importance of small scale paleo oceanographic conditions to interpret changes in size of california mussel mytilus californianus late holocene santa cruz island california abstract several authors have highlighted the difficulties in disentangling human from natural effects when studying shellfish foraging strategies and archeo malacogical records in coastal settings one of the reasons for this difficulty is the lack of understanding of small scale oceanographic conditions and their influence on coastal and marine species used by people in the past the present study evaluated the influence of environmental conditions on shellfish harvesting during the late holocene around santa cruz island southern california considering small scale nearshore oceanographic variability around the island and its effect on m californianus main shellfish species exploited through prehistory along the coast of california fluctuations in size and abundance of m californianus shells through time and local past sea surface temperature sst values from oxygen isotope analysis of mussel shells are correlated throughout the stratigraphy of two shell midden sites 2200 500 cal b p nearby coasts with different paleo oceanographic characteristics despite the fact that human harvesting seems to have been the main force shaping length and availability of m californianus no clear evidence of human pressure was found on archaeological mussel assemblages results also show that fluctuations in regional sst records santa barbara basin marine core do not represent local sst variations oxygen isotope analyses on mussel shells especially if the archaeological site is located on a coast exposed to strong and consistent upwelling activity by re evaluating human impact on mussel beds during the late holocene around santa cruz island the research presented here demonstrates the importance of considering small scale nearshore oceanography for understanding the archaeological evidence of prehistoric human foraging on important intertidal shellfish species

young late amazonian near surface ground ice features near the equator athabasca valles mars abstract a suite of four feature types in a 20 km 2 area near 10 n 204 w in athabasca valles is interpreted to have resulted from near surface ground ice these features include mounds conical forms with rimmed summit depressions flatter irregularly shaped forms with raised rims and polygonal terrain based on morphology size and analogy to terrestrial ground ice forms these athabascan features are interpreted as pingos collapsing pingos pingo scars and thermal contraction polygons respectively thermal infrared mapping spectrometer themis data and geological features in the area are consistent with a sedimentary substrate underlying these features these observations lead us to favor a ground ice interpretation although we do not rule out volcanic and especially glaciofluvial hypotheses the hypothesized ground ice that formed the mounds and rimmed features may have been emplaced via the deposition of saturated sediment during flooding an alternative scenario invokes magmatically cycled groundwater the ground ice implicit in the hypothesized thermal contraction polygons may have derived either from this flooding ground water or from atmospheric water vapor the lack of obvious flood modification of the mounds and rimmed features indicates that they formed after the most recent flood inundated the area analogy with terrestrial pingos suggests that ground ice may be still extant within the positive relief mounds as the water that flooded down athabasca valles emerged via a volcanotectonic fissure from a deep aquifer any extant pingo ice may contain evidence of a deep subsurface biosphere

global chemical erosion during the last glacial maximum and the present sensitivity to changes in lithology and hydrology geographically based calculations for 18 000 years ago 18 ka and today were made to examine the potential effects on terrestrial chemical erosion of changes in lithology and hydrology on glacial interglacial timescales runoff fields were derived from general circulation model predictions of precipitation minus evaporation then global lithologic maps were prepared so that empirical relationships for runoff versus bicarbonate flux for different rock types could be used to calculate global chemical erosion rates assuming that significant chemical erosion does not occur beneath ice sheets we find that chemical erosion in ice free areas at 18 ka was only slightly greater than today this result arises because the amount of land covered by ice sheets is roughly compensated for by exposed shelf areas and because there is little difference in global runoff the small 20 increase in the global chemical erosion rate during glacial conditions is due to exposure on the shelves of a relatively high proportion of carbonates which weather faster than average data on glacial interglacial movements of the calcite compensation depth ccd are inconclusive but seem to indicate little change whereas even a 20 increase in the riverine bicarbonate flux should cause an observable deepening if the ccd did not indeed change then our predicted increase in the bicarbonate flux from land during glaciations would have to be accommodated by other means such as increased carbonate productivity about half of the observed decrease in atmospheric pco2 at 18 ka could be explained if increased silicate chemical erosion accompanied increased total chemical erosion in ice free areas consideration of the maximum possible effect of meltwater at ice margins leads to an 80 increase in the global chemical erosion rate at 18 ka such an increase would lead to a larger and faster drop in atmospheric pco2 but also to an excessive deepening of the global ccd this scenario seems unrealistic our results are contrary to interpretations of a much higher silicate chemical erosion rate during glaciations based on recently published records of quaternary marine sr isotopic ratios therefore if these records are indeed globally representative and entirely due to increased silicate chemical erosion as opposed to changes in source areas or hydrothermal inputs then other factors such as a shift in the global weathering regime which we do not explicitly consider here may be involved sensitivity tests show that considering spatial heterogeneities in lithology and runoff leads to lower predictions of global chemical erosion rates than what one would obtain by considering only global averages in a non spatially resolved calculation

human responses to middle holocene climate change on california s channel islands abstract high resolution archaeological and paleoenvironmental records from california s channel islands provide a unique opportunity to examine potential relationships between climatically induced environmental changes and prehistoric human behavioral responses available climate records in western north america 7 3 8 ka indicate a severe dry interval between 6 3 and 4 8 ka embedded within a generally warm and dry middle holocene very dry conditions in western north america between 6 3 and 4 8 ka correlate with cold to moderate sea surface temperatures sst along the southern california coast evident in ocean drilling program odp core 893a b santa barbara basin an episode of inferred high marine productivity between 6 3 and 5 8 ka corresponds with the coldest estimated ssts of the middle holocene otherwise marked by warm low productivity marine conditions 7 5 3 8 ka the impact of this severe aridity on humans was different between the northern and southern channel islands apparently related to degree of island isolation size and productivity of islands relative to population fresh water availability and on going social relationships between island and continental populations northern channel islanders seem to have been largely unaffected by this severe arid phase in contrast cultural changes on the southern channel islands were likely influenced by the climatically induced environmental changes we suggest that productive marine conditions coupled with a dry terrestrial climate between 6 3 and 5 8 ka stimulated early village development and intensified fishing on the more remote southern islands contact with people on the adjacent southern california coast increased during this time with increased participation in a down the line trade network extending into the western great basin and central oregon genetic similarities between middle holocene burial populations on the southern channel islands and modern california uto aztecan populations suggest middle holocene movement of people at this time from southern california desert environs westward to the southern islands a migration perhaps stimulated by increased continental aridity

climatic and geometric controls on the global distribution of surge type glaciers implications for a unifying model of surging financial support was provided by the conocophillips lundin northern area program project crios

stratigraphical and morphological evidence for pingo genesis in the cerberus plains rootless debris cones or pseudocraters occur in platy patterned ground throughout the cerberus plains of mars and are thought to represent the products of explosive magma ice interaction lanagan et al 2001 geophys res lett 28 2365 2368 fagents et al 2002 in smellie j l chapman m g eds volcano ice interaction on earth and mars in geol soc spec publ vol 202 pp 295 317 requiring lava and water interspersed they are central to theories of multiple magmatic and aqueous flood events burr et al 2002 icarus 159 53 73 berman d c hartmann w k 2002 icarus 159 1 17 and widespread sheet volcanism keszthelyi et al 2000 j geophys res 105 15027 15049 in the region during the late amazonian a region reported to have been occupied by water bodies ranging from lakes to oceans scott et al 1995 map of mars showing channels and possible paleolake basins usgs miscellaneous investigations series map i 2461 1 30 000 000 the nature of the platy substrate is the subject of debate with evidence given for lava keszthelyi et al 2000 j geophys res 105 15027 15049 plescia j b 2003 icarus 164 79 95 and ice brakenridge g r 1993 lunar planet sci xxiv part 1 175 176 rice et al 2002 lunar planet sci xxxiii abstract 2026 murray et al 2005 nature 434 352 355 the superposition relationships of cones and platy deposits in the channels of the athabasca valles precludes a magmatic origin indicating later formation as permafrost mounds or pingos with implications for geologically recent flood volcanism age constraints on young surfaces and recent climate change on mars

climate and vegetation change during the late pleistocene and early holocene in sakhalin and hokkaido northeast asia pollen data from marine isotope stage mis 3 to the early holocene in kenbuchi central hokkaido and khoe central west sakhalin were reviewed and the climate and vegetation compared changes in climate and vegetation during the examined time period in the two regions resembled each other except for latitudinal differences in forest composition during mis 3 cold evergreen needle leaf forests expanded under a cool moist climate the climate then rapidly changed to cool and dry around the mis 3 mis 2 boundary mis 2 was characterized by millennial scale variability in climate heinrich event 2 h2 24 21 ka the last glacial maximum lgm and h1 between 17 and 13 ka were characterized by the dominance of larix and pinus in cold deciduous forests in kenbuchi grassland composed of alpine elements developed in both regions climate was coldest and driest during h1 the bolling allerod interstadial 14 12 ka was characterized by a maritime climate with an abundance of betula in the coastal region the younger dryas 11 5 ka was a minor event in east asia during the pre boreal period around 12 ka cold evergreen needle leaf picea betula forest and mixed quercus abies forest developed in two different regions under a warm moist climate

little ice age glacial activity in the mt waddington area british columbia coast mountains canada the establishment of fourteen little ice age lia glacier chronologies in the mt waddington area led to the development of an extended history of glacial activity in this portion of the southern british columbia coast mountains canada the glaciers were located within four different mountain ranges and were of varying size and aspect dendrochronological and lichenometric techniques were used to provide relative age estimates of moraines formed as glacier termini retreated from advanced positions evidence for pre lia glacial events is best preserved at tiedemann glacier where the oldest glacial advances date to a d 620 and 925 933 soil covered and well vegetated moraines built at cathedral pagoda and siva glaciers date to between a d 1203 and 1226 following this event moraines constructed at ragnarok siva and cathedral glaciers in the mid 14th century suggest glaciers in the region underwent a period of downwasting and retreat before readvancing the majority of moraines recorded in the mt waddington area describe late lia glacial events shown to have constructed moraines that date to a d 1443 1458 1506 1524 1562 1575 1597 1621 1657 1660 1767 1784 1821 1837 1871 1900 1915 1928 and 1942 1946 over the last 500 years these moraine building episodes were shown to occur on average every 65 years and suggest there has been prolonged synchronicity in the glaciological response to persistent climate forcing mechanisms nevertheless our analysis suggests that local factors such as aspect and size play an important role in individual glacial response notably ice termini of medium size glaciers facing eastwards showed a quicker response to climatically induced mass balance changes resume l historique de quatorze glaciers de vallee de la region du mont waddington sud de la chaine cotiere de colombie britannique canada durant le petit ge glaciaire pag fut evalue par l utilisation de techniques dendrochronologiques et lichenometriques procurant un ge minimum pour la formation des moraines laterales et frontales multiples les glaciers a l etude d aspect et de taille differents furent selectionnes a partir de quatre chaines de montagnes les evenements qui predatent le pag sont le mieux preserves sur le site du glacier tiedemann ou les plus vieilles avancees glaciaires date de a d 620 et 925 933 des moraines presentant une pedogenese avancee et recouvertes d une dense couverture vegetale furent datees entre a d 1203 et 1226 des moraines construites dans le milieu du 14 e siecle par les glaciers ragnarok siva et cathedral suggerent que les glaciers de la region se sont retires pour par la suite reavancer la majorite des moraines datees le furent vers la fin du pag soit en a d 1443 1458 1506 1524 1562 1575 1597 1621 1657 1660 1767 1784 1821 1837 1871 1900 1915 1928 et 1942 1946 au cours des 500 dernieres annees en moyenne 65 annees separent les differents episodes glaciaires ce qui suggerent un synchronisme des reponses glaciaires aux mecanismes climatiques des donnees preliminaires suggerent que l orientation et la taille des glaciers jouent un role important dans la reponse individualiste des glaciers en fait les terminus glaciaires des moyens glaciers d orientation est semblent repondre plus rapidement a un ajustement de volume interne glaciaire

delta o 18 of fissurella maxima as a proxy for reconstructing early holocene sea surface temperatures in the coastal atacama desert 25 degrees s abstract fissurella maxima is a keyhole limpet that is abundant and well preserved in archaeological shell midden sites along the coast of chile making it an appropriate species to use for reconstructions of past sea surface temperature sst in the present study we evaluate the potential of f maxima shells as a proxy of sst by analysing 18o of modern shells collected alive from the atacama desert area of taltal 25 s and archaeological shells from two early holocene rockshelter sites 224a and paposo norte 9 reconstructed sst from modern f maxima shells were related to sst obtained from in situ thermometers supporting the use of this mollusc species as a paleotemperature archive mean sst reconstructed from early holocene archaeological shells 14 13 c was 2 86 c cooler than mean temperature recorded in modern shells 16 99 c mean sst reconstructed from modern shells was 1 04 c warmer than the mean temperature of in situ thermometers 15 95 c hence the paleo sst data from archaeological sites 224a and paposo norte 9 enrich the early holocene nearshore paleoceanographic scenario of the pacific coast of south america with mean sst cooler than present day sst our results validate the use of f maxima shells as a sst proxy and contribute to a better understanding of the latitudinal distribution of the coastal upwelling regime during the early holocene temporal changes in the structure of the humboldt current along the holocene and its influence on human adaptation through the prehistory of south america

late holocene vegetation and climate change at moraine bog tiedemann glacier southern coast mountains british columbia moraine bog lies just outside the outermost lateral moraine of tiedemann glacier in the southern coast mountains of british columbia a sediment core taken from the wetland was analyzed for pollen magnetic susceptibility and loss on ignition to reconstruct changes in vegetation and climate during the late holocene vegetation changed little between about 3500 and 2400 14 c years bp a period of local disturbance marked by deposition of a silty clay bed and increases in alnus pollen likely reflecting cooler moister conditions coincides with an extensive holocene advance of tiedemann glacier about 2400 14 c years bp warm dry conditions between about 1900 and 1500 14 c years bp are sug gested by peak values of pseudotsuga pollen and increasing nuphar sclereids the latter suggests lowered water levels this period coincides with a time of drought and increased fire frequency in the southernmost coast mountains about 1300 14 c years bp the forest became more coastal in composition with abundant tsuga heterophylla and abies a n increase in tsuga mertensiana pollen suggests the onset of cool and wet conditions by ca 500 14 c years bp coincident with the little ice age the record of inferred climate change at moraine bog is broadly synchronous with other paleoclimate records from the coast mountains and at the centennial scale with records elsewhere in the world

paleomagnetism and 40ar 39ar ages from volcanics extruded during the matuyama and brunhes chrons near mcmurdo sound antarctica maps of virtual geomagnetic poles derived from international geomagnetic reference field models show large lobes with significant departures from the spin axis these lobes persist in field models for the last few millenia the anomalous lobes are associated with observation sites at extreme southerly latitudes to determine whether these features persist for millions of years paleomagnetic vector data from the continent of antarctica are essential we present here new paleomagnetic vector data and ar 40 ar 39 ages from lava flows spanning the brunhes and matuyama chrons from the vicinity of mcmurdo sound antarctica oriented paleomagnetic samples were collected from 50 lava flows by e mankinen and a cox in the 1965 1966 austral summer season preliminary data based largely on the natural remanent magnetization nrm directions were published by mankinen and cox 1988 we have performed detailed paleomagnetic investigations of 37 sites with multiple fully oriented core samples to investigate the reliability of results from this unique sample collection of these only one site fails to meet our acceptance criteria for directional data seven sites are reversely magnetized the mean normal and reverse directions are antipodal the combined mean direction has d over bar 12 i over bar 86 alpha 4 kappa 37 and is indistinguishable from that expected from a gad field we obtained reproducible absolute paleointensity estimates from 15 lava flows with a mean dipole moment of 49 zam 2 and a standard deviation of 28 zam 2 ar 40 ar 39 age determinations were successfully carried out on samples from 18 of the flows our new isotopic ages and paleomagnetic polarities are consistent with the currently accepted geomagnetic reversal timescales

high energy sedimentation creag aoil spean bridge scotland implications for meltwater movement and storage during loch lomond stadial younger dryas ice retreat this paper examines the origin and significance of loch lomond stadial younger dryas gravel deposits at creag aoil spean bridge scotland sedimentation into ice dammed lakes in glen roy and glen spean associated with shorelines at 260 m 325 m and 350 m is well documented yet little is known about later lower level lakes near spean bridge excavations on the northern flanks of the lundy channel revealed exposures into a 35 40 m thickness of sand and gravel these sediments reflect deposition in a subaqueous environment experiencing repeated short lived periods of high energy subaerial deposition deformation structures within subaqueous deposits are associated with at least two ice push events this study presents new evidence for the existence of ice dammed lakes at elevations between 260 m and 113 m and for periodic jokulhlaups draining southwest via the lundy channel active glacier ice associated with the deposits flowed northwest to southeast driving meltwater across the great glen to the lundy channel glacier retreat was punctuated by periodic minor readvances progressive ice retreat was accompanied by ice thinning and changes in ice flow direction and subglacial meltwater routing these findings add to knowledge of loch lomond stadial deglaciation around spean bridge and have implications for our understanding of lacustrine glacier margins during deglaciation copyright 2003 john wiley sons ltd keywords ice dammed lake subaqueous outwash jokulhlaups ice push structures scotland

seasonal and interannual variation in santa barbara basin water temperatures observed in sediment trap foraminiferal mg ca 1 we have generated a santa barbara basin sediment trap mg ca record to evaluate culture based calibration equations for the temperate subpolar planktonic foraminiferal species globigerina bulloides and neogloboquadrina pachyderma dextral g bulloides and n pachyderma mg ca are significantly correlated with seasonal variations in temperature of the near surface and subthermocline depths respectively the average deviation between mg based and 18o based temperature estimates is 0 6 c for g bulloides and 0 8 c for n pachyderma differences between mg derived temperatures and instrumental temperatures may be due to cleaning methods environmental factors such as seasonal variations in foraminiferal depth habitats or possible secondary effects on mg ca core top mg ca of both g bulloides and n pachyderma is in excellent agreement with average values from the sediment trap lending strong support for the interpretation of downcore mg ca from these species as annual average near surface and thermoclinal temperatures

neoglacial lake alsek lowell glacier a large valley glacier in the st elias mountains of southwestern yukon territory advanced across alsek valley and blocked south flowing alsek river many times during the neoglacial interval the resulting lake termed neoglacial lake alsek extended east of the front of the st elias mountains and inundated parts of dezadeash valley that presently are populated lake alsek at its maximum was about 200 m deep at the glacier dam and over 100 km long staircase flights of beaches wave cut benches layers of driftwood and thin lacustrine sediments provide evidence of the former lake giant dunes and flood terraces on the floor of alsek valley indicate that the lake emptied catastrophically when the lowell glacier dam failed several phases of lake alsek have been identified each was preceded and followed by intervals during which the lake was empty and the present southward drainage pattern in alsek valley prevailed historical records radiocarbon and tree ring dates on driftwood and r

high latitude patterned grounds on mars classification distribution and climatic control patterned grounds such as polygonal features and slope stripes are the signature of the presence of ground ice and of temperature variations in cold regions on earth identifying similar features on mars is important to understand its past climate as well as the ground ice distribution in this study young patterned grounds are classed and mapped from the systematical analysis of mars observer camera high resolution images these features are located poleward of 55 latitude which fits the distribution of ground ice found by the neutron spectrometer onboard mars odyssey thermal contraction due to seasonal temperature variations is the predominant process of formation of polygons formed by cracks which sizes vary from 15 to 300 m the small 40 m widespread polygons are very recent and degraded by the desiccation of ground ice from the cracks which enhances the effect of ice sublimation the large polygons 50 to 300 m located only around the south co2 polar cap indicate the presence of ground ice and thus outline the limit of the co2 ice cap they could be due to the blanketing of water ice deposits by the advances and retreats of the residual co2 ice cap during the last thousand years large 50 250 m and homogeneous polygons similar to ice wedge polygons hillslope stripes and solifluction lobes may indicate that specific environments such as crater floors and hillslopes could have been submitted to freeze thaw cycles possibly related to higher summer temperatures in periods of obliquity higher than 35 these interpretations must be strengthened by higher resolution images such as those of the hirise mission of the mars reconnaissance orbiter because locations with past seasonal thaw could be of major interest as potential landing sites for the phoenix mission

estimates of the magnitude of glacier outburst floods from lake donjek yukon territory canada lake donjek was a large reservoir formed when donjek glacier dammed donjek river although the basin is empty at present a minor advance of donjek glacier could again dam the river and impound app

draining and filling of ice dammed lakes at the terminus of surge type dan zhur donjek glacier yukon canada recent surges of dan zhur donjek glacier have formed lakes at the glacier terminus that have drained catastrophically resulting in hazards to people and infrastructure downstream here we use ai

late glacial and holocene landscapes of central beringia abstract new palynological and sedimentological data from st lawrence island present a rare view into late glacial and holocene environments of the central bering land bridge the late glaciation was a time of dynamic landscape changes in south central beringia with active thermokarst processes including the formation and drainage of thaw lakes the presence of such a wet unstable substrate if widespread probably would have had an adverse impact on food sources and mobility for many of the large mammal populations the establishment of betula shrub tundra on the island suggests late glacial summers that were warmer than present consistent with regional paleoclimatic interpretations however the increasing proximity to the bering sea as postglacial sea levels rose modified the intensity of warming and prevented the establishment of deciduous forest as found in other areas of beringia at this time the mid to late holocene is marked by more stable land surfaces and development of sphagnum and cyperaceae peat deposits the accumulation of organic deposits decline of shrub betula and decrease in thermokarst disturbance suggest that conditions were cooler than the previous a recent decline in peat accumulation at the study sites may relate to local geomorphology but similar decreases have been noted for other arctic regions

circular cryogenic structures from the hirnantian deglaciation sequence anti atlas morocco abstract more than a hundred circular structures are observed at the topmost part of the late ordovician glaciogenic record in the central anti atlas southern morocco the structures were formed in the outer glaciated platform and characterize the hirnantian deglaciation sequence they are distributed within a 20 meter thick stratal interval and at present relicts of them still occupy several square kilometers in map view the circular to ovoidal structures which comprise fluvial sandstone beds and are sealed by shallow marine strata occur in closely spaced clusters they are 13 320 m in diameter with half of them in the 40 90 m range stratal wedging and bending as well as extensional and reverse centimeter to meter scale soft sediment fractures demonstrate that formation processes initially involved synsedimentary uplifts subsequent subsidence and collapse resulted in the formation of circular structures which essentially correspond to localized depocenters in the form of small scale sag basins regarding the overall deglaciation context the circular structures are interpreted as periglacial in origin with vertical movements ascribed to cryogenic processes involving the growth and then decay of bodies of segregation ice the size and diameter distributions which are comparable to the recent younger dryas and current lithalsa structures suggest that hirnantian circular features relate to similar genetic processes and can be referred to as lithalsa like structures a conceptual emplacement model is proposed which considers that a long term sedimentary aggradation over the fluvial plain prevented any significant landforms either a bump or a depression from being expressed at the depositional surface at the time of the circular structure formation the hirnantian lithalsa like structures constitute firm evidence for a late ordovician discontinuous permafrost during the deglaciation stage assuming that the late quaternary meridional zonation is valid it suggests the anti atlas was at latitudes in the 55 65 interval if combined with the rare pingo structures described in the literature which attest that coeval continuous permafrost conditions occurred at higher paleo latitudes the moroccan circular structures provide evidence for an alternate south pole position during the hirnantian 444 ma

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

dating martian climate change abstract geological evidence indicates that low latitude polygonally patterned grounds on mars generally thought to be the product of flood volcanism are periglacial in nature and record a complex signal of changing climate by studying the martian surface stratigraphically in terms of the geometrical relations between surface landforms and the substrate rather than genetically by form analogy with earth we have identified dynamic surfaces across one fifth of martian longitude new stratigraphical observations in the elysium amazonis plains have revealed a progressive surface polygonisation that is destructive of impact craters across the region this activity is comparable to the climatically driven degradation of periglacial landscapes on earth but because it affects impact craters the martian chronometer it can be dated here we show that it is possible to directly date this activity based on the fraction of impact craters affected by polygon formation nearly 100 of craters of all diameters are superposed by polygonal sculpture considering the few 100 ma age of the substrate this suggests that the process of polygon formation was active within the last few million years surface polygonisation in this region often considered to be one of the signs of young plains forming volcanism on mars is instead shown to postdate the majority of impact craters seen we therefore conclude that it is post depositional in origin and an artefact of thermal cycling of near surface ground ice stratigraphically controlled crater counts present the first way of dating climate change on a planet other than earth a record that may tell us something about climate change on our own planet parallel climate change on these two worlds an ice age mars coincident with earth s glacial quaternary period might suggest a coupled system linking both we have previously been unable to generalise about the causes of long term climate change based on a single terrestrial example with the beginnings of a chronology for climate change on our nearest planetary neighbour we can

characteristics of the last five surges of lowell glacier yukon canada since 1948 field observations aerial photographs and satellite images are used to reconstruct the past surges of lowell glacier yukon canada since 1948 based on the timing of terminus advances a total of five surges occurred over this time each with a duration of 1 2 years the time between successive surges ranged from 12 to 20 years and appears to have been shortening over time the relatively short advance and quiescent phases of lowell glacier together with rapid increases in velocity during surges suggest that the surging is controlled by a hydrological switch the 2009 10 surge saw ablation area velocities increase by up to two orders of magnitude from quiescent velocities and the terminus increase in area by 5 1 km 2 and in length by up to 2 85 km this change in area was the smallest since 1948 and follows the trend of decreasing surge extents over time this decrease is likely driven by a strongly negative surface mass balance of lowell glacier since at least the 1970s and means that the current town site of haines junction is very unlikely to be flooded by damming caused by any future advances of the glacier under the current climate regime

oxygen isotopic analysis of archaeological shells to detect seasonal use of wetlands on the southern pacific coast of mexico abstract oxygen isotopic ratios in modern and archaeological marsh clam shells polymesoda radiata from the acapetahua estuary in southwestern mexico record large scale salinity fluctuations caused by alternating wet and dry seasons thus prehistoric patterns of rainfall can be reconstructed and the season of molluscan death can be estimated changes in the oxygen isotopic patterns preserved in marsh clam shells from late archaic period c 3000 1800 bc archaeological deposits indicate that the season of shellfish harvesting changed dynamically through time in this region based on this study and other lines of archaeological evidence we argue that hunter gatherers during the early stages of the late archaic period visited locations in the littoral zone throughout the year with a focus during dry season months through the late archaic period a general trend occurred toward wet season use of these locations this culminated at the end of the late archaic period with the exclusive use of the littoral zone during wet season months these data indicate a fundamental shift in the way these estuarine locations were being used we argue that people living in this region altered their overall subsistence strategy during the late archaic period due to scheduling conflicts that occurred with the adoption of maize agriculture

red abalone collecting and marine water temperature during the middle holocene occupation of santa cruz island california abstract oxygen isotope values derived from prehistoric mussel mytilus californianus shell calcite are used to determine whether sea surface temperatures in the vicinity of the punta arena site ca scri 109 on santa cruz island california were cooler than present between 6300 and 5300 cal bp this site and others in the western sector of the island dating to this period are distinctive because of the presence of large red abalone haliotis rufescens shells a species that historically has been subtidal around santa cruz and the other northern channel islands comparison of temperature values derived from archaeological shells with those from modern mussel shells along with water temperatures derived from satellites indicates that waters were cooler during the 6300 to 5300 cal bp period these results are consistent with a previous study and support the interpretation that collection of red abalone during the 6300 5300 cal bp period was partly the result of cooler water temperatures that made this large mollusk more available to foragers in the intertidal or shallow subtidal zone

factors influencing periglacial fluvial morphology in the northern european russian tundra and taiga the influence of geology discharge regime slope vegetation type vegetation density and permafrost conditions on periglacial channel morphology has been investigated in the usa catchment northern european russia rivers are dominated by meandering or anabranching plan forms and rarely show braiding characteristics despite a nival discharge regime the presence of discontinuous permafrost and locally steep slopes the dense vegetation cover is an important factor in determining the meandering morphology as it inhibits the sediment supply and hence braided conditions differences in vegetation types taiga in the south tundra in the north have no effect on channel plan form copyright 2002 john wiley sons ltd

late holocene sea temperatures along the central california coast mussel shells from central california coastal archaeological sites record changes in sea surface temperatures in the past 2000 years water temperatures inferred from oxygen isotopes in the shells were about 1 c cooler than present and stable between 2000 and 700 yr ago between about 700 and 500 yr ago seasonal variation was greater than present with extremes above and below historic levels water temperatures were 2 3 c cooler than today 500 300 yr ago the interval of variable sea temperatures 700 500 yr ago partially coincided with an interval of drought throughout central california a coincident disruption in human settlement along the coast suggests movements of people related to declining water sources quantities of fish bone in central coast middens dating to this same period are high relative to other periods and the remains of northern anchovies a species sensitive to changing oceanographic conditions are also abundant the continued use of local fisheries suggests that changes in settlement and diet were influenced more by drought than by a decrease in marine productivity as fish provided a staple during an interval of low terrestrial productivity

oxygen isotope seasonality in a temperate estuarine shell midden a case study from ca ala 17 on the san francisco bay california abstract seasonality determination using stable oxygen isotope 18 o analyses in archaeological mollusk shell has been largely limited to aquatic settings where one of the two factors that control shell 18 o water 18 o or salinity and temperature is assumed to be constant open coastal marine environments reflect the former situation and tropical estuaries constitute the latter in an effort to expand stable isotope seasonality to an ecological setting where neither variable remains constant we present a model of annual shell 18 o cycle of aragonite deposition derived from instrumental data on salinity and temperature from san francisco bay california the predicted range of modeled shell 18 o is consistent with observed 18 o values in prehistoric and modern shells when local conditions are considered measurements of 18 o taken at 0 mm and 2 mm from the terminal growth margin were made on 36 archaeological specimens of macoma nasuta from a late holocene hunter gatherer site ca ala 17 and season of collection was inferred using the shell 18 o model we conclude that shellfish exploitation occurred through the year with the exception of fall which may indicate scheduling conflicts with acorn harvesting or other seasonally abundant resources elsewhere the model supports the feasibility of stable isotope seasonality studies in temperate estuaries provided that instrumental records are available to quantify the relevant water conditions at appropriate spatial and temporal scales