quaternary glaciation of the bale mountains ethiopia central ethiopia comprises a high plateau at 2000 3000 m formed from tertiary lava flows and bisected by the eastern african rift ten volcanic mountains rise to altitudes of just over 4000 m but on only three has quaternary glaciation been substantiated by published field observations on the bale mountains 4400 m a previous report based on limited evidence proposed an ice cap extending to 600 km2 based on aerial photographs and ground surveys this paper reports evidence of a more complex situation a wide spread of large erratic boulders on the plateau records a central ice cap of 30 km2 though ice probably extended for a further 40 km2 further north two groups of deeply incised and clearly glaciated valleys contain moraines and roches moutonnees 60 km2 on interfluves between them and on the open north slopes are moraines from an earlier stage of the same glaciation or from a distinct older event altogether about 180 km2 may have been glaciated cores dated by 14c from inside and outside the glaciated area suggest that at least the northern valley glaciers may date from the last glacial maximum estimated equilibrium line altitudes for these glaciers and the ice cap are 3750 4230 m

on the interpretation of caribbean paleo temperature reconstructions during the younger dryas 1 a conundrum exists regarding whether the sea surface temperatures decreased or increased over the southern caribbean and the western tropical atlantic region during the younger dryas when the north atlantic cooled substantially and the atlantic thermohaline circulation was weakened significantly despite the proximity of core locations some proxy reconstructions record a surface cooling while others indicate a warming we suggest that this seemingly paradoxical finding may at least partially be attributed to the competing physical processes that result in opposing signs of temperature change in the region in response to weakened north atlantic meridional overturning circulation our coupled ocean atmosphere model experiments indicate that the temperature response over the southern caribbean and western tropical atlantic regions is complex and can vary considerably in small spatial scales depending on the nature of physical processes that dominate

quaternary glaciers and climate on cerro chirripo costa rica abstract glacial lake sediments and glacial geomorphology in valle de las morrenas a glacial trough on the north face of cerro chirripo costa rica provide evidence on high altitude pleistocene conditions in central america the most recent glacier in the valley chirripo stage i receded very rapidly near the end of the younger dryas chronozone radiocarbon dates on basal organic sediments from lakes beneath upper middle and lower limits of that glacier fall close together and two sigma calibrated ages overlap for the period 9700 9600 cal yr b p earliest datable transition sediments from the central lake date to 12 360 11 230 cal yr b p larger older moraines and associated trimlines allowed reconstruction of three paleoglaciers chirripo stages ii iii and iv computer analysis of hypsometry using published tropical glacier vertical mass balance profiles yields elas of 3506 3523 3515 3537 and 3418 3509 m respectively chirripo ii ela estimate positions applied to chirripo i yield an ela of 3538 3546 m we infer minimal temperature depressions of 7 4 8 0 c for the chirripo i iv stages modeling the behavior of modern tropical glaciers yields basinwide net accumulation estimates of 440 620 550 830 and 960 1760 mm yr 1 for the chirripo ii iii and iv stages

was the younger dryas triggered by a flood draining of a huge lake into the northern atlantic may have triggered a cold period 12 900 years ago the route taken by the flood waters remains unknown

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

evidence for a younger dryas glacial advance in the andes of northwestern venezuela abstract deposits of push moraine outwash and glaciolacustrine sediments recovered from two areas in the northwestern venezuelan andes document the latest pleistocene advance of merida ice underlying peats provide maximum ages on till and outwash evidently emplaced during the younger dryas yd climatic event one example recovered from the humboldt massif where the farthest extent of yd ice buried peat in the surface of late glacial till provides a within glacier advance age of 12 4 ka cal bp the peat lies on moraine deposited during a stillstand event when the humboldt glacier retreated to the area of lago verde at 4000 m a s l approximately 0 5 km upvalley toward lago suero yd till buries peat deposited in glaciolacustrine sediments of presumed late glacial age farther north in the mucunuque mucubaji catchment of the eastern cordillera a push moraine of possible yd age buries older till of late glacial age 0 2 km upvalley outwash of yd age buries glaciolacustrine peat and organic rich alluvial sediment dated to 13 7 and 13 3 ka cal bp the latest merida advance documented here is approximately synchronous with the yd cold event of europe and the north atlantic region ca 11 6 12 7 ka cal bp the yd event in both areas of the northwestern venezuelan andes nearly reestablished earlier late glacial ice positions and termination appears to have been abrupt the valleys in both areas were evacuated of yd ice without emplacement of recessional moraines as during the main deglaciation at the humboldt site equilibrium line altitudes ela s for the late glacial were about 50 m lower than during the inferred yd in the mucunuque mucubaji catchment ela s for the late glacial 3900 m a s l are difficult to establish given the absence of lateral moraines

deglacial changes in ocean circulation from an extended radiocarbon calibration temporal variations in the atmospheric concentration of radiocarbon sometimes result in radiocarbon based age estimates of biogenic material that do not agree with true calendar age this problem is particularly severe beyond the limit of the high resolution radiocarbon calibration based on tree ring data which stretches back only to1 2 about 11 8 kyr before present bp near the termination of the younger dryas cold period if a wide range of palaeoclimate records are to be exploited for better understanding the rates and patterns of environmental change during the last deglaciation extending the well calibrated radiocarbon timescale back further in time is crucial several studies attempting such an extension using uranium thorium dated corals3 4 5 and laminae counts in varved sediments6 7 8 9 show conflicting results here we use radiocarbon data from varved sediments in the cariaco basin in the southern caribbean sea to construct an accurate and continuous radiocarbon calibration for the period 9 to 14 5 kyr bp nearly 3 000 years beyond the tree ring based calibration a simple model compared to the calculated atmospheric radiocarbon concentration and palaeoclimate data from the same sediment core suggests that north atlantic deep water formation shut down during the younger dryas period but was gradually replaced by an alternative mode of convection possibly via the formation of north atlantic intermediate water

rapid oceanic and atmospheric changes during the younger dryas cold period the younger dryas event which began approximately 12 900 years ago was a period of rapid cooling in the northern hemisphere driven by large scale reorganizations of patterns of atmospheric and oceanic circulation 1 3 environmental changes during this period have been documented by both proxy based reconstructions 3 and model simulations 4 but there is currently no consensus on the exact mechanisms of onset stabilization or termination of the younger dryas 5 8 here we present high resolution records from two sediment cores obtained from lake krakenes in western norway and the nordic seas multiple proxies from lake krakenes are indicative of rapid alternations between glacial growth and melting during the later younger dryas meanwhile reconstructed sea surface temperature and salinity from the nordic seas show an alternation between sea ice cover and the influx of warm salty north atlantic waters we suggest that the influx of warm water enabled the westerly wind systems to drift northward closer to their present day positions the winds thus brought relatively warm maritime air to northern europe resulting in rising temperatures and the melting of glaciers subsequent input of this fresh meltwater into the ocean spurred the formation of sea ice which forced the westerly winds back to the south cooling northern europe we conclude that rapid alternations between these two states immediately preceded the termination of the younger dryas and the permanent transition to an interglacial state the impact of freshwater pulses released from northern hemisphere ice sheets on the north atlantic meridional overturning circulation has been suggested as a likely mechanism for the younger dryas cooling 7 11 in addition a responsive sea ice cover has been proposed as a mechanism that could rapidly alter the heat exchange between the ocean and atmosphere during the last glacial period 12 13 the roles of the ocean and the atmosphere in triggering the climate shifts around the younger dryas are much discussed 9 these hypotheses are difficult to resolve partly because the temporal resolution of most palaeoclimate archives is too coarse to enable the anatomy of the younger dryas stadial to be adequately described 14 to address these questions we here present a lake sediment record at sub annual resolution together with new data on the sea surface conditions of the norwegian atlantic current nwac throughouttheyoungerdryasstadial fig 1

glacier climate interaction at low latitudes in the low latitudes there is an absence of major thermal seasonality yet there are three different climate regimes related to global circulation patterns and their seasonal oscillation the humid inner tropics the dry subtropics and intermediate between these two the outer tropics for the respective glacier regimes the vertical profiles of specific mass balance vbps are modeled considering vertical gradients of accumulation air temperature and albedo the duration of the ablation period and a factor for the ratio between melting and sublimation the model is first calibrated with data from hintereisferner austrian alps and is then applied to tropical conditions the simulated vbp matches well the measured profiles from irian jaya and mount kenya due to lack of field evidence the subtropical vbp cannot be verified directly however application of the respective model versions separately to the humid and dry seasons of the outer tropical glaciar uruashraju cordillera blanca peru provides reasonable results glaciers in the humid inner tropics are considered to be most sensitive to variations in air temperature while dry subtropical glaciers are most sensitive to changes in air humidity the two seasons of the outer tropics have to be viewed from these different perspectives

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

phasing of deglacial warming and laurentide ice sheet meltwater in the gulf of mexico evidence is emerging that the tropical climate system played a major role in global climate change during the last deglaciation however existing studies show that deglacial warming was asyn chronous across the tropical band complicating the identification of causal mechanisms the orca basin in the northern gulf of mexico is ideally located to record subtropical atlantic sea surface temperature sst warming in relation to meltwater input from the laurentide ice sheet paired d 18 o and mg ca data on the planktonic foraminifer globigerinoides ruber from core en32 pc6 are used to separate deglacial changes in sst and d 18 o of sea water sst as calculated from mg ca data increased by 3 8c from ca 17 2 to 15 5 ka in association with heinrich event 1 and was not in phase with greenland air temperature subtracting tem perature effects from d 18 o values in g ruber reveals two excur sions representing laurentide meltwater input to the gulf of mex ico one of 1 5 from ca 16 1 to 15 6 ka and a second major spike of 2 5 from ca 15 2 to 13 0 ka that encompassed melt water pulse 1a and peaked ca 13 8 ka during the bolling allerod conversion to salinity through the use of a laurentide meltwater end member of 225 indicates that near surface salinity de creased by 2 4 during these spikes these results suggest that gulf of mexico sst warming preceded peak laurentide ice sheet decay and the bolling allerod interval by 2 k y and that heat was retained in the subtropical atlantic during heinrich event 1 consistent with modulation of deglacial climate by thermohaline circulation

sensitivity of the atlantic intertropical convergence zone to last glacial maximum boundary conditions 1 recent paleoproxy records suggest that the mean latitude of the atlantic intertropical convergence zone itcz varied synchronously with north atlantic climate over a range of timescales throughout the holocene and last glacial maximum we show that the present day meridional mode of atmosphere ocean variability in the tropical atlantic is a potentially useful model for understanding these paleoclimate changes the tropical atlantic in a coupled atmospheric general circulation and slab ocean model responds to last glacial maximum conditions with a southward displacement of the itcz this response arises primarily through the land ice sheet that forces increased north atlantic trades analogous to the forcing on the present day meridional mode changes to sea ice coverage and to ocean heat transport associated with a weakened atlantic thermohaline circulation also cause a meridional mode response though through different mechanisms our results highlight the potential for tropical atlantic paleoclimate to be driven from the high latitude influences in particular land ice on glacial interglacial timescales

metal copper segregation in magmas before precipitating to form porphyry type deposits metals are transported and concentrated into magmas ultimately they can enter crystalline phases or segregate into the volatile phase in both cases partition coefficients determine the partitioning according to the ambient physico chemical conditions metal partitioning between the melt and the magmatic volatile phase mvp is driven by their solubility in this study cu has been selected as a test for metal segregation we evaluate qualitatively the metal s behavior with respect to the melt or to the mvp by comparing the difference in chemical potential and polarizability between the fluid phase and dissolved copper compound maps of polarizability are drawn after computing the chemical reactivity parameters electrophilicity hardness and polarizability for various silicate melts a synthetic fluid phase with water co2 s18 compounds and halogens and cu compounds as a test metal cu compounds show a better affinity with the fluid phase enhanced by the presence of s in its reduced form it explains how cu could segregate into the fluid phase at the magmatic stage before being enriched by diffusion or melt vapor partitioning leading to late hydrothermal precipitation the method should therefore be considered as a model for understanding the behavior of other metals and their segregation during the magmatic stage

a high mountain pollen altitude calibration set for palaeoclimatic use in the tropical andes the numerical relationship between modem pollen assemblages and altitude in high mountain environments from the northern andes is analysed in order to found inference models that allow estimating palaeoaltitudes and palaeotemperatures from past pollen records the calibration set dm consists of a 50 sample altitudinal transect between 2300 and 4600 m altitude the overall and individual pollen responses to altitude were tested by correspondence analysis ca generalized linear regression hof and weighted averaging wa transfer functions were derived by weighted averaging partial least squares wa pls regression overall altitude is the main controlling factor for the composition of pollen assemblages as shown by the high correlation between altitude and the first ca component r 0 88 individually around 35 of the 82 pollen taxa show a significant response to altitude through monotonic or unimodal functions the best transfer function obtained has a good statistical performance as shown b

radiocarbon geochemistry of modern and ancient arctic lake systems baffin island canada the accuracy of arctic lake chronologies has been assessed by measuring the14c activities of modern carbon sources and applying these isotopic mass balances to dating fossil lake materials small 1 km2 shallow 25 m arctic lakes with watersheds 12 km2have soil and peat stratigraphic sections with14c activities ranging from 98 to 51 modern the14c activity of particulate organic carbon dissolved organic carbon and dissolved inorganic carbon from lake and stream waters ranges from 121 to 95 modern the sediment water interface of the studied lakes shows consistent14c ages of 100014c yr although the14c activity of living aquatic vegetation is 115 modern radiocarbon measurements of components of the lacustrine carbon pool imply that the 100014c yr age of the sediment water interface results from deposition of14c depleted organic matter derived from the watershed

abrupt younger dryas cooling in the northern tropics recorded in lake sediments from the venezuelan andes a radiocarbon dated sediment record from laguna de los anteojos a cirque lake in the merida andes of venezuela indicates that warmer and wetter atmospheric conditions occurred in the northern tropics at the onset of the bolling 14 600 cal yr bp and abruptly colder and drier conditions around the time of the younger dryas yd geochemical and clastic sediment analyses from los anteojos show that glaciers advanced at 12 850 cal yr bp reached their yd maximum extent at 12 650 cal yr bp and then retreated until complete deglaciation of the watershed at 11 750 cal yr bp the onset of warmer conditions that ended the coldest phase of the yd occurred several hundred years earlier at los anteojos than in the high latitudes of the northern hemisphere during the peak yd glacial advance glacier equilibrium line altitudes in the region were 360 to 480 m lower and temperature was 2 2 to 2 9 c colder than modern independent palynological evidence from the los anteojos sediment core indicates that the northern andes were more arid and at least 2 3 c colder during the yd the direction and timing of glacial fluctuations in venezuela are consistent with observations of marine sediment records from the cariaco basin that suggest abrupt cooling occurred at 12 850 cal yr bp followed by a shift to higher temperature after 12 300 cal yr bp the timing and pattern of climatic changes in northern south america are also consistent with paleoclimate records from the southern tropical andes that suggest a southward shift in the position of the intertropical convergence zone occurred at the start of the cooling event followed by a return to wetter conditions in northern south america during the late stages of the yd the early warming of the tropical atmosphere and invigoration of the hydrologic cycle likely contributed to the shift to increased temperature in the higher latitudes of the northern hemisphere at the end of the late glacial stage

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

synchronous radiocarbon and climate shifts during the last deglaciation radiocarbon data from the cariaco basin provide calibration of the carbon 14 time scale across the period of deglaciation 15 000 to 10 000 years ago with resolution available previously only from holocene tree rings reconstructed changes in atmospheric carbon 14 are larger than previously thought with the largest change occurring simultaneously with the sudden climatic cooling of the younger dryas event carbon 14 and published beryllium 10 data together suggest that concurrent climate and carbon 14 changes were predominantly the result of abrupt shifts in deep ocean ventilation

geochemical composition and origin of tertiary oils in the yinggehai and qiongdongnan basins offshore south china sea abstract this study comprehensively characterizes the geochemical compositions of tertiary crude oils in the yinggehai and qiongdongnan basins offshore south china sea and differentiates their source properties using chemical and isotopic data the oils in the two basins have distinct source characteristics the majority of the oils from the yacheng yc field in the qiongdongnan basin are commonly marked by high pr ph ratios mostly from 4 5 to 7 0 unusually abundant angiosperm derived compounds and a domination of c29 in diasteranes suggesting a predominantly terrigenous organic source in contrast the oils from the dongfang df and ledong ld fields in the yinggehai basin have relatively lower pr ph values 2 5 5 5 and a low amount of bicadinanes moreover some oils in this basin contain abundant 4 methylsteranes and detectable c30 desmethyl steranes the difference in the molecular composition is also apparent with regard to the aromatic hydrocarbons the former oils contain more abundant biphenyls fluorenes and 2 phenylnaphthalene than the latter ones the oils from the qiongdongnan basin are relatively depleted in 13c and have 13c values of the whole oil in the range of 24 9 to 26 9 consistent with the great terrigenous input in contrast the yinggehai oils are isotopically heavier with 13c values from 21 6 to 23 6 typical of a marine isotope signature correspondingly their n alkane isotopes have different 13c ranges and exhibit distinct distribution profiles based on the oil source rock correlation the oils in the yc field were generated from the coastal plain swamp and shallow marine strata of the oligocene in the qiongdongnan basin while the yinggehai oils were sourced from the miocene shallow marine mudstones in the basin

synchroneity of tropical and high latitude atlantic temperatures over the last glacial termination a high resolution western tropical atlantic sea surface temperature sst record from the cariaco basin on the northern venezuelan shelf based on mg ca values in surface dwelling planktonic foraminifera reveals that changes in sst over the last glacial termination are synchronous within 30 to 90 years with the greenland ice sheet project 2 air temperature proxy record and atmospheric methane record the most prominent deglacial event in the cariaco record occurred during the younger dryas time interval when ssts dropped by 3 to 4 c a rapid southward shift in the atmospheric intertropical convergence zone could account for the synchroneity of tropical temperature atmospheric methane and high latitude changes during the younger dryas