extensive liquid meltwater storage in firn within the greenland ice sheet surface melt water from the greenland ice sheet can become trapped in firn delaying its journey to the sea radar and ice core observations provide direct evidence of a perennial aquifer in the firn layer in southern greenland that represents a potentially significant contribution to the greenland mass budget

vegetation and climate change fire regime shifts and volcanic disturbance in chiloe continental 43 s during the last 10 000 years abstract disentangling the roles of paleofires and explosive volcanism from climatic drivers of past vegetation change is a subject insufficiently addressed in the paleoecological literature the coastal region of the chiloe continental sector of northwestern patagonia is ideal in this regard considering its proximity to active eruptive centers and the possibility of establishing comparisons with more distal upwind sites where volcanic influence is minimal here we present a fine resolution pollen and macroscopic charcoal record from lago teo with the aim of documenting the local vegetation and climate history and assessing the role of disturbance regimes as drivers of vegetation change during the last 10 000 years the lago teo record shows a conspicuous warm dry interval between 7500 and 10 000 cal yrs bp followed by a cooling trend and increase in precipitation that has persisted until the present in agreement with previous studies in the region and interpretations of past southern westerly wind activity at multi millennial scales the presence of 26 tephras throughout the record allows examination of the relationship between explosive volcanism and vegetation change under contrasting climatic states of the holocene we found consistent statistically significant increases in tepualia stipularis after tephra deposition over the last 10 000 years in eucryphia caldcluvia between 7500 and 10 000 cal yrs bp and in hydrangea over the last 7500 years our results indicate a primary role of climate change as driver of long term vegetation change and as a modulator of vegetation responses to volcanic disturbance at multidecadal and centennial timescales

changes in latitudinal sea surface temperature gradients along the southern chilean margin since the last glacial abstract the comparison between different climate model simulations of water hosing experiments under glacial conditions points toward diverging responses in sea surface temperature changes sst especially in the southeast pacific sep this suggests that reconstituting the latitudinal sst gradient in the sep is a critical parameter for a better understanding of the mechanisms behind the abrupt climatic events since the last glacial period here we present high resolution records of sst using planktonic foraminiferal assemblages and alkenone temperature reconstructions and stable oxygen and carbon isotopes from three deep sea sediment cores along a latitudinal transect off the southern chilean coast this allowed us to reconstruct the variations of the latitudinal sst gradient and the subtropical front movements in the sep the sst results suggest a clear antarctic timing consistent with the bipolar seesaw control especially during the late glacial and the deglaciation our records do not suggest a complete oceanic heat transfer signal highlighting the implication of an atmospheric component in the heat transfers between the two hemispheres controlled by the latitudinal movements of the intertropical convergence zone in the atlantic and the associated weaker south pacific westerly split jet furthermore our records indicate variable conditions during the holocene and also emphasize the influence of local fresh water inputs from the patagonian ice sheet and or precipitation on the sst fresh water input estimates along the chilean margin north and south of 49 s from the onset of the deglaciation until 8 kyr cal bp

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

lhasa terrane in southern tibet came from australia the u pb age and hf isotope data on detrital zircons from paleozoic metasedimentary rocks in the lhasa terrane tibet defi ne a distinctive age population of ca 1170 ma with e hf t values identical to the coeval detrital zircons from western australia but those from the western qiangtang and tethyan himalaya terranes defi ne an age population of ca 950 ma with a similar e hf t range the ca 1170 ma detrital zircons in the lhasa terrane were most likely derived from the albany fraser belt in southwest australia whereas the ca 950 ma detrital zircons from both the western qiangtang and tethyan himalaya terranes might have been sourced from the high himalaya to the south such detrital zircon connections enable us to propose that the lhasa terrane is exotic to the tibetan plateau system and should no longer be considered as part of the qiangtang greater india tethyan himalaya continental margin system in the paleozoic reconstruction of the indian plate as current models show rather it should be placed at the northwestern margin of australia these results provide new constraints on the paleogeographic reconstruction and tectonic evolution of southern tibet and indicate that the lhasa terrane evolved as part of the late precambrian early paleozoic evolution as part of australia in a different paleogeographical setting than that of the qiangtang greater india tethyan himalaya system

distributed subglacial discharge drives significant submarine melt at a greenland tidewater glacier this is the publisher s final pdf the article is copyrighted by american geophysical union and published by john wiley sons inc it can be found at http agupubs onlinelibrary wiley com agu journal 10 1002 28issn 291944 8007

full glacial late glacial palaeoclimate of the southern andes evidence from pollen beetle and glacial records palaeoecological studies carried out in the chilean lake district and chilotan archipelago 41 43 s record full glacial and late glacial pollen assemblages beginning just after 21000 and beetle assemblages after 18000 both sets extending until 10000 14c yr bp pollen records indicate that subantarctic parkland the vegetation of the early millennia of record changed after about 14000 yr bp to become open woodland and later north patagonian evergreen forest assemblages of plants and beetles responding more or less in unison to a strong rise in temperature 6 c behaved in accord at around 14000 until 13000 12500 yr bp the beetle fauna displaying a marked increase in obligate forest types during full glacial conditions 17400 16100 and 15300 and 14400 yr bp and in the late glacial interval after about 13000 yr bp however climate evidently coerced populations dissimilarly the pollen sequence showing an increase in plant taxa indicative of colder climate whereas the beetle fauna underwent little or no variation contrasting climate modes implied by plants and beetles may be attributed to differential responses to apparent low order temperature changes 2 3 c

rapid submarine melting of the calving faces of west greenland glaciers widespread glacier acceleration has been observed in greenland in the past few years oceanographic observations taken in summer 2008 show that ocean waters melted a substantial fraction of ice along the calving fronts of three west greenland glaciers indicating that submarine melting has a profound influence on grounding line stability widespread glacier acceleration has been observed in greenland in the past few years1 2 3 4 associated with the thinning of the lower reaches of the glaciers as they terminate in the ocean5 6 7 these glaciers thin both at the surface from warm air temperatures and along their submerged faces in contact with warm ocean waters8 little is known about the rates of submarine melting9 10 11 and how they may affect glacier dynamics here we present measurements of ocean currents temperature and salinity near the calving fronts of the eqip sermia kangilerngata sermia sermeq kujatdleq and sermeq avangnardleq glaciers in central west greenland as well as ice front bathymetry and geographical positions we calculate water mass and heat budgets that reveal summer submarine melt rates ranging from 0 7 0 2 to 3 9 0 8 m d 1 these rates of submarine melting are two orders of magnitude larger than surface melt rates but comparable to rates of iceberg discharge we conclude that ocean waters melt a considerable but highly variable fraction of the calving fronts of glaciers before they disintegrate into icebergs and suggest that submarine melting must have a profound influence on grounding line stability and ice flow dynamics

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

evaluation of cryo hydrologic warming as an explanation for increased ice velocities in the wet snow zone sermeq avannarleq west greenland 1 wintertime satellite derived ice surface velocities from 2001 through 2007 suggest an increase in ice velocity in the wet snow zone of southwest greenland we present a thermomechanical model to evaluate the influence of surface meltwater runoff on englacial temperatures via cryo hydrologic warming chw as a possible mechanism to explain this velocity increase at sermeq avannarleq the model incorporates chw through a previously published dual column parameterization we compare model simulations with i chw active over the entire ice thickness base case chw ii chw active only in the surface 80 m of the ice sheet surface chw and iii no chw to represent a traditional thermomechanical model the horizontal extent of chw is prescribed based on equilibrium line altitude position and thus incorporates the upstream expansion of the ablation zone over the past decade the base case chw simulations reproduce the observed increase in inland ice velocity between 2001 and 2007 reasonably well the no chw and surface chw simulations significantly underestimate observed ice surface velocities in both epochs the higher ice velocities in the base case chw simulations are attributable to both decreased basal ice viscosities associated with increased basal ice temperatures and an increase in the extent of basal sliding permitted by temperate bed conditions only the temperate bed extent predicted by the base case chw simulation is consistent with independent observations of basal sliding based on our sensitivity analysis of chw we evaluate alternative explanations for an increase in inland ice velocity and suggest chw is the most plausible mechanism

the southern oscillation part ix the influence of volcanic eruptions on the southern oscillation in the stratosphere abstract the signal in the winter stratosphere on the northern hemisphere of a warm event in the southern oscillation is a warm polar vortex with a weak westerly circulation this signal failed to appear in two warm events which took place at the time of the eruptions of agung and el chichon we propose that the volcanic emissions affected the development of the warm events in the stratosphere and support this argument by reference to a sensitivity experiment made by m blackmon this experiment used the observed global anomalies of sea surface temperature in december january february 1982 83 but did not consider volcanic aerosols and gasses ejected by el chichon in 1982 the response of the model stratosphere in the experiment resembled the observed signal of the southern oscillation in other years

chironomid and pollen evidence for climate fluctuations during the last glacial termination in nw patagonia abstract we present chironomid and pollen records from the huelmo site 41 30 s nw patagonia to examine in detail the timing and structure of climate changes during the last glacial termination in the southern mid latitudes the chironomid record has the highest temporal and taxonomic resolution for this critical interval and constitutes the first account of midge faunas at the culmination of the last glacial maximum lgm for the region the chironomid record suggests cold and wet conditions during the lgm followed by deglacial warming between 17 6 and 16 8 cal kyr bp relatively warm conditions prevailed between 15 14 cal kyr bp followed by a reversal in trend with cooling pulses at 14 and 13 5 cal kyr bp and warming at the beginning of the holocene cool temperate conditions prevailed during the huelmo mascardi cold reversal hmcr which according to chironomid data exhibits a wet phase 13 5 12 8 cal kyr bp followed by a conspicuous drier phase 12 8 11 5 cal kyr bp the chironomid and pollen records from the huelmo site indicate step wise deglacial warming beginning at 17 6 cal kyr bp in agreement with other paleoclimate records from nw patagonia and isotopic signals from antarctic ice cores peak warmth during the last glacial termination was achieved by 14 5 cal kyr bp followed by a cooling trend that commenced during the antarctic cold reversal which later intensified and persisted during the hmcr 13 5 11 5 cal kyr bp we observe a shift toward drier conditions at 12 8 cal kyr bp superimposed upon the hmcr coeval with intense fire activity and vegetation disturbance during younger dryas time

in situ cosmogenic 10be production rate at lago argentino patagonia implications for late glacial climate chronology abstract when calculated with the commonly accepted average northern hemisphere production rate 10 be dates of surface boulders on moraines in the lago argentino area of patagonia are younger than minimum limiting 14 c ages for the same landforms this disagreement could result from the lack of a regional 10 be production rate calibration site to assess this possibility we here present high precision measurements of 10 be in samples collected from surface boulders on the herminita and puerto bandera moraine complexes deposited alongside lago argentino on the eastern flank of the andes at 50 s in patagonia together with maximum and minimum limiting 14 c ages for the two moraine systems these measurements confine the local 10 be production rate to between 3 60 and 3 82 atoms g yr midpoint 3 71 0 11 atoms g yr when using a time dependent scaling method that incorporates a high resolution geomagnetic model this range includes upper and lower error bounds of acceptable production rates derived from both the herminita and the puerto bandera sites the upper limit of this range is more than 12 below the average northern hemisphere production rate as calculated using the same scaling method given in balco et al quat geochron 3 2008 174 195 other scaling models yield production rates with similarly large offsets from the balco et al 2008 rate on the other hand the range of acceptable production rate values determined from patagonia overlaps at 1 with and encompasses the production rate recently derived in macaulay valley in the southern alps of new zealand a putnam et al quat geochron 5 2010a 392 409 within uncertainties i e overlap at 1 sigma this patagonian production rate range also agrees with a recently determined production rate from low elevation sites in northeastern north america and northern norway when the macaulay production rate is used to calculate patagonian exposure dates 14 c and 10 be chronologies are mutually compatible for late glacial moraine systems both chronologies then indicate that outlet glaciers of the southern patagonian icefield achieved a late glacial maximum in the western reaches of lago argentino at 13 000 cal yr bp at the end of the antarctic cold reversal 14 500 12 900 cal yr bp outlet glaciers subsequently receded to near present day ice margins during the younger dryas stadial 12 900 11 700 cal yr bp this general retreat was interrupted about 12 200 cal yr bp when upsala glacier constructed an interlobate complex of moraine ridges on herminita peninsula mountain glaciers in patagonia and new zealand on both sides of the south pacific ocean exhibited a coherent pattern of late glacial ice margin fluctuations

basal drainage system response to increasing surface melt on the greenland ice sheet surface meltwater reaching the bed of the greenland ice sheet imparts a fundamental control on basal motion sliding speed depends on ice bed coupling dictated by the configuration and pressure of the hydrologic drainage system in situ observations in a four site transect containing 23 boreholes drilled to greenland s bed reveal basal water pressures unfavorable to water draining conduit development extending inland beneath deep ice this finding is supported by numerical analysis based on realistic ice sheet geometry slow meltback of ice walls limits conduit growth inhibiting their capacity to transport increased discharge key aspects of current conceptual models for greenland basal hydrology derived primarily from the study of mountain glaciers appear to be limited to a portion of the ablation zone near the ice sheet margin

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

high resolution marine record of climatic change in mid latitude chile during the last 28 000 years based on terrigenous sediment parameters abstract marine sediment cores from the continental slope off mid latitude chile 33 s were studied with regard to grain size distributions and clay mineral composition the data provide a 28 000 yr14c accelerator mass spectrometry dated record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland these variations can be interpreted in terms of the paleoclimatic evolution of mid latitude chile and are compared to existing terrestrial records glacial climates 28 000 18 000 cal yr b p were generally cold humid with a cold semiarid interval between 26 000 and 22 000 cal yr b p the deglaciation was characterized by a trend toward more arid conditions during the middle holocene 8000 4000 cal yr b p comparatively stable climatic conditions prevailed with increased aridity in the coastal range the late holocene 4000 0 cal yr b p was marked by more variable paleoclimates with generally more humid conditions variations of rainfall in mid latitude chile are most likely controlled by shifts of the latitudinal position of the southern westerlies compared to the holocene the southern westerly wind belt was located significantly farther north during the last glacial maximum less important variations of the latitudinal position of the southern westerlies also occurred on shorter time scales

reconciling the onset of deglaciation in the upper rangitata valley southern alps new zealand abstract enquiry into the detailed timing of paleoclimate events depends on well resolved and reliable chronologies a recently published set of 10be surface exposure ages for moraine boulders in the upper rangitata valley was interpreted to indicate a gradual reduction in glacier surface height between c 21 and c 17 ka without rapid glacier recession beginning c 18 ka as reported from other valleys the dating results were suggested to be consistent with moraine geomorphology and an interpreted lack of post glacial lake formation in the valley in contrast we argue that the geomorphology is consistent with sustained glacier recession and we highlight evidence for a post glacial lake furthermore the upper rangitata moraine chronology was encumbered by inaccurate altitude values assigned to many of the sample sites recalculation of the 10be ages using accurate elevations produces values that are as much as 3000 years younger than originally reported the recalculated values indicate no significant age difference across the c 300 m relative altitudinal spread of sample locations with mean age of all samples c 17 7 0 3 ka the previous inference of slow late glacial ice retreat is not supported by the recalculated chronology rather the revised glacial chronology implies that substantial ice surface lowering of the last glacial maximum rangitata glacier was in progress shortly after c 18 ka the revised upper rangitata chronology is compatible with dating from other eastern valleys of the southern alps indicating moraine formation at c 18 ka followed by sustained glacier recession associated with regional climatic amelioration

climatic controls of holocene fire patterns in southern south america holocene fire climate vegetation linkages are mostly understood at individual sites by comparing charcoal and pollen records with other paleoenvironmental proxy and model simulations this scale of reconstruction often obscures detection of large scale patterns in past fire activity that are related to changes in regional climate and vegetation a network of 31 charcoal records from southern south america was examined to assess fire history along a transect from subtropic to subantarctic biomes the charcoal data indicate that fire activity was greater than present at ca 12 000 cal yr bp and increased further and was widespread at 9500 cal yr bp fire activity decreased and became more spatially variable by 6000 cal yr bp and this trend continued to present atmospheric circulation anomalies during recent high fire years show a southward shift in westerlies and paleoclimate model simulations and data syntheses suggest that such conditions may have prevailed for millennia in the early holocene when the pole to equator temperature gradients were weaker and annual temperatures were higher than present in response to orbital time scale insolation changes

climatic and disturbance influences on the temperate rainforests of northwestern patagonia 40 s since 14 500 cal yr bp abstract we present a detailed record from lago pichilafquen to unravel the vegetation climate and disturbance history of the lowlands of northwestern patagonia 40 s since 14 500 cal yr bp the presence of 30 tephras throughout the record attest for the proximity of the site to active volcanic centres and allows assessment of the role of volcanic disturbance on past vegetation and fire regime shifts we interpret alternations in dominance between north patagonian and valdivian rainforests driven by changes in temperature and precipitation of westerly origin at multi millennial and millennial timescales these trends were punctuated by centennial scale changes most of which were coeval with or immediately followed the deposition of tephras and or paleofires we identify departures of the local vegetation from the regional trend between 2400 and 7100 cal yr bp which we interpret as a response of rainforest vegetation and local fire regimes to the disturbance effect of tephra deposition near lago pichilafquen we also find that volcanic disturbance promoted consistent increases in eucryphia caldcluvia within 30 years and paleofires between 60 and 120 years following tephra deposition comparisons with palynological records having similar span time resolution and age control suggest that regional climate has played a central role on the establishment composition and maintenance of temperate rainforests this influence is overprinted by disturbance regimes at the local and landscape level driving divergences and heterogeneity especially at times of relatively weak climatic forcing

seasonal speedup along the western flank of the greenland ice sheet it has been widely hypothesized that a warmer climate in greenland would increase the volume of lubricating surface meltwater reaching the ice bedrock interface accelerating ice flow and increasing mass loss we have assembled a data set that provides a synoptic scale view spanning ice sheet to outlet glacier flow with which to evaluate this hypothesis on the ice sheet these data reveal summer speedups 50 to 100 consistent with but somewhat larger than earlier observations the relative speedup of outlet glaciers however is far smaller 15 furthermore the dominant seasonal influence on jakobshavn isbrae s flow is the calving front s annual advance and retreat with other effects producing outlet glacier speedups an order of magnitude larger seasonal melt s influence on ice flow is likely confined to those regions dominated by ice sheet flow

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

a continuous record of vegetation fire regime and climatic changes in northwestern patagonia spanning the last 25 000 years abstract we present a high resolution precisely dated terrestrial paleovegetation paleoclimate record from lago pichilaguna northwestern patagonia 40 44 s which spans continuously from the last glacial maximum lgm to the present we find abundant and continuous presence of arboreal pollen chiefly nothofagus during the lgm accompanied by other trees shrubs and alpine herbs these results suggest subantarctic parkland and or scattered woodlands under a cold and hyperhumid climate during the lgm 25 000 17 800 cal yr bp with expansion of nothofagus under relatively warm interstadial conditions between 25 000 and 19 200 cal yr bp this was followed by cooling and a precipitation increase between 19 200 and 17 800 cal yr bp which was contemporaneous with the youngest lgm advance of andean glaciers in the region and maximum influence of the southern westerly wind sww the last glacial termination t1 started at 17 800 cal yr bp and featured the spread of thermophilous trees and ferns characteristic of north patagonian rainforests along with lake level lowering these results suggest a warm pulse and southward shift of the sww concurrent with a rapid collapse of andean glacier lobes subsequent changes led to the establishment of closed canopy rainforests under peak interstadial warmth between 16 000 and 15 000 cal yr bp we detect a shift to cold wet conditions during the antarctic cold reversal 14 800 12 700 cal yr bp and a precipitation decline during younger dryas time followed by maximum temperature relatively lower lake level and minimum sww influence between 11 300 and 7700 cal yr bp precipitation then rose punctuated by centennial scale variations since 6200 cal yr bp chilean european deforestation and spread of invasive exotic species started at 350 cal yr bp aided by fire we conclude that temperate rainforests have persisted with little interruption since t1 with major changes in floristic composition driven by climate change and fires rainforest composition and heterogeneity declined in response to chilean european disturbance during the 1600s and intensified since the 1800s these events constitute the fastest largest magnitude vegetation changes of the last 25 000 years

glacial geomorphology of the torres del paine region southern patagonia implications for glaciation deglaciation and paleolake history abstract the processes affecting paleoclimate variability and pleistocene glacial landscape development in the southern mid latitudes remain poorly understood in part because of the scarcity of comprehensive well studied records glacial landforms are invaluable for reconstructing past ice sheet climate and associated environmental changes along the southern andes but there are significant spatial and temporal gaps in existing data in this paper we present new geomorphic and sedimentologic analyses including surficial maps for the torres del paine region 51 s 73 w southern south america our findings provide a new framework for understanding changes in the regional glacier history and pleistocene landscape development glacial extent during the local last glacial maximum lgm remains unknown but new chronological data supported by geomorphic evidence afford evidence for a larger ice sheet at torres del paine than previously assumed deglaciation from the local lgm was underway by 17 400 200 1 cal yr bp as opposed to previous suggestions we have found that most of the moraines fringing the lakes in the torres del paine national park were deposited during a late glacial expansion that occurred between 14 100 and 12 500 cal yr bp late glacial advances also have been documented recently for the ultima esperanza and lago argentino basins to the south and north of torres del paine respectively suggesting an overall regional ice response to a climate signal the tehuelche paleolake accompanied each of the ice sheet fluctuations in torres del paine new data document at least three main phases of this paleolake which drained eastward to the atlantic ocean while the andes gaps were blocked with ice during the late phase of glacial lake formation when water levels reached 125 155 m a s l the lake likely merged with paleolake consuelo in the ultima esperanza area at the end of the last glaciation lake tehuelche in torres del paine had drained into the pacific ocean by the late glacial period suggesting that ice southwest of torres del paine may have retreated back into the mountains by this time

late glacial holocene climate of the lake district of chile pollen evidence from a 350 cm section of a fen in a moraine belt at rucanancu 39 33 s 72 18 w bears on the controversy regarding interpretation of late glacial and holocene climate in midlatitude chile earlier pollen studies indicating a cooling trend between approximately 11 000 and 10 000 yr b p disagreed with observations of glacier fluctuations which show continuous glacier wastage and by inference warming after 12 500 yr b p and possibly earlier up until neoglaciation beginning after 6850 yr b p fossil beetle assemblage data in this time range support the interpretation of climate made from the observed glacier behavior at rucanancu a pollen assemblage containing upper montane podocarp podocarpus andinus in quantities reaching 34 and dating between 10 440 and 10 000 yr b p implies a cold climate with summer temperatures possibly 5 8 c lower than today s holocene warming began afterward later than the glacier and beetle records indicate and continued until at least 8350 yr b p as suggested by the sequence of assemblages dominated by myrtaceae by aextoxicon punctatum and by gramineae a subsequent assemblage of nothofagus obliqua type implies an increase of moisture until 6960 yr b p following which n dombeyi type under a cool and humid neoglacial climate became dominant

trans pacific glacial response to the antarctic cold reversal in the southern mid latitudes abstract elucidating the timing and regional extent of abrupt climate events during the last glacial interglacial transition 18 11 5 ka is critical for identifying spatial patterns and mechanisms responsible for large magnitude climate events the record of climate change in the southern hemisphere during this time period however remains scarce and unevenly distributed we present new geomorphic chronological and equilibrium line altitude ela data from a climatically sensitive mountain glacier at monte san lorenzo 47 s central patagonia twenty four new cosmogenic 10be exposure ages from moraines provide a comprehensive glacial record in the mid latitudes of south america which constrain the timing spatial extent and magnitude of glacial fluctuations during the antarctic cold reversal acr 14 5 12 9 ka rio tranquilo glacier advanced and reached a maximum extent at 13 9 0 7 ka three additional inboard moraines afford statistically similar ages indicating repeated glacier expansions or marginal fluctuations over the acr our record represents the northernmost robust evidence of glacial fluctuations during the acr in southern south america documenting not only the timing of the acr maximum but also the sequence of glacier changes within this climate event based on ela reconstructions we estimate a cooling of 1 6 1 8 c at the peak of the acr the rio tranquilo record along with existing glacial reconstructions from new zealand 43 s and paleovegetation records from northwestern 41 s and central west 45 s patagonia suggest an uniform trans pacific glacier climate response to an acr trigger across the southern mid latitudes we posit that the equatorial migration of the southern westerly winds provides an adequate mechanism to propagate a common acr signal across the southern hemisphere

radiocarbon chronology of the late glacial puerto bandera moraines southern patagonian icefield argentina abstract we report radiocarbon dates that constrain the timing of the deposition of the late glacial puerto bandera moraine system alongside the western reaches of lago argentino adjacent to the southern patagonian icefield close maximum limiting radiocarbon ages n 11 for glacier advance into the outer moraines with a mean value of 11 100 60 14 c yrs bp 12 990 80 cal yrs bp were obtained from wood in deformation soft till exposed beneath flow and lodgment till in bahia del quemado on the northeast side of brazo norte north branch of western lago argentino other exposures of this basal deformation till in bahia del quemado reveal incorporated clasts of peat along with larger inclusions of deformed glaciofluvial and lacustrine deposits radiocarbon dates of wood included in these reworked peat clasts range from 11 450 45 14 c yrs bp to 13 450 150 14 c yrs bp 13 315 60 to 16 440 340 cal yrs bp the implication is that during this interval glacier fronts were situated inboard of the puerto bandera moraines with the peat clasts and larger proglacial deposits being eroded and then included in the basal till during the puerto bandera advance minimum limiting radiocarbon ages for ice retreat come from basal peat in cores sampled in spillways and depressions generated during abandonment of the puerto bandera moraines glacier recession and subsequent plant colonization were initiated close behind different frontal sectors of these moraines prior to 10 750 75 14 c yrs bp 12 660 70 cal yrs bp east of brazo rico 10 550 55 14 c yrs bp 12 490 80 cal yrs bp in peninsula avellaneda and 10 400 50 14 c yrs bp 12 280 110 cal yrs bp in bahia catalana in addition a radiocarbon date indicates that by 10 350 45 14 c yrs bp 12 220 110 cal yrs bp the brazo norte lobe or former upsala glacier had receded well up the northern branch of lago argentino to a position behind the herminita moraines furthermore glacier termini had receded to just outboard of the outer holocene moraines at lago frias and lago pearson anita prior to 10 400 40 14 c yrs bp 12 270 100 cal yrs bp and 9040 45 14 c yrs bp 10 210 50 cal yrs bp respectively the most extensive recession registered during the early holocene was in agassiz este valley where the upsala glacier had pulled back behind the outer holocene moraine reaching close to the present day glacier terminus before 8290 40 14 c yrs bp 9300 80 cal yrs bp the radiocarbon dated fluctuations of the lago argentino glacier in late glacial time given here are in accord with changes in ocean mixed layer properties predominately temperature derived from the isotopic record given here of odp core 1233 taken a short distance off shore of the chilean lake district it also matches recently published chronologies of late glacial moraines in the southern alps of new zealand on the opposite side of the pacific ocean from lago argentino finally the timing of the late glacial reversal of the lago argentino glacier fits the most recent chronology for the culmination of the antarctic cold reversal acr in the deuterium record of the epica dome c ice core from high on the east antarctic plateau therefore we conclude that the climate signature of the acr was widespread in both the ocean and the atmosphere over at least the southern quarter of the globe

glacier expansion in central patagonia during the antarctic cold reversal followed by retreat and stabilisation during the younger dryas abstract the spatial temporal footprint of millennial scale climate events during the last glacial interglacial transition can yield insights into the underlying drivers of climate change but remains poorly resolved in patagonia here we assess the glacier response to abrupt cold events and palaeolake evolution using geomorphological mapping along with 10 b e ages and optically stimulated luminescence ages from near lago belgrano 47 9 s on the eastern side of monte san lorenzo the former belgrano glacier was sustained by a climatically sensitive ice cap making the site ideal for investigating the glacier response to abrupt cold reversals our data reveal an extensive re advance at 13 1 0 6 ka consistent with cooling and increased precipitation during the antarctic cold reversal acr subsequently ice retreated by at least 10 km and created an ice dammed proglacial lake in the belgrano valley rapid recession was punctuated by smaller advances still stands sufficient to maintain an ice dam for the palaeolake and deposit a lateral moraine dated at 12 4 0 3 ka during the younger dryas yd the final withdrawal of glaciers to the mountains allowed the palaeolake to drain and resulted in an atlantic pacific drainage reversal this marks the final separation of the patagonian ice sheet into the individual ice fields at the yd holocene transition our data demonstrate the dominant acr climate signal in central patagonia but also reveals a co occurrence of the northern hemisphere yd signal albeit of smaller magnitude the acr re advance was primarily climatically controlled but its relative magnitude was likely a consequence of ice divide migration and ice flow re routing during the break up of the patagonian ice sheet

late quaternary tephrostratigraphy of southern chile and argentina abstract the southern and austral volcanic zones of the andes comprise 74 volcanic centres with known post glacial activity at least 21 of these have had one or more large explosive eruptions in the late quaternary dispersing tephra over vast areas these tephra layers therefore have great potential as tephrochronological marker horizons in palaeoenvironmental studies in southern chile and argentina a region that is particularly useful to study climate dynamics of the southern hemisphere however to date tephrochronology has rarely been fully utilised in this region as a correlation and dating tool here we review the existing post glacial tephrostratigraphic record of the southern and austral volcanic zones and compile a database of known occurrences of tephra from these volcanoes in ice and lacustrine marine peat and cave sediment records we address the inconsistencies in and revisions of the tephrostratigraphies presented in prior literature and discuss the challenges in correlating tephras and the limitations of the tephrostratigraphic record in this area this study highlights the many gaps that still exist in our knowledge of the eruptive histories of these volcanoes but also reveals the largely under utilised potential of tephra as a correlation tool in this region this is exemplified by the severe lack of adequate geochemical analysis of tephra layers preserved in many lacustrine and peat sediment sections which are particularly important tephrostratigraphic records in southern chile and argentina due to the paucity of surface preservation

controls on the basal water pressure in subglacial channels near the margin of the greenland ice sheet assuming a channelized drainage system in steady state we investigate the influence of enhanced surface melting on the water pressure in subglacial channels compared to that of changes in conduit geometry ice rheology and catchment variations the analysis is carried out for a specific part of the western greenland ice sheet margin between 668 n and 66830 0 n using new high resolution digital elevation models of the subglacial topography and the ice sheet surface based on an airborne ice penetrating radar survey in 2003 and satellite repeat track interferometric synthetic aperture radar analysis of european remote sensing satellite 1 and 2 ers 1 2 imagery respectively the water pressure is calculated up glacier along a likely subglacial channel at distances of 1 5 and 9 km from the outlet at the ice margin using a modified version of rothlisberger s equation our results show that for the margin of the western greenland ice sheet the water pressure in subglacial channels is not sensitive to realistic variations in catchment size and mean surface water input compared to small changes in conduit geometry and ice rheology

changes in fire regimes since the last glacial maximum an assessment based on a global synthesis and analysis of charcoal data fire activity has varied globally and continuously since the last glacial maximum lgm in response to long term changes in global climate and shorter term regional changes in climate vegetation and human land use we have synthesized sedimentary charcoal records of biomass burning since the lgm and present global maps showing changes in fire activity for time slices during the past 21 000 years as differences in charcoal accumulation values compared to pre industrial there is strong broad scale coherence in fire activity after the lgm but spatial heterogeneity in the signals increases thereafter in north america europe and southern south america charcoal records indicate less than present fire activity during the deglacial period from 21 000 to 11 000 cal yr bp in contrast the tropical latitudes of south america and africa show greater than present fire activity from 19 000 to 17 000 cal yr bp and most sites from indochina and australia show greater than present fire activity from 16 000 to 13 000 cal yr bp many sites indicate greater than present or near present activity during the holocene with the exception of eastern north america and eastern asia from 8 000 to 3 000 cal yr bp indonesia and australia from 11 000 to 4 000 cal yr bp and southern south america from 6 000 to 3 000 cal yr bp where fire activity was less than present regional coherence in the patterns of change in fire activity was evident throughout the post glacial period these complex patterns can largely be explained in terms of large scale climate controls modulated by local changes in vegetation and fuel load

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

aspects of interannual and intraseasonal variability of the tropopause and lower stratosphere radiosonde and national centers for environmental prediction national center for atmospheric research reanalysis data are utilized to consider aspects of large scale variability in tropopause height temperature and pressure this variability is related to coherent dynamical fluctuations in the troposphere and lower stratosphere through the use of linear correlation and regression on interannual time scales significant global scale tropopause fluctuations are tied to variability in sea surface temperature sst associated with the el ni o southern oscillation phenomenon when sst is anomalously high in the central tropical pacific tropopause height pressure is high low throughout the tropics with largest perturbation amplitudes in the subtropical pacific at the same time the tropopause is cold over the tropical and subtropical pacific sector but warm elsewhere in the tropics over the extratropics wave like perturbations in the tropopause are seen with anomalous cyclonic flow corresponding to a lower tropopause height and higher tropopause temperature and pressure and vice versa the sign of the temperature anomalies in the lower stratosphere tends to match that at the tropopause over much of the globe with opposite signed anomalies in the upper troposphere the vertical structure of these perturbations is consistent with the expected potential vorticity anomalies induced by quasi stationary rossby waves and vertically propagating gravity waves forced by displacements of tropical convection similar relationships are associated with the eastward propprotion of tropical convection due to the madden julian oscillation on intraseasonal time scales

asymmetry and nonlinearity of the influence of enso on the northern winter stratosphere 1 observations the el nino southern oscillation enso has significant effects on the extratropical stratosphere this study explores the nonlinearity and the asymmetry of these influences by distinguishing the different effects of four types of enso moderate el nino strong el nino moderate la nina and strong la nina it is revealed that the moderate el nino and the strong la nina are much more efficient than the strong el nino and the moderate la nina respectively in modulating the northern winter stratospheric variability resulting in significant nonlinearity and asymmetry the tropical rainfall anomalies induced by a moderate el nino or a strong la nina are centered over the central equatorial pacific region near the dateline while the convection responses to a strong el nino or a moderate la nina are centered farther eastward accordingly the anomalous pacific north america wave train pattern is modulated by enso in a nonlinear and asymmetric way which leads the large nonlinear and asymmetric components of the vertical eliassen palm e p flux responses to enso the increase of planetary wave activity in the extratropical stratosphere in moderate el nino winters is thus greater than in strong el nino winters whereas a strong la nina gives a larger decrease in propagation than a moderate la nina the relatively strong weak e p flux responses to moderate strong el nino and strong moderate la nina explain the remarkable nonlinearity and asymmetry in the response of the extratropical stratosphere to enso

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

timing and structure of vegetation fire and climate changes on the pacific slope of northwestern patagonia since the last glacial termination abstract by virtue of its location in the southern mid latitudes northwestern patagonia 40 44 s offers the opportunity to unravel the mechanisms involved in the initiation and propagation of paleoclimate signals of hemispheric and global significance of particular importance is deciphering the evolution of the southern westerly winds sww considering their influence at continental zonal hemispheric and global scale here i present a multi decadal record from lago proschle a small closed basin lake located on the pacific slope of northwestern patagonia to examine the timing and structure of vegetation fire and climate change along a continuum since the onset of the last glacial termination t1 the record shows rapid glacier recession during t1 reaching the western andean foothills in 400 years or less nothofagus dominated forests established between 17 4 17 ka followed by closed canopy north patagonian rain forests nprf with shade tolerant thermophilous trees between 16 3 15 4 ka these changes suggest an abrupt warming trend and an increase in precipitation at 16 3 ka associated with a northward shift of the sww subsequent increases in cold tolerant hygrophilous trees between 15 4 12 8 ka imply a shift to cold more humid conditions during the antarctic cold reversal suggesting stronger sww influence this was followed by stand replacing fires brought by a sudden decline in summer precipitation at 12 8 ka associated with a millennial scale southward shift of the sww which was contemporaneous with the onset of the younger dryas dominance of thermophilous summer drought tolerant valdivian rainforest trees and high fire activity ensued between 10 3 7 8 ka suggesting peak warmth and overall decline in annual precipitation associated with weakening of the sww during the early holocene a multi millennial cooling and wetting trend started at 7 8 ka brought by stronger sww influence followed by recurrent centennial scale variations in temperature and precipitation starting at 6 4 ka deforestation fire and spread of non native herbs by chilean european settlers began during the late 18th century abrupt vegetation changes in the lago proschle record were driven by rapid climate changes over the last 17 400 years amplified in some instances by fire disturbance

volcanos and el nino signal separation in northern hemisphere winter the frequent coincidence of volcanic forcing with el nino events disables the clear assignment of climate anomalies to either volcanic or el nino forcing in order to select the signals a set of four different perpetual january gcm experiments was performed control volcano case el nino case and combined volcano el nino case and studied with advanced statistical methods for the northern hemisphere winter the results were compared with observations the signals for the different forcings are discussed for three variables temperature zonal wind and geopotential height and five levels surface 850 hpa 500 hpa 200 hpa and 50 hpa the global el nino signal can be selected more clearly in the troposphere than in the stratosphere in contrast the global volcano signal is strongest in the stratospheric temperature field the amplitude of the perturbation for the volcano case is largest in the atlantic region the observed effect of local cooling due to the volcanic reduction of shortwave radiation over large land areas like asia in subtropical regions the observed advective warming over eurasia and the advective cooling over greenland are well simulated in the model the radiative cooling near the surface is important for the volcano signal in the subtropics but it is weak in high latitudes during winter a statistically significant tropospheric signal of el nino forcing occurs in the subtropics and in the midlatitudes of the north pacific the local anomalies in the el nino forcing region in the tropics and the warming over north america in middle and high latitudes are simulated as observed the combined signal is different from a simple linear combination of the separate signals it leads to a climate perturbation stronger than for forcing with el nino or stratospheric aerosol alone and to a somewhat modified pattern

vegetation fire and climate change in central east isla grande de chiloe 43 s since the last glacial maximum northwestern patagonia abstract we present a detailed record from lago lepue to examine vegetation climate and fire regime changes since the last glacial maximum lgm in central east isla grande de chiloe 43 s northwestern patagonia precipitation in this region correlates with the intensity of the southern westerly winds sww allowing reconstruction of past sww behavior through precipitation sensitive sensors recession from the lgm glacier margins exposed the central east sector of isla grande de chiloe by 17 800 cal yr bp followed by the immediate colonization of pioneer cold resistant herbs shrubs and rapid establishment of closed canopy nothofagus forests by 17 000 cal yr bp broad leaved temperate rainforests have persisted since then with compositional changes driven by changes in temperature hydrologic balance and disturbance regimes we detect low lake levels and enhanced fire activity between 800 2000 4000 4300 8000 11 000 and 16 100 17 800 cal yr bp implying southward shifts and or weaker sww flow that alternated with cold humid phases with muted fire activity covariation in paleoclimate trends revealed by the lago lepue record with tropical and antarctic records since the lgm suggests that the sww have been a highly dynamic component of the climate system capable of linking climate changes from low and high southern latitudes during the last glacial termination and the current interglacial

centennial and millennial scale hydroclimate changes in northwestern patagonia since 16 000 yr bp abstract we examine hydroclimate changes at centennial millennial timescales since 16 000 yr bp in northwestern patagonia based on the pollen and charcoal record from lago el salto a small closed basin lake located in the chilean lake district 41 38 48 02 s 73 5 48 42 w we observe cold wet conditions between 14 500 16 000 yr bp followed by further cooling with increased precipitation until 13 000 yr bp enhanced precipitation seasonality and or variability between 11 600 13 000 yr bp and an extended warm and dry interval between 7600 and 11 300 yr bp with peak paleofire activity colder and wetter than present conditions and muted paleofire activity prevail between 5300 and 7600 yr bp followed by alternating cold wet and centennial scale warm dry phases starting at 5300 yr bp with three conspicuous megadroughts since 2500 yr bp the most recent megadrought occurred during the medieval climate anomaly we identify a cold reversal that spans the antarctic cold reversal acr and the younger dryas yd chrons with stronger than present westerly influence during the former and enhanced variability during the latter these results extend the northern limit of strong cooling and increase in precipitation during the acr and the southern limit of influence of strong hydrologic variations during the yd in terrestrial environments suggesting an overlap in the spheres of influence of processes originating from southern and northern polar latitudes an extended warm southern westerly wind sww minimum interval is evident between 7600 and 11 300 yr bp followed by a rapid shift to cool moist conditions between 5300 and 7600 yr bp brought by a mid holocene sww maximum since then we observe centennial scale hydroclimate variability which has driven biodiversity and fire regime shifts of evergreen temperate rainforests

warming and glacier recession in the rakaia valley southern alps of new zealand during heinrich stadial 1 abstract the termination of the last ice age featured a major reconfiguration of earth s climate and cryosphere yet the underlying causes of these massive changes continue to be debated documenting the spatial and temporal variations of atmospheric temperature during deglaciation can help discriminate among potential drivers here we present a 10be surface exposure chronology and glaciological reconstruction of ice recession following the last glacial maximum lgm in the rakaia valley southern alps of new zealand innermost lgm moraines at big ben have an age of 17 840 240 yrs whereas ice marginal moraines or ice molded bedrock surfaces at distances up valley from big ben of 12 5 km lake coleridge 25 km castle hill 28 km double hill 43 km prospect hill and 58 km reischek knob have ages of 17 020 70 yrs 17 100 110 yrs 16 960 370 yrs 16 250 340 yrs and 15 660 160 yrs respectively these results indicate extensive recession of the rakaia glacier which we attribute primarily to the effects of climatic warming in conjunction with geomorphological maps and a glaciological reconstruction for the rakaia valley we use our chronology to infer timing and magnitude of past atmospheric temperature changes compared to an overall temperature rise of 4 65 c between the end of the lgm and the start of the holocene the glacier recession between 17 840 and 15 660 yrs ago is attributable to a net temperature increase of 4 0 c from 6 25 to 2 25 c accounting for 86 of the overall warming approximately 3 75 c 70 of the warming occurred between 17 840 and 16 250 yrs ago with a further 0 75 c 16 increase between 16 250 and 15 660 yrs ago a sustained southward shift of the subtropical front stf south of australia between 17 800 and 16 000 yrs ago coincides with the warming over the rakaia valley and suggests a close link between southern ocean frontal boundary positions and southern mid latitude climate most of the deglacial warming in the southern alps occurred during the early part of heinrich stadial 1 hs1 of the north atlantic region because the stf is associated with the position of the westerly wind belt our findings support the concept that a southward shift of earth s wind belts accompanied the early part of hs1 cooling in the north atlantic leading to warming and deglaciation in southern middle latitudes

an increase in crevasse extent west greenland hydrologic implications 1 we compare high resolution 1985 and 2009 imagery to assess changes in crevasse extent in the sermeq avannarleq ablation zone west greenland the area occupied by crevasses 2 m wide significantly increased 13 4 over the 24 year period this increase consists of an expansion of existing crevasse fields and is accompanied by widespread changes in crevasse orientation up to 45 we suggest that a combination of ice sheet thinning and steepening are responsible for the increase in crevasse extent we examine the potential impact of this change on the hydrology of the ice sheet we provide a first order demonstration that moulin type drainage is more efficient in transferring meltwater fluctuations to the subglacial system than crevasse type drainage as enhanced basal sliding is associated with meltwater pulses an increase in crevasse extent can therefore be expected to result in a net decrease in basal sliding sensitivity an increase in crevasse extent may also accelerate cryo hydrologic warming and enhance surface ablation

radar mapping of isunnguata sermia greenland ice thickness estimates using advanced nadir sounding and tomographic radar processing techniques are compared and combined in a study of isunnguata sermia glacier greenland using an ensemble of operation icebridge flight lines spaced at 500m intervals and running approximately along the flow direction we find there is a statistically excellent comparison between subglacial terrains derived from two dimensional tomography and gridded nadir sounding analysis shows that tomographic data better capture short wavelength 1 2 km patterns in basal terrain but interpolated nadir sounding data yield more spatially extensive and continuous coverage across the glacier especially in deep subglacial troughs using derived surface and basal topography maps we find that driving stress and measured and modeled surface velocity comparisons indicate that basal sliding is an important component of the glacier motion but is also only weakly coupled to the detailed bed topography save for the deepest troughs as might be expected for this land terminating relatively slow moving glacier the subglacial and proglacial topography is similar suggesting the erosional processes acting on the modern glacier bed once helped sculpt the now exposed land

the deuterium excess records of epica dome c and dronning maud land ice cores east antarctica new high resolution deuterium excess d data from the two epica ice cores drilled in dronning maud land edml and dome c edc are presented here the main moisture sources for precipitation at edc and edml are located in the indian ocean and atlantic ocean respectively the more southward moisture origin for edml is reflected in a lower present day d value compared to edc the edml and edc isotopic records 18o and d show the main climate features common to the east antarctic plateau and similar millennial scale climate variability during the last glacial period however quite large 18o and d differences are observed during mis5 5 and the glacial inception with a long term behaviour a possibility for this long term difference could be related to uncertainties in past accumulation rate which are used in the glaciological models regional climate anomalies between the two sites during mis5 5 could also be consistent with the observed edml edc 18o and d gradient anomalies simulations performed with the general circulation model echam4 for different time slices provide a temporal temperature isotope slope for the edml region in fair agreement to the modern spatial slope tsite and tsource records are extracted from both ice cores using a modelling approach after corrections for past 18o seawater and elevation changes a limited impact of d on antarctic temperature reconstruction at both edml and edc has been found with a higher impact only at glacial inception the aim antarctic isotope maximum events in both ice cores are visible also after the source correction suggesting that these are real climate features of the glacial period the different shape of the aim events between edc and edml as well as some climate features in the early holocene points to a slightly different climate evolution at regional scale a comparison of our temperature reconstruction profiles with the aerosol fluxes show a strong coupling of the nssca fluxes with antarctic temperatures during glacial period and a tighter coupling of 18o and tsite with ssna flux at edml compared to edc during the glacial period and mis5 5

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

influence of volcanic eruptions on the troposphere through stratospheric dynamical processes in the northern hemisphere winter it has been suggested that the zonal mean stratospheric zonal wind anomalies can propagate downward into the troposphere producing considerable changes on the other hand volcanic aerosols are thought to produce a stronger polar vortex in the winter stratosphere if these suggestions are correct the influence of volcanic eruptions can be expected to produce changes in the northern hemisphere winter troposphere through stratospheric process in the present study this idea is examined by analyzing changes in the january circulation after three recent volcanic eruptions regional features of observed changes in tropospheric temperatures due to volcanic eruptions can be explained by the changes in the propagation of stationary waves associated with dipole type anomalies in the zonal mean zonal winds which are similar to those observed in a previous work on the influence of polar night jet

an 18 000 year long eruptive record from volcan chaiten northwestern patagonia paleoenvironmental and hazard assessment implications abstract the 2008 eruption of volcan chaiten vcha in northwestern patagonia was the first explosive rhyolitic eruption to have occurred within a century and provided an unprecedented scientific opportunity to examine all facets of the eruption ranging from magma rheology ascent rates to ash fall effects on biota and infrastructure up to very recently it was thought that the latest eruption prior to the 2008 event occurred c 9750 cal a bp although a number of researchers have recognised additional eruptive products but their stratigraphy age and geochemical attributes have not been systematically described and or recorded in this study we provide a detailed examination of andic cover beds and tephra bearing lake sequences located both proximally and distally to vcha which record a series of hitherto unknown rhyolitic eruptive products and place all previous observations firmly within a coherent stratigraphic framework through major and trace element glass shard geochemistry we are able to confidently verify eruptive source a total of 20 discrete tephra beds are recognised with at least 10 having widespread areal distributions and or depositional imprints broadly comparable to or greater than the 2008 tephra event this record indicates that vcha has been continuously but intermittently active as far back as the end of the last glacial maximum c 18 000 cal a bp with two dominant genetically related magma types and an intermediary mixed type before this the eruptive record has been largely obscured and or erased by widespread andean piedmont glaciation however based on the tempo of vcha activity over the last c 18 000 years older vcha eruptives can be anticipated to occur as well as future hazardous explosive events the new eruptive inventory will ultimately be useful for correlating equivalent aged sequences and refining long term eruptive tempo as well as corresponding temporal changes in magmatic evolution

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

direct observations of evolving subglacial drainage beneath the greenland ice sheet simultaneous observations of moulins and boreholes in western greenland show that water delivery to the base of the ice sheet via moulins affects short term ice velocity fluctuations but not late season ice velocity decelerations increased meltwater delivery to the base of the greenland ice sheet will increase the ice sheet velocity accelerating its inevitable rush towards the ocean and subsequent sea level rise or will it debate on this topic is at the forefront of cryospheric research but has been hampered by the lack of simultaneous observations of hydraulic head in moulins vertical shafts that deliver water to the base of the ice sheet and boreholes which monitor basal water pressure lauren andrews and colleagues now provide these observations from a small region in western greenland and reveal that water delivery by moulins into channelized basal flow is indeed linked to short term fluctuations in ice velocity late season decelerations in ice velocity however seem to be controlled by changes in unchannelized flow rather than any shifts in the moulin system seasonal acceleration of the greenland ice sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed1 2 via crevasses and moulins vertical conduits connecting supraglacial water to the bed of the ice sheet as the melt season progresses the subglacial hydrologic system drains supraglacial meltwater more efficiently1 2 3 4 decreasing basal water pressure4 and moderating the ice velocity response to surface melting1 2 however limited direct observations of subglacial water pressure4 5 6 7 mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby 0 3 2 kilometres away boreholes indicating that moulins connect to an efficient channelized component of the subglacial hydrologic system which exerts the primary control on diurnal and multi day changes in ice velocity our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the paakitsoq region of western greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin connected channels to convey supraglacial melt instead these observations suggest that decreasing late season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt season dynamics affect ice velocity beyond the conclusion of the melt season8 9 10

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

evolution of drainage system morphology at a land terminating greenlandic outlet glacier 1 the influence of meltwater on the dynamics and geomorphic impact of the greenland ice sheet is strongly controlled by the morphology of the ice sheet s drainage system however this system and its evolution through the melt season remain poorly understood here we present the results of an intensive programme of dye tracing experiments undertaken along the lower 14 km of a land terminating greenlandic outlet glacier over a period of four months during the 2010 melt season these data are interpreted in conjunction with observations of proglacial discharge englacial water storage surface melt rates and ice velocity to produce a detailed picture of the changing hydrology of the glacier following the onset of melt in the spring inputs to the drainage system regularly exceed outputs causing the englacial water level to rise to the ice sheet surface during this time there is a rapid transition from distributed to channelized drainage in those parts of the drainage system closed by ice deformation over winter as the melt season progresses channel efficiency increases and englacial storage and ice velocity decrease high velocity events continue to be observed following the channelization of the drainage system however indicating that hydrological forcing of ice velocity occurs despite the existence of channels during periods when meltwater inputs exceed the capacity of the subglacial drainage system

radiocarbon chronology of the last glacial maximum and its termination in northwestern patagonia abstract we examine the timing and magnitude of the last glacial maximum lgm and the last glacial termination lgt in northwestern patagonia situated in the middle latitudes of south america our data indicate that the main phase of the lgt began with abrupt warm pulses at 17 800 and 17 100 cal yrs bp accompanied by rapid establishment of evergreen temperate rainforests and extensive deglaciation of the andes within 1000 years this response shows that south american middle latitude temperatures had approached average interglacial values by 16 800 cal yrs bp the temperature rise in northwestern patagonia coincides with the beginning of major warming and glacier recession in the southern alps of new zealand at southern mid latitudes on the opposite side of the pacific ocean from this correspondence the warming that began at 17 800 cal yrs bp appears to have been widespread in middle latitudes of the southern hemisphere accounting for at least 75 of the total temperature recovery from the lgm to the holocene moreover this warming pulse is coeval with the first half of the heinrich stadial 1 hs1 in the north atlantic region hs1 featured a decline of north atlantic meridional overturning circulation a southward shift of the westerly wind belt in both hemispheres and of the intertropical convergence zone as well as a weakening of the asian monsoon along with the initiating trigger identifying the mechanisms whereby these opposing climate signals in the two polar hemispheres interacted whether through an oceanic or an atmospheric bipolar seesaw or both lies at the heart of understanding the lgt

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

persistent englacial drainage features in the greenland ice sheet 1 surface melting on the greenland ice sheet is common up to 1400 m elevation and in extreme melt years even higher water produced on the ice sheet surface collects in lakes and drains over the ice sheet surface via supraglacial streams and through the ice sheet via moulins water delivered to the base of the ice sheet can cause uplift and enhanced sliding locally here we use ice penetrating radar data to observe the effects of significant basal melting coincident with moulins and calculate how much basal melt occurred we find that more melting has occurred than can be explained by the release of potential energy from the drainage of surface meltwater during one melt season suggesting that these moulins are persistent for multiple years we find only a few persistent moulins in our study area that drain the equivalent of multiple lakes per year and likely remain active over several years our observations indicate that once established these persistent moulins might be capable of establishing well connected meltwater drainage pathways

seasonal variability of submarine melt rate and circulation in an east greenland fjord 1 the circulation in a glacial fjord driven by a large tidewater glacier is investigated using a nonhydrostatic ocean general circulation model with a melt rate parameterization at the vertical glacier front the model configuration and water properties are based on data collected in sermilik fjord near helheim glacier a major greenland outlet glacier the approximately two layer stratification of the fjord s ambient waters causes the meltwater plume at the glacier front to drive a double cell circulation with two distinct outflows one at the free surface and one at the layers interface in summer the discharge of surface runoff at the base of the glacier subglacial discharge causes the circulation to be much more vigorous and associated with a larger melt rate than in winter the simulated double cell circulation is consistent in both seasons with observations from sermilik fjord seasonal differences are also present in the vertical structure of the melt rate which is maximum at the base of the glacier in summer and at the layers interface in winter simulated submarine melt rates are strongly sensitive to the amount of subglacial discharge to changes in water temperature and to the height of the layers they are also consistent with those inferred from simplified one dimensional models based on the theory of buoyant plumes our results also indicate that to correctly represent the dynamics of the meltwater plume care must be taken in the choice of viscosity and diffusivity values in the model

large scale control on the patagonian climate abstractpatagonia located in southern south america is a vast and remote region holding a rich variety of past environmental records but a small number of meteorological stations precipitation over this region is mostly produced by disturbances embedded in the westerly flow and is strongly modified by the austral andes uplift on the windward side leads to hyperhumid conditions along the pacific coast and the western slope of the andes in contrast downslope subsidence dries the eastern plains leading to arid highly evaporative conditions the authors investigate the dependence of patagonia s local climate precipitation and near surface air temperature year to year variability on large scale circulation anomalies using results from a 30 yr long high resolution numerical simulation variations of the low level zonal wind account for a large fraction of the rainfall variability at synoptic and interannual time scales zonal wind also controls the amplitude of the air temperature annual cycle by changi

zonally symmetric changes in the strength and position of the southern westerlies drove atmospheric co2 variations over the past 14 k y terrestrial records from 41 to 52 s across the southern hemisphere reveal nearly synchronous multimillennial trends in moisture derived from the southern westerly winds sww since 14 ka pointing to a marked zonal symmetry in sww changes across a broad swath of the southern middle latitudes the data suggest a southward shift of the sww that coincided with a rapid atmospheric co 2 rise starting ca 12 5 ka a widespread decline in sww strength between ca 10 and 7 ka contemporaneous with an 8 ppm reversal in the deglacial atmospheric co 2 rise followed by stronger sww and a steady multimillennial increase in co 2 until the preindustrial maximum we conclude that zonally symmetric changes in the intensity of the sww at multimillennial time scales have covaried with atmospheric co 2 variations since 14 ka and suggest that changes in the sww southern ocean coupled system have influenced the atmospheric co 2 concentration through wind driven upwelling of co 2 rich deep waters in the high southern latitudes