manifestations and mechanisms of the karakoram glacier anomaly global scale glacier shrinkage is one of the most prominent signs of ongoing climatic change however important differences in glacier response exist at the regional scale and evidence has accumulated that one particular region stands out the karakoram in the past two decades the region has shown balanced to slightly positive glacier budgets an increase in glacier ice flow speeds stable to partially advancing glacier termini and widespread glacier surge activity this is in stark contrast to the rest of high mountain asia where glacier retreat and slowdown dominate and glacier surging is largely absent termed the karakoram anomaly recent observations show that the anomalous glacier behaviour partially extends to the nearby western kun lun and pamir several complementary explanations have now been presented for the anomaly s deeper causes but our understanding is far from complete whether the anomaly will continue to exist in the coming decades remains unclear but its long term persistence seems unlikely in light of the considerable warming anticipated by current projections of future climate glaciers in the karakoram region with their balanced or slightly positive mass balance stand out from global glacier shrinkage but this anomaly is not expected to persist in the long term according to an overview of the possible explanations

sea level pressure variability around antarctica since a d 1750 inferred from subantarctic tree ring records a tree ring chronology network recently developed from the subantarctic forests provides an opportunity to study long term climatic variability at higher latitudes in the southern hemisphere fifty long 1911 1985 homogeneous records of monthly mean sea level pressure mslp from the southern latitudes 15 65 s were intercorrelated on a seasonal basis to establish the most consistent long term trans polar teleconnections during this century variations in summer mslp between the south america antarctic peninsula and the new zealand sectors of the southern ocean are significantly correlated in a negative sense r 0 53 p 0 001 climatically sensitive chronologies from tierra del fuego 54 55 and new zealand 39 47 were used to develop verifiable reconstructions of summer november to february mslp for both sectors of the southern ocean these reconstructions which explain between 37 and 43 of the instrumentally recorded pressure variance indicate that inverse trends in mslp from diametrically opposite sides of antarctica have prevailed during the past two centuries however the strength of this relationship varies over time differences in normalized mslp between the new zealand and the south america antarctic peninsula sectors were used to develop a summer trans polar index stpi which represents an index of sea level pressure wavenumber one in the southern hemisphere higher latitudes tree ring based reconstructions of stpi show significant differences in large scale atmospheric circulation between the nineteenth and the twentieth centuries predominantly negative stpi values during the nineteenth century are consistent with more cyclonic activity and lower summer temperatures in the new zealand sector during the 1800s in contrast cyclonic activity appears to have been stronger in the mid twentieth than previously for the south american sector of the southern ocean recent variations in mslp in both regions are seen as part of the long term dynamics of the atmosphere connecting opposite sides of antarctica a detailed analysis of the mslp and stpi reconstructions in the time and frequency domains indicates that much of the interannual variability is principally confined to frequency bands with a period around 3 3 3 6 y cross spectral analysis between the stpi reconstruction and the southern oscillation index suggests that teleconnections between the tropical ocean and extra tropical mslp variations may be influencing climate fluctuations at southern latitudes

high latitude forcing of the south american summer monsoon during the last glacial the climate of the last glacial period 10 000 to 110 000 years ago was characterized by rapid millennial scale climate fluctuations termed dansgaard oeschger d o and heinrich events we present results from a speleothem derived proxy of the south american summer monsoon sasm from 16 000 to 50 000 years ago that demonstrate the occurrence of d o cycles and heinrich events this tropical southern hemisphere monsoon reconstruction illustrates an antiphase relationship to northern hemisphere monsoon intensity at the millennial scale our results also show an influence of antarctic millennial scale climate fluctuations on the sasm this high resolution precisely dated tropical precipitation record can be used to establish the timing of climate events in the high latitudes of the northern and southern hemispheres

cyclic rapid warming on centennial scale revealed by a 2650 year stalagmite record of warm season temperature 1 a 2650 year bc665 ad1985 warm season mjja may june july august temperature reconstruction is derived from a correlation between thickness variations in annual layers of a stalagmite from shihua cave beijing china and instrumental meteorological records observations of soil co2 and drip water suggest that the temperature signal is amplified by the soil organism co2 system and recorded by the annual layer series our reconstruction reveals that centennial scale rapid warming occurred repeatedly following multicentenial cooling trends during the last millennia these results correlate with different records from the northern hemisphere indicating that the periodic alternation between cool and warm periods on a sub millennial scale had a sub hemispherical influence

contrasting patterns of early twenty first century glacier mass change in the himalayas glaciers are among the best terrestrial climate indicators an important water resource in mountains1 2 and a major contributor to global sea level rise3 4 in the hindu kush karakoram himalaya region hkkh a paucity of appropriate glacier data has prevented a comprehensive assessment of current regional mass balance5 however there are indirect evidences of a complex pattern of glacial responses5 8 in reaction to heterogeneous climate change signals9 here we provide the first coherent data set of detailed glacier thickness changes over the hkkh during 2003 2009 by combining satellite laser altimetry and a global elevation model in the eastern central and south western parts of the hkkh glacier wastage is widespread with regional thinning rates up to 0 66 0 09 m a 1 in the jammu kashmir region conversely in the karakoram glaciers are close to balance with only a slight thinning of 0 07 0 04 m a 1 regionally averaged thinning rates under debris mantled ice are similar to those of clean ice despite insulation by debris covers the 2003 2008 specific mass balance for our hkkh study region is 0 21 0 05 m a 1 water equivalent we significantly less negative than the global average of 0 7 m a 1 we for glaciers and ice caps4 10 this difference is mainly an effect of the balanced glacier mass budget in the karakoram the corresponding hkkh sea level contribution is 0 035 0 009 mm a 1 amounting to 1 of the present day sea level rise11 our 2003 2008 mass budget of 12 8 3 5 gt a 1 is more negative than recent satellite gravimetry based estimates of 5 6 gt a 1 over 2003 2010 ref 12 for the mountain catchments of the indus and ganges basins13 the glacier imbalance contributes 3 5 and 2 0 respectively to the annual average river discharge13 and up to 10 for the upper indus basin14

response of debris covered glaciers in the mount everest region to recent warming and implications for outburst flood hazards abstract in areas of high relief many glaciers have extensive covers of supraglacial debris in their ablation zones which alters both rates and spatial patterns of melting with important consequences for glacier response to climate change wastage of debris covered glaciers can be associated with the formation of large moraine dammed lakes posing risk of glacier lake outburst floods glofs in this paper we use observations of glaciers in the mount everest region to present an integrated view of debris covered glacier response to climate change which helps provide a long term perspective on evolving glof risks in recent decades debris covered glaciers in the everest region have been losing mass at a mean rate of 0 32 m yr 1 although in most cases there has been little or no change in terminus position mass loss occurs by 4 main processes 1 melting of clean ice close to glacier elas 2 melting beneath surface debris 3 melting of ice cliffs and calving around the margins of supraglacial ponds and 4 calving into deep proglacial lakes modelling of processes 1 and 2 shows that everest region glaciers typically have an inverted ablation gradient in their lower reaches due to the effects of a down glacier increase in debris thickness mass loss is therefore focused in the mid parts of glacier ablation zones causing localised surface lowering and a reduction in downglacier surface gradient which in turn reduce driving stress and glacier velocity so the lower ablation zones of many glaciers are now stagnant model results also indicate that increased summer temperatures have raised the altitude of the rain snow transition during the summer monsoon period reducing snow accumulation and ice flux to lower elevations as downwasting proceeds formerly efficient supraglacial and englacial drainage networks are broken up and supraglacial lakes form in hollows on the glacier surface ablation rates around supraglacial lakes are typically one or two orders of magnitude greater than sub debris melt rates so extensive lake formation accelerates overall rates of ice loss most supraglacial lakes are perched above hydrological base level and are susceptible to drainage if they become connected to the englacial drainage system speleological surveys of conduits show that large englacial voids can be created by drainage of warm lake waters along pre existing weaknesses in the ice roof collapses can open these voids up to the surface and commonly provide the nuclei of new lakes thus by influencing both lake drainage and formation englacial conduits exert a strong control on surface ablation rates an important threshold is crossed when downwasting glacier surfaces intersect the hydrological base level of the glacier base level lakes formed behind intact moraine dams can grow monotonically and in some cases can pose serious glof hazards glacier termini can evolve in different ways in response to the same climatic forcing so that potentially hazardous lakes will form in some situations but not others additionally the probability of a flood is not simply a function of lake volume but depends on the geometry and structure of the dam and possible trigger mechanisms such as ice or rockfalls into the lake satellite based measurements of glacier surface gradient and ice velocities allow probable future locations of base level lakes to be identified a base level lake has begun to grow rapidly on ngozumpa glacier west of mount everest and could attain a volume of 10 8 m 3 within the next 2 or 3 decades unless mitigation efforts are undertaken this lake could pose considerable glof hazard potential

repeated cfc sections at the greenwich meridian in the weddell sea 1 repeated observations of the tracer chlorofluorocarbon 11 cfc 11 for a section along the greenwich meridian from antarctica 70 s to about 50 s are presented for the period 1984 1998 the cfc sections display a highly persistent pattern a middepth cfc minimum in the central weddell sea is bounded laterally by elevated levels of dissolved cfcs at the southern margin of the weddell basin and by a column of elevated cfc concentrations around 55 s near to the northern margin part of the latter column covers waters of the antarctic circumpolar current which indicates that a moderate portion of these waters was ventilated in the weddell sea deep cfc maxima adjoining the southern and northern margins of the weddell basin indicate advective cores of recently ventilated waters the southern core supports previous notions of deep water import into the weddell sea from the east for all deep and bottom waters the portions ventilated on the cfc timescale 50 years are small effective initial cfc saturations for these portions are estimated to be between 60 and 70 using in part new data from off the filchner ronne ice shelf for various cfc features along the section mostly advective cores ventilated fractions and mean ages of these fractions were obtained with error limits the procedure was to fit an age distribution of a prescribed form to cfc 11 time series for these features constructed from the various realizations of the cfc section the ages are between 3 and 19 years and the ventilated fractions range between 6 and 23 indicating a rather limited ventilation of the interior weddell sea subsurface layer waters on the cfc timescale it is shown that the concurrent cfc 12 data provide little additional information the work demonstrates a high information content of repeated tracer observations and encourages similar approaches also in other ocean regions

drought reconstructions for the continental united states abstract the development of a 2 lat 3 long grid of summer drought reconstructions for the continental united states estimated from a dense network of annual tree ring chronologies is described the drought metric used is the palmer drought severity index pdsi the number of grid points is 154 and the reconstructions cover the common period 1700 1978 in producing this grid an automated gridpoint regression method called point by point regression was developed and tested in so doing a near optimal global solution was found for its implementation the reconstructions have been thoroughly tested for validity using pdsi data not used in regression modeling in general most of the gridpoint estimates of drought pass the verification tests used in addition the spatial features of drought in the united states have been faithfully recorded in the reconstructions even though the method of reconstruction is not explicitly spatial in its design the drought reconstructions show that the 1930s dust bow

dynamics of the intertropical convergence zone over the western pacific during the little ice age precipitation patterns in the western pacific changed at the onset of the little ice age a synthesis of precipitation reconstructions suggests that this change resulted from a contraction of the intertropical convergence zone

response of karakoram himalayan glaciers to climate variability and climatic change a regional climate model assessment the karakoram and the himalayan mountain range accommodate a large number of glaciers and are the major source of several perennial rivers downstream to interactively describe to response of glaciers to climate change a glacier parameterization scheme has been developed and implemented into the regional climate model remo the scheme simulates the mass balance as well as changes of the areal extent of glaciers on a subgrid scale the parameterization scheme is for the first time applied to the region a regional glacier inventory is compiled and is used to initialize glacier area and volume over the highly complex and data sparse region the simulated mass balance largely agrees with observations including the positive karakoram anomaly the simulated equilibrium line altitude is well captured although a systematic underestimation is apparent remo simulates the glacier climate interaction reasonably well it has clear potential to be used for future climate assessments

mass balance studies on siachen glacier in the nubra valley karakoram himalaya india the hydrological method is used to compute the mass balance of siachen glacier in the nubra valley karakoram himalaya india the method was chosen because of its suitability in rugged terrain analysis of precipitation data from the glacier as a function of altitude shows a power law relationship accumulation estimates based on this relationship show good agreement with the recorded precipitation the discharge data from the glacier show high runoff in the ablation seasons of 1986 87 1987 88 1989 90 and 1990 91 the mass balance calculations for these years are negative the lowest being in 1990 91 1084 mm positive mass balance in 1988 89 358 mm is attributed to comparatively heavy winter snowfall amounts and comparatively low temperatures during the ablation season significantly lower runoff was measured during this season negative mass balance values during 1989 90 and 1990 91 are a result of comparatively dry winters and comparatively warm ablation periods with monthly mean air temperatures 1 4 5 1 c higher at the beginning of the ablation season june and july than the mean of the last 5 years

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

rock avalanches that travel onto glaciers and related developments karakoram himalaya inner asia abstract catastrophic rock slope failures in rugged terrain commonly generate rock avalanches when these occur in glacier basins the extent of landslide run out and its emplacement geometry are affected by movement over ice substantial modifications of glacier activity and sedimentation can follow ice activity leads to rapid modification transport and dispersal of landslide debris the nature of these interactions is described from observations over 20 years at bualtar glacier in the karakoram in august 1986 rock avalanches descended onto the ablation zone of the glacier their moisture content and patterns of deposition were affected by travel over ice glacier movement increased sharply at and below the rock avalanche deposits and within a few months the glacier surged a second surge occurred 2 years later major slope failures and debris flows were triggered beyond the ice margins and ponded melt water led to small outburst floods by 2005 the landslide material had been transported some 9 km about one third of this distance in the surges eventually it was fully reworked to become less readily distinguishable from other heavy supraglacial debris a large area of thickened ice persisted where the debris reduced ablation a positive impact on mass balance equivalent to a 20 increase in annual accumulation however it occurred as a moving segment of the ablation zone in 10 years it had in effect replaced the mass transferred in the surges data for the mid 1980s indicate the rock avalanches exceeded pre existing supraglacial debris by roughly five times and over a 30 year period will equal almost 500 years of normal supraglacial transport to the glacier margins other impacts of the episode suggest a doubling of this contribution to denudation similar developments were observed at three other glaciers where recent rock avalanches occurred and at twenty one prehistoric rock avalanches newly identified as having spread over glaciers it seems inadequate to treat such events only as singular extremes or the landslide and glacial processes separately here they are interpreted as contributing to disturbance regime landscapes whose history reflects episodic and regionally specific responses to strong interference among different earth surface processes they generate polygenetic deposits and landforms that are morphologically complex individual episodes involve decades to millennia their numbers and repetition can over ride or redirect geotectonic and climatic conditions it is suggested they are major but hitherto misread or neglected elements of landform evolution in the karakoram and perhaps in other high mountains

interhemispheric anti phasing of rainfall during the last glacial period abstract we have obtained a high resolution oxygen isotopic record of cave calcite from caverna botuvera 27 13 s 49 09 w southern brazil which covers most of the last 36 thousand years ka with an average resolution of a few to several decades the chronology was determined with 46 u th ages from two stalagmites tests for equilibrium conditions show that oxygen isotopic variations are primarily caused by climate change we interpret our record in terms of meteoric precipitation changes hence the variability of south american monsoon sam intensity the oxygen isotopic profile broadly follows local insolation changes and shows clear millennial scale variations during the last glacial period with amplitudes as large as 3 but with smaller centennial scale shifts 1 during the holocene the overall record is strikingly similar to but strongly anti correlated with a number of records from the northern hemisphere we compared our record to other precisely dated contemporaneous records from hulu cave eastern china minima in 18o wet periods intense sam at our site are synchronous with maxima in 18o dry periods weak east asian monsoon eam in eastern china within precise dating errors and vice versa this anti phased precipitation relationship between two low latitude locations may be interhemispheric in extent based on comparison with records from other sites precipitation anti phasing may be related to north south shifts in the mean position of the intertropical convergence zone itcz and asymmetry in hadley circulation in two hemispheres associated not with seasonal changes as observed today but with millennial scale climate shifts the millennial scale atmospheric see saw patterns that we observe could have important controls and feedbacks on climate within hemispheres because of water vapor s greenhouse properties

southward movement of the pacific intertropical convergence zone ad 1400 1850 tropical rainfall patterns control the subsistence lifestyle of more than one billion people seasonal changes in these rainfall patterns are associated with changes in the position of the intertropical convergence zone which is characterized by deep convection causing heavy rainfall near 10 n in boreal summer and 3 n in boreal winter dynamic controls on the position of the intertropical convergence zone are debated but palaeoclimatic evidence from continental asia africa and the americas suggests that it has shifted substantially during the past millennium reaching its southernmost position some time during the little ice age ad1400 1850 however without records from the meteorological core of the intertropical convergence zone in the pacific ocean quantitative constraints on its position are lacking here we report microbiological molecular and hydrogen isotopic evidence from lake sediments in the northern line islands galapagos and palau indicating that the pacific intertropical convergence zone was south of its modern position for most of the past millennium by as much as 500km during the little ice age a colder northern hemisphere at that time possibly resulting from lower solar irradiance may have driven the intertropical convergence zone south we conclude that small changes in earth s radiation budget may profoundly affect tropical rainfall

renewal and circulation of intermediate waters in the canadian basin observed on the scicex 96 cruise during the summer of 1996 the nuclear submarine uss pogy occupied a line of stations extending through the middle of the canadian basin between about 88 n 44 w lomonosov ridge and about 78 n 144 w center of the canada basin ctd niskin bottle casts extending to 1600 m were carried out at eight stations providing the first high quality temperature salinity cfc tritium and 3he data obtained from this region although xctd data had previously been collected in this region these data along with data from stations at the basin boundary to the south and west reveal the presence of well ventilated intermediate water beneath the halocline in the center of the canada basin indicating renewal times of the order of 1 2 decades the least ventilated intermediate water was observed at the northern end of the canada basin along the southern flank of the alpha ridge intermediate water is derived from the atlantic ocean and enters the arctic ocean through fram strait and the barents sea it flows around the arctic basins in boundary currents and splits in the eastern amundsen basin with one branch crossing the lomonosov ridge and flowing along the east siberian continental slope and the other flowing along the eurasian flank of the lomonosov ridge from the 1996 scientific ice expedition scicex 96 observations we conclude that the branch that flows along the east siberian continental slope transports this water to the chukchi rise where it apparently enters the central canada basin with some flow continuing along the boundary to the southern canada basin the fram strait branch water mixes extensively with waters from the canadian basin during its transit along the east siberian continental slope being diluted by a factor of about 5 by the time it reaches the central canada basin the barents sea branch water does not undergo such extensive mixing and is diluted by a factor of only about 2 when it reaches the central canada basin

ice ablation and meteorological conditions on the debris covered area of baltoro glacier karakoram pakistan during the recent italian expedition k2 2004 50 years later june july 2004 on baltoro glacier karakoram pakistan glaciological field experiments were carried out on the debris covered area of this high elevation glacier the aim was to investigate the ice ablation and its relations with debris thermal properties and meteorological conditions ablation measurements along the glacier up to about 5000 m and within a dedicated test field were combined with meteorological data from two automatic weather stations located at urdukas 4022 m a s l and at k2 base camp 5033 m a s l in addition temperature measurements of the debris cover at different depth levels along the glacier allowed the calculation of debris surface temperature and of the debris thermal resistance r using the air temperature the local mean lapse rate 0 00758 cm 1 and the measured ablation the degree day factors k at different locations on the glacier were calculated the ice ablation rates were related to debris thickness and elevation they are typically on the order of 4 cm d 1 during the observation period however it was found that the surface topography slope aspect has an influence on the total ablation similar to that of the debris thickness thermal resistance of the debris cover and its distribution over the glacier were estimated finally a best guess estimate of the total meltwater production was calculated from available climate data

sea level pressure variability over the southern indian ocean inferred from a glaciochemical record in princess elizabeth land east antarctica 1 a 250 year high resolution multivariate ice core record from lgb65 70 50 07 s 77 04 29 e 1850 m asl princess elizabeth land pel is used to investigate sea level pressure slp variability over the southern indian ocean sio empirical orthogonal function eof analysis reveals that the first eof eof1 of the glaciochemical record from lgb65 represents most of the variability in sea salt throughout the 250 year record eof1 is negatively correlated 95 confidence level and higher to instrumental mean sea level pressure mslp at kerguelen and new amsterdam islands sio on the basis of comparison with ncep ncar reanalysis strong correlations were found between sea salt variations and a quasi stationary low that lies to the north of prydz bay sio comparison with a 250 year long summer transpolar index stpi inferred from sub antarctic tree ring records reveals strong coherency decadal scale slp variability over sio suggests shifting of the polar vortex prominent decadal scale deepening of the southern indian ocean low siol exists circa 1790 1810 1835 1860 1880 1900 and 1940 a d continuously after the 1970s and prominent weakening circa 1750 1795 1825 1850 1870 1890 1910 and 1955 a d the lgb65 sea salt record is characterized by significant decadal scale variability with a strong 21 year periodic structure 99 9 confidence level the relationship between lgb65 sea salt and solar irradiance changes shows that this periodicity is possibly the solar hale cycle 22 years

a new transient tracer measured vertical distribution of ccl2fcclf2 f 113 in the north pacific subarctic gyre the first quantitative marine measurements of trichlorotrifluoroethane f 113 were made in the north pacific subarctic gyre in july of 1986 using a modification of the analytical procedure developed for the transient tracers f 11 and f 12 gammon et al 1982 wisegarver and cline 1985 the measured mixed layer concentration was 0 29 0 02 pm l the corresponding atmospheric mixing ratio was 35 1 pptv rasmussen scale below a subsurface maximum both f 11 and f 113 were found to fall off exponentially with increasing depth f 113 reaching effective blank levels first the significance of adding f 113 to the existing suite of measurable oceanic transient tracers rests in the possibility of age dating water masses by their f 113 f 11 ratio with near annual resolution for the period since 1977

the distribution of tritium and cfcs in the weddell sea during the mid 1980s abstract transient tracer data tritium cfc11 and cfc12 from the southern central and northwestern weddell sea collected during polarstern cruises ant iii 3 ant v 2 3 4 and during andenes cruise nare 85 are presented and discussed in the context of hydrographic observations a kinematic time dependent multi box model is used to estimate mean residence times and formation rates of several water masses observed in the weddell sea ice shelf water is marked by higher tritium and lower cfc concentrations compared to surface waters the tracer signature of ice shelf water can only be explained by assuming that its source water mass western shelf water has characteristics different from those of surface waters using the transient nature of tritium and the cfcs the mean residence time of western shelf water on the shelf is estimated to be approximately 5 years ice shelf water is renewed on a time scale of about 14 years from western shelf water by interaction of this water mass with glacial ice underneath the filchner ronne ice shelf the ice shelf water signature can be traced across the sill of the filchner depression and down the continental slope of the southern weddell sea on the continental slope new weddell sea bottom water is formed by entrainment of weddell deep water and weddell sea deep water into the ice shelf water plume in the northwestern weddell sea new weddell sea bottom water is observed in two narrow deep boundary currents flowing along the base of the continental slope classically defined weddell sea bottom water 0 7 c and weddell sea deep water 0 7 c 0 c are ventilated from the deeper of these boundary currents by lateral spreading and mixing model based estimates yield a total formation rate of 3 5sv for new weddell sea bottom water 1 0 c and a formation rate of at least 11sv for antarctic bottom water 0 5 c

chlorofluoromethanes in the northeast pacific ocean measured vertical distributions and application as transient tracers of upper ocean mixing the vertical distributions of the man made chlorofluoromethanes ccl3f f 11 and ccl2f2 f 12 have been measured at two locations in the eastern north pacific ocean to depths greater than 500 m at both sites 46 n 125 w off the washington oregon coast and 50 n 140 w in the gulf of alaska the halomethane concentrations were found to fall off exponentially with increasing depth below the mixed layer for f 11 at 50 n the surface concentration 3 2 10 12 mol l was found to be in saturation equilibrium with the measured atmospheric concentration 190 pptv the measured chlorofluoromethane profiles have been interpreted in terms of a one dimensional model for the vertical diffusion advection of an exponentially driven conservative tracer into a bottomless ocean in the appropriate limit of transient steady state the projected profiles are simple exponentials described by an advective diffusive scale depth h which is a function of the vertical eddy diffusivity kz the upwelling velocity w and the characteristic time for the exponential growth of the tracer concentration at the boundary at the two ocean locations studied the freon thermocline depth scales were in the range h 120 140 m with f 12 generally 10 20 deeper than f 11 at 50 n the f 11 and f 12 vertical profiles gave consistent values of vertical diffusivity kz 1 2 1 3 cm2 s 1 and upwelling velocity w 12 14 m yr 1 the model also allows a simple scaling from one exponentially driven transient tracer freon to another fossil fuel co2 leading to a predicted mean depth of penetration of fossil fuel co2 of approximately 300 m in the eastern north pacific

how much do we really know about glacier surging some of the ideas about glacier surging are considered mainly but not entirely in the light of observations of temperate glaciers in alaska u s a made within the last 15 years climate has an influence on surge recurrence interval climate and weather also affect surge initiation termination and magnitude regional studies lead to the speculation that subglacial till plays a key role in surging and it has been found under all surge type glaciers studied so far including black rapids and variegated glaciers alaska in most of the glaciers studied till deformation processes dominate the motion in quiescence the linked cavity model of surge triggering and rapid motion is not consistent with these observations but the limited coverage of the observations does not rule it out under parts of the glaciers studied the till observations in alaska raise old questions about the interaction between till and the hydraulic systems of temperate glaciers the role of stored water which observations show to be active even in winter on black rapids glacier is noted

glacial interglacial water cycle global monsoon and atmospheric methane changes the causes of atmospheric methane ch4 changes are still a major contention in particular with regards to the relative contributions of glacial interglacial cycles monsoons in both hemispheres and the late holocene human intervention here we explore the ch4 signals in the antarctic epica dome c and vostok ice records using the methods of timeseries analyses and correlate them with insolation and geological records to address these issues the results parse out three distinct groups of ch4 signals attributable to different drivers the first group 80 variance well tracking the marine 18o record is attributable to glacial interglacial modulation on the global water cycle with the effects shared by wetlands at all latitudes from monsoonal and non monsoonal regions in both hemispheres the second group 15 variance centered at the 10 kyr semi precession frequency is linkable with insolation driven tropical monsoon changes in both hemispheres the third group 5 variance marked by millennial frequencies is seemingly related with the combined effect of ice volume and bi hemispheric insolation changes at the precession bands these results indicate that bi hemispheric monsoon changes have been a constant driver of atmospheric ch4 this mechanism also partially explains the holocene ch4 reversal since 5 kyr bp besides the human intervention in the light of these results we propose that global monsoon can be regarded as a system consisting of two main integrated components one primarily driven by the oscillations of inter tropical convergence zone itcz in response to the low latitude summer insolation changes anti phase between the two hemispheres i e the itcz monsoon component and another modulated by the glacial interglacial cycles mostly synchronous at the global scale i e the glacial interglacial monsoon component although atmospheric ch4 record integrates all wetland processes including significant non monsoonal contributions it is the only and probably the best proxy available to reflect the past changes of global monsoon however the utility of ch4 as a proxy of monsoon changes at any specific location is compromised by its bi hemispheric nature

deep water renewal in lake issyk kul 1 the deep water renewal rates of lake issyk kul are studied using the time dependent anthropogenically produced tracers sulfur hexafluoride sf 6 chlorofluorocarbons cfcs and tritium helium 3 sf 6 and the cfcs are used to calibrate a mixing model from which the vertical age distribution is calculated and found to be comparable to the sf 6 apparent ages based on this model the mean age of the water below 100 m depth is 6 1 yrs the mean oxygen consumption rate for the same depth range is 6 4 mol kg 1 yr 1 and the mean remineralization rates for nitrate phosphate and silicate are 0 53 0 003 and 0 67 mol kg 1 yr 1 respectively

glacier velocities across the central karakoram optical matching of aster advanced spaceborne thermal emission and reflection radiometer satellite image pairs is used to determine the surface velocities of major glaciers across the central karakoram the aster images were acquired in 2006 and 2007 and cover a 60 120 km region over baltoro glacier pakistan and areas to the north and west the surface velocities were compared with differential global position system gps data collected on baltoro glacier in summer 2005 the aster measurements reveal fine details about ice dynamics in this region for example glaciers are found to be active over their termini even where they are very heavily debris covered the characteristics of several surge type glaciers were measured with terminus advances of several hundred meters per year and the displacement of trunk glaciers as surge glaciers pushed into them this study is the first synthesis of glacier velocities across this region and provides a baseline against which both past and future changes can be compared

basin wide circulation and ventilation study in the east sea sea of japan using chlorofluorocarbon tracers abstract near synoptic basin wide distributions of the chlorofluorocarbon cfc tracers were observed during the summer of 1999 in the east sea sea of japan to study its circulation and ventilation the cfcs penetrate throughout the water column and the bottom water bw cfc concentrations have increased over measurements made in 1995 and 1996 indicating a continuous weak renewal of deep waters in the east sea during this recent period the cfc 11 water column inventory estimated in 1999 2000 5500 nmol m 2 is substantially higher than that of the adjacent north pacific ocean a striking anticorrelation between the bw dissolved oxygen and cfc concentrations in the japan basin is attributed to more active vertical mixing along the basin boundary a dynamically isolated deep eastern japan basin and recent changes in deep water ventilation the bw of the eastern japan basin with the lowest cfc content is the oldest water parcel in the east sea although it is colder and contains higher oxygen concentration than the surrounding bw active entrainment of overlying deep water is inferred from the unexpectedly higher bw cfc concentrations in the yamato basin this may explain why the yamato basin bw is warmer and less oxygenated than the other basins in the east sea although it is believed to be a terminus of the ventilated dws mesoscale anticyclonic eddies which have been fused with other deeply convected waters in the northwestern east sea seem to play an important role in transferring surface water properties to depths greater than 2500 m the subsurface cfc maximum centered within the typical east sea intermediate water esiw layer is more widely distributed south of the subpolar front than previously reported the esiw consists primarily of the colder and fresher winter surface water in the northern region that has subducted below the subpolar front

definition of antarctic oscillation index following walker s work about his thmous three oscillations published during the 1920 30s many papers were written about atmospheric oscillations a iburth atmospheric oscillation in the middle and high southern latitudes was lbund and nanted the grotarctic oscillation ao a refiers to a large scale alternation of atmospheric mass between the mid latitudes and high latitudes surthce pressure in order to understand the spatial structure of sea level pressure variation in detail empirical orthogonal fitnction analysis is applied an objective index of the antarctic oscillation index aoi is defined as the diffierence of zonal mean sea level pressure between 40os and 65os the aoi has the potential tbr clarifying climate regimes in the southern hemisphere similar to how the na and the npo has been used in the northern hemisphere were there other oscillation s besides nao npo and s especially in the southern hemisphere it had been supposed that there might be other atmospheric oscillation s in the high southern latitudes although as early as in the first quarter of this century walker 1928 had stated that just as in the north atlantic there is a pressure opposition between the azores and iceland there is an opposition between the high pressure belt across chile and the argentine on the one hand and the low pressure area of weddell sea and the bellingshausen sea on the other the scarcity of data in the southern hemisphere hindered the search tbr new oscillation s during the last two decades more comprehensive data over the southern hemisphere became available and more analyses were carried out see kidson 1975 rogers and van loon 1982 mo and l 7 ite 1985 2 4o 1986 connolley 1997 gong and wang 1998 a tburth atmospheric oscillation in the middle and high southern latitudes was tbund and nanted as the antarctic oscillation a wang 1992 gong and wang 1998 the term ao relrs to a large scale alternation of atmospheric mass between the mid latitude sur hce pressure

can tree ring density data reflect summer temperature extremes and associated circulation patterns over fennoscandia tree ring maximum latewood density mxd records from fennoscandia have been widely used to infer regional and hemispheric scale mean temperature variability here we explore if mxd records can also be used to infer past variability of summer temperature extremes across fennoscandia the first principal component pc1 based on 34 mxd chronologies in fennoscandia explains 50 of the total variance in the observed warm day extremes over the period 1901 1978 variations in both observed summer warm day extremes and pc1 are influenced by the frequency of anomalous anticyclonic pattern over the region summer sea surface temperatures over the baltic north and norwegian seas and the strength of the westerly zonal wind at 200 hpa across fennoscandia both time series are associated with nearly identical atmospheric circulation and sst patterns according to composite map analysis in a longer context the first pc based on 3 millennium long mxd chronologies in central and northern fennoscandia explains 83 of the total variance of pc1 from the 34 mxd chronologies over the period 1901 1978 48 of the total variance of the summer warm day extreme variability over the period 1901 2006 and 36 of the total variance in the frequency of a summer anticyclonic pattern centered over eastern central fennoscandia in the period 1948 2006 the frequency of summer warm day extremes in fennoscandia is likely linked to a meridional shift of the northern mid latitude jet stream this study shows that the mxd network can be used to infer the variability of past summer warm day extremes and the frequency of the associated summer anticyclonic circulation pattern over fennoscandia

glaciological characteristics of the ablation zone of baltoro glacier karakoram pakistan baltoro glacier in the karakoram pakistan is one of the world s largest valley glaciers it drains an area of about 1500 km 2 and is 60km long in 2004 an italian german expedition carried out a glaciological field program on the ablation zone of the glacier focusing on the ablation conditions and the dynamic state of the glacier as baltoro glacier is a debris covered glacier ice ablation also depends on the debris properties stake measurements of ice ablation and debris cover in combination with meteorological data from automatic weather stations close by have been used to determine the local melt conditions results from these calculations have been combined with an analysis of different classes of surface cover and information about precipitation using remote sensing techniques in order to calculate mass fluxes for the upper part of baltoro glacier the dynamic state of the glacier has been investigated by gps based surface velocity measurements along the stake network a comparison of these short term measurements during the melt season with surface velocities computed from feature tracking of satellite images shows a high seasonal variability of the ice motion we have shown that this variability is up to 100 of the annual mean velocity on the basis of these investigations the mass fluxes at the concordia cross section have been quantified this approach can now be used together with the ablation calculations to reconstruct the variability of glacier extent and volume in the past using available climate data from the central karakoram from the comparison of historical measurements and photographs it is shown that the snout of baltoro glacier is oscillating back and forth a couple of hundred metres otherwise it seems not to react with the same magnitude as other glaciers to the climatic change elevation changes at concordia are a few tens of metres at the most

tropical climate changes at millennial and orbital timescales on the bolivian altiplano tropical south america is one of the three main centres of the global zonal overturning circulation of the equatorial atmosphere generally termed the walker circulation1 although this area plays a key role in global climate cycles little is known about south american climate history here we describe sediment cores and down hole logging results of deep drilling in the salar de uyuni on the bolivian altiplano located in the tropical andes we demonstrate that during the past 50 000 years the altiplano underwent important changes in effective moisture at both orbital 20 000 year and millennial timescales long duration wet periods such as the last glacial maximum marked in the drill core by continuous deposition of lacustrine sediments appear to have occurred in phase with summer insolation maxima produced by the earth s precessional cycle short duration millennial events correlate well with north atlantic cold events including heinrich events 1 and 2 as well as the younger dryas episode at both millennial and orbital timescales cold sea surface temperatures in the high latitude north atlantic were coeval with wet conditions in tropical south america suggesting a common forcing

continental scale temperature variability during the past two millennia past global climate changes had strong regional expression to elucidate their spatio temporal pattern we reconstructed past temperatures for seven continental scale regions during the past one to two millennia the most coherent feature in nearly all of the regional temperature reconstructions is a long term cooling trend which ended late in the nineteenth century at multi decadal to centennial scales temperature variability shows distinctly different regional patterns with more similarity within each hemisphere than between them there were no globally synchronous multi decadal warm or cold intervals that define a worldwide medieval warm period or little ice age but all reconstructions show generally cold conditions between ad 1580 and 1880 punctuated in some regions by warm decades during the eighteenth century the transition to these colder conditions occurred earlier in the arctic europe and asia than in north america or the southern hemisphere regions recent warming reversed the long term cooling during the period ad 1971 2000 the area weighted average reconstructed temperature was higher than any other time in nearly 1 400 years

apparent loss of cfc 113 in the upper ocean we report and evaluate data of the chlorofluorocarbon cfc 113 in comparison with concurrent data for cfc 12 from cruises into the temperate north atlantic the tropical western pacific the eastern mediterranean and the weddell sea we consistently find cfc 113 deficiencies in the warmer upper waters which we interpret as cfc 113 depletion at rates of the order of 3 per year with possibly accelerated rates in the mixed layer or near the surface these results severely limit a tracer utility of cfc 113 in the warm upper waters of the ocean tracer applications in the deep waters of the ocean should be much less affected since cfc 113 loss in such waters appears to be far slower this also holds for the eastern mediterranean despite its rather warm deep waters for the weddell sea the data indicate a cfc 113 deficiency 20 in the shelf waters which converts into a similar deficiency in newly formed deep and bottom water such cfc 113 deficiency has to be accounted for in southern ocean tracer work future work is proposed to study cfc 113 loss in the ocean in additional detail and to elucidate the loss mechanism s on which our data give little clue

flow near submarine canyons driven by constant winds circulation over coastal submarine canyons driven by constant upwelling or downwelling wind stress is simulated and analyzed with a primitive equation ocean model astoria canyon on the west coast of north america is the focus of this study and model results are consistent with most major features of mean canyon circulation observed in astoria canyon near surface flow crosses over the canyon while a closed cyclone occurs within the canyon upwelling prevails within the canyon and is larger than wind driven upwelling along the adjacent shelf break water rises from depths reaching 300 m to the canyon rim and subsequently onto the adjacent shelf onshore flow within the canyon is driven by the onshore pressure gradient force due to the free surface slope created by the upwelling wind and is enhanced by the limitation to alongshore flow by the canyon topography density gradients largely compensate the surface slope with realistic stratification but continual upwelling persists near the edges of the canyon within the upper canyon 50 150 m below the canyon rim a cyclone is created by flow turning into the canyon mouth separating from the upstream edge and advecting toward the downstream rim below this layer the cyclone is created by vortex stretching due to the upwelling downwelling winds create nearly the opposite flow in which compression and momentum advection create a strong anticyclone within the canyon momentum advection is found to be important both in creating strong circulation within the canyon and in allowing the surface flow to cross the canyon undisturbed model results indicate that astoria like submarine canyons produce across shore transport of sufficient volume to flush a continental shelf in a few 2 5 years

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

an interdecadal climate dipole between northeast asia and antarctica over the past five centuries climate models emphasize the need to investigate inter hemispheric climatic interactions however these models often underestimate the inter hemispheric differences in climate change with the wide application of reanalysis data since 1948 we identified a dipole pattern between the geopotential heights gphs in northeast asia and antarctica on the interdecadal scale in boreal summer this northeast asia antarctica naa dipole pattern is not conspicuous on the interannual scale probably in that the interannual inter hemispheric climate interaction is masked by strong interannual signals in the tropics associated with the el nino southern oscillation enso unfortunately the instrumental records are not sufficiently long lasting to detect the interdecadal variability of the naa we thus reconstructed gphs since 1565 making using the proxy records mostly from tree rings in northeast asia and ice cores from antarctica the strength of the naa is time varying and it is most conspicuous in the eighteenth century and after the late twentieth century the strength of the naa matches well with the variations of the solar radiation and tends to increase in along with its enhancement in boreal summer enhanced heating associated with high solar radiation in the northern hemisphere drives more air masses from the south to the north this inter hemispheric interaction is particularly strong in east asia as a result of the asian summer monsoon northeast asia and antarctica appear to be the key regions responsible for inter hemispheric interactions on the interdecadal scale in boreal summer since they are respectively located at the front and the end of this inter hemispheric trajectory

glacial interglacial indian summer monsoon dynamics the modern indian summer monsoon ism is characterized by exceptionally strong interhemispheric transport indicating the importance of both northern and southern hemisphere processes driving monsoon variability here we present a high resolution continental record from southwestern china that demonstrates the importance of interhemispheric forcing in driving ism variability at the glacial interglacial time scale as well interglacial ism maxima are dominated by an enhanced indian low associated with global ice volume minima in contrast the glacial ism reaches a minimum and actually begins to increase before global ice volume reaches a maximum we attribute this early strengthening to an increased cross equatorial pressure gradient derived from southern hemisphere high latitude cooling this mechanism explains much of the nonorbital scale variance in the pleistocene ism record