snow megadune fields on the east antarctic plateau extreme atmosphere ice interaction large dune fields occupy more than 500 000 km 2 of the east antarctic plateau the megadunes or long wavelength surface ripples have amplitudes of only a few meters wavelengths of a few kilometers and parallel crests which can extend one hundred kilometers they occur in areas characterized by low accumulation extensively recrystallized snow and strong scattering of the microwave part of the spectrum dune crests are oriented perpendicular to the regional katabatic wind direction snow megadunes are unlikely to be formed by simple wind transport of snow particles

effect of organic carbon flux and dissolved oxygen on the benthic foraminiferal oxygen index bfoi variations in oceanic primary productivity flux of organic carbon to the sediments and dissolved oxygen levels in the water column are thought to be important in the control of benthic foraminiferal test size wall thickness morphology and species composition of assemblages by many foraminiferal paleontologists aspects of these processes should be reflected by the benthic foraminiferal oxygen index bfoi based on these foraminiferal characteristics however analyses indicate that the bfoi correlates most strongly with dissolved oxygen levels in overlying water r2 0 81 weakly with oceanic primary productivity r2 0 55 and weakly with organic carbon flux to the sediments r2 0 51 although both dissolved oxygen and organic carbon flux are main controlling factors for benthic foraminiferal assemblages the bfoi is a useful indicator extracted from benthic foraminiferal assemblages for estimating the condition of dissolved oxygen in cretaceous and cenozoic oceans

a snow transport model for complex terrain as part of the winter environment in middle and high latitude regions the interactions between wind vegetation topography and snowfall produce snow covers of non uniform depth and snow water equivalent distribution a physically based numerical snow transport model snowtran 3d is developed and used to simulate this three dimensional snow depth evolution over topographically variable terrain the mass transport model includes processes related to vegetation snow holding capacity topographic modification of wind speeds snow cover shear strength wind induced surface shear stress snow transport resulting from saltation and suspension snow accumulation and erosion and sublimation of the blowing and drifting snow the model simulates the cold season evolution of snow depth distribution when forced with inputs of vegetation type and topography and atmospheric foreings of air temperature humidity wind speed and direction and precipitation model outputs include the spatial and temporal evolution of snow depth resulting from variations in precipitation saltation and suspension transport and sublimation using 4 years of snow depth distribution observations from the foothills north of the brooks range in arctic alaska the model is found to simulate closely the observed snow depth distribution patterns and the interannual variability

estimating the sensitivity of the atmospheric teleconnection patterns to sst anomalies using a linear statistical method abstractthe pacific north american pna pattern and the north atlantic oscillation nao are known to contain a tropical sea surface temperature sst forced component this study examines the sensitivity of the wintertime nao and pna to patterns of tropical sst anomalies using a linear statistical dynamic method the nao index is sensitive to sst anomalies over the tropical indian ocean the central pacific ocean and the caribbean sea and the pna index is sensitive to sst anomalies over the tropical pacific and indian oceans the nao and pna patterns can be reproduced well by combining the linear operator with the consistent sst anomaly over the indian ocean and the nino 4 regions respectively suggesting that these are the most efficient ocean basins that force the teleconnection patterns during the period of 1950 2000 the nao time series reconstructed by using sst anomalies over the indian ocean nino 4 region caribbean sea or the indian ocean nino 4 region is significantly correlated with t

surface climate variations over the north atlantic ocean during winter 1900 1989 abstract the low frequency variability of the surface climate over the north atlantic during winter is described using 90 years of weather observations from the comprehensive ocean atmosphere data set results are based on empirical orthogonal function analysis of four components of the climate system sea surface temperature sst air temperature wind and sea level pressure an important mode of variability of the wintertime surface climate over the north atlantic during this century is characterized by a dipole pattern in ssts and surface air temperatures with anomalies of one sign cast of newfoundland and anomalies of the opposite polarity off the southeast coast of the united states wind fluctuations occur locally over the regions of large surface temperature anomalies with stronger than normal winds overlying cooler than normal ssts this mode exhibits variability on quasi decadal and biennial time scales the decadal fluctuations are irregular in length averaging 9 years before 1945 and 1

deep air convection in the firn at a zero accumulation site central antarctica abstract ice cores provide unique archives of past atmospheres and climate but interpretation of trapped gas records and their climatic significance has been hampered by a poor knowledge of the prevalence of air convection in the firn layer on top of polar ice sheets in particular the phasing of greenhouse gases and climate from ice cores has been obscured by a discrepancy between empirical and model based estimates of the age difference between trapped gases and enclosing ice which may be due to air convection here we show that deep air convection 23 m occurs at a windy near zero accumulation rate site in central antarctica known informally as the megadunes site 80 77914 s 124 48796 e deep convection is evident in depth profiles of air withdrawn from the firn layer in the observed pattern of the nitrogen isotope ratio 15 n 14 n the argon isotope ratio 40 ar 36 ar and in the mixing ratios of the anthropogenic halocarbons methyl chloroform ch 3 ccl 3 and hfc 134a ch 2 fcf 3 transport parameters diffusivities were inferred and air was dated using measured carbon dioxide co 2 and methane ch 4 mixing ratios by comparing with the law dome atmospheric record which shows that these are the oldest firn air samples ever recovered co 2 mean age 1863 ad the low accumulation rate and the consequent intense metamorphism of the firn due to prolonged exposure to seasonal temperature cycling likely contribute to deep air convection via large grain size and vertical cracks that act as conduits for vigorous air motion the megadunes site provides a possible modern analog for the glacial conditions in the vostok dome fuji and dome c ice core records and a possible explanation for lower than expected 15 n 14 n ratios in trapped air bubbles at these times a general conclusion is that very low accumulation rate causes deep air convection via its effect on firn structural characteristics

surface drag over the snow surface of the antarctic plateau 1 factors controlling surface drag over the katabatic wind region the drag coefficient of the snow surface over the antarctic plateau is evaluated through direct measurement of reynolds stress on the mizuho plateau east antarctica in the austral summer the estimated roughness height z0 varies from 10 l to 10 4 cm even under near neutral conditions large shear stress appears in light wind followed by increased turbulent intensity in the katabatic wind region of the plateau z0 shows symmetric changes with wind direction the average value of z0 in the smoothest direction is 0 0004 cm which is the minimum value previously reported and it increases to 0 015 cm for 40 rotation of wind direction toward the roughest direction the directional dependence of z0 is similar at three stations located nearly 100 km apart unlike the results of jackson and carroll at the south pole the smoothest direction deviates 20 from the mean sastrugi axes and agrees with the direction of the prevailing high wind the 4 m neutral drag coefficient is estimated to be 0 8 10 3 for the smoothest direction and 1 5 10 3 for the roughest direction the effect of snow drift is unimportant a generalized discussion of the results is given in a companion paper

unconformable stratigraphy in east antarctica part i large firn cosets recrystallized growth and model evidence for intensified accumulation unconformable firn stratigraphy exists throughout a 650 km long radar profile that we recorded down flow of megadune fields in the byrd glacier east antarctica catchment profile segments reveal cosets of prograding bedding sequences up to 90 m thick and with lateral along crest dimensions up to tens of kilometers we profiled them in oblique section and nearly parallel to the prevailing wind the prograding snow accumulates on broad low windward slopes located above ice bed depressions which implies long term slope stability the apparent subglacial control implies that the accumulation progrades in balance with ice velocity which we measured at 30 ma 1 the sequences prograde over intensely modified and recrystallized wind glaze firn visible in the profiles as unstratified layers and zones up to several tens of meters thick the intense recrystallization eliminates density stratification and the altered layers appear to thicken into a connected network modeling of coset formation using wind and ice flow reproduces their dimensions and morphology however accumulation rates well above current regional estimates and existing data for megadunes are required because of the measured ice speed and required slope stability the consistent unconformable strata along our traverse show that coset and recrystallized morphology extend far beyond the megadune fields

modis based mosaic of antarctica moa data sets continent wide surface morphology and snow grain size abstract we present digital image mosaics of surface morphology and optical snow grain size for the antarctic continent and surrounding islands assembled from 260 moderate resolution imaging spectroradiometer modis images the products are derived from modis band 1 red light 647 nm and band 2 infrared 857 nm orbit swath data acquired during the 2003 2004 austral summer multiple images of all areas are combined in a data cumulation scheme to improve spatial resolution and increase radiometric content of the mosaics the component images were de striped geo registered and re sampled to the projection grid using the modis swath to grid toolbox ms2gt software a 125 m ground equivalent polar stereographic projection was used identical to previous radar image mosaics and similar to several other continent wide data sets geo location accuracy of the final mosaics is better than 125 m swath acquisition times were limited to the range 05 00 13 30 ut to provide broad but uniform mosaic illumination regions of cloud cover blowing snow and intense forward scattering were masked prior to compositing the moa snow grain size data set image provides the first continent wide semi quantitative map of mean summer snow firn and blue ice grain size optical grain size radius was determined using a normalized difference index derived from modis band 1 and band 2 rad values atmospheric correction adjustments for directional reflectance variation and snow grain size estimation were accomplished by a look up table generated by a combination of published models of snow spectral reflectance and atmosphere radiative transfer validation of the snow grain size image is provided by in situ spectra of snow covered sea ice made in october 2003 we use the new data sets to determine major ice shelf areas and shelf edge coastline and ice grounding line vector files and determine areas of selected blue ice regions these data sets are available for download at http nsidc org data moa

investigation of a large scale mode of ocean atmosphere variability and its relation to tropical pacific sea surface temperature anomalies abstract by examining the linearly coupled atmospheric and oceanic signals related to interannual variability in sea surface temperatures and upper air wind fields a hemispheric scale ocean atmosphere teleconnection mode is isolated that is significantly correlated with equatorial pacific ssts 12 months later the interannual component of this teleconnection mode is related to a basin scale dipole in the upper air wind fields stretching across the extratropical pacific with additional anomalies extending from the eastern tropical pacific over north america and into the atlantic basin in addition it is related to variability in the sst field with warm anomalies found over the tropical subtropical western pacific as well as the equatorial eastern pacific also there are related cold anomalies over the extratropical central north pacific that extend down into the central subtropical tropical pacific diagnostic studies investigating the ocean atmosphere structure for this mode of variability indicate th

observations theory and modeling of the differential accumulation of antarctic megadunes antarctic megadunes are characterized by significant spatial differences in accumulation rate with higher accumulation on the windward side and near zero accumulation on the lee side this leads to spatial differences in physical properties of snow and surface roughness as well as to the upwind migration of the megadunes while previous studies agree that megadunes are a result of complex interactions between wind topography and snow it is not clear how they form or why they accumulate on the windward side here we use icesat observations dimensional analysis and atmospheric flow modeling to investigate what conditions are responsible for the accumulation patterns and upwind migration of the megadunes first we use icesat data to quantify the pattern of differential surface elevation change across the megadunes we then use dimensional analysis based on supercritical flow theory and atmospheric flow modeling to show that the megadunes topography and a stable atmosphere will always lead to upwind dune migration we show that a combination of persistent katabatic winds strong stability and spatial variability in surface roughness is responsible for the accumulation on the upwind slope and hence the upwind migration of the megadunes we further show that spatial differences in surface roughness are the primary control on accumulation magnitudes and hence dune migration velocity the dune migration velocity in turn influences the degree of snow metamorphism and the physical properties of snow that are relevant for paleoclimate records our findings pertain to the ongoing evolution of the megadunes but their genesis remains an open question

near surface environmentally forced changes in the ross ice shelf observed with ambient seismic noise author s chaput j aster r c mcgrath d baker m anthony r e gerstoft p bromirski p nyblade a stephen r a wiens d a das s b stevens l a

deep sea benthic foraminiferal species diversity in the ne atlantic and nw arabian sea a synthesis abstract we present a synthesis of species diversity data fishers alpha index shannon wiener log 2 es 100 rank 1 dominance for live stained foraminifera from five bathyal 1340 m depth and abyssal 4450 4950 m depth sites in the ne atlantic and a 3400 m deep site in the arabian sea three atlantic sites porcupine seabight biotrans porcupine abyssal plain are subject to seasonal phytodetritus inputs that support low diversity populations 8 17 species in other respects the foraminifera are highly diverse the meiofaunal fractions 45 or 63 m including fragmented and phytodetritus species of abyssal atlantic samples yielded 110 and 170 species in the 0 1 cm and 0 10 cm layers respectively the arabian sea sample 0 1 cm layer only yielded 232 species in both cases values for diversity measures were very high diversity was rather lower in bathyal porcupine seabight samples 0 1 cm layer which yielded 500 m porcupine and madeira abyssal plains was also speciose 113 133 species but diversity measures were lower and dominance higher than for the meiofauna all assemblages contained numerous undescribed species many belonging to poorly known monothalamous soft bodied taxa sample diversity was influenced by several factors combining phytodetrital and sediment populations reduced diversity and increased dominance slightly the inclusion of deeper sediment layers and finer sieve fractions had the opposite effect the inclusion of fragments had more impact on macrofaunal than on meiofaunal diversity although in both cases the effect was inconsistent either positive or negative porcupine and madeira abyssal plain multicore samples 63 m fraction contained substantially more foraminiferal species than nematode species the numbers of foraminiferal species in boxcore samples 500 m fraction were comparable to or greater than literature values for macrofaunal taxa such as polychaetes and isopods few of the more abundant species at our atlantic abyssal plain and arabian sea sites are endemic this is consistent with literature evidence that many common deep sea foraminiferal species are cosmopolitan and implies that global foraminiferal diversity may be more modest than the high sample diversity might suggest calcareous foraminifera which are well known taxonomically and have a good fossil record may provide a model for diversity patterns among the deep sea benthic biota in general

the sapropel record of the eastern mediterranean sea results of ocean drilling program leg 160 research on sediments recovered during ocean drilling leg 160 has concentrated on two issues the first concerned the stratigraphy of sapropel formation the second was oriented to clarify specific processes that explain sapropel origin progress has been made in the construction of stratigraphic composites out of sedimentary sequences from individual holes at each of the palaeoceanographic sites on the composites initial work has resulted in the establishment of high resolution and intermediate resolution stratigraphies for three sites 963 964 967 correlation of sedimentary cycles to astronomical insolation cycles extends the stratigraphies to sites 969 and 966 the sapropel occurrences in the marine and land sequences over the entire eastern mediterranean are correlated with the resolution that can be obtained from isotope studies groups of sapropels occurred simultaneously over the entire basin in detail however the temporal and facies patterns of sapropel sequences differ between individual sites and depositional basins the differences may be related to effects of water depth diagenesis and post depositional tectonic attenuation of sequences studies on the geochemistry and facies of sapropels agree that anoxic conditions favoured preservation of organic matter in sapropels caused the enrichment of trace metals associated with sapropels and helped to preserve primary sedimentary structures besides all evidence is consistent with elevated fluxes of organic matter and associated elements during sapropel events

wind borne redistribution of snow across an antarctic ice rise redistribution of snow by the wind can drive spatial and temporal variations in snow accumulation that may affect the reconstruction of paleoclimate records from ice cores in this paper we investigate how spatial variations in snow accumulation along a 13 km transect across lyddan ice rise antarctica are related to wind borne snow redistribution lyddan ice rise is an approximately two dimensional ridge which rises about 130 m above the surrounding ice shelves local slopes on its flanks never exceed 0 04 despite this very smooth profile there is a pronounced gradient in snow accumulation across the feature accumulation is highest on the ice shelf to the east climatologically upwind of the ice rise and decreases moving westward with the lowest accumulation seen to the west climatologically downwind of the ice rise crest superimposed on this broad scale gradient are large 20 30 localized variations in accumulation on a scale of around 1 km that appear to be associated with local variations in surface slope of less than 0 01 the broad scale accumulation gradient is consistent with estimates of wind borne redistribution of snow made using wind speed observations from three automatic weather stations the small scale variability in accumulation is reproduced quite well using a snow transport model driven by surface winds obtained from an airflow model providing that both the wind shear and static stability of the upwind flow are taken into account we conclude that great care needs to be exercised in selecting ice core sites in order to avoid the possibility of blowing snow transport confounding climate reconstructions

seasonal variability in the δ18o and δ13c of planktonic foraminifera from an upwelling environment sediment trap results from the san pedro basin southern california bight stable isotopic analyses 18o and 13crpar on four species of planktonic foraminifera collected from high resolution time series sediment trap sampling indicate that rapid and significant seasonal variability occurred in response to rapid changes in both the hydrographic environment and the isotopic composition of ambient seawater specimens were collected at a depth of 500 m for 28 consecutive 1 week periods in the san pedro basin within the southern california bight a region seasonally influenced by upwelling hydrographic monitoring of the study area revealed a 6 week period late april to mid june during which pulses of upwelling occurred causing significant increases in the oxygen isotopic composition of surrounding waters while decreasing the carbon isotopic composition analyses of globigerina bulloides orbulina universa neogloboquadrina dutertrei and neogloboquadrina pachyderma right coiling indicate that during the upwelling period these species live respectively at the surface in the surface mixed layer within the thermocline and below the thermocline globigerina bulloides ascends from well below the thermocline to the surface at the onset of upwelling and increases production to its maximum simultaneously as its morphology changes to less calcified open forms both n dutertrei and n pachyderma follow isothermal ranges migrating to shallower waters during upwelling and subsequently descending after upwelling ceases neogloboquadrina dutertrei appears to inhabit the region associated with both the thermocline base and chlorophyll maximum when it is most abundant following upwelling orbulina universa increases its depth habitat as solar irradiance increases but this species decreases in abundance during upwelling the 18o signal of o universa appears to be a useful indicator of seasonal temperature variations above the thermocline whereas the 18o of g bulloides documents near surface temperatures during upwelling the 13c signal of both n dutertrei and n pachyderma appears to record the 13c of equilibrium calcite for the regions of the thermocline and just below the thermocline respectively due to the relative preservation potentials of the four species analyzed only n dutertrei and n pachyderma are likely to be preserved in the sedimentary record in regions of oxygenated bottom waters thus an actual record of hydrographic conditions during upwelling as would be found in tests of g bulloides is not preserved instead conditions before n pachyderma and just after n dutertrei are more likely recorded

revisiting the linear theory of sand dune formation a linear stability theory for dune and antidune formation is presented that implements a rotational two dimensional flow model as in previous linear theories the phase lag between sediment transport and bed elevation remains the main mechanism driving instability however it is shown that this phase lag varies significantly in a neighbourhood of the bed moreover since the layer in which sediments are moving has a finite though small thickness it is assumed that the perturbations of the fluid stress driving bedload transport should be evaluated at the top of the layer itself it is shown that such an apparently minor modification of the classical approach alters remarkably the balance between stabilizing and destabilizing effects that drives the instability process this also allows a clarification of the debated role of bedslope on the formation of dunes and antidunes following the above ideas antidunes are shown to form in the absence of suspended sediment load and without any effect associated with sediment inertia the present analysis ultimately allows a successful unification of the theories of dune and antidune formation

the importance of the oxygen minimum zone and sediment geochemistry in the distribution of recent benthic foraminifera in the northwest indian ocean abstract the relationship between the distribution of benthic foraminifera and sediment type and depositional environment in the arabian sea is discussed the benthic foraminiferal fauna were sampled in nineteen recent surface sediment samples and geochemical variables of the sediment of the same samples were measured the water depths for the box core samples varies from 440 to 4040 m a total of 103 species and six species complexes were identified the geochemical properties were found to correspond well to the sediment type and depositional environment and six different sediment depositional environment types could be distinguished analysis of the benthic foraminiferal fauna reveals specific faunal assemblages that are closely related to these sediment depositional environment types

atmospheric flow over a succession of nearly two dimensional ridges and valleys observations of neutral static stability flow in a nearly two dimensional valley are presented upstream and downstream of the valley are a succession of similar ridges and valleys the valley sides have a slope of about 32 to the horizontal and when the wind is nearly perpendicular to the valley there is a marked flow separation the observations of mean flow and turbulence are compared with numerical simulations of flow over periodic two dimensional ridges and valleys

late pliocene to early pleistocene astronomically forced sea surface productivity and temperature variations in the mediterranean abstract principal component analysis of late pliocene to early pleistocene planktonic foraminiferal abundances from the mediterranean yielded two significant components which represent first order approximations for sea surface productivity and temperature this interpretation is confirmed by the good fit between the score plots and sea surface productivity and sea surface temperature proxy records based on selected eutrophic and temperature sensitive species using present day habitat characteristics spectral analysis revealed significant peaks in the orbital frequency bands of the spectrum suggesting that variations in sea surface productivity and temperature are controlled by the quasi periodic variations in the earth s orbit precession forced variations are reflected primarily in sea surface productivity and to a lesser degree in sea surface temperature maxima in sea surface productivity and temperature in this frequency band occurred at times of sapropel formation the sea surface productivity maxima can be explained by an increased input of river borne nutrients and by the shoaling of the pycnocline and the associated intensification of the deep chlorophyll maximum dcm layer precession forced variations in sea surface temperature are not related to glacial cycles since this frequency component is almost completely absent in ice volume proxy records for this time interval sapropel bound sea surface temperature maxima presumably reflect periods of maximum insolation during the northern hemisphere summer the contrasting winter signal corresponds to minimum insolation values which may be reflected by peak abundances ofgloborotalia inflata obliquity forced variations are reflected primarily in sea surface temperature and not in sea surface productivity these temperature fluctuations correspond with ice volume changes registered in the oxygen isotope record at the north atlantic dsdp site 607 this shows that obliquity forced sea surface temperature variations in the mediterranean are primarily driven by glacial cycles

planktic foraminifers and hydrography of the eastern and northern caribbean sea the distribution of living planktic foraminifers and their relation to the hydrography of the caribbean sea was investigated in plankton net tows and surface sediment samples taken along the antilles island arc during april may 1996 the planktic foraminiferal community was strongly influenced by spatial variations in salinity that were largely due to the influx of orinoco river water into the southeastern caribbean sea and inflowing sargasso sea water in the north along the antilles island arc globigerinoides ruber was the dominant species in the surface waters throughout in the southeastern caribbean sea where orinoco river outflow influences the planktic community standing stocks of planktic foraminifers 100 m between 4 and 50 specimens m 3 were medium to low the southeastern faunas between tobago and guadeloupe were characterized by increased proportions of neogloboquadrina dutertrei highest standing stocks of 159 specimens m 3 in the upper 20 m of the water column were recorded in the northeastern caribbean sea and the assemblages were characterized by high proportions of globigerinita glutinata associated with cyclonic eddies in the anegada passage where sargasso sea water flows into the caribbean sea low standing stocks of 18 specimens m 3 indicate oligotrophic conditions together with the oligotrophic surface waters the subtropical underwater enters the caribbean sea through the anegada passage in water depths between 100 and 300 m these waters are characterized by higher concentrations of globorotalia truncatulinoides relative to the adjacent water masses comparison of the living planktic foraminiferal fauna with empty test assemblages from the water column and from surface sediments shows that differences in the faunal composition mostly correspond to the distribution of water masses and to the differential dissolution of species in the vicinity of islands globigerinoides ruber reaches higher relative frequencies than in the open ocean pointing towards a higher tolerance of this species towards neritic conditions than in other species

antidunes on steep slopes 1 when rates of subcritical flow are increased on gentle slopes the bed successively produces ripples dunes and flat beds antidunes defined here as all bed undulations for which the surface gravity waves are in phase with the bed profile appear only in high flow rates and may be found in some extreme natural flow events inversely on steep slopes flume experiment s 1 approximately flows are supercritical and antidunes are observed to appear just after the beginning of sediment motion and to disappear for high flow rates using data from new experiments we seek to improve the prediction of antidune geometry on steep slopes an equation for antidune wavelength was deduced from dimensional analysis and fitted to new experimental data the equation was successfully evaluated using a data set extended to 167 values with data from the literature obtained on both steep and gentle slopes this equation gives results very similar to the usual analytical equation from kennedy when tested on the results from gentle slope experiments but proved to be better adapted for antidune wavelength on steep slopes

the surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

timing and hydrological conditions of sapropel events in the eastern mediterranean as evident from speleothems soreq cave israel this paper explores the connection between the timing of sapropel events in the eastern mediterranean sea and the time of low 18o events in speleothems of the soreq cave israel a new well dated 18o and 13c profile of the soreq cave speleothems for the last 140 kyr reveals five prominent low 18o events dated at 124 to 119 kyr with the main peak at 122 kyr event v 108 to 100 kyr with peaks at 107 and 102 kyr event iv 85 to 79 kyr with peak at 80 kyr event iii 55 to 52 kyr with a peak at 54 kyr event ii and 8 5 to 7 kyr with peaks at 8 5 and 7 kyr event i these events are characteristic of period of enhanced rainfall in the eastern mediterranean area particularly so for events v and i where the marked decrease in 18o and the correspondingly marked increase in 13c indicate very wet conditions the chronology of the low 18o events v iv iii and i match the ages estimated for the formation of sapropels s5 s4 s3 and s1 which are also associated with high hydrological activity thus it is suggested that the low 18o events in the soreq cave speleothems constrain the maximum duration of the sapropel formation pollen data from the sapropel layers and the isotopic pattern of the speleothems indicate that sapropels s5 and s1 were deposited during very wet periods when there were major decrease in the sea surface salinity coupled with frost free winters and drought free summers sapropels s4 and s3 were formed during periods of increased precipitation but ones in which the general climate was mediterranean semi arid

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

faceted crystal formation in the northeast greenland low accumulation region snow pit analysis in the low accumulation region in northeast greenland indicated a mean annual accumulation of 12 1 6 cm it also revealed numerous faceted layers that were not related to the summer horizon of previous years in general the faceted crystals were found under a wind crust these crusts appear to originate during the winter snow and air temperature data from automatic weather stations suggest that the katabatic storms are responsible for the formation of the wind crusts and the faceted layers frequent abrupt temperature changes up to 30 c were observed within two days due to turbulent mixing of cold air inversions the near surface air temperature variations are correlated with wind speed the latter leading the former by 6 9 hours for increasing wind and 1 4 hours for decreasing wind because of low accumulation katabatic storms affect the same snow surface for several months causing repeated air temperature fluctuations this leads to strong vapor pressure gradients and faceted crystal growth in the top snow layer on average we found two faceted layers in addition to the summer layer per year for a 4 year record in addition to its climatological significance in the snow record the formation of these layers is especially important to understand for the interpretation of microwave satellite observations of the firn

global atmospheric sensitivity to tropical sst anomalies throughout the indo pacific basin abstract the sensitivity of the global atmospheric response to sea surface temperature sst anomalies throughout the tropical indian and pacific ocean basins is investigated using the ncep mrf9 general circulation model gcm model responses in january are first determined for a uniform array of 42 localized sst anomaly patches over the domain results from the individual forcing experiments are then linearly combined using a statistically based smoothing procedure to produce sensitivity maps for many target quantities of interest including the geopotential height response over the pacific north american pna region and regional precipitation responses over north america south america africa australia and indonesia perhaps the most striking result from this analysis is that many important targets for seasonal forecasting including the pna response are most sensitive to sst anomalies in the nino 4 region 5 n 5 s 150 w 160 e of the central tropical pacific with lesser and sometimes opposite s

an inventory of active subglacial lakes in antarctica detected by icesat 2003 2008 through the detection of surface deformation in response to water movement recent satellite studies have demonstrated the existence of subglacial lakes in antarctica that fill and drain on timescales of months to years these studies however were confined to specific regions of the ice sheet here we present the first comprehensive study of these active lakes for the antarctic ice sheet north of 868 s based on 4 5 years 2003 08 of nasa s ice cloud and land elevation satellite icesat laser altimeter data our analysis has detected 124 lakes that were active during this period and we estimate volume changes for each lake the icesat detected lakes are prevalent in coastal antarctica and are present under most of the largest ice stream catchments lakes sometimes appear to transfer water from one to another but also often exchange water with distributed sources undetectable by icesat suggesting that the lakes may provide water to or withdraw water from the hydrologic systems that lubricate glacier flow thus these reservoirs may contribute pulses of water to produce rapid temporal changes in glacier speeds but also may withdraw water at other times to slow flow

late holocene deep sea benthic foraminifera from the sea of marmara abstract the benthic foraminiferal assemblages of two cores from the late holocene organic carbon rich and carbonate poor deep sea sediments of the eastern depression of the sea of marmara have been studied they were deposited under high level of primary productivity and poorly oxygenated bottom water conditions they show low diversity and are dominated by a group of species adapted to an infaunal life style with wide bathymetric distribution ca 70 2000 m in the mediterranean sea oxygen deficiency down to about 0 5 ml l does not seem adversely to affect the rate of reproduction of the dominant species belonging to melonis chilostomella buliminids and bolivinitids their distribution is primarily controlled by substrate conditions faunal similarities with fossil assemblages in association with some late quaternary sapropels and related facies from the eastern mediterranean basins suggest that they were deposited under palaeo oceanographic conditions closely similar to those of the modern sea of marmara

seasonality of the north atlantic oscillation abstract monthly sea level pressure slp data from the national centers for environmental prediction reanalysis for 1948 99 are used to develop a seasonally and geographically varying mobile index of the north atlantic oscillation naom naom is defined as the difference between normalized slp anomalies at the locations of maximum negative correlation between the subtropical and subpolar north atlantic slp the subtropical nodal point migrates westward and slightly northward into the central north atlantic from winter to summer the naom index is robust across datasets and correlates more highly than eof coefficients with historical measures of westerly wind intensity across north atlantic midlatitudes as measured by this mobile index the nao s nodes maintain their correlation from winter to summer to a greater degree than traditional nao indices based on fixed stations in the eastern north atlantic azores lisbon iceland when the naom index is extended back to 1873 its annual values during

calcareous nannofossils planktonic foraminifera and oxygen isotopes in the late quaternary sapropels of the ionian sea core m 25 4 12 a long piston core 12 20 m recovered in the ionian sea during cruise m25 4 of the r v meteor summer 1993 at a water depth of 2467 m shows an almost complete sequence of sapropels s 1 s 3 to s 10 over the last 330 ka this paper presents the results of an integrated study based on quantitative biostratigraphic analyses performed on both calcareous nannofossils and planktonic foraminifera coupled with the 18o record a decrease in syracosphaera sp 1 and an increase in the abundance of the genus rhabdosphaera and of helicosphaera carteri florisphaera profunda and of the reworked specimens has been found in the calcareous nannofossil assemblage within the sapropels the planktonic foraminiferal assemblage of the sapropels is characterized by a peak in the frequency of globigerinoides ruber var alba and rosea and neogloboquadrina dutertrei the 18o record of globigerinoides ruber and globigerina bulloides allows recognition of isotope stages 1 to 9 and shows a negative fluctuation that corresponds to the sapropel layers these features support the idea of increased productivity coupled to the presence of reduced salinity surface waters that caused the deposition of the sapropels however the need for a good understanding of the ecological requirements of modern assemblages is stressed this is necessary to correctly interpret fossil assemblages this in turn will allow a better understanding of the palaeoceanographic conditions leading to sapropel deposition

benthic foraminiferal evidence for reduced deep water circulation during sapropel deposition in the eastern mediterranean abstract an analysis of deep sea benthic foraminifera from six eastern mediterranean piston cores was carried out to determine the faunal response to the deposition of sapropel s5 formed between 125 000 and 116 000 yrs b p the pre s5 population is the most diverse being composed of miliolids articulina tubulosa gyroidina spp and various rotaliids an assemblage found near the base and top of s5 is dominated by chilostomella mediterranensis globobulimina affinis and bolivina spp and the post s5 fauna is dominated by a tubulosa and gyroidina spp the faunal data are interpreted in terms of the microhabitat preferences of the fauna based on living stained benthic foraminiferal data and associated morphological characteristics from the north atlantic epifaunal species dominate pre s5 and post s5 sediments and are associated with low organic carbon values ranging from 0 1 to 0 4 infaunal species occurring near or within sapropel layers are found with organic carbon values of 0 7 and live in environments characterized by low dissolved oxygen levels the dominance of epifaunal species within the pre s5 and post s5 sediments is interpreted to reflect low levels of food in a well oxygenated environment while the low abundance and dominance of infaunal taxa at the base and top of s5 reflects low food and low oxygen conditions although an increase in surface productivity may have occurred immediately preceding and during the deposition of s5 the critical factor in deposition of sapropel s5 is anoxia resulting from reduced ventilation of the deep waters the similarity of the faunal patterns in the six cores suggests that bathyal environmental conditions were uniform in the eastern mediterranean at depths ranging from 2042 to 3150 m during deposition of sapropel s5

snow megadunes in antarctica sedimentary structure and genesis 1 megadune fields occupy large areas in the interior of the east antarctic ice sheet and are the result of unusual snow accumulation and redistribution processes they therefore are important to surface mass balance and ice core interpretation field observations gps gpr and surface measurements have provided a detailed description of megadune sedimentation and morphology over a 70 km2 area located 200 km east of dome c a combination of remote sensing analysis using landsat and satellite radar altimetry and field measurements indicate that slope in the prevailing wind direction spwd and climatic conditions play a crucial role in megadune genesis the megadune areas tend to be characterized by slightly steeper regional slope and the presence of highly persistent katabatic winds the megadunes represent 2 to 4 m amplitude waves of 2 to 5 km wavelength formed by variable net accumulation ranging between 25 leeward faces to 120 windward faces of the accumulation in adjacent nonmegadune areas leeward faces are characterized by glazed sastrugi free surfaces and extensive depth hoar formation windward faces are covered by large rough sastrugi up to 1 5 m in height

response of benthic foraminifera to stagnant episodes a quantitative study of core ban 81 23 eastern mediterranean abstract the core investigated was raised from the floor of the ares crater in the western mediterranean ridge cobblestone area 3 at 35 52 03 n 20 47 46 e at a water depth of 3026 m forty one samples were taken from beneath within and above seven sapropel layers identified as s 1 s 3 s 4 s 5 s 6 s 7 and s 8 and two tephra layers ranging in age from approximately 5000 to approximately 250 000 years b p our study shows that the cyclically repeated stagnant episodes resulted in a strong reduction of the faunal density due to the basinal setting some displaced elements were recorded in resedimented beds anomalinoides minimus displays peak abundances in post sapropel layers thus supporting the interpretation that it is an opportunistic species suitable for a rapid repopulation of the bottom after a stagnant episode this taxon along with eponides tumidulus articulina tubulosa and to a lesser extent miliolinella subrotunda dominates the autochthonous deep water fauna other taxa are recorded in high percentages only at definite stratigraphic levels they are epistominella vitrea beneath s 6 and cassidulina laevigata beneath s 1 we consistently recorded a sparse faunule within the sapropels consisting of shallow water epiphytic rotaliforms interpreted as allochthonous transported by floating algae associated with bolivina spp and anomalinoides minimus the occurrence of bolivina spp and of buliminids in general within the sapropels is accounted for by their capability of tolerating very low oxygen levels the topmost part of the multilayered sapropel s 6 in particular is rich in bulimina exilis cassidulinoides tenuis and ellipsopolymorphina sp this sapropel which unlike the other ones originated during glacial conditions is preceded by peak abundances of faunal density a strong increase in productivity of the bottom living fauna is inferred and supported by similar findings in a nearby plateau core where drastic changes in density and diversity are recorded

el nino southern oscillation drives north atlantic oscillation as revealed with nonlinear techniques from climatic indices 1 based on the nonlinear techniques for estimation of coupling between oscillatory systems we investigate the dynamics of climatic modes characterizing global and the northern hemisphere nh processes in particular indices of the north atlantic oscillation nao and el nino southern oscillation enso for 1950 2004 are analyzed the methods based on phase dynamics modeling and nonlinear granger causality are used we infer that enso affects nao during the last half a century with confidence probability higher than 0 95 the influence is characterized with time delay in the range from a couple of months up to three years and increases during the last decade

inhomogeneous precipitation distribution and snow transport in steep terrain 1 the inhomogeneous snow distribution found in alpine terrain is the result of wind and precipitation interacting with the snow surface over topography we introduce and explain preferential deposition of precipitation as the deposition process without erosion of previously deposited snow and thus in absence of saltation a numerical model is developed describing the relevant processes of saltation suspension and preferential deposition the model uses high resolution wind fields calculated with a meteorological model arps the model is used to simulate a 120 h snow storm period over a steep alpine ridge for which snow distribution measurements are available the comparison to measurements shows that the model captures the larger scale snow distribution patterns and predicts the total additional lee slope loading well however the spatial resolution of 25 m is still insufficient to capture the smaller scale deposition features observed the model suggests that the snow distribution on the ridge scale is primarily caused by preferential deposition and that this result is not sensitive to model parameters such as turbulent diffusivity drift threshold or concentration in the saltation layer

stably stratified shear flow over low hills summary an analysis is presented for the mean flow over hills with low slopes for various kinds of stable stratification in the approach flow the froude number f based on the height is always greater than unity the analysis is based on dividing up the flow into different regions with different dynamics we concentrate on the flow in the inviscid outer region of the flow it is shown that in the lower part of the outer region the middle layer where the shear is large the upwind velocity profile and the shape of the hill rather than the upwind density profile largely determine the vertical perturbation velocity in the upper layer the structure of the flow depends largely on the form of the upwind density profile for example this largely determines the location of maximum surface wind new solutions for stable conditions are obtained when there is a constant density gradient when n ub 0 z2 and when there is an elevated inversion layer in the first and third of these cases we compare the results with the hydrostatic approximation and also obtain new general formulae for the near surface winds an approximate formula is developed for surface winds at arbitrary values of f 1 for uniform stable stratification

are productivity and stratification important to sapropel deposition microfossil evidence from late pliocene insolation cycle 180 at vrica calabria we present the results of a micropaleontological study performed on the sapropel sequence associated with insolation cycle 180 from the plio pleistocene vrica sequence calabria italy we performed a high resolution study on the 3 38 m thick layer c from a core drilled close to the classical outcrop section in which we analyze fluctuations in the abundance and composition of calcareous nannofossils and planktic and benthic foraminifera changes in the fossil assemblages reveal at least three major paleoenvironmental phases in layer c the base of the sapropel contains an abrupt decrease in benthic fauna that continues through all of layer c it also has an increase of the coccolithophorids species coccolithus pelagicus planktic foraminifera show at the same depth a peak of the cold species globorotalia scitula these changes are followed by decreases in the carbonate preservation index and in abundances of globigerinita glutinata globigerinita uvula and neogloboquadrina pachyderma sinistral which suggest cold and highly productive upwelling waters a short interval in the middle of the sapropel is characterized by low values of c pelagicus a fluctuating increase of pseudoemiliania lacunosa and among the foraminifera an increase of globigerinoides ruber together with the presence although decreased of g glutinata g uvula and n pachyderma sinistral we interpret these features as suggesting high seasonality with warm stratified and probably oligotrophic waters during summer and relatively cold conditions during winter finally the topmost interval of the vrica layer c exhibits the re appearance of p lacunosa together with abundant siliceous phytoplankton planktic microfauna show the disappearance of the cold species g glutinata g uvula and n pachyderma sinistral thus this interval appears to be characterized by warmer temperature the transition from the laminated to the massive sediment displays a sequence of events including a decrease of the carbonate preservation index and peaks of globorotalia inflata and g scitula suggesting again upwelling and mixing of the whole water column and thus transition to the oxygenated conditions characterizing the massive layer neither increased productivity nor stratification appear to characterize the whole sapropel interval which is however always dysoxic

temporal variability in living deep sea benthic foraminifera a review the deep ocean environment is disturbed by various processes many of which involve episodic inputs of organic matter some inputs e g phytodetritus at mid high latitudes in the north atlantic and northeast pacific are seasonally pulsed others e g falls of whale carcasses are irregular and unpredictable but together they evoke a variety of responses from the benthic biota in the case of deep sea foraminifera only those responses arising from seasonal food pulses have been fairly well documented the population dynamics of deep sea benthic foraminifera total live populations and individual species appear to be controlled largely by two inversely related parameters the flux of organic matter to the seafloor and concentrations of oxygen in the sediment porewater organic matter food inputs are most intense along bathyal continental margins and their oxidation often leads to the depletion of oxygen in surface sediments under these conditions foraminiferal faunas are dominated by low oxygen tolerant infaunal species the abundance of which fluctuate in response to seasonally varying amounts of food and oxygen at some sites e g sagami bay off japan species migrate up and down in the sediments tracking critical oxygen concentrations where oxygen concentrations are consistently low less than about 0 5 ml l 1 as in parts of the california borderland foraminifera may undergo population increases solely in response to food pulses in the abyssal north atlantic and in some continental margin areas of this ocean organic matter inputs are weaker and do not lead to oxygen depletion within surface sediments these systems are food limited and seasonal population fluctuations reflect the availability of food phytodetritus rather than oxygen here the species which respond to phytodetritus are mainly epifaunal or shallow infaunal opportunists which represent a small proportion of highly diverse communities 2 or 3 out of 120 species per core of 25 5 cm2 surface area seasonal phytodetrital pulses to the deep seafloor and hence foraminiferal population dynamics are not entirely predictable being dependent on climatic and upper ocean processes they vary in intensity from year to year and occasionally e g at the porcupine abyssal plain pap in 1997 fail to materialise foraminiferal responses to irregular non seasonal organic matter inputs are poorly known however there is some evidence that whale falls turbidite deposits hydrothermal vents and seeps are exploited by species typical of organically enriched low oxygen environments rather than by a specialised fauna fossil foraminiferal assemblages from bathyal and abyssal environments may provide evidence for an increase or decrease in the seasonality of surface production as well as for longer term changes in palaeoproductivity however the accurate interpretation of this record depends on filling the many gaps which remain in our understanding of relations between benthic foraminiferal ecology and seasonal phenomena in the deep ocean

low frequency variability in the northern hemisphere winter geographical distribution structure and time scale dependence abstract low frequency variability in wintertime 500 mb height is examined with emphasis on its structure geographical distribution and frequency dependence a 39 year record of 500 mb geopotential height fields from the nmc analyses is time filtered to partition the fluctuations into frequency bands corresponding to periods of 10 60 days 60 180 days and 180 days winter is defined as the six month period november through april variance teleconnectivity and anisotropy fields and selected loading vectors derived from orthogonal and oblique rotations of the eigenvectors of the temporal correlation matrix for each band are shown and discussed the variability in all frequency bands exhibits substantial anistropy with meridionally elongated features arranged as zonally oriented wave trains prevailing over the continents and zonally elongated features organized in the form of north south oriented dipole patterns prevailing over the oceanic sectors of the hemisphere the wave trains are most pronounc

the linear sensitivity of the north atlantic oscillation and eddy driven jet to ssts abstractthe north atlantic oscillation nao and eddy driven jet contain a forced component arising from sea surface temperature sst variations due to large amounts of internal variability it i

holocene atmosphere ocean interactions records from greenland and the aegean sea we compare paleoclimate proxy records from central greenland and the aegean sea to offer new insights into the causes timing and mechanisms of holocene atmosphere ocean interactions a direct atmospheric link is revealed between aegean sea surface temperature sst and high latitude climate the major holocene events in our proxies of aegean sst and winter spring intensity of the siberian high gisp2 k record follow an 2300 year spacing recognised also in the 14c record and in worldwide holocene glacier advance phases suggesting a solar modulation of climate we argue that the primary atmospheric response involved decadal centennial fluctuations in the meridional pressure gradient driving aegean sst events via changes in the strength duration and or frequency of northerly polar continental air outbreaks over the basin the observed natural variability should be accounted for in predictions of future climate change and our timeframe for the aegean climate events in addition provides an independent chronostratigraphic argument to middle eastern archaeological studies

observed impact of atlantic sst anomalies on the north atlantic oscillation the large scale patterns of covariability between monthly sea surface temperature sst and 500 mb height anomalies z500 in the atlantic sector are investigated as a function of time lag in the ncep ncar reanalysis 1958 97 in agreement with previous studies the dominant signal is the atmospheric forcing of sst anomalies but statistically significant covariances are also found when sst leads z500 by several months in winter a panatlantic sst pattern precedes the north atlantic oscillation nao by up to 6 months such long lead time covariance is interpreted in the framework of the stochastic climate model reflecting the forcing of the nao by persistent atlantic sst anomalies a separate analysis of midlatitudes 208 708n and tropical 208s 208n sst anomalies reveals that the bulk of the nao signal comes from the midlatitudes a dipolar anomaly with warm sst southeast of newfoundland and cold sst to the northeast and southeast precedes a positive phase of the nao and it should provide a prediction of up to 15 of its monthly variance several months in advance since the forcing sst pattern projects significantly onto the tripole pattern generated by the nao these results indicate a positive feedback between the sst tripole and the nao with a strength of up to 25 mk 21 at 500 mb or 2 3 mb k21 at sea level additionally a warming of the tropical atlantic 208s 208n roughly symmetric about the equator induces a negative nao phase in early winter this tropical forcing of the nao is nearly uncorrelated with and weaker than that resulting from the midlatitudes and is associated with shorter lead times and reduced predictive skill

global sst influence on twentieth century nao variability recent studies have suggested that sea surface temperature sst is an important source of variability of the north atlantic oscillation nao here we deal with four basic aspects contributing to this issue 1 we investigate the characteristic time scales of this oceanic influence 2 quantify the scale dependent hindcast potential of the nao during the twentieth century as derived from sst driven atmospheric general circulation model agcm ensembles 3 the relevant oceanic regions are identified corresponding sst indices are defined and their relationship to the nao are evaluated by means of cross spectral analysis and 4 our results are compared with long term coupled control experiments with different ocean models in order to ensure whether the spectral relationship between the sst regions and the nao is an intrinsic mode of the coupled climate system involving the deep ocean circulation rather than an artefact of the unilateral sst forcing the observed year to year nao fluctuations are barely influenced by the sst on the decadal time scales the major swings of the observed nao are well reproduced by various ensembles from the middle of the twentieth century onward including the negative state in the 1960s and part of the positive trend afterwards a six member echam4 t42 ensemble reveals that the sst boundary condition affects 25 of total decadal mean and interdecadal trend nao variability throughout the twentieth century the most coherent nao related sst feature is the well known north atlantic tripole additional contributions may arise from the southern pacific and the low latitude indian ocean the coupled climate model control runs suggest only the north atlantic sst nao relationship as being a true characteristic of the coupled climate system the coherence and phase spectra of observations and coupled simulations are in excellent agreement confirming the robustness of this decadal scale north atlantic air sea coupled mode

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

tropical atlantic air sea interaction and its influence on the nao an atmospheric general circulation model agcm is forced with a prescribed sst dipole anomaly in the tropical atlantic to investigate the cause of cross equatorial sst gradient cesg variability and its teleconnection to the extratropics the model response bears a striking resemblance to observations in both the tropics and extratropics the tropical response is robust and can act to reinforce the prescribed sst anomalies through wind induced evaporation a new feedback mechanism involving low level stratiform clouds in the subtropics is also identified in the model and observations the tropical sst dipole forces a barotropic teleconnection into the extratropics that projects onto the north atlantic oscillation nao it further induces the extratropical portion of the north atlantic sst tripole when the agcm is coupled with an ocean mixed layer model cesg variability thus appears to be the centerpiece of a pan atlantic climate pattern observed to extend from the south atlantic to greenland

icesat antarctic elevation data preliminary precision and accuracy assessment 1 since first light on february 20th 2003 nasa s ice cloud and land elevation satellite icesat has derived surface elevations from 86 n to 86 s latitude these unique altimetry data have been acquired in a series of observation periods in repeated track patterns using all three geoscience laser altimeter system glas lasers here we focus on antarctic ice sheet elevation data that were obtained in 2003 2004 we present preliminary precision and accuracy assessments of selected elevation data and discuss factors impacting elevation change detection we show that for low slope and clear sky conditions the precision of gla12 laser 2a release 21 data is 2 1 cm and the relative accuracy of icesat elevations is 14 cm based on crossover differences

the dynamics of nao teleconnection pattern growth and decay this investigation performs both diagnostic analyses with ncep ncar re analysis data and forced barotropic model calculations to examine the dynamical mechanisms associated with the growth and decay of the north atlantic oscillation nao teleconnection pattern the diagnostic calculations include projection and composite analyses of each term in the stream function tendency equation the results of the analyses reveal a complete life cycle of growth and decay within approximately two weeks the positive nao phase is found to develop after anomalous wavetrain propagation across the north pacific to the east coast of north america this contrasts with the negative nao phase which appeared to develop in situ both high frequency period 10 days transient eddy fluxes drive the nao growth after the nao anomaly attains its maximum amplitude the high frequency transient eddy fluxes continue to drive the nao anomaly in a manner that is consistent with a positive feedback process the decay of the nao occurs through both the divergence term and the low frequency transient eddy fluxes the temporal and spatial properties of the divergence term are found to be consistent with ekman pumping these results illustrate many important differences between the nao and pacific north american pna teleconnection patterns perhaps most striking being that the nao life cycle is dominated by nonlinear processes whereas the pna evolution is primarily linear in addition the relation between the nao and the zonal index is discussed copyright 2003 royal meteorological society

interannual variability of planktic foraminiferal populations and test flux in the eastern north atlantic ocean jgofs planktic foraminiferal assemblages vary in response to seasonal fluctuations of hydrographic properties between water masses and after periodical changes and episodic events e g reproduction storms distinct annual variability of the planktic foraminiferal flux is also known from sediment trap data in this paper we discuss the short term impacts on interannual flux rates based on data from opening closing net hauls obtained between the ocean surface and 500 m water depth data were recorded during april may june and august at around 47 n 20 w biotrans in 1988 1989 1990 1992 1993 and during may 1989 and 1992 at 57 n 20 22 w species assemblages closely resemble each other when comparing the mixed layer fauna with the fauna of the upper 100 m and the upper 500 m of the water column in addition species assemblages 100 m are almost indistinguishable from assemblages that are 125 m in test size the standing stock of planktic foraminifers at biotrans can vary by more than one order of magnitude over different years however species assemblages may be similar when comparing corresponding seasons early summer assemblages june are distinctly different from late summer assemblages august significant variations in the species composition during spring april may are independent of the mixed layer depth spring assemblages are characterized by high numbers of globigerinita glutinata in particular day to day variations of the number of specimens and in species composition may have the same order of magnitude as interannual variations this appears to be independent of the reproduction cycle species assemblages at 47 n and 57 n are similar during spring although surface water temperatures and salinities differ by up to 10 c and 0 7 psu we suggest that the main factors controlling the planktic foraminiferal fauna are the trophic properties in the upper ocean productive layer planktic foraminiferal carbonate flux as calculated from assemblages reveals large seasonal variations a quasi annual periodicity in flux levels and substantial differences in timing and magnitude of peak fluxes at the biotrans station the average annual planktic foraminiferal caco 3 fluxes at 100 and 500 m depth are estimated to be 22 4 and 10 0 g m 2 yr 1 respectively

barotropic wave propagation and instability and atmospheric teleconnection patterns abstract a global barotropic model linearized about the 300 mb climatological mean january flow is perturbed by applying a series of localized forcings distributed throughout the tropics and subtropics structures which resemble the observed pacific north american and east atlantic teleconnection patterns noted by wallace and gutzler 1981 tend to recur in the responses similar patterns are found to result from the dispersion of isolated initial perturbations placed at a variety of locations in the tropics and midlatitudes it is shown that these structures are related to the most rapidly growing mode associated with barotropic instability of the zonally varying climatological basic state in the absence of damping this mode has an e folding time of about a week and a period close to 50 days in localized regions the instantaneous growth rates can be competitive with those of baroclinic instability these episodes of rapid local barotropic growth are interspersed with intervals in which the local

trophic control of benthic foraminiferal abundance and microhabitat in the bathyal gulf of lions western mediterranean sea surface sediment was sampled at two bathyal sites in the southwestern gulf of lions in the western mediterranean sea in february and august 1997 to study the distribution and microhabitat of living rose bengal stained deep sea benthic foraminifera both standing stock and diversity of the faunas and the microhabitat of distinct species mirror the trophic situation and the depth of the oxidised layer at the different sites our results suggest that the faunas do not comprise highly opportunistic species and are adapted to rather stable environments in the axial channel of the lacaze duthiers canyon organic matter fluxes are enhanced due to advective transport of organic matter resulting in elevated oxygen consumption rates in the surface sediment and a rather thin oxidised layer the corresponding benthic foraminiferal fauna is characterised by rather high standing stock and diversity and a well developed deep infauna in addition to freshly deposited phytodetritus more degraded organic matter seems to be an important food source in contrast at the open slope organic matter fluxes and oxygen consumption rates in the surface sediment are lower and the oxidised layer is much thicker than inside the canyon the corresponding benthic foraminiferal fauna comprises mainly epifaunal and shallow infaunal species with much lower standing stocks and clear differences between february and august in august standing stocks are higher and the average living depths of most species shift towards the sediment surface these differences can be attributed to patchiness or represent a seasonal trophic signal

a dynamic concept for eastern mediterranean circulation and oxygenation during sapropel formation we propose that intermittent bottom water ventilation occurred throughout periods of sapropel deposition and that the recently reported sapropel interruptions represent centennial scale episodes of enhanced frequency intensity of that process in essence the modern high frequency variability in deep water formation affected by climatic variability over the northern basins on seasonal to longer time scales prevailed also at times of sapropel deposition although the overall ventilation state was much reduced this concept is supported by detailed multiple species isotope records for three aegean cores the presence of abundant globorotalia truncatulinoides within especially sapropels s7 and s8 in the western levantine basin observations of three rapid benthic repopulations within sapropel s6 in the deep western levantine basin a report of continuous benthic presence through sapropel s1 at intermediate deep locations offshore libya and further supporting information from the literature in the aegean records concomitant abundance of low oxygen tolerant benthic foraminifera and presence of the more oxyphilic benthic foraminifer uvigerina mediterranea with surface similar 13c values indicate repeated deep water re oxygenation events throughout the deposition of s1 the observations of a continuous benthic presence through s1 offshore from libya imply that no persistent anoxia developed at mid depth levels in that region which is far removed from direct deep ventilation influences the abundance of deep mesopelagic g truncatulinoides through several sapropels from the western levantine basin also suggests the presence of bio available oxygen at many hundreds of meters of depth moreover the rapid intermittent benthic repopulations within sapropels from the deep eastern mediterranean imply that bottom water anoxia was spatially restricted and or of a highly intermittent nature the short time scales of these repopulation events are incompatible with titration of an extensively anoxic water column and subsequent re establishment of water column anoxia we suggest that where anoxic azoic conditions were present they most likely were restricted to a veneer at the sediment water interface the extent of such an anoxic blanket depends on the balance between advective oxygen supply into the deep sea and biological and chemical oxygen demand the demand functions imply a decoupling of oxygenation from water mass advection allowing export production and corg posting rates to the sea floor to delimit the extent of the anoxic blanket in both space and time low productivity regions would develop no anoxic blanket allowing for the observed persistence of deep dwelling planktonic and bottom dwelling benthic faunas

foraminiferal record and environmental changes during the deposition of the early middle pleistocene sapropels in southern italy a foraminiferal investigation documents the palaeoenvironmental changes across the sapropel units associated with insolation cycles 90 and 86 in the early middle pleistocene im fosso 5 agosto section basilicata southern italy three benthic foraminiferal fossil associations associations a b and c identified by performing hierarchical cluster analysis on the quantitative data can be considered diagnostic of the palaeoenvironmental conditions before during and after the sapropel intervals they indicate a gradual decrease of bottom water oxygenation prior to the onset of sapropel deposition and a rapid return to stable environmental conditions at the end of the sapropel events the constant presence of benthic foraminifera throughout the sapropels implies that the bottom environment was not totally anoxic the high resolution distributional pattern of planktonic and benthic foraminifera within the sapropel associated with i cycle 90 documents a surface water cooling with consequent rapid re oxygenation of bottom waters that subdivides this interval in two phases both of them are characterized by an early subphase with warm climate conditions a decrease of salinity in surficial water layers and dominated by the low oxygen tolerant benthic species globobulimina affinis the late subphase shows thermal stratification during summer and a relatively deep and oxygenated mixed layer during winter in this subphase the contemporaneous replacement of g affinis the bless opportunistic but more resistant to low oxygen conditionsq species with bolivina alata bolivina dilatata and brizalina spathulata the bless resistant to low oxygen conditionsq species indicates the relative oxygen improvement in sediment pore water the frequent changes detected in the sapropel associated faunal composition underline the unstable nature of bottom water oxygen content d 2004 elsevier b v all rights reserved

on the glaciological meteorological and climatological significance of antarctic blue ice areas this paper presents the current state of our knowledge about antarctic blue ice areas scattered widely over the antarctic continent yet covering only approximately 1 of its surface area blue ice areas have some peculiar characteristics that make them of particular interest for planetary geologists glaciologists meteorologists and climatologists for instance blue ice areas are subject to net ablation mainly by sublimation since any accumulation is easily swept off their smooth surfaces by winds moreover they are significantly warmer than their surroundings and the wind over them is generally more gusty an important feature of blue ice is its relatively low albedo 0 56 compared with that of snow 0 80 blue ice is probably considerably smoother than snow in the aerodynamic sense with roughness lengths as low as 3 10 6 m which indicates that blue ice is probably the only permanent natural surface over which the air flow is mainly in the aerodynamic smooth regime further since it is likely that very old ice is exposed at the surface of some blue ice areas this ice would be of great interest for paleoclimatic studies it has also been suggested that blue ice areas are sensitive to climate change this would make them useful as antarctic climate indicators because they can easily be monitored by satellite finally this paper addresses several gaps in our knowledge about blue ice areas and gives suggestions for future blue ice area research

analysis of antidune migration direction 1 antidunes are bed forms characteristic of upper regime unidirectional flows contrary to bed forms developed in lower regime flows antidunes not only can propagate in the downstream direction but can propagate upstream or remain stationary in this work we analyze the stable hydraulic conditions that determine each of the three antidune movement possibilities and a new theory is developed for distinguishing the occurrence of each of these conditions the theory is developed from an energy balance over a symmetrical antidune for this the bernoulli equation is applied between the antidune crest and antidune trough and the pressure head is corrected to account for the centrifugal forces generated by curvilinear flow manipulation of the fundamental equations produces an antidune mobility dimensionless number fa dependent on the froude number the mean water depth and the antidune wavelength the critical value of the antidune mobility number fa 1 corresponds to the stationary condition while values higher and lower than the critical correspond to downstream and upstream propagation respectively theory predicts that for a given froude number downstream migrating antidunes are formed for higher water depth wavelength ratios than for upstream migrating antidunes likewise by introducing a restriction for the maximum stationary wave height above antidunes theory predicts that downstream migrating antidunes could attain steeper height wavelength ratios than upstream migrating antidunes comparison with published experimental data in literature largely showed agreement between theory and experimental observations

spiral trough diversity on the north pole of mars as seen by shallow radar sharad we combine observations from ground penetrating radar and optical instruments to conduct a comprehensive survey of spiral troughs on the north polar layered deposits of mars our survey reveals that all north polar troughs have common characteristics but there is strong regional diversity we divide the north polar layered deposits npld into eight regions based on observations of morphology and stratigraphy in order to classify the spiral troughs morphologic features that separate the regions include central promontories topographic undulations bedrock floors and trough asymmetry among others we demonstrate here that the troughs formed during two periods the first generation of troughs formed on the main lobe and in part of gemina lingula during accumulation of 600 m of ice and dust the second generation of troughs formed stratigraphically higher and immediately after large scale erosion in gemini scopuli which we conclude created the slopes necessary for troughs to form we test scenarios of trough evolution and find that only three concurrent processes are required for their formation wind transport insolation induced sublimation and atmospheric deposition our observations are inconsistent with other hypothesized processes to produce spiral troughs including incision after the formation of the npld fracturing due to flowing ice and sublimation driven patterns from insolation

coupled ocean atmosphere response to indian ocean warmth 1 the coupled ocean atmosphere response to indian ocean warmth is studied it is shown with atmospheric models that indian ocean warmth forces a positive polarity phase of the north atlantic oscillation nao confirming results of previous studies coupled model experiments show that this nao response forces a local air sea feedback over the north atlantic ocean which intensifies the nao response this enhancement is realized through a positive feedback between the nao atmospheric circulation anomaly and a tripolar north atlantic sst pattern consistent with other studies on north atlantic air sea interactions it is concluded that the north atlantic and european climate response to indian ocean warming may be considerably greater than hitherto judged from the analyses of atmospheric model experiments alone

eurasian snow cover variability and northern hemisphere climate predictability we present observational evidence demonstrating dynamic interactions and feedbacks between multi seasonal snow cover and winter time circulation anomalies over mid high latitudes the cooling effect of snow cover is associated with a strengthened and more expansive siberian high with more frequent topographically constrained intrusions west and north early season snow cover variability leads to altered general circulation patterns consistent with the dominant mode of winter variability observed in the northern hemisphere troposphere the implications of the surface atmosphere coupling for seasonal to interannual predictability are also discussed

extreme firn metamorphism impact of decades of vapor transport on near surface firn at a low accumulation glazed site on the east antarctic plateau snow and firn properties control the transport of vapor gases and water between the atmosphere and the underlying strata an understanding of this transport and the properties that control it is important for predicting air snow transfer of chemical species and for interpreting ice cores remote sensing images of east antarctica show large areas of alternating light and dark bands these low amplitude long wavelength features have glazed downwind faces and rough upwind faces and are called megadunes the first linked measurements of the permeability and the associated microstructure for a glazed area within a well defined megadune area are reported in this paper permeability and density were measured along with grain scale properties derived from digital image processing of preserved thick sections at this cold low accumulation glazed site a clear layering pattern exists in the top meter the firn density ranges from 0 24 to 0 50 g cm 3 permeability measurements range from 50 x 10 10 to 200 x 10 10 2 several times greater than corresponding profiles from warmer higher accumulation sites like siple dome antarctica it is shown that buoyancy driven natural convection may be important in post depositional processes in very cold low accumulation sites like this

continental scale simulation of the antarctic katabatic wind regime abstract katabatic winds are a common feature of the lower antarctic atmosphere although these drainage flows are quite shallow there is increasing evidence that the low level circulations are an important component in establishing large scale tropospheric motions in the high southern latitudes three dimensional numerical simulations of the antarctic katabatic wind regime and attendant tropospheric circulations have been conducted over the entire continent to depict the topographically forced drainage patterns in the near surface layer of the atmosphere results of the simulation enable a mapping of katabatic wind potential and identification of coastal regions which may experience anomalously intense katabatic winds a large upper level cyclonic circulation forms rapidly in response to the evolving katabatic wind structure in the lower atmosphere suggesting that the drainage circulations are an important component in prescribing the resulting resulting circumpolar vortex these results imply that som

late quaternary paleoceanography as recorded by benthonic foraminifera in strait of sicily sediment sequences at specific times during the late quaternary a widespread low salinity surface water layer was produced over the eastern mediterranean which created stagnant conditions and associated deposition of sapropelic muds in the deep basins the strait of sicily has been positioned above the anoxic deeper water masses and is therefore devoid of sapropel deposits sediment sequences in the region contain a valuable record of upper bathyal 200 1000 m benthonic foraminiferal change during times of deep basin stagnation quantitative examiniation of benthonic foraminiferal assemblages in strait of sicily quaternary cores generally reveals changes coeval with sapropels s1 s2 s4 s5 and s6 the benthonic foraminiferal expression is seen as increases in frequency ofglobobulimina affinis globobulimina pseudospinescens chilostomella mediterranensis bolivina dilatata and otherbolivina species during intervals corresponding to the episodic abyssal stagnation events some cores also display a decrease incassidulina carinata and an increase inarticulina tubulosa similar assemblage changes have been previously documented to be closely associated with the sapropel layers in the deep basins of the eastern mediterranean the actual sapropel layers usually do not contain benthonic foraminifera however in the strait of sicily area the species exhibit less drastic changes than in the deep eastern basins because of the less severe anoxic conditions in the deep eastern basins benthonic foraminifera almost totally disappeared in sapropel layers at the same time there was a general reduction in foraminiferal numbers in the shallower strait area

sedimentation waves on the martian north polar cap analogy with megadunes in antarctica complex interactions between katabatic winds and the cryosphere may lead to the formation of sedimentation waves at the surface of ice sheets these have been first described and named snow megadunes in antarctica here we use topographic data optical images subsurface radar soundings and spectroscopic data acquired by mars orbiters to show that the surface of the martian north polar cap displays two superimposed sets of sedimentation waves with differing wavelengths these sedimentation waves have similarities with antarctic snow megadunes regarding their surface morphology texture grain size asymmetry and internal stratigraphic architecture both sets of martian sedimentation waves present young ice and occasional sastrugi fields indicative of net accumulation on their shallow dipping upwind sides their tops and the intervening troughs old layers of dusty ice indicative of net ablation are exhumed on the steep dipping downwind sides of the larger waves smooth surfaces of coarse grained ice indicative of reduced accumulation associated with sublimation metamorphism cover the steep dipping downwind sides of the smaller waves these surface characteristics and the internal stratigraphy revealed by radar soundings are consistent with the interpretation that both sets of martian sedimentation waves grow and migrate upwind in response to the development of periodic accumulation ablation patterns controlled by katabatic winds the recognition of these sedimentation waves provides the basis for the development of a common model of ice wind interaction at the surface of martian and terrestrial glaciers martian smaller waves characterized by reduced net accumulation on their downwind sides are analogous to antarctic snow megadunes that have been described so far a terrestrial equivalent remains to be discovered for the larger martian waves characterized by net ablation on their downwind sides 2014 elsevier b v

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

impacts of an accumulation hiatus on the physical properties of firn at a low accumulation polar site 1 recent field investigations of a megadune region of east antarctica provide evidence that differences in grain size thermal conductivity and permeability across a megadune profile are due to spatial accumulation variability in the absence of significant microclimate variations the megadunes are low amplitude 2 8 m long wavelength 2 5 km bands with perceptible but low accumulation less than 40 mm water equivalent weq yr 1 and accumulation hiatus within several kilometers proximity as determined by remote sensing surface feature classification and ground penetrating radar profiling our hypothesis that accumulation rate impacts the extent of temperature gradient driven metamorphic growth in low accumulation rate sites is supported by measurements of various firn physical properties relatively small differences in accumulation rate less than 40 mm weq yr 1 result in large differences in physical properties including grain size thermal conductivity and permeability which are apparent in satellite based microwave data from both passive and active sensors the differences in physical snow structure between low accumulation areas and accumulation hiatus areas in the near surface are sufficiently distinct that evidence of past accumulation hiatus should be observable in the physical and chemical properties of an ice core record

palaeoclimate and the formation of sapropel s1 inferences from late quaternary lacustrine and marine sequences in the central mediterranean region abstract synchronous responses to climatic changes during the late pleistocene holocene transition are inferred from marine and lacustrine stratigraphic records in the central mediterranean region new stratigraphic data are presented from well dated sequences in the meso adriatic depression mad two crater lakes in the lazio region and in the tyrrhenian sea the sequences all span the last termination and the holocene but we focus here on the evidence in each record for the time period during which sapropel s1 formed in the mediterranean ca 9 0 to 6 8 cal kyr b p the new records provide evidence of palaeoenvironmental changes on land and sea that can be reconstructed at a high temporal resolution and which throw some light on the processes which led to the formation of s1 the collective evidence indicates that i organic rich sediments occurred in both the marine and the crater lake sites during the time of formation of the s1 sapropel ii there is evidence of increased stratification and anoxia in the sea water column during the period of s1 formation iii the s1 period in the study area is divisible into two sub phases s1a and s1b which reflect short term variations in oceanographic conditions stratification and anoxia iv changes in stratification in the marine column were contemporaneous with regional climate variations that are inferred from the terrestrial records we conclude that the key factor that initiated the formation of s1 was increased discharge of freshwater into the mediterranean following a change post 9 0 cal kyr b p to a warmer and wetter climate furthermore the period of s1 formation was interrupted by a short lived episode ca 500 years of comparatively cooler and drier conditions during the early middle holocene transition emht

air flow over a two dimensional hill studies of velocity speed up roughness effects and turbulence wind tunnel measurements have been made of the streamwise mean and turbulent velocities over a rough bell shaped two dimensional hill with height h and maximum slope 0 26 placed in a neutrally stable boundary layer of thickness 10 h and roughness length zo 0 02 h close agreement is found between the mean velocity and predictions obtained from taylor s 1977 computational model and jackson and hunt s 1975 analytical linearized model for locations at or upwind of the hill top but not in the wake examination of the models shows that the shear stresses are only important in an inner region close to the hill surface so that as suggested by jackson and hunt 1975 the perturbation to the mean flow outside this region is essentially inviscid the theory shows that over very rough surfaces such as wooded or urban terrain the height of this inner region can be of the same order as the height of the roughness elements so that in our experiments no measurements could be made in this region in a second experiment flow over a smooth hill on a rough surface was studied the additional increase of wind speed over the hill top can be estimated by assuming a linear superposition of the velocity changes produced by the changes in elevation and in surface roughness in this case rough to smooth in the lee of a hill however the change in roughness significantly alters the flow with flow separation being suppressed and here a linear superposition is not appropriate finally we consider why observed changes in turbulence structure close to the surface differ from those well above the surface calculations of these changes based on the simple theoretical arguments of equilibrium shear layers and rapidly distorted turbulent flows agree well with turbulence measurements in wind tunnels and in the field

benthic foraminiferal successions across late quaternary mediterranean sapropels abstract benthic foraminiferal records across late quaternary mediterranean sapropels s6 s5 and s1 are reviewed and re considered in the light of recent advances in foraminiferal ecology it is suggested that the main factor controlling the foraminiferal successions that occur immediately before and after sapropel deposition is the amount of time involved in the onset of anoxic conditions and in the re oxygenation of the benthic environment faunas dominated by deep infaunal taxa such as globobulimina and chilostomella reflect a very gradual decrease or increase of bottom water oxygenation post sapropel faunas dominated by small biconvex trochospiral taxa which are inferred to have a much more opportunistic life strategy are typical of a very rapid re oxygenation of the benthic environment after sapropel deposition the time involved in re oxygenation depends upon the mechanism causing sapropel formation the faunal succession found above sapropel s5 suggests a basin with a strong density gradient in the upper part of the water column during sapropel deposition followed by a rapid turnover of the following column and quick re oxygenation of the benthic environment in contrast the faunal succession above sapropel s6 suggests a water column with a more gradual density gradient deeper in the basin a progressive deepening of the halocline and a very slow increase of bottom water oxygenation

impact pressures and flow regimes in dense snow avalanches observed at the vallee de la sionne test site 1 a fundamental problem in avalanche engineering is to determine the impact pressures exerted on structures this task is complicated because snow avalanches flow in a variety of regimes primarily depending on snow temperature and moisture content in this paper we address this problem by analyzing measured impact pressures flow velocities and flow depths of five vallee de la sionne avalanches the measurements are made on a 20 m high tubular pylon instrumented with high frequency pressure transducers and optoelectronic velocity sensors in the observed avalanches we find both subcritical and supercritical flow regimes typical froude numbers were smaller than 6 the subcritical regime fr 1 is characterized by a flow plug riding above a highly sheared basal layer the measured pressures are large and velocity independent in contradiction to calculation procedures pressure fluctuations increase with flow depth indicating a kinematic stick slip phenomena which is largest at the basal layer supercritical flow regimes 1 fr 6 are characterized by a sheared flow all over the avalanche depth in this regime the impact pressure is velocity dependent we derive relationships governing impact pressure as a function of the froude number and therefore flow regime encompassing all the observed avalanches

a consideration of the dune antidune transition in fine gravel hydraulic data defining the dune antidune transition in fine gravel are compared with potential flow theory and information is drawn from published experiments and field based studies attention is given to both transitional bedforms and the development of downstream migrating antidunes in the latter case most data pertain to sand beds and not to gravel empirical data provide some weak support for the theoretical notion that the transition occurs at progressively lower froude numbers at greater relative depths although a critical froude number of 0 84 may reasonably be applied for the beginning of the dune to antidune transformation lag effects and a possible depth limitation ensure that transitional bedforms may persist across a broad range of froude numbers from 0 5 to 1 8 this latter observation has great relevance for palaeohydraulic estimates derived from outcrop data whereas the application of theoretical bedform existence fields based upon potential flow theory to fine gravel was previously purely speculative the addition of experimental and field data to these plots provides a degree of confidence in applying stability theory to practical geological problems for the first time laboratory data pertaining to downstream migrating gravel antidunes are compared with theory these bedforms have been reported from certain experimental near critical flows above sand or gravel beds but have been observed infrequently in natural streams however there are no detailed studies from natural rivers and only a few contentious identifications from outcrops nevertheless the limited hydraulic data conform to theoretical expectations

extent of low accumulation wind glaze areas on the east antarctic plateau implications for continental ice mass balance persistent katabatic winds form widely distributed localized areas of near zero net surface accumulation on the east antarctic ice sheet eais plateau these areas have been called glaze surfaces due to their polished appearance they are typically 2 200km2 in area and are found on leeward slopes of ice sheet undulations and megadunes adjacent leeward high accumulation regions isolated dunes are generally smaller and do not compensate for the local low in surface mass balance smb we use a combination of satellite remote sensing and field gathered datasets to map the extent of wind glaze in the eais above 1500m elevation mapping criteria are derived from distinctive surface and subsurface characteristics of glaze areas resulting from many years of intense annual temperature cycling without significant burial our results show that 11 2 1 7 or 950 143 103 km2 of the eais above 1500m is wind glaze studies of smb interpolate values across glaze regions leading to overestimates of net mass input using our derived wind glaze extent we estimate this excess in three recent models of antarctic smb at 46 82 gt the lowest input model appears to best match the mean in regions of extensive wind glaze

the relationship between the north atlantic oscillation and el nino southern oscillation we have applied a multiresolution cross spectral analysis technique to resolve the temporal relationship between the nao and enso the study shows significant coherence between nao and nino3 sst in about 70 of the warm enso events from 1900 to 1995 of which 33 and 37 are associated with a 5 to 6 year period e1 and a 2 to 4 year period e2 oscillation terms in the spectral decomposition respectively the dominant teleconnection pattern associated with changes in the mean atmospheric circulation during the initial winter of a typical e1 and e2 events is the positive phase of the pacific north american pna pattern non coherence between the nao and enso occurs during relatively weak nino3 sst anomaly with a teleconnection pattern which shows a strong negative phase of the nao and a pattern which resembles a weak eastward shifted negative phase of the pna pattern