quantitative remote sensing study indicates doubling of coastal erosion rate in past 50 yr along a segment of the arctic coast of alaska a new quantitative coastal land gained and lost method uses image analysis of topographic maps and landsat thematic mapper short wave infrared data to document accelerated coastal land loss and thermokarst lake expansion and drainage the data span 1955 2005 along the beaufort sea coast north of teshekpuk lake in the national petroleum reserve in alaska some areas have undergone as much as 0 9 km of coastal erosion in the past 50 yr land loss attributed to coastal erosion more than doubled from 0 48 km2 yr 1 during 1955 1985 to 1 08 km2 yr 1 during 1985 2005 coastal erosion has breached thermokarst lakes causing initial draining of the lakes followed by marine flooding although inland thermokarst lakes show some uniform expansion lakes breached by coastal erosion display lake expansion several orders of magnitude greater than inland lakes

late holocene diatom biostratigraphy and sea level changes in the southeastern beaufort sea late holocene sediments from the atkinson point area were analysed to provide quantitative reconstructions of recent sea level changes in the southeastern beaufort sea the succession of diatom assemblages in five cores revealed paleoenvironmental changes induced by the transgression of the beaufort sea during successive periods of lacustrine conditions breaching and flooding of thermokarst lakes by the sea and the landward migration of sandy spits based on radiocarbon dates and quantitative paleodepth determinations a relative sea level curve for the late holocene has been developed despite a loss of temporal precision due to old carbon contamination an envelope of sea level change has been defined for the last 2 ka bp suggesting a sea level rise in the order of 1 1 mm a 1 for the last millennium this paper presents the first sea level reconstruction inferred from a diatom based transfer function it represents an improvement over traditional methods which were limited to qualitative estimates of

a model of coastal evolution in a transgressed thermokarst topography canadian beaufort sea abstract the coast of the southern canadian beaufort sea consists of bluffs of ice bearing quaternary sediments and of spits and barrier islands enclosing more or less completely lagoons and complex embayments formed by the breaching of thaw lakes the study of the evolution of this coast developed in a thermokarst topography and of the shallow stratigraphy of the inner continental shelf has resulted in the development of a conceptual model of coastal evolution five stages have been defined in this model which form an idealized continuum of coastal evolution according to the model the formation of embayments spits and barrier islands is primarily controlled by the pre existing topography relative sealevel rise and local sediment supply sealevel rise over a topography of thermokarst basins formed in ice bearing sediments leads to the formation of embayments and rapidly eroding headlands from which spits develop geomorphic evidence suggests that barrier islands mainly form by spit breaching or by erosion of tundra islands breached lake basins act as sediment sinks and may restrict the development of coastal accumulation features spits and barrier islands are rapidly retreating landward the mean retreat rates being 2 2 m a 1 and 3 9 m a 1 respectively on an annual time scale spits and barrier islands retreat in response to episodic storm generated overwash events but on a geologic time scale relative sealevel rise in the major forcing mechanism of landward migration while retreating landward these coastal accumulation features may be drowned and possibly partially preserved in breached lake basins during the holocene transgression the shoreface has undergone erosional retreat partly eroding the pre existing topography but preserving the bottom of some breached thaw lakes and lagoons which are now overlain by a transgressive sand sheet on the inner shelf our observations provide the basis of a semi quantitative model of shoreline changes for the barrier coast of the canadian beaufort sea which relates coastal stability to bluff erosion ground ice content sediment texture offshore sediment supply wave energy volume of breached lake basins relative sealevel rise and regional slope

coastal retreat and shoreface profile variations in the canadian beaufort sea the coastline of the southern canadian beaufort sea consists primarily of unconsolidated bluffs although the sea is ice free for 3 months of the year and wave energy is restricted by pack ice the coast is undergoing regional retreat with erosion rates as high as 10 m a 1 in some locations simple and multiple regression analyses were carried out to determine the degree of correlation between the mean retreat rate measured at various locations and the different parameters that may control shoreline recession sediment texture ground ice content cliff height wave energy and shoreface gradient revealed medium to poor correlation with erosion rates showing that the recessive evolution of the coastline can not be explained solely by wave induced and subaerial processes the comparison of nearshore echo sounding records from 1987 with bathymetry from 1971 showed substantial erosion up to 1 m of the submarine profile between 12 and 15 m of water there is strong evidence that this erosion has been caused by sea ice gouging on the seafloor from depths of 5 to 9 m accretion has taken place possibly induced by ice push processes and inshore of the 5 m isobath wave and current erosion of the shoreface has occurred these results suggest that the erosion of the inner shelf by ice gouging drives the erosion observed inshore on the coastal bluffs and nearshore zone as the shoreface profile strives for a state of dynamic equilibrium

influence of the changing lunar orbit on the astronomical frequencies of pre quaternary insolation patterns the sensitivity of the frequencies of the earth s orbital elements involved in the astronomical theory of paleoclimates obliquity and climatic precession to the earth moon distance and consequently to the length of the day and to the dynamical ellipticity of the earth is investigated for the last billions of years but the new frequencies have been computed for the last 440 million years only a time interval over which data and a model of the earth were available moreover we consider only the impact of the changing precessional parameter assuming that the fundamental frequencies of the planetary motion are steady at the geological time scale under such hypotheses the shortening of the earth moon distance and of the length of the day back in time induces a shortening of the fundamental astronomical periods for obliquity and precession a shortening that is larger for longer periods

petrology of ultrahigh pressure eclogites from the zk703 drillhole in the donghai eastern china abstract the 558 m deep zk703 drillhole located near donghai in the southern part of the sulu ultrahigh pressure metamorphic belt eastern china penetrates alternating layers of eclogites gneisses jadeite quartzites garnet peridotites phengite quartz schists and kyanite quartzites the preservation of ultrahigh pressure metamorphic minerals and their relics together with the contact relationship and protolith types of the various rocks indicates that these are metamorphic supracrustal rocks and mafic ultramafic rock assemblages that have experienced in situ ultrahigh pressure metamorphism the eclogites can be divided into five types based on accessory minerals rutile eclogite phengite eclogite kyanite phengite eclogite quartz eclogite and common eclogite with rare minor minerals rutile eclogite forms a thick layer in the drillhole that contains sufficient rutile for potential mining two retrograde assemblages are observed in the eclogites the first stage is characterized by the formation of sodic plagioclase amphibole symplectite or symplectitic coronas after omphacite and garnet plagioclase biotite after garnet or phengite and plagioclase coronas after kyanite the second stage involved total replacement of omphacite and garnet by amphibole albite epidote quartz peak metamorphic p t conditions of the eclogites were around 32 to 40 kbar and 720 c to 880 c the retrograde p t path of the eclogites is characterized by rapidly decreasing pressure with slightly decreasing temperature micro textures and compositional variations in symplectitic minerals suggest that the decompression breakdown of ultrahigh pressure minerals is a domainal equilibrium reaction or disequilibrium reaction the composition of the original minerals and the diffusion rate of elements involved in these reactions controlled the symplectitic mineral compositions

a sea level curve for the canadian beaufort shelf radiocarbon dated peat and peaty clay samples from geotechnical boreholes in the canadian beaufort continental shelf have been used to reconstruct a late quaternary relative sea level rsl curve the samples were carefully selected and evaluated using palynological techniques to ensure that reasonable age error limits could be given to each sample the dated samples were then related to the local geological setting using seismic profiles to determine the environment of deposition the resulting data show a rise of 140 m in rsl since 27 000 years bp a minor lowering of rsl at some time between 20 000 and 10 000 years bp is inferred from acoustic data contributions from basin subsidence sediment loading and consolidation account for 35 m of the total rsl rise the rsl curve is interpreted in the light of recent models of the isostatic and eustatic responses of the earth s crust at the laurentide ice sheet margin ice may have been more extensive during the middle wisconsinan than previously thought a

diatoms as quantitative paleodepth indicators in coastal areas of the southeastern beaufort sea arctic ocean abstract surface sediment diatom assemblages in depth profiles along the southeastern beaufort sea coasts canada were analysed to describe the relationship between species distribution and water depth of deposition the 74 coastal stations sampled were distributed in several sedimentary environments from salt marshes to the inner shelf the relationship between diatom species distribution and water depth was examined using canonical correspondence analysis cca and partial cca the water depth accounted for 9 7 of the variance in the data set the diatom water depth relationship is believed to be controlled by the shoreface circulation which results in a shift in the relative abundance of the epipsammon epipelon and plankton along the water depth gradient upper shoreface assemblages are dominated mainly by epipelic species and a few number of epipsammic taxa whereas deeper environments are dominated by planktonic species a transfer function was derived using weighted averaging regression and calibration to reconstruct the water depth of deposition over the coastal interval from mean sea level to a maximum of 14 m depth on the coastal shelf of the southeastern beaufort sea the transfer function allows relative sea level to be predicted from fossil diatom assemblages with a root mean square error of 1 43 m this model is likely to produce reliable water depth inferences along the southeastern beaufort sea coasts and in other shallow sandy microtidal environments dominated by low energy waves and influenced by freshwater discharge the transfer function was used to provide quantitative paleodepth inferences for late holocene sediments from the atkinson point area based on fossil diatom assemblages

a sediment and organic carbon budget for the canadian beaufort shelf abstract the arctic ocean accounts for 20 of the world s continental shelves because the arctic is sensitive to global change budgets of organic carbon for its shelves are of immediate interest the mackenzie shelf of the canadian beaufort sea is the best north american proxy for the enormous eurasian shelves large area large river input and the only site for which a complete organic carbon budget can be attempted due to an extensive data base a mass balance for the mackenzie shelf has been constructed for sediments terrestrial organic carbon and primary produced carbon we have considered allochthonous inputs from the mackenzie river from coastal erosion from smaller rivers from groundwater from the atmosphere and import by ice the mackenzie river dominates the supply to the beaufort shelf of inorganic sediment 127 mt a 1 and paniculate and dissolved terrestrial carbon 2 1 mt a 1 poc 1 3 mt a 1 doc the combined input from all other sources contributes only about 5 of the mackenzie load using sediment accumulation data we estimate that about half of the sediment supply is trapped in the delta about 40 on the shelf and the remainder escapes the shelf edge by various processes autochthonous primary production in the delta and on the shelf adds a further 3 3 mt a 1 of particulate organic carbon a box model has been constructed to account for sediment terrestrial organic carbon and primary produced carbon whereas about 60 of the terrestrial poc is preserved in delta and shelf sediments it appears that most 97 of the primary produced carbon is recycled and not preserved in sediments confidence in the budget should be improved by focusing future research on the determination of modern sedimentation rates on the delta and shelf measurement of organic carbon content of deltaic sediments determination of primary production on the shelf and determination of the relative proportions of terrestrial and marine organic carbon preserved in sediments

the mackenzie delta sedimentary processes and facies of a high latitude fine grained delta the mackenzie delta is a large fine grained delta deposited in a cold arctic setting the delta has been constructed upon a flooding surface developed on a previous shelf phase delta there are three principal depositional zones the subaerial delta plain the distributary channel mouth region and the subaqeous delta the subaerial delta plain is characterized by an anastomosing system of high sinuosity channels and extensive thermokarst lake development this region is greatly influenced by the annual cycle of seasonal processes including winter freezing of sediments and channels ice jamming and flooding in the early spring and declining river stage during the summer and autumn deposition occurs on channel levees and in thermokarst lakes during flood events and is commonly rhythmic in nature with discrete annual beds being distinguishable in the channel mouth environment deposition is dominated by landward accretion and aggradation of mouth bars during river and storm surge induced flood events the subaqeous delta is characterized by a shallow water platform and a gentle offshore slope sediment bypassing of the shallow water platform is efficient as a result of the presence of incised submarine channels and the predominance of suspension transport of fine grained sediments facies of the shallow platform include silty sand with climbing ripple lamination offshore facies are dominated by seaward fining fine sand to silt tempestites sea ice scouring and sediment deformation are common beyond 10 m water depth where bioturbated muds are the predominant facies the low angle profile of the shallow water platform is interpreted to be the combined response of a fine grained delta to 1 storm sediment dispersal 2 autoretreat as a result of the increasing subaerial and subaqeous area of deposition as the delta progrades out of its glacial valley 3 limited water depth above the underlying flooding surface and 4 efficient nearshore bypassing of sediment through subice channels at the peak of spring discharge several indicators of the cold climate can be used as criteria for the interpretation of ancient successions including thermokarst lake development submarine channel scours freeze thaw deformation and ice scour deformation structures permafrost inhibits compaction subsidence and together with the shallow water setting also limits autocyclic lobe switching the cold climate can thus influence stratal architecture by favouring the development of regional scale clinoform sets rather than multiple smaller scale lobes separated by autocyclic flooding surfaces

modeling 100 000 year climate fluctuations in pre pleistocene time series a number of pre pleistocene climate records exhibit significant fluctuations at the 100 000 year 100 ky eccentricity period before the time of such fluctuations in global ice volume the origin of these fluctuations has been obscure results reported here from a modeling study suggest that such a response can occur over low latitude land areas involved in monsoon fluctuations the twice yearly passage of the sun across the equator and the seasonal timing of perihelion interact to increase both 100 ky and 400 ky power in the modeled temperature field the magnitude of the temperature response is sufficiently large to leave an imprint on the geologic record and simulated fluctuations resemble those found in records of triassic lake levels

toward reconciliation of late ordovician 440 ma glaciation with very high co2 levels although phanerozoic glaciations usually coincided with times of estimated low atmospheric co2 the late ordovician 440 ma glaciation is a significant exception co2 levels during that time may have been as much as 10 times greater than present in an earlier paper we suggested that the unique geographic configuration of gondwanaland may explain such a response as the edge of the supercontinent was essentially tangent to the south pole and the moderating effect of the nearby ocean may have suppressed the magnitude of summer warming on the landmass thereby allowing glacial inception one limitation to the earlier study was that it used a linear energy balance model ebm in this paper we further test the above hypothesis in a suite of experiments with a nonlinear ebm that allows for snow albedo feedback we also utilize updated estimates for co2 levels decreases in solar luminosity and variations in orbital forcing baseline experiments with no changes in luminosity or co2 resulted in an ice covered area of 6 3 106 km2 53 of the estimated area covered by the ordovician ice sheet additional experiments for different combinations of orbital forcing 7x 13x co2 and 3 5 5 0 luminosity yielded 0 35 of the estimated ice area in the late ordovician a crude estimate of possible topographic influences increased these numbers to7 47 of total estimated ice area additional factors related to ice sheet growth should increase these values somewhat these results provide additional support for the high co2 glaciation explanation with the caveat that even the partial success occurs only when parameters are at the extreme end of their permissible range the estimated duration of ordovician glaciation is also consistent with the migration of gondwanaland across the south pole with a centrally located pole yielding ice free conditions in the summer thus identical levels of external forcing yield either glaciated or ice free conditions with the solution dependent on location of the landmass although more work is required on this topic our experiments suggest that there may be a relatively parsimonious explanation for this perplexing paleoclimate paradox the results lend further support to the proposition that paleogeography significantly modifies the role of co2 in the long term evolution of climate

geochemistry and fluxes of hydrocarbons to the beaufort sea shelf a multivariate comparison of fluvial inputs and coastal erosion of peat using principal components analysis abstract the allochthonous inputs of hydrocarbon to the canadian beaufort shelf were studied by applying principal components analysis pca to well validated and rigorously blank corrected samples incorporation of a wide range of perdeuterated n alkanes and pah into the analysis scheme ensured that only reliably quantified variables were used to interpret the hydrocarbon geochemistry application of pca to mackenzie river samples demonstrated a homogeneous system from which we infer coupling or equilibrium between the river particulate hydrocarbons and the dissolved fraction particulate particle size 0 7 m hydrocarbon flux from the mackenzie river is by far the most important terrestrially derived source of hydrocarbons to the beaufort sea the mackenzie river particulates have a distinct n alkane signature which can be used to identify the riverine influence on the hydrocarbon geochemistry of the beaufort sea shelf based on one year s data the flux of total alkanes is 440 94 tonne a and pah is 49 8 tonne a uncertainties are one standard deviation of the sampling and analytical variation the particulate flux exceeds the accompanying dissolved hydrocarbon flux by two orders of magnitude and has a strong seasonal cycle winter contributes less than an estimated 0 6 of total annual flux deltaic silt from the western mackenzie delta and the smaller amounts of detritus from coastal erosion of peat are minor hydrocarbon sources and contribute in total less than 10 to the budget for most alkanes an important exception with regard to shelf geochemistry is the significant quantity of peat derived higher plant n alkanes

sediment budget calculation to estimate holocene coastal changes on the southwest baltic sea germany abstract the tide less sw baltic sea has a paraglacial coast alternating pleistocene cliff sections and holocene barrier systems separate shallow lagoons from the open sea more than 300 cores penetrating the holocene coastal sequence allowed for detailed reconstruction of the palaeogeographic evolution the sequence formed in response to transgression in the early holocene 8000 year bp the barrier cliff system evolution is described as four stages over these stages dependencies of sedimentation processes to the rate of sea level rise are obvious to reconstruct palaeo coast configurations mass balance calculations were applied retreating cliff sections are seen as the main source for coastal sediment starting from mapped volumes of sand incorporated in barriers cliff retreat in the last 8000 years is calculated to total 2400 m at maximum sediment supply to the coastal zone averaged over the larger part of the holocene is approximately three times smaller than for the last hundreds years this signals accelerated rise of sea level since c 1000 years and hints on what to expect when sea level rises faster in the future such will cause intensified coastal erosion and eventually the formation of new inlets a general drowning of the coastal landscape as observed in the early holocene is unlikely

milankovitch fluctuations on supercontinents observational and modeling studies support the concept of significant milankovitch fluctuations in the pre pleistocene many of these studies have focused on the mid cretaceous a time of high sea level and moderately dispersed land sea distribution in this paper we utilize a two dimensional energy balance climate model to examine the potential effects of milankovitch fluctuations for a supercontinent configuration early jurassic 195 ma we calculate that milankovitch variations can modulate the magnitude of summer warming by as much as 14 16 c on pangaea with large changes occurring in both the northern and southern hemispheres these values are comparable to or slightly larger than the calculated range for the present eurasian landmass for the pleistocene in addition mean monthly summer temperatures of 25 c reach 65 paleolatitude for hot orbit configurations this latter result suggests that some organisms may have been able to migrate into higher latitudes during precession half cycles of 10 000 years duration and a potential bias should be considered when evaluating evidence for past high latitude warmth our results indicate that general circulation model gcm runs for past time periods which use only one orbital configuration may be missing a substantial amount of the potential variance on large land masses

milankovitch climatic origin of mid cretaceous black shale rhythms in central italy the earth s orbital variations reflected in pleistocene ice volume were also recorded in non glacial times carbonate production in pelagic mid cretaceous sediments quantified by calcium carbonate and optical densitometry time series reflects the orbital eccentricity and precessional cycles minimal eccentricity brought deep sea anoxia most of the sedimentary variability of this 100 myr old sequence lies within the milankovitch orbital frequency band

application of portable free fall penetrometer for geotechnical investigation of arctic nearshore zone the arctic is currently undergoing rapid changes with regard to sea ice extent permafrost thaw and coastal erosion in addition to hydrodynamic processes the sediments in the arctic nearshore zon

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

collapse of a hercynian tibetan plateau into a late palaeozoic european basin and range province the large width the importance of crustal shortening and the likelihood of thick crust in the late palaeozoic hercynian or variscan belt of southern europe suggest a tectonic evolution analogous to the evolution of the tibetan plateau and its neighbouring himalaya1 and of the altiplano and other high plateaux of the andes here we extend dewey and burke s analogy1 of the hercynian chain with tibet to include the subsequent stage of pervasive normal faulting and crustal extension and thinning which characterize the active tectonics of tibet parts of the high andes and the basin and range province of western north america it appears that normal faulting and rifting also characterize the late palaeozoic tectonic activity of the hercynian chain

terrain controls on the occurrence of coastal retrogressive thaw slumps along the yukon coast canada retrogressive thaw slumps rtss are among the most active landforms in the arctic their number has increased significantly over the past decades while processes initiating discrete rtss are well identified the major terrain controls on the development of coastal rtss at a regional scale are not yet defined our research reveals the main geomorphic factors that determine the development of rtss along a 238 km segment of the yukon coast canada we 1 show the current extent of rtss 2 ascertain the factors controlling their activity and initiation and 3 explain the spatial differences in the density and areal coverage of rtss we mapped and classified 287 rtss using high resolution satellite images acquired in 2011 we highlighted the main terrain controls over their development using univariate regression trees model coastal geomorphology influenced both the activity and initiation of rtss active rtss and rtss initiated after 1972 occurred primarily on terrains with slope angles greater than 3 9 and 5 9 respectively the density and areal coverage of rtss were constrained by the volume and thickness of massive ice bodies differences in rates of coastal change along the coast did not affect the model we infer that rates of coastal change averaged over a 39 year period are unable to reflect the complex relationship between rtss and coastline dynamics we emphasize the need for large scale studies of rtss to evaluate their impact on the ecosystem and to measure their contribution to the global carbon budget

late quaternary sequence stratigraphy of the mackenzie delta the late wisconsinan and holocene sequence stratigraphy of the mackenzie delta provides insights into the glacial history of the region the base of the described succession is a hummocky regional reflector interpreted to be a flooding surface formed immediately after retreat of glacial ice from the mackenzie trough above this flooding surface two progradational parasequences are present the first assigned to the transgressive systems tract is correlated with the tutsieta lake readvance of the ice sheet at approximately 13 000 bp a flooding surface forming the upper boundary of this parasequence extends inland to at least inuvik developing as a response to glacial retreat and early holocene relative sea level rise the second parasequence of holocene deltaic deposits is assigned to the highstand systems tract and is characterized by progressive progradation of the delta into the mackenzie trough to a position seaward of the present delta coastline a distinct reduction in gradient of the most recen

coastal changes in the arctic the arctic s climate system is changing air temperatures major river discharges and open water season length have increased and storm intensities and tracks are changing thirteen quantitative studies of the rates of coastline position change throughout the arctic show that recently observed changes have not increased coastal erosion rates which currently range between 0 and 2 m yr when averaged for the arctic shelf seas current data is probably insufficient both spatially and temporally however to capture change at decadal to sub decadal time scales in this context we describe the current understanding of arctic coastal geomorphodynamics with an emphasis on erosional regimes of coasts with ice rich sedimentary deposits in the laptev east siberian and beaufort seas where local coastal erosion can reach 30 m yr we also examine coasts with lithified rocky substrates where geomorphodynamics are intensified by rapid glacial retreat coastlines of svalbard greenland and the canadian archipelago are less frequently studied than ice rich continental coasts of north america and siberia and studies often focus on coastal sections composed of unlithified material as air temperature and sea ice duration and extent change longer thaw and wave seasons will intensify coastal dynamics in the arctic

the small ice cap instability in diffusive climate models abstract simple climate models employing diffusive heat transport and ice cap albedo feedback have equilibrium solutions with no stable ice cap smaller than a certain finite size for the usual parameters used in these models the minimum cap has a radius of about 20 degrees on a great circle although it is traditional to remove this peculiar feature by various ad hoc mechanisms it is of interest because of its relevance to ice age theories this paper explains why the phenomenon occurs in these models by solving them in a physically appealing way if an ice free solution has a thermal minimum and if the minimum temperature is just above the critical value for formation of ice then the artificial addition of a patch of ice leads to a widespread depression of the temperature below the critical freezing temperature therefore a second stable solution will exist whose spatial extent is determined by the range of the influence function of a point sink of heat due to the albedo shift in the patch the rang

a model for atmospheric co 2 over phanerozoic time a new model has been constructed for calculating the level of atmospheric co sub 2 over phanerozoic time which is much simpler mathematically than the blag model but more complex geologically and biologically results suggest that there has been a notable pattern of varying atmospheric co sub 2 level over the past 570 my with high levels during the mesozoic and early paleozoic and low levels during the permo carboniferous and late cenozoic sensitivity analysis shows that within reasonable limits of the principal governing parameters this qualitative trend of varying co sub 2 is relatively insensitive to the actual values chosen for these parameters causes of the co sub 2 variation are multiple and no single geological or biological process can be called upon to explain all co sub 2 variation for all time the calculated trend of co sub 2 over time agrees well with independent estimations of paleoclimates thus the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study

filtering of milankovitch cycles by earth s geography abstract earth s land sea distribution modifies the temperature response to orbitally induced perturbations of the seasonal insolation we examine this modification in the frequency domain by generating 800 000 yr time series of maximum summer temperature in selected regions with a linear two dimensional seasonal energy balance climate model previous studies have demonstrated that this model has a sensitivity comparable to general circulation models for the seasonal temperature response to orbital forcing on land although the observed response in the geologic record is sometimes significantly different than modeled here differences attributable to model limitations and feedbacks involving the ocean atmosphere cryosphere system there are several results of significance 1 in mid latitude land areas the orbital signal is translated linearly into a large 10 c seasonal temperature response 2 although the modeled seasonal response to orbital forcing on antarctica is 6 c the annual mean temperature effect

a guide to phanerozoic cold polar climates from high latitude ice rafting in the cretaceous the high latitude extent of warm climate indicators at certain times in earth history has been considered as evidence that the globe was ice free for long intervals despite theoretical considerations and results from numerical modelling experiments1 2 indicating that this was unlikely one of the warmest periods the cretaceous displays faunal and floral evidence for cool temperate to sub tropical conditions very near to the poles however our studies of lower cretaceous mudstones of central australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice rafting implying that high latitude ice was present at sea level strata of a similar origin of mid jurassic to mid cretaceous age occur on other continents that were positioned between 65 and 78 palaeolatitude indeed there is a record of high latitude ice rafting throughout the phanerozoic suggesting that ice was present on earth for much of its history and that ice free conditions could have been at most only episodic over the past 600 myr

wind forced seiche events on great slave lake hydrologic implications for the slave river delta nwt canada a limited amount of research has focused on northern lacustrine deltas and the impacts of basin processes prevalent at these deltas wind forced seiche events have received little focus in deltaic studies the slave river delta located on the south shore of great slave lake gsl nwt is an ideal environment to study the prevalence of wind forced seiche events and the impact of seiche events on the hydrodynamics of the delta this paper presents an historical analysis of seiche activity on gsl and the effect of seiches on water levels of the slave river delta the seasonality frequency and magnitude of seiche events on the lake are quantified a description of the wind characteristics that force these events is included the radial distributary pattern of the delta suggests that water level response to seiche events within the delta may be particularly complex hydrologic data from delta distributaries illustrate the temporal and spatial dynamics of seiche response during the open water season seiche response in the delta is affected by the seasonal hydrograph of the slave river and wind conditions spatially the slope of delta distributaries governs seiche response responses are most similar among zones in the delta rather than among different distributaries copyright 2006 john wiley sons ltd

influence of ground ice and permafrost on coastal evolution richards island beaufort sea coast n w t a long term sediment budget 1947 1985 for northern richards island shows that when ground ice and offshore erosion are accounted for there is a near balance between headland erosion and coastal deposition excess ice constitutes about 20 of the total volume of eroded material from the headlands with massive ground ice contributing nearly 9 and segregated ice lenses and ice wedges making up the remainder coastal response to major storms in 1987 and 1993 suggests that erosion is episodic with short periods of intense disruption followed by readjustment of cliff profiles processes characteristic of this environment include mechanical erosion of ice bonded sediments creating unstable erosional niches mechanical failure of niches along ice wedge planes and longer term thermal erosion of ice bonded sediments where ice contents are high localized thaw slumps initiated by coastal erosion may retreat at rates substantially higher than those observed at other sections of the coast cliff top retreat r

pangaean climates megamonsoons of the megacontinent the climate for a highly idealized geographic representation of the megacontinent of pangaea corresponding to the period 250 200 m y ago is explored using a low resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth with a provision for sea ice formation and decay soil moisture is included as a predicted variable on the continent because there are large uncertainties about key factors that might influence the pangaean climate sensitivity experiments are used to examine the climate for two different mean elevations 0 and 1000 m two different snowcover prescriptions and two different levels of implied greenhouse heating and solar luminosity modern co2 concentration and modern solar luminosity fivefold increase in modern co2 concentration and a 1 decrease in modern solar luminosity in all of the experiments the large bipolar land masses of laurasia and gondwanaland joined near the equator in the west and separated by the tethys sea in the east exhibit extreme continentality with hot summers cold winters and large scale summer and winter monsoon circulations year round or seasonal aridity is simulated for all but the eastern coastal regions the tropical western coast and the regions poleward of 40 latitude the simulated climate of the idealized pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late permian and triassic however the model results serve mainly to indicate the importance of various climate forming factors geography topography heating detailed comparisons will require new experiments with better models and more accurate geologic boundary conditions

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

temporal and spatial variability in coastline response to declining sea ice in northwest alaska abstract arctic sea ice is declining in extent leaving coastlines exposed to more storm wave events there is an urgent need to understand how these changes affect geomorphic processes along arctic coasts here we describe spatial and temporal patterns of shoreline changes along two geomorphologically distinct storm wave dominated reaches of the chukchi sea coastline over the last 64 years one study area encompasses the west to southwest facing coarse clastic shoreline and ice rich bluffs of cape krusenstern cakr the other covers the north facing sandy shorelines on barrier islands ice rich bluffs and the cape espenberg spit in the bering land bridge national park bela both study areas lie within the zone of continuous permafrost which exists both on and offshore and outcrops as ice rich bluffs along the bela coast we mapped changes in coastal geomorphology over three observation periods 1950 1980 1980 2003 and 2003 2014 using aerial and satellite imagery we then compared these geomorphic changes to changes in sea ice coverage which declined 10 days per decade between 1979 and 2016 in the southern chukchi sea changes in coastal geomorphology in both bela and cakr exhibited high spatial variability over the study period between 2003 and 2014 shorelines of barrier islands in bela exhibited the highest mean rates of change 1 5 m yr 1 while coarse clastic barrier beaches in cakr showed only minimal change overall shorelines in both bela and cakr became more dynamic increasing erosion or increasing accumulation after ca 2003 with spatial variability in shoreline changes roughly doubling between the first period of observation 1950 1980 and the last 2003 2014 this increase in coastal dynamism may signal a transitional period leading to new state of geomorphic equilibria along these ice affected coastlines

sensitivity of climate to late cenozoic uplift in southern asia and the american west numerical experiments experiments with general circulation models with no mountains half mountains and full modern mountains show the sensitivity of atmospheric circulation patterns to progressive amounts of uplift the experiments were motivated by geologic evidence for large kilometer scale uplift in the late cenozoic in southern asia and the american west particularly within the last 10 m y in january the amplitude of the mid latitude upper tropospheric planetary waves increased with uplift and the low level winds were progressively blocked or diverted around the topographic features in july the progressive uplift caused monsoonlike circulations to develop in the vicinity of the colorado and tibetan plateaus atmospheric heating rates midtroposphere vertical motion and upper tropospheric planetary wave amplitudes varied approximately linearly with progressive uplift these results suggest that geologically recent kilometer scale uplift may have had climatic consequences comparable in magnitude and pattern to those of earlier stages of uplift comparison of the simulated climatic effects of uplift with the geologic evidence for late cenozoic climatic change especially for the last 10 m y is given in accompanying papers

paleoclimate of the kimmeridgian tithonian late jurassic world i results using a general circulation model abstract the kimmeridgian tithonian 154 7 145 6 ma middle and late late jurassic was a time of expanded continental rifting increased sea floor spreading and a relatively high eustatic sea level stand these processes collectively caused the fragmentation and flooding of the megacontinent pangea as well as the alteration of the global paleoclimate using a version of the community climate model ccm from the national center for atmospheric research we report two kimmeridgian tithonian paleoclimate seasonal simulations with geologically inferred paleotopography one using a co 2 concentration of 280 ppm pre industrial level and the other 1120 ppm increasing the co 2 four fold warms virtually the entire planet the greatest warming occurs over the higher latitude oceans and the least over the equatorial and subtropical regions simulation of a warmer planet with an elevated greenhouse effect fits the distribution of paleoclimatically sensitive faunas floras and sedimentary rocks model results indicate that sea ice was restricted to the high latitudes of the boreal and austral seas making landfall only in restricted areas the trade winds bring heavy rainfall in december january february to eastern gondwana and in june july august to the tethys sea margins a strong june july august monsoon occurs over southeast asia the distribution of coals correlates to precipitation sufficient to maintain gymnosperm forests and coastal areas where water saturated sediments are a result of eustatic high stands of sea level evaporites are localized to areas of negative precipitation evaporation runoff is restricted to regions of intense precipitation overall the 1120 ppm co 2 simulation provides a reasonable paleoclimate for the kimmeridgian tithonian and provides a standard until a ccm with oceanic heat transport a coupled atmospheric oceanic model or one with a finer grid cell configuration is available the results need further scrutiny in areas with more detailed geologic information

variability in rates of coastal change along the yukon coast 1951 to 2015 to better understand the reaction of arctic coasts to increasing environmental pressure coastal changes along a 210 km length of the yukon territory coast in north west canada were investigated shoreline positions were acquired from aerial and satellite images between 1951 and 2011 shoreline change rates were calculated for multiple time periods along the entire coast and at six key sites additionally differential global positioning system dgps measurements of shoreline positions from seven field sites were used to analyze coastal dynamics from 1991 to 2015 at higher spatial resolution the whole coast has a consistent spatially averaged mean rate of shoreline change of 0 7 0 2 m a with a general trend of decreasing erosion from west to east additional data from six key sites shows that the mean shoreline change rate decreased from 1 3 0 8 1950s 1970s to 0 5 0 6 m a 1970s 1990s this was followed by a significant increase in shoreline change to 1 3 0 3 m a in the 1990s to 2011 this increase is confirmed by dgps measurements that indicate increased erosion rates at local rates up to 8 9 m a since 2006 ground surveys and observations with remote sensing data indicate that the current rate of shoreline retreat along some parts of the yukon coast is higher than at any time before in the 64 year long observation record enhanced availability of material in turn might favor the buildup of gravel features which have been growing in extent throughout the last six decades

morphology of the canadian beaufort sea coast a study of the canadian beaufort sea coast alaskan yukon border to baillie island was conducted to provide a regional summary of a coastal morphology b coastal stability and c coastal processes a total of 2077 km of coastline was mapped using aerial photographs low altitude and oblique aerial video imagery and information from previous field studies the coast can be adequately characterized by six repetitive coastal types four of which are erosional landforms and comprise 60 of the coast ice rich cliffs ice poor cliffs low tundra cliffs and inundated tundra two repetitive coastal types are accretional landforms and comprise 40 of the coast barrier islands and spits and deltas the deltas in the study area are retreating rapidly and therefore over 80 of the coast is considered erosional and less than 20 accretional over 1000 measurements of coastal stability indicate wide scale coastal retreat most sections of the coast show mean coastal retreat rates in excess of 1 m yr 1 despite very low annual wave exposure levels near active areas of the mackenzie river delta mean retreat rates are in excess of 2 m yr 1 and a maximum retreat rate of 18 m yr 1 was documented near shallow bay the presence of significant quantities of ice in the coastal sediments both in the form of pore ice and massive ice beds appears to be the primary cause of the wide scale regional retreat of the coast although a relative sea level rise in the region may also be important

fifty years of coastal erosion and retrogressive thaw slump activity on herschel island southern beaufort sea yukon territory canada abstract patterns of coastal erosion in the arctic differ dramatically from those coasts in more temperate environments thick sea ice and shore fast ice limit wave based erosional processes to a brief open water season however despite this permafrost coasts containing massive ice ice wedges and ice bonded sediments tend to experience high rates of erosion these high rates of erosion reflect the combined thermal mechanical processes of thawing permafrost melting ground ice and wave action climate change in the arctic is expected to result in increased rates of coastal erosion due to warming permafrost increasing active layer depths and thermokarst rising sea levels reduction in sea ice extent and duration and increasing storm impacts with the most ice rich permafrost in the canadian arctic the southern beaufort sea coast between the tuktoyaktuk peninsula and the alaskan border is subject to high rates of erosion and retrogressive thaw slump activity under many climate change scenarios this area is also predicted to experience the greatest warming in the canadian arctic this paper presents results of a remote sensing study on the long term patterns of coastal erosion and retrogressive thaw slump activity for herschel island in the northern yukon territory using orthorectified airphotos from 1952 and 1970 and an ikonos image from 2000 corrected with control points collected by kinematic differential global positioning system and processed using softcopy photogrammetric tools mean coastal retreat rates of 0 61 m yr and 0 45 m yr were calculated for the periods 1952 1970 and 1970 2000 respectively the highest coastal retreat rates are on north west facing shorelines which correspond to the main direction of storm related wave attack during the period 1970 2000 coastal retreat rates for south to south east facing shorelines displayed a distinct increase even though these are the most sheltered orientations however south to south east facing shorelines correspond to the orientations where the highest densities of retrogressive thaw slumps are observed differences in rates of headwall retreat of retrogressive thaw slumps and coastal erosion results in the formation of larger thermokarst scars and the development of polycyclic thaw slumps on south to south east exposures the number and the total area of retrogressive thaw slumps increased by 125 and 160 respectively between 1952 and 2000 as well the proportion of active retrogressive thaw slumps increased dramatically polycyclic retrogressive thaw slumps appear to develop in a periodic fashion related to retrogressive thaw slump stage and maximum inland extent

a review of mesozoic climates there is overwhelming evidence based on the distribution of distinctive sediments and fossils and oxygen isotope data that the climate of the mesozoic world was appreciably more equable than that of today with no polar ice caps but precise quantitative data are not available except for an episode of late cretaceous cooling there is no good documentation of any significant change in global temperature distributions through the era the distribution of coals and evaporites together with other criteria indicates a pattern of humid arid and zones appreciably different in important respects from that of today during the triassic and jurassic western pangaea in low to middle latitudes was largely arid but in the early cretaceous the lands on the margin of the newly opening central atlantic and western tethys experienced a humid climate by late cretaceous times arid zones had become very restricted in extent because of insufficient suitable data attempts at climatic modelling have had only modest success and only to a limited extent can the major long term changes in climate between the permian and the present be explained in terms of changing geography the most probable explanation of mesozoic equability is an increased atmospheric co 2 content a number of enigmas remain such as the existence of flourishing forests in polar palaeolatitudes whereas for the late cenozoic short term climatic changes can be related successfully to variations in the geometry and mechanics of the earth sun system there is a long way to go before comparable success can be claimed for the mesozoic