reconstructing the siluro devonian coastline of gondwana insights from the sedimentology of the port stephens formation falkland islands silurian and lower devonian sedimentary successions are uncommon within the remnants of gondwana the port stephens formation the basal unit of the middle palaeozoic west falkland group presents a rare opportunity to study gondwanan material of siluro devonian age the formation on west falkland is c 2560 m thick and consists of five members plantation albemarle mount alice south harbour and fish creek thirty five lithofacies are defined using variations in grain size and bedding characteristics the distribution of these lithofacies and their associated ichnofacies between the various members lead us to suggest terrestrial and shallow marine deposition on an extensive gently shelving alluvial to coastal plain vertical facies trends through the port stephens formation and into the base of the overlying fox bay formation record a complex superposition of subenvironments within a distinct overall transgressive regressive transgressive pattern with the bulk of sediment accumulating during the regressive phase palaeocurrents indicate a basin to the present day ne throughout these results together with lithostratigraphic correlations between the port stephens formation and the nardouw subgroup in south africa are consistent with a reconstructed position off eastern south africa and on the palaeo pacific margin of gondwana requiring a near 180 rotation of the falkland island microplate during break up in agreement with previous models we suggest that global changes in sea level during the mid late silurian and early devonian strongly influenced changes in the depositional environment enhanced erosion of the continental margin and extensive sediment bypass during the regressive phase of this cycle could help to explain the low abundance of preserved gondwanan material of this age

the development of antarctic glaciation and the neogene paleoenvironment of the maurice ewing bank abstract a micropaleontologic magnetostratigraphic and sedimentologic analysis of 56 piston cores provides the basis of a geologic study of the late miocene to holocene depositional and erosional history of the intermediate depth maurice ewing bank meb located at the eastern extremity of the falkland malvinas plateau southwest atlantic ocean sedimentation on the meb is controlled presently by the position of the polar front and strong bottom currents beneath the axis of the antarctic circumpolar current acc fluctuations in the position of the polar front and in the intensity of the acc are inferred to have largely controlled deposition on the meb since the initiation of acc flow over the bank in the miocene the sedimentary record of the meb is used to infer the late miocene to holocene oceanographic and climatic conditions in the south atlantic sector of the southern ocean the meb suffered major erosion by intense acc flow during late miocene time which exposed cretaceous miocene sediment near the surface and shaped the present configuration of the bank this erosional event is inferred to have occurred during late miocene to early pliocene time 7 2 4 7 m y b p with the major phase of erosion occurring between middle magnetostratigraphic chron 7 and late chron 6 7 2 6 2 m y b p we suggest that the miocene sedimentary record of the meb and other paleoenvironmental evidence from the circum antarctic region precludes the existence of a west antarctic ice sheet or extensive ice shelves along the antarctic margin prior to the late miocene during the late miocene a west antarctic ice shelf formed in the former west antarctic sea and rapidly thickened until it grounded below sea level to form the west antarctic ice sheet formation of this ice sheet with floating and partially grounded extensions ice shelves in the ross and weddell embayments led to the first major production of true antarctic bottom water formed in a manner similar to today which permanently altered global abyssal circulation late miocene changes in oceanic ccd levels and a permanent shift in the oceanic 13 c 12 c composition may be attributed to this major change in abyssal circulation a decrease in acc velocity during an early pliocene amelioration of climate led to resumption of deposition on the bank from 4 7 to 3 9 m y b p intensification of the acc during the late gilbert and early gauss chrons again resulted in limited deposition and widespread erosion and or non deposition over most of the meb from 4 0 to 3 2 m y b p acc velocity apparently began to wane during the middle of the gauss chron and allowed widespread deposition on the bank during late gauss time 2 9 2 48 m y b p and over more limited areas during earliest matuyama time 2 48 to about 2 2 m y b p during middle to late matuyama time bottom current intensity reached its greatest post miocene level forming a regional disconformity between sediments of about 2 0 and 1 0 m y in age this increased circumpolar circulation and associated erosion is inferred to have peaked during the late matuyama chron 1 2 1 0 m y b p and is approximately the same age as the tentatively dated greatest patagonian glaciation in nearby southern argentina between 1 0 and 0 7 m y b p the bank was blanketed with a coarse erosion resistant layer of ice rafted detritus which armored the older sediment thereby protecting it from major subsequent erosion sedimentation on the meb during the bruhnes chron 720 000 yr b p present was intermittent and finally culminated with the deposition of a veneer of carbonate ooze during or since latest pleistocene time

slope induced errors in radar altimetry over continental ice sheets ranges obtained by radar altimetry from a satellite to a sloping surface on the earth are not measurements of the surface elevation at the subsatellite point instead the reflecting point is displaced upslope from the subsatellite point causing a slope induced error between the true range to the subsatellite point and the indicated range for the seasat 1 altimeter this range error is nearly 80 m for a 0 8 degree slope ice sheet surface slopes are frequently large enough to cause errors of 10 m or more in addition undulations in the surface about a mean slope cause pronounced variations in these errors altimeter measurements of ranges to modeled irregular surfaces are simulated and two correction schemes are used to reconstruct the modeled surfaces from the simulated data the results illustrate the fundamental limitations inherent in single beam radar altimetry for mapping irregular surfaces in the simpler two dimensional case for which cross track slopes are neglected a relocation scheme which constructs a surface consistent with the altimeter ranges removes 85 of the rms error the mean error along profiles of about 75 km or longer is usually reduced more than the rms error an alternate slope correction scheme which uses the local slope to calculate the expected error is less effective in the two dimensional case however over a simulated three dimensional surface where groundtracks are widely spaced and cross track slopes are significant the slope correction method must be used in at least the cross track direction the effectiveness of the three dimensional correction depends on the relative size of the errors caused by the local slope on surface undulations in comparison to the regional slope

late devonian glaciation in south america abstract an ice age in famennian late devonian time is documented by the presence of diamictites with striated faceted and polished pebbles rhythmites with dropstones erratic boulders and striated pavements and deformed sandstones the glacigenic beds occur in three huge intracratonic basins solimoes amazonas and parnaiba and in one pericratonic basin acre in northern brazil other possible late devonian diamictites may occur elsewhere in brazil and africa which if confirmed would extend considerably the area affected by this glacial age the onset of the late devonian glaciation caused a global narrowing of the warm climatic belts sharp regression increased clastic sedimentation massive biotic extinction reduced biochemical deposition and unconformities this resulted in important facies changes in the world geological record ice centers moved from northern africa to southwestern south america from late ordovician to early silurian time from mid silurian to early late devonian time no record of glaciation is known in late late devonian time intermittent glaciation began again in central south america and from late late devonian to early late permian time ice centers migrated towards antarctica across south america and south africa the devonian and ordovician silurian glaciations together with the better known permo carboniferous glaciations may all have primarily resulted from the shifting position of the gondwana continent with respect to the south pole

devonian sea level change in bolivia a high palaeolatitude biostratigraphical calibration of the global sea level curve article i nfo available online xxxx during the devonian period the cool water malvinokaffric realm was located at high palaeolatitudes in the southern hemisphere the realm is defined by its highly endemic marine benthic fauna which makes extra malvinokaffric correlations problematic investigation of the devonian palynomorphs from an extensive regional sub surface dataset 24 wells in the chaco basin bolivia reveals the presence of a number of stratigraphically restricted and regionally correlative epiboles peak abundances of the distinctive palynomorphs bimerga bensonii crucidia camirense evittia sommeri petrovina connata and ramochitina magnifica these palynomorph epiboles were then located at outcrop by a high resolution palynological investigation 225 samples of two bolivian outcrop localities in the chaco basin bermejo santa cruz department and campo redondo chiquisaca department the important evittia sommeri epibole in the basal los monos formation is related to a marine transgression that is present in both these outcrop sections additional chronostratigraphic control on this marine transgression comes from the occurrence of rare goniatites in the base of the huamampampa formation at campo redondo which are at least early eifelian in age post chot c event based on the goniatite together with spore data the marine transgression with evittia sommeri in the basal los monos formation can be tentatively assigned to the mid devonian mid late eifelian kacak event the presence of a datable malvinokaffric goniatite has shown that key spore taxa which are used zonally in both laurussia and gondwana do not all have coincident first occurrences in both areas furthermore despite the appearance of some cosmopolitan elements in the microflora mid and late devonian spore assemblages in bolivia are distinct from other regions in being relatively impoverished in both progymnosperm and lycopod spores this floral difference is attributable to the malvinokaffric realm continuing to retain a distinctive cool climatic signature throughout this interval however the sporadic occurrences of extra malvinokaffric macrofauna in restricted stratigraphic intervals of the middle devonian in south america and south africa are significant the oldest known occurrence of the extra malvinokaffric brachiopod tropidoleptus in bolivia is coincident with the late eifelian basal los monos formation transgression hence there was a relationship between influxes of this fauna and marine transgressions i e temporary periods of reduced climatic gradient the migration of devonian spores and particularly heterosporous spores between gondwana and laurussia clearly occurs during the mid and late devonian this is at variance with models claiming a wide rheic ocean during much of the devonian

on the reconstruction of pleistocene ice sheets a review abstract pleistocene ice sheets can be reconstructed through three separate approaches 1 evidence based on glacial geological studies such as erratic trains till composition crossing striations and exposures of multiple tills nonglacial sediments 2 reconstructions based on glaciological theory and observations these can be either two or three dimensional models they can be constrained by known ice margins at specific times or they can be open ended with the history of growth and retreat controlled by parameters resting entirely within the model 3 glacial isostatic rebound after deglaciation provides a measure of the distribution of mass ice across a region a best fit ice sheet model can be developed that closely approximates a series of relative sea level curves within an area of a former ice sheet in addition the model should also provide a reasonable sea level fit to relative sea level curves at sites well removed from glaciation this paper reviews some of the results of a variety of ice sheet reconstructions and concentrates on the various attempts to reconstruct the ice sheets of the last wisconsin weischelian wurm devensian glaciation evidence from glacial geology suggests flow patterns at variance with simple single domed ice sheets over north america and europe in addition reconstruction of ice sheets from glacial isostatic sea level data suggests that the ice sheets were significantly thinner than estimates based on 18 ka equilibrium ice sheets cf denton and hughes 1981 the review indicates it is important to differentiate between ice divides which control the directions of glacial flow and areas of maximum ice thickness which control the glacial isostatic rebound of the crust upon deglaciation recent studies from the laurentide ice sheet region indicate that the center of mass was not over hudson bay that a major ice divide lay east of hudson bay so that flow across the hudson bay and james bay lowlands was from the northeast that hudson bay was probably open to marine invasions two or three times during the wisconsin glaciation and that the laurentide ice sheet was thinner than an equilibrium reconstruction would suggest

analysis and retracking of continental ice sheet radar altimeter waveforms the seasat i radar altimeter data set acquired over both the antarctic and greenland continental ice sheets is analyzed to obtain corrected ranges to the ice surface the radar altimeter functional response over the continental ice sheets is considerably more complex than over the oceans causal factors identified in this complicated response include sloping surfaces undulating ice surfaces with characteristic wavelengths on the same spatial scale as the altimeter beam limited footprint off track reflections and dynamic lag of the altimeter tracking circuit retracking methods using the altimeter return pulse waveforms give range corrections that are typically several meters the entire set of seasat i altimetry over the continental ice sheets is being retracked by fitting a multi parameter function to each waveform many waveforms have double ramps indicating near normal reflections from two distinct portions of the ice surface within the altimeter beam two independent range measurements differing by less than 25 m are obtained from retracking the double ramp waveforms

nine centuries of microparticle deposition at the south pole abstract the analysis of microparticles in a 101 m core from amundsen scott south pole station antarctica has revealed a substantial increase in total particle concentration between approximately 1450 and 1850 a d a period encompassing the latest neoglacial interval or little ice age it is likely that this reflects a simultaneous increase in the concentration of particulate material in the antarctic atmosphere this is important climatologically for the antarctic atmosphere may represent the closest approximation to the natural background aerosol thus cores from east antarctica may contain long and detailed records of the natural global background aerosol such records are unavailable from any other medium additionally a cyclical variation which appears to be annual has been detected in the south pole particle record these features allow construction of a relative time scale for ice cores older than 100 yr from regions of low accumulation 1 where many traditional techniques are not applicable this is especially significant as the comparison of climatic data extracted from ice cores with other records of proxy data depends upon the ability to assign an accurate time scale to the ice core an estimated nine century record of net annual accumulation at the south pole has been compiled and the calculated error in the time scale is 90 yr

reappraisal of sea ice distribution in atlantic and pacific sectors of the southern ocean at 18 000 yr bp the question of the distribution of winter and summer sea ice cover during the last glacial maximum 18 000 yr bp is important in climatic modelling of the glacial world we have now compared satellite derived 5 yr monthly averages of per cent summer sea ice cover in the atlantic and pacific sectors of the southern ocean with the distribution of reported sedimentological indicators of sea ice cover at the sediment water interface these data strongly suggest that sediment type cannot be used to identify summer sea ice limits neither in recent sediments nor in sediments of the last glacial maximum rather the data seem to indicate that sediment type can be used to identify spring sea ice limits for these two time intervals

blame it on the goats desertification in the near east during the holocene the degree to which desertification during the holocene resulted from climatic deterioration or alternatively from overgrazing has puzzled quaternary scientists in many arid regions of the world i

late palaeozoic to mesozoic structural evolution of the falkland islands a displaced segment of the cape fold belt the falkland islands lie on a displaced crustal block presently forming part of the south american plate the islands possess two roughly orthogonal structural grains the relative chronology of which is here unequivocally established for the first time d1 structures form a southerly verging permo triassic age fold belt striking e w to wnw ese which represents a displaced segment of the gondwanian orogenic belt the strike swing from e w to wnw ese is coincident with a decrease in deformation intensity toward the west on west falkland d1 folds are superimposed by the early mesozoic d2 ne sw trending hornby mountains anticline producing localized kilometre scale type i and iii fold interference patterns the hornby mountains anticline is interpreted to be the result of dextral transpressive reactivation of a pre existing ne sw basement fault if the falkland islands are rotated 180 the structure of the d1 fold belt and tectono sedimentary features of the permian age lafonian supergroup display a remarkable correlation with the structural style and tectonic evolution of the eastern cape fold belt of south africa our data therefore support a 180 tectonic rotation of the falkland islands and reaffirm their pre gondwana break up position adjacent to the southeast coast of south africa in such a reconstruction the falkland islands constrain the easterly extension and eventual lateral termination of the cape fold belt

geobiology and paleobiogeography tracking the coevolution of the earth and its biota abstract paleobiogeographic research is an important area of geobiology that involves the study of the coevolution of the earth and its biota by considering how tectonic and climatic changes have affected the evolution and distribution of organisms the intellectual heritage of the discipline stretches back well before darwin phylogenetic approaches to paleobiogeography have played an important part in the expansion of the field and recent analyses have incorporated geographic information systems gis each of these approaches by enhancing the precision of paleobiogeography helps make the discipline more relevant to geobiology the interaction occurring between the geological and biological sciences in paleobiogeography is apparent in several areas first there is the emergence of new techniques such as the ability to analyze ancient dna sequences also paleobiogeographers and biogeographers have realized that geo dispersal a biogeographic process first identified through studies of the fossil record can powerfully influence the evolution and distribution of biotas finally biogeographers have recognized that paleontological incompleteness and extinction constrain our ability to reconstruct biogeographic patterns in the fossil record and the extant biota respectively each of these developments suggests that further growth in paleobiogeography will involve important interactions between studies involving the fossil record and the extant biota and this along with the discipline s commitment to studying how tectonic and climatic changes have influenced evolution reaffirms the validity of the synthetic field that is geobiology

role of glacial arctic ocean ice sheets in pleistocene oxygen isotope and sea level records abstract a comparison of the oxygen isotope signal in deep sea benthic foraminifera with the record of glacio eustatic sea level for the last 160 000 years reveals that the amplitude of the benthic 18 o records predicts more continental ice volume than appears to be reflected in lowered sea level stands these differences between the benthic 18 o ice volume estimates and radiometrically dated records of eustatic sea level are consistent with the presence of a large floating arctic ocean ice mass during glacial intervals the presence of an arctic ocean ice sheet during glacial intervals may account for the two climatic modes observed in oxygen isotope records which span the entire pleistocene the early pleistocene 1 8 to 0 9 myr b p interval is characterized by low amplitude high frequency 18 o fluctuations between glacial and interglacial periods while the late pleistocene 0 9 myr b p to present is characterized by large amplitude low frequency 18 o changes these two climatic modes can be explained by the initiation of earth orbital conditions favoring the co occurrence of glacial period arctic ocean ice sheets and large continental ice sheets approximately 900 000 years before present

research on snow and ice this review unlike its predecessor martinelli et al 1979 is an intentionally selective survey of recent advances in selected areas of snow and ice research i have chosen to concentrate on studies relating to large scale aspects of the cryosphere and to consider their wider significance for other disciplines results obtained by new measurement techniques and the application of remote sensing methods are also stressed at the same time the broad lines of advance in glaciological research as represented in books conference themes and major field or laboratory programs are noted and a detailed bibliography is appended

a paleozoic pangaea paleozoic paleogeographies should be consistent with all available reliable data however comparison of three different devonian paleogeographies that are based largely or wholly on the data of remanent magnetism show them to be inconsistent in many regards when these three paleogeographies are provided with possible ocean surface current circulation patterns and have added to them lithofacies and biogeographic data they also are shown to be inconsistent with such data a pangaeic reconstruction positioned in the southern hemisphere permits the lithofacies and biogeographical data to be reconciled in a plausible manner

the micromorphological identification of faecal spherulites from archaeological and modern materials abstract microscopic calcium carbonate spherulites from animal dung are now regularly found in archaeological micromorphology samples they have a particular set of morphological and optical characteristics including a fixed cross of extinction which is always pseudo uniaxial negative this paper gives details of these characteristics and provides methodologies for using them to distinguish faecal spherulites from similar materials e g coccoliths and related biominerals such as plant derived calcium oxalate druses and avian reptilian uric acid spheres simple predictions are made concerning the effect of thin section versus liquid mount preparations on maximum retardation diameter plots these are confirmed by the pattern of the real data but a discrepancy remains between the measured birefringence of the spherulite material and the expected birefringence from radial calcite using morse donnay s 1932 american journal of science 23 421 461 calculation possible reasons for this discrepancy are discussed

on some possible interactions between internal waves and sea ice in the marginal ice zone the ice edges of the world ocean are generally the site at times when winds are blowing off the ice of regularly spaced surface bands of ice floes these bands have size scales of the order of 1 10 km and their long axes are oriented approximately normal to the wind direction available oceanic temperature and salinity data from the bering and greenland sea ice edge regions suggest that these ice bands are commonly underlain by a two layered density structure which is maintained by net melting along the ice edges linear internal wave theory is applied to these data to compute first mode interfacial wave phase speeds a simple analytical model is developed that demonstrates the feasibility of generation of such interfacial internal waves by the stress discontinuity due to off ice winds blowing over either a stationary or a moving ice edge it is qualitatively shown that the computed internal wave phase speeds and wavelengths are under many conditions compatible with the speeds and spacings of the surface ice bands this compatibility suggests in turn that coupling between internal waves and ice bands may commonly occur some possible implications of the generation and presence of these internal waves upon other ice edge processes such as air sea heat and momentum transfer are qualitatively discussed

quantitative phytolith study of hearths from the natufian and middle palaeolithic levels of hayonim cave galilee israel abstract a study of the mineralogy and phytolith assemblages of hearths and their associated sediments in hayonim cave israel shows that wood ash is a major component of the sediments of both the natufian approximately 12 000 bp and the mousterian deposits approximately 100 to 250 000 bp interestingly phytolith analyses show that in the natufian deposits grasses are the second most abundant form of vegetation preserved whereas in the mousterian deposits leaves of dicotyledonous plants are the second most abundant form of vegetation preserved significant differences were repeatedly observed in phytolith assemblages from closely associated but different stratigraphic layers showing that vertical mixing of intact sediments is not intensive and that there was a diverse input of vegetation over relatively short time periods no consistent differences were observed in the mineralogy and the phytolith assemblages between hearths and their associated sediments both contain abundant ash components this study demonstrates that quantitative analyses of phytoliths together with mineralogical analyses can provide much information on the use of plants for fuel and other purposes by the cave occupants

basin fill evolution and paleotectonic patterns along the samfrau geosyncline the sauce grande basin ventana foldbelt argentina and karoo basin cape foldbelt south africa revisited as integral parts of du toit s 1927 samfrau geosyncline the sauce grande basin ventana foldbelt argentina and karoo basin cape foldbelt south africa share similar paleoclimatic paleogeographic and paleotectonic aspects related to the late paleozoic tectono magmatic activity along the panthalassan continental margin of gondwanaland late carboniferou earliest permian glacial deposits were deposited in the sauce grande sauce grande formation and karoo dwyka formation basins and falkland malvinas islands lafonia formation during an initial sag phase of extension the pre breakup position of the falkland malvinas islands on the easternmost part of the karoo basin immediately east of the coast of south africa is supported by recent paleomagnetic data lithofacies associations paleoice flow directions and age similarities between the dwyka and the lafonia glacial sequences the desintegration of the gondwanan ice sheet gis triggered widespread transgressions reflected in the stratigraphic record by the presence of inter basinally correlatable open marine fine grained deposits piedra azul formation in the sauce grande basin prince albert formation in the karoo basin and port sussex formation in the falkland islands capping glacial marine sediments these early postglacial transgressive deposits characterised by fossils of the eurydesma fauna and glossopteris flora represent the maximum flooding of the basins cratonward foreland subsidence was triggered by the san rafael orogeny ca 270 ma in argentina and propogated along the gondwanan margin this subsidence phase generated sufficient space to accommodate thick synorogenic sequences derived from the orogenic flanks of the sauce grande and karoo basins compositionally the initial extensional phase of these basins was characterized by quartz rich craton derived detritus and was followed by a compressional foreland phase characterized by a paleocurrent reversal and dominance of arc foldbelt derived material in the sauce grande basin tuffs are interbedded in the upper half of the synorogenic foldbelt derived tunas formation early early late permian likewise the first widespread appearance of tuffs in the karoo basin is in the whitehill formation of late early permian 260 ma age silicic volcanism along the andes and patagonia choiyoi magmatic province peaked between the late early permian and late permian a link between these volcanics and the consanguineous airborne tuffs present in the sauce grande and karoo basins is suggested on the basis of their similar compositions and ages

monthly and seasonal variability in the ocean ice atmosphere systems of the north pacific and the north atlantic four regional indices of sea ice variability and thirty years of monthly sea surface temperature sst and sea level pressure slp data are used to evaluate the large scale interactions within the ocean ice atmosphere systems of the north pacific and the north atlantic a direct association between positive negative sst anomalies and light heavy ice in the bering sea is indicated the sst ice coupling in the northern alaskan waters is also statistically significant the sst anomalies in both the north pacific and the north atlantic appear as persistent responses to atmospheric forcing the slp distributions over both oceans correlate significantly with the arctic slp distribution although the midlatitude atmospheric circulation shows no systematic tendency to lead or lag the arctic circulation sea ice fluctuations correlate most highly with the atmospheric forcing over antecedent periods of approximately 9 months in the northern alaskan waters 3 4 months in the bering sea and 5 7 months in the east greenland sea the strength of the 9 month mean onshore air flow component describes over 70 of the northern alaskan ice variance

on the seasonal sea ice cover of the sea of okhotsk free of ice 4 months of the year the sea of okhotsk begins to freeze over in a few coastal locations in november attains its maximum ice coverage usually in mid march and by june retains ice in only a few coastal regions this sequence is well recorded by satellite imagery from the electrically scanning microwave radiometer esmr on board nimbus 5 four years of esmr data reveal significant interannual variations in the maximum ice cover and in the smoothness of the growth and retreat periods of the years 1973 1976 the heaviest ice cover occurred in 1973 and the growth period most interrupted by temporary ice edge retreats was in 1974 comparison of the general features of the cycle of sea ice distribution with basic oceanographic factors shows that ice forms first in cold shallow low salinity waters and then seems to drift in a direction approximating the okhotsk kuril current system two basic patterns of ice edge positioning which occur frequently in the esmr data are identified as a rectangular structure and a wedge structure each of these is strongly correlated with the bathymetry of the region and with the known current system suggesting that convective depth and ocean currents play an important role in determining ice patterns certain major interannual variations in the ice extents are accounted for by interannual contrasts in the atmospheric pressure fields

geomorphic changes leading to natural desertification versus anthropogenic land conservation in an arid environment the negev highlands israel the negev highlands in southern israel are currently under an erosive regime causing degradation of soil and vegetation a process which has often been attributed to land mismanagement and overgrazing caused by the local bedouin population to estimate the anthropogenic role in the erosional processes in the negev highlands two similar drainage basins were selected and studied one undisturbed with almost no human impact and the other with intensive human modification including the establishment of roman to early islamic agriculture field observations and luminescence dating indicate that during the late pleistocene glacial period ois 4 and 3 deposition of fluvio loess sediments with minor erosion cycles occurred in the negev highlands severe erosion started during ois 2 and continued into the holocene as the climate shifted during the termination of the pleistocene to the present interglacial phase higher rain intensity generated the incision of gullies and channels into the fine grained alluvial sediments of the previous phase causing extended soil erosion and reducing the natural biomass and the agricultural potential establishment of runoff harvesting farms in the 3rd century interrupted the holocene natural erosion and gully incision and led to the redeposition of up to 3 5 m of fine alluvial loess sediments originating from late pleistocene loess sections this accumulation is not related to any late holocene pluvial climatic phase and is solely the result of farming we conclude that since the end of the pleistocene a dynamic change in the soil rock ratio related to the long term process of adjustment of the geomorphologic system to the holocene climate has been taking place within the drainage basins in the negev highlands the fluvio loess sediments deposited in the region during ois 4 and 3 have been eroding since the latest pleistocene throughout the holocene this process causes degradation of the biomass and agricultural potential and leads onto natural desertification of the region the historical intervention by establishment of runoff harvesting agriculture which as a by product resulted in the accumulation of redeposited loess sediments counteracted the natural trend of soil erosion this was in fact a land conservation act applied by the ancient farmers in the semi arid regions of the middle east deserts this activity and its geomorphic consequences are in contrast to the well documented land degradation trend generated by recent anthropogenic impact on marginal lands elsewhere in any case the human impact either contributing to land degradation or to soil conservation is super imposed on the natural long term trend leading toward desertification

evidence for long term climate change in upper devonian strata of the central appalachians abstract the highest 1 to 200 m of the upper devonian famennian catskill and equivalent hampshire formations exhibit a noticeable vertical or stratigraphic change in color and a shift in lithologic character the lower part of the unit is characterized by typically red channel phase sandstones and overbank siltstone and mudstone containing thin calcareous paleosols these lithologies give way to greenish gray sandstone containing abundant coaly plant fragments coalified logs and pyrite interbedded with thick intervals of non calcareous paleo vertisols the increase in the prominence of preserved terrestrial organic matter suggests that there was a corresponding increase in the abundance of plants in terrestrial ecosystems the stratigraphic change in lithology within the upper part of the catskill hampshire succession suggests the onset of environmental conditions that became increasingly wet in response to elevated humid climatic conditions during the final stages of catskill alluvial plain deposition the sedimentological signature suggesting increased climatic wetness within the uppermost catskill and hampshire formations is nearly contemporaneous with the initiation of late devonian gondwanan glaciation in the paleo high latitudes the appalachian climate record indicates that this change began during the fa2c and continued through the latest famennian reaching its peak during the fa2d when glacial deposits are recorded in the paleo mid latitudes of the appalachian basin evidence of this late famennian increase in precipitation also is recorded in the adjacent marine environments equivalent age marine units in ohio and kentucky record progressive increases in both total organic carbon and the percentage of terrestrially derived organic carbon this suggests that there was a late famennian increase in terrestrial organic matter productivity and that during the late famennian there were elevated levels of runoff produced by the interpreted increase in precipitation that washed progressively higher amounts of terrestrial organic matter into the local marine environments the late famennian climate changes identified within the appalachian basin strata have been recognizable globally and appear to have had both positive and negative effects on the earth s biota some marine groups exhibit sharp diversity drops or even extinction coincident with the maximum development of the late famennian ice age conversely terrestrial biota appears to have been more positively affected by the late famennian increased wetness that accompanied this progressive climate change marked diversification and evolutionary innovation which appear to coincide with this climatic deviation can be recognized within terrestrial plant communities and early tetrapod amphibians

the falkland islands a key element in gondwana paleogeography stratigraphic and sedimentological fieldwork on the falkland islands confirms that they were originally part of south africa east and west falkland have contrasting geological and deformation histories and are separated by the falkland sound fault which marks a significant deformation edge to the cape fold belt the degree of structural deformation and metamorphism in west falkland is substantially less than that of east falkland adjustments to differential shortening between the two islands being reflected by structures developed along the falkland sound fault prior to fragmentation of gondwana the falkland platform and maurice ewing bank were positioned in the natal valley adjacent to the east coast of south africa this predrift reconstruction shows that the falkland islands have subsequently been rotated by 180 relative to south africa and complements recent paleomagnetic data there was a complete overlap of the maurice ewing bank and falkland platform to the exclusion of the falkland plateau basin which is a small oceanic basin formed during the jurassic fragmentation of gondwana extension in this basin was accommodated by movements along the aghulas falkland fracture zone and the gastre fault system predrift restoration of these faults shows that patagonia was positioned closer to both africa and antarctica the falkland plateau basin was an integral component of the west gondwana jurassic microplate system and provides an invaluable insight into the evolution of its western margin at some time prior to the main opening of the south atlantic the falkland platform was rotated clockwise by 120 against the agulhas falkland fracture zone such that the falkland islands were translated some 300 km to the south the driving force for this rotation is not known but could possibly have been initiated by periodic stress buildups in the falkland plateau basin as the gastre fault system within continental crust became unable to accommodate the continuous dextral shear in the agulhas falkland fracture zone the falkland islands represent an outboard extension of the eastern cape and are significant for understanding the paleogeography of both the cape and karoo supergroups east falkland is closely similar to south africa in its geology while west falkland shows significant contrasts with both the devonian and permian successions being more proximal in character but still demonstrate the eastward continuation of the cape and karoo basins

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

sea ice displacement from seasat synthetic aperture radar images obtained by a synthetic aperture radar on seasat have been used to measure sea ice displacements over a three day interval in october 1978 the position of a natural ice feature was measured on 5 october and again on october 8 the difference in these two positions is a displacement the displacement of many features was measured the tracked features lie roughly along a line and are quite dense about 2 km apart over a distance of 865 km the displacements are about 20 km displacement errors grow with distance from shore becoming as large as 3 km the graph of displacement versus distance has occasional discontinuities of several kilometers displacement discontinuities are accurate to 0 07 km along track and 3 of their magnitude across track

the human impact in geomorphology 50 years of change abstract concern with the human impact in geomorphology has a long history what is new is that since 1969 a number of developments have taken place that have led to an increasing realisation of its importance these developments are in four main areas i intellectual and policy related ii technological developments that alter geomorphological processes iii demographic trends and iv the proliferation of techniques for the study of landform and process change there has been a realisation of the role of humans in landscape transformation in ancient times the human impact has developed through time but particularly notable are the potential early effects of fire extinctions and deforestation on geomorphological processes the spread of european agriculture particularly in the nineteenth century transformed erosion and sedimentation rates in many parts of the world notwithstanding the importance of some of these changes in prehistoric and historic times recent researches have demonstrated that humans have become an increasingly important agent of geomorphological change during the period of the great acceleration of the past five or six decades the interest in global warming that has developed since the early 1980s has created considerable interest in its consequences for a range of geomorphological phenomena it is also becoming apparent that anthropogenic geomorphological change is having an impact on the earth system as a whole finally geomorphologists have taken an increasing interest in how they can make an impact in the field of landscape conservation

analysis of multiple angle microwave observations of snow and ice using cluster analysis techniques the nimbus 6 satdlite carries the scanning microwave spectrometer experiment scams which continuously maps the earth s surface at two frequencies 22 235 and 31 65 ghz and at six angles besides nadir cluster analysis was applied to these observations to determine the influence of various geophysical parameters on the radiometric brightness temperatures characteristic microwave signatures for a variety of terrain were obtained by this method discrete clusters were distinguished for sea ice with sub cla ses for ice age and fractional ice cover and firn with accumulation rate sub classes the availability of the angular data greatly facilitated separate determinations of the extent of continuous sea ice and mixtures of sea ice and water resume analyse d observations aux micro ondes sous des angles multiples de neige et de glace par les techniques de reconnaissance desformes le satdlite nimbus 6 transporte un spectrometre a balayage a micro onde scanning microwave spectrometerscams qui cartographie continuellement la surface de la terre a deux frequences 22 235 et 31 65 ghz et sous six angles en sus du nadir on a applique i analyse de groupe aces observations pour determiner 1 influence de parametres geophysiques varies sur les temperatures de brillance adiometrique on a obtenu par cette methode les signatures caracteristiques aux micro ondes pour divers terrains on a distingue des groupes speciaux pour la glace de mer qui se subdivisent selon i age de la glace et le decoupage de la couverture de glace et le neve avec des sous classes selon la vitesse d accumulation le fait de disposer de donnees prises sous divers angles facilite beaucoup la distinction des etendues a glace de mer noninterrompue et des melanges de glace de mer et d eau zusammenfassung analyse von beobachtungen mit mikrowellenabtastern uber schnee und eis unter anwendung van verfahren der mustererkennung der satellit nimbus 6 triigt das mikrowellen abtasterspektrometer scams das die erdoberfliiche dauernd in zwei frequenzen 22 235 und 31 65 ghz und unter sieben nadirdistanzen aufnimmt zur bestimmung des einflusses verschiedener geophysikalischer grossen auf die radiometrischen strahlungstemperaturen wurde die cluster analyse angewandt fur eine reihe von oberfliichen liessen sich charakteristische mikrowellen signaturen feststellen meereis mit unterklassen fur alter und dichtigkeit und firn mit unterklassen fur die akkumulationsrate ergaben diskrete hiiufungsstellen cluster die verfugbarkeit der winkeldaten erleichtert getrennte bestimmungen des vorkommens von geschlossenem meereis und mischlagen von meereis und wasser erheblich

temporal variability of microparticle properties in polar ice sheets abstract four recent ice core studies reveal a consistently recurring temporal correlation between increased microparticle concentrations and lower global temperatures more negative 13 o 16 o ratios a continuous 900 year record of particle deposition from the 101 m south pole core was obtained by analyzing 6218 samples the concentration of insoluble particles with diameters 0 63 m increases substantially between a d 1450 and 1850 a period of slightly reduced global temperatures encompassing the latest neoglacial or little ice age there is evidence suggesting that some of the additional material may be volcanic although further substantiation is required the microparticle analyses of selected sections from three deep cores coupled with the respective 18 o measurements reveal that in all three cores the last glacial or late wisconsin ice contained great quantities of microparticles the ratio of the average microparticle concentration in wisconsin sections to that in holocene sections is 6 for the 905 m dome c antarctica core 3 for the 2164 m byrd station antarctica core and 12 for the 1387 m camp century greenland core microparticle increases of this magnitude can not be accounted for merely by a reduction in net accumulation these data suggest that the global atmosphere was heavily laden with suspended particulates near the end of the last major glaciation

late devonian glacial deposits from the eastern united states signal an end of the mid paleozoic warm period abstract a late devonian polymictic diamictite extends for more than 400 km from northeastern pennsylvania across western maryland and into east central west virginia the matrix supported unbedded locally sheared diamictite contains subangular to rounded clasts up to 2 m in diameter the mostly rounded clasts are both locally derived and exotic some exhibit striations faceting and polish the diamictite commonly is overlain by laminated siltstone mudstone facies associations laminites the laminites contain isolated clasts ranging in size from sand and pebbles to boulders some of which are striated the diamictite laminite sequence is capped by massive coarse grained pebbly sandstone that is trough cross bedded a stratigraphic change from red calcic paleo vertisols in strata below the diamictite to non calcic paleo spodosols and coal beds at and above the diamictite interval suggests that the climate became much wetter during deposition of the diamictite the diamictite deposit is contemporaneous with regressive facies that reflect fluvial incision during the late devonian of the appalachian basin these deposits record a late devonian episode of climatic cooling so extreme that it produced glaciation in the appalachian basin evidence for this episode of climatic cooling is preserved as the interpreted glacial deposits of diamictite overlain by glaciolacustrine varves containing dropstones and capped by sandstone interpreted as braided stream outwash the appalachian glacigenic deposits are contemporaneous with glacial deposits in south america and suggest that late devonian climatic cooling was global this period of dramatic global cooling may represent the end of the mid paleozoic warm interval that began in the middle silurian

domestic activities and spatial distribution in ain abū nukhayla wadi rum southern jordan the use of phytoliths and spherulites studies abstract the pre pottery neolithic b site of ayn ab nukhayla wadi rum jordan contains structural installations loci composed of inter connected oval rock walled pithouses questions that arose from their study centered on how to identify possible herding and agricultural activities and to assess any differences in how the loci were used the combined study of phytoliths and spherulites identified from different loci are presented here the results of quantitative morphologic and morphometric analyses of phytoliths and spherulites identified in the different loci are discussed cereal processing is evident in some loci by the concentration of the inflorescent parts of festucoid grass phytoliths associated with the presence of handstones and querns these loci appear to have encompassed specific areas in which domestic activities including the grinding of cereals and the preparation of other plant resources were undertaken in contrast other loci such as locus 20 seem to have been used as pens for herd animals sheep goats as indicated by very high densities of spherulites the results of this study provide new insights on plant uses herding practices and the economic diversity of early neolithic communities in the levant

taphonomy and taphofacies analysis of lingulid brachiopods from devonian sequences of the parana basin brazil abstract the extreme abundance of lingulid valves in some outcrops of the devonian sequences of the parana basin and their absence in others where other benthic taxa dominate was the starting point to the present research twenty one outcrops were sampled and characterized taphonomically these outcrops record an epeiric muddy sea influenced by episodic storms in twelve out of the 21 outcrops the devonian sequences b c d and e massive occurrences of complete and fragmented valves of lingulids oriented parallel to the bedding plane were documented the occurrence of fragments together with complete but disarticulated valves suggests that the post mortem sorting and transport is unlikely to have been notable this claim is also supported by the fact that in situ preserved lingulid valves were always recorded even if in low numbers however some time averaging may have occurred this is because entire valves presumably removed from their burrows just prior to burial and fragmented ones probably reworked or exposed on sediment water interface for some days or a few weeks were found together rosette and stringer arrangements of the lingulid pavements represent the first record of distal reworking of this kind of bioclastic material the devonian lingulid outcrops studied here represent fossil accumulations that likely formed with contributions from multiple factors however the extrinsic physico chemical factors are difficult to infer by analogy with modern environments because of the unique setting that typified palaeozoic epeiric seas on the other hand an actualistic approach can be used to assess some of the taphonomic controls exerted by intrinsic characteristics of lingulid brachiopods including shell thickness and life habit the lingulid rich units with their distinct taphonomical signatures represent a clearly definable taphofacies lingulid taphofacies characterized by abundant often complete occurrence of lingulid valves parallel to the bedding plane in light grey and dark grey siltstones and rare occurrences of lingulid valves in black shales the lingulid taphofacies is associated with a range of proximal marine settings ranging from the lower shoreface lowermost intertidal to the distal transitional offshore shallow subtidal zones the pattern of patchy distribution of lingulids observed in some present day environments was rarely seen in the studied sequences

a field and laboratory study of wave damping by grease ice in a field and laboratory study we discuss the formation growth and wave absorption properties of grease ice our field observations show that grease ice formation occurs under cold windy conditions in both leads and polynyas in leads grease ice forms in the open water then is herded to the down wind edge of the lead in polynyas a langmuir circulation herds the grease ice into long plumes parallel to the wind in the laboratory we grow grease ice in a wave tank and measure its wave absorption properties for single frequency two dimensional waves on a large scale we find that the thickness of the grease ice which increases away from the paddle is determined by a balance between the wave momentum flux and the free surface tilt on a small scale our photographs show that the crystals which make up the grease ice consist of discs measuring about 1 mm in diameter and 1 10 m thick which at low rates of shear sinter together into larger clumps yielding a viscosity increase to measure this non linear viscosity we study the decay of wave amplitude between two critical distances measured inwards from the leading edge the first occurs when the depth of grease ice exceeds k 1 where k is the wave number the second further distance is a line of transition from liquid to solid behavior which we call the dead zone between these two distances the wave amplitude decays with a linear slope which increases as a 0 k 2 where a0 is the wave amplitude in open water concurrent measurements of ice concentration show that it increases from values of 18 22 at the leading edge to a local maximum of 32 44 at the dead zone while the values at the dead zone increase non linearly with a0k finally comparison of the observed to that calculated from a yield stress viscosity model shows if the yield stress coefficient is proportional to the incident wave momentum flux the model predicts the observed

recovery brachiopod associations from the lower silurian of south china and their paleoecological implications a recovery brachiopod fauna occurs in the lower niuchang formation upper rhuddanian lower aeronian llandovery of the xinglongchang section meitan county northern guizhou province south china nine collections were made at the section all of which are dominated by brachiopods and three associations are recognized here and their paleoecology is discussed paleoenvironmental analysis shows a shallowing upward trend for the lower niuchang formation although a global transgression was happening at that time the balance between the global transgression and the regional qianzhong uplift guaranteed a stable environment for the formation of the niuchang formation and the recovery of brachiopods in south china after the end ordovician mass extinction in addition to the traditional methods of principal component analysis and cluster analysis a relatively new technique to paleontology network analysis is applied successfully in this study it is suggested that network analysis could be used as one o

evidence for a former large ice sheet in the orville coast ronne ice shelf area antarctica the orville coast area of the antarctic peninsula was extensively glacierized in the past striations polished rock surfaces and erratics on nunatak summits indicate that this area was covered by a broad regional ice sheet whose grounded ice margin was on the continental shelf in the present day ronne ice shelf area if the glacial history of antarctica has been controlled by eustatic sea level changes the destruction of this ice sheet would have been contemporaneous with that of the ross sea ice sheet due to the world wide rise of eustatic sea level at the end of the wisconsin glaciation shelf area of the weddell sea denton and borns 1974 field evidence found in the course of reconnaissance geologic mapping during the austral summer of 1977 78 indicated that the orville coast area of the antarctic peninsula was extensively g lacierized in the past data from the behrendt hauberg merrick sweeney and wilkins mountains and sky hi nunataks fig i indicate that a large ice sheet whose grounding line was on the present day continental shelf at least 65 km and perhaps several hundred kilometers from the present coast existed in the past almost the entire study area 30 000 km2 is located in the accumulation area of a large ice field blue ice was encountered only in areas where wind erosion is common the few mountain ranges and isolated nunataks comprise approximately i of the study area the present day ice field was superimposed upon a pre glacial topography and has modified the mountain ranges and nunataks into aretes horns and broad cols in the hauberg mountains a number of valleys trend nearly due north approximately parallel to a major joint system pre glacial valleys

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

early middle devonian brachiopod provincialism and bioregionalization at high latitudes a case study from southwestern gondwana the paleobiogeography of early middle devonian pragian eifelian brachiopods from west gondwana was assessed to determine any potential controls regional climatic differences or global eustasy that may have driven bioregionalization the pragian eifelian interval of west gondwana was examined because work by previous authors suggested that this was a period when regionally extensive areas of provincialism among marine invertebrates were present and most pronounced factors of particular interest in this study were the controls over brachiopod bioregionalization at high 60 90 southern latitudes which the malvinokaffric realm is thought to have entirely occupied a large presence absence data matrix was compiled consisting of the occurrences of 206 genera from 17 localities across west gondwana and an array of multivariate methods cluster analysis nonmetric multidimensional scaling and network analysis was employed to assess regional bioregionalization trends the results of our study suggest that regional climatic differences brought on by latitudinal effects were the determining driver for bioregionalism of brachiopods during the pragian eifelian and these trends were coincident with a global cooling period during the early middle devonian our study further suggests that of the three regional paleobiogeographic realms thought to be present in west gondwana during the early middle devonian eastern americas old world and malvinokaffric only the malvinokaffric realm is valid as a single biogeographic area its area however is reduced it is interpreted to have been a second order biogeographic area and not a first order area as suggested by previous authors given these factors we suggest a new demonym for this area the malvinoxhosan given the racially charged connotations of malvinokaffric we present a new biogeographic framework for west gondwana that is free of preconceived biogeographic area and rank biases with the understanding that a more globally expansive study should be undertaken to elucidate these areas and their rank within the correct hierarchy two first order paleobiogeographic areas are recognized in west gondwana and are named according to their latitudinal extent namely the high latitude 60 s 90 s and temperate latitude 30 s 60 s bioregions the temperate latitude bioregion consists of a single second order paleobiogeographic area the colombian west african bioregion two second order bioregions are present in the high latitude bioregion namely the amazonian and malvinoxhosan bioregions here the amazonian 50 s 70 s compositionally was an intermediate region between the colombian west african 30 s 50 s and malvinoxhosan 70 s 90 s end members latitudinal effects may also have been responsible for dividing the malvinoxhosan bioregion into two tentative third order paleobiogeographic areas namely the andeo south african 70 s 80 s and the parana 80 s 90 s bioregions

late holocene landscape instability in the breckland england drift sands abstract this research investigates the landscape instability associated with the drift sands which are widespread across north western europe it focuses on breckland uk using new sites along with existing geomorphic archaeological and historical data this shows landscape instability of drift sands occurred at 5240 1040 years bce 600 100 1150 50 1600 and 1790 ce comparison of these phases to climate records show no clear patterns with drifting occurring during dry wet as well as cold warm periods additionally similar climatic shifts lead to diverging reactions of landscapes in different regions throughout europe at the regional scale land usage and population pressures also may not be the direct cause of sand drifting suggesting that complex responses or different triggers at different times were responsible within this society s unawareness of the inherent landscape instability and the threat posed by the sand hazard may have been important as it affected whether mitigation measures were or could be implemented in breckland initial instability may have been due to the establishment of the open field system on virgin soil later changes in land ownership and associated power within the society led to an inability of communities to implement mitigation measures and large land owners abstaining from tackling the sand hazard whilst the widespread coversands and climatic extremes provide the underlying susceptibility to sand drifting it would appear that drift sands of the last 2000 years may provide less of a sedimentary archive of late holocene climatic changes and more a record of land management changes

mapping ice sheet margins from radar altimetry data the seasat radar altimeter which was designed to measure ranges to the sea surface has also provided the most accurate available maps of ice sheet eleva tion seasat operated for three months during the austral winter of 1978 when antarctica was girdled by sea ice as the satellite approached the continent from the ocean the altimeter obtained very strong reflections from the sea ice and it continued to measure ranges to the sea ice even for a short time after passing over the ice front the measured ranges are oblique distances to the nearest portion of sea ice and the sequence of oblique ranges gives the position of the sea ice along the ice front after the satellite crossed the ice front travelling sea ward oblique ranges were measured to the nearest portion of ice shelf examples are given from seasat orbits crossing the amery and fimbul ice shelves the entire seasat data set provides an opportunity for mapping most of the east antarctic coastline to an absolute horizontal accuracy of 0 1 1 km the resulting map would effectively be an instantan eous view of the ice margin requiring no adjustment for ice movement during the survey period introduction the radar altimeter aboard seasat was designed to measure ranges to the ocean surface it transmitted short radar pulses with a beam width to 3 db attenu ation of 1 6 degrees of arc pulse length was 3 125 ns equivalent to 1 m and pulse rate was 1 020 s l ranges were obtained from the time delay between pulse transmission and receipt of the reflected pulse return energy was measured during a data acquisition window of about 188 ns duration high resolution was achieved by dividing this window into 63 time gates in operation the altimeter initially undertook a low resolution search for the ocean surface and then located the center of the high resolution acquisition window to coincide with the time of the return pulse leading edge there after the altimeter maintained track of the ocean present address california institute of technology pasadena california 91109 usa surface by continually adjusting the timing of the acquisition window as dictated by the rate of change of previous measured ranges the tracking worked well over the oceans where measured ranges changed very slowly however over sloping or undulating terrain the servo tracking circuit was not sufficiently agile to monitor the rapidly changing ranges and the alti meter frequently lost track of the return pulse this resulted in short periods usually a few seconds when no useful data were obtained nevertheless more than 600 000 surface elevations were measured on the portions of greenland and antarctica that lie between 72 latitude these are undergoing systematic correction for tracking errors and slope induced errors as part of the research program of the oceans and ice branch at the goddard space flight center zwally and others in press in this paper we show how radar altimetry data can be used to map ice sheet margins seaward ice fronts of the ice shelves and ice margins generally are associated with a step change in surface eleva tion mapping the ice front would be straightforward if the altimeter responded immediately to the abrupt change in surface elevation however the seasat radar altimeter responded slowly and usually lost track for a few seconds nevertheless the ice front position can be inferred accurately from the rela tionship between satellite position and measured range prior to losing track as the satellite passed over the ice front from seaward it continued to record the return signal from the sea or sea ice that lay within the seaward portion of the beam limited radar footprint radius approximately 11 km consequently the measured range was the oblique distance from the satellite to the sea surface next to the ice front the variation of measured distance with time gives the ice front position to within 100 to 1000 m depending on data quality and the length of time during which oblique ranges were measured in addition the data give an indication of the shape of the nearby ice front as related to the orbit track when the satellite crossed the ice front travel ling seaward oblique ranges were similarly obtained jet propulsion laboratory 4800 oak grove drive

enhanced zoogeomorphological processes in north africa in thehuman impacted landscapes of the anthropocene abstract new zoogeomorphological features discovered in dryland landscapes of northern africa reflect human animal agency since prehistory and attest to complex networked activities over great distances we discuss the role of zoogeomorphology in shaping earth s surface since the beginning of the anthropocene the timeframe when natural processes shifted and landscape evolution became more human dominated we focus on contexts in arid and semiarid lands of northern africa which are metastable sensitive ecosystems that are prone to modifications triggered by climatic and anthropogenically forced factors studying the geoarchaeological record in context of landscape impact and animal procurement by people throughout antiquity is important for reconstructing domestication and husbandry of cattle sheep and goats in this region among the features we recognize in association with transhumance pastoralism and herding are trails trackways footholds animal daybeds stables animal dwellings rockshelters game blinds and monuments to name a few related activities with landscape scale impacts include herding transport corralling and browsing of cattle bos sp goats and sheep ovicaprines as well as pasturage activities like cropping fire setting and manuring these activities were disturbances that affected surface processes like erosion and dust mobilization as well as reduced vegetation and ecosystems productivity in dryland africa and especially in the sahara intensive herding led to the alteration of the pristine aspects of bare rock surfaces and of the stone desert pavement i e the hamada many regions preserved evidence of middle late holocene animal daybeds trampled areas and barren tracks and trails we suggest that human and herd animal activities affected geomorphic surfaces that affected slope stability intensified erosion and dust mobilization and enhanced dust export from the african continent offshore we reinterpret the increased dust emission from north africa during the mid holocene at the end of the african humid period as has been interpreted from ocean cores aridification of the green sahara followed the insolation forced monsoonal maximum and was exacerbated by human animal activities across the sahara and the sahel we argue that the spread of human activities and intensive husbandry of cattle and caprines goat and sheep in this region significantly influenced the geomorphic stability ecosystem and landscape sustainability in a comparable manner of overuse observed in present day arid and marginal environments where pastoral overgrazing pressure increases erosion processes and enhances dust mobilization we suggest that human animal activities have amplified dust generation from the north african continental interior since 7 ka bp this evidence of prehistoric human impacts on surface processes in north africa supports arguments for an early beginning of the anthropocene

an overview of seasonal snow metamorphism the grains in seasonal snow undergo rapid and radical transformations in size shape and cohesion these grain characteristics affect all of the basic properties of snow snow is characterized as either wet or dry depending on the presence of liquid water wet snow is markedly different at low and high liquid contents dry snow is characterized as either an equilibrium form or a kinetic growth form that is it is either well rounded or faceted of course many snow grains display either transitional features between two of these categories or features which arise from other processes snow is classified depending on the dominant processes of its metamorphism