dinoflagellate cyst assemblages as tracers of sea surface conditions in the northern north atlantic arctic and sub arctic seas the new n 677 data base and its application for quantitative palaeoceanographic reconstruction the distribution of dinoflagellate cyst dinocyst assemblages in surface sediment samples from 677 sites of the northern north atlantic arctic and sub arctic seas is discussed with emphasis on the relationships with sea surface parameters including sea ice cover salinity and temperature of the coldest and warmest months difficulties in developing a circum arctic data base include the morphological variation within taxa e g operculodinium centrocarpum islandinium cezare and polykrikos sp which probably relate to phenotypic adaptations to cold and or low salinity environments sparse hydrographical data together with large interannual variations of temperature and salinity in surface waters of arctic seas constitute additional limitations nevertheless the use of the best analogue technique with this new dinocyst data base including 677 samples permits quantitative reconstruction of sea surface conditions at the scale of the northern north atlantic and the arctic domain the error of prediction calculated from modern assemblages is 1 3 ca nd 1 8 c for the temperature of february and august respectively 1 8 for the salinity and 1 5 months yr 1 for the sea ice cover application to late quaternary sequences from the western and eastern subpolar north atlantic labrador sea and barents sea provide reconstructions compatible with those obtained using the previous dinocyst data base n 371 which mainly included modern data from the northern north atlantic copyright 2001 john wiley sons ltd journal of quaternary science

monsoon related variations in zaire congo sediment load and influence of fluvial silicate supply on marine productivity in the east equatorial atlantic during the last 200 000 years two sediment cores from the zaire fan and the angola margin have been investigated for their composition of terrigenous and biogenic constituents respectively for the late quaternary kaolinite feldspar ratios and variations of terrigenous element ratios of zr ti k rb and al reveal that the composition of zaire river sediment load has fluctuated in tune with precessional variations of boreal summer insolation in particular the correspondence of high kaolinite feldspar and al k ratios with low latitude insolation maxima strongly corroborates the assumption that west african monsoonal precipitation and chemical weathering was enhanced during periods of increased central african heating the most striking feauture observed is that opal accumulation has been 2 to 10 times higher in zaire fan sediments than outside in continental margin sediments off angola although biogenic ba and corg fluctuations from both areas indicate that changes of total paleoproductivity were of the same magnitude in the zaire river plume and off angola from this we infer that the contribution of biogenic opal production to total paleoproductivity has been significantly higher within the zaire river plume than in the oceanic upwelling regime farther to the south off angola over the last 200 000 years the pattern of opal accumulation rates with respect to that of marine organic carbon implies that enhanced opal production off the zaire river to a great extent was the result of additional fluvial supply of dissolved silica during humid climates characterized by more intense chemical weathering on the continent while total paleoproductivity created by oceanic upwelling was high in periods of increased zonal trade wind intensity at precessional insolation minima and during cold more arid glacial climate conditions we presume that paleoproductivity off the zaire was controlled by the following two sources of nutrients 1 marine nutrients including nitrate and phosphate as well as the uptake of ba on particulate corg caused by upwelling and 2 silica mainly delivered by the zaire river dissolved silicate hence our results underline the importance of dissolved silicate in large rivers for marine silicate cycling in the tropical to subtropical atlantic at a millenial timescale

glacial interglacial variablity in the benguela upwelling system spatial distribution and budgets of organic carbon accumulation 1 modern sedimentary total organic carbon toc content as a proxy for surface water export production was mapped on the shelf and on the upper continental slope of the benguela upwelling system using 137 core tops shelf maxima in toc can be correlated with maxima in surface water productivity on the slope high toc contents are observed offshore from sites of strong modern upwelling estimates of modern toc mass accumulation rates mar show that approximately 85 of the total is accumulating on the shelf toc mar were calculated mapped and budgeted for the holocene and for the last glacial maximum lgm using 19 sediment cores from the continental slope during the lgm centers of deposition and production have migrated offshore with respect to their holocene positions toc accumulation on the continental slope was approximately 84 higher during the lgm than during the holocene possibly reflecting enhanced productivity the toc distribution patterns and sediment echo sounding data suggest that undercurrents strongly influence the sedimentation off namibia winnowing and focusing result in great lateral heterogeneity of sedimentation rates and sediment properties individual cores therefore do not necessarily reflect general changes in export production these results highlight the need for detailed regional studies based on a large number of sediment cores for highly heterogeneous high productivity areas in order to derive general statements on total fluxes

methodology of the last climatic cycle reconstruction in france from pollen data abstract a numerical method has been devised to reconstruct the climate of the last climatic cycle from pollen data reliable annual reconstructions have been published recently for the two french long sequences of la grande pile and les echets covering the last 140 millennia this paper gives more details on the method used it proposes new reconstructions based on an extended modern pollen data base these reconstructions are consistent with the previous ones especially detailed information is obtained on the seasonal characteristics of climate computations of gcm on the climate variations from 125 kyr to 115 kyr b p are confirmed for western europe the insolation variations have induced at that time a decrease of seasonality accompanied by an increased cyclonic activity in winter this has been the beginning of the first ice growth after the last interglacial other glacier growth phases are detected at the end of substage 5c and particularly at the end of substage 5a

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

land sea correlation by means of terrestrial and marine palynomorphs from the equatorial east atlantic phasing of se trade winds and the oceanic productivity abstract sporomorphs and dinoflagellate cysts from site gik16867 in the northern angola basin record the vegetation history of the west african forest during the last 700 ka in relation to changes in salinity and productivity of the eastern gulf of guinea during most cool and cold periods the afromontane forest rather than the open grass rich dry forest expanded to lower altitudes partly replacing the lowland rain forest of the borderlands east of the gulf of guinea except in stage 3 when oceanic productivity was high during a period of decreased atmospheric circulation high oceanic productivity is correlated to strong winds the response of marine productivity in the course of a climatic cycle however is earlier than that of wind vigour and makes wind stress induced oceanic upwelling in the area less likely monsoon variation is well illustrated by the pollen record of increased lowland rain forest that is paired to the dinoflagellate cyst record of decreased salinity forced by increased precipitation and run off

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

temporal trends in avalanche activity in the french alps and subregions from occurrences and runout altitudes to unsteady return periods we present an analysis of temporal trends in 55 000 avalanches recorded between 1946 and 2010 in the french alps and two north south subregions first bayesian hierarchical modelling is used to isolate low intermediate and high frequency trends in the mean avalanche occurrence and runout altitude per year winter variables are then combined to investigate their correlation and the recent evolution of large avalanches comparisons are also made to climatic and flow regime covariates the results are important for risk assessment and the development of new high altitude climate proxies at the entire french alps scale a major change point exists in 1978 at the heart of a 10 year period of high occurrences and low runout altitudes corresponding to colder and snowier winters the differences between this change point and the beginning end of the study period are 0 1 avalanche occurrences per winter and per path and 55 m in runout altitude trends before after are well correlated leading to enhanced minimal altitudes for large avalanches at this time a marked upslope retreat 80 m for the 10 year return period runout altitude accompanied by a 12 decrease in the proportion of powder snow avalanches has occurred since then interrupted from about 2000 the snow depth and temperature control on these patterns seems significant r 0 4 0 6 but is stronger at high frequencies for occurrences and at lower frequencies for runout altitudes occurrences between the northern and southern french alps are partially coupled r 0 4 higher at low frequencies in the north the main change point was an earlier shift in 1977 and winter snow depth seems to be the main control parameter in the south the main change point occurred later 1979 84 was more gradual and trends are more strongly correlated with winter temperature

vegetation change in equatorial west africa time slices for the last 150 ka abstract drawing on marine and terrestrial palynological data vegetation maps of equatorial west africa are presented for eleven time slices over the last 150 000 years long marine records are used as a basis for the regional picture and provide a chronology for the last glacial cycle much shorter terrestrial records help fill in the picture for the most recent periods and facilitate interpretation of regional patterns for the longer timescale temporal and spatial variation is revealed in relation to global patterns of climate change rain forest was widespread during oxygen isotope stages 1 and 5 but strongly reduced during stages 3 and 4 and especially during stages 2 and 6 when open grass rich vegetation prevailed glacial rain forest refuges are found in the southwest of the guinean mountains and along the eastern coast of the gulf of guinea miombo woodland of the zambezian vegetation zone expanded during stage 5 especially during the first half podocarpus forest had its largest expansion during substages 5d 115 to 105 ka and 5b 95 to 85 ka the last occurrence of podocarpus in the guinean mountains is during stage 5a the distribution of mangrove swamps was extremely reduced during glacial times during stage 6 savanna and open dry forest covered large areas along the northern coast of the gulf of guinea the southern saharan desert reached far to the south and the namib desert far to the north the area of rain forest was restricted mangrove swamps were strongly reduced and the area of podocarpus forest fluctuated during stage 5 large changes in the area of afromontane forest rain forest dry open forest and savanna occurred rain forest was widespread and mangroves were extensive along the coast during the last interglacial substage 5e podocarpus forest area strongly extended during substages 5d and 5b in substages 5c and 5a rain forest reclaimed areas it had lost in the previous substages 5d and 5b respectively mangrove swamps were less widespread in the later substages of stage 5 than during substage 5e during stage 4 the rain forest area was again strongly reduced and recovered only slightly during the following stage 3 also the mangrove swamp area was reduced except along the ivory coast and along the northwestern coast of the gulf of guinea podocarpus forest only occurred in angola and may be in congo during stage 4 again forest was much reduced during stage 2 and open vegetation types covered large parts of equatorial west africa mangrove swamps must have been rare at the beginning of the holocene mangrove swamps had recovered and reached their largest extension also the rain forests area increased in the early holocene and guinean and congolian rain forests were probably not separated by a savanna corridor now existing in togo and benin

oceanographic control of diatom abundances and species distributions in surface sediments of the tropical and southeast atlantic abstract this paper is a descriptive account of the diatomaceous component of pelagic sediments from the tropical and southeast atlantic ocean geographic patterns of diatom abundances whole and fragment forms per gram major species relative abundances and diatom assemblages resolved by q mode factor analysis are presented comparisons drawn to sea surface temperature salinity and productivity distributions suggest that i diatom abundances primarily reflect surface productivity with no apparent dissolution effects due to water depth ii relative abundances of major species vary in their ecologic dependence but do reflect major oceanographic features of the surface waters and iii of the five diatom assemblages resolved four finely delineate the complexity of the low latitude oceanography these assemblages in decreasing order of statistical importance are associated with 1 warm waters of moderate to high primary productivity 2 the oceanward margin of the benguela current a region of high primary production with a maximum in austral summer 3 low salinity waters off the mouths of the zaire and niger rivers and 4 subtropical to tropical waters of lower productivity mostly in the western equatorial atlantic the fifth factor represents the equatorward advection of subantarctic to antarctic diatoms by deep ocean currents

late holocene snow avalanche activity in southern norway interpreting lichen size frequency distributions using an alternative to simulation modelling recent work by mccarroll 1993 1994 suggests that a new approach to lichenometry can be used to date diachronous surfaces size frequency distributions of largest lichens obtained from the diachronous surfaces of avalanche boulder ramparts comprise two elements an equilibrium population growing on boulders deposited throughout the holocene and overlapping populations growing on groups of boulders deposited by events during the last 300 years in this study almost 10000 lichens were measured on two groups of closely similar ramparts the number of very large lichens is used to predict the form of the equilibrium distribution which is then removed leaving a corrected distribution which reflects the age frequency of surface boulders deposited during the little ice age the results confirm that maximum avalanche activity occurred during the 19th century but a minor peak at one site suggests that avalanche activity was enhanced during the mid 18th century

stelladinium bifurcatum n sp a distinctive extant thermophilic heterotrophic dinoflagellate cyst from the late quaternary of the eastern pacific and east equatorial atlantic oceans abstract stelladinium bifurcatum n sp is a large and distinctive brown heterotrophic dinoflagellate cyst recorded from upper pleistocene through modern sediments of the eastern pacific modern sediments of the western bay of bengal and sediment traps from the south china sea and upper pleistocene through middle holocene deposits of the east equatorial atlantic it is distinguished by prominent apical and antapical horns numerous long processes distributed along the cingulum tips of horns and processes that are characteristically solid or thickened and taper to points a prominent flagellar scar and an archeopyle formed by the second anterior intercalary plate with the operculum adnate along the right lateral margin stelladinium bifurcatum has been recorded in the literature under several names including stelladinium reidii and the cyst of protoperidinium stellatum from which it differs in having abundant cingular processes at least one of which usually has a strongly divergent bifurcation re examination of published records shows stelladinium bifurcatum to have a tropical subtropical neritic distribution in modern sediments of the eastern pacific margin and to be associated with high biological productivity similarly in pleistocene holocene sediments off west equatorial africa stelladinium bifurcatum is linked to elevated sea surface temperatures during the last deglaciation and it serves as a marker of river discharge associated with an increase in monsoonal dynamics at this time

quaternary forest associations in lowland tropical west africa terrestrial fossil pollen records are frequently used to reveal the response of vegetation to changes in both regional and global climate here we present a fossil pollen record from sediment cores extracted from lake bosumtwi west africa this record covers the last c 520 thousand years ka and represents the longest terrestrial pollen record from africa published to date the fossil pollen assemblages reveal dynamic vegetation change which can be broadly characterized as indicative of shifts between savannah and forest savannah formations are heavily dominated by grass poaceae pollen 55 typically associated with cyperaceae chenopodiaceae amaranthaceae and caryophyllaceae forest formations are palynologically more diverse than the savannah with the key taxa occurring in multiple forest zones being moraceae celtis uapaca macaranga and trema the fossil pollen data indicate that over the last c 520 ka the vegetation of lowland tropical west africa has mainly been savannah however six periods of forest expansion are evident which most likely correspond to global interglacial periods a comparison of the forest assemblage composition within each interglacial suggests that the holocene 11 0 ka forest occurred under the wettest climate while the forest which occurred at the time of marine isotope stage 7 probably occurred under the driest climate

a 30 000 yr record of land ocean interaction in the eastern gulf of guinea abstract a 30 000 yr dinocyst and pollen record from the eastern equatorial atlantic off cameroon has been investigated in order to identify land ocean linkages during the last deglacial transition a strong correlation between the abundance of brigantedinium spp and the ca fe ratio during the last glacial period suggests enhanced marine productivity in association with cool seawater temperatures and nutrient input linked to coastal upwelling and or a proximal river mouth dry conditions are recorded on the adjacent continent with a significant representation of open vegetation indicators and the afromontane taxon podocarpus after 17 cal ka bp these indicators register a sharp decline as a result of a climatic transition from the dry cooler conditions of the last glacial period to the wetter warmer conditions of the deglaciation simultaneously dinocysts show a significant shift from dominant heterotrophs to an increasing abundance of autotrophs reflecting warmer conditions significant changes are observed during the younger dryas with a return to drier conditions and higher salinities the start of the holocene is marked by very low salinity conditions reflecting optimal monsoonal conditions over west equatorial africa the end of the african humid period is observed between 6 and 5 cal ka bp followed by significant fluctuations in both terrestrial and oceanic proxies

high resolution last deglaciation record from the congo fan reveals significance of mangrove pollen and biomarkers as indicators of shelf transgression abstract high abundances of mangrove pollen have been associated with transgressive cycles on tropical margins but the detailed relations between systems tracts and the taphonomy of the pollen are unclear we report here the occurrence and high abundance of rhizophora pollen in association with taraxerol a rhizophora sourced biomarker from a high resolution congo fan core covering the last deglaciation an age model based on 14c dates enables the temporal changes in taraxerol content and the percentage frequencies and flux pollen grains pg cm 2 103 yr 1 of mangrove pollen to be compared quantitatively with the lateral rate of transgression across the flooding surface derived from glacio hydro isostatic model output and the bathymetry of the margin rhizophora pollen concentrations and taraxerol content of the sediment are very strongly positively correlated with the lateral rate of transgression and indicate independently of any sequence stratigraphic context that mangrove pollen spikes are associated with the transgressive systems tract rather than the highstand systems tract or maximum flooding surface lower resolution longer term records from this margin indicate an association between taraxerol concentrations and transgressive rather than regressive phases the flux of these materials to the congo fan is interpreted as a function of the erosion of flooded mangrove swamp on the shelf and less importantly changing extent of mangrove habitat during sea level rise congo river palaeoflood events also result in reworking of mangrove pollen and supply to the fan but this mechanism is subdominant rhizophora pollen has been underestimated in many palynological studies undertaken on cores from the african margin because of inappropriate sieve mesh size used during laboratory preparation

modelling late holocene snow avalanche activity incorporating a new approach to lichenometry where snow avalanches descend steeply into large rivers displacing bedload avalanche boulder ramparts may accumulate retaining a record of late holocene snow avalanche frequency the age frequency of surface boulders on 12 such features in upper jostedalen southern norway was investigated using the size frequency distribution of lichens a model was constructed to simulate the influence of variations in avalanche frequency since ad 1325 on lichen size frequency distributions using this modelling approach it is not possible to define a unique pattern of avalanche activity to account for the observed lichen size frequency distributions but it is possible to place strict limits on the range of scenarios that are acceptable the results suggest that maximum avalanche activity occurred during the 19th century after the peak of the little ice age this conflicts with historical records of avalanche damage to property at lower altitude in nearby valleys which may reflect avalanche activity only during a short period of extreme climatic conditions close agreement between the records of snow avalanches and debris flows suggests that both reflect periods of high winter snowfall and rapid spring melting rather than low temperature future greenhouse warming may therefore result in increased avalanche activity in southern norway

rapid palaeoceanographic changes in the benguela upwelling system for the last 160 000 years as indicated by abundances of planktonic foraminifera abstract two sediment cores retrieved from the continental slope in the benguela upwelling system geob 1706 19 33 7 s 11 10 5 e and geob 1711 23 18 9 s 12 22 6 e reveal striking variations in planktonic foraminiferal abundances during the last 160 000 years these fluctuations are investigated to assess changes in the intensity and position of the upwelling centres off namibia four species make up over 95 of the variation within the core and enable the record to be divided into episodes characterized by particular planktonic foraminiferal assemblages the fossil assemblages have meaningful ecological significance when compared to those of the modern day and the relationship to their environment the cold water planktonic foraminifer neogloboquadrina pachyderma sinistral n pachyderma s dominates the modern day coastal upwelling centres and neogloboquadrina pachyderma dextral and globigerina bulloides characterize the fringes of the upwelling cells globorotalia inflata is representative of the offshore boundary between newly upwelled waters and the transitional reduced nutrient levels of the subtropical waters in the fossil record episodes of high n pachyderma s abundances are interpreted as evidence of increased upwelling intensity and the associated increase in nutrients the n pachyderma s record suggests temporal shifts in the intensity of upwelling and corresponding trophic domains that do not follow the typical glacial interglacial pattern periods of high n pachyderma s abundance describe rapid discrete events dominating isotope stages 3 and 2 the timing of these events correlates to the temporal shifts of the angola benguela front jansen et al 1997 situated to the north of the walvis ridge absence of high abundances of n pachyderma s from the continental slope of the southern cape basin indicates that southern ocean surface water advection has not exerted a major influence on the benguela current system the coincidence of increased upwelling intensity with the movement of the angola benguela front can be interpreted mainly by changes in strength and zonality of the trade wind system

sea ice cover sea surface salinity and halo thermocline structure of the northwest north atlantic modern versus full glacial conditions abstract seasonal sea ice develops along the eastern continental margins in the northern north atlantic where freshwater and or meltwater outflow are responsible for relatively low salinity in surface waters and very pronounced water mass stratification sea ice constitutes a major parameter in the marine ecosystem since the duration and extent of its seasonal spreading constrain the plankton distribution and the related microfossil assemblages on the sea floor organic walled dinoflagellate cysts that are highly resistant to dissolution were recovered from surface sediments of the northern north atlantic and used to develop transfer functions best analogue method for the reconstruction of the seasonal spreading and duration of sea ice cover in addition to salinity and temperature of the warmest month of the year application of the best analogue approach to cores from the labrador sea reveals large variations in sea ice cover and sea surface conditions throughout the last glacial stage and during the early holocene isotopic analyses in epipelagic and mesopelagic planktonic foraminifers also suggest important changes in salinity and temperature gradients between the surface and sub surface water masses specific study of the last glacial maximum lgm time slice 16 20 ka on a 14 c time scale in the northwestern north atlantic shows much more extensive sea ice than at present with perennial sea ice lying along the continental margins of eastern canada seasonal spreading of the cover of sea ice offshore was accompanied by large seasonal contrasts in temperature with very cold winters but relatively warm summers a pattern linked to strong stratification between a buoyant low saline surface layer having a low thermal inertia and the underlying intermediate oceanic waters

reconstruction of sea surface conditions at middle to high latitudes of the northern hemisphere during the last glacial maximum lgm based on dinoflagellate cyst assemblages abstract a new calibration database of census counts of organic walled dinoflagellate cyst dinocyst assemblages has been developed from the analyses of surface sediment samples collected at middle to high latitudes of the northern hemisphere after standardisation of taxonomy and laboratory procedures the database comprises 940 reference data points from the north atlantic arctic and north pacific oceans and their adjacent seas including the mediterranean sea as well as epicontinental environments such as the estuary and gulf of st lawrence the bering sea and the hudson bay the relative abundance of taxa was analysed to describe the distribution of assemblages the best analogue technique was used for the reconstruction of last glacial maximum lgm sea surface temperature and salinity during summer and winter in addition to sea ice cover extent at sites from the north atlantic n 63 mediterranean sea n 1 and eastern north pacific n 1 three of the north atlantic cores from the continental margin of eastern canada revealed a barren lgm interval probably because of quasi permanent sea ice six other cores from the greenland and norwegian seas were excluded from the compilation because of too sparse assemblages and poor analogue situation at the remaining sites n 54 relatively close modern analogues were found for most lgm samples which allowed reconstructions the new lgm results are consistent with previous reconstructions based on dinocyst data which show much cooler conditions than at present along the continental margins of canada and europe but sharp gradients of increasing temperature offshore the results also suggest low salinity and larger than present contrasts in seasonal temperatures with colder winters and more extensive sea ice cover whereas relatively warm conditions may have prevailed offshore in summer from these data we hypothesise low thermal inertia in a shallow and low density surface water layer

marine production in the congo influenced se atlantic over the past 30 000 years a novel dinoflagellate cyst based transfer function approach abstract the sediments from the congo deep sea fan contain valuable information about past environmental conditions of the east equatorial atlantic during the transition from the last glacial maximum lgm to present day climatic conditions the high resolution marine organic walled dinoflagellate cysts dinocysts and terrestrial pollen palynological records from two cores off equatorial west africa covering the last 30 000 years document three major phases in surface productivity 1 during the lgm relative sea level was low nutrient enrichment due to seasonal coastal upwelling prevailed off the congo mouth and high aridity prevailed in the catchment area 2 at around 15 2 cal ka bp monsoonal precipitation strengthened over the congo basin generating high river discharges river induced upwelling and increased nutrient flux to the ocean in parallel erosion of shelf sediments during shelf transgression further enhanced nutrient flux 3 at around 9 8 cal ka bp rainforest vegetation inhibited soil erosion depleted nutrient supply and restricted marine productivity to its modern levels the study presents the application of modern analogues and a dinocyst transfer function to the reconstruction of primary palaeoproductivity pp in a region of freshwater influence a database of recent dinocyst assemblages comprising of 208 sites in the equatorial atlantic enabled the reconstruction of sea surface annual pp 1 3 times higher during the lgm and also during the deglaciation between 15 2 and 13 2 cal ka bp the reconstruction is independent of and thus provides corroboration for other biological and geochemical proxies

dinoflagellate cyst distribution in high latitude marine environments and quantitative reconstruction of sea surface salinity temperature and seasonality a data base of 179 reference sites documents the relations between the assemblages of organic walled dinoflagellate cysts and sea surface temperature salinity and seasonality throughout the north atlantic adjacent subpolar basins labrador sea baffin bay irminger and iceland basins and epicontinental environments off eastern canada estuary and gulf of st lawrence hudson bay principal component analyses show close relationships between dinoflagellate cyst data and sea surface conditions the first component 71 1 of the variance correlates with the winter temperature salinity and seasonal duration of sea ice cover whereas the second component 11 3 of the variance appears mainly related to summer temperature transfer functions using the best analogue method were tested by reconstructing modern sea surface conditions on the basis of the reference dinoflagellate cyst assemblages the correlation coefficient between instrumental averages and reconstructed values ranges from 0 87 august tem

african monsoonal precipitation modulated by interhemispheric temperature gradients the deglacial pattern of a high resolution alkenone derived temperature record from the southeastern tropical atlantic was compared with one from the northeastern subtropical atlantic during termination 1b surface waters in the eastern tropical atlantic 6 s reached modern temperatures whereas those in the subtropical northeastern atlantic 21 n were still considerably colder than today this asymmetrical warming may reflect meltwater induced reductions in the northward heat transport and helps to explain rapid changes in monsoonal precipitation over africa during the early holocene

late quaternary climate changes in central africa as inferred from terrigenous input to the niger fan time series of terrigenous source elements al k ti zr from core geob4901 8 recovered from the deep sea fan of the niger river record variations in riverine sediment discharge over the past 245 000 yr although the flux rates of all the elements depend on physical erosion which is mainly controlled by the extent of vegetation coverage in central africa element al ratios reflect conditions for chemical weathering in the river basin maximum sediment input to the ocean occurs during cold and arid periods when precipitation intensity and associated freshwater runoff are reduced high carbonate contents during the same periods indicate that the sediment supply has a positive effect on river induced marine productivity in general variations in the terrestrial signals contain a strong precessional component in tune with changes in low latitude solar radiation however the terrestrial signal lags the insolation signal by several thousand years k al ti al and zr al records reveal that african monsoonal precipitation depends on high latitude forcing we attribute the shift between insolation cycle and river discharge to the frequently reported nonlinear response of african climate to primary orbital configurations which may be caused by a complex interaction of the secondary control parameters such as surface albedo and or thermohaline circulation

an expanded modern dinoflagellate cyst dataset for the southwest pacific and southern hemisphere with environmental associations organic walled dinoflagellate cyst dinocyst assemblages were examined in 120 sea floor sediment samples from the southwest sw pacific to highlight dinocyst distribution in the region from these 120 samples census counts of 40 samples were added to previously published census data from the southern hemisphere to form a modern dataset of 311 samples sh 311 cluster analysis k means clustering of a 98 sample sub set from the sw pacific nz 98 reveals four distinct assemblages which coincide with modern subantarctic surface water the subtropical front and two clusters from subtropical surface water a similar clustering of the sh 311 dataset reveals an additional three assemblages two associated with polar waters colder than those sampled in the sw pacific and one that may be endemic to the south atlantic ocean multivariate ordination canonical correspondence analysis and redundancy analysis indicates that the dinocyst assemblages change most along a sea surface temperature sst gradient in both the regional sw pacific and southern hemisphere datasets sst accounts for 38 to 56 of the species environmental relationship after removal of covarying variables and contributes 2 3 times the explainable inertia than the other environmental variables tested both modern datasets sh 311 and nz 98 are suitable as a training set for quantitative palaeotemperature transfer functions applied to late quaternary records with the caveat that the modern assemblage also displays sensitivity to productivity shoreline proximity bottom water oxygen and water mass variation that may be exploited in certain situations c 2013 elsevier b v all rights reserved

nw african climate variations during the last 47 000years evidence from organic walled dinoflagellate cysts nw african climate shows orbital and millennial scale variations which are tightly connected to changes in marine productivity we present an organic walled dinoflagellate cyst dinocyst record from a sediment core off cape yubi at about 27 n in the canary basin covering the time period from 47 to 3 ka before present bp the dinocyst record reflects differences in upwelling intensity and seasonality as well as the influence of fluvial input sea level changes play an important role for the upwelling pattern and productivity signals at the core site within the studied time interval four main phases were distinguished 1 from 45 to 24 ka bp when sea level was mostly about 75 m lower than today high relative abundances of cysts of heterotrophic taxa point to enhanced upwelling activity especially during heinrich events while relatively low dinocyst accumulation rates indicate that filament activity at the core location was strongly reduced 2 at sea level lowstand during the lgm to h1 dinocyst accumulation rates suggest that local filament formation was even more inhibited 3 from the early holocene to about 8 ka bp extraordinary high accumulation rates of most dinocyst species especially of lingulodinium machaerophorum suggest that nutrient supply via fluvial input increased and rising sea level promoted filament formation at the same time the upwelling season prolongated 4 a relative increase in cysts of photoautotrophic taxa from about 8 ka bp onwards indicates more stratified conditions while fluvial input decreased our study shows that productivity records can be very sensitive to regional features from the dinocyst data we infer that marine surface productivity off cape yubi during glacial times was within the scale of modern times but extremely enhanced during deglaciation

major and trace elements of river borne material the congo basin the congo river basin is the second largest drainage basin in the world after the amazon the materials carried by its main rivers provide the opportunity to study the products of denudation of a large fraction of the upper continental crust of the african continent this paper presents the chemical composition of the different phases carried in the congo rivers and is followed by a companion paper devoted to the modelling of major and trace elements the congo river between bangui and brazzaville as well as its main tributaries including a few organic rich rivers also called black rivers were sampled during the 1989 high water stage the three main phases suspended load dissolved load and bedload were analysed for twenty five major and trace elements concentrations normalized to the upper continental crust show that in each river suspended sediments and dissolved load are chemical complements for the most soluble elements ca na sr k ba rb and u while these elements are enriched in the dissolved loads they are considerably depleted in the corresponding suspended sediments this is consistent with their high mobility during weathering another type of complementarity is observed for zr and hf between suspended sediments and bedload related to the differential velocity of suspended sediments and zircons which are concentrated in bedloads compared to other rivers absolute dissolved concentrations of ca na sr k ba rb and u are remarkably low surprisingly high dissolved concentrations are found in the congo waters for other trace elements e g rees especially in the black rivers on a world scale these concentrations are among the highest measured in rivers and are shown to be ph dependent for a number of dissolved trace elements the dissolved loads are systematically normalized to the suspended loads for each river in order to remove the variations of the element abundances owing to source rock variations normalized diagrams for rees are presented and extended to the other elements they strongly support the argument that the apparent higher solubility of trace elements in the congo waters is due to the presence in the dissolved load of a colloidal phase as a result of 0 2 m filtration an important result is that these colloids are strongly depleted in fe and al with respect to the other elements finally the comparison of the dissolved suspended and sandy transport fluxes of each element in the congo basin rivers shows that although the proportions of for example the rees in the dissolved loads of the majority of the congo basin rivers is close to 10 of the total transport flux up to 80 of the rees are transported by the so called dissolved load in the black rivers

environmental control of pollen grain distribution patterns in the gulf of guinea and offshore nw africa the areas of marine pollen deposition are related to the pollen source areas by aeolian and fluvial transport regimes whereas wind transport is much more important than river transport pollen distribution patterns ofpinus artemisia chenopodiaceae amaranthaceae and asteraceae tubuliflorae trace atmospheric transport by the northeast trades pollen transport by the african easterly jet is reflected in the pollen distribution patterns of chenopodiaceae amaranthaceae asteraceae tubuliflorae andmitracarpus grass pollen distribution registers the latitudinal extension of sahel savannas and dry open forests marine pollen distribution patterns of combretaceae melastomataceae alchornea andelaeis reflect the extension of wooded grasslands and transitional forests pollen from the guinean congolian zambezian forest and from the sudanian guinean vegetation zones mark the northernmost extension of the tropical rain forest rhizophora pollen in marine sediments traces the distribution of mangrove swamps only near the continent pollen ofrhizophora mitracarpus chenopodiaceae amaranthaceae and pollen from the sudanian and guinean vegetation zones are transported by the upwelling under current and the equatorial under current where those currents act as bottom currents the distribution of pollen in marine sediments reflecting the position of major climatic zones desert dry tropics humid tropics can be used in tracing climatic changes in the past

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

increased upwelling off portugal during the last glaciation diatom evidence abstract quantitative studies have been carried out on opaline microfossils and diatom assemblage composition and preservation in two latest quarternary 100 ka to p d cores from the continental slope of portugal the sites are located in an area of modern summer coastal upwelling created by northerly trade winds the spatial patterns and intensity of this upwelling system are accurately recorded by the diatom abundances and taxonomic composition in the surface sediments the diatom record in these sequences indicates that coastal upwelling intensity was similar to present day during late holocene interglacial stage 3 and late stage 5 higher during stage 2 and lower in the early holocene paleoproductivity estimates are consistent with the diatom accumulation rates from stage 3 to the recent this indicates that both the diatom and the organic carbon content of the sediments mainly reflect the biological productivity in the euphotic zone

land sea comparisons during the last glacial interglacial transition pollen records from west tropical africa abstract land sea correlation off nw africa is investigated from both modern and late pleistocene holocene pollen records pollen spectra from modern soil surface samples from senegal and mauritania and from modern bottom sediment samples from the offshore eastern atlantic 21 12 n record accurately the latitudinal vegetation zonation of west tropical africa by showing the maximum percentages of the phytogeographical groups and the same characteristic taxa as the adjacent vegetation zones a strong correlation between marine core m 16017 2 near cap blanc and continental sebkha of chemchane mauritania pollen signals is also observed for the evolution of the late glacial holocene vegetation zonation at 21 n the differing sensitivities of each sedimentary environment for recording local and or subcontinental vegetation changes are discussed

marine dinocysts acritarchs and less well known npp tintinnids ostracod and foraminiferal linings copepod and worm remains

integrated marine and terrestrial evidence for abrupt congo river palaeodischarge fluctuations during the last deglaciation we present a high resolution reconstruction of tropical palaeoenvironmental changes for the last deglacial transition 18 to 9 cal kyr bp based on integrated oceanic and terrestrial proxies from a congo fan core pollen grass cuticle pediastrum and dinoflagellate cyst fluxes sedimentation rates and planktonic foraminiferal 18o ratios u37k sea surface temperature and alkane alkenone ratio data highlight a series of abrupt changes in congo river palaeodischarge a major discharge pulse is registered at around 13 0 cal kyr bp which we attribute to latitudinal migration of the intertropical convergence zone itcz during deglaciation the data indicate abrupt and short lived changes in the equatorial precipitation regime within a system of monsoonal dynamics forced by precessional cycles the phases of enhanced congo discharge stimulated river induced upwelling and enhanced productivity in the adjacent ocean copyright 2001 john wiley sons ltd

reconstructing pathways of aeolian pollen transport to the marine sediments along the coastline of sw africa the distribution of pollen in marine sediments is used to reconstruct pathways of terrigenous input to the oceans and provides a record of vegetation change on adjacent continents the wind transport routes of aeolian pollen is comprehensively illustrated by clusters of trajectories isobaric 4 day backward trajectories are calculated using the modelled wind field of echam3 and are clustered on a seasonal basis to estimate the main pathways of aeolian particles to sites of marine cores in the south eastern atlantic trajectories and clusters based on the modelled wind field of the last glacial maximum hardly differ from those of the present day trajectory clusters show three regional and two seasonal patterns determining the pathways of aeolian pollen transport into the south eastern atlantic ocean mainly transport out of the continent occurs during austral fall and winter when easterly and south easterly winds prevail south of 25 s winds blow mostly from the west and southwest and aeolian terrestrial input is very low generally a good latitudinal correspondence exists between the distribution patterns of pollen in marine surface sediments and the occurrence of the source plants on the adjacent continent the northern angola basin receives pollen and spores from the congolian and zambezian forests mainly through river discharge the zambezian vegetation zone is the main source area for wind blown pollen in sediments of the angola basin while the semi desert and desert areas are the main sources for pollen in sediments of the walvis basin and on the walvis ridge a transect of six marine pollen records along the south western african coast indicates considerable changes in the vegetation of southern africa between glacial and interglacial periods important changes in the vegetation are the decline of forests in equatorial africa and the north of southern africa and a northward shift of winter rain vegetation along the western escarpment

distribution of dinoflagellate cysts in surface sediments of the northern north atlantic in relation to nutrient content and productivity in surface waters abstract analyses of dinoflagellate cyst assemblages from the surface sediments of 371 sites from the north atlantic ocean were performed in order to define relationships with nitrate phosphate silica and productivity in the upper water layer statistical analyses reveal close links between dinocyst assemblages and nitrate content in february that provide a measurement of nitrate availability amongst the taxa in the assemblages nematosphaeropsis labyrinthus which positively correlates with nutrients shows an eutrophic relationship whereas impagidinium aculeatum impagidinium patulum spiniferites ramosus spiniferites mirabilis and lingulodinium machaerophorum have a rather oligotrophic relationship on these grounds transfer functions were tested using multiple regressions and the best analogue technique to reconstruct nitrate content both methods yielded reasonable estimates and allow the reconstruction of the nitrate concentrations in february with an accuracy better than 1 45 mol m 3 at the scale of the study area there are also tenuous links between the dinocyst assemblages and productivity transfer functions were tentatively tested for the reconstruction of annual productivity and yield estimates with an accuracy of about 26 5 gc m 2 year 1 these results demonstrate that dinocyst assemblages can be used for the reconstruction of productivity and nitrates

an overview and brief description of common marine organic walled dinoflagellate cyst taxa occurring in surface sediments of the northern hemisphere abstract organic walled resting cysts of planktonic dinoflagellates occur commonly in modern marine sediment where they represent with rare exceptions the only geologically preservable part of the life cycle although many species do not produce fossilizable resting cysts upper quaternary sediments contain a diverse cyst record that is used frequently for paleoenvironmental reconstruction and stratigraphic analysis reconstructions of past sea surface conditions rely on an understanding of the distributions of dinoflagellate cysts in modern sediments linked to their respective environmental parameters underpinned by sound taxonomy and standardized nomenclature stratigraphic studies additionally require knowledge of morphological details to distinguish extant from similar extinct taxa here 51 dinoflagellate cyst species and two informal cyst morphotypes that are commonly encountered during routine palynological analysis of upper quaternary marine sediments from the northern hemisphere are briefly described taxonomically and illustrated in addition their lowest stratigraphic occurrences are provided

the north atlantic oscillation and snow avalanching in iceland 1 the number of snow avalanche cycles occurring in iceland is correlated to a major source of variability in climate the north atlantic oscillation a new index for this oscillation is produced that reflects the cumulative effect of snow build up in a starting zone an analysis of the time series for this index shows that recent avalanche tragedies in iceland are linked to a rise in this index consequently estimations of avalanche return periods and thus avalanche hazard zones may need re evaluation because the oscillation has an impact upon climate throughout the northern hemisphere this may be necessary in a number of other countries

on the accuracy of lichenometric dates an assessment based on the little ice age moraine sequence of nigardsbreen southern norway families of lichenometric dating curves are constructed using four historically dated moraine ridges on the glacier foreland of nigardsbreen jostedalsbreen ice cap southern norway a further 20 little ice age moraine ridges are dated in terms of median predicted dates derived from the families of curves four approaches are used to assess the accuracy of the median predicted dates 1 the extent to which the dates form a temporal sequence 2 the extent to which they agree with local independent evidence of glacier variations 3 the extent to which dates agree when the moraine sequences on the two sides of the glacier foreland are dated separately and 4 the extent to which they agree when section rhizocarpon is differentiated from lichens of the rhizocarpon subgenus as a whole it is concluded that under conditions favourable for lichenometric dating median predicted dates have attained an accuracy of 10 on the little ice age timescale realistic error limits are considered to be of the o

changing surface water conditions for the last 500 ka in the southeast atlantic implications for variable influences of agulhas leakage and benguela upwelling the southeast atlantic ocean is an important component of global ocean circulation as it includes heat and salt transfer into the atlantic through the agulhas leakage as well as the highly productive benguela upwelling system here we reconstruct sea surface temperatures ssts from ocean drilling program odp site 1087 in the southeast atlantic to investigate surface ocean circulation patterns during the late pleistocene 0 500 ka the uk 37 index and dinoflagellate cyst assemblages are used to reconstruct ssts dalkenone is used to reconstruct changes in sea surface salinity and mass accumulation rates of alkenones and chlorine pigments are quantified to detect changing marine export productivity the greatest amplitude of sst warming precedes decreases in benthic 18o and therefore occurs early in the transition from glacials to interglacials the dalkenone as a salinity indicator increases before ssts suggesting that the pattern of agulhas leakage is more complex than suggested by sst proxies marine isotope stage mis 10 shows an anomalous pattern it is marked by a pronounced increase in chlorine concentration which may be related to enhanced expanded benguela upwelling reaching the core site we find no evidence of an absence of agulhas leakage throughout the record suggesting that there is no agulhas cutoff even during mis 10 finally the odp site 1087 record shows an increasing strength of agulhas leakage towards the present day which may have impacted the intensity of the atlantic meridional overturning circulation as a result the new analyses from odp site 1087 demonstrate a complex interaction between influences of the benguela upwelling and the agulhas leakage through the late pleistocene which are inferred here to reflect changing circulation patterns in the southern ocean and in the atmosphere

anomalous occurrences of neogloboquadrina pachyderma left in a 420 ky upwelling record from walvis ridge se atlantic abstract core t89 40 eastern walvis ridge between the subtropical gyre and benguela coastal upwelling system contains three types of levels of abundant left coiled neogloboquadrina pachyderma a cold eutrophic species next to subtropical species type a peaks 362 110 and 53 43 ky bp are accompanied with high percentages of other eutrophic species they are attributed to intensified upwelling in the northern benguela region type b peaks 129 and 92 ky bp are accompanied by moderate the highest c peaks up to 38 are associated with strongly reduced percentages of other eutrophic species and with abundant subtropical species marine isotopic stage 11 3 401 ky and 9 3 326 ky the subtropical species preceeded the c peaks by ca 8 ky we argue that the c peaks were not produced by local reproduction but expatriated from the northern benguela upwelling cells here more nutrient rich waters may have produced a mono specific neogloboquadrina pachyderma left fauna during strong polewards shifts of the frontal systems in the south atlantic which could have been transported 700 km offshore to the core location unadmixed with eutrophic species from the surrounding waters we propose meandering shelf edge jets strong contour jets as a mechanism for the transport the timing of the c peaks and associated subtropical peaks agrees with the known precessional cyclicity of the se atlantic front movements and zonality of the trade winds which supports the shelf edge jet hypothesis

use of selective degradation to separate preservation from productivity the assessment of diagenetic influences on the sedimentary record is problematic despite its crucial importance for accurate environmental reconstruction and understanding of biochemical cycles we propose a general applicable method that uses differences in degradation rates of organic components to separate degradation and productivity we demonstrate this method on a southeastern atlantic sediment core covering the past 145 k y the new method solves discrepancies between existing organic matter silica and carbonate based productivity reconstructions and emphasizes the importance of bottom and pore water characteristics for transformation of the sedimentary record

cosmogenic 10be and 26al ages of holocene moraines in southern norway ii evidence for individualistic responses of high altitude glaciers to millennial scale climatic fluctuations abstract 10be and 26al exposure ages are reported for boulder moraine ridges in front of two high altitude cirque glaciers austanbotnbreen jotunheimen and ostre tundradalskyrkjabre breheimen in southern norway ages and 1 external uncertainties for austanbotnbreen moraines range from 7 4 0 75 ka to 8 7 0 9 ka when no adjustment for snow shielding is made with the maximum conceivable snow cover effect 2 m thick a density of 0 2 g cm3 6 months duration at the exposed site the resulting adjusted 7 7 0 8 to 10 9 1 3 ka as well as unadjusted ages suggest moraine formation possibly during both the 8 2 ka event finse event in southern norway and the erdalen event c 10 0 ka in contrast ages obtained for the outer ridges of the large moraine complex in front of ostre tundradalskyrkjabre range from 1 1 0 3 ka to 1 9 0 4 ka assuming no snow shielding assuming extreme snow lie conditions 4 m thick 0 2 g cm3 density 6 months duration at this more sheltered site the adjusted ages

late quaternary history of continental climate and the benguela current off south west africa abstract late quaternary sediments from the southwest african continental slope were analyzed for their coarse fraction diatom and clay mineral content and composition changes in the flow pattern of the benguela current were inferred from the abundance and preservation of opaline microfossils and diatom species composition the benguela current turned westward in the general latitude of 24 s during oxygen isotope stages 1 and 3 this flow pattern caused transportation of opaline microorganisms from the near shore area to the continental slope area or caused increased upwelling phenomena further offshore during oxygen isotope stage 2 on the other hand the westward deflection of the benguela current was moved further to the north two sources of terrigenous material were determined one is local with supply from the namib desert the other one is distant with supply from the orange river mouth material from the orange river mouth might have been transported to the north by the benguela current the local terrigenous supply from the namib desert increased during oxygen isotope stage 2 as evidenced by the increased amounts of terrigenous matter by an increase of illite and by greater grain sizes occurrence of wood fibres in oxygen isotope stage 3 indicates a denser continental vegetation over the present namib desert

dinoflagellate cyst assemblages from the northern shelf sediments of the east china sea an indicator of marine productivity abstract the dinoflagellate cyst assemblages from the northern shelf of the east china sea were examined to assess their potential use as indicators of marine productivity in shelf environments a characteristic disparity in the species compositions of dinoflagellate cysts between coastal sediments and outer shelf sediments was observed coastal areas affected by fluvial freshwater input adjacent to the changjiang river mouth were dominated by protoperidinioid species whereas open sea shelf areas were dominated by gonyaulacoid species the rarity of protoperidinioid cysts in the shelf sediment is primarily attributable to the deficit of silicate in the waters overlying the northern east china sea shelf associated with low supplies of suspended particulate matter from the adjacent continent this would limit the growth of the protoperidinioid species which feed on diatoms in contrast a constant supply of nitrogen generated by microbial nitrogen fixation appeared to have played an important role in supporting the production of gonyaulacoid species in this shelf region thus it was determined that dinoflagellate cyst assemblages in marine sediments are closely linked to significant changes in nutrient composition leading to a selective advantage for the growth of favored taxa this result suggests that gonyaulacoid dinoflagellate cysts are a potentially useful proxy indicator for low nutrient concentration levels especially of silicate in the shelf environment

a new approach to lichenometry dating single age and diachronous surfaces a new approach to lichenometry based on large samples of the single largest lichen on each boulder is presented on surfaces of uniform age lichen sizes measured in this way are near normally distributed so the mean value can be used in constructing lichenometric dating curves by combining mean values from several sites statistically defined confidence limits can be assigned to predicted dates in a pilot study dates obtained for little ice age moraines of two glaciers in southern norway are consistent with those obtained using other approaches unlike standard lichenometry the new approach can be used to investigate the age frequency of boulders on diachronous surfaces formed by continuous or periodic accretion or disturbance it has been used successfully to access the record of late holocene snow avalanche activity retained on avalanche boulder ramparts in upper jostedalen western norway pilot studies are also presented of its use on a talus slope solifluction lobes and periglacial pattern

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

dinoflagellate cyst based reconstructions of mid to late holocene winter sea surface temperature and productivity from an anoxic fjord in the ne pacific ocean abstract published contemporary dinoflagellate distributional data from the ne pacific margin and estuarine environments n 136 were re analyzed using canonical correspondence analysis cca and partial canonical correspondence analysis pcca these analyses illustrated the dominant controls of winter temperature and productivity on the distribution of dinoflagellate cysts in this region dinoflagellate cyst based predictive models for winter temperature and productivity were developed from the contemporary distributional data using the modern analogue technique and applied to subfossil data from two mid to late holocene 5500 calendar years before present present cores tul99b03 and tul99b11 collected from effingham inlet a 15 km long anoxic fjord located on the southwest coast of vancouver island that directly opens to the pacific ocean through barkley sound sedimentation within these basins largely comprises annually deposited laminated couplets each made up of a winter deposited terrigenous layer and spring to fall deposited diatomaceous layer the effingham inlet dinoflagellate cyst record provides evidence of a mid holocene gradual decline in winter sst ending with the initiation of neoglacial advances in the region by 3500 cal bp a reconstructed late holocene increase in winter sst was initiated by a weakening of the california current which would have resulted in a warmer central gyre and more el nino like conditions

lichens lichenometric dating of diachronous surfaces this paper describes software to accompany mccarroll d 1993 modelling late holocene snow avalanche activity incorporating a new approach to lichenometry earth surface processes and landforms18 527 539 and mccarroll d matthews j a and shakesby r a 1995 late holocene snow avalanche activity in southern norway interpreting lichen size frequency distributions using an alternative to simulation modelling earth surface processes and landforms20 465 471

late quaternary sea surface conditions at dsdp hole 594 in the southwest pacific ocean based on dinoflagellate cyst assemblages investigation of organic walled dinoflagellate cyst distribution in 118 surface sediments from the southern ocean documents the relatively high diversity of cyst taxa 46 species and distinct cyst assemblages in relation to surface water masses and temperature gradient the antarctic water is characterised by the dominance of selenopemphix antarctica accompanied by brigantedinium spp and impagidinium pallidum the subantarctic water association consists mainly of nematosphaeropsis labyrinthus impagidinium paradoxum and impagidinium sphaericum whereas the subtropical water association is dominated by operculodinium centrocarpum and spiniferites membranaceus multivariate analyses non metric multidimensional scaling demonstrate the relationships with sea surface conditions and enable the application of the best analogue method on the southern ocean dinoflagellate cyst data base for reconstructing past sea surface conditions the dinoflagellate cyst record from dsdp 594 45 31 41 s 174 56 88 e 1204 m southern margin of the chatham rise shows important fluctuations in species composition from glacial to interglacial over the last 140 000 yr reconstruction of winter and summer ssts reveals much lower temperature than present by 6 to 10 c during marine oxygen isotope stages 6 4 and 2 and higher temperature by 2 3 c during substage 5e copyright 2001 john wiley sons ltd journal of quaternary science

dinoflagellate cysts from two sediment traps east of new zealand abstract two discontinuous sediment trap records of organic walled dinoflagellate cyst dinocyst flux each sampling 300 days within the years 2005 2009 were derived from two time incremental traps deployed at 1500 m water depth east of new zealand the traps sampled flux from beneath two distinct surface water masses on either side of the subtropical front i warm seasonally macronutrient depleted subtropical and ii cold micronutrient limited subantarctic waters nineteen dinocyst taxa or taxonomic groups were identified from the trap samples trap assemblages at both sites were dominated by cysts of protoperidiniaceae notably brigantedinium spp which comprised almost 98 of the dinocyst flux the seasonality of the dinocyst flux differed between the traps with a pronounced spring flux in the subtropical trap while seasonal variation in the subantarctic trap was relatively muted in subtropical waters moderate correlation was observed between protoperidiniaceae cyst flux and chlorophyll a concentrations in surface waters in the 3 4 weeks prior to sampling in subantarctic waters there was a weak correlation between protoperidiniaceae cyst flux and reduced intensity of storm induced turbulence during the preceding 2 3 weeks there was a large discrepancy between dinocyst assemblages in the traps and those observed in nearby sea floor sediments protoperidiniaceae dinocysts particularly echinidinium and brigantedinium were highly under represented in the sea floor assemblages these forms are more susceptible to degradation in oxygenated sediments than other dinocysts but inter annual variability in cyst flux or short term variation not covered by sampling discontinuities in the current study could also have contributed to this discrepancy the major differences in the seasonality of dinocyst fluxes between the two water masses examined in this initial study suggest that mean annual rather than seasonal climatologies are more appropriate for dinocyst based quantitative palaeoenvironmental reconstructions in the new zealand region

land sea correlation in southeastern brazil during the last 7 4 cal ka bp vegetational climatic and oceanographic inferences abstract the vegetation history and climate in southeastern brazil as well as the oceanic dynamics of the tropical atlantic ocean offshore were reconstructed for the last 7 4 cal ka bp this reconstruction was based on pollen fern spores and dinoflagellate cysts identified in a marine core cf10 04b it was possible to verify the presence of an ombrophilous forest from 7 4 cal ka bp near the base of the pi zone low concentrations of pollen and fern spores are recorded along with low frequencies of forest taxa and fern spores and an increase in pollen types of open vegetation suggesting less humid climatic conditions than currently observed in the coastal regions of southeastern brazil the assemblages of dinoflagellate cysts suggest a neritic zone with warm upper column temperature high salinity and oligotrophic environment evidenced by the presence of o centrocarpum spiniferites spp and l machaerophorum an increase in tropical waters tw and the approximation of the brazilian current bc in the middle shelf of southeastern brazil in the mid holocene probably influenced the low accumulation of cysts pollen grains fern spores and their associations it is still possible to verify that at approximately 4 6 cal ka bp an increase in the rainfall in the southeastern brazilian region was probably the fundamental factor for the expansion of vegetation mainly based on the considerable increases in hygrophytic and aquatic plants the marked increase in the accumulation of dinoflagellate cysts with the dominance of autotroph taxa mainly o centrocarpum followed by spiniferites spp evidences the warmer waters of the bc and more intense surface upwelling of the south atlantic central water sacw

contrasting paleoceanographic conditions off morocco during heinrich events 1 and 2 and the last glacial maximum abstract past hydrological and primary productivity regimes on the basis of dinocyst and foraminiferal fossil assemblages as well as on stable isotopes o c and alkenones were investigated over the last 30 ka at upwelling site md04 2805 cq off morocco the results show highest upwelling intensity during heinrich event he 1 time coeval with a distinct plateau of heavy planktonic 13 c values high concentrations of pinus pollen and heterotrophic dinocysts caused by an increased northern wind regime in addition we also present regional reconstructions of paleo sea surface temperatures ssts using three different proxy tools dinocyst and foraminiferal transfer functions as well as alkenones u k 37 sst the reconstructed ssts depict coherent scenarios as modulated by the typical northern hemisphere climatic fluctuations furthermore specific occurrences of the dinocyst spiniferites lazus and of the foraminifer turborotalita quinqueloba are noted for he 2 he 1 and the younger dryas whereas in the alboran sea and in peri iberian waters these cold events were accompanied by the dinocyst bitectatodinium tepikiense and the subpolar foraminifer neogloboquadrina pachyderma s both implying a marked southward shift in the planktonic population in response to the migration of polar water masses this very pronounced demarcation between the planktonic communities better seems to attest the presence of a distinct hydrological structure in proximity of the strait of gibraltar which separated at that time african north of morocco from european southern iberia water masses

dinoflagellate cysts as environmental indicators in surface sediments from the congo deep sea fan and adjacent regions abstract forty nine surface sediment samples from the congo deep sea fan and adjacent hydrographic environments were prepared palynologically and analyzed for fossilizable dinoflagellate cysts the main objective was to investigate the extent to which cysts reflect present day hydrography and therefore may be used downcore as paleoceanographic indicators the region sampled covers a range of marine environments including the congo river plume the area of pronounced upwelling off west central africa and a nearshore offshore gradient from coastal to oceanic waters this is the first study of the effect of a major tropical river plume on associated cyst assemblages cyst counts were low particularly near the river mouth and furthest offshore a combination of statistical treatments was used to analyze the surface cyst assemblages including cluster analysis correspondence analysis and canonical correspondence analysis this helped to identify five distinctive sample groupings representing the main ecological signals in the cyst assemblage data group a dominated by spherical brown protoperidinioid cysts is an upwelling signal group b dominated by the cosmopolitan species o centrocarpum is the main signal for the river plume effect interpreted as reflecting the environmental instability this creates group c dominated by s delicatus with accessory o centrocarpum characterizes the outer plume somehow reflecting the mixing of progressively diluted river plume water and the surrounding oceanic waters group d with high proportions of impagidinium and nematosphaeropsis together with o centrocarpum and s delicatus characterizes the location of the angola benguela front group e with mainly impagidinium species is an oceanic signal the identification of nutrients and water stability as main determining factors influencing cyst signals has implications for cyst based paleoenvironmental interpretations using transfer functions which are developed almost exclusively from comparisons with more easily available data for sea surface temperature salinity and sea ice

minor element and ca isotope composition of calcareous dinoflagellate cysts of cultured thoracosphaera heimii abstract we investigated the influences of temperature salinity and ph on the calcium isotope as well as trace and minor element uranium strontium magnesium to ca ratios on calcium carbonate cysts of the calcareous dinoflagellate species thoracosphaera heimii grown in laboratory cultures the natural habitat of this species is the photic zone preferentially at the chlorophyll maximum depth of temperate to tropical oceans and it is abundant in deep sea sediments over the entire cenozoic in our experiments temperatures ranged from 12 to 30 c salinity from 36 5 to 38 8 and ph from 7 9 to 8 4 the 44 40ca of t heimii cysts resembles that of other marine calcifiers including coccolithophores foraminifers and corals however its temperature sensitivity is considerably smaller and statistically insignificant and t heimii might serve as a recorder of changes in seawater 44 40ca over geologic time the sr ca ratios of t heimii cysts show a pronounced temperature sensitivity 0 016 mmol mol c 1 and have the potential to serve as a palaeo sea surface temperature proxy no clear temperature and ph dependences were observed for mg ca u ca seems to be influenced by temperature and ph but the correlations change sign at 23 c and ph 8 2 respectively

summer monsoon intensity controls c4 c3 plant abundance during the last 35 ka in the chinese loess plateau carbon isotope evidence from bulk organic matter and individual leaf waxes the natural abundance of c3 and c4 plants is affected by multiple environmental factors including temperature moisture balance and atmospheric pco2 the relative importance of these factors is a subject of considerable debate and may vary in different natural ecosystems previous studies generally focus on single loess sequences in the chinese loess plateau and conflicting conclusions on c4 c3 have been reached when studying carbon isotope ratios in carbonate and organic matter in this paper we report a comprehensive carbon isotopic characterization of total organic carbon toc and individual higher plant leaf waxes from five loess sequences spanning the last 35 ka from the chinese loess plateau clp the five coring sites encompass large gradients of annual mean temperature 9 2 13 9 c and precipitation 402 673 mm allowing us to assess the controlling mechanisms on c4 c3 plant ratios glacial interglacial sequences provide carbon isotope data for comparison with other climatic and environmental proxies such as lithology and magnetic susceptibility our results demonstrate that increased c4 c3 ratios are positively correlated with higher temperature and increased summer rainfall which characterize stronger summer monsoon in all five sites we conclude c4 abundance increases from the last glacial to the holocene in response to greater monsoon activity and that the c4 expression is suppressed in the cold and drier intervals

seven centuries of avalanche activity at echalp queyras massif southern french alps as inferred from tree rings the purpose of this study was to reconstruct spatiotemporal patterns of avalanche events in a forested avalanche path of the queyras massif echalp avalanche path southeast french alps analysis of past events was based on tree ring series from 163 heavily affected multicentennial larch trees larix decidua mill growing near or next to the avalanche path a total of 514 growth disturbances such as tangential rows of traumatic resin ducts the onset of compression wood as well as abrupt growth suppression or release were identified in the samples indicating 38 destructive snow avalanches between 1338 and 2010 the mean return period of snow avalanches was 22 years with a 4 probability that an avalanche occurs in a particular year on a temporal plan three maxima in snow avalanche frequency were reconstructed at the beginning of the 16th and 19th centuries and around 1850 correlating with below average winter temperatures and glacier advances analysis of the spatial distribution of disturbed trees contributed to the determination of four preferential patterns of avalanche events the comparison of dendrogeomorphic data with historical records demonstrate that at least 18 events six of which were undocumented reached the hamlet of echalp during the last seven centuries but no significant temporal trend was detected concerning the frequency of these extreme events

evidence for congo river freshwater load in late quaternary sediments of odp site 1077 5 s 10 e abstract late quaternary fluctuations in the intensity of congo river freshwater load were reconstructed using three different proxies marine and freshwater diatoms and the 18o record of globigerinoides ruber preserved in the sediments of ocean drilling program odp site 1077 located at the northern rim of the congo river fan 5 10 s 10 26 e an abrupt change in the diatom assemblage is evident at termination ii a two to four fold increase in a the relative abundance of a marine planktonic diatom tolerant of low salinity conditions cyclotella litoralis and b in the concentration of freshwater diatoms the microfossil data suggest a change in the environmental conditions surrounding site 1077 from predominantly marine to mixed marine brackish fresh the 18o record of the planktic foraminifera g ruber pink revealed negative deviations from the global oxygen isotope signal since termination ii which occurred during warm stage 1 and substages 3 2 5 1 5 3 and 5 5 comparison of the isotopic signal of odp site 1077 with the record from a pelagic location core geob1041 at 3 48 s 7 05 w confirms these results the construction of an artificial 18o curve using alkenone derived sea surface temperature sst data from a nearby core geob1008 at 6 s 10 e allowed us to estimate salinity and temperature effects on the odp site 1077 isotopic signal although increased ssts may account for lighter 18o values during warmer periods they do not explain the extremely light values documented in the sediments of site 1077 we used the oxygen isotope difference 18o between our site and geob1041 as a proxy for freshwater input a general trend in the 18o was observed with more negative values since termination ii in addition conspicuous 18o negative pulses coincided with periods of northern hemisphere summer insolation maxima over the african continent suggesting an increase in the freshwater discharge from the congo river due to enhanced precipitation on the hinterland here we propose that the abrupt change in environmental conditions at site 1077 since termination ii is a consequence of a major reorganization in the depositional environment of the congo river delta this reorganization involved sustained equatorward displacement of the angola benguela front causing a northward deflection of the congo river plume thus moving plume waters further north than normal and over site 1077

pleistocene variations in dust input and marine productivity in the northern benguela current evidence of evolution of global glacial interglacial cycles abstract we infer variations in paleoproductivity and eolian input at odp site 1082 in the walvis basin from stable oxygen isotope compositions of the planktonic foraminifera globorotalia inflata total organic carbon mass accumulation rates toc mar and x ray fluorescence analyses of fe content the most pronounced paleoclimatic changes correspond to the time at about 0 9 ma when glacial conditions in the northern hemisphere nh led to the onset of pronounced 100 kyr glacial interglacial cycles we used fe intensity as a proxy for eolian terrigenous input and toc mar as a paleoproductivity indicator paleoproductivity and eolian input show generally higher amplitude variations of glacial interglacial cyclicity from 1 5 to 0 58 ma indicating pronounced variations in upwelling favorable winds in this area at 0 58 ma paleoproductivity and eolian input shifted abruptly to lower amplitude variations with a periodicity of 100 kyr while 18o values show a trend toward more negative isotope values for the past 0 65 myr especially during glacial periods oxygen isotope values indicate increasingly warmer sea surface temperatures toward the end of the pleistocene to evaluate the relative influences of nh glaciation and southern hemisphere sh insolation as potential forcing mechanisms for variations of eolian input and productivity in the northern benguela system we filtered our proxy records at orbital frequencies the filtered records of fe intensity and toc mar indicate a strong influence of the 100 kyr and 41 kyr frequency bands supporting our assumption that strong ice buildup in the nh is the dominant trigger for climate changes on the continent and probably in trade wind intensity sh insolation and low latitude precession related insolation changes were important for paleoproductivity variations in the northern benguela system modifying the nutrient supply by southern ocean intermediate waters and the zonal direction of upwelling inducing trades by the african monsoon system respectively

late quaternary paleoproductivity changes off the congo deduced from stable carbon isotopes of planktonic foraminifera a detailed record 2 kyr intervals of the difference in stable carbon isotopes 13c between globigerina bulloides and globigerinoides ruber pink is used to reconstruct changes in upwelling intensity off the congo river for the last 190 000 yr comparisons of the oxygen and carbon isotope data from this core with records from the niger fan and from pelagic cores in the eastern equatorial south atlantic indicate that the congo fan isotope records do not contain a strong freshwater signal as is described off other major rivers the temporal pattern of the 13c signal correlates with the marine organic carbon record from the congo fan thus the planktonic 13c record reflecting past changes in upwelling intensity and nutrient content corroborates the signal provided by sedimentary organic carbon which is presumed to indicate changes in the amount of biological productivity and export flux to the seafloor the planktonic 13c signal is characterized by a dominant 23 kyr periodicity which provides evidence for a strong response of upwelling fluctuations off the congo to precessional forcing minima in the 13c record are aligned with periods of minimum boreal summer insolation over central africa reflecting an increase of upwelling and biological productivity off the congo at periods of enhanced zonal intensity of southeast trades and corresponding weak southeast monsoon over the eastern south atlantic a strong response to changes in river discharge probably did not occur indicating that fertilization by river derived nutrients has played only a minor role with respect to late quaternary changes in the total amount of primary productivity off the congo

environmental changes on the inner northeastern black sea shelf off the town of gelendzhik over the last 140 years abstract a comprehensive multi proxy study of mini core ash 2009 08 from the inner shelf of the northeastern black sea allowed us to define recent environmental changes in the area on a sub decadal resolution the age model of the core based on radionuclide 210pb and 137cs measurements suggests an average sedimentation rate of 2 mm y and consequently a sedimentary record spanning the last 140 years overall four fossil groups studied from the core indicate subtle environmental changes the dinocyst assemblages show stable surface water conditions with a possible cooling in the 1930s 1950s and a slight decline in salinity from the 1960s which corresponds to an increase in precipitation and the fresh water balance of the black sea known from the published instrumental data a gradually increasing abundance of the heterotroph species suggests a nutrient increase from the 1920s ostracods and molluscs demonstrate rather stable bottom water salinity and biotopes over the last 75 years changes in abundance of ostracods and benthic foraminifers as well as changes in the mollusc diversity most likely reflect variations in trophic conditions with the higher food supply to the sea floor in the 1940s 1960s and from the late 1990s enhanced bottom water energy is inferred from the mollusc enrichment and a relatively high content of the fine sand grain size fraction in the 1990s in the pollen assemblages trees mainly represented by pinus strongly prevail over herbs throughout the record however the trees to herbs ratio demonstrates a slight decline from the 1920s most likely resulting from human impact on the vegetation of the nearby land

palaeo and rock magnetic investigations of late quaternary sediments from the upper congo deep sea fan on the difficulty in obtaining palaeomagnetic secular variation records from low latitudes we report here on results of palaeo and rock magnetic investigations of two sediment cores from the upper congo deep sea fan the sediments have a high organic content and contain a heterogeneous fe mineral assemblage with biogenic magnetite and detrital ti magnetite as the main magnetic carrier minerals pyrite hematite and fe oxyhydroxides were identified by comparing high temperature magnetic susceptibility curves with those from fe minerals of known composition according to ams 14c dates the 6 8 m long profile spans the last 37 kyr sediments older than 20 ka are affected by reductive diagenesis that has led to a loss of the fine grained magnetic mineral fraction sediments younger than 20 ka have stable magnetizations characteristic remanent magnetization records of inclination and declination were obtained for each core there is a little agreement between these records modelled curves and other sediment records from equatorial africa so no composite record could be established the cores are not ideal relative palaeointensity recorders and estimates using different normalizers did not yield consistent signals from both cores normalization methods used for relative palaeointensity estimation were not developed for sediments that contain large amounts of ultra fine grained biogenic magnetite therefore the relative palaeointensity estimates should be considered with caution however in view of the incoherent picture given by the scarce available palaeointensity information from the region off south west africa the geob6517 2 record may provide a tentative relative palaeointensity record for comparison at least for the past 10 kyr

a 220 000 year climatic record for the east equatorial atlantic ocean and equatorial africa evidence from diatoms and opal phytoliths in the zaire congo deep sea fan accumulation rates of microfossil associations are independent of each other and in addition to percentages give indispensable information about the significance of micropaleontological data marine diatoms reveal that coastal upwelling in the zaire fan region was strong during glacial stages and weaker during interglacial stages oceanic upwelling was intense in stages 6 and 2 and at the stage 5d 5c transition but not in stage 4 the benguela current did not penetrate into the gulf of guinea during the last 220 000 years the phfd index based on the contribution of freshwater diatoms and phytoliths is a measure of aridity in equatorial africa the production in the low salinity river plume was high in the most humid periods on land and low when the continent was arid on the long term nutrient supply of the zaire river to the ocean was probably larger in humid than in arid periods periods of strong seasonal variability in river fluxes and coastal upwelling coincide with arid intervals except in the very humid interval with strong seasonal contrasts 35 000 20 000 years b p

diatom response to oceanographic and climatic changes in the congo fan area equatorial atlantic ocean during the last 190ka bp changes in siliceous productivity in the eastern equatorial atlantic ocean off the western african margin over the last several glacial cycles have been either related to global to regional oceanographic changes upwelling intensity or climate changes precipitation and river discharge based on diatom assemblages in core kzai 02 located to the south of the mouth of the congo river integrated with a selection of geochemical proxies we show that siliceous productivity in the southeastern angola basin responded to non linear interactions between both oceanographic and climate changes over the last 190 000 years high diatom accumulation rates were recorded in the middle part of mis 6 in cold substage mis 5d and in mis 3 2 during these intervals high diatom productivity was sustained essentially by nutrients including dissolved silica injected by the congo river into the ocean the highest productivity was observed during mis 3 when nutrients were sourced both from the river and regional upwelling low diatom accumulation rates were recorded during early and late mis 6 mis 5e early mis 4 and during the holocene these resulted either from low river discharge and overall low nutrient stocks in the angola basin despite evidence for upwelling or from extremely high river discharge in the case of the latter the terrigenous load drastically increased the turbidity of the surface waters in the southeastern angola basin and lowered phytoplankton productivity despite the presence of sufficient dissolved silica

cretaceous calcareous dinoflagellate cysts as recorder of δ44 40caseawater and paleo temperature using sr ca thermometry abstract we evaluate the potential of calcareous dinoflagellates as archives for sr ca based paleo temperature reconstructions and 44 40caseawater fluctuations on sediments from ocean drilling program expedition 113 hole 690c weddell sea southern ocean between 73 and 68 ma sr ca ratios of two cretaceous dinoflagellate species pirumella krasheninnikovii and orthopithonella globosa show a pronounced decrease consistent with a significant drop in sea surface temperature as reflected by the 18o of planktic foraminifers the apparent temperature sensitivity of the dinoflagellate cysts sr ca is 0 06 and 0 08 mmol mol c 1 using 18o derived paleo sea surface temperatures which is significant and large enough to resolve paleoenvironmental temperature changes at current analytical precision as the chemical composition of the cyst calcite appears to have a good preservation the sr ca of calcareous dinoflagellates has a potential to serve as paleo temperature proxy although the chemical composition of the cretaceous seawater and potential impacts on the cyst geochemistry is pending further inspection the ca isotope composition of the two dinoflagellate species shows identical trends of increasing 44 40ca between 73 and 67 ma the planktic foraminifer archaeoglobigerina australis and the benthic foraminifer nuttallides truempyi reveal the same increase of about 0 4 but are offset relative to the dinoflagellates by about 0 5 presumably due to species specific ca isotope fractionation bulk carbonate sediment shows significant scatter likely caused by changes in faunal composition and does not reproduce the trend revealed by the dinoflagellate and foraminifer records these observations demonstrate the importance of taxon specific records and careful determination of fractionation factors of selected archives and highlight complications arising from utilizing less suitable archives such as bulk sediments for 44 40caseawater reconstructions our records indicate strong changes in the marine ca cycle associated with the global temperature decrease towards the end of the cretaceous

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

distribution of common modern dinoflagellate cyst taxa in surface sediments of the northern hemisphere in relation to environmental parameters the new n 1968 database abstract we present a new version of the standardized northern hemisphere modern dinoflagellate cyst dinocyst database which includes abundances of 71 taxa at 1968 sites across the northern hemisphere cross referenced with 17 environmental parameters extracted mostly from the 2013 world ocean atlas several taxa with tropical to warm temperate affinities were added to the previous database version dinocyst concentrations in the surface sediments reach 106 cysts g 1 with maximum values along the continental margins and minimum values offshore in distal open ocean settings assemblages are characterized by the co occurrence of phototrophic n 41 and heterotrophic taxa n 30 with maximum proportions of heterotrophic taxa in high productivity regions notably at the sea ice edge and in upwelling regions the main pattern of assemblage distributions includes north south and nearshore offshore gradients with maximum diversity of species along the continental margins and towards the south in warm temperate and tropical areas canonical correspondence analyses performed on heterotrophic and phototrophic taxa independently yield consistent results hence suggesting similar but not identical ecological affinities for both taxonomic groups for both groups sea surface temperature and sea ice are the most determining parameters but the phototrophic taxa seem more sensitive to onshore offshore gradients marked by salinity changes productivity related parameters also determine dinocyst distribution especially primary productivity in the fall and winter with a stronger relationship for the combined dataset of phototrophic and heterotrophic taxa

little ice age variations of outlet glaciers from the jostedalsbreen ice cap southern norway a regional lichenometric dating study of ice marginal moraine sequences and their climatic significance complex moraine ridge sequences in front of seven outlet glaciers of the jostedalsbreen ice cap austerdalsbreen bergsetbreen fabergstolsbreen lodalsbreen stegaholbreen tuftebreen bodalsbreen are dated using families of lichenometric dating curves established previously at an eighth outlet nigardsbreen applicability of the nigardsbreen curves at the regional level is tested using independent historical evidence moraines deposited during the present century are dated to an accuracy of 9 4 yr 16 0 and most of them are dated to an accuracy of 5 5 yr 9 4 results from the moraine sequences are combined to form a composite jostedalsbreen record median predicted dates for moraine ridges cluster around ad 1939 2 yr 1929 3 1908 3 1886 5 1875 2 1867 4 1855 3 1842 5 1822 5 1807 4 and 1785 5 at least four glaciers reached their little ice age maxima prior to ad 1780 two nigardsbreen and bodalsbreen at ca 1750 one fabergstolsbreen at ca 1705 stegaholbreen attained its maximum ca 1863 since the little ice age maximum and despite large differences in glacier size frontal variations of the various outlets have exhibited a high degree of synchroneity which suggests that the moraine sequences contain a sensitive record of high frequency climatic variations over the last ca 250 yr during the early twentieth century measured readvances of the order of 5 150 m over 1 10 yr led to moraine formation dendroclimatic evidence indicates that since the late eighteenth century moraine ridges formed about 5 yr after summer temperature minima and correlate with runs of cool summers temperature depression of 0 5 1 0 c below the ad 1700 1950 average almost simultaneous glacier advances appear to have been caused by reduced ablation this near immediate response to climatic variation by glacier tongues that descend to relative low altitudes is superimposed upon the longer term dynamic response of the ice cap to climate

surface water conditions in the northern benguela region se atlantic during the last 450 ky reconstructed from assemblages of planktonic foraminifera planktonic foraminiferal records from site 1083 odp leg 175 were used to investigate changes in surface water conditions in the northern benguela region over the past 450 ky the assemblages of planktonic foraminifera are dominated by four species sinistral coiling neogloboquadrina pachyderma dextral coiling n pachyderma globigerina bulloides and globorotalia inflata besides tropical species deliver a small contribution to the assemblage the most prominent temporal variations displayed by n pachyderma s d represent changes in the coastal upwelling and the presence of cold nutrient rich waters over the core site neogloboquadrina pachyderma s d shows cyclic variability in the eccentricity and to a less extent precession frequencies the changes indicate increased upwelling intensity in glacial maxima and precession maxima and correlate well with the wind strength record of stuut et al 2002 during glacial maxima steep temperature gradients over the southern hemisphere caused strong se trade winds and strong upwelling precession maxima cause a weak monsoonal circulation more zonal se trade winds strong coastal upwelling and nutrient rich surface waters over odp site 1083 advection of angola current ac surface water into the walvis basin indicated by the tropical species occurs when the angola benguela front abf is positioned southward occasionally this happened during glacial maxima as can be explained with the reconstructed and predicted meridional movements of the abf the amount of ac water was never sufficient to suppress the marine biological production at the core site the contribution of benguela current bc water reflected by globorotalia inflata is greatly determined by the upwelling in periods of strong upwelling the bc influence is suppressed in several glacial substages the temperature of the upwelling south atlantic central water sacw may have been increased as suggested by the dominance of neogloboquadrina pachyderma d in the upwelling record this phenomenon may be due to intensified subduction in the central south atlantic that induces the formation of sacw or to larger contributions of eastern sacw to the upwelling water around 250 200 ky bp a long term shift to higher productivity occurred that is absent in the upwelling record it was accompanied with a transition from a precession and obliquity variability to an eccentricity dominated variability in the

diatom record of late quaternary climatic change in the eastern equatorial atlantic and tropical africa over the last 160 000 years diatom productivity in the equatorial atlantic has been high during glacial stages 2 4 and 6 and moderate during parts of substages 5b and 5d approximately 96 000 and 117 000 years b p productivity of diatoms is particularly low in substage 5e and in the middle of stage 1 higher productivity implies more vigorous trade winds during glacial intervals leading to stronger upwelling and enhanced lateral advection of surface waters the influence of the benguela current near the equator was strongest during stage 2 a separate regime of coastal upwelling may have existed in the gulf of guinea at this time upwelling and advection may not always respond to the same forcing as sea surface temperature results support the hypothesis that ethmodiscus rex oozes result from high diatom productivity runoff from the zaire and niger rivers was highest at the stage 2 1 transition and just prior to the stage 6 5 transition due to intensification of the african monsoon several other times of increased runoff are indicated periods of increased surface water circulation in the eastern equatorial atlantic appear to correspond to times of aridity in tropical africa conversely intervals of decreased circulation in the eastern equatorial atlantic coincide with times of humidity in tropical africa precessional forcing of continental climate is suggested however precessional forcing of surface ocean circulation can be neither confirmed nor refuted based on the records examined here influx of antarctic bottom water to the eastern equatorial atlantic has been insignificant throughout the last 160 000 years

the lavrion pb zn ag rich vein and breccia detachment related deposits greece involvement of evaporated seawater and meteoric fluids during postorogenic exhumation