variability of the north atlantic thermohaline circulation during the last interglacial period studies of natural climate variability are essential for evaluating its future evolution greenland ice cores suggest that the modern warm period the holocene has been relatively stable for the past 9 000 years much less is known about other warm interglacial periods which comprise less than 10 of the climate record during the past 2 5 million years here we present high resolution ocean sediment records of surface and deep water variables from the bermuda rise spanning the last interglacial period about 118 000 127 000 years ago in general deep water chemical changes are coincident with transitions in surface climate at this site the records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates the relatively stable interglacial period begins and ends with abrupt changes in deep water flow we estimate using 230 th measurements to constrain the chronology that transitions occur in less than 400 years

eemian cooling in the norwegian sea and north atlantic ocean preceding continental ice sheet growth changing conditions in the north atlantic region may drive global climate changes1 2 according to previous reconstructions of the last interglacial the eemian north atlantic sea surface tempera tures ssts were similar to present day values3 in the norwegian sea even warmer conditions appeared as a single pulse of short duration4 5 whereas the greenland ice record suggests that the warm interglacial air temperatures were interrupted by several cold periods6 here we use faunal and stable isotope analyses of foraminifera in two sediment cores from the north atlantic ocean and norwegian sea to reconstruct high resolution records of sst and sea surface salinity sss during the eemian interglacial our results which differ significantly from the greenland record6 show a sharp decrease in sst and sss of the norwegian sea associated with a more moderate cooling and freshening of the north atlantic at the middle of isotope substage 5e several millennia before the beginning of continental ice sheet growth changes in the norweg ian sea surface conditions appear to have represented an important climate change affecting global atmospheric and thermohaline circulations

direct comparison of marine and terrestrial climate variability during marine isotope stages 6 and 5 results from santa barbara basin odp hole 893a 1 planktonic foraminiferal 1 8 o pollen and opal records from santa barbara basin are used to evaluate climate changes in the northeast pacific during marine isotope stages mis 6 and 5 while the oak and foraminifera record the major glacial interglacial changes opal is not correlated with these large scale transitions surface water warming in the basin was synchronous with terrestrial warming but earlier than ice sheet melting and increasing northern hemisphere insolation at termination ii during and immediately after deglaciation our marine proxies indicate the presence of an isothermal upper water column later in substage 5e the water column became thermally stratified surface productivity increased and laminated sediments began accumulating sediment trap and hydrographic data suggest these changes were due to the onset of a strong seasonal cycle similar to that seen today in the basin a series of rapid coolings within mis 5 appears to be synchronous with north atlantic ice rafting events and greenland stadials

evidence from u th dating against northern hemisphere forcing of the penultimate deglaciation milankovitch proposed that summer insolation at mid latitudes in the northern hemisphere directly causes the ice age climate cycles1 this would imply that times of ice sheet collapse should correspond to peaks in northern hemisphere june insolation but the penultimate deglaciation has proved controversial because june insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier2 3 4 5 6 7 8 there is a clear signature of the penultimate deglaciation in marine oxygen isotope records but dating this event which is significantly before the 14c age range has not been possible here we date the penultimate deglaciation in a record from the bahamas using a new u th isochron technique after the necessary corrections for recoil mobility of 234u and 230th and a small age correction for sediment mixing the midpoint age for the penultimate deglaciation is determined to be 135 2 5 kyr ago this age is consistent with some coral based sea level estimates but it is difficult to reconcile with june northern hemisphere insolation as the trigger for the ice age cycles potential alternative driving mechanisms for the ice age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean atmosphere system or changes in atmospheric co2 concentration controlled by a process in the southern hemisphere

climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

oxygen isotopic composition of multiple species of planktonic foraminifera recorders of the modern photic zone temperature gradient abundances of 12 species of planktonic foraminifera collected in two plankton tows from the east tropical atlantic are compared to the chlorophyll content and the temperature of the sea water from which they were collected as expected from previous work in the tropics all dominant tropical species occur in greatest abundance within the photic zone many species occur in greatest abundances in the seasonal thermocline in association with the maximum chlorophyll concentration while a few algal symbiont bearing species occur in greatest abundance in the mixed layer the 18o measurements of planktonic foraminifera shells from core top sediment samples confirm the vertical stratification within the photic zone that is suggested by the relationship between hydrography and abundances found in the plankton tows and found in the statistical study by ravelo et al 1990 comparison between the measured 18o values of planktonic foraminifera with the predicted 18o profiles of the overlying water column at three core locations indicate that species abundances in the sediment record the seasonally integrated conditions of the photic zone and suggests that the abundance of a species in the sediment depends on whether the preferred ecological conditions of that species may be found within the photic zone of the overlying water column sometime during the year species which calcify below the photic zone have only trace relative abundances finally it appears that the total range of 18o values of the dominant species approximates the predicted annual 18o of calcite range in the upper 80 m of the water column

devils hole nevada δ18o record extended to the mid holocene abstract the mid to late pleistocene devils hole 18 o record has been extended from 60 000 to 4500 yr ago the new 18 o time series in conjunction with the one previously published is shown to be a proxy of pacific ocean sea surface temperature sst off the coast of california during marine oxygen isotope stages mis 2 and 6 the devil hole and sst time series exhibit a steady warming that began 5000 to 10 000 yr prior to the last and penultimate deglaciations several possible proximate causes for this early warming are evaluated the magnitude of the peak 18 o or sst during the last interglacial lig is significantly greater 1 per mill and 2 to 3 c respectively than the peak value of these parameters for the holocene in contrast benthic 18 o records of ice volume show only a few tenths per mill difference in the peak value for these interglacials statistical analysis provides an estimate of the large shared information variation between the devils hole and eastern pacific sst time series from 41 to 2 n and enforces the concept of a common forcing among all of these records the extended devils hole record adds to evidence of the importance of uplands bordering the eastern pacific as a source of archives for reconstructing pacific climate variability

thorium 230 profiling in deep sea sediments high resolution records of flux and dissolution of carbonate in the equatorial atlantic during the last 24 000 years variations in carbonate flux and dissolution which occurred in the equatorial atlantic during the last 24 000 years have been estimated by a new approach that allows the point by point determination of paleofluxes to the seafloor an unprecedented time resolution can thus be obtained which allows sequencing of the relatively rapid events occurring during deglaciation the method is based on observations that the flux of unsupported 230th into deep sea sediments is nearly independent of the total mass flux and is close to the production rate thus excess 230th activity in sediments can be used as a reference against which fluxes of other sedimentary components can be estimated the study was conducted at two sites ceara rise western equatorial atlantic and sierra leone rise eastern equatorial atlantic in cores raised from three different depths at each site from measurements of 230th and caco3 changes in carbonate flux with time and depth were obtained a rapid increase in carbonate production starting at the onset of deglaciation was found in both areas this event may have important implications for the postglacial increase in atmospheric co2 by increasing the global carbonate carbon to organic carbon rain ratio and decreasing the alkalinity of surface waters and possibly the north atlantic deep water increased carbonate dissolution occurred in the two regions during deglaciation followed by a minimum during mid holocene and renewed intensification of dissolution in late holocene during the last 16 000 years carbonate dissolution was consistently more pronounced in the western than in the eastern basin reflecting the influence of antarctic bottom water in the west this trend was reversed during stage 2 possibly due to the accumulation of metabolic co2 below the level of the romanche fracture zone in the eastern basin

pollen based evidence of extreme drought during the last glacial 32 6 9 0 ka in coastal southern california abstract high resolution pollen analyses of sediment core ledc10 1 from lake elsinore yield the first well dated terrestrial record of sub centennial scale ecologic change in coastal southern california between 32 and 9 ka in the lake elsinore watershed the initial mesic montane conifer forests dominated by pinus and cupressaceae with trace amounts of abies and picea were replaced by a sequence of multiple extended severe mega droughts between 27 5 and 25 5 ka in which halophytic and xerophytic herbs and shrubs occupied an ephemeral lake this prolonged and extended dry interval which corresponds with warm waters offshore imply strengthening of the north pacific high and persistent below average winter precipitation the subsequent contrasting monotonic occurrence of montane conifers reflects little variation in cold mesic climate until 15 ka postglacial development of quercus woodland and chaparral mark the return to more xeric warmer conditions at this time a brief reversal at 13 1 12 1 ka as reflected by an expansion of pinus is correlative with the younger dryas and interrupts development of warm postglacial climate subsequent gradual expansion of xeric vegetation post younger dryas denotes the establishment of a winter hydroclimate regime in coastal southern california that is more similar to modern conditions pollen based reconstructions of temperature and precipitation at lake elsinore are generally correlative with pollen based paleoclimatic reconstructions and foraminifera based sea surface temperatures from santa barbara basin in marine core odp 893 the conspicuous absence of the 27 5 25 5 ka glacial mega drought in the santa barbara basin pollen record highlights the sensitivity of lake elsinore to hydroclimate change and thus the importance of this new record that indicates that mega drought can occur during the full glacial when climatic boundary conditions and forcings differed substantially from the present

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

orbital scale stratigraphy and high resolution analysis of biogenic components and deep water oxygenation conditions in the japan sea during the last 640 kyr abstract paleoceanographic conditions in the japan sea changed drastically during the late quaternary in association with orbital and suborbital cycles and glacio eustatic sea level changes however few studies have examined long term sediment records older than 160 ka because of the lack of long and continuous cores and the difficulty in constructing high resolution age models in this study we first constructed an orbital scale stratigraphy of the sediments covering the last 640 kyr by comparing the specmap 18o curve and the 18o curve of planktonic foraminifera 18opf in the japan sea together with the combination zones of dominant planktonic foraminifera species then we reconstructed temporal variations in biogenic silica biosil and biogenic carbonate biocarb contents calculated from high resolution major element analysis data determined by an xrf microscanner in order to evaluate the deep water oxygenation conditions we also defined excess s as the difference between the content of s in the sediments and that for normal marine sediments calculated from the organic carbon content corg estimated from lightness l by assuming a total sulfur content stotal corg ratio of 0 36 and examined its variability biosil shows orbital scale variation and is generally low except during interglacial maxima when global sea level was high enough to allow a strong influx of the tsushima warm current biocarb shows orbital and suborbital scale variations and tends to be higher in dark layers deposited during glacial stages whereas the relationship is reversed during interglacial stages the low biocarb in dark layers deposited during interglacial stages is probably due to dissolution of biogenic carbonate caused by the increase in surface productivity as a result of the strong influx of nutrient rich east china sea coastal water and consequent increase in surface productivity and decomposition rate of organic matter in the intermediate water excess s tends to be higher in thicker dark layers deposited during glacial maxima when the sea level dropped below 90 m compared to adjacent light layers suggesting development of euxinic deep water conditions during these periods the results demonstrated the presence of orbital and suborbital scale variations in biosil and biocarb and their association with dark and light layers in the japan sea that reflect variations in the nature and strength of inflow through the tsushima strait controlled by both climatic and sea level changes whereas higher excess s reflects the development of euxinic deep water condition during glacial maxima in association with glacio eustatic sea level drops below 90 m during the last 640 kyr

anabranching rivers their cause character and classification anabranching rivers consist of multiple channels separated by vegetated semi permanent alluvial islands excised from existing floodplain or formed by within channel or deltaic accretion these rivers occupy a wide range of environments from low to high energy however their existence has never been adequately explained they occur concurrently with other types of channel pattern although specific requirements include a flood dominated flow regime and banks that are resistant to erosion with some systems characterized by mechanisms to block or constrict channels thereby triggering avulsion the fundamental advantage of an anabranching river is that by constructing a semi permanent system of multiple channels it can concentrate stream flow and maximize bed sediment transport work per unit area of the bed under conditions where there is little or no opportunity to increase gradient on the basis of stream energy sediment size and morphological characteristics six types of anabranching river are recognized types 1 3 are lower energy and types 4 6 are higher energy systems type 1 are cohesive sediment rivers commonly termed anastomosing with low w d ratio channels that exhibit little or no lateral migration they are divisible into three subtypes based on vegetative and sedimentary environment type 2 are sand dominated island forming rivers and type 3 are mixed load laterally active meandering rivers type 4 are sand dominated ridge forming rivers characterized by long parallel channel dividing ridges type 5 are gravel dominated laterally active systems that interface between meandering and braiding in mountainous regions type 6 are gravel dominated stable systems that occur as non migrating channels in small relatively steep basins anabranching rivers represent a relatively uncommon but widespread and distinctive group that because of particular sedimentary energy gradient and other hydraulic conditions operate most effectively as a system of multiple channels separated by vegetated floodplain islands or alluvial ridges

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

sedimentation under deep sea storms fast currents high concentrations of suspended sediment and grooved mud beds are associated with erosion in frequent abyssal storms where a fast deep mean flow is augmented or reversed by intense intermittent currents this occurs about 5 km below the gulf stream or its rings the waning phase of a storm results in development of bedforms and rapid deposition of a mud blanket several other regions of the world ocean display evidence of abyssal storm activity

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

latest quaternary north pacific surface water responses imply atmosphere driven climate instability a full sequence of brief interstadials dansgaard oeschger d o cycles are recorded from 60 to 25 ka in santa barbara basin california ocean drilling program hole 893a by planktonic foraminiferal isotopic and assemblage changes at unparalleled high resolution for the oceans synchronous climatic response between north pacific surface waters and the greenland ice sheet during d o cycling is strongly indicated by remarkable similarities in speed magnitude and character of rapid oceanic and atmospheric reorganizations inferred sea surface temperature warmings of as much as 5 c within a few decades and brief warming overshoots of as much as 3 c suggest involvement of an atmospheric amplification top down in situ atmospheric warming of the ocean is implied by differential responses partial decoupling in the changes recorded in surface and thermoclinal waters

structure of the penultimate deglaciation along the california margin and implications for milankovitch theory the detailed structure and timing of the penultimate deglaciation are insufficiently defined yet critical for understanding mechanisms responsible for abrupt climate change here we present oxygen isotope records from planktonic and benthic foraminifera at unprecedented resolution encompassing late marine oxygen isotope stage mis 6 and termination ii ca 150 120 ka from the santa barbara basin supported by additional southern california margin records a region highly sensitive to millennial scale climate oscillations during the last deglaciation these records reveal millennial and centennial scale climate variability throughout the interval including an interstadial immediately preceding the deglaciation a brief warm event near the beginning of termination ii and a bolling allerod younger dryas like climate oscillation midway through the deglaciation recognition of these events in an oxygen isotope record from a 230th dated stalagmite allows the adoption of this radiometric chronology for the california margin records this chronology supports the milankovitch theory of deglaciation the suborbital history of climate variability during termination ii may account for records of early deglaciation

vegetation response to southern california drought during the medieval climate anomaly and early little ice age ad 800 1600 abstract high resolution studies of pollen in laminated sediments deposited in santa barbara basin sbb core spr0901 02kc reflect decadal scale fluctuations in precipitation spanning the interval from ad 800 1600 from ad 800 1090 during the medieval climate anomaly mca sbb sediments were dominated by xeric vegetation types drought resistant coastal sagebrush and chaparral implying reduced precipitation in the southern california region drought adapted vegetation abruptly decreased at ad 1090 and was rapidly replaced by mesic oak quercus woodlands associated with an increased pollen flux into the basin after a mesic interval lasting 100 years pollen flux and the relative abundance of quercus pollen dropped abruptly at ad 1200 when the rapid rise of chaparral suggests a significant drought similar to that of the mca ad 800 1090 this brief resurgence of drought adapted vegetation between ad 1200 1270 marked the end of the mca droughts a gradual increase in mesic vegetation followed characterizing cool hydroclimates of the little ice age lia in coastal southern california the presence of xeric vegetation in sbb coincides with major drought events recorded in tree rings and low lake levels elsewhere in california except for the brief drought between ad 1130 1160 correlative diatom and terrigenous sediment input proxy records from sbb are largely supportive of the pollen record predominantly linking the mca with drought and la nina like conditions and the lia with wetter more el nino like conditions differences between paleoclimate proxies pollen diatoms and terrigenous sediment in sbb exist however possibly reflecting the temporal and spatial differences in the generation of each proxy record as well as their individual sensitivity to climate change

water mass conversion in the glacial subarctic pacific 54 n 148 w physical constraints and the benthic planktonic stable isotope record benthic uvigerina spp cibicidoides spp gyroidinoides spp and planktonic n pachyderma sinistral g bulloides stable isotope records from three core sites in the central gulf of alaska are used to infer mixed layer and deepwater properties of the late glacial subarctic pacific glacial interglacial amplitudes of the planktonic 18o records are 1 1 1 3 less than half the amplitude observed at core sites at similar latitudes in the north atlantic these data imply that a strong negative w anomaly existed in the glacial subarctic mixed layer during the summer which points to a much stronger low salinity anomaly than exists today if true the upper water column in the north pacific would have been statically more stable than today thus suppressing convection even more efficiently this scenario is further supported by vertical i e planktic versus benthic 18o and 13c gradients of 1 which suggest that a thermohaline link between pacific deep waters and the subarctic pacific mixed layer did not exist during the late glacial epibenthic 13c in the subarctic pacific is more negative than at tropical subtropical pacific sites but similar to that recorded at southern ocean sites suggesting ventilation of the deep central pacific from mid latitude sources e g from the sea of japan and sea of okhotsk still convection to intermediate depths could have occurred in the subarctic during the winter months when heat loss to the atmosphere sea ice formation and wind driven upwelling of saline deep waters would have been most intense this would be beyond the grasp of our planktonic records which only document mixed layer temperature salinity fields extant during the warmer seasons also we do not have benthic isotope records from true intermediate water depths of the subarctic pacific

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

milankovitch forcing of the last interglacial sea level during the last interglacial sea level was as high as present 4000 to 6000 years before peak northern hemisphere insolation receipt 126 000 years ago the sea level results are shown to be consistent with climate models which simulate a 3 to 4 c july temperature increase from 140 000 to 130 000 years ago in high latitudes with all northern hemisphere land areas being warmer than present by 130 000 years ago the early warming occurs because obliquity peaked earlier than precession and because precession values were greater than present before peak precessional forcing occurred these results indicate that a fuller understanding of the milankovitch climate connection requires consideration of fields other than just insolation forcing at 65 n

residual ages of modern sediments in an hyperarid region israel modern sediments from a variety of depositional environments in the hyperarid southern arava region israel were analyzed for their residual equivalent dose d colluvial and uvial sediments from drainage systems of di erent sizes and parent materials were collected and alkali feldspars were measured using the single aliquot additive dose protocol all samples showed a large scatter in the d s for most types of the sediments the average d is between 2 and 11 gy equivalent to residual ages of 1 5 ka the lowest d is usually in the range of 0 1 4 gy con rming that the single aliquot protocol can identify the best bleached grains newly weathered material from active channels gave the largest d s of up to 30 gy reworked uvial sediments derived from terraces and fans gave progressively smaller d s with increasing level of recycling the degree of bleaching of colluvial sediments strongly depends on the face of the slope the high d s and the large scatter result from the mode of sediment transport brief rain episodes result in ash oods where large volumes of sediment are transported over short distances and only a small part of the sediment is exposed at any time to the sun only repeated cycles of transportation can homogenize the sediment and fully expose all its particles to the sun single grain or small aliquot protocols can overcome the high and variable residual d values and enable better dating of sediments in hyperarid environments 2000 elsevier science ltd all rights reserved

high resolution climate records from the north atlantic during the last interglacial the two deep ice cores recovered by the grip1 and gisp22 projects at summit greenland agree in detail over the past 100 000 years3 and demonstrate dramatic climate variability in the north atlantic region during the last glacial before the current period of holocene stability this glacial climate instability has subsequently been documented in the marine sedimentary record of surface ocean conditions in the north atlantic4 before 100 kyr ago the two ice core records are discrepant however casting doubt on whether the oxygen isotope fluctuations during the last interglacial eemian seen in the grip core1 5 represent a true climate signal here we present high resolution records of foraminiferal assemblages and ice rafted detritus from two north atlantic cores for the interval 65 kyr to 135 kyr ago extending the surface ocean record back to the eemian the correlation between our records and the greenland ice core records is good throughout the period in which the two ice cores agree suggesting a regionally coherent climate response during the eemian our marine records show a more stable climate than that implied by the grip ice core suggesting that localized phenomena may be responsible for the variability in the latter record during the eemian

precambrian basement complexes in the north central scandinavian caledonides and their pre caledonian tectonic evolution precambrian basement lithology as exposed in four tectonic windows of the northcentral scandinavian caledonides comprises uniform sequences of metasedimentary mica schists and gneisses borgefjell as well as mica schists dominated by acid metavolcanics bangonaive with minor basic rocks the major part however is made up of intrusive rocks older granites are distributed in the borgefjell area and to the east of it obviously related to the svecofennian revsund granites younger granodiorites quartzsyenites subordinate in the borgefjellet dominate the bangonaive window

late holocene upper bounds of flood magnitudes and twentieth century large floods in the ungauged hyperarid alluvial nahal arava israel abstract the impact of large twentieth century floods on the riparian vegetation and channel morphology of the relatively wide anabranching and braided nahal arava southern israel was documented as part of developing tools to a identify recent large floods b determine these flood s respective magnitudes in alluvial ungauged streams and c determine long term upper bounds to flood stages and magnitudes along most of its course nahal paran a major tributary that impacts the morphology floods and sediments of nahal arava at the study reach is a coarse gravel braided ephemeral stream downstream of the arava paran confluence aeolian and fluvial sand delivered from eastern arava valley alters the channel morphology the sand has accreted up to 2 5 m above the distinct current channels facilitating the recording of large floods this sand enhances the establishment of denser riparian vegetation mainly tamarix nilotica and haloxylon persicum that interacts with floods and affects stream morphology a temporal association was found between specific floods recorded upstream and tree ring ages of re growth of flood damaged tamarix trees sigafoos trees in the past 30 years this association can be utilized for developing a twentieth century flood chronology in hyperarid ungauged basins in the region the minimum magnitude of the largest flood that covered the entire channel width estimated from flood deposits is approximately 1700 1800 m 3 s 1 this is a larger magnitude than the largest gauged flood of 1150 m 3 s 1 that occurred in 1970 about 30 km upstream in nahal paran our estimation agrees with flood magnitude estimated from the regional envelope curve of the largest floods based on holocene alluvial stratigraphy and osl dating in the study reach we also conclude that flood stages did not reach the late holocene 2 2 ka surface and therefore we estimate a non exceedance upper bound of 2000 m 3 s 1 flood magnitudes for nahal arava during that interval this study indicates that in unfavorable areas the combination of hydrology fluvial morphology and botanic evidence can increase our understanding of ungauged basins and give information crucial for hydrology planning

ecogeomorphology in the australian drylands and the role of biota in mediating the effects of climate change on landscape processes and evolution

stages and rate of the gravel shattering process by salts in desert reg soils abstract gravel shattering by salts is a common process in gravelly young to mature desert reg soils the shattered gravel is found on the surface and in the b and c horizons down to a maximum depth of 50 cm field studies on the process of salt weathering in deserts are scarce therefore the objectives of this study are to present the stages of development of the gravel shattering process by salts in desert reg soils and to discuss factors influencing the rate of development under natural conditions prevailing in the negev desert the studied reg soils were developed on two alluvial fan chronosequences in the negev desert the fan of nahal ze elim and the fan of nahal shehoret the development of the shattering process can be divided into five stages a e based on chemical physical and micromorphological features of the reg soils stages a d very young yo young reg soils represent the early holocene to the present some 14 000 years salinity values are between 0 27 16 mmho cm and the percentage of the shattered gravel is between 20 and 70 the shattered gravel however still maintains its original shape stage e mature reg soil represents the middle pleistocene to early holocene or 500 000 years salinity values at this stage reach 62 mmho cm although part of the gravel does not keep its original shape and starts to disperse in the profile the percentage of shattered gravel is only 75 80 it was found that the process of salt shattering in reg soils does not depend on concentrations or mineralogy of the salts but on the micro environmental conditions of the soil profile the process requires extreme and rapid variations of temperatures and moisture conditions such as found close to the soil surface to cause salt crystallization in a confined system with time the sealing of the soil surface through the development of desert pavement and a gravel free b horizon results in a change in the soil micro environment this change impedes the process irrespective of the amounts concentrations and types of salt minerals which exist in the profile the fact that in extreme arid regions the gravel shattering process develops primarily close to the reg soil surface suggests that it can be used to identify buried reg soils and to reconstruct climatic and micro environmental conditions of paleosols

δ18o of atmospheric oxygen measured on the grip ice core document stratigraphic disturbances in the lowest 10 of the core 18 o measured on oxygen in the bubble air from ice cores is a proxy for continental ice volume and is used to synchronize cores from greenland and antarctica a record measured on ice samples from the central greenland deep ice core grip spanning the last glacial maximum and the holocene shows that 18 o of atmospheric oxygen lags 18 o of ice by about 4000 to 1000 years the smooth isotope record of atmospheric oxygen shows a steady ice sheet decay beginning around 18 000 years bp taking the time lag into account however measurements performed on ice from the grip core older than 100 kyrs do not correlate with the corresponding vostok record and show transitions too fast to be typical for ice sheet build up or decay furthermore the expected time lag between 18 o atm and 18 o of seawater or 18 o of ice is absent or has even turned into a lead climatic interpretation of the fast 18 o ice transitions is not consistent with our 18 o atm results the stratigraphy is possibly irregular and if so this stops us from constructing a steady age depth relation in the deepest part of the grip ice core

brief interstadial events in the santa barbara basin ne pacific during the past 60 kyr the instability of the northern hemisphere glacial climate over the past 100 kyr has been revealed by at least 20 brief warm interstadial episodes called dansgaard oeschger events recorded in greenland ice cores1 3 and in north atlantic sedimentary records4 5 a few of these events have been recognized elsewhere6 8 here we describe a record of ocean oxygenation and circulation from the santa barbara basin in the northeast pacific ocean which correlates well with the greenland ice core records we see 19 of the 20 dansgaard oeschger events in the form of laminated sediments deposited under anoxic conditions and we can correlate at least 16 of these with the 17 ice core interstadials of the past 60 kyr thus these short term events were not restricted to the north atlantic region the events had substantial ecological and oceanographic effects in the santa barbara basin including changes in benthic faunal populations and in the age and composition of bottom waters similar ventilation changes have been seen in the gulf of california9 10 suggesting that these changes may have been widespread and synchronous along the northeast pacific margin these results suggest sensitivity of broad areas of the ocean atmosphere cryosphere system to short term climate change

a late pleistocene linear dune dam record of aeolian fluvial dynamics at the fringes of the northwestern negev dunefield abstract a late pleistocene aeolian fluvial record within a rare vegetated linear dune like structure at the fringe of the northwestern negev dunefield israel provides direct evidence of dune damming dynamics within the structure and its environs study methods included high resolution morphology and stratigraphy micromorphology and sedimentological analyses chronology was based on eight archaeological sites from the structure and the inqua dune atlas chronologic database low energy fine grained fluvial deposits underlying the structure and extending from its flanks indicate deposition by low energy hyper concentrated flows in a floodplain environment and later in water bodies that formed by dune damming of a mid sized drainage basin interbedded sand with fine grained deposits within the linear structure indicates interchanging dominances between aeolian sand incursion and seasonal floods sand deposition during dune elongation led to structure growth and dune damming of its drainage system that in turn formed water bodies and upstream fine grained deposition following seasonal floods calculations of current sediment yields indicate that fine grained deposits accretion up to the structure s brim could possibly have rapidly occurred over a total time span of decades however artifacts dating to the geometric kebaran 17 5 12 9 cal kyr bp and harifian 12 9 11 2 cal kyr bp archaeological periods on the structure s surface indicates intermittent repetitive and short term camping utilizing adjacent water bodies over a time period of 4000 5000 years fluctuating high winds and precipitation during a time window of increased fluvial availability of fine grained sediment from the hinterland generated ample fine grained deposition after 11 cal kyr bp the abundance and recurrence of dammed water bodies decreased when reduced wind power constrained dune dam maintenance after sediment accommodation space dissipated fluvial flow of the drainage basin led to dune dam destruction and partial fluvial erosion of the fine grained deposits that continues today

seasonal and interannual variation in santa barbara basin water temperatures observed in sediment trap foraminiferal mg ca 1 we have generated a santa barbara basin sediment trap mg ca record to evaluate culture based calibration equations for the temperate subpolar planktonic foraminiferal species globigerina bulloides and neogloboquadrina pachyderma dextral g bulloides and n pachyderma mg ca are significantly correlated with seasonal variations in temperature of the near surface and subthermocline depths respectively the average deviation between mg based and 18o based temperature estimates is 0 6 c for g bulloides and 0 8 c for n pachyderma differences between mg derived temperatures and instrumental temperatures may be due to cleaning methods environmental factors such as seasonal variations in foraminiferal depth habitats or possible secondary effects on mg ca core top mg ca of both g bulloides and n pachyderma is in excellent agreement with average values from the sediment trap lending strong support for the interpretation of downcore mg ca from these species as annual average near surface and thermoclinal temperatures

deformation of the baltic continental crust during caledonide intracontinental subduction views from seismic reflection data deep seismic profiling in norway and sweden provides documentation of the amount and style of deformation of the baltic crust in response to caledonian intracontinental subduction the seismic data demonstrate that the preserved caledonide allochthon in central scandinavia is 15 to 20 km thick considerably greater than the 2 to 5 km predicted from surface geologic data much of the thickness of allochthonous rocks results from imbrication of the baltic basement within a thin skinned style thrust complex seismic data across the skardora antiform one of the basement windows in the central caledonides indicate that the window represents an antiformal stack of thrust sheets involving basement and cover rocks these data suggest that many of the basement windows in the scandinavian caledonides may result from similar thrust culminations and that the basement windows do not expose autochthonous baltic basement documentation of the response of the baltic crust during intracontinental subduction provides new constraints on reconstructions of the scandinavian caledonides and insights into the style of deformation occurring in other collisional orogens

accumulation rates of th 230 pa 231 and some transition metals on the bermuda rise abstract measurements of 238u 234u 230th 232th 231pa mn fe co ni cu and zn were made on 23 samples from core gpc 5 a 29 m giant piston core from a water depth of 4583 m on the northeastern bermuda rise 33 41 2 n 57 36 9 w this area is characterized by rapid deposition of sediment transported by abyssal currents unsupported 230th and 231pa are present throughout the core but because of large variations in the sedimentation rate show marked departures from exponential decay with depth the trend with depth of the 231 pa ex 230 th ex ratio is consistent with the average accumulation rate of 36 cm 1000 y reported earlier on the basis of radiocarbon dating and caco3 stratigraphy when expressed on a carbonate free basis concentrations of mn co ni cu zn 230thex and 231paex all show cyclic variations positively correlated with those of caco3 the correlations can be explained by a model in which all of these constituents including caco3 are supplied to the sediments from the water column at a constant rate concentration variations are controlled mainly by varying inputs of terrigenous detritus with low inputs occurring during interglacials and high inputs during glacials relationships between the metal and 230thex concentrations permit estimates of the rates at which the metals are removed to the sediment by scavenging from the water column the results in g cm2 1000 y are 4300 1100 for mn 46 16 for ni and 76 26 for cu these rates are somewhat larger than ocean wide averages estimated by other methods and the absolute rate of 230th accumulation in gpc 5 averages about nine times higher than production in the overlying water column this part of the bermuda rise and similar bottom current deposits may act as important accumulators of elements scavenged from seawater

global ice volume fluctuations north atlantic ice rafting events and deep ocean circulation changes between 130 and 70 ka multiproxy data from north atlantic deep sea sediment core neap18k provide a detailed record of climate through oxygen isotope stage ois 5 seven distinct large scale episodes of ice rafting c25 c19 were identified between 126 and 70 ka global ice volume reconstructions based on high resolution benthic 18 o records indicate that major ice rafting events were not confined to ice volume maxima at ois 5d and 5b but also occurred during periods of ice sheet growth and disintegration however iceberg discharges were restricted to times when sea levels were 40 65 m below present values ice rafting episode c25 the first large scale cooling of mid atlantic surface waters after the last interglacial occurred during the gradual buildup of continental ice sheets at the ois 5e 5d transition major ice sheet collapses allied to ice rafting events c24 and c21 were associated with rapid sea level increases of 20 and 40 m respectively suborbital climatic fluctuations in the neap18k sedimentary record denoted by prominent 7 5 4 5 and 3 k y cyclicities appear to correlate with both greenland atmospheric temperatures and changes in thermohaline circulation patterns inferred from benthic 13 c values and hence provide clear evidence of a highly interconnected north atlantic climatic regime during ois 5

increased northeast pacific climatic variability during the warm middle holocene 1 we use a pair of decadally resolved planktonic foraminiferal 18o records from santa barbara basin sbb to show that the warmest interval of the current interglacial the middle holocene was characterized by increased decadal to centennial scale climatic variability modern relationships between the pacific decadal oscillation pdo the el nino southern oscillation enso and upper water conditions in sbb also suggest a preference of the northeast ne pacific climate during the warm mid holocene toward the warm phase of the pdo and more intense enso warm events el ninos in the context of future climate this study suggests increasing decadal to centennial scale climatic variability in a globally warmed world

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

variability in vertical distributions of planktonic foraminifera in the california current relationships to vertical ocean structure 1 geochemical records from planktonic foraminifera are among the few means available to infer past changes in the upper ocean although interpretations can be confounded by variability in foraminifera habitat depths the principal environmental factors affecting foraminiferal vertical distributions were examined through 28 vertically stratified plankton tows taken off southern california in winter spring and summer each species has a dynamic range of preferred habitat depth from the mixed layer to the thermocline characterized by a unique relationship with environmental properties globigerina bulloides neogloboquadrina pachyderma dextral and neogloboquadrina dutertrei can live near the surface but frequently live deeper as stratification increases and a particular isotherm deepens globigerinoides ruber and orbulina universa vary more closely with the depth of the thermocline than the depth of a given isotherm the shifts in habitat depth are of sufficient magnitude to affect 18o records the effects of such shifts are observed for g bulloides and n pachyderma in santa barbara basin sediments geochemical signatures from multiple species of foraminifera each with a different predicted response to environmental change can permit the detection of changes in habitat depth of a given species and thus more accurately indicate past changes in hydrographic structure

optical dating of holocene sediments from a variety of geomorphic settings using single grains of quartz this paper presents an improved method for the optical dating of holocene sediments from a variety of geomorphic settings we have measured the equivalent dose de in individual grains of quartz using green laser light for optical stimulation and have simulated the de distributions for multiple grain synthetic aliquots using the single grain data for 12 samples of known independent age we show that application of a minimum age model to the single grain and small 10 grain aliquot de data provides the most accurate estimate of the burial dose for nine of the samples examined 3 aeolian 5 fluvial and 1 marine the weighted mean de as obtained using the central age model gives rise to burial age overestimates of up to a factor of 10 for these nine samples whether single grains small aliquots or large 100 grain aliquots are used for the other three samples two aeolian and one fluvial application of either the minimum age model or the central age model to the single grain small aliquot and large aliquot de data yields burial ages in accord with the independent age control we infer that these three samples were well bleached at the time of deposition these results show that heterogeneous bleaching of the optical dating signal is commonplace in nature and that aeolian transport offers no guarantee that the sample will be well bleached at the time of deposition we also show that grains sensitive to infrared ir stimulation can give rise to low de values which will result in significant underestimation of the burial dose and hence of the age of deposition we demonstrate that use of a modified single aliquot regenerative dose protocol incorporating ir stimulation prior to green light stimulation deals effectively with contamination by ir sensitive grains we conclude that application of the modified protocol to single grains or small aliquots of quartz using the lowest de population to estimate the burial dose is the best means of obtaining reliable ages for holocene sediments from a wide range of depositional environments d 2003 elsevier b v all rights reserved

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

chilean and southeast pacific paleoclimate variations during the last glacial cycle directly correlated pollen and δ18o records from odp site 1234 abstract joint pollen and oxygen isotope data from ocean drilling program site 1234 in the southeast pacific provide the first continuous record of temperate south american vegetation and climate from the last 140 ka located at 36 s 65 km offshore of concepcion chile site 1234 monitors the climatic transition zone between northern semi arid summer dry winter wet climate and southern year round rainy cool temperate climate dominance of onshore winds suggests that pollen preserved here reflects transport to the ocean via rivers that drain the region and integrate conditions from the coastal mountains to the andean foothills down hole changes in diagnostic pollen assemblages from xeric lowland deciduous forest characterized by grasses herbs ferns and trees such as deciduous beech nothofagus obliqua mesic valdivian evergreen forest including conifers such as the endangered prumnopitys andina and subantarctic evergreen rainforest comprised primarily of southern beech n dombeyi reveal large rapid shifts that likely reflect latitudinal movements in atmospheric circulation and storm tracks associated with the southern westerly winds during glacial intervals mis 2 4 and 6 rainforests and parkland dominated by nothofagus moved northward into the region at the mis 6 5e transition coeval with the rapid shift to lower isotopic values rainforest vegetation was rapidly replaced by xeric plant communities associated with mediterranean type climate an increased prominence of halophytic vegetation suggests that mis 5e was more arid and possibly warmer than mis 1 although rainforest pollen rises again at the end of mis 5e lowland deciduous forest pollen persists through mis 5d and 5c into mis 5b substantial millennial scale variations occur in both interglacial and glacial regimes attesting to the sensitivity of the southern westerly belt to climate change comparison of the cool mesic n dombeyi rainforest assemblage from site 1234 with 18 o in the byrd ice core shows that on time scales longer than 10 ka cool moist conditions in central chile were coherent with and occurred in phase with antarctic cooling this is also likely at millennial scales although rainforest pollen lags antarctic cooling with exponential response times of about 1000 years which plausibly reflects the ecological response time to regional climate change

nitrogen isotope variations in santa barbara basin sediments implications for denitrification in the eastern tropical north pacific during the last 50 000 years nitrogen isotope variations preserved in santa barbara basin sediments are used to evaluate changes in denitrification in the eastern tropical north pacific etnp during the last 50 000 years a significant component of the subsurface waters 100 400 m that presently fill the santa barbara basin is derived from the low oxygen denitrifying zone in the etnp and the nitrate in these waters has a 15n value of 8 9 during the last glacial the 15n values of santa barbara basin sediments were typically 6 7 indicating decreased denitrification in the etnp and a better oxygenated intermediate water mass in the santa barbara basin at this time this reduced denitrification during the last glacial would have increased the pool of fixed nitrogen and may have contributed to the higher productivity previously reported for various regions of the global ocean during this period at the onset of deglaciation sediment 15n values increase by more than 2 indicating increased denitrification in the etnp during younger dryas time 15n values decreased by 3 and record a brief return to better ventilated conditions in the subsurface waters of the etnp this is followed by an increase in 15n to over 9 at 10 000 years ago indicating intense denitrification at the beginning of the holocene

duration and structure of the past four interglaciations reanalysis and additional dating of the devils hole 18o paleotemperature record confirm that the last interglaciation in the great basin the continental analog of marine isotopic substage 5e lasted 22 000 yr consistent with the vostok paleotemperature record which suggests a duration of 19 000 yr for this event in antarctica the three preceding interglaciations in the devils hole record analogs of marine isotopic substages 7e 9c and 11c range from 20 000 to 26 000 yr in duration a 20 000 yr duration for the last interglaciation is consistent with tims uranium series dated sea level high stands thus the widely held view that interglaciations were of 11 000 to 13 000 yr duration and constituted only about 10 of mid to late pleistocene climatic cycles needs reexamination the warmest portion of each interglaciation in the devils hole time series is marked by a 18o plateau signifying apparent climatic stability for periods of 10 000 to 15 000 yr duration

climate variability in northwest greece during the last interglacial isotopic and palynological data over the period 115 000 to 135 000 years ago from a lacustrine sequence in northwest greece show distinct oscillations during the intervals leading into and out of the full interglacial whereas in between changes were less pronounced but included a brief fluctuation after peak interglacial conditions temperatures decreased and precipitation increased in a series of steps these data suggest that eemian climate variability was similar to that of the holocene both in terms of amplitude and possibly of pacing

biotic response to late quaternary rapid climate switches in santa barbara basin ecological and evolutionary implications benthic foraminiferal assemblages from santa barbara basin exhibit major faunal and ecological switches associated with late quaternary millennial to decadal scale global climate oscillations repeated turnovers of entire faunas occurred rapidly 40 400 yr without extinction or speciation in conjunction with dansgaard oeschger shifts in thermohaline circulation ventilation and climate confirming evolutionary model predictions of roy et al consistent faunal successions of dysoxic taxa during successive interstadials reflect the extreme sensitivity and adaptation of the benthic ecosystem to the rapid environmental changes that marked the late quaternary and possibly other transitional intervals in the history of the earth s ocean atmosphere cryosphere system these data support the hypothesis that broad segments of the biosphere are well adapted to rapid climate change

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

marine core evidence for reduced deep water production during termination ii followed by a relatively stable substage 5e eemian we present oxygen and carbon isotope records of benthic foraminifera from the glacial stage 6 through interglacial substage 5e eemian sections of several cores from the subpolar north atlantic the cores range in water depth from 1451 to 2658 m in one core we generated estimates of sea surface temperature sst and of ice rafted detritus ird delivery for all of stage 5 we reconstruct bathymeric profiles of 13c for stage 6 termination ii and three time slices of substage 5e the 13c profiles indicate that local deep water geometry during stage 6 was similar to that of the last glaciation with glacial north atlantic intermediate water gnaiw overlying deeper waters partially of southern origin an anomalously large peak in ird coupled with planktonic 18o evidence for iceberg melting immediately precedes termination ii and is otherwise similar to stage 2 and 3 heinrich events during the termination low 13c values are observed in cores near and above 2 km providing evidence of reduced gnaiw production in association with deglacial melting in the shallowest cores low 13c values persist into early substage 5e indicating that the southward retreat of southern source waters was not completed until well after the beginning of the substage in contrast to termination i ssts remained cold until the end of the deglaciation this may be why there is little evidence from marine and terrestrial sequences for a pronounced climate reversal on termination ii despite what is now clear evidence of a significant reduction in ocean ventilation the faunal data suggest that ssts during early 5e were about 7 c warmer than during the glaciation sst rose several degrees from early to middle substage 5e peaked in middle substage 5e at about 10 c above glacial values and then gradually declined by about 5 c these changes were linked to variations in water mass configuration as interpreted from benthic 13c evidence most of the evidence suggests that oscillations superimposed on the gradual sst trend were 1 2 c in contrast to the larger sst changes 3 4 c documented for substage 5d

devonian orogen parallel opposed extension in the central norwegian caledonides comment and reply braathen et al 2000 1 described early to middle devonian extensional faults around the central norway basement window one of many tectonic windows exposing basement in the scandinavian caledonides here these basement rocks are called tectonic window basement extension was orogen parallel

mesoproterozoic dyke swarms in foreland and nappes of the central scandinavian caledonides structure magnetic fabric and geochemistry as an example of microstructural and magnetic fabric evolution and geochemistry of mafic dykes during a subsequent orogenic overprint a major mesoproterozoic dyke complex in scandinavia the vasterbotten complex of the central scandinavian dolerite group is traced westwards into the crystalline nappes of the early phanerozoic caledonian orogen using geophysical field microscopic magnetic and geochemical information dykes and sills are characterized and their overprint during caledonian orogeny documented the vasterbotten complex is composed of sets of dykes trending ne sw nw se and wnw ese respectively similar dykes are exposed in allochthonous positions lower and middle allochthons in the caledonian fold and thrust belt the autochthonous dykes are generally undeformed and retain both their primary texture and mineralogy chilled margins are well preserved in the caledonian lower and middle allochthons similar dykes in crystalline basement rocks are progressively faulted and sheared when proceeding from the marginal to the interior parts of the orogen dyke margins are more likely to be sheared than the interior parts of dykes in the lower allochthon under very low and low grade metamorphic conditions dykes are distinctly less competent than granitic host rocks thick dykes are more competent than gneisses thin dykes do not show such competence contrasts in the middle allochthon metre scale dykes with patches of altered plagioclase phenocrysts can still be discerned in low strain domains highly sheared dykes are drawn out to thin layers of centimetre thickness dykes are deformed together with the crystalline country rocks under greenschist grade metamorphic conditions without major competence contrasts magnetic fabrics show an evolution similar to the silicate mineral fabrics the magnetic fabrics in the dykes are transformed successively from ferromagnetic magmatic in the autochthon to ferromagnetic deformational in the lower allochthon and finally paramagnetic deformational in the middle allochthon as a consequence the magnetic susceptibility decreases for several orders of magnitude geochemically the dykes are dominantly sub alkaline basalts typical for continental tholeiites and can be distinguished from the neoproterozoic dykes in the sarv nappe equivalents highest part of the middle allochthon which show a more morb like e morb magmatic signature preliminary age information from a dyke in the lower allochthon of the borgefjell area and the middle allochthon is consistent with the assumption that these dykes are time equivalent with the central scandinavian dolerite group therefore the studied dykes may represent an extension of the vasterbotten complex or a new complex of the central scandinavian dolerite group according to section restorations the caledonian allochthons were situated further wnw relative to their present position and originally the mafic dykes cut across all of the fennoscandian lithosphere at least to the present atlantic margin and the earlier passive margin of the baltica terrane as a consequence these dykes may provide a link for pre caledonian and pre grenvillian plate reconstructions

direct u th dating of marine sediments from the two most recent interglacial periods a knowledge of the age of marine sediments is necessary to determine the timing of events and rates of processes in the marine realm and the relationships among marine and other climatically sensitive records the establishment of an accurate chronology for pleistocene marine sediments beyond the range of radiocarbon dating approximately the past 45 kyr has therefore been a goal of palaeoceanographers for decades early attempts1 2 based on measurements of the radionuclides 230th and 231pa were beset with problems and subsequent studies focused on tying fluctuations in marine sediment oxygen isotope records to events such as the formation of coral reef terraces and changes in the earth s magnetic polarity3 4 and tuning the resultant chronologies to the earth s orbitally driven insolation variations5 8 but these chronologies especially the age and duration of the last interglacial period have been challenged by several studies9 12 raising questions about the fundamental cause of pleistocene climate fluctuations here we report the direct u th dating of aragonite rich marine sediments from the bahamas and present an accurately dated marine oxygen isotope record for the last two interglacials we obtain dates of 120 127 kyr bp for the last interglacial and 189 190 kyr bp for the late stage 7 interglacial these dates are in accord with the general theory of orbitally forced climate fluctuations and demonstrate the potential of our direct dating approach for developing an absolute chronology for the pleistocene marine oxygen isotope record

modern alluvial history of the paria rver drainage basin southern utah abstract stream channels in the paria river basin were eroded and partially refilled between 1883 and 1980 basin wide erosion began in 1883 channels were fully entrenched and widened by 1890 this erosion occurred during the well documented period of arroyo cutting in the southwest photographs of the paria river channel taken between 1918 and 1940 show that the channel did not have a floodplain and remained wide and deep until the early 1940s a thin bar

rapid fluctuations in sea level recorded at huon peninsula during the penultimate deglaciation about 140 000 years ago the breakup of large continental ice sheets initiated the last interglacial period sea level rose and peaked around 135 000 years ago about 14 meters below present levels a record of last interglacial sea levels between 116 000 years to 136 000 years ago is preserved at reef vii of the uplifted coral terraces of huon peninsula in papua new guinea however corals from a cave situated about 90 meters below the crest of reef vii are 130 000 2000 years old and appear to have grown in conditions that were 6 c cooler than those at present these observations imply a drop in sea level of 60 to 80 meters after 130 000 years sea level began rising again in response to the major insolation maximum at 126 000 to 128 000 years ago the early about 140 000 years ago start of the penultimate deglaciation well before the peak in insolation is consistent with the devils hole chronology

dating floodplain sediments using tree ring response to burial floodplain sediments can be dated precisely based on the change in anatomy of tree rings upon burial when a stem of tamarisk tamarix ramosissima or sandbar willow salix exigua is buried subsequent annual rings in the buried section resemble the rings of roots rings become narrower vessels within the rings become larger and transitions between rings become less distinct we combined observations of these changes with tree ring counts to determine the year of deposition of sedimentary beds exposed in a 150 m long trench across the floodplain of the rio puerco a rapidly filling arroyo in new mexico this method reliably dated most beds thicker than about 30 cm to within a year of deposition floodplain aggradation rates varied dramatically through time and space sediment deposition was mostly limited to brief overbank flows occurring every few years the most rapid deposition occurred on channel margin levees which migrated laterally during channel narrowing at the decadal timescale the cross section average sediment deposition rate was steady but there was a shift in the spatial pattern of deposition in the 1980s from 1936 to 1986 sediment deposition occurred by channel narrowing with little change in elevation of the thalweg after 1986 sediment deposition occurred by vertical aggradation from 1936 to 2000 about 27 per cent of the arroyo cross section filled with sediment the rate of filling from 1962 to 2000 was 0 8 vertical m decade or 85 m2 decade published in 2005 by john wiley sons ltd

collapse of the california current during glacial maxima linked to climate change on land time series of alkenone unsaturation indices gathered along the california margin reveal large 4 to 8 c glacial interglacial changes in sea surface temperature sst over the past 550 000 years interglacial times with ssts equal to or exceeding that of the holocene contain peak abundances in the pollen of redwood the distinctive component of the temperate rainforest of the northwest coast of california in the region now dominated by the california current ssts warmed 10 000 to 15 000 years in advance of deglaciation at each of the past five glacial maxima ssts did not rise in advance of deglaciation south of the modern california current front glacial warming along the california margin therefore is a regional signal of the weakening of the california current during times when large ice sheets reorganized wind systems over the north pacific both the timing and magnitude of the sst estimates suggest that the devils hole nevada calcite record represents regional but not global paleotemperatures and hence does not pose a fundamental challenge to the orbital milankovitch theory of the ice ages

polyorogenic 40 ar 39 ar mineral age record in the seve and koli nappes of the gaddede area northwestern jamtland central scandinavian caledonides in the scandinavian caledonides eugeoclinal terranes represented in the koli nappes were thrust 500 km onto the baltoscandian platform during the early to middle paleozoic immediately underlying thrust sheets of the seve nappe complex are suspected to have been derived from the outer margin of continent baltica contrasting tectonothermal histories are recorded in seve and koli nappes exposed in the gad dede area northern jamtland county sweden eclogite bearing seve rocks underwent an initial amphibolite grade regional metamorphism smi with different structural units experiencing contrasting high to intermediate pressure conditions subsequent ductile imbrication sm2 of high and intermediate pressure structural units occurred prior to 460 470 ma cooling through temperatures required for intracrystalline retention of argon in hornblende a later thermal overprint sm3 everywhere rejuvenated seve biotite and muscovite and locally hornblende argon systems at 430 pm 5 ma 40 ar 39 ar plate

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

distribution and sources of polycyclic aromatic hydrocarbons pahs in laminated santa barbara basin sediments abstract the santa barbara basin sbb preserves a high resolution sediment record that is varved down to ca 1700 ce and laminated for at least 2500 years the distributions of 25 polycyclic aromatic hydrocarbons pahs were investigated in a suite of samples from sediment cores representing different depositional scenarios varves laminae terrigenous flood layers and marine turbidites the concentrations of these pahs were determined using gas chromatography mass spectrometry in selected ion mode and evaluated in terms of their distributions diagnostic ratios and loadings recognized by principal component analysis pca two biogenic pahs perylene and retene provided the greatest variation in their downcore concentration values perylene concentrations increased downcore exhibiting markedly higher abundance in sediments older than 300 ce consistent with the interpretation that perylene is formed diagenetically in reducing sediments a modest increase in perylene concentrations in sediments from the late 1960s may be associated with flood derived transport of higher amounts of degraded terrestrial organic matter from fire denudated landscapes into the coastal environment the markedly higher concentrations of retene in flood layers and turbidites relative to varves laminae suggest that these lithologies are more effective in transporting pyrogenic pahs and can be interpreted as a proxy for wildfires in sbb changes in key diagnostic ratios reveal the shift from a dominance of petrogenic pahs in older sediments to a strong pyrogenic signal beginning in the latter half of the 20th century statistical analysis using pca of the pah distributions in the samples revealed that modern sediments showed a strong positive relationship with pc1 which represents the greatest variation among the samples whereas flood layers showed a strong relationship with the second major variable pc2 thus statistical approaches provide the capability to elucidate modern anthropogenic signatures within the complex pah distributions of sbb and also establish a pah profile that characterizes the lithological signature of flood layers

modern and last glacial maximum eolian sedimentation patterns in the atlantic ocean interpreted from sediment iron oxide content eolian dust derived from the desert regions of north africa is blown far into the tropical atlantic ocean by persistent easterly and northeasterly winds in this paper we demonstrate that the iron oxides hematite and goethite are a worthwhile addition to proxy monitors of eolian sedimentation in the tropical atlantic iron oxides are identified by diffuse reflectance spectrophotometry a technique capable of identifying these minerals in concentrations as low as 0 01 by weight we analyze samples from both the modern and last glacial maximum lgm synoptic levels from 178 sample locations yielding a total of 356 samples distributed throughout the atlantic ocean to determine the relative contribution of the iron oxides we factor analyzed the modern and lgm levels as a single data set the iron oxide factor explains about 25 of the variance in the combined core top and lgm data set mapped factor scores for the lgm and modern ocean indicate high iron oxide values are present in just two regions one off eastern north america and the other off northwest africa in the region off eastern north america iron oxide occurs primarily during the lgm as the previously noted brick red lutite a unique sediment type derived from the erosion of permo carboniferous red beds in atlantic canada a larger lobe shaped area of iron oxide rich sediment is present off northwest africa in both the modern and lgm levels the modern iron oxide lobe is coincident with the distribution of eolian dust as determined by observations from ships satellites and analysis of air samples during the lgm iron oxides exhibit a similar distribution except the southern margin of the region shifts equatorward and iron oxide concentration increases

rapid oscillations in western north america vegetation and climate during oxygen isotope stage 5 inferred from pollen data from santa barbara basin hole 893a abstract chronologically controlled high resolution 200 yr average sampling interval pollen data from a core in the santa barbara basin sbb provide evidence of millennial scale climate variability on the southern california coast from 70 to 140 ka b p the first climate event inferred from a brief reversal in the glacial interglacial shift from montane conifer to lowland oak assemblages occurred during the oxygen isotope stage ois 6 5 transition in ois 5e oak dominated assemblages imply conditions similar to or slightly warmer than present cooler conditions that gradually replaced the relatively stable warm mediterranean climate that continued across the ois 5e 5d transition ended abruptly just before the end of ois 5d warming inferred from oak expansion continued in ois 5c this lengthy cyclic sequence of high amplitude warming events which peaked below interglacial values extended into the first part of ois 5b similar oscillations occurred in ois 5a these pollen data that are directly correlated with isotopic data from the same sediment samples from hole 893a support previous observations that the last interglacial sensu stricto on the west coast of north america was correlative with oxygen isotope substage 5e in addition pollen data show that significant warming events reflected in terrestrial vegetation also occurred in different background states of the climate system during processes of ice growth as well as ice decay

the palaeoflood record of a hyperarid catchment nahal zin negev desert israel the palaeohydrology of nahal zin a 1400 km2 catchment in the hyperarid negev desert is inferred from slackwater deposits and palaeostage indicators in a canyon near its lower end the palaeoflood record augmented by the instrumental and historical records of the last decade includes 28 floods ranging from 200 to 1500 m3s 1 over the last 2000 years this helps to reanalyse the frequency of floods in this drainage system the clusters of floods around 1000 years bp and again during the last 60 years are characterized by high flow magnitudes periods with many floods correspond well to periods with high dead sea levels and are probably relatively wet periods while periods with few floods correspond well to low dead sea levels indicating a drier climate fluctuations in the frequency of floods are typical of periods of transition from one climate regime to another copyright 2000 john wiley sons ltd

the role of the deep ocean in north atlantic climate change between 70 and 130 kyr ago the suggestion1 that changes in north atlantic deep water nadw production are linked through surface heat flux to the atmospheric temperature over greenland is supported by earlier indications2 3 that nadw production decreased during glacial times and by the subsequent finding4 6 that it declined during the younger dryas cool period at the end of the last glaciation changes in north atlantic surface temperatures have been found7 to mirror high frequency temperature changes recorded in greenland ice cores over the past 80 kyr but the connection to abyssal circulation has yet to be established except for one or two isolated oscillations8 9 here we present carbon and oxygen isotope analyses of benthic foraminifera in a high resolution north atlantic deep sea sediment core for the period 70 130 kyr ago these data allow us to reconstruct the history of nadw production which shows a close correlation with greenland climate variability for much of this time interval suggesting that the climate influence of nadw variability was widespread we see no evidence however for changes in nadw production during substage 5e the eemian interglacial period in contrast with recent ice core data10 which suggest severe climate instability in greenland during this time period our results may support suggestions based on data from a second ice core that this apparent instability is an artefact caused by ice flow11 alternatively the eemian climate instability may have had a different origin from the subsequent climate events

planktonic foraminiferal fluxes in the santa barbara basin response to seasonal and interannual hydrographic changes results of a three year time series sediment trap experiment in the santa barbara basin indicate linkages between water column dynamics and variations in plankton fluxes on both seasonal and interannual time scales the two week collection interval utilized for this study allows evaluation of high frequency changes in the production and flux of planktonic foraminifera which are compared to those of siliceous microorganisms diatoms radiolaria and silicoflagellates annual hydrographic conditions in santa barbara basin are influenced by seasonal changes in insolation the wind field and source waters this study includes periods of weak to moderate el nino conditions followed by a transitional period to a non el nino state planktonic foraminiferal fluxes and species turnover are related to seasonal and interannual changes in source waters and water column conditions globigerina bulloides g quinqueloba and neogloboquadrina pachyderma dextral dominate the planktonic foraminiferal population in this location and are present throughout the year globigerina bulloides and g quinqueloba have similar flux patterns and highest fluxes occur in association with diatom blooms the flux patterns of g bulloides and g quinqueloba in general are inversely related to that of n pachyderma dextral globigerina quinqueloba seems to respond earlier to the onset of upwelling than g bulloides three temperature limited species neogloboquadrina dutertrei orbulina universa and globigerinoides ruber are present in lower numbers and show more restricted seasonal ranges in the thermal regime of the santa barbara basin n dutertrei like o universa disappears during upwelling neogloboquadrina dutertrei occurs in highest abundance when the water column is thermally stratified and there is a well developed deep chlorophyll maximum increased fluxes of globigerinoi ruber the most thermally restricted of the dominant species in the basin are associated with the presence of warm oceanic diatoms and warm water radiolarians total planktonic foraminiferal fluxes were lower in 1995 than during the previous two years which were characterized by el nino conditions

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

geological effects of the gulf stream system on the northern bermuda rise abstract the gulf stream system contains a clockwise rotating set of bottom currents which influence the sea bed in the northern north american basin it is possible to interpret the present day and historical record of current activity in this basin in terms of the deep flow of the gulf stream this interpretation provides a much more satisfactory and consistent explanation of the geologic record than previous interpretations based strictly on the influence of the classic abyssal circulation the present day circulation of the gulf stream actively resuspends large quantities of sediment on and near the northern bermuda rise and it is suggested that this resuspension may be due to the eddy field which is embedded in the westward flowing return flow during the late cenozoic the gulf stream system was responsible for depositing and shaping the major acoustic sedimentological units on the relatively smooth surface of the horizon a complex fine grained mont morillionite rich sediments derived from the chemically weathered saprolites of the hudson and st lawrence drainage basins were injected into the deep ocean basins by turbidity currents during the late paleogene and the neogene fine grained turbidites from the st lawrence spread southward down the southeastern sohm abyssal plain across the eastward flowing gulf stream and its westward flowing return flows portions of these fine grained sediments were entrained by the main and return flows and deposited downstream as acoustically non laminated accumulations on the corner and bermuda rises respectively the hudson river input was injected into the deep basin through the hudson canyon system the interaction of these fine grained turbidites with the northward flowing deep flow of the gulf stream system led to the formation of the gulf stream outer ridge here defined for the first time during the late neogene or early pleistocene the gulf stream outer ridge was partially eroded by the gulf stream system and portions subsequently covered by coarse grained pleistocene turbidites the coarse grained illite rich turbidites that flowed across the southeastern sohm abyssal plain also crossed the main and return flows of the gulf stream system the finer portions of these sediments were entrained and deposited as pleistocene acoustically laminated sediments on the plateaus of the bermuda and corner rises

millennial pulsing of environmental change in southern california from the past 24 k y a record of indo pacific enso events century long variations in coastal california vegetation inferred from polliniferous sediments deposited in the santa barbara basin record a succession of brief 14 c yr b p ka these millennial scale pulses many of which correspond with western great basin hydrological fluctuations are also linked to events of southwest monsoon intensification in southern asia we suggest that these correlative high frequency variations in the asian summer and northeast pacific winter climates may reflect submillennial scale el nino southern oscillation enso type forcing involving water vapor transport over the indian and pacific oceans

ice ages the california current and devils hole at the end of an ice age climate changes across the globe but this response is not uniform in some parts of the world oceanic and atmospheric temperatures started to rise well before continental ice sheets began to melt in his perspective lea 1 highlights the report by herbert et al 2 who show that ocean temperatures in the california current led ice volume change by 10 000 to 15 000 years the data support earlier results from a terrestrial record at devils hole helping to reconcile them with the leading theory of ice age cycles 1 http www sciencemag org cgi content full 293 5527 59 2 http www sciencemag org cgi content short 293 5527 71

mineral age record of a polyorogenic evolution within the seve and koli nappes trondelag norway abstract in the central scandinavian caledonides eugeoclinal terranes represented in the koli nappes were thrust 500 km onto the baltoscandian platform during the early to middle paleozoic immediately underlying thrust sheets of the seve nappe complex are suspected to have been derived from the outer margin of continent baltica hornblende within amphibolite at one locality within westernmost exposures of seve nappe units in trandelag norway displays an internally discordant 40 ar 39 ar age spectrum which suggests a polyphase thermal evolution including 1 1 initial post metamorphic cooling through argon retention temperatures at c 475 480 ma 2 2 partial rejuvenation during a silurian c 400 425 ma thermal overprint muscovite within the exposure was more extensively rejuvenated during the silurian overprint at twelve other trandelag sample locations hornblende muscovite and biotite within both the seve and koli nappe complexes record post metamorphic cooling ages between 420 and 435 ma and display no direct evidence of a pre silurian thermal record however the widespread occurrence of intracrystalline extraneous argon components and textural complexities clearly point toward a pre silurian tectonothermal history comparison with 40 ar 39 ar mineral ages reported elsewhere in the central scandinavian caledonides suggests a polyorogenic evolution consisting of 1 1 variable high pressure metamorphism of distal baltoscandian miogeoclinal sequences during entrainment in an accretionary wedge which developed in the late cambrian early ordovician over a west dipping subduction zone related arc volcanic activity occurred in more outboard western sectors 2 2 ductile imbrication of high and intermediate pressure sequences within the accretionary wedge diachronous cooling and or chronologically distinct tectonic episodes are indicated throughout the early and middle ordovician 3 3 ultimate accretion of a variety of eugeoclinal terranes along the baltica continental margin 4 4 imbrication and metamorphism of the eugeoclinal terranes and previously deformed portions of the miogeocline during eastward translation onto the baltoscandian platform in the silurian crystalline baltica basement and overlying structural cover units were depressed to significant crustal depths during eastward nappe transport with resultant formation of high temperature eclogues previously reported crystallization ages of c 425 ma suggest that the eclogites formed at approximately the same time as minerals within the superencumbent nappe units cooled through argon closure temperatures following eastward nappe transport the basement experienced rapid uplift and resultant adiabatic decompression this was followed by rapid cooling through argon retention temperatures at 390 400 ma

a high magnitude storm and flood in a hyperarid catchment nahal zin negev desert israel in october 1991 a high magnitude rainstorm flood estimated return period 40 years occurred in nahal zin a 1400 km2 catchment in the hyperarid negev desert the meso scale structure of the storm was a curved squall line that developed from a thunderstorm in accordance with the topography of the catchment divide by which it was strongly affected tropical moisture reached the area via the subtropical jet stream in conjunction with a lower level northward intrusion of the red sea trough rst n into the mediterranean sea rainfall as measured at the few and sparse gauging stations was much too small to account for the resulting large flood peak flow and other hydraulic characteristics of the flood were indirectly reconstructed the techniques of palaeoflood hydrology used were based on sedimentological evidence of fine grained flood sediments deposited in back flooded tributaries as well as on other stage indicators the hec 2 procedure was employed to determine water surface profiles the spatial and temporal characteristics of the event were studied through a combination of rainstorm analysis remote sensing hydrological and sedimentological data they jointly explain the magnitude and timing of tributary contributions producing the integrated flood in the main channel the flood as reconstructed reveals a three peak hydrograph two peaks were generated by the same storm but had different floodwave arrival times in the main channel the third resulted from a local rainstorm which occurred on the following day and covered only one tributary the curved structure of the storm and its dynamics in relation to catchment orientation resulted in storm move ment in tandem with the floodwave the synchronous contribution from all main tributaries preserved evidence of the floodwave both in stage and volume by replacing the transmission losses in the sections with thick alluvium other high magnitude floods on record for the large negev desert catchments are caused by a cold upper air incursion associated with the rst n most of them occur in the autumn and are caused by storms with high intensity rainfall this is in stark contrast with the flooding behaviour of the semi arid zone further north which is linked primarily to the core of the mediterranean winter the complexities involved in the generation of a large desert flood as revealed by this study illustrate the fallacy of applying routine hydrological modelling to such events and underline the need to study the processes involved in adequate detail 1998 john wiley sons ltd

sediment fluxes and varve formation in santa barbara basin offshore california results from a year long sediment trap study provide the first direct observations of seasonal variability in sediment fluxes to the sea floor in santa barbara basin offshore california and are used to evaluate varve formation in this basin sediment fluxes throughout the year are dominated by lithogenic material biogenic sediments primarily silica are of secondary importance we conclude that the combination of high lithogenic fluxes and low biogenic fluxes during the fall winter period results in the deposition of dark laminae the onset of upwelling and high surface productivity in the spring results in high biogenic silica fluxes that last into the summer the relative contribution of silica to the total sediment flux is highest during this spring summer period and we suggest that light laminae are formed at that time this is consistent with previous suggestions that sediment input is the primary factor controlling varve formation in this basin

reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records a major discrepancy between the late quaternary sea level changes derived from raised coral reef terraces at the huon peninsula in papua new guinea and from oxygen isotopes in deep sea cores is resolved the two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka ka 1000 yr before present but between 70 and 30 ka the isotopic sea levels are 20 40 m lower than the huon peninsula sea levels derived in earlier studies new high precision u series age measurements and revised stratigraphic data for huon peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic 18o data using the sea level and deep sea isotopic data oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from greenland ice cores the record of ice volume changes through the last glacial cycle now appears to be reasonably complete