europa s dynamic icy crust abstract europa s icy crust records active resurfacing by tectonic and thermal processes over tens of millions of years as rapidity demonstrated by a paucity of craters tidal working causes rotational torque surface stress internal heating and orbital evolution which can explain the formation of observed tectonic crack patterns ridges crustal displacement and chaotic terrain by processes involving connections between the surface and the underlying ocean through cracks melt sites and occasional impacts these processes were recent and thus most likely continue today the permeability of the crust allows exchange of materials including oxidants and exogenic organics from the surface and endogenic substances from the ocean such that a habitable biosphere might extend to within a few centimeters of the surface continual changes in environmental conditions in the ice crust such as deactivation of individual cracks after thousands of years due to non synchronous rotation and crustal thawing releasing any trapped organisms could provide drivers for biological adaptation as well as opportunity for evolution

copper isotope fractionation in sedimentary copper mineralization timna valley israel abstract copper isotopes 65 cu 63 cu are potentially powerful new geochemical proxies for oxidation reduction processes and metallic cycling this research presents a cu isotope study of mineralization in historically mined stratiform sediment hosted copper ssc ore deposits of the precambrian and cambrian rocks of the timna valley southern israel these deposits provide a natural laboratory for studying isotopic fractionations between cu sulphides and cu ii minerals copper carbonates hydroxides and silicates formed during sequential cycles of low temperature alteration of igneous copper porphyries marine sedimentary diagenesis and epigenetic mobilization in sandstones isotopic measurements were made using mc icp ms after ion chromatographic separation of the copper from matrix elements in accord with abiogenic experimental studies showing that there should be a negative isotopic fractionation between reduced and oxidized copper minerals 65 cu values of cu sulphides are significantly lower 3 4 to 1 2 than coexisting cu ii carbonates and hydroxides 1 2 to 0 5 cu ii silicates which should only show a very small isotopic fractionation relative to parent cu ii solutions give average 65 cu values of 0 09 0 24 consistent with the fact that the primary source of sedimentary copper was the precambrian igneous rocks isotopic zoning profiles in cu sulphides of the cambrian dolomites suggest they were formed through the interaction of small disconnected cu solution reservoirs with h 2 s formed by bacterial reduction of sulphate containing pore waters mass balance modeling based on the measured cu isotope compositions and experimental fractionation factors shows that the main copper reservoir is the cambrian sandstone shale sequence and that the cu sulphide reservoirs are relatively small thus most of the copper transport occurred in relatively oxidized conditions the calculated reservoir sizes are in agreement with field observations and confirm that copper isotopes are able to trace both the oxidation reduction cycles and mass transfer during sedimentary copper mineralization

manganese nodules nod a 1 and nod p 1 implications of pre treatment on oxygen isotopes and mineralogy abstract manganese nodules are a type of ferromanganese chemical precipitate containing a plethora of economically important metals increasingly being used in the high and green technology sectors by measuring oxygen isotope ratios in these materials we can increase our understanding of how they form and constrain which metals are likely to be present in them there is a lack of suitable reference materials for use in oxygen isotopic studies of samples dominated by mn oxide minerals i e mn nodules and crusts and therefore a need for their development the samples nod a 1 and nod p 1 united states geological survey mn nodules from the atlantic and pacific oceans respectively provide the best opportunity for such a reference material but their application has been hampered by their incomplete mineralogical characterization and lack of consensus on how to pre treat if at all these type of samples for 18o analysis we have performed a detailed mineralogical study using scanning electron microscopy energy dispersive spectroscopy sem eds powder x ray diffraction pxrd and raman spectroscopy on these reference materials in sample nod a 1 todorokite goethite and or hematite mg calcite phillipsite or chabazite quartz and barite were identified the minerals todorokite birnessite asbolane vernadite goethite pyrochroite quartz phillipsite or chabazite anorthite kaolinite and barite were identified in nod p 1 we conducted experiments to assess the effect on 18o and mineralogy resulting from acidification with hydrochloric acid hcl pre fluorination with bromine pentafluoride brf5 at ambient temperature or both acidification and pre fluorination treatments results from samples given both treatments were deemed most meaningful to the study of mn crusts and nodules and therefore nodule research in general by providing 18o values representative of the relatively pure oxide silicate fraction only we report a 18o value of 11 0 1 0 for the oxide silicate fraction of nod a 1 and a value of 11 1 0 7 for the same fraction in nod p 1 with results showing a 18o shift of up to 10 3 as a function of nodule and the pre treatment used the 18o values of samples given both treatments converge and are substantially 18o depleted relative to that of corresponding untreated material which was found to contain various 18o enriched phases such as carbonate minerals and non stoichiometric water based on our results we recommend that for all future analyses of mn nodules and crusts the samples receive both treatments to ensure accurate and consistent results

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

liquid water and active resurfacing on europa voyager images of the jovian moon europa show a bright icy surface transected by a complex pattern of long linear fracture like markings with a slightly lower albedo1 very few impact craters are observed with sizes generally hi the range 10 20 km indicators of surface composition and texture include deep ir h2o absorption features2 uv absorption features characteristic of sulphur in a water matrix on the trailing hemisphere3 and a photometric function indicating much more homogeneous scattering than areas of equal albedo on ganymede and callisto4 europe s mean density is 3 03 g cm 3 indicating a primarily silicate composition however if the density of the silicates is the same as for io the h2o mass fraction would be 6 enough to form an outer layer of h2o 100 km thick if completely differentiated several models have been suggested for the evolution and present state of europa5 8 we present here arguments for recent resurfacing by h2o from a liquid layer based on new interpretations of recent spacecraft and earth based observations and revised theoretical calculations

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

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

oxygen isotope variations in phosphate of biogenic apatites ii phosphorite rocks abstract phosphorites from sedimentary sequences ranging in age from archaean to recent were analysed for 18 o in both the po 4 18 o p and co 3 18 o c in the apatite lattice the oxygen isotope record is considerably better preserved in phosphates than in either carbonates or cherts the use of the longinelli and nuti 8 temperature equation yields temperatures for recent phosphorites that are in good agreement with those measured in the field the 18 o p values of ancient phosphorites decrease with increasing age these changes with time are not likely to be due to post depositional exchange changes in 18 o values of seawater and variations of temperature with time can account for the 18 o p time trend but the latter explanation is preferred in ancient phosphorites 18 o c in structurally bound carbonate in apatite is not a reliable geochemical indicator

is there evidence for polar wander on europa abstract the orientations of the albedo lineaments bands and lineations on europa s surface have been compared in previous studies with the global stress fields set up by orbital eccentricity orbital recession and nonsynchronous rotation of these orbital and rotational effects nonsynchronous rotation combined with an offsetting of the tidal bulge comes closest to providing agreement between the stress field generated and the lineation orientations if the lineations trace tension or extension fractures mcewen 1986 nature321 49 51 however inferred minimum principal stress directions for a broad region of wedge shaped bands near the anti jove point cannot satisfactorily be accounted for by any of the stress fields above but are consistent with the stresses resulting from a rotation of europa s ice shell about an axis through the sub and anti jove points clockwise as seen from the anti jove hemisphere p m schenk and w b mckinnon 1989 icarus79 75 100 calculations by ojakangas and stevenson 1989 icarus81 220 241 of the thermal state of europa s ice shell indicate that spatial variations in the thickness of the shell may cause it to undergo such a reorientation we have investigated whether any reorientation of the shell about an axis through the sub and anti jove points produces a stress field consistent with the full global set of prominent lineations on europa s surface we find that no such reorientation provides a good fit between the lineations and plausible fracture orientations derived from the principal stress trajectories topographic ridges identified in a limited zone south of the anti jove point are roughly consistent with compression due to clockwise polar wander but the orientations of these ridges may be strongly biased by illumination direction within the limitations of the presently available imagery nonsynchronous rotation is still the most likely cause of the prominant fractures on europa s surface and the best specific albeit regionally limited tectonic evidence consistent with recent polar wander remains the wedge shaped bands

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

lead and uranium isotopic behavior in diagenetic and epigenetic manganese nodules timna basin israel determined by mc icp ms abstract isotope ratios of u and pb were measured in two types of mn nodules from the cambrian timna formation israel type a nodules are mainly composed of pyrolusite and hollandite with mn ba pb and u concentrations of 30 60 0 2 2 5 0 2 1 0 and 500 3500 ppm respectively whereas type b nodules were formed by alteration of the former and contain mainly coronadite with mn ba pb and u concentrations of 7 48 0 2 7 0 6 5 and 10 160 ppm respectively the isotopic composition of u and pb was measured by mc icp ms on mn rich solutions up to 100 mg l without and with chromatographic separation the values for the 207 206 and 208 206 ratios have been determined with precisions of up to 50 ppm and those of 206 204 207 204 and 208 204 up to 200 ppm the values for the 234 238 ratios have been determined with precisions of 0 4 1 the results of the separated and unseparated solutions were shown to be equal within the error thus there is no significant matrix effect while measuring u and pb in mn rich solution using the mc icp ms the isotopic composition of pb and u support the distinction between the two types of mn nodules type a nodules have a wide range of 206pb 204pb ratios 18 278 19 776 and an almost constant ratio of 208pb 204pb in contrast type b nodules have almost constant 206pb 204pb ratios and a wide range of 208pb 204pb ratios 37 986 38 079 type a nodules form a linear array on a 207pb 204pb vs 206pb 204pb diagram while type b nodules form a tight group characterized by lower pb isotope ratios that slightly deviate from the type a array the 234u 238u ratio differs between the two types of nodules type a nodules exhibit a uniform and close to equilibrium 234u 238u ratio while type b nodules show a wide range of 234u 238u ratios above and below the equilibrium value the isotopic composition of pb in type a nodules might reflect pb contributions from plutonic rock weathering exposed at the time of deposition or later to the cambrian sea these nodules have remained unaffected by processes that occurred since the cambrian the higher 208pb 204pb values of type b indicate that these nodules were formed from a th enriched solution probably during epigenetic processes which occurred also during the last 1 ma thus the two isotopic systems of u and pb can record formation leaching and redeposition of mn ores

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

observational selection effects in europa image data identification of chaotic terrain abstract the identification of terrains on images of europa is highly dependent on the image resolution and illumination angle both of which are quite variable due to the observational selection constraints of the galileo mission higher resolution images allow for the identification of smaller patches of chaotic terrain which are indistinguishable from surrounding tectonic terrain in most other galileo imagery the incidence angle of light also introduces an observational bias in the identification of chaotic terrain images acquired closer to europa s terminator generally reveal more chaos features than images taken with higher sun proper accounting for selection effects has implications for the size distribution and chronology of chaotic terrain and the geologic history of the satellite at 200 m pixel 30 of europa s surface appears as chaotic terrain but with the effects of lighting and resolution taken into account the portion is 40 or more bias correction eliminates the 10 km size peak that had been the basis of an earlier thick ice model mottled terrain and lenticulae appear to be the same as chaotic terrain even though they have been mapped separately in the past and accounting for how observational bias affects the freshness of appearance of chaotic terrain and the identification of tectonic modification of chaotic terrain demonstrates that the formation of tectonic and chaotic terrain have been concurrent processes throughout europa s surface history

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

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

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

trace metal remobilization in the interstitial waters of red clay and hemipelagic marine sediments interstitial water samples from the guatemala basin and the coast of baja california have been analyzed for manganese iron copper nickel and nitrate the data provide a systematic look at changes in trace metal diagenesis proceeding from red clay to highly reducing nearshore sediments in red clay sediments the nitrate concentrations suggest that only aerobic respiration is occurring manganese and iron are below detection nickel concentrations remain the same as in bottom seawater but copper shows a pronounced maximum just at the sediment water interface proceeding to hemipelagic sediments denitrification becomes increasingly important and manganese and iron remobilization occur in the sediments the linear manganese and nitrate profiles suggest regions of production or consumption separated by zones of diffusion this differs from the conventional picture of a continuous series of reactions within the sediments manganese reduction always occurs before iron reduction the pore water nickel correlates well with manganese in these sediments suggesting that nickel is associated with mno2 in the solid phase the pore water flux ratio of manganese and nickel agrees well with the ratio in solid phase authigenic oxides copper still displays a core top concentration maximum as well as a second maximum associated with the remobilized manganese the calculated ratio of the cu c flux ratios support the argument for copper remobilization during organic carbon oxidation comparison of the upward and downward diffusive fluxes with the rate of copper buried by sedimentation shows that at least half of the copper buried must be of diagenetic origin and less than 25 of the copper reaching the sediments is buried

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

isotopic constraints on fluid evolution and precipitation mechanisms for the boleo cu co zn district mexico stable and radiogenic isotope composition of stratiform cu co zn mineralization and associated sedimentary rocks within the boleo district of the miocene santa rosalia basin baja california sur constrains the evolution of seawater and hydrothermal fluids and the mechanisms responsible for sulfide and oxide deposition stable isotope geochemistry of limestone and evaporite units indicates a strong paleogeographic influence on the chemistry of the water column near shore limestone at the base of the boleo formation is characterized by modified marine carbon 13cpdb 6 0 to 4 4 and oxygen 18osmow 19 5 to 26 2 isotope composition due to the influx of 13c and 18o depleted fluvial water sulfate sulfur isotope composition 34scdt 17 21 to 22 3 and 18osmow 10 7 to 13 1 for basal evaporite and claystone facies are similar to miocene seawater strontium isotopes are less radiogenic than expected for miocene seawater due to interaction with volcanic rocks low s c ratios high mn contents and sedimentological evidence indicate the basin water column was oxidizing the oxygenated basin restricted sulfide precipitation to within the sedimentary pile by replacement of early diagenetic framboidal pyrite and pore space filling by cu co zn sulfides to produce disseminated sulfides quartz mn oxide oxygen isotope geothermometry constrains mineralization temperature between 18 and 118 c sulfur isotopes indicate the following sources of sulfide 1 bacterial sulfate reduction within the sedimentary pile produced negative 34s values 20 in framboidal pyrite and 2 bacterial sulfate reduction at high temperature 80 118 c within the sedimentary pile during the infiltration of the metal bearing brines produced cu co zn sulfides with negative but close to 0 34s values isotope modeling of fluid rock reaction and fluid mixing indicates 1 sedimentary and marine carbonates 13c 11 6 to 3 2 and 18o 19 0 to 21 8 precipitated from basin seawater pore water that variably mixed with isotopically depleted meteoric waters and 2 hydrothermal calcite 13c 7 9 to 4 3 and 18o 22 1 to 25 8 formed by dissolution and replacement of authigenic marine calcite by downward infiltrating metalliferous brine and brine sediment exchange that prior to reaction with calcite had mixed with isotopically depleted pore water the downward infiltration of metalliferous brine is inferred from lateral and stratigraphic metal distributions and from the concentration of cu sulfides along the upper contact of pyrite bearing laminae the co existence and textural relationships among framboidal pyrite base metal sulfides carbonate and mn fe oxides including magnetite within mineralized units are consistent with carbonate replacement and high temperature bacterial reduction within the sedimentary pile occurring simultaneously below a seawater column under predominantly oxygenated conditions

polar wander and surface convergence of europa s ice shell evidence from a survey of strike slip displacement two global issues regarding europa are addressed by a survey of strike slip faults first a common type of terrain that appears to represent convergent sites of surface removal which may help compensate for substantial widespread dilation along tectonic bands elsewhere thus helping resolve the problem of conserving global surface area is identified second evidence for polar wander may provide the first confirmation of that theoretically predicted phenomenon these results among others come from an extensive survey of strike slip faults over the portion of the surface where galileo images at 200 m pixel resolution were obtained for regional mapping purposes the images cover two broad swaths that run from the far north to the far south one in the leading hemisphere and the other in the trailing hemisphere among the faults that have been mapped are a fault 170 km long with a strike slip offset of 83 km the greatest yet identified on europa and a quasi circular strike slip fault that surrounds a 500 km wide plate which has undergone rotation as a rigid unit reconstruction of specific examples of strike slip reveals sites of lateral convergence because europa is unique in many ways these sites are not similar to compression features on other bodies which may explain why they had previously been difficult to identify the distribution of strike slip in both hemispheres when compared with predictions of the theory of tidal walking provides evidence for polar wander the crust of europa appears to have slid as a single unit relative to the spin axis such that the site on the crust that was previously at the north rotational pole has wandered probably during the last few million years to a location currently in the leading hemisphere about 30 away from the spin axis such polar wander probably also explains symmetry patterns in the distribution of chaotic terrain pits and uplift features

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

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

temperatures on europa from galileo photopolarimeter radiometer nighttime thermal anomalies galileo observations of europa s thermal emission show low latitude diurnal brightness temperatures in the range of 86 to 132 kelvin nighttime temperatures form an unexpected pattern with high temperatures on the bright ejecta blanket of the crater pwyll and an equatorial minimum in temperatures after sunset uncorrelated with surface albedo or geology the nighttime anomalies may be due to regional thermal inertia variations of an unknown origin which are equivalent to a two to threefold variation in thermal conductivity or to endogenic heat fluxes locally reaching 1 watt per square meter endogenic heat flow at this high level although consistent with some geological evidence is theoretically unlikely

low temperature thermochronology of francolite insights into timing of dead sea transform motion cambrian siliciclastic sequences along the dead sea transform dst margin in southern israel and southern jordan host both detrital fluorapatite d apatite and u rich authigenic carbonate fluorapatite francolite a apatite d apatite and underlying neoproterozoic basement apatite yield fission track ft data reflecting paleozoic mesozoic sedimentary cycles and epeirogenic events and dispersed u th sm he ahe ages a apatite which may partially or completely replace d apatite yields an early miocene ft age suggesting formation by fracturing hydrothermal fluid ascent and intra strata recrystallisation linked to early dst motion the dst separating the african and arabian plates records 105 km of sinistral strike slip displacement but became more transtensional post 5 ma helium diffusion measurements on a apatite are consistent with thermally activated volume diffusion indicating tc 52 56 10 c cooling rate 10 c myr a apatite ahe data record pliocene cooling 35 40 c during the transtensional phase of movement this suggests that timing of important milestones in dst motion can be discerned using a apatite low temperature thermochronology data alone

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

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

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

ferromanganese crusts as recorders of marine dissolved oxygen abstract the distinct triple oxygen isotope composition of tropospheric o2 relative to seawater is the result of biogeochemical reactions e g primary productivity respiration exchange with the stratosphere and the relative size of different oxygen containing reservoirs namely o2 o3 and co2 this difference in isotopic composition gives tropospheric o2 utility as a record of biogeochemical and atmospheric processes and may also be used for determining where in the rock record isotopic fingerprints of tropospheric oxygen may be preserved the isotopic record of tropospheric oxygen in previous studies is largely limited to analyses of gas trapped in continental glaciers and a patchwork of other proxies most notably the triple oxygen signature of sulfate here we show the uppermost layers of hydrogenetic deep ocean ferromanganese crusts from each of the major ocean basins have a triple oxygen isotope composition consistent with the direct incorporation of dissolved oxygen the range of 18o and 17o in ferromanganese crusts suggests the mn oxide endmember contains a near 50 50 mixture of oxygen from water and dissolved o2 our data indicate this signal also persists into older layers of the crusts potentially preserving near 75 million years of the oxygen isotopic composition of the lower troposphere and subsequent deep ocean respiration our analysis of oxygen isotope values bulk chemistry and estimated local dissolved oxygen for crust top samples reveals that variations in bulk chemistry ultimately exhibit more influence on the oxygen mass balance than changes in dissolved oxygen presenting a challenge for unambiguous determination of local dissolved oxygen although analytical challenges remain these widespread layered deposits of ferromanganese crust may offer a viable path for future interrogation of the history or relative history of the oxygen cycle of the troposphere and deep ocean millions of years into the past

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

evidence for separation across a gray band on europa abstract thynia linea a gray band on europa is found to be a 25 km wide and 900 km long region of lithospheric separation which has been infilled by relatively dark material roughly a dozen older features and the cuspate segments that form its outline appear to have been displaced across its width displacement azimuths indicate a best fit pole of opening near 79 s 200 w however displacement magnitude decreases toward either end of the gray band indicating that it is more akin to a tear in a nonrigid europan lithosphere opening was in response to nw se directed tensile stress in accord with the stress predictions of nonsynchronous rotation observations of thynia linea are consistent with a laterally mobile brittle lithosphere decoupled from ductile or liquid material below as previously suggested to account for opening of wedge shaped bands in europa s antijovian region lithospheric separation and contemporaneous emplacement of new material offers a possible volcano tectonic scenario for resurfacing europa if this process is ongoing resurfacing can be accomplished on a time scale consistent with the satellite s surface age if one gray band or zone of wedge shaped bands forms every 10 3 10 4 yr and becomes unrecognizable with age this would imply that features on europa brighten with age as through continuous deposition of frost onto the surface

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

europa s petrological thermal history the thermal evolution of europa is described by a new path of geophysical development petrological considerations suggest that heat may have been transported within europa by sub solidus convection and that a large fraction of europa s water content is retained as hydrated silicates

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

fluid speciation controls of low temperature copper isotope fractionation applied to the kupferschiefer and timna ore deposits article i nfo mass balance amongreducedandoxidizedsolutionspeciesexertsastrongcontrol ontheisotopiccompositionof sulphide minerals we explore this issue for copper isotopic fractionation in sedimentary copper sulfide deposits through fluid speciation isotopic eh ph calculations based on the thermodynamic stability of copper chloride aqueous solution complexes and experimentally measured copper isotope fractionation factors applying these speciation diagrams to mc icp ms copperisotope data on the kupferschiefer sw partof thelubin sieroszowice copper district and timna s israel sediment hosted stratiform copper deposits ssc identifies differences in ore formation redox conditions timna valley copper sulfides have light cu isotopic compositions of 65 cu 2 04 0 44 2 relatively to srm 976 copper standard which are shown to correspond to eh values of 0 5 to 0 6 v at formation conditions t 40 c ph b6 these eh values indicate precipitation at relatively oxidized conditions where the cu i solution complex cucl3 2 i sb10 of the total solution species in contrast the kupferschiefer cu sulfides analyzed in this work dominantly show significantly higher 65 cu values 0 39 0 36 corresponding to eh values of 0 4 to 0 5 v at formation conditions t 100 c ph 6 3 in these eh conditions most copper in solution occurs as cucl3 2 complexes 80 the above observations are in accord with field relations showing that cu ii minerals dominate the timna system but cu sulfides are the major minerals of the kupferschiefer deposits fluid speciation isotopic calculations show that copper isotopes can be used as effective tracers of redox conditionsandthisapproach can bepotentiallyappliedtovarioushydrothermal oredeposits such as black smokers and volcanic hosted massive sulphide deposits and to other metallic isotope systems however the isotopic fractionation mayalso be strongly influenced by the types ofligand bondingofcopper ions and these effects need to be fully evaluated before the isotope geochemistry of copper ores can be fully understood

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

holocene dolomitization of calcium carbonate sediments from the coastal sabkhas of abu dhabi u a e a stable isotope study secondary dolomitization of holocene calcium carbonate sediments occurs beneath the coastal sabkhas of abu dhabi u a e a stable isotope study of the sabhka sediments and brines indicates that the

hydrothermal mn deposits of the franciscan assemblage ii isotope and trace element geochemistry and implications for hydrothermal convection at spreading centers abstract major element trace element and sr nd pb and o isotopic data for a franciscan mn deposit suggest an origin by seafloor hydrothermal circulation based on q mode factor analysis the cherts and mn lenses of the blue jay mine formed from a combination of 4 components representing 1 biogenic 1 hydrothermal and 2 detrital sources rb sr u th pb and o isotopic systematics in the mn lenses were affected by input from the hydrothermal circulation of material leached from the underlying basalts nd isotopic compositions in both cherts and mn lenses are identical and within the range measured for pacific ocean water suggesting the ree were not mobilized by hydrothermal activity correlation of 18 o with sio 2 and mno 2 in the mn lenses implies the lenses formed by simple mixing of hydrothermally derived mn oxides with seawater and biogenic silica 18 o of the cherts is both uniform and depleted relative to dsdp jurassic cherts but similar to microquartz bearing cherts of the monterey formation this suggests that diagenetic activity exerted more control on oxygen isotope compositions then hydrothermal alteration or metamorphism finally a well defined rb sr isochron of 158 5myr was obtained for these cherts and opens the possibility of determining absolute radiometric ages for similar cherts throughout the geologic record

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

europa stratigraphy and geological history of the anti jovian region from galileo e14 solid state imaging data a tidal bulge and associated deformation are predicted to occur in europa s anti jovian region voyager data showed polygonal low albedo bands in this region it was demonstrated that when the low albedo material comprising these bands was removed the margins could be reconstructed suggesting that fracturing and lateral separation has occurred higher resolution galileo images of a 300 000 km2 portion of the anti jovian region permit recognition and mapping of a variety of features and documentation of the geological history we identify background ridged plains several distinctive types of bands and ridges lenticulae and regions of chaotic terrain these images are at relatively low incidence angles thus albedo variations predominate over topography this presents a challenge to morphologically based mapping but does not preclude development of a regional stratigraphy stratigraphic relationships show that dark bands crosscut the bright ridged plains and are themselves disrupted by lenticulae and chaos suggesting a geological history beginning with background ridged plains followed by a period dominated by band formation with the most recent history predominantly characterized by formation of lenticulae and chaos the paucity of impact craters in this region indicates that the entire sequence of units is geologically recent

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

chemical remanent magnetism related to the dead sea rift evidence from precambrian igneous rocks of mount timna southern israel a paleomagnetic and mineralogical study of shallow intrusive basement rocks on mount timna arabo nubian massif in sinai shows that although all the igneous rocks are of late precambrian age a remanent magnetic direction similar to the subrecent field miocene to present is identified in samples of quartz monzodiorite monzodiorite dikes of various composition and altered gabbro the average direction of these rock units is d i 359 41 95 4 and the pole is at 83 6 n 223 2 e the subrecent direction appears both as an overprint direction and as the sole stable vector in dolerite rhyolite and andesite dikes the magnetic mineral assemblage of these rocks includes secondary minerals such as hematite and goethite which formed by oxidation and hydration of the original magnetite and ti magnetite the subrecent direction is interpreted to have been acquired as a chemical remanent magnetization crm by hydrothermal activity and circulation of thermal brines through fractures related to the adjacent dead sea transform the hydrothermal activity occurred before uplift and erosion exposed the basement rocks i e in the middle miocene during the early stages of activity of the dead sea rift the north trending declinations indicate that mount timna has not rotated about a vertical axis after acquisition of the crm a conclusion that confirms a previous structural analysis an absence of reversals implies that the duration of crm acquisition was probably less than 1 m y the maximum length of normal polarities since the oligocene other field directions were found in an alkali granite one site 343 14 95 22 in a dolerite dike one site 318 0 95 2 and in a gabbro seven sites 303 56 95 6 the field direction in the granite is similar to that for early cretaceous a time of magmatic activity in timna northwest trending declinations and shallow inclinations found in several samples of the dikes are carried by unaltered parts of the rocks these directions are interpreted as late precambrian early cambrian in age indicating a near equatorial location of the region at that time

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

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

early organic diagenesis the significance of progressive subsurface oxidation fronts in pelagic sediments abstract porewater and solid phase geochemical data at two contrasting ne atlantic stations are reported station 10552 on the cape verde abyssal plain is a site of slow pelagic accumulation ca 0 4 cm kyr 1 molecular oxygen is present in the sediment column to at least 2 m and probably much deeper labile organic carbon is almost totally consumed in the upper few centimetres of the sediment by contrast at station 10554 on the madeira abyssal plain the pelagic sequence has been interrupted by the occasional deposition of organic rich turbidites porewater oxygen and nitrate profiles show that subsurface organic metabolism of the organic carbon associated with the uppermost turbidite layer is a significant fraction of the overall metabolism in the sediment column this metabolism occurs at a relatively thin reaction front which progresses deeper into the turbidite with time this phenomenon exerts a controlling influence on the present nutrient profile and redox succession in a less extreme form substrate distributions of this latter type are not uncommon in atlantic sediments a model has been developed which is controlled by both oxygen and nitrate data this model permits a vertical profile of metabolic activity to be derived and also gives estimates of the reaction rate constants and solid phase mixing rates at these two contrasting stations about 30 of the total activity at station 10554 is located within the turbidite at the deepening reaction front this is a non steady state condition in fact it is found that the integrated metabolic activity at the two stations is not dissimilar ca 1 2 10 13 moles cm 2 sec 1 the striking differences in redox profile are therefore primarily attributable to differences in the distribution of metabolic activity within the column

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

stable isotopic characterisation of francolite formation stable isotopic data are presented for 112 samples of francolite from 18 separate phosphate deposits values of 13c and 34s in most offshore deposits suggest formation within oxic or suboxic environments either by carbonate replacement or direct precipitation of francolite from water of normal marine compositions the exceptions are concretionary francolite from namibia which has an isotopic composition in keeping with its formation within organic rich sediments and that from offshore morocco which has an isotopic signature of the anoxic suboxic interface onshore deposits from jordan mexico south africa and possibly the permian phosphoria formation in the western u s a are substantially depleted in18o they appear to be too altered for deductions to be made about their environments of formation in other onshore deposits which are unaltered or minimally altered the isotopic composition suggests that some formed within sulphate reducing sediments sedhura morocco whilst francolite from the georgina basin of australia formed at the oxic anoxic boundary where oxidation of biogenic h2s decreases the 34s of pore water in general pelletal samples show non oxic isotopic signatures whilst non pelletal samples show oxic isotopic signatures but samples from namibia peru ica plateau and the californian and moroccan margins are exceptions to this rule morphology may therefore be a misleading indicator of francolite genesis as no definitive relation exists between phosphorite type and isotopic signature

tectonics and water on europa the tectonics of europa one of jupiter s moons are complex this satellite probably hosts a subsurface water ocean but the thickness of the outer ice crust is poorly constrained and the episodic presence of liquid water at the surface is debated we argue that some surface features of europa are formed by soft ice that is heated by viscous dissipation of tidal motion along faults and do not depend on a shallow ocean our model suggests that transient pockets of liquid water or brine could form at shallow depths in the crust

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

does europa have a subsurface ocean evaluation of the geological evidence it has been proposed that jupiter s satellite europa currently possesses a global subsurface ocean of liquid water galileo gravity data verify that the satellite is differentiated into an outer h2o layer about 100 km thick but cannot determine the current physical state of this layer liquid or solid here we summarize the geological evidence regarding an extant subsurface ocean concentrating on galileo imaging data we describe and assess nine pertinent lines of geological evidence impact morphologies lenticulae cryovolcanic features pull apart bands chaos ridges surface frosts topography and global tectonics an internal ocean would be a simple and comprehensive explanation for a broad range of observations however we cannot rule out the possibility that all of the surface morphologies could be due to processes in warm soft ice with only localized or partial melting two different models of impact flux imply very different surface ages for europa the model favored here indicates an average age of 50 myr searches for evidence of current geological activity on europa such as plumes or surface changes have yielded negative results to date the current existence of a global subsurface ocean while attractive in explaining the observations remains inconclusive future geophysical measurements are essential to determine conclusively whether or not there is a liquid water ocean within europa today

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

europa s differentiated internal structure inferences from four galileo encounters radio doppler data from four encounters of the galileo spacecraft with the jovian moon europa have been used to refine models of europa s interior europa is most likely differentiated into a metallic core surrounded by a rock mantle and a water ice liquid outer shell but the data cannot eliminate the possibility of a uniform mixture of dense silicate and metal beneath the water ice liquid shell the size of a metallic core is uncertain because of its unknown composition but it could be as large as about 50 percent of europa s radius the thickness of europa s outer shell of water ice liquid must lie in the range of about 80 to 170 kilometers

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

chemical and stable isotope fractionation in manganese oxide phosphorite mineralization timna valley israel element carbon and oxygen isotope fractionations have been studied in laminated deposits manganese nodules and phosphorite lenses in clastic sediments of the cambrian timna formation southern israel comparisons of element abundances show that only manganese phosphorus and uranium were mobilized and concentrated during diagenesis element fractionations among the diagenetic manganese components particularly resemble those observed in present day suboxic pelagic marine sediments epigenetic processes involving reducing solutions reversed the diagenetic geochemical trends with the redox sensitive elements manganese and uranium showing considerable depletions in nodules and iron and lead showing corresponding enrichments the manganese oxides of nodules have calculated 18 o compositions varying from 1 6 to 3 1 these compositions are significantly lower than a 18 o value of 7 9 obtained for the manganese oxides of an ocean floor nodule and are taken to largely represent temperature differences between the ocean floor and the shallow marine timna conditions slight decreases in 18 o accompany the transformation from diagenetic type a to epigenetic type b manganese nodules corresponding shifts to lower 18 o are also inferred for the structural carbonate of apatites such shifts are compatible with re equilibration accompanying a slight temperature increase and or low temperature meteoric water alteration 13 c values of 7 to 12 obtained for the apatites of laminated deposits and phosphorite lenses are consistent with phosphorite diagenesis in suboxic to anoxic pore waters early diagenetic redox conditions are indicated to be major controls governing the development of the assemblages

isotope geochemistry of oxygen and carbon in phosphate and carbonate of phosphorite francolite oxygen isotope ratios in phosphate delta sup 18 o sub p were determined in 219 samples of phosphoritic rocks from all major phosphogenic provinces of the world ranging in age from lower proterozoic to recent in 58 samples oxygen was analyzed in the two oxygen lattice sites of francolite both in phosphate and in structural carbonate delta sup 18 o sub c delta sup 13 c was also analyzed in the latter and in coexisting calcite for 10 of them both delta sup 18 o sub p and delta sup 18 o sub c decrease sharply from the recent to the cretaceous and decrease with a gentler slope to the precambrian the nature of the time variation is elucidated by means of a delta sup 18 o sub p vs delta sup 18 o sub c plot which suggests that a the main cause of the time trends is the increase in temperature between recent and the cretaceous b the pre cretaceous trend is overprinted by both low temperature nonequilibrium exchange between sup 18 o depleted water and the rocks and higher temperature exchange between phosphate and carbonate c the observed trend cannot be explained by sup 18 o depleted cretaceous and paleozoic oceans the calcite coexisting with apatite in phosphatic rocks is similar in both delta sup 18 o and delta sup 13 c to the structural carbonatemore of the apatite even though phosphate may exchange its oxygen with environmental water to a greater extent than the authors originally claimed it is probably still a very good isotopic recorder of sedimentary environments less

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