late quaternary benthic foraminifera and deep water paleoceanography in the south china sea abstract recent and late quaternary deep sea benthic foraminifera in the south china sea scs have been quantitatively studied in order to approach some disputable questions about the glacial deep circulation of the pacific from the paleoceanographic records of a marginal sea for example whether or not there existed the north pacific deep water npdw during glacials based on the quantitative data of deep sea benthic foraminiferal faunas from sixty six surface sediment samples of the scs a q mode factor analysis indicates that the globocassidulina subglobosa assemblage the astrononion novozealandicum and bulimina aculeata assemblages and the eggerella bradyi assemblage are associated with the intermediate water mass iwm deep water mass dwm and the deep water below ccd in the scs respectively the factor assemblages resulted from surface sample data were then applied to the quantitative analysis of late quaternary deep sea benthic foraminifera in eight cores from the scs and western pacific the results show a generally increased contribution of the dwm assemblage relative to that of the iwm assemblage during glacials which implies that the influence of the dwm increased and that of the iwm decreased in the scs and western pacific however there were two major deep water paleoceanographic changes during the late quaternary 1 the deep sea carbonate dissolution of the scs and western pacific was intensified during 18 0 stages 4 5 evidenced by the higher arenaceous calcareous ratios of benthic foraminifera and relative abundance of eggerella bradyi 2 the influence of the pacific dwm above 2500 m greatly increased during the last glacial maximum lgm inferred from the increased abundances of the pacific dwm benthic foraminiferal assemblage as compared to those of the pacific iwm and pacific bottom water mass assemblages in the western pacific particularly the water in which favocassidulina favus was distributed could not enter the scs since the lgm meanwhile the great changes had taken place in the dwm of the scs during the lgm reflected in the occurrence of a clearly cooled and ventilated dwm and the replacement of a novozealandicum and b aculeata assemblages by b aculeata melonis barleeanum assemblage at water depths of 1000 2500 m these significant changes during the lgm may be related to the formation of the npdw

benthic foraminiferal response to changes in bottom water oxygenation and organic carbon flux in the eastern mediterranean during lgm to recent times abstract we present a high resolution study of benthic foraminiferal abundances in 4 cores from the central aegean and ne levantine seas spanning the interval from 30 ka bp to the present the benthic foraminiferal faunas indicate that during lgm times bottom waters were well ventilated while organic flux to the sea floor was significantly higher than today from 30 to 10 2 ka bp faunal density and composition suggest a gradual decrease in organic flux to the sea floor this trend is interrupted by a short return to higher organic flux levels during the younger dryas 12 8 11 5 ka bp the faunas immediately preceding the early to middle holocene organic rich layer sapropel s1 are very similar to late holocene faunas indicating oligotrophic conditions the transition from well ventilated bottom waters to anoxic levantine basin or strongly dysoxic aegean sea bottom waters appears to take place within a time span of only 600 years from 10 8 to 10 2 ka bp sapropel s1 10 2 6 4 ka bp is characterized by extended periods of bottom water anoxia in the levantine basin and by strongly dysoxic conditions punctuated by episodic re ventilation events in the aegean sea re establishment of fully oxygenated bottom water conditions after sapropel s1 was extremely rapid the ensuing late holocene faunas are very similar to recent faunas found in the aegean sea suggesting much lower fluxes of organic matter to the sea floor than during glacial times

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

ages of 24 widespread tephras erupted since 30 000 years ago in new zealand with re evaluation of the timing and palaeoclimatic implications of the lateglacial cool episode recorded at kaipo bog abstract tephras are important for the nz intimate project because they link all three records comprising the composite inter regional stratotype developed for the new zealand climate event stratigraphy nz ces here we firstly report new calendar ages for 24 widespread marker tephras erupted since 30 000 calendar cal years ago in new zealand to help facilitate their use as chronostratigraphic dating tools for the nz ces and for other palaeoenvironmental and geological applications the selected tephras comprise 12 rhyolitic tephras from taupo nine rhyolitic tephras from okataina one peralkaline rhyolitic tephra from tuhua and one andesitic tephra each from tongariro and egmont taranaki volcanic centres age models for the tephras were obtained using three methods i 14 c based wiggle match dating of wood from trees killed by volcanic eruptions these dates published previously ii flexible depositional modelling of a high resolution 14 c dated age depth sequence at kaipo bog using two bayesian based modelling programs bacon and oxcal s p sequence function and the intcal09 data set with sh offset correction 44 17 yr and iii calibration of 14 c ages using oxcal s tau boundary function and the shcal04 and intcal09 data sets our preferred dates or calibrated ages for the 24 tephras are as follows youngest to oldest all mid point or mean ages of 95 probability ranges kaharoa ad 1314 12 taupo unit y ad 232 10 mapara unit x 2059 118 cal yr bp whakaipo unit v 2800 60 cal yr bp waimihia unit s 3401 108 cal yr bp stent unit q 4322 112 cal yr bp unit k 5111 210 cal yr bp whakatane 5526 145 cal yr bp tuhua 6577 547 cal yr bp mamaku 7940 257 cal yr bp rotoma 9423 120 cal yr bp opepe unit e 9991 160 cal yr bp poronui unit c 11 170 115 cal yr bp karapiti unit b 11 460 172 cal yr bp okupata 11 767 192 cal yr bp konini bed b 11 880 183 cal yr bp waiohau 14 009 155 cal yr bp rotorua 15 635 412 cal yr bp rerewhakaaitu 17 496 462 cal yr bp okareka 21 858 290 cal yr bp te rere 25 171 964 cal yr bp kawakawa oruanui 25 358 162 cal yr bp poihipi 28 446 670 cal yr bp and okaia 28 621 1428 cal yr bp secondly we have re dated the start and end of the lateglacial cool episode climate event nzce 3 in the nz ces previously referred to as the lateglacial climate reversal as defined at kaipo bog in eastern north island new zealand using both bacon and oxcal p sequence modelling with the intcal09 data set the ca 1200 yr long cool episode indicated by a lithostratigraphic change in the kaipo peat sequence to grey mud with lowered carbon content and a high resolution pollen derived cooling signal began 13 739 125 cal yr bp and ended 12 550 140 cal yr bp mid point ages of the 95 highest posterior density regions bacon modelling the oxcal modelling generating almost identical ages confirmed these ages the lateglacial cool episode ca 13 8 12 6 cal ka bp thus overlaps a large part of the entire antarctic cold reversal chronozone ca 14 1 12 4 cal ka bp or ca 14 6 12 8 cal ka bp and an early part of the greenland stadial 1 younger dryas chronozone ca 12 9 11 7 cal ka bp the timing of the lateglacial cool episode at kaipo is broadly consistent with the latitudinal patterns in the antarctic cold reversal signal suggested for the new zealand archipelago from marine and terrestrial records and with records from southern south america

boundary lines within petrologic diagrams which use oxides of major and minor elements use of some petrologic diagrams applied to analyses of volcanic rocks is unnecessarily difficult due to lack of data for construction of discriminant lines between rock series coordinates are provided for sufficient points to enable accurate plotting of the boundary lines within seven diagrams viz 1 tas total alkalies na2o k2o vs sio2 2 k2o vs sio2 3 afm 4 jensen 5 ktp k2o tio2 p2o5 6 fms feo mgo vs sio2 and 7 taktip k2o na2o k2o vs tio2p2o5 different versions of these boundaries are collated to indicate their variable position and it is demonstrated that inter laboratory analytical precision suffices to account for almost all of their spread on the tas and k2o vs sio2 diagrams

deepwater circulation on blake outer ridge western north atlantic during the holocene younger dryas and last glacial maximum three depth transects containing a total of 33 sediment cores were investigated along the blake outer ridge in the western subtropical north atlantic sortable silt mean grain size and stable isotope records were used to assess the position and relative intensity of the western boundary undercurrent wbuc during the holocene the last glacial maximum lgm and the younger dryas yd intervals the holocene reconstruction is consistent with modern physical and chemical hydrographic measurements in the area suggesting a deep position for the fast flowing core of the wbuc 3000 4000 m deepening to 4500 m water depth on the ridge flanks and a water column dominated by north atlantic deep water nadw the lgm and yd reconstructions show that a comparable hydrographic regime was present during both these intervals suggesting a similar mode of circulation that was appreciably different from the holocene reconstruction the wbuc s zone of maximum flow speed during these intervals is suggested to have shifted above 2500 m water depth consistent with nutrient depleted glacial north atlantic intermediate water formation with an increasing influence of southern source water ssw beneath below 4000 m water depth results hint at increased ssw flow vigor during both the lgm and yd with higher flow speeds than during the holocene this study provides a framework for aiding the interpretation of time series records of paleocurrent flow speed changes in the region of the wbuc

productivity and paleoceanographic implications on the tore seamount iberian margin during the last 225 kyr foraminiferal evidence foraminifera counts and climatic assemblages from the tore seamount are used to approach the glacial and interglacial changes in temperature and productivity on the iberian margin over the last 225 kyr chronostratigraphy is based on globigerinoides ruber and globigerina bulloides oxygen isotopes and supported by foraminifera and carbonate stadial fluctuations foraminifera indicate cooling from late interglacial stage 5 to the beginning of termination i ti neogloboquadnna pachyderma s reflects cold conditions during glacial stages 4 2 in contrast glacial stage 6 is dominated by warmer n pachyderma d and dutertrei and a restricted arctic assemblage past sea surface temperatures confirm the general cooling reaching 4 3 c simmax 28 during stage 2 multiple productivity proxies such as organic carbon productivity related foraminifera and 13c constrain the changes observed a productivity increase occurs after interglacial stage 5 enhanced from late glacial stage 3 to ti present day satellite detected phytoplankton plumes off portugal would have accounted in the past glacial stages for the general productivity increase over the tore on top of this welldefined peaks of organic carbon and productivity related foraminifera correspond with heinrich events 1 4

changes in the water column structure and paleoproductivity in the western south atlantic ocean since the middle pleistocene evidence from benthic and planktonic foraminifera abstract based on an integrated approach planktonic and benthic foraminifera and stable isotopes carried out in two cores collected on continental slope of santos basin central brazil the paleoceanographic oscillations of the last 570 ka are documented benthic foraminiferal isotopic records coupled with foraminiferal assemblages analyses show 100 ky long term oscillation in the superficial productivity along the middle pleistocene these long term oscillations are interrupted by 30 ky short term changes that mark the transition periods of higher productivity 425 400 ka and 190 160 ka and lower 290 260 ka the planktonic foraminifera species allowed the recognition of changes in the water column structure and in the superficial productivity observed in the area those changes in the superficial waters promoting different organic matter export to the sea floor might have resulted in changes on the more abundant and phytodetritus opportunist benthic taxa epistominella exigua and alabaminella weddellensis

vegetation and climate history inferred from a qinghai crater lake pollen record from tengchong southwestern china abstract a palynological investigation of a 514 cm long continuous core section from qinghai crater lake western yunnan province southwestern china was performed in order to reconstruct regional vegetation and climate from 15 8 cal kyr bp to the present the results show that the area was covered with deciduous broadleaved forest dominated by deciduous quercus between 15 8 and 12 8 cal kyr bp suggesting slightly cold and dry conditions from 12 8 to 8 3 cal kyr bp the vegetation continued to be dominated by deciduous broadleaved forest but there was also a sudden increase in castanopsis lithocarpus and a slight drop in deciduous quercus and alnus reflecting a gradual increase in both temperature and humidity during the period 8 3 4 6 cal kyr bp the mixed deciduous forests became more diverse and dense with thermophilous and hygrophilous species expanding to their maximum extents implying a warm and rather humid climate from 4 6 to 0 5 cal kyr bp the vegetation was succeeded by open mixed deciduous forest dominated by alnus with a retreating evergreen broadleaved forest indicating a cool and slightly dry climate after 0 5 cal kyr bp the vegetation became less diverse and more open but evergreen broadleaved trees increased their spread markedly suggesting that the climate had become warmer and drier in recent decades human activity resulted in a large increase in alnus and pinus around this lake basin specifically we concluded that the warm and moist climate detected between 8 3 and 4 6 cal kyr bp may have occurred in response to the high sea surface temperatures and high sea levels in the bay of bengal existent at that time

tracking the key parameters stimulating organic carbon productivity accumulation rate and preservation based on foraminiferal proxies in the subsurface miocene sediments in north sinai egypt abstract productivity redox conditions and sedimentation rate constrain the enrichments of organic matters and under suitable conditions they can trigger larger enrichments these parameters are tracked in the subsurface miocene sediments in four wells on east to west transect across north sinai these wells are abu roda 1 misfaq 1 teffah 1 and einab 1 the miocene sections cover the aquitanian burdigalian langhian serravalian and tortonian the tracking is based on the proxies of planktonic and benthic foraminifera that offer many solutions in the application of the equations used to calculate these parameters the first of these parameters is the sedimentation rate which is calculated for different time segments based on the planktonic foraminifera bioevents the sedimentation rates are correlated throughout the basin the second parameter is the water depth that is obtained from conversion of the scores of component 1 resulted during the routine statistical analysis of the benthic foraminifera by cluster and principal component analyses these analyses are used also in assessment of redox condition and eutrophication the sedimentation rates and water paleobathymetry alongside the measured corg are used to calculate the paleoproductivity and to determine four stratigraphic sequences seq1 seq2 seq3 and seq4 the tracking of these parameters reveal higher productivity levels in the seq1 aquitanian and burdigalian accompanied with dysoxic and mesotrophic conditions however the lower sedimentation rates are not optimum to stimulate enough burial efficiency that reduced values of corg in the younger sequences seq2 4 the higher sedimentation rates increase the burial efficiency and values of corg despite the lower paleoproductivity and oxic oligotrphic conditions

on the late pleistocene ocean geochemistry and circulation a box model of the atmosphere and ocean was developed to investigate how geochemical distributions extant during the late pleistocene may have come about the model simulates the regional distribution of calcium carbonate dissolution as well as the chemical oceanography and atmospheric co2 13c and radiocarbon if the downward biological flux of particulate carbon increases by a factor of 2 to 3 in the antarctic and if this increase is combined with a relative increase of the atlantic sector antarctic bottom water aabw versus north atlantic deep water nadw source ratio from 1 3 to about 2 1 then the model predicts several changes that seem to be recorded in the sedimentary record as follows 1 a global redistribution of nutrients and 12c from the intermediate to deep water takes place with the atlantic intermediate water phosphate decreasing 0 6 mole kg 1 and the 13c increasing 0 3 to 0 5 2 the dissolved oxygen level of the deep sea is reduced from an average of about 180 to 70 mole kg 1 but the intermediate water oxygen declines only a small amount 3 the decrease in intermediate water nutrient concentration results in lower average organic carbon and calcium carbonate production in the warm surface ocean 4 the atmospheric co2 decreases by 90 to 110 ppm 5 initially a global increase in calcium carbonate dissolution occurs which is followed by a relaxation toward better preservation than exists for the present ocean in the model in this paper the reduction of nadw by itself does not produce these effects rather the nutrient decrease that does occur is found mostly in north pacific intermediate water and the model atmospheric co2 decrease is only 10 to 30 ppm it is observed that 92 of the atmospheric co2 change takes place according to a 200 year time constant in the model this corresponds to the response time of the upper ocean and atmosphere to a change in the stationary state atmospheric pco2 thus according to this model the time lag between the nutrient based cause and the atmospheric co2 response is not expected to be particularly large

deep sea benthic foraminifera and biogenic opal glacial to postglacial productivity changes in the western equatorial pacific the accumulation rate of benthic foraminifera in deep sea sediments is strongly correlated with the productivity of the surface ocean core tops from diverse deep sea settings straddling different export production levels are used in this study for the calibration between the organic carbon flux to the seafloor jsf flux and the benthic foraminifera accumulation rate bfar the correlation can be used to reconstruct organic carbon flux to the seafloor in the past and hence the productivity of past oceans these results are compared with the accumulation rates of carbonate and biogenic opal in the sediments it is found that biogenic opal is more sensitive to productivity changes in the modern ocean than is carbonate the appropriate equations are derived for the equatorial pacific using core material fromeurydice erdc indomed inmd andpleiades plds expeditions these equations are then applied to two selected time horizons in sediments from the ontong java plateau a western equatorial pacific pelagic depth transect the last transition lt and the last glacial lg it is found that productivity was higher during the last glacial relative to the late holocene by a factor between 1 6 and 2 during the last transition productivity was intermediate between glacial and recent values we do not see any corresponding increase in the rates of accumulation of carbonate or biogenic opal during the last glacial this observation questions the importance of ocean productivity as the main controlling factor of carbonate and biogenic opal accumulation rates back through geological time

recent benthic foraminifera from the continental margin of northwest africa community structure and distribution abstract sediment grab samples were collected at 107 locations along the continental margin of northwest africa these samples form a series of depth transects between the straits of gibraltar and dakar senegal the greater than 250 m size fraction was retained for a census of both the live and dead foraminifera after deleting trace occurrences jaccard and correlation coefficient based cluster analyses were performed to decipher the community structure for this margin the geographic distribution of the four major faunal provinces recognized is conventional in that for both the live and dead assemblages three are related to depth upper slope and shelf middle slope and lower slope and continental rise the biotopes and thanatotopes within these provinces are strongly restricted along vertical or latitudinal boundaries when the data are analysed using jaccard coefficients dendrograms constructed from correlation coefficients emphasize depth related faunal communities dominant species such as cibicides lobatulus trifarina fornasinii planulina ariminensis uvigerina finisterrensis and c wuellerstorfi are generally distributed within a definite depth range along this margin and strongly influence the correlation coefficient based dendrograms other distributions are clearly not depth related but correspond to various environmental variables for example cancris auriculus coarse substrate bolivina subaenariensis oxygen minimum cibicidoides kullenbergi and hoeglundina elegans low organic carbon uvigerina peregrina is also a notable exception to depth dependence in that this dominant species and the province it represents are generally confined to the continental slope south of cape blanc its preference for that region may arise from the high organic carbon and fine grain size of the sediment there from low salinity of the bottom water or from other unknown variables the most important vertical faunal boundary occurs between cape barbas and cape blanc between 22 and 21 n latitude in contrast the canary island ridge intersects the continental margin at a saddle depth of about 1500 m but that physiographic barrier has little effect on provincialism of the deep water benthic foraminifera

shallow marine sediment cores record climate variability and earthquake activity off lisbon portugal for the last 2000 years abstract sea surface temperature sst river discharge and biological productivity have been reconstructed from a multi proxy study of a high temporal resolution sedimentary sequence recovered from the tagus deposition center off lisbon portugal for the last 2000 years sst shows 2 c variability on a century scale that allows the identification of the medieval warm period mwp and the little ice age lia high iron fe and fine sediment deposition accompanied by high n alkane concentrations and presence of freshwater diatoms during the lia 1300 1900 ad science 292 2001 662 suggest augmented river discharge whereas higher total alkenone concentrations point to increased river induced productivity during the mwp 550 1300 ad science 292 2001 662 larger mean grain size and low values of magnetic susceptibility and concentrations of fe n alkanes and n alcohols are interpreted to reflect decreased runoff at the same time increased benthic and planktonic foraminifera abundances and presence of upwelling related diatoms point to increased oceanic productivity on the basis of the excellent match found between the negative phases of the north atlantic oscillation nao index and the intensified tagus river discharge observed for the last century it is hypothesized that the increased influx of terrigenous material during the lia reflects a negative nao like state or the occurrence of frequent extreme nao minima during the milder few centuries of the mwp stronger coastal upwelling conditions are attributed to a persistent positive nao like state or the frequent occurrence of extreme nao maxima the peak in magnetic susceptibility centered at 90 cm composite core depth ccd is interpreted as the result of the well known 1755 ad lisbon earthquake the lisbon earthquake and accompanying tsunami are estimated to have caused the loss of 39 cm of sediment 355 years of record most of the lia and the instantaneous deposition of a 19 cm sediment bed

abyssal ne atlantic benthic foraminifera during the last 15 kyr relation to variations in seasonality of productivity abstract benthic foraminiferal faunas 63 m and stable isotopes from the last 15 kyr were studied in bengal programme high resolution temporal and spatial study of the benthic biology and geochemistry of a north eastern atlantic abyssal locality kasten core 13078 16 from the porcupine abyssal plain ne atlantic 48 49 91 n 16 29 94 w water depth 4844 m changes occurred in the accumulation rates species composition diversity and stable isotopes during the last 15 kyr today the area is strongly influenced by seasonal inputs of phytodetritus following the spring blooms in surface water primary productivity variations in the relative abundance of the two most abundant species epistominella exigua and alabaminella weddellensis which today show significant increases in abundance with the presence of phytodetritus on the sea floor are interpreted as resulting from changes in the seasonality of productivity seasonal productivity was higher during the holocene than during the last deglaciation and younger dryas probably coinciding with the retreat of the polar front to higher latitudes this hypothesis is consistent with simultaneous decreases in the percentage of the polar planktic foraminifera neogloboquadrina pachyderma s and increases in the percentage of globigerina bulloides a warmer water planktic foraminifera indicative of phytoplankton blooms and enhanced productivity the relative abundance of the phytodetritus species e exigua and a weddellensis covary between 14 7 and 8 1 kyr but not between 7 8 and 1 2 kyr major decreases in the numbers per gram and accumulation rates of planktic and benthic foraminifera occurred at 12 8 5 kyr and at 4 kyr which correspond to decreases in the sediment coarse fraction and published data on inorganic carbon contents suggesting that dissolution may have increased at these times relationships between benthic foraminiferal faunas and benthic stable isotope records suggest no simple relationship between faunal abundances and test isotope chemistry for example the abundances of phytodetritus species do not show strong correlations with either the 13c values of e exigua or the 13c e exigua p wuellerstorfi record which have previously been suggested as indicative of seasonality of productivity

the impact of african aridity on the isotopic signature of atlantic deep waters across the middle pleistocene transition abstract a high resolution analysis of benthic foraminifera as well as of aeolian terrigenous proxies extracted from a 37 m long marine core located off the mauritanian margin spanning the last 1 2 ma documents the possible link between major continental environmental changes with a shift in the isotopic signature of deep waters around 1 0 0 9 ma within the so called mid pleistocene transition mpt time period the increase in the oxygen isotopic composition of deep waters as seen through the benthic foraminifera 18o values is consistent with the growth of larger ice sheets known to have occurred during this transition deep water mass 13c changes also estimated from benthic foraminifera show a strong depletion for the same time interval this drastic change in 13c values is concomitant with a worldwide 0 3 decrease observed in the major deep oceanic waters for the mpt time period the phase relationship between aeolian terrigeneous signal increase and this 13c decrease in our record as well as in other paleorecords supports the hypothesis of a global aridification amongst others processes to explain the deep water masses isotopic signature changes during the mpt in any case the isotopic shifts imply major changes in the end member 18o and 13c values of deep waters

trends in caribbean paleoproductivity related to the neogene closure of the central american seaway abstract this study tests the hypothesis that the late miocene to early pliocene constriction and closure of the central american seaway cas connecting the tropical atlantic and east quatorial pacific eep caused a decrease in productivity in the caribbean due to decreased coastal upwelling and an end to the connection with high productivity tropical pacific waters the present study compared paleoceanographic proxies for the interval between 8 3 and 2 5 ma in 47 samples from south caribbean odp site 999 with published data on eep dsdp site 503 proxies for site 999 include the relative abundance of benthic foraminiferal species representing bottom current velocity and the flux of organic matter to the sea floor the ratio of infaunal epifaunal benthic foraminiferal species and benthic foraminifer accumulation rates bfars in addition we calculated resistant planktic foraminifers species and used the previously published sand fraction and benthic carbon isotope values from site 999 during early shoaling of the isthmus 8 3 7 9 ma the caribbean was under mesotrophic conditions with little ventilation of bottom waters and low current velocity the pre closure interval 7 6 4 2 ma saw enhanced seasonal input of phytodetritus with even more reduced ventilation and enhanced dissolution between 6 8 and 4 8 ma during the post closure interval 4 2 2 5 ma in the caribbean paleoproductivity decreased current velocity was reduced and ventilation improved while the seasonality of phytodetrital input was reduced dramatically coinciding with the establishment of the atlantic pacific salinity contrast at 4 2 ma our data support the hypothesis that late miocene constriction of the cas at 7 9 ma and its closure at 4 2 ma caused a gradual decrease in paleoproductivity in the caribbean consistent with decreased current velocity and seasonality of the phytodetrital input

late quaternary palaeoceanography of the tasman sea the benthic foraminiferal view abstract the benthic foraminiferal content of four gravity cores from the east tasman plateau 2450 m and 2667 m water depth and the lord howe rise 1349 m and 1448 m water depth was examined in order to determine late quaternary palaeoceanographic changes in the tasman sea in all cores benthic foraminifera demonstrate the glacial interglacial cyclicity through changes in assemblages and abundance abundances range from about 400 to 1200 specimens per gram of dry sediment over the last 400 kyr abundance patterns differ between the northern between 31 s and 33 s and the southern sites between 43 s and 44 s in the southern cores a significantly increased benthic foraminiferal abundance indicates high nutrient flux and quality perhaps continuously during stage 5 the northern cores on the other hand display this signal for stage 6 this reversed pattern is recognizable for other glacial episodes as well as for interglacials but the trend is less distinctive enhanced sea surface productivity in the tasman sea during the last glacial cycle is recognized from benthic foraminiferal assemblages but the pattern appears highly variable and complex the data suggest that for the past relocation of recent high productive oceanographic features sensu yoder et al 1994 in the tasman sea such as the tasman front the subtropical convergence the east australian current and perhaps the east australian eddy field tranter et al 1982 are reflected in the benthic formainiferal abundances in the cores increased foraminiferal abundance during glacials on the lord howe rise indicate a slight northward shift of the tasman front data from the east tasman plateau show a more complex situation the faunal pattern in the cores probably reflect a southward shift of the eddy field during glacials and a slight northward shift of the subtropical convergence during interglacials

x radiography of archaeological soil and sediment profiles abstract x radiography is surprisingly not commonly used in the examination of archaeological soils and sediments the technique is simple rapid inexpensive and non destructive and provides a permanent record of the internal structure of core and monolith samples it reveals structural and stratigraphic details that are invisible or unclear from ordinary visual inspection and photography features such as the nature of stratigraphic boundaries and their precise locations signs of disturbance mixing and redeposition and variations in sediment density may be highlighted apparently homogenous deposits may be shown to contain stratigraphic and structural information the technique is therefore a very useful adjunct to any palaeoenvironmental analysis helping to elucidate the depositional and post depositional context of palaeoenvironmental samples and helping to guide the initial choice of sub sampling levels

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

ocean ventilation and sedimentation since the glacial maximum at 3 km in the western north atlantic 1 stable isotope sedimentological and radiocarbon data from cores at 3 km water depth on the blake ridge western subtropical north atlantic reveal the history of deep water ventilation since the last glacial maximum lgm bulk sediment accumulation rates varied locally by a factor of 2 under the influence of bottom currents in this sediment drift environment but the sand flux mostly foraminifera was nearly identical at a given time this suggests that the rain rate of foraminifera mostly planktonic was constant that transport of foraminifera was negligible and that current controlled differences in clay and silt transport drive bulk accumulation in two of the cores flux peaks in the benthic foraminifera cibicidoides and uvigerina peregrina occurred during the younger dryas yd cold event and at 18 2 19 6 21 1 25 0 and 28 1 ka radiocarbon measurements on those benthic foraminifera show the ventilation age of bottom waters was 1000 years during the yd and for older events it was as great as 2000 years these results contrast with holocene ventilation which was 500 years and 700 years at 1500 years and 7100 years before present respectively

benthic foraminiferal abundance and stable isotope changes in the indian ocean sector of the southern ocean during the last 20kyr paleoceanographic implications abstract benthic foraminiferal faunas and benthic stable isotopes during the last 20 kyr were investigated in core md02 2488 46 28 8 s 88 01 3 e 3420 m water depth from the southeast indian ocean sector of the southern ocean in order to document paleoceanographic changes from the last glacial through deglaciation and into the holocene variations occurred in the accumulation rates species composition diversity and stable isotopes during the last 20 kyr the benthic 18o and 13c records during the last 28 kyr show that no significant deep water circulation changes took place before 15 6 calendar kyr ka the 13c increase at 15 6 ka is interpreted as reflecting the arrival of better ventilated deep waters at the site and is associated with the progressive increase in of miliolids from 15 ka to 0 ka an interval 16 15 ka of low benthic foraminiferal accumulation rates bfars and an increase in the relative abundance of stainforthia complanata deep waters were 2 2 0 4 c colder during the last glacial than at present carbonate dissolution proxies indicate that carbonate dissolution was higher during the last glacial than during the last deglacial and holocene bfars and the percentage of species indicative of high productivity suggest that the flux of organic matter resulting from surface water productivity was generally higher between 20 and 13 ka than between 12 and 0 ka consistent with the observed higher proportion of biosiliceous sediment at 20 14 ka and published records the combined percentages of the two most abundant species alabaminella weddellensis and epistominella exigua phytodetritus species suggest that seasonality of productivity intermittency of primary productivity fluctuated over the last 20 kyr and was higher during the last glacial and deglaciation 20 10 ka compared with the holocene 10 0 ka the relative abundances of a weddellensis and e exigua do not covary over the last 20 kyr an observation also reported from other areas

petrological reconstruction of triassic seamounts oceanic islands within the palaeotethys geochemical implications from the karakaya subduction accretion complex northern turkey abstract subduction accretion complexes provide unique insight into the tectonic assembly of continental margins and oceanic basins as they record the tectonic stacking and juxtaposition of materials derived from distinct tectonic environments the karakaya complex exposed throughout northern turkey is a good example of an ancient subduction accretion complex that includes a number of pre liassic units that characterize the closure of palaeotethys defining the components of this complex is of crucial importance to understanding the geodynamic evolution of palaeotethys in the eastern mediterranean region in this study we explore the geochemistry of metabasic rocks within the karakaya complex redefining and evaluating one of its main constituents known as the nilufer unit new geochemical results combined with previously published data suggest that the nilufer unit is dominated by oceanic island basalt oib and enriched mid ocean ridge basalt e morb type metabasic rocks which are variably enriched in the most highly incompatible elements relative to normal morb n morb associated alkaline oib type basalts are characterized by highly fractionated and variable rare earth element ree patterns la yb n 4 8 16 2 suggesting melting across the garnet spinel transition derivation from a heterogeneous mantle source and or dynamic melting of a homogeneous source similar nb y zr y systematics of spatially associated oib and e morb type samples may indicate involvement of a shared enriched mantle source s combining both geological and geochemical evidence we suggest that the oib and e morb type assemblages defining the nilufer unit represent seamounts and oceanic islands formed on palaeotethyan oceanic crust which was finally incorporated into a forearc accretionary prism during latest triassic and became a component of the karakaya complex

benthic foraminiferal diversity response to the climate induced changes in the eastern arabian sea oxygen minimum zone during the last 30kabp abstract a high resolution record of deep sea benthic foraminiferal diversity variations in the eastern arabian sea for the last 30 ka bp was obtained from two sediment cores sk17 and md131 retrieved from the present day oxygen minimum zone omz in the indian margin off goa the benthic foraminiferal diversity is represented in terms of sander s rarefaction number s 100 shannon wiener index h s equitability e and alpha index records of diversity indices exhibit millennial scale changes during the late glacial and deglacial periods corresponding to the northern hemisphere climatic events we compared the faunal diversity with proxy records of primary productivity c org and bottom water oxygen low o 2 taxa we suggest that benthic foraminiferal diversity in the eastern arabian sea omz is largely controlled by the primary productivity induced organic carbon flux and strength of bottom water oxygenation the less diverse fauna along with increased percentages of c org and low o 2 taxa during the last glacial maximum 18 22 5 ka bp suggest eutrophic and oxygen poor benthic environment attributed mainly to a strong omz associated with intense winter monsoon wind induced productivity and a weak deep ocean circulation the intervals of distinct increase in diversity closely correspond with north atlantic cold heinrich events when eastern arabian sea experienced significant declines in monsoon driven productivity and better deep sea ventilation due to enhanced inflow of antarctic intermediate water aaiw

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

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

late quaternary deep sea ostracodes in the polar and subpolar north atlantic paleoecological and paleoenvironmental implications two sediment cores from the northern north atlantic one from the iceland plateau and one from the rockall plateau were investigated in order to examine the response of deep sea benthic ostracodes to climate related environmental changes since marine isotope stage mis 7 ostracode fauna was divided into three factor assemblages by using q mode factor analyses and diversity was calculated using the shannon wiener index the iceland plateau revealed an interglacial assemblage dominated by henryhowella a transitional assemblage dominated by eucythere and a background assemblage that consists of the common taxa krithe and cytheropteron the presence of henryhowella is linked to conditions that prevailed during the peak interglacial periods mis 5e and 1 characterized by increased food supply well oxygenated bottom water and lateral advection the presence of eucythere mainly during the interstadial periods appears to be related to slightly increased food supply whereas the background assemblage is considered to be opportunistic and able to cope with decreased food supply as interpreted for glacial times on the rockall plateau the opportunistic background assemblage consisting mainly of krithe argilloecia and cytheropteron shows no obvious relation to climate changes the interglacial assemblage consists of several taxa dominated by pelecocythere but as on the iceland plateau it also contains henryhowella the third assemblage is the glacial assemblage that consists of a variety of taxa several of which are known from the modern arctic ocean and the greenland sea shelf thus this assemblage indicates glacial conditions on the rockall plateau that are comparable to those found in the present day arctic ocean diversity calculations revealed higher ostracode diversities in glacial than in interglacial episodes in both cores and particularly high diversities during periods of increased input of iceberg rafted debris ird in the rockall plateau core both cores reveal lower surface water productivity during the glacial compared to the interglacial periods and particularly low productivity during the ird events as inferred from carbonate contents we assume therefore that ostracode diversity in the study areas is negatively correlated with food flux

species composition and glacial interglacial variations in the ostracode fauna of the northeast atlantic during the past 200 000 years sediment core m23414 from the rockall plateau north atlantic covering the last two climatic cycles marine isotope stages mis 7 to 1 was investigated for glacial interglacial variations in the deep sea benthic ostracode fauna a highly diversified ostracode fauna including 98 species was found two climate related assemblages were identified associated with interglacial and peak glacial periods respectively the interglacial group occurs during the end of mis 7 5 and 1 and is composed of the genera henryhowella pelecocythere echinocythereis cytherella bradleya aversovalva and eucytherura the glacial group consists of the genera acetabulastoma which is known as sea ice indicator in the modern arctic ocean polycope bythoceratina rhombobythere and some species possibly belonging to the genus pseudocythere and is found during mis 6 4 and 2 these longer term variations within the ostracode fauna seem related to the particular glacial and interglacial climate conditions that affected both deep water production as well as primary production in the surface waters however a detailed comparison of ostracode abundances with the occurrence of events marked by increased ice rafted debris reveals also much shorter term climate related changes in the ostracode fauna thus the temporal fluctuations within ostracode assemblages reflect long and short term alterations of the deep sea environment that are clearly linked to climate changes

late quaternary history of atmospheric and oceanic circulation in the eastern equatorial pacific abstract four radiolarian assemblages have been defined in recent seafloor sediments of the equatorial pacific ocean the distribution of these assemblages corresponds to the modern pattern of oceanic circulation and water mass structure in this region the eastern pacific shallow permanent thermocline and the equatorial undercurrent peru current upwelling and the oxygen minimum the subtropical water mass warm western tropical water and the north equatorial countercurrent in twelve cores chosen to transect the region both longitudinally and latitudinally the distribution of these four assemblages has been reconstructed for six time intervals during the last 127 000 years 18 000 b p glacial stage 2 36 000 b p and 52 000 b p interstadial stage 3 65 000 b p glacial stage 4 82 000 b p and 120 000 b p interglacial stage 5 atmospheric and oceanic circulation changes through time have been inferred from the reconstructed microfossil assemblage distributions changes in assemblage distributions indicate that variations in intensity direction and mean position of the tradewinds caused marked changes in the oceanic circulation patterns through the last glacial cycle near the end of interglacial stage 5 the disappearance of the north equatorial countercurrent from the eastern pacific suggests that the mean position of the tradewinds was shifted to the south approximately 5 of latitude relative to the modern position so that the northeast trades prevented the flow of the north equatorial countercurrent into the eastern pacific near the end of interstadial stage 3 a change in wind direction occurred from predominantly zonal winds which enhance equatorial divergence and surfacing of the equatorial undercurrent to more meridional winds which enhance coastal upwelling associated with the peru current in the tropical pacific ocean late quaternary changes in atmospheric and oceanic circulation are linked with times of continental ice sheet growth in the northern hemisphere i e the interglacial to glacial transitions across oxygen isotope stage boundaries 5 4 and 3 2 the major changes in circulation seem to occur a few thousand years in advance of the glacial episodes at or near periods of ice sheet growth this relationship indicates that changes in atmospheric circulation in the tropics led and influenced the development of conditions suitable for polar and continental ice sheet growth in the northern hemisphere

ion microprobe dating of zircons from active dayingshan volcano tengchong se tibetan plateau time scales and nature of magma chamber storage abstract the rare occurrences of active volcanoes on the tibetan plateau provide a unique opportunity to investigate time scales of magma chamber processes for post collisional potassic volcanism this research utilizes high spatial resolution u th disequilibrium dating methods to date zircons from the active dayingshan volcano tengchong se tibetan plateau which erupted last during the holocene zircon crystal ages can be used to provide constraints on the magma chamber storage time measured zircon interiors yielded an isochron age of 87 5 6 5 ka while zircon outermost rims yielded an isochron age of 58 13 ka the calculated zircon crystal storage time for the most recent eruption is 48 ka at least two separate late pleistocene zircon crystallization events have occurred where the older age population represents antecrysts remobilized from an earlier magmatic episode but protracted crystallization cannot be ruled out regardless the similarity in zircon age populations between dayingshan volcano and maanshan volcano 13 km apart in the tengchong volcanic field suggests a synchronous thermal history of the magma reservoir possibly in an extensive interconnected magma chamber beneath the tengchong volcanic field

benthic foraminiferal assemblage response to the onset of northern hemisphere glaciation paleoenvironmental changes and species trends in the northeast atlantic abstract the response of the benthic foraminiferal community in the northeast atlantic to the late pliocene onset of northern hemisphere glaciation was investigated using closely spaced samples from dsdp ipod site 548 factor analysis of quantitative species abundance data shows that the replacement of aglobocassidulina subglobosa assemblage first bybulimina mexicana and then bymelonis uvigerina dominated assemblages accompanied the onset of glaciation also the benthic assemblages became much more variable with progressive climatic deterioration in order to examine benthic foraminifera species responses to changing paleoenvironmental variables measurements of planktonic foraminifera species abundances benthic foraminifera stable isotope values and sediment grain size and composition were made the planktonic data and oxygen isotope values were used to quantify paleoclimatic changes and changes in bottom water properties the sediment analyses were used to quantify changes in the substrate and a combination of planktonic assemblage data and benthic carbon isotope values were used to estimate changes in food supply surface ocean productivity canonical correlation analysis of the species data and the independent paleoenvironmental indicators shows a strong relationship between planktonic assemblage diversity and the long term benthic trend of assemblage replacement this trend could be a response to changing bottom water properties but it might also reflect increasing food supply at the sea bed in addition the benthic assemblages show a strong relationship to changes in the carbonate content of the sediments this latter fluctuates due to varying terrigenous input changes in substrate at site 548 may influence the benthic foraminiferal assemblage there remains however a significant fraction of species abundance variability particularly in theuvigerina species that cannot be explained with the paleoenvironmental indicators used in this study

anatomy of the organic carbon related to the miocene syn rift dysoxia of the rudeis formation based on foraminiferal indicators and palynofacies analysis in the gulf of suez egypt abstract the syn rift deposits from the gulf of suez witness different episodes of anoxia and dysoxia conditions in many areas the sediments of rudeis formation that represent the deposition in the time of maximum rift subsidence are considered as the principal organically rich and oil prone sources while in other areas they are not these differences are attributed to relative positions to the location of the syn rift dysoxia and amounts of the carbon flux during active paleoproductivity time in the present study an extensive analysis of the syn rift dysoxia and paleoproductivity during the miocene is conducted in burdigalian rudeis formation in ramadan 1 well to determine their influence on the accumulation of organic carbon the analysis depends on the statistical investigation of the benthic foraminiferal assemblages the foraminiferal assemblages are discriminated into two biofacies in r mode suboxic and dysoxic and three biotopes in q mode suboxic s dysoxic da and db sample groups the sediments are divided into three stratigraphic sequences five oxygen minimum zones are determined at the extreme oxygen depletion intervals and they are defined by suboxic s and dysoxic da sample groups in descendent order of oxygen depletion intensity and mostly coincide with the high sea levels the distribution of the organic matter showed large enrichment with partial fluorescence amorphous organic matter indicating kerogen type ii in the three biotopes as clarified from palynofacies analysis the organic carbon enrichment from the studied samples ranged from fair to very good 0 51 and 2 38 wt and the relatively larger enrichments are found to be correlated with dysoxic sample group da of intermediate oxygen depletion the pyrolysis gas chromatography pgc specifies the algal rich type i kerogen that deposited in oxygen depleted marine environment the mathematical calculation of the paleoproductivity oligotrophic to eutrophic range 106 352 gcm 2yr 1 carbon flux 13 77 and 36 19 gcm 2yr 1 indicates that higher levels of organic productivity are correlated with dysoxic sample group da the larger organic carbon values are found in the rudeis formation when the dysoxic conditions from the deeper topographic lows extend to the higher tectonic position of ramadan 1 well during the sea level rise that furthermore enhances the paleoproductivity

u series ages of young volcanoes from the southeastern tibetan plateau holocene eruptions and magma evolution timescales abstract the tengchong volcanic field in southwestern china represents rare quaternary volcanic eruptions and associated active geothermal activities on the southeastern margin of the tibetan plateau the reported eruption ages for the 3 youngest tengchong volcanoes heikongshan dayingshan maanshan are highly variable 3 0 482 ka because of the challenge to accurately and precisely date young volcanic rocks by radiometric methods here we use high resolution 238u 230th 226ra disequilibria to constrain the eruption ages and magma evolution timescales all 3 young volcanoes exhibit whole rock 226ra 230th disequilibrium ranging from 1 27 to 1 71 indicating eruption ages of 230th ages of zircons from heikongshan dayingshan and maanshan zircon age populations are 54 6 13 ka and 94 9 4 1 ka for heikongshan 59 6 5 8 and 90 1 8 4 for dayingshan and 53 8 8 7 ka and 76 5 11 ka for maanshan magma residence times for all 3 volcanoes are 50 kyr for a shallow stage and 85 kyr for a deep stage in a two stage magma chamber system below tengchong the similar zircon age distributions for the 3 volcanoes from tengchong indicate simultaneous magmatism at 90 ka and 55 ka and imply interconnected nature of these volcanoes

recent benthic foraminiferal associations and ecology of the scotia sea and argentine basin abstract we investigated 88 surface sediment samples taken with a multiple corer from the southwestern south atlantic ocean for their live rose bengal stained and dead benthic foraminiferal content using q mode principal component analysis six live and six dead associations are differentiated live and dead association distributions correspond fairly well differences are mainly caused by downslope transport and selective test destruction in addition four potential fossil associations are calculated from the dead data set after removal of non fossilizable species these potential fossil associations are expected to be useful for paleoceanographic reconstructions environments are described in detail for the live and potential fossil associations and for selected species along the upper argentine continental slope strong bottom currents control the occurrence of live dead and potential fossil angulogerina angulosa associations here particles of a high organic carbon flux rate remain suspended below this high energy environment live dead and potential fossil uvigerina peregrina dominated associations correlate with enhanced sediment organic carbon content and still high organic carbon flux rates the live a angulosa and u peregrina associations correlate with high standing crops furthermore live and dead epistominella exigua nuttallides umbonifer associations were separated dominance of a nuttallides umbonifer potential fossil association relates to coverage by antarctic bottom water aabw and lower circumpolar deep water lcdw above the calcite compensation depth ccd three associations of mainly agglutinated foraminifera occur in sediments bathed mainly by aabw or cdw a reophax difflugiformis association was found in mud rich and diatomaceous sediments below the ccd a psammosphaera fusca association occurs in coarse sediments poor in organic carbon while a cribrostomoides subglobosus ammobaculites agglutinans association covers a more variable environmental range with mud contents exceeding 30 one single eggerella bradyi martinottiella communis association poor in both species and individuals remains from the agglutinated associations below the ccd if only preservable species are considered for calculation

environmental changes and growth history of a cold water carbonate mound propeller mound porcupine seabight on and off mound sediment cores from propeller mound hovland mound province porcupine seabight were analysed to understand better the evolution of a carbonate mound the evaluation of benthic foraminiferal assemblages from the off mound position helps to determine the changes of the environmental controls on propeller mound in glacial and interglacial times two different assemblages describe the holocene and marine isotope stage mis 2 and late mis 3 31 kyr bp the different assemblages are related to changes in oceanographic conditions surface productivity and the waxing and waning of the british irish ice sheet biis during the last glacial stages the interglacial assemblage is related to a higher supply of organic material and stronger current intensities in water depth of recent coral growth during the last glaciation the benthic faunas showed high abundances of cassidulinid species implying cold bottom waters and a reduced availability of organic matter high sedimentation rates and the domination of elphidium excavatum point to shelf erosion related to sea level lowering 50 m and the progradation of the biis onto the shelf a different assemblage described for the on mound core is dominated by discanomalina coronata gavelinopsis translucens planulina ariminensis cibicides lobatulus and to a lower degree by hyrrokkin sarcophaga these species are only found or show significantly higher relative abundances in on mound samples and their maximum contribution in the lower part of the record indicates a higher coral growth density on propeller mound in an earlier period they are less abundant during the holocene however this dataset portrays the boundary conditions of the habitable range for the cold water coral lophelia pertusa which dominates the deep water reefal ecosystem on the upper flanks of propeller mound the growth of this ecosystem occurs during interglacial and interstadial periods whereas a retreat of corals is documented in the absence of glacial sediments on mound glacial conditions with cold intermediate waters a weak current regime and high sedimentation rates provide an unfavourable environmental setting for lophelia corals to grow a late pleistocene decrease is observed in the mound growth for propeller mound which might face its complete burial in the future as it already happened to the buried mounds of the magellan mound province further north

benthic foraminifera off west africa 1 n to 32 s do live assemblages from the topmost sediment reliably record environmental variability abstract recent benthic foraminifera 125 m were investigated from multicorer samples on a latitudinal transect of 20 stations between 1 n and 32 s along the upper slope off west africa samples were selected from a narrow water depth interval between 1200 and 1500 m so that changes in water masses are minimized but changes in surface productivity are important and the only significant environmental variable live rose bengal stained benthic foraminifera were counted from the surface sediment down to a maximum of 12 cm dead foraminifera were investigated in the top 5 cm of the sediment only five live and five dead benthic foraminiferal assemblages were identified using q mode principal component analysis matching distinct primary productivity provinces characterized by different systems of seasonal and permanent upwelling differences in seasonality quantity and quality of food supply are the main controlling parameters on species composition and distribution of the benthic foraminiferal faunas to test the sensitivity of foraminiferal studies based on the uppermost centimeter of sediment only a comparative q mode principal component analysis was conducted on live and dead foraminiferal data from the top 1 cm of sediment it has been demonstrated that on the upper slope off west africa most of the environmental signals as recorded by species composition and distribution of the total live and dead assemblages i e including live and dead foraminifera from the surface sediment down to 12 cm and 5 cm respectively can be extracted from the assemblages in the top centimeter of sediment only on the contrary subsurface abundance maxima of live foraminifera and dissolution of empty tests strongly bias quantitative approaches based on the calculation of standing stocks and foraminiferal numbers in the topmost centimeter

glacial interglacial variations in sediment organic carbon accumulation and benthic foraminiferal assemblages on the bermuda rise odp site 1063 during mis 13 to 10 glacial times organic d 13 c values are less negative during mis 12 and mis 10 than during mis 11 which is consistent with greater glacial stage marine productivity high relative abundances of oridorsalis umbonatus during glacial intervals probably records a low but sustained flux of highly degraded organic material large recurrent fluctuations in the abundance of epistominella exigua at the beginnings of the mis 12 and mis 10 glaciations suggest a marked increase in local phytoplankton blooms at these times and consequent delivery of phytodetritus to the seafloor the most likely causes of these variations are changes in the position and strength of the gulf stream and its associated cold ring eddies combined with increased advection of terrigenous sediments from northerly locations during glacial lowstands

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

age of a late quaternary 13 6 cal kyr bp eruption and associated marker tephra of the tengchong volcanoes yunnan province southwestern china abstract the tengchong volcanoes in western yunnan province are some of the youngest volcanoes in china and determining their eruption ages would further our understanding of their genesis and historical activity in this study the age of a late quaternary eruption of dayingshan volcano was obtained by dating organic rich sediments that envelope a 5 cm thick visible tephra layer found in the yubi peat section compositionally the purified glass shards extracted from the layer by density separation are calc alkaline trachyandesite and trachyte trachydacite which is consistent with the composition of the dayingshan lava an age depth model of the yubi section was constructed from accelerator mass spectrometry ams 14c dating of peat samples and poisson models of deposition p sequence functions using oxcal with the intcal 13 database this yielded an age for the tephra layer of 13 642 84 cal yr bp a nearly identical tephra layer occurs in the qinghai crater lake sediments the yubi tephra is now a reliable age and stratigraphic marker layer useful for regional paleoclimate and tephrochronology research

deep sea benthic foraminiferal assemblage response to a surface ocean productivity gradient a test a transect of samples from the eastern equatorial pacific where surface ocean productivity is the only changing environmental variable was used to test the response of benthic foraminiferal assemblages to an open ocean productivity gradient the transect runs along the east pacific rise from the highly productive waters near the equator to the oligotrophic south pacific subtropical gyre surface sediment benthic assemblages show progressive change along the transect with strong compositional shifts corresponding to the rapid productivity gradient near the equator and to the position of the southern convergence near 18 19 s the relationship of the assemblages to surface ocean productivity was tested by statistical regression of quantitative estimates of productivity on the assemblage principal component scores calculated for each sampling location the regression yielded an r squared of 0 87 demonstrating a clear relationship between surface ocean productivity and deep sea benthic foraminiferal assemblage composition the species most important to this relationship display a consistent response to oceanic productivity for long stretches of geologic time this conservative behavior and the results of the regression analysis indicate that benthic foraminiferal assemblages can be used to estimate surface ocean productivity for the geologic past

ne atlantic surface water mass changes over the last 15 kyr planktic foraminiferal faunas 150 m and stable isotopes from the last 15 kyr were studied in kasten core 13078 16 from the porcupine abyssal plain ne atlantic 48 49 91 n 16 29 94 w water depth 4844 m in order to document changes in surface waters the faunas were dominated 80 by four species neogloboquadrina incompta n pachyderma dextral globigerina bulloides n pachyderma n pachyderma sinistral and globorotalia inflata and their abundances fluctuated strongly over the last 15 kyr other species g truncatulinoides right and left coiling forms and globigerinoides ruber white had low abundances typically 6 the polar species n pachyderma dominated 60 the terminal glacial interval when surface conditions were cold decreased to 25 35 during the deglaciation and remained low 2 throughout the holocene the relative abundance of n incompta increased over the last 15 kyr and shows an inverse relationship with n pachyderma the increase in 13c values of g bulloides g inflata and g truncatulinoides over the last 15 kyr is consistent with the whole ocean shift due to the expansion of the terrestrial biosphere indicating that the upper oceanic 13c values did not change significantly during this time between the deglaciation and the holocene the negative shift 1 0 in 18o values of g inflata and g truncatulinoides equates to the global ice volume shift suggesting that there was no significant warming of the deeper surface waters or that the species migrated to occupy a similar temperature water mass during this time in contrast the negative shift 1 7 in 18o values of g bulloides corresponds to a local shift of 0 7 equivalent to a 3 c warming of surface waters between 10 kyr and 5 kyr the positive 18o increases in g inflata and g truncatulinoides suggest a decrease in deeper surface water temperatures in the order of 1 0 1 5 c a change not evident in the shallow surface water 18o record of g bulloides water mass stratification changes revealed by the 18o g inflata g bulloides and 18o g truncatulinoides g bulloides records suggest that the waters of the upper water column were more mixed during the last deglaciation than during the holocene and that there was a trend towards increasing water stratification over the last 15 kyr with a peak at 4 kyr intervals of enhanced carbonate dissolution at 12 8 5 kyr and 4 kyr previously reported are not clearly reflected in changes in solution susceptible planktic foraminiferal species such as g ruber

a new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments abstract tephrochronology a key tool in the correlation of quaternary sequences relies on the extraction of tephra shards from sediments for visual identification and high precision geochemical comparison a prerequisite for the reliable correlation of tephra layers is that the geochemical composition of glass shards remains unaltered by natural processes e g chemical exchange in the sedimentary environment and or by laboratory analytical procedures however natural glasses particularly when in the form of small shards with a high surface to volume ratio are prone to chemical alteration in both acidic and basic environments current techniques for the extraction of distal tephra from sediments involve the cleaning of samples in precisely such environments and at elevated temperatures the acid phase of the cleaning process risks alteration of the geochemical signature of the shards while the basic phase leads to considerable sample loss through dissolution of the silica network here we illustrate the degree of alteration and loss to which distal tephras may be prone and introduce a less destructive procedure for their extraction this method is based on stepped heavy liquid flotation and which results in samples of sufficient quality for analysis while preserving their geochemical integrity in trials this method out performed chemical extraction procedures in terms of the number of shards recovered and has resulted in the detection of new tephra layers with low shard concentrations the implications of this study are highly significant because i the current database of distal tephra records and their corresponding geochemical signatures may require refinement and ii the record of distal tephras may be incomplete due to sample loss induced by corrosive laboratory procedures it is therefore vital that less corrosive laboratory procedures are developed to make the detection and classification of distal glass tephra more secure

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

late quaternary icelandic tephras in ireland and great britain detection characterization and usefulness microscopic studies of late quaternary tephras from iceland yield a detailed tephrochronology in deposits of the british isles where the quantities of volcanic glass employed are much less than those used to construct almost any other late quatemary tephrochronology we summarize improved methods of isolating extremely sparse glass shards for light microscope and electron microprobe analysis and provide major element geochemistry for 20 volcanic glass layers detected in ireland including those which comprise an outline historic tephrochronology for ireland the paper highlights possible limitations of chronology construction when attempting to separate dated tephras whose major element geochemistries are almost identical tephras in other parts of the british isles and europe are used with those in ireland to demonstrate further applications of tephrochronology especially for dating deposits where other dating methods e g radiocarbon have proved difficult

microhabitat preferences and stable carbon isotopes of endobenthic foraminifera clue to quantitative reconstruction of oceanic new production seventeen surface sediment samples from the north atlantic ocean off ne greenland between 76 and 81 n and nine samples from the south atlantic ocean close to bouvet island between 48 and 55 s were taken with the aid of a multiple corer and investigated for their live rose bengal stained benthic foraminiferal content within the upper 15 cm of sediment preferentially endobenthic melonis barleeanum m zaandami and bulimina aculeata as well as preferentially epibenthic lobatula lobatula were counted from 1 cm thick sediment slices each and analyzed for stable carbon and oxygen isotopic compositions of their calcareous tests live and dead specimens were counted and measured separately the carbon isotopic composition of the foraminifera was compared to that of the dissolved inorganic carbon dic of simultaneously sampled bottom water during a period of one month one station off ne greenland was replicately sampled once every week and samples were processed as above live specimens of lobatula lobatula are confined to the uppermost two centimeters of sediment live specimens of melonis spp are found down to eight centimeters within the sediment but with a distinct sub surface maximum between two and five centimeters the down core distribution of live bulimina aculeata shows a distinct surface maximum in the top centimeter and constant but low numbers down to 11 cm subbottom depth the average stable carbon isotopic composition d13c per mil vpdb of live l lobatula off ne greenland is by 0 4 0 1 per mil higher than the d13cdic of the ambient bottom water at the time of sampling there is evidence that this species calcify before the ice free season when bottom water d13cdic is supposed to be higher this would reconfirm the one to one relationship between d13c of ambient water dic and cibicids widely used by paleoceanographers live m barleeanum show a negative offset from bottom water dic of 1 7 0 6 per mil in the uppermost sediment and of 2 2 0 5 per mil in three to four centimeters subbottom depth all d13c values of live melonis spp decrease within the upper four centimeters regardless of the time of sampling and site investigated the offset of live b aculeata from bottom water d13cdic values of eight stations rather constantly amounts 0 6 0 1 per mil no matter what subbottom depth the specimens are from at one station however where is strong indication of elevated organic carbon flux the negative offset averaged over all sub bottom depths increases to 1 5 0 2 per mil buliminids actively move within the sediment and by this either record an average isotope signal of the pore water or the signal of one specific calcification depth the recorded signal however depends on the organic carbon flux and reflects general but site specific pore water d13cdic values if compared with epibenthic d13c values from the same site not influenced by pore water and related phytodetritus layer effects bulimina d13c values bear some potential as a paleoproductivity proxy specimens of melonis spp seem to prefer a more static way of life and calcify at different but individually fix depths within the sediment although live specimens thus record a stratified pore water d13c signal there is no means yet to correct for bioturbational and early diagenetic effects in fossil faunas

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research