average seasonal variation of the atlantic equatorial currents from historical ship drifts abstract surface currents in the tropical atlantic were studied using historical ship drift data these are the only available data capable of resolving the long term seasonal fluctuations of currents over a broad geographical region the north equatorial countercurrent was found to extend as a continuous eastward flowing current across the atlantic in the band 5 8 n from july to december the maximum average eastward velocity was 30 cm s 1 during july september east of 20 w the countercurrent continued throughout the year west of 20 w and from january to june the countercurrent disappeared and westward currents were observed average westward velocity reached 20 cm 1 in april and may centered near 40 w the annual cycle in surface velocity 20 cm s 1 amplitude agrees closely with that of geostrophic velocity inferred from variations in thermocline depth across the counter current jets centered near 2 n and 4 s separated by a minimum near 1 s the northern jet has a large 14 cm s 1 semiannual v

variability in the canary islands area of filament eddy exchanges abstract the physical background to a suite of biological studies carried out in the canary islands upwelling region is presented the area is unique in that the coastal transition zone is spanned by an archipelago of islands that shed mesoscale eddies of diameter 50 100 km into the alongshore flow a recurrent filament and eddy system was sampled intensively to study the changing properties of waters as they are advected towards the open ocean in the filament and to investigate the exchanges between filament and eddies the system was more complex than previously revealed in early august a single filament extended offshore from near cape juby two weeks later a second filament had developed slightly farther north and extended offshore to merge with the first at 100 km offshore the merged filament was entrained around a recurrent topographically trapped cyclonic eddy and interacted with transient cyclonic and anticyclonic eddies shed from the island of gran canaria between the two filaments and the coast a pair of counter rotating eddies re circulated water parcels for several weeks surface layer drifters cycled around this near shore re circulation several times before following convoluted paths that demonstrate significant exchange between continental shelf and open ocean waters

extratropical forcing of sahel aridity during heinrich stadials 1 in order to investigate a possible link between tropical northeast ne atlantic sea surface temperature sst atlantic meridional overturning circulation amoc and drought in the sahel during the past 44 thousand years kyr we used alkenone paleothermometry and 13c of c wuellerstorfi of a marine sediment core from the continental slope off senegal our data show periods of low sst and reduced amoc that coincided with drought in the sahel during north atlantic heinrich stadials hs the coldest period was hs1 ca 15 18 kyr before present bp when sst decreased by more than 2 c moreover the sst off senegal lagged variations in sahel aridity which is in agreement with results from a freshwater hosing experiment we conclude that variations in tropical ne atlantic sst were not the initial trigger of millennial scale sahel droughts of the past 44 kyr instead it is thought that these droughts were induced by substantial coolings of the extratropical north atlantic

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

millennial scale northwest african droughts related to heinrich events and dansgaard oeschger cycles evidence in marine sediments from offshore senegal 1 we present a suite of new high resolution records 0 135 ka representing pulses of aeolian fluvial and biogenic sedimentation along the senegalese continental margin a multiproxy approach based on rock magnetic element and color data was applied on three cores enclosing the present day northern limit of the itcz a strong episodic aeolian contribution driven by stronger winds and dry conditions and characterized by high hematite and goethite input was revealed north of 13 n these millennial scale dust fluxes are synchronous with north atlantic heinrich stadials fluvial clay input driven by the west african monsoon predominates at 12 n and varies at dansgaard oeschger time scales while marine productivity is strongly enhanced during the african humid periods and marine isotope stage 5 from latitudinal signal variations we deduce that the last glacial itcz summer position was located between core positions at 12 26 and 13 40 n furthermore this work also shows that submillennial periods of aridity over northwest africa occurred more frequently and farther south than previously thought

assessment of geochemical and micropaleontological sedimentary parameters as proxies of surface water properties in the canary islands region abstract the canary islands region occupies a key position with respect to biogeochemical cycles with the zonal transition from oligotrophic to nutrient rich waters and the contribution of saharan dust to the particle flux we present the distribution of geochemical proxies toc carbonate 15n 13corg c n ratio and micropaleontological parameters diatoms dinoflagellates foraminifera pteropods in 80 surface sediment samples in order to characterise the influence of coastally upwelled water on the domain of the subtropical gyre results of the surface sediment analyses confirmed the high biomass gradient from the coast to the open ocean inferred from satellite data of surface chlorophyll or sst the distribution of total dinoflagellate cysts the planktic foraminifera species globigerina bulloides the diatom resting spore chaetoceros spp and toc concentration coincided well with the areas of strong filament production off cape ghir and cape yubi the warm water planktic foraminifera globigerinoides ruber white the diatom nitzschia spp and the 15n values showed the opposite trend with high values in the open ocean factor analyses on the planktic foraminifera species distribution indicated three major assemblages in the canary islands region that represent the present surface water conditions from the upwelling influenced region via a mixing area towards the subtropical gyre

error analysis of paleosalinity calculations a detailed error analysis is performed for the calculation of open ocean salinity changes from carbonate oxygen 18 proxy data measurement errors are generally negligible however errors due to the goodness of fit of various regressions used in the calculation are significant depending on the method used and on the proxies available error bars 1 for the salinity range from 0 6 to 1 8 in particular expected errors for the midlatitude and tropical salinity differences at the last glacial maximum are around 1 1 to 2 5 the largest errors occur because of the differences between temporal and spatial seawater oxygen 18 salinity relationships and through the use of nonconcurrent temperature measurements methods of improving paleosalinity estimates should focus on eliminating these large sources of uncertainty

paleosalinity confidence limits and future applications error propagation is investigated through the only commonly applied technique for reconstruction of paleosalinity based on oxygen isotope residuals although this technique is known to be fairly inaccurate there remained a need for thorough assessment of confidence limits in a variety of global settings here it is found that a theoretical minimum error bar of between 0 3 and 0 7 applies to paleosalinity estimates and that real life practical limits are rarely better than 0 6 best results are expected in the latitudinal ranges 50 n and 70 s taking care to avoid the sea ice margin confidence intervals at low and mid latitudes including marginal seas are very wide at least 1 8 for the mediterranean and 2 2 for the equatorial atlantic it appears that oxygen isotope distributions are best used in their own right to investigate circulation and advective processes in coupled ocean atmosphere cryosphere models instead of calibrating them to paleosalinity to define restoring boundary conditions however isotope residual based paleosalinity maps from large numbers of regionally averaged studies in the above mentioned latitudinal bands may help in defining initial conditions and first order validation arguments for models

surface water temperature salinity and density changes in the northeast atlantic during the last 45 000 years heinrich events deep water formation and climatic rebounds we developed a new method to calculate sea surface salinities sss and densities ssd from planktonic foraminiferal 18o and sea surface temperatures sst as determined from planktonic foraminiferal species abundances sst sss and ssd records were calculated for the last 45 000 years for biogeochemical oceanic flux study bofs cores 5k and 8k recovered from the northeast atlantic the strongest feature is the dramatic drop in all three parameters during the heinrich ice rafting events we modelled the possibility of deepwater formation in die northeast atlantic from the ssd records by assuming that the surface waters at our sites cooled as they flowed further north comparison with modelled north atlantic deepwater densities indicates that there could have been periods of deepwater formation between 45 000 and 30 000 14c years b p interrupted by iceberg meltwater input of heinrich event 3 and 4 at 27 000 and 38 000 14c years b p and during the holocene no amount of cooling in the northeast atlantic between 30 000 and 13 000 years could cause deep water to form because of the low salinities resulting from the high meltwater inputs from icebergs our records indicate that after each heinrich event there were periods of climatic rebound with milder conditions persisting for up to 2000 years as indicated by the presence of warmer and more saline water masses after these warm periods conditions returned to average glacial levels these short term cold and warm episodes in the northeast atlantic are superimposed on the general trend towards colder conditions of the last glacial maximum lgm heinrich event 1 appears to be unique as it occurs as insolation rose and was coeval with the initial melting of the fennoscandian ice sheet we propose that meltwater input of heinrich event 1 significantly reduced north atlantic deep water formation reducing the heat exchange between the low and high latitudes thus delaying deglaciation by about 1500 radiocarbon years 2000 calendar years

orbital forcing of dust supply to the north canary basin over the last 250kyr abstract the canary basin lies in a region of strong interaction between the atmospheric and ocean circulation systems trade winds drive seasonal coastal upwelling and dust storm outbreaks from the neighbouring sahara desert are the major source of terrigenous sediment to investigate the forcing mechanisms for dust input and wind strength in the north canary basin the temporal pattern of variability of sedimentological and geochemical proxy records has been analysed in two sediment cores between latitudes 30 30 n and 31 40 n spectral analysis of the dust proxy records indicates that insolation changes related to eccentricity and precession are the main periods of temporal variation in the record si al and grain size of the terrigenous fraction show an increase in glacial interglacial transitions while al concentration and fe al ratio are both in phase with minima in the precessional index hence the results obtained show that the wind strength was intensified at terminations at times of maxima of northern hemisphere seasonal insolation when the african monsoon was enhanced the north canary basin also received higher dust input this result suggests that the moisture brought by the monsoon may have increased the availability of dust in the source region

sound velocities in olivine at earth mantle pressures the independent elastic constants of an upper mantle mineral san carlos olivine mg1 8fe0 2 sio4 were measured from 0 to 12 5 gigapascals evidence is offered in support of the proposition that the explicit temperature dependence of the bulk modulus is small over the range of temperatures and pressures thought to prevail above the 400 kilometer discontinuity and thus the data can be extrapolated to estimate the properties of olivine under mantle conditions at a depth of 400 kilometers in the absence of high temperature data at high pressures estimates are made of the properties of olivine under mantle conditions to a depth of 400 kilometers in contrast with low pressure laboratory data the predicted covariance of shear and compressional velocities as a function of temperature nearly matches the seismically estimated value for the lower mantle

persistent summer expansion of the atlantic warm pool during glacial abrupt cold events palaeoclimate records and numerical model simulations indicate that changes in tropical and subtropical sea surface temperatures and in the annual average position of the intertropical convergence zone are linked to high latitude climate changes on millennial to glacial interglacial timescales it has recently been suggested that cooling in the high latitudes associated with abrupt climate change events is evident primarily during the northern hemisphere winter implying increased seasonality at these times8 however it is unclear whether such a seasonal bias also exists for the low latitudes here we analyse the mg ca ratios of surface dwelling foraminifera to reconstruct sea surface temperatures in the northeastern gulf of mexico for the past 300 000 years we suggest that sea surface temperatures are controlled by the migration of the northern boundary of the atlantic warm pool and hence the position of the intertropical convergence zone during boreal summer and are relatively insensitive to winter conditions our results suggest that summer atlantic warm pool expansion is primarily affected by glacial interglacial variability and low latitude summer insolation because a clear signature of rapid climate change events such as the younger dryas cold event is lacking in our record we conclude that high latitude events seem to influence only the winter caribbean climate conditions consistent with the hypothesis of extreme northern hemisphere seasonality during abrupt cooling events

elastic wave velocities of a pyrope majorite garnet to 3 gpa abstract the pressure dependence of the elastic wave velocities for a polycrystalline specimen 100 theoretical density of majorite pyrope garnet py 62 mj 38 has been determined at room temperature to 3 gpa by ultrasonic phase comparison interferometry pressure derivatives of the adiabatic bulk modulus dk s dp 5 3 and shear modulus dgdp 2 0 are derived from the travel times of the compressional p and shear s waves these derivatives clearly demonstrate that pressure has a more pronounced effect on the elasticity of the majorite rich garnet than on the pure pyrope end member presumably in response to the coupled substitution of si and mg for al on the octahedral site in the garnet structure when combined with plausible values for the as yet unmeasured temperature derivatives these new data can be used to calculate velocity depth profiles along a 1400 c adiabat for the range of depths in which majorite is expected to be stable in the transition zone of the earth s mantle 450 600 km for shear waves these majorite gradients match those from regional seismic models much better than those for a pure olivine mantle more reliable calculations of elastic wave velocities at mantle temperatures and pressures await measurement of the temperature derivatives of elastic modulus

mineral assemblages of basalt in the lower mantle high pressure x ray diffraction and analytical transmission electron microscopy of laser heated diamond cell samples show temperature dependent phase assemblages in mid ocean ridge basalt morb at lower mantle pressures the assemblage observed below 2250 k consists of only stishovite plus an orthorhombic perovskite phase space group pbnm or cmcm having a composition close to that of morb but slightly depleted in sio2 with increasing temperature the assemblage transforms to orthorhombic and cubic perovskites plus stishovite and then at 3250 k to orthorhombic and cubic perovskites plus stishovite and the cafe2o4 phase all of these assemblages could be present in slabs that have penetrated deep into the mantle and can therefore contribute to the seismological heterogeneity of the lower mantle

p v vp vs t measurements on wadsleyite to 7 gpa and 873 k implications for the 410 km seismic discontinuity the compressional p and shear wave s velocities for mg2sio4 wadsleyite have been measured to 7 gpa and 873 k using simultaneous ultrasonic interferometry and in situ x ray diffraction techniques from the velocity measurements we obtained the pressure and temperature derivatives for the elastic shear g and adiabatic bulk ks moduli g p t 1 5 1 g t p 0 017 1 gpa k ks 173 2 gpa ks p t 4 2 1 and ks t p 0 012 1 gpa k for the p and s waves we obtained vs p t 0 021 1 km s gpa vs t p 0 035 2 km s k vp p t 0 065 2 km s gpa and vp t p 0 038 2 km s k values in parentheses are standard deviations e g 1 5 1 1 5 1 independent equation of state analysis of p v t data provided an estimation of the temperature dependence for the isothermal bulk modulus of kt t p 0 022 12 gpa k and thermal expansion a bt coefficients of a 2 10 5 k 1 and b 2 5 10 8 k 2 using these data along with elastic properties for other mantle phases a velocity depth profile for a pyrolite model to 670 km depth is constructed using a finite strain method along a 1673 k adiabat in the transition zone the pyrolite model has a smaller gradient between 410 and 660 km than the body wave models from synthetic waveform analyses but converges with the seismic profiles at the bottom of the transition zone just above the 660 km discontinuity the pyrolite model has velocity jumps of 6 9 and 7 9 for p and s waves respectively over a thickness of 10 km for the phase transformation from olivine to wadsleyite which is in good agreement with short period p wave reflection data and a recent fine structure model c4 for both the velocity jumps and the thickness of the 410 km seismic discontinuity

a revised picture of the structure of the monsoon and land itcz over west africa this article presents an overview of the land itcz intertropical convergence zone over west africa based on analysis of ncar ncep reanalysis data the picture that emerges is much different than the classic one the most important feature is that the itcz is effectively independent of the system that produces most of the rainfall rainfall linked directly to this zone of surface convergence generally affects only the southern sahara and the northern most sahel and only in abnormally wet years in the region a second feature is that the rainbelt normally assumed to represent the itcz is instead produced by a large core of ascent lying between the african easterly jet and the tropical easterly jet this region corresponds to the southern track of african easterly waves which distribute the rainfall this finding underscores the need to distinguish between the itcz and the feature better termed the tropical rainbelt the latter is conventionally but improperly used in remote sensing studies to denote the surface itcz over west africa the new picture also suggests that the moisture available for convection is strongly coupled to the strength of the uplift which in turn is controlled by the characteristics of the african easterly jet and tropical easterly jet rather than by moisture convergence this new picture also includes a circulation feature not generally considered in most analyses of the region this feature a low level westerly jet termed the african westerly jet plays a significant role in interannual and multidecadal variability in the sahel region of west africa included are discussions of the how this new view relates to other aspects of west africa meteorology such as moisture sources rainfall production and forecasting desertification climate monitoring hurricanes and interannual variability the west african monsoon is also related to a new paradigm for examining the interannual variability of rainfall over west africa one that relates changes in annual rainfall to changes in either the intensity of the rainbelt or north south displacements of this feature the new view presented here is consistent with a plethora of research on the synoptic and dynamic aspects of the african easterly waves the disturbances that are linked to rainfall over west africa and spawn hurricanes over the atlantic and with our knowledge of the prevailing synoptic and dynamic features this article demonstrate a new aspect of the west africa monsoon a bimodal state with one mode linked to dry conditions in the sahel and the other linked to wet conditions the switch between modes appears to be linked to an inertial instability mechanism with the cross equatorial pressure gradient being a critical factor the biomodal state has been shown for the month of august only but this month contributes most of the interannual variability this new picture of the monsoon and interannual variability shown here appears to be relevant not only to interannual variability but also to the multidecadal variability evidenced in the region between the 1950s and 1980s

variationally induced breathing equations of state of pyrope grossular and majorite garnets we have completed the first non empirical fully optimized calculations of the equations of state for pyrope grossular and mgsio3 majorite garnets the static gibbs free energy of the 160 atom unit cell was minimized relative to all 27 structural parameters for the tetragonal structure zero point vibration and thermal effects were estimated with a debye like model and debye temperatures obtained from the equations of state calculated zero pressure densities differ from experimental values by less than 1 while the bulk moduli are systematically larger than those obtained spectroscopically nevertheless the calculations strongly support experimental evidence that the bulk modulus of mgsio3 majorite is close to that of pyrope and further indicate that its kt p o is not distinctly larger than that of other silicate garnets if these properties are close to those of real majorite the steep gradient of the bulk modulus in the transition zone is at best marginally consistent with a iherzolitic composition

single crystal elasticity of iron bearing majorite to 26 gpa implications for seismic velocity structure of the mantle transition zone abstract single crystal elastic moduli of synthetic iron bearing majoritic garnet were measured using brillouin spectroscopy up to a pressure of 26 gpa we found that the iron bearing majoritic garnet mg 0 79 fe 0 08 al 0 30 si 0 84 o 3 remains elastically isotropic throughout the pressure range of this study the shear and adiabatic bulk moduli and their pressure derivatives at zero pressure were determined to be 0 88 7 7 gpa k s0 166 2 gpa p 0 1 28 8 k p 0 4 2 2 these values are almost indistinguishable within the experimental uncertainties from those obtained in previous studies of pure mgsio 3 majorite and other solid solutions of the majorite pyrope join our direct acoustic velocity measurements of iron bearing majorite indicate that the incorporation of iron into majoritic garnet does not drastically affect its elastic moduli and their pressure derivatives the measured pressure derivatives of iron bearing majorite are about 3 6 times lower than required to account for the high seismic velocity gradients observed in the mantle transition zone

marine and terrestrial biomarker records for the last 35 000 years at odp site 658c off nw africa several high resolution proxy environmental records have been obtained for the last 35 kyr from odp hole 658c a well studied site ca 200 km oa cap blanc nw africa the collective assessment based on the marine proxies u k 0 37 sst contents of toc and chlorins upwelling radiolarian index and the percentage of florisphaera profunda surprisingly indicates that the last glacial maximum lgm was characterized by warmer sea surface temperature sst weaker upwelling and lower marine productivity compared with the preceding older glacial and subsequent deglaciation periods of the terrigenous proxies the mean grain size of the non carbonate fraction and the terrigenous alkane content indicate that wind strength and aridity were high the weaker upwelling at the 658 site during the lgm may have resulted from changes in the strength and direction of the wind systems and or shifts in the position and geometry of the upwelling cell 2000 elsevier science ltd all rights reserved

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

the upper mantle beneath the north east pacific rim a comparison with the gulf of california summary seismograms from 22 earthquakes along the north east pacific rim recorded in southern california form the data set for investigation of the upper mantle beneath the cascade range juan de fuca region a transitional area encompassing both very young ocean floor and a continental margin these data consist of 853 seismograms 6 a 42 which produce 1068 travel times and 40 ray parameter estimates we compare these data directly to another large suite of records representative of structure beneath the gulf of california an active spreading centre we use the spreading centre model gca as a starting point in wkbj synthetic seismogram modelling and perturb gca until the ne pacific data are matched application of wavefield continuation to these two groups of data provides checks on the model s con sistency with the data as well as an estimate of the resolvability of differences between the two areas the resulting ne pacific model cjf is very similar to gca disparities in travel times and waveforms from 16 to 22 however are interpretable in ierms of lateral structural variations between the two regions from 200 to 410 km depth cjf features velocities from 200 to 350 km that are inter mediate between the very low values of gca and the more moderate values of t7 a model for the inland western united states models of continental shield regions have even higher velocities in this depth range but all four model types are similar below 450 km this regular pattern observed in the rate of velocity increase with tectonic regime suggests an inverse relationship between velocity gradient and lithospheric age above 400 km depth

topographic features and stratified soil characteristics of a hillslope with fissures formed by the 2016 kumamoto earthquake abstract we examined topographic and stratified soil characteristics of a hillslope with fissures formed by the 2016 kumamoto earthquake in japan numerous fissures were developed on mountainous areas and concentrated along convex topography of ridgelines in addition to the occurrence of many landslides within a 6 20 m plot depth of fissures ranged from 0 3 to 0 4 m near the ridgeline and from 0 6 to 0 8 m in the lower part of hillslope adjacent to a landslide of the same depth on the lower slope width of fissures ranged from 0 4 to 2 2 m mean 1 4 m standard deviation 0 6 m between fissures soil blocks rotated downslope and remained on the slope the soil matrix within the plot consisted of the four sequences of tephra with various thicknesses andisol layers with higher organic matter 16 6 were found between tephra deposits with lower organic matter 11 2 particularly at shallow depths 0 5 and 1 5 m soil bulk density was low in most andisol layers 0 55 0 15 g cm3 while mean bulk density of tephra deposits was slightly higher 0 66 0 14 g cm3 bulk density was negatively correlated to organic matter content the wet conditions 133 37 gravimetric moisture in the andisol layer 1 0 m depth which corresponds to the landslide failure plane are related to higher organic matter content and lower bulk density compared to the tephra layers situated above and below this layer differences in the depths of fissures along the ridgeline suggested that the development of fissures was associated with combinations of topographic factors and soil sequences findings from detailed topography and soil surveys provide insights into fissure formation processes and slope stability assessment

single crystal elasticity of majoritic garnets stagnant slabs and thermal anomalies at the base of the transition zone abstract the elastic properties of two single crystals of majoritic garnet mg 3 24 al 1 53 si 3 23 o 12 and mg 3 01 fe 0 17 al 1 68 si 3 15 o 12 have been measured using simultaneously single crystal x ray diffraction and brillouin spectroscopy in an externally heated diamond anvil cell with ne as pressure transmitting medium at conditions up to 30 gpa and 600 k this combination of techniques makes it possible to use the bulk modulus and unit cell volume at each condition to calculate the absolute pressure independently of secondary pressure calibrants substitution of the majorite component into pyrope garnet lowers both the bulk k s and shear modulus g the substitution of fe was found to cause a small but resolvable increase in k s that was accompanied by a decrease in k s p the first pressure derivative of the bulk modulus fe substitution had no influence on either the shear modulus or its pressure derivative the obtained elasticity data were used to derive a thermo elastic model to describe v s and v p of complex garnet solid solutions using further elasticity data from the literature and thermodynamic models for mantle phase relations velocities for mafic harzburgitic and lherzolitic bulk compositions at the base of earth s transition zone were calculated the results show that v s predicted by seismic reference models are faster than those calculated for all three types of lithologies along a typical mantle adiabat within the bottom 150 km of the transition zone the anomalously fast seismic shear velocities might be explained if laterally extensive sections of subducted harzburgite rich slabs pile up at the base of the transition zone and lower average mantle temperatures within this depth range

paleoceanography of the mauritanian margin during the last two climatic cycles from planktonic foraminifera to african climate dynamics abstract the last 220 ka of the md03 2705 18 05 81 n 21 09 19 w sedimentary sequence retrieved off the cape verde islands was investigated using a multiproxy approach planktonic foraminifera assemblage analyses coupled with isotopic measurements 18 o from benthic planulina wuellerstorfi and planktonic globigerinoides ruber foraminifera monospecific samples were conducted along the topmost 11 m of the sequence high resolution x ray fluorescence measurements 0 5 cm resolution giving access to major element ratio have completed the geochemical analyses along the core seasonal and annual past sea surface temperatures sst were quantitatively reconstructed local sea surface salinity sss changes were then estimated by coupling sst with planktonic 18 o data our data provide a set of both oceanic and continental markers of environmental changes along the north western african margin the major changes detected in our record are discussed in the light of the regional paleoceanographic and paleoclimatic history of the last 220 ka coupled oceanographic and atmospheric processes portray the climatic evolution of the area and show strong links among the regional oceanography water mass advection the upwelling dynamics and the intertropical convergence zone itcz migration an increased upwelling activity or influence of upwelling filaments is noted at the end of the two last glacial periods probably in response to a more southerly position of the itcz higher sss are recorded over the area during arid intervals and were tentatively interpreted as signing a southward shift of the cape verde frontal zone a detailed coupling between dust advection and sss values over the site of study was noted during mis6 5

simmax a modern analog technique to deduce atlantic sea surface temperatures from planktonic foraminifera in deep sea sediments we present a data set of 738 planktonic foraminiferal species counts from sediment surface samples of the eastern north atlantic and the south atlantic between 87 n and 40 s 35 e and 60 w including published climate long range investigation mapping and prediction climap data these species counts are linked to levitus s 1982 modern water temperature data for the four caloric seasons four depth ranges 0 30 50 and 75 m and the combined means of those depth ranges the relation between planktonic foraminiferal assemblages and sea surface temperature sst data is estimated using the newly developed simmax technique which is an acronym for a modern analog technique mat with a similarity index based on 1 the scalar product of the normalized faunal percentages and 2 a weighting procedure of the modern analog s ssts according to the inverse geographical distances of the most similar samples compared to the classical climap transfer technique and conventional mat techniques simmax provides a more confident reconstruction of paleo ssts correlation coefficient is 0 994 for the caloric winter and 0 993 for caloric summer the standard deviation of the residuals is 0 90 c for caloric winter and 0 96 c for caloric summer at 0 m water depth the sst estimates reach optimum stability standard deviation of the residuals is 0 88 c at the average 0 to 75 m water depth our extensive database provides sst estimates over a range of 1 4 to 27 2 c for caloric winter and 0 4 to 28 6 c for caloric summer allowing sst estimates which are especially valuable for the high latitude atlantic during glacial times an electronic supplement of this material may be obtained on adiskette or anonymous ftp from kosmos agu org login toagu s ftp account using anonymous as the username and guestas the password go to the right directory by typing cd append typels to see what files are available type get and the name of the file toget it finally type exit to leave the system paper 95pa01743 simmax a modern analog technique to deduce atlantic sea surfacetemperatures from planktonic foraminifera in deep sea sediments uwepflaumann josette duprat claude pujol and laurent d labeyrie diskette may be ordered from american geophysical union 2000florida avenue n w washington dc 20009 payment mustaccompany order

variability of the antarctic intermediate waters in the northern canary box abstract several chemical parameters were measured during four seasonal cruises in 1997 and 1998 within the canary islands acores gibraltar observations project along the transects within the so called northern canary box ncb this area is enclosed between the african coast latitudes 29 n and 32 n and longitude 18 w to the north of the canary islands spain the nutrient and oxygen concentration data are used in order to establish the atlantic antarctic intermediate water aaiw distribution in the area by means of an anomaly method it is established that this water mass is widely found in this zone particularly new to the african coast a volumetric budget indicates that the aaiw volume flowing into the ncb is of the same order as the mediterranean water mw inflow the results indicate that only 40 of the aaiw mass reaching the box flows northwards through the 32 n section whereas 20 returns southwards through the 29 n section

canary current and north equatorial current from an inverse box model 1 the large scale canary basin circulation is estimated from a box inverse model applied to hydrographic data from a quasi synoptic survey carried out in september 2003 the cruise consisted of 76 full depth ctd and oxygen stations circulation is required to nearly conserve mass and anomalies of salinity and heat within layers bounded by neutral surfaces it permits advective and diffusive exchange between layers and an adjustment of the ekman transport and the freshwater flux divergences the canary current at the thermocline layer transports a net mass of 4 7 0 8 sv southward north of the canary islands from the african coast to 19 w it is divided into a northward circulation at a rate of 1 1 0 5 sv between the african coast and lanzarote island and a southward transport of 5 8 0 6 sv it transports north atlantic central water and organic matters advected offshore by the filaments protruding from the upwelling system off northwest africa at 24 n the canary current feeds the north equatorial current that transports a mixture of north and south atlantic central waters westward in the intermediate layer a southwestward flow of 1 2 1 1 sv transports mediterranean water to the subtropical gyre though the highest salt flux is transported by a meddy oxygen distribution and mass transport suggest a northeastward deep flow of a water mass colder than 2 2 c consisting of diluted antarctic bottom water the heat and freshwater divergences and the average dianeutral velocity and diffusion between the sections and the african coast are negligible

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

elasticity of a majorite pyrope solid solution the elastic properties of a solid solution consisting of 59 mole percent pyropic garnet and 41 mg sub 4 si sub 4 o sub 12 majorite a high pressure form of pyroxene have been measured by brillouin spectroscopy under ambient conditions values of the adiabatic bulk modulus k sub s 164 plus minus 15 gpa and shear modulus g 89 4 plus minus 3 7 gpa are similar to those for low pressure aluminosilicate garnets the enstatite majorite reaction is characterized by a large 49 increase in k sub s and a much smaller 13 increase in g the properties of low pressure garnets suggest that the contrast in shear moduli for this reaction is probably larger in ca rich systems taken at face value the stp properties of these phases imply that large quantities of ca rich clinopyroxene are needed in order to satisfy seismologically determined shear modulus gradients in the transition zone this suggestion is however subject to considerable uncertainties in the pressure and temperature derivatives of elastic properties for mantle minerals and the velocity structure of the transition zone

chemical accumulation variations under the peru current during the past 130 000 years the titanium to aluminum ratio in core v19 29 is correlated with aluminosilicate accumulation rates this correlation may be due to pleistocene eolian transport fluctuations which alter the mean grain size of sedimented eolian material the relation between aluminum accumulation rate and ti al established from accumulation rates integrated over 11 000 50 000 year intervals can be inverted to compute a high resolution record of aluminosilicate and calcium carbonate accumulation rates over the past 130 000 years carbonate accumulation rates are closely related to the oxygen isotope record in the core with a phase lag and damping constant that is compatible with the response time shown to be only 6000 years of calcium carbonate in the ocean carbonate sedimentation at this site responds to several processes independently correlated with climatic change the relative importance of these processes for carbonate sedimentation at this site can be constrained by the record in this core and other lines of evidence 15 of the increased carbonate deposition at this site during glacial periods may be due to diminished nadw north atlantic deep water formation 10 is due to carbonate productivity decreases in the north atlantic 25 may be due to a diminished shallow sea carbonate sink and the residual 50 must be due to a local productivity increase these assignments are consistent with observations on carbonate paleoceanography in the north atlantic aluminosilicate accumulation rate variations correlate with the record of eolian quartz deposition near northwest africa and in a general way with the climatic record but in detail the record differs substantially from the oxygen isotope record and may provide independent evidence on the nature of climate dynamics

the eastern boundary current system between the canary islands and the african coast to study the easternboundarycurrentsystem off northwest africa in detail several ctd adcp sections and long term mooring work were carried out in the channel between lanzarote and africa the observations are compared with a fine resolution model which was developed in the framework of the canigo project the water masses which are observed in this area are characterised and classified in density ranges the current field shows a high spatial and temporal variability with maximum velocities of about 35 cm s seasonal means as well as currents averaged across the channel are only a few cm s in the surface water a steady southward flow in the middle of the channel indicates the canarycurrent in this area during fall a strong northward current is observed close to the african shelf though the canarycurrent strengthens during summer and fall due to an increase of the trade winds the transport in the channel decreases or turns northward during that time due to the enhanced poleward current at the eastern side a northward undercurrent with a mean velocity of 2 3 cm s is observed at the african slope in 950 m depth the poleward transport of aaiw increases during fall and a strong influence of relatively fresh aaiw is observed during that time most of the observations fit well to the results of the canigo model but the occurrence of mw at the bottom of the channel and the corresponding southward flow cannot be resolved by the model

glacial mediterranean sea surface temperatures based on planktonic foraminiferal assemblages we present a new reconstruction of mediterranean sea surface temperatures sst during the last glacial maximum lgm a calibration data set based on census counts of 23 species of planktonic foraminifera in 129 north atlantic and 145 mediterranean core top samples was used to develop summer winter and annual average sst reconstructions using artificial neural networks anns and the revised analogue method ram prediction errors determined by cross validation of the calibration data set ranged between 0 5 and 1 1 c with both techniques being most successful in predicting winter ssts glacial reconstructions are based on a new expanded data set of 273 samples in 37 cores with consistent minimum level of age control the new lgm reconstructions suggest that the east west temperature gradient during the glacial summer was 9 c whereas during the glacial winter the gradient was 6 c both some 4 c higher than that existing today in contrast to earlier studies our results tend to suggest much cooler sst estimates throughout the glacial mediterranean particularly in the eastern basin where previous sst reconstructions indicated a decrease of only 1 c our new sst reconstructions will provide the modelling community with a detailed and updated portrayal of the mediterranean sea during the lgm setting new targets on which glacial simulations can be tested

elasticity of majorite and a majorite pyrope solid solution to high pressure implications for the transition zone 1 high seismic velocity gradients in the transition zone have been attributed to large pressure derivatives of the elastic moduli of transition zone minerals such as majorite garnet here we present brillouin scattering measurements of the elasticity of polycrystalline mg majorite mj100 mg4si4o12 and a mj50py50 majorite pyrope solid solution to pressures similar to those at the top of the transition zone 15 1 1 gpa and 12 8 1 gpa respectively the pressure derivatives of the adiabatic bulk ks and shear moduli of both mj50py50 and mj100 are 4 2 3 and 1 4 2 respectively and are equal to those of pyrope within the experimental uncertainties we conclude that neither the adiabatic compression of majorite garnet nor any other likely transition zone phase is able to produce the high velocity gradients observed seismically high velocity gradients are consistent with gradual transformations between minerals with very different elastic properties the transformation of 25 or more of clinopyroxene into majorite above 520 km and the formation of ca silicate perovskite below 520 km could produce the observed seismic gradients

a model for the layered upper mantle abstract numerical modeling of mantle convection by liu 1994 science 264 1904 1907 favors a two layer convection if the results are reinterpreted for the correct phase relations in mg fe 2sio4 the resulting chemical isolation of the upper and lower mantle suggests a highly differentiated and layered upper mantle to account for the discrepancy between the observed compositions of mantle xenoliths and the cosmic abundances of elements it is shown that a layered upper mantle with a hidden reservoir can have a structure consistent with the observed seismic velocity profiles and an average bulk composition corresponding to the cosmic abundances the evolution of the upper mantle and the origin of komatiites are discussed in the context of the proposed model

spinel elasticity and seismic structure of the transition zone of the mantle there is continuing debate about whether the upper mantle is chemically stratified and whether the seismic discontinuity at 400 km depth represents a chemical boundary a phase change of the mg fe 2sio4 component from the phase olivine to the p phase or a combination of both recent developments in high pressure synthesis1 2 and ultrasonic interferometry3 4 have made possible measurements of elastic wave velocities in small poly crystalline samples of high pressure phases by combining our new acoustic measurements on the spinel phase of mg2 sio4 with existing data for the and phases we present here velocity profiles for the m2sio4 component of the mantle where m represents mg or fe to depths of about 600 km we find it to be unlikely that any seismologically observable velocity discontinuity at about 520 km depth can be attributed to this component although the contrast in impedance the product of density and velocity might be sufficient for the transformation to be observed in long period seismic reflection studies at near normal incidence5 the velocity gradients in the transition zone particularly for shear waves are steeper than would be expected for simple adiabatic compression of likely mantle compositions suggesting that alternative explanations including chemical heterogeneity and anelastic relaxation need to be explored

evidence for immiscibility in majorite garnet from experiments at 13 15 gpa abstract the compositions of coexisting aluminous garnet clinoenstatite and either jadeitic clinopyroxene or a second silica rich garnet were experimentally determined in the system na2o cao feo mgo al2o3 sio2 at 1450 1650 c and 13 15 gpa using a split sphere anvil apparatus ussa 2000 the pyroxene content of the aluminous garnet increases from 50 at 13 gpa to 100 at 15 gpa for bulk compositions with a high na ca ratio the trends of the observed variation in the compositions of both garnet and clinopyroxene exhibit a major change with increasing pressure at 14 gpa this is consistent with the stabilization of a second silica rich garnet which replaces jadeitic clinopyroxene in the assemblage with aluminous garnet and clinoenstatite the transformation from clinopyroxene to silica rich garnet is almost isochemical and occurs near the composition na0 8ca0 3 fe mg 2 25al0 5si4 15o12 due to the observed immiscibility in the garnet solution the transformation from pyroxene to garnet could produce a sharp seismic discontinuity in the earth s mantle at 400 km depth

the upwelling area off northwest africa a description of phenomena related to coastal upwelling abstract this paper presents a brief review of the oceanography along the upwelling coast of northwest africa the description contains information on seasonal variations of large scale winds ocean circulation and some gross of features of the hydrography characteristic meso scale patterns of currents during the upwelling season between 16 n and 26 n air and water temperature differences during upwelling season diurnal and semi diurnal variations of temperature atmospheric pressure wind and current regional peculiarities canyons and the banc d arguin

sahel megadroughts triggered by glacial slowdowns of atlantic meridional overturning 1 the influence of the large scale ocean circulation on sahel rainfall is elusive because of the shortness of the observational record we reconstructed the history of eolian and fluvial sedimentation on the continental slope off senegal during the past 57 000 years our data show that abrupt onsets of arid conditions in the west african sahel were linked to cold north atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with heinrich stadials climate modeling suggests that this drying is induced by a southward shift of the west african monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric african easterly jet

tem observations of several spinel garnet assemblies toward the rheology of the transition zone in order to better identify the mineral phase which controls the rheology of the transition zone between 410 and 660 km depth transmission electron microscopy observations were made on several coexisting spinel garnet assemblies alkremite xenolith pyrope rich mgo 1 1al2o3 spinel assembly deformed at 1173k 800 mpa in a griggs apparatus mg fe 3 al mg si 2si3o12 majorite mg fe 2sio4 spinel assembly synthesized in a laser heated diamond anvil cell it was found that garnet crystals systematically remain undeformed while spinel crystals are plastically deformed these results are in accord with the assumption that the rheology of majorite is stronger than the rheology of spinel in the conditions of the transition zone

upwelling intensity and ocean productivity changes off cape blanc northwest africa during the last 70 000 years geochemical and micropalaeontological evidence abstract the accumulation of biogeochemical organic carbon calcium carbonates molybdenum and iodine micropalaeontological benthic foraminifera and terrigenous markers grain size si al zr al k al over the last 70 000 years in one core sedorqua 11k on the northwest african margin off cap blanc has been used to reconstruct past variations of local upwelling intensity and oceanic productivity the study demonstrates that productivity in this area increased during stage 3 particularly between 40 000 and 50 000 yr b p and during the last deglaciation between 6000 and 15 000 yr b p during most of isotopic stage 2 and particularly during the last glacial maximum productivity was much lower these variations can be attributed to changes in local wind stress and seasonality that are related to variability in monsoon pressure intensity because of the establishment of upwelling cells over the shelf due to high sea level the conditions of sedimentation during the last 5 6 thousend years on the upper slope site 11k are largely dominated by advection from the shelf leading to strong sorting prior to deposition advection seems to have been minor during the other periods of enhanced productivity a conceptual model is proposed to link the productivity variations to atmospheric circulation in particular to the wind stress direction and seasonality

a synthetic pollen record of the eastern mediterranean sapropels of the last 1 ma implications for the time scale and formation of sapropels abstract the quaternary climate of southern europe south italy and greece is investigated by pollen analysis of the sapropels which were deposited in the deep eastern mediterranean sea during the last 1 million year ma the time scale of core kc01b in the ionian sea has been established by tuning its oxygen isotopic record to the ice volume model of imbrie and imbrie 1980 for the last 250 000 year 250 ka the previous pollen studies and astronomical tuning have been confirmed sapropels were deposited under a large range of mediterranean climates fully interglacial fully glacial and intermediary as revealed mainly by the balance between the respective pollen abundances of oak quercus and sage brush artemisia the high value of the oak reveals the warm and wet climate of an interglacial and the high value of the sage brush the dry and cold climate of a glacial whereas the mediterranean climate is directly related to the variation of the high latitude ice sheets the deposition of sapropels is not so in contrast with the wide climatic range sapropels were deposited only when summer insolation in the low latitudes reached its highest peaks however between 250 ka and 1 ma that stable pattern is not yet established only six sapropels are observed many expected ones do not appear even as ghosts signalled by peaks of barium abundance that remain after the post deposition oxidation of organic matter the pattern of sapropel formation in stable and direct relationship to highest insolation does not seem to apply for five of those sapropels neither climate extremes are observed they mainly formed during intermediary types of mediterranean climate in contrast one sapropel and one ghost relates to a relatively low peak of insolation and its climate is of a unique composite type not seen later this might suggest an unsuspected more complex pattern linking the formation of mediterranean sapropels to the astronomical configuration

simulation of intense monsoons under glacial conditions paleoenvironmental and paleoclimatological proxy data indicate that strong continental monsoons took place under glacial conditions during marine isotopic stage 6 5 175 ka bp so far no climate model has explored the possible coexistence of glacial conditions at mid and high latitudes and of interglacial monsoons in the tropics here we use an atmospheric general circulation model and clearly demonstrate that high insolation can generate increased monsoon activity even with surface glacial conditions our experiments show that indian and african monsoons at 175 ka were stronger than nowadays and induced an increase in outflow of the nile river to the mediterranean sea this freshwater supply combined with the local low glacial evaporation may explain the stagnation of the eastern mediterranean sea leading to the deposit of sapropel s6 our simulations show also increased surface winds in the northern atlantic and pacific oceans which may have affected the bioproductivity in these areas

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

the p wave upper mantle structure beneath an active spreading centre the gulf of california summary detailed analysis of short period travel time dt d and wave form data reveals the upper mantle structure beneath an oceanic ridge to depths of 900 km more than 1400 digital seismograms from earthquakes in mexico and central america recorded at scarlet yield 1753 travel times and 58 direct measurements of dt d as well as high quality stable waveforms the 29 events combine to form a continuous record section from 9 to 40 with an average station spacing of less than 5 km first the travel times are inverted using the tau method of bessonova et al the resultant model is adjusted to agree with the experimental p values further constraints arise from the observed relative amplitudes of mantle phases which are modelled by trial and error using wkbj synthetic seismograms chapman wiggins model gca which is appropriate for western mexico north of 20 latitude is similar to existing upper mantle models for shield tectonic continental and arc trench regimes below 400 km but differs significantly in the upper 350 km gca velocities are very low in this depth range the model catches up with the others with a very large velocity gradient from 225 to 390 km this well resolved feature is consistent with the shear wave model tna for western north america of grand helmberger the abundant data from 20 to 30 control the detailed shape of the 660 km discontinuity very large velocity gradients lie both above 620 660 km and below 661 680km a 2 8 per cent velocity change

phasing of deglacial warming and laurentide ice sheet meltwater in the gulf of mexico evidence is emerging that the tropical climate system played a major role in global climate change during the last deglaciation however existing studies show that deglacial warming was asyn chronous across the tropical band complicating the identification of causal mechanisms the orca basin in the northern gulf of mexico is ideally located to record subtropical atlantic sea surface temperature sst warming in relation to meltwater input from the laurentide ice sheet paired d 18 o and mg ca data on the planktonic foraminifer globigerinoides ruber from core en32 pc6 are used to separate deglacial changes in sst and d 18 o of sea water sst as calculated from mg ca data increased by 3 8c from ca 17 2 to 15 5 ka in association with heinrich event 1 and was not in phase with greenland air temperature subtracting tem perature effects from d 18 o values in g ruber reveals two excur sions representing laurentide meltwater input to the gulf of mex ico one of 1 5 from ca 16 1 to 15 6 ka and a second major spike of 2 5 from ca 15 2 to 13 0 ka that encompassed melt water pulse 1a and peaked ca 13 8 ka during the bolling allerod conversion to salinity through the use of a laurentide meltwater end member of 225 indicates that near surface salinity de creased by 2 4 during these spikes these results suggest that gulf of mexico sst warming preceded peak laurentide ice sheet decay and the bolling allerod interval by 2 k y and that heat was retained in the subtropical atlantic during heinrich event 1 consistent with modulation of deglacial climate by thermohaline circulation

relative strength of the pyrope majorite solid solution and the flow law of majorite containing garnets even though the garnet phase is the second most abundant phase in the upper mantle and transition zone no previous studies have directly measured the effect of majorite content on the strength of garnet under mantle conditions here we report the results of constant strain rate and stress relaxation experiments on garnets in the pyrope majorite solid solution which constrain the strength of majoritic containing garnets relative to pyrope as a function of majorite content and temperature we find that at temperatures below 650 degrees c both pure pyrope and majoritic garnets have the same strength conversely above 650 degrees c we find that majoritic garnets are initially stronger than pure pyrope but weaken with increasing temperature and majorite content and with significant majorite contents are weaker than pyrope above approximately 800 degrees c we develop a flow law for the entire pyrope majorite solid solution as a function of temperature and majorite content c 2010 elsevier b v all rights reserved

low latitude dusty events vs high latitude icy heinrich events it has been proposed that tropical events could have participated in the triggering of the classic high latitude iceberg discharge heinrich events he we explore low latitude heinrich events equivalents at high resolution in a piston core recovered from the tropical north western african margin they are characterized by an increase of total dust lacustrine diatoms and fibrous lacustrine clay minerals thus low latitude events clearly reflect severe aridity events that occurred over africa at the saharan latitudes probably induced by southward shifts of the inter tropical convergence zone at a first approximation it seems that there is more likely synchronicity between the high latitude heinrich events hes and low latitude events lle rather than asynchronous behaviours

elastic wave velocities of pyrope majorite garnets py62mj38 and py50mj50 to 9 gpa abstract polycrystalline specimens of two pyrope majorite garnets 2 py 62 mj 38 and py 62 mj 38 were synthesized in a 2000 ton uniaxial split sphere apparatus ussa 2000 at pressures of 16 gpa and temperatures of 1670 k for run durations of about 2 h using homogeneous glasses as starting materials ultrasonic interferometric measurements on these specimens were conducted at pressures up to 9 gpa at room temperature using a 1000 ton uniaxial split cylinder apparatus usca 1000 with bi as an internal pressure marker from the measurements of the travel times for compressional p and shear s waves the velocities and elastic moduli are calculated using length density changes determined from the travel time data third order eulerian finite strain analysis of these data yield the longitudinal l and shear g moduli and their pressure derivatives m 0 m p t for py 62 mj 38 l 0 291 6 gpa and l 0 9 1 0 6 g 0 90 1 gpa and g 0 1 9 0 2 from which we calculate the values for the adiabatic bulk modulus k l 4 3 g to be k 0 171 5 gpa and k 0 6 2 0 5 these new data for the shear modulus and its pressure derivative are in agreement with the previous values for the same composition rigden s m gwanmesia g d liebermann r c 1994 elastic wave velocities of a pyrope majorite garnet to 3 gpa phys earth planet inter 86 35 44 but the p wave velocity the bulk modulus and its pressure derivative are somewhat higher for the py 50 mj 50 composition these values are l 0 289 6 gpa l 0 9 2 0 7 g 0 89 1 gpa g 0 2 1 0 2 k 0 170 5 gpa and k 0 6 4 0 5 the high pressure derivatives of k and g for these py mj garnets may be important in explaining the high velocity gradients observed in seismic models of the transition zone of the earth s mantle

climatic conditions during marine oxygen isotope stage 6 in the eastern mediterranean region from the isotopic composition of speleothems of soreq cave israel at several times during marine oxygen isotope stage 6 the eastern mediterranean region was influenced by two extreme climatic systems the large ice sheet over northern europe and the wet tropics associated with african monsoons during this interval two major climatic events occurred in the region the sapropel s6 layer formed ca 176 ka in the eastern mediterranean basin owing to the increase in the african monsoon and another event although not large enough to form sapropel occurred ca 151 ka the isotopic composition of soreq cave speleothems seems to record these events as very low 18 o 13 c values dated as ca 178 and 152 ka the very low 18 o 13 c values of 6 and 11 to 12 respectively are typical of interglacial intervals but here they were recorded during a glacial interval such low peaks indicate that in this part of the eastern mediterranean region i e israel the rainfall amount increased dramatically moreover the isotopic record of the speleothems also shows that during the entire stage 6 although the climate was as cold as much of the last glacial the conditions were never as dry

an experimental investigation of the pyroxene garnet transformation in a pyrolite composition and its bearing on the constitution of the mantle abstract the pyroxene garnet transformation in a model pyrolite composition has been investigated over the pressure interval 4 0 to 17 5 gpa at temperatures of 1200 1400 c the transformation is largely completed in the pressure interval 14 16 gpa and a single phase aluminum deficient garnet majorite becomes stable above 16 gpa the mineral assemblages and the density and seismic velocity distributions for pyrolite are calculated as a function of depth on the basis of this and other recent experimental data density and seismic velocity profiles calculated for pyrolite are consistent with models based on seismic observations to a depth of 550 km if the existence of a high density velocity gradient between 550 km and 650 km is confirmed the presence of further phase transformations in majorite and or some degree of chemical heterogeneity in this depth interval would be indicated

the transition zone of the canary current upwelling region abstract like all the major upwelling regions the canary current is characterised by intense mesoscale structure in the transition zone between the cool nutrient rich waters of the coastal upwelling regime and the warmer oligotrophic waters of the open ocean the canary island archipelago which straddles the transition introduces a second source of variability by perturbing the general southwestward flow of both ocean currents and trade winds the combined effects of the flow disturbance and the eddying and meandering of the boundary between upwelled and oceanic waters produce a complex pattern of regional variability on the basis of historical data and a series of interdisciplinary field studies the principal features of the region are described these include a prominent upwelling filament originating near 28 n off the african coast cyclonic and anti cyclonic eddies downstream of the archipelago and warm wake regions protected from the trade winds by the high volcanic peaks of the islands the filament is shown to be a recurrent feature apparently arising from the interaction of a topographically trapped cyclonic eddy with the outer edge of the coastal upwelling zone its role in the transport and exchange of biogenic material including fish larvae is considered strong cyclonic eddies observed throughout the year drift slowly southwestward from gran canaria one sampled in late summer was characterised by large vertical isopycnal displacements apparent surface divergence and strong upwelling producing a fourfold increase in chlorophyll concentrations over background values such intense eddies can be responsible for a major contribution to the vertical flux of nitrogen the lee region of gran canaria is shown to be a location of strong pycnocline deformation resulting from ekman pumping on the wind shear boundaries which may contribute to the eddy formation process

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

transformation of enstatite diopside jadeite pyroxenes to garnet the high pressure stability of enstatite en diopside di jadeite jd pyroxenes has been investigated experimentally with a split sphere anvil apparatus ussa 2000 on the enstatite pyrope join the compositions of garnet coexisting with enstatite were determined at 100 165 kbar and 1450 1850 c the results indicate complete solubility between enstatite and pyrope in the system cao mgo al2o3 sio2 cmas the compositions of coexisting pyroxenes and garnet were determined at 100 165 kbar and 1250 1750 c at 157 kbar 1650 c garnet with the composition en79di21 mol forms on the en di join in the system na2o mgo al2o3 sio2 nmas the compositions of coexisting pyroxenes and garnet were determined at 60 160 kbar and 1200 1850 c on the en jd join the first garnet has the composition en48jd52 at 135 kbar 1650 c and en53jd47 at 140 kbar 1500 c on the di jd join the first garnet with the composition di63jd37 forms around 170 kbar 1650 c in the en di jd system the first appearance of garnet with the composition en42di9jd49 is estimated at 133 kbar 1650 c the new pyroxene with the composition namg0 5si2 5o6 napx transforms to garnet at 154 kbar 1650 c the experimental results indicate that the transformation of a twopyroxene assemblage to garnet and residual pyroxene in the en di jd system could occur at pressures consistent with the 400 km seismic discontinuity and in a pressure interval of 0 3 kbar

phase lag between intertropical convergence zone migration and subtropical monsoon onset over the northwestern indian ocean during marine isotopic substage 6 5 mis 6 5 high resolution faunal and isotopic analyses of foraminifera were performed on core md96 2073 10 94 n 52 62 e 3142 m depth located close to socotra island in the upwelling area of the somali basin nw indian ocean this work focuses on marine isotopic stage 6 5 in order to reconstruct paleo upwelling changes and their links with the arabian sea summer monsoon and the migration of the intertropical convergence zone itcz correspondence and cluster analyses of planktonic foraminiferal abundances partly controlled by temperature and water mass productivity together with an upwelling intensification index show the occurrence of a strong upwelling between 176 and 165 ka this upwelling intensification responds to a northward migration of the itcz an isotopic depletion in the planktonic foraminifera 18o records occurring between 180 and 167 ka is interpreted as proof of a large salinity decrease in the surface waters probably linked to a strong input of fresh rainfall waters induced by an intense monsoon activity the lag between the onset of upwelling intensification and the strong monsoonal impact over the same area suggests a decoupling between both phenomena the migration of the itcz is influenced by obliquity and precessional forcing while the arabian sea summer monsoon precipitation depends only on precessional forcing

hydrological conditions over the western mediterranean basin during the deposition of the cold sapropel 6 ca 175 kyr bp a new oxygen isotope record is reported from a stalagmite collected in the argentarola cave located on the tyrrhenian coast of italy as shown from observations and numerical modeling of n 18 o in modern precipitation the recorded n 18 o variability for this zone is dominated by the amount of precipitation so called amount effect the n 18 o profile measured in the stalagmite is characterized by a prominent negative excursion ca 2 3x between 180 and 170 kyr bp this paleoclimatic feature is interpreted as being due to a relatively wet period which occurred during the penultimate glacial period more precisely during marine isotope stage 6 5 this pluvial phase is shown to correspond chronologically to the deposition of the sapropel event 6 s6 although this particular sapropel event occurred during a cold phase the n 18 o excursion is similar to those corresponding to other sapropels s4 s3 and s2 the evidence for humid conditions during s6 in the western mediterranean basin agrees with previous studies based on deep sea sediment cores taken collectively the data suggest that during sapropel events dilution of ocean surface waters was not restricted to the output of the river nile but was rather widespread over the entire mediterranean sea due to increased rainfall 2002 elsevier science b v all rights reserved

late quaternary upwelling off tropical nw africa new micropalaeontological evidence from odp hole 658c planktonic foraminifera and radiolaria have been analysed in a late quaternary 40 0 ka sediment sequence from ocean drilling program odp hole 658c located under a coastal upwelling system near cap blanc offshore northwest africa in order to document the palaeoceanographic history of the area temporal variations in species abundance and faunal assemblage analysis reveal a tripartite phased sequence of palaeoceanographic change through the late quaternary phase 1 spans 40 14 5 ka and is characterised by moderate upwelling but heinrich event 2 is distinguished as a brief episode of strengthened upwelling phase 2 begins with a change in a number of variables at ca 14 5 ka and extends to ca 5 5 ka this phase is characterised by a general strengthening of upwelling but may be subdivided into three minor phases including a the recognition of the younger dryas marked by a temporary reduction in upwelling strength followed by b an intensification of upwelling and c upwelling and high productivity between 8 and 5 5 ka this phase of upwelling corresponds with maximum holocene cooling possibly triggered by the collapse of the laurentide ice sheet phase 3 extends from 5 5 to 0 ka and is characterised by weak upwelling and significant calcite dissolution these phases are related to climatic events particularly the african humid period ahp which is coincident with phase 2 the ahp is characterised by increased precipitation linked to an intensification of the african monsoon that enhances north east trade wind driven coastal upwelling and is associated with the expansion of continental vegetation across north africa copyright 2006 john wiley sons ltd

geochemical and geophysical implications of the radiocarbon calibration abstract a precise and accurate chronological framework is crucial to study the dynamics of a variety of phenomena which occurred during the last 45 000 years although the 14 c dating method has been widely applied since the 1950s it is recognized that the atmospheric 14 c 12 c ratio has not been stable during the past in order to calculate accurate ages these fluctuations have to be corrected by means of a calibration curve obtained by comparing raw 14 c measurements with true calendar ages provided by independent dating methods the calibration curve obtained so far is characterized by a long term trend with raw 14 c ages being significantly younger than calendar ages during most of the last 45 000 years abrupt 14 c shifts which occurred over centuries to millennia are superimposed on this long term trend of decreasing atmospheric 14 c 12 c ratio to a certain extent it is possible to outline the different causes of atmospheric 14 c variations by considering complementary information obtained from other cosmogenic nuclides studied at different latitudes 1 most high frequency changes in the atmospheric 14 c 12 c ratio are linked to magnetic fluctuations of solar origin as revealed by studying the last three centuries for which direct observations of the sun are available a similar conclusion is derived by comparing 14 c 12 c events with 10 be and 36 cl concentration maxima in polar ice cores 2 the long term trend shift of 14 c ages is due to a long period of decreased shielding effect of the geomagnetic dipole field which occurred over the interval between 10 000 and 40 000 years bp this interpretation is supported by paleomagnetic measurements performed on volcanic and sedimentary rocks and by 10 be and 36 cl analysed in low and high latitude records 3 a prominent and rapid atmospheric 14 c 12 c excursion occurred between 13 000 and 11 500 cal yr bp thus corresponding to the younger dryas cold period by contrast with the 14 c variability mentioned above which is linked to 14 c production changes this so called 14 c age plateau is probably due to an abrupt variation in the rates of exchange within the global carbon cycle this interpretation is supported by independent geochemical proxies and by numerical modelling of the carbon cycle

water masses and currents in the upper tropical northeast atlantic off northwest africa recent current measurements in the tropical eastern north atlantic reproduce the components of the large scale flow field however the observations as well as the 1 12 flame model computations indicate that a lot of eddy scale variability is superimposed on the mean flow field despite of the disturbance by variability the signature of the guinea dome is well present in november 2002 the guinea dome transport from direct observations was about 2 8 sv above 25 8 kg m3 and 4 sv between 25 8 and 27 1 kg m3 the oxygen minimum in the shadow zone comprises the central water and the antarctic intermediate water aaiw layers and is located between the equatorial current system and the north equatorial current the north equatorial counter and undercurrents at 3 to 6 n are major oxygen sources for the central water layer of the low oxygen regions in the northeastern tropical atlantic a second northern north equatorial countercurrent nnecc band exists at 8 to 10 n the nnecc carries oxygen rich water from the southern hemisphere eastward but with an admixture of water from the northern hemisphere a float at 200 m depth was spreading eastward in the north equatorial undercurrent neuc at 28 w it shifted northward into the nnecc and then was trapped in the guinea dome region for more than 3 years the model indicates the region 22 to 32 w as the area of exchange between the necc neuc and the nnecc bands in the aaiw layer the northern intermediate countercurrent acts as oxygen source for the oxygen minimum zone

phase relations in the transition zone phase relations in the systems mgo al2o3 sio2 and cao mgo sio2 have been investigated experimentally at 166 226 kbar pressures and 1350 2500 c temperatures with a split sphere anvil apparatus ussa 2000 mgsio3 ilmenite is stable to lower pressures 175 kbar than found previously casio3 perovskite forms at p bar 15t c 151 000 three new high pressure phases are reported a phase with the diopsidic composition the cm phase a high pressure polymorph of al2o3 and superphase b with the tentative composition mg10si3o14 oh f 4 the invariant point for coexisting majorite mg4si4o12 perovskite mgsio3 beta phase mg2sio4 and liquid has been located at 224 kbar 2430 c with the eutectic melt composition on the enstatite forsterite join at 40 44 wt of forsterite the melting temperature of mgsio3 perovskite at 225 kbar is predicted to be 2600 c the new data made possible the calculation of a temperature pressure phase diagram for the system cao mgo al2o3 sio2 cmas in the pressure range 0 280 kbar the mineralogy of the earth s mantle and the possible mechanisms for producing large seismic velocity gradients in the transition zone are discussed on the basis of the derived phase relations

on the origin of the azores current the azores current south of the azores archipelago is part of the subtropical north atlantic gyre using an international hydrographic data set we analyze mean and seasonal geostrophic transport fields in the upper 800 m of the ocean in order to determine the origin of the azores current in the western basin and seasonal changes in the related flow geostrophic currents are obtained by using the method applied by stramma 1984 in the eastern basin the azores current is found to originate in the area of the southwest newfoundland rise figure 10 in winter an almost uniform current connects this region of origin with the azores current while a branching into two current bands is observed in summer with the southern band forming a marked cyclonic loop within the upper 800 m all of the transport in the northern band and about 70 of the transport in the southern band recirculates in the eastern basin additionally expendable bathythermograph data from the azores current region indicate an increase of eddy potential energy from winter to summer

reconstruction of sea surface temperatures from assemblages of planktonic foraminifera multi technique approach based on geographically constrained calibration data sets and its application to glacial atlantic and pacific oceans abstract we present a conceptual framework for a new approach to environmental calibration of planktonic foraminifer census counts this approach is based on simultaneous application of a variety of transfer function techniques which are trained on geographically constrained calibration data sets it serves to minimise bias associated with the presence of cryptic species of planktonic foraminifera and provides an objective tool for assessing reliability of environmental estimates in fossil samples allowing identification of adverse effects of no analog faunas and technique specific bias we have compiled new calibration data sets for the north n 862 and south n 321 atlantic and the pacific ocean n 1111 we show evidence that these data sets offer adequate coverage of the sea surface temperature sst and faunal variation range and that they are not affected by the presence of pre holocene samples and or calcite dissolution we have applied four transfer function techniques including artificial neural networks revised analog method and simmax with and without distance weighting on faunal counts in a last glacial maximum lgm data set for the atlantic ocean 748 samples in 167 cores based on the glamap 2000 compilation and a new data set for the pacific ocean 265 samples in 82 cores and show that three of these techniques provide adequate degree of independence for the advantage of a multi technique approach to be realised the application of our new approach to the glacial pacific lends support to the contraction and perhaps even a cooling of the western pacific warm pool and a substantial 3 c cooling of the eastern equatorial pacific and the eastern boundary currents our results do not provide conclusive evidence for lgm warming anywhere in the pacific the atlantic reconstruction shows a number of robust patterns including substantial cooling of eastern boundary currents with considerable advection of subpolar waters into the benguela current a cooling of the equatorial atlantic by 5 c and steep sst gradients in the mid latitude north atlantic the transfer function techniques generally agree that subtropical gyre areas in both hemispheres did not change significantly since the lgm although the ann technique produced glacial sst in the southern gyre 1 2 c warmer than today we have revisited the issue of sea ice occurrence in the nordic seas and using the distribution of subpolar species of planktonic foraminifera in glacial samples we conclude that the norwegian sea must have been ice free during the summer

impacts of warm and cold situations in the mediterranean basins on the west african monsoon observed connection patterns 1979 2006 and climate simulations using both empirical and numerical ensemble approaches this study focuses on the mediterranean west african relationship in northern summer statistical analyses utilize skin temperature sea surface temperature in situ and satellite rainfall outgoing longwave radiation olr observations and reanalyzed data winds and specific humidity on isobaric surfaces numerical investigations are based on a large set of sensitivity experiments performed on four atmospheric general circulation models agcm arpege climat3 echam4 lmdz4 and ucla7 3 model outputs are compared to observations discussed model by model and with an ensemble multi model approach as in previous studies the anomalous mediterranean warm events are associated with specific impacts over the african monsoon region i e a more intense monsoon enhanced flux convergence and ascendances around the itcz a strengthening of low level moisture advection and a more northward location of ascending motion in west africa the results show also new features 1 thermal variability observed in the two mediterranean basins has unalike impacts i e the western mediterranean covaries with convection in gulf of guinea while the eastern mediterranean can be interpreted as sahelian thermal forcing 2 although observations show symmetry between warming and cooling modelling evidences only support the eastern warming influence 3 anomalous east warm situations are associated with a more northward migration of the monsoon system accompanied by enhanced southwertely flow and weakened northeasterly climatological wind 4 the multi model response shows that anomalous east warm surface temperatures generate an enhancement of the overturning circulation in low and high levels an increase in tej tropical eeasterly jet and a decrease in aej african eeasterly jet

density and thermal expansion of a peridotite melt at high pressure abstract density of a feo rich peridotite ma a model composition of martian mantle melt was investigated by high pressure experiments conducted at 6 3 18 0 gpa and 1800 2570 c we adopted the sink float method i e the sinking and flotation of a certain crystal density marker in the silicate melt is judged from its position in the run product recovered from high pressure and high temperature conditions the density marker moves in a vertical direction driven by the density difference between the melt and the marker we used olivine and diamond for the density marker the third order birch murnaghan equation of state was applied for a feo rich peridotite melt and its thermal expansion coefficients at 1980 c and bulk moduli at 1980 c and 2330 c were determined from the constraints obtained by sinking and flotation of olivine and diamond assuming that the pressure derivative of bulk modulus k equals 10 1 as the same value as that of fayalite melt agee 1992a the thermal expansion coefficients at 1980 c are 6 2 2 0 10 5 k 1 at 8 1 gpa and 5 9 1 8 10 5 k 1 at 15 1 gpa and the isothermal bulk moduli are 17 9 3 3 gpa at 1980 c and 17 7 4 5 gpa at 2330 c the density relations between the martian mantle melt and the liquidus crystals obtained in the present study suggest the enrichment of olivine at 600 km depth and of majorite at the bottom of the mantle in the crystallizing martian magma ocean

benthic δ18o records in the north atlantic over the last glacial period 60 10 kyr evidence for brine formation four high resolution benthic isotope records from north atlantic and south norwegian sea cores are compared for the past 60 kyr the benthic records show light 18o peaks simultaneously to or following the heinrich events the amplitude of these light peaks varies between 1 for the most northern core enam93 21 and 0 35 for the deep north atlantic cores the high 18o gradient between the north atlantic cores and the pacific core v19 30 suggests a regional influence of 18o depleted meltwater to deeper depth during periods of iceberg discharges the most likely process for transferring 18o depleted meltwater to depth is sea ice formation induced by brine formation during heinrich events 4 and 3 this mecanism was of major importance compared to open ocean convection in the southern norwegian sea and at the northern boundaries of the atlantic leading to intermediate to deep water formation other 18o excursions appearing in all the records point to the contribution of both brine formation and global changes in the 18o of seawater associated with the heinrich event periods

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

computation of seismic profiles from mineral physics the importance of the non olivine components for explaining the 660 km depth discontinuity the recent increasing number of experimental works leads us to review the elastic properties and mineralogical transformations of mantle minerals the updated data set is used to compute seismic profiles for two petrological models along three adiabatic temperature profiles these profiles are chosen to stress out the influence of non olivine minerals on seismic parameters and to represent cold and horizontally averaged temperature profiles of the earth s mantle in a first part starting compositions of pyrolite and piclogite and a single layer convection are assumed the results clearly point out the importance of the non olivine part of the mineralogy two scenarios are found to explain the 660 km depth discontinuity

melting experiments on the enstatite pyrope join at 80 152 kbar melting temperatures of the assemblage pyroxene garnet on the enstatite pyrope join were experimentally determined at 11 different pressures between 80 and 152 kbar with a split sphere anvil apparatus ussa 2000 the compositions of pyroxene garnet and melt coexisting along the solidus were also determined comparison with previous data at lower temperatures revealed a large temperature dependence of the compositions of garnet coexisting with pyroxene it is proposed that the observed variation in the garnet composition is caused by disorder in garnet the obtained alumina contents of orthopyroxene coexisting with garnet on the solidus at 80 110 kbar contributed to an improvement of the garnet peridotite thermobarometry an internally consistent set of thermodynamic parameters was derived which allows calculation of the temperature pressure phase diagram for the enstatite pyrope join at 20 260 kbar

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

african climate change and faunal evolution during the pliocene pleistocene abstract environmental theories of african faunal evolution state that important evolutionary changes during the pliocene pleistocene interval the last ca 5 3 million years were mediated by changes in african climate or shifts in climate variability marine sediment sequences demonstrate that subtropical african climate periodically oscillated between markedly wetter and drier conditions paced by earth orbital variations with evidence for step like 0 2 ma increases in african climate variability and aridity near 2 8 ma 1 7 ma and 1 0 ma coincident with the onset and intensification of high latitude glacial cycles analysis of the best dated and most complete african mammal fossil databases indicates african faunal assemblage and perhaps speciation changes during the pliocene pleistocene suggesting more varied and open habitats at 2 9 2 4 ma and after 1 8 ma these intervals correspond to key junctures in early hominid evolution including the emergence of our genus homo pliocene pleistocene shifts in african climate vegetation and faunal assemblages thus appear to be roughly contemporary although detailed comparisons are hampered by sampling gaps dating uncertainties and preservational biases in the fossil record further study of possible relations between african faunal and climatic change will benefit from the accelerating pace of important new fossil discoveries emerging molecular biomarker methods for reconstructing african paleovegetation changes tephra correlations between terrestrial and marine sequences as well as continuing collaborations between the paleoclimatic and paleoanthropological communities

planktonic foraminifera from modern sediments reflect upwelling patterns off iberia insights from a regional transfer function abstract quantitative and qualitative analyses of planktonic foraminiferal assemblages from 134 core top sediment samples collected along the western iberian margin were used to assess the latitudinal and longitudinal changes in surface water conditions and to calibrate a sea surface temperature sst transfer function for this seasonal coastal upwelling region q mode factor analysis performed on relative abundances yielded three factors that explain 96 of the total variance factor 1 50 is exclusively defined by globigerina bulloides the most abundant and widespread species and reflects the modern seasonal may to september coastal upwelling areas factor 2 32 is dominated by neogloboquadrina pachyderma dextral and globorotalia inflata and seems to be associated with the portugal current the descending branch of the north atlantic drift factor 3 14 is defined by the tropical sub tropical species globigerinoides ruber white globigerinoides trilobus trilobus and g inflata and mirrors the influence of the winter time eastern branch of the azores current in conjunction with satellite derived sst for summer and winter seasons integrated over an 18 year period the regional foraminiferal data set is used to calibrate a sst transfer function using imbrie kipp mat and simmaxndw techniques similar predicted errors rmsep correlation coefficients and residuals deviation from sst estimated for both techniques were observed for both seasons all techniques appear to underestimate sst off the southern iberia margin an area mainly occupied by warm waters where upwelling occurs only occasionally and overestimate sst on the northern part of the west coast of the iberia margin where cold waters are present nearly all year round the comparison of these regional calibrations with former atlantic and north atlantic calibrations for two cores one of which is influenced by upwelling reveals that the regional one attests more robust paleo ssts than for the other approaches

african monsoon enhancement during the penultimate glacial period mis 6 5 170 ka and its atmospheric impact 1 a reconstruction of northwest african summer monsoon strength during the cold marine isotopic stage mis 6 indicates a link to the seasonal migration of the intertropical convergence zone itcz high resolution studies of eolian dust supply and sea surface temperature recorded in marine core md03 2705 on the mauritanian margin provide a better understanding about the penultimate glacial history of northwestern african aridity humidity and upwelling coastal activity today site md03 2705 experiences increased upwelling and dust flux during the winter months when the itcz is in a southerly position analyses of foraminifera isotopic composition suggest that during mis 6 5 180 168 ka the average position of the itcz migrated north marked by an increase in the strength of the summer monsoon which decreased eolian dust transport and the coastal upwelling activity the northward migration is in phase with a specific orbital combination of a low precessional index with a high obliquity signal high resolution analysis of stable isotopes 18o and 13c and microscale resolution geochemical ti al and quartz grain counts determinations reveal that the transition between monsoonal humid mis 6 5 and dry mis 6 4 conditions has occurred in less than 1 3 ka such rapid changes suggest a nonlinear link between the african monsoonal rainfall system and environmental changes over the continent this study provides new insights about the influence of vegetation and oceanic temperature feedbacks on the onset of african summer monsoon and demonstrates that during the penultimate glacial period changes in tropical dynamics had regional and global impacts

mediterranean pluvial periods and sapropel formation over the last 200 000 years abstract three mediterranean deep sea cores have been studied to reconstruct the hydrological conditions at the time of deposition of interglacial and glacial sapropels during the time interval 200 60 kyr bp the isotopic and sea surface temperature records of planktonic foraminifera were used to estimate the oxygen isotopic composition of surface water w in the tyrrhenian sea and levantine basin our results show a strong w salinity decrease in both basins associated with each sapropel these w decreases reflect a drastic change in the local freshwater budget and were comparable to that observed during the last sapropel s 1 centred at ca 8 kyr bp a strong precipitation increase transformed the whole mediterranean sea into a non concentration basin the low surface salinity was responsible for the water column stratification while nutrients brought in by the runoff enhanced productivity it resulted in a significant reduction in the rate of deep water oxygenation and sapropel formation in the eastern basin in addition the mediterranean sea 18 o record is very similar to that of the bay of bengal as the latter is very sensitive to the summer monsoon rain this similarity suggests that both glacial and interglacial sapropels result from enhanced monsoon like precipitation due to an increase in summer insolation driven by precession variations

upper mantle p velocity structure of the canadian shield waveform modeling of the phases pnl p and pp is used to determine the p wave upper mantle structure beneath the canadian shield long period recordings at world wide standard seismograph network long range seismic measurement and canadian network stations in north america are used with earthquakes within and just outside the shield as sources the p data set is incomplete due to the scarcity of large events within the shield and the inclusion of pp provides much more data using the wkbj approach to calculate the mantle response the pp waveforms can be modeled almost as well as the p the phase pnl persists to large distances in shield regions and the interference of pnl with triplication range p helps constrain the structure in the upper 400 km important features of our model which is designated s25 are 1 a thick high q high velocity lid to 165 km 2 a deep low velocity zone and 3 discontinuities of 5 at 405 km and 4 at 660 km the lid and low velocity zone create an unusual b branch arrival not seen in other regions which persists well beyond 30 only slight lateral variation is noted within the shield region the major features of the model are similar to those of grand and helmberger s s wave model for the canadian shield