taphonomic signatures and patterns of test degradation on tropical intertidal benthic foraminifera the preservational condition of benthic foraminifera from tropical intertidal sediments in cleveland bay north queensland australia was examined in order to provide systematic descriptions of taphonomic signatures and semi quantitative estimates of test degradation the primary aim was to improve understanding of the processes of test degradation experienced by intertidal foraminifera during early burial eight common tropical intertidal foraminiferal species were examined arenoparrella mexicana miliammina fusca miliammina obliqua and trochammina inflata from two upper mangrove stations and ammonia aoteana elphidium excavatum clavatum pararotalia venusta and parrellina hispidula from two mudflat stations taphonomic alteration was broadly divided into surface textural features and larger scale structural losses to tests surface alteration of calcareous tests was dominated by the etching and roughening associated with dissolution processes with limited evidence for bioerosion and abrasion both surficial etching and larger scale structural damage were closely related to test architecture with degradation most intense on porous chamber walls as opposed to non porous areas interlocular walls and chamber tips furthermore all calcareous species exhibited consistent pathways of degradation whereby the most recently formed chambers were the most vulnerable to degradation the correspondence between larger scale test loss and these patterns of surface textural alteration suggests calcareous test degradation is primarily driven by dissolution degradation of agglutinated tests contrasts in a number of ways pristine tests of all four species examined exhibited a smooth outer organic coating which may be missing from other specimens the extent to which this initial loss effects further test breakdown is uncertain but appears to differ between species m obliqua and some specimens of a mexicana exhibited structural damage which corresponded to clear cement losses and agglutinant disaggregation more generally agglutinated species displayed fracturing and test breakages which bore no conspicuous relation to cement loss furthermore neither surface alteration nor structural loss affected any part of agglutinated tests preferentially and therefore pathways of degradation were inconsistent across specimens the fact that agglutinated tests degrade in a more arbitrary manner compared with calcareous tests is taken as evidence that their degradation is 1 not entirely controlled by test architecture and 2 at least partially driven by physical mechanical processes we suggest that if agglutinated tests are not already inherently weaker than their calcareous counterparts the loss of organic cements may sufficiently weaken agglutinated tests so as to increase susceptibility to physical damage tests were also graded according to the extent to which they were structurally degraded average taphonomic grades and taphonomic variability i e standard deviation for all species at cocoa creek were statistically invariant with depth contrary to expectations based on the concept of progressive burial through a taphonomically active zone this indicates that shallow sub surface sediments are significantly homogenised and that sediment mixing and infaunal test production imparts a considerable effect on the development of surface and sub surface dead assemblages at the study site

paleoenvironmental changes at the lower pleistocene montalbano jonico section southern italy global versus regional signals abstract integrated high resolution data from calcareous plankton assemblages foraminifera and nannofossils together with geochemical and mineralogical investigations have been collected at the on land montalbano jonico section southern italy in order to reconstruct the paleoenvironmental changes through marine isotope stages mis 23 37 time series analysis on globigerina bulloides and cassidulina carinata 18o records and on selected calcareous plankton proxies mainly revealed the occurrence of precession and obliquity forcing the deposition of sapropel layers which are interbedded in the montalbano jonico section was driven by water column stratification insolation cycle i 104 and enhanced sea surface water productivity insolation cycle i 112 i 102 and i 86 different paleoenvironmental conditions mark the sedimentary evolution of the section from 1240 to 1082 ka mis 37 mis 32 high percentage abundances of warm and oligotrophic planktonic foraminifera and calcareous nannofossil taxa indicate the establishment of oligotrophic and stratified surface water conditions a key paleoenvironmental change occurred during mis 31 from about 1080 to 1065 ka which was a very warm interglacial characterized by an increase of tropical subtropical globigerinoides ruber group and globigerinoides trilobus and low salinity braarudosphaera bigelowii sea surface water taxa during this interval more humid climate conditions coupled with changes in local paleomorphology may have triggered a higher and unusual freshwater input and the creation of a new entry point for sediment supply into the basin from a different drainage area from about 1065 to 1010 ka mis 30 mis 29 a cool and dry climate prevailed in the circum mediterranean area during a time of precession maxima this favored lowered sea surface temperatures and an increase of polar water neogloboquadrina pachyderma left coiling there are also indications of a reduction of the terrigenous input from the new source area from 1010 ka upward mis 28 mis 23 the higher abundances of globigerina bulloides turborotalita quinqueloba and calciosolenia spp indicate enhanced productivity conditions probably related to high turbidity of sea surface waters triggered by a more conspicuous sediment input from land analysis of the long term trends in the multiproxy patterns suggests that the major paleoenvironmental changes occurred as a consequence of the combined effect of orbitally controlled global climate and regional processes

glacial interglacial ocean climate variability from planktonic foraminifera during the mid pleistocene transition in the temperate southwest pacific odp site 1123 abstract planktonic foraminiferal assemblages and artificial neural network estimates of sea surface temperature sst at odp site 1123 41 47 2 s 171 29 9 w 3290 m deep east of new zealand reveal a high resolution history of glacial interglacial g i variability at the subtropical front stf for the last 1 2 million years including the mid pleistocene climate transition mpt most g i cycles of 100 kyr duration have short periods of cold glacial and warm deglacial climate centred on glacial terminations followed by long temperate interglacial periods during glacial deglacial transitions maximum abundances of subantarctic and subtropical taxa coincide with sst minima and maxima and lead ice volume by up to 8 kyrs such relationships reflect the competing influence of subantarctic and subtropical surface inflows during glacial and deglacial periods respectively suggesting alternate polar and tropical forcing of southern mid latitude ocean climate the lead of ssts and subtropical inflow over ice volume points to tropical forcing of southern mid latitude ocean climate during deglacial warming this contrasts with the established hypothesis that southern hemisphere ocean climate is driven by the influence of continental glaciations based on wholesale changes in subantarctic and subtropical faunas the last 1 2 million years are subdivided into 4 distinct periods of ocean climate 1 the pre mpt 1185 870 ka has high amplitude 41 kyr fluctuations in sst superimposed on a general cooling trend and heightened productivity reflecting long term strengthening of subantarctic inflow under an invigorated antarctic circumpolar current 2 the early mpt 870 620 ka is marked by abrupt warming during mis 21 followed by a period of unstable periodicities within the 40 100 kyr orbital bands decreasing sst amplitudes and long intervals of temperate interglacial climate punctuated by short glacial and deglacial phases reflecting lower meridional temperature gradients 3 the late mpt 620 435 ka encompasses an abrupt decrease in the subantarctic inflow during mis 15 followed by a period of warm equable climate poorly defined low amplitude g i variations in ssts during this interval are consistent with a relatively stable stf and evenly balanced subantarctic and subtropical inflows possibly in response to smaller less dynamic polar icesheets 4 the post mpt 435 0 ka is marked by a major climatic deterioration during mis 12 and a return to higher amplitude 100 kyr frequency sst variations superimposed on a long term trend towards cooler ssts and increased mixed layer productivity as the subantarctic inflow strengthened and polar icesheets expanded

braarudosphaera rich sediments on the exmouth plateau eastern indian ocean calcareous nannofossil assemblages enriched in braarudosphaera occur in lower oligocene to lower miocene sediments at ocean drilling program sites 762 and 763 on the central exmouth plateau although beds of braarudosphaera rich sediments are well known in the oligocene of the south atlantic the braarudosphaera chalk this is the first published report of this phenomenon in the easter indian ocean braarudosphaerids appear rather abruptly in the lower oligocene in zone np 21 on the exmouth plateau they reach their greatest numbers in the lower oligocene in zones np 22 and np 23 where they comprise up to 10 of some samples braarudosphaera bigelowii is the overwhelmingly dominant species occurring together with rare specimens of b discula and micrantholithus pinguis the holococcoliths peritrachelina joidesa and lanternithus minutus are also associated with the braarudosphaera enrichment there are two populations of b bigelowii one of normal size 10 14 mu m and one of large specimens 20 22 mu m the larger braarudosphaerids are more common than the smaller forms braarudosphaera rich sediments are absent at the nearby wombat plateau sites during the same time interval the authors attribute this to latitudinal control since the wombat sites are about 4 degree north of the central exmout plateau sites the occurrencemore of braarudosphaerids on the exmouth plateau is related to an oligocene to early miocene oceanographic event stable isotope and trace element analyses suggest that upwelling of cool low salinity nutrient rich water along a divergent zone created the braarudosphaera rich sediments in the indian ocean less

overview of the montalbano jonico area and section a proposal for a boundary stratotype for the lower middle pleistocene southern italy foredeep abstract in the southernmost part of the southern apennine foredeep crops out a well exposed and continuous succession about 500 m thick of muds and muddy silts and several interbedded volcaniclastic layers on the basis of nannofossil biostratigraphy it ranges from large gephyrocapsa to pseudoemiliania lacunosa zones that indicate the upper part of the lower pleistocene and the lower part of the middle pleistocene the vertical distribution of both invertebrate fossil assemblages and teleostean otoliths points out changes in the primary environmental parameters particularly bathymetry sedimentation rate and oxygen concentration the observations allowed the reconstruction of several deepening shallowing cycles within a general regressive framework the montalbano jonico composite section is likely to represent a regressive portion of a third order cycle in which relevant tectonic pulses should be the main reason for the general shallowing possibly related to the beginning of the filling up phase of the southern part of the apennines foredeep the two recognized fourth order cycles could be related to tectonoeustatic causes the higher frequency cyclicity represented by several fifth order cycles seems to be mainly connected with astronomical relationships the montalbano jonico section could be suitable for defining the lower middle pleistocene boundary stratotype the potential gssp could be located close to the small gephyrocapsa p lacunosa zonal boundary near a biohorizon rich in delectopecten vitreus a muddy dark grey sapropelitic layer rich in chondrites ichsp and in oxygen isotopic stage 25 another potential location of the gssp of middle pleistocene could be near the volcaniclastic horizon v4 close to the isotopic stage 19 boundary

conflicting coccolithophore and geochemical evidence for productivity levels in the eastern mediterranean sapropel s1 abstract the cyclic development of anoxic conditions in the eastern mediterranean deep sea waters is one of the most fascinating research topics in paleoceanographic studies in combination with bottom water stagnation enhanced primary production is a common explanation for the deposition of organic rich layers sapropels this is supported by extensive evidence from both geochemical and micropaleontological studies the correspondence of recent sapropel layers with peaks of the lower photic zone coccolithophore species florisphaera profunda has been interpreted as a proxy for the development of a deep chlorophyll maximum dcm due to the pycnocline nutricline shallowing into the lower part of the photic zone we present millennial scale data for coccolithophore assemblages from sediments across the most recent sapropel s1 in the odp hole 964b drilled in the ionian sea relative and absolute abundances of taxa are compared with selected elemental composition of the bulk sediments the mn al and ba al profiles are used to determine the original thickness of the s1 interval and show that the upper part of s1 was affected by post depositional oxidation of organic matter the nannofossil accumulation rate defined by the number of coccoliths cm 2 kyr 1 suggests that there is no evidence of increased productivity within most of the sapropel layer in fact coccolithophore production was at its minimum in the lower part minimum coccolith concentrations are reached despite the increase in f profunda in both relative and absolute abundance we suggest that the dcm deduced from the increased productivity of this species did not significantly contribute to the putative overall increased primary productivity during the deposition of most of the sapropel layer within the upper oxidized part of s1 coccolith accumulation was at least five times higher than in the lower part this period of high coccolith productivity finds a counterpart in the increase of the ba al ratio the total concentration of coccoliths is again controlled by the amount of e huxleyi but it is also supported by concomitant increases in all the other groups suggesting that coccolithophore productivity increased throughout the year and through the total vertical extent of the photic zone at site 964 this is apparently the only moment when coccolithophores contributed substantially to the increased primary productivity generally assumed for the s1 layer

phyto_ and zooplankton paleofluxes during the deposition of sapropel s1 eastern mediterranean biogenic carbonate preservation and paleoecological implications abstract the relative and absolute abundances and accumulation rates of foraminifera and calcareous nannofossils were quantified in a box core containing sapropel s1 from the florence rise area se of cyprus 2302 m water depth the main objective of this study was to reconstruct in detail variations in paleoecological conditions of water masses during the deposition of this sapropel in particular we qualitatively evaluated the importance of carbonate dissolution on planktonic assemblages to better interpret the abundance profiles obtained from the two investigated taxa selective carbonate corrosion in the core is shown by 1 the decrease in shell mass weight of selected species of planktonic foraminifera 2 the decrease in accumulation rate of dissolution susceptible holococcoliths and coccolith species and 3 the absence of pteropods however the presence of other relatively dissolution susceptible coccolith species throughout all of the s1 interval suggests moderate dissolution florisphaera profunda shows a marked increase in paleofluxes within the sapropel coupled with a decrease in the accumulation rate of the upper middle photic zone coccoliths suggesting an ecological depth separation of the water column probably characterised by higher nutrient availability at depth and nutrient depleted surface waters between 10 and 6 5 kyr bp in the same interval turborotalita quinqueloba and globigerina bulloides two foraminiferal species frequently occurring during periods of high fertility increase in relative abundance the maximum increase in relative abundance of globigerinoides ruber var alba and rosea marks the climatic optimum phase and the maximum stratification in surface water that occurred at the beginning of sapropel s1 deposition when the bottom waters were anoxic an important change in foraminiferal assemblages occurs at 8 kyr bp and corresponds with a negative shift in caco 3 ba and c org contents this short interval marks the establishment of relatively less anoxic conditions in the bottom water introducing the last phase of sapropel formation after 6 5 kyr bp a progressive re establishment of normal oceanographic conditions occurred before the real end of the sapropel s1 this transition is well recorded by the reoccurrence and major accumulation rate of the mixing indicator foraminiferal species globorotalia inflata and by the gradual decrease in abundance of f profunda

chemical cycles in pliocene sapropel bearing and sapropel barren eastern mediterranean sediments abstract high resolution 3 4 cm investigations of major and minor elements were carried out on sediment cores from odp leg 160 sites 964 ionian basin 969 mediterranean ridge 967 and 966 northern slope and top of eratosthenes seamount south of cyprus at site 967 element al ratios display pronounced cyclic records that are related to astronomically forced climatic variations sediments from the top of eratosthenes seamount site 966 show a similar pattern to those from site 967 but they are more disturbed by bioturbation and also strongly influenced by long term variations in sediment dispersal sediments from site 969 display similar trends to those from site 964 i e they are characterized by higher mg al slightly higher k al and lower ti al ratios during sapropel formation higher ti al ratios at site 969 compared with sediments from site 964 may be explained by a westward transport of material from a source in the east where ti al ratios are highest sites 966 and 967 elevated mg al ratios at site 969 during sapropel intervals are due to river derived material transported through the kithira strait between peloponnesus and crete from the northwestern aegean sea which originates from ultramafic rocks a change in intermediate water currents current reversal during sapropel formation may explain the enhanced supply of mg rich and the relatively diminished supply of ti rich material we propose that during deposition of the reddish intervals at site 969 a change in circulation did not occur because a drastic decrease in ti al ratios is not evident in these sediments ba peaks indicative of former sapropels are not present ba enrichments in the same sapropel barren intervals at site 967 northern slope of eratosthenes seamount suggest that during such intervals the burn down process was more effective than during the sapropel bearing intervals mn contents in all investigated pliocene sediments correlate with the carbonate contents higher mn contents of the sapropel barren sediments suggest that during time intervals of sapropel formation either mn accumulation at the margins of the permanently oxic upper water column or mn export into the western mediterranean might have occured the latter could only be explained by sub or anoxic conditions in large parts of the water column

shell size variation of the planktonic foraminifer neogloboquadrina pachyderma sin in the norwegian greenland sea during the last 1 3 myrs implications for paleoceanographic reconstructions we present measurements of the maximum diameter of the planktonic foraminifer neogloboquadrina pachyderma sin from six sediment cores ocean drilling program sites 643 644 907 909 985 and 987 from the norwegian greenland sea our data show a distinct net increase in mean shell size of n pachyderma sin at all sites during the last 1 3 ma with largest shell sizes reached after 0 4 ma external factors such as glacial interglacial variability and carbonate dissolution alone cannot account for the observed variation in mean shell size of n pachyderma sin we consider the observed shell size increase to mirror an evolutionary trend towards better adaptation of n pachyderma sin to the cold water environment after 1 1 1 0 ma probably the mid pleistocene climate shift and the associated change of amplitude and frequency of glacial interglacial fluctuations have triggered the evolution of this planktonic foraminifer oxygen and carbon stable isotope analyses of diverent shell size classes indicate that the observed shell size increase could not be explained by the functional concept that larger shells promote increasing sinking velocities during gametogenesis for paleoceanographic reconstructions the evolutionary adaptation of neogloboquadrina pachyderma sin to the cold water habitat has significant implications carbonate sedimentation in highest latitudes is highly dependent on the presence of this species in the norwegian greenland sea carbonate poor intervals before 1 1 ma are therefore not necessarily related to severe glacial conditions they are probably attributed to the absence of this not yet polar adapted species further transfer function and modern analog techniques used for the reconstruction of surface water conditions in high latitudes could therefore contain a large range of errors if they were applied to samples older than 1 1 1 0 myrs 2000 elsevier science b v all rights reserved

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

glacial variability over the last two million years an extended depth derived agemodel continuous obliquity pacing and the pleistocene progression abstract an agemodel not relying upon orbital assumptions is estimated over the last 2 ma using depth in marine sediment cores as a proxy for time agemodel uncertainty averages 10 ka in the early pleistocene 2 1 ma and 7 ka in the late pleistocene 1 ma to the present twelve benthic and five planktic 18 o records are pinned to the agemodel and averaged together to provide a record of glacial variability major deglaciation features are identified over the last 2 ma and a remarkable 33 out of 36 occur when earth s obliquity is anomalously large during the early pleistocene deglaciations occur nearly every obliquity cycle giving a 40 ka timescale while late pleistocene deglaciations more often skip one or two obliquity beats corresponding to 80 or 120 ka glacial cycles which on average give the 100 ka variability this continuous obliquity pacing indicates that the glacial theory can be simplified an explanation for the 100 ka glacial cycles only requires a change in the likelihood of skipping an obliquity cycle rather than new sources of long period variability furthermore changes in glacial variability are not marked by any single transition so much as they exhibit a steady progression over the entire pleistocene the mean variance skewness and timescale associated with the glacial cycles all exhibit an approximately linear trend over the last 2 ma a simple model having an obliquity modulated threshold and only three adjustable parameters is shown to reproduce the trends timing and spectral evolution associated with the pleistocene glacial variability

calcareous nannofossils planktonic foraminifera and oxygen isotopes in the late quaternary sapropels of the ionian sea core m 25 4 12 a long piston core 12 20 m recovered in the ionian sea during cruise m25 4 of the r v meteor summer 1993 at a water depth of 2467 m shows an almost complete sequence of sapropels s 1 s 3 to s 10 over the last 330 ka this paper presents the results of an integrated study based on quantitative biostratigraphic analyses performed on both calcareous nannofossils and planktonic foraminifera coupled with the 18o record a decrease in syracosphaera sp 1 and an increase in the abundance of the genus rhabdosphaera and of helicosphaera carteri florisphaera profunda and of the reworked specimens has been found in the calcareous nannofossil assemblage within the sapropels the planktonic foraminiferal assemblage of the sapropels is characterized by a peak in the frequency of globigerinoides ruber var alba and rosea and neogloboquadrina dutertrei the 18o record of globigerinoides ruber and globigerina bulloides allows recognition of isotope stages 1 to 9 and shows a negative fluctuation that corresponds to the sapropel layers these features support the idea of increased productivity coupled to the presence of reduced salinity surface waters that caused the deposition of the sapropels however the need for a good understanding of the ecological requirements of modern assemblages is stressed this is necessary to correctly interpret fossil assemblages this in turn will allow a better understanding of the palaeoceanographic conditions leading to sapropel deposition

enso like forcing on oceanic primary production during the late pleistocene late pleistocene changes in oceanic primary productivity along the equator in the indian and pacific oceans are revealed by quantitative changes in nanoplankton communities preserved in nine deep sea cores we show that variations in equatorial productivity are primarily caused by glacial interglacial variability and by precession controlled changes in the east west thermocline slope of the indo pacific the precession controlled variations in productivity are linked to processes similar to the southern oscillation phenomenon and they precede changes in the oxygen isotopic ratio which indicates that they are not the result of ice sheet fluctuations the 30 000 year spectral peak in the tropical indo pacific ocean productivity records is also present in the antarctica atmospheric co2 record suggesting an important role for equatorial biological productivity in modifying atmospheric co2

chemical weathering and boulder mantles karkevagge swedish lapland abstract a deposit of giant boulders covers much of the floor of karkevagge an alpine valley in the swedish arctic these mica schist and garnet mica schist boulders apparently have been there since the waning stages of glaciation in the valley about 13 000 to 9000 years ago according to cosmogenic dating boulder elevations range from 665 to 825 m asl with the higher and possibly younger boulders situated farther up the valley we used total chemical analyses of rock and incipient soils forming on the boulders to determine relative weathering intensity on the tops of 20 boulders arrayed across lower middle and upper valley positions an additional three boulders from a deposit of giant boulders damming lake rissajaure at the valley head were also analyzed the dam may be a later deposit as indicated by preliminary cosmogenic dates or may be part of the larger valley deposit as other interpretations surmise total chemistry was not significantly different between the mica schist and garnet mica schist boulders however total chemistry did vary by position boulders at the lowest positions were chemically more similar to those at the dam than to the other positions this difference was removed when calculating the overall weathering indices by taking the ratio of weathering indices of the c horizon to exposed rock a clear trend in the weathering was revealed by the analyses lower valley boulders show significantly more weathering than the upper group and the middle group is intermediate this indicates that weathering rates differ because of elevation or age of the boulders strewn down the valley however boulders on the lake rissajaure dam complicate those simple interpretations because they show as much weathering evidence as the lower boulders all of the weathering indices exhibited this same trend elevated levels of fe in the two more weathered positions indicate influence of pyrite a known weathering accelerant and undoubtedly the factor controlling boulder weathering in karkevagge

calcareous nannofossil paleoecology in the sapropel s1 of the eastern ionian sea paleoceanographic implications a high resolution study performed by means of calcareous nannofossils on two box cores located in the south eastern ionian basin allowed recognition of fluctuations in the assemblage which can be related to the climatic and paleoceanographic changes that occurred during the deposition of the holocene sapropel s1 this study reports a decrease of the coccolith abundance and of the genus reticulofenestra in the s1 sapropel interval considered as whole with its mn and fe oxidized intervals florisphaera profunda shows an increase at the base of the dark corg rich interval while helicosphaera carteri and rhabdosphaera claviger show an increase in abundance within the fe enriched interval of the oxidized sapropel braarudosphaera bigelowii is very rare in the interval studied as a whole however it shows a small but significant increase in abundance in the mn enriched interval of the oxidized sapropel sapropel deposition is probably related to important climatic changes that influenced the abundance of the various nannofossil species as a function of their paleoecological preferences our results indicate that three different paleoceanographic phases exist in s1 suggesting eutrophication at the beginning of s1 deposition followed by an intermediate stage characterized by nutrient depletion and finally by stagnation

the whole rock cerium anomaly a potential indicator of eustatic sea level changes in shales of the anoxic facies abstract the whole rock cerium anomaly tested for outer shelf upper slope stratigraphic sections from the middle ordovician through the lower silurian of scotland is proposed as an empirical technique to develop a eustatic 3rd order or finer scale sea level curve this interval was chosen as it straddles the well documented late ordovician glaciation and can be defined by graptolite zones the anomaly is calculated from neutron activation analysis of low carbonate phosphate free fossil free field identified shales of the graptolite facies by comparison of the normalized cerium content with the linearized trend of the normalized composition of other rare earth elements in order of atomic number for sections originally deposited in the main pycnocline below the surface mixed layer values of the anomaly for a given sample would indicate its position on the redox curves developed for the early paleozoic by wilde 1987 changes in the anomaly that are positive with time would indicate a lowering of sea level as the apparent depth on the redox curve would reflect more oxic conditions relative changes negative with time would indicate a rise in sea level as the apparent depth reflects more anoxic conditions depending on the vertical sample spacing and the time interval sampled resolution of the order of 1 m y might be achieved thus the vail et al 1977 curves of the 3rd order 1 to 10 m y or of finer scale could be obtained by this technique with the proper choice of section accordingly for the early through middle paleozoic when the main pycnocline was anoxic this geochemical technique could be used to develop eustatic sea level curves and additionally offer an independent calibration for seismic stratigraphy as well as an indicator of glacial interglacial climatic sequences or eustatic changes due to fluctuations in global ridge crest volumes

pronounced mid pleistocene southward shift of the polar front in the atlantic sector of the southern ocean abstract ocean drilling program odp site 1094 situated in the atlantic sector of the antarctic region below the polar front pf is dominated by silica rich sediments during the pleistocene but does contain occasional calcium carbonate rich intervals the analysis of the coccolithophore assemblages of one of these intervals in the mid pleistocene allows us to interpret a prominent southward displacement of the pf an age model constructed using paleomagnetic and biostratigraphic information places this event around 1 ma close to the jaramillo subchron in an interval of strong eccentricity and high amplitude in the insolation record we distinguish five intervals based on coccolithophore assemblage and abundances according to the age model used this calcium carbonate rich period should include marine isotope stage 31 the most significant interglacial period recorded at this time however this model cannot decipher if adjacent isotope stages are partially represented interval v the oldest is interpreted as an episode with progressive abundance of coccolithophores with a characteristic assemblage from the polar front zone pfz but with dominance of siliceous micro organisms interval iv contains the maximum abundance of coccolithophores with an assemblage characteristic of the subantarctic zone saz with peaks in abundance of calcidiscus leptoporus coccolithus pelagicus helicosphaera carteri and syracosphaera spp related with the proximity of the subantarctic front saf the southward displacement of the frontal system linked to an increase in sea surface temperature produced increases in diversity and in productivity conversely we consider that the presence of some coccolithophore taxa linked in other environments with anomalies in salinity could reflect a pulse in the melting of west antarctic ice sheet as suggested previously for this interval interval iii is characterized by a pfz assemblage reflecting again a northward shift of the pf interval ii is considered in this context as another southward pulse but less important than interval iv and with the absence of saf and or melting related taxa interval i is considered a transition from a situation similar to the present day pfz to the antarctic zone conditions as consequence of a northward displacement of pf and weddell gyre antarctic circumpolar current boundary

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

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

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

foraminiferal record and environmental changes during the deposition of the early middle pleistocene sapropels in southern italy a foraminiferal investigation documents the palaeoenvironmental changes across the sapropel units associated with insolation cycles 90 and 86 in the early middle pleistocene im fosso 5 agosto section basilicata southern italy three benthic foraminiferal fossil associations associations a b and c identified by performing hierarchical cluster analysis on the quantitative data can be considered diagnostic of the palaeoenvironmental conditions before during and after the sapropel intervals they indicate a gradual decrease of bottom water oxygenation prior to the onset of sapropel deposition and a rapid return to stable environmental conditions at the end of the sapropel events the constant presence of benthic foraminifera throughout the sapropels implies that the bottom environment was not totally anoxic the high resolution distributional pattern of planktonic and benthic foraminifera within the sapropel associated with i cycle 90 documents a surface water cooling with consequent rapid re oxygenation of bottom waters that subdivides this interval in two phases both of them are characterized by an early subphase with warm climate conditions a decrease of salinity in surficial water layers and dominated by the low oxygen tolerant benthic species globobulimina affinis the late subphase shows thermal stratification during summer and a relatively deep and oxygenated mixed layer during winter in this subphase the contemporaneous replacement of g affinis the bless opportunistic but more resistant to low oxygen conditionsq species with bolivina alata bolivina dilatata and brizalina spathulata the bless resistant to low oxygen conditionsq species indicates the relative oxygen improvement in sediment pore water the frequent changes detected in the sapropel associated faunal composition underline the unstable nature of bottom water oxygen content d 2004 elsevier b v all rights reserved

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

coccolithophores in surface sediments of the arabian sea in relation to environmental gradients in surface waters abstract one hundred surface sediment samples of the arabian sea indian ocean were investigated and relative abundances of coccoliths were compared to mean annual gradients of temperature salinity chlorophyll po4 and mixed layer depth total coccolith concentrations ranged from 42 106 g sediment in coastal areas to more than 19 000 106 g sediment in oceanic regions the general distribution does not seem to be dependent on coccolithophore productivity in surface waters alone but also on the diluting input of terrigenous material a total of 27 taxa were identified the main species dominating the assemblages were gephyrocapsa oceanica emiliania huxleyi and florisphaera profunda with a combined average abundance of more than 70 several species and species groups reflect with their distribution the environmental parameters of the overlying water masses and may be successfully used to improve palaeoclimatic reconstructions e g a f profunda exhibits a high similarity or even positive correlation to the mean annual mixed layer depth b calciosolenids can be described as coastal or shelf species while temperature and salinity gradients do not seem to be crucial for coccolithophores in this region the mean mixed layer depth as well as the po4 concentration representative for total nutrient availability may control in part the coccolithophore assemblages according to the results of a cluster analysis and the distribution pattern of all species it was possible to differentiate three main coccolithophore assemblages a g oceanica dominated assemblage mainly occurs in the northern part of the study area and can be described as high nutrient assemblage the second assemblage dominated by f profunda may be typical for oligotrophic and stable conditions in open ocean waters a third assemblage with high amounts of coastal species characterises coastal conditions on the shelves

paleoenvironmental changes during sapropel 19 i cycle 90 deposition evidences from geochemical mineralogical and micropaleontological proxies in the mid pleistocene montalbano jonico land section southern italy an integrated micropaleontological geochemical and mineralogical study has been performed across the mid pleistocene sapropel 19 i cycle 90 from the montalbano jonico land section southern italy to reconstruct the paleoenvironmental conditions at time of its formation the sapropel interval is characterized by two oxygen depletion phases phase a and c interrupted by a temporary re oxygenation interval phase b the beginning and the end of sapropel deposition are dated at 957 0 81 kyr and 950 0 86 kyr respectively the duration of the interruption is estimated to 0 350 0 32 kyr the multiproxy approach highlights that deposition of sapropel 19 reflects a period of enhanced freshwater runoff induced by a wetter climate as a consequence of a more efficient fluvial erosion a higher terrigenous input mostly ascribable to a southern apennines source and an increased turbidity of surface waters accompanied most of sapropel deposition biotic and abiotic proxies document that different paleoenvironmental conditions occur through phases a c the beginning of phase a is characterized by warm on land paleoclimate as well as warm and oligotrophic surface water conditions during the upper part of phase a temperature starts decreasing and surface waters appear more productive this change probably represents the prelude to cooler and drier conditions characterizing phase b which displays a river supply reduction and an eolian input increase sahara dust during phase c the restored depleted oxygen environment at the bottom sediments is clearly coupled with the re establishment of humid conditions and increased river supply at the same time enhanced mixing of water column a cooler paleoclimate and increased productivity of surface waters are recorded the latter likely favored by the enhanced mixing of water column and also increased delivery of land derived nutrients the end of phase c is marked by a restored normal run off enhanced productivity in surface waters and low oxygen conditions at the bottom sediments persist slightly above phase c the overall results suggest that the onset of sapropel deposition is related to water stratification that caused low oxygen exchanges with the sea bottom although enhanced productivity characterizes most of the sapropel deposition it was not the primary factor triggering sapropel deposition

mafic gneissic complex batholithic root in the southernmost sierra nevada california a mafic complex of hornblende rich gneissic to granoblastic amphibolite to granulite grade metamorphic rocks and associated mafic to felsic magmatic rocks is exposed over an area of some 300 km2 in the southernmost sierra nevada the mafic complex probably reflects a deeper exposed crustal level than is represented by the dominantly granitic terrane of the sierra nevada batholith to the north and it may be the upper part of the root zone and metamorphic substrate of the sierra nevada batholith xenoliths of gneiss amphibolite and granulite from subbatholithic levels transported upward and preserved in volcanic rocks in the central sierra nevada are possible analogues of some of the rocks of the southernmost sierra nevada mafic complex

palaeoceanography of the last deglaciation in the alboran sea western mediterranean stable isotopes and planktonic foraminiferal records abstract oxygen isotope changes of the foraminiferal species globigerina bulloides and uvigerina peregrina eleven radiocarbon dates on the sediment fraction above 50 m and 13 biostratigraphical events allow us to correlate and to date the sediment record of the last climatic cycle in four cores from the alboran sea nine ecozones are recognized which differ from those previously established for atlantic sediments cored immediately west of gibraltar these ecozones can be grouped into two broad phases from the last glacial maximum up to near 9 500 yr b p cold north atlantic microfaunas are the major component of the assemblages during this interval dominant species replace each other according to the varying temperature and density stratification of the water masses from 9 500 yr b p up to the present time subtropical forms from the central atlantic dominate the northern atlantic forms an abrupt increase in the percentages of g inflata occurred near 7 000 b p this event was diachronous within the mediterranean during the last glacial g inflata was endemic inside the mediterranean and its abrupt increase near the end of the deglaciation did not result from replenishment from the atlantic between 4 000 and 5 000 yr b p percentages of g bulloides also increased abruptly warming conditions associated with the onset of a seasonal thermal stratification and a contrasting winter vertical convection are strongly suggested

vegetation changes during the late early pleistocene at montalbano jonico province of matera southern italy based on pollen analysis pollen analysis of the early pleistocene montalbano jonico section in southern italy reveals cyclic changes driven by climate and eustasy as illustrated by mesothermic vs steppe elements for climate and pinus vs caryophyllaceae amaranthaceae chenopodiaceae and ephedra for eustasy these results are directly compared with oxygen isotope data on globigerina bulloides constrained within a biostratigraphic framework based on nannofossils and foraminifers facilitating a new age calibration for the section marine isotopic stages 37 to 23 1 250 0 900 ma are recorded and compared with global and mediterranean oxygen isotope curves high frequency changes in pollen are related to the mediterranean curve globigerinoides ruber from odp site 967 and superimposed the lr04 stack curve during the early pleistocene pollen recorded global and regional climate changes related to obliquity and precession respectively and regional tectonic evolution precession forcing was caused by mediterranean wetness related to precession the intensified precession effect over climatic cycles that is expected during the middle pleistocene transition is not recorded in the montalbano jonico interval a vegetation changes

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

stratigraphy and sedimentation in the mediterranean ridge diapiric belt abstract two basic sediment types are recorded in the mediterranean ridge diapiric belt the host sediment and the mud breccia the host sediment consists of hemipelagic marl as dominant lithology associated with sapropels and tephras as minor isochronous lithologies a high resolution stratigraphy which allows much more detailed and precise correlations than those based on biostratigraphy essentially calcareous nannofossils is applicable to the over 20 cores considered in this study that were obtained during cruise ttr3 leg 2 in 1993 the mud breccia is matrix supported and contains submillimetric to pluricentimetric clasts in various amounts staffini et al 1993 this lithology is consistently related to doming physiographic features of different size and shape camerlenghi et al 1992 and to high reflectivity patches recorded on long range side scan sonar the mud breccia can be intruded or extruded the massive course nature of the mud breccia recorded in the large majority of the 16 cores that contain this lithology may suggest intrusion cores from napoli dome which is typically an active mud volcano cita et al 1994 are fine grained and very gaseous contacts between the mud breccia and the host sediment are mostly distinct but may be gradational two cores document interlayering of the mud breccia with pelagic sediments but not turbidites were ever recovered among the main results of the study we mention the strong slope instability documented by the pelagic host sediments from the ridge diaperic belt hiatuses microfaults hardgrounds the wide distribution of diapiric features across the ridge axis from the inner deformation front to the toronto dome some 50 km to the south the age of the mud breccia matrix essentially which is consistently early middle miocene with some older elements but strictly middle to late cretaneous for the southernmost toronto dome

causes and consequences of a middle pleistocene origin of the modern planktonic foraminifer neogloboquadrina pachyderma sinistral switches in coiling direction of shells of the planktonic foraminifer neogloboquadrina pachyderma have been extensively used as a paleotemperature proxy from the late miocene through the quaternary exploiting the specific modern polar affinity of the sinistrally coiled form here we have reexamined the origin of the modern sinistral form in pliocene and pleistocene sediments from ocean drilling program site 1014 in the eastern north pacific by using morphometric and stable isotope data we show that pliocene and pleistocene sinistral forms of n pachyderma are morphologically and ecologically different and that modern type sinistral form first appeared ca 1 ma these findings suggest that n pachyderma sinistral should not be used for calibrated paleoceanographic reconstructions prior to the middle pleistocene and reinforce the need to assess the origin of specific ecological affinities of other modern planktonic foraminifer species the first appearance of the modern form and the subsequent evolution of its mean shell size appear to have been synchronous in the north pacific and the north atlantic such hemispheric evolutionary synchronicity implies existence of trans arctic gene flow the modern type shell morphology and the specific cold water affinity of n pachyderma sinistral may have evolved in response to the onset of the 100 k y climate regime in the middle pleistocene

oceanic surface conditions recorded on the sea floor of the southwest pacific ocean through the distribution of foraminifers and biogenic silica over 180 surface sediment samples from the southwest pacific ocean were investigated for their planktonic foraminiferal 149 m opaline and terrigenous sediment content with the aim to determine the oceanic conditions at the sea surface above the sampling sites high concentrations of biogenic opal are related to high productivity levels recognised in tropical surface waters the abundance of this biogenic opal found within the sediments on the ocean floor shows a slight decrease as one approaches the australian landmass and also poleward from the equatorial belt the distribution of major species of planktonic formainifers reflects different surface water masses q mode factor analysis of planktonic foraminiferal percentage data from 63 core tops permits identification of several characteristic formainiferal assemblages for the southwest pacific ocean four factors explain up to 95 5 of the total variance factor 1 66 is dominated by the tropical subtropical species globigerinoides sacculifer and globigerinoides ruber the transitional to subpolar species globorotalia inflata is important in factor 2 12 the temperate cool factor 3 13 is characterised by turborotalia quinqueloba and globigerinita glutinata factor 4 which explains 3 of the total variance and which is represented by several species is assigned to the high productive equatorial and coastal waters off the australian continental margin palaeoecological equations permitting an estimate of sea surface temperatures and salinities are presented the correlation coefficients between modern data adapted from literature and estimated by transfer function fp 4 transfer function for planktonic formainifers are 0 95 for temperature and 0 77 for salinity

holocene millennial scale productivity variations in the sicily channel mediterranean sea 1 the calcareous nannofossil assemblages of ocean drilling program hole 963d from the central mediterranean sea have been investigated to document oceanographic changes in surface waters the studied site is located in an area sensitive to large scale atmospheric and climatic systems and to high and low latitude climate connection it is characterized by a high sedimentation rate the achieved mean sampling resolution is 70 years that allowed the sicily channel environmental changes to be examined in great detail over the last 12 ka bp we focused on the species florisphaera profunda that lives in the lower photic zone its distribution pattern shows repeated abundance fluctuations of about 10 15 such variations could be related to different primary production levels given that the study of the distribution of this species on the sicily channel seafloor demonstrates the significant correlation to productivity changes as provided by satellite imagery productivity variations were quantitatively estimated and were interpreted on the basis of the relocation of the nutricline within the photic zone led by the dynamics of the summer thermocline productivity changes were compared with oceanographic atmospheric and cosmogenic nuclide proxies the good match with holocene master records as with ice rafted detritus in the subpolar north atlantic and the near 1500 year periodicity suggest that the sicily channel environment responded to worldwide climate anomalies enhanced northern hemisphere atmospheric circulation which has been reported as one of the most important forcing mechanisms for holocene coolings in previous mediterranean studies had a remarkable impact on the water column dynamics of the sicily channel

revised tuning of ocean drilling program site 964 and kc01b mediterranean and implications for the δ18o tephra calcareous nannofossil and geomagnetic reversal chronologies of the past 1 1 myr 1 high resolution color reflectance records of kc01 and kc01b calabrian ridge ionian sea are presented and compared with a modified spliced high resolution color reflectance record of ocean drilling program odp site 964 this comparison revealed that kc01b is characterized by intensive deformation between 27 and 28 5 m piston depth and that some sapropels are tectonically reduced in thickness moreover the piston coring has caused considerable stretching in the top of kc01 and kc01b using a new splice of odp site 964 as guide previous astronomical tuned timescales of kc01b and odp site 964 were evaluated this evaluation resulted in a new sapropel based astronomical timescale for the last 1 1 myr the new timescale implies a much more uniform change in sedimentation rate for the ionian sea cores two prominent excursions to lighter values in the 18o record of the planktonic foraminiferal species globigerinoides ruber occur during marine isotopic stages 12 and 16 applying the new timescale these shifts correspond with maxima in obliquity and are punctuated by minima in the precession cycle they are absent in global ice volume records and are interpreted as reflecting a summer low salinity surface water lens that floats on top of extremely saline intermediate and deep waters at times of the very low sea levels during these glacial periods all biostratigraphic and magnetostratigraphic events found in kc01b and odp site 964 were re dated according to the new timescale and the ages of 33 tephra layers were reviewed the new ages for the calabrian ridge 2 and 3 magnetic events in the brunhes are concordant with minima in the global sint800 composite record derived from worldwide deep sea records of relative paleointensity and have been attributed to the big lost and la palma excursions respectively

export production of coccolithophores in an upwelling region results from san pedro basin southern california borderlands a seven month long time series sediment trap project was carried out in san pedro basin southern california borderlands in order to evaluate the response of calcareous nannoplankton to seasonal hydrographic changes this region is periodically influenced by upwelling particularly during the spring and early summer the highest fluxes of both whole coccospheres and individual coccoliths occurred during winter january february a period when the fluxes of diatoms and planktic foraminifera were low the highest coccolithophore fluxes were recorded in the mid february with 860 106 coccoliths m 2 day 1 8 106 whole coccospheres m 2 day 1 and 80 mg of coccolith carbonate m 2 day 1 coccolith carbonate fluxes in january and february account for most of the total carbonate fluxes measured during this period the season of maximum coccolithophore production in this region winter is correlated with weak stratification of the upper water column low total primary production low nutrient contents and low temperatures emiliania huxleyi and florisphaera profunda are the two most abundant species in this region while e huxleyi displays no distinct seasonal changes in flux f profunda shows a clear preference for cold low nutrient water conditions and low light levels helicosphaera spp flux is positively correlated to the total coccosphere fluxes and is indicative of high coccolithophore productivity

distribution of coccoliths in surface sediments of the south eastern south atlantic ocean ecology preservation and carbonate contribution abstract recent coccoliths from 52 surface sediment samples recovered from the south eastern south atlantic were examined qualitatively and quantitatively in order to assess the controlling mechanisms for their distribution patterns such as ecological and preservational factors and their role as carbonate producers total coccolith abundances range from 0 2 to 39 9 coccoliths 109 g 1 sediment four assemblages can be delineated by their coccolith content characterising the northern benguela the middle to southern benguela the walvis ridge and the deeper water distinctions are based on multivariate ordination techniques applied on the relative abundances of the most abundant taxa emiliania huxleyi calcidiscus leptoporus gephyrocapsa spp coccolithus pelagicus and subtropical to tropical species the coccolith distribution seems to be temperature and nutrient controlled co varying with the seaward extension of the upwelling filament zone in the benguela a preservation index cex based on the differential dissolution behaviour of the delicate e huxleyi and gephyrocapsa ericsonii versus the robust c leptoporus is applied in order to detect the position of the coccolith lysocline although some samples were recognised as dissolution affected the distribution of the coccoliths in the surface sediments reflects the different oceanographic surface water conditions mass estimations of the coccolith carbonate reveal coccoliths to be only minor contributors to the carbonate preserved in the surface sediments the mean computed coccolith carbonate content is 17 wt equivalent to a mean contribution of 23 to the bulk carbonate

the mid pleistocene climate transition onset of 100 ka cycle lags ice volume build up by 280 ka the mid pleistocene climate transition mpt is the complex climatic change which brought the late pleistocene ice ages we explore the mpt in the time and frequency domains by new methods of time series analysis high resolution oxygen isotope records reveal that the ice volume related increase in 18o mean amplitude 0 29 0 05 1 transition midpoint 922 12 ka duration 40 9 ka significantly preceded the abrupt increase in the amplitude of the 100 ka cycle at 641 9 ka this finding can be quantitatively simulated using a simple ice bedrock model in which due to the additional ice the calving threshold is exceeded the simulated calving events prior to 650 ka are separated by 77 ka whereas after 650 ka they occur pseudo periodically with a mean period of nearly 100 ka the cause for the delay of the 100 ka calving cycle was not a slow bedrock relaxation rather the coincidental combination of insolation existing ice mass and bedrock depression