undulating topography on the antarctic ice sheet revealed by noaa avhrr images undulating topography on the east antarctic ice sheet was clearly revealed by noaa avhrr the following three patterns of undulating topography were detected by using high pass filtered images from the visible to thermal infrared channels in coastal regions below 2000 m a s l undulation can be clearly detected by the fluctuation of reflectance in visible channel it has wavy structure with spacing less than 10 km and alignment at a right angle to the ice flow lines in the katabatic zone from 2000 m a s to 3000 m a s well defined fluctuations of albedo stpectrum can be seen with spacing from 10km to 20km aligned at right angles to the ice flow lines or prevailing katabatic wind direction ground survey data show that the undulating topography is associated with large variations of net accumulation rate on the inland plateau above 3000 m a s l undulation can be clearly seen in the fluctuation of thermal infrared channel in winter ground survey data show that the signal corresponds to the undulating topography the alignment of the undulation is at a right angle to the ice flow lines and the spacing is longer than 20 km the characteristics of these undulations represent the ice flow dynamics and

gravity wave propagation characteristics 60 120 km as determined by the saskatoon mf radar gravnet system 1983 85 at 52 n 107 w abstract gravity waves gw have been detected and their characteristics measured by observations with the saskatoon multiple bistatic system gravnet data are available from 50 days for two height ranges 64 97 km 100 115 km and for the four seasons of 1983 85 wave characteristics include horizontal wavelength phase velocity period and amplitude background wind data allows the corresponding intrinsic parameters to be calculated many waves are doppler shifted to near their critical levels altitude and seasonal variations in the gw characteristics are shown the strongest variation is in the horizontal direction of wave propagation with southward directions dominating but significant eastward westward fluxes in summer winter below 100 km

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

modis based mosaic of antarctica moa data sets continent wide surface morphology and snow grain size abstract we present digital image mosaics of surface morphology and optical snow grain size for the antarctic continent and surrounding islands assembled from 260 moderate resolution imaging spectroradiometer modis images the products are derived from modis band 1 red light 647 nm and band 2 infrared 857 nm orbit swath data acquired during the 2003 2004 austral summer multiple images of all areas are combined in a data cumulation scheme to improve spatial resolution and increase radiometric content of the mosaics the component images were de striped geo registered and re sampled to the projection grid using the modis swath to grid toolbox ms2gt software a 125 m ground equivalent polar stereographic projection was used identical to previous radar image mosaics and similar to several other continent wide data sets geo location accuracy of the final mosaics is better than 125 m swath acquisition times were limited to the range 05 00 13 30 ut to provide broad but uniform mosaic illumination regions of cloud cover blowing snow and intense forward scattering were masked prior to compositing the moa snow grain size data set image provides the first continent wide semi quantitative map of mean summer snow firn and blue ice grain size optical grain size radius was determined using a normalized difference index derived from modis band 1 and band 2 rad values atmospheric correction adjustments for directional reflectance variation and snow grain size estimation were accomplished by a look up table generated by a combination of published models of snow spectral reflectance and atmosphere radiative transfer validation of the snow grain size image is provided by in situ spectra of snow covered sea ice made in october 2003 we use the new data sets to determine major ice shelf areas and shelf edge coastline and ice grounding line vector files and determine areas of selected blue ice regions these data sets are available for download at http nsidc org data moa

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

10be derived sub milankovitch chronology of late pleistocene alluvial terraces along the piedmont of sw tian shan abstract using topographic maps and terrestrial cosmogenic nuclide tcn 10be exposure dating methods we reconstructed a chronology with robust age constraints based on four alluvial terrace abandonment features in two study sites along the sw piedmont of kepingtage mountain in sw tian shan agreement between alluvial terrace abandonment ages and guliya ice core 18o lr04 stack of benthic 18o epica dome c ch4 and solar insolation records suggests that alluvial terraces with 10be age sequences at 63 7 5 9 ka 40 9 3 84 ka 36 2 3 4 ka and 22 1 5 1 4 7 ka correspond to three wetter climate intervals possibly triggered by intensified south asian summer monsoons since the late pleistocene given that the active thrust kepingtage fault experienced sustained uplift during this period we suggest that the abandonment of alluvial terraces that formed since 22 1 5 1 4 7 ka may be related to sudden tectonic uplift the occurrence of these four younger well preserved alluvial terraces may also be related to the fact that the transient climatic incision has been no higher than the temporary tectonic uplift since 22 1 5 1 4 7 ka

on the possible influence of extraterrestrial volatiles on earth s climate and the origin of the oceans abstract a consideration of observational and circumstantial evidence suggests that earth may be subject to high influx rates 1011 1012 kg yr of extraterrestrial sourced volatile elements carbon hydrogen oxygen nitrogen derived from comets or other primitive solar system material the total extraterrestrial influx rate may be four to five orders of magnitude greater than previously thought large enough to account for today s total near surface inventories of water and carbon the possibility of high rates of extraterrestrial volatile accretion suggests a new climatic paradigm wherein earth s surface temperature is influenced by conflicting internal and external processes a variable influx of volatile elements tends to warm the earth while terrestrial processes cool the planet by absorbing these gasses at a more uniform rate variations in extraterrestrial influx rates may explain the variation of sea level and mean global temperature over geologic time as well as some types of climate change the occurrence of the pleistocene ice ages and the asymmetry of the phanerozoic climate record sudden warmings slow coolings the extraterrestrial influx rate may also act as the pacemaker of terrestrial evolution at times leading to mass extinctions through climatic shifts induced by changes in accretion rates with concomitant disruptions of the carbon and nitrogen cycles life on earth may be balanced precariously between cosmic processes which deliver an intermittent stream of life sustaining volatiles from the outer solar system or beyond and biological and tectonic processes which remove these same volatiles from the atmosphere by sequestering water and carbon in the crust and mantle

earth s precession cycle and quaternary climatic change in tropical africa high abundances of the freshwater diatom melosira spp reflecting eolian input from dry lake beds in tropical africa occur in deep sea sediments of the equatorial atlantic at discrete times during the late quaternary1 2 we report here an approximately 260 kyr record of melosira accumulation in an equatorial atlantic sediment core and demonstrate significant influence of the earth s precessional cycle on the climate of tropical africa

average infiltration at yucca mountain over the next million years 1 an uncertainty distribution is developed to describe areal average infiltration at yucca mountain averaged over the next million years the distribution uses infiltration tabulator for yucca mountain itym model results to estimate uncertainty in net infiltration given decadal average climate driven with two independent estimates for potential future climatic sequences both future climatic sequences use orbital mechanics linked to paleoclimatic proxies to estimate future climate states but one uses primarily biotic indicators and the other uses primarily abiotic indicators to link paleoclimate to orbital stage abiotic indicators suggest that present day climate variation by latitude in the great basin is reasonably analogous to glacial scale climate variation at a single location once orographic lake effect and insolation influences are accounted for in the southern sierra nevada abiotic indicators suggest that mean annual precipitation was 1 7 1 9 times larger than present and mean annual temperature was 5 6 7 c cooler than present at the last glacial maximum the influence of decadal to millennial scale variability is estimated using the 8000 year methuselah walk tree ring record which suggests that even large inferred fluctuations over the holocene only modestly increase 8000 year average infiltration combining the future climate projections with the infiltration model uncertainty distribution yields approximately lognormal uncertainty distributions for projected million year areal average net infiltration with a mean of 41 mm yr and coefficient of variation of 0 81 even if anthropogenic effects significantly alter climatic patterns relative to past climate cycles the projected anthropogenic period is sufficiently brief that million year averages are not likely to be substantially influenced

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

recent contributions to the climatology of the last glacial interglacial cycle based on french pollen sequences abstract new pollen data derived from three long french sequences and methodological improvements in the methods used to reconstruct past climates are summarized here after a short presentation of the study sites and pollen diagrams estimated climate parameters during the major episodes of the last 140 000 years are shown to be coherent between sites analysis of the seasonality variations provides much additional information in particular it is shown that the advection from the ocean has governed the last climatic cycle on the european continent

greenland ice sheet surface properties and ice dynamics from ers 1 sar imagery c band synthetic aperture radar sar imagery from the european space agency s ers 1 satellite reveals the basic zonation of the surface of the greenland ice sheet the zones have backscatter signatures related to the structure of the snowpack which varies with the balance of accumulation and melt at various elevations the boundaries of zones can be accurately located with the use of this high resolution imagery the images also reveal a large flow feature in northeast greenland that is similar to ice streams in antarctica and may play a major role in the discharge of ice from the ice sheet

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

500 000 year stable carbon isotopic record from devils hole nevada the record of carbon 13 delta 13 c variations in dh 11 vein calcite core from devils hole nevada shows four prominent minima near glacial terminations glacial interglacial transitions v to ii the delta 13 c time series is inversely correlated with the dh 11 oxygen isotope ratio time series and leads it by as much as 7000 years the delta 13 c variations likely record fluctuations in the delta 13 c of dissolved inorganic carbon of water recharging the aquifer how such variations are transported 80 kilometers to devils hole without obliteration by water rock reaction remains an enigma the record may reflect i global variations in the delta 13 c of atmospheric co 2 and hence the delta 13 c of continental biomass or ii variations in extent and density of vegetation in the southern great basin in the latter case delta 13 c minima at 414 334 246 and 133 thousand years ago mark times of maximum vegetation

a 250 000 year climatic record from great basin vein calcite implications for milankovitch theory a continuous record of oxygen 18 18o variations in the continental hydrosphere during the middle to late pleistocene has been obtained from a uranium series dated calcitic vein in the southern great basin the vein was deposited from ground water that moved through devils hole an open fault zone at ash meadows nevada between 50 and 310 ka thousand years ago the configuration of the 18o versus time curve closely resembles the marine and antarctic ice core vostok 18o curves however the u th dates indicate that the last interglacial stage marine oxygen isotope stage 5 began before 147 3 ka at least 17 000 years earlier than indicated by the marine 18o record and 7 000 years earlier than indicated by the less well dated antarctic 18o record this discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine 18o chronology may need revision and that orbital forcing may not be the principal cause of the pleistocene ice ages

a glaciological map of filchner ronne ice shelf antarctica a set of landsat 5 multispectral scanner mss images of filchner ronne ice shelf was commissioned by the institut fur angewandte geodasie and recorded over a short period in early 1986 a mosaic of digitally enhanced images was constructed using all available ground control in due course it is planned to use the data for the production of a series of digital image maps at a scale of 1 1 000 000 meanwhile a line map has been prepared at a scale of 1 2 000 000 to show the principal glaciological features the new mosaic shows much more detail than earlier landsat images and extends coverage to higher latitudes more of the poorly known southern boundary of the ice shelf can be identified but floating ice still extends beyond the limit of coverage extensive ice rumples are revealed many of them undetected in earlier imagery flow bands can be tracked without a break from their ice stream source to the ice front over distances of up to 800 km even minor tributaries and sheet flow from the inland ice sheet between the ice streams yield narrow but identifiable flow bands ice thickness velocity and mass flux data are reviewed in order to underline their dependence on good mapping

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

the coral record of last interglacial sea levels and sea surface temperatures abstract the rise and fall of the last interglacial li sea levels and sea surface temperatures ssts are evaluated using u series dating combined with sr ca ratios in corals from both stable and tectonically uplifted sites along the stable coastal margin of western australia an extensive series of li coral reefs occur at heights of 2 3 m above present day sea level these corals have a very tight cluster of 234u 230th ages ranging from 129 1 to 119 1 ka as well as a narrow range of initial 234u values of 150 5 similar to modern seawater bahamas which is also a stable site has an essentially identical pattern of u series ages from 130 1 to 120 1 ka barbados and huon peninsula are tectonically active sites where the li terraces are found at elevations of 50 and 200 m respectively u series ages from corals exposed in the lower footwall of these uplifted reefs allow better constraints to be placed on the rate of sea level rise which initiated the li corals from the huon peninsula constrain sea level at 80 10 m at 131 2 ka and from barbados at 30 5 m at 129 1 ka combined with constraints from stable sites these observations require an exceedingly rapid rise in sea level of 30 50 m per 1000 years at 130 1 ka this indicates that large scale catastrophic melting of the once massive continental ice sheets occurred in phase with the rapidly increasing northern hemisphere nh summer insolation consistent with the orbital forcing being the main driver of glacial interglacial climate change there is also some evidence from huon peninsula although still not conclusive for a precursor oscillation in sea level during the penultimate deglaciation that may have been within 20 m of present day levels at 135 ka ssts for the li porites corals from the huon peninsula and western australia have mean annual temperatures and seasonal ranges that are remarkably similar to present day patterns the tropical site of huon peninsula has ssts of 29 1 c which is indistinguishable from the ssts given by modern corals at ningaloo reef in western australia similar mean annual 24 c and summer maximum ssts of 27 29 c are found in both li and modern corals the only significant difference is the 1 c cooler winter minimum ssts of 21 c for the li compared to present day minimums of 22 c li ssts from these southern hemisphere sh sites were thus very similar or at most only slightly cooler than today despite sea levels being up to 4 m higher this maybe indicative of asymmetric warming of the earth with the increased nh insolation during the li period being responsible for the extensive melting of the mainly nh based ice sheets and hence higher global sea levels the observation of relatively high sea levels in the li together with the rapid pulses of sea level rise indicates that the potential now exists for greenhouse warming to initiate increases in sea level of at least several metres on relatively short time scales 102 years

investigating tidal flexure on an ice shelf using kinematic gps the positions of ice stream grounding zones are uniquely sensitive to changes in the mass balance of the ice sheet present methods for locating groundingzone features are either imprecise or require considerable effort in interpretation and so are of little value for change studies we present a new method which uses the kinematic gps technique to locate the position of the limit of tidal flexure the method involves the collection of at least two surface elevation profiles along the same track through the grounding zone at different times during the tidal cycle the elevation profiles obtained coincide upstream of the limit of flexure but diverge downstream of the limit of flexure subtracting the profiles produces a tidal def1ection profile which shows directly the response of the ice shelf to the tidal forcing we present two examples of the use of this method both on rutford ice stream antarctica the first is across the grounding zone and shows that the method is capable of measuring grounding positions to around 200 m precision the second taken across an active shear margin shows a tidal deflection profile with an absence of steps that would indicate the presence of fracture planes penetrating from the ice base to sea level

timing and duration of the last interglacial evidence for a restricted interval of widespread coral reef growth abstract we report new mass spectrometric u series ages for eight last interglacial fossil reefs along the continental margin of western australia corals were selected in growth position from localities that are characterized by apparently low levels of diagenesis and relative tectonic stability so that the fossil reefs provide critical information on last interglacial sea levels without requiring corrections for tectonic movements in addition we have improved the constraint on the timing of onset of reef growth by recovering drill core coral from the base of the reefs uranium and thorium isotopes were measured with high levels of precision leading to improvements in age resolution and allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified and discarded these data supplement our previous results for rottnest island and leander point leading to more than seventy mass spectrometric u series ages from which constraints can be placed on the timing duration and character of the last interglacial sea level highstand reliable ages show that reef growth started contemporaneously at 128 1 ka along the entire western australian coastline while relative sea levels were at least 3 m above the present level because western australia is located far from the former penultimate glacial maximum ice sheets and are not significantly effected by glacial unloading these data constrain the timing of onset of the last interglacial period to 128 1 ka assuming reef growth started soon after sea level approached interglacial levels a unique regressive reef sequence at mangrove bay constrains the timing of termination of the last interglacial period to 116 1 ka the major episode of reef building however both globally and locally along the western australian coast is restricted to a very narrow interval occurring from 128 ka and 121 ka suggesting that global ocean surface temperatures were warm and or sea levels were stable enough to allow prolific reef growth only during the earlier part of the last interglacial

radiation windows as indicators of an astronomical influence on the devil s hole chronology orbitalexplanationsofpaleoclimaticrecordstraditionallyfocusondailyinsolationat 60 n we exemplify how insolation at different latitudes and different times of day can explain the timing of the devil s hole d 18 o record we combine winter tropical noontime insolation associated with the source region for wintertime precipitation and summer extra tropicalnoontimeinsolation producingnoontimeheattowarmterrestrialsurfaces periodsoflowwinterandhighsummerinsolationarecalled radiationwindows andyield drier warmer conditions in the northern hemisphere mid latitudes when radiation windows are compared with the dh 11 record the apparent contradiction with milankovitch winogradetal 1992 mayberesolved themiddle latitudecontinentalclimatesignal as recordedbydh 11 tendstowardacoolingstateuntilinterruptedbyatermination inevery instance where the dh 11 record is warming before a radiation window a termination occurs if radiation windows occur with antecedent cooling then there is a complex response of warming with a variable lag effect yet there are no cases where cooling follows a radiation window

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

a synthesis of remote sensing data on wilkins ice shelf antarctica wilkins ice shelf has an area of 16000 km2 and lies off the west coast of the antarctic peninsula bounded by alexander latady charcot and rothschild islands several ice shelves including wilkins exist close to a climatic limit of viability the recent disintegration of the neighbouring wordie ice shelf has been linked to atmopsheric warming observed on the antarctic peninsula the limit of ice shelf viability thus appears to have migrated south should this continue the question arises how long will wilkins ice shelf survive compared with the other ice shelves on the antarctic peninsula few surface glaciological data have been collected on wilkins ice shelf we compare contrast and combine a variety of remotely sensed data the recently declassified geosat geodetic mission altimetry landsat mss and tm imagery and radio echo sounding data res to study its structure and mass balance regime we find that this shelf has an unusual mass balance regime and relies heavily for sustenance on in situ accumulation its response to a continued atmospheric warming may be significantly different from that of wordie ice shelf wordie ice shelf was fed by several dynamic outlet glaciers which accelerated the disintegration process when the ice shelf fractured wilkins ice shelf by contrast is almost stagnant and is expected to respond by normal calving at the ice front changes in the accumulation rate or basal melt rate may however dominate any dynamic effect over the last two decades the ice front positions have remained stable

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

the surface topography of large ice masses from landsat imagery les images de landsat mss de l antarctique et du svalbard ont ete comparees a des mesures altimetriques effectuees a partir d avion

role of orbitally induced changes in tundra area in the onset of glaciation the link between glacial interglacial cycles and changes in insolation due to variations in the earth s orbital parameters is well established1 4 but of the attempts to simulate incipient glaciation using three dimensional general circulation models gcms driven by orbital forcing alone5 10 only one10 has been successful gcm experiments7 11 show that reduced summer insolation 115 000 years ago during an interglacial to glacial climate shift produces sufficient high latitude cooling to cause expansion of tundra at the expense of boreal forest11 which in turn can induce more cooling11 14 here we show using a global climate model that the increase in surface albedo under snow covered conditions that results from a biome model estimate11 of tundra expansion 115 000 years ago is sufficient to induce glaciation over extreme northeastern canada if the additional cooling from this estimated tundra expansion induces further expansion then widespread glaciation occurs at latitudes above 65 n these results suggest that the climate feedback from high latitude tundra expansion might have contributed to the onset of the most recent glaciation

potential reconciliation of devils hole and deep sea pleistocene chronologies the standard model of pleistocene climate fluctuations being driven by orbital insolation changes has been challenged by results from a high precision radiometrically dated deposit from devils hole nevada although the devils hole record agrees with a previously derived ice volume record for most of the last 500 000 years clear indication of warming prior to the orbitally dated onset of the last interglacial forms the prime basis for this conclusion i suggest that early warming at devils hole needs to be understood in light of the prior very extensive glaciation at 150 000 b p marine records in both the north pacific and north atlantic from the same latitude as devils hole indicate that the subpolar fronts during the penultimate glaciation 150 000 years ago were 5 father south than during the last glaciation continental glaciation may also have been more extensive at this time the first phase of ice retreat 145 000 years ago is associated with a northward shift of these fronts which results in full interglacial sea surface temperatures in the north atlantic the early warming at devils hole may reflect the northward movement of the ice margins and associated fronts if so both the devils hole and deep sea chronologies may be correct with differences between 130 000 and 150 000 years ago reflecting a regionally varying response to climate shifts associated with a very extensive glaciation

orbital signals in the diurnal cycle of radiation time of day plays a critical role in determining the dominance of the earth s orbital parameters involving eccentricity precession and obliquity extension of orbital radiation data to the diurnal cycle permits the recognition of well defined temporally separate signals corresponding to all three major orbital parameters and to combinations of these parameters past research involving computed radiation changes at the daily and seasonal scales has not shown significant eccentricity cycles results of this study show 1 at the solstices a marked change in dominance from precession for the solar elevation classes associated with early morning late afternoon to obliquity for the elevation class containing solar noon occurs in solar radiation 2 at the equinoxes cycles corresponding to those associated with eccentricity are evident in the radiation data at all individual time intervals of the day past studies have shown that the daily radiative total reflects only the influence of precession a third set of cycles at the equinoxes centered near 11 kyr corresponds to a combination of orbital signals these results imply that paleoclimatic proxy data displaying strong spectral peaks corresponding to eccentricity 100 kyr and obliquity 41 kyr such as records of global ice volume may be related to radiation changes occurring in the solar elevation class containing solar noon while paleoclimatic proxy data displaying strong spectral peaks corresponding to precession for example sea surface temperatures appear to be showing the dominance of precession on the daily total radiation

climatic hydrologic oscillations since 155 000 yr b p at owens lake california reflected in abundance and stable isotope composition of sediment carbonate abstract sediment grain size carbonate content and stable isotopes in 70 cm long 1500 yr channel samples from owens lake core ol 92 record many oscillations representing climate change in the eastern sierra nevada region since 155 000 yr b p to first order the records match well the marine 18o record at owens lake however the last interglaciation appears to span the entire period from 120 000 to 50 000 yr b p according to our chronology and was punctuated by numerous short periods of wetter conditions during an otherwise dry climate sediment proxies reveal that the apparent timing of glacial interglacial transitions notably the penultimate one is proxy dependent in the grain size and carbonate content records this transition is abrupt and occurs at 120 000 yr b p in contrast in the isotopic records the transition is gradual and occurs between 145 000 and 120 000 yr b p differences in timing of the transition are attributed to variable responses by proxies to climate change

geothermal evidence from canada for a cold period before recent climatic warming three deep boreholes in a small area in quebec each having two high accuracy temperature logs separated by 22 years allow reliable determination of the ground surface temperature history during the past few centuries the temperature logs show that the recent climatic warming was preceded by a cold period near the end of the 19th century in this area the presence of such a cold period is also suggested by borehole temperature data from other areas in canada

links between climate and sea levels for the past three million years the oscillations between glacial and interglacial climate conditions over the past three million years have been characterized by a transfer of immense amounts of water between two of its largest reservoirs on earth the ice sheets and the oceans since the latest of these oscillations the last glacial maximum between about 30 000 and 19 000 years ago approximately 50 million cubic kilometres of ice has melted from the land based ice sheets raising global sea level by approximately 130 metres such rapid changes in sea level are part of a complex pattern of interactions between the atmosphere oceans ice sheets and solid earth all of which have different response timescales the trigger for the sea level fluctuations most probably lies with changes in insolation caused by astronomical forcing but internal feedback cycles complicate the simple model of causes and effects

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