the meteoritical bulletin no 81 1997 jul meteoritical bulletin no 81 lists 181 new meteorites noteworthy among these are a new lunar meteorite dar al gani 262 four observed falls dong ujimqin qi galkiv mount tazerzait and piplia kalan four irons albion great sand sea 003 hot springs and mont dieu two mesosiderites dong ujimqin qi and lamont an acapulcoite fro 95029 a eucrite piplia kalan two probably paired ureilites dar al gani 164 and 165 an r chondrite hammadah al hamra 119 an ungrouped type 3 chondrite hammadah al hamra 180 a highly unequilibrated ordinary chondrite wells ll3 3 and a variety of carbonaceous and unequilibrated ordinary chondrites from libya and antarctica all italicized abbreviations refer to addresses listed in the appendix

monsoon fluctuations in two 20 000 yr b p oxygen isotope pollen records off southwest india abstract two marine pollen diagrams for sediments off the southwest coast of india provide a 20 000 yr history of the nearby continental vegetation determined by the monsoon climate within the framework of the isotopic stratigraphy two important phases of the evolution of the monsoon climate are a very arid period about 22 000 18 000 yr b p and a very humid period culminating at 11 000 yr b p the very arid period corresponds to the lowest pollen representation of mangrove vegetation which is used here as an indirect indicator of monsoonal runoff this aridity is due to a very weak southwest airflow a great reduction of summer monsoonal rainfall and reduced runoff of the western ghats rivers the extension of the monsoon over india after the last glacial maximum has been a gradual process following the northward progression of the intertropical convergene zone the very humid period corresponding to the highest pollen representation of mangrove vegetation and the heaviest summer rainfall is a climatic response to the maximum summer insolation of the northern hemisphere at 11 000 yr b p

spatial variability of major frontal systems in the north atlantic norwegian sea area 1980 81 abstract locations of strong frontal systems in the upper 350 m of the north atlantic norwegian sea area are identified using data from nearly 2300 axbts deployed over a period spanning both winter and summer seasons approximate bounds on frontal widths and frontal meandering are given and the variations in frontal locations with depth are also described seasonal variations in the horizontal and vertical structure of the fronts are examined sea surface expression of fronts is shown to decrease in summer months and a general dependence of frontal locations on bathymetry is seen

microdistributions and petrogenetic implications of rare earth elements in polymict ureilites polymict ureilites contain various mineral and lithic clasts not observed in monomict ureilites including plagioclase enstatite feldspathic melt clasts and dark inclusions this paper investigates the microdistributions and petrogenetic implications of rare earth elements rees in three polymict ureilites elephant moraine eet 83309 eet 87720 and north haig focusing particularly on the mineral and lithic clasts not found in monomict ureilites as in monomict ureilites olivine and pyroxene are the major heavy h ree carriers in polymict ureilites they have light l ree depleted patterns with little variation in ree abundances despite large differences in major element compositions the textural and ree characteristics of feldspathic melt clasts in the three polymict ureilites indicate that they are most likely shocked melt that sampled the basaltic components associated with ureilites on their parent body simple ree modeling shows that the most common melt clasts in polymict ureilites can be produced by 20 30 partial melting of chondritic material leaving behind a ureilitic residue the plagioclase clasts as well as some of the high ca pyroxene grains probably represent plagioclase pyroxene rock types on the ureilite parent body however the variety of ree patterns in both plagioclase and melt clasts cannot be the result of a single igneous differentiation event multiple processes probably including shock melting and different sources are required to account for all the ree characteristics observed in lithic and mineral clasts the c rich matrix in polymict ureilites is lree enriched like that in monomict ureilites the occurrence of ce anomalies in c rich matrix dark inclusions and the presence of the hydration product iddingsite imply significant terrestrial weathering a search for 26mg excesses from the radioactive decay of 26al in the polymict ureilite eet 83309 was negative

role of microtopography in the formation of sodic soils in the semi arid part of the indo gangetic plains india abstract in the northwestern part of the indo gangetic plains igp india non sodic and moderately sodic soils occur on microhigh mh and highly sodic soils on microlow ml positions under a semi arid climate the main soil forming processes have been clay illuviation deposition of pedogenic calcium carbonate and concomitant development of sodicity the microlows are repeatedly flooded with surface water during brief high intensity showers so the soils are subject to cycles of wetting and drying this provides a steady supply of alkalis by hydrolysis of feldspars leading to precipitation of calcium carbonate at high ph and development of subsoil sodicity this impairs the hydraulic conductivity of soils and eventually leads to the development of natrustalfs with exchangeable sodium percentages increasing rapidly up the profile the semi arid climate and topography interact to facilitate greater penetration of bicarbonate rich water in microlow than microhigh positions thin sections show deformational pedofeatures such as cross and reticulate striation of plasmic fabric disruption of clay pedofeatures and carbonate nodules and elongation of voids as a result of tectonic activity during the holocene in view of the persistent build up of stresses in the igp in general and the study area in particular it seems that the neotectonics have caused the microtopographical variations 0 5 1 m that control the formation of sodic soils

quantitative skill of quasi geostrophic forecasts of a baroclinically unstable iceland faroe front using initialization and validation conditions from hydrographie surveys of the iceland faroe front in august 1993 shipboard quasi geostrophic model forecasts executed in real time are evaluated for quantitative skill in terms of anomaly correlation coefficient and rms error the prototype dynamical forecasts are synoptically initialized from two observed initial states and validated against observations obtained 3 4 days later the forecasts correlate with the validating observations yielding anomaly correlation coefficients of 0 75 0 80 which beat persistence of day zero forecasts by 0 07 0 30 depending on the region of interest and the initial state thus this quasi geostrophic model is able to forecast the rapidly evolving currents of this front with quantitative skill the forecast fields of stream function are also used to diagnose the physical processes of the frontal current variations energetic diagnostics clearly reveal that the frontal current evolution is controlled by baroclinic instability processes baroclinic wave disturbances at middepth serve to transfer available gravitational energy to kinetic energy which then is transferred through the water column resulting in the observed and modeled rapid changes in the frontal current

role of neotectonics and climate in development of the holocene geomorphology and soils of the gangetic plains between the ramganga and rapti rivers abstract fifteen soil geomorphic units have been delineated from the gangetic plains between the ramganga and rapti rivers they were identified by remote sensing and field checks on the basis of degree of profile development their soils are grouped into five members qgh1 to qgh5 qgh5 being the oldest of a soil chrono association tentative ages assigned to qgh1 to qgh5 are 500 2500 8000 and 13 5000 yr b p respectively from the early holocene to about 6500 yr b p a cold arid to semi arid climate prevailed and pedogenic calcrete developed over large areas in the gangetic plains later a warm and humid climate and improved drainage resulted in complete removal of calcrete from soil profiles in some areas or its dissolution and re precipitation in lower horizons in other areas neotectonics seems to have played a significant role in the evolution of the geomorphology and soils of the area it determined areas of active sedimentation pedogenesis and erosion in upland regions it led to tilting and sagging of large blocks resulting in shifting and increase in sinuosity of the rivers tectonic slopes faults determined the courses of large rivers

temporal variability of the subarctic front near the charlie gibbs fracture zone we document temporal variability of the northernmost branch of the north atlantic current known as the north subarctic front nsaf for the period 1976 1985 the front s location and temperature salinity t s parameters were determined from 120 repeat transects along three standard sections occupied by russian ships 1 ocean weather station ows c 52 75 n 35 5 w to st john s newfoundland 2 along 35 w from 52 n to 36 5 n and 3 ows c to cape st vincent portugal the nsaf exhibits significant interannual variability of its location shifting 200 km to 300 km in a few months along the ows c st john s section the front reached its southernmost location in 1976 1977 then experienced two 250 to 300 km northward shifts in 1978 1979 and 1980 1981 all of the three shifts peaked in wintertime these events nearly coincide with events of the opposite sign along the ows c cape st vincent section the northernmost location in 1976 1977 and two 200 km southward shifts in 1978 1979 and 1980 1981 the nsaf s behavior is thus coherent near the charlie gibbs fracture zone at the 500 km scale frontal time series associated with the moving front of t and s at the 200 m level for the cold side of the nsaf reveal two events an s200 minimum in the winter of 1976 1977 which might be a manifestation of the great salinity anomaly of the 1970s and a sharp drop of s200 in early 1984 which might signal the arrival of another large salinity anomaly the great salinity anomaly of the 1980s

radiolarian faunal provinces in surface sediments of the greenland iceland and norwegian gin seas the overall abundance and species composition of the polycystine and phaeodarian radiolaria have been determined in 63 surface sediment samples from the gin seas these results are compared to chemical and physical properties of the overlying water masses there are three abundance maxima in the distribution of radiolarian skeletal debris preserved in these surface sediments centered on the iceland plateau southern norwegian basin and northern norwegian basin the most commonly encountered species were a spumellarida actinomma boreale a leptoderma larcospira minor and phorticium clevei b nassellarida amphimelissa setosa artobotrys boreale lithomelissa setosa lithocampe platycephala pseudodictyophimus gracilipes cycladophora davisiana a ndlithomitra lineata based on factor analysis of the core top assemblages the radiolarian species were grouped into three associations factor 1 a polar and arctic water association dominated by amphimelissa setosa varimax factor score 5 269 high factor component values are found in the iceland plateau area and in a wedge just north of the iceland faeroe ridge factor 2 an atlantic water association dominated by pseudodictyophimus gracilipes 3 247 lithomelissa setosa 2 731 and actinomma boreale 1 851 high factor component values are found in the eastern part of the norwegian sea particularly in the area under the influence of the norwegian current and factor 3 an atlantic and arctic water mixed association dominated by lithocampe platycephala 3 251 lithomelissa setosa 2 176 actinomma leptoderma 1 994 and artobotrys boreale 1 504 high factor component values are found immediately to the east of the iceland plateau in correspondence to the deepest part of the norwegian basin the correlation coefficients obtained between seasonal sea surface temperature and factors 1 r 2 d 0 835 a nd 2 r 2 d 0 891 show a good fit whilst for factor 3 there was a less marked r 2 d 0 497 but still significant at the 5 confidence level correlation for fifth degree polynomial regression functions the factors correlated better with the summer than the winter sea surface temperatures however at 20 50 100 and 200 m depth the correlation became increasingly better particularly so for the winter situation the highest species richness for polycystine radiolarians 28 species was found in the warm atlantic domain the lowest 24 species was found in the colder arctic and polar domains whilst an area approximating the position of the arctic front had between 24 and 28 species 1998 elsevier science b v all rights reserved

sea surface temperature variability of the iceland faeroe front correction in a previous study by niiler et al 1992 advanced very high resolution radiometer avhrr images were used for locating the iceland faeroe front temperature distributions and gradients in that study the satellite sensed sea surface temperatures were found to contain an error after an atmospheric correction algorithm was applied this was determined through a regression fit of avhrr data against in situ aircraft deployed expendable bathythermograph axbt and conductivity temperature depth measurements recently minnett 1993 pointed out that an error occurred in that fit as a result we decided to repeat the comparisons of avhrr sea surface temperature sst data against in situ measurements after correcting several errors we still find a shift of about 2 c in the scatter of avhrr against axbt sst data the bias mean difference was 1 73 c and the standard deviation was 0 3 c

comment on sea surface temperature variability of the iceland faeroe front by pearn p niiler steve piacsek lucas neuberg and alex warn varnas

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

late quaternary palaeoclimatic reconstruction from the lacustrine sediments of the sambhar playa core thar desert margin india the sambhar playa in rajasthan india located at the eastern fringe of the thar desert records multiple phases of clastic and evaporite dominated deposition as revealed from a 23 m deep core drilled in the center of the playa seven evaporite facies identified from the mineralogical data reflect variable brine chemistry throughout the history of the playa the complete absence of gypsum rich facies in the upper 5 m and dominance of carbonate and gypsum rich facies in the lower parts of the core reflect fluctuations in salinity level induced by climate change stable isotope data on carbonates d 18 o values correlate with the mgo mgo cao ratio geochemical ratios na al na ti na k and the evaporite mineralogy these data coupled with ams chronology of the organic fraction of the core sediments have been integrated to interpret evaporation inflow ratios which reflect humid and arid climatic conditions our data reconstruct the palaeoclimatic fluctuations in the thar desert margin for the last 30 ka and show significant spatial variation from the available lacustrine records from the thar desert the sambhar playa does not show any evidence of complete desiccation throughout its history although we record arid phases during the lgm and between ca 7500 and 6800 years d 2005 elsevier b v all rights reserved

soil development in till of various ages in northeastern pennsylvania abstract eleven well drained soils formed in till parent materials of varying ages in northeastern pennsylvania were studied to determine changes in the soils with time four profiles three lackawanna and one bath were formed in woodfordian till 15 000 yr b p and two leck kill were formed in altonian till 28 000 75 000 yr b p in these soils the extractable iron oxide extractable aluminum oxide and kaolinite contents increase with age as do the total clay and fine total clay ratio with increasing age the maximum accumulation of these constituents is found deeper in the profile the extractable silicon oxide distribution is constant with depth but it decreases in overall amount with time gibbsite is found only in small amounts in the a horizon of altonian soils but occurs throughout the profile of pre wisconsinan soils although only in small amounts in general differences were found in these soils which separated them into three groups representing varying degrees of soil development a regression equation was derived to predict the age of soils formed from the altonian till based on a clay accumulation index value for soils of known woodfordian and holocene ages the equation log y 1 80 0 992 log x best fit the data with an r 2 value of 0 913 using this equation a mean age of 41 000 yr was calculated for the altonian soils this date was used to derive a second equation to predict ages for pre wisconsinan soils the equation with the highest r 2 value 0 934 was log y 1 81 0 998 log x dates for soils developed in the white deer till and the laurelton till of the pre wisconsinan stage were calculated to be 86 000 and 91 000 yr b p respectively these dates fall within ages estimated for the sangamon interglaciation and thus would appear to be too young for pre sangamonian materials the probable reason for the too young age is that the c horizon material of the pre wisconsinan soils was weathered and did not provide an accurate estimate of clay accumulation for the prediction equation

the subtropical front satellite observations during fronts 80 satellite derived sea surface temperature in situ hydrography data and satellite tracked drifter data collected during winter 1979 1980 as part of the fronts 80 experiment are used to describe the spatial structure of the north pacific subtropical front northeast of hawaii the satellite observations reveal a deformation scale meander 85 km 32 km in association with the front having an evolution time scale of 60 days the satellite measurements of the change in sea surface temperature across the front are typically 1 c within a distance of 10 km the correlation coefficients between the satellite data and the in situ hydrographic data were computed and found to be significantly nonzero above 800 m the high correlation at deep levels indicates that the satellite was viewing a feature with sizable vertical extent not just a surface phenomenon additionally the hydrographic data and drifter trajectories were combined with the satellite derived sea surface temperature data together they demonstrate that the feature observed by the satellite was nearly stationary during the experiment period in addition they also indicate that the flow along the front was nearly in geostrophic balance

the frontier mountain meteorite trap antarctica the frontier mountain blue ice field is an important antarctic meteorite trap which has yielded 472 meteorite specimens since its discovery in 1984 remote sensing analyses and field campaigns from 1993 to 1999 have furnished new glaciological data on ice flow ice thickness bedrock topography ice ablation and surface mass transport by wind along with detailed descriptions of the field situation at the trap this solid set of data combined with an updated meteorite distribution map and terrestrial ages available from literature allows us to better describe the nature of the concentration mechanism in particular we observe that the meteorite trap forms in a blue ice field 1 located upstream of an absolute and a shallow sub ice barriers 2 characterized by compressive ice flow with horizontal velocities decreasing from 100 to 10 cm year on approaching the obstacle 3 undergoing mean ablation rates of 6 5 cm year 4 nourished by a limited snow accumulation zone extending 20 km upstream of the blue ice area we also draw the following conclusions 1 the origin of the meteorite trap can be explained according to the present day glaciological situation 2 the meteorite concentration develops according to the general principles of the ice flow model 3 the accumulation model can be described as stagnant ice or slow moving ice against an absolute and submerged barriers according to the descriptive schemes present in literature 4 the frontier mountain ice field is an effective trap for meteorites weighing more than 200 g for smaller masses the combination of wind and glacial drift may remove meteorites in less than a few tens of thousands of years 5 although the activation age of the frontier mountain trap is not yet constrained we infer that one of the most important findsites may be as old as 50 ka predating the last glacial maximum

frontier mountain meteorite specimens of the acapulcoite lodranite clan petrography pairing and parent rock lithology of an unusual intrusive rock in this paper we reconstruct the heterogeneous lithology of an unusual intrusive rock from the acapulcoite lodranite al parent asteroid on the basis of the petrographic analysis of 5 small 8 3 g meteorite specimens from the frontier mountain ice field antarctica although these individual specimens may not be representative of the parent rock lithology due to their relatively large grain size by putting together evidence from various thin sections and literature data we conclude that frontier mountain fro 90011 fro 93001 fro 99030 and fro 03001 are paired fragments of a medium to coarse grained igneous rock which intrudes a lodranite and entrains xenoliths the igneous matrix is composed of enstatite fs13 3 0 4 wo3 1 0 2 cr rich augite fs6 1 0 7 wo42 3 0 9 and oligoclase ab80 5 3 3 or3 2 0 6 the lodranitic xenoliths show a fine grained average grain size 488 201 m granoblastic texture and consist of olivine fa9 5 0 4 and fe ni metal and minor amounts of enstatite fs12 7 0 4 wo1 8 0 1 troilite chromite schreibersite and ca phosphates crystals of the igneous matrix and lodranitic xenoliths are devoid of shock features down to the scanning electron microscope scale from a petrogenetic point of view the lack of shock evidence in the lodranitic xenoliths of all the studied samples favors the magmatic rather than the impact melting origin of this rock fro 95029 is an acapulcoite and represents a separate fall from the al parent asteroid i e it is not a different clast entrained by the fro 90011 fro 93001 fro 99030 and fro 03001 melt as in genomict breccias common in the meteoritic record the specimen to meteorite ratio for the al meteorites so far found at frontier mountain is thus 2 5

polygenetic soils of the north central part of the gangetic plains a micromorphological approach abstract micromorphology indicates that soils of the central part of the gangetic plains are polygenetic they occur on surfaces originating at 13 500 8000 2500 500 and

clay minerals in soils as evidence of holocene climatic change central indo gangetic plains north central india clay mineral assemblages of a soil chrono association comprising five fluvial surface members qgh1 to qgh5 of the indo gangetic plains between the ramganga and rapti rivers north central india demonstrate that pedogenic interstratified smectite kaolin sm k can be considered as a potential indicator for paleoclimatic changes during the holocene from arid to humid climates on the basis of available radiocarbon dates thermoluminescence dates and historical evidence tentative ages assigned to qgh1 to qgh5 are 500 yr b p 2500 yr b p 8000 tl yr b p and 13 500 tl yr b p respectively during pedogenesis two major regional climatic cycles are recorded relatively arid climates between 10 000 6500 yr b p and 3800 yr b p were punctuated by a warm and humid climate biotite weathered to trioctahedral vermiculite and smectite in the soils during arid conditions and smectite was unstable and transformed to sm k during the warm and humid climatic phase 7400 4150 cal yr b p when the humid climate terminated vermiculite smectite and sm k were preserved to the present day the study suggests that during the development of soils in the holocene in alluvium of the indo gangetic plains climatic fluctuations appear to be more important than realized hitherto the soils older than 2500 yr b p are relict paleosols but they are polygenetic because of their subsequent alterations

meanders of the gulf stream downstream from cape hatteras 1975 1978 abstract weekly gulf stream paths within 1000 km downstream of cape hatteras were obtained for 1975 78 from the navy s weekly eofa charts based on satellite ir imagery they displayed two dominant meander modes first a standing meander energetic over periods between 4 months and at least 4 years and second down stream propagating meanders that were most energetic at periods of several weeks the long period standing meander was confined between nodes located at the separation point near cape hatteras i e where the stream s mean path turns seaward and at a point about 600 km farther downstream the rms amplitude was 36 km at the antinode the amplitude of propagating meanders increased rapidly in the first 200 km downstream of the separation point where the capture of warm core eddies was common farther down stream the predominant meanders had a wavelength averaging 330 km a period averaging 1 5 month a phase speed averaging 8 cm s 1 a downstream group speed averaging 17 cm s 1 and downstrea

evidence for common breakup events of the acapulcoites lodranites and chondrites acapulcoites and lodranites are believed to originate on a common parent body and to represent some of the earliest events in the differentiation of the chondritic asteroids we have conducted isotopic studies of the noble gases he ne ar kr and xe and determinations of the concentrations of the major elements and of the radionuclides 10be 26al and 36cl in an attempt to constrain the cosmic ray exposure history of two members of the acapulcoite lodranite clan recovered in antarctica frontier mountain fro 95029 and graves nunataks gra 95209 from cosmic ray produced 3he 21ne and 38ar and appropriate production rates we derive parent body breakup times of 4 59 0 60 and 6 82 0 60 ma for for 95029 and gra 95209 respectively these times are consistent with those obtained from the pairs 10be 21ne and 26al 21ne whereas the times inferred from the pair 36cl 36ar are slightly longer perhaps because the 36cl activities decreased as a result of decay on earth terrestrial ages up to 50 ka for the two meteorites are consistent with the measured 36cl activities of the metal phases all acapulcoites and lodranites dated until now show cosmic ray exposure ages in the range of 4 10 ma this is the same range as that found for the major exposure age cluster of the h chondrites as a common parent body is improbable on the basis of the o isotopic systematics a common set of impactors might have affected the asteroid belt 4 10 ma ago

meteorite and meteoroid new comprehensive definitions abstract meteorites have traditionally been defined as solid objects that have fallen to earth from space this definition however is no longer adequate in recent decades man made objects have fallen to earth from space meteorites have been identified on the moon and mars and small interplanetary objects have impacted orbiting spacecraft taking these facts and other potential complications into consideration we offer new comprehensive definitions of the terms meteorite meteoroid and their smaller counterparts a meteoroid is a 10 m to 1 m size natural solid object moving in interplanetary space a micrometeoroid is a meteoroid 10 m to 2 mm in size a meteorite is a natural solid object larger than 10 m in size derived from a celestial body that was transported by natural means from the body on which it formed to a region outside the dominant gravitational influence of that body and that later collided with a natural or artificial body larger than itself even if it is the same body from which it was launched weathering and other secondary processes do not affect an object s status as a meteorite as long as something recognizable remains of its original minerals or structure an object loses its status as a meteorite if it is incorporated into a larger rock that becomes a meteorite itself a micrometeorite is a meteorite between 10 m and 2 mm in size meteorite a solid substance or body falling from the high regions of the atmosphere craig 1849 a mass of stone and iron that ha s been directly observed to have fallen down to the earth s surface translated from cohen 1894 a solid bod y which came to the earth from space farrington 1915 a mass of solid matter too small to be considered an asteroid either traveling through space as an unattached unit or having landed on the earth and still retaining its identity nininger 1933 a meteoroid which has reached the surface of the earth without being vaporized 1958 international astronomical union iau definition quoted by millman 1961 a solid body which has arrived on the earth from outer space mason 1962 a solid bod y which reach es the earth or the moon mars etc from interplanetary space and is large enough to survive passage through the earth s or mars etc atmosphere gomes and keil 1980 a meteoroid that survive s passage through the atmosphere and fall s to earth burke 1986 a recovered fragment of a meteoroid that has survived transit through the earth s atmosphere mcsween 1987 a solid bod y of extraterrestrial material that penetrate s the atmosphere and reach es the earth s surface krot et al 2003

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

feldspathic clast populations in polymict ureilites stalking the missing basalts from the ureilite parent body abstract polymict ureilites dag 164 165 dag 319 dag 665 and eet 83309 are regolith breccias composed mainly of monomict ureilite like material but containing 2 vol of feldspathic components we characterized 171 feldspathic clasts in these meteorites in terms of texture mineralogy and mineral compositions based on this characterization we identified three populations of clasts each of which appears to represent a common igneous generally basaltic lithology and whose mafic minerals show a normal igneous fractionation trend of near constant fe mn ratio over a range of fe mg ratios that extend to much higher values than those in monomict ureilites the melts represented by these populations are unlikely to be impact melts because the ubiquitous presence of carbon in polymict ureilites the regolith of the ureilite parent body implies that impact melts would have crystallized under conditions of carbon redox control and therefore have highly magnesian mafic mineral compositions with constant mn mg ratio therefore these melts appear to be indigenous products of igneous differentiation on the ureilite parent body upb complementary to the olivine pigeonite residues represented by the majority of monomict ureilites the most abundant population is characterized by albitic plagioclase in association with pyroxenes phosphates ilmenite silica and incompatible element enriched glass model calculations suggest that it formed by extensive fractional crystallization of the earliest melt s of precursor materials from which the most magnesian shallowest olivine pigeonite ureilites formed a less abundant population characterized by labradoritic plagioclase may have formed from melts complementary to more ferroan olivine pigeonite ureilites and derived from deeper in the upb the third population characterized by the presence of olivine and augite could only have formed from melts produced at greater depths in the upb than the olivine pigeonite ureilites many other feldspathic clasts cannot be positively associated with any of these three populations because their mafic mineral compositions exhibit carbon redox control however they may be products of early crystallization of basaltic melts produced on the upb before carbon was exhausted by reduction partial melting on the ureilite parent body was a fractional or incremental process melts were produced early in upb history and most likely extracted rapidly thus preserving primitive chemical and oxygen isotopic signatures in the residues

the gin sea a synthesis of its physical oceanography and literature review 1972 1985 abstract a synthesis and review of the physical oceanography of the gin sea greenland iceland and norwegian seas is presented an accompanying bibliography is included from 1972 through 1985 some 1986 works are also noted emphasis is placed on describing the gin sea as a major semi enclosed basin that plays a role unique among the world s oceans by providing a strong two way advective exchange between the ice covered polar sea and the north atlantic ocean and at the same time acting as the primary site for northern hemisphere bottom water formation the water masses for the gin sea are defined in a manner as consistent as possible with the literature the large scale oceanographic and meteorological factors influencing the water mass formation and circulation are described a sample calculation of the various horizontal and vertical thermohaline driven exchanges is given

lateglacial and holocene environmental changes in ganga plain northern india abstract stable isotope elemental geochemistry and pollen analysis of a sediment profile from sanai lake central ganga plain were used to document climatic oscillations during the last 15 000 yr in indian subcontinent micaceous sandy sediments at the base of the profile indicate an active channel and humid conditions before 15 000 14c yr bp the channel was abandoned during comparatively arid conditions 15 000 13 000 14c yr bp and converted into a swamp enhanced humidity around 13 000 14c yr bp led to submergence of marshes and establishment of a large lake a dry phase is also identified around an estimated age of 11 500 10 500 14c yr bp which might correspond to the younger dryas event witnessed globally the early to mid holocene climatic optimum 10 000 5800 14c yr bp is characterised by a lake environment occurence of warmth loving aquatic plants lower 18o values of gastropod aragonite heavier 13corg values indicate a sensitive response of the lake ecology to the climatic warming and increased rainfall this is followed by an arid event during 5000 2000 14c yr bp and from 1700 14c yr bp there is evidence of climatic amelioration the sequence and magnitude of the millenium scale climatic oscillations documented along the lake profile correlate well with records from other parts of the indian subcontinent indicating that the recorded changes are an expression of broad scale probably global and climatic change

historical geomorphology and pedology of the gandak megafan middle gangetic plains india the gandak megafan of eastern uttar pradesh and northwestern bihar lies in the middle gangetic plains the gandak river has shifted about 80 km to the east due to tilting in the last 5000 years this has created a soil chronoassociation similar to the chronosequences found on some flights of river terraces this chronoassociation has five members qgd1 5 they are distinguished on the basis of profile development clay mineralogy and calcium carbonate content chlorite transforms to vermiculite on a large scale from qgd1 to qgd3 and decreases drastically in member qgd4 kaolinite and interstratified kaolinite smectite are abundant in the older members of the chronoassociation the youngest soils qgd1 500 b p while qgd3 soils like those on the older gandak plain and old rapti plains date back to 2500 b p qgd4 soils like those on the oldest gandak plain are dated as 5000 years b p whilst the oldest qgd5 soils as on the old ghaghra plain and ganga ghaghra interfluve date back to 10000 b p these soils which include pedogenic calcite and a saline epipedon indicate a dry climatic spell during the period 9000 11000 b p faults developed on the megafan are not related to the basement structures

observations of seasonal subduction at the iceland faroe front the polar front in the north atlantic is bound to the ridge between iceland and the faroe islands where about one half of the northward transport of warm atlantic water into the nordic seas occurs as well as about one sixth of the equatorward dense overflow we find a low salinity water mass at the surface of the iceland faroe front iff which in wintertime subducts along outcropping isopycnals and is found in much modified form on the atlantic side of the iceland faroe ridge ifr crest the features found on the atlantic side of the crest at depth have temperature and salinity characteristics which are clearly traceable to the surface outcrop of the iff the presence of coherent low salinity layers on the atlantic side of the ifr crest has not been previously reported warm waters above the ifr primarily feed the faroe current and injection of a low salinity water mass may play an early role in the water mass transformation taking place in the nordic seas the seasonality of the intrusive features suggests a link between winter convection mixed layer instability and deep frontal subduction these low salinity anomalies as well as a low oxygen water mass from the iceland basin can be used as tracers of the intermediate circulation over the ifr

relict olivine grains chondrule recycling and implications for the chemical thermal and mechanical processing of nebular materials chondrules and isolated forsterites in five low subtype ordinary chondrites nwa 3127 ll3 1 sahara 97210 ll3 2 wells ll3 3 chainpur ll3 4 and sahara 98175 ll3 5 were studied using petrographic empa and sims techniques to better constrain the origin of chondrules and the olivine grains within them our results imply that igneous crystallization vapor fractionation redox e ects and open system behavior were important processes all olivine grains including normal relict and isolated forsterite grains show evidence for igneous fractionation under disequilibrium conditions with olivine crystallizing during rapid cooling closer to 2000 c h than to 100 c h vapor fractionation is manifested by anti correlated abundances between refractory elements al sc y ti ca v and volatile elements cr mn p rb fe in olivine redox e ects are evidenced in various ways and imply that fe co ni and p were partitioned more into metal and v was partitioned more into olivine under reducing conditions in the most feo poor melts there is no obvious evidence for systematic variations in olivine composition according to meteorite subtype but shock melting in sahara 97210 resulted in the injection of glass derived melt into olivine resulting in artificially high abundances of ba sr na ti and some other incompatible elements in olivine terrestrial weathering in a hot desert environment may have mobilized ba and sr in some glasses our data suggest that chondrules in ordinary chondrites experienced repeated thermal chemical and mechanical processing during a recycling process over an extended time period which involved multiple episodes of melting under fluctuating redox and heating conditions and multiple episodes of chondrule break up in some cases forsterite grains including normal grains in forsterite bearing type i chondrules the cores of isolated forsterites and relict forsterite in type ii chondrules all crystallized from similar refractory melts under reducing conditions relict mg olivine and isolated forsterite grains were thus derived from type i chondrules olivine in type ii chondrules including normal grains and ferroan overgrowths on relict mgolivine crystallized from more volatile rich oxidized and relatively unfractionated melts relict dusty olivine grains in type i chondrules were derived from type ii chondrules during incomplete melting episodes involving reduction and some vaporization with clear non dusty grains in dusty olivine bearing chondrules crystallizing from the reduced and partly vaporized melts melt compositions parental to normal olivine grains in type i and ii chondrules are systematically enriched in refractory elements compared to bulk chondrule compositions implying that chondrules often experienced open system exchange with more volatile rich surroundings after some olivine had crystallized possibly while the chondrules were still partly molten type ii chondrules could have been derived from type i chondrules by the addition of relatively volatile rich material followed by re melting and little evaporation under oxidizing conditions in contrast type i chondrules could have been derived from type ii chondrules by re melting involving more or less evaporation under reducing conditions chemical oxygen

pedogenic processes on the ganga deoha ghaghara interfluve upper gangetic plains india abstract the ganga deoha ghaghara interfluve in the upper gangetic plains india has been investigated by satellite image analysis and digital terrain modelling field observations and laboratory analysis of soils to identify 24 soil geomorphic units these units were grouped into five members of a morphostratigraphic sequence based on the infra red stimulated luminescence irsl dating and these members with typical soils are grouped into i qgms i 1 7 ka fluvaquents ustifluvents and haplustepts ii qgms ii 1 8 3 6 ka fluvaquents and haplustepts iii qgms iii 4 6 6 4 ka haplustalfs haplustepts and rarely natraqualfs iv qgms iv 6 8 10 ka haplustalfs and ochraqualfs and v qgms v 10 ka haplustalfs calcrete formation starts at the base of piedmont zone further downslope to the south significant alkalization starts still further south salinization starts and continues to the distal end of the interfluve with increased intensity these processes are active in the present dry sub humid climate though earlier they mainly occurred in semiarid regions a combination of factors including dry sub humid climate and shallow impervious layers leading to water logging in microdepressions occurring over large areas sub surface flow from proximal to distal parts and higher evaporation from topographic microlows leads to the concentration of salts in the soils of the interfluve these phenomena occur in the qgms i and ii soils and older soils occurring in the low lying areas in western parts of the upper half and the whole of the lower half of the study area micromorphology and clay mineral studies suggest polygenetic nature of these soils due to the climatic changes since the late pleistocene soils 10 ka old on loamy material seem to have reached a mature stage in respect of thicknesses of solum bhorizon and argillans ferriargillans

quasigeostrophic forecasting and physical processes of iceland faroe frontal variability abstract using a hydrocast survey of the iceland faroe front iff from october 1992 quasigeostrophic forecasts are studied to validate their efficacy and to diagnose the physical processes involved in the rapid growth of a cold tongue intrusion explorations of 1 the choice of initial objective analysis parameters 2 the depth of the unknown level of no motion 3 the effects of surrounding mesoscale activity 4 variations in the boundary conditions and 5 simple assimilation of newly acquired data into the forecasts are carried out using a feature validation technique which incorporates a 1 validating hydrocast survey 2 satellite sst images and 3 surface drifter observations most of the forecasts are found to perform well in capturing the key events of the validation strategy particularly the development of the cold tongue intrusion though it tends to develop somewhat more weakly and slightly farther downstream than observed sharp resolution of frontal structure to capture seed anomali

a study of the iceland faeroe frontal variability using the multiscale energy and vorticity analysis the multiscale nonlinear interactive iceland faeroe frontal iff variability during 14 22 august 1993 is investigated for complex dynamics with the localized multiscale energy and vorticity analysis ms eva in terms of multiscale window transform the cold meandering intrusion observed in the iff experiment is represented on a mesoscale window the resulting mesoscale energetics for the deep layer show an isolated center of transfer of potential energy from the large scale window into the mesoscale window in the study domain this large to mesoscale potential energy transfer or bc for short is a baroclinic instability indicator by the ms eva based stability theory signatures on other energetics maps and the reconstructed mesoscale structures all support this baroclinic instability on the bc map the transfer hotspot originally resides near the western boundary it travels along the front into the interior domain in a form of convective instability and then on 19 august changes into another instability that is absolute in character correspondingly disturbances switch from a spatial growing pattern into a time growing mode culminating on 21 august the day just before the intrusion matures the whole process lasts for about five days limited within a small horizontal region and beneath a depth of approximately 150 m by interaction analysis the energy locally gained from this process goes to the submesoscale window as well but most of it remains in the mesoscale window serving to fuel the growth of the meandering intrusion

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

near surface circulation of the nordic seas as measured by lagrangian drifters in the period june 1991 to august 1993 107 argos tracked drifters drogued to 15 m depth were released in the nordic seas or greenland iceland and norwegian seas the drifter movements revealed the strong and spatially confined current systems along the surface salinity fronts of the iceland faroe frontal zone and of the norwegian coast and along the continental margins and their extensions to the barents sea and spitsbergen the norwegian atlantic current is composed of three distinct streams two continental margin and one coastal branches which join into one single swift mean current west of the lofoten and vesteralen islands where the strongest measured currents are in excess of 110 cm s 1 in addition to the general cyclonic gyre circulation in the nordic seas the drifters indicate smaller cyclonic circulation patterns in all the major subbasins i e the iceland plateau the norwegian the lofoten and the greenland basins no surface signature of the east icelandic current is disclosed by the drifters interpolated and low pass filtered position data were used to construct maps of 15 m depth ensemble mean velocity velocity variability and residence time vigorous eddy fields are dominant in the strong currents and in the lofoten basin eulerian correlations indicate that they tend to propagate to the west in contrast the iceland plateau appears quiescent both in the mean and eddy velocities single particle diffusivities are computed and are found to be in the range 1 7 107 cm2 s 1 the corresponding lagrangian timescale and space scale are 1 3 days and 10 40 km respectively these lagrangian drifter measurements compose the first basin scale accurate near surface velocity data set of the nordic seas

idealized study on the effect of bottom topography on the seasonality of the stability of the iceland faeroe front abstractwe investigate the effects of bottom topography on the instability eddy driven heat flux and overturning of a front that sits atop a ridge by varying the initial location of an idealized

the halting effect of baroclinicity in vortex merging abstract we study the quasigeostrophic merging dynamics of axisymmetric baroclinic vortices to understand how baroclinicity affects merging rates and the development of the nonlinear cascade of enstrophy the initial vortices are taken to simulate closely the horizontal and vertical structure of gulf stream rings a quasigeostrophic model is set with a horizontal resolution of 9 km and 6 vertical levels to resolve the mean stratification of the gulf stream region the results show that the baroclinic merging is slower than the purely barotropic process the merging is shown to occur in two phases the first which produces clove shaped vortices and diffusive mixing of vorticity contours and the second which consists of the sliding of the remaining vorticity cores with a second diffusive mixing of the internal vorticity field comparison among nof cushman roisin polvani et al and dewar and killworth merging events indicates a substantial agreement in the kinematics of the process parameter sensitivi

cross frontal cold jets near iceland in water satellite infrared and geosat altimeter data this paper reports detailed in water observations and satellite infrared images which are approximately coincident with a single geosat altimeter track across the iceland faeroes frontal zone the are thermistor chain covered the upper 300 m of the ocean along the track and the first two of a long sequence of noaa satellite infrared images were obtained all within 24 hours of the geosat overpass the data are interpreted as showing cold cross frontal jets related to the formation of cold eddies south of the main frontal boundary implications for the use of altimetry for ocean monitoring are considered

sea surface temperature variability of the iceland faeroe front several advanced very high resolution radiometer avhrr images with spatial resolution of 1 1 3 3 km together with several concurrent aircraft deployed expendable bathythermograph axbt surveys and conductivity temperature depth ctd stations from spring 1989 are used to describe the iceland faeroe sea surface temperature sst front in the avhrr images sst fronts are located by maximizing sst single large gradient segments of the sst front do exist with some exceeding 100 km in length indicating a multiple frontal structure these single frontal lines are also segments where 2sst is small and they can be followed uniquely by a single isotherm eastward from iceland for a distance of 300 km with a 35 km sampled axbt survey two small subsurface cold eddies were located south of the surface front in an area 170 km 270 km east of iceland from a may 1987 avhrr image on 1 1 km resolution a population of seven such cold eddies are found between iceland and the faroes they appear to be generated along the surface expression of the iceland faroes front and populate the northern slope of the iceland faroes ridge historical data from towed high resolution instruments suggest that the cold eddies are 30 50 km in size and uplift the main thermocline by 150 m

lithofacies and palaeosol analysis of the middle and upper siwalik groups plio pleistocene haripur kolar section himachal pradesh india abstract the middle upper siwalik groups plio pleistocene are exposed at haripur kolar himachal pradesh india the succession is 2800 m thick and has been subdivided into unit m1 of the middle siwalik and four units u1 u4 of the upper siwalik group on the basis of facies associations and type and degree of development of palaeosols the available magnetostratigraphic ages for bases of units u1 u3 and u4 are 5 5 2 6 and 1 77 ma respectively the top of the section has been dated as 19 ka lithofacies association and palaeocurrent analysis indicates that the middle and upper siwalik groups were formed mainly by a basin transverse fluvial system two types of river systems which differ in their size can be documented in unit m1 unit u1 and unit u2 one trunk river system similar to the modern kosi and the other smaller river system which formed tributaries to the former the large rivers were mainly braided in nature the unit u3 and lower part of unit u4 were deposited in the piedmont depositional system mainly by small braided streams and the upper part of the unit u4 was deposited during a period of arid climate by sediment gravity flows integration of fluvial lithofacies and pedofacies helps to identify two fluvial depositional systems from the modern indo gangetic plains the lowland system involved deposition on alluvial megafans and interfan areas which resulted in sand rich and mud rich sequences with weekly developed soils the upland system allowed large tracts to act as high ground for thousands of years thereby giving rise to sandstone poor intervals with moderately to strongly developed soils occurrence of moderately to strongly developed soils was controlled by uplifting and tilting of large tectonic blocks without any relation to distance from the main channels rate of subsidence apparently controlled the occurrence of lowland and upland systems deposition of the unit m1 unit u1 and unit u2 took place under upland and lowland systems very similar to those identified from the modern indo gangetic plains the warm and humid climate between 5 3 and 2 6 ma led to the formation of red alfisols with calcrete nodules at places slightly cooler and drier climate starting at about 2 6 ma and approximately coinciding with the onset of global scale glaciation produced poorly developed yellow soil with common development of nodular calcretic horizon and calcitc material disseminated in the groundmass at ca 0 9 ma a probable significant change to still drier and cooler climate produced typical sediment gravity flows in the piedmont system that continued until at least up to 19 ka

rumuruti chondrites noble gases exposure ages pairing and parent body history in this paper we present concentration and isotopic composition of the light noble gases he ne and ar as well as of 84kr 132xe and 129xe in bulk samples of 33 rumuruti r chondrites together with previously published data of six r chondrites exposure ages are calculated and compared with those of ordinary chondrites a number of pairings especially between those from northwest africa nwa are suggested so that only 23 individual falls are represented by the 39 r chondrites discussed here eleven of these meteorites or almost 50 contain solar gases and are thus regolithic breccias this percentage is higher than that of ordinary chondrites howardites or aubrites this may imply that the parent body of r chondrites has a relatively thick regolith concentrations of heavy noble gases especially of kr are affected by the terrestrial atmospheric component which resides in weathering products compared to ordinary chondrites 129xe 132xe ratios of r chondrites are high

the ungrouped chondrite el medano 301 and its comparison with other reduced ordinary chondrites abstract el medano 301 em 301 is an ungrouped chondrite with overall texture and trace element distribution similar to those of ordinary chondrites ocs but with silicate olivine and low ca pyroxene compositions that are more reduced than those in ocs with average olivine and low ca pyroxene of fa3 9 0 3 and fs12 8 4 9 respectively these values are far lower than the values for ocs and even for chondrites designed as reduced chondrites low ca pyroxene is the dominant mineral phase and shows zoning with higher mgo contents along the crystal rims and cracks reverse zoning the co content of kamacite is also much lower than the concentrations observed in ocs below detection limit of 0 18 wt versus 0 44 37 wt oxygen isotopic composition is 17o 0 79 0 78 and slightly different from that of ocs the lower modal olivine pyroxene ratio different infrared ir spectra lower co content of kamacite lower mean feo contents of olivine and pyroxene different kamacite texture and different oxygen isotopic composition show that em 301 does not belong to a known oc group em 301 shows similarities with chondritic clasts in cumberland falls aubrite and with northwest africa 7135 nwa 7135 and acfer 370 ungrouped chondrites however dissimilar to nwa 7135 and the clasts it does not contain highly reduced mineral phases like daubreelite our observations suggest the formation of em 301 in a nebular region compositionally similar to ocs but with a different redox state with oxygen fugacity o2 in this region lower than that of ocs and higher than that of enstatite chondrites condensation region a second possibly nebular phase of reduction by the production of reducing gas phases e g c rich could be responsible for the subsequent reduction of the primary material and the occurrence of reverse zoning in the low ca pyroxene and lower average fa fs ratio based on the ir spectra of em 301 we suggest the possibility that the parent body of this chondrite was a v type asteroid

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

oceanographic conditions east of iceland circulation and hydrography on the shelf east of iceland and on the western portion of the iceland faeroe ridge is described by a series of surveys using temperature salinity profilers moored current meters and satellite tracked drifters the dominant surface current of the region is the northeastward flow of north atlantic water at the shelf break southeast of iceland as it leaves the shelf to join the iceland faeroe front on the bottom beneath it flowing in the opposite direction is a strong steady current composed of water from the nordic seas that has overflowed the ridge and followed along bathymetric contours north of the front three comparatively weak currents are identified formed by splitting of the north icelandic irminger current after it has rounded the northeast corner of iceland one branch the east icelandic current is confined to the shelf and produces a mean southward flow until it turns eastward to join the iceland faeroe front another leaves the shelf to form the shallow southeastward flowing icelandic current the third follows deeper contours of the continental slope and renews waters on the northern flank of the iceland faeroe ridge

monnig collection meteorites from forestburg davy harrison township and gurram kond we report the histories and classifications of poorly known meteorites from the oscar monnig meteorite collection forestburg a texas is an l4 s2 ordinary chondrite forestburg b texas is a shock blackened l5 s5 ordinary chondrite containing an impact melt clast davy a texas l4 s2 is represented by several highly weathered stones davy b texas is a single stone classified as h4 s2 harrison township kansas l6 s4 was found in the vicinity of several meteorites grouped as ladder creek but appears distinct we have identified the second and largest fragment of the 1814 october gurram konda india l6 s3 meteorite fall and uncovered details of its early history

evolution and classification of acapulcoites and lodranites from a chemical point of view we examined 15 bulk samples of the acapulcoite lodranite clan for their major minor and trace element concentrations using inaa techniques among the analyzed meteorites are 2 new acapulcoites dhofar dho 290 thiel mountains til 99002 as well as an additional acapulcoite that has been described previously only in very brief form graves nunataks gra 98028 the petrographic attributes of these 3 samples are addressed thoroughly we also include petrographic information on 2 acapulcoites from africa northwest africa nwa 725 and nwa 1058 in general our study strongly supports the widely accepted idea that acapulcoites and lodranites evolved through partial melting and melt migration of metal sulfide phases and plagioclase furthermore we concur with previous researchers that the original bimodal classification scheme for acapulcoites and lodranites proves to be too simple based on our data set we introduce an alternative extended scheme with respect to their elemental distribution patterns we distinguish 5 subtypes comprising primitive typical transitional and enriched acapulcoites on one hand and lodranites on the other the chemical distinction between the primitive typical and transitional acapulcoites is rather subtle and gradual it stands in contrast to the clear modifications observed for the signatures of the enriched acapulcoites and the lodranites the definition of subcategories basically reflects the concentrations of 2 key elements k and se we note however that the assignment of subgroups may not be exclusively inferred from elemental abundances but should also consider additional petrographic information

dynamics of the north brazil current retroflection region from the western tropical atlantic experiment observations hydrographic and velocity observations of the north brazil current nbc retroflection region during the 1990 1991 western tropical atlantic experiment westrax are examined with the intent of extracting dynamical information about the nbc eddy shedding a comparison is performed between the depth structure of empirical orthogonal functions and the dynamical normal modes of the nbc retroflection region on a beta plane centered on 5 n the barotropic and first two baroclinic modes account for about 75 of the vertical structure of the nbc flow thus a three layer model of the nbc region is suitable for dynamical studies of the nbc retroflection in terms of flow structure the upper layer represents the retroflection of the surface layers of the nbc to feed the north equatorial countercurrent the middle layer represents the separating subthermocline waters of the nbc which feed the north equatorial undercurrent the third layer represents a weak meandering flow that may be thought of as the deep western boundary current signature in the three layer ocean in terms of pv a well defined front separates the nbc waters from the north equatorial current in the upper layer both upper and middle layers present closed pv contours associated with the eddy in the process of pinching off from the retroflecting nbc the nbc separation region although equatorial complies reasonably well with the basic quasigeostrophic qg assumptions therefore qg methods are applied to investigate the nbc meander growth by isolating the effect of pv anomalies in each of the layers on each of the layers baroclinic growth is verified to occur during the nbc eddy shedding

recirculating components to the deep boundary current of the northern north atlantic abstract the meridional overturning system of the north atlantic is conventionally thought of as transporting warm water 4 c to high latitudes and covd water to low latitudes the northern cold water sources for this system are dense overflow from the nordic seas and less dense water from the labrador sea lsw the overflow components are carried westward by a deep northern boundary current dnbc that is shown here actually to begin southeast of the overflow regions the dnbc lies along the southern side of a system of islands and submarine ridges that divides the nordic seas from the subpolar basins the overflows act to increase the transport of the dnbc and this transport is further increased through the entrainment of warm waters once inside the labrador sea the dnbc is joined by lsw before continuing south to low latitudes as a cold deep western boundary current dwbc however published transport estimates are larger than can be explained by warm water entrainment alone thus indicating entrainment also of recirculating cold components the subject of this paper their sources are shown to be the lsw and cold abyssal waters originating from the southern hemisphere the lsw is entrained downward into the denser part of the dnbc and laterally into the upper part of the dwbc whereas the cold abyssal waters are supplied by an eastern intensified northward flow in the eastern atlantic that serves as the initial source of the dnbc and by a similar northward flow in the western atlantic the meridional overturning system described includes recirculations and poleward transport of cold water in addition tothe components described by the conventional system the cold abyssal waters in both the eastern and western basins have relatively low levels of oxygen and high concentrations of silicate reflecting their southern origin but their influence in the northwestern atlantic is somewhat obscurred by strong recirculating cyclonic gyres in the newfoundland and labrador basins this influence is detected by a deep silicate maximum extending poleward from the mid latitude western atlantic through the two gyres with eastern concentration and recirculating back diluted toward the south in the dwbc within the respective basins such a maximum also extends northward through the irminger basin into the dnbc but there is an ambiguity as to whether this is a direct extension of the signal from the south in the western basin or if it comes from the mid latitude eastern basin by way of westward flow through the charlie gibbs fracture zone it is perhaps consequence of both estimates of the volume transports of the various recirculating cold components indicate that they supply about as much water to the deep boundary currents as do the combined cold water sources in the north

sea surface structure of north brazil current rings derived from shipboard and moored acoustic doppler current profiler observations 1 in the western tropical atlantic the north brazil current retroflection periodically sheds large anticyclonic rings which then propagate northwestward between 1998 and 2000 the north brazil current rings experiment sampled a large number of these rings by shipboard and moored acoustic doppler current profiler ten of the sampled rings are analyzed in this study focusing on their sea surface dynamic properties the rings exhibit a radial structure consisting of two regimes an inner core region in near solid body rotation and an outer ring regime with an approximately exponentially decaying structure the observations show a sharp change in vorticity at the regime transition and the presence of a strong opposite vorticity shield bounding the inner solid body core we show that gaussian models commonly used to represent the surface expression of these and other rings are adequate for determining the sea surface height anomaly but tend to poorly estimate other properties such as the maximum swirl velocity therefore we propose a new two part model as a better approximation of the rings radial structure according to the cyclogeostrophic balance approximation the sea surface height distribution across the inner ring has a parabolic shape while the outer ring has an exponential structure similar to the velocity field interestingly many of the observed rings have an intensity very close to the theoretical limit for anticyclones at these latitudes which is believed to be due to inertial instability

a three dimensional ocean mesoscale simulation using data from the semaphore experiment mixed layer heat budget a primitive equation model is used to simulate the mesoscale circulation associated with a portion of the azores front investigated during the intensive observation period iop of the structure des echanges mer atmosphere proprietes des heterogeneites oceaniques recherche experimentale semaphore experiment in fall 1993 the model is a mesoscale version of the ocean general circulation model ogcm developed at the laboratoire d oceanographie dynamique et de climatologie lodyc in paris and includes open lateral boundaries a 1 5 level order turbulence closure scheme and fine mesh resolution 0 11 for latitude and 0 09 for longitude the atmospheric forcing is provided by satellite data for the solar and infrared fluxes and by analyzed or reanalyzed for the wind atmospheric data from the european centre for medium range weather forecasts ecmwf forecast model the extended data set collected during the iop of semaphore enables a detailed initialization of the model a coupling with the rest of the basin through time dependent open boundaries and a model data comparison for validation the analysis of model outputs indicates that most features are in good agreement with independent available observations the surface front evolution is subject to an intense deformation different from that of the deep front system which evolves only weakly an estimate of the upper layer heat budget is performed during the 22 days of the integration of the model each term of this budget is analyzed according to various atmospheric events that occurred during the experiment such as the passage of a strong storm this facilitates extended estimates of mixed layer or relevant surface processes beyond those which are obtainable directly from observations surface fluxes represent 54 of the heat loss in the mixed layer and 70 in the top 100 m layer while vertical transport at the mixed layer bottom accounts for 31 and three dimensional processes account for 14

dhofar 081 a new lunar highland meteorite the lunar meteorite dhofar 081 found as a single fragment of 174 g in the dhofar region of oman is a shocked feldspathic fragmental highland breccia dominated by anorthosite rich lithic and mineral clasts embedded into a fine grained mostly shock melted clastic matrix major mineral phases in the bulk rock are ca rich plagioclase an96 5 99 5 pyroxene fs21 9 46 2wo3 0 41 4 and olivine fa29 3 47 8 accessory phases include fe ni metal ilmenite and ti cr rich spinel dhofar 081 contains subordinate crystalline fragments of large anorthosites intersertal impact melt rocks microporphyritic impact melt breccias dark fine grained impact melt breccias large cataclastic feldspars and irregularly shaped brown glass clasts mafic components are rare and no genuine regolith components were found in the sections studied minerals in dhofar 081 show homogeneously distributed shock features intergranular recrystallization strong fracturing and mosaicism in feldspar as well as a high density of mostly irregular fractures in pyroxene and olivine localized impact melting caused by one or several impacts led to a strong lithification based on these effects an equilibration shock pressure of about 15 20 gpa is estimated for the strongest shock event in dhofar 081 devitrification of the glassy material in the rock indicates thermal annealing after shock melting suggesting that the 15 20 gpa shock event predated the ejection event according to the concentrations of implanted solar noble gases dhofar 081 represents a polymict clastic breccia deposit with possibly a minor regolith component a similar noble gas record of dhofar 081 and macalpine hills 88104 05 suggests the possibility of a source crater pairing of both meteorites as indicated by noble gas measurements pairing of dhofar 081 with the other lunar meteorites found in oman dhofar 025 and dhofar 026 is unlikely

thermoluminescence sensitivity and thermal history of type 3 ordinary chondrites eleven new type 3 0 3 1 chondrites and possible explanations for differences among h l and ll chondrites we review induced thermoluminescence tl data for 102 unequilibrated ordinary chondrites uocs many data just published in abstracts in order to identify particularly primitive uocs and further explore tl systematics that may have implications for the history of the chondrites and their parent body we have identified 11 uocs of petrologic types 3 0 3 1 adrar 003 elephant moraine eet 90066 eet 90161 grosvenor mountains gro 95502 lewis cliff lew 88477 meteorite hills met 96503 yamato y 790787 y 791324 y 791558 y 793565 and y 793596 these samples represent an important new resource for researchers interested in the nature of primitive solar system materials previously reported trends in which tl sensitivity increases with tl peak temperature and tl peak width which we interpret in terms of crystallization of feldspar in the ordered or disordered forms during metamorphism are confirmed by the new data importantly the present data strengthen the trend described earlier in which the mean level of metamorphism experienced by uocs increases along the series ll l and h this suggests either different burial depths for the uocs from each class or formation at similar depths in regoliths of different thickness

sharp decrease in summer monsoon strength 4000 3500 cal yr b p in the central higher himalaya of india based on pollen evidence from alpine peat age constrained pollen data and magnetic susceptibility of an alpine peat profile from the garhwal higher himalaya display a continuous record of climate and monsoon trends for the past 7800 yr about 7800 cal yr b p dominance of evergreen oak quercus semecarpifolia alder alnus and grasses in the pollen record reflect a cold wet climate with moderate monsoon precipitation from 7800 to 5000 cal yr b p vegetation was progressively dominated by conifers indicating ameliorated climate with a stronger monsoon a warm humid climate with highest monsoon intensity from 6000 4500 cal yr b p represents the mid holocene climatic optimum between 4000 and 3500 cal yr b p the abundance of conifers sharply decreased with the greatest increase in evergreen oak this trend suggests progressive cooling with a decrease in the monsoon to its minimum about 3500 cal yr b p two relatively minor cold dry events at ca 3000 and 2000 cal yr b p marked step wise strengthening of the monsoon until ca 1000 cal yr b p after a cold dry episode that culminated ca 800 cal yr b p the monsoon again strengthened and continued until today a sharp decrease in temperature and rainfall at 4000 3500 cal yr b p represents the weakest monsoon event of the holocene record this cold dry event correlates with proxy data from other localities of the indian subcontinent arabian sea and western tibet

paleoclimatic implications of pedogenic carbonates in holocene soils of the gangetic plains india abstract this study attempts to reconstruct the holocene climatic history of the indo gangetic plains based on micromorphological characteristics and stable isotope composition of calcretes in a soil chronoassociation between the ramganga and rapti rivers the calcrete from the b2 horizon of older soils qgh4 qgh5 6500 13 500 year bp consists of septaric and irregularly shaped nodules of dense micrite and diffused needles associated with the illuvial clay pedofeatures fabric of the calcretes of older soils show inclusion of soil constituents and precipitation of carbonates in between weathered layers of micas formation of this calcrete took place during the pedogenesis in an arid to semi arid climate that also influenced vegetation and c4 type biomass such as chenopodium and typha angustata spread in the area a change to warm and humid phase at 6500 year bp led to dissolution and reprecipitation of the calcretes this led to the formation of blocky crystals and needles of calcite in voids and coarsening of the fabric in the lower horizons the vegetation pattern also changed to woodland with anogeissus and tecomella spp the younger soils bp show secondary carbonate accumulation associated mainly along the voids in lower parts of the profiles these are relatively coarse textured with little or no inclusion of soil constituents this coarse grained calcrete results from capillary rise from a fluctuating water table in a sub humid climate similar to present carbon and oxygen isotope data suggest that the formation of pedogenic carbonate in old soils qgh4 and qgh5 by evapotranspiration during arid to semi arid climate in the upper horizons the carbonates are depleted in 13c as their formation was influenced by the sparse vegetation and low soil respiration rate in the lower horizons the carbonates show enrichment of 13c due its extensive dissolution reprecipitation during the humid climate the younger soils showed the enrichment of 13c in their calcretes and support their formation from fluctuating shallow groundwater table the oxygen isotope values similar to that of meteoric water of the area indicate calcrete precipitation in equilibrium with the soil water

geomorphology pedology and sedimentology of the deoha ganga ghaghara interfluve upper gangetic plains himalayan foreland basin extensional tectonic implications abstract regional mapping of soils helped to identify and map 24 soil geomorphic units on the deoha ganga ghaghara interfluve in the upper gangetic plains himalayan foreland basin on the basis of luminescence ages soil geomorphic units can be grouped into five members of a morphostratigraphic sequence with ages of 1 7 ka 1 8 3 6 ka 4 6 6 4 ka 6 8 10 ka and 10 ka except for two units with sandy parent material all the members with loamy parent materials show systematic increase in the degree of soil development from member qgms i to v major pedogenic processes are salinization alkalinization illuviation calcrete development and gleying and degradation of some micromorphological features is observed in the oldest soils regional mapping and dating of soils show that the interfluve between the deoha ganga ghaghara rivers is bounded by longitudinal faults along the bounding rivers the major longitudinal faults trend n s or nne ssw in the northern region turn n s in the central region and take easterly to see direction in the south giving the interfluve a curvilinear shape strike of a set of six transverse extensional normal faults changes from approximately e w to nee sww in the southernmost region of the interfluve downthrown sides are to the south and to the east in northern region and western region respectively due to the activity of different segments of various transverse faults during a probably dry sub humid to semi arid climatic period of 10 5 ka terminal fans were deposited on the downthrown blocks thus role of extensional tectonics in an overall compressional regime is significant also tilting of smaller blocks leading to the shifting away of large rivers seems to be an additional control on the distribution of soils and sedimentation on the interfluve

decadal variability in the outflow from the nordic seas to the deep atlantic ocean the global thermohaline circulation is the oceanic overturning mode which is manifested in the north atlantic ocean as northward flowing surface waters which sink in the nordic greenland iceland and norwegian seas and return southwards after overflowing the greenland scotland ridge as deep water this process has been termed the conveyor belt and is believed to keep europe 5 8 c warmer than it would be if the conveyor were to shut down the variability of today s conveyor belt is therefore an important component of climate regulation the nordic seas are the only northern hemisphere source of deep water and a previous study has revealed no long term variability in the outflow of deep water from the nordic seas to the atlantic ocean here i use flows derived from hydrographic data to show that this outflow has approximately doubled and then returned to previous values over the past four decades i present evidence which suggests that this variability is forced by variability in polar air temperature which in turn may be connected to the recently reported arctic warming

dynamical interpolation of mesoscale flows in the topex poseidon diamond surrounding the u s joint global ocean flux study bermuda atlantic time series study site an open boundary ocean model is configured in a domain bounded by the four topex poseidon t p ground tracks surrounding the u s joint global ocean flux study bermuda atlantic time series study bats site this implementation facilitates prescription of model boundary conditions directly from altimetric measurements both t p and ers 2 the expected error characteristics for a domain of this size with periodically updated boundary conditions are established with idealized numerical experiments using simulated data a hindcast simulation is then constructed using actual altimetric observations during the period october 1992 through september 1998 quantitative evaluation of the simulation suggests significant skill the correlation coefficient between predicted sea level anomaly and ers observations in the model interior is 0 89 that for predicted versus observed dynamic height anomaly based on hydrography at the bats site is 0 73 comparison with the idealized experiments suggests that the main source of error in the hindcast is temporal undersampling of the boundary conditions the hindcast simulation described herein provides a basis for retrospective analysis of bats observations in the context of the mesoscale eddy field

dynamics of deep thermocline jets in the polymode region abstract we present the study of a series of very energetic events which occur in the 360 days of the polymode synoptic dynamics experiment dataset the method consists of the assimilation of data by a quasi geostrophic open boundary model so that dynamically adjusted fields are produced they are used to study local dynamical vorticity and energy balances during 20 to 30 day benchmark forecast experiments the data and forecasts show the presence of strong jets at the thermocline levels 100 1400 meters which intensify via a process of baroclinic conversion of available gravitational energy into kinetic energy the formation together with strengthening of these jets is explained in terms of amplifying short scale baroclinic waves growing along the sheared borders of larger eddies associated with the local steepening or the frontal areas there is a cyclone development processes that results from the growth of these short baroclinic waves thus the area at the southern boundary of the gulf stream r