ice age simulations with a calving ice sheet model abstract variations of ice sheet volume during the quaternary ice ages are simulated using a simple ice sheet model for the northern hemisphere the basic model predicts ice thickness and bedrock deformation in a north south cross section with a prescribed snow budget distribution shifted uniformly in space to represent the orbital perturbations an ice calving parameterization crudely representing proglacial lakes or marine incursions can attack the ice whenever the tip drops below sea level the model produces a large 100 000 yr response in fair agreement correlation coefficient up to 0 8 with the 18o deep sea core records to increase confidence in the results several of the more uncertain model components are extended or replaced using an alternative treatment of bedrock deformation a more realistic ice shelf model of ice calving and a generalized parameterization for such features as the north atlantic deglacial meltwater layer much the same ice age simulations and agreement with the 18o records as with the original model are still obtained the model is run with different types of forcing to identify which aspect of the orbital forcing controls the phase of the 100 000 yr cycles first the model is shown to give a 100 000 yr response to nearly any kind of higher frequency forcing although over the last 2 million yrs the model phase is mainly controlled by the precessional modulation due to eccentricity over just the last 500 000 yr the observed phase can also be simulated with eccentricity held constant a definite conclusion on the phase control of the real 100 000 yr cycles is prevented by uncertainty in the deep sea core time scales before 600 000 yr b p the model is adapted to represent west antarctica and yields unforced internal oscillations with periods of about 50 000 yr

a high resolution proxy record of rainfall and enso since ad 1550 from layering in stalagmites from anjohibe cave madagascar two stalagmites from anjohibe cave have annual layers made up of inclusion rich calcite over inclusion free calcite or of darker aragonite over clear aragonite geochemical evidence indicates that the basal units are deposited slowly in the wet season and the upper units more rapidly in the dry season for the period with rainfall and temperature data ad 1951 1992 layer thickness correlates well with the southern oscillation index soi as well as rainfall water surplus and actual evapotranspiration aet at nearby majunga com parison of the layer record for one stalagmite with 1866 1994 soi data indicates that layer thickness correlates best with the frequency and intensity of warm low phase so el nino events not with average soi conditions in addition the 415 year layer thickness time series from that speleothem agrees remarkably well with historical records of el nino frequency with galapagos ecuador coral records of sea surface temperature in the eastern pacific and with accumulation

the influence of whitecapping waves on the vertical structure of turbulence in a shallow estuarine embayment abstract the vertical distribution of the turbulent kinetic energy dissipation rate was measured using an array of four acoustic doppler velocimeters in the shallow embayment of grizzly bay san francisco bay california owing to the combination of wind and tide forcing in this shallow system the surface and bottom boundary layers overlapped whitecapping waves were generated for a significant spectral peak steepness greater than 0 05 or above a wind speed of 3 m s 1 under conditions of whitecapping waves the turbulent kinetic energy dissipation rate in the upper portion of the water column was greatly enhanced relative to the predictions of wind stress wall layer theory instead the dissipation followed a modified deep water breaking wave scaling near the bed bottom 10 of the water column the dissipation measurements were either equal to or less than that predicted by wall layer theory stratification due to concentration gradients in suspended sediment was identified as the likely cause for t

intra and inter annual growth rate of modern stalagmites we measure the factors that determine growth rate temperature drip rate calcium ion concentration for 31 waters that feed stalagmites within six cave systems throughout europe water samples were collected at a frequency of at least 1 month to permit the modelling of both inter and intra annual growth rate variations utilising the theory of wolfgang dreybrodt chem geol 29 1980 89 105 chem geol 32 1981 237 245 dreybrodt w 1988 processes in karst systems springer verlag berlin 288 pp inter annual growth rates were measured using the stalagmites that were associated with the analysed water samples growth rate was determined from annual lamina counting specific time markers within the stalagmites and location of bomb 14c when compared to theoretically predicted values a good agreement between theoretical and measured stalagmite growth rates is observed r2 0 69 when compared to site climate and geochemical parameters a good correlation is observed between measured growth rate and mean annual temperature for five sites r2 0 63 and dripwater calcium content r2 0 61 but not drip rate r2 0 09 the good correlation with both calcium and temperature is due to soil co2 production being primarily determined by surface temperature and soil moisture however when we compare our data to that in the grotte de clamouse a site that has little soil cover we observe that the growth rate temperature relationship breaks down due to either the lack of soil co2 production or prior calcite precipitation intra annual data demonstrates that maximum growth rate occurs when calcium concentrations are high and that this occurs under different seasons depending on the hydrology of each site our results demonstrate a stronger dependence of intra annual stalagmite growth rate on dissolved calcium ion concentrations than drip rate for the range of drip rates investigated here 0 01 t 2drip s 1 but for lower drip rates this factor becomes important in controlling growth rate we suggest that for well monitored and understood sites stalagmite growth rate variations can provide useful information for palaeoclimate reconstruction

modelling the last ice age cycle with 2 d climate models we compare the results of 2 zonally averaged climate models designed to simulate the ice age cycles of the pleistocene one model was developed at louvain la neuve university lln model the other model is now running at the university of bremen ub model in the lln model the atmosphere ocean sub system is treated in a rather sophisticated way with a simplified formulation of ice sheet dynamics the ub model explicitly calculates ice flow and ice temperature within the ice sheet but contains a simplified atmosphere and no ocean the two model simulations of the last ice age cycle the last 120 000 years show the strong link between the variations in the insolation and the modelled variations of the ice sheet volume however this link is non linear the transformation of the insolation changes into changes of the global ice volume depends on the modelled state of the ice sheet

the younger dryas an intrinsic feature of late pleistocene climate change at millennial timescales abstract a box model of the north atlantic ocean exhibits self sustained oscillations of the large scale ocean circulation which are reminiscent of dansgaard oeschger do style oscillations the freshwater forcing of this ocean model depends on mean climate state represented by global ice volume this is computed by a one dimensional ice sheet model subject to changes in high latitude northern hemisphere summer insolation at low large ice volume the ocean ice system stays in a permanent interstadial stadial mode millennial scale do style oscillations result at intermediate ice volume values which thus define a do window during an interglacial to glacial transition this do window is crossed sufficiently slow to allow for sustained do style oscillations to develop in contrast during a glacial termination the system moves relatively rapid through the do window resulting in an intermittent re appearance of do style oscillations which resemble the sequence of events surrounding the younger dryas yd when forced with modeled ice volume evolution over the last 800 thousand years our model predicts younger dryas type cooling events for each major glacial termination accordingly the younger dryas does not appear to be a one time event

surface wave effects on high frequency currents over a shelf edge bank abstractseveral acoustic doppler current profilers and vertical strings of temperature conductivity and pressure sensors deployed on and around the east flower garden bank efgb were used to examine surface wave effects on high frequency flows over the bank and to quantify spatial and temporal characteristic of these high frequency flows the efgb about 5 km wide and 10 km long is located about 180 km southeast of galveston texas and consists of steep slopes on southern and eastern sides that rise from water depths over 100 m to within 20 m of the surface three dimensional flows with frequencies ranging from 0 2 to 2 cycles per hour cph were observed in the mixed layer when wind speed and stokes drift at the surface were large these motions were stronger over the bank than outside the perimeter the squared vertical velocity w2 was strongest near the surface and decayed exponentially with depth and the e folding length of w2 was 2 times larger than that of stokes drift the 2 h averaged w2 i

a sea ice climate switch mechanism for the 100 kyr glacial cycles a box model of the ocean atmosphere sea ice land ice climate system is used to study a novel mechanism for self sustained oscillations of the climate system on a time scale of 100 000 years without external forcing the oscillation in land ice volume has the familiar sawtooth shape of climate proxy records the most novel aspect of the climate oscillations analyzed here is the crucial role played by the sea ice the sea ice acts as a switch of the climate system switching it from a growing land glaciers mode to a retreating land glaciers mode and shaping the oscillation s sawtooth structure a simple explanation of the 100 kyr timescale is formulated on the basis of the mechanism seen in the model finally rapid sea ice changes such as those seen in our model and their drastic effects on the climate system may provide an explanation to some of the rapid climate changes observed to be a part of the variability at all timescales in the paleorecord

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

a 780 year annually resolved record of indian ocean monsoon precipitation from a speleothem from south oman 1 meteorological records of monsoon rainfall in the indian ocean are generally less than 100 years long the relative brevity of these records makes it difficult to investigate monsoon variation on decadal and centennial timescales to determine what factors influence the intensity of rainfall on these timescales or to place possible changes in the twentieth century into a broader historical context development of a geologic proxy for rainfall that records annual variation in the monsoon over much longer time periods than are covered by instrumental records would be a significant step forward we have developed an annually resolved record of monsoon rainfall variation for the past 780 years based on annual layer thickness and stable isotope analyses of a laminated stalagmite from southern arabia our results show that monsoon variation over the past century is not outside of the range of the past 800 years decreasing monsoon rainfall over the past century is related to increasing sea surface temperature in the indian ocean spectral analyses of the record are dominated by cycles that are similar to those observed in records of solar activity on centurial timescales decadal to interannual cycles in the record appear to originate in the tropical pacific ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 3354 meteorology and atmospheric dynamics precipitation 1854 1620 global change climate dynamics 3309 1699 global change general or miscellaneous keywords monsoon paleoclimate rainfall indian ocean speleothem oxygen isotopes

a thousand year speleothem proxy record of north atlantic climate from scotland luminescent organic matter in stalagmites may form annual bands allowing growth rate to be precisely determined stalagmite growth rate is controlled by precipitation so annual bands can be used to derive long precipitation records a continuously banded stalagmite from a cave in nw scotland was used to provide a 1100 year high resolution record of precipitation the location of the cave means that precipitation is closely linked to the north atlantic oscillation for which a record is also derived this suggests that changes in the north atlantic oscillation state was an important control on european climate over the past millennium

carbon and oxygen isotope study of the active water carbonate system in a karstic mediterranean cave implications for paleoclimate research in semiarid regions abstract in a semiarid climatic zone such as the eastern mediterranean region annual rainfall variations and fractionation processes in the epikarst zone exert a profound influence on the isotopic compositions of waters seeping into a cave consequently the isotopic compositions of speleothems depositing from cave waters may show complex variations that need to be understood if they are to be exploited for paleoclimate studies this is confirmed by a four year study of the active carbonate water system in the soreq cave israel the 18o smow values of cave waters range from 6 3 to 3 5 the highest 18o values occur at the end of the dry season in waters dripping from stalactites and reflect evaporation processes in the epikarst zone whereas the lowest values occur in rapidly dripping fast drip waters at the peak of the rainy seasons however even fast drip waters are about 1 5 heavier than the rainfall above the cave which is taken to reflect the mixing of fresh with residual evaporated water in the epikarst zone 13c pdb values of dissolved inorganic carbon dic vary from 15 6 to 5 4 with fast drip waters having lower 13c values mostly 15 6 to 12 and higher dic concentrations relative to pool and stalactite drip water the low 13c values of fast drip waters and their supersaturation with respect to calcium carbonate indicates that the seepage waters have dissolved both soil co2 derived from overlying c3 type vegetation and marine dolomite host rock the 18o pdb values of various types of present day low magnesium calcite lmc speleothems range from 6 5 to 4 3 and 13c values from 13 to 5 5 and are not correlated with speleothem type an analysis of 18o values of present day calcite rafts and pool waters shows that they form in oxygen isotope equilibrium similarly the measured ranges of 13c and 18o values for all types of present day speleothems are consistent with equilibrium deposition at cave temperatures the 13c 18o range of contemporary lmc thus reflects the variations in temperatures and isotopic compositions of the presentday cave waters the 10 variation in the 13c values in waters can be modeled by a simple rayleigh calculation of the carbon isotope fractionation accompanying co2 degassing and carbonate precipitation these variations may obscure the differences in the carbon isotopic composition of speleothems that could arise when vegetation cover changes from c3 to c4 type plants this consideration emphasizes that it is necessary to characterize the full range of 13c values associated with contemporaneous speleothems in order to clarify the effects of degassing from those due to differing vegetation types isotopic studies of a number of different types of fossil lmc speleothems show many of them to exhibit isotopic trends that are similar to those of present day lmc but others show both higher and lower 18o ranges in particular the higher 18o range has been shown by independent age measurements to be associated with a period of drier conditions the results of the study thus indicate that it is necessary to work on a well calibrated cave system in semiarid climates and that the fossil speleothem record should be obtained from different types of contemporaneous deposit in order to fully characterize the 18o 13c range representative of any given climatic period

measurements of turbulence in the upper ocean mixing layer using autosub abstract the rate of dissipation of turbulent kinetic energy has been measured with airfoil probes mounted on an autonomous vehicle autosub on constant depth legs at 2 10 m below the surface in winds up to 14 m s 1 the observations are mostly in an area limited by fetch to 26 km where the pycnocline depth is about 20 m at the operational depths of 1 55 15 9 times the significant wave height hs and in steady winds of about 11 6 m s 1 when the wave age is 11 7 17 2 dissipation is found to be lognormally distributed with a law of the wall variation with depth and friction velocity breaking waves leaving clouds of bubbles in the water are detected ahead of the autosub by a forward pointing sidescan sonar and the dissipation is measured when the clouds are subsequently reached bands of bubbles resulting from the presence of langmuir circulation are identified by a semiobjective method that seeks continuity of band structure recognized by both forward and sideways pointing sidescan sonars the times

modeling the oxygen isotopic composition of the north american ice sheet and its effect on the isotopic composition of the ocean during the last glacial cycle contribution to the change of seawater d 18 o dw between the last glacial maximum lgm and the holocene and to evaluate the effect of nonequilibrium isotopic composition of the nais on the relationship between ice volume variations and the ocean isotopic enrichment the enrichment due to the nais at the lgm was 0 63 corresponding to 60 of the lgm sea level lowstand and to a mean d 18 o of the nais of approximately 31 the modeled nais volume variations and the induced dw changes over the past 120 000 years indicated no significant time lag the inaccuracy associated with linearly inferring ice volume variations from dw changes was generally less than 10 citation sima a a paul m schulz and j oerlemans 2006 modeling the oxygen isotopic composition of the north american ice sheet and its effect on the isotopic composition of the ocean during the last glacial cycle geophys res lett 33 l15706 doi 10 1029 2006gl026923

the effect of wave breaking on surf zone turbulence and alongshore currents a modeling study the effect of breaking wave generated turbulence on the mean circulation turbulence and bottom stress in the surf zone is poorly understood a one dimensional vertical coupled turbulence k and mean flow model is developed that incorporates the effect of wave breaking with a time dependent surface turbulence flux and uses existing published model closures no model parameters are tuned to optimize model data agreement the model qualitatively reproduces the mean dissipation and production during the most energetic breaking wave conditions in 4 5 m water depth off of a sandy beach and slightly underpredicts the mean alongshore current by modeling a cross shore transect case example from the duck94 field experiment the observed surf zone dissipation depth scaling and the observed mean alongshore current although slightly underpredicted are generally reproduced wave breaking significantly reduces the modeled vertical shear suggesting that surf zone bottom stress cannot be estimated by fitting a logarithmic current profile to alongshore current observations model inferred drag coefficients follow parameterizations manning strickler that depend on the bed roughness and inversely on the water depth although the inverse depth dependence is likely a proxy for some other effect such as wave breaking variations in the bed roughness and the percentage of breaking wave energy entering the water column have a comparable effect on the mean alongshore current and drag coefficient however covarying the wave height forcing and dissipation and bed roughness separately results in an alongshore current drag coefficient only weakly strongly dependent on the bed roughness because of the competing effects of increased turbulence wave forcing and orbital wave velocities

cyclic rapid warming on centennial scale revealed by a 2650 year stalagmite record of warm season temperature 1 a 2650 year bc665 ad1985 warm season mjja may june july august temperature reconstruction is derived from a correlation between thickness variations in annual layers of a stalagmite from shihua cave beijing china and instrumental meteorological records observations of soil co2 and drip water suggest that the temperature signal is amplified by the soil organism co2 system and recorded by the annual layer series our reconstruction reveals that centennial scale rapid warming occurred repeatedly following multicentenial cooling trends during the last millennia these results correlate with different records from the northern hemisphere indicating that the periodic alternation between cool and warm periods on a sub millennial scale had a sub hemispherical influence

measurements of enhanced near surface turbulence under windrows abstractobservations of waves winds turbulence and the geometry and circulation of windrows were made in a shallow bay in the winter of 2018 outside of rimouski quebec water velocities measure

drought reconstructions for the continental united states abstract the development of a 2 lat 3 long grid of summer drought reconstructions for the continental united states estimated from a dense network of annual tree ring chronologies is described the drought metric used is the palmer drought severity index pdsi the number of grid points is 154 and the reconstructions cover the common period 1700 1978 in producing this grid an automated gridpoint regression method called point by point regression was developed and tested in so doing a near optimal global solution was found for its implementation the reconstructions have been thoroughly tested for validity using pdsi data not used in regression modeling in general most of the gridpoint estimates of drought pass the verification tests used in addition the spatial features of drought in the united states have been faithfully recorded in the reconstructions even though the method of reconstruction is not explicitly spatial in its design the drought reconstructions show that the 1930s dust bow

vertical structure of dissipation in the nearshore abstract the vertical structure of the dissipation of turbulence kinetic energy was observed in the nearshore region 3 2 m mean water depth with a tripod of three acoustic doppler current meters off a sandy ocean beach surface and bottom boundary layer dissipation scaling concepts overlap in this region no depth limited wave breaking occurred at the tripod but wind induced whitecapping wave breaking did occur dissipation is maximum near the surface and minimum at middepth with a secondary maximum near the bed the observed dissipation does not follow a surfzone scaling nor does it follow a log layer surface or bottom boundary layer scaling at the upper two current meters dissipation follows a modified deep water breaking wave scaling vertical shear in the mean currents is negligible and shear production magnitude is much less than dissipation implying that the vertical diffusion of turbulence is important the increased near bed secondary dissipation maximum results from a decrease in the tu

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

antarctic ice and sediment flux in the oligocene simulated by a climate ice sheet sediment model abstract a model of deforming sediment is added to a climate ice sheet model and applied to the eocene oligocene transition in antarctic ice volume around 34 ma the coupling between the global climate and ice sheet models is asynchronous with a climate simulation performed once every 10 000 years and only for the first 40 000 years these global climate model solutions are re used to perform runs of 400 000 years in length with orbital forcing and different levels of co2 the sediment model includes bulk transport under ice generation of sub ice till and river transport and predicts the continental scale evolution of sediment thickness and coastal discharge for the first few 10 000 s of years after the onset of substantial ice triggered by co2 falling below 3 pre industrial level sediment discharge to the ocean is relatively uniform around the coast derived from nearby pre existing regolith after that most discharge is concentrated into 4 sites at the mouths of major trough systems with orbitally paced pulses on 104 yr scales these sites and the average magnitudes of the fluxes agree generally with those deduced from offshore seismic and core data although longer 10 my integrations are needed to model the real sediment evolution

late holocene annual growth in three alpine stalagmites records the influence of solar activity and the north atlantic oscillation on winter climate annual growth rates and the ratio of dark to light colored calcite within single annual laminae in three contemporaneously deposited holocene speleothems from grotta di ernesto an alpine cave in northern italy respond to changes in surface temperature rather than precipitation based on monitoring of present day calcite growth and correlation with instrumental data for surface climatic conditions we interpret a higher ratio of dark to light colored calcite and the simultaneous thinning of annual laminae as indicative of colder than present winters such dark and thin laminae occur in those parts of the three stalagmites deposited from ad 1650 to 1713 and from ad 1798 to 1840 as reconstructed through lamina counting these periods correspond to the well known maunder and dalton minima of solar activity an 11 yr cyclicity in growth rate coupled with reduced calcite deposition during the historic minima of solar activity is indicative of a solar influence on lamina thickness spectral analysis of the lamina thickness data also suggests that the north atlantic oscillation variability influenced winter temperatures based on the present day controls on cave calcite formation we infer that high frequency changes in solar activity modulated the seasonal duration of soil co2 production

testing theoretically predicted stalagmite growth rate with recent annually laminated samples implications for past stalagmite deposition annually laminated stalagmites deposited over the last 30 160 years are analysed to determine their growth rate three natural and artificial cave sites in england france and belgium were chosen for their wide range of variability in growth rate determining variables and multiple samples were taken from each site the annual nature of laminae deposition within the stalagmite calcite was confirmed by comparison to the date of cave void opening 14c analyses or by using dated event horizons measured stalagmite growth rate was determined from annual laminae thickness measurements and compared to that theoretically predicted from the chemical kinetics of the calcite precipitation reaction a good agreement is observed between empirical observations and theoretical predictions although two complicating factors variations in calcite porosity and seasonal cessation of the water supply to the samples both affect the growth rate implications for the extraction of palaeoclimate information from stalagmite growth rate are discussed

a new second order turbulence closure scheme for modeling the oceanic mixed layer a new second order turbulence closure scheme is proposed for the oceanic mixed layer the scheme is similar in complexity to a mellor yamada level 2 5 scheme in that the turbulent kinetic energy is the only turbulence quantity treated prognostically with the others determined diagnostically the main difference lies in the treatment of the turbulent fluxes while momentum fluxes are assumed to be downgradient the other turbulent fluxes allow for nonlocal and countergradient contributions the model was tested against several idealized forcing experiments for wind deepening heating and cooling cases and also against observational data taken from ocean weather stations november and papa the simulations reveal good agreement with other models the present scheme also performs reasonably well in reproducing the observed sea surface temperature and boundary layer depth for the year 1961 at stations november and papa also proposed are ways of incorporating near surface processes such as langmuir circulation and wave breaking simulations have shown that wave breaking leads to negligible deepening of the mixed layer while the inclusion of langmuir circulations causes further deepening to occur

high precision and high resolution carbonate 230th dating by mc icp ms with sem protocols abstract to facilitate the measurement of u th isotopic compositions suitable for high precision and high resolution 230th dating of coral and speleothem carbonates secondary electron multiplier sem protocol techniques for multicollector inductively coupled plasma mass spectrometry mc icp ms have been developed the instrumental sensitivities are 1 2 with a precision of 1 2 2 for abundance determination of 50 200 fg 234u 1 4 ng 238u or 230th this method features chemistry refinements improvements to procedural and instrumental blanks spectral inference reductions and careful consideration of non linear sem behavior measurement consistency of this mc icp ms combined with previous mass spectrometric results on u th standards and a variety of carbonates demonstrates the validity of the sem protocol method for fossil corals a routine u th isotopic determination at permil level precision requires only 10 50 mg of carbonate as little as 200 mg of young coral with an age of less than 20 yr can be dated with a precision of 0 3 0 8 yr about 20 200 mg speleothem samples with sub ppm to ppm u are required to earn a 5 precision on ages from 5 to 100 kyr requirement of small sample size 10 100s mg carbonate can permit high temporal resolution to date speleothems with slow growth rates i e 1 10 mm kyr this high precision 230th chronology is critical to accurately establish age models date events and splice geochemical proxy time series records from multiple samples in the fields of paleoclimatology and paleoceanography the u th isotopic determination techniques described here can also be applied to different environmental samples such as waters rocks and sediments

oceanic turbulence dissipation measurements in swade abstract recent experiments measuring turbulence dissipation rates in the upper ocean can be divided into two types those supporting an analogy between the upper ocean and lower atmosphere with dissipation rates following wall layer behavior and those finding oceanic dissipation rates to be much higher than wall layer predictions in an attempt to reconcile these two diverse acts of observations terray et al proposed a wave dependent scaling of the dissipation rate based on the significant wave height and the rate of energy input from the wind to the waves their parameterization was derived from observations of strongly forced fetch limited waves although they conjectured that it would apply in typical oceanic conditions as well this paper reports new measurements of turbulent kinetic energy dissipation made in the north atlantic ocean from a swath ship during the recent surface waves dynamics experiments swade these data support the scaling of terray et al verifying its validity when applied

formation of a diurnal thermocline in the ocean mixed layer simulated by les the formation of a diurnal thermocline in the ocean mixed layer under a stabilizing buoyancy flux was simulated successfully by large eddy simulation reproducing various features consistent with observation the analysis of the simulation result revealed that the formation of a diurnal thermocline passes through two different phases the formation of a thermocline formation stage and increasing thickness of the thermocline thereafter growth stage turbulent kinetic energy tke flux dominates tke production within the mixed layer but turbulencemaintained by shear production at the thermoclinecausesstratification below the mixed layer in addition once the thermocline is formed both the gradient and flux richardson numbers maintain constant values at the thermocline it was also found that a diurnal thermocline cannot be formed in the absence of both wave breaking and langmuir circulation furthermore the effects of stratification on turbulencewereinvestigatedbasedonthetimeseriesofvariousphysicalvariablesofturbulenceatthediurnal thermocline and within the mixed layer and the mechanism for diurnal thermocline formation is discussed

glacial terminations in the oxygen isotope record of deep sea cores hypothesis of massive antarctic ice shelf destruction abstract glacial terminations i and ii in the deep sea core foraminiferal oxygen isotope ratios though not similar in form are each characterized by a short interval of about 3 ka during which a large negative change occurred in the ratios after correcting for temperature effects we estimate that each change was equivalent to a glacial disintegration capable of causing a 50 60 m eustatic sea level rise in the termination i interval 16 13 ka b p the estimated equivalent sea level rise is much larger than that suggested by the best evidence of deglacial ice loss from the laurentide ice sheet which is thought to dominate pleistocene glacial ice volume changes moreover in termination ii about 125 ka b p the estimated equivalent sea level rise is much larger than that inferred from the stratigraphy of coral reefs and beaches on new guinea and other locations which suggests quite high sea levels for 10 ka prior to this termination to reconcile these severely conflicting lines of evidence we propose that the rapid negative isotope ratio changes were largely caused by the disintegration of massive floating antarctic ice shelves which masqueraded as land ice in the oceanic isotope ratios but which contributed no sea level change we propose that such shelves were formed when oceanic circulation changes in the north atlantic under glacial conditions greatly reduced the formation of relatively warmer north atlantic deep water and its injection into circumpolar antarctic regions and that the shelves disintegrated rapidly with the resumption of large scale formation of this deep water and its input into the antarctic we find that high sea levels in the 125 135 ka b p interval prior to termination ii which imply very little northern ice then are well supported by dated coral reef stratigraphy although these ages were not accepted by the climap study of the last interglacial ocean minimal northern ice volumes at that time imply that strong milankovitch summer insolation is not always required for northern deglaciation a promising additional deglacial mechanism is the prolonged viscous depression of the crust beneath the laurentide ice sheet combined with atmospheric oceanic circulation factors

oceanic mechanisms for amplification of the 23 000 year ice volume cycle situated adjacent to the largest northern hemispher ice sheets of the ice ages the mid latitude north atlantic ocean has an important role in the earth s climate history it provides a significant local source of moisture for the atmosphere and adjacent continents forms a corridor that guides moisture bearing storms northward from low latitudes and at times makes direct contact along its shorelines with continental ice masses evidence of major ice ocean air interactions involving the north atlantic during the last 250 000 years is summarized outflow of icebergs and meltwater initially driven by summer insolation over the ice sheets affects midlatitude ocean temperatures summer heat storage winter sea ice extent and global sea level these oceanic responses in turn influence the winter moisture flux back to the ice sheets as well as ablation of land ice by calving spectral data indicate that the oceanic moisture and sea level feedbacks in part controlled by glacial melt products amplify milankovitch insolation forcing of the volumetrically dominant mid latitude ice sheets at the 23 000 year precessional cycle

ice age terminations 230th dated oxygen isotope records of stalagmites from sanbao cave china characterize asian monsoon am precipitation through the ends of the third and fourthmost recent ice ages as a result am records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments establishing the timing and sequence of major events in all four cases observations are consistent with a classic northern hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets meltwater and icebergs entering the north atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon causing increases in atmospheric co2 and antarctic temperatures that drive the termination in the southern hemisphere increasing co2 and summer insolation drive recession of northern ice sheets with probable positive feedbacks between sea level and co2

summer monsoon precipitation variations in central china over the past 750 years derived from a high resolution absolute dated stalagmite abstract a 2 3 year resolution record of stalagmite oxygen isotope variations from the south flank of the qinling mountains central china has revealed the asian summer monsoon asm precipitation variations in the investigated area over the past 750 years the summer monsoon precipitation gradually increased since 1249 ad reaching its highest values in the period 1535 1685 ad and then decreased with substantial decadal to centennial scale fluctuations the monsoon precipitation increased again between 1920 and 1970 ad three intervals of high monsoon precipitation were identified 1535 1685 ad 1755 1835 ad and 1920 1970 ad three intervals of low precipitation were inferred in 1249 1325 ad 1390 1420 ad and 1890 1915 ad the 18 o composition and lithological features of the stalagmite coincidently indicate a wetter climate during the little ice age lia which is also confirmed by climate records from chinese historical documents within this area a comparison with other high resolution speleothem records indicates regional differences in monsoon precipitation variability from the south to the north of central china in the last 750 years on decadal to centennial scale power spectrum analysis of the 18 o record shows significant 117 8 34 6 14 10 3 and 6 year periodicities these periodicities are widely observed in the climate records from asm controlled areas of china and are consistent with the gleissburg periodicity br ckner periodicity sunspot periodicity of solar activity and el nino southern oscillation enso periodicity these correlations suggest that both solar activity and enso periodicity may have had important influences on asm precipitation in china over the past 750 years

extension of summer june august temperature records for northern inner mongolia 1715 2008 china using tree rings this paper presents a spatially and temporally improved reconstruction of mean summer june august temperature derived from tree ring width data of dahurian larch larix gmelinii rupr from the northern great xing an mountains northeast china three new chronologies were added to the original 2011 reconstruction and the reconstruction extended back to ad 1715 the reconstruction was generated using a simple linear regression method verified by independent meteorological data and accounts for 47 0 of the actual temperature variance during the common period 1957 2008 the reconstruction captures decadal and century scale regional temperature variability such as cold decades 1940s 1930s 1790s 1950s and 1850s warm decades 2000s 1870s 1750s 1980s and 1840s a cold half century ca 1750 1799 and a warm half century ca 1900 1949 it also reveals slightly higher frequency of cold years 20 4 than warm years 18 0 and a recent warming trend compared to the original 2011 reconstruction this reconstruction has lower inter annual temperature variability high explained variance and high representativeness of regional climate the reconstruction also correlates with the east asian monsoon and the pacific ocean signals and indicates the feasibility of using tree rings from high latitude northeast china to reconstruct summer temperature in permafrost forest environments

a coupled climate ice sheet model applied to the quaternary ice ages a coupled climate ice sheet model is used in an attempt to simulate the northern hemispheric ice sheet volume variations implied by deep sea core records over the last several 105 years the climate model consists of a global one level diffusive energy balance equation with seasonal variation and land ocean contrast using a severely truncated series of associated legendre functions the ice sheet model uses a standard vertically averaged flow law and predicts ice thickness in a north south cross section bedrock deformation under the ice is included as linear flow confined to a thin asthenospheric channel the climate model is tuned to the modern climate and tested against results from atmospheric general circulation models for 18 000 and 10 000 yr b p it is suggested that the lack of sea ice variations causes the biggest departures from the gcm results the sensitivities to the orbital perturbations of the coupled model and of the ice sheet model alone with a prescribed snow budget distribution are examined some qualitative differences are found in the latitudinal forms of these sensitivities despite these differences however the two types of models produce similar ice age simulations over the last 700 thousand years in response to the orbital perturbations in particular fairly realistic simulations with strong 100 kyr cycles similar to those obtained by adding an ice calving mechanism to the ice sheet model in pollard 1982a are again produced in the coupled model

sea state dependent wind work on the oceanic general circulation 1 we examine sea state dependent wind work on the oceanic general circulation using a wave hindcast dataset quikscat winds and geostrophic and total ocean surface currents from 1 aviso and 2 ecco2 model products for wind work on surface geostrophic currents estimated from aviso or ecco2 sea state dependent wind stress increases an average of 24 0 17tw or 23 0 15tw compared with estimates that exclude sea state effects for wind work on the total surface currents the sea state dependent wind stress increases the wind work by about 24 0 4tw in terms of spatial distribution the increase in wind power input occurs mainly in high wind tropical regions and the mid latitude storm track regions like the antarctic circumpolar current region where the relatively rough ocean surface is characterized by young waves and high winds by comparison in some regions with relatively low winds and mature ocean waves there is a slight reduction in estimated wind power input

estimates of dissipation in the ocean mixed layer using a quasi horizontal microstructure profiler abstract some recent measurements of the mixed layer in oceans and lakes have indicated that the rate of the dissipation of turbulent kinetic energy e is much higher than expected from a purely shear driven wall layer this enhancement has usually been attributed to wave breaking in this study measurements of dissipation in the open ocean mixed layer on the continental shelf off nova scotia are integrated with air sea flux estimates and directional wave spectra to further study this issue a microstructure profiler gliding quasi horizontally provides estimates of e starting within 2 m of the ocean surface as it slowly descends through the mixed layer dissipation rates were found to be enhanced relative to the wind stress production and indicated that 6 of the wind energy at 10 m is dissipated in the ocean mixed layer in addition results from this experiment demonstrate that the waves scaling for e based on wind and wave parameters is valid for the case of a simple windsea in which the swell can

high resolution record of paleoclimate since the little ice age from the tibetan ice cores climate changes during the little ice age were studied based on oxygen isotope values 18o measured from ice cores recovered on and nearby the qinghai tibetan plateau three cold periods have been identified and are supported by three widely existing moraine ridges formed during the little ice age importantly the amplitude of the three cold periods differ in the cores studied in the dunde ice core the coldest period occurred in the 17th century while it occurred in the 19th century in the guliya ice core all the ice cores recovered from the tibetan plateau and nearby regions show strong climatic warming in the 20th century

origin of the middle pleistocene transition by ice sheet erosion of regolith the transition in the middle pleistocene 0 9 ma seen in 18o deep sea core records from relatively low amplitude high frequency 41 kyr to high amplitude low frequency 100 kyr ice volume variations under essentially the same orbital forcing can be attributed to a change from an all soft bedded to a mixed hard soft bedded laurentide ice sheet through glacial erosion of a thick regolith and resulting exposure of unweathered crystalline bedrock a one dimensional ice sheet and bedrock model which includes transport of sediment and ice by subglacial sediment deformation demonstrates that a widespread deforming sediment layer maintains thin ice sheets before the transition which respond linearly to the dominant 23 and 41 kyr orbital forcing progressive removal of the sediment layer eventually causes a transition to thicker ice sheets whose dominant timescale of change 100 kyr reflects nonlinear deglaciation processes in model simulations over the last 3 ma initialized with no ice and a uniform 50 m sediment layer the time series of ice volume and extent agree in several important aspects with the observed records

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

a paleoclimate model of northern hemisphere ice sheets abstract a model for predicting the growth and decay of ice sheets based on the astronomical theory of climate change is presented the purpose of the study in part is to isolate the role of the ice sheet physics and earth response under varying ice load by simplifying to the extreme the role of the hydrosphere atmosphere ice sheet physics and the response of the lithosphere asthenosphere under the ice load are modeled explicitly insolation anomalies taken at a fixed latitude directly force latitudinal displacement of the snow line accumulation rate a and ablation rate a evaluated at mean sea level are specificed as external constants a a decrease linearly with ice sheet elevation rough tuning of the model to the general shape of the ice volume record of the last two major glacials determines the external constants model predictions of the ages of several events in the last major glaciation compare well with the radiological ages the six glacial terminatios i vi over the last 600 000 yr are identified and the predicted ages compare reasonably well with the 18 o record for two deep sea cores a direct comparison of model power spectra of ice volume as a function of period with spectra of the 18 o record shows apparent underprediction of power near 100 000 yr when a quantitative but heuristic method for taking into account the red noise spectrum evident in the geological records is used a much more favorable comparison is possible the model prediction lends support to the hypothesis that the nonlinearity of the ice sheet physics is responsible for the 100 000 yr periodicity in the geological record of the late pleistocene

brunhes matuyama magnetic reversal dated at 790 000 yr b p by marine astronomical correlations abstract the presence of the brunhes matuyama magnetic reversal in deep sea core sediments makes possible an alternative to the usual k ar radioistope method of dating the reversal as found in rocks the alternative method uses correlations of northern hemisphere summer insolation with oxygen isotope ratios from tropical cores the latitude dependent insolation variations are calculated from planetary mechanics and thus provide a highly accurate astronomical time scale the insolation variations strongly influence glacial ice volume fluctuations that dominate the oxygenisotope ratio changes recorded in core sediments the summer half year insolation variations are identified with corresponding isotope ratio changes in cores from the present through glacial stage 20 misleading effects of discontinuities or major nonuniformities of sediment deposition are avoided by an analysis of the uniformity of v28 238 and v28 239 the principal cores studied and by comparisons with other cores the top section stages 1 to 10 of v28 238 is uniformly deposited and for this section an isotope ratio time scale is chosen that agrees with the thorium uranium date for the high sea stand of the last interglacial extreme over this interval major glacial extremes strong isotope ratio minima coincide consistently with major insolation minima at times of low orbital eccentricity in addition interstadials are directly associated with precessional insolation peaks and the envelope of isotope ratio peaks resembles the envelope of precessionally dominated insolation peaks the assumption that the glacial extremes depended similarly on insolation minima during stages 10 to 20 permits minor age shifts of strong isotope ratio minima in the two cores relative to ages based on uniform overal deposition to match the ages of low eccentricity insolation minima the age shifts reflect residual nonuniformities of deposition the validity of this matching procedure is supported by a resulting consistent identification of principal isotope ratio peaks with high and low latitude coincident insolation maxima the brunhes matuyama reversal is found intinterglacial stage 19 and is dated on the astronomical time scale at 790 000 5000 yr b p

a climate model with cryodynamics and geodynamics we present a highly simplified zero dimensional model of the climatic system the model attempts to incorporate mechanisms important on the time scale of glaciation cycles namely 104 105 years in particular the radiation balance of the ocean atmosphere the plastic flow of continental ice sheets and the viscous flow of the upper mantle are taken into account the stress is on the interaction between the cryosphere ice sheets and the asthenosphere upper mantle which had not been taken into account in previous energy balance or ice sheet models of climate weertman 1976 kallen et al 1979 the model exhibits free self sustained oscillations of an amplitude and period comparable to those found in the paleoclimatic record of glaciations viz o 10 deg k and o 104 years respectively such oscillations had already been found in the simpler model of kallen et al 1978 1979 the fact that nonlinear self sustained oscillations also obtain for the present slightly more complex model is interesting it offers mild support to the idea that unforced oscillations can actually exist in the real climatic system itself these oscillations are characterized by a quarter phase lag between ice extent and global temperature given that the climatic system is a nonlinear oscillator with a period of o 104 years it is expected that astronomical forcing at 19 000 23 000 and 41 000 years will lead to subharmonic oscillations with a period close to 100 000 years the dominant period of glaciation cycles such effects have already been noticed in the work of birchfield and weertman 1978 with an even simpler model including only glacial dynamics the careful study of the interplay between internal mechanisms and external forcing with comparable time scales represents an interesting challenge to the theory of ice ages the results of such theoretical studies can also provide guidance for observational work in particular periodicities of o 104 years in the climate record and phase lags between ice volume and temperature appear to be supported by the most recent paleogeochemical investigations ruddiman and mclntyre 1981

seascape level variation in turbulence and wave generated hydrodynamic signals experienced by plankton abstract plankton exhibit diverse and dramatic responses to fluid motions and these behaviors are likely critical for survival and fitness fluid motions can be generated by organisms or by physical processes including turbulence and surface gravity waves physical processes vary geographically in their intensity and generate hydrodynamic signals experienced by plankton as fluid forces on their sensory receptors in this synthesis we review how turbulence and waves vary in space the scales and statistics of their motions and the forces exerted on plankton we then quantify the hydrodynamic signals produced by turbulence and waves in four seascape types surf zones inlets and estuaries the continental shelf and the open ocean using published dissipation rates wind and wave data from buoys and observations from two coastal sites in massachusetts usa we relate these geographic patterns in signals to the observed behaviors of example species and to the forces sensed by typical plankters with different receptor types turbulence generated shears are largest in the surf zone inlets and estuaries while wave generated accelerations are larger offshore as a result each seascape exhibits some range of combined shears and accelerations that is distinct these signals generate forces on plankton that vary among habitats and with plankton size and swimming speed spatial patterns in fluid forces create a potential mechanism for dispersing larvae to distinguish habitats by their hydrodynamic signatures however turbulence can be strong in all seascapes and may cause widespread interference in signaling among predators and prey plankton with a single receptor type could identify nearshore habitats while those with multiple receptor types potentially could distinguish inshore vs offshore seascapes or decode signals produced by physical processes and by other organisms

a simple ice sheet model yields realistic 100 kyr glacial cycles records of global ice volume for the past 700 kyr based on oxygen isotopic data from deep sea cores and reflecting mainly the changing northern hemispheric ice sheets show a dominant cycle of roughly 100 kyr period the records also show smaller amplitude oscillations with spectral peaks at roughly 40 and 20 kyr periods which are well correlated with the milankovich insolation variations due to perturbations in the earth s orbital parameters however no model has accurately simulated the 100 kyr glacial cycle recently birchfield et al 1 and oerlemans2 have obtained encouraging agreement with some features of the glacial cycle by using a simple ice sheet model with a realistic time lag in the response of the bedrock to the ice load this study extends their basic model first by including topography to represent high ground in the north improved results can then be obtained but only with unrealistic parameter values and for some aspects of the record further improvements areobtained by crudely parameterizing possible calving at the equatorward ice sheet tip during deglaciation by proglacial lakes and or marine incursions from the atlantic as emphasized by andrews3 the resulting ice volume curves agree fairly well with the observed records and their power spectra over the past 700 kyr

carbonate time series of the quaternary and late miocene sediments in the pacific ocean a spectral comparison abstract the variance of the quaternary carbonate record of core rc11 209 from the equatorial pacific is almost twice as large as that for the upper miocene of dsdp site 158 from the same region spectral analysis of the carbonate time series shows that the miocene record is dominated by very low frequency components with a concentration of variance near the frequency corresponding to a period of about 400 kyr the quaternary record is also dominated by low frequency components but has in addition concentrations of variance spectral peaks at frequencies corresponding to periods near 100 and 40 kyr cross spectral analysis indicates that both records are coherent with the calculated record of eccentricity of the earth s orbit and that the quaternary record in addition shows coherence with the calculated record of axial tilt these variations in the earth s orbital parameters can then be used to tune the time scales of these two records based on the similarity in the amount of variance in the two records near the 400 kyr period and the observed relationship between carbonate fluctuations and variations in global ice volume as indicated by oxygen isotope measurements it is proposed that the dominant 400 kyr cycle has been associated directly or indirectly with long term fluctuations in the antarctic ice cap since its formation in mid miocene times the major difference in the quaternary carbonate spectrum lies in the marked increase in variance at frequencies associated with the 100 kyr period this increase is thought to be linked directly or indirectly with glacial to interglacial fluctuations of the northern hemisphere ice sheets

climatic importance of the modulation of the 100 kyr cycle inferred from 16 m y long miocene records the variations of the amplitude of the 100 kyr cycle are not yet clearly understood although the timing of the appearance of these cycles in the pleistocene is well established very little is known about the occurrence of such cycles and their evolution in most of the neogene two detailed and continuous 16 m y long miocene records of paleoceanographic significance are analyzed in order to study the dynamics of the 100 kyr cycle one record results from counts of the relative abundance of the calcareous nannoplankton coccolithus pelagicus in about 1000 samples taken in the neogene section recovered from ocean drilling program site 747 southern indian ocean this record in which the chronologic resolution is 17 kyr is interpreted as reflecting migrations of the antarctic polar front through time the record of the wet bulk density in the same section which is interpreted as reflecting variations of paleoproductivity constitutes the second 16 m y record it has a chronologic resolution of 3 5 kyr the two series reveal the presence of 100 kyr cycle during the miocene this cycle is not stable through time and vary similarly in the two series the amplitude of the 100 kyr cycle fluctuates quasi periodically with primary periods close to 2 38 1 14 and 0 8 m y equivalent to those of the modulation of the orbital parameters obliquity and eccentricity in addition the amplitude of the 100 kyr cycle is stronger during cooler times the interactions between climate and modulation of the eccentricity or the obliquity cycles are good candidates to explain that change in amplitude it is concluded that the long term modulation of the orbital parameter has a significant influence on global climate

simulations of temperature and turbulence structure of the oceanic boundary layer with the improved near surface process an improved model for the oceanic boundary layer is presented in view of the recent observation of the microstructure of the upper ocean including the high dissipation rate near the sea surface in the new model the surface boundary conditions for both the turbulent kinetic energy flux and the roughness length scale are modified the parameterization of stratification effects on turbulence is improved and the convective process is reformulated on the basis of the observation of uniform temperature and velocity profiles within the convective mixed layer evolutions of the profiles of both the dissipation rate and temperature of the observation data patches experiment as well as the time series of the sea surface temperature over the observation days are successfully simulated during a diurnal cycle for the first time it is also shown that the model reproduces various important features of the oceanic boundary layer for example the formation of a diurnal thermocline the profiles of buoyancy flux and the magnitudes of the buoyancy gradients both within the mixed layer and at the diurnal thermocline performance of the model is compared with that of the widely used mellor yamada model

simulation of the last glacial cycle by a coupled sectorially averaged climate ice sheet model 2 response to insolation and co2 variations a two dimensional climate model which links the northern hemisphere atmosphere ocean mixed layer sea ice and continents has been asynchronously coupled to a model of the three main northern ice sheets and their underlying bedrock the coupled model has been used to test the influence of several factors including snow surface albedo over the ice sheets in producing plausible ice age simulations using astronomically derived insolation and co2 data from the vostok ice core the impact of potentially important processes such as the water vapor transport clouds and deep sea circulation was not investigated in this study after several sensitivity experiments designed to identify the main mechanism governing surface temperature and ice accumulation the model is first run with ice sheet feedback by forcing it only with the astronomical insolation over the past 122 kyr large variations of ice volume are simulated between 122 and 55 kyr b p with a rapid latitudinal extension of the north american and eurasian ice sheets starting at 120 kyr b p the simulated last glacial maximum is at 19 kyr b p the model is able to simulate deglaciation as well the simulated evolution of the three northern ice sheets is generally in phase with geological reconstructions the major discrepancy between the simulation and paleoclimate reconstructions lies in the underestimation of temperature variations linked with an underestimation of the ice sheet extent and an excess in the prescribed co2 concentration sensitivity experiments show that ablation is more important to the ice sheet response than snow precipitation variations in the model a key mechanism in the deglaciation after the last glacial maximum appears to be the aging of snow which decreases its albedo the other factors which play an important role are in decreasing level of importance the ice sheet altitude insolation taiga cover and ice sheet extent a final set of experiments addresses the effects of co2 on the simulated climate of the last glacial maximum and on a new long term experiment covering the last 122 kyr this last experiment is made by forcing the model with both insolation and co2 variations this additional forcing improves the temperature and ice volume results despite the limitations inherent to the present modeling approach the sensitivity experiments performed can provide insight into the relative importance of possible mechanism responsible for the building and melting of huge ice sheets during the last glacial interglacial cycle

measurements of turbulent vertical kinetic energy in the ocean mixed layer from lagrangian floats d asaro in previous work using nearly neutrally buoyant lagrangian floats in a wind forced mixed layer found w2 5 where w2 is the mean square vertical velocity and u is the friction velocity estimated 2 au from shipboard meteorological measurements using bulk formulas depth profiles of a z 5 w 2 z within 2 u the mixed layer showed a maximum value of a z of about 2 which is 1 75 2 times that measured in solidwall turbulent boundary layers driven by a wall stress alone this result implied that the ocean mixed layer was more energetic than shear driven turbulent boundary layers driven by the same stress here these results are verified using observations of vertical velocity in the mixed layer from 72 float days of data from two lagrangian floats in the north pacific ocean in the autumn of 2000 these floats were more neutrally buoyant than those used previously by d asaro thus reducing possible biases wind stress was estimated from quick scatterometer satellite measurements and is thus subject to errors and biases different from those in d asaro s previous work despite these instrumental differences the new results are very similar to those of the previous work except that no corrections for internal wave velocities are needed the values of w 2

surface wave effects on the translation of wind stress across the air sea interface in a fetch limited coastal embayment abstractthe role of surface gravity waves in structuring the air sea momentum flux is examined in the middle reaches of chesapeake bay observed wave spectra showed that wave direction in chesapeake bay is strongly correlated with basin geometry waves preferentially developed in the direction of maximum fetch suggesting that dominant wave frequencies may be commonly and persistently misaligned with local wind forcing direct observations from an ultrasonic anemometer and vertical array of advs show that the magnitude and direction of stress changed across the air sea interface suggesting that a stress divergence occurred at or near the water surface using a numerical wave model in combination with direct flux measurements the air sea momentum flux was partitioned between the surface wave field and the mean flow results indicate that the surface wave field can store or release a significant fraction of the total momentum flux depending on the direction of the wind when wind blew across dominant fetc

abrupt changes heinrich events in late quaternary north atlantic marine environments a history and review of data and concepts in the last several years evidence has mounted that a series of abrupt changes in sediment delivery and palaeoceanography effected the north atlantic they are recorded in a variety of proxy records but most dramatically in changes of grain size and mineralogy associated with postulated iceberg rafting events specifically heinrich h events this review paper examines the evidence for such evidence prior to the development of the heinrich event concept 1988 1992 and then examines the explosion of data and correlations that stemmed from the acceptance and use of this paradigm specific attention is focused on ideas pertaining to the cause s of glaciological mechanisms sediment delivery and sediment source and major gaps in our understanding of the underlying glaciological glacial geological and glacial marine processes are stressed abrupt changes across boundaries associated with h 2 in the labrador sea are illustrated from core hu87033 009lcf the case is made that correlations between records need to be more rigorous especially within the range of radiocarbon dating but it appears that abrupt changes in the delivery of iceberg rafted debris which characterize these intervals are multisourced it is unclear how global climate can simultaneously influence the abrupt behaviour of ice margins in different parts of the world for marine based margins changes in relative sea level are one possibility a qualitative model is presented for triggering h events which includes global changes in mass balance changes in relative sea level at ice margins due to glacial isostasy and changes in the basal thermal regime of tidewater ice streams 1998 john wiley sons ltd

a 53 year seasonally resolved oxygen and carbon isotope record from a modern gibraltar speleothem reconstructed drip water and relationship to local precipitation abstract the response of a climate proxy against measured temperature rainfall and atmospheric circulation patterns at sub annual resolution is the ultimate test of proxy fidelity but very few data exist showing the level of correspondence between speleothem climate proxies and the instrumental climate record cave sites on the gibraltar peninsula provide a unique opportunity to calibrate speleothem climate proxies with the longest known available precipitation isotopes and instrumental records an actively growing speleothem sampled from new st michaels cave in 2004 is composed of paired laminae consisting of light columnar calcite and a darker microsparitic calcite stable isotope analysis of samples micromilled in 100 m steps at the equivalent of bi monthly intervals reveals fabric correlated annual cycles in carbon isotopes oxygen isotopes and trace elements responding to seasonal changes in cave microclimate hydrology and ventilation patterns calcite 13 c values reach a minimum in the light columnar fabric and evidence from trace element behaviour and cave monitoring indicates that this grows under cave winter conditions of highest p co 2 whereas the dark microsparitic calcite characterised by elevated 13 c and 18 o values grows under low summer p co 2 conditions drip water 13 c dic reaches a minimum in march april at which time the attenuated 18 o signal becomes most representative of winter precipitation an age model based on cycle counting and the position of the 14 c bomb carbon spike yields a precisely dated winter oxygen isotope proxy of cave seepage water for comparison with the gnip and instrumental climate record for gibraltar the 18 o characteristics of calcite deposited from drip water representing winter precipitation for each year can be derived from the seasonally resolved record and allows reconstruction of the 18 o drip water representing winter precipitation for each year from 1951 2004 these data show an encouraging level of correspondence r 2 0 47 with the 18 o of rainfall falling each year between october and march and on a decadal scale the 18 o of reconstructed winter drip water mirrors secular change in mean winter temperatures

pervasive autocorrelation of the chemical index of alteration in sedimentary profiles and its palaeoenvironmental implications the chemical index of alteration has been used widely for reconstruction of the palaeoclimate however the mechanisms and environmental factors controlling the chemical index of alteration of sediments are not yet fully understood in this study autocorrelations of the chemical index of alteration in nine sedimentary profiles from both the land and the sea spanning different geological times are discussed the sediments of these profiles have different origins dust fluvial or ocean sediments and are from various climate situations and sedimentary environments autocorrelations of chemical index of alteration series are ubiquitously evident in all profiles it is suggested here that autocorrelations may be caused by post depositional changes such as persistent weathering and diagenesis as a result the chemical index of alteration may not reflect climatic conditions during the time of sediment deposition this study strongly recommends the confirmation of the reliability and veracity of the chemical index of alteration before it is adopted to evaluate the weathering degree of parent rocks and to reconstruct the past climate significant autocorrelations in loess profiles were specifically observed suggesting that the existing understanding of loess deposition in terms of climate conditions requires re examination and that previous reconstructions of rapid climate changes for example in centennial millennial scales should be treated with caution

wind wave effects on estuarine turbulence a comparison of observations and second moment closure predictions abstractobservations of turbulent kinetic energy dissipation and turbulent stress were collected in the middle reaches of chesapeake bay and were used to assess second moment closure predictions

observations of small scale processes associated with the internal tide encountering an island current meter temperature and microstructure observations of the large amplitude internal tide shoaling on the continental shelf of the east coast of northern new zealand show the complexity of the internal kinematics and mixing the propagation speed of the main internal wave was around 0 3 m s 1 and nonstationary time series analysis was used to locate the trailing short wavelength internal waves in frequency periods of around 40 min and tidal phase space the average energy dissipation rate 5 10 8 m 2 s 3 was an order of magnitude smaller than that observed on the open shelf in other studies but peaks in dissipation rate were measured to be much greater the vertical diffusivity of heat was around 10 4 m 2 s 1 comparable to or greater than other studies examples of the scale and sporadic nature of larger mixing events were observed the behavior was complicated by the nearby steeply shoaling coast of the poor knight islands consistent reflected wave energy was not apparent

palaeo climate reconstruction from stable isotope variations in speleothems a review abstract speleothems are now regarded as valuable archives of climatic conditions on the continents offering a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores they are ideal materials for precise u series dating yielding ages in calendar years thereby circumventing the radiocarbon calibration problems associated with most other continental records stable isotope studies in speleothems have shifted away from attempting to provide palaeo temperature reconstructions to the attainable goal of providing precise estimates for the timing and duration of major o isotope defined climatic events characterised by high signal to noise ratios e g glacial interglacial transitions dansgaard oeschger oscillations the 8200 year event unlike the marine records speleothem data sets are not tuned and their independent chronology offers opportunities to critically assess leads and lags in the climate system that in turn can provide important insights into forcing and feedback mechanisms improved procedures for the extraction and measurement of stable isotope ratios in fluid inclusions trapped in speleothems are likely to provide in the near future a much enhanced basis for the quantitative interpretation of o isotope ratios in speleothem calcite the latter developments open up once again the tantalising prospect of palaeo temperature estimates but more importantly perhaps provide a direct test for a new generation of general circulation models whose hydrological cycles will incorporate the water isotopes the literature is reviewed briefly to provide for the reader a sense of the current state of the art and to provide some pointers for future research directions

multiple instabilities and modes of glacial rhythmicity in the plio pleistocene a general theory of late cenozoic climatic change it has been noted that several distinct modes of glacial oscillation have existed during the past few million years ranging from low amplitude high frequency oscillations in the early pliocene through relatively high amplitude predominantly near 40 ky period oscillations in the late pliocene and early pleistocene to the major near 100 ky period oscillations of the late pleistocene in addition to other plausible mechanisms suggested previously to explain aspects of this multirhythmic phenomenon we now illustrate another possible contributor to this type of behavior based on the hypothesis that the slow response climatic system is bistable and that two kinds of internal instability may be operative along with externally imposed forcing due to earth orbital milankovitch radiation changes and slow tectonically induced changes in atmospheric carbon dioxide these two instabilities have been discussed previously one is due to positive feedback in the global carbon cycle leading to near 100 ky free oscillations of the ice sheets and the other is due to the potential for ice calving catastrophes associated with bedrock variations that can lead to oscillations of a period near 40 ky independent of obliquity forcing within the framework of a dynamical model containing the possibility for these two instabilities as well as for stable modes we show 1 how milankovitch radiative changes or stochastic forcing influencing ice sheets can induce aperiodic chaotic transitions between the possible stable and unstable modes and more significantly 2 how progressive long term tectonically induced changes in carbon dioxide acting in concert with earth orbital radiative variations in high northern hemisphere latitudes can force systematic transitions between the modes such systematic changes can result in an ice mass chronology for the past 5 my that is qualitatively similar to the observed record of global ice mass in essence we have constructed a minimum dynamical model of the late cenozoic climatic changes containing what are believed to be the main physical factors determining these changes ice mass bedrock depression atmospheric carbon dioxide concentration deep ocean thermohaline state milankovitch radiation forcing and slow tectonically induced carbon dioxide forcing this model forms the basis for a coherent theory for the complex climatic events of this long period

scaling surf zone turbulence 1 turbulence in the surf zone the shallow region adjacent to the shoreline has a key role in beach erosion fertilization dispersal and larval settlement of marine invertebrates and microbial contamination dilution in beach waters breaking wave generated the dominant source surf zone turbulence is understood poorly a new surf zone turbulent dissipation rate scaling is derived that collapses new field surf zone observations with relatively high skill compared to other scalings the vertically uniform length scale is 1 6 the water depth and 15 of the wave energy flux gradient is dissipated below the mean surface field and laboratory surf zone turbulence observations are shown to be consistent using the scaling the non dimensional surf zone diffusivity and suspended sediment profile can be applied to sediment transport and a range of biological processes including microbial pathogen contamination of beach waters

long periodic variations in the earth s obliquity and their relation to third order eustatic cycles and late neogene glaciations abstract evolutive spectra of four high resolution climatic proxy records reveal that the spectral power in the obliquity frequency band increases during five well defined intervals in the last 5 3 million years these intervals correspond to periods of high amplitude variations in the tilt obliquity of the earth s axis connected with a 1 2 myr cycle and to sea level lowstands of third order eustatic cycles in the haq et al 1987 curve this implies that the development of major plio pleistocene glaciations proceeded episodically and that third order cycles are glacio eustatically controlled in at least two of these intervals sinistrally coiled neogloboquadrinids entered the mediterranean at times of glacial periods one interval starts around 2 8 ma and is characterized by the first occurrence of n atlantica s another interval begins at the plio pleistocene boundary around 1 8 ma and is characterized by the common occurrence of sinistrally coiled n pachyderma also during the late miocene third order cycles correlate well with the 1 2 myr cycle of obliquity a significant drop in the third order eustatic curve starting at the tortonian messinian boundary for instance coincides with a period of high amplitude variations in the obliquity time series connected with the 1 2 myr cycle

applications of stalagmite laminae to paleoclimate reconstructions comparison with dendrochronology climatology abstract laminated stalagmites observed in either ultra violet or visible light or recognized via trace elements are now widely recognized as a common deposition form annually laminated stalagmites should be expected in caves which have an overlying climate that has a strong seasonality similar climate zones to where trees grow with distinct annual rings continuous laminated stalagmite chronologies up to several thousand years should be expected where some mixing of stored water occurs such stalagmites can be used to reconstruct climate particularly through variations in lamina width such climate records would be relatively damped by mixing of event water with stored groundwater constraining the amount of high frequency climate signals contained in the stalagmite but relatively long continuous lamina sequences permit the preservation of low frequency centennial scale climate signals this contrasts with numerous tree ring climate records which are frequently limited in preserving multi centennial trends due to the necessary removal of age related noise from relatively short tree segments laminated stalagmites and tree rings should therefore to some degree provide complementary climate information appropriate methods for compiling stalagmite layer chronologies and climatologies are presented

turbulence from breaking surface waves at a river mouth abstractobservations of surface waves currents and turbulence at the columbia river mouth are used to investigate the source and vertical structure of turbulence in the surface boundary layer tu

asthenospheric ice load effects in a global dynamical system model of the pleistocene climate in a previous dynamical model the late cenozoic climate variations were simulated taking into account free and forced variations of atmospheric carbon dioxide acting in concert with changes in global ice mass and the deep ocean thermal state all under the influence of the known earth orbital radiative changes this model is now extended by adding another relevant variable bedrock asthenosphere depression including its associated ice calving effects within the context of this extended model we 1 demonstrate the main results of previous bedrock ice sheet models in what we believe is the simplest possible manner 2 show how these previous models can exhibit the mid pleistocene transition with the inclusion of co2 effects 3 discuss the limitations of these previous bedrock models and 4 illustrate the possibility of removing some of these limitations and accounting for further aspects of the paleoclimate record by using the full dynamical system that includes forced and free effects of co2 as well as effects of bedrock depression and milankovitch forcing as one example of a new possibility with bedrock effects included in the full system we can obtain a solution characterized by irregularly spaced intermittent episodes in which the behavior is dominated either by near 40 kyr period oscillations or by near 100 kyr periods such as prevailed over the pleistocene

modeling the influence of wave enhanced turbulence in a shallow tide and wind driven water column 1 the ability of one dimensional hydrodynamic models to reproduce dissipation of turbulent kinetic energy and velocity profiles for conditions of whitecapping waves in a shallow water tide and wind forced environment was assessed the models were forced with the conditions experienced during a month long field experiment in a shallow estuarine embayment and the results were compared with the observed dissipation and mean velocity profiles three turbulence models were assessed the k model and two k l models with different prescribed bilinear relationships for the turbulent length scale l the k turbulence model was found to best replicate the measured decay of dissipation with depth with a surface roughness length z0s 1 3hs and wave energy parameter 60 the k l model achieved equally as good reproduction of the observations as the k model when the proportionality constant in the prescribed linear length scale relationship for the upper half of the water column was modified from the traditionally employed von karman s constant 0 4 to 0 25 the model results show that the whitecapping waves often supplied the dominant source of turbulent kinetic energy over the majority of the water column in the shallow tide and wind forced system

quantitative temperature reconstruction based on growth rate of annually layered stalagmite a case study from central china we used the annual growth rate of a stalagmite xl21 collected from xianglong cave central china to quantitatively reconstruct regional terrestrial temperature changes over the last 95 years 1912 2006 ad based on a significant positive correlation between the growth rate and the observed temperature a transfer function was designed and the temperature from the previous september to may p9 5 was reconstructed with an explained variance of 43 5 our results show an increasing trend in temperature during the last century and especially over the last 30 years the temperature variability from central china recorded here bears a striking similarity to that in the northern hemisphere and also to global trends however the cooling between the 1980s and the early 1990s seen in the stalagmite record which interrupted the warming trend that began in the 1960s is not observed in the mean conditions found in china the northern hemisphere neither globally this methodology for reconstructing historical temperature from stalagmite growth rates overcomes the limitation of the short meteorological observation period and supports the potential of stalagmite lamina climatology

breaking surface wave effects on river plume dynamics during upwelling favorable winds this study examines the dynamics of a buoyant river plume in upwelling favorable winds concentrating on the time after separation from the coast a set of idealized numerical simulations is used to examine the effects of breaking surface gravity waves on plume structure and cross shore dynamics inclusion of a wavebreaking parameterization in the two equation turbulence submodel causes the plume to be thicker and narrower and to propagate offshore more slowly than a plume in a simulation with no wave breaking in simulations that include wave breaking the plume has much smaller vertical gradients of salinity and velocity than in the simulation without breaking this leads to decreased importance of shear dispersion in the plumes with wave breaking much of the wideningrate of the plume is explainedby divergentekmanvelocities at the off and onshore edges some aspects of plume evolution in all cases are predicted well by a simple theory based on a critical richardson number and an infinitely deep ocean however because the initial plume in thesesimulationsisincontactwiththeseafloorintheinnershelf somedetailsarepoorlypredicted especially around the time that the plume separates from the coast

paleoclimate reconstruction based on the timing of speleothem growth and oxygen and carbon isotope composition in a cave located in the rain shadow in israel high resolution th 230 u 234 ages and delta 18 o and delta 13 c compositions of speleothems in ma ale efrayirn cave located to the east of the central mountain ridge of israel enable us to examine the nature of the rain shadow aridity during glacial and interglacial intervals speleothem growth occurred during marine glacial isotopic periods with no growth during the two last marine isotope interglacial intervals and during the peak of the last glacial maximum this contrasts with speleothem growth in caves located on the western flank of the central mountain ridge in the eastern mediterranean semiarid climatic zone which continued throughout the last 240 000 yr thus during glacial periods water reached both sides of the central mountain ridge a comparison of the present day rain and cave water isotopic compositions and amounts at the ma ale efrayim cave site with those on the western flank shows that evaporation and higher temperatures on the eastern flank are major influences on isotopic composition and the lack of rainfall the delta 18 o and delta 13 c profiles of the speleothems deposited between 67 000 and 25 000 yr b p match the general trends of the isotopic profiles of soreq cave speleothems suggesting a similar source eastern mediterranean sea and similar climatic conditions thus during glacial periods the desert boundary effectively migrated further south or east from its present day location on the eastern flank whereas interglacial periods appear to have been similar to the present with the desert boundary at the same position the decrease in overall temperature and a consequent reduction in the evaporation to precipitation ratios on the eastern flank are viewed as the major factors controlling the decay of the rain shadow effect during glacial periods c 2003 elsevier science usa all rights reserved

quantifying the value of laminated stalagmites for paleoclimate reconstructions 1 from the permian through to the modern day stalagmites are an important archive of environmental change annually laminated stalagmites provide both a precise chronology and a paleoclimate proxy the rate of annual vertical growth of stalagmites is recorded in changes of calcite fabric annual fluxes of fluorescent organic matter or annual variations in trace element composition the processes governing stalagmite growth are the flux of water the co2 saturation of drip water relative to the cave atmosphere and the temperature although these processes are well understood they depend on the specific hydrogeological flow routing of individual stalagmites therefore although past climates are recorded in the vertical growth lamina thickness the climatic signal is perturbed by noise related to local hydrologic factors to separate local from global factors we used geostatistical tools to analyze annual growth rate data from eleven stalagmites located on four continents variogram analyses permit the quantification of the signal content contained within the growth rate records the information content ranges from 23 to 87 analysis of the growth derivative shows a negative correlation at a 1 year lag meaning that acceleration in growth rate tends to be systematically followed by deceleration in growth rate and vice versa we call this behavior flickering growth and argue that it is related to the size of the store feeding the stalagmite variogram analysis and flickering are used to screen which types of signals can potentially be recorded in a given speleothem

abrupt climatic change related to unstable ice sheet dynamics toward a new paradigm ice streams are fast currents of ice that drain some 90 of present day ice sheets and probably drained a similar percent of ice from former ice sheets ice streams may have life cycles akin to but much longer than surge cycles of certain mountain glaciers the floating tongues of marine ice streams coalesce to form floating ice shelves that buttress marine ice sheets and the grounded lobes of terrestrial ice streams stabilize terrestrial ice sheets ice shelves and ice lobes form during the life cycles of ice streams and disintegrate rapidly to initiate new life cycles successive life cycles continue until the ice sheet collapses a new paradigm is postulated in which abrupt climatic change is driven by iceberg outbursts associated with life cycles of marine ice streams and dust storms associated with life cycles of terrestrial ice streams for pleistocene northern hemisphere ice sheets these mechanisms regulated north atlantic surface temperatures and salinity and perhaps planetary albedo and atmospheric co2 and thereby drove climatic change which tended to be abrupt because ice stream life cycles began and ended abruptly ice streams proliferated along the margins of northern hemisphere ice sheets after they advanced beyond the crystalline shields of north america and eurasia and spread over softer sedimentary rocks overlain by thick ice cemented sediments that progressively thawed especially along river valleys and marine troughs an increasing fraction of these ice sheets was then subjected to the unstable life cycles of ice streams as seen in the pronounced spikiness of the late glacial oxygen isotope stratigraphy in the greenland ice core at dye 3 life cycles of greenland ice streams during the holocene seem to be linked to episodes of regional climatic cooling most recently the little ice age when superimposed on the present milankovitch hemicycle of reduced insolation over the north atlantic this could abruptly initiate a new worldwide glaciation cycle in the aftermath of present day co2 greenhouse warming proliferation of antarctic ice stream life cycles during the period of greenhouse warming may also trigger global climatic change by forcing a reorganization of circumpolar thermohaline circulation in the southern ocean

on the vertical structure of wind driven sea currents abstract the vertical structure of wind driven sea surface currents and the role of wind wave breaking in its formation are investigated by means of both field experiments and modeling analysis of drifter measurements of surface currents in the uppermost 5 m layer at wind speeds from 3 to 15 m s 1 is the experimental starting point of this study the velocity gradients beneath the surface are found to be 2 to 5 times weaker than in the wall boundary layer surface wind drift identified via drift of an artificial slick with respect to 0 5 m depths is about 0 7 which is even less than the velocity defect over the molecular sublayer in the wall boundary layer at a smooth surface to interpret the data a semiempirical model describing the effect of wave breaking on wind driven surface currents and subsurface turbulence is proposed the model elaborates on the idea of direct injection of momentum and energy from wave breaking including microscale breaking into the water body momentum and energy tran

the co 2 induced thickening thinning of the greenland and antarctic ice sheets as simulated by a gcm ccmi and an ice sheet model scaling analysis shows that the mean thickness of an ice sheet depends on the product of two poorly known quantities the ice viscosity and the net snow accumulation rate we adjust the viscosity of an ice sheet in order to get a consistent value of this product for the present day ice sheet volume and area given the net snow accumulation rate calculated by an atmospheric general circulation model gcm we then hold this artificial rheology constant in further numerical experiments we hope that in doing so we can partially compensate for systematic gcm errors in simulating the snow accumulation rate and therefore thickening thinning of ice sheets will depend mostly on the tendency in the net accumulation change rather than on its absolute value using this approach the response of the greenland and antarctic ice sheets to doubling co2 concentration is simulated and the horizontal distribution of possible thickening thinning of polar ice obtained we find that initially the region of thickening ice is close to the area of increased snowfall rate but later it significantly changes under the influence of internal ice flow dynamics the sea level changes predicted by our experiments agree with some empirical estimates the sensitivity experiment with assigned basal sliding does not show significant changes in the large scale ice topography meaning for example that there is no indication of a possible disintegration of the west antarctic ice sheet at the same time the regional thickening thinning of ice and consequently the sea level change depends strongly on processes at the ice sheet bottom