links between marine and atmospheric processes oscillating on a millennial time scale a multi proxy study of the last 50 000 yr from the alboran sea western mediterranean sea abstract the large dataset obtained from the extensive study of images core md95 2043 recovered from the alboran sea western mediterranean shows the periodicities and phase relationships of oceanographic and atmospheric processes on a millennial time scale the 1470 yr cycle is the most significant with the exception of the records reflecting climatic or environmental changes on land which show statistically significant 3300 and 8000 frequency bands the investigation of these core records on a millennial scale resolution allows us to establish the evolution of oceanographic and atmospheric mechanisms that influenced the western mediterranean region in the course of the dansgaard oeschger cycles accordingly possible land sea interactions can be identified and situated in the context of the temporal succession of the different climatic processes for instance saharan dust supply from northern africa appears to lead high latitude climate changes suggesting that low latitude feedback processes were involved in forcing the millennial climatic variability in the westernmost mediterranean

warming trends in the continental shelf of malaga bay alboran sea 1 temperature time series from 1992 to 2001 ecomalaga project show an intense warming trend in deep layers 200m depth of malaga bay 0 02 c yr data from medatlas show that this trend is 0 005 c yr throughout the whole century another striking change in malaga bay is the disappearance of the cold western intermediate water wiw after 1992 this could be the responsible of temperature changes in the malaga continental shelf

the advection of submesoscale thermal features in the alboran sea gyre abstract noaa 7 infrared and nimbus 7 multi spectral visible imagery of the alboran sea collected as part of the donde va experiment during the period 6 20 october show the advection of submesoscale cold water features about the alboran sea gyre continuous monitoring of thew cold water features using satellite imagery is possible because of the twice daily every 12 h spacing of the noaa 7 coverage of the area after registration to a mercator projection and atmospheric correction analysis of the displacement of the cold water features in successive images shows their apparent origin to be just east of gibraltar their movement at average speeds of 0 4 m s 1 around the gyre and their apparent re entrainment into the incoming atlantic water east of gibraltar the nimbus 7 czcs imagery supplements the analysis by adding details of the movement and the theory on where the cold water features originate during the 15 day period nine cold water features were thermally distinct enough to be tracked for

the mw 6 3 2003 lefkada earthquake greece and induced stress transfer changes abstract a large earthquake of magnitude mw 6 3 occurred on 14 august 2003 nw of the lefkada island which is situated at the ionian sea western greece the source parameters of this event are determined using body wave modeling the focal depth was found equal to 9 km the constrained focal mechanism revealed dextral strike slip motion 15 80 and 170 the duration of the source time function was 8 s and the seismic moment 2 9 1025 dyn cm the earthquake occurred close to the northern end of the kefallinia transform fault where the 1994 moderate event and its aftershock sequence were also located the epicentral distribution of the 2003 aftershock sequence revealed the existence of two clusters the first one is located close to the epicentral area of the mainshock while the second southern close to the northwestern coast of the kefallinia island a gap of seismicity is observed between the two clusters the length of the activated zone is approximately 60 km the analysis of data revealed that the northern cluster is directly related to the mainshock while the southern one was triggered by stress transfer caused by the main event

the sapropel record of the eastern mediterranean sea results of ocean drilling program leg 160 research on sediments recovered during ocean drilling leg 160 has concentrated on two issues the first concerned the stratigraphy of sapropel formation the second was oriented to clarify specific processes that explain sapropel origin progress has been made in the construction of stratigraphic composites out of sedimentary sequences from individual holes at each of the palaeoceanographic sites on the composites initial work has resulted in the establishment of high resolution and intermediate resolution stratigraphies for three sites 963 964 967 correlation of sedimentary cycles to astronomical insolation cycles extends the stratigraphies to sites 969 and 966 the sapropel occurrences in the marine and land sequences over the entire eastern mediterranean are correlated with the resolution that can be obtained from isotope studies groups of sapropels occurred simultaneously over the entire basin in detail however the temporal and facies patterns of sapropel sequences differ between individual sites and depositional basins the differences may be related to effects of water depth diagenesis and post depositional tectonic attenuation of sequences studies on the geochemistry and facies of sapropels agree that anoxic conditions favoured preservation of organic matter in sapropels caused the enrichment of trace metals associated with sapropels and helped to preserve primary sedimentary structures besides all evidence is consistent with elevated fluxes of organic matter and associated elements during sapropel events

marine isotope stage 11 palaeoclimates palaeoenvironments and its role as an analogue for the current interglacial abstract interglacials of the quaternary period are currently the focus of a great deal of attention within the scientific community this is primarily because they play a vital role in distinguishing between natural and human climate change in the current interglacial and in understanding how the holocene would evolve in the absence of anthropogenic greenhouse warming in this respect marine isotope stage 11 mis 11 ca 410 000 yr bp is one of the key interglacial stages of the past 450 000 yr the pattern of insolation variability that occurs during mis 11 matches that which occurs in the holocene more closely than in any other warm stage of the past half a million years in addition there is now an extensive range of evidence for mis 11 palaeoclimates and palaeoenvironments from marine ice core lacustrine and terrestrial sequences the aim of this paper is to provide a comprehensive review of the current state of our understanding of mis 11 this is the first paper to provide a detailed review of mis 11 that incorporates the wide range of marine ice core long lacustrine and terrestrial records that have been generated over the last ten years since the last major overview crucially it is the first review of mis 11 that incorporates a detailed synthesis of the high resolution terrestrial sequences of western and central europe this paper therefore provides a holistic integration of a diverse range of proxies and archives to provide a detailed understanding of the expression of mis 11 in the earth system in particular the review focuses on 1 the climatic background of mis 11 2 the robustness of the identification of mis 11 in a diverse range of sequences 3 the climatic structure of mis 11 4 the magnitude of warmth that occurred in this warm stage 5 mis 11 sea level magnitude and variability 6 the duration of mis 11 7 evidence for abrupt climatic events within the interglacial of mis 11 and 8 precipitation patterns and trends during this interglacial the paper concludes by considering how useful mis 11 is as an analogue for holocene climates and compares it with other proposed analogues such as mis 19 with particular reference to the early anthropogenic hypothesis

four climate cycles of recurring deep and surface water destabilizations on the iberian margin centennial climate variability over the last ice age exhibits clear bipolar behavior high resolution analyses of marine sediment cores from the iberian margin trace a number of associated changes simultaneously proxies of sea surface temperature and water mass distribution as well as relative biomarker content demonstrate that this typical north south coupling was pervasive for the cold phases of climate during the past 420 000 years cold episodes after relatively warm and largely ice free periods occurred when the predominance of deep water formation changed from northern to southern sources these results reinforce the connection between rapid climate changes at mediterranean latitudes and century to millennial variability in northern and southern polar regions

meteorologically induced mesoscale variability of the north western alboran sea southern spain and related biological patterns hydrographic mesoscale structures in the north western alboran sea show a high variability induced by a number of different factors one of the most important is the differences in atmospheric pressure over the mediterranean basin when compared to the gulf of cadiz this difference modulates the zonal wind field in the alboran sea and the intensity of the atlantic inflow through the strait of gibraltar also affecting the formation and extension of the western alboran gyre wag when westerly winds are dominant lower atmospheric pressure in the mediterranean enhances the inflow of atlantic waters causing the atlantic jet to be located in the vicinity of the spanish shore creating a well defined frontal zone in front of estepona cove in this situation the coastal upwelling is enhanced leading to a minimum in sea surface temperature and a maximum of surface nutrient concentrations located in the coastal area the vertical position of the chlorophyll maximum found in these circumstances appeared to be controlled by the nutrient availability on the other hand when easterly winds prevail higher atmospheric pressure in the mediterranean leads to a reduced inflow and the oceanographic and biological structures are clearly different the atlantic jet moves southward flowing in a south eastern direction changing the structure of the currents resulting in an enhanced cyclonic circulation extending throughout the north western alboran sea basin these physical alterations also induce changes in the distribution of biogeochemical variables maximum nutrient and chlorophyll concentrations are located further off the coast in the central area of the newly created cyclonic gyre during these easterlies periods coastal upwelling stops and the distribution of phytoplankton cells seems to be mainly controlled by physical processes such as advection of coastal waters to the open sea

sea surface temperatures did not control the first occurrence of hudson strait heinrich events during mis 16 1 hudson strait hs heinrich events ice rafting events in the north atlantic originating from the laurentide ice sheet lis are among the most dramatic examples of millennial scale climate variability and have a large influence on global climate however it is debated as to whether the occurrence of hs heinrich events in the eastern north atlantic in the geological record depends on greater ice discharge or simply from the longer survival of icebergs in cold waters using sediments from integrated ocean drilling program iodp site u1313 in the north atlantic spanning the period between 960 and 320 ka we show that sea surface temperatures ssts did not control the first occurrence of hs heinrich like events in the sedimentary record using mineralogy and organic geochemistry to determine the characteristics of ice rafting debris ird we detect the first hs heinrich like event in our record around 643 ka marine isotope stage mis 16 which is similar as previously reported for site u1308 however the accompanying high resolution alkenone based sst record demonstrates that the first hs heinrich like event did not coincide with low ssts thus the hs heinrich like events do indicate enhanced ice discharge from the lis at the end of the mid pleistocene transition not simply the survivability of icebergs due to cold conditions in the north atlantic

late pleistocene carbonate stratigraphy on ontong java plateau in the western equatorial pacific abstract late pleistocene carbonate cycles on ontong java plateau are characterized by maxima during deglaciations deglacial preservation spikes and by minima during transitions from interglacial to glacial conditions ice growth dissolution spikes superimposed on these short period fluctuations there is a long term oscillation of carbonate contents with a period of nearly 400 ky the brunhes dissolution cycle dissolution related sand fraction profiles 63 m indicate that the lysocline was at a water depth of about 3 6 km during deglacial transitions and that it rose up to 2 6 km during the stages of ice growth a fluctuation of the lysocline by 1 km can account for more than half of the total amplitude of the observed carbonate cycles assuming a linear increase in carbonate dissolution rates with increasing water depth below the lysocline and a constant ccd a shoaling of the lysocline during ice buildup may result from downward transfer of metabolic co 2 from intermediate waters to greater depths in the water column enhanced carbonate dissolution below 2 6 km increases alkalinity in deep waters predisposing the system toward reducing atmospheric co 2 partial pressure during a subsequent period

phase relationship and surface water mass change in the northeast atlantic during marine isotope stage 11 mis 11 planktic foraminiferal census data faunal sea surface temperatures ssts and oxygen isotopic and lithic records from a site in the northeast atlantic were analyzed to study the interglacial dynamics of marine isotope stage mis 11 a period thought to closely resemble the holocene on the basis of orbital forcing interglacial conditions during mis 11 persisted for approximately 26 ka after the main deglacial meltwater processes ceased a 10 to 12 ka long transitional period marked by significant water mass circulation changes occurred before surface waters finally reached their thermal maximum this sst peak occurred between 400 and 397 ka inferred from the abundance of the most thermophilic foraminiferal species and was coincident with lowest sea level according to benthic isotope values the ensuing stepwise sst decrease characterizes the overall climate deterioration preceding the increase in global ice volume by 3 ka this cooling trend was followed by a more pronounced cold event that began at 388 ka and that terminated in the recurrence of icebergs at the site around 382 ka because the water mass configuration of early mis 11 evolved quite differently from that of the early holocene there is little evidence that mis 11 can serve as an appropriate analogue for a future holocene climate despite the similarity in some orbital parameters

a 20 m middle pleistocene sea level highstand bermuda and the bahamas due to partial collapse of antarctic ice marine deposits at 20 3 m on the tectonically stable coastlines of bermuda and the bahamas support the hypothesis of a partial collapse of the antarctic ice sheet during the middle pleistocene beach sediments fill a sea cave at 22 m in bermuda and horizontal fenestrae filled beds crop out on platforms at two sites as high as 21 m in eleuthera bahamas carbonate beach sands are bound by an early generation of isopachous fibrous cement that is characteristic of a phreatic marine environment amino acid racemization and tims thermal ionization mass spectrometry dates constrain the age of the deposits to between 390 and 550 ka while proxy evidence supports a correlation with oxygen isotope stage 11 this direct geologic evidence of a 20 decrease in polar ice during the middle pleistocene has important implications for the stability of ice sheets during warm interglaciations

improved accuracy of cross borehole radar velocity models for ice property analysis cross borehole radar xbhr is widely used for the quantification of pore scale liquid water in geologic materials inferred from bulk velocity variations caused by differences in electromagnetic properties between the water and the surrounding material the xbhr can accurately and repeatedly measure variation at depth with sampled material remaining under natural stresses while maintaining good lateral sampling however even small errors in measured radar velocities result in large errors in water content estimates emphasizing the need to quantify and minimize errors we have rigorously assessed the sources of uncertainty in xbhr surveys undertaken in a glaciological setting we have summarized and quantified the three main areas of uncertainty in data collection 1 instrument time drift 2 first break picking and 3 borehole geometry our analysis of field data indicated that contemporary acquisition procedures can produce velocity errors of 3 0 0 0050 m ns equivalent to 0 84 vol water content we have developed several revisions to produce improved data acquisition through enhancement of existing techniques the velocity uncertainties were improved to 1 5 we also found the measurement of borehole diameter during hot water drilling which could hypothetically further reduce the velocity uncertainty to 0 8 equivalent to 0 2 vol water content the need for such precise measurement is clear because an increase in englacial water content from 0 to 0 8 has been proven to triple the strain rate and soften the ice liquid water between ice crystals has also been linked to faster velocities in ice streams and surging events

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

late holocene climate variability in the adriatic sea central mediterranean planktic and benthic foraminifera assemblages from a set of sediment cores collected on the adriatic shelf and the southern adriatic deep basin provide compelling evidence of submillennial scale environmental changes during the last 6000 years repeated peaks in globigerinoides sacculifer represent warm dry intervals including the mediaeval warm period the roman age the late bronze age and the copper age the last occurrence lo of g sacculifer 550 years bp approximates the base of the little ice age lia significant turnovers in the structure of the water column reflect changes in the rate of formation and depth of flow of the north adriatic dense water naddw and the levantine intermediate water liw about 7500 years bp the benthic oxygen isotope records mark the timing when the naddw formation intensified on the slope and shifted to its modern route about 5500 years bp when sea level reached its modern high stand oxygen isotope records of intermediate planktic dwellers indicate a northward intrusion of the liw on the slope the oscillating isotope trends during the last five millennia document a discontinuous invasion of liw into the central adriatic possibly reflecting short term climate changes with weakened liw production during colder and wetter intervals

on the upper layer circulation in the alboran sea we present new experimental results and assemble them with previous results in order to develop an improved picture of the upper layer circulation in the alboran sea it is suggested that the key idea to understanding this upper layer circulation is the tendency of the atlantic jet aj to have negative curvature local interactions with the western alboran gyre wag or the african coast can however counterbalance this tendency and modify the anticyclonic path of the aj it is also proposed that the density gradients in the wag can be maintained in part by means of an intermittent surface cross gyre current which results in an input mixing and renewal of atlantic water the static stability at the bottom of the gyre increases because of the mixing of atlantic water with western mediterranean deep water which is uplifted close to the african coast this mixing process thereby acts as a local source of potential vorticity we also report the existence in the alboran sea of subsurface anticyclonic eddies located between 100 and 400 m of relatively cold water that appear to be detached from the iberian shelf regarding the large scale variability of the aj wag system we present evidence of an eastward migration of the wag and the subsequent formation of a new anticyclonic gyre in the western alboran basin on a timescale of 1 month this eastward gyre migration process temporarily allows the simultaneous presence of three anticyclonic gyres in the alboran sea

millennial scale ice rafting events and hudson strait heinrich like events during the late pliocene and pleistocene a review abstract various types of abrupt millennial scale climate variability such as dansgaard oeschger and heinrich events characterized the last glacial period over the last decade a number of studies demonstrated that such millennial scale climate variability was not limited to the last glacial but inherent to quaternary climate here we review the occurrence and origin of millennial ice rafting events in the north atlantic during the late pliocene and pleistocene last 3 4 ma with a special focus on north atlantic hudson strait hs heinrich like events we show that heinrich layers 5 4 2 and 1 in marine sediment cores from across the north atlantic all bear the organic geochemical fingerprint of the hudson area using this framework and combining previously published results detailed investigations into the organic and inorganic chemistry of ice rafted debris ird found across the north atlantic demonstrate that prior to mis 16 650 ka ird in the north atlantic did not originate from the hudson area of northern canada the signature of this early ird is distinctly different compared to that of hs heinrich layers rather ice rafting events during the late pliocene and early pleistocene predominantly emanated from the calving of the greenland and fennoscandian ice sheets and possibly minor contributions from local ice streams from the north american and british ice sheets compared to north atlantic hs heinrich events these early pleistocene ird events had a limited impact on surface water characteristics in the north atlantic north atlantic hs heinrich like events first occurred during mis 16 at the same time the dominant frequency in silicate rich ird accumulation shifted from the obliquity 41 ka to a 100 ka frequency across the north atlantic iceberg survivability or a change in iceberg trajectory likely did not control this change in ird regime these results lend further support for the existing hypothesis that an increase in size thickness of the laurentide ice sheet controls the occurrence of north atlantic hs heinrich events favoring an internal dynamic mechanism for their occurrence

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

arctic front shifts in the subpolar north atlantic during the mid pleistocene 800 400ka and their implications for ocean circulation abstract surface water conditions at the integrated ocean drilling program iodp site u1314 southern gardar drift 56 21 8 n 27 53 3 w 2820 m depth were inferred using planktic foraminifer assemblages between marine isotope stage mis 19 and 11 ca 800 400 ka factor analysis of the planktic foraminifer assemblages suggests that the assemblage was controlled by three factors the first factor which explained 49 of the variance is dominated by transitional and subpolar species and points to warm and salty surface water conditions atlantic water the second factor 37 is dominated by neogloboquadrina pachyderma sin and has been associated with the presence of cold and low saline surface waters arctic water finally the third factor 9 linked to a significant presence of turborotalita quinqueloba reflects the closeness of the arctic front the boundary between atlantic and arctic water the position of the arctic and polar fronts has been estimated across the glacial interglacial cycles studied according to planktic foraminifer abundances from site u1314 and their factor analysis combined with a synthesis of planktic foraminifer and diatom data from other north atlantic sites regarding at the migrations of the arctic front and the surface water masses distribution across each climatic cycle we determined five phases of development furthermore deep ocean circulation changes observed in glacial interglacial cycles have been associated with each phase the high abundance of transitional subpolar foraminifers above 65 at site u1314 during the early interglacial phase indicated that the arctic front position and surface water masses distribution were similar to present conditions during the late interglacial phase n pachyderma sin and t quinqueloba slightly increased indicating that winter sea ice slightly expanded southwestwards whereas the ice volume remained stable or was still decreasing n pachyderma sin increased rapidly above 65 at site u1314 at the first phase of glacial periods indicating the expansion of the arctic waters in the western subpolar north atlantic during the second phase of glacial periods the transitional subpolar assemblage throve again in the central subpolar north atlantic associated with strong warming events that followed ice rafting events the third phase of glacial periods corresponds to full glacial conditions in which n pachyderma sin dominated the assemblage for the whole subpolar north atlantic this division in phases may be applied to the last four climatic cycles

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

impact of climate and sea level changes on the ventilation of intermediate water and benthic foraminifer assemblages in the gulf of lions off south france during mis 6 and 7 abstract benthic and planktic foraminifer assemblages together with oxygen stable isotope were studied in the prgl1 borehole promess1 drilled on the upper slope of the gulf of lions with a view to reconstruct the impact of climate changes on surface and bottom waters between mis7 and mis6 foraminifer species were grouped by r mode principal components analysis we obtained 3 factors in benthic assemblages that were related to eutrophic mesotrophic and oxygenated environments in the planktic foraminifer assemblages four factors were considered that explained the changes of sea surface temperature productivity and turbulence in the water column variations in the terrestrial organic carbon supply associated with eustatic sea level changes mainly controlled oxygen consumption and the benthic communities during mis7 the benthic communities were mainly mesotrophic owing to the low supply of terrestrial organic carbon because the coastline was distant from the slope however during mis6 the sea level drop caused a rapid progradation of the river rhone prodelta and dramatically increased the supply of terrestrial organic carbon resulting in a pronounced increase in eutrophic foraminifers apart from the effect of the river discharge which contributed to the reduced oxygen content we recognized periods of intense bottom ventilation during mis 6 and to a lesser extent in the substadial stages of mis 7 the ventilation events are well matched by higher turbulence and convection in the water column during cold episodes associated with an intensification of the northwesterlies in contrast during the short millennial scale warming events of mis6 the stratification of the water column rapidly reduced bottom ventilation these results are consistent with those reported in previous studies that point to enhanced dense water formation in the gulf of lions during cold stages

variability of surface water characteristics and heinrich like events in the pleistocene midlatitude north atlantic ocean biomarker and xrd records from iodp site u1313 mis 16 9 1 a reconstruction of milankovitch to millennial scale variability of sea surface temperature sst and sea surface productivity in the pleistocene midlatitude north atlantic ocean marine isotope stage mis 16 9 and its relationship to ice sheet instability was carried out on sediments from integrated ocean drilling program iodp site u1313 this reconstruction is based on alkenone and n alkane concentrations u37k index total organic carbon toc and carbonate contents x ray diffraction data magnetic susceptibility and accumulation rates increased input of ice rafted debris occurred during mis 16 12 and 10 characterized by high concentrations of dolomite quartz and feldspars and elevated accumulation rates of terrigenous matter minimum input values of terrigenous matter on the other hand were determined for mis 13 and 11 peak values of dolomite coinciding with quartz plagioclase and kalifeldspar peaks and maxima in long chain n alkanes indicative for land plants are interpreted as heinrich like events related to sudden instability of the laurentide ice sheet during early and late deglacial phases of the glacials the coincidence of increased toc values with elevated absolute concentrations of alkenones suggests increased glacial productivity probably due to a more southern position of the polar front alkenone based sst reached absolute maxima of about 19 c during mis 11 3 and absolute minima of 10 c during mis 12 and 10 within mis 11 prominent cooling events mis 11 22 and 11 24 occurred the absolute sst minima recorded directly before and after the glacial maxima mis 10 2 and 12 2 are related to heinrich like event meltwater pulses as supported by the coincidence of sst minima and maxima in c37 4 alkenones and dolomite these sudden meltwater pulses especially during terminations iv and v probably caused a collapse of phytoplankton productivity as indicated by the distinct drop in alkenone concentrations ice sheet disintegration and subsequent surges and outbursts of icebergs and meltwater discharge may have been triggered by increased insolation in the northern high latitudes

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

western mediterranean planktonic foraminifera events and millennial climatic variability during the last 70 kyr abstract detailed study of associations of planktonic foraminifera in cores md95 2043 and odp 977 located in the alboran sea mediterranean sea has allowed the identification of 29 new faunal events defined by abrupt changes in the abundances of neogloboquadrina pachyderma right and left coiling turborotalita quinqueloba globorotalia scitula globorotalia inflata globigerina bulloides and globigerinoides ruber white and pink varieties the age model for odp 977 was based on that of md95 2043 cacho et al 1999 paleoceanogr 14 698 705 on the isotopic stratigraphy and on two ams 14c measurements sea surface temperatures ssts were estimated for the last 54 kyr using the modern analog technique mat and were compared with the ssts provided by the uk 37 method the uk 37 record is very similar to the mat annual mean temperature record for the last 8 kyr however for older times alkenone derived temperatures are consistently higher than the annual mat temperatures this offset may be due to an underestimation of the sst provided by the planktonic foraminiferal method for glacial times to an overestimation of the uk 37 record or to changes in the seasonal production of alkenones most of the variability in the fauna is related to the millennial variability of heinrich and dansgaard oeschger d o events during heinrich events hes and most of the other d o stadials g bulloides t quinqueloba and g scitula increased while n pachyderma right coiling g inflata and g ruber decreased by contrast n pachyderma left coiling was only abundant in the hes the main component of the associations n pachyderma right coiling follows a general trend similar to that of sea level and 18o this species reached its highest abundance during the last glacial maximum when sea level was at a lower position the occurrence of a shallower nutricline owing to a shallowing of the interface between atlantic inflowing and mediterranean outflowing waters could have favoured the development of neogloboquadrinids in the vicinity of the strait of gibraltar

changes in planktic and benthic foraminifer assemblages in the gulf of lions off south france response to climate and sea level change from mis 6 to mis 11 1 a multidisciplinary study involving micropaleontological and geochemical tools was carried out in borehole prgl1 promess 1 with the aim of reconstructing the impact of climate change and sea level variation between 133 ka and 406 ka in the upper slope of the gulf of lions we used factor analysis to obtain three main benthic assemblages related to eutrophic mesotrophic and oxygenated environments planktic foraminifers were grouped as warm water and cold turbulent species these results were compared with records of caco3 and major and trace elements al ca k sr as well as the c n ratio of organic matter power and cross spectral analysis showed a straightforward relationship between precession minima and thermal stratification of the water column as well as the occurrence of eutrophic bottom conditions during lowstand periods and mesotrophic environments at times of highstand these eutrophic mesotrophic oscillations usually driven by global eustatic change also involved regional variations in caco3 source to this environment during periods of precession maxima enhancement of northwesterly winds increased primary productivity by mixing enhancing the percentage of cold turbulent species in the water column and the proportion of oxygenated benthic species on the bottom during interglacial stages these events were recorded by lower biogenic carbonate at the expense of higher silicate related components most likely due to a higher supply from pyrenees rivers the record of oxygenated benthic species can be a good proxy to monitor past changes in winter intermediate water dynamics driven by northwesterly winds

calcareous nannofossil changes during the mid pleistocene revolution paleoecologic and paleoceanographic evidence from north atlantic site 980 981 abstract new quantitative data on calcareous nannofossil assemblages through 583 1138 thousand years ago kyr have been acquired in high sample resolution 2 3 ky at northern atlantic odp ocean drilling program site 980 981 assemblage composition reflects a temperate paleobioprovince suggesting significant influx of warm north atlantic current at the site location during the mid pleistocene transition between marine isotope stage mis 35 and 15 three intervals have been described based on changes in nannofossil composition and abundance fluctuations of taxa reticulofenestrids are abundant just in the first interval mis 35 22 which is also characterised by the absence of gephyrocapsa 4 m and c pelagicus s l the latter occurring in upper mis 24 only the second interval corresponds to the expanded warm mis 21 that is accompanied by high carbonate content absence of both nannofossil reworking and ice rafted debris ird higher abundance of c leptoporus 5 8 m and h carteri and absence of c pelagicus s l and medium gephyrocapsids the third interval mis 20 15 records the occurrence of c pelagicus s l and medium gephyrocapsa generally higher abundance and higher amplitude fluctuations of helicoliths and absence of reticulofenestrids the major changes in nannofossil assemblages seem to be the result of combined paleoenvironmental factors related to sea surface water features temperature and nutrient availability sea ice cover and possibly to deep and intermediate water production of both northern and southern hemisphere origin during glacial and interglacial phases complex inter relationships between environmental parameters and evolutionary ecological factors are inferred to explain the patterns of coccolithus pelagicus subspecies whose distribution and abundance fluctuations are compared with the available patterns of turborotalia quinqueloba and neogloboquadrina pachyderma left coiled at site 980 and with the c pelagicus subspecies patterns from north atlantic dsdp deep sea drilling project site 607 and south atlantic odp site 1090 data collected provide additional information on stratigraphic distribution of selected taxa the first occurrence fo of gephyrocapsa omega is confirmed as a diachronous event even in the atlantic ocean while the first and last common occurrence fco lco of r asanoi appear as diachronous and synchronous events respectively on a global scale

synchroneity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the mediterranean region land sea climatic proxies have been obtained from the last glacial section of images core md95 2043 western mediterranean sea vegetation and alkenone derived sst curves indicate rapid 150 years and synchronous terrestrial and marine climatic changes paralleling the dansgaard oeschger d o climatic variability over greenland this frequency of climate change can be related to shifts between the two modes of operation of the north atlantic oscillation nao transfer functions applied to the pollen data indicate that there was an amplification of the climatic signal during heinrich events hes in comparison with other d o stadials the development and persistence of both scandinavian and atlantic mobile polar highs over southwestern europe may explain the extreme cooling 10 c and dryness 400 mm during heinrich events 5 and 4 in the mediterranean region comparison of the results of core md95 2043 with similar climatic data from images core md95 2042 located off portugal indicates that thermal and precipitation gradients occurred between the mediterranean and the atlantic sides of iberia within hes hes 4 and 5 are associated with more humid conditions in the atlantic by 200 mm than in the mediterranean site as is the case at the present time this comparison also illustrates the different behaviour of these areas during the d o stadials in contrast with the mediterranean site the atlantic site shows similar precipitation and temperature drops for all the d o stadials including those related to the hes here we propose the operation of different mobile polar highs mph as the driving mechanism for this difference in behaviour between the atlantic and mediterranean sides of iberia hes are related to a stronger influence of the scandinavian mph forcing a severe aridification and cooling of the full iberian peninsula the atlantic mph may have been dominant during the other stadials which would preferentially affect southwestern iberia

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

clues from mis 11 to predict the future climate a modelling point of view simulations performed with the lln two dimensional northern hemisphere climate model have confirmed that climate is largely triggered by changes in insolation forcing although atmospheric co concentration also plays an important role in particular in the amplitude of the simulated variations marine isotope stage 11 mis 11 some 400 kyr ago and the future share a common feature related to climate forcing i e the insolation at these times displays small similar variations mis 11 can be considered an analogue for future natural climate changes different simulations were performed to identify the conditions constraining the length of the mis 11 simulated interglacial clearly its length strongly depends on the phase relationship between insolation and co2 variations it is only when insolation and co act together towards a cooling i e they both decrease together that the climate enters quickly into glaciation and that the interglacial may be short otherwise each forcing alone is not able to drive the system into glaciation and the climate remains in an interglacial state the same situation applies for the future however we already know that co2 and insolation do not play together indeed insolation has been decreasing since 11 kyr bp and co2 concentration remains above 260 ppmv with a general increasing trend over the last 8000 yr therefore we conclude that the long interglacial simulated for the future is a robust feature and the earth will not enter naturally into glaciation before 50 kyr ap c 2003 elsevier science b v all rights reserved

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

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

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

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

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

enhanced seasonality of precipitation in the mediterranean during the early part of the last interglacial the deposition of sapropels in the eastern mediterranean sea is thought to occur during intervals of intensified african monsoon and increased precipitation in the mediterranean borderlands speleothem and pollen records however reveal conflicting evidence for a mediterranean wide precipitation increase suggesting that seasonal changes in the hydrological regime may be important using a multiproxy record we present the first independent evidence for seasonality of precipitation during the early last interglacial ca 130 119 ka from the tenaghi philippon peatland in northeast greece during the early part of the interglacial mineralogical macrofossil and pollen records from the same core show a shift from mire to lacustrine conditions simultaneous with an expansion of sclerophyllous vegetation and the presence of acicular aragonite indicating the onset of highly evaporative summer conditions this indicates enhanced seasonality of precipitation and reconciles the apparent incongruity between mediterranean pollen and speleothem records it also provides evidence for significantly increased winter precipitation coeval with the deposition of sapropel s5 one of the most prominent sapropels of the pleistocene we suggest that in addition to the summer african monsoon component increased winter precipitation from the northern mediterranean borderlands may have contributed to maintaining reduced surface water salinities in the mediterranean sea over the entire year

pleistocene fluctuations in the northern benguela current system as revealed by coccolith assemblages late pleistocene coccolith data of odp site 1082 from the eastern south atlantic off namibia were analysed to document spatial and temporal changes in surface ocean circulation upwelling intensity and associated productivity the studied site is located on the continental slope close to prominent oceanographic features such as the coastal upwelling mixing area the openoceanic realm and the warm water regime of the angola current highest numbers of total coccoliths up to 30 10 9 coccoliths g 1 sediment were observed during relatively warm periods characterised bydecreased upwellingintensity these elevatednumbers ofcoccoliths are due to highersurface water temperatures anddocumentadomainprobablyinfluencedbylowernutrientconcentrationsinanareawhereoceanicandfilamentouswatermix in contrast low numbers of coccoliths during glacial periods probably characterise time intervals of enhanced upwelling accompanied byabroad filamentous mixing area coccoliths of the genusgephyrocapsaarethe most abundant taxain samples of site 1082 their occurrences are characterised by abrupt changes in the investigated time interval in addition calcidiscus leptoporus pseudoemilinia lacunosa and reticulofenestra asanoi contribute a common part of the assemblage coccoliths accountformorethanhalfofthecarbonate withpeakcontributionofupto 80 intheinterval560to280kawhengephyrocapsa caribbeanica is the major caco3 producer increased carbonate accumulation during this time interval point to an overall weakening of the coastal upwelling intensity accompanied by a reduction of the mixing zone influencing the site location during this event d 2004 elsevier b v all rights reserved

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

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels

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

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

biological and geochemical signatures associated with the water circulation through the strait of gibraltar and in the western alboran sea previous hydrological investigations of the gibraltar strait have left some questions unanswered as regards the composition of the mediterranean outflow into the atlantic ocean in the present study nutrient oxygen and chlorophyll distributions are used to characterize the main water masses flowing through the strait of gibraltar and the alboran sea with particular reference to levantine intermediate water liw and western mediterranean deep water wmdw high chlorophyll a concentrations reaching 3 g l 1 at the subsurface are observed in the northern part of the anticyclonic alboran sea gyre the salinity subsurface minimum 36 located temporarily in the strait corresponds to high nutrient concentrations 7 8 g at l 1 diagram analysis shows that in the upwelling area off the spanish coast nutrients are largely transported into the photic zone and that photosynthetic nitrate consumption actually takes place consequently the formation of the alboran sea o2 extraminimum can be related to the enhanced new production most of the lowest o2 values 4 00 ml l 1 also correspond to a slight nutrient maximum po4 and no3 comparative diagram analysis of biologically affected parameters oxygen and nutrients versus salinity as a conservative property confirms and expands results from the classical s analysis oxygen and silicate exhibit the best tracer qualities for the circulation pattern demonstrating in particular that during the period of observations water rich in liw feeds the mediterranean outflow

modeling the paleocirculation of the mediterranean the last glacial maximum and the holocene with emphasis on the formation of sapropel s 1 an ocean general circulation model is used to simulate the thermohaline circulation in the mediterranean sea during the last glacial maximum and the holocene when the sapropel s1 was deposited the model is forced by prescribed surface temperatures and salinities where present day values lead to very realistic surface buoyancy fluxes different paleoreconstructions for the surface salinity and temperature distributions during these periods are tested in both periods under all reconstructions antiestuarine flow is maintained at gibraltar and sicily the holocene circulation has fresh intermediate water produced in the adriatic and an upward salt flux from the old waters below help maintain its outflow at sicily the depth of ventilation around the basin is broadly consistent with the shallowest sapropel layers observed shoaling of the eastern pycnocline occurs in all experiments in both periods possibly indicating enhanced productivity although the reasons for this are different in each case

north atlantic intermediate to deep water circulation and chemical stratification during the past 1 myr benthic foraminiferal carbon isotope records from a suite of drill sites in the north atlantic are used to trace variations in the relative strengths of lower north atlantic deep water lnadw upper north atlantic deep water unadw and southern ocean water sow over the past 1 myr during glacial intervals significant increases in intermediate to deep 13c gradients commonly reaching 1 2 are consistent with changes in deep water circulation and associated chemical stratification bathymetric 13c gradients covary with benthic foraminiferal 18o and covary inversely with vostok co2 in agreement with chemical stratification as a driver of atmospheric co2 changes three deep circulation indices based on 13c show a phasing similar to north atlantic sea surface temperatures consistent with a northern hemisphere control of nadw sow variations however lags in the precession band indicate that factors other than deep water circulation control ice volume variations at least in this band

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

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

mediterranean river systems of andalusia southern spain and associated deltas a source to sink approach abstract the northern shores of the semi isolated mediterranean sea with its low tidal range and a relatively voluminous fluvial supply of sediments constitute an ideal delta forming environment in this paper we examine the present day and multi decadal behaviour of 26 river systems from andalusia southern spain forming deltas in the alboran sea the westernmost basin in the mediterranean sea eastern central and western andalusian watersheds have been defined based on geomorphological climatological and hydrological characteristics a comprehensive data set has been compiled including satellite images aerial photographs a digital elevation model thematic maps time series of precipitation temperature and water discharge and the damming history of individual river basins this data set has been used to analyse basin morphology and hydrology and anthropogenic impact several modelling approaches have been applied to obtain the water budget and mean annual sediment yield of 12 of the 26 studied river systems in addition the periodicities of water discharge events and their possible link with north atlantic oscillation nao fluctuations have been also studied a decreasing trend has been observed in most water discharge time series during the last decades which has been attributed to natural factors although it could have been expected that the diminution of water discharge may have caused a reduction in sediment load calculated sediment discharge time series do not show any significant tendency in general sediment yield shows an opposite relationship with basin area a comparative analysis of spanish mediterranean deltas indicates that in terms of sediment transport andalusian river systems are quite efficient despite the small size of their catchments repetitive flood events and the consequent suspension plumes off river mouths play a major role in the development of deltaic and prodeltaic bodies nowadays 42 of the study area is regulated although to date the effect of dam building is hardly noticeable on river mouths

a sustained 21 m sea level highstand during mis 11 400 ka direct fossil and sedimentary evidence from bermuda abstract a small protected karstic feature exposed in a limestone quarry in bermuda preserved abundant sedimentary and biogenic materials documenting a transgressive phase still stand and regressive phase of a sea level in excess of 21 3 m above present during marine isotope stage mis 11 400 ka as determined by u th dating and amino acid racemization cobbles and marine sediments deposited during the high energy transgressive phase exhibit rim cements indicating a subsequent phreatic environment this was succeeded stratigraphically by a still stand deposition of fine calcareous lagoonal sediments containing bioclasts of red algae and benthic and planktonic foraminifera that was intensely burrowed by marine invertebrates probably upogebiid shrimp that could not be produced under any condition other than sustained marine submergence overlying this were pure carbonate beach sands of a low energy regressive phase containing abundant remains of terrestrial and marine vertebrates and invertebrates the considerable diversity of this fauna along with taphonomic evidence from seabird remains indicates deposition by high run up waves over a minimum duration of months if not years the maximum duration has yet to be determined but probably did not exceed one or two thousand years the most abundant snails in this fauna are two species indicative of brackish water and high tide line showing that a ghyben herzberg lens must have existed at 20 m the nature of these sediments and fossil accumulation is incompatible with tsunami deposition and given the absence of evidence for tectonic uplift of the bermuda pedestal or platform provide proof that sea level during mis 11 exceeded 20 m a fact that has widespread ramifications for geologists biogeographers and human demographics along the world s coastlines

seven ambiguities in the mediterranean palaeoenvironmental narrative abstract a review of seven outstanding issues on mediterranean palaeoenvironments is presented these are related to the dominant orbital pacing of climate variability the length of the interglacial vegetation succession the influence of the african summer monsoon the seasonality of precipitation during boreal insolation maxima the moisture balance during glacial maxima and the appearance of the mediterranean type climate rhythm and evolution of mediterranean sclerophyllous plants what emerges is that 1 marine 18oplanktonic and sst records show that precession has been a fundamental tempo of mediterranean climate change representing both a low latitude signal runoff from north africa and the direct influence of insolation at mediterranean latitudes but high latitude glacial effects 41 kyr and 100 kyr cycles became superimposed after 2 8 ma sapropel and dust deposition patterns in marine cores reveal that obliquity also has an effect on mediterranean climate through dry wet oscillations which are independent of glacial interglacial variability 2 the temperate part of interglacial vegetation succession has a duration of approximately half a precession cycle this persisted during the interval of obliquity dominated glacial cycles 2 8 1 ma with distinct forest successions following the precessional cycles however these are not always separated by an open vegetation phase because of minimal ice growth producing an impression of a prolonged interglacial forest interval 3 the effect of an enhanced african monsoon during summer insolation maxima has been mainly indirect in terms of nile discharge and runoff along the north african coast leading to increased freshwater input into the mediterranean sea reduced deep water ventilation and sapropel deposition 4 the notion of an accentuated summer rain regime in the northern mediterranean borderlands also contributing to a freshening of the mediterranean sea during boreal insolation maxima is not supported by the available evidence which suggests increased summer aridity 5 recent improvements in chronological precision and data resolution point to an increase in aridity and decreased temperatures during the last glacial maximum 21 2 ka but suggest an increase in effective moisture during the immediately preceding interval of 24 27 ka 6 the mediterranean type climate is not exclusively a post 3 6 ma phenomenon but may have appeared intermittently during the course of the tertiary or before 7 if that is the case then the paradigm that the sclerophyllous evergreen habit represents a pre adaptation to summer drought may need re evaluation

centennial to millennial scale climate oscillations in the central eastern mediterranean sea between 20 000 and 70 000 years ago evidence from a high resolution geochemical and micropaleontological record abstract here we present a high resolution faunal floral and geochemical stable isotopes and trace elements record from the sediments of ocean drilling program site 963 central mediterranean basin which shows centennial millennial scale resemblance to the high northern latitude rapid temperature fluctuations documented in the greenland ice cores between 20 and 70 kyr bp oxygen and carbon isotopes planktic foraminifera and calcareous nannofossil distributions suggest that dansgaard oeschger d o and heinrich events he are distinctly expressed in the mediterranean climate record moreover recurrent though subdued oscillations not previously identified in the lateglacial mediterranean sediments document a significant centennial scale climate variability in the basin that is greater than previously thought alternations between climate regimes dominated by polar outbreaks during d o stadials and warm d o interstadials with associated intensification of continental runoff are well expressed in the odp site 963 these place the mediterranean basin as an often overlooked recorder of the interplay between large and regional scale climate controls at intermediate latitudes and of the possible interactions between different components of the climate system significant changes in ba ca values measured in globigerinoides ruber shells from a number of d o stadials and interstadials suggest enhanced freshwater input from the north eastern mediterranean borderland during the d o interstadials however the short duration of 3d stratification events never led to complete oxygen consumption along the water column but clear effects of sluggish 3d circulation in the basin are testified to by negative excursions in 13c measured in selected species of planktic and benthic foraminifera hes are constantly associated with lightening in the 18o record of planktic foraminifera possibly because of the impact of iceberg melting in the iberian margin on mediterranean thermohaline circulation interestingly in two cases in particular he2 and he5 fresher water inputs also affected deeper horizons of intermediate waters suggesting a basin wide impact

microplankton response to environmental conditions in the alboran sea western mediterranean one year sediment trap record abstract the present work analyses the seasonal evolution of planktonic assemblages and particle fluxes through the water column in the eastern alboran sea western mediterranean at 35o55 47 n 01o30 77 w a sediment trap was deployed below the influence of the almeria oran front aof a semi permanent geostrophic front during july 1997 to june 1998 overall the temporal variability of coccolithophore planktonic foraminifer diatom benthic and wind carried biogenic particle fluxes is linked to the seasonal evolution of sea surface hydrological structures maximum planktonic fluxes were found during high productivity periods and wind induced upwelling following a trimodal pattern with maximum fluxes in july 1997 november december 1997 and april may 1998 these periods were characterized by vertical mixing and the full development of anticyclonic gyres in the alboran sea the annual flux of coccolithophores was dominated by the small gephyrocapsa group and emiliania huxleyi whereas turborotalita quinqueloba and globigerina bulloides dominated the foraminiferal fluxes and chaetoceros resting spores rs were predominant in the diatom assemblage benthic specimens were also collected with the sediment trap suggesting a variable influence of bottom water activity wind driven particles phytoliths and fresh water diatoms were collected along the year but their fluxes followed the local wind regime the high sea surface temperature sst during fall due to weaker than usual westerly winds and the pressure anomaly prevailing in the alboran sea during early winter were reflected in the planktonic assemblages by the proliferation of warm lower photic layer inhabitants and or oligotrophic taxa of coccolithophores florisphaera profunda planktonic foraminifers globigerinoides ruber and globorotalia inflata and diatoms leptocylindrus danicus these unusual climatic conditions in the eastern alboran sea must have been caused by the 1997 1998 enso event

prediction of sea surface temperatures in the western mediterranean sea by neural networks using satellite observations 1 we use artificial neural networks anns to predict sea surface temperatures ssts in the western mediterranean sea the anns are trained with meteorological variables as input and concurrent satellite derived ssts as target the trained anns predict well both the seasonal and the interannual variability of sst in that region we also reproduce the impact of the heat wave that occurred during the summer of 2003 on the ssts of the western mediterranean sea the ann technique allows us to predict sst maps in the western alboran sea for time coordinates before sst satellite availability the presence and later partial collapse of the western alboran gyre throughout 1980 is detected with good agreement by both the ann predictions and the concurrent results from a 3 d circulation model the same methodology is used to reconstruct incomplete sst satellite images

coccolithophores in the equatorial atlantic ocean response to seasonal and late quaternary surface water variability abstract the present study was initiated to ascertain the significance of coccolithophores as a proxy for paleoceanographic and paleoproductivity studies in the equatorial atlantic data from a range of different samples from the plankton surface sediments as well as sediment cores are shown and compared with each other in general the living coccolithophores in the surface and subsurface waters show considerable variation in cell numbers and distribution patterns cell densities reached a maximum of up to 300 103 coccospheres l in the upwelling area of the equatorial atlantic here emiliania huxleyi is the dominant species with relatively high cell numbers whereas umbellosphaera irregularis and umbellosphaera tenuis are characteristic for oligotrophic surface waters although they are observed in high relative abundances these species only occur in low absolute numbers the lower photic zone is dominated by high abundances and considerable cell numbers of florisphaera profunda the geographical distribution pattern of coccoliths in surface sediments reflects the conditions of the overlying surface water masses however abundances of the oligotrophic species umbellosphaera irregularis and umbellosphaera tenuis are strongly diminished causing an increase in relative abundance of the lower photic zone taxa florisphaera profunda and gladiolithus flabellatus during the past 140 000 years the surface water circulation of the equatorial atlantic has changed drastically as can be seen from changes in the coccolithophore species composition absolute coccolith numbers as well as coccolith accumulation rates significant increases in coccolith numbers and accumulation rates is observed in the southern equatorial atlantic during the last glacial interval oxygen isotope stages 2 4 which we attribute to enhanced upwelling intensities and advection of cool nutrient rich waters at this site in the western equatorial atlantic we observe an opposite trend with decreasing numbers of coccoliths during glacial periods which probably is caused by a deepening of the thermocline

iberian margin sea surface temperature during mis 15 to 9 580 300 ka glacial suborbital variability versus interglacial stability 1 past sea surface water conditions of the western iberian margin were reconstructed based on biomarker analyses of a marine deep sea core md03 2699 from the estremadura spur north off lisbon providing new insights into orbital and suborbital scale climate variability between marine isotope stage mis 15 to mis 9 580 to 300 ka we use biomarker based proxy records such as the alkenone unsaturated index to estimate sea surface temperature sst the total alkenone concentration to reconstruct phytoplankton productivity and terrestrial biomarkers to evaluate the continental input the results extend the existing biomarker record namely the sst for the iberian margin back to the sixth climatic cycle 580 ka a general trend of stable interglacials contrasts with glacial periods and glacial inceptions which are marked by high frequency variability thus several short lived climatic coolings were identified by large sst decreases the occurrence of ice rafted detritus and high percentages of the tetraunsaturated alkenone c37 4 some of these events were extremely cold and similar in their general trends to the well known heinrich events of the last glaciation we identified eight heinrich type events between 580 and 300 ka the general deglaciation pattern detected between mis 15 and mis 9 is similar in their general trends to that characterizing the more recent climatic cycles i e marked by two coolings separated by a short warming episode which may reflect the southward northward and southward migration of the polar front

atmospheric methane southern european vegetation and low mid latitude links on orbital and millennial timescales abstract pollen records from marine and terrestrial sequences in southern europe reveal a strong coherence between changes in tree populations and atmospheric methane concentrations over the last 800 thousand years variations in the continental hydrological balance provide a link for the observed patterns leading to concomitant changes in southern european vegetation and low latitude wetland extent and methane volatile organic compound emissions although additional contributions to the methane budget from extratropical sources are not excluded here we propose that the close coupling between low and mid latitude hydrological changes reflects shifts in the mean latitudinal position of the intertropical convergence zone which determines the extent to which southern europe is dominated by subtropical or mid high latitude influences this provides a conceptual framework within which to view vegetation variability in southern europe on orbital and millennial timescales

a paleoecological and paleobiogeographic evaluation of helicosphaera inversa gartner theodoridis and the diachrony of its first occurrence abstract the distribution pattern of helicosphaera inversa gartner theodoridis is examined from a mid latitude north atlantic core md01 2446 and two mediterranean cores ocean drilling program odp site 975 and core kc01b through marine isotope stage mis 13 to 9 the earliest rare occurrences are observed from the uppermost part of mis 12 while common and continuous abundances characterize mis 11 the paleoenvironmental framework of the study cores suggests that the taxon thrived in warm surface waters correlation with new data from planktonic foraminifera also suggests that h inversa may have only flourished within a limited salinity range comparison with previous findings highlights major diachrony in the fo of the taxon between low and mid latitude records it first occurred at lower latitude in the pacific as early as 0 8 ma while in the mid latitude north atlantic regions it is not recorded before 0 51 ma the distribution of the taxon in the north atlantic ocean also apparently varies in relation with surface water masses and hydrographic fronts the results suggest that the fo of h inversa is ecologically controlled and needs to be used with caution in worldwide stratigraphic correlation nevertheless the distribution of the species within the mediterranean basin can produce an invaluable ecostratigraphical signal

abrupt climate events 500 000 to 340 000 years ago evidence from subpolar north atlantic sediments subpolar north atlantic proxy records document millennial scale climate variations 500 000 to 340 000 years ago the cycles have an approximately constant pacing that is similar to that documented for the last glacial cycle these findings suggest that such climate variations are inherent to the late pleistocene regardless of glacial state sea surface temperature during the warm peak of marine isotope stage 11 mis 11 varied by 0 5 to 1 c less than the 4 to 4 5 c estimated during times of ice growth and the 3 c estimated for glacial maxima coherent deep ocean circulation changes were associated with glacial oscillations in sea surface temperature

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

a study of an intense density front in the eastern alboran sea the almeria oran front abstract studies of satellite imagery and space shuttle photographs of the western mediterranean have indicated that the main path of inflowing atlantic water is around two large anticyclonic gyres in the alboran sea and along the algerian coast these studies have also shown that a strong ocean front is present between almeria spain and oran algeria which is part of the easternmost segment of the eastern alboran gyre based on these satellite studies the first in situ investigation of the front called here the almeria oran front was conducted in march 1986 as part of the winter campaign of the western mediterranean circulation experiment wmce analyses of the resulting data show that the almeria oran front is a large scale density front formed by the convergence of two distinct water masses and controlled by the geographic position and strength of the eastern alboran gyre physical and biochemical data indicate that the front is limited to the upper 300 m with a strong southward baroclinic jet

foraminiferal faunal estimates of paleotemperature circumventing the no analog problem yields cool ice age tropics the sensitivity of the tropics to climate change particularly the amplitude of glacial to interglacial changes in sea surface temperature sst is one of the great controversies in paleoclimatology here we reassess faunal estimates of ice age ssts focusing on the problem of no analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods a new calibration strategy developed here which uses past variability of species to define robust faunal assemblages solves the no analog problem and reveals ice age cooling of 5 o to 6oc in the equatorial current systems of the atlantic and eastern pacific oceans classical transfer functions underestimated temperature changes in some areas of the tropical oceans because core top assemblages misrepresented the ice age faunal assemblages our finding is consistent with some geochemical estimates and model predictions of greater ice age cooling in the tropics than was inferred by climate long range investigation mapping and prediction climap 1981 and thus may help to resolve a long standing controversy our new foraminiferal transfer function suggests that such cooling was limited to the equatorial current systems however and supports climap s inference of stability of the subtropical gyre centers

detrital input productivity fluctuations and water mass circulation in the westernmost mediterranean sea since the last glacial maximum 1 by presenting sea surface temperatures planktonic oxygen isotope profiles and bulk geochemical composition of core sediments we offer a multiparameter reconstruction of western mediterranean oceanography from the last glacial maximum until the middle holocene 20 000 5000 cal years b p sediments from ocean drilling program site 975 in the algero balearic basin have been compared with three alboran basin cores ttr 300g ttr 302g and ttr 304g all of them investigated at high resolution this multiproxy approach has allowed two different modes of circulation to be recognized 1 during the lgm and from 8 0 cal ka b p onward no surface gradient in 18og bulloides is found associated with low productivity in close analogy to modern conditions 2 during the bolling allerod and early holocene significant surface isotopic gradients are found with periods probably indicating an unstable water column associated with enhanced productivity and low bottom oxygen conditions the close synchrony between the occurrence of the surface isotopic offset and organic rich layer formation implicates that the origin of these features is linked probably via shoaling of the regional thermohaline circulation paleo ssts derived from planktonic foraminifer assemblages indicate abrupt changes in surface conditions during the analyzed time interval fluctuations in marine productivity based on ba and total organic carbon are related to water column stability and atmospheric conditions a sharp warming and 18og bulloides excursion at the end of the younger dryas is probably linked to glacial meltwater influence the riverine input has been reconstructed using the mg al ratio and mg al peaks during arid periods greenland stadial 2a and younger dryas related to bypass margin processes

time and space variability in the eastern alboran sea from march to may 1990 an intensive field experiment was carried out from march 6 to april 30 1990 in the eastern alboran sea to understand the relationship between the large scale circulation and the location of the transition zone between new and longer resident modified atlantic water maw the detection of a strong jet 80 cm s 1 of new maw with anticyclonic curvature near the morocco coast suggests that the eastern alboran gyre eag was not fully developed a new state of the circulation in the eastern alboran basin intermediate between the eag viudez et al 1995 and the lanoix 1974 state is presented also important is that the almeria oran front was not present in the upper layer that small scale instabilities were detected in the northern region and that significant nongeostrophic flows were observed all these features are clearly indicative of the high spatial and temporal variability of a region where complex adjustments among density velocity and topography occur