integration of ice core marine and terrestrial records for the australian last glacial maximum and termination a contribution from the oz intimate group the degree to which southern hemisphere climatic changes during the end of the last glacial period and early holocene 30 8 ka were influenced or initiated by events occurring in the high latitudes of the northern hemisphere is a complex issue there is conflicting evidence for the degree of hemispheric teleconnection and an unresolved debate as to the principle forcing mechanism s the available hypotheses are difficult to test robustly however because the few detailed palaeoclimatic records in the southern hemisphere are widely dispersed and lack duplication here we present climatic and environmental reconstructions from across australia a key region of the southern hemisphere because of the range of environments it covers and the potentially important role regional atmospheric and oceanic controls play in global climate change we identify a general scheme of events for the end of the last glacial period and early holocene but a detailed reconstruction proved problematic significant progress in climate quantification and geochronological control is now urgently required to robustly investigate change through this period copyright c 2006 john wiley sons ltd

coccolithophore response to oceanographic changes in the equatorial atlantic during the last 200 000 years a deep sea core from the eastern equatorial atlantic meteor core 16772 1 21 s 11 58 w revealed strong primary productivity variations 70 230 gc m2 year based on the relative abundance of the deep living coccolithophore florisphaera profunda with productivity maxima following temperature minima during the last 200 000 years the response of the coccolithophore flora was investigated by relative and absolute abundance records of coccoliths the wind strength and the resulting equatorial upwelling intensity are thought to comprise the most important control of coccolith abundance and species composition which reflects the different abundance of coccolithophores living in the upper or lower photic zone relative abundances of the different species varies widely throughout the core although a wide range of species were present in the different samples three different taxa dominated the assemblage the lower photic zone species f profunda was the most abundant with a mean relative abundance of 49 4 throughout the core the upper photic zone flora were divided into three groups emiliania huxleyi together with small gephyrocapsa 3 m was the second most abundant species group mean 20 8 gephyrocapsa oceanica was the third most important species in the core and had a mean relative abundance of 16 8 all other species together represented a mean of 13 highest absolute abundance of coccoliths number gram sediment occurs in sediments deposited during periods of high sst mainly in warm isotope stages 1 and 5 the accumulation rates of coccoliths number cm2 ky show peaks in isotope stages 1 and 5 but also in some parts of cool isotope stages 4 and 6 high relative and absolute abundance of f profunda were found in warm isotope stages which suggests that a deep nutricline existed and that primary productivity was low absolute and relative abundance records of e huxleyi and small gephyrocapsa 3 m mainly showed higher values in sediments from warm periods the other upper photic zone coccolith species were generally more abundant during periods of low sst particularly in isotope stages 2 4 and 6 which were times of high primary productivity and a shallow nutricline this suggest that e huxleyi and small gephyrocapsa probably were able to live deeper in the water column than most other species during periods of low nutrient supply to the upper photic zone in summary the composition of the coccolith flora can be explained by the nutricline depth level with three different assemblages being recognized a deep photic zone assemblage consisting of f profunda a middle upper photic zone assemblage of e huxleyi and small gephyrocapsa and an upper photic zone assemblage consisting of all other species

benthic foraminifera from the carnarvon ramp reveal variability in leeuwin current activity western australia since the pliocene abstract benthic foraminiferal assemblages from a 300 m deep core from an outer carbonate ramp site off western australia international ocean discovery program core u1460a were examined to reconstruct the paleoceanographic evolution of the carnarvon ramp and the warm surficial leeuwin current lc for the last 3 54 ma of the identified 179 benthic foraminiferal species occurrences of the 15 most abundant taxa were assessed using q mode cluster analysis and non metric dimensional scaling diversity equitability planktonic benthic index microhabitat preference and sedimentary parameters such as lithology and sponge spicule content were analyzed to gather information about past intermediate and surface water circulation relative abundances of infaunal and epifaunal species were applied to indicate changes in organic matter supply and oxygenation at the sea floor influence of upwelling was recognized by a high infaunal species ratio with dominance by uvigerina peregrina lagena annellatrachia and trifarina bradyi epifaunal species such as hanzawaia nipponica and hyalinea florenceae gradually became more abundant around 1 14 ma indicating increased ventilation and establishment of the paleo lc a more substantial change was initiated by 0 91 ma as marked by key species spirorutilus carinatus and rotorbinella sp together with increased faunal diversity benthic foraminiferal accumulation rates and evidence for suspension feeding sponges with the lc flow suppressing upwelling and better ventilated waters entering the shelf the environment favored epifaunal agglutinates rotalids and miliolids while buliminids decreased under high flow conditions of the lc sponge spicules and skeletal carbonate production reached an optimum at 0 6 ma before returning to modern conditions supported by these observations we propose the following paleoceanographic evolution of the carnarvon ramp during the late pliocene to mid pleistocene 3 54 0 91 ma conditions of deep water upwelling from the western australian current and indian ocean gyre indicate the absence of the capping lc on the outer carbonate ramp a transitional phase started in the mid pleistocene 1 14 0 61 ma the paleo lc triggered gradual oxygenation at the sediment water interface which coincided with an increase in carbonate sedimentation rates and waning sea surface productivity during a third phase mid pleistocene to present 0 91 0 ma the lc s intensity and flow rates peaked at 0 6 ma benthic foraminiferal accumulation rates reached a high then decreased to present day rates for short periods sea surface productivity was moderately enhanced likely due to fluctuating lc persistence or landward shift during glacial maxima

monsoonal dynamics and evolution of the primary productivity in the eastern arabian sea over the past 30 ka abstract this study presents a high resolution primary productivity record for the last 30 ka in the eastern arabian sea eas based on the coccolithophore assemblage at sk 17 core in the continental slope off goa india coccolithophores were proposed as indicators of primary productivity and nutricline position and the results were used to reconstruct the monsoonal dynamics which is a main factor controlling productivity changes in the eas both seasons in the indian monsoon winter and summer monsoon exert a strong control over the primary productivity in the arabian sea an increased productivity was recorded during the late glacial period in the eas contrasting with records obtained in the western and northern arabian sea this enhanced productivity was related to strengthened winter monsoon winds planktonic foraminifera data suggested a weakened winter mixing during the last deglaciation which would reduce productivity in the area however our coccolithophore data reveal a high primary productivity during the deglaciation provably maintained by the nutrient supply from the continental runoff due to the presence of enhanced summer monsoon regarding the holocene surface waters were highly stratified since 10 5 ka our data were compared with ice cores isotopic records from high latitudes of both hemispheres allowing us to observe a good correlation between the stratification of the eas and the climate variability over high latitude regions in the northern hemisphere however there has been some inconsistency between our coccolithophore data and planktonic foraminiferal records particularly during the short time intervals corresponding to the heinrich cold events described in the north atlanctic region

pleistocene variability of the subtropical convergence at east tasman plateau evidence from planktonic foraminiferal mg ca odp site 1172a combined measurements of mg ca and stable oxygen isotopes in tests of the planktonic foraminifer g bulloides from ocean drilling program odp site 1172a east tasman plateau allowed us to reconstruct sea surface temperature sstmg ca sea surface salinity sss and hence variations in the subtropical convergence stc in the southwestern tasman sea over the last four major glacial interglacial changes during interglacials the commonly enhanced sstmg ca and sss correspond to a lowered marine productivity and a lowered terrigenous flux implying that the stc separating cool high nutrient subantarctic surface water from warm saline oligotrophic subtropical surface water and hence the band of zonal westerlies responsible for the eolian dust flux were located south of east tasman plateau the warm east australian current was well established during warm periods and propagated far south during glacial times sstmg ca and sss were lower while both marine productivity and eolian flux increased such conditions prevailed during glacial marine isotope stages mis 12 mis 10 and to a lesser degree mis 6 and implied the extended northward influence of subantarctic surfacewater and a shift of the stc to 44 s the overall climatic signal at site 1172a appears to be largely attenuated when compared to published climate records from comparable latitudes to the west and to the east sstmg ca amplitudes were more pronounced in the subantarctic indian ocean and at chatham rise they exhibit a consistent pattern suggesting that latitudinal shifts of the stc occurred synchronously in the subantarctic indian ocean and at chatham rise but were largely damped at east tasman plateau due to the influence of the east australian current

calcareous plankton and the mid brunhes climate variability in the alboran sea odp site 977 abstract quantitative calcareous plankton analyses have been performed at the ocean drilling program site 977 in the alboran sea through the mid brunhes interval 300 540 ka the results evidence orbital suborbital and millennial scale climate variability which primary reflects temperature change the patterns of increase decrease of coccolithophore and planktonic foraminifera warm water taxa reproduce the stage and substage climate variability in the planktonic 18o in good agreement with other planktonic isotope records from mediterranean sea and atlantic ocean variable conditions characterized by alternating cool nutrient rich or warm and stable sea surface waters occurred during interglacial marine isotope stage mis 13 in response to high amplitude oscillations of insolation during obliquity maximum and to north africa monsoon strength influencing distribution of taxa mis 13a resulted warmer than mis 13c based on the higher abundances of warm water taxa they increase just after insolation maxima suggesting a primary response of calcareous plankton to precessional orbital control following short term warm mis 11e and more humid mis 11d phases a climate optimum lasting about 16 kyr is recognized during mis 11c when major tropical subtropical water arrival into the alboran sea occurred as evidenced by the presence of trilobatus sacculifer mis 11c records unstable climate condition that persisted up to the late mis 11 indicating multiple pulses of southward migrations of subpolar front following the full interglacial mis 11c warm and oligotrophic conditions occurred during mis 9 as during mis 11 especially in mis 9e although without a climate optimum reduced abundance of warm water taxa and decrease of globorotalia inflata highlight colder surface water conditions and decreased atlantic mediterranean water exchange during glacials especially during the prominent sea level low stand of mis 12 short term prominent peaks of the polar subpolar neogloboquadrina pachyderma and coccolithus pelagicus ssp pelagicus and additional key taxa preferring fresher and turbid water together with minima in total nannofossil accumulation rate and enhanced coccolith reworking sustain a correlation with the north atlantic heinrich type ht events ht1 ht1a ht3 ht4 6 thus documenting the sensitiveness of the alboran sea in recording european and laurentide ice sheet dynamics the comparable chronology of most of these cold spells in the available balearic and ionian calcareous plankton records highlights that atlantic melt water entering alboran basin through gibraltar strait may have reached the central mediterranean preserving some of its original polar signature

late quaternary nannofossil indicators of climate change in two deep sea cores associated with the leeuwin current off western australia the stratigraphic variations in nannoflora observed in the two deep sea cores recovered from the offshore western australia revealed a sequence of paleoceanographic changes for the last 250 kyr the dominance of small placolith taxa in the upper photic flora indicates continuous mild upwelling for the isotope stages 7 5 in this region the most important controlling factor for the abundance variation of florisphaera profunda in this region is considered to be the lower photic temperature rather than the stability of water column or the water turbidity the significant reduction in the abundance of f profunda combined with the stable in the northern core rs96gc21 and reduced in the southern core rs9 150 abundance of the small taxa suggest an intensified upwelling for the penultimate glaciation the sharp increase in f profunda abundance indicates a weakening of upwelling at the last interglacial climax lic offshore western australia after isotope stage 5 the existence of upwelling is not clear except in stage 2 when it was not strong enough to produce blooms of emiliania huxleyi among the subordinate taxa calcidiscus leptoporus calciosolenia murrayi neosphaera coccolithomorpha and oolithotus fragilis provide meaningful paleoceanographic signals supporting the conclusions of previous studies a weakening or cessation of leeuwin current for the glacial periods the shift of dominance from small gephyrocapsa mostly g ericsonii to small reticulofenestra mostly r parvula can be an useful datum event offshore western australia the reduced diversity of nannoflora during the interglacial periods can be explained by a lessened competition within nannoplankton community caused by particularly favorable conditions for the opportunists such as e huxleyi f profunda and small placoliths the variations in nannofossil abundance suggests an increased aeolian flux at the stages 6 and 2 offshore north west cape as well as at stage 6 offshore southwestern australia

calcareous nannofossils and the origin of eastern mediterranean sapropels a quantitative analysis of calcareous nannofossil assemblages was carried out with an optical microscope on four deep sea cores raised from the eastern mediterranean and selected to form a nw se transect a total of 748 samples were studied including a very detailed analysis of sapropels s5 and s6 in two out of the four cores this paper is restricted to the discussion of the results obtained on florisphaera profunda which provided important insights on the mechanisms of sapropel formation an intricated and unravelled puzzle for the scientists of the last decades on the basis of abundance variations of f profunda the only species of calcareous nannoplankton which inhabits the lower part of the photic zone i suggest that sapropel formation was triggered by increased primary production either confined to a deep chlorophyll maximum dcm a concept previously introduced by rohling and gieskes 1989 or extended to a thicker layer of the photic zone when increased primary production was confined to the dcm sapropel s3 s4 s5 s7 and s1 this latter only in the eastern part of the basin the abundance of f profunda was enhanced greatly with respect to all other species living in the higher part of the photic zone on the contrary when the increased primary production was extended to a thicker layer of the photic zone glacial sapropels s6 and s8 the production of most nannoplankton species was favored decreasing the relative proportion of f profunda

avo in transversely isotropic media an overview the amplitude variation with offset avo responses of elastic transversely isotropic media are sensitive to contrasts in both of thomsen s anisotropic parameters and e the equation describing p p reflections indicates that the smaller the contrasts in isotropic properties compressional velocity shear velocity and density and the larger the contrasts in and e across an interface of reflection the greater the effects of anisotropy on the avo signature contrasts in are most important under small to medium angles of incidence as previously described by banik 1987 while contrasts in e can have a strong influence on amplitudes for the larger angles of incidence commonly encountered in exploration 20 degrees and beyond consequently using rutherford and williams avo classification of isotropic gas sands type i gas sands overlain by a transversely isotropic ti shale exhibit a larger decrease in avo than if the shale had been isotropic and type iii gas sands overlain by a transversely isot

florisphaera profunda and the origin and diagenesis of carbonate phases in eastern mediterranean sapropel units high relative concentrations of the lower photic zone nannofossil florisphaera profunda have been reported in all recent eastern mediterranean sapropels in the most recent sapropel s1 high bulk sediment sr ca ratios occur along with high f profunda contents toward the base of the unit exemplified here in four cores from 1 5 3 5 km water depth co occurring biogenic carbonates contain insufficient sr to account for these high sr concentrations and x ray diffraction and selective leaching show that the high sr ca ratios are due to aragonite the caco3 polymorph that is rarely preserved in deep marine sediments with 1 wt sr the possible sources of this aragonite include 1 precipitation with surface ocean production 2 detrital input from shallow water sediments by high continental runoff or 3 postdepositional diagenetic formation driven by increased pore water alkalinity resulting from sulphate reduction the third formation mechanism for the aragonite is favored in which case the similarity in the positions of the aragonite and f profunda abundance maxima in sapropels is probably related to corg accumulation and resulting sulphide diagenesis that produces high pore water alkalinity there is clear micropaleontological evidence that dissolution of the less soluble biogenic low mg caco3 is occurring or has occurred during early diagenesis in these sediments despite the coexistence of the more soluble high mg calcite and aragonite polymorphs similar sr ca maxima are also found associated with older sapropels always located close both to local minima in surface ocean 18o that signal maximum monsoon driven runoff and to maxima in diagenetic sediment sulphide contents high freshwater flows from monsoons are believed to drive eastern mediterranean sapropel formation through water column stabilization that favors f profunda production and later through development of deep water column dysoxia anoxia because of reduced ventilation the relative abundances of f profunda are high between 5 and 11 14c kyr b p with a maximum at 9 14c kyr b p the surface ocean production changes marked by f profunda therefore begin earlier and finish later than the formation of the s1 sapropel which only develops between 6 and 10 14c kyr b p

changes in calcareous nannofossil assemblages during the mid pleistocene revolution the distribution of calcareous nannofossils are quantitatively analysed in high resolution deep sea core samples from north atlantic dsdp site 607 and eastern mediterranean odp site 967 between marine oxygen isotope stage mis 35 and 15 in order to observe the response of calcareous nannofossils to the mid pleistocene revolution mpr nannofossil abundance patterns show major variations through mis 25 22 and distinct higher amplitude changes from mis 21 upward sometime clearly correlatable to glacial interglacial cycles high amplitude short term fluctuations of small placoliths and f profunda characterize the interval through mis 24 to 22 21 suggesting strong instability in nutricline dynamics and surface water productivity principal component analysis and shannon weaver indices diversity and dominance highlight significant shifts mainly related to variations in the characteristics of surface waters in both sites a minimum in diversity is recorded at mis 22 21 corresponding to a maximum in the dominance of reticulofenestra spp at site 607 and of pseudoemiliania lacunosa at site 967 above mis 21 the increase in abundance of various taxa c leptoporus umbilicosphaera spp syracosphaera spp rhabdosphaera spp oolithotus spp and a general increase in diversity are related to a distinct trend toward more stable and oligotrophic surface waters in contrast to the higher productivity and less stratified surface waters of the early pleistocene in addition power spectral analysis was performed on calcareous nannofossil abundances shannon index diversity values and factor 1 of principal component analysis these show significant peaks in the obliquity 41 kyr and eccentricity 100 kyr frequency bands indicating that the quasi periodic oscillations in the climate proxy data are controlled by these orbital parameters a relationship between changes in abundance of calcareous nannofossils and production of glacial north atlantic deep water is inferred

variation of frontal and precipitation structure along a cold front a diagnostic study is presented to illustrate the sequence of events in which a warm conveyor belt wcb flow is drawn into the circulation of a developing extratropical cyclone and interacts with dry air aloft to produce distinctive precipitation structures the poleward boundary of the upstream end of the wcb was associated with a classical ana cold frontal structure the other end of the wcb flow closer to the cyclone centre was overrun by a dry intrusion of low wet bulb potential temperature air to give a split kata cold front the orientation of the surface cold front i e the wcb boundary changed significantly between these two parts but the orientation of the surface geostrophic flow within the wcb changed relatively little between the two parts the surface cold front was characterized in most places by a narrow cold frontal rainband composed of shallow line convection elements precipitation cores aligned nearly parallel to the surface geostrophic flow in the wcb the changing relationship between the frontal orientation and the direction of the surface flow accounts for the fact that the line convection elements occurred end to end to give almost two dimensional line convection along the classical ana part of the cold front but were non aligned and widely spaced along the split cold front part

the calcareous nannofossil crisis in northern spain asturias province linked to the early toarcian warming driven mass extinction abstract quantitative analysis of late pliensbachian early toarcian calcareous nannofossil assemblages from the west rodiles section asturias northern spain has been performed in order to interpret the paleoenvironmental changes that occurred during this time interval characterized by a major extinction event and especially around the lower toarcian tenuicostatum serpentinum zonal and extinction boundary nannofossil data were statistically treated the shannon diversity index was calculated and results were compared to the stable isotope data and the total organic carbon content to determine the changes recorded in the entire nannofossil communities a principal component analysis was applied during the latest pliensbachian the nannofossil assemblages were dominated by schizosphaerella sp and tubirhabdus patulus followed by the dominance of calcivascularis jansae taxa that probably thrived in rather cold waters the progressive decrease in the relative abundances of both schizosphaerella sp and c jansae coincides with a progressive increase in paleotemperatures during the extinction interval as indicated by the 18o values measured on diagenetically screened belemnite calcite biscutum spp dominated the nannofossil assemblages during the early toarcian tenuicostatum ammonite zone when seawaters were warm in the west rodiles section the extinction boundary coincides with the deposition of the laminated shales where especially high relative abundances of calyculus spp were recorded after the extinction boundary c jansae becomes extinct the relative abundance of biscutum spp sharply decreases and the nannofossil assemblages become dominated by the crepidolithus and lotharingius species which have been interpreted as opportunistic taxa the shannon index fluctuates throughout the studied section although it is especially high after the extinction boundary the covariance between the nannofossil crisis and the evolution of 18obel based seawater paleotemperatures as well as the fact that none of the explanations proposed by other authors seems to explain our observations suggest a clear relationship between the increase in paleotemperature and the changes recorded in our nannofossil assemblages nevertheless we do not discard possible changes in other paleoenvironmental parameters related or not to warming

effects of superficial layers on coseismic displacements for a dip slip fault and geophysical implications summary we study the effect of a superficial layer overlying a half space on the surface displacements created by a dip slip dislocation on a planar rectangular fault using a 2 d finite element model the effect of the density and poisson s ratio is negligible on the other hand the contrast in young s modulus between the top layer and the half space below significantly affects the modelled coseismic displacements the horizontal displacements are more sensitive than the vertical displacements to the existence of the top layer near the fault a low rigidity layer with a young s modulus of 10 gpa can increase the horizontal displacements by up to 40 per cent an analytical 3 d half space model is used to interpret this effect in terms of an equivalent homogeneous model the presence of a top layer can be partly simulated in a homogeneous half space by perturbing the depth and the slip on the fault from their real values to equivalent values for a given displacement field observed at the surface the perturbations in fault depth and slip can reach 1 km and 25 per cent respectively the fault dip angle is not model dependent we conclude that for the accurate estimation of fault depth and slip from coseismic geodetic data rigidity contrasts existing within the upper crust must be taken into account not taking into account the effect of an existing low rigidity layer also leads to an underestimation of seismic moment release this may in part be the cause of apparent discrepancies between seismic and geodetic moment releases in particular areas such as the gulf of corinth greece

pliensbachian early jurassic calcareous nannofossils from the peniche section lusitanian basin portugal a clue for palaeoenvironmental reconstructions abstract quantitative analysis of early jurassic calcareous nannofossil assemblages from the peniche section in portugal have been performed in order to interpret palaeoenvironmental changes occurring in the lusitanian basin during the late pliensbachian davoei margaritatus and spinatum ammonite zones nannofossil data are compared to already published carbon and oxygen stable isotope data organic matter content wt total organic carbon toc and biomarker analysis a significant change in calcareous nannofossil assemblages and species diversity at the transition between the margaritatus and spinatum ammonite zones matches with the pattern shown by geochemical data this suggests that a profound change in environmental conditions occurred at that time in the davoei and margaritatus ammonite zones in a context of general sea level rise the lusitanian basin was characterized by water column stratification that favoured the sedimentation and preservation of organic matter biomarkers and oxygen isotope trends suggest that stratification of water masses occurred because of low salinity in surface waters the shallowest part of the water column characterized by oligotrophic conditions was inhabited by the probable calcareous dinocyst schizosphaerella spp while the deep dweller crepidolithus crassus flourished in the lower photic zone layers in the spinatum ammonite zone a regressive trend occurred and a salinity increase is inferred on the basis of oxygen isotope values water masses were probably less stratified at that time the upper photic zone nannofossil assemblages were still dominated by schizosphaerella spp whilst in the deep photic zone mitrolithus jansae a mediterranean taxon replaced c crassus a taxon with nw european affinity this pattern may indicate a change in palaeoceanographic conditions related to surface current circulation the sea level fall occurring during the spinatum ammonite zone may have resulted in the partial isolation of the lusitanian basin from the nw europe basins because of the creation of a threshold alternatively tectonic drowning of north african carbonate platforms in the late pliensbachian may have promoted better exchanges of nannoplankton between the lusitanian basin and the mediterranean tethys via the creation of new seaway connections

millennial scale coccolithophore paleoproductivity and surface water changes between 445 and 360 ka marine isotope stages 12 11 in the northeast atlantic abstract a high resolution coccolithophore study was carried out in order to improve the understanding of the paleoceanographic evolution and changes in paleoproductivity occurring off the iberian margin im between 445 and 360 ka i e during late marine isotope stage 12 to 11 coccolithophore assemblages allowed reconstructing surface water changes characterized by millennial scale oscillations 1 5 kyr cycles involving portugal or iberian poleward currents pc and ipc prevalence changes in paleoproductivity possibly related to the upwelling of eastern north atlantic central waters enacw of sub tropical enacwst or sub polar origin enacwsp were also recognized this study also permitted detecting abrupt events stadial interstadial type oscillations and revealed that changes in paleoproductivity are related to opposite dynamics during glacial and interglacial stages with the reversed setting being established during the deglaciation furthermore a possible control of half and fourth precessional cycle components on the occurrence of abrupt changes within the assemblages structure during the deglaciation is proposed on the basis of wavelet analysis results applied to selected taxa

nannoplankton successions in the northern red sea during the last glaciation 60 to 14 5 ka bp reactions to climate change abstract due to its restricted connection with the indian ocean the desert enclosed red sea is extremely sensitive to global sea level changes and thus ideally suited for paleoceanographic studies of what occurred during the last glaciation the understanding of its glacial history is however still limited a serious obstacle to obtain satisfactory paleoecological information has been the rarity of microfossil proxy species caused by high salinities here we present a continuous and well dated calcareous nannoplankton record from the northern red sea covering the interval from 60 14 5 ka bp our investigation shows that the composition of the calcareous nannoplankton community varied between 32 ka bp and 14 5 ka bp in response to rapid environmental changes which are closely correlated to climatic fluctuations described from the north atlantic region heinrich events h3 h2 and h1 are dominated by emiliania huxleyi gephyrocapsa oceanica and especially gephyrocapsa ericsonii are abundant between h3 h2 and h2 h1 a less pronounced response of the calcareous nannoplankton to the high latitudinal climatic oscillations is documented prior to 32 ka bp suggesting that a strong atmospheric coupling between the northern red sea and the north atlantic realm was established in the late marine isotope stage 3 in contrast to the previously held view of a sea level related salinity increase as the major cause for changes of the plankton communities within the glacial red sea we interpret the documented variations as being caused by local hydrographic changes under the atmospheric control from the extratropics temperature changes and especially variations of the water stratification appear to be critical selective factors for the calcareous nannoplankton composition

surface and deep water variability in the western mediterranean odp site 975 during insolation cycle 74 high resolution calcareous plankton and molecular biomarker signals abstract we reconstructed changes in productivity and surface subsurface and deep water dynamics in the western mediterranean through a multi proxy study of ocean drilling program site 975 between late marine isotope stage mis 20 and early interglacial mis 19 our high resolution study down to 200 year resolution combines calcareous plankton assemblages coccolithophores and foraminifera biomarkers c37 alkenones n alkanes n alcohols and elemental proxies total organic carbon total nitrogen calcium carbonate surface water conditions are derived i from high resolution 18o and 13c records obtained from the planktonic foraminifer globigerina bulloides and ii from summer and winter foraminifera based sea surface temperature reconstructions sstjas foram sstjfm foram achieved through transfer function the integration of the whole dataset makes it possible to identify in the balearic sea and to accurately characterize for the first time an organic rich layer orl during latest mis 20 early mis 19 close to i cycle 74 its presence is marked firstly by higher values of total nitrogen tn and an increase of total c37 alkenone and total organic carbon toc preserved in the sediments the multi proxy approach reveals that the deglacial phase played a prominent role for orl formation that was characterized by centennial scale phases the alcohol preservation index api suggests that the shoaling of the circulation which boosted marine productivity started in the deglaciation and in combination with freshening by atlantic water inflow riverine input and surface water buoyancy during sea level rising culminated during the orl event at this time calcareous plankton proliferated on subsurface surface waters benefiting from ameliorating conditions which promoted maximum marine productivity and higher organic matter preservation on the seafloor

precessional forcing of nutricline dynamics in the equatorial atlantic climate control of nutricline depth in the equatorial atlantic can be monitored by variations in the abundance of the phytoplankton species florisphaera profunda a conceptual model based on in situ evidence associates high abundances of f profunda with a deep nutricline and low abundances with a shallow nutricline a 200 000 year record of f profunda relative abundances obtained from a deep sea core sited beneath the region of maximum equatorial divergence at 10 w has 52 percent of its variance centered on the 23 000 year precessional band cross spectral analysis between the signals of f profunda and sea surface temperature independently derived from zooplankton species shows their 23 000 year cycles to be coherent and nearly in phase abundance minima of f profunda coincide with times of december perihelion whereas abundance maxima coincide with june perihelion these relations indicate that nutricline dynamics in the divergence region of the equatorial atlantic are controlled by variations in the tropical easterlies forced by the precessional component of orbital insolation on time scales greater than 10 000 years

ocean surface water response to short term climate changes revealed by coccolithophores from the gulf of cadiz ne atlantic and alboran sea w mediterranean the response of coccolithophore assemblages to short term millennial and centennial climatic changes over the last 50 kyr is studied in core m39029 7 from the gulf of cadiz atlantic ocean and core md95 2043 from the alboran sea western mediterranean sea the nannoplankton data are compared with oxygen isotopes u37k sst and other biogeochemical and sedimentological proxies to obtain a new perspective of the paleoceanography and paleoecology of the area during these short term climatic changes coccolithophores indicate that heinrich events he were characterised by the presence of cold low salinity and turbid water masses on both sides of the strait of gibraltar high abundances of the lower photic zone lpz species florisphaera profunda in the gulf of cadiz synchronous with he are interpreted as being an evidence of upper water column stratification on the atlantic side these episodes coincided with input of terrigenous material especially during h2 surface waters during dansgaard oeschger do stadials were also cold and turbid while most of do interstadials were characterised by warm water flora the increase in small placoliths small gephyrocapsa and emiliania huxleyi 4 m which is considered here as a cold water indicator the sharp decrease in large specimens of e huxleyi related to the warming trend in the last deglaciation can be used as a biostratigraphic reference level that marks at least approximately the deglaciation and the beginning of the holocene peaks of f profunda are observed during termination 1 t1 in the alboran sea they are isochronous with the organic rich layer 1 recognised in the western mediterranean in this interval the water column of the region was stratified as a consequence of the global increase in the sea level following the deglaciation quantitative analyses of the coccolithophore assemblage allow us to interpret that coccolithophore production has been higher in the alboran sea than in the gulf of cadiz during the holocene

late quaternary paleoceanography deduced from coccolith assemblages in a piston core recovered off the central japan coast abstract nannofossil assemblages from the last 144 ka marine isotope stage mis6 were studied in a piston core md01 2421 from the nw pacific 36 01 4 n 141 46 8 e wd 2 224 m off the coast of central japan the site is influenced by both the subtropical kuroshio and the subarctic oyashio currents and is located just north of the kuroshio front this study attempted to reconstruct paleoceanographic changes in the region by illustrating the past migration patterns of the kuroshio current which is considered to be one of the strongest western boundary currents in the pacific in order to reconstruct the past migration patterns of the kuroshio current relative abundance values of several taxa classified as either kuroshio species or oyashio species were used as indices using these species a ratio tn nannofossils temperature index representing the mixing of the kuroshio and oyashio currents was calculated to express quantitatively the influence of the kuroshio current tn values fluctuated widely ranging from 1 45 135 ka to 86 9 115 3 ka and corresponds to the warm cold cycles obtained by oxygen isotope analysis the fluctuation pattern of percentage abundance of umbellosphaera spp shows a strong similarity to that of the precessional cycle it may indicate that subtropical water has influenced the japanese coast during these warm intervals possibly due to the expansion of subtropical divergence also the fluctuation pattern of tn shows a similar time transgressive trend to that of the precessional cycle this implies that latitudinal displacement of the kuroshio front was related to subtropical climatic variability the ratio between tn and tp planktonic foraminifera temperature index drastically increased at about 20 ka in mis2 with small peaks in mis6 this suggests that a thin layer of warm water may have covered the study area during these intervals an increased preservation of organic matter i e caco3 preservation possibly affected the absolute coccolith abundance coccolith g dry sediment although other factors controlling absolute coccolith abundance e g nutrient levels need to be taken into consideration

variations in deep sea benthic foraminifera at odp hole 756b southeastern indian ocean evidence for changes in deep ocean circulation abstract seventy three core samples of 10 cc volume were analysed from ocean drilling program odp site 756 hole b with an average interval of 236 kyr per sample factor and cluster analyses of 37 high ranking species of benthic foraminifera enabled us to identify four clusters representing four biofacies biofacies sl om is characterised by stilostomella lepidula orthomorphina modesta robulus gibbus bulimina miolaevis and cibicides cf lucidus this biofacies dominates the latest oligocene to early miocene interval 24 21 ma and 18 75 16 5 ma indicating low to intermediate dissolved oxygen organic carbon rich environment warm and sluggish deep waters during 21 18 75 ma the biofacies gp nu globocassidulina pacifica nuttallides umbonifera trifarina angulosa quinqueloculina weaveri robulus gibbus and pullenia bulloides dominates the benthic assemblage at hole 756b this biofacies also has a short lived presence at 16 5 ma this was an interval of intense circulation of cold and corrosive deep water similar to antarctic intermediate water aaiw and intermediate to high flux of organic matter to hole 756b the antarctic circumpolar current acc initiated during this time from 16 5 to 10 6 ma the benthic assemblage at hole 756b is dominated by biofacies ub gs characteristic species uvigerina buzasi globocassidulina subglobosa laticarina pauperata indicating intermediate to high food supply and cold deep water this interval coincides with the middle miocene positive oxygen isotope shift and permanent build up of antarctic ice sheets the late miocene interval 10 6 6 5 is characterised by biofacies ec bs dominant species ehrenbergina carinata bolivina spathulata osangularia culter and pullenia osloensis indicating low oxygen condition with high food supply in the study area this corresponds to an interval of global biogenic bloom

aragonite cycles diagenesis caught in the act organic biomarker and nannofossil assemblages are used in combination with sedimentary petrology to identify the role of diagenesis for the formation of a rhythmic calcareous succession a record from the early pliocene of the maldives ocean drilling program odp leg 115 is presented containing precession and eccentricity cycles expressed as variable aragonite content additional sub milankovitch cycles are caused by rhythmic precipitation of calcite cement in the lower part of the interval comparison with palaeo productivity indicators nannofossils chlorin total organic carbon suggests that cementation occurs preferentially in intervals characterized by increasing or decreasing productivity the coupled variability in productivity and carbonate diagenesis is attributed to the effect of organic matter degradation in the sediment the observed combination of primary and diagenetic factors hampers the interpretation of the cyclicity on milankovitch and sub milankovitch scales diagenetically stable proxies for palaeo productivity such as nannofossil assemblage data were used to distinguish between palaeoclimate and diagenetic influences

coccolithophore productivity and surface water dynamics in the alboran sea during the last 25kyr abstract coccolithophore productivity and surface water dynamics for the last 25 kyr in the alboran sea western mediterranean are described in a study of high resolution sedimentary records from two cores her gc t1 and ceuta10pc08 whose locations are currently characterized by different hydrographic conditions fossil coccolithophore assemblages and oxygen isotopes and alkenone and planktonic foraminifera derived sea surface temperature sst records allowed a reconstruction of the properties of the inflowing atlantic water aw which have proved to be a primary control of the variations in productivity in the neighborhood of the strait of gibraltar other local factors such as fluvial discharge wind induced and eddy induced upwelling are proposed to have influenced marine productivity in more distant areas the entrance of cold and less saline aw during the stadials associated with heinrich events 2 and 1 prevented primary productivity which increased along the last glacial maximum probably due to a greater fluvial discharge during terminations 1a and 1b the upper water column was affected by stratification although wind induced upwelling occurred locally the bolling allerod was characterized by a gradual increase in productivity and the development of the organic rich layer two phases of the younger dryas are recognized a first phase which was colder followed by a second phase which was warmer and wetter differences in productivity between both locations during these two phases can be attributed to fluvial discharge and the changing properties of the aw local hydrography such as the dynamics of the western anticyclonic gyre gained greater importance in determining productivity and its variations during the holocene which was the most productive period

reconstruction of paleoceanographic conditions in the northwestern pacific ocean over the last 500kyr based on calcareous nannofossil and planktic foraminiferal assemblages calcareous nannofossil and planktic foraminiferal assemblages from odp hole 1210a in the northwestern pacific ocean were used to reconstruct surface water conditions for the past 500 kyr stratigraphic control was provided by calcareous nannofossil events that are thought to be synchronous over a broad range of latitudes calcareous nannofossil and planktic foraminiferal assemblages and abundance patterns indicate the unlikelihood of long term milankovitch scale latitudinal shifts of the kuroshio extension over the last 500 kyr and illustrate two successive surface water mass states one that prevailed prior to 300 ka and one that existed after 300 ka the relative abundance of very small placoliths and the absolute abundance of the upper photic zone upz coccolith species decrease abruptly at approximately 300 ka the relative abundance of the lower photic zone lpz species florisphaera profunda greatly increases at the same time although intervals during which the relative abundance of this taxon is very low or absent also occur prior to 300 ka the absolute abundance of planktic foraminifera gradually increased after the 300 ka boundary including peaks of globoconella inflata these assemblage and abundance changes suggest significant modifications to the surface water mass structure surface water was weakly stratified prior to 300 ka but alternated between intensely stratified and vertically mixed after 300 ka changes in the surface water mass structure suggest an intensification of the east asian summer and winter monsoon after 300 ka

paleoceanography of the mid pleistocene the fossil record of the pleistocene calcareous nannoplankton indicates that during the mid pleistocene 0 93 1 25 my occurred an episode of overwhelming dominance of smallgephyrocapsa during this episode normally abundant large size specimens of this genus mainlygephyrocapsa oceanica were virtually excluded from the phytoplankton of tropical and subtropical oceans the best modern analog of this dominantly smallgephyrocapsa assemblage is the subpolaremiliania huxleyi assemblage which implies that nutrient content was significantly greater and water temperature was lower in the photic water column of the tropical oceans than they are today increased equatorial upwelling in the oceans on a scale much greater than today may explain the above pattern to achieve such broad equatorial upwelling there must be a source and a drive for cold dense water the arctic ocean which was probably seasonally free of ice during this interval of the mid pleistocene is capable of providing the requisite source as well as a drive for the inferred equatorial upwelling the energy balance of a predominantly ice free arctic ocean requires an approximately three to seven fold increase of hydrospheric heat transport from the north atlantic to the arctic ocean which dictates a corresponding or even greater increase in the volume of warm water entering the arctic ocean at the surface and cold dense water exiting at depth to the north atlantic such enhanced dense water formation in the arctic ocean could drive the intensified equatorial upwelling implied by the smallgephyrocapsa dominance interval if the above scenario is correct then the climate of the earth s northern hemisphere during the mid pleistocene may have been very different from the younger pleistocene climate one manifestation of this difference may be the mid pleistocene shift in climatic cycle periodicity from 40 ky to 100 ky another important aspect is that the enhanced greenhouse effect expected during the next century because of an increase of atmospheric co2 is thought to lead directly to melting of the arctic ocean ice cover and of the greenland ice sheet thus the greenhouse arctic ocean and its attendant ocean circulation would resemble the inferred mid pleistocene conditions

seismic velocities of unconsolidated sands part 2 influence of sorting and compaction induced porosity variation unaccounted for porosity variation in unconsolidated sediments can cloud the interpretation of the sediment s seismic velocities for factors such as fluid content and pressure however an understanding of the effects of porosity variation on the velocities can permit the remote characterization of porosity with seismic methods we present the results of a series of measurements designed to isolate the effects of sorting and compaction induced porosity variation on the seismic velocities and their pressure dependences in clean unconsolidated sands we prepared a set of texturally similar sand and glass bead samples with controlled grain size distributions to cover an initial porosity range from 0 26 to 0 44 we measured the compressional and shear wave velocities and porosity of dry samples over a series of hydrostatic pressure cycles from 0 1 to 20 mpa over this rangeof porosities the velocities of the dry samples at a given pressure vary by 15 however the water saturated compressional wave ve

a physical model for shear wave velocity prediction the clay sand mixture model of xu and white is shown to simulate observed relationships between s wave velocity or transit time porosity and clay content in general neither s wave velocity nor s wave transit time is a linear function of porosity and clay content for practical purposes clay content is approximated by shale volume in well log applications in principle the model can predict s wave velocity from lithology and any pair of p wave velocity porosity and shale volume although the predictions should be the same if all measurements are error free comparison of predictions with laboratory and logging measurements show that predictions using p wave velocity are the most reliable the robust relationship between s and p wave velocities is due to the fact that both are similarly affected by porosity clay content and lithology moreover errors in the measured p wave velocity are normally smaller than those in porosity and shale volume both of which are subject to errors introduced by imperfect models and imperfect parameters when estimated from logs because the model evaluates the bulk and shear moduli of the dry rock frame by a combination of kuster and toksoz theory and differential effective medium theory using pore aspect ratios to characterize the compliances of the sand and clay components the relationship between p and s wave velocities is explicit and consistent consequently the model sidesteps problems and assumptions that arise from the lack of knowledge of these moduli when applying gassmann s theory to this relationship making it a very flexible tool for investigating how the v p v s relationship is affected by lithology porosity clay content and water saturation numerical results from the model are confirmed by laboratory and logging data and demonstrate for example how the presence of gas has a more pronounced effect on p wave velocity in shaly sands than in less compliant cleaner sandstones

high resolution palaeoenvironmental reconstruction of odp hole 963d sicily channel during the last deglaciation based on calcareous nannofossils abstract a palaeoenvironmental reconstruction of ocean drilling program odp hole 963d sicily channel has been obtained on the basis of quantitative abundance fluctuations in the calcareous nannofossil assemblages the studied hole is characterized by a very high sedimentary resolution and covers the last ca 20 kyr a new palaeoclimatic curve based on the gephyrocapsa muellerae upper photic zone upz group ratio permitted the detection of the rapid climatic fluctuations that characterized the last deglaciation cold water masses occupied the sicily channel during the glacial period and the younger dryas whereas they were generally warm during the bolling allerod and the holocene an approach based on a direct relationship between actualistic data water samples and palaeontological records in the coccolithophores has been attempted in order to obtain the palaeoecological characterization with the proposition of two floristic groups pertaining to the upper photic zone and the lower photic zone lpz further information has been provided by several additional taxa during the investigated time interval stratification in the water column and oligotrophic conditions are always linked to the warm periods while high productivity caused by continuous convection of nutrient fluxes existed during the cold periods finally a simple model with two end members is proposed to explain the relative abundance of the deep dwelling species florisphaera profunda relative to other coccolithophores and to the physical conditions of the photic zone

a high resolution record of the last deglaciation in the sicily channel based on foraminifera and calcareous nannofossil quantitative distribution abstract relative abundance fluctuations in planktic foraminiferal and calcareous nannofossil assemblages are reported on the basis of a high resolution study of odp leg 160 hole 963d drilled in the sicily strait near capo rossello southern sicily with its 8 m of undisturbed sediments the core covers the interval from 1 5 to 23 kyr allowing a 50 100 yr sampling resolution all the short warm and cold events and sub events recorded in this time interval in the grip greenland ice core and at several mediterranean sites were recognized on this basis a total number of nine ecozones based on planktic foraminifera and seven ecozones based on calcareous nannofossils were identified a short interval of climatic amelioration identified above the base of the holocene precedes the segment contemporaneous with the deposition of sapropel s1 which has no lithological expression in the local sedimentary record this segment has been subdivided into the two warm s1a and s1b phases separated by a cold intermediate event a gradual climatic deterioration is recorded above the top of the interval correlated with sapropel s1 it is interrupted by short cold spells tentatively correlated with similar short duration cold events reported for this interval in the recent literature

velocity porosity relationships for water saturated siliciclastic sediments seeking a global empirical relationship between compressional wave velocity and porosity for siliciclastic sediments we have brought together an extensive suite of both new and published log and core based data we undertook a detailed statistical analysis of ocean drilling program data from amazon fan to examine variables affecting compressional velocity in shallow unconsolidated sediments we identify three dominant variables porosity shale fraction and consolidation history and present two empirically determined boundary curves one for normally consolidated sediments and a second for highly consolidated environments e g accretionary prisms these two empirical relationships predict the compressional velocity of siliciclastic sedimentary rocks with water filled pores as a function of porosity and clay content for the full range of observed porosities velocities of siliciclastic sedimentary rocks decrease rapidly with both increasing porosity and increasing clay content at fractional porosities higher than about 0 4 fluid dominates the elastic properties and velocity exhibits a subtle dependence on porosity remarkably the amazon fan data show that clay content has no direct influence on velocity at high porosities both clay content and sorting do indirectly affect velocity through their control of porosity burial affects velocity not only by compaction related porosity decrease but also by pressure induced increase of intergrain coupling because of the sensitivity of velocity to consolidation history particularly at intermediate fractional porosities of about 0 30 0 40 no single velocity porosity relationship can apply to all high porosity sediments the two proposed relationships fit the majority of published and new data they are applicable however only for normally pressured in situ conditions and water filled pores

coccolithophores as proxy of seawater changes at orbital to millennial scale during middle pleistocene marine isotope stages 14 9 in north atlantic core md01 2446 quantitative coccolithophore analyses were performed in core md01 2446 located in the midlatitude north atlantic to reconstruct climatically induced sea surface water conditions throughout marine isotope stages mis 14 9 the data are compared to new and available paleoenvironmental proxies from the same site as well as other nearby north atlantic records that support the coccolithophore signature at glacial interglacial to millennial climate scale total coccolithophore absolute abundance increases during interglacials but abruptly drops during the colder glacial phases and deglaciations coccolithophore warm water taxa wwt indicate that mis11c and mis9e experienced warmer and more stable conditions throughout the whole photic zone compared to mis13 mis11 was a long lasting warmer and stable interglacial characterized by a climate optimum during mis11c when a more prominent influence of the subtropical front at the site is inferred the wwt pattern also suggests distinct interstadial and stadial events lasting about 4 10 kyr the glacial increases of gephyrocapsa margereli g muellerae 3 4 m along with higher values of corg additionally supported by the total alkenone abundance at site u1313 indicate more productive surface waters likely reflecting the migration of the polar front into the midlatitude north atlantic distinctive peaks of g margereli muellerae 4 m c pelagicus pelagicus neogloboquadrina pachyderma left coiling and reworked nannofossils combined with minima in total nannofossil accumulation rate are tracers of heinrich type events during mis12 and mis10 additional heinrich type events are suggested during mis12 and mis14 based on biotic proxies and we discuss possible iceberg sources at these times our results improve the understanding of mid brunhes paleoclimate and the impact on phytoplankton diversity in the midlatitude north atlantic region

modeling elastic properties of siliciclastic rocks we have modeled the effective elastic moduli and hence the compression and shear wave velocities of dry sandstones the modeling is distinctly different in two ranges of porosity from zero to the consolidation limit con consolidated regime where the rock is treated as continuous material containing pores and cracks and from con to the critical porosity c where the rock is transitioning to a granular material unconsolidated regime in the consolidated regime the modeling is micromechanics based and yields the moduli in terms of porosity pore shape factor and crack density based on the noninteraction approximation with the mori tanaka correction for interactions by necessity it contains empirical parameters reflecting highly irregular shapes of pores and microcracks in the unconsolidated regime we propose empirical relations of the mori tanaka type where pore shape factors assume large values consistent with very soft concave pore shapes typical in this regime combined the two

late quaternary oceanic fronts along chatham rise indicated by phytoplankton assemblages and refined calcareous nannofossil stratigraphy for the mid latitude sw pacific abstract a quantitative analysis was carried out of planktonic diatoms biogenic opal and calcareous nannofossils biogenic calcite in late quaternary sediments mis 1 6 from four cores along a n s transect east of new zealand from 39 50 s to 50 04 s across the e w trending submarine ridge the chatham rise this was done to trace movements of oceanic fronts and to improve calcareous nannofossil stratigraphy for the last 130 000 yr in the sw pacific sites odp 1123 and q 858 are below present day subtropical surface waters north of chatham rise site dsdp 594 is below present day mixed temperate subantarctic surface water south of the rise and site odp 1120 is below subantarctic surface water the more diverse and opportunistic planktonic diatoms provided marker species for subtropical surface waters alveus marina fragilariopsis doliolus rhizosolenia bergonii and azpeitia nodulifer and others for subantarctic surface waters nitzschia kerguelensis thalassiosira lentiginosa application of these tracers permits the following conclusions 1 subtropical conditions persisted north of chatham rise throughout the past 130 000 yr in spite of the cooling of surface waters during colder periods 2 during warm times mis 5 and mis 3 and in mis 1 the sporadic occurrence of subtropical species south of chatham rise indicates occasional admixture of subtropical surface waters that far south 3 subantarctic waters extended to the southern slopes of the chatham rise during mis 5b late mis 5a to early mis 4 during the warmer time intervals in early mis 3 and during latest mis 3 to early mis 2 4 subantarctic frontal conditions existed over southern chatham rise during early mis 4 and late mis 3 to early mis 2 and 5 it is probable that during cooler times mis 6 mis 5b and in mis 2 intensified particle transport from the bounty trough to the northern flank of chatham rise occurred by intensified boundary currents the larger abundance fluctuations in both microfossil groups at the sites south of chatham rise than north of chatham rise reflect northward shifts of the circumpolar subantarctic water csw and a contemporaneous disappearance of australasian subantarctic water asw implying an elevated temperature gradient between the surface water masses north and south of the chatham rise at the times of such northward shifts of csw calcareous nannofossils are less diverse than diatoms and are less specialised some calcareous nannofossil species show abundance shifts at the same time at different latitudes two of these abundance shifts can be used for correlation between subtropical and subantarctic sediments in the sw pacific 1 reversal in the relative abundance of calcidiscus leptoporus and coccolithus pelagicus associated with the mis 2 1 boundary and 2 drop in abundance of gephyrocapsa muellerae or medium sized gephyrocapsa at the mis 4 3 boundary an additional abundance shift seems to be restricted to subtropical to mixed temperate subtropical subantarctic surface waters 3 increase in abundance of g muellerae or medium sized gephyrocapsa at the beginning of mis 2 below the okareka tephra

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones part v the substructure of narrow cold frontal rainbands abstract the organization and structure of a narrow cold frontal rainband ncfr on the small mesoscale and the microscale have been investigated through quantitative radar reflectivity doppler radar observations airborne observations and surface measurements the ncfr was composed of small mesoscale regions of heavy precipitation called precipitation cores pcs oriented at an angle to the synoptic scale cold front in horizontal cross section the pcs were roughly elliptical in shape areas of lighter precipitation called gap regions grs separated the pcs the pcs were so oriented that their loading edges were regions of strong low level convergence the weather associated with the passage of a pc resembled that of a squall line gust front with concurrent windshifts and pressure checks occurring 5 min before heavy precipitation and a fall in temperature the changes in surface weather that accompanied the passage of a gr were more variable but tended to be less marked than for pcs thus the se

ultrasonic velocities in sands revisited ultrasonic compressional and shear wave velocities of isotropic sands are shown to be dependent on their mineralogy their porosity their fluid content and their state of consolidation under fixed temperature and pressure conditions this leads to a distinction between two broad classes of sands those that are well consolidated and those that are loosely consolidated changes in elastic velocities reflect changes in the ratio of bulk and shear moduli to density in response to lithologic variations we decouple the two effects by examining changes in elastic moduli with respect to changes in lithology and we observe three main points 1 for consolidated sandstones the effects of mineralogy and porosity can be approximated both empirically and theoretically by a modified isostrain theory the dry bulk and shear moduli of the rock aggregate follow a mixing law being linear combinations of the respective moduli of the individual constituents the dry elastic moduli of families of clean sands and s

variability in the vertical structure of the water column and paleoproductivity reconstruction in the central western mediterranean during the late pleistocene abstract a sedimentary sequence spanning marine isotope stage mis 6 to mis 2 in core lc07 recovered in the central mediterranean has been investigated in order to produce a high resolution paleoceanographic reconstruction the changes in productivity deduced from calcareous plankton relative abundances and independently confirmed by the ba xs fluctuations are linked to the stability of the water column which is mainly controlled by the water mass temperature during glacial intervals productivity was generally enhanced oligotrophic and warmer water masses with a deepened seasonal thermocline can be inferred for most of mis5 the magnetic properties of the sediment show increased occurrences of north africa dust in the central mediterranean during cold phases likely as a consequence of a more efficient erosive process triggered by southward displacement of the intertropical convergence zone although increases in both productivity and saharan dust occurred during cold periods the atmospheric inputs do not seem to contribute significantly to the fertilization of primary producers a shannon index curve has been used to tentatively synthesize the variations of calcareous nannofossil assemblages through the last 150 kyr the assemblage diversity sharply increased coincident with the transition from the penultimate glacial to the last interglacial subsequently low diversity was gradually reached again in the last glacial

the warm interglacial marine isotope stage 31 evidences from the calcareous nannofossil assemblages at site 1090 southern ocean article i nfo calcareous nannofossil assemblages have been investigated at ocean drilling program odp site 1090 located in the modern subantarctic zone through the pleistocene marine isotope stages mis 34 29 between 1150 and 1000 ka a previously developed age model and new biostratigraphic constraints provide a reliable chronological framework for the studied section and allow correlation with other records two relevant biostratigraphic events have been identified the first common occurrence of reticulofenestra asanoi distinctly correlated to mis 31 32 the re entry of medium gephyrocapsa at mis 29 unexpectedly similar to what was observed at low latitude sites the composition of the calcareous nannofossil assemblage permits identification of three intervals i iii intervals i and iii correlated to mis 34 32 and mis 30 29 respectively are identified as characteristic of water masses located south of the subtropical front and reflecting the southern border of subantarctic zone at the transition with the polar front zone this evidence is consistent with the hypothesis of a northward shift of the frontal system in the early pleistocene with respect to the present position and therefore a northernmost location of the subantarctic front during interval ii which is correlated to mis 31 calcareous nannofossil assemblages display the most significant change characterized by a distinct increase of syra cosphaera spp and helicosphaera carteri lasting about 20 ky an integrated analysis of calcareous nannofossil abundances and few mineralogical proxies suggests that during interval ii site 1090 experienced the influence of subtropical waters possibly related to a southward migration of the subtropical front coupled with an expansion of the warmer agulhas current at the core location this pronounced warming event is associated to a minimum in the austral summer insolation the present results provide a broader framework on the mid pleistocene dynamic of the ocean frontal system in the atlantic sector of the southern ocean as well as additional evidence on the variability of the indian atlantic ocean exchange

coccolithophore assemblages during the holocene climatic optimum in the ne mediterranean aegean and northern levantine seas greece paleoceanographic and paleoclimatic implications recent paleoceanographic findings suggest that during the holocene ne mediterranean climate was less stable than previously thought several recently generated aegean paleoceanographic records of sapropel s1 suggest that during the holocene short term potentially global cooling episodes reflecting the n atlantic climatic fluctuations and possibly related to solar variability are superimposed on the underlying regional subtropical tropical control on the hydrography and ecosystems detailed quantitative analyses of coccolithophores have been performed on the deep sea deposits of the ne mediterranean sea four gravity core records from north aegean sea sl 152 se aegean ns 14 ns 18 and south cretan continental margin northern levantine sea hcmr 2 22 respectively with a focus on the regional expression of sapropel s1 deposition in all sites higher values of florisphaera profunda helicosphaera carteri braarudosphaera bigelowii and the increase of stratification s index within sapropel intervals can be interpreted as the result of elevated marine production in the deep photic zone and enhanced inflow of fresh water input during the s1 period the stratification s index is significantly higher in the north aegean in respect to se aegean and the south cretan margin scm reflecting increased coccolithophore productivity at the lower photic zone being associated with a remarkably stratified water column the concomitant increased presence of b bigelowii indicates the prominent riverine input in the north aegean basins and possible influx of black sea waters after 9 0 ka bp consequently the increased stratification of the water column is linked to the significant freshening of the north aegean surface waters particularly during the early stages of the holocene climatic optimum s1a depositional interval a series of cooling events detected towards the end of sapropelic conditions 7 2 ka bp mostly in the north aegean site may be linked to outbursts of cold northerly air masses and relevant pulses in the deep intermediate water ventilation that caused the enhancement of surface marine productivity and the temporary cessation of s1 at 8 0 ka bp in contrast in the se aegean and the northern levantine sea the water column remains still warm and stratified influenced by moderate fresh water input for at least 1 more ky

application of theoretically derived rock physics relationships for clastic rocks to log data from the wilmington field ca relationships between porosity and shear modulus are applied to logs recorded in the miocene upper terminal formation of the wilmington field ca to predict porosity from shear wave velocity data recorded through casing using a dipole sonic logging tool a relationship based on a modified hashin shtrikman lower bound appropriate for the unconsolidated nature of the formation allows determination of porosity from the shear modulus the results are similar to those obtained using standard log analysis in sands standard logs predict higher porosities in smectite bearing wackes because of the inclusion in the standard analysis of bound water or micro porosity in the clays which is not included in the porosity value derived from the shear wave velocity

origin of late pleistocene bryozoan reef mounds great australian bight bryozoan rich biogenic mounds grew periodically on the prograding carbonate slope of the central great australian bight throughout pliocene pleistocene time cores from three odp leg 182 drill sites provide a record of mound growth during the last 300 000 years over a stratigraphic thickness of similar to 150 m these mounds the first such structures described from the modern ocean grew between paleodepths of 100 and 240 m we infer that the upper limit of growth was established by swell wave base and the lower boundary was fixed by an oligotrophic water mass detailed chronostratigraphy based on radiometric and u series dating benthic foraminifer stable isotope stratigraphy and planktonic foraminifer abundance ratios confirms that buildups flourished during glacial lowstands even numbered marine isotope stages but were largely moribund during interglacial highstands and are not extant today mound floatstones are compositionally a mixture of in situ bryozoans comprising 96 genera and characterized by fenestrate flat robust branching encrusting nodular arborescent and delicate branching growth forms the packstone matrix comprises autochthonous and allochthonous sand size bryozoans benthic and planktonic foraminifers serpulids coralline algae sponge spicules peloids and variable glauconite and quartz grains together with mud size ostracods tunicate spicules bioeroded sponge chips and coccoliths intermound allochthonous packstone and local grainstone contain similar particles but they are conspicuously worn abraded blackened and bioeroded an integrated model of mound accretion during sea level lowstands begins with delicate branching bryozoan floatstone that increases in bryozoan abundance and diversity upward over a thickness of 5 10 m culminating in thin intervals of grainstone characterized by reduced diversity and locally abraded fossils mound accumulation was relatively rapid 30 67 cm ky and locally punctuated by rudstones and firmgrounds intermound highstand deposition was comparatively slow 17 25 cm ky and typified by meter scale fining upward packages of packstone and grainstone or burrowed packstone with local firmgrounds overlain by characteristically abraded particles mound growth during glacial periods is interpreted to have resulted from increased nutrient supply and enhanced primary productivity such elevated trophic resources were both regional and local and thought to be focused in this area by cessation of leeuwin current flow together with northward movement of the subtropical convergence and related dynamic mixing

atmospheric patterns driving holocene productivity in the alboran sea western mediterranean a multiproxy approach high resolution paleoproductivity variations have been reconstructed in a productive cell in the alboran sea for the holocene fossil coccolithophore assemblages have been studied along with the u37k estimated sea surface temperature sst and other paleoenvironmental proxies the appearance of this cell is suggested at 7 7 ka cal bp and was linked to the establishment of the western anti cyclonic gyre from that time until the present the nannofossil accumulation rate of florisphaera profunda has revealed successive episodes of weakening and strengthening of upwelling conditions in the alboran sea that have been simultaneous to changes in western mediterranean deep water wmdw formation in the gulf of lions a two phase scenario operating at millennial centennial time scale is proposed to explain this climatic and oceanographic variability 1 coeval with more arid climate conditions weaker northerlies or north westerlies blowing over the gulf of lions would have triggered a slackening of wmdw form

climatic variability in the southwest pacific during the last termination 20 10 kyr bp the degree to which palaeoclimatic changes in the southern hemisphere co varied with events in the high latitude northern hemisphere during the last termination is a contentious issue with conflicting evidence for the degree of teleconnection between different regions of the southern hemisphere the available hypotheses are difficult to test robustly however because there are few detailed palaeoclimatic records in the southern hemisphere here we present climatic reconstructions from the southwestern pacific a key region in the southern hemisphere because of the potentially important role it plays in global climate change the reconstructions for the period 20 10 kyr bp were obtained from five sites along a transect from southern new zealand through australia to indonesia supported by 125 calibrated c 14 ages two periods of significant climatic change can be identified across the region at around 17 and 14 2 cal kyr bp most probably associated with the onset of warming in the west pacific warm pool and the collapse of antarctic ice during meltwater pulse 1a respectively the severe geochronological constraints that inherently afflict age models based on radiocarbon dating and the lack of quantified climatic parameters make more detailed interpretations problematic however there is an urgent need to address the geochronological limitations and to develop more precise and quantified estimates of the pronounced climate variations that clearly affected this region during the last termination c 2005 elsevier ltd all rights reserved

climatic changes in the northern red sea during the last 22 000 years as recorded by calcareous nannofossils 1 we present a high resolution record of calcareous nannofossils from the northern red sea for the last 22 kyr extreme conditions with enhanced salinities during the last glacial maximum are characterized by high values of gephyrocapsa ericsonii the dominance of emiliania huxleyi in heinrich event 1 indicates a climatic cooling favoring the bloom of opportunistic species the calcareous nannofossils record a two step onset of the postglacial humid climate punctuated by the younger dryas both steps show an early oligotrophic phase dominated by florisphaera profunda and gladiolithus flabellatus and a subsequent fertile phase characterized by e huxleyi the younger dryas is described by high values of gephyrocapsa oceanica indicating an increased mixing of the water column in the late holocene repetitive increases in abundance of f profunda and g flabellatus reflect restricted oligotrophic conditions caused by the high aridity following the holocene humid period

holocene climate variability of the western mediterranean surface water dynamics inferred from calcareous plankton assemblages a high resolution study centennial scale has been performed on the calcareous plankton assemblage of the holocene portion of the ocean drilling program site 976 alboran sea with the aim to iden

subtropical front fluctuations south of australia 45 09 s 146 17 e for the last 130kayears based on calcareous nannoplankton abstract calcareous nannoplankton assemblages from a late quaternary deep sea core gc07 46 09 s 146 17 e south of australia provide information on regional palaeoceanography and palaeoclimate changes in the southern ocean in particular the movement of the subtropical front for the past 130 ka years marine isotope stages 1 5 are identified through changes in calcareous nannoplankton assemblages supported by 14c dates and oxygen isotope and caco data two distinct assemblages are recognised a warm water assemblage with higher abundances of calcidiscus leptoporus emiliania huxleyi helicosphaera carteri syracosphaera pulchra gephyrocapsa caribbeanica and gephyrocapsa oceanica and a cold water assemblage with higher abundances of gephyrocapsa muellerae and coccolithus pelagicus alternation between these two assemblages downcore in gc07 reflect movement of the subtropical front across the location and can be correlated to marine isotope stages mis 1 5 sediments with a cold water assemblage indicate the position of the subtropical front equatorward of the site when transitional to sub antarctic waters were overlying the site conversely sediments with a warm water assemblage indicate the subtropical front was poleward of gc07 when warmer subtropical waters were over the site mis 1 and 5 are interpreted as warmer than mis 3 based on species composition with the subtropical front more poleward than for mis 3 during mis 3 the subtropical front is interpreted as adjacent to or immediately poleward of gc07 some species including c leptoporus and c pelagicus show negative covariance and are considered to be reliable species in identifying glacial and interglacial intervals in this region comparison with established biostratigraphy based on calcareous nannoplankton showed the datum event for the reversal between e huxleyi and g muellerae of 73 ka in transitional waters is not applicable in this region the reversal between these two species occurs between 48 and 30 cm downcore in gc07 with a 14c date of 11 020 year bp at 49 48 cm i e the reversal event is younger than this date

calcareous plankton response to orbital and millennial scale climate changes across the middle pleistocene in the western mediterranean abstract the paleoenvironmental conditions through mis 15 9 at the mediterranean ocean drilling program odp site 975 were interpreted by high resolution study of calcareous plankton assemblages compared with available 18o and 13c records and high resolution paleoclimate proxies from the atlantic ocean sea surface temperatures ssts have been estimated from planktonic foraminiferal assemblages using the artificial neural networks method calcareous plankton varied dominantly on a glacial interglacial scale as testified by the sst record foraminiferal diversity total coccolith abundance and changes in warm water calcareous nannofossil taxa a general increase in foraminiferal diversity and of total coccolith abundance is observed during interglacials warmest ssts are reached during mis 11 while mis 12 and mis 10 represent the coldest intervals of the studied record during mis 12 one of the most extreme glacials of the last million years occurrence of globorotalia inflata and of neogloboquadrinids indicates a shoaling of the interface between atlantic inflowing and mediterranean outflowing waters among calcareous nannofossils the distribution of gephyrocapsa margereli gephyrocapsa muellerae 4 m also supports a reduced atlantic mediterranean exchange during mis 12 superimposed on glacial interglacial variability six short term coolings are recognized during mis 12 and 10 which appear comparable in their distribution and amplitude to the heinrich type events documented in the atlantic ocean in the same interval during these h type events neogloboquadrina pachyderma s and g margereli g muellerae 4 m increase as a response to the enhanced inflow of cold atlantic water into the mediterranean via the strait of gibraltar mediterranean surface water hydrography appears to have been most severely affected at termination v during the h type event ht4 possibly as a response to a large volume of atlantic meltwater inflow via the strait of gibraltar and or to freshwater terrigenous input deriving from local mountain glaciers three additional sst coolings are recorded through mis 14 16 but these are not well correlated with heinrich type events documented in the atlantic ocean in the same interval during these cooling episodes only the subpolar turborotalita quinqueloba increases these results highlight the sensitive response of the mediterranean basin to millennial scale climate variations related to northern hemisphere ice sheet instability and support the hypothesis that the tight connection between high latitude climate dynamics and mediterranean sea surface water features can be traced through the middle pleistocene

southern ocean deglacial record supports global younger dryas abstract in northern hemisphere deglaciation records the transition from the last glacial to the holocene indicates a rapid return to near glacial conditions during the younger dryas whereas their southern hemisphere ice core counterparts record two separate cooling events the antarctic cold reversal and the oceanic cold reversal spatial distribution and relative timing of these events in both hemispheres are central for our understanding of causes and mechanisms of abrupt climate change to date no marine record from the southern mid latitudes conclusively demonstrates that the younger dryas was a significant event in the southern ocean here we present high resolution oxygen isotope and iron content records of a radiocarbon dated sedimentary sequence from the great australian bight which constrains oceanic and atmospheric changes during the last deglaciation oxygen isotopes from planktonic foraminifera indicate two rapid cold reversals between 13 1 and 11 1 kyr bp separated by a brief warming the sedimentary iron content interpreted as a proxy for wind strength indicates a simultaneous change in atmospheric circulation pattern both records demonstrate the existence of cooling events in the southern hemisphere which are synchronous with the northern hemisphere younger dryas cold reversal between 12 9 and 11 5 kyr bp such evidence for the spatial distribution and timing of abrupt climatic fluctuations is essential data for groundtruthing results derived from global climate models

calcareous nannofossil biostratigraphy biochronology and paleoecology at the tortonian messinian boundary of the faneromeni section crete abstract a detailed calcareous nannofossil analysis was performed on 180 samples from the astronomically dated faneromeni section to identify the most important calcareous nannofossil events across the tortonian messinian t m boundary in the mediterranean and to date and correlate them precisely to the previously observed sections here we confirm the reliability of the genus amaurolithus the successive entries of amaurolithus primus amaurolithus aff amplificus and amaurolithus delicatus have been dated at 7 430 7 388 and 7 250 ma respectively the first occurrence and the first common occurrence of reticulofenestra rotaria are further confirmed bioevents dated at 7 421 and 7 264 ma these events improve the biostratigraphic resolution in the t m boundary interval at least for the mediterranean quantitative analysis revealed marked changes in the calcareous nannofossil assemblage associated with the sapropels as previously observed in other sections of the same time interval a decrease in the total number of coccoliths but an increase in abundance of the genera rhabdosphaera and helicosphaera characterize sapropels the observed fluctuations are comparable to the previous findings in neogene mediterranean sapropel sediments and suggest that similar mechanisms were responsible for their formation during this interval the possible influence of preservation on nannofossil assemblages is discussed

the last interglacial ocean the final effort of the climap project was a study of the last interglaciation a time of minimum ice volume some 122 000 yr ago coincident with the substage 5e oxygen isotopic minimum based on detailed oxygen isotope analyses and biotic census counts in 52 cores across the world ocean last interglacial sea surface temperatures sst were compared with those today there are small sst departures in the mid latitude north atlantic warmer and the gulf of mexico cooler the eastern boundary currents of the south atlantic and pacific oceans are marked by large sst anomalies in individual cores but their interpretations are precluded by no analog problems and by discordancies among estimates from different biotic groups in general the last interglacial ocean was not significantly different from the modern ocean the relative sequencing of ice decay versus oceanic warming on the stage 6 5 oxygen isotopic transition and of ice growth versus oceanic cooling on the stage 5e 5d transition was also studied in most of the southern hemisphere the oceanic response marked by the biotic census counts preceded led the global ice volume response marked by the oxygen isotope signal by several thousand years the reverse pattern is evident in the north atlantic ocean and the gulf of mexico where the oceanic response lagged that of global ice volume by several thousand years as a result the very warm temperatures associated with the last interglaciation were regionally diachronous by several thousand years these regional lead lag relationships agree with those observed on other transitions and in long term phase relationships they cannot be explained simply as artifacts of bioturbational translations of the original signals

late quaternary marginal marine palaeoenvironments of northern australia as inferred from cluster analysis of coccolith assemblages abstract cluster analyses r and q mode were applied to upper quaternary coccolith assemblages in a sediment core md972132 collected in the gulf of carpentaria northern australia this shallow gulf is influenced by the australian monsoon is tectonally stable and represents an important link between marine and terrestrial palaeoenvironments the gulf of carpentaria is linked to the pacific ocean to the east by torres strait 12 m water depth and to the indian ocean to the west by the arafura sill 53 m water depth and therefore has been separated from both oceans during sea level low stands resulting in the formation of lake carpentaria coccolith assemblages in the gulf are similar to modern assemblages in the region and correspond to typical assemblages in marginal seas the cluster analysis defines six species assemblages r mode and six groups of samples i e defined by depth in core depth q mode some with sub groups which were deposited under similar environmental conditions we thus recognised four major environmental facies over the past 125 ka corresponding to closed lake carpentaria stages the transitional periods while active channels sporadically connected lake carpentaria to the indian ocean and the opening of the gulf of carpentaria to the ocean over either one or both of the sills lake carpentaria was isolated from both oceans through marine isotope stages mis 5d mis 4 and mis 2 and the gulf of carpentaria was connected to both oceans during mis 5c and mis 1 torres strait was emergent during mis 5b was flooded again during mis 5a and persisted as land bridge from mis 4 to mis 1 the arafura sill was opened from mis 5c to mis 5a and episodically connected the gulf to the indian ocean during mis 3

coccolithophore paleoproductivity and ecology response to deglacial and holocene changes in the azores current system 1 in order to test the sensitivity of marine primary productivity in the midlatitude open ocean north atlantic to changes in the atlantic meridional overturning circulation amoc we investigated two spliced sediment cores from a site south of the azores islands at the northern rim of the north atlantic subtropical gyre for this purpose we analyzed coccolithophore assemblages diatom abundances alkenones and conducted x ray fluorescence xrf core scanning during times of reduced amoc especially during heinrich event 1 h1 and the younger dryas we observe a strong increase in productivity as evidenced by high coccolith accumulation rates high alkenone concentrations accumulation rates high ba ti ratios high abundances of diatoms and low abundances off profunda the increased productivity is partly caused by a more southern position of the azores front azf and hence by a less northward extension of the subtropical gyre as deduced from high abundances of the temperate coccolithophore species g muellerae and low abundances of subtropical species oolithotus spp umbellosphaera spp umbilicosphaeraspp however to explain the full range of the observed productivity increase other factors like increased westerly winds and advection of nutrient rich surface waters have also to be considered because this pattern can also be observed in other sediment cores from the midlatitude north atlantic we propose that during times of reduced amoc there has been a band of strongly increased productivity across the north atlantic at the northern rim of the contracted subtropical gyre which partly counteracts the decreased organic carbon pump in the high northern latitudes

ocean surface and wind dynamics in the atlantic ocean off northwest africa during the last 140 000 years abstract a combined micropaleontological analysis of core camel 1 from the oligotrophic sierra leone rise area has allowed reconstruction of the paleoclimatic and paleoceanographic history of the region for the last 140 kyr the ratio n between the reticulofenestrids coccolithophore indicators of relatively high nutrient contents versus florisphaera profunda a lower photic zone coccolithophore allowed us to monitor changes in the nutricline depth these results were compared with those obtained for marine diatom and planktic foraminifera assemblages thus a shallow nutricline thermocline and high productivity during stages 6 5d 5b 4 and 2 is proposed this situation can be correlated with maximum input of biosiliceous wind transported particles fresh water diatoms and phytoliths in sea sediments the shallow nutricline is correlated with an intensification in atlantic divergence and or a north equatorial current intensification when the ne trades were enhanced for glacial and stadials cold periods a clear precessional component is observed in the surface water dynamics during the last climatic cycle minima in the n ratio coinciding with minimum insolation during winter in the boreal hemisphere during mis 5 4 and 2 dry conditions were dominant on the northern african continent corresponding to a more intense ne trade wind circulation the increased phytolith concentrations during mis 6 are consistent with a more intense seasonality on the african continent cold planktic foraminifera assemblages show an eccentricity component linked to northern ice sheet dynamics this situation is enhanced in isotope stages 6 and 3 due to an intensification in the north equatorial current the eccentricity component is also observed both in the n ratio coccolithophore related and in the total planktic foraminifera

paleoceanography for the last 195 000 years in the solomon sea odp site 1109 by means of calcareous nannofossils abstract the paleoceanography of the solomon sea for the last 195 000 years was investigated based on the observations of 21 taxonomic groups of calcareous nannofossils in 144 samples taken from ocean drilling program odp cores 1109a 1h and 1109c 2h oxygen isotope ratios in tests of the planktonic foraminifer globigerinoides ruber allow us to assign the cores to oxygen isotope stages 7 1 past sea surface temperatures sst were estimated qualitatively using the composition of three gephyrocapsa coccolith morphotypes the high intermediate and low angle types that are classified based on the bridge angle of coccolith can be used as proxies for warm intermediate and cold temperatures respectively abundance of the high angle type coccoliths increased and decreased during the interglacial and glacial periods respectively this tendency is consistent with the expected change of the western pacific warm pool wpwp development however a large shift in the abundance of the high angle type coccolith recorded during early stage 3 did not correspond to the oxygen isotope record the ratio of small

the effect of systematic diagenetic changes on the mechanical behavior of a quartz cemented sandstone abstracta key goal of petrophysical studies of sandstones is to relate common field measurements particularly seismic or sonic velocities to parameters defining the rock s mechanical and hydrologic characteristics these include elastic and inelastic mechanical properties porosity and permeability we explored relationships among these properties in variably quartz cemented mature arenites of the st peter sandstone with porosities ranging from 9 to 25 in a previous paper we described microstructural changes accompanying progressive quartz cementation and related porosity and permeability reduction in this sample suite here we report ultrasonic velocities ultrasonic velocities dynamic and static elastic properties confined compressive strength and tensile strength analyses of these data demonstrated that factors controlling permeability also fundamentally determined the elastic and inelastic mechanical properties we found that the number of grain contacts or bonds per number of grains vi

abnormal carbonate diagenesis in holocene late pleistocene sapropel associated sediments from the eastern mediterranean evidence from emiliania huxleyi coccolith morphology in studying the holocene late pleistocene record of the eastern mediterranean considerable emiliania huxleyi size shape variation not clearly assignable to primary or secondary calcification was observed accordingly different morphotypes were distinguished by light microscope lm a subsequent scanning electron microscope sem analysis of selected samples has indicated that emiliania huxleyi coccoliths are variably affected by carbonate diagenesis in these sediments a series of diagenetic stages were qualitatively defined comprising well preserved specimens three overgrowth og1 to og3 and one etching e1 stage comparing sem and lm observations a tentative correlation between the e huxleyi calcified lm morphotypes and e huxleyi sem overgrowth stages is proposed here our study not only indicates that emiliania huxleyi coccoliths are strongly influenced by carbonate diagenesis but also that they show effects of carbonate precipitation and dissolution much more clearly than other coccoliths the relative abundances of the different lm morphotypes were used to define an e huxleyi overgrowth index exo that qualitatively estimates carbonate precipitation dissolution on coccoliths in this sediment this resulted in definition of five diagenetic intervals d1 to d5 deposition of sapropel s1 was a time of good preservation with variable dissolution and no overgrowth of e huxleyi coccoliths whereas calcite overgrowth was high during the last glacial maximum lgm and interglacial period and to a lesser extent during the younger dryas and through the last 5 ka d 2004 elsevier b v all rights reserved

sediment waves with a biogenic twist in pleistocene cool water carbonates great australian bight abstract sediment waves composed of fine grained carbonate ooze with in place bryozoans are a characteristic element of the pleistocene of the great australian bight gab the low amplitude and strongly elongate sediment waves are up to 10 km long 1 km wide 40 m high and oriented sub parallel to contours immediately off the shelf slope break they are asymmetrical showing up slope migration and mainly occur in trains the sediment waves were drilled during odp leg 182 in 1998 and were interpreted as biogenic reef mounds new high quality seismic and multibeam bathymetry data were acquired on the galathea 3 expedition in 2006 allowing description of the morphology and internal architecture of the sediment waves in unprecedented detail leading to an alternative interpretation of their formation most sediment waves were initiated by preferential deposition on the landward side of irregular erosion surfaces sediment wave accretion took place under the influence of density driven currents which decelerated up the landward dipping flanks and accelerated down the seaward dipping flanks of the sediment waves the currents are interpreted as dense water cascades formed by summer evaporation and strong winter cooling by analogy with oceanographic processes in the present day gab the lithological composition varied with climate and sea level but sediment wave formation did not sediment waves formed and accreted during both glacials and interglacials in contrast to the previous interpretations which involved growth in glacial periods only bryozoans influenced the depositional environment by adding sediment trapping fine grained particles and stabilizing the muddy sea floor this caused the sediment waves to gain a more prominent sea floor relief than most muddy siliciclastic sediment waves formed by similar depositional processes the interpretation of the sediment waves as purely biogenic build ups is rejected and the sediment waves are most appropriately described as biogenically influenced sediment waves

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

large scale reorganization of ocean currents offshore western australia during the late quaternary abstract the history of coastal surface currents in the eastern indian ocean over the last 130 kyr has been studied through the application of the fi 2 transfer function to planktic foraminifera in deep sea cores in a n s transect offshore western australia the concept of sea surface temperature sst gradient residuals is the amount by which the sea surface temperature gradient of a given time differs from that in the modern sea the sst gradient residuals for several episodes of climate extremes in the late quaternary the last glacial maximum 20 kyr b p the last interglacial maximum 122 120 kyr b p and at the end of the penultimate glaciation 130 kyr b p indicate that areas north of 18 s off western australia have changed very little during the extremes in climate over the last 130 kyr while south of 18 s there have been significant changes in surface water temperatures large areas of anomalously cool surface water were established off north west cape 22 s 24 s during both glacial and interglacial extremes these reflect the increased influence of the west australian current on the surface water circulation during the last glacial maximum and at the end of the penultimate glaciation cold sea surface temperature anomalies were established near to the coast indicating that the leeuwin current did not warm the coastal zone as it does today during the last interglacial maximum the leeuwin current flowed as an intensified current in a narrow zone close to the coast but did not significantly warm surface waters offshore as far as 20 25 s where a zone of cold water was maintained

climatic records over the past 30 ka from temperate australia a synthesis from the oz intimate workgroup temperate australia sits between the heat engine of the tropics and the cold southern ocean encompassing a range of rainfall regimes and falling under the influence of different climatic drivers despite this heterogeneity broad scale trends in climatic and environmental change are evident over the past 30 ka during the early glacial period 30 22 ka and the last glacial maximum 22 18 ka climate was relatively cool across the entire temperate zone and there was an expansion of grasslands and increased fluvial activity in regionally important murray darling basin the temperate region at this time appears to be dominated by expanded sea ice in the southern ocean forcing a northerly shift in the position of the oceanic fronts and a concomitant influx of cold water along the southeast including tasmania and southwest australian coasts the deglacial period 18 12 ka was characterised by glacial recession and eventual disappearance resulting from an increase in temperature deduced from terrestrial records while there is some evidence for climatic reversals e g the antarctic cold reversal in high resolution marine sediment cores through this period the high spatial density of holocene terrestrial records reveals an overall expansion of sclerophyll woodland and rainforest taxa across the temperate region after 12 ka presumably in response to increasing temperature while hydrological records reveal spatially heterogeneous hydro climatic trends patterns after 6 ka suggest higher frequency climatic variability that possibly reflects the onset of large scale climate variability caused by the el nino southern oscillation

evidence for eutrophication in the northwestern pacific and eastern indian oceans during the miocene to pleistocene based on the nannofossil accumulation rate discoaster abundance and coccolith size distribution of reticulofenestra abstract to reconstruct the cenozoic paleoceanographic evolution in particular temporal changes in nutrient levels we studied calcareous nannofossil assemblages from ocean drilling program holes 1210a located in the northwestern pacific ocean and 762b situated in the eastern indian ocean at each site we focused on the relationships among the nannofossil accumulation rate nar relative abundance of discoaster and coccolith size of the genus reticulofenestra the co occurrence of a low nar high discoaster abundance and presence of large reticulofenestra suggest a deep thermocline and nutricline typical of oligotrophic conditions conversely the co occurrence of a high nar low discoaster abundance and presence of small reticulofenestra indicate a shallow thermocline and nutricline typical of eutrophic conditions the combination of these three parameters suggests that the gradual eutrophication and collapse of sea surface stratification occurred in the northwestern pacific ocean at 7 9 6 4 and 5 0 ma in contrast abrupt eutrophication is indicated at 8 8 ma in the eastern indian ocean although the timing of eutrophication differs between the pacific and indian ocean sites it roughly coincides with tectonic and or climatic events around the two oceans this finding suggests that tectonic and climatic events are capable of causing an increase in the terrestrial input and or coastal upwelling of nutrients that subsequently leads to the eutrophication of sea surface waters

paleoceanographic significance of deep sea benthic foraminiferal species diversity at southeastern indian ocean hole 752a during the neogene abstract diversity parameters of neogene deep sea benthic foraminifera were measured at ocean drilling program odp hole 752a southeastern indian ocean water depth of 1086 3 m using information function h equitability e number of species s and sander s rarefaction values these parameters combined with population abundance of dominant benthic foraminifera bulimina macilenta nuttallides umbonifera cibicides wuellerstorfi cibicides lobatulus bolivina pusilla ehrenbergina carinata gavelinopsis lobatulus cassidulina laevigata globocassiulina subglobosa reveal significant paleoceanographic changes in the southeastern indian ocean during the neogene the values of all the diversity parameters show a decrease from 25 to 23 ma and thereafter an increase with peak values at 13 5 ma the late oligocene to earliest miocene was an interval of more unstable conditions at hole 752a dominated by species characteristic of low organic carbon well ventilated carbonate corrosive high energy conditions the highest values of diversity parameters coincide with the early middle miocene climatic optimum all these parameters show a declining trend and gradual decrease from 13 5 to 4 5 ma coinciding with the major build up of ice sheets in the antarctic region major increase in b pusilla and e carinata population during this time suggests high nutrient levels and low oxygen conditions at hole 752a this interval corresponds with the so called biogenic bloom and an intense oxygen minimum zone as observed throughout the indo pacific region deep waters were warmer from 4 5 to 3 ma marked by an increase in species diversity values coinciding with the early middle pliocene warmth the species diversity values abruptly decreased in the younger interval contemporaneous with the major northern hemisphere glaciation during this time species characteristics of high energy bottom currents and relatively cold deep water were dominant

response of nannoplankton to major changes in sea surface temperature and movements of hydrological fronts over site dsdp 594 south chatham rise southeastern new zealand during the last 130 kyr abstract a high resolution history of paleoceanographic changes in the subpolar waters of the southern margin of the subtropical convergence zone during the last 130 kyr is present in foraminiferal assemblages of dsdp site 594 the foraminifera indicate that sea surface temperatures during the last interglacial climax were warmer than today and that between substage 5d through to the end of isotope stage 2 temperatures were mostly cooler than holocene temperatures the paleotemperatures suggest that 1 the subtropical convergence was located over the site during substage 5e later moving further north then moving southwards to near the site during the holocene and 2 the polar front was positioned over the site during glacial stages 6 4 2 and possibly parts of stage 3 several major events are indicated by the nannofloral assemblages during these large changes in sea surface temperature and associated reorganization of ocean circulation first the time progressive trends between e huxleyi and medium to large gephyrocapsa are unique to this site with e huxleyi dominating over medium gephyrocapsa during stages 5c a middle part of stage 4 and after the middle point of stage 3 this unusual trend may at least partly be caused by the shift of the polar front across the site second upwelling flora e huxleyi and small placoliths increase in abundance during stages 1 3 and 5 suggesting that upwelling or disturbance of water stratification took place during the interglacials thirdly there are no significant differences between the distribution patterns of the various morphotypes of medium to large gephyrocapsa and the combined value of all medium gephyrocapsa increases in abundance during glacials stages 2 and 4 and the end of stage 6 similar to the abundance trends in benthic foraminifera finally subordinate nannofossil taxa also show distinctive climatic trends during the last glacial cycle 1 syracosphaera spp are present in increased abundance during warmer extremes in climate substages 5e 5a and stage 1 2 coccolithus pelagicus and calcidiscus leptoporus dominate the subordinate nannofossil taxa and their relative proportions seem to provide a useful paleoceanographic index with c pelagicus dominating when the polar front zone is over the site stages 6 4 and 2 whilst c leptoporus is relatively more abundant when the stc is positioned over the site stages 1 and 5e increased abundance of c pelagicus also can indicate intensified coastal upwelling

quantitative analysis of quaternary nannoplankton in the subtropical northwestern pacific ocean abstract time progressive changes of nannoflora and biometry of coccoliths for the last 1 3 m y were investigated for a piston core recovered from the west mariana ridge the species compositions were quantitatively investigated under an electron microscope and six assemblages assemblages a through f were identified significant changes in relative abundances of various types of genus gephyrocapsa are the main cause for the stratigraphic change of the flora a dominant occurrence of gephyrocapsa protohuxleyi var a which can be identified only under an electron microscope was observed for the first time in a thin sequence which corresponds to the lowest part of the brunhes epoch 0 75 0 62 ma because of this characteristic occurrence assemblage d was further subdivided into three subassemblages the dominant occurrence of small gephyrocapsa which is well known in the small gephyrocapsa zone of the equatorial pacific ocean was not observed but the almost complete absence of medium to large gephyrocapsa during approximately 200k years of the middle pleistocene was confirmed a stratigraphically restricted occurrence of a large form of reticulogenestra was also confirmed by the biostratigraphic study under a light microscope and the last and first occurrences of the largest form reticulofenestra sp a 6 5 m were identified at 0 81 and 0 98 ma respectively in addition to these four events precise ages for another five well known evolutionary events were also calibrated these ages are generally in good agreement with previously reported ages from other world oceans and diachronism was not evident for most of these evolutionary events

a middle pleistocene northeast atlantic coccolithophore record paleoclimatology and paleoproductivity aspects abstract changes in paleoclimate and paleoproductivity patterns have been identified by analysing in conjunction with other available proxy data the coccolithophore assemblages from core md03 2699 located in the portuguese margin in the time interval from the marine isotope stage mis 13 14 boundary to mis 9 535 to 300 ka during the mid brunhes event the assemblages associated with the eccentricity minima are characterised by higher nannoplankton accumulation rate nar values and by the blooming of the opportunistic genus gephyrocapsa changes in coccolithophore abundance are also related to glacial interglacial cycles higher nar and numbers of coccoliths g mainly occurred during the interglacial periods while these values decreased during the glacial periods superimposed on the glacial interglacial cycles climatic and paleoceanographic variability has been observed on precessional timescales the structure of the assemblages highlights the prevailing long term influence of the portugal pc and iberian poleward ipc currents following half and full precession harmonics related to the migration of the azores high ah pressure system small gephyrocapsa and coccolithus pelagicus braarudii are regarded as good indicators for periods of prevailing pc influence gephyrocapsa caribbeanica syracosphaera spp rhabdosphaera spp and umbilicosphaera sibogae denote periods of ipc influence our data also highlights the increased percentages of coccolithus pelagicus pelagicus during the occurrence of episodes of very cold and low salinity surface water probably related to abrupt climatic events and millennial scale oscillations of the ah icelandic low il system

high frequency climate fluctuations over the last deglaciation in the alboran sea western mediterranean evidence from calcareous plankton assemblages abstract a high resolution study with a centennial scale resolution has been performed on the calcareous plankton assemblage coccolithophores and planktonic foraminifera at ocean drilling program site 976 alboran sea western mediterranean focusing on the interval between 20 and 9 ka in order to reconstruct changes in surface and subsurface water dynamics and productivity the biotic surface water proxies integrate the extremely detailed multi decadal scale geochemical data set and the pollen record already available at the core thus providing a complete paleoenvironmental paleoceanographic reconstruction the results highlight the sensitivity of the calcareous plankton in recording stadial interstadial phases and higher frequency climatic events that produced changes in sea water features wind induced upwelling and river discharge during the last glacial period favored nutrient availability and moderate productivity during heinrich stadial 1 hs1 the arrival of cold and fresher waters from iceberg melting in the north atlantic significantly hampered productivity at its lowest values of the whole investigated interval calcareous plankton behavior supports the hypothesis that hs1 is a composite event marked by three phases hs1a characterized by the coldest sst polar atlantic water inflow into the basin and a first step toward a dry climate on the continent hs1b recording enhanced freshwater inflow and drought on land and hs1c indicating reduced polar water influx the bolling allerod ba interstadial sees the highest rate of productivity in the entire interval and accompanies the deposition of organic rich layer 1 during the ba coccolithophore assemblage also marks higher frequency changes in hydrographic conditions apparently in relation with greenland interstadial i gi i high variability the younger dryas stadial yd is characterized by refunding cold and dry conditions although not as severe as during hs1 and by enhanced detrital input in surface water during drier conditions on land the holocene onset records climate amelioration both in the marine and continental environment although coccolithophore productivity is not as high as during the ba the rapid shifts in climate sensitive taxa support the hypothesis that each of the climate phases subphases is characterized by a complex pattern forced by strong interaction between ice sheet instability meltwater discharge entering the gibraltar strait north atlantic westerlies and moisture availability clearly impacting over surface water temperature productivity and land masses

paleoenvironmental conditions at core kc01b ionian sea through mis 13 9 evidence from calcareous nannofossil assemblages quantitative analyses on calcareous nannofossil assemblages on high temporal resolution 600e800 years have been carried out from core kc01b in the ionian sea eastern mediterranean throughout marine isotope stage mis 13e9 between 500 and 300 ka this is an interval of considerable climate changes known as the mid brunhes event which includes mis 11 considered as a possible analogue for future interglacial conditions in the mediterranean core the interval is characterized by the dominance of gephyrocapsaspp as also known fromocean records calcareous nannofossil abundance fluctuations have been interpreted in terms of modification of sea surface primary productivity water stratification and temperature specifically the increase in abundance of gephyrocapsa caribbeanica and small gephyrocapsa coupled with decreases of florisphaera profunda syracosphaera spp and rhabdosphaera spp suggests enhanced primary productivity mixed surface waters during interglacial stages and at the terminations which can be interpreted in terms of interaction between climate changes and mesoscale oceanographic circulation on the other hand distributions of calciosolenia spp oolithotus spp and umbilicosphaera sibogae which are inphase with d 18 o curve showing higher abundances at the lighter values of the marine

middle to late miocene fluctuations in the incipient benguela upwelling system revealed by calcareous nannofossil assemblages odp site 1085a middle to late miocene calcareous nannofossil data of odp site 1085 from the eastern south atlantic off namibia were analysed to document spatial and temporal changes in surface ocean circulation upwelling initiation and associated productivity our data show that calcareous nannofossils constitute a significant part of the carbonate fraction throughout the investigated interval from 12 5 to 7 7 million years ma highest numbers of calcareous nannofossils up to 38 000 10 6 nannofossils g 1 sediment were observed during the intervals 9 9 to 9 7 and 8 7 to 8 0 ma these elevated numbers of calcareous nannofossils may generally be linked to the initiation of upwelling at about 10 ma in the studied region in contrast diminished numbers of calcareous nannoplankton as in the interval 9 6 to 9 0 ma probably characterise time intervals of weaker productivity resulting in a decrease of nannofossil carbonate contents in the sediments of site 1085 this decrease in nannofossil production could be one possible explanation for the major caco3 depression in between 9 6 and 9 0 ma coccoliths of the genus reticulofenestra are the most abundant taxa their occurrences are characterised by changes in the investigated time interval in addition coccolithus pelagicus calcidiscus leptoporus and umbilicosphaera spp contribute a common part of the assemblage calcareous nannofossils account for more than half of the carbonate with peak contribution up to 80 at 8 8 ma d 2005 elsevier b v all rights reserved

florisphaera profunda a possible nannoplankton indicator of late quaternary changes in sea water turbidity at the northwestern margin of the pacific three piston cores from the ryukyu trench slope northwestern margin of the pacific ocean contain nearly continuous paleoceanographic records of the last 320 165 and 105 kyr ages of the cores are constrained by planktic 18o stratigraphy and roughly substantiated by the presence of two calcareous nannofossil events spectral analysis of the changes in relative abundance offlorisphaera profunda a nannoplankton species presently living in the lower euphotic zone reveals a maximum power at 0 01 cycles kyr corresponding to the 100 kyr cycle of orbital eccentricity much lower power is observed at the 23 kyr precessional band this differs from the equatorial atlantic ocean variations which show dominant power in the 23 kyr precessional band in the changes off profunda abundances molfino and mcintyre 1990a besides our cores were taken outside the equatorial divergence zone we also show a rather close relationship betweenf profunda abundance and sea water transparency secchi depth in the present northwest pacific based on data from 204 sites of surface sediment samples because sea water transparency is primarily affected by bio productivity change in open ocean stratigraphic changes off profunda abundances in our cores seem to have been caused by productivity change as well pointed out by molfino and mcintyre 1990a b a mechanism proposed by them for its change however is not applied to our cases due to differences in spectral analysis results and in geographic situation alternatively we suggest that geographic change of the northwestern margin of the pacific during the late quaternary causedf profunda abundance change through the sea water turbidity change which has been affected not only by bio productivity but also by land origin particles supply

history of the last deglaciation in the alboran sea western mediterranean and adjacent north atlantic as revealed by coccolith floras abstract a series of cores recovered from the alboran sea western mediterranean and the adjacent part of the north atlantic has revealed very high rates of accumulation which have enabled us to identify the stages of the last deglaciation in great detail isotopic analyses of the cores show the two steps of the deglaciation terminations 1a and 1b separated by the bolling allerod warm phase 14 c dating of the cores has allowed the dating og the climatic succession we have identified each event of the deglaciation on the basis of changes in the coccolith flora especially in species of the genus gephyrocapsa such changes reflect surface water changes since coccolith live only in the photic zone the abundance of g muellerae in the cold intervals prior to each termination is greater than that in the bolling allerod and holocene warm intervals which follow the terminations coversely g oceanica is virtually absent during cold intervals but becoms more common during the warmer periods during the first deglacial warming there is a large influx of fine grained detrital material presumably derived from increased run off from the nearby mountains of southern spain and north west africa in the alboran sea cores with the most expanded sections there is a marked increase in the percentage of syracosphaera histrica at the beginning of this increase of detritus no increase was found in the atlantic core at this time

response of deep sea benthic foraminifera to late quaternary climate changes southeast indian ocean offshore western australia the late quaternary benthic foraminifera of four deep sea cores off western australia odp 122 760a odp122 762b bmr96gc21 and rc9 150 have been examined for evidence of increased surface productivity to explain the anomalously low sea surface paleotemperatures inferred by planktic foraminifera for the last and penultimate glaciations the 13c trends ofcibicidoides wuellerstorfi and differences between the 13c trends of planktics globigerinoides sacculifer and benthicsc wuellerstorfi in the four cores indicate that during stage 6 bottom waters were significantly depleted in 13c and strong 13c gradients were established in the water column while during stage 2 and the last glacial maximum 13c trends did not differ greatly from that of the holocene two main assemblages of benthic foraminifera were identified by principal component analyses one dominated byuvigerina peregrina another dominated byu proboscidea abundance of these uvigerinids and of taxa preferring an infaunal microhabitat and ofepistominella exigua andbulimina aculeata indicate that episodes of high influx of particulate organic matter were established in most sites during glacial episodes and particularly so during stage 6 while evidence for upwelling during the last glacial maximum is less strong the penultimate glaciation upwellings were established within the areas of low sea surface paleotemperature indicated by planktic foraminifera during the last interglacial climax upwelling appears to have been established in an isolated region offshore from a strengthened leeuwin current off north west cape last glacial maximum 13c values ofc wuellerstorfi at waterdepths of less than 2000 m show smaller than global mean glacial interglacial changes suggesting the development of a deep hydrological front a similar vertical stratification bathyal front was also established during the penultimate glaciation

floral and solution patterns of coccoliths in surface sediments of the north pacific coccolith assemblages from core top samples of the north pacific seafloor follow the distribution of surface water masses gephyrocapsa caribbeanica umbellosphaera tenuis and coccolithus pelagicus are the most important identifiers of surface water mass different multivariate statistical techniques group shallow samples in somewhat different spatial patterns factor analysis condenses the information contained in sixteen ies percentages to four new variables that can be interpreted as species assemblages by canonical correlation analysis these assemblages can in turn be related to the environment the first canonical correlation indicates that factor 2 the g caribbeanica assemblage is represented in samples underlying cooler surface water a second possible correlation describes a direct relationship between factor 3 the umbilicosphaera sibogae assemblage and the remaining environmental variable surface water salinity factor 1 the g oceanica assemblage and factor 4 the emiliania huxleyi assemblage are not as closely related to the selected environmental measures of temperature salinity dissolved oxygen and inorganic phosphate phosphorus as are factor 2 and factor 3 because samples were coded according to their overlying water mass group separations produced by discriminant analysis are easily interpreted in terms of the environment overlap of group assignments occurs for samples from the south china sea and extreme western pacific even partially dissolved samples retain the signature of surface water mass group assignment for those samples is generally reliable with the exception of samples from the central water mass where almost half of the shallow and half of the deep samples show strongest affinities with one of the other three water masses selective solution therefore only partially obscures the record of floral provinciality partial dissolution of coccolith assemblages does not proceed according to one systematic rank order the sequence of species removal is variable from region to region the more abundant species tend to consistently appear at an extreme of the ranking for example umbilicosphaera sibogae is among the least resistant and c leptoporus and g oceanica are among the most resistant species maximum depths of coccolith lysocline and compensation depth occur generally in the central part of the basin and shoal towards its margins as previously observed for planktonic foraminifera

calculating erosion by deep sea turbidity currents during initiation and flow turbidity currents transport massive amounts of sediment from continental margins to the deep sea individual flows can catastrophically remove and redeposit as turbidites many hundreds of cubic kilometres of material1 2 with the larger events reaching the bottom of the continental slope to form the abyssal plains3 here we show that the age range of sediments in individual turbidites can be used directly to estimate both the thickness of failed sediment in the source region even when its exact location is unknown and the extent to which the turbidity current caused erosion of the sea bed our method involves the comparison of the abundance ratios of microfossil coccolith species in turbidites with those in the ocean margin sediments of the source region analysis of a recently emplaced turbidite on the madeira abyssal plain shows that it contains a mixture of sediments with an age range of about 200 000 years equivalent to the failure of a block of sediment about 15 m deep radiocarbon dating and coccolith ratios show that the turbidite contains only about 12 of recent near surface sediment indicating that this turbidity current caused surprisingly little erosion en route

coccolithophore export in three deep sea sites of the aegean and ionian seas eastern mediterranean biogeographical patterns and biogenic carbonate fluxes abstract coccolithophore export fluxes were investigated via the analysis of sinking matter obtained from eastern mediterranean time series sediment traps moored in three open sites of the north eastern mediterranean sea located in the athos basin of north aegean m2 site cretan sea of south aegean m3 site and at ionian sea nestor site the aim of our study was to determine the spatial temporal and seasonal variability in coccolithophore fluxes as well as to estimate coccolith biogenic carbonate contribution to the sedimentation process data from an additional time series sediment trap located in the southwestern black sea were also considered for the comparison of the oligotrophic eastern mediterranean setting with the eutrophic black sea coccolithophore fluxes revealed a highly seasonal pattern during february march in the north aegean peak in late february 2015 85 6 x 105 coccospheres m 2 day 1 27 9 x 108 coccoliths m 2 day 1 during march may in the cretan sea peak in late march 2015 33 7 x 105 coccospheres m 2 day 1 19 5 x 108 coccoliths m 2 day 1 and during february march and may june in the ionian sea peak in late may 2012 14 3 x 105 coccospheres m 2 day 1 1 53 x 108 coccoliths m 2 day 1 the recorded maxima coincide with low sea surface temperatures increased precipitation and high pic fluxes coccosphere fluxes were dominated by emiliania huxleyi comprising 70 of the total abundance in the north aegean and 50 in the cretan and ionian seas syracosphaera pulchra was also prominent in the study sites where its abundance reached 14 in the north aegean and 10 in the cretan and ionian seas respectively florisphaera profunda represented one of the major taxa in the coccolith fluxes of all three eastern mediterranean sites 25 in north aegean 20 in cretan and ionian seas while algirosphaera robusta and umbilicosphaera sibogae were the most abundant among the minor taxa the north aegean sea exhibited a considerably higher coccolith flux when compared to other sediment traps due to the prominent seasonal peak of e huxleyi during winter february march 95 of the total abundance in contrast to the eastern mediterranean sediment traps the time series data from the black sea showed presence of monospecific e huxleyi assemblage increasing its abundance during late september november max 320 x 105 coccospheres m 2 day 1 at least 7 79 x 108 coccoliths m 2 day 1 coccolith flux derived only from coccospheres converted to coccoliths in the eastern mediterranean biogenic carbonate fluxes followed the general pattern of the total mass flux in all investigated areas with the black sea coccolithophore caco3 flux being the lowest due to low the e huxleyi coccolith mass overall in the north aegean sea coccolithophore fluxes are strongly dependent on surface waters nutrients enrichment due to winter vertical water column mixing riverine inputs and black sea water inflows while the fertilization and or formation of fast sinking aggregates due to episodic dust input event are affecting the coccolithophore fluxes in the cretan and ionian seas the intercomparison of the coccolith export fluxes in the studied ne sw mooring transects implies a north south and east west decreasing pattern depending on the variable oceanographic regimes and the associated environmental factors controlling the investigated areas

reconstructing nutricline dynamics of mid cretaceous oceans evidence from calcareous nannofossils from the niveau paquier black shale se france abstract a high resolution calcareous nannofossil record is presented from the lower albian niveau paquier black shale from the vocontian basin se france the niveau paquier black shale represents the regional equivalent of the supraregionally distributed oceanic anoxic event 1b oae 1b to reconstruct surface water fertility a nutrient index based on zeugrhabdotus erectus discorhabdus rotatorius high fertility indicators and watznaueria barnesae low fertility indicator was established using principal component analysis in addition the distribution of nannoconus spp and absolute abundances of coccoliths coccoliths per gram were used for reconstructing nutricline dynamics of the surface waters high surface water fertility coincides with low percentages of nannoconids and vice versa moreover high percentages of nannoconids correlate with low absolute abundances of all other coccoliths based on the observed nannoplankton distribution pattern and a suggested similarity in ecological requirements between nannoconids and the modern taxon florisphaera profunda a model is proposed that couples nannoconid abundances with dynamics of the nutricline time series analyses of the nutrient index show fluctuations within the precessional band the precession controlled fluctuations of the surface water fertility may represent a monsoonal signal with the nutrient supply in the surface waters depending on the strength of monsoonal activity during periods of enhanced monsoonal activity which were characterized by humid conditions and stronger winds mixing of the upper water column was enhanced during that time the abundance of nannoconids decreased as a consequence of enhanced wind stress that improved vertical mixing and led to an entrainment of nutrients into the surface waters this resulted in an increase of primary production during periods of reduced monsoonal activity marked by drier conditions and reduced wind stress the surface waters were depleted in nutrients as a result of a deep nutricline and a reduced nutrient supply to the upper photic zone in a stratified water column percentages of nannoconids increased according to the mechanisms outlined above fluctuations of the nutrient index and nannoconid percentages have been used as a proxy for reconstructing the physical structure of mid cretaceous oceans steered by precession forced monsoonal activity the results of the study show that the formation of the lower albian oae 1b from the vocontian basin occurred under strongly fluctuating surface waters fertility

numerical study of precipitation core gap structure along cold fronts abstract the mechanism responsible for the core gap structure of precipitation along narrow cold frontal rainbands ncfrs is investigated through analyses of idealized cloud resolving simulations of cold fronts the control simulation in which the prefrontal thermal stratification is characterized by a weak convective instability at low levels with convective available potential energy cape of 60 j kg 1 reproduces the typical alongfront variability of observed ncfrs the simulated ncfr is broken up into regularly spaced ellipsoidal cores oriented at a clockwise angle to the cold front while horizontal shear instability hsi has frequently been proposed as a mechanism leading to the alongfront variability of ncfrs no characteristic features of hsi are recognized in the simulated vertical vorticity field at the leading edge of the cold front the alongfront variability in precipitation is attributed to the formation of a wavelike disturbance just above the leading edge of the cold front the wave

nutricline variation in the equatorial atlantic coincident with the younger dryas variations in nutricline depth during the last deglaciation are recorded by the phytoplankton species florisphaera profunda a stacked record of six deep sea cores shows that across the entire equatorial atlantic there was a brief shallowing of the nutricline centered on 11 ka coincident with the younger dryas this shallowing is linked with high latitude north atlantic deglacial events we invoke high albedo and cool sea surface temperatures in the northern latitudes during 11 ka which steepened an already higher than expected winter insolation and hence temperature gradient for a time of june perihelion we postulate that the resultant increased pressure gradient caused an intensification of the northern hemisphere winter tropical easterlies which in turn caused equatorial divergence to occur in boreal winter

quaternary bryozoan reef mounds in cool water upper slope environments great australian bight bryozoan reef mounds are common features in the geological record occurring within mid ramp slope paleoenvironments especially in paleozoic carbonate successions but until now have not been recorded from the modern ocean recent scientific drilling in the great australian bight ocean drilling program leg 182 has confirmed the existence of shallow subsurface bryozoan reef mounds in modern water depths of 200 350 m these structures have as much as 65 m of synoptic relief and occur both as single mounds and as mound complexes they are unlithified have a floatstone texture and are rich in delicate branching encrusting and or nodular arborescent flat robust branching fenestrate and articulated zooidal bryozoan growth forms the muddy matrix is composed of foraminifers serpulids fecal pellets irregular bioclasts sponge spicules and calcareous nannofossils the 14c accelerator mass spectrometry dates of 26 6 35 1 ka indicate that the most recent mounds the tops of which are 7 10 m below the modern seafloor flourished during the last glacial lowstand but perished during transgressive sea level rise this history reflects changing oceanographic current patterns strong upwelling during lowstands and reduced upwelling and lowered trophic resources during highstands large specimens of benthic foraminifers restricted to the mounds confirm overall mesotrophic growth conditions the mounds are similar in geometry scale general composition and paleoenvironments to older structures but lack obvious microbial influence and extensive synsedimentary cementation such differences reflect either short term local conditions or long term temporal changes in ocean chemistry and biology