applications of geophysical techniques to improve a groundwater conceptual model in an outcrop area of the guarani aquifer system in brazil the comprehension of groundwater flow depends on the knowledge of hydrogeological features and water cycle especially the recharge process geophysical techniques can provide useful hydrogeological information e g water table and base aquifer toward improving the water balance in groundwater models this study conducted in an outcrop area of the guarani aquifer system gas in sao paulo state brazil applied ground penetrating radar gpr and geoelectrical techniques for structuring a conceptual groundwater model a gpr with 200 mhz antenna 4 vertical electrical soundings ves with schlumberger array and 12 electrical resistivity tomographies ert with dipole dipole array were used geophysical techniques soil samples and water level from monitoring wells helped the definition of two different hydraulic conductivity regions and a flux boundary condition for the groundwater flow model

south american cold surges types composites and case studies abstract this paper examines the climatological large scale and synoptic scale aspects of south american cold surges using ncep ncar gridded reanalyses for the 1992 96 period three common cold surge types are identified on the basis of a thickness 1000 850 hpa criteria type 1 a transient surge associated with weak anticyclone development east of the andes in the absence of ridging aloft type 2 a strong and persistent surge associated with dynamic anticyclogenesis aloft and strong surface anticyclone development east of the andes and type 3 a surge east of the brazilian coastal mountains cold surges are most common during the winter and spring jun nov accounting for 189 of the 256 events 74 case studies of two events 19 22 jul 1992 and 12 14 apr 1993 are conducted from both a conventional isobaric and a potential vorticity pv perspective the upper air flow pattern in the july 1992 type 2 case is characterized by the presence of a strong ridge trough couplet which amplifies and becomes

the last glaciation in central magellan strait southernmost chile abstract glacial landforms and drift stratigraphy in central magellan strait southernmost chile document repeated fluctuations during the last glacial cycle of outlet lobes from an ice cap centered over the southern andes the lobes developed comparatively low gradient profiles because of low basal shear stresses over soft deformable beds and this made them sensitive to even small scale changes in the mass balance such low profiles and rapid calving in deep proglacial lakes during deglaciation may have made the magellan ice lobe particularly responsive to climatic fluctuations during the last glacial cycle and to advance and retreat over considerable distances study of the glacial landforms and drift stratigraphy has led to the identification of at least five glacier advances to limits at and south of the segunda angostura fragments of mollusc shells contained in basal till indicate marine incursions between some advances thus documenting extensive deglaciation a partial chronology based on amino acid studies and radiocarbon dating suggests that five of these advances occurred during the last glacial cycle the most extensive advances may have culminated during substages of marine isotope stage 5 substage 5b or 5d and or during stage 4 slightly less extensive advances occurred between ca 28 000 and 14 000 yr b p

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

a holocene record of environmental change from rio zeballos central patagonia there are few continuous palaeoenvironmental records spanning the holocene in andean southern patagonia near the northern patagonian ice field 47 s insights into the environmental context for h

the magnitude and rapidity of the climate change marking the end of the pleistocene in the mid latitudes of south america abstract the chi squared test of independence and cluster analysis of otsuka similarity coefficients of fossil beetle assemblages from the chilean lake region in the mid latitudes of south america support the following conclusions 1 the mean summer temperature of the glacial climate was 4 5 c lower than today s climate 2 the climatic change from glacial to interglacial mode was in a single step centered on about 14 000 yr b p 3 the climatic change was rapid and within 1500 years the biota of a moorland had been completely replaced by a biota of a rain forest 4 by 12 500 yr b p the low elevation beetle fauna of the chilean lake region was similar in composition to that of the present day and 5 no reversal in the postglacial warming trend equivalent in age to the younger dryas stade was detected

air sea interaction at the southern brazilian continental shelf in situ observations the influence of the cross shelf oceanographic front occurring between the brazil current bc and the brazilian coastal current bcc on the local marine atmospheric boundary layer mabl is investigated here this front is typical of wintertime in the southern brazilian continental shelf sbcs and this is the first time that its effects are investigated over the above mabl here we analyze variability vertical structure and stability of mabl as well as heat fluxes at air sea interface across five oceanographic transects in the sbcs made during a winter 2012 cruise local thermal gradients associated with mixing between distinct water masses play an essential role on mabl modulation and stability although weaker when compared with other frontal regions the cross shelf thermal gradients reproduce exactly what is expected for open ocean regions stronger weaker winds lower higher sea level pressure and a more unstable stable mabl are found over the warm cold side of the oceanographic front between the bc warm and coastal cold waters our findings strongly support the coexistence of both known mabl modulation mechanisms the static and hydrostatic mabl stability this is the first time that these modulation mechanisms are documented for this region turbulent fluxes were found to be markedly dependent on the cross shelf sst gradients resulting in differences of up to 100 w m 2 especially in the southernmost region where the gradients were more intense

atmospheric circulation associated with extreme generalized frosts persistence in central southern south america generalized frosts gf in central southern south america have a strong impact due to their spatial extension and they are especially important when they become persistent this paper aims at identifying the atmospheric circulation features that determine the extreme gf persistence i e very persistent and without persistence and the differences between them during the 1961 1990 winters since the gf without persistence group outnumbers the other one two subgroups are composed with events selected from winters with maximum and minimum frequency of gf occurrence respectively additionally the individual event of july 1988 within the very persistent gf group is analyzed due to its exceptional persistence gf persistence is mainly conditioned by two large scale dynamic factors one is the rossby wave train propagation across the pacific ocean and the other one is the location with respect to the continent and the magnitude of the confluence in the jet entrance region in subtropical latitudes a predominantly meridional rossby wave train propagation with a confluence region to the west of the continent prior to the event favors gf with intermediate null persistence depending on the greater lesser jet acceleration this is conditioned by the magnitude of the confluence which in turn depends on the disposition of the wave train propagation pattern instead an essentially zonal propagation with a confluence region to the east of the continent favors the gf persistence for several days yet if there is no confluence the event does not persist the greatest persistence of an event combines the confluence diffluence of the jet entrance exit region which depends on the disposition with respect to the continent of the zonally propagating rossby wave trains

exploring the interplay between infiltration dynamics and critical zone structures with multiscale geophysical imaging a review abstract infiltration is the process of water entering into and routings through the subsurface it has a profound impact on water flux in the earth s critical zone cz influencing phenomena such as overland flow stream generation plant available water and groundwater recharge as well as the associated cz processes and functions of weathering erosion slope stability and food production however reliable measurement of infiltration in structured geomedia soils and regolith with hidden subsurface features remain challenging the increasing availability of geophysical techniques has helped them emerge as viable options for minimally invasive determination of infiltration at the pedon to hillslope or catchment scales geophysical methods replace the educated guesswork of interpreting field data from traditional infiltrometers with direct visualization and quantification this paper provides a comprehensive literature review of various applications of geophysical techniques used to 1 visualize infiltration relevant structures 2 monitor non uniform or preferential infiltration patterns and 3 map soil moisture distribution after infiltration it then proposes a new conceptualization form and function dualism for subsurface hydrology to link preferential infiltration to cz structures with the goal of formulating more realistic infiltration theories related to subsurface structural heterogeneity the characterization of both subsurface structures form and infiltration dynamics function via geophysical imaging should help infiltration models currently emphasizing macroscale behaviors rooted in the continuum concept expand to accommodate the microscale nature of preferential flow integrating multiple geophysical approaches and developments into the new generation of geophysical techniques will further enhance our ability to see into the fabric of the subsurface and capture the dynamics of non uniform infiltration through the hidden half of the cz this approach offers exciting opportunities for understanding the complex interactions between cz structures and cz processes

soil moisture content estimation using ground penetrating radar reflection data abstract ground penetrating radar gpr reflection travel time data were used to estimate changes in soil water content under a range of soil saturation conditions throughout the growing season at a california winery data were collected during three data acquisition campaigns over an 80 by 180 m area using 100 mhz surface gpr antennas gpr reflections were associated with a thin low permeability clay layer located 0 8 1 3 m below the ground surface that was identified from borehole information and mapped across the study area field infiltration tests and neutron probe logs suggest that the thin clay layer inhibited vertical water flow and was coincident with high volumetric water content vwc values the gpr reflection two way travel time and the depth of the reflector at the borehole locations were used to calculate an average dielectric constant for soils above the reflector a site specific relationship between the dielectric constant and vwc was then used to estimate the depth averaged vwc of the soils above the reflector compared to average vwc measurements from calibrated neutron probe logs over the same depth interval the average vwc estimates obtained from gpr reflections had an rms error of 0 018 m3 m 3 these results suggested that the two way travel time to a gpr reflection associated with a geological surface could be used under natural conditions to obtain estimates of average water content when borehole control is available and the reflection strength is sufficient the gpr reflection method therefore has potential for monitoring soil water content over large areas and under variable hydrological conditions

the planetary and synoptic scale interactions in a southeast pacific blocking episode using pv diagnostics abstract the synoptic and planetary scale forcing in two blocking anticyclones occurring over the southeast pacific ocean was examined using potential vorticity diagnostics while many studies have examined the dynamic and thermodynamic forcing associated with blocking events in the northern hemisphere nh very few studies have examined blocking in the southern hemisphere sh climatological analysis suggests sh blocking events in the pacific region have similar characteristics to their nh counterparts however the occurrence of blocking is rare elsewhere in the sh and these events are relatively short lived some studies of nh blocking dynamics have also shown that the extent to which the planetary and synoptic scale and planetary synoptic scale interaction forcing that contribute to the genesis and maintenance of pacific and atlantic region events can be different thus a study of the relevant atmospheric dynamics associated with blocking events in the sh was carried out in order to determine wh

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

dynamics of former ice lobes of the southernmost patagonian ice sheet based on a glacial landsystems approach reconstructions of former ice masses from glacial geomorphology help to constrain the nature and timing of glaciation in relation to climatic forcing this paper presents a new reconstruction of the glacial history of five ice lobes in southernmost south america the bahia inutil san sebastian magellan otway skyring and rio gallegos ice lobes we use previous geomorphological mapping of glacial landforms to reconstruct former glacial limits and proglacial lakes demarcate flow sets from the distribution of glacial lineations and evaluate glacial landsystem signatures and their palaeoglaciological implications evidence suggests that the ice lobes predominantly reflect active temperate glacial landsystems which may have switched to polythermal systems when periods of cold based ice developed ephemerally this complex landsystem signature implies that the ice lobes were sensitive to regional climate variability with active re advances during overall retreat of the ice margins there is also evidence for periods of fast ice flow and possible surge like activity in the region followed by the rapid retreat or even collapse of some of the ice lobes in association with proglacial lakes constraining our new reconstruction with published chronological information suggests that at least some of the ice lobes advanced before the global last glacial maximum glgm ca 26 5 19 ka during the last glacial cycle our new reconstruction demonstrates a more complex picture of ice dynamics than has previously been portrayed and one in which the advance and retreat of the ice lobes was likely to have been primarily driven by changes in climate as such ice advances before the glgm in the southernmost part of the patagonian ice sheet are likely to indicate a wider climatic forcing at this time

a review of glacial and holocene paleoclimate records from southernmost patagonia 49 55 s southern south america is the only landmass intersecting the southern westerly wind belt sww that influences the large scale oceanography and controls for example the outgassing of co2 in the southern ocean therefore paleo reconstructions from southernmost patagonia are of global interest and an increasing number of paleoclimate records have been published during the last decades we provide an overview on the different records mostly covering the holocene but partly extending into the late glacial based on a large variety of archives and proxies we particularly discuss possible reasons for regionally diverging palaeoclimatic interpretations and summarize potential climate forcing mechanisms the deglacial and holocene temperature evolution of the region including the adjacent pacific ocean indicates antarctic pattern and timing consistent with glacier re advances during the antarctic cold reversal some records indicate a significant accumulation control on the glacier fluctuations related to changes in sww strength and or position reconstructions of holocene changes in the sww behaviour provide partly inconsistent and controversially discussed pattern while records from the hyperhumid side point to a stronger or southward displaced sww core during the early holocene thermal maximum records from the lee side of the andes show either no long term trend or the opposite suggesting enhanced westerlies during the late holocene neoglacial likewise centennial scale global or hemispheric cold intervals such as the little ice age have been interpreted in terms of enhanced and reduced sww strength some sww variations can be linked to changes in the el nino southern oscillation enso consistent with instrumental climate data sets and might be ultimately forced by solar variability resolving these inconsistencies in southernmost patagonian sww records is a prerequisite for improving hemispheric comparisons and links to atmospheric co2 changes

an influence of extreme southern hemisphere cold surges on the north atlantic subtropical high through a shallow atmospheric circulation previous studies have attributed inter hemisphere influences of the atmosphere to the latitudinal propagation of planetary waves crossing the equator to the triggering of equatorial kelvin waves or to monsoonal circulation over the american atlantic sector such cross equatorial influences rarely occur during boreal summer due to unfavorable atmospheric conditions we have observed that an alternative mechanism provides an inter hemisphere influence when episodes of extreme cold surges and upper tropospheric westerly winds occur concurrently over southern hemisphere amazonia cold surges from extratropical south america can penetrate deep into southern amazonia although they do not appear to influence upper tropospheric circulation of the northern hemisphere extremely strong southerly cross equatorial advection 2 of cold and dense air in the lower troposphere can reach as least 10 n such cold advection increases the northward cross equatorial pressure gradient in the lower to middle troposphere thus shallow northerly return flow below 500 hpa this return flow and the strong lower tropospheric southerly cross equatorial flow form an anomalous shallow meridional circulation spanning from southern amazonia to the subtropical north atlantic with increased geopotential height anomalies exceeding 1 standard deviation to at least 18 n it projects onto the southern edge of the nash increasing its pressure and leading to equatorward expansion of nash s southern boundary these anomalies enhance the north atlantic subtropical high nash leading to its equatorward expansion these extreme cold surges can potentially improving the predictability of weather patterns of the tropical and subtropical atlantic including the variability of the nash s southern edge

frost record in tree rings linked to atmospheric circulation in northern patagonia abstract cold air incursions over subtropical south america are the precursor conditions for frost a recognized extreme thermal weather event affecting plant growth damaging agricultural production over the whole argentinian territory given that sub freezing temperatures occurring during the active growing season may harm the cambium tissues and their daughter cells frost injury can be recorded in annual tree rings in the form of anatomical anomalies for this study six forest sites of araucaria araucana a multi centennial tree species from nw patagonia were considered from 321 trees 1374 frost injuries in the growth rings named frost rings were identified and their calendar dating allowed the development of a regional chronology of frost rings covering the period ad 1256 to ad 1993 738 yrs this represents the longest record at present of extreme low thermal events for patagonia frost injuries were mostly restricted to the middle section of the growth rings suggesting the incidence of late spring frosts moreover frost rings were observed mainly in the juvenile portions

climatic inferences from glacial and palaeoecological evidence at the last glacial termination southern south america there is uncertainty about the interhemispheric timing of climatic changes during the last glacial interglacial transition different hypotheses relying on different lines of evidence point variously to the northern hemisphere leading the southern hemisphere and vice versa or to synchrony between the hemispheres southern south america is well placed to test the various alternatives using both glacial and palaeoecological evidence we argue here from a synthesis of key proxy records that there was a sudden rise in temperature that initiated deglaciation sychronously over 16 of latitude at 14 600 14 300 14 c yr bp 17 500 17 150 cal yr there was a second step of warming in the chilean lake district at 13 000 12 700 14 cy r bp 15 650 15 350 cal yr which saw temperatures rise to close to modern values a third warming step particularly clear in the south occurred at ca 10 000 14 c yr bp 11 400 cal yr the latter achieving holocene levels of warmth following the initial warming there was a lagged response in precipitation as the westerlies after a delay of ca 1600 yr migrated from their northern glacial location to their present latitude which was attained by 12 300 14 cy r bp 14 300 cal yr the latitudinal contrasts in the timing of maximum precipitation are reflected in regional contrasts in vegetation change and in glacier behaviour the large scale of a 80 km glacier advance in the strait of magellan at 12 700 10 300 14 c yr bp 15 350 12 250 cal yr which spans the antarctic cold reversal and the younger dryas was influenced by the return of the westerlies to southern latitudes the delay in the migration of the westerlies coincides with the heinrich 1 iceberg event in the north atlantic the suppressed global thermohaline circulation at the time may have affected sea surface temperatures in the south pacific and the return of the westerlies to their present southerly latitude only followed ocean reorganisation to its present interglacial mode copyright 2000 john wiley sons ltd

late glacial ice advances in the strait of magellan southern chile abstract during the last glacial cycle low gradient glaciers repeatedly drained north eastward into the strait of magellan and dammed extensive proglacial lakes in the central section of the strait this paper focuses on the two most recent glacial advances in the strait culminating over 150 and 80 km from the present ice limits the timing of the first of the two advances has up to now been ambiguous and depended on the interpretation of anomously older dates of 16 590 15 800 yr bp for deglaciation at puerto del hambre here we show there is evidence from seismic data and truncated shorelines that the puerto del hambre basin has been tectonically displaced and that the dates do not represent minimums for deglaciation several other dates show that the advance occurred sometime before 14 260 yr bp the timing of the second advance has been investigated using a refined tephrochronology for the region which has also enabled a palaeoshoreline and glaciolacustrine sediments to be linked to a moraine limit 14c dating of peat and a key tephra layer above and below the glaciolacustrine deposits respectively suggest that the advance culminated in the strait of magellan between 12 010 and 10 050 yr bp

subsurface lateral preferential flow network revealed by time lapse ground penetrating radar in a hillslope subsurface lateral preferential flow lpf has been observed to contribute substantially to hillslope and catchment runoff however the complex nature of lpf and the lack of an appropriate investigation method have hindered direct lpf observation in the field thus the initiation persistence and dynamics of lpf networks remain poorly understood this study explored the application of time lapse ground penetrating radar gpr together with an artificial infiltration to shed light on the nature of lpf and its dynamics in a hillslope based on our enhanced field experimental setup and carefully refined gpr data postprocessing algorithms we developed a new protocol to reconstruct lpf networks with centimeter resolution this is the first time that a detailed lpf network and its dynamics have been revealed noninvasively along a hillslope real time soil water monitoring and field soil investigation confirmed the locations of lpf mapped by time lapse gpr surveys our results indicated the following 1 increased spatial variations of radar signals after infiltration suggested heterogeneous soil water changes within the studied soil which reflected the generation and dynamics of lpf 2 two types of lpf networks were identified the network at the location of soil permeability contrasts and that formed via a series of connected preferential flow paths and 3 the formation and distribution of lpf networks were influenced by antecedent soil water condition overall this study demonstrates clearly that carefully designed time lapse gpr surveys with enhanced data postprocessing offer a practical and nondestructive way of mapping lpf networks in the field thereby providing a potentially significant enhancement in our ability to study complex subsurface flow processes across the landscape

the role of cold fronts in the onset of the monsoon season in the south atlantic convergence zone the onset of the south american monsoon season culminates with the abrupt establishment of the south american convergence zone sacz the impact of cold fronts on the abrupt establishment of the sacz is studied using an 11 year composite analysis of the dynamic and thermodynamic structures intensity and propagation of cold fronts that occur prior to during and after monsoon onset in the sacz a significant change in the structure and propagation of cold fronts is observed at the time of monsoon onset in the sacz with cold fronts suddenly stalling and becoming stationary in southeastern brazil it is proposed that this regime change of the structure and propagation of cold fronts causes the abrupt onset of the monsoon in the sacz a mechanism for this sudden change in cold front behaviour is suggested by analyzing changes in the observed upper level structure of midlatitude waves our observations show that at the time of monsoon onset in the sacz midlatitude waves develop a thinning trough behaviour with upper level troughs becoming thinner westward tilted and sometimes forming cut off lows this behaviour is characteristic of midlatitude waves that develop in the region of anticyclonic shear on the equatorward side of the upper level midlatitude jet during the austral spring the upper level midlatitude jet over south america migrates southward leaving subtropical south america in the equatorward anticyclonic shear side of the jet it is hypothesized that as the meridional shear on the equatorward side of the upper level jet gradually becomes more anticyclonic it suddenly crosses the critical threshold of horizontal shear that has been shown to produce a sudden transition to a thinning trough midlatitude wave regime at this time a regime change occurs whereby the character of frontal systems crossing south america changes abruptly causing the onset of the monsoon season in the sacz copyright 2011 royal meteorological society

imaging rainfall drainage within the miami oolitic limestone using high resolution time lapse ground penetrating radar 1 the vadose zone of the miami limestone is capable of draining several centimeters of rainfall within a fraction of an hour once the water enters the ground little is known about the flow paths in the oolitic rock a new rotary laser positioned ground penetrating radar gpr system enables centimeter precise and rapid acquisition of time lapse surveys in the field two dimensional 2 d gpr time lapse surveying at a 3 min interval before during and after rainfall shows how buried sand filled dissolution sinks efficiently drain the bulk of the rainwater hourly repeated 3 d imaging of a dissolution sink in response to surface infiltration shows how the wetting front propagates at a rate of 0 6 1 2 m h traversing the 5 m thick vadose zone within hours at the same time some of the water migrates laterally into the host rock guided by stratigraphic unit boundaries average lateral propagation measured over a 28 hour period was of the order of 0 1 m h on a seasonal time frame redistribution involves the entire rock volume comparing 3 d surveys acquired after wet summer and dry winter conditions shows good gpr event correspondence but also time shifts up to 20 ns caused by the change of overall water content within the vadose zone high precision time lapse gpr imaging can therefore be used to noninvasively characterize natural drainage inside the vadose zone ranging from transient loading to seasonal variation

the last glacial maximum and deglaciation in southern south america abstract this paper models the extent of the patagonian icesheet during the last glacial maximum lgm and its subsequent deglaciation it constrains a new coupled icesheet climate numerical model with empirical evidence and simulates the icesheet at the lgm and at stages of deglaciation under lgm conditions an icesheet with a modelled volume slightly in excess of 500 000 km3 builds up along the andes there is a marked contrast between the maritime and continental flanks of the modelled icesheet with positive mass balance exceeding 2 m in the west and declining tenfold to the east modelled ice velocities commonly reach 400 m yr 1 in the western fjords the model is most sensitive to variations in temperature and good agreement between modelled ice extent and empirical evidence was achieved by applying a temperature decrease of 6 c relative to present day temperatures with constant wind fields over the model domain assuming a stepped start to deglaciation modelled ice volumes declined sharply contributing 1 2 m to global sea level 80 of it within 2000 years the empirical record suggests that such a stepped warming occurred around 17 500 17 150 cal yr ago

palaeoenvironmental change in southern patagonia during the lateglacial and holocene implications for forest refugia and climate reconstructions abstract a high resolution palynological record from punta yartou fuego patagonia 53 51 s 70 08 w supported by lithostratigraphy radiocarbon dating and tephrochronology was examined to reconstruct the vegetation changes during the last glacial interglacial transition and the holocene following deglaciation from the last glacial maximum sometime before c 23 070 cal yr bp the vegetation was initially dominated by ericaceous shrubs and following modest climate amelioration between c 20 480 and 14 820 cal yr bp the environment favoured the spread of acaena the trend to a warmer and more humid climate was interrupted between c 14 820 and 13 560 cal yr bp when the vegetation community was dominated by cold tolerant herbs such as poaceae and asteraceae subfamily asteroideae suggesting an open treeless landscape with colder climatic conditions coeval with the antarctic cold reversal after c 13 560 cal yr bp a gradual rise in temperature and humidity is inferred from the colonisation of nothofagus a further warming and increase is inferred from the establishment of the forest steppe ecotone by c 12 900 cal yr bp the early holocene was then characterised by increasing development of nothofagus open canopy forest however between c 8080 and 5060 cal yr bp there was a significant reduction in the forest cover and high values of charcoal which suggest an intense arid phase leading to increased availability of dry fuel between c 5060 and 2170 cal yr bp there were centennial scale periods of increased wetter and colder climatic conditions the punta yartou record demonstrates the sensitivity of fuego patagonian forest to changes in the proximity and intensity of the southern westerly winds

rerewhakaaitu tephra a land sea marker for the last termination in new zealand with implications for global climate change abstract the rerewhakaaiutu tephra erupted from okataina volcanic centre north island new zealand at 14 700 95 14 c yr bp ca 17 600 cal yr bp at a time of rapid re organisation of earth s climate system at the end of the last glacial termination i it provides a distinctive isochron in a range of different environments in north island and in adjacent south pacific ocean sediments terrestrial evidence based on fluvial aggradation and downcutting relationships loess accumulation rates palaeovegetation patterns and buried soil development and mineralogy shows that marked amelioration of climate occurred shortly before the rerewhakaaitu tephra was deposited similarly marine evidence from around this time shows major changes in accumulation rates of sediment and aeolian quartz and in the abundance of various marine organisms while foraminiferal oxygen and carbon isotope records indicate that the arrival of the glacial meltwater signal occurred close to or just after the deposition of the rerewhakaaitu tephra these changes are discussed in relation to controls on climate by oceanic and atmospheric mechanisms the re organisation of climate commencing at ca 15 000 14 500 14 c yr bp ca 18 000 17 400 cal yr bp is detected elsewhere in the southern hemisphere and evidently was linked to orbitally forced warming which is thought to have initiated ice retreat in both hemispheres

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

latest pleistocene and holocene glacier fluctuations in southernmost tierra del fuego argentina abstract some researchers propose that summer insolation controls long term changes in glacier extent during the holocene if this hypothesis is correct the record of glacier fluctuations at high latitudes in the southern hemisphere should differ from that in the northern hemisphere although the chronology of holocene glacier fluctuations in the northern hemisphere is well established much uncertainty remains in the ages of holocene glacier fluctuations in the southern hemisphere especially south america here we report on latest pleistocene and holocene glacier fluctuations at the southern end of the andes north and west of ushuaia argentina surface exposure ages 10 be from glaciated bedrock beyond cirque moraines indicate that alpine areas were free of ice by ca 16 9 ka one and in some cases two closely spaced moraines extend up to 2 km beyond little ice age moraines within many of the cirques in the region the mean age of five 10 be ages from two pre little ice age moraines is 14 27 12 67 ka whereas a minimum limiting radiocarbon age for a smaller recessional moraine in one cirque is 12 38 12 01 ka our ages imply that following glacier retreat beginning about 18 52 17 17 ka cirque glaciers first advanced during the antarctic cold reversal 14 5 12 9 ka and may have later advanced or stabilized in the younger dryas chronozone 12 9 11 7 ka based on the distribution of thick geochemically distinct and well dated hudson tephra no holocene moraines appear to be older than 7 96 7 34 ka at some sites there is evidence for one or more advances of glaciers sometime between 7 96 7 34 ka and 5 29 5 05 ka to limits only tens of meters beyond little ice age maximum positions taken together the data 1 do not support the summer insolation hypothesis to explain holocene glacier fluctuations in southernmost patagonia 2 confirm paleobotanical evidence for a warm dry early holocene and 3 suggest that some glaciers in the region reached extents comparable to those of the little ice age shortly before 5 29 5 05 ka

tephra geochemistry a discussion of some persistent analytical problems distal tephrochronological studies are reliant upon precise and accurate geochemical quantitation this quantitation can involve difficulties not often encountered in more conventional petrology solving these problems is of particular importance in the holocene and late quaternary of northwest europe where numerous tephra layers of icelandic origin have been detected in peat bogs and lake and marine sediments electron probe microanalysis epma has proved the most applicable analytical technique when insufficient quantities of tephra are available for bulk analysis standard epma techniques require fine tuning to the tephra problem as the geochemical instability of glass is a common feature in many previous studies geochemical data of avoidably low quality have been produced and little attention appears to have been directed to modification of epma methods it is suggested that the black box approach to geochemical analysis should be avoided by the consideration of several factors these include

holocene sea level changes along the strait of magellan and beagle channel southernmost south america abstract radiocarbon dated marine sediments from five coastal sites along the strait of magellan and beagle channel in southernmost chile permit construction of a curve of relative sea level fluctuations during the holocene morphologic and stratigraphic data point to coastal submergence during the early holocene as the sea rose to a maximum level at least 3 5 m higher than present about 5000 yr ago progressive emergence then followed during the late holocene data from widely separated localities define a smooth curve the form of which is explainable in terms of isostatic and hydroisostatic deformation of the crust resulting from changing ice and water loads apparently anomalous data from one site located more than 100 km behind the outer limit of the last glaciation may reflect isostatic response to deglaciation the sea level curve resembles one derived by clark and bloom 1979 in proceedings of the 1978 international symposium on coastal evolution in the quaternary sao paulo brasil pp 41 60 sao paulo using a spherical earth model both in amplitude and in the timing of the maximum submergence

comment on the last glacial maximum and deglaciation in southern south america by n r j hulton r s purves r d mcculloch d e sugden m j bentley quaternary science reviews 21 2002 233 241

application of ground penetrating radar methods in soil studies a review abstract applications of ground penetrating radar gpr in soil surveys promise cost and time benefits together with the possibility of repeating surveys at the same locations due to the method s non destructiveness to the ground surface after its successful application to earth sciences surveying of the deep subsurface gpr was used in soil surveys however its application in soil surveys has been difficult this paper aims to provide an overview of the application of gpr in soil surveys this paper focuses on methods to estimate the soil water content by various approaches such as determining the electromagnetic signal velocity in a soil by analyses of reflections ground wave or guided wave approaches and the full waveform inversion method to characterize soil and peat stratigraphy with an emphasis on organic horizons and to detect tree roots gprs have been relatively successfully applied in a wide spectrum of surveys but under favourable conditions more complex techniques using numerical modelling that have emerged in recent years might have the potential to be more successful

soil layering and preferential flow impacts on seasonal changes of gpr signals in two contrasting soils abstract experimental evidence has shown that soil layering can significantly alter water movement through soil profiles especially in sloping landscapes detailed knowledge of soil layering and its position in the landscape is therefore necessary for determining dynamic subsurface flow in this study we used ground penetrating radar gpr in combination with high resolution real time soil water monitoring to investigate seasonal changes in gpr signals to identify soil horizon interfaces and their impacts on water flow in two contrasting soils the results showed that 1 in the deep rushtown soil located in a concave hillslope gpr reflections in the bw bc and bc c horizon interfaces became clearer as soil became wetter such increased contrast along interfaces was due to the presence of water associated with water restricting bc horizon and lateral flow from upslope area and 2 in the shallow weikert soil located in a planar hillslope gpr reflections in the soil bedrock interface and the weathered unweathered rock interface become intermittent as soil became wetter this scattering of gpr reflection was due to the non uniform distribution of water in fractured shale bedrock and possible tree root effects while wet condition permitted the enhanced detection of water distribution in both soil profiles optimal time for detecting soil layering was different for these two soils wet condition was more suited for detecting water restricting dense layer in the deep rushtown soil while dry season was optimal for identifying the soil bedrock interface in the shallow weikert soil overall this study demonstrates the value of repeated gpr surveys in different seasons to capture subsurface hydrologic processes and the impacts of soil layering and preferential water distribution on seasonal changes of gpr signals it also provides a useful reference for selecting optimal time for gpr survey in the field

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

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

recent fault movement and palaeoseismicity in western scotland abstract field study at two locations in western scotland is described and gives evidence for fault movement and seismic activity during the late and post glacial epochs the evidence comprises levelling survey of raised marine shorelines remote sensing study of lineaments radiocarbon dating of quaternary sediment and detailed field examination of faults and fault gouge material vertical fault displacements of up to 3 m are observed on a c 10 500 year old raised marine shoreline on the isle of mull and repeated predominantly lateral movement is observed on a prominent 14 km long fault lineament active since ice retreat and as recently as c 2000 yrs b p the fault movements are located close to the edge of the area formerly covered by the loch lomond readvance ice cap 11 000 10 000 yrs b p they are considered to have been caused by rapid rates of isostatic rebound soon after deglaciation

revisiting wintertime cold air intrusions at the east of the andes propagating features from subtropical argentina to peruvian amazon and relationship with large scale circulation patterns this study investigates the spatial and temporal characteristics of cold surges that propagates northward along the eastern flank of the andes from subtropical to tropical south america analysing wintertime in situ daily minimum temperature observations from argentina bolivia and peru and era 40 reanalysis over the 1975 2001 period cold surges usually last 2 or 3 days but are generally less persistent in the southern la plata basin compared to tropical regions on average three to four cold surges are reported each year our analysis reveals that 52 of cold episodes registered in the south of la plata basin propagate northward to the northern peruvian amazon at a speed of around 20 m s 1 in comparison to cold surges that do not reach the tropical region we demonstrate that these cold surges are characterized before they reach the tropical region by a higher occurrence of a specific circulation pattern associated to southern low level winds progression toward low latitudes combined with subsidence and dry condition in the middle and low troposphere that reinforce the cold episode through a radiative effect finally the relationship between cold surges and atmosphere dynamics is illustrated for the two most severe cold intrusions that reached the peruvian and bolivian amazon in the last 20 years

geochemical stability of fine grained silicic holocene tephra in iceland and scotland this paper tests two assumptions fundamental to the use of fine grained silicic tephras from iceland for creating chronological frameworks in northwest europe it is shown firstly that glass shards can retain their overall chemical integrity on at least a four millennial time scale in contrasting depositional environments in iceland and scotland and secondly that an acid digestion process the most practical method for extracting tephra from peat does not significantly bias the results of major element analysis by electron microprobe the implication is that there is great potential and an appropriate method for developing both the resolution and the spatial coverage of chronologies based on silicic icelandic tephras in northwest europe

a geochemical and sedimentary record of high southern latitude holocene climate evolution from lago fagnano tierra del fuego abstract situated at the southern margin of the hemispheric westerly wind belt and immediately north of the antarctic polar frontal zone tierra del fuego is well positioned to monitor coupled changes in the ocean atmosphere system of the high southern latitudes here we describe a holocene paleoclimate record from sediment cores obtained from lago fagnano a large lake in southern tierra del fuego at 55 s to investigate past changes in climate related to these two important features of the global climate system we use an ams radiocarbon chronology for the last 8000 yr based on pollen concentrates thereby avoiding contamination from bedrock derived lignite our chronology is consistent with a tephrochronologic age date for deposits from the middle holocene volcan hudson eruption combining bulk organic isotopic 13 c and 15 n and elemental c and n parameters with physical sediment properties allows us to better understand sediment provenance and transport mechanisms and to interpret holocene climate and tectonic change during the last 8000 yr co variability and long term trends in c n ratio carbon accumulation rate and magnetic susceptibility reflect an overall holocene increase in the delivery of terrestrial organic and lithogenic material to the deep eastern basin we attribute this variability to westerly wind derived precipitation increased wind strength and precipitation in the late holocene drives the nothofagus forest eastward and enhances run off and terrigenous inputs to the lake superimposed on the long term trend are a series of abrupt 9 negative departures in c n ratio which constrain the presence of seismically driven mass flow events in the record we identify an increase in bulk 13 c between 7000 and 5000 cal yr bp that we attribute to enhanced aquatic productivity driven by warmer summer temperatures the lago fagnano 13 c record shows similarities with holocene records of sea surface temperature from the mid latitude chilean continental shelf and antarctic air temperatures from the taylor dome ice core record in east antarctica mid holocene warming occurred simultaneously across the antarctic frontal zone and in particular in locations currently influenced by the antarctic circumpolar current

pleistocene glacitectonic landforms and sediments around central magellan strait southernmost chile evidence for fast outlet glaciers with cold based margins abstract proglacial and subglacial glacitectonic sediments and landforms around the margins of the strait of magellan southernmost chile record the advance and retreat of outlet glaciers of the patagonian ice cap during the last glacial cycle the spatial arrangement of glacitectonic landforms in the area is inferred to have resulted from the advance of ice lobes with cold based margins and wet based interiors as the ice advanced subglacial basins were excavated beneath the glacier margins and the eroded material was pushed up into thrust moraines probably because frozen bed conditions formed a thermal dam against the free drainage of subglacial meltwater these ice marginal glacitectonic landforms were then overridden and streamlined into drumlins and flutes as thicker wet based ice passed over the area evidence for permafrost near sea level in patagonia during the last glaciation suggests that mean annual temperatures were several degrees lower than indicated by recent modelling studies the results indicate that future modelling experiments should incorporate more realistic basal boundary conditions particularly the presence of a weak deforming layer at the glacier bed to improve climatic reconstructions of southern south america

glacial sediment landform associations and paleoclimate during the last glaciation strait of magellan chile abstract glacial sediments and landforms preserved beside the strait of magellan record repeated advances of an outlet of the patagonian icefield during and following the last glacial maximum lgm 25 000 14 000 14c yr b p ice marginal landform assemblages consist of thrust moraine complexes kame and kettle topography and lateral meltwater channels very similar to those found at the margins of modern subpolar glaciers taken together with other forms of paleoenvironmental evidence the landform assemblages show that during the lgm and late glacial time permafrost occurred near sea level in southernmost south america this finding implies that mean annual temperatures were 7 8 c lower than at present somewhat lower than those reconstructed by current glacier climatic models comparison with precipitation temperature relationships for modern glaciers suggests in addition that precipitation levels were lower than today reduced glacial age precipitation may have resulted from a precipitation shadow induced by the patagonian icefield an equatorward migration of the average position of westerly cyclonic storm tracks in the southern midlatitudes or both these factors

seismic stratigraphy and glacial cycles in the inland passages of the magallanes region of chile southernmost south america abstract we present results of a marine geophysical survey that imaged submarine sedimentary and geomorphic features of the main inland channels of the magallanes region of chile in southernmost south america this region holds a remarkable terrestrial and marine record of glacial variations in the closest landmass to antarctica we report evidence for grounded ice along the main channels associated with two ice lobes that flowed from cordillera darwin part of the austral andes into central estrecho de magallanes and seno almirantazgo multibeam data show drumlins and glacial lineations in whiteside channel the northern continuation of seno almirantazgo and iceberg plough marks in central estrecho de magallanes multichannel seismic data show a complex array of seismic facies interpreted as representing two main types of sedimentary units glacimarine sediments corresponding to glacial periods and pelagic sediments corresponding to interglacial periods we find that there are two interglacial glacial cycles represented in this marine sedimentary record chronologically 1 the youngest glacial unit corresponds to the last regional glaciation 31 18 ka 2 these passageways deglaciated with the retreat from regional glacial limit d 17 18 ka and 3 there is no marine sedimentary or morphological evidence that the magallanes glaciers readvanced into the main passageways during the antarctic cold reversal 14 13 ka these findings suggest that final deglaciation of southernmost south america was driven by the atmospheric and ocean warming that started 18 ka as recorded in antarctic ice core records and sea surface temperature proxies offshore the magallanes region

hydropedological investigations with ground penetrating radar gpr estimating water table depths and local ground water flow pattern in areas of coarse textured soils in coarse textured soils ground penetrating radar gpr can provide continuous high resolution records that chart the depth to water tables the use of this information can increase confidence in hydropedological site assessments and reduce the number of wells needed for water table depth and ground water flow determinations ground penetrating radar was used to map spatial and temporal variations in water table depths and ground water flow patterns within an unconfined aquifer located beneath an eolian landscape in northwestern indiana compared with the data collected at a limited number of wells the greater number of observations with gpr provided more comprehensive site coverage and mapped more intricate local ground water flow patterns over a 2 year period gpr revealed systematic temporal and spatial variations in water table depths and local ground water flow patterns

historical climatic extremes as indicators for typical scenarios of holocene climatic periods in the pampean plain abstract the holocene has been marked by two different climatic periods in the pampas one 8 5 3 5 kyr b p characterized by temperatures and precipitation higher than today and the other 3 5 1 4 kyr b p semiarid generating parabolic dunes the humid period produced intense pedogenesis down to 40 lat s and a mobilization of iron oxides to 30 lat s which means tropical climate with temperatures above 20 c and precipitation higher than 2000 mm yr sand deflation and development of parabolic dunes occur under climates with 300 400 mm yr this contribution is based on geological and physical proxies typical weather scenarios of those climates are sporadically reproduced today during extremely humid or dry periods on that basis meteorological parameters of years beyond the thresholds of 2000 and 400 mm yr were processed dry periods were characterized by a large thermal amplitude frosts and stronger winds reproducing the continental anticyclonic circulation of the late holocene humid extremes were warmer than normal lower thermal amplitude with rains produced by local convection processes typical scenarios with precipitation above 2000 mm yr are 21 c mean temperature ca 1 c higher than the present record 27 c maximal annual temperatures 16 c minimal annual temperatures more than 1 c higher than the present as a consequence thermal amplitude was smaller than today virtually without frosts characteristic parameters of the late holocene were mean annual precipitation ca 350 mm yr 15 c mean temperature 22 c maximal annual temperatures 8 c minimal annual temperatures showing significative shifts in the dry season lower than normal monthly maximal and mean temperatures higher than today the result is a thermal amplitude larger than today probably higher quantity of frosts per year stronger winds and lower relative air humidity in comparison with the humid climate extreme complete the scenario

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

vegetation and fire history during the last 18 000 cal yr b p in southern patagonia mallin pollux coyhaique province aisen 45 41 30 s 71 50 30 w 640 m elevation to better understand the climate vegetation and fire history of southern south america since the last deglaciation sediment characteristics diatoms pollen microscopic and macroscopic charcoal and magnetic susceptibility were analyzed in a 14 m long sediment core from a closed basin fen at lago pollux aisen province southern chile 45 41 30 s lat 71 50 30 w long 640 m elev sediment characteristics absence of diatoms and scarce pollen suggest that before 18 000 cal yr bp glacier meltwaters were feeding the small basin when local glaciers were at their maximum position from 18 000 to ca 14 000 cal yr bp the site was a shallow productive pond surrounded by a sparse scrub steppe and accompanied some fire activity this period was markedly drier but warmer than before by 14 000 cal yr bp the fen developed and a species rich steppe expanded suggesting a moderate increase in effective moisture and temperature high fluctuations of terrestrial and aquatic pollen taxa occur between 14 000 and 11 000 cal yr bp attesting to climate variability at this time between 11 000 and 7500 cal yr bp nothofagus steppe woodland developed and fire activity was very high with several large local events precipitation must have increased but most likely summers were drier than today with high frequency of convective storms after 7500 cal yr bp present day closed nothofagus forest became established and fire activity decreased suggesting establishment of present day equable precipitation regime the forest was more open between 4000 and 1500 cal yr bp than before and shrubs or trees grew on the fen forest clearance and grazing only began in the mid 20th century both in terms of timing and character of past changes in vegetation and fire activity the record from m pollux takes an intermediate position between records from high southern latitudes versus those from mid latitudes indicating the different latitudinal expression of the southern westerly storm tracks during the last 18 000 cal yr bp 2007 elsevier b v all rights reserved

faunistic changes between the middle late pleistocene and the holocene on the atlantic coast of tierra del fuego molluscan evidence abstract the marine terraces located on the atlantic coast of tierra del fuego argentina were previously assigned to different sea level highstands from the middle pleistocene to the holocene this study is focused on the analysis of the mollusc assemblages recovered from those terraces when comparing middle late pleistocene mollusc assemblages with adjacent holocene modern ones ecological changes in the fauna were recognized the pleistocene assemblages are less diverse and are dominated by infaunal bivalves whereas holocene and modern assemblages are more diverse and are dominated by epifaunal taxa with a higher presence of gastropods however on a biogeographic scale the fact that pleistocene taxa with the probable exception of retrotapes sp are living today in the region is attributed to the location of the study sites at the centre of the magellan biogeographic unit with species far away from the edges of their ranges of distribution regional faunistic changes and the local disappearance of retrotapes in post glacial benthic communities in the area are therefore interpreted on the basis of regional and local causes most probably associated to substrate changes and not on a global trend related to large scale patterns

gpr based detection of pleistocene periglacial slope deposits at a shallow depth test site abstract pleistocene periglacial slope deposits ppsd almost completely cover the mountainous regions of germany and are the parent material for soil formation it is therefore necessary to map their thickness and spatial distribution the mapping of periglacial slope deposits can be performed more quickly than conventional probing by drilling or soil profile analysis if ground penetrating radar gpr is used because the use of gpr to map soils or soil depth depends to a large degree on the suitability of soil properties the performance of gpr in mapping layered substrates was evaluated at a test site with varying water content and substrate properties we focus on the efficiency of gpr in mapping loess rich layers above layers with a high stone content within a depth range of 1 m different materials such as loess metabasalt and slates including heavily weathered slates saprolite were studied the test site was equipped with several time domain reflectometry tdr probes to monitor soil water content changes for the period of one year systematic investigations of the reflection patterns were performed with 100 200 400 500 and 900 mhz antennae with respect to the quality of measurement dielectric coefficient and soil water content of different material combinations it became clear that the 400 mhz antenna is most suitable for creating images of loess and stone layers at the depth range of 1 m and under natural climatic conditions the results prove that the most important effect the substrates at the test site have on gpr is produced by the differences in water content of bordering layers making the soil water capacity of the materials a decisive parameter for evaluating gpr performance the water content dependent dielectric permittivities show higher values for saprolite heavily weathered slate compared to loess by a factor of 1 3 to 2 with water content increasing from 15 to 40 vol respectively in doing so we discovered the dielectric permittivity of loess to be 1 2 to 1 5 times higher than that of unweathered slate at the same water content we were able to locate horizontal layer boundaries at the test site starting at a minimum of 0 5 vol water content difference and a reflection coefficient r 0 02 between the layers the results obtained at the test site show the ability of gpr to detect layering in ppsd at different water contents and help to predict the performance of gpr measurements in mapping of ppsd

shallow subsurface storm flow in a forested headwater catchment observations and modeling using a modified topmodel transient perched water tables in the shallow subsurface are observed at the south fork brokenback run catchment in shenandoah national park virginia crest piezometers installed along a hillslope transect show that the development of saturated conditions in the upper 1 5 m of the subsurface is controlled by total precipitation and antecedent conditions not precipitation intensity although soil heterogeneities strongly influence local response the macroporous subsurface storm flow zone provides a hydrological pathway for rapid runoff generation apart from the underlying groundwater zone a conceptualization supported by the two storage system exhibited by hydrograph recession analysis a modified version of topmodel is used to simulate the observed catchment dynamics in this model generalized topographic index theory is applied to the subsurface storm flow zone to account for logarithmic storm flow recessions indicative of linearly decreasing transmissivity with depth vertical drainage to the groundwater zone is required and both subsurface reservoirs are considered to contribute to surface saturation

the role of magnesite spatial distribution patterns in determining dissolution rates when do they matter we systematically explore the role of magnesite distribution patterns in dictating its dissolution rates under an array of flow velocity and permeability contrast conditions using flow through column experiments and reactive transport modeling columns were packed with magnesite distributed within quartz matrix in different spatial patterns the mixed column has uniformly distributed magnesite while the zonation columns contain magnesite in different number of zones parallel to the main flow dissolution rates are highest under conditions that maximize water flowing through the magnesite zone this occurs under fast flow and high permeability or uniformly distributed magnesite zones under high flow and low permeability magnesite conditions dissolution only occurs at the magnesite quartz interface leading to rates an order of magnitude lower in the one zone columns than those in the mixed columns spatial patterns do not make a difference under low flow conditions when the system approaches equilibrium v 0 36 m d or under conditions where magnesite zones have higher permeability than quartz zone the bulk column scale rate depends on ae through rmgco3 b mol s 10 9 60 ae where ae is the surface area that effectively dissolves with iap keq 0 1 the rate constant of 10 9 60 is very close to 10 10 0 mol m 2 s under well mixed conditions suggesting the potential resolution of laboratory field rate discrepancy when ae instead of the total bet surface area at i s used the ae values are 1 3 orders of magnitude lower than at the effectively dissolving magnesite quartz interface areas vary between 60 and 100 of ae pointing the importance of reactive interfaces in heterogeneous porous media this work quantifies the significance of magnesite spatial distribution patterns it has important implications in understanding biogeochemical processes in the critical zone and in the deep subsurface where spatial variations in mineral properties prevail

effect of the andes cordillera on precipitation from a midlatitude cold front the effects of the andes cordillera the major mountain range in south america on precipitation patterns of baroclinic systems approaching from the southeast pacific remain largely unstudied this study focuses on a case in late may 2008 when an upper level trough and surface cold front produced widespread precipitation in central chile the primary goal was to analyze the physical mechanisms responsible for the structure and evolution of the precipitation weather research and forecasting wrf model simulations indicate that as an upper level trough approached central chile midtropospheric flow below 700 hpa was blocked by the high topography and deflected poleward in the form of a barrier jet this northerly jet had wind maxima in excess of 15 m s 21 was centered around 925 hpa and extended westward 200 km from the mountains it intersected the cold front which approached from the south near the coast thereby increasing convergence along the frontal surface slowing its equatorward progress and enhancing rainfall over central chile another separate region of heavy precipitation formed over the upwind slopes of the cordillera a trajectory analysis confirmed that the barrier jet moved low level parcels from their origin in the moist southeast pacific boundary layer to the coast when model topography was reduced to twenty percent of its original height the cold front advanced more rapidly to the northeast generated less precipitation in central chile between 338 and 368s and produced minimal orographic precipitation on the upwind andean slopes based on these findings the high topography appears responsible for not only orographic precipitation but also for substantially increasing precipitation totals over the central coast and valley

upper quaternary geology of the lower carcarana basin north pampa argentina abstract the geological evolution of the lower carcarana basin reflects a sequence of dry and humid climates from a geomorphological point of view the area belongs to the pampean eolian system the geomorphological units comprise several fluvial geoforms partially masked by a loess carpet on which eolian erosive forms developed the sedimentary record is not simple the typical profile begins with a predominantly eolian unit composed of silty sand and including two pedogenic levels carcarana fm the formation is the result of the reworking of a dune field in the pampean sand sea is4 it is upper pleistocene in age is 3 another somewhat different climatic deterioration followed related to the begining of the last glacial maximum is 2 which caused the deposition of a loessic mantle tezanos pinto fm subsequent evolution of the climate involved a shift to humid conditions during the hypsithermal period generating a well developed soil at the top of the formation an upper holocene eolian layer san guillermo fm covers the whole sequence at the river margins of the basin the late pleistocene lower holocene eolian deposits are replaced by a complex silty clayey sequence mainly paludal with a soil complex in the middle of the section lucio lopez fm

glaciation in the andes during the lateglacial and holocene this review updates the chronology of andean glaciation during the lateglacial and the holocene from the numerous articles and reviews published over the past three decades the andes which include some of the world s wettest and driest mountainous regions offer an unparalleled opportunity to elucidate spatial and temporal patterns of glaciation along a continuous 68 degree meridional transect the geographic and altitudinal extent of modern glaciers and the sensitivity of both modern and former glaciers to respond to changes in specific climatic variables reflect broad scale atmospheric circulation and consequent regional moisture patterns glaciers in the tropical andes and in the mid latitude andes are likely to have been far more sensitive to changes in temperature than glaciers in the dry subtropical andes broad scale temporal and spatial patterns of glaciation during the lateglacial are apparent in the southernmost andes the lateglacial chronology appears to have a strong antarctic signature with the best dated moraines correlating closely with the antarctic cold reversal the southernmost andes do not appear to have experienced a significant ice advance coeval with the younger dryas yd climatic reversal at the other end of the andes from w 0t o 9 n a stronger yd connection may exist but critical stratigraphic and geochronologic work is required before a yd ice advance can be fully demonstrated in the central andes of peru well dated moraines record a significant ice readvance at the onset of the yd but ice was retreating during much of the remaining yd interval the spatial temporal pattern of holocene glaciation exhibits tantalizing but incomplete evidence for an early to mid holocene ice advance s in many regions but not in the arid subtropical andes where moraines deposited during or slightly prior to the little ice age lia record the most extensive advance of the holocene in many regions there is strong evidence for neoglacial advances in the interval between 1 0 and 2 5 ka moraines that correlate with the lia of the northern hemisphere are seen in all presently glacierized mountain ranges most of these date to within the past 450 years outboard of these moraines in many regions are moraines of a slightly more extensive advance that occurred several hundred years prior to the onset of the lia priorities for future work include filling in several prominent spatial gaps in the distribution of chronologic studies for the lateglacial these gaps include the arid regions of northern chile and argentina the southern peruvian andes between 11 5 and 13 5 s and the andes of northern peru and

architecture of the deep critical zone in the rio icacos watershed luquillo critical zone observatory puerto rico inferred from drilling and ground penetrating radar gpr

late glacial and holocene palaeoenvironmental change in the central strait of magellan southern patagonia abstract high resolution palaeoenvironmental data for the wisconsin late glacial and early holocene is provided from two sites puerto del hambre and estancia esmeralda ii in the central section of the strait of magellan southern chile palaeoecological and lithostratigraphical evidence is correlated with other palaeoenvironmental data from the magellan region using 14 c dating and tephrochronology the oldest record from puerto del hambre commences at 14 470 14 c yr bp 17 330 cal yr bp following retreat of the magellan glacier climatic warming after that time is indicated by ice retreat from the central section of the strait of magellan and palynological evidence however mean annual temperature continued to be cooler than present until c 10 300 14 c yr bp 12 270 12 110 cal yr bp the magellan environment was relatively humid between c 14 100 and c 12 550 14 c yr bp 16 910 and 15 170 14 410 cal yr bp at c 12 550 14 c yr bp there was a sharp decrease in effective moisture levels of humidity fluctuated but remained relatively low until c 10 300 14 c yr bp this period of cool and drier climate is contemporary with a significant glacier advance dated to between c 12 700 and 10 300 14 c yr bp 15 330 and 12 270 12 110 cal yr bp which would have produced an enhanced rainshadow effect around 10 300 14 c yr bp a shift to warmer conditions occurred between c 10 300 and 8550 14 c yr bp 12 270 12 110 and 9530 cal yr bp an extreme arid phase is recorded which led to an increase in fires at c 8550 14 c yr bp an increase in available moisture allowed the eastward spread of nothofagus forest at 8265 14 c yr bp 9270 9160 cal yr bp there was a relative rise in sea level in the strait of magellan this marine incursion lasted until 3970 14 c yr bp 4420 cal yr bp reaching its maximum around c 6450 14 c yr bp 7420 7340 cal yr bp

fluctuations of outlet and valley glaciers in the southern andes argentina during the past 13 000 years abstract in the southern argentine andes ten advances of valley glaciers were used to reconstruct the late glacial and holocene glacier history the accumulation areas of these glaciers lie in the precordillera and are thus independent of fluctuations of the south patagonian icefield like the viedma outlet glacier the valley glaciers advanced three times during late glacial time 14 000 10 000 yr b p the youngest advance correlates with the younger dryas stade based on two minimum ams 14 c dates of 9588 and 9482 yr b p the second oldest advance occurred before 11 800 yr b p during the first half of the holocene ca 10 000 5000 yr b p advances culminated about 8500 8000 7500 and 5800 5500 yr b p during the second half of the holocene advances occurred between ca 4500 and 4200 yr b p as well as between 3600 and 3300 yr b p in the rio condor valley three subsequent advances have been identified