successions of invertebrate microfossils and the late quaternary deglaciation of the central st lawrence lowland canada and united states abstract foraminiferal and ostracode assemblages in late glacial and early post glacial sediments of the central st lawrence lowland show that a proglacial lake glacial lake st lawrence preceded the champlain sea in some parts of the lowland and that the champlain sea was in contact with the laurentide ice sheet during deglaciation of other parts of the lowland glaciolacustrine and glaciomarine environments were followed by marine environments with salinity as high as 24 34 the higher salinity water in the champlain sea was part of a salt water wedge extending from the gulf of st lawrence into the central st lawrence lowland the beginning of the champlain sea is placed between 11 4 and 11 6 ka bp on the basis of radiocarbon ages for the arrival of the salt water wedge in the central st lawrence lowland the distribution of rhythmites associated with glacial lake st lawrence shows that subaqueous outwash fans in the ottawa area were deposited in glacial lake st lawrence rather than in the champlain sea

the last 7500 cal yr b p of westerly rainfall in central chile inferred from a high resolution pollen record from laguna aculeo 34 s abstract we report multiproxy analyses of a sediment core obtained from laguna aculeo that spans the past 7500 years laguna aculeo 33 50 s 70 55 w is one of the few natural inland lakes located in the mediterranean zone of central chile near the northern margin of the influence of the southern westerlies the record shows elevated pollen counts of halophytes and seasonally drying of the lake basin prior to 5700 cal yr b p indicating severe aridity and warmer than present conditions this was followed by the establishment of a fresh water lake along with an increase in arboreal and herbaceous plant diversity between 5700 and 3200 cal yr b p an intensification of this trend started at 3200 cal yr b p along with the abrupt decrease of halophytes until 100 cal yr b p within this humid period pollen accumulation rates show large amplitude fluctuations coeval with numerous turbidite layers suggesting a highly variable and torrential rainfall pattern this intense and variable precipitation regime is probably associated with the el nino southern oscillation enso phenomenon we suggest that the modern mediterranean climate of central chile was established at 3200 cal yr b p paleovegetation and paleolimnological changes starting at 100 cal yr b p correlate with documented human activity surrounding the lake

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

ostracod assemblages in late quaternary varved glaciomarine clay of the baltic sea yoldia stage in eastern middle sweden abstract four cored sites in eastern middle sweden have been analysed for their content of calcareous fossils the investigated sediments consist of late quaternary varved clay deposited during the baltic sea yoldia stage four regional palaeoecological units a d have been established unit a reflects ice proximal conditions unit b optimal conditions for the benthic fauna and unit c the termination of a saline phase in unit c oxygen deficiency might have occurred in the fourth unit d no fossils were found the fauna recorded is poor in taxa and indicates a weak marine influence the salinity was higher in the western part of the investigated area due to the proximity to the inlet of marine water the meltwater influx was high and the salinity probably fluctuated considerably the ostracod cytheromorpha macchesneyi brady and crosskey is reported for the first time in quaternary deposits from northwestern europe and indicates that a connection could have existed between the baltic and the white sea in late glacial times

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

postglacial vegetation fire and climate dynamics at central chilean patagonia lake shaman 44 s a 19 cal ka bp pollen and charcoal record from lake shaman 44 s 71 w chile was analyzed to establish vegetation fire and climate dynamics of the forest steppe ecotone in central chilean patagonia lake shaman record indicates that the upper rio cisnes valley was free of ice at around 19 cal ka bp from this date and until 14 8 cal ka bp a grass steppe with high proportions of shrubs associated to colder and drier conditions than present developed in this area a continuous increase of nothofagus accompanied by a decline in the steppe shrubs and sudden dominance of paludal over aquatic plants from 11 cal ka bp was associated to effective moisture increase but still under modern values the replacement of the cold dry grass shrub steppe by a similar than present forest steppe ecotone suggests an increase in temperature indicating the onset of the holocene at the same time moderate fire activity suggested by the charcoal record could be related to major fuel availability as consequence of nothofagus forest expansion between 8 and 3 cal ka bp the record indicates the easternmost position of the forest steppe ecotone suggesting the highest effective moisture with the establishment of seasonality between 5 and 3 cal ka bp from 3 cal ka bp the record indicates a retraction of the forest steppe ecotone accompanied by a high pollen record variability and an increased fire activity these late changes suggest decreased effective moisture associated with a high climatic variability at regional and extra regional scale climatic changes at lake shaman s record are mostly associated to changes latitudinal shifts and or strengthening weakening of past southern westerlies that were previously recorded along patagonia from the lateglacial to the mid holocene during the late holocene a regional pattern characterized by high record variability emerges throughout central chilean patagonia this variability would be related to 1 low magnitude southern westerlies changes probably associated to enso and or sam or 2 the complex relationships between vegetation fire and human occupations during the last 3 cal ka

three late quaternary pollen diagrams from southern patagonia and their palaeoecological implications abstract diagrams of fossil pollen in three deposits postdating glacial recession of the last ice age provide an account of late glacial and holocene vegetation and palaeoclimate in southern patagonia sites are mires located along the estrecho de magallanes at punta arenas 53 09 s 70 57 w and puerto del hambre 53 36 s 70 55 w and an intermittent lake some 300 km to the north at torres del paine 50 59 s 72 40 w chronostratigraphy is controlled by 20 radiocarbon dates the oldest site puerto del hambre covering close to 16 000 years charcoal from the sites and carbonate torres del paine as well as tephra layers and an instance of marine incursion puerto del hambre supply additional data of interpretive value accompanying the fossil pollen records is a reference survey of modern pollen fallout from 43 surface sample localities late glacial vegetation during deglaciation consisted mostly of tundra dominated by communities of empetrum acaena gunnera and tubuliflorae compositae under a relatively cold dry climate nothofagus although present in numbers initially at puerto del hambre did not expand until the close of the late glacial at punta arenas expansion of nothofagus was episodic occurring during apparent warmer intervals of the last three millennia of steppe tundra holocene vegetation is depicted at first as a patchwork of nothofagus woodland and steppe subject to climate of relative warmth and limited moisture except at torres del paine where moisture levels were apparently higher than at sites to the south closed nothofagus forest communities subsequently are best developed in the late holocene under a climate with generally cooler wetter parameters fire believed to be caused mostly by palaeoindians has had an important role in shaping vegetation sequences in the holocene formidable however in the development of vegetation are the latitudinal displacements variable intensities of atmospheric conditions caused by shifting storm tracks of the southern westerlies

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

abrupt vegetation changes during the last glacial to holocene transition in mid latitude south america a pollen record from the huelmo site ca 41 30 s shows that vegetation and climate changed at millennial time scales during the last glacial to holocene transition in the mid latitude region of western south america the record shows that a nothofagus parkland dominated the landscape between 16 400 and 14 600 14c yr bp along with magellanic moorland and cupressaceous conifers evergreen north patagonian rainforest taxa expanded in pulses at 14 200 and 13 000 14c yr bp following a prominent rise in nothofagus at 14 600 14c yr bp highly diverse closed canopy rainforests dominated the lowlands between 13 000 and 12 500 14c yr bp followed by the expansion of cold resistant podocarps and nothofagus at ca 12 500 and 11 500 14c yr bp local disturbance by fire favoured the expansion of shade intolerant opportunistic taxa between 10 900 and 10 200 14c yr bp subsequent warming pulses at 10 200 and 9100 14c yr bp led to the expansion of thermophilous summer drought resistant valdivian rainforest trees until 6900 14c yr bp our results suggest that cold and hyperhumid conditions characterised the final phase of the last glacial maximum lgm between 16 400 and 14 600 14c yr bp the last ice age termination commenced with a prominent warming event that led to a rapid expansion of north patagonian trees and the abrupt withdrawal of andean ice lobes from their lgm positon at ca 147 000 14c yr bp hyperhumid conditions prevailed between 16 400 and 13 000 14c yr bp what we term the extreme glacial mode of westerly activity this condition was brought about by a northward shift and or intensification of the southern westerlies the warmest driest conditions of the last glacial interglacial transition occurred between 9100 and 6900 14c yr bp during this period the westerlies shifted to an extreme interglacial mode of activity via a poleward migration of stormtracks our results indicate that a highly variable climatic interval lasting 5500 14c years separate the opposite extremes of vegetation and climate during the last glacial interglacial cycle i e the end of the lgm and the onset of the early holocene warm and dry period copyright 2003 john wiley sons ltd

succession of late pleistocene and holocene ostracode assemblages in a transgressive environment a study at a coastal locality of the southern baltic sea germany abstract the present study documents the hydrological and coastal evolution of a southern baltic sea lagoon by analyzing ostracode associations six ostracode zones were distinguished from a 13 5 m long vibro core in the pudagla lowland ne germany using splitinf binary divisive clustering zonation sediments of a pleistocene freshwater stage are overlain by deposits of a preboreal brackish water environment which are not related directly to the development of the baltic sea different boreal freshwater habitats developed in the study area until marine water protruded the pudagla site in the course of the littorina transgression a gradual succession in the species assemblage reflects the subsequent transgression freshwater species i e metacypris cordata fabaeformiscandona protzi and herpetocypris sp are substituted in pre littorina inland waters ca 7 2 14 c ka bp by halotolerant species i e candona angulata sarscypridopsis aculeata and plesiocypridopsis newtoni ca 6 5 14 c ka bp and finally the ostracode fauna is dominated by cyprideis torosa associated with cytheromorpha fuscata and loxoconcha elliptica when brackish marine water conditions are established ca 6 4 14 c ka bp

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

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

deglacial holocene svalbard paleoceanography and evidence of meltwater pulse 1b abstract better understanding of deglacial meltwater pulses mwps is imperative for future predictions of human induced warming and abrupt sea level change because of their potential for catastrophic damage however our knowledge of the second largest meltwater pulse mwp 1b that occurred shortly after the start of the holocene interglacial remains very limited here we studied fossil ostracods as paleoenvironmental indicators of water depth salinity and temperature in two marine sediment cores from storfjorden svalbard margin the arctic ocean to investigate near field i e areas located beneath continental ice sheets at the last glacial maximum evidence of mwp 1b the depositional environment changed from a cold bathyal environment to a warmer bathyal environment at 11 300 yr bp indicating incursion of warm atlantic water into the nordic seas and eventually to a cold neritic environment by 11 000 yr bp because of melting of the svalbard barents sea ice sheet and resultant isostatic rebound this process corresponds to rapid relative sea level fall of 40 80 m of mwp 1b from 11 300 to 11 000 yr bp

deglaciation shore displacement and early holocene vegetation history in eastern middle sweden the sedimentary record at lake vibysjo lake basin is situated close to the narke strait where the main water exchange occurred between the vanern basin and baltic basin during the middle and late phases of the yoldia sea stage of the baltic sea c 10 000 9500 14c years bp the area was deglaciated in a glaciomarine environment as reflected by the occurrence of benthic calcareous fossils foraminifera ostracods and the mollusc portlandia arctica gray in the lower most clay units the estimated date of deglaciation 10 440 clay varve years bp suggests that a saline bottom water current entered the baltic basin shortly after the high areas south of lake vibysjon became free of ice the brackish water fauna occurs during a regional betula empetrum hippophae pollen zone which in southern sweden is correlated with the early preboreal the isolation of the lake vibysjon basin is dated to 8100 14c years bp and occurred during the last part of the ancylus lake stage based on investigations of other bas

integrated reconstruction of holocene millennial scale environmental changes in tierra del fuego southernmost south america abstract this study presents new paleoenvironmental data obtained from sedimentary cores from lago fagnano an elongated lake located at 54 s in southernmost south america data from palynomorphs pollen spores and algae and associated palynofacies as well as from diatom taxa retrieved from these cores compared with other regional proxies contribute to evaluate the similarities and differences in the climate patterns based on different proxies from southernmost patagonia the pollen analysis reveals that a grass steppe environment existed during the early holocene 11 300 8000 cal a bp followed by a major vegetation change characterized by development of forest steppe ecotone communities between 8000 and 6500 cal a bp under more humid conditions between 6500 and 4000 cal a bp expansion and colonization by nothofagus forests reflect an increase in effective moisture levels while openness in the forest communities characterizes the region after 1100 cal a bp the palynological organic matter combined with the algal content reflects hydrological changes occurring in the lake and its nutrient status probably in close relation with past climate oscillations all these past ecological changes are closely related to oscillations in precipitation and temperature as a response to the variations in the latitudinal position and or strength of the southern westerlies wind belt during the holocene

palaeoenvironment during preboreal boreal in narke south central sweden abstract four sites have been investigated to illustrate the shore displacement and vegetation history during the yoldia sea stage in an area east of the narke strait diatom analysis shows that two of the localities at 165 170 m and 147 m altitude were located above the highest shore line formed during the yoldia sea stage and that only freshwater diatom assemblages were registered in the sediments deposited during the preboreal and boreal chronozones acidification of the water seems to have taken place rather early according to the composition of the diatom flora the basin ladfallet at 142 m was situated slightly above or at the yoldia limit and might have been temporarily influenced by the yoldia sea as the diatom flora contains the slightly brackish littoral taxon mastogloia smithi v lacustris grunow the basin skelnabackakarret at 127 m was isolated from a bay of the yoldia sea which is clearly reflected by the brackish marine diatom flora the composition of the pollen flora illustrates that the isolation occurred during the betula empetrum pollen assemblage zone radiocarbon datings of the sediments deposited at the isolation gave too high ages but the spread of corylus and alnus were dated approximately 9400 and 8500 bp respectively the pollen flora at the four sites studied indicates a vegetational succession from open herb and shrub communities with betula nana and empetrum followed by a phase of open birch forests with juniperus before the immigration of pinus corylus and alnus

laminations from the palmer deep a diatom based interpretation 1 highly laminated holocene age diatomaceous sediments are characteristic of the palmer deep western antarctic peninsula ocean drilling program odp leg 178 site 1098 from 10 000 years b p to the present laminations are comprised of several groups of diatoms chaetoceros resting spores the dominant laminae former result from intense spring blooms rhizosolenia proboscia thalassiothrix and corethron are common also the consequence of summer production marked by a well stratified water column each lamination represents a single productivity event but laminations are not necessarily annual high concentrations of a subpolar form of eucampia antarctica in laminations between 9000 and 6700 years b p suggest early holocene warmth a consequence of southward intrusion of more subpolar waters the glacial interglacial transition is distinguished by pairs of laminae most likely deposited annually laminations with an overwhelming dominance of chaetoceros resting spores alternate with more terrigenous laminae representing alternation of intense spring blooms with more mixed deposition during the summer proximity to retreating glacial ice results in the supply of silt and sand that provides a marker bed between successive blooms

tracking abrupt climate change in the southern hemisphere a seismic stratigraphic study of lago cardiel argentina 49os lake sediments from a closed basin in southern patagonia argentina provide a continental archive with which to reconstruct climate change and to test the interhemispheric synchroneity of abrupt events high resolution sub bottom seismic profiles of lago cardiel indicate substantial lake level changes since the late pleistocene which were identified and dated in a series of long piston cores these data allow the reconstruction of the regional water balance at 49 s since the late glacial the seismic stratigraphy reveals a dry late glacial climate with a desiccation of the basin around 11 220 yr bp 14 c lake level rapidly increased by 135 m at the holocene transition following the early holocene highstand at 55 m lake level never dropped significantly below modern level the palaeoclimate changes implied by the lago cardiel record are out of phase with those implied by records from tropical south america and demonstrate considerable latitudinal asynchroneity in the climate evolution of this continent

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

fluctuations of the ultima esperanza ice lobe 52 s chilean patagonia during the last glacial maximum and termination 1 abstract we present a new record from the ultima esperanza region 51 25 52 25 s southwestern patagonia to unravel the timing and structure of glacial fluctuations during the last glacial termination t1 this sector of southern south america represents the only windward facing continental landmass in the southern hemisphere that intersects the core of the southern westerly wind belt geomorphic stratigraphic and geochronological evidence indicate the following stages during and since the last glacial maximum lgm i deposition of prominent moraine complexes during at least two advances dated between 39 and 17 5 ka ii development of an ice dammed proglacial lake glacial lake puerto consuelo accompanying ice recession iii active deposition of moraine complexes at intermediate positions followed by recession at 15 2 ka iv lake level drop and subsequent stabilization between 15 2 12 8 ka v a glacial readvance in glacial lake puerto consuelo between 14 8 12 8 ka vi ice recession stabilization and lake level lowering between 12 8 10 3 ka and vii glacial withdrawal and disappearance of glacial lake puerto consuelo prior to 10 3 ka by comparing our results with the chronologies from neighboring regions we explore whether there was a consistent temporal geographic pattern of glacial fluctuations during the lgm and t1 and examine their implications at regional hemispheric and global scales the correspondence of these variations with key paleoclimate events recorded in the southern and the northern hemispheres suggest a common forcing that most likely propagated through the atmosphere regional heterogeneities at millennial timescales probably reflect the influence of processes related to deep ocean circulation and changes in the position intensity of the antarctic polar front and southern westerly winds

synchronized terrestrial atmospheric deglacial records around the north atlantic on the basis of synchronization of three carbon 14 c 14 dated lacustrine sequences from sweden with tree ring and ice core records the absolute age of the younger dryas preboreal climatic shift was determined to be 11 450 to 11 390 80 years before the present a 150 year long cooling in the early preboreal associated with rising delta 14 c values is evident in all records and indicates an ocean ventilation change this cooling is similar to earlier deglacial coolings and box model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the north atlantic heat conveyor although the younger dryas may have begun as an anomalous meltwater event

recent ostracoda from the laptev sea arctic siberia species assemblages and some environmental relationships ostracod assemblages from coretop sediments collected at 26 localities at different depths of the laptev sea shelf and upper continental slope were investigated for assemblage studies a total of 41 species belonging to 19 genera and 12 families have been identified three assemblages have been established that could be linked to environmental factors such as water depth bottom salinities water mass circulation and sea ice transportation the species rich and abundant assemblages of the western and central laptev sea were related to the atlantic waters occupying the upper continental slope these include relatively deep water forms that show clear affinities to north atlantic and arctic ocean assemblages cytheropteron biconvexa c testudo c simplex c nodosoalatum c inflatum c porterae krithe glacialis k minima pseudocythere caudata polycope punctata p orbicularis in the eastern middle shelf region the assemblage is comprised of acanthocythereis dunelmensis together with other normal marine species semicytherura complanata elofsonella concinna cluthia cluthae this assemblage seems connected to the winter flaw polynya which is believed to be the main area of sediment entrainment into sea ice the inner shelf assemblage of the southern laptev sea is dominated by shallow water euryhaline species paracyprideis pseudopunctillata and heterocyprideis sorbyana with admixture of the brackish water species roundstonia macchesneyi the unusual occurrence of a number of shallow water ostracod species on the upper continental slope may be explained by ice rafting which these ostracods are probably able to survive

an event stratigraphy for the last glacial holocene transition in eastern middle sweden results from investigations of varved clay and terrestrial sequences this paper presents an event stratigraphy for the last glacial holocene transition in eastern middle sweden the event stratigraphy for eastern middle sweden comprises ten events and covers the tim

marine conditions in central sweden during the early preboreal as inferred from a stable oxygen isotope gradient the marine benthic fauna and the 18 oc of foraminifers and ostracods from six sites situated on a west east transect through central sweden have been analysed in order to estimate the palaeosalinity and palaeocirculation in this shallow marine environment the measurements have been undertaken on material from the early preboreal when the baltic basin was in contact with the north sea through straits in central sweden the 18 oc values have a more negative value towards the east indicating decreasing salinity this was the result of limited possibilities for marine water to penetrate into the baltic basin and the mixing with freshwater from the melting fennoscandian ice sheet four water masses existed in the area a surface layer of freshwater marine water from the north sea brackish marine intermediate water on the swedish west coast and brackish yoldia sea water in the baltic basin the chronology is based on radiocarbon dates of marine fossils and at one site on the occurrence of the vedde ash 10 400 10 300 14 c yr bp this is the first record from marine settings in sweden copyright 2001 john wiley sons ltd journal of quaternary science

postglacial marine diatom record of the palmer deep antarctic peninsula odp leg 178 site 1098 1 total diatom abundance 1 late pleistocene to holocene climate variability in the antarctic peninsula is described from ocean drilling program odp leg 178 site 1098 palmer deep using total diatom abundance valves per gram dry sediment as a paleoproductivity proxy diatom frustules are absent in the diamicton at the base of the core which was deposited prior to age calibrated circa 13 2 ka immediately above the diamicton frustules are in low abundance as rare fragments and become increasingly more abundant and well preserved up core a rapid and major increase in productivity after circa 12 8 ka is evident from distinctly laminated sediments that overlie the diamicton the strongly laminated section was deposited during a deglaciation phase that followed the retreat of grounded ice after the last glacial maximum diatom productivity decreased during a climatic cooling and or change in meltwater supply until circa 9 0 ka between 9 0 and 4 4 ka productivity increased steadily again with diatom abundance maxima reached during a mid holocene climatic optimum the optimum is interrupted by a brief cold event of 1000 years duration 6 0 5 0 ka after 4 4 ka productivity generally decreased and the last 500 years have experienced the lowest diatom productivity of the postglacial period the palmer deep sediment is compared to ice core and lake sediment records from other regions around the antarctic peninsula these diverse data sets confirm that the antarctic peninsula has been a region of rapid and variable climate fluctuation since the last glacial maximum

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

renewed glacial activity during the antarctic cold reversal and persistence of cold conditions until 11 5 ka in southwestern patagonia resolving the timing direction and magnitude of paleoclimate changes in the southern midlatitudes is a prerequisite for determining the mechanisms underlying abrupt and widespread climate changes between the hemispheres during the last glacial interglacial transition lgit this issue is still debated with previous studies producing apparently discordant fi ndings here we show evidence for a glacial readvance and a cold episode between ca 14 8 and 12 6 ka in southwestern patagonia 50 s contemporaneous with the antarctic cold reversal this was followed by ice recession under cold but relatively milder conditions until ca 11 5 ka when paleovegetation records indicate the onset of warm interglacial conditions these fi ndings differ from those reported in northern patagonia 40 s where deteriorating conditions before 13 5 ka were followed by the coldest part of the lgit that lasted until ca 11 5 ka we interpret the apparent blend of greenlandic and antarctic cold phases as evidence for their co occurrence in the southern middle latitudes in patagonia and hypothesize that the position of the antarctic polar front modulated the strength of these cold events in regions to the north or south of it

late weichselian early holocene stratigraphy and environmental conditions in southwestern varmland sweden reflected by benthic foraminifera and molluscs abstract the biostratigraphy at two sites lake uppsalstjarnet and lake osten southwestern varmland southwestern sweden has been investigated the main interest is put on glaciomarine and marine sediments deposited shortly after deglaciation foraminifera and molluscs were present at the deglaciation and some hundred years after arctic faunas dominate in the lowermost layers deposited close to the ice front a transition to faunas affected by increased meltwater influence and higher temperature is recorded higher up in the sequences ams datings of bivalves and foraminifera have yielded ages between ca 10 100 and 9750 bp which infers that southwestern varmland was deglaciated during the latest part of the younger dryas to early preboreal the marine sediments are overlain by varved and sulphide stained clay units deposited when a connection with the sea still was open but the ingression of saline water had ceased

liquefaction and varve deformation as evidence of paleoseismic events and tsunamis the autumn 10 430 bp case in sweden coastal seismic events generate instantaneous changes in relative sea level i e land level vs sea level tsunamis may cause disastrous damage to coasts and coastal habitation liquefaction and deformations of annually varved sediments provide information on paleoseismic events the evidence for a major earthquake and associated tsunami waves in sweden are explored thanks to the varve chronology liquefaction structures and varve deformations caused by this event can be dated at the autumn 10 430 varve years bp the magnitude is estimated at 8 or more on the richter scale the tsunami washed the previously blocked outlet of the baltic free of icebergs and pack ice so that marine water could suddenly invade the entire baltic forming the yoldia sea

postglacial marine diatom record of the palmer deep antarctic peninsula odp leg 178 site 1098 2 diatom assemblages 1 the distribution of late pleistocene to holocene diatom assemblages from ocean drilling program odp leg 178 site 1098 palmer deep is described and compared using multivariate statistical methods cluster analysis and analysis of variance five assemblages are identified from site 1098 which are correlated with the climatic zones identified previously in the palmer deep domack et al 2001 a thalassiosira diatom assemblage characterizes the deglaciation phase 13 2 11 0 ka and was deposited during glacial retreat at the end of the regional last glacial maximum a well preserved rhizosolenia assemblage was deposited during a climatic reversal 11 0 9 0 ka and indicates periods of seasonally open water with diatom blooms an open water fragilariopsis kerguelensis assemblage characterizes the mid holocene climatic optimum 9 0 3 7 ka in the neoglacial late holocene 3 7 ka climatic cooling increased sea ice cover and increased wind are inferred from a cocconeis assemblage during the climatic optimum neoglacial transition 4 4 1 8 ka laminae characterized by corethron criophilum were preserved it is uncertain whether the laminae represent short lived interannual bloom events with high settling rates or have been deposited over longer time periods

southern westerlies during the holocene deduced from geomorphological and pedological studies in the norte chico northern chile 27 33 s abstract in the norte chico precipitation is controlled by atmospheric perturbations and frontal systems associated with the belt of westerly wind circulation the holocene climatic history of the region can be reconstructed from geomorphic and pedologic investigations in comparison to modern climatic conditions increased influence of the westerlies is deduced for the time periods prior to 7300 yr b p between 5000 3700 yr b p 3000 1800 yr b p and around 270 yr b p it remains uncertain whether the increased influence of the westerlies was the consequence of northward shifts of the westerlies as a whole of a meridional expansion of the westerly belt or only of intensity changes of the atmospheric dynamics almost synchronous with changes in the westerlies the coastal fogs in the region were apparently reduced or the fog belt in the coastal range was elevated probably due to a weakened upwelling and warmer water conditions in the eastern pacific in general the climate of the norte chico has become more variable since 5000 yr b p especially since 3000 yr b p with frequent changes of the geoecological conditions

deglacial paleoclimate of the american sector of the southern ocean late glacial holocene records from the latitude of canal beagle 55 s argentine tierra del fuego abstract paleoclimate at the time of deglaciation 14 000 10 000 14 c yr b p in different sectors of the southern ocean has followed a continuous warming trend but also warming broken by a transitory episode the younger dryas stadial event during which on the order of a millennium colder conditions prevailed evidence is from antarctic ice cores deep sea cores glacier fluctuations and pollen and beetle records reasons for the apparent nonuniformity include differential sensitivity of each sector to climatic change uneven dating control and the variable forcing response nature of biota used as climatic indicators establishing the late glacial paleoclimate of the southern ocean is of significance as it bears on comprehending the character of deglaciation in a global context with the object of investigating further the sequence of deglacial climatic events pollen stratigraphic studies at canal beagle at the southern extremity of south america were extended westward to the vicinity of ushuaia and lapataia supplementing work done previously at caleta robalo puerto harberton and bahia moat at ushuaia pollen frequency and influx records of the late glacial as well as the holocene chronologically controlled by 25 14 c age determinations are from four sphagnum empetrum mires results obtained at sites dating from 12 500 to 12 000 yr b p show late glacial climatic variability most indicative among tundra communities of grass and dwarf shrub heath is a drop both in frequency and influx of the singular arboreal component nothofagus at the time of the younger dryas when estimated summer january temperature was 3 c lower than at present at ushuaia in general terms the late glacial pattern is not unlike the northwestern european sequence sensu walker 1995 which exhibits a late glacial interstadial 13 000 11 000 yr b p followed by a younger dryas stadial 11 000 10 000 yr b p within limits of the chronology in the american sector there is no indication as shown by marine cores from the southern ocean and by antarctic ice cores that deglacial climatic events at higher latitudes of the southern hemisphere exemplified by the younger dryas lead similar events in the northern hemisphere uninterrupted warming evident in the marine and ice cores occurred after 11 600 11 500 yr b p at canal beagle in contrast the trend toward steadily milder climate indicated by continuous expansion of nothofagus frequency followed in the early holocene after 10 000 yr b p early holocene nothofagus woodland containing grass and composites replaced tundra under a warmer and drier set of conditions coupled with burning estimated summer temperature averaged 1 c higher than today and annual precipitation 100 mm less pollen influx remained generally low until about 5000 yr b p when the rate of nothofagus greatly increased together with increase in the rate of empetrum a characteristic mire component the implication is of late holocene spread of both closed forest and mire the result of greater precipitation and lower temperatures while burning abated summer temperatures evidently varied within about 0 5 c and precipitation by 100 mm compared with the present renewed albeit fluctuating glacial activity is recorded after 5000 yr b p under a variable cooler and more humid late holocene climatic regime

early to mid holocene aridity in central chile and the southern westerlies the laguna aculeo record 34 s abstract central chile 32 35 s lies at the northern border of strong westerly influence and thus exhibits a steep precipitation gradient therefore the palaeoclimatic archives in the region are suitable for detecting past moisture changes the study of laguna aculeo 33 50 s 70 54 w presents a multiproxy holocene lake record including sedimentology geochemistry mineralogy pollen diatoms and radiocarbon dating 17 dates results indicate an arid early to mid holocene period about 9500 5700 cal yr b p after 5700 cal yr b p effective moisture increased progressively and around 3200 cal yr b p modern humid conditions were established numerous intercalated clastic layers reflect flood deposition during rainy winters a fluvial unit was deposited shortly before 9000 cal yr b p subsequently flood events were absent until 5700 but have become frequent since 3200 cal yr b p the frequency of flood layers possibly points to weak or no el nino activity during the early and mid holocene with a subsequent increase during the late holocene during the early and mid holocene the westerlies were probably blocked and hence deflected southward by the subtropical high pressure cell higher precipitation during the last 3200 yr seems strongly related to a weakened subtropical high pressure cell with intensified westerlies and possibly increased el nino activity

palaeohydrology of laguna de tagua tagua 34 30 s and moisture fluctuations in central chile for the last 46 000 yr central chile 32 35 s lies at the northern border of the strong influence of the westerly circulation belt and thus exhibits a steep rainfall gradient a new core from laguna de tagua tagua 34 30 0 s provides a sedimentologic geochemical and palynological record of regional hydrologic balance for the last 46 000 cal yr bp according to our age model relatively humid conditions occurred during glacial times before 43 500 cal yr bp and from 40 000 to 21 500 cal yr bp reduced moisture conditions and likely lower temperatures occurred from 42 400 40 100 cal yr bp higher lake levels and pollen assemblages with valdivian rainforest taxa imply much higher precipitation during glacial times 40 100 21 000 cal yr bp compared to today and therefore enhanced westerly activity in northern central chile afterwards the general decrease in moisture was punctuated by two abrupt arid periods at 21 000 19 500 cal yr bp and 17 000 15 000 cal yr bp and two more humid intervals 19 500 17 000 almost coincident with the global last glacial maximum lgm and 13 500 11 500 cal yr bp the early and mid holocene were the most arid periods in central chile for the studied time interval millennial scale palaeohydrological reconstructions from tagua tagua are consistent with regional climatic records copyright 2005 john wiley sons ltd

holocene tephrochronology record of large explosive eruptions in the southernmost patagonian andes for regionally widespread holocene tephra layers in southernmost patagonia correlations based on both chemical and chronological data indicate their derivation from five large volume 1 km3 explosive eruptions of four different volcanoes in the southernmost andes bulk tephra and tephra glass major and trace element chemistry and sr isotopic ratios unambiguously distinguish different source volcanoes and imply that two of the regionally widespread tephra mb1 and mb2 were derived from mt burney 52 s one r1 from reclus 51 s one a1 from aguilera 50 s and one h1 from hudson volcano 46 s the h1 tephra derived from the hudson volcano which is located at the southern end of the andean southern volcanic zone svz 33 46 s contains distinctive greenish andesitic glass with feo 4 5 wt and tio2 1 2 wt in contrast rhyolitic glass in tephra derived from the eruptions of mt burney reclus and aguilera volcanoes which are located in the andean austral volcanic zone avz 49 55 s is clear and transparent and has significantly lower feo and tio2 tephra derived from these three avz volcanoes all contain plagioclase orthopyroxene minor clinopyroxene and amphibole biotite occurs only in the aguilera a1 tephra which also has the highest bulk tephra and tephra glass k2o and rb contents averages of new and published 14c ages determined on organic material in soil and sediment samples above and below these tephra constrain the uncalibrated 14c age of the r1 eruption of reclus volcano to 12 685 260 years bp the mb1 and mb2 eruptions of mt burney to 8 425 500 and 3 830 390 years bp the hudson h1 eruption to 6 850 160 years bp and the a1 eruption of aguilera volcano to 3 000 100 years bp the volume of the largest of these eruptions h1 of the hudson volcano is estimated as 18 km3 the volume of the reclus r1 eruption is estimated at 10 km3 the aguilera a1 eruption at between 4 and 9 km3 and the younger mt burney mb2 eruption at 2 8 km3 the volume of the older mb1 mt burney eruption is the least well constrained but must have been larger than the younger mb2 eruption the data indicate that the frequency of explosive activity of volcanic centers in the avz is lower than in the southern svz

a review of the history of the baltic sea 13 0 8 0 ka bp abstract the dynamic history of the baltic sea during the millennia following the last deglaciation has been one of the main topics for many generations of quaternary geologists around the baltic sea based on the present state of knowledge and certain hypotheses a model for the development during the baltic ice lake yoldia sea and ancylus lake stages are presented the oresund strait was the threshold of the initial stage of the baltic ice lake and was eroded down to bedrock as a result of the isostatic uplift the emerging threshold forced the baltic ice lake to rise above sea level at ca 12 0 ka bp this gradual up damming ended at ca 11 2 ka bp when the large glacial lake was lowered 5 10m by possible subglacial drainage at mt billingen a glacial readvance during the younger dryas ended a ca 400 year long land bridge between sweden and the continent by blocking the former drainage route once again the baltic ice lake had to rise above sea level to be drained over the oresund strait at ca 10 5 ka bp a gradual ice recession began and 200 years later when the receding ice sheet could not withhold the up dammed water masses the final drainage of the baltic ice lake occurred which rapidly lowered the water level within the baltic basin with ca 25 m and ended the baltic ice lake stage the next stage the yoldia sea was characterized by a complex pattern of relative sea level changes with large differences within the baltic basin a very restricted baltic sea in the south and thus an extensive landbridge at ca 9 9 ka bp a short 100 200 years saline ingression is seen in the baltic sediment records from stockholm in the north to the southernmost parts of the yoldia sea the gradually shallower strait in south central sweden the narke strait ended the saline influence 300 400 years later the two remaining outlets west of lake vanern gota alv and otteid steinselva had become too shallow to swallow the outflowing yoldia sea waters at this stage the baltic lake vanern level could thus not fall in pace with the relative sea level fall outside the outlet areas this was the isolation of lake vanern and the baltic from the sea and the beginning of the ancylus lake since the water depth of the larger gota alv outlet had to be more or less maintained the ancylus lake level had to rise in pace with the uplift of the outlet region this caused a significant and rapid transgression 10 30 m in ca 300 years in the southern baltic which flooded large areas with recently immigrated pine forests since the oresund strait during the yoldia sea stage had been uplifted more than southerly areas the ancylus transgression ended with a new drainage pathway at ca 9 2 ka bp through the darss sill area in the southern baltic and northwards through the store belt strait this so called dana river had cut off the former large land bridge the quaternary deposits of this new threshold were eroded and a fairly rapid regression set in at ca 9 0 ka bp the dana river had eroded down to the sea level which isolated lake vanern from the ancylus lake and created a land bridge between southern sweden and northwards ca 800 years later when the sea level rose above the oresund threshold marine water could enter the baltic and at ca 8 0 ka bp brackish water characterized the southern baltic this marks the end of the ancylus lake

late and postglacial vegetation and fire history in southern patagonia and tierra del fuego abstract two 17 000 yr old peat bog records from low elevation sites in tierra del fuego harberton 54 54 s and southern patagonia rio rubens 52 4 48 s and one c 14 000 cal yr bp record from the upper treeline in tierra del fuego paso garibaldi 54 43 s were analyzed for pollen charcoal and plant macrofossils to reconstruct changes in regional and local vegetation fire frequency and bog hydrology respectively past environmental changes in both lowland records and in the upper treeline record are interpreted in terms of variations in effective moisture during the late glacial period effective moisture changes at both low and high elevation sites were interpreted from comparable shifts between mesic herb rich grasslands and arid empetrum heath or shrub grassland with abundant disturbance indicators the late glacial effective moisture changes were primarily driven by temperature changes during the early holocene expansion of open nothofagus woodlands in the lowlands in present day areas of dense forest was related to a marked precipitation increase however precipitation must have remained highly variable with century long periods of increased summer drought as evidenced by repeated intervals when bogs dried out and fire frequency was high up slope shifts of the nothofagus forest andean tundra ecotone at 11 000 and 9000 cal yr bp also appear to reflect precipitation increases precipitation variability however must not have affected the upper treeline environments as no fires were recorded and the present day nothofagus forest had become established after 9000 cal yr bp upper treeline apparently was below present from 8000 to 7000 and 2500 to c 400 cal yr bp during those times low elevation environments did not register change which suggests that the upper treeline may have been affected by lower temperatures after c 5000 cal yr bp fires became rare in the lowlands suggesting a shift to an equable precipitation regime with only minor intervals of summer drought no simultaneous change was recorded at the upper treeline thus for the late glacial and early holocene the upper and lower treeline environments apparently responded similarly to primarily moisture changes only during the mid and late holocene environmental changes at high and low elevations differed suggesting responses to different climate signals precipitation in the lowlands and temperature at high elevation

the dynamics of chironomid assemblages and vegetation during the late quaternary at laguna facil chonos archipelago southern chile abstract we compare high resolution pollen and chironomid records from the last 15 000 yr in laguna facil southern chile major vegetation and chironomid changes are recorded between ca 14 900 and 14 700 cal yr bp during the lateglacial changes in the chironomid stratigraphy lag behind changes in the pollen stratigraphy suggesting that the chironomids are responding to changes in the tree canopy or in soil chemistry brought about by vegetational development at about 7200 cal yr bp there is a change in the chironomid stratigraphy in advance of changes in the vegetation this suggests that the response is to regional climatic change the relatively close correlation of the chironomid and pollen stratigraphies with changes in charcoal concentrations also implicates the importance of fire and or vulcanism in influencing the dynamics of forest and limnological systems there is no clear evidence of cooling during the younger dryas chronozone in laguna facil

anastomosis and the continuum of channel pattern anastomosing rivers are characterized by multiple channels separated by islands excised from the floodplain their status relative to the continuum concept of channel pattern is assessed with channel pattern defined in terms of three variables flow strength bank erodibility and relative sediment supply using an ordinal scaling l ow m oderate h igh the traditional forms of straight meandering and braided have respective representations of l l l m l m l m and h h m h in terms of those variables the anastomosing pattern is on average represented by l l m h but not so definitively as other forms specification of the third element sediment supply is particularly hampered by the paucity of data but aggradation a characteristic of many anastomosing rivers can be thought of as symptomatic of a moderately high rate of supply relative to the ability for onward transport a sufficiently high rate of supply to a channel with low flow strength and resistant banks would induce shoaling and or lateral constriction that locally forces flow out of the main channel and ultimately leads to the cutting of anabranches a flow regime characterized by concentrated floods of relatively large magnitude is also regarded as highly conducive to the formation of new channels where low bank erodibility constrains channel capacity anastomosis may in certain cases represent a transitional form of channel pattern but there is no denying the longevity of some anastomosing systems

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

deglacial changes of the southern margin of the southern westerly winds revealed by terrestrial records from sw patagonia 52 s much of the ongoing discussion regarding synchrony or bipolar asynchrony of paleoclimate events has centered on the timing and structure of the last glacial termination in the southern mid latitudes in particular the southwestern patagonian region 50 e55 s its location adjacent to the drake passage and near the southern margin of the southern westerly winds sww allows examining the postulated links between the southern oceanesww coupled system and atmospheric co2 variations through the last glacial termination results from two sites located in the ultima esperanza area 52

different phases of the yoldia sea in the north western baltic proper four sediment cores from the north western baltic proper covering the time from the weichselian deglaciation to the present have been studied main interest is focused on the yoldia stage and especially the duration of the marine phase of this stage the lithological compositions of the sediments and results of different analyses magnetic carbonate ostracods and foraminifera have resulted in a subdivision into five stratigraphical units a e from older to younger unit a was deposited in a glaciolacustrine environment probably during the first non saline phase of the yoldia stage the first ingression of saline water is recorded in unit b brackish water ostracods and foraminifera occur exclusively in this unit which represents the only saline phase of the yoldia stage this phase lasted for less than 120 clay varve years unit c was deposited in fresh water probably during the last phase of the yoldia stage and the ancylus stage the uppermost units d and e are of holocene age and represent different phases of the litorina and post litorina stages

interaction of the south american monsoon system and the southern westerly wind belt during the last 14 kyr abstract surface currents and sediment distribution of the se south american upper continental margin are under the influence of the south american monsoon system sams and the southern westerly wind belt swwb both climatic systems determine the meridional position of the subtropical shelf front stsf and probably also of the brazil malvinas confluence bmc we reconstruct the changing impact of the sams and the swwb on sediment composition at the upper rio grande cone off southern brazil during the last 14 cal kyr bp combining sedimentological geochemical micropaleontological and rock magnetic proxies of marine sediment core geob 6211 2 sharp reciprocal changes in ferri and paramagnetic mineral content and prominent grain size shifts give strong clues to systematic source changes and transport modes of these mostly terrigenous sediments our interpretations support the assumption that the sams over se south america was weaker than today during most of the late glacial and entire early holocene while the swwb was contracted to more southern latitudes resembling modern austral summer like conditions in consequence the stsf and the bmc were driven to more southern positions than today s favoring the deposition of fe rich but weakly magnetic la plata river silts at the rio grande cone during the mid holocene the northern boundary of the swwb migrated northward while the stsf reached its northernmost position of the last 14 cal kyr bp and the bmc most likely arrived at its modern position this shift enabled the transport of antarctic diatoms and more strongly magnetic argentinean shelf sands to the rio grande cone while sediment contributions from the la plata river became less important during the late holocene the modern el nino southern oscillation set in and the sams and the austral tradewinds intensified causing a southward shift of the stsf to its modern position this reinforced a significant deposition of la plata river silts at the rio grande cone these higher magnetic silts with intermediate fe contents mirror the modern more humid terrestrial climatic conditions over se south america

lateglacial of lake onega contribution to the history of the eastern baltic basin abstract new stratigraphy data especially diatom analyses are presented from the area north of lake onega relevant to the discussion on possible lateglacial connection between the baltic sea and white sea following the deglaciation 12 000 11 000 years ago lake onega basin was occupied by a system of ice dammed lakes which drained to the lake ladoga basin when the ice retreated from the threshold leading to the white sea 11 000 years ago the water level dropped and since that the lake was controlled by its thresholds to the white sea and the baltic basin lake onega has remained distinctly above the sea level and no late weichselian sea connection existed between the white sea and baltic basins the marine diatoms frequently found in sediments are reworked older fossils as also suggested by some earlier workers lake onega drained to the white sea basin over the maselga threshold and also to lake ladoga between 11 000 and 10 000 radiocarbon years ago and to the white sea alone between 10 000 and 9500 years ago and the present outlet of lake onega river svir originated 9500 years ago

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