dust a diagnostic of the hydrologic cycle during the last glacial maximum dust concentrations in ice of the last glacial maximum lgm are high in ice cores from greenland and antarctica the magnitude of the enhancements can be explained if the strength of the hydrologic cycle during the lgm was about half of that at present this notion is consistent with a large decrease 5 c in ocean temperature during the lgm as recently deduced from measurements of strontium and calcium in corals

the role of time versus climate in the formation of deep soils of the apennine fringe of the po valley italy abstract two very deep red soils on a loess mantled fluvial terrace of the trebbia river in northern italy were sampled and analyzed to determine their history and pedologic significance magnetostratigraphy confirms that the upper part of the terrace gravel and all of the 4 m thick loess cover is normally magnetized and therefore less than about 780 000 yr artifacts collected from the oldest loess suggest an age of about 400 000 yr for the inception of loess deposition in this area the soil horizons in loess dominantly have argillic or albic character with redoximorphic features that include mottles glossic tongues and zones of ferromanganese concretions soil colors become progressively redder with depth in the loess cover and are most red a 2 5 yr color hue in the top of the terrace gravel the upper horizons in gravel have abundant ghosts of completely weathered marl and sandstone rubification and weathering of stones diminishes with depth to fresh slightly carbonate enriched parent material at 12 m the heavy mineral composition of the sand fraction suggests minor discontinuities in loess derived horizons abundance of opaque heavy minerals and picotite which are resistant to weathering increases from the soil surface to the base of the loess is highest in the upper part of the terrace gravel and decreases from there to the c horizon in gravel depth functions of major elements to si in the medium silt fraction 10 30 m indicate a downward increase in degree of decalcification and of dissolution of primary minerals micromorphology adds detail to the interpretation of these complex soils yellow complex ferriargillans are present in almost all horizons they are rare at the top of the sequence in loess and become progressively more abundant with depth reaching a maximum in the upper 3 m of the gravel and then decreasing with further depth to 12 m we interpret this peak in abundance of yellow cutans to result from long continued clay illuviation to this depth from a succession of eluvial zones in the aggrading loessial sequence above distinctive red hematite rich argillans are abundant only in the upper horizons in the gravel the red argillans relate to initial development of the soil in gravel because they are included as pedorelicts in the deepest loess layer where they are embedded in the yellow argillans stratigraphic and pedologic evidence indicates that these soils began forming in terrace gravel for perhaps 300 000 yr during the early middle pleistocene from this relict core these soils continued developing both downward by continuing deep decalcification and argilluviation and upward as a sequence of wet alfisols developed in a succession of loess layers that began aggrading about 400 000 yr ago a paleoclimatic record can be perceived weakly in these soils mainly by thick horizons of fe mn nodules that mark boundaries between episodes of loess deposition that took place during glacial cold phases paleofeatures from one unit to another are similar in kind and intensity indicating a degree of continuity of a basic set of pedogenic processes principally declcification argilluviation and redoximorphism these soils can be regarded as vetusols because a single dominant set of pedogenic features are represented in all parts of these soils and deeper parts of these aggrading super profiles have never been isolated from continuing pedogenic change to the present

vegetation zones in nw africa during the brunhes chron reconstructed from marine palynological data abstract six east atlantic sites between 9 and 35 n allow the reconstruction of the latitudinal position and extension of the nw african vegetation zones during the last 0 7 ma the response of the vegetation to alternating glacial dry and interglacial humid climatic conditions has been recorded the vegetation response to a climatic amelioration starts with the northward expansion of the tropical rain forest followed by the northward shift of the saharan sahelian boundary and ends with the southward shift of the saharan mediterranean transitional steppes and the expansion of the mediterranean oak forests most sensitive is the reaction of the saharan sahelian boundary to climatic change large shifts of the saharan sahelian boundary seem to occur faster than small ones annual precipitation estimates for the latitude of dakar 15 n range from 100 to 1000 mm at 24 n yearly precipitation probably ranged from 0 to 150 mm smallest extent of the guinean tropical rain forest probably occurred during the arid conditions of isotope stages 2 and 6 reducing the carbon fixation of these forests to a minimum large extent of the guinean tropical rain forest occurred during most of the odd isotope stages more humid interglacials

spatial arrangement of soil mantle in glacis de buenavista mexico as a product and record of landscape evolution abstract factors controlling spatial soil organization have recently attracted the attention of soil scientists because they can contribute to regional management of soil resources we present here a case study in the glacis de buenavista mexico an extended volcanic piedmont in order to develop an integral understanding of its soil cover as a product and at the same time as a record of the main stages of landscape evolution three phenomena were considered luvisol and vertisol type soils and pedosediments all of them analyzed in terms of their development degree clay content macro and micromorphology selective extractions of fe fe d fe o silicon si o and aluminum al o weathering index and clay mineralogy luvisols represented in the ahuatenco mexicapa and buenavista sections are located in the northern and central part of the area they are red clayey polygenetic soils that show strong weathering with high kaolinitic clay content and high weathering index values clay illuviation and reductomorphic processes combined with vertic features in some parts of the profiles vertisols dominate the central and southern portion of the glacis they exhibit cracking angular blocks with wedge like shapes slickensides and stress cutans the pedogenesis of the vertisol type is clearly associated with the presence of smectitic minerals in the clay fraction as a product of neoformation factors controlling this pedodiversity are relief which affects bioclimatic differentiation within the studied landsurface and defines the lateral redistribution of moisture and dissolved substances and time luvisols represent a longer pedogenetic phase that started in the late pleistocene according to the age of buried paleosols while vertisols mainly originated in the late holocene according to the age of buried organic horizons pedosediments are located in the central area of the glacis here past and present geomorphic processes interact to produce the greatest soil diversity the recent human induced erosion partly destroyed polycyclic luvisols and exposed ancient subsurface pedosedimentary strata at the same time it produced patches of unconsolidated pedosediments consisting mostly of redeposited luvisol materials

paleomagnetism of the dewey lake formation late permian northwest texas end of the kiaman superchron in north america the remanent magnetization of red beds of the late permian dewey lake formation from northwest texas was investigated using thermal chemical and alternating field demagnetization after removal of a small present day viscous overprint the dewey lake shows univectorial decay of the remanence revealing a dual polarity characteristic direction of d 152 4 i 11 1 k 39 5 95 5 9 n 16 sites three polarity transitions were observed defining at least four polarity zones the observed polarity zones are roughly layer parallel and may correlate with the illawarra magnetozone at the end of the kiaman if this is so k ar age determinations of an interbedded ash layer kolker and fracasso 1985 suggest that the kiaman superchron ended before 251 4 ma the paleopole located at 51 4 n 126 2 e confirms the reliability of previously reported late permian poles from southwest united states which fall significantly off the late permian segment of the paleomagnetic euler pole pep track of gordon et al 1984 this implies that a more segmented set of small circles is required to model the north american apparent polar wander path diminishing the usefulness of the pep method

palaeomagnetism and magnetostratigraphy of uppermost permian strata southeast new mexico usa correlation of the permian triassic boundary in non marine environments summary continental red sandstone and siltstone rocks of the dewey lake quartermaster formation at maroon cliffs near carlsbad new mexico are characterized by two components of magnetization with partially overlapping laboratory unblocking temperature spectra both magnetizations display high coercivities 100 mt probably residing in haematite a north directed magnetization with steep positive inclination unblocks between 100 and 650 c isolating a predominantly northwest directed magnetization with shallow inclination of near uniform normal polarity and maximum unblocking temperatures of 680 c we collected samples from 24 palaeomagnetic sites i e individual beds from a 60 m thick section of flat lying strata disconformably overlying carbonate and evaporite rocks of the rustler formation the upper member of the rustler formation contains a late permian early changxingian marine invertebrate and conodont fauna of the sampled sites four yield only steep magnetizations interpreted to be recent overprints eight sites did not yield well grouped site means and were excluded from the final calculations the formation mean dec 337 7 inc 9 2 k 31 6 a 95 7 8 n 12 sites defines a palaeomagnetic pole located at 55 2 n 117 5 e in good agreement with other late permian north american cratonic poles correlation of the short polarity sequence of this section of dewey lake strata is unambiguous compared with the polarity stratigraphy of marine sections in asia and supported by isotopic age determinations on a widespread bentonite bed in dewey lake strata in west texas approximately 251 ma and fossil data for the underlying rustler formation the magnetostratigraphy is consistent with deposition of the dewey lake formation during the latest changxingian late permian stage

durations of soil formation and soil development indices in a holocene mediterranean floodplain abstract holocene and late pleistocene alluvial sequences of the mid medjerda floodplain northern tunisia reveal three types of soils with gradual transitions fluvisols calcaric cambisols calcaric and calcic luvisols chromic stratigraphic cross correlations palaeomagnetic secular variation and 14 c and irsl dating enable detailed information about ages and durations of soil formation in the floodplain weakly developed fluvisols calcaric commonly reveal late holocene ages with soil formation durations lasting between 100 and 300 years hence holocene soil formation is detectable in the exposures from durations of around 100 years onwards cambisols show predominantly mid holocene ages the durations of soil formation are between 800 and 5000 years calcic luvisols chromic feature late pleistocene ages with durations of soil formation between 10 000 and 40 000 years profile development indices were computed from simple field parameters like soil structure soil colour horizon thickness and leaching features the derived development indices show good correlation r 2 0 804 with the calculated durations of soil formation field parameters are well suited for a quantitative development index of holocene soil formation even if very weak developed soils are predominant the study shows that maturity stages of holocene alluvial soils in a homogeneous mediterranean environment are predominantly driven by soil formation duration

the holocene and upper pleistocene pollen record from padul granada spain a new study two borings were made at the site of padul granada pollen analysis of 200 spectra from two successive sequences 14 8 and 8 m deep enables a description of the vegetational and climatic history of this region the most southern one in europe from early wurmian times the chronology is supported by twenty one 14c dates original equivalents are found for the great european prewurm interstadials a markedly arid though thermically not extreme episode exactly equivalent to stage 4 of the marine isotopic stratigraphy closes this relatively temperate period the middle part of the last glacial shows climatic fluctuations that are poorly characterized as is often the case in europe for this period a long section very probably corresponding to the complete last pleniglacial does not show any climatic amelioration towards 15 000 yr b p a change in the diagram is noted that can only be interpreted as reflecting a larger expansion of a regional steppe cover this event also reported on three occasions in southeast france marks the beginning of the oldest dryas the climatic amelioration of ca 13 000 yr b p is far more pronounced here than anywhere else in europe whereas that at 10 000 yr b p is not so clearly marked this unexpected result may be accounted for by the fact that padul is the first continental site so far south and so near pleniglacial refuges to be known on the other hand this result is consistent with what is known from oceanic isotopic stratigraphy a quite new late glacial and holocene vegetational history is revealed characterized by the early appearance and dominance of quercus ilex oak forests of a southern type and the early occurrence of quercus suber and olea it is the first account of a complete history of the postglacial reafforestation in a region with a modern semi arid mediterranean climate from the palaeoclimatic point of view it shows that the hot and humid holocene optimum was attained slightly before 8000 yr b p and that the holocene climatic fluctuations were of but small amplitude

paleopedology of terrae rossae rodoxeralfs from quaternary calcarenites in nw morocco abstract selected terrace rossae or rhodoxeralfs from calcarenites in all probability of mid pleistocene age in the vicinity of rabut show a strong mineral weathering and a considerable to extensive formation of clay minerals especially of kaolinites main sources of pedogenic kaolinites mostly of a disordered structure and poor cristallinity are primary feldpars 2 m and smectites 2 0 2 and

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

nepheloid and suspended particulate matter in south eastern lake michigan a persistent benthic nepheloid layer with high total suspended matter tsm and high total particulate surface area was observed in south eastern lake michigan the layer thickens from a few metres near the shelf slope boundary to greater than 10 m at the base of the slope when compared to the hypolimnion tsm increases by a factor of 2 20 at 1 m above the bottom the greatest increase detected at the slope basin boundary sediment trap profiles within the nepheloid layer show that the particulate flux increases exponentially from about 10 m above the bottom to 1 m above the bottom suggesting that a large fraction of the collected material came from resuspension a nepheloid layer is created during the formation of the thermal bar and maintained during the stratified period apparently through the action of weak but persistent currents this layer is supplemented by lakeward transport of fine particles resuspended near the shelf slope boundary due to impingement of the thermocline on the bottom or during higher energy events

response of the benthic nepheloid layer to near inertial internal waves in southern lake michigan 1 time series measurements of water transparency water temperature and current velocity were made at a station located in 58 m of water in southern lake michigan during the summer of 1995 currents generated by near inertial internal waves are correlated with variations in the thickness and in the vertical distribution of suspended sediment in the benthic nepheloid layer although a direct causal link between internal wave action and changes in the nepheloid layer could not be established the data suggest that local resuspension by shoaling internal waves maintains the layer during the stratified period the origin and maintenance of the benthic nepheloid layer is most likely the result of local resuspension due to a combination of internal wave action and longer term processes

loess like and palaeosol sediments from lanzarote canary islands spain indicators of palaeoenvironmental change during the late quaternary abstract on lanzarote canary islands quaternary saharan dust and weathered local volcanic material were trapped in miocence to pliocene valleys dammed by younger volcanic edifices these sediments show sequences of alternating reddish clayey and loess like yellowish silty material in order to investigate if reddish clayey layers contain material derived from local pedogenesis and if so which pedogenetic processes were active we performed sedimentological micromorphological and environmental magnetic analyses the analyses demonstrate that these layers contain material derived from local soils these soils were characterised by clay formation rubefication and the formation of superparamagnetic particles during periods of enhanced soil moisture thus they can serve as natural archives in order to reconstruct the terrestrial palaeoclimatic history of lanzarote the distribution of soil material in the profiles shows that cold periods of the late quaternary were characterised by more humid conditions than today using palaeontological remains and a comparison with recent soils on tenerife we can roughly estimate maximal palaeoprecipitation values during more humid periods

the major and minor element geochemistry of lake baikal funding for u s participation in the fieldwork and sample collection was provided by the u s national science foundation funding for the analytical work was obtained by various means

the use of234th 238 disequilibrium to examine the fate of particle reactive species on the yangtze continental shelf measurements of234th t1 2 24 1d in water column and seabed samples from an area near the mouth of the yangtze river people s republic of china provide the following information 1 most of the234th in waters near the mouth of the yangtze river is in particulate form and horizontal transport and sedimentation of234th bearing particles dominate the234th budget in this area a model incorporating processes in at least two dimensions is required to understand the fate of particle reactive species on the yangtze continental shelf 2 the residence times of particle reactive species with respect to scavenging range from 0 3 days nearshore to 4 0 days offshore the residence times with respect to removal to the seabed range from 0 5 day nearshore to 11 0 days offshore 3 scavenging residence times for234th decrease as the concentration of suspended particles increases the time for removal of234th to the seabed increases with distance from shore a variable which integrates such factors as scavenging rate bathymetry and frequency of resuspension

paleomagnetism of the moenkopi formation colorado plateau basis for long term model of acquisition of chemical remanent magnetism in red beds paleomagnetic studies of moenkopi samples from several sites on the colorado plateau including a complete 427 m section at sinbad valley western colorado reveal the following 1 the presence of both normal and reversed triassic components in many of the same samples at many localities 2 the close correlation of the magnetic polarity and intensity of magnetic remanence with the lithologic characteristics in the sinbad valley section 3 a streaked pattern of the remanence directions in any one member in the sinbad valley section similar to that expected from polar wander 4 a lack of progressive change from the base upward and 5 the common intermediate remanence directions of weak intensity suggesting the presence of two or more nearly balanced anti parallel components throughout the formation the results of our investigation combined with previously reported petrographic and paleomagnetic studies of the moenkopi formation have led us to conclude that the principal remanence carried by the formation is chemical remanent magnetism crm acquired diagenetically over a geologically long time interval from the available data we have formulated the following model to explain how the crm was acquired through natural processes acting intermittently at geologically reasonable rates when initially deposited the moenkopi sediments consisted primarily of first cycle detritus containing a few percent of iron bearing accessory minerals such as biotite hornblende magnetite and ilmenite at some time after deposition under favorable subsurface conditions intrastratal alteration began involving breakdown of iron bearing silicate and oxide minerals partial replacement of some iron rich silicate grains by hematite martitization of magnetite growth of hematite pods and blebs in ilmenite and biotite and precipitation of crystalline hematite in both primary and secondary voids the authigenesis spanned at least two polarity events and probably continued over several tens of millions of years stratigraphic units with grossly similar lithologies underwent similar diagenetic alterations at rates and to extents that were different from other stratigraphic units having different lithologies because of variations in the rate and duration of alteration and variations in the length of normal versus reversed polarity events any given lithologic unit tended to be dominated by one polarity the model given above seems to be capable of explaining not only those magnetic and petrographic features found in the moenkopi formation but also those of most other red beds

vegetation history and palaeoclimate of the last glacial period at lago grande di monticchio southern italy a high resolution palynological study of a 51 m core from lago grande di monticchio southern italy has provided a palaeonvironmental record for the last glacill a annual lamination based chronology supported by radiometric and tephrochronological dates provides an absolute timescale for this record that spans 76 300 years correlations are established between the pollen stratigraphy the grip ice core 18o record and foraminiferal assemblages from atlantic core v23 81 both dansgaard oeschger and heinrich events are reflected by changes in the pollen stratigraphy revised dates are estimated for heinrich events h1 h6 a quantitative palaeoclimate reconstruction based upon the pollen data provides evidence of the climate changes in southern italy associated with these and other fluctuations during the last glacial

quaternary sedimentation and subsidence history of lake baikal siberia based on seismic stratigraphy and coring the long continuous high latitude stratigraphic record of lake baikal was deposited in three broad sedimentary environ ments defined by high resolution seismic reflection and coring meth ods 1 turbidite depositional systems by far the most widespread characterizing most of the margins and floors of the main basins of the lake 2 large deltas of major drainages and 3 tectonically or topographically isolated ridges and banks holocene sedimentation rates based on radiocarbon ages vary by more than an order of mag nitude among these environments from less than about 0 03 mm yr on ridges and banks to more than about 0 3 mm yr on basin floors ex trapolating these rates with a correction for compaction yields ten tative estimates of about 25 and 11 ma for the inception of rifting in the central and north basins respectively and less than 6 ma for the 200 m sediment depth on academician ridge the selenga delta has the distinctive form of a classic prograding gilbert type delta but its history appears to represent a complex com bination of tectonism and sedimentation the central part of the delta is underlain by prograding shallow water sequences now several hun dred meters below the lake surface these deposits and much of the delta slope are mantled by fine grained deep water hemipelagic de posits whose base is estimated to be about 650 000 years old modern coarse grained sediment bypasses the delta slope through fault con trolled canyons that feed large subaqueous fans at the ends of the south and central basins these relations along with abundant other evidence of recent faulting and the great depths of the central and south basins suggest that these two rift basins have experienced a period of unusually rapid subsidence over the last 650 000 years dur ing at least part of which sedimentation has failed to keep pace

uranium series disequilibrium sedimentation diatom frustules and paleoclimate change in lake baikal abstract the large volume of water approximately one fifth of the total surface fresh water on the planet contained in lake baikal in southeastern siberia is distinguished by having a relatively high concentration of uranium ca 2 nm and together with the surface sediments an unusually high234u238u alpha activity ratio of 1 95 about 80 of the input of uranium to the lake with a234u238u ratio of 2 0 comes from the selenga river profiles of uranium as well as the extent of isotopic disequilibrium in a 9 m sediment core collected on academic ridge generally show high values during interglacial periods corresponding to high diatom frustule numbers difr and biogenic silica bsi data that have been reported elsewhere during glacial periods low difr and bsi uranium progeny 234u and230th were in secular equilibrium with low concentrations of their parent238u radionuclide distributions were interpreted in terms of a quantitative model allowing for adsorption of riverine inputs of uranium onto two classes of sedimenting particles with differing238u232th ratios and uranium progeny in secular equilibrium if the234u238u activity ratio of adsorbed uranium has remained constant mean sedimentation rates can be independently estimated as 3 6 0 6 and 3 7 0 9 cm kyr 1 for the decay of234u and in growth of230th respectively these rates are consistent with a mean rate of 3 76 cm kyr 1 calculated by optimization of the correspondence between adsorbed238u and 18o in dated oceanic sediments the adsorbed uranium apparently tracks variable river flow during interglacials and is drastically reduced during periods of glaciation evidently uranium has not been significantly redistributed within baikal sediments over at least the past 250 kyr and is a unique biologically non essential tracer for climate sensitive processes which provide their own internal geochronometers potentially useful for ages up to 1 myr bp

modes of cross shore sediment transport on the shoreface of the middle atlantic bight the mechanisms responsible for onshore and offshore sediment fluxes across the shoreface zone seaward of the surf zone were examined in a 3 year field study the study was conducted in the southern part of the middle atlantic bight in the depth region 7 17 m using instrumented tripods supporting electromagnetic current meters pressure sensors suspended sediment concentration sensors and sonar altimeters the observations embraced fairweather moderate energy swell dominated and storm conditions cross shore mean flows ranged from near zero during fairweather to 20 cm s 1 during the storm oscillatory flows were on the order of 10 cm s 1 during fairweather and 100 cm s 1 during the storm suspended sediment concentrations at about 10 cm above the bed were 5 kg m 3 during the storm three methods were applied to evaluate the relative importance of incident waves long period oscillations mean flows and gravity in effecting shoreward or seaward sediment flux 1 an energetics transport model was applied to instantaneous near bottom velocity data 2 higher moments of near bottom flows were estimated and compared and 3 suspended sediment fluxes were estimated directly from the instantaneous products of cross shore velocity and suspended sediment concentration the results show that measurable contributions were made by all four of the processes most significantly mean flows were seen to dominate and cause offshore fluxes during the storm and to contribute significantly to onshore and offshore flux during fairweather and moderate energy incident waves were in all cases the major source of bed shear stress but also caused shoreward as well as seaward net sediment advection low frequency effects involving wave groups and long period waves made secondary contributions to cross shore sediment flux contrary to expectations low frequency fluxes were just as often shoreward as seaward whereas cross correlations between suspended sediment concentration and the instantaneous near bottom current speed were high and in phase under storm conditions they were weak and out of phase during fairweather conditions this suggests that simple energetics models are probably inadequate for predicting fairweather transport of suspended sediment

sediment resuspension and transport in lake michigan during the unstratified period instrumented moorings were deployed during the winter of 1994 95 at three depths 28 58 and 101 m in southern lake michigan storms during the observation period were not unusually severe so the processes observed are typical of those that occur during an average winter time series observations of water temperature beam attenuation coefficient a measure of water transparency and current velocity show that local resuspension of bottom sediment occurred frequently after the breakdown of the thermocline resuspension was most frequent close to the shore but was also observed at the 58 m station local resuspension did not occur at the 101 m station but advection to the site of material resuspended at shallower sites was observed these observations do not support the hypothesis proposed by previous investigators that local resuspension at depths of 100 m or greater occurs during the unstratified period it is more likely that fine grained material resuspended by storm action in intermediate water depths 30 60 m is transported into the deeper parts of the lake by the general lake circulation

pre drift extension of the atlantic margins of north america and europe based on paths of permo triassic apparent polar wander summary we reconstruct the relative configuration of north america and europe prior to separation using paths of apparent polar wander apw for the interval 300 to 200 ma the bullard et al 1965 reconstruction closely superimposes the 300 ma points on the two apw paths but leaves the 200 ma points far apart conversely anomaly based reconstructions for later times approximately superimpose the 200 ma ends of the paths but leave the older ends far apart this indicates that separation of the interiors of the two continents began during the interval 300 to 200 ma long before surficial rifting commenced in the late mesozoic this in turn requires pre rift extension in the two continental margins extension appears to have occurred in two phases of approximately equal magnitude but significantly different direction the change in direction occurred at about 200 ma the earlier 300 to 200 ma episode of extension appears to have involved a strong element of sinistral shear based on our preferred reconstruction the total amount of pre rift extension of the two continental margins may have been as much as 1400 km

permo triassic magnetostratigraphy in china the type section near taiyuan shanxi province north china summary a palaeomagnetic study has been made of samples collected from the permo triassic type section near taiyuan shanxi province in the north china block no results were obtained from the upper carboniferous shanxi and taiyuan formations results from the permian lower and upper shihezi and shiqianfeng formations and from the lower triassic liujiagou formation were restricted mainly to the red shale and red mudstone horizons that were preferentially sampled for this study after thermal demagnetization the following pole positions were obtained lower permian lower shihezi formation n 11 samples 20 9 n 1 4 e with dp 6 1 and dm 12 2 upper permian combined upper shihezi and shiqianfeng formations n 89 samples 47 8 n 357 4 e with dp 2 3 and dm 4 3 lower triassic liujiagou formation n 25 samples 50 0 n 351 o e with dp 3 7 and dm 7 0 the sequence crosses the younger boundary of the permo carboniferous reversed kiaman superchron and the polarity sequence observed suggests that this superchron ended in mid ufimian times a minimum of 13 polarity zones seven normal and six reverse then follow before the permo triassic boundary this is in excellent agreement with currently available observations worldwide

a rock magnetic record from lake baikal siberia evidence for late quaternary climate change rock magnetic measurements of sediment cores from the academician ridge region of lake baikal siberia show variations related to late quaternary climate change based upon the well dated last glacial interglacial transition variations in magnetic concentration and mineralogy are related to glacial interglacial cycles using a conceptual model interglacial intervals are characterized by low magnetic concentrations and a composition that is dominated by low coercivity minerals glacial intervals are characterized by high magnetic concentrations and increased amounts of high coercivity minerals the variation in magnetic concentration is consistent with dilution by diatom opal during the more productive interglacial periods we also infer an increased contribution of eolian sediment during the colder windier and more arid glacial conditions when extensive loess deposits were formed throughout europe and asia eolian transport is inferred to deliver increased amounts of high coercivity minerals as staining on eolian grains during the glacial intervals variations in magnetic concentration and mineralogy of lake baikal sediment correlate to the specmap marine oxygen isotope record the high degree of correlation between baikal magnetic concentration mineralogy and the specmap oxygen isotope record indicates that lake baikal sediment preserves a history of climate change in central asia for the last 250 ka this correlation provides a method of estimating the age of sediment beyond the range of the radiocarbon method future work must include providing better age control and additional climate proxy data thereby strengthening the correlation of continental and marine climate records

mineralogical and clay mineralogical aspects of loess research abstract mineralogical and clay mineralogical investigations under certain circumstances allow conclusions regarding the rate and kind of pedogenetic weathering especially clay mineral formation together with soil physical and chemical and mainly micromorphological investigations paleoclimatic conclusions can be drawn in central european holocene and pleistocene loess soils as well as in relict loess soils in the central and northern part of the great plains of the u s a smectite is the dominant pedogenetically formed mineral in the fine clay fraction

palaeoenvironmental history of lake baikal during the last 23000 years abstract a sediment core recovered from lake baikal was studied in an attempt to elucidate the palaeoenvironmental history of an intra continental lake under the control of last glacial to post glacial climatic fluctuations the lake conditions were characterised by subdued primary production and increased turbidity conditions during the last glacial maximum terrestrial vegetation and the development of soil layers were reduced in the drainage areas the deglaciation suggested by increased terrigenous sand influx and biological productivity took place at around 18 000 yr b p responding to the increased insolation in the northern hemisphere high latitude the onset of wet and warm conditions at ca 12 000 yr b p brought on a maximum of aquatic production and forestal expansion between 7 000 and 6 000 yr b p since 5 000 yr b p enhanced blooming of diatoms has occurred due to an increased nutrient supply and dissolved silica input into the lake

vertical and horizontal particle transport in the coastal waters of a large lake an assessment by sediment trap and thorium 234 measurements 1 the horizontal and vertical flux of particulate material in the nearshore of southern lake michigan 0 40 m was estimated with the naturally occurring radionuclide 234th horizontal fluxes of 234th supplemented apparent vertical fluxes of 234th in the water column based on local 234th 238u disequilibria by a factor of 7 14 reinforcing the importance of lateral transport in coastal environments calculated onshore transport of particulate material across the 40 m isobath was as high as 1 1 106 kg km 1 d 1 and exceeds estimates of terrigenous riverine and bluff erosion loading estimates of onshore flux of organic carbon exceeded areal primary productivity by as much as 300 and should be considered in nearshore carbon budgets bottom tethered sediment traps placed 5 m above the bottom measured sedimentation rates that were 1 order of magnitude lower than 234th derived mass fluxes from the water column and 2 orders of magnitude lower than 234th derived mass fluxes to the lakebed we ascribe this difference to under collecting by the sediment trap either because of trap hydrodynamics or flux occurring below the trap capture plane cross shore fluxes showed a periodicity of 4 days and correlated strongly with a topographic vorticity wave that is present throughout the year in southern lake michigan the impact of this wave as a driver of bidirectional cross shore flux on biogeochemical cycling and both nearshore and offshore food webs has not yet been explicitly considered

does 234th 238u disequilibrium provide an accurate record of the export flux of particulate organic carbon from the upper ocean the magnitude of the flux of biogenic particulate organic carbon poc exported from the surface waters of the world ocean and remineralized at depth is critical to constraining models of the global carbon cycle yet remains controversial the use of upper ocean sediment traps is still one of the primary tools for determining this export flux although trap fluxes have been shown to vary significantly because of hydrodynamic and sample collection biases over the past decade 234 th increasingly has been used as a tracer to estimate poc export from the euphotic zone by multiplying the depth integrated 234 th flux by the poc 234 th ratio of sinking particles the accuracy of this technique is highly dependent on the natural variability in the poc 234 th ratio and 234 th flux yet the significance of this variability to estimates of poc export remains uncertain based on an analysis of new 234 th and poc data from the labrador sea and a review of 25 previous independent field studies we report that poc export fluxes can vary 2 10 times or more solely because of variability in the poc 234 th ratio and procedures used to estimate the 234 th flux recommended improvements include studies of the biological chemical and physical mechanisms controlling 234 th organic matter interactions in seawater detailed comparisons of poc 234 th ratios in size fractionated and sediment trap material increased spatial and temporal sampling density of 234 th and more standardized procedures to calculate the 234 th export flux

correlation and comparison of seawater δ34ssulfate records at the permian triassic transition abstract correlation of carbonate associated sulfate cas 34 s analysed permian triassic p tr sections via conodont biostratigraphy and sequence stratigraphy shows distinct phases in the oceanic 34 s sulfate evolution during the period 1 million years m y either side of the p tr boundary a 34 s sulfate rise in the changhsingian prior to the end permian mass extinction is followed by a period of about 350 000 years of erratic and substantial 34 s sulfate movements range 1 to 28 the mass extinction occurring in the middle of this period the sharp swings in this phase indicate severe changes in the oceanic sulfur geochemistry and perhaps stages of ocean inhomogeneity low 34 s sulfate values coincide with the mass extinction horizon suggesting the extinction is related to an input of relatively 32 s enriched sulfur into the oceanic sulfate reservoir the source of this sulfur most likely being h 2 s from euxinic waters after the erratic 34 s sulfate phase there is a stabilisation of 34 s sulfate values 17 until the later griesbachian however there is a possibility of discrepant panthalassan and tethyan data sets during the early to mid griesbachian but this requires further work for confirmation 34 s sulfate values are erratic in the late griesbachian to early dienerian suggesting further perturbation of the sulfur cycle the poorly age constrained smithian record shows a wide range of 34 s sulfate values probably indicating swings during that time also the 34 s sulfate movements from the changhsingian to smithian indicate the permian triassic transition is a time of intense changes in the sulfur fluxes to and from the oceans and perhaps stages of ocean inhomogeneity

centennial to millennial scale climate shifts in continental interior asia repeated between warm dry and cool wet conditions during the last three interglacial states evidence from uranium and biogenic silica in the sediment of lake baikal southeast siberia abstract we observed timescale dependent changes in the correlations between biogenic silica biosi and uranium concentrations of bulk sediment from the buguldeika saddle lake baikal there was a positive correlation for the glacial interglacial 100 kyr scales over the 180 kyr with inverse correlations for centennial to millennial scales during the last three interglacial states mis 5 3 and 1 the distinction of these correlations between the time scales suggests that the sedimentation processes of biosi and u differ from each other the baikal biosi concentration record is generally regarded as a paleotemperature proxy reflecting the diatom production of the lake on the other hand we concluded that the temporal variation of the u concentration in the sediment reflected the weathering intensity in the south of lake baikal watershed associated with changes in the rainfall moisture levels based on the paleoclimate proxies from lake baikal climates in continental interior asia are identified as having dry and wet conditions during the glacial and interglacial periods respectively this accounts for the rhythms in growth and retreat of ice sheets in eurasia on glacial interglacial scales in the interglacial periods mis 5 3 and 1 the continental interior is contrary to the glacial interglacial climate changes characterized by alternating warm dry and cool wet climates with periods in tens of thousands years in particular such shifts in the climate stand out prominently at the beginning of mis 5d the detrended u record for the last 5 2 kyr shows wet events at 4 3 3 7 3 2 2 3 1 8 1 2 and 0 8 0 3 kyr these events coincide with the timing of the north atlantic ice rafted debris events which were possibly related to solar activity all this evidence suggests that climate in the continental interior followed significantly different fluctuation patterns in the glacial interglacial and shorter time scales

widespread inclination shallowing in permian and triassic paleomagnetic data from laurentia support from new paleomagnetic data from middle permian shallow intrusions in southern illinois usa and virtual geomagnetic pole distributions abstract recent paleomagnetic work has highlighted a common and shallow inclination bias in continental redbeds the permian and triassic paleomagnetic records from laurentia are almost entirely derived from such sedimentary rocks so a pervasive inclination error will expectedly bias the apparent polar wander path of laurentia in a significant way the long standing discrepancy between the apparent polar wander paths of laurentia and gondwana in permian and triassic time may be a consequence of such a widespread data pathology here we present new middle permian paleomagnetic data from igneous rocks and a contact metamorphosed limestone from cratonic laurentia the exclusively reversed middle permian magnetization is hosted by low ti titanomagnetite and pyrrhotite and yields a paleomagnetic pole at 56 3 s 302 9 e a95 3 8 n 6 this pole which is unaffected by inclination shallowing suggests that a shallow inclination bias may indeed be present in the laurentian records to further consider this hypothesis we conduct a virtual geomagnetic pole distribution analysis comparing theoretical expectations of a statistical field model tk03 gad against published data sets this exercise provides independent evidence that the laurentian paleomagnetic data is widely biased likely because of sedimentary inclination shallowing we estimate the magnitude of this error from our model results and present and discuss several alternative corrections

magnetostratigraphy of the permo triassic boundary section at shangsi guangyuan sichuan province china continous marine sedimentation characterizes many late permian to early triassic sections on the yangtze terrane in south china the permo triassic p tr boundary section at shangsi sichuan province consists of limestones intercalated with clays and mudstones which belong to the wuchiapingian and changxingian upper permian and the griesbachian and dienerian lower triassic stages the p tr boundary is formed by a clay horizon with an unusually high iridium concentration the intensity of natural remanent magnetization is very low with a mean of 0 15 ma m 1 about 40 of the samples contain secondary or unstable magnetization components only whereas the remaining samples carry a characteristic remanent magnetization thought to reflect the polarity of the geomagnetic field during deposition with sufficient accuracy normal and reversed polarity of the characteristic magnetization constitute a pattern of at least six polarity zones the p tr boundary being situated very close to the transition from a reversed to a normal polarity zone the shangsi polarity sequence represents part of the illawarra interval of mixed polarity the exact beginning of which has still to be determined

late quaternary climatic reconstruction for the maghreb north africa abstract the paleoclimatic evolution of the maghreb since 40 000 yr b p is not yet known in great detail for that purpose data from more than 35 sites have been collected although only about 11014c dates and a few prehistoric remains can be used to correlate these data however the sites are well distributed over the maghreb and the convergent results from paleosoils paleolakes alluvian or eolian deposits pollen analysis etc induce one to draw up a certain pattern in climatic evolution for the period between 40 000 and 20 000 yr b p the data are still fragmentary but are concordant in indicating wetter environments generalized as far as the northern sahara the effect of dropping temperatures on the increasing water budget and soil moisture is not yet clear but rainfall could have been more regular and more abundant as a consequence of the shifting of middle latitude cyclone paths towards the south in both summer and winter the environmental indicators show that between about 20 and 18 000 yr b p rainfall progressively became more irregular however proofs of aridity in the south maghreb and the northern sahara is evident only for the period between 12 10 000 yr b p at that time the saharan high pressure belt was reinforced and well established at higher latitudes than at present this dry climate lasted more or less until the thermal optimum after 6000 yr b p there is some evidence that the climate became wetter again but the environmental conditions were rather different from those of before 20 000 yr b p for instance the middle holocene dark humic sois are the result of a pedogenesis different from that of the late pleistocene reddish paleosoils for the last two millennia it is not easy to distinguish between a natural trend towards aridification and desertification through man s intervention

permian triassic magnetostratigraphy new results from south china abstract continuous marine sediments of permian to triassic age are widely distributed over large areas in southern china they offer the potential for developing magnetostratigraphic columns to investigate the polarity status of the palaeomagnetic field three carbonate sections on the yangtze platform which represent mainly the upper permian but also parts of the lower triassic and possibly parts of the uppermost lower permian contain a long term main r n r n r polarity succession throughout the permian this signal is hidden under strong overprint magnetizations of variable origin and can be mostly obtained only from directional trends of the natural remanent magnetization during demagnetization rather than from clear stable end point directions the new chinese polarity sequences are in accord with magnetostratigraphic records from the former ussr and pakistan depending on stratigraphic assignment of the lithological formations studied either they include the boundary between the lower and upper permian and give evidence that the kiaman reversed polarity superchron had ended before the upper permian or the formations all belong stratigraphically to the upper permian with the oldest reversed interval to be correlated with the reversed zone in the midian stage of the palaeontologically well dated nammal section in pakistan this zone is preceded by at least one normal polarity zone at nammal so that the end of the kiaman superchron would not be observed in the new chinese sections

late permian to early triassic magnetostratigraphy a late permian to early triassic magnetostratigraphic reference section is presented the lower triassic part is based on results from marine limestone sections in south china published earlier 1 2 reliable new permian data are added here which have been collected in the nammal gorge salt range northwest pakistan where marine sediments have been deposited quasi continuously with occasional minor hiatuses during the late palaeozoic to early mesozoic about 50 of the permian samples from the nammal section contain hidden beneath a strong recent or tertiary overprint a characteristic remanent magnetization chrm which is very likely of permian age this component which was imprinted on the southern hemisphere has normal as well as reversed polarity with a normal mean direction decl 289 3 incl 50 3 95 4 3 n 113 which is in close agreement with the palaeofield direction expected for a site belonging to the indian plate as part of gondwanaland during the permian in the lower upper permian several normal polarity zones are recognized this contradicts the current assumption that rocks of this age belong to the long reversely polarized kiaman hyperzone the kiaman interval must end and the illawarra hyperzone of mixed polarity must begin in or prior to the lowermost upper permian the permian triassic boundary at nammal as well as in the chinese sections is situated very close to a transition from a reversed to a normal polarity zone the upper permian at nammal together with the lower triassic south china sections is estimated to cover about 20 ma nearly 30 polarity changes are observed which result in an average reversal frequency very similar to that observed during the early tertiary the reversal rate after the end of the long lasting reversed kiaman hyperchron apparently increases in a manner similar to that after the end of the cretaceous long normal superchron only a few polarity zones are found in the lower upper permian while progressively more frequent reversals follow in the lower triassic

circulation during winter and northerly storm events in southern lake michigan 1 moored observations of winds currents and temperature made off the southeastern lake michigan shore during 1998 to 2000 winter spring periods are studied to describe the mean winter circulation and episodic circulation during northerly storms in lake michigan late winter spring sediment plumes in southeastern lake michigan were attributed to these episodic circulation features the winter spring currents in southeastern lake michigan are quite depth independent and the mean currents flow predominantly alongshore and toward the north the observed currents show the signature of a forced two gyre circulation in the southeastern basin the interannual variability of mean and fluctuating currents is mainly due to the variability of prevailing wind forcing the intermittent episodic circulation influenced by northerly storms causes significant asymmetry to the mean circulation during northerly storm episodes the mean current speeds increased significantly and the currents within 10 km of shore followed the surface wind stress while farther offshore the circulation was oppositely directed during these episodes it is also observed that the combination of directly wind forced currents and northward propagating vorticity wave generates significant offshore transport in this region

continental climate response to orbital forcing from biogenic silica records in lake baikal changes in insolation caused by periodic changes in the earth s orbital parameters provide the primary forcing for global ice ages1 6 but it is not clear to what extent the climates in continental interiors are controlled directly by regional variations in insolation and to what extent they are driven instead by the highly nonlinear response of the oceans and ice sheets here we investigate this question using the record of biogenic silica in lake baikal as a proxy for climate change in this high latitude mid continental region we find a good correlation between this record and that of marine oxygen isotopes4 over the past 250 kyr the baikal record exhibits both a strongly nonlinear component manifested in a 100 kyr periodicity and weaker direct insolation components manifested in the 41 kyr obliquity and 23 and 19 kyr precession orbital cycles these results show that even though extreme continental climates such as this are influenced directly by insolation variations they are dominated by the nonlinear rhythm of the oceans and ice sheets

a palaeoecological study in the western mediterranean area the upper pleistocene pollen record from cova beneito alicante spain abstract results are presented of palynological analyses of pleistocene deposits at cova beneito an archaeological site on the southern slopes of the sierra de benicadell alicante province se spain 650 m a s l with a wsw orientation the chronology is supported by radiocarbon dating archaeological evolution previous local sequences and recourse to several wider correlations for the first time in the region a warming event is defined in the mid last glacial stage during this event vegetation took on a mediterranean character with sclerophyllous elements such as quercus olea phillyrea rhamnus helianthemum etc the rest of the sequence shows a predominance of pinus within the ap phases of steppe like character and an aridity crisis immediately after the climate improvement due to local conditions forest cover was never very great

vetusols and paleosols natural versus man induced environmental change in the atlantic coastal region of morocco abstract surface terrae rossae rhodoxeralfs and a terra fusca petrocalcic palexeralf developed on mid quaternary calcarenites in the moister region of rabat show substantial pedogenic formation of clay minerals particularly kaolinite mainly in the fraction m for the most part the pedogenic kaolinites show poor crystallinity of the fireclay type they are mainly formed from feldspars and perhaps also amphiboles and pyroxenes in the fractions 2 m and from smectites inherited from the calcarenite residual loam in the coarse 2 0 2 m and fine clay fractions m in one terra rossa soil formation was interrupted twice by deposition of eolian materials and it is regarded as a polycyclic pedocomplex eolian input was much less important during development of the other surface terrae rossae on younger calcarenites 100 ka near the coast three rendzinas typic calcixerolls show only slight mineral weathering and pedogenic clay formation in spite of a varied spectrum of primary minerals in one example kaolinite formation has just started the calcixerolls were probably recalcified by addition of eolian material as a result of anthropogenic thinning of the vegetation and or due to the vicinity of the coast these results suggest that at least in this region the younger terrae rossae of the coastal area were formed over much of the brunhes epoch in areas farther from the coast they have been developing for almost all of the brunhes epoch because climatic fluctuations in the quaternary were generally slight in this region the direction of soil formation was constant therefore we regard the rhodoxeralfs in the northern part of our study area as vetusols according to our expanded definition vetusols are surface soils which underwent almost constant processes of soil formation under an almost constant constellation of soil forming factors especially climate and vegetation over a long period of time including at least some part of the pleistocene consequently the present patchy distribution of terrae rossae is hardly a result of climatically induced periods of geomorphological activity and stability but the result of the removal of an earlier dense forest cover followed by severe soil erosion the human impact on the ecosystem is much more serious than any climatic fluctuations in the southwestern part of the study area between el jadida and agadir the soil moisture regime is dry xeric to aridic and terrae rossae occur only in small areas mostly in depressions however two selected rhodoxeralfs in the vicinity of tamanar show considerable pedogenic mineral weathering and clay mineral formation though hardly any kaolinite the strong weathering and clay illuviation must have been preceded by decalcification implying a distinctly moister climate here in the past however micromorphological features of recent recalcification are common in these rhodoxeralfs suggesting that their main properties are not in equilibrium with the present climate and the soils should be regarded as nonburied paleosols or relict paleosols

90y 90sr disequilibrium in surface waters investigating short term particle dynamics by using a novel isotope pair abstract we demonstrate the use of the disequilibrium between 90 sr t 1 2 29 1 yr and its particle reactive daughter 90 y t 1 2 64 h to estimate particle removal rates and settling velocities in the epilimnion of a freshwater lake during varying conditions of stratification caused by seasonal changes the estimated rates of removal obtained from the 90 sr 90 y disequilibrium showed good agreement with a measured rates of mass removal obtained from settling particle fluxes in sediment traps and the inventories of suspended material and b independently obtained removal coefficients for the scavenging behavior of two different isotopes of particle reactive plutonium present in the water column because of different processes because 90 sr is widespread and readily measurable in freshwater systems as a result of fallout from nuclear weapons testing the 90 sr 90 y disequilibrium is a potentially valuable resource for examining particle dynamics in surface waters

a year of internal poincare waves in southern lake michigan 1 a unique set of full year deep water observations from the middle of lake michigan s southern basin are analyzed to quantify the seasonal variability of the dominant near inertial internal poincare wave at this mid lake location the poincare wave is seen to describe more than 80 of the observed surface current variability for much of the year with characteristic near inertial frequency and clockwise rotating velocities the dominance of the near inertial seiche on the flow decreases with depth the wave persists during the stratified period roughly may through late december and is supported by as few as 1 2 degrees of thermal stratification over 150 m only after complete water column mixing does the wave go dormant for january through april the strongest poincare wave activity is seen to correspond to the period of strongest summer thermal stratification august in spite of the relatively weak winds at this time a simple inertial slab model optimized with linear friction is shown to capture the seasonal variability of the near inertial energy at this location reasonably well the vertical structure of the wave shows good agreement with that calculated with a standard normal modes formulation which is in turn used to characterize the potential shear and mixing caused by the wave late spring and summer events of elevated poincare wave activity are shown to generate sufficiently strong shear with persistent periods of sub 1 richardson numbers within the thermocline suggesting that the near inertial seiche is likely generating thermocline instabilities in the lake s interior

palaeoclimate and palaeoenvironmental responses in the western mediterranean over the last 140 ka evidence from mallorca spain climatic change in the western mediterranean basin over the last 140 ka has been investigated from sediment and soil sequences along the coast of the northeastern part of mallorca spain palaeoclimate and palaeoenvironments are reconstructed from sediment and soil structures marine and terrestrial molluscan fauna grain size distributions mineral magnetics sediment and soil chemistry sem and oxygen isotope values dating is by osl and amino acid geochronometry along with marine molluscan faunal assemblages all oxygen isotope stages and substages from ois 6 to 1 are recorded mean annual temperatures m a t of c 19 2 c for the climatic optimum of the last interglacial compare with c 17 3 c for the present and are associated with high sea level extensive woodland and stable soils although wide temperature ranges are detected during this stage with values as low as c 10 3 c through ois 5d to 5a m a t fluctuated from 8 2 c to 17 9 c low sea level open vegetation effective river activity and aeolian sand and dust deposition characterize 5d and 5b while relatively high sea level and soil development on stable landscapes dominate ois 5c and 5a ois 4 is represented by m a t of c 4 9 c with aeolian sand and loess deposition limited river activity and weak soil development loess deposition persisted into ois 3 but at this time the m a t was c 13 c and with higher humidity and vegetation growth during the lgm ois 2 m a t was c 8 1 c and effective river slope and aeolian processes along with associated with limited vegetation cover were responsible for the most extensive changes in the landscape major rates of change occur during periods of climatic deterioration when the high levels of geomorphic energy were imposed on a landscape undergoing a breakdown of vegetation cover

abrupt increase in precipitation and weathering of soils in east siberia coincident with the end of the last glaciation 15 cal kyr bp abstract an abrupt increase in the temperature in greenland in the wake of the initiation of the bolling allerod warm phase at ca 15 cal kyr bp was followed after a few decades by a dramatic increase in the concentration of methane in the atmosphere of the earth resulting from an increase in humidity in the tropics j p severinghaus e j brook science 286 1999 930 934 analysis of a sediment core from lake baikal east siberia spanning the end of the last glacial period and the holocene revealed an abrupt stepwise 1 3 3 4 fold decrease in the concentration of several soluble elements such as na k mg ca and si in hot nitric acid extracts of small intervals 3 cm this chemical change appears to have occurred over the same time span based on similarities in the profiles of silica and diatoms found in other 14 c dated cores this suggests that the calcium rich mammoth steppe landscape r d guthrie quat sci rev 20 2001 549 573 of siberia created during the last glaciation underwent a dramatic transformation at the end of this period at the beginning of the bolling allerod warm phase due to an increase in precipitation within a time interval of less than 300 yr

particle delivery to the benthos of coastal lake michigan a 2 d non steady state model was applied to measured profiles of 234th 238u and 90y 90sr disequilibria in a shallow 22 m water column of coastal lake michigan downward fluxes of 234th and 90y were primarily driven by onshore horizontal advection concordance between 234th and 90y derived mass flux estimates from the water column could only be realistically achieved under a nuclide scavenging scenario dominated by direct sorption on bottom or near bottom sediment and vertical convection in the water column not sinking particles an estimated vertical 234th 90y flux ratio of 0 31 in the water column agreed with measured 234th 90y activity ratios on collected ejecta from bottom dwelling dreissenid mussels 0 26 0 05 and not with water column particles 3 3 1 3 a similar 238u 90sr parent nuclide activity ratio of 0 30 0 02 suggests that both 234th and 90y are scavenged in toto below the maximum sampling depth 17 m and near the sediment water interface determining the mechanism by which particles are transported to the bottom is important for understanding not only how benthos are supplied with water column material but also how particle fluxes should be measured and calculated

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