a 1 000 year ice core record of interannual to multidecadal variations in atmospheric circulation over the north atlantic interannual to multidecadal modes in ocean atmosphere dynamics in the north atlantic region have been identified using sea salt aerosol proxy records from northern greenland ice cores over the last 1 000 years sea salt concentrations show a consistent relationship with anomalies in the meridional pressure gradient over the north atlantic region over all considered time scales these pressure anomalies are connected to shifts in storm tracks leading to lower pressure and higher storm activity hence higher sea salt export over the greenland ice sheet two modes of long term variability with a period of 10 4 years and 62 years could be identified the latter is connected to long term changes in sea surface temperature sst as documented by a high correlation of north atlantic sst with our sea salt record over the last 150 years long term reconstruction of these modes shows that the 10 4 year cycle has been a phenomenon persistent over the last millennium while the 62 year cycle has been mainly active after 1700 accordingly the longer term persistence of this multidecadal variability in sea salt points also to significant variations in sst over the last 300 years

late pleistocene and holocene palaeogeography of the lower tagus valley portugal effects of relative sea level valley morphology and sediment supply abstract because of the deep glacial incision the lower tagus valley hosts a sedimentary record since 20 000 cal bp making this a unique site along the european atlantic margin with respect to palaeogeographic and sea level changes based on nine cross sections and 55 radiocarbon dates together with a newly created relative sea level curve we constructed five palaeogeographic maps of the infill of the lower tagus valley since 20 000 cal bp we illustrate that relative sea level rise and fluvial sediment supply were the prime forcing factors determining the depositional history and palaeogeographic changes around 20 000 cal bp a deeply incised braided river existed which was directly connected to the ocean across the narrow continental shelf after that 12 000 cal bp the gradually moister and warmer climate caused a change to a single channel river during the following period 12 000 7000 cal bp relative sea level rise resulted in a transgression in the lower tagus valley and the establishment of extensive tidal environments after relative sea level rise had ended 7000 cal bp the valley was progressively filled by a fluvial wedge and tidally influenced bayhead delta since 1000 cal bp the valley fill history was dominated by increased sediment input due to human induced degradation of catchment slopes generally climate was of subordinate importance during the entire studied period merely causing a single channel river resulting from the change from the cold heinrich event 1 to the temperate bolling allerod interstadial despite the tectonic activity in the region neotectonic uplift or subsidence was limited as supported by the horizontal relative sea level curve since 7000 cal bp neotectonics played a minor role due to the large distance from the fennoscandian ice sheet and the narrow continental shelf which prohibited strong glacio and hydro isostatic movements

biomarkers as proxies for plant inputs to peats an example from a sub boreal ombrotrophic bog lipid distributions in modern peat forming plants were determined and compared to biomarkers recovered from a ca 2800 year old peat deposited in a dutch ombrotrophic bog the peat section spans a well constrained shift in local hydrology and vegetation and potential molecular proxies for plant inputs were directly tested against the macrofossil record based on the analyses of modern plants low molecular weight lmw n alkanes c23 c25 and high molecular weight n alkanes c33 are proposed as potential biomarkers for sphagnum and non sphagnum inputs respectively consistent with this in the bargerveen peat core lmw n alkane abundances increase and hmw n alkane abundances decrease coincident with the shift to sphagnum dominated peat additional potential proxies include the abundances of c22 alkanedioic acid and phytenyl phytenoate as sphagnum indicators and the abundances of the triterpenoids taraxer 14 ene and taraxast 20 ene as biomarkers for ericaceae rootlets

major storm periods and climate forcing in the western mediterranean during the late holocene abstract big storm events represent a major risk for populations and infrastructures settled on coastal lowlands in the western mediterranean where human societies colonized and occupied the coastal areas since the ancient times the variability of storm activity for the past three millennia was investigated with a multi proxy sedimentological and geochemical study from a lagoonal sequence mappings of the geochemistry and magnetic susceptibility of detrital sources in the watershed of the lagoon and from the coastal barriers were undertaken in order to track the terrestrial or coastal marine origin of sediments deposited into the lagoon the multi proxy analysis shows that coarser material low magnetic susceptibility and high strontium content characterize the sedimentological signature of the paleostorm levels identified in the lagoonal sequence a comparison with north atlantic and western mediterranean paleoclimate proxies shows that the phases of high storm activity occurred during cold periods suggesting a climatically controlled mechanism for the occurrence of these storm periods besides an in phase storm activity pattern is found between the western mediterranean and northern europe spectral analyses performed on the sr content revealed a new 270 year solar driven pattern of storm cyclicity for the last 3000 years this 270 year cycle defines a succession of ten major storm periods sp with a mean duration of 96 54 yr periods of higher storm activity are recorded from 680 to 560 cal yr bc sp10 end of the iron age cold period from 140 to 820 cal yr ad sp7 to sp5 with a climax of storminess between 400 and 800 cal yr ad dark ages cold period and from 1230 to 1800 cal yr ad sp3 to sp1 little ice age periods of low storm activity occurred from 560 cal yr bc to 140 cal yr ad sp9 and sp8 roman warm period and from 820 to 1230 cal yr ad sp4 medieval warm period

a thousand year speleothem proxy record of north atlantic climate from scotland luminescent organic matter in stalagmites may form annual bands allowing growth rate to be precisely determined stalagmite growth rate is controlled by precipitation so annual bands can be used to derive long precipitation records a continuously banded stalagmite from a cave in nw scotland was used to provide a 1100 year high resolution record of precipitation the location of the cave means that precipitation is closely linked to the north atlantic oscillation for which a record is also derived this suggests that changes in the north atlantic oscillation state was an important control on european climate over the past millennium

sand invasion along the portuguese coast forced by westerly shifts during cold climate events phases of higher aeolian activity are responsible for the formation and movement of large transgressive dunefields well reported phases of aeolian activity in northwest europe are coincident with global cooling events and were related to enhanced westerly winds and storminess however the extent to which these climatic episodes influenced dunefield dynamics in southwest europe remains an open question ground penetrating radar gpr was used to image the stratigraphy of a cliff top coastal transgressive dunefield in portugal and reconstruct former windfield regimes using optically stimulated luminescence osl five major phases of aeolian activity were dated at 12 6 5 6 1 2 0 4 and 0 3 ka and related to coastal instability and enhanced westerlies these phases were later reconciled to favorable patterns of atmospheric circulation simulated by global and regional climate models at both synoptic and local scales respectively the results prove that major phases of aeolian activity in southwest europe are associated with the onset of cold climate events of global distribution coinciding with aeolian accumulation in northwest europe this implies the dominance of zonal westerlies along the western coast of europe from denmark to portugal during the onset of cold climate events model simulations suggest that the pattern of atmospheric circulation during periods of enhanced aeolian activity is compatible with prolonged negative phases of the north atlantic oscillation nao

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

application of new technology liquid scintillation spectrometry to radiocarbon dating of tephra deposits new zealand abstract two major technological advances in the radiocarbon dating method have recently enhanced its potential application to tephra studies the advent of accelerator mass spectrometry and the development of new technology liquid scintillation ls spectrometry the new technology ls spectrometer represents a significant refinement of the conventional dating method based on liquid scintillation counting of benzene it improves upon conventional ls counting by allowing spectral analysis and by providing a high degree of counting stability and efficiency in an ultra low level background radiation environment these attributes enable radiocarbon dating with greater accuracy and statistical precision and also allow the determination of both smaller and older samples than previously possible by conventional radiometric methods the new wallac oy quantulus ls spectrometer has been in operation at the university of waikato radiocarbon dating laboratory since 1988 the instrument achieves ultra low background levels by both passive and active forms of shielding the shielding comprises a massive asymmetric passive lead shield surrounding an aticoincident liquid scintillation guard in addition the quantulus contains dual multichannel analyzers which allow spectral analysis and windowless data acquisition the quantulus ls spectrometers at the waikato laboratory have been used to date a variety of carbonaceous materials associated with tephra deposits in new zealand ranging in age from ca 0 1 55 ka in particular we have tested the capability of the quantulus for determining ages of samples that are typically more difficult or impossible to date by conventional methods 1 very young samples e g tarawera tephra erupted ca 100 years ago 2 older samples e g mangaone tephra erupted ca 30 ka and 3 samples containing only sparse carbon e g lake sediments associated with tephra layers aged ca 20 ka or less the quantulus ls spectrometer is both more accurate and precise statistical counting errors are reduced than conventional instruments is capable of extending the limits of detection at both ends of the age scale and has a smaller sample handling ability analyses can be obtained at comparatively low cost such advances are potentially beneficial to tephrochronology and volcanology and a wide range of applications in quaternary research

aeolian sediment in raised bog deposits halland sw sweden a new proxy record of holocene winter storminess variation in southern scandinavia cores of peat taken from two raised bogs in the near coastal part of halland sw sweden were examined for their content of wind transported clastic material the boarps mosse core has a length of 262 cm and covers the last 2850 years age model based on three radiocarbon dates while the hyltemossen core has a length of 347 cm and records the last 7000 years age model based on eight radiocarbon dates the peat contains aeolian quartz silt and sand from trace amount to more than 10 weight of the dry peat sample and the grain size composition of the minerogenic sediment indicates that the material is composed of both far travelled dust and local wind eroded silt and sand grains larger than 0 2mm are present in many intervals and probably record niveo aeolian transport in connection with severe snowstorms a systematic count of quartz grains between 0 2 0 35mm and larger than 0 35mm was carried out to determine variations in aeolian sand influx asi and winter wind climate with time the boarps m

holocene interdependences of changes in sea surface temperature productivity and fluvial inputs in the iberian continental shelf tagus mud patch 1 sea surface temperature sst marine productivity and fluvial input have been reconstructed for the last 11 5 calendar cal ka b p using a high resolution study of c37 alkenones coccolithophores iron content and higher plant n alkanes and n alkan 1 ols in sedimentary sequences from the inner shelf off the tagus river estuary in the portuguese margin the sst record is marked by a continuous decrease from 19 c at 10 5 and 7 ka to 15 c at present this trend is interrupted by a fall from 18 c during the roman and medieval warm periods to 16 c in the little ice age river input was very low in the early holocene but increased in the last 3 cal ka b p in association with an intensification of agriculture and deforestation and possibly the onset of the north atlantic oscillation atlantic multidecadal oscillation modes of variability river influence must have reinforced the marine cooling trend relative to the lower amplitude in similar latitude sites of the eastern atlantic the total concentration of alkenones reflects river induced productivity being low in the early holocene but increasing as river input became more important rapid cooling of 1 2 c occurring in 250 years is observed at 11 1 10 6 8 2 6 9 and 5 4 cal ka b p the estimated age of these events matches the ages of equivalent episodes common in the ne atlantic mediterranean region this synchronicity reveals a common widespread climate feature which considering the twentieth century analog between colder ssts and negative north atlantic oscillation nao is likely to reflect periods of strong negative nao

8000 years of environmental evolution of barrier lagoon systems emplaced in coastal embayments nw iberia the rocky and indented coast of nw iberia is characterized by the presence of highly valuable and vulnerable small and shallow barrier lagoon systems structurally controlled the case study was se

the impact of north atlantic storminess on western european coasts a review abstract instrumental and documentary records of storminess along the atlantic coast of western europe show that storm activity exhibits strong spatial and temporal variability at annual and decadal scales there is evidence of periods of increased storminess during the little ice age lia ad 1570 1990 and archival records show that these periods are also associated with sand movement in coastal areas independent evidence of sand movement during the lia is derived from dating the coastal sand deposits using luminescence or radiocarbon methods the holocene record of sand drift in western europe includes episodes corresponding to periods of northern hemisphere cooling particularly at 8 2 ka and provides the additional evidence that these periods like the lia were also stormy

oxygen and hydrogen isotope signatures of northeast atlantic water masses abstract only a few studies have examined the variation of oxygen and hydrogen isotopes of seawater in ne atlantic water masses and data are especially sparse for intermediate and deep water masses the current study greatly expands this record with 527 18o values from 47 stations located throughout the mid to low latitude ne atlantic in addition d was analyzed in the 192 samples collected along the geotraces north atlantic transect ga03 ga03 e kn199 4 and the 115 iberia forams cruise samples from the western and southern iberian margin an intercomparison study between the two stable isotope measurement techniques cavity ring down laser spectroscopy and magnetic sector isotope ratio mass spectrometry used to analyze ga03 e samples reveals relatively good agreement for both hydrogen and oxygen isotope ratios the surface 0 100 m and central 100 500 m water isotope data show the typical evaporation related trend of increasing values equatorward with the exception for the zonal transect off cape blanc nw africa off cape blanc surface water isotope signatures are modified by the upwelling of fresher antarctic intermediate water aaiw that generally has isotopic values of 0 0 to 0 5 for 18o and 0 to 2 for d along the iberian margin the mediterranean outflow water mow is clearly distinguished by its high 18o 0 5 1 1 and d 3 6 values that can be traced into the open atlantic isotopic values in the ne atlantic deep water neadw are relatively low 18o 0 1 to 0 5 d 1 to 4 and show a broader range than observed previously in the northern and southern convection areas the neadw is best observed at ga03 e stations 5 and 7 in the central ne atlantic basin antarctic bottom water isotope values are relatively high indicating modification of the original antarctic source water along the flow path the reconstructed 18o salinity relationship for the complete data set has a slope of 0 51 i e slightly steeper than the 0 46 described previously by pierre et al 1994 j mar syst 5 2 159 170 for the tropical to subtropical northeast atlantic this slope decreases to 0 46 for the subtropical north atlantic central water nacw and the mow and to 0 32 for the surface waters of the upper 50 m the d salinity mixing lines have estimated slopes of 3 01 for the complete data 1 26 for the mow 3 47 for the nacw and 2 63 for the surface waters the slopes of the 18o d relationship are significantly lower than the one for the global meteoric water line with 5 6 for the complete data set 2 30 for the mow 4 79 for the nacw and 3 99 for the surface waters the lower slopes in all the relationships clearly reflect the impact of the evaporation surplus in the subtropics

holocene interplay between a dune field and coastal lakes in the quiaios tocha region central littoral portugal coastal dune fields and dune body associated lakes were studied through sedimentological malacological and palynological analyses lake deposits and palaeosoil horizons gave new information about phases of aeolian activity and dune building coastline and sea level vegetation history and cultural impact after a period of intense aeolian activity late pleistocene that limited soil forming processes a wet aeolian field recorded by podzolized sands and interdune wetland deposits was present in the region around 5000 to 4000 yr bp sea level reached the current level and the coastline was situated c 1 km further inland compared with the present situation subsequently lagoon barrier island systems developed c 4000 yr bp vegetation in the region during this time was a pine oak forest between 4000 and 1600 yr bp the forest was replaced by a semi natural heathland later the heathland was degraded allowing dune migration and finally formation of a desert like landscape this process was probably a c

last interglacial vegetation and climate history from the portuguese coast we examine the atlantic maritime vegetation history from praia rei cortico portugal to understand natural vegetation patterns and infer climatic conditions during the transition from the last interglacial to early glacial periods optically stimulated luminescence dating of quartz grains from sediments surrounding the 1 3 m thick organic deposit date the section to within 120 89 ka pollen data were used to reconstruct the vegetation history and determine a range of possible past climates using an ensemble of seven modern analogue approaches a five part environmental sequence transitioned from heath pine dominated communities deciduous hardwood forests and pine forests to heathlands surrounded by steppe like environments mixed temperate and mediterranean forest elements existed during the last interglacial period at praia rei cortico suggesting a proximal limit to these floras abundant fagus pollen 6 suggests local beech populations existed within maritime forests of the iberian atlantic margin representing a greater distribution of this genus during interglacial periods than has previously been recognized climate reconstructions indicate that variations in moisture availability may have been a major driver of the observed environmental changes

hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability abstract hydrogen isotope ratios were measured on n alkanes n c12 to n c31 extracted from recent lake surface sediments along a n s european transect to test if modern climate variability is recorded in these biomarkers d values of the n alkanes are compared to d values of meteoric water from the iaea gnip database spanning a range from 119 in northern sweden to 41 in southern italy to lake water d values and to mean annual temperatures varying between 2 0 c in the north and 13 7 c in the south d values of the short chained n alkanes n c12 to n c20 excluding algal derived n c17 and n c19 are higher in the north and lower in the south the isotopic fractionation e for hydrogen between meteoric water and the short chained n alkanes is increasing from n to s by more than 100 and is significantly correlated to mean annual temperature for n c16 and n c18 this suggests that these n alkanes may originate from a different source in the northern lakes possibly due to petroleum contamination or are synthesized using a different biochemical pathway the n c17 and n c19 alkanes of algal origin the n c21 and n c23 alkanes originating from water plants and the long chain n alkanes n c25 n c27 n c29 and n c31 of terrestrial origin clearly correlate with d values of meteoric water lake water and mean annual temperature indicating that they excellently record the d value of meteoric water the mean hydrogen isotope fractionation ec17 w of 157 sd 13 between n c17 and meteoric water is fairly constant over the wide range of different climates and lake environments suggesting only minor influence of environmental factors on this biochemical fractionation this suggests that d values of n c17 are suitable to reconstruct the isotopic composition of source water the mean fractionation between the long chain n alkanes and water is 128 sd 12 the mean difference of 31 between both e values is likely due to evaporative enrichment of deuterium in the leaf water if this is the only influence on the enrichment the difference between the d values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment

evaluating dynamic mechanisms and formation process of freshwater lenses on reclaimed atoll islands in the south china sea abstract groundwater on remote coral atoll islands in tropical oceans occurs in the form of freshwater groundwater lenses fgls that serve as an important water resource for local inhabitants and ecosystems continuous recharge of freshwater from rainfall can flush out salt water and eventually create a fgl beneath the natural or reclaimed island however the process whereby a fgl grows in reclaimed islands and the dynamic mechanisms and formation process are unclear this study used numerical modeling for a reclaimed island in the south china sea to evaluate the process of mixing between freshwater and saltwater dynamic mechanisms and the formation process of fgls influenced by tidal action our results revealed that the long term average flow lines of fgls were superimposed by short term tidal fluctuations beneath the atoll island the tidal signals move rapidly inland from the lower aquifer and are then propagated upwards to drive the water level in the holocene sediments this causes an oscillation of the fgls and increased mixing between salt and fresh water the formation of the fgls can be divided into three stages preparatory formation and pseudo steady state yongshu island a reclaimed island was used as a case study the island s preparatory phase lasted approximately 2 5 years and will take 20 years to form a stable fgl with a thickness of about 15 m recharge rates and the nature of the contact between the holocene and the underlying pleistocene aquifers determine the shape of the fgls beneath the island abstraction during the formative period of the fgls will increase the time required to reach a stable state the results obtained enhance the understanding of the formation of fgls and can provide a reference for the management of freshwater resources on atoll islands

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

plant wax d h ratios in the southern european alps record multiple aspects of climate variability we present a younger dryas holocene record of the hydrogen isotopic composition of sedimentary plant waxes d wax from the southern european alps lake ghirla n italy to investigate its sensitivity to climatic forcing variations in this mid latitude region 45 n a modern altitudinal transect of d values of river water and leaf waxes in the lake ghirla catchment is used to test present day climate sensitivity of d wax while we find that altitudinal effects on d wax are minor at our study site temperature precipitation amount and evapotranspiration all appear to influence d wax to varying extents in the lake sediment record d wax values vary between 134 and 180 over the past 13 kyr the long term holocene pattern of d wax parallels the trend of decreasing temperature and is thus likely forced by the decline of northern hemisphere summer insolation shorter term fluctuations in contrast may reflect both temperature and moisture source changes during the cool younger dryas and little ice age lia periods we observe unexpectedly high d wax values relative to those before and after we suggest that a change towards a more d enriched moisture source is required during these intervals in fact a shift from northern n atlantic to southern n atlantic western mediterranean sea sources would be consistent with a southward migration of the westerlies with climate cooling prominent d wax fluctuations in the early and middle holocene are negative and potentially associated with temperature declines in the late holocene 4 kyr bp excursions are partly positive as for the lia suggesting a stronger influence of moisture source changes on d wax variation in addition to isotopic fractionations of the hydrological cycle changes in vegetation composition in the length of the growing season and in snowfall amount provide additional potential sources of variability although we cannot yet quantitatively assess these in the paleo record we conclude that while our d wax record from the alps does contain climatic information it is a complicated record that would require additional constraints to be robustly interpreted this also has important implications for other water isotope based proxy records of precipitation and hydro climate from this region such as cave speleothems

plant wax δd values record changing eastern mediterranean atmospheric circulation patterns during the 8 2 kyr b p climatic event abstract throughout the holocene the climate of the mediterranean region has been strongly influenced by variability in the atmospheric circulation of the high and low latitudes a prominent example for such holocene climate perturbations is the 8 2 kyr b p climatic event reorganization of northern hemisphere atmospheric circulation patterns resulted in variations of temperature and precipitation distribution across the mediterranean the effects of changing high and low latitude atmospheric circulation on mediterranean climate in relation to the 8 2 kyr b p climatic event are however not well understood here we present a high resolution record of stable hydrogen isotope composition of plant wax n alkanes dwax across the 8 2 kyr b p climatic event from the tenaghi philippon peat deposit ne greece in order to characterize patterns of precipitation and changes in atmospheric circulation in the eastern mediterranean region our record reveals pronounced changes in dwax that correlate closely with previously published palynological data a long term decline in dwax values characterizes the lower part of the section the 8 2 kyr b p climatic event itself is connected to two distinct positive dwax excursions a minor shift in dwax around 8 2 kyr b p and a major shift in dwax between ca 8 1 and 8 0 kyr b p the upper part of the section shows a progressive trend towards higher dwax values we link shifts in dwax to changes in mediterranean air mass trajectories supplying precipitation to ne greece caused by variations in the relative contributions of northerly derived d depleted moisture and southerly derived d enriched moisture possible control mechanisms for alternating air mass trajectories include changes in the influence of the siberian high and differences in the influence of the african and asian monsoon circulation on anticyclonic conditions in the mediterranean region as well as regional inflow of moist air masses from the aegean sea

impacts of paleohydrological changes on n alkane biomarker compositions of a holocene peat sequence in the eastern european russian arctic coupled analyses of n alkane biomarkers and plant macrofossils from a peat plateau deposit in the northeast european russian arctic were carried out to assess the effects of past hydrology on the m

holocene vegetation climate and history of a raised bog complex northern new zealand based on palynology plant macrofossils and tephrochronology a holocene history of vegetation climate and ombrogenous mire development is presented from pollen and plant macrofossil analyses of sediments at kopouatai bog a large raised restiad bog in northern new zealand tephra layers of established ages supplemented by numerous radiocarbon dates provide a secure chronology the earliest peats overlying last glacial sediments and dated at c 11700 radiocarbon years bp with extensive accumulation after c 10360 bp are dominated by pollen of warm temperate podocarp angiosperm forest indicating a moist mild early holocene climate the bog began as a series of small soligenous mires within lowland podocarp dominated swamp forest but was mostly oligotrophic by c 8500 bp peat accumulation rates have varied spatially and temporally averaging 0 9 mm yr 1 in central and southern areas the deposition of deltaic muds in the northern part of the bog accompanied a marine transgression c 6500 5000 bp while elsewhere an associated groundwater table rise result

rerewhakaaitu tephra a land sea marker for the last termination in new zealand with implications for global climate change abstract the rerewhakaaiutu tephra erupted from okataina volcanic centre north island new zealand at 14 700 95 14 c yr bp ca 17 600 cal yr bp at a time of rapid re organisation of earth s climate system at the end of the last glacial termination i it provides a distinctive isochron in a range of different environments in north island and in adjacent south pacific ocean sediments terrestrial evidence based on fluvial aggradation and downcutting relationships loess accumulation rates palaeovegetation patterns and buried soil development and mineralogy shows that marked amelioration of climate occurred shortly before the rerewhakaaitu tephra was deposited similarly marine evidence from around this time shows major changes in accumulation rates of sediment and aeolian quartz and in the abundance of various marine organisms while foraminiferal oxygen and carbon isotope records indicate that the arrival of the glacial meltwater signal occurred close to or just after the deposition of the rerewhakaaitu tephra these changes are discussed in relation to controls on climate by oceanic and atmospheric mechanisms the re organisation of climate commencing at ca 15 000 14 500 14 c yr bp ca 18 000 17 400 cal yr bp is detected elsewhere in the southern hemisphere and evidently was linked to orbitally forced warming which is thought to have initiated ice retreat in both hemispheres

storminess variation during the last 6500 years as reconstructed from an ombrotrophic peat bog in halland southwest sweden cores taken from an ombrotrophic peat bog in the coastal zone of halland southwest sweden were examined for wind transported mineral grains pollen and humidity indicators the core covers the period from 6500 cal yr bp to present ombrotrophic conditions existed from ca 4200 cal yr bp onwards bog surface wetness fluctuated strongly until ca 3700 cal yr bp with an apparent dominance of dry summer conditions from 4800 4500 cal yr bp local wet shifts occurred around 4300 2800 2400 and 1500 cal yr bp whereas the most recent 600 years of the record show increasingly dry conditions mineral grain content interpreted as aeolian sand influx asi was used as a proxy for winter storm frequency and intensity until ca 1500 cal yr bp after which increasing human impact as reconstructed by pollen analysis became a second important potential cause for increased sand drift strongly increased storminess occurred at 4800 4200 2800 2200 1500 1100 and 400 50 cal yr bp indicating a dominance of cold and stormy winters during these periods many of these storm periods apparently coincide with storm events in other sites in southwestern scandinavia suggesting that our asi record reflects a regional scale climatic signal furthermore these stormy periods correlate to well known cold phases in the north atlantic region suggesting a link to large scale fluctuations in atmospheric circulation patterns less

late pleistocene raised beaches of coastal estremadura central portugal abstract we present new stratigraphic sedimentological and chronological data for a suite of tectonically raised beaches dating to marine isotope stages 5 4 and 3 along the estremadura coast of west central portugal the beach deposits are found in association with ancient tidal channels and coastal dunes pollen bearing mud and peat and middle paleolithic archaeological sites that confirm occupation of the coastal zone by neanderthal populations the significance of these deposits is discussed in terms of the archaeological record the tectonic and geomorphic evolution of the coast and correlation with reconstructions of global climate and eustatic sea level change direct correlation between the estremadura beach sections is complicated by the tectonic complexity of the area and the age of the beach deposits which are near or beyond the limit of radiocarbon dating evidence from multiple sites dated by ams radiocarbon and optical luminescence methods suggests broad synchroneity in relative sea level changes along this coast during marine isotope stage 3 two beach complexes with luminescence and radiocarbon age control date to about 35 ka and 42 ka recording a rise in relative sea level around the time of heinrich event 4 at 39 ka depending on assumptions about eustatic sea level at the time they were deposited we estimate that these beaches have been uplifted at rates of 0 4 4 3 mm yr 1 by the combined effects of tectonic halokinetic and isostatic processes uplift rates of 1 2 mm yr 1 are likely if the beaches represent sea level stands at roughly 40 m below modern as suggested by recent eustatic sea level reconstructions evidence from coastal bluffs and the interior of the study area indicates extensive colluvial fluvial and aeolian sedimentation beginning around 31 ka and continuing into the holocene these geomorphic adjustments are related to concomitant changes in climate and sea level providing context that improves our understanding of late pleistocene landscape change and human occupation on the western iberian margin

7000 years of paleostorm activity in the nw mediterranean sea in response to holocene climate events abstract a high resolution record of paleostorm events along the french mediterranean coast over the past 7000 years was established from a lagoonal sediment core in the gulf of lions integrating grain size faunal analysis clay mineralogy and geochemistry data with a chronology derived from radiocarbon dating we recorded seven periods of increased storm activity at 6300 6100 5650 5400 4400 4050 3650 3200 2800 2600 1950 1400 and 400 50 cal yr bp in the little ice age in contrast our results show that the medieval climate anomaly 1150 650 cal yr bp was characterised by low storm activity the evidence for high storm activity in the nw mediterranean sea is in agreement with the changes in coastal hydrodynamics observed over the eastern north atlantic and seems to correspond to holocene cooling in the north atlantic periods of low ssts there may have led to a stronger meridional temperature gradient and a southward migration of the westerlies we hypothesise that the increase in storm activity during holocene cold events over the north atlantic and mediterranean regions was probably due to an increase in the thermal gradient that led to an enhanced lower tropospheric baroclinicity over a large central atlantic european domain

north atlantic holocene climate evolution recorded by high resolution terrestrial and marine biomarker records abstract holocene climatic change is driven by a plethora of forcing mechanisms acting on different time scales including insolation internal ocean e g atlantic meridional overturning circulation amoc and atmospheric e g north atlantic oscillation nao variability however it is unclear how these driving mechanisms interact with each other here we present five biomarker based paleoclimate records air sea surface temperature and precipitation from a fjordic sediment core revealing north atlantic terrestrial and marine climate in unprecedented detail the early holocene 10 7 7 8 kyrs bp is characterised by relatively high air temperatures while ssts are dampened by melt water events and relatively low precipitation the middle holocene 7 8 3 2 kyrs bp is characterised by peak ssts declining air temperatures and high precipitation a pronounced marine thermal maximum occurs between 7 5 5 kyrs bp 3000 years after the terrestrial thermal maximum driven by melt water cessation and an accelerating amoc the neoglacial cooling between 5 8 and 3 2 kyrs bp leads into the late holocene we demonstrate that an observed modern link between icelandic precipitation variability during different nao phases may have existed from 7 5 kyrs bp a simultaneous decoupling of both air and sea surface temperature records from declining insolation at 3 2 kyrs bp may indicate a threshold after which internal feedback mechanisms namely the nao evolved to be the primary drivers of icelandic climate on centennial time scales

late pleistocene and holocene environmental changes in the coastal zone of northwestern portugal this paper examines the quaternary changes in the coastal zone of northwestern portugal through the relationship between sediments and landforms by interpolating the available data from geomorphology lithostratigraphy sedimentology and geochronology it was possible to reconstruct existing palaeoenvironments the oldest of which date back to the last interglacial the main landforms are a high and a low platform bounded by scarps river sands and silty sediments formed in a lacustrine environment antas formation mis 5 are associated with the high platform two deposits are associated with the low platform the cepaes formation mis 3 consisting of a lower set of river sand beds and an upper gravel beach bed and the agucadoura formation mis 1 consisting of holocene lagoonal beds copyright 2006 john wiley sons ltd

groundwater lens dynamics of atoll islands a variable density groundwater model is used to analyze the effects of various controls on the size of the freshwater lens the structure of the transition zone and the propagation of tidal fluctuations in a two layer atoll island groundwater system modeling results indicate that mixing of fresh water and saltwater occurs primarily as a result of oscillating vertical flow due to tidal fluctuations and depends to a lesser extent on transverse dispersion along the dominantly horizontal recharge discharge path of flow the controls on the amount of mixing are 1 the accumulated vertical distance which increases with tidal range and is restricted by vertical permeabilities and 2 vertical longitudinal dispersion comparison of cross sectional simulations of atoll islands using nontidal and tidal models shows that the nontidal model must use artificially high values of transverse dispersivity to compensate for the lack of tidally driven vertical mixing processes although the tidal model has high computational requirements it can be used to calibrate vertical permeabilities and is best suited for problems dealing with groundwater resource evaluations hydrologic events and hydrologic processes the limitations of the nontidal model are that it cannot be used for calibration of vertical permeabilities and will not realistically simulate those cases in which transition zones are thick or recharge low

postglacial sea level rise and sedimentary response in the guadiana estuary portugal spain border abstract the study of sedimentological features foraminifera and molluscan fauna in samples recovered from four rotary boreholes permitted after 14 c dating the first assessment of the post glacial transgression in guadiana river estuary the holocene sequence is underlain by coarse sediments from delta fan enclosing continental swamp deposits dated 16 980 year bp the holocene sedimentary sequence was deposited either directly on this delta fan gravels or on top of fluvial sands deposited probably between 11 000 and 10 000 yr bp an accelerated phase of the estuary infilling by clayey sediments containing the salt marsh foraminifer trochammina began ca 9800 year bp when sea level was about 39 m below present between 7500 and 7000 year bp the central part of the estuary started to accommodate coarser sediments partially introduced from the continental shelf the first phase of holocene sea level rise at a rate of 0 85 m century terminated ca 6500 year bp since then lagoonal sediments in the vicinity of the estuary have been enclosed behind sand spits and predominantly sandy sedimentation was initiated within the estuary after a second phase of slower rise at the rate of 0 3 m century which lasted until ca 5000 year bp the sea approached the present level

persistent non solar forcing of holocene storm dynamics in coastal sedimentary archives considerable climatic variability on decadal to millennial timescales has been documented for the past 11 500 years of interglacial climate1 2 3 this variability has been particularly pronounced at a frequency of about 1 500 years with repeated cold intervals in the north atlantic1 3 however there is growing evidence that these oscillations originate from a cluster of different spectral signatures4 ranging from a 2 500 year cycle throughout the period to a 1 000 year cycle during the earliest millennia here we present a reappraisal of high energy estuarine and coastal sedimentary records from the southern coast of the english channel and report evidence for five distinct periods during the holocene when storminess was enhanced during the past 6 500 years we find that high storm activity occurred periodically with a frequency of about 1 500 years closely related to cold and windy periods diagnosed earlier1 2 3 we show that millennial scale storm extremes in northern europe are phase locked with the period of internal ocean variability in the north atlantic of about 1 500 years4 however no consistent correlation emerges between spectral maxima in records of storminess and solar irradiation we conclude that solar activity changes are unlikely to be a primary forcing mechanism of millennial scale variability in storminess

a 35 myr north american leaf wax compound specific carbon and hydrogen isotope record implications for c4 grasslands and hydrologic cycle dynamics article i nfo hydrology source region and timing of precipitation are important controls on the climate of the great plains of north america and the composition of terrestrial ecosystems moisture delivered to the great plains varies seasonally and predominately derives from the gulf of mexico atlantic ocean with minor contributions from the pacific ocean and arctic region for this work we evaluate long term relationships for the past 35 million years between north american hydrology climate and floral change using isotopic records and average carbon chain lengths of higher plant n alkanes from gulf of mexico sediments dsdp site 94 we find that carbon isotope values 13 c of n alkanes corrected for variations in the 13 c value of atmospheric co2 provide minor evidence for contributions of c4 plants prior to the middle miocene a sharp spike in c4 input is identified during the middle miocene climatic optimum and the influence of c4 plants steadily increased during the late miocene into the pleistocene consistent with other north american records chain length distributions of n alkanes indicative of the composition of higher plant communities remained remarkably constant from 33 to 4 ma however a trend toward longer chain lengths occurred during the past 4 million years concurrent with an increase in 13 c values indicating increased c4 plant influence and potentially aridity the hydrogen isotope values d of n alkanes are relatively invariant between 33 and 9 ma and then become substantially more negative 75 from 9 to 2 ma changes in the plant community and temperature of precipitation can solely account for the observed variations in d from 33 to 5 ma but cannot account for plio pleistocene d variations and imply substantial changes in the source region of precipitation and seasonality of moisture delivery we posit that hydrological changes were linked to tectonic and oceanographic processes including the shoaling and closure of the panamanian seaway amplification of north atlantic deep water production and an associated increase of meridional winds the southerly movement of the intertropical convergence zone near 4 ma allowed for the development of a near modern pressure storm track system driving increased aridity and changes in seasonality within the north american interior

influence of sea level rise on freshwater lenses of different atoll island sizes and lens resilience to storm induced salinization summary human populations inhabiting remote coral atoll islands in the tropical pacific ocean rely heavily on thin unconfined fresh groundwater lenses fwls as their main natural source of potable water potential threats to the continuing viability of atoll fwls may be associated with eustatic sea level rise slr but little is known about the influence of slr on the fwls of different atoll island sizes and the resilience of fwls to salinization caused by storm induced wave washover of low lying land here numerical modelling is carried out to generate steady state fwl configurations at three chosen island sizes 400 600 and 800 m widths upon which a 40 cm slr scenario is imposed followed by transient simulations to assess saline damage and recovery over a 1 year period after a storm washover event on a 600 m wide island two different approaches are tested for taking into account the existence of a freshwater swamp formed where a topographic depression exposes the central region of a fwl above the ground surface these groundwater window and specified flux approaches yield similar results implying that complex integrated surface and groundwater modelling may be unnecessary to develop realistic models of fwl configuration where central freshwater swamps exist thereafter steady state solutions indicate how fwl dimensions are not related in a linear manner to atoll island size such that smaller islands develop much more restricted lenses than larger islands partly in consequence smaller fwls display greater potential for disturbance by slr while larger and more robust fwls may show more resilience results from simulation of saline damage caused by storm washover produce a somewhat counterintuitive finding in a post slr situation it is apparent that fwl vulnerability to washover salinization may actually be reduced owing to the thinner layer of unsaturated substrate lying above the water table i e fwl surface into which saline water can infiltrate and accumulate during a storm washover event

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

high spatial resolution of pollen and charcoal in relation to the c 600 year bp kaharoa tephra implications for polynesian settlement of great barrier island northern new zealand analysis of high spatial resolution of nine pollen profiles 150 m 6 5 km apart from great barrier island shows that between 7500 and 600 calibrated year bp the island had a low frequency of natural fires compared with elsewhere in the northern north island except for one site which has locally sourced pre kaharoa charcoal source of this charcoal in the awana kaitoke area is uncertain if local pre kaharoa burning did occur at other sites in this area it was patchy occurring at different times in different places and was small scale charcoal was first recorded c 1700 year bp then again after c 1200 year bp pre kaharoa charcoal on great barrier may be interpreted as either an increased frequency of natural fires in the region due to climatic change to drier conditions or small scale localized initial human impact or some combination of these factors major post kaharoa burning in the awana kaitoke area was also patchy commencing at different times in different places the presence of the kaharoa tephra on great barrier island allows the commencement of major sustained polynesian deforestation at awana kaitoke to be reliably dated to c 600 year bp at some sites and possibly up to 50 years later at other sites

late quaternary behavior of the east african monsoon and the importance of the congo air boundary both atlantic and indian ocean climate dynamics exert influence over tropical african hydroclimate producing complex patterns of convergence and precipitation to isolate the indian ocean influence on african paleohydrology we analyzed the deuterium hydrogen ratio of higher plant leaf waxes delta d wax in a 25 000 year sediment record from lake challa 3 degrees s 38 degrees e in the easternmost area of the african tropics whereas both the seismic record of inferred lake level fluctuations and the branched and isoprenoidal tetraether bit index proxy record changes in hydrology within the challa basin delta d wax as a proxy for the isotopic composition of precipitation delta d p is interpreted as a tracer of large scale atmospheric circulation that integrates the history of the moisture transported to the lake challa area specifically based on modern day isotope rainfall relationships we argue that lake challa delta d wax reflects the intensity of east african monsoon circulation the three hydrological proxy records show generally similar trends for the last 25 000 years but there are important differences between them primarily during the middle holocene we interpret this deviation of delta d wax from local hydrological history as a decoupling of east african monsoon intensity which heavily influences the isotopes of precipitation in east africa today from rainfall amount in the challa basin in combination the hydrological proxy data from lake challa singularly highlight zonal gradients in tropical african climate that occur over a variety of timescales suggesting that the congo air boundary plays a fundamental role in controlling hydroclimate in the african tropics

effects of storminess sand supply and the north atlantic oscillation on sand invasion and coastal dune accretion in western portugal holocene forested coastal dunes fringe the atlantic coast of western portugal mapping of dunes in the field and using air photographs shows a range of forms reflecting dominant northwest and westerly onshore wind regimes planting of maritime pine forests in the thirteenth and twentieth centuries was initiated because of sand invasion causing problems for human settlement and agriculture early holocene dunes have a well developed podsol and date to 9 7 and 8 2 ka suggesting at least some of these sands may have been emplaced during a global cooling event significant transgressive dune accretion at 2 2 and 1 5 ka implies abundant sand supply and strong onshore winds the most recent dune building period dates to ad 1770 1905 and coincides with a predominantly negative winter north atlantic oscillation index naoi accretion of dunes along the portuguese coast appears out of phase with dune development in southwest france which may reflect different atlantic storm tracks driven by changes in the domin

accelerator mass spectrometry the new revolution in radiocarbon dating abstract the development of accelerator mass spectrometry ams during the last ten years has created a new revolution in the fields of radiocarbon 14c dating and other types of radioisotope analysis the radiocarbon dating method can be used to determine the ages of many types of carbonaceous material of up to about 50 ka in age an ams instrument has been in operation at the nsf arizona accelerator facility for radioisotope analysis of the university of arizona since 1982 it has been used almost exclusively to measure carbon 14 the greatest advantage of radiocarbon dating by ams is the ability routinely to measure samples containing 1 mg or less of elemental carbon while previous methods have required nearly 1000 times that amount in addition the ability of ams to measure the numbers of individual 14c atoms present rather than having to wait to detect the small numbers of 14c atoms decaying makes the measurement time very much shorter for ams the precision attainable for a one hour counting time for a sample 5 ka in age is about 0 6 or 50 years ams radiocarbon dating is of value to multiple areas of quaternary research these include archaeology oceanography hydrology geology and paleoclimatology while ams dating of archaeological and geological samples was once seen as the biggest application of the method studies of global change atmospheric oceanic climatological changes in the past with potentially important applications to predicting future changes now contribute the largest share of samples for analysis by this laboratory other isotopes that have been analyzed using ams include 10be 26al 36cl 41ca and 129i the research applications of these isotopes are much the same as for 14c but are useful for studying processes of time scales greater than the limit of 14c dating

fragility of western mediterranean landscapes during holocene rapid climate changes abstract in this paper we explore the evidence for holocene rapid climate changes rccs in western mediterranean records examining similarities and differences in the timing and nature of impacts on different components of the natural environment vegetation fluvial and coastal sedimentation fire activity soil formation marine lacustrine and fluvial archives of the western mediterranean iberian peninsula and northwest africa provide evidence for both pervasive millennial scale climatic variability and abrupt decadal to centennial scale transitions we focus in particular on three rccs characterised by high latitude cooling glacier advances and north atlantic ice rafting events the mid holocene rcc interval 6 5 cal ka bp the late holocene rcc interval 3 5 2 5 cal ka bp and the historical rcc interval known as the little ice age lia 1300 1950 ad evidence from multiple records indicates wide ranging impacts of rccs in the western mediterranean region the three rcc intervals were characterised however by contrasting hydrological situations in the western mediterranean with prevailing dry conditions including marked aridification events during the rcc intervals 6 5 and 3 5 2 5 cal ka bp and prevailing or recurrent wet conditions during the lia we examine issues of proxy sensitivity in palaeoecological and geomorphological records and evaluate examples of contrasting geomorphological responses to regional climatic triggers between humid and semi arid sectors of the western mediterranean finally we consider the long term sensitivity of the region to rapid climate change the role of threshold changes and the extent to which this region represents a fragile landscape

the geological record of environmental changes in southwestern portuguese coastal lagoons since the lateglacial abstract the multidisciplinary study sedimentology palaeoecology geochemistry isotopic dating of the sedimentary infill of selected coastal lagoons of the southwestern portuguese coast suggests that during the early holocene eustasy was the dominating element forcing coastal change and controlled the sedimentation patterns of these areas the strong decrease of the mean sea level rise rate observed in the middle holocene defined an important threshold of regional significance the flooded lowlands developed terminal barriers and started to silt up initially driven by natural forcing factors e g climate sediment supply of local expression which were later added or overwhelmed by anthropic influence the latter relates with deforestation and agriculture inducing changes of sedimentation rates and sediment delivery to the coast human interference with the natural rhythms of barrier breaching generated significant change of the whole physico chemical setting of the lagoonal basins that translated into sediments water quality and depth and local ecosystem s structure this paper presents examples of the impacts of global versus local factors and natural versus anthropic influences as driving factors of coastal change since the lateglacial the available data suggest that this line of research is crucial to support objective and accurate models of past and future coastal evolution

evidence of high energy events in the geological record mid holocene evolution of the southwestern donana national park sw spain abstract four phases are distinguished in the mid holocene evolution of the southwestern donana national park sw spain based on the multidisciplinary study of sediments in drill cores in the oldest phase 5500 5400 cal years bp a coastal brackish lagoon occupied the central part of the study area partly enclosed by the donana spit and limited by fluvial levees an evolution from subtidal to intertidal conditions characterized the areas located close to the inner side of the donana spit during the same phase the following phase 5400 5200 cal years bp is characterized by a high energy event tsunami which caused the breakthrough of the donana spit and the creation of new littoral strands in the inner areas in the first period of the third phase 5200 4200 cal years bp estuarine infilling was probably the dominant process with the accumulation of phyllosilicate rich clays in the lagoon bed this was followed by a renewed phase of instability 4200 4100 cal years bp indicated by the presence of fine storm lain deposits and thicker probably tsunami induced shelly deposits the last phase 4100 3700 cal years bp comprises a an infilling period with a diminution of the marine influence and b two new high energy events which caused the erosion of the donana spit and the creation of new cheniers in the last 7000 years the comparison of these results with a revision of both geological and historical records has revealed the occurrence of twenty tsunamis at least during this period in portugal and southern spain evidences of these high energy events are washover fans bioclastic coarse sized layers within salt marsh deposits or the presence of giant boulders and pebbles the determination of the recurrence period is very difficult owing to the very scarce data although our data and other authors do not discard a possible periodicity of 2000 years for a cycle of two events separated by 300 400 years

differential hydrogen isotopic ratios of sphagnum and vascular plant biomarkers in ombrotrophic peatlands as a quantitative proxy for precipitation evaporation balance abstract we have developed a new approach to quantitatively reconstruct past changes in evaporation based on compound specific hydrogen isotope ratios of vascular plant and sphagnum biomarkers in ombrotrophic peatland sediments we show that the contrast in h isotopic ratios of water available to living sphagnum top 20 cm and in the rooting zone of peatland vascular plants can be used to estimate the fraction of water remaining after evaporation vascular plant leaf waxes record h isotopic ratios of acrotelm water which carries the d h ratio signature of precipitation and is little affected by evaporation whereas the sphagnum biomarker c 23 n alkane records h isotopic ratios of the water inside its cells and between its leaves which is strongly affected by evaporation at the bog surface evaporation changes can then be deduced by comparing h isotopic ratios of the two types of biomarkers we calibrated d h ratios of c 23 n alkane to source water with lab grown sphagnum we also tested our isotopic model using modern surface samples from 18 ombrotrophic peatlands in the midwestern united states finally we generated a 3000 year downcore reconstruction from minden bog michigan usa our new record is consistent with records of other parameters from the same peatland derived from different proxies and allows us to differentiate precipitation supply and evaporative loss

windiness spells in sw europe since the last glacial maximum abstract dunefields have a great potential to unravel past regimes of atmospheric circulation as they record direct traces of this component of the climate system along the portuguese coast transgressive dunefields represent relict features originated by intense and frequent westerly winds that largely contrast with present conditions clearly dominated by weaker northwesterly winds optical dating and subsurface stratigraphy document three age clusters indicating main episodes of dune mobilization during the last termination 20 11 6 ka middle holocene 5 6 ka and late holocene 1 2 0 98 and 0 4 0 15 ka we find reconstructed windfields to be analogous during all episodes and dominated by strong westerlies yet larger grain size diameters and dune volumes documented for the last termination support amplified patterns compatible with a southward shift and intensification of the north atlantic westerlies during winters conversely dunes deposited after the middle holocene are compatible with more variable windfields and weakened patterns controlled by interannual shifts towards low values of the north atlantic oscillation nao this work demonstrates that present windfield regimes in southern europe are not compatible with past aeolian activity indeed present day analogs indicate that wind intensities compatible with past aeolian activity are rare at present sediment transport potentials below estimates in the aeolian record but can occur if the jet stream is diverted to the south i e 30 n with negative nao index or if very deep cyclones anchor around 50 n extending their influence to the western portuguese coast relatively low nao index however these conditions represent temporary patterns lasting around one day while we suggest that the identified episodes of aeolian activity may represent semi permanent conditions

tarawera 1886 new zealand a basaltic plinian fissure eruption abstract new zealand s biggest and most destructive volcanic eruption of historical times was that of tarawera in 1886 the resulting scoria fall has a dispersal very similar in extent to that of the vesuvius a d 79 pumice fall and is one of the few known examples of a basaltic deposit of plinian type a new estimate of the volume 2 km 3 is significantly greater than previous estimates the basalt came mainly from a 7 km length of fissure and emission and exit velocity were fairly uniform along at least 4 km of it this is one of the few documented examples of a plinian eruption from a fissure vent primary welding of the scoria fall resulted where the accumulation rate exceeded about 250 mm min 1 a model of the eruption dynamics is proposed which leads to an estimate of 28 km for the height of the eruption cloud and implies a magma volatile fraction of 1 5 3 violent phreatic explosions occurred in the southwestern extension of the fissure across the rotomahana geothermal field and it is thought that some of the water responsible for the power of the plinian eruption came from this source though its amount was not sufficient to turn the eruption into a phreatoplinian one

molecular proxies for paleoclimatology we summarize the applications of molecular proxies in paleoclimatology marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments loess deposits and ice cores the fundamentals of this approach are the molecular parameters the compound abundances and carbon hydrogen nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts these afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation we discuss two types of proxy those of terrigenous and those of aquatic origin and exemplify their application in the study of marine sediments through the medium of ten case studies based in the atlantic mediterranean and pacific oceans and in antarctica the studies are mainly for periods in the present the holocene and particularly the last glacial interglacial but they also include one study from the cretaceous the terrigenous proxies which are measures of continental vegetation are based on higher plant leaf wax compounds i e long chain circa c30 hydrocarbons alcohols and acids they register the relative contributions of c3 vs c4 type plants to the vegetation in the source areas the two marine proxies are measures of sea surface temperatures sst the longer established one u37k is based on the relative abundances of c37 alkenones photosynthesized by unicellular algae members of the haptophyta the newest proxy tex86 is based on c86 glycerol tetraethers gdgts synthesized in the water column by some of the archaeal microbiota the crenarchaeota

identification of the main driving mechanisms in the evolution of a small coastal wetland traba galicia nw spain since its origin 5700 cal yr bp this paper examines the interdependence among the different forcing factors in the evolution of the traba coastal wetland galicia nw spain based on lithofacies and diatom analyses of three cores reaching the basement according to radiocarbon data the wetland originated 5700 cal yr bp a time when similar systems on the atlantic coast of the iberian peninsula were formed diatom assemblage data allow the estimation of the sea level position at 5700 cal yr bp at least 7 m below present day mean sea level attenuation of the sea level rise at that time was a major driving mechanism that permitted the establishment of an incipient beach dune complex causing water logging in the traba basin however the location of this incipient wetland on a basement high which prevented an open connection to the sea made topographic inheritance the main forcing factor in the subsequent evolution of the wetland thus traba was never a coastal lagoon system as it has sometimes been defined the maximum permeability of the beach dune complex enclosing the wetland was recorded after its origin until 2900 cal yr bp when increased stormy conditions affected the galician shelf waters since then the evolution of the wetland has been mainly controlled by more local factors especially the continental sediment supply changes in land use in the basin have accelerated the infilling of the water body since the 19th century this rapid infilling makes the whole system more prone to total encroachment in the short term rather than to sea drowning palaeoenvironmental analyses showing the main trends in the long term evolution of coastal wetlands can be of key importance in any management decisions aimed at preserving these kinds of sensitive coastal environments