climate fluctuations of the weddell sea and its surroundings in a transient climate change scenario the response of the weddell sea and antarctic peninsula to anthropogenic forcing simulated by a global climate model is analyzed the model despite its low resolution is able to capture several aspects of the observed regional pattern of climate change a strong warming and depletion of the sea ice cover in the western weddell sea contrasts with a slight cooling and a sea ice extension in the eastern weddell sea this simulated long term climate change is modulated by interdecadal variability but also affected by some abrupt regional changes in the oceanic mixed layer depth between 1960 and 2030 a reorganization of the deep convection activity in the weddell sea sustains the opposition between the eastern and western weddell sea the deep convection collapses in the western weddell sea in the 2030s the sea ice retreat trend is then followed by an increase of the sea ice cover in the western weddell sea in the eastern weddell sea another abrupt collapse of the deep convection activity occurs around 2080 this event is followed by a rapid cooling and sea ice extension during the next 20 years most of the surface changes are associated with large scale atmospheric circulation changes that project on the dominant mode of natural variability but also with oceanic convection and circulation changes

soil formation in coastal continental antarctica wilkes land recent antarctic soil studies suggest that in terrestrial ecosystems of coastal regions soil formation and chemical weathering occur to a greater extent than predicted by former models this paper summarizes pedogenic findings from the casey area on the coast of east antarctica and presents a proposal of soil formation sequences on a large scale data base soil organic matter accumulation and podzolization are important soil forming processes in regions outside the antarctic cold desert of the ross sea section the results suggest some correlations between the soil development and vegetation patterns nutrient supply in soil is affected by the high contents and availability of nitrogen phosphorus potassium and magnesium due to an input by seabirds the us soil taxonomy 8th edn gelisol order and the recently adopted world reference base for soil resources wrb cryosol soil group suggest a different understanding of impact of permafrost on soil formation according to the wrb and the us soil taxonomy organic permafrost affected soils are not cryosols but gelisols lithic haplorthels as well as haploturbels and to some extent aquaturbels and organic gelisols are suggested to be representative of the casey area in addition podzols occur to a great extent however the recent keys to soil taxonomy do not reflect the podzolization process in an adequate way and a classification is not possible according to a former version these soils would be lithic or pergelic haplocryods whereas according to the newly adopted wrb system these soils are spodic haplic cryosols

distribution of soil taxa in antarctica a preliminary analysis abstract only 0 35 49 500 km2 of antarctica is ice free these areas are scattered around the periphery of the continent and in interior mountain ranges making soil mapping difficult here we compile the results of mapping in five of the nine ice free areas that account for 79 of the ice free area on a reconnaissance scale and interpret the distribution of soil subgroups in soil taxonomy soils of antarctica are contained in four orders dominantly gelisols 84 13 suborders 27 great groups and 76 subgroups forty five percent of the soils of antarctica are orthels gelisols that show minimal cryoturbation and occur in dry landscape positions 38 of the soils are turbels showing cryoturbation and occurring in more moist landscape positions only 16 of the soils of antarctica lack permafrost in the control section and are classified as entisols gel great groups inceptisols gelepts suborder or gelaquepts or histosols gel great groups these soils occur almost exclusively along the western antarctic peninsula and at elevations below 30 m in the south shetland islands ssi and south orkney islands soi typic anhyorthels are the dominant soil subgroup comprising nearly 15 340 km2 or 31 of the soils in antarctica these soils occur primarily in central and southern victoria land but also occur in the thiel and pensacola mountains and shackleton range the prince charles mountains and the mountains of queen maud land typic haploturbels and typic anhyturbels occupy 14 and 13 of the soils of ice free regions of antarctica respectively most abundant in central victoria land they are common in most mountainous regions of antarctica the dominant soil processes of maritime antarctica are cryoturbation gleization melanization podzolization paludization and phosphatization in coastal east antarctica the major soil processes are rubification salinization calcification pervection and gleization the predominant soil forming processes in the transantarctic mountains include rubification salinization desert pavement formation and permafrost development measures of pedodiversity will be valuable in the selection of protected areas in antarctica

detection of temperature and sea ice extent changes in the antarctic and southern ocean 1949 96 abstract some global climate models indicate that future global warning from increased atmospheric concentrations of greenhouse gases may be greatest in the polar regions over areas where the sea ice cover is reduced the reduction of sea ice area in the models also gives rise to a strong positive feedback to the warming from the increase of atmospheric greenhouse gas concentration to date and the results of transient climate models an estimate of the expected change in the antarctic temperatures and sea ice extent can be made the existing data for observed changes in temperatures of the antarctic and southern ocean extending back to approx 1956 and approx 1945 respectively are analyzed along with the data of sea ice cover commencing in 1973 to examine the extent to which the anticipated warming trends and sea ice decrease are being realized in spite of high temporal and spatial variability the data does support small significant trends of temperature increase and sea ice cover decrease compatible in magnitude to those expected as a consequence of atmospheric greenhouse gas increase the seasonal cycle shows a delayed period of autumn winter sea ice growth with a longer period of open water this supports a mechanism for positive feedback between decreasing sea ice cover and increasing temperature

ordovician and silurian global geography presidential address delivered 3 may 2000 the main palaeocontinents during the early ordovician were gondwana laurentia baltica and siberia and a brief survey is made of their limits in the ordovician and silurian in particular gondwana by far the largest continent is analysed as including a core of south america antarctica africa australia and peninsular india and also the marginal terranes all of which show faunal links with but which may not have been attached to the core of avalonia ibero armorica and other european fragments turkey arabia and terranes from the far east including south china sibumasu and parts of australasia changes within the benthic faunas reveal that baltica whilst isolated in the early ordovician became united with avalonia by the end ordovician and the two with laurentia by the mid silurian to form the new supercontinent of laurussia island arcs had distinctive faunas during the ordovician in particular those in the iapetus between laurentia baltica and gondwana and the huge kipchak arc which ran from baltica to siberia as the period progressed the iapetus arcs became subducted beneath or accreted to their neighbouring cratons and the kipchak arc gradually collapsed to form the core of the new kazakhstania terrane gondwana drifted over the south pole and this movement is reflected in the cratonic benthic faunas particularly brachiopods and trilobites which in the early ordovician had formed a cline between the high latitude faunas of north africa and the equatorial faunas of the far east and australia but by the devonian lived in much warmer seas in southern europe and cooler waters in antarctica the faunas also reflect the global palaeoclimates which were warm in the early to mid ordovician and mid to late silurian but which were much colder in the half million year period of the late ordovician and early silurian particularly in the latest ordovician hirnantian ice age with its attendant widespread hirnantia brachiopod fauna the relative closeness of the chief palaeocontinents by the early silurian enabled brachiopod and trilobite larvae to cross the narrower oceans enabling a relatively cosmopolitan benthic fauna to be established over much of the globe apart from the cooler water higher latitude clarkeia fauna to the south and the tuvaella fauna to the north

diagenetic alteration of the structure and δ18o signature of palaeozoic fish and conodont apatite potential use for corrected isotope signatures in palaeoenvironmental interpretation abstract the oxygen isotopic compositions of carboniferous conodonts and fish microfossils ichthyoliths from identical samples were analysed in tandem in order to test whether these phosphatic media can be reliably used for palaeoclimatic reconstruction the structure of conodonts and of most ichthyoliths analysed are somewhat analogous to the enamel and dentine bone tissue respectively of modern mammals therefore the diagenetic susceptibilities of the taxa analysed may provide important clues to other palaeoclimatic studies utilising a variety of biogenic apatite thermal maturation indices and scanning electron microscopy were used to characterise the preservation of biogenic apatite despite a high conodont colour alteration index cai of 5 5 conodont elements appear to have been only mildly affected by diagenetic alteration in contrast ichthyoliths were commonly recrystallised and exhibited diagenetic apatitic overgrowths containing amorphous pyrolytic carbon interpreted as indicating that at least some overgrowth material derived from the original biogenic apatite diagenetic alteration has resulted in ichthyolith 18 o values being systematically lower by on average 2 9 1 0 3 relative to conodont apatite conodont samples yielded regionally correlatable isotope values which can be interpreted in terms of more palaeoenvironmentally sensible palaeotemperatures relative to ichthyolith values densely crystalline enamel like conodont elements are interpreted as the more robust phosphatic medium to preserve original isotopic compositions the strong correlation r 0 8 of the 18 o values of the more structurally pristine conodont and commonly recrystallised ichthyolith apatite indicates that i despite diagenetic lowering of absolute isotope values original palaeoenvironmental records may be preserved and ii diagenetic overprinting may result in a stable offset and therefore be correctable locally

thickness distribution of antarctic sea ice 1 ship based observations are used to describe regional and seasonal changes in the thickness distribution and characteristics of sea ice and snow cover thickness around antarctica the data set comprises 23 373 observations collected over more than 2 decades of activity and has been compiled as part of the scientific committee on antarctic research scar antarctic sea ice processes and climate aspect program the results show the seasonal progression of the ice thickness distribution for six regions around the continent together with statistics on the mean thickness surface ridging snow cover and local variability for each region and season a simple ridge model is used to calculate the total ice thickness from the observations of level ice and surface topography to provide a best estimate of the total ice mass including the ridged component the long term mean and standard deviation of total sea ice thickness including ridges is reported as 0 87 0 91 m which is 40 greater than the mean level ice thickness of 0 62 m analysis of the structure function along north south and east west transects revealed lag distances over which sea ice thickness decorrelates to be of the order of 100 300 km which we use as a basis for presenting near continuous maps of sea ice and snow cover thickness plotted on a 2 5 5 0 grid

studies of the antarctic sea ice edge and ice extent from satellite and ship observations abstract passive microwave derived ice edge locations in the antarctic are assessed against in situ observations from ships between 1989 and 2000 during the growth season march october the ship data agrees with satellite data very well with r2 values of 0 99 and 0 97 for the bootstrap and team algorithms respectively during the melt season november february the agreement is not so good with the passive microwave ice edge typically 1 2 of latitude south of the observations this is due to the low concentration and saturated nature of the ice and the r2 values for this period are 0 92 and 0 80 for the bootstrap and team algorithms respectively sensitivity studies show that such an offset in the summer ice edge location can cause significant errors in trend studies of the extent of sea ice cover in the southern ocean the passive microwave ice concentration at the ice edge observed by ship varies greatly averaging 14 for the team algorithm and 19 for the bootstrap comparisons between passive microwave data and sar landsat and ols data during the ice growth season show that while small scale details in ice edge location are lost the passive microwave data generally provide good and consistent representation of the higher resolution imagery

variations of surface air temperature and sea ice extent in the western antarctic peninsula region the western antarctic peninsula wap region has experienced a statistically significant warming trend during the past half century in addition a statistically significant anticorrelation between air temperatures and sea ice extent as determined from satellite passive microwave data during the past two decades has been observed for this region consistent with this strong coupling sea ice extent in the wap area has trended down during this period of satellite observations further much of the variability in both air temperature and sea ice in the wap region has been shown to be influenced by contrasting maritime warm moist and continental cold dry climate regimes as part of the palmer long term ecological research program the ecological influence of these trends and variability is being studied and effects have already been demonstrated at all trophic levels here we extend earlier observations to include the past decade and focus on the annual cycles of air temperature and sea ice extent for the past few years with the aim of placing these recent observations within the context of changes seen in the longer term records the more recent years have seen an increasing maritime influence in the wap region with corresponding effects on the marine ecosystem

the dependence of southern ocean meridional overturning on wind stress an eddy resolving numerical model of a zonal flow meant to resemble the antarctic circumpolar current is described andanalyzedusing the framework of j marshallandt radko in additionto windand buoyancy forcing at the surface the model contains a sponge layer at the northern boundary that permits a residual meridional overturning circulation moc to exist at depth the strength of the residual moc is diagnosed for different strengths of surface wind stress it is found that the eddy circulation largely compensates for the changes in ekman circulation the extent of the compensation and thus the sensitivity of the moc to the winds depend on the surface boundary condition a fixed heat flux surface boundary severely limits the ability of the moc to change an interactive heat flux leads to greater sensitivity to explain the moc sensitivity to the wind strength under the interactive heat flux transformed eulerian mean theory is applied in which the eddy diffusivity plays a central role in determining the eddy response a scaling theory for the eddy diffusivity based on the mechanical energy balance is developed and tested the average magnitude of the diffusivity is found to be proportional to the square root of the wind stress the moc sensitivity to the winds based on this scaling is compared with the true sensitivity diagnosed from the experiments

a recent sea ice retreat west of the antarctic peninsula satellite passive microwave data show a record decrease in sea ice extent in the bellingshausen sea from mid 1988 through early 1991 the change coincides with more southerly surface winds increased cyclonic activity and rising surface air temperatures which reached historic highs along the west coast of the antarctic peninsula in 1989 preceded by high ice cover in 1986 87 the retreat was most evident during summer in the formerly perennial sea ice field over the continental shelf ocean heat storage probably contributed to the persistence and coastal propagation of this anomaly

the early palaeozoic geography of europe in the early ordovician three main continents are recognized by faunas in europe laurentia northwest of the closed suture of the iapetus ocean which was tropical baltica north of the general area of the trans european suture zone which was temperate and gondwana south of the tesz which was high latitude as the ordovician progressed various terranes separated and drifted away from the gondwana supercontinent at different times namely avalonia which was probably originally part of gondwana near south america iberia armorica perunica bohemia and various alpine fragments each terrane developed progressively different faunas as time went by avalonia collided with baltica near the end of ordovician confirmed by faunas tectonics and palaeomagnetism and subsequently avalonia baltica collided with laurentia to form laurussia from the mid silurian to the early devonian the ibero armorica perunica and alpine terranes did not join the european collage until the devonian the modern sites of the terrane boundaries bear little direct relationships to the original palaeogeographical boundaries in the early palaeozoic

direct dating of mylonite evolution a multi disciplinary geochronological study from the moine thrust zone nw scotland rb sr dating of sub closure temperature syn deformationly crystallized white micas from the moine mylonites knockan and dundonnell has yielded ages which vary from 437 ma to 408 ma morphological and major element analyses of the micas indicate that all the micas within the analysed samples were re crystallized during the moine thrust shearing the ages yielded are therefore interpreted as marking the end of crystal plastic deformation associated with shearing on the moine thrust the variation in ages between samples is significantly greater than the individual analytical errors and may be a product of strain localization within the shear zone alternatively it may indicate flow of strontium rich fluids derived from outside the shear zone implying that feldspars may act as potentially unreliable initial isotopic reservoirs even in very high strain samples within the greenschist facies shear zones however the rb sr age are internally consistent and compatible broadly with existing geological and geochronological data for the region suggesting that even if the feldspars have not acted as perfect initial isotopic reservoirs the resulting errors were minimal the general cessation of ductile deformation at c 430 ma probably dates the general initiation of imbrication within footwall to the moine thrust the age of 430 ma is therefore likely to be a time of significant brittle displacement on the underlying ben more thrust k ar dating of the re crystallized moine mylonite micas yielded anomalously old ages in comparison to rb sr values as a result of incorporation of excess ar during shearing the degree of incorporated excess ar decreases away from the base of the shear zone into the hanging wall becoming indiscernible at c 1 5 km structurally above the base of the shear zone the distance c 1 5 km may represent the distance that fluid can have flowed out of the shear zone during deformation

rock weathering processes and landform development in the sor rondane mountains antarctica abstract field observations of weathering processes and the related landforms combined with laboratory analyses of weathering products permit a synthetic evaluation of late cenozoic weathering environments in the sor rondane mountains antarctica an arid upland characterized by low temperatures and strong winds rates and character of weathering depend mainly on moisture availability and the bedrock geology under the humid weathering regime that occurs only locally around the margin of the present sheet frequent diurnal freeze thaw cycles in summer cause relatively rapid rock fragmentation most of the mountains are situated in the arid weathering regime under which rock breakdown is very slow unless the rock contains plenty of salts salt weathering becomes more intensive and extensive with exposure age as a result of salt accumulation in rock eventually producing soils as small as fine silt size lack of clay mineralization even in weathered rocks having been exposed above the ice sheet prior to 4 ma ago indicates that hydrolysis or carbonation of rock minerals has been insignificant during the past 4 ma the final products of weathering are due mainly to salt action and reflect the parent lithology resistant fine grained granite forms strongly oxidized tors carved with tafoni or fields of mushroom like boulders overlying the fractured bedrock less resistant rocks like biotite gneiss and amphibolite produce stone pavements underlain by saline silty soils up to 30 40 cm thick the thickness of which corresponds to the maximum thaw depth

palaeobiogeography and the ordovician and mesozoic cenozoic biotic radiations curves of taxonomic diversity through geological time consistently show major evolutionary radiations during the ordovician period and from the mid mesozoic to the present day both intervals were characterized by marked biotic provincialism reflecting episodes of major continental break up and global tectonism and their later histories featured steep global climatic gradients the ordovician radiation can be recognized at a wide spectrum of taxonomic levels from species to class and the biogeographical patterns associated with the radiation of individual clades reflect a complex combination of plate distribution tectonic activity sedimentary environment sea level rise and ultimately glaciation the true scale of the mid mesozoic cenozoic biotic radiation is currently a topic of intense debate but there is no doubt that it affected plants and animals in both the marine and terrestrial realms the role of land bridges and ocean gateways in controlling the for mation of biodiversity patterns has been a persistent theme in mesozoic cenozoic bio geography and a complex set of neogene tectonic events probably aided the development of both latitudinal and longitudinal provinces during the cenozoic the present volume highlights some of the successes across a spectrum of approaches to unravelling the ordovician and mesozoic cenozoic radiations within the context of palaeobiogeography

the effect of snow on antarctic sea ice simulations in a coupled atmosphere sea ice model the effect of a snow cover on sea ice accretion and ablation is estimated based on the zero layer version sea ice model of semtner and is examined using a coupled atmosphere sea ice model including feedbacks and ice dynamics effects when snow is disregarded in the coupled model the averaged antarctic sea ice becomes thicker when only half of the snowfall predicted by the atmospheric model is allowed to land on the ice surface sea ice gets thicker in most of the weddell and ross seas but thinner in east antarctic in winter with the average slightly thicker when twice as much snowfall as predicted by the atmospheric model is assumed to land on the ice surface sea ice also gets much thicker due to the large increase of snow ice formation these results indicate the importance of the correct simulation of the snow cover over sea ice and snow ice formation in the antarctic our results also illustrate the complex feedback effects of the snow cover in global climate models in this study we have also tested the use of a mean value of 0 16 wm 1 k 1 instead of 0 31 for the thermal conductivity of snow in the coupled model based on the most recent observations in the eastern antarctic and bellingshausen and amundsen seas and have found that the sea ice distribution changes greatly with the ice becoming much thinner by about 0 2 m in the antarctic and about 0 4 m in the arctic on average this implies that the magnitude of the thermal conductivity of snow is of considerable importance for the simulation of the sea ice distribution an appropriate value of the thermal conductivity of snow is as crucial as the depth of the snow layer and the snowfall rate in a sea ice model the coupled climate models require accurate values of the effective thermal conductivity of snow from observations for validating the simulated sea ice distribution under the present climate conditions

modeling the enso modulation of antarctic climate in the late 1990s with the polar mm5 abstract the polar fifth generation pennsylvania state university ncar mesoscale model mm5 is employed to examine the el nino southern oscillation enso modulation of antarctic climate for july 1996 june 1999 which is shown to be stronger than for the mean modulation from 1979 to 1999 and appears to be largely due to an eastward shift and enhancement of convection in the tropical pacific ocean this study provides a more comprehensive assessment than can be achieved with observational datasets by using a regional atmospheric model adapted for high latitude applications polar mm5 the most pronounced enso response is observed over the ross ice shelf marie byrd land and over the weddell sea ronne filchner ice shelf in addition to having the largest climate variability associated with enso these two regions exhibit anomalies of opposite sign throughout the study period which supports and extends similar findings by other investigators the dipole structure is observed in surface temperature meridio

simulations of southern hemisphere warming and antarctic sea ice changes using global climate models a combination of modelling techniques is used in conjunction with the limited available observational data to examine antarctic sea ice changes with global warming over the past century firstly a coupled global climate model is forced by prescribing the effect of increasing greenhouse gases from last century to the present secondly the gisst u k meteorological office global sea ice and sea surface temperature observational dataset is used to force an atmosphere sea ice model to compute changes in the antarctic sea ice from last century to the present thirdly the global sea surface temperature sst anomalies derived from the coupled model are used to force the atmosphere sea ice model over the same period the change in the southern hemisphere annual mean surface temperature simulated by the coupled model with greenhouse gas forcing is about 0 6 c which is similar to the observed change over the antarctic poleward of 60 s the corresponding simulated change is about 0 7 c which also appears compatible with observations the reduction in summer sea ice extent simulated by the csiro commonwealth scientific and industrial research organisation coupled model is 0 44 lat which is in general less than the observed change for the two sst forcing cases the changes are in general larger than indicated by the observations it is concluded that future changes of reduced sea ice extent from increasing greenhouse gases as simulated by the csiro coupled model are not expected to be overestimates

soil distribution in the mcmurdo dry valleys antarctica abstract the mcmurdo dry valleys mdvs are the largest ice free area ca 6692 km 2 in antarctica here we present a reconnaissance scale 1 2 million soil map of the mdvs the soil map units are subgroups as identified in the u s department of agriculture soil taxonomy the dominant soil subgroups in the mdvs are typic anhyorthels 43 typic haploturbels 36 and typic anhyturbels 14 soils of the mdvs represent an evolutionary sequence that include glacic haploturbels anhyturbels on holocene surfaces typic haploturbels anhyturbels on late quaternary surfaces typic anhyorthels on late to mid quaternary surfaces salic anhyorthels on mid to early quaternary surfaces and petrosalic petrogypsic petronitric anhyorthels on pliocene and older surfaces soils on silt rich tills of pliocene and older age generally are typic or salic anhyorthels they feature less weathering than younger soils because i they are derived from quartzose materials largely devoid of weatherable minerals and ii they have been subject to considerable wind erosion

the great ordovician biodiversification event gobe the palaeoecological dimension abstract the great ordovician biodiversification event gobe saw a spectacular increase in marine biodiversity at all taxonomic levels largely within the phyla established much earlier during the so called cambrian explosion the diversification was probably the result of a combination of several geological and biological processes and the positive feedbacks resulting from them the present paper reviews the palaeoecological dimension of the gobe it involved major increases in s and biodiversity largely associated with the rise of the paleozoic evolutionary fauna dominated by suspension feeders and involving a greater occupation of ecospace and more complex ecological structures in the ecological evolutionary units p1 and p2 in the benthos these include more complex food webs than those of the cambrian greater tiering especially above the sediment water interface and the development of guild structures indicating increased competition between taxa for particular resources the ordovician is characterized by a profound change in reef composition with a switch from microbial dominated reefs in the early and middle ordovician to metazoan dominated reefs in the late ordovician increases in complexity of deep water trace fossil assemblages began in the early ordovician and mark the increasing exploitation in that environment and the development of hardgrounds permitted bioerosion and encrusting strategies together with the appearance of cryptic communities within the water column the gobe involved a significant increase in the diversity of the phytoplankton and the development of a diverse zooplankton including planktotrophic larvae from a range of invertebrate clades this revolution in the plankton enabled the establishment of a diverse fauna of pelagic vertebrates molluscs and arthropods and promoted the rise of suspension feeders in the benthos an escalation amongst predators and thus community evolution may also have been a major driver of biodiversification

covariation of sea ice and methanesulphonic acid in wilhelm ii land east antarctica sea ice plays an important role in ocean atmosphere heat exchange global albedo and the marine ecosystem knowledge of variation in sea ice extent is essential in order to understand past climates and to model possible future climate scenarios this paper presents results from a short firn core spanning 15 years collected from near mount brown wilhelm ii land east antarctica variations of methanesulphonic acid msa at mount brown were positively correlated with sea ice extent from the coastal region surrounding mount brown 60 1208 e and from around the entire antarctic coast 0 3608 e previous results from law dome identified this msa sea ice relationship and proposed it as an antarctic sea ice proxy curran and others 2003 with the strongest results found for the local law dome region our data provide supporting evidence for the law dome proxy at another site in east antarctica but a deeper mount brown ice core is required to confirm the sea ice decline suggested by curran and others 2003 results also indicate that this deeper record may also provide a more circum antarctic sea ice proxy

global ordovician vertebrate biogeography abstract cambrian ordovician vertebrate and supposed vertebrate occurrences have been repeatedly claimed during recent decades with confirmed taxa bearing mineralized tissues with a vertebrate histomorphology still relatively rare the only biogeographic province that we can presently recognize is the gondwana endemic assemblage gea with possible late cambrian fragmentary remains from australia but more definite early ordovician arenigian to early late ordovician caradocian arandaspids i e sacabambaspis arandaspis and other taxa known from south america and australia certain chondrichthyans sharks at first without teeth and which might not constitute a monophyletic group might have originated in east gondwana province and then are found in the late ordovician and early silurian of mongolia tarim and south china the gea fauna proper disappears by middle late caradocian and vertebrates do not reappear in gondwana until mid late silurian late ordovician 455 myr or earlier vertebrates are also known with certainty from laurentia viz north america pteraspidomorphs astraspis eriptychius and various gnathostome like taxa including chondrichthyan placoderm and acanthodian like remains and siberia astraspid like microremains with an unusual histology which might correspond to a new group of lower vertebrates as well as scales from putative loganiid and thelodontidid thelodonts from north america and russia timan pechora the severnaya zemlya archipelago and siberia this is defined as the laurentia baltica siberia assemblage lbsa we also mention one enigmatic reference to a late ordovician anaspid in south africa there is no clear association of taxa between the gea and lbsa despite a small overlap in time various recent palaeogeographic models published for the ordovician are critically analyzed and considered within four groups the archetypal palaeogeographic reconstructions two alternative solutions and a compact version habitats of vertebrates in mostly ba1 marine intertidal to ba3 shallow subtidal environments and their dispersal capabilities are evaluated with regard to those models the main feature of ordovician vertebrate biogeography is endemism furthermore the present lack of complete descriptions of most taxa which are often represented only by isolated microremains and the need for a thorough phylogenetic analysis preclude any phylogenetic palaeobiogeographic study in such a framework we also evaluate possible links between external physical factors and the ordovician radiation of vertebrates the late proterozoic deposition of oceanic phosphate and the early cambrian increase in oxygen on earth might have been the spur for vertebrate evolution before the phase when hard tissues appeared the sharp decline of the marine strontium isotope ratio during the middle to late ordovician transition interpreted as having been controlled primarily by continental collisional tectonics and its associated erosion and weathering has been proposed as the consequence of a possible mantle superplume event which could have caused the prominent caradocian transgressive phase this might have been a factor in the changeover from a gondwanan to a laurentian focus for vertebrates

ice shelf advance and retreat rates along the coast of queen maud land antarctica we mapped ice shelf margins along the queen maud land coast antarctica in a study of ice shelf margin variability over time our objective was to determine the behavior of ice shelves at similar latitudes but different longitudes relative to ice shelves that are dramatically retreating along the antarctic peninsula possibly in response to changing global climate we measured coastline positions from 1963 satellite reconnaissance photography and 1997 radarsat synthetic aperture radar image data for comparison with coastlines inferred by other researchers who used landsat data from the mid 1970s we show that these ice shelves lost 6 8 of their total area between 1963 and 1997 most of the areal reduction occurred between 1963 and the mid 1970s since then ice margin positions have stabilized or even readvanced we conclude that these ice shelves are in a near equilibrium state with the coastal environment

the little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap the analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent annual variations in visible dust layers oxygen isotopes microparticle concentrations conductivity and identification of the historical a d 1600 huaynaputina ash permit accurate dating and time scale verification the fact that the little ice age about a d 1500 to 1900 stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event

observations of change in the southern ocean the southern ocean has been in a state of disequilibrium with its atmosphere and cryosphere during recent decades ocean station and drifting float observations have revealed rising temperatures in

anomalous peak in antarctic sea ice area winter 1998 coincident with enso the results of an updated satellite analysis of hemispheric and regional antarctic sea ice cover are presented based on october 1987 september i999 special sensor microwave imager ssm i data these show an ongoing slight but significant hemispheric increase of 3 7 0 3 in extent and 6 6 1 5 in area in the two principal sectors weddell sea ice extent area decreased by 3 4 1 0 3 9 4 6 and ross sea ice extent area increased by 10 9 1 0 18 3 4 6 hemispheric ross sea and western pacific ocean ice peaks in september 1998 were anomalously high and may have been related to atmospheric and oceanic anomalies in the pacific ocean and beyond associated with that year s exceptionally strong enso preliminary comparison of antarctic sea ice concentration data with european centre for medium range weather forecasts ecmwf operational analyses fields suggests that the unusually extensive sea ice in winter 1998 was concomitant with an equatorward shift of the circumpolar westerly surface winds over the southern pacific ocean

the obduction of equatorial 13 c water in the pacific identified by a simulated passive tracer the obduction of equatorial 13 degrees c water in the pacific is investigated using a simulated passive tracer of the consortium for estimating the circulation and climate of the ocean ecco the result shows that the 13 degrees c water initialized in the region 8 degrees n 8 degrees s 130 degrees 90 degrees w enters the surface mixed layer in the eastern tropical pacific mainly through upwelling near the equator in the costa rica dome and along the coast of peru approximately two thirds of this obduction occurs within 10 years after the 13 degrees c water being initialized with the upper portion of the water mass reaching the surface mixed layer in only about a month the obduction of the 13 degrees c water helps to maintain a cool sea surface temperature year round equivalent to a surface heat flux of about 6 0 w m 2 averaged over the eastern tropical pacific 15 degrees s 15 degrees n 130 degrees w eastern boundary for the period of integration 1993 2006 during el nino years when the thermocline deepens as a consequence of the easterly wind weakening the obduction of the 13 degrees c water is suppressed and the reduced vertical entrainment generates a warming anomaly of up to 10 w m 2 in the eastern tropical pacific and in particular along the coast of peru providing explanations for the warming of sea surface temperature that cannot be accounted for by local winds alone the situation is reversed during la nina years

the early paleozoic evolution of the argentine precordillera as a laurentian rifted drifted and collided terrane a geodynamic model paleontologic and stratigraphic evidence points to the early paleozoic precordilleran terrane of western argentina as being the conjugate rift pair of the appalachians stratigraphic similarities of the cambrian and early arenig carbonate series and very strong affinities among trilobite conodont and brachiopod faunas show their close relationship the most probable provenance areas are the appalachian ouachita rifted margin and the newfoundland appalachians although the former fits better with geometric and drifting paths suggested by faunal affinities increasing celtic and baltic brachiopod genera and divergent stratigraphy since the arenig indicate the drifting of the precordilleran terrane collisional foredeeps developed on collapsed former platform carbonates as flexural subsidence progressed the collision of the precordillera with western gondwana occurred during the mid llanvirn to llandeilo a magmatic arc related to eastward subduction present coordinates was active in the famatina range east of the precordillera this region of celtic affinity shows faunal exchange with the precordilleran terrane since the late arenig and may represent accreted intra iapetus volcanic island arc complexes the rifting and drifting stages are consistent with paleoclimatic and paleomagnetic data that show the migration of the precordilleran terrane from periequatorial to peripolar latitudes between the cambrian and latest ordovician the deep ocean to the west of the precordillera started to close by the late ordovician with the eastward drift of the chilenian terrane absence of volcanic or pyroclastic arc derived rocks in the precordillera indicate west dipping subduction as chilenia approached the continental margin a new forebulge was established on the former collided precordilleran terrane developing an erosional unconformity in central precordillera talacasto tambolar arch a gondwanic signature was fully developed by the middle silurian when the malvinokaffric clarkeia fauna flourished before then the late ordovician glacial record and associated hirnantia fauna were the first clear tie to gondwana during the silurian the marginal basin behaved as a foreland with lithosphere rheology and eustasy governing the sequence stratigraphy wrench faulting along its eastern boundary displaced the precordillera toward the south continued shortening during closure with the chilenian terrane in the mid devonian produced thrust loading of the basin and generated a thick graywacke succession final accretion of chilenia late devonian generated a regional angular unconformity between the lower and upper paleozoic new eastward subduction was initiated west of the accreted chilenian terrane during the late permian triassic as indicated by the choiyoi volcanic complex which presently outcrops in the frontal cordillera

siluro devonian paleomagnetic results from the tuva terrane southern siberia russia implications for the paleogeography of siberia new paleomagnetic data from seven sections of siluro devonian age sedimentary sequences in the tuva terrane south siberia russia reveal the presence of up to three different components of magnetization component a is of recent or late mesozoic cenozoic origin and component b identified unambiguously in 25 samples from one section yields a sample mean direction declination inclination of 300 6 54 7 k 42 2 95 4 5 in geographic and 283 9 63 5 k 45 4 95 4 3 in stratigraphic coordinates however since the results of the fold test are inconclusive no further attempt has been made to assign an age to this magnetization component c with unblocking temperatures of 500 680 c is identified in all seven sections and with dual polarity after bedding correction the section mean directions all plot along a common small circle in stereographic projection with a mean inclination of 42 1 n 7 sites k 184 2 95 2 9 it passes the inclination only fold test the within site fold test both on the 95 significance level and the reversal test and is thus interpreted as being primary in origin and siluro devonian in age adopting the normal polarity option for component c yields a paleolatitude of 24 n 2 for the tuva terrane on the basis of geological evidence the tuva terrane was clearly accreted to siberia by early silurian times the results obtained in this study therefore indicate lower paleolatitudes for siberia than those predicted from previously published apparent polar wander paths for the siberian platform and demonstrate that siberia was positioned between the equator and 30 n during latest silurian earliest devonian times these new results are also supported by paleoecological and paleoclimatological evidence the dispersion of declinations along a small circle is indicative of clockwise block rotations within the tuva terrane of up to 72 with respect to siberia

late pleistocene and holocene landscape evolution and environmental change in the lake sulivan area falkland islands south atlantic abstract late pleistocene and holocene landscape evolution around lake sulivan falkland islands south atlantic is assessed using morphological stratigraphical palaeoecological and 14c dating evidence data indicate a complex landscape history involving frost related activity ventifact development growth and degradation of peat terrain expansion and contraction of lakes and the development stabilisation and subsequent reworking of alluvial and aeolian sand bodies late pleistocene cold conditions favoured production of sandy diamicts on hillslopes and ventifacts on outcrops and blockfield clasts lateglacial climatic amelioration was marked by early growth of peat ca 16 500 cal yr bp since then peat accumulation changes in lake areas and depths and alluvial and or aeolian sand deposition have been recurring and dominant features of landscape change which throughout the late pleistocene and early holocene may have been a response to near synchronous climatic fluctuations along the south america antarctica axis marked landscape changes around lake sulivan coincided with intervals of glacier readvance in south america and south georgia at ca 3200 1900 and 700 100 cal yr bp with lower lake levels and aeolian sand transport from exposed lakebeds and shorelines implying greater aridity in the falklands than at present

soil characteristics on varying lithological substrates in the south shetland islands maritime antarctica abstract soils in ice free areas of livingston island have been forming since the last deglaciation in a maritime warmer climate that is more humid than in interior antarctica a soil survey was carried out on byers and hurd peninsulas to characterize the soils and investigate the processes soils were sampled on two different substrates mudstones and volcanic rocks in byers peninsula and greywackes in hurd peninsula sampling sites were located on raised beaches platforms and on volcanic outcrops across an altitudinal range from few m to 150 m a s l the ph electrical conductivity carbonates and organic matter showed similar patterns in each geomorphic unit but their values differed between bedrocks the sand silt and clay contents differed greatly in the soils on mudstones and volcanic rocks the elemental composition was closely related to mineralogy of parent materials mg k zn mn and fe were similar in the soils on all bedrocks the al content was highest on the volcanic rocks the largest difference in the ca content was between the soils on greywackes and mudstones the na pb and ba contents in soils on the mudstones differed greatly from the rest of bedrocks geochemical and mineralogical characteristics suggest that the main process involved in soil development was the mechanical disintegration of bedrock although there was also some leaching cryogenic processes play a key role in soil development but chemical weathering processes were also involved in soil evolution although limited in extent due to the restriction of water circulation to summer

ice core evidence for antarctic sea ice decline since the 1950s the instrumental record of antarctic sea ice in recent decades does not reveal a clear signature of warming despite observational evidence from coastal antarctica here we report a significant correlation p

continental shelf drift deposit indicates non steady state antarctic bottom water production in the holocene a late quaternary current lain sediment drift deposit over 30 m in thickness has been discovered on the continental shelf of east antarctica in an 850 m deep glacial trough off george vth land radiocarbon dating indicates that a period of rapid deposition on the drift averaging 290 cm kyr occurred in the mid holocene between about 3000 and 5000 yr before present slower rates of around 10 cm kyr during the past 0 3000 yr and from 5000 to about 13000 yr bp coincides with deposition of bioturbated ice rafted debris ird rich sandy mud under an energetic bottom current regime in contrast the mid holocene 3000 5000 yr bp sediments are fine grained laminated to cross laminated with minimal ird content and are contemporaneous with a period of warmer marine conditions with less sea ice production this pattern suggests that bottom currents were weaker than present day in the mid holocene and that the rate of dense bottom water production was reduced at that time this scenario is consistent with the hypothesis of non steady state rates of antarctic bottom water production through the holocene as recently proposed by broecker and his colleagues

investigation of the dynamic sea ice component of a coupled atmosphere sea ice general circulation model this paper discusses the development of a coupled atmospheric ice model with a comprehensive ice dynamics cavitating fluid rheology and an open water parameterization the results center on the ice thickness and concentration distribution in the arctic basin where the inclusion of ice rheology has maximum impact the influence of the wind stresses calculated by an atmospheric model with stability dependent surface drag coefficients is discussed along with the role of the ocean currents and ocean ice drag coefficient under winter wind stress conditions the model had a tendency to buildup ice on the siberian coast the introduction of a partial slip condition at land ice boundaries in the model designed to prevent this buildup is discussed and the best choice for the amplitude of the slip at the land boundaries in this model is found to be 0 4 the ice model results are compared with the available observational data sets on ice thickness concentration and ice velocity fields to test the validity of the model simulations

geomorphology and soils distribution under paraglacial conditions in an ice free area of admiralty bay king george island antarctica abstract the main pedological geomorphological and cryogenic features of keller peninsula part of admiralty bay king george island maritime antarctica were mapped and quantified with emphasis on the relationship between the ice retreat process melt out landform development and soil distribution moraines protalus scree slopes inactive glacial cirques uplift marine terraces biogenic landforms aretes and felsenmeer were mapped scree slope is the main landform covering approximately 25 of the peninsula indicating prominent paraglacial features inherited glacial landforms such as lateral moraines highland plateau and exhumed u shaped valleys are now being exposed in north keller by ice shrinkage of former ice protecting cover landforms influenced soil formation and stability cryosols and leptosols wrb roughly corresponding to gelisols and entisols sss respectively are the most common soil classes with an overall tendency of absent permafrost in the coastal areas changing to sporadic permafrost at mid slope and discontinuous permafrost with greater altitude and substrate stability

primary results of glaciological studies along an 1100 km transect from zhongshan station to dome a east antarctic ice sheet the chinese national antarctic research expedition ghinare carried out three traverses from zhongshan station to dome a princess elizabeth land and inaccessible area east antarctic ice sheet during the 1996 97 to 1998 99 antarctic field seasons the expeditions are part of the chinese international trans antarctic scientific expedition program in this project glaciological investigations of mass balance ice temperature ice flow stratigraphy in snow pits and snow firn ice cores as well as the glaciochemical study of surface snow and shallow ice cores have been carried out in the 1998 99 field season chinare extended the traverse route to 1128 km inland from zhongshan station the density profiles show that firnification over princess elizabeth land and inaccessible area 290 1100 km along the route is fairly slow and the accumulation rate recovered from snow pits along the initial 460 km of the route is 4 6 21 cm 46 210 kg m 2a 1 water equivalent the initial 460 km of the route can be divided into four sections based on the differences of accumulation rate this pattern approximately coincides with the study on the lambert glacier basin lgb by australian scientists during the past 50 years the trends of both air temperature and accumulation rate show a slight increase in this area in contrast to the west side of the lgb data on surface accumulation rates and their spatial and temporal variability over ice drainage areas such as the lgb are essential for precise mass balance calculation of the whole ice sheet and are important for driving ice sheet models and testing atmospheric models

modeling of antarctic sea ice in a general circulation model a dynamic thermodynamic sea ice model is developed and coupled with the melbourne university general circulation model to simulate the seasonal cycle of the antarctic sea ice distribution the model is efficient rapid to compute and useful for a range of climate studies the thermodynamic part of the sea ice model is similar to that developed by parkinson and washington the dynamics contain a simplified ice rheology that resists compression the thermodynamics is based on energy conservation at the top surface of the ice snow the ice water interface and the open water area to determine the ice formation accretion and ablation a lead parameterization is introduced with an effective partitioning scheme for freezing between and under the ice floes the dynamic calculation determines the motion of ice which is forced with the atmospheric wind taking account of ice resistance and rafting the simulated sea ice distribution compares reasonably well with observations the seasonal cycle of ice extent is well simulated in phase as well as in magnitude simulated sea ice thickness and concentration are also in good agreement with observations over most regions and serve to indicate the importance of advection and ocean drift in the determination of the sea ice distribution

atlantic salinity budget in response to northern and southern hemisphere ice sheet discharge the impact of an idealised scenario of future mass release of major ice sheets on the atlantic ocean is studied a freshwater forcing is applied to the ocean surface in a coupled climate model forced in accordance with a high end future climate projection for mass loss from the greenland and antarctic ice sheet together with the rcp8 5 emission scenario the added freshwater dilutes the entire ocean by increasing total volume but changes in freshwater budget are non linear in time especially in the atlantic ocean in the atlantic the initial dilution mainly comes from greenland freshwater but the increase in mass is counteracted by the mass flux across the boundaries of the atlantic with the outflow into the southern ocean becoming larger than the inflow through bering strait associated with this mass divergence salt is exported to the southern ocean by the barotropic flow further freshening is associated with more freshwater import by the atlantic meridional overturning circulation across the southern boundary of the atlantic also the subtropical gyre exports salt and imports freshwater across the atlantic s southern boundary especially when freshwater from the antarctic ice sheet arrives at the boundary of the basin it appears that the response to northern hemisphere nh sources the greenland ice sheet and southern hemisphere sh sources the antarctic ice sheet are opposite in the case of nh only freshwater forcing sea surface height ssh increases in the arctic causing a reduction of the ssh gradient over the bering strait and hence the barotropic throughflow across the arctic atlantic basin reduces in case of sh only freshwater forcing ssh increases in the pacific enhancing the barotropic throughflow in the arctic atlantic when both nh and sh freshwater forcings are present the response in the atlantic is dominated by nh forcing changes in overturning transport to either nh or sh forcing counteract the response to changes in barotropic transport these changes are not due to volume transport but mainly due to salinity changes in particular across the southern boundary of the atlantic only when both sh and nh freshwater forcing are present changes in barotropic transport and overturning transport reinforce each other the barotropic transport more strongly reacts to nh forcing while the overturning transport reacts more strongly to sh forcing

scales of thelodont and shark like fishes from the ordovician of colorado the phylogeny of primitive vertebrates has been investigated over the past fifteen years1 3 and there has been a notable increase in the amount of data by which such phylogenies can be tested4 7 stratigraphic data should provide constraints to such analyses and we record here descriptions of putative shark and thelodont scales from the harding sandstone caradoc late ordovician of colorado the fossil record of sharks is extended back from the llandovery lower silurian by some 25 million years and that of thelodonts by 10 million years from the ashgill late ordovician the new data indicate that a major radiation of lower vertebrates took place during the ordovician

deep water properties and surface buoyancy flux as simulated by a z coordinate model including eddy induced advection abstract a parameterization for the adiabatic transport effect of eddies is introduced into a world ocean model based on the bryan cox code the model topography is only lightly smoothed and retains realistic sill depths and representation of continental shelves commensurate with the model s 1 6 latitude by 2 8 longitude resolution the parameterization allows the model to be run without horizontal diffusivity though only under certain conditions as discussed a first control run features a typical horizontal diffusivity and no eddy induced transport a second run features the eddy induced transport scheme and zero horizontal diffusivity substantial changes occur between the runs in subsurface temperature salinity and density throughout the model ocean the most profound changes occur in the deep ocean and feature a marked increase in density in the second run associated with a substantial decline in temperature especially in the atlantic and an increase in salinity especially in the southern

state of the antarctic and southern ocean climate system this paper reviews developments in our understanding of the state of the antarctic and southern ocean climate and its relation to the global climate system over the last few millennia climate over this and earlier periods has not been stable as evidenced by the occurrence of abrupt changes in atmospheric circulation and temperature recorded in antarctic ice core proxies for past climate two of the most prominent abrupt climate change events are characterized by intensification of the circumpolar westerlies also known as the southern annular mode between 6000 and 5000 years ago and since 1200 1000 years ago following the last of these is a period of major trans antarctic reorganization of atmospheric circulation and temperature between ad1700 and 1850 the two earlier antarctic abrupt climate change events appear linked to but predate by several centuries even more abrupt climate change in the north atlantic and the end of the more recent event is coincident with reorganization of atmospheric circulation in the north pacific improved understanding of such events and of the associations between abrupt climate change events recorded in both hemispheres is critical to predicting the impact and timing of future abrupt climate change events potentially forced by anthropogenic changes in greenhouse gases and aerosols special attention is given to the climate of the past 200 years which was recorded by a network of recently available shallow firn cores and to that of the past 50 years which was monitored by the continuous instrumental record significant regional climate changes have taken place in the antarctic during the past 50 years atmospheric temperatures have increased markedly over the antarctic peninsula linked to nearby ocean warming and intensification of the circumpolar westerlies glaciers are retreating on the peninsula in patagonia on the sub antarctic islands and in west antarctica adjacent to the peninsula the penetration of marine air masses has become more pronounced over parts of west antarctica above the surface the antarctic troposphere has warmed during winter while the stratosphere has cooled year round the upper kilometer of the circumpolar southern ocean has warmed antarctic bottom water across a wide sector off east antarctica has freshened and the densest bottom water in the weddell sea has warmed in contrast to these regional climate changes over most of antarctica near surface temperature and snowfall have not increased significantly during at least the past 50 years and proxy data suggest that the atmospheric circulation over the interior has remained in a similar state for at least the past 200 years furthermore the total sea ice cover around antarctica has exhibited no significant overall change since reliable satellite monitoring began in the late 1970s despite large but compensating regional changes the inhomogeneity of antarctic climate in space and time implies that recent antarctic climate changes are due on the one hand to a combination of strong multi decadal variability and anthropogenic effects and as demonstrated by the paleoclimate record on the other hand to multi decadal to millennial scale and longer natural variability forced through changes in orbital insolation greenhouse gases solar variability ice dynamics and aerosols model projections suggest that over the 21st century the antarctic interior will warm by 3 4 1oc and sea ice extent will decrease by 30 ice sheet models are not yet adequate enough to answer pressing questions about the effect of projected warming on mass balance and sea level considering the potentially major impacts of a warming climate on antarctica vigorous efforts are needed to better understand all aspects of the highly coupled antarctic climate system as well as its influence on the earth s climate and oceans

chemical and biological properties formation occurrence and classification of spodic cryosols in a terrestrial ecosystem of east antarctica wilkes land abstract soils with the morphological features of podzols are widespread in coastal east antarctica neither the world reference base of soil resources wrb nor soil taxonomy st adequately classify these soils so we recommend the addition of spodic cryosol at the second hierarchical level in wrb and spodorthel at the great group level of st we divide the spodic cryosols into ornithogenic and non ornithogenic spodic cryosols based on inorganic chemistry soil organic matter composition and microbiology the occurrence of spodic cryosols depends on parent materials soil texture surface pattern solar energy input and vegetation patterns antarctic spodic cryosols form on solid rocks outwash sediments and abandoned penguin rookeries and represent 20 of the soil landscape of wilkes land with one third ornithogenic and two thirds non ornithogenic ornithogenic spodic cryosols are related to tectonically uplifted abandoned penguin rookeries all spodic cryosols contain large amounts of carbon and nitrogen during pedogenesis iron complexed with organic matter in the topsoils has been altered to oxides and crystalline iron minerals but aluminium remains almost entirely 100 organically bound throughout the profile meltwater and a moss cover are essential for podzolization on the non ornithogenic sites and at the ornithogenic sites the chemically aggressive solution from dissolved guano has bleached the uppermost ae horizon and translocated iron and aluminium into the subsoil the low salinity suggests that downward leaching exceeds upward transport by evaporation intensity of podzolization is determined by microclimate soil microbial effects and parent materials the permafrost table may cause precipitation of organic matter in the subsoil mg and p levels are high the p level is very high in the ornithogenic soils k p ph base saturation bs and bacterial colonization reflect the influence of guano in the ae horizon of ornithogenic soils colonization by lichens and or mosses depresses bacterial activity the mean c n ratio of approximately 11 and the abundance of carboxylic carbon compounds probably derive from organic acids and oxidized carbohydrates migration of organic acids non humified carbohydrates and n containing compounds is suggested as the main mechanism of podzolization

recent southern indian ocean climate variability inferred from a law dome ice core new insights for the interpretation of coastal antarctic isotopic records stable isotopes in water have been measured along a very high accumulation ice core from law dome on the east antarctic coast these enable a detailed comparison of the isotopic records over sixty years 1934 1992 with local antarctic station data and remote meteorological observations atmospheric reanalyses and sea surface temperature estimates on a seasonal to inter annual time scale using both observations and isotopic atmospheric general circulation model gcm results we quantify the relationships between stable isotopes 18o d and deuterium excess d d 8 18o with site and source temperature at seasonal and decadal time scales showing the large imprint of source conditions on law dome isotopes these calibrations provide new insights for the quantitative interpretation of temporal isotopic fluctuations from coastal antarctic ice cores an abrupt change in the local meridional atmospheric circulation is clearly identified from law dome deuterium excess during the 1970s and analysed using gcm simulations

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

genesis mineralogy and ecological significance of ornithogenic soils from a semi desert polar landscape at hope bay antarctic peninsula abstract large amounts of organic matter of marine origin are seasonally deposited on ice free soils by birds and mammals especially penguins in some restricted antarctic terrestrial ecosystems the incorporation of this material into the mineral soil matrix becomes the main pathway for the widespread formation of phosphate minerals and ornithogenic soils enhancing local biodiversity and complexity these soils have been well studied in maritime antarctica and comparatively neglected in the cold dry polar antarctica hence we studied the influence of penguins on soil and landscape formation at hope bay a transition climatic zone in antarctic peninsula where no previous pedological study has been undertaken with regards to soil phosphatization ten pedons nine of which are ornithogenic were described sampled and analyzed for physical chemical and mineralogical properties results indicate that the slow mineralization of bird guano coupled with high levels of organic matter and reduced leaching notably ca contribute to reduced soil acidification and low exchangeable al3 content unlike ornithogenic soils from maritime antarctica phosphate minerals typical of the phosphatization process such as taranakite minyulite leucophosphite struvite and fluorapatite were detected in hope bay they are subjected to very slow rates of dissolution neoformation of secondary phosphatic minerals and mineralogical transformation and leaching processes ornithogenesis is viewed as a mechanism of sea land nutrient transfer enriching the latter since the parent rocks are chemically poor sedimentary materials on the other hand the presence of kaolinite indicates wetter climate conditions in the past with periods with greater moisture and weathering compared with the current semi polar desert environment we conclude that the phosphatization process overprints previously weathered sedimentary materials

did the taconic appalachians continue into southern south america the appalachian mountains now terminating abruptly at the gulf of mexico coastal plain may have formerly continued into southern south america rocks forming the basement of the argentine andes can be interpreted as remnants of an early paleozoic orogen the famatinian belt not unlike the taconic appalachians both orogens are bordered to the west present coordinates by lower paleozoic carbonate platforms bearing the olenellid trilobite fauna that is characteristic of laurentia paleomagnetic and geologic data indicate that they could have formed as one continuous mountain chain possibly extending into antarctica during ordovician closure of an ocean basin southern iapetus between laurentia and gondwana the taconic and famatinian segments of the chain may have been truncated during late ordovician separation of laurentia and gondwana along the preexisting late neoproterozoic to cambrian rift system that initiated formation of the ouachita embayment and the southern margin of north america

genesis properties and classification of cryosols from admiralty bay maritime antarctica abstract soils from maritime antarctica are different than those from other antarctic climatic zones and are among the least studied soils in antarctica we here present analytical and morphological data for the main soils found in admiralty bay king george island in the south shetland group fifty six 56 pedons were described sampled and analyzed according to standard international methods and classified according to both u s soil taxonomy and the wrb the soils are generally weakly developed and have chemical physical and morphological characteristics strongly influenced by the parent material we identify four main soil groups i basaltic andesitic ii acid sulfate iii weakly ornithogenic and iv ornithogenic soils small adjustments are proposed for both classification systems for allowing a more adequate classification for maritime antarctica greyish colored eutric lithic and typic haploturbels turbi leptic cryosols with neutral to alkaline reaction are the most common soils in admiralty bay and are usually developed from basaltic andesitic tills yellowish acid dystric sulphuric haploturbels turbi thionic cryosols are restricted to areas affected by pyritized andesites umbriturbels turbi umbric cryosols only occur at sites under bird influence ornithogenic soils are the most developed soils in admiralty bay and show pronounced chemical physical and morphological alteration of parent materials with formation of umbric epipedons and phosphatic b horizons fibristels organo turbic cryosols are restricted to hydromorphic areas under thick moss carpets

the southern hemisphere westerlies in the australasian sector over the last glacial cycle a synthesis abstract the southern hemisphere westerlies in the southwest pacific are known to have waxed and waned numerous times during the last two glacial cycles though even semi continuous histories of the westerlies extend back no more than about 20 000 years we have good evidence for at least three scales of events a westerly maximum occurs at the last glacial maximum there is less conclusive evidence for another westerly maximum in the late holocene and for a minimum at ca 11 ka it is too early to ascribe even a cycle to these data but there are grounds to suggest that milankovitch precessional forcing may underlie the observed pattern there is also a quasi 2600 year cycle present in antarctic ice cores that appears to correlate to variation in westerly flow there is strong centennial scale variability in historical times the little ice age lia ca 1400 1850 was associated with a poleward shift in the circumpolar trough in the southern ocean strengthened westerly circulation over tasmania and a strengthening of southwesterly circulation and neoglaciation in southern new zealand while the preceding period 800 1400 ad was less certainly marked by reduced westerly flow from modern records we know that decadal and inter annual variability is important e g pacific decadal oscillation high latitude mode also known as the antarctic oscillation el nino southern oscillation only a minority of the proxies examined can identify changes on these temporal scales but data from tree rings ice cores and laminated lake sediments do indicate systematic changes in these phenomena through time rossby wave patterns are shown to play a critical role in long duration events as well as at the synoptic scale we conclude that westerly circulation is as strong now as at any time in the last glacial cycle in addition changes in latitudinal boundaries in the westerlies may be nearly as large in inter annual zonal shifts ca 2 maximum as in glaciation interglaciation movements ca 3 4 there is however reasonable evidence of strengthening weakening across much of the westerly belt at westerly maxima minima such as the lia early holocene

a new silurian palaeolatitude for eastern avalonia and evidence for crustal rotations in the avalonian margin of southwestern ireland summary palaeomagnetic data are presented from mid silurian homerian upper wenlock 425 ma sediments from the dingle peninsula sw ireland which forms part of thenorthern margin of the palaeozoic microcontinent of avalonia three remanencecomponents were recognized after removal of a low temperature component l oriented parallel to the present earth eld at the sampling area two higher stabilitycomponents were isolated an intermediate unblocking temperature component i with mean in situ d 196 9 i 11 0 a95 10 8 with a corresponding palaeopole at330 0 e 30 6 s dp 5 6 dm 11 0 and a high unblocking temperature component h with mean tilt corrected d 218 6 i 22 1 a95 7 9 with a correspondingpalaeopole at 309 5 e 18 3 s dp 4 4 dm 8 4 a primary wenlock age is indicatedfor the h component by a positive intraformational conglomerate test whereas the i component is thought to be a secondary mid carboniferous partial remagnetization these data con rm that the sector of the iapetus ocean between avalonia andlaurentia was essentially closed within the limits of palaeomagnetic resolution by thewenlock there is still however a discrepancy between the declinations recorded bysimilar aged sequences to the north and south of the iapetus suture these point toeither an approximately 30 clockwise rotation of the entire avalonian microcontinentrelative to laurentia during closure or local vertical axis rotations of the samplingsites in southern britain

a generalized transport theory water mass composition and age abstract a general theory to describe and understand advective and diffusive ocean transport is reported it allows any passive tracer field with an atmospheric source to be constructed by superposing sea surface contributions with a generalized green s function called the boundary propagator of the passive tracer equation the boundary propagator has the interpretation of the joint water mass and transit time distribution from the sea surface the theory thus includes the classical oceanographic idea of water mass analysis and extends it to allow for a distribution of transit times from the sea surface the joint water mass and transit time distribution contains complete information about the transport processes in the flow it captures this information in a more accessible way than using velocity and diffusivity fields however at least for the case of sequestration and transport of dissolved material by the ocean circulation the boundary propagator is thus the natural quantity to consider when discus

climate variability in the amundsen and bellingshausen seas satellite data reveal a 20 decline in sea ice extent in the amundsen and bellingshausen seas in the two decades following 1973 this change is negatively correlated with surface air temperatures on the west side of the antarctic peninsula which have increased 0 58c decade21 since the mid 1940s the recession was strongest during summer when monthly average minima in 1991 92 removed much of the incipient multiyear ice over the continental shelf this would have lowered the regional mean ice thickness impacting snow ice formation brine production and vertical heat flux the northern ice edge contracted by 18 of latitude in all seasons from 1973 79 to 1987 93 returning toward mean conditions in 1993 95 the decline included multiyear cycles of several years in length superimposed on high interannual variability a review of atmospheric forcing shows winds consistent with mean and extreme ice extents and suggests links to larger scale circulation changes in the south pacific historical ocean measurements are sparse in this sector but mixed layer depths and upper pycnoclines beneath the sea ice resemble those in the weddell sea weaker surface currents or changes in the upwelling of circumpolar deep water on the continental shelf could have contributed to the anomaly persistence

el nino suppresses antarctic warming here we present new isotope records derived from snow samples from the mcmurdo dry valleys antarctica and re analysis data of the european centre for medium range weather forecasts era 40 to explain the connection between the warming of the pacific sector of the southern ocean jacka and budd 1998 jacobs et al 2002 and the current cooling of the terrestrial ross sea region doran et al 2002a our analysis confirms previous findings that the warming is linked to the el nino southern oscillation enso kwok and comiso 2002a 2002b carleton 2003 ribera and mann 2003 turner 2004 and provides new evidence that the terrestrial cooling is caused by a simultaneous enso driven change in atmospheric circulation sourced in the amundsen sea and west antarctica

the spatial and temporal diversification of early palaeozoic vertebrates recent discoveries have dramatically altered traditional views of the stratigraphic distribution and phylogeny of early palaeozoic vertebrates and permit a reappraisal of biogeographic patterns and processes over the first 120 million years of vertebrate evolution stratigraphic calibration of the phylogenetic trees indicates that most of the pre silurian record can be inferred only through ghost ranges assessment of the available data suggests that this is due to a shift in ecological niches after the latest ordovician extinction event and a broadening of geographical range following the amalgamation of euramerica during the early silurian two major patterns are apparent in the bio geographic data firstly the majority of jawless fishes with dermoskeletal plated armour were highly endemic during cambrian ordovician time with arandaspids restricted to gondwana galeaspids to china and anatolepids astraspids and possibly heterostracans confined to laurentia these laurentian groups began to disperse to other continental blocks as the old red sandstone continent amalgamated through a series of tectonic collisions the second maj or pattern in contrast encompasses a number of microsquamous and naked jawed and jawless primitive vertebrates such as conodonts thelodonts placo derms chondrichthyans and acanthodians which dispersed rapidly and crossed oceanic barriers to attain cosmopolitan distributions although many have laurentian origins a clear difference in dispersal potential exists between these two types of fishes overall the development of biogeographic patterns in early palaeozoic vertebrates involved a complex interaction of dispersal vicariance and tectonic convergence

holocene climate variability in antarctica based on 11 ice core isotopic records a comparison is made of the holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east antarctica vostok dome b plateau remote komsomolskaia dome c taylor dome dominion range d47 km105 and law dome and west antarctica byrd with temporal resolution from 20 to 50 yr the long term trends possibly reflect local ice sheet elevation fluctuations superimposed on common climatic fluctuations all the records confirm the widespread antarctic early holocene optimum between 11 500 and 9000 yr in the ross sea sector a secondary optimum is identified between 7000 and 5000 yr whereas all eastern antarctic sites show a late optimum between 6000 and 3000 yr superimposed on the long time trend all the records exhibit 9 aperiodic millennial scale oscillations climatic optima show a reduced pacing between warm events typically 800 yr whereas cooler periods are associated with less frequent warm events pacing 1200 yr

eight centuries of volcanic signal and climate change at talos dome east antarctica 1 during the 1996 programma nazionale di ricerche in antartide international trans antarctic scientific expedition traverse two firn cores were retrieved from the talos dome area east antarctica at elevations of 2316 m td 89 m long and 2246 m st556 19 m long cores were dated by using seasonal variations in non sea salt nss so42 concentrations coupled with the recognition of tritium marker level 1965 1966 and nss so42 spikes due to the most important volcanic events in the past pinatubo 1991 agung 1963 krakatoa 1883 tambora 1815 kuwae 1452 unknown 1259 the number of annual layers recognized in the td and st556 cores was 779 and 97 respectively the d record obtained from the td core has been compared with other east antarctic isotope ice core records dome c epica south pole taylor dome these records suggest cooler climate conditions between the middle of 16th and the beginning of 19th centuries which might be related to the little ice age lia cold period because of the high degree of geographical variability the strongest lia cooling was not temporally synchronous over east antarctica and the analyzed records do not provide a coherent picture for east antarctica the accumulation rate record presented for the td core shows a decrease during part of the lia followed by an increment of about 11 in accumulation during the 20th century at the st556 site the accumulation rate observed during the 20th century was quite stable

little ice age neoglacial paleoenvironmental conditions at siple station antarctica the 550 year records of 18 o and dust concentrations from siple station antarctica suggest warmer and less dusty atmospheric conditions from 1600 to 1830 a d which encompasses much of the northern hemisphere little ice age lia dust and 18 o data from south pole station indicate that the opposite conditions e g cooler and more dusty were prevalent there during the lia meteorological data from 1945 85 show that the lia temperature opposition between amundsen scott and siple inferred from 18 o is consistent with the present spatial distribution of surface temperature there is some observational evidence suggesting that under present conditions stronger zonal westerlies produce a temperature pattern similar to that of the lia these regional differences demonstrate that a suite of spatially distributed high resolution ice core records will be necessary to characterize the lia in antarctica

isolating the role of mesoscale eddies in mixing of a passive tracer in an eddy resolving model 1 this study examines the role of mesoscale eddies in distribution of chlorofluorocarbon cfc in a numerical model of the north atlantic our main conclusions are based on a comparison of two eddy resolving experiments one with and one without eddy advection of cfc the cfc distributions in these two experiments exhibit substantial differences within the subpolar gyre in particular in the presence of eddies the horizontal distribution of cfc in the upper 1000 m is more uniform and the cfc concentration is lower in the lower 1500 m our analysis demonstrates that these basin wide differences are caused by the interactions of eddy advection with convection and mean advection in several isolated locations the corresponding eddy flux divergence terms are spatially non uniform in magnitude their effects are often nonlocal and sometimes work against the spreading of cfc being carried out by the mean advection these conclusions are further confirmed by a third experiment in which the eddy advection was replaced by a down gradient diffusive parameterization our results demonstrate that advection by mesoscale eddies is crucial to the mixing of atmospheric gasses into the ocean and outline difficulties in representing eddies by the down gradient diffusion

on the role of wind driven sea ice motion on ocean ventilation abstract simulations with a coupled ocean atmosphere sea ice model are used to investigate the role of wind driven sea ice motion on ocean ventilation two model experiments are analyzed in detail one including and the other excluding wind driven sea ice transport model simulated concentrations of chlorofluorocarbons cfcs are compared with observations from the weddell sea the southeastern pacific and the north atlantic the authors show that the buoyancy fluxes associated with sea ice divergence control the sites and rates of deep and intermediate water formation in the southern ocean divergence of sea ice along the antarctic perimeter facilitates bottom water formation in the weddell and ross seas neglecting wind driven sea ice transport results in unrealistic bottom water formation in drake passage and too strong convection along the southern ocean sea ice margin whereas convection in the weddell and ross seas is suppressed the freshwater fluxes implicitly associated with sea ice export also