circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

two basin filling boxes the convection induced by turbulent buoyant plumes in a rectangular filling box baines and turner 1969 is extended to situations where the lower depths of the box are divided into two basins by a vertical barrier the barrier restricts horizontal spreading and allows the interbasin exchange of water to occur only in the common region above the barrier height one and two plume systems are considered in the two plume case it is assumed that each of the plumes arises from an independent buoyancy source above each basin the resulting two basin circulation is characterized by different stratifications in each basin and by an overflow from one basin into the other the spreading depths of the plumes and ambient stratification depend on the barrier height relative basin sizes and in the two plume case the relative strengths of the two buoyancy fluxes these results may be of relevance to multibasin seas and oceans where the circulation produced by near surface sources of intermediate and deep water is influenced by underwater ridges

interhemispheric synchrony of late glacial climatic instability as recorded in proglacial lake mascardi argentina several high resolution continental records have been reported recently in sites in south america but the extent to which climatic variations were synchronous between the northern and southern hemispheres during the late glacial holocene transition and the causes of the climatic changes remain open questions previous investigations indicated that east of the andes the middle and high latitudes of south america warmed uniformly and rapidly from 13 000 14c yr bp with no indication of subsequent climate fluctuations equivalent for example to the younger dryas cooling here we present a multiproxy continuous record radiocarbon dated by accelerated mass spectroscopy from proglacial lake mascardi in argentina the results show that unstable climatic conditions comparable to those described from records obtained in the northern hemisphere dominated the late glacial holocene transition in argentina at this latitude furthermore a significant advance of the tronador ice cap which feeds lake mascardi occurred during the younger dryas chronozone this instability suggests a step wise climatic history reflecting a global rather than regional forcing mechanism the lake mascardi record therefore provides strong support for the hypothesis that ocean atmosphere interaction rather than global ocean circulation alone governed interhemispheric climate teleconnections during the last deglaciation 1997 john wiley sons ltd

effects of strait mixing on ocean stratification the density distribution in the abyssal atlantic ocean suggests that mixing associated with overflows across deep sills may account for substantial amounts of deep mixing estimates of the strait mixing are made from published estimates of the overflows and the difference between antarctic bottom water densities across the vema channel and the romanche fracture zone to demonstrate that the strait mixing is an order of magnitude larger than the abyssal mixing estimated for a standard diffusivity of 1 times 10 ndash 4 m2 s ndash 1

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

comment on glacial geomorphology and chronology of deglaciation south georgia sub antarctic by m j bentley d j a evans c j fogwill j d hansom d e sugden p w kubik

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

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

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

circulation and deep water export at the western exit of the subpolar north atlantic the current system east of the grand banks was intensely observed by world ocean circulation experiment woce array acm 6 during 1993 95 with eight moorings reaching about 500 km out from the shelf edge and covering the water column from about 400 m depth to the bottom more recently a reduced array by the institut fur meerskunde ifm at kiel germany of four moorings was deployed during 1999 2001 focusing on the deep water flow near the western continental slope both sets of moored time series each about 22 months long are combined here for a mean current boundary section and both arrays are analyzed for the variability of currents and transports a mean hydrographic section is derived from seven ship surveys and is used for geostrophic upper layer extrapolation and isopycnal subdivision of the mean transports into deep water classes the offshore part of the combined section is dominated by the deep reaching north atlantic current nac with currents still at 10 cm s 1 near the bottom and a total northward transport of about 140 sv sv 106 m3 s 1 with the details depending on the method of surface extrapolation used the mean flow along the western boundary was southward with the section mean north atlantic deep water outflow determined to be 12 sv below the 27 74 kg m 3 isopycnal however east of the deep western boundary current dwbc the deep nac carries a transport of 51 sv northward below 27 74 kg m 3 resulting in a large net northward flow in the western part of the basin from watermass signatures it is concluded that the deep nac is not a direct recirculation of dwbc water masses transport time series for the dwbc variability are derived for both arrays the variance is concentrated in the period range from 2 weeks to 2 months but there are also variations at interannual and longer periods with much of the dwbc variability being related to fluctuations and meandering of the nac a significant annual cycle is not recognizable in the combined current and transport time series of both arrays the moored array results are compared with other evidence on deep outflow and recirculation including recent models of different types and complexity

basin modelling of the sw barents sea abstract the sw barents sea is an epicontinental platform consisting of n to nne oriented basins separated by basement highs the basins were formed during four distinct rift phases in the carboniferous late permian late jurassic early cretaceous and paleocene eocene progressive rifting culminated in continental breakup and seafloor spreading along the north atlantic axis approximately at 55 ma we present tectonic and thermal models of basin evolution along two seismic profiles crossing the sw barents sea the thermal and isostatic history of basins is constrained through time forward basin modelling based on an automated inverse basin reconstruction approach we estimate the effects of continental breakup and near margin processes magmatic underplating and sill intrusions on the thermal history and kerogen maturity below the vestbakken volcanic province basin models are calibrated against well data the results imply that both breakup and underplating alter the thermal and isostatic history of sediments along the margin the hydrocarbon potential of source rocks modelled along the margin suggests breakup has a permanent thermal effect on the present day sediments promoted by lateral heat flow while heat conduction by underplating is more diffuse inhibited to some degree by deeply buried low conductivity shales and limestones

a shift towards wetter and windier conditions in southern sweden around the prominent solar minimum 2750 cal a bp a variety of palaeoclimatic records show a shift towards cooler wetter and windier conditions in europe around 2800 cal a bp the shift broadly coincides with an increase of the atmospheric c 14 concentration suggesting a connection between solar activity variations and climate change here we investigate a peat record from undarsmosse in southern sweden in a previous study based on a low resolution chronology this record showed increased aeolian sand influx and sphagnum spore content around 2800 cal a bp indicating high storm activity and wetter conditions we applied the c 14 wiggle match dating technique on the same record to construct a robust chronology to evaluate the temporal relationship to solar forcing in addition we performed plant macrofossil analysis to determine local vegetation changes based on the new chronology a shift to a sphagnum dominated bog representing wetter conditions and the onset of a period with increased storminess occurred around 2700 cal a bp these changes are within age model uncertainties synchronous with climatic changes inferred from other sites in europe suggesting a shift in the larger scale atmospheric circulation possibly triggered by decreased solar activity less

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

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

transdimensional change point modeling as a tool to investigate uncertainty in applied geophysical inference an example using borehole geophysical logs recently developed methods for inferring abrupt changes in data series enable such change points in time or space to be identified and also allow us to estimate noise levels of the observed data the inferred probability distributions of these parameters provide insights into the capacity of the observed data to constrain the geophysical analysis and hence the magnitudes and likely sources of uncertainty we carry out a change point analysis of sections of four borehole geophysical logs density neutron absorption sonic interval time and electrical resistivity using transdimensional bayesian markov chain monte carlo to sample a model parameter space the output is an ensemble of values which approximate the posterior distribution of model parameters we compare the modeled change points borehole log parameters and the variance of the noise distribution of each log with the observed lithology classes down the borehole to make an appraisal of the uncertainty characteristics inherent in the data our two examples one with well defined lithology changes and one with more subtle contrasts show quantitatively the nature of the lithology contrasts for which the geophysical borehole log data will produce a detectable response in terms of inferred change points we highlight the different components of variation in the observed data due to the geologic process dominant lithology changes that we hope to be able to infer geologic noise due to variability within each lithology and analytical noise due to the measurement process this inference process will be a practical addition to the analytical tool box for borehole and other geophysical data series it reveals the level of uncertainties in the relationships between the data and the observed lithologies and would be of great use in planning and interpreting the results of subsequent routine processing

sensitivity analysis in thermal and maturity modelling abstract knowledge about the present and past thermal structure in sedimentary basins is central to understanding the evolution of sedimentary basins and for success in hydrocarbon exploration the possibilities and limitations in resolving the palaeothermal structure by inversion of downhole temperature and vitrinite reflectance data are discussed by means of an example from the danish central trough the prediction of petroleum generation is sensitive to uncertainties in source rock temperature history and the kinetic parameters of kerogen degradation the effects of uncertainties in surface temperature heat flow depth of burial thermal resistivity structure and kinetic parameters are investigated using a previously developed stochastic method regarding the state of petroleum generation the number of safe statements based on numerical modelling essentially are reduced to three 1 the source rock has not generated significant amounts of petroleum 2 the source rock has released most of its petroleum potential or 3 the source rock has released some of its petroleum potential in the latter case the state of petroleum generation is best described by a cumulative distribution function of source rock transformation which reflects the effects of uncertainties in the basic modelling parameters the probability of occurrence of a particular transformation ratio value like those derived in traditional deterministic modelling is zero an example of application from the danish central trough is given

moho depth of the british isles a probabilistic perspective summary we present a new moho depth model of the british isles and surrounding areas from the most up to date compilation of moho depth estimates obtained from refraction reflection and receiver function data we use a probabilistic trans dimensional and hierarchical approach for the surface reconstruction of moho topography this fully data driven approach allows for adaptive parametrization assessment of relative importance between different data types and uncertainties quantification on the reconstructed surface our results confirm the first order features of the moho topography obtained in previous work such as deeper moho 29 36 km in continental areas e g ireland and great britain and shallower moho 12 22 km offshore e g in the atlantic ocean west of ireland resolution is improved by including recent available data especially around the porcupine basin onshore ireland and great britain ne trending features in moho topography are highlighted above the rockall high about 28 km and the rockall trough with a ne directed deepening from 12 to about 20 km a perpendicular se oriented feature moho depth 26 28 km is located between the orkney and the shetland extending further sw in the north sea onshore our results highlight the crustal thinning toward the n in ireland and an e w oriented transition between deep 34 km and shallow about 28 km moho in scotland our probabilistic results are compared with previous models showing overall differences around 2 km within the posterior uncertainties calculated with our approach bigger differences are located where different data are used between models or in less constrained areas where posterior uncertainties are high

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

the last termination in the south indian ocean a unique terrestrial record from kerguelen islands 49 s situated within the southern hemisphere westerly belt the awareness of the significance of the southern ocean in the earth s climate system has become increasingly obvious the deglacial atmospheric co2 rise during warming periods in antarctica has been attributed to co2 ventilation from the deep ocean caused by enhanced upwelling around the antarctic divergence it has been hypothesized that more intense southern hemisphere westerly winds aligned with the antarctic circumpolar current due to a southward shift of the wind belt from its last glacial maximum equator ward position are the main drivers reconstructions of past changes in atmospheric circulation in the southern hemisphere are still scarce and the overall picture is patchy with sometimes contradictory results for obvious reasons most terrestrial records originate from southern south america and new zealand here we present a terrestrial record from the indian sector of the southern ocean from kerguelen islands located at 49 s a peat record is investigated using a multi proxy approach pollen and plant macrofossils magnetic susceptibility xrf analyses biogenic silica content rock eval6 analysis and humification degree peat accumulation starts at about 16 000 cal yr bp with relatively warm and dry conditions the most prominent change in our proxy data occurs at 13 600 cal yr bp when peat ponds were established on the peat surface resulting in lacustrine type deposits as a result of very high humidity and with proxies implying very windy conditions within chronological uncertainties this onset coincides with the onset of the so called oceanic cold reversal based on the deuterium excess data in the epica dome c ice core record kerguelen islands are located in the moisture source area of dome c and a change in atmospheric circulation at that time could explain both records around 12 900 cal yr bp at the end of the antarctic cold reversal pond lake sediments give way to more peaty deposits with proxies suggesting slightly drier less windy and probably warmer conditions kerguelen islands became less influenced by the southern hemisphere westerly winds and these conditions were amplified during the early holocene climate optimum as found in antarctic ice core records

a bayesian approach for thermal history reconstruction in basin modeling we present a novel method for the joint inversion of thermal indicator data vitrinite reflectance and apatite fission track and additional data bottom hole temperature and porosity for thermal history reconstruction in basin modeling a transdimensional and hierarchical bayesian formulation is implemented with a reversible jump markov chain monte carlo algorithm with a 1 d transient thermal model the objective of the inverse problem is to infer the heat flow history below a borehole given the data and a set of geological constraints e g burial histories and physical properties of the sediments the algorithm incorporates an adaptive data driven parametrization of the heat flow history allows for automatic estimation of the relative importance of each data type and quantification of parameter uncertainties and trade offs our approach deals with uncertainties on the imposed geological constraints in two ways first the amount of erosion and timing of an erosional event are treated as independent parameters second uncertainties on compaction parameters and surface temperature history are directly propagated into the final solution synthetic tests show that porosity data can be used to reduce uncertainties on the amount of erosion this work illustrates a truly probabilistic analysis of the trade off between the magnitude of erosion and variations in heat flow histories which is key in basin modeling the algorithm is then applied to real data from a well in the barents sea our algorithm can reconcile estimates of erosion from the thermal indicator and porosity data which is a difficult and subjective task in basin modeling

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

a bayesian partition modelling approach to resolve spatial variability in climate records from borehole temperature inversion summary collections of suitably chosen borehole profiles can be used to infer large scale trends in ground surface temperature gst histories for the past few hundred years these reconstructions are based on a large database of carefully selected borehole temperature measurements from around the globe since non climatic thermal influences are difficult to identify representative temperature histories are derived by averaging individual reconstructions to minimize the influence of these perturbing factors this may lead to three potentially important drawbacks the net signal of non climatic factors may not be zero meaning that the average does not reflect the best estimate of past climate the averaging over large areas restricts the useful amount of more local climate change information available and the inversion methods used to reconstruct the past temperatures at each site must be mathematically identical and are therefore not necessarily best suited to all data sets in this work we avoid these issues by using a bayesian partition model bpm which is computed using a trans dimensional form of a markov chain monte carlo algorithm this then allows the number and spatial distribution of different gst histories to be inferred from a given set of borehole data by partitioning the geographical area into discrete partitions profiles that are heavily influenced by non climatic factors will be partitioned separately conversely profiles with climatic information which is consistent with neighbouring profiles will then be inferred to lie in the same partition the geographical extent of these partitions then leads to information on the regional extent of the climatic signal in this study three case studies are described using synthetic and real data the first demonstrates that the bayesian partition model method is able to correctly partition a suite of synthetic profiles according to the inferred gst history in the second more realistic case a series of temperature profiles are calculated using surface air temperatures of a global climate model simulation in the final case 23 real boreholes from the united kingdom previously used for climatic reconstructions are examined and the results compared with a local instrumental temperature series and the previous estimate derived from the same borehole data the results indicate that the majority 17 of the 23 boreholes are unsuitable for climatic reconstruction purposes at least without including other thermal processes in the forward model

the intercept is a poor estimate of a calibrated radiocarbon age intercept based methods of generating a point estimate of a calibrated radiocarbon date are very popular but exhibit undesirable behaviour they are highly sensitive to the mean of the radiocarbon date and to adjustments of the calibration curve other methods give more stable results the weighted average of the probability distribution function is recommended as the best central point estimate but more consideration should be given to using the full probability distribution rather than a point estimate in developing age depth models

topographic control of oceanic flows in deep passages and straits saddle points between neighboring deep ocean basins are the sites of unidirectional flow from one basin to the next depending on the source of bottom water flow in these sites appears to be topographically controlled so the interface between the bottom water and the water above adjusts itself to permit bottom water flow from the basin that contains a source of bottom water into the next examples in the atlantic include flow in the romanche fracture zone the vema channel the ceara abyssal plain the anegada jungfern passage and the discovery gap but there are many more theoretical predictions of volume flux using a method that requires only conductivity temperature depth data archives and detailed knowledge of bathymetry near the saddle point are compared with volume flux estimates using current meters and or geostrophic estimates for seven cases the ratio of prediction to volume flux estimate ranges from 1 0 to 2 7 some ocean straits that separate adjacent seas are also found to critically control bidirectional flows between basins theory of the influence of rotation on such critical flows is reviewed predictions of volume flux in eight cases are compared with ocean estimates of volume flux from traditional methods

when do marginal seas and topographic sills modify the ocean density structure 1 we ask what effect marginal seas at high latitudes have on the abyssal densities and stratification of the oceans although marginal seas are not necessary for the formation of dense abyssal waters topographic sills tend to restrict exchange flows and increase density differences laboratory experiments with a steady state large scale overturning circulation forced by a gradient in surface temperatures or heat fluxes show that a marginal sea and topographic sill influence the abyssal density when the sill depth is less than twice the oceanic thermocline depth the overflow over shallow sills interacts directly with the surrounding thermocline stratification decreasing the abyssal density relative to an ocean with no marginal sea and increasing the density difference between the sea and the ocean experiments show that the effect of the sill depends on the surface boundary conditions and indicate a larger response for conditions approaching a prescribed distribution of temperature rather than of heat flux application of the results to the north atlantic circulation suggests that the greenland scotland ridge is shallow enough to lead to a significant reduction of the density of north atlantic deep water and this is consistent with the conclusions from an analysis of water mass properties the greenland scotland ridge is therefore likely to have a significant effect on the density structure and heat transport in the global oceans

stochastic thermal history modelling 1 constraining heat flow histories and their uncertainty we introduce a novel application of the markov chain monte carlo mcmc method to address the problem of characterising uncertainties in modelled thermal histories as real data are never perfect uncertainties in measurement will be propagated through to final estimates of hydrocarbon volumes types and locations and therefore it is important to characterise the nature of the uncertainty at each stage of the modelling process here we specifically consider heat flow parameters used to generate thermal history models and illustrate the use of the mcmc method on both synthetic and real well data we show that this technique is able to both recover a good data fitting model and perhaps more importantly to characterise the uncertainties on every heat flow model parameter the approach described here is generally applicable for characterising the parameter uncertainties in various other aspects of basin modelling

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

terrestrial and submarine evidence for the extent and timing of the last glacial maximum and the onset of deglaciation on the maritime antarctic and sub antarctic islands this paper is the maritime and sub antarctic contribution to the scientific committee for antarctic research scar past antarctic ice sheet dynamics pais community antarctic ice sheet reconstruction the overarching aim for all sectors of antarctica was to reconstruct the last glacial maximum lgm ice sheet extent and thickness and map the subsequent deglaciation in a series of 5000 year time slices however our review of the literature found surprisingly few high quality chronological constraints on changing glacier extents on these timescales in the maritime and sub antarctic sector therefore in this paper we focus on an assessment of the terrestrial and offshore evidence for the lgm ice extent establishing minimum ages for the onset of deglaciation and separating evidence of deglaciation from lgm limits from those associated with later holocene glacier fluctuations evidence included geomorphological descriptions of glacial landscapes radiocarbon dated basal peat and lake sediment deposits cosmogenic isotope ages of glacial features and molecular biological data we propose a classification of the glacial history of the maritime and sub antarctic islands based on this assembled evidence these include type i islands which accumulated little or no lgm ice type ii islands with a limited lgm ice extent but evidence of extensive earlier continental shelf glaciations type iii seamounts and volcanoes unlikely to have accumulated significant lgm ice cover type iv islands on shallow shelves with both terrestrial and submarine evidence of lgm and or earlier ice expansion type v islands north of the antarctic polar front with terrestrial evidence of lgm ice expansion and type vi islands with no data finally we review the climatological and geomorphological settings that separate the glaciological history of the islands within this classification scheme

exchange through the strait of gibraltar to measure the exchange between the atlantic and mediterranean through the strait of gibraltar an array of current meter moorings was deployed for a year in the strait during 1985 1986 a novel aspect of these measurements is the inclusion of conductivity as well as temperature and pressure sensors on each current meter so that the salinity of the flows could be monitored continuously these salinity measurements determine the water mass characteristics of the flows crossing the sill they allow definition of the 37 psu isohaline as the interface between inflowing fresher atlantic water and outflowing saltier mediterranean water and they enable time series to be developed for the depth of this interface for the upper layer inflow and for the lower layer outflow from these measurements the time averaged outflow of mediterranean water is estimated to be 0 68sv 1sv 1 106m3s 1 and the outflow salinity transport defined to be the outflow times the salinity excess above a basic atlantic water salinity of 36 1 psu is estimated to be 1 50 103m3s 1 1sv 1psu 1 103m3s 1 equivalent to a net evaporation over the mediterranean basin of 52cm y 1 extrapolated measurements of the inflow from current meters generally deployed below 100m depth yield an estimate for the time averaged inflow of 0 93sv which is believed to be unrealistically high in view of the better measured outflow and net evaporation thus a more realistic estimate of the inflow is 0 72sv equal to the sum of the outflow and net evaporation as required by the mass budget for the mediterranean sea such estimates of the exchange are smaller by almost a factor of 2 than previous values for the exchange by lacombe and richez 1982 the exchange across the gibraltar sill is found to be due in nearly equal parts to the mean currents and to the tidal fluctuations the mean currents are smaller than had been expected reaching a peak value of only about 60 cm s 1 in the deep outflow over the sill the tidal exchange is due to a strong correlation over the tidal period between the depth of the interface and the strength of the inflowing currents for the m2 tide at the sill the amplitude of the interface depth is 51 m and the amplitude of the tidal currents is 1 2m s 1 furthermore the inflow and interface depth have similar phases as a consequence the upper layer is deep on the inflowing tide so that a large slug of atlantic water crosses the sill into the mediterranean on the outflowing tide the interface is shallow so that a large slug of mediterranean water crosses the sill into the atlantic similar processes occur for the s2 o1 and k1 tides though the amplitude are smaller in this manner tidal oscillations lead to a time averaged exchange of water masses across the gibraltar sill the inflow and outflow defined to be the instantaneous transports above and below the 37psu isohaline interface exhibit m2 tidal amplitudes of 2 3 sv and 1 3sv respectively thus the tides are large enough to reverse the mean upper layer inflow and lower layer outflow daily averaged inflow and outflow transports exhibit low frequency fluctuations with standard deviations of 0 37sv and 0 22sv respectively such low frequency fluctuations have been shown previously to be associated with barotropic flows through the strait of gibraltar compensating for sea level variations over the mediterranean due to atmospheric pressure fluctuations candela winant and bryden 1989 finally from these measurements there appear to be little fortnightly or annual period fluctuations in the exchange through the strait of gibraltar

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

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

intense mixing of the faroe bank channel overflow 1 the continuous swift flow of cold water across the sill of the faroe bank channel the deepest passage from the nordic seas to the north atlantic ocean forms a bottom attached dense plume overflow the amount and distribution of entrainment and mixing that the overflow encounters during its descent influence the ventilation of the deep north atlantic however remain poorly known due to lack of direct measurements using the first direct turbulence measurements we describe the dynamic properties and mixing of the overflow plume as it descends toward the iceland basin the vigorously turbulent plume is associated with intense mixing and enhanced turbulent dissipation near the bottom and at the plume ambient interface but with a quiescent core our measurements show a pronounced transverse circulation consistent with rotating plume dynamics a strong lateral variability in entrainment velocity and a vertical structure composed of order 100 m thick stratified interface and comparably thick well mixed bottom boundary layer with significant transport and entrainment

submaximal exchange between a convectively forced basin and a large reservoir if a sill enclosed basin connected to a large reservoir is suddenly subjected to a de stabilizing surface buoyancy flux it will first mix vertically by turbulent convection before the resulting lateral buoyancy gradient generates a horizontal exchange flow across the sill we present a study which examines the unsteady adjustment of such a basin under continued steady forcing it is shown through theoretical development and laboratory experimentation that two consecutive unsteady regimes characterized by different dynamic balances are traversed as the flow approaches a steady state once established the exchange flow is controlled at the sill crest where it is hydraulically critical in the absence of a lateral contraction the single control at the sill crest allows a range of submaximal exchange states with the flow at the sill being dependent not only on the forcing and geometrical parameters but also on mixing conditions within the basin which are in turn dependent on the sill exchange the sill basin system is therefore strongly coupled although it remains isolated from the external reservoir conditions by a region of internally supercritical flow results from the laboratory experiments are used to demonstrate the link between the forcing and the exchange flow at the sill steady state measurements of the interior mean velocity and buoyancy fields are also compared with previous analytical models

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

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

transformations of landscape and peat forming ecosystems in response to late holocene climate change in the western antarctic peninsula we used subfossil mosses and peats to document changes in regional climate cryosphere and terrestrial ecosystems in the western antarctic peninsula at 65 s latitude we find that most peat forming ecosystems have initiated since 2800 cal b p in response to warmer summers and increasing summer insolation the period at 900 600 cal b p was coldest as indicated by ice advance abundance of kill ages from ice entombed mosses exposed recently from retreating glacial ice and apparent gap in peatbank initiation furthermore the discovery of a novel antarctic hairgrass deschampsia antarctica peatland at 2300 1200 cal b p from the mainland antarctic peninsula suggests a much warmer climate than the present a warming and wetting climate in the 1980s caused very high carbon accumulation in a polytrichum strictum moss peatbank our results document dramatic transformations of landscape and ecosystems in response to past warmer climate providing a telltale sign for what may come in the future

faroe bank channel overflow 1995 2005 abstract the faroe bank channel fbc is the deepest passage across the greenland scotland ridge and there is continuous overflow of dense water through the channel which provides a substantial contribution to the global thermohaline circulation since november 1995 acoustic doppler current profilers adcps have been moored at the sill of the channel continuously except for short annual servicing periods in addition to this ctd sections have regularly been occupied across the channel and instruments recording temperature and salinity have been moored for short periods these observations demonstrate that the channel due to its small width can be monitored fairly well with only one adcp mooring and they allow the generation of a time series of overflow volume flux for the 1995 2005 period the kinematic overflow flux defined solely from the velocity field was found to have an average value of 2 1 0 2 sv with a seasonal and with inter annual variations of approximately 10 amplitude but with no discernible trend for the whole period the average flux of water with potential density exceeding 27 8 kg m 3 was found to be 1 9 0 3 sv with average properties 0 25 c s 34 93 28 01 kg m 3 for this period no evidence was found for a weakening overflow flux but the salinity of the fbc overflow especially the warmer parts has increased substantially during the period which implies an increased average density on the order of 0 01 kg m 3 previous observations of a helical cross channel circulation are confirmed and may explain the thin pycnocline layer but shear instability induces intensive mixing that puts a lower limit on the layer thickness critical control at one point of the sill cross section rather than friction seems to govern the overflow dynamics and simple layered models can explain much of the observed features as well as the seasonal variation but potential vorticity as defined for a single overflow layer is not conserved a previously suggested 1950 2000 weakening of the fbc overflow which was partly based on a subset of the data presented here is not supported by the full dataset

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

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

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

phase relationships between antarctic and greenland climate records comparison of climate records from antarctic and greenland ice cores shows that the two regions respond asynchronously during millennial scale climate changes the apparent out of phase relationship between the records has been described as a climate seesaw in which cooling in the northern hemisphere is balanced by warming in the southern hemisphere the same relationship has also been attributed to the initiation of climate change events in the southern hemisphere rather than the north atlantic as is conventionally assumed a simple statistical approach band pass filtering combined with lag correlation tests used to examine the phase relationships in more detail shows that neither an anti phase nor a phase lag relationship adequately describes the observations whereas antarctic and greenland climate records do exhibit approximate anti phase behavior about 50 of the time they are generally in phase during cooling a phase lead of southern hemisphere climate of 1000 1600 years is statistically indistinguishable from a lag of 400 800 years whether for dansgaard oeschger heinrich or longer duration events the seesaw or southern lead appearance of the data arises from the fundamentally different characteristics of the climate time series most importantly the absence of rapid warming events in antarctica comparable to those in greenland to be consistent with the observations climate models will need to capture these characteristics in addition to reproducing the correct phase relationships

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

the flux of dense cold overflow water southeast of iceland abstract from the period commencing midsummer 1990 and lasting for 13 months 13 current meters were deployed on seven moorings at depths between 1000 and 2300 m southeast of iceland 63 09 n 17 18 w to 61 44 n 15 24 w the purpose of the array designated woce acm8 was to measure the overflow of dense water downstream of the source in the faeroe bank channel and downstream of any sources on the iceland faeroe ridge in the depth range 1300 2100 m three of the moorings showed a bottom intensified current that was persistent and directed to the southwest at the other moorings the current was erratic and weak the records were combined to form a transport time series for water denser than 0 27 8 kg m 3 in the direction 240 a mean value of 3 2 0 5 sv was found with considerable variability near a period of seven days but there was no convincing evidence for a seasonal signal the amount of pure norwegian sea water present in the overflow was estimated at 1 6 0 15 sv close to previous determina

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

bi polar ocean linkages evidence from late holocene antarctic marine and greenland ice core records a continuous 14c dated palaeoenvironmental 4000 year proxy from the antarctic peninsula glacial marine record demonstrates pronounced cycles of elevated palaeoproductivity warm events that rec

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