geochemical characteristics of deep sea sediments from the arabian sea a high resolution study abstract five deep sea cores from the arabian sea covering a time interval of 170 ky were sampled at high resolution and analysed for major and trace elements the stratigraphy of the cores was obtained by comparing the ba al ratio with the specmap data this method is based on the close correlation between ba concentrations or ba al ratios and oxygen isotope ratios 18o of foraminifera in arabian sea sediments ba al ratios used as a productivity proxy are variable but high in all deep sea cores of the arabian sea indicating a basin wide influence of nutrient rich water masses compared to glacial intervals the warmer periods are characterised by higher element al ratios of proxies which are directly ba ca sr p i e hard parts of organisms or indirectly u 230thex related to biological productivity 230thex provides evidence for intense boundary scavenging caused by high productivity due to enhanced upwelling and terrigenous input from the indus fan the mn distribution in a core from the western arabian sea shows enrichments during interglacial periods and may indicate mn export owing to the presence of a stronger oxygen minimum zone several processes limit the applicability of proxies intercalated turbidites in the deep sea cores can be identified by means of si al ti al and zr al ratios versus depth due to the enrichment of quartz ti minerals and zircon in the basal layer these elements are also important for the reconstruction of the history and extent of the eolian dust input diagenetic redistribution of redox sensitive elements occurs at the boundaries between turbidites and normal pelagic sedimentation and may mask or destroy primary signals

deep ocean fluxes and their link to surface ocean processes and the biological pump abstract intense studies of upper and deep ocean processes were carried out in the northwestern indian ocean arabian sea within the framework of jgofs and related projects in order to improve our understanding of the marine carbon cycle and the ocean s role as a reservoir for atmospheric co2 the results show a pronounced monsoon driven seasonality with enhanced organic carbon fluxes into the deep sea during the sw monsoon and during the early and late ne monsoon north of 10 n the productivity is mainly regulated by inputs of nutrients from subsurface waters into the euphotic zone via upwelling and mixed layer deepening deep mixing introduces light limitation by carrying photoautotrophic organisms below the euphotic zone during the peak of the ne monsoon nevertheless deep mixing and strong upwelling during the sw monsoon provide an ecological advantage for diatoms over other photoautotrophic organisms by increasing the silica concentrations in the euphotic zone when silica concentrations fall below 2 mol l 1 diatoms lose their dominance in the plankton community during diatom dominated blooms the biological pathway of uptake of co2 the biological pump appears to be more efficient than during blooms of other organisms as indicated by organic carbon to carbonate carbon rain ratios due to the seasonal alternation of diatom and non diatom dominated exports spatial variations of the annual mean rain ratios are hardly discernible along the main jgofs transect data based estimates of the annual mean impact of the biological pump on the fco2 in the surface water suggest that the biological pump reduces the increase of fco2 in the surface water caused by intrusion of co2 enriched subsurface water by 50 70 the remaining 30 to 50 are attributed to co2 emissions into the atmosphere rain ratios up to 60 higher in river influenced areas off pakistan and in the bay of bengal than in the open arabian sea imply that riverine silica inputs can further enhance the impact of the biological pump on the fco2 in the surface water by supporting diatom blooms consequently it is assumed that reduced river discharges caused by the damming of major rivers increase co2 emission by lowering silica inputs to the arabian sea this mechanism probably operates in other regions of the world ocean also

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

measurements of katabatic winds between dome c and dumont d urville dumont d urville on the antarctic coast is an area well known for the presence of strong katabatic winds since the austral summer 1979 80 a us french joint experiment has been investigating the katabatic wind in this region in early 1980 three automatic weather stations aws were installed along a trajectory from dome charlie to dumont d urville measurements from these stations include air pressure temperature wind speed and direction at ground level only to supplement these data with information regarding the vertical structure and the advective changes in the katabatic flow two airborne missions were undertaken in november 1980 along a route from dome charlie dome c to dumont d urville

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

effect of surface roughness on bidirectional reflectance of antarctic snow the angular pattern of sunlight reflected by snow is altered by surface roughness which in the interior of antarctica is usually in the form of meter scale longitudinal erosional features sastrugi whose axes align with the direction of strong winds the bidirectional reflectance distribution function brdf changes over the course of a day as the solar azimuth changes relative to the sastrugi axis the normalized brdf or anisotropic reflectance factor r was measured at south pole station from a 22 m tower at 600 660 and 900 nm wavelengths the r pattern was similar at the three wavelengths it probably varies little from 300 to 900 nm measurements were made at solar zenith angles 0 from 67 to 90 over the full range of viewing zenith angle r azimuth angle between sun and view and azimuth angle between sun and sastrugi sas variation of r with sas was notable sastrugi oriented perpendicular to the solar beam cause a reduction of the forward peak and sastrugi at an oblique angle cause r to lose its symmetry about the solar azimuth however the effects of sastrugi are mostly restricted to large viewing zenith angles so remote sensing of albedo and atmospheric properties can be carried out accurately without knowledge of sastrugi height and orientation if only near nadir views are used this recommendation is opposite that for observations of broken clouds over dark surfaces for which large r is preferred a parameterization of r is developed valid for viewing angles r 50 sastrugi can cause a reduction of the snow albedo by altering the angle of incidence and by trapping of photons for the small sastrugi of the antarctic plateau the albedo is unaffected at visible wavelengths but can be reduced by a few percent at near infrared wavelengths when the sun is low

the confluence zone of the intense katabatic winds at terra nova bay antarctica as derived from airborne sastrugi surveys and mesoscale numerical modeling the surface wind field inland of the intense coastal kataba c wind regime at terra nova bay antarctica has been studied both observationally and numerically airborne surveys of windinduced features on the snow surface have been used to construct the time averaged winter surface airflow pattern the surface motion field has also been simulated by a mesoscale primitive equation model using terrain slopes with a horizontal resolution of 32 km both methods of analys s demonstrate that the intense katabatic airstream at terra nova bay is forced by converging air currents in the continental interior the broadscale confluence zone becomes organized into two regions within about 180 km of the coast the primary route for katabatic mass transport into the terra nova bay area is reeves glacier valley but an important secondary source is provided by airflow down david glacier the former is generated by the coriolis induced concentration of mass transport on the left side looking downwind of the broadscale confluence zone as well as by the near coastal mountain deflection of airflow into the valley head the confluence zone feeding into david glacier valley stretches over 100 km into the interior and is forced by the broadscale terrain configuration of the ice sheet source areas for the two airstreams differ with reeves glacier valley being fed by cold air formed well into the interior whereas the airflow down david glacier is sustained by radiative cooling over lower parts of the ice sheet which are much closer to the ross sea evaluation of the observational and modeling results reveals both the strengths and weaknesses of each approach airborne surveys of sastrugi orientations are a highly successful method for establishing the detailed pattern of surface airflow however a systematic examination of sastrugi dimensions suggests that such work could also be carried out using spot type satellite observations which is a more cost effective approach than aircraft surveying the double jet structure of katabatic airflow into the terra nova bay area is well represented by the primitive equation modeling but much finer grids are needed to resolve the near coastal drainage details

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

snowdrift landscape patterns an arctic investigation between 2012 and 2018 we mapped near peak seasonal snow depths across two swaths covering 126 km in northern alaska using aerial structure from motion photogrammetry and lidar surveys the surveys

reconstruction of sea surface temperature variations in the arabian sea over the last 23 kyr using organic proxies tex86 and u37k well established u37 0 based on long chain unsaturated ketones synthesized by haptophyte algae and the newly proposed tex86 derived from the membrane lipids of crenarchaeota comparison of niop905 and 74kl core top data with present day sst 0 10 m values indicates that both proxies yield temperatures similar to local annual mean ssts however tex86 and u37 0 sst down core records derived from the same cores differ in magnitude and phasing the alkenone sst record of niop905 shows small changes in sst 0 5 c over the last 23 kyr while that of core 74kl shows a 2 c increase from the last glacial maximum lgm 23 19 calendar cal kyr b p through the holocene the last 11 5 cal kyr b p synchronous with changes in the northern hemisphere in contrast the tex86 records of both cores show a large increase in sst from 22 23 c in the lgm to 28 30 c during termination i 19 11 5 cal kyr b p decreasing to present day annual means of 26 c a cold phase between 14 5 and 12 cal kyr b p that may correspond to the antarctic cold reversal is also observed this implies a southern hemisphere control on tropical sst reconstructed by the tex86 possibly related to sw monsoon our results suggest that the application of both tex86 and u37 0 give different but complementary information on sst developments in past marine environments

the phytoplankton bloom in the northwestern arabian sea during the southwest monsoon of 1979 the biological variability of the northwestern arabian sea during the 1979 southwest monsoon has been investigated by the synthesis of satellite ocean color remote sensing with analysis of in situ hydrographic and meteorological data sets and the results of wind driven modeling of upper ocean circulation the phytoplankton bloom in the northwestern arabian sea peaked during august september extended from the oman coast to about 65 e and lagged the development of open sea upwelling by at least 1 month in total the pigment distributions hydrographic data and model results all suggest that the bloom was driven by spatially distinct upward nutrient fluxes to the euphotic zone forced by the physical processes of coastal upwelling and offshore ekman pumping coastal upwelling was evident from may through september yielded the most extreme concentrations of phytoplankton biomass and along the arabian coast was limited to the continental shelf in the promotion of high concentrations of phytoplankton upward ekman pumping to the northwest of the somali jet axis stimulated the development of a broad open sea phytoplankton bloom oceanward of the oman shelf vertical mixing during the 1979 southwest monsoon was apparently not a primary cause of the regional scale phytoplankton bloom

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

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

snow dunes a controlling factor of melt pond distribution on arctic sea ice 1 the location of snow dunes over the course of the ice growth season 2007 08 was mapped on level landfast first year sea ice near barrow alaska landfast ice formed in mid december and exhibited essentially homogeneous snow depths of 4 6 cm in mid january by early february distinct snow dunes were observed despite additional snowfall and wind redistribution throughout the season the location of the dunes was fixed by march and these locations were highly correlated with the distribution of meltwater ponds at the beginning of june our observations including ground based light detection and ranging system lidar measurements show that melt ponds initially form in the interstices between snow dunes and that the outline of the melt ponds is controlled by snow depth contours the resulting preferential surface ablation of ponded ice creates the surface topography that later determines the melt pond evolution

dissolved organic carbon doc fluxes of deep sea sediments from the arabian sea and ne atlantic abstract diffusive flux of dissolved organic carbon doc from deep sea sediments is a poorly constrained component of the global marine carbon cycle but may play an important role for doc concentrations in the oceans during six cruises between the years 1995 and 2000 we measured doc concentrations in pore waters of surface sediments and the ambient bottom waters at five stations in the deep arabian sea water depths 3190 4420 m and at two sites in the ne atlantic 4500 4800 m pore water doc concentrations were usually one order of magnitude greater than in bottom waters with maximum doc contents between 509 and 1526 mol l in the uppermost sediment interval 0 0 5 cm doc values generally decrease towards 3 cm core depth with slightly increasing concentrations in deeper layers under sub oxic to anoxic conditions calculated benthic doc effluxes into the bottom water caused by concentration gradients ranged between 59 8 and 223 9 mol m 2 d 1 in the arabian sea and 47 2 and 121 2 mol m 2 d 1 in the ne atlantic doc efflux rates were highly correlated with the annual vertical particle flux rates at the sites and thus appear to be a function of the regional productivity taking an average global oceanic doc efflux rate between 50 5 and 78 1 mol m 2 d 1 we calculated that the doc release is in the order of 70 103 1012 g c yr 1 from sediments below 2000 m water depth thus deep sea sediments have the potential to represent a significant source of doc in the oceans

the meteoritical bulletin no 85 2001 september meteoritical bulletin no 85 lists information for 1376 newly classified meteorites comprising 658 from antarctica 409 from africa 265 from asia 262 of which are from oman 31 from north america 7 from south america 3 from australia and 3 from europe information is provided for 11 falls dergaon dunbogan gujba independence itqiy moravka oued el hadjar sayama sologne valera and worden noteworthy non antarctic specimens include 5 martian meteorites dar al gani 876 northwest africa 480 and 817 and sayh al uhaymir 051 and 094 6 lunar meteorites dhofar 081 280 and 287 and northwest africa 479 482 and 773 an ungrouped enstatite rich meteorite itqiy a bencubbin like meteorite gujba 9 iron meteorites and a wide variety of other interesting stony meteorites including ch ck cm co cr cv r enstatite and unequilibrated ordinary chondrites primitive achondrites hed achondrites and ureilites

the forcing of antarctic katabatic winds abstract the temporal and spatial development of katabatic winds along an idealized slope representative of anmtarctic terrain is examined using a hydrostatic two dimensional primitive equation model with explicit longwave radiation parameterization a detailed diagnosis is made of a simulation in which katabatic flow develops from rest due to the strong radiational cooling of the underlying surface significant thermodynamic and dynamic differences are seen between the gravity driven flows over the gently sloping interior and over the steep ice slopes near the coast the strongest temperature inversions and largest static stabilities are found over the interior of the continent although the net cooling of the katabatic layer and magnitude of the downslope directed horizontal pressure gradient force are greatest at the coast the interior is characterized by low rossby number quasi geostrophic type flows while more intense near antitriptic winds occur at the coast model results are in reasonable agr

modeling of pleistocene european ice sheets some experiments with simple mass balance parameterizations abstract a vertically integrated ice flow model suitable for use in climate studies is formulated large continental ice sheets may be characterized by two fundamental quantities the height to width ratio and the steepness of the edge so it is natural to develop a model containing two parameters that can be chosen to give the right values of those characteristic quantities the result is a model that is close to m a w mahaffy s journal of geophysical research 81 1059 1066 1976 the model is used to study glaciation in europe dropping the level of zero mass balance creates small stable ice caps in the alps and the scandinavian mountains if the drop exceeds 600 m with respect to present day conditions the feedback between ice sheet height and mass balance becomes dominating and the fennoscandian ice sheet keeps growing it does not reach an equilibrium state within 60 000 yr an experiment simulating rapid onset of a glacial cycle shows that the growth of ice volume in europe is smaller than that in northern america j t andrews and m a w mahaffy quaternary research 6 167 183 1976 after 10 000 yr the volume of the fennoscandian ice sheet 2 10 15 m 3 is about half the volume of the laurentide ice sheet this leaves the observed sea level lowering in the period 125 000 115 000 yr b p estimates center around 50 m unexplained

live rose bengal stained and dead benthic foraminifera from the oxygen minimum zone of the pakistan continental margin arabian sea live rose bengal stained and dead benthic foraminiferal communities hard shelled species only from the pakistan continental margin oxygen minimum zone omz have been studied in order to determine the relation between faunal composition and the oxygenation of bottom waters during r r s charles darwin cruises 145 and 146 12 march to may 28 2003 11 multicores were taken on the continental margin off karachi pakistan two transects were sampled constituting a composite bathymetric profile from 136 m above the omz in spring 2003 down to 1870 m water depth cores surface area 25 5 cm2 were processed as follows for stations situated above and in the upper part of the omz sediment slices were taken for the 0 0 5 and 0 5 1 cm intervals and then in 1 cm intervals down to 10 cm for the lower part of the omz the second centimetre was also sliced in half centimetre intervals each sample was stored in 10 borax buffered formalin for further processing onshore the samples were wet sieved over 63 m 150 m and 300 m sieves and the residues were stained for one week in ethanol with rose bengal after staining the residue was washed again the stained faunas were picked wet in three granulometric fractions 63 150 m 150 300 m and 300 m down to 10 cm depth to gain more insight into the population dynamics we investigated the dead unstained foraminifera in the 2 3 cm level for the fractions 150 300 m and 300 m the fractions 300 m and 150 300 m show nearly the same faunal distribution and therefore the results are presented here for both fractions combined i e the 150 m fraction live foraminiferal densities show a clear maximum in the first half centimetre of the sediment only few specimens are found down to 4 cm depth the faunas exhibit a clear zonation across the pakistan margin omz down to 500 m water depth uvigerina ex gr u semiornata and bolivina aff b dilatata dominate the assemblages these taxa are largely restricted to the upper cm of the sediment they are adapted to the very low bottom water oxygen values ab 0 1 ml l in the omz core and the extremely high input of organic carbon on the upper continental slope the lower part of the omz is characterized by cosmopolitan faunas containing also some taxa that in other areas have been described in deep infaunal microhabitats

sensitivity experiments with a model of the ice age cycle the response to milankovitch forcing abstract we address the question of the extent to which a simple one dimensional time dependent climate model is able to explain the fluctuations of continental ice volume which have occurred during the last quarter of the pleistocene epoch the model includes explicit ice physics based on the glen flow law and explicit glacial isostatic adjustment based on a realistic viscoelastic field theory when the model is forced by the milankovitch variations of insulation it delivers ice volume fluctuations which are very similar to those implied by the specmap 18o record in particular the model appears capable of explaining the observed correlation between eccentricity and ice volume variations the dominance of the 105 year period in the power spectrum of the ice volume time series and the thickness and latitudinal extents of the continental ice sheets which existed at wurm wisconsin maximum 18 000 years ago

foraminiferal response to the northeast monsoon in the western and southern arabian sea abstract sediments from the western and southern part of the arabian sea were collected periodically in the spring intermonsoon between march and may 1997 and additionally at the end of the northeast monsoon in february 1998 assemblages of rose bengal stained living deep sea benthic foraminifera their densities vertical distribution pattern and diversity were analysed after the northeast monsoon and short time changes were recorded in the western arabian sea foraminiferal numbers increased steadily between march and the beginning of may especially in the smaller size classes 30 63 m 63 125 m at the same time the deepening of the foraminiferal living horizon variable diversity and rapid variations between dominant foraminiferal communities were observed we interpret these observations as the time dependent response of benthic foraminifera to enhanced organic carbon fluxes during and after the northeast monsoon in the southern arabian sea constant low foraminiferal abundances during time no distinctive change in the vertical distribution reduced diversity and more stable foraminiferal communities were noticed which indicates no or little influence of the northeast monsoon to benthic foraminifera in this region

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

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

surface roughness and bulk heat transfer on a glacier comparison with eddy correlation more than 100 simultaneously measured profiles of wind speed and temperature were analyzed to determine the aerodynamic and thermal roughness lengths of glacier ice the results proved to be extremely sensitive to measurement height which is difficult to define precisely on the hummocky terrain of a glacier therefore aerodynamic roughness lengths were estimated from the microtopography of the surface yielding 2 46 mm for ice and 5 5 mm for snow despite the indeterminate nature of the profile analysis it did support the view that the thermal roughness length must decrease as the roughness reynolds number increases a relationship which has been modelled in the literature good agreement between bulk transfer estimates and eddy correlation measurements of fhe sensible heat flux density on melting ice and snow was obtained by combining the aerodynamic roughness length with a suitable model for thermal roughness length

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

measurement and parameterization of aerodynamic roughness length variations at haut glacier d arolla switzerland spatial and temporal variations in aerodynamic roughness length z0 on haut glacier d arolla switzerland during the 1993 and 1994 ablation seasons are described based on measure ments of surface microtopography the validity of the microtopographic z0 measurements is established through comparison with independent vertical wind profile z0 measurements over melting snow slush and ice the z0 variations are explained through correlation and regression analyses using independent measurements of meteorological and surface variables and parameterizations are developed to calculate z0 variations for use in surface energy balance melt models several independent variables successfully explain snow z0 variation through their correlation with increasing surface roughness caused by ablation hollow formation during snow melt non linear parameterizations based on either accumulated melt or accumulated daily maximum temperatures since the most recent snowfall explain over 80 of snow z0 variation the z0 following a fresh snowfall on an ice surface is parameterized based on relationships with the underlying ice z0 snow depth and accumulated daily maximum temperatures none of the independent variables were able to successfully explain ice z0 variation although further comparative studies are needed the results lend strong support to the microtopo graphic technique of measuring z0 over melting glacier surfaces

coupling between sw monsoon related surface and deep ocean processes as discerned from continuous particle flux measurements and correlated satellite data particle flux data obtained by time series sediment traps deployed at water depths of approximately 3000 m in the western central and eastern arabian sea since 1986 were compared with wind speeds derived from measurements made by microwave radiometer flying on polar orbiting satellites and sea surface temperatures ssts provided by the physical oceanography distributed active archive center at jet propulsion laboratory this comparison has allowed us to trace the link between the oceanographic and biological processes related to the development of the sw monsoon with the pattern and interannual variability of particle fluxes to the interior of the arabian sea we could recognize the well known upwelling systems along the coasts of somalia and oman as well as open ocean upwelling at the beginning of the sw monsoon both open ocean upwelling and coastal upwelling off oman cause a cooling of surface waters at our western and central arabian sea stations when ssts fall below their long term average an increase in fluxes which are dominated by coccolithophorid derived carbonates occurs the timing of this increase is determined by the rate of surface water cooling further intensification of upwelling as the sw monsoon progresses causes additional increases in biogenic opal fluxes denoting diatom blooms in the overlying waters the total fluxes during this period are the highest measured in the open arabian sea at the central arabian sea location the fluxes are only randomly affected by these blooms the particle flux in the eastern arabian sea is as high as in the central arabian sea but is influenced by a weaker upwelling system along the indian coast the observed interannual variability in the pattern of particle fluxes during the sw monsoons is most pronounced in the western arabian sea this is controlled by the intensity of the upwelling systems on the one hand and the transport of cold nutrient poor south equatorial water into the oman region on the other the latter effect which is strongest during the sw monsoon with highest recorded wind speeds reduces the influence of upwelling and the related particle fluxes at the western arabian sea station where highest fluxes occur during sw monsoons with moderate wind speeds thus coastal and open ocean upwelling are most effective in transferring biogenic matter to the deep sea during the sw monsoons of intermediate strength

modeling the effect of sastrugi on snow reflectance a snow reflectance model was developed to assess the bidirectional reflectance distribution function brdf of snow over anisotropic rough surfaces such as fields of sastrugi commonly encountered in some areas of the ice sheets of antarctica and greenland the sastrugi are modeled as regularly spaced identical rectangular protrusions with the same orientation interfacet multiple scattering is ignored each model sastruga has vertical walls and a small width compared to its length and to its height the input data for the model are the sun and the viewing directions the number of sastrugi per pixel their dimensions and the bidirectional reflectance for a flat snow surface the latter is computed by a multiple scattering model and snow particles are assumed to be spherical mie theory in order to compare the model results with ground measurements acquired at the south pole by grenfell et al 1994 and brandt et al 1991 atmospheric effects were taken into account the model reproduces the global influence of sastrugi on the shape of the brdf the influence of sastrugi is clearly visible for zenith viewing angles larger than 50

the influence of the sw monsoon on the deep sea organic carbon cycle in the holocene abstract results from long term sediment trap experiments carried out since 1986 in the western central and eastern arabian sea are combined with satellite derived wind fields and paleoceanographic information to link the intensity of the sw monsoon to organic carbon fluxes and its preservation in sediments the sw monsoon is characterized by the low level jet findlater jet that crosses the arabian sea almost parallel to the arabian coast the intensity of the findlater jet mainly controls the velocities of upwelling that occurs to the northeast of the jet since up welling in turn mainly governs the organic carbon fluxes in the western arabian sea variation in the strength of the findlater jet is the dominant factor determining the organic carbon fluxes on seasonal time scales changes in the subsurface nutrient concentrations due to variations in the surface ocean current systems seem to be another factor influencing the organic carbon fluxes mostly on interannual time scales the translation of sedimentary organic carbon burial rates into organic carbon fluxes according to jahnke 1996 global biogeochemical cycles 10 71 88 allows us to extend our reflections also to a millennium time scale this indicates that changes in the sw monsoon intensity as observed during the last decade could almost account for the range of organic carbon fluxes deciphered from the holocene record

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

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

quantifying carbonate dissolution and calibration of foraminiferal dissolution indices in the somali basin two sediment traps moored off somalia in 1992 1993 collected similar settling fluxes of carbonate and siliceous shells formed by various plankton groups planktic foraminifera showed large seasonal variations with more than 74 of the total planktic foraminifera flux collected during the sw monsoon summer upwelling when globigerina bulloides was dominating along with globigerinita glutinata and neogloboquadrina dutertrei the intermonsoon and ne monsoon assemblages were dominated by globigerinoides ruber we used the trap records as our no dissolution reference for comparison with three boxcore recorders in order to quantify the carbonate dissolution along a depth transect dissolution increases downslope from station 905 to 907 and 915 at depths of 1567 m 2807 m and 4035 m respectively the carbonate fraction of the sediment at station 915 which is located near the ccd is the most affected by dissolution with more than 97 of the planktic foraminifera dissolved here the planktic foraminifera assemblage is strongly modified with thick walled species such as n dutertrei globorotalia tumida and pulleniatina obliquiloculata as the most resistant it is not representative of the settling assemblage the planktic foraminiferal assemblages of the sediment surface at stations 905 and 907 remain similar to the trap assemblages and the foraminifera are well preserved although only 25 of foraminifera are apparently preserved at station 905 and 8 at station 907 those numbers are surprisingly low and infer that only a small fraction of the foraminiferal carbonate production is buried and removed from the carbon cycle this discrepancy between the export and buried flux is partly be due to bio mechanical destruction by benthic processes and to supralysoclinal dissolution due to metabolic co2 generated by the benthic organisms another important factor is the interannual variability of the productivity well known in the arabian sea the calibration of commonly used foraminiferal dissolution indices percentage of foraminiferal fragments percentage of resistant species foraminiferal dissolution index fdx to our data only shows reliable results for high dissolution levels 97 off somalia the most accurate of the proxies is the percentage of foraminiferal fragments compared to the other methods tested i e fdx planktic foraminiferal loss l percentage of radiolarians and diatoms percentage of benthic foraminifera the species assemblage appears to be not significantly modified by dissolution unless the estimated shell loss is high 92 of the arriving shells in our samples this level is expressed in the percentage of fragmentation the percentage of radiolarians and diatoms the percentage of resistant foraminifera species and fdx as 80 35 25 and 1 8 respectively the relative abundance of globigerina bulloides is a valid sw monsoon upwelling proxy only when dissolution is moderate 92 globigerina bulloides and globigerinoides ruber have similar burial efficiencies and susceptibilities to dissolution thus the ratio g bulloides g ruber is a valid proxy for past changes in the intensity of the sw monsoon even in the strongly dissolved samples in our sediment record the ratio g bulloides g ruber indicates that the sw monsoon was stronger in the recent past than in 1992 93

climate sensitivity to continental ice sheet size and configuration abstract a version of the ncar community climate model ccm has been used to carry out a study of climate sensitivity to the size and distribution of continental ice sheets by comparing two perpetual season fixed sea surface temperature sst winter simulations of the climate at a glacial maximum the two simulations differ only in the size and configuration of the continental ice sheet boundary conditions these conditions represent minimum and maximum ice sheet extent for a glacial maximum as presently constrained by the geologic evidence all other boundary conditions are as specified by climap 1981 for winter surface conditions during the last glacial maximum lgm the ice sheets specified by climap 1981 used by many previous researchers to simulate ice age climate conditions are intermediate in size between the minimum and maximum ice sheets used for the simulations described here the maximum case simulation resulted in unexpected positive temperature anomalies over the northern hemisphere

snow bedforms a review new data and a formation model snow bedforms like sand bedforms consist of various shapes that form under the action of wind on mobile particles throughout a year they can cover up to 11 of the earth surface concentrated toward the poles these forms impact the local surface energy balance and the distribution of precipitation only a few studies have concentrated on their genesis their size ranges from 2 cm ripple marks to 2 5 m tall whaleback dunes we counted a total of seven forms that are widely recognized among them sastrugi an erosional shape is the most widespread from laser scans we compared scaling of snow versus sand barchan morphology we found that both have proportionally the same footprint but snow barchans are flatter the key difference is that snow can sinter immobilizing the bedform and creating an erodible material using a model we investigated the effect of sintering on snow dune dynamics we found that sintering limits their size because it progressively hardens the snow and requires an ever increasing wind speed to maintain snow transport from the literature and results from this model we have reclassified snow bedforms based on two parameters wind speed and snow surface conditions the new data show that snow dune behavior mirrors that of sand dunes with merging calving and collision however isolated snow barchans are rare with most of the snow surfaces encountered in the field consisting of several superimposed bedforms formed sequentially during multiple weather events spatially variable snow properties and geometry can explain qualitatively these widespread compound snow surfaces

26al survey of antarctic meteorites abstract an 26 al survey by non destructive gamma ray spectrometry was conducted as part of the preliminary examination effort for antarctic meteorites a total of 220 samples were studied the majority of the samples were from the allan hills area however samples from several other sites including the yamato mountains were studied compared to worldwide falls and finds the antarctic group shows a clear trend toward lower 26 al levels at leasr 10 of the samples studied were clearly undersaturated in 26 al the frequency of undersaturated samples suggests that terrestrial ages of several hundred thousand years are common among the antarctic meteorite collection the absence of samples with extremely low 26 al implies that the upper limit for terrestrial ages in the antarctic is on the order of 1 million years

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

particulate organic carbon fluxes compilation of results from the 1995 us jgofs arabian sea process study by the arabian sea carbon flux group abstract organic carbon fluxes in the arabian sea were measured as a function of depth season and distance from the coast of oman we present here a compilation of measurements of primary production water column export flux and sediment accumulation of organic carbon over a full annual monsoon cycle on a 1500 km transect from the coast of oman toward the central arabian sea this represents an integration of measurements spanning one day primary production to 1000 yr sediments and gives a broad overview of organic carbon removal and remineralization in the highly productive seasonally varying region of the northern indian ocean organic carbon fluxes decreased from the surface to the sediments by a factor of 500 10 000 with the largest rates of change in the upper ocean and at the sediment seawater interface organic carbon fluxes generally decreased with distance offshore with the largest gradient between surface and seafloor being at the offshore station sediment accumulation rates of organic carbon differed by a factor of 40 between nearshore and offshore while primary productivity varied only by a factor of 2 the decrease in carbon flux with depth that occurs between the deepest traps and the sediment becomes a greater proportion of the total loss with increasing distance from shore thus the influence of processes at the sediment water interface on the proportion of primary productivity preserved in the sediment increases offshore relative to upper water column processes carbon fluxes changed greatly with season with highest fluxes during the southwest monsoon export fluxes varied more with season than primary productivity or mid water fluxes

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

surficial sediments of the arabian sea abstract coarse grained low carbonate sediments with high abundances of quartz and feldspar in the northerly areas of the arabian sea close to land reflect significant terrigenous sediment in fluxes primarily from the indus river and to some extent from other sources carbonate content of sediments increases gradually from the northernmost areas to about 18 21 n and reflects the waning influence of terrigenous sediment supply southward in areas farther from significant terrigenous influences the carbonate distribution also clearly reflects bathymetric control thus whereas the caco3 content is high on ridges it becomes less than 10 at about 4800 m ccd in the arabian basin a low carbonate band extends from the areas opposite the indus river to the deep areas 2000 3000 m southward and is confined to the easternmost indus fan valley relatively high bottomwater turbidities in this valley suggest that the low carbonate band may result in part from dilutions due to the influxes of terrigenous sediments transported and deposited by deep turbid water flows although high amounts of organic matter occur in the sediments of westerly northerly and easterly areas close to land it is along the indian continental margin at 200 1500 m water depths that the highest organic carbon values 5 10 are observed however high nutrient abundances in the surface waters and high contents of opal and siliceous fossil remains in the sediments off the arabian peninsula gulf of aden clearly reflect higher biogenic productivities in this region than along the indian margin the high organic matter content in the sediments of the indian margin is primarily due to its preservation which results from the impingement of low oxygenated waters on the sea floor at 200 1500 m water depths and from the high sedimentation rates calculations suggest that the degree of preservation of organic matter along the indian margin is about 15 80 times higher than that in the region off the arabian peninsula

high rates of benthic carbon remineralisation in the abyssal arabian sea during the large scale deep sea programme bigset in situ measurements of sediment community oxygen consumption scoc were carried out during three cruises between 1995 1998 at five abyssal sites 3190 4450 m water depth in the deep arabian sea in order to elucidate the regional and temporal variation of benthic carbon remineralisation scoc ranged from 0 9 6 3 mmol o2 m 2 d 1 with highest values in the western and northern arabian sea and lowest values in the southern arabian sea for the central arabian sea intermediate oxygen uptake rates were detected this regional pattern mirrors the overall regional pattern of primary productivity in surface waters and vertical particulate organic carbon poc flux at 1000 mab primary productivity in arabian sea surface waters and particulate flux into the deep sea are controlled by the monsoon system and the flux maxima during the sw and ne monsoon are among the highest particle fluxes recorded in the deep open ocean highest flux rates were recorded in the western and northern arabian sea and decreased towards the central and southern arabian sea scoc at our western northern and eastern arabian sea stations wast nast and east were considerably higher than so far detected in other abyssal areas of the global oceans and vertical poc flux can account for only 20 50 of benthic carbon remineralisation bcr possible explanations for the high rates of bcr at these stations that are situated close to the continental margins are discussed the accelerated deposition of very labile organic matter due to eolian dust particles enhanced rain efficiencies and lateral advection a significant temporal variability in scoc only could be detected at the eastern and western arabian sea stations wast and east

changes in surface productivity and subsurface denitrification during the holocene a multiproxy study from the eastern arabian sea spatial and temporal variations in the intensity of subsurface denitrification in the water column of the eastem arabian sea have been investigated using chemical and isotopic proxies the data show a steady increase in the denitrification intensity from 10 ka to 2 ka bp probably caused by changes in surface productivity fuelled by strengthening of upwelling monsoonal intensity in addition changes in redox conditions and detrital material input are assessed using abundances of a suite of major and trace elements the temporal variations in some of the monsoonal proxies are characterized by periodicities of 1400 and 700 years similar to those reported in the south asian chinese monsoon and high latitude climate north atlantic region

theory of metamorphism of dry snow the growth of ice particles in dry seasonal snow is caused by vapor diffusion among particles due to temperature gradients imposed on the snow cover the diffusion is calculated by using the potential field solutions for electrostatically charged particles the stereography of snow is represented by using a log normal distribution function for a geometrical enhancement factor defined here reasonable crystal growth rates and supersaturations are found the transition between the growth of highly faceted crystals and the growth of highly rounded crystals is determined by the critical supersaturation for the onset of dislocation aided growth thermal convection and the continuous movement of vapor around the particles due to the imposed temperature gradient are accommodated in the theory although both have little effect relative to the interparticle diffusion the growth of a layer of faceted crystals just below semi permeable crusts is explained by showing that crusts can cause the local supersaturation to exceed the critical value faceted crystals are shown to grow most rapidly in the lower warmer portions of the snow cover because of temperature effects on growth rate

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

did the indo asian summer monsoon decrease during the holocene following insolation a few studies from the western arabian sea indicate that the indian summer or southwest monsoon ism after attaining its maximum intensity at ca 9 ka declined during the holocene as did insolation in contrast earlier and later observations from both the eastern and the western arabian sea do not support this inference analysis of multiple proxies of productivity in a new sediment core from the western arabian sea fails to confirm the earlier single proxy e g abundance of globigerina bulloides based inference of the holocene weakening of ism following insolation the reason for the observed decreasing trend in foraminiferal abundance the basis for the earlier inference could be the favouring of silicate rather than carbonate productivity by the increased ism wind strength although ism exhibits several multi millennial scale fluctuations there is no evidence from several multi proxy data to conclude that it declined during the holocene this is consistent with the phase lag analysis of longer time series of monsoon proxies thus on sub milankovitch timescales ism did not follow insolation highlighting the importance of internal feedbacks a comparison with east asian summer monsoon easm records suggests that both ism and easm varied in unison implying common forcing factors on such longer timescales copyright 2010 john wiley sons ltd

stable sulfur isotopes indicate net sulfate reduction in near surface sediments of the deep arabian sea depth profiles of the stable sulfur isotopic composition of dissolved sulfate in near surface sediments were measured at five stations of the deep arabian sea between 1918 and 4426 m water depth wast wast top cast sast nast sampled in april 1997 the results clearly indicate that net microbial sulfate reduction took place in the sediments at stations wast and nast below about 12 cm depth sulfate reduction at wast was more pronounced compared to station nast most likely due to higher organic carbon content in turbiditic sediments no net sulfate reduction took place within the upper 10 cm of the surface sediments at all stations and no significant isotopic indication for sulfate reduction was found down to 30 cm bsf at station sast results are in accordance with accumulation of reduced isotopically light sulfur species below about 6 cm bsf at station wast it is concluded that the sulfur isotopic composition of remaining sulfate is more sensitive to net sulfate reduction than the so4 cl ratio the sulfur isotopic composition of a vertical profile for dissolved sulfate through the water column at station wast was essentially constant 250 4047 m full size image 1 k vs v cdt n 8 a similar constancy 20 4565 m water depth full size image 1 k vs v cdt n 15 was found for the station biotrans in the northeastern atlantic 47 11 19 33w indicating that the oxygen minimum zone in the arabian sea has no influence on the sulfur isotopic composition of dissolved sulfate

the fall of the st robert meteorite the st robert quebec canada meteorite shower occurred on 1994 june 15 at 0h02m ut accompanied by detonations audible for 200 km from the fireball endpoint the fireball was recorded by visual observers in vermont new york state new hampshire quebec and ontario as well as by optical and infrared sensors in earth orbit penetration to an altitude of 36 km occurred 60 km to the northeast of montreal where the bolide experienced several episodes of fragmentation a total of 20 fragments of this h5 chondrite comprising a total mass of 25 4 kg were recovered in an ellipse measuring 8 3 5 km one fragment of the shower partially penetrated the aluminum roof of a shed interpretation of the visual and satellite data suggests that the fireball traveled from south southwest to north northeast with a slope from the horizontal of 55 61 a statistical evaluation of the likely heliocentric orbits for the body prior to collision with the earth coupled with theoretical modeling of the entry suggests an entry velocity in the range of 12 7 13 3 km s the meteoroid had moved in a low inclination orbit with orbital perihelion located extremely close to the earth s orbit from satellite optical data it is found that the photometric mass consumed during the largest detonation is 1200 kg estimation of the amplitude of the acoustic signal detected by the most distant observer yields a source energy near 0 5 kt tnt equivalent energy which corresponds to a mass of order 10 metric tonnes this measure is uncertain to approximately one order of magnitude theoretical modeling of the entry of the object suggests a mass near 1600 kg cosmogenic radionuclide activities constrain the lower initial mass to be 700 kg with an upper limit near 4000 kg seismic data possibly associated with the fireball suggest extremely poor coupling between the airwave and the ground the total mass estimated to have reached the ground is 100 kg in material comprising 55 g fragments while the preatmospheric mass is found to be most probably in the range of 1200 2000 kg

radionuclide fluxes in the arabian sea the role of particle composition we investigated the influence of the composition of the vertical particle flux on the removal of particle reactive natural radionuclides th 230 and pa 231 from the water column to the sediments radionuclide concentrations determined in sediment traps moored in the western central and eastern arabian sea were related to the major components carbonate particulate organic matter poc opal lithogenic material of the particle flux these data were combined with sediment trap data previously published from the southern ocean equatorial pacific and north atlantic z chase r f anderson m q fleisher p w kubik the influence of particle composition and particle flux on scavenging of th pa and be in the ocean earth planet sci lett 204 2002 215 229 j c scholten f fietzke s vogler m rutgers van der loeff a mangini w koeve j waniek p stoffers a antia j kass trapping efficiencies of sediment traps from the deep eastern north atlantic the th 230 calibration deep sea research 1148 2001 2383 2408 the correlations observed between the particle dissolved distribution coefficients k d of th 230 and pa 231 and the concentrations of the particle types depend on the sediment trap data set used this result suggests that scavenging affinities of the nuclides differ between oceanic regions several factors k d values reactive surface areas of particles inter correlations in closed data set can however influence the observed relationships and thus hamper the interpretation of these correlation coefficients as a measure of relative scavenging affinities of the nuclides to the particle types investigated the mean fractionation factor f pa th k d pa k d th from the equatorial pacific f 0 11 0 03 is similar to that from the north atlantic f pa th 0 077 0 026 and both are lower than the factors from the arabian sea f pa th 0 35 0 12 and from the southern ocean f pa th 0 87 0 4 for opal concentrations exceeding similar to60 an increase in the fractionation factors is observed causing a higher mean fractionation factor for the southern ocean trap data set for the other areas investigated differences in the mean fractionation factors cannot be related to the particles types considered in the arabian sea seasonally variable pa 231 ex th 230 ex ratios observed in the sediment traps as well as differences of the ratios between recently deposited phytodetritus fluff and normal surface sediments indicate seasonal changes in scavenging processes which the generally accepted reversible scavenging models do not envisage we assume that variable sinking rates of particles and or particles not considered in this study e g colloids manganese oxides transparent exopolymer particles may play an important but as yet unexplored role in deep water scavenging processes c 2004 elsevier b v all rights reserved

increased ablation at the margin of the greenland ice sheet under a greenhouse effect climate increased ablation under a greenhouse effec t climate is calculated by an energy balance model for two sites at the margin of the greenland ice sheet nordbogletscher south greenland and qaman lrssop sermia west greenland the change in summer ablation is nearly linear with change in summer temperature with gradients of 0 43 and 0 57 m water a i deg i for nordbogletscher and qamanarssup sermia respectively however the increase in ablation rate must be less in the higher parts of the ice sheet a future climatic warming will therefore cause a rapid retreat of the ice sheet margin and a steeper ice sheet profile

late quaternary biogenic productivity and organic carbon deposition in the eastern arabian sea abstract paleoproductivity variations in the eastern arabian sea during the late quaternary period 42 ka bp to present have been studied using accumulation rates of sedimentary biogenic components organic carbon corg nitrogen n caco3 sr and ba such a multi proxy approach reveals decreased surface productivity during the last glacial interglacial transition the observed change of surface water productivity during the last glacial interglacial period is in antiphase to those observed in other low and mid latitude upwelling areas however consistent with some of the upwelling regions like nw africa and nw mexico sedimentary corg and n are found to be decoupled from surface productivity trend with significant enrichments in corg and n during the last glacial maximum lgm this is interpreted in terms of increase in sedimentation rates by a factor of 3 4 resulting in the better preservation of corg during the lgm

initiation of northern hemisphere glaciation and strengthening of the northeast indian monsoon ocean drilling program site 758 eastern equatorial indian ocean the indian monsoon system as recorded by ocean floor biota benthic foraminifera at ocean drilling program site 758 in the eastern equatorial indian ocean has varied dramatically over the past 5 5 m y long after the onset of the monsoons at 10 8 ma benthic foraminifera that thrive with high productivity year round were common before the formation of northern hemisphere continental ice sheets ca 3 1 2 5 ma indicating that the summer southwest monsoon had high intensity and long seasonal duration ca 2 8 ma benthic faunas became dominated by taxa that flourish with a seasonally strongly fluctuating food supply indicating that the northeast winter monsoon during which primary productivity is relatively low increased in duration and strength to form a system similar to that of today the change occurred coeval with the initiation of the northern hemisphere glaciation documenting a close link between the development of the indian monsoon and northern hemisphere glaciation

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

the worden meteorite a new ordinary chondrite fall from michigan usa an ordinary chondrite fall in southeast michigan usa near the crossroads hamlet of worden in northeast washtenaw county penetrated the garage roof of a private home on 1997 september 1 the worden chondrite comprises silicate matrix mineral fragments chondrules chondrule fragments and opaque primary phases electron microprobe analyses olivine fa23 9 orthopyroxene fs20 1 en78 8 w01 indicate diagnostic l chondrite silicate mineral compositions recognizable chondrules and chondrule fragments constitute up to 42 vol chondrule boundaries are readily discernable especially where chondrules have rims of opaque material but not sharp and discrete plagioclase crystals are visible in the devitrified mesostasis of barred olivine chondrules together these characteristics suggest petrologic type s the spatially averaged ensemble of shockrelated features optical extinction of olivine grains minor localized shock melt suggests assignment of a shock stage of s3 the 26 al and 22na activities are typical for an l chondrite worden fell near the most recent solar minimum in 1997 and the 22na production rate should have been at a level approaching the maximum levels due to solar modulation of the galactic cosmic ray flux the low value for the worden 22na activity relative to those observed in chondrite falls associated with the 1969 solar maximum and 1976 solar minimum suggests a relatively small preatmospheric size the 60co activity confirms the indication of a small body the 56co activity was essentially zero indicating that none of the recovered meteorite contained material exposed to solar cosmic rays the worden chondrite is the fourth documented fall in michigan and the fourth stony meteorite recovered in michigan all other michigan meteorites are finds not observed falls and are iron meteorites all michigan falls to date are ordinary chondrites the three falls prior to worden were allegan hs fell 1899 rose city hs brecciated black dark matrix fell 1921 and coleman l6 veined shocked osborn et ai 1997 fell 1994 worden has a much lighter matrix than rose city and is less extensively thermally and shock metamorphosed than either rose city stoffler et ai 1991 or coleman

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

igneous rims on low feo and high feo chondrules in ordinary chondrites abstract many ordinary chondrite oc chondrules are surrounded by rims that show evidence of appreciable melting and can be called igneous these rims formed after the melting and solidification of the host chondrule we studied thirteen igneous rims on low feo chondrules fa or fs 10 mol in ordinary chondrites of petrographic type 3 5 by electron microprobe analysis and scanning electron microscopy in both sets olivine and pyroxene compositions of the rims are similar to or moderately higher in feo than those in the host igneous rims around low feo chondrules show evidence of large degree 80 melting including 1 resorbed chondrule surfaces 2 rounded metal troilite nodules and feldspathic mesostasis 3 euhedral and subhedral morphology of olivine and pyroxene and limited ranges in grain sizes and 4 a rarity of relict grains most low feo chondrules have olivine as their major phase but pyroxene is commonly the predominant phase in their rims rims on high feo chondrules generally have smaller grain sizes and exhibit lower degrees of melting than rims around low feo chondrules mg rich relict grains are observed in high feo rims most low feo chondrules have matrix like rims around the igneous rims but matrix like rims are rare around rims on high feo chondrules there is a continuum between igneous rims and enveloping secondaries of compound chondrules the existence of both sets of objects supports the view that in the oc region most mm size grain assemblages experienced more than one melting event the precursors melted to produce the igneous rims on low feo chondrules differ from those that comprise the rims on high feo chondrules a sizeable fraction of the precursors of low feo rims are from the host chondrule most high feo rims appear to consist largely of melted matrix like materials if the rim precursors are mainly independent the similar fa and fs contents in mafic minerals of rims and host chondrules indicate that 1 oc nebular subregions bounded in space and or in time were dominated by well mixed solids 2 many chondrules experienced multiple heating events during a short period and were then withdrawn from the chondrule forming region and 3 chondrules formed at different times were mixed before agglomeration to form chondrites if the host chondrules were the main source of the low feo rim materials the fact that pyroxene is generally more abundant than in the host suggests that sio 2 normative matrix was also an important ingredient and or that kinetics favored pyroxene crystallization in the rim rims around high feo chondrules were heated to lower temperatures than rims around low feo chondrules the rarity of matrix like rims around high feo igneous rims may indicate that the dust chondrule ratio was lower where they formed

katabatic wind intensity and direction over antarctica derived from scatterometer data although satellite radar scatterometers are initially designed to measure ocean surface wind speed and direction they also provide important observations over continental ice sheets data from the seasat scatterometer analysed over a sector of antarctica show that the signal is strongly dependent on the incidence angle of observation but that it also depends on azimuth ledroit et al 1992 the minimum values of the backscatter coefficient the ratio of backscattered versus incident power are always observed in the direction of katabatic winds a theoretical analysis shows that the backscatter coefficient must be very sensitive to the sastrugi slopes and orientations which are streamlined features formed on the snow surface in the wind direction parish and bromwich 1987 satellite scatterometers can thus map the characteristics of sastrugis of importance for the interpretation of microwave measurements above ice sheets this indirectly provides the intensity and direction of these very persistent and strong winds which play a important role in the behaviour of the atmosphere and ocean in high southern latitudes

fall recovery and description of the coleman chondrite a 0 5 kg stony meteorite associated with a bright bolide seen over southeastern michigan on 1994 october 20 has been recovered the circumstances of the fall and recovery of this chondrite named coleman are presented the most likely trajectory from the observations of the event implies preatmospheric orbital parameters typical of meteorites gamma ray spectrometry of the cosmogenic radionuclides showed that the recovered mass was an interior fragment of a larger body and revealed abnormally high 22na and 26al activity electron microprobe analysis yielded compositions of fa24 1 and fs20 3 which are consistent with an l chondrite classification petrographically the presence of chondrules the observed mineralogy and the degree of chondrule matrix integration suggests assignment to petrologic type 6

the influence of continental ice sheets on the climate of an ice age the climate influence of the land ice that existed 18 000 years before present 18k b p is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean simulated climates are obtained from two versions of the model one with the land ice distribution of the present and the other with that of 18k b p in the northern hemisphere the tropospheric flow field is strongly influenced by the laurentide ice sheet and features a split flow straddling the ice sheet with a strong jet stream forming the southern branch the northern branch of the flow brings very cold air over the north atlantic ocean where thick sea ice is maintained the distribution of sea surface temperature sst difference between the two experiments in the northern hemisphere resembles the difference between the sst at 18k b p and at present as estimated by the climap project 1981 the 18k b p ice sheets have very little influence upon atmospheric temperature and sst in the southern hemisphere this is because the interhemispheric heat transport hardly changes as the loss of heat energy due to the reflection of solar radiation by continental ice sheets in the northern hemisphere is almost completely counterbalanced by the in situ reduction of upward terrestrial radiation hydrologic changes in the model climate are also found with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in north america and eurasia these findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum

sedimentation in the western arabian sea the role of coastal and open ocean upwelling monsoon induced coastal and open ocean upwelling explain 84 of the variations of the organic carbon fluxes measured in the deep western arabian sea in this paper sea level measurements satellite derived wind speeds sea surface temperatures and nutrient profiles are used to discern the relative importance of these factors on fluxes measured during nine years of continuous sediment trap deployments this exercise shows i the increase in fluxes observed during the initial stages of the sw monsoons are caused by open ocean upwelling which develops faster than the coastal upwelling ii coastal upwelling triggers diatom blooms from nutrients from subsurface water and sediment resuspension and more importantly by injecting resting stages of diatoms back into the euphotic zone iii silica depletion resulting from diatom blooms in laterally advecting water masses leads to a replacement of diatoms by other nitrate limited organisms iv organic carbon fluxes to the deep arabian sea increase in response to an intensification of both coastal and open ocean upwelling weak coastal upwelling and strong open ocean upwelling also increase organic carbon fluxes the varying dominance of their influence is reflected in the timing and the composition of the peak fluxes v the link between organic carbon flux and monsoon strength is non linear probably due to changes in the surface currents and to vigorous turbulence in the surface water during strong sw monsoons these processes could reduce the organic carbon flux in the western arabian sea by about 65

new evidence for enhanced preservation of organic carbon in contact with oxygen minimum zone on the western continental slope of india paropkari a l prakash babu c and mascarenhas a 1993 new evidence for enhanced preservation of organic carbon in contact with oxygen minimum zone on the western continental slope of india mar geol i 11 7 13 in order to evaluate the reason for organic enrichment on the western continental slope of india we provide rock eval pyrolysis data of 25 surficial sediment samples from this area results show that the organic matter on the slope is hydrogenrich type ii kerogen which suggests that the organic carbon there is mostly marine the low productivity of overlying waters rules out surface productivity as a possible cause of organic enrichment the association of higher hydrogen index hi values average 306 and higher organic carbon contents av 3 28 wt with the sediments of the upper slope in contact with the oxygen minimum zone omz clearly indicates enhanced preservation under reducing conditions in the anoxic waters of the omz it is suggested that the sediments of the upper slope in contact with the omz have excellent hydrocarbon generation potential and that these slope beds deserve preferential attention for hydrocarbon exploration

millennial centennial scale thermocline ventilation changes in the indian ocean as reflected by aragonite preservation and geochemical variations in arabian sea sediments abstract the formation and temporal variability of the oxygen minimum zone omz of the arabian sea is a subject of intense research we contribute to the discussion by studying modern seawater profiles of the indian ocean salinity o2 ph aragonite saturation nitrate deficit nutrients which show that subantarctic mode and antarctic intermediate waters samw aaiw have a strong influence on the omz characteristics of the arabian sea to obtain a better grasp of the range of possible omz variations we studied a 50 kyr record in the ne arabian sea core md042876 from a site at 828 m water depth within the thermocline in this core aragonite is preserved during north atlantic heinrich events hes and dansgaard oeschger do stadials while it is absent during do interstadials and most of the holocene considering the excellent correlation between aragonite content and sr ca ratio as well as the presence of fine grained aragonitic needles and the isotopic composition 13c of carbonates in the fine fraction we infer that essentially all aragonite originates as fine sr rich debris from shallow water a comparison with other records from the ne arabian sea sr ca 15n indicates that aragonite variability in the cores is rather controlled by omz intensity variations as forcing mechanism while changes in aragonite supply seem to play a minor role the strong correlation of aragonite content with changes in millennial scale ventilation of the indian ocean as well as a comparison with modern oceanographic conditions supports the theory that omz intensity variations are controlled by changes in the formation of samw aaiw and are not only due to monsoonal changes thus during hes and do stadials the thermocline arabian sea experienced a strengthened influx of o2 rich samw aaiw on the other hand omz conditions during do interstadials and the holocene seem best explained by analogy with the present day situation low supply of o2 combined with elevated o2 demand controlled by monsoon related productivity

variability in upwelling fields in the northwestern indian ocean 1 model experiments for the past 18 000 years a nonlinear reduced gravity ocean model is used to assess the effects of changes in the monsoon winds during glacial and interglacial conditions on the seasonal circulation in the northwestern indian ocean winds from the national center for atmospheric research community climate model simulations for 18 kyr b p the most recent glacial maximum and a period of weaker monsoon winds 9 kyr b p near the beginning of the present interglacial and a period of stronger monsoon winds and present day 0 kyr b p conditions are used to drive the model to a steady seasonal cycle strength of upwelling fields are inferred in each case by integrating upward displacements of the model pycnocline over the primary upwelling season of mid april to mid august in both the 0 kyr b p and the 9 kyr b p cases a broad band of upwelling and decreased model upper layer thickness extends along the coast of the arabian peninsula out 350 500 km offshore during the southwest monsoon this upwelling is driven by the strongly positive wind stress curl beneath the cyclonic side of the atmospheric findlater jet located to the north and west of the jet axis farther offshore in the anticyclonic region to the south and east of the jet axis the negative wind stress curl drives downwelling and increased upper layer thickness in the 9 kyr b p case the atmospheric jet is much stronger and narrower than in the 0 kyr b p case with stronger values of both positive and negative curl to the northwest and southeast respectively of the jet axis this drives much stronger upwelling to the northwest of the jet axis and downwelling to the southeast in the 18 kyr b p case the findlater jet is very weak and upwelling patterns are uniformly weak across the basin the spatial distribution and temporal variation of the upwelling fauna in the sediment record is consistent with the model upwelling fields in all three cases the ocean model thus provides the link between the climate model and the sedimentation data verifying the hypothesis that variations in upwelling driven by variations in the strength of the monsoon jet are responsible for the observed variations in the sediment record

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport

contrasting sea surface temperature of summer and winter monsoon variability in the northern arabian sea over the last 25 ka abstract the seasonal monsoon cycle with winds from the southwest sw in summer and from the northeast ne in winter strongly impacts on modern regional sea surface temperature sst patterns in the arabian sea northern indian ocean to reconstruct the temporal and spatial variation in the dynamically coupled winter and summer monsoon strength over the last 25 ka we analyzed alkenone derived sst variations in one sediment core from the northwestern arabian sea that is influenced by the summer monsoon sst affected by upwelling processes and in one core from the northeastern arabian sea where sst is mainly governed by the winter monsoon no upwelling comparison of the sst records reveals an antagonistic relationship of summer and winter monsoon strength throughout the late deglaciation and the holocene upwelling along the arabian peninsula associated with peak sw monsoonal wind strength was strongest during the early holocene climate optimum between 11 and 8 ka and coincided with the northernmost position of the intertropical convergence zone itcz marked by maximum precipitation over northern oman the sw monsoon weakened over the middle to late holocene while the ne monsoon gained strength this different evolution was caused by the southward displacement of the itcz throughout the holocene superimposed over the long term trend are variations in northeast monsoon wind strength at time scales of centuries that were synchronous with late holocene climate variations recorded on the asian continent and in the high latitude northern hemisphere their likely driving forces are insolation changes associated with sunspot cycles enhanced by feedback mechanisms e g land sea thermal contrast they enforced centennial scale fluctuations in wind strength and temperature in the northern arabian sea monsoon system

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

surface drag over the snow surface of the antarctic plateau 2 seasonal change of surface drag in the katabatic wind region the seasonal change of the surface drag coefficient cd over the snow surface in the antarctic katabatic wind region was evaluated from year round wind profile measurements at mizuho station east antarctica in 1979 the average stability is near neutral throughout the year roughness heights z0 are estimated from hourly averaged wind speeds at four heights 8 4 2 1 and 1 m assuming a logarithmic law values of z0 do not vary significantly with wind direction in winter but they show marked symmetric directional dependence with the smoothest direction around 90 in azimuth in summer the smoothest direction is formed by the prevailing high wind in a narrow directional range in summer but it is not formed by high winds in winter because of the scatter over a wider directional range the results of the first paper can be used throughout the year cd10 is estimated to be 0 0013 but decreases to 0 00075 in the smoothest direction in summer the winter value is similar to previous results over a polar snow surface but the minimum value in summer is smaller than any previous values in the literature

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation