biogeography of terminal cretaceous deep sea benthic foraminifera from the atlantic and pacific oceans abstract most species of late cretaceous deep sea benthic foraminifera are believed to be cosmopolitan and therefore to exhibit only minor biogeographical differences in this preliminary report six deep sea drilling project dspd sites from different oceans paleolatitudes and paleodepths were analyzed for terminal cretaceous abyssal bathyal benthic foraminifera in order to investigate their assumed cosmopolitan distribution and the question of whether different faunal compositions are related to time different paleolatitudes and or different paleodepths the material studied was obtained from the low latitude site 465 pacific ocean and the intermediate latitude sites 384 north atlantic and 356 516 525 and 527 south atlantic the material analyzed represents a time slice encompassing the last 20 50 k y of the cretaceous the faunas contain numerous velasco type species such as gavelinella beccariiformis white cibicidoides velascoensis cushman nuttallides truempyi nuttall gaudryina pyramidata cushman and various gyroidinoids and buliminids the results contradict the general assumption of the cosmopolitan nature of late cretaceous deep sea benthic foraminifera advocated in the literature only about 9 of the taxa identified were found to be truly cosmopolitan through their occurrence at all the sites analyzed on the basis of correspondence analysis and relative abundance data three assemblages and three subassemblages were recognized 1 a bathyal abyssal assemblage nuttallinella sp a cibicidoides hyphalus fisher valvalabamina sp evolute form and gyroidinoides spp at the south atlantic sites 356 516 525 and 527 divided into three subassemblages namely a a middle bathyal subassemblage eouvigerina subsculptura mcneil and caldwell tritaxia aspera cushman and g pyramidata at sites 516 and 525 b a lower bathyal subassemblage osangularia sp pyramidina rudita cushman and parker and quadrimorphina camerata brotzen at site 356 and c an abyssal subassemblage gyroidinoides sp c hyperammina bathysiphon gyroidinoides beisseli white and globorotalites sp b at site 527 2 an abyssal assemblage buliminella cf plana cushman and parker and bulimina incisa cushman at the north atlantic site 384 and 3 a middle bathyal assemblage vulvulina sp a osangularia navarroana cushman alabamina sp bulimina velascoensis cushman spiroplectammina spp calcereous forms and bulimina trinitatensis cushman and jarvis at the pacific site 465

estimating wind speed and direction using wave spectra compact wave buoys are increasingly used to provide monitoring of coastal and oceanic conditions by measuring surface waves in real time due to their relatively compact size they are generally not suited to measure wind directly however since the wave field is intrinsically coupled to the wind field wave measurements can serve as a proxy observation of ocean surface winds in this study we use spectral wave observations to estimate wind speed and direction based on the assumption of a universal shape of the wave energy spectrum in the equilibrium range and the presence of a logarithmic wind speed profile above the ocean surface the wind speed and direction were estimated between 2014 and 2017 at more than a 100 coastal sites with colocated wave and wind observations estimates of wind speed and direction based on wave measurements have a root mean square error of 2 m s for wind speeds between 3 and 12 m s and a relative error of 17 for wind speeds between 10 and 20 m s and up to 20 for wind speeds between 10 and 20 m s the accuracy of proxy measurements of wind depends on fetch wave steepness wave age directional alignment between wind and dominant waves and temporal variability of the wind further we show that estimates of wind speed and direction improve considerably as the size of the buoy is reduced

an abrupt change in the african monsoon at the end of the younger dryas 1 high resolution studies of variations in the elemental and stable carbon and nitrogen isotope composition of organic matter in cores from lakes malawi tanganyika and bosumtwi tropical africa indicate an abrupt change in the wind driven circulation of these lakes that within the limits of available chronologies was contemporaneous with the end of the younger dryas in the northern hemisphere the change was also coincident with shifts in surface winds recorded in cores from off the west and northeast coasts of africa a range of other proxies indicate that these changes in wind regime were accompanied by a marked increase in precipitation in the northern tropics africa south of 5 10 s on the other hand initially suffered drought conditions together the evidence suggests an abrupt northward translation of the african monsoon system at circa 11 5 0 25 ka b p the data assembled here contribute to a growing body of work showing that the younger dryas was a major climatic excursion in tropical africa furthermore they add substance to recent suggestions that climatic events in the southern hemisphere may have played a significant role in the abrupt demise of the younger dryas

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

middle cretaceous calcareous nannofossil biogeography and preservation in the atlantic and indian oceans implications for paleoceanography abstract the quantitative study of calcareous nannofossil preservation and biogeographic distribution puts constraints on paleoceanographic models for the atlantic and indian oceans during the middle cretaceous we establish a dissolution ranking of middle cretaceous calcareous nannofossils based on susceptibility to dissolution a positive correlation of organic carbon content of the sediments and the relative abundance of watznaueria indicates that much of the carbonate dissolution was caused by the release of carbon dioxide during oxidation of organic matter the depth distribution of the most dissolution resistant species watznaueria barnesae shows relative abundance maxima at the deepest sites and a maximum where intermediate waters impinge on slopes this reflects stagnant oxygen poor bottom waters and possibly a mid water oxygen minimum zone with increased deposition and catabolic breakdown of organic matter factor analyses are performed on various data sets for three different time slices ranging in age from late aptian to early albian middle albian and late albian to cenomanian the resulting factors can be related to paleoceanographic conditions such as colder water at high latitudes high fertility upwelling conditions and neritic conditions for all three time intervals a wide tropical to subtropical zone was flanked by boreal and austral zones upwelling conditions probably existed along the north african margin and over the falkland plateau zonal upwelling is tentatively postulated for the northwestern and northeastern margin of the north atlantic in the middle albian and for the eastern margin of the north atlantic off western europe for the late albian to cenomanian we speculate on surface water current patterns location of upwelling regions and haline driven deep circulation for the middle cretaceous

late quaternary paleoclimate in the eastern mediterranean region from stable isotope analysis of speleothems at soreq cave israel abstract the eastern mediterranean continental paleoclimate during the past 25 000 years was determined by a high resolution petrographic stable isotopic and age study of speleothems from soreq cave israel 18o 13c trends indicate that all speleothems older than 7000 yr formed under conditions that differ from those of today the period from 25 000 to 17 000 yr b p was characterized by the highest 18o and 13c values which indicate deposition at temperatures of 12 16 c annual rainfall of 300 450 mm and vegetation typical of a mixed c3 c4type from 17 000 to 10 000 yr b p deglaciation in northern europe 18o values dropped progressively correlative with warming 2 3 c and a gradual increase in precipitation a simultaneous decrease in 13c gives a range expected for c3 type vegetation this period also shows significant 18o and 13c spikes which are correlatable with global events e g heinrich events and the younger dryas stade the speleothems that grew between 10 000 and 7000 yr b p have a unique petrography showing irregular thin laminae of various colors and much detritus they have the lowest 18o corresponding to 1000 mm rain coupled with the highest 13c caused by flooding events which stripped the soil cover from 7000 to 1000 yr b p conditions became closer to those of today this study demonstrates that global events which were recognized in northern europe and north africa are also evident in the eastern mediterranean and are reflected principally by large changes in the rainfall rate

palaeoecological evidence for holocene environmental change from the virunga volcanoes in the albertine rift central africa abstract this study presents two new well dated sedimentary pollen and charcoal records from high altitude crater sites in the virunga volcanoes located in the albertine rift central africa currently part of one of the world s most biodiverse areas here we argue that holocene vegetation changes in a ca 8000 year palaeoenvironmental record from a crater swamp at an altitude of 3474 m and a ca 2800 year record from a crater lake at an altitude of 4127 m are linked to variations in both climate and human activity climatic changes during the mid to late holocene are reflected in the high altitude sites and more widely in adjacent parts of the albertine rift vegetation changes comprising a decline in ericaceous vegetation at ca 5000 cal yrs bp and subsequent expansion of afroalpine vegetation together with a later increase in taxa associated with lower montane forest particularly podocarpus reflect increasing aridity during the mid to late holocene human induced environmental change in the virunga volcanoes is apparent only within the last millennium despite the long history of human occupation of the area both study sites record significant forest clearance at ca 900 cal yrs bp involving a reduction in lower montane forest taxa and increases in disturbance indicators changes in the composition of upper montane forest and particularly the expansion of hagenia are possibly linked to anthropogenic induced changes in the fire regime and are apparent from ca 900 cal yrs bp human induced environmental modification from the early part of the last millennium likely associated with onset of the late iron age appears to have extended to high altitudes the importance of natural long term climate change as a major cause of environmental change in the albertine rift has been eclipsed within the last millennium by human induced environmental effects

climate drying and associated forest decline in the lowlands of northern guatemala during the late holocene abstract palynological studies document forest disappearance during the late holocene in the tropical maya lowlands of northern guatemala the question remains as to whether this vegetation change was driven exclusively by anthropogenic deforestation as previously suggested or whether it was partly attributable to climate changes we report multiple palaeoclimate and palaeoenvironment proxies pollen geochemical sedimentological from sediment cores collected in lake peten itza northern guatemala our data indicate that the earliest phase of late holocene tropical forest reduction in this area started at 4500 cal yr bp simultaneous with the onset of a circum caribbean drying trend that lasted for 1500 yr this forest decline preceded the appearance of anthropogenically associated zea mays pollen we conclude that vegetation changes in peten during the period from 4500 to 3000 cal yr bp were largely a consequence of dry climate conditions furthermore palaeoclimate data from low latitudes in north africa point to teleconnective linkages of this drying trend on both sides of the atlantic ocean

paleoceanography of the cretaceous tertiary boundary event inferences from stable isotopic and other data we report the results of new stable oxygen and carbon isotope analyses on carbonate fine fraction whole rock and benthic foraminifers caco3 and coarse fraction percentage determinations and trace element sr analyses on carbonate constituents across the cretaceous tertiary k t boundary in deep sea drilling project dsdp sites 47 2 356 384 and 577 and compare them with published results from k t boundary sections in other dsdp sites we used the trace element data and scanning electron microscope examination to evaluate possible diagenetic alteration and relative preservation of the samples analyzed in this study the 18o data when interpreted as isotopic paleotemperatures indicate relative stable surface water and deepwater temperatures in the late maestrichtian followed by somewhat fluctuating temperatures in the early paleocene however there is no indication of either a significant warming or cooling at or following the k t boundary several sites do exhibit somewhat heavier 18o values by about 0 5 across the boundary which might suggest a 2 3 c cooling at most however we interpret these somewhat heavier 18o values as reflecting slightly better preservation of 18o of carbonate constitutents in relatively clay rich intervals e g lower diagentic potential characteristic of the k t boundary the 13c values of carbonate fine fraction and planktonic foraminifers indicate a major negative excursion in surface water total dissolved carbon across the boundary the surface water and deepwater 13c values from benthic foraminifers combined with calculated decreases in carbonate accumulation rates at all sites in the earliest paleocene are consistent with a major decrease in productivity across the k t boundary the decrease in caco3 accumulation rates is due not to increased rates of dissolution but to decreased production in surface waters the low productivity episode lasted at least 1 m y beyond the k t boundary crisis suggesting that hypothesized catastrophic events alone such as impact of an apollo object are not the only explanation for the observed long term decrease in productivity there is also an indication in the 13c curves from several sites that the surface water 13c decrease began in the latest maestrichtian suggesting that the decrease in productivity may have been independent of a hypothesized impact event

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

early maastrichtian benthic foraminiferal assemblages from the western north atlantic blake nose and their relation to paleoenvironmental changes benthic foraminiferal faunas from the lower maastrichtian globotruncana falsostuarti gansserina gansseri planktic foraminiferal zone of dsdp site 390 blake nose western north atlantic were investigated in order to characterize changes in organic matter flux and bottom water oxygenation and their relation to paleoceanographic changes benthic foraminiferal faunas in the lower part of the studied succession show high abundances of praebulimina reussi and nuttallides truempyi and are proposed to reflect fluctuations in organic matter flux to the seafloor meso to eutrophic under oxygenated bottom water conditions the middle interval is characterized by very low numbers of benthic foraminiferal specimens but a dominance of thick walled species e g lenticulinids laevidentalinids may reflect carbonate dissolution in contrast to the lower part benthic foraminifera from the upper part of the succession show well oxygenated bottom waters the most dominant species during this interval are gavelinella beccariiformis reussella szajnochae and n truempyi parallel to this change in the benthic foraminiferal assemblages the number of inoceramid shells decreases reflecting a significant increase in bottom water oxygenation based on these data we speculate that the observed changes in benthic foraminiferal assemblages towards a well oxygenated environment within the early maastrichtian of dsdp site 390 could reflect the onset of a shift from low latitude to high latitude deep water sources this speculation will predate the major reorganization of the oceanic circulation resulting in a circulation mode similar to today at the early late maastrichtian boundary by 1 ma

rapid climate shifts in the southern african interior throughout the mid to late holocene a detailed climate proxy record based on 18o 13o and grey index of a well dated stalagmite from cold air cave in the makapansgat valley of north eastern south africa suggests that regional precipitation temperatures and vegetation oscillated markedly and rapidly over the last 6500 years on centennial and multi decadal scales the mid holocene prior to 5200 years ago was humid and warm a fundamental transition occurred 3200 years ago leading to drier and cooler conditions that culminated at 1750 ad comparisons with ice core records suggest synchronous changes implicating rapid global teleconnections

multiple deep water sources and trophic regimes in the latest cretaceous deep sea evidence from benthic foraminifera benthic foraminifera from 24 dsdp odp sites were investigated to assess their global horizontal and vertical distribution in the deep sea environment at the end of the cretaceous period the samples analyzed are from the late maastrichtian and within the planktic forammiferal abathomphalus mayaroensis zone from a wide range of oceans and paleolatitudes including the low latitude sites 10 and 384 atlantic ocean 47 171 305 and 465 pacific ocean the mid latitude sites 20 111 356 363 516 525 527 548 and 605 atlantic ocean 216 217 and 758 indian ocean and the high latitude sites 208 pacific ocean 689 698 700 738 and 750 southern ocean correspondence analysis based on the 75 most common taxa shows a clear biogeographic trend along the first correspondence axis by arranging the sites in paleolatitudinal order the assemblages from the tethyan realm i e low latitudes are marked by abundant heavily calcified buliminids such as bulimina incisa b trinitatensis b velascoensis and reussella szajnochae and aragonia spp whereas high latitude faunas are characterized by abundant alabamina creta gyroidinoides quadratus and pullenia coryelli the results indicate that the faunas at low and high latitudes respectively were influenced by quite different environmental conditions this is based on the much higher abundance of infaunal morphotypes at low and mid latitudes compared to high latitudes suggesting that the biogeographic trend found in the data set coincides with the trophic regime at the various sites the results also provide support for the hypothesis that postulates two simultaneous sources and mechanisms for deep water formation during the late cretaceous including warm saline deep water produced by evaporation at low equatorial latitudes in contrast to the formation of cold deep waters at high southern latitudes

benthic foraminiferal ecomarker species of the terminal cretaceous late maastrichtian deep sea tethys abstract benthic foraminiferal distribution patterns throughout the late maastrichtian tethyan deep sea are analyzed many species are ubiquitously distributed throughout this region and therefore it is hard to assess their ecological preferences however five species show distribution patterns which suggest that they may have distinctive paleoenvironmental preferences these preferences are interpreted from hypothesized surface circulation and upwelling patterns additional information comes from recent benthic foraminiferal ecology and from responses to the cretaceous paleogene k pg boundary event this enables us to assess the ecological preferences of these late maastrichtian taxa and establish them as ecological marker ecomarker species for paleoenvironmental interpretation of the late maastrichtian bathyal abyssal tethyan realm 1 eouvigerina subsculptura is suggested to be indicative of reasonably oxygenated upper middle bathyal environments though with high abundance of utilizable organic matter 2 sliteria varsoviensis is linked to areas of late maastrichtian upwelling and seems to have been an epibenthic species with an opportunistic life mode 3 gavelinella beccariiformis and 4 nuttallides truempyi are considered to be indicative of oligotrophic conditions unless they occur with a large proportion of endobenthic morphotypes 5 gavelinella pertusa is proposed to indicate neritic middle bathyal environments of the boreal realm which might be influenced by more seasonal food fluxes and by higher oxygen levels than similar settings in the sub tropics finally the anomalous high abundances of the buliminid species sitella cf plana in deep open ocean environments is discussed in terms of possible mechanisms permitting such a morphologically opportunistic species to thrive in such an assumedly oligotrophic environment

late quaternary lowstands of lake bosumtwi ghana evidence from high resolution seismic reflection and sediment core data results from the first high resolution single channel seismic reflection survey of tropical lake bosumtwi ghana and sedimentological data from a 14c dated sediment piston core were used to revise and extend the basin s late quaternary lake level history we report four seismic sequence boundaries and an exposure surface from a sediment core which are interpreted as erosional surfaces formed at times of drastic low lake level the youngest erosional surface occurs as much as 31 m below present lake level bpll and up to 0 7 m below the present sediment water interface this most recent unconformity observed in the seismic data is interpreted to be coeval with the basin wide late holocene dry period between 0 5 and 1 cal ky bp calendar years before present another exposure surface observed in a sediment core is based on an abrupt contact separating low density wet clay rich sediments from underlying high density compact silt rich and rootlet rich sediments and is interpreted to have developed prior to 16 8 cal ky bp when the lake was 60 m bpll three older erosional surfaces occur at depths of 92 3 102 3 and 107 4 m bpll suggesting numerous lowstands in lake bosumtwi during the late pleistocene by extrapolation of average sedimentation rates 0 41 m ky from the upper 10 5 m of sediment we estimate the ages of these older lowstands to be 65 86 108 cal ky bp the lowstands of lake bosumtwi evidenced from the seismic and sediment core data are interpreted as a response to increased aridity in this part of the equatorial tropics and may correlate to other observed continent wide shifts in african climate over the past 100 ky and possibly to rapid climatic shifts observed at high latitudes determining the precise timing of these lowstands will ultimately reveal much about the drought dynamics of tropical and subtropical africa

differential dissolution of upper cretaceous deep sea benthonic foraminifers from the angola basin south atlantic ocean abstract material from the deep sea drilling project dsdp site 527 from the angola basin south atlantic ocean has been analyzed to determine whether upper cretaceous benthonic foraminiferal taxa are differentially sensitive to calcite dissolution and if so to rank their order of susceptibility two regimes of dissolution established on the basis of the degree of planktonic foraminiferal fragmentation representing stronger and less prominent dissolution within the section studied were used as a framework for reference a total of 60 calcareous and eight agglutinated benthonic foraminiferal taxa were identified at the species or genus level of these twenty three calcareous and five agglutinated taxa were selected for the dissolution study relative abundance of each of the various taxa was tested statistically using t test between dissolution regimes to assess the significance of the change induced by increased dissolution nuttallides truempyi and neoeponides sp intermediate form are interpreted as resistant to dissolution pullenia spp alabamina sp a anomalina sp a praebulimina sp fusiform and nuttallinella sp a are susceptible to dissolution the majority of the taxa 16 in number are unaffected by dissolution because they show no change between dissolution regimes among the agglutinated taxa gaudryina pyramidata is resistant to dissolution whereas the remaining four taxa are unaffected by dissolution at the level of superfamilies one calcareous superfamily discorbacea is resistant two orbitoidacea and cassidulinacea are unaffected and two nodosariacea and buliminacea are susceptible to dissolution

late holocene drought responsible for the collapse of old world civilizations is recorded in an italian cave flowstone a severe drought in parts of low latitude northeastern africa and southwestern asia 4200 yr ago caused major disruption to ancient civilizations stable isotope trace element and organic fluorescence data from a calcite flowstone collected from the well watered alpi apuane karst of central western italy indicate that the climatic event responsible for this drought was also recorded in mid latitude europe although the timing of this event coincides with an episode of increased ice rafted debris to the subpolar north atlantic the regional ocean atmosphere response seems atypical of similar holocene ice rafting events furthermore comparison of the flowstone data with other regional proxies suggests that the most extreme part of the dry spell occurred toward the end of a longer term climate anomaly

benthic foraminiferal turnover across the cretaceous paleogene boundary at agost southeastern spain paleoenvironmental inferences abstract we studied upper cretaceous and lower paleogene benthic foraminifera from the agost section southeastern spain to infer paleobathymetrical changes and paleoenvironmental turnover across the cretaceous paleogene k p transition benthic foraminifera indicate uppermost bathyal depths at agost during the abathomphalus mayaroensis biochron from about 400 kyr before the k p boundary through the early plummerita hantkeninoides biochron about 120 150 kyr before that boundary the depth increased to middle bathyal for the remainder of the cretaceous and remained so for the danian part of the studied section parasubbotina pseudobulloides biochron at least 200 kyr after the k p boundary there were no perceivable bathymetrical changes at the k p boundary where 5 of the species became extinct and the species composition of the benthic foraminiferal fauna changed considerably below the boundary infaunal morphogroups constitute up to 65 73 of the faunas directly above the boundary in the black clays of the lower guembelitria cretacea biozone benthic foraminifera are rare several opportunistic taxa e g the agglutinant haplophragmoides sp have short peaks in relative abundance possibly reflecting low oxygen conditions as well as environmental instability with benthos receiving food from short lived local blooms of primary producers above the clays through the end of the studied interval epifaunal morphogroups dominate up to 70 of the assemblages or there is an even mixture or epifaunal and infaunal morphogroups infaunal groups do not recover to pre extinction relative abundances indicating that the food supply to the benthos did not recover fully over the studied interval about 200 kyr after the k p boundary the benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact which severely destabilized primary producers and the oceanic food web that was dependent upon them

deep circulation in the late cretaceous oxygen isotope paleotemperatures from inoceramus remains in d s d p cores abstract inoceramus is an epibenthic bivalve which lived in a wide variety of paleoenvironments encompassing a broad range of paleodepths a survey of all cretaceous sediments from deep sea drilling project legs 1 69 and 75 revealed over 500 inoceramus specimens at twenty sites of these 47 well preserved late cretaceous specimens from the south atlantic pacific and indian oceans were analyzed for oxygen and carbon isotopes the specimens exhibit small internal isotopic variability and oxygen isotopic paleotemperatures that are consistent with a deep sea habitat paleotemperatures ranging from 5 to 16 c show that late cretaceous oceans were significantly warmer than the present oceans the data suggest that deep water was formed both by cooling at high latitudes and by evaporation in the subtropics

paleoenvironments of the latest cretaceous oil shale sequence southern tethys israel as an integral part of the prevailing upwelling system abstract the late cretaceous succession in israel is part of an extensive high productivity upwelling regime that persisted over 20 m y in the southern margins of tethys the deposition of a 40 m thick organic rich carbonate oil shale sequence in the negev israel indicates a major change in the evolution of this high productivity regime and reorganization of the marine ecosystem during the latest campanian early maastrichtian time the main objective of this study was to reconstruct changes in surface water productivity and seafloor oxygenation during the deposition of the oil shale member osm and transitions with the underlying phosphate and overlying marl members using high resolution records of planktic and benthic foraminifera and total organic carbon toc content the updated age of the osm determined by integrating planktic foraminifera calcareous nannofossils and inoceramids suggests that this sequence spans a maximum of 1 85 m y from 71 6 to 69 85 ma with a sedimentation rate of at least 2 4 cm kyr five distinct planktic p types and benthic b type foraminiferal assemblages were distinguished in the studied sequence the change from p type 5 to p type 1 along the sequence correlates with a distinct decrease in toc content 18 0 0 1 wt and signifies an upward decline in surface productivity based on this relationship it was inferred that species of globigerinelloide s principally globigerinelloides asper are the best tracers for extreme eutrophic surface water whereas heterohelicids are associated with more mesotrophic conditions the transition in time from assemblages b types 5 to 1 mainly reflects a change from the predominance of praebuliminids and neobuliminids to a more diversified rotaliid dominated assemblage indicating an increase in bottom water aeration the appearances of planktic foraminifera coincident with the establishment of benthic rotaliid fauna at the phosphate oil shale member transition mark the most prominent change in the upwelling sequence this change probably reflects moderate weakening of the eutrophic surface water productivity and a regional sea level rise resulting in seafloor deepening and improved seafloor aeration a further step in the decrease in toc content to 5 5 8 wt occurs in the uppermost part of the osm latest campanian and corresponds to the transitions to assemblages p type 1 and b type 1 this change suggests a shift to mesotrophic conditions additional increase in bottom and pore water aeration and thus the demise of the upwelling activity in the southern tethys

the response of benthic foraminifera to the k pg boundary biotic crisis at elles northwestern tunisia abstract the high resolution quantitative study of benthic foraminifera from the elles section nw tunisia that contains one of the most complete cretaceous paleogene k pg boundary transition and spans about 357 kyr provides detailed data on the palaeoenvironmental turnover across the k pg boundary benthic foraminifera indicate outer neritic uppermost bathyal depths without perceivable bathymetrical changes throughout uppermost maastrichtian assemblages are well preserved and highly diversified indicating stable environment and mesotrophic to weakly eutrophic conditions during the latest cretaceous benthic foraminifera underwent a major faunal turnover in coincidence with the k pg boundary where a dramatic and sudden decrease in the percentage of both infaunal morphogroups and buliminids as well as in diversity heterogeneity and genus and species richness of the assemblages are recorded indicating overall oligotrophic conditions benthic foraminifera do not show significant extinction at the end of the cretaceous with only about 3 of the species clearly becoming extinct together with the temporary disappearance of some taxa a stepped pattern of faunal recovery and restructuring is recognizable during the lowermost danian reflecting the gradual restabilization of the environmental conditions after the k pg boundary event the nature and the abundance of food supply to the sea floor conditioned the faunal turnover in the earliest paleogene which reflects not only a sudden collapse of the food web due to the extinction of calcareous primary producers but also a major rapid change in composition and abundance of food supply just after the k pg boundary short term blooms of some opportunistic species within the g cretacea zone and the lowermost part of the ps pseudobulloides zone would reflect instability in the benthic assemblages that might be related to the transfer to the sea floor of food supply not easily used by the benthos through short term large blooms or changes in abundance of opportunistic various phytoplankton groups the major environmental instability at the sea floor that just follows the k pg boundary event may have been thus related to changes in the phytoplankton composition and abundance and would have taken place over a period of about 25 kyr benthic foraminiferal assemblages appear to stabilize in the lowermost part of zone ps pseudobulloides 65 kyr after the k pg boundary event the sea floor ecosystem at least at outer neritic uppermost bathyal depths may have recovered over a considerably shorter period than commonly suggested even if the food delivery to the sea floor had not fully recovered the pre k pg levels as indicated by the lower percentages of infaunal morphogroups and buliminids this would be also in agreement with the rapid recovery of terrestrial ecosystems following the biotic crisis at the k pg boundary the drastic change of benthic foraminiferal assemblages coincident with the k pg boundary at elles and their staggered reorganization during the lowermost paleogene are largely compatible with the catastrophic effects of a huge asteroid impact on earth at the k pg boundary that severely destabilized the oceanic phytoplankton based food web

contrasting compositions of saharan dust in the eastern atlantic ocean during the last deglaciation and african humid period abstract during the african humid period ahp much of the modern hyperarid saharan desert was vegetated and covered with numerous lakes in marine sediments off northwestern africa the ahp is represented by markedly reduced siliciclastic sediment flux between 12 3 and 5 5 ka changes in the origin of this terrigenous sediment fraction can be constrained by sediment chemistry and radiogenic isotope tracers at ocean drilling program odp site 658 hole c 20 44 95 n 18 34 85 w 2263 mbsl the neodymium nd isotope composition of terrigenous detritus shows little variability throughout the last 25 kyr indicating that the contributing geological terranes have not changed appreciably since the last glacial period in contrast there were large and abrupt changes in strontium sr isotope ratios and chemical compositions associated with the ahp during which 87 sr 86 sr ratios were markedly less radiogenic and sediments show higher chemical indices of alteration we show that sediment geochemical changes during the ahp cannot be attributed to changes in the source terranes physical sorting or intensity of chemical weathering the low 87 sr 86 sr and high sr concentrations of ahp age samples also conflict with the interpretation of increased fine grained fluvially derived sediments we propose that the most significant compositional changes at odp 658c are due to the addition of an aluminosilicate component that has a highly altered major element signature but is enriched in soluble elements like sr and magnesium mg compared to aluminum al and has low 87 sr 86 sr relative to local terrigenous source areas we interpret these characteristics to reflect authigenic sediment supply from extensive north african paleolake basins that were prevalent during the ahp

west african monsoon variability during the last deglaciation and the holocene evidence from fresh water algae pollen and isotope data from core kw31 gulf of guinea abstract the study of aquatic and mangrove pollen grains and algae from freshwater environments from core kw31 recovered off the mouth of the niger river 3 31 1 n 05 34 1 e 1181 m water depth documents large scale changes in river discharge linked to variations of atlantic monsoon rainfall during the last glacial interglacial transition and the holocene two main taxa dominate the algal record pediastrum which records the strongest river input from 14 500 to 7100 cal b p and botryococcus which indicates surficial runoff in more arid periods particularly at the onset of the deglaciation and during the younger dryas several dry events punctuated the first and more intense phase of the so called african humid period 14 500 cal b p 9800 cal b p during the younger dryas 13 400 12 100 cal b p then around 11 400 11 200 cal b p indicating major climate instability freshwater discharges decreased after 7100 cal b p and definitely dropped to modern values after 3500 cal b p in agreement with land data the microfossil record of core kw31 shows that the increase in freshwater input to the ocean and correlative rainfall over western tropical africa were gradual in response to insolation forcing at the transition from glacial to interglacial situations

benthic foraminifera and environmental turnover across the cretaceous paleogene boundary at blake nose odp hole 1049c northwestern atlantic sediments recovered at lower bathyal odp site 1049 on blake nose northwestern atlantic offer an opportunity to study environmental changes at the cretaceous paleogene k p boundary relatively close to the chicxulub impact structure on the yucatan peninsula mexico in hole 1049c the boundary is located at the base of a 9 cm thick layer with abundant spherules considered to be impact ejecta uppermost maastrichtian oozes below and lowermost danian pelagic oozes above the spherulebed contain well preserved bathyal benthic foraminifera the spherule bed itself in contrast contains a mixture of shallow neritic and deeper bathyal species and specimens vary strongly in preservation this assemblage was probably formed by reworking and down slope transport triggered by the k p impact across the spherule bed i e the k p boundary only f7 of benthic foraminiferal species became extinct similar to the low extinction rates of benthic foraminifera worldwide quantitative analysis of benthic foraminiferal assemblages and morphogroups in the 63 am size fraction indicates a relatively eutrophic stable environment during the latest maastrichtian interrupted by a sudden decrease in the food supply to the benthos at the k p boundary and a decrease in diversity of the faunas followed by a stepped recovery during the earliest danian the recovery was probably linked to the gradual recovery of surface dwelling primary producers d 2004 elsevier b v all rights reserved

a revised 30 000 year paleoclimatic and paleohydrologic history of lake albert east africa abstract new geochemical and palynological data and a sedimentological reinterpretation of two cores from lake albert allow a revision of the paleoclimatic and paleohydrologic history of northwest uganda over the last 30 000 14 c yr bp our findings document one and possibly three periods of significantly reduced inflow to the nile river system from the white nile based on sediment fabric and mineralogy shifts in percentages of total organic carbon toc and total organic nitrogen ton hydrogen index hi and 13 c and 15 n as well as poor preservation of sporopollenin and siliceous microfossils we recognize two mature paleosols that formed between 18 000 and 12 500 14 c yr bp at the surface of exposed lacustrine muds a thin fossiliferous zone between the two soils documents a brief period of flooding lake albert was below the level of the coring site and thus a closed basin for several thousand years during the late pleistocene around 12 500 14 c yr bp the younger vertisol was flooded by a major rise in lake level relatively deep water conditions were established soon after this transgression but an apparent change in sedimentation rate sometime between 8 000 and 3 400 14 c yr bp may reflect another briefer period of low water which resulted in interruption of sedimentation at the coring site palynological data document a rapid and abrupt shift to drier conditions around lake albert from 11 400 to 9 900 14 c yr bp coincident with the cool younger dryas event of the northern hemisphere geochemical evidence suggests that throughout the terminal pleistocene and early holocene and again in the late holocene the water column was relatively well mixed with little tendency to persistent anoxia

benthic foraminiferal faunal turnover across the cretaceous tertiary boundary at agost southeastern spain paleoenvironmental inferences we studied upper cretaceous and lower paleogene benthic foraminifera from the agost section southeastern spain to infer paleobathymetrical changes and paleoenvironmental turnover across the cretaceous paleogene k p transition benthic foraminifera indicate uppermost bathyal depths at agost during the abathomphalus mayaroensis biochron from about 400 kyr before the k p boundary through the early plummerita hantkeninoides biochron about 120 150 kyr before that boundary the depth increased to middle bathyal for the remainder of the cretaceous and remained so for the danian part of the studied section parasubbotina pseudobulloides biochron at least 200 kyr after the k p boundary there were no perceivable bathymetrical changes at the k p boundary where v5 of the species became extinct and the species composition of the benthic foraminiferal fauna changed considerably below the boundary infaunal morphogroups constitute up to 65 73 of the faunas directly above the boundary in the black clays of the lower guembelitria cretacea biozone benthic foraminifera are rare several opportunistic taxa e g the agglutinant haplophragmoides sp have short peaks in relative abundance possibly reflecting low oxygen conditions as well as environmental instability with benthos receiving food from short lived local blooms of primary producers above the clays through the end of the studied interval epifaunal morphogroups dominate up to 70 of the assemblages or there is an even mixture or epifaunal and infaunal morphogroups infaunal groups do not recover to pre extinction relative abundances indicating that the food supply to the benthos did not recover fully over the studied interval about 200 kyr after the k p boundary the benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact which severely destabilized primary producers and the oceanic food web that was dependent upon them 2003 elsevier science b v all rights reserved

orbital controls on the el nino southern oscillation and the tropical climate the global synchroneity of glacial interglacial events is one of the major problems in understanding the link between milankovitch forcing and the climate of the late quaternary in this study we isolate a part of the climate system the tropical pacific and test its sensitivity to changes in solar forcing associated with changes in the earth s orbital parameters we use a simplified coupled ocean atmosphere model that is run for the past 150 000 years and forced with milankovitch changes in the solar insolation this system responds primarily to the precessional cycle in solar forcing and is capable of generating a mean response to the changes in the seasonal distribution of solar radiation even while the annual mean insolation is roughly constant the mean response to the precessional forcing is due to an interaction between an altered seasonal cycle and the el nifio southern oscillation enso changes in the enso behavior result in a mean tropical climate change the hypothesis is advanced that such a change in the tropical climate can generate a globally synchronous climate response to milankovitch forcing

from phytoplankton to oil shale reservoirs a 19 million year record of the late cretaceous tethyan upwelling regime in the levant basin abstract the complexity of sedimentary organic matter formation its source to burial and influence on bottom water communities are addressed in this study of the 19 million years long upper cretaceous tethyan upwelling regime in the levant a multi proxy approach is amalgamated into a model through which the paleoceanographic complexity of an intense and long lasting upwelling system is better understood a shift in primary producer assemblages and reorganization of the bottom water bacterial consortium followed the campanian maastrichtian boundary enforcing conspicuous sedimentological and faunal changes the siliceous and phosphatic bearing sediments of the campanian gave way to maastrichtian uniform and regionally distributed organic rich carbonates accompanied by an increase in sedimentation rates from 1 to 6 cm kyr this has facilitated both the increase in organic matter production and its excellent preservation and through diagenetic pathways affected its elemental composition these paleoceanographic modifications have also affected foraminiferal assemblages from massive blooms of triserial buliminid benthic foraminifera during the campanian which have sequestered diatom chloroplasts to diverse trochospiral forms during the maastrichtian using nitrate instead of oxygen for their respiratory pathways we propose that shifts in the type of primary producers promote a change in the amount and type of preserved organic matter in bottom water communities on the lithological composition of the rock mass and ultimately on the hydrocarbon generation potential of the studied source rock the continued rise of southern tethyan sea level and global highstands during the upper maastrichtian culminating into arabian plate wide maximum flooding surfaces cause the migration of upwelling activity away from the study area terminating the high productivity sequence in the levant

biogeographic patterns in terminal cretaceous planktonic foraminifera from tethyan and warm transitional waters abstract biogeographic patterns in terminal cretaceous planktonic foraminifera have been analyzed from their faunal compositions at a time slice spanning the upper parts of the calcareous nannofossil micula prinsii zone approximately the latest 20 60 k y of the cretaceous at dsdp sites from low 16 through middle 37 paleolatitudes in either the northern or the southern hemisphere the study is based on relative abundance data of 26 species at sites 356 516f 525a and 527 from the south atlantic ocean sites 384 and 548a from the north atlantic and sites 465a and 577a from the north pacific cretaceous tertiary k t boundary sections at site 516f and 577a are poorly preserved which prevented quantitative faunal analysis two major faunal assemblages one tethyan assemblage and one transitional assemblage are distinguished from the quantitative distribution patterns the tethyan assemblage dominating at sites 465a 356 and 384 is composed of heterohelix striata globotruncana aegyptiaca pseudoguembelina kempensis p costulata an undescribed form of heterohelix with relict apertural flanges along medium suture rugoglobigerina hexacamerata and trinitella scotti among these species p kempensis p costulata and h sp exhibit enhanced abundances at site 465a and constitute a warm tethyan subassemblage whereas r hexacamerata and t scotti which are most abundant at sites 356 and 384 represent a cool tethyan subassemblage seven species show greater relative abundances at sites 525a and 527 and are referred to a warm transitional subassemblage abathomphalus mayaroensis gublerina cuvillieri pseudotextularia elegans rugoglobigerina rugosa racemiguembelina fructicosa globotruncana arca and planoglobulina acervulinoides in addition an assemblage marked by the heterohelix glabrans h carinata complex h globulosa globigerinelloides multispina and rosita contusa may represent a shallower water subassemblage within warm transitional waters site 548a

coupled ocean atmosphere surface variability and its climate impacts in the tropical atlantic region this study examines time evolution and statistical relationships involving the two leading ocean atmosphere coupled modes of variability in the tropical atlantic and some climate anomalies over the tropical 120 w 60 w region using selected historical files 75 y near global ssts and precipitation over land more recent observed data 30 y sst and pseudo wind stress in the tropical atlantic and reanalyses from the us national centers for environmental prediction ncep ncar reanalysis system on the period 1968 1997 surface air temperature sea level pressure moist static energy content at 850 hpa precipitable water and precipitation the first coupled mode detected through singular value decomposition of the sst and pseudo wind stress data over the tropical atlantic 30 n 20 s expresses a modulation in the thermal transequatorial gradient of sst anomalies conducted by one month leading wind stress anomalies mainly in the tropical north atlantic during northern winter and fall it features a slight dipole structure in the meridional plane its time variability is dominated by a quasi decadal signal well observed in the last 20 30 ys and when projected over longer term sst data in the 1920s and 1930s but with shorter periods the second coupled mode is more confined to the south equatorial tropical atlantic in the northern summer and explains considerably less wind stress sst cross covariance its time series features an interannual variability dominated by shorter frequencies with increased variance in the 1960s and 1970s before 1977 correlations between these modes and the enso like nino3 index lead to decreasing amplitude of thermal anomalies in the tropical atlantic during warm episodes in the pacific this could explain the nonstationarity of meridional anomaly gradients on seasonal and interannual time scales overall the relationships between the oceanic component of the coupled modes and the climate anomaly patterns denote thermodynamical processes at the ocean atmosphere interface that create anomaly gradients in the meridional plane in a way which tends to alter the north south movement of the seasonal cycle this appears to be consistent with the intrinsic non dipole character of the tropical atlantic surface variability at the interannual time step and over the recent period but produces abnormal amplitude and or delayed excursions of the intertropical convergence zone itcz connections with continental rainfall are approached through three ncep ncar and observed rainfall indexes over the nordeste region in brazil and the guinea and sahel zones in west africa these indices appear to be significantly linked to the sst component of the coupled modes only when the two atlantic modes the enso like nino3 index are taken into account in the regressions this suggests that thermal forcing of continental rainfall is particularly sensitive to the linear combinations of some basic sst patterns in particular to those that create meridional thermal gradients the first mode in the atlantic is associated with transequatorial pressure moist static energy and precipitable water anomaly patterns which can explain abnormal location of the itcz particularly in northern winter and hence rainfall variations in nordeste the second mode is more associated with in phase variations of the same variables near the southern edge of the itcz particularly in the gulf of guinea during the northern spring and winter it is primarily linked to the amplitude and annual phase of the itcz excursions and thus to rainfall variations in guinea connections with sahel rainfall are less clear due to the difficulty for the model to correctly capture interannual variability over that region but the second atlantic mode and the enso like pacific variability are clearly involved in the sahel climate interannual fluctuations anomalous dry wet situations tend to occur when warmer cooler waters are present in the eastern pacific and the gulf of guinea in northern summer which contribute to create a northward southward transequatorial anomaly gradient in sea level pressure over west africa

winds near the surface of waves observations and modeling abstractthe concept of a constant flux layer is usually employed for vertical profiling of the wind measured at some elevation near the ocean surface the surface waves however modify the balance

wave follower field measurements of the wind input spectral function part ii parameterization of the wind input abstract nearly all of the momentum transferred from wind to waves comes about through wave induced pressure acting on the slopes of waves known as form drag direct field measurements of the wave induced pressure in airflow over water waves are difficult and consequently rare those that have been reported are for deep water conditions and conditions in which the level of forcing measured by the ratio of wind speed to the speed of the dominant spectral peak waves is quite weak u10 cp 3 the data reported here were obtained over a large shallow lake during the australian shallow water experiment auswex the propagation speeds of the dominant waves were limited by depth and the waves were correspondingly steep this wider range of forcing and concomitant wave steepness revealed some new aspects of the rate of wave amplification by wind the so called wind input source function in the energy balance equation for wind driven water waves it was found that the exponential growth rate parameter fra

formal subdivision of the holocene series epoch a discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommission on quaternary stratigraphy international commission on stratigraphy this discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommision on quaternary stratigraphy sqs of the international commission on stratigraphy ics considers the prospects for a formal subdivision of the holocene series epoch although previous attempts to subdivide the holocene have proved inconclusive recent developments in quaternary stratigraphy notably the definition of the pleistocene holocene boundary and the emergence of formal subdivisions of the pleistocene series epoch mean that it may be timely to revisit this matter the quaternary literature reveals a widespread but variable informal usage of a tripartite division of the holocene early middle or mid and late and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology we propose an early middle holocene boundary at 8200 a bp and a middle late holocene boundary at 4200 a bp each of which is linked to a global stratotype section and point gssp should the proposal find a broad measure of support from the quaternary community a submission will be made to the international union of geological sciences iugs via the sqs and the ics for formal ratification of this subdivision of the holocene series epoch copyright 2012 john wiley sons ltd

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

wind stress from wave slopes using phillips equilibrium theory abstract an open ocean deep water air sea interaction experiment was conducted in the gulf of alaska wave amplitude and slope data were measured using a wavec heave pitch and roll buoy that was let drift in the alaska gyre wind stress estimates were obtained from a fast sample anemometer using the dissipation technique and from synoptic measurements through a boundary layer model the fundamental correlation and predictive relationships between wind friction velocity and wave spectral properties were established a comparison of the slope spectrum to simultaneous wind stresses allowed us to estimate the phillips proposed universal constant reintroducing this constant into the phillips slope spectrum and using measured slope spectral characteristics an inferred wind stress was calculated that was shown to agree well with both the dissipation and model stresses thereby validating both phillips theory and the boundary layer model any discrepancies with the model stresses were attributed to second

food supply to the seafloor in the pacific ocean after the cretaceous paleogene boundary event article i nfo deep sea benthic foraminifera show important but transient assemblage changes at the cretaceous paleogene k pg boundary when many biota suffered severe extinction we quantitatively analyzed benthic foraminiferal assemblages from lower bathyal upper abyssal 1500 2000 m northwest pacific odp site 1210 shatsky rise and compared the results with published data on assemblages at lower bathyal 1500 m pacific dsdp site 465 hess rise to gain insight in paleoecological and paleoenvironmental changes at that time at both sites diversity and heterogeneity rapidly decreased across the k pg boundary then recovered species assemblages at both sites show a similar pattern of turnover from the uppermost maastrichtian into the lowermost danian 1 the relative abundance of buliminids indicative of a generally high food supply increases towards the uppermost cretaceous and peaks rapidly just above the k pg boundary coeval with a peak in benthic foraminiferal accumulation rate bfar a proxy for food supply 2 a peak in relative abundance of stensioeina beccariiformis a cosmopolitan form generally more common at the middle than at the lower bathyal sites occurs just above the buliminid peak 3 the relative abundance of nuttallides truempyi a more oligotrophic form decreases at the boundary then increases above the peak in stensioeina beccariiformis the food supply to the deep sea in the pacific ocean thus apparently increased rather than decreased in the earliest danian the low benthic diversity during a time of high food supply indicates a stressed environment this stress might have been caused by reorganization of the planktic ecosystem primary producer niches vacated by the mass extinction of calcifying nannoplankton may have been rapidly b10 kyr filled by other possibly opportunistic primary producers leading to delivery of another type of food and or irregular food delivery through a succession of opportunistic blooms the deep sea benthic foraminiferal data thus are in strong disagreement with the widely accepted hypothesis that the global deep sea floor became severely food depleted following the k pg extinction due to the mass extinction of primary producers strangelove ocean model or to the collapse of the biotic pump living ocean model

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

a high resolution palaeoclimatic record for the last 27 500 years in tropical west africa from the carbon and nitrogen isotopic composition of lacustrine organic matter variations in the carbon and nitrogen isotopic composition of bulk organic matter in the sediments of lake bosumtwi ghana reflect climatically induced changes to the lake and the catchment flora cores spanning the last 27 5 kyr of sedimentation in the lake show large oscillations in 13corg pdb and 15norg air the late pleistocene record is particularly detailed showing changes of ca 20 in carbon and ca 10 in nitrogen isotopic compositions these variations are of complex origin although different in magnitude major isotopic excursions in the two records are generally in phase and reveal the occurrence of two major dry intervals at and immediately following the last glacial maximum the allerod younger dryas period also seems to have been marked by generally dry conditions in this part of tropical west africa nitrogen isotopic evidence suggests that during the period 9 2 3 2 kyr the lake had an extremely stable water column probably due to the absence of a windy or cool dry season or both regular circulation of the water column recommenced during the late holocene and has persisted until the present day

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

deep sea benthonic foraminiferal faunal turnover near the eocene oligocene boundary abstract eocene oligocene deep sea benthonic foraminifera in d s d p site 277 in the southwest pacific have been analyzed to determine the benthonic foraminiferal response to the development of the psychrosphere near the eocene oligocene boundary biostratigraphic ranges of 41 taxa show that 23 taxa are found throughout the late eocene to early oligocene sequence while 18 taxa exhibit first or last occurrences comparison of the faunal changes in site 277 with a benthonic foraminiferal oxygen isotope record shows that the development of the psychrosphere did not have a profound effect upon the benthonic foraminifera and the overall faunal change preceding and subsequent to the bottom water circulation event occurred gradually the inferred water mass event affected the relative abundance of one species epistominella umbonifera the lack of major faunal changes at the eocene oligocene boundary in site 277 probably reflects either wide environmental tolerances of the benthonic foraminifera or a bottom water temperature change less than 3 c examination of previously published benthonic foraminiferal biostratigraphic data from d s d p sites 167 171 357 360 363 and 400a and deep sea ostracode data from d s d p leg 3 show faunal changes occurred during discrete intervals in the middle eocene early oligocene the faunal patterns from these data and from site 277 show that the eocene oligocene cooling event did not cause rapid catastrophic changes of the benthonic faunas of the open ocean although significant faunal changes are associated with the water mass event in sites 167 171 and 400a the benthonic faunal changes in middle eocene early oligocene time are consistent with the gradual decrease of inferred bottom water temperatures based on previously published oxygen isotopic data the 18 o eocene oligocene enrichment of 0 76 is a major event in the southern ocean oxygen isotopic record but is considerably less in magnitude than the 1 75 2 00 change that occurred gradually from mid early eocene to the eocene oligocene boundary the benthonic foraminiferal and isotopic data indicate that bottom water circulation may have developed during the middle eocene to early oligocene interval with the 3 c bottom water cooling near the eocene oligocene boundary representing part of this development

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

multivariate data analysis in palaeoecology and palaeobiogeography a review abstract palaeoecologists and palaeobiogeographers are often confronted with large multivariate data sets from which fossil communities assemblages or associations or faunal provinces are to be recognized the complex multidimensional nature of these data sets the recognition of the enormous variation of communities and environments both in space and time and the difficulties of dealing with these problems by the human mind justify the use of multivariate statistical methods in palaeoecology and palaeobiogeography concepts and basic procedures of several commonly used multivariated statistical methods of palaeoecology and palaeobiogeography are reviewed in the wider context of quantitative community ecology and biogeography basic assumptions about data structure and theoretical and practical limitations are discussed the emphasis is on evaluation of binary similarity coefficients and two multivariate approaches cluster analysis and ordination thirty nine binary similarity coefficients are evaluated against nine criteria jaccard s coefficient of community is found most suitable as a similarity measure between samples under the conditions tested algorithmic procedures of cluster analysis especially the agglomerative hierarchical cluster analysis techniques and indirect ordinations particularly polar ordination principal component analysis principal coordinate analysis correspondence analysis detrended correspondence analysis and nonmetric multidimensional scaling are outlined and their applicability to palaeoecological and palaeobiogeographical data is discussed where the data are appropriate an integration of cluster analysis and ordination is suggested to be applied to the same data

late holocene climatic changes in western equatorial africa inferred from pollen from lake sinnda southern congo abstract pollen analysis of two cores from the lake sinnda located in one of the driest areas of the southern congo reveals a history of vegetation and climate in this region during the past 5000 yr a major change centered around 3000 2500 yr b p is indicated by an abrupt decrease in forest pollen and by a corresponding increase in grassland pollen concurrent drying up of the lake shows that climate in particular aridity was the major cause of this change this paleoclimatic reconstruction conforms with evidence for drier conditions in other parts of western equatorial africa such as the development of isolated enclosed savannas and of heliophilous forested formations the aridity is recorded more fully at lake sinnda than at the previous studied ones it probably lasted longer from 4200 to 1300 yr b p and was more progressive than previously inferred the aridity predates agriculture marked by pollen of the oil palm at lake sinnda

dynamics of the west african monsoon under mid holocene precessional forcing regional climate model simulations abstract the african humid period ahp about 14 800 yr ago 14 8 5 5 ka ka 1000 yr ago was a time of increased humidity over africa paleoclimate evidence suggests that the west african summer monsoon was stronger and more extensive 6 ka than today and that the saharan desert was green here a regional climate model that produces an excellent simulation of today s climate over northern africa is used to study the dynamics of the monsoon 6 ka changes in insolation atmospheric co2 and vegetation are used to impose 6 ka conditions and the role of each forcing is isolated vegetation is not interactive and the large scale circulation and ssts are fixed at present day values for the 6 ka simulations the regional model produces precipitation increases across the sahel and sahara that are in good agreement with the paleodata however unobserved drying is simulated over the guinean coast region where paleodata are sparse precipitation increases in the sahel are related to a northward shift of th

primary and diagenetic carbonates in the anoxic sediments of lake bosumtwi ghana cores of organic rich muds from the tropical meteorite crater lake bosumtwi ghana contain laminae of authigenic calcite polyhedra and aragonite needles as well as scattered diagenetic calcite mg calcite spherulites and aggregates of dolomite crystals their respective origins are traced by analyses of oxygen and carbon stable isotopes anoxic dolomite and mg calcite formed in pore waters reflecting highest degrees of evaporative concentration and high rates of methanogenesis carbon dioxide reduction must have been the dominant methanogenic pathway producing diagenetic carbonates with delta sup 13 c values up to 27 pdb this example shows the inherent problems of interpreting bulk samples with progressive mineralogical sequences of calcite to mg calcite to aragonite to dolomite merely in terms of mg sup 2 ca sup 2 in lake waters it provides a model for the interpretation of ancient lacustrine carbonates from organic rich environments

pollen evidence of late quaternary vegetation and inferred climate changes in congo a detailed palynological analysis of two cores recovered from a swamp in the southern bateke plateaux congo provides information on the botanical history of this region during the last 24 000 yr b p rich and well diversified pollen counts exhibit changes in the vegetational communities related to hydrological and climatic fluctuations around 24 000 yr b p the occurrence of hydromorphous forest elements gives evidence of a humid phase between 24 000 and around 13 000 yr b p swampy herbaceous communities expanded indicating slightly drier climatic conditions from approximately 13 000 yr b p onward the beginning of a humid episode is reflected by the development of mesophilous forests the decrease of these forests is documented since 3000 yr b p grasslands are found to extend locally whereas elaies guineensis oil palm spreads out indicating both climatic change but also anthropogenic activities

on the age and origin of lake ejagham cameroon and its endemic fishes lake ejagham is a small shallow lake in cameroon west africa which supports five endemic species of cichlid fishes in two distinct lineages genetic evidence suggests a relatively young age for the species flocks but supporting geologic evidence has thus far been unavailable here we present diatom geochemical mineralogical and radiocarbon data from two sediment cores that provide new insights into the age and origin of lake ejagham and its endemic fishes radiocarbon ages at the base of the longer core indicate that the lake formed approximately 9 ka ago and the diatom record of the shorter core suggests that hydroclimate variability during the last 3 millennia was similar to that of other lakes in cameroon and ghana these findings establish a maximum age of ca 9 cal ka bp for the lake and its endemic species and suggest that repeated cichlid speciation in two distinct lineages occurred rapidly within the lake local geology and west african paleoclimate records argue against a volcanic chemical or climatic origin for lake ejagham although not conclusive the morphometry of the lake and possible signs of impact induced effects on quartz grains are instead more suggestive of a bolide impact

palaeoenvironmental turnover across the palaeocene eocene boundary at the stratotype section in dababiya egypt based on benthic foraminifera the global stratotype section and point for the palaeocene eocene p e boundary was defined at dababiya quarry egypt at the base of the carbon isotope excursion cie we present the first detailed analysis of palaeocene eocene benthic foraminifera from dababiya in order to infer the palaeoenvironmental turnover across the p e boundary at dababiya the cie coincides with a major turnover in foraminiferal assemblages the last occurrence of angulogavelinella avnimelechi at the base of the cie may be correlated to the main phase of extinction of deep sea benthic foraminifera benthic foraminifera indicate that stressful conditions such as oxygen deficiency carbonate dissolution and changes in food supply persisted at the sea floor over most of the cie interval the main phase of recovery of benthic foraminifera is recorded c 250 cm above the p e boundary and it may be linked to increased productivity and oxygenation at the sea floor

mineralogical organic and isotopic composition as palaeoenvironmental records in the lake sediments of two lakes the plitvice lakes croatia abstract six sediment cores the top 30 40 cm from two lakes of different sizes lake prosce and lake kalu erovac situated in the karst region of the plitvice lakes system croatia were studied by mineralogical and structural c n and total organic carbon toc and isotopic analyses a14c and 13c of carbonate and organic fractions the study of the two karst lakes where sediment composition is mainly calcite showed that organic matter om also plays an important role and that both fractions analysed simultaneously give a good overview of the processes in the lakes the morphological and structural properties of the calcite particles at micron and submicron levels indicate that the calcite mineral phase is formed by active authigenic precipitation in the studied lake systems in the small lake kalu erovac the measured distributions of carbonate and om fractions c n toc and a14c and 13c values of both fractions along the sediment depth showed similar values for all three cores with small variations in each core indicating very homogenous precipitation of autochthonous calcite inside the lake without allochthonous fraction in the bigger lake prosce the large difference in sediment composition of the three cores indicated different conditions of sediment precipitation inside the lake significant fractions of land derived carbonate and om were recognized by mineralogical c n a14c and 13c values in the shallow coastal area indicating that the sediment was a mixture of allochthonous and autochthonous fractions in contrast the composition of the deep water sediment in the same lake indicated in situ calcite precipitation and aquatic om produced in the lake sedimentation rates of 0 7 cm yr and from 0 3 to 0 7 cm yr for lake prosce and lake kalu erovac respectively were determined based on the a14c of macrofossils extreme hydrological events in 1981 and 2010 were identified by disturbances in carbon isotopes distributions in sediment profiles no evidence of anthropogenic influence in either lake on the local level was found but the response to the global 14c contamination was observed by a14c peaks in both carbonate and organic fractions increased bioproductivity in the recent decades was observed in lake prosce which can be correlated with a slight increase in lake water temperature in the last three decades this process can be associated with enhanced eutrophication in lake prosce

climate change and the collapse of the akkadian empire evidence from the deep sea the akkadian empire ruled mesopotamia from the headwaters of the tigris euphrates rivers to the persian gulf during the late third millennium b c archeological evidence has shown that this highly developed civilization collapsed abruptly near 4170 150 calendar yr b p perhaps related to a shift to more arid conditions detailed paleoclimate records to test this assertion from mesopotamia are rare but changes in regional aridity are preserved in adjacent ocean basins we document holocene changes in regional aridity using mineralogic and geochemical analyses of a marine sediment core from the gulf of oman which is directly downwind of mesopotamian dust source areas and archeological sites our results document a very abrupt increase in eolian dust and mesopotamian aridity accelerator mass spectrometer radiocarbon dated to 4025 125 calendar yr b p which persisted for 300 yr radiogenic nd and sr isotope analyses confirm that the observed increase in mineral dust was derived from mesopotamian source areas geochemical correlation of volcanic ash shards between the archeological site and marine sediment record establishes a direct temporal link between mesopotamian aridification and social collapse implicating a sudden shift to more arid conditions as a key factor contributing to the collapse of the akkadian empire

the cretaceous tertiary boundary sedimentology and micropalaeontology at el mulato section ne mexico in the el mulato section ne mexico the upper cretaceous marly mendez and the lower palaeogene marly velasco formations are separated by a clastic unit benthic foraminifera from both marly formations indicate lower bathyal depths the clastic unit in contrast contains platform sands muddy pebbles and neritic shallow faunas mixed with microspherules indicating that it was allochthonously deposited into the deep basin the diversity and the variability in origin of the components in the clastic unit and its sedimentological features support a model of deposition by turbidity currents related to mass wasting processes triggered by the creta ceous tertiary k t boundary impact planktic foraminifera were affected by a catastrophic extinction at the k t boundary whereas benthic foraminifera show reorganization of the community structure rather than significant extinction the benthic faunal turnover may have resulted from the drop in primary productivity after the asteroid impact at the end of the cretaceous

numerical investigation of spectral evolution of wind waves part i wind input source function abstract this paper is dedicated to the investigation and calibration of the parameterized form for the wind input source term sin proposed earlier on the basis of field observations at lake george australia the main objective of this study was to obtain spectral forms for the wind input source function sin which incorporates the novel observation based features and at the same time satisfies the important physical constraint that the total integrated wind input must agree with independently observed magnitudes of the wind stress within this approach a new methodology a dynamic self adjusting routine was developed for correction of the wind input source function sin this correction involves a frequency dependent adjustment to the growth rate f based on extrapolations from field data the model results also show that light winds require higher rate adjustments of the wind input than strong winds

radiocarbon dating of pollen by accelerator mass spectrometry radiocarbon dating of bulk sediments has been the standard method for establishing chronologies in the studies of lake sediment cores which have contributed significantly to our knowledge of late quaternary paleo environments these bulk sediment dates are presumed to be direct ageindicators for the speciments e g pollen or macrofossils which are actually being studied however several recent studies have reinforced long standing apprehensions concerning this presumption in this study we demonstrate for the first time the radiocarbon dating of pollen concentrate samples by accelerator mass spectrometry the dates obtained by this method should provide more reliable radiocarbon chronologies for paleo environmental studies than have been obtainable by bulk sediment dating

an international and multidisciplinary drilling project into a young complex impact structure the 2004 icdp bosumtwi crater drilling project an overview the bosumtwi impact crater in ghana arguably the best preserved complex young impact structure known on earth displays a pronounced rim and is almost completely filled by lake bosumtwi a hydrologically closed basin it is the source crater of the ivory coast tektites the structure was excavated in 2 1 2 2 gyr old metasediments and metavolcanics of the birimian supergroup a drilling project was conceived that would combine two major scientific interests in this crater 1 to obtain a complete paleoenvironmental record from the time of crater formation about one million years ago at a near equatorial location in africa for which very few data are available so far and 2 to obtain a complete record of impactites at the central uplift and in the crater moat for ground truthing and comparison with other structures within the framework of an international and multidisciplinary drilling project led by the international continental scientific drilling program icdp 16 drill cores were obtained from june to october 2004 at six locations within lake bosumtwi which is 8 5 km in diameter the 14 sediment cores are currently being investigated for paleoenvironmental indicators the two impactite cores lb 07a and lb 08a were drilled into the deepest section of the annular moat 540 m and the flank of the central uplift 450 m respectively they are the main subject of this special issue of meteoritics planetary science which represents the first detailed presentations of results from the deep drilling into the bosumtwi impactite sequence drilling progressed in both cases through the impact breccia layer into fractured bedrock lb 07a comprises lithic in the uppermost part and suevitic impact breccias with appreciable amounts of impact melt fragments the lithic clast content is dominated by graywacke besides various metapelites quartzite and a carbonate target component shock deformation in the form of quartz grains with planar microdeformations is abundant first chemical results indicate a number of suevite samples that are strongly enriched in siderophile elements and mg but the presence of a definite meteoritic component in these samples cannot be confirmed due to high indigenous values core lb 08a comprises suevitic breccia in the uppermost part followed with depth by a thick sequence of graywacke dominated metasediment with suevite and a few granitoid dike intercalations it is assumed that the metasediment package represents bedrock intersected in the