a high resolution record of the last deglaciation in the central mediterranean sea palaeovegetation and palaeohydrological evolution abstract a high resolution palynological and stratigraphical record of a marine deep sea core in the adriatic sea documents marine and continental palaeoenvironmental changes in the basin during the last deglaciation and early holocene a chronology is derived from the oxygen isotope stratigraphy three periods of aridity marked by the development of a semi desert rich in artemisia occurred between 18 5 and 16 kyr between 14 4 and 12 7 kyr and between 11 1 and 9 7 kyr consistent with the last glacial maximum the oldest dryas and the younger dryas they are correlated with increases in productivity and intensification of the levantine water formation in the eastern mediterranean basin during the warmer bolling allerod 12 7 11 1 kyr the presence of the cold temperate dinocyst bitectatodinium tepikiense is interpreted as indicating the establishment of a strong seasonal thermal gradient probably linked to seasonal cold freshwater runoff from the po river attested by the unique presence of pollen of freshwater plants the expansion of forest and the development of the warmer dinocysts start with termination ib during the holocene three tree phases are recognized and are contemporaneous with the preboreal boreal and atlantic chronozones of europe the two phases of sapropel deposition are marked by higher pollen and dinocyst concentrations and a high representation of brigantedinium spp which indicate higher preservation of organic material and or freshwater runoff of the po river

residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

paleoenvironmental changes in the western mediterranean since the last glacial maximum high resolution multiproxy record from the algero balearic basin abstract the present study uses a multiproxy approach in order to further understand the evolution of climate responses in the western mediterranean as of the last glacial maximum sediments from odp site 975 in the algero balearic basin have been analysed at high resolution both geochemically and mineralogicallly the resulting data have been used as proxies to establish a sedimentary regime primary marine productivity the preservation of the proxies and oxygen conditions fluctuations in detrital element concentrations were mainly the consequence of wet arid oscillations productivity has been established using ba excess according to which marine productivity appears to have been greatest during cold events heinrich 1 and younger dryas the s1 time interval was not as marked by increases in productivity as was the eastern mediterranean in contrast the s1 interval was first characterized by a decreasing trend and then by a fall in productivity after the 8 2 ky bp dry cold event since then productivity has remained low here we report that there was an important redox event in this basin probably a consequence of the major oceanographic circulation change occurring in the western mediterranean at 7 7 ky bp this circulation change led to reventilation as well as to diagenetic remobilization of redox sensitive elements and organic matter oxidation comparisons between our paleoceanographic reconstruction for this basin and those regarding other mediterranean basins support the hypothesis that across the mediterranean there were different types of responses to climate forcing mechanism the algero balearic basin is likely to be a key area for further understanding of the relationships between the north atlantic and the eastern mediterranean basins

metal diagenesis in oxic marine sediments the metal nutrient relationships observed for nickel and cadmium in the deep ocean are continued at the interface between seawater and oxidizing pore water this continuum results in pore water concentrations of these metals which are only slightly greater than near bottom seawater levels manganese concentrations in these oxidizing pore waters are also extremely low less than three times bottom water in contrast release in the boundary layer produces a maximum of dissolved copper which is 10 40 times ambient seawater assuming these pore waters are at steady state flux estimates based on these measurements suggest that the manganese in todorokite rich nodules of the central equatorial pacific was not supplied by upward diffusion through pore waters below the interface most nodular nickel is precipitated with manganese while nodular copper is supplied by diffusion

eastern mediterranean sapropel s1 interruption an expression of the onset of climatic deterioration around 7 ka bp we discuss the palaeoclimatic interpretation of unprecedented high resolution micropalaeontological studies of shortterm 2 to 4 centuries interruptions within early holocene organic rich layer sapropel s1 from the eastern mediterranean results for cores from the adriatic and aegean seas that contain double s1 sapropels indicate that these interruptions which are centred roughly around 7000 years 14 cnc bp are genuine and related to climatic deterioration this interpretation is endorsed by a coeval dry event recorded in terrestrial records and indications of climatic deterioration affecting human migration patterns and early societies in egypt the presence of sapropel interruptions in the two major source areas of deep water for the entire eastern mediterranean likely implies that similar intervals may be found throughout the basin provided that sedimentation rates and sampling resolutions allow the detection of events with a duration of only several centuries moreover our results show that the sapropel mode of circulation comprises a delicate balance between reduced ventilation and enhanced productivity which is easily disturbed through surface water cooling triggering a short time of improved deep water ventilation 1999 elsevier science b v all rights reserved

holocene climatic changes in the western mediterranean from south east france to south east spain abstract holocene climatic changes along coastal regions from south east france to south east spain were studied using pollen ratios comparing modern pollen rain vegetation and climate along selected transects from the atlantic ocean to the mediterranean we obtained threshold values of two different ratios corresponding to the different climatic conditions along the transects these pollen ratios and threshold values were employed to characterize the holocene climatic changes from nine mediterranean coastal sites the results were compared with data from marine and continental pollen sequences distributed in the western mediterranean basin and with additional regional data independent of human activity lake level fluctuations alpine glacier advance and retreat chronology 14 c anomaly and cooling phases in eastern france and central europe the role of anthropogenic activities and climate on the changes in vegetation is discussed six major changes in vegetation cover were identified they correspond to aridification phases that occurred around 9500 9000 yr bp 10 900 9700 cal bp 7500 7000 yr bp 8400 7600 cal bp 4500 4000 yr bp 5300 4200 cal bp 3700 3300 yr bp 4300 3400 cal bp 2600 1900 yr bp 2850 1730 cal bp and 1300 1000 yr bp 1300 750 cal bp these arid episodes were regional responses to more global climatic changes and determined the changes in the vegetation cover humans undoubtedly enhanced the vegetation changes but none the less had to adapt to these new climatic conditions

dansgaard oeschger and heinrich event imprints in alboran sea paleotemperatures past sea surface temperature sst evolution in the alboran sea western mediterranean during the last 50 000 years has been inferred from the study of c37 alkenones in international marine global change studies md952043 core this record has a time resolution of 200 years allowing the study of millennial scale and even shorter climatic changes the observed sst curve displays characteristic sequences of extremely rapid warming and cooling events along the glacial period comparison of this alboran record with 18o from greenland ice greenland ice sheet project 2 core shows a strong parallelism between these sst oscillations and the dansgaard oeschger events five prominent cooling episodes standing out in the sst profile are accompanied by an anomalous high abundance of neogloboquadrina pachyderma sinistral which is confined to the duration of these cold intervals these features and the isotopic record reflect drastic changes in the surface hydrography of the alboran sea in association with heinrich events hl 5

the mediterranean mare nostrum of earth sciences the mediterranean area is one of the most appealing natural laboratories in the world to study geodynamic and paleoclimatic processes on different scales consequently the mediterranean sea can be considered as the mare nostrum our sea of earth sciences its semi enclosed land locked configuration in a convergent setting between africa in europe in combination with its latitudinal position makes the mediterranean extremely suitable to study both fundamental plate tectonic processes and astronomically induced oscillations in climate for many years to come the mediterranean will certainly remain a fascinating area where an integrated and multi disciplinary approach will increasingly contribute to our understanding of geological geophysical geodetical and geochemical processes in an accurate and high resolution time frame

deposition of sapropel s1 sediments in oxic pelagic and anoxic brine environments in the eastern mediterranean differences in diagenesis and preservation sediments from a boxcore in the previously anoxic brine filled poseidon basin eastern mediterranean have been studied and compared to sediments deposited in a normal eastern mediterranean environment the boxcore can be divided into three main sedimentary intervals based on ams radiocarbon ages foraminiferal and geochemical zonations from the base of the core upwards these are 1 12 3 31 2 cm organic rich sediments redeposited from within the brine 2 6 6 12 3 cm sediment containing a cold foraminifera fauna redeposited from above the brine into the basin while the brine was still present 3 0 6 6 cm oxic pelagic sediment accumulated since the reoxygenation of poseidon basin which occurred1800 yrs bp near the base of the latter unit a mn oxide peak has formed and it marks the present boundary between oxic and suboxic environments a progressive downward oxidation front which is usually found in normal sapropel s1 sediments has never formed in poseidon basin sediments this has resulted in the preservation of the relationship between organic carbon and organic related trace elements e g se in the organic rich sediments of poseidon basin whereas such a relationship has been obliterated in normal sapropel s1 sediments on the basis of the carbonate content as well as the sr ca ratio preservation of carbonates appears to be better in the brine sapropel sediments of bc15 than it is in normal sapropel s1 sediments the high opal content of bc15 shows that biogenic opal is also much better preserved the overall lower corg ba ratio in bc15 suggests a better preservation of barite relative to that of organic carbon in shallow brine sediments but is as yet inconclusive for the organic carbon preservation potential of brine relative to normal unoxidised sediments 1999 elsevier science b v all rights reserved

duration of s1 the most recent sapropel in the eastern mediterranean sea as indicated by accelerator mass spectrometry radiocarbon and geochemical evidence slowly accumulated 5 cm kyr 1 and rapidly accumulated 5 20 cm kyr 1 sediments have been compared to define the initiation and termnation times of the most recent sapropel s1 in the eastern mediterranean sea the ba a1 ratio has been employed as a more persistent index of productivity than cg accelerator mass spectrometry radiocarbon dating of pelagic foraminifera indicates a maximum duration for increased ba a1 levels in s 1 from 9500 6000 uncorrected radiocarbon convention years b p in the rapidly accumulated sediments and 9500 5300 years b p in the slowly accumulated sediments this difference is ascribed to bioturbation affecting the slower accumulated s1 sediments in the two most rapidly accumulated s1 units from the adriatic and aegean seas there is a saddle of lower values centered on 7500 years b p in the corg and ba ai profiles so that the visual s 1 unit appears as a doublet geochemical evidence indicates that this intervening period is best interpreted as an episode of increased ventilation and bottom water oxygenation during the period of sapropel accumulation

particulate manganese and iron in recent sediments of the gulf of lions continental margin north western mediterranean sea deposition and diagenetic process abstract this study aims at apprehending the major forcing factors which govern the spatial and vertical mn and fe distributions in ten cores from the gulf of lions speciation by chemical leaching experiments helps understanding their chemical behaviour during the early diagenetic processes in a marine environment under strong continental influence the distribution and chemical behaviour of mn and fe differ drastically the strong dependence of mn distribution on chemical conditions is expressed by a marked solid phase mn enrichment in the oxic layers of sediment deposits this enrichment increases with decreasing sedimentation rate increasing water depth it is illustrated by an enhanced portion of total mn in the reducible phase and the precipitation of todorokite on calcareous supports in the upper part of the deepest cores as a result 65 of the margin total particulate mn is thought to be stored in slope deposits in a relatively strongly held association conversely the low chemical mobility of iron in the sedimentary column is indicated by uniform depth profiles and an exclusive location in the residual chemical phase in all the studied sites the fe distribution is largely controlled by the dispersion of particulate material on the margin from the rhone river main source a budget of mn and fe accumulation based on the average amount of total mn and fe content of sediments deposited during the last 100 yr has been made taking into account diagenetic readjustments the total mn and fe amount stored on the margin during the last century is estimated to be 1 5 106 and 54 106 t respectively these values are seven times higher than the total secular external inputs calculated on the basis of present day riverine and atmospheric fluxes this large discrepancy is mainly explained by the sharp decrease of the rhone river discharge after dam buildings between 1950 and 1958 a residual discrepancy dating before 1950 is likely to be due to seafloor erosion and gravity induced mechanisms

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

evidence for basin restriction during syn collisional basin formation in the silurian arisaig group nova scotia the arisaig basin in nova scotia canada provides a regional sedimentary record of an early silurian basin subsidence on the microcontinent of avalon the lower members of the arisaig group beechill cove and lower ross brook formations are likely to be deposited in a basin formed during syn to post collisional rifting subsidence driven by the collision of avalon and baltica the evolution of this constricted basin can be tracked by examining the geochemistry of the sedimentary rocks deposited within the basin here we report on the chemostratigraphy of the arisaig group a series of siliciclastics with a focus on understanding the redox chemistry during sedimentation the trace and major element geochemistry of this group provides insight into the oceanographic and geological processes that were influencing its depositional environment in particular concentrations of u v mo ni cd and pb indicate regional shifts in ocean redox state which serve as a proxy for changes in ocean circulation and regional tectonic activity we find evidence for anoxic conditions near the base of ross brook formation and attribute this anomaly in redox status to a significant change in physical mixing in the region trace element concentrations indicate that this anoxic event was associated with poor circulation rather than elevated productivity and organic matter burial based on these data we confirm that these sediments are deposited in a tectonically formed basin during a period of limited ocean circulation

the inorganic geochemistry of cretaceous black shales dsdp leg 41 in comparison to modern upwelling sediments from the gulf of california

geochemical evidence for enhanced productivity during s1 sapropel deposition in the eastern mediterranean the geochemistry of the youngest mediterranean sapropel layer suggests changes in productivity and water column oxygen conditions during sapropel deposition the ba enriched interval is broader than the organic carbon rich interval of this sapropel we suggest that the ba enriched horizon records the original thickness of the sapropel prior to subsequent partial oxidation the main carrier of ba is barite as microcrystals 0 5 5 m having a morphology characteristic of marine barite particularly abundant beneath high productivity regions ba concentrations do not change at the sapropel layer oxidation front and diagenetic barite crystals are absent thus the ba enriched layer reflects original oceanic conditions of increased biological productivity during sapropel deposition and not diagenetic ba remobilization paleoredox indicators point to restricted oxygenated bottom water but not to fully anoxic conditions detrital elements within this layer indicate a lower eolian terrigenous input enhanced humidity and increased precipitation runoff thus likely higher nutrient supply supporting table is available on diskette or via anonymous ftp from kosmos agu org directory apend username anonymous password guest diskette may be ordered by mail from agu 2000 florida ave n w washington dc 20009 or by phone at 800 966 2481 15 00 payment must accompany order

concentration vertical flux and remineralization of particulate uranium in seawater abstract concentrations and fluxes of particulate u were measured throughout the water column at several locations in the atlantic and pacific oceans with in situ filtration systems and sediment traps the results indicate that dissolved u is fixed to particles in surface seawater organic matter appears to be the carrier phase formation of particulate authigenic u below the surface waters could not be detected authigenic u is remineralized within the bathypelagic layers at the open ocean sites studied in the panama basin an upwelling area with high biological productivity remineralization of authigenic u in the deep water column was not observed the rate of remineralization of authigenic u in the deep sea is insufficient to produce a measurable concentration gradient between surface and deep waters within the mixing time of the oceans formation of authigenic u in the water column in areas such as the panama basin is not a significant sink for u on an ocean wide basis

what do we learn from peaks of uranium and of manganese in deep sea sediments abstract uranium and manganese are two redox sensitive trace elements with complementary behavior under anoxic conditions u is immobile while reduced mn is dissolved in pore water of sediments uranium diffuses from sea water into reducing sediments and is enriched there the depth of the reducing layers and the sediment accumulation rate determine the enrichment of authigenic uranium on the contrary mn is dissolved in the reducing sediment sections diffuses in pore water and forms peaks of mn oxide as soon as oxygen is available thus the profiles of both mn and authigenic u record the depth of the redoxcline during periods of oxygen limitation in the sediments estimates of the depth of incorporation of uranium during the last glacial were derived for several cores at localities in the atlantic numerical modeling of the redoxcline as a function of the oxygen content of the water column and of the flux of organic matter to the sediments constrains these values during periods of extreme shallow redoxcline depths burn down of organic matter and deepening of the redoxcline during the holocene may have significantly altered the organic matter and uranium signals of glacial sediments at present day conditions sediments accumulating at rates smaller than 2 cm ky 1 may have lost the u signals peaks of manganese are then the only reliable record for a less ventilated sediment column in the past

modeling a 200 yr interruption of the holocene sapropel s1 an oceanic general circulation model previously used to simulate the conditions associated with the holocene sapropel s1 is used to simulate the effects of a climate deterioration represented as a cooling event on the sapropelic circulation mode the enhanced cooling 2 3 c induces deep convection in the adriatic and the gulf of lions and intermediate water formation in the aegean where in all cases there had previously been only stagnant unventilated waters the depths of ventilation to 1250 m are in agreement with core data from this period the short decadal timescales involved in modifying the sapropelic circulation suggest that such a climatic deterioration may be associated with the interruption of s1 between 7100 and 6900 14c yr b p which divided the sapropel into two subunits

why some mediterranean sapropels survived burn down and others did not abstract we have evaluated using a numerical model the burn down depth depth of post depositional oxygenation of organic matter rich sapropels under aerobic conditions at the seafloor the model suggests that sapropels may be erased by burn down to depths of at least 5 cm after 10 kyr of bottom water reoxygenation a test of the sensitivity shows that the parameters exerting a major control over the burn down process are the flux of freshly sedimenting organic carbon the oxygen concentration of the bottom water the amount of organic matter in the sapropel and the sedimentation rate in comparison bioturbation is of minor importance the result implies that burial of elevated concentrations of non refractory organic carbon is generally improbable when the sedimentation rate is lower than 1 2 cm kyr 1 the record of sapropel deposition in the mediterranean sea and elsewhere may thus be biased towards depositional environments where the sedimentation rate is large enough to shield the organic rich layer from oxygenation

abrupt environmental oscillations during the early weichselian recorded at lago grande di monticchio southern italy abstract this study presents multi proxy data from a new core from lago grande di monticchio italy extending back to about 100 000 calendar years bp the time scale of this record is independent from deep sea and ice core chronologies and has been established from a combination of varve counts and high resolution sedimentation rate calculations based on microscopic sediment investigation this paper focuses on environmental variability between 100 000 and 65 000 calendar years bp several abrupt cold periods have been recognised and correlated to other terrestrial as well as to ice core and deep sea records the longest of the monticchio cold phases corresponds to marine isotopic stage 5b and lasted from ca 87 000 to 84 000 calendar years bp two shorter events about 1000 years long occurred during the transition from interstadial to full glacial conditions between 79 000 and 75 000 calendar years bp the increased frequency of cold events during this time interval probably indicates a higher degree of climatic instability in periods of major changes dating discrepancies between monticchio grip and deep sea chronologies range between a few hundred to a few thousand years however these differences in dating are not constant but vary significantly for different sections of the records nevertheless the good match of environmental fluctuations at monticchio with atmospheric variability at the greenland summit as well as variations in the oceanic circulation pattern suggests a close link of the mediterranean to the atlantic climate regime

millennial scale variability in the productivity signal from the alboran sea record western mediterranean sea primary productivity of the alboran sea western mediterranean is reconstructed for the time interval 48 000 to 28 000 years bp using the following geochemical proxies calcium carbonate barium excess baexcess total organic carbon toc and alkenone concentration the records show a consistent pattern that indicates enhanced productivity during dansgaard oeschger d o warm periods at the same time deep water conditions were favorable for organic matter preservation in the sediments as indicated by the variation in redox sensitive elements such as mn cr or v and by the 13c record of benthic foraminifers the alboran sea productivity variation during d o cycles is explained by the succession of two climatic scenarios that led to latitudinal shifts of the westerly wind system this mechanism would also account for the variability in the deep water ventilation of the western mediterranean sea

palaeoclimatic cyclicity in central mediterranean pliocene sediments the mineralogical signal abstract a high resolution x ray mineralogical study of four pliocene sediment sections from the central mediterranean punta piccola sicily monte singa and vrica calabria odp hole 964 a ionian sea shows cyclic opposite abundance variations of two groups of clay minerals the first is dominated by palygorskite and kaolinite whose abundance maxima can be interpreted as resulting from periods of aridity on the african continent allowing their transport as wind blown dust the second is dominated by smectite whose abundance maxima can be interpreted as indicative of periods of abundant rainfall on the mediterranean borderlands these variations in abundance show a 22 ky cyclicity implying a control by the precession of the earth s orbit sapropels and sapropelic layers always occur in the smectite rich beds and therefore appear to have been deposited during the wet periods

late pleistocene sedimentation in the western mediterranean sea implications for productivity changes and climatic conditions in the catchment areas abstract sediment cores from the western mediterranean sea wms have been analyzed for their bulk element composition 18o values of planktic foraminiferal tests and 87sr 86sr and 143nd 144nd ratios of their bulk lithogenic components the investigated time interval comprises the last 215 kyr si al and ti al ratios as well as radiogenic isotope compositions indicate changes in the provenance of the lithogenic components between glacial intervals and interglacial phases comparison with modern data indicates that detrital input from the northwestern and northeastern sahara may have dominated during interglacial phases in contrast during glacial periods the accumulation rate of terrigenous sediment is high and changes in the sediment source areas are evident that may be related to changes in the prevailing atmospheric circulation over the basin and its source areas a productivity reconstruction based on bio mediated barium accumulation rates reveals increased surface productivity during glacial phases intervals time equivalent to sapropel formation in the eastern mediterranean sea ems show no changes in surface productivity compared to the intervening intervals comparison of the productivity patterns between the wms and ems suggests a decoupling during late pleistocene sapropel formation and highlights the importance of more localized factors such as the freshwater drainage basin

the azores front since the last glacial maximum the spatial distribution of warm surface water in the atlantic ocean reflects the state of the thermohaline circulation the azores current front which is a recirculation of the gulf stream marks the northeastern boundary of the north atlantic subtropical gyre its position is therefore diagnostic of the width of the atlantic warm water sphere here we report high resolution stable isotope and faunal abundance records of planktonic foraminifera in a sediment core from the gulf of cadiz southwest spain which reflects shifting of the azores front since the last glacial maximum lgm today the azores front does not penetrate into the gulf of cadiz even though the front resides at the same latitude as the gulf of cadiz in the atlantic our results indicate that the azores front is a robust feature of the atlantic surface circulation and that is present both in interglacial times and during the lgm at roughly the same latitude however during the lgm prior to 16 ka bp and during the younger dryas the azores front did penetrate eastward into the gulf of cadiz

circulation patterns and transport of the azores front current system in this paper different types of new data sets hydrography lagrangian and eulerian current measurements and quasi geostrophic model results obtained after altimetric data assimilation are used to study the structure and variability of the azores current and frontal system the azores current was observed to transport between 11 0 and 18 0 sv eastwards and the associated counter current some 2 0 10 0 sv to the west resulting in a net value of about 8 9 sv furthermore both data and model results revealed a meandering azores current where some freely rotating eddies were also identified these hydrographic and lagrangian results exhibit space and time scales that agree fairly well with the dynamics shaped by baroclinic instability current meters moored across the azores current system delineated a mean counter current flowing westwards with a maximum subsurface core of about 2 0 cm s at a mean depth of 800 dbar this is in excellent agreement with previous studies which explains this azores counter current as the rectification process of the geostrophic turbulence occurring north of the main azores current stream a new scheme is proposed for the formation mechanism of the freely rotating cyclonic eddies observed south of the azores it is shown that the north south contrast thickness of the 17 19 c water layer across the azores front decreases downstream this will create in turn a downstream increase of the most unstable wavelength in a non linear baroclinic instability context as a consequence both large cyclonic and anticyclonic features are able to form at the eastern side of the azores current around 19 w while at the western side around 35 w only large anticyclones will survive western generated cyclones will be small enough to be quickly dissipated this means that the eastern cyclones of the azores current may live longer than the shorter western ones however because longer lived cyclonic eddies propagate westwards with a mean speed of 2 5 km day they may be observed south of azores and of the main stream several months later although they were not formed there

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

sequential extraction of iron manganese and related elements in s1 sapropel sediments eastern mediterranean a detailed sequential extraction scheme mesex was developed to distinguish fe and mn phases in eastern mediterranean sediments after calibration and validation using single natural minerals and a mixed mineral standard mesex was applied to holocene eastern mediterranean sediments from 1 a former brine basin and 2 a normal setting including the organic rich sapropel s1 in both sediments the mn ii mn iii iv redox boundary is clearly distinguished with carbonate related mn being enriched below and mn oxides occurring only above it a clear fe ii fe iii redox boundary is present in the normal eastern mediterranean sediments and is located just below the mn ii mn iii iv redox boundary the fe ii fe iii boundary closely coincides with the visible boundary between the lower unoxidised and the upper oxidised burned down part of the original sapropel s1 interval pyrite is only present within the unoxidised interval whereas fe oxides are abundant above it the fe ii fe iii redox boundary in the former brine sediments resides on top of the organic enriched sediments as deduced from the distribution of fe oxides and pyrite as a result of burn down of the sapropel s1 unit in the normal sediments a vanadium peak has been formed below the oxidation front whereas no such v peak was observed in the former brine sediments this together with the location of the mn ii mn iii iv redox boundary well above the organic enriched sediments suggests that no burn down has taken place into the sapropelic sediments of the former brine basin resulting in the preservation of the relationships of trace metal to organic carbon or pyrite in these latter sediments mn and co appear to be associated with pyrite whereas ni cu and zn as well as v are more related to organic matter on the basis of mesex variations have also been detected in the terrigenous component i e aluminosilicates fe al clay mg al clay and several trace metal to al ratios are higher in sapropelic than in non sapropelic sediments these results indicate that sources of terrestrial material have been different during sapropel times compared to the period immediately after it on the other hand the fairly constant k alclay ratio suggests that no major changes may have occurred in the relative illite contribution

high resolution geochemical and micropalaeontological profiling of the most recent eastern mediterranean sapropel abstract a combined geochemical and micropalaeontological study of the most recently deposited sapropel s1 from the eastern mediterranean sea is reported from two cores in which the s1 sapropel units were rapidly deposited 15 and 20 cm ky 1 such rapid accumulation rates have largely protected the two s1 units from post depositional oxidation effects and allow a high resolution investigation of conditions before during and after s1 formation the cores are from the adriatic and aegean seas and both record a simultaneous diminution in intensity of sapropel development at 7500 conventional radiocarbon years that divides both visual s1 units into two approximately equal lobes detailed foraminiferal analysis of the aegean core reveals fluctuations in benthic foraminifera species that indicate anoxic or near anoxic bottom water conditions during formation of the upper and lower lobes the central s1 section shows a temporary repopulation by an opportunistic benthic species g orbicularis indicative of improved bottom water oxygen levels the appearance and disappearance of this species in the central section and its reappearance just before the end of s1 times also coincides with increases in abundance of pelagic foraminifera characteristic of cooler surface water conditions and with local mn peaks in the sapropel these features are interpreted as indications of increased deep water ventilation and bottom water o 2 levels centred during s1 time although the s1 c org contents are low at 1 2 wt because of dilution by high detrital fluxes a set of elements ba cr cu mo ni s se u v and zn generally present in other s1 units older sapropels and black shales is clearly present at enhanced levels sulfur enrichment is well correlated with the c org content throughout s1 and fes 2 formation accounts for the bulk of the observed s enrichment

hydrogeochemical and isotopic evidence of groundwater evolution and recharge in aquifers in beijing plain china an investigation was conducted in beijing to identify the groundwater evolution and recharge in the quaternary aquifers water samples were collected from precipitation rivers wells and springs for hydrochemical and isotopic measurements the recharge and the origin of groundwater and its residence time were further studied the groundwater in the upper aquifer is characterized by ca mg hco3 type in the upstream area and na hco3 type in the downstream area of the groundwater flow field the groundwater in the lower aquifer is mainly characterized by ca mg hco3 type in the upstream area and ca na mg hco3 and na ca mg hco3 type in the downstream area the d and 18o in precipitation are linearly correlated which is similar to wmwl the d and 18o values of river well and spring water are within the same ranges as those found in the alluvial fan zone and lay slightly above or below lmwl the d and 18o values have a decreasing trend generally following the precipitation surface water shallow groundwater spring water deep groundwater direction there is evidence of enrichment of heavy isotopes in groundwater due to evaporation tritium values of unconfined groundwater give evidence for ongoing recharge in modern times with mean residence times 50 a it shows a clear renewal evolution along the groundwater flow paths and represents modern recharge locally from precipitation and surface water to the shallow aquifers 150 m in contrast according to 14c ages in the confined aquifers and residence time of groundwater flow lines the deep groundwater is approximately or older than 10 ka and was recharged during a period when the climate was wetter and colder mainly from the piedmont surrounding the plain the groundwater exploitation is considered to be mined unsustainably because more water is withdrawn than it is replenished

active post depositional oxidation of the most recent sapropel s1 in sediments of the eastern mediterranean sea abstract over a wide area of the eastern mediterranean basin two mn rich layers have been observed above the most recent sapropel s1 one immediately above the sapropel top and one a few centimetres closer to the sediment surface different mechanisms have been proposed to explain the occurrence of these two mn peaks either both peaks have a diagenetic origin in which case the upper mn peak is actively forming or the lower peak is actively forming and the upper peak has a different formation mechanism high resolution porewater including a gel sampler used for the first time in marine sediments and solid phase data are now used to demonstrate that the oxidation front is located at the level of the lower mn peak which therefore is presently being formed a barium organic carbon relationship is used to calculate the initial organic carbon profile of the s1 sapropel the palaeoproductivity profiles generated by this method demonstrate that the original sapropel unit was bounded by the upper mn peak this implies that the interval between the two mn peaks where a low organic carbon content is now observed was originally part of the sapropel the initially deposited organic carbon has been oxidised by a progressive downwards moving oxidation front the penetration depth of this oxidation front i e the distance between the two mn peaks is mainly determined by the organic carbon content the sediment accumulation rate and the bioturbation depth the upper mn peak appears to have formed as a result of either mn precipitation upon oxygenation of previously anoxic eastern mediterranean deep water or preservation of a surficial mn peak at the end of the high productivity episode in either case the upper mn peak marks the end of sapropel formation as indicated by the ba profiles this means that formation of the s1 sapropel ceased more recently than is indicated by radiocarbon dating of the visible top of s1

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

the last 100 000 years in the western mediterranean sea surface water and frontal dynamics as revealed by coccolithophores a quantitative analysis was carried out on coccolith assemblages from two pleistocene cores k1 and k10 from the western mediterranean the distribution of selected coccolithophore species provides new paleoclimatic and paleoceano graphic data a continuous sequence from the top of isotope stage 5 to the holocene was recorded the reversal in dominance between gephyrocapsa muellerae and emiliania huxleyi was dated in both cores at ca 73 ka at about 47 ka e huxleyi shows a regular increase whereas g muellerae progressively decreases in abundance during interglacial periods high concentrations of coccoliths are observed whereas in glacial times coccoliths are more diluted and the percentage of reworked forms increases as a consequence of the higher terrigenous input after taking careful account of the dilution factor we conclude that the production of coccolithophores was higher during warm periods maxima in coccolith concentrations coincide with highstand episodes probably as a result of the intensification of the atlantic flux into the mediterranean across the gibraltar strait this intensification could have produced an increase in nutrient content in the surface mediterranean waters during cold periods the western mediterranean front underwent a reduction in activity probably due to an increase in the saline and or thermal gradients between the superficial waters and intermediate waters in the liguro provencal basin

a comparative study of the geochemical and mineralogical characteristics of the s1 sapropel in the western and eastern mediterranean sapropels which are dark sediments with organic carbon content s 2 wt are common in eastern mediterranean sections in some western mediterranean sites however even organic rich layers orls are not detected in sections spanning the s1 sapropel deposition event 9500 6000 yr bp we compare geochemical and mineralogical compositions in cores from the eastern ionian sea and western alboran sea and south balearic basin mediterranean basins to determine the causes for the lack of orl deposition during s1 in the western basin in particular we investigate whether the differences between the eastern and western sites are due to preservation or productivity variations using mineralogical and geochemical data mineral abundances major and trace element concentrations and ratios organic carbon content ba and barite accumulations and sea surface temperature data along with information about the sedimentary regimes sedimentation rates and water depths at these sites we conclude that the lack of s1 sapropel formation in the western mediterranean is due to lower export production fluxes in this basin accordingly the response to regional climate changes through time must be different in the eastern and western mediterranean identifying the exact causes for these differences may lead to an understanding of the variations in export production rates in response to basin wide versus regional climate changes in the mediterranean region

uranium removal in oceanic sediments and the oceanic u balance pore water uranium data from the nw atlantic ocean cariaco trench black sea and san clemente basin are used to calculate fluxes across the sediment water interface all samples were collected in situ and show depletions in pore water u relative to the overlying water concentration the uptake rate of u derived from pore water gradients reflects the redox environment with lowest fluxes 10 g cm 2 ky in oxic su ic sediments of the nw atlantic dominated by no 3 reduction and higher fluxes 25 70 g cm 2 ky in the anoxic sulfate reducing sediments of the cariaco trench black sea and san clemente basin the anoxic fluxes compare well with previous estimates based on solid phase data calculations indicate that the areally integrated removal of u into su ic hemipelagic sediments is of greater magnitude than that into anoxic sulfate reducing sediments these fluxes are discussed in the context of the oceanic u balance the removal of u in all oceanic sediments is estimated to account for about 65 of the riverine input and this sink plus removal of u in altered oceanic crust balances the most probable value for riverine input

high resolution lacustrine record of the late glacial holocene transition in central europe abstract in this paper we present the high resolution record of proxy climatic data in central europe during the final stages of the last deglaciation derived from the annually laminated sediments of lake go ciaz central poland the isotopic palynological and other microfossil data confirm sudden changes of climate at the onset and termination of the younger dryas completed within 150 and 70 years respectively in close agreement with the previous estimates derived from the polar ice cores and marine sediments in the upper yd some amelioration of climate took place already about 600 years before the main yd preboreal transition counting of annual varves in the lake sediments allows a direct estimate of the duration of the younger sdryas in central europe it lasted approximately 1640 years substantially longer than suggested by previous estimates derived from laminated lake sediments and glacial varves but agreeing with the radiocarbon calibration data obtained for barbados corals the calendar ages of the boundaries of the yd 12 920 and 11 280 cal bp are tentatively set

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

meridional heat advection due to mixed rossby gravity waves in the equatorial indian ocean abstractthis study examines heat advection due to mixed rossby gravity waves in the equatorial indian ocean using moored buoy observations at 0 80 5 e and 0 90 e and an ocean general circulation model ogcm output variability associated with mixed rossby gravity waves is defined as that at periods of 10 30 days where both observations and the ogcm results show high energy in meridional velocity and meridional gradient of temperature the 10 30 day variability in meridional velocity causes convergence of heat flux onto the equator the net effect of which amounts to 2 5 c month 1 warming at the depth of the thermocline detailed analysis shows that the wave structure manifested in temperature and velocity is tilted in the x z plane which causes the phase lag between meridional velocity and meridional temperature gradient to be a half cycle on the equator and results in sizable thermocline warming an experiment with a linear continuously stratified model shows that the contributions of many bar

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

variability of the large scale general circulation of the mediterranean sea from observations and modelling a review abstract in this paper we present an overview of the most recent findings about the mediterranean sea present day circulation structure both historical observations and numerical model simulations are presented outlining the differences and agreement the model simulations are presented for both an eddy resolving and a coarse resolution numerical model and the results are intercompared the importance of the mesoscales in modifying the large scale flow field is elucidated the critical point is the discovery of the large amplitude interannual variability of the circulation and water mass structure associated with the anomalies of atmospheric forcing over the basin the seasonal variability can be strictly related to changes in heat and momentum fluxes while the interannual variability has a component which is related to the mesoscale field the latter is very intense in the algerian current region and levantine basin but different in structure in the two regions results are shown which confirm the importance of wind driving in establishing the kinetic energy of the flow field by comparing the current transport at the strait of corsica with observations in conclusion the essential characteristics of the present day circulation are associated with the atmospheric forcing and the basin topographic structure results from palaeoceanographic simulations for the last 20 000 years show that changing the atmospheric forcing can cause large changes in the circulation structure which may have affected sapropel formation

a dynamic explanation for the origin of the western mediterranean organic rich layers the eastern mediterranean sapropels are among the most intensively investigated phenomena in the paleoceanographic record but relatively little has been written regarding the origin of the equivalent of the sapropels in the western mediterranean the organic rich layers orls orls are recognized as sediment layers containing enhanced total organic carbon that extend throughout the deep basins of the western mediterranean and are associated with enhanced total barium concentration and a reduced diversity dysoxic but not anoxic benthic foraminiferal assemblage consequently it has been suggested that orls represent periods of enhanced productivity coupled with reduced deep ventilation presumably related to increased continental runoff in close analogy to the sapropels we demonstrate that despite their superficial similarity the timing of the deposition of the most recent orl in the alboran sea is different than that of the approximately coincident sapropel indicating that there are important differences between their modes of formation we go on to demonstrate through physical arguments that a likely explanation for the origin of the alboran orls lies in the response of the western mediterranean basin to a strong reduction in surface water density and a shoaling of the interface between intermediate and deep water during the deglacial period furthermore we provide evidence that deep convection had already slowed by the time of heinrich event 1 and explore this event as a potential agent for preconditioning deep convection collapse important differences between heinrich like and deglacial like influences are highlighted giving new insights into the response of the western mediterranean system to external forcing

paleoproductivity variations related to climatic conditions in the alboran sea western mediterranean during the last glacial interglacial transition the diatom record the present study addresses the analysis of changes in marine primary productivity derived from climatic variability over the last 30 000 yr the study area is the alboran sea this is the westernmost basin of the mediterranean sea and was a very sensitive area to changes in sea levels and atmospheric configuration during the last glacial interglacial transition we report the results from four sediment cores recovered in both the western and eastern alboran basins this allowed us to monitor the w e evolution of the hydrological structures the study is mainly based on the diatom record although total organic carbon toc isotopes and uk 0 37 sst were also used to gain further information paleoceanographic conditions favoured high paleoproductivity rates during the last glacial maximum although this occurred at termination 1a and during the younger dryas event yd increasing towards the easternmost sites during these periods meteorological conditions with increased westerlies intensified the flow to the east driving an eastward migration of the western anticyclonic gyre a possible displacement of the north alboran upwelling system is also considered the major component of the diatom assemblage during the yd are the resting spores of leptocylindrus danicus which suggest the presence of cooler and less saline surface waters the opposite behaviour between planktonic and benthic proxies in addition to the high toc values allows us to infer a phase of reduced deep water renewal between 16 5 and 9 cal ky bp fresh water diatoms and opal phytoliths were used as indicators of aridity and humid land conditions respectively during the glacial period and until 14 cal ky bp we observed a gradual climatic deterioration accompanied by a loss of grass belts climatic conditions were warmer and moister during the bolling allerod while the yd was dry the re establishment of vegetation belts and replenishment of lakes was observed at 8 cal ky bp q 2001 elsevier science b v all rights reserved

retreat velocity of the north atlantic polar front during the last deglaciation determined by 14 c accelerator mass spectrometry the glacial oscillations which dominate the quaternary global climate are closely related to changes in incoming solar radiation but the details of palaeoclimatic spectra suggest that other parameters usually referred to as feedback have significantly increased the climatic response to extraterrestrial forcing1 the last deglaciation appears to be one of the more characteristic examples of nonlinearity because its abruptness strongly contrasts with the smooth shape of the associated solar radiation maximum dated at 11 000 yr bp in addition the presence of the younger dryas cold event concomitant with the solar radiation maximum could be interpreted as a transitory phenomenon caused by the rapid meltwater influx linked to the first phase of the ice sheet s disintegration2 3 here using accelerator mass spectrometry we date precisely the movements of the polar front during the whole period of glacial retreat 15 000 8 000 yr bp our results show that the polar front has moved between 35 n and 55 n in 1 000 yr for the earliest retreat 12 500 12 000 bp and moved almost instantaneously that is 400 yr during the two abrupt climatic changes associated with the younger dry as cold event

neogene sapropels in the mediterranean a review for 50 years the existence of sapropels organic carbon rich sediments deposited within plio pleistocene sediments of the mediterranean sea has been known initially research concentrated on material recovered in relatively short gravity piston cores taken from the eastern basins where sequences were found to be well developed preserved and had extensive spatial coverage in the main previous studies concentrated upon establishing a workable stratigraphy spatial correlation of individual layers and determining the probable depositional mechanisms however despite a plethora of research papers some issues still remain unresolved this is in part due to a lack of agreement between investigators sampling and analytical short comings restricted sample size and the fact that in many instances like was not being compared with like recently the limit of sapropels in the western basin has been further extended as a result the palaeoceanographic palaeoclimate models which had previously been developed for deposition of sapropels in the eastern basin have been modified most recently strong links have been established between astronomical cyclicity and sapropel formation this review paper provides a summary of sapropel research to date and ongoing sapropel research in the mediterranean some of which appears in this thematic issue of marine geology it is fitting that this thematic issue of marine geology be dedicated to the memory of colette vergnaud grazzini and rob kidd who in many ways helped to initiate the resurgence in sapropel studies in the 1970s in the mediterranean perhaps in 50 more years we will know all of the answers 1999 elsevier science b v all rights reserved

near surface meanders in the equatorial indian ocean abstract drifting buoys were released in the western indian ocean from 1979 to 1982 they reveal meanders of the eastward flowing monsoon drift in august september 1979 1980 and 1981 oscillating meridional buoy drifts reach 80 cm s 1 and meridional displacements can exceed 3 for motions at a period close to 25 days in 1979 this is related to oscillation below the thermocline sensed by an array of current meters in the western equatorial indian ocean it is likely that the origin of the oscillations is in the surface currents north of the equator the currents change in october with the formation of an intense eastward equatorial current in which most of the buoys are entrained as the buoys drift rapidly towards the eastern indian ocean meridional motions are still present but at shorter periods 12 days than is observed below the thermocline 25 days it is possible that is still a manifestation of the same oscillations but with doppler shifting and a strong influence of nonlinearities waves a

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

evidence for enhanced mediterranean thermohaline circulation during rapid climatic coolings molecular biomarkers c37 alkenones n nonacosane and n hexacosanol and toc are used together with benthic 18o and 13c data to document the hydrographic response of the western mediterranean sea to rapid climatic variability these proxies are recorded in core md 95 2043 alboran sea affording the study of the dansgaard oeschger d o and heinrich he variability during the last glacial period the results suggest that rapid changes in the western mediterranean thermohaline circulation occurred in parallel to sea surface temperature oscillations enhanced deep water ventilation occurred during cold intervals he and d o stadials probably driven by a strengthening of north westerly wind over the north western mediterranean sea in contrast decreased intensity of the thermohaline circulation is detected during warm intervals d o interstadials which led to low oxygenated deep water masses and better preservation of the organic matter in the sediment

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

variability of the western mediterranean sea surface temperature during the last 25 000 years and its connection with the northern hemisphere climatic changes sea surface temperature sst profiles over the last 25 kyr derived from alkenone measurements are studied in four cores from a w e latitudinal transect encompassing the gulf of cadiz atlantic ocean the alboran sea and the southern tyrrhenian sea western mediterranean the results document the sensitivity of the mediterranean region to the short climatic changes of the north atlantic ocean particularly those involving the latitudinal position of the polar front the amplitude of the sst oscillations increases toward the tyrrhenian sea indicating an amplification effect of the atlantic signal by the climatic regime of the mediterranean region all studied cores show a shorter cooling phase 700 years for the younger dryas yd than that observed in the north atlantic region 1200 years this time diachroneity is related to an intra yd climatic change documented in the european continent minor oscillations in the southward displacement of the north atlantic polar front may also have driven this early warming in the studied area during the holocene a regional diachroneity propagating west to east is observed for the sst maxima 11 5 10 2 kyr b p in the gulf of cadiz 10 9 kyr b p in the alboran sea and 8 9 8 4 kyr b p in the thyrrenian sea a general cooling trend from these sst maxima to present day is observed during this stage which is marked by short cooling oscillations with a periodicity of 730 40 years and its harmonics

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

contrasting sulfur geochemistry and fe al and mo al ratios across the last oxic to anoxic transition in the cariaco basin venezuela an abrupt transition from oxic to anoxic sulfidic euxinic marine bottom waters occurred in the cariaco basin in response to increasing productivity resulting from the late pleistocene post glacial rise in sea level and corresponding increase in surface water nutrient availability the microlaminated sediments of the euxinic interval which span the last f14 5 ky suggest a predominance of water column syngenetic pyrite formation based on 1 high pyrite sulfur spy concentrations in the surficial sediment layers 2 values for degree of pyritization dop that generally do not increase appreciably with increasing burial 3 ratios of total iron fet to al that are elevated above the continental baseline recorded in the underlying oxic sediments and 4 spy isotope trends that largely mimic the d 34 shsof the modern water column intermediate dop values in the microlaminated deposits and fet al ratios that are slightly above continental levels indicate an iron reservoir controlled by scavenging during syngenetic pyrite formation in combination with intermediate rates of fe bearing siliciclastic accumulation as predicted from the relative rates of siliciclastic delivery fet al and dop data lie between end member values observed in the modern black sea as viewed broadly fet al and dop relationships in euxinic sediments reflect the balance between syngenetic fe scavenging and temporal and spatial gradients in siliciclastic input pyrite concentrations are generally low in the underlying oxic marine deposits because of limitations in the supply of organic carbon corg however the upper 80 cm of the fe rich corg poor bioturbated sediment show evidence for a strong diffusional hsoverprint from the overlying fe limited euxinic marine environment this post glacial transition manifests in pyrite overprints that are strongly 34 s depleted relative to those in restricted presently euxinic marine settings elsewhere in the world such as the black sea where the sedimentary sequence spanning the last glacial interglacial transition begins with a shift from freshwater to corg poor oxic marine deposition and thus dominantly sulfate diffusion trends for mo al ratios in the microlaminated sediments suggest that mo is enriched by roughly two orders of magnitude above the continental levels recorded in the oxic deposits organic matter plays a role by enhancing hsproduction and or by providing a substrate for mo scavenging significant mo enrichment via diffusion into the upper portion of the bioturbated zone was not observed despite hs rich pore waters as recorded in the heavy iron sulfide overprint we have

observational evidence of lower frequency yanai waves in the central equatorial indian ocean the analysis of long time series current meter data from a mooring at 77 0 e and equator during 20032007 along with mean sea level anomaly msla data throws light on the occurrence of the lower frequency yanai wave 24 40 day in the upper water column of the central equatorial indian ocean eio during the positive indian ocean dipole iod years of 2003 2004 2006 and 2007 and its absence during the negative iod year of 2005 this result is in contrast with the earlier studies that observed only the higher frequency biweekly period yanai wave in this region we propose a new notion for the generation of the lower frequency yanai wave in the upper central eio due to the positive iod phenomenon the strong meridional current shear created by the northward shifting and strengthening of the westward flowing south equatorial current sec associated with positive iod and the eastward flowing southwest monsoon current provides energy for the generation of lower frequency yanai waves the vertical stratification of the water column appears to be responsible for the trapping of different frequency of yanai wave with only the higher frequency yanai wave in the region of lower pycnocline during positive iod the strongly stratified upper water column responds to the lower frequency yanai wave while the deeper ocean 4000m exhibited longer period 47 day oscillation the expected surface signature of madden julian oscillation mjo seems to be suppressed by strong easterlies during the positive iod years

redistribution and geochemical behaviour of redox sensitive elements around s1 the most recent eastern mediterranean sapropel the youngest eastern mediterranean sapropel s1 is generally believed to have formed 7 9 14c ky b p the distribution of redox sensitive elements above in and below the sharply defined organic rich unit reveal that s 1 has already suffered heavy diagenetic alteration its present thickness based on its dark colour is only a fraction of its original thickness in one core visual evidence of s1 with an inferred initial thickness of 6 cm has been destroyed and a similar thickness appears to have been lost from the tops of another two examples this is caused by oxidation of the upper reaches of s 1 by a progressive oxidation front which commenced 5 2 5 4 14c ky ago and still appears to be active in the three cores studied diagenetic relocation of many redox sensitive elements has occurred most elements expected to be enriched in sapropels or sulphide rich sediments already have maximum concentrations above or below rather than in the present s 1 layers similarities are observed in the geochemical behaviour of as fe and p of co cu mn ni and zn and of cd mo sb ti u and v the behaviour of ba is distinctive and its immobility as barite makes it an indicator for palaeoproductivity and the original high s1 corg content the elements se and i exhibit particularly large sharp concentration peaks and together are proposed as useful indicators of the present boundary between oxic and post oxic conditions

temperature and salinity variations of mediterranean sea surface waters over the last 16 000 years from records of planktonic stable oxygen isotopes and alkenone unsaturation ratios alkenone unsaturation ratios and planktonic d18o records from sediment cores of the alboran ionian and levantine basins in the mediterranean sea show pronounced variations in paleo temperatures and salinities of surface waters over the last 16 000 years average sea surface temperatures ssts are low during the last glacial averages prior to 13 000 years 11 15 c vary rapidly at the beginning of the holocene and increase to 17 18 ca t all sites during s1 formation dated between 9500 and 6600 calendar years the modern temperature gradient 2 3 c between the mediterranean sub basins is maintained during formation of sapropel s1 in the eastern mediterranean sea after s1 ssts have remained uniform in the alboran sea at 18 c and have fluctuated around 20 c in the ionian and levantine basin sites the d18o of planktonic foraminifer calcite decreases by 2 from the late glacial to s1 sediments in the ionian basin and by 2 8 in the levantine basin in the alboran sea the decrease is 1 7 of the 2 8 decrease in the levantine basin the evect of global ice volume accounts for a maximum of 1 05 and the temperature increase explains only a maximum of 1 3 the remainder is attributed to salinity changes we use the temperature and salinity estimates to calculate seawater density changes they indicate that a reversal of water mass circulation is not a likely explanation for increased carbon burial during s1 time instead it appears that intermediate and deep water formation may have shifted to the ionian sea approximately 2000 years before onset of s1 deposition because surface waters were as cold but saltier than surface water in the levantine basin during the younger dryas sapropel s1 began to form at the same time when a significant density decrease also occurred in the ionian sea 2000 elsevier science b v all rights reserved

cyclic variations in the chemical composition of eastern mediterranean pliocene sediments a key for understanding sapropel formation abstract two pliocene mediterranean sediment cores from ocean drilling program odp leg 160 sites 964 pisano plateau ionian basin and 967 lower northern slope of eratosthenes seamount south of cyprus have been analyzed for major and minor elements si ti al fe mg ca k ba cr ni v zn zr by x ray fluorescence analysis at a depth resolution of 3 to 4 cm a total of 430 samples core 964c 9h comprises five sapropels with up to 9 7 total organic carbon toc one 2 5 m thick turbidite and a 50 cm segment of a second turbidite whereas core 967b 9h contains eight sapropels with toc contents of up to 6 7 cyclic variations in carbonate content and detrital matter composition are evident at both sites at site 964 pisano plateau terrigenous detrital matter chemistry reflects periods of stronger saharan dust input higher si al and zr al ratios alternating with fluvial input from the northern borderlands higher mg al ratios cyclicity is not well expressed at this location because turbidites and winnowing occur site 967 eratosthenes seamount sediments are strongly influenced by discharge from the nile river during humid periods low k al and mg al ratios at site 967 sapropels occur only during periods of enhanced nile discharge with correspondingly lower si al ti al mg al k al and zr al ratios accumulation rates of carbonate and terrigenous detrital matter were 30 lower during such episodes because of the reduction in eolian input and carbonate production and or carbonate dissolution periodical ba enrichments which are not only seen in the sapropels but in every k al minimum document the association of enhanced bioproductivity and sapropel formation as calculated from excess ba concentrations productivity increased by up to a factor of five during intervals of intensified nile runoff fluviatile discharge seems to be responsible for an enhanced input of nutrients and suspended matter containing low mg al and k al ratios based on organic carbon concentrations episodes of sapropel formation lasted at least from 1000 to 4000 years at site 964 and from 2000 to 6000 years at site 967 periods of enhanced bio productivity as defined by ba enrichments lasted from 8000 to 12 000 years at site 967 episodes of high river discharge and corresponding nutrient input as well as conditions of sapropel formation seem to have lasted longer in the eastern part of the basin site 967 than at the pisano plateau site 964

impact of iceberg melting on mediterranean thermohaline circulation during heinrich events down core samples of planktonic and benthic foraminifera were analyzed for oxygen and carbon isotopes in international marine past global changes study images core md99 2343 in order to study the interactions between climate change in the northern hemisphere and the western mediterranean thermohaline circulation at times of heinrich events he our results confirm the antiphase correlation between enhanced north atlantic deep water formation and low ventilation in the mediterranean however this study reveals that this antiphase relationship in deepwater formation between the north atlantic and mediterranean was interrupted during times of he when the injection of large volumes of water from melting icebergs reached the entrance to the mediterranean these events which lasted less than 1000 years are represented by pronounced decreases in both planktonic d18o and benthic d13c signals lower salinities of mediterranean surface water resulted in a slowdown of western mediterranean deepwater overturn even though cold sea surface temperatures and drier climate should have resulted in enhanced deepwater formation

oxygenation history of bottom waters in the cariaco basin venezuela over the past 578 000 years results from redox sensitive metals mo v mn and fe we present results from analyses of the redox sensitive metals mo v mn and fe in sediment recovered from the cariaco basin ocean drilling program leg 165 site 1002 results are interpreted in the context of previous studies of 15n export production percent total organic carbon eolian input and hemipelagic deposition in the basin variations in redox metal ratios over the past 578 000 years were compared to variations in 18o at milankovitch frequencies and show a strong relationship between glacial interglacial cycles in sea level governed by the shallow sills encircling cariaco basin and bottom water oxygen content during 100 kyr and 41 kyr cyclicity enrichments of mo and v occur during highly productive interglacials indicating bottom water anoxia during glacials sediments are less depleted or enriched in mn and fe relative to the interglacials reflecting oxic conditions during 23 kyr and 19 kyr cyclicity however these redox metal patterns are not observed indicating that the cariaco basin responds differently to the higher frequency climate changes

palaeoclimate and the formation of sapropel s1 inferences from late quaternary lacustrine and marine sequences in the central mediterranean region abstract synchronous responses to climatic changes during the late pleistocene holocene transition are inferred from marine and lacustrine stratigraphic records in the central mediterranean region new stratigraphic data are presented from well dated sequences in the meso adriatic depression mad two crater lakes in the lazio region and in the tyrrhenian sea the sequences all span the last termination and the holocene but we focus here on the evidence in each record for the time period during which sapropel s1 formed in the mediterranean ca 9 0 to 6 8 cal kyr b p the new records provide evidence of palaeoenvironmental changes on land and sea that can be reconstructed at a high temporal resolution and which throw some light on the processes which led to the formation of s1 the collective evidence indicates that i organic rich sediments occurred in both the marine and the crater lake sites during the time of formation of the s1 sapropel ii there is evidence of increased stratification and anoxia in the sea water column during the period of s1 formation iii the s1 period in the study area is divisible into two sub phases s1a and s1b which reflect short term variations in oceanographic conditions stratification and anoxia iv changes in stratification in the marine column were contemporaneous with regional climate variations that are inferred from the terrestrial records we conclude that the key factor that initiated the formation of s1 was increased discharge of freshwater into the mediterranean following a change post 9 0 cal kyr b p to a warmer and wetter climate furthermore the period of s1 formation was interrupted by a short lived episode ca 500 years of comparatively cooler and drier conditions during the early middle holocene transition emht

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

mediterranean quaternary sapropels an immediate response of the african monsoon to variation of insolation abstract in the subsurface of the east mediterranean sea eleven discrete basin wide organic rich black sapropels were deposited during the last 465 000 years they are dated by oxygen isotopic chronostratigraphy the most recent sapropel has been shown to be the consequence of heavy nile river summer floods due to increased monsoonal summer precipitation over ethiopia and not of scandinavian ice sheet meltwater influx into the east mediterranean sea as was previously believed while most sapropels were deposited during interglacials two thick sapropels formed during glacial periods as shown by their position in the oxygen isotopic stratigraphy and by their pollen record in core rc9 181 the new evidence presented here is that the sapropel sequence in this core including the two glacial sapropels correlates on a one to one basis with the highest values of an index of insolation on top of the atmosphere the concept of this index derives from an analysis of the african monsoon process the index variation is computed for the last 465 000 years from the caloric northern summer insolation in the tropical latitudes controlled by variations of the earth s orbital parameters it is conjectured that this index might be linked through the climate system to the monsoonal precipitation which in africa produces the nile river summer flood

glacial to interglacial fluctuations in productivity in the equatorial pacific as indicated by marine barite an empirical correlation between marine barite baso4 accumulation rate in core top sediment samples from two equatorial pacific transects at 140 w and 110 w and the estimated primary productivity of the overlying water column were used to evaluate glacial to interglacial changes in productivity fluctuations in barite accumulation rates down core indicate that during glacial periods of the past 450 000 years the productivity in the central and eastern equatorial pacific was about two times that during intervening interglacial periods this result is consistent with other evidence that productivity was high in the eastern and central equatorial pacific during the last glacial