late pleistocene holocene climatic and vegetational history of the brazilian caatinga the fossil dunes of the middle sao francisco river palynological studies of a peat bog sequence with a basal date of 10 990 80 yr b p provide a history of vegetational and climatic changes in the icatu river valley located inside a large system of stabilized sand dunes at the middle sao francisco river at 10o24 0 s 43o13 0 w in northeastern brazil the present day vegetation of the valley is vereda a mauritia vinifera palm swamp forest bordered by a narrow strip of semi deciduous tropical forest the adjacent dunes are stabilized by arboreal caatinga and cerrado vegetation in some areas the palynological profile of the saquinho locality within this valley was divided into five pollen zones zone sa1 10 990 10 540 yr b p contains pollen of taxa found in present amazonian and atlantic forests as well as from montane taxa thus suggesting very humid climatic conditions synchronous with more reduced temperatures zone sa2 10 540 6790 yr b p has pollen spectra from a vegetation type dominated by mauritia suggesting progressive warming and high humidity levels the period between 8920 and 8910 yr b p has rapid sedimentation rate few thermoluminescence tl dates pronounced increase of mauritia and ilex pollen suggesting a very moist climate from 8910 to 6790 yr b p there is a progressive decline in forest taxa and a gradual increase of caatinga and cerrado taxa on the landscape zone sa3 6790 ca 6230 yr b p does not contain palynomorphs possibly indicating semi arid conditions zone sa4 ca 6230 ca 4535 yr b p marks the return of mosaic vegetation composed of gallery forest cerrado and caatinga taxa indicating moister climatic conditions a marked decline in moisture levels characterizes the period between 4240 yr b p and present as suggested by an increase in caatinga and cerrado species and a decline in gallery forest taxa zone sa5 ca 4535 yr b p present establishes the present vegetational and climatic pattern of the icatu river valley 1999 elsevier science b v all rights reserved

amazon fan biomarker evidence against the pleistocene rainforest refuge hypothesis ocean drilling program leg 155 site 942 on the amazon fan is an ideal location for monitoring palaeoclimatic changes within a significant proportion of the amazon basin we present n alkane d 13 c and taraxerol and laevoglucosan concentration records from this site covering the last 38 ka the entire n alkane d 13 c record is constrained between 31 and 34 which is well within the isotopic range occupied by c3 vegetation the concentration and relative abundance of taraxerol a mangrove indicator varies by over an order of magnitude but seems to have had no effect on the n alkane d 13 c record the laevoglucosan concentrations are extremely low during the last glacial period suggesting a relatively low occurrence of forest fires laevoglucosan concentrations are highest between 13 5 and 12 5 ka suggesting an increased incidence of amazon forest fires at the very end of the younger dryas these records combined with previously published pollen records from site 932 reveal no evidence for massive incursions of grasslands into amazonia during the last glacial period despite evidence of reduced outflow of the amazon river indicating more arid conditions we therefore suggest that savannah encroachment as proposed by the pleistocene refuge hypothesis can be refuted as an explanation for high species endemism within the amazon basin and alternative explanations are required copyright 2012 john wiley sons ltd

seasonal variation of counterclockwise eddies downstream of the tsushima islands abstract the seasonal variation of counterclockwise eddies downstream of the tsushima islands in the tsushima straits was investigated from 2004 to 2008 using long term acoustic doppler current profiler adcp data eddy activity was high from summer to autumn july november the eddies were formed in short term intervals of 5 8 days almost corresponding to the formation cycle of karman vortices the eddy activity varied on a longer time period about 13 days the mean kinetic energy mke converted to eddy kinetic energy eke at current shears between the eastern and western channels of the tsushima straits the counterclockwise eddies that formed downstream of the tsushima islands were intensified and maintained by energy conversion from mke to eke at the northern shear of the current core in the eastern channel the countercurrent east of the tsushima islands from summer to autumn was intensified by energy conversion from eke to mke

study of the impact of ice formation in leads upon the sea ice pack mass balance using a new frazil and grease ice parameterization abstractleads are cracks in sea ice that often form because of deformation during winter months leads expose the ocean to the cold atmosphere resulting in supercooling and the formation of frazil ice crystals within the mixed layer here the authors investigate the role of frazil ice formation in leads on the mass balance of the sea ice pack through the incorporation of a new module into the los alamos sea ice model cice the frazil ice module considers an initial cooling of leads followed by a steady state formation of uniformly distributed single size frazil ice crystals that precipitate to the ocean surface as grease ice the grease ice is pushed against one of the lead edges by wind and water drag that the authors represent through a variable collection thickness for new sea ice simulations of the sea ice cover in the arctic and antarctic are performed and compared to a model that treats leads the same as the open ocean the processes of ice formation in the new module slow down the refreezing o

evidence for a transgressive barrier within a regressive strandplain system implications for complex coastal response to environmental change clastic depositional strandplain systems have the potential to record changes in the primary drivers of coastal evolution climate sea level and the frequency of major meteorological and oceanographic events this study seeks to use one such record from a southern brazilian strandplain to highlight the potentially complex nature of coastal sedimentological response to small changes in these drivers following a 2 to 4 m highstand at ca 5 8 ka in southern brazil falling sea level reworked shelf sediment onshore forcing coastal progradation smoothing the irregular coastline and forming the 5 km wide pinheira strandplain composed of ca 500 successive beach and dune ridges sediment cores grab samples and 11 km of ground penetrating radar profiles reveal that the strandplain sequence is composed of well sorted fine to very fine quartz sand since the mid holocene highstand the shoreline prograded at a rate of ca 1 to 2 m yr 1 through the deposition of a 4 to 6 m thick shoreface unit a 1 to 3 m thick foreshore unit containing ubiquitous ridge and runnel facies and an uppermost beach and foredune unit however the discovery of a linear 100 m wide barrier ridge with associated washover units a 3 to 4 m deep lagoon and 250 m wide tidal inlet within the strandplain sequence reveals a period of shoreline transgression at 3 3 to 2 8 ka during the otherwise regressive developmental history of the plain the protected nature of pinheira largely buffered it from changes in precipitation patterns wave energy and fluvial sediment supply during the time of its formation however multiple lines of evidence indicate that a change in the rate of relative sea level fall probably due to either steric or ice volume effects may have affected this coastline thus whereas these other potential drivers cannot be fully discounted this study provides insights into the complexity of decadal scale to millennial scale coastal response to likely variability in sea level change rates

measuring the sea ice floe size distribution sea ice is broken into floes whose diameters range from meters to a hundred kilometers this fragmentation affects the resistance of the ice cover to deformation and the melting at floe sidewalls in summer floes are broken by waves and swell near the ice edge and throughout the pack by isostatic imbalances thermal cracking winds and currents in winter they are welded together by freezing floe size can be measured by several properties p for instance area or mean caliper diameter two definitions of floe size distribution seem useful f p the fraction of area covered by floes no smaller than p and n p the number of floes per unit area no smaller than p f p can be measured by sets other than areas such as the fraction of a line or of a point set covered by floes no smaller than p if n behaves like for small where is mean caliper diameter must be greater than 2 so that the small floes occupy finite area if 2 1 the perimeter of small floes is infinite several summertime distributions have been measured on a log log graph their slopes local values of range from 1 7 to 2 5 one distribution follows a power law the others have steeper slopes for larger floes and more gradual slopes for smaller floes another sampling strategy is to measure the lengths of line segments on floes the distribution of these chord lengths is equivalent to the distribution of floe diameters the variance of an estimate of the fraction g of area covered by floes in any size range is g 1 g k 1 where k is the equivalent number of independent samples k can be found from the autocovariance of the indicator function for the chosen size range for line sampling of a narrow range of floe diameters k is the ratio of the sample length to the floe diameter

evaluation of last glacial maximum sea surface temperature reconstructions through their influence on south american climate 1 the consistency of land based and ocean based last glacial maximum lgm proxy evidence on and near south america is evaluated by utilizing a regional climate model rcm the relatively high resolution of the rcm brings model output closer to the spatial scales of the geological reconstructions this is important because proxy sites only a few tens of kilometers apart can yield markedly different interpretations of lgm climate along with differences in orbital parameters co2 concentrations and vegetation four versions of lgm sea surface temperatures ssts climate long range investigation mapping and prediction climap schafer neth and paul s 2003 core version paul and schafer neth s 2003 line version and coupled gcm output from shin et al 2003 are used to generate four realizations of the lgm climate in the model mean annual surface temperature mean temperature of the coldest month and aridity differences from a present day simulation are compared with the geological reconstructions over south america to evaluate the consistency of the land and ocean based reconstructions model results suggest that the tropical atlantic during the lgm was not significantly cooler than climap s original estimates simulations utilizing tropical atlantic lgm ssts cooler than climap estimates yield unrealistically warm lgm surface conditions over the equatorial amazon basin reductions in evaporation and the atmosphere s moisture content over too cold tropical oceans lead to a reduction in cloud cover over the amazon and increases in solar heating of the surface all of the lgm sst simulations produce drier conditions over tropical south america however the extent of the aridity is associated with the degree of cooling in the surrounding oceans especially the tropical atlantic the line version lgm ssts of paul and schafer neth 2003 are recommended

summer transport through the tsushima korea strait transport variations through the korea tsushima strait are examined from two lines of bottom moored acoustic doppler current profilers adcps deployed southwest and northeast of tsushima island in may 1999 almost full depth velocity profiles are measured an optimal interpolation oi scheme is used to interpolate the data spatially and to provide error estimates along each section the strong northeastward current core through the southern section lies approximately in the center of the strait and small southwestward flows occur sporadically near both the korea and japan coasts much of the flow through the northern line occurs near the korea and japan coasts with a weak southwestward mean flow and large variability in the strait center on the leeside of tsushima island the estimated mean transport is 2 9 sverdrups sv through the southern line and 2 5 sv through the northern line the northern line does not extend close to the korea coast where there is significant flow expected errors in the transport estimates at any time are about 0 5 sv rms for each mooring line the gradual transport increase through the summer is carried through the center of the southern line and on the korea side of the strait through the northern line

late quaternary palaeoecology and palaeoclimatology from pollen records of the savannas of the llanos orientales in colombia abstract pollen analysis of sediment cores from laguna angel 4 28 n 70 34 w 200 m elevation and laguna sardinas 4 58 n 69 28 w 80 m a s l in the savannas of the llanos orientales of colombia are presented the pollen record of laguna angel includes 7 radiocarbon dates and shows the holocene vegetation and climatic history since 10 030 yr b p the record of laguna sardinas includes 7 radiocarbon dates and shows the late glacial and holocene history since 11 570 yr b p both pollen records show that the present day savanna vegetation dominated by grassland poaceae with only few woody savanna taxa e g curatella bryrsonima was present since the late glacial indicating dry climatic conditions with a marked dry season shrubs and trees of forest and or gallery forest e g mauritia mauritiella moraceae urticaceae melastomataceae alchornea and myrtaceae are well represented during the recorded period the proportions between forest and savanna were subject to change in the past but also the composition of the forest and savanna ecosystems changed laguna sardinas shows a greater abundance during the late glacial holocene transition than today for alchornea especially from 10 680 to 10 070 yr b p for this interval synchronous to the el abra stadial younger dryas equivalent in colombia more humid climatic conditions have been inferred which are primarily the result of higher moisture levels under colder conditions during the early and middle holocene from 9730 to 5260 yr b p in laguna angel and from 9390 to 6390 yr b p in laguna sardinas the maximum expansion of grassland occurred indicating very dry climatic conditions the following period from 5260 to 3890 yr b p in laguna angel and from 6390 to 3680 yr b p in laguna sardinas shows a decrease of savanna herbs and an increase of forest and gallery forests reflecting a wetter period probably with a shorter annual dry season in both lake records the period after ca 3500 yr b p is incomplete but is characterized by a high representation of the palm genera mauritiella in laguna angel and mauritia in laguna sardinas this marked change has been interpreted as evidence of strong a anthropogenic influence on the vegetation but also wetter climatic conditions than during the late glacial and early and middle holocene periods

pack ice drift off east antarctica and some implications three satellite tracke d data buoys were deployed between 700 and 800e south of 65 os in february march 1985 these buoys were subsequently trapped within the expanding seasonal sea ice and drifted with the ice the buoys measured air temperature and pressure and water temperatures to 100 m depth data from the buoys are used to describe the ice drift and environment within the winter sea ice zone in this region both north and south of the antarctic divergence additional preliminary data from a further six buoys deployed in the same area in march 1987 are also presented besides providing information on the broad scale drift of the ice in the prydz bay region data from the buoys have shown i the important role that ice drift plays in determining the autumn and winter expansion of antarctic sea ice ii the highly mobile nature of the ice even hundreds of kilometres from the ice edge iii the role that ocean bottom topography has in determining ice drift over the continental shelf and iv the modifying influence that an ice cover has on regional climate a qualitative assessment is made of importance of the major forces driving the ice data are insufficient for a detailed study dynamics

correlated millennial scale changes in surface hydrography and terrigenous sediment yield inferred from last glacial marine deposits off northeastern brazil abstract the stable isotope composition of planktonic foraminifera correlates with evidence for pulses of terrigenous sediment in a sediment core from the upper continental slope off northeastern brazil stable oxygen isotope records of the planktonic foraminiferal speciesglobigerinoides sacculiferandglobigerinoides ruber pink reveal sub milankovitch changes in sea surface hydrography during the last 85 000 yr warming of the surface water coincided with terrigenous sedimentation pulses that are inferred from high xrf intensities of ti and fe and which suggest humid conditions in northeast brazil these tropical signals correlate with climatic oscillations recorded in greenland ice cores dansgaard oeschger cycles and in sediment cores from the north atlantic heinrich events trade winds may have caused changes in the north brazil current that altered heat and salt flux into the north atlantic thus affecting the growth and decay of the large glacial ice sheets

long term vegetation climate and ocean dynamics inferred from a 73 500 years old marine sediment core geob2107 3 off southern brazil abstract long term changes in vegetation and climate of southern brazil as well as ocean dynamics of the adjacent south atlantic were studied by analyses of pollen spores and organic walled dinoflagellate cysts dinocysts in marine sediment core geob2107 3 collected offshore southern brazil covering the last 73 5 cal kyr bp the pollen record indicates that grasslands were much more frequent in the landscapes of southern brazil during the last glacial period if compared to the late holocene reflecting relatively colder and or less humid climatic conditions patches of forest occurred in the lowlands and probably also on the exposed continental shelf that was mainly covered by salt marshes interestingly drought susceptible araucaria trees were frequent in the highlands with a similar abundance as during the late holocene until 65 cal kyr bp but were rare during the following glacial period atlantic rainforest was present in the northern lowlands of southern brazil during the recorded last glacial period but was strongly reduced from 38 5 until 13 0 cal kyr bp the reduction was probably controlled by colder and or less humid climatic conditions atlantic rainforest expanded to the south since the lateglacial period while araucaria forests advanced in the highlands only during the late holocene dinocysts data indicate that the brazil current bc with its warm salty and nutrient poor waters influenced the study area throughout the investigated period however variations in the proportion of dinocyst taxa indicating an eutrophic environment reflect the input of nutrients transported mainly by the brazilian coastal current bcc and partly discharged by the rio itajai the major river closest to the core site this was strongly related to changes in sea level a stronger influence of the bcc with nutrient rich waters occurred during marine isotope stage mis 4 and in particular during the late mis 3 and mis 2 under low sea level evidence of nothofagus pollen grains from the southern andes during late mis 3 and mis 2 suggests an efficient transport by the southern westerlies and argentinean rivers then by the malvinas current and finally by the bcc to the study site major changes in the pollen spore and dinocyst assemblages occur with similar pacing indicating strongly interlinked continental and marine environmental changes proxy comparisons suggest that the changes were driven by similar overarching factors of which the most important was orbital obliquity

on the accuracy of hf radar measurement in the tsushima strait 1 the accuracy of hf radar measurement in the tsushima strait is investigated a comparison between radial velocities measured by hf radar and acoustic doppler current profiler adcp which provides an upper bound of hf radar measurement error shows that the root mean square rms velocity difference obtained from the principal component analysis is 6 62 11 3 cm s 1 a comparison of velocities measured by two facing hf radars which provides a lower bound of hf radar measurement error shows that the variance error of hourly radial velocity is 5 75 13 3 cm s 1 the bias error of hf radar measurement is also found to be reasonably small through a comparison of tidal ellipses estimated from 1 year of hf radar data with those from 5 years of adcp data these results suggest that the variance error of hf radar measurement is the dominant source of the velocity difference found between adcp and hf radar

transport variability across the korea tsushima strait and the tsushima island wake abstract transport variations are calculated across the korea tsushima strait using continuous current measurements made between may 1999 and march 2000 twelve bottom mounted acoustic doppler current profilers provide velocity profiles along two sections one section south line at the strait entrance southwest upstream of tsushima island and the other section north line at the strait exit northeast downstream of tsushima island transport variations across the strait are large particularly in the lee of tsushima island where a countercurrent commonly exists the tsushima current transport averaging 2 65 sverdrups sv 1 sv 10 6 m 3 s 1 is split into two cores by tsushima island which divides the strait into eastern and western channels transport in the western channel is 23 higher than in the eastern channel over the measurement period some seasonality in transport variability is observed for both the western and eastern channels transports are largest in fall and smallest during winter the single velocity core observed upstream of tsushima island is estimated to split directly behind tsushima island over an aperture of about 31 km along the south line a wake zone that averages 40 km in width is observed downstream of tsushima island and appears to follow island wake zone dynamics reynolds numbers can range from 22 to 90 in the wake zone and eddy shedding can occur throughout the year

the vitoria eddy and its relation to the brazil current in late austral summer 1991 a cyclonic thermocline eddy was detected in the subtropical western south atlantic off the brazilian shelf near the city of vitoria this vitoria eddy was tracked for 55 days by surface drifters drogued at 100 m depth the drifters had been deployed in the western boundary current regime by fs meteor as part of a basinwide surface current study the analysis of a combined ctd xbt section across the vitoria eddy together with drifter data and satellite images of the thermal surface structure revealed the unexpected complexity of the region the eddy interacted not only with the local topography and the brazil current located farther offshore but also with an extended upwelling regime north of cabo frio the hydrographic and kinematic properties and anomalies of the vitoia eddy are analyzed and compared with similar vortices described elsewhere in literature

antarctic sea ice concentrations inferred from nimbus 5 esmr and landsat imagery a quantitative comparison is made of antarctic sea ice concentration derived from the nimbus 5 electrically scanning microwave radiometer esmr and from the landsat 1 and landsat 2 mss 7 near infrared band images the set of images includes regions near the ice edge and near the continental boundary during late winter or spring the ice covered areas in the southern ocean exhibit microwave brightness temperature predominantly characteristic of first year sea ice with emissivity of 0 92 the percentage ice cover is derived from the microwave data using an algorithm that uses this emissivity and interpolated climatological physical temperatures and that is not dependent on spatial resolution classification of ice floes and open water in cloud free landsat images provides an alternative determination of large scale ice concentrations but the limitations of this method are shown in various areas especially near the ice edge landsat data are limited in their ability to resolve individual ice floes a classification procedure for landsat data based on a threshold radiance level for water overestimates the ice concentration because this method tends to classify mixtures of open water and unresolved ice floes as fully ice covered a proportional classification based on observed reflectance gives better agreement with the esmr ice concentration values because it does not require that each open water area be resolved in the landsat imagery the derived ice concentrations from the esmr and landsat data using the proportional classification method agree to 15 with the largest uncertainties occurring in regions of low concentration

seasonal variations in the properties and structural composition of sea ice and snow cover in the bellingshausen and amundsen seas antarctica sixty three ice cores were collected in the bellingshausen and amundsen seas in august and september 1993 during a cruise of the r v nathaniel b palmer the structure and stable isotopic composition 18 o 16 o of the cores were investigated in order to understand the growth conditions and to identify the key growth processes particularly the contribution of snow to sea ice formation the structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the bellingshausen sea in march 1992 are reassessed frazil ice and congelation ice contribute 44 and 26 respectively to the composition of both the winter and summer ice core sets evidence that the relatively calm conditions that favour congelation ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil ice growth and pancake ice formation both frazil and congelation ice layers have an av erage thickness of 0 12 m in winter evidence that congelation ice and pancake ice thicken primarily by dynamic processes the thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover snow ice layers have a mean thickness of 0 20 and 0 28 m in the winter and summer cores respectively and the contribution of snow ice to the winter 24 and summer 16 core sets exceeds most quantities that have been reported previously in other antarctic pack ice zones the thickness and quantity of snow ice may be due to a combination of high snow accumulation rates and snow loads environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow ice interface and bottom melting losses being compensated by snow ice formation layers of superimposed ice at the top of each of the summer cores make up 4 6 of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice the accumulation of superimposed ice is evidence that melting in the snow cover on antarctic sea ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass

late quaternary vegetation and climate dynamics in the serra da bocaina southeastern brazil abstract late quaternary vegetation fire and climate dynamics were studied by pollen and charcoal analysis in the serra da bocaina in the coastal ranges of southeastern brazil rio de janeiro and sao paulo states samples were taken from two cores serra da bocaina 1 and 2 seven radiocarbon dates indicate deposits of late pleistocene to holocene age during the period between 18 570 and 14 570 cal bp wide spread grassland campos with frequent fires existed in the higher serra da bocaina taken together with other evidence this indicates relatively dry and cold climatic conditions for this period upper montane forest occurred in protected valleys or on slopes at lower elevations the conifer araucaria angustifolia has been present in the serra da bocaina since the late pleistocene but populations have fluctuated an erosion hiatus in the late glacial period evidenced by reworked deposits lacking pollen was probably caused by increased rainfall during the younger dryas period upper montane forest taxa expanded during the holocene especially after 7260 cal bp indications are that the early and mid holocene were dry and relatively warm with an annual dry season longer than present day modern patches of campos in the serra da bocaina are remnants of more expansive grasslands during glacial times

dynamic boundary monsoon intensity hypothesis evidence from the deglacial amazon river discharge record glacioeustatic and temperature corrected planktonic foraminiferal oxygen isotope d 18 o records from odp site 942 on the amazon fan provide a means of monitoring past changes in the outflow of the amazon river this study focuses on the last deglaciation and reveals that during this period there were significant variations in the outflow which implies large changes in moisture availability in the amazon basin aridity in the amazon basin seems to occur between 20 5 ka calendar to 17 0 ka and 13 6 ka to 11 ka the second arid period correlates with the start of the antarctic cold reversal and aridity continues throughout the younger dryas period we find that the large scale trends in amazon river outflow are dissimilar to high latitude variability in either hemisphere instead high resolution variations correlate with the d 18 o difference between greenland and antarctica ice core temperature records this suggests a link between hemispheric temperature gradients and moisture availability over the amazon based on our results and previously published work we present a new testable dynamic boundary monsoon intensity hypothesis which suggests that tropical moisture is not a simple belt that moves north or south rather the northern and southern boundaries of the south american summer monsoon sasm are independently dynamic and driven by temperature gradients within their individual hemispheres the intensity of rainfall within the sasm however is driven by precessionally modulated insolation and the resultant convection strength combining these two influences produces the dynamic heterogenic changes in the moisture availability observed over tropical south america since the last glacial maximum

east antarctic sea ice albedo thickness distribution and snow cover characteristics of springtime sea ice off east antarctica were investigated during a cruise of the australian national antarctic research expedition in october through december 1988 the fractional coverage of the ocean surface the ice thickness and the snow cover thickness for each of several ice types were estimated hourly for the region near the ship these observations were carried out continuously during the 4 weeks the ship was in the ice thin and young ice types were prevalent throughout the region and the observations show a systematic increase in the total area weighted pack ice thickness including open water area from only 0 2 m within 50 km of the ice edge to 0 45 m close to the coast ice thickness averaged over the ice covered region only is also relatively thin ranging from 0 35 m near the ice edge to 0 65 m in the interior these values are probably typical of average winter thickness for the area the average snow cover thickness on the ice increased from 0 05 m near the ice edge to 0 15 m in the interior average ice concentration increased from less than 6 10 near the ice edge to 8 10 in the interior the ship observed concentrations were in good agreement with concentrations derived from passive microwave satellite imagery except in some regions of high concentration in these regions the satellite derived concentrations were consistently lower than those estimated from the ship possibly because of the inability of the satellite sensors to discriminate the appreciable percentage of very thin ice observed within the total area spectral albedo was measured for nilas young grey ice grey white ice snow covered ice and open water at wavelengths from 420 to 1000 nm allwave albedo was computed by using the spectral measurements together with estimates of near infrared albedo and modeled spectral solar flux area averaged albedos for the east antarctic sea ice zone in spring were derived from representative allwave albedos together with the hourly observations of ice types these area averaged surface albedos increased from about 0 35 at the ice edge to about 0 5 at 350 km from the edge remaining at 0 5 to the coast of antarctica the low average albedo is in part due to the large fraction of open water within the pack but extensive fractions of almost snow free thin ice also play an important role

low frequency current observations in the korea tsushima strait abstract high resolution continuous current measurements made in the korea tsushima strait between may 1999 and march 2000 are used to examine current variations having time periods longer than 2 days twelve bottom mounted acoustic doppler current profilers provide velocity profiles along two sections one section at the strait entrance southwest of tsushima island and the second section at the strait exit northeast of tsushima island additional measurements are provided by single moorings located between korea and tsushima island and just north of cheju island in cheju strait the two sections contain markedly different mean flow regimes a high velocity current core exists at the southwestern section along the western slope of the strait for the entire recording period the flow directly downstream of tsushima island contains large variability and the flow is disrupted to such an extent by the island that a countercurrent commonly exists in the lee of the island the northeastern section is marked b

evidence of dry and cold climatic conditions at glacial times in tropical southeastern brazil last glacial paleoenvironments have been reconstructed from a pollen and charcoal record analyzed in organic sediments and dated between ca 18 000 and 48 00014c yr b p the site is located near the village catas altas in the lower highland region of southeastern brazil the last glacial landscape was covered by extensive areas of subtropical grasslands and small areas of gallery forests along the rivers where tropical semideciduous forests and cerrado ecosystems exist today the subtropical gallery forests were composed ofaraucariaforest trees such asaraucaria angustifolia podocarpus drimys ilex andsymplocos paleofires were frequent the record indicates that subtropical grassland vegetation which today is found in patches on the highlands in southern brazil especially in the state of santa catarina expanded from southern brazil to southeastern brazil over a distance of more than 750 km from latitudes of about 28 s to at least 20 s the completely different last glacial environment in comparison to the present day environment reflects a dry and cold climate with strong frosts during the winter months temperatures of 5 7 c below those of the present are inferred for the last glaciation

late quaternary vegetational and climate dynamics in southeastern brazil inferences from marine cores geob 3229 2 and geob 3202 1 abstract late quaternary palaeoenvironments from southeastern se brazil have been reconstructed by pollen analysis of two marine sediment cores the core geob 3229 2 19 38 5 s 38 43 0 w 780 mbsl from the central depression south of the abrolhos bank is 505 cm long and 80 kyr bp old the core geob 3202 1 21 37 0 s 39 58 7 w 1090 mbsl from the upper continental slope off rio paraiba do sul is 495 cm long and 52 kyr bp old chronological control for core geob 3202 1 is based on seven ams radiocarbon dates from individuals of the foraminiferal species globigerinoides sacculifer the age scale for core geob 3229 2 was obtained by the detailed correlation of the oxygen isotope and x ray fluorescence records of both cores the two marine pollen records document vegetational changes in the drainage areas of two major se brazilian rivers the rio doce and the rio paraiba do sul which probably transported most of the pollen and spores deposited in the marine sediments during glacial times grassland vegetation dominated the landscape and atlantic rainforest and semideciduous forest were markedly reduced small areas of subtropical araucaria forest occurred in southeastern se brazil while cerrado vegetation was rare maximal grassland expansion and atlantic rainforest reduction were found during the last glacial maximum reflecting cold and relatively dry climatic conditions during the late glacial period grassland decreased and lowland forest taxa increased indicating wetter and warmer conditions comparison between the two marine pollen records with terrestrial records from the two river drainage areas confirms that grassland dominated the glacial age landscape reconstructed from terrestrial records

a new pleistocene bird assemblage from the southern pampas buenos aires argentina abstract in the present paper we report the most complete fossil avifauna from the southern cone of south america the specimens here described were collected in the paso otero locality at the middle stream of the quequen grande river pampean region buenos aires province argentina the fossiliferous levels belong to the la chumbiada member of lujan formation 37 800 2300 yr bp late pleistocene the assemblage is represented by 60 specimens belonging to at least 22 taxa the radiocarbon age indicates that paso otero birds represent the oldest late pleistocene avifauna known from the south american continent and the first coming from a clear interstadial event mis3 available evidence indicates similar environmental conditions during the mis3 interstadial in the pampean region of argentina and the post last glacial maximum stadials in southeastern brazil the absence of significant extinction events in the latest pleistocene early holocene avifaunas of brazil and argentina suggests that the main avifaunal composition along southeastern continental lowlands may not be affected by the cyclic retraction and extension of open environments on the contrary the fossil record of peru and ecuador demonstrates that a large number of taxa including aquatic and predatory scavenger birds have gone extinct along andean environments at the pacific coast and late pleistocene climatic oscillations may have played a more dramatic impact in these avian communities

regional and global benthic δ18o stacks for the last glacial cycle although detailed age models exist for some marine sediment records of the last glacial cycle 0 150 ka age models for many cores rely on the stratigraphic correlation of benthic 18o which measures ice volume and deep ocean temperature change the large amount of data available for the last glacial cycle offers the opportunity to improve upon previous benthic 18o compilations such as the lr04 global stack not only are the age constraints for the lr04 stack now outdated but a single global alignment target neglects regional differences of several thousand years in the timing of benthic 18o change during glacial terminations here we present regional stacks that characterize mean benthic 18o change for 8 ocean regions and a volume weighted global stack of data from 263 cores age models for these stacks are based on radiocarbon data from 0 to 40 ka correlation to a layer counted greenland ice core from 40 to 56 ka and correlation to radiometrically dated speleothems from 56 to 150 ka the regional 18o stacks offer better stratigraphic alignment targets than the lr04 global stack and furthermore suggest that the lr04 stack is biased 1 2 kyr too young throughout the pleistocene finally we compare global and regional benthic 18o responses with sea level estimates for the last glacial cycle

late quaternary vegetational and climate dynamics in northeastern brazil inferences from marine core geob 3104 1 abstract late quaternary paleoenvironments from northeastern ne brazil have been studied by pollen analysis of marine sediment the studied core geob 3104 1 3 40 s 37 43 w 767 m b s l from the upper continental slope off ne brazil is 517 cm long and 42 000 14 c yr bp old chronological control was obtained by 12 radiocarbon ams dates from individuals of the foraminiferal species globigerinoides sacculifer modern pollen analogs were received from 15 river lake and forest soil surface samples from ne brazil marine pollen dates indicate the predominance of semi arid caatinga vegetation in ne brazil during the recorded period between 42 000 and 8500 14 c yr bp the increased fluvial input of terrigenous material with high concentrations of pollen and specially fern spores into the marine deposits about 40 000 33 000 and 24 000 14 c yr bp and between 15 500 and 11 800 14 c yr bp indicate short term periods of strong rainfall on the ne brazilian continent the expansion of mountain floodplain and gallery forests characterize the interval between 15 500 and 11 800 14 c yr bp as the wettest recorded period in ne brazil which allowed floristic exchanges between atlantic rain forest and amazonian rain forest and vice versa the paleodata from core geob 3104 1 confirm the in general dry pre last glacial maximum lgm and lgm conditions and the change to wet lateglacial environments in tropical south america the annual movement of the intertropical convergence zone over ne brazil the strong influence of the antarctic cold fronts and changes of the high pressure cell over the southern atlantic may explain the very wet lateglacial period in ne brazil the documented ne brazilian short term signals correlate with the documented dansgaard oeschger cycles and heinrich events from the northern hemisphere and suggest strong teleconnections

what do yellowish brown soils and stone layers tell us about late quaternary landscape evolution and soil development in the humid tropics a field study in the serra dos orgaos southeast brazil abstract the occurrence spatial distribution and properties of yellowish brown soils and stone layers allow deriving conclusions about landscape evolution and soil development in the humid tropics in this study standard soil profiles and saprolite and subsoil samples along an altitudinal gradient from the high mountain ranges 1500 m a s l to the lowlands 8 m a s l in the serra dos orgaos mountain range in the brazilian state of rio de janeiro are analyzed field mapping techniques and laboratory methods are used to analyze the samples and reconstruct late quaternary landscape and soil development processes it is suggested that the formation of stone layers is polygenetic with dissolution processes geogenic bioturbation pedogenic and slope processes including coverage of terrace gravels geomorphic as possible mechanisms yellowing of the upper soil horizons is assumed to be the result of bio chemical processes xanthization chelation which took and take place in periods of wet climate conditions and closed forest cover in the late quaternary it can be distinguished between pre colonial and modern yellowish brown colluvial deposits with or without stone layer s it is suggested that the deposition of pre colonial colluvial soils primarily took place in dryer periods and forest retreat during the late pleistocene and holocene however it is proposed that the model of cyclic changes between geomorphic activity with colluviation on the one hand and stability and pedogenesis on the other hand need to be further differentiated due to small scale temporal and spatial climatic changes and sensitive vegetation responses to these fluctuations moreover it is suggested that due to the very steep relief and intense rainfall in the central mountain ranges of the serra dos orgaos accelerated displacement of soil material by landslides and mudslides took also place under closed forest cover in the late holocene modern colluvial deposits have originated from deforestation and land use intensification processes within the last 300 years they cover wide parts of the lower slopes foothills and depressions and indicate massive erosion and deposition processes since the european colonization

a new mechanism for millennial scale positive precipitation anomalies over tropical south america abstract continental and marine paleoclimate archives from northwestern and northeastern south america recorded positive precipitation anomalies during heinrich stadials hs these anomalies have been classically attributed to enhanced austral summer monsoon precipitation however the lack of marine paleoclimate records off eastern south america as well as inconsistencies between southeastern south american continental and marine records hamper a comprehensive understanding of the mechanism responsible for sub tropical south american hydroclimate response to hs here we investigate piston core m125 95 3 collected off eastern south america 10 94 s and simulate south american hs conditions with a high resolution version of an atmosphere ocean general circulation model further meridional changes in precipitation over sub tropical south america were assessed with a thorough compilation of previously available marine paleorecords our ln ti ca and ln fe k data show increases during hs6 younger dryas it is the first core off eastern south america and the southernmost from the atlantic continental margin of south america that unequivocally records hs related positive precipitation anomalies based on our new data model results and the compilation of available marine records we propose a new mechanism for the positive precipitation anomalies over tropical south america during hs the new mechanism involves austral summer precipitation increases only over eastern south america while the rest of tropical south america experienced precipitation increases during the winter challenging the widely held assumption of a strengthened monsoon south american precipitation changes were triggered by dynamic and thermodynamic processes including a stronger moisture supply from the equatorial north atlantic tropical south atlantic in austral winter summer

a numerical study of barotropic instability associated with the soya warm current in the sea of okhotsk abstract numerical model experiments have been carried out in an attempt to elucidate the generation mechanism of the eddy or wave street in the soya warm current we use a barotropic model incorporating bottom topography under realistic conditions the model produces waves whose properties are within range of the observed ones the generation mechanism of the waves proposed in this experiment is as follows when the current is driven by the mean water level difference between the japan sea and the sea of okhotsk the flow separates from the cape in the soya strait in the region of the flow separation strong positive vorticity is produced by the frictional torques occurring as the water flows through the strait and by vortex stretching as the water is pushed out to deeper depths this strong vorticity or horizontal shear induces barotropic instability in which the waves are generated in brief the system of the soya warm current accompanied by an eddy street is interpreted as a good geophysical ex

late quaternary environmental dynamics inferred from marine sediment core geob6211 2 off southern brazil abstract vegetation and climate changes in southern brazil as well as the dynamics of the adjacent south atlantic were investigated through the analyses of pollen spores and dinocysts from marine sediment core geob6211 2 that covers the last 19 3 kyr the pollen record indicates the dominance of grassland campos in southeastern south america sesa reflecting cold and or dry conditions during the last glacial maximum forests mainly gallery forests expanded slightly during heinrich stadial 1 suggesting slightly wetter conditions a stronger expansion of the atlantic lowland rainforest is noticed in the record after ca 5 5 cal kyr bp likely due to wetter conditions the relatively high amount of exotic nothofagus pollen transported by wind rivers and then by oceanic currents northwards to the study site as well as the dinocyst brigantedinium spp indicate a noticeable influence of the brazilian coastal current from the south between 19 3 and 14 8 cal kyr bp after that the decrease in nothofagus and brigantedinium spp together with the increase in dinocyst operculodinium centrocarpum indicate that the brazil current from the north dominated the coring site the abundance of freshwater algae between ca 19 3 and 17 0 cal kyr bp suggests that the rio de la plata mouth was located close to the coring site during this period and its discharge of nutrient rich freshwaters strongly affected the upper water column sea level rise decreased this impact during the late glacial phase by moving the coastline further away from the core site the presence of the brazil current at the core site became stronger after ca 15 cal kyr bp and strongest after 9 cal kyr bp in summary the pollen spores and dinocyst records from core geob6211 2 provide important climatic records to reconstruct the environmental changes in sesa

distribution of diatoms in surface sediments of prydz bay antarctica abstract four diatom assemblages are identified from the surface sediments of prydz bay and the mac robertson shelf using multivariate analysis a coastal assemblage is characterised by the sea ice diatoms fragilariopsis curta f angulata f cylindrus and pseudonitzschia turgiduloides a continental shelf assemblage is characterised by sea ice and ice edge diatoms and an oceanic assemblage is characterised by the open water diatoms fragilariopsis kerguelensis thalassiosira lentiginosa t gracilis var expecta and trichotoxin reinboldii the cape darnley assemblage contains both sea ice and open water diatoms but all are characteristically large and heavily silicified multiple regression has been used to identify the relationships between the diatom assemblages and known environmental variables there are strong correlations between the coastal shelf and oceanic assemblages and ecological conditions including latitude sea ice distribution and ocean currents the cape darnley assemblage is thought to represent an assemblage from which the smaller and more lightly silicified species have been removed by current winnowing

related changes in biodiversity insolation and climate in the atlantic rainforest since the last interglacial abstract the long term colonia record is located in the atlantic rainforest domain in brazil 23 52 s 46 42 20 w 900 m a s l the 780 cm long core co3 provides a coverage of a complete interglacial glacial cycle for the first time in a neotropical rainforest information on the behavior of tropical climates compared to global changes in temperatures indicates specific climate responses in terms of precipitation at these latitudes winter extratropical circulation was very active during the last interglacial and most of the glacial floristic composition of the rainforest changed several times in each phase of expansion twice during the interglacial and three times during glacial episodes araucaria was well developed in the area of sao paulo until the beginning of the first dry phase of the glacial at ca 50 000 yr b p changes in insolation controlled the expansion of the rainforest and the tropical hydrological cycle as evidenced by a strong precession signal however precession had no impact on regional climatic features the two interglacials mis 5e and holocene showed completely different patterns attesting to the continuous evolution of the forest the biodiversity index shannon wiener index remained high during both the interglacial and glacial attesting to the permanence of small patches of rainforest refugia during drier phases the lowest shannon wiener indexes were recorded between 23 000 and 12 000 yr b p and 40 000 and 30 000 yr b p and characterize two marked phases of stress for the rainforest

an ice water vortex at the edge of the east greenland current during the y mer 80 cruise in august 1980 we observed an ice feature of 60 km diameter having the shape of a breaking wave it lay at the edge of the east greenland drift ice in fram strait with its center at 79 15 n 00 38 e and the wave was breaking upstream relative to the east greenland current two conductivity temperature and depth sections across the feature in n s and e w directions revealed warm up to 4 3 c water some 60 km inside the polar front in lenses centered at 40 m depth but with an effect to beyond 600 m the temperature anomalies were accompanied by salinity anomalies so that there was little net effect on the density profile the form of the sections together with the ice distribution observed by vertical photography from a helicopter and surface motion observed by tracking four radar transponders all suggest that the feature is a vortex produced by an instability in the polar front it has similar characteristics to vortices investigated experimentally and theoretically by griffiths and linden 1981a b 1982 and observationally by wadhams et al 1979

late quaternary vegetation climate and fire history from the tropical mountain region of morro de itapeva se brazil late quaternary paleoenvironments have been interpreted from a 35 000 yr b p pollen and charcoal record from morro de itapeva 22 47 s 45 32 w 1850 m a s l in the se brazilian highlands changes in taxa composition and elevational shifts in high elevation grassland campos de altitude araucaria forest cloud forest and atlantic rain forest all of which can be found in the study area today indicate climatic changes in the past expanded high elevation grasslands absence of araucaria forest cloud forest and atlantic rain forest during the recorded last glacial period ca 35 000 17 000 yr b p suggest a climate markedly cooler and drier than today development of a sphagnum peat bog rare presence of araucaria forest taxa and existence of a narrow cloud forest and rain forest belt at lower elevations during the late glacial period 17 000 ca 10 000 yr b p indicate a change to a cool and somewhat moister climates during the early holocene cloud forest developed close to the study site reflecting a warm and moist climate on the east facing slopes but a drier climate on the highland plateau evidenced by the rare presence of araucaria and podocarpus only during the late holocene moisture increases in the highlands suggested by the higher frequency of araucaria and podocarpus fires were more frequent during the last glacial than during the holocene

winter sea ice properties in marguerite bay antarctica abstract during the winter 2001 and 2002 cruises of the so globec experiment we investigated the morphological properties growth processes and internal permeability of sea ice in the marguerite bay area of the western antarctic peninsula there was considerable interannual variability in ice thickness with average values of 62 cm in 2001 and 102 cm in 2002 with medians of 43 and 68 cm respectively snow depth averaged 16 cm in 2001 and 21 cm in 2002 at 40 of the thickness holes in 2001 and 17 in 2002 a combination of deep snow and thin ice resulted in negative freeboard and the potential for surface flooding ice production was strongly influenced by the snow cover deep snow resulted in negative freeboard surface flooding and the formation of snow ice but also limited columnar ice growth on the bottom of the ice a stratigraphic analysis of ice thin sections showed that more than half of the ice sampled was granular and that virtually all of the upper 20 cm of the ice cover was granular stable isotope 18 o analysis of samples from 2001 indicated that snow ice formation at the surface contributed significantly to ice formation two thirds of the cores had some snow ice and 15 of the ice sampled in 2001 was snow ice for 95 of the ice sampled the combination of warm ice temperatures and large salinities resulted in brine volumes that were greater than the percolation threshold of 5 autonomous mass balance buoys indicated that the ice was above the percolation threshold throughout late winter and spring the exceeding of the percolation threshold allows continuous flooding to occur throughout the late winter spring period the wap sea ice therefore represents a warm end member of the sea ice covers of antarctica an expected consequence of the lengthy flooding condition at the snow ice interface is an earlier onset of an algal bloom in the flooded snow than elsewhere in antarctic sea ice

the movement and decay of ice edge bands in the winter bering sea during periods of off ice winds the winter bering sea ice edge consists of ice bands that measure 1 10 km in length 0 1 1 km in width and are oriented at approximately right angles to the wind the bands are composed of small floes 10 20 m in diameter and 1 5 m in thickness in march 1981 working from the noaa ship surveyor we mounted two radar transponders 4 km apart on ice floes within such a band and then tracked them for 46 h over an 80 km distance as the band moved into warmer water and melted comparison of the band position with that of a satellite tracked argos station deployed in the ice interior shows that the band moved 30 faster than the interior ice analysis of our observations strongly suggest that the cause of the speed increase is the wind wave radiation stress on the upwind side of the band we also observed that wind waves contribute to band ablation by the following mechanism at the upwind edge these waves break up the floes into small pieces because these pieces are no longer good wave reflectors or absorbers they drift in the upwind direction away from the band to melt so that the band width as well as the individual floe thicknesses decrease with time in summary because the bands provide an efficient way for the export and ablation of sea ice the bands play a major role in the maintenance of the ice edge position

the deglacial history of the western tropical atlantic as inferred from high resolution stable isotope records off northeastern brazil abstract the western south atlantic boundary currents represent a sensitive system within the global thermohaline circulation thc we investigated the impact of deglacial thc changes on the western tropical atlantic studied in six high resolution sediment cores from the upper continental slope of brazil the stratigraphy of the cores is mainly based on 14c ams dating of monospecific foraminiferal samples changes in the upper layer tropical ocean during the deglaciation are inferred from stable oxygen isotope measurements on planktic and benthic foraminifera variations in the 18o residuals are assumed to be mainly temperature related during the oldest and younger dryas cooling periods two major deglacial thc disturbances are reported from north atlantic sediment cores concomitant to the repeated thc slowdown we observe an upper layer warming in the tropical ocean a reduced northward heat export from the tropical areas during these periods weak north brazil current is additionally reflected by low meridional gradients in the stable oxygen records this generally agrees with results from coupled ocean atmosphere models

evidence for a prolonged retroflection of the north brazil current during glacial stages the importance of the role played by the tropics in driving and propagating climate change between hemispheres has long been the focus of attention in a bid to evaluate ocean atmosphere interactions on glacial interglacial timescales the amazon fan and ceara rise in the western equatorial atlantic ocean lie directly in the flowpath of the north brazil current nbc which as a conduit for the cross equatorial transport of heat and salinity is a key component for the heat budget of the north atlantic mg ca palaeothermometry and stable oxygen isotope analysis of planktonic foraminifera sampled from 15 sites across the amazon fan and ceara rise reveal variations in oceanic surface currents and of the dispersal of freshwater from the river amazon over five timeslices modern early holocene younger dryas late glacial and marine isotope stage 3 sea surface temperature reconstructions reveal progressive climatic amelioration over the last similar to 30 ka indicating a temperature increase of similar to 3 2 1 1 degrees c since the late glacial in conjunction with this warming values of delta delta o 18 a proxy for water column stratification indicates increased vertical mixing of the glacial ocean the spatial distribution of values of delta 18 w the isotopic composition of ambient seawater is used to infer surface current variations and demonstrates an oceanward shift in the river outflow plume in cold climates representing a prolongation or possibly permanent continuation in the duration of the seasonal retroflection of the nbc causing the curtailment of cross equatorial transport a prolongation of this retroflection could have resulted from a mean southward migration of the southern boundary of the itcz c 2011 elsevier b v all rights reserved

evidence for lake formation as a response to an inferred holocene climatic transition in brazil abstract geochemical mineralogical and palynological records from a holocene sediment core 12 7 m long from lake silvana southeastern brazil served to identify the source of detrital sediments within catchment soils the lake basin was first flooded in the early holocene 9400 14 c yr b p when a gibbsite rich b soil horizon started to accumulate four distinct hydrologic phases are consistent with vegetational changes indicated by pollen data phases of slope instability colluviation and low lake level correspond to pollen free intervals and point to a severe retreat of the vegetation cover the rapid sedimentation of slope wash sediments alternating with alluvial sediments appears to have formed a tributary fan 7 8 m thick that dammed the lake silvana basin 8500 14 c yr b p probably as a response to a drastic increase in precipitation rates

geochemical and geophysical implications of the radiocarbon calibration abstract a precise and accurate chronological framework is crucial to study the dynamics of a variety of phenomena which occurred during the last 45 000 years although the 14 c dating method has been widely applied since the 1950s it is recognized that the atmospheric 14 c 12 c ratio has not been stable during the past in order to calculate accurate ages these fluctuations have to be corrected by means of a calibration curve obtained by comparing raw 14 c measurements with true calendar ages provided by independent dating methods the calibration curve obtained so far is characterized by a long term trend with raw 14 c ages being significantly younger than calendar ages during most of the last 45 000 years abrupt 14 c shifts which occurred over centuries to millennia are superimposed on this long term trend of decreasing atmospheric 14 c 12 c ratio to a certain extent it is possible to outline the different causes of atmospheric 14 c variations by considering complementary information obtained from other cosmogenic nuclides studied at different latitudes 1 most high frequency changes in the atmospheric 14 c 12 c ratio are linked to magnetic fluctuations of solar origin as revealed by studying the last three centuries for which direct observations of the sun are available a similar conclusion is derived by comparing 14 c 12 c events with 10 be and 36 cl concentration maxima in polar ice cores 2 the long term trend shift of 14 c ages is due to a long period of decreased shielding effect of the geomagnetic dipole field which occurred over the interval between 10 000 and 40 000 years bp this interpretation is supported by paleomagnetic measurements performed on volcanic and sedimentary rocks and by 10 be and 36 cl analysed in low and high latitude records 3 a prominent and rapid atmospheric 14 c 12 c excursion occurred between 13 000 and 11 500 cal yr bp thus corresponding to the younger dryas cold period by contrast with the 14 c variability mentioned above which is linked to 14 c production changes this so called 14 c age plateau is probably due to an abrupt variation in the rates of exchange within the global carbon cycle this interpretation is supported by independent geochemical proxies and by numerical modelling of the carbon cycle

enhanced chlorophyll associated with island induced cyclonic eddies in the eastern channel of the tsushima straits the relationship between island induced cyclonic eddies and chlorophyll a chl a was investigated using field data and satellite images in the eastern channel of the tsushima straits the maximum chl a concentration around the leeward eddy of the tsushima islands was two or three times greater than that of outside the eddy two different mechanisms of chl a enhancement associated with island induced cyclonic eddies were found in the post bloom periods in summer when nutrients were depleted in the surface layer eddy pumping increased the nutrient supply in the euphotic zone resulting in enhanced chl a around the shallow thermocline near the eddy core in late autumn when the mixed layer deepened over the euphotic zone the mixed layer depth became shallow due to the doming effect of the cyclonic eddy therefore the improved irradiance condition led to an increase in the chl a concentration in the surface mixed layer nighttime satellite visible images showed a number of fishing vessels in the lee region of the tsushima islands implying that the enhanced phytoplankton biomass may have resulted in good feeding conditions for fishes and squids in the tsushima straits

the brazilian continental margin abstract the brazilian continental margin with its interesting morphology structure and sediments has become better known only during the last two decades six physiographical provinces can be recognized at the continental margin and the adjacent coast 1 cabo orange parnaiba delta 2 parnaiba delta cabo sa o roque 3 cabo sa o roque belmonte 4 belmonte cabo frio 5 cabo frio cabo santa marta and 6 cabo santa marta chui the shelf is rather wide near the amazon mouth becoming narrower eastwards continuing very narrow along the northeastern and eastern coast and becoming wider again in the south towards the plate river prominent morphological features along the margin are the amazon cone the marginal plateaus off northeastern brazil the sa o francisco cone and canyon the abrolhos bank and the deep sea plateaus of pernambuco and sa o paulo on the shelf proper a number of relief elements exist such as sand waves east of the amazon submarine terraces at various places and irregularities of structural origin the shelf break is rather smooth in the far north and south more abrupt in the remainder surface sediments of the brazilian shelf show five distinct facies types littoral quartz sands mud transition sand mud coralline algae and biodetrital the terrigenous elastic fractions dominate off the amazon and in southern brazil between these areas they occupy a very narrow strip near the coast the carbonate facies predominantly composed of calcareous algae is abundant between the parnaiba delta and cabo frio to the south this facies is more biodetrital and restricted to the outer shelf economically important on the brazilian continental margin besides oil are sands and gravels carbonate deposits evaporites and some subsurface coal other possible mineral resources could be phosphate heavy minerals and clays for ceramics

paleoenvironmental dynamics in south amazonia brazil during the last 35 000 years inferred from pollen and geochemical records of lago do saci abstract paleoenvironmental changes for the last 35 000 years were reconstructed from palynological sedimentological and organic geochemical evidence from a well dated sediment core from lago do saci south amazonia dry climatic conditions occurred between 35 000 and 18 200 cal yr bp as recorded by high frequencies of open savanna taxa and low lake level indicated by sagittaria and low total organic carbon content cold temperatures are indicated by the presence of podocarpus and ilex a sedimentation hiatus observed between 18 200 and 9200 cal yr bp was likely related to dry conditions the beginning of the holocene was marked by rainforest expansion and an increase in carbon content that represented high lake levels and warmer and wetter climate conditions between 7500 and 5000 cal yr bp the expansion of open savanna seasonal forest elements and abundant black carbon suggests a dry phase after 5000 cal yr bp rainforest expansion and higher lake levels indicate a return to wetter conditions a reduction of flooding taxa celtis and mauritia between 1800 and 1300 cal yr bp high lake level conditions and maintenance of a forest physiognomy suggests a decrease of regional precipitation and subsequent reduction of the flooded areas in a still humid climate regime

the tsushima warm current through tsushima straits estimated from ferryboat adcp data abstract current structures across the tsushima straits are studied using results from long term acoustic doppler current profiler adcp observations by a ferryboat between hakata and pusan conducted since february 1997 two maxima of the northeastward current are observed in the central parts of the eastern and western channels and the maximum velocity in the western channel is stronger than that of the eastern channel downstream of the tsushima islands a southwestward countercurrent is observed associated with a pair of cyclonic and anticyclonic eddies in the western channel the deep countercurrent is observed pronouncedly on the bottom slope of the korean side from summer to winter the volume transport of the tsushima warm current through the straits has strong seasonal variation with a minimum in january and two maxima from spring to autumn double peaks the spring peak of the volume transport through the eastern channel is more pronounced than the autumn peak and the autumn peak of the west

late quaternary palaeosol records from subtropical 38 s to tropical 16 s south america and palaeoclimatic implications abstract loess and palaeosols in the subtropical lowlands of south america 23 38 s have a large potential to serve as archives of late quaternary environmental and climate changes at present mean annual precipitation generally decreases from n to s and from e to w though with a complex seasonal pattern with austral summer rainfall related to the monsoonal circulation and with austral winter rainfall related to the se trades in this paper we present results of multiproxy geochemical analyses from three representative eolian alluvial soil profiles along a s n transect aiming at the reconstruction of past climate changes i profile chasico at the southern border of the subtropics 38 s ii d4 in misiones at the northern border of the subtropics 27 s and for comparison iii laguna sucuara in the savannas of the bolivian lowlands 16 s our results show that before 16 ka bp conditions were likely very cold and dry except for in d4 loess or soils are not preserved due to rather scarce vegetation cover and resultant deflation in chasico accumulation of sands directly overlying the tertiary starts only during the late glacial indicating increasing temperatures and increased monsoonal precipitation coinciding with the tauca wet phase on the altiplano in d4 a palaeosol is preserved below the late glacial sediments and the deflation hiatus this palaeosol is dated to 40 ka bp and documents an earlier but less intensive southward reaching phase of monsoonal precipitation inca huasi on the altiplano whereas the seasonality during the late glacial seems to have been very pronounced conditions for organic matter production and preservation became much more favourable at chasico and d4 during the early holocene we suggest that extra tropical winter precipitation played a more important role than before and than today between 7 5 and 3 ka bp the expansion of c4 plants along the s n transect suggests increasing aridity probably due to a weakening of the extra tropical circulation in combination with a relatively weak monsoonal circulation only after 3 ka bp climate became more humid again due to the re strengthening of the monsoon

late quaternary vegetation and coastal environmental changes at ilha do cardoso mangrove southeastern brazil abstract a 190 cm mangrove sediment core from the ilha do cardoso state park state of sao paulo southeastern brazil was analyzed for pollen diatoms as well as carbon and nitrogen isotopes the goal was to determine the dynamics of the coastal terrestrial aquatic ecosystems vegetation history and climate change in this region of the brazilian atlantic rainforest during the late pleistocene and holocene the values for total organic carbon toc from 3 up to 40 c n ratios from 10 up to 130 and 15n 0 to 8 are associated with well preserved aquatic and terrestrial organic matter and possibly influenced by nitrogen cycling e g denitrification that caused 15n enrichment between 40 000 cal yr b p and 23 000 cal yr b p depleted 13c values 28 0 are also observed and indicate the predominance of c3 plants during this time interval the pollen analysis reveals the presence of the genera ilex alchornea weinmannia myrsine symplocos drimys and podocarpus on a site currently occupied by mangrove vegetation these data suggest that in the past prevailed a colder and more humid climate than today with a low relative sea level from 23 000 cal yr b p to 2200 cal yr b p a sedimentary hiatus likely occurred related to an erosive event associated to the post glacial sea level rise since at least 2200 cal yr b p sediments are marked by relatively low c n ratios from 2 to 27 exhibit more enriched 13c from 26 0 to 24 0 and 15n up to 7 values and are characterized by the presence of marine diatoms this indicates the return of the marine coastal line to its current position and consequently the development of mangrove

late quaternary variability of the sedimentary record in the sao tome deep sea system south brazilian basin abstract very few sediment records allow addressing the paleoceanographic changes that took place on orbital and or sub milankovitch time scales in the south west atlantic here a set of sediment cores located across a deep channel levee system in the south brazilian basin 3700 3900 m depth is used to infer the sediment dynamics that prevailed on this system during the late quaternary and to relate this pattern to climate changes the spatial distribution of deposits changes in mineralogy texture structure and sedimentation rate according to the morphology indicates bulk of sediment supplies is distributed on the sao tome system by bottom advective processes the silty sandy layers originate undoubtedly from turbidity currents whereas the fine grained muds and oozes that form the major part of the deposits are controlled by deep geostrophic currents in addition to variations forced by the orbital cycles more turbidites less carbonates and higher sedimentation rate during glacials the sediment records chiefly the caco 3 record document outstanding higher frequency regional changes in sedimentation according to the location of the cores at the present day interface between nadw and aabw we infer that changes in sedimentation are related to pulses of aabw versus nadw production these changes commonly marked by asymmetric carbonate pattern of about 10 kyr suggest that the relative influence of nadw versus aabw followed throughout the last 190 kyr a repetitive sequence of progressive increase and sharp decrease the rather sharp shut down observed during the late glacial could be associated to heinrich events when nadw production stopped but similar events are also well expressed during mis 5 mis 6 and at the end of mis 7

antarctic sea ice microwave signatures and their correlation with in situ ice observations the general characteristics and microwave radiative properties of sea ice in the weddell sea region during the onset of spring are studied by using the nimbus 7 scanning multichannel microwave radiometer smmr and other satellite sensors in conjunction with in situ observations from the mikhail somov the position of the ice edge the gradient of ice concentration and the width of the marginal ice zone are inferred from the microwave data and are found to be consistent with ship observations especially at 18 ghz the sensitivities of the various smmr frequencies to surface and other effects are investigated by using multi spectral cluster analysis the results show considerable variability in emissivity especially at 37 ghz likely associated with varying degrees of surface wetness ice concentrations are derived by using two methods one that assumes fixed emissivities for consolidated ice and an iterative procedure that accounts for the variable emissivities observed by using the procedure that allows the emissivities to be variable gives ice concentrations that are more consistent with qualitative field observations

a multiproxy approach to the climate and marine productivity variations along mis 5 in se brazil a comparison between major components of calcareous nannofossil assemblages and geochemical records abstract in this study changes in terrigenous input based on geochemical elementary ratios e g fe ca ti ca ba ca fe k and on marine primary productivity based on calcareous nannofossil assemblages from the southeastern brazilian continental margin are analyzed for the time interval 140 to 55 ka mis 6 to mis 4 variation in the terrigenous input follows the continental paleoclimate records based on speleothems from se brazil and the summer insolation curve from low latitudes for the southern hemisphere in turn marine productivity shows a high correlation with terrigenous input terrigenous input maxima correlate to increased marine productivity during sub stages 5d and 5b both terrigenous input and marine productivity would be strongly controlled by changes in the intertropical convergence zone and winds associated with the south atlantic convergence zone thus ne winds would have prevailed promoting humidity and precipitation rates over se brazil as well as an intensified wind driven upwelling and eddies associated with the brazil current which favored the presence of a shallow nutricline our results are consistent with that of different proxies presented in other studies providing estimates of changes on the precipitation rate of se brazil and changes on marine productivity in the south atlantic ocean during mis 5