holocene rainfall variability in southern chile a marine record of latitudinal shifts of the southern westerlies geochemical and clay mineral parameters of a high accumulation marine sediment core from the chilean continental slope 41 s provide a 7700 yr record of rainfall variability in southern chile related to the position of the southern westerlies we especially use the iron content measured with a time resolution of ca 10 yr on average of 14 caccelerator mass spectrometry dated marine sediments as a proxy for the relative input of iron poor coastal range and iron rich andean source rocks variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position based on these interpretations we find a pronounced rainfall variability on multicentennial to millennial time scales superimposed on generally more arid conditions during the middle holocene 7700 to 4000 cal yr b p compared to the late holocene 4000 to present this variability and thus changes in the position of the southern westerlies are first compared to regional terrestrial paleoclimate data sets from central and southern chile in order to derive possible wider implications and forcing mechanisms of the holocene latitudinal shifts of the southern westerlies we then compare our data to ice core records from both tropical south america and coastal antarctica these records show similar bands of variability centered at ca 900 and 1500 yr comparisons of band pass filters suggest a close connection of shifts of the southern westerlies to changes within the tropical climate system the correlation to climate conditions in coastal antarctica shows a more complicated picture with a phase shift at the beginning of the late holocene coinciding with the onset of the modern state of el nin o southern oscillation system the presented data provide further evidence that the well known millennial scale climate variability during the last glacial continued throughout the holocene fl 2001 elsevier science b v all rights reserved

peat bank growth holocene palaeoecology and climate history of south georgia sub antarctica based on a botanical macrofossil record botanical macrofassil analysis of a more than 9000 years old radiocarbon dated peat sequence of a moss peat bank from south georgia shows a clear evolution in the vegetation seven ecological phases could be distinguished and they can be interpreted in terms of climate development during the holocene until 2200 years ago warnstorfia fontinatiopsis was the dominant moss species pointing to a wet environment lower numbers of this species in association with the presence of drier species are assumed to indicate drier periods such as occurring between ca 6000 5200 and 4400 3400 cal yr br the most prominent and definitive vegetation change took place around 2200 cal yr bp a polytilchum chollsodontium moss peat bank was formed which is still growing there today the forcing mechanism for this vegetation change is thought to be a temperature decrease rather than a precipitation decrease this conclusion is mainly based on the fact that today moss peat banks have their optimal occurrence range in the maritime antarctic a region were the mean annual temperature is ca 4 degrees c lower than on south georgia the remarkable change in the moss bank vegetation at 2200 cal yr bp raises the question whether this moment was only a short climatic deterioration or a definitive change to a cooler and wetter climate after a holocene climatic optimum period c 2008 elsevier ltd all rights reserved

on the response of the ocean to a moving storm the nonlinear dynamics abstract a novel and efficient numerical method is used to investigate the nonlinear equations of motion for the upper layer of a two layer ocean in which the lower layer is infinitely deep and at rest the efficiency is achieved by seeking solutions that are in a steady state translating in equilibrium with the storm oscillations are found in the wake of the storm two features of the response are attributed to the nonlinear terms in the equation of motion 1 a rapid transition from a maximum in the downwelling phase to a maximum in the upwelling phase of each oscillation followed by a gradual relaxation to the next downwelling maximum and 2 a displacement of the maximum response usually to the right of the storm track by 40 km it is shown that the horizontal pressure gradient terms can be neglected from the momentum equations for fast large storms in which case a lagrangian integration can be performed following fluid particles this enables feature 1 to be attributed to the along tra

holocene glacial and climate history of prince gustav channel northeastern antarctic peninsula the antarctic peninsula is one of the most rapidly warming regions on earth as evidenced by a recent increase in the intensity and duration of summer melting the recession of glaciers and the retreat and collapse of ice shelves despite this only a limited number of well dated near shore marine and lake sediment based palaeoenvironmental records exist from this region so our understanding of the longer term context of this rapid climate change is limited here we provide new well dated constraints on the deglaciation history and changes in sea ice and climate based on analyses of sedimentological proxies diatoms and fossil pigments in a sediment core collected from an isolation basin on beak island in prince gustav channel ne antarctic peninsula 63 36 s 57 20 w twenty two radiocarbon dates provided a chronology for the core including a minimum modelled age for deglaciation of 10 602 cal yr bp following the onset of marine sedimentation conditions remained cold and perennial sea ice persisted in this part of prince gustav channel until c 9372 cal yr bp this was followed by a seasonally open marine environment until at least 6988 cal yr bp corresponding with the early retreat and disintegration of the ice shelf in southern prince gustav channel following isolation of the basin from 6988 cal yr bp a relatively cold climate persisted until 3169 cal yr bp a mid late holocene climate optimum occurred between 3169 and 2120 cal yr bp inferred from multiple indicators of increased biological production this postdates the onset of the mid late holocene climate optimum in the south shetland islands 4380 cal yr bp and the south orkney islands 3800 cal yr bp suggesting that cooler climate systems of the weddell sea gyre to the east of the peninsula may have buffered the onset of warming climate deterioration is inferred from c 2120 cal yr bp until 543 cal yr bp this was followed by warming superimposed on this warming trend the instrumental record of recent warming at nearby hope bay is mirrored by a recent increase in the lake s primary production and a shift in the diatom communities in the uppermost 3 cm of sediments suggesting that this is amongst the first records to show an ecological response to recent rapid temperature increase these new constraints on glaciological and climate events in prince gustav channel are reviewed in the context of wider changes in the antarctic region

multiproxy summer and winter surface air temperature field reconstructions for southern south america covering the past centuries we statistically reconstruct austral summer winter surface air temperature fields back to ad 900 1706 using 22 20 annually resolved predictors from natural and human archives from southern south america ssa this represents the first regional scale climate field reconstruction for parts of the southern hemisphere at this high temporal resolution we apply three different recon struction techniques multivariate principal component regression composite plus scaling and regularized expectation maximization there is generally good

development of a regional glycerol dialkyl glycerol tetraether gdgt temperature calibration for antarctic and sub antarctic lakes a b s t r a c t a regional network of quantitative reconstructions of past climate variability is required to test climate models in recent studies temperature calibration models based on the relative abundances of sedimentary glycerol dialkyl glycerol tetraethers gdgts have enabled past temperature reconstructions in both marine and terrestrial environments nevertheless to date these methods have not been widely applied in high latitude environments due to poor performance of the gdgt temperature calibrations at lower temperatures to address this we studied 32 lakes from antarctica the sub antarctic islands and southern chile to 1 quantify their gdgt composition and investigate the environmental controls on gdgt composition and 2 develop a gdgt temperature calibration model for inferring past temperatures from antarctic and sub antarctic lakes gdgts were found in all 32 lakes studied and in 31 lakes branched gdgts brgdgts were the dominant compounds statistical analyses of brgdgt composition in relation to temperature ph conductivity and water depth showed that the composition of brgdgts is strongly correlated with mean summer air temperature msat this enabled the development of the first regional brgdgt temperature calibration for use in antarctic and sub antarctic lakes using four brgdgt compounds gdgt ib gdgt ii gdgt iii and gdgt iiib a key discovery was that gdgt iiib is of particular importance in cold lacustrine environments the addition of this compound significantly improved the model s performance from r2 0 67 rmsep loo leave one out 2 23 c rmsep h h block 2 37 c when applying the re calibrated global gdgt

estimates of late holocene soil production and erosion in the snowy mountains australia soil production in actively uplifting or high precipitation alpine landscapes is potentially rapid however these same landscapes are also susceptible to erosion and can be sensitive to changes in climate and anthropogenic activity which can upset the balance between soil production and erosion the snowy mountains southeastern australia are a tectonically stable low relief moderate precipitation mountain environment the alpine area is extensively blanketed by soil that has been subjected to more intensive episodes of erosion during past periods of anthropogenic disturbance and under cold climate conditions of the late quaternary in this study rates of soil development and hillslope erosion were investigated using radiocarbon dating fallout radionuclides and sediment cores collected from lakes and reservoirs estimated holocene soil development rates were 20 220 t km y erosion rates determined from the radionuclides cs and pb were equivocal due to the inherent spatial variability of radionuclide inventories relative to apparent erosion rates estimated average erosion rates over the past 100 years determined from pb inventories were 60 t km y 95 ci 10 90 inventories of cs observed at the same site implied that more recent erosion rates over the past 60 years was below the detection limits of the sampling method applied here i e 70 t km y the upper estimate of 90 t km y is comparable to the mean erosion rate estimated using the radionuclide method for uncultivated sites in australia and is significantly lower than that measured at sites were vegetation cover was disturbed by livestock grazing prior to its exclusion from the alpine area in the 1940s ce low erosion and high soil production rates relative to the lowland soils are likely related to extensive vegetation cover which in this context protects soils against erosion and contributes to the formation of organic alpine soils that rapidly accumulate organic matter by comparison to other soil types

millennial scale variability in southern hemisphere westerly wind activity over the last 5000 years in sw patagonia abstract here we report results from a high resolution palynological record and stratigraphic geochronologic data related to a neoglacial event in torres del paine national park southern chile 51 s 71 w to investigate climatic variations in southwest patagonia during the last 5000 years the record reveals a stepwise expansion of nothofagus dominated woodlands and forests with discrete pulses at 4400 2900 1300 and 570 cal yr bp superimposed upon this trend we identify a relative opening of the woodlands between 4100 2900 and 2300 1300 cal yr bp closed canopy forests dominated the landscape between 570 60 cal yr bp followed by a rapid decline at the end of the 19th century that coincided with intense fire activity and the appearance of rumex cf acetocella an exotic species introduced by european settlers we interpret these changes as variations in the intensity and or position of the southern margin of the westerly winds which culminated with a net eastward shift of the forest steppe ecotone during the little ice age we propose that millennial scale changes in either the latitudinal position and or the overall strength of the southern westerlies may be responsible for vegetation changes fire occurrence and the dynamic behavior of patagonian glaciers during the last 5000 years because the modern maximum in near surface wind velocities and precipitation is located between 48 and 50 s we suggest that the core of the southern westerlies may have achieved this modern position 570 years ago

is palynology a credible climate proxy in the subantarctic pollen and spore analysis is the most successfully used palaeobotanical discipline for reconstructing holocene vegetation and climate history throughout the world subantarctic islands are very specific areas they are located in the circum antarctic southern ocean in latitudes that are under strong influence of the southern westerly winds and are characterised by a treeless phanerogam poor flora palynological research on many of these islands has resulted in diverging conclusions about how to infer climate history from pollen data in this study we compare pollen data with macrofossil data on the one hand and the palaeoenvironmental history based on a multiproxy record on the other hand of two peat sequences from two different subantarctic islands south georgia and ile de la possession iles crozet we conclude that palynology must be used with caution as a proxy for climate change on these islands especially when no other proxy data are available the upland lowland principle as it has been applied in pollen studies in the south indian ocean islands results in erroneous conclusions about climate change on ile de la possession more palaeoclimatic multiproxy and pollen studies in combination with pollen vegetation relationship studies can however contribute to a more reliable model of how to interpret pollen data in the subantarctic we want to stress that our conclusions are only based on holocene records consequently the question remains if palynology can be used as a palaeoclimatic proxy when climatic changes were more pronounced such as during the last glacial interglacial transition

glacial geomorphology and chronology of deglaciation south georgia sub antarctic we mapped and dated the glacial geomorphology of north east south georgia in the maritime sub antarctic the aim was to examine the timing of deglaciation of the island in the context of inter hemispheric phasing of climate change former glacier limits are restricted to the inner fjords and our detailed mapping of them has demonstrated a consistent geomorphological pattern that is similar across several different glacier types and sizes the pattern comprises three suites of moraines categories a c not all of which are represented at every site because the outer suite is often overridden by younger suites category a is an outer wide low amplitude moraine ridge category b comprises 2 4 sharp crested bouldery moraines that are often located close to or even over riding a and category c is a series of lower amplitude moraines with overprinted streamlined landforms such as flutings analysis of in situ cosmogenic 10be in boulders on these moraines has allowed us to determine a deglacial chronology for the older two moraine groups the age of the inner youngest group has been estimated from soil development the cosmogenic nuclide ages show that the outermost moraine was deposited ca 12 2 1 5 ka bp but that a subsequent readvance in the mid holocene ca 3 6 1 1 ka bp reached and in places over rode this earlier moraine this latter advance coincides with the mid holocene hypsithermal a final late holocene advance reached closely similar limits to the previous two fluctuations and is estimated from soil data to have an age of ca 1 1 ka bp we suggest that the close concordance of late glacial and interglacial limits in this case associated with warming can be explained by a change in dominant forcing during glacials extensive sea ice limits precipitation availability and so glaciers are restricted to the inner fjords during interglacials precipitation is not limited in the same way by sea ice cover and so during warming precipitation increases and tidewater glaciers on the island have responded by advancing this study emphasises the importance of a clear understanding of geomorphology in order to interpret chronological information

holocene environmental change in south georgia evidence from lake sediments the holocene environmental history of south georgia is important because of the island s location in the southern westerlies in an oceanic zone of the world devoid of high resolution terrestrial records this is the first attempt to interpret a palaeoenvironmental record from lake sediments in south georgia it is based on a wide variety of analyses undertaken on cores from two lakes both are in the same unglaciated drainage basin but one is at 80 m above sea level and near the altitudinal limit for vegetation growth whereas the other is at 25 m and within the zone of continuous vegetation cover results from both lakes indicate shifts of vegetation boundaries which together with evidence for changing biotic productivity within the lakes themselves are interpreted as indicating climatic changes radiocarbon dates on the main changes identify a climatic optimum beginning before 5620 290 14c yr bp and ending at around 4815 330 14c yr bp when conditions in the upper part of the catchment were more conducive to plant growth than they are today the record obtained from the lower lake was shorter but indicates two periods of harsher climate relative to the present since 4000 yr bp this interpretation of the lake evidence agrees with other dated evidence of environmental change from peat sections glacial stratigraphy and geomorphology in south georgia together the work allows an overall reconstruction of environmental change in the holocene

late holocene palaeoclimatic records from lake sediments on james ross island antarctica sediment profiles from several lakes ponds in the northern ice free area of james ross island antarctica were the subject of a multi disciplinary palaeoenvironmental investigation the results obtained from lithological geomagnetic geochemical and diatom analyses and the frequency of branchinecta eggs were evaluated with multivariate statistics and provide a fairly detailed picture of climate change during the last 5000 years new radiocarbon dates are combined with previously published 14c dates so as to date the palaeoenvironmental and palaeohydrological changes identified by the stratigraphic studies in combination with the findings of glacial geological studies our data suggest that the brandy bay glacier began to recede rapidly just before 5000 yr b p due to calving and moisture starvation caused by cold and arid conditions in one of the ponds studied gypsum began to precipitate as a consequence of these conditions when the influence of glacial meltwater ceased this hypothesis was tested by hydrochemical modeling at approximately 4200 yr b p the climate became more humid and warmer and the pond supported a fairly diverse biota which included a variety of diatom species and for example branchinecta gaini a crustacean that feeds on benthic cyanobacterial mats the brandy bay glacier probably advanced during this humid period but the advance was interrupted by subsequent arid conditions which started at 3000 yr b p during this arid phase glaciers became completely absent from the study area as a result formerly large lakes fed by glacial meltwater transformed into small enclosed brackish water bodies that contained b gaini the arid and fairly cold conditions lasted for 1500 2000 years until approximately 1200 yr b p when the aquatic systems expanded and their salinity was lowered as a result of increased snow accumulation and glacial expansion the increased deposition of minerogenic matter caused by glacial erosion and meltwater inflow probably caused the disappearance of branchinecta on james ross island we regard this most recent phase as a period of increased humidity and warmth compared to the previous period although the conditions appear to be less warm and humid than those which prevailed during the climatic optimum between 4200 and 3000 yr b p in spite of certain correlation problems we tentatively correlate our results to other studies of holocene environments in antarctica and from that it can be suggested that the climatic optimum was of circumpolar significance therefore the climatic oscillations recorded in sediments on james ross island may reflect oscillations in the anticyclonic stormtracks and the strength of the high pressure cell over the inland ice sheet

middle tertiary extension recorded by lacustrine fan delta deposits plush ranch basin western transverse ranges california abstract the plush ranch formation upper oligocene and lower miocene consists of more than 1800 m of nonmarine sedimentary and volcanic rocks that record the history of an extensional basin referred to here as the plush ranch basin distinctive depositional facies provenance and sediment transport directions along each basin margin suggest an asymmetric basin shape that is consistent with a half graben origin the northern basin margin consists of sandstone dominated alluvial plain deposits 0 1 1 5 m thick normally graded lenticular sandstone beds small deltaic sequences 1 2 m thick were formed where these alluvial systems flowed southward into a lake lenses of massive boulder rich granitic breccia that represent rockslide deposits derived from a nearby northern granitic provenance nterfinger with the alluvial plain facies in contrast to the northern margin the southern basin margin is represented by coarse grained fan delta deposits matrix and clast supported lenticular conglomerate beds 0 2 5 m thick with interbedded trough cross bedded pebbly sandstone represent braided stream and flood flow and or noncohesive debris flow deposits of alluvial fans that drained a highland area to the south the alluvial fan deposits interfinger to the north with several types of subaqueous sediment gravity flow facies including turbidite sandstone beds and matrix supported debris flow conglomerate each of the basin margin depositional systems grades basinward and to the east into lacustrine deposits that include organic rich dark shale evaporite and limestone the lacustrine deposits represent the central and eastern parts of the plush ranch basin which received little coarse siliciclastic sediment basalt deposits that are at least 50 m thick in the west and thicken eastward are interbedded mainly with the lacustrine facies the southern margin of the plush ranch basin formed along a north dipping normal slip fault along which dip separation increased toward the southwest the northern margin developed on the tilted hanging wall block of this fault this fault was later reactivated in post middle miocene time as the present left lateral strike slip big pine fault the plush ranch is one of several extensional and transtensional basins that formed in southern california and western arizona about 25 20 ma as a response to the change from a convergent to a strikeslip tectonic regime along western north america

palaeoclimate southern westerlies and co2 the southern hemisphere westerly winds affect the exchange of carbon dioxide between the ocean and atmosphere climate reconstructions from the southern mid latitudes may reveal variability in the strength and position of the wind belt since the last glacial maximum

the three dimensional steady circulation in a homogenous ocean induced by a stationary hurricane based on the classical ekman layer theory a simple analytical solution of the steady flow induced by a stationary hurricane in a homogenous ocean is discussed the model consists of flow converging in an inward spiral in the deeper layer and diverging in the upper layer the simple analytical model indicates that both the upwelling flux and the horizontal transport increase linearly with increasing radius of maximum winds furthermore they both have a parabolic relationship with the maximum wind speed the coriolis parameter also affects the upwelling flux the response to a hurricane is stronger at low latitudes than that at middle latitudes numerical solutions based on a regional version of an ocean general circulation model are similar to the primary results obtained through the analytical solution thus the simplifications made in formulating the analytical solution are reasonable although the analytical solution in this paper is sought for a rather idealized ocean it can help to make results from the more complicated numerical model understandable these conceptual models provide a theoretical limit structure of the oceanic response to a moving hurricane over a stratified ocean

the medieval climate anomaly in antarctica abstract the medieval climate anomaly mca is a well recognized climate perturbation in many parts of the world with a core period of 1000 1200 ce here we are mapping the mca across the antarctic region based on the analysis of published palaeotemperature proxy data from 60 sites in addition to the conventionally used ice core data we are integrating temperature proxy records from marine and terrestrial sediment cores as well as radiocarbon ages of glacier moraines and elephant seal colonies a generally warm mca compared to the subsequent little ice age lia was found for the subantarctic islands south of the antarctic convergence the antarctic peninsula victoria land and central west antarctica a somewhat less clear mca warm signal was detected for the majority of east antarctica mca cooling occurred in the ross ice shelf region and probably in the weddell sea and on filchner ronne ice shelf spatial distribution of mca cooling and warming follows modern dipole patterns as reflected by areas of opposing temperature trends main drivers of the multi centennial scale climate variability appear to be the southern annular mode sam and el nino southern oscillation enso which are linked to solar activity changes by nonlinear dynamics

isotopic evidence for hydrologic change related to the westerlies in sw patagonia chile during the last millennium abstract the southern hemisphere westerly winds influence the spatial distribution of precipitation in southern south america and play a significant role in the global carbon cycle yet little is known about how this important atmospheric circulation feature has varied in the past here we present a sediment core record of late holocene variability from lago guanaco a small closed basin lake located in torres del paine national park chilean patagonia the park is located in the core of the modern wind field and variations in the intensity of the atmospheric circulation directly influence the hydrology of this region we combine stable isotopic measurements of biogenic carbonate and bulk organic matter to identify two periods of increased evaporation between 900 550 and 400 50 calendar years before present cal yr bp the first interval is coincident with the medieval climate anomaly mca while the more recent period is broadly coincident with the timing of the little ice age lia during the lia interval we observe simultaneous monotonic increases in the 18 o of biogenic carbonate and nothofagus dombeyi type pollen which we interpret as indicative of significant changes in the intensity of the southern westerlies during the last millennium the isotopic and palynological variations in the guanaco record are coincident with geochemical variations found in an antarctic ice core record from siple dome suggesting that the signal preserved in lago guanaco is regional rather than local and that the lia intensification was accompanied by a poleward shift in the southern margin of the westerlies in addition we interpret four periods of increased lake productivity centered on 900 650 500 and 200 cal yr bp from simultaneous increases in the 13 c of bulk organic material and biogenic carbonate these increases in lake productivity are most likely tied to increases in summer temperatures

millennial scale climate changes on south georgia southern ocean abstract the location of south georgia 54 s 36 w makes it a suitable site for the study of the climatic connections between temperate and polar environments in the southern hemisphere because the mass balance of the small cirque glaciers on south georgia primarily responds to changes in summer temperature they can provide records of changes in the south atlantic ocean and atmospheric circulation we use grey scale density weight loss on ignition and grain size analyses to show that the proportion of glacially eroded sediments to organic sediments in block lake was highly variable during the last 7400 cal yr b p we expect that the glacial signal is clearly detectable above noise originating from nonglacial processes and assume that an increase in glacigenic sediment deposition in block lake has followed holocene glacier advances we interpret proglacial lake sediment sequences in terms of summer climate warming and cooling events prominent millennial scale features include cooling events between 7200 and 7000 5200 and 4400 and 2400 and 1600 cal yr b p and after 1000 cal yr b p comparison with other terrestrial and marine records reveals that the south georgian record captures all the important changes in southern hemisphere holocene climate our results reveal a tentative coupling between climate changes in the south atlantic and north atlantic because the documented temperature changes on south georgia are anti phased to those in the north atlantic

palynological evidence for interglacial vegetation cover on marion island subantarctic abstract peats and organic rich sediments found intercalated with glacial deposits on subantarctic marion island yielded pollen spectra indicating vegetation and climatic conditions similar to present these deposits are considered to have formed under interglacial conditions a few palynomorph types of plants not recorded on the island were found in the samples these could have been introduced through long distance dispersal but one of them might belong to an extinct taxon zonation in the pollen profile suggests that during the interglacial phase the ocean shore was close to its present position and that it moved some distance away at the onset of the glacial stage

a 2 300 year long annually resolved record of the south american summer monsoon from the peruvian andes decadal and centennial mean state changes in south american summer monsoon sasm precipitation during the last 2 300 years are detailed using an annually resolved authigenic calcite record of precipitation 18o from a varved lake in the central peruvian andes this unique sediment record shows that 18o peaked during the medieval climate anomaly mca from a d 900 to 1100 providing evidence that the sasm weakened considerably during this period minimum 18o values occurred during the little ice age lia between a d 1400 and 1820 reflecting a prolonged intensification of the sasm that was regionally synchronous after the lia 18o increased rapidly particularly during the current warm period cwp a d 1900 to present indicating a return to reduced sasm precipitation that was more abrupt and sustained than the onset of the mca diminished sasm precipitation during the mca and cwp tracks reconstructed northern hemisphere and north atlantic warming and a northward displacement of the intertropical convergence zone itcz over the atlantic and likely the pacific intensified sasm precipitation during the lia follows reconstructed northern hemisphere and north atlantic cooling el nino like warming in the pacific and a southward displacement of the itcz over both oceans these results suggest that sasm mean state changes are sensitive to itcz variability as mediated by western hemisphere tropical sea surface temperatures particularly in the atlantic continued northern hemisphere and north atlantic warming may therefore help perpetuate the recent reductions in sasm precipitation that characterize the last 100 years which would negatively impact andean water resources

palaeolimnological evidence for marked holocene environmental changes on signy island antarctica lake sediment cores from heywood and sombre lakes on signy island south orkney islands antarctica have yielded a conformable radiocarbon chronology for the holocene and a high resolution record of environmental change the lakes share a common climate and geology but have distinct catchments this provides an opportunity for using lake sediments to differentiate between local within lake catchment events and those at a regional scale analyses of various biological and physical remains from the lakes suggest that both catchments have undergone considerable changes during the last 5700 years macrofossils moss and crustacean remains are more abundant in the late holocene being associated with a period of high sediment accumulation which is related to diatom evidence for more nutrient rich conditions at the sites this is inter preted as a response to a holocene climate optimum at c 3800 1300 14 c yr bp the record is consistent with other lake ice and ocean core studies although the climate optimum appears to have persisted for a longer period at signy island

17 000 years of vegetation fire and climate change in the eastern foothills of the andes lat 44 s abstract paleoenvironmental records from patagonia reveal the importance of latitude longitude and elevation in shaping the response of vegetation to climate change we examined the vegetation fire and watershed history from two sites at lat 44 s as inferred from pollen charcoal and lithologic data these reconstructions were compared with independent paleoenvironmental records to better understand ecosystem dynamics along the southeastern andes lat 41 50 s our results show that at lat 44 s late glacial heath steppe was colonized by trees at 14 200 cal yr bp and forests became more closed at 11 500 cal yr bp differences in forest cover between the two sites were likely due to elevation dependent disparities in humidity and fire north of lat 44 s increasing precipitation favored initial forest development at 16 500 cal yr bp while dry conditions restricted tree expansion in the south until 7000 cal yr bp the time transgressive pattern is attributed to a gradual southward shift in the southern westerlies resulting from deglaciation and increasing annual insoltion present day vegetation developed at all latitudes during the middle to late holocene when the core of the southern westerlies reached its modern position 50 s asynchronous forest expansions north and south of lat 45 s between 5000 and 3000 cal yr bp are ascribed to centennial cycles of contraction and expansion of the southern westerlies which led to seasonal variations in precipitation at the core and northern border of the wind belt synchronous oscillations in tree abundance along the eastern andes prevailed during the last 3000 years decreased forest cover at all latitudes between 2500 and 1500 cal yr bp is concurrent with la nina like conditions and high solar irradiance these climate drivers likely decreased effective moisture and favored fires at all latitudes

a study of tropical cyclone influence on the generation of internal tides 1 an investigation is made into modifications of the semidiurnal internal tide on the western australian shelf by a passing tropical cyclone current mooring observations are presented taken during the passage of tropical cyclone bobby 1995 over these mooring locations the observations reveal large vertical excursions at near inertial frequency of the isotherm during and following the cyclone s passage this coincides with diminishing semidiurnal baroclinic tides to gain dynamical insight into the observations a fully three dimensional free surface nonlinear hydrostatic model is applied to the western australian shelf the model is initialized with realistic stratification and forced by representative tides and cyclone winds the wind forcing is derived from an idealized analytical cyclone model prescribed from observed cyclone track and central pressure data and the tidal forcing allows for the generation of internal tides the cyclone modifies stratification by turbulent mixing upwelling downwelling and density advection up or down the shelf slope this results in significant changes to internal tide characteristic paths and hence the internal tide generation process on the continental slope mixing is enhanced over the shelf due to shallow topography with respect to the shelf slope region creating a strong density front at the shelf edge observations and modeling show that the water column response to the cyclone passage is most abrupt in shallow water at 125 m then at 300 m depth the model reproduces the main features of the observed inertial oscillations concomitant with the dampening of m2 internal tides after the passage of the cyclone

estimate of ocean mixed layer deepening after a typhoon passage over the south china sea by using satellite data abstractthe ocean responses to typhoon cimaron which influenced the south china sea scs from 1 to 8 november 2006 are analyzed based on satellite observed sea surface temperature sst and climatological temperature profiles in the scs mixed layer deepening an important parameter characterizing turbulent mixing and upwelling driven by strong typhoon winds is derived corresponding to the sst drop of 4 4 c on 3 november 2006 the mixed layer deepened by 104 5 m relative to the undisturbed depth of 43 2 m which is consistent with a simulation result from a mixed layer model furthermore baroclinic geostrophic velocity and vorticity are calculated from the surface temperature gradient caused by the typhoon the negative vorticity associated with the typhoon cooling indicated an anticyclonic baroclinic circulation strongest at the base of the mixed layer and at the depth of 50 m the geostrophic speed reached as high as 0 2 m s 1 typhoon cimaron proceeded slowly 1 7 m s 1 when it was making a s

late glacial and holocene glacier fluctuations and environmental change on south georgia southern ocean south georgia provides a terrestrial record of postglacial environmental change from a largely oceanic zone of the earth the record is representative of the southern westerlies and provides a link between antarctica and the temperate zones of southern south america evidence from glacial geomorphology slope stratigraphy and analyses of environmental indicators in peat and lake cores is used to interpret this record wastage of the full glacial ice cap was interrupted by a late glacial stade of the outlet and valley glaciers before ca 10 000 yr b p plant growth had begun at low altitude 50 m on the sheltered lee side northeast coast within the late glacial moraine limits by 9700 yr b p environmental conditions on slopes above 80 m probably were too rigorous for a stable vegetation cover until ca 6400 yr b p this was followed by a period from 5600 to 4800 yr b p when conditions were warmer than at present by up to 0 6 c periods of climatic cooling occurred at ca 4800 3800 yr b p ca 3400 1800 yr b p and within the last 1400 yr the most extensive holocene advance of south georgia glaciers culminated just before 2200 yr b p these holocene temperature changes of between 0 5 and 1 0 c are comparable in scale and timing to those identified from recent analyses of vostok ice cores from the antarctic ice sheet

mid late holocene monsoonal records from the partially active mudflat of diu island southern saurashtra gujarat western india abstract the mid late holocene period is seldom known for any drastic climatic perturbations but witnessed significant anthropogenic growth and thus has been a subject of scientific importance in this study sediment core raised from an active mudflat of diu island southern saurashtra coast gujarat with a climatic history for the last 4100 yr bp has been investigated based on geochemical proxies productivity weathering and detrital results indicate warm and humid conditions during holocene climate optimum hco between 4105 and 2640 cal yr bp as a result of monsoon intensification followed by an arid conditions between 2640 and 1930 cal yr bp later during 1930 355 cal yr bp the region regained warm and humid conditions the mudflat responded in accordance with the global climatic perturbations during last 2000 yr witnessing signatures of roman warm period and medieval warm period additionally cool and humid climatic conditions persisted during little ice age followed by modern warming period witnessed during last 300 yr

hurricane generated currents on the outer continental shelf 2 model sensitivity studies a numerical model described and verified in part 1 of this two part series cooper and thompson this issue is applied to study the sensitivity of hurricane generated currents on the outer shelf and slope numerical experiments are performed in a simple basin with a straight shelf the sensitivity of the response to changes in storm parameters direction of storm approach and topography is quantified response is measured in terms of the mixed layer velocity and depth at sites along the storm track results reveal the most important factors are in decreasing order wind speed storm translation speed direction of storm approach asymmetry in the wind field entrainment parameterization and advection at slower storm translation speeds response is largely insensitive less than 10 to radius of maximum wind shelf and slope configuration bottom friction atmospheric pressure gradients and further reductions in the model grid size for a storm approaching cross shelf the response is primarily baroclinic greater than 90 and only weakly dependent less than 10 on the water depth at the site

subantarctic peatlands and their potential as palaeoenvironmental and palaeoclimatic archives subantarctic islands are located within the antarctic circumpolar current and the southern westerly wind belt the latter called southern westerlies making them unique terrestrial archives to investigate past changes in oceanic and atmospheric circulation patterns in the southern mid latitudes the islands are characterised by a treeless phanerogam poor flora in which bryophytes are of major importance several peat based holocene palaeoenvironmental and palaeoclimatic studies have recently been published for south georgia and ile de la possession iles crozet a range of techniques have been used in these studies mainly plant macrofossil analysis but also analyses of diatoms pollen and non pollen microfossils geochemical and geomagnetic measurements the records are chronologically constrained by radiocarbon dating this paper brings together these data in order to give an overview of the subantarctic peat based palaeoclimatic records a new plant macrofossil record for the island of south georgia is added evidence for millennial scale holocene climate variability was found for both islands of which the most striking one occurred in the late holocene however within the uncertainty of the age depth models the timing for this climate shift to wetter and or colder conditions on south georgia and windier wetter conditions on ile de la possession is different for both islands ile de la possession iles crozet seems to follow the northern hemisphere climate evolution as the event was dated to w2800 cal bp a well known climate event present in many peat based records in north western europe in contrast the south georgian late holocene climate records reveal a shift around w2200e2000 cal bp

a geochemical and sedimentary record of high southern latitude holocene climate evolution from lago fagnano tierra del fuego abstract situated at the southern margin of the hemispheric westerly wind belt and immediately north of the antarctic polar frontal zone tierra del fuego is well positioned to monitor coupled changes in the ocean atmosphere system of the high southern latitudes here we describe a holocene paleoclimate record from sediment cores obtained from lago fagnano a large lake in southern tierra del fuego at 55 s to investigate past changes in climate related to these two important features of the global climate system we use an ams radiocarbon chronology for the last 8000 yr based on pollen concentrates thereby avoiding contamination from bedrock derived lignite our chronology is consistent with a tephrochronologic age date for deposits from the middle holocene volcan hudson eruption combining bulk organic isotopic 13 c and 15 n and elemental c and n parameters with physical sediment properties allows us to better understand sediment provenance and transport mechanisms and to interpret holocene climate and tectonic change during the last 8000 yr co variability and long term trends in c n ratio carbon accumulation rate and magnetic susceptibility reflect an overall holocene increase in the delivery of terrestrial organic and lithogenic material to the deep eastern basin we attribute this variability to westerly wind derived precipitation increased wind strength and precipitation in the late holocene drives the nothofagus forest eastward and enhances run off and terrigenous inputs to the lake superimposed on the long term trend are a series of abrupt 9 negative departures in c n ratio which constrain the presence of seismically driven mass flow events in the record we identify an increase in bulk 13 c between 7000 and 5000 cal yr bp that we attribute to enhanced aquatic productivity driven by warmer summer temperatures the lago fagnano 13 c record shows similarities with holocene records of sea surface temperature from the mid latitude chilean continental shelf and antarctic air temperatures from the taylor dome ice core record in east antarctica mid holocene warming occurred simultaneously across the antarctic frontal zone and in particular in locations currently influenced by the antarctic circumpolar current

holocene changes in the position and intensity of the southern westerly wind belt the position and intensity of the southern westerly wind belt varies seasonally as a consequence of changes in sea surface temperature during the austral winter the belt expands northward and the wind intensity in the core decreases conversely during the summer the belt contracts and the intensity within the core is strengthened reconstructions of the westerly winds since the last glacial maximum however have suggested that changes at a single site reflected shifts throughout the entire southern wind belt 1 4 here we use sedimentological and pollen records to reconstruct precipitation patterns over the past 12 500 yr from sites along the windward side of the andes precipitation at the sites located in the present core and northern margin of the westerlies is driven almost entirely by the wind belt 5 and can be used to reconstruct its intensity rather than varying coherently throughout the holocene epoch we find a distinct anti phasing of wind strength between the core and northern margin over multi millennial timescales during the early holocene the core westerlies were strong whereas the northern margin westerlies were weak we observe the opposite pattern in the late holocene as this variation resembles modern seasonal variability we suggest that our observed changes in westerly wind strength can best be explained by variations in sea surface temperature in the eastern south pacific ocean chile is ideally located to reconstruct past variability of the southern westerly wind belt sww as the sww almost entirely controls precipitation on the western side of the andes in southern south america with an extreme northsouth

reconstructing atmospheric circulation over southern new zealand establishment of modern westerly airflow 5500 years ago and implications for southern hemisphere holocene climate change abstract late twentieth century changes in the intensity and migration of southern hemisphere westerly winds have been implicated in spatially complex variability in atmospheric and ocean circulation and ice sheet dynamics across the mid to high latitudes a major uncertainty however is whether present day hemispheric wide symmetrical airflow is representative of past behaviour here we report a multi proxy study from stewart island and southern fiordland new zealand 46 47 s reconstructing holocene changes at the northern limit of westerly airflow increased minerogenic input and a pronounced shift in cool loving vegetation around 5500 years ago is consistent with the establishment of westerly airflow at this latitude in the southwest pacific in marked contrast stronger winds are reported further south over the subantarctic auckland 50 s and campbell 52 s islands from 8000 years ago intriguingly reconstructions from the east pacific suggest a weakening of core westerly airflow after 8500 years ago but an expansion along the northern limits sometime after 5500 years ago our results suggest similar atmospheric circulation changes have been experienced in the pacific since 5500 years ago but indicate an expanded network of sites is needed to comprehensively test the driver s and impact s of holocene mid latitude westerly winds across the southern hemisphere

inertial wave dynamics in the north atlantic subtropical zone doppler current profiler observations of an inertial wave packet are presented from a region where a cold core ring impinges on a front in this intense current a drogue is deployed to mark one region of the fluid as the drogue is advected by the current the ship follows it zigzagging across the drogue s trajectory along this ship track vertical rotary velocity spectra indicate the presence of a downgoing intertial wave with a vertical wavelength which slowly changes from 50 to 100 m as time progresses the wave s intrinsic frequency was measured for the first time ever a horizontally synoptic data set is obtained at the drogue depth by correcting for frontal advection and the temporal rotation of the wave velocity examination of these synoptic data indicates the presence of a southgoing near inertial wave with horizontal wavelength 20 km the wave is confined to a 25 km region supplementary ray tracing calculations through objective maps of the ring flow field indicate that the wave is strongly influenced by doppler shifting this is accompanied by a slow counterclockwise turning of the horizontal wave number vector a decrease in the intrinsic frequency and an increase in the vertical wavelength in qualitative agreement with the data a companion paper marmorino et al this issue details the effect of this inertial wave upon the small scale temperature activity with horizontal length scales of 1 3 m

satellite observations of sea surface cooling by hurricanes sea surface cooling associated with 13 hurricanes in the western north atlantic between september 1981 and december 1984 is examined using satellite derived sea surface temperature fields some surface cooling is observed in all cases however because of cloud cover and the fairly weak signal in some cases we see pronounced cooling along an extensive and continuous portion of the storm path for only three strong hurricanes the persistence of cooling following the passage of a hurricane varies from a few days to at least 16 days the amplitude of cooling is moderately well correlated with hurricane strength and is as large as 3 5 c when the hurricanes move rapidly the maximum cooling occurs well to the right of the track approximately 70 km whereas for slowly moving hurricanes the maximum cooling occurs near or on the track because western north atlantic hurricanes are often found in close proximity to high pressure systems daytime satellite images must be made with some care because of diurnal warming

holocene climate and glacial history of the northeastern antarctic peninsula the marine sedimentary record from a long shaldril core abstract a high resolution record of holocene deglacial and climate history was obtained from a 77 m sediment core from the firth of tay antarctic peninsula as part of the shaldril initiative this study provides a detailed sedimentological record of holocene paleoclimate and glacial advance and retreat from the eastern side of the peninsula a robust chronostratigraphy was derived from thirty three radiocarbon dates on carbonate material this chronostratigraphic framework was used to establish the timing of glacial and climate events derived from multiple proxies including magnetic susceptibility electric resistivity porosity ice rafted debris content organic carbon content nitrogen content biogenic silica content and diatom and foraminiferal assemblages the core bottomed out in a stiff diamicton interpreted as till gravelly and sandy mud above the till is interpreted as proximal glaciomarine sediment that represents decoupling of the glacier from the seafloor circa 9400 cal yr bp and its subsequent landward retreat this was approximately 5000 yr later than in the bransfield basin and south shetland islands on the western side of the peninsula the firth of tay core site remained in a proximal glaciomarine setting until 8300 cal yr bp at which time significant glacial retreat took place deposition of diatomaceous glaciomarine sediments after 8300 cal yr bp indicates that an ice shelf has not existed in the area since this time the onset of seasonally open marine conditions between 7800 and 6000 cal yr bp followed the deglacial period and is interpreted as the mid holocene climatic optimum open marine conditions lasted until present with a minor cooling having occurred between 6000 and 4500 cal yr bp and a period of minor glacial retreat and or decreased sea ice coverage between 4500 and 3500 cal yr bp finally climatic cooling and variable sea ice cover occurred from 3500 cal yr bp to near present and it is interpreted as being part of the neoglacial the onset of the neoglacial appears to have occurred earlier in the firth of tay than on the western side of the antarctic peninsula the medieval warm period and little ice age were not pronounced in the firth of tay the breadth and synchroneity of the rapid regional warming and glacial retreat observed in the antarctic peninsula during the last century appear to be unprecedented during the holocene epoch

holocene palaeoecology and climate history of south georgia sub antarctica based on a macrofossil record of bryophytes and seeds the results are presented of a detailed plant macrofossil analysis of a c 14 dated holocene organic sequence from a sub antarctic island south georgia in the peat infilling of a rock basin 31 bryophyte species and many of the principal species of the present day angiosperm flora associated with bog communities have been identified the zonation of the bryophytes and the seeds and fruits shows a striking correspondence with the sediment stratigraphy and indicates five ecological phases the first four reflect a succession from a minerotrophic shallow pool to an ombrotrophic warnstorfia polytrichum bog after the deposition of a greyish brown layer c 2200 c 14 years bp a wet deschampsia warnstofia sanionia rostkovia bog came into existence which is still present today the ecological phases are radiocarbon dated they can be interpreted in terms of climate development during the holocene climate ameliorated rapidly at about 10 000 c 14 years bp followed by a drier period around 7000 c 14 years bp the climate became wetter and the following c 2500 years probably represent the climatic optimum between 4500 and 2600 c 14 years bp drier conditions prevailed at the study site the most striking change occurred at 2600 c 14 years bp when a marked change in vegetation and ecology indicates much wetter conditions less

late glacial to middle holocene climatic record of lacustrine biogenic silica oxygen isotopes from a southern ocean island late glacial to middle holocene climatic record of lacustrine biogenic silica oxygen isotopes from a southern ocean island

vegetation and fire history during the last 18 000 cal yr b p in southern patagonia mallin pollux coyhaique province aisen 45 41 30 s 71 50 30 w 640 m elevation to better understand the climate vegetation and fire history of southern south america since the last deglaciation sediment characteristics diatoms pollen microscopic and macroscopic charcoal and magnetic susceptibility were analyzed in a 14 m long sediment core from a closed basin fen at lago pollux aisen province southern chile 45 41 30 s lat 71 50 30 w long 640 m elev sediment characteristics absence of diatoms and scarce pollen suggest that before 18 000 cal yr bp glacier meltwaters were feeding the small basin when local glaciers were at their maximum position from 18 000 to ca 14 000 cal yr bp the site was a shallow productive pond surrounded by a sparse scrub steppe and accompanied some fire activity this period was markedly drier but warmer than before by 14 000 cal yr bp the fen developed and a species rich steppe expanded suggesting a moderate increase in effective moisture and temperature high fluctuations of terrestrial and aquatic pollen taxa occur between 14 000 and 11 000 cal yr bp attesting to climate variability at this time between 11 000 and 7500 cal yr bp nothofagus steppe woodland developed and fire activity was very high with several large local events precipitation must have increased but most likely summers were drier than today with high frequency of convective storms after 7500 cal yr bp present day closed nothofagus forest became established and fire activity decreased suggesting establishment of present day equable precipitation regime the forest was more open between 4000 and 1500 cal yr bp than before and shrubs or trees grew on the fen forest clearance and grazing only began in the mid 20th century both in terms of timing and character of past changes in vegetation and fire activity the record from m pollux takes an intermediate position between records from high southern latitudes versus those from mid latitudes indicating the different latitudinal expression of the southern westerly storm tracks during the last 18 000 cal yr bp 2007 elsevier b v all rights reserved

holocene variability in climate and oceanic conditions in the winter rainfall zone of south africa inferred from a high resolution diatom record from verlorenvlei

late holocene climatic changes in tierra del fuego based on multiproxy analyses of peat deposits a ca 1400 yr record from a raised bog in isla grande tierra del fuego argentina registers climate fluctuations including a medieval warm period although evidence for the little ice age is less clear changes in temperature and or precipitation were inferred from plant macrofossils pollen fungal spores testate amebae and peat humification the chronology was established using a 14c wiggle matching technique that provides improved age control for at least part of the record compared to other sites these new data are presented and compared with other lines of evidence from the southern and northern hemispheres a period of low local water tables occurred in the bog between a d 960 1020 which may correspond to the medieval warm period date range of a d 950 1045 generated from northern hemisphere tree ring data a period of cooler and or wetter conditions was detected between ca a d 1030 and 1100 and a later period of cooler wetter conditions estimated at ca cal a d 1800 1930 which may correspond to a cooling episode inferred from law dome antarctica

surface front displacement in the gulf stream by hurricane tropical storm dennis using airborne radiation thermometer measurements and air dropped expendable bathythermographs the near surface thermal structure of a section of the gulf stream northeast of cape hatteras was monitored before and immediately after the passage of hurricane tropical storm dennis in august 1981 the passage of dennis increased the average horizontal separation between the surface and subsurface gulf stream fronts from about 1 to 19 km this increase in separation between the two fronts was apparently caused by wind driven cross stream advection in the mixed layer

changes in holocene climate and the intensity of southern hemisphere westerly winds based on a high resolution palynological record from sub antarctic south georgia sub antarctic south georgia is a key region for studying climate variability in the southern hemisphere because of its position at the core of the southern hemisphere westerly wind belt and between the antarctic circumpolar current and the polar frontal zone here we present a 5 8 m long high resolution pollen record from fan lake on annenkov island dominated by local sub polar vegetation with acaena and poaceae being present throughout the last 7000 years palynological and sedimentological analyses revealed a warm late holocene climate optimum between 3790 and 2750 cal yr bp which was followed by a gradual transition to cool and wet conditions this cooling was interrupted by slightly warmer environmental conditions between 1670 and 710 cal yr bp that partly overlap with the northern hemisphere medieval climate anomaly increases in non native and long distance pollen grains transported from south america e g nothofagus podocarpus indicate that stronger southern hemisphere westerly winds over south georgia possibly occurred during some colder phases of the late holocene most notably between c 2210 and 1670 cal yr bp and after 710 cal yr bp

upper ocean response to typhoon kalmaegi 2014 typhoon kalmaegi passed over an array of buoys and moorings in the northern south china sea in september 2014 leaving a rare set of observations on typhoon induced dynamical and thermohaline responses in the upper ocean the dynamical response was characterized by strong near inertial currents with opposite phases in the surface mixed layer and in the thermocline indicating the dominance of the response by the excitation of the first baroclinic mode the thermohaline response showed considerable changes in the mean fields in addition to a near inertial oscillation in particular temperature and salinity anomalies generally exhibited a three layer vertical structure with the surface layer becoming cooler and saltier the subsurface layer warmer and fresher and the lower layer cooler and saltier again the response in the surface and subsurface layers was much stronger to the right of the typhoon track while that in the lower layer was stronger along the track and to the left these features of the upper ocean response were grossly reproduced by a three dimensional numerical model a model based heat budget analysis suggests that vertical mixing was mainly responsible for the surface cooling and subsurface warming while upwelling was the cause of cooling from below both observations and model results indicate that the whole upper ocean experienced an overall cooling in the wake of typhoon kalmaegi

have the southern westerlies changed in a zonally symmetric manner over the last 14 000 years a hemisphere wide take on a controversial problem the prevailing view in the palaeoclimate literature of the last 20 years is that the southern westerly winds sww were intensified over southern australia and tasmania during the warmer than present early holocene 11e8 ka at similar latitudes on the opposite side of the southern mid latitudes palaeoclimate studies have suggested a poleward shift of the northern edge of the westerlies and focusing at 49 s in southern south america this zonal asymmetry contrasts with the modern day zonal symmetry displayed by the sww and poses a formidable challenge to an understanding of the modes of climatic variability of the southern extra tropics this paper presents an updated synthesis of continuous radiocarbon dated palaeoenvironmental data from the westerlies zone of influence in all southern hemisphere continents synchronous multi millennial trends in moisture vegetation fire and hydrologic balance are remarkably consistent with the way the sww changes impact upon the climate in southern hemisphere landmasses in the modern climate considering the modern relationships between local precipitation and zonal wind speeds it is suggested that the sww changed in a zonally symmetric manner at multi millennial scale between 14 and 5 ka regional asymmetry develops after 5 ka across the southern hemisphere with a pattern of precipitation anomalies akin to the modern functioning of el nino e southern oscillation which started w6200 years ago

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

late holocene glacier reconstruction reveals retreat behind present limits and two stage little ice age on subantarctic south georgia observational data show that climate in the southern ocean region is rapidly changing however past the instrumental period our understanding of climate variability in the region is limited by a scarcity of highresolution palaeoclimate records alpine glaciers present on many southern ocean islands may provide such data because changes in their mass balance extent and erosion rates often mark a response to climate shifts rock flour the fine grained fraction of the glacial erosion process is suspended in meltwater streams and transferred into the sediments of downstream lakes continuously recording glacier variations here we utilize this relationship to present a reconstruction of the late holocene glacier history of subantarctic south georgia using sediments from the glacier fed middle hamberg lake to fingerprint a glacial erosion size signal we used titanium counts validated against changes in sediment density and grain size allowing a continuous reconstruction of glacier variations over the past similar to 1250 years together with local moraine evidence and supporting evidence from other southern hemisphere glaciers on new zealand and in patagonia our findings reveal a series of consecutively diminishing late holocene advances in addition to a glacier maximum before 1250 cal a bp these include a twostage litle ice age with advances around 300 and 120 cal a bp in line with evidence from southern patagonia in addition we present evidence for an unreported retreat behind present limits around 500 cal bp

covariability of the southern westerlies and atmospheric co2 during the holocene a suite of mechanisms has been proposed to account for natural variations in atmospheric co 2 during the holocene all of which have achieved limited success in reproducing the timing direction and magnitude of change recent modeling studies propose that changes in the latitudinal position and strength of the southern hemisphere westerly winds sww can greatly influence large scale ocean circulation and degassing of the deep ocean via changes in wind driven upwelling in the southern ocean the extent to which the hypothesized sww southern ocean coupled system could account for changes in atmospheric co 2 is uncertain because of a lack of observations on the behavior of the sww in the past the paucity of appropriate records of productivity changes in the southern ocean and our limited understanding of the sensitivity of the southern ocean biological and or physical system to sww forcing here we report a reconstruction of the behavior of the sww during the past 14 k y based on terrestrial ecosystem proxies from western patagonia south america the reconstructed variations in the intensity of zonal flow correspond to the timing and structure of atmospheric co 2 changes and are consistent with the modeled magnitude of co 2 changes induced by varying strengths of the sww the close match between data and models supports the view that the sww southern ocean coupled system underpins multimillennial co 2 variations during the current interglacial and possibly during glacial cycles over the past 800 k y

mechanisms of holocene palaeoenvironmental change in the antarctic peninsula region the antarctic peninsula is one of the three fastest warming regions on earth here we review holocene proxy records of marine and terrestrial palaeoclimate in the region and discuss possible forcing mechanisms underlying past change with a specific focus on past warm periods our aim is to critically evaluate the mechanisms by which palaeoclimate changes might have occurred in order to provide a longer term context for assessing the drivers of recent warming two warm events are well recorded in the holocene palaeoclimate record namely the early holocene warm period and the mid holocene hypsithermal mhh whereas there are fewer proxy data for the mediaeval warm period mwp and the recent rapid regional rrr warming we show that the early holocene warm period and mhh might be explained by relatively abrupt shifts in position of the southern westerlies superimposed on slower solar insolation changes a key finding of our synthesis is that the marine and terrestrial records in the ap appear to show markedly different behaviour during the mhh this might be partly explained by contrasts in the seasonal insolation forcing between these records circumpolar deep water cdw has been implicated in several of the prominent changes through the holocene but there are still differences in interpretation of the proxy record that make its influence difficult to assess further work is required to investigate contrasts between marine and terrestrial proxy records east west contrasts in palaeoclimate the history of cdw to retrieve a long onshore high resolution record of the holocene and determine the role of sea ice in driving or modulating palaeoclimate change along with further efforts to study the proxy record of the rrr and the mwp

multi proxy analyses of a peat bog on isla de los estados easternmost tierra del fuego a unique record of the variable southern hemisphere westerlies since the last deglaciation we have analyzed an almost 14 000 year old peat sequence on the island of isla de los estados 55 degrees s 64 degrees w east of tierra del fuego in the core of the southern hemisphere westerlies a multitude of methods have been used high resolution c 14 dating detailed lithologic descriptions including humification degree loss on ignition magnetic susceptibility bulk density pollen and spore analysis and determination of aeolian sand influx by combining proxies for wind and precipitation we have been able to reconstruct how the westerlies have varied over time in the atlantic sector of the southern ocean it shows that this westerly wind belt was most intense at the onset of the record 13 600 13 200 cal bp coinciding with the mid to late part of the antarctic cold reversal followed by a gradual decline at 12 200 cal bp the westerlies seem to have shifted to a position south of tierra del fuego and this phase the calmest and driest period on the island throughout the sequence ended at 10 000 cal bp when the westerlies moved equatorward again since then the westerlies have been present but with a variable impact on the 55 degrees s latitude of the atlantic mostly conditions have been fairly similar to today but occasionally with a wider or narrower and or weaker or stronger wind belt at 7200 cal bp wind intensity began to increase and between 4500 and 3500 cal bp these southern latitudes experienced a distinct wind and precipitation maximum both in terms of perseverance and intensity our results show a both wide and strong wind belt with possible niveo aeolian activity in tierra del fuego in winter and possibly creating milder summers around the antarctic peninsula in the later part of the holocene expansion contraction phases of the wind belt especially in winter seem to have been a common phenomenon c 2012 elsevier ltd all rights reserved

holocene palaeoclimates of southern patagonia limnological and environmental history of lago cardiel argentina multiproxy palaeoenvironmental and palaeolimnological analyses of two holocene age sediment cores from the margin of lago cardiel a 76 m deep closed basin lake in southern patagonia latitude 49 s provide information on lake level changes that can be related to regional palaeoclimate scenarios sedimentol ogic magnetic susceptibility organic and inorganic carbon content and environmental indicators pollen dia toms ostracodes and stable isotopes on ostracodes show lake levels markedly higher than today during the early holocene following a rapid lake level rise after a desiccation phase prior to 11 000 bp after about 6000 bp lake levels were generally lower but underwent repeated e uctuations these inferred changes support the previously proposed view that the southern westerly stormtracks were focused zonal north of latitude 50 s during the early holocene allowing for antarctic cold fronts to bring easterly moisture to southern patagonia whereas during the late holocene the stormtracks shifted seasonally with an overall more meridional behaviour resulting in less and more variable moisture at these latitudes

a diatom conductivity transfer function for reconstructing past changes in the southern hemisphere westerly winds over the southern ocean sub antarctic islands are ideally placed to reconstruct past changes in southern hemisphere westerly wind behaviour they lie within their core belt 50 60 s and the strong winds deliver sea salt ions to the islands resulting in a west to east conductivity gradient in their water bodies this means that the stronger or weaker the winds the higher or lower the conductivity values measured in the water bodies a survey of the water chemistry and diatom assemblages of lakes and ponds on sub antarctic campbell island 52 32 s 169 8 e revealed that similar to other sub antarctic islands conductivity was the most important statistically significant ecological variable explaining turnover in diatom community structure based on this a diatom conductivity transfer function was developed simple weighted averaging with inverse deshrinking r2 0 86 r2jack 0 66 rmsep 0 25 log10 s cm 1 this transfer function will be applied to lake sediment cores from the western edge of the campbell island plateau to reconstruct past conductivity sea spray and therefore directly reconstruct changes in southern hemisphere westerly wind strength within their core belt

holocene glacier fluctuations and environmental changes in subantarctic south georgia inferred from a sediment record from a coastal inlet the subantarctic island of south georgia provides terrestrial and coastal marine records of climate variability which are crucial for the understanding of the drivers of holocene climate changes in the subantarctic region here we investigate a sediment core co1305 from a coastal inlet on south georgia using elemental lipid biomarker diatom and stable isotope data to infer changes in environmental conditions and to constrain the timing of late glacial and holocene glacier fluctuations because of the scarcity of terrestrial macrofossils and the presence of redeposited and relict organic matter in the sediments age control for the record was obtained by compound specific radiocarbon dating of mostly marine derived n c 16 fatty acids a basal till layer recovered in little jason lagoon was likely deposited during an advance of local glaciers during the antarctic cold reversal after glacier retreat an oligotrophic lake occupied the site which transitioned to a marine inlet around 8 0 0 9 ka because of relative sea level rise from 7 0 0 6 to 4 0 0 4 ka reduced vegetation coverage in the catchment as well as high siliciclastic input and deposition of ice rafted debris indicates glacier advances in the terrestrial catchment and likely in the adjacent fjord a second less extensive period of glacier advances occurred in the late holocene after 1 8 0 3 ka