biogenic silica fluxes and accumulation rates in the gulf of california the gulf of california though small in size plays an important role in the global silica cycle the seasonal pattern of biogenic silica flux in the gulf is closely related to that of phytoplankton biomass levels and is controlled by changes in weather and hydrographic conditions the highest opal fluxes approximately 0 35 g center dot m sup minus 2 center dot d sup minus 1 occur during winter and spring and they are comparable to those measured in some of the most productive ecosystems of the world approximately 15 25 of the biogenic silica produced in surface waters is preserved in gulf sediments a figure significantly higher than the average global ocean preservation rate however the flux of opal at 500 m water depth is less than 25 of that being produced at the surface suggesting that most of the recycling of biogenic silica in the gulf of california occurs in the upper water column 28 refs 3 figs

globorotalia truncatulinoides growth and chemistry as probes of the past thermocline 1 shell size this work identifies features of the life history of the deep living planktonic foraminifer globorotalia truncatulinoides that offer possibilities for reconstructing characteristics of the past ocean s main thermocline part 1 considers two aspects of variation in shell size the predictability of growth related size changes which we need to calculate changes in shell chemistry and a model for environmentally forced changes in shell size frequency which suggests how shell size may be a direct source of paleoceanographic information even though size variation among shells of g truncatulinoides at the same stage of growth same number of chambers exceeds the size difference between successive growth stages growth related size changes are predictable because shells tend to grow at the same rate variation in initial shell size is sufficient to account for the large size variation found among shells at the same stage of growth several lines of evidence suggest that g truncatulinoides reproduces at 600 m in the water column and it appears that vertical mixing to that depth is required to return juvenile shells to the surface anything that prevents this such as shallowing of the thermocline can interfere with g truncatulinoides life history in such a way that its shell size frequency distributions are altered among shells falling to the seafloor from a reproducing population are large numbers of both juvenile and adult sizes and if reproduction is inhibited the frequencies of those sizes are reduced and the relative frequency of intermediate sized shells increases a paleoceanographically useful result of this is that the topography of the main thermocline tends to be reflected in the size frequency distribution of g truncatulinoides shells from the underlying sediments in areas where the top of the main thermocline is shallower than 600 m production of juveniles 125 177 m and reproductive adults 425 m is reduced leaving predominantly intermediate sized 212 355 m shells

varieties of a single cosmopolitan diatom species associated with surface water masses in the north pacific abstract a time series of 65 sediment trap samples representing 48 month changes in diatom flora and 62 sediment core tops from the western north pacific ocean were analyzed varieties of a single diatom species were found to be characteristic of two surface water masses bounded by the kuroshio current thalassionema nitzschioides var incurvata var inflata and var parva dominate in warm saline waters in the subtropical gyre while t nitzschioides sensu stricto is abundant in less saline waters northwest of this current time series data on percent abundances for the three t nitzschioides varieties in the t nitzschioides complex are compared with path variations of the current south of japan inter annual fluctuations in percent abundance are linked to changes in surface water masses over the sediment traps in association with migration of the kuroshio paths this finding makes the percent abundance a useful tool for deciphering path migrations of the kuroshio current in the geologic past down core analyses of two sediment cores collected beneath the modern kuroshio current were performed a sharp increase in percent abundances from 12 to 9 kyr bp with an abrupt change around 11 kyr bp records the previously reported transition of the kuroshio current from a predominantly offshore path to its modern path path migrations of the kuroshio current may be inferred from percent abundances of these diatoms which comprise a new proxy for delineating the paleoclimate of the northwestern pacific in relation to changes in northward heat transport from the western equatorial pacific ocean by the western boundary current

vertical fluxes of diatoms and silicoflagellates in the eastern equatorial atlantic and their contribution to the sedimentary record abstract sediment trap data from water depths of 853 m and 3921 m retrieved from the eastern equatorial atlantic 01 47 5 n 11 07 6 w sampling time march 1 1989 to march 16 1990 reveal seasonal changes in the vertical flux of opal biogenic opal constitutes 3 20 of the total flux at 853 m and 10 19 at 3921 m important contributors to the opal fraction are diatoms and to a lesser extent silicoflagellates at 853 m the fluxes of both siliceous groups show a distinct seasonal pattern related to upwelling and the location of the itcz the flux values are highest between march and april and in august september the seasonal pattern with the spring and summer peaks can be recognized in the samples from 3921 m in a modified form the flux curve is smoother and the time lag varies between 0 and 95 days higher flux values for diatoms silicoflagellates and total particles in the lower trap suggests an additional source of material lateral advection of particles from the coastal regime seems to be an important factor at 3921 m adding material at depth and distorting the original record also freshwater diatoms were relatively important in the spring and winter samples at 853 m and throughout the year at 3921 m suggesting continental influence a total of 202 diatom taxa were identified at both depths only a few were responsible for 50 of the total diatom assemblage nitzschia bicapitata dominated the assemblage differences in the relative abundances of strongly and weakly silicified diatom taxa between trap levels indicate dissolution in the water column however comparison between trap and sediment surface assemblages point to extreme dissolution at the sediment water interface approximately 98 of the siliceous shells are lost to the sedimentary record despite this loss the changes between the surface sediment assemblages reflect the overlying hydrographic conditions of the surface waters

modeling tsunami hazards from manila trench to taiwan abstract the 2006 dual pingtung earthquake event and the 2004 south asia tsunami highlighted the potential tsunami hazards from manila trench manila trench is only about 100 km away from taiwan therefore one shall punctuate the importance of thorough study on all possible tsunami scenarios for hazard mitigation based on the faults parameters issued by usgs and the seismic record from global cmt this study creates a hypothetical earthquake tsunami scenario caused by seismic motion at manila trench the magnitude of the earthquake is 9 35 mw the total length is 990 km and the maximum initial free surface height is 9 3 m the initial displacement profile is provided in this paper an open source code comcot is adopted to perform the simulation of the tsunami propagation runup and inundation around taiwan nested grid system and moving boundary technique are adopted to study runup and inundation the result shows that the maximum wave height is 11 m in southern taiwan serious flooding is observed in the southwest coast of taiwan tsunami inundation is able to reach 8 5 km inlandward due to the refraction effect 8 m wave height is noted in the northeast coast of taiwan the detailed tsunami behavior around taiwan is described in the context

planktonic foraminiferal assemblages in surface sediments from the southwest african continental margin abstract the relative abundance and distribution of planktonic foraminifera species on the southwest african continental margin have been determined from 152 surface sediment samples of the 23 recorded taxa only 8 make a significant contribution to the foraminiferal assemblages individual species proportions are closely related to the surface water hydrography of the benguela system and the associated upwelling phenomena three foraminiferal assemblages can be distinguished by correlation analysis on the abundances of the major taxa species composition of these assemblages range from polar taxa in the upwelling area left coiling neogloboquadrina pachyderma and globigerina quinqueloba to transitional taxa in the offshore oligotrophic environment globorotalia inflata and globorotalia truncatulinoides globigerina bulloides and right coiling neogloboquadrina pachyderma are preferentially distributed in the highly productive intermediate zone of the benguela system where upwelled and oligotrophic offshore waters mix variability of the hydrological processes upwelling intensity strength of the frontal features may be inferred from frequency variations of individual species and diversity patterns

origins and variability of the benguela current a subset of the benguela sources and transports best 1992 1993 data is analyzed to study the magnitude and variability of the large scale transports in the area the data consist of inverted echo sounder series and conductivity temperature depth stations the mean 16 month transport values for the upper 1000 m indicate that of the 13 sv northward transport within the benguela current 50 is derived from the central atlantic which from geometry may be chiefly south atlantic water 25 comes from the indian ocean which may be chiefly agulhas water and the remaining 25 may be a blend of agulhas and tropical atlantic water a simple schematic of the transport pattern with a somewhat restricted corridor for agulhas eddies translation is envisioned to the west of the eddy corridor flows the south atlantic source for the benguela current to the east is the agulhas indian ocean source the corridor is breached by south atlantic and indian water as the transient eddy field stirs these water masses

seasonal associations of phytoplankton and planktic foraminifera in an upwelling region and their contribution to the seafloor abstract seasonal occurrences of both phytoplankton and zooplankton are closely associated with upwelling and stabilization in waters overlying the san pedro basin this region is situated within the southern california bight and is affected by variations in the general southward flowing california current and variable intrusion of oceanic waters increased northerly wind stress in spring and early summer results in upwelling of deeper nutrient rich waters into the photic zone a seven month time series sediment trap experiment revealed clear patterns in seasonal succession of both phytoplankton and planktic foraminifera several distinct high and low flux periods occurred over the study period some of which can be related to rapid changes in the hydrographic environment caused by upwelling and subsequent surface water stratification factor analysis of relative abundances of combined phytoplankton and foraminiferal taxa defines seven assemblages reflecting seven stages of production which range in duration from two to five weeks factor scores describe phytoplankton and foraminiferal taxa indicative of specific production stages periods of high flux of the more abundant diatoms and planktic foraminifera also illustrate preferred production stages and compare well with percentage based results a comparison of the sediment trap assemblage with local sediment from an oxygenated portion of the basin suggests that long term phytoplankton accumulation in this region is dominated by taxa associated with winter bloom and post upwelling bloom production implying that brief but massive episodic events overwhelm and dominate the annually averaged diatom species assemblage found in the sediments foraminifera however are modified by dissolution to the extent that the high production periods of late spring and during upwelling are poorly represented rather species indicative of early spring and post upwelling conditions dominate the planktic foraminiferal sedimentary assemblage

the silica cycle during the last ice age abstract qualitative and quantitative investigations of the silica geochemistry in the ocean and its cycles and changes during the quaternary have been carried out based on more than 4000 sample determinations the present si cycle within the ocean balance and annual silica accumulation were determined the main part of silica has accumulated on the ocean bottom in three silica accumulation belts southern equatorial and northern the changes of the belts were synchronous for the northern and the southern hemispheres and were caused by climatic changes connected with glaciation

settling dissolution and burial of biogenic silica in the sediments off somalia northwestern indian ocean abstract particle fluxes of biogenic silica through the water column silica burial fluxes into the sediments and the flux of dissolved silica across the sediment water interface estimated from pore water profiles are used to assess the behaviour of biogenic silica at two stations 80 and 270 km offshore along a transect off the somali coast in the northwestern indian ocean particulate biogenic silica fluxes varied from 0 3 mmol m 2 day 1 in the non upwelling season to 6 mmol m 2 day 1 during upwelling on the somali slope fluxes were lower in the somali basin from 0 2 to 2 3 mmol m 2 day 1 evaluation of the dissolution curves derived by wet chemical leaching in sediment trap and sediment samples shows that the km values the apparent reactivity rates in alkaline medium are higher for the shallow sediment traps than for deep trap and boxcore sediments modelling of pore water profiles shows that in the sediment most dissolution occurs in the top halfcentimetre and pore water effluxes are in close agreement with those from in situ benthic incubations our results show that less than 10 of the biogenic silica arriving on the somali margin is buried in the sediments giving a burial efficiency lower than the approximately 20 reported from the open arabian sea

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

lunar cycles and seasonal variations in deposition fluxes of planktic foraminiferal shell carbonate to the deep south atlantic central walvis ridge abstract several authors have argued that lunar reproductive cycling controls the shell fluxes of planktic foraminifera one of the major carbonate producing groups in the global pelagic ocean a time series sediment trap at 2700 m depth on the central walvis ridge below the south atlantic central gyre demonstrate for the first time that shell deposition fluxes of hastigerina pelagica are synchronous with lunar periodicity spectral analysis of the 6 month time series with 8 day resolution showed a strong 30 day cyclicity in the flux maxima of h pelagica arriving at the ocean floor on average 12 5 days after each full moon given a shell settling velocity of about 400 m day 1 which implies about 7 days for settling this coincides with the pronounced endogenous reproduction rhythm of 5 2 days after full moon as originally observed in laboratory cultured isolates from off bermuda in the north atlantic by contrast no endogenous or exogenous lunar periodicity was observed in the deposition flux or size distribution of any of the 27 other shell species from austral winter august 2000 to austral summer february 2001 instead the deposition fluxes of shell species the bulk carbonate and the total mass were dominated by a seasonal maximum during austral spring without any periodicity in the 16 90 day domain of this study since h pelagica exhibits low fluxes with a low burial efficiency and continuous re production is shown by the deposition fluxes of other species lunar reproductive cycling appears not to affect pelagic carbonate productivity and deep ocean sedimentation fluxes

quantifying carbonate dissolution and calibration of foraminiferal dissolution indices in the somali basin two sediment traps moored off somalia in 1992 1993 collected similar settling fluxes of carbonate and siliceous shells formed by various plankton groups planktic foraminifera showed large seasonal variations with more than 74 of the total planktic foraminifera flux collected during the sw monsoon summer upwelling when globigerina bulloides was dominating along with globigerinita glutinata and neogloboquadrina dutertrei the intermonsoon and ne monsoon assemblages were dominated by globigerinoides ruber we used the trap records as our no dissolution reference for comparison with three boxcore recorders in order to quantify the carbonate dissolution along a depth transect dissolution increases downslope from station 905 to 907 and 915 at depths of 1567 m 2807 m and 4035 m respectively the carbonate fraction of the sediment at station 915 which is located near the ccd is the most affected by dissolution with more than 97 of the planktic foraminifera dissolved here the planktic foraminifera assemblage is strongly modified with thick walled species such as n dutertrei globorotalia tumida and pulleniatina obliquiloculata as the most resistant it is not representative of the settling assemblage the planktic foraminiferal assemblages of the sediment surface at stations 905 and 907 remain similar to the trap assemblages and the foraminifera are well preserved although only 25 of foraminifera are apparently preserved at station 905 and 8 at station 907 those numbers are surprisingly low and infer that only a small fraction of the foraminiferal carbonate production is buried and removed from the carbon cycle this discrepancy between the export and buried flux is partly be due to bio mechanical destruction by benthic processes and to supralysoclinal dissolution due to metabolic co2 generated by the benthic organisms another important factor is the interannual variability of the productivity well known in the arabian sea the calibration of commonly used foraminiferal dissolution indices percentage of foraminiferal fragments percentage of resistant species foraminiferal dissolution index fdx to our data only shows reliable results for high dissolution levels 97 off somalia the most accurate of the proxies is the percentage of foraminiferal fragments compared to the other methods tested i e fdx planktic foraminiferal loss l percentage of radiolarians and diatoms percentage of benthic foraminifera the species assemblage appears to be not significantly modified by dissolution unless the estimated shell loss is high 92 of the arriving shells in our samples this level is expressed in the percentage of fragmentation the percentage of radiolarians and diatoms the percentage of resistant foraminifera species and fdx as 80 35 25 and 1 8 respectively the relative abundance of globigerina bulloides is a valid sw monsoon upwelling proxy only when dissolution is moderate 92 globigerina bulloides and globigerinoides ruber have similar burial efficiencies and susceptibilities to dissolution thus the ratio g bulloides g ruber is a valid proxy for past changes in the intensity of the sw monsoon even in the strongly dissolved samples in our sediment record the ratio g bulloides g ruber indicates that the sw monsoon was stronger in the recent past than in 1992 93

siliceous phytoplankton of the western equatorial atlantic sediment traps and surface sediments abstract we present information on seasonal interannual and latitudinal variations of total mass caco 3 and biogenic opal in the western equatorial atlantic from time series sediment traps deployed between 550 and 850 m water depth at the equator wa 0 4 s wa 4 s and 7 s wa 7 s in addition species composition and downward fluxes of diatoms and silicoflagellates were determined significant seasonal variations in export production were observed between the equator and wa4 s and were substantially diminished at wa7 s oligotrophic site caco 3 dominates sedimentation followed by lithogenic particle and biogenic opal diatom and silicoflagellate maxima coincide with the southernmost position of the intertropical convergence zone january march and with the equatorial upwelling season of july september mainly reflected at wa4 s where mean diatom and silicoflagellate fluxes are highest interannual variability may be more common than generally assumed for oligotrophic central ocean gyres on a yearly basis total particle and caco 3 fluxes covary and show opposite latitudinal trends high annual fluxes at wa4 s in 1994 correspond with low values at wa7 s and vice versa for 1993 and 1995 annual diatom and silicoflagellate fluxes observed only at the oligotrophic site wa7 s were one order of magnitude higher in 1993 than those of 1994 and 1995 lightly silicified small diatoms of the nitzschia bicapitata group are the most abundant contributors to the diatom flux because these organisms are not preserved in the sedimentary record significant discrepancies between trapped and preserved assemblages were seen a substantial enrichment of the moderately robust species representative of the period of low diatom export characterizes the assemblages of the surface sediments differences in total particle and diatom fluxes between the western and eastern basins of the equatorial atlantic reflect basin to basin asymmetry with w e increase in primary productivity estimates organic carbon fluxes and silicate content in the subsurface waters and the w e shallowing of the thermocline depth despite flux differences siliceous phytoplankton species composition remained constant along the equatorial atlantic

planktonic response to main oceanographic changes in the alboran sea western mediterranean as documented in sediment traps and surface sediments abstract in order to determine the influence of seasonal oceanographic changes to the export of particulates and the flux of organisms as well as its corresponding integrated signal left in the bottom sediments of the alboran sea western mediterranean two mooring lines alb 1f and alb 1d were deployed from july 1997 to may 1998 on the continental slope south of malaga at 36 01 n 04 16 w and 36 14 n 04 28 w and a water depth of 1004 and 958 m respectively the mooring locations are under the influence of the incoming atlantic surface water asw at the northern and productive edge of the western alboran gyre wag and of the wind induced upwelling offshore the spanish coast additionally a total of five core tops located in the same area were studied the results are compared to information based on seawifs images of chlorophyll a concentration sst meteorological data on wind direction and intensity and fluvial discharges from the main rivers of the alboran basin the temporal oceanographic evolution of the alboran sea during the studied period was divided into five episodes e1 july 1997 e2 august october 1997 e3 november to mid december 1997 e4 december march 1998 and e5 april may 1998 the episodes represent different oceanographic conditions in the alboran sea during the studied period detailed analyses of the recorded pattern of bulk components calcareous nannoplankton planktonic foraminifera diatoms and phytoliths reflect seasonal changes in the main hydrographic regimes in the western alboran sea all biogenic bulk components as well as the annual evolution of the floral and faunal assemblages follow a tri modal pattern with maximum fluxes recorded during e1 e3 and e5 representing periods of higher productivity and wind induced upwelling during these periods species such as the small gephyrocapsa group gephyrocapsa muellerae and calcidiscus leptoporus the foraminifer globigerina bulloides and the diatom chaetoceros resting spores rs were dominant gephirocapsa oceanica and globorotalia inflata were coupled to the evolution of the atlantic surface water asw or related to surface water stability e2 and e4 the diatom leptocylindrus danicus responded to upwelling relaxation and water stratification e1 e2 and e4 and benthic diatoms were related to eddy intensity at bottom phytolith fluxes were directly related to wind intensities and the prevailing westerly winds e3 and e5 the distribution of microfossils in surface sediments differs from the biogenic assemblages recorded in the sediment traps in this sense during 1997 1998 the strongest el nino event in the last century took place which could have forced an unusual seasonality in the alboran sea reflecting an exceptional micropaleontological signal not observed in the surface sediments

alkenone and coccolithophorid species changes in late quaternary sediments from the walvis ridge implications for the alkenone paleotemperature method abstract sea surface temperatures ssts derived from the alkenone u37 record of quaternary sediments may be subject to bias if algae with different temperature sensitivities have contributed to the sedimentary alkenone record the alkenone derived sst records are usually based on a u37 temperature relationship which was measured in culture experiments using the coccolithophorid emiliania huxleyi f g prahl l a muehlhausen and d l zahnle 1988 further evaluation of long chain alkenones as indicators of paleoceanographic conditions geochim cosmochim acta 52 2303 2310 to assess possible effects of past species changes on the u37 temperature signal we have analysed long chain alkenones and coccolithophorids in a late quaternary sediment core from the walvis ridge and compared the results to sst estimates extracted from the 18o record of the planktonic foraminifer globigerinoides ruber alkenones and isotopes were determined over the entire 400 kyr core record while the coccolithophorid study was confined to the last 200 kyr when the most pronounced changes in alkenone content occurred throughout oxygen isotope stages 6 and 5 species of the genus gephyrocapsa were the predominating coccolithophorids e huxleyi began to increase systematically in relative abundance since the stage 5 4 transition became dominant over gephyrocapsa spp during stage 3 and reached the highest abundances in the holocene carbon normalized alkenone concentrations are inversely related to the relative abundances of e huxleyi and directly related to that of gephyrocapsa spp suggesting that species of this genus were the principal alkenone contributors to the sediments nevertheless sst values obtained from the u37 temperature relationship for e huxleyi compare favourably to the isotope derived temperatures the recently reported u37 temperature relationship for a single strain of gephyrocapsa oceanica j k volkman s m barrett s i blackburn and e l sikes 1995 alkenones in gephyrocapsa oceanica implications for studies of paleoclimate geochim cosmochim acta 59 513 520 produces unrealistically high sst values indicating that the temperature response of the examined strain is not typical for the genus gephyrocapsa this is supported by the c37 c38 alkenone ratios of the sediments which are comparable to average ratios reported for e huxleyi but significantly higher than for the g oceanica strain most notably the general accordance of the alkenone characteristics between sediments and e huxleyi persists through stages 8 to 5 and even in times that predate the first appearance of this species 268 ka h r thierstein k r geitzenauer and b molfino 1977 global synchroneity of late quaternary coccolith datum levels validation by oxygen isotopes geology 5 400 404 our results suggest that u37 temperature relationships based on e huxleyi produce reasonable paleo sst estimates even for late quaternary periods when this species was scarce or absent because other alkenone synthesizing algae e g of the genus gephyrocapsa responded similarly to temperature changes

interannual variability of planktic foraminiferal populations and test flux in the eastern north atlantic ocean jgofs planktic foraminiferal assemblages vary in response to seasonal fluctuations of hydrographic properties between water masses and after periodical changes and episodic events e g reproduction storms distinct annual variability of the planktic foraminiferal flux is also known from sediment trap data in this paper we discuss the short term impacts on interannual flux rates based on data from opening closing net hauls obtained between the ocean surface and 500 m water depth data were recorded during april may june and august at around 47 n 20 w biotrans in 1988 1989 1990 1992 1993 and during may 1989 and 1992 at 57 n 20 22 w species assemblages closely resemble each other when comparing the mixed layer fauna with the fauna of the upper 100 m and the upper 500 m of the water column in addition species assemblages 100 m are almost indistinguishable from assemblages that are 125 m in test size the standing stock of planktic foraminifers at biotrans can vary by more than one order of magnitude over different years however species assemblages may be similar when comparing corresponding seasons early summer assemblages june are distinctly different from late summer assemblages august significant variations in the species composition during spring april may are independent of the mixed layer depth spring assemblages are characterized by high numbers of globigerinita glutinata in particular day to day variations of the number of specimens and in species composition may have the same order of magnitude as interannual variations this appears to be independent of the reproduction cycle species assemblages at 47 n and 57 n are similar during spring although surface water temperatures and salinities differ by up to 10 c and 0 7 psu we suggest that the main factors controlling the planktic foraminiferal fauna are the trophic properties in the upper ocean productive layer planktic foraminiferal carbonate flux as calculated from assemblages reveals large seasonal variations a quasi annual periodicity in flux levels and substantial differences in timing and magnitude of peak fluxes at the biotrans station the average annual planktic foraminiferal caco 3 fluxes at 100 and 500 m depth are estimated to be 22 4 and 10 0 g m 2 yr 1 respectively

increasing seasonal upwelling in the subtropical south atlantic over the past 700 000 yrs evidence from deep living planktonic foraminifera abstract the distribution and character of deep living planktonic foraminifera such asgloborotalia truncatulinoides andg hirsuta are particularly sensitive to the structure of the upper ocean because of the wide range of water depths over which their life cycles extend like other planktonic foraminifera the deep living species begin growing in shallow surface waters but unlike the other species they continue growing while sinking into much deeper water their reproduction is synchronized with the seasonal deep mixing and upwelling of nutrient rich waters that precedes spring bloom where deep mixing is curtailed the abundances of the deeper dwelling species g hirsuta the deeper dwelling varieties e g left coilingg truncatulinoides and the larger presumably faster sinking shells are reduced leading to an apparent acceleration in shell development these changes are observed today in transects from the seasonally deep mixed subtropical gyres to the seasonally stable surface waters equatorward of the subtropical convergences past changes in the abundance and character of these deep living planktonic foraminifera have been measured in a late pleistocene record from the subtropical western south atlantic ocean over the past 700 kyrs abundances of these species have increased g truncatulinoides has changed from the predominantly shallower dwelling right coiling to the deeper dwelling left coiling variety and the accelerated shell development characteristic of shallow mixing has shifted toward the rates normally associated with deep mixing all this indicates that the structure of the upper ocean in the subtropical south atlantic before 700 kyrs ago was more like that nearer the equator today where mixing is limited to the upper 100 200 m since that time the scale of mixing has gradually increased to more than 400 m this implies a gradual increase through the late pleistocene in the seasonal upwelling of nutrients in the subtropical south atlantic and consequently in the intensity of the seasonal maximum in organic productivity

preservation of siliceous microplankton in surface sediments of the northern red sea abstract we studied the siliceous microplankton assemblages mainly diatoms from plankton tows mesh size 20 m and surface sediment samples collected along a n s transect in the northern red sea 28 21 n in addition we analyzed differences similarities between plankton and sediment assemblages within a brine filled basin the southern basin of the shaban deep and compared these assemblages with those from outside the brine plankton samples revealed the overwhelming dominance of diatoms over other siliceous groups diatoms accounted for ca 97 of all biosiliceous particles at 120 20 m vs 2 9 silicoflagellates and 0 4 radiolarians and ca 94 at 200 120 m vs 4 5 silicoflagellates and 1 6 radiolarians in general a marine warm water tropical subtropical diatom assemblage characterizes the plankton samples representatives of the nitzschia bicapitata group are by far the most abundant contributors at both depth intervals average 43 ranging from ca 30 in the north to ca 60 in the south biogenic opal content in non brine surface sediments is very low below 0 2 wt sio2 and concentration of siliceous microorganisms is also low and of the order of 5 103 104 microorganisms g 1 dry sediment diatoms are the main contributors to the opal signal in the 20 40 m fraction while they share dominance with radiolarians in the 40 m fraction total diatom concentrations average 1 2 104 valves g 1 in the 20 40 m fraction and 4 103 valves g 1 in the 40 m fraction robust taxa of warm water affinity alveus marinus azpeitia neocrenulata azpeitia nodulifera and roperia tesselata characterize the surface sediments in contrast biogenic opal content in brine surface sediment samples is much higher than in the non brine samples ranging from 2 8 to 3 8 wt sio2 and concentration of siliceous microorganisms is 3 4 orders of magnitude higher in addition here diatoms dominate the opal signal the taxa found in these samples are a mixture of non brine and plankton samples and fragile forms e g n bicapitata group neodelphineis indica are well preserved in these sediments thus brine sediments in this region seem to offer a great potential for palaeoenvironmental studies

quantified sensitivity of small lake sediments to record historic earthquakes implications for paleoseismology seismic hazard assessment is a critical but challenging issue for modern societies a key parameter to be estimated is the recurrence interval of damaging earthquakes this requires the establishment of earthquake records long enough to be relevant i e far longer than historical observations we study how lake sediments can be used for this purpose and explore conditions that enable lake sediments to record earthquakes this was achieved i through the compilation of eight lake sediment sequences from the european alps to reconstruct chronicles of mass movement deposits and ii through the comparison of these chronicles with the well documented earthquake history this allowed 24 occurrences of mass movements to be identified of which 21 were most probably triggered by an earthquake however the number of earthquake induced deposits varies between lakes of a same region suggesting variable thresholds of the lake sequences to record earthquake shaking these thresholds have been quantified by linking the mass movement occurrences in a single lake to both intensity and distance of the triggering earthquakes this method offers a quantitative approach to estimate locations and intensities of past earthquake epicenters finally we explored which lake characteristics could explain the various sensitivities our results suggest that sedimentation rate should be larger than 0 5 mm yr 1 so that a given lake records earthquakes in moderately active seismotectonic regions we also postulate that an increasing sedimentation rate may imply an increasing sensitivity to earthquake shaking hence further paleoseismological studies should control carefully that no significant change in sedimentation rates occurs within a record which could falsify the assessment of earthquake recurrence intervals

seasonal export and sediment preservation of diatomaceous foraminiferal and organic matter mass fluxes in a trophic gradient across the se atlantic abstract seasonal deposition fluxes of sinking phytoplankton zooplankton and major mass compounds i e calcium carbonate biogenic opal and organic matter intercepted by deep moored sediment traps are contrasted with their sediment accumulation rates over the 2700 m deep central walvis ridge in the oligotrophic se atlantic these data provide the first seasonally resolved record of biogenic particle fluxes in the south atlantic central gyre and serve as the oligotrophic end member of a gradient across the benguela system to the highly productive coastal upwelling off namibia maximum fluxes at the central walvis ridge were deposited in early austral spring following winter deepening of the surface mixed layer and associated nutrient entrainment nearly 25 of the annual mass flux arrived in october when sea surface temperature rose deep vertical mixing halted and surface production collapsed the annual flux of diatoms was dominated by small specimens of nitzschia bicapitata 60 whereas globorotalia inflata dominated the foraminiferal fluxes 25 diatom diversity dropped significantly during the bloom periods when up to 80 was composed of small n bicapitata but foraminiferal diversity remained about constant the diatom flux maximum together with those of biogenic silica and organic matter preceded those of the foraminifera pteropods carbonate and total mass by 1 week fluxes of the left and right coiled shells of the deep dwelling foraminifer globorotalia truncatulinoides peaked in different seasons a distinctive ecological behaviour which merits their taxonomic recognition as separate species these findings testify to recent evidence for the existence of several genetic species within g truncatulinoides and now suggest that such species may also have different seasonal responses the benguela trophic gradient showed a shoreward increase in particle fluxes but differences were surprisingly small testifying to only moderately enhanced export productivity and deposition at the namibian margin relative to the oligotrophic central gyre from the open ocean toward coastal upwelling small and weakly silicified diatoms were substituted by other larger and more heavily silicified species possibly in response to decreased silica limitation foraminiferal deposition fluxes were increasingly dominated by g inflata accompanied by a change over from many warm to few cold water minor species the late winter maximum at the namibian margin and the early spring maximum at the central walvis ridge were generated by the same process of collapsing surface productivity in response to the shut down of nutrient entrainment at the winter to summer transition although delayed by up to 2 months in the central gyre at the sediment water interface intense degradation of organic matter and biogenic silica resulted in poor preservation accompanied by pronounced changes in the species composition of siliceous phytoplankton of all particle groups at the central walvis ridge only the export of foraminiferal shells appeared to be fully transferred into the sediment and through their species assemblage to provide a sedimentary record of past seasonal productivity conditions of the upper ocean

particle settling rates increase with depth in the ocean abstract time and depth scales of particulate organic carbon degradation and caco3 and biogenic opal dissolution are critical to understanding the depth distribution of co2 and dissolved nutrients in the ocean the speed at which particles sink and the factors that control sinking speed are of primary importance to the distribution of oceanic nutrient concentrations and to the preservation of biogenic material in the sediment record sequencing sediment trap collectors deployed at us jgofs sites in the equatorial pacific and arabian sea provided a time series of particle fluxes from which particle settling rates were estimated a comparison of settling velocities obtained from 100 500 m pilskaln et al deep sea research 45 1998 1803 to settling velocities obtained for depths between 1000 and 3500 m indicate an increase of a factor of 2 10 between 100 and 2000 m and an increase of 15 60 between 2000 and 3500 m the increase in settling velocity in the deep ocean is generally correlated with the loss of corg with depth lithogenic content does not appear to impact particle settling rate variability in particle settling rate is systematically related to physical forcing of the surface ocean in the equatorial pacific but not in the arabian sea the increase in particle settling rate with depth likely influences the delivery of caco3 to the sea floor

planktonic foraminiferal flux seasonality in subantarctic sediment traps a test for paleoclimate reconstructions sediment trap moorings deployed during 1997 and 1998 in the subantarctic to polar frontal regions of the southern ocean reveal distinct seasonality in foraminiferal flux foraminiferal assemblages vary between each site yet major species exhibit very similar patterns of seasonal succession which can be associated with changes in mixed layer depth enhanced foraminiferal productivity is also associated with periods of high biogenic silica and particulate organic carbon flux on a broader scale foraminiferal assemblages are strongly delineated by temperature temperature estimates derived from the assemblages using the modern analog technique mat are mostly within 2 5 c of the satellite advanced very high resolution radiometer temperatures observed during the deployment period this indicates that core top sediments included in the mat database do reflect modern observed conditions at the sea surface providing a robust technique for estimating past temperature change from foraminiferal assemblages in southern ocean environments

oxygen isotope ecology of recent planktic foraminifera at the central walvis ridge se atlantic 1 above the walvis ridge in the se atlantic ocean we collected living plantkic foraminifera from the upper water column using depth stratified plantkon tows the oxygen isotope composition 18oc in shells of foraminifera and shell concentration profiles show seasonal and depth habitats of individual species the tow results are compared with the average annual deposition 18oc from sediment traps and the interannual average 18oc of fossil specimens in top sediments at the same site the species globigerinita glutinata best reflects the austral winter spring sea surface temperature sst its 18oc signal in top sediments remains pristine in contrast tow results also show that globigerinoides ruber continues to calcify below the surface mixed layer sml i e down to the deep chlorophyll maximum dcm hence its 18oc signature of exported specimens reflects the sst only when sml incorporates the dcm deep tow and sediment trap results show that both globorotalia truncatulinoides and globorotalia inflata record the temperature between 150 and 350 m depending on the season and the shell size however for all fossil taxa in sediments apart from globigerinita glutinata we observe a positive 18oc shift with respect to the sediment trap and plankton tow values likely related to the interannual flux changes and deep encrustation