climate variations since the last interglacial recorded in czech loess 1 magnetic susceptibility organic matter content and grain size were measured on a loess palaeosol sequence deposited since the last interglacial at the dolni vestonice section in the czech republic high values in magnetic susceptibility and organic matter content in palaeosols pk0 pk2 and pk3 indicate that they were strongly influenced by long term pedogenesis and high vegetation density linked to interglacials or interstadials grain size variations record a series of cold wind strengthened events during the last glacial which we interpret as a record of the distinctive younger dryas episode and millennial scale climate oscillations that correlate with the grip ice core 18o record and north atlantic heinrich events these climate events as indicated by grain size peaks combined with previous climate records at french massif central and lago grande di monticchio in italy suggest that the climate over these areas might have undergone synchronous oscillations with the shifts in sea surface temperatures of the north atlantic and air temperature changes above greenland

a high resolution paleointensity stack of the past 14 to 68 ka from black sea sediments abstract detailed paleo and mineral magnetic analyses of a sediment composite record from the southeastern black sea yielded a high resolution well dated paleointensity record though hampered by some larger hiatuses in some cores and contaminated by diagenetically formed greigite the paleomagnetic composite record obtained from the preserved primary detrital magnetite phase reflects a highly dynamic geomagnetic field during the last glacial period relative variations of paleointensity inferred from the sediments magnetisations were converted into a record of the virtual axial dipole moment vadm lowest vadm values are linked with the laschamp 0 50 10 22 a m 2 at 41 0 ka the norwegian greenland sea 1 5 10 22 a m 2 at 64 5 ka and the mono lake 3 0 10 22 a m 2 at 34 5 ka geomagnetic excursions the fully reversed field during the laschamp excursion exhibits a vadm of 2 0 10 22 a m 2 which is more than 25 of the present day axial dipole moment 7 628 10 22 a m 2 rates of change calculated from the black sea vadm record also give some information on how to assess the global decay of the present day geomagnetic field which is significantly enhanced in the area of the south atlantic anomaly comparison with provided c 14 and 10 be records confirm partly in the very detail the non linear anti correlation of geomagnetic field intensity and the production of cosmogenic radionuclides in the earth s upper atmosphere however discrepancies in the timing of lows and highs in the compiled records points out that the combination of different data sets from different archives remains a challenge

climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

conceptual model for millennial climate variability a possible combined solar thermohaline circulation origin for the 1 500 year cycle dansgaard oeschger and heinrich events are the most pronounced climatic changes over the last 120 000 years although many of their properties were derived from climate reconstructions the associated physical mechanisms are not yet fully understood these events are paced by a 1 500 year periodicity whose origin remains unclear in a conceptual model approach we show that this millennial variability can originate from rectification of an external solar forcing and suggest that the thermohaline circulation through a threshold response could be the rectifier we argue that internal threshold response of the thermohaline circulation thc to solar forcing is more likely to produce the observed do cycles than amplification of weak direct 1 500 year forcing of unknown origin by thc one consequence of our concept is that the millennial variability is viewed as a derived mode without physical processes on its characteristic time scale rather the mode results from the linear representation in the fourier space of nonlinearly transformed fundamental modes

evidence for an east west regional gravity trend in northern tunisia insight into the structural evolution of northern tunisian atlas abstract the atlas orogeny in northern algeria and tunisia led to the destruction of tethys oceanic lithosphere and cumulated in a collision of microplates rifted off the european margin with the north african continental margin the location of the boundary between african plate and kabylian microplate is expressed in northern algeria by a crustal wedge with double vergence of thrust sheets whereas in northern tunisia the geologic environment is more complex and the location of the plate boundary is ambiguous in this study we analyzed gravity data to constrain the crustal structure along the northern margin of tunisia the analysis includes a separation of regional and residual gravity anomalies and the application of gradient operators to locate density contrast boundaries the horizontal gradient magnitude and directional gradient highlight a prominent regional e w gravity gradient in the northern tunisian atlas interpreted as a deep fault active since at least the early mesozoic having a variable kinematic activity depending on the tectonic regime in the region the main e w gravity gradient separates two blocks having different gravitational and seismic responses the southern block has numerous gravity lineaments trending in different directions implying several density variations within the crust whereas the northern block shows a long wavelength negative gravity anomaly with a few lineaments taking into account the geologic context of the western mediterranean region we consider the e w prominent feature as the boundary between african plate and kabylian microplate in northern tunisia that rifted off europe this hypothesis fits most previous geological and geophysical studies and has an important impact on the petroleum and mineral resource prospection as these two blocks were separated by an ocean and they did not belong to the same margin

geochronologies and environmental records of quaternary fluvial sequences in the guadalope basin northeast spain based on luminescence dating

evidence for climate instability during the younger dryas interval in the hengduan mountains yunnan southwestern china abstract the younger dryas yd is the most recent abrupt climatic event recognized during the transition from the last glaciation to the holocene growing evidence from the middle and high latitudes of europe and north america shows that the climate within the yd event was highly unstable until recently however climate instability during this event has received little attention elsewhere in the world here we present evidence of a climatically unstable yd based on pollen climate transfer function and redfit spectral analysis of pollen data from haligu in the hengduan mountains of southwestern china a low latitude temperate biodiversity hotspot our data show that the climate fluctuated significantly during the yd with three warm peaks recognized at 11 5 11 7 and 12 3 cal kyr bp in particular we estimate a gradual rise in mean annual temperature by 3 7 c between the end of the yd and the early holocene 11 2 10 9 cal kyr bp in response to this the subalpine conifer forest dominated by picea and abies may have migrated about 610 m upwards we also detected that the climate fluctuations during the yd holocene transition show significant centennial periodicities of 76 yr 84 yr 91 yr 95 yr and 638 yr the former four cycles are possibly related to the gleissberg around 80 yr solar cycle which was also detected in the hongyuan peat the pc 6 core of the east china sea and the gisp2 ice core these new findings enhance our understanding of millennial scale abrupt climate events which may be of great significance in predicting the impact of future climate change on mountainous ecosystems in southwestern china the warming at the end of the yd may provide a potential analog for global warming in the near future during which the upward migration of vegetation zones will likely lead to the loss of habitat for threatened species we therefore should take action to restore habitats and provide protected areas for species at risk

the tolsta interstadial scotland correlation with d o cycles gi 8 to gi 5 abstract organic sediments buried by till at tolsta head in north lewis in the scottish outer hebridean islands have been re investigated radiocarbon dates of 32 26 kyr bp indicate correlation with the denekamp interstadial of the netherlands and the sandnes alesund interstadial of norway the organic sediments contain an unusually detailed record of the dominantly open grassland vegetation during the interstadial variations in palaeotemperature inferred from the pollen assemblages and sedimentology are provisionally matched with the 18o record of the gisp2 ice core and correlation with the dansgaard oeschger cycles gi 8 gi 5 is proposed the interstadial starts at 38 1k cal yr and 32 8k radiocarbon years the termination of the interstadial and the build up of the late devensian weichselian ice sheets in scotland and north west europe dates from 32k cal yr and 28 7k radiocarbon years whether the tolsta and other contemporaneous episodes are intervals or interstadials is also considered

growth of an intermittent ice sheet in iceland during the late pliocene and early pleistocene abstract deep sea paleoclimatic records show that the quaternary climate around iceland was and probably still is very sensitive to rapid shifts in north atlantic oceanic circulation studies of several key sections in iceland indicate that similar oscillations are reflected in the late pliocene and early pleistocene terrestrial stratigraphy correlations between six rock sequences in western northern eastern and southern iceland show a fairly distinct trend during the pliocene pleistocene transition indicating the progressive growth of an ice sheet from southeast toward the north and west the correlations are based on k ar dates and paleomagnetic studies a total of 11 glacial horizons are recorded in a stratigraphic column from eastern iceland extending back 6 5 myr in western iceland 7 glacial horizons are preserved in a rock section dated from 7 0 to 1 8 myr and in northern iceland 14 glacial horizons are identified in a section that extends back to 9 0 myr well over 20 glacial horizons have been identified in the stratigraphic column in iceland full scale glacial interglacial cyclicity with regional ice cover is indicated at approximately 2 6 myr a further amplification leading to islandwide glaciations is identified at 2 2 2 1 myr these results show that changes in the ice cover in iceland correlate with the deep sea oxygen isotope records from benthic and planktonic foraminifera as well as ird studies from the north atlantic

halokinesis and structural evolution of the major features in eastern and southern tunisian atlas abstract the eastern and southern tunisian atlas is marked by the presence of three major faults the n s axis fault the nw se gafsa fault and the e w northern chott fault seismic lines crossing these structures show the existence of significant halokinetics that began in the early jurassic the aim of this paper is to study and better understand the triassic salt movements which are mainly linked to periods when the major basement faults were reactivated resulting in extension compression transtension or and transpression analysis of the seismic data allows us to conclude that the triassic salt migration started in the early jurassic and continued during the late jurassic and the early cretaceous although these periods are characterized by an extensional tectonic regime the synsedimentary halokinesis is accompanied by thickening and thinning of the overlying series salt remobilization was accentuated during the compressional deformation which occurred from the late tertiary to quaternary and resulted in local diapiric extrusions along the major structural features

superlakes megafloods and abrupt climate change about 8200 years ago the climate of much of the northern hemisphere cooled abruptly for a period of about 200 years in their perspective clarke et al examine the most likely culprit for this cooling an outburst of fresh water from a vast ice dammed glacial lake in north america the superlake had formed when the kilometers thick ice sheet covering much of north america disintegrated when the ice dam became unstable fresh water flooded from the lake into the north atlantic it remains unclear how this fresh water affected ocean circulation or whether the outburst occurred in more than one stage but the timing points strongly to the outburst flood as the trigger of the 8200 year climate event

tectonic evolution of the northern african margin in tunisia from paleostress data and sedimentary record abstract a reconstruction of the tectonic evolution of the northern african margin in tunisia since the late permian combining paleostress tectonic stratigraphic and sedimentary approaches allows the characterization of several major periods corresponding to consistent stress patterns the extension lasting from the late permian to the middle triassic is contemporaneous of the rifting related to the break up of pangea during liassic times regional extensional tectonics originated the dislocation of the initial continental platform in northern tunisia the evolution of the liassic ne sw rifting led during dogger times to the north african passive continental margin whereas in southern tunisia a n s extension associated with e w trending subsiding basins lasted from the jurassic until the early cretaceous after an upper aptian early albian transpressional event ne sw to ene wsw trending extensions prevailed during late cretaceous in relationship with the general tectonic evolution of the northeastern african plate the inversions started in the late maastrichtian paleocene in northern tunisia probably as a consequence of the africa eurasia convergence two major nw se trending compressions occurred in the late eocene and in the middle late miocene alternating with extensional periods in the eocene oligocene early middle miocene and pliocene the latter compressional event led to the complete inversion of the basins of the northwestern african plate originating the maghrebide chain such a study supported by a high density of paleostress data and including complementary structural and stratigraphic approaches provides a reliable way of determining the regional tectonic evolution

timing and dynamics of the last deglaciation from european and north african δ13c stalagmite profiles comparison with chinese and south hemisphere stalagmites abstract the last deglaciation and its climatic events such as the bolling allerod ba and the younger dryas yd have been clearly recorded in the 13 c profiles of three stalagmites from caves from southern france to northern tunisia the three 13 c records dated by thermal ionization mass spectrometric uranium thorium method tims show great synchroneity and similarity in shape with the chinese cave 18 o records and with the marine tropical records leading to the hypothesis of an in phase between 15 5 and 16 ka 0 5 ka postglacial warming in the northern hemisphere up to at least 45 n the ba transition appears more gradual in the speleothem records than in the greenland records and the allerod seems warmer than the bolling showing here close similarities with other marine and continental archives a north south gradient is observed in the ba trend it cools in greenland and warms in our speleothem records several climatic events are clearly recognizable a cooler period at about 14 ka older dryas od the intra allerod cold period at about 13 3 ka the yd cooling onset between 12 7 and 12 9 0 3 ka similar to the ba the yd displays a gradual climate amelioration just after its onset at 12 75 0 25 ka up to the preboreal and is punctuated by a short climatic event at 12 15 ka even though the southern hemisphere stalagmite records seem to indicate that the postglacial warming started about 3 ka 1 8 ka earlier in new zealand 41 s and about 1 to 2 ka earlier in south africa 24 1 s large age uncertainties essentially due to slow growth rates make the comparison still perilous the overall 13 c speleothem record seems to follow a baseline temperature increase controlled by the increase in insolation and punctuated by cold events possibly due to the n america freshwater lake discharges

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

vegetation history and palaeoclimate of the last glacial period at lago grande di monticchio southern italy a high resolution palynological study of a 51 m core from lago grande di monticchio southern italy has provided a palaeonvironmental record for the last glacill a annual lamination based chronology supported by radiometric and tephrochronological dates provides an absolute timescale for this record that spans 76 300 years correlations are established between the pollen stratigraphy the grip ice core 18o record and foraminiferal assemblages from atlantic core v23 81 both dansgaard oeschger and heinrich events are reflected by changes in the pollen stratigraphy revised dates are estimated for heinrich events h1 h6 a quantitative palaeoclimate reconstruction based upon the pollen data provides evidence of the climate changes in southern italy associated with these and other fluctuations during the last glacial

textures and fabrics in the grip ice core a comprehensive study of textures and fabrics has been carried out on the greenland ice core project grip ice core crystal sizes and c axis orientations have been measured on thin sections with conventional techniques yielding new information on the growth rotation and recrystallization of ice crystals in the greenland ice sheet normal grain growth is found to persist to a depth of 700 m in the core where the onset of polygonization due to increasing strain prevents a further increase in grain size in the holocene ice smaller crystals are observed in the wisconsin ice larger crystals are found in the eemian ice and the crystal size is found to vary with climatic parameters in these periods this dependence which probably results from variable impurity content in the ice persists to a depth of 2930 m coarse grained ice probably resulting from rapid growth of crystals at comparatively high temperatures is found in the lowest 100 m of the core the data on c axis orientations reveal a steady evolution of the fabric from random near the surface to a strong single maximum in the lower part of the ice sheet a significant strengthening is not observed at the holocene wisconsin transition the fabric development indicates that vertical compression at the ice divide is the main mode of deformation down to a depth of 2850 m the evolution toward a single maximum fabric hardens the ice against vertical compression but softens it against simple shear evidence of simple shear deformation is clearly observed between 2850 m and 2950 m depth stretched fabrics in coarse grained ice in the lowest 100 m could be due to tensional stresses this ice is unlikely to be undergoing any significant horizontal deformation at the present time

a salt oscillator in the glacial atlantic 1 the concept as shown by the work of dansgaard and his colleagues climate oscillations of one or so millennia duration punctuate much of glacial section of the greenland ice cores these oscillations are characterized by 5 c air temperature changes severalfold dust content changes and 50 ppm co2 changes both the temperature and co2 change are best explained by changes in the mode of operation of the ocean in this paper we provide evidence which suggests that oscillations in surface water conditions of similar duration are present in the record from a deep sea core at 50 n based on this finding we suggest that the greenland climate changes are driven by oscillations in the salinity of the atlantic ocean which modulate the strength of the atlantic s conveyor circulation

using holo hilbert spectral analysis to quantify the modulation of dansgaard oeschger events by obliquity abstract astronomical forcing obliquity and precession has been thought to modulate dansgaard oeschger do events yet the detailed quantification of such modulations has not been examined in this study we apply the novel holo hilbert spectral analysis hhsa to five polar ice core records quantifying astronomical forcing s time varying amplitude modulation of do events and identifying the preferred obliquity phases for large amplitude modulations the unique advantages of hhsa over the widely used windowed fourier spectral analysis for quantifying astronomical forcing s nonlinear modulations of do events is first demonstrated with a synthetic data that closely resembles do events recorded in greenland ice cores ngrip grip and gisp2 cores on gicc05 modelext timescale the analysis of paleoclimatic proxies show that statistically significantly more frequent do events with larger amplitude modulation in the greenland region tend to occur in the decreasing phase of obliquity especially from its mean value to its minimum value in the eastern antarctic although statistically significantly more do events tend to occur in the decreasing obliquity phase in general the preferred phase of obliquity for large amplitude modulation on do events is a segment of the increasing phase near the maximum obliquity implying that the physical mechanisms of do events may be different for the two polar regions additionally by using cross spectrum and magnitude squared analyses greenland do mode at a timescale of about 1400 years leads the antarctic do mode at the same timescale by about 1000 years

interhemispheric anti phasing of rainfall during the last glacial period abstract we have obtained a high resolution oxygen isotopic record of cave calcite from caverna botuvera 27 13 s 49 09 w southern brazil which covers most of the last 36 thousand years ka with an average resolution of a few to several decades the chronology was determined with 46 u th ages from two stalagmites tests for equilibrium conditions show that oxygen isotopic variations are primarily caused by climate change we interpret our record in terms of meteoric precipitation changes hence the variability of south american monsoon sam intensity the oxygen isotopic profile broadly follows local insolation changes and shows clear millennial scale variations during the last glacial period with amplitudes as large as 3 but with smaller centennial scale shifts 1 during the holocene the overall record is strikingly similar to but strongly anti correlated with a number of records from the northern hemisphere we compared our record to other precisely dated contemporaneous records from hulu cave eastern china minima in 18o wet periods intense sam at our site are synchronous with maxima in 18o dry periods weak east asian monsoon eam in eastern china within precise dating errors and vice versa this anti phased precipitation relationship between two low latitude locations may be interhemispheric in extent based on comparison with records from other sites precipitation anti phasing may be related to north south shifts in the mean position of the intertropical convergence zone itcz and asymmetry in hadley circulation in two hemispheres associated not with seasonal changes as observed today but with millennial scale climate shifts the millennial scale atmospheric see saw patterns that we observe could have important controls and feedbacks on climate within hemispheres because of water vapor s greenhouse properties

some comments on climatic reconstructions from ice cores drilled in areas of high melt poor consideration has been given in many arctic circum polar ice core studies to the effect of summer snow melt on chemistry stable isotope concentrations and time scales many of these corps are drilled close to the firn line where melt is intense some come from below the firn line where accumulation is solely in the form of super imposed ice in all cases seasonal signals are reduced or removed and in some time gaps develop during periods of excessive melting which situate the drill site in the ablation zone consequently cross correlations of assumed synchronous events among the cores are invalid so that time scales along the same cores differ between authors by factors of over 2 many so called climatic signals are imaginary rather than real by reference to published analyses of cores from the superimposed ice zone on devon ice cap koerner 1970 and meighen ice cap koerner and paterson 1974 it is shown how melt affects all the normally well established ice core proxies and leads to their misinterpretation despite these limitations the cores can give valuable low resolution records for all or part of the holocene they show that the thermal maximum in the circum polar arctic occurred in the early holocene this maximum effected negative balances on all the ice caps and removed the smaller ones cooler conditions in the second half of the holocene have caused the regrowth of these same ice caps

physical properties of reykjanes ridge sediments and their linkage to high resolution greenland ice sheet project 2 ice core data five gravity cores taken from the reykjanes ridge have been used to establish a link between sediment physical properties and atmospheric records documented by 18o variations in greenland ice cores over the last 45 000 calendar years marine gamma ray attenuation porosity evaluator density and magnetic susceptibility variations could be linked with the ice core dansgaard oeschger and bond cycles this is supported by ice rafted detritus ird grain size the quartz feldspar ratio and carbonate isotopic and foraminiferal records the covariation of the sediment physical properties and 18o in greenland ice indicates a coupling of atmospheric temperature and paleocirculation variations gradual reduced bottom currents iceland scotland overflow water and enhanced iceberg discharges have been reconstructed for cold atmospheric periods relative to interstadial times in the study area the magnetic susceptibility signal is not related to the ice rafted detritus input but most probably reflects the variations of the iceland scotland overflow water intensity transporting titanomagnetite into the reykjanes ridge region

monsoon and dust signals recorded in dasuopu glacier tibetan plateau during summer 1997 a 15 m firn core was recovered from dasuopu glacier 28 23 n 85 44 e 7000 m a s l on the northwest margin of xixabarngma feng in the central himalaya oxygen isotope values and concentrations of ca 2 mg 2 nh 4 so 4 2 and no 3 were measured over the 10 years of snow accumulation captured in the firn core the seasonal variations of 18 o values and major ion concentrations in the dasuopu core indicate that summer monsoon and dust signals are clearly recorded in dasuopu glacier annual variations in 18 o values are controlled by the amount effect with more negative i e lighter 18 o values representing summer monsoon precipitation characteristic of tropical regions higher concentrations of ca 2 mg 2 and so 4 2 reflect the influx of mineral aerosols from the vast arid and semi arid desert regions to the north and west during the spring dust storm period high spring concentrations of nh 4 and no 3 appear to reflect changes in regional biogenic source strength

description and esr dating of the holsteinian interglaciation abstract the classical region of the holsteinian interglacial is in the vicinity of hamburg and the lower elbe it is defined on the basis of pollen and is clearly distinguishable from the eemian interglacial hallik 1960 muller 1974 the holsteinian interglacial is represented by a sequence of sediments up to 100 m in thickness these consist of limnic fluvial and marine beds and show a transgression up to the height of present sea level twenty seven molluscs from holsteinian deposits were used for esr dating the ages show that the holsteinian may be correlated with stage 7 of the deep sea record v28 238 shackleton and opdyke 1973

sampling the oxygen minimum zone off pakistan glacial interglacial variations of anoxia and productivity preliminary results sonne 90 cruise during cruise sonne 90 the well developed oxygen minimum zone omz in the northeastern arabian sea was sampled in great detail to study surface ocean productivity and organic carbon accumulation preservation during the last hundred to hundred thousands of years nearly anoxic conditions on and below the seafloor are indicated by the lack of macrobenthos and nekton absence of bioturbation high marine organic carbon accumulation and preservation of laminated sediments between about 300 and 1000 m water depth on the steep continental slope this pattern approximately coincides with the zone of extremely low o2 concentrations presently observed in the water column accumulation of organic material on the deeper slope near the lower boundary of the omz is enhanced by downslope transport downcore we observe a complex alternation of dark colored laminated and light colored homogeneous facies in general laminated organic carbon rich intervals were deposited under suboxic bottom water and enhanced productivity conditions mainly during warm stages e g bolling allerod and holocene from 8000 yrs b p to recent the homogeneous bioturbated intervals indicate normal bottom water oxygen levels and reduced productivity during or just after cold stages e g terminations ia and b and younger dryas the striking facies similarities of the sedimentary record in cores collected from different areas and water depths suggest a unique pattern of late pleistocene corg accumulation in the northeastern arabian sea which depends mainly on regional surface ocean productivity and intermediate water oxygenation however the sedimentary record is also influenced by variations in sediment supply from the makran and karachi shelf and from indus river discharge during rapid sea level changes

gravity contributions to the understanding of salt tectonics from the jebel cheid area dome zone northern tunisia detailed gravity measurements integrated with geological data were computed to constrain the mechanisms that were active during the emplacement of the triassic evaporite bearing folds of jebel cheid from the salt dome zone in the atlassic region the gravity analysis consists in mapping the contrasting gravity responses complete bouguer anomaly residual anomaly and derivative maps the main results display a positive amplitude gravity anomaly as the response of triassic evaporite bodies and important ne sw trending features at the boundaries between the triassic outcrops and their enveloping strata in contrast with gravity calculations of a salt dome structure usually resulting in negative gravity anomaly models the jebel cheid clearly expresses a positive gravity anomaly furthermore this result is supported by synthetic gravity interpretation

a role for north pacific salinity in stabilizing north atlantic climate 1 a simple ocean atmosphere feedback may reduce the amplitude of climate variability in around the north atlantic during interglacial compared to glacial states when climate is warm in the north atlantic region the intertropical convergence zone has a relatively northward position and moisture is exported from the tropical atlantic to the tropical pacific at the same time the east asian summer monsoon is strong which helps maintain a positive balance of precipitation over evaporation in the subpolar north pacific this is thought to account for lower salinity in the north pacific relative to the north atlantic which in turn drives northward flow through the bering strait to the northern north atlantic freshening in the north atlantic by water of pacific origin suppresses the meridional overturning circulation and reduces the heat flux the opposite situation exists during cold climate thus the combination of atmospheric vapor transport and flow through bering strait tends to cool the north atlantic region when warm and warm the region when cool

mineralogical and geo chemical characterization of a diapiric formation in the north of spain abstract we have selected seven profiles located in a diapiric formation in the north of spain the profiles have been analyzed for the mineralogy and the chemical composition of original materials soils developed above them and clay fractions three soils formed on basic rock of volcanic origin ophite and rich in alterable minerals three others formed on clay marl and one soil formed on gypsiferous marl plagioclases pyroxenes vermiculites and biotites are the main minerals found in the soil samples and ophitic rocks biotite smectite chlorite and interstratified chlorite vermiculite make up the predominant mineralogical association in the clay fraction of the soils calcite biotite and on top of all chlorite are the main minerals in the marls and the soils developed on them with gypsum predominant in the gypsiferous marl the mineralogy of its clay fraction is comprised mainly of chlorite and biotite the variations in content of al2o3 tio2 and na2o in the ophites are considered to be associated with the differences in the evolution of the pyroxenes the variability of the chemical composition of the keuper sediments and the soils is attributed more to the chaotic disposition of the triassic materials in the formation of the diapir than to intense chemical weathering the low concentrations of silica iron and aluminum extractable with ammonium oxalate indicate the low proportion of non crystalline products fundamentally it is the semiarid conditions in the study zone together with the processes of extrusion and hydrothermal activity affecting the formation of the diapir that are responsible for the genesis of the minerals

last 40ka climate changes as deduced from the lacustrine sediments of lake biwa central japan abstract sequential changes of aeolian dust and lake primary productivity since the last 40 ka observed in lacustrine sediment core from lake biwa central japan and provide high resolution climate changes in relation to the asian monsoon activities and the westerlies in east asia quartz content is very useful as a proxy record for reconstructing aeolian dust changes influenced by paleointensity of the asian winter monsoon and the westerlies since the last glacial on the other hand total organic carbon toc and opal a contents are useful as a proxy record for reconstructing primary biological production by paleo precipitation influenced by paleointensity of the asian summer monsoon activities aeolian dust and toc records in biw95 4 core indicated the millennial scale variation of the asian winter and summer monsoon activities and the westerlies during the last 40 ka suggesting good correlations with global cooling events in the last glacial period found in the north atlantic region the asian summer monsoon activities during the holocene are frequent and increased at 9 6 after 2 ka and decreased at 4 ka

geometry and structural evolution of lorbeus diapir northwestern tunisia polyphase diapirism of the north african inverted passive margin detailed geologic mapping structural analysis field cross sections new dating based on planktonic foraminifera in addition to gravity signature of lorbeus diapir are used to characterize polyphase salt diapirism this study highlights the role of inherited faulting which controls and influences the piercement efficiency and the style and geometry of the diapir and also the localization of evaporite early ascent displaying diapiric growth during extension salt was extruded along the graben axis developed within extensional regional early cretaceous tectonic associated with the north african passive margin evolution geologic data highlight reactive diapirism during albian time most extreme extension period and passive diapirism during the late cretaceous post rift stage northeastern maghreb salt province gives evidences that contractional deformations are not associated with significant diapirism during shortening the initial major graben deforms as complex anticlines where diapirs are squeezed and pinched from their feeding

continental oxygen isotopic record of the last 170 000 years in jerusalem abstract a long radiometrically dated oxygen isotopic record of continental climatic variations since the penultimate glaciation was obtained from a stalagmite deposited in a sealed cave in jerusalem this record shows that speleothems have the potential of assigning dates to long and short term climatic events with possible refining of milankovitch tuning of ice and marine records which themselves are not datable short term 1000 yr events are very significant in the region reaching 50 of glacial interglacial fluctuations the mediterranean sea was the most probable source of local precipitation throughout the last glacial cycle

the structure of jebel el mourra tunisia a diapiric structure causing a positive gravity anomaly detailed gravity data integrated with geological data and mining well data are analysed to constrain the shape of the triassic evaporitic body at jebel el mourra northern tunisian atlas and the mechanism of its emplacement at the surface the gravity data analysis included the construction of a gravity anomaly maps and synthetic and forward 2 5d gravity models the complete bouguer and residual gravity anomaly maps indicate a positive amplitude gravity anomaly over the triassic evaporitic outcrops and prominent ne sw trending features associated with the boundary of the triassic rocks and surrounded layers a nw se trending gravity model that crosses the triassic evaporitic outcrop at jebel el mourra shows that the positive gravity anomaly can be explained by a deep rooted salt diapir conventional models of salt dome formation suggest that they produce negative gravity anomalies however this study shows that this model is not universal the studied area is an example of a diapir expressed by positive gravity anomaly and this result is supported by synthetic gravity models at different stages of salt piercing

asynchronous deposition of ice rafted layers in the nordic seas and north atlantic ocean instabilities in ice stream flow within the north american laurentide ice sheet leading to the periodic release of armadas of icebergs into the north atlantic ocean over the past 60 000 years have produced extensive layers of coarse grained iceberg rafted debris heinrich layers in north atlantic sediments1 2 correlation of these layers with iceberg discharge events from the ice sheets on greenland iceland and scandinavia suggested in previous studies for some heinrich layers and in some areas3 4 5 would imply that ice sheet instability had been synchronous across the north atlantic presumably in response to a common environmental cause here we show a lack of widespread systematic correlations both between ice rafted debris layers in different sediment cores from the nordic seas and between the nordic layers and the north atlantic heinrich layers this suggests that the full glacial nordic ice sheets did not exhibit unstable behaviour coincident with iceberg discharge from the vast hudson bay drainage basin of the laurentide ice sheet6 7 off the hudson strait significant ice sheet discharge of melt water is indicated by size sorted sandy and muddy turbidite sediments different from the poorly sorted debris flows which dominate sedimentation on the margins of the nordic seas8 9 10 together these results suggest that the dynamics of quaternary ice sheets surrounding the nordic seas were different from the outlet glacier draining the hudson bay basin and they provide evidence against a common circum north atlantic mechanism driving the discharge of icebergs

late quaternary bottom current activity in the south aegean sea reflecting climate driven dense water production abstract the eastern mediterranean transient emt represents a recent early 1990s to today water circulation phenomenon during which more arid climatic conditions in the mediterranean lead to the production of very dense surface water masses in the north aegean sea the produced north aegean dense water nadw sinks to seafloor flows to the south aegean sea and then spills into the eastern mediterranean sea through the cretan straits contributing to the rejuvenation of the bottom water a large dataset of vintage high resolution seismic reflection profiles indicates that the floors of the basins in the southwest aegean sea are characterised by late quaternary erosional gullies abraded surfaces and channel related sediment drifts such structures provide evidence for the presence of strong bottom currents which originate from the southward propagation of nadw masses the basins have depths of 300 m to 1000 m and are connected to each other by narrow a few km straits and sills the dominance of abraded surfaces and erosional gullies on the northern flank of the basins and in the narrow straits sills between them provides evidence that the southward propagation of the nadw occurs by the filling and flooding of each basin by dense water which then spills and cascades into the next basin southward seismic stratigraphy suggests that the formation of the drifts started at marine isotope stage mis 11 420 ka bp the coincidence of at least three erosional surfaces within the sediment drifts with interglacial mis 11 5 and 1 respectively suggests that bottom currents were mostly active during high sea level stands and sluggish during glacial low sea level stands a 90 100 m drop of the sea level below the current level would have resulted in the emergence of the eastern cyclades plateau and thus in the disconnection of the southwest aegean sea from the north aegean sea several 0 05 0 5 m thick beds of gravelly sand with algal and mollusc debris laminated to mottled sand and mottled mud are observed in the sediment cores analysed in this paper these beds can be confidently correlated from core to core and are interpreted as bottom current deposits the separation of these beds by hemipelagic sediments indicates that bottom current activity in the southwest aegean is not permanently established but episodic six episodes of intense bottom current activity are recorded in the mis 2 4 10 80 ka sediments and they appear to correlate well with the cold and dry younger dryas and heinrich 3 4 5 6 and 7 events in contrast at least three episodes of intense bottom current activity are recorded in the cores during the holocene the higher frequency of strong bottom current episodes in the southwest aegean sea during the holocene is attributed to the higher sea level stand that makes the circulation of water masses in the aegean sea more sensitive to climatic changes

gravity constraints on the structure of the northern margin of tunisia implications on the nature of the northern african plate boundary summary bouguer gravity data were analysed to determine the general crustal and upper mantle structure in northern tunisia residual gravity anomalies were determined by removing the gravitational effect of crustal thickness variations imaged by regional seismic experiments residual gravity anomalies contain short wavelength anomalies superimposed on a long wavelength component that decreases in amplitude northward towards the tunisian coastline an edge enhancement analysis e g enhanced analytic signals of the short wavelength anomalies suggests a previously unknown east west trending gravity anomaly south of 37 n with source depths of between 3 and 7 km modelling of residual and bouguer gravity anomalies indicate that there are two possible solutions for the residual gravity decrease in northern tunisia 1 thickening of cenozoic and mesozoic sediments north of a strike slip fault or 2 a crustal and uppermantle low density zone interpreted as being crustal material of the remnant subducted african plate the latter result is favoured based on seismic tomographic images of the mediterranean region which implies that subducting material exists under the african coast geological interpretations suggesting that the tell atlas may be a thrust wedge accreted by underplating of the african continental crust and seismic refraction models indicating a thinning of sediments in northern tunisia the east west trending gravity anomalies south of 37 n correspond to an important structural feature that may be related to either a structural boundary e g a transform fault or subduction beneath the african plate

evidence for triassic salt domes in the tunisian atlas from gravity and geological data abstract detailed gravity data were analyzed to constrain two controversial geological models of evaporitic structures within the triassic diapiric zone triassic massifs of jebel debadib and ben gasseur of the northern tunisian atlas based on surface observations two geological models have been used to explain the origin of the triassic evaporitic bodies 1 salt dome diapiric structure or 2 a salt glacier the gravity analysis included the construction of a complete bouguer gravity anomaly map horizontal gravity gradient hgg map and two and a half dimensional 2 5d forward models the complete bouguer gravity anomaly map shows a prominent negative anomaly over the triassic evaporite outcrops the hgg map showed the location of the lateral density changes along northeast structural trends caused by triassic cretaceous lithological differences the modeling of the complete bouguer gravity anomaly data favored the diapiric structure as the origin of the evaporitic bodies the final gravity model constructed over jebel debadib indicates that the triassic evaporitic bodies are thick and deeply rooted involving a dome diapiric structure and that the triassic material has pulled upward the younger sediment cover by halokinesis taking in account kinematic models and the regional tectonic events affecting the northern margin of africa the above diapirs formed during the reactive to active to passive stages of continental margin evolution with development of sinks otherwise this study shows that modeling of detailed gravity data adds useful constraints on the evolution of salt structures that may have an important impact on petroleum exploration models

millennial scale variability to 735 ka high resolution climate records from santa barbara basin ca 1 determining the ultimate cause and effect of millennial scale climate variability remains an outstanding problem in paleoceanography partly due to the lack of high resolution records predating the last glaciation recent cores from santa barbara basin provide 2500 5700 year windows of climate with 10 50 year resolution ages for three cores determined by seismic stratigraphic correlation oxygen isotope stratigraphy and biostratigraphy date to 293 ka mis 8 450 ka mis 12 and 735 ka mis 18 these records sample the late pleistocene during which the 100 kyr cycle strengthened and the magnitude of glacial interglacial cyclicity increased thus these records provide a test of the dependence of millennial scale behavior on variations in glacial interglacial cyclicity the stable isotopic 18o composition of planktonic foraminifera shows millennial scale variability in all three intervals with similar characteristics duration cyclicity to those previously documented during mis 3 at this site stadial g bulloides 18o values are 2 75 1 75 average 2 25 and interstadial values are 1 75 0 5 average 1 with rapid decadal scale interstadial and stadial initiations of 1 2 as in mis 3 interstadials lasted 250 1600 years and occurred every 650 1900 years stadial paleotemperatures were 3 5 9 5 c and interstadial paleotemperatures were 7 5 13 c upwelling evidenced by planktonic foraminiferal assemblages and 13c increased during interstadials similar to mis 3 high productivity during some stadials was reminiscent of the last glacial maximum this study builds upon previous records in showing that millennial scale shifts were an inherent feature of northern hemisphere glacial climates since 735 ka and they remained remarkably constant in the details of their amplitude cyclicity and temperature variability

crustal structure beneath the tell and atlas mountains algeria and tunisia through the analysis of gravity data abstract bouguer and isostatic residual gravity anomaly maps were analyzed for the general crustal structure under the tell and atlas mountains of algeria and tunisia two dimensional gravity models and profiles of topography free air and bouguer gravity anomalies were constructed to provide estimates of the crustal thickness and the degree of isostatic compensation the thickest crust 38 40 km was found beneath the saharian atlas in northern algeria whereas under the tunisian atlas it is approximately 34 36 km there is little evidence of crustal thickening due to the formation of the tell mountains large amplitude negative bouguer small amplitude positive free air gravity and small amplitude positive isostatic residual gravity anomalies suggest that saharian and tunisian atlas are partially isostatically compensated with regions of possible overcompensation in algeria the boundary between the saharian and tunisian atlas is characterized by negative isostatic residual anomalies suggesting overcompensation and a thick crustal root however the cause may be low density material in the upper crust the amplitude and width of bouguer gravity anomalies and two dimensional gravity models across the saharian and tunisian atlas indicate that there was a greater amount of crustal shortening in algeria than in tunisia

climate variability and vadose zone controls on damping of transient recharge abstract increasing demand on groundwater resources motivates understanding of the controls on recharge dynamics so model predictions under current and future climate may improve here we address questions about the nonlinear behavior of flux variability in the vadose zone that may explain previously reported teleconnections between global scale climate variability and fluctuations in groundwater levels we use hundreds of hydrus 1d simulations in a sensitivity analysis approach to evaluate the damping depth of transient recharge over a range of periodic boundary conditions and vadose zone geometries and hydraulic parameters that are representative of aquifer systems of the conterminous united states u s although the models were parameterized based on u s aquifers findings from this study are applicable elsewhere that have mean recharge rates between 3 65 and 730 mm yr 1 we find that mean infiltration flux period of time varying infiltration and hydraulic conductivity are statistically significant predictors of damping depth the resulting framework explains why some periodic infiltration fluxes associated with climate variability dampen with depth in the vadose zone resulting in steady state recharge while other periodic surface fluxes do not dampen with depth resulting in transient recharge we find that transient recharge in response to the climate variability patterns could be detected at the depths of water levels in most u s aquifers our findings indicate that the damping behavior of transient infiltration fluxes is linear across soil layers for a range of texture combinations the implications are that relatively simple homogeneous models of the vadose zone may provide reasonable estimates of the damping depth of climate varying transient recharge in some complex layered vadose zone profiles

role of the thermohaline circulation in the abrupt warming after heinrich events evidence of rapid climate oscillations during the last glacial period has been identified in climate records from greenland ice cores1 2 and ocean sediments in the north atlantic3 4 these records show that periods of gradual cooling are terminated by abrupt warming events5 with the coldest periods coinciding with the deposition of ice rafted debris so called heinrich events throughout the north atlantic heinrich events are thought to be a signature of massive iceberg discharges owing to collapse of the laurentide ice sheet bond et al 5 have proposed that the decrease in meltwater flux following collapse and retreat of the ice sheet enhanced the ocean s thermohaline circulation6 thereby increasing advection of heat from the tropics and giving rise to abrupt climate warming here we test this idea using a simple ocean model coupled to a model of a periodically surging ice sheet we find that massive discharges of icebergs first stop the thermohaline circulation because of the consequent freshwater influx cooling the north atlantic region this is followed by a rapid restart of the circulation leading to abrupt warming thus our model can reproduce the qualitative features of the climate oscillations seen in the ice core and ocean records

millennial variability in an idealized ocean model predicting the amoc regime shifts abstracta salient feature of paleorecords of the last glacial interval in the north atlantic is pronounced millennial variability commonly known as dansgaard oeschger events it is believed that these events are related to variations in the atlantic meridional overturning circulation and heat transport here the authors formulate a new low order model based on the howard malkus loop representation of ocean circulation capable of reproducing millennial variability and its chaotic dynamics realistically it is shown that even in this chaotic model changes in the state of the meridional overturning circulation are predictable accordingly the authors define two predictive indices which give accurate predictions for the time the circulation should remain in the on phase and then stay in the subsequent off phase these indices depend mainly on ocean stratification and describe the linear growth of small perturbations in the system thus monitoring particular indices of the ocean state could help predict

subsidence history in basins of northern algeria abstract the tellian foreland in algeria represents a part of the southern tethyan margin during the mesozoic its tectonic evolution includes a rifting stage during the triassic and liassic times characterised by tilted blocks and early diapiric events during the liassic a post rift regime from middle jurassic up to the late cretaceous and basin inversion during the tertiary related to the african and european plates convergence the subsidence modelling supported by surface and subsurface data integration emphasises different subsidence phases 1 liassic subsidence phase under tethyan and atlantic control related to crustal thinning 2 late jurassic cretaceous and tertiary subsidence phases where the first one is linked to diapiric events and the second in eastern algeria to the effects of the rifting event developed more easterly in the gulf of gabes and sirte the last one is flexural and occurs in foreland basins during the tertiary taking into account the subsidence record of each structural domain a correlation between tectonic events and the subsidence phases can be established

spreading of salt structures in the gulf of mexico abstract past and present overhangs on diapirs ductile intrusions of salt are potential hydrocarbon traps and increasing numbers of larger overhangs are being recognised as seismic acquisition and processing improves salt overhangs develop by three process drag by ductile surroundings sinking around salt diapirs thinning of diapiric stems or the topic considered here gravity spreading gravity spreads salt where it is easier for salt to flow sideways than it is to float or sink the potential level to which individual salt diapirs rise depends on the pressure applied to their source by the overburden load and any lateral forces the potential level to which salt diapirs rise can be independent of both the top free surface and the level of neutral buoyancy of the salt even the most vigorous diapirs cannot rise indefinitely they gravitationally spread at barriers they cannot penetrate below at or above their level of neutral buoyancy it has been suggested that salt diapirs spread below their level of neutral buoyancy in weak layers beneath stiff barriers however no case of deep subsurface salt spreading appears to have been documented instead shales rise with salt along the us gulf coast some salt diapirs in the gulf of mexico may simulate ductile ice flows and spread both upwards and downwards to a subsurface level of neutral buoyancy in surroundings of similar strain rate however most diapirs in the gulf are driven above their level of neutral buoyancy so that they spread downwards back towards it these spread over denser or stifter layers in less dense and weaker barriers of air water or unconsolidated sediments this work focuses on the geological implications of the shapes of the tops of small scale secondary salt bodies that spread superficially in weaker and less dense barriers under the northern gulf of mexico analytical material and natural models are used to show that the shape of the top free surface of spreading salt contains information about both the properties of the materials involved and their kinematics many salt diapirs in the gulf spread downslope from viscous salt fountains in muds over sand salt flowing downslope towards a lower level of neutral buoyancy exhibits dynamic extrusion the temporary dynamic nature of salt sheets is emphasised by restating standard arguments for overburden strength in terms of low strain rates contrary to recent views that salt spreading occurs in weak horizons during fast sedimentation it is argued that most salt spreads superficially during periods of slow sedimentation small salt laccoliths advance downslope at long term rates between 1 and 5 mm a after burial spreading and gliding of their overburdens can detach such laccoliths from their source and smear them to salt sills that advance downslope at 8 mm a as development wells are likely to be complicated by such active salt flow we should begin now direct measurements of the rates at which salt spreads at superficial levels beneath the northern gulf of mexico

diapirism in northern tunisia abstract the diapirs of northern tunisia composed mainly of evaporitic triassic material are the result of a complex evolution initiated by local basement movements of nne ssw faults which at the end of the early cretaceous this first uplift occurring during a period without any folding of the sedimentary series is purely halokinetic such diapiric activity remained in active progress throughout the cretaceous and early tertiary causing local disturbance in the related series and then during the alpine atlas orogeny the diapiric structures underwent deformation according to their position in the orogenic area

structural setting of northern tunisia insights from gravity data analysis jendouba case study detailed gravity data in conjunction with available surface geology are analyzed to infer the organization of the underlying structures in jendouba area gravity data analysis benefits from the gravity bouguer anomaly upward continuations residual distribution derivatives and euler deconvolved maps the main results display a positive amplitude gravity anomaly as the response of triassic evaporitic bodies and important ne trending features at the boundaries between the triassic outcrops and their enveloping strata integration of gravity geological and structural maps let to the identification of major structural directions and trends of the study area it confirms some structural elements gathered from outcrops it defines also new ones

response of bushy tailed woodrats neotoma cinerea to late quaternary climatic change in the colorado plateau abstract temperature profoundly influences the physiology and life history characteristics of organisms particularly in terms of body size because so many critical parameters scale with body mass long term temperature fluctuations can have dramatic impacts we examined the response of a small mammalian herbivore the bushy tailed woodrat neotoma cinerea to temperature change from 20 000 yr b p to present at five sites within the colorado plateau our investigations focused on the relationship between temperature plant composition and abundance and woodrat size body size was estimated by measuring fossil fecal pellets a technique validated in earlier work we found significant and highly covariable patterns in body mass over the five locations suggesting that responses to temperature fluctuations during the late quaternary have been very similar although woodrat mass and the occurrence of several plant species in the fossil record were significantly correlated in virtually all instances changes in woodrat size preceded changes in vegetational composition these results may be due to the greater sensitivity of woodrats to temperature or to the shorter generation times of woodrats as compared to most plants an alternative hypothesis is that winter temperatures increased before summer ones woodrats are highly sensitive to warmer winters whereas little response would be expected from forest woodland plants growing at their lower limits our work suggests that woodrat size is a precise paleothermometer yielding information about temperature variation over relatively short term temporal and regional scales

transient response of the moc and climate to potential melting of the greenland ice sheet in the 21st century 1 the potential effects of greenland ice sheet gris melting on the atlantic meridional overturning circulation moc and global climate in the 21st century are assessed using the community climate system model version 3 with prescribed rates of gris melting only when gris melting flux is strong enough to be able to produce net freshwater gain in upper subpolar north atlantic does the moc weaken further in the 21st century otherwise this additional melting flux does not alter the moc much relative to the simulation without this added flux the weakened moc doesn t make the late 21st century global climate cooler than the late 20th century but does reduce the magnitude of the warming in the northern high latitudes by a few degrees moreover the additional dynamic sea level rise due to this weakened moc could potentially aggravate the sea level problem near the northeast north america coast

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

submarine salt glacier of northern tunisia a case of triassic salt mobility in north african cretaceous passive margin stratigraphical sedimentological and structural data and a bouguer gravity map of medjez el bab meb in northern tunisia are used to illustrate a cretaceous example of salt extrusion on a passive continental margin located just south of the teboursouk thrust front a preferential decollement surface used by the continuous tertiary shortening in this area the meb structure is a simple n40 e box anticline removing the two tertiary foldings eocene and miocene leads to the exposure of the original feature of a simple submarine salt glacier the triassic salt rocks appear as an albian interstratified body between two cretaceous series with stratigraphic normal polarity suggesting a bedding parallel extrusion at the sediment water interface of the triassic salt in cretaceous times the formation of such salt extrusions are associated with extensional faulting probably both in the cover and basement the presence of a slope and basinwards salt flow this scenario is similar to the allochthonous salt described in other salt provinces characterizing passive margins

sediment color record from the northeast atlantic reveals patterns of millennial scale climate variability during the past 500 000 years a 500 000 yr long deep sea sediment color record from the northeast atlantic was investigated to reconstruct the evolution of late pleistocene climate variability on millennial time scales variations of the red green color intensity are probably caused by climatically induced changes in the ice rafted input of red colored iron bearing terrigenous material to the core site the resolution of the age model impedes the detection of distinct spectral features at sub milankovitch periodicities hence millennial scale climate variability is quantified as time dependent variance of the high pass filtered color time series the course of the estimated variance shows distinct patterns which can be linked to continental ice mass during the past 500 000 yr large amplitude millennial scale climate variability occurs only if continental ice mass exceeds a threshold level equivalent to sea level at approximately 40 of the lowering during the last glacial maximum

transferring radiometric dating of the last interglacial sea level high stand to marine and ice core records in order to derive a radiometric age marker for the end of the penultimate glacial interglacial transition we compiled published u series isotope measurements on corals from the period extending from stage 6 to the middle of the last interglacial and computed the corresponding open system ages using thompson et al model thompson w g spiegelman m w goldstein s l speed r c an open system model for u series age determinations of fossil corals earth planet sci lett 210 2003 365 381 we obtain a global mean age of 126 calendar kyr bp ka 1 7kyr 2 for the beginning of the last interglacial sea level high stand after showing that the phase relationships observed between changes in sea level north atlantic benthic and planktonic foraminifera oxygen isotopic records and atmospheric methane over the last deglaciation were likely also valid over the penultimate deglaciation we derive an age of 131 2ka 2kyr 2 for the abrupt increase in atmospheric ch4 and north atlantic surface temperature marking the end of the penultimate glacial interglacial transition this age is consistent with u th dates of the penultimate glacial interglacial transition recorded in speleothems from sites where speleothems isotopic records are synchronous with north atlantic temperature records over the last deglaciation finally we show that the phase obtained between the climatic response and northern hemisphere summer insolation is not constant from termination ii to termination i implying that northern hemisphere summer insolation alone cannot explain the timing of terminations

evidence for triassic salt domes in the tunisian atlas from gravity and geological data by c jallouli et al tectonophysics 396 2005 209 225 evidence for triassic salt domes in the tunisian atlas from gravity and geological data by c jallouli et al tectonophysics 396 2005 209 225 discussion

structural evolution of djebel debadib anticline a clue to the regional tectonic style of the tunisian atlas djebel debadib is a northeast trending anticline in the tunisian atlas near el kef tunisia the core of the anticline consists of a deformed triassic gypsum matrix breccia containing clasts of supratidal dolomite terrigeneous clastic rocks and ophites metabasites locally low grade metasedimentary rocks occurring as clasts in the evaporite may represent fragments of basement rock plucked from salt subcrop during deep seated flowage the multiply deformed triassic rocks are juxtaposed against cretaceous or younger rocks and jurassic and neocomian strata are not present in outcrop these characteristics have been cited in many studies to suggest a history of diapirism to explain both the internal structure of the triassic rocks and the contact relations with the younger rocks a previously unreported unconformity developed on the triassic rocks and overlain by aptian albian strata indicates that an important period of piercement occurred during the early cretaceous for the djebel debadib diapir from the mid cretaceous to the late eocene the continental margin of northern tunisia was a regional basin in which a thick sequence of carbonate rocks was deposited beginning in late oligocene time sandy clastic sediments accumulated on the older carbonate rocks above a regional unconformity and during the middle miocene atlas orogeny numerous northeast southwest folds deformed the rocks of the tunisian trough including the diapiric triassic masses these folds commonly boxlike in geometry were extensively faulted during the late miocene and pliocene a four phase tectonic model is recognized for the tunisian atlas 1 early mesozoic rifting of the north african continental margin 2 diapiric emplacement of the late triassic liassic evaporites into overlying strata beginning in the early cretaceous 3 folding of the cover strata in response to regional compression culminating in the middle miocene atlas orogeny 4 the development of transvers grabens during late orogenic normal faulting latest miocene to recent a major regional decollement is not considered necessary to account for the shortening of the sedimentary cover during the middle miocene deformation rather the principal driving mechanism of regional crustal shortening was the reactivation of early mesozoic normal faults as reverse faults that displaced basement rocks this model implies that the small amount of shortening recorded in the tunisian atlas involved active shortening and structural thickening of basement and the concurrent deformation of the sedimentary cover

autochthonous versus allochthonous upper triassic evaporites in the sbiba graben central tunisia abstract two dimensional seismic data and well data from the sbiba graben in central tunisia north africa reveal its asymmetrical structural geometry affected by e w n s nw se and ne sw master strike slip faults these faults have been intruded by upper triassic evaporites which can be classified into the following three types 1 sealed evaporite anticlines and domes along folded structures 2 extrusional wrinkles of salt walls at the borders of the graben related to along strike displacement of the master fault zone and 3 evaporite outpouring at the center of the graben interpreted as the result of fault and diapir movement detailed seismic stratigraphic analysis highlights a complex interplay between fault growth and evaporite movement which strongly controlled the evolution of the graben during the mesozoic tectonic stresses induced multidirectional faulting along inherited faults the vertical rising of the upper triassic evaporites was initiated locally at the intersection of master faults during regional extensional and transtensional events in the sub evaporite basement the interaction of normal faulting and evaporite diapirism caused lateral outpouring of surface piercing evaporites this phenomenon is well expressed in upper cretaceous upper cenomanian to lower turonian strata the master faults which cut the diapir at the border and the crest have caused the extrusion of evaporites the downward gravity driven flow of these evaporites across the slope surface and subsequent accumulation and preservation in mesozoic sediments is related to the fault escarpment and the adjacent fault induced depression there is an apparent relation between tectonic inheritance and inversions of the graben where interconnected deep faults and diapirs have been reactivated during extensional and contractional tectonic episodes causing evolution of the structures with the associated sedimentary lapouts several autochthonous triassic evaporites and associated fault escarpments have induced salt canopy structures

the lacustrine sedimentary sequence in sygneskardvatnet western norway a continuous high resolution record of the jostedalsbreen ice cap during the holocene abstract two lacustrine sediment cores from sygneskardvatnet sunndalen confirm that at least the northern part of the jostedalsbreen ice cap melted away during the atlantic chronozone between 6475 and 5300 14 c yr bp 7340 and 6150 cal bp possibly interrupted for short intervals of glacier activity around 6000 and 5800 14 c yr bp 6900 and 6700 cal bp prior to this periods of glacier expansion culminated at ca 8500 8400 8200 7750 7600 and 7400 cal bp the 8400 8200 cal bp advances are correlated with the widespread 8200 event finse event recorded in greenland ice cores lacustrine and proglacial sites and marine sediments during the early part of the holocene periods of glacier contraction culminated at ca 8450 8300 7900 7500 and 6250 cal bp of which the last represents climatic optimum conditions lowest supply of minerogenic sediments and or highest organic production the sedimentary record also shows that the ice cap has existed continuously since 5300 14 c yr bp 6150 cal bp neoglaciation involved three main phases 1 6150 4500 cal bp 2 4500 2700 cal bp 3 2700 cal bp to the present and a series of low amplitude glacier advances which occurred at 6000 5800 5700 5600 5500 5200 5100 4900 4800 4700 4550 4450 4300 4200 4150 4050 4000 3900 3800 3550 3300 2550 2450 2350 2250 2150 2000 1800 1700 1600 1400 1300 1150 1050 and the 1000 cal bp including the little ice age loss on ignition analyses indicate however that episodes of less glacier activity occurred during the mid and late holocene at around 5900 5800 5550 5450 5300 5050 4850 4750 4500 4400 4100 3950 3700 3450 3100 2650 2500 2400 2300 2200 1850 1700 1550 1350 1250 1050 1000 cal bp and during the twentieth century altogether the lacustrine record from sygneskardvatnet indicates that the holocene has been interrupted by 41 periods of increased glacier activity mean return period of ca 150 years and by 36 events of glacier contraction mean return period of 210 years spectral analysis of the loi data show peaks at periods of about 50 85 110 250 285 500 and 2000 calendar years the mean time resolution in core sygneskardvatnet 2 is ca 20 yr cm 1 while the mean sedimentation rate is 0 5 mm yr 1

50 000 years of vegetation and climate history on the colorado plateau utah and arizona usa sixty packrat middens were collected in canyonlands and grand canyon national parks and these series include sites north of areas that produced previous detailed series from the colorado plateau the exceptionally long time series obtained from each of three sites n48 000 14 cy r bp to present include some of the oldest middens yet discovered most middens contain a typical late wisconsinan glaciation mixture of mesic and xeric taxa evidence that plant species responded to climate change by range adjustments of elevational distribution based on individual criteria differences in elevational range from today for trees and shrubs ranged from no apparent change to as much as 1200 m difference the oldest middens from canyonlands np however differ in containing strictly xeric assemblages including middens incorporating needles of arizona single leaf pinyon far north of its current distribution similar aged middens from the eastern end of grand canyon np contain plants more typical of glacial climates but also contain fossils of one seed juniper near its current northern limit in arizona holocene middens reveal the development of modern vegetation assemblages on the colorado plateau recording departures of mesic taxa from low elevation sites and the arrival of modern dominant components much later published by university of washington

millennial scale dynamics of the east asian winter monsoon during the last 200 000 years the primary productivity dynamics of the last 200 000 years in the sulu sea was reconstructed using the abundance of the coccolithophore florisphaera profunda in the images md97 2141 core we find that primary productivity was enhanced during glacial periods which we suggest is due to a stronger east asian winter monsoon during the last 80 kyr eight significant increases in primary productivity pp in the sulu sea are similar to east asian winter monsoon changes recorded in chinese loess the pp maxima are not linked with heinrich events he in the north atlantic although four pp peaks are synchronous with he the pp oscillations have frequencies near those of the dansgaard oeschger cycles in northern hemisphere ice records and indicate a teleconnection of the east asian winter monsoon with greenland climate in this sulu sea record the east asian winter monsoon oscillates with periodicities of6 4 2 3 4 2 3 and 1 5 kyr in particular the 1 5 kyr cycle exhibits a strong and pervasive signal from stage 6 to the holocene without any ice volume modulation this stationarity suggests that the 1 5 kyr cycle is not driven by some high latitude forcing

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

role of preexisting faults in the geodynamic evolution of northern tunisia insights from gravity data from the medjerda valley abstract the middle medjerda valley belongs to the tellian zone of tunisia it behaves as a post orogenic basin where surface structural indices are almost completely absent it is noteworthy to recall that alpine and atlasic tectonic prints are well expressed on both sides of this basin this paper presents an integrated study comprising geology and gravity data subsurface geological modeling was based on gravity data interpretation including the complete bouguer anomaly upward continuation residual and derivatives 2 5d gravity modeling was essential for subsurface geometric features characterization in spite of its sub horizontal and smooth topography and the low density of the homogenous quaternary series covering the area well contrasted and variable gravity responses are observed reflecting the heterogeneities of the geological substratum the enhanced horizontal gravity gradient confirms structural systems that are already evidenced by surface geology it supports also the presence of new masked fault systems the main structural features inferred are i nw directed grabens located at mellegue and s ez zaouam depressions ii triassic diapirs associated to ne thrust faults of el merdja bousalem ben bechir and mjez el assa these structures are generally covered by the quaternary series the presence of both distensive and compressive structures within a compressive regime is explained by the solicitation of preexisting fault systems in the area during the nw directed shortening occurred at the upper miocene age the geodynamic evolution of northern tunisia was dominated by strike slip thrust movements through the reactivation of deep major inherited faults e g i the dextral ew oriented fault system of ghardimaou thibar and ii the sinister ns accident of dehmani bousalem ras rajel these accidents shaped the medjerda basin and contribute to its complex geological architecture

paleoenvironmental conditions and strontium isotope stratigraphy in the paleogene gafsa basin tunisia deduced from geochemical analyses of phosphatic fossils fossil shark teeth and coprolites from three major phosphorite occurrences in the gafsa basin southwestern tunisia were investigated for their geochemical compositions to improve local stratigraphy and to better assess paleoenvironmental conditions 87sr 86sr isotope ratios of shark teeth from the early maastrichtian el haria formation and from the early eocene metlaoui s s formation yielded sr isotope ages of 68 1 and 47 9 1 3 ma respectively which accord with the expected stratigraphic positions of these sediments conversely shark teeth from the paleocene eocene chouabine formation have large variation in sr isotope ratios even within individual layers after statistical treatment and then elimination of certain outlier samples three age models are proposed and discussed the most reasonable solution includes three subsequent sr ages of 61 8 2 2 ma 57 2 1 8 and 54 6 1 6 for layer ix layers viii v and layers iv 0 respectively three scenarios are discussed for explanation of the presence of the outliers 1 diagenesis 2 re working and 3 locally controlled seawater sr isotope ratio the most plausible account for the higher 87sr 86sr ratios relative to the global ocean in some fossils is enhanced intrabasinal re working due to low sea level conversely the sample with lower 87sr 86sr than the global seawater may link to diagenesis or to seawater influenced by weathering of late cretaceous marine carbonates which latter is supported by model calculation as well the end values of these fossils are very similar to those reported for paleogene and late cretaceous tethyan seawater and are compatible with the above interpretations the relatively low oxygen isotope values in shark teeth from the topmost phosphate bed of the chouabine formation together with the sr isotope results point toward recovering better connections with the open sea these 18o data reflect elevated ambient temperature which may link to the early eocene climatic optimum

evidence for warm wet heinrich events in florida analyses of pollen and plant macrofossils from a new core spanning the past 60 000 years from lake tulane florida show a strong antiphase relationship in temperature between florida and the north atlantic region during the pleistocene oak scrub and prairie phases were coeval with long intense dansgaard oeschger interstadials warm periods that initiated bond cycles pine phases were coeval with the north atlantic long stadials cold periods that ended bond cycles and were terminated by heinrich events lake levels were higher during pine phases and climate was wetter however climate in florida was also warmer during these phases which were cold periods in the north atlantic perhaps diminution of thermohaline circulation before and during heinrich events reduced northward heat transport and retained warmth in the subtropical atlantic and gulf of mexico

physical modelling of overburden deformation around salt diapirs abstract salt diapirs produce highly complex deformation patterns in the surrounding overburden which are difficult to image seismically or model numerically to further the understanding of deformation around salt structures we have used physical models with brittle granular overburdens and simulated sedimentation accompanying diapiric rise rigid linear indentors produce a crestal horst above the indentor with two flanking graben large amounts of indentation produce predominantly reverse faults along the margins of the diapir and extensional faults over the crest in contrast hemispherical indentors produced inward dipping concentric reverse faults forefully intruded polymer diapirs produce a narrow crestal graben above the diapir crest downbuilt polymer diapirs produce extensional faults on the flanks of the diapirs which offset the diapir walls no clear secondary rim synclines were developed as polymer is withdrawn evenly from the whole of the polymer layer across the model strong and anisotropic layered overburden were simulated using cohesive clay and mica respectively detachments were formed along mica layers which suppressed faults with large throws cohesive layer deformation began with tensile fractures permitting rotation of fractured rafts around the sides of the diapir these progressively slip off the crest and create large gaps in the stratigraphy

crustal structure of the eastern algerian continental margin and adjacent deep basin implications for late cenozoic geodynamic evolution of the western mediterranean the karukera spur is an easternmost submerged rise of the lesser antilles fore arc in the guadeloupe archipelago culminating about 4000 m above the fore arc basin 150 km west of the deformation front the analysis of 3500 km 2d high resolution multichannel seismic reflection and multibeam bathymetric data and the study of 14 core samples allow for the first time to reconstruct its sedimentary anatomy and tectonic evolution seven seismic units us1 to us7 are evidenced organised into four major depositional sequences separated by erosional surfaces units us1 to us4 thicken to the south southeast on the spur the sedimentary deposits rest upon a deeply eroded metamorphic basement of the caribbean plate as in la desirade island sequence 1 units us1 and us2 remains unknown in its lower part because it does not outcrop its upper part comprises early miocene shallow water carbonates sequence s2 unit us3 only comprises an upper miocene transgressive systems tract deposited into basinal environment it is bounded by major erosional surfaces sb2 and sb3 sequence 3 us4 to us6 is zanclean to pleistocene it is dominantly composed of shallow water reefal deposits sequence 4 corresponds to recent deposits the karukera spur experienced three main extensional episodes with alternations between uplift and subsidence periods uplifts are responsible for emersions and erosions subsidence severely drowned shallow water deposits the first extensional episode led to the formation of horsts and grabens in the basement prior to early miocene deposits the second extensional episode occurred during upper miocene in accordance with data in surrounding islands the third tectonic episode developed since calabrian noticeable is the constant reactivation of n130 n150 n150 n180 and n40 trending faults since early miocene and the neoformation of e w trending faults since calabrian our results suggest that at the latitude of guadeloupean archipelago the lesser antilles subduction zone is an erosional margin because of the successive sweepings of the santa lucia then tiburon ridges

gravity analysis of salt structures an example from the el kef ouargha region northern tunisia triassic outcrops in the atlassic zone of northern tunisia may be modelled in two ways salt bodies piercing through cretaceous terrains or triassic salt flows stratified within an albian series both models find support from gravity data and are debatable to evaluate the mass distribution changes with depth the bouguer anomaly of the el kef ouargha region was successively decomposed into regional and residual components to construct multiple pseudo depth slices and apparent density maps analyses of gravity lows clearly show a vertical continuity of less dense materials below the triassic salt outcrops these features can be explained by salt diapirism during mesozoic and cenozoic further gravity data tend to indicate less dense materials below aptian outcropping in jebel aite oued bou adila thus suggesting triassic materials occurring at depth in addition dense entities were recognized under mio pliocene and quaternary deposits which are thought to correspond to cretaceous paleoshoals currently collapsed by non outcropping faults our findings lend support to a diapir model intruding overburden rather than the salt glacier model stratified in the albian series proposed by some authors as the genetic structural model for triassic material bearing series in the north of tunisia

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr