mediterranean planktonic foraminiferal faunas during the last glacial cycle this paper highlights the planktonic foraminiferal abundance variations during the last glacial cycle from six new cores along a roughly west east transect in the mediterranean sea together with results from previous studies multivariate statistical analysis describes a first significant axis that indicates a general sea surface temperature sst gradient from west to east as expected lower sst values are recorded in glacial times but the eastern and western basins seem to have reacted differently to glacial conditions the western basin shows a sst decrease from the alboran sea to the central mediterranean whereas the eastern basin records a west to east increase that is similar to the present day eastern mediterranean gradient these new results show that 1 few almost basin wide faunal trends may be recognised but these are interrupted by local anomalies with opposing trends and 2 major abundance variations are distinctly diachronous in some species and virtually synchronous in others the implication is that over the glacial interglacial timescale concerned biostratigraphy should only be used on a local rather than basin wide scale unless it is supported by other independent dating methods

chemical element imaging for speleothem geochemistry application to a uranium bearing corallite with aragonite diagenesis to opal eastern siberia russia abstract two complementary image based microanalysis methods digital autoradiography of radioactive elements and x ray fluorescence microspectroscopy micro xrf were used to study the geochemistry of a speleothem from eastern siberia our objective was to show the interest of these micro chemical methods to investigate the distribution of u and some other elements as ca sr and si in speleothems the sample studied was a corallite concretion that formed slowly by the precipitation of minerals from moisture that had condensed underground polished sections of the sample revealed alternating laminas of gray calcite and white aragonite the concretion which is older than 400 kyr u th tims showed no signs of detrital contamination 230 th 232 th 10 000 digital autoradiography and xrf analyses indicated exceptionally high uranium contents ranging from 3 10 to more than 1300 g g 1 in different areas of the sample element maps for calcium ca uranium u strontium sr and silicon si showed inverse correlations between ca and u and between ca and si but there is a strong correlation between si and u under the optical microscope the low ca appears as corrosion voids which were found to contain uranium enriched amorphous silica replacing areas of aragonite and in some cases calcite this postgenetic amorphous and uraniferous silica is composed of two kinds of opal opal a formed by large microspheres of 30 40 m in diameter and a gray opal ct with irregular lepispheres this late opal dated around 385 412 kyr is probably due to a special volcanic event formed by uraniferous glass ashes easily soluble by meteoric waters as suggested by the presence of volcanic suite in the fine fraction of the opal opal precipitated after speleothem crystallization by evaporation or cryogenic supersaturation the study of this exceptional concretion shows the value of direct chemical imaging methods as they easily revealed the presence and distribution of u in the concretion and allowed an unusual case of opal diagenesis in a carbonate speleothem to be described given the value of speleothems as geo chronometers and recorders of environmental changes at different time scales from season to isotopic stage this methodology opens new perspectives in understanding the geochemical system and consequently the validity of radiometric datings u th and u pb especially in speleothem samples

crustal thickness in antarctica from champ gravimetry abstract champ flying at an altitude of about 400 km is the first of a new generation of satellites dedicated to earth gravity field observation the high quality data have generated new gravity field models eigen 1s in 2001 and eigen 2s more recently the gravitational potential is decomposed into spherical harmonic coefficients and in this study we use the free air gravity anomalies reconstituted up to degree 60 at zero altitude the anomalies for the antarctic continent range from 57 to 65 mgal we have modeled the gravity effect from the ice the ocean and the bedrock using a 666 km cut off filter to simulate the resolution obtained by champ computing the differences between this terrain effect and the champ map provides a map of the bouguer anomalies because of the dominant influence of the crust we first used a crustal thickness model from seismology this gives a map of the mantle bouguer anomalies the range of which is still large between 255 and 216 mgal indicating imperfections in the crust model by appealing to isostasy we then imposed the condition that this mantle bouguer anomaly should vanish and therefore solve for a new resulting crustal thickness this gravity based crust model gives thicknesses from 8 5 to 42 6 km in the zone of interest there is a good general agreement with seismological models but our models shows more detail particularly in the western part of the continent these details are in agreement with geological studies

evidence of sapropel s1 formation from holocene lacustrine sequences in lake vrana in dalmatia croatia abstract the sediment core from lake vrana between 1000 and 500 cm on the eastern adriatic coast was analyzed using palynological and geochemical approaches to detect environmental changes during the holocene the deepest sediments between 1000 and 967 cm in lake vrana could correspond to late pleistocene to holocene transition although this interval is not dated it is indicated by the palynological record after that the holocene warming is evident and the observed dark layers are identified as holocene sapropel s1 known in the eastern mediterranean 10 8 6 1 cal kyr bp sapropelic layer s1a in lake vrana sediment core is evident between 905 and 790 cm and it ended at 7 9 cal kyr bp it is formed in a very shallow freshwater ecosystem dominated by cyanobacteria gleocapsa and terrigenous detritus as a consequence of runoff periodically anoxic condition occurred the geochemical signature of sapropelic layer s1a from lake vrana is consistent with post depositional oxidation due to transition to the bottom water oxygenation evidenced in elevated mn and mn peak at the end of sapropelic layer s1a deposition sapropelic layer s1b deposited between 7 4 and 6 4 cal kyr bp is characterized by amorphous organic matter the two sapropelic layers are separated by the horizon at 7 9 7 4 cal kyr bp corresponding to the drier climate conditions indicated by the presence of poaceae ericaceae juniperus and pistacia this horizon reflects regional climatic cooling associated with reduced levels of precipitation that interrupted a period of generally higher precipitation based on geochemical data total organic carbon toc and nitrogen n the sapropelic layers are characterized by elevated values comparing to the rest of the core the new records allow reconstruction of paleoenvironmental changes on land which give insight into the processes and climate conditions that led to the formation of s1 the evidence indicates that i s1 sapropelic layer in lake vrana sediments is an organic poor deposit ii the s1 period in the study area can be divisible into two sub phases s1a and s1b the key factor that initiated the formation of s1 was increased discharge of freshwater into the lake vrana basin during warmer and wetter climate in the early holocene

evidence of 550 year and 1000 year cyclicities in north atlantic circulation patterns during the holocene sedimentological colour data obtained from north atlantic deep sea sediment core neap15k pro vide a continuous climate record for the last 11500 yr with a mean sampling interval of 15 yr variations in sediment lightness a proxy for changes in north atlantic deep water nadw circulation are characterized by high frequency fluctuations with periodicities equivalent to 550 and 1000 yr as well as a 1600 yr cyclicity comparable to that reported in other studies of holocene climate cross spectral analysis suggests that the 550 yr and 1000 yr cyclical variations in nadw circulation were coherent with fluctuations in atmospheric con ditions over greenland where both these periodicities have been identified previously in the holocene gisp2 d18o record stuiver et al 1995 a similar statistical comparison provides evidence that high frequency 550 yr variability in nadw circulation patterns may have been linked to short term variations in atmospheric 14c values during the holocene in general nadw pro

eastern turkish high plateau as a small turkic type orogen implications for post collisional crust forming processes in turkic type orogens abstract post collisional magmatism may be generated by extensive crustal melting in tibet type collisional environments or by falling out of slabs from under giant subduction accretion complexes in turkic type collisional orogens giving rise to decompression melting of the asthenospheric mantle replacing the removed oceanic lithosphere in turkic type post collisional magmatism the magmatic products are dominantly alkalic to peralkalic and greatly resemble those of extensional regions giving rise to much confusion especially in interpreting old collisional orogenic belts such magmatic regions are also host to a variety of economically valuable ore deposits including gold one place in the world where today active turkic type post collisional magmatism is present is the eastern anatolian high plateau produced after the terminal arabia eurasia collision in the late miocene the plateau is mostly underlain by the late cretaceous to oligocene east anatolian accretionary complex which formed south of the rhodope pontide magmatic arc this subduction accretion complex has been further shortening since the collision but it has also since been domed and became almost entirely covered by at least 15 000 km3 of volcanic rocks the volcanic rocks are calc alkalic in the north transitional in the middle and alkalic in the south of the plateau where the crust is thinnest today less than 38 km the volcanics are derived almost entirely from an enriched mantle the ages of the volcanics also become younger from north to south from about 11 ma to possibly 17th century ad we interpret the origin of the magmatic rocks as the result of decompression melting of the asthenospheric mantle sucked towards the exposed base of the east anatolian accretionary complex as the oceanic lithosphere beneath it fell out the lower density of the hot asthospheric material was the cause of the doming we believe that similar processes dominated the post collisional tectonics of such vast turkic type orogens as the altaids of central asia the late devonian early carboniferous lachlan belt in southeastern australia and the pan african collage of northeast afro arabia it is likely that archaean collisions were dominated by turkic type post collisional events rather than tibetan ones that only became common in the proterozoic

northern levantine and adriatic quaternary planktic foraminifera reconstruction of paleoenvironmental gradients rohling e j jorissen f j vergnaud grazzini c and zachariasse w j 1993 northern levantine and adriatic quaternary planktic foraminifera reconstruction of paleoenvironmental gradients mar micropaleontol 21 191 218 a detailed study of the planktic foraminiferal records of three cores recovered near crete shows very consistent changes unfortunately the record of t87 2 13g our shallowest core is bioturbated too much for detailed comparisons but it can still be used to discuss the general trends the mutual record of the other two cores t87 2 20g and t87 2 27g extends back to about 125 000 yr b p principal components analyses performed on the combined records of t87 2 20g and t87 2 27g yield two axes that can be interpreted paleoecologically namely a temperature axis and an annual stability axis the latter is a measure of stratification within the euphoric layer in this study we consider t87 2 20g and t87 2 27g to be reference cores for the eastern mediterranean subsequently we interprete the faunal variation in two cores from the adriatic sea in 68 5 and in 68 9 containing records extending back to 15 000 and 18 000 yr b p in the context of these reference cores this is done by calculating scores of the adriatic records along the two relevant pca axes derived from the northern levantine records also cluster analyses of the adriatic and northern levantine records are compared on the average the adriatic sea appears to have been considerably colder than the region around crete during the past 18 000 years this temperature difference was largest during the pleniglacial and only small during the holocene we found no distinct expression of a younger dryas cooling event in the adriatic records neither on our pca axis nor in the oxygen isotope record this contradicts previous paleoclimatic reconstructions based mainly on paleobotanical evidence which suggests that the younger dryas event greatly influenced circum mediterranean areas as yet we have no ready explanation for this discrepancy low annual stability values dominate both the pleniglacial and the holocene intervals of the adriatic records this suggests that homothermal conditions were as prevalent in the adriatic euphoric layer at pleniglacial times as they are at present in the present day adriatic homothermal conditions are associated with deep convection and subsequent eastern mediterranean deep water emdw formation and therefore our data suggest that emdw formation was as effective at pleniglacial times as it is at present high annual stability values in the transitional interval from 12 700 to 9600 yr b p in the adriatic records are suggestive of low emdw formation rates at that time in combination with high productivity throughout the eastern mediterranean which has previously been inferred from the planktic foraminiferal record these low emdw formation rates may have preconditioned the eastern mediterranean for sapropel formation

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

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

controls on phosphorus regeneration and burial during formation of eastern mediterranean sapropels the carbon c and phosphorus p geochemistry of sapropels from four sites in the eastern mediterranean sea was determined to obtain more insight into the role of differences in sediment accumulation rates and bottom water anoxia on p regeneration and burial in sediments sediment corg porg with org organic ratios above redfield indicate enhanced regeneration of p relative to c from organic matter during formation of the most recent sapropel s1 and a pliocene sapropel odp site 969e i 282c release of p from fe oxides was relatively unimportant increased burial of ca p authigenic carbonate fluorapatite and or biogenic hydroxyapatite occurred but was of minor importance compared to the enhanced p release from organic matter for sapropel s1 corg porg and corg preac with reac reactive defined as the sum of organic fe bound authigenic and biogenic ca p ratios decreased with increasing sedimentation rate and oxygen exposure and decreasing water depth whether the water column in the deep basin was dysoxic semi euxinic s1 or euxinic pliocene does not appear to affect the estimated burial efficiencies of porg and preac enhanced corg burial under the euxinic water column explains the much higher corg porg and corg preac ratios in the pliocene sapropel on average 2860 and 760 respectively compared to sapropel s1 on average 530 and 160 respectively

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

recent results on modelling the spatial and temporal structure of the earth s gravity field the earth s gravity field plays a central role in sea level change in the simplest application a precise gravity field will enable oceanographers to capitalize fully on the altimetric datasets collected over the past decade or more by providing a geoid from which absolute sea level topography can be recovered however the concept of a static gravity field is now redundant as we can observe temporal variability in the geoid due to mass redistribution in or on the total earth system temporal variability associated with interactions between the land oceans and atmosphere can be investigated through mass redistributions with for example flow of water from the land being balanced by an increase in ocean mass furthermore as ocean transport is an important contributor to the mass redistribution the time varying gravity field can also be used to validate global ocean circulation models this paper will review the recent history of static and temporal gravity field recovery from the 1980s to the present day in particular mention will be made of the role of satellite laser ranging and other space tracking techniques satellite altimetry and in situ gravity which formed the basis of gravity field determination until the last few years with the launch of challenging microsatellite payload and gravity and circulation experiment grace our knowledge of the spatial distribution of the earth s gravity field is taking a leap forward furthermore grace is now providing insight into temporal variability through monthly gravity field solutions prior to this data we relied on satellite tracking global positioning system and geophysical models to give us insight into the temporal variability we will consider results from these methodologies and compare them to preliminary results from the grace mission

dysaerobic conditions during heinrich events 4 and 5 evidence from phosphorus distribution in a north atlantic deep sea core abstract reactive phosphorus undergoes diagenetic transformation once transferred into marine sediments the degree of regeneration and redistribution of phosphorus depends on early diagenetic and environmental conditions which may be linked to larger scale phenomena such as bottom water circulation water column ventilation and organic carbon flux phosphorus phases of the

impact of the circulation on sapropel formation in the eastern mediterranean the role of the thermohaline circulation in controlling export production oxygenation of deep waters and hence possible sapropel formation in the eastern mediterranean is examined using a simple nutrient cycling model the model is driven by velocity fields from a general circulation model and receives fluxes of nutrient from river run off and atmospheric deposition the model is used to study three scenarios a strong anti estuarine circulation a weakened anti estuarine circulation and a weak estuarine circulation nutrient transports ventilation of oxygen and deposition of organic matter are investigated in each case with a present day circulation the model provides reasonable agreement with observed phosphate and oxygen profiles and for export production with the weakened anti estuarine circulation consistent with surface salinity reconstructions for the most recent sapropel s1 there is a modest increase in export production and reduced ventilation leading to anoxia in intermediate and deep waters sapropel formation is possible near the coastal margins particularly if there is enhanced river run off with an estuarine circulation there is significant increase in export production in addition to anoxia below a shallow winter mixed layer while both the latter circulations allow sapropel formation in the model the estuarine case is distinguished by higher organic carbon deposition and anoxia in the near surface waters

a new global earth s gravity field model from satellite orbit perturbations grim5 s1 a new model of the earth s gravity field called grim5 s1 was prepared in a joint german french effort the solution is based on satellite orbit perturbation analysis and exploits tracking data from 21 satellites to solve simultaneously for the gravitational and ocean tide potential and tracking station positions the satellite only solution results in a homogeneous representation of the geoid with an approximation error of about 45 cm in terms of 5 5 degree block mean values and performs globally better in satellite orbit restitution than any previous gravity field model the grim5 normals which were generated taking into account the latest computational standards shall be the reference for use during the coming geopotential satellite mission champ and should provide new standards in computing orbits of next altimetric missions like jason and envisat the grim5 s1 normals also give the basis for the tracking surface data combined solution grim5 c1

the marine phosphorus cycle phosphorus introduced to the ocean must ultimately be removed if a steady state is to be maintained over geologic time aeolian input is insignificant and there is evidently no hydrothermal contribution rivers dominate p input to the ocean the fluvial p flux is poorly quantified due to the interactions of two factors 1 man s influence on river nutrient fluxes and 2 inherent complexities in understanding the biological and inorganic associations of p in estuarine and coastal waters our best estimate of the natural or pre man p input flux is about 10 x 10 sup 9 moles p cm sup 2 ocean surface year of the identified flux of phosphorus to the sediments about 90 percent is in the form of biogenic debris or its regeneration products the burial of phosphatic fish debris is negligible p removal by direct reaction of phosphate in seawater with sea floor basalts during mid ocean ridge hydrothermal circulation is insignificant p removal by processes such as sorption on clay surfaces or formation of authigenic fe and al phosphate phases is presently unquantified and remains a serious uncertainty in the phosphorus cycle the identified sources and sinks approximately balance yielding a residence time for p in the oceans of about 10 sup 5 yrs

sedimentary phosphorus record from the oman margin new evidence of high productivity during glacial periods 1 the northern region of the arabian sea is one of the biologically most fertile regions of the world oceans with present productivity rates varying between 150 and 2500 mgc m2 day madhupratap et al 1996 this is related to the influence of the southwesterly summer monsoon which causes vigorous upwelling along the oman margin upwelling ceases during northeasterly winter monsoon activity productivity rates however remain relatively high about 800 mgc m2 day related to deep water mixing madhupratap et al 1996 the goal of this study is to verify if during the last glacial period a period in which winter monsoon conditions prevailed productivity rates were similarly high with an analysis of phosphorus phases stable nitrogen isotopes organic matter content and bulk mineralogy of the upper 10 m of the cores of odp hole 724c corresponding to the last 140 000 years sample resolution is 5 kyr we provide new evidence of high productivity during this last glacial period marine isotopic stages 2 3 and 4 this was probably related to the combined effect of 1 increased eolian input of iron containing dust due to dryness on the adjacent continent and stronger winter monsoon and 2 regeneration and diffusion of dissolved phosphorus from the sediments to the water column due to variations in the position and intensity of the oxygen minimum zone these findings suggest that there is no one to one relationship between summer monsoon activity and productivity which emerges to be a quasi persistent phenomenon across glacial and interglacial stages

sedimentary organic carbon to phosphorus ratios as a redox proxy in quaternary records from the mediterranean abstract in this study organic carbon to organic phosphorus c org p org and total phosphorus c org p tot ratios as bottom water redox proxies are explored for two eastern mediterranean sediment records extending back 600 700 kyrs cores kc19c 19 6 m long 2750 m water depth and kc01b 37 0 m long 3643 m water depth contain numerous organic rich layers sapropels throughout the two cores variations found in the c org p ratios correspond to those for other redox proxies such as total s contents and v al ratios accordingly these are interpreted as variations in bottom water oxygenation and inter sapropel redox variability in core kc19c the original c org p signals seem to have been preserved despite intense post depositional sulfidization high resolution p fractionation data of sapropel s5 from a third core ps25pc 3304 m water depth showing high and relatively stable c org p org ratios indicate that sapropel s5 at this deep location was deposited under permanently reducing conditions while p regeneration from organic matter was intense net p burial increased in the sapropel due to enhanced burial of inorganic calcium phosphate likely biogenic ca p sediment p contents and c org p tot ratios in s5 are variable reflecting short term changes in marine conditions productivity redox and sediment chemistry the c org p org and c org p tot ratios thus provide valuable insight into paleoceanographic conditions and pathways of p cycling for mediterranean sediment records extending back at least 600 700 kyrs

testing solar forcing of pervasive holocene climate cycles the temporal and spatial extent of holocene climate change is an area of considerable uncertainty with solar forcing recently proposed to be the origin of cycles identified in the north atlantic region to address these issues we have developed an annually resolved record of changes in irish bog tree populations over the last 7468 years which together with radiocarbon dated bog and lake edge populations extend the dataset back to 9000 yr ago the irish trees underpin the internationally accepted radiocarbon calibration curve used to derive a proxy of solar activity and allow us to test solar forcing of holocene climate change tree populations and age structures provide unambiguous evidence of major shifts in holocene surface moisture with a dominant cyclicity of 800 yr similar to marine cycles in the north atlantic indicating significant changes in the latitude and intensity of zonal atmospheric circulation across the region the cycles however are not coherent with changes in solar activity both being on the same absolute timescale indicating that holocene north atlantic climate variability at the millennial and centennial scale is not driven by a linear response to changes in solar activity copyright 2005 john wiley sons ltd

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

field based validation of a diagenetic effect on g ruber mg ca paleothermometry core top results from the aegean sea eastern mediterranean recent work across the mediterranean sea has illustrated the salinity and overgrowth effects on planktonic foraminiferal mg ca which potentially confound the use of this as a temperature proxy for paleoceanographic reconstructions to test and verify these effects we present new aegean sea results which reveal mg ca values that were unreasonably high to be explained by temperature or salinity variations alone confirming that foraminiferal mg ca is affected by diagenesis we have specifically targeted globigerinoides ruber w sensu stricto from a series of modern core tops spanning a strong sea surface salinity gradient and a minor sea surface temperature range along a north south aegean sea transect scanning electron microscopy analyses show that g ruber specimens were covered by microscale euhedral crystallites of inorganic precipitates this secondary calcite phase seems to be responsible for the anomalously high mg ca ratios and likely formed near the sediment water interface from caco3 supersaturated interstitial seawater we also have clear evidence of diagenetic alteration in a north south direction along the aegean sea possibly depending on salinity and calcite saturation state gradients these observations illustrate the necessity of alternative techniques e g flow through time resolved analysis or laser ablation inductively coupled plasma mass spectrometry to potentially overcome these diagenetic issues and develop a more reliable and sensitive temperature proxy in similar subtropical settings characterized by high salinity excessive evaporation and restricted circulation

simulations of ecosystem response during the sapropel s1 deposition event abstract a one dimensional ecosystem numerical model is used to simulate the ecosystem changes that could have occurred in the open ocean areas of the eastern mediterranean sea during the climatic optimum interval 9500 6000 b p mercone et al mercone d thomson j croudace i w siani g paterne m troelstra s 2000 duration of s1 the most recent sapropel in the eastern mediterranean sea as indicated by accelerator mass spectrometry radiocarbon and geochemical evidence paleoceanography 15 336 347 in this period the s1 sapropel was deposited s1 is the most recent sapropel in the succession of organic carbon rich layers intercalated in normal neogene sedimentary sequences different theories have been invoked in order to explain the deposition of this peculiar layer our simulations seem to indicate that the modified thermohaline circulation supplying oxygen only in the first 500 m of the water column is responsible for the sapropel deposition when higher productivity is allowed in the euphotic zone the model shows the importance in this process of bacteria that consume oxygen by decomposing the particulate organic matter pom produced in the upper water column the sinking velocity of pom partially regulates the timescale of the occurrence of anoxia at the bottom and in the whole water column allowing the relatively rapid onset of sapropel deposition

review of recent advances in the interpretation of eastern mediterranean sapropel s1 from geochemical evidence abstract the sediments of the eastern mediterranean basin contain c org enriched layers sapropels interbedded with the c org poor sediments which form by far the greater part of the record while it is generally appreciated that different surface ocean productivity and bottom water conditions are necessary for the formation and preservation of these two sediment types less attention has been paid to diagenetic effects which are an expected consequence of transitions between dramatically different bottom water oxygenation levels a geochemical interpretation has emerged of post depositional oxidation of the most recent sapropel s1 initially based on the relationship of the mn fe c org and s concentration depth profiles observed around s1 and the characteristic shapes of these elemental profiles known from other situations this indicates that post depositional oxidation has removed approximately half of the visual evidence of the sapropel 6 cm from a total of 12 cm in the deep basin the oxidation interpretation from redox sensitive element redistribution profiles has subsequently been consolidated with evidence from pore water o 2 no 3 mn 2 and fe 2 studies from characteristic solid phase ba profiles which yield palaeoproductivity records and from oxidation sensitive indicator trace elements i and se so far these geochemical observations have been concentrated in the deeper central parts of the basin where sediment accumulation rates are lower than on the basin margins and radiocarbon dating indicates that s1 formation occurred between 5 3 and 9 0 ky uncorrected conventional radiocarbon time it remains to be demonstrated whether or not these times are applicable to the entire e mediterranean basin the implications of these findings to guide sampling in future work on the s1 productivity episode and on older sapropels for palaeoenvironmental investigations are discussed

the nsuze group pongola sequence south africa geochemical evidence for archaean volcanism in a continental setting abstract the archaean nsuze group in southeast south africa represents an important volcano sedimentary succession that is markedly different compositionally and lithologically from older and contemporaneous sequences elsewhere in southern africa the nsuze volcanic rocks cropping out in the vicinity of the pongola river in northern natal display a complete spectrum of chemical compositions from basalt to rhyolite with lavas of intermediate compositions predominant but ultramafic lavas absent flows of different compositions are complexly interdigitated the uppermost rocks of the nsuze group reflect a gradual decrease in volcanic activity accompanied by an increase in sedimentation the nsuze lavas are tholeiitic with total fe as fe 2 o 3 contents approaching 17 in the basaltic andesites all lithologies are characterized by moderate to strong light rare earth element ree enrichment heavy ree slopes range from moderate in the basalts and basaltic andesites to flat in the rhyolites with the exception of two basaltic andesites and a dacite which have flat heavy ree slopes basalts have small or no negative eu anomalies but increasingly larger negative anomalies are a feature of the intermediate and acid lavas variations in cr content appear to be related to stratigraphic position basalts and basaltic andesites in the lower part of the volcanic sequence have higher cr contents by a factor of six to eight times than lavas with similar mgo abundances in the upper part of the sequence provisional modelling of the available chemical data favours low pressure crystal fractionation from and evolved basaltic parent that could be derived by initial non modal melting of a garnet lherzolite source variable degrees of crustal contamination of the evolved magmas are considered probable

origin and transformation of organic matter in pliocene pleistocene mediterranean sapropels organic geochemical evidence reviewed abstract drilling of deep water post messinian sedimentary sequences by odp legs 160 and 161 in the mediterranean sea has shown that occurrence of organic carbon rich sapropels and sapropel like sediments extends from the levantine basin westward into the alboran basin in the eastern mediterranean sapropel deposition started in the early pliocene whereas in the western basin the onset of sapropel formation occurred later in the early pleistocene precessional cycles are apparently the primary external forcing for sapropel formation nevertheless the pattern of sapropel occurrence suggests that the precessional influence is modulated by the glaciation cycles large differences were observed in the organic carbon contents of sapropels recovered in the eastern and western mediterranean correspondence between organic carbon contents rock eval hydrogen index values and elemental c n ratios indicate that both variations in the production and preservation of marine organic matter have led to the accumulation of high amounts of organic matter in sapropels molecular organic geochemical compositions of sapropels from the eastern mediterranean further confirm that the major fraction of organic matter in sapropels is derived from marine algal sources and has undergone variable oxidation enhanced marine productivity and improved preservation of organic matter is central to sapropel formation accumulation of increased amounts of land derived material at times of sapropel formation is also evidenced supporting the hypothesis of significant periodic freshwater discharges

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

tectonic controls on tholeiitic and calc alkaline magmatism in the aleutian arc the tectonic position of aleutian arc volcanic centers and their magmatic differentiation trends calc alkaline or tholeiitic appear to correlate from 160 w to 175 e the volcanoes form four major arc segments that coincide with earthquake aftershock zones and major geographic features on both the upper and lower plates the tholeiitic volcanoes are large primarily basaltic centers that occur between or at the end of segments where magmas can more easily reach the surface and undergo shallow closed system differentiation the calc alkaline volcanoes are smaller more andesitic centers that occur in the middle of segments where transit through the upper plate is apparently more difficult differentiation is deeper and the intrusive to extrusive ratios are higher than in the tholeiitic centers the chemistry of the least differentiated basalts at both types of centers is similar and suggests a common parent magma probably derived from mantle peridotite conditions for the derivation of the two trends through crystal fractionation support the proposed model the tholeiitic magmas show characteristics i e no hydrous phenocrysts fe enrichment trend parallel ree patterns vitrophyric and esites and dacites consistent with low pressure high temperature crystallization in large shallow magma chambers the calc alkaline magmas show characteristics i e some hydrous phenocrysts no fe enrichment trend nonparallel rare earth patterns porphyritic lavas consistent with higher pressure and lower temperature of crystallization than the tholeiitic series tertiary plutons also show both calc alkaline and tholeiitic trends and appear to be chemically similar to the quaternary volcanoes the larger plutons are calc alkaline and probably represent the extensive 1002 km magma chambers of the small calc alkaline volcanoes the small shallow tholeiitic plutons complement the large tholeiitic volcanoes and reflect the greater percent of extrusive rocks in the tholeiitic series

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

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

enhanced regeneration of phosphorus during formation of the most recent eastern mediterranean sapropel s1 phosphorus regeneration and burial fluxes during and after formation of the most recent sapropel s1 were determined for two deep basin low sedimentation sites in the eastern mediterranean sea organic c p ratios and burial fluxes indicate enhanced regeneration of p relative to c during deposition of sapropel s1 this is largely due to the enhanced release of p from organic matter during sulfate reduction release of p from fe bound p also increased but this was only a relatively minor source of dissolved p pore water hpo4 concentrations remained too low for carbonate fluorapatite formation an increased burial of biogenic ca p i e fish debris was observed for one site estimated benthic fluxes of p during sapropel formation were elevated relative to the present day 900 to 2800 vs 70 to 120 mol m 2 yr 1 the present day sedimentary p cycle in the deep basin sediments is characterized by two major zones of reaction 1 the zone near the sediment water interface where substantial release of hpo4 from organic matter takes place and 2 the oxidation front at the top of the s1 where upward diffusing hpo4 from below the sapropel is sorbed to fe oxides the efficiency of aerobic organisms in retaining p is reflected in the low organic c p ratios in the oxidized part of the sapropel burial efficiencies for reactive p were significantly lower during s1 times compared with the present day 7 to 15 vs 64 to 77 budget calculations for the eastern mediterranean sea demonstrate that the weakening of the antiestuarine circulation and the enhanced regeneration of p both contributed to a significant increase in deep water hpo 4 concentrations during sapropel s1 times provided that sufficient vertical mixing occurred enhanced regeneration of p at the seafloor may have played a key role in maintaining increased productivity during sapropel s1 formation copyright 2002 elsevier science ltd

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

a spectral assessment review of current satellite only and combined earth gravity models 1 the realization over the last decade of dedicated gravity field satellite missions enabled the production of a series of new satellite only and combined models for the earth s gravity field using different sensors measurement techniques and algorithmic procedures the final product in each case is a set of spherical harmonic coefficients representing the series expansion of the gravitational potential up to a certain maximum degree depending on the mission characteristics and the range of the available data the present review performs a detailed quantified analysis of a representative selection of currently available champ challenging minisatellite payload grace gravity recovery and climate experiment goce gravity field and steady state ocean circulation explorer and combined earth gravity models in this comparative analysis we also include the so called topographic isostatic gravity models that represent the contribution of global digital elevation maps for the topography and ocean bathymetry applying a range of available spatial and spectral accuracy and assessment measures such as correlation per degree and order smoothing per degree and order signal to noise ratio gain degree variances and error degree variances one gains a quantified peek inside the quality of these models spanning over their whole spectrum the applied error and assessment measures are defined both in an absolute and relative manner with respect to other similar models or some reference earth gravity models furthermore the nature of the performed analysis degree wise order wise and cumulative permits the identification of distinct spectral bandwidths in these models enables the quantification of some standard features of the observed field such as its long wavelength short wavelength or very high frequency part and specifies the attenuation of the gravity signal with increasing altitude from the earth s surface an examination of the assessment quantities reveals certain bandwidths of these models with characteristic statistical features a band limited synthesis of these bandwidths in the space domain quantifies the corresponding contributions in terms of selected gravity field functionals including second order derivatives at goce altitude

some thermal problems associated with magma migration abstract the mechanisms by which magma migrates from the point in the earth s interior where melting occurs to the earth s surface are poorly understood in this paper several aspects of this problem are examined magma can migrate upward due to its differential buoyancy on the scale of crystalline grains or as large dispairs magma transport is an effective means of heat transport magma transport at a rate of 0 15 cm yr is equivalent to a heat flow of 10 6 cal cm 2 s if magma encounters country rock witha lower melting point the original magma is likely to solidify while melting the country rock this would be an effective mechanism of purging silicic rocks and incomparable elements from the lower crust under some circumstances magma must penetrate up to 100 km or more of cold lithospheric rock in order for this magma to reach the surface without solidification a heated path must be provided the heating of this path requires the solidification of some magma it is estimated that magma penetrates the lithosphere in about 5000 years and that the crack is lined by several hundred meters of frozen basalt

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

late pleistocene holocene sedimentation in the nw aegean sea a palaeoclimatic palaeoceanographic reconstruction sedimentological particle size organic carbon calcium carbonate clay mineralogy and radiocarbon dating and micropalaeontological investigation of 9 cores from the nw aegean sea eastern mediterranean have enabled five main lithological units to be identified the units cover a period from the late pleistocene to the present day on the basis of these results and reference to other studies a palaeo reconstruction is presented for the area the reconstruction takes into account the increase in sea level during the period the decrease in fluvial inputs issuing to the area from the north mediterranean coastline and the possible influence of water issuing from the black sea it is concluded that the sedimentological and oceanographic regimes of the area were strongly influenced by a fluvial component during the late pleistocene and early holocene whereas today the sedimentary record is more indicative of an open oceanic environment

organic carbon accumulation in bannock basin evaluating the role of productivity in the formation of eastern mediterranean sapropels abstract three sediment cores from bannock basin a hypersaline anoxic basin in the eastern mediterranean have been studied to evaluate the importance of productivity on organic carbon accumulation and sapropel formation in this region organic carbon accumulation rates were determined for two cores from within the anoxic hypersaline zone and for one core from the oxygenated portion of this basin organic carbon accumulation rates are higher by an order of magnitude in the surficial sediments of the anoxic zone due to better preservation an empirically derived preservation factor which allows calculation of paleoproductivity during the deposition of the most recent sapropel si indicates that productivity increased by an order of magnitude during the formation of si we conclude that increased productivity was coupled with a density stratification and a circulation reversal in the eastern mediterranean which together led to sapropel formation

a dynamic concept for eastern mediterranean circulation and oxygenation during sapropel formation we propose that intermittent bottom water ventilation occurred throughout periods of sapropel deposition and that the recently reported sapropel interruptions represent centennial scale episodes of enhanced frequency intensity of that process in essence the modern high frequency variability in deep water formation affected by climatic variability over the northern basins on seasonal to longer time scales prevailed also at times of sapropel deposition although the overall ventilation state was much reduced this concept is supported by detailed multiple species isotope records for three aegean cores the presence of abundant globorotalia truncatulinoides within especially sapropels s7 and s8 in the western levantine basin observations of three rapid benthic repopulations within sapropel s6 in the deep western levantine basin a report of continuous benthic presence through sapropel s1 at intermediate deep locations offshore libya and further supporting information from the literature in the aegean records concomitant abundance of low oxygen tolerant benthic foraminifera and presence of the more oxyphilic benthic foraminifer uvigerina mediterranea with surface similar 13c values indicate repeated deep water re oxygenation events throughout the deposition of s1 the observations of a continuous benthic presence through s1 offshore from libya imply that no persistent anoxia developed at mid depth levels in that region which is far removed from direct deep ventilation influences the abundance of deep mesopelagic g truncatulinoides through several sapropels from the western levantine basin also suggests the presence of bio available oxygen at many hundreds of meters of depth moreover the rapid intermittent benthic repopulations within sapropels from the deep eastern mediterranean imply that bottom water anoxia was spatially restricted and or of a highly intermittent nature the short time scales of these repopulation events are incompatible with titration of an extensively anoxic water column and subsequent re establishment of water column anoxia we suggest that where anoxic azoic conditions were present they most likely were restricted to a veneer at the sediment water interface the extent of such an anoxic blanket depends on the balance between advective oxygen supply into the deep sea and biological and chemical oxygen demand the demand functions imply a decoupling of oxygenation from water mass advection allowing export production and corg posting rates to the sea floor to delimit the extent of the anoxic blanket in both space and time low productivity regions would develop no anoxic blanket allowing for the observed persistence of deep dwelling planktonic and bottom dwelling benthic faunas

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

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

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

organic carbon variations of the eastern mediterranean holocene sapropel a key for understanding formation processes abstract this work reports on the organic carbon content of the s1 holocene sapropel the youngest and most extensively researched of the eastern mediterranean sapropels the peak organic carbon percentage of the s1 sapropel varies between 1 2 and 3 4 at varying locations these variations could not be correlated with sapropel thickness or with spatial location in contrast there was a close linear correlation with water depth the deeper samples containing the highest values of organic carbon within the s1 layer the highest values were found in the top of the sapropel even if primary productivity increased during the s1 sapropelic period the main factors responsible for sapropel deposition were changes in the degradation and preservation of organic matter in the water column and at the sediment water interface water column stratification created an oxygenated surficial layer 0 350 400 m thick and a stagnant deep water layer the majority of the organic material escaping the surficial layer was remineralised either at the sediment water interface or just below it organic matter preserved in sapropelic sediments can be assumed to have remained for a significantly longer time 1000 years within the benthic boundary layer than in the water column organic flux decreased with depth through the stagnant deep water layer when stagnation was established water exchanges either did not exist or were limited vertical oxidant transport depended on eddy diffusion while oxidant fluxes at the sediment water interface decreased with depth the organic matter mineralisation rate also decreased and the burial efficiency increased the linear relationship between sapropel organic content and depth was reflected in a linear decrease in oxidant flux regardless of location the same organic carbon percentage was preserved at the same depth in contrast in the same area but at different depths organic carbon content ranges between 1 2 and 3 4 this observation suggests that primary productivity was of the same order of magnitude basinwide the organic carbon concentration of sediment should be used with caution as a quantitative record of palaeoproductivity

organic carbon distribution and isotopic composition in three records from the eastern mediterranean sea during the holocene we investigated the distribution of organic carbon toc and bulk organic 13 c org values in two cores from the aegean sea and one from the libyan sea eastern mediterranean sea ems with a focus on the timing and regional expression of sapropel s 1 deposition in the early holocene our data indicate that the onset of s 1 occurred earlier in the libyan sea 9 8 kyr bp than in the aegean sea 8 9 kyr bp implying that dysoxia anoxia started earlier in the deeper sites of the ems than in the shallower sites in the aegean sea accumulation rates of organic matter om during the s 1 period have a clear decreasing gradient from north to south with higher values in the aegean sea and toc contents higher in the deep basin the three sedimentary sequences exhibit 13 c org values that fall within the range of algal om 25 to 20 shifts to lighter 13 c org values within sapropel intervals in the aegean sites can be interpreted as the result of elevated marine production enhanced inflow of light terrestrial dissolved inorganic carbon and or of the shoaling of the pycnocline along with the presence of a deep chlorophyll maximum dcm during the s 1 period

the glacial interglacial transition and holocene environmental changes in sediments from the gulf of taranto central mediterranean abstract an extensive high resolution sedimentological geochemical survey was done using geo acoustics xrf core scans icp aes ams 14c dating and grain size analyses of sediments in 11 cores from the gulf of taranto the southern adriatic sea and the central ionian sea spanning the last 16 cal ka bp comparable results were obtained for cores from the gallipoli shelf eastern gulf of taranto and the southern adriatic sea suggesting that the dominant provenance of gallipoli shelf sediments is from the western adriatic mud belt the 210pb and 14c dated high accumulation rate sediments permit a detailed reconstruction of climate variability over the last 16 cal ka bp although the glacial interglacial transition is generally dry and stable these conditions are interrupted by two phases of increased detrital input during the bolling allerod and the late younger dryas the event during the younger dryas period is characterized by increased sediment inputs from southern italian sources this suggests that run off was higher in southern compared to northern italy at approximately 7 cal ka bp increased detrital input from the adriatic mud belt related to sea level rise and the onset of deep water formation in the adriatic sea is observed and is coincident with the end of sapropel s1 formation in the southern adriatic sea during the mid to late holocene we observed millennial scale events of increased detrital input e g during the roman humid period and of decreased detrital input e g medieval warm period these dry wet spells are consistent with variability in the north atlantic oscillation nao a negative state of the nao and thus a more advanced penetration of the westerlies into the central mediterranean that result in wet conditions in the research area concord with events of high detrital input e g during the roman humid period in contrast a positive state of the nao resulting in dry conditions in the mediterranean dominated during events of rapid climate change such as the medieval warm period and the bronze age

paleoclimatic and paleoceanographic conditions leading to development of sapropel layer s1 in the aegean sea abstract sapropel s1 occurs as 25 35 cm thick black weakly laminated muds in aegean sea cores s1 was deposited between 9600 and 6400 yr b p during a period of isotopically depleted and relatively cool surface waters micro faunal and floral data indicate a major reduction in surface waters salinity during the deposition of s1 and oxygen isotopic data show a northerly fresh water source relatively light 13 c org and high pollen spore concentrations in s1 suggest increased influx of terrestrial organic carbon probably supplied by major rivers draining into the northern aegean sea benthic foraminifera indicate high nutrient low oxygen bottom waters for s1 and together with silt sized hematite and manganese coatings suggest that during the deposition of s1 surface sediments were oxic visual and xrd evidence of pyrite in s1 together with enrichments in s cu zn as ni cr and fe suggest that subsurface conditions were sufficiently reducing for so 4 2 reduction to occur probably by diffusion from surface oxic into subsurface anoxic sediments palynomorphs in s1 show large increases in terrestrial pollen and spores with the floral assemblage indicating significant influx from northern european rivers and minor african components associated with increased summer monsoonal rain abundance of dinoflagellates and amorphogen suggests some increase in primary productivity in response to increased influx of humic compounds however there is no evidence of upwelling the clay fraction in s1 shows notable decreases in smectite and kaolinite and reciprocal increases in illite and chlorite the combined data suggested that the evolution of s1 in the aegean sea largely resulted from stagnation of the surface waters during the final disintegration of the continental ice sheets rather than an increase in primary productivity and higher preservation of organic carbon on the sea floor

seasonal effect on vertical positioning by satellite laser ranging and global positioning system and on absolute gravity at the oca geodetic station grasse france summary we present a comparison of the vertical displacement monitored by independent techniques at the geodetic observatory of grasse france both satellite laser ranging and global positioning system gps vertical position time series over the period 1998 2003 show a prominent annual signal with a magnitude of 5 6 mm and reaching a maximum every year in july results from 14 absolute gravity measurements are also discussed we investigate the possible origin of the observed signal by comparing it with predictions from various local and regional contributions gps results from a local network indicate that the periodic annual elastic deformation of the 1270 m high karstic plateau due to local water storage loading does not exceed 1 2 mm in contrast a combination of global model prediction for atmospheric and hydrological loading explains more than 70 per cent of the annual and semi annual observed signals

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

interpreting rock eval pyrolysis data using graphs of pyrolizable hydrocarbons vs total organic carbon kerogen the major organic component of sedimentary rocks is commonly analyzed by rock eval pyrolysis plotting the data on a graph of s 2 vs total organic carbon toc and determining the regression equation is the best method for determining the true average hydrogen index and measuring the adsorption of hydrocarbon by the rock matrix such a plot also indicates the type of kerogen present and avoids the problem of increasing hydrogen index with total organic carbon content with the s 2 vs toc diagram the organic component of different suites of samples may be compared and their petroleum generation potentials established as an example the diagrams are used to evaluate the sedimentary environments and petroleum potential of the paleogene evaporitic sediments of the mulhouse basin alsace france

magmatic processes under arcs and formation of the volcanic front temperature structure and stress under arcs are simulated in a two dimensional cross section taking into account the flow induced by the subducting slab in the mantle wedge results of the calculations show three important features with respect to magmatic processes under arcs 1 temperature structure in the crust and the mantle wedge under arcs is insensitive to the angle and velocity of slab subduction the temperature structure of the slab and that of the back arc region this indicates that physical conditions such as temperature and pressure are similar under various arcs it is thus inferred that primary magmas generated under various arcs should have similar chemical compositions if chemical composition and the flux rate of fluid from the slab are similar and the chemical compositions of mantle wedge materials are the same 2 calculated deviatoric stress magnitude is relatively large more than a few tens of megapascals in the partially molten mantle cracks may open under high differential stress and magma can easily segregate and accumulate through interconnected cracks while the buoyancy driven compaction of partially molten mantle proceeds 3 the deviatoric stress values in the region over the partially molten mantle are relatively large and the direction of the principal stress changes horizontally the direction of the maximum compressional stress is nearly vertical under the volcanic zone and is nearly horizontal under the fore arc region it is considered that magma segregated in partially molten mantle migrates upward through the brittle mantle and crust by the magma fracturing mechanism the propagation direction of magma filled fissures is controlled by the stress field in the crust and mantle and is parallel to the maximum principal stress the calculated stress is highly compressive horizontally on the trench side while it becomes tensile on the back arc side the location of this stress transition coincides with that of the volcanic front the location of this transition indicates that the volcanic front marks a change in the ease of upward migration of the magma filled cracks under relatively high differential stress field

geochemical evidence for high resolution variations during deposition of the holocene s1 sapropel on the cretan ridge eastern mediterranean abstract major and minor element distributions and solid phase phosphorus contents were measured in a sediment core from the cretan ridge that contains the holocene s1 sapropel micro xrf ultra high resolution analysis reveals multiple mn peaks in the oxidized upper portion of the sapropel which implies either a non steady state upward remobilization of mn or not constant downward diffusion of bottom water oxygen sequential extraction allowed the identification of different phosphorus phases detrital phosphorus increases in the sapropel layer suggesting enhanced delivery from land during sapropel deposition higher organic carbon to organic phosphorus ratios in the sapropel indicate enhanced regeneration of phosphorus relative to carbon under low oxygen conditions fourier analysis on the ultra high resolution xrf data reveals frequencies that are provisionally assigned to millennial to decennial solar cycles although these cycles have been reported from several continental and marine archives they have never been documented from sapropel s1 in the eastern mediterranean

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

holocene millennial centennial scale multiproxy cyclicity in temperate eastern australian estuary sediments we have undertaken a comparative study of down core variation in multiproxy palaeoclimate data magnetic susceptibility calcium carbonate content and total organic carbon from two coastal water bodies myall and tuggerah lakes in temperate eastern australia to identify local regional and global forcing factors within holocene estuarine sediments the two lakes lie within the same temperate climate zone adjacent to the tasman sea but are not part of the same catchment and drain different geological provinces one is essentially a freshwater coastal lake whereas the other is a brackish back barrier lagoon despite these differences data from two sites in each of the two lakes have allowed us to investigate and compare cyclicity in otherwise uniform single facies sediments within the frequency range of 200 2000 years limited by the sedimentation rate within the lakes and our sample requirements we have auto and cross correlated strong periodicities at 360 years 500 530 years 270 290 years 420 450 years and 210 years and subordinate periods of 650 years 1200 1400 years and 1800 years our thesis is that climate is the only regionally available mechanism available to control common millennial and centennial scale cyclicity in these sediments given the geographical and other differences however regional climate may not be the dominant effect at any single time and either location within the range of frequency spectral peaks we have identified several fall within known long term periodical fluctuations of sun spot activity however feedback loops associated with short term orbital variation such as dansgaard oeschger cycles and the relationship between these and palaeo enso variation are also possible contributors copyright 2005 john wiley sons ltd

climatically linked oscillations in arabian sea denitrification over the past 1 m y implications for the marine n cycle water column and core top 15n data show that arabian sea denitrification produces large nitrogen isotopic enrichments that are regionally recorded with fidelity in the sediments these results facilitate interpretation of a 1 m y 15n record for ocean drilling program site 722b on the owen ridge in terms of climatically linked oscillations in denitrification at the major orbital periods as at present denitrification was greatest during interglacial periods and apparently was not active during most glacial intervals cross spectral analysis of 15n with foraminiferal 18o global climate sea level index and lithogenic grain size monsoon strength index suggests forcings by changes in hydrography and productivity acting through the extent and intensity of the oxygen minimum zone the data suggest that denitrification may be an internal forcing mechanism for climate change during major glacial interglacial transitions through influence on marine n inventory and atmospheric co2 however compensation or amplification may occur from other sinks sediment denitrification or sources nitrogen fixation

a theoretical model of hotspot volcanism control on volcanic spacing and patterns via magma dynamics and lithospheric stresses many linear island chains are thought to be the result of the steady motion of the lithospheric plates over stationary hotspots the occurrence of discrete nearly regularly spaced volcanoes rather than continuous ridges are assumed to be caused by the interaction of flexural stresses due to the volcanic loads with magma percolation a parameter study is performed on a simple model that incorporates these effects in addition to dike wall erosion it is demonstrated that the strength of the erosional feedback determines whether the model generates discrete volcanoes or a continuous ridge the intervolcanic spacing depends not only on the elastic thickness of the lithosphere but also on the magma pressure at the base of the lithosphere the size of the eruptive region of the individual volcanoes is controlled by the elastic response of the lithosphere to magma overpressurization if an initial off axis edifice is introduced the model is able to preserve this asymmetry and produce an alternating series of volcanoes a small initial perturbation grows over time resulting in double lines or wider patterns depending on the width of the magma source region single lines of volcanoes therefore indicate very narrow magma source regions

the cenozoic evolution of the strontium and carbon cycles relative importance of continental erosion and mantle exchanges the past variations of the seawater 87sr86sr isotopic ratio are related to changes in the relative contribution of the mantle sr input to the ocean and the sr supply from continental weathering recently it has been postulated that the cenozoic increase in the seawater 87sr86sr isotopic ratio was associated with the uplift of the himalayan and andean mountains at that time these orogenies may have changed the sr isotopic ratio of the continental rocks undergoing weathering as a result of extensive metamorphism increased the river flux of sr through enhanced weathering in these regions and possibly caused the global climatic cooling trend of the cenozoic a model of the major geochemical cycles coupled to an energy balance climate model is used to explore the possible causes of the mesozoic cenozoic fluctuations in the seawater 87sr86sr isotopic ratio the contribution of the mantle exchanges at mid ocean ridges of the recycling of seafloor carbonates through plate margin volcanism and of the alteration of seafloor basalts to the fluctuations of the seawater 87sr86sr isotopic ratio are studied finally this model tentatively describes the impact of the himalayan orogeny on the geochemical cycles of sr and c some possible effects of the extensive metamorphism associated with the india asia collision and of the himalayan uplift are modelled the model reproduces the cenozoic increase of the seawater 87sr86sr isotopic ratio however the impact of the himalayan orogeny on the c cycle appears to be limited and insufficient to generate the global climatic cooling of the cenozoic rather in the model the cenozoic cooling is mostly due to the reduction of the co2 emission from mid ocean ridge volcanism and to changes in the chemical weathering rates in the rest of the world excluding the himalayas

pliocene holocene evolution of depositional conditions in the eastern mediterranean role of anoxia vs productivity at time of sapropel deposition a multiproxy geochemical study of nine sapropel layers from odp hole 964a odp leg 160 in the eastern mediterranean spanning the pliocene holocene time interval provides new insights into the evolution of sapropel deposition paleoenvironmental proxies were used for reconstruction of productivity ba derived from marine barite oxygen conditions trace metal ratios and sedimentary regime clay minerals detrital elements these proxies reveal a significant increase in river runoff relative to decreasing aeolian input during sapropel deposition over the whole time interval ba excess supports the argument that a significant increase in export productivity is the main triggering mechanism for sapropel deposition although preservation also played an important role furthermore major differences exist in depositional conditions including both oxygenation and productivity since the pliocene productivity fluctuated substantially and was higher during the pliocene and pleistocene than during the holocene at the same time decreasing oxygen availability parallels the enhanced productivity dysoxic to anoxic conditions appear to coincide with marine productivity maxima thus suggesting that oxygen depletion may be linked to greater consumption rather than restricted circulation this correspondence supports the hypothesis that productivity fluctuations resulting from climate oscillations were the main cause of enhanced organic matter contents and also a main controlling factor for reduced oxygen availability

evidence for enhanced phosphorus regeneration from marine sediments overlain by oxygen depleted waters phosphorus regeneration and burial fluxes determined from in situ benthic flux chamber and solid phase measurements at sites on the californian continental margin peruvian continental slope north carolina continental slope and from the santa monica basin california are reported comparison of these sites indicates that o2 depleted bottomwaters enhance p regeneration from sediments diminishing overall phosphorus burial efficiency based on these observations a positive feedback linking ocean anoxia enhanced benthic phosphorus regeneration and marine productivity is proposed on shorter timescales these results also suggest that o2 depletion in coastal regions caused by eutrophication may enhance p regeneration from sediments thereby providing additional p necessary for increased biological productivity

trace elemental derived paleoceanographic and paleoclimatic conditions for pleistocene eastern mediterranean sapropels abstract eastern mediterranean sediments are characterized by cyclic deposition of organic rich sediments known as sapropels enhanced primary productivity combined with bottom water oxygen depletion are thought to be the main drivers for sapropel deposition we selected sapropel layers from a suite of odp leg 160 cores and applied a set of geochemical proxies to determine paleo productivity variations redox conditions of the water column during deposition and provenance of detrital material high sedimentary ba al and corg contents indicate enhanced primary production whereas the sedimentary la lu ratio points to an enhanced contribution from a north african riverine source during sapropel formation these features are especially pronounced on sapropels s5 and s7 deposited during a particularly warm climatic interval this indicates a more intense north african drainage weathering and consequently run off for those sapropels that have the most enhanced expression of productivity too correspondingly the latter has also resulted in bottom water redox conditions that have been more severe during these sapropels than during others deepwater formation from adriatic and aegean areas thought to be mainly controlled by sustained cooling of preconditioned surface waters triggers the onset of bottomwater ventilation thus sapropel duration our data therefore suggest that the intensity of sapropel formation is determined by the north african monsoonal system whereas their duration is directed by northern borderlands climatic conditions