late quaternary vegetation and climate of southern tierra del fuego vegetation and climate over approximately the past 13 000 yr are reconstructed from fossil pollen in a 9 4 m mire section at caleta robalo on beagle channel isla navarino 54 56 s 67 38 w southern tierra del fuego fifty surface samples reflecting modern pollen dispersal serve to interpret the record chronologically controlled by nine radiocarbon dates fossil pollen assemblages are empetrum gramineae gunnera tubuliflorae zone 3b 13 000 11 850 yr b p gramineae empetrum assorted minor taxa zone 3a 11 850 10 000 yr b p nothofagus gramineae tubuliflorae polypodiaceae zone 2 10 000 5000 yr b p nothofagus empetrum zone 1b 5000 3000 yr b p and empetrum nothofagus zone 1a 3000 0 yr b p assemblages show tundra under a cold dry climate zone 3 followed by open woodland zone 2 as conditions became warmer and less dry and later with greater humidity and lower temperatures by closed forest and the spread of mires zone 1 comparisons drawn with records from antarctica new zealand tasmania and the subantarctic islands demonstrate broadly uniform conditions in the circumpolar southern hemisphere the influences of continental and maritime antarctic air masses were apparently considerable in tierra del fuego during cold late glacial time whereas holocene climate was largely regulated by interplay between maritime polar and maritime tropical air

the evolution of the patagonian ice sheet from 35 ka to the present day patice abstract we present patice a gis database of patagonian glacial geomorphology and recalibrated chronological data patice includes 58 823 landforms and 1 669 geochronological ages and extends from 38 s to 55 s in southern south america we use these data to generate new empirical reconstructions of the patagonian ice sheet pis and subsequent ice masses and ice dammed palaeolakes at 35 ka 30 ka 25 ka 20 ka 15 ka 13 ka synchronous with the antarctic cold reversal 10 ka 5 ka 0 2 ka and 2011 ad at 35 ka the pis covered of 492 6 x103 km2 had a sea level equivalent of 1 496 mm was 350 km wide and 2090 km long and was grounded on the pacific continental shelf edge outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams the pis reached its maximum extent by 33 28 ka from 38 s to 48 s and earlier around 47 ka from 48 s southwards net retreat from maximum positions began by 25 ka with ice marginal stabilisation then at 21 18 ka which was then followed by rapid irreversible deglaciation by 15 ka the pis had separated into disparate ice masses draining into large ice dammed lakes along the eastern margin which strongly influenced rates of recession glacial readvances or stabilisations occurred at least at 14 13 ka 11 ka 6 5 ka 2 1 ka and 0 5 0 2 ka we suggest that 20th century glacial recession a 1 is occurring faster than at any time documented during the holocene

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

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

holocene glacier fluctuations in south america and antarctica abstract glacial geologic evidence indicates that glaciers throughout the andes and antarctica fluctuated during the holocene radiocarbon dating and other age determinations suggest that glaciers readvanced significantly only during the last 5 ka reaching positions from several 100 m to a few kilometres beyond their present limits in south america tenuous evidence from radiocarbon dates with dendrochronological data and environmental interpretations from pollen analyses indicate four main periods of neoglacial advance culminating 5000 4000 bp 3000 2000 bp 1300 1000 bp and 15th late 19th centuries smaller advances may have occurred at ca 8400 bp ca 7500 bp and ca 6300 bp the meagre data are consistent in indicating broad synchrony throughout the andes during the last 5 ka suggesting response to global climatic changes anomalies exist in patagonia where some tide water glaciers reached their maximal holocene limits recently this century the broad spectrum of differing antarctic environments produces interesting contrasts some local glaciers in the mcmurdo sound area of the east artarctic continent are more extensive now than during the global glacial maximum ca 18 ka bp when they were starved of precipitation consistent agreement among 14 radiocarbon dates from the south shetland islands indicates two main holocene glacier advances the most extensive 2 3 km peaking in the 12th century the other culminating in the 18th 19th century glaciers in south georgia reached their most advanced holocene limits before 2200 bp moraine fjord glacier which culminated as a 6 km advance between 1460 1700 radiocarbon bp may have lagged 400 650 years behind the climatic forcing because it could only advance in its deep water fjord by building a moraine bank smaller advances in south georgia culminated in the 17th 19th centuries and during the 1920s 30s there is no firm evidence of glacier advances before 3 ka bp in the southern ocean sub antarctic domain but broad synchrony in glacier advances during the last ca 3000 years appears to have occurred throughout the andes antarctic transect caution is required in the interpretation and correlation of moraines associated with calving glaciers and of those with poorly constrained dating

fuegian floating tree ring chronology from subfossil nothofagus wood the discovery of subfossil nothofagus wood buried in several peat bogs of argentine tierra del fuego is reported a provisional fragmented floating tree ring width chronology covering the last 1400 years has been obtained statistical and spectral analysis revealed no significant differences between the present and floating tierra del fuego tree ring chronologies some cyclical growth peculiarities found in both modern and floating chronologies are discussed

microbial origin of early animal trace fossils abstract elongate surface trails that abound in late ediacaran and early paleozoic sandstone and siltstone are often attributed to early animals these trails commonly exist on the same beds as wrinkle structures millimeter to centimeter size ridges and pits that are interpreted as evidence of the former presence of microbial mats here we show that interactions between oscillatory flow and centimetric microbial aggregates produce elongate trails on the surface of a sediment bed trails left by moving microbial aggregates share a number of characteristics with some presumed trace fossils of the earliest animals elevated edges zig zag patterns smooth curves reversals intersections with other trails series of pits and paths that terminate abruptly and restart nearby under the same flow conditions millimetric microbial aggregates generate wrinkle structures thus the interaction between flow and microbial aggregates on a sediment bed can produce a number of structures that are commonly interpreted as evidence of early animal locomotion

spatial distribution of 17o excess in surface snow along a traverse from zhongshan station to dome a east antarctica the influence of temperature on the triple isotopic composition of oxygen in water is still an open question and limits the interpretation of water isotopic profiles in antarctic ice cores the main limitation arises from the lack of 17o excess measurements in surface snow and especially for remote regions characterized by low temperature and accumulation rate in this study we present new 17o excess measurements of surface snow along an east antarctic traverse from the coastal zhongshan station to the highest point of the antarctic ice sheet at dome a the 17o excess data significantly decrease inland with a latitudinal gradient of 1 33 0 41 per meg degree an altitudinal gradient of view the mathml source and a temperature gradient of view the mathml source theoretical calculations performed using a rayleigh model attribute this inland decrease to kinetic isotopic fractionation occurring during condensation from vapor to ice under supersaturation conditions at low temperatures however large heterogeneity of 17o excess in antarctic precipitation cannot only be explained by temperature at condensation and or influences of relative humidity in the moisture source region

changes in the critical erosion velocity for sediment colonized by biofilm in flowing water the incipient motion of sediment can be affected by the presence of microbial biofilm growth this article documents a series of flume experiments using non uniform sediments in which sediment entrainment was investigated for cases where the sediment was immersed in deionized water so that no biofilm developed and for cases where a bio sediment was cultivated by placing the sediment in a mixture of natural water and nutrient solution differences in entrainment and the velocity at incipient motion were measured over an eight week period as biofilm grew it was found that the incipient motion phenomena were quite distinct between the two kinds of sediment sediment with biofilm was more stable and over time incipient velocity increased to a threshold level before declining biofilm development is clearly an important control on the stability of sediments especially in eutrophic water bodies two incipient velocity formulas were derived for sliding and rolling conditions film water theory was utilized to describe the cohesive force between sediment particles and the adhesive force generated by biofilm was introduced into the formula derivation the time variation characteristics of biofilm strength and the features of the substrate were also taken into consideration such analyses can help to predict sediment transport changes due to biofilm presence in nutrient rich water bodies

the role of endolithic cyanobacteria in the formation of lithified laminae in bahamian stromatolites the microboring activity of endolithic cyanobacteria plays a major role in the formation of the dominant lithified laminae in modern marine stromatolites in the exuma cays bahamas these stromatolites are composed primarily of fine grained carbonate sand that is trapped and bound by the filamentous cyanobacteria schizothrix sp periodic introduction of coccoid endolithic cyanobacteria solentia sp during hiatuses in stromatolite growth associated with very low rates of sedimentation results in the formation of lithified horizons 200 1000 lm thick these layers consist of micritized grains that are welded together at point contacts the micritization is caused by extensive microboring and carbonate precipitation within boreholes concurrent with endolithic activity grain welding occurs when boreholes cross from one grain to another at point contacts thus microboring destroys original grain textures but at the same time plays a constructional role in stromatolite growth by forming lithified layers of welded grains these lateral bands of fused carbonate grains help to stabilize and preserve the stromatolite deposits

interannual evolution of multiple longshore sand bars in a mesotidal environment truro massachusetts usa abstract multiple longshore bars 0 30 1 5 m in amplitude are present in the nearshore zone off truro ma in cape cod bay these bars exist in a mesotidal environment with a tidal range of 3 0 m a detailed interannual investigation of these bars over a 16 year time period using orthorectified vertical aerial photography has been carried out to characterize the behavior of multiple bars forming in a mesotidal environment over a temporal scale of observation not generally achieved by direct field study this investigation reveals that the bars are dynamic over the time interval studied with offshore extents of up to 660 m and wavelengths of 45 150 m generally increasing in the seaward direction at any one location 4 to 10 bars are present with an apparent addition of bars at the southern end of the study area in addition the bars are consistently parallel to offshore bathymetric contours and comparison of more recent photographs with a 1960 image reveals a 0 5 km alongshore zone without bars that has persisted and grown since 1960 the characteristics of the truro multiple bar field are consistent with several existing theories of multiple bar formation including formation by breaking waves standing infragravity waves and edge waves the demonstrated dynamic nature of the truro multiple bar field over a long temporal scale suggests that field experiments designed to distinguish between possible formation theories may provide an explanation for the continuing modern creation and modification of this and similar multiple bar fields occurring in mesotidal environments

late glacial history of lago argentino argentina and age of the puerto bandera moraines in the west central part of lago argentino the puerto bandera moraines are clearly detached from longer more prominent moraines of the last glaciation and from shorter and smaller neoglacial moraines scientists have long speculated about the age of the puerto bandera moraines detailed geomorphologic studies in the western area of lago argentino including stratigraphic profiles at bahia del quemado in the northern branch brazo norte indicate that the puerto bandera moraines were deposited by three pulses of ice each of the three pulses is represented by single moraine ridges and belts of tightly arranged ridges the timing of the three glacier advances was established by radiocarbon dating including data published by john mercer the oldest moraine system formed during the puerto bandera i substade was deposited ca 13 000 14c yr b p moraines of the puerto bandera ii substade were deposited ca 11 000 14c yr b p the youngest moraine system was deposited during a minor readvance shortly before 10 390 c14 yr b p and thus appears to have occurred some time during the european younger dryas interval after this third substade the ice tongues retreated into the interior branches of lago argentino and have remained there since evidence found at bahia del quemado together with data provided by other authors attests to a significant climatic change by the middle holocene which we believe occurred during the herminita advance the first holocene glacial readvance recognized within the area

relationships between terrestrial animal exploitation marine hunter gatherers and palaeoenvironmental conditions during the middle late holocene in the beagle channel region tierra del fuego abstract palaeoenvironmental information collected from zooarchaeological guanaco exploitation and palynological pollen and fungal remains records from tierra del fuego and isla de los estados allowed us to reconstruct the natural scenarios during the holocene to better understand the human behavioral patterns and cultural changes we have seen that changes in subsistence and guanaco exploitation would not have necessarily been synchronous with climatic variations however there is evidence of great climatic and environmental variability in the fuegian archipelago during the last 6000 years that would have influenced the distribution of the hunter gatherer societies in particular the little ice age lia event could have caused a reorganization of subsistence activities of the hunter gatherer societies the stress caused by this severe climatic episode might have changed the availability of the guanaco population over the inland and coastal areas along the beagle channel indeed the colder conditions would have significantly impacted on both the animal population and the availability of their food sources in summary the guanaco availability decreased under those colder and intense winters which is clearly reflected in the substantial drop in the zooarchaeological record

comment on record of δ18o and 17o excess in ice from vostok antarctica during the last 150 000 years by amaelle landais et al

late quaternary palaeoenvironmental change in western staaten island 54 5 s 64 w fuegian archipelago abstract late glacial holocene environmental conditions were interpreted in western isla de los estados staaten island from geomorphological and palynological analysis the geomorphological data from caleta lacroix 54 50 s 64 40 w indicate the presence of a fossil dune field that suggest exposition of a larger land surface and stronger wind intensity predominantly from sw and w probably during late glacial times when sea level was lower than today deglaciation and onset of peat formation in the western coastal area began prior to 12 600 cal bp in response to warmer conditions the pollen data indicates initial treeless herbaceous and paludal vegetation with scarce empetrum ericaceae type heaths and scrubs as a result of plant invasion and short term succession vegetal communities spreading over the shoreline areas under locally more humid conditions the vegetation between 10 300 and 8300 cal bp included dwarf shrub heaths scrubs cushion plants and grasses with scattered trees under warmer and drier climate conditions than today after 8300 cal bp more humid conditions allowed the expansion of an open nothofagus forest associated with dwarf shrub heath communities it was followed at 6700 cal bp by a gradual closed forest development in association with drimys winteri and shrub and herb vegetation indicative of subantarctic evergreen forest magellanic moorland vegetation transition under cold and wet conditions after 5500 cal bp the rate of evergreen beech forest greatly increased with the development of almost pure subantarctic evergreen forest communities these vegetation changes accompanied a modification of the climate toward colder and wetter conditions after 2700 cal bp the closed forest was replaced by an open nothofagus forest indicative of warm and dry conditions the minimum of nothofagus pollen registered between 1000 and 500 cal bp may correspond to the medieval climate anomaly mca period all these vegetation changes are in turn related to the positioning and intensity of the southern westerlies wind belt sea ice antarctic extent and changes in the sea level

seasonal variations of 17 o excess and d excess in snow precipitation at vostok station east antarctica the use of water isotopes in polar regions is essential for reconstructing past climate over glacial interglacial cycles in addition to d do rd 18 o linearly related to condensation temperature the second order parameters d excess and 17 o excess provide important information on the climatic conditions of the source of precipitations in order to best interpret the glacial interglacial records of d excess and 17 o excess in polar ice cores it is important to document their present variability especially in remote and cold regions of east antarctica indeed the current climatic conditions encountered in these regions provide a good analogy with glacial climatic conditions in a large part of antarctica here we present the first seasonal variations of 17 o excess and d excess at vostok station on an event basis i e samples were collected immediately after each precipitation event over 1 year these records show strong correlation between 17 o excess and d 18 o over the course of the year with an amplitude 40 per meg 10 3 in the 17 o excess seasonal cycle and strong anticorrelation between d excess and d 18 o with d excess variations up to 20 the d excess and 17 o excess variations can be explained by the influence of kinetic fractionation at very low temperatures the comparison with simple isotopic models confirms this explanation but cannot explain the link between 17 o excess d excess and temperature without 1 a particular relationship between condensation and surface temperature and or 2 seasonal changes in the climatic conditions of the source regions

characteristics distribution and morphogenesis of subtidal microbial systems in shark bay australia abstract the distribution nature and extent of microbial deposits in hamelin pool shark bay have been investigated and mapped with emphasis on the occurrence external morphologies internal fabrics constructional mechanisms microbial communities growth rates and sediment associations in the intertidal and previously little researched subtidal zone detailed georeferenced substrate mapping revealed extensive subtidal microbial deposits occupying approximately 300 km 2 of the total holocene 1400 km 2 area of hamelin pool the microbial pavement covers 227 km 2 of the subtidal substrate that together with columnar structures reveals a subtidal microbial habitat which occupies an area 10 times larger than the area of the intertidal deposits microbial carbonate is composed of aragonite 80 98 that reveals high positive values of 13 c 4 46 to 5 88 and 18 o 3 06 to 3 88 as a characteristic of the highly evaporative environment with extensive microbial activity oldest dated heads are 1915 and 1680 14 c years bp and the overall system was deposited in two stages the first between 2000 and 1200 and the last from 900 years bp to the present slow growth rates vary from less than 0 1 mm year to 0 5 mm year different internal fabrics were constructed according to their position in relation to the littoral zone by distinct microbial communities and lateral fabric relations have been established evidence of shallowing upward fabric sequences of microbial origin reflects relative falling sea levels during the late holocene and is likely useful in ancient environmental interpretation a sequence of events and mechanisms are described emphasizing differences between the stromatolitic thrombolitic and cryptomicrobial deposits in shark bay the new substrate map and depositional history for this distinctive and peculiar microbial habitat establish the significance of subtidal structures and emphasize the geoscientific importance of hamelin pool especially with respect to early life studies and ancient analogues for understanding microbial activity deposit characteristics fenestral fabrics and distribution

late quaternary vegetation of southern isla grande de chiloe chile late glacial holocene forest history of southern isla chiloe latitude 43 10 s was reconstructed on the basis of pollen analysis in three profiles laguna soledad laguna chaiguata puerto carmen prior to 12 500 yr b p pollen records are dominated by plant taxa characteristic of open habitats zone i from 12 500 yr b p to the present tree species predominate in the pollen records zones ii v between 12 500 and 9500 yr b p ombrophyllous taxa nothofagus podocarpus nubigena myrtaceae fitzroya pilgerodendron and drimys are frequent in all pollen diagrams suggesting a wetter and colder climate than the present between 9000 and 5500 yr b p valdivian forest elements such as nothofagus dombeyi type weinmannia and eucryphia caldcluvia dominate indicating a period of drier and warmer climate from 5500 yr b p onward the expansion of mixed north patagonian subantarctic forest elements and the increased frequence of tepualia suggest increased rainfall and temperatures oscillating around the modern values the change from open to forest vegetation ca 12 500 yr b p probably represents the most pronounced climatic change in the record and can be interpreted as the glacial postglacial transition in the study area

pleistocene glaciation in the southern lake district of chile relative age criteria permit deposits of successive andean glacier advances in the southern lake district of chile to be divided into four mappable drift sheets the oldest two of which overlie tertiary bedrock along the eastern flank of the cordillera de la costa only the youngest drift llanquihue is datable by radiocarbon during the most extensive ice advance of the last glaciation the lago llanquihue glacier was about 95 km long and reached an estimated maximum thickness of between 1000 and 1300 m glacier equilibrium lines at that time lay about 1000 m below their present level and rose eastward with a gradient of about 5 m km successive ice advances in the lago llanquihue basin which resulted in construction of end moraines and associated outwash plains beyond the lake margin culminated sometime before about 20 000 yr ago and between 20 000 and 19 000 yr ago a later readvance inferred from the sedimentary record of lake level fluctuations in the basin had begun by about 15 000 yr ago and culminated shortly after 13 000 yr ago a comparable but less closely dated record of ice advances is found northwest of seno reloncavi and on isla chiloe deglaciation following the latest advance is likely to have been rapid for the major glacier lobes fronted on deep water bodies that would have promoted extensive calving

seabed wave resonance and sand bar growth the interaction of surface water waves with undulating sea bed topography is of fundamental importance to coastal engineersand sedimentologists for example wave reflection from submerged bars on beaches may provide a mechanism for protecting the beach from further wave attack additionally the interaction of surface water waves with other tidally or wave generated bedforms such as sandwaves on offshore banks may modify wave climates on adjacent coastlines while there have been numerous studies of the interaction of sea waves with engineering structures such as breakwaters piers and jetties there have been comparatively few investigations of wave interactions with naturally occurring bedforms predictions have recently been made of the amount of wave energy reflected as a result of resonant interactions between surface water waves and undulating sea bed topography but with no supporting experimental proof i describe here preliminary results from what are believed to be the first published laboratory measurements of resonant interactions between surface water waves and submerged bars which show that significant and large amounts of wave energy may be reflected and that these reflections are brought about by resonant interactions between surface water waves and the bedforms in particular at resonance incident surface water wavelengths are approximately twice the bedform wavelengths these results have implications not only in terms of wave reflection from naturally occurring bedforms say bars on beaches but also for sediment transport processes in general

rhythmic topography in a mesotidal low wave energy environment abstract the intertidal zone in craig bay extends 1200 m offshore making it the broadest non estuarine tidal flat on the east coast of vancouver island british columbia canada superimposed on the low gradient foreshore 1 360 are up to fourteen low amplitude 0 6 m ridges with an average wavelength of 86 3 m these are permanent fixtures of the intertidal zone exhibiting considerable stability in both form and position they are generally symmetrical in cross section and in no instance is a landward slip face evident the ridges have developed in medium to fine sand atop a coarse deltaic platform the thickness of this surficial sand unit is often equal only to the height of the ridges and the gravel sustrate is frequently exposed in the depressions the morphology sediments and hydraulic environment of this rhythmic foreshore were examined to provide insight into the factors controlling ridge development and maintenance although the maximum tidal range exceeds 5 0 m tidal currents are of limited importance only in the major runnels are velocities sufficient to initiate sediment transport waves within the strait of georgia are locally generated h1 3 3 0 m t1 3 7 0 s and appear to the the prime agent responsible for the formation and maintenance of this variant of ridge and runnel morphology the dominant bedform across the intertidal zone is the wave formed ripple although current ripples may locally predominate small scale cross stratification which is associated with these bedforms is the most common primary physical sedimentary structure in the surficial sand unit however a large proportion of the cores were structureless this is attributed to bioturbation by sand dollars dendraster excentricus and to a lesser extent to air entrapment and water escape

palaeoenvironmental conditions during the early peopling of southernmost south america late glacial early holocene 14 8 ka b p abstract environmental conditions in southernmost south america the patagonian andes and the extra andean plains during the early peopling of the region in late glacial early holocene times are herein described different glacial advances or stabilization phases in valley glaciers occurred several millennia after the last glacial maximum lgm as a consequence of regional cold climatic episodes according to clapperton 1993 two advances during the late glacial took place ca 15 14 14 c ka and 12 10 14 c ka b p a cold event during this last period probably correlative with the younger dryas episode in the northern hemisphere has been observed in the palynological record a tundra environment dominated until ca 13 10 14 c ka b p afterwards a gramineous steppe with forest refuges developed the transition steppe forest lasted to the middle holocene when the nothofagus forest took over the arrival of man in southernmost south america ca 13 14 c ka b p or even before probably took place while glaciers were still present in most andean valleys sea level was much lower than today and tundra environments dominated the extra andean plains moreover peopling in the isla grande de tierra del fuego would have occurred not later than 11 8 14 c ka b p when the present magellan straits valley was still occupied by a meltwater discharge braided stream fed by the receding magellan glacier

note on sediment sorting in a sandy bed under standing water waves we present new quantitative data on the sorting of sediments on a sandy seabed under standing waves starting from a flat bed composed of a homogeneous mixture of a coarse and a fine sand with mean diameters 0 11 and 0 21 mm we observed simultaneous ripple and sand bar formation and sand sorting on the seabed over days of wave action sand bars formed with crests beneath the surface wave nodes and flat plateaus flanked by mounds beneath the antinodes bar crests were composed of sand coarser on average than 0 21 mm while the flat plateaus were covered by sand finer on average than 0 11 mm comparison with two experiments involving sand beds of more homogeneous size distributions shows that the mounds are characteristic of the motion of fine suspensions

facies architecture and sequence stratigraphic features of the tumbiana formation in the pilbara craton northwestern australia implications for depositional environments of oxygenic stromatolites during the late archean abstract the tumbiana formation ca 2 7 ga is a succession developed in response to late archean crustal extension in the pilbara craton northwestern australia the formation is characterized by intercalations of stromatolitic carbonates and provides a perspective of the evolution of photosynthetic organisms which are interpreted to have been responsible for the oxygenation of earth surface environments in early earth here we investigated the depositional setting of the stromatolitic carbonates for the better understand of the environments which may have controlled the massive development of oxygenic photosynthesis we studied lithofacies and sequence stratigraphic features of the tumbiana formation in the redmont area a southern margin of the northern pilbara craton on the basis of three dimensional analyses of onshore outcrops the tumbiana formation as much as 170 m thick unconformably overlies the early to middle archean basement rocks and is unconformably overlain by the maddina formation that consists of mafic tuffaceous sediments and basalt lavas the lower part of the tumbiana formation is characterized by planar and trough cross stratified conglomerates which are interpreted to be an alluvial fan deposit shed from the northern hinterlands and developed mainly in local depressions of the basement rocks during late lowstand and early transgressive stages the base of the middle part is defined by a transgressive surface of erosion overlain by conglomerates and or breccias that pass upward to mafic tuffaceous mudstones and sandstones intercalated with accretionary lapillis breccias and basalt pillow lavas mudstones are commonly laminated and sandstones contain current and wave ripple lamination parallel lamination hummocky cross stratification and trough cross stratification in general the middle part exhibits an overall fining and coarsening upward pattern and is interpreted to indicate transgressive and regressive shelf to coastal lithofacies successions in particular the uppermost horizon of the middle part is characterized by sandstone beds with herringbone structures and desiccation cracks and is interpreted to indicate an intertidal deposit developed during late highstand and or following falling stages the middle part of the formation in general thickens to the northern proximal area and eventually flattened out the topographic irregularity of the basement rocks the upper part is characterized by stromatolitic carbonates associated with minor mudstones and wave and current rippled sandstones and does not exhibit distinct lateral variation in thickness and vertical lithofacies organization the base of the upper part is characterized by a transgressive lag deposit the ensuing transgression over the intertidal deposits of the uppermost middle part is interpreted to have developed a new accommodation space for the vertical stacking of stromatolites with different external shapes from elongated small domal and columnar types associated with desiccation cracks to stratiform and large domal types these changes may have responded to the increase in paleowater depth possibly from intertidal to subtidal environments in conclusion stromatolites in the upper tumbiana formation in the redmont area are interpreted to have developed in coastal and shallow marine environments in response to the rise in relative sea level rather than in ephemeral saline lakes as proposed by previous studies however the outcome of the present research does not necessarily deny the previously proposed interpretation but suggests spatial variations in depositional environments of the tumbiana formation from the north to south

the deglaciation of the americas during the last glacial termination this paper reviews current understanding of deglaciation in north central and south america from the last glacial maximum to the beginning of the holocene together with paleoclimatic and paleoceanographic data we compare and contrast the pace of deglaciation and the response of glaciers to major climate events during the global last glacial maximum glgm 26 5 19 ka average temperatures decreased 4 to 8 c in the americas but precipitation varied strongly throughout this large region many glaciers in north and central america achieved their maximum extent during the glgm whereas others advanced even farther during the subsequent heinrich stadial 1 hs 1 glaciers in the andes also expanded during the glgm but that advance was not the largest except on tierra del fuego hs 1 17 5 14 6 ka was a time of general glacier thickening and advance throughout most of north and central america and in the tropical andes however glaciers in the temperate and subpolar andes thinned and retreated during this period during the bolling allerod interstadial b a 14 6 12 9 ka glaciers retreated throughout north and central america and in some cases completely disappeared many glaciers advanced during the antarctic cold reversal acr 14 6 12 9 ka in the tropical andes and patagonia there were small advances of glaciers in north america central america and in northern

fine grained agglutinated elongate columnar stromatolites tieling formation ca 1420 ma north china the mesoproterozoic tieling formation near jixian northern china contains thick beds of vertically branched laterally elongate columnar stromatolites carbonate mud is the primary component of both the stromatolites and their intervening matrix its abundance is attributed to water column whiting precipitation stimulated by cyanobacterial photosynthesis neomorphic microspar gives the stromatolites a streaky microfabric and small mud flakes are common in the matrix the columns consist of low relief mainly non enveloping laminae that show erosive truncation and well defined repetitive lamination in plan view the columns form disjunct elongate ridges 10 cm wide separated by narrow matrix filled runnels the stromatolite surfaces were initially cohesive rather than rigid and prone to scour and are interpreted as current aligned microbial mats that trapped carbonate mud the pervasive ridge runnel system suggests scale dependent biophysical feedback between i carbonate mud supply ii current duration strength and direction and iii growth and trapping by prolific mat growth together these factors determined the size morphology and arrangement of the stromatolite columns and their laminae as well as their branching patterns alignment and ridge runnel spacing ridge runnel surfaces resemble ripple mark patterns but whether currents were parallel and or normal to stromatolite alignment remains unclear the formation and preservation of tieling columns required plentiful supply of carbonate mud mat building microbes well adapted to cope with this abundant sediment and absence of both significant early lithification and bioturbation these factors were time limited and tieling stromatolites closely resemble coeval examples in the belt purcell supergroup of laurentia the dynamic interactions between mat growth currents and sediment supply that determined the shape of tieling columns contributed to the morphotypical diversity that characterizes mid late proterozoic branched stromatolites this article is protected by copyright all rights reserved

polar perspective of late quaternary climates in the southern hemisphere abstract late quaternary paleoecological and glacial evidence from the higher latitudes of the southern hemisphere implies overall uniformity of large scale glacial and interglacial climatic fluctuations for the past 40 000 yr climate of the last glacial maximum variously dated between 30 000 and 11 000 yr b p was relatively cold and dry compared with the warmer more humid climate of the holocene and the interstade preceding the last glacial maximum conditions were apparently coldest during millennia centered around 20 000 yr b p and warmest in the early holocene recorded small scale fluctuations frequently variable for any given time interval are less consistent a cold late glacial episode estimated as occurring between ca 13 000 and 11 000 yr b p in antarctica possibly was coeval with the younger dryas stade in northwestern europe and may be correlative with a climatic episode in southern south america and perhaps in new zealand and south georgia however there is no evidence for the event in tasmania general atmospheric circulation models for the polar latitudes at the time of the last glacial maximum show an intensification of the southern westerlies apparently a result of the expansion of ice cover in antarctica and of sea ice in the southern ocean

interannual variation of water isotopologues at vostok indicates a contribution from stratospheric water vapor combined measurements of water isotopologues of a snow pit at vostok over the past 60 y reveal a unique signature that cannot be explained only by climatic features as usually done comparisons of the data using a general circulation model and a simpler isotopic distillation model reveal a stratospheric signature in the 17o excess record at vostok our data and theoretical considerations indicate that mass independent fractionation imprints the isotopic signature of stratospheric water vapor which may allow for a distinction between stratospheric and tropospheric influences at remote east antarctic sites

feedbacks between flow sediment motion and microbial growth on sand bars initiate and shape elongated stromatolite mounds abstract elongated stromatolites are often used as indicators of current direction and shoreline orientation especially in paleoenvironmental reconstructions however mechanisms that create shore parallel m scale elongated stromatolite mounds in carbonate sand are not well understood we propose that this geometry is initiated by microbial growth on the parts of sand bars that experience low wave induced bed shear stresses we test this idea by growing microbial mats on carbonate sand bars in a laboratory wave tank cyanobacterial mats grow on the bar runnels where sediment motion is negligible but are absent from the bar ridges where the waves generate migrating ripples when microbially promoted lithification reinforces and preserves this initial pattern elongated stromatolites should initiate in the runnels of sand bars with long wavelengths 5 100 m and small width to wavelength ratios 0 3 these dimensions are consistent with modern shore parallel stromatolites in hamelin pool western australia and with patterns of microbial colonization in other sandy sediments this model of elongated stromatolite mounds can inform paleoenvironmental reconstructions by clarifying and quantifying feedbacks among waves sediment transport and microbial growth

cold climatic episode of younger dryas age in tierra del fuego pronounced climatic change during the last glacial maximum is recognized as global in extent and has been attributed to orbital forcing1 not readily explained in a global context because of the equivocal nature of the evidence are the late glacial climatic events of short 100 1 000 yr duration the cold climate of the younger dryas chron 11 000 10 000 yr bp for example is known to have been particularly pronounced over the north atlantic and parts of europe and north america2 3 whereas in the southern hemisphere cold conditions for that time are not well established here we present evidence for late glacial climatic cooling in southernmost south america from studies of radiocarbon dated glacial and pollen stratigraphy at sites along the beagle channel in tierra del fuego where a forest tundra tension zone in the region is especially sensitive to shifting climate we conclude that the cold episode corresponds with the time of the younger dryas in europe when a drop in temperature ascribed most recently to colder sea surface temperatures and production rate of deep water in the north atlantic4 5 apparently occurred worldwide

morphodynamics of intertidal bars in wave dominated coastal settings a review abstract intertidal bar systems are ubiquitous features on wave dominated beaches in coastal settings with a significant 1 m tidal range depending primarily on the wave conditions and the tidal range and to a lesser extent on the nearshore gradient they can assume a variety of forms slip face bars represent the most pronounced and dynamic intertidal bar morphology and are generally found on their own around the mean high tide level they usually form low on the intertidal beach after storm induced beach erosion and develop into a berm under prolonged calm wave conditions low amplitude ridges and sand waves represent multiple bar morphologies the bars occur across the entire intertidal profile and they remain present throughout the year multiple intertidal bars tend to be rather subdued and relatively static especially sand waves and their origin remains unclear the morphological response of intertidal bars to changing wave conditions is largely forced bars build up and migrate onshore under calm waves and are flattened and may migrate offshore during storms the morphological response is however significantly affected by relaxation time effects and morphological feedback particularly on beaches with multiple intertidal bars despite their morphological differences the intertidal bar types exhibit pronounced similarities in their morphodynamics sediment transport processes and morphological response are principally controlled by the tidal water levels on the beach because these together with the offshore wave energy level and the beach morphology determine the type intensity and duration of the wave processes operating on the cross shore profile it is the dominant importance of tidal water level variations and wave processes in shallow water depths swash and surf zone bores rather than wave height variability and deeper water wave processes breaking and shoaling waves that constitutes the main difference between intertidal and subtidal bar morphodynamics

climate and chronology of antarctica and adjacent south america over the past 30 000 yr abstract well dated records of paleoclimate essential for developing general circulation models of the atmosphere during the quaternary are limited in the subpolar southern hemisphere for antarctica where dating is particularly restricted records from distal south america provide a measure to assess antarctic ice sheet chronology and to establish the timing of past climatic events of the continental and insular land masses in the middle latitudes south america lies closest to antarctica and most reflects conditions in the polar region close interval dating of a pollen record at harberton 54 52 s 67 53 w in southern tierra del fuego strengthens implications drawn from paleoecological data and from fluctuations of glaciers to show a climatic parallel with isotope temperature climate data developed from antarctic ice cores over the time span of approximately 30 000 yr since before the full glacial coldest conditions both in antarctica and south america appear centered at 20 000 yr b p warming of climate occurred in the late glacial after 15 000 yr b p interrupted by a cold episode between about 13 000 and 10 500 yr b p with maximum warmth at 9000 yr b p in the early holocene after which temperatures were lower varying only moderately until the present this deglacial pattern although inconsistent in other southern hemisphere records is reproducible on a global scale

extensive recession of cordillera darwin glaciers in southernmost south america during heinrich stadial 1 abstract the geographic expression and phasing of events during the last termination are important for isolating mechanisms that caused earth to emerge from the last ice age heinrich stadial 1 hs1 14 600 18 000 yr bp is a key because of the central role that its far field effects had on the last termination in the southern hemisphere here we present new data from cordillera darwin that show rapid glacier recession in southern south america during hs1 this retreat was coeval with ice recession elsewhere in south america and new zealand with increased upwelling in the southern ocean with warming of ssts offshore of chile and with a rise in atmospheric co2 together these data indicate a coherent and rapid response to the effects of hs1 in the middle and high latitudes of the southern hemisphere

bragg reflection of ocean waves from sandbars 1 resonant bragg reflection of ocean surface waves by a field of natural shore parallel sandbars was observed in cape cod bay ma waves transmitted through the bars were reflected strongly from the steep shoreline and the observed cross shore variations in the onshore and offshore directed energy fluxes are consistent with theory for resonant bragg reflection including a 20 decay of the incident wave energy flux that is an order of magnitude greater than expected for wave orbital velocity induced bottom friction bragg reflection was observed for a range of incident wave conditions including storms when sediment transported toward and away from nodes and antinodes caused by the reflecting waves might result in growth and maintenance of the sandbars

temperature and precipitation record in southern chile extended to 43 000 yr ago southern chile 41 56 s in the belt of westerly winds receives mostly heavy precipitation reaching 8 500 mm yr 1 near 50 s and decreasing northwards and southwards from this latitude to 1 500 mm mean january summer temperatures near sea level along the latitudinal gradient are 8 16 c refs 1 2 dense rain forest covers much of the region to 48 s south to cape horn magellanic moorland prevails and rain forest becomes limited modern pollen measured in surface samples reflects the distribution of plant species in the vegetation we have now applied regression equations relating present day pollen to temperature and precipitation to fossil pollen data at taiquemo to assess climatic conditions during the quaternary the results extend our previous record of the past 16 000 yr at alerce3 beyond the lateglacial to 43 000 yr bp for the 27 000 yr interval they show mean january temperatures of 10 12 c and mean annual precipitation centred around 1 000 mm except during the time span of 31 000 43 000 yr bp when amounts increased to 4 000 mm in general fluctuations correspond to the isotopic climatic reconstruction in antarctica4 and to changes inferred from pollen data at comparable latitudes in tasmania5 8 and new zealand9 10

the biogeomorphology of shark bay s microbialite coasts abstract the world heritage microbialites coquinas and microbialitic sediments of hamelin pool shark bay western australia form through complex community and environmental interactions resulting in surficial co2 sequestration predicted climate change impacts threaten the stability of this setting and the balance of biogeomorphological processes that generate them in this setting long term surficial co2 sequestration occurs through the combination of biomineralisation organomineralisation and lithification which locks atmospheric co2 into caco3 rocks and sediments biogeomorphological processes that control the distribution and effectiveness of these mechanisms including biostabilisation bioconstruction bioerosion and bioturbation have not been addressed in this setting to date a three dimensional biogemorphological mapping unit framework is defined at three locations in hamelin pool within the shallow subtidal to supratidal zones based on historical and recent multiscale datasets this framework is used to review the complex distribution of geomorphological and biogeomorphological processes the distribution of lithification within a biogeomorphological process context is examined and current geological analogue models of microbialite and coquina development are expanded to include biogeomorphological processes the framework is used to understand the impacts of increased water elevation in response to intensification of the leeuwin current during the 2010 2012 ningaloo nino event potential climate change impacts are identified including reduced intertidal bioconstruction and a shift from microbialitic structure generation to increased grain generation reducing stromatolite development review of the uncertainty of impacts of ocean acidification and temperature shifts on biomineralisation organomineralisation and lithification processes crucial to the maintenance of the outstanding universal values in this world heritage location suggests urgent research is required

geomorphological evidence of different glacial stages in the martial cirque fuegian andes southernmost south america abstract the geomorphological features of a cirque partially occupied by receding ice bodies are presented as evidences of different glacial stages in the fuegian andes summits since the last glaciation ios 2 a glacierization scheme involving i regional glacier accumulation basin ii glacier individualization from a main regional ii a stillstand during the general retreat and iii two advancing stages are suggested geomorphic and sedimentary units named martial i ii iii and iv have been distinguished as a consequence of the glacial scheme unfortunately the lack of datable materials has impeded establishment of an absolute chronology recognized glacier advances in the region are discussed the palaeoclimatic framework for the surroundings based on previous studies is presented

glacier readvances in the andes at 12 500 10 000 yr bp implications for mechanism of late glacial climatic change radiocarbon dates from two sites in the andes ecuador and peru confirm that glaciers culminated a readvance after 11 000 yr bp a moraine stage equivalent in altitude and position relative to existing glaciers is present in most glacierized ranges but its age is equivocal broadly limiting dates from colombia and peru suggest that the stage may be late glacial as it is younger than 12100 yr bp but formed before the early holocene in southern chile a comparable moraine stage is older than ca 9100 yr bp andean glaciers appear to have advanced at least twice during the late glacial interval glacier reconstruction from these moraine limits suggests depression of the equilibrium line altitude by at least 300 400 m in the northern and north central andes and possibly less than this farther south late glacial climatic change occurred globally and possibly reflects north atlantic temperature and circulation changes forced by deglaciation of the northern ice sheets migrations north and south of the atlantic polar front and the switching off and on of a dust pump in low midlatitudes

sandbar formation under surface waves theory and experiments 1 we report a combined theoretical and experimental study of sandbar formation under simple harmonic surface waves for coarse grains and weak waves an established empirical rule of bed load transport is used with an asymptotic theory for the fluid flow the surface waves are governed by potential theory and a depth linear eddy viscosity is employed in the turbulent boundary layer at the seabed the derived bed stress is used to predict the sand bed evolution laboratory experiments and corresponding numerical simulations for both high and low beach reflection are discussed for weak reflection the shear stress associated with the return current is found to be important partial simulation of a field record in cape cod bay is also described

the glacial geomorphology and pleistocene history of south america between 38 s and 56 s abstract this paper presents new mapping of the glacial geomorphology of southern south america between latitudes 38 s and 56 s approximately the area covered by the former patagonian ice sheets glacial geomorphological features including glacial lineations moraines meltwater channels trimlines sandur and cirques were mapped from remotely sensed images landsat 7 etm pan sharpened landsat 7 and aster the landform record indicates that the patagonian ice sheets consisted of 66 main outlet glaciers together with numerous local cirque glaciers and independent ice domes in the surrounding mountains in the northern part of the mapped area in the chilean lake district 38 42 s large piedmont glaciers developed on the western side of the andes and the maximum positions of these outlet glaciers are in general marked by arcuate terminal moraines to the east of the andes between 38 s and 42 s outlet glaciers were more restricted in extent and formed alpine style valley glaciers along the eastern flank of the andes south of 45 s a series of large fast flowing outlet glaciers drained the ice sheet the location of these outlet glaciers was topographically controlled and there was limited scope for interactions between individual lobes west of the andes at this latitude there is geomorphological evidence for an independent ice cap close to sea level on the taitao peninsula the age of this ice cap is unclear but it may represent evidence of glacier growth during the antarctic cold reversal and or younger dryas chronozone maximum glacier positions are difficult to determine along much of the western side of the andes south of 42 s because of the limited land there and it is assumed that most of these glaciers had marine termini in the south east of the mapped area in the fuegan andes cordillera darwin the landform record provides evidence of ice sheet initiation by adding published dates for glacier advances from the literature we present maps of pre last glacial maximum lgm glacier extent lgm extent and the positions of other large mapped moraines younger than lgm in age a number of large moraines occur within the known lgm limits the age of these moraines is unknown but since many of them lie well outside the established maximum neoglacial positions the possibility that they reflect a return to glacial climates during the younger dryas chronozone or antarctic cold reversal cannot be discounted

deglacial palaeoclimate at puerto del hambre subantarctic patagonia chile the primary objective of this study is to further substantiate multistep climatic forcing of late glacial vegetation in southern south america a secondary objective is to establish the age of deglaciation in estrecho de magallanes bahia inutil pollen assemblages at 2 cm intervals in a core of the mire at puerto del hambre 53 36 21 s 70 55 53 w provide the basis for reconstructing the vegetation and a detailed account of palaeoclimate in subantarctic patagonia chronology over the 262 cm length of core is regulated by 20 ams radiocarbon dates between 14 455 and 10 089 14c yr bp of 13 pollen assemblage zones the earliest representing the oldest dryas chronozone 14 455 13 000 14c yr bp records impoverished steppe with decreasing frequencies and loss of southern beech nothofagus successive 100 yr long episodes of grass herbs and of heath empetrum ericaceae before 14 000 14c yr bp infer deglacial successional communities under a climate of increased continentality prior to the establishment of grass dominated steppe the bolling allerod 13 000 11 000 14c yr bp is characterised by mesic grassland under moderating climate that with abrupt change to heath dominance after 12 000 14c yr bp was warmer and not as humid at the time of the younger dryas 11 000 10 000 14c yr bp grass steppe expanded with a return of colder more humid climate later with gradual warming communities were invaded by southern beech the puerto del hambre record parallels multistep deglacial palaeoclimatic sequences reported elsewhere in the southern andes and at taylor dome in antarctica deglaciation of estrecho de magallanes bahia inutil is dated close to 14 455 14c yr bp invalidating earlier dates of between 15 800 and 16 590 14c yr bp copyright 2000 john wiley sons ltd

archean microbial mat communities much of the archean record of microbial communities consists of fossil mats and stromatolites critical physical emergent properties governing the evolution of large scale centimeters to meters topographic relief on the mat landscape are a mat surface roughness relative to the laminar sublayer and b cohesion these properties can be estimated for fossil samples under many circumstances a preliminary analysis of archean mat cohesion suggests that mats growing in shallow marine environments from throughout this time had cohesions similar to those of modern shallow marine mats there may have been a significant increase in mat strength at the end of the archean

a field guide to finding fossils on mars the martian surface is cold dry exposed to biologically harmful radiation and apparently barren today nevertheless there is clear geological evidence for warmer wetter intervals in the past that could have supported life at or near the surface this evidence has motivated national aeronautics and space administration and european space agency to prioritize the search for any remains or traces of organisms from early mars in forthcoming missions informed by 1 stratigraphic mineralogical and geochemical data collected by previous and current missions 2 earth s fossil record and 3 experimental studies of organic decay and preservation we here consider whether how and where fossils and isotopic biosignatures could have been preserved in the depositional environments and mineralizing media thought to have been present in habitable settings on early mars we conclude that noachian hesperian fe bearing clay rich fluvio lacustrine siliciclastic deposits especially where enriched in silica currently represent the most promising and best understood astropaleontological targets siliceous sinters would also be an excellent target but their presence on mars awaits confirmation more work is needed to improve our understanding of fossil preservation in the context of other environments specific to mars particularly within evaporative salts and pore fracture filling subsurface minerals

reply to comment by martin f miller on record of δ18o and 17o excess in ice from vostok antarctica during the last 150 000 years that this excess was lower in glacial than in interglacial times we further suggested that the change in 17 o excess indicates smaller effect of kinetics signifying higher normalized humidity in the oceanic source region during glacials in his comment miller 2008 questions the validity of these conclusions on three grounds first he emphasizes that the measurements are reported with respect to the vsmow standard and not with respect to ocean water and therefore 17 o excess with respect to the ocean may not exist we note however that this point was raised by us landais et al 2008 p 3 and we emphasized the need for precise calibration with respect to seawater recently we luz and barkan 2008 have made precise calibration and reported that the triple oxygen isotope composition of vsmow is similar to seawater therefore we conclude that antarctic precipitation unambiguously contains 17 o excess with respect to the ocean

record of δ18o and 17o excess in ice from vostok antarctica during the last 150 000 years 1 we measured 17 o and 18 o in recent antarctic snow and down the vostok ice core and calculated the excess of 17 o with respect to vsmow the magnitude of the 17 o excess in the holocene and the last interglacial is 45 per meg and it remains constant in a transect from the coast to the continental interior analysis of the transect data shows that the 17 o excess is not sensitive to temperature variations over the continent there are significant shifts in 70 excess from low values in glacial to high values in interglacial times the observed shifts suggest higher normalized relative humidity and or wind speeds over the source oceanic regions in glacial times

facies relations depositional environments and diagenesis in a major early proterozoic stromatolitic carbonate platform to basinal sequence campbellrand subgroup transvaal supergroup southern africa the campbellrand subgroup and its correlative the malmani subgroup of the transvaal supergroup represent a major 2300 2600 ma old carbonate buildup it is on average between 1500 and 1700 m thick and covers an area of approximately 190 000 km2 on the kaapvaal craton the original depository probably extended across the entire 600 000 km2 surface area of the craton and beyond the buildup consists essentially of two major lithofacies assemblages namely a basinal non stromatolitic laminated carbonate and shale sequence with minor chert iron formation and mafic tuff interbeds off the craton to the west and a shallow water stromatolitic carbonate sequence on the craton proper growth faults along the edge of the craton controlled the platform margin defined by columnar stromatolite oolite and carbonate arenite shoal deposits these are flanked basinward by reef like giant subtidal stromatolitic mounds elongated perpendicular to the platform margin and grading into slope deposits consisting of laminated carbonates with interbeds of chaotic dolomite breccia and conophyton stromatolites platform lagoonal deposits consist of dark grey laminoid fenestrate stratified stromatolites interfingering to the interior of the craton with intertidal to supratidal light grey cherty dolomite units with a variety of structures such as domal and stratified stromatolites laminoid fenestrae tepee structures and flat pebble conglomerates the buildup consisted primarily of limestone which was replaced by early diagenetic dolomite the chemical composition of the dolomite is related to depofacies platform margin and lagoonal dolomites are manganese rich basinal dolomites are iron rich and intertidal to supratidal deposits are virtually free of iron and manganeses indications are that the carbonate buildup developed from an early carbonate ramp stage into a mature rimmed carbonate shelf eventually the carbonate shelf was drowned by a major transgression followed by the deposition of the kuruman iron formation

megafauna extinction in south america a new chronology for the argentine pampas abstract the megafauna extinction in south america was one of the most profound events with the loss of 50 genera 83 three orders disappeared notoungulata proboscidea litopterna as did all large xenarthrans but how this fits into global extinction is uncertain mainly due to the lack of chronological resolution in recent years there has been an increase in the number of radiocarbon dating at archeological and paleontological sites but this information varies greatly from area to area in south america and few data can be considered to constitute a taxon date the timing of the late pleistocene extinction in the pampas is poorly established most taxa only appear in the biostratigraphic context and many reported 14 c dates do not meet rigorous criteria for accepting dates including reports suggesting survival of megafauna into the holocene in the present paper we evaluate the published radiocarbon dates in the pampas and present 20 new radiocarbon dates for paleontological sites in order to establish a more accurate extinction window for the key taxa these new dates are sufficiently robust to assess correspondences among last appearance records of megafauna first appearance records of humans and the younger dryas to holocene climatic transition in the argentine pampas these results highlight the need for greater effort in taxa selection for dating

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

variations of 17o 16o and 18o 16o in meteoric waters the variations of d 17 o and d 18 o in recent meteoric waters and in ice cores have proven to be an important tool for investigating the present and past hydrologic cycle in order to close significant information gaps in the present distribution ofd 17 o and d 18 o of meteoric water we have run precise measurements with respect to vsmow on samples distributed globally from low to high latitudes based on the new and existing data we present the global meteoric water line gmwl ford 17 o andd 18 o as ln d 17 o 1 0 528 ln d 18 o 1 0 000033 r 2 0 99999 in addition to meteoric water we carried out the first measurements of seawater from the pacific and atlantic oceans with respect to vsmow the obtained results show that the slope of the trend line ln d 17 o 1 vs ln d 18 o 1 of seawater samples is 0 528 the same as for meteoric water but the regression intercept is 5 per meg thus the positive intercept in the gmwl indicates an excess of 17 o in meteoric waters with respect to the ocean an excess or depletion of 17 o in water is defined as 17 o excess ln d 17 o 1 0 528 d 18 o 1 most meteoric water samples have positive 17 o excess of varying magnitudes with an average of 37 per meg with respect to vsmow we explain how these positive values originate from evaporation of sea water into marine air which is undersaturated in water vapor and how subsequent increase of 17 o excess occurs when atmospheric vapor condenses to form liquid and solid precipitation we also clarify the effect of excessive evaporation on 17 o excess finally based on the new results on 17 o excess of seawater we recalculated the relationship of d 17 o vs d 18 o in vapor diffusion in air as 18 adiff 1 0096

cenozoic glaciation in the southern hemisphere with the end of glaciation in gondwana in early permian time a prolonged interval began when the earth was without ice sheets though not necessarily free of mountain glaciers not until sometime during the tertiary era did ice sheets build up once more first in antarctica and later in the northern hemisphere the fundamental cause of the cooling that led to the formation of the antarctic ice sheet and eventually to major glaciation in lower latitudes is generally held to have been the increasing thermal isolation of antarctica as australia and later south america separated from it allowing zonal oceanic circulation to develop rifting between australia and antarctica began between 1 10 and 90 m y ago cande mutter 1982 but not until much later probably sometime between 30 and 25 m y ago had it progressed far enough for deep circulation to begin as the south tasman rise cleared north victoria land kennett et a1 1974 kennett 1977 weissel et ai 1977 however antarctica did not reach its present high level of thermal isolation until south america had separated from it enabling the antarctic circumpolar current to become established savin et ai 1975 according to barker burrell 1977 1982 coherent spreading between the antarctic peninsula and tierra del fuego started about 29 m y ago and deep circulation began 23 5 2 5 m y ago thereafter increasing in volume the initial ice fields and ice caps that later expanded to become the

middle late holocene palynology and marine mollusks from archipielago cormoranes area beagle channel southern tierra del fuego argentina abstract the palynology and marine mollusks of a marine sequence from rio ovando 54 51 s 68 35 w archipielago cormoranes beagle channel has been studied in order to reconstruct paleoenvironmental conditions during the middle late holocene the dinoflagellate cyst assemblages from rio ovando sequence reflect fjord estuarine environments close to terrestrial ice field affected by glacier meltwater discharge and characterized by short term oscillations of sea surface water parameters the base of the section which is dated at about ca 4160 14 c yr b p 4736 cal yr b p palynological subzone ro 2c is characterized by a high species diversity of dinocyst and mollusks and it is immediately followed by an interval palynological subzone ro 2b characterized by the presence of the echinidinium islandinium complex and the monospecific mytilus mollusk assemblage this subzone registers an inverse correlation between nothofagus dombeyi type and echinidinium islandinium complex concentration values during ca 4160 14 c yr b p 4736 cal yr b p 4064 14 c yr b p 4540 cal yr b p suggesting a variable climatic condition probably related to neoglacial episodes occurred in the southern patagonia andes during this interval the pollen assemblages permit direct correlations with the onshore palynostratigraphy from southern of tierra del fuego the high percentages of nothofagus dombeyi type recorded throughout most of the profile strongly suggest the presence of a closed forest confirming the existence of a variable cool and wet climate for the archipielago cormoranes area during the middle late holocene

precipitation regime influence on oxygen triple isotope distributions in antarctic precipitation and ice cores abstract the relative abundance of 17o in meteoric precipitation is usually reported in terms of the 17o excess parameter variations of 17o excess in antarctic precipitation and ice cores have hitherto been attributed to normalised relative humidity changes at the moisture source region or to the influence of a temperature dependent supersaturation controlled kinetic isotope effect during in cloud ice formation below 20 c neither mechanism however satisfactorily explains the large range of 17o excess values reported from measurements a different approach based on the regression characteristics of 10 3 ln 1 17 o versus 10 3 ln 1 18 o is applied here to previously published isotopic data sets the analysis indicates that clear sky precipitation diamond dust which occurs widely in inland antarctica is characterised by an unusual relative abundance of 17o distinct from that associated with cloud derived synoptic snowfall furthermore this distinction appears to be largely preserved in the ice core record the respective mass contributions to snowfall accumulation on both temporal and spatial scales provides the basis of a simple first order explanation for the observed oxygen triple isotope ratio variations in antarctic precipitation surface snow and ice cores using this approach it is shown that precipitation during the last major deglaciation both in western antarctica at the west antarctic ice sheet wais divide and at vostok on the eastern antarctic plateau consisted essentially of diamond dust only despite a large temperature differential and thus different water vapour supersaturation conditions at the two locations in contrast synoptic snowfall events dominate the accumulation record throughout the holocene at both sites

the impact of cold north atlantic sea surface temperatures on climate implications for the younger dryas cooling 11 10 k the sensitivity of global climate to colder north atlantic sea surface temperatures is in vestigated with the use of the giss general circulation model north atlantic ocean temperatures 18 000 b p resembling those prevalent during the younger dryas were incorporated into the model of the present climate and also into an experiment using orbital parameters and land ice characteristic of 11 000 b p the results show that with both 11 000 b p and present conditions the colder ocean temperatures produce cooling over western and central europe in good agreement with younger dryas paleoclimatic evidence cooling also occurs over extreme eastern north america although the precise magnitude and location depends upon the specification of ocean temperature change in the western atlantic despite the presence of increased land ice and colder ocean temperatures the younger dryas summer air temperatures at northern hemisphere midlatitudes in the model are warmer than those of today due to changes in the orbital parameters chiefly precession and atmospheric subsidence at the perimeter of the ice sheets

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

multiple longshore sand bars in the upper chesapeake bay abstract in the upper chesapeake bay maryland u s a field surveys were conducted at 18 multiple longshore sand bar sites the multiple bar systems were found in water depths less than approximately 2 m mean sea level and exhibited mild bottom slopes of 0 0052 or less the number of bars composing each system ranged from four to 17 and the spacing between the crests typically increased in the offshore direction ranging from 12 to 70 m bar height also typically increased with distance offshore and ranged from 0 03 to 0 61 m a grain size analysis of crest and trough sediment did not reveal any significant differences and the sediment was categorized as fine sand a review of the literature data indicated that the chesapeake bay multiple bars possessed similar characteristics to those found in gelding bay baltic sea similarities in fetch wave height and tidal range between the two bays may account for this finding the surf scaling parameter indicated that the multiple bar systems were extremely dissipative with regard to wave energy and wave height appeared to be an important factor in controlling bar spacing and bar height a multiple wave break point hypothesis was discussed as a possible mechanism for the formation of chesapeake bay multiple longshore bars and limited observational evidence appeared to support such a mechanism

langmuir turbulence in shallow water part 1 observations during extended deployment at an ocean observatory off the coast of new jersey a bottom mounted five beam acoustic doppler current profiler measured large scale velocity structures that we interpret as langmuir circulations filling the entire water column these circulations are the large eddy structures of wind wave driven turbulent flows that occur episodically when a shallow water column experiences prolonged strong wind forcing many observational characteristics agree with former descriptions of langmuir circulations in deep water the three dimensional velocity field reveals quasi organized structures consisting of pairs of surface intensified counter rotating vortices aligned approximately downwind maximum downward velocities are stronger than upward velocities and the downwelling region of each cell defined as a pair of vortices is narrower than the upwelling region maximum downward vertical velocity occurs at or above mid depth and scales approximately with wind speed the estimated crosswind scale of cells is roughly 3 6 times their vertical scale set under these conditions by water depth the long axis of the cells appears to lie at an angle 10 20 to the right of the wind a major difference from deep water observations is strong near bottom intensification of the downwind jets found typically centred over downwelling regions accessible observational features such as cell morphology and profiles of mean velocities turbulent velocity variances and shear stress components are compared with the results of associated large eddy simulations reported in part 2 of shallow water flows driven by surface stress and the craik leibovich vortex forcing generally used to represent generation of langmuir cells a particularly sensitive diagnostic for identification of langmuir circulations as the energy containing eddies of the turbulent flow is the depth trajectory of invariants of the turbulent stress tensor plotted in the lumley triangle corresponding to realizable turbulent flows when langmuir structures are present in the observations the lumley map is distinctly different from that of surface stress driven couette flow again in agreement with the large eddy simulations les unlike the les observed velocity fields contain two distinct and significant scales of variability documented by wavelet analysis of observational records of vertical velocity variability with periods of many minutes is that expected from langmuir cells drifting past the instrument at the slowly time varying crosswind velocity shorter period variability of the order of 1 2 min has roughly the observed periodicity of surface wave groups suggesting a connection with the wave groups themselves and or the wave breaking associated with them in high wind conditions

expansion of magellanic moorland during the late pleistocene palynological evidence from northern isla de chiloe chile the late quaternary vegetation of northern isla de chiloe is inferred from palynological analysis of a section in the rio negro drainage 42 03 s 73 50 w at ca 30 500 yr b p maxima of astelia and donatia occurred suggesting wetland development from that time until ca 27 000 yr b p steppe indicators such as compositae gramineae dominated suggesting drier conditions after 27 000 yr b p the moorland shrub dacrydium gradually increased reaching a maximum by 18 000 yr b p at this time astelia increased again suggesting development of cushion bog during cold and wet conditions the glacial postglacial transition is characterized by a marked change from peaty sediments to clays a decrease in the cushion bog flora and the prevalence of gramineae compositae and swamp taxa this vegetation prevailed until ca 7000 yr b p when forest taxa became dominant the floristic pattern inferred from the pollen spectra of the rio negro section suggests that the late pleistocene vegetation of chiloe resembled modern magellanic moorland vegetation 52 56 lat s based on climatic conditions presently associated with magellanic moorland its occurrence in chiloe at low elevations during the late pleistocene implies a decrease in average temperature of at least 4 c and an increase in annual precipitation of at least 1500 mm

the meaning of stromatolites stromatolites document microbial interactions with sediments and flowing water throughout recorded earth history and have the potential to illuminate the long term history of life and environments modern stromatolites however provide analogs to only a small subset of the structures preserved in archean and proterozoic carbonates thus interpretations of secular trends in the shapes and textures of ancient columnar stromatolites require nonuniformitarian scale dependent models of microbial responses to nutrient availability seawater chemistry influx of sediment grains shear and burial models that integrate stromatolite scales macroscopic organization and shapes could also help test the biogenicity of the oldest stromatolites and other structures whose petrographic fabrics do not preserve direct evidence of microbial activity an improved understanding of stromatolite morphogenesis in the presence of oxygenic and anoxygenic microbial mats may illuminate the diversity of microbial metabolisms tha

quaternary of tierra del fuego southernmost south america an updated review abstract the quaternary of tierra del fuego is represented by glacial glaciofluvial glaciolacustrine marine and aeolian deposits six drift units have been described the oldest dating from the late pliocene these are starting from the oldest the rio grande sierra de los frailes cabo virgenes punta delgada primera angostura and segunda angostura drifts neoglacial and little ice age events are represented in cirques and higher mountain valleys marine deposits and raised beaches were formed during middle pleistocene late pleistocene and holocene interglacial stages after the definitive ice retreat 10 ka ago vegetation changed from tundra and cold steppe to subantarctic forest environments marine deposits reflect also colder conditions than the present ones aeolian processes prevailed in northern tierra del fuego where semiarid conditions and the frequent westerlies favoured the retransportation of finer materials coming from pre existing deposits before the opening of the magellan straits earliest human colonization occurred in northern tierra del fuego ca 11 ka bp in tundra like environmental conditions pedestrian hunters of camelids and foxes co existed with pleistocene fauna that became extinct during late glacial earliest holocene times the steppe area inland and atlantic coast was successively occupied since then until recent times on the other hand the beagle channel coasts were occupied since 6 ka bp by hunter gatherer groups adapted to maritime littoral conditions finally the easternmost area of the island was inhabited at least since 1 5 ka bp the human settlements in these latter areas occurred under environmental conditions similar to the present ones when the fuegian forest was definitively established

estuarine biofilm patterns modern analogues for precambrian self organization this field and laboratory study examines whether regularly patterned biofilms on present day intertidal flats are equivalent to microbially induced bedforms found in geological records dating back to the onset of life on earth algal mats of filamentous vaucheria species functionally similar to microbial biofilms cover the topographic highs of regularly spaced ridge runnel bedforms as regular patterning is typically associated with self organization processes indicators of self organization are tested and found to support this hypothesis the measurements suggest that biofilm induced sediment trapping and biostabilization enhance bedform relief strength and multi year persistence this demonstrates the importance of primitive organisms for sedimentary landscape development algal covered ridges consist of wavy crinkly laminated sedimentary deposits that resemble the layered structure of fossil stromatolites and microbially induced sedimentary structures in addition to layering both the morphological pattern and the suggested formation mechanism of the recent bedforms are strikingly similar to microbialite strata found in rock records from the precambrian onwards this implies that self organization was an important morphological process in times when biofilms were the predominant sessile ecosystem these findings furthermore emphasize that self organization dynamics such as critical transitions invoking ecosystem emergence or collapse might have been captured in fossil microbialites influencing their laminae this notion may be important for paleoenvironmental reconstructions based on such strata

glacial geomorphology of the pleistocene lake fagnano ice lobe tierra del fuego southern south america abstract a regional geomorphological study is presented of the southern and eastern coast of lake fagnano one of the most extensive glacial areas of tierra del fuego island at the southernmost tip of south america a palaeoglacial reconstruction is made based on the location of erosional and depositional glacial landforms the outlet glacier flowing eastwards from the darwin cordillera fuegian andes chile had more than 50 tributary glaciers an alpine type landscape including aretes cirques truncated spurs and hanging valleys developed in the western region of the present lake whereas a piedmont type landscape including lateral moraines glaciofluvial and glaciolacustrine terraces and an ice disintegration landscape developed in the eastern region the glacier spread over the low ranges and lowlands through three different lobes and was drained by four main outwash basins directly into the atlantic ocean the ice covered area is estimated at 4000 km 2 the maximum length of the main lobe at 132 km and the general slope at 8 four terminal positions of the glacier were recognized and related to the inutil bay and beagle channel glacial areas located to the north and south respectively 14 c dates from basal peats show that most of the area especially the easternmost part and the southern coast were free of ice by 12 300 years b p fossil peat contained in the lower basal till deposits yield 14 c dates of 31 000 48 200 years b p indicating that a glacial advance occurred in the area prior to the last glacial maximum ca 25 000 23 000 cal years b p

holocene glacier variations in new zealand a review abstract in the central southern alps of new zealand ice surface lowering has exposed extensive sections of lateral moraines allowing investigation of moraine stratigraphy and genesis the presence of multiple superposed palaeosurfaces within moraine sequences allows recognition of any disturbances displacements or contamination of till layers and interbedded organic material radiocarbon dating of buried wood and soils allows comparison between the holocene glacial history of the eastern ranges and that of the westland region the periodicity of glacier response has been similar to both areas although the precise timing of events has differed due to local climatic and environmental factors in general glaciers in new zealand expanded about 5000 4500 4200 3700 3500 3000 2700 2200 1800 1700 1500 1100 900 700 600 and 400 100 bp

a 150 000 year climatic record from antarctic ice during much of the quaternary the earth s climate has undergone drastic changes most notably successive glacial and interglacial episodes the past 150 kyr includes such a climatic cycle the last interglacial the last glacial and the present holocene interglacial a new climatic time series for this period has been obtained using 18 o data from an antarctic ice core

climate induced changes as registered in inorganic and organic sediment components from laguna potrok aike argentina during the past 51 ka total organic carbon total inorganic carbon biogenic silica content and total organic carbon total nitrogen ratios of the laguna potrok aike lacustrine sediment record are used to reconstruct the

multiproxy record of holocene paleoenvironmental change tierra del fuego argentina abstract we interpret holocene environmental conditions in a subantarctic high andean valley from palynological and diatom analysis peat stratigraphy and local geomorphology the multiproxy data from las cotorras mire 54 41 13 s 68 02 51 w 420 m a s l indicate the development of a soligenous mire as a result of a fine grained tephra layer deposition over the mineral soils sometime prior to 8000 cal yr bp the paleoecological conditions in the mire after 8000 cal yr bp show a rapid succession from a limnic to a telmatic stage as the mire is colonized by sedges cyperaceae and herbaceous communities the upland vegetation changed from cushion and shrub heaths to an expansion of nothofagus forest at high altitudes after 6500 cal yr bp the peat is interbedded with clastic sediment that originates from mass wasting events or floods these depositional changes affected the mire ecosystem water table level and nutrient status oligotrophic and or eutrophic conditions maxima in total pollen influx at about 2800 1100 and 700 cal yr bp coincide with heightened mineral flux and these changes are related to precipitation and slope processes the major vegetational change registered in the pollen record is the decline of nothofagus pollen after 1000 cal yr bp which reaches a minimum between ca 680 and 300 cal yr bp this minimum was likely caused by cool wet conditions that coincided with the little ice age lia in the southern hemisphere our results indicate the sensitivity of subantarctic nothofagus forest and mire ecosystems to changes during the holocene

late holocene and little ice age palaeoenvironmental change inferred from pollen analysis isla de los estados argentina we present pollen and spore analysis from a peat bog section from southwestern isla de los estados staaten island tierra del fuego to better understand late holocene environmental change in southernmost patagonia the island s position as the easternmost landmass at the southernmost of south america places it squarely within the influence of the southern westerly winds sww and the antarctic circumpolar current and so makes the island a unique location to document the palaeoecological response to climate change during the late quaternary we compare our nothofagus pollen record from bahia franklin with other nothofagus pollen records from isla de los estados and tierra del fuego nothofagus has been shown to respond to changes in mean annual temperature in the southern latitudes under cooler climate with little seasonality in precipitation we also evaluate the correspondence between these changes in vegetation to other late holocene environmental proxies that include variations in sea surface temperature sst from the beagle channel and records of past glacier fluctuations our results show that low concentrations of nothofagus pollen existed at bahia franklin at about 4000 cal yr bp climate ameliorated between ca 3500 and 500 cal yr bp based on an increase in frequency and concentration values of nothofagus and drimys winteri between about 500 and 50 cal yr bp the pollen record revealed a noticeable decline in the forest density we interpret the decline in forest density in isla de los estados between 500 and 50 yr cal bp as a response to cold and windy conditions during the little ice age lia our interpretation from our nothofagus pollen record broadly agrees with regional cooling recorded in reconstructed sst of the beagle channel and with glacier expansion in the fuegian cordillera

microbial shaping of sedimentary wrinkle structures wrinkle structures in ancient sedimentary environments are enigmatic wave tank experiments suggest that wrinkle structures are shaped by microbial mat fragments that are moved by waves over sandy bed surfaces and thus are morphological biosignatures

lateglacial and holocene wet dry cycles in southern patagonia chronology sedimentology and geochemistry of a lacustrine record from laguna potrok aike argentina a high resolution multiproxy geochemical approach was applied to the sediments of laguna potrok aike in an attempt to reconstruct moist and dry periods during the past 16 000 years in south eastern patagonia the age depth model is inferred from ams 14 c dates and tephrochronology and suggests moist conditions during the lateglacial and early holocene 16 000 8700 cal bp interrupted by drier conditions before the beginning of the holocene 13 200 11 400 cal bp data also imply that this period was a major warm phase in southeastern patagonia and was approximately contemporane ous with the younger dryas chronozone in the northern hemisphere 12 700 11 500 cal bp after 8650 cal bp a major drought may have caused the lowest lake level of the record since 7300 cal bp the lake level rose and was variable until the little ice age which was the dominant humid period after 8650 cal bp