sand dunes as a major proximal dust source for late pleistocene loess in the negev desert israel grain size analyses of three hilltop primary eolian loess sequences in the negev desert southern israel show a bimodal grain size distribution at 50 60 m and 3 8 m using analyses of mineralogy and osl ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time suggesting an enhancement of a time transgressive proximal dust source compared to a distal saharan fine grain dust the only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into sinai and the negev concurrently with the loess accretion during the late pleistocene as a result of the exposure of the mediterranean shelf we therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea this relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as northern africa china and australia

evidence of saharan dust in upper pleistocene reworked palaeosols of north west sardinia italy palaeoenvironmental implications abstract a multi disciplinary approach was followed to investigate two thick palaeosolstrata that alternate with wind blown dominated deposits developed along thealghero coast north west sardinia italy optically stimulated luminescenceages reveal that both palaeosols were developed during cooler drier periods the rst one at around 70 ka marine isotope stage 4 and the latter around 50 ka marine isotope stage 3 in contrast the pedological features indicate that thepalaeosols underwent heavy weathering processes under warm humid to sub humid conditions characteristic of the sardinian climate during the lastinterglacial stage marine isotope stage 5e to reconcile this apparent datadiscrepancy a range of sedimentological and pedological analyses wereconducted these analyses reveal that the palaeosols possess a complexhistory with accumulation and weathering occurring during marine isotopestage 5e and erosion colluviation and nal deposition taking place during thefollowing cold stages thus even if these reddish palaeosols were last formedduring the glacial period the sediments building up these strata probablyrecord the climate of the last interglacial stage marine isotope stage 5e traceelement and x ray diffraction analyses together with scanning electronmicroscope images reveal the presence of saharan dust in the parentmaterial of the palaeosols however no evidence of any far travelled africandust has been observed in the marine isotope stage 4 3 aeolian deposits it ispossible to conclude that in the west mediterranean islands saharan dustinput even if of modest magnitude is preserved preferentially in soilsaccumulated and weathered during interglacial stages keywords marine isotopic stage mediterranean osl dating trace elementgeochemistry xrd analysis sedimentology 2012 59 917 938

development of vegetation in the central mojave desert of california during the late quaternary vegetation analysis of 47 neotoma packrat middens from the core of the central mojave desert of california reveal changes in desert plant community composition over the last ca 24 000 years bp one of the lowest and most arid locations in north america habitat currently dominated by mojave desert larrea tridentata creosote bush was occupied prior to ca 11 500 years bp by pinus monophylla pinon juniperus osteosperma utah juniper purshia mexicana bitterbush cercocarpus ledifolius mountain mahogany and prunus fasciculata desert almond woodland above 1000 m p monophylla juniperus woodland was widespread over the southern and central mojave desert however less than 150 km north of the central mojave j osteosperma steppe dominated the landscape paleoecologic records spanning latitude 358n ca 378n document a biogeographic boundary between milder moister environments to the south and the colder drier environments to the north at elevations b1000 m desert scrub species of lycium cooperi wolfberry salvia mojavensis mojave sage and the mesophytic prosopis juliflora mesquite occurred near the shore of pluvial lake mojave from ca 8810 to 8430 years bp larrea is not recorded on the xeric carbonate substrates 605 m until ca 6990 years bp then took over 2000 years to dominate the regional landscape modern vegetation associates such as thamnosma montana desert rue and atriplex confertifolia shadscale were established by ca 4500 years bp late holocene vegetation changes document neoglacial cooling and wetter conditions than today between ca 3490 and 2640 years bp paralleling the regional pluvial lake highstands and marsh deposit records decreases of mesophytic mojave desert associates in the granite mountains suggest climates similar to today s aridity between ca 1970 and 1440 years bp mesophytic species increase in middens

multidecadal variations in the early holocene outflow of red sea water into the arabian sea we present holocene stable oxygen isotope data from the deep arabian sea off somalia at a decadal time resolution as a proxy for the history of intermediate upper deep water these data show an overall 18o reduction by 0 5 between 10 and 6 5 kyr b p superimposed upon short term 18o variations at a decadal centennial timescale the amplitude of the decadal variations is 0 3 prior and up to 0 6 subsequent to 8 1 kyr b p we conclude from modeling experiments that the short term 18o variations between 10 and 6 5 kyr b p most likely document changes in the evaporation precipitation balance in the central red sea changes in water temperature and salinity cause the outflowing red sea water to settle roughly 800 m deeper than today

transition from arid to hyper arid environment in the southern levant deserts as recorded by early pleistocene cummulic aridisols abstract the time at which deserts established their current arid or hyper arid conditions remains a fundamental question regarding the history of earth cosmogenic isotope exposure ages of desert pavement and welded calcic gypsic salic reg soils that developed on relatively flat alluvial surfaces 2 ma ago in the negev desert indicate long geomorphic stability under extremely dry conditions over a short interval during their initial stage of development between 1 2 ma these cumulative soils are characterized by calcic soils reaching maximum stage iii of carbonate morphology this interval is the only period when calcic soil horizons formed on stable abandoned alluvial surfaces in the southern negev desert since 1 ma pedogenesis changed toward more arid soil environment and the formation of gypsic salic soil horizons that were later followed by dust accumulation the dichotomy of only moderately developed calcic soil stages ii iii during a relatively long time interval 105 106 years indicates an arid environment that does not support continuous development but only occasional calcic soil formation the very low 18o and relatively high 13c values of these early pedogenic carbonates support soil formation under arid climatic conditions such an environment was probably characterized by rare and relatively longer duration rainstorms which occasionally allowed deeper infiltration of rainwater and longer retention of soil moisture this in turn enabled the growth of sparse vegetation that enhanced deposition of pedogenic carbonate at 1 ma these rare events of slightly wetter conditions ceased and less atmospheric moisture reached the southern negev desert leading to deposition of soluble salts and dust deposited in the soils the combination of long term hyperaridity scarcity of vegetation and lack of bioturbation salts cementation dust accumulation and tight desert pavement cover has protected the surfaces from erosion forming one of the most remarkably stable landscapes on earth a landscape that essentially has not eroded but accumulated salt and dust for more than 106 yr

compositions of modern dust and surface sediments in the desert southwest united states 1 modern dusts across southwestern united states deserts are compositionally similar to dust rich av soil horizons depths of 0 0 5 cm and 1 4 cm at 35 sites for common crustal elements but distinctly different for some trace elements chemical compositions and magnetic properties of the soil samples are similar among sites relative to dust sources geographic areas and lithologic substrates exceptions are li u and w enriched in owens valley california and mg and sr enriched in soils formed on calcareous fan gravel in southeast nevada the av horizons are dominated by dust and reflect limited mixing with substrate sediments modern dust samples are also similar across the region except that owens valley dusts are higher in mg ba and li and dusts both there and at sites to the north on volcanic substrates are higher in sb and w thus dust and av horizons consist of contributions from many different sources that are well mixed before deposition modern dusts contain significantly greater amounts of as cd cr cu ni pb and sb than do av horizons which record dust additions over hundreds to thousands of years these results suggest that modern dust compositions are influenced by anthropogenic sources and emissions from owens dry lake after its artificial desiccation in 1926 both modern dusts and av horizons are enriched in as ba cu li sb th u and w relative to average crustal composition which we interpret to indicate that the geologic sources of dust in the southwestern united states are geochemically distinctive

paleoclimates off northwest africa 28 35 n about 18 000 yr b p based on continental eolian deposits abstract most conceptual models of atmospheric circulation deduced from bottom sediments or isopollen maps off nw africa assume the occurrence of intensified nne trade winds about 18 000 yr b p in latitudes of 28 35 n and oversimplify the glacial atmospheric circulation over africa an alternative method for reconstructing paleowinds of the last glacial maximum in these latitudes was recently put forward and uses sedimentological records from the canary islands and coastal regions of morocco the continental data do not agree with the previous models and show the prevalence of westerlies all the data from deep sea cores reduction of sea surface temperature increase of biogenic opal accumulation distribution patterns of pollen or dinoflagellate cysts and xeric conditions on the adjacent continent can be explained without increased activity of the trade winds but with a discharge current of cold meltwater from the european and north american ice sheets the model is backed up by a comparison with the present day humboldt current off subtropical south america

geochemical and mineralogical evidence for sahara and sahel dust additions to quaternary soils on lanzarote eastern canary islands spain africa is the most important source of dust in the world today and dust storms are frequent on the nearby canary islands previous workers have inferred that the sahara is the most important source of dust to canary islands soils with little contribution from the sahel region soils overlying a late quaternary basalt flow on lanzarote canary islands contain in addition to volcanic minerals quartz and mica exotic to the island s bedrock kaolinite in the soils also likely has an exotic origin trace element geochemistry shows that the soils are derived from varying proportions of locally derived basalt and african dust major element geochemistry clay mineralogy and interpretation of satellite imagery suggest that dust additions to the canary islands come not only from the sahara desert but also from the sahel region

glacial to interglacial contrasts in the northern indian ocean differences between the 18o 16o ratios of planktonic foraminifera deposited during the last glacial maximum about 18 000 yr ago and those deposited during the holocene show that in the indian ocean the south west monsoon was weaker than today but that the north east monsoon was stronger the upwelling observed in modern conditions along the southern coast of arabia had disappeared because of the low speed of the southwestern winds during glacial summers the reduction in rainfall and runoff over the continent caused a reduction of the salinity gradient in the bay of bengal and along the western coast of india increased precipitation fell on the sea south of 10 n while strong evaporation over the northernmost arabian sea produced an enhanced salinity gradient in that area

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

chronology sedimentology and microfauna of groundwater discharge deposits in the central mojave desert valley wells california during the late pleistocene emergent groundwater supported persistent and long lived desert wetlands in many broad valleys and basins in the american southwest when active these systems provided important food and water sources for local fauna supported hydrophilic and phreatophytic vegetation and acted as catchments for eolian and alluvial sediments desert wetlands are represented in the geologic record by groundwater discharge deposits which are also called spring or wetland deposits groundwater discharge deposits contain information on the timing and magnitude of past changes in water table levels and thus are a source of paleohydrologic and paleoclimatic information here we present the results of an investigation of extensive groundwater discharge deposits in the central mojave desert at valley wells california we used geologic mapping and stratigraphic relations to identify two distinct wetland sequences at valley wells which we dated using radiocarbon luminescence and uranium series techniques we also analyzed the sediments and microfauna ostracodes and gastropods to reconstruct the specifi c environments in which they formed our results suggest that the earliest episode of high water table conditions at valley wells began ca 60 ka thousands of calendar yr b p and culminated in peak discharge between ca 40 and 35 ka during this time cold 4 12 c emergent groundwater supported extensive wetlands that likely were composed of a wet sedge rush tussock meadow mixed with mesic riparian forest after ca 35 ka the water table dropped below the ground surface but was still shallow enough to support dense stands of phreatophytes through the last glacial maximum lgm the water table dropped further after the lgm and xeric conditions prevailed until modest wetlands returned briefl y during the younger dryas cold event 13 0 11 6 ka we did not observe any evidence of wet conditions during the holocene at valley wells the timing of these fl uctuations is consistent with changes in other paleowetland systems in the mojave desert the nearby great basin desert and in southeastern arizona near the border of the sonoran and chihuahuan deserts the similarities in hydrologic conditions between these disparate locations suggest that changes in groundwater levels during the late pleistocene in desert wetlands scattered throughout the american southwest were likely driven by synopticscale climate processes

response of red sea deep water agglutinated foraminifera to water mass changes during the late quaternary abstract the distribution of deep water agglutinated foraminifera was determined in core material taken in the central red sea by the r v meteor cruise 5 leg 2 the sedimentary record represents the last 380 kyr which includes four glacial interglacial cycles the agglutinate assemblage is of low diversity and in general is a minor component of the benthic foraminifera it comprises 14 species belonging to the following genera ammobaculites lagenammina plotnikovina pseudogaudryina reophax sahulia siphotextularia spiroplectinella textularla and a doubtful genus of unknown taxonomic position psammosphaera three sub groups were identified in the core according to their occurrence either in interglacial stages or in both glacial and interglacial intervals reflecting mainly tolerance to salinity variations exceptional bottom water conditions during the last 60 kyr caused a remarkable decrease in the abundance and diversity of this group the development of dysaerobic bottom water between approx 60 and 26 kyr the presence of a deep water mass of extremely high salinity ca 55 between 26 and 13 kyr and the occurrence of anoxic bottom sediments between 12 9 and 9 6 kyr seem to have caused the extreme impoverishment during the last 9 6 kyr the agglutinated foraminifera gradually recolonized the deep water a diverse assemblage composed of the above mentioned genera is found in holocene sediments only in the core top sample in addition small 63 149 m noncanaliculate organic cemented agglutinated foraminifera belonging to the genera ammodiscus cribrostomoides eggerella glomospira haplophragmoides morulaeplecta spiroplectammina paratrochammina and trochammina are preserved preferentially only in the uppermost part of the core 0 28 cm depth in sediments younger than 3 kyr

change in atmospheric mineral aerosols in response to climate last glacial period preindustrial modern and doubled carbon dioxide climates desert dust simulations generated by the national center for atmospheric research s community climate system model for the current climate are shown to be consistent with present day satellite and deposition data the response of the dust cycle to last glacial maximum preindustrial modern and doubled carbon dioxide climates is analyzed only natural non land use related dust sources are included in this simulation similar to some previous studies dust production mainly responds to changes in the source areas from vegetation changes not from winds or soil moisture changes alone this model simulates a 92 33 and 60 change in dust loading for the last glacial maximum preindustrial and doubled carbon dioxide climate respectively when impacts of carbon dioxide fertilization on vegetation are included in the model terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions probably due to the lack of simulation of glaciogenic dust sources in order to include the glaciogenic dust sources as a first approximation we designate the location of these sources and infer the size of the sources using an inversion method that best matches the available data the inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2 1 to 3 3 times current deposition

understanding the red sea response to sea level here we outline a new pragmatic methodology to derive relative sea level estimates from central red sea oxygen isotope records based on a previously published model in this paper the methodology is described in detail and it is shown that sea level change is the dominant factor responsible for the recorded variability in red sea 18o pdb for sea level changes greater than 12 m variables such as temperature or net evaporation are shown to have relatively small effects on the oxygen isotope record the modelled 18o pdb to sea level relationship is given in terms of a fifth order polynomial which may be used to describe relative sea level from central red sea oxygen isotope records we show how established sea level records from fossil reef terraces for the last 20 kyr are successfully simulated from central red sea oxygen isotope records we also examine the spatial variability of 18o pdb in the basin over the last 13 kyr

the last interglacial period on the pacific coast of north america timing and paleoclimate new high precision u series ages of solitary corals balanophyllia elegans coupled with molluscan faunal data from marine terraces on the pacific coast of north america yield information about the timing and warmth of the last interglacial sea level highstand balanophyllia elegans takes up u in isotopic equilibrium with seawater during growth and shortly after death corals from the second terrace on san clemente island offshore southern california the third terrace on punta banda on the pacific coast of northern baja california and the discovery point formation on isla de guadalupe in the pacific ocean offshore baja california date to the peak of the last interglacial period and have u series ages ranging from ca 123 to 114 ka the first terrace on punta banda has corals with ages ranging from ca 83 to 80 ka which corresponds to a sea level highstand formed in the late last interglacial period u series analyses of corals from the cayucos terrace central california and the nestor terrace at point loma southern california show that these fossils have evidence of open system history similar to what has been reported by other workers for the same localities nevertheless a model of continuous secondary u and th uptake shows that two ages of corals are likely present at these localities representing the ca 105 and ca 120 ka sea level highstands reported elsewhere u series ages of last interglacial corals from the pacific coast overlap with but are on average younger than the ages of corals from barbados the bahamas and hawaii this age difference is explained by the nature of the geomorphic response to sea level change fringing or barrier reefs on low latitude coastlines have an accretionary growth style that keeps pace with rising sea level whether on a tectonically rising or stable coastline in contrast midlatitude high energy coastlines are sites of platform cutting during the early part of a sea level high stand and terrace scouring and concomitant sediment and fossil deposition as sea level starts to recede the youngest ages of corals from the pacific coast suggest that sea level was still relatively high at ca 116 ka which is not in agreement with other estimates of relatively large global ice volume at that time reliably dated ca 120 ka marine terrace deposits on the pacific coast have fossil mollusks that indicate water temperatures as warm or warmer than at present in contrast ca 80 ka marine deposits reported here and elsewhere have fossil mollusks indicating cooler than modern water temperatures the presence of both ca 105 ka and ca 120 ka corals on the nestor and cayucos terraces explains a previously enigmatic mixture of warm water and cool water mollusks at ca 105 ka a relatively high sea level with cool waters may have captured the terrace formed during the 120 ka sea level highstand in areas of low uplift rate the inference of cooler than modern waters off the pacific coast of north america at ca 80 ka and ca 105 ka based on marine terrace faunas does not agree with estimates of sea surface temperatures derived from alkenone studies in the santa barbara basin however cooler water temperatures at these times are in agreement with paleotemperature estimates from planktonic foraminiferal data for the santa barbara basin all records from central california to baja california whether from marine terraces or offshore cores indicate at least seasonably warmer than modern waters during the peak of the last interglacial period at ca 120 ka

variations in trace element including rare earth element concentrations with grain sizes in loess and their implications for tracing the provenance of eolian deposits the concentrations of rare earth elements rees and other 28 trace elements were determined in seven grain size fractions from four loess samples collected from the tibetan plateau the sichuan basin and the chinese loess plateau the results indicate that concentrations of rees except for heavy rare earth elements hrees are almost grain size independent however rees show clear fractionation with grain size middle rare earth element mree depletion increases with decreasing grain size whereas hree enrichment increases with decreasing grain size excluding rees and y most of the other trace element concentrations tend to increase with decreasing grain sizes the trace element geochemistry indicates that the potential sources of eolian deposits from the sichuan basin the chinese loess plateau and the tibetan plateau differ from one another this comparative study confirmed that the eolian materials from the asian continent are the source of the terrigenous component of the central north pacific sediments and the loess from the chinese loess plateau could represent the average composition of eolian dust from the asian continent in contrast the eolian deposits in the sichuan basin and in the tibetan plateau are mainly of local origin with short distance eolian transport

aeolian origin and palaeoclimatic implications of the red clay north china as evidenced by grain size distribution the red clay is an important deposit underlying the quaternary loess palaeosol sequence in the chinese loess plateau being regarded as an excellent record of palaeoclimate changes in the late tertiary several properties of the red clay have been measured previously in order to derive climatic information however the sedimentary processes involved and the origin of the materials remain controversial here we present results of grain size analyses of the red clay from four representative sites in the chinese loess plateau in particular their grain size distribution is compared with that of typical quaternary aeolian loess palaeosol as well as lacustrine and fluvial sediments it appears from the sedimentological evidence that the major part of the red clay is of aeolian origin it is rather similar in some of its properties to the quaternary loessic palaeosols the dust forming the red clay was transported by a wind system that was weaker than that involved in the accretion of the quaternary loess furthermore the red clay sediment has been modified by post depositional weathering copyright 2001 john wiley sons ltd

geochemistry of the xining xifeng and jixian sections loess plateau of china eolian dust provenance and paleosol evolution during the last 140 ka abstract loess and paleosol samples from three distant sections xining xifeng jixian of the chinese loess plateau were analyzed for chemical and nd sr isotopic compositions in order to obtain information about the paleoclimatic variation during the last 140 ka these three sections represent three different climatic conditions from arid in the west xining to more humid in the east jixian across the loess plateau isotopic analyses show that all the three sections display a restricted range of 143 nd 144 nd ratios or e nd 10 0 5 indicating the dominance of relatively young and uniform upper crustal sources for the eolian dust the loess and paleosol samples have typical upper crustal 87 sr 86 sr ratios 0 714 0 718 and their variation can partly be attributed to different carbonate silicate ratios in the samples ree data from the three sections are indistinguishable from each other they show typical upper crust patterns characterized by la yb n 10 and eu eu 0 65 the high degree of chemical and isotopic homogeneity suggests that the dust source region must have undergone multiple recycling and thorough sedimentary mixing processes various chemical indicators have been used to monitor the pedogenetic intensity in these sections although results for the jixian section agree reasonably well with the known climatic conditions on the loess plateau the other two sections yield results not in agreement with some well accepted proxies like magnetic susceptibility or grain size distribution some chemical proxy indicators established in our previous work on the luochuan section such as the systematic u depletion and negative ce anomalies in ree patterns in soils are not clearly recorded in the present case the discrepancy between different climatic proxies could be related to the effective soil water budget temperature as well as the rate of development of each proxy

recent abyssal benthic foraminiferal biofacies of the eastern equatorial indian ocean abstract study of recent abyssal benthic foraminifera from core top samples in the eastern equatorial indian ocean has identified distinctive faunas whose distribution patterns reflect the major hydrographic features of the region above 3800 m indian deep water idw is characterized by a diverse and evenly distributed biofacies to which globocassidulina subglobosa pyrgo spp uvigerina peregrina and eggerella bradyi are the major contributors nuttalides umbonifera and epistominella exigua are associated with indian bottom water ibw below 3800 m within the ibw fauna n umbonifera and e exigua are characteristic of two biofacies with independent distribution patterns nuttalides umbonifera systematically increases in abundance with increasing water depth the e exigua biofacies reaches its greatest abundance in sediments on the eastern flank of the ninetyeast ridge and in the wharton cocos basin the hydrographic transition between idw and ibw coincides with the level of transition from waters supersaturated to waters undersaturated with respect to calcite and with the depth of the lysocline carbonate saturation levels possibly combined with the effects of selective dissolution on the benthic foraminiferal populations best explain the change in faunas across the idw ibw boundary and the bathymetric distribution pattern of n umbonifera the distribution of the e exigua fauna cannot be explained with this model epistominella exigua is associated with the colder more oxygenated ibw of the wharton cocos basin the distribution of this biofacies on the eastern flank of the ninetyeast ridge agrees well with the calculated bathymetric position of the northward flowing deep boundary current which aerates the eastern basins of the indian ocean

geochemical evidence for african dust and volcanic ash inputs to terra rossa soils on carbonate reef terraces northern jamaica west indies abstract the origin of red or reddish brown clay rich terra rossa soils on limestone has been debated for decades a traditional qualitative explanation for their formation has been the accumulation of insoluble residues as the limestone is progressively dissolved over time however this mode of formation often requires unrealistic or impossible amounts of carbonate dissolution therefore where this mechanism is not viable and where local fluvial or colluvial inputs can be ruled out an external source or sources must be involved in soil formation on the north coast of the caribbean island of jamaica we studied a sequence of terra rossa soils developed on emergent limestones thought to be of quaternary age the soils become progressively thicker redder more fe and al rich and si poor with elevation furthermore although kaolinite is found in all the soils the highest and oldest soils also contain boehmite major and trace element geochemistry shows that the host limestones and local igneous rocks are not likely source materials for the soils other trace elements including the rare earth elements ree show that tephra from central american volcanoes is not a likely source either however trace element geochemistry shows that airborne dust from africa plus tephra from the lesser antilles island arc are possible source materials for the clay rich soils a third as yet unidentified source may also contribute to the soils we hypothesize that older more chemically mature jamaican bauxites may have had a similar origin the results add to the growing body of evidence of the importance of multiple parent materials including far traveled dust to soil genesis

late quaternary biostratigraphy and paleotemperatures of the red sea and the gulf of aden based on planktonic foraminifera and pteropods abstract the quantitative distributions of planktonic foraminifera and pteropods were analyzed in seven red sea cores and two deep sea cores from the gulf of aden and off sokotra island biostratigraphic intervals were distin guished corresponding to oxygen isotope stages 1 5 in the red sea and stages 1 3 in the gulf of aden the faunal assemblages demonstrate that in the red sea hydrological conditions changed significantly during the late quaternary especially at the last glacial maximum when water exchange at the bab el mandeb straits was at a minimum and at the pleistocene holocene boundary at the end of deglaciation water exchange renewal and pluvial conditions resulted in surface salinity decrease and stable stratification which was followed by a rise in planktonic fauna abundance and stagnation of bottom waters the more constant composition of rather cold water subtropical faunal assemblages in the gulf of aden during the last 40 000 50 000 yrs points to more stable hydrological parameters and to local upwelling or influx of arabian upwelling waters during the last stadial mean annual sea surface temperatures fell by at least 5 c compared to the present in the central part of the red sea and by 3 5 c in the western gulf of aden

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

aeolian dust in colorado plateau soils nutrient inputs and recent change in source aeolian dust windblown silt and clay is an important component in arid land ecosystems because it may contribute to soil formation and furnish essential nutrients few geologic surfaces however have been characterized with respect to dust accumulation history and resultant nutrient enrichment we have developed a combination of methods to identify the presence of aeolian dust in arid regions and to evaluate the roles of this dust in ecosystem processes unconsolidated sandy sediment on isolated surfaces in the canyonlands region of the colorado plateau differs greatly in mineralogical and chemical composition from associated bedrock mainly aeolian sandstone detrital magnetite in the surficial deposits produces moderately high values of magnetic susceptibility but magnetite is absent in nearby bedrock a component of the surficial deposits must be aeolian to account for the abundance of magnetite which formed originally in far distant igneous rocks particle size analysis suggests that the aeolian dust component is typically as much as 20 30 dust inputs have enriched the sediments in many elements including p mg na k and mo as well as ca at sites where bedrock lacks calcite cement soil surface biologic crusts are effective dust traps that apparently record a change in dust sources over the past several decades some of the recently fallen dust may result from human disturbance of land surfaces that are far from the canyonlands such as the mojave desert some land use practices in the study area have the potential to deplete soil fertility by means of wind erosion removal of aeolian silt

a 560 year record of santa ana fires reconstructed from charcoal deposited in the santa barbara basin california microscopic charcoal from varved santa barbara basin sediments was used to reconstruct a 560 yr record a d 1425 to 1985 of santa ana fires comparison of large 3750 m2 charcoal with documented fire records in the santa barbara ranger district shows that high accumulations correspond to large fires 20 000 ha that occurred during santa ana conditions the charcoal record reconstructed a minimum of 20 large fires in the santa barbara region during the study period the average time between fires shows no distinct change across three different land use periods the chumash period apparently characterized by frequent burning the spanish early american period with nominal fire control and the 20th century with active fire suppression pollen data support the conclusion that the fire regime has not dramatically changed during the last 500 yr comparison of large charcoal particle accumulation rates and precipitation reconstructed from tree rings show a strong relationship between climate and fire history with large fires consistently occurring at the end of wet periods and the beginning of droughts

microfossil evidence for changing salinity patterns in the bay of bengal over the last 20 000 years the monsson climate characterizing the northern indian ocean produces salinity gradients that are large compared with those in other open ocean areas these gradients are substantially independent of thermal and other ecologically important gradients this situation makes it possible not only to isolate the effect of salinity on sea bed distribution patterns of planktonic foraminifera but also to investigate past salinity changes along a north south transect of piston cores in the bay of bengal analysis of 152 surface sediment samples reveals that at least three factors other than salinity are important in controlling foraminiferal distribution sea bed dissolution surface productivity and surface temperature of these dissolution is the most important therefore in order to reconstruct past salinity patterns in the bay of bengal faunal indices need to be developed that isolate the effect of salinity we have developed two independent approaches the first uses ternary diagrams of the three dominant dissolution resistant species globoquadrina dutertrei globorotalia menardii pulleniatina obliquiloculata high values of g dutertrei are associated with low surface salinities the second approach uses dissolution buffered salinity transfer functions based on the total foraminiferal fauna in the 152 surface samples from the northern indian ocean applied to downcore samples these methods show the same basic historical pattern of salinity variation which is in turn consistent with independent inferences based on preliminary oxygen isotope data duplessy 1980 historical changes in the bay of bengal salinity are reconstructed along a north south transect of seven cores at 90 e the stratigraphy of the transect is controlled by oxygen isotope profiles that are similar to the generalized patterns observed in other areas over the past 20 000 yr salinity gradients are reconstructed for three time intervals 1 the last glacial maximum lgm 2 the mid termination mt and 3 the holocene during the lgm interval salinity was highger in the bay of bengal particularly in the north thus reducing the north south salinity gradient during the mt the middle of the transition from glacial to interglacial global climatic regimes northern bay of bengal surface salinity was considerably reduced while salinity to the south was generally similar to today thus the salinity gradient between 10 n and 15 n was considerably steeper than today in contrast the holocene gradient was approximately the same as the modern gradient with absolute values along the transect being slightly but uniformly higher these changes in the pattern of salinity are explained in terms of changes in the local patterns of precipitation and river run off during the lgm the salinity pattern probably results from decreased precipitation and decreased run off by the ganges brahmaputra river system during the mt decreased salinity in the northern bay of bengal is caused by increased precipitation and run off rather than by the influx of glacial meltwater the steeper mt salinity gradient in the central bay of bengal suggests increased eastward advection of equatorial surface waters by a southwest monsoon current somewhat more vigorous than today these patterns can be correlated with faunal evidence from the western arabian sea that suggest decreased upwelling during the lgm and increased upwelling during the mt this coupling of events may be associated with changes in the pattern or intensity of circulation during the southwest monsoon decreased intensity at the lgm 18 000 b p and increased intensity at the mt 10 500 to 12 500 b p

influences of quaternary climatic changes on processes of soil development on desert loess deposits of the cima volcanic field california summary soils formed in loess are evidence of both relict and buried landscapes developed on pliocene to latest pleistocene basalt flows of the cima volcanic field in the eastern mojave desert california the characteristics of these soils change systematically and as functions of the age and surface morphology of the lava flow four distinct phases of soil development are recognized phase 1 weakly developed soils on flows less than 0 18 m y old phase 2 strongly developed soils with thick argillic horizons on 0 18 0 7 m y old flows phase 3 strongly developed soils with truncated argillic horizons massively impregnated by carbonate on 0 7 to 1 1 m y old flows and phase 4 degraded soils with petrocalcic rubble on pliocene flows a critical aspect of the development of stage 1 soils is the evolution of a vesicular a horizon which profoundly affects the infiltration characteristics of the loess parent materials laboratory studies show that secondary gypsum and possibly other salt accumulation probably occurred during the period of phase 1 soil development slight reddening of the interiors of peds from vesicular a horizons of phase 1 soils and presence of weakly developed b horizons indicates a slight degree of in situ chemical alteration however clay and fe oxide contents of these soils show that these constituents as well as carbonates and soluble salts are incorporated as eolian dust in contrast to phase 1 soils chemical and mineralogical analysis of argillic horizons of phase 2 soils indicate proportionally greater degrees of in situ chemical alteration these data the abundant clay films and the strong reddening in the thick argillic horizons suggest that phase 2 and phase 3 soils formed during long periods of time and periodically were subjected to leaching regimes more intense than those that now exist flow age data and soil stratigraphic evidence also indicate that several major loess deposition events occurred during the past 1 0 m y loess events are attributed to past changes in climate such as the pleistocene to holocene climatic change that periodically caused regional desiccation of pluvial lakes reduction of vegetational density and exposure of loose unconsolidated fine materials during times of warmer interglacial climates precipitation infiltrates to shallower depths than during glacial periods extensive saline playas which developed in the mojave desert during the holocene are a likely source of much of the carbonates and soluble salts that are accumulating at shallow depths both in phase 1 soils and in the formerly noncalcareous nongypsiferous argillic horizons of phase 2 and 3 soils

paleoceanographic record of the last glacial interglacial cycle in the red sea and gulf of aden abstract hydrographic conditions in the red sea are strongly controlled by regional climatic conditions and the restricted water exchange with the gulf of aden indian ocean in turn intermediate and deep water masses in the gulf of aden reflect the nature of red sea outflow planktonic and benthic foraminiferal faunas and the lithology and mineralogy of red sea and gulf of aden sediments were studied in order to evaluate changes in water mass conditions in the two basins during the last 18 000 years the results indicate that changes in the local climate and circulation regime during this period resulted in significant hydrographic changes in surface and bottom waters in the red sea and intermediate waters in the gulf of aden during the last glacial maximum high aridity and glacio eustatic sea level lowering resulted in surface and bottom water salinities in the red sea which were considerably higher than at present in the gulf of aden glacial surface salinities and temperatures remained similar to holocene values while surface water productivity may have been lower surface salinities in the red sea decreased after 18 000 years b p as the connection between the red sea and gulf of aden was reestablished however bottom water salinities remained high until at least 11 000 years b p pluvial conditions during deglaciation enhanced the density difference between surface and bottom waters in the red sea and resulted in a decrease in the oxygen content of the bottom waters hydrographic conditions in the western gulf of aden reflect a change in the properties of outflowing red sea water during deglaciation

salinity tolerance or marine organisms deduced from red sea quaternary record abstract the oxygen isotopic record and microfossils from deep sea cores raised in the hypersaline 41 salinity gulf of aqaba indicate that during late quaternary glacial time salinity rose considerably due to sea level fall and strait dynamics reaching values of more than 50 during the last glacial maximum about 18 ka b p the salinity dependent sequence of disappearance of various species of foraminifera pteropods and coccolithophorids can be used to determine upper salinity tolerance limits of different taxa only the pteropod creseis acicula and various benthonic foraminifera are able to withstand high salinities like those during the last glacial maximum

geochemical evidence for airborne dust additions to soils in channel islands national park california there is an increasing awareness that dust plays important roles in climate change biogeochemical cycles nutrient supply to ecosystems and soil formation in channel islands national park california soils are clay rich vertisols or alfi sols and mollisols with vertic properties the soils are overlain by silt rich mantles that contrast sharply with the underlying clay rich horizons silt mantles contain minerals that are rare or absent in the volcanic rocks that dominate these islands immobile trace elements sc th la and ta nd cr and rare earth elements show that the basalt and andesite on the islands have a composition intermediate between upper continental crust and oceanic crust in contrast the silt fractions and to a lesser extent clay fractions of the silt mantle have compositions closer to average upper continental crust and very similar to mojave desert dust island shelves exposed during the last glacial period could have provided a source of eolian sediment for the silt mantles but this is not supported by mineralogical data we hypothesize that a more likely source for the silt rich mantles is airborne dust from mainland california and baja california either from the mojave desert or from the continental shelf during glacial low stands of sea although average winds are from the northwest in coastal california easterly winds occur numerous times of the year when santa ana conditions prevail caused by a high pressure cell centered over the great basin the eolian silt mantles constitute an important medium of plant growth and provide evidence that abundant eolian silt and clay may be delivered to the eastern pacifi c ocean from inland desert sources

carbonate sedimentation beneath the antarctic circumpolar current during the late quaternary abstract calcium carbonate content and planktonic foraminiferal fragmentation have been studied in four late quaternary eltanin piston cores e48 22 e48 28 e49 18 and e49 23 taken from the southeast indian ridge between 3200 and 3400 m waterdepth beneath the antarctic circumpolar current the calcium carbonate records in the two southernmost cores e49 18 and e49 23 show distinct glacial interglacial cycles with the glacial intervals and intermediate cool intervals having low carbonate values relative to the interglacial times however the carbonate records of e48 22 and e48 28 are largely independent of the paleoclimatic records and may be influenced by input of volcanic ash from the st paul or amsterdam islands located less than 700 km upwind of the cores planktonic formainiferal fragmentation considered to be a dissolution index indicates that dissolution generally increased during glacial intervals relative to the interglacial intervals in e49 18 and e49 23 in e48 22 and e48 28 the dissolution records do not follow glacial interglacial patterns but instead dissolution was greatest during oxygen isotope stage 9 the stage 9 8 boundary the early part of stage 8 and during stage 7 no relationship exists between benthonic formainiferal changes and the fragmentation records in three cores e48 22 e48 28 and e49 23 indicating that deep water circulation changes had minimal or no influence on these dissolution records however in e49 18 the benthonic foraminiferal and the dissolution records are closely matched from oxygen isotope stages 12 to 5 t 440 000 120 000 yrs b p deep water circulation changes may have influenced the dissolution record in e49 18 or the two variables may be unrelated but may have independently responded to glacial interglacial climatic changes

atmospheric dust in modern soil on aeolian sandstone colorado plateau usa variation with landscape position and contribution to potential plant nutrients rock derived nutrients in soils originate from both local bedrock and atmospheric dust including dust from fardistant sources distinction between fine particles derived from local bedrock and from dust provides better understanding of the landscape scale distribution and abundance of soil nutrients sandy surficial deposits over dominantly sandstone substrates covering vast upland areas of the central colorado plateau typically contain 5 40 silt plus clay depending on geomorphic setting and slope excluding drainages and depressions aeolian dust in these deposits is indicated by the presence of titanium bearing magnetite grains that are absent in the sedimentary rocks of the region thus contents of far traveled aeolian dust can be estimated from magnetic properties that primarily reflect magnetite content such as isothermal remanent magnetization irm isothermal remanent magnetization was measured on bulk sediment samples taken along two transects in surficial sediment down gentle slopes away from sandstone headwalls one transect was in undisturbed surficial sediment the other in a setting that was grazed by domestic livestock until 1974 calculation of far traveled dust contents of the surficial deposits is based on measurements of the magnetic properties of rock surficial deposits and modern dust using a binary mixing model at the undisturbed site irm based calculations show a systematic down slope increase in aeolian dust ranging from 2 to 18 of the surface soil mass similar to the down slope increase in total fines 18 39 of surface soil mass a combination of winnowing by wind during the past and down slope movement of sediment likely accounts for the modern distribution of aeolian dust and associated nutrients at the previously grazed site dust also increases down slope 5 11 in sediment with corresponding abundances of 13 25 fines estimates of the contributions of aeolian dust to the total soil nutrients range widely depending on assumptions about grain size partitioning of potential nutrients in weathered bedrock nevertheless aeolian dust is important for this setting contributing roughly 40 80 of the rock derived nutrient stocks p k na mn zn and

geochemical evidence for the origin of late quaternary loess in central alaska loess is extensive in central alaska but there are uncertainties about its source and the direction of paleo winds that deposited it both northerly and southerly winds have been inferred the most likely sources of loess are the tanana river south the nenana river southeast and the yukon river north late quaternary loess in central alaska has immobile trace element compositions cr sc th ta th sc th u eu eu gdn ybn that indicate derivation mostly from the tanana river however other ratios as sb zr hf lan ybn and quantitative modeling indicate that the yukon river was also a source during the last glacial period there may have been a longer residence time of the siberian and canadian high pressure cells along with a strengthened aleutian low pressure cell this would have generated regional scale northeasterly winds and explains derivation of loess from the yukon river however superim posed upon this synoptic scale circulation there may have been strong southerly katabatic winds from expanded glaciers on the northern flank of the alaska range these winds could have provided eolian silt from the tanana river yukon river and tanana river sediments are highly calcareous whereas fairbanks area loess is not this suggests that carbonate leaching in loess kept ahead of sedimentation and that late quaternary loess in central alaska was deposited relatively

calcium carbonate suspended in arabian gulf and red sea waters biogenic and detrital not chemogenic the warm saline waters of the arabian gulf and red sea are supersaturated with respect to aragonite and magnesian calcite despite the local dominance of these phases in the arabian gulf sediment and their general abundance in southern red sea sediments little or no evidence of chemogenic carbonate is found in the overlying waters suspended carbonate grains are either biogenic or detrital precipitation of calcium carbonate appears limited to bottom or interstitial waters

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

oxygenation changes in the deep western arabian sea during the last 190 000 years productivity versus deepwater circulation 1 fluctuations in the abundance of selected foraminiferal indicator species and diversity allowed the reconstruction of changes in deepwater oxygenation and monsoon driven organic matter fluxes in the deep western arabian sea during the last 190 kyr times of maximum surface production coincide with periods of intensified sw monsoon as shown by the abundance of globigerina bulloides and enhanced carbonate corrosion benthic ecosystem variability in the deep arabian sea is not exclusively driven by variations in monsoonal upwelling and related organic matter supply to the seafloor but also by changes in deepwater ventilation deepening of the base of the oxygen minimum zone omz below 1800 m water depth is strongly coherent on the precessional band but lags proxies of sw monsoon strength by 4 to 6 kyr the out of phase relationship between omz deepening and maximum sw monsoon strength is explained by temporal changes in the advection of oxygen rich deepwater masses of north atlantic and antarctic origin this process affected the remineralization and burial efficiency of organic matter in the deep arabian sea resulting in the observed phase lag between maximum monsoon strength and organic carbon preservation

active sand seas and the formation of desert loess abstract loess is a widespread eolian deposit dominated by coarse silt and very fine sand quartz grains 20 80 m that serve as an important archive of information on quaternary climate change despite the intensive research during the past century on desert loess formation its origin remains poorly understood and is still a fundamental problem in sedimentology the ongoing debate is focused on the first stage of loess formation the production of coarse silt quartz grains although laboratory experiments indicate the potential of dunes with their abundant quartz sand grains as a primary source for generating coarse silt grains this concept has been generally rejected because field based evidence of abrasion from sand grains eolian abrasion is scarce here we have adopted a global view of the sand sea loess association and examine in detail several well known late pleistocene loess regions in different subtropical deserts africa the middle east and arabia this analysis demonstrates that all these loess regions are located downwind of adjacent sand seas together with evidence of mineralogical similarity between the loess and the sand dunes and the contemporaneous deposition of the loess and movement of the dunes these observations suggest that sand seas are an important source for desert loess because there is only limited silt storage in sand dunes we postulate that the silt grains comprising most of the loess are not reworked from the dunes but are generated probably through active eolian abrasion of the sand grains under past climates characterized by intensified winds as a result the role of sand dunes and eolian abrasion in the formation of desert loess may be more important than previously thought

late quaternary deep ocean circulation a review of paleoceanographic studies dealing with late quaternary deep water circulation in the oceans is presented these studies which are based on the analysis of deep sea benthic foraminiferal faunal and geochemical data and sedimentological data are discussed in light of physical oceanographic conditions in the modern ocean we include in this review a re evaluation of benthic foraminiferal data from north atlantic and southern ocean piston cores and suggest that the dominance of uvigerina during glacial intervals reflects increased amounts of organic carbon at the sea floor compared to modern values a number of geochemical studies have suggested that the production or characteristics of north atlantic deep water nadw changed during glacial times although these changes have been thought to result from a cessation of overflow water from the norwegian greenland seas it is suggested here that seasonal sea ice cover was possible over southern portions of the norwegian sea during glacial intervals the presence of seasonally open water would have allowed norwegian sea overflow water to have been produced although perhaps at lower volumes and with different hydrographic properties than at present the record of antarctic bottom water aabw circulation does not show a simple relationship with paleoclimatic oscillations indicating that changes in oceanographic conditions in the southern ocean had little effect on aabw formation the aabw record contrasts with the glacial interglacial cycles of nadw suggesting no direct link between aabw and nadw circulation a variety of data suggests that changes in pacific deep water circulation occurred as a result of glacial production of north pacific deep water or from an increased flux of southern ocean water

imprints of high salinity water plumes originating from the red sea during termination ii abstract the investigation of a core collected in the socotran area western indian ocean provides new insights into water mass exchanges between the red sea and the gulf of aden through the strait of bab el mandeb during the penultimate deglaciation the benthic oxygen isotope record documents the occurrence of stillstands and possibly reversals within the general trend of sea level rise plumes of warm and salty waters are recorded at the surface of the arabian sea and as far as the socotran coast for each increase in sea level these plumes disappeared whenever global sea level stopped rising or showed a brief lowering according to their high salinities these plumes can only originate in the red sea the sill of bab el mandeb becoming deeper and wider during the deglaciation allowed greater exchange between both seas and stronger flow out of the red sea at each episode of sea level rise isotopic and faunal evidence suggest a strengthening of coastal upwelling in the arabian sea during these periods this increase in upwelling activity may explain how plumes of highly saline waters were maintained at the surface moreover the high salinity surface plumes may have facilitated upwelling activity through the destabilisation of density stratification in the upper water column the occurrence of at least high salinity salty water outflows during termination ii confirms the step wise non linear structure of the penultimate deglaciation providing a perfect example of the threshold concept in rapid climate changes

mineralogical composition of african dust delivered by red rains over northeastern spain the african dust deposition mineralogy source regions and influence on rain chemistry were analyzed for a site in the montseny mountains catalonia northeastern spain for the period august 1 1983 through august 1 1994 dust deposition was highly variable two events collected on november 9 11 1984 and march 22 25 1991 accounted for 62 of the total dust input in the 38 red rain events recorded in the period the average annual dust deposition was 5 3 g m 2 se 2 6 three source regions in the african continent were identified with back trajectory analysis 1 western sahara 2 moroccan atlas and 3 central algeria events from the moroccan atlas predominated in terms of number of events amount of rainfall and dust deposition the meteorological situations during red rains were identified western sahara events occurred principally with a depression at high latitudes 50 n forming a trough in the north atlantic moroccan atlas events occurred with a depression in front of portugal and events from central algeria were associated with a depression over spain or north africa by order of abundance median of n 13 the minerals identified in the dust by x ray diffraction were as follows illite quartz smectite palygorskite kaolinite calcite dolomite feldspars differences in mineralogy between source regions were significant for smectite kaolinite quartz and dolomite smectite and kaolinite content was highest in the algerian events while quartz and dolomite content was lowest events from the moroccan atlas had the lowest smectite and kaolinite the red rain soluble chemistry was clearly influenced by the dissolution of calcite high alkalinity calcium concentration and basic ph and by marine components high na cl arid mg 2 concentrations because of the very alkaline character of red rains they had a strong weight on the annual mean ph of rainwater this was reflected by the significant relationship r 0 71 p 0 01 between the percentage of annual precipitation as red rain and annual mean precipitation ph red rains provided 25 45 of the annual dissolved input of the major ions in precipitation and 34 of the calcium required for holm oak quercus ilex l forest growth at the study site

sediment provenance of the wilderness barrier dunes southern cape coast south africa trace element geochemistry has been used to discern the provenance of sediments derived from geologically distinct sources found in a range of depositional settings this study investigates whether this approach can also identify provenance signatures in sediments derived from clastic sedimentary rocks of similar origins within a complex coastal transport environment the potential local sediment sources of a coastal barrier dune in south africa were analysed to assess their relationships with the barrier and whether these have varied with time results indicate that the oldest part of the barrier partly formed during mis 6 when sea levels were lower than at present has a closer affinity to fluvial sediment provided by local rivers than either younger samples from the barrier s seaward flank or the holocene dunes atop its crest both formed during sea level highstands constraints on the timing of barrier formation provided by osl dating proved helpful in discriminating between provenance and weathering signals terra nova 00 000 000 2010

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

the geochemistry of loess asian and north american deposits compared abstract loess is widely distributed over asia and north america and constitutes one of the most important surficial deposits that serve as terrestrial records of the quaternary the oldest pleistocene loess in china is likely 2 6 ma thus spanning much or all of the pleistocene in north america most loess is no older than the penultimate glacial period with the exception of alaska where the record may go back to 3 0 ma on both continents loess deposits date primarily to glacial periods and interglacial or interstadial periods are represented by paleosols both glacial and non glacial sources of silts that comprise the bulk of loess deposits are found on both continents although loess has been considered to be representative of the average upper continental crust there are regionally distinctive compositions of loess in both asia and north america loess deposits in asia from yakutia tajikistan and china have compositionally distinct major element compositions due to varying abundances of silicate minerals carbonate minerals and clay minerals in north america loess in the mississippi river valley the great plains and alaska are also distinguishable with regard to major element composition that reflects highly diverse source sediments trace element geochemistry sc th zr and the rare earth elements also shows regional diversity of loess bodies in both asia and north america on both continents most loess bodies show significant contributions from later cycle altered sedimentary rocks as opposed to direct derivation from igneous rocks further some loess bodies have detectable contributions from mafic igneous rocks as well as major contributions from average upper crustal felsic rocks intercalated paleosols in loess sections show geochemical compositions that differ significantly from the underlying loess parent materials ratios of soluble to insoluble elements show depletions in paleosols due to chemical weathering losses of calcite dolomite plagioclase mica apatite and smectite in asia and north america the last interglacial paleosol is more weathered than equivalent modern soils which could be due either to a climate that was warmer and more humid a longer period of pedogenesis or both in asia early pleistocene loess and paleosols are both more weathered than those from the middle and late pleistocene forming prior to a mid pleistocene aridification of asia from uplift of the tibetan plateau understanding the geochemistry of loess and paleosols can tell us much about past atmospheric circulation past temperature and moisture regimes and even tectonic processes

stratigraphic and paleoceanographic significance of late quaternary pteropods from deep sea cores in the gulf of aqaba elat and northernmost red sea abstract the quantitative distribution of 16 thecosomatous pteropod species from four deep sea cores recovered from the gulf of aqaba elat and northernmost red sea is summarized the distribution facilitates a relatively high resolution stratigraphic subdivision of the 6 8 m long core sequences and their correlation the sequences of pteropod assemblages can be related to oxygen isotope curves and thus dated beyond the radiocarbon range the oldest strata penetrated are dated at about 150 000 yr b p considering the present day distribution of the species recognized the core assemblages are of a tropical subtropical character throughout the late quaternary on the basis of the composition of the living pteropod populations in the hypersaline 41 moderately oligotrophic and desert enclosed gulf of aqaba the pteropod core assemblages associated foraminiferal assemblages and the oxygen isotope values determined on both groups a sequence of paleoceanographic changes during the late quaternary is derived these changes are primarily influenced by productivity of the waters and pertain less to temperature and salinity the glacial periods isotope stages 2 3 4 and upper 6 were characterized by lower temperature than at present higher salinity and greater fertility of the waters during the glacial maxima monospecific creseis acicula assemblages characterize periods of metahaline more than 50 salinity conditions in highly productive waters although not identical in detail the last interglacial stage 5 assemblages are similar to the holocene warm water oligotrophic ones between 8000 and 3000 yr b p a short period of slightly higher productivity is indicated

aeolian processes and the biosphere ravi s d odorico p breshears d d field j p goudie a s huxman t e li j okin g s swap r j thomas a d pelt s v whicker j j zobeck t m 2011 aeolian processes and the biosphere reviews of geophysics 49 3

sea surface temperature pattern reconstructions in the arabian sea from throughout the arabian sea for four distinct time intervals 0 ka 8 ka 15 ka and 20 ka with the aim of understanding the history of the indian monsoon and the climate of the arabian sea region this was accomplished through the use of paired mg ca and d 18 o measurements of the planktonic foraminifer globigerinoides ruber by analyzing basin wide changes and changes in cross basinal gradients we assess both monsoonal and regional scale climate changes sst was colder than present for the majority of sites within all three paleotime slices furthermore both the indian monsoon and the regional arabian sea mean climate have varied substantially over the past 20 kyr the 20 ka and 15 ka time slices exhibit average negative temperature anomalies of 2 5 3 5 c attributable in part to the influences of glacial atmospheric co2 concentrations and large continental ice sheets the elimination of the cross basinal sst gradient during these two time slices likely reflects a decrease in summer monsoon and an increase in winter monsoon strength changes in d 18 ow that are smaller than the d 18 o signal due to global ice volume reflect decreased evaporation and increased winter monsoon mixing ssts throughout the arabian sea were still cooler than present by an average of 1 4 ci n the 8 ka time slice these cool ssts along with lower d 18 ow throughout the basin are attributed to stronger than modern summer and winter monsoons and increased runoff and precipitation the results of this study underscore the importance of taking a spatial approach to the reconstruction of processes such as monsoon upwelling

on the late pleistocene holocene sapropel record of climatic and oceanographic variability in the eastern mediterranean sapropels and intercalated marls in a piston core from the eastern mediterranean are chemically and mineralogical distinct kaolinite smectite and total s contents fe a1 ba a1 co a1 mo a1 and v a1 are higher whereas quartz mg calcite illite contents si a1 ti a1 k a1 rb a1 and zr a1 are lower in the sapropels missing and ghost sapropels are identified by mineralogical and chemical properties that are not prone to diagenesis primary production was higher ba a1 and bottom water and or interstitial oxygenation was lower co a1 mo a1 ni a1 and v a1 during sapropel formation wind speeds quartz clay si a1 and zr a1 and bottom water salinities mg calcite calcite were higher during periods of marl formation sapropels represent a fundamentally different sedimentary facies whose formation is linked to changes in the hydrological balance in the basin driven by precessionally modulated changes in monsoon strength and subtropical precipitation changes which altered circulation production and sediment source areas

the vesicular layer and carbonate collars of desert soils and pavements formation age and relation to climate change abstract the vesicular fine grained a horizon av is the widespread ubiquitous surficial horizon of desert soils in diverse landforms and parent materials of varying ages now known to form mostly through accumulation of eolian dust recent studies show that dust accumulation and concomitant soil development are genetically linked to stone pavement formation changes in the magnitude of eolian activity and effective leaching related to quaternary climatic changes are also hypothesized to have influenced the evolution of the av horizon numerical modeling geochronologic and field laboratory studies elucidate the nature of pedogenic processes controlling compositional evolution of av how the changing av horizon increasingly influences soil infiltration and carbonate translocation and accumulation and the control that clasts of the evolving pavement exert on pedogenic processes results of a model that determines soil bulk chemical composition based on mixing of estimated proportions of externally derived eolian material and parent materials imply that the evolution of the soil bulk composition is strongly influenced by av horizon formation the early development of a weakly to moderately developed av horizon directly over gravelly parent material in late and middle holocene soils moderately influences soil infiltration but significant leaching of very soluble materials and some carbonate in dust are permitted in older pleistocene soils however the texturally more mature av and underlying cumulic nongravelly horizons more strongly limit the rate and depth of leaching and soil bulk composition therefore more closely approximates a simple mixture of dust and parent material other aspects of av horizon development and its relations to the pavement are evaluated through studies of pavement clasts with coatings of soil carbonate referred to as carbonate collars development of a numerical model that integrates soil hydrology a co2 production diffusion model calcite kinetics and thermodynamic considerations composition and thermal characteristics of pavement clasts and the textural and structural properties of the surface horizon provides the basis for testing a hypothesis of collar formation model results combined with results of 13c and 18o analyses of collar carbonate demonstrate how precipitation of calcite on pavement clasts and within the av is favored at a depth much shallower than that indicated by the classic carbonate depth climate relationship of jenny and leonard jenny h j leonard c d 1935 functional relationships between soil properties and rainfall soil science 38 363 381 and arkley arkley r j 1963 calculations of carbonate and water movement in soil from climatic data soil science 96 239 248 or simulated by numerical models of carbonate accumulation simultaneous development of thick carbonate collars and the av horizon requires the sustained pavement clast av horizon coupling for at least centuries to possibly millennia new thermoluminescence ages also indicate that much of the av horizon formed in the holocene and that it is certainly much younger than the older pleistocene pavements this supports the previously proposed hypothesis that increased dust flux during the pleistocene to holocene transition triggered and or greatly accelerated av horizon development an understanding of the genesis of collars provides not just an understanding of how carbonate can accumulate in surface environments but it also provides important clues into processes of pavement evolution and preservation of av horizons during long glacial periods the av horizon is not merely an insignificant surficial zone of recent dust accretion instead its development profoundly influences the genesis of desert soils and pavements

quaternary soils and dust deposition in southern nevada and california eoliandustconstitutesmuchofthepedogenic material in late pleistocene and holocene soils of many arid regions of the world comparisonofthecompositionsand influx rates of modern dust with the eolian component of dated soils at 24 sites in southern nevada and california yields informationon 1 thecompositionandinflux rate of dust in late pleistocene and holocene soils 2 paleoclimate and its effects on the genesis of aridic soils especially with regard to dustfall events 3 the timing and relative contribution of dust from playa sources versus alluvial sources and 4 the effects of accumulation of dust in soil horizons the 2mmfractionsofaandbhorizons of soils formed on gravelly alluvial fan deposits in the study area are similar to moderndustingrainsize contentofcaco3and salt majoroxides andclaymineralogy thus they are interpreted to consist largely of dust the major oxide compositions of the shallow soil horizons are nearly identical to that of the modern dust but the compositions of progressively deeper horizons approachthatoftheparentmaterial theclay mineralogyofmoderndustatagivensiteis similar to that of the av horizons of nearby holocene soils but is commonly different from the mineralogies of deeper soil horizonsandoftheavhorizonsofnearbypleistocenesoils theseresultsareinterpretedto indicate that dust both accumulates and is transformed in av horizons with time changes in soil accumulation rates provide insights into the interplay of paleoclimate dustsupply andsoil formingprocesses modern dust deposition rates are more than large enough to account for middle and late holocene soil accumulation rates at nearly all sites however the early holocene soil accumulation rates in areas near late pleistocene pluvial lakes are much higher than modern rates and clearly indicate a dust deflation and deposition event that caused rapid formation offine grained shallow soil horizons on uppermost pleistocene and lower holocene deposits we interpret late pleistocene soil accumulation rates to indicate that dust deposition rates were low during this period but that increased effective moisture during the late wisconsinan favored translocation of clay andcaco3fromnearthesurfacetodeeper inthesoilprofile pre latepleistocenerates are very low in most areas mainly due to a pedogenic threshold that was crossed when accumulations of silt clay and caco3 began to inhibit the downward transport of eolian material but in part due to erosion

geochemistry of eolian dust in pacific pelagic sediments implications for paleoclimatic interpretations geochemical data rees th sc were determined for the operationally defined eolian dust oded fraction 63 m of late quaternary sediment samples n 57 from the north and equatorial pacific ocean paleoclimate studies commonly have assumed that this sediment fraction represents eolian materials from continental source regions this study shows on the basis of geochemical data published mineralogical data and mixing models that the oded fraction actually is a mixture of materials from two endmember sources the continental crust eolian transported weathering products and the oceanic crust primarily volcanogenic material mixing model results show that the average ash content is significant in the oded fraction equatorial pacific 43 north pacific 24 we have used this information to reconsider and refine the results of previous paleoclimate studies in the northwest pacific the flux of the eolian fraction is greater during glacial stages and shows a latitudinal maximum between 35 n and 42 n eolian fluxes are greatest during interglacial periods in the equatorial pacific these results are consistent with previous interpretations in contrast to previous assumptions eolian mass accumulation rates may not be a valid indicator of paleo aridity because they are correlated with grain size furthermore the relative abundance of the two endmembers is correlated with the average grain size of the dust fraction the continental crust component is associated with larger grains this compositional effect should be considered in future studies which commonly utilize grain size as a proxy indicator of paleo wind intensity

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

climatic cycles inferred from the aminostratigraphy and aminochronology of quaternary dunes and palaeosols from the eastern islands of the canary archipelago aminochronological and aminostratigraphical methods have been used to study the quaternary a e o l i a n deposits f r om the islands located east of the canary archipelago fuerteventura and lanzarote islands and la graciosa montana clara and alegranza islets t h e extent of racemisation epimerisation of four amino acids isoleucine aspartic acid phenylalanine and glutamic acid was measured in land snail shells of the genus theba the age calculation algorithms of these amino acids h a v e b e e n determined to permit t he numerical dating of these deposits eight a m i n o z o n e s e a ch defining dune palaeosol formation episodes have been distinguished and dated at 4 8 6 6 4 42 5 6 0 37 8 4 6 29 4 4 8 22 4 4 5 14 9 3 6 11 0 4 0 and 5 4 1 1 ka b p t h e first f i ve of t h em defining c y c l e s of 5 7 ka the alternation of palaeosols and a e o l i a n deposits w h i c h are related to abrupt transitions from humid to arid conditions are t he reflection of globally induced changes in north africa palaeoenvironmental conditions linked to the effect of african palaeomonsoons on the trade w i n d s and the saharan air layer probably these a eolian cycles with a recurrence neriod of 5 7 ka are t he expression of multiples of the 2 4 ka solar cycle

on the formation of desert loess sequences of quartz rich coarse 20 63 m silt occur in many low and midlatitude unglaciated arid and semiarid areas and have been termed desert loess the processes by which these deposits are generated have been debated for decades all hypotheses to explain their origin seek to provide mechanisms for the generation of silt sized material without glacial grinding which is the main process involved in the production of coarse silt at high latitudes possible mechanisms for the formation of coarse silt in arid regions include derivation from preexisting siltstones mechanical weathering of silicate rocks and abrasion of sand grains in active dune environments during intense transport events examination of the characteristics of desert loess and field and laboratory experiments to assess the role of dune areas as a source of coarse silt by abrasion and or resuspension of residual fines suggests that many loess sequences are dominated by locally derived coarse silt improvements in the characterization of desert loess particle size mineralogy and geochemistry are needed however to identify sources and sinks of coarse silt especially when combined with climatic back trajectory analysis properly scaled experiments and modeling of particle collisions will also help to better quantify the effectiveness of abrasion in the generation of coarse silt in support of field observations

oxygen minimum zone edge effects evidence from the central california coastal upwelling system geologic and biological data from box cores gravity cores and bottom photographs across the modern coastal upwelling system of central california reveal that biogeochemical activity increases along the edges of the oxygen minimum zone omz 0 5 ml 1 o2 macrofauna and benthic foraminifers as well as relative concentrations of calcium carbonate glauconite and fecal pellets all display edge effects the major controls appear to be a combination of dissolved oxygen concentration of near bottom waters bottom currents and possibly bacterially mediated nutrient recycling as well as food supplies omz edge effects should be recognizable in the rock record and may prove to be powerful paleoenvironmental paleoecological indicators

accumulation of impact markers in desert wetlands and implications for the younger dryas impact hypothesis the younger dryas impact hypothesis contends that an extraterrestrial object exploded over north america at 12 9 ka initiating the younger dryas cold event the extinction of many north american megafauna and the demise of the clovis archeological culture although the exact nature and location of the proposed impact or explosion remain unclear alleged evidence for the fallout comes from multiple sites across north america and a site in belgium at 6 of the 10 original sites excluding the carolina bays elevated concentrations of various impact markers were found in association with black mats that date to the onset of the younger dryas black mats are common features in paleowetland deposits and typically represent shallow marsh environments in this study we investigated black mats ranging in age from approximately 6 to more than 40 ka in the southwestern united states and the atacama desert of northern chile at 10 of 13 sites we found elevated concentrations of iridium in bulk and magnetic sediments magnetic spherules and or titanomagnetite grains within or at the base of black mats regardless of their age or location suggesting that elevated concentrations of these markers arise from processes common to wetland systems and not a catastrophic extraterrestrial impact event

isotopic evidence for the eolian origin of quartz and mica in soils developed on volcanic materials in the canary archipelago quartz and mica contents of soils developed on volcanic materials in the canary archipelago lanzarote tenerife gomera and la palma islands off western africa are often higher in surficial horizons with higher rainfall and older landscape age the soil quartz particles are fine grained less than 53 m in diameter and well sorted the oxygen isotopic abundance 18osmow of fine aerosol sized quartz 1 10 m in diameter showed a range of 16 0 to 18 2 the values are compatible with those of the same sized quartz from two holocene deep sea sediments in cape verde rise 16 0 and 16 1 and saharan dusts 15 8 la laguna tenerife 16 2 barbados west indies a distinct 87sr 86sr ratio of 0 717 for a micaceous horizon from lanzarote is comparable with those of saharan dusts 0 715 to 0 721 but not with reported values 0 7032 from local volcanics these geochemical parameters show that the fine grained quartz together with mica in soils of the canary archipelago are transported from north african sahara deserts by trade winds and negate both possibilities of authigenesis and inheritance from weathering of local volcanics

airborne dust transport to the eastern pacific ocean off southern california evidence from san clemente island 1 islands are natural dust traps and san clemente island california is a good example soils on marine terraces cut into miocene andesite on this island are clay rich vertisols or alfisols with vertic properties these soils are overlain by silt rich mantles 5 20 cm thick that contrast sharply with the underlying clay rich subsoils the silt mantles have a mineralogy that is distinct from the island bedrock silt mantles are rich in quartz which is rare in the island andesite the clay fraction of the silt mantles is dominated by mica also absent from local andesite and contrasts with the subsoils dominated by smectite ternary plots of immobile trace elements sc th la and ta nd cr show that the island andesite has a composition intermediate between average upper continental crust and average oceanic crust in contrast the silt and to a lesser extent clay fractions of the silt mantles have compositions closer to average upper continental crust the silt mantles have particle size distributions similar to loess and mojave desert dust but are coarser than long range transported asian dust we infer from these observations that the silt mantles are derived from airborne dust from the north american mainland probably river valleys in the coastal mountains of southern california and or the mojave desert although average winds are from the northwest in coastal california easterly winds occur numerous times of the year when santa ana conditions prevail caused by a high pressure cell centered over the great basin examination of satellite imagery shows that easterly santa ana winds carry abundant dust to the eastern pacific ocean and the california channel islands airborne dust from mainland north america may be an important component of the offshore sediment budget in the easternmost pacific ocean a finding of potential biogeochemical and climatic significance

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

moisture evolution in central asia since 26 ka insights from a kyrgyz loess section western tian shan abstract central asia ca is located in the hinterland of the eurasian continent and faces an extreme risk of continued aridification under the current global warming trend to predict future climate change in ca paleoclimate studies provide essential references however the mechanisms underlying climate changes in ca remain relatively poorly known here we investigate moisture variations in ca as recorded in a 6 m loess section in the western tian shan kyrgyzstan which has accumulated since 26 ka based on the radiometric ams 14c dating we reconstructed the evolution of the wind regime and moisture conditions in the western tian shan with a modified grain size index gsim and a new l proxy l while the frequency dependent magnetic susceptibility fd redness a and yellowness b did not provide reliable paleoclimatic indicators due to weak pedogenesis and other controlling factors the gsim records demonstrated a precipitation maximum in summer before 15 ka shifting to a maximum in spring after 15 ka probably associated with large scale modulation of the latitudinal climatic zones and atmospheric circulation in response to retreat of the northern hemisphere ice sheets based on the l records we place emphases on the important role of temperature modulated evaporation in moisture evolution across ca however this has only influenced moisture evolution in spring and summer with little effect on winter moisture conditions moreover the l records may also indicate that atmospheric humidity can partly affect the long term effective moisture variations

grain size variation on dunes in the southwest kalahari southern africa abstract grain size parameters mean standard deviation skewness and kurtosis were determined for 83 sediment samples from six dune cross profiles and one 28 km long profile on dunes in the southwest kalahari desert in southern africa although some studies elsewhere and previous studies in the kalahari have reported significant grain size variation over dune cross profiles data presented here show no systematic variation of grain size parameters except that sediments from the crest of a dune are almost invariably better sorted indicated by the standard deviation of the sample than samples from the base or plinth of the dune the proportion of fines 63 m in plinth sediments is also greater than in crest samples there is no significant trend in grain size parameters along the length of a linear dune this lack of significant pattern corresponds with similar findings for central australian dunes

dominant synoptic disturbance in the extreme rainfall at cherrapunji northeast india based on 104 years of rainfall data 1902 2005 abstractthe characteristics of active rainfall spells arss at cherrapunji northeast india where extreme high rainfall is experienced and their relationships with large scale dynamics were studied using daily rainfall data from 1902 to 2005 and japanese 55 year reanalysis from 1958 to 2005 extreme high daily rainfalls occur in association with arss the extremely large amounts of rainfall in the monsoon season are determined by the cumulative rainfall during arss arss start when anomalous anticyclonic circulation aac at 850 hpa propagates westward from the south china sea and western north pacific and covers the northern bay of bengal the aac propagates farther westward and suppresses convection over central india during arss at cherrapunji and continues for 3 to 14 days consequently a northward shift of the monsoon trough during the break in the indian core region occurs the westerly wind which prevails in the northern portion of the aac transports moisture toward northeast india and en

geochemical evidence for african dust inputs to soils of western atlantic islands barbados the bahamas and florida 1 we studied soils on high purity limestones of quaternary age on the western atlantic ocean islands of barbados the florida keys and the bahamas potential soil parent materials in this region external to the carbonate substrate include volcanic ash from the island of st vincent near barbados volcanic ash from the islands of dominica and st lucia somewhat farther from barbados the fine grained component of distal loess from the lower mississippi river valley and wind transported dust from africa these four parent materials can be differentiated using trace elements sc cr th and zr and rare earth elements that have minimal mobility in the soil forming environment barbados soils have compositions that indicate a complex derivation volcanic ash from the island of st vincent appears to have been the most important influence but african dust is a significant contributor and even mississippi river valley loess may be a very minor contributor to barbados soils soils on the florida keys and islands in the bahamas appear to have developed mostly from african dust but mississippi river valley loess may be a significant contributor our results indicate that inputs of african dust are more important to the genesis of soils on islands in the western atlantic ocean than previously supposed we hypothesize that african dust may also be a major contributor to soils on other islands of the caribbean and to soils in northern south america central america mexico and the southeastern united states dust inputs to subtropical and tropical soils in this region increase both nutrient holding capacity and nutrient status and thus may be critical in sustaining vegetation

environmental distribution of recent benthic foraminifera on the northeast united states continental slope several bathymetrically consistent recent benthic foraminiferal biofacies have been recognized from the continental slope south east of cape cod faunal assemblages are dominated by globobulimina bulimina upper slope less than 1 000 m and uvigerina peregrina lower slope uppermost rise water depths between 1 000 and 2 500 m the globobulimina bulimina assemblage coincides with the oxygen minimum zone this agrees with the occurrence of globobulimina in mediterranean sapropels organic rich sediments deposited under anoxic conditions previous studies have noted the association of u peregrina with bathyal water depths deep water temperatures of 3 to 4 c and water of low oxygen content however correlations between abundance of u peregrina and water depth or temperature are not the same everywhere and no correlation with dissolved oxygen in the water column is seen on the united states continental slope and rise the highest abundances of u peregrina coincide with maxima of organic carbon and silt within the slope sediments this suggests that the distribution of u peregrina in this region may be influenced more by low oxygen in the sediments rather than by low oxygen content of the overlying water

new insights into geochemical behaviour in ancient marine carbonates upper jurassic ammonitico rosso novel proxies for interpreting sea level dynamics and palaeoceanography elemental concentrations in phanerozoic sea water are known to fluctuate both in time and space with regard to carbonates precipitated from marine fluids elemental concentrations in the carbonate crystal lattice are affected by a complex array of equilibrium and non equilibrium as well as post depositional alteration processes to assess the potential of carbonate elemental chemostratigraphy seven upper jurassic sections were investigated along a proximal to distal transect across the south east iberian palaeomargin the aim was to explore stratigraphic and spatial variations in calcium strontium magnesium iron and manganese elemental abundances the epicontinental geochemical record is influenced by the combination of continental runoff and a significant diagenetic overprint in contrast the epioceanic geochemical record agrees with reconstructed open marine sea water values reflecting a moderate degree of syn depositional to early marine pore water diagenesis establishing a fair degree of preservation of matrix micrite a thorough statistical approach was applied and elemental associations tested for their environmental significance principal component and hierarchical cluster analyses revealed a persistent relation between carbonate magnesium iron and strontium abundances processes related to early diagenetic nodulation in ammonitico rosso facies most probably account for the incorporation of these elements in the calcium carbonate lattice the clear decoupling of carbonate manganese abundance with respect to the remaining elements is documented and related to high sea floor spreading rates and hydrothermal activity during the late jurassic the investigation of potential time fluctuation of geochemical patterns was approached through variogram computation the observed temporal behaviour is most likely to be forced by relative sea level dynamics reflecting late jurassic palaeoceanographic conditions and potential planetary interactions the data obtained in this study highlight the utility of elemental data from carbonate matrix micrites as geochemical proxies for studying the influence of remote trigger factors

dirtmap the geological record of dust atmospheric dust is an important feedback in the climate system potentially affecting the radiative balance and chemical composition of the atmosphere and providing nutrients to terrestrial and marine ecosystems yet the potential impact of dust on the climate system both in the anthropogenically disturbed future and the naturally varying past remains to be quantified the geologic record of dust provides the opportunity to test earth system models designed to simulate dust records of dust can be obtained from ice cores marine sediments and terrestrial loess deposits although rarely unequivocal these records document a variety of processes source transport and deposition in the dust cycle stored in each archive as changes in clay mineralogy isotopes grain size and concentration of terrigenous materials although the extraction of information from each type of archive is slightly different the basic controls on these dust indicators are the same changes in the dust flux and particle size might be controlled by a combination of a source area extent b dust emission efficiency wind speed and atmospheric transport c atmospheric residence time of dust and or d relative contributions of dry settling and rainout of dust similarly changes in mineralogy reflect a source area mineralogy and weathering and b shifts in atmospheric transport the combination of these geological data with process based forward modelling schemes in global earth system models provides an excellent means of achieving a comprehensive picture of the global pattern of dust accumulation rates their controlling mechanisms and how those mechanisms may vary regionally the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap data base has been established to provide a global palaeoenvironmental data set that can be used to validate earth system model simulations of the dust cycle over the past 150 000 years

dissolved iron and macronutrient distributions in the southern california current system 1 the distribution of dissolved iron in the southern california current system sccs is presented from seven research cruises between 2002 and 2006 dissolved iron concentrations were generally low in most of the study area 0 5 nm although high mixed layer and water column dissolved iron concentrations up to 8 nm were found to be associated with coastal upwelling both along the continental margin and some island platforms a significant supply of iron was probably not from a deep remineralized source but rather from the continental shelf and bottom boundary layer as identified in previous studies along the central and northern california coast with distance offshore dissolved iron decreased more rapidly relative to nitrate in a transition zone 10 250 km offshore during spring and summer resulting in relatively high ratios of nitrate dissolved iron higher nitrate dissolved iron ratios could be the result of utilization and scavenging in addition to an overall lower supply of iron relative to nitrate in the offshore transition zones the low supply of iron leads to phytoplankton iron limitation and a depletion in silicic acid relative to nitrate in the coastal upwelling and transition zones of the sccs

thorium derived dust fluxes to the tropical pacific ocean 58 ma abstract eolian dust in pelagic deep sea sediments can be used to reconstruct ancient wind patterns and paleoenvironmental response to climate change traditional methods to determine dust accumulation involve isolating the non dissolvable aluminosilicate minerals from deep sea sediments through a series of chemical leaches but cannot differentiate between minerals from eolian authigenic and volcanogenic sources other geochemical proxies such as sedimentary 232th and crustal 4he content have been used to construct high resolution records of atmospheric dust fluxes to the deep sea during the quaternary here we use sedimentary th content as a proxy for terrigenous material eolian dust in 58 myr old sediments from the shatsky rise odp site 1209 and compare our results with previous dust estimates generated using the traditional chemical extraction method and sedimentary 4hecrustal concentrations we find excellent agreement between th based dust estimates and those generated using the traditional method in addition our results show a correlation between sedimentary th and 4hecrustal content which suggests a source older than present day asian loess supplied dust to the central subtropical pacific ocean during the early paleogene

soil mineralogy trends in california landscapes california s diverse environmental gradients serve as natural experiments for examining controls on soil mineral distribution in landscapes in this paper we use example soilscapes from throughout california to examine how lithology climate topography and duration of pedogenesis interact to produce distinctive weathering environments and characteristic suites of soil minerals seven soil geomorphic sequences were assembled from the literature to illustrate major soil mineralogical trends 1 granitic terrain of the peninsular ranges 2 granitic terrain of the central sierra nevada 3 andesitic terrain of the northern sierra nevada 4 fluvial terraces on the east side of the great valley 5 marine terraces of the central coast 6 ultramafic terrain of the klamath mountains and 7 an alluvial fan in the mojave desert results of this analysis show that kaolin is present in virtually all pedons irrespective of climate parent material age or topographic position kaolin does not form in ultramafic soils due to insufficient aluminum many secondary clay minerals reflect the state s strong climatic influence with palygorskite smectite and vermiculite in the dry hot environments hydroxy interlayered minerals gibbsite and short range ordered minerals in the cool moist environments in arid and semi arid regions the distribution of calcite gypsum and soluble salts is strongly related to patterns of eolian dust deposition and water infiltration and leaching

geochemistry of the pliocene red clay formation in the chinese loess plateau and implications for its origin source provenance and paleoclimate change abstract recent field observations and sedimentological studies suggest the eolian origin of the late tertiary red clay formation underlying the pleistocene loess soil sequence in the loess plateau thereby extending the wind blown record from 2 6 ma down to 7 0 ma in north central china to address the source provenance of the red clay major and trace element concentrations were analyzed on the samples from a north south loess transect of the loess plateau and a red clay section at jiaxian results show that there is a good agreement of both major and trace element compositions between the last glacial interglacial loess soil units and the jiaxian red clay record the ree distribution patterns of the loess soil and red clay samples are remarkably similar in shape with enriched lree and fairly flat hree profiles and clear negative eu anomaly the geochemical features of the red clay are also identical to those of upper continental crust these chemical characteristics provide further evidence for eolian sedimentation of the red clay from the relations both between na2o al2o3 and k2o al2o3 ratios and between u pb and th pb ratios the eolian loess and red clay materials must have been subject to thorough sedimentary differentiation and moderate chemical weathering in the source area the chemical similarity between soil unit s1 and the red clay implies that such an environment as occurred in the last interglacial period may have already formed in northwestern china during the late tertiary comparison of down section variations in elemental ratios with field observations of pedogenic development of the red clay suggests that cao al2o3 sr rb and sr ba are more sensitive to climate changes than magnetic susceptibility and can be used to reconstruct the climate history of the late cenozoic

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

benthic foraminiferal faunal and isotopic changes as recorded in holocene sediments of the northwest indian ocean 1 historically the holocene has been considered an interval of relatively stable climate however recent studies from the northern arabian sea netherlands indian ocean program 905 suggested high amplitude climate shifts in the early and middle holocene based on faunal and benthic isotopic proxy records we examined benthic foraminiferal faunal and stable isotopic data from ocean drilling program odp site 723 and total organic carbon data from odp site 724 oman margin 808 and 593 m water depths respectively at site 723 the mid holocene shift in 18o values of infaunal benthic species uvigerina peregrina 1 4 is 3 times larger than that of epifaunal benthic species cibicides kullenbergi recorded at site niop 905 off somalia however none of the five other benthic species we measured at hole 723a exhibits such a shift in 18o we speculate that the late holocene 18o decrease in u peregrina represents species specific changes in ecological habitat or food preference in response to changes in surface and deep ocean circulation while the stable isotopic data do not appear to indicate a middle holocene climatic shift our total organic carbon and benthic faunal assemblage data do indicate that the early holocene deep arabian sea was influenced by increased ventilation perhaps by north atlantic deep water and or circumpolar deep water incursions into the indian ocean leading to remineralization of organic matter and a relatively weak early holocene oxygen minimum zone in the northwest arabian sea in spite of strong summer monsoon circulation

impact of late quaternary environmental changes on deep sea benthic foraminiferal faunas of the red sea abstract fluctuations in abundance diversity and species composition of benthic foraminifera from two sites of the northern and southern red sea indicate strong variability of deep sea ecosystems during the last four glacial to interglacial cycles in total five and four different benthic foraminiferal assemblages have been identified in the northern core and southern core respectively comparison with recent faunas from the red sea and adjacent oceans allowed the reconstruction of temporal changes in deep water ventilation salinity and food availability at the seafloor generally the abundance of infaunal and miliolid taxa increase during glacial intervals indicating increased organic matter fluxes oxygen decrease and salinity increase in deep waters during these times these fluctuations are attributed to enhanced oxygen consumption rates and temporarily reduced deep water formation in the northern red sea during glacial intervals the recorded environmental changes are a reflection of both high and low latitude climate changes the northern red sea is mainly influenced by glacio eustatic sea level fluctuations that control deep water formation rates and by mid latitude climate changes of the mediterranean region that control surface productivity in contrast deep sea ecosystem variability of the southern red sea is additionally influenced by low latitude climate changes attributed to the ne monsoon intensity that drives the inflow of nutrient rich surface waters from the gulf of aden these results demonstrate the high sensitivity of deep sea ecosystems of the red sea to both global and regional climate changes

holocene sediment budgets for the basins of the california continental borderland abstract two holocene sediment budgets have been compiled for the california continental borderland the first detailed budget includes the six northern inshore and central basins that capture almost 40 of the total sediment input to the entire borderland in the second budget the data for the six basins has been added to estimates of accumulation for the remaining borderland area to produce a total regional budget of lower precision than the smaller six basin region natural river influx to the borderland approximates 13 1010 tons for the holocene epoch and biological input has been estimated at about 2 1010 tons eolian and ocean current influx have each been estimated at about 1 1010 tons in sum the total deposited volume for 104 yrs is about 14 1010 tons and the estimated total influx is of the order of 17 1010 tons which suggests that a net of 1 3 101010 tons for the holocene high sea level period the six high accumulation rate basins are located adjacent to the largest river sources the major zones of coastal upwelling and the main northern eddies of the california current these high accumulation sites are typically also areas where mass movement and fan development are localized the sediment accumulation rate is much larger than subsidence rate and flat floored basins are typical in contrast the southern and outer low accumulation basins are areas of draped sediment with accumulation rate less than subsidence rate and are the sites of penecontemporaneous deformation of the accumulating fine hemipelagic sediments few fans or major mass movements are seen significant sedimentation is mainly confined by topography to less than 20 of total margin area thus the moderate to low total sediment influx is amplified by the restricted receiving area to produce locally thick deposits of limited areal extent this pattern is characteristic of neogene southern california basins and illustrates that stratigraphic thickness is not a valid indicator of sediment influx

major change in atlantic deep and bottom waters 700 000 yr ago benthonic foraminiferal evidence from the south atlantic abstract in the modern south atlantic the transition between deep water and bottom water is marked by a clear change in the associated benthonic foraminiferal fauna uvigerina and globocassidulina characterize oxygen poor circumpolar deep water which has long been isolated from the surface planulina and miliolids are found associated with the more newly formed oxygen rich north atlantic deep water antarctic bottom water is characterized by epistominella umbonifera analysis of the benthonic foraminiferal faunas in two sediment cores recovered from the vema and hunter channels in the western south atlantic shows that the level of the transition between deep and bottom waters shallowed sharply about 700 000 yr ago this rise indicates a sharp sustained increase in the volume of bottom water flowing through the south atlantic after this time prior to about 700 000 yr ago the amount of antarctic bottom water entering the western south atlantic was greatly reduced and circumpolar deep water apparently accounted for the bulk of northward flow production of southward flowing north atlantic deep water seems not to have been affected the timing of this change in circulation regime suggests a possible causal link to similar changes in records of terrestrial and sea surface climate

a soil chronosequence on quaternary marine terraces san clemente island california a soil chronosequence on marine terraces was examined on san clemente island california in an arid mediterranean climate in order to see which soil properties differ most systematically with time ages of the geomorphic surfaces were determined by radiocarbon uranium series and amino acid racemization techniques and range from 1 000 000 yrs soils on surfaces 200 000 yrs old are vertisols or alfisols with vertic properties such as slickensides and cracks and they exhibit both prismatic and angular blocky sphenoidal or only angular blocky structure solum thickness increases linearly with age of geomorphic surface clay soluble salts ald smectite mica ratios in the clay fraction and quartz plagioclase ratios in the silt fraction when expressed as profile summations show increases with age of geomorphic surface the best fit regression equations are linear with the exception of ald which is best expressed as a power function important soilforming processes appear to be alteration of mica to smectite accumulation at depth of soluble salts derived from marine aerosols possibly additions of eolian materials clay illuviation in the younger soils and pedoturbation in the older soils the observations reported here allow the following conclusions to be drawn about soils in this environment 1 certain soil properties which show distinct trends with time can be used for relative age dating in geomorphic and stratigraphic studies 2 soils have not reached a steady state condition with respect to many of their properties and 3 alfisols and mollisols with natric b horizons may be precursors to vertisols

the role of african dust in the formation of quaternary soils on mallorca spain and implications for the genesis of red mediterranean soils abstract african dust additions explain the origin of terra rossa soils that are common on the carbonate platform island of mallorca spain mineralogical and geochemical analyses indicate that quaternary carbonate eolianites on mallorca have a very high purity usually composed of more than 90 carbonate minerals calcite dolomite and aragonite in contrast terra rossa soils developed on these eolianites have lower carbonate contents and contain higher concentrations of quartz and other silicates analyses of immobile trace elements indicate that the non carbonate fractions of the eolianites have distinctive zr hf la yb cr sc and th ta values that differ from the superjacent terra rossa soils these observations indicate that even if sufficient dissolution of the eolianite had taken place to create the soils by residual accumulation immobile element ratios in the soils require an external source however zr hf la yb cr sc and th ta values in the soils fall within the range of values for these element ratios in african dust collected on barbados and mainland spain we conclude that the silicate fractions of terra rossa soils on mallorca are derived mainly though not wholly from far traveled african dust and this process may explain the origin of other terra rossa soils found in southern europe

red sea isolation history suggested by plio pleistocene seismic reflection sequences abstract high evaporation rates in the desert climate of the red sea ensure that during glacial sea level lowstands when water exchange with the indian ocean was more restricted water salinity and 18 o became unusually extreme modeling of the effect on red sea sedimentary 18 o has been used previously to reconstruct relative sea level to 500 ka and now poses the question of whether that sea level model could be extended if continuous core material of older sediment became available we attempt to address this question here by examining seismic reflection data the upper pleistocene hemipelagic sediments in the red sea contain intervals of inorganic aragonite precipitated during supersaturated conditions of sea level lowstands seismic impedance changes associated with boundaries to those aragonite rich layers appear to explain seismic reflection sequences a segment of chirp sediment profiler data from the central red sea reveals prominent reflections at 1 5 23 26 and 36 ms two way travel time twt from the seabed based on depths to the glacial marine isotope stages mis in cores we relate the upper three reflections to the tops of aragonite rich layers and hence the sea level rises immediately following mis 2 6 and 12 the reflection at 26 ms is related to an unusually rapid fall into mis 12 predicted by one sea level reconstruction which may have created an abrupt lower boundary to the mis 12 aragonite rich layer with the aid of seismogram modeling we tentatively associate the 36 ms reflection with the top of an aragonite rich layer formed during mis 16 furthermore some segments of lower frequency airgun and sparker seismic data from the central and southern red sea show a lower earlier plio pleistocene pp interval that is less reflective than the upper late pp interval this implies less variability in sediment impedance and that extreme variability in water salinity did not develop water exchange with the indian ocean likely continued throughout this interval these results suggest that viable relative sea level reconstructions may be recovered from red sea sediment 18 o data to at least mis 16 and perhaps even as far back as the early pliocene

relations between morphology air flow sand flux and particle size on transverse dunes taklimakan sand sea china field experiments on two isolated transverse dunes with different scales in the taklimakan sand sea show that particle size and slope control the threshold shear velocity and sand flows on the stoss of the dunes the decreased threshold shear velocity and the unsaturated sand flows are the main reasons why sands are not deposited at the toe of the dunes the particle size controls sand flux through its influence on the aerodynamic roughness elements and threshold shear velocities the sand flux is different for dune surfaces with different particle size distributions under the control of the medium to low stress of the drifting sand winds the results of the field experiments and particle size analysis showed that sand transport had little influence on the particle size distributions the mean particle size being transported on the stoss is lower than that on the dune surface it is difficult to determine whether or not the wind is fully saturated with sands when sand flux calculation is mainly dependent on the shear velocity and the mean particle size the sands within some range of the particle size are transported and developed into simple transverse dunes and then the interdune surface is coarsened and alternated with the draas in the taklimakan sand sea copyright 2002 john wiley sons ltd

sediment and pollen evidence for an early to mid holocene humid period in the eastern sahara a major problem in the study of holocene palaeoenvironments of the arid and wind deflated sahara is the low preservation potential of sediments from which a record of past climatic change can be established several indirect and imprecisely dated pieces of evidence have suggested humid episodes in the holocene that may have supported more productive ecosystems and denser human populations than today searches for reliable proxy data on past climates however have failed to yield satisfactory results we report here the discovery of buried lake muds in north west sudan in the hyperarid core of the eastern sahara which yield sedimentological and palynological data clearly interpretable as recording an early to mid holocene humid episode that supported a relatively deep stratified lake surrounded by tropical savanna woodland vegetation