intensification of northern hemisphere glaciations in the circum atlantic region 3 5 2 4 ma ice rafted detritus evidence abstract records of ice rafted detritus ird from ocean drilling program sites 644 and 907 in the nordic seas and deep sea drilling program sites 610 and 607 in the north atlantic ocean are used to determine the growth and history of northern hemisphere glaciations spanning the interval from 3 6 to 2 4 ma the records document that the initiation of large scale glaciation in the circum atlantic region occurred stepwise between 3 5 and 2 4 ma with greenland leading the other areas the first major pulse of ird occurs at 3 3 ma suggesting a distinct expansion of the greenland ice sheet progressive increases in ird occur from 3 0 ma with a synchronous ice sheet development between the greenland scandinavian and north american regions starting around 2 72 2 75 ma the regional records of ird correspond to major trends in the oxygen isotope record suggesting a tight connection between the record of global ice volume and evidence for expanding glaciers in the northern hemisphere it appears as if widespread ird distribution occurs when the global ice volume surpasses certain thresholds similar to the late quaternary situation

geochemistry geochronology and tectonic setting of early cretaceous volcanic rocks in the northern segment of the tan lu fault region northeast china abstract we present new geochemical and geochronological data for volcanic and related rocks in the regions of the jia yi and dun mi faults in order to constrain the late mesozoic tectonic evolution of the northern segment of the tan lu fault zircon u pb dating shows that rhyolite and intermediate mafic rocks along the southern part of the jia yi fault formed at 124 and 113 ma respectively whereas the volcanic rocks along the northern parts of the jia yi and dun mi faults formed at 100 ma the rhyolite has an a type granitoid affinity with high alkalis low mgo ti and p contents high rare earth element ree contents and ga al ratios enrichments in large ion lithophile liles e g rb th and u and high field strength element hfses e g nb ta zr and y and marked negative eu anomalies these features indicate that the rhyolites were derived from partial melting of crustal material in an extensional environment the basaltic rocks are enriched in light rees and liles e g rb k th and u and depleted in heavy rees hfses e g nb ta ti and p and sr these geochemical characteristics indicate that these rocks are calc alkaline basalts that formed in an intraplate extensional tectonic setting the dacite is a medium to high k calc alkaline i type granite that was derived from a mixed source involving both crustal and mantle components in a magmatic arc therefore the volcanic rocks along the jia yi and dun mi faults were formed in an extensional regime at 124 100 ma early cretaceous and these faults were extensional strike slip faults at this time

present day south american climate abstract this paper documents the main features of the climate and climate variability over south america on the basis of instrumental observations gathered during the 20th century it should provide a modern reference framework for paleoclimate research in south america targeting high resolution proxies over the past few centuries several datasets suitable for present day climate research are first described highlighting their advantages as well as their limitations we then provide a basic physical understanding of the mean annual cycle of the precipitation and atmospheric circulation over the continent and the adjacent oceans in particular the diversity of precipitation temperature and wind patterns is interpreted in terms of the long meridional extent of the continent and the disruption of the large scale circulation caused by the andes cordillera the contrasting oceanic boundary conditions and the landmass distribution similarly the intensity and timing of the interannual and interdecadal climatic fluctuations exhibit considerable geographical dependence as some regions are more influenced by large scale phenomena rooted in the tropical oceans while others are more influenced by high latitude phenomena the impact of these large scale phenomena over south america is documented by a regression analysis between selected atmospheric indices and the precipitation and temperature fields we have included a discussion on the seasonality and long term stability of such impacts and complemented our general description by an updated review of the literature on climate variability over specific regions

a distributed temperature index ice and snowmelt model including potential direct solar radiation hourly melt and discharge of storglaciaren a small glacier in sweden were computed for two melt seasons applying temperature index methods to a 30 m resolution grid for the melt component the classical degree day method yielded a good simulation of the seasonal patient of discharge but the pronounced melt induced daily discharge cycles were not captured modelled degree day factors calculated for every hour and each gridcell from melt obtained from a distributed energy balance model varied substantially both diurnally and spatially a new distributed temperature index model is suggested attempting to capture both the pronounced diurnal melt cycles and the spatial variations in melt due to the effects of surrounding topography this is accomplished by including a radiation index in terms of potential clear sky direct solar radiation and thus without the need for other data besides air temperature this approach improved considerably the simulation of diurnal discharge fluctuations and yielded a more realistic spatial distribution of melt rates the incorporation of measured global radiation to account for the reduction in direct solar radiation due to cloudiness did not lead to additional improvement in model performance

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

simulating late pliocene northern hemisphere climate with the lln 2 d model deep sea sediment records suggest northern hemisphere glaciation intensified at approximately 2 75 ma in this paper we simulate the fluctuations of the late pliocene northern hemisphere ice sheets volume using the lln 2 d model forced by the astronomically derived insolation and by scenarios of co2 concentrations the model simulates the waxing and waning of the northern hemisphere ice volume in an acceptable agreement with geological reconstructions and in particular supports the geological evidence that the development of significant northern hemisphere ice sheets started between 2 75 and 2 55 ma a time interval accompanied by quite high and stable eccentricity values and increased obliquity amplitude when the co2 concentration is lower than a threshold value the milankovitch forcing explains the suddenness and specific timing of this entrance into the ice age during the late pliocene

suitability of a constant air temperature lapse rate over an alpine glacier testing the greuell and bohm model as an alternative near surface air temperature typically measured at a height of 2 m is the most important control on the energy exchange and the melt rate at a snow or ice surface it is distributed in a simplistic manner in most glacier melt models by using constant linear lapse rates which poorly represent the actual spatial and temporal variability of air temperature in this paper we test a simple thermodynamic model proposed by greuell and bohm in 1998 as an alternative using a new dataset of air temperature measurements from along the flowline of haut glacier d arolla switzerland the unmodified model performs little better than assuming a constant linear lapse rate when modified to allow the ratio of the boundary layer height to the bulk heat transfer coefficient to vary along the flowline the model matches measured air temperatures better and a further reduction of the root mean square error is obtained although there is still considerable scope for improvement the modified model is shown to perform best under conditions favourable to the development of katabatic winds few clouds positive ambient air temperature limited influence of synoptic or valley winds and a long fetch but its performance is poor under cloudy conditions

glacial interglacial changes in equatorial pacific surface water structure during the plio pleistocene intensification of northern hemisphere glaciation the late pliocene early pleistocene intensification of northern hemisphere glaciation inhg represents the most recent major tipping point in earth s climate history in the equatorial pacific the inhg has been suggested to mark the transition from a warm pliocene climate state in which the pacific warm pool was greatly expanded relative to today giving rise to a surface ocean temperature field akin to modern el nino conditions to a climate state with strong upwelling in the east of the basin and stronger zonal temperature gradients here we examine this transition by presenting new high resolution 800 yr planktic foraminiferal mg ca and 18 18o based sea surface temperature sst and salinity sss based on 18o 18o residuals 18oivc sw 18oivc sw records from eastern equatorial pacific eep ocean drilling program site 849 spanning 2 75 2 4 ma our study interval contains the first large amplitude 1 in benthic 18 18o early pleistocene glacial interglacial cycles marine isotope stages 100 96 representing the culmination of inhg in this study we investigate west to east equatorial pacific sst and sss gradients we find that the zonal sst gradient increased by 1 5 c from 2 75 to 2 4 ma through eep cooling no glacial interglacial pattern is seen in this gradient on the other hand we document obliquity paced oscillations in the 18oivc sw 18oivc sw sss gradient we hypothesize that these oscillations originated from a response to a glacial southward and interglacial northward migration of the intertropical convergence zone over the eep

u pb dating of a terminal pliocene coral from the indonesian seaway abstract pristine detrital platygyra corals were discovered in an exhumed package of syn orogenic marine sediments on the island of timor in the eastern indonesian region and dated using u pb techniques a single coral from the upper part of the sequence yields a 238 u 206 pb 207 pb 206 pb concordia age of 2 66 0 14 2 ma that is supported by coral 87 sr 86 sr chemostratigraphy and foraminiferal biostratigraphy from bounding strata minor u series disequilibrium is best explained by u mobility within the last 150 ka as pore water chemistry was altered during exhumation and is unlikely to have affected 238 u 206 pb and the apparent sample age by more than 1 2 the ability to date corals beyond the limits of 14 c and u th techniques provides the opportunity to improve the temporal resolution of associated marine chronostratigraphic records in this instance we refine the timing of timor s emergence from beneath the waters of the indonesian seaway is and the initiation of turbiditic deposition at the study site to between ca 3 35 and 2 66 ma these results have implications for the evolution of topography and is oceanic pathways in the active orogenic belts along the northern fringes of the australian plate

interaction of katabatic winds and near surface temperatures in the antarctic 1 a two dimensional mesoscale model was applied to simulate wintertime katabatic winds in the antarctic coastal region simulations were made for a constant slope angle with the slope height varying and for fixed slope heights with the slope angle varying thermal wind opposed the katabatic flow near the foot of the slope but enhanced it over the high plateau the steeper and higher the slope the stronger the effect on the plateau the 2 m potential temperature decreased down the slope toward sea ice because 1 the katabatic wind resulted in the accumulation of cold near surface air over the sea ice and the lower parts of the slope 2 over the flat sea ice zone the stratification was stronger and 3 the shallow slope was within the strong surface inversion from over the sea ice with a slope aspect ratio of 5 m km 1 and a slope height below 1000 m 2 m temperature t2m decreased down the slope but for slope heights of 1500 m and more t2m increased down the slope adiabatic warming and because of the stronger wind enhanced turbulent mixing of the warmer air from aloft contributed to the warming for slope angles ranging from 1 to 20 m km 1 with a small slope height of 500 m t2m decreased down the slope but not monotonically whereas with a slope height of 2000 m yielding stronger winds and larger adiabatic warming t2m increased monotonically down the slope the model results were supported by observations from several antarctic sites with different topographic conditions

neogene carbonate burial in the pacific ocean 1 i have compiled caco3 mass accumulation rates mars for the period 0 25 ma for 144 deep sea drilling project and ocean drilling program drill sites in the pacific in order to investigate the history of caco3 burial in the world s largest ocean basin this is the first synthesis of data since the beginning of the ocean drilling program sedimentation rates caco3 contents and bulk density were estimated for 0 5 myr time intervals from 0 to 14 ma and for 1 myr time intervals from 14 to 25 ma using mostly data from initial reports volumes there is surprisingly little coherence between caco3 mar time series from different pacific regions although regional patterns exist a transition from high to low caco3 mar from 23 20 ma is the only event common to the entire pacific ocean this event is found worldwide the most likely cause of lowered pelagic carbonate burial is a rising sea level trend in the early miocene the central and eastern equatorial pacific is the only region with adequate drill site coverage to study carbonate compensation depth ccd changes in detail for the entire neogene the latitude dependent decrease in caco3 production away from the equator is an important defining factor of the regional ccd which shallows away from the equatorial region examination of latitudinal transects across the equatorial region is a useful way to separate the effects of changes in carbonate production productivity from changes in bottom water chemistry dissolution upon carbonate burial

final closure of panama and the onset of northern hemisphere glaciation abstract the greenland ice sheet is accepted as a key factor controlling the quaternary glacial scenario however the origin and mechanisms of major arctic glaciation starting at 3 15 ma and culminating at 2 74 ma are still controversial for this phase of intense cooling ravelo et al 1 a c ravelo d h andreasen m lyle a o lyle m w wara regional climate shifts caused by gradual global cooling in the pliocene epoch nature 429 2004 263 267 proposed a complex gradual forcing mechanism in contrast our new submillennial scale paleoceanographic records from the pliocene north atlantic suggest a far more precise timing and forcing for the initiation of northern hemisphere glaciation nhg since it was linked to a 2 3 c surface water warming during warm stages from 2 95 to 2 82 ma these records support previous models g h haug r tiedemann effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation nature 393 1998 673 676 2 claiming that the final closure of the panama isthmus 3 0 2 5 ma j groeneveld s steph r tiedemann d nurnberg d garbe schonberg the final closure of the central american seaway geology in prep 3 induced an increased poleward salt and heat transport associated strengthening of north atlantic thermohaline circulation and in turn an intensified moisture supply to northern high latitudes resulted in the build up of nhg finally culminating in the great irreversible climate crash at marine isotope stage g6 2 74 ma in summary there was a two step threshold mechanism that marked the onset of nhg with glacial to interglacial cycles quasi persistent until today

enhanced circulation during a warm period the early pliocene is the most recent interval in which equilibrium oceanic conditions can be studied in the context of global warmth relative to today to characterize thermohaline circulation during this warm period 4 4 3 1 ma we combined new benthic foraminiferal isotopic data from the southeast atlantic with published data and reconstructed pacific and atlantic ocean nutrient distributions the data indicate enhanced ventilation of the deep atlantic and intermediate pacific during the early pliocene enhanced ventilation implies that delivery of surface water to high latitudes in western boundary currents of north pacific and atlantic subtropical gyres was probably also enhanced future modeling of this warm period needs to reconcile reduced meridional surface temperature gradients with enhanced subtropical gyre and thermohaline circulation

simulating the ice thickness distribution in a coupled climate model climate simulations in a global coupled model are investigated using a dynamic thermodynamic sea ice and snow model with sophisticated thermodynamics and a subgrid scale parameterization for multiple ice thicknesses in addition to the sea ice component the model includes a full primitive equation ocean and a simple energy moisture balance atmosphere we introduce a formulation of the ice thickness distribution that is lagrangian in thickness space the method is designed to use fewer thickness categories because it adjusts to place resolution where it is needed most and it is free of diffusive effects that tend to smooth eulerian distributions experiments demonstrate that the model does reasonably well in simulating the mean arctic climate we find the climate of the arctic and northern north atlantic is sensitive to resolving the ice thickness distribution when comparing the model results to a simulation with a two level sea ice model the ice thickness distribution causes ice export through fram strait to be more variable and more strongly linked to meridional overturning in the north atlantic ocean the lagrangian formulation of the ice thickness distribution allows for the inclusion of a vertical temperature profile with relative ease compared to an eulerian method we find ice growth rates and ocean surface salinity differ in our model with a well resolved vertical temperature profile in the ice and snow and an explicit brine pocket parameterization compared to a simulation with semtner zero layer thermodynamics although these differences are important for the climate of the arctic the effects of an ice thickness distribution are more dramatic and extend into the northern north atlantic sensitivity experiments indicate that five ice thickness categories with 50 cm vertical temperature resolution capture the effects of the ice thickness distribution on the heat and freshwater exchange across the surface in the presence of sea ice in these simulations

early oligocene initiation of north atlantic deep water formation dating the onset of deep water flow between the arctic and north atlantic oceans is critical for modelling climate change in the northern hemisphere1 2 and for explaining changes in global ocean circulation throughout the cenozoic era3 from about 65 million years ago to the present in the early cenozoic era exchange between these two ocean basins was inhibited by the greenland scotland ridge3 4 but a gateway through the faeroe shetland basin has been hypothesized3 5 previous estimates of the date marking the onset of deep water circulation through this basin on the basis of circumstantial evidence from neighbouring basins have been contradictory5 6 7 8 9 ranging from about 35 to 15 million years ago here we describe the newly discovered southeast faeroes drift which extends for 120 km parallel to the basin axis the onset of deposition in this drift has been dated to the early oligocene epoch 35 million years ago from a petroleum exploration borehole we show that the drift was deposited under a southerly flow regime and conclude that the initiation of deep water circulation from the norwegian sea into the north atlantic ocean took place much earlier than is currently assumed in most numerical models of ancient ocean circulation

miocene to pliocene development of surface and subsurface temperatures in the benguela current system 1 the initiation of the benguela upwelling has been dated to the late miocene but estimates of its sea surface temperature evolution are not available this study presents data from ocean drilling program odp site 1085 recovered from the southern cape basin samples of the middle miocene to pliocene were analyzed for alkenone based u37k sstuk and glycerol dialkyl glycerol tetraether gdgt based tex86 temptex water temperature proxies in concordance with global cooling during the miocene sstuk and temptex exhibit a decline of about 8 c and 16 c respectively the temperature trends suggest an inflow of cold antarctic waters triggered by antarctic ice sheet expansion and intensification of southern hemisphere southeasterly winds a temperature offset between both proxies developed with the onset of upwelling which can be explained by differences in habitat alkenone producing phytoplankton live in the euphotic zone and record sea surface temperatures while gdgt producing thaumarchaeota are displaced to colder subsurface waters in upwelling influenced areas and record subsurface water temperatures we suggest that variations in subsurface water temperatures were driven by advection of cold antarctic waters and thermocline adjustments that were due to changes in north atlantic deep water formation a decline in surface temperatures an increased offset between temperature proxies and an increase in primary productivity suggest the establishment of the benguela upwelling at 10 ma during the messinian salinity crisis between 7 and 5 ma surface and subsurface temperature estimates became similar likely because of a strong reduction in atlantic overturning circulation while high total organic carbon contents suggest a biogenic bloom in the pliocene the offset between the temperature estimates and the cooling trend was reestablished

a short circuit in thermohaline circulation a cause for northern hemisphere glaciation the cause of northern hemisphere glaciation about 3 million years ago remains uncertain closing the panamanian isthmus increased thermohaline circulation and enhanced moisture supply to high latitudes but the accompanying heat would have inhibited ice growth one possible solution is that enhanced moisture transported to eurasia also enhanced freshwater delivery to the arctic via siberian rivers freshwater input to the arctic would facilitate sea ice formation increase the albedo and isolate the high heat capacity of the ocean from the atmosphere it would also act as a negative feedback on the efficiency of the conveyor belt heat pump

widespread intense turbulent mixing in the southern ocean observations of internal wave velocity fluctuations show that enhanced turbulent mixing over rough topography in the southern ocean is remarkably intense and widespread mixing rates exceeding background values by a factor of 10 to 1000 are common above complex bathymetry over a distance of 2000 to 3000 kilometers at depths greater than 500 to 1000 meters this suggests that turbulent mixing in the southern ocean may contribute crucially to driving the upward transport of water closing the ocean s meridional overturning circulation and thus needs to be represented in numerical simulations of the global ocean circulation and the spreading of biogeochemical tracers

biotic and geochemical evidence for a global latitudinal shift in ocean biogeochemistry and export productivity during the late pliocene during the late pliocene 3 to 2 5 ma oceanic records of opal and c37 alkenone accumulation from around the world show a secular shift towards lower values in the high latitudes and higher values in the low and mid latitudes these shifts are broadly coincident with the intensification of northern hemisphere glaciation and are suggestive of changes in export productivity with potential implications for pliocene atmospheric carbon dioxide concentrations the interpretation of a global latitudinal shift in productivity however requires testing because of the potential uncertainties associated with site to site comparisons of records that can be influenced by highly nonlinear processes associated with production export and preservation here we assess the inferred pliocene latitudinal productivity shift interpretation by presenting new records of c37 alkenone accumulation from ocean drilling program odp site 982 in the north atlantic and biotic assemblages calcareous nannoplankton from this site and odp site 846 in the eastern tropical pacific our results corroborate the interpretation of c37 alkenone accumulation as a proxy for gross export productivity at these sites indicating that large scale productivity decreases at high latitudes and increases at tropical sites are recorded robustly we conclude that the intensification of northern hemisphere glaciation during the late pliocene was associated with a profound reorganisation of ocean biogeochemistry

reorganization of miocene deep water circulation in response to the shoaling of the central american seaway 1 the response of ocean circulation to the shoaling of the central american seaway cas is investigated using the massachusetts institute of technology mit ocean general circulation model ogcm in contrast to earlier model studies it is found that significant amounts of deep water are formed in the north atlantic prior to the closure of the cas however the circulation pattern is fundamentally different from the modern ocean in the upper layers of the cas there is a relatively strong geostrophic flow from the pacific to the atlantic controlled by the pressure difference across the seaway however when the cas is deeper than the level of north atlantic deep water nadw outflow a significant amount of nadw passes through the cas to the pacific ocean in the pacific the deep water traverses the basin from east to west in a relatively narrow zonal jet and becomes a southward flowing western boundary current before it joins with the antarctic circumpolar current acc to the south this implies that deep sea sediment records from the miocene pacific ocean could have been influenced by relatively young nadw and provides a new framework for the interpretation of geochemical tracer data diversification of benthic foraminifer fauna suggests that the cas shoaled to a depth of about 1000 m toward the end of the middle miocene this would have prevented the passage of nadw to the pacific and established the modern deep water circulation pattern at that time

sensitivity of net mass balance estimates to near surface temperature lapse rates when employing the degree day method to estimate glacier melt glacier mass balance models that employ the degree day method of melt modeling are most commonly driven by surface air temperatures that have been downscaled over the area of interest using digital elevation models and assuming a constant free air lapse rate that is often taken to be the moist adiabatic lapse rate malr 6 58 ck m 1 air temperature lapse rates measured over melting glacier surface are however consistently less steep than free air values and have been shown to vary systematically with lower tropospheric temperatures in this study the implications of including a variable near surface lapse rate in a 26 year 1980 2006 degree day model simulation of the surface mass balance of devon ice cap nunavut canada are examined and compared with estimates derived from surface air temperatures downscaled using a constant near surface lapse rate equal to the measured summer mean 4 98 ck m 1 and the malr our results show that degree day models are highly sensitive to the choice of lapse rate when compared with 23 years of surface mass balance measurements from the northwest sector of the ice cap model estimates are significantly better when surface air temperatures are downscaled using a modeled daily lapse rate rather than a constant lapse equal to either the summer mean or the malr

spatial and temporal variability of air temperature on a melting glacier atmospheric controls extrapolation methods and their effect on melt modeling juncal norte glacier chile 1 temperature data from three automatic weather stations and twelve temperature loggers are used to investigate the spatiotemporal variability of temperature over a glacier its main atmospheric controls the suitability of extrapolation techniques and their effect on melt modeling we use data collected on juncal norte glacier central chile during one ablation season we examine temporal and spatial variability in lapse rates lrs together with alternative statistical interpolation methods the main control over the glacier thermal regime is the development of a katabatic boundary layer kbl katabatic wind occurs at night and in the morning and is eroded in the afternoon lrs reveal strong diurnal variability with steeper lrs during the day when the katabatic wind weakens and shallower lrs during the night and morning we suggest that temporally variable lrs should be used to account for the observed change they tend to be steeper than equivalent constant lrs and therefore result in a reduction in simulated melt compared to use of constant lrs when extrapolating from lower to higher elevations in addition to the temporal variability the temperature elevation relationship varies also in space differences are evident between local lrs and including such variability in melt modeling affects melt simulations extrapolation methods based on the spatial variability of the observations after removal of the elevation trend such as inverse distance weighting or kriging do not seem necessary for simulations of gridded temperature data over a glacier

model study of the spatial distribution of the energy and mass balance of morteratschgletscher switzerland to investigate the spatial distribution of the energy and mass balance fluxes of a glacier a two dimensional mass balance model was developed and applied to morteratschgletscher switzerland the model is driven by meteorological input from four synoptic weather stations located in the vicinity of morteratschgletscher the model results were compared to observations made on the glacier the calculated mean specific mass balance is 0 47 m w e for 1999 and 0 23 m w e for 2000 net shortwave radiation shows a minimum at around 3350 m a s l due to the effects of shading slope aspect reflection from the slopes and obstruction of the sky ignoring these effects results in a 37 increase in the annual incoming shortwave radiation on the glacier causing 0 34 m w e more ablation a 1 c change in the air temperature results in a shift of 0 67 m w e in the mean specific mass balance while altering the precipitation by 10 causes a change of 0 17 m w e

the geology of the darien panama and the late miocene pliocene collision of the panama arc with northwestern south america the geology of the darien province of eastern panama is presented through a new geologic map and detailed biostratigraphic and paleobathymetric analysis of its upper cretaceous to upper miocene sediments the sequence of events inferred from the stratigraphic record includes the collision of the panama arc the southwestern margin of the caribbean plate and south american continent three tectonostratigraphic units underlie the darien region 1 precollisional upper cretaceous eocene crystalline basement rocks of the san blas complex form a series of structurally complex topographic massifs along the northeastern and southwestern margins of the darien province these rocks formed part of a 20 m y submarine volcanic arc developed in a pacific setting distant from the continental margin of northwestern south america the northerly basement rocks are quartz diorites granodiorites and basaltic andesites through dacites to rhyolites indicating the presence of a magmatic arc the southerly basement rocks are an accreted suite of diabase pillow basalt and radiolarian chert deposited at abyssal depths precollisional arc related rocks of eocene to lower miocene age consist of 4000 m of pillow basalts and volcaniclastics and biogenic calcareous and siliceous deep water sediments they consist of the eocene oligocene darien formation the oligocene porcona formation and the lower middle miocene clarita formation postcollisional deposits are mostly coarse to fine grained siliciclastic sedimentary rocks and turbiditic sandstone of upper middle to latest miocene age this 3000 m thick sedimentary sequence is deformed as part of a complexly folded and faulted synclinorium that forms the central chucunaque tuira basin of the darien the sedimentary package reveals general shallowing of the basin from bathyal to inner neritic depths during the 12 8 7 1 ma collision of the panama arc with south america the sediments are divided into the upper middle miocene tapaliza formation the lower upper miocene tuira and membrillo formations the middle upper miocene yaviza formation and the middle to upper miocene chucunaque formation the precollisional open marine units of late cretaceous middle miocene age are separated from the overlying postcollisional sequence of middle to late miocene age by a regional unconformity at 14 8 12 8 ma this unconformity marks the disappearance of radiolarians the changeover of predominantly silica deposition from the atlantic to the pacific the initiation of the uplift of the isthmus of panama and the onset of shallowing upward coarser clastic deposition this pattern is also recorded from the southern limon basin of caribbean costa rica to the atrato basin of northwestern colombia by the middle late miocene neritic depths were widespread throughout the darien region and a regional unconformity suggests completion of the central american arc collision with south america by 7 1 ma no pliocene deposits are recorded from either the darien or the panama canal basin and no sediments younger than 4 8 ma have been identified in the atrato basin of colombia suggesting rapid uplift and extensive emergence of the central american isthmus in the latest miocene northward movement of the eastern segment of the panama arc along a now quiescent panama canal zone fault during eocene oligocene time may have dislocated the pre collision arc since collision the portion west of this fault chorotega block has remained stable without rotation to the east in the darien region compression has been accommodated through formation of a panama microplate with convergent boundaries to the north north panama deformed belt and south south panama deformed belt and suturing with south america along the atrato valley deformation within the microplate has been accommodated in the darien province by several major left lateral strike slip faults that were active until the early pliocene since when the plate has behaved rigidly

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

mid pliocene warmth stronger greenhouse and stronger conveyor abstract three million years ago prior to the onset of northern hemisphere glaciation global mean temperatures may have been as much as 3 5 c warmer than at present we present evidence based on the carbon isotopic composition of marine organic matter that atmospheric co2 levels at this time were on average only about 35 higher than the preindustrial value of 280 ppm we also present carbon isotopic evidence for stronger thermohaline circulation in the atlantic ocean during the warmest intervals and propose that the north atlantic conveyor belt may act as a positive feedback to global warming by enhancing sea ice retreat and decreasing high latitude albedo based on our results it seems unlikely that the mid pliocene warm period was a doubled co2 world

the use of bulk and profile methods for determining surface heat fluxes in the presence of glacier winds a one dimensional second order closure model and in situ observations on a melting glacier surface are used to investigate the suitability of bulk and profile methods for determining turbulent fluxes in the presence of the katabatic wind speed maximum associated with glacier winds the results show that profile methods severely underestimate turbulent fluxes when a wind speed maximum is present the bulk method on the other hand only slightly overestimates the turbulent heat flux in the entire region below the wind speed maximum and is thus much more appropriate for use on sloping glacier surfaces where katabatic winds dominate and wind speed maxima are just a few meters above the surface

neogene stratigraphy paleoceanography and paleobiogeography in northwest south america and the evolution of the panama seaway abstract the atrato basin in the pacific coastal region of nw south america colombia exhibits stratigraphic and biostratigraphic characteristics similar to other neogene pacific coastal basins of southern central america and northern south america an evaluation of the neogene stratigraphy and foraminiferal biostratigraphy with emphasis on paleoceanographic and paleobiogeographic phenomena indicate the following 1 previous to the middle miocene well aerated deep and open oceanic conditions and free and active water circulation prevailed along the steep continental margins of nw south america 2 during the early middle miocene right after the neogene hiatus nh 2 15 2 ma tectonic disturbances triggered the initial uplift of the panama sill bottom water circulation foraminiferal and sedimentation changes are observed in both the pacific and caribbean coastal areas of nw south america 3 during the middle miocene coinciding with the neogene hiatus nh 3 12 9 11 8 ma an abrupt paleobathymetric change from lower to middle bathyal depths indicates a major uplift of the panama sill to about 1000 m reflecting the middle miocene tectonic disturbances in nw south america 4 during the late middle miocene immediately following this uplift a distinctive pacific benthic foraminiferal fauna abruptly appeared and extended from ecuador to california because these assemblages do not occur in the adjacent caribbean region a circulation barrier between the atlantic and pacific oceans as a result of intensification of the cool marginal california current is proposed anoxic middle to upper bathyal environments prevailed under well aerated cool surface waters in the pacific coastal areas of nw south america 5 during the latest miocene immediately following the neogene hiatus nh 6 7 0 6 3 ma surface water circulation between the caribbean and the pacific was re established and the previous influence of the california current disappeared a rapid filling and shallowing of the basin to mostly neritic depths is indicated along the pacific and caribbean coastal basins of colombia as well as a progressive increase in similarity between the coastal pacific and caribbean benthic biotas this shallowing in the early late miocene also appears to have been associated with the earliest terrestrial interchange of ground sloths to north america and raccoons and their allies to south america 6 immediately following early pliocene time the panamanian isthmus became completely emergent providing a terrestrial environment favourable for intermingling of terrestrial faunas and floras between north and south america i correlate this pliocene uplift with the neogene hiatus nh 8 3 7 3 1 ma four regional unconformities associated with tectonic disturbances in the nw corner of south america have also been recognized and correlated with neogene hiatuses recorded from the oceans early middle miocene middle miocene late miocene and early pliocene

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

a coastal upwelling seesaw in the atlantic ocean as a result of the closure of the central american seaway 1 based on coupled climate model experiments we suggest an antiphase relationship between the two major coastal upwelling zones in the atlantic ocean off northwestern and southwestern africa we describe this as an upwelling seesaw the state of the coastal upwelling seesaw is controlled by variations in the oceanic meridional heat transfer between south and north atlantic in particular we suggest that the pliocene closure of the central american seaway induced a large scale redistribution of heat in the atlantic ocean leading to an intensification weakening of upwelling off southwest northwest africa

mass balance estimates for haut glacier d arolla switzerland from 2000 to 2006 using dems and distributed mass balance modeling a distributed mass balance modeling approach is required to assess the impact of future climate scenarios on water availability in glaciated basins accurate estimation of water stored within the snow firn and ice of such basins requires knowledge of the distributed snow and ice mass balance throughout the year in this study we estimate the annual mass balance and runoff for haut glacier darolla switzerland from 2000 to 2006 our estimations are based on observed elevation changes from three digital elevation models dems derived from aerial photographs in september 1999 and 2005 and october 2006 in addition to these estimations we implement a combined field observation and a distributed mass balance modeling approach an energy balance model driven by meteorologi cal variables from automatic weather stations inside the catchment area including gravitational snow transport is run for the period 2005 06 the model results are validated with direct snow water equiv alent measurements as well as with runoff measurements combining the mass balance measurements energy balance calculations and measured runoff we estimate the contribution from ice melt to the runoff for this period to be 25 30 the contribution from snowmelt 50 60 and the contribution from rain 15 25 our model results also show that the snow distribution affects both snow and ice melt it is therefore important for water resources management to understand the distribution of snow in alpine catchments as it seems to be the controlling factor for the timing of streamflow throughout the year as well as for the total availability of water

evolution of a deep water ferromanganese nodule in the south china sea in response to pacific deep water circulation and continental weathering during the plio pleistocene abstract the south china sea scs is connected to the west pacific through a deep channel in the luzon strait thus the scs deep water is sensitive to the evolution of pacific ocean circulation which significantly influences the global climate system geochemical data pb isotope and redox sensitive elements data and magnetic data were determined for a fe mn nodule obtained from jiaolong seamount in the central scs these records reflect interactions between changes in ice sheets deep pacific circulation and weathering inputs to the deep scs during the pliocene and quaternary our results show that the scs deep water environment can be divided into three major stages stages 1 3 stage 1 4 8 1 4 ma was characterized by a well oxygenated pacific deep water pdw and lower dust inputs then moderate stable deep water ventilation and greater inputs of asian dust occurred during stage 2 1 4 0 9 ma during stage 3

a distributed surface energy balance model for a small valley glacier i development and testing for haut glacier d arolla valais switzerland this paper describes the development and testing of a distributed surface energy balance model used to calculate rates of surface melting at haut glacier d arolla valais switzerland the model uses a digital elevation model dem of the glacier surface and surrounding topography together with meteorological data collected at a site in front of the glacier to determine hourly or daily totals of the energy balance components and hence of melting over the entire surface of the glacier with a spatial resolutio of 20 m the model can also be used to determine temporal and spatial variations in snow depth snow line position and glacier surface albedo calculations from the model are compared with observations made along the glacier centre line in 1990 and in general the model performs very well the correlation coefficients between calculated and measured snow line elevation albedo and ablation are 0 99 0 85 and 0 81 respectively the main source of error between modelled and measured values of these variables is probably inadequacies in the parameterization of albedo used in the model

melt and surface sublimation across a glacier in a dry environment distributed energy balance modelling of juncal norte glacier chile previous estimates of melt and surface sublimation on glaciers of the subtropical semiarid andes 29 34 s have been obtained at few specific locations but it is not clear how ablation components vary across the entire extent of a glacier in this dry environment here we simulate the distributed energy and mass balance of juncal norte glacier 33 s during a 2 month summer period forcing fields of near surface air temperature and wind speed are generated using two methods accounting for the main physical processes that shape their spatial variations simulated meteorological variables and ablation agree well with observations on the glacier tongue and reveal complex patterns of energy and mass fluxes ablation decreases from 70 mm w e d 1 at the low albedo glacier terminus 3000 m where almost 100 of total ablation corresponds to melt to 75 of total ablation our simulations provide the first glacier scale estimates of ablation components on a glacier in the study region and better reproduce the observed and expected spatial variations of melt and surface sublimation in comparison with more simple assumptions such as linear gradients and uniform wind speeds

including debris cover effects in a distributed model of glacier ablation 1 distributed glacier melt models generally assume that the glacier surface consists of bare exposed ice and snow in reality many glaciers are wholly or partially covered in layers of debris that tend to suppress ablation rates in this paper an existing physically based point model for the ablation of debris covered ice is incorporated in a distributed melt model and applied to haut glacier d arolla switzerland which has three large patches of debris cover on its surface the model is based on a 10 m resolution digital elevation model dem of the area each glacier pixel in the dem is defined as either bare or debris covered ice and may be covered in snow that must be melted off before ice ablation is assumed to occur each debris covered pixel is assigned a debris thickness value using probability distributions based on over 1000 manual thickness measurements locally observed meteorological data are used to run energy balance calculations in every pixel using an approach suitable for snow bare ice or debris covered ice as appropriate the use of the debris model significantly reduces the total ablation in the debris covered areas however the precise reduction is sensitive to the temperature extrapolation used in the model distribution because air near the debris surface tends to be slightly warmer than over bare ice overall results suggest that the debris patches which cover 10 of the glacierized area reduce total runoff from the glacierized part of the basin by up to 7

air temperature distribution and energy balance modelling of a debris covered glacier near surface air temperature is an important determinant of the surface energy balance of glaciers and is often represented by a constant linear temperature gradients tgs in models spatiotemporal variability in 2 m air temperature was measured across the debris covered miage glacier italy over an 89 d period during the 2014 ablation season using a network of 19 stations air temperature was found to be strongly dependent upon elevation for most stations even under varying meteorological conditions and at different times of day and its spatial variability was well explained by a locally derived mean linear tg mg tg of 0 0088 c m 1 however local temperature depressions occurred over areas of very thin or patchy debris cover the mg tg together with other air tgs extrapolated from both on and off glacier sites were applied in a distributed energy balance model compared with piecewise air temperature extrapolation from all on glacier stations modelled ablation using the mg tg increased by 4 using the environmental lapse rate ice melt under thick debris was relatively insensitive to air temperature while the effects of different temperature extrapolation methods were strongest at high elevation sites of thin and patchy debris cover

testing the influence of the central american seaway on orbitally forced northern hemisphere glaciation 1 utilizing a climate model of intermediate complexity we test the hypothesis that the pliocene closure of the central american seaway was a necessary precondition for orbitally triggered northern hemisphere glaciation we conduct a series of sensitivity experiments in order to analyze the isolated and combined effects of panama closure and orbital forcing on northern hemisphere perennial snow cover while orbital forcing efficiently controls the extension of perennial snow cover the model results suggest that the closure of the central american seaway did not intensify orbitally forced glaciation in high northern latitudes

control of north atlantic deep water circulation by the greenland scotland ridge coherent bathymetric features along the reykjanes ridge indicate that there were significant changes in the flux of buoyant material within the icelandic hot spot during the neogene the radial extent of the topographic swell associated with this hot spot is of the order of 1000 to 2000 km and therefore these changes affected the greenland scotland ridge gsr at present sill depths along the gsr are generally less than 500 m with the deepest passage being less than 1000 m making the overflow water sensitive to even small changes in the ridge depths reconstructions of neogene mantle plume activity correlate with the deepwater circulation patterns in the north atlantic times of high mantle plume activity caused northern component water ncw production to cease ncw fluxes resumed once this phase of high mantle plume activity slowed the long term climate change during the neogene must be controlled by factors other than ncw production however climatic optima during the late early miocene and early pliocene appear to have been augmented by high ncw fluxes while subsequent middle miocene and middle pliocene coolings correlate with uplifts on the gsr and reduced ncw flux we suggest that reductions in ncw may have contributed to both of these cooling events

late neogene benthic stable isotope record of ocean drilling program site 999 implications for caribbean paleoceanography organic carbon burial and the messinian salinity crisis we report on epibenthic foraminiferal 18o and 13c and percentage coarse fraction records from caribbean ocean drilling program odp site 999 12 44 n 78 44 w water depth 2828 m spanning the interval from 8 5 to 5 3 ma low epibenthic 13c values and low amounts of sand sized particles mostly foraminifer shells indicate a poorly ventilated deep caribbean throughout the late miocene at this time the deep caribbean was dominated by a nutrient rich and corrosive water mass a generally constant 13c gradient between the caribbean and deep atlantic records during the late miocene suggests that the fluctuations in 13c reflect global changes in 13c of the dissolved inorganic carbon due to varying erosion of organic carbon from terrigenous soils and shelf sediments the observed 100 kyr cyclicity of epibenthic 13c is in good accordance with the variability of terrigenous input to the equatorial atlantic as recorded by magnetic susceptibility records of the ceara rise however some short term gradient changes between 7 0 and 4 5 ma indicate a poorer ventilation of the deep atlantic related to a reduced production of deep water in the atlantic the messinian salinity crisis between 6 0 and 5 3 ma did not affect the intermediate to deep water gradient between the caribbean and the atlantic comparison to the bahama platform record of odp site 1006 however indicates a poorer ventilation of the shallower northern caribbean basins coincident with the isolation of the mediterranean sea

influence of vertical mixing on the thermohaline hysteresis analyses of an ogcm the thermohaline hysteresis response to varying north atlantic freshwater forcing is studied by means of a three dimensional global ocean general circulation model ogcm the influence of vertical diffusivity is examined using a wide range of mixing coefficients for sufficiently large vertical diffusivity the model shows a pronounced hysteresis behavior so that two equilibrium states of the thermohaline circulation are found one mode with intense deep water formation in the north atlantic on mode and one mode with strongly reduced convective activity off mode by decreasing the diffusivity the two branches of the hysteresis merge in addition the effect of numerical diffusion is analyzed by applying different advection schemes a positive feedback between overturning strength and the numerical diffusivity of upstream advection is found resulting in a reduced stability of the on mode comparing the results with those from zonally averaged models exhibits substantial differences regarding the stability properties of the thermohaline circulation freshwater transports by horizontal gyres have an important effect on the overturning circulation in the ogcm

modelling seasonal and spatial variations in the surface energy balance of haut glacier d arolla switzerland the impact of spatial and temporal variations in the surface albedo and aerodynamic roughness length on the surface energy balance of haut glacier d arolla switzerland was examined using a semi distributed surface energy balance model arnold and others 1996 the model was updated to incorporate the glacier wide effects of albedo and aerodynamic roughness length variations using parameterizations following brock 1997 after the model s performance was validated the glacier wide patterns of the net shortwave turbulent and melt energy fluxes were examined on four days representative of surface conditions in late may june july and august in the model meteorological conditions were held constant on each day in order that the impact of albedo and aerodynamic roughness length variations could be assessed independently a late summer snowfall event was also simulated albedo and aerodynamic roughness length variations particularly those associated with the migration of the transient snowline and the decay of the winter snowpack were found to exert a strong influence on the magnitude of the surface energy fluxes the importance of meteorological conditions in suppressing the surface energy fluxes and melt rate following a fresh snowfall was highlighted

the initiation of northern hemisphere glaciation for well over a century scientists have speculated that variations in the atmospheric concentration of radiatively important trace gases such as carbon dioxide could control the earth s climate e g arrhenius 1 896 recent observations of significant glacial interglacial variation in atmo spheric co2 in ice cores put this idea on a firm observational as well as theoretical footing e g barnola et ai1 987 in this century as atmospheric co2 levels creep steadily upwards in response to the burning of fossil fuels and forests the specter of manmade global climate change looms before us ipcc 1990 a possibility that has heightened interest in the natural variability of climate in the past in particular the 3 c warming pre dicted for the next century has stimulated interest in past warm climates such as the middle pliocene around 3 0 million years ma ago an interval that has often been invoked as a greenhouse world budyko et al 1985 in this paper the climate transition from the warm mid pliocene around 3 2 ma to the onset of northern hemisphere ice ages around 2 4 ma is examined evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe while the cause of individual glacial interglacial oscillations is tied to milankovitch variations in the earth s orbit around the sun e g imbrie et ai 1 992 these insolation changes cannot account for the long term cooling trend which culminated in northern hemisphere glaciation in the final section of this paper mechanisms of long term climate change

2 m temperatures along melting mid latitude glaciers and implications for the sensitivity of the mass balance to variations in temperature in calculations of the variation in the 2 m temperature along glaciers the lapse rate is generally assumed to be constant this implies that the ratio of changes in the 2 m temperature above a glacier to changes in the temperature outside the thermal regime of that glacier climate sensitivity is equal to 1 however data collected during the ablation season on several mid latitude glaciers show that this sensitivity is smaller than 1 the lowest measured value 0 3 was obtained on the tongue of the pasterze a glacier in austria the measured temperature distribution along the pasterze cannot be described by a constant lapse rate either however there is almost a linear relationship between potential temperature and the distance along die glacier this paper introduces a simple analytical thermodynamic glacier wind model which can be applied to melting glaciers and which explains the observed climate sensitivities and temperature distributions much better than calculations based on a constant lapse rate this way of modelling the 2 m temperatures has implications for the sensitivity of the surface mass balance to atmospheric warming outside the thermal regime of the glacier the magnitude of this sensitivity is computed with a surface energy balance model applied to the pasterze when a constant lapse rate is used instead of the proposed glacier wind model to compute changes in the 2 m temperature along the glacier the negative change in mass balance due to 1 c warming is overestimated by 22

paleoclimatic response of the closing of the isthmus of panama in a coupled ocean atmosphere model the paleoclimatic effects of the closure of the isthmus of panama 3 ma are investigated using a coupled atmosphere ocean model consistent with earlier ocean only modelling studies it is shown that prior to closure there is an absence of deep water formation in the north atlantic hence there is a reduction in oceanic heat transport this is largely compensated for by the atmosphere such that only small changes in total planetary heat transport occur the model climate of the north atlantic is significantly warmer after isthmus closure in addition the regions surrounding the pacific ocean and south atlantic are generally cooler while the indian ocean is generally warmer in the model present day climate finally possible relationships to glaciation and initiation of northern hemisphere glacial cycles are discussed

oligocene miocene basin evolution in se anatolia turkey constraints on the closure of the eastern tethys gateway the oligocene miocene was a time characterized by major climate changes as well as changing plate configurations the middle miocene climate transition 17 to 11 ma may even have been triggered by a plate tectonic event the closure of the eastern tethys gateway the marine connection between the mediterranean and indian ocean to address this idea we focus on the evolution of oligocene and miocene foreland basins in the southernmost part of turkey the most likely candidates to have formed this gateway in addition we take the geodynamic evol ution of the arabian eurasian collision into account the musand elazog u basins located to the north of the bitlis zagros suture zone were most likely connected during the oligocene the deepening of both basins is biostratigraphically dated by us to occur during the rupelian early oligocene deep marine conditions between 350 and 750 m prevailed until the chattian late oligocene when the basins shoaled rapidly to subtidal intertidal environment in tropical to subtropical conditions as indicated by the macro fossil assemblages we conclude that the emergence of this basin during the chattian severely restricted the marine connection between an eastern indian ocean and western mediterranean marine domain if a connection persisted it was likely located south of the bitlis zagros suture zone the kahramanmarasbasin located on the northern arabian promontory south of the bitlis zagros suture zone was a foreland basin during the middle and late miocene possibly linked to the hatay basin to the west and the lice basin to the east our data indicates that this fore land basin experienced shallow marine conditions during the langhian followed by a rapid dee pening during langhian serravallian and prevailing deep marine conditions between 350 and 750 m until the early tortonian we have dated the youngest sediments underneath a subduc tion related thrust at c 11 ma and suggest that this corresponds to the end of underthrusting in the kahramanmarasregion i e the end of subduction of arabia this age coincides in time with the onset of eastern anatolian volcanism uplift of the east anatolian accretionary complex and the onset of the north and east anatolian fault zones accommodating westward escape tec tonics of anatolia after c 11 ma the foreland basin south of the bitlis formed not or no longer a deep marine connection along the northern margin of arabia between the mediterranean sea and the indian ocean we finally conclude that a causal link between gateway closure and global climate change to a cooler mode recorded in the mi3b event d 18 o increase dated at 13 82 ma cannot be supported

centreline and cross glacier air temperature variability on an alpine glacier assessing temperature distribution methods and their influence on melt model calculations the spatio temporal distribution of air temperature over mountain glaciers can demonstrate complex patterns yet it is often represented simplistically using linear vertical temperature gradients vtgs extrapolated from off glacier locations we analyse a network of centreline and lateral air temperature observations at tsanteleina glacier italy during summer 2015 on average vtgs are steep 1 but they are shallow under warm ambient conditions when the correlation between air temperature and elevation becomes weaker published along flowline temperature distribution methods explain centreline observations well including warming on the lower glacier tongue but cannot estimate lateral temperature variability application of temperature distribution methods improves simulation of melt rates rmse in an energy balance model by up to 36 compared to the environmental lapse rate extrapolated from an off glacier station however results suggest that model parameters are not easily transferable to glaciers with a small fetch without recalibration such methods have potential to improve estimates of temperature across a glacier but their parameter transferability should be further linked to the glacier and atmospheric characteristics furthermore cold spots which can be 2 c cooler than expected for their elevation whose occurrence is not predicted by the temperature distribution models are identified at one quarter of the measurement sites

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

modeling 2 m air temperatures over mountain glaciers exploring the influence of katabatic cooling and external warming air temperature is one of the most relevant input variables for snow and ice melt calculations however local meteorological conditions complex topography and logistical concerns in glacierized regions make the measuring and modeling of air temperature a difficult task in this study we investigate the spatial distribution of 2 m air temperature over mountain glaciers and propose a modification to an existing model to improve its representation spatially distributed meteorological data from haut glacier d arolla switzerland place canada and juncal norte chile glaciers are used to examine approximate flow line temperatures during their respective ablation seasons during warm conditions off glacier temperatures well above 0 c observed air temperatures in the upper reaches of place glacier and haut glacier d arolla decrease down glacier along the approximate flow line at juncal norte and haut glacier d arolla an increase in air temperature is observed over the glacier tongue while the temperature behavior over the upper part can be explained by the cooling effect of the glacier surface the temperature increase over the glacier tongue may be caused by several processes induced by the surrounding warm atmosphere in order to capture the latter effect we add an additional term to the greuell and bohm gb thermodynamic glacier wind model for high off glacier temperatures the modified gb model reduces root mean square error up to 32 and provides a new approach for distributing air temperature over mountain glaciers as a function of off glacier temperatures and approximate glacier flow lines

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

a distributed surface energy balance model for complex topography and its application to storglaciaren sweden a grid based surface energy balance mass balance model has been developed to simulate snow and ice melt in mountainous regions with an hourly resolution the model is applied to storglaciaren a valley glacier in sweden using a 30 m resolution digital elevation model emphasis is directed towards computing the radiation components these are modelled individually considering the effects of slope angle aspect and effective horizon a new parameterization for snow albedo is suggested modifying the albedo of the preceding hour as a function of time after snowfall air temperature and cloudiness the model is used to provide the meltwater input for discharge modelling and to assess the influence of the individual components on melt results are validated by means of observed melt rates patterns of snow line retreat and proglacial discharge in general simulations are in good agreement with observations in particular the diurnal and seasonal fluctuations of discharge are simulated remarkably well

north atlantic deep water export to the southern ocean over the past 14 myr evidence from nd and pb isotopes in ferromanganese crusts the intensity of north atlantic deep water nadw production has been one of the most important parameters controlling the global thermohaline ocean circulation system and climate here we present a new approach to reconstruct the overall strength of nadw export from the north atlantic to the southern ocean over the past 14 myr applying the deep water nd and pb isotope composition as recorded by ferromanganese crusts and nodules we present the first long term nd and pb isotope time series for deep southern ocean water masses which are compared with previously published time series for nadw from the nw atlantic ocean these data suggest a continuous and strong export of nadw or a precursor of it into the southern ocean between 14 and 3 ma an increasing difference in nd and pb isotope compositions between the nw atlantic and the southern ocean over the past 3 myr gives evidence for a progressive overall reduction of nadw export since the onset of northern hemisphere glaciation nhg the nd isotope data allow us to assess at least semiquantitatively that the amount of this reduction has been in the range between 14 and 37 depending on location

derivation of melt factors from glacier mass balance records in western canada melt factors for snow k s and ice k i were derived from specific mass balance data and regionally interpolated daily air temperature series at nine glaciers in the western cordillera of canada fitted k s and k i were relatively consistent across the region with mean values standard deviations of 3 04 0 38 and 4 59 0 59 mm d 1 c 1 respectively the interannual variability of melt factors was investigated for two long term datasets calculated annually snow and ice melt factors were relatively stable from year to year standard deviations for snowmelt factors were 0 48 17 and 0 42 18 at peyto and place glaciers respectively while standard deviations of ice melt factors were 1 17 25 and 0 81 14 while fitted values of k s are comparable to those presented in previous observational and modeling studies fitted k i are substantially and consistently lower across the region fitted melt factors were sensitive to the choice of lapse rate used in the air temperature interpolation melt factors fitted to mass balance data from a single site place glacier provided reasonable summer balance predictions at most other sites representing both maritime and continental climates although there was a tendency for under prediction at several sites the combination of regionally interpolated air temperatures and a degree day model appears capable of generating first order estimates of regional summer balance which can provide a benchmark against which to judge the predictive ability of more complex e g energy balance models applied at a regional scale mass balance sensitivity analyses indicate that a temperature increase of 1 k will increase summer ablation in the region by 0 51 m w e a 1 on average

an enhanced temperature index glacier melt model including the shortwave radiation balance development and testing for haut glacier d arolla switzerland an enhanced temperature index glacier melt model incorporating incoming shortwave radiation and albedo is presented the model is an attempt to combine the high temporal resolution and accuracy of physically based melt models with the lower data requirements and computational simplicity of empirical melt models represented by the degree day method and its variants the model is run with both measured and modelled radiation data to test its applicability to glaciers with differing data availability five automatic weather stations were established on haut glacier d arolla switzerland between may and september 2001 reference surface melt rates were calculated using a physically based energy balance melt model the performance of the enhanced temperature index model was tested at each of the four validation stations by comparing predicted hourly melt rates with reference melt rates predictions made with three other temperature index models were evaluated in the same way for comparison the enhanced temperature index model offers significant improvements over the other temperature index models and accounts for 90 95 of the variation in the reference melt rate the improvement is lower but still significant when the model is forced by modelled shortwave radiation data thus offering a better alternative to existing models that require only temperature data input

early pliocene closing of the indonesian seaway evidence from north east indian ocean and tropical pacific deep sea cores abstract deep sea cores from sites 214 and 758 a ninetyeast ridge north east indian ocean 761 b wombat plateau north east indian ocean and 586 b ontong java plateau tropical pacific are ideally located for comparison of late neogene planktic foraminiferal biogeography and paleoceanographic records of tropical indian and pacific oceans to infer the timing of closing of the indonesian seaway a consistent stratigraphy was developed between sites 214 and 586 b using graphic correlation and was integrated with the paleomagnetic time scale of berggren et al 1985 to provide an accurate chronology to compare interocean stratigraphic ranges of late neogene planktic foraminifera tropical planktic foraminifera occur throughout each sequence at all sites at each site the miocene pliocene boundary is defined by the first appearance of globorotalia tumida 5 2 ma the early late pliocene boundary by the first appearance of globigerinoides fistulosus 3 2 ma and the pliocene pleistocene boundary by the last appearance of g fistulosus 1 6 ma neogene planktic foraminiferal assemblages at sites 214 758a 761 b and 586b are generally similar until the beginning of the pliocene 5 2 ma when the faunal record indicates divergence a notable difference is complete absence of early pliocene taxon pulleniatina spectabilis from all the indian ocean sites this difference suggests that the indonesian seaway became an effective biogeographic barrier to planktic foraminifera at the beginning of the pliocene however there is still exchange of surface waters through this seaway earlier studies suggested a middle to late miocene occurrence for this biogeographic barrier p spectabilis evolved from p primalis in the equatorial pacific at about 5 2 ma it is a short ranging early pliocene species spanning about 1 3 my and occurred only in pacific unlike earlier suggestions of a broader distribution into the indian ocean

variability of air temperature over a debris covered glacier in the nepalese himalaya estimates of melt from debris covered glaciers require distributed estimates of meteorological variables and air temperature in particular meteorological data are scarce for this environment and spatial variability of temperature over debris is poorly understood based on multiple measurements of air and surface temperature from three ablation seasons 2012 14 we investigate the variability of temperature over lirung glacier nepal in order to reveal how air temperature is affected by the debris cover and improve ways to extrapolate it we investigate how much on glacier temperature deviates from that predicted from a valley lapse rate lr analyse on glacier lrs and test regression models of air temperature and surface temperature air temperature over the debris covered glacier tongue is much higher than what a valley lr would prescribe so an extrapolation from off glacier stations is not applicable an on glacier lr is clearly defined at night with strong correlation but not during the day when the warming debris disrupts the elevation control an alternative to derive daytime air temperature is to use a relationship between air and surface temperature as previously suggested we find strong variability during daytime that should be accounted for if these regressions are used for temperature extrapolation

high mixing rates in the abyssal southern ocean mixing of water masses from the deep ocean to the layers above can be estimated from considerations of continuity in the global ocean overturning circulation but averaged over ocean basins diffusivity has been observed to be too small to account for the global upward flux of water and high mixing intensities have only been found in the restricted areas close to sills and narrow gaps here we present observations from the scotia sea a deep ocean basin between the antarctic peninsula and the tip of south america showing a high intensity of mixing that is unprecedented over such a large area using a budget calculation over the whole basin we find a diffusivity of 39 plus minus 10 x 104 m2 s 1 averaged over an area of 7 x 105 km2 the scotia sea is a basin with a rough topography situated just east of the drake passage where the strong flow of the antarctic circumpolar current is constricted in width the high basin wide mixing intensity in this area of the southern ocean may help resolve the question of where the abyssal water masses are mixed towards the surface

simulating the impact of the panamanian seaway closure on ocean circulation marine productivity and nutrient cycling abstract the closure of the panama isthmus 14 3 ma caused large reorganizations of ocean circulation here we use a global climate ocean ecosystem model to investigate the effects of the closing gateway on ocean circulation marine productivity and nutrient distributions several sensitivity experiments with different sill depths and vertical diffusivities are performed consistent with previous model studies we find constricted throughflow due to shallowing of the sill leads to intensification of the north atlantic thermohaline overturning we demonstrate a strong coupling between the flows through the tropical gateways of panama and indonesia in a way that reduced outflow of upper ocean pacific waters via the panama gateway into the atlantic is compensated by increased flow through the indonesian archipelago the simulated rates of north atlantic deep water formation strongly depend on the vertical diffusion in the model particularly for a deep sill for the first time we document by model results shifts in nutrient distributions associated with reorganizations of ocean circulation with repercussions on marine productivity patterns reduced flow of nutrient rich sub surface waters from the pacific into the atlantic reduces biological productivity in the north atlantic in the eastern tropical pacific restriction of the nutrient rich outflow leads to nutrient accumulation which in turn maintains a strong increase in productivity these results seem to be largely consistent with the paleoproductivity proxy record a massive drop of opal accumulation rates however as found in north pacific sediments for the time of the final closure 2 75 ma cannot be simulated generally global marine net primary productivity npp is found to increase with proceeding gateway closure

air temperature variability in a high elevation himalayan catchment air temperature is a key control of processes affecting snow and glaciers in high elevation catchments including melt snowfall and sublimation it is therefore a key input variable to models of land surface atmosphere interaction despite this importance its spatial variability is poorly understood and simple assumptions are made to extrapolate it from point observations to the catchment scale we use a dataset of 2 75 years of air temperature measurements from may 2012 to november 2014 at a network of up to 27 locations in the langtang river nepal catchment to investigate air temperature seasonality and consistency between years we use observations from high elevations and from the easternmost section of the basin to corroborate previous findings of shallow lapse rates seasonal variability is strong with shallowest lapse rates during the monsoon season diurnal variability is also strong and should be taken into account since processes such as melt have a pronounced diurnal variability use of seasonal lapse rates seems crucial for glacio hydrological modelling but seasonal lapse rates seem stable over the 2 3 years investigated lateral variability at transects across valley is high and dominated by aspect with south facing sites being warmer than north facing sites and deviations from the fitted lapse rates of up to several degrees local factors e g topographic shading can reduce or enhance this effect the interplay of radiation aspect and elevation should be further investigated with high elevation transects

role of panama uplift on oceanic freshwater balance comparison between planktic foraminiferal oxygen isotope records from the caribbean sea ocean drilling program odp site 999 and the equatorial east pacific odp site 851 suggests an increase in caribbean surface water salinity between 4 7 and 4 2 ma the modern atlantic pacific salinity contrast of about 1 became fully established at 4 2 ma as reflected by a 0 5 planktic foraminifera 18o enrichment in the caribbean sea this is interpreted as the result of restricted surface water exchange between the tropical atlantic and pacific in response to the shoaling of the central american seaway as a consequence the atlantic and pacific surface ocean circulation regime changed as did the freshwater balance between the major ocean basins simultaneous shifts in benthic carbon isotope records in the caribbean sea suggest an intensification in north atlantic thermohaline circulation these results indicate that the panamanian isthmus formation caused several new ocean atmosphere feedback mechanisms that have affected climate since the early pliocene

changes in caribbean surface hydrography during the pliocene shoaling of the central american seaway pliocene d18o records of shallow and deep dwelling planktonic foraminifers from the caribbean ocean drilling program sites 999 and 1000 the tropical east pacific sites 1241 and 851 and the atlantic site 925 ceara rise and site 1006 western great bahama bank were used to examine atlantic caribbean pacific atmospheric and oceanic linkages associated with the progressive closure of the central american seaway 5 5 3 ma comparisons indicate the development of an inner caribbean salinity gradient in the mixed layer and salinity changes on precessional periodicities after 4 4 ma site 1000 when the pacific caribbean throughflow became significantly restricted the high amplitude variability in salinity is also observed at site 1006 monitoring the caribbean outflow into the atlantic comparisons of caribbean and atlantic planktonic d18o records suggest the north atlantic subtropical gyre as a major source for high salinity surface waters precession induced variations in the volume transport of pacific surface water masses through the panamanian seaway are considered a main factor to explain the caribbean salinity minima results from a coupled climate model point to changes in the el nin o southern oscillation state as a potential trigger for changes in the amount of pacific inflow into the caribbean

recent glacier variations at the aconcagua basin central chilean andes the majority of glaciers in central chile have receded in recent decades from 50 m to only a few meters per year mainly in response to an increase in the 08c isotherm altitude the aconcagua river basin 338 s is one of the major glaciated basins in central chile with 121 km 2 of ice in 2003 an earlier inventory using 1955 aerial photographs yielded a total surface area of 151 km 2 implying a reduction in glacier area of 20 0 63 km 2 a 1 over the 48 years photographic stereo models high resolution satellite images landsat aster and srtm data have been used to delineate glacier basins a focus on glaciar juncal norte one of the largest glaciers in the basin allows a more detailed analysis of changes the glacier has exhibited a smaller reduction 14 between 1955 and 2006 and the resulting elevation changes over this smaller period are not significant the above reduction rates are lower than in other glaciers of central chile and argentina this trend emphasizes water runoff availability in a river where most of the water in the dry summers is generated by glaciers and snowpack and where most of the superficial water rights are already allocated ongoing hydrological research including modelling of future water runoff will improve our understanding