middle to late holocene moisture changes in the desert of northwest namibia derived from fossil hyrax dung pollen new pollen results and radiocarbon dating from fossil hyrax middens derived from the edge of the northern namib desert address the shortage of continental palaeobotanical evidence in arid namibia by providing evidence for the environmental conditions during the mid to late holocene in the region the results obtained reflect long term stability in the area throughout most of the sequence higher than modern moisture availability is suggested between c 6 and 1 ka bp by the increased abundance of poaceae cyperaceae or chenopodiaceae which respond rapidly by flowering after modest quantities of rainfall around 1 ka and recently arid conditions seem to have prevailed with a decrease in poaceae and an increase in acanthaceae other palaeoecological evidence from the local and regional surroundings that focused on fluvial deposits marine palynology and mineralogy confirms this mid holocene increase in more effective rainfall

two mode ionospheric response and rayleigh wave group velocity distribution reckoned from gps measurement following mw 7 8 nepal earthquake on 25 april 2015 the coseismic induced ionospheric total electron content tec perturbations were analyzed following the mw 7 8 nepal earthquake 28 147 n 84 708 e depth 15 km that occurred on 25 april 2015 at 06 11 26 utc the ionospheric response is due to both the modes i e shock acoustic waves slow mode and rayleigh wave induced fast mode the continuous global positioning system gps data at about 60 sites from various gps networks have been used in the present study all the sites within epicentral distance of 2400 km and 70 170 azimuth recorded the rayleigh wave induced tec response while the sites within 400 2200 km in the same azimuth recorded the response from both the modes the maximum coseismic induced peak to peak tec amplitude is 1 2 total electron content unit 1 tecu 1016 el m 2 from hodochron plot the apparent rayleigh wave velocity has been determined as 2400 m s on the average and the acoustic wave velocity as 1180 m s both these waves being discernible beyond 1200 km of epicentral distance as also evident from hodochron plot and wavelet spectrographs we reckoned the rayleigh wave group velocities using ionospheric response at selected radial pairs of stations and validated the ionospheric response distribution seen mainly depending on the epicentral distance satellite geometry directivity of radiation pattern and the upper crustal heterogeneity this study highlights the characteristics of ionospheric response consequent to the 2015 nepal earthquake

modelling glacial climatic millennial scale variability related to changes in the atlantic meridional overturning circulation a review abstract since the discovery of glacial abrupt variability in greenland and the north atlantic about two decades ago its modelling remains a conceptual and technical challenge while the global climatic signature of heinrich events can reasonably be ascribed to the fresh water discharge related to the massive iceberg armadas released by the laurentide ice sheet in the north atlantic the existence of such a triggering mechanism is elusive as far as dansgaard oeschger type variability is concerned even if other mechanisms have been proposed the majority of modelling attempts to better understand glacial climate variability has assumed it to be linked to abrupt variations in the atlantic meridional overturning circulation amoc in this review we introduce the rationale behind this approach i e the possible existence of several deep ocean circulation equilibria associated with distinct climate signatures we then review the published fresh water hosing experiments and the mechanisms at work to explain the climate differences related to the different amoc states most of these works have been performed under pre industrial boundary conditions the few hosing experiments run under glacial conditions show that the sensitivity of the climate system to fresh water hosing is very dependent on the background climate state in order to rigourously compare several types of experiments equilibrium runs vs transient runs with pre industrial vs glacial boundary conditions we present experiments especially run for this review with two climate models of intermediate complexity uvic and loveclim although there are similarities between the responses simulated by these models there are also many differences which would benefit being compared to reconstructions such as those presented in this special issue however a strict comparison will require to consider boundary conditions as realistic as possible for marine isotopic stage 3 modelling glacial variability to compare model results with paleoclimatic data remains a big challenge

interhemispheric climate links revealed by a late glacial cooling episode in southern chile understanding the relative timings of climate events in the northern and southern hemispheres is a prerequisite for determining the causes of abrupt climate changes but climate records from the patagonian andes1 2 3 4 and new zealand5 6 7 8 for the period of transition from glacial to interglacial conditions about 14 6 10 kyr before present as determined by radiocarbon dating show varying degrees of correlation with similar records from the northern hemisphere it is necessary to resolve these apparent discrepancies in order to be able to assess the relative roles of northern hemisphere ice sheets and oceanic atmospheric and astronomical influences in initiating climate change in the late glacial period here we report pollen records from three sites in the lake district of southern chile 41 s from which we infer conditions similar to modern climate between about 13 and 12 2 14c kyr before present bp followed by cooling events at about 12 2 and 11 4 14c kyr bp and then by a warming at about 9 8 14c kyr bp these events were nearly synchronous with important palaeoclimate changes recorded in the north atlantic region9 supporting the idea that interhemispheric linkage through the atmosphere was the primary control on climate during the last deglaciation in other regions of the southern hemisphere where climate events are not in phase with those in the northern hemisphere local oceanic influences may have counteracted the effects that propagated through the atmosphere

holocene aeolian activity in the southwestern kalahari desert southern africa significance and relationships to late pleistocene dune building events little is known about the timing of dune building episodes in the southwestern kalahari desert previously arid phases when dune activity occurred have been inferred from gaps in chronologies derived from information that attests to former humid periods to redress this optically stimulated luminescence osl dating was applied to sediment samples taken from a range of aeolian landforms in the sw kalahari four periods of dune building are identified in the late pleistocene and holocene holocene aeolian activity at 6 ka and 1 2 ka led to the construction of localised dune forms in contrast to late pleistocene times when the extensive field of linear dunes that dominates the region was emplaced late holocene aridity was however sufficient to allow rapid emplacement of the lunette dune at witpan the record of aeolian activity is evaluated in the context of humid chronologies and an ocean atmosphere model of holocene climate change with good agreement obtained it is concluded that the application of

a high resolution 15 600 year pollen and microcharcoal record from the cederberg mountains south africa abstract the cederberg mountains western cape province south africa are located within the fynbos biome which exhibits some of the highest levels of species richness and endemism in the world the region s post glacial vegetation history however remains largely unknown presented here are high resolution pollen and microcharcoal records spanning the last 15 600 years obtained from the de rif rock hyrax midden from the driehoek valley of the central cederberg in this region previous pollen studies have shown muted variability in vegetation community composition during periods of globally marked climatic variability e g the last glacial interglacial transition in our record however significant changes in vegetation composition are apparent most notably they indicate a shift from ericaceous restioid fynbos present from 15 600 to 13 300 cal yr bp to a brief but prominent development of proteoid fynbos at the beginning of the holocene around 11 200 cal yr bp this vegetation shift is associated with increased moisture at the site and coincides with reduced fire frequency as indicated by the microcharcoal record at 10 400 cal yr bp there is a marked reduction in protea type pollen which is replaced by thicket characterised by dodonaea which became the dominant arboreal pollen type this shift was likely the result of a long relatively fire free period coupled with warmer and wetter climates spanning much of the early holocene a brief but marked decrease in water availability around 8500 8000 cal yr bp resulted in the strong decrease of dodonaea pollen the vegetation of the mid to late holocene is characterised by the increased occurrence of asteraceae and succulent taxa suggesting substantially drier conditions these data give unprecedented insight into the vegetation dynamics across a period of substantial rapid climate change and while they confirm the presence of fynbos elements throughout the last 15 600 years the results highlight significant fluctuations in the vegetation that were triggered by changes in both climate and fire regimes

palynology of hyrax middens 2000 years of palaeoenvironmental history in namibia abstract well preserved and dateable faunal middens in rock shelters of dry areas in southern africa occur as desiccated urine rich masses under local conditions which exclude microbial decomposition and oxidation urine cements together faecal pellets and other inclusions nine radiocarbon dated hyrax procavia capensis dung middens from the kuiseb river basin of the namib desert were sub sampled and analysed for fossil pollen some contain small proportions of rat droppings but not many macro fossils comparative modern pollen in faecal samples were also studied most plant macro fossils are severely digested but seeds are well preserved some insect inclusions were identified small scale changes in vegetation over the last two millennia were observed representing environmental fluctuations in cycles of ca 100 200 years the fluctuations partly agree with other palynological data from southern africa and with geomorphologic evidence for environmental changes in the desert region

multiphase plumes in a stratified ambient we report on experiments of turbulent particle laden plumes descending through a stratified environment we show that provided the characteristic plume speed b 0 n 1 4 exceeds the particle fall speed where the plume buoyancy flux is b 0 and the brunt vaisala frequency is n then the plume is arrested by the stratification and initially intrudes at the neutral height associated with a single phase plume of the same buoyancy flux if the original fluid phase in the plume has density equal to that of the ambient fluid at the source then as the particles sediment from the intruding fluid the fluid finds itself buoyant and rises ultimately intruding at a height of about 0 58 pm 0 03 of the original plume height consistent with new predictions we present based on classical plume theory we generalise this result and show that if the buoyancy flux at the source is composed of a fraction f s associated with the buoyancy of the source fluid and a fraction 1 f s from the particles then following the sedimentation of the particles the plume fluid intrudes at a height 0 58 0 22f s pm 0 03 h t where h t is the maximum plume height this is key for predictions of the environmental impact of any material dissolved in the plume water which may originate from the particle load we also show that the particles sediment at their fall speed through the fluid below the maximum depth of the plume as a cylindrical column whose area scales as the ratio of the particle flux at the source to the fall speed and concentration of particles in the plume at the maximum depth of the plume before it is arrested by the stratification we demonstrate that there is negligible vertical transport of fluid in this cylindrical column but a series of layers of high and low particle concentration develop in the column with a vertical spacing which is given by the ratio of the buoyancy of the particle load and the background buoyancy gradient small fluid intrusions develop at the side of the column associated with these layers as dense parcels of particle laden fluid convect downwards and then outward once the particles have sedimented from the fluid with a lateral return flow drawing in ambient fluid as a result the pattern of particle rich and particle poor layers in the column gradually migrates upwards owing to the convective transport of particles between the particle rich layers superposed on the background sedimentation we consider the implications of the results for mixing by bubble plumes for submarine blowouts of oil and gas and for the fate of plumes of waste particles discharged at the ocean surface during deep sea mining

numerical simulations of rotating bubble plumes in stratified environments the effects of system rotation on the turbulent dynamics of bubble plumes evolving in stratified environments are numerically investigated by considering variations in both the system rotation rate and the gas phase slip velocity the turbulent dispersion of a passive scalar injected at the source of a buoyant plume is strongly altered by the rotation of the system and the nature of the buoyancy at the source when the plume is driven by the density defect associated with the presence of slipping gas bubbles the location of the main lateral intrusion decreases with respect to the single phase case with identical inlet volume momentum and buoyancy fluxes enhanced downdrafts of carrier phase fluid result in increased turbulent mixing and short circuiting of detraining plume water that elevate near field effluent concentrations similarly rotation fundamentally alters dynamic balances within the plume leading to the encroachment of the trapping height on the source and an increase in turbulent dispersion in the near field system rotation even at modest rossby numbers produces a sustained robust anticyclonic precession of the plume core the effects of rotation and the presence of bubbles are cumulative the vertical encroachment of the primary intrusion and the overall dispersion of effluent are greatest at smallest rossby numbers and largest slip velocities the main characteristic feature in rotating single phase plumes namely the robust anticyclonic precession persists in bubble plumes analysis of the momentum budgets reveal that the mechanism responsible for the organized precession i e the establishment of an unstable vertical hydrostatic equilibrium related to radial cyclostrophic balance does not differ from the single phase case

last deglacial sea surface temperature evolution in the southeast pacific compared to climate changes on the south american continent abstract applying the alkenone method we estimated sea surface temperatures ssts for the past 33 kyr in two marine sediment cores recovered from the continental slope off mid latitude chile the sst record shows an increase of 6 7 c from the last ice age lia to the holocene climatic optimum while the temperature contrast between lia and modern temperatures is only about 3 4 c the timing and magnitude of the last deglacial warming in the ocean correspond to those observed in south american continental records according to our sst record the existence of a younger dryas equivalent cooling in the southeast pacific is much more uncertain than for the continental climate changes a warming step of about 2 5 c observed between 8 and 7 5 cal kyr bp may have been linked to the early to mid holocene climatic transition 8 2 7 8 cal kyr bp also described from equatorial africa and antarctica in principal variations in the latitudinal position of the southern pacific westerlies are considered to be responsible for sst changes in the peru chile current off mid latitude chile

palynological evidence for late quaternary warming episodes in southern africa abstract polleniferous sediments from southern africa associated with past warm episodes before the last glacial maximum are rare interpretation of environmental conditions during these phases are complicated by difficulties of dating in sediments from the northern areas north of 28 s the prominence of tropical woodland pollen suggests that the period between 7000 and 6500 yr b p was associated with optimal temperatures during the holocene identifying the warmest phase in the southern high lying grasslands and semi arid karoo shrublands south of 28 s is difficult because unlike the savanna areas of the north they do not yield good pollen indicators for changes in temperature such as those of frost sensitive trees however some pollen sequences from further south along the southern coast of africa 34 s and at marion island in the southern ocean 47 s suggest that the holocene temperature optimum occurred at about the same time in the sub antarctic area in the south and the subtropical regions in the north the advent of moister conditions in southern africa during the early to middle holocene is generally recorded earlier ca 7500 6500 yr b p in the north at ca 26 s than around 31 s ca 5000 yr b p this change is provisionally associated with a relative shift in seasonality from a predominance of all season precipitation to a greater proportion of summer rainfall which apparently reached the southern karoo areas two thousand years later than the northern bushveld region

harmonic excitation of mantle rayleigh waves by the 1991 eruption of mount pinatubo philippines an unusually long at least two hours seismic wave train having periods of about 230 sec was recorded at many worldwide seismic stations during the major eruption of mount pinatubo in the philippines on june 15 1991 this wave train exhibits two sharp spectral peaks at 228 and 270 sec the group velocity phase velocity and the particle motion of this wave train indicate that it is a rayleigh wave the most probable excitation mechanism is acoustic coupling of atmospheric oscillations that were set off by continuous thermal energy flux from the volcano the two spectral peaks correspond to the characteristic periods of acoustic and gravity modes of the earth s atmosphere the magnitude of the vertical single force equivalent to the acoustic coupling is 1 6 10 17 dynes over a frequency band of 0 003 to 0 01 hz the results suggest the possibility of using acoustically coupled rayleigh waves for detection characterization and quantification of volcanic eruptions acoustic coupling of the atmosphere and the solid earth provides a unique seismic source with long duration

geomorphological palaeoenvironments of the sneeuberg range great karoo south africa sedimentary sequences within headwater valleys on the landward side of the great escarpment of south africa are elucidated and their significance as indicators of environmental change is assessed this study focuses on the sneeuberg range the most prominent mountain range in the semi arid central great karoo valley fills of a hitherto unrecognised complexity and of a greater age than any previously recorded in the central great karoo are reported three phases of deposition spanning the late pleistocene up to the present are documented from sites where gully erosion has incised the valley fills the earliest depositional phase is represented by deeply weathered calcretised gravel deposits which probably were emplaced by debris flow and fluvial processes in the form of a fan these deposits subsequently were buried by finer grained largely unconsolidated sediment with much of this emplacement occurring during the holocene there is evidence for phases of landscape stability and instability within this facies finally sheetwash has removed fine grained sediments from valley flanks and has deposited it either on valley bottoms or in presently active gullies this process appears to be ongoing and is the subject of current investigation the sedimentary deposits are interpreted as representing a wide range of palaeoenvironmental conditions that have prevailed within the central great karoo since the penultimate glaciation copyright 2003 john wiley sons ltd

holocene climate change in southernmost south africa rock hyrax middens record shifts in the southern westerlies abstract south africa s southern coastal margin is recognised as being a highly dynamic climatic region that plays a critical role in both regional and global atmospheric and oceanic circulation dynamics our understanding of the past dynamics of this system however has been limited by the number and nature of datasets available that can be used to infer changes in key climatic parameters in the region in this paper we present new high resolution 13c and 15n data from two independently dated rock hyrax procavia capensis middens from seweweekspoort in south africa s groot swartberg mountains these data provide information regarding both past vegetation and hydroclimatic change and allow a regional integration of available data that explore the long term dynamics of mid latitude circulation systems in the african sector of the southern hemisphere combined a negative relationship is apparent between temperature and humidity in this area of the southern cape and these changes can for the first time be clearly linked to variations in antarctic sea ice extent and shifts in the southern westerly storm track this dynamic is particularly evident between 5 and 7 cal kbp when a reduction in sea ice extent and a southward shift of the westerlies are manifested regionally by increased temperatures and a phase of marked aridity

from sumatra 2004 to tohoku oki 2011 the systematic gps detection of the ionospheric signature induced by tsunamigenic earthquakes the recent tsunamigenic earthquake in tohoku 11 march 2011 strongly affirms one more time after the sumatra event 26 december 2004 the necessity to open new paradigms in oceanic monitoring detection of ionospheric anomalies following the sumatra tsunami demonstrated that ionosphere is sensitive to the tsunami propagation observations supported by modeling proved that tsunamigenic ionospheric anomalies are deterministic and reproducible by numerical modeling via the ocean neutral atmosphere ionosphere coupling mechanism in essence tsunami induces internal gravity waves propagating within the neutral atmosphere and detectable in the ionosphere most of the ionospheric anomalies produced by tsunamis were observed in the far field where the tsunami signature in the ionosphere is clearly identifiable in this work we highlight the early signature in the ionosphere produced by tsunamigenic earthquakes and observed by gps measuring the total electron content close to the epicenter we focus on the first hour after the seismic rupture we demonstrate that acoustic gravity waves generated at the epicenter by the direct vertical displacement of the source rupture and the gravity wave coupled with the tsunami can be discriminated with theoretical support we illustrate the systematic nature of those perturbations showing several observations nominally the ionospheric perturbation following the tsunamigenic earthquakes in sumatra on 26 december 2004 and 12 september 2007 in chile on 14 november 2007 in samoa on 29 september 2009 and the recent catastrophic tohoku oki event on 11 march 2011 based on the analytical description we provide tracks for further modeling efforts and clues for the interpretation of complex and thus often misleading observations the routine detection of the early ionospheric anomalies following the rupture highlights the role of ionospheric sounding in the future ocean monitoring and tsunami detection

ionospheric plasma response to m w 8 3 chile illapel earthquake on september 16 2015 the lithosphere and the atmosphere ionosphere continuously exchange energy through various coupling mechanisms in particular the earth surface displacement caused by earthquakes volcanoes and tsunamis can manifest as ionospheric plasma perturbations we investigate the coseismic induced ionospheric total electron content tec perturbations following the m w 8 3 illapel thrust earthquake that occurred on september 16 2015 the continuous global positioning system gps data at 48 sites from centro sismologico nacional and international gnss service gps networks have been used in this study the nearest gps site recorded the ionospheric response 10 min after the occurrence of this earthquake the maximum vertical coseismic induced tec amplitude is 1 4 tecu and the perturbations are pronounced in the northern region of the epicenter and confined to less than 1500 km radius the average horizontal acoustic wave velocity has been determined as 1260 m s we also observed acoustic resonance recorded by prn 12 at 4 3 mhz corresponding to the first overtone of acoustic mode and lasting for about 30 min in this study we present characteristics of gps derived ionospheric plasma perturbations following illapel earthquake

ionospheric remote sensing of the denali earthquake rayleigh surface waves 1 using the global positioning system we have detected ionospheric disturbances associated with the long period rayleigh waves from the 2002 denali earthquake ms 7 9 the dense california gps networks allowed us to map the ionospheric perturbations and to compute the group velocity with a high spatial resolution above the pacific coasts due to a low sampling rate a large error in the velocity determination remains nonetheless it demonstrates that bi static remote sensing measurements of seismic waves with gps networks can be performed monostatic measurements with a dedicated satellite could possibly be used to record in the ionosphere surface waves originating from large earthquakes such a space based remote sensing of the local group velocity of rayleigh surface waves would effectively complement the seismic networks for high resolution global tomography of the earth s lithosphere

late holocene environmental change in the northwestern namib desert margin new fossil pollen evidence from hyrax middens abstract the lack of anoxic environments in arid lands makes well preserved fossil pollen difficult to find the scarcity of continental palaeobotanical data in tropical arid zones restricts the understanding of aridification processes in these endangered ecosystems it is essential to improve the knowledge about their environmental histories during the holocene and therefore we attempt to investigate the causes and describe the patterns of vegetation change in northern namibia with that aim we analyzed pollen from fossil hyrax dung that accumulated over long periods of time by sampling stratigraphically coherent sequences in five radiocarbon dated middens the fossil hyrax middens were found in rock shelters on the eastern desert edge in the northwestern kaokoveld within the so called nama karoo biome this is an ecotonal area between the namib desert and the savanna biomes which reflects features from both systems and its life form composition largely depends on an erratic rainfall pattern thirty three samples were analyzed for pollen and the pollen record reflects a non continuous vegetation history over the last 5200 yr with a hiatus between ca 4200 and 1690 yr bp the pollen spectra reflect arid savanna vegetation with a marked increase in the tree grass ratio from ca 1300 cal yr bp the most likely cause for this change is a decline in moisture that we relate to intrinsic savanna dynamics with early pastoralism megahervibore migration and changes in the hyrax diet playing a minor role

reconstruction of se trade wind intensity based on sea surface temperature gradients in the southeast atlantic over the last 25 kyr 1 a prominent feature in the southeast atlantic is the angola benguela front abf the convergence between warm tropical and cold subtropical upwelled waters at present the sea surface temperature sst gradient across the abf and its position are influenced by the strength of southeasterly se trade winds here we present a record of changes in the abf sst gradient over the last 25 kyr variations in this sst contrast indicate that periods of strengthened se trade wind intensity occurred during the last glacial maximum the younger dryas and the mid to late holocene while heinrich event 1 the early part of the bolling allerod and the early holocene were periods of weakened se trade winds

ionospheric gps total electron content tec disturbances triggered by the 26 december 2004 indian ocean tsunami 1 tsunami ionospheric disturbances tids of the 26 december 2004 mw 9 3 sumatra earthquake are detected by the total electron content tec of ground based receivers of the global positioning system gps in the indian ocean area it is found that the tsunami waves triggered atmospheric disturbances near the sea surface which then traveled upward with an average velocity of about 730 m s 2700 km hr into the ionosphere and significantly disturbed the electron density within it results further show that the tids which have maximum height of about 8 6 17 2 km periods of 10 20 min and horizontal wavelengths of 120 240 km travel away from the epicenter with an average horizontal speed of about 700 km hr 190 m s in the ionosphere

rock hyrax middens a palaeoenvironmental archive for southern african drylands abstract like many of the world s subtropical regions southern africa is highly sensitive to changes in the earth s climate system but a dearth of reliable palaeoenvironmental records means that relatively little is known about how regional environments have been affected over centennial to multi millennial timescales to a large extent this sensitivity is a function of the position of these regions at the interface between temperate and tropical circulation systems the resulting seasonality and irregularity of rainfall have limited the development of suitable archives such as lakes and wetlands for the preservation of palaeoenvironmental proxies this paper reviews and evaluates the value of rock hyrax middens as novel palaeoenvironmental archives in southern africa considered are 1 the contemporary taxonomy distribution and ecology of hyraxes 2 the mechanisms of hyrax midden development their physical and chemical structure rates of accumulation and age and 3 the palaeoenvironmental proxies preserved within hyrax middens including fossil pollen stable isotopes and biomarkers the interpretive constraints and opportunities offered by these various midden characteristics are assessed with a view to demonstrating the potential of these deposits widespread as they are through arid and semi arid southern africa in providing a more detailed and chronologically resolved view of late quaternary palaeoenvironments across the subcontinent

role of slip velocity in the behavior of stratified multiphase plumes this paper presents direct measurements of multiphase plumes in stratification and correlates characteristic plume properties with the nondimensional slip velocity un un is defined as the ratio of the bubble slip velocity us to a characteristic plume fluid rise velocity bn 1 4 b is the total kinematic buoyancy flux and n is the buoyancy frequency un is derived by dimensional analysis and is compared to other nondimensional parameters for multiphase plumes in the literature to investigate correlations of the nondimensional numbers with plume properties laboratory experiments were conducted in linear stratification using dispersed phases of air oil and glass beads creating an inverted plume a new type of plume behavior is identified called type 1 in which the horizontal motion in the first detrainment event disperses the relatively weak bubbles creating a diffuse bubble plume that forms out of the intrusion measurements from these and previous experiments for type behavior trap height

energetic bubble plumes in arbitrary stratification field and laboratory experiments were performed to investigate the mixing induced by energetic point source bubble plumes in water columns of arbitrary stable stratification published data from various sources were also used in the present study to increase the parameter range it was found that the bubble plume surface signatures were marked by a central unsteady core consisting of an air water mixture surrounded by an annular up thrusting flow consisting of water only outside this the rising plume water spread radially plunged below the surface and then flowed outward as an intrusive gravity current at a level of neutral buoyancy by equating the observed arbitrary stratification to a linear profile of equal potential energy the radial extent of the plunge point and the net detrainment rate could be parameterized using natural scales of the problem these formulas were verified using field and laboratory data and may thus be used in air diffuser design procedures

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

formation dynamics of subsurface hydrocarbon intrusions following the deepwater horizon blowout 1 hydrocarbons released following the deepwater horizon dh blowout were found in deep subsurface horizontal intrusions yet there has been little discussion about how these intrusions formed we have combined measured or estimated observations from the dh release with empirical relationships developed from previous lab experiments to identify the mechanisms responsible for intrusion formation and to characterize the dh plume results indicate that the intrusions originate from a stratification dominated multiphase plume characterized by multiple subsurface intrusions containing dissolved gas and oil along with small droplets of liquid oil unlike earlier lab measurements where the potential density in ambient water decreased linearly with elevation at the dh site it varied quadratically we have modified our method for estimating intrusion elevation under these conditions and the resulting estimates agree with observations that the majority of the hydrocarbons were found between 800 and 1200 m

interhemispheric atlantic seesaw response during the last deglaciation the asynchronous relationship between millennial scale temperature changes over greenland and antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the atlantic ocean here we present new records from the south atlantic that show rapid changes during the last deglaciation that were instantaneous within dating uncertainty and of opposite sign to those observed in the north atlantic our results demonstrate a direct link between the abrupt changes associated with variations in the atlantic meridional overturning circulation and the more gradual adjustments characteristic of the southern ocean these results emphasize the importance of the southern ocean for the development and transmission of millennial scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide

pollen indications of holocene palaeoenvironments at florisbad spring in the central free state south africa mid to late holocene pollen data from florisbad in the central free state south africa reveal a number of moisture fluctuations commencing at c 6500 bp the pollen sequence indicates an arid climate but shows more availability of moisture under grassy conditions from summer rain at c 6300 bp and again at c 4420 bp the interval between these dates is characterized by a dry episode with karroid shrubs some time between 5500 and 4500 bp possibly as a result of less marked summer seasonality after 4220 bp moisture conditions gradually fluctuated in intensity or seasonal availability until c 2100 1700 bp when strong summer evaporation is indicated at the upper end of the sequence the data are complemented by previously published results on environmental change from the nearby deelpan site to the west although some distinct events correlate regionally over south africa summer rains appear to have been significant at florisbad at an earlier stage in the mid holocene than in the karoo to the south

holocene pollen from swamp cave and hyrax dung deposits at blydefontein kikvorsberge karoo south africa abstract pollen analysis of material from a variety of sediment types including those from ponds streams a rock shelter and hyrax dung accumulations in the blydefontein basin 31 09 s 25 05 e fig 1b provide a record of vegetation change in the eastern karoo over the last 10 000 years the pollen composition fluctuated as a result of different taphonomic processes inherent in the various sampled deposits results further demonstrate that long term vegetation changes alternated between karoo shrub and grassland plant communities karoo shrubs suggesting relatively dry conditions were generally prominent in the early holocene until ca 5400 yr bp when more grassy vegetation began to flourish presumably in response to increased summer rain conditions pollen representation of the early holocene is not detailed enough to trace millennial scale variations during this period but more detailed middle to late holocene data show millennial or shorter scale shifts between grassland and drier karroid veld

ongoing methane discharge at well site 22 4b north sea and discovery of a spiral vortex bubble plume motion highlights mega ebullition of biogenic methane from an abandoned offshore gas well north sea evidence for midwater bubble plume intrusion fallback and short circuiting of the plume effective trapping of seabed released methane underneath the thermocline first observation of a spiral vortex methane plume and marginal turbulences megaplumes appear less efficient in terms of vertical methane transport than previously thought abstract first direct evidence for ongoing gas seepage activity on the abandoned well site 22 4b northern north sea 57 55 n 01 38 e and discovery of neighboring seepage activity is provided from observations since 2005 a manned submersible dive in 2006 discovered several extraordinary intense seepage sites within a 60 m wide and 20 m deep crater cut into the flat 96 m deep seafloor capture and isotope chemical analyses of the gas bubbles near the seafloor revealed in situ concentrations of methane between 88 and 90 vol with 13c ch4 values around 74 vpdb indicating a biogenic origin bulk methane concentrations throughout the water column were assessed by 120 niskin water samples showing up to 400 000 nm ch4 in the crater at depth in contrast concentrations above the thermocline were orders of magnitude lower with a median value of 20 nm a dye tracer injection into the gas seeps revealed upwelling bubble and water motion with gas plume rise velocities up to 1 ms 1 determined near the seabed however the dissolved dye did not pass the thermocline but returned down to the seabed measurements of direct bubble mediated atmospheric flux revealed low values of 0 7 0 3 kty 1 much less than current state of the art bubble dissolution models would predict for such a strong and upwelling in situ gas bubble flux at shallow water depths i e 100 m acoustic multibeam water column imaging data indicate a pronounced 200 m lateral intrusion at the thermocline together with high methane concentration at this layer a partly downward orientated bubble plume motion is also visible in the acoustic data with potential short circuiting in accordance to the dye experiment this observation could partly explain the observed trapping of most of the released gas below the well established thermocline in the north sea moreover 3d analyses of the multibeam water column data reveal that the upwelling plume transforms into a spiral expanding vortex while rising through the water column such a spiral vortex motion has never been reported before for marine gas seepage and might represent an important process with strong implication on plume dynamics dissolution behavior gas escape to the atmosphere and is considered very important for respective modeling approaches

northern hemisphere forcing of southern hemisphere climate during the last deglaciation changes in ocean circulation are the most plausible explanation for the early southern hemisphere deglacial warming and its lead over northern hemisphere temperature milankovitch theory which was developed to explain the relationship between earth s movement and the climate holds that glacial cycles are ultimately controlled by variations in northern hemisphere summer insolation exposure to the sun s rays spectral analyses of palaeoclimate records support this theory but a mechanistic test has been elusive other lines of evidence also show that climate changes in the southern hemisphere may have led those in the northern hemisphere casting doubt on the main theory here feng he and colleagues use a coupled ocean atmosphere model to show that the last deglaciation was indeed triggered by northern hemisphere insolation changes amplified by albedo co2 and ocean circulation changes according to the milankovitch theory changes in summer insolation in the high latitude northern hemisphere caused glacial cycles through their impact on ice sheet mass balance1 statistical analyses of long climate records supported this theory but they also posed a substantial challenge by showing that changes in southern hemisphere climate were in phase with or led those in the north2 although an orbitally forced northern hemisphere signal may have been transmitted to the southern hemisphere3 insolation forcing can also directly influence local southern hemisphere climate potentially intensified by sea ice feedback4 5 6 suggesting that the hemispheres may have responded independently to different aspects of orbital forcing signal processing of climate records cannot distinguish between these conditions however because the proposed insolation forcings share essentially identical variability7 here we use transient simulations with a coupled atmosphere ocean general circulation model to identify the impacts of forcing from changes in orbits atmospheric co2 concentration ice sheets and the atlantic meridional overturning circulation amoc on hemispheric temperatures during the first half of the last deglaciation 22 14 3 kyr bp although based on a single model our transient simulation with only orbital changes supports the milankovitch theory in showing that the last deglaciation was initiated by rising insolation during spring and summer in the mid latitude to high latitude northern hemisphere and by terrestrial snow albedo feedback the simulation with all forcings best reproduces the timing and magnitude of surface temperature evolution in the southern hemisphere in deglacial proxy records8 9 amoc changes associated with an orbitally induced retreat of northern hemisphere ice sheets10 is the most plausible explanation for the early southern hemisphere deglacial warming and its lead over northern hemisphere temperature the ensuing rise in atmospheric co2 concentration provided the critical feedback on global deglaciation9 11

detection and modeling of rayleigh wave induced patterns in the ionosphere 1 global positioning system gps allows the detection of ionospheric disturbances associated with the vertical displacements of most of the major shallow seismic events we describe a method to model the time and space distributions of rayleigh wave induced total electron content tec patterns detected by a dense gps array we highlight the conditions for which a part of the ionospheric pattern can be directly measured at teleseismic distance and above the epicenter in particular a satellite elevation angle lower than 40 is a favorable condition to detect rayleigh wave induced ionospheric waves the coupling between the solid earth and its atmosphere is modeled by computing the normal modes of the solid earth atmosphere system we show the dependency of the coupling efficiency on various atmospheric conditions by summation of the normal modes we model the atmospheric perturbation triggered by a given earthquake this shows that a part of the observation is a rayleigh induced radiation pattern and therefore characteristic of the seismic rupture through atmosphere ionosphere coupling we model the ionospheric perturbation after the description of the local geomagnetic field anisotropic effects we show how the observation geometry is strongly affecting the radiation pattern this study deals with the related data for two earthquakes with far field and near field observations using the japanese gps network geonet after the 12 may 2008 wenchuan earthquake china and after the 25 september 2003 tokachi oki earthquake japan respectively waveforms and patterns are compared with the observed tec perturbations providing a new step toward the use of ionospheric data in seismological applications

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

seismo ionospheric observations modeling and backprojection of the 2016 kaikōura earthquake we processed global navigation satellite system gnss time series data to extract total electron content tec perturbations of the ionosphere caused by the kaik ura earthquake we used ray based modeling to infer which part of the earth s surface coupled significant energy from the solid earth into the atmosphere we compared modeled tec data with the observed time series data and determined that significant coupling occurred north northeast of the initial slip this work corroborates existing analysis made with geodetic and interferometric synthetic aperture radar insar data the tec data suggested that the initial rupture coupled some energy into the atmosphere but later surface displacements 60 s after the initiation caused more significant ionospheric perturbations using an array of gnss stations we were able to track the moveout of the acoustic wave through the ionosphere we used a method commonly used in seismological studies called backprojection to estimate the location of the source of the tec perturbation on earth s surface this is the first time that this method has been applied to tec data and the results are promising the backprojection results are slightly shifted in space from the known area of maximum uplift and we attribute this small discrepancy to the fact that we did not account for horizontal winds in the atmosphere nor the 3d heterogeneity of the real atmosphere in the travel time modeling

holocene palaeoecology of the northern flinders ranges south australia based on stick nest rat leporillus spp middens a preliminary overview eight stick nest rat leporillus spp middens from three locations in the northern flinders ranges south australia provide a discontinuous palaeoecological record spanning the holocene evidence from radiocarbon dates pollen plant macrofossils and animal macrofossils is presented both pollen and plant macrofossils show that in the early to mid holocene c 8 8 5 3 ka woodlands with grassy understoreys were more widespread than present this accords with other studies suggesting wetter conditions at this time samples dating of the pleistocene holocene transition 10 9 9 ka are dominated by halophytes it is not yet clear whether this is due to the continuation of pleistocene aridity changes in rainfall seasonality or local influences on vegetation

radial spreading of turbulent bubble plumes weak bubble plumes carry liquid from the environment upwards and release it at multiple intermediate levels in the form of radial intrusive currents in this study laboratory experiments are performed to explore the spreading of turbulent axisymmetric bubble plumes in a liquid with linear density stratification the thickness volumetric flowrate and spreading rates of multiple radial intrusions of plume fluid were measured by tracking the movement of dye injected at the source of bubbles the experimental results are compared with scaling predictions our findings suggest that the presence of multiple intrusions reduces their spreading rate compared to that of a single intrusion this work is of relevance to the spreading of methane plumes issuing from the seabed in the arctic ocean above methane hydrate deposits the slower multiple spreading favours the presence of methane rich seawater close to the plume which may reduce the dissolution of methane in the bubbles and thus promote the direct transport of methane to the atmosphere this article is part of the theme issue stokes at 200 part 2

on the co seismic ionospheric disturbances cids in the rapid run ionosonde observations over allahabad following mw 7 8 nepal earthquake on april 25 2015

paleocean circulation during the last deglaciation a bipolar seesaw hughen et al 1998 have documented that during the first 200 years of younger dryas time the 14c content of atmospheric co2 increased by 50 and that during the remainder of this 1200 year duration cold event it steadily declined the initial increase in 14c c was likely the result of a reduction in the atlantic s conveyor circulation however were the subsequent radiocarbon decline due to the rejuvenation of this potent heat pump then it is difficult to understand why the climate conditions in the northern atlantic basin remained cold throughout the younger dryas modeling exercises by stocker and wright 1996 mikolajewicz 1998 and schiller et al 1998 show that if the conveyor is terminated the transfer of radiocarbon into the deep sea shifts to the southern ocean thereby stabilizing the atmospheric 14c c ratio paleoclimatic evidence from the antarctic continent suggests that this model based scenario might have been played out in the real world while the younger dryas cooling has been documented in many places around the world including new zealand denton and hendy 1994 sowers and bender 1995 using their 18o in o2 based correlation between the ice core 18o in ice records for antarctica and greenland have demonstrated that in antarctica the younger dryas was a time of maximum warming the point of this paper is that the steep rise in 18o rise in antarctic ice which commenced close to the onset of the younger dryas might have been caused by heat released to the atmosphere in response to an increase in deep sea ventilation in the southern ocean

nostradamus the radar that wanted to be a seismometer 1 surface waves emitted after large earthquakes are known to induce by dynamic coupling atmospheric infrasonic waves propagating upward through the neutral and ionized atmosphere those waves have been detected in the past at ionospheric heights using a variety of techniques such as hf doppler sounding or gps receivers the hf doppler technique particularly sensitive to the ionospheric signature of rayleigh waves is used here to show ionospheric perturbations consistent with the propagation of rayleigh wave phases r1 and r2 following the sumatra earthquake on the 28 march 2005 m 8 6 this is in our knowledge the first time that the phase r2 is detected by ionospheric sounding in addition we prove here that the ionospheric signature of r2 is also observed by over the horizon oth radar the latter was never used before to detect seismic signature in the ionosphere adding the oth radar to the list of the ionospheric seismometers we discuss and compare the performances of the three different instruments mentioned above namely hf doppler sounding gps receivers and oth radar

low latitude control of interhemispheric sea surface temperature contrast in the tropical atlantic over the past 21 kyears the possible role of se trade winds to stimulate a discussion on the role of tropical atmospheric circulation versus thermohaline circulation changes for tropical atlantic sea surface temperature sst variations we present a record of the sst contrast sst between the tropical northwest and southeast atlantic from the last glacial maximum to the late holocene the sst was calculated from two alkenone derived sst records one from the caribbean sea and the other from the angola basin changes in the cross equatorial sst were then compared with an abundance record of florisphaera profunda from the equatorial atlantic which is indicative of se trade wind induced variations in thermocline depth in the equatorial divergence zone this comparison implies that the last glacial maximum the younger dryas and the mid to late holocene were periods of strong se trade winds which led to an intense upwelling related cooling in the southeast atlantic and concurrently enhanced advection of warm tropical south atlantic waters into the western tropical atlantic accordingly a coupled ocean atmospheric process has probably created a dipole like sst distribution pattern in the tropical atlantic during these three distinct climatic periods in contrast heinrich event 1 the bolling allerod and the early holocene were intervals of weakened se trade winds causing a warming in the southeast atlantic however synchronous warming in both regions during heinrich event 1 can be partially attributed to a weakening of thermohaline overturning which caused a reduced northward heat transport from the low latitude to the high latitude north atlantic

ionospheric and geomagnetic disturbances caused by the 2008 wenchuan earthquake a revisit previous works have shown that coseismic ionospheric disturbances cids after the tsunamigenic 2011 tohoku earthquake tohoku eq mw9 1 covered a vast area and were observed thousands of kilometers away from the epicenter for the purpose of making a comprehensive comparison between powerful oceanic and inland eqs we conduct a retrospective investigation of cids and geomagnetic responses to the 2008 wenchuan eq mw7 9 using a combination of techniques total electron content hf doppler and ground magnetometer it is the very first study to present cids recorded by different techniques at co located sites and profiled with regard to changes of both ionospheric plasma and current geomagnetic field simultaneously the integrated observation also shows that 1 in the wenchuan case most of the ionospheric and geomagnetic disturbances were observed within 1000 km distance which is far less than the tohoku case 2 two groups of cids were found with maximum amplitudes in the direction of azimuth 150 and 135 respectively and 3 the geomagnetic changes were only registered by three magnetometers located to the east and southeast of the epicenter all the facts indicate that the main directional lobe of wenchuan eq energy propagation is to southeast and perpendicular to the direction of the fault rupture but this kind of directivity is not that distinct in the tohoku case we suggest that the different fault slip inland or submarine affecting the way of couplings of lithosphere with atmosphere may contribute to the discrepancies between the two events

paleohydraulics of the last outburst flood from glacial lake agassiz and the 8200 bp cold event abstract during the last deglaciation of north america huge proglacial lakes formed along the southern margin of the laurentide ice sheet the largest of these was glacial lake agassiz which formed about 11 7 14 c kyr and drained into hudson bay about 7 7 14 c kyr 8 45 cal kyr overflow from these lakes was variably directed to the mississippi st lawrence and mackenzie drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events when the ice dam across hudson bay finally was breached a massive flood drained lake agassiz which was routed through hudson strait to the labrador sea in terms of stored water volume the largest reservoir was associated with the kinojevis level of lake agassiz for this maximum filling the impounded water volume available to produce floods is estimated as 40 000 151 000 km 3 depending on the location of the ice margin and route used the timing of this rapid release of stored freshwater just precedes the early holocene cooling event at 8 2 cal kyr bp we use the spring hutter theory to simulate flood hydrographs for floods that originate in subglacial drainage conduits and find that flood magnitude and duration are 5 sv and 0 5 yr multiple fillings and floods are possible as are single floods having a complex multipulse structure modelling results suggest that the outburst flood from lake agassiz may have terminated before the lake surface elevation dropped to sea level and that the flood ended when a stable drainage channel was established connecting lake agassiz to the tyrrell sea

evidence of younger dryas and neoglacial cooling in a late quaternary palaeotemperature record from a speleothem in eastern victoria australia a calcitic stalagmite collected from a limestone cave in the buchan area of eastern victoria has been dated by three mass spectrometric uranium series analyses two growth phases are represented the older from 13 4 to 10 6 ka and the younger from 3 2 to 2 1 ka oxygen isotope analysis reveals that temperatures were below present day values at all times but particularly cool conditions are indicated between 12 3 and 11 4 ka and neoglacial conditions occurred at about 3 ka the older cold climate event is clearly synchronous with the younger dryas in europe and this is the first time that strong evidence for this event has been found in australia carbon isotope variations are interpreted as indicating changes in plant productivity on the surface and are most likely controlled by variations in summer rainfall they indicate particularly high levels of plant productivity from 11 5 to 11 0 ka 1996 john wiley sons ltd

a 19 5 kyr vegetation history from the central cederberg mountains south africa palynological evidence from rock hyrax middens abstract in arid and semi arid areas such as southern africa rock hyrax procavia capensis middens represent an exceptionally valuable source of late quaternary palaeoenvironmental information pollen and stable isotope data derived from two rock hyrax middens extracted from de rif in the cederberg mountains of the southwestern cape casts new light on climatic changes that occurred across the last glacial interglacial transition lgit and the holocene 19 5 0 7 cal kbp and how the region s vegetation responded to these changes significant changes in vegetation community composition would be expected in response to environmental changes characteristic of the contrast between glacial and interglacial climates however the pollen assemblages in general indicate that mountain fynbos remained dominant throughout the record and that most of the pollen taxa exhibited only muted frequency variations this finding could be considered to be inconsistent with indications of marked climatic variations recorded in the stable isotope records for the same midden an analysis of the geological setting and the bioclimatic affinities of the taxa suggest that the explanation for this inconsistency may lie in the dominating influence of sandstone substrates and the relative resilience of mountain fynbos vegetation to climate change

large eddy simulation and parameterization of buoyant plume dynamics in stratified flow characteristics of laboratory scale bubble driven buoyant plumes in a stably stratified quiescent fluid are studied using large eddy simulation les as a bubble plume entrains stratified ambient water its net buoyancy decreases due to the increasing density difference between the entrained and ambient fluids a large fraction of the entrained fluid eventually detrains and falls along an annular outer plume from a height of maximum rise peel height to a neutral buoyancy level trap height during which less buoyant scalars e g small droplets are trapped and dispersed horizontally forming quasi horizontal intrusion layers the inner outer double plume structure and the peel intrusion process are found to be more distinct for cases with small bubble rise velocity while weak and unstable when the slip velocity is large les results are averaged to generate distributions of mean velocity and turbulent fluxes these distributions provide data for assessing the performance of previously developed closures used in one dimensional integral plume models in particular the various les cases considered in this study yield consistent behaviour for the entrainment coefficients for various plume cases furthermore a new continuous peeling model is derived based on the insights obtained from les results comparing to previous peeling models the new model behaves in a more self consistent manner and it is expected to provide more reliable performance when applied in integral plume models

a minimum thermodynamic model for the bipolar seesaw 1 the simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of antarctic ice cores the model results from the classic bipolar seesaw by coupling it to a heat reservoir in this thermal bipolar seesaw the heat reservoir convolves northern time signals with a characteristic timescale applying the model to the data of grip and byrd we demonstrate that maximum correlation can be obtained using a timescale of about 1000 1500 years higher correlations are obtained by first filtering out the long term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw the model resolves the apparent confusion whether northern and southern climate records are in or out of phase synchronous or time lagged

palynological analysis of hyrax middens from southern africa abstract hyrax middens in relatively dry parts of africa preserve plant material which includes pollen the bottoms of two stratified hyrax dung middens from blydefontein basin in the karoo shrubland of south africa were dated by radiocarbon to ca 300 yr b p and ca 1130 yr b p comparison of midden pollen spectra with pollen from alluvial sediments near one of the hyrax middens and in modern surface samples indicates that middens contain pollen which reflects local vegetation and that diet probably does not have a major influence on pollen spectra changes in pollen composition probably reflect climatic conditions during the early history of the older midden profile grass dominated spectra suggest moist conditions existed between 1200 and 300 yr b p and an interval of slightly more shrubby karoid vegetation possibly points to a minor dry spell at 1000 yr b p a sharp increase of karoid shrub vegetation and a decrease of grass since 300 yr b p is reflected in both middens the change was apparently triggered by relatively dry conditions and later during the last 150 years it was enhanced by overgrazing from european domestic stock

a record of rapid holocene climate change preserved in hyrax middens from southwestern africa the discovery of sensitive paleoenvironmental proxies contained within fossilized rock hyrax middens from the margin of the central namib desert africa is providing unprecedented insight into the region s environmental history high resolution stable carbon and nitrogen isotope records spanning 0 11 700 cal calibrated yr b p indicate phases of relatively humid conditions from 8700 7500 6900 6700 5600 4900 and 4200 3500 cal yr b p with a period of marked aridity occurring from 3500 until ca 300 cal yr b p transitions between these phases appear to have occurred very rapidly often within 200 years of particular importance are 1 the observed relationship between regional aridifi cation and the decline in northern hemisphere insolation across the holocene and 2 the signifi cance of suborbital scale variations in climate that covary strongly with fl uctuations in solar forcing together these elements call for a fundamental reexamination of the role of orbital forcing on tropical african systems and a reconsideration of what factors drive climate change in the region the quality and resolution of these data far surpass any other evidence available from the region and the continued development of this unique archive promises to revolutionize paleoenvironmental studies in southern africa

patterns and implications of plant soil δ13c and δ15n values in african savanna ecosystems abstract southern african savannas are mixed plant communities where c3 trees co exist with c4 grasses here foliar 15n and 13c were used as indicators of nitrogen uptake and of water use efficiency to investigate the effect of the rainfall regime on the use of nitrogen and water by herbaceous and woody plants in both dry and wet seasons foliar 15n increased as aridity rose for both c3 and c4 plants for both seasons although the magnitude of the increase was different for c3 and c4 plants and for two seasons soil 15n also significantly increased with aridity foliar 13c increased with aridity for c3 plants in the wet season but not in the dry season whereas in c4 plants the relationship was more complex and non linear the consistently higher foliar 15n for c3 plants suggests that c4 plants may be a superior competitor for nitrogen the different foliar 13c relationships with rainfall may indicate that the c3 plants have an advantage when competing for water resources the differences in water and nitrogen use likely collectively contribute to the tree grass coexistence in savannas such differences facilitate interpretations of palaeo vegetation composition variations and help predictions of vegetation composition changes under future climatic scenarios

holocene environmental changes in namibia inferred from pollen analysis of swamp and lake deposits spring deposits exposed during building operations in downtown windhoek and lake sediments retrieved from underneath 50 m of water in a sinkhole lake otjikoto contain pollen profiles which reflect environmental changes in namibia during the holocene at windhoek moist local conditions are reflected by pollen in the spring deposits which were radiocarbon dated to between ca 7000 and 6000 bp they remained relatively favourable until 5630 bp despite signs of drying weedy compositae lactucoideae or liguliflorae increased until the end of this record ca 2410 bp indicating local disturbance deposits from lake otjikoto were dated to the late holocene although an accurate chronology could not be estabiished for the sequence due to unexpected results with radiocarbon measurements pollen accumulation values and composition indicate relatively dry conditions after 3500 bp which were followed temporarily by a wetter climate during more recent times

detection of ruptures of andaman fault segments in the 2004 great sumatra earthquake with coseismic ionospheric disturbances 1 near field coseismic perturbations of ionospheric total electron content tec caused by direct acoustic waves from focal regions can be observed with global positioning system gps they appear 10 15 min after the earthquake with typical periods of 4 5 min and propagate as fast as 1 km s toward directions allowed by ambient geomagnetic fields ionospheric disturbance associated with the 2004 december 26 great sumatra andaman earthquake was recorded with nine continuous gps receiving stations in indonesia and thailand here we explore the possibility to constrain the rupture process of the earthquake with the observed ionospheric disturbances we assumed linearly distributed point sources along the zone of coseismic uplift extending 1300 km from sumatra to the andaman islands that excited acoustic waves sequentially as the rupture propagate northward by 2 5 km s tec variations for several satellite receiver pairs were synthesized by simulating the propagation of acoustic waves from the ground to the ionosphere and by integrating the tec perturbations at intersections of line of sights and the ray paths the tec perturbations from individual point sources were combined using realistic ratios and the total disturbances were compared with the observed signals prescribed ratios based on geodetically inferred coseismic uplifts reproduced the observed signals fairly well similar calculation using a rupture propagation speed of 1 7 km s degraded the fit suppression of acoustic waves from the segments north of the nicobar islands also resulted in a poor fit which suggests that ruptures in the northern half of the fault were slow enough to be overlooked in short period seismograms but fast enough to excite atmospheric acoustic waves coseismic ionospheric disturbance could serve as a new indicator of faulting sensitive to ruptures with timescale up to 4 5 min

ionospheric detection of the 25 may 2009 north korean underground nuclear test 1 the total electron content tec measurements of the global navigation satellite system gnss revealed traveling ionospheric disturbances tid that locate north korea s underground nuclear explosion une of 25 may 2009 to within about 3 5 km of its seismically determined epicenter the random chance for this pattern of tids to register across the eleven gnss stations is roughly 1 in 19 billion monte carlo analysis of nearly 1 300 tids from a 7 station subset of the 11 gnss stations supports the statistical strength of the array s signature the une was also detected by seismic stations and possibly a local infrasound network of the international monitoring system ims of the comprehensive nuclear test ban treaty organization ctbto but no radionuclide evidence was found thus global gnss infrastructure enables mapping spatial and temporal variations of tec that augment and complement other methods of detecting and locating clandestine unes

three dimensional waveform modeling of ionospheric signature induced by the 2004 sumatra tsunami 1 the sumatra december 26th 2004 tsunami produced internal gravity waves in the neutral atmosphere and large disturbances in the overlying ionospheric plasma to corroborate the tsunamigenic hypothesis of these perturbations we reproduce with a 3d numerical modeling of the ocean atmosphere ionosphere coupling the tsunami signature in the total electron content tec data measured by the jason 1 and topex poseidon satellite altimeters the agreement between the observed and synthetic tec shows that ionospheric remote sensing can provide new tools for offshore tsunami detection and monitoring

evidence for progressive holocene aridification in southern africa recorded in namibian hyrax middens implications for african monsoon dynamics and the african humid period abstract presented here are stable nitrogen isotope data from a rock hyrax procavia capensis middens from northwestern namibia that record a series of rapid aridification events beginning at ca 3800 cal yr bp and which mark a progressive decrease in regional humidity across the holocene strong correlations exist between this record and other terrestrial and marine archives from southern africa indicating that the observed pattern of climate change is regionally coherent combined these data indicate hemispheric synchrony in tropical african climate change during the holocene with similar trends characterising the termination of the african humid period ahp in both the northern and southern tropics these findings run counter to the widely accepted model of direct low latitude insolation forcing which requires an anti phase relationship to exist between the hemispheres the combined dataset highlights 1 the importance of forcing mechanisms influencing the high northern latitudes in effecting low latitude climate change in africa and 2 the potential importance of solar forcing and variations in the earth s geomagnetic shield in determining both long term and rapid centennial scale climate changes identifying a possible mechanism for the variations marking the ahp termination in both the southern and northern tropics

evolving southwest african response to abrupt deglacial north atlantic climate change events abstract climate change during the last deglaciation was strongly influenced by the bipolar seesaw producing antiphase climate responses between the north and south atlantic however mounting evidence demands refinements of this model with the occurrence of abrupt events in southern low to mid latitudes occurring in phase with north atlantic climate improved constraints on the north south phasing and spatial extent of these events are therefore critical to understanding the mechanisms that propagate abrupt events within the climate system we present a 19 400 year multi proxy record of climate change obtained from a rock hyrax midden in southernmost africa arid anomalies in phase with the younger dryas and 8 2 ka events are apparent indicating a clear shift in the influence of the bipolar seesaw which diminished as the earth warmed and was succeeded after 14 6 ka by the emergence of a dominant interhemispheric atmospheric teleconnection

liquid volume fluxes in stratified multiphase plumes this paper presents an optimization scheme to estimate the internal entrained fluid fluxes for multiphase plumes in stratification from indirect experimental measurements and applies the results to field scale plumes experiments were conducted in linear stratification using dispersed phases of air bubbles and glass beads the latter creating an inverted plume comparison of pre and postexperiment salinity profiles provided direct measurements of the net liquid fluxes in the plume fluorescence profiles provided direct measurements of the fluxes of passive tracer to separate the net flux measurements into upward and downward flows this paper applies a constrained bayesian estimation technique based on a conceptual model of the plume this method provides estimates of the ambient and counterflowing entrained fluid fluxes the peeling efficiency percent of entrained fluid that detrains and the buoyancy flux continuing above the first peel these quantities correlate with the non dimensional slip veloci

modeling of atmospheric coupled rayleigh waves on planets with atmosphere from earth observation to mars and venus perspectives acoustic coupling between solid earth and atmosphere has been observed since the 1960s first from ground based seismic pressure and ionospheric sensors and since 20 years with various satellite measurements including with global positioning system gps satellites this coupling leads to the excitation of the rayleigh surface waves by local atmospheric sources such as large natural explosions from volcanoes meteor atmospheric air bursts or artificial explosions it contributes also in the continuous excitation of rayleigh waves and associated normal modes by atmospheric winds and pressure fluctuations the same coupling allows the observation of rayleigh waves in the thermosphere most of the time through ionospheric monitoring with doppler sounders or gps the authors review briefly in this paper observations made on earth and describe the general frame of the theory enabling the computation of rayleigh waves for models of telluric planets with atmosphere the authors then focus on mars and venus and give in both cases the atmospheric properties of the rayleigh normal modes and associated surface waves compared to earth the authors then conclude on the observation perspectives especially for rayleigh waves excited by atmospheric sources on mars and for remote ionospheric observations of rayleigh waves excited by quakes on venus

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

gnss ionospheric seismology recent observation evidences and characteristics abstract the detail and nature of earthquakes are still challenging from traditional technique observations e g seismometers and strong motion accelerographs nowadays the ionospheric total electron content tec can be obtained from ground based global navigation satellite systems gnss and space borne gnss radio occultation which can be used to investigate the seismo ionospheric disturbances and may provide insights on the earthquake in this paper gnss ionospheric seismology is presented and reviewed including methods observation results and characteristics case studies of the 2008 wenchuan earthquake and 2011 japan earthquake are presented using ground based gnss observations significant co post seismic ionospheric anomalies are found from continuous gnss observations near the epicenters showing that the seismic ionospheric total electron content tec disturbances were derived mainly from the main shock the detailed pattern and evolution of the ionospheric disturbance are revealed by denser gnss observations some simulations explore the nature of the ionospheric perturbation highlighting that acoustic gravity waves are generated close to the epicenter and that surface rayleigh waves and tsunamis generate in the atmosphere ionosphere acoustic and gravity waves respectively these waves are induced by solid earth ocean and atmosphere coupling at the ground or ocean interface with the atmosphere propagating upward until the ionosphere create strong perturbation in plasma density and plasma velocity

virtual array beamforming of gps tec observations of coseismic ionospheric disturbances near the geomagnetic south pole triggered by teleseismic megathrusts we identified co seismic ionospheric disturbances cid in antarctica generated by the 2010 maule and the 2011 tohoku oki earthquakes analyzing tec data with a modified beamforming technique beamforming in antarctica however is not straightforward due to the effects of array deformation and atmospheric neutral wave ionospheric plasma coupling we take these effects into account and present a method to invert for the seismically generated acoustic wave using tec observations the back azimuths speeds and waveforms obtained by the beamform are in excellent agreement with the hypothesis that the tec signals are generated by the passage of rayleigh waves from the maule and tohoku oki earthquakes the tohoku oki earthquake is 12 500 km from antarctica making this the farthest observation of cids to date using gps

detection of the 2012 havre submarine eruption plume using argo floats and its implications for ocean dynamics abstract more than 85 of the earth s volcanism and geothermal heat release occurs underwater at mid ocean ridges intra plate hotspots and oceanic island arcs however we lack a clear understanding of how a submarine eruption interacts with the overlying water column the structure of the submarine eruptive plume and the transport of volcanic products in the ocean by these plumes we describe here the detection of eruption derived temperature increase and salinity decrease from the 2012 havre submarine caldera eruption by an existing array of temperature salinity profiling floats known as argo the argo floats observed the signal significant at 3 sigma level with respect to the background ocean variability noise at ocean depths of 1750 2000 m deeper than the eruptive vent itself in order to understand this signal we develop a new conceptual submarine plume model which suggests that the sub vent level temperature and salinity anomalies are caused by large scale ocean mixing induced by the eruptive plume rather than heating directly from the eruption using results from scaling analysis and a modified numerical plume gravity current model we show that submarine eruptions can efficiently advect water masses from the deep ocean closer to the surface and form multiple subsurface intrusions during the process consequently the submarine eruptive plumes can initiate significant ocean mixing a process with significant implications for both long and short term influence of submarine volcanism on ocean chemistry dynamics and ecology finally our model confirms that a detectable anomaly would persist out to 100s of km from the eruption location comparable to argo s spatial sampling given the global ocean coverage and a decadal baseline the argo floats and other similar datasets in concert with hydrophone and seismic arrays can provide significant new constraints on subaqueous volcanism eruption dynamics and the impact on earth systems through enhanced ocean mixing and nutrient supply e g during submarine large igneous provinces

geomagnetic dependence of ionospheric disturbances induced by tsunamigenic internal gravity waves summary a series of ionospheric anomalies following the sumatra tsunami has been recently reported in the literature these anomalies show the signature in the ionosphere of tsunami generated internal gravity waves igw propagating in the neutral atmosphere over the ocean all these anomalies observed in the total electron content tec measured by gps or altimeters show geographical heterogeneity in the perturbed tec amplitude and suggest a dependence on geomagnetic latitude this latitudinal dependence has been taken into account in the previous 3 d modelling used for the interpretation of the tec topex and jason data here we present an accurate description of the ocean atmosphere ionosphere coupling method and focus on the properties of the propagation of tsunamigenic igw in the neutral atmosphere and their interaction with the ionospheric plasma the analytical dependence on the geomagnetic field in the neutral plasma coupling discussed in detail and quantitative modelling is used to describe the propagation of a simple tsunami wave at the global scale what emphasize the role of geomagnetic field within the neutral plasma coupling at the equatorial and mid latitude regions the results presented here in terms of electron density and tec variations show a strong geometric dependance involving the magnetic field inclination and the propagative direction of the tsunami if the strongest electron density and tec perturbations are located around 15 0 and 15 north the structure and amplitude of the modelled perturbation changes in the two

ionospheric response following the mw 7 8 gorkha earthquake on 25 april 2015 a detailed observation of the coseismic ionospheric disturbances cids after the mw 7 8 gorkha earthquake has been carried out using total electron content tec data from 333 gps stations this inland earthquake occurred on 25 april 2015 at a depth of 15 km following the quake at 6 11 ut groups of cids were observed from 06 18 to 07 00 ut the cids we observed could be classified into three groups cids related to gravity waves gws cids related to acoustic waves aws and cids related to seismic rayleigh surface waves the gw related cids traveled at a velocity of 500 m s they were mainly observed to the south and north of the epicenter within 600 km of the event with a maximum amplitude of 0 18 tecu the aw related cids traveled at a velocity of 700 1400 m s they could be observed for 1000 km in all directions from the epicenter with an amplitude of 0 3 tecu the cids related to rayleigh waves could be observed only to the east of the epicenter at a maximum distance of 1800 km they had an apparent velocity of 2 0 2 3 km s through comparing the seismogram data from iris to the tec data we found the azimuthal characteristics of the ground vibrations agree with the directivity of the cids related to rayleigh surface waves

glacier retreat in new zealand during the younger dryas stadial the younger dryas a period of sudden cooling in the northern hemisphere about 12 900 years ago is perhaps the best known example of abrupt climate change but the global extent of the younger dryas is a topic of intense debate particularly in the record of glacial behaviour in new zealand a new reconstruction of the growth and retreat patterns of glaciers in the southern alps in new zealand at the time of the younger dryas supports the suggestion that temperature reductions in the north caused warming and glacial retreat in the southern hemisphere through a series of climate feedbacks the younger dryas during which northern hemisphere temperatures cooled drastically in just a few years is perhaps the best known example of abrupt climate change but its global extent is under debate particularly in the record of glacial behaviour in new zealand these authors present evidence for glacial retreat in new zealand during the younger dryas supporting the hypothesis that northern hemisphere climate changes caused southern hemisphere warming through a series of climate feedbacks millennial scale cold reversals in the high latitudes of both hemispheres interrupted the last transition from full glacial to interglacial climate conditions the presence of the younger dryas stadial 12 9 to 11 7 kyr ago is established throughout much of the northern hemisphere but the global timing nature and extent of the event are not well established evidence in mid to low latitudes of the southern hemisphere in particular has remained perplexing1 2 3 4 5 6 the debate has in part focused on the behaviour of mountain glaciers in new zealand where previous research has found equivocal evidence for the precise timing of increased or reduced ice extent1 2 3 the interhemispheric behaviour of the climate system during the younger dryas thus remains an open question fundamentally limiting our ability to formulate realistic models of global climate dynamics for this time period here we show that new zealand s glaciers retreated after 13 kyr bp at the onset of the younger dryas and in general over the subsequent 1 5 kyr period our evidence is based on detailed landform mapping a high precision 10be chronology7 and reconstruction of former ice extents and snow lines from well preserved cirque moraines our late glacial glacier chronology matches climatic trends in antarctica southern ocean behaviour and variations in atmospheric co2 the evidence points to a distinct warming of the southern mid latitude atmosphere during the younger dryas and a close coupling between new zealand s cryosphere and southern high latitude climate these findings support the hypothesis that extensive winter sea ice and curtailed meridional ocean overturning in the north atlantic led to a strong interhemispheric thermal gradient8 during late glacial times in turn leading to increased upwelling and co2 release from the southern ocean9 thereby triggering southern hemisphere warming during the northern younger dryas

vegetation history inferred from pollen in late quaternary faecal deposits hyraceum in the cape winter rain region and its bearing on past climates in south africa abstract pollen analysis shed light on vegetation community structure over the last 23 000 year in the western cape the pollen from dated hyrax faecal accumulations hyraceum relates to the evolution of climate and contributes to proxy records in southern africa principal components analyses of the pollen data and 13c values of the hyrax dung samples show millennial and shorter scale temperature moisture and seasonality variations in the winter rain region the moisture availability at times do not parallel that in previously studied proxy records in the summer rain region showing an asynchronous moist event in the early holocene and drier conditions in the middle holocene anomalies in climate between the two regions may depend on the degree of northward or southward shifting of winter and summer rain circulation systems scenarios with winter rain or cool growing seasons mostly typify the dung sequence but do not exclude the possibility of southward displacement of the westerly belt under precessional strength with slight summer rain increases during the last glacial maximum limited southward displacement is also possible during the mid holocene

effects of rotation on turbulent buoyant plumes in stratified environments we numerically investigate the effects of rotation on the turbulent dynamics of thermally driven buoyant plumes in stratified environments at the large rossby numbers characteristic of deep oceanic releases when compared to nonrotating environments rotating plumes are distinguished by a significant decrease in vertical buoyancy and momentum fluxes leading to lower and thicker neutrally buoyant intrusion layers the primary dynamic effect of background rotation is the concentration of entraining fluid into a strong cyclonic flow at the base of the plume resulting in cyclogeostrophic balance in the radial momentum equation the structure of this cyclogeostrophic balance moving upward from the well head is associated with a net adverse vertical pressure gradient producing an inverted hydrostatic balance in the mean vertical momentum budgets the present simulations reveal that the primary response to the adverse pressure gradient is an off axis deflection of the plume that evolves into a robust organized anticyclonic radial precession about the buoyancy source the off axis evolution is responsible for the weaker inertial overshoots the increased thickness of lateral intrusion layers and the overall decrease in the vertical extent of rotating plumes at intermediate rossby numbers compared to the nonrotating case for inlet buoyancy forcings and environmental rossby numbers consistent with those expected in deepwater blowout plumes the speed of the organized precession is found to be as large as typical oceanic cross flow speeds

normal modes modelling of post seismic ionospheric oscillations since 1960 several experiments have shown strong perturbations of the ionosphere after earthquakes for the biggest quakes doppler ionospheric soundings have revealed displacements of several tens of meter of the ionized layers e and f an accurate modelling of these phenomena was however never described we present here synthetic displacements of such oscillations and compare it with experimental data realistic models of the atmosphere including viscosity are used as well as realistic earth and seismic source model these ionospheric oscillations are computed by normal modes summation taking explicitly into account the coupling between the solid earth and the open atmosphere they are associated to the rayleigh fundamental surface waves we obtain a good agreement between synthetics and observations so it should be possible to use this method to study the ionospheric post seismic perturbations and possibly the high altitude profile of the density and the viscosity of the atmosphere

double plume integral models for near field mixing in multiphase plumes we present a generalized integral model for multiphase plumes in stratified ambient conditions based on the double plume approach where the plume is composed of a rising multiphase core plume surrounded by a counterflowing outer ring plume of dense fluid the generalized model captures as limiting cases the current approaches in the literature including two fluid and mixed fluid equations continuous and discrete detrainment dispersed phase mass transfer and two models for entrainment in the counterflow region these modeling approaches are compared and validated against both laboratory and field scale data in unstratified conditions all model formulations perform equally well in stratification entrainment in the counterflow region is best represented by correlation to the inner plume velocity instead of the difference between the inner and outer plume velocities the vertical distribution of the exchange between the inner and outer plumes in the models differs from that measured in the prototype due to enhanced entrainment at the detrainment zone and forced entrainment from the collapsing intrusion layer nonetheless the models predict well the length scales and volume fluxes at the detrainment zone and intrusion layer applications are demonstrated for reservoir air bubble plumes the mass transfer and near field mixing in the double plume integral model prove sufficiently accurate to predict the depth of maximum plume rise both the locations of total dissolution of the bubbles and the maximum height of the decelerating plume and the volume flux dissolved constituent mass flux and trap height of the intrusion

did tsunami launched gravity waves trigger ionospheric turbulence over arecibo 1 we report on measurements of ionospheric plasma dynamics conducted at the arecibo observatory between 20 00 and 24 00 local time lt on december 25 and 26 2004 using the 430 mhz incoherent scatter radar isr for interpretive purposes these measurements are supported by data from two nearby ionosondes and global positioning system gps satellites the isr detected different ionospheric behaviors during the vertical transmission periods on the consecutive magnetically quiet nights on the night of december 25 the ionosphere descended smoothly and spread f signatures faded for about two hours on the following evening the bottomside ionosphere rose by 50 km inducing plasma irregularities and intense spread f alternating cycles of bottom side plasma rising and falling persisted through the remainder of the experiments we postulate that this sinusoidal behavior is a response to gravity waves propagating above puerto rico nearly simultaneous data from two nearby stations show that gps signals were modified by variations in total electron content tec indicating the presence of traveling ionospheric disturbances tids the december 26 experiments were conducted about a day after an mw 9 2 earthquake launched tsunami waves first across the indian then into the atlantic and pacific oceans we suggest that coupling at the tsunami sea air interface launched gravity waves that propagated for great distances beneath the mesopause gps data recorded tec variation in asia europe and the caribbean suggesting that tids were induced on a global scale at the wake of tsunami launched gravity waves energy from imperfectly ducted gravity waves leaked into the ionosphere partially over puerto rico the wind velocity field of these gravity waves caused local ionospheric plasma to rise seeding bottomside irregularities via the generalized rayleigh taylor instability

glacier advance in southern middle latitudes during the antarctic cold reversal the geographic extent of cooling associated with the antarctic cold reversal is unclear dating of glacial moraines in new zealand suggests that the cooling extended into the southern mid latitudes possibly as a result of the northward migration of the southern subtropical front

evidence of increased rainfall prior to 3500 years bp as revealed by river borne terrigenous flux a study from west coast of india abstract the study has been conducted for insoluble residue and calcium carbonate content in a 4 80 m long shallow water at 22 m water depth sediment core at 22 m water depth off central west coast of india to reconstruct palaeo monsoonal precipitation linked with river discharge the down core profile of carbonate content shows that it is generally less than 28 below ca 3 00 m whereas above 3 00 m it is generally more than 28 and this showing an general upward trend on the contrary the average insoluble residue is marked by higher value 72 below ca 3 00 m while above 3 00 m it is low

size variation in the rock hyrax procavia capensis and late quaternary climatic change in south africa abstract the average adult size of the rock hyrax varies greatly across south africa regression analysis suggests that mean hyrax size is more closely linked to precipitation than to temperature probably because precipitation has a much greater impact on preferred hyrax food plants the relationship between mean size and precipitation is curvilinear such that size increases up to about 700 mm annum and declines thereafter this parallels a tendency for less palatable grasses to replace more palatable ones where rainfall exceeds 700 mm annum in conjunction with other indicators of past climate hyrax size variation can be used to reconstruct precipitation history near deeply stratified south african late quaternary sites including elands bay cave die kelders cave 1 and nelson bay cave

sea surface temperature fluctuations during the holocene off the south coast of africa implications for terrestrial climate and rainfall models of southern african palaeoclimate implicate surface atmospheric circulation anoma lies as forcing large scale changes during the late quaternary the available proxy data are insufficient to test the models since they provide information about temperature and rainfall rather than surface circulation a conceptual model is proposed which links coastal ocean temperatures with atmospheric circulation and allows a history of surface circulation to be inferred from sea temperature data a holocene sea surface temperature sst record was constructed by measuring the oxygen isotope composition of marine mollusc shells preserved in an archaeological cave deposit on the coast of the eastern agulhas bank southern africa radiocarbon dating of individual shells allowed definition of the timing and timespan of events in the record by serially sampling along the growth axis of each shell information was obtained about intra annual variability as well as millennial scale trends during the early holocene th