applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

paleoproductivity of eastern lake ontario over the past 10 000 years we evaluated relative levels of paleo primary productivity in eastern lake ontario during the past 10 000 yr via analysis of inorganic and organic sediment from the rochester basin there was significant natural variability in primary production correlative with holocene climate change the cold post younger dryas interval 10 9 4 ka was a time of minimal levels of primary production the warm holocene hypsithermal interval 9 4 5 3 ka had much higher levels of primary production but was more variable including five well defined cycles that have an average period of 750 yr the largest negative anomaly in primary productivity occurred during the 8 2 ka climate event 8 4 8 0 ka a time of cold dry conditions another negative anomaly occurred in association with the nipissing flood 6 3 5 3 ka which triggered a regional cooling event the cool holocene neoglacial interval 5 3 ka to 1850 a d was characterized by lower but more stable levels of primary production as well as by a cessation of calcite precipitation and the onset of diatom productivity during the historic interval 1850 1940 a d there was a dramatic increase in primary production to unprecedented levels over the past 10 000 yr as well as a 30 fold increase in sediment accumulation rates these large abrupt changes occurred in response to regional deforestation anthropogenic nutrient loading and increased chemical weathering due to acid rain we project that during 21st century global warming eastern lake ontario will evolve into an ecosystem similar to that during the holocene hypsithermal the level of primary productivity in eastern lake ontario is of great importance to the region s present and future economy including sport fishing recreation and water quality there is not however a simple relationship between the level of primary productivity in the lake and various economic and environmental interests proper assessment of both present and future levels of primary productivity in lake ontario will be necessary for addressing scientific and management issues during the 21st century in a series of papers published during the 1980s 1990s

boundary mixing associated with tidal and near inertial internal waves abstract moorings deployed on the south august november 2002 and north november 2002 june 2003 flanks of the kaena ridge hawaii are used to document the flow variability associated with mixing within 200 m from the boundary deep along the ridge as part of the hawaii ocean mixing experiment home at both sites strong temperature inversions are detected with vertical scales of 100 m a thorpe scale analysis of the overturns yields a time averaged dissipation near the bottom at the south site 1 2 10 8 w kg 1 that is 10 times higher than the north site 1 9 10 9 w kg 1 with both higher than the dissipation at similar depths 30 km from the ridge on the south flank observed horizontal currents and vertical displacements are dominated by the semidiurnal internal tide on the north flank the semidiurnal tide is less energetic than on the south with a different vertical structure as tidal amplitudes decrease toward the boundary these differences are attributed to greater separation from th

tidal mixing events on the deep flanks of kaena ridge hawaii abstract a 3 month mooring deployment august november 2002 was made in 2425 m depth on the south flank of kaena ridge hawaii to examine tidal variations within 200 m of the steeply sloping bottom horizontal currents and vertical displacements inferred from temperature fluctuations are dominated by the semidiurnal internal tide with amplitudes of 0 1 m s 1 and 100 m respectively a series of temperature sensors detected tidally driven overturns with vertical scales of 100 m a thorpe scale analysis of the overturns yields a time averaged dissipation near the bottom of 1 2 10 8 w kg 1 10 100 times that at similar depths in the ocean interior 50 km from the ridge dissipation events much larger than the overall mean up to 10 6 w kg 1 occur predominantly during two phases of the semidiurnal tide 1 at peak downslope flows when the tidal stratification is minimum n 5 10 4 s 1 and 2 at the flow reversal from downslope to upslope flow when the tidal stratification is ordinarily increasi

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

the mediaeval warm period drought recorded in lake huguangyan tropical south china the geochemistry of dated sediment cores from lake huguangyan 21o9 n 110o17 e tropical south china reveals distinct stratigraphical patterns in total organic and inorganic carbon toc tic biogenic silica bs and total nitrogen tn over the past 1400 years in this hydrologically closed lake tic variations may reeect changes in the precipitation evaporation ratio which controls the evaporative enrichment of carbonate toc bs and tn in the sediment are proxy indicators of lake productivity and nutrient input which we believe are linked to local precipitation high tic content correlates with low concentrations of toc bs and tn and indicates two drought episodes dated to ad 670 760 and ad 880 1260 in the sediments of lake huguan gyan local historical chronicles support these data suggesting that the climate of tropical south china was dry during the mediaeval warm period mwp and wet during the little ice age lia the detected mwp drought is temporally correlated with evidence for lower precipitation on the guliya china and quelccaya peru ice caps and with increased salinity in moon lake us great plains

breaking internal lee waves at kaena ridge hawaii shallow water oscillatory flows and deep ocean steady flows have both been observed to give rise to breaking internal lee waves downstream of steep seafloor obstacles a recent theory also predicts the existence of high mode oscillatory internal lee waves in deep water but they have not previously been directly observed here we present repeated spatial transects of velocity isopycnal displacement and dissipation rate measured with towed instruments on the south flank of a supercritical ridge in hawaii known as kaena ridge and compare them with predictions from a 3 d numerical model with realistic tidal forcing bathymetry and stratification the measured and modeled flow and turbulence agree well in their spatial structure time dependence and magnitude confirming the existence and predicted nature of high mode internal lee waves turbulence estimated from thorpe scales increases 2 orders of magnitude following downslope tidal flow when the internal lee wave begins to propagate upslope and breaks

deep sea currents driven by breaking internal tides on the continental slope mooring data collected on the continental slope of the south china sea show that along slope deep sea bottom currents are generated when large spring internal tides internal waves with tidal frequency are observed with the maximum velocity amplitude exceeding 0 15m s the observations are consistent with predictions that near bottom breaking of internal waves can result in generation of along slope flows when these waves obliquely approach the slope a linear internal tide model in one horizontal dimension with realistic topography and stratification is used to show that the breaking of internal tides is likely due to near critical reflection on the slope combining the mooring observations and the model simulation an along slope near bottom transport of similar to 0 5sv is estimated along slope bottom flows caused by breaking internal waves potentially provide a significant way to deform continental slopes and affect deep water exchange between the marginal sea and open ocean

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

tectonic development of the eastern mediterranean region an introduction the eastern mediterranean is one of the key regions for the understanding of fundamental tectonic processes including continental rifting passive margins ophiolites subduction accretion collision and post collisional exhumation it is also ideal for under standing the interaction of tectonic sedimentary igneous and metamorphic processes through time that eventually lead to the development of an orogenic belt below we will outline some milestones in the development of tectonic related research in the eastern mediterranean region we will mention how studies of the eastern mediterranean contrib ute to our understanding of fundamental tectonic processes and indicate how papers in this volume contribute to this aim current and emerging research themes will be highlighted we will also outline the main alternative tectonic reconstructions of the region see fig 1 and mention which of these the different contributors favour tethyan nomenclature remains controversial and we will suggest an appropriate informal terminology for the various oceanic basins that existed an entr6e to some of the key literature sources is also provided citations here are mainly to edited volumes which provide access to this large subject area many of the papers in this book integrate and synthesize large amounts of geological information for extended periods of geological time the papers are ordered in a general time sequence with a view to linking those that consider comparable tectonic setting and pro cesses the locations of the areas are shown in figures 2 and 3 figure 2 also shows the main sutures and figure 3 illustrates the main neotectonic elements of the region

high resolution seismic reflection evidence for middle holocene environmental change owasco lake new york abstract approximately 70 km of new decimeter resolution seismic reflection profile data from owasco lake new york define a middle holocene 4600 14c yr b p erosion surface in the north end of the lake at water depths as great as 26 m beneath the lake post glacial sediments are up to 9 m thick and represent about 10 of the total sediment fill early to middle holocene sediments 6 m thick contain biogenic gas at the south end of the basin and a large 4 km 300 m 15 m subaqueous slide deposit along the east central portion of the lake late holocene sediments are thinner or absent particularly at the north end of the lake the middle holocene erosion surface may have been produced by a drop in lake level alternatively it may represent a change in climate during the transition between the relatively warm holocene hypsithermal and cool neoglacial at this time 4600 14c yr b p circulation in owasco lake appears to have evolved from sluggish to active the increased circulation which persists today probably resulted from atmospheric cold fronts with strong southwesterly winds that piled up water at the north end of the lake the increased water circulation may have been ultimately driven by decreasing insolation which produced an increased pole to equator thermal gradient and thus stronger global winds that began at the transition between the hypsithermal and neoglacial

geochemistry of daihai lake sediments inner mongolia north china implications for provenance sedimentary sorting and catchment weathering abstract to advance the understanding of sediment distribution catchment weathering hydraulic sorting and sediment provenance in a tectonically stable basin the geochemistry of surface sediment samples from daihai lake in north china is presented mud bulk sediments were analyzed for 10 major and 30 trace elements organic carbon and nitrogen and for 87sr 86sr ratios in silicate fraction acid insoluble ai and carbonates acid soluble as enrichment in fe2o3 cao mno mgo k2o and p2o5 and their positive correlation with al2o3 rb sr ratios and bivariate discrimination diagrams of k vs rb and th u vs th suggest low chemical weathering intensity under semiarid conditions in the daihai catchment accumulation of clays in deeper water sites by sedimentary sorting results in an evident distribution of sediment composition with the lake water depth although similar chondrite normalized ree rare earth element patterns of lake sediment samples with lree light rare earth element enrichment negative eu anomalies and an almost flat hree heavy rare earth element pattern may suggest similar sedimentary source rocks original sediment provenance can be recognized on the basis of their distinctive 87sr 86sr ai ratios and immobile th zr ti and nb trace element signature separating from weathering and sedimentary processes as well as from grain size effect

tidal mixing processes amid small scale deep ocean topography the nature of tide topography interaction reflects the topographic scales experienced by water parcels during their tidal excursions in the deep ocean these scales are typically subkilometer yet direct observations of tidal processes on such scales are lacking at one site a saddle amid steep and complex mid atlantic ridge topography observations reveal tidally pulsed bottom trapped fronts overflows and lee waves in response to a tide combined with a mean flow of similar amplitude the tidal pulsing of the fronts and overflows was only evident locally and their phase became unpredictable over scales of hundreds of meters enhanced turbulence in a 100 200 m thick bottom boundary layer had an estimated dissipation rate of 2 6 10 2 w m 2 exceeding the large scale average of tidal dissipation in mid ocean ridge environments but by less than an order of magnitude this site was not a dissipation hotspot and the processes observed could provide widely distributed mixing to the meridional overturning circulation

thermal fronts generated by internal waves propagating obliquely along the continental slope abstract rapid temperature falls occurring at semidiurnal periods are observed close to the bottom above the continental slope in the bay of biscay simultaneous current measurements reveal that the abrupt temperature decrease o 0 5 k within one minute is associated with a brief downslope current contrary to previous observations it is suggested that the flow field associated with internal waves propagating obliquely downslope is responsible for advecting denser water higher on the slope than lighter fluid resulting in a gravitationally unstable stratification the collapse of this stratification is observed as a thermal front passing the moored instruments

middle holocene dry period in the northern midwestern united states lake levels and pollen stratigraphy abstract four cores from lake mendota in the yahara river valley of south central wisconsin provide pollen charcoal and sediment stratigraphic evidence of a middle holocene dry period in the northern midwest the lake level was lower between about 6500 and 3500 yr b p indicating that runoff from the upper yahara river basin may have ceased during the drier seasons of the year derived estimates of precipitation between 6500 and 3500 yr b p indicate a decrease of about 10 down to about 700 mm from the present precipitation value of 800 mm a warming between 6500 and 3500 yr b p is also interpreted based on a change of vegetation from rich mesophytic forest before 6500 yr b p to quercus savanna with increased charcoal abundances after that time after 3500 yr b p a closed quercus forest and decreased charcoal suggest a cooler and wetter climate the qualitative paleoecological interpretations quantitative precipitation reconstructions based on pollen from the region including the lake mendota data and estimates of hydrologic budget based on lake level changes all show indications of a dry and warm middle holocene evidence from a large regional array of sites also supports these interpretations

historic calcite record from the finger lakes new york impact of acid rain on a buffered terrane most previous studies on the effects of acid rain have been conducted in areas with low acid neutralizing or buffering capacity in contrast significantly less study has occurred in calcareous terrane that has high buffering capacity and that has traditionally been thought to be insensitive to the effects of acid rain to address this fundamental inequity we have conducted a comprehensive study of near surface 1 m historic age 200 yr sediments in the finger lakes of central new york state a high buffering capacity area that has received significant quantities of acid rain in particular we have focused on authigenic calcite contained in historic bottom sediment as well as water column geochemistry between 1972 and 1999 results indicate that the open water precipitation of calcite whitings returned to 7 of the 11 finger lakes during historic time following an 4500 14c yr hiatus only those lakes with calcite in the near surface sediment have calcareous soils and or limestone outcrops in their drainage basins and summer surface waters that are supersaturated with respect to calcite water column data indicate that the saturation state of summer surface waters has increased in at least seven finger lakes between 1972 and 1999 and that calcium loading to lakes lacking calcite has also increased over the same time interval we hypothesize that acid rain has increased carbonate weathering in the finger lakes region leading to an increase in supersaturation of summer surface waters with respect to calcite the precipitation of calcite in summer is triggered by evaporation temperature increase and or photosynthetic removal of carbon dioxide this new chemical weathering hypothesis contrasts with but is not mutually exclusive of the traditional cultural eutrophication model that suggests that increased nutrient loading biological productivity and co2 removal are the primary causal mechanisms for historic calcite precipitation stable carbon isotope and water column geochemical data from the finger lakes indicate decreasing levels of primary production since at least the 1960s and there are statistically significant correlations between co2 so2 and nox emissions and calcite content of bottom sediments historic calcite precipitation in the finger lakes began as early as the 1820s suggesting that naturally acidic rain falling on freshly deforested and tilled landscapes increased chemical weathering and brought these lakes to supersaturation there was also a rapid increase in calcite precipitation beginning in ca 1940 coincident with increased industrialization and acidic rainfall associated with world war ii that continued into the 1990s during the mid to late 1990s calcite precipitation decreased in the finger lakes following the introduction of zebra mussels unlike regions with low acid neutralizing capacity where acid rain results in the acidification of lakes acidic deposition across well buffered terrane may result in the alkalization of lakes

water and sediment geochemistry of major kumaun himalayan lakes india four major himalayan lakes in kumaun region in india namely nainital bhimtal sattal and naukuchiatal have been studied to understand water and sediment geochemistry the lakes are characterised by varying degrees of natural and human influences the nainital is intensively used and is a major tourist destination whereas the other three lakes have attracted much attention lately the lakes have a tectonic origin and are characterised by dolomites limestones shales and silicate rocks the water chemistry is dominated by ca mg and hco3 an indication of a carbonate lithology source for the water composition about 55 80 of na and only 30 40 of ca in the lakes are derived from silicate lithology the nainital lake is also characterised by a high chemical index of alteration which is reflected in its high carbonate and the clay mineral content of the sediments model calculations show that 33 and 67 of nitrate in sattal lake is contributed by agriculture and cultural effects respectively the 87sr 86sr ratios in the lakes are very high 0 72 with samples from sattal lake being extremely radiogenic 0 82 similar to many himalayan rivers the 1 sr 87sr 86sr in sediments show two major sources for sr silicates and carbonates the contributions of sr from carbonate and silicate lithology is estimated to be 25 and 60 respectively in bhimtal lake

holocene climatic change in the northern midwest pollen derived estimates mapping of holocene pollen data in the midwestern united states has revealed several broadscale vegetational changes that can be interpreted in climatic terms these changes include 1 the early holocene northward movement of the spruce dominated forest and its later southward movement after 3000 yr b p and 2 the eastward movement of the prairie forest border into southwestern wisconsin by 8000 yr b p and its subsequent westward retreat after 6000 yr b p when certain basic assumptions are met multiple regression models can be derived from modern pollen and climate data and used to transform the pollen record of these vegetational changes into quantitative estimates of temperature or precipitation to maximize the reliability of the regression equations we followed a sequence of procedures that minimize violations of the assumptions that underlie regression analysis reconstructions of precipitation during the holocene indicated that from 9000 to 6000 yr b p precipitation decreased by 10 to 25 over much of the midwest while mean july temperature increased by 0 5 to 2 0 c at 6000 yr b p precipitation was less than 80 of its modern values over parts of wisconsin and minnesota after 6000 yr b p precipitation generally increased while mean july temperature decreased in the north and increased in the south the time of the maximum temperature varies within the midwest and is earlier in the north and later in the south

a lacustrine carbonate record of holocene seasonality and climate annually laminated varved holocene sediments from derby lake michigan display variations in endogenic calcite abundance reflecting a long term millennial scale decrease in burial punctuated with frequent short term decadal scale oscillations due to carbonate dissolution since 6000 cal yr b p sediment carbonate abundance has followed a decreasing trend while organic carbon abundance has increased the correlation between organic carbon abundance and the sum of march april october november insolation has an r 2 value of 0 58 we interpret these trends to represent a precession driven lengthening of the holocene growing season that has reduced calcite burial by enhancing net annual organic matter production and associated calcite dissolution correlations with regional paleoclimate records suggest that changes in temperature and moisture balance have impacted the distribution of short term oscillations in carbonate and organic matter abundance superimposed on the precession driven trends

a 250 ka sedimentary record from a small karstic lake in the northern levant yammouneh lebanon paleoclimatic implications the levant influenced by both the mediterranean sea and the saharan arabian deserts is a key region for understanding climatic changes in response to glacial interglacial boundary conditions that have greatly affected regional hydrology here we present the first long term paleoenvironmental record from the northern levant presently much wetter than the southern levant our record derives from the multi proxy study of a sediment core 36 m long retrieved from the small intra mountainous tectonic basin of yammouneh lebanon which is mainly supplied by karstic springs sediments consist of a thick accumulation of brownish to greenish clayey silts interrupted by intervals of whitish marls composed of caco3 rich material the core chronology is based on radiometric dating 14c and u th and paleomagnetic techniques the sedimentary sequence spans approximately the last two glacial interglacial cycles 250 ka carbonate content is relatively high throughout the profile due to a perennial input of detrital calcite from the watershed but varies significantly the marls are mostly composed of authigenic and biogenic calcite and reflect lacustrine environments with high carbonate productivity during peaks of interglacial periods their occurrence suggests low physical erosion of the basin slopes which were covered by arboreal vegetation and intense karstic water circulation under warm and relatively wet conditions in agreement with pollen data the clayey silts are dominated by quartz and clay minerals and a few amounts of k feldspars and dolomite they are characterized by high concentration in magnetic particles and high relative concentrations of si al k and fe considered as strictly of detrital origin due to the carbonated nature of the watershed quartz and k feldspars are attributed to eolian origin from a distal source the clayey silt intervals generally suggest palustrine conditions with abrupt flows responsible for runoff derived material or subaerial environments and low local water availability in particular during the last glacial maximum high si al and k al ratios during interglacials are attributed to relatively high eolian dust contribution due to the decrease of local detrital inputs our study reveals significant differences between yammouneh and lake records from the dead sea basin southern levant the latter showing high low levels during glacial interglacial periods these hydrological differences might reflect either changes in the north south ns rainfall gradient in response to the development of the northern ice sheet and the southward migration of the westerly belt or local factors i e a decrease in efficient precipitation and water availability at yammouneh during the coldest glacial periods e g the last glacial maximum due to water storage by ice caps on the mount lebanon range and frozen soils in the yammouneh basin

tethyan vs cordilleran ophiolites a reappraisal of distinctive tectono magmatic features of supra subduction complexes in relation to the subduction mode abstract supra subduction zone ssz ophiolites deserve special attention because they represent fundamental markers of intraoceanic convergence and generation of new lithosphere above subduction zones moreover owing to their structural characteristics and location in the overriding plate these complexes are far better represented and preserved than mid ocean ridge basalt morb ophiolites in orogenic belts in terms of their structure tectonics and magmatic features ssz ophiolites may be classified in two main types 1 tethyan complexes such as those of the albanide hellenide belt which mostly consist of complete and extensive volcanic dyke plutonic and mantle sections with prevalent island arc tholeiitic iat affinity and the significant presence of boninites obducted as relatively intact lithospheric slabs onto collisional continental margins 2 cordilleran complexes including the circum caribbean ophiolites of guatemala cuba and venezuela mostly represented by dismembered sections of arc volcanic plutonic and subordinate mantle sequences with tholeiitic to calc alkaline iac magmatic affinity and acidic differentiates commonly associated with metamorphic subduction complexes and tectonically emplaced onto or juxtaposed against the continental margin within polygenetic terranes these two types appear to be related to significantly different subduction modes and intraoceanic plate dynamics whereby ssz ophiolites were generated the tethyan complexes can best be compared with west pacific type subduction with accentuated steepening and retreat of the subducted slab accompanied by progressive decoupling of the converging plates intense mantle diapirism and tensional events in the upper plate with generation of large iat sheeted dike complexes in open oceanic spreading systems continuous slab sinking and roll back allow increasing asthenospheric diapirism and interarc spreading from the arc axis to the forearc region with generation of boninites and back arc basin basalts babb with intermediate morb iat composition by contrast the genesis of the cordilleran complexes requires a subduction mode characterized by a steady state regime with moderate and constant dip of the subducted slab and limited extension in the backarc region the magmatic evolution of these ophiolites from iat to iac and the significant presence of rhyodacite and tonalite differentiates coherently indicate a more mature stage of arc magmatism as well as the occurrence of efficient differentiation processes developing under nearly closed system conditions in independent magma chambers tethyan complexes are likely to be obducted as large and relatively intact slabs onto the continental margins through the interposition of metamorphic soles which represent relics of the morb lithosphere underplating the ssz ophiolites on the other hand the common emplacement of cordilleran complexes within polygenetic terranes appears to be controlled by prolonged accretionary mechanisms that trap against the continental margin parts of the arc structure subduction complexes melanges and volcanoclastic products

the terminology and the concepts of gypsum rich soils abstract many terms in earth sciences and their underlying ideas have been developed in temperate humid countries both geological and climatic reasons cause gypsum rich soils to occur in dry lands soil science has paid little attention to gypseous soils and this limited knowledge is reflected in the direct loan of customary terms of soil science that can lead to misconceptions on the composition and behaviour of soils with large proportions of gypsum elements for discussion on the use of sundry terms about soils containing gypsum are presented here and some of their implicit assumptions discussed some generic terms are examined as well as several expressions used by organizations devoted to soil survey and classification the transformations occurring in gypseous soils are discussed in particular the effects from exposure the refinements herein proposed aim to help understand the role of gypsum in local and global earth surface processes

biologically induced calcite and its isotopic composition in lake ontario we studied water sediment trap and core samples from eastern lake ontario to reconstruct the factors controlling the biologically induced production and sedimentation of calcite during so called whiting events calcite accumulation and its isotopic composition are controlled by a complex set of interrelated factors including temperature primary productivity and the abundance of pica cyanobacteria during the stratified period calcite precipitation is highly correlated to lake temperature because physical and biological factors interact to produce conditions favorable for whitings during warm years when the lake stratifies early in the seasonal cycle carbonate stratigraphies in multiple cores from eastern lake ontario revealed similar patterns of historical variation in percent carbonate an exponential rise in carbonate accumulation occurred in nine cores after 1930 culminating in peak values in the early 1980s this rise was related to historic increases in primary productivity resulting from increased phosphorus loading to lake ontario superimposed upon this rise were four peaks centered on 1940 1942 1957 1961 1971 1977 and 1983 that correlate with maxima in summer air temperature anomalies from the great lakes region and with strong el niiio events these peaks are also associated with maxima in s c values and minima in s180 values of carbonate lending support to our model that more calcite is precipitated with higher 6 c values during warm years when thermal stratitication occurs early in the seasonal cycle beginning in the mid 1980s calcite accumulation and its 6 c ratio began to decrease suggesting a reduction in primary productivity in surface waters probably related to lower phosphate concentrations in epilimnetic waters of lake ontario during the stratified period reduced summer p loading may be explained either by a lagged response to p abatement measures that began in the late 1970s or by decreased p loading from upstream lake erie beginning in the late 1980s as a result of the establishment of filter feeding zebra mussels

environmental change controls of lacustrine carbonate cayuga lake new york dated sediment cores from cayuga lake new york state document that biologically mediated precipitation of calcite has been controlled by environmental change both natural and anthropogenic over the past 10 000 yr during the holocene hypsithermal 9 4 ka 14 c milankovitch forcing of summer insolation in the northern hemisphere resulted in a broad increase to 55 then decrease to 5 of calcite content in bottom sediment warmer summers resulted in earlier onset of thermal stratification of the water column which increased the duration of primary production as well as the abundance of picoplankton which in turn increased the amount of calcite precipitated at the end of the hypsithermal ca 3500 yr ago global cooling greatly reduced the amount of calcite precipitated however since a d 1940 calcite contents in cayuga lake sediments have risen up to 20 one hypothesis is that this recent increase in calcite is the result of cultural eutrophication nutrient loading however this rise in calcite also closely tracks the anthr opogenic rise of atmospheric carbon dioxide suggesting a possible link to global environmental change further research on hard water lake basins will be needed to test which of these two hypotheses is corr ect

alongslope current generated by obliquely incident internal gravity waves a simple laboratory experiment in stratified salt water demonstrates that an obliquely incident internal gravity wave generates a mean horizontal current when approaching a sloping boundary from above the alongslope current is in the same direction as the transverse component of wave propagation and coexists with a turbulent bore propagating diagonally up and along the slope mean flow generation is observed for vertical angles of incidence above and below the critical angle as well as for steeper angles in which the viscous dissipation of waves is smaller initially

a simple parameterization of turbulent tidal mixing near supercritical topography abstract a simple parameterization for tidal dissipation near supercritical topography designed to be applied at deep midocean ridges is presented in this parameterization radiation of internal tides is quantified using a linear knife edge model vertical internal wave modes that have nonrotating phase speeds slower than the tidal advection speed are assumed to dissipate locally primarily because of hydraulic effects near the ridge crest evidence for high modes being dissipated is given in idealized numerical models of tidal flow over a gaussian ridge these idealized models also give guidance for where in the water column the predicted dissipation should be placed the dissipation recipe holds if the coriolis frequency f is varied as long as hn w f where n is the stratification h is the topographic height and w is a width scale this parameterization is not applicable to shallower topography which has significantly more dissipation because near critical processes dominate the observed turbul

estimates of holocene precipitation for rajasthan india based on pollen and lake level data abstract a pollen profile obtained from lake sediments at lunkaransar rajasthan in northwest india was used along with a pollen climate calibration function to estimate past precipitation between 10 500 and 3500 yr b p the estimated precipitation was about 500 mm yr or about 200 mm yr above the modern value a model was used for the energy and hydrologic budget of a lake basin and lake at sambhar located 240 km se of lunkaransar to calculate that a 200 mm yr increase in rainfall above the modern amount would have raised the lake level about 20 m above the modern level topographic charts and satellite imagery provided some evidence in support of an enlarged paleolake of that elevation but field exploration would be required to confirm the size and date of a former lake after about 3500 yr b p the lunkaransar profile indicated a desiccated lake bed because no pollen was preserved the pollen climate calibration function was of no use for estimating the amount of the precipitation decline a reduction of precipitation of about 200 mm yr below the modern amount was estimated from the energy and hydrologic budget for paleolake sambhar by assuming that the lake was one tenth of its present size during the dry interval

erosion and infill of new york finger lakes implications for laurentide ice sheet deglaciation a comprehensive seismic reflection profile investigation of the new york finger lakes has revealed the extent of bedrock erosion and nature of sediment fill beneath the lakes bedrock deepens to the south where gorgelike profiles have been eroded to as much as 304 m below sea level and infilled with up to 275 m of late quaternary age 14 ka sediment we propose a working hypothesis that invokes ice streaming and pressurized subglacial meltwater and sediment to account for regional geomorphology this working hypothesis is consistent with recent concepts of the collapse of continental ice sheets via ice streaming and the marine isotopic record for a meltwater spike at 13 14 ka the finger lakes may provide a critical testing ground for deglaciation models of the southern laurentide ice sheet because they contain a thick well preserved and now seismically defined record of the deglaciation process

estuarine processes and their stratigraphic record paleosalinity and sedimentation changes in the hudson estuary north america paleosalinity estimates and rates of sedimentation inferred from core samples from the hudson estuary for the interval between 6 4 and 1 3 ka indicate a possible role for the estuarine turbidity maximum etm in influencing patterns of estuarine sedimentation at centennial to millennial time scales currently in the estuary sedimentation is localized via sediment trapping particularly in the vicinity of the etm 13 26 km upstream from battery park fbp at the southern tip of manhattan in water depths greater than 4 m and on the western side of the estuary data presented in this paper are from cores located within the segment of the estuary 29 50 km fbp age constraints are provided by c 14 dating paleoenvironmental interpretations are based upon paleosalinity estimates grain size variability and sedimentary structures paleosalinity was inferred on the basis of foraminiferal biofacies analysis and a new method for estimating summertime paleosalinity using oxygen isotope measurements in bivalve shell material the isotopic analysis of a narrow size fraction 1 0 1 7 mm representing summer growth of a single bivalve species gemma gemma reduces the uncertainty related to annual changes in temperature data from f45 km fbp indicate a gradual decrease in summertime paleosalinity between 6 4 and 2 0 ka from 25 20x to 15 10x the latter is similar to present day values these results are consistent with the conclusion of an earlier low resolution study sedimentation rates are generally low and are similar to the rate of sea level rise in the hudson river lowest sedimentation rates are noted in short 2 3 to f1 3 ka we hypothesize that the observed pattern in sediment accumulation relates to a location for the etm some 20 km upstream of its present position at 3 ka downstream migration of the etm since 3 ka is ascribed to shoaling of the estuary effectively squeezing the marine saltwater wedge in the same direction and off marginal flats into the channel such shoaling would have enhanced the role of waves in mixing marine and fresher surface water and reduced the effect of the etm in

internal tide generation in nonuniformly stratified deep oceans we present numerical and experimental studies of the conversion of tidal motions of an exponentially stratified fluid over two dimensional knife edge gaussian and complex bottom topography to radiated internal waves in a model of the deep ocean we compare the radiated internal wave power for cases of strong stratification where the buoyancy frequency profile n z proportional to the square root of the density gradient is much larger than the tidal frequency to the power radiated for weak stratifications we consider particularly internal wave generation for topography below a turning depth ztd where n ztd for z ztd although the radiated power in these waves is much weaker than in cases without turning depths the radiated power is predicted well by prior analytical theory if the nonuniform stratification is averaged over depths spanning from the bottom boundary up to an effective height zeff in the absence of a turning depth we find zeff is approximately equal to the height of the topography indicating that only the stratification for depths spanned by the topography is relevant however in the presence of a turning depth the vertical scale of the internal tide becomes larger and zeff increases approximately linearly with the turning depth height toward values comparable to the total fluid depth

a downslope propagating thermal front over the continental slope in the ocean internal frontal bores above sloping topography have many appearances depending on the local density stratification and on the angle and source of generation of the carrier wave however their common characteristics are a backward breaking wave strong sediment resuspension andrelatively cool denser water moving more or less upslope underneath warm less dense water in thispaper we present a rare example of a downslope moving front of cold water moving over near bottomwarm water large backscatter is observed in the downslope moving front s trailing edge rather than theleading edge as is common in upslope moving fronts time series observations have been made during afortnight in summer using a 101 m long array of high resolution temperature sensors moored with anacoustic doppler current profiler at 396 m depth in near homogeneous waters near a small canyon in thecontinental slope off the malin shelf west scotland uk occurring between fronts that propagate upslopewith tidal periodicity the rare downslope propagating one resembles a gravity current and includes strongconvective turbulence coming from the interior rather than the more usual frictionally generated turbulencearising from interaction with the seabed its turbulence is 3 10 times larger than that of more commonupslope propagating fronts as the main turbulence is in the interior with a thin stratified layer close tothe bottom little sediment is resuspended by a downslope propagating front the downslope propagatingfront is suggested to be generated by oblique propagation of internal tidal waves and flow over a nearbyupstream promontory

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

buoyancy frequency profiles and internal semidiurnal tide turning depths in the oceans 1 we examine the possible existence of internal gravity wave turning depths depths below which the local buoyancy frequency n z becomes smaller than the wave frequency at a turning depth incident gravity waves reflect rather than reaching the ocean bottom as is generally assumed here we consider internal gravity waves at the lunar semidiurnal m2 tidal frequency m2 profiles of n2 z the quantity in the equations of motion are computed using conductivity temperature and depth data obtained in the world ocean circulation experiment woce values for n2 z computed using gibbs seawater routines in two thermodynamically equivalent expressions for n2 z are found to yield values that are in excellent accord but differ significantly from n2 z computed from often used but inexact expressions that involve potential density uncertainties in n2 z are estimated using a monte carlo method where the data are averaged over a range in depth 80 200 m which is determined by minimizing a cost function our principal result reached from an analysis of all 18 000 woce casts is that turning depths are common for zonal east west propagating internal tides in the deep oceans inclusion of the full coriolis effect i e not making the so called traditional approximation leads to the conclusion that turning depths cannot occur for meridional and near meridional internal tides but the non traditional component has little impact on turning depths for internal tides that are near zonal i e propagating within about 30 of the east west direction at low and midlatitudes

development of concepts concerning the genesis and emplacement of tethyan ophiolites in the eastern mediterranean and oman regions this article uses evidence mainly from the eastern mediterranean and oman to help understand the origin and emplacement of ophiolites field studies in these regions emphasize the diversity of ophiolite related sedimentary and tectonic processes topics to be discussed here include the sedimentary covers of ophiolites their metamorphic soles related melanges and emplaced continental margin slope rise units modes of ophiolite emplacement will also be considered and tectonic reconstructions that have a direct bearing on the origin and emplacement of ophiolites the writer argues that there is compelling evidence that many ophiolites formed by spreading above intraoceanic subduction zones evidence from their intact sedimentary covers however indicates that such subduction was only incipient in most cases as directly associated volcanic arcs or back arc basins are rare metamorphic soles record fragments of oceanic lithosphere derived from settings ranging from open ocean to continental slope rise settings underlying melanges record the subduction of most of the ocean lithosphere formed at spreading ridges continental margin units beneath ophiolites demonstrate that these ophiolites were formed in ocean basins that were mainly initiated by continental rifting in the eastern mediterranean and oman regions ophiolite emplacement was commonly achieved by trench margin collision although strike slip transpression and large scale accretion along subducting margins played a role in some cases taking account of the mesozoic palaeotectonic setting of the eastern mediterranean region it is widely believed that ophiolites of two main ages mid jurassic and late cretaceous were formed in several small oceanic basins separated by rifted microcontinents the history of tethys in pre mesozoic time remains more open to question lastly giant subduction related ophiolites as in oman cyprus or the balkans may not be forming anywhere in the world ocean today but may instead relate to rare events in earth history when regional to global plate boundaries were drastically reorganised

do greenland ice cores reflect nw european interglacial climate variations the climatic evolution during the eemian and the holocene in western europe is compared with the sea surface conditions in the norwegian sea and with the oxygen isotope derived paleotemperature signal in the grip and renland ice cores from greenland the records show a warm phase ca 3000 yr long early in the eemian substage 5e this suggests that the greenland ice sheet in general recorded the climate in the region during this time rapid fluctuations during late stage 6 and late substage 5e in the grip ice core apparently are not recorded in the climatic proxies from western europe and the norwegian sea this may be due to low resolution in the terrestrial and marine records and or long response time of the biotic changes the early holocene climatic optimum recorded in the terrestrial and marine records in the norwegian sea nw european region is not found in the summit grip and gisp2 ice cores however this warm phase is recorded in the renland ice core due to the proximity of renland to the norwegian sea this area is probably more influenced by changes in polar front positions which may partly explain this discrepancy a reduction in the elevation at summit during the holocene may however be just as important the high amplitude shifts during substage 5e in the grip core could be due to atlantic water oscillating closer to and also reaching the coast of east greenland during the holocene atlantic water was generally located farther east in the norwegian sea than during the eemian

temporal variability of microparticle properties in polar ice sheets abstract four recent ice core studies reveal a consistently recurring temporal correlation between increased microparticle concentrations and lower global temperatures more negative 13 o 16 o ratios a continuous 900 year record of particle deposition from the 101 m south pole core was obtained by analyzing 6218 samples the concentration of insoluble particles with diameters 0 63 m increases substantially between a d 1450 and 1850 a period of slightly reduced global temperatures encompassing the latest neoglacial or little ice age there is evidence suggesting that some of the additional material may be volcanic although further substantiation is required the microparticle analyses of selected sections from three deep cores coupled with the respective 18 o measurements reveal that in all three cores the last glacial or late wisconsin ice contained great quantities of microparticles the ratio of the average microparticle concentration in wisconsin sections to that in holocene sections is 6 for the 905 m dome c antarctica core 3 for the 2164 m byrd station antarctica core and 12 for the 1387 m camp century greenland core microparticle increases of this magnitude can not be accounted for merely by a reduction in net accumulation these data suggest that the global atmosphere was heavily laden with suspended particulates near the end of the last major glaciation

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

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

evidence from north west canada for an early holocene milankovitch thermal maximum according to the milankovitch theory of global climatic change maximum summer solar radiation at high latitudes of the northern hemisphere occurred at 10 000 yr bp refs 1 2 in particular it predicts summer solstice radiation greater by 9 10 preliminary climate simulation experiments with these increased values of radiation confirm that high latitude land surfaces received maximal insolation at 10 000 yr refs 3 4 paradoxically however the large volume of fossil pollen and other evidence from north america indicates a maximum of holocene warmth at 7 000 6 000 yr ref 5 and a recent review of the evidence from new england suggests that the warming began at 9 000 and ended at 5 000 yr but also stresses the difficulties of interpretation in terms of climate change6 we summarize here data from sites in the north west corner of mainland canada fig 1 that directly support the milankovitch hypothesis

the impact of cold north atlantic sea surface temperatures on climate implications for the younger dryas cooling 11 10 k the sensitivity of global climate to colder north atlantic sea surface temperatures is in vestigated with the use of the giss general circulation model north atlantic ocean temperatures 18 000 b p resembling those prevalent during the younger dryas were incorporated into the model of the present climate and also into an experiment using orbital parameters and land ice characteristic of 11 000 b p the results show that with both 11 000 b p and present conditions the colder ocean temperatures produce cooling over western and central europe in good agreement with younger dryas paleoclimatic evidence cooling also occurs over extreme eastern north america although the precise magnitude and location depends upon the specification of ocean temperature change in the western atlantic despite the presence of increased land ice and colder ocean temperatures the younger dryas summer air temperatures at northern hemisphere midlatitudes in the model are warmer than those of today due to changes in the orbital parameters chiefly precession and atmospheric subsidence at the perimeter of the ice sheets

stable isotope response to lake eutrophication calibration of a high resolution lacustrine sequence from baldeggersee switzerland stable isotope analyses of discrete seasonal layers from a 108 yr annually laminated freeze core from baldeg gersee a small eutrophic lake in central switzerland provide information on the climatological and environmental factors including lake eutrophication that control oxygen and carbon isotopic composition of epilimnic biologically induced calcite precipitate during the last 100 yr baldeggersee has undergone major increases in productivity and eutrophication in response to nutrient loading from agriculture and industrialization in the lake s watershed calibration of the isotopic signal in baldeggersee to historical limnological data quantitatively links evidence of isotopic depletion in the sedimented calcite to trophic state of the lake 18o values from the spring summer light sediment layers steadily diverged to more depleted values in response to historical eutrophication measured 18o values were up to 21 5 more negative than calculated equilibrium 18o values evidence for 13c depletion in the calcite relative to equilibrium values is more difficult to ascertain because of an overall dominance of isotopic enrichment in the dissolved inorganic pool as productivity in baldeggersee increases a positive association exists between the degree of oxygen 18 depletion and the calcite crystal size thus large amorphous calcite grains can be used as a proxy for recognizing apparent isotopic nonequilibrium in sediment sequences from highly productive lacustrine environments from all geologic time scales in contrast to the light layers the oxygen isotopic composition of the calcite in the late summer fall dark sediment layers is unaffected by the apparent isotope nonequilibrium oxygen and carbon isotope values from the dark laminae in the baldeggersee sediment therefore provide environmental and climatological proxies that can be calibrated with known environmental and regional climate data for the last century

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

stable isotope record from seneca lake new york evidence for a cold paleoclimate following the younger dryas a radiocarbon controlled stable isotope record from seneca lake new york has defined a relatively cold paleoclimate 10 1 8 2 ka that was younger and regionally of greater magnitude than the well known younger dryas cold interval these new isotope results are supported by published pollen records from throughout the great lakes region that also define a relatively cold paleoclimate at this time this cold paleoclimate occurred during global meltwater pulse ib when large volumes of cold isotopically light low 18 o meltwater flowed into the great lakes from the rapidly retreating laurentide ice sheet the discharge of cold glacial meltwaters into the great lakes during pulse ib suppressed downwind summer temperatures in the finger lakes region and provided a source of isotopically light precipitation published proxy data from greenland norway and alaska also record relatively cold paleoclimates following the younger dryas suggesting widespread northern hemisphere cooling as a direct result of the rapid melting of the laurentide ice sheet between 10 and 8 ka

burst resuspension of seabed material at the foot of the continental slope in the rockall channel to better understand the relationship between near bottom hydrodynamics and sediment resuspension in the transition zone between the continental slope and the abyssal plain an array of three moorings equipped with near bottom sediment traps and current meters was deployed in a triangular configuration of at the foot of the south east slope of the rockall channel north atlantic in addition a fast sampling adcp was moored in the centre of the triangle microscopic observations combined with grain size analysis revealed that the material intercepted by the traps was mainly composed of loose phytodetritus and aggregates organic carbon and 13corg analyses further indicate that this material is relatively fresh and hence probably only transported over short distances the total mass flux measured by the traps suggests input from either laterally advected or resuspended material during the deployment period the measured flux was variable in time and space with a strong increase at the deepest site at the very foot of the slope the measured flux did not correlate significantly with daily averaged current speed suggesting that processes other than those related to elevated bed shear stress are involved in the resuspension mechanism rapid changes in the hydrodynamics probably related to internal motions are evidenced by abrupt bursts in the current velocity and in the near bottom turbidity their occurrence at slack tidal waters appears to be at the origin of the resuspension observed at the foot of the slope of the rockall channel high resolution current velocity measurements suggest that resuspension is dominated by energetic highly localised and short term resuspension events despite the abyssal depths part of these events resemble in many ways the solibores which have been previously observed to enhance sediment transport at much shallower depths over the continental slope while others rather appear to be associated to gravity waves

sensing of upslope passages of frontal bores across the trench slope break of the japan trench the circum pacific trench slope system is one of the most spectacular topographic features of the earth we report the relatively frequent occurrence of upslope passages 50 times a year of internal bores in the japan trench system observations were made using a triaxial accelerometer a tiltmeter and a current meter at the seafloor 3400 m deep during 10 months from 2013 to 2014 we detected 42 tilt events from the records of the accelerometer and confirmed their consistency with the tiltmeter records the tilt occurred always landward by 1 10 rad with a rise time on the order of 1000 s and return to the original with a much longer recovery time the current and temperature records available for the first two events indicated that landward tilting was associated with an upslope current with a speed of several cm s and a temperature drop of several tens of m c the temperature remained cold even after the current had diminished all of these observations implied the frontal passages of upslope advancing bores which caused the instrument to be tilted landward the observational site was located at the trench slope break separating the trench slope sloping supercritically or near critically for the m2 internal tide from the fore arc basin sloping subcritically this unique locality suggested the internal tide origin of the observed bores although other possibilities could not be precluded bores generated on the trench slope may play a role for upslope transportation of suspended sediments stirred up by deep submarine landslides

calibration of radiocarbon ages and the interpretation of paleoenvironmental records abstract calibration of the radiocarbon timescale of paleoecological records is essential if they are to be explained correctly in terms of their governing ecological or climatological controls the differences between calendar ages and radiocarbon ages that arise from variations in 14c production through time can distort the chronologies of individual records and the interpretations based on them misleading impressions of synchrony or diachrony of events among multiple records can result and estimates of the apparent duration of episodes and rates of sedimentation and local population changes can be biased displays of the temporal patterns of migration or extinction may also be affected spurious correlations may arise between records with radiocarbon controlled chronologies and time series of potential controls that are expressed on a calendar time scale support for particular explanations of features in a paleoecological record may vary depending on whether radiocarbon ages are calibrated or not this situation is illustrated using the eastern beringian populus subzone as an example when the radiocarbon ages that control the timing of the populus subzone are calibrated the contemporaneous decrease in ice volume and increase in summer insolation are implicated as the ultimate controls of the occurrence of the subzone

a 250 ka sedimentary record from a small karstic lake in the northern levant yammouneh lebanon paleoclimatic implications the levant influenced by both the mediterranean sea and the saharan arabian deserts is a key region for understanding climatic changes in response to glacial interglacial boundary conditions that have greatly affected regional hydrology here we present the first long term paleoenvironmental record from the northern levant presently much wetter than the southern levant our record derives from the multi proxy study of a sediment core 36 m long retrieved from the small intra mountainous tectonic basin of yammouneh lebanon which is mainly supplied by karstic springs sediments consist of a thick accumulation of brownish to greenish clayey silts interrupted by intervals of whitish marls composed of caco3 rich material the core chronology is based on radiometric dating 14c and u th and paleomagnetic techniques the sedimentary sequence spans approximately the last two glacial interglacial cycles 250 ka carbonate content is relatively high throughout the profile due to a perennial input of detrital calcite from the watershed but varies significantly the marls are mostly composed of authigenic and biogenic calcite and reflect lacustrine environments with high carbonate productivity during peaks of interglacial periods their occurrence suggests low physical erosion of the basin slopes which were covered by arboreal vegetation and intense karstic water circulation under warm and relatively wet conditions in agreement with pollen data the clayey silts are dominated by quartz and clay minerals and a few amounts of k feldspars and dolomite they are characterized by high concentration in magnetic particles and high relative concentrations of si al k and fe considered as strictly of detrital origin due to the carbonated nature of the watershed quartz and k feldspars are attributed to eolian origin from a distal source the clayey silt intervals generally suggest palustrine conditions with abrupt flows responsible for runoff derived material or subaerial environments and low local water availability in particular during the last glacial maximum high si al and k al ratios during interglacials are attributed to relatively high eolian dust contribution due to the decrease of local detrital inputs our study reveals significant differences between yammouneh and lake records from the dead sea basin southern levant the latter showing high low levels during glacial interglacial periods these hydrological differences might reflect either changes in the north south ns rainfall gradient in response to the development of the northern ice sheet and the southward migration of the westerly belt or local factors i e a decrease in efficient precipitation and water availability at yammouneh during the coldest glacial periods e g the last glacial maximum due to water storage by ice caps on the mount lebanon range and frozen soils in the yammouneh basin

pollen studies in the junin area central peruvian andes laguna junin is a large lake 675 km long but only 4 m deep located in the grass covered altiplano at an altitude of 4 100 m northeast of lima pollen analysis of a 30 m core indicates that from about 12 000 yr ago until some time after 3 000 yr ago about 30 of the pollen was carried in by easterly winds from the east andean forests which today are at least 600 m lower in elevation contemporaneous pollen deposition in lakes on moraines of the last glaciation west of the junin plain was dominated by local grassland types and had little contribution from this easterly source at some time after 3 000 yr ago perhaps about 1 200 yr ago the pollen influx to laguna junin from this distant forest source greatly diminished perhaps because of deforestation by increased human populations between about 12 000 and 24 000 yr ago in the junin core the sparse pollen concentration was dominated by grassland types supplemented by polylepis acaena alnus and compositae blown in from the sub puna shrublands that may have occupied much of the east andean slopes in place of the humid forest that occurs there today the silty sediment in this section of the core is interpreted as outwash from piedmont glaciers that invaded the plain especially from the cordillera to the west these glaciers left a distinctive pattern of moraines and outwash fans which served to dam tine lake basin an unconformity in the sediment covers the time from about 24 000 to 39 000 yr ago when the lake was probably dry before this time the silty sediment and the dominance of grassland and shrubland pollen types indicates an earlier interval of glaciation recorded on the landscape by an older set of moraines and outwash fans which initially dammed the lake basin

paleoclimatic estimates from water and energy budgets of east african lakes abstract the turkana nakuru elmenteita and naivasha basins in the rift valley of east africa experienced high water levels during the period of 10 000 7000 yr b p analyses of the modern hydrologic and energy budgets for these basins along with that of lake victoria were used to infer the amount of precipitation that would have been required to maintain the enlarged paleolakes of the early holocene precipitation must have been at least 150 300 mm yr 15 to 35 above the modern average the precipitation estimates were fairly consistent among the various basins but no quantitative estimate was made for the additional precipitation required to account for overflow from the rift valley lake basins discharge from the lake victoria basin around 1880 a d was considerably above the more recent average and the increased discharge into the white nile for that period might have been similar to that of the early holocene a sensitivity analysis showed that temperature changes were probably not too important for changing the hydrologic energy budget changes of albedo bowen ratio and cloudiness were likely to have been of greater importance

non traditional reflection of internal waves from a sloping bottom and the likelihood of critical reflection 1 the problem of internal inertio gravity wave reflection from an arbitrarily orientated uniform slope is solved in a linear setting and with coriolis effects fully included that is the horizontal component of the earth rotation vector is taken into account a new criterion is derived for critical reflection the presence of creates a specific anisotropy the criterion depends on the orientation of the bottom slope in the horizontal geographical plane while it does not depend on the horizontal orientation of the incident wave using an empirical based bottom slope distribution the probability of critical reflection is calculated for diurnal and semi diurnal internal tide bands for a range of latitudes and for various values of stratification the probability is largest near the inertial latitudes i e when the internal tides are near inertial it is explained how the inclusion of gives significant changes in the probability near these latitudes especially for weak stratification

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

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

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation

multiple early holocene climate oscillations at silver lake new jersey and their possible linkage with outburst floods abstract episodic discharges from the laurentide ice sheet are considered to be one of the major causes of climate oscillations during the glacial to interglacial transition these outburst floods disrupted thermohaline circulation and might have caused cooling events in the north atlantic region and beyond including the younger dryas preboreal oscillation and 8 2 ka events however few terrestrial sedimentary records show regional climate changes directly linked to outburst floods during the early holocene here we present lithologic and isotopic data from silver lake in northern new jersey to document temperature and moisture changes during the early holocene and to discuss possible linkage with outburst flooding events the lithologic record shows multiple intervals with coupled decreases in carbonate and increases in organic matter during the early holocene suggesting lower lake levels and drier climate conditions simultaneous with these changes were decreases in carbonate 18 o values likely reflecting a decrease in air temperature during these dry periods the apparent correlation of these sedimentary events at silver lake with documented outburst floods from the melting ice sheet suggests a possible causal connection implying that the climate in the mid atlantic region was extremely sensitive to perturbations of ocean circulation