tropical glaciers recorders and indicators of climate change are disappearing globally in this paper we review the interaction of el nino southern oscillation enso variability and warming trends recorded in ice core records from high altitude tropical glaciers discuss the implications of the warming trends for the glaciers and consider the societal implications of glacier retreat enso has strong impacts on meteorological phenomena that directly or indirectly affect most regions on the planet and their populations many tropical ice fields have provided continuous annually resolved proxy records of climatic and environmental variability preserved in measurable parameters especially oxygen and hydrogen isotopic ratios d 18 o dd and the net mass balance accumulation these records present an opportunity to examine the nature of tropical climate variability in greater detail and to extract new information on linkages between rising temperatures on tropical glaciers and equatorial pacific sea surface temperatures in critical enso indicator regions the long term climate records from a collection of high altitude tropical ice cores provide the longer term context essential for assessing the significance of the magnitude and rate of current climate changes that are in large measure driving glacier retreat the well documented ice loss on quelccaya in the peruvian andes naimona nyi in the himalaya kilimanjaro in eastern africa and the ice fields near puncak jaya in papua indonesia presents a grim future for low latitude glaciers the ongoing melting of these ice fields response is consistent with model predictions for a vertical amplification of temperature in the tropics driver and has serious implications for the people who live in these areas

palaeoreconstruction of the amazon river freshwater and sediment discharge using sediments recovered at site 942 on the amazon fan a continuous reconstruction of palaeoclimate has been generated for the last 12 000 c 14 yr bp from odp site 942 5 degrees 45 n 49 degrees 6 w at a water depth of 3346 m drilled to the west of the amazon fan records from the site suggest that during the younger dryas the amazon basin was extremely dry and amazon river discharge was low this increased aridity is hypothesised to be due predominantly to reduced precipitation in addition there is evidence for a discharge event at the end of the younger dryas coeval with termination 1b that produced an estimated amazon river outflow equivalent to present day values and an increase in sediments derived from the andes the timing of this event coincident with the warming of the andean ice sheet suggests that it was at least partly driven by meltwater produced by the retreat of andean glaciers but also required an increase in regional rainfall resulting from changes in climate site 942 also demonstrates that the sediment input to the western part of the amazon fan from the river ceased between 9900 and 9500 c 14 yr bp at a time when sea level was 40 50 m below the present level if this value is truly indicative of the sea levels at which the sediment supply to the fan switched off then it is far greater than the 30 m below current sea level suggested previously copyright c 2000 john wiley sons ltd

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

a major widespread climatic change around 5300 cal yr bp at the time of the alpine iceman palaeoenvironmental and archaeological data from arbon bleiche lake constance switzerland give evidence of a rapid rise in lake level dated by tree ring and radiocarbon to 5320 cal yr bp this rise event was the latest in a series of three successive episodes of higher lake level between 5550 and 5300 cal yr bp coinciding with glacier advance and tree limit decline in the alps this west central european climate change may have favoured the quick burial and the preservation of the alpine iceman recently found in the tyrolean alps it has possible equivalents in many records from various regions in both hemispheres dating to 5600 5000 cal yr bp and corresponds to global cooling and contrasting patterns of hydrological changes this major mid holocene climate event marks the hypsithermal neoglaciation transition possibly resulting from a combination of different factors including orbital forcing changes in ocean circulation and variations in solar activity copyright 2004 john wiley sons ltd

post glacial arid episodes in ethiopia have implications for climate prediction several lines of geomorphological and stratigraphical evidence suggest that the widespread early post glacial wet phase in tropical africa between 12 500 and 5 000 yr bp refs 1 2 was interrupted by severe dry episodes during the intervals 11 000 10 000 8 500 6 500 and 6 200 5 800 yr bp refs 3 9 the magnitude of the second event has recently been questioned10 we present new stratigraphical and dating evidence from the ziway shala lake basin ethiopia indicating the severity and timing of dry phases during the interval 12 000 5 000 yr bp our findings have important implications for predictions of the climatic impact of increasing atmospheric levels of co2

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

holocene environmental changes in bangong co basin western tibet part 4 discussion and conclusions abstract a 12 4 m core taken in lake bangong provides a continuous holocene climatic record we summarize information on changes in stable isotope and radiocarbon balances in the lake hydrobiology and vegetal cover in the catchment deduced from detailed analytical results given in the three preceding papers the bangong record is then compared with the environmental history of the neighbouring lake sumxi also constructed from multidisciplinary analyses the two records show a major environmental change at 10 9 5 ka b p attributed to a rapid strengthening of the summer monsoonal circulation which led to wet warm conditions this event was followed by a long term trend toward aridity which culminated around 4 3 ka b p in western tibet maximum monsoon rainfall seems to have occurred from 9 5 to 8 7 ka b p and from 7 2 to 6 3 ka b p as two wet pulses separated by a reversal event centered on 8 0 7 7 ka b p our results broadly agree with the records from lake seling in central tibet and lake qinghai at the plateau s northeastern margin and with palaeoclimatic studies in western china which document conditions wetter and warmer than those of today during the early middle holocene the environmental fluctuations recorded in western tibet appear in phase with climatic changes recognized in tropical north africa suggesting that the 8 0 7 7 ka b p and the 4 0 3 0 ka b p dry events were caused by abrupt disequilibrium in the climatic system

radiocarbon dating of glacial dust layers and soils at kilimanjaro s northern ice field as the african climate history recorded in kilimanjaro s northern ice field nif is rapidly lost the age of the glacier remains disputed current age estimates from ice core data and glacial dynamics modeling disagree by an order of magnitude 11 700 vs 1000 years old we present radiocarbon dates of glacial dust and proximal soil samples collected from in and around the edge of the nif that support the hypothesis that the peripheral portions of the nif glacier are younger and more dynamic than the center samples of a dust rich ice layer 1 5 m above the base at the edge of the 40 m high glacier ice cliff were found to be 1600 790 years old these dates agree with the prediction of significant growth and shrinkage in glacial coverage over the last millennium the variation in radiocarbon ages likely arises from heterogeneity in the summit volcanic soils the main source of the dust recovered from the glacier and cryoconite microbial activity sediment samples of a supraglacial pond had modern radiocarbon ages further demonstrating the impact of cryoconite microbial communities on radiocarbon measurements of glacial samples after accounting for the variability in the sample ages and the effects of microbial activity we contend that the lower i e younger limit of the radiocarbon age range is the most reliable assessment of the age of the ice in which it was trapped

late glacial holocene diatom record of water chemistry and lake level change from the tropical east african rift lake abiyata ethiopia abstract diatom study of a 12 6 m long sediment core ab95ii from lake abiyata ethiopian rift 8 n revealed large amplitude changes in the water level and chemistry over the past 13 4 cal kyr bp past water conductivity ph and water chemical facies reflected by ionic ratios are quantitatively reconstructed based on diatom transfer functions previously established conductivity has varied from 400 to 21 500 s cm 1 ph from 8 to 10 5 the anion hco 3 co 3 2 cl so 4 2 and cation na k ca 2 mg 2 ratios ranged between 0 9 4 and 0 5 275 respectively a high water salinity oscillation is recorded at the base of the sequence the extrapolated age of this interval 12 7 12 0 cal kyr bp corresponds to the younger dryas chronozone the early middle holocene registers a high stand freshwater lake between 12 and 5 4 cal kyr bp changes in diatom assemblages suggest minor changes in water depth lake mixing and or nutrient content during this interval post 5 4 cal kyr bp shallow saline conditions generally predominate short term regressive events are recorded at 5 6 and 3 0 cal kyr bp our results are roughly consistent with previous works in the region they refine the timing of the hydrochemical changes and quantify their amplitude thus providing inputs for modelling approaches

the oxygen isotopic composition of uranium minerals a review abstract uranium ore is an essential material in the preparation of nuclear fuel for civilian as well as military uses uranium is first extracted from uranium bearing minerals using a variety of reagents and is precipitated from solutions as yellow cake prior to isotope enrichment processes the disintegration of the former eastern bloc in the 1990s and frequent unrest in the middle east have underscored the need for better characterizing source uranium ores for forensic and attribution purposes the world s major deposits of u occur in several distinctly different geological environments fourteen principal types of u deposits and rocks with elevated uranium contents are recognized with more than 40 subtypes combining our own analysis and literature data we have amassed over 250 oxygen isotope data from 13 major u producing countries which vary widely from 32 to 11 however interpreting the oxygen isotopic composition of uraninite in terms of the composition of the fluid from which it precipitated or interacted with requires knowledge of the fractionation factor and temperature of interactions which are not always available since each deposit type occurs within a unique geologic setting and is generally formed from chemically distinct fluids the chemical compositions of the uranium ores are also distinct uranium deposits that form in igneous rocks have higher trace element compositions relative to sandstone hosted deposits our data shows that one of the most useful techniques for distinguishing between uranium ore is to use a combination of 18 o values and rare earth elements e g la yb ratios these methods may allow investigators to trace uranium ore back to the source

deglaciated areas of kilimanjaro as a source of volcanic trace elements deposited on the ice cap during the late holocene abstract ice fields on kilimanjaro 5895 m a s l tanzania are retreating and 85 of the ice cover has been lost since 1912 the degree to which this recession is exceptional during the holocene is uncertain as age control of the entire ice stratigraphy exists only for the very shallow and very bottom ice of the northern ice field this empirical evidence suggests that the kilimanjaro ice cover may be a persistent holocene feature while a model based on maximum possible extent and a constant shrinkage rate of the summit glaciers suggests a cyclic decay time on the order of one to two centuries today the mass balance of these ice fields is negative and no persistent ice accumulation zones are observed over multiannual scales the expanding deglaciated area within the kilimanjaro caldera should act as an increasingly larger and productive source of volcanic origin aeolian dust that is quickly deposited onto the surface of the adjacent ice fields particularly in the seasonal absence of caldera snow cover variations in the local dust influx may directly influence albedo and the energy balance of these ice fields investigating the characteristics of insoluble material entrapped in the ice remnants of kilimanjaro can thus provide insights into the extent of ice and or continuity of the summit snow cover through time here we report the trace element composition linked to the insoluble particles entrapped in holocene kilimanjaro ice in the context of the current understanding of the past ice accumulation processes including solid precipitations and ablation contributing to build the horizontal caldera ice fields for this purpose we analysed an ice core drilled to bedrock from the northern ice field thought to span the late holocene 2200 bc 1950 ad the ultra low trace element concentrations recorded in this kilimanjaro core are consistent with a generally low volcanic dust source availability i e limited exposure of the deglaciated area in the caldera and fairly continuous ice accumulation during the late holocene in contrast the maximum concentrations for most of the trace elements recorded in the surface ice section suggest that the current lack of ice accumulation on the kilimanjaro ice fields is unusual over the last 4 ka

sm nd direct dating of the collins bay hydrothermal uranium deposit saskatchewan primary pitchblende mineralization from the collins bay unconformity type uranium deposit in northern saskatchewan has been dated using the sm nd method the mineral isochron age of 1281 80 ma is in good agreement with other geologic and geochronological data and demonstrates the potential of the sm nd technique for the direct dating of hydrothermal mineral deposits 23 references 5 figures 7 tables

rare earth element distributions in uraninites implications for ore genesis abstract analysis of the rare earth element ree distributions in uraninites from a variety of hydrothermal mineral deposits indicates that wide variations are to be anticipated although crystal structure must exert a fundamental influence upon ree substitution in uraninite the present study suggests that other factors in particular hydrothermal fluid chemistry may be of equal importance total ree ree contents range from 15 000 ppm in uraninites from ultrametamorphic deposits to eu eu lree hree 0 08 1 10 they are interpreted to result from variations in the oxygen fugacity and the nature of the anionic complexes in the hydrothermal fluids responsible for ore transport additionally in uraniferous quartz pebble conglomerates the ree patterns of the detrital uraninites provide direct evidence regarding the provenance of these sedimentary u ores

comment on recent glacial recession in the rwenzori mountains of east africa due to rising air temperature by richard g taylor lucinda mileham callist tindimugaya abushen majugu andrew muwanga and bob nakileza

the history of south american tropical precipitation for the past 25 000 years long sediment cores recovered from the deep portions of lake titicaca are used to reconstruct the precipitation history of tropical south america for the past 25 000 years lake titicaca was a deep fresh and continuously overflowing lake during the last glacial stage from before 25 000 to 15 000 calibrated years before the present cal yr b p signifying that during the last glacial maximum lgm the altiplano of bolivia and peru and much of the amazon basin were wetter than today the lgm in this part of the andes is dated at 21 000 cal yr b p approximately coincident with the global lgm maximum aridity and lowest lake level occurred in the early and middle holocene 8000 to 5500 cal yr b p during a time of low summer insolation today rising levels of lake titicaca and wet conditions in amazonia are correlated with anomalously cold sea surface temperatures in the northern equatorial atlantic likewise during the deglacial and holocene periods there were several millennial scale wet phases on the altiplano and in amazonia that coincided with anomalously cold periods in the equatorial and high latitude north atlantic such as the younger dryas

tropical climate instability the last glacial cycle from a qinghai tibetan ice core an ice core record from the guliya ice cap on the qinghai tibetan plateau provides evidence of regional climatic conditions over the last glacial cycle 36 cl data suggest that the deepest 20 meters of the core may be more than 500 000 years old the 18 o change across termination i is 5 4 per mil similar to that in the huascaran peru and polar ice cores three guliya interstadials stages 3 5a and 5c are marked by increases in 18 o values similar to that of the holocene and eemian 124 000 years ago the similarity of this pattern to that of ch 4 records from polar ice cores indicates that global ch 4 levels and the tropical hydrological cycle are linked the late glacial stage record contains numerous 200 year oscillations in 18 o values and in dust nh 4 and no 3 levels

tropical ice core records evidence for asynchronous glaciation on milankovitch timescales over the last 28 years ice core records have been systematically recovered from ten high elevation ice fields nine of which are located in the low latitudes each core has provided new information about the regional climate and environmental change and together their records challenge existing paradigms about the earth s climate system when viewed collectively these ice core histories provide compelling evidence that the growth glaciation and decay deglaciation of large ice fields in the lower latitudes are often asynchronous both between the hemispheres and with high latitude glaciation that occurs on milankovitch timescales although stable isotopic records suggest that global scale cooling occurred during the last glacial stage lgs we contend that precipitation is the primary driver of glaciation in the low latitudes this is consistent with the time transgressive nature of precession driven changes in insolation and hence precipitation such that glaciers advance retreat in the tropics north of the equator while glaciers retreat advance in the tropics south of the equator thus the coeval inter hemispheric retreat of glaciers in the 20th century and the beginning of the 21st century is atypical copyright 2005 john wiley sons ltd

a 25 000 year tropical climate history from bolivian ice cores ice cores that were recovered from the summit of sajama mountain in bolivia provide carbon 14 dated tropical records and extend to the late glacial stage lgs oxygen isotopic ratios of the ice decreased 5 4 per mil between the early holocene and the last glacial maximum which is consistent with values from other ice cores the abrupt onset and termination of a younger dryas type event suggest atmospheric processes as the probable drivers regional accumulation increased during the lgs during deglaciation and over the past 3000 years which is concurrent with higher water levels in regional paleolakes unlike polar cores sajama glacial ice contains eight times less dust than the holocene ice which reflects wetter conditions and extensive snow cover

recent glacial recession in the rwenzori mountains of east africa due to rising air temperature based on field surveys and analyses of optical spaceborne images landsat5 landsat7 we report recent decline in the areal extent of glaciers in the rwenzori mountains of east africa from 2 01 0 56 km 2 in 1987 to 0 96 0 34 km 2 in 2003 the spatially uniform loss of glacial cover at lower elevations together with meteorological trends derived from both station and reanalysis data indicate that increased air temperature is the main driver clear trends toward increased air temperatures over the last four decades of similar to 0 5 degrees c per decade exist without significant changes in annual precipitation extrapolation of trends in glacial recession since 1906 suggests that glaciers in the rwenzori mountains will disappear within the next two decades

east african soil erosion recorded in a 300 year old coral colony from kenya 1 soil erosion is a key socio economic and environmental problem in kenya which has been poorly documented due to the lack of long continuous records here we present ba ca records from porites corals from the malindi coral reef documenting the flux of suspended sediment from the sabaki river with a sub weekly resolution for the last 300 years while sediment flux from the sabaki river is almost constant between 1700 and 1900 a continuous rise in sediment flux is observed since 1900 first due to british settlements and afterwards due to steadily increasing demographic pressure on land use the peak in suspended sediment load and hence soil erosion occurred between 1974 and 1980 when there is a five to tenfold increase relative to natural levels this is attributed to the combined effects of dramatically increasing population unregulated land use deforestation and severe droughts in the early 1970 s we conclude that despite laudable attempts to instigate soil conservation measures it is unlikely that there will be a sustainable reduction in soil erosion without a significant improvement in socio economic conditions

climate change and the collapse of the akkadian empire evidence from the deep sea the akkadian empire ruled mesopotamia from the headwaters of the tigris euphrates rivers to the persian gulf during the late third millennium b c archeological evidence has shown that this highly developed civilization collapsed abruptly near 4170 150 calendar yr b p perhaps related to a shift to more arid conditions detailed paleoclimate records to test this assertion from mesopotamia are rare but changes in regional aridity are preserved in adjacent ocean basins we document holocene changes in regional aridity using mineralogic and geochemical analyses of a marine sediment core from the gulf of oman which is directly downwind of mesopotamian dust source areas and archeological sites our results document a very abrupt increase in eolian dust and mesopotamian aridity accelerator mass spectrometer radiocarbon dated to 4025 125 calendar yr b p which persisted for 300 yr radiogenic nd and sr isotope analyses confirm that the observed increase in mineral dust was derived from mesopotamian source areas geochemical correlation of volcanic ash shards between the archeological site and marine sediment record establishes a direct temporal link between mesopotamian aridification and social collapse implicating a sudden shift to more arid conditions as a key factor contributing to the collapse of the akkadian empire

source of the detrital components of uraniferous conglomerates quirke ore zone elliot lake ontario canada large volumes of pyritic quartz pebble conglomerate in the elliot lake district of ontario contain at least 300 000 tonnes u3o8 recoverable at a grade of 0 1 ref 1 with much greater tonnages available at lower recovery grades the quirke zone alone contains in excess of 224 000 tonnes u3o8 at 0 1 refs 2 4 and is accordingly one of the world s largest known uranium deposits situated 40 km north of the north channel of lake huron 400 km north west of toronto ore conglomerates occur in the matinenda formation locally the basal unit of the huronian supergroup and although their age is not well constrained they are probably close to 2 350 myr old 5 uraninite the most important primary ore mineral occurs as poorly rounded to euhedral grains 0 05 0 2 mm across within the matrix between quartz pebbles while its chemical and morphological characteristics have led most workers to consider that the uraninite is detrital5 7 there has hitherto been no attempt to characterize its source lithology a matter of considerable significance as regards mineral exploration this was the aim of the present study we have examined the mineral and fluid inclusions observed in the quartz pebbles in the conglomerate and conclude that they were derived from a pegmatitic potassic alaskitic granite we have also demonstrated that in this source lithology pebble sized quartz was spatially associated with radioactive minerals by inference uraninite the postulated characteristics of such a source are remarkably similar in several respects to the uraniferous alaskites of the rossing deposit in namibia

an andean ice core record of a middle holocene mega drought in north africa and asia an ice core from the nevado huascaran col in the cordillera blanca of northern peru contains high resolution time series of dust concentrations and size distributions since the end of the last glacial stage a large dust peak dated 4500 years ago is contemporaneous with a widespread and prolonged drought that apparently extended from north africa to eastern china evidence of which occurs in historical archeological and paleoclimatic records this event may have been associated with several centuries of weak asian indian african monsoons possibly linked with a protracted cooling in the north atlantic during the second half of the 20th century high austral summer dust concentrations in the huascaran record are significantly correlated with atmospheric conditions such as sea level pressure and zonal wind velocities that are consistent with el nino southern oscillation enso and positive north atlantic oscillation nao indices and with aridity in north africa southwest asia and the middle east therefore the dominant submicron fraction of the dust may have been transported by more intense northeasterly trade winds from the african dry regions across the tropical atlantic during a period of frequent and or intense enso activity the proposed enso conditions that may have been linked with drought in the monsoon region may also have contributed to aridity in tropical south america including the cordillera blanca

groundwater residence time and paleorecharge conditions in the deep confined aquifers of the coastal watershed south east tanzania summary analysis of radiocarbon and stable isotopes of c h and o in groundwater samples from the coastal watershed of southeastern tanzania is used to decipher the age of groundwater and the climatic conditions at the time of recharge radiocarbon dating was corrected on the basis of stable carbon isotope ratios and hydrochemical data two main recharge periods are recognised 1 a recent recharge period with residence times dated to younger than 1 3 ka bp for the shallow aquifer and some deep groundwater aquifers and 2 a paleorecharge occurring during the late pleistocene to holocene transition between 6 and 13 ka bp for the lower confined aquifer the climatic excursions arid and humid phases identified in this study match well with those identified from studies of paleo climatic records in tanzania and east africa the oxygen 18 and radiocarbon results show that there is a potential mixing of groundwater of varying ages along flow paths in the coastal aquifer system this has also been shown by redox parameters in some of the deeper aquifer samples the data also revealed that there is relatively simple pattern of lateral groundwater flow in the deeper confined aquifer isotopic evidence from this study and related studies in paleolimnology improves our knowledge of the past climates the data suggests that the paleorecharge to the confined aquifer was from inland under wetter climatic conditions than present therefore paleorecharge from the adjacent mountain regions to coastal area like ifakara morogoro and udzungwa mountains could be important parts of recharge area of the kimbiji aquifer however the hinterland mountains of dar es salaam mainly pugu mkuranga ruvu and kisarawe could also play an important role in replenishing the kimbiji coastal aquifers in contrast recharge in the shallow unconfined aquifer is characterized by local rainfall and river water infiltration this study is the first of its kind assessing fingerprinting of paleoclimates in southeastern coastal tanzania using the isotopic composition of deep groundwater aquifers the freshwater resources in the neogene aquifer contain paleo groundwater aquifers that have been mixed with recently recharged flow systems hence the resources may be sustainable this study also provides information that may be useful for designing optimum strategies for a sustainable management of groundwater resources in the coastal aquifer and it testifies to the importance of groundwater as a paleoclimatic archive such information is also essential for consideration by modellers in their attempts to simulate the hydrogeological processes in confined aquifers over very long time spans

a late quaternary diatom record of tropical climatic history from lake titicaca peru and bolivia abstract a composite high resolution diatom stratigraphy from three piston cores and one box core in the deep sub basin of lake titicaca reveals large moisture variations during the past 30 kyr in the altiplano region diatom sequences indicate orbital and millennial scale variability in water level and salinity the pelagic freshwater diatom species cyclotella andina and cyclotella stelligera dominate glacial age sediments suggesting that the lake was above its present outlet generally wet conditions continued until 11 000 cal yr bp as indicated by high percentages of freshwater planktonic diatoms large pulses of benthic diatom species between about 11 000 and 10 000 cal yr bp suggest brief intervals of large amplitude declines in lake level during the early holocene 10 000 8500 cal yr bp a freshwater diatom assemblage suggests overflowing conditions pelagic freshwater diatoms are replaced ca 8500 cal yr bp by the salinity indifferent species cyclotella meneghiniana and by benthic taxa indicating the beginning of lake regression during the mid holocene 6000 3500 cal yr bp the abundance of the saline taxon chaetoceros muelleri coupled with high abundances of epiphytic and epipelic diatoms indicates maximum salinity and lowest lake levels in the entire 30 000 year record lake transgression began ca 4000 cal yr bp and the lake achieved modern levels by about 1500 cal yr bp these water level changes imply changes in effective moisture most likely resulting from large precipitation changes precipitation was high throughout the last glacial maximum 21 000 18 000 cal yr bp likely due to an enhanced south american summer monsoon during peak summer insolation in the southern hemisphere in contrast the mid holocene transition was dryer than today in association with an austral summer insolation minimum and the subsequent weakening of the summer monsoon

late twentieth century warming in lake tanganyika unprecedented since ad 500 lake tanganyika has become warmer increasingly stratified and less productive over the past 90 years analyses of lake sediments show that this recent warming is unprecedented within the past 1 500 years

isotopic evidence for late quaternary climatic change in tropical south america the tropical hydrologic cycle affects atmospheric trace gases and global climate change and thus records of hydrologic change encompassing a variety of time scales from the low latitudes are important in paleoclimatology isotopic analysis of calcite from lake junin peru provides a record of hydrologic variability that spans the last glacial interglacial transition in the southern tropics the record reveals a 6 enrichment in 18 o calcite during the late glacial followed by a gradual depletion during the holocene which can be interpreted as a decrease followed by a long term increase in effective moisture close agreement between 18 o calcite and rainy season insolation indicates that long term changes in tropical hydrology were linked to orbital variations furthermore hydrologic change was out of phase in the northern and southern tropics over this time period

climate change at the 4 2 ka bp termination of the indus valley civilization and holocene south asian monsoon variability 1 planktonic oxygen isotope ratios off the indus delta reveal climate changes with a multi centennial pacing during the last 6 ka with the most prominent change recorded at 4 2 ka bp opposing isotopic trends across the northern arabian sea surface at that time indicate a reduction in indus river discharge and suggest that later cycles also reflect variations in total annual rainfall over south asia the 4 2 ka event is coherent with the termination of urban harappan civilization in the indus valley thus drought may have initiated southeastward habitat tracking within the harappan cultural domain the late holocene drought cycles following the 4 2 ka bp event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14c production rates this suggests that solar variability is one fundamental cause behind holocene rainfall changes over south asia

the eastern mediterranean paleoclimate as a reflection of regional events soreq cave israel the climate of the eastern mediterranean region of the last 60 ky was determined by a high resolution study of the oxygen and carbon isotopic composition 1500 measurement pairs of speleothems from the soreq cave israel with chronology provided by 53 precise 230 th 234 u tims ages the high precision of the speleothem tims ages permits us to determine the timing of regional climatic events in the eastern mediterranean region and to see if they correlate with global events during the period from 60 to 17 ky the 18 o and 13 c values were generally 2 2 5 higher than during the period from 17 ky to present this is consistent with the climatic transition from glacial to interglacial within the 60 to 17 ky period the soreq cave stable isotope profile includes four cold peaks at 46 35 25 and 19 ky and 2 warm peaks at 54 and 36 ky in addition the period 17 ky has two more cold peaks at 16 5 and from 13 2 to 11 4 ky the ages of four of the six cold peaks correlate well with the ages of three heinrich events h1 h2 h5 and with the age of the younger dryas however the other two heinrich events are not reflected in the soreq cave record several other isotope peaks which appear during the last 7 ky are contemporaneous with regional climatic events in the middle east and north africa in addition to the drop in 18 o and 13 c observed between the last glacial and the holocene sharp simultaneous drops in 234 u 238 u 0 ratios sr concentrations and in 87 sr 86 sr are also observed suggesting that the latter are climate related these variations are interpreted in terms of major changes in the temperature the mean annual rainfall and its isotopic composition the isotopic composition of the mediterranean vapor source the soil moisture conditions and in the mixing proportions of sources with different 87 sr 86 sr ratios sea spray dust particles and dolomitic host rock

a paleoclimatic perspective on the 21st century glacier loss on kilimanjaro tanzania assessing the significance of current glacier loss on kilimanjaro tanzania demands a well constrained temporal perspective that context is provided by direct measurements ancillary observations of the ice fields and the analyses of the ice cores collected from them ice retreat mechanisms observed there today are consistent with the preservation of the oldest ice 11 7 ka in the central deepest part of the northern ice field nif this ice core derived paleoclimate history published by thompson and others 2002 is further confirmed by more recent paleoclimate records from tropical east africa mounting evidence suggests that the anticipated loss of the entire nif will be unprecedented within the past 10 000 years new evidence bears directly on the mechanisms driving the current ice loss measurements made in 2000 on the nif document that air temperature at 0 5 and 1 5 m above the surface remained below 58c while a surface temperature of 0 08c was sustained for up to 8 hours d 1 under clear conditions consistent with observations of melting on all kilimanjaro summit ice fields the linear relationship between oxygen and hydrogen isotopic ratios for all six ice cores drilled in 2000 lies very close to the global meteoric waterline and does not support sublimation evaporation as a major driver of ice loss today or in the past on kilimanjaro