living planktonic foraminifera in the eastern south atlantic during spring indicators of water masses upwelling and the congo zaire river plume abstract planktonic foraminifera were collected from pumped surface water samples and net tows over the upper 150 m of the water column in the eastern south atlantic ocean during october and november 1989 of the 24 recorded species 12 occur abundantly and form 6 foraminiferal assemblages the assemblages correlate with the physico chemical properties of the 6 vapor surface water masses the correlation of species with low salinity is due to properties co variant with salinity at several locations high concentrations of planktonic foraminifera were observed caused by frontal mixing or reproduction the g sacculifer g ruber white assemblage marks the south equatorial under current minor contribution of g menardii and n dutertrei to this assemblage reflects the subsurface equatorial under current the n dutertrei g siphonifera assemblage reflects the south equatorial counter current and equatorial under current the n pachyderma g bulloides assemblage reflects the coastal upwelling over the shelf and the filaments of mixed oceanic and upwelled water in the coastal of the benguela current bc the angola benguela front at the interface of the warm currents and the bc is reflected by the g inflata g bulloides assemblage an unusual coincidence of g sacculifer g bulloides in one assemblage results from the interaction of the subtropical gyre and the oceanic branch of the bc the g rubber pink n dutertrei assemblage is attributed to the warm low saline plume in front of the congo zaire river

biotic and geochemical δ 18 o δ 13 c mg ca ba ca responses of globigerinoides ruber morphotypes to upper water column variations during the last deglaciation gulf of mexico abstract within the gulf of mexico gom the bryant canyon is exceptional in that rapid sedimentation sustained by high rates of terrigenous sediment delivery and surface marine productivity make this basin an excellent recorder of paleoenvironmental and paleoclimatic conditions we present a new 21 kyr record of sea surface temperature sst and local salinity changes from the nw gom core jpc 26 approximated from combined globigerinoides ruber morphotype specific 18 o and mg ca as well as ba ca which reflect the subtropical gom hydrographic dynamics and their relationship to both mississippi river discharges and climate evolution during the last deglaciation overall the reconstructed sst and sss related patterns reveal notable variations in amplitude between the analyzed morphotypes adding valuable insights to previously published g ruber w mixed gom records especially during the deglaciation bryant canyon meltwater flooding events bcdfs and associated sea surface freshening seem to be more pronounced than the sst reduction our mg ca derived sst records of both morphotypes g ruber sensu stricto s s and g ruber sensu lato s l show comparable general trends but with important sst differences t we interpret down core t as a record of changing upper water column hydrography with particular influence from the deglacial meltwater bcdfs or holocene bchfs flooding events during the warm intervals the deeper thicker and probably more seasonally persistent mixed layer led to more uniform thermal conditions for both g ruber morphotypes and therefore to a minimum t on the contrary during the cold and low salinity periods the shallower mixed layer favored more habitat divergence and caused a maximum thermal gradient in the well stratified upper water column overall this supports the notion that g ruber s s is consistently calcifying in warmer waters than g ruber s l either due to a shallower depth habitat or to a more summer weighted seasonal distribution moreover intra specific paired 13 c and ba ca differences show that g ruber s l is more sensitive to river water influence than g ruber s s due to its ability to change its depth habitat and therefore exploit optimal temperature salinity productivity stratification conditions during the low salinity events overall our observations support the current practice of treating the two g ruber morphotypes separately and further illustrate the necessity to map both their spatial and temporal distribution

the link between tectonic and paleoclimatic events at 2 8 2 5mabp in the lake baikal region abstract the records of diatom abundance clay fraction content and magnetic susceptibility from lake baikal drill core bdp 96 1 reflect the climate driven plio pleistocene evolution of the lake baikal sedimentation system in addition to the dramatic variations in the proxy records in response to the northern hemisphere ice ages the baikal record also indicates climatic deterioration from 2 8 to 2 5 ma bp with evidence for an early siberian glaciation around the matuyama gauss paleomagnetic reversal boundary the drill core data also allow correlation of this early glacial interval with the basin wide seismic sequence boundary b10 which marks the unconformity produced by the active neotectonic phase in the baikal rift zone at the bdp 96 drill site however the strong b10 acoustic reflection was produced not by an erosional boundary but instead by deposition of glacial clay layers the paleomagnetic age scale of bdp 96 1 constrains the upper age of the neobaikalian uplift subsidence phase in the baikal sayan region at ca 2 5 ma bp the coincident timing of the paleoclimatic and tectonic events recorded in lake baikal sediments suggests a close causal link between regional tectonics and climate and indicate that the late pliocene uplift contributed to the initiation of the early glaciation in southeast siberia between 2 8 and 2 6 ma bp by creating an elevated terrain with lower snowline favorable for alpine glaciation and by changing the heat balance of the region

planktonic foraminifera as indicators of oceanographic complexity on the southern caribbean sea continental shelf abstract the southern caribbean sea over the northern south american continental shelf is oceanographically complex it is subject to 1 widespread coastal upwelling 2 wakes and eddies in the nw flowing guiana and caribbean currents to the lee of islands and 3 the hypopycnal orinoco river plume upwelled water is dispersed nw along high productivity filaments offshore northern trinidad an intra plume front separates higher productivity orinoco derived water to the west from lower productivity amazon derived water this paper examines planktonic foraminiferal assemblages in surface sediment samples a below upwelling foci in the gulf of venezuela gov north of lake maracaibo and b at an upwelling focus in the north coast marine area ncma offshore northern trinidad near but west of the intra plume front the samples were collected for previous studies and only certain size fractions which differed between the study areas were available for current study samples from the gov 250 m fraction taken using an alpine corer or a petersen dredge were assigned a priori to groups underlying upwelled and non upwelled water discriminant analysis after cluster analysis confirmed these assignments total recovery was dominated by neogloboquadrina dutertrei with lesser globigerinoides ruberpink and the upwelling indicator globigerina bulloides all four non upwelled samples co dominated by n dutertrei and gs ruberpink reflect seasonal freshwater outflow from lake maracaibo five upwelled area samples were dominated by g bulloides with subdominant n dutertrei or globigerinoides ruber morphotype b the remaining two upwelled samples dominant n dutertrei subdominant gs ruber morphotype a apparently reflect the transition between upwelling and non upwelling areas the mean proportions of assemblages as trilobatus sacculifer morphotype a did not differ markedly between the upwelled and non upwelled gov clusters this morphotype was absent from the gulf proper but present to the north ncma total recovery 150 m fraction samples taken using a van veen grab was dominated by gs ruber morphotype b cluster analysis here indicated three clusters cluster 1 proximal to the intra plume front cluster 2 distal to the intra plume front and cluster 3 scattered throughout the ncma upwelling was pervasive canonical variate analysis cva verifying that g bulloides did not differentiate the clusters instead these clusters were differentiated by gs ruber morphotype b only the proportional abundance of which was highest in cluster i and lowest in cluster 2 this pattern indicates that the influence of the orinoco plume on assemblage composition is stronger than that of upwelling cluster 1 reflecting higher productivity near the front

planktic foraminifers and hydrography of the eastern and northern caribbean sea the distribution of living planktic foraminifers and their relation to the hydrography of the caribbean sea was investigated in plankton net tows and surface sediment samples taken along the antilles island arc during april may 1996 the planktic foraminiferal community was strongly influenced by spatial variations in salinity that were largely due to the influx of orinoco river water into the southeastern caribbean sea and inflowing sargasso sea water in the north along the antilles island arc globigerinoides ruber was the dominant species in the surface waters throughout in the southeastern caribbean sea where orinoco river outflow influences the planktic community standing stocks of planktic foraminifers 100 m between 4 and 50 specimens m 3 were medium to low the southeastern faunas between tobago and guadeloupe were characterized by increased proportions of neogloboquadrina dutertrei highest standing stocks of 159 specimens m 3 in the upper 20 m of the water column were recorded in the northeastern caribbean sea and the assemblages were characterized by high proportions of globigerinita glutinata associated with cyclonic eddies in the anegada passage where sargasso sea water flows into the caribbean sea low standing stocks of 18 specimens m 3 indicate oligotrophic conditions together with the oligotrophic surface waters the subtropical underwater enters the caribbean sea through the anegada passage in water depths between 100 and 300 m these waters are characterized by higher concentrations of globorotalia truncatulinoides relative to the adjacent water masses comparison of the living planktic foraminiferal fauna with empty test assemblages from the water column and from surface sediments shows that differences in the faunal composition mostly correspond to the distribution of water masses and to the differential dissolution of species in the vicinity of islands globigerinoides ruber reaches higher relative frequencies than in the open ocean pointing towards a higher tolerance of this species towards neritic conditions than in other species

aridization of the transbaikalia in the context of global events during the pleistocene and its effect on the evolution of small mammals abstract the features of the earliest climate aridization and the onset of the arid open landscapes in the transbaikalian region are shown by the early early pleistocene mammalian faunas of the itantsinian complex and by geological data the climate deterioration intensified through the middle and late pleistocene the uplift of mountains surrounding lake baikal is considered to be the main cause for the deep aridization of the western transbaikalia because they became the major orographic barrier preventing humid west atlantic cyclones from reaching the transbaikalian area comparative analyses of successive early middle and late pleistocene faunas have shown that they differ significantly in species composition and in stages of the evolution of taxa belonging to different lineages however the dominant species of faunas demonstrate similar evolutionary trends such as the development of complex shaped teeth structure due to adaptation to feeding on coarse grass and to inhabit arid landscapes

late quaternary benthic foraminifera and the orinoco plume abstract the bathyal benthic foraminiferal palaeoecology east of trinidad is currently unknown the area is oceanographically complex comprising a pro delta deep sea fan building across a transpressional plate boundary outflow from the orinoco river forms a high productivity surface plume that abuts low productivity water of the tropical western atlantic ocean across a laterally extensive but sharp front the plume s areal extent differs between the rainy and dry seasons which are governed by the position of the inter tropical convergence zone itcz upper quaternary benthic foraminifera are examined in two 4 m long piston cores taken near the eastern edge of the plume chirp profiles show that core bgt086 water depth 626 m comprised in situ material throughout while the lower part of core bgt096 water depth 700 m consisted of slumped material benthic foraminiferal assemblages in bgt086 were examined quantitatively while those in bgt096 were examined qualitatively only for comparison core bgt086 shows a transition from a low diversity cibicidoides pachyderma dominated community with subdominant cassidulina curvata to a later high diversity low dominance bulimina alazanensis osangularielloides rugosa epistominella exigua community the former is indicative of low productivity and the latter of high productivity surface water the restriction of e exigua to the core s upper part may reflect a change from an aseasonal to a seasonal organic flux the faunal change was detected by both she and cluster analyses and an assemblage turnover index ati it may be related to either a expansion of the orinoco plume due to northward migration of the itcz approximately 600 yr after the end of the younger dryas b eastward progradation of the orinoco delta which would in turn push the front of the orinoco plume eastward or c both no other boundary detected was common to all three procedures a boundary between 124 and 130 cm below the seafloor detected by she analysis might equate to the 8000 7500 yr bp meltwater pulse 1c while some specialist species were restricted to the c pachyderma or the b alazanensis o rugosa e exigua communities the percentage abundance of some others concluded to be relative generalists e g bulimina aculeata and sphaeroidina bulloides varied little through the core the undisturbed section of core bgt096 showed the same general faunal succession as core bgt086 the slumped material in this core was rich in eponides regularis which was rare elsewhere this species shows that the allochthonous sediment was derived from the outer shelf and upper slope 100 400 m water depth during late pleistocene time

pliocene and pleistocene biostratigraphic succession of transbaikalia with emphasis on small mammals this paper deals with the pliocene pleistocene and holocene mammalian faunas of the transbaikal area for which 15 successive mammalian faunas are recognized this review is based on the study of new paleontological materials obtained from several late cenozoic localities and reexamination of existing faunal data stratigraphically the oldest fauna is known as udunginian it contains mostly fossils of forest inhabitants and few arvicolids this fauna was replaced by the next pliocene hipparion assemblage known as the chikoi faunistic complex characterized by the dominance of forest steppe and open landscape inhabitants as well as by the abundance and diversity of rooted arvicolids the itantsinian complex is the following faunistic level of the late pliocene it is characterized by the first appearance of equus and spermophilus and by the presence of progressive taxa of rooted voles the early pleistocene fauna is characterized by the appearance and abundance of rootless arvicolids and by the continued existence of the latest rooted voles the middle pleistocene tologoi faunistic complex is distinguished from the preceding one by the disappearance of rooted voles the late pleistocene fauna featured a diversity of microtus taxa and an abundance of lasiopodomys and ochotona species the majority of the late pleistocene small mammals belong to recent species although some of them were distributed over a greater area at that time than at present

seasonal associations of phytoplankton and planktic foraminifera in an upwelling region and their contribution to the seafloor abstract seasonal occurrences of both phytoplankton and zooplankton are closely associated with upwelling and stabilization in waters overlying the san pedro basin this region is situated within the southern california bight and is affected by variations in the general southward flowing california current and variable intrusion of oceanic waters increased northerly wind stress in spring and early summer results in upwelling of deeper nutrient rich waters into the photic zone a seven month time series sediment trap experiment revealed clear patterns in seasonal succession of both phytoplankton and planktic foraminifera several distinct high and low flux periods occurred over the study period some of which can be related to rapid changes in the hydrographic environment caused by upwelling and subsequent surface water stratification factor analysis of relative abundances of combined phytoplankton and foraminiferal taxa defines seven assemblages reflecting seven stages of production which range in duration from two to five weeks factor scores describe phytoplankton and foraminiferal taxa indicative of specific production stages periods of high flux of the more abundant diatoms and planktic foraminifera also illustrate preferred production stages and compare well with percentage based results a comparison of the sediment trap assemblage with local sediment from an oxygenated portion of the basin suggests that long term phytoplankton accumulation in this region is dominated by taxa associated with winter bloom and post upwelling bloom production implying that brief but massive episodic events overwhelm and dominate the annually averaged diatom species assemblage found in the sediments foraminifera however are modified by dissolution to the extent that the high production periods of late spring and during upwelling are poorly represented rather species indicative of early spring and post upwelling conditions dominate the planktic foraminiferal sedimentary assemblage

the influence of shelf vicinity on the distribution of planktic foraminifera south of puerto rico abstract the effects of water masses and depth on the distribution of planktic foraminifera across the island slope of southwestern puerto rico were studied in holocene surface sediments samples from the depth range of 432 4700 m covered 0 5 95 km distance from the shelfbreak shallower samples in this region are altered by winnowing plankton net tows through the upper 120 m of the water column sampled the living planktic foraminiferal population in the same area they contained shallow water benthic foraminifera that were probably brought into suspension on the shelf and transported seawards with the shelf outflow water illustrating the exchange of water and suspended particles from the shelf to the slope the grain size spectrum of the sediment samples shows no depth related trend the sand fraction 63 m consists of foraminifera pteropoda and on the upper slope of reef detritus the bulk carbonate content varies from 51 to 73 the abundance of planktic foraminifera per gram sediment increases with depth while the number of benthic foraminifera decreases with water depth the composition of the benthic assemblage shows an increase of the ratio of agglutinated versus calcareous perforate forms the planktic foraminiferal assemblage 150 m is dominated by globigerinoides ruber and shows no obvious trend over the sampled depth range the plankton benthos ratio increases with depth from 0 63 to 0 99 as a result of opposite trends in accumulation rates of benthic and planktic foraminifera accumulation rates of planktic foraminifera increase with distance from the shelfbreak and with water depth from 10 000 to 30 000 specimens cm 2 ka indicating the influence of ecological and or depositional processes on their distribution it is suggested that the tests of planktic foraminifera are displaced in a seaward direction by lateral advection therefore their place of deposition does not lie directly underneath the place of production

a 2000 year record of caribbean and tropical north atlantic hydrographic variability 1 here we present near annually resolved oxygen isotope records from two species of planktic foraminifera from the cariaco basin that reflect sea surface temperature sst and intertropical convergence zone itcz precipitation related salinity variations over the caribbean and tropical north atlantic spanning the last 2000 years a strong broad spatial pattern of correlation exists between foraminiferal 18o and ssts over the period of instrumental overlap but the correlations weaken as they are extended back in time and instrumental sst records become discontinuous a long term trend in the globigerinoides ruber 18o record can be explained by two different but equally plausible scenarios first the increase in 18o may indicate that tropical summer fall ssts have cooled by as much as 2 c over the last 2000 years possibly as a result of a long term increase in upwelling intensity alternately comparisons to other studies of itcz and regional evaporation precipitation variability suggest that much of the 18o record is influenced by decadal to centennial scale variations in the mean annual position of the itcz and associated rainfall patterns similarities between the g bulloides 18o record and the 11 year sunspot cycle support prior studies that suggest solar variability plays a role in influencing the hydrologic balance of the circum caribbean

ecosystem analysis of baikal siberia using palaeolithic faunal assemblages to reconstruct mis 3 mis 2 environments and climate abstract integrated studies of the geological context and fauna of palaeolithic sites made it possible to reconstruct climate and environments of baikal siberia during mis 3 mis 2 the main constituents of the faunal assemblages are small mammals which are a reliable bioindicator of landscapes and climates of the past in the fore baikal area fauna recovered from archaeological sites presents a mixture of ecological indicators its components presently inhabiting different natural zones the sediments studied at the bol shoi naryn and gerasimov s sites and dated to mis 3 yielded fauna with a large proportion of tundra species its composition suggests mosaic landscapes of tundra forest meadow steppes and a cold humid climate at the time of human habitation fauna from the malta site mis 2 is indicative of tundra steppe and harsh climate at the beginning of the sartan glaciation evidence from the end of the pleistocene and postglacial indicates the climate becoming warmer and wetter tundra animals are absent from mis 3 sites of transbaikalia according to faunal evidence dry steppe and arid climates existed at the early sartan mis 2 and taiga animal species appeared and increased in importance towards the end of pleistocene when the forests had wide distribution fauna from mis 3 sites in the southwestern baikal area near baikal area is similar to transbaikalia lacking tundra species and dominated by indicators of dry steppe and arid climates the southwestern baikal is more similar to fore baikal area both having a higher proportion of forest species than in transbaikalian assemblages the fauna distribution displays features of mosaic landscapes with distinctly identified zones forest and meadow steppe along rivers and dry steppe and semi desert on south facing slopes of mountains the climate was milder than in the transbaikal and warmer than in the fore baikal area unfortunately we have little data on the fauna of mis 2

comparison of ba ca and as freshwater proxies a multi species core top study on planktonic foraminifera from the vicinity of the orinoco river mouth past river run off is an important measure for the continental hydrological cycle and the assessment of freshwater input into the ocean however paleosalinity reconstructions applying different proxies in parallel often show offsets between the respective methods here we compare the established foraminiferal ba ca and view the mathml source salinity proxies for their capability to record the highly seasonal orinoco freshwater plume in the eastern caribbean for this purpose we obtained a data set comprising ba ca and view the mathml source determined on multiple species of planktonic foraminifera from core tops distributed around the orinoco river mouth our findings indicate that interpretations based on either proxy could lead to different conclusions in particular ba ca and view the mathml source diverge in their spatial distribution due to different governing factors apparently the orinoco freshwater plume is best tracked by ba ca ratios of g ruber pink and sensu lato morphotypes while view the mathml source based on the same species is more related to the local precipitation evaporation balance overprinting the riverine freshwater contribution other shallow dwelling species g sacculifer o universa show a muted response to the freshwater discharge most likely due to their ecological and habitat preferences extremely high ba ca ratios recorded by g ruber are attributed to ba2 desorption from suspended matter derived from the orinoco samples taken most proximal to the freshwater source do not show pronounced ba ca or view the mathml source anomalies here the suspension loaded freshwater lid developing during maximum discharge suppresses foraminiferal populations both proxies are therefore biased towards dry season conditions at these sites when surface salinity is only minimally reduced

planktonic foraminifera as recorders of past surface water stratification the 18 o difference between shallow and deep living planktonic foraminifera is a proxy for the stratification of surface waters in holocene sediments from the atlantic this difference increases from about 0 in subpolar regions to 3 in the tropics the 18 o values of the shallow dwellers globigerinoides sacculifer and neogloboquadrina pachyderma mainly reflect surface water conditions the calcification depth of the deep living species globorotalia truncatulinoides right coiling is affected by the stratification of the water column in the subtropics shell formation of g truncatulinoides right coiling begins in weakly stratified surface waters in the tropics the initial shell is secreted below the mixed layer this hydrographically induced difference in calcification depth allows the use of the isotopic difference between g truncatulinoides and the shallow species as a proxy for the stratification of surface waters the 18 o between g truncatulinoides and g sacculifer from tropical gravity core geob 1523 1 was significantly lower during isotope stage 2 this suggests that the glacial temperature stratification of western equatorial atlantic surface waters was significantly reduced relative to the holocene

an 8 century tropical atlantic sst record from the cariaco basin baseline variability twentieth century warming and atlantic hurricane frequency 1 we present the first direct comparison and calibration of a downcore foraminiferal mg ca record to historical instrumental sea surface temperature sst mg ca measured on the planktic foraminifer globigerina bulloides from a cariaco basin sediment core strongly correlate with spring march may instrumental ssts between a d 1870 and 1990 a mg ca sst equation is derived and a paleo sst record is presented spanning the last 8 centuries an interval that includes the end of the medieval warm period and the little ice age the long term record displays a surprising amount of variability the temperature swings are not necessarily related to local upwelling variability but instead represent wider conditions in the caribbean and western tropical atlantic the mg ca sst record also captures the decadal and multidecadal variability observed in records of global land and sea surface temperature anomalies and atlantic tropical storm and hurricane frequency over the late nineteenth and twentieth centuries a divergence between the sst proxy record and atlantic storm frequency around 1970 appears to reflect a fundamental change in atlantic hurricane behavior noted in historical data on average twentieth century temperatures are not the warmest in the entire record but they do show the largest increase in magnitude and fastest rate of sst change over the last 800 a

records of magnetic properties in quaternary loess and its paleoclimatic significance a brief review due to the successive deposition quaternary loess paleosol sequences potentially provide one of the best terrestrial records of paleoclimatic changes magnetostratigraphy and paleoclimate are two major aspects of magnetic investigation in northern china and other regions of the world the classic loess sections across the chinese loess plateau indicate that wind blown loess deposition began close to the base of matuyama 2 6 ma however progress has also been made in extending the record below the loess into the red clay and the aeolian record can now be carried back beyond 7 ma the surprising similarity between the initial susceptibility is curve obtained from numerous loess paleosol sequences and the oxygen isotope fluctuation from the deep sea sediments provides impressive evidence of the global significance of the magnetic record as a useful proxy in paleoclimatic studies magnetic susceptibility ms has been extensively used to reconstruct the paleoclimate however the actual mechanism of ms enhancement of paleosols remains controversial the important questions why does is fluctuate in loess sections and what are the causes of the is enhancement in paleosols have been matters of debate in the last 10 years currently the viewpoint that pedogenesis plays an important role in the ms enhancement of paleosols has been generally accepted pedogenic magnetite is an important contributor to the ms enhancement is is not only simply controlled by the abundance of strong magnetic minerals but also by their grain size distributions the increment of superparamagnetic sp grains o0 1mm which is induced by pedogenesis could enhance the is of paleosols the formation of sp minerals has been debated as either biotic or abiotic it is now possible to propose a quantitative model for the reconstruction of paleoclimate according to the paleoprecipitation deduced from proxy indicators such as is fluctuation grain size stable isotope composition caco3 content rb sr and ratio of citrate bicarbonatedithionite extractable fe2o3 to total fe2o3 fed fet r 2002 elsevier science ltd and inqua all rights reserved

tologoi key section a unique archive for pliocene pleistocene paleoenvironment dynamics of transbaikalia bikal rift zone abstract the multi layered key section of tologoi is situated on the selenga river left bank 15 km southwest of ulan ude city 51o45 n 107o29 e in the western transbaikal region it holds a long record of quaternary sedimentation since early late pliocene through holocene with the only minor gap in the beginning of early pleistocene comprehensive studies have been carried out on the lithology geochemistry fauna succession and paleoenvironment reconstructions this paper summarizes the data acquired on the geology and stratigraphy of the tologoi section the authors investigated the composition structure and formation conditions of the section as well as the intensity of weathering rock geochemistry grain size and biostratigraphy

tidal dynamics in a coupled ocean lake system abstract barotropic tides were studied in the lake maracaibo system venezuela the system consists of two larger water bodies the gulf of venezuela and lake maracaibo connected by the strait of maracaibo and tablazo bay the dominant semi diurnal tide resonates in the gulf and co oscillates roughly 180 out of phase in the lake the narrow strait and shallow bay regulate their dynamical interaction two and three dimensional finite element models are used in conjunction with a fresh analysis of tidal data at seven stations several of which lie in the strait and bay a coupled model of the whole system is necessary to properly interpret these data which show the influence of small scale near field effects superimposed on the larger scale dynamics of the gulf and lake the detailed geometry at the connections with the gulf and the lake also plays a significant role in the local response in the strait and bay co tidal charts are presented for nine major astronomical and shallow water tidal constituents found in the data the velocity structure derived under simple eddy viscosity assumptions is shown to be highly dynamic a characteristic phase lead is found in velocities at depth and near the shore where vertical shear dominates over inertia in the force balance

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

late quaternary paleoenvironmental reconstruction and paleoclimatic implications of the aegean sea eastern mediterranean based on paleoceanographic indexes and stable isotopes the late quaternary palaeoenvironmental evolution and the main palaeoceanographic changes of the aegean sea was reconstructed using planktonic foraminifera obtained from the sediments of a northern sk 1 and a southern ns 14 core site multivariate statistical approach including q mode cluster and principal component pca analyses gives an insight into the relationships between sea surface environmental changes between the north and south aegean and furthermore serves as a baseline data set for palaeoclimatic and palaeoceanographic reconstructions of the eastern mediterranean sea stable isotope analyses coupled with additional paleoceanographic sea surface temperature sst productivity ssp stratification s index upwelling u index seasonality sn index proxies provide insights into the sedimentological hydrographic and trophic evolution and ecosystem dynamics of the aegean sea and furthermore serve as a baseline data set for palaeoclimatic and palaeoceanographic reconstructions of the eastern mediterranean sea concentrating on the last 19 ka faunal and isotopic data concur suggesting a series of climatic zones corresponding to well known climatic phases of the last glacial cycle cold and arid conditions during the late glacial period were followed by a warmer and wetter climate trend during deglacial time a marked seasonality characterized by homogenous water column favored by efficient upwelling during the winter and by warm stratified water column during the summer has also been recognized during this period bolling allerod b a in both basins an abrupt switch to cool arid climatic event younger dryas yd suggests a strengthening of winter convection around 12 9 ka which seems to be more evident in the north aegean core however the more pronounced environmental changes between the north and south aegean sea were identified during the holocene and they coincide with the deposition of sapropel s1 and sapropel mid holocene smh the comparison between sk 1 and ns 14 records indicated significant changes in both the productivity and stratification patterns with the former the main factor in north aegean and the latter in south aegean for s1 deposition regarding the localized deposition of smh in the semi enclosed shallow south aegean site the fully oxygenated and less productive water column conditions prevailing during that time 5 4 4 3 ka in the north aegean were the limiting factor for its deposition

vertical movements following a dip slip earthquake fault motion during a dip slip earthquake induces elastic stresses in the earth which are well modeled by elastic dislocation theory shortly after the earthquake flow in the asthenosphere begins to relax these stresses and leads to postseismic motions observable at the earth s surface recent work has led to apparently contradictory results on the sign of the vertical motion following a dip slip earthquake some workers find downwarping in the region overlying a thrust fault others find upwarping this controversy is now resolved by a finite element study of postseismic rebound following a thrust earthquake on a 30 dip fault in an initially planar elastic lithosphere which overlies a maxwell viscoelastic asthenosphere if the fault penetrates less than 0 68 of the way through the lithosphere downwarping follows the earthquake if the fault penetrates more than 0 68 of the lithosphere upwarping results the magnitude as well as the sign of the postseismic rebound is a sensitive indicator of the ratio between the thickness of the elastic lithosphere and the fault depth observations of postseismic rebound may thus be used to measure lithosphere thicknesses at time scales on the order of years