late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

amazonia during the last glacial abstract new data on the vegetational history and quaternary geology of amazonia permit an improved reconstruction of past environments in amazonia during the last glacial period although limited data from rondonia carajas and guyana show that in certain areas savanna type vegetation and savanna forest had replaced the rain forest during the late pleniglacial ca 22 000 13 000 yr b p the amazonian forest may have been split up into one major west amazonian and several other medium size forest areas this suggests a decline in rainfall of 500 to 1000 mm a reduction of 25 to 40 temperatures may also have been 2 to 6 c 4 2 c lower than today possibly substancially influencing amazonian vegetation during the humid middle pleniglacial 55 000 26 000 yr b p rivers carried a lot of water and sediment resulting in the deposition of lower terrace sediments with one dry interruption around 40 000 yr b p carajas and katira in carajas there is evidence of dry periods ocurring at about 40 000 yr b p and during the early pleniglacial ca 60 000 yr b p rivers carried little water and incised into the low terrace sediments during the dry late pleniglacial water levels rose during the late glacial 13 000 10 000 yr b p or at the beginning of the holocene 10 000 yr b p sedimentation in and of the present inundation valleys commenced after that

cool kaolins in finland we use d h and 18o 16o ratios to explore the age of kaolins on the fennoscandian shield sub cretaceous kaolins in southern scandinavia have isotopic compositions indicative of weathering under warm mean annual temperatures mats of 15 c deep kaolins on the shield surface in finland previously also have been regarded as products of humid tropical weathering of mesoproterozoic to eocene age new oxygen and hydrogen isotope ratios indicate however weathering by cool groundwater under mats of 13 15 c isotope ratios are also not consistent with deep 1 km burial by cover rocks indicating that a very old age for the weathering is unlikely palaeotemperatures are below cretaceous mats yet substantially above plio pleistocene mats comparisons with palaeotemperatures in n europe and around the arctic ocean indicate that the finnish kaolins developed on the shield surface in the palaeogene or alternatively miocene deep weathering was selectively developed in highly fractured shield rocks and took place in response to latest cretaceous and palaeogene uplift and after stripping of palaeozoic cover rocks the cool kaolins in finland indicate that previous routine attributions of kaolinitic weathering products in the geological record to humid tropical environments should be closely scrutinised

water isotopes in precipitation data model comparison for present day and past climates abstract variations of hdo and h2 18 o concentrations are observed in precipitation both on a geographical and on a temporal basis these variations resulting from successive isotopic fractionation processes at each phase change of water during its atmospheric cycle are well documented through the iaea wmo network isotope concentrations are in middle and high latitudes linearly related to the annual mean temperature at the precipitation site paleoclimatologists have used this relationship to infer paleotemperatures from isotope paleodata extractable from ice cores deep groundwater and other such sources for this application to be valid however the spatial relationship must also hold in time at a given location as the location undergoes a series of climatic changes progress in water isotope modeling aimed at examining and evaluating this assumption has been recently reviewed jouzel et al 1997 with a focus on polar regions and more specifically on greenland we extend this review in comparing the results of two different isotopic agcms nasa giss and echam and in examining with a more global perspective the validity of the above assumption i e the equivalence of the spatial and temporal isotope temperature relationships these results confirm the dominating role of local temperature changes on the paleo isotope signal in most regions however the exact calibration of this valuable paleothermometer is biased by for example the seasonality of precipitation and other factors we forced the two models by the climatic boundary conditions of the mild holocene at 6 kyr bp which only slightly differs from today s climate the isotope response on this weak forcing is quite heterogeneous the only robust common response is the intensification of the hydrological cycle in low latitudes and therefore isotopically more depleted precipitation in the tropics and subtropics we also examine recent progress made in modeling the relationship between the conditions prevailing in moisture source regions for precipitation and the deuterium excess of that precipitation

tropical climates at the last glacial maximum a new synthesis of terrestrial palaeoclimate data i vegetation lake levels and geochemistry palaeodata in synthesis form are needed as benchmarks for the palaeoclimate modelling intercomparison project pmip advances since the last synthesis of terrestrial palaeodata from the last glacial maximum lgm call for a new evaluation especially of data from the tropics here pollen plant macrofossil lake level noble gas from groundwater and delta 18 o from speleothems data are compiled for 18 2 ka c 14 32 degrees n 33 degrees s the reliability of the data was evaluated using explicit criteria and some types of data were re analysed using consistent methods in order to derive a set of mutually consistent palaeoclimate estimates of mean temperature of the coldest month mtco mean annual temperature mat plant available moisture pam and runoff p e cold month temperature mat anomalies from plant data range from 1 to 2 k near sea level in indonesia and the s pacific through 6 to 8 k at many high elevation sites to 8 to 15k in s china and the se usa mat anomalies from groundwater or speleothems seem more uniform 4 to 6 k but the data are as yet sparse a clear divergence between mat and cold month estimates from the same region is seen only in the se usa where cold air advection is expected to have enhanced cooling in winter regression of all cold month anomalies against site elevation yielded an estimated average cooling of 2 5 to 3 k at modern sea level increasing to approximate to 6 k by 3000m how ever neotropical sites showed larger than the average sea level cooling 5 to 6 k and a non significant elevation effect whereas w and s pacific sites showed much less sea level cooling 1 k and a stronger elevation effect these findings support the inference that tropical sea surface temperatures ssts were lower than the climap estimates but they limit the plausible average tropical sea surface cooling and they support the existence of climap like geographic patterns in sst anomalies trends of pam and lake levels indicate wet lgm conditions in the w usa and at the highest elevations with generally dry conditions elsewhere these results suggest a colder than present ocean surface producing a weaker hydrological cycle more arid continents and arguably steeper than present terrestrial lapse rates such linkages are supported by recent observations on freezing level height and tropical ssts moreover simulations of greenhouse and lgm climates point to several possible feedback processes by which low level temperature anomalies might be amplified aloft

oxygen isotope evidence of climate change from pedogenic clay minerals in the himalayan molasse abstract in this study we examine the oxygen isotope ratios of smectite and kaolinite in a stratigraphic sequence of paleosols in the siwalik himalayan molasse on the potwar plateau northern pakistan there is a 3 4 o increase in the smectite 18 o values synchronous with a 3 5 o increase in 18 o values of pedogenic calcite at 8 5 6 5 ma previously observed by quade et al 1989 the covariation of the 18 o values of smectite with calcite gd 18 o values through time strongly suggests a pedogenic origin of smectite and that its 18 o values reflect the oxygen isotope ratio of the soil water present during pedogenesis these data show that the 18 o values of clay minerals in paleosols in aggrading sedimentary sequences are viable paleoclimate indicators kaolinite 18 o values are similar to smectite 18 o values as would be expected for pedogenic kaolinite but there is greater variation in these data which we attribute to incomplete mineral separation the measured permil oxygen isotope fractionation between calcite and smectite within individual paleosols is on average 3 o higher than the equilibrium fractionation this isotopic disequilibrium can be explained by the calcite forming predominantly during the dry winter season and the smectite forming predominantly during the wet summer season the synchronous 3 5 o increase in oxygen isotope ratios of smectite and calcite at 8 5 6 5 ma indicates that this 18 o 16 o increase is not due to diagenesis but rather results from a climate change the most likely causes of the 18 o 16 o increase in smectite and calcite are either increased aridity resulting in increased soil water evaporation thus 18 o enrichment and or a change from more continental to more marine sourced precipitation the tibetan plateau which is suggested to have undergone rapid uplift around 8 ma e g harrison et al 1992 may have acted as an effective orographic barrier to low 18 o precipitation originating from central asia causing higher 18 o values of the precipitation falling on the potwar plateau currently it is impossible to distinguish between these two potential causes of the 18 o 16 o increase at 8 5 6 5 ma but these clay mineral 18 o values support that there was a significant climate change in this region

building the pamir tibetan plateau crustal stacking extensional collapse and lateral extrusion in the central pamir 2 timing and rates geothermochronologic data outline the temperature deformation time evolution of the muskol and shatput gneiss domes and their hanging walls in the central pamir prograde metamorphism started before 35 ma and peaked at 23 20 ma reflecting top to n thrust sheet and fold nappe emplacement that tripled the thickness of the upper 7 10 km of the asian crust multimethod thermochronology traces cooling through 700 100 c between 22 and 12 ma due to exhumation along dome bounding normal sense shear zones synkinematic minerals date normal sense shear zone deformation at 22 17 ma age versus elevation relationships and paleoisotherm spacing imply exhumation at 3 km myr south of the domes mesozoic granitoids record slow cooling and or constant temperature throughout the paleogene and enhanced cooling 7 31 c myr starting between 23 and 12 ma and continuing today integrating the central pamir data with those of the east chinese pamir kongur shan and muztaghata domes and with the south pamir shakhdara dome implies i regionally distributed paleogene crustal thickening ii pamir wide gravitational collapse of thickened crust starting at 23 21 ma during ongoing india asia convergence and iii termination of doming and resumption of shortening following northward propagating underthrusting of the indian cratonic lithosphere at 12 ma westward lateral extrusion of pamir plateau crust into the hindu kush and the tajik depression accompanied all stages deep seated processes e g slab breakoff crustal foundering and underthrusting of buoyant lithosphere governed transitional phases in the pamir and likely the tibet crust

biogeochemical characteristics of lacustrine sediments reflecting a changing alpine neotropical ecosystem during the pleistocene abstract continuous lacustrine deposits of the funza ii core from the bogota basin colombia 5 n74 w record late pleistocene climatic variations providing an opportunity to assess the influence of glacial interglacial climate changes on alpine ecosystems in equatorial south america biogeochemical response of this tropical alpine system to climate change was inferred from changes in elemental concentrations and ratios and isotopic signatures in the upper 120 m of the lacustrine funza core values of 13 c org exhibit eight abrupt positive shifts that are thought to reflect rapid expansions of c 4 grasses in the tropical andes and algal blooms one of these excursions interpreted to correspond to c 4 vegetation expansion occurred in sediments accumulated during the last glaciation 30 000 50 000 yr b p and implies a downslope shift of the upper andean treeline regardless of prevailing temperatures sedimentary carbon sulfur ratios are low and indicate significant sequestering of sulfur monosulfides are the dominant constituent of sedimentary sulfur during relatively humid intervals when increased supply of iron caused by enhanced weathering favored the formation of monosulfide minerals under strongly reducing conditions in contrast organosulfur compounds dominate the sedimentary sulfur species in relatively drier intervals when mildly reducing conditions and limited iron input promoted the diagenetic incorporation of sulfur in organic matter dry events inferred from the sulfur record typically correlate with glacial maxima whereas glacial terminations are usually associated with wet periods

eastern tropical pacific hydrologic changes during the past 27 000 years from d h ratios in alkenones 1 the tropical pacific plays a central role in the climate system by providing large diabatic heating that drives the global atmospheric circulation quantifying the role of the tropics in late pleistocene climate change has been hampered by the paucity of paleoclimate records from this region and the lack of realistic transient climate model simulations covering this period here we present records of hydrogen isotope ratios dd of alkenones from the panama basin off the colombian coast that document hydrologic changes in equatorial south america and the eastern tropical pacific over the past 27 000 years a and the past 3 centuries in detail comparison of alkenone dd values with instrumental records of precipitation over the past 100 a suggests that dd can be used as a hydrologic proxy on long timescales our records indicate reduced rainfall during the last glacial period that can be explained by a southward shift of the mean position of the intertropical convergence zone and an associated reduction of pacific moisture transport into colombia precipitation increases at 17 ka in concert with sea surface temperature sst cooling in the north atlantic and the eastern tropical pacific a regional coupled model forced by negative sst anomalies in the caribbean simulates an intensification of northeasterly trade winds across central america increased evaporative cooling and a band of increased rainfall in the northeastern tropical pacific these results are consistent with the alkenone sst and dd reconstructions that suggest increasing precipitation and sst cooling at the time of heinrich event 1

oxygen isotope systematics in a multiphase weathering system in haiti abstract physical and chemical partial dissolution techniques have been applied to a suite of young karst bauxite and laterite samples from the southern peninsula of haiti the 18o values have been obtained for nine mineral species and range from 1 0 for anatase rutile to 33 4 for authigenic quartz on one hand results for quartz calcite kaolinite gibbsite and boehmite compare favourably with 18o values predicted from accepted mineral water fractionation factors assuming modern temperatures 25 2 c and water 18o values 3 1 0 5 on the other hand the 18o values measured for anatase illite smectite chlorite smectite and some iron oxide samples do not compare favourably with predicted values departures from expected values for these minerals may be related to crystallization from water with a different 18o value than modern water an imprecise knowledge of some mineralwater fractionation factors under surficial conditions or nonattainment of isotopic equilibrium between mineral and water during formation partial dissolution techniques hold considerable promise for obtaining quantitative 18o values of individual minerals in single samples of complex fine grained regolith material

the pliocene and quaternary of the high plain of bogota colombia a history of tectonic uplift basin development and climatic change abstract the high plain of bogota in the eastern cordillera of colombia represents a large tectonic basin that is filled with hundreds of metres of lacustrine and fluvial sediments in the centre of the basin the sediment sequence attains a thickness of nearly 600 m and covers a time span of the last 3 ma late pliocene quaternary still older sediments of mainly fluvial origin cover the adjacent mountain slopes the age of these sediments reaches back into the late miocene to 6 ma and older the sediment sequence of the bogota area has been the subject of extensive stratigraphical and palynological studies for decades the results of these studies have provided a unique picture of the pliocene quaternary geological history of a tropical montane region three main factors have influenced the evolution of the landscape sedimentation and vegetation development these are the tectonic uplift of the andes between ca 5 and 3 ma the development of the large tectonic sedimentary basin of bogota after ca 3 5 ma and the quaternary climatic fluctuations and glaciations starting shortly after ca 2 7 ma

late pliocene high sulfidation epithermal gold mineralization at the la bodega and la mascota deposits northeastern cordillera of colombia la bodega and la mascota are plio pleistocene high to intermediate sulfidation epithermal gold deposits hosted in proterozoic gneisses and mesozoic granites of the santander massif eastern cordillera of colombia and are part of the california vetas mining district coeval volcanic rocks are not recognized in the district and volumetrically minor granodiorite porphyries dated at 10 1 ma are the only igneous rocks younger than jurassic known from the vicinity of the epithermal deposits as of 2010 la bodega and la mascota contained an inferred resource of 3 47 moz au 19 2 moz ag and 84 4 mlbs cu at a 2 g t au cut off mineralization exhibits ne trending nw dipping structural control associated with the right lateral strike slip la baja fault mineralization at la bodega is composed of vein networks and tectonic hydrothermal breccias while at la mascota it is largely contained in tabular fault controlled tectonic hydrothermal breccia bodies alteration and sulfide assemblages can be assigned to six distinct hydrothermal episodes which comprise early porphyry style phases and a late epithermal style phase with up to four distinct stages porphyry phases comprise stages 1 and 2 stage 1 is characterized by propylitic alteration with epidote chlorite calcite specularite veins minor pyrite and chalcopyrite molybdenite from veins collected 0 7 km southwest of la mascota yielded an re os age of 10 14 ma which constrains the age of stage 1 stage 2 is related to a separate younger magmatic hydrothermal system and characterized by phyllic alteration sericite illite quartz pyrite associated with quartz pyrite veins and its age is constrained by 40 ar 39 ar geochronology on hydrothermal muscovite i e sericite to 3 4 ma the epithermal phase comprises stages 3 through 6 and is related to multiphase hydrothermal breccia development and quartz alunite alteration stage 3 is defined by presence of copper sulfides such as bornite covellite and chalcopyrite stage 4 by wolframite stage 5 by enargite and stage 6 by sphalerite pyrite quartz and alunite are common to all epithermal stages residual vuggy quartz is scarce gold silver mineralization took place during stages 3 through 5 with some gold introduced during stage 2 alunite 40 ar 39 ar ages constrain epithermal mineralization to between 2 6 and 1 6 ma primary fluid inclusion assemblages representative of hydrothermal stages 4 and 5 contain liquid and vapor rich inclusions and together with quartz vein textures suggest that boiling was an important ore precipitating mechanism homogenization temperatures of these range from 143 and 238 c and salinities from 0 5 to 5 6 wt nacl equiv pyrite 34 s ranges from 16 9 to 11 3 at la mascota and 8 3 to 6 1 at la bodega the strongly negative sulfur isotope signature can be explained by fluid boiling or alternatively by biogenic sulfur source from the proterozoic paragneisses based on 18 o and d data alunite was precipitated from magmatic fluids and only stage 6 alunite shows clear evidence for mixing of the hydrothermal fluid with meteoric water

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

unraveling climatic changes from intraprofile variation in oxygen and hydrogen isotopic composition of goethite and kaolinite in laterites an integrated study from yaou french guiana an integrated study of o and h isotopes in the lateritic profile of yaou french guiana was undertaken to investigate the usefulness of stable isotopes as tracers of climatic changes in continental environments the studied profile is composed of a 27 m thick saprolite mostly developed in the past under wet and dry tropical climate in association with a duricrust overlain by a 3 m thick yellow latosol formed more recently under present equatorial hot and humid climate 18o d values determined for weathering goethite pseudomorphs after pyrite and kaolinite microcrystalline clay groundmass throughout the 30 m deep profile reflect formation temperatures consistent with present 25 c and realistic past climatic temperatures 20 c 30 c indicating that weathering minerals formed in isotopic equilibrium with their genetic environment and were not subjected to significant isotope exchange after formation a distinct shift downward 2 for 18o 15 for d from low to high 18o d values occurs around 20 m depth in the saprolite it is interpreted as recording the change from the past tropical to the present equatorial climate goethite and kaolinite in the 5 10 m thick saprolite interval immediately above the active basement weathering front are in isotopic equilibrium with modern water and must have formed under present equatorial humid conditions in contrast goethite and kaolinite found higher up in the saprolite and in the duricrust formed in the past under tropical wet and dry climate from waters distinctly depleted in 18o and d relative to modern water the marked depletion of paleo meteoric water at yaou most likely reflects a more contrasted or monsoonal character of the ancient tropical climate the present study shows that ancient weathering minerals in lateritic profiles preserve their 18o d values and carry a time signal the time signal is best expressed in minerals formed rapidly at the weathering front and not subjected to post formational remobilization such as the goethite pseudomorphs after pyrite occurring at yaou groundmass kaolinite is more susceptible to partial remobilization through successive dissolution precipitation reactions which may obliterate the paleoclimatic signal unraveling the climatic record carried by weathering minerals in old soil systems is greatly enhanced by studying both oxygen and hydrogen isotopic compositions

astronomical forcing of contrasting rainfall changes in tropical south america between 12 400 and 8800 cal yr b p abstract today precipitation over tropical south america is largely controlled by the seasonal movements of the inter tropical convergence zone itcz during the summer the itcz is shifted southward due to the warming of the continent paleoclimate data from southeastern amazonia and the central andes indicate that these two areas evolved similarly during the last 30 000 yr however between 12 400 and 8800 cal yr b p eastern amazonia received substantial moisture whereas the bolivian altiplano was arid this suggests that the itcz during summer was then farther north than it is today

isotopic evidence for cooler and drier conditions in the tropical andes during the last glacial stage documentation of paleoclimatic conditions during the last glacial stage in the tropical andes is sparse despite the importance of understanding past climate changes in the tropics to reconstruct paleoenvironmental conditions in the alpine neotropics we measured the oxygen 18o and hydrogen d isotopic composition of authigenic kaolinite within weathering profiles of the bogota basin colombia because of the strong dependence of isotopic values on both surface temperature and rainfall while kaolinite isotope data from holocene soils in the basin reflect modern mean annual temperature and mean weighted rainwater isotopic composition of the basin kaolinite isotope data from paleosols developed during the last glacial stage suggest 6 2 c cooler temperatures moreover the isotope data indicate higher isotopic values of paleorainwater interpreted to reflect drier conditions the combination of reduced rainfall temperature and p co2 significantly affected the distribution of tropical montane flora during the last glacial stage

the hydrogen and oxygen isotope geochemistry of pedogenic clay minerals principles and theoretical background abstract the 18 o 16 o and d h ratios of the structural oxygen and hydrogen of naturally occurring clay minerals carry information about the conditions under which the minerals formed clays generally form in isotopic equilibrium with the environment and hence have isotopic compositions that reflect the temperature of formation and the 18 o 16 o and d h ratios of water in the micro environment the isotopic signature of water in the weathering environment is a reflection of the climate once formed clays are resistant to isotopic alteration under surface and near surface conditions except when they undergo subsequent mineralogical alteration in some instances this alteration may be subtle as in the case of conversion of kaolinite with a high degree of crystalline order as measured by the hinckley index to kaolinite of low crystalline order in a pedogenic profile isotopic studies of pedogenic clays may be expected to yield more information about pedogenesis and paleoclimate when both 18 o 16 o and d h ratios of the clays are measured however few studies have incorporated the use of the two isotope ratios

high resolution δ13c stratigraphy of the chuar group ca 770 742 ma grand canyon implications for mid neoproterozoic climate change a high resolution c isotope record based on 13 c org from organic rich shales and 13 c carb from dolomites in the ca 770 742 ma chuar group provides important new data for evaluating the signifi cance of large magnitude c isotope anomalies in neoproterozoic climate change three successive large magnitude isotopic excursions 8 15 are interpreted to represent primary seawater values based on a series of diagenetic tests and they are not associated with evidence of signifi cant long term 10 6 10 7 m y sea level change nor glaciomarine deposits intrabasinal correlation of 13 c org values suggests that most chuar shales record primary values and is consistent with previously reported h c ratios of 0 49 indicating that chuar shales experienced minimal thermal alteration although some chuar dolomites reveal early diagenetic alteration their 13 c dol values typically fall near those of coeval least altered dolomites or organic rich shales relative to dolomite values the chuar carbon record is interpreted to refl ect predominantly primary organic carbon 13 c values and contains suf

evidence for a prolonged retroflection of the north brazil current during glacial stages the importance of the role played by the tropics in driving and propagating climate change between hemispheres has long been the focus of attention in a bid to evaluate ocean atmosphere interactions on glacial interglacial timescales the amazon fan and ceara rise in the western equatorial atlantic ocean lie directly in the flowpath of the north brazil current nbc which as a conduit for the cross equatorial transport of heat and salinity is a key component for the heat budget of the north atlantic mg ca palaeothermometry and stable oxygen isotope analysis of planktonic foraminifera sampled from 15 sites across the amazon fan and ceara rise reveal variations in oceanic surface currents and of the dispersal of freshwater from the river amazon over five timeslices modern early holocene younger dryas late glacial and marine isotope stage 3 sea surface temperature reconstructions reveal progressive climatic amelioration over the last similar to 30 ka indicating a temperature increase of similar to 3 2 1 1 degrees c since the late glacial in conjunction with this warming values of delta delta o 18 a proxy for water column stratification indicates increased vertical mixing of the glacial ocean the spatial distribution of values of delta 18 w the isotopic composition of ambient seawater is used to infer surface current variations and demonstrates an oceanward shift in the river outflow plume in cold climates representing a prolongation or possibly permanent continuation in the duration of the seasonal retroflection of the nbc causing the curtailment of cross equatorial transport a prolongation of this retroflection could have resulted from a mean southward migration of the southern boundary of the itcz c 2011 elsevier b v all rights reserved

gold contents of sulfide minerals in granitoids from southwestern new brunswick canada the abundance of gold and selected trace elements in magmatic sulfide and rock forming minerals from silurian devonian granitoids in southwestern new brunswick were quantitatively analyzed by laser ablation inductively coupled plasma mass spectrometry gold is mainly hosted in sulfide minerals i e chalcopyrite pyrrhotite and pyrite in some cases perhaps as submicron inclusions nanonuggets gold is below detection 0 02 ppm in major rock forming minerals i e plagioclase k feldspar biotite hornblende and muscovite and oxides i e magnetite and ilmenite gold distribution coefficients between sulfide and granitoid melt are calculated empirically as d text cpy melt text au 948 pm 269 text d text po melt text au 150 pm 83 text and d text py melt text au 362 pm 96 this result suggests that gold behavior in the granitoid systems is controlled by the conditions of sulfur saturation during magmatic evolution the threshold of physiochemical conditions for sulfur saturation in the melts is a key factor affecting gold activity gold behaves incompatibly prior to the formation of sulfide liquids or minerals but it becomes compatible at their appearance gold would be enriched in sulfur undersaturated granitoid magmas during fractionation partitioning into evolved magmatic fluids and favoring the formation of intrusion related gold deposits however gold becomes depleted in residual melts if these melts become sulfur saturated during differentiation leading to gold precipitation in the early sulfide phases of a granitoid suite late stage cl bearing magmatic hydrothermal fluids with low ph and relatively high oxidation state derived from either progressively cooling magmas at depth or convective circulation of meteoric water buffered by reduced carbon bearing sediments may scavenge gold from early sulfide minerals if a significant amount of gold produced in this manner is concentrated in a suitable geological environment e g shear zones or fracture systems intrusion related gold deposits may also be generated exploration for intrusion related gold systems should focus on the areas around evolved phases of granitoid suites that remained sulfur undersaturated for sulfur saturated granitoid suites the less differentiated phase and associated structures are the most prospective targets

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

the orbital tuned marine oxygen isotope record applied to the middle and late pleistocene pollen record of funza colombian andes abstract assuming that orbital variations are the main external cause of the succession of late pleistocene ice ages deep sea stratigraphers developed an orbital tuned chronology of the marine oxygen isotope record the pollen record of funza eastern cordillera colombia displays in great detail long range altitudinal shifts of the forest line being also an expression of long range fluctuating global temperatures both records of palaeotemperature were visually correlated 48 isotopic events are assumedly reflected in the pollen record this enables an orbital tuning of the initial time frame of the pollen record which was based on 14 dated volcanic ash horizons and provides a detailed record of changes in sediment accumulation in the sedimentary basin of bogota inferences for the time frame of the pollen record of paramo de agua blanca from the same area are discussed

pleistocene precipitation balance in the amazon basin recorded in deep sea sediments abstract terrigenous sediments from ceara rise in the western tropical atlantic ocean record pleistocene amazon basin climate variability iron oxides and oxyhydroxides in this region originate mainly from chemically leached amazon lowland soils concentrations of goethite and hematite in the terrigenous fraction consistently peak during transitions from glacial to interglacial periods suggesting an increased proportion of erosive products derived from the amazon lowlands compared to the physically weathered highlands lowland amazon basin precipitation changes monitored by the percentage of goethite relative to total iron oxides lead ice age extremes with maximum aridity during ice growth and maximum precipitation during ice melt rapid climate changes over the amazon basin may reflect shifts in the position of the intertropical convergence zone forced by northern hemisphere insolation at precessional 1 23 000 yr 1 and obliquity 1 41 000 yr 1 frequencies variance in the orbital eccentricity bands 1 100 000 and 1 413 000 yr 1 may be explained by nonlinear amplification of insolation forcing at precessional frequencies the early response of amazon precipitation to insolation ahead of high latitude ice volume 18o at all orbital frequencies suggests that tropical aridity is part of the chain of events leading to ice ages rather than a response to glacier oscillations

foraminiferal faunal estimates of paleotemperature circumventing the no analog problem yields cool ice age tropics the sensitivity of the tropics to climate change particularly the amplitude of glacial to interglacial changes in sea surface temperature sst is one of the great controversies in paleoclimatology here we reassess faunal estimates of ice age ssts focusing on the problem of no analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods a new calibration strategy developed here which uses past variability of species to define robust faunal assemblages solves the no analog problem and reveals ice age cooling of 5 o to 6oc in the equatorial current systems of the atlantic and eastern pacific oceans classical transfer functions underestimated temperature changes in some areas of the tropical oceans because core top assemblages misrepresented the ice age faunal assemblages our finding is consistent with some geochemical estimates and model predictions of greater ice age cooling in the tropics than was inferred by climate long range investigation mapping and prediction climap 1981 and thus may help to resolve a long standing controversy our new foraminiferal transfer function suggests that such cooling was limited to the equatorial current systems however and supports climap s inference of stability of the subtropical gyre centers

a high resolution late quaternary upwelling record from the anoxic cariaco basin venezuela results are presented of a high resolution study of the planktonic foraminiferal faunas from two piston cores recovered from the cariaco basin in the southern caribbean sea the cariaco basin is a small anoxic marine basin on the northern continental margin of venezuela in an area today characterized by both seasonal trade wind induced upwelling and pronounced dry and wet seasons our data indicate that large changes in the intensity of upwelling and hence trade wind strength occurred in this region during the last glacial interglacial transition and throughout the holocene during the last glacial lowstand of sea level the cariaco basin was effectively isolated from the open caribbean along its northern margin by the then largely emergent tortuga bank oxic conditions existed in the deep cariaco basin at this time and surface productivity was low about 12 600 years ago the abrupt initiation of strong upwelling over the basin and the onset of permanent anoxia in the deep waters are coincident with the rapid rise of sea level that accompanied the peak interval of meltwater discharge from the laurentide ice sheet into the gulf of mexico strong upwelling between 12 600 and about 10 000 years ago may be related to intensified trade winds resulting in part from cooler sea surface temperatures in the caribbean and gulf of mexico after about 10 000 years ago upwelling intensity was reduced though highly variable a preliminary frequency domain analysis of the holocene portion of the cariaco basin time series suggests that solar forcing may explain a significant component of the century scale variability observed in the record of upwelling and trade wind strength