late quaternary palaeoenvironmental change in the year round rainfall zone of south africa derived from peat sediments from vankervelsvlei abstract due to the scarcity of natural archives for palaeoenvironmental studies the climatic evolution of south africa during the late quaternary remains the subject of considerable debate peat deposits provide excellent archives to investigate past environmental and climate variability vankervelsvlei a fen near the southern cape coast located 152 m above mean sea level within the year round rainfall zone of south africa is ideally suited to investigate past environmental changes in this region a 14 6 m long sediment sequence was retrieved from the fen from which 8 85 m of sediment have been analysed using a multi proxy approach this includes elemental macrofossil and micropalaeontological analyses as a novelty in palaeoenvironmental reconstruction in this region leaf wax n alkanes and their compound specific stable carbon and hydrogen isotopes were also investigated the chronology of the sequence is based on 13 radiocarbon ages and reveals a basal age of 37 430 1 570 1 710 cal bp the top of the investigated sequence has an age of 1 180 340 170 cal bp leaf wax n alkane abundances and their compound specific stable carbon and hydrogen isotopes as well as various in organic bio geochemical parameters indicate that the older section of the sequence 37 430 1 570 1 710 28 050 510 600 cal bp which is composed of strongly degraded peat represents a rather dry phase during mis 3 this is followed by a hiatus of around 20 000 years 28 050 510 600 to 8 360 730 810 cal bp reflecting the driest conditions during mis 2 by comparing to supra regional archives this is hypothesised to have resulted from a larger extension of the antarctic sea ice which caused an equatorward shift of the westerlies blocking the tropical easterlies and resulting in drier conditions along the south coast and the adjacent coastal platform during the early holocene the input of reworked soil into the depression and subsequently renewed peat formation from 6 820 305 365 cal bp to 1 180 340 170 cal bp in vankervelsvlei point to moister climatic conditions contraction of antarctic sea ice and a poleward shift of the westerlies during the holocene is consistent with this interpretation climatic driving forces are suggested to differ between centennial millennial and orbital time scales evapotranspirative enrichment through stronger winds is assumed to be the main driver on centennial to millennial time scale within this hydrological system however a combination of evapotranspiration and precipitation amount seems to be the most prominent driver on the orbital time scales

change in climate ocean and ice sheet conditions in the ross embayment antarctica at 6 ka evidence from the ross embayment antarctica suggests an abrupt cooling and a concomitant increase in sea ice cover at about 6000 sp 6 ka stable isotope delta d concentrations in the taylor dome ice core at the western edge of the ross embayment decline rapidly after 6 ka and continue to decline through the late holocene methanesulfonic acid concentrations at taylor dome show opposite trends to delta d sediment cores from the western ross sea show a percentage minimum for the sea ice diatom fragilariopsis curta between 9 and 6 ka when taylor dome delta d values are highest followed by an increase through the late holocene radiocarbon dates from raised beach deposits indicate that the retreat of ice shelves in the ross embayment ceased atabout 6 ka coincident with the environmental changes inferred from the sediment and ice core records the similarity in timing suggests an important role for climate in controlling the evolution of ice shelf margins following the end of the last 9 glaciation

a multiproxy study of the ocean atmospheric forcing and the impact of sea level changes on the southern cape coast south africa during the holocene abstract a multiproxy approach focusing on biological proxies was undertaken to determine the influence of sea level changes along the southern cape coast and the variability of water masses over the central agulhas bank region during the holocene a 30 47 m sedimentary core extracted from the coastal lake eilandvlei shows continuous deposition for the last 9000 years microfossils were classified based on salinity and habitat diatoms were further defined by their temperature preferences as either warm or cold water species the composition of the assemblages is strongly linked to fluctuations in marine inflow into the system and the extent of freshwater inputs to the lake as recorded at the core site paleoproductivity improved during periods of equatorward migration of the westerlies notably from 5800 to 5000 cal yr b p when surface water mixing increased spectral analysis revealed periodicities associated with solar cycles namely gleissberg and de vries the system remained predominantly marine and submerged in response to an early mid holocene transgression until 4700 cal yr b p when sea level fluctuations and landscape modification restricted marine incursions modified the exposed landscape and shifted the system toward a lagoon state this multiproxy record provides insights into oceanic exchanges surface water conditions and the mechanisms that govern them during the holocene

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

pollen evidence for variations in the southern margin of the westerly winds in sw patagonia over the last 12 600 years we report pollen and charcoal records from vega nandu 51 0 s 72 45 w a small mire located near the modern forest steppe ecotone in torres del paine national park southern chile the record shows an open landscape dominated by low shrubs and herbs between 12 600 and 10 800 cal yr bp under cold and relatively humid conditions nothofagus experienced frequent large amplitude oscillations between 10 800 and 6800 cal yr bp indicating recurrent transitions between shrubland parkland environments under warm and highly variable moisture conditions a sustained increase in nothofagus started at 6800 cal yr bp punctuated by step wise increases at 5100 and 2400 cal yr bp implying further increases in precipitation we interpret these results as indicative of variations in the amount of precipitation of westerly origin with prominent increases at 6800 5100 and 2400 cal yr bp these pulses led to peak precipitation regimes during the last two millennia in this part of sw patagonia our data suggest variations in the position and or strength of the southern margin of the westerlies most likely linked to variations in the extent and or persistence of sea ice and sea surface temperature anomalies in the southern ocean over the last two centuries the record shows a forest decline and expansion of rumex acetosella an exotic species indicative of european disturbance 2007 university of washington all rights reserved

sea ice and wind variability during the holocene in east antarctica insight on middle high latitude coupling abstract micropaleontological and biomarker data from two high accumulation marine sites from the coastal and continental shelf zone ccsz off east antarctica adelie land at 140 e and eastern prydz bay at 77 e are used to reconstruct holocene changes in sea ice and wind stress at the basin wide scale these data demonstrate congruent increase in sea ice concentration persistence and wind stress related sea surface turbulence in the two regions since 7 cal ka bp with a particularly strong signal since 4 5 3 5 cal ka bp comparison of these high latitude records with sea ice and turbulence records from the southern mid latitudes highlights distinctive climatic evolutions according to the different latitudinal bands sea ice persistence and turbulence increase in east antarctica ccsz are opposite to sea surface warming and sea ice retreat recorded after 4 5 3 5 cal ka bp in the east atlantic and indian sector between 55 and 45 s at the same period paleodata suggest sst cooling in all major coastal upwelling systems of the southern hemisphere caused by the northward transport of subpolar surface waters as a response to southern westerlies reinforcement we therefore propose as suggested for the northern hemisphere that holocene changes in the latitudinal insolation gradient primarily forced by obliquity and precession and amplified by sea ice and glacial ice expansions in the antarctic realm are responsible for the observed contrasted latitudinal patterns of southern latitudes

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

a review of holocene solar linked climatic variation on centennial to millennial timescales physical processes interpretative frameworks and a new multiple cross wavelet transform algorithm article i nfo wereportontheexistenceandnature of holocene solar andclimaticvariationson centennialto millennial time scales we introduce a new solar activity proxy based on nitrate no3 concentration from the talos dome ice core east antarctica we also use a new algorithm for computing multiple cross wavelet spectra in time fre quency space that is generalized for multiple time series beyond two our results provide a new interpretive framework for relating holocene solaractivity variations on centennial to millennial timescales to co varying cli mate proxies drawn from a widespread area around the globe climatic proxies used represent variation in the north atlantic ocean western pacific warm pool southern ocean and the east asian monsoon regions our wavelet analysis identifies fundamental solar modes at 2300 yr hallstattzeit 1000 yr eddy and 500 yr unnamed periodicities leaves open the possibility that the 1500 1800 yr cycle may either be fundamental or derived and identifies intermediary derived cycles at 700 yr and 300 yr that may mark rectified responses of the atlantic thermohaline circulation to external solar modulation and pacing dating uncertainties suggest that the 1500 yr and 1800 yr cycles described in the literature may represent either the same or two separate cycles but in either case and irrespective too of whether it is a fundamental or derived mode in the sense of dima and lohmann 2009 the 1500 1800 yr periodicity is widely represented in a large number of paleoclimate proxy records it is obviously premature to reject possible links between changing solar activity at these multiple scales and the variations that are commonly observed in paleoclimatic records

triple water isotopologue record from wais divide antarctica controls on glacial interglacial changes in 17oexcess of precipitation measurements of the 17oexcess of h2o were obtained from ice cores in west and east antarctica combined with previously published results from east antarctica the new data provide the most complete spatial and temporal view of antarctic 17oexcess to date there is a steep spatial gradient of 17oexcess in present day precipitation across antarctica with higher values in marine influenced regions and lower values in the east antarctic interior there is also a spatial pattern to the change in 17oexcess between the last glacial maximum lgm and holocene periods at coastal locations there is no significant change in 17oexcess at both the west antarctic ice sheet divide site and at vostok east antarctica the lgm to early holocene change in 17oexcess is about 20 per meg atmospheric general circulation model gcm experiments show that both the observed spatial gradient of 17oexcess in modern precipitation and the spatial pattern of lgm to early holocene change can be explained by kinetic isotope effects during snow formation under supersaturated conditions requiring a high sensitivity of supersaturation to temperature the results suggest that fractionation during snow formation is the primary control on 17oexcess in antarctic precipitation variations in moisture source relative humidity play a negligible role in determining the glacial interglacial 17oexcess changes observed in antarctic ice cores additional gcm experiments show that sea ice expansion increases the area over which supersaturating conditions occur amplifying the effect of colder temperatures temperature and sea ice changes alone are sufficient to explain the observed 17oexcess glacial interglacial changes across antarctica

the last deglaciation in the southern ocean the isotopic and micropaleontological deglacial records of three deep sea cores from 44 s to 55 s have been dated by accelerator mass spectrometry the available records did not allow accurate dating of the initiation of the deglaciation by 13 000 years b p sea surface temperatures reached values similar to the present values a cool oscillation abruptly interrupted this warm phase between 12 000 and 11 000 years b p initiation of this cooling therefore preceded the northern hemisphere younger dryas by approximately 1000 years complete warming was reached by 10 000 years b p more or less synchronous with the northeast atlantic ocean

holocene climate in the atlantic sector of the southern ocean controlled by insolation or oceanic circulation abstractthe holocene climate of the southern ocean is not well un derstood mainly because of the lack of high resolution reconstruc tions of ocean surface properties here we present a 12 500 yr long decadal scale record of holocene sea surface temperatures and sea ice presence from the polar front of the east atlantic southernocean the record shows gradual climate change with no abruptneoglacial cooling and an unprecedented late holocene warming the dominant forcing factor appears to be precessional insolation northern hemisphere summer insolation correlates to at least theearly to middle holocene climate trend spectral analysis revealscentennial scale cyclic climate changes with periods of 1220 1070 400 and 150 yr the record shows good correlation to east ant arctic ice cores and to climate records from south georgia andbunger oasis however the record shows out of phase behaviorwith regard to climate records from the western antarctic penin sula and the peru chile current such behavior hints at a climaticdivide through patagonia the drake passage and between westand east antarctica keywords southern ocean paleoclimate diatoms modern analogtechnique holocene insolation antarctic polar front introductionthe holocene climate variability has received less attention thanthe more dramatic changes during the last glacial period the holoceneis generally assumed to be a stable interglacial period when climatechanges in the north atlantic are transmitted to the rest of the worldthrough a strong thermohaline circulation imbrie et al 1992 thelarge uctuations of the last glacial period appear to continue into thisinterglacial although in a subdued manner bond et al 2001 the southern ocean has received even less attention than the highnorthern latitudes oceanic records are few and coarse they generallydisplay a warm early holocene followed by cooling labracherie etal 1989 pichon et al 1992 hodell et al 2001 similar to northatlantic climate e g koc and jansen 1994 high resolution recordsare restricted to antarctic ice cores which mostly display little climatevariability during the holocene jouzel et al 2001 an exception isthe taylor dome deuterium record in which the holocene appears tobe split by an abrupt cooling event ca 5 5 5 ka steig et al 1998 this cooling appears to t the late holocene global cooling trend por ter 2000 as a nonlinear response from the climate system to insolationchanges demenocal et al 2000 hodell et al 2001 high resolution holocene records available for southern oceanclimate reconstruction are rarely from the antarctic circumpolar cur rent proper e g domack et al 2001 stenni et al 2001 lamy et al 2002 with the exception of a multiproxy approach to holocene cli mate that includes a high resolution description of lithic fragments hodell et al 2001 we present data from site tn057 17 near the polar front in theeast atlantic southern ocean it is based on quantitative estimates ofsummer sea surface temperature ssst and sea ice presence sip utilizing the down core variability of diatom assemblages the recordshows good correlation to antarctic ice cores but a gradual change inphase relationships during the early holocene the record shows anin phase relationship with the ross sea region ice cores during thelate holocene the record shows an in phase relationship with the eastantarctic region ice cores antarctic polar frontthe antarctic polar front apf fig 1 is an important climateboundary in terms of air sea uxes and the heat and salt budgets ofthe oceans at the surface the apf is a steep sea surface temperaturegradient while the subsurface expression is the southern limit for sub duction of cold fresh antarctic surface water below warmer and moresaline subantarctic surface water orsi et al 1995 globally the apfcould be the southern limit of synchrony with northern hemisphereclimate broecker 1996 the apf is subject to large spring and sum mer blooms of diatoms fischer et al 2002 and achieves the largestbiogenic sedimentation rates of the diatom ooze belt of the southernocean burckle and cirilli 1987 it is these high sedimentation ratesof diatomaceous oozes and the sensitivity of diatoms especially to lightand temperature that make sites in the apf region suitable for pro ducing high resolution records of climate change

holocene subsurface temperature variability in the eastern antarctic continental margin 1 we reconstructed subsurface 45 200 m water depth temperature variability in the eastern antarctic continental margin during the late holocene using an archaeal lipid based temperature proxy tex86l our results reveal that subsurface temperature changes were probably positively coupled to the variability of warmer nutrient rich modified circumpolar deep water mcdw deep water of the antarctic circumpolar current intrusion onto the continental shelf the tex86lrecord in combination with previously published climatic records indicates that this coupling was probably related to the thermohaline circulation seasonal variability in sea ice extent sea temperature and wind associated with high frequency climate dynamics at low latitudes such as internal el nino southern oscillation enso this in turn suggests a linkage between centennial enso like variability at low latitudes and intrusion variability of mcdw into the eastern antarctic continental shelf which might have further impact on ice sheet evolution

real time measurements of sediment transport and bed morphology during channel altering flow and sediment transport events abstract real time measurements of bed changes over a reach are a missing piece needed to link bed morphology with sediment transport processes during unsteady flows when the bed adjusts quickly to changing transport rates or visual observation of the bed is precluded by fine sediment in the water column a new technique is presented that provides continuous measurement of sediment movement over the length of a flume a bedload monitoring system blms was developed that makes use of pressure pillows under a false flume bottom to measure sediment and water weights over discrete flume channel sections throughout a flow event this paper details the construction of the blms and provides examples of its use in a laboratory setting to reconstruct bed slopes during unsteady flows and to create a real time record of sediment transport rates across the flume channel bed during a sediment transporting flow data gathered from the blms compared well against techniques commonly in use in flume studies when the blms was analyzed in conjunction with bed surface dems and differenced dems a complete transport and bed adjustment picture was constructed the difference dems provided information on the spatial extent of bed morphology changes the blms supplied the data record necessary to reconstruct sediment transport records through the downstream channel including locations and time periods of temporary sediment storage and supply the blms makes it possible to construct a continuous record of the spatial distribution of sediment movement through the flume including areas of temporary aggradation and degradation exciting implications of future research that incorporates a blms include a more informed management of river systems as a result of improved temporal predictions of sediment movement and the associated changes in channel slope and bed morphology

deglacial changes in flow and frontal structure through the drake passage the oceanic gateways of the drake passage and the agulhas current are critical locations for the inflow of intermediate depth water masses to the atlantic which contribute to the shallow return flow that balances the export of deep water from the north atlantic the thermohaline properties of northward flowing intermediate water are ultimately determined by the inflow of water through oceanic gateways here we focus on the less well studied cold water route through the drake passage we present millennially resolved bottom current flow speed and sea surface temperature records downstream of the drake passage spanning the last 25 000 yr we find that prior to 15 ka bottom current flow speeds at sites in the drake passage region were dissimilar and there was a marked anti phasing between sea surface temperatures at sites upstream and downstream of the drake passage after 14 ka we observe a remarkable convergence of flow speeds coupled with a sea surface temperature phase change at sites upstream and downstream of drake passage we interpret this convergence as evidence for a significant southward shift of the sub antarctic front from a position north of drake passage this southward shift increased the through flow of water from the pacific likely reducing the density of atlantic intermediate water the timing of the southward shift in the sub antarctic front is synchronous with a major re invigoration of atlantic meridional overturning circulation with which we argue it may be linked

model data comparison for the 8 2 ka bp event confirmation of a forcing mechanism by catastrophic drainage of laurentide lakes abstract to improve our understanding of the mechanism behind the 8 2 ka bp cooling event we compare proxy evidence with climate model simulations in which the thermohaline ocean circulation is perturbed by a freshwater pulse into the labrador sea both the proxy data and model results show a cooling that is mainly concentrated in the north atlantic region ranging from more than 5 c cooling in the nordic seas to about 0 5 1 c over europe and less than 0 5 c over the subtropical north atlantic data and model also indicate a weakening of the summer monsoon and generally a drier circum north atlantic over the south atlantic ocean the model simulates a slight warming mostly less than 0 5 c which falls within the uncertainty of proxy data and thus could not be confirmed to examine in detail the structure of the 8 2 ka bp event we also compare the modeled climatological evolution at two locations with high quality records revealing a generally consistent picture the good model data agreement confirms the hypothesis that the 8 2 ka bp event was forced by a freshwater induced weakening of the thermohaline circulation other forcings are unlikely since they would result in an alternative geographical distribution and expression of the climate response

onset of neoglaciation in the southern hemisphere a review of evidence documenting an early neoglacial mid holocene advance of mountain glaciers in south america and new zealand reveals that of 16 glaciers for which radiocarbon age control exists only two have associated dates that may approximate the culmination of an advance advances of the remaining glaciers are controlled only by minimum or maximum limiting ages additional dates for several new zealand glaciers are based on weathering rind measurements having large potential errors twelve of the glaciers now terminate or have terminated in lakes or in tidewater and are subject to instabilities associated with calving termini an extensive debris cover in the ablation zone of nearly half of the glaciers makes their moraine succession potentially suspect as a record of detailed climatic variation the two glaciers with seemingly reliable age control are located in valleys where large rock avalanches could affect glacier mass balance and lead to random advances or where rock avalanche deposits might easily be mistaken for moraines and tills the early neoglacial interval has been defined primarily based on this set of data the ages taken at face value suggest that the early neoglacial advance culminated between ca 5400 and 4900 cal yr ago ca 4600 4400 14c yr bp this chronology however should remain provisional until improved age control is obtained for a large population of glaciers based on closely bracketing radiocarbon dates and or an adequate number of cosmogenic isotope ages data from calving glaciers and those subject to rock avalanche activity should be avoided or assessed critically copyright 2000 john wiley sons ltd

uplift of the western altiplano plateau evidence from the precordillera between 20 and 21 s northern chile 1 we present a quantitative reconstruction of uplift of the western flank of the altiplano plateau central andes one of the largest monoclines on the earth on the basis of an analysis of tectonic structures syntectonic deposits and geophysical data uplift occurred on a west vergent slowly propagating system of high angle reverse faults merging into a joint detachment that ramps down to midcrustal levels below the plateau edge the upper ramps determine local fold geometries while the lower ramp controls large scale surface tilting and uplift at 20 s this fault system was active between 30 ma and 5 10 ma with maximum shortening rates of 0 22 mm yr between 17 and 10 ma it generated some 2600 m of surface uplift with only minor shortening of 3000 m its activity was largely synchronous to eruption of large volume ignimbrites from a midcrustal source geophysical data indicate that the fault system localized deformation at the boundary between a cool strong forearc crust and a presumably fluid rich and or partially molten zone underneath the plateau area the systematic relation between crustal melting and shortening with uplift at the western plateau margin can be traced along most of the plateau flank with a stepwise decrease in age of deformation and magmatism toward the south indicating discontinuous addition of plateau segments crustal thickening to as much as 70 km from westward underthrusting in the back arc parts of the plateau isostatically compensated the tectonic surface uplift and monocline formation with respect to a stable forearc which only reacted with minor tilting

deglacial environmental changes on isla de los estados 54 4 s southeastern tierra del fuego the island of isla de los estados is situated at 54 5 degrees s 64 degrees w east of argentinian tierra del fuego and is located in a sensitive geographic position in relation to the zonal circulation between antarctica and south america its terrestrial records of the last deglaciation recording atmospheric conditions but within an oceanic setting can help to clarify changes of regional circulation patterns both atmospheric and marine here we present geochemical analyses from 16 10 ka cal bp of a peat core from lago galvarne bog at the northern coast of the island and a lake sediment core from laguna cascada 3 kin further south the data comprise tc tn loss on ignition analyses and continuous xrf scanning on both cores as well as age depth modeling based on ams c 14 dating deglaciation and onset of peat formation in the coastal areas began before 16 ka cal bp followed by a rapid glacial retreat and the start of lacustrine sedimentation further inland data suggest initially windy conditions with permafrost succeeded by gradually warmer and wetter conditions until ca 14 5 ka cal bp the warming trend slows down until ca 13 5 ka cal bp followed by arid conditions culminating around 12 8 ka cal bp our data suggest fairly warm conditions and the establishment of denser peat and forest vegetation ca 10 6 ka cal bp contemporaneous with the onset of the antarctic thermal optimum this indicates large scale shifts in the placement of zonal flow and the westerlies at the beginning of the holocene c 2008 elsevier ltd all rights reserved

surface water temperature changes in the high latitudes of the southern hemisphere over the last glacial interglacial cycle a set of numerical equations is developed to estimate past sea surface temperatures sst from fossil antarctic diatoms these equations take into account both the biogeographic distribution and experimentally derived silica dissolution the data represent a revision and expansion of a floral data base used previously and includes samples resulting from progressive opal dissolution experiments factor analysis of 166 samples 124 holocene core top and 42 artificial samples resolved four factors three of these factors depend on the water mass distribution one subantarctic and two antarctic assemblages factor 4 corresponds to a dissolution assemblage inclusion of this factor in the data analysis minimizes the effect of opal dissolution on the assemblages and gives accurate estimates of sst over a wide range of biosiliceous dissolution a transfer function dtf 166 34 4 is derived from the distribution of these factors versus summer sst its standard error is 1 c in the 1 to 10 c summer temperature range this transfer function is used to estimate sst changes in two southern ocean cores 43 s and 55 s which cover the last climatic cycle the time scale is derived from the changes in foraminiferal oxygen and carbon isotopic ratios the reconstructed sst records present strong analogies with the air temperature record over antarctica at the vostok site derived from changes in the isotopic ratio of the ice this similarity may be used to compare the oceanic isotope stratigraphy and the vostok time scale derived from ice flow model the oceanic time scale if taken at face value would indicate that large changes in ice accumulation rates occurred between warm and cold periods

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

a new 27 ky high resolution east antarctic climate record the ice core recently drilled at the dome concordia site on the east antarctic plateau provides a new high resolution isotope record covering part of the last glacial the last transition and the holocene the two step shape of the deglaciation is remarkably similar for all the ice cores now available on the east antarctic plateau the first warming trend ends about 14000 years ago and is followed by the well marked antarctic cold reversal acr with a secondary peak common to all records during the deglaciation there are more similarities between the near coastal site of taylor dome and inland east antarctica than between taylor dome and central greenland however the results for epica do appear to confirm the taylor dome timescale after about 14 ka showing cooling into the acr roughly in phase between greenland and antarctica while the overall deglacial pattern is asynchronous this suggests that the now classical picture of a temperature seesaw between antarctica and greenland may be too simplistic

abrupt cooling of antarctic surface waters and sea ice expansion in the south atlantic sector of the southern ocean at 5000 cal yr b p antarctic surface waters were warm and ice free between 10 000 and 5000 cal yr b p as judged from ice rafted debris and microfossils in a piston core at 53 s in the south atlantic this evidence shows that about 5000 cal yr b p sea surface temperatures cooled sea ice advanced and the delivery of ice rafted detritus ird to the subantarctic south atlantic increased abruptly these changes mark the end of the hypsithermal and onset of neoglacial conditions they coincide with an early neoglacial advance of mountain glaciers in south america and new zealand between 5400 and 4900 cal yr b p rapid middle holocene climate changes inferred from the taylor dome ice core antarctica cooling and increased ird in the north atlantic and the end of the african humid period the near synchrony and abruptness of all these climate changes suggest links among the tropics and both poles that involved nonlinear response to gradual changes in northern hemisphere insolation sea ice expansion in the southern ocean may have provided positive feedback that hastened the end of the hypsithermal and african humid periods in the middle holocene

on the strength of interplate coupling and the rate of back arc convergence in the central andes an analysis of the interseismic velocity field 1 we interpret the interseismic crustal velocity field of the central andes using a simple three plate model in which the andean mountain belt is treated as a rigid microplate located between the nazca and south american soam plates we assume that the euler vectors associated with these plates are strictly coaxial and that the surface velocity field can be decomposed into an elastic loading field driven by locking of the main plate boundary and a smaller contribution associated with back arc convergence we obtain our best fit to the geodetic velocities if the main plate boundary is fully 100 locked between depths of 10 50 km and 8 5 of nazca soam plate convergence is achieved in the back arc by underthrusting of the brazilian shield beneath the subandean zone

seasonal and subseasonal climate changes recorded in laminated diatom ooze sediments adelie land east antarctica a 40 m long sediment core covering the 1000 9600 years bp period was retrieved from the dumont d urville trough off adelie land east antarctica during the md 130 images x cado cruise this sedimentary sequence allows the documentation of changes in climate seasonality during the holocene here we show preliminary results of diatom communities lithic grain distribution and titanium content measured on two 30 cm long sequences of thin sections the two sequences originate from two different climate regimes the colder neoglacial and the warmer hypsithermal proxies were measured at microscale resolution on 25 laminations for the neoglacial and 14 laminations for the hypsithermal the two sequences reveal alternating light green and dark green laminae light laminae result from low terrigenous input and high sea ice edge diatom fluxes and are interpreted to represent the spring season dark laminae result from high terrigenous input mixed with a diversified open ocean diatom flora and are interpreted to represent the summer autumn season the two sequences therefore resolve annual couplets composed of one light plus one dark lamina variations in the relative thickness of laminations and annual couplets associated with diatom assemblage changes are observed in each sequence and between the two sequences giving information on interannual to millennial changes in environmental conditions

early holocene laurentide ice sheet deglaciation causes cooling in the high latitude southern hemisphere through oceanic teleconnection the impact of the early holocene laurentide ice sheet lis deglaciation on the climate at southern hemisphere high latitudes is studied in three transient simulations performed with a global climate model of the coupled atmosphere ocean vegetation system considering the lis deglaciation we quantify separately the impacts of the background meltwater fluxes and the changes in topography and surface albedo in our model the meltwater input into the north atlantic results in a substantial weakening of the atlantic meridional overturning circulation associated with absence of deep convection in the labrador sea northward ocean heat transport by the atlantic ocean is reduced by 28 this weakened ocean circulation leads to cooler north atlantic deep water nadw upwelling of this cool nadw in the southern ocean results in reduced surface temperatures by 1 degrees c to 2 degrees c here between 9 and 7 ka compared to an experiment without lis deglaciation poleward of the polar front zone this advective teleconnection between the southern and northern hemispheres overwhelms the effect of the classical bipolar seesaw mechanism these results provide an explanation for the relatively cold climatic conditions between 9 and 7 ka reconstructed in several proxy records from southern hemisphere high latitudes such as antarctic ice cores

an integrated palaeoenvironmental investigation of a 6200 year old peat sequence from ile de la possession iles crozet sub antarctica a 6200 year old peat sequence cored in a volcanic crater on the sub antarctic ile de la possession iles crozet has been investigated based on a multi proxy approach the methods applied are macrobotanical mosses seeds and fruits and diatom analyses complemented by geochemical rock eval6 and rock magnetic measurements the chronology of the core is based on 5 radiocarbon dates when combining all the proxy data the following changes could be inferred from the onset of the peat formation 6200 cal yr bp until ca 5550 cal yr br biological production was high and climatic conditions must have been relatively warm at ca 5550 cal yr bp a shift to low biological production occurred lasting until ca 4600 cal yr br during this period the organic matter is well preserved pointing to a cold and or wet environment at ca 4600 cal yr bp biological production increased again from ca 4600 cal yr bp until ca 4100 cal yr bp a hollow and hummock micro topography developed at the peat surface resulting in the presence of a mixture of wetter and drier species in the macrobotanical record after ca 4100 cal yr bp the wet species disappear and a generally drier acidic bog came into existence a major shift in all the proxy data is observed at ca 2800 cal yr br pointing to wetter and especially windier climatic conditions on the island probably caused by an intensification and or latitudinal shift of the southern westerly belt caused by a stronger wind regime erosion of the peat surface occurred at that time and a lake was formed in the peat deposits of the crater which is still present today c 2008 elsevier b v all rights reserved less

millennial to centennial scale changes in sea surface temperature in the tropical south atlantic throughout the holocene abstract we performed 18oc globigerinoides ruber 250 300 m white and sst modern analogue technique paleoceanographic reconstructions for the western tropical south atlantic ocean at the northeast brazilian margin to assess millennial to centennial scale climatic shifts that may be propagated by the thermohaline circulation the results show a progressive sst increase 1 c over the holocene with a prominent shift occurring during the mid holocene that may be linked to changes in insolation distribution furthermore spectral and coherency analyses reveal several centennial to millennial scale modes of variability that are similar in both proxy records 4 1 3 8 kyr 1 5 1 0 kyr 700 yr 570 560 yr 390 yr 350 yr and 330 yr such variability could be the result of 1 solar induced atmospheric changes at northern high latitudes possibly propagated southward by the meridional overturning circulation and hence inducing shifts in tropical 18oc and sea surface temperature and or 2 salinity anomalies propagated from the southern atlantic ocean and transmitted to the study site through the agulhas leakage these climate oscillations may have had substantive effects on the holocene climate system especially over the tropical western south atlantic ocean and the south american continent our data show that the western tropical south atlantic may respond to multi centennial to millennial oscillations that are possibly triggered by external solar and internal northern and southern high latitudes climate forcing further investigations are necessary to illuminate the role of the western tropical south atlantic in inter hemispheric heat transfer

productivity cycles of 200 300 years in the antarctic peninsula region understanding linkages among the sun atmosphere oceans sea ice and biota compared to the rest of the world9s oceans high resolution late holocene paleoclimatic data from the southern ocean are still rare we present a multiproxy record from a sediment core retrieved from a deep basin on the western side of the antarctic peninsula that reveals a dramatic perspective on paleoclimatic changes over the past 3700 yr analyses completed include measurement of magnetic susceptibility and granulometry bed thickness particle size percent organic carbon bulk density and microscopic evaluation of diatom and benthic foraminiferal assemblages and abundances downcore variability of these parameters demonstrates the significance of both short term cycles which recur approximately every 200 yr and longer term events 2500 yr cycles that are most likely related to global climatic fluctuations in the upper 600 cm of the core lower values of magnetic susceptibility ms are correlated with lower bulk density the presence of thinly laminated units specific diatom assemblages and generally higher total organic carbon content below 600 cm magnetic susceptibility is uniformly low though variability in other parameters continues the magnetic susceptibility signal is controlled primarily by dilution of ferromagnetic phases with biosiliceous material this signal may be enhanced further by dissolution of magnetite in the magnetic susceptibility lows high total organic carbon the role of variable primary productivity and its relationship to paleoclimate is assessed through the diatom data in particular magnetic susceptibility lows are characterized by higher than normal abundances of chaetoceros resting spores corethron criophilum and or rhizosolenia spp also are found as is a higher ratio of the most common species of fragilariopsis versus species of thalassiosira these assemblages are indicative of periods of high primary productivity driven by the presence of a meltwater stabilized water column the 200 yr cyclicity noted in other paleoclimatic records around the world suggests a global forcing mechanism possibly solar variability in addition to the cyclic changes in productivity overall elevated productivity is noted below 600 cm or prior to ca 2500 yr b p this increased productivity may represent the tail end of a holocene climatic optimum which is widely recognized in other parts of the world but as yet is poorly documented in antarctica

holocene migration of oceanic front systems over the conrad rise in the indian sector of the southern ocean there has been limited previous research about holocene climate variability in the indian sector of the southern ocean here we examine centennial scale changes in diatom assemblages and stable isotopic ratios since 10 000 cal a bp in a high accumulation rate sediment core from the conrad rise although abundances of dominant diatom taxa fragilariopsis kerguelensis and thalassiothrix antarctica are comparatively constant relative abun dances of secondary taxa fluctuate before c 9900 cal a bp winter sea ice and cold water covered the conrad rise following deglaciation the sea ice retreated from the conrad rise lagging that of the atlantic and eastern indian sectors by about 1500 a the polar front moved southward during the early holocene optimum and north antarctic zone waters covered the conrad rise for about 650 a after 9300 cal a bp solar insolation strongly influenced sea surface temperature and primary productivity in the southern ocean in the high latitude indian sector productivity increased 1500 a after the onset of late holocene neoglaciation periodic d 18 o and cold water diatom taxa spikes at intervals of 200 and 300 500 a respectively occurred after 9300 cal a bp probably associated with solar activity fluctuations in short term sea surface temperature and cold water taxa are synchronous with changes in dd observed in an east antarctic ice core copyright 2011 john wiley sons ltd

assessing the link between coastal morphology wave energy and sea ice throughout the holocene from antarctic raised beaches post glacial rebound has preserved beaches across many ice free parts of the antarctic coastline these beaches typically contain gravel to boulder sized deposits and are built by high magnitude waves five new ages from the western antarctic peninsula were added to a compilation of 282 published ages from antarctic beaches a reduced compilation based solely on those ages that date beach formation is used to assess variations in beach formation throughout the holocene around antarctica we suggest the clustering of beach ages centered at 0 8 and 2 4 ka in the antarctic peninsula 1 5 3 6 and 6 0 ka in the ross sea and a broad peak from 2 7 to 6 3 ka in east antarctica indicates periods of heightened wave exposure leading to increased beach formation measurements of clast roundness from raised beaches show more rounded material is coincident with periods of heightened beach formation providing an independent means of assessing wave climate a comparison of periods of increased beach formation with available sea ice proxies suggests beach formation is synchronous with reduced sea ice conditions and thus higher wave climate as the presence or absence of sea ice determines open water conditions the factors that control sea ice directly influence antarctic coastal evolution

late quaternary sea ice history in the indian sector of the southern ocean as recorded by diatom assemblages abstract a modern analog technique mat5201 31 has been applied to fossil diatom assemblages to provide down core estimates of february sea surface temperatures ssts and of sea ice duration over the past 220 000 years at 56 40 s 160 14 e at the core location sea ice progression lagged the sst drop by 1 ka at interglacial glacial transitions and sea ice retreat was almost synchronous to the sst increase at glacial interglacial terminations sea ice increased continuously during glacial periods to reach its maximum extent at the end of glacial times although ssts were almost constant during glacials this indicates that ssts are the major parameter determining the advance and retreat of sea ice at transitions but that the sea ice advance during glacial conditions may be related to positive feedbacks of the ice on albedo air temperature and meridional wind stress the strong correlation r 0 75 between sea ice duration at the core location and the vostok co2 record argues for a control of antarctic sea ice extent on atmospheric co2 concentration via the modification of the ocean to atmosphere gas balance

holocene deglaciation and climate history of the northern antarctic peninsula region a discussion of correlations between the southern and northern hemispheres holocene deglaciation and climate history of the northern antarctic peninsula region a discussion of correlations between the southern and northern hemispheres

post glacial regional climate variability along the east antarctic coastal margin evidence from shallow marine and coastal terrestrial records we review the post glacial climate variability along the east antarctic coastline using terrestrial and shallow marine geological records and compare these reconstructions with data from elsewhere nearly all east antarctic records show a near synchronous early holocene climate optimum 11 5 9 ka bp coinciding with the deglaciation of currently ice free regions and the optimum recorded in antarctic ice and marine sediment cores shallow marine and coastal terrestrial climate anomalies appear to be out of phase after the early holocene warm period and show complex regional patterns but an overall trend of cooling in the terrestrial records a mid to late holocene warm period is present in many east antarctic lake and shallow coastal marine records although there are some differences in the regional timing of this warm period it typically occurs somewhere between 4 7 and 1 ka bp which overlaps with a similar optimum found in antarctic peninsula terrestrial records the differences in the timing of these sometimes abrupt warm events in different records and regions points to a number of mechanisms that we have yet to identify nearly all records show a neoglacial cooling from 2 ka bp onwards there is no evidence along the east antarctic coastline for an equivalent to the northern hemisphere medieval warm period and there is only weak circumstantial evidence in a few places for a cool event crudely equivalent in time to the northern hemisphere s little ice age there is a need for well dated high resolution climate records in coastal east antarctica and particularly in terre adelie dronning maud land and enderby land to fully understand the regional climate anomalies the disparity between marine and terrestrial records and to determine the significance of the heterogeneous temperature trends being measured in the antarctic today 2010 elsevier b v

holocene climate evolution in the high latitude southern hemisphere simulated by a coupled atmosphere sea ice ocean vegetation model the holocene climate is simulated in a 9000 yr long transient experiment performed with the ecbilt clio vecode coupled atmosphere sea ice ocean vegetation model this experiment is forced with annually varying orbital parameters and atmospheric concentrations of co2 and ch4 the objective is to study the impact of these long term forcings on the surface temperature evolution during different seasons in the high latitude southern hemisphere we find in summer a thermal optimum in the mid holocene 6 3 ka bp with temperatures locally 3 degrees c above the preindustrial mean in autumn the temperatures experienced a long term increase particularly during the first few thousand years the opposite trend was simulated for winter and spring with a relatively warm southern ocean at 9 ka bp in inter up to 3 5 degrees c above the preindustrial mean and a warm continent in spring 3 degrees c followed by a gradual cooling towards the present these long term temperature trends can be explained by a combination of 1 a delayed response to orbital forcing with temperatures lagging insolation by i to months owing to the thermal inertia of the system and 2 the long memory of the southern ocean this long memory is related to the storage of the warm late winter spring anomaly below the shallower summer mixed layer until next winter sea ice plays an important role as an amplifying factor through the ice albedo and ice insulation feedbacks our experiments can help to improve our understanding of the holocene signal in proxies for instance the results suggest that in contrast to recent propositions teleconnections to the northern hemisphere appear not necessarily to explain the history of southern hemisphere temperature changes during the holocene

holocene glacier and deep water dynamics adelie land region east antarctica abstract this study presents a high resolution multi proxy investigation of sediment core md03 2601 and documents major glacier oscillations and deep water activity during the holocene in the adelie land region east antarctica a comparison with surface ocean conditions reveals synchronous changes of glaciers sea ice and deep water formation at milankovitch and sub milankovitch time scales we report 1 a deglaciation of the adelie land continental shelf from 11 to 8 5 cal ka bp which occurred in two phases of effective glacier grounding line retreat at 10 6 and 9 cal ka bp associated with active deep water formation 2 a rapid glacier and sea ice readvance centred around 7 7 cal ka bp and 3 five rapid expansions of the glacier sea ice systems during the mid to late holocene associated to a long term increase of deep water formation at milankovich time scales we show that the precessionnal component of insolation at high and low latitudes explains the major trend of the glacier sea ice ocean system throughout the holocene in the adelie land region in addition the orbitally forced seasonality seems to control the coastal deep water formation via the sea ice ocean coupling which could lead to opposite patterns between north and south high latitudes during the mid to late holocene at sub milankovitch time scales there are eight events of glacier sea ice retreat and expansion that occurred during atmospheric cooling events over east antarctica comparisons of our results with other peri antarctic records and model simulations from high southern latitudes may suggest that our interpretation on glacier sea ice ocean interactions and their holocene evolutions reflect a more global antarctic holocene pattern

late holocene dynamics of sea surface temperature and terrestrial hydrology in southwestern africa southwest africa is an important region for paleo climatic studies being influenced by both tropical and temperate climate systems and thus reflecting the interplay of variable controls the aim of this study was to unravel the interaction of sea surface temperature sst changes in the southernmost benguela upwelling system with precipitation changes in south africa s winter rainfall zone wrz during the late holocene therefore a marine sediment core from the southernmost benguela upwelling system was investigated to reconstruct climate changes in this region for the past 2000 years grain size and geochemical analyses were conducted to reconstruct changes in fluvial sediment discharge and weathering intensity while sst changes were estimated using alkenone paleo thermometry results show that the southernmost benguela behaves distinctly in comparison with the rest of the benguela system reflecting amplified sst changes decreasing ssts accompanied increasing river discharge during times of increas

abrupt climate warming in east antarctica during the early holocene we report a centennial scale warming event between 8600 and 8400 cal bp from amery oasis east antarctica that is documented by the geochemical record in a lacustrine sediment sequence the organic carbon content the c s ratio and the sedimentation rate in this core have distinctly elevated values around 8500 y ago reflecting relatively warm and ice free conditions that led to well ventilated conditions in the lake and considerable sedimentation of both autochthonous and allochthonous organic matter on the lake bottom this abrupt warming event occurred concurrently with reported warm climatic conditions in the southern ocean while the climate in central east antarctic remained cold the comparison of the spatial and temporal variability of warm climatic periods documented in various terrestrial marine and glacial archives from east antarctica elucidates the uniqueness of the centennial scale warming event in the amery oasis we also discuss a possible correlation of the amery warming event with the abrupt climatic deterioration around 8200 cal bp on the northern hemisphere 2007 elsevier ltd all rights reserved

late holocene multi proxy records of environmental change on the south atlantic island tristan da cunha sediment stratigraphies from three sites one lake one overgrown lake and an exposed section on the island tristan da cunha in the temperate south atlantic were analysed by means of pollen analysis total carbon nitrogen and sulphur content determination magnetic susceptibility measurements and detailed radiocarbon dating the aim of these studies was to reconstruct the late holocene vegetation and climatic variations the oldest sediment sequence extends back to 2300 cal years bp the vegetation was relatively stable up to the arrival of humans in the 17th century the appearance of the introduced taxon rumex acetosa acetosella at c 300 cal years bp and a subsequent decline in forest cover on the lowland plain provide evidence of substantial human influence on the vegetation well before the establishment of the first permanent settlement in the 19th century before the first anthropogenic influence centennial scale fluctuations in the proxy records are interpreted as reflections of local hydrological changes probably caused by variations in precipitation as inferred mainly from changing proportions of pollen derived from telmatic and terrestrial taxa and corresponding changes in the deposition of mineral matter by fluvial erosion lake levels were low between c 1450 and 1050 cal years bp and high between c 1050 and 300 cal years bp these variations coincide with known climatic changes in southern africa and in the north atlantic suggesting that the inferred hydrological changes on tristan da cunha were related to large scale variations in the general oceanic and atmospheric circulation in the atlantic region

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

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

climate response to basin specific changes in latitudinal temperature gradients and implications for sea ice variability we use experiments with the giss general circulation model to investigate how changes in latitudinal temperature gradients affect atmospheric circulation in different ocean basins with particular attention paid to the implications for high latitude sea ice the results are relevant to both estimated past climate changes current climate gradient changes e g el nino southern oscillation events and proposed future climate responses to greenhouse gases sea surface temperature gradients are increased decreased in all ocean basins and in the pacific and atlantic separately without changing sea ice or global average temperature additional experiments prescribe sea ice growth reduction with global cooling warming as expected increased gradients strengthen the subtropical jet stream and deepen the subpolar lows in each hemisphere but results in the northern and southern hemispheres differ in fundamental ways in the northern hemisphere increased storm intensities occur in the ocean basin with the increased gradient in the southern hemisphere the deeper storms occur in the ocean basin with the decreased gradient alterations of the gradient in one ocean basin change longitudinal temperature gradients an increased gradient in one basin from tropical heating results in subsidence in the tropics in the other basin mimicking the effect of a decreased gradient in that basin the subtropical jet is therefore strengthened over the basin with the increased gradient and decreased over the other ocean basin hence in many respects regional effects such as the strength of subpolar lows in an individual basin are amplified when the gradient changes are of opposite sign in the two ocean basins the southern hemisphere response occurs because gradient increases in one ocean basin by strengthening the subtropical jet shift storm tracks equatorward and away from the potential energy source associated with cold air advection from antarctica at the same time with a weaker subtropical jet in the other basin storms move poleward and strengthen this latter effect may explain observed sea ice variations that are out of phase in the atlantic and pacific ocean basins in the southern hemisphere referred to as the antarctic dipole as well as upper ocean variability in the weddell gyre gradient changes produce little effect on sea level pressure in the arctic unless sea ice is changed with arctic sea ice reductions the sea ice response acts as a positive feedback inducing cyclonic circulation changes that would enhance its removal as may be occurring due to the current high phase of the north atlantic oscillation

sea ice seasonality during the holocene adelie land east antarctica abstract thin sections of laminated cores from different antarctic coastal areas have demonstrated the potential of diatom species to document climate change at the seasonal scale here we present the relative abundances of four diatom species and species groups fragilariopsis curta group as a proxy for yearly sea ice cover f kerguelensis as a proxy for summer sea surface temperature chaetoceros hyalochaete resting spores as a proxy for spring sea ice melting and the thalassiosira antarctica group as a proxy for autumn sea ice formation in core md03 2601 retrieved off adelie land on the antarctic continental shelf these abundances were compared to surface temperatures and sea ice cover modelled over the last 9000 years both the marine records and the simulated climate demonstrated a cooler early holocene 9000 7700 years bp a warmer mid holocene 7700 4000 years bp and a colder late holocene 4000 1000 years bp yearly sea ice cover followed an inverse pattern to temperatures with less sea ice during the mid holocene hypsithermal than during the late holocene neoglacial however diatom census counts and model output indicate that sea ice spring melting happened earlier in the season as expected but that autumn sea ice formation also occurred earlier in the season during the hypsithermal than during the colder neoglacial thereby following seasonal changes in local insolation

holocene long and short term climate changes off adelie land east antarctica diatom data from a marine sediment core give insight on holocene changes in sea surface conditions and climate at high southern latitudes off adelie land east antarctica the early to mid holocene was warmer than the late holocene with a transition at 4000 calendar years b p sea ice was less present and spring summer growing season was greater during the warm period relative to the cold one thus limiting sea ice diatom production and favoring more open ocean diatom to develop the long term holocene climatic evolution in east antarctica is explained by a combination of a delayed response to local seasonal insolation changes coupled to the long memory of the southern ocean abrupt variations of the diatom relative abundances indicating rapid climate changes are superimposed to the holocene long term trends spectral analyses calculate robust frequencies at 1600 a where a is years 1250 a 1050 a 570 a 310 a 230 a 150 125 a 110 a 90 a and 66 a such periods are very close to solar activity cyclicities except for the periods at 310 a and 1250 a which are close to internal climate variability cyclicities wavelet analyses estimate the same periods but indicate nonstationary cyclicities rapid climate changes at high southern latitudes may therefore be explained by a combination of external solar and internal thermohaline circulation forcings

high and low latitude climate control on the position of the southern peru chile current during the holocene 1 we reconstructed changes of temperature salinity and productivity within the southern peru chile current during the last 8000 years from a high resolution sediment core recovered at 41 s using alkenones isotope ratios of planktic foraminifera biogenic opal and organic carbon paleotemperatures and paleosalinities reached maximum values at 5500 years ago and thereafter declined to modern values whereas paleoproductivity continuously increased throughout the last 8000 years we ascribe these long term holocene trends primarily to latitudinal shifts of the antarctic circumpolar current acc the concurrence with shifts in the position of the southern westerlies points to a common response of atmospheric and oceanographic circulation patterns off southern chile millennial to centennial scale fluctuations of paleotemperatures and paleosalinities on the other hand lag displacements in the position of the southern westerlies but reveal a significant correlation to short term temperature changes in antarctica indicating a high latitude control of the acc at these timescales

holocene environmental changes on nightingale island south atlantic based on diatom floristic changes in an infilled pond a holocene diatom stratigraphy of 2nd pond a small filled pond on nightingale island 37 degrees 25 s 12 degrees 29 w was analyzed and interpreted to infer paleolimnological changes on tristan da cunha south atlantic the diatom assemblage of 2nd pond has the character of an acidic oligotrophic wetland and the diatom record suggests that 2nd pond most likely has been a bog wetland throughout most of the holocene the flora is largely dominated by pinnularia viridis a species typically found in peat bogs the flora also includes benthic and epiphytic gomphonema sp achnanthes saxonica frustulia cf rhomboides staurosira venter as well as pinnularia cf divergens var decrescens and eunotia paludosa var paludosa peaks of aerophytic diatom i e mostly diadesmis spp and luticola spp abundances and concentrations correspond to increased magnetic susceptibility and slightly higher c n ratios and are interpreted to be the result of increased catchment erosion due to precipitation and following increased in wash of terrestrial diatoms the diatom record suggests dry conditions in the early holocene followed by recurrent periods of increased precipitation in the region at 8600 5600 cal a bp and at 2200 1700 cal a bp the main causes for these hydrological changes are probably changes in intensity and or position of the southern hemisphere west wind belt c 2013 elsevier b v all rights reserved less

last glacial holocene climate variability in the atlantic sector of the southern ocean abstract the southern ocean plays a major role in the glacial interglacial global carbon cycle however there is a substantial lack of information from its antarctic zone south of the polar front pf to understand key climate processes e g sea ice variability productivity changes co2 source region shifts of the southern westerly wind active in this region during the glacial interglacial transition due to the limited high resolution sediment records from this area to close this gap we investigated high resolution diatom records from a series of sediment cores from the atlantic and western indian sectors of the southern ocean between the modern pf and the winter sea ice wsi edge summer sea surface temperature ssst and sea ice information spanning the past 30 thousand years were derived from diatom transfer functions and indicators which augment comprehensive information on past surface ocean conditions and related ocean and atmospheric circulation as well as opal deposition these complementary lines of evidences also provide important environmental boundary conditions for climate simulations understanding the past climate development in the high latitudes southern ocean our reconstructions show that the last glacial lg sssts south of the modern pf are 1 3 c colder than modern conditions wsi expanded to the modern pf our data suggests effective carbon export in the antarctic zone during the lg deglacial two steps of warming support the bipolar seesaw mechanism antarctic zone is an important source region for the co2 deglacial increase the warming was more suppressed towards south due to continuous ice discharge from antarctica the sssts exceeded modern values during the early holocene optimum when wsi extent probably retreated south of its modern position the southern boundary of maximum opal deposition zone may have shifted to south of 55 s in the bouvet island area at this time the mid late holocene cooling with wsi re expanding to the bouvet island area probably related to enhanced cold water export by the weddell gyre from the developing cavity under the west antarctic ice shelf the cooling also suggests a northward shift of the southern westerly wind at least its southern boundary

seismic imaging of a convergent continental margin and plateau in the central andes andean continental research project 1996 ancorp 96 1 a 400 km long seismic reflection profile andean continental research project 1996 ancorp 96 and integrated geophysical experiments wide angle seismology passive seismology gravity and magnetotelluric depth sounding across the central andes 21 s observed subduction of the nazca plate under the south american continent an east dipping reflector nazca reflector is linked to the down going oceanic crust and shows increasing downdip intensity before gradual breakdown below 80 km we interpret parts of the nazca reflector as a fluid trap located at the front of recent hydration and shearing of the mantle the fluids being supplied by dehydration of the oceanic plate patches of bright quebrada blanca bright spot to more diffuse reflectivity underlie the plateau domain at 15 30 km depth this reflectivity is associated with a low velocity zone p to s wave conversions the upper limits of high conductivity and high vp vs ratios and to the occurrence of neogene volcanic rocks at surface we interpret this feature as evidence of widespread partial melting of the plateau crust causing decoupling of the upper and lower crust during neogene shortening and plateau growth the imaging properties of the continental moho beneath the andes indicate a broad transitional character of the crust mantle boundary owing to active processes like hydration of mantle rocks in the cooler parts of the plate margin system magmatic underplating and intraplating under and into the lowermost crust mechanical instability at moho etc hence all first order features appear to be related to fluid assisted processes in a subduction setting

holocene climate and vegetation dynamics on nightingale island south atlantic an apparent interglacial bipolar seesaw in action abstract high resolution analyses of a sediment sequence from an in filled lake on nightingale island at 37 s in the south atlantic have revealed hydrological variations during the last 10 700 cal yr bp which are linked to shifts in the southern hemisphere westerlies and the meridional overturning circulation moc in the atlantic the lowermost part of the sequence 10 700 8600 cal yr bp consists of peat the peat is overlaid by gyttja which continues up to the final overgrowing of the basin around 500 years ago the transition from peat to gyttja at 8600 cal yr bp implies a significant increase in effective humidity probably caused by a northward shift of the southern hemisphere westerlies after the end of the antarctic thermal optimum recurring phases of increased erosion with high deposition of minerogenic particles terrestrial organic matter high c n ratios and pollen grains from plant taxa growing in more distal parts of the catchment indicate periods with higher precipitation these high precipitation periods correspond to periods of southward shifted southern hemisphere westerlies inferred from south america and with periods of weaker moc in the north atlantic therefore we conclude that these periods also characterized by decreased influence from marine aerosols were not caused by the stronger westerlies but by weaker moc and less heat transport from the south to the north atlantic causing warmer sea surface temperatures ssts and increased precipitation in the south atlantic this is the expression of the bipolar seesaw mechanism and implies that it may have been operational also during interglacial conditions

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

ice core evidence for secular variability and 200 year dipolar oscillations in atmospheric circulation over east antarctica during the holocene two holocene ice core records from east antarctica vostok and epica dome c were analysed for dust concentration and size distribution at a temporal resolution of 1 sample per 50 years a series of volcanic markers randomly distributed over the common part of the ice cores from 9 8 to 3 5 kyear bp ensures accurate relative dating 33 years dust size records from the two sites display oscillations structured in cycles with sub millennial and secular scale frequencies that are apparently asynchronous the power spectra of the composite sum of the two dust size records display spectral energy mostly for 150 to 500 year periodicities on the other hand the 200 year band is common to both records and the 200 year components of the two sites are out of phase 100 year lead or lag over 5 5 kyear a phenomenon also reflected by a significant 99 conf lev band in the power spectra of the composite difference of the two size records during long range transport mineral dust originating from the southern hemisphere continents is graded to a variable extent depending on the altitude and duration of atmospheric transport relatively coarse dust is associated with air mass penetration from the middle lower troposphere and conversely relatively fine dust with upper troposphere air masses or the influence of subsidence over the antarctic plateau a hypothesis already proposed for the changes that occurred during the last glacial maximum to holocene transition delmonte et al 2004b moreover we assume that the overall fluctuation of air mass advection over antarctica depends on the meridional pressure gradient with respect to low latitudes i e the antarctic oscillation aao we therefore suggest a regional variability in atmospheric circulation over east antarctica the 150 500 year power spectrum of the composite parameter represents the long term variability of the aao imprinted by secular internal oscillations probably related to the southern ocean climatic system on the other hand the dust composite parameter suggests a persistent atmospheric dipole over east antarctica delivering coarser finer dust particles alternatively to vostok and dome c regions with a bi centennial periodicity indeed a seesaw phenomenon in dust size distribution was already observed at three east antarctic sites during the last deglaciation delmonte et al 2004b and was interpreted as a progressive reduction of the eccentricity of the polar vortex with respect to the geographic south pole interestingly the parameter shows a pronounced 200 year oscillation mode throwing new light on the unresolved question of a possible relationship between climate and solar activity

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

high resolution record of holocene climate change dynamics from southern africa s temperate tropical boundary baviaanskloof south africa abstract south africa s southern cape is a highly dynamic climatic region that is influenced by changes in both temperate and tropical atmospheric and oceanic circulation dynamics recent research initiatives suggest that the major elements of the regional climate system have acted both independently and in combination to establish a mosaic of distinct climate regions and potentially steep climate response gradients across the southern cape to consider this further we present new high resolution 13c and 15n data from a rock hyrax procavia capensis midden from baviaanskloof in the cape fold mountains of south africa s eastern cape province spanning the last 7200 years these data provide detailed information regarding environmental changes in the mid and late holocene allowing us to assess the spatio temporal nature of climate change anomalies across the wider region throughout the full duration of the record a negative correlation between humidity and palaeotemperature reconstructions from nearby cango cave is observed in conjunction with correlations with southern ocean sea surface temperatures and sea ice presence we infer a dominant influence of the southern westerlies in determining multi millennial scale hydroclimate variability at shorter multi centennial to millennial timescales the baviaanskloof data indicate a clearer expression of tropical influences highlighting a delicate balance between the mechanisms driving regional climate dynamics across timescales and the sensitivity of the region to changes in global boundary conditions

deglacial environments in eastern prydz bay east antarctica abstract a high resolution continuous record of diatom census counts and diatom specific biomarkers in sediment core nbp0101 jpc24 allows assessment of oceanographic and environmental conditions in eastern prydz bay during the deglaciation 11 100 9000 cal yr bp at decadal timescale our study improves previous snapshots investigations based on resin embedded thin sections and presents a new proxy that compliments the diatom census counts our results suggest that the ice sheet retreat over the core site is dated at 11 100 cal yr bp setting the onset of local deglaciation and subsequent open marine conditions the glacial retreat in prydz bay is due to global warming initiated at 18 cal ka bp and the regional development of the prydz bay cyclonic gyre our results further demonstrate that the deglaciation in eastern prydz bay can be separated in four phases the first between 11 100 and 10 900 cal yr bp when the ice shelf was proximal and sea ice was almost perennial the second and the third phases between 10 900 10 400 cal yr bp and 10 400 9900 cal yr bp respectively when the ice shelf retreated and seasonal sea ice cycle consequently developed promoting warmer water to pump into the bay within the gyre which in turn forced the ice shelf recession and the yearly sea ice cycle establishment and the fourth between 9900 and 9000 cal yr bp when holocene condition were set with a recurrent seasonal sea ice cycle and a well established prydz bay gyre

holocene antarctic climate variability from ice and marine sediment cores insights on ocean atmosphere interaction abstract holocene climate variability in the southeast atlantic sector of the southern ocean and antarctic is assessed and quantified through integration of available marine sediment core and antarctic ice core data we use summer sea surface temperature ssst and sea ice presence sip reconstructions from two marine sediment cores recovered north 50 s and south 53 2 s of the present day antarctic polar front apf as well as an atmospheric temperature and sea ice proxy from the epica ice core from dronning maud land edml we find reasonably good agreement in the timing of climate evolution in the analyzed series almost all records show a gradual glacial to holocene climate transition interrupted by the antarctic cold reversal around 13 000 cal yr bp and early holocene climatic optimum hco at about 11 000 cal yr bp during the early hco the seasonal ice cover retreats to south of 53 s it then readvances in the course of the mid to late holocene the maximum winter sea ice edge position during the recent 10 000 years varied mainly within 51 53 s with sporadic growth to north of 50 s a position similar to that during the last glacial the onset of the neoglacial period after ca 4000 yr bp is associated with a steepening of the ssst gradient between the marine core sites strengthening of the westerlies and cooling in the inland ice sheet the agreement in timing between elevated ssst during the early hco and decreased deuterium excess in edml and other ice cores from different locations in the east antarctic suggests that the retreat of sea ice during the early hco and weakening of the apf was a general feature of the east antarctic climate during that time

late holocene palaeolimnological and climate dynamics at princessvlei south africa evidence from diatoms the cape flats region situated in the winter rainfall zone of south africa is a low lying tombolo underlain by recent fluvial and aeolian sands and characterised by numerous small lakes and wetlands one of these is princessvlei a eutrophic freshwater coastal lake the lake lies in an inter dunal depression encroached on in the more recent past by high density residential industrial and agricultural land uses a 210 cm core extracted from the lake periphery yielded high diatom fossil concentrations for the upper 174 cm princessvlei appears to oscillate between two ecologically stable states namely a state characterised by clear water oligotrophic benthic communities and a turbid state dominated by eutrophic planktonic species the two stable ecological states are interpreted to be a function of the relative dominance of catchment precipitation or groundwater influx which augments the open water conditions from 2600 to 1500 cal bp 173 135 cm the system is predominantly turbid with greater

application of modern analog technique to marine antarctic diatoms reconstruction of maximum sea ice extent at the last glacial maximum modern analog technique mat applied to antarctic diatoms is a new approach for quantitative sea ice paleoreconstructions in the southern ocean in a first step we show that mat is a better approach than the imbrie and kipp method to reconstruct the modern sea ice pattern we then use this approach to reconstruct sea ice presence in number of months per year during the last glacial maximum lgm at this time sea ice presence was greater than today leading to a shorter diatom growing season the maximum sea ice extent inferred from quantitative values of sea ice presence was located 5 8 north of its actual position leading to double the surface of modern winter sea ice this greater sea ice extent may have played a significant role on atmospheric and surface oceanic circulations and therefore on southern mid latitude and high latitude climates it may also have reduced the amount of heat moisture and co2 from the ocean to the atmosphere thus participating in the lowering of atmospheric co2 during the lgm

evidence from wavelet analysis for a mid holocene transition in global climate forcing a strong mid holocene transition has been identified by wavelet analyses in several sea ice cover records from the circum antarctic area ice core records taylor dome byrd and tropical marine records the results are compared with those previously published in a synthesis of north atlantic records and with 4 new records from the norwegian and icelandic seas and from a coastal site in ireland these new records confirm the previous pattern for the north atlantic area extend this pattern nearly to the arctic circle and include a continental record we further tested the possibility of extending this scheme using continental records from south america the holocene pattern proposed here confirms the importance of external forcing during the early holocene solar activity 1000 years cyclicity and 2500 years during the entire holocene even if the signal is disturbed by meltwater fluxes the second part of the holocene is then marked by the gradual appearance of internal forcing thermohaline circulation around 1500 years associated with a stabilisation of the signal coupling between ocean and atmosphere seems to play a fundamental role in the observed frequencies which vary accordingly in the atlantic circum antarctic and pacific areas the north atlantic area seems to be the instigator of thermohaline circulation as shown by its sensitivity to meltwater discharges during the early holocene even though each sector is independent with regards to its frequency content around 1600 years for atlantic area around 1250 years for antarctica the holocene methane pattern still under debate ruddiman w f 2003a orbital insolation ice volume and greenhouse gases quaternary science review 22 1597 1629 ruddiman w f 2003b the anthropogenic greenhouse era began thousands of years ago climatic change 61 261 293 could be explained by a more efficient thermohaline circulation around the mid holocene with an anthropogenic effect initiated at not vert similar2500 bp as shown by the inter hemispheric gradient

response of the high latitude northern hemisphere to orbital climate forcing evidence from the nordic seas sediment cores from the nordic greenland iceland and norwegian seas provide evidence that this area acts as an initial responder to the forcing effect of orbitally driven changes in insolation on the climate system as postulated by j imbrie et al the 18 o record of the cores documents a widespread initial deglacial signal in the area between 15 and 13 ka 1000 yr before other deglacial signals from other parts of the northern hemisphere an even earlier meltwater event has been dated to 16 090 185 yr b p north of iceland at the initial rise of northern hemisphere insolation after the last glacial maximum during the period with lowered surface salinities the nordic seas were still cold reconstructions of the surface water conditions of the area show that as the summer insolation values of the northern hemisphere reached half of maximum values a sea ice free corridor opened along norway at 13 4 ka nearly contemporaneous fluctuations of the polar front and the sea surface temperatures with the insolation changes indicate that the nordic seas are very sensitive to insolation forcing especially in regions close to the sea ice margin a decrease in sea surface temperature and an increase in the areal extent of sea ice cover since 7 ka indicate that the area is currently on the way to glacial conditions supporting the predictions made earlier by j imbrie et al

global characterization of the holocene thermal maximum we analyze the global variations in the timing and magnitude of the holocene thermal maximum htm and their dependence on various forcings in transient simulations covering the last 9000 years 9 ka performed with a global atmosphere ocean vegetation model in these experiments we consider the influence of variations in orbital parameters and atmospheric greenhouse gases and the early holocene deglaciation of the laurentide ice sheet lis considering the lis deglaciation we quantify separately the impacts of the background melt water fluxes and the changes in topography and surface albedo in the analysis we focus on the intensity of the maximum temperature deviation relative to the preindustrial level its timing in the holocene and the seasonal expression in the model the warmest htm conditions are found at high latitudes in both hemispheres reaching 5 c above the preindustrial level while the smallest htm signal is seen over tropical oceans less than 0 5 c this latitudinal contrast is mostly related to the nature of the orbitally forced insolation forcing which is also largest at high latitudes and further enhanced by the polar amplification the holocene timing of the htm is earliest before 8 ka bp in regions not affected by the remnant lis particularly nw north america e asia n africa n south america the middle east ne siberia and australia compared to the early holocene insolation maximum the htm was delayed by 2 3 ka over ne north america and regions directly downwind from the lis a similar delay is simulated over the southern ocean while an intermediate lag of about 1 ka is found over most other continents and oceans the seasonal timing of the htm over continents generally occurs in the same month as the maximum insolation anomaly whereas over oceans the htm is delayed by 2 3 months exceptions are the oceans covered by sea ice and north africa were additional feedbacks results in a different seasonal timing the simulated timing and magnitude of the htm are generally consistent with global proxy evidence with some notable exceptions in the mediterranean region sw north america and eastern eurasia 2012 elsevier ltd

an oceanic cold reversal during the last deglaciation a detailed deuterium excess profile measured along the dome c epica european project for ice coring in antarctica core reveals the timing and strength of the sea surface temperature changes at the source regions for dome c precipitation we infer that an oceanic cold reversal took place in the southern indian ocean 800 years after the antarctic cold reversal the temperature gradient between the oceanic moisture source and antarctica is similar to the dome c sodium profile during the deglaciation illustrating the strong link between this gradient and the strength of the atmospheric circulation

holocene southern ocean surface temperature variability west of the antarctic peninsula the antarctic peninsula is currently one of the fastest warming locations on earth but its long term variability has remained unclear amelia shevenell and colleagues now use the tex86 proxy a palaeothermometer that tracks membrane lipids of the marine picoplankton crenarchaeota to show that a long term cooling of about 4 c occurred in waters near the tip of antarctic peninsula over the past 12 000 years this is consistent with orbitally controlled changes in insolation shorter term variability in temperature seems to have been strongly influenced by the position of the westerly winds this work suggests that the present influence of the el nino southern oscillation system on the antarctic peninsula is a relatively recent phenomenon dating to the late holocene the antarctic peninsula is currently one of the fastest warming locations on earth but its long term variability has remained unclear this study uses tex86 sea surface temperature proxy evidence to show that a long term cooling of about 3 4 c occurred in waters near the tip of the antarctic peninsula over the past 12 000 years consistent with orbitally controlled changes in insolation shorter term variability in temperature at the antarctic peninsula appears to have been strongly influenced by the position of westerly winds the present influence of the el nino southern oscillation system on the antarctic peninsula may have arisen only during the late holocene the disintegration of ice shelves reduced sea ice and glacier extent and shifting ecological zones observed around antarctica1 2 highlight the impact of recent atmospheric3 and oceanic warming4 on the cryosphere observations1 2 and models5 6 suggest that oceanic and atmospheric temperature variations at antarctica s margins affect global cryosphere stability ocean circulation sea levels and carbon cycling in particular recent climate changes on the antarctic peninsula have been dramatic yet the holocene climate variability of this region is largely unknown limiting our ability to evaluate ongoing changes within the context of historical variability and underlying forcing mechanisms here we show that surface ocean temperatures at the continental margin of the western antarctic peninsula cooled by 3 4 c over the past 12 000 years tracking the holocene decline of local 65 s spring insolation our results based on tex86 sea surface temperature sst proxy evidence from a marine sediment core indicate the importance of regional summer duration as a driver of antarctic seasonal sea ice fluctuations7 on millennial timescales abrupt sst fluctuations of 2 4 c coincide with globally recognized climate variability8 similarities between our ssts southern hemisphere westerly wind reconstructions9 and el nino southern oscillation variability10 indicate that present climate teleconnections between the tropical pacific ocean and the western antarctic peninsula11 strengthened late in the holocene epoch we conclude that during the holocene southern ocean temperatures at the western antarctic peninsula margin were tied to changes in the position of the westerlies which have a critical role in global carbon cycling9 12

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

deep sea sedimentary analogs for the vostok ice core 1 many applications of the vostok ice core depend critically on the ability to make stratigraphic ties to marine records in the adjacent southern ocean here we present oxygen isotopic records from high accumulation rate sites in the south atlantic sector of the southern ocean collected for the purpose of complementing the recently extended d record from the vostok ice core the combination of several planktonic foraminiferal 18o records from northern subantarctic piston cores demonstrates that all of the millennial scale oscillations expressed in the vostok ice core over the last 60 ky are also present in marine records the observations also support the assumption that the millennial scale oscillations common to both marine and ice archives are synchronous thus providing a rationale for extending the marine ice core comparison through the last 400 000 years making use of a marine drilled core odp site 1089 by aligning the phase of these common abrupt events we anchor the vostok chronology to an orbitally tuned marine sediment chronology a refinement that allows examination of a variety of paleoclimatological issues such as the relationship between deep ocean variability and antarctic polar climate for example this exercise suggests that over at least the 4 major deglaciation events the primary orbital scale changes in the chemistry and most likely the temperature of the deep southern ocean were synchronous with changes in atmospheric pco2 and polar air temperatures we also find that the deuterium excess in the ice core resembles marine foraminiferal 13c records and that the deuterium excess is synchronous with an anomalous foraminiferal 18o signal the residual between normalized versions of vostok d and foraminiferal 18o these observations demand a tight link between the vostok isotopic record and the air sea interaction of the subantarctic zone

chronology of the palmer deep site antarctic peninsula a holocene palaeoenvironmental reference for the circum antarctic palmer deep sediment cores are used to produce the first high resolution continuous late pleistocene to holocene time series from the antarctic marine system the sedimentary record is dated using accelerator mass spectrometer radiocarbon methods on acid insoluble organic matter and foraminiferal calcite fifty four radiocarbon analyses are utilized in the dating which provides a calibrated timescale back to 13 ka bp reliability of resultant ages on organic matter is assured because duplicates produce a standard deviation from the surface age of less than laboratory error i e 50 years in addition surface organic matter ages at the site are in excellent agreement with living calcite ages at the accepted reservoir age of 1260 years for the antarctic peninsula spectral analyses of the magnetic susceptibility record against the age model reveal unusually strong periodicity in the 400 200 and 50 70 year frequency bands similar to other high resolution records from the holocene but so far unique f

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

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

holocene sea surface temperature variability in the chilean fjord region here we provide three new holocene 11 0 cal ka bp alkenone derived sea surface temperature sst records from the southernmost chilean fjord region 50 53 s sst estimates may be biased towards summer temperature in this region as revealed by a large set of surface sediments the holocene records show consistently warmer than present day ssts except for the past 0 6 cal ka bp however they do not exhibit an early holocene temperature optimum as registered further north off chile and in antarctica this may have resulted from a combination of factors including decreased inflow of warmer open marine waters due to lower sea level stands enhanced advection of colder and fresher inner fjord waters and stronger westerly winds during the mid holocene pronounced short term variations of up to 2 5 c and a cooling centered at 5 cal ka bp which coincides with the first neoglacial glacier advance in the southern andes are recorded the latest holocene is characterized by two pronounced cold events centered at 0 6 and 0 25 cal ka bp i e during the little ice age these cold events have lower amplitudes in the offshore records suggesting an amplification of the sst signal in the inner fjords

late cenozoic deformation and uplift of the western flank of the altiplano evidence from the depositional tectonic and geomorphologic evolution and shallow seismic activity northern chile at 19 30 s 1 we analyze the west vergent thrust system wts along the western flank of the altiplano in northern chile 18 s 21 s in our study area 19 20 s 19 50 s the wts consists of three thrust propagation monocline folds flexures developing growth strata the relative uplift accommodated by the flexures is rapid between 26 and 8 ma 0 1 mm yr diminishing to 0 02 mm yr after 8 ma approximately 2000 m of relative surface uplift was accommodated by the flexures since the late oligocene sedimentological and geomorphological analysis shows that westward tilting of the forearc occurred after 10 ma coeval with the shifting of deformation from the altiplano to the sub andean zone where the underthrusting of the brazilian craton would have resulted in crustal thickening surface uplift in the orogen and westward ductile subcrustal flow forearc tilting is accommodated by east vergent thrusts ets issued from the benioff zone beneath the central depression emerging into the western cordillera contributing 500 1400 m of surface uplift the wts connects the ets in the brittle ductile crustal transition 25 km depth continuing farther east as the altiplano low velocity zone configuring the western altiplano as a crustal scale fault bend fold forearc tilting would be caused by westward ductile flow in the lower crust pushing the rigid forearc in the ets meanwhile between 19 s and 21 s the wts accommodates dextral strike slip and 3 km of n s shortening occurred in the coastal cordillera transcurrence and strain partitioning are probably the result of slight plate convergence obliquity strong coupling within the interplate zone westward continental concavity and high elevation opposing horizontal contraction