cyclic sedimentation in the southern alpine rhaetic the importance of climate and eustasy in controlling platform basin interactions uppermost triassic rhaetic facies as developed in the southern alpine region of northern italy were deposited in a rapidly subsiding fault dissected trough the lombardy basin bounded by carbonate platforms the main part of the rhaetic succession consists of 10 m scale asymmetric cycles each divided into three parts a lower shale portion a central rhythmic portion consisting of repeated marl limestone couplets the limestone parts of which thicken upward and an upper wholly carbonate unit a study of the diagenetic history of the series demonstrates that both the major asymmetric cyclicity and the limestone marl couplets of the central rhythmic member together constituting a compound cyclic form are fundamentally depositional in nature it is suggested that this compound cyclicity resulted from the superposition of a low frequency approximately 100 000 year periodicity asymmetric carbonate mud signal with a higher frequency terrigenous mud signal field petrographic and geochemical investigations suggest that the basinal carbonate is predominantly allochthonous in origin having been derived as relatively pure aragonitic mud from adjacent carbonate platforms it is postulated that the asymmetric carbonate signal was linked to the ecological effects of eustatic fluctuation on platform carbonate systems repeated subaerial exposure of subtidal muds in shallow areas indicates that such sea level variations occurred a model is presented in which the basinward export of carbonate was negligible in the deepening phase increased to a maximum during shallowing and was finally halted by the emergence of large platform flats in contrast the higher frequency terrigenous mud signal of the basin is thought to have been climatically modulated fluctuations of a shorter period than those predicted by the milankovitch theory affected hinterland precipitation and runoff particularly rapid subsidence and high depositional rates may have allowed the preservation of this signal

eolian sediment responses to late quaternary climate changes temporal and spatial patterns in the sahara abstract this paper presents a compilation of eolian based records of late quaternary climate changes in the sahara although the data are relatively sparse when viewed as a whole they reveal a general pattern of widespread eolian sediment mobilization prior to 11 000 cal years bp eolian sediment stabilization from 11 000 to 5000 cal years bp and a return to widespread eolian sediment mobilization after 5000 cal years bp furthermore an eolian based record from southern tunisia reveals the existence of millennial scale changes in eolian sediment behavior these millennial scale variations provide examples of eolian sediment responses to climate changes at a scale intermediate between seasonal and orbital milankovitch changes and they are also coincident with abrupt atmospheric and oceanic changes the general synchroneity of the eolian stratigraphic records and their coincidence with various oceanic and atmospheric changes suggest that global forcing mechanisms have influenced late quaternary eolian sediment behavior in the sahara

martian south polar layered deposit stratigraphy and implications for accumulation history 1 we examine the stratigraphy of the martian south polar layered deposits spld exposed on scarp walls throughout the deposit using themis visible 17 m pxl images from the mars odyssey spacecraft by correlating marker layers and packets of layers among multiple locations we are able to identify three sequences of layers within the spld each with a different areal extent while certain layers are correlatable over hundreds of km implying widespread deposition of polar material the absence of several identified layer sequences in some regions notably the promethei lingula region as well as the presence of several unconformities indicates that deposition and sublimation or erosion of these deposits has not been uniform around the spld this is further supported by the fact that individual layers display variations in thickness greater than a factor of 4 over hundreds of kilometers using these observations we propose an internal structure for the spld with individual layers roughly following a dome like shape toward the center of the deposit and becoming more planar toward the margins we infer that the spld underwent at least three major periods of layer accumulation each period is distinguished by a change in areal extent of net accumulation the changes in areal extent of the layer sequences may be due to changes in martian climate causing episodes of significant erosion of the spld between the deposition of each sequence or causing wide variations in accumulation zones of the spld over the history of these deposits

stabilization of the earth s obliquity by the moon according to milankovitch theory1 2 the ice ages are related to variations of insolation in northern latitudes resulting from changes in the earth s orbital and orientation parameters precession eccentricity and obliquity here we investigate the stability of the earth s orientation for all possible values of the initial obliquity by integrating the equations of precession of the earth we find a large chaotic zone which extends from 60 to 90 in obliquity in its present state the earth avoids this chaotic zone and its obliquity is essentially stable exhibiting only small variations of 1 3 around the mean value of 23 3 but if the moon were not present the torque exerted on the earth would be smaller and the chaotic zone would then extend from nearly 0 up to about 85 thus had the planet not acquired the moon large variations in obliquity resulting from its chaotic behaviour might have driven dramatic changes in climate in this sense one might consider the moon to act as a potential climate regulator for the earth

variations in solar magnetic activity during the last 200 000 years is there a sun climate connection abstract the production of 10be in the earth s atmosphere depends on the galactic cosmic ray influx that in turn is affected by the solar surface magnetic activity and the geomagnetic dipole strength using the estimated changes in 10be production rate and the geomagnetic field intensity variations in solar activity are calculated for the last 200 ka large variations in the solar activity are evident with the sun experiencing periods of normal enhanced and suppressed activity the marine 18o record and solar modulation are strongly correlated at the 100 ka timescale it is proposed that variations in solar activity control the 100 ka glacial interglacial cycles however the 10be production rate variations may have been under estimated during the interval between 115 ka and 125 ka and may have biased the results future tests of the hypothesis are discussed

north polar cap of mars polar layered deposit characterization and identification of a fundamental climate signal of the cap 6 10 5 km 2 in the 13 images analyzed to date 3 assessment of geometric relationships shows that layers are not horizontal but rather have an apparent dip of approximately 0 5 degrees we interpret these results as follows 1 the fundamental 30 m signal is interpreted as a climate signal that may correspond to a 51 kyr insolation cycle 2 the lateral correlation and broad distribution of these layer sequences strongly imply that layer accumulation processes are widespread across the cap rather than confined within a single trough or region 3 local to regional variability in individual layer thicknesses and thus accumulation and sublimation rates is typically less than a factor of 2 5 providing the ability to study regional trends but often making it difficult to correlate visually the vertical sequences in individual cores finally initial examination of layers located deeper in the stratigraphic sequence within the north polar cap than the 300 m thick zone 1 provides evidence for a unit less than 100 m thick zone 2 in which the fundamental 30 m sequence is not detected we interpret this as a deposit having formed during a recent high obliquity phase of mars during which time polar volatiles underwent mobilization and were transport equatorward leaving a polar lag of dust rich material the most recent ice age 0 5 2 ma offers a plausible candidate for this period of ice cap removal and lag deposit formation an underlying zone 3 200 m contains a dominant 35 m signal and a lowermost zone 4 200 m contains multiple signals but no dominant one together these four zones represent 800 m of vertical stratigraphic section about one fourth of the total thickness of the cap these findings support earlier interpretations that orbital parameter variations could cause significant erosion and possibly complete removal of the polar caps the interpreted crater retention ages of the layered terrain are consistent with the correlations and vertical sequences described here suggesting that the polar caps wax and wane throughout geological history depending on the evolution of orbital parameters definition of the 30 m unit signal holds promise for determining 1 the detailed origin of individual layer types 2 the nature of deposition and sublimation processes and their relation to insolation geometry across the polar cap and 3 correlation with and comparison to the south polar layered terrain record

astronomical theory of the pleistocene ice ages a brief historical review abstract this paper traces the evolution of the astronomical theory of the pleistocene ice ages from its origin in the work of adhemar and croll through its quantitative transformation in the hands of milankovitch to its current renaissance emphasis is given to the interplay between climatic theory and geologic observation from 1941 when milankovitch published his final version of the theory until the early 1970s most attempts to test the theory empirically were carried out in the time domain by comparing the geologic record of climate with predicted climate curves these attempts ran into serious difficulties particularly the inaccuracy of the geologic time scale and the ambiguity of climate predictions early attempts to evaluate the theory with simple radiation balance models appeared to indicate that the climatic response to secular changes in the orbit would be too small to be observed geologically but by the mid 1970s the advent of an improved time scale for pleistocene marine deposits and the availability of long closely sampled records made it possible to arrange generalized but unambiguous tests of the theory in the frequency domain by comparing orbital and climatic spectra these results decisively confirmed the idea that orbital variations significantly influenced the earth s climate during the pleistocene but they did not tell us how this influence was exercised the emphasis of current work has therefore shifted to the identification and quantitative modeling of physical mechanisms by which the climate system responds so dramatically to the predicted rather subtle changes in radiative boundary conditions

the intensification of glaciation in the mid pliocene and the earth s obliquity variation the intensification of glaciation in the northern hemisphere during the past 3 myr has clearly been confirmed by 18o record for deep sea sediment cores extending over the past 5 6 myr for earth models with a lower mantle viscosity of greater than 1022 pa s inferred from several geophysical observables perturbations in the earth s dynamic ellipticity in response to this long term climatic change might have produced an increase of the average earth s obliquity 0 06 through the resonant effect associated with the orbits of jupiter and saturn this predicted obliquity change may consequently operate as a negative feedback on solar insolation resulting in a reduction of the intensification of glaciation

variability of mars north polar water ice cap i analysis of mariner 9 and viking orbiter imaging data abstract previous studies interpreted differences in ice coverage between mariner 9 and viking orbiter observations of mars north residual polar cap as evidence of interannual variability of ice deposition on the cap however these investigators did not consider the possibility that there could be significant changes in the ice coverage within the northern residual cap over the course of the summer season our more comprehensive analysis of mariner 9 and viking orbiter imaging data shows that the appearance of the residual cap does not show large scale variance on an interannual basis rather we find evidence that regions that were dark at the beginning of summer look bright by the end of summer and that this seasonal variation of the cap repeats from year to year our results suggest that this brightening was due to the deposition of newly formed water ice on the surface we find that newly formed ice deposits in the summer season have the same red to violet band image ratios as permanently bright deposits within the residual cap we believe the newly formed ice accumulates in a continuous layer to constrain the minimum amount of deposited ice we used observed albedo data in conjunction with calculations using mie theory for single scattering and a delta eddington approximation of radiative transfer for multiple scattering the brightening could have been produced by a minimum of 1 a 35 m thick layer of 50 m sized ice particles with 10 dust or 2 a 14 m thick layer of 10 m sized ice particles with 50 dust

the effects of martian orbital variations upon the sublimation and relaxation of north polar troughs and scarps abstract the north polar layered deposits pld of mars are climatologically significant because they represent the largest actively exchanging reservoir of martian water the kilometer scale topography of the north pld is dominated by troughs and scarps which exhibit highly correlated surface slopes and total depths the most widespread theories of pld evolution presume that the asymmetrical nature of north pld troughs characterized by equatorward facing slopes that are generally steeper than poleward facing slopes is the result of preferential h 2 o sublimation from equatorward facing trough walls however our orbitally modulated simulations indicate that there is no long term sublimation advantage of equatorward facing trough walls because of the effects of obliquity upon the slope dependence of sublimation rate in contrast we propose that viscous relaxation of subsurface water is consistent with the slope and depth distributions of north pld troughs and scarps the results of our finite element simulations suggest that a mere 2 k difference in the subsurface temperatures of opposing trough walls is sufficient to produce the observed slope disparity due to the slower rate of uplift of colder poleward facing trough walls both our sublimation and relaxation simulations indicate that present day north pld troughs have formed since 5 ma and are not sites of long term deposition additionally our results imply that glacial flow may govern the large scale evolution of the north pld especially at high obliquity

turbidite sedimentation during alpine thrusting the taveyannaz sandstones of eastern switzerland the taveyannaz sandstones of eastern switzerland are a succession of turbidites found within the tertiary north helvetic flysch system they represent a portion of the early underfilled stage of the north alpine foreland basin the taveyannaz sandstones were deposited in two sub basins inner and outer basins separated by a topographic high trending ene wsw parallel to the subsequent structural strike of the region interpreted as an emergent thrust tip that propagated into the basin the southerly inner basin is therefore considered as a piggy back basin comprising a 140 m thick succession dominated by approximately 12 very thick bedded sandstones with thick mudstone caps these very thick bedded sandstone mudstone couplets are interpreted as having resulted from the ponding of megaturbidite flows in the topographically confined inner basin intercalated with the very thick bedded sandstones are thin to medium bedded sandstones the outer northerly basin comprises at least 240 m of turbidites characterized by sandstone packets 5 50 m thick with extensive amalgamation of beds and a dominantly symmetrical vertical bed thickness and grain size profile intercalated between the sandstone packets are laminated graded siltstones and mudstones the inner basin sediments underwent localized deformation on the sea floor generating an irregular surface topography which was then capped by a mud sheet emplaced by superficial sliding during the emplacement of the mud sheet large sandstone blocks up to 130 m across were incorporated from the underlying succession the resultant geometry of the upper surface of the inner basin sandstones exhibits vertical walls which truncate and are perpendicular to the underlying beds the depositional style and structural control of the taveyannaz sandstones in association with the emplacement of superficial mud sheets reflect processes that are highly analogous to those occurring in modern accretionary wedge environments the sandstone packets of the outer basin reflect a cyclical pattern of sedimentation alternating between deposition of sandstones and mudstones the autocyclical or allocyclical controls on these high frequency alternations are difficult to interpret likely mechanisms include lobe switching climatic variations eustatic sea level fluctuations and changes of horizontal in plane deviatoric stress on the lithosphere in this example an alternative mechanism is speculated upon this is based on the analogy with accretionary wedge processes in this hypothesis it is proposed that high frequency fluctuations in the accommodation space available on the shelf may result from fluctuations in the topographic slope of an accretionary wedge around its critical taper hence during periods of accelerated frontal accretion the taper angle of the thrust wedge becomes subcritical resulting in a broad low angle topographic slope and increased shelfal accommodation consequently sediment becomes trapped in a relatively landward position the necessary rejuvenation of the surface slope of the thrust wedge to a critical taper is achieved through internal reactivation resulting in tectonic uplift and hence a relative fall in sea level this leads to the reworking of sediment to the base of slope or outer trench repeated alternations of relative sea level between a subcritical highstand and a supercritical lowstand are considered to be sufficient to generate the observed alternations between sandstone and mudstone packages in the turbidite basin

an initial study of the sensitivity of modeled cretaceous climate to cyclical insolation forcing some cretaceous rhythmic sedimentation such as the colorado greenhorn formation deposited in the western interior seaway u s may have been produced by cyclic precipitation intensity change responding to orbitally produced insolation forcing to test this hypothesis a general circulation model was forced with the seasonal maximum and minimum insolation calculated from assumed cretaceous orbital parameters geographic comparisons for july and january of surface temperature surface pressure and precipitation were prepared for january maximum land sea contrast produced an increase of more than 6 mm day precipitation over the interior seaway however the july maximum simulation did not produce precipitation increase despite an anticipated monsoonlike circulation over the region north america appears to be very arid during cretaceous northern hemisphere summer

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

pre pleistocene glaciation on earth implications for climatic history of mars the history of ice ages on earth extending back more than 2 ga 109 years has been established by the recognition in strata of many ages of the assemblage of erosional features and deposits generated by glacial activity the most useful indicators are widespread diamictite striated and faceted clasts polished and striated pavements and laminites containing dropstones inferred to be ice rafted the chronology of ancient glaciation is limited by our ability to recognize the results of glacial activity in an incomplete geologic record and by the age resolution attainable with available dating methods ice ages are currently known from the early proterozoic 2 5 2 1 ga ago several intervals in the middle to late proterozoic 1 0 0 57 ga the late ordovician to late silurian 440 415 ma or 106 years possibly latest devonian 360 345 ma permo carboniferous 335 245 ma and late cenozoic 26 ma ago to the present however the timing of pre phanerozoic ice ages occurring before 0 57 ga ago is known only approximately and glacial events would have been shorter than is suggested by the bracketing ages a generally warm climate seems to have prevailed for the remainder of earth history although mesozoic cenozoic seismic stratigraphic evidence suggests that a small ice sheet may have been a persistent feature near the south pole throughout the last 500 ma terrestrial climatic fluctuations occur on several time scales the occurence of ice ages on a time scale of 108 109 years and possibly higher frequency fluctuations 106 107 years appears to be controlled by changes in solar output and atmospheric composition and by the rearrangement of continents and oceans as a result of the motion of lithospheric plates climatic changes on a time scale of 104 105 years are driven by perturbations of the earth s orbital parameters the principal evidence suggesting that significant climate changes have occured on mars consists of widespread dry channels 3 5 0 5 ga and of geologically young dust ice layered terrains in the polar regions 10 ma by analogy with the earth polar layered terrains have probably existed episodically on mars for a considerable time although there is little direct evidence for this factors affecting a potential sedimentary record are the degree to which ice sublimed or melted the effectiveness of eolian destruction of layering and in contrast to the present polar terrains the tendency for ice to flow and slide over its substrate as on earth climate changes on mars have probably been induced by the long term evolution of the atmosphere by changes in solar luminosity and by variations in orbital parameters major tectonic events may have affected martian climate through changes in planetary obliquity

integrating radar stratigraphy with high resolution visible stratigraphy of the north polar layered deposits mars abstract shallow radar sharad on board nasa s mars reconnaissance orbiter has successfully detected tens of reflectors in the subsurface of the north polar layered deposits npld of mars radar reflections are hypothesized to originate from the same material interfaces that result in visible layering as a first step towards verifying this assumption this study uses signal analyses and geometric comparisons to quantitatively examine the relationship between reflectors and visible layers exposed in an npld outcrop to understand subsurface structures and reflector geometry reflector surfaces have been gridded in three dimensions taking into account the influence of surface slopes to obtain accurate subsurface geometries these geometries reveal reflector dips that are consistent with optical layer slopes distance elevation profiling of subsurface reflectors and visible layer boundaries reveals that reflectors and layers demonstrate similar topography verifying that reflectors represent paleosurfaces of the deposit statistical and frequency domain analyses of the separation distances between successive layers and successive reflectors confirms the agreement of radar reflector spacing with characteristic spacing of certain visible layers direct elevation comparisons between individual reflectors and discrete optical layers while necessary for a one to one correlation are complicated by variations in subsurface structure that exist between the outcrop and the sharad observations as inferred from subsurface mapping although these complications have prevented a unique correlation a genetic link between radar reflectors and visible layers has been confirmed validating the assumption that radar reflectors can be used as geometric proxies for visible stratigraphy furthermore the techniques for conducting a stratigraphic integration have been generalized and improved so that the integration can be undertaken at additional locations

a resonance in the earth s obliquity and precession overthe past 20 myr drivenbymantle convection the motion of the solar system is chaotic to the extent that the precise positions of the planets are predictable for a period of only about 20 myr ref 1 the earth s precession obliquity and insolation parameters over this time period1 2 3 4 5 6 can be influenced by secular variations in the dynamic ellipticity of the planet which are driven by long term geophysical processes such as post glacial rebound5 7 8 9 10 here we investigate the influence of mantle convection on these parameters we use viscous flow theory to compute time series of the earth s dynamic ellipticity for the past 20 myr and then apply these perturbations to the nominal many body orbital solution of laskar et al 5 we find that the convection induced change in the earth s flattening perturbs the main frequency of the earth s precession into the resonance associated with a secular term in the orbits of jupiter and saturn5 and thus significantly influences the earth s obliquity we also conclude that updated time series of high latitude summer solar insolation diverge from the nominal solution for periods greater than the past 5 myr our results have implications both for obtaining precise solutions for precession and obliquity and for procedures that adopt astronomical calibrations to date sedimentary cycles and climatic proxy records

tropical mountain glaciers on mars altitude dependence of ice accumulation accumulation conditions formation times glacier dynamics and implications for planetary spin axis orbital history abstract fan shaped deposits up to 166 000 km 2 in area are found on the northwest flanks of the huge tharsis montes volcanoes in the tropics of mars recent spacecraft data have confirmed earlier hypotheses that these lobate deposits are glacial in origin increased knowledge of polar latitude terrestrial glacial analogs in the antarctic dry valleys has been used to show that the lobate deposits are the remnants of cold based glaciers that formed in the extremely cold hyper arid climate of mars mars atmospheric general circulation models gcm show that these glaciers could form during periods of high obliquity when upwelling and adiabatic cooling of moist air favor deposition of snow on the northwest flanks of the tharsis montes we present a simulation of the tharsis montes ice sheets produced by a static accumulation pattern based on the gcm results and compare this with the nature and extent of the geologic deposits we use the fundamental differences between the atmospheric snow accumulation environments mass balance on earth and mars geological observations and ice sheet models to show that two equilibrium lines should characterize ice sheet mass balance on mars and that glacial accumulation should be favored on the flanks of large volcanoes not on their summits as seen on earth predicted accumulation rates from such a parameterization together with sample spin axis obliquity histories are used to show that obliquity in excess of 45 and multiple 120 000 year obliquity cycles are necessary to produce the observed deposits our results indicate that the formation of these deposits required multiple successive stages of advance and retreat before their full extent could be reached and thus imply that spin axis obliquity remained at these high values for millions of years during the late amazonian period of mars history spin axis obliquity is one of the main factors in the distribution and intensity of solar insolation and thus in determining the climate history of mars unfortunately reconstruction of past climate history is inhibited by the fact that the chaotic nature of the solution makes the calculation of orbital histories unreliable prior to about 20 ma ago we show however that the geological record combined with glacial modeling can be used to provide insight into the nature of the spin axis orbital history of mars in the late amazonian and to begin to establish data points for the geologically based reconstruction of the climate and orbital history of mars

sea surface temperature during the quaternary at odp sites 976 and 975 western mediterranean abstract based on the relative abundances of the planktonic foraminifera species found in quaternary samples from odp sites 976 alboran sea and 975 menorca rise and using a modern analog technique winter and summer sea surface temperatures were estimated frequency distributions of temperatures are asymmetrical more so at odp site 976 where there is a greater abundance of samples from the warm part of the temperature range during the quaternary there is a general tendency for temperatures to fall with an overall diminution of 1 c for the winters and of more than 2 c for the summers overall mean temperatures and those of the biostratigraphic intervals identified are higher at odp site 975 than at 976 when differences are statistically significant the q1 interval i e the oldest in the quaternary is colder than the upl i e terminal pliocene and the q2 interval the q3 interval is also colder than the q2 interval and the q4 interval i e the most recent interval differences between intervals general trends and the asymmetries of frequency distributions cannot be explained as linear responses to insolation the stratigraphic series from odp site 976 was dated by correlating the relative maxima and minima of the summer temperature series with those of insolation during the month of july at 65 n it was found that 26 2 of the variance of the time series of temperatures was concentrated in the harmonics related to precession and obliquity while 19 was located in those related to eccentricity there are indications of the need to add lags and leads to the age of temperature spikes with respect to insolation but such delays and leads cannot be quantified precisely

north american continental seasonality during the last millennium high resolution analysis of sagittal otoliths abstract 18 o caco 3 values of late holocene sagittal fish otoliths from lake erie provide a record of seasonal temperature variation for mid western north america freshwater drum aplodinotus grunniens sagittal otoliths obtained from paleo indian middens ranging in age from a d 985 to a d 1530 as well as a recent specimen were sampled at a resolution representing time averaging of as little as 3 5 days to estimate seasonal climatic variation over the last thousand years regional differences in climate as well as asynchronous variation inferred by comparison with historical records of europe greenland and iceland suggest that the climate trends of eastern north america may not always correspond to those of europe or even the north atlantic results suggest that summer temperatures of the laurentian great lakes region at the beginning of the millennium were 2 6 c warmer while winter temperatures may have been nearly 2 c cooler than the 20th century average by the late 1200s summer temperatures decreased to nearly modern values in the 1400s and through the 1500s summer maxima exhibited enhanced intra annual variation as well as temperatures which were as much as 8 c cooler while winter temperatures were 0 4 2 7 c warmer than 20th century values an additional outcome of this research is the estimation of lake water 18 o values for several time periods throughout the holocene mean annual temperatures inferred from 18 o h 2 o values display a decrease from a d 985 through at least a d 1530 concomitant with summer temperature trends the long residence time of these large lakes suggests that secular trends in 18 o values must represent long term variation in climate which can be used in concert with the short term high resolution temperature record for a comprehensive estimation of climatic trends temperature variation and paleohydrology of the great lakes region is discussed in terms of variation in storm tracks and source region with time 18 o values of lake water coupled with paleotemperature data suggest that changing climate is the result of secular variation in the position shape and strength of the circumpolar vortex

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

short term orbital forcing a quasi review and a reappraisal of realistic boundary conditions for climate modeling abstract the aim of this paper is to provide geoscientists with the most accurate set of the earth s astro climatic parameters and daily insolation quantities able to describe the short term orbital forcing stof as represented by the ever changing incoming solar radiation we provide an updated review and a pragmatic tool database using the latest astronomical models and orbital ephemeris for the entire holocene and 1 kyr into the future our results are compared with the most important database produced for studying long term orbital forcing showing no systematic discrepancies over the full thirteen thousand years period studied our detailed analysis of the periods present in stof as perturbed by solar system bodies yields a very rich dynamical modulation on annual to decadal timescales when compared to previous results in addition we addressed for the first time the error committed considering daily insolation as a continuous function of orbital longitudes with respect to the nominal values i e calculating the corresponding daily insolation with orbital longitudes tabulated at noon we found important relative differences up to 5 which correspond to errors of 2 5 w m 2 in the daily mean insolation for exactly the same calendar day and set of astro climatic parameters this previously unrecognized error could have a significant impact in both the initial and boundary conditions for any climate modeling experiment

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

synthetic coral reef terraces and variations of quaternary sea level abstract coral reef terraces on tectonically elevated coasts provide important data on variations of sea level in this paper a systematic approach is presented for the construction of synthetic reef terraces idealized reef terraces are generated assuming a constant rate of tectonic uplift and a harmonic variation of sea level with amplitudehwo and period it is further assumed that coral terraces grow only during periods of relative sea level rise the behavior is governed by the parameter u 2 hwo if u 1 no reef terraces form if 0 217

storm dominated mixed carbonate siliciclastic shelf sequence displaying cycles of hummocky cross stratification late proterozoic wonoka formation south australia abstract the regressive late proterozoic wonoka formation of the adelaide geosyncline in south australia contains a thick mixed carbonate siliciclastic interval of middle to inner shelf origin the shelf was storm dominated and displays abundant hummocky cross stratification hcs of varying scales and other wave formed sedimentary structures some parts of this sequence are notably cyclic two kinds of cycles are described here the first average cycle 8 m thick consists of the alternation of silty and argillaccous limestone with fine grained hummocky cross stratified calcareous sandstone climatic cyclicity e g milankovitch cycles involving alternate wet and dry periods or minor sealevel fluctuations along a low gradient shoreline are considered the most likely cause of the observed sediment cyclicity carbonate deposition predominated during dry periods or high sealevel followed by influxes of sand from deltaic sources during wet periods or times of low sealevel the prevalence of hcs in the sandstones is most likely due to much slower rates of lithification in comparison to the limestones which give evidence of rapid lithification on the seafloor the second type of cycle average cycle 5 10 m thick is characterised by the cyclic appearence of red hummocky cross stratified glauconitic and phosphatic limestones within a sequence dominated by grey green stylonodular limestone tempestites the most likely origin of the red limestone involves contributions of volcanic ash fall material the resulting sediment did not undergo the rapid seafloor lithification of the associated grey green limestones and thus was involved in considerable storm wave reworking before deposition the micritic shelf carbonates of the wonoka formation are considered to represent direct inorganic precipitation into the middle shelf environment rather than reworking of detrital material from shallow carbonate banks

astronomical theory of paleoclimates and the last glacial interglacial cycle in the 19th century croll and pilgrim stressed the importance of severe winters as a cause of quaternary ice ages later on mainly during the first half of the 20th century koppen spitaler and milankovitch regarded high winter and low summer insolation as favoring glaciation after koppen and wegener related the milankovitch new radiation curve to penck and bruckner s subdivision of the quaternary there was a long lasting debate whether or not such changes in the insolation can explain the quaternary glacial interglacial cycles in the 1970s with the improvements of radiometric dating and of acquiring and interpreting the long continuous geological records with the advent of computers and with the development of more sophisticated astronomical and climate models the astronomical theory and in particular its milankovitch version were revived over the last 5 years most geological astronomical and climatological obstacles have been overcome and the causal role of the orbital variations in long term variation of climate is taken almost universally for granted models of different categories of complexity from conceptual ones to 3 d atmospheric general circulation models and 2 d time dependent models of the whole climate system have now been astronomically forced in order to test the physical reality of the astronomical theory for example experiments with both low and high resolution gcms show that the increased seasonality at 9 000 bp leads to intensified summer monsoon circulation of africa and southern asia on the other hand seasonal models for simulating the transient response of the climate system to astronomical forcing are also developed and the output of these most recent modeling efforts compares favorably with data of the past 400 000 years accordingly the model predictions for the next 100 000 years are used as a basis for forecasting how climate would evolve when forced by orbital variations in the absence of anthropogenic disturbances the long term cooling trend which began some 6 000 years ago will continue for the next 5 000 years this first temperature minimum will be followed by an amelioration around 15 000 ap after present by a cold interval centered al 23 000 ap and by a major glaciation at around 60 000 ap

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

the middle late jurassic forced regression and disconformity in central portugal eustatic tectonic and climatic effects on a carbonate ramp system successions across the middle upper jurassic disconformity in the lusitanian basin west central portugal are highly varied and were probably developed on a large westward inclined hangingwall of a half graben the disconformity is preceded by a complex forced regression showing marked variations down the ramp and provides an example of the effects of rapid relative sea level falls on carbonate ramp systems in the east middle jurassic inner ramp carbonates candeeiros facies are capped by a palaeokarstic surface veneered by ferruginous clays or thick calcretes in the west mid outer ramp marls and limestones brenha facies are terminated by two contrasting successions 1 a sharp based carbonate sandbody capped by a minor erosion surface overlain by interbedded marine lagoonal deltaic deposits with further minor erosion exposure surfaces 2 a brachiopod rich limestone with a minor irregular surface overlain by marls lignitic marls with marine and reworked non marine fossils and charophytic limestones with further minor irregular surfaces and capped by a higher relief ferruginous erosional surface the age ranges from late bathonian in the east to late callovian in the west this disconformity assemblage is succeeded by widespread lacustrine lagoonal limestones with microbial laminites and evaporites cabacos facies attributed to the middle oxfordian over the whole basin increasingly marine facies were deposited afterwards in middle jurassic inner ramp zones in the east the overall regression is marked by a major exposure surface overlain by continental sediments in middle jurassic outer ramp zones to the west the regression is represented initially by open marine successions followed by either a sharp marine erosion surface overlain by a complex sandbody or minor discontinuities and marginal marine deposits in both cases capped by the major lowstand surface reflooding led to a complex pattern of depositional conditions throughout the basin from freshwater and brackish lagoonal to marginal and shallow marine settings additional complications were produced by possible tilting of the hangingwall of the half graben the input of siliciclastics from westerly sources and climate change from humid to more seasonally semi arid conditions the middle late jurassic sea level fall in the lusitanian basin is also recorded elsewhere within the iberian and other peri atlantic regions and matches a transgressive to regressive change in eustatic sea level curves indicating that it is related in part to a global event

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

towards a high resolution global deep sea chronology for the last 750 000 years abstract variations in the ratio of 18 o 16 o as measured in shells of marine calcareous microfossils are primarily dominated by changes in global ice volume hence these variations provide a set of global time lines in deep sea sediments it is likely that the timing of major changes in oxygen isotope values is strongly influenced if not controlled by variations in the geometry of the earth s orbit since the variation of orbital parameters can be accurately calculated the opportunity exists for transforming this orbital chronology into a geological chronology through careful correlation of oxygen isotope records in a set of deep sea cores from the sub antarctic south atlantic and equatorial pacific we have assembled a composite isotopic section spanning the last 750 000 years with an average sedimentation rate of 2 3 cm 1000 years a new chronology for this time period was developed by adjusting the ages of the oxygen isotope stage boundaries in this composite section so as to extend the consistent phase relationships that exist between variations in oxygen isotope ratios and changes in obliquity and precession during the last 300 000 years to the entire 750 000 year record previously identified difficulties in phase locking precession with the filtered isotopic signal between 365 000 and 465 000 years b p have been resolved with the recognition that precessional variations have an average period of 19 000 years and not 23 000 years during this interval since this new age model yields the best match between variations in obliquity and precession and their corresponding frequency components in the oxygen isotope record we believe that it presents the most accurate chronology yet developed for deep sea sediments with this new age model providing the time control power spectral analyses of south atlantic and sub antarctic chemical and biotic indices show that there is a strong tendency for variance to be concentrated at frequencies corresponding to periods of 100 000 41 000 and 23 000 years

pleistocene climatic variability at astronomical frequencies abstract spectral analysis of geological records show periodicities corresponding to those calculated for the eccentricity 400 and 100 ka the obliquity 41 ka and the climatic precession 23 and 19 ka it is precisely the geological observations of this bi partition of the precessional peak confirmed to be real in astronomical computations which was one of the most impressive of all tests for the milankovitch theory concerning the question of whether or not the observed cycles account for most of the climatic variability having periods in the range predicted by the astronomical theory substantial evidence from cross spectral analysis coherency analysis and modelling is provided that at least near frequencies of variation in obliquity and precession a considerable fraction of the climate variance is driven in some way by insolation changes accompanying changes in the earth s orbit the variance components centered near a 100 ka cycle dominate most ice volume records and seem in phase with the eccentricity cycle although the exceptional strength of this cycle needs a non linear amplification by the glacial ice sheets themselves and associated feedbacks as the insolation spectra change with latitudes and with the type of parameters considered the diversity of the spectra of different climatic proxy data recorded in different places of the world over different periods is used to better understand how the climate system responds to the insolation forcing this study of the physical mechanisms involved is also achieved through the analysis of the log log shape of the geological records and through the comparison in frequency domain between simulated climatic time series and proxy data the evidence both in the frequency and in the time domain that orbital influences are felt by the climate system implies that the astronomical theory may provide a clock with which to date quaternary sediments with a precision several times greater than is now possible

orbital forcing of the inception of the laurentide ice sheet according to the astronomical theory of palaeoclimates the glacial interglacial oscillations of the pleistocene have their origin in the insolation forcing caused by the orbital variations of the earth1 the potential response of the climatic system to the resulting insolation perturbations has been investigated mainly using zonally averaged energy balance models ebm 2 6 atmospheric general circulation models gcm include many essential processes such as the hydrological cycle neglected in ebms but because of their high computational cost can be used only for snapshot reconstructions of climate at certain times in the past we show here that the climatic transition at the end of the last interglacial is a particularly relevant period for gcm studies of the sensitivity of climate to the astronomical variations of insolation we have used a low resolution spectral gcm to simulate two annual cycles with the insolation conditions of 125 000 yr bp and 115 000 yr bp for the 115 kyr simulation we find an annual mean cooling over canada of more than 2 k and increased precipitation we suggest that such a pattern of response to the insolation changes would favour the extension of permanent snow cover over the labrador area and could have triggered formation of the laurentide ice sheet

tree ring responses to the 1978 earthquake at stephens pass northeastern california the 1978 earthquake at stephens pass northeastern california dropped a series of grabens that average 4 5 m in width extend up to 1 m in depth and are found intermittently along a 2 km long rupture zone the formation of this graben series killed or otherwise affected many trees growing in or immediately adjacent to the rupture zone nine trees responded to the 1978 earthquake with anomalously narrow ring widths beginning in 1979 and continuing for several years one tree responded with anomalously wide latewood relative to total ring width this example of tree ring responses to a normal fault earthquake complements other cases of tree growth responses to earthquakes of thrust and strike slip tectonic settings the 1978 earthquake at stephens pass was unique in that it caused tree ring responses even though it was only moderate magnitude 4 6 this study serves as a specific calibration example for dendrochronologically studying prehistoric earthquakes as well as eruptions at the nearby medicine lake highlands medicine lake has been seismically and volcanically active during the past 1000 yr and it supports a forest of several coniferous tree species that can be used for dendrochronologically studying geomorphological processes