the 9 june 94 bolivian deep earthquake an exceptional event in an extraordinary subduction zone we investigate the physical setting of the bolivian shock based on the history of the subducting nazca plate intraslab seismicity deep seismic moment release and seismic tomography south america has two broad regions of reverse arc curvature subduction constrained to this unique geometry produces slab kinking contortions that may cause unusual slab thickening as they sink to the bottom of the transition zone and encounter resistance to penetration into the lower mantle such contortions are observed at intermediate depths upstream from the slab source regions of both the great 1970 colombian and 1994 bolivian events thickening helps explain how the nazca slab accommodates large seismic source dimensions at depths of 625 650 km

assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures though many studies on the mg contents in the calcitic tests of foraminifers exist the processes controlling its uptake are still a matter of debate laboratory cultures offer an excellent opportunity to reveal these mechanisms the mg concentrations within single chambers of the planktic foraminifer globigerinoides sacculifer brady maintained under controlled laboratory conditions were measured 1 at variable temperatures 19 5 29 5 c and constant salinity and 2 at variable salinity 22 45 and constant temperature the experimental results suggest that under natural conditions temperature is the leading mechanism controlling the mg ca ratio temperature and magnesium are related proportionally a temperature increase of ca 10 c gives rise to an increase of the magnesium concentrations of ca 130 drastic unnatural salinity changes dominate the effects of temperature a 110 change in the mg ca ratio was observed when salinity was elevated or reduced by more than ca 10 specimens which underwent gametogenesis reveal significantly higher mg concentrations than specimens that did not release gametes partition coefficients for mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite when comparing observed mg ca ratios of foraminiferal tests with predicted mg ca ratios calculated according to empirical equations it becomes evident that foraminiferal tests are undersaturated with respect to mg for the water temperature they have experienced apparently foraminifers are capable of controlling their mg concentration the physiological processes presumably responsible for such depressed mg ca ratios appear to be temperature controlled as deduced from the close relationship of the observed mg ca ratios and water temperature this study demonstrates that variations in temperature and salinity are definitely reflected in the mg content of foraminiferal tests magnesium may thus serve as a paleo proxy for past surface water temperatures as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded

mountain building in the central andes the central andes is the middle part of the andean chain between about 13 s and 27 s characterized by the parallel running high mountain chains the western and eastern cordilleras at the edges of high plateaus with a height of about 4000 m and a width of 200 to 450 km the altiplano puna from the examination of geophysical and geological data in this area including earthquakes deformation gravity anomaly volcanism uplift history and plate motion we conclude that the continued plate subduction with domination of compressive stress over the entire arc system is the main cause of the tectonic style of the central andes we propose that the present cycle of mountain building has continued in the cenozoic with the most active phase since the miocene and that the present subduction angle 30 is not typical in that period but that subduction with more shallowly dipping oceanic lithosphere has prevailed at least since the miocene because of the young and buoyant slab involved this situation is responsible for the production of a broad zone of partial melt in the mantle above the descending slab addition of volcanic materials was not restricted to the western edge where active volcanoes of the western cordillera exist but extended to the western and central portion of the altiplano puna the western half of the central andes is essentially isostatic because the heat transferred with the volcanic activities softened the crust there in the eastern edge the thermal effect is small and the crust is strongly pushed by the westward moving south american plate this caused the shortening of crustal blocks due to reverse faulting and folding in the eastern cordillera and amazonian foreland the magmatism and crustal accretion are dominant at the western end of the mountain system and decrease eastward while the compression and consequent crustal shortening are strongest at the eastern end and wane toward west these two processes are superposed between the two mountain chains and form high plateaus there the altiplano of bolivia and peru and the puna of argentina this interpretation is supported by the observation that 1 neogene sedimentary formations have been uplifted to high elevations without heavy distortion in the altiplano and the western cordillera 2 no significant reverse fault systems are observed on the altiplano 3 neogene volcanic rocks and volcanic centers since the miocene are not restricted to the western cordillera but are widely distributed over most of the altiplano 4 most of the altiplano is in a zone of high heat flow values 5 thick paleozoic rocks are strongly folded and faulted in the eastern cordillera with little volcanism and no large scale plutonism in the cenozoic age 6 crustal earthquakes with reverse fault mechanisms are concentrated on the eastern flank of the eastern cordillera and amazonian foreland and 7 the crustal thickness suddenly decreases at the junction of the eastern cordillera and the amazon basin exactly at the place of reverse earthquakes

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

attenuation of high frequency seismic waves beneath the central andean plateau observed patterns of high frequency seismic wave attenuation suggest that near 22 s the upper mantle structure beneath the central andean plateau changes along strike to the south contrasting regions of high and low upper mantle seismic wave attenuation beneath the plateau are identified based on striking azimuthal variations in the character and frequency content of p and s waves propagating beneath the plateau to a portable seismic network deployed in jujuy province argentina 24 s 65 w ray paths from intermediate depth earthquakes located north and northwest of the network transmit seismic waves with a higher frequency content than ray paths from earthquakes at similar depths and distances but located west and south of the network the estimated apparent q values fall into two categories qp 500 and qs 350 for the high q paths and qp 350 and qs 200 for the low q paths in addition sn phases from regional crustal earthquakes in the subandean foreland fold thrust belt to the north propagate efficiently to the jujuy network while sn is not observed from foreland earthquakes located at similar distances to the south of the network these observations combined with data from previously reported wave propagation studies suggest that south of about 22 s the upper mantle beneath the plateau and its adjacent foreland thrust belt is more highly attenuating than the upper mantle farther north forward modeling of the q measurements made at jujuy indicates that the observations can be explained either by a variable thickness high q upper plate beneath the plateau or by a thin variable width very low q zone in the asthenospheric wedge above the subducted slab this lateral variation in upper mantle structure coincides with two physiographically distinct segments of the central andean plateau and its adjacent foreland thrust belt to the east the bolivian altiplano and subandean ranges in the north and the argentine puna and santa barbara system in the south we interpret the north south change in upper mantle attenuation and the corresponding changes in physiography topography and tectonic style at the surface to be due to a mantle lid that is thicker beneath the altiplano and the subandean belt than beneath the puna and the santa barbara ranges

seismotectonics of the loma prieta california region determined from three dimensional v p v p v s and seismicity three dimensional vp and vp vs velocity models for the loma prieta region were developed from the inversion of local travel time data 21 925 p arrivals and 1 116 s arrivals from earthquakes refraction shots and blasts recorded on 1700 stations from the northern california seismic network and numerous portable seismograph deployments the velocity and density models and microearthquake hypocenters reveal a complex structure that includes a san andreas fault extending to the base of the seismogenic layer a body with high vp extends the length of the rupture and fills the 5 km wide volume between the loma prieta mainshock rupture and the san andreas and sargent faults we suggest that this body controls both the pattern of background seismicity on the san andreas and sargent faults and the extent of rupture during the mainshock thus explaining how the background seismicity outlined the along strike and depth extent of the mainshock rupture on a different fault plane 5 km away new aftershock focal mechanisms based on three dimensional ray tracing through the velocity model support a heterogeneous postseismic stress field and can not resolve a uniform fault normal compression the subvertical or steeply dipping san andreas fault and the fault surfaces that ruptured in the 1989 loma prieta earthquake are both parts of the san andreas fault zone and this section of the fault zone does not have a single type of characteristic event

lithospheric scale structure across the bolivian andes from tomographic images of velocity and attenuation for p and s waves we have developed a three dimensional lithospheric scale model across the bolivian andes at 20 s based on tomographic images of velocity and attenuation for both p and s waves observations of travel time and attenuation for this study are from regional mantle earthquakes in the subducted nazca plate recorded on a portable broadband seismic array broadband andean joint experiment and seismic exploration of the deep andes in bolivia and chile the shallow mantle under the altiplano from 18 s to 21 s is high velocity and moderately high q vp 8 3 vs 4 7 qp 500 and qs 200 suggesting lithospheric mantle high velocity material in the altiplano extends to a depth of 125 150 km the shallow mantle of the western cordillera is characterized by high vp vs 1 83 suggesting a correlation between vp vs and arc volcanism seismic velocity in the western cordillera mantle is on average only slightly reduced from global averages however velocity and attenuation anomalies are locally strong vp 7 8 vs 4 3 qp 200 and qs 100 consistent with partial melt conditions under the los frailes volcanic field in the eastern cordillera shallow mantle velocity and q decrease drastically from the neighboring altiplano vp 7 8 vs 4 3 qp 300 qs 100 however high vp vs is not as pervasive as it is in the western cordillera we believe that slab derived water and perhaps other volatiles strongly influence the western cordillera while the eastern cordillera low velocity region is more affected by partial melt and or compositional changes average velocity and q in the shallow mantle across the bolivian andes where the tomographic images are best resolved are significantly higher than in most mantle wedge environments where corresponding images are available this is likely the result of a compressional back arc setting in the andes this implies that lithospheric shortening and thickening associated with the formation of the andes has profoundly influenced the shallow mantle structure across the range shallow mantle structure is locally influenced by the subduction processes particularly under the western cordillera however the differing volcanism and seismic character under the two cordilleras suggest that the volcanic process in the eastern cordillera may be distinct from arc volcanism tertiary volcanism in the eastern cordillera is located in the region where mantle shortening is suspected to be greatest both the timing and location of volcanism are consistent with upward migration of mantle wedge asthenosphere following the removal of over thickened lithosphere

variability of mg ca and sr ca between and within the planktonic foraminifers globigerina bulloides and globorotalia truncatulinoides the variability in mg ca and sr ca within individual tests and chambers of tests and samples consisting of differing numbers of individuals was determined for globigerina bulloides and globorotalia truncatulinoides in a north atlantic core top sample 52 918 n 16 917 w the variability in mg ca and sr ca within individual tests and chambers was determined by electron microprobe and samples consisting of variable sample size were measured using inductively coupled plasma optical emission spectrometer icp oes large compositional heterogeneity was found within individual chambers and within the test as a whole of the two species and the presence of regions with up to 10 mmol mol mg ca especially in g bulloides mean mg ca decreases in successive chambers of g bulloides especially the 300 355 m fraction and is accompanied by decreasing variance but is not statistical significant sr ca is much more homogeneously distributed with a normal distribution and shows no differences from chamber to chamber the variability of mg ca and sr ca decreases with increasing sample size from single to five to twenty tests per sample approximately as for a normal distribution with greater variability for g bulloides than for g truncatulinoides equivalent to uncertainties in temperature n 20 of 1 1 c and 0 7 c for the two species within the whole of the sediment mixed layer

three dimensional p and s wave velocity structures of southern peru and their tectonic implications in 1981 an 18 station regional array was operated in southern peru above the area where the dip of the subducted nazca plate changes from virtually horizontal in the northwest to about 30 in the southeast arrival times of compressional p and shear s waves from microearthquakes recorded by this array are used in this paper to investigate the three dimensional velocity structure of the crust and upper mantle in the region between the coast and the cordillera occidental the results suggest a crustal thickness of about 40 km beneath the coast increasing to about 70 km beneath the cordillera occidental this change in thickness occurs abruptly in the northwest but is gradual in the southeast the inverse correlation between the dip of the moho and the dip of the slab suggests a broad scale causal relation between the two at the same time free air gravity anomalies suggest that the steepening of the moho in the northwest may occur only in the region under the array because the crust is thicker in the southeast than originally surmised a suite of earthquakes previously thought to occur in the mantle now appears to be confined to the crust the association of these earthquakes with a shallow dipping moho is suggestive of ongoing crustal deformation to the west of the andes however other seismological and geological observations make the role of these earthquakes in crustal deformation unclear s wave velocities in the mantle between 70 and 130 km depth above the 30 dipping slab are low suggesting the presence of partially melted asthenosphere that may be responsible for the magmatic activity observed in southern peru

composition of the crust and upper mantle in the central andes 19 30 s inferred from p wave velocity and poisson s ratio the present day crustal structure of the andean chain results from deformation processes and magmatic activity since the onset of subduction one line of investigation to resolve questions about the mechanism of crustal thickening is to get information about the composition of the crust and upper mantle by imaging the structures in velocity and poisson s ratio or vp vs a high density seismic network was operated during six months in 1994 across the whole andean chain the p and s travel times of the best located local earthquakes mainly situated in the subduction zone have been inverted for vp and vp vs using thurber s 3d iterative simultaneous inversion method the resulting models giving short scale information about the crustal and upper mantle composition provide new limits on the respective involvement of crustal shortening and magmatism in the thickening of the andean crust beneath the western cordillera the seismic properties are well explained by typical active volcanic arc processes and the thickening of the crust is explained by magmatic addition conversely beneath the central altiplano basin and the eastern cordillera our results preclude significant volume of magmatic addition from the mantle and reinforce crustal shortening as the main thickening process moreover cratonic lower crust and subcontinental lithospheric upper mantle are observed under the eastern cordillera up to 67 w evidence of the underthrusting of the brazilian craton which drives the crustal shortening beneath the central altiplano basin a thin lithospheric mantle is observed above a well marked asthenospheric wedge which extends in depth below the western part of the eastern cordillera thus partial melt is observed in the shallow mantle west of the western cordillera up to the brazilian craton

salinity controls on na incorporation in red sea planktonic foraminifera whereas several well established proxies are available for reconstructing past temperatures salinity remains challenging to assess reconstructions based on the combination of in organic temperature proxies and foraminiferal stable oxygen isotopes result in relatively large uncertainties which may be reduced by application of a direct salinity proxy cultured benthic and planktonic foraminifera showed that na incorporation in foraminiferal shell calcite provides a potential independent proxy for salinity here we present the first field calibration of such a potential proxy living planktonic foraminiferal specimens from the red sea surface waters were collected and analyzed for their na ca content using laser ablation quadrupole inductively coupled plasma mass spectrometry using the red sea as a natural laboratory the calibration covers a broad range of salinities over a steep gradient within the same water mass for both globigerinoides ruber and globigerinoides sacculifer calcite na ca increases with salinity albeit with a relatively large intraspecimen and interspecimen variability the field based calibration is similar for both species from a salinity of 36 8 up to 39 6 while values for g sacculifer deviate from this trend in the northernmost transect it is hypothesized that the foraminifera in the northernmost part of the red sea are partly expatriated and hence should be excluded from the na ca salinity calibration incorporation of na in foraminiferal calcite therefore provides a potential proxy for salinity although species specific calibrations are still required and more research on the effect of temperature is needed

adaptation of a flow through leaching procedure for mg ca paleothermometry 1 mg ca ratios in planktonic foraminifera reflect calcification temperatures and are thus useful for sea surface temperature sst reconstructions despite the obvious utility of this paleoceanographic tracer problems of dissolution gametogenic calcification and contaminant phases have thus far limited confidence in mg ca based reconstructions here we show strong evidence of mg heterogeneity in foraminiferal calcite by sequentially measuring the composition of different forms of calcite ontogenetic gametogenic diagenetic in the same shells while monitoring and removing contaminant phases a new flow through method combines chromatographic technology and inductively coupled plasma mass spectrometry icp ms in a series of cleaning and dissolution reactions monitored continuously with time resolved analysis tra this combination of slow controlled dissolution and tra provides a complete elemental description of contaminant phases and sorts the cleaned calcium carbonate based on dissolution sensitivity examination of partially dissolved shells with electron microscopy suggests that the flow through method simulates the natural dissolution sequence and effectively separates the different calcite domains within a single foraminiferal shell heterogeneity of mg ca in foraminiferal calcite is clearly demonstrated in flow through analysis foraminiferal shells have initially high mg levels that decrease steadily throughout dissolution later dissolution yields lower mg ca which is likely due to a combination of subsurface calcification and biomineralization effects mg ca ratios from the most dissolution sensitive high mg portions of surface dwelling species in core tops are used to calculate calcification temperatures a comparison of late holocene core top data with world ocean atlas sst data indicates that the flow through method does yield viable sst estimates furthermore a depth transect in the eastern tropical pacific suggests that this approach provides the opportunity to extract initial calcification temperatures despite partial dissolution of foraminiferal shells

three hundred eighty thousand year long stable isotope and faunal records from the red sea influence of global sea level change on hydrography stable isotope and faunal records from the central red sea show high amplitude oscillations for the past 380 000 years positive 18o anomalies indicate periods of significant salt buildup during periods of lowered sea level when water mass exchange with the arabian sea was reduced due to a reduced geometry of the bab el mandeb strait salinities as high as 53 and 55 are inferred from pteropod and benthic foraminifera 18o respectively for the last glacial maximum during this period all planktonic foraminifera vanished from this part of the red sea environmental conditions improved rapidly after 13 ka as salinities decreased due to rising sea level the foraminiferal fauna started to reappear and was fully reestablished between 9 ka and 8 ka spectral analysis of the planktonic 18o record documents highest variance in the orbital eccentricity obliquity and precession bands indicating a dominant influence of climatically driven sea level change on environmental conditions in the red sea variance in the precession band is enhanced compared to the global mean marine climate record specmap suggesting an additional influence of the indian monsoon system on red sea climates

probing connections between deep earth and surface processes in a land locked ocean basin transformed into a giant saline basin the mediterranean gold project during the last decade the interaction of deep processes in the lithosphere and mantle with surface processes erosion climate sea level subsidence glacio isostatic readjustment has been the subject of heated discussion the use of a multidisciplinary approach linking geology geophysics geodesy modelling and geotechnology has led to the awareness of coupled deep and surface processes deep earth dynamics topography erosion tectonics are strongly connected to natural hazards such as earthquakes landslides and tsunamis sedimentary mass transfers have important consequences on isostatic movements and on georesources geothermal energy repartitions the ability to read and understand the link between deep earth dynamics and surface processes has therefore important societal impacts ground truthing at carefully selected sites of investigation is imperative to better understand these connections due to its youth 30 ma and its subsidence history the almost land locked gulf of lion sardinia continental margins system provides a unique record of sedimentary deposition from the miocene to present due to its high subsidence rate palaeoclimatic variations tectonic events and vertical evolution are all recorded here at very high resolution the late miocene isolation and desiccation of the mediterranean the youngest and most catastrophic event the messinian salinity crisis msc induced drastic changes in marine environments widespread deposition of evaporite gypsum anhydrite and halite in the central basin and intense subaerial erosion along its periphery these extraordinary mass transfers from land to sea induced strong isostatic re adjustments that are archived in the sedimentary record and represent a window to the lithospheric rheology and the deep processes the gold gulf of lion drilling project proposes to explore this unique sedimentary record as well as the nature of the deep crustal structure providing valuable information about the mechanisms underlying vertical motions in basins and their margins

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

systematic change of foraminiferal mg ca ratios across a strong salinity gradient abstract the mg ca ratio of foraminiferal calcite is an important proxy for estimating past ocean temperatures used in conjunction with 18 o of foraminiferal calcite it allows deconvolution of temperature and ice volume signals to infer past ocean temperatures and salinities assuming the relationship between seawater 18 o and salinity is known such work assumes that temperature is the only or at least the dominant environmental controller of foraminiferal mg ca the semi enclosed mediterranean sea where salinity varies from 36 to 40 psu over a seasonal temperature range of between only 5 c to 8 c provides a relevant setting to test this assumption outside the laboratory in this study planktonic foraminifera o universa g siphonifera g bulloides and g ruber white and pink were picked from 11 box core tops spanning the mediterranean salinity gradient and analysed for their trace element concentrations mg ca ratios are higher for the associated calcification temperatures than in other regions where calibrations have been conducted and correlate poorly with calcification temperature mg ca ratios are particularly high for samples from the eastern mediterranean where salinity is unusually high correlations of mg ca with the calcification salinity are statistically significant with mg ca changing by 15 59 per psu suggesting that salinity may act as a control on mg ca ratios in addition to the dominant temperature control we show that contamination by non carbonate material and diagenetic high mg carbonate overgrowths cannot account for the observed trend of increasing mg ca with salinity a relationship between mg ca and salinity is also suggested by re analysis of calibrations from open ocean settings these new mediterranean results are from a region with unusually high salinity but suggest that the effects of salinity on the mg ca palaeothermometer should be considered even in open ocean settings particularly where large salinity changes occurred in the past

eocene seasonality and seawater alkaline earth reconstruction using shallow dwelling large benthic foraminifera abstract intra test variability in mg ca and other trace elements within large benthic foraminifera lbf of the family nummulitidae have been investigated using laser ablation inductively coupled plasma mass spectrometry la icpms these foraminifera have a longevity and size facilitating seasonal proxy retrieval and a depth distribution similar to surface dwelling planktic foraminifera coupled with their abundance in climatically important periods such as the paleogene this means that this family of foraminifera are an important but under utilised source of palaeoclimatic information we have calibrated the relationship between mg ca and temperature in modern operculina ammonoides and observe a 2 increase in mg ca c 1 o ammonoides is the nearest living relative of the abundant eocene genus nummulites enabling us to reconstruct mid eocene tropical sea surface temperature seasonality by applying our calibration to fossil nummulites djokdjokartae from java our results indicate a 5 6 c annual temperature range implying greater than modern seasonality in the mid eocene bartonian this is consistent with seasonal surface ocean cooling facilitated by enhanced eocene tropical cyclone induced upper ocean mixing as suggested by recent modelling results analyses of fossil n djokdjokartae and operculina sp from the same stratigraphic interval demonstrate that environmental controls on proxy distribution coefficients are the same for these two genera within error using previously published test seawater alkaline earth metal distribution coefficients derived from an lbf of the same family raitzsch et al 2010 and inorganic calcite with appropriate correction systematics for secular mg casw variation evans and muller 2012 we use our fossil data to produce a more accurate foraminifera based mg casw reconstruction and an estimate of seawater sr ca we demonstrate that mid eocene mg casw was 2 mol mol 1 which is in contrast to the model most commonly used to correct deep time mg ca data from foraminifera but in agreement with most other paleogene proxy and model data this indicates that mg casw has undergone a substantial 3 4 rise over the last 40 ma

environmental controls on mg ca in neogloboquadrina incompta a core top study from the subpolar north atlantic magnesium calcium paleothermometry is an established tool for reconstructing past surface and deep sea temperatures however our understanding of non thermal environmental controls on the uptake of mg into the calcitic lattice of foraminiferal tests remains limited here we present a combined analysis of multiple trace element calcium ratios and stable isotope 18o and 13c geochemistry on the subpolar planktonic foraminifera neogloboquadrina incompta to assess the validity of mg ca as a proxy for surface ocean temperature we identify small size specific offsets in mg ca and 18oc values for n incompta that are consistent with depth habitat migration patterns throughout the life cycle of this species additionally an assessment of non thermal controls on mg ca values reveals that 1 the presence of volcanic ash 2 the addition of high mg abiotic overgrowths and 3 ambient seawater carbonate chemistry can have a significant impact on the mg ca to temperature relationship for carbonate ion concentrations of values 200 mol kg 1 we find that temperature exerts the dominant control on mg ca values while at values 200 mol kg 1 the carbonate ion concentration of seawater increases the uptake of mg thereby resulting in higher than expected mg ca values at low temperatures we propose two independent correction schemes to remove the effects of volcanic ash and carbonate ion concentration on mg ca values in n incompta within the calibration data set applying the corrections improves the fidelity of past ocean temperature reconstructions

mediterranean climate and oceanography and the periodic development of anoxic events sapropels mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding sediments which are organic poor sapropels occur quasi periodically in sedimentary sequences of the last 13 5 million years and exist both in the eastern and western mediterranean sub basins they have been the subject of extensive study based on records from both short conventional and long ocean drilling program sediment cores and from a wide variety of uplifted marine sediment sequences on the basin margins and islands previous syntheses in the 1990s and 2000s have discussed how the formation of sapropels is commonly ascribed to deep sea anoxia enhanced export productivity or a combination of these effects however a wealth of new evidence and insights has emerged during the past 1 2 decades based on traditional and novel proxy data as well as modelling which has revealed intriguing new aspects and nuances to the reconstructed conditions hence it is timely to present a new synthesis of current understanding of the processes behind the formation of sapropels which have over the past decade also become a matter of commercial interest in sub salt hydrocarbon exploration in this review we present a context of modern mediterranean climate and oceanography followed by an integrated assessment of the growing understanding of climatological and ocean circulation changes that were associated with sapropel deposition we find that sapropels predominantly formed during astronomically timed episodes when climatic and oceanographic conditions and ecological responses broadly preconditioned the basin for sapropel deposition there is strong correspondence with times of monsoon intensification fuelling runoff from north africa into the mediterranean sea while preconditioning due to sea level rise and regional precipitation and runoff may have contributed as well within these broad episodes of surface buoyancy gain and resultant decline in deep water ventilation specific deposition under dysoxic anoxic or even euxinic conditions occurred within a clearly dynamic system that was characterised by complex spatial and depth dependent patterns gradients with distinct temporal variability on at least decadal to centennial millennial timescales in the final section we evaluate the implications of different modes of deep water removal from silled basins to investigate why sapropels are more frequently and often more intensely developed in the eastern mediterranean than in the western mediterranean

further constraints on the diagenetic influences and salinity effect on globigerinoides ruber white mg ca thermometry implications in the mediterranean sea we analyzed mg ca ratios of the planktonic species globigerinoides ruber white picked from 49 box core samples covering the whole mediterranean sea and 2 core tops from the atlantic ocean over the entire data set we found no significant correlation between mg ca and 18o derived calcification temperatures this lack of correlation is chiefly due to the presence of an early diagenetic mg rich calcite coating which can constitute up to 20 of the total shell calcite in the central and eastern mediterranean basin and result in anomalously high mg ca values and a high scattering in the western mediterranean sea however g ruber mg ca scattering shows smaller amplitude and mg rich calcite remains under the xrd detection limit sem observations indicate that only a few samples are affected by trace amounts of post mortem calcite overgrowths most of this calcite being likely removed during the chemical cleaning for mg ca analyses using core top sediments from the western mediterranean sea we performed an empirical calibration exercise which confirms that g ruber mg ca is not only related to temperature but it is also significantly affected by sea surface salinity this salinity effect is not specific to high salinity environments such as the mediterranean sea since it appears to be coherent with recent results obtained on indo pacific and atlantic surface sediments which suggest that a 1 psu change in sss results in a 1 7 c mg ca temperature bias this sensitivity to salinity is significantly higher than those deduced from culture experiments

ecological and temperature controls on mg ca ratios of globigerina bulloides from the southwest pacific ocean we present mg ca data for globigerina bulloides from 10 core top sites in the southwest pacific ocean analyzed by laser ablation inductively coupled plasma mass spectrometry la icpms mg ca values in g bulloides correlate with observed ocean temperatures 7 degrees c 19 degrees c and when combined with previously published data an integrated mg ca temperature calibration for 7 degrees c 31 degrees c is derived where mg ca mmol mol 0 955 x e 0 068 x t r 2 0 95 significant variability of mg ca values 20 30 was found for the four visible chambers of g bulloides with the final chamber consistently recording the lowest mg ca and is interpreted in part to reflect changes in the depth habitat with ontogeny incipient and variable dissolution of the thin and fragile final chamber and outermost layer concomitantly added to all chambers caused by different cleaning techniques prior to solution based icpms analyses may explain the minor differences in previously published mg ca temperature calibrations for this species if the lower mg ca of the final chamber reflects changes in depth habitat then la icpms of the penultimate or older chambers will most sensitively record past changes in near surface ocean temperatures mean size normalized g bulloides test weights correlate negatively with ocean temperature t 31 8 x e 30 5xwtn r 2 0 90 suggesting that in the southwest pacific ocean temperature is a prominent control on shell weight in addition to carbonate ion levels

gulf stream subtropical gyre properties across two dansgaard oeschger cycles salinity increase in the subtropical gyre system may have pre conditioned the north atlantic ocean for a rapid return to stronger overturning circulation and high latitude warming following meltwater events during the last glacial period here we investigate the gulf stream subtropical gyre system properties over dansgaard oeschger do cycles 14 to 12 including heinrich ice rafting event 5 during the holocene and last glacial maximum a positive gradient in surface dwelling planktonic foraminifera 18o globigerinoides ruber can be observed between the gulf stream and subtropical gyre due to decreasing temperature increasing salinity and a change from summer to year round occurrence of g ruber we assess whether this gradient was a common feature during stadial interstadial climate oscillations of marine isotope stage 3 by comparing existing g ruber 18o from odp site 1060 subtropical gyre location and new data from odp site 1056 gulf stream location between 54 and 46 ka our results suggest that this gradient was largely absent during the period studied during the major warm do interstadials 14 and 12 we infer a more zonal and wider gulf stream influencing both odp sites 1056 and 1060 a gulf stream presence during these major interstadials is also suggested by the large vertical 18o gradient between shallow dwelling planktonic foraminifera species especially g ruber and the deep dwelling species globorotalia inflata at site 1056 which we associate with strong summer stratification and gulf stream presence a major reduction in this vertical 18o gradient from 51 ka until the end of heinrich event 5 at 48 5 ka suggests site 1056 was situated within the subtropical gyre in this mainly cold period from which we infer a migration of the gulf stream to a position nearer to the continental shelf indicative of a narrower gulf stream with possibly reduced transport

field based validation of a diagenetic effect on g ruber mg ca paleothermometry core top results from the aegean sea eastern mediterranean recent work across the mediterranean sea has illustrated the salinity and overgrowth effects on planktonic foraminiferal mg ca which potentially confound the use of this as a temperature proxy for paleoceanographic reconstructions to test and verify these effects we present new aegean sea results which reveal mg ca values that were unreasonably high to be explained by temperature or salinity variations alone confirming that foraminiferal mg ca is affected by diagenesis we have specifically targeted globigerinoides ruber w sensu stricto from a series of modern core tops spanning a strong sea surface salinity gradient and a minor sea surface temperature range along a north south aegean sea transect scanning electron microscopy analyses show that g ruber specimens were covered by microscale euhedral crystallites of inorganic precipitates this secondary calcite phase seems to be responsible for the anomalously high mg ca ratios and likely formed near the sediment water interface from caco3 supersaturated interstitial seawater we also have clear evidence of diagenetic alteration in a north south direction along the aegean sea possibly depending on salinity and calcite saturation state gradients these observations illustrate the necessity of alternative techniques e g flow through time resolved analysis or laser ablation inductively coupled plasma mass spectrometry to potentially overcome these diagenetic issues and develop a more reliable and sensitive temperature proxy in similar subtropical settings characterized by high salinity excessive evaporation and restricted circulation

incorporation and preservation of mg in globigerinoides sacculifer implications for reconstructing the temperature and 18o 16o of seawater using bathymetric transects of surface sediments underlying similar sea surface temperatures but exposed to increasing dissolution we examined the processes which affect the relationship between foraminiferal mg ca and 18o we found that globigerinoides saccculifer calcifies over a relatively large range of water depth and that this is apparent in their mg content on the seafloor foraminiferal mg ca is substantially altered by dissolution with the degree of alteration increasing with water depth selective dissolution of the chamber calcite formed in surface waters shifts the shell s bulk mg ca and 18o toward the chemistries of the secondary crust acquired in colder thermocline waters the magnitude of this shift depends on both the range of temperatures over which the shell calcified and the degree to which it is subsequently dissolved in spite of this shift the initial relationship between mg ca and 18o determined by their temperature dependence is maintained we conclude that paired measurements of 18o and mg ca can be used for reconstructing 18owater though care must be taken to determine where in the water column the reconstruction applies

tomography of the andean crust and mantle at 20 s first results of the lithoscope experiment abstract in 1994 a temporary network of 41 short period seismic stations operated for 6 months along an east west profile in northern chile and bolivia the profile crossed the entire andean chain at a latitude of 20 s we present the results of the teleseismic tomography of the crust and mantle along an east west vertical cross section beneath the profile the most striking feature of the tomographic image is the identification of the subducted nazca plate it appears as a zone of high velocities which is continuous over the aseismic part of the slab down to the 660 km discontinuity in the continental lithosphere strong lateral p wave velocity variations are found in the crust whereas the upper mantle shows only small velocity variations major lateral changes in crustal velocity coincide with the limits of the main structural units of the andean range the distribution of velocity anomalies in the crustal layer matches the lateral changes in crustal thickness and average velocity deduced from refraction surveys a comparison with a previous tomographic experiment in northern bolivia confirms that the northern and southern segments of the bolivian orocline have different lithospheric structures

variations in mg ca and sr ca ratios of planktonic foraminifera caused by postdepositional dissolution evidence of shallow mg dependent dissolution a comparative study has been made of two species of planktonic foraminifera g tumida and g sacculifer in a depth transect on the ontong java plateau western equatorial pacific g tumida tests from core top sediments showed decreasing mg ca 2 65 1 25 mmol mol and sr ca 1 50 1 16 mmol mol ratios with increasing water depth 1600 4400 m while no such variation was found in g sacculifer tests in excess of 355 m average mg ca 3 6 mmol mol sr ca 1 4 mmol mol artificial dissolution of g tumida tests led to a decrease in both mg ca and sr ca but in g sacculifer there was no significant change in the ratios analyses by electron microprobe revealed that mg ca of the inner chamber calcite in g tumida tests was much higher than that of the calcite crust keel whereas sr ca was only slightly elevated there were no consistent spatial differences in either mg ca or sr ca for g sacculifer tests dissolution in the oceans gives rise to the removal of the chamber calcite in g tumida about 30 of the total calcite leaving the keel calcite although g tumida is thought of as a dissolution resistant form the majority of mg ca and sr ca depletion and chamber loss occurs above the lysocline it is also possible that much of the mg enriched gametogenic calcite has been lost by dissolution from g sacculifer above 1600 m mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera calculations show that the saturation horizon for mg rich parts of tests may be elevated by several hundred meters compared with normal calcite

preferential dissolution of benthic foraminiferal calcite during laboratory reductive cleaning we have investigated the effect of cleaning procedures on eight element ca ratios in three widely used benthic foraminifera species from core top and down core sediments two cleaning techniques were employed 1 comparison between mg cleaning and cd cleaning methods and 2 comparison between the various constituent reagents li ca b ca and sr ca ratios remained unchanged for samples subjected to different treatments but mg ca mn ca zn ca cd ca and u ca were substantially decreased when foraminifera shells were cleaned with reagents containing citrate in contrast no significant decreases in element ca ratios were observed for samples cleaned in n2h4 without citrate indicating that the role of n2h4 was insignificant during reductive cleaning and that citrate is responsible for decreases of mg ca mn ca zn ca cd ca and u ca decreases in these ratios are most likely due to 1 removal of contaminant particles enriched in mg mn zn cd and u and or 2 preferential leaching of caco3 by the formation of stable metal complexes through chelation between citrate and metals heterogeneously distributed in foraminiferal shells due to the negligible effect of n2h4 and preferential dissolution of caco3 during reductive cleaning it is suggested that the reductive cleaning step should be omitted and the mg cleaning method barker et al 2003 could be employed to clean foraminiferal shells for trace element measurements

on the fidelity of shell derived δ18oseawater estimates article i nfo 18 oseawater a robustproxyforsurfacesalinity we assessthe fidelity of shell derived 18 oseawater estimates for the surface dwelling foraminifer globigerinoides ruber white using an atlantic meridional coretop transect spanning basin scale temperature and salinity gradients shell derived and observed 18 oseawater values are well correlated r 2 0 77 but a large systematic bias is observed shell mg ca ratios are significantly elevated above values expected from observed and isotopic calcification temperatures in the saline subtropical gyres of both hemispheres this temperature independent shell mg ca ratio variability termed excess mg ca i s highly correlated with surface salinity r 2 0 77 and the observed salinity dependence 27 4 is much higher than indicated by culture studies 6 2 our coretop data are used to develop new atlantic basin temperature and salinity calibration equations that are accurate 1 1 c and 0 20 respectively precise r 2 0 82 and 0 81 respectively and verifiable using previously published data these results are valid for the relatively high salinities of the subtropical atlantic 35 5 37 3 we discover that inclusion of other published data from lower salinity regions b35 indicates little or no excess mg ca taken together these results point to a strongly non linear positive salinity effect on shell mg ca ratios that significantly affects the accuracy of sst and 18

holocene climate variability in the labrador sea formation of labrador sea water proper commenced about 7000 years ago during the holocene interglacial to test whether fresher surface water conditions may have inhibited labrador sea water convection during the early holocene we measured planktonic foraminiferal globigerina bulloides oxygen isotopes 18 o and mg ca ratios at orphan knoll cores hu91 045 093 and md95 2024 3488 m in the labrador sea to reconstruct shallow subsurface summer conditions temperature and seawater 18 o lighter foraminiferal 18 o values are recorded during the early holocene between 11000 and 7000 years ago part of these lighter foraminiferal 18 o values can be explained by increased calcification temperatures reconstructed seawater 18 o values were however still on average 0 5 lighter compared with those of recent times confirming that fresher surface waters in the labrador sea were probably a limiting factor in labrador sea water formation during the early holocene

meridional shifts in the marine itcz and the tropical hydrologic cycle over the last three glacial cycles 1 paleoproxy studies show a strong correlation between tropical climate and high latitude temperature variability recorded in the greenland ice cores over the last glacial cycle in particular abrupt cooling events in the greenland ice sheet project ii 18o ice record appear synchronous with a southward migration of the intertropical convergence zone itcz in the atlantic a weakening of the indian and east asian monsoon systems and a strengthening of the south american monsoon system because this high to low latitude climate teleconnection significantly alters the tropical hydrologic cycle around the globe it plays a critical role in regulating global climate on glacial interglacial time scales we compare 18oseawater reconstructions a salinity proxy generated from previously published mg ca and oxygen isotope data on globigerinoides ruber white var obtained from western caribbean core odp 999a and western equatorial pacific core 806b across the last three glacial cycles to show that systematic variations in surface salinity at these sites suggest the tropical hadley cell hydrologic system undergoes systematic reorganizations that differ dramatically between warm interglacial and cold glacial periods furthermore cross spectral and phase angle analyses of the ice volume corrected caribbean and western pacific 18osw records reveal a 100 kyr frequency in both records that is almost 180 out of phase and a 23 kyr frequency that is nearly in phase this results in the development of a very large 18osw gradient between the caribbean and the western equatorial pacific on glacial interglacial time scales that is best explained by a southward shift in both the atlantic and pacific itcz during north atlantic cold phases

mg ca in the planktonic foraminifera globorotalia inflata and globigerinoides bulloides from western mediterranean plankton tow and core top samples abstract due to its strong gradient in salinity and small temperature gradient the mediterranean provides an ideal setting to study the impact of salinity on the incorporation of mg into foraminiferal tests we have investigated tests of globorotalia inflata and globigerina bulloides in plankton tow and core top samples from the western mediterranean using icp oes for bulk analyses and la icp ms for analyses of individual chambers in single specimens mg ca observed in g inflata are consistent with existing calibrations whereas g bulloides had significantly higher mg ca than predicted particularly in core top samples from the easterly stations scanning electron microscopy and laser ablation icp ms revealed secondary overgrowths on some tests which could explain the observed high core top mg ca we suggest that the mediterranean intermediate and deep water supersaturated with respect to calcite cause these overgrowths and therefore increased bulk mg ca however the different species are influenced by diagenesis to different degrees probably due to different test morphologies our results provide new perspectives on reported anomalously high mg ca in sedimentary foraminifera and the applicability of the mg ca paleothermometry in high salinity settings by showing that 1 part of the signal is generated by precipitation of inorganic calcite on the foraminifer test due to increased calcite saturation state of the water and 2 species with high surface to volume shell surfaces are potentially more affected by secondary mg rich calcite encrustation

the use of paleoceanographic proxies in carbonate periplatform settings opportunities and pitfalls in a sediment core from the leeward side of the great bahama bank ocean drilling program odp leg 166 1006a 24h early pliocene several paleoceanographic proxies were compared with carbonate mineralogy the proxies measured on the planktonic foraminifera species globigerinoides sacculifer are mg ca and sr ca elemental ratios and 18o values these proxies are widely used in pelagic sediments to derive parameters of water masses such as paleo temperature and salinity to produce quantitative estimates it is necessary to verify that the primary shell mineralogy of the foraminifera was not altered diagenetically diagenetic alteration can be rapid in periplatform settings relative to pelagic deep sea sediments since the meta stable carbonate phases provide an additional driving force for recrystallisation we show that the sr ca ratio of foraminiferal calcite can be used to assess the degree of diagenetic alteration of their shell chemistry using this method we demonstrate that the primary signal in the oxygen isotope ratios is preserved in the studied core in the mg ca record the relative change of foraminiferal mg ca ratios seems to be preserved but absolute values are influenced by diagenesis the second set of proxies comprises 13c and c n ratios of organic carbon these are used in pelagic sediments in order to assess the origin of organic carbon terrestrial or marine phytoplankton it is demonstrated here that a simple two end mixing model cannot explain the observed co occurrence of relatively high 13corg and c n values as the 13corg values co vary with the aragonite content we attribute this signature to varying contribution of organic carbon from benthic algae which are also the major aragonite producers on the platform top

palaeoenvironments in the southern baltic sea basin during marine isotope stage 3 a multi proxy reconstruction abstract sediment cores from kriegers flak in the southwestern baltic sea provide a unique possibility to study the middle weichselian history of the baltic basin three weichselian interstadial units have been identified and are attributed to marine isotope stage 3 mis 3 60 25 ka the oldest unit a is characterized by a deglaciation sequence gradually turning into brackish water clay the low diversity benthic foraminiferal fauna stable oxygen isotope values and mg ca ratios indicate low temperature and salinity for unit a a hiatus separates unit a from the overlying unit b which was deposited in wetlands and shallow lakes between 42 and 36 cal ka bp macrofossil and pollen analyses indicate deposition of unit b in an area dominated by a tree less open tundra environment possibly with some birch and pine in sheltered positions the uppermost unit c is characterized by clay deposition including redeposition of material from older sediments unit b optically stimulated luminescence osl ages indicate deposition of unit c between 26 and 28 5 ka radiocarbon ages of 39 and 40 cal ka bp for unit c are considered to be too old the following depositional model is suggested i isostatic depression of the region after an advance of the scandinavian ice sheet sis most likely the ristinge ice advance previously dated to c 55 50 ka enabled an inflow of marine waters into the baltic basin during the deposition of unit a ii isostatic rebound caused a regression at kriegers flak and a hiatus between units a and b iii wetlands and smaller lakes formed in the uplifted area between 42 and 36 cal ka bp unit b iv deposition of glaciolacustrine clays at kriegers flak demonstrates that a growing sis dammed kattegat and the baltic basin c 28 5 to 26 ka the new evidence from kriegers flak provides a solid framework for future mis 3 palaeoenvironmental reconstructions in the circum baltic area

controls on shell mg ca and sr ca in cultured planktonic foraminiferan globigerinoides ruber white mg ca and sr ca ratios were determined on a single species of planktonic foraminiferan globigerinoides ruber white collected from the gulf of eilat and cultured in seawater at five different salinities 32 to 44 five temperatures 18 to 30 c and four ph values 7 9 to 8 4 the mg ca temperature calibration of cultured g ruber with an exponential slope of 8 3 c agrees well with previously published calibrations from core tops and sediment traps however the dependence of mg ca on salinity with an exponential slope of 5 3 psu is also significant and should be included in the calibration equation with this purpose we calculated a calibration equation for g ruber dependent on both temperature and salinity within the 95 confidence limits mg ca mmol mol exp 0 06 0 02 s psu 0 08 0 02 t c 2 8 1 0 r2 0 95 the influence of ph on mg ca ratios is negligible at ambient seawater ph 8 1 to 8 3 however we observe a dominating ph control on shell mg ca when the ph of seawater is lower than 8 0 sr ca in g ruber shows a significant positive correlation with average growth rate presumably part of the variability in shell sr ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions

refining globigerinoides ruber mg ca paleothermometry in the atlantic ocean abstract the mg ca ratio of the planktonic foraminifera globigerinoides ruber white has become a widely used proxy for reconstructing sea surface temperature sst as numerous studies have shown that temperature is the primary control on mg ca ratios in foraminiferal calcite however a recent study of core top sediments across an atlantic meridional transect suggests that salinity might have a stronger control on foraminiferal mg ca ratios than previously thought by analyzing mg ca ratios and o 18 values in g ruber white arbuszewski et al 2010 found a 27 increase in g ruber mg ca ratios per 1 salinity unit increase for seawater salinities above 35 5 here we use shell weight analyses and sem images from a subset of the core tops used in the arbuszewski et al 2010 study across a narrow depth range 3197 3733 m to show that g ruber shells from the equatorial region are highly dissolved compared to those from the subtropical north and south atlantic gyres significantly impacting their mg ca ssts shell weights from the higher productivity equatorial region of the atlantic are on average 20 and 15 lower than those from the oligotrophic north and south atlantic gyres respectively given the large preservation gradient along the transect studied by arbuszewski et al 2010 application of a single dissolution corrected mg ca sst calibration equation dekens et al 2002 on cores from the subtropical gyres and the equatorial region is not appropriate when regional differences in preservation are considered as well as realistic habitat depths and calcification seasons for g ruber in temperate latitudes we find a strong correlation between observational ssts and calculated g ruber mg ca ssts in core top samples spanning 43 n to 25 s in the atlantic in addition our re calibrated mg ca ssts are more strongly correlated with isotopic calcification temperatures across the transect than originally reported by arbuszewski et al 2010 this study provides evidence that regional differences in preservation rather than salinity significantly affects g ruber mg ca ssts in the atlantic and supports culturing experiments that found salinity only has a minor influence on foraminiferal mg ca ratios

three dimensional models of p wave velocity and p to s velocity ratio in the southern central andes by simultaneous inversion of local earthquake data the pisco 94 proyecto de investigation sismologica de la cordillera occidental 1994 seismological network of 31 digital broad band and short period three component seismometers was deployed in northern chile between the coastal cordillera and the western cordillera more than 5300 local seismic events were observed in a 100 day period a subset of high quality p and s arrival time data was used to invert simultaneously for hypocenters and velocity structure additional data from two other networks in the region could be included the velocity models show a number of prominent anomalies outlining an extremely thickened crust about 70 km beneath the forearc region an anomalous crustal structure beneath the recent magmatic arc western cordillera characterized by very low velocities and a high velocity slab a region of an increased vp vs ratio has been found directly above the wadati benioff zone which might be caused by hydration processes a zone of lower than average velocities and a high vp vs ratio might correspond to the asthenospheric wedge the upper edge of the wadati benioff zone is sharply defined by intermediate depth hypocenters while evidence for a double seismic zone can hardly be seen crustal events between the precordillera and the western cordillera have been observed for the first time and are mainly located in the vicinity of the salar de atacama down to depths of about 40 km

mg ca paleothermometry in high salinity environments planktonic foraminiferal mg ca ratios have become a fundamental temperature proxy in past climate reconstructions however in the highly evaporative seas of the tropics and subtropics anomalously high planktonic foraminiferal mg ca ratios arise possibly linked to high salinities the extent to which salinity affects mg uptake into foraminiferal calcite remains disputed some studies suggest only minor salinity effects whereas others suggest a dominant role here we present new data from the highly saline 40 red sea which separate pure foraminiferal calcite from other phases the results show that high mg ca ratios 7 to 13 mmol mol found by conventional analysis of planktonic foraminifera from a red sea sediment core are not caused by increased mg uptake into foraminiferal calcite in a high salinity setting e g beyond those predicted by culturing studies but instead result from secondary high mg calcite overgrowths the overgrowths likely formed near the sediment seawater interface from caco3 supersaturated interstitial seawater

late cretaceous granitic intrusions and associated deposits in the yidun arc of the eastern tibetan plateau abstract the yidun arc is an important tectonic unit and polymetallic metallogenic belt in the sanjiang tectono magmatic belt in which many cretaceous 138 75 ma granites and associated polymetallic deposits are distributed along a nw trending belt the queershan cuomolong rongyicuo and genie granitic intrusions and the associated sn pb zn ag polymetallic deposits are distributed in the changtai and xiangcheng arcs whereas the xiuwacu relin hongshan and tongchanggou granitic intrusions and the associated cu mo w deposits are mainly distributed in the geza arc this study presents new zircon u pb hf o isotopic data for the queershan cuomolong rongyicuo genie xiuwacu and tongchanggou granitic intrusions combined with the structural analysis of the xiuwacu granitic complex to discuss the differences in the petrogenesis and metallogenesis of these granitic intrusions as well as the geodynamic processes that controlled the formation of the late cretaceous intrusions and related deposits hf o isotopic characteristics indicate that the highly fractionated granites hfg in the changtai and xiangcheng arcs were mainly derived from the partial melting of metasedimentary crustal materials with a minor input from mantle components while the i type granites ig in the geza arc were predominantly derived from the partial melting of ancient lower crustal material the spatial distributions of the different types of deposits in the yidun arc were probably controlled by the magma sources reduced magmas produced by the partial melting of the sedimentary crust in the changtai and xiangcheng arcs are favorable for w sn pb and zn mineralization whereas oxidized magmas produced by the partial melting of the lower crust in the geza arc are conducive to the enrichment of cu au and mo the geochronological data indicate that the emplacement ages of the late cretaceous granites in the yidun arc gradually decrease from north to south ranging from 106 to 73 ma reflecting the southward lateral tectonic migration the structural analysis of the xiuwacu w mo deposit in combination with previous studies demonstrated that the late cretaceous granites in the yidun arc were likely formed in a regional extensional setting which was probably related to the slab break off of the bangong nujiang oceanic slab or the subduction of the yarlung zangbo oceanic slab

composition of the crust in the grenville and appalachian provinces of north america inferred from v p v s ratios we use the ratios between p and s wave velocities vp vs derived from seismic refraction data to infer the composition of the crust in the grenville and the appalachian provinces of north america the crust exhibits vp vs increasing with depth from 1 64 to 1 84 there is a clear distinction between the grenville province average vp vs 1 81 and the appalachian province average vp vs 1 73 which persists at all depths the boundary between these provinces is east dipping extending for 100 km east of the champlain thrust in the appalachian province the increase in vp vs ratios with depth from 1 67 to 1 74 0 02 may reflect a normal decrease of silica content in the continental crust in the grenville province beneath the central granulite terrane an anomalous vp vs ratio of 1 82 0 02 is observed extending to a depth of 10 km this correlates with the abundance of ca plagioclase in the marcy anorthosite at greater depth 15 20 km where seismic lamination and high electrical conductivity is observed vp vs is 1 84 0 02 and correlates with the tahawus complex a layered mafic intrusion within the 25 km thick lower crust of the grenville province the vp vs is 1 84 0 02 and p velocity is 7 0 0 1 km s which are typical for plagioclase bearing rocks gabbro norite the high vp vs ratio in the grenville province has not been reported in crust of any other age since the grenville province contains 75 of the world s known anorthosites high vp vs ratio is related to high plagioclase we suggest that the composition of the grenville lower crust was significantly modified by the emplacement of the anorthosites in the mid proterozoic

crustal structure of the altiplano from broadband regional waveform modeling implications for the composition of thick continental crust we have modeled the full waveforms from six intermediate depth and two shallow earthquakes recorded at regional distances by the banjo broadband andean joint experiment banjo and seismic exploration of the deep altiplano seda portable seismic networks in the central andes in this study we utilize data from those banjo and seda stations located within the altiplano and eastern cordillera we used reflectivity synthetic seismograms and a grid search to constrain four parameters of the altiplano eastern cordillera lithosphere crustal thickness average crustal velocity vp and crustal and upper mantle poisson s ratios crust and mantle using our grid search we investigated the crustal and upper mantle structure along 36 individual event station paths and applied forward modeling to 56 event station paths robust models for the altiplano that provide the best overall fit between the data and synthetic seismograms are characterized by an average vp of 5 75 6 25 km s crustal thicknesses of 60 65 km crust 0 25 and mantle 0 27 0 29 we find a north south variation in the structure of the altiplano with the crust south of the banjo transect characterized by either lower than average crustal p wave velocities or a slightly higher crust relative to crust north of the banjo transect these results are consistent with a model of crustal thickening caused predominantly by tectonic shortening of felsic crust rather than by underplating or magmatic intrusion from the mantle

the influence of salinity on mg ca in planktic foraminifers evidence from cultures core top sediments and complementary δ18o the mg ca ratio in foraminiferal calcite is one of the principal proxies used for paleoceanographic temperature reconstructions but recent core top sediment observations suggest that salinity may exert a significant secondary control on planktic foraminifers this study compiles new and published laboratory culture experiment data from the planktic foraminifers orbulina universa globigerinoides sacculifer and globigerinoides ruber in which salinity was varied but temperature ph and light were held constant combining new data with results from previous culture studies yields a mg ca sensitivity to salinity of 4 4 2 3 4 7 1 2 and 3 3 1 7 per salinity unit 95 confidence respectively for the three foraminifer species studied here comparison of these sensitivities with core top data suggests that the much larger sensitivity 27 4 per salinity unit derived from atlantic core top sediments in previous studies is not a direct effect of salinity rather we suggest that the dissolution correction often applied to mg ca data can lead to significant overestimation of temperatures we are able to reconcile culture calibrations with core top observations by combining evidence for seasonal occurrence and latitude specific habitat depth preferences with corresponding variations in physico chemical environmental parameters although both mg ca and 18o yield temperature estimates that fall within the bounds of hydrographic observations discrepancies between the two proxies highlight unresolved challenges with the use of paired mg ca and 18o analyses to reconstruct paleo salinity patterns across ocean basins the first step towards resolving these challenges requires a better spatially and seasonally resolved 18osw archive than is currently available nonetheless site specific reconstructions of salinity change through time may be valid

influences of temperature and secondary environmental parameters on planktonic foraminiferal mg ca a new core top calibration the accuracy of the mg ca paleothermometer is contested over the influences of secondary environmental parameters such as salinity and ph recent calibrations based on compiled sediment trap and laboratory culture data suggest moderate influences from salinity and ph core tops are the best analogues to downcore samples used for paleoceanographic reconstruction with well constrained environmental parameters and thus can be used to validate sediment trap and laboratory culture calibrations here we calibrate new core top mg ca data in globigerinoides ruber white and trilobatus sacculifer without final sac like chamber with sea surface temperature salinity and ph part of these coretops were previously used to argue for a large salinity effect on g ruber w mg ca arbuszewski et al 2010 http 10 0 3 248 j epsl 2010 10 035 our new g ruber w mg ca data are on average 12 lower than the previous results our calibrations yield mg ca temperature sensitivities of 8 1 0 7 c for g ruber w and 6 6 0 8 c for t sacculifer w o sac and mg ca salinity effects of 4 7 2 4 for g ruber w and 5 5 2 3 for t sacculifer w o sac these results agree well with culture experiments but discount the large salinity effects reported in previous core top studies our data reveal insignificant ph effects on mg ca in both species overall our core top calibrations for g ruber w and t sacculifer w o sac lend strong support to previous calibrations strengthening our confidence in the use of planktonic mg ca as a reliable proxy for sea surface temperature reconstructions less

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

lower bound on the amount of crustal shortening in the central bolivian andes balanced cross sections across the cordillera oriental and subandean zone of the central bolivian andes indicate that crustal shortening probably has played the dominant role in orogeny in this convergent margin setting a minimum amount of shortening 210 km is documented which can account for two thirds of the present day crustal cross sectional area along a transect spanning the entire mountain range substantial crustal shortening may also require loss of the lower lithosphere to the asthenosphere a large minimum amount of crustal shortening in the bolivian andes shows contrary to common assumptions about orogeny that 1 magmatic addition may be volumetrically less important in orogeny in andean type margins and 2 crustal shortening is not uniquely associated with continental or island arc collision

northern and southern hemisphere controls on seasonal sea surface temperatures in the indian ocean during the last deglaciation 37 are consistently warmer than those derived from mg ca by 2 3 c except for the heinrich event 1 in addition the initial timing for the deglacial warming of alkenone sst started at 15 6 ka which lags behind that of mg ca temperatures by 2 5 kyr we argue that the discrepancy between the two sst proxies reflects seasonal differences between summer and winter rather than postdepositional processes or sedimentary biases the u k 37 sst record clearly mimics the deglacial sst trend recorded in the north atlantic region for the earlier part of the termination indicating that the early deglacial warming trend attributed to local summer temperatures was likely mediated by changes in the atlantic meridional overturning circulation at the onset of the deglaciation in contrast the glacial to interglacialsstpatternrecordedbyg rubermg ca probably reflectscoldseasonssts this indicates that the cold season ssts was likely mediated by climate changes in the southern hemisphere as it closely tracks the antarctic timing of deglaciation therefore our study reveals that the tropical southwestern indian ocean seasonal sst was closely linked to climate changes occurring in both hemispheres the austral summer and winter recorded by each proxy is further supported with seasonal sst trends modeled by atmosphere ocean general circulation models for our core site our interpretation that the alkenone and mg ca ssts are seasonally biased may also explain similar proxy mismatches observed in other tropical regions at the onset of the last termination

benthic foraminiferal mg ca paleothermometry a revised core top calibration core top samples from different ocean basins have been analyzed to refine our current understanding of the sensitivity of benthic foraminiferal calcite magnesium calcium mg ca to bottom water temperatures bwt benthic foraminifera collected from hawaii little bahama bank sea of okhotsk gulf of california ne atlantic ceara rise sierra leone rise the ontong java plateau and the southern ocean covering a temperature range of 0 8 to 18 c were used to revise the cibicidoides mg ca temperature calibration the mg ca bwt relationship of three common cibicidoides species is described by an exponential equation mg ca 0 867 0 049 exp 0 109 0 007 bwt stated errors are 95 ci the temperature sensitivity is very similar to a previously published calibration however the revised calibration has a significantly different preexponential constant resulting in different predicted absolute temperatures we attribute this difference in the preexponential constant to an analytical issue of accuracy some genera notably uvigerina show apparently lower temperature sensitivity than others suggesting that the use of constant offsets to account for vital effects in mg ca may not be appropriate downcore mg ca reproducibility as determined on replicate foraminiferal samples is typically better than 0 1 mmol mol 1 2 s e thus considering the errors associated with the cibicidoides calibration and the downcore reproducibility bwt may be estimated to within 1 c application of the revised core top mg ca bwt data to cenozoic foraminiferal mg ca suggests that seawater mg ca was not more than 35 lower than today in the ice free ocean at 50 ma

strong crustal heterogeneity in the bolivian altiplano as suggested by attenuation of lg waves using the seismological data of four temporary networks installed across the andes of bolivia and chile between 1990 and 1995 we study the amplitudes of the lg phase for 45 regional events located at crustal depths this analysis reveals that lg is strongly attenuated for most of the ray paths crossing the altiplano independent of the azimuth of propagation to map the anomalies and evaluate their frequency dependence we conduct a regionalization of the crustal average qs factor using a damped least squares inversion technique in the frequency range 0 6 5 hz the resulting maps delineate regions with contrasting values of apparent attenuation the altiplano is characterized by strong attenuation with an average qs of 100 at 1 hz whereas the cordilleras are regions of weaker attenuation the frequency dependence of qs is investigated in an attempt to separate the source of the apparent attenuation into scattering and anelastic absorption within the hypothesis of a weak frequency dependence of the intrinsic q we show that at 1 hz scattering plays a major part in the attenuation of lg waves whereas at 4 hz both mechanisms are of equal importance these results indicate that the attenuation of lg waves in the altiplano is due more to scattering by small scale heterogeneities than to a high percentage 1 of partial melt involving a large part of the crust

globorotalia truncatulinoides dextral mg ca as a proxy for gulf of mexico winter mixed layer temperature evidence from a sediment trap in the northern gulf of mexico abstract three years of weekly to biweekly resolved sediment trap data show that almost 90 of the total flux of tests of the planktic foraminifer globorotalia truncatulinoides to sediments in the northern gulf of mexico occurs in january and february comparison of 18 o from tests of non encrusted gl truncatulinoides in sediment trap samples with calculated calcification depths indicates that the non encrusted individuals secrete their test in the winter surface mixed layer most likely at the bottom of the surface mixed zone mg ca temperature estimates from non encrusted gl truncatulinoides in sediment trap samples are consistent with observed temperatures at the calcification depths inferred from the 18 o data in contrast mg ca temperature estimates from encrusted gl truncatulinoides in sediment trap samples indicate the crust is formed in cooler deeper waters a preliminary study in a core recovered near the sediment trap site demonstrates that non encrusted and encrusted forms of gl truncatulinoides in sediment samples show a similar offset in mg ca values as observed in sediment trap samples a short 100 years mg ca record from non encrusted gl truncatulinoides indicates a warming trend that coincides with a warming trend in mean annual sea surface temperature recorded by mg ca in globigerinoides ruber white from the same core these findings suggest mg ca from non encrusted gl truncatulinoides has clear potential as a proxy for past winter mixed layer temperature

dominant northern hemisphere climate control over millennial scale glacial sea level variability abstract based on a radiocarbon and paleomagnetically dated sediment record from the northern red sea and the exceptional sensitivity of the regional changes in the oxygen isotope composition of sea water to the sea level dependent water exchange with the indian ocean we provide a new global sea level reconstruction spanning the last glacial period the sea level record has been extracted from the temperature corrected benthic stable oxygen isotopes using coral based sea level data as constraints for the sea level oxygen isotope relationship although the general features of this millennial scale sea level records have strong similarities to the rather symmetric and gradual southern hemisphere climate patterns we observe in constrast to previous findings pronounced sea level rises of up to 25 m to generally correspond with northern hemisphere warmings as recorded in greenland ice core interstadial intervals whereas sea level lowstands mostly occur during cold phases corroborated by climber 2 model results the close connection of millennial scale sea level changes to northern hemisphere temperature variations indicates a primary climatic control on the mass balance of the major northern hemisphere ice sheets and does not require a considerable antarctic contribution

la icp ms depth profiling perspective on cleaning protocols for elemental analyses in planktic foraminifers 1 measurements of trace metal ratios in foraminiferal calcite are routinely used to reconstruct paleoceanographic conditions analyses using solution based inductively coupled plasma mass spectrometry icp ms require dissolution of the entire foraminifer shell the potential exists for contamination from adherent clays mineralized coatings and other diagenetic components that confound the biogenic trace metal signal we present results from a cleaning experiment on fossil specimens of the planktic foraminifer orbulina universa that were cracked into several shell fragments and subjected to different cleaning protocols we use laser ablation icp ms la icp ms depth profiling to evaluate the effects of reductive oxidative and chelating diethylene triamine pentaacetic acid cleaning protocols on shell mg ca and ba ca ratios using the natural pattern of intrashell mg ca heterogeneity exhibited by o universa we demonstrate that reductive and oxidative cleaning can dissolve shell calcite from available surfaces although intrashell mg ca minima and maxima are unaffected high resolution depth profiles can be used to identify areas of heterogeneous intrashell ba ca which can be excluded from computations of whole shell ba ca the size and density of shell pores plays a major role in the degree of contamination from sedimentary material we demonstrate an approach for computing whole shell me ca ratios from la icp ms depth profiles that accounts for potential contamination and diagenetic overprinting

foraminiferal mg ca increase in the caribbean during the pliocene western atlantic warm pool formation salinity influence or diagenetic overprint we constructed a high resolution mg ca record on the planktonic foraminifer globigerinoides sacculifer in order to explore the change in sea surface temperature sst due to the shoaling of the isthmus of panama as well as the impact of secondary factors like diagenesis and large salinity fluctuations the study covers the latest miocene and the early pliocene 5 6 3 9 ma and was combined with 18o to isolate changes in sea surface salinity sss before 4 5 ma sstmg ca and sss show moderate fluctuations indicating a free exchange of surface ocean water masses between the pacific and the atlantic the increase in 18o after 4 5 ma represents increasing salinities in the caribbean due to the progressive closure of the panamanian gateway the increase in mg ca toward values of maximum 7 mmol mol suggests that secondary influences have played a significant role evidence of crystalline overgrowths on the foraminiferal tests in correlation with aragonite sr ca and productivity cyclicities indicates a diagenetic overprint on the foraminiferal tests laser ablation inductively coupled plasma mass spectrometry analyses however do not show significantly increased mg ca ratios in the crystalline overgrowths and neither do calculations based on pore water data conclusively result in significantly elevated mg ca ratios in the crystalline overgrowths alternatively the elevated mg ca ratios might have been caused by salinity as the 18o record of site 1000 has been interpreted to represent large fluctuations in sss and cultivating experiments have shown an increase in mg ca with increasing salinity we conclude that the mg ca record 4 5 ma can only reliably be considered for paleoceanographical purposes when the minimum values not showing any evidence of secondary influences are used resulting in a warming of central caribbean surface water masses after 4 5 ma of 2 c

three dimensional υp and υp υs structure of the hengill triple junction and geothermal area iceland and the repeatability of tomographic inversion we investigate the crustal structure of the hengill triple junction in southwestern iceland applying tomographic methods to local earthquake data recorded in two field experiments with different network geometries and instrumentation data from the two experiments enable us to derive three dimensional models of the compressional wave speed p and the wave speed ratio p s well resolved high p bodies correlate with sites of gabbroic intrusions a small reduction in p s associated with the high temperature part of the geothermal area is probably due to mineral alteration or supercritical fluids the rms difference between the two p models about 0 26 km s 1 indicates the approximate repeatability that may be expected of good tomographic inversions

the late pliocene benguela upwelling status revisited by means of multiple temperature proxies as compared to the late pleistocene alkenone based sea surface temperature sst in the benguela region revealed relatively warm and stable sst recorded between approximate to 3 5 and 2 0 ma and coincide with a period of increasing biological productivity as revealed by increasing deposition of biogenic opal we assess how the hydrological patterns recorded in sst proxies are embedded in the geological record by performing a proxy proxy comparison we used laser ablation inductively coupled plasma mass spectrometry to measure the mg ca on the planktonic foraminifera species globigerina bulloides allowing in situ measurements of mg ca on individual foraminiferal tests mg ca derived temperatures provide much colder temperatures than alkenone derived sst by up to 10 degrees c we build a scenario involving contrasting sensitivities of paleothermometers upon the annual cycle namely alkenones preferentially capturing sst when the surface ocean is warmer than the mean annual average sst and g bulloides capturing sst when upwelling intensifies multichamber analysis also suggests that g bulloides migrates below the sea surface while calcifying its last chambers prior to gametogenesis allowing the extraction of both surface and subsurface temperature from mg ca measured on different chambers the range of temperatures recorded between our multiple sst proxies is supported by the range of temperatures simulated with a general circulation model when different seasons different water depth and different orbital configurations occurring during the late pliocene are considered a greater seasonal cycle in sst during the pliocene can account for alkenone and mg ca derived temperature contrast pointing to a radically different mode of upwelling activity in the benguela region compared to today

diagenetic mg rich calcite in mediterranean sediments quantification and impact on foraminiferal mg ca thermometry abstract mg ca ratios in planktonic foraminifera have been developed into a powerful tool in paleoceanography to reconstruct past sea surface temperatures sst however additional factors that might have an influence on mg ca like dissolution salinity diagenesis and carbonate ion effects have come into focus in this paper the occurrence of diagenetic calcification and its potential effects on mg ca have been studied using 20 well preserved core tops recovered from the mediterranean sea analyses were performed on two planktonic foraminifer species globigerinoides ruber and globigerina bulloides using icp aes mg ca measurements sem observations and x ray diffractometry analyses foraminiferal mg ca values are higher than those obtained in the open sea the highest values were found in the eastern mediterranean basin these anomalies cannot be simply explained by a salinity effect because mg ca ratios when corrected for temperature influence do not display any significant correlation with salinity our results seem to indicate that diagenesis can account for anomalously high mg ca values indeed sem observations show aggregates of rhombohedral crystals that could be interpreted as secondary calcite overgrowths we note also the occurrence of numerous coccoliths trapped in foraminifer walls and covered with a secondary mineral phase x ray diffraction diagrams of numerous foraminiferal samples exhibit peak of mg rich calcite 10 12 associated with the usual foraminifer calcite peak it has been demonstrated that this calcite highly rich in mg is compatible with an inorganic calcite precipitated directly from seawater the deconvolution of the main xrd peak 104 shows that the percentage of mg rich calcite can reach up to 21 of the total foraminiferal calcite in the eastern basin whereas in the western mediterranean sea proportions do not exceed 5 in addition we demonstrate that the diagenetic process is very heterogeneous even at the sample scale and is not simply a reflection of co 3 at the sea bottom thus the high mg ca ratios measured from mediterranean sea planktonic foraminifera does not appear to be caused by increased mg uptake in a high salinity setting but instead result chiefly from the presence of mg rich calcite 10 12 deposited during early diagenetic processes

aplanktonic zones in the red sea abstract we use micropalaeontological and stable isotope results for a series of cores from north to south through the red sea to assess temporal and spatial patterns of change in planktonic foraminiferal faunas leading up to the remarkable full glacial red sea aplanktonic zones aplanktonic zones reflect salinities in the red sea in excess of the lethal 49 p s u limit caused by reduced exchange transport through the strait of bab el mandab due to glacial sea level lowering concerning the last glacial cycle aplanktonic conditions began at 39 ka bp in the north where salinities eventually reached 55 57 p s u paradoxically planktonic faunas are reported to have survived the last glacial maximum in the northern gulf of aqaba suggesting a poorly understood freshwater dilution at that time aplanktonic conditions s 49 p s u reached the south central red sea by 22 ka bp while planktonic foraminiferal faunas continued albeit in very low abundances and limited diversity s 45 p s u in the southernmost red sea during marine isotope stage mis 6 the 49 p s u isohaline appears to have resided in the central red sea between cores kl11 and md921017 we observe a systematic sequence of species disappearances before all glacial maxima of the last 500 kyr absence of a logical relationship with sea levels suggests that the disappearance sequences are not related to a general salinity increase instead we argue that the sequences were driven by complex reorganisations in hydrography stratification productivity food availability and subsurface oxygenation reproduction habitats the onset is marked by dramatic basin wide expansion of conditions that today are restricted to only the southern red sea suggesting an expansion of the dominance of ne monsoonal circulation over the entire red sea this expansion occurred 15 or more kyr before the aplanktonic zones of mis 12 6 and 2 and also before mis 10 and 8 which never reach the aplanktonic stage regarding the last glacial cycle this event occurred as early as 75 ka bp mis 4 5 boundary after this major climatic reorganisation we reconstruct progressive intensification of the new conditions especially marked by northward expansion and intensification of the subsurface oxygen minimum zone omz during the last glacial cycle a shallow and very distinct omz affected the central red sea as early as 68 ka bp and the north as late as 55 ka bp the omz expansion intensification appears to have been interrupted by episodes of increased ventilation

seismic gravity and petrological evidence for partial melt beneath the thickened central andean crust 21 23 s on the basis of seismic refraction investigations and gravimetric data we have modelled the crustal structure of the southern central andes 21 23 s a pronounced variation in crustal parameters is seen in n s and w e crossing seismic profiles over the entire andean orogene characterized by a crustal thickness of up to 70 km under the magmatic arc and backarc strongly reduced seismic velocities and a bouguer minimum of 450 mgal anomalously low velocities of 5 9 6 0 km s in the deeper crust of the western cordillera and altiplano regions lead to an over compensation of the bouguer minima resulting in values of crustal densities higher than estimates based purely on seismic velocity measurements in an attempt to reconcile these differences the behavior of crystalline rocks based on published laboratory data was studied under varying pressure and temperature conditions up to the range of partial melting if the temperature is increased above the melting point a rapid decrease in seismic velocity is accompanied by a slow decrease in density for the central andes a good fit of the observed and calculated bouguer anomalies is obtained if the densities of the rocks from the low velocity zone lvz beneath the western cordillera and the altiplano are varied model calculations lead to a velocity density relation for partial molten rocks that allows the melt proportions of rocks to be estimated model calculations indicate that 15 20 vol of basaltic to andesitic melt at depth is necessary to explain the lvz and bouguer anomaly beneath the arc and parts of the backarc high heat flow values 100 mw m2 support the idea that large areas of the deeper andean crust are strongly weakened by the presence of partially molten rocks resulting in reduced seismic velocities with the western cordillera the active volcanic arc of the andean mountain range acting as a ductile buffer between the two more rigid crustal blocks of the forearc and backarc regions

anomalous crust of the bolivian altiplano central andes constraints from broadband regional seismic waveforms a one year deployment of broadband seismographs in the bolivian altiplano recorded numerous intermediate depth earthquakes at near regional distances we modeled the associated broadband waveforms of two earthquakes to estimate an average crustal structure for the altiplano the resulting model is characterized by an anomalously low mean p velocity of 6 0 km s a low poisson s ratio of 0 25 and a crustal thickness of 65 km the combination of the low mean velocity and low poisson s ratio can be explained only by a predominantly quartz rich felsic bulk composition this constraint precludes significant volumes of magmatic addition from the mantle contributing to the great thickness of the altiplano crust but is consistent with thickening by compressive shortening concentrated in a weak felsic layer

transition from basement involved to thin skinned thrusting in the cordillera oriental of southern bolivia the eastern flank of the central andes in southern bolivia and northern argentina is underlain by a fold and thrust belt of neogene age it comprises an external thin skinned segment with basal detachment in silurian shales subandean ranges and an internal segment where units as deep as precambrian metasedimentary and igneous rocks are involved in thrusting eastern cordillera oriental between the cordillera oriental and the subandean ranges an intermediate segment interandean zone intervenes north of the argentinian bolivian border 22 s the structure of the interandean zone is characterized by folded and thrust faulted cambrian to triassic strata balanced cross sections across the western subandean ranges the interandean zone and the eastern cordillera oriental are based on previously available data and recent field work they suggest that the geological structure can be interpreted in terms of two major basement involved thrusts here referred to as interandean and subandean thrusts the more internal interandean thrust caused the development of broad basement anticlines in the eastern cordillera oriental however at shallower levels its displacement was accommodated by thin skinned folding and thrusting in the interandean zone in sequence activation of the subandean thrust uplifted the interandean zone on top of an imbricate basement sheet and caused the development of the thinskinned subandean ranges farther east published radiometric data and subsidence history of the subandean foreland basin suggest that the interandean thrust was active between about 10 ma and 5 ma the subandean thrust is still active southward displacement transfer from the subandean thrust onto the interandean thrust and a southward dipping lateral ramp of the interandean thrust result in the gradual transition from the interandean zone north of 22 s to the cordillera oriental of northern argentina a similar but larger scale transfer may be involved in the southern termination of the thin skinned subandean ranges of argentina at 23 s shortening in the western part of the thrust belt is of the order of 80 90 km total shortening in the eastern andean thrust belt from the undeformed foreland to the eastern margin of the cordillera oriental is 140 150 km

paleoceanography of the atlantic mediterranean exchange overview and first quantitative assessment of climatic forcing 1 the mediterranean sea provides a major route for heat and freshwater loss from the north atlantic and thus is an important cause of the high density of atlantic waters in addition to the traditional view that loss of fresh water via the mediterranean enhances the general salinity of the north atlantic and the interior of the eastern north atlantic in particular it should be noted that mediterranean water outflowing at gibraltar is in fact cooler than compensating inflowing water the consequence is that the mediterranean is also a region of heat loss from the atlantic and contributes to its large scale cooling uniquely this system can be understood physically via the constraints placed on it by a single hydraulic structure the gibraltar exchange here we review the existing knowledge about the physical structure of the gibraltar exchange today and the evidential basis for arguments that it has been different in the past using a series of quantitative experiments we then test prevailing concepts regarding the potential causes of these past changes we find that 1 changes in the vertical position of the plume of mediterranean water in the atlantic are controlled by the vertical density structure of the atlantic 2 a prominent early holocene contourite gap within the gulf of cadiz is a response to reduced buoyancy loss in the eastern mediterranean during the time of sapropel 1 deposition 3 changes in buoyancy loss from the mediterranean during mis3 caused changes in the bottom velocity field in the gulf of cadiz but we note that the likely cause is reduced freshwater loss and not enhanced heat loss and 4 strong exchange at gibraltar during atlantic freshening phases implies that the gibraltar exchange provides a strong negative feedback to reduced atlantic meridional overturning given the very counterintuitive way in which the strait of gibraltar system behaves we recommend that without quantitative supporting work qualitative interpretations of how the system has responded to past external forcing are unlikely to be robust

environmental versus biological controls on mg ca variability in globigerinoides ruber white from core top and plankton tow samples in the southwest pacific ocean 1 laser ablation inductively coupled plasma mass spectrometry was used to analyze the individual chambers from tests of foraminiferal fossil and plankton tow globigerinoides ruber from the southwest pacific ocean from latitudes 3 s to 42 s the variability of mg ca between chambers of an individual intraindividual and individuals of the same population interindividual is such that when converted to temperature the extent of intra individual and interindividual variability appears to exceed that attributable to either calcification or seasonal temperature variability the pooled mean chamber mg ca from each core top and plankton tow site demonstrates a significant p 0 05 positive correlation with temperature we derive chamber specific calibrations where mg cach f 2 0 798 exp0 070 t mg cach f 1 0 891 exp0 067 t and mg cach f 0 590 exp0 072 t we do not observe any bias between the two morphotypes gs ruber ruber and gs ruber pyramidalis the chamber specific calibrations potentially offset mg ca based temperature reconstructions if used on bulk whole test mg ca or applied to misidentified chambers nevertheless these calibrations can be used to reliably estimate sea surface temperature although there is a general overriding temperature control on mg ca we show that removal of the effect of temperature at each site reveals a lognormal mg ca distribution this suggests that mg ca variability at each site is also affected by biological mechanism s that may control the distribution of interindividual mg ca in addition other te ca data al ca and mn ca from laser ablation trace element depth profiles can be used to identify detrital or diagenetic phases that may bias the trace element ca signal

offset timing of climate oscillations during the last two glacial interglacial transitions connected with large scale freshwater perturbation multidecadal to centennial planktic 18o and mg ca records were generated at ocean drilling program site 976 odp976 in the alboran sea the site is in the flow path of atlantic inflow waters entering the mediterranean and captured north atlantic signals through the surface inflow and the atmosphere the records reveal similar climatic oscillations during the last two glacial to interglacial transitions albeit with a different temporal pacing glacial termination 1 t1 was marked by heinrich event 1 h1 post h1 bolling allerod warming and younger dryas yd cooling during t2 the h11 18o anomaly was twice as high and lasted 30 longer than during h1 the post h11 warming marked the start of mis5e while the subsequent yd style cooling occurred during early mis5e the post h11 temperature increase at odp976 matched the sudden asian monsoon termination ii at 129 ka b p extending the 230th dated speleothem timescale to odp976 suggests glacial conditions in the northeast atlantic region were terminated abruptly and interglacial warmth was reached in less than a millennium the early mis5e cooling and freshening at odp976 coincided with similar changes at north atlantic sites suggesting this was a basin wide event by analogy with t1 we argue that this was a yd type event that was shifted into the early stages of the last interglacial period this scenario is consistent with evidence from northern north atlantic and nordic sea sites that the continuing disintegration of the large saalian stage mis6 ice sheet in eurasia delayed the advection of warm north atlantic waters and full strength convective overturn until later stages of mis5e

mg ca of globorotalia inflata as a recorder of permanent thermocline temperatures in the south atlantic 1 we present a species specific mg ca calcification temperature calibration for globorotalia inflata from a suite of 38 core top samples from the south atlantic from 8 s to 49 s g inflata is a deep dwelling planktonic foraminifer commonly occurring in subtropical to subpolar conditions which qualifies it for reconstructions of the permanent thermocline apparent calcification depths and calcification temperatures were determined by comparing measured 18o with equilibrium 18o of calcite based on water column properties based on our core top samples g inflata apparent calcification depth is constant throughout the south atlantic midlatitudes with a depth of 350 400 m within the permanent thermocline the resulting mg ca calcification temperature calibration is mg ca 0 72 0 045 0 042 exp 0 076 0 006 calcification temperature r2 0 81 and covers the temperature range 3 1 c 16 5 c we applied our mg ca calibration to gravity core ps2495 3 from the mid atlantic ridge at 41 s to test its validity by reconstructing a low resolution record covering the last two glacial interglacial cycles our paleotemperature record reveals large changes in temperature for terminations i and ii when permanent thermocline temperature increased by as much as 8 c the g inflata paleotemperature record suggests that oceanic fronts repeatedly migrated over the location of core ps2495 3 during the last 160 kyr this study shows the potential of g inflata mg ca to reconstruct paleotemperatures in the permanent thermocline

determination of multiple element calcium ratios in foraminiferal calcite by quadrupole icp ms a method has been developed for rapid and precise simultaneous determination of nine element ca ratios in foraminiferal tests directly from intensity ratios using external matrix matched standards on a quadrupole inductively coupled plasma mass spectrometer icp ms all quantification isotopes are determined in pulse mode to avoid cross calibration small argide 40ar26mg interferences on 66zn are corrected by using two additional mg and zn standards a stable signal conducive for high precision measurements is obtained by cone conditioning variable calcium concentration has negligible effect on li al mn and sr but ca concentrations for standards and samples need to be constrained at a similar level for precise measurements of zn cd and u aliquots of samples are first analyzed for ca concentrations on an inductively coupled plasma atomic emission spectrometer icp aes and the remaining solutions are diluted to ca concentration of 100 ppm for ratio measurements to assure data quality the long term reproducibility of the method yielded precisions of li ca 2 4 b ca 4 2 mg ca 1 4 al ca 14 mn ca 0 9 zn ca 2 8 1 2 7 8 mol mol and 5 1 0 5 1 2 mol mol sr ca 0 9 cd ca 2 4 0 07 0 24 mol mol and 4 8 0 01 0 07 mol mol and u ca 2 5 for foraminiferal samples as small as 60 g

neogene shortening contribution to crustal thickening in the back arc of the central andes to illustrate the neogene shortening distribution in the back arc units of the central andes and to estimate the contribution of the shortening to crustal thickening two balanced crustal cross sections have been constructed across the northern and southern branches of the bolivian orocline total neogene shortening which varies from 191 to 231 km is accommodated by a crustal duplex below the cordillera oriental but is insufficient to produce the 70 km of crustal thickness evidenced by geophysical data below the altiplano the best explanation for this anomalous thickening seems to be crustal underplating by material tectonically eroded from the continental margin this process probably caused the altiplano uplift the subduction of oceanic lithosphere coupled with this underplating and a brief episode of gravity spreading of the altiplano constituted the driving forces that produced neogene shortening and development of the central andes

taphonomic and ontogenetic effects on na ca and mg ca in spinose planktonic foraminifera from the red sea as a recorder of the hydrological cycle and ocean circulation salinity is one of the most wanted parameters in paleoceanography current paleosalinity reconstructions mostly rely on the interpretation of stable oxygen isotope signals combined with an independent paleotemperature proxy due to error propagation this indirect approach is associated with large uncertainties recent culture studies and a red sea field study have shown that incorporation of na in foraminiferal shell calcite depends on salinity providing a potential direct proxy for salinity however application of a na ca based salinity proxy requires further calibration which should also consider settling of foraminifera through the water column and burial in the sediment here we compare na ca in living specimens from red sea surface waters with specimens collected from 0 to 500 m water depth and sedimentary specimens from core tops this shows that na ca in globigerinoides ruber and trilobatus sacculifer shells decrease with increasing water depth and until the sediment surface for both species laser ablation icp q ms measurements combined with electron probe microanalysis show that na is enriched in the spines loss of spines during settling of foraminifera through the water column hence provides a mechanistic explanation for the observed na decrease in bulk specimens with water depth in contrast average mg ca values increase toward the seafloor in both species coinciding with deposition of gametogenic calcite which is enriched in mg but has na ca values similar to that in lamellar calcite both spine shedding and gametogenic calcite addition hence affect the average minor trace element composition of foraminiferal calcite