did the last sea level lowstand always lead to cross shelf valley formation and source to sink sediment flux 1 it is commonly believed that the efficiency of sediment flux from continents to oceans is maximized during relative sea level rsl lowstands by means of cross shelf valleys that are directly connected to the continental slope and deep marine environment while such conditions have been documented for the last rsl lowstand along several continental margins there is increasing evidence that radically different conditions persisted during the last glacial maximum lgm elsewhere with lowstand shorelines that remained on the continental shelf here we analyze the relationship between the lgm 21 ka shoreline and the shelf edge for the gulf of mexico off the united states and the bay of biscay off france a geophysical model is used to compute shoreline positions corrected for isostatic movements and the shelf edge position is quantified by means of curvature the conditions in the two study areas differed markedly throughout the gulf of mexico study area lgm sea level dropped to a point commonly 40 m below the shelf edge consistent with conventional sequence stratigraphic models while in the bay of biscay the modeled lgm shoreline remained well landward of the shelf edge in places separated by hundreds of kilometers these observations hint at potentially significant implications for 1 the source to sink sediment flux from continents to oceans and its variation in time and space 2 sequence stratigraphic models that predict deep marine sedimentation as being particularly prominent during rsl lowstands and 3 the occurrence of paleovalleys and related features on the continental shelf in addition our findings raise fundamental questions about the mechanics of shelf edge formation

changes in biological productivity along the northwest african margin over the past 20 000 years the intertropical convergence zone and the african monsoon system are highly sensitive to climate forcing at orbital and millennial timescales both systems influence the strength and direction of the trade winds along northwest africa and thus directly impact coastal upwelling sediment cores from the northwest african margin record upwelling related changes in biological productivity connected to changes in regional and hemispheric climate we present records of 230th normalized biogenic opal and corg fluxes using a meridional transect of four cores from 19 n 31 n along the northwest african margin to examine changes in paleoproductivity since the last glacial maximum we find large changes in biogenic fluxes synchronous with changes in eolian fluxes calculated using end member modeling suggesting that paleoproductivity and dust fluxes were strongly coupled likely linked by changes in wind strength opal and corg fluxes increase at all sites during heinrich stadial 1 and the younger dryas consistent with an overall intensification of the trade winds and changes in the meridional flux gradient indicate a southward wind shift at these times biogenic fluxes were lowest and the meridional flux gradients were weakest during the african humid period when the monsoon was invigorated due to precessional changes with greater rainfall and weaker trade winds over northwest africa these results expand the spatial coverage of previous paleoproxy studies showing similar changes and they provide support for modeling studies showing changes in wind strength and direction consistent with increased upwelling during abrupt coolings and decreased upwelling during the african humid period

slope water current over the laurentian fan on interannual to millennial time scales the strength and position of surface and deep currents in the slope water south of newfoundland are thought to vary as a coupled system in relation to the dipole in atmospheric sea level pressure known as the north atlantic oscillation nao paleoceanographic data from the laurentian fan used as a proxy for sea surface temperature reveal that surface slope waters north of the gulf stream experienced warming during the little ice age of the 16th to 19th centuries and support the notion of an nao driven coupled system the nao may be a useful model for millennial scale ocean variability during interglacial climate states

major storm periods and climate forcing in the western mediterranean during the late holocene abstract big storm events represent a major risk for populations and infrastructures settled on coastal lowlands in the western mediterranean where human societies colonized and occupied the coastal areas since the ancient times the variability of storm activity for the past three millennia was investigated with a multi proxy sedimentological and geochemical study from a lagoonal sequence mappings of the geochemistry and magnetic susceptibility of detrital sources in the watershed of the lagoon and from the coastal barriers were undertaken in order to track the terrestrial or coastal marine origin of sediments deposited into the lagoon the multi proxy analysis shows that coarser material low magnetic susceptibility and high strontium content characterize the sedimentological signature of the paleostorm levels identified in the lagoonal sequence a comparison with north atlantic and western mediterranean paleoclimate proxies shows that the phases of high storm activity occurred during cold periods suggesting a climatically controlled mechanism for the occurrence of these storm periods besides an in phase storm activity pattern is found between the western mediterranean and northern europe spectral analyses performed on the sr content revealed a new 270 year solar driven pattern of storm cyclicity for the last 3000 years this 270 year cycle defines a succession of ten major storm periods sp with a mean duration of 96 54 yr periods of higher storm activity are recorded from 680 to 560 cal yr bc sp10 end of the iron age cold period from 140 to 820 cal yr ad sp7 to sp5 with a climax of storminess between 400 and 800 cal yr ad dark ages cold period and from 1230 to 1800 cal yr ad sp3 to sp1 little ice age periods of low storm activity occurred from 560 cal yr bc to 140 cal yr ad sp9 and sp8 roman warm period and from 820 to 1230 cal yr ad sp4 medieval warm period

climate variability during the last 2000 years in the tagus prodelta western iberian margin benthic foraminifera and stable isotopes abstract a high resolution sedimentary sequence recovered in the tagus prodelta has been studied in order to reconstruct paleoenvironmental conditions on the western iberian margin portugal through the last ca 2000 years including the historical time when anthropogenic influence became significant benthic foraminiferal assemblages as well as stable isotopic composition of the benthic foraminifera uvigerina sp were investigated considerable environmental fluctuations are indicated by all these proxies between ad 400 and 1400 1550 550 cal year bp during a period including the medieval warm period bottom water temperatures as reconstructed from uvigerina sp were high 13 3 c in this time interval species typical for shelf environments cassidulina laevigata nonion asterizans and hyalinea balthica maintained a high abundance along with opportunistic species like bolivina dilatata and bolivina pacifica the most abundant species in the record a faunal change occurred at around ad 1300 1400 650 550 cal year bp at the beginning of the little ice age after this the environment became more variable in the tagus prodelta as reflected by a decrease in faunal diversity and benthic foraminiferal composition and flux values after about ad 1800 150 cal year bp bottom water temperatures rose to maximum values of the record the disappearance of certain benthic taxa and the appearance of the species saidovina karreriana indicate a change in bottom water conditions during the last 100 years possibly induced by anthropogenic pollution

cryptic sequence boundaries in braided fluvial successions in braided fluvial deposits consisting of monotonous successions of sandstone or conglomerate it may be difficult to distinguish regionally significant bounding surfaces sequence boundaries from autogenic channel scour surfaces major surfaces may be characterized by erosional relief and draped by lag deposits but not all sequence boundaries show these characteristics other clues to the presence of a major surface are sharp changes in detrital composition shifts in regional palaeocurrent trends and evidence of early diagenesis of the sandstones immediately below the sequence boundary examples of these attributes of cryptic sequence boundaries are illustrated from three mesozoic units in the colorado plateau area of the united states in the chinle formation triassic near moab utah angular intraformational unconformities overlie sandstones showing evidence of early diagenesis in the castlegate sandstone upper cretaceous of east central utah a cryptic sequence boundary can be discriminated from other erosion surfaces by the evidence of detrital petrography and early diagenesis palaeocurrent data indicate changes in regional palaeoslope at two sequence boundaries within this unit evidence of early diagenesis is also present at a sequence boundary in the kayenta formation jurassic of westernmost colorado

geologic factors controlling co2 storage capacity and permanence case studies based on experience with heterogeneity in oil and gas reservoirs applied to co2 storage a variety of structural and stratigraphic factors control geological heterogeneity inferred to influence both sequestration capacity and effectiveness as well as seal capacity structural heterogeneity factors include faults folds and fracture intensity stratigraphic heterogeneity is primarily controlled by the geometry of depositional facies and sandbody continuity which controls permeability structure the permeability structure in turn has implications for co2 injectivity and near term migration pathways whereas the long term sequestration capacity can be inferred from the production history examples of gulf coast oil and gas reservoirs with differing styles of stratigraphic heterogeneity demonstrate the impact of facies variability on fluid flow and co2 sequestration potential beach and barrier island deposits in west ranch field in southeast texas are homogeneous and continuous in contrast seeligson and stratton fields in south texas examples of major heterogeneity in fluvial systems are composed of discontinuous channel fill sandstones confined to narrow sinuous belts these heterogeneous deposits contain limited compartments for potential co2 storage although co2 sequestration effectiveness may be enhanced by the high number of intraformational shale beds these field examples demonstrate that areas for co2 storage can be optimized by assessing sites for enhanced oil and gas recovery in mature hydrocarbon provinces

abrupt post glacial climate events in west asia and north africa monsoon domains regions beyond the present or past penetration of the indian and african monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14c kyr pollen and lake records from west asia western tibet and rajasthan east africa ethiopia and west africa western sahara sahel and subequatorial africa were selected on the basis of chronological control sensitivity of both site and environmental indicators to climate change the continuity of the record and interdisciplinary control of the palaeoclimatic interpretation conditions wetter than those of today prevailed during the early mid holocene period but major dry spells are recorded at all sites during the intervals 11 0 9 5 kyr bp 8 7 kyr bp and 3 4 kyr bp several records also suggest dry events of minor amplitude around 6 kyr bp potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed the solar radiation accounts for the general envelop of the post glacial monsoon fluctuations but explains neither the timing nor the amplitude of the short term changes in spite of apparent covariation between fluctuations in sea surface conditions in the north atlantic and the monsoon record no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength changes in tropical land surface conditions soil moisture negative feedback and changes in ch4 production from wetlands provide a more satisfactory hypothesis for explaining abrupt reversal events

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

late holocene variability of upper north atlantic deep water temperature and salinity 1 magnesium calcium ratios in benthic foraminifera cibicidoides pachyderma from a sediment core on the laurentian slope 1854 m exhibit strong millennial scale fluctuations during the past 4000 years we convert these data to seawater paleotemperatures using a new monospecific linear equation results suggest that the temperature of upper north atlantic deep water dominated by labrador seawater today has varied by at least 2 c during the late holocene millennial scale coolings coincide with previously identified periods of increased drift ice and regional glacier advances including the little ice age paired oxygen isotope measurements indicate that salinity and perhaps density were reduced during the cold periods we discuss possible mechanisms for transmitting this cold fresh signal from surface waters to intermediate depths our reconstructed late holocene ranges in upper north atlantic deep water properties greatly exceed those of the instrumental record and imply that large changes may be yet to come

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

synsedimentary faults and amalgamated unconformities insights from 3d seismic and core analysis of the lower triassic middle buntsandstein ems trough north western germany the late permian early triassic succession of the central european basin ceb was repeatedly affected by the tectonic pulses associated with the earliest phases of tethyan and arctic north atlantic rifting effects of the differential tectonic subsidence are particularly well recorded by unconformities which form widespread sequence boundaries such unconformities are most obvious in areas occupied by fault controlled intra basinal highs swells in that areas stratigraphic loss may comprise entire lower and middle buntsandstein formations and in places remnant middle buntsandstein successions directly rest on permian strata analysis of 3d seismic data and well logs combined with high resolution sedimentological logging of drillcores at the western margin of the ems trough nw germany reveals details of synsedimentary tectonic control on sequence development early triassic extensional faulting of basement blocks provided stepwise addition of accommodation space for continental sequences by growth faulting along north south oriented fault zones blocks on the flanks of the east netherlands high this process is most evident during the development of the hardegsen unconformity which is characterised by an amalgamation of succeeding unconformity surfaces in areas of structurally controlled intrabasinal highs

diagenetic signatures of stratal surfaces in the upper jurassic fulmar formation central north sea ukcs sedimentation rate and changes in relative sea level affect early diagenetic cementation along key stratal surfaces within the deeply buried upper jurassic fulmar formation south central graben ukcs as a result of the bioturbated nature of the shallow marine strata variations in ichnofabrics and cross cutting relationships between trace fossils are important in identifying and correlating stratal surfaces two transgressive and two regressive surfaces sequence boundaries were studied using petrographical mineralogical and geochemical techniques cements including early diagenetic pyrite framboids grain rimming apatite microcrystalline dolomite and ankerite occur at above and immediately below both transgressive and forced regressive surfaces sequence boundaries breaks or subdued rates of sedimentation associated with both types of surfaces meant that the sediment package resided within early diagenetic zones for prolonged periods of time enhancing diagenetic reactions at and below the surfaces the distribution of ankerite despite being a deep burial cement was primarily controlled by concentrations of bioclasts that are particularly abundant at transgressive surfaces the diagenetic character of the forced regressive surfaces sequence boundaries is more complex than that of the transgressive surfaces both in terms of mineralogy and paragenesis this is attributed to the superimposition of diagenetic assemblages as a result of erosion re sedimentation and sediment by passing although the diagenetic signature of the surfaces has been modified by dissolution replacement reactions during deep burial early diagenetic signatures can still be distinguished

high resolution alkenone sea surface temperature variability on the north icelandic shelf implications for nordic seas palaeoclimatic development during the holocene the palaeoceanography of the northern icelandic shelf for the holocene period was reconstructed from alkenone indices measured in core jr51 gc35 this contains a continuous record of holocene sedimentation spanning 0 10 2 cal kyr bp with a resolution of 20 yr cm we have identified a general holocene cooling trend that has superimposed millennial scale oscillations of 28c their timing is in close agreement with the timing of glacier advances in northern iceland for the later half of the holocene the alkenone sea surface temperature sst record from jr51 gc35 correlates with proxy data for the strength of nadw formation recorded in cores south of iceland this is interpreted as evidence of a close connection existing between north icelandic sea surface temperatures and the north atlantic meridonal overturning circulation the timing of the millennial scale sst variability in our core off north iceland is found to be out of phase or anti phased with the sst variability of a record in the eastern nordic seas md952011 this suggests that the evolution of holocene climate in the nordic seas was more complex than previously proposed and it is likely to be caused by differential responses of the irminger and norwegian currents and modulated by changes in atmospheric circulation analogous to the north atlantic oscillation

estimating pliocene sea surface temperatures in the mediterranean an approach based on the modern analogs technique the possibilities of adapting the modern analogs technique mat based on planktonic foraminifers for estimating sea surface temperatures sst in the mediterranean during the pliocene are discussed in this article the calibration database used comprises 684 core top samples distributed in the north atlantic and the mediterranean mat estimates show an imperceptible bias 0 03 c 0 59 and a low mean error of estimates 0 42 c 0 42 when applied over the samples of the calibration dataset the procedure used for assimilating the pliocene taxonomic categories to those of the modern assemblages results in an increase from 17 to 40 in the number of samples showing an error n2 c when applied over the calibration database however the precision of mat does not diminish when these samples are removed from the dataset this methodology was used for obtaining sst estimates of late middle pliocene earliest pleistocene samples from odp site 975 menorca area which have close modern analogs within the calibration database in order to compare this technique with an additional proxy we measured also 18 o values of g bulloides tests from these samples the results obtained show a good agreement on the whole which corroborates the validity of the technical approach proposed 2006 elsevier b v all rights reserved

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

chronological uncertainty severely complicates the identification of cyclical processes in radiocarbon dated time series abstract cycles are widely considered to be an important feature of environmental and human history over the last 50 000 years however there is an overlooked problem in the investigation of cyclicity in this time period the standard statistical methods for identifying cycles assume that observations are precisely dated but the main relevant dating technique radiocarbon dating often yields dates with large and highly irregular uncertainties here we present the results of a massive simulation study that explored the impact of radiocarbon dating uncertainty on our ability to identify cycles in time series our results suggest there is indeed a problem we found that at best we could correctly identify known cycles only 42 of the time and that the false positive rate was as high as 90 this indicates that an individual analysis of a single time series is very likely to return false positive cycles one implication of this is that many of the environmental and sociopolitical cycles that have been identified may not be real consequently a program of reassessment is needed

faunal and alkenone reconstructions of subtropical north atlantic surface hydrography and paleotemperature over the last 28 kyr two techniques for estimating past variations in sea surface temperature sst have been used to investigate climatic change in biogeochemical oceanic flux study bofs core 31k 19 n 20 w from the eastern subtropical atlantic high resolution sst records for the last 28 kyr have been produced using planktonic foraminiferal assemblages based on the imbrie kipp transfer function technique and the uk 37 index derived from abundances of c37 alkenones biosynthesized by prymnesiophyte algae modern observations suggest that these indices reflect particular hydrographic conditions in the upper ocean the uk 37 index corresponds to the temperature at the time of maximum coccolith productivity typically late spring early summer in the study area today whereas the faunal transfer function is calibrated for seasonal maximum and minimum temperatures in general the faunal and biomarker paleotemperature records display comparable sst variations during the last glacial and deglacial but although the overall trends are similar differences exist in the magnitude and timing of these temperature changes most notably the faunal twarm and uk 37 sst estimates diverge by 3 c between 8 ka and 6 ka and this offset persists through the late holocene this difference cannot be adequately explained by uncertainties associated with either the calibration data sets or fluctuating preservation levels we therefore propose that the deviation in sst estimates is linked to a switch in the seasonal timing of maximum coccolith production from the summer in the glacial ocean to the late spring early summer in the modern ocean our results suggest that a dual approach to sst estimation based on faunal and biomarker proxies can provide a valuable means of evaluating mixed layer and productivity changes associated with the movement of oceanographic frontal zones during the late quaternary

molecular stratigraphy of cores off northwest africa sea surface temperature history over the last 80 ka the molecular stratigraphy of biogeochemical oceanic flux study core 31k 19 n 20 10 w and ocean drilling program hole 658c 20 45 n 18 35 w has been studied for c37 alkenone abundances over the past 80 ka at high resolution circa 200 500 years the derived uk37 sea surface temperature record for both cores shows a range of temperatures from about 18 c during the last glacial to 21 5 c during the early holocene both records also reveal changes in sea surface temperature as much as 2 4 c over a few hundred years which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the ne atlantic associated with heinrich events our results indicate that meltwater produced by these ice rafting events was transmitted southward by the canary current where it had considerable impact on sea surface temperatures in the subtropical eastern atlantic

holocene climate and vegetation dynamics on nightingale island south atlantic an apparent interglacial bipolar seesaw in action abstract high resolution analyses of a sediment sequence from an in filled lake on nightingale island at 37 s in the south atlantic have revealed hydrological variations during the last 10 700 cal yr bp which are linked to shifts in the southern hemisphere westerlies and the meridional overturning circulation moc in the atlantic the lowermost part of the sequence 10 700 8600 cal yr bp consists of peat the peat is overlaid by gyttja which continues up to the final overgrowing of the basin around 500 years ago the transition from peat to gyttja at 8600 cal yr bp implies a significant increase in effective humidity probably caused by a northward shift of the southern hemisphere westerlies after the end of the antarctic thermal optimum recurring phases of increased erosion with high deposition of minerogenic particles terrestrial organic matter high c n ratios and pollen grains from plant taxa growing in more distal parts of the catchment indicate periods with higher precipitation these high precipitation periods correspond to periods of southward shifted southern hemisphere westerlies inferred from south america and with periods of weaker moc in the north atlantic therefore we conclude that these periods also characterized by decreased influence from marine aerosols were not caused by the stronger westerlies but by weaker moc and less heat transport from the south to the north atlantic causing warmer sea surface temperatures ssts and increased precipitation in the south atlantic this is the expression of the bipolar seesaw mechanism and implies that it may have been operational also during interglacial conditions

mid holocene climate change in lake bosumtwi ghana lake bosumtwi is one of the most widely studied palaeoclimate archives in west africa results from numerous ams 14c dates of samples from four piston cores from lake bosumtwi show that an abrupt sedimentary transition from a mid holocene sapropel to calcareous laminated muds occurred at about 3200 cal yr b p high resolution analyses of the nitrogen isotopic composition of organic matter across this transition confirm its abrupt nature and suggest that the change may signal a step toward increased aridity and intensified surface winds that affected western equatorial africa from ghana to the congo basin northern and eastern africa experienced a similar abrupt shift toward aridity during the late holocene but at about 5000 cal yr b p a difference in timing that illustrates the regional nature of climate changes during the holocene and the importance of feedback mechanisms in regulating holocene climate variability furthermore an abrupt change at about 3000 cal yr b p occurs at several sites adjacent to the tropical and subtropical atlantic which may hint at major changes in the surface temperatures of the tropical atlantic and or pacific at this time

controls on the stratigraphic framework and paleoenvironmental change within a holocene estuarine system pamlico sound north carolina usa abstract this study examines the holocene stratigraphic record and paleoenvironmental evolution of a large estuarine system at high temporal and spatial resolution in the context of changing climate sea level and hydrodynamics new data are used to examine two time periods of increased marine influence within pamlico sound in northeastern north carolina interpreted to be the result of extensive barrier island segmentation synchronous with periods of rapid climate change during the late holocene the study reveals the controls on the stratigraphic development and the highly dynamic character of the coastal system in response to climate and sea level change as it interacts with paleotopography these findings can be used to inform projections of future environmental changes estuarine waters occupied paleovalleys in the pamlico sound region as early as ca 7500 cal bp and pleistocene interfluves separated the paleovalleys from the atlantic ocean until ca 5500 cal bp when they were flooded by rising sealevel forming the broad shallow pamlico sound initial barrier islands and shoals likely formed sometime between 5500 and 5000 cal bp providing the geomorphic setting for continued estuarine conditions behind the barriers at ca 4000 cal bp an increase in marine influence and sand content is detected in multiple cores and is correlated to seismic data within the pamlico sound basin this change is interpreted to be the result of increased segmentation of barrier islands thus a greater number of inlets or wider inlets which is consistent with a rapid transgression seen in other areas of the u s east coast the segmentation may have been partially facilitated by a rapid increase in lagoonal area and tidal prism by overtopping of interfluves greater barrier island continuity is evident from 3500 to 1200 cal bp as indicated by muddy deposits with low brackish estuarine foraminiferal assemblages at ca 1200 cal bp seismic sedimentological and micropaleontological data suggest an increase in wave and current energy and marine influence throughout southeastern pamlico sound these changes are interpreted to represent extensive segmentation of the barrier islands during the medieval climate anomaly mca since ca 500 cal bp the pamlico sound system has returned to a more restricted state as inlets have closed currently only three major inlets segment the outer banks the barrier island system fronting pamlico sound but warming climate and increasing rates of sea level rise suggest that another episode of barrier island segmentation began about a half century ago and appears that it may extend into the near future

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

signatures of the late holocene neoglacial cold event and their marine terrestrial linkage in the northwestern pacific margin marine microfossil assemblages in core sediments from the northern east china sea ecs were investigated to understand late holocene paleoclimatic changes in the northwestern pacific margin we find a pronounced alternation of ocean condition during the late holocene characterized by an abrupt decrease in dinoflagellate cysts and kuroshio water species of planktonic foraminifera centered at ca 4000 2500 14c yr bp compilation and merger of new and previously published data show that this oceanic event corresponds with terrestrial cooling and dry episodes in the northern china the synchronicity between marine and terrestrial records is considered to be linked to a weakened kuroshio influence that is in coupled with intensified winter monsoon highlighting a significance of oceanic atmospheric dynamics in determining moisture and heat distribution over both oceanic and terrestrial domains superimposed on the late holocene the synchronicity between this particular climatic shift in the northwestern pacific and the neoglacial cold events in the northern high latitude regions is tentatively indicative of a global climate signal possibly associated with dynamics of the north pacific gyre system and the high latitude north atlantic thermohaline circulation and therefore positions of the mean latitude of the kuroshio extension

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

first high resolution multi proxy palaeoenvironmental record of the late glacial to early holocene transition in the ria de arousa atlantic margin of nw iberia abstract a 322 cm long sedimentary sequence obtained in the shallow marine basin of the ria de arousa a submerged unglaciated river valley on the atlantic margin of northwestern iberia was analysed using a multi proxy approach to study how climatic and sea level changes affected the coastal ecosystems during the last glacial interglacial transition past sedimentation vegetation and marine productivities were inferred from palynological radiocarbon seismic and lithological data a substantial reduction in the pollen and dinoflagellate cyst accumulation rates is observed at 12 700 to 11 700 cal a bp suggesting lower marine and vegetation productivities likely as a response to the younger dryas cooling event overall the regional vegetation changed from cold tolerant open woodlands pinus sylvestris p nigra and betula dominating before 10 200 cal a bp to coastal wetlands and the regional spread of quercus dominated forests after 9800 cal a bp cluster analysis and principal component analysis allowed the identification of several small environmental oscillations such as the 11 4 ka and 10 5 ka cooling events after that a conspicuous heath expansion was likely favoured by the palaeotopography the increased precipitation and the relative sea level rise which might have caused a profound change in the coastal configuration concurrently both the dinoflagellate cyst and non pollen palynomorph records reveal variations in the marine productivity and coastal hydrodynamics that also agree with a period of marked marine transgression warming and increasing river flow new sedimentary data highlight the high sensitivity of the ria s ecosystems to environmental oscillations and show a close temporal correspondence between terrestrial and marine responses to climate change

simulation of an abrupt change in saharan vegetation in the mid holocene climate variability during the present inter glacial the holocene has been rather smooth in compar ison with the last glacial nevertheless there were some rather abrupt climate changes one of these changes the desertication of the saharan and arabian region some 4 6 thousand years ago was presumably quite important for human society it could have been the stimulus leading to the foundation of civilizations along the nile euphrat and tigris rivers here we argue that saharan and arabian de sertication was triggered by subtle variations in the earth s orbit which were strongly amplied by atmosphere vegeta tion feedbacks in the subtropics the timing of this tran sition however was mainly governed by a global interplay between atmosphere ocean sea ice and vegetation

hydrological changes and paleoproductivity in the gulf of california during middle and late holocene and their relationship with itcz and north american monsoon variability abstract this study investigates changes in precipitation patterns and variations in paleoproductivity in the tropical pacific region associated with the north american monsoon intertropical convergence zone itcz latitudinal migration and changes in insolation during the middle and late holocene major and trace element records al ba c k si and ti and zr al and ba al ratios in a core from alfonso basin southern gulf of california are used as proxies of terrigenous input and bio productivity records reveal an increase in precipitation and low bio productivity ca 6200 to 2400 cal yr bp associated with the strengthening of monsoonal precipitation and northward shift of the itcz mean position in the eastern tropical pacific a multi centennial drought from ca 2400 to 1900 cal yr bp and a dry and cold interval ca 700 and 500 cal yr bp are characterized by strong aeolian input and enhanced productivity associated with diminution of the summer monsoonal precipitation and reduced insolation in the northern hemisphere and more southerly itcz position correlation of alfonso basin records with other records in the gulf of california and the pigmy and cariaco basins in the gulf of mexico and central atlantic provides constraints on nam itcz migration and insolation driven changes

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

late quaternary paleoceanography of the tropical atlantic 2 the seasonal cycle of sea surface temperatures 0 20 000 years b p foraminiferal species abundances are used to estimate seasonal variability of late quaternary sea surface temperatures in the tropical atlantic ocean empirical orthogonal functions analysis of 28 time series isolates two patterns modes of variation the dominant mode 1 reflects seasonal temperature contrast of the south equatorial current region 5 6 c higher at the glacial maximum than at present probably indicating larger seasonal variations of the southern trade winds forcing for this pattern may have come from equatorward compression of glacial climate zones due to high latitude cooling in both hemispheres and or suppression of meridional monsoonal circulation via feedback from northern hemisphere ice cover when compared with climap estimates of lower seasonal variations of glacial age sea ice fronts in antarctica mode 1 suggests decoupling of low and high latitude seasonal cycles in the southern hemisphere on a glacial interglacial scale mode 2 variations reflect seasonal contrast in sea surface temperature of 2 3 c less 9000 to 14 000 years b p than at present along the equator and in the eastern subtropical atlantic perhaps related to an equatorial position of the intertropical convergence zone weakened trade winds and or strengthened monsoonal circulation during deglaciation our findings emphasize the need to isolate spatially coherent and thus dynamically linked patterns of climate change from a complex record of multiple climatic effects only then can effective tests of hypotheses be made with a coupled strategy of data acquisition and climate modeling

dinoflagellate cyst distribution in marine surface sediments off west africa 17 6 n in relation to sea surface conditions freshwater input and seasonal coastal upwelling abstract an organic walled dinoflagellate cyst analysis was carried out on 53 surface sediment samples from west africa 17 6 n to obtain insight in the relationship between their spatial distribution and hydrological conditions in the upper water column as well as marine productivity in the study area multivariate analysis of the dinoflagellate cyst relative abundances and environmental parameters of the water column shows that sea surface temperature salinity marine productivity and bottom water oxygen are the factors that relate significantly to the distribution patterns of individual species in the region the composition of cyst assemblages and dinoflagellate cyst concentrations allows the identification of four hydrographic regimes 1 the northern regime between 17 and 14 n characterized by high productivity associated with seasonal coastal upwelling 2 the southern regime between 12 and 6 n associated with high nutrient waters influenced by river discharge 3 the intermediate regime between 14 and 12 n influenced mainly by seasonal coastal upwelling additionally associated with fluvial input of terrestrial nutrients and 4 the offshore regime characterized by low chlorophyll a concentrations in upper waters and high bottom water oxygen concentrations our data show that cysts of polykrikos kofoidii selenopemphix quanta dubridinium spp echinidinium species cysts of protoperidinium monospinum and spiniferites pachydermus are the best proxies to reconstruct the boundary between the ne trade winds and the monsoon winds in the subtropical eastern atlantic ocean the association of bitectatodinium spongium lejeunecysta oliva quinquecuspis concreta selenopemphix nephroides trinovantedinium applanatum can be used to reconstruct past river outflow variations within this region