oxygen and carbon isotope record of east pacific core v19 30 implications for the formation of deep water in the late pleistocene north atlantic abstract a detailed oxygen and carbon isotope record has been obtained from benthic foraminifera in core v19 30 from the carnegie ridge on the south side of the panama basin expressing these records and the oxygen and carbon isotope records previously published for atlantic core m 12392 on a common timescale it is apparent that the oxygen isotope records are very similar but that the carbon isotope records are quite different by obtaining the carbon isotope gradient between the two sites as a function of time we show that the production of north atlantic deep water has varied over a wide range during the late pleistocene and that the pattern of variation is not simply related to the well known oxygen isotope record although the two oxygen isotope records are very similar changes in the interoceanic gradient are detectable and support the hypothesis that in the glacial mode the north atlantic was colder and less oxygenated than it is today shackleton s 1 1977 interpretation whereby the carbon isotope record from the atlantic core reflects changes in the terrestrial biomass is an over simplification however the record from the pacific core v19 30 probably can be explained in these terms since it probably approximates the carbon isotope record of global mean oceanic dissolved co 2

oxygen isotope analyses and pleistocene ice volumes abstract the oxygen isotope record from fossil foraminifera in deep sea sediments is commonly used as a proxy for global ice volume the linkage between 18 o and ice volume however is probably nonlinear we have developed a simple numerical model of the isotopic response of the oceans to ice volume change the major features it simulates are 1 the changing mean isotopic composition of snow as a function of ice volume colder snow temperatures forced by climate change and higher elevation accumulation areas imply more negative mean 18 o 2 the nonequilibrium isotopic composition of ice sheets the past history of an ice sheet is integrated into its mean isotopic composition which introduces a lag of isotopic ice volume i e the measured 18 o record scaled to ice volume units behind true ice volume 3 selective preservation of isotopically more negative colder higher latitude ice this geographic effect can selectively amplify or dampen the isotopic response to the ice volume signal we illustrate the response of our model to simple hypothetical ice volume transitions of ice growth and ice decay sensitivity tests are illustrated for all model parameters the results suggest that oxygen isotope records reproduce the general patterns of ice volume change fairly accurately the foraminiferal isotope record however may misrepresent the true amplitude of the ice volume signal and lag true ice volume by 1000 to 3000 yr

observed and modelled effects of ice lens formation on passive microwave brightness temperatures over snow covered tundra abstract immediately before an april 2007 snow survey and passive microwave radiometer field campaign in the northwest territories canada a rain on snow event deposited a thin 3 mm continuous layer of ice on the surface of the snowpack at eight sites the brightness temperature t b of the undisturbed snow pack was measured with a multi frequency dual polarization 6 9 19 37 and 89 ghz ground based radiometer system the ice lens was then carefully removed and the t b s were measured again the individual v pol channels and the 37 v 19 v difference were largely unaffected by the presence of the ice lens exhibiting a systematic shift of about 3 k in comparison the ice lens had a considerable effect on the h pol t b at all frequencies with a mean difference ice lens present ice lens removed of 9 k 5 3 k at 6 9 ghz 40 k 11 3 k at 19 ghz 33 k 7 6 k at 37 ghz and 19 k 8 0 k at 89 ghz the effect of the ice lens on h pol measurements was also observed with spaceborne data from the advanced microwave scanning radiometer amsr e satellite data simulations of t b were produced for each site using a new two layer formulation of the helsinki university of technology hut snow emission model the ice lens was used as the top layer and the underlying snowpack considered as a homogenous second layer the agreement between observations and simulations was variable with agreement strongest at 19 ghz a comparison with simulations produced using the microwave emission model of layered snowpacks memls suggests hut model uncertainty is related not to the ice lens but to difficulties in simulating emission from deep snow overall the observations and simulations suggest h pol measurements are capable of detecting new ice layers across the tundra snowpack while v pol measurements are more appropriate for snow water equivalent swe retrievals due to their relative insensitivity to ice layers

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

quaternary correlations in arctic canada in the hudson bay james bay lowlands along the coasts of banks island and along the eastern coast of baffin island are continuous and extensive sections in quaternary sediments these sections are rich in marine fossils buried peats and soils and contain a wide variety of glaciagenic sediments together with glacial marine units and littoral deposits lake muds are also fairly common all three areas possess very long records that may extend to the early quaternary and pliocene the events of the last glaciation wisconsinan foxe amundsen are interpreted in terms of lithostratigraphy biostratigraphy and aminostratigraphy relative and absolute dating control is provided by radiocarbon dating of events that span the last 50 ka and in particular the last 11 ka and some age control is also provided by several u series dates on marine molluscs regional correlations are based on comparisons of amino acid ratios from marine shells suggested correlations during the last glaciation wisconsinan foxe amundsen are ka banks island hudson bay lowland baffin island 8 tyrrell sea sediments inugsuin regression 10 russell stade upper tills baffinland stade 40 friday creek sediments iron stand event till 80 fawn river gravels quajon interstade m clure stade adam till ayr lakde stade 120 cape collinson interglaciation missinaibi formation kogalu cape broughton interglaciation

the great cenozoic ice sheet abstract ocean floor sediments contain a record of quaternary continental glaciations in which global cooling prevails over a 100 000 year cycle and the intensity of the last glacial maximum is as strong as any of the earlier glaciations yet the areal extent of quaternary glacial drift in north america and eurasia during the last glaciation is much less extensive than during several earlier glaciations in an attempt to explore this problem two versions of a great cenozoic ice sheet were reconstructed the minimum version transformed a frozen bed beneath high interior ice domes and along southern margins during the last glaciation into a thawed bed during more extensive earlier glaciations this allowed thinner ice to cover a larger area with little change in ice volume thereby satisfying both the continental and oceanic records of quaternary glaciation the maximum version extended frozen basal conditions beneath high interior ice domes and along southern margins so that a greater areal extent could only be accommodated by thicker ice a greater ice volume is required in this case and would seem to put the great cenozoic ice sheet in the late tertiary where some evidence for global cooling on a 400 000 year cycle exists and might provide the longer timespan needed to produce a larger ice sheet

late weichselian and holocene relative sea level history of broggerhalvoya spitsbergen abstract radiocarbon dated whalebones from raised beaches record a relative sea level history for broggerhalvoya western spitsbergen that suggest a two step deglaciation on svalbard at the end of the late weichselian glaciation the late weichselian marine limit was reached at about 13 000 yr b p and was followed by relatively slow emergence until about 10 000 yr b p either in response to ice unloading in the barents sea initial retreat of local fjord glaciers or some combination of the two rare whale skeletons dating between 13 000 and 10 000 yr b p indicate that the norwegian sea was at least seasonally ice free during that interval deglaciation of spitsbergen is recorded by the rapid emergence of broggerhalvoya after 10 000 yr b p this was followed by a transgression during the mid holocene here named the talavera transgression and another in modern times raised beach morphologies suggest striking differences in nearshore depositional processes before and after 10 000 yr b p that are probably related to changes in the rate of uplift and in sea ice conditions

thrust faults and back thrusts in madison range of southwestern montana foreland in the rocky mountain foreland of southwestern montana a zone of late cretaceous thrust faults named the hilgard fault system extends along the west side of the madison range from hebgen lake northward for about 50 mi 80 km the thrust faults are steep at their leading edges but flatten westward beneath the associated plates where they commonly dip 25 30 structural lows and highs are apparent beneath the beaver creek plate the major thrust sheet of the system and correlate with salients and reentrants of the plate the beaver creek plate consists primarily of archean metamorphic rocks but phanerozoic strata are preserved along the northern part of the plate s leading edge only the forward part of the plate is preserved in the madison range because c nozoic normal faults of the madison range fault system dropped much of the plate beneath the madison valley on the west the kirkwood plate lies east of and beneath the beaver creek plate and contains structures of the eastern part of the hilgard system the central segment of the leading edge of the kirkwood plate is not completely detached from underlying strata the leading edge of the northern part of the plate defined by the cache creek fault is flanked on the west by an associated anticline the southern end of the cache creek fault is an eastward dipping back thrust which abruptly steepens on the west adjacent to the anticline both the fault and the anticline are believed to have formed above a concealed detachment fault the southern part of the kirkwood plate displays structures interpreted to represent displacement transfer from the beaver creek plate back thrusts are associated with both thrust plates and played a key role in accommodating strain associated with folding the strata at the leading edges of the plates the back thrusts project upward from the main thrust fault beneath each plate they dip eastward at moderate angles in their lower segments but steepen at structurally higher levels they become overturned locally and dip westward in their uppermost segments the northern part of the study area contains the northwest trending buck creek reverse fault which dips steeply to the northeast movement on this structure ceased before the north trending thrust faults of the hilgard system were emplaced

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

sensitivity experiments with a model of the ice age cycle the response to milankovitch forcing abstract we address the question of the extent to which a simple one dimensional time dependent climate model is able to explain the fluctuations of continental ice volume which have occurred during the last quarter of the pleistocene epoch the model includes explicit ice physics based on the glen flow law and explicit glacial isostatic adjustment based on a realistic viscoelastic field theory when the model is forced by the milankovitch variations of insulation it delivers ice volume fluctuations which are very similar to those implied by the specmap 18o record in particular the model appears capable of explaining the observed correlation between eccentricity and ice volume variations the dominance of the 105 year period in the power spectrum of the ice volume time series and the thickness and latitudinal extents of the continental ice sheets which existed at wurm wisconsin maximum 18 000 years ago

assessing the global meltwater spike abstract l v worthington 1968 meteorological monographs 8 63 67 hypothesized that a low salinity lid covered the entire world ocean by deconvolving isotopic curves from the western equatorial pacific and equatorial atlantic w h berger r f johnson and j s killingley 1977 nature london 269 661 663 and w h berger 1978 deep sea research 25 473 480 reconstructed meltwater spikes similar to those actually observed in the gulf of mexico and thus apparently confirmed the worthington hypothesis it is shown that this conclusion is unwarranted the primary flaw in the reconstructed meltwater spikes is that the mixing intensity used in the deconvolution operation is overestimated as a result structure recorded in the mixed isotopic record becomes exaggerated in the attempt to restore the original unmixed record this structure can be attributed to variable ice volume decay during deglaciation effects of differential solution on planktonic foraminifera temporal changes in abundance of the foraminifera carrying the isotopic signal and analytical error an alternative geographic view to the global low salinity lid is offered a map showing portions of the ocean potentially affected by increased deglacial meltwater at middle and high latitudes and by increased precipitation induced runoff at low and middle latitudes

comparison of snow mass estimates from a prototype passive microwave snow algorithm a revised algorithm and a snow depth climatology abstract while it is recognized that no single snow algorithm is capable of producing accurate global estimates of snow depth for research purposes it is useful to test an algorithrn s performance in different climatic areas in order to see how it responds to a variety of snow conditions this study is one of the first to develop separate passive microwave snow algorithms for north america and eurasia by including parameters that consider the effects of variations in forest cover and crystal size on microwave brightness temperature a new algorithm gsfc 1996 is compared to a prototype algorithm chang et al 1987 and to a snow depth climatology sdc which for this study is considered to be a standard reference or baseline it is shown that the gsfc 1996 algorithm compares much more favorably to the sdc than does the chang et al 1987 algorithm for example in north america in february there is a 15 difference between the gsfc 1996 algorithm and the sdc but with the chang et al 1987 algorithm the difference is greater than 50 in eurasia also in february there is only a 1 3 difference between the gsfc 1996 algorith rn and the sdc whereas with the chang et al 1987 algorithm the difference is about 20 as expected differences tend to be less when the snow cover extent is greater particularly for eurasia the gsfc 1996 algorithln performs better in north america in each month than does the chang et al 1987 algorithm this is also the case in eurasia except in april and may when the chang et al 1987 algorithm is in closer accord to the sdc than is the gsfc 1996 algorithm

thermal maturation of the lower palaeozoic strata of northern greenland from conodont colour alteration index cai data implications for burial history and hydrocarbon exploration conodont colour alteration data for the lower palaeozoic strata of the north greenland carbonate platform indicate a pattern of increased thermal maturity northwards within the franklinian basin there is little variation in values through the canadian llandovery lower ordovician lower silurian interval at any given locality a simplified thermal model for the platform suggests that the predominant control of conodont colour alteration and thermal maturation was maximum depth of burial which occurred during the mid to late silurian a preliminary integrated scheme for conodont and organic thermal maturity indicators can be compiled from the data now available from north greenland

snow stratigraphic heterogeneity within ground based passive microwave radiometer footprints implications for emission modeling two dimensional measurements of snowpack properties stratigraphic layering density grain size and temperature were used as inputs to the multilayer helsinki university of technology hut microwave emission model at a centimeter scale horizontal resolution across a 4 5 m transect of ground based passive microwave radiometer footprints near churchill manitoba canada snowpack stratigraphy was complex between six and eight layers with only three layers extending continuously throughout the length of the transect distributions of one dimensional simulations accurately representing complex stratigraphic layering were evaluated using measured brightness temperatures large biases 36 to 68 k between simulated and measured brightness temperatures were minimized 0 5 to 0 6 k within measurement accuracy through application of grain scaling factors 2 6 to 5 3 at different combinations of frequencies polarizations and model extinction coefficients grain scaling factors compensated for uncertainty relating optical specific surface area to hut effective grain size inputs and quantified relative differences in scattering and absorption properties of various extinction coefficients the hut model required accurate representation of ice lenses particularly at horizontal polarization and large grain scaling factors highlighted the need to consider microstructure beyond the size of individual grains as variability of extinction coefficients was strongly influenced by the proportion of large hoar grains in a vertical profile it is important to consider simulations from distributions of one dimensional profiles rather than single profiles especially in sub arctic snowpacks where stratigraphic variability can be high model sensitivity experiments suggested that the level of error in field measurements and the new methodological framework used to apply them in a snow emission model were satisfactory layer amalgamation showed that a three layer representation of snowpack stratigraphy reduced the bias of a one layer representation by about 50

relation between grain size and correlation length of snow in the past it has often been difficult to compare results of different types of snow structural information grain size and correlation length are such parameters of granular media and there exist different definitions and different measurement methods for both of them the relation between these parameters is analyzed from theoretical and from experimental points of view considering optical and microwave properties for spherical ice grains the connecting formulas are simple but for other shapes the two parameters are not directly related care must be taken in the measurement procedure especially if grain size is regarded as the maximum extent of connected ice particles the results are likely to lead to extreme overestimates therefore it is concluded that grain size should be complemented by an additional size parameter namely the surface to volume ratio of equivalent spheres i e a measure of the correlation length methods to determine this quantity in the laboratory have been known for a long time methods to obtain such measurements in the field are described here

source rock potential of middle cretaceous rocks in southwestern montana the middle cretaceous in southwestern montana is composed of a marine and nonmarine succession of predominantly clastic rocks that were deposited along the western margin of the western interior seaway in places middle cretaceous rocks contain appreciable total organic carbon toc such as 5 59 for the mowry shale and 8 11 for the frontier formation in the madison range most samples however exhibit less than 1 0 toc the genetic or hydrocarbon potential s1 s2 of all the samples analyzed except one yield less than 1 mg hc g rock strongly indicating poor potential for generating commercial amounts of hydrocarbons out of 51 samples analyzed only one a thermopolis shale sample from the snowcrest range showed a moderate petroleum potenti l of 3 1 mg hc g rock most of the middle cretaceous samples are thermally immature to marginally mature with vitrinite reflectance ranging from about 0 4 to 0 6 r0 maturity is high in the pioneer mountains where vitrinite reflectance averages 3 4 r0 and at big sky montana where vitrinite reflectance averages 2 5 r0 at both localities high r0 values are due to local heat sources such as the pioneer batholith in the pioneer mountains

late pleistocene eolian sand sheets in alaska abstract nonglaciated lowlands in central and southwestern alaska contain extensive deposits of upper quaternary eolian sand derived largely from major outwash rivers although surface dunes are common deep exposures consistently reveal that subhorizontally stratified sand and silt deposits dominate over dune cross strata we hypothesize that 1 many of the subhorizontally stratified deposits represent full glacial eolian sand sheets formed when sand supply was limited by seasonally variable combinations of ice cementation snow cover high groundwater tables and vegetation and 2 many surface dunes reflect late glacial and postglacial reworking under conditions of increased short term availability of loose sand the morphology of some surface dunes may therefore reflect mainly the intensity of reworking since the last glacial maximum rather than full glacial paleowind vectors or the age of the bulk of the underlying deposits

volume loss and defluidization history of barbados the basal complex of barbados island is a tectonic amalgam of eocene strata accreted at an outer deformation front at the end of eocene time the structures and porosity depth function of such sediments give clues to the succession of pore volume loss episodes each of which must have been accompanied by defluidization the basal complex evolved as a perpetually shallow low temperature mass which underwent little or no unroofing in its 36 m y history in the accretionary prism in its early phase of deformation the accretionary structure formed by thrust imbrication perhaps with little concurrent volume loss burial compaction followed tectonic thickening during accretion causing probable large pore volume loss within limits of 0 70 of the initial volume of the imbricate stack a late phase of tectonics has affected barbados and a wide region of the structural high since 20 ma such tectonics reactivated faults in the basal complex which acted as channelways for deep seated and perhaps shallow fluids to emerge from the structural high the late stage tectonics also caused local basins for deposition of sediment cover and emplacement of thrust nappes of forearc basin strata above the basal complex such top loading caused a renewed phase of burial compaction and loss of about 37 or more of the pore volume that existed at the onset of late stage tectonics

structure burial history and petroleum potential of frontal thrust belt and adjacent foreland southwest montana the frontal thrust belt in the lima area of southwestern montana consists of blind nonsurfacing thrusts of the lima thrust system beneath the lima anticline and the tendoy thrust sheet to the west the tendoy sheet involves mississippian through cretaceous rocks of the southwest plunging nose of the mesozoic blacktail snowcrest uplift that are thrust higher northeast onto the uplift the front of the tendoy sheet west of lima locally has been warped by later compressive deformation which also involved synorogenic conglomerates of the structurally underlying beaverhead formation to the north recent extension faulting locally has dropped the front of the tendoy sheet beneath quaternary gravels rocks of the exposed tendoy sheet have never been deeply buried based on itrinite reflectance of the laramide blacktail snowcrest uplift east of the frontal thrust belt is asymmetric its southeast steeper limb is exposed along the snowcrest range this limb extends southwestward in the complexly deformed snowcrest structural terrane northwest dipping thrusts on this limb involve basement rocks and probably merge with depth into a major sub snowcrest range thrust this major thrust borders and is chiefly responsible for the blacktail snowcrest uplift and adjacent ruby synclinorium to the southeast uniform conodont cai values of 1 from both the southeast and northwest flanks of the blacktail snowcrest uplift indicate that no thick cover of upper cretaceous or younger rocks extended over the flanks of the uplift during mississippian through permian time the area of later laram de uplift underwent more rapid subsidence than the area of the laramide ruby syncline and the centennial basin to the southeast the inferred sub snowcrest range thrust fault apparently represents a reactivated zone of basement weakness the intersection of thrust belt and foreland trends similar to the uinta uplift area to the south probably formed a number of structural traps for hydrocarbons which have not yet been tested potential petroleum source beds and reservoir rocks are both present in southwest montana however remnants of tertiary lava flows through much of the area tertiary to recent basin and range faulting and supermaturity with respect to oil of permian and older rocks in the western centennial uplift area are additional factors which must be considered in any estimate of hydrocarbon potential of the cordilleran overthrust belt and adjacent foreland in extreme southwestern montana

glacial isostatic adjustment and the free air gravity anomaly as a constraint on deep mantle viscosity summary a gravitationally self consistent theory for relative sea level variations forced by pleistocene deglaciation events is employed to explore the extent to which rsl and free air gravity observations together constrain the viscosity of the mantle beneath the seismic discontinuity at 670 km depth a trade off is revealed between errors in the assumed deglaciation history and errors in the inferred value of the viscosity of the lower mantle taking full account of such uncertainty plausible values of the viscosity beneath the transition region are bounded above by 1023 poise cgs units the preferred value is at least a factor of 2 lower than this and is strongly constrained by the observed free air gravity anomaly over hudson bay the calculations described in detail here show for the first time that the relatively large gravity anomalies observed over sites of wurm wisconsin deglaciation do not require any pronounced increase of mantle viscosity with depth in order to explain them

extra basinal fluid infiltration mass transfer and volume strain during folding insights from the idaho montana thrust belt finite strain and geochemical variations along strain gradients were used to study cleavage development in carbonates in the lost river range idaho deformation accommodating layer parallel shear was partitioned into thin deforma tion zones during folding of willow creek anticline cleavage intensity is strong to very strong in deformation zones and weak in surrounding rocks strain magnitudes range from e s0 32 1 15 0 93 0 73 x y z principal axes of strain outside to e s0 64 1 29 0 80 0 52 inside deformation zones we found a positive linear correlation between strain cleavage development and negative dilation volume loss at a cubic centimeter scale ranges from 12 percent to 49 percent cleavage selvages are depleted in ca and 18 o and enriched in other elements relative to microlithons and less deformed protolith carbonates mass balance considerations indicate that cleavage was formed by incongruent pressure solution leading to a passive concentration of less soluble components during ca loss and metasomatic additions of si al and k to produce authigenic clay minerals in selvages data for the willow creek locality and elsewhere in the lost river range davidson and others 1998 pioneer mountains and the tendoy range bebout and others 2001 show that across the sevier orogen fluid infiltration was heterogeneous at centimeter kilometer scales and resulted from positive feedback between deforma tion and far traveled surficial fluids metasomatic strain softening enhanced deforma tion zone development which generated increased permeability as the thrust belt evolved from a porosity based closed system to a discontinuity based open system increased fluid infiltration and isotopic exchange was associated with volume loss increasingly prolate strains and crystallization of clays to produce the cleavage selvages mass transfer was accommodated by diffusion early and advection later in the deformation history mesoscopic structures deformation zones faults veins focused fluid flow and were kinematically related to larger scale structures faults fault related folds the inferred addition of surficial fluids to depths of 7 kilometers in the thrust belt implies a fluid regime involving significant topographically driven recharge deformed whole rocks and microsamples are lower in 18 o than unde formed samples which have o and c isotope compositions similar to those of marine carbonates veins are even lower in 18 ov smow with minimum values of 5 permil reflecting penetration of the crust by ocean derived precipitation with 18 o near to somewhat lower than 0 permil range of 7 5 to 2 5 calculated for h2 oi n equilibrium with these veins the inferred penetration into the thrust belt of nearshore meteoric waters is consistent with proximity to the reconstructed western interior seaway later fluid infiltration locally lowered the 18 o of carbonates even further based on the o isotope compositions of veins related to younger compres sional deformation and to the onset of crustal scale extension in the eocene this progression toward lowered 18 o of the surficial waters is compatible with the retreat of the seaway during emergence of the thrust wedge and paleogene extension uplift and subaerial volcanism

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

spatial variability of snowmelt timing from amsr e and ssm i passive microwave sensors pelly river yukon territory canada spring snow melt run off in high latitude and snow dominated drainage basins is generally the most significant annual hydrological event melt timing duration and flow magnitude are highly variable and influence regional climate geomorphology and hydrology arctic and sub arctic regions have sparse long term ground observations and these snow dominated hydrologic regimes are sensitive to the rapidly warming climate trends that characterize much of the northern latitudes passive microwave brightness temperatures are sensitive to changes in the liquid water content of the snow pack and make it possible to detect incipient melt diurnal melt refreeze cycles and the approximate end of snow cover on the ground over large regions special sensor microwave imager ssm i and advanced microwave scanning radiometer for eos amsr e passive microwave brightness temperatures tb and diurnal amplitude variations dav are used to investigate the spatial variability of snowmelt onset timing in two stages dav onset and melt onset and duration for a complex sub arctic landscape during 2005 the satellites are sensitive to small percentages of liquid water and therefore represent incipient melt a condition somewhat earlier than a traditional definition of a melting snowpack incipient melt dates and duration are compared to topography land cover and hydrology to investigate the strength and significance of melt timing in heterogeneous landscapes in the pelly river a major tributary to the yukon river microwave derived melt onset in this region in 2005 occurred from late february to late april upland areas melt 1 2 weeks later than lowland areas and have shorter transition periods melt timing and duration appear to be influenced by pixel elevation aspect and uniformity as well as other factors such as weather and snow mass distribution the end of the transition season is uniform across sensors and across the basin in spite of a wide variety of pixel characteristics copyright 2007 john wiley sons ltd

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

siberia snow depth climatology derived from ssm i data using a combined dynamic and static algorithm abstract one of the major challenges in determining snow depth sd from passive microwave measurements is to take into account the spatiotemporal variations of the snow grain size static algorithms based on a constant snow grain size cannot provide accurate estimates of snow pack thickness particularly over large regions where the snow pack is subjected to big spatial temperature variations a recent dynamic algorithm that accounts for the dependence of the microwave scattering on the snow grain size has been developed to estimate snow depth from the special sensor microwave imager ssm i over the northern great plains ngp in the us in this paper we develop a combined dynamic and static algorithm to estimate snow depth from 13 years of ssm i observations over central siberia this region is characterised by extremely cold surface air temperatures and by the presence of permafrost that significantly affects the ground temperature the dynamic algorithm is implemented to take into account these effects and it yields accurate snow depths early in the winter when thin snowpacks combine with cold air temperatures to generate rapid crystal growth however it is not applicable later in the winter when the grain size growth slows combining the dynamic algorithm to a static algorithm with a temporally constant but spatially varying coefficient we obtain reasonable snow depth estimates throughout the entire snow season validation is carried out by comparing the satellite snow depth monthly averages to monthly climatological data we show that the location of the snow depth maxima and minima is improved when applying the combined algorithm since its dynamic portion explicitly incorporate the thermal gradient through the snowpack the results obtained are presented and evaluated for five different vegetation zones of central siberia comparison with in situ measurements is also shown and discussed

a 10 000 yr b p extensive ice shelf over viscount melville sound arctic canada abstract late wisconsinan age glacial landforms and deposits indicate that an ice shelf of at least 60 000 km 2 flowed northwestward into viscount melville sound probably from the m clintock dome of the laurentide ice sheet the ice shelf overlapped coastal areas and laid winter harbour till up to 125 m above present sea level on the southern coast of melville island to 135 m on byam martin island to possibly 90 m on the northeast tip of banks island and to 150 m on the north coast of victoria island the contemporary sea level was 50 to 100 m higher than present it now rises eastward a maximum age of 10 340 150 yr b p for the till and thus the ice shelf advance is provided by shells in marine sediments which underlie it whereas a minimum age of 9880 150 yr b p is provided by overlying shells that postdate the ice advance the major advance of shelf ice into viscount melville sound may be the result of the rapid disintegration of the m clintock dome while the climate ameliorated in the western arctic

pleistocene deglaciation and the global gravity field the present day global geoid and free air gravity anomaly signals induced by pleistocene deglaciation have been computed along with their secular variations a revised green function has been derived for the free air gravity anomaly and we find that an earth model with a lower mantle viscosity moderately larger than the upper mantle value satisfies observations of the anomaly over both hudson s bay and fennoscandia using this preferred earth model the predicted global geoid anomaly map is characterized by peak negative values of 36 7 9 4 and 21 9 m over hudson s bay northern europe and antarctica respectively and by a smooth small amplitude 2 5 m upwarping over the major ocean basins although the field has an order of magnitude less power than the observed there is a significant spatial correlation between the two inferences of mantle viscosity based upon comparisons between the observed geoid and the computed deglaciation induced anomaly are hampered by the large contribution from the convective circulation in the earth s mantle we have subtracted a predicted convection signal based on seismic tomography from the observed field however the residual geoid thus obtained is still too inaccurate to allow a useful comparison in contrast a filtered version of the observed geoid over canada which retains harmonic coefficients in the degree range 10 22 provides a relatively uncontaminated by convection datum that is indeed satisfied by the preferred earth model secular variations in the earth s gravitational field are naturally dominated by the signal from pleistocene deglaciation in this respect we compute zonal harmonics in the expansion of the present day rate of change of the geopotential and in particular we predict amplitudes comparable to that for the previously analysed j2 for j4 j5 j7 and j9 all of which reflect in large part the response due to the melting of the massive laurentide ice sheet this analysis suggests that measurement of these higher order secular variations of the zonal harmonics based upon analysis of long time series of lageos ranging data could provide very useful additional constraints on the radial variation of mantle viscosity these constraints along with all others described in this paper are shown to be relatively insensitive to assumptions concerning the deflection during the glacial isostatic adjustment process of the 400 and 670 km density discontinuities within the mantle

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

conodont geothermometry and tectonic overburden in the northernmost east greenland caledonides kronprins christian land lies at the northernmost limit of the east greenland caledonides and may be divided into four main tracts foreland parautochthon thin skinned thrust sheets containing neoproterozoic sediments and thick skinned thrust sheets of crystalline basement the eastern part of the foreland and the parautochthon are composed of ordovician silurian shelf carbonates overlain by llandovery lower wenlock turbidites deposited at the southern margin of the franklinian basin deformation of the parautochthon occurred beneath a major detachment the vandredalen thrust with neoproterozoic sediments of the rivieradal group lying in the hanging wall the rivieradal group was deposited in an e facing half graben and was displaced westwards across its rift shoulders during caledonian thrusting extensive sampling for conodonts has been carried out within the lower palaeozoic rocks of the foreland and parautochthon in order to increase the precision of structural interpretations and to provide data on maximum burial temperature and in turn the thickness of overburden in contrast to earlier studies conodont colour alteration indices cai show a gradual and continuous increase from cai 3 in the eastern part of the foreland to cai 5 in the easternmost parts of the parautochthon the isopleths are not disrupted or truncated by thrusting as previously suspected indicating that the heating is not attributable to pre thrusting stratigraphic overburden furthermore considerations of the regional geology indicate that there was no significant accumulation of sedimentary overburden in post caledonian time the predominant component is thus considered to be loading by thrust sheets modelling of the overburden thickness suggests that prior to erosion it increased from 3 9 km cai 3 in the easternmost foreland to a maximum of 12 5 km beneath the vandredalen thrust sheet in the easternmost part of the area providing constraints for restoring cross sections across the orogen

late cretaceous and tertiary history and the dynamic crushing of cobbles black butte area southwestern montana black butte is an early miocene basaltic volcanic neck that forms a prominent landmark as the highest peak of the gravelly range southwestern montana the intrusion cuts mid cenozoic and older sedimentary rocks near the eastern margin of the overthrust belt after erosional removal of the late cretaceous frontier formation quartzite rich detritus from ultimate sources probably far to the west was deposited in the area and now forms a diamicton that rests on striated bedrock this unit previously interpreted as a till and as a mudflow deposit probably represents upper cretaceous or lower tertiary syntectonic alluvial fan sediments these were deposited after the gravelly arch had begun to rise and were deformed during overthrusting from the west or possibly during mass movement as the basal part of a landslide scattered cobbles of hard quartzite in the diamicton are crushed if this crushing occurred within aggregates of coarse clasts that were momentarity in point contact with one another it does notrequire either overthrusting or mass movement of extremely thick depositional overburden but if a major thrust sheet did move over the diamicton the leading edge of the overthrust belt must extend considerably further east of where it is currently recognized in this area volcanic and volcaniclastic rocks were deposited in the area throughout much or all of oligocene time these include tuffaceous mudstone as much as 265 m thick that contains vertebrate fossils of chadronian through whitneyan age the kar age of biotite in an airfall tuff within this section at nearby lion mountain is 31 4 ma and the kar age of an alkaline basaltic flow at the top of the lion mountain section is 30 8 ma these tuffaceous rocks and basalt on lion mountain correlate with volcaniclastics in wyoming and as far east as nebraska and the dakotas eruptions at black butte dated previously at 22 9 ma begun with phreatomagmatic explosions that deposited tuff across an irregular topographic surface cut in the section of tuffaceous mudstone into which the black butte plug was emplaced the alkali basalt magma differentiated to yield the relatively rare rock typetephritic phonolite during fractional crystallization and segregation in situ of potassic late liquids lava flows from black butte and the nearby lion mountain volcanic center may have covered much of this part of the gravelly range but have been mostly removed owing to erodability of the thick blanket of mudstone on which they rested removal of mudstone that contained the black butte intrusion involved massive slumping mass movement of the diamicton beneath the mudstone is occurring today as an earthflow down the west dipping structural and topographic slope of the range

isostatic adjustments in a full glacial sea during the last glaciation an ice free corridor existed between the northeast ellesmere island and northwest greenland ice sheets this corridor constituted a peripheral depression in which the marine limit marks the uppermost extent of a full glacial sea the full glacial sea is characterized by 1 14c dates on in situ marine shells that predate initial emergence unloading followed by 2 synchronous emergence from the marine limit throughout the peripheral depression relative sea level curves from the full glacial sea confirm previous morphostratigraphic and glacioisostatic evidence for limited ice extent during the last glaciation these curves also document the history of glacial unloading and the form of the relative sea level curve that one would theoretically expect in the peripheral depression the form of the curves presented here is unlike any other published emergence curves from arctic canada or from fennoscandia the relative sea level curves for northeast ellesmere island show three segme

evidence from fram strait 78 n for early deglaciation recent syntheses of the history of the last northern hemisphere glaciation and deglaciation illustrate that understanding of the mechanisms and timing of deglaciation before approximately 12 000 years bp1 5 is limited after 12 000 yr bp however there is sufficient evidence from radiocarbon dated moraines raised beaches varved lake sediments and pollen records to provide a reasonable temporal and geographic picture of the decay of the ice sheets here we report on the first oxygen isotope record from the norwegian greenland sea that is radiocarbon dated directly by accelerator mass spectrometry a significant light oxygen isotope event is recorded at approximately 15 000 years bp which suggests that the marine based barents shelf ice sheet disintegrated rapidly at this time recent studies6 7 have estimated that the decay of this ice sheet could have contributed as much as 15 metres to eustatic sea level rise the decay of the barents shelf ice sheet is the earliest major deglacial event yet dated and may have triggered subsequent deglacial events through eustatic sea level effects