minerals such as from the kuril kamchatka margin the systematics of these profiles suggest a consistently strong lateral advection of labile mn and fe from redox mobilized labile sources at the continental shelf supplemented by a more variable source of fe from the upper continental slope this subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing and is likely a key source of bioavailable fe to the hnlc north pacific

mechanical models for correlation of ring fracture eruptions at pantelleria strait of sicily with glacial sea level drawdown recent k ar dating of eruptions at pantelleria a peralkaline volcanic island in the strait of sicily shows a correlation between eruption of pantellerite lavas from caldera ring fractures and low stands of sea level as determined from 18o stratigraphy post caldera pantellerite lavas associated with an 114 ky old caldera erupted along the ring fracture zone during a major low stand of sea level at about 67 ka the most recent episode of lava flow emplacement began about 20 ky ago during the last glacial maximum magma vented along the ring fault of a 45 ky old caldera from fractures radial to the caldera and along faults formed by intracaldera trapdoor uplift two mechanical models based on elasticity theory are presented to explain the correlation of post caldera ring fracture eruptions at pantelleria with lowering of sea level a simple analysis of a bending circular plate of thickness t r and radius r representing the magma chamber roof block shows that tensile stress is concentrated by a factor of 0 75r 2 t 2 at the lower perimeter of the plate when sea level drops stress changes may be even greater ift r is effectively less than the stratigraphic thickness due to layering of rocks in the roof block calculated stress changes due to a 100 m drawdown of sea level are similar in magnitude to stresses associated with dike propagation more realistic model geometries including different chamber shapes a conical volcanic edifice and sea level drawdown beyond the surface projection of the magma chamber were tested using the boundary element method lowering sea level generates a horizontal tensile stress above the chamber even when sea water is removed outboard of the magma chamber for some chamber geometries the magnitude of the tensile stress maximum is greater than the 1 mpa pressure of the 100 m of removed water and is of the right order of magnitude for dike propagation dikes initiated by the change of the stress field may originate and propagate along fractures inboard of the chamber margin the magnitudes of tensile maxima along the top of the chamber decrease as original sea level is moved outboard of the chamber margin and as the chamber thickness decreases when the depth to the top of the magma chamber reaches a critical value dependent on chamber geometry the propagation of dikes to the surface is inhibited

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

radiocarbon calibration beyond 20 000 14c yr b p by means of planktonic foraminifera of the iberian margin we present a new set of 14c ages obtained by accelerator mass spectrometry ams on planktonic foraminifera from a deep sea core collected off the iberian margin md952042 this site at 37 n is distant from the high latitude zones where 14c reservoir age is large and variable many independent proxies alkenones magnetic susceptibility ice rafted debris foraminifera stable isotopes abundances of foraminifera pollen and dinoflagellates show abrupt changes correlative with dansgaard oeschger and heinrich events of the last glacial period the good stratigraphic agreement of all proxies from the fine to the coarse size fractions indicates that the foraminifera 14c ages are representative of the different sediment fractions to obtain reliable 14c ages of foraminifera beyond 20 000 14c yr b p we leached the shells prior to carbonate hydrolysis and subsequent analysis for a calendar age scale we matched the iberian margin u37k profile with that of greenland summit 18o both are proxies for temperature which in models varies synchronously in the two areas the match creates no spurious jumps in sedimentation rate and requires only a limited number of tie points except for ages older than 40 000 14c yr b p greenland s gisp2 and grip records yield similar calendars the 14c and imported calendar ages of the iberian margin record are then compared to data from lacustrine annual varves and from corals and speleothems dated by u th previously used to extend the calibration beyond 20 000 14c yr b p the new record follows a smooth pattern between 23 000 and 50 000 cal yr b p we find good agreement with the previous data sets between 23 000 and 31 000 cal yr b p in the interval between 33 000 and 41 000 cal yr b p for which previous records disagree by up to 5000 cal yr the iberian margin record closely follows the polynomial curve that was previously defined by an interpolation of the coral ages and runs between the lake suigetsu and the bahamian speleothem data sets

origin of the first global meltwater pulse following the last glacial maximum well dated sea level records show that the glacioeustatic rise following the last glacial maximum was characterized by two or possibly three brief intervals of rapid sea level rise separating periods with much lower rates these very high rates of sea level rise indicate periods of exceptionally rapid deglaciation of remaining ice sheets the laurentide ice sheet is commonly targeted as the source of the first and largest of the meltwater pulses mwp ia between 14 200 12 200 14c years b p and 13 700 years ago 11 700 14c years b p in all oceanic records of deglaciation of the former northern hemisphere ice sheets that we review only those from the gulf of mexico and the bermuda rise show evidence of low 18o values at the time of mwp ia identifying the southern laurentide ice sheet as a potential source for mwp ia we question this source for mwp ia however because 1 ice sheet models suggest that this sector of the ice sheet contributed only a fraction 10 of the sea level needed for mwp ia 2 melting this sector of the ice sheet at the necessary rate to explain mwp ia is physically implausible and 3 ocean models predict a much stronger thermohaline response to the inferred freshwater pulse out of the mississippi river into the north atlantic than is recorded this leaves the antarctic ice sheet as the only other ice sheet capable of delivering enough sea level to explain mwp ia but there are currently no well dated high resolution records to document this hypothesis these conclusions suggest that reconstructions of the laurentide ice sheet in the ice 4g model which are constrained to match the sea level record may be too low for time periods younger than 15 000 years ago furthermore 18o records from the gulf of mexico show variable fluxes of meltwater from the southern margin of the laurentide ice sheet which can be traced to the opening and closing of eastward draining glacial lake outlets associated with surging ice sheet behavior these variable fluxes through eastern outlets were apparently sufficient to affect formation of north atlantic deep water thus underscoring the sensitivity of this process to changes in freshwater forcing

cadmium calcium and carbon isotope reconstructions of the glacial northeast atlantic ocean the 13c and cd measurements from benthic foraminifera from biogeochemical ocean flux study bofs northeast atlantic ocean sediment cores are presented the 13c values in glacial foraminifera are consistent with those from elsewhere in the north atlantic ocean for intermediate water 1000 2000 m water depth 13c values were higher at the last glacial maximum than in present north atlantic deep water nadw whereas for deep water 2000 m they were lower during the glacial maximum the cd concentrations of glacial northeast atlantic intermediate water were lower than those of present nadw however deepwater cd concentrations increased to values between nadw and present pacific deep water pdw the 13c and cd data are consistent and show that the northeast atlantic ocean was strongly stratified with 13c enriched low cd intermediate water overlying 13c depleted high cd deep water the glacial water column comprised two different water masses deep water similar in character to present antarctic bottom water aabw and intermediate water different in character from both aabw and nadw and any present intermediate depth north atlantic water the characteristics of glacial intermediate water were however similar to present near surface waters in the north atlantic which suggests rapid ventilation of the glacial ocean to depths of up to 2000 m by cold nutrient depleted young surface waters

centennial scale holocene climate variability revealed by a high resolution speleothem δ18o record from sw ireland evaluating the significance of holocene submillennial 18 o variability in the greenland ice cores is crucial for understanding how natural climate oscillations may modulate future anthropogenic warming a high resolution oxygen isotope record from a speleothem in southwestern ireland provides evidence for centennial scale 18 o variations that correlate with subtle 18 o changes in the greenland ice cores indicating regionally coherent variability in the early holocene evidence for previously undetected early holocene cooling events is presented but mid to late holocene ice rafting in the north atlantic appears to have had little impact on 18 o at this ocean margin site

the age and origin of the younger dryas climate event in greenland ice cores 230th 234u and 14c dating of barbados corals has extended the calibration of 14c years b p to calendar years b p beyond the 9200 year tree ring series bard et al 1990 this now permits the conversion of 14c chronozones which delimit major climate shifts in western europe to calendar years the younger dryas chronozone defined as 11 000 to 10 000 14c years b p corresponds to 13 000 to 11 700 calendar years b p this calibration affects the interpretation of an intensely studied example of the younger dryas climate event the 18o anomaly between 1785 and 1793 m in dye 3 ice core the end of the 18o anomaly in dye 3 ice core has been dated by measurements of 14c in air bubbles andree et al 1984 1986 and by annual layer counting hammer et al 1986 the older 14c dates fall out of the range of the tree ring calibration series but can now be calibrated to calendar years using the barbados 230th 234u calibration the 14ccorrected age for the end of the 18o event is 10 300 400 calendar years b p compared to the annual layer counting age of 10 720 150 years b p thus the younger dryas event in the dye 3 ice core ends in the preboreal chronozone 11 700 to 10 000 calendar years b p and is not correlative with the end of the younger dryas event identified in pollen records marking european vegetation changes the end of the dye 3 18o event is however correlative with the end of meltwater pulse ib fairbanks 1989 marking a period of intense deglaciation with meltwater discharge rates exceeding 13 000 km yr

dissolved iron anomaly in the deep tropical subtropical pacific evidence for long range transport of hydrothermal iron abstract dissolved iron profiles along a north south transect along 158 w in the tropical pacific show evidence of two deepwater anomalies the first extends from station aloha 22 78 n to the equator at 1000 1500 m and lies below the maximum apparent oxygen utilization and nutrient n p concentrations the feature is not supported by vertical export processes but instead corresponds with the lateral dilution field of 3 he derived from the loihi seamount hawaii though a sediment source associated with the hawaiian island chain cannot be entirely ruled out the second deeper 2000 3000 m anomaly occurs in tropical south pacific waters 7 s and also does not correlate with the depths of maximum nutrient concentrations or apparent oxygen utilization but it does coincide closely with 3 he emanating from the east pacific rise more than 5000 km to the east we hypothesize that these anomalies represent the long range 2000 km transport of hydrothermal iron residuals stabilized against scavenging by complexation with excess organic ligands in the plume source regions such trace leakage of hydrothermal iron to distal plume regions would have been difficult to identify in most hydrothermal vent mapping studies because low analytical detection limits were not needed for the proximal plume regions these findings suggest that hydrothermal activity may represent a major source of dissolved iron throughout the south pacific deep basin today as well as other regions having high mid ocean spreading rates in the geologic past in particular we hypothesize that high spreading rates along the south atlantic and southern ocean mid oceanic ridges combined with the upwelling ventilation of these distal hydrothermal plumes may have increased ocean productivity and carbon export in the southern ocean assessing the magnitude and persistence of dissolved hydrothermal iron in basin scale deep waters will be important for understanding the marine biogeochemistry of iron and potentially on ocean productivity and climate change during the geologic past

quantification of paleotemperature changes during isotopic stage 2 in the la draga continental sequence ne spain based on the mg ca ratio of freshwater ostracods past summer temperature changes are quantified from the la draga sequence banyoles ne spain during stage 2 24 10 ka bp using trace element content in lacustrine ostracod valves the high resolution results from this new method are compared to summer paleotemperature reconstructions from sequences from the north atlantic area providing a discussion about the magnitudes of some temperature changes in ne spain and offshore portugal the coldest part of stage 2 is not documented at the classical date of similar to 18 c 14 ka bp similar to 21 5 calendar ka bp but rather occurred later date of ca 17 15 ka cal bp in the north atlantic area the onset of the bolling allerod interstadials was relatively synchroneous at similar to 14 6 ka cal bp although the magnitude of the bolling allerod improvement was more important in the southern area than in the northern area the duration of the younger dryas is discussed even if different durations are reported from calendar ages it seems that the summer temperature cooling of the younger dryas was similar around the north atlantic area c 1996 elsevier science ltd

reconstructing paleosalinity from δ18o coupled model simulations of the last glacial maximum last interglacial and late holocene reconstructions of salinity are used to diagnose changes in the hydrological cycle and ocean circulation a widely used method of determining past salinity uses oxygen isotope ow residuals after the extraction of the global ice volume and temperature components this method relies on a constant relationship between ow and salinity throughout time here we use the isotope enabled fully coupled general circulation model gcm hadcm3 to test the application of spatially and time independent relationships in the reconstruction of past ocean salinity simulations of the late holocene lh last glacial maximum lgm and last interglacial lig climates are performed and benchmarked against existing compilations of stable oxygen isotopes in carbonates oc which primarily reflect ow and temperature we find that hadcm3 produces an accurate representation of the surface ocean oc distribution for the lh and lgm our simulations show considerable variability in spatial and temporal ow salinity relationships spatial gradients are generally shallower but within 50 of the actual simulated lh to lgm and lh to lig temporal gradients and temporal gradients calculated from multi decadal variability are generally shallower than both spatial and actual simulated gradients the largest sources of uncertainty in salinity reconstructions are found to be caused by changes in regional freshwater budgets ocean circulation and sea ice regimes these can cause errors in salinity estimates exceeding 4 psu our results suggest that paleosalinity reconstructions in the south atlantic indian and tropical pacific oceans should be most robust since these regions exhibit relatively constant ow salinity relationships across spatial and temporal scales largest uncertainties will affect north atlantic and high latitude paleosalinity reconstructions finally the results show that it is difficult to generate reliable salinity estimates for regions of dynamic oceanography such as the north atlantic without additional constraints

paleosalinity and δ18o a critical assessment in paleoceanography a traditional application of oxygen isotope ratios in fossil carbonate from deep sea cores concerns the reconstruction of paleotemperatures recently isotopic data have been increasingly employed in the reconstruction of paleosalinities as well this application involves a number of basic assumptions a critical review of which is presented here as the calculation of paleosalinity from 18o residuals assumes constant and linear surface water salinity s 18o relationships we investigate this basic assumption for areas with important and variable freshwater budget and or sea ice influences we show that it is particularly unwarranted to assume such temporally invariant linearity in temperate and subpolar seas because of the effects of freezing and melting more critically we argue that the determinant of many regions s 18o is advection not the local water balance so that the basic 18o of seawater in many regions of the world ocean would likely have changed in a manner somewhat different from that expected from the ice volume record although the differences may not be significant for the gross reconstruction of such features as past sea level we believe they do potentially bias paleosalinity reconstructions mostly toward high salinities to fully exploit the potential of oxygen isotope records as quantitative paleosalinity indicators both the spatial and temporal variabilities need to be constrained hence we recommend that 1 for any time slice of specific interest to paleoceanographic and paleoclimatological studies a coupled ocean atmosphere isotope model or at least an ocean isotope model driven by a paleoclimate isotope model should be used to define the distribution of the base mixing end member 18o of sea water 2 much further regional scale research is needed on flux rates and isotopic compositions of the various terms in the freshwater budget as well as on the variability in the various advective terms the latter variability may be assessed from reconstructions of past seaice distributions and of volume fluxes isotopic compositions of outflow from marginal seas and through sea straits passages

volcanoes the stratosphere and climate abstract a list of volcanic eruption plumes observed to ascend into or near the stratosphere since 1883 shows that the volcanoes divide readily into two groups one at low and one at higher latitudes a model for the rise of a buoyant volcanic plume rise as applied to volcanic eruptions is corrected for realistic temperature profiles and for the finite vertical extent of the resultant debris clouds the utility of the model can be questioned however owing to the highly uncertain and variable nature of the efficiency of use of heat energy of buoyant rise the observed correlation of stratospheric plumes with climatic effects indicates that those plumes nearer the equator have the largest impact on surface temperatures analysis of the observations also suggests that injection of debris into the stratosphere is more important in determining the effect on climate than either the total volcanic explosivity of the eruption or the actual height reached within the stratosphere

multi isotopic age assessment of dirty speleothem calcite an example from altamira cave spain the dating of dirty speleothem calcite of late pleistocene or holocene age can be problematic this is notably the case with the 14 c method due to uncertainties in the initial 14 c activity of the cave co2 and withth e 230 th 234 u method due to either low u contents in the authigenic calcite and or to the presence of heterogeneous detrital particles containing high concentrations of u and thseries isotopes frequently out of secular equilibrium in this study of a b60 cm thick flowstone sealing archaeological remains of the magdalenian period in the altamira cave nw spain we used a combination of isotopic approaches and analytical techniques to confront dating methods and finally tried to validate chronological interpretations based on stable isotope paleoclimate constraints u series data indicate the presence of a relatively important and heterogeneous detrital fraction resulting in 232 th 230 th mass ratios generally too high 0 1 0 25 10 6 to allow precise tims measurements mc icp ms measurements provided more reliable results and allowed the calculation of 230 th 234 u isochron ages of 11 870 8 ka in the upper part of the flowstone and of b22 ka in the lower part of it in view of the calibrated 14 c ages of these layers b13 and b15 ka bp respectively the isochron age of the lower unit of the flowstone seems erroneous suggesting the presence of an isotopically heterogeneous contaminating fraction in this layer 226 ra 230 thratio measurements indicate near secular equilibrium conditions seriate stable isotope measurements indicate calcite precipitation in isotopic equilibrium with ambient waters they suggest that flowstone deposition ended at the very onset of the younger dryas this transition seems to have occurred here at 11 870 8 72s ka based on th u isochron and 10 770 08 71s uncalibrated 14 c kiloyears the 14 c activity for the cave co2 seems to have been near that of atmospheric co2 during the precipitation interval it is concluded that the 14 c data provide here relatively reliable ages in spite of the fact that they partly fall into a period characterized by 14 c plateau effects but that other isotopic data revealed essential in validating them

the chronology of the last deglaciation implications to the cause of the younger dryas event it has long been recognized that the transition from the last glacial to the present interglacial was punctuated by a brief and intense return to cold conditions this extraordinary event referred to by european palynologists as the younger dryas was centered in the northern atlantic basin evidence is accumulating that it may have been initiated and terminated by changes in the mode of operation of the northern atlantic ocean further it appears that these mode changes may have been triggered by diversions of glacial meltwater between the mississippi river and the st lawrence river drainage systems we report here accelerator mass spectrometry ams radiocarbon results on two strategically located deep sea cores one provides a chronology for surface water temperatures in the northern atlantic and the other for the meltwater discharge from the mississippi river our objective in obtaining these results was to strengthen our ability to correlate the air temperature history for the northern atlantic basin with the meltwater history for the laurentian ice sheet

chronology of early archaean granite greenstone evolution in the barberton mountain land south africa based on precise dating by single zircon evaporation abstract we report precise 207 pb 206 pb single zircon evaporation ages for low grade felsic metavolcanic rocks within the onverwacht and fig tree groups of the barberton greenstone belt bgb south africa and from granitoid plutons bordering the belt dacitic tuffs of the hooggenoeg formation in the upper part of the onverwacht group yield ages between 3445 3 and 3416 5 ma and contain older crustal components represented by a 3504 4 ma old zircon xenocryst fig tree dacitic tuffs and agglomerates have euhedral zircons between 3259 5 and 3225 3 ma in age which we interpret to reflect the time of crystallization a surprisingly complex xenocryst population in one sample documents ages from 3323 4 to 3522 4 ma we suspect that these xenocrysts were inherited during the passage of the felsic melts to the surface from various sources such as greenstones and granitoid rocks now exposed in the form of tonalite trondhjemite plutons along the southern and western margins of the bgb and units predating any of the exposed greenstone or intrusive rocks several of the granitoids along the southern margin of the belt have zircon populations with ages between 3490 and 3440 ma coeval with or slightly older than onverwacht felsic volcanism while the kaap valley pluton along the northwestern margin of the belt is coeval with fig tree dacitic volcanism these results emphasize the comagmatic relationships between greenstone felsic volcanic units and the surrounding plutonic suites some of the volcanic and plutonic units contain zircon xenocrysts older than any exposed rocks these indicate the existence of still older units possibly stratigraphically lower and older portions of the greenstone sequence itself older granitoid intrusive rocks or bodies of older unrelated crustal material our data show that the onverwacht and fig tree felsic units have distinctly different ages and therefore do not represent a single tectonically repeated unit as proposed by others unlike the late archaean abitibi greenstone belt in canada which formed over about 30 ma exposed rocks in the bgb formed over a period of at least 220 ma the complex zircon populations encountered in this study imply that conventional multigrain zircon dating may not accurately identify the time of felsic volcanic activity in ancient greenstones a surprising similarity in rock types tectonic evolution and ages of the bgb in the kaapvaal craton of southern africa and greenstones in the pilbara block of western australia suggests that these two terrains may have been part of a larger crustal unit in early archaean times

high resolution stratigraphy of the faeroe shetland channel and its relation to north atlantic paleoceanography the last 87 kyr abstract two piston cores from the faeroe shetland channel have been investigated for stratigraphic and paleoceanographic correlation with atlantic ocean and norwegian sea records the high resolution cores have been analyzed for the downcore distribution of planktic and benthic foraminifera and oxygen isotopes ams 14 c dates and the position of ash layers i and ii form the basis for the correlation core na81 10 covers the period from isotope stage 3 to recent stage 1 while core na81 04 covers isotope stages 5a to 1 the holocene is well represented in core na81 10 by 2 m of sediment whereas it is only 50 cm in core na81 04 which is situated directly under the main core of the norwegian sea deep water outflow the transition of isotope stage 2 to stage 1 is affected by dissolution and thus is less clearly represented ams 14 c dates show that termination ia begins at 16 ka and ends at about the 13 ka level the last glacial maximum lgm defined at 19 16 ka is characterized by an ird peak faunal planktic foraminifera maxima dated at 17 3 and 18 25 ka and a high percentage of globigerina quinqueloba apparently open water conditions and circulation within the norwegian sea prevailed at least from 22 5 to 14 8 ka during the greatest part of stage 2 including the lgm and well onto termination ia a preservation maximum is observed throughout stage 2 isotope stage 3 with a nearly complete record of isotope substages is well represented in both cores oxygen isotope depletion peaks correlate with fauna minima and in time to north atlantic heinrich events h5 h1 faunal data indicate that deep water is generated within the norwegian greenland sea repeatedly since 26 ka with stops prior to 26 ka 22 5 20 8 20 5 ka and between 14 9 and 13 ka h3 h2 and h1 all isotope depletion peaks since ca 50 ka are anticorrelated with fauna and are mainly controlled by surface salinity changes isotope stages and substages are directly correlated to fauna peaks and temperature between 87 and ca 50 ka the faeroe shetland channel record shows that repeated presences of atlantic surface water and deep convection alternating with convection shutdowns have occurred within the norwegian sea greenland sea from the beginning of stages 5a to 1

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

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

foraminiferal magnesium in globeriginoides sacculifer as a paleotemperature proxy foraminiferal magnesium shows increasing promise as a paleothermometer but the accuracy and precision are limited by biases introduced by partial dissolution salinity variations mg rich gametogenic calcite and contaminant phases we improved cleaning methods and reduced errors introduced by partial dissolution by sampling from well preserved cores in the equatorial atlantic and the caribbean sea with different dissolution histories all cores reveal a synchronous 25 increase in mg ca from the stage 2 3 boundary to the holocene core top indicating that dissolution is not a controlling factor modern temperatures estimated from core top mg ca are 24 5 25 0 c equal to mean annual water temperatures at 50 100 m we estimate that sea surface temperature increased by 2 6 c 1 3 from the last glacial maximum to the holocene holocene values were comparable to those during isotope stage 5e our data indicate that biases from contaminant phases and partial dissolution can be reduced this paleothermometer holds promise if uncertainties introduced by salinity variations and gametogenic calcite can be constrained

instabilities in the labrador sea water mass structure during the last climatic cycle in the modern labrador sea the north atlantic deep water components are found below the 2 km deep intermediate labrador sea water lsw mass which is renewed locally through winter convective mixing this water mass structure remained relatively stable since 9 5 14 c ka bp as indicated by isotopic studies of foraminifer assem blages from deep sea cores almost constant differences in 18 o values are observed between major species these av erage 0 5 between the epipelagic species globigerina bulloides and the mesopelagic species neogloboquadrina pachyderma left coiled and 1 between neogloboquadrina pachydermaand the benthic species cibicides wuellerstorfi after correction for cibicides wuellerstorfi specific fractionation these isotopic compositions represent thermohaline conditions in surface waters in the pycnocline with the lsw and in the deep component of the north atlantic deep water respectively a drastically different structure characterized the glacial labrador sea differences in 18 o values of 2 to 2 5 are then observed between globigerina bulloides and benthic species indicative of a strong halocline between the corresponding water masses thus for reduced production of intermediate waters during the same interval neogloboquadrina pachydermashows 13 c and 18 o fluctuations of 1 to 1 5 amplitude in phase with heinrich bond events and higher frequency climate oscillations the 18 o values in neogloboquadrina pachyderma vary between those of globigerina bulloides and of benthic foraminifers suggesting large amplitude bathymetric fluctuations of the halo thermocline above and below the bathymetric range occupied by neogloboquadrina pachyderma minimum 18 o values in neogloboquadrina pachydermamatch intervals of maximum ice rafting deposition such as the late heinrich events thus intervals with a deeper more dilute buoyant surface water layer