the ultrapotassic rocks from southeastern spain the ultrapotassic rocks of orenditic affinity from southeastern spain have variable sio2 and mgo contents high k2o p2o5 ni cr ba ce th zr values and high k2ona2o nimgo ratios on the contrary tio2 nb y are moderate and feot cao v sc are low the parent magmas possibly generated from a phlogopite bearing mantle source enriched in many incompatible elements by metasomatic processes and probably they were characterized by very co2 co2 h2o ratio the low tip ratio and the moderate tio2 and nb contents in spite of the high alkaline element contents of the magmas suggest that titanium and niobium were retained in the source of the metasomatic fluids the low na contents may depend in part on the loss of this element via naf separation during the latest stage of crystallization crustal contamination cannot be excluded

composition of aqueous fluid coexisting with mantle minerals at high pressure and its bearing on the differentiation of the earth s mantle in order to understand the role of aqueous fluid on the differentiation of the mantle the compositions of aqueous fluids coexisting with mantle minerals were investigated in the system mgo sio2 h2o at pressures of 3 to 10 gpa and temperatures of 1000 to 1500 c with an ma8 type multianvil apparatus phase boundaries between the stability fields of forsterite aqueous fluid forsterite enstatite aqueous fluid and enstatite aqueous fluid were determined by varying the bulk composition at constant temperature and pressure the composition of aqueous fluid coexisting with forsterite and enstatite can be defined by the intersection of these two phase boundaries the solubility of silicate components in aqueous fluid coexisting with forsterite and enstatite increases with increasing pressure up to 8 gpa from about 30 wt at 3 gpa to about 70 wt at 8 gpa it becomes almost constant above 8 gpa the mg si weight ratio of these aqueous fluids is much higher than at low pressure 0 2 at 1 5 gpa and almost constant 1 2 at pressures between 3 and 8 gpa at 10 gpa it becomes about 1 4 aqueous fluid migrating upward through the mantle can therefore dissolve large amounts of silicates leaving modified mg si ratios of residual materials it is suggested that the chemical stratification of mg si in the earth may have been formed as a result of aqueous fluid migration

late cenozoic palaeobathymetry and geohistory analysis of central west timor eastern indonesia abstract results of quantitative correlations between late cenozoic benthic foraminiferal faunas from central west timor and recent faunas from the australian irian jaya continental margin provide high resolution palaeobathymetric criteria for geohistory analysis for the last 3 ma two periods of uplift were found in parts of the central basin on west timor one from 2 4 to 1 6 ma b p which decelerated from 5 to 0 5 mm per year and a second which started about 750 ka ago and then accelerated to acquire rates of up to 20 mm per year during the last 100 ka the step wise uplift history documents the response of this part of the foreland basin to the collision of the australian continental margin with the banda arc

fluxes of planktic foraminifera in response to monsoonal upwelling on the somalia basin margin abstract sediment trap samples collected off somalia bi weekly from early june 1992 through mid february 1993 show large seasonal variations in the shell flux and species composition of planktic foraminifera these variations mirror the monsoon driven circulation which resulted in massive upwelling and offshore eddy transport in summer during the sw monsoon june september and accounted for nearly 90 of the estimated annual shell flux of planktic foraminifera g bulloides dominated the sw monsoon along with g glutinata t quinqueloba n dutertrei and t iota in a fauna rich species but with a low diversity and equitability during the autumn intermonsoon november december the ocean became stratified and the nutrient exhausted whereas during the ne monsoon january march a warm surface mixed layer developed with the nutrients entrained by deep wind mixing it was dominated by g ruber in association with g tenella g aequilateralis g trilobus g sacculifer and g menardii in a fauna poorer in species but with a higher diversity and equitability consequently the ratio in the abundance of g bulloides and g ruber follows the monsoonal cycle closely as both species persist throughout the year only the rare g theyeri seems to be restricted to the sw monsoon in october at the end of the sw monsoon the trap at 265 m above the bottom intercepted massive amounts of fine grained carbonate m resuspended from the shelf and upper slope it contained extreme fluxes of bioclastic fragments benthic foraminifera and benthic ostracods as well as enhanced fluxes of small sized planktic foraminifera m notably g rubescens integrated over the year the species composition intercepted by the trap shows a very good match with the shell fauna in a core top sediment from the same site apparently the year estimated monsoonal record of planktic foraminifera which is strongly dominated by the sw monsoon production survives burial intact consequently the species composition of planktic foraminifera and measures such as the bulloides ruber ratio can be applied as a proxy for past changes in the intensity of the sw monsoon off somalia compared to the modern condition

migration of fluid phases and genesis of basalt magmas in subduction zones dehydration and hydration reactions in both the downgoing lithosphere and the overlying mantle wedge have been examined in order to understand the role of h2o in the production of magmas at convergent plate boundaries the subduction of oceanic lithosphere occurring with increasing pressures and rising temperatures causes liberation of h2o from the slab amphibole which can be stable to the highest pt conditions among hydrous phases in the slab decomposes at around 90 km depth it follows that the subducted lithosphere is essentially anhydrous beneath volcanic arcs lying more than 110 km above the slab and that the supply of slab derived h2o is not a direct trigger for the production of arc magmas instead the h2o released from downgoing lithosphere reacts with the forearc mantle wedge to crystallize hydrous minerals serpentine talc amphibole chlorite and phlogopite this hydrated peridotite is dragged downward on the slab toward higher pt regions and releases h2o to shallower potential magma source regions in the mantle wedge combining experimental data on the stability of serpentine and talc with the thermal structure in the mantle wedge it is concluded that those minerals decompose beneath the forearc region on the other hand high pt experimental and thermodynamic data suggest that dehydration of amphibole and chlorite in the downdragged hydrated peridotite can take place just beneath a volcanic front phlogopite in the peridotite decomposes to release h2o at a deeper level about 200 km h2o liberated from the hydrated peridotite causes partial melting of overlying mantle wedge peridotites along with the migration of h2o through the above processes subduction components especially large ion lithophile elements can be overprinted on the magma source region which governs the geochemical characteristics of arc magmas

mg si ratios of aqueous fluids coexisting with forsterite and enstatite based on the phase relations in the mg2sio4 sio2 h2o system direct observation of aqueous fluids coexisting with mgsio 3 enstatite and or mg2sio4 forsterite was performed at 0 5 5 8 gpa and 800 1000 c with an externally heated diamond anvil cell and synchrotron x rays at 1000 c in the mgsio3 h2o system forsterite crystallizes below 3 gpa but not above that pressure at 1000 c in the mg2sio4 h2o system forsterite congruently dissolves into the aqueous fluids up to 5 gpa these observations suggest that the aqueous fluids coexisting with enstatite and forsterite have mg si 1 below 3 gpa and 1 mg si 2 above that pressure comparison with the previous studies reporting mg si ratios of the aqueous fluid coexisting with enstatite and forsterite indicates that the mg si ratios change rapidly from sio2 rich to mgo rich at around 3 gpa and 1000 c this change can be related to possible structural changes of liquid water under these conditions the aqueous fluids coexisting with enstatite and forsterite do have mg si ratios similar to those found in the partial melts of h2o saturated peridotite somewhere within the upper mantle these two fluids unite to form a single regime and cannot be distinguished from each other

sedimentation under deep sea storms fast currents high concentrations of suspended sediment and grooved mud beds are associated with erosion in frequent abyssal storms where a fast deep mean flow is augmented or reversed by intense intermittent currents this occurs about 5 km below the gulf stream or its rings the waning phase of a storm results in development of bedforms and rapid deposition of a mud blanket several other regions of the world ocean display evidence of abyssal storm activity

late quaternary paleoproductivity and deep water circulation in the eastern south atlantic ocean evidence from benthic foraminifera abstract two late quaternary sediment cores from the northern cape basin in the eastern south atlantic ocean were analyzed for their benthic foraminiferal content and benthic stable carbon isotope composition the locations of the cores were selected such that both of them presently are bathed by north atlantic deep water nadw and past changes in deep water circulation should be recorded simultaneously at both locations however the areas are different in terms of primary production one core was recovered from the nutrient depleted walvis ridge area whereas the other one is from the continental slope just below the coastal upwelling mixing area where present day organic matter fluxes are shown to be moderately high recent data served as the basis for the interpretation of the late quaternary faunal fluctuations and the paleoceanographic reconstruction during the last 450 000 years nadw flux into the eastern south atlantic ocean has been restricted to interglacial periods with the strongest dominance of a nadw driven deep water circulation during interglacial stages 1 9 and 11 at the continental margin high productivity faunas and very low epibenthic 13c values indicate enhanced fluxes of organic matter during glacial periods this can be attributed to a glacial increase and lateral extension of coastal upwelling the long term glacial interglacial paleoproductivity cycles are superimposed by high frequency variations with a period of about 23 000 yr enhanced productivity in surface waters above the walvis ridge far from the coast is indicated during glacial stages 8 10 and 12 during these periods cold nutrient rich filaments from the mixing area were probably driven as far as to the southeastern flank of the walvis ridge

the system tonalite peridotite h 2 o at 30 kbar with applications to hybridization in subduction zone magmatism we present data on the phase relationships of mixtures between natural tonalite and peridotite compositions with excess h2o at 30 kbar and on the composition of the piercing point where the peridotite tonalite mixing line intersects the l ga opx reaction boundary these data in conjunction with earlier analogous data along peridotite granite and basalt granite mixing lines permit construction of a pseudoternary liquidus projection that is relevant to interaction of peridotite with slab derived magmas knowledge of the liquidus phase and temperature for a range of compositions within this projection enables us to map primary crystallization fields for quartz garnet orthopyroxene clinopyroxene and olivine and to estimate the distribution of isotherms across the projection using this projection we explore the consequences of peridotite assimilation by mafic to intermediate basalt to dacite hydrous slab derived melts progressive assimilation under isothermal conditions results in garnet precipitation as the melt composition traverses the garnet liquidus surface and then garnet orthopyroxene crystallization once the melt reaches the l ga opx field boundary the melt is constrained to remain on this field boundary and further assimilation of peridotite simply results in continued precipitation of garnet orthopyroxene until the melt is consumed the product is a hybrid solid assemblage consisting of ga opx it is noteworthy that this process drives the melt composition in a direction nearly perpendicular to the mixing line between peridotite and the initial melt if assimilation occurs with increasing temperature as might occur if a slab derived magma rises into the hotter mantle wedge intermediate magmas e g andesites will again precipitate garnet until they reach the l ga opx reaction boundary at which point ga re dissolves and orthopyroxene precipitates as the melt composition moves up temperature along this boundary the product of this process is a hybrid solid assemblage with garnet subordinate to orthopyroxene for more mafic initial compositions e g basalts originally plotting in the cpx field it appears possible to avoid field boundaries involving garnet and shift in composition more directly toward peridotite if assimilation is accompanied by a sharp increase in temperature considering published ree evidence arguing against garnet playing a significant role in the genesis of many subduction related magmas in light of our results it appears unlikely that peridotite assimilation by intermediate magmas under conditions of constant or increasing temperature is an important process in subduction zones however if assimilation is accompanied by an increase in temperature our data do permit the derivation of high mg basalts from less refractory precursors e g high al basalts by peridotite assimilation

multi stage metasomatism of diamondiferous eclogite xenoliths from the udachnaya kimberlite pipe yakutia siberia the primary garnet pyrope almandine omphacite cpx 1 6 5 7 wt na2o sulfide fe ni co mss assemblage of the two diamondiferous eclogite xenoliths studied u33 1 and ux 1 experienced two mantle metasomatic events the metasomatic event i is recorded by the formation of platy phlogopite 10 wt k2o prior to incorporation of the xenoliths in the kimberlite the bulk of the metasomatic alteration consisting of spongy textured clinopyroxene cpx 2a 1 3 wt na2o coarser grained clinopyroxene cpx 2b 2 5 wt na2o pargasitic amphibole 0 8 wt k2o 3 3 5 wt na2o kelyphite cpx 3 mostly 1 wt na2o and zoned mg fe al spinel sodalite calcite k feldspar djerfisherite k5 95na0 02fe18 72ni2 36co0 01cu4 08s26cl and a small amount of k ca fe mg glass is ascribed to the metasomatic event ii that occurred also in the upper mantle but after the xenoliths were incorporated in the kimberlite a pervasive chloritic alteration mainly clinochlore magnetite that overprints earlier assemblages probably took place in the upper crustal environment the diamonds are invariably associated with secondary clinopyroxene and chlorite but the diamonds formed before the entrainment of the xenoliths in the udachnaya kimberlite

hydrous phases and water transport in the subducting slab arc volcanoes are typically located 90 180 km above the surface of downgoing slabs as shown by wadati benioff deep seismic foci gill 1981 tatsumi 1989 the intimate relationship between the dip angles of the subducting slab and the locations of volcanic arcs indicates that subduction zone magmatism is triggered by material input from the subducting slab tatsumi and eggins 1995 the slab derived components are thought to be aqueous fluids or h2o rich partial melts of subducted oceanic crust therefore knowledge of the stability of hydrous phases and the chemical and physical properties of aqueous fluids in downgoing slabs is essential to understand the material transport in subduction zones in this section i will review the stability of hydrous phases in downgoing peridotite basalt and sediment systems and the chemical and the wetting properties of aqueous fluids recent experimental studies indicate that 3 4 gpa equivalent to 90 120 km depth is a key pressure where 1 the chemical compositions of silicate components dissolved in aqueous fluids equilibrated with mantle minerals approach the composition of mantle peridotite itself stalder et al 2001 mibe et al 2002 kawamoto et al 2004 2 the dihedral angle between olivine and aqueous fluids starts becoming smaller than 60 watson et al 1990 mibe et al 1998 1999 and 3 the immisciblity gap between peridotitic melts and aqueous fluids disappears and consequently hydrous minerals liberate supercritical aqueous fluids mibe et al 2004a 2006 the similarity between these pressures and the depths of downgoing slab underneath volcanic fronts where the maximum numbers of volcanoes are formed 124 38 km gill 1981 or 112 19 km tatsumi 1986 suggests that subduction zone magmatism can be triggered by the input of supercritical fluids from the downgoing peridotite and basalt many hydrous crystalline phases

aspects of atmospheric circulation the late pleistocene 0 950 000 yr record of eolian deposition in the pacific ocean rea d k 1990 aspects of atmospheric circulation the late pleistocene 0 950 000 yr record of eolian deposition in the pacific ocean palaeogeogr palaeoclimatol palaeoecok 78 217 227 the eolian component of pelagic sediments provides a proxy record of atmospheric circulation intensity and of dust transport examination of those records indicates that the atmosphere responds to orbital forcing but that during the past 875 000 years the variability in atmospheric circulation is at much shorter periods than the 100 000 year variation in ice volume the mid brunhes climatic event is well characterized in the eolian grain size records and in records of sea surface phenomena it is not seen in proxy indicators of either deep water or ice volume variability the increase in the amplitude of paleoclimatic variability that denotes the early late pleistocene transition occurs suddenly about 875 000 years ago in the eolian grain size record which is about 20 000 to 25 000 years earlier than the transition in the deep sea caco3 dissolution record or in the 8180 proxy record of ice volume

variations of the northwest australian summer monsoon over the last 300 000 years the paleohydrological record of the gregory mulan lakes system abstract monsoon rains in the kimberley region feed an interconnected chain of lake basins the gregory lakes system in northwestern australia a terminal system surrounded by dunefields of the great sandy desert this semi arid region records a sequence of quaternary climatic changes at times much wetter at times much drier than today a morphostratigraphic sequence defines episodic formation of dunes and related sediments reflecting past hydrologic and climatic changes which caused them thermoluminescence dating provides a broad temporal framework identifying major hydrologic changes of the past 300 ka ancient foreshore dunes define shorelines of mega lake phases the largest of which covered some 6500 km2 with ages near 300 ka later lacustral expansions near 200 and 100 ka reflect wet phases broadly comparable to marine isotope stages 7 and 5 with a trend towards increasing aridity through time longitudinal quartz dune formed within the mega lake confines between successive wet phases with at least two dune building episodes near or just before 230 and 70 ka monsoon activity today produces short lived flood events such as recorded in 1993 climates of the mega lake phases need not be drastically different from today s although a substantial increase in the frequency of high magnitude events was certainly involved

the importance of the oxygen minimum zone and sediment geochemistry in the distribution of recent benthic foraminifera in the northwest indian ocean abstract the relationship between the distribution of benthic foraminifera and sediment type and depositional environment in the arabian sea is discussed the benthic foraminiferal fauna were sampled in nineteen recent surface sediment samples and geochemical variables of the sediment of the same samples were measured the water depths for the box core samples varies from 440 to 4040 m a total of 103 species and six species complexes were identified the geochemical properties were found to correspond well to the sediment type and depositional environment and six different sediment depositional environment types could be distinguished analysis of the benthic foraminiferal fauna reveals specific faunal assemblages that are closely related to these sediment depositional environment types

atmospheric hydrospheric mechanisms of climate anomalies in the western equatorial indian ocean atmosphere ocean mechanisms of rainfall anomalies at the coast of eastern africa are studied using long term ship observations in the indian ocean surface current measurements subsurface casts upper air analyses by the european centre for medium range weather forecasts rain gauge series in eastern africa and india and an index of the southern oscillation so the high so phase being defined by anomalously high low pressure at tahiti darwin the causalities of precipitation anomalies at the coast of eastern africa differ for the two rainy seasons centered on april may and october november and only the latter is strongly related to the so in the high so phase april may pressure is low over the entire indian ocean domain whereas in october november pressure is high in the west and low in the east concomitantly surface waters are anomalously cold in the west and strong westerlies sweep the equatorial zone of the indian ocean eastern african rainfall anomalies are related to the so through a combination of cooperative mechanisms that function most effectively in the boreal autumn rainy season of eastern africa 1 equatorial westerly winds are conducive to lower tropospheric divergence over equatorial east africa and in the high so phase these are accelerated especially in october november owing to the anomalous eastward pressure gradient 2 the equatorial westerly winds drive the eastward equatorial jet in the upper hydrosphere which entails cold water upwelling in the western extremity of the basin where sea surface temperature further hydrostatically affects the zonal pressure gradient and thus feeds back into the equatorial westerly winds 3 in addition cold water anomalies in the western indian ocean most pronounced in october november during the high so phase also suppress convection 4 in the high so phase the indian summer monsoon tends to be strong leaving behind an anomalously cold western indian ocean which in turn feeds into mechanisms 1 to 3 the eastward equatorial jet thus has a role to play in feedback mechanisms contributing to the anomalies of the boreal autumn rains at the coast of eastern africa

rapid quench hydrothermal experiments at mantle pressures and temperatures new experimental methods for the encapsulation extraction and analysis of large volumes of aqueous fluids enable studies of mineral solubilities and dissolution kinetics with the piston cylinder apparatus quench rates and volumes of experimental fluids with these methods are comparable with those used in modern hydrothermal experiments employing cold seal vessels analyses of fluid compositions are reproducible and consistent with independent results the techniques permit experimental investigations that will better characterize fluid rock interaction in such environments as subducting slabs the mantle wedge barrovian metamorphic belts and middle to lower crustal granulites

an early miocene atlantic wide foraminiferal palaeoceanographic event abstract in the lower miocene deep sea record of the atlantic ocean a foraminiferal assemblage dominated by small smooth thin walled bolivinids occurs at several sites in different regions from 20 17 ma no modern deep sea analogues are known but such assemblages are present in modern environments in the upper bathyal zone within the oxygen minimum zone we interpret this as reflecting lowered oxygen conditions in the deep atlantic ocean perhaps resulting from a period of sluggish bottom water circulation in the early miocene ocean this was a period of major change in global 13 c equivalent to the beginning of the monterey carbon excursion

the ecology of living stained deep sea benthic foraminifera from the sulu sea the distribution of living rose bengal stained deep sea benthic foraminifera was determined in the upper 20 cm of sediments of eight soutar box cores taken from two depth transects 510 4515 m in the thermospheric 10 c sulu sea despite the uniformity of bottom water temperatures salinities and dissolved oxygen levels below 1000 m significant faunal differences exist at different depths in the low oxygen 1 25 ml l below 1000 m basin the shallowest site 510 m is dominated 10 of the calcareous fauna by cibicidoides uvigerina 150 m and bolivina 63 m while siphonina is codominant with cibicidoides and uvigerina in the 1005 m core the 2000 m cores are dominated by cibicidoides gyroidinoides and oridorsalis while cibicidoides bradyi and oridorsalis umbonatus dominate the 3000 and 4000 m cores infaunal assemblages of valvulineria mexicana are found in the sediments of the 4515 m core relatively low bottom water oxygen values do not necessarily yield typical low oxygen taxa such as bolivina uvigerina chilostomella bulimina and globobulimina changes in the abundances of these taxa in fossil assemblages have been used as indicators of changes in ancient bottom water oxygen levels but may instead reflect organic carbon contents of the sediments an examination of the vertical distributions of foraminiferal assemblages from the 63 m and 150 m fractions reveals that taxa have microhabitat preferences similar to those observed in other regions taxa found in the upper 0 to 1 cm interval epifaunal include cibicidoides wuellerstorfi and hoeglundina elegans while taxa such as chilostomella and globobulimina reach maximum abundances in subsurface sediments and have infaunal microhabitat preferences cibicidoides bradyi and o umbonatus live in sediment depths from 0 to 4 cm and have transitional preferences with both epifaunal and infaunal occurrences intrageneric differences in test morphologies including pore distribution rounded peripheries and variable spire height are observed in cibicidoides and gyroidinoides and are suggested to be related to microhabitat preferences vertical distributions of a number of taxa found in both the 63 to 150 m and 150 m fractions are similar suggesting that juveniles and adults live under similar microhabitat conditions ontogenetic changes in microhabitat preferences of most species are not observed in this study and therefore would not be expected to account for isotopic vital effects reported for some taxa in previous studies

sediment waves in the eastern equatorial atlantic sediment record during late glacial and interglacial times standing and migrating sediment waves along the west african continental rise 3000 4500 m water depth are characterized by a regular spacing of wave length periods that are multiples of 280 m and by long term pelagic sediment composition interpretations of their origin must account for the following evidence 1 the wave crests generally run parallel or oblique to the continental rise and also to prevailing net currents as confirmed by sea beam data 2 migrating waves along the west african continental margin are directed only upslope i e towards the east 3 the waves have been accreting for a long time 1 ma 4 glacial to interglacial differences in the evolution of sediment accumulation rates on crests and troughs may indicate that the accreting regime was intermittent and that the waves were more levelled prior to 7500 years bp due to increased deposition of siliciclastic matter in the troughs 5 absent patterns of grain size sorting in the fine grained muds contradict conventional models of current related sediment transport a superposition of large tidal components and slow thermohaline net currents lonsdale 1978 secondary current processes unsold pers comm or a superposition of internal waves and thermohaline currents kolla et al 1980 are regarded as the most probable modes of origin

association of bathyal foraminifera with water masses in the northwestern gulf of mexico abstract q mode cluster analysis and r mode factor analysis of benthic foraminiferal data from 120 core tops from the northwestern gulf of mexico 87 1361 m 26 4 29 0 n 88 5 96 4 w distinguish separate thanatotopes and faunal assemblages related to the five water masses present within the depth range of the samples these water masses are the surface mixed layer sml gulf water gw oxygen minimum water omw subantarctic intermediate water saiw and caribbean midwater cmw reussella atlantica bigenerina irregularis and angulogenerina bella are particularly associated with sml bulimina spicata planulina foveolata and cibicidoides umbonatus with gw sphaeroidina bulloides bulimina mexicana and siphonina bradyana with omw epistominella exigua with saiw and gyroidinoides laevis cibicides wuellerstorfi pullenia subsphaerica bulimina aculeata gyroidinoides polius and laticarinina pauperata with cmw cluster analysis also indicates the presence of three faunal groups related to water depth and bottom water oxygen content within the omw assemblage an additional assemblage recognized in the mississippi river delta area may be related to low oxygen conditions above the normal depth for the oxygen minimum the close correspondence between the results of cluster and factor analyses suggests that similar numerical analyses of fossil data should be useful in deciphering ancient bathyal assemblages influenced by water mass properties

uvigerina proboscidea abundances and paleoceanography of the northern indian ocean dsdp site 214 during the late neogene abstract this study attempts to understand the significance of uvigerina proboscidea in paleoceanographic reconstructions at the northern tropical indian ocean dsdp site 214 from the late miocene through the pleistocene in this interval at this site u proboscidea is the most abundant species of the benthic assemblage and shows abrupt frequency changes about 1 74 based on relative percentages of u proboscidea calibrated with oxygen and carbon isotope record and the sediment accumulation rates the modern distribution of the species in the indian ocean and other evidence the peaks of abundance of u proboscidea are inferred to represent times of high surface productivity this productivity is related to intensified trade winds during strong southwest sw indian monsoons causing widespread upwelling along equatorial divergence in the indian ocean the sudden increase of u proboscidea abundance at approximately 8 5 7 5 ma reflects significant upwelling at the equatorial divergence this event corresponds to the permanent build up of west antarctic ice sheets and a major increase in sw indian monsoons related upwelling in the northwestern indian ocean the chron 6 carbon shift at approximately 6 2 ma is marked by another peak of abundance reflecting widespread ocean fertility the highest abundances of u proboscidea and highest sediment accumulation rates occur between 5 8 and 5 1 ma which coincides with the greatest development of antarctic ice sheets and strong southwest monsoons the higher percentages at 3 2 3 1 ma approximately 2 4 ma and 1 6 ma all represent phases of high productivity at the equatorial divergence

the role of sea surface temperature as a control on carbonate platform development in the western coral sea the derivation of a detailed sea surface paleotemperature curve for the middle miocene holocene 10 0 ma from odp site 811 on the queensland plateau northeast australia has clarified the role of sea surface temperature fluctuations as a control on the initiation and development of the extensive carbonate platforms of this region this curve was derived from isotopic analyses of the planktonic foraminifer globigerinoides ruber and converted to temperature using the surface water paleotemperature equation accounting for variations in global ice volume the accuracy of these data were confirmed by derivation of paleotemperatures using the water column isotopic gradient 13o corrected for salinity and variations in seafloor water mass temperature results indicate that during this period surface water temperatures were on average greater than the minimum required for tropical reef growth 20 c veron 1986 with the exception of the late miocene and earliest early pliocene 10 4 9 ma when there were repeated intervals of temperatures between 18 20 c tropical reef growth on the queensland plateau was extensive from the early to early middle miocene 21 13 ma after which reef development began to decline a lowstand near 11 ma probably exposed shallower portions of the plateau after re immersion near 7 ma the areal extent of reef development was greatly reduced 50 paleotemperature data from site 811 indicate that decreased sea surface temperatures were likely to have been instrumental in reducing the area of active reef growth on the queensland plateau reduced reefal growth rates continued until the late pliocene or quaternary despite the increase of average sea surface paleotemperatures to 22 23 c studies on modern corals show that when sea surface temperatures are below 24 c as they were from the late miocene to the pleistocene off northeast australia corals are stressed and growth rates are greatly reduced consequently when temperatures are in this range corals have difficulty keeping pace with subsidence and changing environmental factors in the late pliocene sedimentation rates increased due to increases in non reefal carbonate production and falling sea levels it was not until the mid quaternary 0 6 0 7 ma that sea surface paleotemperatures increased above 24 c as a result of the formation of a western coral sea warm water pool because of age discrepancies it is unclear exactly when an effective barrier developed on the central great barrier reef the formation of the warm water pool was likely to have either assisted the formation of this barrier and or permitted increased coral growth rates fluctuations in sea surface temperature can account for much of the observed spatial and temporal variations of reef growth and carbonate platform distribution off northeast australia and therefore we conclude that paleotemperature variations are a critical control on the development of carbonate platforms and must be considered an important cause of ancient platform drowning

recent benthic foraminifera from the eastern south atlantic ocean dependence on food supply and water masses abstract sixty surface sediment samples from the eastern south atlantic ocean including the walvis ridge the angola and cape basins and the southwest african continental margin were analysed for their benthic foraminiferal content to unravel faunal distribution patterns and ecological preferences live stained with rose bengal and dead faunas were counted separately and then each grouped by q mode principal component analysis into seven principal faunal end members then multiple regression technique was used to correlate recent assemblages with available environmental variables and to finally differentiate between four principal groups of environmental agents acting upon the generation of benthic foraminiferal assemblages 1 seasonality of food supply and organic carbon flux rates together with oxygen content in the pore and bottom waters 2 lateral advection of deep water masses 3 bottom water carbonate corrosiveness and 4 energetic state at the benthic boundary layer and grain size composition of the substrate food supply and corresponding dissolved oxygen contents in the pore and bottom waters turned out to be the most important factors which control the distribution pattern of the recent benthic foraminifera at the continental margin in the zone of coastal upwelling and its mixing area benthic foraminiferal assemblages are dominated by stenobathic high productivity faunas characterized by elevated standing stocks low diversities and a large number of endobenthic living species at the continental shelf and upper continental slope the live assemblages are characterized by rectuvigerina cylindrica uvigerina peregrina s 1 uvigerina auberiana and rhizammina spp while the dead assemblages are characterized by cassidulina laevigata bolivina dilatata bulimina costata and b mexicana at the lower continental slope strong influence of high organic matter fluxes on the species composition is restricted to the area off the cunene river mouth where the live assemblage is dominated by uvigerina peregrina s 1 the corresponding dead assemblage by melonis barleeanum and m zaandamae in the adjacent areas of the lower continental slope the biocoenosis is characterized by reophax bilocularis and epistominella exigua which becomes dominant in the corresponding dead assemblage at the walvis ridge and in the abyssal angola and cape basins where organic matter fluxes are low and highly seasonal benthic foraminiferal assemblages reflect both the oligotrophic situation and the deep and bottom water mass configuration the top and flanks of the walvis ridge are inhabited by the rhizammina psammosphaera and r bilocularis live assemblages the corresponding dead assemblages are dominated by g subglobosa on the ridge top and e exigua on the flanks within the highly diverse e exigua dead assemblage several associated epibenthic species coincide with the core of nadw between about 1600 and 3700 m water depth these species include osangularia culter cibicidoides kullenbergi melonis pompilioides bolivinita pseudothalmanni and bulimina alazanensis the assemblages of the abyssal cape and angola basins are characterized by nuttallides umbonifer and a high proportion of agglutinated species these species are adapted to very low organic matter fluxes and a carbonate corrosive environment

factors influencing the distribution patterns of recent deep sea benthic foraminifera east of new zealand southwest pacific ocean abstract this study investigates which combination of environmental factors most strongly influences the distribution patterns of benthic foraminferal tests 0 63 m in a region bisected by the subtropical front east of new zealand seafloor sample sites extend from outer shelf 90 m to abyssal 4700 m depths across substrates ranging from biogenic terrigenous gravelly sand to hemipelagic mud and occur under the influence of antarctic intermediate water aaiw and circumpolar deep waters as well as receiving detritus from both subtropical and subantarctic surface water masses elevated values of the planktic foraminiferal fragmentation index and reworked small paleogene planktic foraminifera at outer shelf and bathyal depths coincide with areas of strong bottom currents q mode cluster analysis on the census counts of 398 benthic species clusters the 66 samples into three large groups shallow bathyal abyssal and at a lower level 10 mappable associations are recognised a combination of canonical correspondence analysis and a correlation coefficient matrix was used to relate the faunal data to a set of measured environmental proxies these analyses show that factors that have a relationship with depth are the most significant in determining foraminiferal distribution the principal environmental factors which appear to most strongly influence this benthic foraminiferal distribution are dissolved oxygen content in bottom waters sustainability of organic carbon flux rates seasonality of food supply lateral advection of water masses bottom water carbonate corrosiveness energetic state at the benthic boundary layer grain size composition of substrate salinity and temperature of the bottom waters shallow water associations 90 1250 m dominated by cassidulina carinata and trifarina angulosa occur within coarse substrates under well oxygenated high energy regimes and sustained food input the occurrence of the bathyal associations 230 2840 m dominated by c carinata alabaminella weddellensis and abditodentrix pseudothalmanni closely mirrors the distribution of aaiw within a region of variable food supply the sustainability of food supply combined with bottom water type and associated ventilation and dissolution strongly influence the composition of abyssal associations 1200 4700 m mostly dominated by epistominella exigua and a weddellensis

globally increased pelagic carbonate production during the mid brunhes dissolution interval and the co2 paradox of mis 11 the mid brunhes dissolution interval mbdi represents a period of global carbonate dissolution lasting several hundred thousand years centred around marine isotope stage mis 11 here we report the effects of dissolution in odp core 982 taken from 1134 m in the north atlantic paradoxically records of atmospheric co2 from antarctic ice cores reveal no long term trend over the last 400 kyr and suggest that co2 during mis 11 was no higher than during the present interglacial we suggest that a global increase in pelagic carbonate production during this period possibly related to the proliferation of the gephyrocapsa coccolithophore could have altered marine carbonate chemistry in such a way as to drive increased dissolution under the constraints of steady state an increase in the production of carbonate in surface waters would cause a drawdown of global carbonate saturation and increase dissolution at the seafloor in order to reconcile the record of atmospheric co2 variability we suggest that an increase in the flux of organic matter from the surface to deep ocean associated with either a net increase in primary production or the enhanced ballasting effect provided by an increased flux of caco3 could have countered the effect of increased calcification on co2

a record of fire vegetation and climate through the last three glacial cycles from lombok ridge core g6 4 eastern indian ocean indonesia abstract charcoal elemental carbon and clastic particle analyses have been undertaken on tropical marine core g6 4 collected from the eastern indian ocean between the lesser sunda islands of indonesia and northwestern australia to help interpret an existing pollen record in addition a new oxygen isotope record has been constructed and several radiocarbon dates produced to allow a refinement of the chronology of the core the record covers the last 300 000 years with three clear glacial interglacial cycles however the new oxygen isotope record and radiocarbon dates suggest a hiatus and it appears that most isotope stage 3 is missing interglacials are characterised by higher values of mangrove fern and rainforest pollen indicating wetter conditions than intervening glacials which have higher cyperaceae and chenopodiaceae values gramineae percentages are also generally higher during glacials but there is a sustained increase in grasses relative to eucalyptus about 185 000 years ago originally interpreted as a change to drier conditions an increase in burning from about 200 000 years ago from charcoal evidence suggests that fire may have been an important contributing factor this and subsequent increases in charcoal may reflect anthropogenic burning and are considered in relation to archaeological evidence for possible times of arrival of people within australia the elemental carbon record shows major differences to that from charcoal and further research is needed to interpret its meaning little consistent evidence for changes in climate or vegetation disturbance is provided by clastic particle influx which may well reveal a record of volcanicity within the region

research perspectives of sediment waves and drifts monitors of global change in deepwater circulation the purpose of this special section in paleoceanography is to present interdisciplinary approaches for contributing to the reconstruction of ocean circulation and its response to climate changes a high priority objective for understanding the causes and mechanisms of climate change is the monitoring of past ocean circulation and oceanic heat and nutrient transport lehman and keigwin 1992 have shown that cooling for example during the younger dryas event may have culminated in a cessation of the oceans conveyor circulation the cooling in the north atlantic was apparently the result of reduced northward heat transport in the upper water masses of the north atlantic conveyor belt in contrast intervals with a strong surface and deepwater circulation were marked by a high northward heat transport for the understanding of the causes and the timing of such rapid highfrequency events marine records of high deposition ratecores are needed these cores should provide evidence for changes in abyssal circulation and heat transport as well as arecord of surface and deepwater characteristics the sediment drifts of the north atlantic and in other ocean basins are one of the major targets for the recovery of sediments with high deposition rates 10 cm kyr and for reconstructing the role of both intermediate and deepwater production in the conveyor belt that is drawing low latitude heat northward we stress the need for international programs targeting high deposition rate areas on sediment drifts and sediment waves in order to understand 1 the evolution of the conveyor belt and 2 its dynamics and variability the north atlantic where sediment drifts are concentrated will provide ideal study areas with time resolutions comparable to those of ice core records but with records linked directly to the record of changing bottom water flow therefore one can address the changes in circulation heat and carbon budget on high and ultrahigh resolution records

indian ocean high productivity event 10 8 ma linked to global cooling or to the initiation of the indian monsoons uplift of the himalayas and tibetan plateau ca 10 8 ma has been said to be the main cause of the origin or intensification of the indian monsoon system because mountains modulate the land sea thermal contrast the intensification of the monsoons in turn is seen as the cause of major changes in fauna and flora on land as a result of changing precipitation patterns as well as in the indian ocean where the monsoons drive increased upwelling and thus increased productivity we argue that the interactions between the elevation of the himalayas and tibetan plateau the onset of the monsoons and their effects on the indian ocean biota remain uncertain the timing of these events uplift monsoons and biotic change is not well constrained neogene deep sea benthic foraminiferal faunal and isotope records of the ninetyeast ridge combined with published data show that a major increase in bio genic productivity occurred at 10 8 ma throughout the indian ocean the equatorial pacific and southern atlantic we suggest that this indian ocean high productivity event was not simply the result of monsoon induced upwelling or nutrient delivery from the weathering of newly uplifted mountains but may have been caused by strengthened wind regimes resulting from global cooling and the increase in volume of the antarctic ice sheets

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

temporal variability in living deep sea benthic foraminifera a review the deep ocean environment is disturbed by various processes many of which involve episodic inputs of organic matter some inputs e g phytodetritus at mid high latitudes in the north atlantic and northeast pacific are seasonally pulsed others e g falls of whale carcasses are irregular and unpredictable but together they evoke a variety of responses from the benthic biota in the case of deep sea foraminifera only those responses arising from seasonal food pulses have been fairly well documented the population dynamics of deep sea benthic foraminifera total live populations and individual species appear to be controlled largely by two inversely related parameters the flux of organic matter to the seafloor and concentrations of oxygen in the sediment porewater organic matter food inputs are most intense along bathyal continental margins and their oxidation often leads to the depletion of oxygen in surface sediments under these conditions foraminiferal faunas are dominated by low oxygen tolerant infaunal species the abundance of which fluctuate in response to seasonally varying amounts of food and oxygen at some sites e g sagami bay off japan species migrate up and down in the sediments tracking critical oxygen concentrations where oxygen concentrations are consistently low less than about 0 5 ml l 1 as in parts of the california borderland foraminifera may undergo population increases solely in response to food pulses in the abyssal north atlantic and in some continental margin areas of this ocean organic matter inputs are weaker and do not lead to oxygen depletion within surface sediments these systems are food limited and seasonal population fluctuations reflect the availability of food phytodetritus rather than oxygen here the species which respond to phytodetritus are mainly epifaunal or shallow infaunal opportunists which represent a small proportion of highly diverse communities 2 or 3 out of 120 species per core of 25 5 cm2 surface area seasonal phytodetrital pulses to the deep seafloor and hence foraminiferal population dynamics are not entirely predictable being dependent on climatic and upper ocean processes they vary in intensity from year to year and occasionally e g at the porcupine abyssal plain pap in 1997 fail to materialise foraminiferal responses to irregular non seasonal organic matter inputs are poorly known however there is some evidence that whale falls turbidite deposits hydrothermal vents and seeps are exploited by species typical of organically enriched low oxygen environments rather than by a specialised fauna fossil foraminiferal assemblages from bathyal and abyssal environments may provide evidence for an increase or decrease in the seasonality of surface production as well as for longer term changes in palaeoproductivity however the accurate interpretation of this record depends on filling the many gaps which remain in our understanding of relations between benthic foraminiferal ecology and seasonal phenomena in the deep ocean

late pleistocene to holocene productivity changes in the western equatorial pacific sulu sea philippines from calcareous nannofossils abstract we present a new calcareous nannofossil paleoproductivity reconstruction of the southeastern margin of the sulu sea to understand how marine productivity varied through time in one of the major fishing grounds of the philippine archipelago the study is based on two sediment cores obtained from two different hydrographic locations in the western equatorial pacific region an upwelling region off zamboanga peninsula u gc12 and a non upwelling area off panay island nu gc14 covering the past 18 000 years before present b p calcareous nannofossil assemblages in the investigated areas were of low diversity and largely dominated by gephyrocapsa oceanica and florisphaera profunda followed by small placolith bearing taxa emiliania huxleyi small gephyrocapsa and reticulofenestra minuta upwelling episodes off the zamboanga peninsula were recorded several times in the past as shown by an increase in the abundance of high productivity indicator species g oceanica small gephyrocapsa e huxleyi and of bulk sediment caco3 and a concomitant decline in the total organic carbon toc the high abundance of low surface water productivity species f profunda and umbellosphaera irregularis indicates a stratified water column with a deeper nutricline probably caused by the reduced upwelling intensity this condition was corroborated by the decrease in caco3 and an increase in toc we propose that the modern day high productivity conditions off zamboanga peninsula started at 2500 years b p whereas the low productivity off panay island was recorded from 4000 years b p and persists to the present day evidence of the younger dryas yd event was recorded from 11 100 to 10 400 years b p in u gc12 synchronous to the yd event reported from other areas in the northern hemisphere and in accordance with the timing in the sulu sea as reported from previous studies in this region this event in the sulu sea is characterized by a decrease in total nannofossil abundance and estimated primary productivity together with an increase in caco3 and a decrease in toc we interpreted that dilution caused by the increase in precipitation experienced in the southeast asian region during the yd event could have led to the decline of the total calcareous nannofossils whereas the recorded increase in caco3 is attributed to the high abundance of planktonic foraminifera during this interval

formation of ultrafine particles from impact generated supercritical water abstract shock recovery experiments were performed targeting an olivine iron and water mixture to simulate a low velocity ocean impact event the maximum pressure in the sample container reached 20 gpa during the experiments ultrafine particles ups of olivine and metal oxides were newly formed even at pressures less than their vaporization pressure 150 200 gpa impedance match and thermodynamic calculations suggest that supercritical water formed during the shock wave traversal such supercritical water dissolves impacted materials and precipitates ups results of our experiments further suggest that many extraterrestrial objects that have impacted on oceans might have been converted to large masses of ups and probably influenced the climate and uv shielding especially during the late hadean and early archean eras

the distribution of living benthic foraminifera on the continental slope and rise off southwest norway abstract surface sediment samples taken by corer from 45 stations on the norwegian continental margin and in the norway basin have been investigated for their benthic foraminiferal content unlike previous studies the living benthic foraminiferal fauna was differentiated from empty tests comprising the foraminiferal death assemblage factor analysis of both the living and dead faunal data reveals six living species assemblages and five corresponding dead assemblages the additional living assemblage is characterized by the arenaceous speciescribrostomoides subglobosum that dominates between 1400 and 2000 m water depth but is rare in the dead faunal data trifarina angulosa and to a lesser extent cibicides lobatulus characterize the shallowest foraminiferal assemblage from 200 to 600 m water depth where it is associated with strong bottom currents and warm saline atlantic water of the north atlantic drift on the slope between 600 and 1200 m water depth themelonis zaandami species assemblage dominates particularly in areas characterized today by rapid sedimentation of terrigeneous material between 1000 and 1400 m depth where the slope is covered by fine grained organic rich terrigeneous mud the living foraminiferal assemblage is characterized bycassidulina teretis andpullenia bulloides below 1400 m three foraminiferal assemblages are found c subglobosum is found from 1400 to 2000 m cibicidoides wuellerstorfi andepistominella exigua predominantly live from 2000 to 3000 m water depth and below 3000 m oridorsalis umbonatus andtriloculina frigida dominate the fauna all of theelphidium excavatum tests found in this study and thecassidulina reniforme tests found above 500 m water depth were found to be reworked analysis of the sediment grain size distribution and the organic carbon content in surface samples from the deepest stations suggest that the abundance ofc wuellerstorfi ande exigua is positively correlated to relatively coarse caused by planktic foraminifera and organic rich sediments whereas high frequencies ofo umbonatus andt frigida coincide with low organic carbon content we suggest thatc wuellerstorfi is adapted to deep sea environments with relatively high food supply tolerating relatively low interstitial water oxygen content whereaso umbonatus may tolerate lower food supply prefering well oxygenated interstitial waters

mid holocene evolution and paleoenvironments of the shoreface offshore transition north eastern argentina new evidence based on benthic microfauna abstract a sedimentary record spanning 5792 5511 cal yr bp and 3188 2854 cal yr bp was recovered at 36 45 43 s 56 37 13 w south west south atlantic the sedimentological features and micropaleontological benthic foraminifera and ostracoda content were analyzed in order to reconstruct paleoenvironmental conditions considerable environmental fluctuations are indicated by all these proxies five different stages were distinguished stage 1 ca 5800 5000 cal yr bp consists of muddy sand with abundant microfossils in this interval species typical for inner marine shelf environments maintained a high abundance stage 2 consists of plastic light greenish grey clays barren of microfossils and probably represents fluvial input from the de la plata river to the shelf contemporaneous of a lowering of sea level stage 3 is composed of brownish yellow sandy silts and represents increasing marine conditions in the area as reflected by higher faunal diversity and typical foraminifera of inner shelf environments stage 4 is made of homogeneous mud barren of microfossil which represents a new pulse of fluvial input to the shelf in consequence of a new fall in sea level the final part of the core stage 5 is a coarsening upward sequence grading from greeny brown clayey sandy silts to coarse shelly sands and represents the modern sedimentation in the area this interpretation strengthens the stepped model of late holocene sea level fall between 5511 5792 cal yr bp and 2854 3188 cal yr bp in buenos aires coast and agrees with the relative sea level history previously proposed by some authors from western south atlantic coasts

the influence of the ne winter monsoon on productivity changes in the gulf of aden nw arabian sea during the last 530ka as recorded by foraminifera abstract benthic and selected planktic foraminifera and stable isotope records were determined in a piston core from the gulf of aden nw arabian sea that spans the last 530 ka the benthic foraminifera were grouped into four principal assemblages using q mode principal component analyses comparison of each of these assemblages with the fauna of the nearby regions enabled us to identify their specific environmental requirements as a function of variability in food supply and strength of the oxygen minimum zone and by that to use them as indicators of surface water productivity the benthic foraminiferal productivity indicators coupled with the record of globigerina bulloides a planktic foraminifer known to be sensitive to productivity changes in the region all indicate higher productivity during glacial intervals and productivity similar to present or even reduced during interglacial stages this trend is opposite to the productivity pattern related to the sw summer monsoon of the arabian sea and indicates the role of the ne winter monsoon on the productivity of the gulf of aden a period of exceptionally enhanced productivity is recognized in the gulf of aden region between 60 and 13 kyr indicating the intensification of the ne winter monsoon to its maximal activity contemporaneous indication of increased productivity in other parts of the arabian sea unexplained so far by the sw summer monsoon variability might be related to the intensification of the ne winter monsoon another prominent event of high productivity second in its extent to the last glacial productivity event is recognized between 430 and 460 kyr these two events seem to correspond to periods of similar orbital positioning of rather low precession and eccentricity amplitude for a relatively long period glacial boundary conditions seem to control to a large extent the ne winter monsoon variability as also indicated by the dominance of the 100 ka cycle in the investigated time series secondary in their importance are the 23 and 41 ka cycles which seem also to contribute to the ne monsoonal variability following the identification of productivity events related to the ne winter monsoon in the gulf of aden it is possible now to extend this observation to other parts of the arabian sea and consider the contribution of this monsoonal system to the productivity fluctuations preserved in the sedimentary records

late quaternary productivity changes in the equatorial indian ocean odp hole 716a abstract the equatorial indian ocean is swept by the indian ocean equatorial westerlies iew which intensify in monsoon transitions during april may and october november driving eastward equatorial current eec to the upper ocean the eec brings significant changes in the surface productivity in the equatorial region influencing the life style of the surface and deep sea fauna this study is aimed at understanding 300 kyr record 450 150 kyrs ago of productivity changes linked to variations in iew eec in the equatorial indian ocean using high resolution microfaunal record from integrated ocean drilling program iodp hole 716a maldives ridge in total 451 core samples of 10 cm 3 volume from the 300 kyr long sequence ranging 450 150 kyrs ago were analyzed at every 1 cm interval to generate census data of the benthic foraminiferal fauna factor and cluster analyses using percentages of 53 highest ranked benthic foraminiferal species were run that enabled us to identify five biofacies indicating the varied nature of deep sea environments during the late quaternary the results show a major shift roughly 300 kyr ago across marine isotope stages 9 and 8 mis 9 8 recorded in this study as mid brunhes transition at hole 716a the present study also combines published planktic foraminiferal fauna and pteropod records from hole 716a to understand if the surface to shallow and intermediate water paleoenvironments were coupled with deep water changes during the late quaternary in the maldivian archipelago biofacies robulus nicobarensis trifarina reussi rn tr uvigerina porrecta reussella simplex upo rs and cymbaloporetta squammosa bolivinita sp cs bsp dominate before the mid brunhes transition and document high organic flux with relatively low oxygen paleoenvironment similar to the planktic foraminifer globigerina bulloides population while benthic foraminiferal biofacies hoeglundina elegans miliolinella subrotunda he ms and uvigerina peregrina quinqueloculina seminulum upe qs record high seasonality in food supply with well oxygenated deep water following the mid brunhes climatic transition 300 kyr ago at hole 716a these changes are also recorded in the population of planktic foraminiferal species globigerinoides ruber and neogloboquadrina dutertrei as well as pteropods organic carbon flux linked to changes in the iew eec strength appears to be the most plausible factor controlling faunal assemblages and hence paleoproductivity dynamics in the maldivian region our results suggest that the strength of the iew is inversely related with the indian ocean dipole iod the iod strengthened across mis 9 8 during which time the iew weakened leading to major changes at hole 716a

sodium rich metasomatism in the upper mantle implications of experiments on the pyrolite na2o rich fluid system at 950 c 20 kbar abstract sodium rich metasomatism in the upper levels of the mantle has been modelled by reacting pyrolite with alkali bearing h2o fluids containing minor co2 and concentrations of na2o and na2o k2o k k na 0 1 up to 4 0 g alkalies 10 g h2o at 20 kbar and 950 c with increasing alkali concentration the amounts of amphibole pargasite edenite and olivine increase as orthopyroxene and clinopyroxene decrease amphiboles show progressive increases in na and k and si concentrations and decreases in al and ca concentrations suggesting the dominant substitution mechanism is na k sial ca these results and least squares mass balance calculations suggest the reaction of clinopyroxene orthopyroxene spinel produces amphibole olivine in nature upper mantle spinel lherzolite is commonly veined by a variety of rock types which may contain ti pargasite as a magmatic crystallization product pargasite edenite occurs interstitially in spinel iherzolite often spatially related to ti pargasite and may be produced by hydrous fluids evolved during late stage crystallization of the veined rocks this is supported by the close compositional correlation between the natural pargasite edenite amphiboles and those produced in this study the present study suggests that up to 43 wt amphibole may be accommodated in pyrolite in the presence of na2o rich h2o co2 fluids this represents 0 8 wt h2o and 1 7 wt na2o in the hydrated pyrolite composition and indicates the importance of sodium in determining the extent of metasomatism sodium also lowers the solidus temperature of pyrolite by more than 50 c over the h2o saturated pyrolite system at 20 kbar

insolation cycles as a major control of equatorial indian ocean primary production analysis of a continuous sedimentary record taken in the maldives indicates that strong primary production fluctuations 70 to 390 grams of carbon per square meter per year have occurred in the equatorial indian ocean during the past 910 000 years the record of primary production is coherent and in phase with the february equatorial insolation whereas it shows diverse phase behavior with 18o depending on the orbital frequency eccentricity obliquity or precession examined these observations imply a direct control of productivity in the equatorial oceanic system by insolation in the equatorial indian ocean productivity is driven by the wind intensity of westerlies which is related to the southern oscillation therefore it is suggested that a precession forcing on the southern oscillation is responsible for the observed paleoproductivity dynamics

paleoceanographic changes during the past 1 9 myr at dsdp site 238 central indian ocean basin benthic foraminiferal proxies abstract deep sea benthic foraminifera have been quantitatively analyzed in samples 125 m size fraction from ocean drilling program odp site 238 to understand paleoceanographic changes in the central indian basin over the past 1 9 myr factor and cluster analyses of the 25 highest ranked species made it possible to identify five biofacies characterizing distinct deep sea environmental settings the environmental interpretation of each biofacies is based on the ecology of recent deep sea benthic foraminifera the benthic faunal record indicates fluctuating deep sea conditions in environmental parameters including oxygenation surface productivity and organic food supply these changes appear to be linked to indian summer monsoon variability the main climatic feature of the indian ocean region the benthic assemblages show a major shift at 0 7 to 0 6 ma marked by major turnovers in the relative abundances of species coinciding with an increased amplitude of glacial cycles these cycles appear to have influenced low latitude monsoonal climate as well as deep sea conditions in the central indian ocean basin

latest miocene pleistocene productivity and deep sea ventilation in the northwestern indian ocean deep sea drilling project site 219 knowledge of the biology of deep sea benthic foraminifera was used to interpret the results of multivariate analyses factor and cluster on relative abundance data of benthic foraminifera at deep sea drilling project site 219 southeastern arabian sea 1764 m depth in combination with carbon and oxygen isotope data faunal data document major changes in deep sea ventilation and productivity over the past 5 5 ma including the end of the miocene pliocene indo pacific biogenic bloom period at 4 0 ma interestingly there is no simple correlation between high productivity and low oxygenation productivity fluctuated but became overall more pulsed whereas overall oxygenation increased we interpret the records as a combination of local to regional fluctuations in productivity probably caused by changes in monsoonal development particularly its seasonality and changes in oxygenation of intermediate depth waters in the indian ocean caused by global changes in climate and ocean circulation

abyssal bedforms as indicators of changing bottom current flow examples from the u s east coast continental rise direct indications of circulation patterns in the deep sea especially along continental rises and sediment drifts can be obtained through the analysis of abyssal bedforms such as furrows and mud waves such direct evidence of current flow will supplement indirect indicators of circulation provide by paleochemical indicators preserved in ocean sediments water that sinks in the northern north atlantic forms part of the western boundary undercurrent along the continental rise of eastern north america and the understanding of temporal changes in the speed and depth of flow along this continental rise can provide important information on how the speed at which the global conveyor system is operating changes with time studies of furrows and mud waves along the blake bahama outer ridges show that they are active sedimentary features today and that bottom flow speeds near the time of the younger dryas were increased over later intervals a more detailed analysis of bedform structure and sediments is needed to more clearly show the timing and reason for this change in sedimentation pattern

late quaternary milankovitch scale climatic change and variability and its impact on monsoonal australasia four pollen and charcoal records derived from marine cores around the northern perimeter of australia are examined to provide a regional picture of patterns causes and impacts of climate change over the last 100 300 ka the availability of radiocarbon dates and oxygen isotope records for the cores provides primary chronological control spectral analysis of components of these records demonstrates an overall importance of milankovitch frequencies with clear glacial interglacial cyclicity dominated by variation in precipitation in addition a number of pollen taxa as well as charcoal particles exhibit a 30 ka frequency that is considered from its relationship with biomass burning and with results of past modelling to reflect changes in the intensity of el nino southern oscillation enso variability pollen components of all records show a decline frequently stepwise in more fire sensitive vegetation and its replacement with more fire tolerant vegetation there is some evidence that this trend is linked to an onset or general increase in enso activity and perhaps also to variation in monsoon activity dating from about 300 ka bp that was caused by changes to oceanic circulation within the indonesian region the trend may have accelerated within the last 45 ka due to burning by indigenous people c 2003 elsevier b v all rights reserved

east west similarities and differences in the surface and deep northern arabian sea records during the past 21kyr abstract this study analyses monsoon proxy globigerina bulloides from ocean drilling program odp hole 723a western arabian sea and hole abp 25 02 northeastern arabian sea as well as dominant benthic foraminifera pteropods total organic carbon toc inorganic carbon ic and stable isotope values of benthic foraminifera from hole abp 25 02 to understand summer monsoon driven changes in the western and eastern arabian sea and their impacts on deep sea ventilation during the past 21 kyr we have also combined published toc data from odp hole 724b to understand if deep sea conditions in the arabian sea were same throughout the region during the studied interval the summer monsoon was generally weaker during cold intervals including the last glacial maximum the younger dryas and the bond events of the holocene from 20 to 10 kyr the deep northeastern arabian sea was better oxygenated with less organic carbon supply except during 14 12 5 kyr when toc values increased indicating a weaker summer monsoon and a weak oxygen minimum zone omz the toc values and the abundance of the eutrophic benthic foraminiferal species bulimina aculeata melonis barleeanum and uvigerina peregrina increased during the late holocene whereas well oxygenated low organic carbon benthic species sphaeroidina bulloides as well as pteropods decreased indicating an intense omz and an increased supply of refractory organic material to the arabian sea it is important to note that although the surface response to monsoon variability was more or less similar in the western and northeastern arabian sea the deep sea conditions show a marked contrast in the two regions during the past 21 kyr

variations of oxygen minimum and primary productivity recorded in sediments of the arabian sea abstract two deep sea sediment cores from the northeastern and the southeastern arabian sea were studied in order to reconstruct the palaeoenvironments of the past glacial cycles core 136kl was recovered from the high productivity area off pakistan within the modern oxygen minimum zone omz by contrast modern primary productivity at the site of md900963 close to maldives is moderate and bottom waters are today well oxygenated for both cores we reconstructed the changes in palaeoproductivity using a set of biomarkers alkenones dinosterol and brassicasterol the main result is that primary productivity is enhanced during glacial stages and lowered during interstadials the proxies associated with productivity show a 23 kyr cyclicity corresponding to the precession related insolation cycle palaeoredox conditions were studied in both cores using a new organic geochemical parameter c35 c31 n alkane ratio developed by analysing surface sediments from a transect across the omz off pakistan the value of this ratio in core 136kl shows many variations during the last 65 kyr indicating that the omz was not stable during this time it disappeared completely during heinrich and the younger dryas events pointing to a connection between global oceanic circulation and the stability of the omz the c35 c31 ratio determined in sediments of core md900963 shows that bottom waters remained rather well oxygenated over the last 330 kyr which is confirmed by comparison with authigenic metal concentrations in the same sediments a zonally averaged circulation biogeochemical ocean model was used to explore how the intermediate indian ocean responds to a freshwater flux anomaly at the surface of the north atlantic as suggested by the geochemical time series both the abundance of southern ocean water and the oxygen concentration are significantly increased in response to this freshwater perturbation

benthic foraminiferal successions across late quaternary mediterranean sapropels abstract benthic foraminiferal records across late quaternary mediterranean sapropels s6 s5 and s1 are reviewed and re considered in the light of recent advances in foraminiferal ecology it is suggested that the main factor controlling the foraminiferal successions that occur immediately before and after sapropel deposition is the amount of time involved in the onset of anoxic conditions and in the re oxygenation of the benthic environment faunas dominated by deep infaunal taxa such as globobulimina and chilostomella reflect a very gradual decrease or increase of bottom water oxygenation post sapropel faunas dominated by small biconvex trochospiral taxa which are inferred to have a much more opportunistic life strategy are typical of a very rapid re oxygenation of the benthic environment after sapropel deposition the time involved in re oxygenation depends upon the mechanism causing sapropel formation the faunal succession found above sapropel s5 suggests a basin with a strong density gradient in the upper part of the water column during sapropel deposition followed by a rapid turnover of the following column and quick re oxygenation of the benthic environment in contrast the faunal succession above sapropel s6 suggests a water column with a more gradual density gradient deeper in the basin a progressive deepening of the halocline and a very slow increase of bottom water oxygenation

latest pliocene through holocene paleoceanography of the eastern indian ocean benthic foraminiferal evidence multivariate analyses of latest pliocene through holocene benthic foraminifera from 61 samples from deep sea drilling project dsdp site 214 eastern indian ocean were carried out the 46 highest ranked species were used in r mode factor analysis which has enabled to the identification of three environmentally significant assemblages at site 214 assemblage 1 is characterized by uvigerina hispido costata osangularia culter gavelinopsis lobatulus cibicides wuellerstorfi and karreriella baccata as principal species this assemblage is inferred to reflect high energy well oxygenated and probably low organic carbon deep sea environment at site 214 assemblage 2 is defined principally by globocassidulina pacifica and u proboscidea and is considered to indicate an organic carbon rich environment which resulted from high surface productivity irrespective of dissolved oxygen content assemblage 3 is marked by oridorsalis umbonatus textularia lythostrota hoeglundina elegans pyrgo murrhina and pullenia quinqueloba as principal species this assemblage is inferred to indicate a low organic carbon environment with high pore water oxygen concentration leading to better preservation of deep sea sediments

south equatorial current sec driven changes at dsdp site 237 central indian ocean during the plio pleistocene evidence from benthic foraminifera and stable isotopes abstract this study attempts to analyse paleoceanographic changes in the central indian ocean deep sea drilling project site 237 linked to monsoon variability as well as deep sea circulation during the plio pleistocene we used factor and cluster analyses of census data of the 34 most dominant species of benthic foraminifera that enabled us to identify five biofacies astrononion umbilicatulum uvigerina proboscidea au up pullenia bulloides bulimina striata pb bs globocassidulina tumida nuttallides umbonifera gt nu gyroidinoides nitidula cibicides wuellerstorfi gn cw and cassidulina carinata cassidulina laevigata cc cl biofacies knowledge of the environmental preferences of modern deep sea benthic foraminifera helped to interpret the results of factor and cluster analyses in combination with oxygen and carbon isotope values the biofacies indicative of high surface productivity resulting from a stronger south equatorial current au up and pb bs biofacies dominate the early pliocene interval 5 6 4 5 ma of global warmth an intense indo pacific biogenic bloom and strong oxygen minimum zone extended to intermediate depths 1000 2000 m over large parts of the indian ocean in the early pliocene since 4 5 ma the food supply in the central indian ocean dropped and fluctuated while deep waters were corrosive biofacies gt nu gn cw the pleistocene interval is characterized by an intermediate flux of organic matter cc cl biofacies

spheroidal textures in igneous rocks textural consequences of h2o saturation in basaltic melts abstract when melts reach h 2 o saturation before they are emplaced at the earth s surface they exsolve a hydrous fluid phase at elevated pressure and high temperature a hydrous fluid is not pure h 2 o but can contain some quantities of silicate and metal oxide solute notably if fluid saturation occurs at high pressure chemically and physically fluid saturated basalts behave like any other system with liquid immiscibility textures that can result after solidification are globules of former fluid dispersed in a former silicate melt or silicate melt orbs embedded in a former fluid matrix the troodos ophiolite on the island of cyprus generated in a back arc basin above a wet intra oceanic subduction zone carries in its magmatic stratigraphy lithologies distinctly orbicular and globular in shape many melt compositions parental to the ophiolite were h 2 o saturated near their liquidus temperatures before they reached their depths of emplacement within the ophiolite sequence spheroids are not uncommon in magmatic rocks but still debated as to how they form we propose that globular and orbicular textures in igneous worldwide may result when melts reach h 2 o saturation and exsolve an immiscible solute bearing h 2 o dominated fluid phase at elevated temperature and pressure before or while they are emplaced

impact of productivity events on the benthic foraminiferal fauna in the arabian sea over the last 150 000 years we have studied the sediment geochemistry and benthic foraminiferal fauna in a piston core from the northwest arabian sea covering the last 150 000 years and compared the results with the stable isotopic record from both benthic uvigerina peregrina and planktonic globigerinoides sacculifer foraminifera the 18o record of the planktonic foraminiferal species shows excursions towards heavier 18o values when compared to the benthic record and the specmap stack particularly in stage 3 between approximately 30 and 45 50 kyr we call this the stage 3 event species diversity and relative abundance data on benthic foraminifera reveal that some species e g cibicidoides wuellerstorfi oridorsalis umbonatus pullenia bulloides pyrgo spp and the uvigerinids increased in relative abundance during glacial stages 2 and 4 and during the stage 3 event whereas other e g astrononion novozealandicum cibicidoides bradyi eggerella bradyi gyroidina altiformis hoeglundina elegans pullenia subcarinata and sigmoilina edwardsii decreased using correspondence analysis we determined that approximately 50 of the total sample variation may be accounted for by three first factors which all are interpreted as primarily related to surface water productivity and the quality of the organic matter that reaches the seafloor the relative abundance of some species appears to vary on a precessional cycle perhaps responding to monsoon driven upwelling and associated increased food supply whilst the abundances of other species are related to the 100 kyr ice volume cycle and may be responding to changes in intermediate and deep water chemistry geochemical paleoproductivity tracers such as the ba content of the sediment have a very similar distribution to specific foraminiferal factors in both time and frequency domains certain planktonic foraminifera e g globigerina bulloides also display obvious maxima in the stage 3 event the stage 3 event occurs at a time of reduced rate of amplitude change in both solar radiation and monsoon pressure index we conclude that there was a period 15 to 20 kyr duration during stage 3 with cooler than normal surface waters enhanced productivity and rapid settling of biogenic matter

a glimpse of the quaternary monsoon history from india and adjoining seas abstract the evolution of the monsoon is briefly summarized taking into account previous studies conducted on both terrestrial and marine records recovered from the indian subcontinent and the adjoining seas while the initiation of the monsoon is debated it seems clear that a major intensification of the summer monsoon occurred at 8 2 ma a seasonal monsoon circulation with distinct summer and winter monsoon phases was established at 2 8 ma in the late quaternary the summer monsoon weakens during glacial periods as compared to interglacial periods the centennial to sub centennial scale changes in the monsoon during both glacial and interglacial periods suggest strong links between high latitude processes and the tropical monsoon and its role in modulating northern hemispheric climate the glacial terminations are marked by weak monsoon activity the summer monsoon weakened during the middle holocene after the early holocene optimum a change in the monsoon intensity though alters the salinity of the seas surrounding india the quantitative paleosalinity reconstructions still have large associated uncertainties and an effort should be made to lower them

sedimentation and climate induced sediments on feni ridge northeast atlantic ocean abstract feni ridge has been studied in detail in the area between 54 and 56 n and 12 and 16 w by using high resolution profiling water column sampling with transmissometer and ctd and by piston and box core sampling the crest of feni ridge is absent in the north of the study area but on passing towards the south it begins to take shape and to increase in height its distance from the rockall slope also increases towards the south on the lower southeastern flank a secondary ridge crest has locally developed and sediment waves along the flanks have amplitudes of up to 45 m the highest and steepest waves are found in the south the waves in the north being somewhat lower bottom nepheloid layers of 175 m near the foot of rockall plateau and 125 m near the crest are attributed to a norwegian sea overflow water current with a core at 2100 m bottom nepheloid layers of 75 100 m on the lower flanks of the ridge are thought to have been caused by northeast atlantic deep water piston cores reflect alternations of glacial and interglacial periods interglacials have a high carbonate and corg content a positive eu anomaly and negative ce anomaly and a low rb la ratio they are dominated by a subpolar and transitional foraminiferal assemblage glacials show a low carbonate and corg content a reduced eu anomaly and a high rb la ratio suggesting increasingly continental sediment sources these deposits are dominated by a polar planktonic foraminiferal assemblage characterized by n pachyderma s and g quinqueloba sedimentation rates reflect differential deposition at crestal station na 87 25 rates are 17 1 cm k y for stage 1 14 6 cm k y for stage 2 3 4 cm k y for stage 3 and 5 4 cm k y for stage 4 stage 5a e has a mean sedimentation rate of 6 1 cm k y over the last 125 k y the development of feni ridge has taken place under a relatively low energy current regime

mid brunhes strengthening of the indian ocean dipole caused increased equatorial east african and decreased australasian rainfall 1 the tropical indian ocean is an important component of the largest warm pool marked by changes in sea surface temperatures and depths of thermocline and mixed layer in its western and eastern extremities leading to the development of a dipole mode the indian ocean dipole iod a narrow band of westerlies 7 n to 7 s sweep the equatorial indian ocean during the april may and october november transitions between the summer and winter monsoon seasons these indian ocean equatorial westerlies iew are closely related to the iod intensifying the upper ocean eastward equatorial current also known as wyrtki jets the strength of the iod iew determines the moisture content in east africa a major decrease in the strength of the iew strengthening or positive mode of the iod during the mid brunhes epoch 300 250 kyr bp coincides with a wetter equatorial east africa a drier australasia and a stronger indian summer monsoon indicating that the iod iew play a significant role in driving climate change in east africa australasia and south asia

late quaternary millennial scale variability in pelagic aragonite preservation off somalia abstract in order to better understand late quaternary pelagic aragonite preservation in the western arabian sea we have investigated a high resolution sediment core 905 off somalia pteropod preservation is enhanced in times of reduced monsoon driven productivity indicated by low amounts of corg and low barium to aluminium ba al ratios all periods corresponding to heinrich events in the north atlantic are represented by maxima in shell preservation of the common pteropod limacina inflata ldx values 2 66 good shell preservation is also found during stadials at 52 1 53 2 36 33 2 and 31 9 ka relative abundance of pteropods and their fragments in the coarse fraction reaches maxima during marine isotope stage mis 5 2 during time equivalents of heinrich events 4 6 and in stadials at 53 42 5 and 41 4 ka on longer time scales the pteropod abundance corresponds to the indo pacific carbonate preservation type with poor preservation during interglacials and better preservation during glacials late mis 5 to early mis 4 sections 84 1 64 8 ka and the late holocene interval 6 5 0 ka of core 905 contain only traces of pteropods the early holocene 9 2 6 5 ka part is characterized by low pteropod amounts between 64 8 and 43 4 ka strong fluctuations occur and an intermediate average relative pteropod abundance is revealed between 43 4 and 9 2 ka the highest amounts in relative pteropod abundance in core 905 are observed besides the regional monsoonal influence on deepwater chemistry changes in deepwater circulation occurring on glacial interglacial and stadial interstadial time scales might have affected pteropod preservation however it remains elusive whether 1 deep water formation in the arabian sea 2 inflow of glacial north atlantic intermediate water or 3 change in water mass properties of the circumpolar deep water which is the water mass currently bathing this site contributed to the observed pteropod preservation pattern

late pleistocene paleoclimatology of the central equatorial pacific sea surface response to the southeast trade winds proxy indicators of sea surface temperature and equatorial divergence based on radiolarian assemblage data and of trade wind intensity based on eolian grain size data show similar aspects of variability during the late pleistocene all indicators fluctuate at higher frequencies than the 100 000 year glacial interglacial cycle display reduced amplitude variations since 300 000 years ago exhibit a change in the record character at about 300 000 years ago the mid brunhes climatic event and have higher amplitude variations in sediments 300 000 850 000 years old time series analyses were conducted to determine the spectral character of each record 18o of planktonic foraminifer sea surface temperature values equatorial divergence indicators and wind intensity indicators and to quantify interrecord coherence and phase relationships the record was divided at the 300 000 year clear change in climatic variability nonstationarity the 18o based time scale is better lower in the core so our spectral analyses concentrated on the interval from 402 000 774 000 years the 18o spectra show 100 000 and 41 000 year power in the younger portion 0 300 000 years and 100 000 41 000 and 23 000 year power in the older interval all highly coherent and in phase with the specmap average stacked isotope record unlike the isotope record the dominant period in both the eolian grain size and equatorial divergence indicators is 31 000 years this period is also important in the sea surface temperature signal where the dominant spectral peak is 100 000 years the 31 000 year spectral component is coherent and in phase between the eolian and divergence records confirming the link between atmospheric and ocean surface circulation for the first time in the paleoclimate record since the 31 000 year power appears in independent data sets within this core and also appears in other equatorial records j imbrie personal communication 1987 we assume it to be real and representative of both a nonlinear response to orbital forcing possibly a combination of orbital tilt and eccentricity and some resonance phenomenon required to amplify the response at this period so that it appears as a dominant frequency component the mid brunhes climatic event is an important aspect of these records but its cause remains unknown

benthic foraminiferal response to late glacial and holocene sea level rise and rainfall variability off east africa analogous to west and north africa east africa experienced more humid conditions between approximately 12 and 5 kyr bp relative to today while timing and extension of wet phases in the north and west are well constrained this is not the case for the east african humid period here we present a record of benthic foraminiferal assemblages and sediment elemental compositions of a sediment core from the east african continental slope in order to provide insight into the regional shallow indian ocean paleoceanography and east african climate history of the last 40 kyr during glacial times the dominance of a benthic foraminiferal assemblage characterized by bulimina aculeata suggests enhanced surface productivity and sustained flux of organic carbon to the sea floor during heinrich stadial 1 h1 the nuttallides rugosus assemblage indicates oligotrophic bottom water conditions and therefore implies a stronger flow of southern sourced aaiw to the study site during the east african humid period the saidovina karreriana assemblage in combination with sedimentary c n and fe ca ratios suggest higher river runoff to the indian ocean and hence more humid conditions in east africa between 8 5 and 8 1 kyr contemporaneous to the globally documented 8 2 kyr event a severe reduction in river deposits implies more arid conditions on the continent comparison of our marine data with terrestrial studies suggests that additional moisture from the atlantic ocean delivered by an eastward migration of the congo air boundary during that time period could have contributed to east african rainfall since approximately 9 kyr the gaining influence of the millettiana millettii assemblage indicates a redevelopment of the east african fringe reefs

initiation of northern hemisphere glaciation and strengthening of the northeast indian monsoon ocean drilling program site 758 eastern equatorial indian ocean the indian monsoon system as recorded by ocean floor biota benthic foraminifera at ocean drilling program site 758 in the eastern equatorial indian ocean has varied dramatically over the past 5 5 m y long after the onset of the monsoons at 10 8 ma benthic foraminifera that thrive with high productivity year round were common before the formation of northern hemisphere continental ice sheets ca 3 1 2 5 ma indicating that the summer southwest monsoon had high intensity and long seasonal duration ca 2 8 ma benthic faunas became dominated by taxa that flourish with a seasonally strongly fluctuating food supply indicating that the northeast winter monsoon during which primary productivity is relatively low increased in duration and strength to form a system similar to that of today the change occurred coeval with the initiation of the northern hemisphere glaciation documenting a close link between the development of the indian monsoon and northern hemisphere glaciation

on deep current and hydrographic observations from a mudwave region and elsewhere in the argentine basin near bottom current measurements from both sides of a mudwave in an extensive mudwave region of the mid argentine basin are examined for evidence of lee waves such waves appear to exist when the across crest flow exceeds a critical value predicted by flood 1988 deep sea research 35 973 983 of about 9 cm s 1 the observations agree with the predictions of blumsack and weatherly 1989 deep sea research 36 155 172 in three of four cases however if it is assumed that the flow perturbations induced by lee waves are shifted slightly downcurrent from that predicted by the blumsack and weatherly model then there is agreement in all four cases the mudwave region is characterized as having a strong 10 cm s 1 steady eddy kinetic energy mean kinetic energy current the westward flow is consistent with the anticyclonic abyssal gyre centered about the zapiola drift inferred by flood and shor 1987 deep sea research 35 973 983 near bottom flow measurements made further to the west in the region of confluence of the brazil and malvinas current extensions reveal relatively energetic fluctuations and equatorward flowing deep western boundary currents along the continental slope along the continental rise a poleward flow is observed consistent with that inferred by reid 1989 progress in oceanography 23 149 244 too cold bottom layers were found to be common only on the lower continental slope 4000 m depth and at the mid basin mudwave site

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

the contourite depositional system of the gulf of cadiz a sedimentary model related to the bottom current activity of the mediterranean outflow water and its interaction with the continental margin the present paper is mostly a synthesis of work conducted on the continental margin of the gulf of cadiz using a broad database collected by several cruises and projects supported by the spanish research council and the nrl and naval oceanographic office usa including bathymetry sidescan sonar imagery seismic profiles sediment cores submarine photographs and physical oceanographic data these data have enabled us to establish a detailed understanding of the morphologic development of the margin its pliocene and quaternary stratigraphy and a full characterization of the contourite depositional system cds generated by the mediterranean outflow water mow the northern margin of the gulf of cadiz shows the following distinct features a an active compressive framework where the cadiz allocthonous unit provides an unstable substratum for late miocene pliocene and quaternary sedimentation b a relative lack of submarine canyons except in the western area of the algarve margin c a very broad continental slope that lacks a marked continental rise d a middle slope dominated by along slope processes driven by the mow which has generated a complex cds during the pliocene and quaternary and e an irregular lower slope and abyssal plain region dominated by down slope processes that is partly detached from an upper slope source region the cds is composed of both depositional and erosive features the main depositional features are characterised by sedimentary wave fields sedimentary lobes mixed drifts plastered drifts elongated mounded and separated drifts and sheeted drifts the main erosive features are contourite channels furrows marginal valleys and moats these various depositional and erosive features have a specific location along the margin and their detailed distribution is essential to understand the present and past interaction of the mow with the middle slope based on this distribution five morphosedimentary sectors have been identified within the cds which from east to west are 1 proximal scour and sand ribbons 2 overflow sedimentary lobe 3 channels and ridges 4 active contourite drifts and 5 submarine canyons the development of the cds has been controlled in general by the pliocene and quaternary environmental and paleoceanographic changes and by the morphology of the margin but in detail the development of each of these sectors is related to systematic deceleration of the mow as it flows westwards to the interaction with the margin bathymetry and to the effects of coriolis force our comprehensive sedimentary model for the cds defines the gulf of cadiz margin as a mixed contourite turbidite system with a detached combined drift fan morphology this is different from many other contourite influenced margins where the contourite processes are dominant on the middle slope and separated from the down slope processes which are characteristic on the lower slope and abyssal plains

response to the comment by r stalder on composition of aqueous fluid coexisting with mantle minerals at high pressure and its bearing on the differentiation of the earth s mantle

carbon reservoir changes preceded major ice sheet expansion at the mid brunhes event the beginning of the mid brunhes event ca 430 ka coincided with the largest amplitude change in d 18 o in the global ocean over the past 6 m y this large d 18 o change recorded a major ice sheet expansion that cannot be explained by small changes in orbital forcing our recent studies at ocean drilling program site 1143 from the south china sea show that this large d 18 o change was preceded by a significant negative d 13 c shift a global survey of long deep sea records has revealed periodic d 13 cmax episodes i e maximum positive values of d 13 c and both major ice sheet expansion events in the pleistocene the mid brunhes event and the middle pleistocene revolution were preceded by d 13 cmax ep isodes followed by negative d 13 c shifts this new finding suggests that disturbance in carbon reservoirs leads to major growth of ice sheet size and challenges the prevalent concept of arctic control of glacial cycles because earth is now passing again through a d 13 cmax episode it is crucial to understand the causal relationship between the successive d 13 c changes and ice sheet growth events

compositions of aqueous fluids in equilibrium with pyroxenes and olivines at mantle pressures and temperatures solubility experiments were performed at 30 kbars in the system mg2sio4 sio2 h2o and at 20 and 30 kbars on omphacitic pyroxene water mixtures they confirm that the solubility of the forsterite component in aqueous fluids remains rather low up to 5 wt whereas the solubility of the sio2 component from solids of appropriate sio2 rich compositions in the system mg2sio4 sio2 h2o increases with temperature up to some 75 at 1 100 c at this temperature a simplified harzburgite consisting of forsterite and enstatite coexists with a fluid containing about 35 mgo sio2 hydrous fluids coexisting with omphacitic clinopyroxenes leach sodium silicate component from the solid leaving less jadeitic pyroxenes behind most interestingly the amount of sodium leached at constant temperature increases with decreasing pressure comparison of the results with previous solubility studies in the system k2o mgo al2o3 sio2 h2o indicates that hydrous fluids in the mantle must be alkaline rather than silicanormative alkali metasomatism caused by such fluids would lead to potassium enrichment in deeper portions of the upper mantle and to sodium enrichment at shallower levels where amphiboles become stable this k na fractionation in the upper mantle may explain the generation of k rich or of na rich magmas through partial melting at different depths

magnetic mineral dissolution recorded in a lacustrine sequence from the heqing basin sw china and its relationship with changes in the indian monsoon abstract the dissolution of magnetic oxides is an important process in many lake environments understanding this phenomenon is crucial for the paleoenvironmental interpretation of the magnetic properties of lake sediments in order to reveal its effects on sedimentary magnetic properties and to assess the possible associated paleoenvironmental implications we carried out detailed rock magnetic analyses of the selected samples from a 920 kyr lacustrine sequence from the heqing basin sw china the results indicate that the sedimentary magnetic properties are controlled by the concentration and grain size of magnetite and maghemite high magnetic susceptibility intervals contain more fine grained magnetite and maghemite while low intervals contain only minor amounts of residual magnetite the decreased content of fine grained maghemite from high to low intervals reflects the dissolution of magnetic oxides during deposition intervals affected by strong magnetic dissolution have a high toc content and correspond to times of high antarctic temperatures suggesting that magnetic mineral dissolution intensity was associated with variations in the strength of the indian summer monsoon ism notably the ism is sensitive to southern hemisphere warming weak magnetic dissolution indicates a dry climate occurred since 320 kyr in the heqing basin this dry cool event was widespread across the eastern bay of bengal equatorial indian ocean and northern australia and was linked to a strengthened indian ocean dipole iod since the moisture source of the heqing basin was mainly from the above regions we infer that the influence of the iod extended northwards to sw china

relationship of surface sediments and benthic foraminiferal distribution patterns in the norwegian channel northern north sea abstract our study of the distribution of benthic foraminifers in surface sediment samples from the norwegian channel has shown that eight species and five different assemblages are important the assemblages are dominated by uvigerina peregrina bolivina skagerrakensis cassidulina laevigata elphidium excavatum and bulimina marginata respectively hyalinea balthica melonis barleeanum and trifarina angulosa are also abundant the first four assemblages and their dominant species can be related to certain water masses with known characteristics two species are related to certain types of substrate m barleeanum seems to prefer a fine grained substrate while t angulosa occurs most abundantly where the content of silt and clay is low b skagerrakensis and h balthica occur most abundantly in sediments with a high content of organic carbon while t angulosa shows inverse correlation to the organic carbon content

sea surface temperatures and the history of monsoon upwelling in the northwest arabian sea during the last 500 000 years abstract arabian sea sediments record changes in the upwelling system off arabia which is driven by the monsoon circulation system over the nw indian ocean in accordance with climate models and differing from other large upwelling areas of the tropical ocean a 500 000 yr record of productivity at odp site 723 shows consistently stronger upwelling during interglaciations than during glaciations sea surface temperatures ssts reconstructed from the alkenone unsaturation index uk 37 are high up to 27 c during interglaciations and low 22 24 c during glaciations indicating a glacial interglacial temperature change of 3 c in spite of the dampening effect of enhanced or weakened upwelling the increased productivity is attributed to stronger monsoon winds during interglacial times relative to glacial times whereas the difference in ssts must be unrelated to upwelling and to the summer monsoon intensity the winter ne monsoon was more effective in cooling the arabian sea during glaciations then it is now

the capacity of hydrous fluids to transport and fractionate incompatible elements and metals within the earth s mantle both silicate melts and aqueous fluids are thought to play critical roles in the chemical differentiation of the earth s crust and mantle yet their relative effects are poorly constrained we have addressed this issue by measuring partition coefficients for 50 trace and minor elements in experimentally produced aqueous fluids coexisting basanite melts and peridotite minerals the experiments were conducted at 1 0 4 0 gpa and 950 1200 c in single capsules containing either 40 or 50 wt h2o and trace element enriched basanite glass this allowed run products to be easily identified and analyzed by a combination of electron microprobe and lam icp ms fluid and melt compositions were reconstructed from mass balances and published solubility data for h2o in silicate melts relative to the basanite melt the solutes from h2o fluids are enriched in sio2 alkalis ba and pb but depleted in feo mgo cao and ree with increasing pressure the mutual solubility of fluids and melts increases rapidly with complete miscibility between h2o and basanitic melts occurring between 3 0 and 4 0 gpa at 1100 c although lree are favored over hree in the fluid phase they are less soluble than the hfse nb ta zr hf and ti thus the relative depletions of hfse that are characteristic of arc magmas must be due to a residual phase that concentrates hfse e g rutile otherwise h2o fluids have the capacity to impart many of the geochemical characteristics that distinguish some rocks and melts from the deep mantle lithosphere e g marid and lamproites

comment on k mibe t fujii and a yasuda 2002 composition of aqueous fluid coexisting with mantle minerals at high pressure and its bearing on the differentiation of the earth s mantle geochimica et cosmochimica acta 66 2273 22851

benthic foraminiferal assemblages from the eastern south atlantic polar front region between 35 and 57 s distribution ecology and fossilization potential abstract surface sediment samples taken with a multiple corer from the polar front region along two profiles in the eastern south atlantic sector between 35 and 57 s have been investigated for their benthic foraminiferal content live fauna was differentiated from the death assemblage based on the dead assemblages potential fossil assemblages dead fauna reduced by non resistant agglutinants were calculated for comparison with upper neogene core material the distribution of the potential fossil assemblages defined byq mode principal component analysis mirrors the recent hydrographic as well as the trophic situation in the eastern south atlantic ocean circulation and productivity two southern component bottom water faunas reflect the northward flow of antarctic bottom water aabw and lower circum polar deep water lcdw an assemblage dominated by the arenaceousmultifidella nodulosa below the calcite compensation depth ccd and anuttallides umbonifer dominated assemblage above the ccd in the region of highest bio silicious primary productivity south of the polar front and north of the winter sea ice limit these faunas are overprinted by a southern high productivity fauna dominated by infaunal species such aspullenia bulloides melonis pompilioides andm zaandamae north atlantic deep water nadw meets the circum polar deep water cdw at intermediate depth as reflected in the distribution of the northern component deep water fauna dominated byepistominella exigua the high productivity assemblage overprinting this fauna the northern high productivity fauna is dominated by the shallow endobenthicbulimina aculeata a strong bottom current fauna dominated byangulogerina angulosa characterizes areas between 400 and 900 m water depth with sandy sediment independent from water mass characteristics and food supply

climate variability and land ocean interactions in the indo pacific warm pool a 460 ka palynological and organic geochemical record from the timor sea climatic conditions in the western timor sea and the adjacent northwestern part of australia are reconstructed for the last 460 ka based oil geochemical and palynological proxy records of paleoproductivity and land vegetation precipitation from images core md01 2378 reduced precipitation and elevated productivity characterize glacial stages whereas enhanced precipitation and reduced productivity are typical of interglacial stages a long term reduction in precipitation over the last 320 ka occurred in two steps at approximately 300 ka and 180 ka bp that are clearly recognizable in the pollen record variations in paleoproductivity and paleoclimate in the timor sea and adjacent landmasses appear to be driven by similar mechanisms that are related to the precession control led australian monsoon system c 2005 elsevier b v all rights reserved

benthic foraminifera as proxies of organic matter flux and bottom water oxygenation a case history from the northern arabian sea abstract benthic foraminifera have been quantified in two sediment cores from a topographic high murray ridge in the northern arabian sea one core is from a station within the present day oxygen minimum zone omz the other from a station below the omz changes in the intensity of the omz linked to monsoonal climate variability had a strong impact on benthic foraminiferal composition and accumulation rates at the shallower omz station 920 m an intensification of the omz resulted in lower diversities and high dominances of low oxygen tolerant species the deeper station 1470 m was far less affected though at least once during the last 225 000 years the benthic faunal composition and accumulation rates show evidence for a deepening of the base of the omz to a level close to or even below 1470 m we suggest that percentages of miliolids can be used for rapid reconstruction of periods of increased ventilation in the northern arabian sea and are a promising proxy for tracing changes in bottom and pore water oxygenation in general omz conditions are characterised by high abundances of deep infaunal species and increased burial efficiency of organic matter the proportion of deep infaunal species appears to be a measure for the anoxic burial efficiency of organic matter and not a direct measure for the arriving flux at the seabed results furthermore show that benthic foraminiferal accumulation rates cannot be used as a proxy for surface water productivity under the prevalence of severe dysoxia

high latitude influence on the eastern equatorial pacific climate in the early pleistocene epoch many records of tropical sea surface temperature and marine productivity exhibit cycles of 23 kyr orbital precession and 100 kyr during the past 0 5 myr refs 1 5 whereas high latitude sea surface temperature records display much more pronounced obliquity cycles at a period of about 41 kyr ref 6 little is known however about tropical climate variability before the mid pleistocene transition about 900 kyr ago which marks the change from a climate dominated by 41 kyr cycles7 when ice age cycles and high latitude sea surface temperature variations were dictated by changes in the earth s obliquity8 9 to the more recent 100 kyr cycles of ice ages here we analyse alkenones from marine sediments in the eastern equatorial pacific ocean to reconstruct sea surface temperatures and marine productivity over the past 1 8 myr we find that both records are dominated by the 41 kyr obliquity cycles between 1 8 and 1 2 myr ago with a relatively small contribution from orbital precession and that early pleistocene sea surface temperatures varied in the opposite sense to local annual insolation in the eastern equatorial pacific ocean we conclude that during the early pleistocene epoch climate variability at our study site must have been determined by high latitude processes that were driven by orbital obliquity forcing

recent deep sea benthic foraminiferal distributions in the south china and sulu seas thirty nine surface sediment samples collected from the south china and sulu seas were examined to determine the bathymetric distribution of benthic foraminifera in these two basins and the factors responsible for these distributions the benthic foraminiferal faunas of both basins are highly diverse but have low absolute abundances benthic number and species diversity systematically decrease with increasing water depth four faunal assemblages were identified for each basin byq mode principal component analysis theglobocassidulina subglobosa uvigerina assemblage 1500 m and theuvigerina assemblage 1400 m represent the shallowest assemblages in the south china sea and sulu sea respectively and are found within the oxygen minimum zone of each basin where the sedimentary organic carbon content is highest and the pore water oxygen penetration depth zo is shallowest thebulimina aculeata assemblage occurs at water depths between 1700 and 2000 m in the southeastern south china sea and is also associated with relatively high sedimentary organic carbon content theastrononion pusillum assemblage is found in south china sea at the depths between 1500 and 3200 m below the lysocline 3200 m in the south china sea this assemblage is replaced by the agglutinatedrhabdammina abyssorum assemblage this assemblage reflects the presence of a water mass that is highly undersaturated with respect to calcite in the sulu sea thepyrgo murrhina assemblage occupies water depths from 1400 to 2200 m below 2200 m two deep water assemblages are present that are both dominated byoridorsalis umbonatus a correlation between various environmental and benthic foraminiferal variables indicates that salinity temperature sediment grain size water depth and bottom water oxygen concentration are not key factors controlling the benthic foraminiferal distribution in either the south china sea or the sulu sea rather organic carbon content and oxygen penetration depth in sediments appear to play important roles in determining the distribution of benthic foraminifera in both basins

australian dust deposits modern processes and the quaternary record abstract dust raising and transport are common and important processes in australia today the aridity of the australian continent and high climatic variability result in widespread dust raising in the arid and semi arid areas and transport to the humid margins and surrounding oceans the supply of erodible particles appears to be the greatest limitation on total flux of transported dust dust raising is greatest in the lake eyre basin including the simpson desert and murray darling basin where internal drainage renews supplies of fine particles to the arid zone in the west and northwest dust entrainment is low despite considerable aridity the marine record of dust flux shows at least a threefold increase in dust flux compared with the holocene in the last glacial maximum in both tropical and temperate australia driven by weakened australian monsoon rains and drier westerly circulation respectively despite the widespread confirmation of aeolian dust deposits in southeastern and southwestern australia dated or quantified records are extremely rare the dominant model of australian dust deposits the clay rich parna is shown to be poorly substantiated while modern and ancient dust deposits examined in detail are shown to bear a strong similarity to conventional definitions of loess

orbital and suborbital variability in the equatorial indian ocean as recorded in sediments of the maldives ridge odp hole 716a during the past 444 ka this study is aimed at understanding past 444 ka record of climate variability in the equatorial indian ocean using high resolution records of planktic and benthic foraminifera and pteropods from ocean drilling program hole 716a maldives ridge southeastern arabian sea in total 892 samples of 10 cm 3 volume from 444 ka old sequence were analysed at 1 cm intervals to generate census data of the foraminiferal fauna and pteropods the percent and detrended time series of mixed layer species globigerinoides ruber and globigerinoides sacculifer and thermocline species neogloboquadrina dutertrei benthic foraminifera cymbaloporetta squammosa sphaeroidina bulloides and uvigerina proboscidea and pteropods from odp hole 716a reveal significant changes in wind intensity during the past 444 ka an abrupt decrease in the cymbaloporetta squammosa population at c 300 ka across mis 8 9 suggests a weakening of equatorial wind intensity which could be linked to indian monsoon and may have driven pronounced changes in the oxygen minimum zone in the maldivian region these changes were contemporaneous with the mid brunhes climatic event the beginning of aridity in the indonesian australian region and the onset of a humid phase in equatorial east africa as observed in several oceanic and continental records this strengthens a connection between equatorial indian ocean wind intensity the indian monsoon and indonesian australian african climates