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

vertical mixing in the ocean the thermohaline circulation of the ocean results primarily from downwelling at sites in the nordic and labrador seas and upwelling throughout the rest of the ocean the latter is often described as being due to breaking internal waves here we reconcile the difference between theoretical and observed estimates of vertical mixing in the deep ocean by presenting a revised view of the thermohaline circulation which allows for additional upwelling in the southern ocean and the separation of the north atlantic deep water cell from the antarctic bottom water cell the changes also mean that much less wind and tidal energy needs to be dissipated in the deep ocean than was originally thought

retreat of glaciers on puncak jaya irian jaya determined from 2000 and 2002 ikonos satellite images puncak jaya irian jaya indonesia contains the only remaining tropical glaciers in east asia the extent of the ice masses on puncak jaya has been mapped from high resolution ikonos satellite images acquired on 8 june 2000 and 11 june 2002 exclusive of southwall hanging glacier the ice extent on puncak jaya was 2 326km 2 and 2 152km 2 in 2000 and 2002 respectively from 2000 to 2002 the puncak jaya glaciers lost a surface area of 0 174km 2 or 7 48 of their 2000 ice extent comparison of the ikonos based glacier extents with previous glacier extents demonstrates a continuing reduction of ice area on puncak jaya by 2000 ice extent on puncak jaya had reduced by 88 of its maximum neoglacial extent between 1992 and 2000 meren glacier disappeared entirely all remaining ice masses on puncak jaya continue their retreat from their neoglacial maxima comparison of 2000 2002 ice extents with previous extents suggests that these glaciers have not experienced accelerating rates of retreat during the last half of the 20th century if the recession rates observed from 2000 to 2002 continue the remaining ice masses on puncak jaya will melt within 50 years

solar radiation maintained glacier recession on kilimanjaro drawn from combined ice radiation geometry modeling 1 in the context of investigating modern glacier recession on kilimanjaro which began around 1880 this study addresses the glacier regime of the vertical ice walls that typically form the margins of kilimanjaro s summit glaciers these walls have suffered a continuous lateral retreat during the twentieth century to evaluate the role of solar radiation in maintaining glacier recession on kilimanjaro a radiation model is applied to an idealized representation of the 1880 ice cap the combined process based model calculates the spatial extent and geometry of the ice cap for various points in time after 1880 support for input data and fundamental assumptions are provided by an automatic weather station that has operated on the summit s northern icefield since february 2000 even in a simple climatic scenario only forced with an annual cycle of clouds the basic evolution in spatial distribution of ice bodies on the summit is modeled well the northern and southern icefields form in characteristic east west orientation which verifies the basic idea behind the model forcing the model with further climate related phenomena improves the results it then additionally reproduces the eastern icefield the third big ice entity on the summit this study qualitatively demonstrates that solar radiation is the main climatic parameter maintaining modern glacier recession on kilimanjaro summit but also suggests that retreat on the inner ice cap margin might have been supported by a secondary energy source the need for additional field measurements is emphasized in order to better understand the complex processes of glacier climate interaction on kilimanjaro index terms 1620 global change climate dynamics 3309 1827 hydrology glaciology 1863 3309 meteorology and atmospheric dynamics climatology 1620 3359 meteorology and atmospheric dynamics radiative processes 9305 information related to geographic region africa keywords tropical glaciers kilimanjaro climate change glacier retreat solar radiation modeling

global ocean meridional overturning abstract a decade mean global ocean circulation is estimated using inverse techniques incorporating air sea fluxes of heat and freshwater recent hydrographic sections and direct current measurements this information is used to determine mass heat freshwater and other chemical transports and to constrain boundary currents and dense overflows the 18 boxes defined by these sections are divided into 45 isopycnal neutral density layers diapycnal transfers within the boxes are allowed representing advective fluxes and mixing processes air sea fluxes at the surface produce transfers between outcropping layers the model obtains a global overturning circulation consistent with the various observations revealing two global scale meridional circulation cells an upper cell with sinking in the arctic and subarctic regions and upwelling in the southern ocean and a lower cell with sinking around the antarctic continent and abyssal upwelling mainly below the crests of the major bathymetric ridges

improved estimates of glacier change rates at nevado coropuna ice cap peru accurate quantification of rates of glacier mass loss is critical for managing water resources and for assessing hazards at ice clad volcanoes especially in arid regions like southern peru in these regions glacier and snow melt are crucial dry season water resources in order to verify previously reported rates of ice area decline at nevado coropuna in peru which are anomalously rapid for tropical glaciers we measured changes in ice cap area using 259 landsat images acquired from 1980 to 2014 we find that coropuna ice cap is presently the most extensive ice mass in the tropics with an area of 44 1 km 2 and has been shrinking at an average area loss rate of 0 409 km 2 a 1 0 71 a 1 since 1980 our estimated rate of change is considerably lower than previous studies 1 4 km 2 a 1 or 2 43 a 1 but is consistent with other tropical regions such as the cordillera blanca located 850 km to the nw 0 68 a 1 thus if glacier recession continues at its present rate our results suggest that coropuna ice cap will likely continue to contribute to water supply for agricultural and domestic uses until 2120 which is nearly 100 years longer than previously predicted

turbulence and diapycnal mixing in drake passage abstractdirect measurements of turbulence levels in the drake passage region of the southern ocean show a marked enhancement over the phoenix ridge at this site the antarctic circumpolar current acc is constricted in its flow between the southern tip of south america and the northern tip of the antarctic peninsula observed turbulent kinetic energy dissipation rates are enhanced in the regions corresponding to the acc frontal zones where strong flow reaches the bottom in these areas turbulent dissipation levels reach 10 8 w kg 1 at abyssal and middepths the mixing enhancement in the frontal regions is sufficient to elevate the diapycnal turbulent diffusivity acting in the deep water above the axis of the ridge to 1 10 4 m2 s 1 this level is an order of magnitude larger than the mixing levels observed upstream in the acc above smoother bathymetry outside of the frontal regions dissipation rates are o 10 10 w kg 1 comparable to the background levels of turbulence found throughout most mid and

global energy conversion rate from geostrophic flows into internal lee waves in the deep ocean a global estimate of the energy conversion rate from geostrophic flows into internal lee waves in the ocean is presented the estimate is based on a linear theory applied to bottom topography at o 1 10 km scales obtained from single beam echo soundings to bottom stratification estimated from climatology and to bottom velocity obtained from a global ocean model the total energy flux into internal lee waves is estimated to be 0 2 tw which is 20 of the global wind power input into the ocean the geographical distribution of the energy flux is largest in the southern ocean which accounts for half of the total energy flux the results suggest that the generation of internal lee waves at rough topography is a significant energy sink for the geostrophic flows as well as an important energy source for internal waves and the associated turbulent mixing in the deep ocean

experimental study on the river blockage and landslide dam formation induced by rock slides abstract rock slides triggered by strong earthquake or heavy rainfall may cause different degrees of blockage in flow channels resulting in a significant impact on the continuity of mountainous rivers based on the extent of blocking the blockage type is divided into three categories in this paper no blockage submerged dam partial blockage and complete blockage the accumulation process of sliding materials in the course of rock slides is an important issue for understanding the formation of landslide dams in this study rock slide and river valley models are developed to investigate the typical kinematic process and emplacement of rock slides and the factors that dictate the formation of landslide dams are critically analyzed the experimental study suggests that there is a positive correlation between the deposit height and the rock slide volume despite differences of rock fragmentation and flow condition in addition the less fragmented rocks result in larger maximum deposit height maxi dh and smaller minimum deposit height mini dh while the better fragmented rocks result in smaller maxi dh and larger mini dh furthermore the water depth has a significant impact on the river blockage type a new blockage index bi that combines the landslide volume and the wet cross sectional area is proposed to assess the damming capacity of rock slides then a method for predicting the river blockage type of rock slides is developed based on the relationship between blockage index and the ratio of maxi dh or mini dh and water depth the model proposed in this work can be used to assist estimating the formation of landslide dam for similar rock slides in the future

small glaciers disappearing in the tropical andes a case study in bolivia glaciar chacaltaya 16 o s glaciar chacaltaya is an easily accessible glacier located close to la paz bolivia since 1991 information has been collected about the evolution of this glacier since the little ice age with a focus on the last six decades the data considered in this study are monthly mass balance measurements yearly mappings of the surface topography and a map of the glacier bed given by ground penetrating radar survey a drastic shrinkage of ice has been observed since the early 1980s with a mean deficit about 1 m a 1 w e from 1992 to 1998 the glacier lost 40 of its average thickness and two thirds of its total volume and the surface area was reduced by 40 with a mean estimated equilibrium line altitude lying above its upper reach the glacier has been continuously exposed to a dominant ablation on the whole surface area if the recent climatic conditions continue a complete extinction of this glacier in the next 15 years can be expected glaciar chacaltaya is representative of the glaciers of the bolivian eastern cordilleras 80 of which are small glaciers 0 5 km2 a probable extinction of these glaciers in the near future could seriously affect the hydrological regime and the water resources of the high elevation basins

tropical climate and glacier hydrology a case study in bolivia runoff from intertropical glaciers is highly variable indicating that they are greatly affected by climatic changes peculiar to tropical climates the 3 km2 basin presented in this case study lies in the cordillera real of bolivia and is 77 covered by glacier ice ranging in elevation from 6000 to 4830 m a s l a comparison of 2 years of study demonstrates the peculiar feature of intertropical glaciers that accumulation and melting periods coincide during the rainy season during the first hydrological year 1991 1992 runoff was 1793 mm for an average precipitation on the glacier of approximately 916 mm during the second year 1992 1993 runoff was 1080 mm for a precipitation of 1060 mm solar radiation and daily mean duration with positive temperature on the ablation zone are the parameters best explaining variation in monthly runoff gauge readings taken downstream enable discharge from the glacier to be established over a period of nearly 20 years the most prominent events coincide with significantly negative values of the southern oscillation index often linked to el nino southern oscillation enso phenomena in conclusion results show that these intertropical glaciers are receding rapidly as precipitation does not compensate for loss from melting

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

monthly balance and water discharge of an inter tropical glacier zongo glacier cordillera real bolivia 16 s measurements of mass balance were performed every month on zongo glacier bolivia simultaneously water discharge temperature and precipita tion data were obtained the first year of the survey 1991 92 was marked by an enso el nino southern oscillation event with high temperature and low precipitation whilst the following year 1992 93 was normal results point to the early and late wet season october december and march may as playing a critical role in the determination of the annual mass balance the wet season is the warmest period of the year and consequently the duration of the wet season is a highly relevant variable in determining mass balance both glaciological and hydrological methods for the determination of the mass balance provide similar results our study confirms that enso events have a major influence on the rapid glacier retreat currently affecting this part of the andes

dating groundwater with trifluoromethyl sulfurpentafluoride sf5cf3 sulfur hexafluoride sf6 cf3cl cfc 13 and cf2cl2 cfc 12 1 a new groundwater dating procedure using the transient atmospheric signal of the environmental tracers sf5cf3 cfc 13 sf6 and cfc 12 was developed the analytical procedure determines concentrations of the four tracers in air and water samples sf5cf3 and cfc 13 can be used to date groundwaters in some environments where the cfcs and sf6 have previously failed because these new tracers have increasing atmospheric input functions no known terrigenic source and are believed to be stable under reducing conditions sf5cf3 has a dating range from 1970 to modern the mixing ratio mole fraction in north american air has increased from the detection limit of 0 005 parts per trillion ppt to the 2006 mole fraction of about 0 16 ppt no evidence was found for degradation of sf5cf3 in laboratory anaerobic systems the solubility of sf5cf3 was measured in water from 1 to 35 c groundwater samples that contained large amounts of terrigenic sf6 did not contain terrigenic sf5cf3 cfc 13 is a trace atmospheric gas with a dating range in groundwater of about 1965 to modern cfc 13 has been used primarily in very low temperature refrigeration thus groundwater environments are less likely to be contaminated with nonatmospheric sources as compared to other widely used cfcs because of the low solubility of sf5cf3 and cfc 13 in water an excess air correction must be applied to the apparent ages the new dating procedure was tested in water samples from wells and springs from maryland virginia and west virginia

rapid cross density ocean mixing at mid depths in the drake passage measured by tracer release diapycnal mixing across density surfaces is an important process in the global ocean overturning circulation1 2 3 mixing in the interior of most of the ocean however is thought to have a magnitude just one tenth of that required to close the global circulation by the downward mixing of less dense waters4 some of this deficit is made up by intense near bottom mixing occurring in restricted hot spots associated with rough ocean floor topography5 6 but it is not clear whether the waters at mid depth 1 000 to 3 000 metres are returned to the surface by cross density mixing or by along density flows7 here we show that diapycnal mixing of mid depth 1 500 metres waters undergoes a sustained 20 fold increase as the antarctic circumpolar current flows through the drake passage between the southern tip of south america and antarctica our results are based on an open ocean tracer release of trifluoromethyl sulphur pentafluoride we ascribe the increased mixing to turbulence generated by the deep reaching antarctic circumpolar current as it flows over rough bottom topography in the drake passage scaled to the entire circumpolar current the mixing we observe is compatible with there being a southern component to the global overturning in which about 20 sverdrups 1 sv 106 m3 s 1 upwell in the southern ocean with cross density mixing contributing a significant fraction 20 to 30 per cent of this total and the remainder upwelling along constant density surfaces the great majority of the diapycnal flux is the result of interaction with restricted regions of rough ocean floor topography

evidence for enhanced mixing over rough topography in the abyssal ocean the overturning circulation of the ocean plays an important role in modulating the earth s climate but whereas the mechanisms for the vertical transport of water into the deep ocean deep water formation at high latitudes and horizontal transport in ocean currents have been largely identified it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise however measurements of the internal wave field the main source of energy for mixing and of turbulent dissipation rates have typically implied diffusivities across surfaces of equal density of only approximately 0 1 cm2 s 1 too small to account for the return flow here we report measurements of tracer dispersion and turbulent energy dissipation in the brazil basin that reveal diffusivities of 2 4 cm2 s 1 at a depth of 500 m above abyssal hills on the flank of the mid atlantic ridge and approximately 10 cm2 s 1 nearer the bottom this amount of mixing probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry may be large enough to close the buoyancy budget for the brazil basin and suggests a mechanism for closing the global overturning circulation

disappearance of the last tropical glaciers in the western pacific warm pool papua indonesia appears imminent the glaciers near puncak jaya in papua indonesia the highest peak between the himalayas and the andes are the last remaining tropical glaciers in the west pacific warm pool wpwp here we report the recent rapid retreat of the glaciers near puncak jaya by quantifying the loss of ice coverage and reduction of ice thickness over the last 8 y photographs and measurements of a 30 m accumulation stake anchored to bedrock on the summit of one of these glaciers document a rapid pace in the loss of ice cover and a 5 4 fold increase in the thinning rate which was augmented by the strong 2015 2016 el nino at the current rate of ice loss these glaciers will likely disappear within the next decade to further understand the mechanisms driving the observed retreat of these glaciers 2 32 m long ice cores to bedrock recovered in mid 2010 are used to reconstruct the tropical pacific climate variability over approximately the past half century on a quasi interannual timescale the ice core oxygen isotopic ratios show a significant positive linear trend since 1964 ce 0 018 0 008 per year p 0 03 and also suggest that the glaciers retreat is augmented by el nino southern oscillation processes such as convection and warming of the atmosphere and sea surface these papua glaciers provide the only tropical records of ice core derived climate variability for the wpwp

mixing of a tracer in the pycnocline a patch of sulfur hexafluoride was released in may 1992 in the eastern north atlantic on an isopycnal surface near 300 m depth and was surveyed over a period of 30 months as it dispersed across and along isopycnal surfaces the diapycnal eddy diffusivity k estimated for the first 6 months was 0 12 0 02 cm2 s while for the subsequent 24 months it was 0 17 0 02 cm2 s the vertical tracer distribution remained very close to gaussian for the full 30 months as the root mean square rms dispersion grew from 5 to 50 m lateral dispersion was measured on several scales the growth of the rms width of the tracer streaks from less than 100 m to approximately 300 m within 2 weeks implies an isopycnal diffusivity of 0 07 m2 s at scales of 0 1 to 1 km larger than expected from the interaction between vertical shear of the internal waves and diapycnal mixing teasing of the overall patch initially about 25 km across into streaks with an overall length of 1800 km within 6 months supports predictions of exponential growth by the mesoscale strain field at a rate of 3 0 5 10 7 s 1 the rms width of these streaks estimated as 3 km and maintained in the face of the streak growth indicates an isopycnal diffusivity of 2 m2 s at scales of 1 to 10 km much greater than expected from internal wave shear dispersion the patch was painted in albeit streakily by 12 months confirming expectations from analytical and numerical models homogenization of the patch continued during the subsequent 18 months while the patch continued to spread with an effective isopycnal eddy diffusivity on the order of 1000 m2 s acting at scales of 30 to 300 km

spatial variability of mixing in the southern ocean 1 strain variance from standard hydrographic profiles in the southern hemisphere oceans shows that turbulent mixing is vertically and spatially non uniform in the south atlantic indian and south pacific oceans enhanced diffusivities are found over rough topography consistent with internal tide generated mixing the water column diffusivity returns to background levels 500 m to 1000 m off the sea floor in the southern ocean enhanced diffusivities throughout the entire water column below 1500 m are found in the antarctic circumpolar current over complex topography differences in the vertical extent of enhanced diffusivity profiles in the antarctic circumpolar current between the parameterizations based on tidal models and topography and of the present estimate of strain variance imply that elevated vertical diffusivity profiles in the southern ocean are due to the interaction between the mean geostrophic current and bottom topography