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

bathyal demersal fishes of the charlie gibbs fracture zone region 49 54 n of the mid atlantic ridge iii results from remotely operated vehicle rov video transects demersal fish were assessed by remotely operated vehicle rov video transects at sites to the ne nw 54 n se and sw 49 n of the charlie gibbs fracture zone cgfz at ca 2500 m depth on the mid atlantic ridge at each site three different slope categories flat 10 slope and 30 slope were sampled with four transects each surveying 2000 m3 of suprabenthic water this resulted in 12 high definition video transects at every site covering a total of 24 000 m3 suprabenthic water six species were observed which was fewer than in surveys using baited landers 19 species and trawls 26 species in the same area bathysaurus ferox halosauropsis macrochir antimora rostrata and polyacanthonotus challengeri did not vary in density between sites while coryphaenoides brevibarbis and coryphaenoides armatus were significantly more abundant at the northern sites the latter supporting findings using baited landers the halosaur h macrochir was the only species affected by slope the majority of observed fish showed no reaction to one or more of the stimuli produced by the rov however burst swimming was observed at least once in all species except b ferox the most abundant species c brevibarbis was particularly affected by the presence of the rov

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

modelling rip current flow and bather escape strategies across a transverse bar and rip channel morphology abstract rip currents are a hazard to bathers on surf beaches worldwide yet due to logistical and ethical concerns there has been minimal examination of how bathers caught in them should attempt to escape this study presents the first numerical model of simulated bathers escaping from a rip current an understanding of the underlying coastal geomorphology and hydrodynamics form a critical basis for the model with the intention that outcomes of the model should be evaluated from a physical science perspective field observations of a transverse bar rip channel were used as model inputs escape simulations were performed with moderate energy h s 1 m oblique offshore wave forcing used to generate two non stationary asymmetric flow fields dominant surfzone exits and dominant recirculation the model treats bathers as particles that move with the underlying flow with an additional swimming velocity added iterating until a safety condition based on depth and current speed is satisfied or until a maximum time limit is reached simulations compared the strategies of stay afloat and various fixed swim directions using two bather heights and four swim speeds up to 0 4 m s the overall optimal escape strategy was to swim parallel in the direction of alongshore flow time to safety was less for i recirculating flow ii taller bathers and iii greater swim speeds across all simulations 44 of floaters reached safety within 10 min while 80 of slow swimmers 0 2 m s succeeded in the same time interval this suggests that slow sustainable swimming may be a preferable escape action to floating optimal swim direction varied with start location from onshore near the shoreline parallel to shore mid rip channel and diagonally onshore outer rip channel at lower swim speeds the optimal swim direction had greater dependence on the underlying flow field as opposed to distance to safety therefore choice of direction is more complex for slower swimmers critically no strategy succeeded in all scenarios at all locations across the surfzone and small changes to input conditions water level start time and location swim direction had major impacts on outcomes future modelling efforts should examine additional surf zone rip current morphologies and wave tide inputs with a goal of determining generalised rip escape principles that may be communicated to the general public

a self similar scaling for cross shelf exchange driven by transient rip currents transient rip currents episodic offshore flows from the surf zone to the inner shelf present a recreational beach hazard and exchange material across the nearshore ocean the magnitude and offshore extent of transient rip current induced exchange and its relative importance to other inner shelf exchange processes are poorly understood here 120 model simulations with random normally incident directionally spread waves spanning a range of beach slopes and wave conditions show that the transient rip current exchange velocity is self similar the nondimensional exchange velocity surf zone flushing time and cross shore decay length scale are scaled by beach slope and wave properties depending strongly on wave directional spread transient rip current driven exchange can be compared to other cross shelf exchange processes for example transient rip current driven exchange is stronger than wave induced stokes drift driven exchange up to six surf zone widths from shore

the ecology and biogeography of discospirina tenuissima foraminifera in the atlantic and indian oceans the large 1 cm diameter miliolid foraminifera discospirina tenuissima carpenter and jeffreys 1870 is common at four sites nw ne sw and se located on either side of the mid atlantic ridge to the north 54 n and south 49 n of the charlie gibbs fracture zone the white discoidal tests of this epifaunal species were visible in video surveys of flat and gently 10 sloping sediment covered areas of seafloor replicate 500 m long transects 1000 m2 surface area obtained using the remote operated vehicle isis average densities varied from 0 07 se site to 1 12 nw ind m 2 for sloped transects and 0 02 nw to 1 75 sw ind m 2 for flat transects considerable variation was also evident between individual transects 0 2 25 ind m 2 the tests displayed no consistent dispersion pattern both significantly random and clumped patterns were observed in some cases within a single site isis was also used to make detailed in situ observations of d tenuissima and to collect individual specimens the delicate test margin sometimes exhibited angular notches and other signs of damage presumably a result of megafaunal activity in some cases the damage had been repaired specimens perforated by a large central hole occurred at the se site smaller sessile organisms including agglutinated foraminifera and occasional brachiopods use d tenuissima tests as a substratum for attachment in all areas some tests were surrounded by a ring of sediment presumably surface material collected by pseudopodia we interpret these features as being comparable to the feeding cysts created by other foraminiferal species they were particularly common at the se site where one or two abandoned rings indicated that some tests had moved distances of several centimetres across the seafloor most previous records of d tenuissima are from well oxygenated sites in the ne atlantic we provide the first records from the indian ocean here this species occurs at bathyal depths in the northwest 1980 m and northeast 938 m arabian sea where bottom water oxygen concentrations are depressed

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

extreme erosion on high energy embayed beaches influence of megarips and storm grouping abstract megarips have long been recognised as an important yet poorly documented mechanism of beach erosion on high energy embayed beaches the persistence and cumulative effect of megarips during storm groups are described from three embayed beaches arrifana mt clerigo and amoreira exposed to high energy wave conditions in the mesotidal bedrock dominated southwestern coast of portugal morphological changes determined by topographic monitoring and supplemented by interpretation of digital imagery over two years revealed the development of storm induced megarips which exerted a major influence on beach erosion differences in megarip influence within and between beaches are related to embayment geometry and orientation which significantly influence the nearshore wave field rip location is topographically controlled being determined by alongshore variations in breaking wave height and obliquity along with interaction of wave driven circulation patterns and embayment nearshore topography moderate beach sand loss during individual storms was linked to the development of megarips with associated rip neck and feeder channels extreme erosion however occurred when megarips and feeder channels persisted during successive storms promoting continued erosion and seaward sediment export observations show that once initiated megarip channels persist for several months and continue to act as conduits for offshore sediment transport under non storm conditions the maintenance of such rip circulation systems driven by morphodynamic feedback reduces beach recovery ability until the rip neck and feeder channels are infilled

the ecosystem of the mid atlantic ridge at the sub polar front and charlie gibbs fracture zone eco mar project strategy and description of the sampling programme 2007 2010 the work was supported by the uk natural environment research council consortium grant no ne c512961 1 and the census of marine life

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

topographically controlled breaking wave induced macrovortices part 2 changing geometries this is the second part of a series examining the behaviour of breaking wave induced macrovortices the first part examined theoretically general behaviours during startup conditions and gave computational results for macrovortex generation and their evolution on widely spaced breakwaters in this paper we extend and test qualitatively and quantitatively some of the basic results of part 1 in particular the initial longshore vortex transport for a wide range of geometries ranging from narrow rip current topographies to isolated breakwaters accounting for the presence of a shoreline is found to be necessary for the representation of longshore vortex transport results show vortex motion ranging from strongly offshore in the case of a narrow rip current to strongly longshore in the case of an isolated breakwater even with the significant approximations inherent in the analytical predictions numerical computations using time domain boussinesq type equations and laboratory experiments confirm the trends part 3 examines the horizontal mixing features of wave induced flows over isolated single breakwater configuration or multiple ripcurrent configuration submerged structures

sedimentary labile organic carbon and pore water redox control on species distribution of benthic foraminifera a case study from lisbon setubal canyon southern portugal abstract rose bengal stained benthic foraminifera were studied from 11 cores collected along two depth transects off southern portugal one in the lisbon setubal canyon and the other along the canyon edge the total standing stocks and distribution of foraminifera were investigated in relation to sediment and pore water geochemistry nitrate was used as a redox indicator sedimentary chlorophyll a and cpe chloroplastic pigment equivalents contents as a measure of labile organic matter and total organic carbon as a measure of bulk organic matter availability the canyon sediments were enriched in organic carbon and phytopigments at all water depths in comparison with the canyon edge water depth seemed to control sedimentary phytopigment content but not total organic carbon no significant correlation was seen between pigment and total organic carbon content the abundance of calcareous foraminifera correlated with the phytodetritus content whereas a weaker correlation was observed for the agglutinated taxa therefore calcareous foraminifera appear to require a fresher food input than agglutinated taxa the foraminiferal species composition also varied with pigment content and nitrate penetration depth in the sediment in line with the trox concept phytopigment rich surficial cpe content 20 g cm3 sediments with a shallow nitrate penetration depth 1 cm depth were inhabited by generally infaunal species such as chilostomella oolina melonis barleeanus and globobulimina spp as the nitrate penetration increased to 2 cm depth in sediment and the pigment content remained relatively high 15 g cm3 uvigerina mediterranea and uvigerina elongatastriata became dominant species with declining cpe content and increasing nitrate penetration depth the foraminiferal assemblages changed from the mesotrophic cibicides kullenbergi uvigerina peregrina assemblage to the oligotrophic abyssal assemblage mainly consisting of agglutinated taxa

variability of particulate flux over the mid atlantic ridge abstract the magnitude and composition of the sinking particle flux were studied over the northern mid atlantic ridge mar from june 2007 to july 2010 four moorings equipped with dual sediment traps 100 m and 1000 m above the sea floor sampled regions north and south of the charlie gibbs fracture zone between 49 n and 54 n and east and west of the mar biogenic data were coupled with satellite estimates of primary production and modelled particle source to assess the variability in export flux large variations were found in the seasonality chemical composition magnitude and source of sinking particulate material between mooring sites the northern moorings recorded both greater mean primary production and greater particle mass flux than the southern moorings although the large inter annual variability within the sites exceeded inter site differences while estimates of primary production and organic carbon fluxes are comparable to other investigations of this type they are notably lower than previous estimates for the abyssal plain of the north atlantic the deeper traps consistently recorded a higher mass flux compared to the shallower traps however we suggest that the overall flux recorded by the shallower traps was reduced by trapping inefficiency which in the light of the low current velocities may largely be due to the physical nature of the sinking material although deep trap flux estimates may be more susceptible to errors due to re suspended and advected material from nearby topography mass flux and current velocity are not linked in addition the relatively low aluminium concentration of the deep trap material indicates that this contribution is relatively small the organic carbon flux to the ne nw se and sw station was 0 8 1 2 1 1 and 1 1 g m 2 y 1 respectively corresponding to an export flux of 0 6 over this region of the mar

morphodynamics of a large scale rip current system at muriwai beach new zealand abstract field measurements of rip spacing nearshore morphology water surface elevation and eulerian and lagrangian flows were made in order to investigate the morphodynamics of a large scale rip current system at muriwai beach new zealand muriwai is a high energy meso tidal beach characterised by modal breaker wave heights of 2 5 m and incident wave periods of 10 15 s the monitored rip system was characterised by a 400 m long 75 m wide longshore feeder channel and a 150 m wide rip neck channel oriented obliquely to the shore and extending over a distance of almost 400 m during the experiment the beach evolved from a longshore bar trough and rip state to a transverse bar and rip configuration mean eulerian flow velocities obtained from ducted flowmeters deployed on the margin of the feeder channel and rip neck were on the order of 1 m s 1 and instantaneous flows were commonly in excess of 2 m s 1 mean lagrangian surface flow velocities extending from the base of the feeder through to the rip head were obtained by tracking rip floaters and were on the order of 0 7 m s 1 with maximums in the rip neck region of 1 4 m s 1 a distinct tidal modulation of rip current flow existed with maximum velocities occurring at low tide and minimum velocities at high tide comparison with other rip studies suggests that although the magnitude of the morphodynamic and hydrodynamic processes occurring within large scale rip systems is extreme the behaviour of these rip systems is very similar to low energy rips with much smaller spatial scales there is evidence to suggest that distinct morphodynamic scaling relationships exist between these environments

small scale distribution of deep sea demersal nekton and other megafauna in the charlie gibbs fracture zone of the mid atlantic ridge abstract videotapes from manned submersibles diving in the area of the charlie gibbs fracture zone of the mid atlantic ridge were used to investigate the distribution of fishes large crustaceans epifaunal and sessile organisms and environmental features along a series of transects submersibles mir 1 and mir 2 conducted paired dives in an area of mixed sediment and rock beginning depth ca 3000 m and on a large pocket of abyssal like sediments depth ca 4000 m in the shallower area the submersibles passed over extremely heterogeneous terrain with a diversity of nekton epifaunal forms and sessile forms in the first pair of dives mir 1 rose along the mid atlantic ridge from 3000 to 1700 m while mir 2 remained near the 3000 m isobath nekton seen in these relatively shallow dives included large and small macrourids genus coryphaenoides shrimp infraorder penaeidea halosauropsis macrochir aldrovandia sp antimora rostrata and alepocephalids the last two were more characteristic of the upper areas of the slope reached by mir 1 as it rose along the mid atlantic ridge to depths less than 3000 m distributions of some forms seemed associated with depth and or the presence of hard substrate sessile organisms such as sponges and large cnidaria were more likely to be found in rocky areas the second pair of dives occurred in an abyssal area and the submersibles passed over sediment covered plains with little relief and many fewer countable organisms and features the most evident of these were holes mounds small cerianthid anemones small macrourids and the holothurian benthodytes sp a few large macrourids and shrimp also were seen in these deeper dives as well as squat lobsters munidopsis sp sponges and larger cnidaria were mostly associated with a few small areas of rocky substrate holes and mounds showed distributions suggesting large scale patterning over all dives most sessile and epifaunal forms showed clumped distributions however large holothurians and large nekton often had distributions not significantly different from random

infragravity rip current pulsations 1 the origins of rip current pulsations within the infragravity frequency band 0 004 0 04 hz are determined from measurements made with arrays of colocated pressure and velocity sensors deployed on a beach with persistent rip current channels the observations indicate significant energy in cross shore infragravity velocities that varies spatially in the alongshore due to the presence of rip channels infragravity velocities are smaller within the rip channel than on the shore connected shoal owing to differences in water depth rip current pulsations at infragravity frequencies are linked to standing infragravity motions but not to the ponding and subsequent release of water by wave group pumping

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

boussinesq modelling of transient rip currents the flow on a plane beach with a random directionally spread wave field was simulated with a boussinesq model the random wave spectra were directionally symmetric with their central direction perpendicular to the beach so no constant longshore current was generated variable wave averaged currents were generated because of the spatially variable wave field and sometimes formed offshore directed rip currents that appear in variable longshore locations the rip currents are associated with a vortex pair which is generated within the surfzone and subsequently propagates offshore analysis of the vorticity balance show that the main vorticity input occurs within the inner surfzone three different beach slopes and four different wave spectra are simulated the frequency duration and intensity of the transient rips depend on both the beach slope and the incident wave spectra the results have important engineering implications for the transport of material in the nearshore zone in particular on longshore uniform beaches

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

trawled megafaunal invertebrate assemblages from bathyal depth of the mid atlantic ridge 48 54 n we investigated the effects of contrasting surface primary production on the benthic invertebrate megafauna at four sites on the mid atlantic ridge the sites designated nw ne sw and se were located to the west and east of the ridge axis and to the north and south of the charlie gibbs fracture zone benthic megafauna were sampled in 2007 and 2009 with a semi balloon otter trawl at a target depth of 2 500 m the total biomass and density of major taxonomic groups did not differ significantly between sites despite those to the north being characterised by greater surface productivity than those to the south however the density and biomass of individual taxonomic groups as well as diversity and body size all showed significant differences between sites diversity was highest at the se and lowest at the ne site most species were larger to the north community composition was significantly different between all sites with the greatest number of unique species found at the se and noticeably fewer unique species at the northern sites there was no clear correlation between the surface productivity and community structure suggesting complex ecological controls on the communities it is speculated that in addition to the energy supply drivers such as strong currents and sediment characteristics play an important role in shaping the communities at the different sites to what extent the ridge acts as a dispersal barrier for benthic invertebrate fauna remains unclear however high numbers of species unique to the southern site suggest a limited dispersal between the northern and southern areas

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

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

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

lagrangian observations of circulation on an embayed beach with headland rip currents abstract this study describes the first comprehensive measurements of nearshore current patterns across the entire extent of an embayed beach bounded by headland rip currents a field experiment at whale beach nsw australia provides valuable insights into i embayment wide spatial and temporal flow behaviour ii rates of cross and alongshore water exchange and iii the influence of geological control by headlands on morphology and circulation lagrangian flow data was obtained using 34 gps drifters with 293 individual deployments over a single ebbing tidal cycle during moderate low energy h s 1 m oblique wave forcing in situ wave and current data and bathymetric data were also collected beach morphology was dominated by a large mid beach rip channel with lesser headland rip channels mean flow rates were 0 6 ms 1 in the mid beach channel and 0 4 ms 1 in the headland channels with the majority of cross shore water volume flux 60 through the central channel a weak alongshore current o 0 1 ms 1 was forced by the oblique offshore wave angle rip current velocities flow variability and rate of surfzone exits by lagrangian drifters increased as water level decreased transient currents on a planar bar along the northern half of the beach with velocity standard deviation up to 0 2 ms 1 were not tidally modulated lagrangian time series were used to differentiate four current regimes rip cell rip head planar bar and offshore low energy zone based on mean velocity velocity variability and degree of tidal modulation an increase in surfzone exit rates by drifters was observed from south upwave to north downwave with exit rates per drifter deployment of 22 at the south headland rip 65 at the mid beach open rip and 80 at the north headland rip the high rate of drifter exits contrasts previous observations on open coast beaches observed flow behaviours are attributed to wave shadowing at the upwave protected end of the beach and longshore currents forced by oblique waves deflected offshore at the downwave headland these field observations are in good agreement with recent numerical modelling a relationship between bathymetric variability and current intensity was determined with cross shore average mean velocity correlating with a parameterisation of bathymetric alongshore non uniformity this study demonstrates that flow behaviour and exchange rates can vary along the length of an embayed beach due to geological control this research has implications for transport of organisms nutrients and pollutants is relevant to beach safety practitioners and can be used in calibration of numerical models

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

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

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

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

nearshore circulation over transverse bar and rip morphology with oblique wave forcing there is a paucity of field data to describe the transition in nearshore circulation between alongshore meandering and rip current systems a combination of in situ current meters and surf zone drifters are used to characterize the nearshore circulation over a transverse bar and rip morphology at pensacola beach florida in the presence of relatively low energy oblique waves current speeds vary in response to the relative wave height ratio hs h which defines the degree and extent of breaking over the shoal in the absence of wave breaking the nearshore circulation was dominated by an alongshore current driven by the oblique waves as waves begin to break across the shoal 0 2 0 5 the meandering current is replaced by an unsteady rip circulation that moves offshore between the shoals before turning alongshore in the direction of wave advance outside the surf zone the increase in wave dissipation is associated with an increase in very low frequency vlf variations in the current speed across the shoal and in the rip channel that caused the circulation to oscillate between an offshore and an alongshore flow the unsteady nature of the nearshore circulation is responsible for 55 of all surf zone exits under these more dissipative conditions in contrast only 29 of the drifters released from the shoal exited the surf zone and bypassed the adjacent shoal with the alongshore meandering current while the currents had a low velocity maximum of 0 4 m s 1 and would not pose a significant hazard to the average swimmer the results of this study suggest that the transverse bar and rip morphology is sufficient to create an alongshore variation in wave dissipation that forces alongshore meandering and low energy rip circulation systems under oblique wave forcing copyright 2013 john wiley sons ltd

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

the flux of overflow water through the charlie gibbs fracture zone we report the results of a set of measurements made within the charlie gibbs fracture zone in 1988 1989 the principal data sources are year long current meter records 16 in number and 23 conductivity temperature depth stations the aim was to determine the flux of overflow water passing westward out of the iceland basin in the eastern north atlantic within the fracture zone overflow water is defined either as having salinity greater than 34 94 at the present time or more generally as having a potential density 0 27 8 kg m3 in 1988 1989 the core salinity had a value equal to that reported in 1981 and 1983 but was fresher by about 0 02 than was found in 1964 the flux was estimated twice per day and was found to fluctuate strongly with energy spread in a broad band of periods ranging from 10 to 400 days no annual signal could be detected the mean value was 2 4 0 5 sv less than all previous estimates based on hydrography alone it is suggested that hydrography may systematically overestimate transport because diffusion is neglected flux estimates from current meter arrays are rarely used in initializing numerical ocean models consequently measurements like those reported here are an independent and important means for assessing the performance of such models at the deepest levels water enters the two transform valleys of the fracture zone from the west in the northern valley the flow is periodically flushed out by energetic bursts of overflow water a critical value of an inverse froude number is shown to define the flushing threshold

mean lagrangian flow behavior on an open coast rip channeled beach a new perspective article i nfo the accepted view of rip currents is that they are an efficient mechanism for transporting material out of the surf zone previous rip current campaigns on natural beaches have focused on eulerian measurements with sparse in situ pressure and current meter arrays here for the first time spatially synoptic estimates of rip current flow patterns vorticity and lagrangian transport behavior are measured in the field using a fleet of 30 position tracking surfzone drifters during multiple rip current occurrences on an open coast beach in monterey ca contrary to the classic view shepard et al 1941 the rip current flow field consisted of semi enclosed large scale vortices that retained the drifters and resulted in a high number of lagrangian observations that are temporally and spatially repeated approximately 19 of the drifters deployed in the rip currents exited the surf zone per hour on average during the experiments the observed surf zone retention of drifters is consistent with measurements from different open coast beach rip current systems 14 at meso macrotidal truc vert france and 16 at macrotidal perranporth united kingdom the three hour average cross shore rip current velocity at monterey was 30 cm s with peak time averaged velocities of 40 60 cm s depending on wave and tidal conditions drifters that episodically exited the surf zone were transported approximately 2 surf zone widths offshore at 20 cm s published by elsevier b v

benthic biological and biogeochemical patterns and processes across an oxygen minimum zone pakistan margin ne arabian sea abstract oxygen minimum zones omzs impinging on continental margins present sharp gradients ideal for testing environmental factors thought to influence c cycling and other benthic processes and for identifying the roles that biota play in these processes here we introduce the objectives and initial results of a multinational research program designed to address the influences of water depth the omz 150 1300 m and organic matter om availability on benthic communities and processes across the pakistan margin of the arabian sea hydrologic sediment and faunal characterizations were combined with in situ and shipboard experiments to quantify and compare biogeochemical processes and fluxes om burial efficiency and the contributions of benthic communities across the omz in this introductory paper we briefly review previous related work in the arabian sea building the rationale for integrative biogeochemical and ecological process studies this is followed by a summary of individual volume contributions and a brief synthesis of results five primary stations were studied at 140 300 940 1200 and 1850 m water depth with sampling in march may intermonsoon and august october late to postmonsoon 2003 taken together the contributed papers demonstrate distinct cross margin gradients not only in oxygenation and sediment om content but in benthic community structure and function including microbial processes the extent of bioturbation and faunal roles in c cycling hydrographic studies demonstrated changes in the intensity and extent of the omz during the sw monsoon with a shoaling of the upper omz boundary that engulfed the previously oxygenated 140 m site oxygen profiling and microbial process rate determinations demonstrated dramatic differences in oxygen penetration and consumption across the margin and in the relative importance of anaerobic processes but surprisingly little seasonal change a broad maximum in sediment om content occurred on the upper slope roughly coincident with the omz but the otherwise poor correlation with bottom water oxygen concentrations indicated that other factors are important in determining sediment om distributions downcore profiles generally showed little clear evidence of in situ om alteration and there was little sign of om enrichment resulting from the southwest monsoon in sediments collected in the late to postmonsoon sampling this is interpreted to be due to rapid cycling of labile om organic geochemical studies confirmed that sediment om is overwhelmingly of marine origin across the margin but also that it is heavily altered with only small changes in degradation state across the omz more negative stable c isotopic compositions in surficial sediments at hypoxic sites within the omz core are attributed to a chemosynthetic bacterial imprint dramatic changes in benthic community structure occurred across the lower omz transition apparently related to om availability and quality as well as to do concentrations high resolution sampling biomarkers and isotope tracer studies revealed that oxygen availability appears to exert threshold type controls on benthic community structure and early faunal c processing biomarker studies also provided evidence of faunal influence on sediment om composition together the results offer strong evidence that benthic fauna at sites across the margin play important roles in the early cycling of sediment om through differential feeding and bioturbation activities

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

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

low energy rip currents associated with small bathymetric variations we show for the first time that low energy waves can induce a rip current system over subtle alongshore bathymetric variations comprehensive field measurements across a rip current that morphologically migrated 12 m day through a coherent cross and alongshore array of co located pressure and velocity sensors were obtained the rip current is associated with a small bathymetric surfzone non uniformity 1 in 300 alongshore variation the circulation was kinematically non uniform for 5 of the time over the course of the 20 day experiment and was present at low tides associated with increases in rip current activity the presence of the rip current and mild sloped rip channel induce statistically significant alongshore variations in hrms wave direction directional spreading infragravity waves and very low frequency motions changes in the directional spreading are correlated with the presence of very low frequency motions influenced by the presence of the rip current

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

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

dense aggregations of a hexactinellid sponge pheronema carpenteri in the porcupine seabight northeast atlantic ocean and possible causes dense aggregations of the hexactinellid sponge pheronema carpenteri were encountered in the porcupine seabight at depths between about 1000 and 1300m in restricted areas within this bathymetric range the sponges attain numerical abundances of more than 1 5m 2 and an estimated biomass of up to 372g m 2 wet weight or about 10g m 2 ash free dry weight these recently acquired samples together with historical data suggest that pheronema occurs close to but not within regions of the upper continental slope where the bottom topography is expected to result in significant enhancement of the near bottom tidal current velocities it is suggested that the sponges may not be able to withstand the enhanced currents but may nevertheless be dependent upon the resuspended or undeposited organic matter carried to them from these regions of increased tidal energy

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