the onset of islandscapes in the balearic islands a study case of addaia northern minorca spain abstract paleoenvironmental and archaeological data show that mediterranean landscapes result from long term socio environmental interactions mediterranean islands constitute a place of passage where the creation of cultural landscapes can be traced through colonization and anthropization histories palynological studies carried out in the balearic islands highlight a deep vegetation change from the mid to late holocene but the climate environmental human interactions are not fully understood yet in this study we aim to disentangle the causalities of landscape changes during the last six millennia using a multi proxy approach on an off site core for the first time in minorca island we find that during the mid holocene the climate was wetter than today with less rainfall seasonality than in the current mediterranean this climate favoured the expansion of box formations and the predominance of forested formations with minimal anthropized conditions first agropastoral activities appeared in the sequence between ca 3500 2650 cal bce in north eastern minorca coinciding with other sporadic archaeological evidence cova dels morts rock shelter which support the possibility of a pre chalcolithic discovery and frequentation of the island we record deep environmental change during the third millennium cal bce reflected in the substitution of the former mesophytic vegetation by mediterranean maquis formations dominated by wild olive trees heathers mastic and cistaceae we propose that maquis garrigues and open land vegetation were favoured by human action in a context of increasing climatic dryness and seasonality promoting vegetation flammability and substitution of former mesic communities to more adapted termophilous vegetation the comparison of our new record from addaia with other pollen studies from the balearic islands highlights the resilience of mesic vegetation to climate change this is shown by the survival of box formations to the increased aridification initiated at ca sixth fifth millennium cal bce ca 7 6 cal kyr bp in the western mediterranean which culminated at ca fourth third millennium cal bce ca 5 4 cal kyr bp additionally whilst sporadic human presence versus stable occupation are difficult to detect in archaeological records the coupling with paleoenvironmental studies may offer new scenarios and information for human arrival in the balearic islands

contrasting styles of explosive eruption at sete cidades sao miguel azores in the last 5000 years hazard implications from modelling abstract the deposits of three eruptions in the last 5000 years are described in detail in order to constrain eruptive parameters and allow a quantitative assessment of the hazard from a range of explosive eruption types at sete cidades volcano sao miguel azores these deposits include the caldeira seca eruption p17 which occurred around 600 yr bp which was the last explosive event from inside the sete cidades caldera the p11 eruption dated at 2220 70 yr bp and the undated p8 eruption our studies reveal that the caldeira seca eruption p17 produced ash rich deposits probably as the result of hydromagmatic eruptions and several lapilli fall layers dispersed in different directions the lapilli fall layers were derived from eruption columns up to10 km high evidence indicates pyroclastic density currents pdcs only moved outside of the caldera on to the western flank the p11 deposit represents one of the largest eruptions at sete cidades in the last 5000 years the deposits are composed of two units the main lower one is a lapilli fall deposit inferred to be derived from an eruption column 18 km high evidence for pdcs outside of the caldera occurs to the southeast and northwest the p8 deposits are composed of numerous alternating lapilli and ash layers representing a highly pulsatory eruption almost all of which are of a fallout origin the lapilli are inferred to be derived from eruption columns up to 8 km in height using the eruptive parameters derived from these deposits we use hazmap macedonio g costa a longo a 2005 a computer model for volcanic ash fallout and assessment of subsequent hazard comput geosci 31 837 845 to constrain the probability of fallout of different loads and thicknesses two end member scenarios were used with hazmap one representing a p17 eruption and another representing a p11 eruption both scenarios use wind profile data averaged over 25 years for a p17 type event there is a 5 chance of tephra fallout exceeding 15 cm thickness in ponta delgada the capital of sao miguel indicating that roof collapse associated with such an event is unlikely the larger magnitude and higher intensity p11 type eruption provides a 5 probability that tephra loads thicknesses would exceed 92 cm in ponta delgada and that roof collapse could be a major problem to assess the distribution of pdcs from future eruptions we use a gis application of the energy line model toyos g cole p d felpeto a marti j 2006 a gis based methodology for hazard mapping of small volume pyroclastic density currents nat hazards 41 99 112 the model indicates that individual pdcs of up to 10 7 m 3 derived from a vent located centrally within the caldera and a fountain collapse height of 500 m above the caldera floor could be completely contained within the caldera however pdcs derived from a vent located at caldeira seca in the western part of the caldera show individual pdcs 10 5 m 3 would travel out of the caldera and down the western flank as the vent location from a future eruption within the sete cidades caldera is unknown the hazard from pdcs is high for anywhere on the immediate flanks of the volcano

atlas of pollen spores and further non pollen palynomorphs recorded in the glacial interglacial late quaternary sediments of lake suigetsu central japan abstract the record of well preserved palynomorphs from sediment samples of lake suigetsu mirrors temporal changes in the flora around the lake and spatial changes in the vegetation cover of central japan during the late quaternary this study presents photographic images of 169 identifiable types of moss lycophyte and fern spores and pollen of gymnospermous and angiospermous plants from the sg06 core sediment obtained at a standard magnification of ca 750 additionally non pollen palynomorphs npps which appeared in the pollen slides are documented including remains of fungi rhizopods arthropods rotifers flatworms as well as green algae and plant tissue fragments all documented taxa are presented in taxonomical order on 66 plates including 55 plates for pollen and spores of higher plants and 11 plates for npps this study renders an overview on quality of preservation and on the range of palynomorphs found in the last glacial interglacial sediments of lake suigetsu and furthermore may serve as a handy and thorough guide for palynological investigations aiming at the reconstruction of past vegetation environmental and climate dynamics

multiple post caledonian exhumation episodes across nw scotland revealed by apatite fission track analysis abstract the post caledonian exhumation history of nw scotland is a controversial issue with some studies advocating largely continual emergence whereas others suggest dominantly early palaeogene plume driven exhumation apatite fission track analysis afta data for samples of precambrian basement and permian cretaceous sediments from onshore and offshore reveal multiple phases of post caledonian cooling triassic beginning 245 225 ma cretaceous 140 130 ma 110 90 ma and cenozoic 65 60 ma 40 25 ma 15 10 ma all of which are interpreted at least in part as recording exhumation basement and sedimentary cover rocks display similar thermal histories emphasizing the regional nature of these episodes and implying that sedimentary outliers represent the remnants of previously more extensive sequences significant thicknesses of jurassic rocks may once have covered nw scotland palaeocene palaeothermal effects are most pronounced in the vicinity of igneous centres probably reflecting combined effects of heating by elevated heat flow deeper burial and hydrothermal activity most of the region underwent kilometre scale neogene exhumation contrary to the common assumption of monotonic cooling and denudation histories integration of geological evidence with afta data defines an episodic thermal history involving repeated cycles of burial and exhumation we suggest that onshore passive margins and continental interiors may also best be characterized by similar histories

neogene stratigraphy and the sedimentary and oceanographic development of the nw european atlantic margin a regional correlation of neogene stratigraphy has been attempted along and across the nw european atlantic continental margin between mid norway and sw ireland two unconformity bounded successions are recognised these are referred to as the lower and upper neogene successions and have been dated as miocene early pliocene and early pliocene holocene respectively in age their development is interpreted to reflect plate wide tectonically driven changes in the sedimentary oceanographic and latterly climatic evolution of the ne atlantic region the lower neogene succession mainly preserves a record of deep water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities within this succession on both sides of the eastern greenland scotland ridge from the mid miocene this is interpreted to record enhanced deep water exchange through the faroe conduit deepest part of the southern gateway and can be linked to compressive inversion of the wyville thomson ridge complex thus a pervasive interconnected arctic north atlantic deep water circulation system is a neogene phenomenon the upper neogene succession records a regional change at about 4 ma in the patterns of contourite sedimentation submarine erosion new depocentres coeval with the onset of rapid seaward progradation of the continental margin by up to 100 km this build out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin associated changes in deep water circulation may be part of an atlantic wide reorganisation of ocean bottom currents glacial sediments form a major component of the prograding shelf margin shelf slope sediment wedges but stratigraphic data indicate that the onset of progradation pre dates significant high latitude glaciation by at least 1 ma and expansive northern hemisphere glaciation by at least 3 ma

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

discussion on multiple post caledonian exhumation episodes across nw scotland revealed by apatite fission track analysis journal vol 167 675 694 the question of the former extent of jurassic strata over the scottish highlands has been debated since the nineteenth century discussion by arkell 1933 arkell s conclusion that the main part of the highlands was land during that period has been followed by subsequent palaeogeographers wills 1951 ziegler 1990 bradshaw et al 1992 although underhill partington 1993 emphasized the greater effect of doming in the north sea in delivering jurassic sediments to the adjacent basins and postulated a marine connection between the moray firth and hebridean basins along the line of the great glen apatite fission track analysis afta is a powerful method for assessing the former existence of substantial thicknesses of strata over areas where they have subsequently been stripped by uplift and erosion the paper by holford et al 2010 is a welcome application of this technique to nw scotland the authors conclude that thick jurassic rocks may once have covered nw scotland abstract and our results imply that comparable successions with the 2 5 km in the north minch basin were deposited where jurassic rocks are now missing

late holocene environmental change and the anthropization of the highlands of santo antao island cabo verde abstract cabo verde was the first tropical archipelago colonized by europeans historians have suggested that the first colonizers initiated archipelago wide ecosystem degradation loss of vegetation cover and erosion however the human environment interactions that led to the archipelago s current environmental status remain poorly understood here we report the first palaeoecological study of past vegetation change and disturbance regimes for cabo verde we present a 2130 yr old sediment sequence from a volcanic caldera cova de paul located at 1200 m asl on santo antao island for which we analyzed fossil pollen non pollen palynomorphs npps charcoal silica bodies and grain size distribution our analyses do not show evidence of the presence of temperate tropical or subtropical forests growing on the summits of santo antao in pre human times the pollen record shows that scrubland and grasslands dominated the highlands and underwent compositional changes ca 1850 and 1300 cal yr bp these shifts overlap with erosion phases and are linked to intensified seasonality steady rates of sedimentation marked the period 1230 to ca 350 cal yr bp but an increase in charcoal concentrations indicate a drying phase increases in regional and local fire peaks of coprophilous fungi and the presence of new world crop pollen zea mays are interpreted as the onset of portuguese settlement of the highlands after 450 bp sustained erosion between ca 350 and 100 cal yr bp indicate soil degradation and the pollen record shows the increase in introduced herbaceous taxa rosaceae centaurea verbenaceae and exotic tree taxa e g pinus while shifting abundances of coprophilous fungi indicate changes in land use the record shows stabilization of soils in the last century due to recent afforestation of the highlands further palaeoecological studies have the potential to provide further detail of the long term dynamics of cabo verde ecosystems and to inform conservation initiatives

organic maturation thermal history and hydrocarbon generation in the orcadian basin scotland the devonian orcadian basin contains thick sequences of organic rich lacustrine sediments of interest as hydrocarbon source rocks throughout the basin the range of organic maturation is large spore colours vary from yellow orange to black and vitrinite reflectance for type iii kerogens ranges from 0 7 to 10 5 maximum palaeotemperatures are estimated to range from those typical of moderate burial diagenesis 100 c to those characteristic of greenschist facies metamorphism 400 c the highest maturities are related to contact metamorphism by devonian plutons and it is postulated that a large pluton underlies much of caithness high and low maturity regions are often juxtaposed across major faults which were active during variscan inversion regionally the lowest maturity is about 0 8 r o implying uplift and erosion of 2 3 km of cover basin wide this cover was probably a sequence of late devonian and carboniferous rocks removed largely during variscan uplift geothermal gradients were high but variable during devonian extension this together with the contact metamorphic affects of the devonian plutons resulted in early maturation metamorphism of large areas of the basin most of the onshore sequence entered the oil window during devonian and carboniferous times significant generation of hydrocarbons from orcadian lacustrine facies offshore during subsequent mesozoic burial will have occurred only in those areas which escaped maturation during the palaeozoic

late pleistocene and holocene environmental change inferred from the cocha caranga sediment and soil records in the southeastern ecuadorian andes abstract late pleistocene and holocene vegetation climate and fire dynamics of mountain forest and paramo ecosystems as well as human impact are presented from the cocha caranga area at 2710 m elevation in the podocarpus national park southeastern ecuadorian andes palaeoenvironmental changes inferred from two sediment cores and a soil core were investigated by pollen spore algae and charcoal analyses during the transition from late pleistocene to early holocene between ca 14 500 to 9700 cal yr bp upper mountain forest vegetation expanded suggesting increasing temperature and moisture this expansion abruptly stopped with increasing fires at ca 9700 cal yr bp and open grassy vegetation became established the period from ca 9700 to 1300 cal yr bp of strong fire intensity indicate that vegetation components mainly weinmannia and myrica react sensitively to past probably human caused fires during the last few centuries modern vegetation established characterised by open grassy areas with forest patches and small mires the green algae botryococcus braunii isoetes and cyperaceae were used to identify lake level fluctuation to reconstruct holocene wet dry phases drier climatic conditions occurred from ca 9700 to 6900 cal yr bp and from ca 4200 to 1300 cal yr bp from ca 6900 to 4200 cal yr bp and from ca 1300 cal yr bp to modern times wetter climatic conditions occurred

diatom inferred ecological responses of an oceanic lake system to volcanism and anthropogenic perturbations since 1290 ce abstract the impacts of natural and human induced processes on lake ecosystems in remote oceanic islands remain to be fully elucidated these lakes are excellent candidates to analyze the importance of anthropogenic vs natural forces driving lacustrine long term ecological evolution from previous pristine pre colonized conditions disentangling the effects of both is particularly relevant in highly active volcanic areas where catastrophic eruptions can act as an atypical natural driver altering the lake s long term ecological trajectories in this paper we study past ecological changes occurring in lake azul sao miguel island a crater lake from the remote azorean archipelago to address which were the main causes of its long term trophic history we analyzed diatom assemblages sedimentology and bulk organic matter of sediments deposited since ca 1290 ce when a huge local eruption occurred this episode drove the evolution of lake azul through six distinct phases commencing with a restart of ecological succession after tephra deposition disrupted biogeochemical cycling the alteration was so profound that the lake underwent a state of oligotrophic conditions for approx 650 yr nutrients were sourced by fish induced internal recycling and the overflow of the near lake verde during this period rather than by allochthonous nutrient inputs modulated by climate variability and or vegetation cover changes in the watershed after the official portuguese colonization it was only after recent artificial fertilization when the system overcame the volcanic induced long term resilience this over fertilization and a reduction in water turnover exacerbated the recent symptoms of eutrophication after 1990 ce contrary to other studies lake azul constitutes an uncommon case of long term resilience to trophic change induced by a cataclysmic volcanic eruption it brings new insights into the fate of lake ecosystems which might be affected by similar events in the future

stable isotopic composition of precipitation over the northern slope of the central himalaya stable water isotope data 6d and 18 o from three groups of samples fresh snow and snow pit samples collected on qomolangma mount everest and xixabangma during field seasons 1997 1998 and 2001 and precipitation samples collected at tingri station during summer 2000 are presented and used to survey the isotopic composition of precipitation over the northern slope of the central himalaya multi year snow pit samples on qomolangma have a local meteoric water line slope 8 close to the global value deuterium excess d d 8 18 o values at tingri are much lower than those in fresh snow from qomolangma probably due to differences in moisture source and air mass trajectories as well as local weather conditions there is no obvious seasonal trend for d values in the qomolangma region a negative relationship exists between 18 o and d values in both fresh snow on qomolangma and precipitation at tingri fresh snow samples collected from different altitudes on xixabangma allow us to investigate the altitude effect on 18 o values in snow of four storm events only one has an obvious altitude effect on 18 o variation and a very low gradient of 0 1 per 100 m elevation

kaolins in gravels and saprolites in north east scotland evidence from stable h and o isotopes for palaeocene miocene deep weathering stable isotope ratios can provide important evidence for estimating groundwater temperatures during the formation of clay minerals in response to chemical weathering of rocks at the landsurface in this paper we investigate weathering kaolins found in buchan ne scotland stable oxygen and hydrogen isotopes for kaolins from weathered clasts in post cretaceous fluvial gravels and from clay rich saprolites developed in dalradian metamorphic and caledonian igneous rocks indicate weathering under warm groundwater temperatures of 23 5 c comparisons with cenozoic palaeotemperatures derived from north sea sediments indicate that weathering took place under humid tropical climates of the palaeocene eocene the 25 m deep weathering profiles in the buchan gravels indicate that these coarse quartzite and flint bearing gravels are older than previously thought and were likely deposited by rivers which also fed thick palaeocene early eocene deep water sand fans in the western north sea basin a later phase of kaolin weathering at lower temperatures of 15 5 c took place in the middle miocene kaolinitic weathering remnants are largely confined to elevations of 100 m in eastern buchan and define a well preserved deeply weathered cenozoic landscape in north east scotland

groundwater recharge environments and hydrogeochemical evolution in the jiuquan basin northwest china the groundwater recharge environments and hydrogeochemical characteristics in the quaternary aquifer of jiuquan basin was investigated using a combination of chemical indicators stable isotopes and radiocarbon dating the d excess values of winter precipitation and surface water revealed that the meltwater from snow and ice played the dominant role in the basin s surface water supply the unconfined groundwater showed gradual enrichment of heavy isotopes along the flow path but delta o 18 and delta h 2 values were similar to those of surface water suggesting recent recharge as a result of rapid seepage along rivers combined with the effects of high evaporation the c 14 pmc values of unconfined groundwater was between 71 5 and 90 9 and since 80 modern carbon probably represents the upper limit of initial c 14 activity this suggests that the groundwater is relatively young the confined groundwater was depleted in heavy isotopes coupled with low c 14 values similar to 20 53 indicating that the groundwater was mainly recharged as palaeowater during the late pleistocene and holocene epochs under a cold climate the surface water and most groundwater samples were fresh rather than saline with tds 490 and 1000 mg l 1 respectively the chemistry of unconfined groundwater changed from hco3 dominated to no dominant ions and then to so42 dominated moving along the flow path from the jiuquan jiayuguan basin to the jinta basin and the confined water was so42 dominated the results have important implications for groundwater management in the basin where a high proportion of the water being used is in effect being mined i e extracted faster than its replacement rate thus significant changes are urgently needed in the regional water use strategy c 2012 elsevier ltd all rights reserved

palynological signal of the younger dryas in the tropical venezuelan andes the occurrence or not of the younger dryas cold reversal in the tropical andes remains a controversial topic this study reports a clear signal for this event in the venezuelan andes employing high resolution palynological analysis of a well dated sediment core from laguna de los anteojos situated around 3900 m elevation within grass paramo vegetation the lake is surrounded by some polylepis forests which are close to their upper distribution limit the section of the core discussed here is 150 cm long and dated between about 14 68 and 9 35 cal kyr bp using a polynomial age depth model based on six ams radiocarbon dates between 12 86 and 11 65 cal kyr bp an abrupt shift occurred in the pollen assemblage manifested by a decline of podocarpus polylepis and huperzia combined with an increase in poaceae and asteraceae the aquatic pteridophyte isoetes also decreased and disappeard and the algae remains show their minimum values pollen assemblages from the younger dryas interval show maximum dissimilarity values compared with today s pollen assemblage and are more similar to modern analogs from superparamo vegetation growing at elevations 400 500 m higher a lowering of vegetation zones of this magnitude corresponds to a temperature decline of between 2 5 and 3 8 c during this colder interval lake levels may have been lower suggesting a decrease in available moisture the vegetation shift documented in anteojos record between 12 86 and 11 65 cal kyr bp is comparable to the el abra stadial in the colombian andes but it differs in magnitude the anteojos shift is better dated and coincides with the younger dryas chron as recorded in the cariaco basin sea surface temperature reconstructions and records of continental runoff as well as in the oxygen isotope measurements from the greenland ice cores when compared to other proxies of quasi immediate response to climate the time lag for the response of vegetation to climate is found to be negligible at a centennial scale the polylepis pollen curve is especially noteworthy as it reproduces the overall pollen trends and matches well with paleoclimatic reconstructions based on other proxies hence polylepis might be used as a reliable paleoclimatic indicator in lake sediments close to its uppermost distribution boundary

vegetation and landscape dynamics under natural and anthropogenic forcing on the azores islands a 700 year pollen record from the sao miguel island abstract the azores archipelago has provided significant clues to the ecological biogeographic and evolutionary knowledge of oceanic islands palaeoecological records are comparatively scarce but they can provide relevant information on these subjects we report the palynological reconstruction of the vegetation and landscape dynamics of the sao miguel island before and after human settlement using the sediments of lake azul the landscape was dominated by dense laurisilvas of juniperus brevifolia and morella faya from ca 1280 ce to the official european establishment 1449 ce after this date the original forests were replaced by a complex of erica azorica myrsine africana forests shrublands and grassy meadows which remained until ca 1800 ce extractive forestry cereal cultivation rye maize wheat and animal husbandry progressed until another extensive deforestation ca 1774 ce followed by the large scale introduction 1845 ce of the exotic forest species cryptomeria japonica and pinus pinaster which shaped the present day landscape fire was a significant driver in these vegetation changes the lake levels experienced a progressive rise during the time interval studied reaching a maximum by ca 1778 1852 ce followed by a hydrological decline likely due to a combination of climatic and anthropogenic drivers our pollen record suggests that sao miguel were already settled by humans by ca 1287 ce approximately one century and a half prior to the official historically documented occupation of the archipelago the results of this study are compared with the few palynological records available from other azores islands pico and flores

fracture controls on valley persistence the cairngorm granite pluton scotland valleys are remarkably persistent features in many different tectonic settings but the reasons for this persistence are rarely explored here we examine the structural controls on valleys in the cairngorms mountains scotland part of the passive margin of the eastern north atlantic we consider valleys at three scales straths glens and headwater valleys the structural controls on valleys in and around the cairngorm granite pluton were examined on satellite and aerial photographs and by field survey topographic lineaments including valleys show no consistent orientation with joint sets or with sheets of microgranite and pegmatitic granite in this granite landscape jointing is not a first order control on valley development instead glens and headwater valleys align closely to quartz veins and linear alteration zones lazs lazs are zones of weakness in the granite pluton in which late stage hydrothermal alteration and hydro fracturing have greatly reduced rock mass strength and increased permeability lazs which can be kilometres long and 700 m deep are the dominant controls on the orientation of valleys in the cairngorms lazs formed in the roof zone of the granite intrusion although the cairngorm pluton was unroofed soon after emplacement the presence of old red sandstone ors outliers in the terrain to the north and east indicates that the lower relief of the sub ors basement surface has been lowered by 1 km of vertical erosion and for 400 myr this valley persistence is a combined product of regionally low rates of basement exhumation and of the existence of lazs in the cairngorm pluton and sub parallel caledonide fractures in the surrounding terrain with depths that exceed 1 km

a holocene lacustrine record in the central north atlantic proxies for volcanic activity short term nao mode variability and long term precipitation changes a holocene lacustrine record in the central north atlantic proxies for volcanic activity short term nao mode variability and long term precipitation changes

the effect of refreezing on the isotopic composition of melting snowpack the isotopic composition of solid and liquid portions of natural melting snowpack is investigated in detail by the separating of liquid water from snow grains at different depths of the snowpack the slope of the d 18o line for the liquid phase is found to be lower than for the solid phase this is proved to be due to the isotopic fractionation occurring in the melt freeze mass exchange within the snowpack melting of the snowpack has no clear impact on the d 18o line for the solid phase but the slope of the d 18o line for the liquid shows an overall slight decrease in the melting period when the snowpack is refrozen the refreezing process would inevitably cause the slope of the solid phase to decrease because of the discrepancy between the slopes of the two phases thus the slope of the solid would become lower and lower as the diurnal melt freeze episodes cycle throughout the melting season this effect is then demonstrated by looking into the isotopic composition changes of glacier firn the extent of the effect depends on the snowpack properties and environmental conditions the slope changes also result in a decreasing trend in deuterium excess copyright 2007 john wiley sons ltd

the late quaternary decline and extinction of palms on oceanic pacific islands late quaternary palaeoecological records of palm decline extirpation and extinction are explored from the oceanic islands of the pacific ocean despite the severe reduction of faunal diversity coincidental with human colonisation of these previously uninhabited oceanic islands relatively few plant extinctions have been recorded at low taxonomic levels recent faunal extinctions on oceanic islands are concentrated in larger bodied representatives of certain genera and families fossil and historic records of plant extinction show a similar trend with high representation of the palm family arecaceae late holocene decline of palm pollen types is demonstrated from most islands where there are palaeoecological records including the cook islands fiji french polynesia the hawaiian islands the juan fernandez islands and rapanui a strong correspondence between human impact and palm decline is measured from palynological proxies including increased concentrations of charcoal particles and pollen from cultivated plants and invasive weeds late holocene extinctions or extirpations are recorded across all five of the arecaceae subfamilies of the oceanic pacific islands these are most common for the genus pritchardia but also many sedis fossil palm types were recorded representing groups lacking diagnostic morphological characters

linking onshore and offshore structures mesozoic extension in the scottish highlands geological relationships in the offshore basins flanking northern scotland suggest that a regional caledonian control on the structure of these basins is far from proven but conversely mesozoic faults of the offshore set may extend onshore the strathconnon fault long held to be late caledonian may be mesozoic in age forming the principal kinematic link between the east and west coast basins of northern scotland the numerous outcrops of precambrian basement within the minch hebrides basin nearly all lie in the uplifted footwalls of mesozoic faults similar fault controls on the distribution of onshore outcrop within the precambrian may exist

quantitative determination of tertiary sediment supply to the north sea basin sediment supply comprises a major family of regime variables that influence geomorphic surface grade spatial and temporal changes in total sediment supply and sediment texture gravel sand mud ratio will cause reconfiguration of depositional and erosional profiles potentially creating or influencing the sequence stratigraphic framework of the basin sequence grain volume which is defined as the volume of sedimentary grains in an individual stratigraphic sequence total sequence volume minus cement and porosity volume has been quantitatively determined for each of 16 genetic stratigraphic sequences in the north sea basin rates of total sediment supply to the basin in both time and space were then calculated sand grain volume and sand mud ratio were also calculated for each sequence these data define four principal episodes of tertiary sediment supply the most significant episode occurred in the late paleocene and was followed by secondary episodes in the eocene and oligocene a fourth neogene episode extends through the present all episodes correlate to source terrain tectonic pulses related to evolution of the north atlantic basin to intraplate stress changes associated with successive phases of the alpine orogeny or to the late cenozoic epeirogenic uplift of scandinavia the major episodes in turn contain secondary sequence to sequence variations that correspond to changes in spatial or temporal values of one or both of the supply regime variables again most changes closely reflect details within the histories of the principal tectonic phases the history of changing source area relief and resulting topographic grades and related changes in sediment yield into the basin was a principal control on north sea cenozoic sequence development source basin relief in turn was largely determined by regional tectonism

anatomy of a dansgaard oeschger warming transition high resolution analysis of the north greenland ice core project ice core large and abrupt temperature oscillations during the last glacial period known as dansgaard oeschger do events are clearly observed in the greenland ice core record here we present a new high resolution chemical 2 mm and stable isotope 20 mm record from the north greenland ice core project ngrip ice core at the onset of one of the most prominent do events of the last glacial do 8 observed 38 000 years ago the unique subannual resolution ngrip record provides a true sequence of change during a do warming with detailed annual layer counting of very high depth resolution geochemical measurements used to determine the exact duration of the transition the continental ions indicative of long range atmospheric loading and dustiness from east asia are the first to change followed by the snow accumulation the moisture source conditions and finally the atmospheric temperature in greenland the sequence of events shows that atmospheric and oceanic source and circulation changes preceded the do warming by several years

a compartmental mixing cell approach for the quantitative assessment of groundwater dynamics in the otway basin south australia abstract transient groundwater fluxes as calculated by a groundwater flow model modflow are used as input into a compartmental mixing cell cmc model to simulate the transport of hydrochemical and isotopic species in regional groundwater systems good agreement between modeled and measured concentrations of solutes in groundwater provides greater confidence in estimating aquifer parameters for the flow model the cmc model is currently developed for multi layered groundwater systems and allows for both recharge to the uppermost aquifer and upward or downward leakage between individual aquifers the combination of the cmc approach and modflow allows chemical and hydraulic data to be analysed simultaneously to allow for improved conceptualization of the groundwater system the use of transient fluxes reflects the temporal scale and variability of the chemical tracers as well as the temporal variability of hydraulic conditions the model is applied to a transect in the gambier embayment of the otway basin in south australia to quantify mixing between two main aquifer systems this groundwater system is hydraulically connected to the ocean in the west and as a result would have been affected by sea level changes over the last 30 000 yr radiocarbon simulations helped to quantify a major zone of downward leakage to the confined aquifer with modeled rates of leakage ranging 2 9 mm yr

late cretaceous unroofing of the white mountains new hampshire usa an episode of passive margin rejuvenation the growing recognition that many passive margins have experienced periods of post rift uplift has raised new questions about the nature of the tectonic processes that drive such uplift the eastern north america margin is of particular interest because it is a classic atlantic style margin that has long been suspected of tectonic rejuvenation yet the timing of post rift uplift events remains elusive to address this question we present apatite u th he and fission track ages from a 1300 m vertical transect in the white mountains of new hampshire usa including a 910 m deep bore hole thermal modeling suggests a period of accelerated denudation from ca 85 to 65 ma this timing is broadly similar to the timing of accelerated exhumation and compression on passive margins elsewhere in the atlantic raising the question of whether a common mechanism such as a change in lateral stresses changes in mantle convection or climate change could be responsible

deuterium excess record from central greenland over the last millennium hints of a north atlantic signal during the little ice age a stacked water isotope record for summit central greenland has been established covering approximately the last 900 years measurements of 18o and d in the grip deep ice core and the 230 m core s93 allow the reconstruction of a millennial record of the deuterium excess in a near annual resolution a short period of particularly high values of the deuterium excess at the beginning of the fourteenth century may be associated with the medieval warm period mwp the little ice age lia might be represented by a 100 year period of very low excess values in the sixteenth and seventeenth centuries using a simple isotope model 18o and deuterium excess are interpreted in terms of surface temperature variations over central greenland and over the subtropical north atlantic greenland s principal vapor source region an estimated cooling of 0 7 c of subtropical sea surface temperatures ssts during the little ice age and a warming of 0 6 c during the short warm period in the medieval is in agreement with previous studies over periods of about 100 years an antiphasing between gradually decreasing 18o and increasing deuterium excess is observed interannual to decadal scale variability associated to the north atlantic oscillation may be responsible for this anti phase relationship an alternative explication is a north south oscillation in north atlantic sea surface temperatures associated with short term changes in the thermohaline circulation

changes of 2 h and 18 o enrichment of meteoric water and pleistocene glaciation recent theoretical modelling1 has suggested that the well documented d 18o relationship for modern meteoric waters may have changed during the pleistocene glacial periods in response to increased ocean surface air humidity here we present isotopic data on fluid inclusions and host speleothem which support this hypothesis depositional temperatures can be determined for speleothems formed in equilibrium conditions from the temperature dependence of the calcite water 18o fractionation by isotopic analysis of both entrapped fluid inclusions and host calcite palaeotemperatures for five areas of east central north america and bermuda calculated assuming the present d 18o meteoric water relationship for fluid inclusion waters are observe dto be too low during late pleistocene glacial periods in some instances falling below 0 c by contrast interglacial palaeotemperatures are largely equivalent to those in the areas at present as speleothem deposition cannot occur at subzero temperatures a possible solution to this dilemma is a shift in the intercept of the meteoric water relationship

volcanic lakes of the azores archipelago portugal geological setting and geochemical characterization abstract a representative set of 30 lakes from the azores archipelago portugal has been studied to obtain data on their volcanic setting and water geochemistry the majority of the studied lakes are located inside volcanic craters and subsidence calderas while the remaining lakes are located in topographic depressions not associated with volcanic centres in depressions of tectonic origin and inside lava caves in general the azorean volcanic lakes are small with surface areas between 8 94 10 4 km 2 and 4 35 km 2 and volumes between 2 4 10 3 and 4 78 10 7 m 3 median 3 99 10 4 m 3 presenting maximum depths between 0 8 and 33 m mostly of the na cl to na hco 3 type the lake waters are generally low temperature 11 9 24 6 c very dilute tds range between 11 0 and 356 2 mg l median 36 8 mg l and a clear exception is furna do enxofre lake graciosa island that shows a mg trend two types of lake waters can be recognized 1 one is characterized by na cl ratio close to the seawater value and have evolved and evolve by marine contribution and 2 na hco 3 type waters that in addition to sea salt input have been influenced by other processes e g water rock interaction hydrothermal seepage into the lake bottom evident from higher total co 2 content 365 1 mg l and sio 2 content 74 9 mg l as well demonstrated by in the furna do enxofre lake nevertheless volcanic contribution cannot be excluded for some lakes as furna do enxofre vertical profiles made at the deepest lakes of sao miguel reveal that major ion content varies little with depth largely independent of the occurrence of thermally driven density stratification in summer for some lakes however dissolved co 2 increases with depth and is kept in the hypolimnion in summer whereas the hco 3 content is stable suggesting that co 2 release exceeds acidity neutralization by water rock interaction during winter without stratification the dissolved co 2 increase is less sharp for the majority of the lakes with the exception of furnas and furna do enxofre lakes the co 2 enrichment observed for certain lakes e g furna do enxofre and furnas implies a volcanic input moreover as these lakes themselves are located near hydrothermal surface manifestations they therefore offer good targets of volcano monitoring in the azores

cenozoic post rift sedimentation off northwest britain recording the detritus of episodic uplift on a passive continental margin the cenozoic sedimentary basins on the atlantic margin of nw britain contain a remarkable record of tectonically influenced post breakup sedimentation we have mapped the distribution and quantified the solid grain volume of four unconformity bound successions in the region the eocene 6 8 104 km3 oligocene 2 104 km3 miocene lower pliocene 4 5 104 km3 and lower pliocene holocene 4 5 104 km3 complementing previous work on the paleocene succession approximately 80 of the total cenozoic sediment volume on the atlantic margin of nw britain was deposited in eocene and later times the relative volumes of the cenozoic succession do not support previous claims that the paleocene was the main period of cenozoic uplift and erosion of sediment source areas rather the cenozoic sedimentary basins on the atlantic margin of nw britain record the detritus of four major episodes of cenozoic uplift of the british isles paleocene eocene oligocene miocene and pliocene pleistocene

the last 5000 years of activity at sete cidades volcano sao miguel island azores implications for hazard assessment abstract sete cidades is a central volcano with a summit caldera at the western end of sao miguel island azores its stratigraphy comprises two main geological groups the inferior group the units of which date from more than 200 000 years ago through to 36 000 years before present consisting of thick lava flows and subaerial volcaniclastic deposits that built the base of the central volcano and the superior group which comprises all the activity from the last 36 000 years including pumice and scoria fallout and pdc deposits with minor lava flows the volcanostratigraphy is divided into six main formations risco ajuda bretanha lombas santa barbara and lagoas each defined by different activity phases in the volcano s evolution the present caldera developed in three phases associated with massive paroxysmal eruptions which occurred approximately 36 000 29 000 and 16 000 years before present since the last caldera forming event eruptive activity has been predominantly explosive and a variety of deposits have been produced by different eruptive styles associated with three specific settings 1 pumice fall deposits pyroclastic density currents and hydromagmatic events from eruptions inside the caldera 2 lava domes cinder cones and basaltic lava flows from eruptions on the volcano flanks 3 tuff ring and tuff deposits from surtseyan eruptions offshore the more recent history of the volcano is marked by a change in the intracaldera activity from dominantly magmatic behaviour to a hydromagmatic character which happened about 5000 years ago since then at least 15 basaltic subaerial and submarine eruptions have occurred on the volcano flanks and 17 trachytic s l explosive eruptions have occurred within the caldera the most recent of which took place about 700 years ago this eruptive frequency makes sete cidades probably the most active volcanic centre in the azores in this paper we present the stratigraphy and a description of the deposits which originate from the last 5000 years in order to delineate sete cidades recent eruptive history for the purpose of estimating the hazard associated with this volcano an event tree has been designed to systematize possible future eruptive scenarios and to aid the assessment of relative probabilities of occurrence of different potential eruptive styles the probabilities for all nodes on the event tree together with their associated uncertainties were obtained by expert elicitation providing results that accord with the geologic record these probability estimates indicate that 1 basaltic strombolian and submarine eruptions are the most likely to occur 2 trachytic activity from the central volcano magmatic system is more probable in the intracaldera environment than on the flanks and 3 explosive activity is more likely than effusive for the trachytic system worst case scenario and maximum expected events are identified according to the eruptive scenarios and their probabilities of occurrence

a comparison of deep antarctic ice cores and their implications for climate between 65 000 and 15 000 years ago abstract three ice cores drilled in the central part of the antarctic continent extend back to the last glacial period one from west antarctica byrd and two from east antarctica vostok and dome c this period is also partly covered by a few cores from the coastal areas in these cores climatic information is mostly derived from the isotopic profiles d or 18 o from which surface temperature and more indirectly precipitation rate can be estimated the main objective has been to compare thoroughly the three deep ice cores for the main part of the last glacial period from ca 65 000 15 000 yr b p the time scales have been examined in detail and a new 40 000 yr chronology for the dome c core adopted special emphasis is placed on the link between the concentration of 10 be and past accumulation changes and on the use of peaks in the concentration of this cosmogenic isotope as stratigraphic markers elevation changes of the ice sheet derived from gas content and isotopic data bear directly on interpretations of past temperature and precipitation rate changes

holocene changes in tropical wind intensity and rainfall evidence from southeast ghana abstract remnants of a fixed aeolian dune ridge occur along the southeast coast of ghana just behind the present shoreline aeolian sands also cover extensive areas of the accra plains no dunes are present here the sands mainly occurring as sheets which blanket an early holocene landscape the sediments are of mid holocene age and were deposited during the interval 4500 b p 3800 yr b p when the southwesterly winds were stronger than they are at present and much of tropical africa seems to have been subject to marked aridity the onset of drier windier conditions around 4500 yr b p brought to an end the more equable climates than had characterized much of west africa during the earlier holocene aridity intensified winds and desert expansion between 4500 and 3800 yr b p parallel environmental conditions in tropical continental areas at the height of the late pleistocene glaciation

vegetation changes and human settlement of easter island during the last millennia a multiproxy study of the lake raraku sediments earlier palynological studies of lake sediments from easter island suggest that the island underwent a recent and abrupt replacement of palm dominated forests by grasslands interpreted as a deforestation by indigenous people however the available evidence is inconclusive due to the existence of extended hiatuses and ambiguous chronological frameworks in most of the sedimentary sequences studied this has given rise to an ongoing debate about the timing and causes of the assumed ecological degradation and cultural breakdown our multiproxy study of a core recovered from lake raraku highlights the vegetation dynamics and environmental shifts in the catchment and its surroundings during the late holocene the sequence contains shorter hiatuses than in previously recovered cores and provides a more continuous history of environmental changes the results show a long gradual and stepped landscape shift from palm dominated forests to grasslands this change started c 450 bc and lasted about two thousand years the presence of verbena litoralis a common weed which is associated with human activities in the pollen record the significant correlation between shifts in charcoal influx and the dominant pollen types suggest human disturbance of the vegetation therefore human settlement on the island occurred c 450 bc some 1500 years earlier than is assumed climate variability also exerted a major influence on environmental changes two sedimentary gaps in the record are interpreted as periods of droughts that could have prevented peat growth and favoured its erosion during the medieval climate anomaly and the little ice age respectively at c ad 1200 the water table rose and the former raraku mire turned into a shallow lake suggesting higher precipitation evaporation rates coeval with a cooler and wetter pan pacific ad 1300 event pollen and diatom records show large vegetation changes due to human activities c ad 1200 other recent vegetation changes also due to human activities entail the introduction of taxa e g psidium guajava eucalyptus sp and the disappearance of indigenous plants such as sophora toromiro during the two last centuries although the evidence is not conclusive the american origin of v litoralis re opens the debate about the possible role of amerindians in the human colonisation of easter island

diffuse co2 flux emission in two maar crater lakes from sao miguel island azores portugal abstract santiago and congro are two maar crater lakes located at sao miguel the largest island of the azores archipelago santiago lake is located on the sete cidades volcano at an altitude of 364 m presenting a surface area of 0 25 km2 and a maximum depth of 33 m congro lake is located on the congro fissural volcanic system at an altitude of 420 m and has a surface area of 0 04 km2 and a maximum depth of 22 m both lakes are monomictic in character with low mineralized waters of meteoric origin being the temperature in the range between 12 4 c winter period and 23 8 c summer period the main water type is na hco3 and the relative major ion composition is hco3 cl so42 f for anions and na k mg2 ca2 for cations four sampling surveys were carried out between 2013 and 2016 in each lake in order to estimate surface diffuse co2 degassing a total of 1612 and 713 co2 flux measurements were made with an accumulation chamber at santiago and congro lakes respectively the higher co2 fluxes were measured during the winter surveys 0 2 t d 1 in congro and 5 6 t d 1 in santiago while the lowest values 0 1 t d 1 and 0 2 t d 1 respectively in congro and santiago lakes were recorded in the summer these seasonal differences observed in both lakes are associated with the monomictic character of the lakes as the co2 is not able to ascend to the surface when the water column is stratified during the warmer period due to the physical processes that occur in both lakes the co2 emission is mostly associated to a biogenic origin but the higher co2 emissions measured in santiago lake suggest that a volcanic influence cannot be excluded as also shown through the heavier 13c isotopic measured in this water body the tectonic structures that cross santiago lake probably enable the observed degassing

a seasonal deuterium excess signal at law dome coastal eastern antarctica a southern ocean signature the snow isotopic composition 18o and d of two shallow cores from the high accumulation summit region of law dome east antarctica was measured at monthly resolution over the 1980 1992 period while the 18o or d signals clearly reflect the local temperature cycle the deuterium excess d d 8 18o is shifted with respect to 18o cycle by a 4 months lag interpretation of this phase lag is investigated using both an atmospheric general circulation model agcm which includes the water isotopic cycles and a simple isotopic model which better describes the microphysical processes within the cloud using this dual approach we show that the seasonality of 18o and d at law dome summit results from a combination of the southern ocean temperature cycle shifted by 2 3 months with respect to the local insolation and seasonal moisture origin changes due to a strong contribution of the local ocean when ice free both approaches are consistent with a dominant temperate to subtropical moisture origin we thus demonstrate from our present day subseasonal study that the record of d in the dome summit south dss deep ice core represents a potential tool for identifying changes in southern ocean temperatures and or sea ice cover at the scale of the past thousand years

late pleistocene and holocene palaeoenvironments in and around the middle caspian basin as reconstructed from a deep sea core this article has been made available through open access by the brunel open access publishing fund

the reunion subchron vegetation and climate history of the northeastern russian arctic inferred from the lake el gygytgyn pollen record abstract the 318 m thick sediment record from lake el gygytgyn provides unique opportunities for a detailed examination of environmental changes during the reunion subchron polarity reversal event 2 1384 2 1216 myr bp in the northeastern russian arctic the paper describes vegetation and climate fluctuations between 2 15 and 2 10 myr bp as inferred from palynological data biome reconstructions indicate that throughout this interval the tundra tund biome generally has higher affinity scores as compared to cold steppe step or cold deciduous forest clde an exception is the climatic optimum between 2 139 and 2 131 myr bp coinciding with marine isotope stage 81 approximately the reunion subchron when the clde biome has the highest scores landscape openness indices suggest that more closed vegetation characterized most of the interval between 2 146 and 2 127 myr bp when deciduous forest and shrubs expanded in the regional vegetation and climate was relatively warm and wet peaks in green algal colonies botryococcus and zygnema type spores 2 150 2 146 2 131 2 123 and 2 112 2 102 myr bp indicate expansions of shallow water habitats and lowered lake levels comparisons with biome reconstructions from other interglacial intervals at lake el gygytgyn suggest that precession related summer insolation intensity and obliquity related duration of summer daylight are major controls on the onset of interglaciations whereas obliquity probably plays a more significant role on vegetation succession at northern high latitudes during the pleistocene

evidence from apatite fission track analysis for the post devonian burial and exhumation history of the northern highlands scotland abstract devonian and older rock samples from outcrops in the northern scottish highlands have undergone protracted cooling since they reached palaeotemperatures of 110 c or more in the late palaeozoic to early mesozoic the results not only suggest that the northern highlands region has experienced kilometre scale exhumation since the late palaeozoic but also that devonian and possibly permo carboniferous sedimentation was probably more extensive than current outcrop patterns would imply a permian outcrop sample from the minches basin reached a maximum palaeotemperature of 70 90 c prior to the onset of cooling in the early tertiary while data from devonian and older samples suggest an acceleration in the rate of cooling in the early tertiary the magnitude of early tertiary palaeotemperatures on the mainland adjacent to the inner moray firth imf indicate similar amounts of tertiary exhumation to those derived from compaction analyses for the imf however to the west the magnitude of tertiary cooling cannot be solely ascribed to exhumation and a contribution of heating due to hydrothermal effects and or elevated heat flow associated with the tertiary igneous complex may also need to be invoked

macroholes in stalagmites and the search for lost water 1 fluid microinclusions in stalagmites have provided samples of paleowaters present during the growth of the stalagmite but only in microliter amounts genty et al 2002 discovered much larger water filled macroinclusions in some stalagmites using computerized tomographic ct x ray scanning and magnetic resonance imaging mri we searched for such macroinclusions in 21 stalagmites from diverse localities in north and central america and the caribbean we show that most stalagmites contained numerous mm to cm sized internal cavities macroholes these do not penetrate the outer surfaces which in most cases are deceptively unblemished some stalagmites have up to 10 average internal porosity two types of macroholes are distinguishable axial holes formed during growth due to slower calcite accumulation at the axial drip site off axis holesformed penecontemporaneously with growth in discrete layers these cut previous growth laminae showing that they are post depositional using mri on uncut apparently sealed specimens we find that very few of these cavities contain significant quantities of water although they were clearly formed while the stalagmite was being continuously bathed by drip water presumably the water has escaped post depositionally through micro fissures extensive connected hole system crystal boundaries or other defects

cenozoic erosion of the scottish highlands orkney shetland area implications for uplift and previous sediment cover the scottish highlands are both an ancient mountain belt and more recently part of a passive continental margin both features where the long term controls on topography are uncertain during the mesozoic the area may have been either a net sediment source or at least in parts a net sediment sink balancing preserved sediment volumes in surrounding basins with the palaeo surface area of the highlands exposed to erosion suggests that a c 2000 2400 m average thickness of zero porosity rock has been eroded from the highlands in the cenozoic assuming that a change from sand dominated sediments in the paleocene and eocene to later mud dominated sediment corresponds to the change from the erosion of sediment to erosion of metamorphic basement then 1900 2400 m average thickness of clastic sediment was present at the start of the cenozoic plus any overlying chalk this has been subsequently eroded away except along the east and west coasts where preserved mesozoic sequences suggest a more extensive original cover prior to uplift associated with rifting of the north atlantic the highlands may have been an area of sediment filled half graben much like the inner hebrides at the present day

the upper jurassic boulder beds and related deposits a fault controlled submarine slope ne scotland during the late jurassic kimmeridgian rifting in the north sea large scale normal faults developed to form relatively deep marine basins the north western margin of one of these basins defined by the helmsdale fault is described to show the nature of sedimentation associated with a submarine fault scarp subsidence to the se of the helmsdale fault led to a fault scarp down which various sediment mass flows moved including debris flow rockfall high and low concentration turbidity currents and possible storm surge wash over deposits redeposition by soft sediment sliding was important as a slope accretion process deep channels were incised into the slope and infilled by coarse grained elastics contemporaneous small scale submarine fans located farther off in the present north sea may have developed as a result of slope bypassing sediment flows down such channels the succession is characterized by extreme sediment heterogeneity compared to many deep water environments and it may be part of an ancient fan delta the main influences upon slope accretion were the synsedimentary movements on the helmsdale fault and the nature of the available sediment input such that the succession represents structurally controlled and sedimentologically modified slope development

climate imprints during the medieval climate anomaly and the little ice age in marine records from the alboran sea basin an integrated multiproxy analysis from westernmost mediterranean hemipelagic sediments has provided further insights into natural climate variability and forcing mechanisms in this region during th

deuterium excess in an east antarctic ice core suggests higher relative humidity at the oceanic surface during the last glacial maximum a continuous deuterium excess profile d d 8 18o was obtained from the dome c ice core spanning 32 000 yr it exhibits significant variations over this period in particular d was 4 5 lower around 18 000 yr bp than over the past 7 500 yr interpreted as reflecting higher relative humidity estimated 90 over the oceanic areas providing moisture for antarctic precipitation

the deuterium excess records of epica dome c and dronning maud land ice cores east antarctica new high resolution deuterium excess d data from the two epica ice cores drilled in dronning maud land edml and dome c edc are presented here the main moisture sources for precipitation at edc and edml are located in the indian ocean and atlantic ocean respectively the more southward moisture origin for edml is reflected in a lower present day d value compared to edc the edml and edc isotopic records 18o and d show the main climate features common to the east antarctic plateau and similar millennial scale climate variability during the last glacial period however quite large 18o and d differences are observed during mis5 5 and the glacial inception with a long term behaviour a possibility for this long term difference could be related to uncertainties in past accumulation rate which are used in the glaciological models regional climate anomalies between the two sites during mis5 5 could also be consistent with the observed edml edc 18o and d gradient anomalies simulations performed with the general circulation model echam4 for different time slices provide a temporal temperature isotope slope for the edml region in fair agreement to the modern spatial slope tsite and tsource records are extracted from both ice cores using a modelling approach after corrections for past 18o seawater and elevation changes a limited impact of d on antarctic temperature reconstruction at both edml and edc has been found with a higher impact only at glacial inception the aim antarctic isotope maximum events in both ice cores are visible also after the source correction suggesting that these are real climate features of the glacial period the different shape of the aim events between edc and edml as well as some climate features in the early holocene points to a slightly different climate evolution at regional scale a comparison of our temperature reconstruction profiles with the aerosol fluxes show a strong coupling of the nssca fluxes with antarctic temperatures during glacial period and a tighter coupling of 18o and tsite with ssna flux at edml compared to edc during the glacial period and mis5 5

cainozoic geology and landscape evolution of north east scotland memoir of the british geological survey sheets 66e 67 76e 77 86e 87w 87e 95 96w 96e and 97 scotland

water isotopes as tools to document oceanic sources of precipitation the isotopic composition of precipitation in deuterium oxygen 18 and oxygen 17 depends on the climatic conditions prevailing in the oceanic regions where it originates mainly the sea surface temperature and the relative humidity of air this dependency applies to present day precipitation but also to past records which are extracted for example from polar ice cores in turn coisotopic measurements of deuterium and oxygen 18 offer the possibility to retrieve information about the oceanic origin of modern precipitation as well as about past changes in sea surface temperature and relative humidity of air this interpretation of isotopic measurements has largely relied on simple rayleigh type isotopic models and is complemented by lagrangian back trajectory analysis of moisture sources it is now complemented by isotopic general circulation models igcm in which the origin of precipitation can be tagged we shortly review published results documenting this link between the oceanic sources of precipitation and their isotopic composition we then present experiments performed with two different igcms the giss model ii and the lmdz model we focus our study on marine water vapor and its contribution to precipitation over antarctica and over the andean region of south america we show how igcm experiments allow us to relate climatic conditions prevailing in the oceanic source of precipitation to its isotopic composition such experiments support at least qualitatively the current interpretation of ice core isotopic data in terms of changes in sea surface temperature additionally we discuss recent studies clearly showing the added value of oxygen 17 measurements key points link between the isotopic content of precipitation and its oceanic origin application of this method to polar ice cores andean precipitation potential of combining deuterium excess and oxygen 17 excess 2013 american geophysical union all rights reserved

vitrinite reflectance and molecular geochemistry of jurassic sediments the influence of heating by tertiary dykes northwest scotland vitrinite reflectance measurements from sedimentary rocks adjacent to six dykes from sites across the inner hebrides indicate that the lateral extent of thermal alteration is reasonably similar and proportional to dyke thickness d t with alteration starting to take effect at 70 d t detailed sampling of a jurassic siltstone adjacent to a 0 9 m dyke reveals that the zone of maximum extractable organic matter eom wt g rock equivalent to the oil window is relatively narrow ca 25 of the d t the position of this oil window relative o the vitrinite reflectance profile is comparable with that from burial maturation gas chromatograms of the aliphatic hydrocarbon fractions reveal i a shift from branched and cyclic dominated hydrocarbons to an increasing predominance of straight chain components and ii the carbon number distribution of the n alkanes shifts towards the shorter chain homologues with decreasing distance from the dyke contact apart from the methylphenanthrene index mpi1 changes in each of the molecular maturity parameters are initiated by the the thermal effects of the dyke between 80 and 70 d t from the contact the mpi1 parameter was the most sensitive maturity indicator in that it responded to the dyke emplacement even in the distal samples i e distance from dyke contact 140 d t a significant reduction in toc at the dyke contact suggests that the synthesis gas reaction may have occurred i e the reaction of organic matter with steam resulting in the formation of carbon monoxide this reaction may be associated with the vitrinite reflectance reversal this study suggests that these particular dykes have had only a local effect on the maturity of the intruded sediments

a global oxygen isotope model semi empirical zonally averaged a simple model which is zonally averaged for the transport of atmospheric water vapour is presented which uses as input the zonally averaged evaporation field and the mean meridional travel distance of tropospheric water vapour as functions of latitude the model demonstrates that for polar regions each of the 10 latitude strips poleward of 25 is of equal importance as a moisture source the model is used to predict zonal averages of 6 1s 0 for the present day and 18 ka bp both annual average values and seasonal amplitudes are presented and compared to observations sea ice cover is an important factor in determining both annual averages and seasonal amplitudes today and at 18 ka bp an earlier model jouzel and others 1983 linking 6eso the deuterium excess and sea salt content in an antarctic ice core to the relative humidity of the source region is based on a single source atmospheric water vapour cycle type model and is re ev aluated using the present model

episodic cenozoic tectonism and the development of the nw european passive continental margin the north atlantic margins are archetypally passive yet they have experienced post rift vertical movements of up to kilometre scale the cenozoic history of such movements along the nw european margin from ireland to mid norway is examined by integrating published analyses of uplift and subsidence with higher resolution tectono stratigraphic indicators of relative movements including results from the stratagem project three episodes of epeirogenic movement are identified in the early mid and late cenozoic distinct from at least one phase of compressive tectonism two forms of epeirogenic movement are recognised referred to as tilting coeval subsidence and uplift rotations 1 over distances of 100s of kilometres and sagging strongly differential subsidence rotations up to 4 over distances 100 km each epeirogenic episode involved relatively rapid 10 ma km scale tectonic movements that drove major changes in patterns of sedimentation to find expression in regional unconformity bounded stratigraphic units early cenozoic tilting late paleocene to early eocene c 60 50 ma caused the basinward progradation of shelf slope wedges from elongate uplifts along the inner continental margin and from offshore highs mid cenozoic sagging late eocene to early oligocene c 35 25 ma ended wedge progradation and caused the onset of contourite deposition in deep water basins late cenozoic tilting early pliocene to present 4 0 5 ma again caused the basinward progradation of shelf slope wedges from uplifts along the inner margin including broad dome like features and from offshore highs the early mid and late cenozoic epeirogenic episodes coincided with atlantic plate reorganisations but the observed km scale tectonic movements are too large to be accounted for as flexural deflections due to intra plate stress variations mantle lithosphere interactions are implied but the succession of epeirogenic episodes of differing form are difficult to reconcile with the various syn to post rift mechanisms of permanent and or transient movements proposed in the hypothetical context of a plume beneath iceland the epeirogenic movements can be explained as dynamic topographic responses to changing forms of small scale convective flow in the upper mantle tilting as coeval upwelling and downwelling above an edge driven convection cell sagging as a loss of dynamic support above a former upwelling the inferred cenozoic succession of epeirogenic tilting sagging and tilting is proposed to record the episodic evolution of upper mantle convection during ocean opening a process that may also be the underlying cause of plate reorganisations the postulated episodes of flow reorganisation in the ne atlantic region have testable implications for epeirogenic movements along the adjacent oceanic spreading ridge and conjugate continental margin as well as on other atlantic type passive margins

climate reconstruction for the last two millennia in central iberia the role of east atlantic ea north atlantic oscillation nao and their interplay over the iberian peninsula abstract a multi proxy characterization of the uppermost sedimentary infill of an iberian alpine lake cimera 2140 m a s l was performed to establish the climatic and environmental conditions for the iberian central range icr over the last two millennia this multi proxy characterization was used to reconstruct the intense runoff events lake productivity and soil erosion in the lake catchment and interpret these factors in terms of temperature and precipitation variability the roman period rp 200 bce 500 ce beginning was characterized by an alternation between cold and warm periods as indicated by short lived oscillations of intense runoff conditions and soil erosion although warm conditions dominated the end of the period and the early middle age ema 500 900 ce onset in the icr a noticeable decrease in intense runoff events and a progressive decrease in soil erosion during the late ema indicated a shift to colder temperatures in terms of precipitation both the rp and ema climate periods displayed a transition from dry to wet conditions that led to a decrease in lake productivity the medieval climate anomaly mca 900 1300 ce was characterized by warm and dry conditions with frequent intense runoff episodes and increases in lake productivity and soil erosion whereas the little ice age lia 1300 1850 ce showed the opposite characteristics the industrial era 1850 2012 ce presented an increase in lake productivity that likely demonstrates the influence of global warming the spatio temporal integration of the cimera record with other iberian reconstructions has been used to identify the main climate drivers over this region during the rp and ema n s and e w humidity gradients were dominant whereas during the mca and lia these gradients were not evident these differences could be ascribed to interactions between the north atlantic oscillation nao and east atlantic ea phases during the rp the general warm conditions and the e w humidity gradient indicate a dominant interplay between a negative nao phase and a positive ea phase nao ea whereas the opposite conditions during the ema indicate a nao ea interaction the dominant warm and arid conditions during the mca and the cold and wet conditions during the lia indicate the interplay of the nao ea and nao ea respectively furthermore the higher solar irradiance during the rp and mca may support the predominance of the ea phase whereas the opposite scenario during the ema and lia may support the predominance of the ea phase which would favour the occurrence of frequent and persistent blocking events in the atlantic region during these periods

fidelity of alkenone paleotemperatures in southern cape basin sediment drifts 0 in two drift cores tn057 21 and ocean drilling program site 1089 are nearly identical during the interval of overlapping analyses mis 4 5c ssts in a nearby nondrift core tn057 6 covary with those in core tn057 21 throughout mis 1 5c while climatological ssts overlying tn057 21 and tn057 6 are similar and consistent with reconstructed holocene ssts in the nondrift core surface waters overlying tn057 21 are 6 c colder than holocene alkenone ssts in the drift core temperatures remain 6 c warmer in tn057 21 relative to tn057 6 during the 100 kyr duration of the records we hypothesize that alkenone derived ssts in tn057 21 are higher than climatological ssts in the overlying surface water and those in tn057 6 as a result of the winnowing and focusing of sedimentary alkenones produced in warmer waters to the north climatological ssts in the central and northern cape basin are 16 20 c a 1 5 offset of fine fraction d 18 o values relative to planktonic foraminifera in tn057 21 supports this hypothesis temporal changes in sediment focusing were evaluated directly using uranium series radioisotopes while higher sediment focusing factors would be expected to result in higher alkenone derived ssts if sediment advection were the primary control on down core changes in alkenone derived ssts 230 th derived focusing factors indicate no such correlation exists we conclude that alkenone paleotemperature reconstructions from southern cape basin drifts reliably record regional sst variations in the cape basin index terms 4267 oceanography general paleoceanography 1055 geochemistry organic geochemistry 1040 geochemistry isotopic composition chemistry 3022 marine geology and geophysics marine sediments processes and transport keywords alkenones cape basin thorium