the southern westerlies during the last glacial maximum in pmip2 simulations the southern hemisphere westerly winds are an important component of the climate system at hemispheric and global scales variations in their intensity and latitudinal position through an ice age cycle have been proposed as important drivers of global climate change due to their influence on deep ocean circulation and changes in atmospheric co2 the position intensity and associated climatology of the southern westerlies during the last glacial maximum lgm however is still poorly understood from empirical and modelling standpoints here we analyse the behaviour of the southern westerlies during the lgm using four coupled ocean atmosphere simulations carried out by the palaeoclimate modelling intercomparison project phase 2 pmip2 we analysed the atmospheric circulation by direct inspection of the winds and by using a cyclone tracking software to indicate storm tracks the models suggest that changes were most significant during winter and over the pacific ocean for this season and region three out four models indicate decreased wind intensities at the near surface as well as in the upper troposphere although the lgm atmosphere is colder and the equator to pole surface temperature gradient generally increases the tropospheric temperature gradients actually decrease explaining the weaker circulation we evaluated the atmospheric influence on the southern ocean by examining the effect of wind stress on the ekman pumping again three of the models indicate decreased upwelling in a latitudinal band over the southern ocean all models indicate a drier lgm than at present with a clear decrease in precipitation south of 40 s over the oceans we identify important differences in precipitation anomalies over the land masses at regional scale including a drier climate over new zealand and wetter over nw patagonia

glacial to holocene implications of the new 27000 year dust record from the epica dome c east antarctica ice core insoluble dust concentrations and volume size distributions have been measured for the new 581 m deep dome c epica ice core antarctica over the 27000 years spanned by the record microparticle measurements from 169 levels to date confirm evidence of the drastic decrease in bulk concentration from the last glacial maximum lgm to the holocene interglacial by a factor of more than 50 in absolute value and of about 26 in flux unique new features revealed by the epica profile include a higher dust concentration during the antarctic cold reversal phase acr by a factor of 2 with respect to the holocene average this event is followed by a well marked minimum that appears to be concomitant with the methane peak that marks the end of the younger dryas in the northern hemisphere particle volume size distributions show a mode close to 2 m in diameter with a slight increase from the lgm to the holocene the lgm holocene concentration ratio appears to be dependent on particle size and for diameters from 2 to 5 m it changes from 50 to 6 glacial samples are characterised by well sorted particles and very uniform distributions while the interglacial samples display a high degree of variability and dispersion this suggests that different modes of transport prevailed during the two climatic periods with easier penetration of air masses into antarctica in the holocene than during glacial times assuming that southern south america remained the main dust source for east antarctica over the time period studied the higher dust content recorded during the acr which preceded the younger dryas period represents evidence of a change in south america environmental conditions at this time a wet period and likely mild climate in south america is suggested at circa 11 5 11 7 kyr bp corresponding to the end of the younger dryas the holocene part of the profile also shows a slight general decrease in concentration but with increasingly large particles that may reflect gradual changes at the source

constraints on the magnitude and patterns of ocean cooling at the last glacial maximum observation based reconstructions of sea surface temperature from relatively stable periods in the past such as the last glacial maximum represent an important means of constraining climate sensitivity and evaluating model simulations1 the first quantitative global reconstruction of sea surface temperatures during the last glacial maximum was developed by the climate long range investigation mapping and prediction climap project in the 1970s and 1980s refs 2 3 since that time several shortcomings of that earlier effort have become apparent4 here we present an updated synthesis of sea surface temperatures during the last glacial maximum rigorously defined as the period between 23 and 19 thousand years before present from the multiproxy approach for the reconstruction of the glacial ocean surface margo project5 we integrate microfossil and geochemical reconstructions of surface temperatures and include assessments of the reliability of individual records our reconstruction reveals the presence of large longitudinal gradients in sea surface temperature in all of the ocean basins in contrast to the simulations of the last glacial maximum climate available at present6 7

climate and marine carbon cycle response to changes in the strength of the southern hemispheric westerlies 1 it has been previously suggested that changes in the strength and position of the southern hemisphere westerlies could be a key contributor to glacial interglacial atmospheric co2 variations to test this hypothesis we perform a series of sensitivity experiments using an earth system model of intermediate complexity a strengthening of the climatological mean surface winds over the southern ocean induces stronger upwelling and increases the formation of antarctic bottom water enhanced ekman pumping brings more dissolved inorganic carbon dic rich waters to the surface however the stronger upwelling also supplies more nutrients to the surface thereby enhancing marine export production in the southern hemisphere and decreasing the dic content in the euphotic zone the net response is a small atmospheric co2 increase 5 ppmv compared to the full glacial interglacial co2 amplitude of 90 ppmv roughly the opposite results are obtained for a weakening of the southern hemisphere westerly winds

sensitivity of southern hemisphere circulation to lgm and 4 co2 climates 1 this paper investigates the effect of last glacial maximum lgm versus high co2 world boundary condition on the southern hemisphere atmospheric circulation in particular on the strength and latitudinal position of the near surface southern westerly winds sww pmip2 and pmip3 experiments as well as the abrupt 4 co2 simulations from cmip5 were analyzed robust findings include poleward expansion of the mean meridional circulation mmc and intensified and poleward shifted sww in the 4 co2 simulations consistent with recent observations and 21st century climate change projections and for the lgm stronger and southward shifted northern hemisphere mmc and weakened southern hadley cell however six of the eight lgm simulations show a decrease in the sww the other two models simulate the opposite a critical difference between the models is strong coupling between sea ice extent surface temperature gradients sww and ferrel cell in the two models with stronger and poleward shifted sww

displacement of surface monuments vertical motion several measurements of vertical ground motion at pinon flat observatory california indicate the overall weakness and instability of the earth s weathered surface with respect to the underlying rock cumulative long period motions of order 0 5 mm per year dominate these records though smaller elastic deformations caused by precipitation loading atmospheric loading and tidal strains are evident at higher frequencies all of these help to characterize the near surface material the long period records suggest that near surface weathering is the dominant influence on monument motion at least at this site on crystalline rock in a semi arid environment rainfall loading gives an average vertical modulus of 2 6 gpa for the material in the uppermost 26 m of the ground compared with 88 gpa for granite under moderate confining stress atmospheric loading gives similar results but indicates the ground is permeable to airflow at periods longer than a few hours earth tide records show poisson s ratio to be 0 09 in contrast to the normative range of 0 2 0 25 establishing that horizontal strains couple only weakly into vertical ones so that vertical strains near the surface are a poor measure of areal strain the form of the ground surface displacement power spectrum indicates that analyses of geodetic surveys would be improved with the inclusion of a monument positioning error budget that increases with time because of ground instability and the generally small rate of crustal tectonic motions deeply emplaced monuments will be needed for observational programs designed to detect short term changes in crustal deformation over baselengths of order 10 km and less

connecting antarctic sea ice to deep ocean circulation in modern and glacial climate simulations antarctic sea ice formation plays a key role in shaping the abyssal overturning circulation and stratification in all ocean basins by driving surface buoyancy loss through the associated brine rejection changes in antarctic sea ice have therefore been suggested as drivers of major glacial interglacial ocean circulation rearrangements here the relationship between antarctic sea ice buoyancy loss deep ocean stratification and overturning circulation is investigated in last glacial maximum and preindustrial simulations from the paleoclimate modelling intercomparison project pmip the simulations show substantial inter model differences in their representation of the glacial deep ocean state and circulation which is often at odds with the geological evidence we argue that these apparent inconsistencies can largely be attributed to differing and likely insufficient antarctic sea ice formation discrepancies can be further amplified by short integration times deep ocean equilibration and sea ice representation should therefore be carefully evaluated in the forthcoming pmip4 simulations

monument motion and measurements of crustal velocities it is usually assumed in geodetic studies that measurement errors are independent from one measurement to the next and that the rate of deformation velocity is constant over the duration of the experiment any temporal correlation between measurements can substantially affect the uncertainty in this velocity estimate when it is determined from the time series of measurements one source of possible long term correlation is motion of the geodetic monument with respect to the deep crust available measurements suggest that this motion introduces errors that have the form of a random walk process we show how such errors affect the uncertainty of velocity estimates for a geodetic experiment of set duration we calculate the velocity uncertainty as a function of the number of observations and of the relative amount of correlated and uncorrelated noise we find that 1 neglecting long term temporal correlations makes the uncertainty in the estimated velocities much too small and that 2 when the correlated and independent noise sources are of similar magnitude the expected improvement in uncertainty from having more measurement is not realized there is almost no improvement in some cases we have also examined the effect of outliers blunders on the velocity uncertainty for a frequency of outliers typical of geodetic field campaigns the previous two conclusions remain unchanged these results suggest that long term correlations have a large effect on estimating deformation rates unless these correlations are small frequent observations give little advantage if frequent observations are planned the amount of correlated noise due to monument instability must be kept small if the full capabilities of the measurement technique are to be realized

palaeoclimates in central and south america since 18 000 bp based on pollen and lake level records abstract the last 18 ka of palaeoclimates are discussed at 3 ka intervals based on palaeoenvironmental changes shown in pollen and lake level records from central and south america a total of 61 pollen records fulfill the requirements of continuity and chronology to be used in this synthesis 8 records from tropical and subtropical lowlands in central and south america 7 records from the central american highlands 26 records from the high andes north and south of the equator 2 records from the southern subtropics and 18 from the southern andes and subantarctic islands palaeoclimatic interpretation of the pollen records is semiquantitative based on bioclimatic parameters such as e g elevational temperature gradients or latitudinal precipitation gradients that can be related to vegetation zonation additional palaeoclimatic information is obtained from lake level records derived either from dated shorelines or from the limnological history of lake sediment sections large scale palaeoclimatic comparison of the proxy data records indicates that full and late glacial climates throughout central and south america were cooler than today by about 4 to 5 c but that moisture patterns showed regional differentiation thus in both the southern subtropics and high latitudes in southern chile conditions were substantially moister than today during full and late glacial times whereas everywhere else conditions were far drier than today in terms of palaeocirculation this scenario can be interpreted as a poleward shift of the subtropical as well as the westerly circulation a scenario that has been suggested by palaeoclimatic simulations from general circulation models gcm another major palaeoclimatic aspect predicted by the gcm simulations is the suppressed early holocene summer monsoon in the southern subtropics although proxy records are few from this zone their palaeoenvironmental history during that time shows a period of aridity that would support the model one of the most controversial aspects of south american palaeoclimates concerns the existence of a younger dryas equivalent a cold period between 11 and 10 ka bp based on the existing data from south america that show a great diversity of palaeoclimatic trends the concept of an interval that is characterized by the same climatic signal as documented for the north atlantic seems too simplistic moreover at this point only very few records have been analysed in sufficient detail to yield unambiguous climatic information for the interval in question the principal outcome of this palaeoenvironmental and palaeoclimatic synthesis is the better understanding of the type and quality of data available at present and the realization of regions and periods where much more and concerted effort is needed to address problems of intra and interhemispheric palaeoclimatic correlations only then can questions concerning the mechanism of climatic change be tackled successfully

last glacial sea surface temperatures and sea ice extent in the southern ocean atlantic indian sector a multiproxy approach 1 on the basis of the quantitative study of diatom radiolarian and planktic foraminiferal assemblages we estimated summer sea surface temperature ssst and sea ice extent at 50 sediment core localities in the atlantic and western indian sector of the southern ocean to reconstruct the last glacial environment at the glamap 18 to 15 ka equal to 21 500 to 18 000 calendar cal years bp and epilog 19 5 to 16 0 ka equal to 23 000 to 19 000 cal years bp time slices stratigraphic identification of the time slices was accomplished by a combination of ams 14c measurements benthic isotope and siliceous microfossil abundance records while the ssst estimates reveal greater surface water cooling than reconstructed by climap 1981 reaching a maximum in the area of the present subantarctic zone the sea ice reconstruction indicates that climap overestimated the expansion of the antarctic sea ice field especially for austral summer during winter the sea ice field was expanded by 60 70 compared to the present last glacial summer sea surface isotherms indicate a northward shift of the zonal bands of the antarctic circumpolar current and a relative expansion of the cold water realm south of the subantarctic front by 5 in latitude this coincides with a northward displacement of the zone of enhanced biogenic silica deposition and iceberg occurrence as a result of northward expansion of antarctic cold waters and a relatively small displacement of the subtropical front thermal gradients were steepened during the last glacial in the area of the present subtropical front the northward displacement of antarctic cold waters and the related deflection of southern ocean waters along the eastern boundary of south america may have resulted in a weakened cold water route across the drake passage in contrast the transport of warm and salty surface water from the indian into the atlantic ocean via the warm water route was not blocked allowing continuous but reduced import of heat into the south atlantic

a sea level curve for the canadian beaufort shelf radiocarbon dated peat and peaty clay samples from geotechnical boreholes in the canadian beaufort continental shelf have been used to reconstruct a late quaternary relative sea level rsl curve the samples were carefully selected and evaluated using palynological techniques to ensure that reasonable age error limits could be given to each sample the dated samples were then related to the local geological setting using seismic profiles to determine the environment of deposition the resulting data show a rise of 140 m in rsl since 27 000 years bp a minor lowering of rsl at some time between 20 000 and 10 000 years bp is inferred from acoustic data contributions from basin subsidence sediment loading and consolidation account for 35 m of the total rsl rise the rsl curve is interpreted in the light of recent models of the isostatic and eustatic responses of the earth s crust at the laurentide ice sheet margin ice may have been more extensive during the middle wisconsinan than previously thought a

a sediment and organic carbon budget for the canadian beaufort shelf abstract the arctic ocean accounts for 20 of the world s continental shelves because the arctic is sensitive to global change budgets of organic carbon for its shelves are of immediate interest the mackenzie shelf of the canadian beaufort sea is the best north american proxy for the enormous eurasian shelves large area large river input and the only site for which a complete organic carbon budget can be attempted due to an extensive data base a mass balance for the mackenzie shelf has been constructed for sediments terrestrial organic carbon and primary produced carbon we have considered allochthonous inputs from the mackenzie river from coastal erosion from smaller rivers from groundwater from the atmosphere and import by ice the mackenzie river dominates the supply to the beaufort shelf of inorganic sediment 127 mt a 1 and paniculate and dissolved terrestrial carbon 2 1 mt a 1 poc 1 3 mt a 1 doc the combined input from all other sources contributes only about 5 of the mackenzie load using sediment accumulation data we estimate that about half of the sediment supply is trapped in the delta about 40 on the shelf and the remainder escapes the shelf edge by various processes autochthonous primary production in the delta and on the shelf adds a further 3 3 mt a 1 of particulate organic carbon a box model has been constructed to account for sediment terrestrial organic carbon and primary produced carbon whereas about 60 of the terrestrial poc is preserved in delta and shelf sediments it appears that most 97 of the primary produced carbon is recycled and not preserved in sediments confidence in the budget should be improved by focusing future research on the determination of modern sedimentation rates on the delta and shelf measurement of organic carbon content of deltaic sediments determination of primary production on the shelf and determination of the relative proportions of terrestrial and marine organic carbon preserved in sediments

noise in gps displacement measurements from southern california and southern nevada 1 time series of position changes estimated from data from 236 continuously recording gps receivers operating in southern california and southern nevada are evaluated for noise models that characterize their temporal correlations the lengths of the time series range between 3 5 and 10 years after adjusting these data for postseismic deformation offsets and annual periodicities i find that about one half of the time series have temporal correlations that are categorized as either flicker or random walk noise the remaining time series can be best categorized as either a combination of flicker and random walk power law noise first order gauss markov plus random walk noise or power law plus broadband seasonal noise a variety of geodetic monuments are used in southern california and nevada including deeply braced designs cement piers pins drilled in outcrop and buildings when i evaluate the noise for each time series in terms of an estimate of the standard error in velocity i find that the sites with the smallest errors are those located in nevada using deeply braced monuments sites that are installed within regions of active pumping both for groundwater and oil had the largest standard errors in velocity comparison of monument stability as measured by standard error in rate with average annual rainfall nearby indicates a marginally significant correlation in addition even though regional filtering removed much of the common mode signals in these time series there still remains a common mode seasonal signal which can and should be removed

a gps velocity field for fennoscandia and a consistent comparison to glacial isostatic adjustment models in fennoscandia the process of glacial isostatic adjustment gia drives ongoing crustal deformation crustal velocities from gps observations have proved to be a useful tool in constraining gia models however reference frame uncertainties plate tectonics intraplate deformations as well as other geophysical processes contaminate the results former studies have shown that different international terrestrial reference frames have large discrepancies especially in the vertical component which hamper geophysical interpretation we present new velocity estimates for the fennoscandian and north european gps network our gps velocity field is directly realized in a gia reference frame using this method named the gia frame approach we are able to constrain gia models with minimal influence of errors in the reference frame or biasing signals from plate tectonics the drawbacks are more degrees of freedom that might mask real but unmodeled signals monte carlo tests suggest that our approach is robust at the 97 level in terms of correctly separating different models of ice history but depending on deformation patterns the identified earth model may be slightly biased in up to 39 of cases we compare our results to different one and three dimensional gia models employing different global ice load histories the gia models generally provide good fit to the data but there are still significant discrepancies in some areas we suggest that these differences are mainly related to inaccuracies in the ice models and or lateral inhomogeneities in the earth structure under fennoscandia thus gia models still need to be improved but the gia frame approach provides a base for further improvements

last glacial jetting of cold waters through the subtropical convergence zone in the southwest pacific off eastern new zealand and some geological implications recent evidence suggests that the subtropical convergence stc zone east of new zealand shifted little from its modern position along chatham rise during the last glaciation and that offshore surface waters north of the stc zone cooled only slightly however at nearshore core site p69 2195 m depth 115 km off the east coast of north island and ca 300 km north of the modern stc zone planktonic foraminiferal species transfer function data and stable oxygen and carbon isotope records suggest that surface waters were colder by up to 6 c during the late last glacial period compared to the holocene and included a strong upwelling signature presently site p69 is bathed by south flowing subtropical waters in the east cape current the nearshore western end of chatham rise supports a major bathymetric depression the mernoo saddle through which some exchange between northern subtropical and southern subantarctic water presently occurs it is proposed that as a result of much intensified current flows south of the rise during the last glaciation a consequence of more compressed subantarctic water masses lowered sea level and an expanded and stronger westerly wind system there was accelerated leakage northwards of both australasian subantarctic water and upwelled antarctic intermediate water over mernoo saddle in a modified and intensified southland current the expanded cold water masses displaced the south flowing warm east cape current off southeastern north island and offshore divergence was accompanied by wind assisted upwelling of nutrient rich waters in the vicinity of p69 a comparable kind of inshore cold water jetting possibly characterised most glacial periods since the latest miocene and may account for the occasional occurrence of subantarctic marine fossils in onland late cenozoic deposits north of the stc zone rather than invoking wholesale major oscillations of the oceanic stc itself

geochemistry and fluxes of hydrocarbons to the beaufort sea shelf a multivariate comparison of fluvial inputs and coastal erosion of peat using principal components analysis abstract the allochthonous inputs of hydrocarbon to the canadian beaufort shelf were studied by applying principal components analysis pca to well validated and rigorously blank corrected samples incorporation of a wide range of perdeuterated n alkanes and pah into the analysis scheme ensured that only reliably quantified variables were used to interpret the hydrocarbon geochemistry application of pca to mackenzie river samples demonstrated a homogeneous system from which we infer coupling or equilibrium between the river particulate hydrocarbons and the dissolved fraction particulate particle size 0 7 m hydrocarbon flux from the mackenzie river is by far the most important terrestrially derived source of hydrocarbons to the beaufort sea the mackenzie river particulates have a distinct n alkane signature which can be used to identify the riverine influence on the hydrocarbon geochemistry of the beaufort sea shelf based on one year s data the flux of total alkanes is 440 94 tonne a and pah is 49 8 tonne a uncertainties are one standard deviation of the sampling and analytical variation the particulate flux exceeds the accompanying dissolved hydrocarbon flux by two orders of magnitude and has a strong seasonal cycle winter contributes less than an estimated 0 6 of total annual flux deltaic silt from the western mackenzie delta and the smaller amounts of detritus from coastal erosion of peat are minor hydrocarbon sources and contribute in total less than 10 to the budget for most alkanes an important exception with regard to shelf geochemistry is the significant quantity of peat derived higher plant n alkanes

the last glacial maximum and deglaciation in southern south america abstract this paper models the extent of the patagonian icesheet during the last glacial maximum lgm and its subsequent deglaciation it constrains a new coupled icesheet climate numerical model with empirical evidence and simulates the icesheet at the lgm and at stages of deglaciation under lgm conditions an icesheet with a modelled volume slightly in excess of 500 000 km3 builds up along the andes there is a marked contrast between the maritime and continental flanks of the modelled icesheet with positive mass balance exceeding 2 m in the west and declining tenfold to the east modelled ice velocities commonly reach 400 m yr 1 in the western fjords the model is most sensitive to variations in temperature and good agreement between modelled ice extent and empirical evidence was achieved by applying a temperature decrease of 6 c relative to present day temperatures with constant wind fields over the model domain assuming a stepped start to deglaciation modelled ice volumes declined sharply contributing 1 2 m to global sea level 80 of it within 2000 years the empirical record suggests that such a stepped warming occurred around 17 500 17 150 cal yr ago

correlated errors in geodetic time series implications for time dependent deformation analysis of frequent trilateration observations from the two color electronic distance measuring networks in california demonstrate that the noise power spectra are dominated by white noise at higher frequencies and power law behavior at lower frequencies in contrast earth scientists typically have assumed that only white noise is present in a geodetic time series since a combination of infrequent measurements and low precision usually preclude identifying the time correlated signature in such data after removing a linear trend from the two color data it becomes evident that there are primarily two recognizable types of time correlated noise present in the residuals the first type is a seasonal variation in displacement which is probably a result of measuring to shallow surface monuments installed in clayey soil which responds to seasonally occurring rainfall this noise is significant only for a small fraction of the sites analyzed the second type of correlated noise becomes evident only after spectral analysis of line length changes and shows a functional relation at long periods between power and frequency of 1 where is frequency and 2 with 2 this type of correlated noise is termed random walk noise and its source is mainly thought to be small random motions of geodetic monuments with respect to the earth s crust though other sources are possible because the line length changes in the two color networks are measured at irregular intervals power spectral techniques cannot reliably estimate the level of 1 noise rather we also use here a maximum likelihood estimation technique which assumes that there are only two sources of noise in the residual time series white noise and random walk noise and estimates the amount of each from this analysis we find that the random walk noise level averages about 1 3 mm yr and that our estimates of the white noise component confirm theoretical limitations of the measurement technique in addition the seasonal noise can be as large as 3 mm in amplitude but typically is less than 0 5 mm because of the presence of random walk noise in these time series modeling and interpretation of the geodetic data must account for this source of error by way of example we show that estimating the time varying strain tensor a form of spatial averaging from geodetic data having both random walk and white noise error components results in seemingly significant variations in the rate of strain accumulation spatial averaging does reduce the size of both noise components but not their relative influence on the resulting strain accumulation model

southern ocean sea ice extent productivity and iron flux over the past eight glacial cycles sea ice and dust flux increased greatly in the southern ocean during the last glacial period palaeorecords provide contradictory evidence about marine productivity in this region but beyond one glacial cycle data were sparse here we present continuous chemical proxy data spanning the last eight glacial cycles 740 000 years from the dome c antarctic ice core these data constrain winter sea ice extent in the indian ocean southern ocean biogenic productivity and patagonian climatic conditions we found that maximum sea ice extent is closely tied to antarctic temperature on multi millennial timescales but less so on shorter timescales biological dimethylsulphide emissions south of the polar front seem to have changed little with climate suggesting that sulphur compounds were not active in climate regulation we observe large glacial interglacial contrasts in iron deposition which we infer reflects strongly changing patagonian conditions during glacial terminations changes in patagonia apparently preceded sea ice reduction indicating that multiple mechanisms may be responsible for different phases of co2 increase during glacial terminations we observe no changes in internal climatic feedbacks that could have caused the change in amplitude of antarctic temperature variations observed 440 000 years ago

last glacial maximum and holocene climate in ccsm3 abstract the climate sensitivity of the community climate system model version 3 ccsm3 is studied for two past climate forcings the last glacial maximum lgm and the mid holocene the lgm approximately 21 000 yr ago is a glacial period with large changes in the greenhouse gases sea level and ice sheets the mid holocene approximately 6000 yr ago occurred during the current interglacial with primary changes in the seasonal solar irradiance the lgm ccsm3 simulation has a global cooling of 4 5 c compared to preindustrial pi conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at lgm tropical sea surface temperature sst cools by 1 7 c and tropical land temperature cools by 2 6 c on average simulations with the ccsm3 slab ocean model suggest that about half of the global cooling is explained by the reduced lgm concentration of atmospheric co2 50 of present day concentrations there is an increase in the antarctic circumpolar current an

on the position of southern hemisphere westerlies at the last glacial maximum an outline of agcm simulation results and evaluation of their implications abstract the paper evaluates the claim of a poleward displacement of the southern hemisphere mid latitude westerly circulation at the last glacial maximum lgm the claim was initially based on the interpretation of the late quaternary paleoenvironmental records of southern south america and drew on conceptual paleo circulation reconstructions and the results of early agcm simulations a guide to likely lgm changes in the position of the southern hemisphere westerlies can in principle be obtained through a modelling of associated storm tracks a detailed analysis of the position of the southern hemisphere storm tracks at the lgm was undertaken using the ugamp gcm the results of the experiment suggest that a general poleward displacement of the zonal maximum of the southern hemisphere westerlies occurred at the lgm but this is a generalization and in detail the changes in the westerly circulation are more far ranging with significant regional differences

a transient subduction zone slip episode in southwest japan observed by the nationwide gps array 1 we investigate the spatiotemporal variation of fault slip on the subduction interface in southwest japan following the two 1996 hyuganada earthquakes m 6 7 using continuous gps observations a silent thrust slip event has been reported by hirose et al 1999 following these earthquakes approximately 100 km to the north beneath the bungo channel we employ the network inversion filter to rigorously invert for the fault slip distribution in space and time the gps time series is modeled as a sum of 1 secular deformation 2 coseismic station displacements 3 transient fault slip 4 random benchmark motion 5 reference frame shifts and 6 observational errors nonnegativity constraints effectively prohibit normal faulting on the subduction interface spatial and temporal smoothing parameters are estimated by the extended kalman filter the estimated fault slip rate images postseismic slip following the two hyuganada earthquakes slip associated with the silent thrust event began roughly 1 month after the second earthquake but initiated 100 km to the northeast of the hyuganada earthquakes the slow event propagated southwest and downdip beneath the bungo channel lasting approximately 1 year with maximum slip rates of 0 6 m yr the equivalent seismic moment was mw 7 2 we can rule out the possibility that slip propagated from the source region of the hyuganada earthquakes to the location of the silent earthquake however the timing of the events suggests a causal connection perhaps due to static stress transfer this kind of transient event or silent earthquake may reflect different fault zone characteristics and may be responsible for accommodating strain that would otherwise be released in large earthquakes

southern hemisphere westerly wind changes during the last glacial maximum model data comparison the southern hemisphere sh westerly winds are thought to be critical to global ocean circulation productivity and carbon storage for example an equatorward shift in the winds though its affect on the southern ocean circulation has been suggested as the leading cause for the reduction in atmospheric co2 during the last glacial period despite the importance of the winds it is currently not clear from observations or model results how they behave during the last glacial here an atmospheric modelling study is performed to help determine likely changes in the sh westerly winds during the last glacial maximum lgm using lgm boundary conditions the maximum in sh westerlies is strengthened by 1 m s 1 and moved southward by 2 at the 850 hpa pressure level boundary layer stabilisation effects over equatorward extended lgm sea ice can lead to a small apparent equatorward shift in the wind band at the surface further sensitivity analysis with individual boundary condition changes indicate that changes in sea surface temperatures are the strongest factor behind the wind change the hadam3 atmospheric simulations along with published pmip2 coupled climate model simulations are then assessed against the newly synthesised database of moisture observations for the lgm although the moisture data is the most commonly cited evidence in support of a large equatorward shift in the sh winds during the lgm none of the models that produce realistic lgm precipitation changes show such a large equatorward shift in fact the model which best simulates the moisture proxy data is the hadam3 lgm simulation which shows a small poleward wind shift while we cannot prove here that a large equatorward shift would not be able to reproduce the moisture data as well we show that the moisture proxies do not provide an observational evidence base for it

chilean and southeast pacific paleoclimate variations during the last glacial cycle directly correlated pollen and δ18o records from odp site 1234 abstract joint pollen and oxygen isotope data from ocean drilling program site 1234 in the southeast pacific provide the first continuous record of temperate south american vegetation and climate from the last 140 ka located at 36 s 65 km offshore of concepcion chile site 1234 monitors the climatic transition zone between northern semi arid summer dry winter wet climate and southern year round rainy cool temperate climate dominance of onshore winds suggests that pollen preserved here reflects transport to the ocean via rivers that drain the region and integrate conditions from the coastal mountains to the andean foothills down hole changes in diagnostic pollen assemblages from xeric lowland deciduous forest characterized by grasses herbs ferns and trees such as deciduous beech nothofagus obliqua mesic valdivian evergreen forest including conifers such as the endangered prumnopitys andina and subantarctic evergreen rainforest comprised primarily of southern beech n dombeyi reveal large rapid shifts that likely reflect latitudinal movements in atmospheric circulation and storm tracks associated with the southern westerly winds during glacial intervals mis 2 4 and 6 rainforests and parkland dominated by nothofagus moved northward into the region at the mis 6 5e transition coeval with the rapid shift to lower isotopic values rainforest vegetation was rapidly replaced by xeric plant communities associated with mediterranean type climate an increased prominence of halophytic vegetation suggests that mis 5e was more arid and possibly warmer than mis 1 although rainforest pollen rises again at the end of mis 5e lowland deciduous forest pollen persists through mis 5d and 5c into mis 5b substantial millennial scale variations occur in both interglacial and glacial regimes attesting to the sensitivity of the southern westerly belt to climate change comparison of the cool mesic n dombeyi rainforest assemblage from site 1234 with 18 o in the byrd ice core shows that on time scales longer than 10 ka cool moist conditions in central chile were coherent with and occurred in phase with antarctic cooling this is also likely at millennial scales although rainforest pollen lags antarctic cooling with exponential response times of about 1000 years which plausibly reflects the ecological response time to regional climate change

the de correlation of westerly winds and westerly wind stress over the southern ocean during the last glacial maximum motivated by indications from paleo evidence this paper investigates the changes of the southern westerly winds sww and westerly wind stress between the last glacial maximum lgm and pre industrial in the pmip3 cmip5 simulations highlighting the role of antarctic sea ice in modulating the wind effect on ocean particularly a de correlation occurs between the changes in sww and westerly wind stress caused primarily by an equatorward expansion of winter antarctic sea ice that undermines the efficacy of wind in generating stress over the liquid ocean such de correlation may reflect the lgm condition in reality in view of the fact that the model which simulates this condition has most fidelity in simulating modern sww and antarctic sea ice therein two models stand out for their agreements with paleo evidence regarding the change of sww and the westerly wind stress they simulate strengthened and poleward migrated lgm sww in the atmosphere consistent with the indications from dust records whilst in the ocean they well capture an equatorward shifted pattern of the observed oceanic front shift with most pronounced equatorward shifted westerly wind stress during the lgm

antarctic timing of surface water changes off chile and patagonian ice sheet response marine sediments from the chilean continental margin are used to infer millennial scale changes in southeast pacific surface ocean water properties and patagonian ice sheet extent since the last glacial period our data show a clear antarctic timing of sea surface temperature changes which appear systematically linked to meridional displacements in sea ice westerly winds and the circumpolar current system proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore but reveal a variable glacier response time of up to 1000 years which may explain some of the current discrepancies among terrestrial records in southern south america

a coupled climate model simulation of the last glacial maximum part 2 approach to equilibrium the climate of the last glacial maximum lgm is simulated with a coupled climate model the simulated climate undergoes a rapid adjustment during the first several decades after imposition of lgm boundary conditions as described in part 1 and then evolves toward equilibrium over 900 model years the climate simulated by the coupled model at this period is compared with observationally based lgm reconstructions and with lgm results obtained with an atmosphere mixed layer slab ocean version of the model in order to investigate the role of ocean dynamics in the lgm climate global mean surface air temperature and sea surface temperature sst decrease by about 10 c and 5 6 c in the coupled model which includes ocean dynamics compared to decreases of 6 3 and 3 8 c in slab ocean case the coupled model simulates a cooling of about 6 5 c over the tropics which is larger than that of the climap reconstruction 1 7 c and larger than that of the slab ocean simulation 3 3 c but which is in reasonable agreement with some recent proxy estimates the ocean dynamics of the coupled model captures features found in the climap reconstructions such as a relative maximum of ocean cooling over the tropical pacific associated with a mean la nina like response and lead to a more realistic sst pattern than in the slab model case the reduction in global mean precipitation simulated in the coupled model is larger 15 than that simulated with the slab ocean model 10 in conjunction with the enhanced cooling some regions such as the usa and the mediterranean region experience increased precipitation in accord with proxy paleoclimate evidence the overall much drier climate over the ocean leads to higher sea surface salinity sss in most ocean basins except for the north atlantic where sss is considerably lower due to an increase in the supply of fresh water from the mississippi and amazon rivers and presumably a decrease in salt transport by the weakened north atlantic overturning circulation the north atlantic overturning stream function weakens to less than half of the control run value the overturning is limited to a shallower depth less than 1000 m and its outflow is confined to the northern hemisphere in the southern ocean convection is much stronger than in the control run leading to a stronger overturning stream function associated with enhanced antarctic bottom water formation as a result southern ocean water masses fill the entire deep ocean the antarctic circumpolar current acc transport through the drake passage increases by about 25 the acc transport despite weaker zonal winds is enhanced due to changes in bottom pressure torque the weakening of the overturning circulation in the north atlantic and the accompanying 30 decrease in the poleward ocean heat transport contrasts with the strengthening of the overturning circulation in the southern ocean and a 40 increase in heat transport as a result sea ice coverage and thickness are affected in opposite senses in the two hemispheres the lgm climate simulated by the coupled model is in reasonable agreement with paleoclimate proxy evidence the dynamical response of the ocean in the coupled model plays an important role in determining the simulated and undoubtedly the actual lgm climate

change in atmospheric mineral aerosols in response to climate last glacial period preindustrial modern and doubled carbon dioxide climates desert dust simulations generated by the national center for atmospheric research s community climate system model for the current climate are shown to be consistent with present day satellite and deposition data the response of the dust cycle to last glacial maximum preindustrial modern and doubled carbon dioxide climates is analyzed only natural non land use related dust sources are included in this simulation similar to some previous studies dust production mainly responds to changes in the source areas from vegetation changes not from winds or soil moisture changes alone this model simulates a 92 33 and 60 change in dust loading for the last glacial maximum preindustrial and doubled carbon dioxide climate respectively when impacts of carbon dioxide fertilization on vegetation are included in the model terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions probably due to the lack of simulation of glaciogenic dust sources in order to include the glaciogenic dust sources as a first approximation we designate the location of these sources and infer the size of the sources using an inversion method that best matches the available data the inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2 1 to 3 3 times current deposition

particulate matter in pack ice of the beaufort gyre ice observations and sediment samples were collected in the beaufort gyre in 1988 fine sediment occurred in very small patches of turbid ice as thin spotty surface layers in mud pellets or in old snowdrifts the latter were widespread south of 74 n containing an estimated 22 tonnes of silt and clay km 2 average particle concentration in sea ice 40 mg l 1 was much higher than in sea water 0 8 mg l 1 or in new snow but the sediment load was significantly smaller and of finer texture compared to that observed in a shelfal source area after a major entrainment event

a simulation of the last glacial maximum climate using the ncar ccsm the national center for atmospheric research community climate system model ncar ccsm is used in a coupled atmosphere ocean sea ice simulation of the last glacial maximum lgm around 21 000 years ago climate in the tropics the simulation shows a moderate cooling of 3 c over land and 2 c in the ocean in zonal average this cooling is about 1 c cooler than the climap sea surface temperatures ssts but consistent with recent estimates of both land and sea surface temperature changes subtropical waters are cooled by 2 2 5 c also in agreement with recent estimates the simulated oceanic thermohaline circulation at the lgm is not only shallower but also weaker than the modern with a migration of deep water formation site in the north atlantic as suggested by the paleoceanographic evidences the simulated northward flow of antarctic bottom water aabw is enhanced these deep circulation changes are attributable to the increased surface density flux in the southern ocean caused by sea ice expansion at the lgm both the gulf stream and the kuroshio are intensified due to the overall increase of wind stress over the subtropical oceans the intensified zonal wind stress and southward shift of its maximum in the southern ocean effectively enhances the transport of the antarctic circumpolar current acc by more than 50 simulated ssts are lowered by up to 8 c in the midlatitudes simulated conditions in the north atlantic are warmer and with less sea ice than indicated by climap again in agreement with more recent estimates the increased meridional sst gradient at the lgm results in an enhanced hadley circulation and increased midlatitude storm track precipitation the increased baroclinic storm activity also intensifies the meridional atmospheric heat transport a sensitivity experiment shows that about half of the simulated tropical cooling at the lgm originates from reduced atmospheric concentrations of greenhouse gases

dirtmap the geological record of dust atmospheric dust is an important feedback in the climate system potentially affecting the radiative balance and chemical composition of the atmosphere and providing nutrients to terrestrial and marine ecosystems yet the potential impact of dust on the climate system both in the anthropogenically disturbed future and the naturally varying past remains to be quantified the geologic record of dust provides the opportunity to test earth system models designed to simulate dust records of dust can be obtained from ice cores marine sediments and terrestrial loess deposits although rarely unequivocal these records document a variety of processes source transport and deposition in the dust cycle stored in each archive as changes in clay mineralogy isotopes grain size and concentration of terrigenous materials although the extraction of information from each type of archive is slightly different the basic controls on these dust indicators are the same changes in the dust flux and particle size might be controlled by a combination of a source area extent b dust emission efficiency wind speed and atmospheric transport c atmospheric residence time of dust and or d relative contributions of dry settling and rainout of dust similarly changes in mineralogy reflect a source area mineralogy and weathering and b shifts in atmospheric transport the combination of these geological data with process based forward modelling schemes in global earth system models provides an excellent means of achieving a comprehensive picture of the global pattern of dust accumulation rates their controlling mechanisms and how those mechanisms may vary regionally the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap data base has been established to provide a global palaeoenvironmental data set that can be used to validate earth system model simulations of the dust cycle over the past 150 000 years

southern hemisphere westerly wind changes during the last glacial maximum paleo data synthesis changes in the strength and position of southern hemisphere westerly winds during the last glacial cycle have been invoked to explain both millennial and glacial interglacial climate fluctuations however neither paleo models nor paleodata agree on the magnitude or even the sign of the change in wind strength and latitude during the most studied glacial period the last glacial maximum lgm compared to the recent past this paper synthesizes paleo environmental data that have been used to infer changes in lgm winds data compilations are provided for changes in terrestrial moisture dust deposition sea surface temperatures and ocean fronts and ocean productivity and existing data on southern hemisphere ocean circulation changes during the lgm are summarized we find that any hypothesis of lgm wind and climate change needs to provide a plausible explanation for increased moisture on the west coast of continents cooler temperatures and higher productivity in the subantarctic zone and reductions in agulhas leakage around southern africa our comparison suggests that an overall strengthening an equatorward displacement or no change at all in winds could all be interpreted as consistent with observations if a single cause related to the southern westerlies is sought for all the evidence presented then an equatorward displacement or strengthening of the winds would be consistent with the largest proportion of the observations however other processes such as weakening or poleward shifts in winds a weakened hydrological cycle extended sea ice cover and changed buoyancy fluxes cannot be ruled out as potential explanations of observed changes in moisture surface temperature and productivity we contend that resolving the position and strength of westerly winds during the lgm remains elusive based on data reconstructions alone however we believe that these data reconstructions of environmental conditions can be used in conjunction with model simulations to identify which processes best represent westerly wind conditions during the lgm

southern california permanent gps geodetic array error analysis of daily position estimates and site velocities we analyze time series of daily positions estimated from data collected by 10 continuously monitoring global positioning system gps sites in southern california during the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes each time series exhibits a linear tectonic signal and significant colored noise spectral power at frequencies in the range 5 yr 1 to 0 5 d 1 is dominated by white noise or possibly fractal white noise and is several orders of magnitude higher than what would be expected from random walk noise in this short period range attributed by others to geodetic monument motions estimating a single slope for the time series power spectra suggests fractal white noise processes with spectral indices of about 0 4 site velocity uncertainties assuming this fractal white noise model are 2 4 times larger than uncertainties obtained assuming a purely white noise model a combination white noise plus flicker noise spectral index of 1 model also fits the data and suggests that the velocity uncertainties should be 3 6 times larger than for the white noise model we cannot adequately distinguish between these two noise models nor can we rule out the possibility of a random walk signal at the lowest frequencies these questions await the analysis of longer time series in any case reducing the magnitude of low frequency colored noise is critical and appears to be best accomplished by building sites with deeply anchored and braced monuments otherwise rate uncertainties estimated from continuous gps measurements may not be improved significantly compared to those estimated from infrequent campaign mode measurements

morphology of the canadian beaufort sea coast a study of the canadian beaufort sea coast alaskan yukon border to baillie island was conducted to provide a regional summary of a coastal morphology b coastal stability and c coastal processes a total of 2077 km of coastline was mapped using aerial photographs low altitude and oblique aerial video imagery and information from previous field studies the coast can be adequately characterized by six repetitive coastal types four of which are erosional landforms and comprise 60 of the coast ice rich cliffs ice poor cliffs low tundra cliffs and inundated tundra two repetitive coastal types are accretional landforms and comprise 40 of the coast barrier islands and spits and deltas the deltas in the study area are retreating rapidly and therefore over 80 of the coast is considered erosional and less than 20 accretional over 1000 measurements of coastal stability indicate wide scale coastal retreat most sections of the coast show mean coastal retreat rates in excess of 1 m yr 1 despite very low annual wave exposure levels near active areas of the mackenzie river delta mean retreat rates are in excess of 2 m yr 1 and a maximum retreat rate of 18 m yr 1 was documented near shallow bay the presence of significant quantities of ice in the coastal sediments both in the form of pore ice and massive ice beds appears to be the primary cause of the wide scale regional retreat of the coast although a relative sea level rise in the region may also be important

instantaneous global plate motion model from 12 years of continuous gps observations 1 we estimate a global plate motion model for 17 major and minor tectonic plates solely on the basis of analysis of data from 106 globally distributed continuous gps stations spanning the period from january 1991 to july 2003 site positions estimated from 24 hour segments of data are aligned day by day to the international gps service igs realization of the itrf2000 reference frame using a similarity transformation thereby ensuring that the itrf2000 no net rotation condition is preserved linear velocities of a carefully selected set of stations are estimated from the position time series along with annual and semiannual fluctuations and position offsets due to gps instrument changes a white noise plus flicker noise model is applied to estimate realistic uncertainties for the site velocities which are then propagated into the derived plate motion model parameters we also examine the vertical velocities in the site selection process at the scripps orbit and permanent array center we have implemented a procedure whereby the plate motion model is updated on a regular monthly basis to improve its precision and reliability as new data become available and as a baseline against which anomalous motions can be detected

apparent stability of gps monumentation from short baseline time series 1 long running short 1 km gps baselines offer an insight into the accuracy budget of geophysical estimates inferred from gps coordinate time series in this paper we report on analysis of 10 short baselines using data spanning several years and examine deviations from a constant baseline length annual signals with amplitude 0 5 mm are evident in various coordinate components at 6 of the 10 sites with amplitudes exceeding 2 5 mm on two baselines these signals are largely invariant to elevation cutoff angle multipath and phase center model errors are shown to probably have negligible effects at most sites at annual periods they are therefore likely real monument motions although linear thermal expansion is negligible at most sites linear trends 0 25 mm yr 1 are evident on four baselines in at least one coordinate component subdaily signals are present at all sites at k1 and its higher harmonics time correlated noise possibly in the form of flicker noise dominates despite many common signals being eliminated as a result of the small baseline lengths although it is around 1 order of magnitude smaller than for single site ppp solutions we constrain monument random walk motion to be no more than 0 5 mm yr 1 2 if these baseline motion results were representative of the 300 currently active igs sites 180 would have annual signals 0 5 mm in at least one coordinate component 120 would have linear rates 0 25 mm yr 1 and almost all sites would have subdaily k1 k2 signals of 0 1 mm each solely due to local site effects

precursory transient slip during the 2001 mw 8 4 peru earthquake sequence from continuous gps 1 two hour position estimates from a continuous gps station located at arequipa peru document precursory deformation beginning 18 hours prior to an mw 7 6 aftershock of the june 23rd 2001 mw 8 4 earthquake this preseismic signal appears on the north and east components as a slow displacement with an amplitude twice that of the subsequent coseismic analysis of three years of 18 hour rate measurement shows this signal to be unprecedented and beyond four standard deviations from the mean rate the best fitting centroid is directionally consistent with slow slip along the plate interface and suggests the preseismic deformation arises from creep near the aftershock rupture this implies the nazca south american plate interface slipped slowly prior to seismogenic faulting these observations indicate the mw 7 6 earthquake grew out of slow slip along the plate interface and clearly demonstrate the breadth of slip rates accommodated by subduction zone plate interfaces

sensitivity of southern hemisphere westerly wind to boundary conditions for the last glacial maximum abstract the southern hemisphere sh westerly wind change in the lgm is critical in understanding the glacial interglacial carbon cycle since its strength and position influence the upwelling of the carbon rich deep water to the surface to examine the change in sh westerly wind in the lgm we adopted cam5 atmosphere general circulation model gcm and performed lgm simulation with sensitivity experiments by specifying the lgm sea ice in the southern ocean so ice sheet over antarctica and tropical pacific sea surface temperature the sh westerly response to lgm boundary conditions in the cam5 was compared with those from cmip5 lgm simulations in the cam5 lgm simulation the sh westerly wind substantially increases between 40 s and 65 s while the zonal mean zonal wind decreases at latitudes higher than 65 s the position of the sh maximum westerly wind moves poleward by about 8 in the lgm simulation sensitivity experiments suggest that the increase in sh westerly winds is mainly due to the increase in sea ice in the so that accounts for 60 of total wind change in the cmip5 pmip3 lgm experiments most of the models show the slight increase and poleward shift of the sh westerly wind as in the cam5 experiment the increased and poleward shifted westerly wind in the lgm obtained in the current model result is consistent with previous model results and some lines of proxy evidence though opposite model responses and proxy evidence exist for the sh westerly wind change

the glaciogenic origin of the pleistocene calcareous dust in argentina on the basis of field mineralogical textural and geochemical analyses calcareous dust occurs in argentina as layers and pockets closely associated with pleistocene deposits and periglacial features from southernmost patagonia to at least the mendoza precordillera and has been traditionally interpreted as a soil horizon resulting from postdepositional pedogenesis during interglacials detailed field and microscopic observations and sedimentological and geochemical analyses of more than 100 samples collected from lower to upper pleistocene deposits between 51 s and 33 s and from near sea level to 2800 m asl allow us to interpret the dust as synchronous with the host sediment all observations and analyses lead us to conclude that 1 the cryogenic morphology and the chemical signatures of the calcite component show that the dust is glaciogenic 2 the dust was carried by southeasterly antarctic winds and 3 it was deposited over most of southern and central argentina field observations geomorphic evidence and radiocarbon dates suggest that the dust was deposited during several pleistocene glacial episodes