noble gases in individual l chondritic micrometeorites preserved in an ordovician limestone we have measured the he and ne concentrations and isotopic ratios of individual sediment dispersed extraterrestrial chromite grains 63 180 mu m in diameter from an ordovician limestone in southern sweden in the same sediment many fossil meteorites were found and have been attributed to the l chondrite parent body breakup event similar to 470 ma ago in this analysis of 37 individual extraterrestrial chromite grains of l chondritic major element composition at least 35 similar to 95 contain surface implanted helium and neon of fractionated solar wind composition implying that these grains are relict parts of fossil micrometeorites of asteroidal origin similar to what has been observed in recent micrometeorites collected in the polar regions significant amounts of cosmogenic ne 21 were found in several grains resulting in cosmic ray exposure cre ages of up to similar to 77 myr these ages exceed both dynamical lifetimes for asteroidal micrometeorites of this size as well as cre ages observed in chromites from fossil meteorites from the same sediment beds significant contributions from terrestrial sources like nucleogenic and cosmic ray muon induced ne 21 can be excluded in the extraterrestrial chromites since 11 terrestrial chrome spinel grains from the same sediment beds did not contain any measurable ne 21 excesses having found micrometeorites of undisputed asteroidal origin with cosmic ray exposure ages of several 10 7 years implies that high cosmic ray exposure ages alone are not a good indicator of cometary origin in opposition to what has been suggested for recent micrometeorites and idps we propose instead that these grains collected their cosmogenic ne 21 while residing in the regolith layer of their parent body c 2009 elsevier b v all rights reserved less

a wind forced ekman spiral as a good statistical fit to low frequency currents in a coastal strait ekman s classical analysis of wind driven currents is a fundamental component of the modern circulation theory of the oceans but there have been few good observations of the predicted ekman spiral where the velocity vector rotates clockwise in direction in the northern hemisphere and decays exponentially in magnitude with increasing depth an analysis of recent cyclesonde velocity measurements based on the use of empirical orthogonal functions however suggests that a classical ekman spiral was a good statistical fit to a significant portion of the low frequency current fluctuations in the strait of georgia british columbia for fluctuation periods of about 5 to 10 days

the micrometeorite flux to earth during the frasnian famennian transition reconstructed in the coumiac gssp section france abstract we have reconstructed the distribution of extraterrestrial chrome spinels in a marine limestone section across the frasnian famennian stratotype section at coumiac in southern france providing the first insights on the types of micrometeorites and meteorites that fell on earth at this time the data can test whether the small cluster of roughly coeval large impact structures is related to an asteroid breakup and shower with possible bearings also on the late devonian biodiversity crisis a total of 180 extraterrestrial spinel grains 32 m were recovered from 957 kg of rock noble gas measurements of individual grains show high solar wind content implying an origin from decomposed micrometeorites element analyses indicate a marked dominance of ordinary chondritic over achondritic grains similar to the recent flux the relation between h l and ll meteorites is 29 58 13 similar to the late silurian flux 31 63 6 but different from the distribution 45 45 10 in the recent and the cretaceous flux our data show no indication of a generally enhanced late devonian micrometeorite flux that would accompany an asteroid shower however in a single limestone bed that formed immediately before the upper kellwasser horizon that represents the main end frasnian species turnover event we found an enrichment of 10 ordinary chondritic grains 63 m per 100 kg of rock compared to the 1 3 grains per 100 kg that characterise background the anomalously abundant grains are of mixed h l and ll types and may be related to an enhanced flux of extraterrestrial dust during postulated minima in both the 405 ka and 2 4 ma earth orbit eccentricity cycles at the onset of the upper kellwasser event in the present solar system the dust accretion at earth is the highest at eccentricity minima because of the spatial distribution of dust bands of the zodiacal cloud besides this small grain anomaly the data here and in previous studies support a stable meteorite flux through the late silurian and devonian in contrast to the mid ordovician when achondritic meteorites that are rare on earth today were common followed by the influx of a flood of debris related to the breakup of the l chondrite parent body our accumulated data for six time windows through the phanerozoic indicate that the ordinary chondrites make up a major fraction in the meteorite flux since at least the mid ordovician we note that the sources in the asteroid belt of the h and l meteorites the two most common types of meteorites today and through much of the phanerozoic remain elusive

laser probe 40ar 39ar studies of the peace river shocked l6 chondrite abstract samples of matrix and melt glass from the shocked l6 chondrite peace river have been subjected to 40ar 39ar analysis using both stepped heating and localised outgassing by a laser probe stepped heating studies of three distinct samples of matrix gave indistinguishable and unusually well defined low temperature 40ar 39ar plateaux corresponding to an age of 450 30 ma in an attempt to investigate whether or not this plateau age is meaningful i e the time of a major collision event involving the parent body or is an artefact resulting from partial degassing during the fragmentation of the parent body which commenced the exposure of peace river to cosmic rays 40 ma ago we have used a laser probe to analyse ar from single 80 m diameter laser pits which release gas from a few micrograms of sample on this scale no areas have ages younger than the plateau age supporting the view that it is not an artefact measurements on the melt glass gave variable and meaningless ages in some cases greater than the age of the solar system due to retention of 40ar and loss of k during melting followed by rapid quenching this observation indicates the danger of attempts to date impact melt glass directly the observation that argon has been retained by the glass and lost by the matrix can be understood in terms of a range of plausible annealing histories

direct evidence for an ekman balance in the california current moored acoustic doppler current profiler velocity estimates and buoy wind observations made during a period of moderate southward winds were used to test the ekman balance at a site in the california current as in prior studies the wind driven flow was separated from the total flow by subtraction of a deep reference current the wind driven flow was shown to be in an ekman balance on daily timescales over a period of several months the mean observed transport was to the right of the wind and agreed to within 3 in magnitude and 4 in phase with the predicted ekman transport although the error bar was about 20 the mean velocity profile was a smooth spiral qualitatively similar although flatter than the theoretical ekman spiral prom the observed mean momentum balance profiles of the turbulent stress and eddy viscosity were inferred eddy viscosity estimates within the wind mixed layer were o 100 cm2 s 1

the ordovician chondrite from brunflo central sweden iii geochemistry of terrestrial alteration the fossil h chondrite brunflo found in a slab of ordovician limestone from central sweden is pervasively altered to an assemblage dominated by calcite and barite the meteorite is surrounded by a 15 20 cm wide zone of lighter colors than the unaffected limestone due to dissolution of hematite here we present detailed geochemical analyses of two meteorite samples 14 limestone samples at distances from 0 to 29 cm along two profiles from the meteorite and a reference sample of brunflo limestone element concentrations in brunflo and surrounding bleached limestone have been strongly disturbed during two stages of alteration early oxygenated and deep burial in the meteorite the ni rco ratio has changed from an initial value of 20 to 0 8 and redox sensitive elements like v as mo re and u are strongly enriched the sulfur isotope 34 composition of barite from brunflo d s sq 35 indicates initial loss of meteoritic sulfide followed by later accumulation of sea water sulfate as barite during deep burial under more reducing conditions reduction processes supported by an externally derived reductant possibly derived from alum shale underlying the limestone were largely responsible for the observed redox phenomena in spite of massive redistribution of many elements concentrations of pt ir and au remain at chondritic levels the geochemistry and mineralogy of alteration determined for brunflo are similar to

turbulent mixing under drifting pack ice in the weddell sea by providing cold dense water that sinks and mixes to fill the abyssal world ocean high latitude air sea ice interaction is the main conduit through which the deep ocean communicates with the rest of the climate system a key element in modeling and predicting oceanic impact on climate is understanding the processes that control the near surface exchange of heat salt and momentum in 1992 the united states russian ice station weddell 1 traversed the western weddell sea during the onset of winter providing a platform for direct measurement of turbulent heat flux and reynolds stress in the upper ocean data from a storm early in the drift indicated i well formed ekman spirals in both velocity and turbulent stress ii high correlation between mixed layer heat flux and temperature gradients iii that eddy viscosity and eddy thermal diffusivity were similar about 0 02 square meters per second and iv that the significant turbulent length scale 2 to 3 meters through most of the boundary layer was proportional to the wavelength at the peak in the weighted vertical velocity spectrum the measurements were consistent with a simple model in which the bulk eddy viscosity in the neutrally buoyant mixed layer is proportional to kinematic boundary stress divided by the coriolis parameter

geochemistry of meteorite rich marine limestone strata and fossil meteorites from the lower ordovician at kinnekulle sweden abstract thirteen fossil meteorites 1 5 9 cm have been found in lower ordovician orthoceratite limestone at kinnekulle sweden the meteorites were recovered from a 3 5 m thick quarried interval in the middle of a 30 m thick section of orthoceratite limestone the section formed in an epicontinental sea at very slow sedimentation rates 0 2 cm ka the limestones of the lower two thirds of the section are reddish brown except in the quarried interval where a conspicuous 1 m thick grey limestone bed occurs ten of the meteorites were found in a thin bed below the grey limestone one was found in the grey limestone and two in the red limestone above the meteorites are almost completely pseudomorphosed primarily by calcite and barite they were identified by their content of chromite grains and chondrule pseudomorphs the central part of one of the meteorites shows iridium 800 ppb gold 550 ppb and chromium 4400 ppm concentrations in typical chondritic abundances centimeter resolution profiles for iridium and eight other elements have been established through the quarried interval at a site at 4 km distant from the meteorite producing quarry in the reddish brown parts ir concentrations carbonate free basis lie typically in the range 300 400 ppt compared with 50 ppt ir in average shale in the grey limestone the ir concentrations are lower around 100 150 ppt iridium correlates with iron and appears to be related to sedimentation rate and or iron redox state rather than to any variations in the composition of the siliciclastic fraction with estimated sedimentation rates as above the excess ir flux to the sediment was 30 ng cm 2 ma which is a factor 2 3 higher than the present total ir flux and one order of magnitude higher than the extraterrestrial ir flux to the pacific sea floor our data cannot discriminate to what extent the ordovician ir enrichments are related to extraterrestrial matter or to precipitation of ir from seawater in recent deep sea sediments seawater derived ir enrichments are associated with mn oxides but no similar association occurs in the orthoceratite limestone the ten meteorites in the bed below the grey limestone reflect minimum meteorite accumulation rates of one meteorite per 150 m 2 and 175 ka probably the ten meteorites are related to a local strewn field rather than to background influx minimum accumulation rates calculated on three meteorite finds 20 g in the entire quarried interval give one meteorite per 570 m 2 and 1 17 ma which is one order of magnitude higher than present day large area averaged meteorite influx rates the probability is low that the small area 2 of the sea floor studied would happen to be one where an unusually high number of meteorites struck our results may reflect that meteorite and possibly also extraterrestrial ir influx rates were substantially higher than at the present during a period in the early ordovician enhanced influx rates could be related to an asteroid collision in space

extraterrestrial chromite in latest maastrichtian and paleocene pelagic limestone at gubbio italy the flux of unmelted ordinary chondrites the distribution of sediment dispersed extraterrestrial ordinary chondritic chromite ec grains 63 m has been studied across the latest maastrichtian and paleocene in the bottaccione gorge section at gubbio italy this section is ideal for determining the accumulation rate of ec because of its condensed nature and well constrained sedimentation rates in a total of 210 kg of limestone representing eight samples of 14 28 kg distributed across 24 m of the bottaccione section only 6 ec grains were found an average of 0 03 ec grains kg 1 in addition one probable pallasitic chromite grain was found no ec grains could be found in two samples at the cretaceous tertiary k t boundary which is consistent with the k t boundary impactor being a carbonaceous chondrite or comet low in chromite the average influx of ec to earth is calculated to 0 26 grain m 2 kyr 1 this corresponds to a total flux of 200 tons of extraterrestrial matter per year compared to 30 000 tons per year as estimated from os isotopes in deep sea sediments the difference is explained by the ec grains representing only unmelted ordinary chondritic matter predominantly in the size range from 0 1 mm to a few centimeters in diameter sedimentary ec grains can thus give important information on the extent to which micrometeorites and small meteorites survive the passage through the atmosphere the average of 0 03 ec grain kg 1 in the gubbio limestone contrasts with the up to 3 ec grains kg 1 in mid ordovician limestone that formed after the disruption of the l chondrite parent body in the asteroid belt at 470 ma the two types of limestone were deposited at about the same rate and the difference in ec abundance gives support for an increase by two orders of magnitude in the flux of chondritic matter directly after the asteroid breakup

the subinertial momentum balance of the north atlantic subtropical convergence zone abstract the upper ocean to forcing by pressure gradients and wind stress is examined using observations from the frontal air sea interaction experiment a moored way acquired time series of winds upper ocean currents temperatures and salinities between winter and late spring in a region of the sargasso sea known for the presence of upper ocean fronts these fronts have timescales of 10 days and dominate current variance while winds varied with the 4 day timescale of passing weather systems employing a frequency domain regression model it is found that gestrophy accounts for most of the low frequency 100 h current variance in the seasonal pycnoclino but wind forced shear becomes important nearer the surface in particular currents oriented in the typical ne sw alonfront direction display geostrophic balance while those perpendicular to them do not wind forcing can produce geostrophic currents indirectly through ekman pumping and knowledge of the geostrophic shear is required to distinguish be

wind driven ocean currents and ekman transport oceanographic engineering of the woods hole oceanographic institution and the massachusetts institute of technology woods hole ma 02543 oceanographers have long sought to verify the theoretical ekman transport relation which predicts that a steady wind stress acting together with the coriolis force will produce a transport of water to the right of the wind in situ measurements of wind and ocean currents provide a detailed view of this phenomenon by separating the wind driven current from the measured total current and by averaging over a long record it is found that the observed transport is consistent with theoretical ekman transport to within about 10 percent in this case the wind driven transport is strongly surface trapped with 95 percent occurring in the upper 25 meters as a result of fair summer weather

the mid ordovician osmussaar breccia in estonia linked to the disruption of the l chondrite parent body in the asteroid belt the middle ordovician 466 ma osmussaar breccia situated along the northwestern coast of estonia is rich in angular chromite grains of extraterrestrial origin 13 grains kg 1 and shocked quartz the angularity of the chromite grains implies that they have not been transported or reworked to any large extent connoting that the brecciation is the result of a contemporary impactor either as a direct consequence of the impact or as a result of an earthquake triggered by the impact and thus is not as previously suggested redeposited material from the nearby similar to 70 m y older neugrund impact structure the chemical composition of the chromite indicates that the impactor was an ordinary chondrite of l type which concurs well with the hypothesis that the influx of large bodies to earth increased during this period due to the breakup of the l chondrite parent body this in turn gives support to the recent suggestion that abundant coeval mega breccias worldwide are impact triggered the presence of extraterrestrial chromite also strengthens the theory that physical pieces of a large celestial body can survive upon impact with earth less

asteroid breakup linked to the great ordovician biodiversification event the great ordovician biodiversification event coincides 470 million years ago with the break up of a large asteroid and the resultant frequent bombardment of earth with asteroid fragments

a global rain of micrometeorites following breakup of the l chondrite parent body evidence from solar wind implanted ne in fossil extraterrestrial chromite grains from china previous studies of limestone beds of mid ordovician age from both sweden and china show that the earth saw an at least two orders of magnitude increase in the influx of extraterrestrial material approximately 470 ma following the disruption of an l chondrite parent body in the asteroid belt recovered extraterrestrial material consists of fossil meteorites and sediment dispersed extraterrestrial chromite sec grains both with l chondritic origin ne isotope analysis of sec grains from one of the swedish limestone sections revealed that the vast majority of the grains were delivered to earth as micrometeorites in this study we extend the previous work both in time and geographically by measuring concentrations and isotopic ratios of ne in individual sec grains 60120 mu m in diameter from three different beds from a contemporary middle ordovician limestone section in china all of the chinese sec grains 44 in total contain surface implanted ne of fractionated solar wind composition implying that these grains were as in the case of the swedish sec grains delivered to earth as micrometeorites this gives further compelling evidence that the two to three orders of magnitude increase in the influx of micrometeoritic material following the breakup of the l chondrite parent body was indeed a global event the rain of micrometeorites prevailed for at least 2 myr the estimated time of the deposition of the topmost chinese bed after the breakup event less

ekman drift in homogeneous water measurements made with satellite tracked buoys drogued in different layers between the sea surface and 30 m depth under homogeneous winter conditions in the north sea allow analysis of the ekman currents under a large variety of wind conditions the experiment lasted from november 20 1991 until february 29 1992 the first 4 weeks of this period during which the buoys stayed close together are used to determine the ekman stresses the total current field is a superposition of barotropic currents due to sea level variations and ekman currents the classical ekman theory is not able to describe properly the observed deflection of the currents to the right of the wind direction and their decay with depth this deflection is 10 near the sea surface and increases to approximately 50 in 25 m depth the relation between wind stress and the stress field in the interior of the water is given by a tensor which describes the rotation and the variation of the stress with increasing depth the concept of eddy viscosity is applicable if a viscosity tensor is used to relate stress and vertical shear the viscosity tensor is a function of the vertical coordinate only and is independent from the wind stress it shows maximum values in 15 to 20 m depth and may be due to langmuir circulation cells further studies are needed to determine the physics of this tensor its magnitude in the interior of the mixed layer exceeds 1000 cgs units consequently ekman currents are weak and may not be the dominant currents within the mixed layer

a single asteroidal source for extraterrestrial ordovician chromite grains from sweden and china high precision oxygen three isotope sims analysis we examined oxygen three isotope ratios of 48 extraterrestrial chromite ec grains extracted from mid ordovician sediments from two different locations in sweden and one location in south central china the ages of the sediments similar to 470 ma coincide with the breakup event of the l chondrite parent asteroid elemental compositions of the chromite grains are generally consistent with their origin from l or ll chondrite parent bodies the average delta o 17 parts per thousand deviation from the terrestrial mass fractionation line measured in situ from 15 mu m spots by secondary ion mass spectrometry sims of ec grains extracted from fossil meteorites from thorsberg and brunflo are 1 17 0 09 parts per thousand 2 sigma and 1 25 0 16 parts per thousand respectively and those of fossil micrometeorites from thorsberg and puxi river are 1 10 0 09 parts per thousand and 1 11 0 12 parts per thousand respectively within uncertainty these values are all the same and consistent with the l chondrite group average delta o 17 1 07 0 18 parts per thousand but also with the ll chondrite group average delta o 17 1 26 0 24 parts per thousand clayton et al 1991 we conclude that the studied ec grains from correlated sediments from sweden and china are related and most likely originated in the same event the l chondrite parent body breakup we also analyzed chromites of modern h l and ll chondrites and show that their delta o 17 values coincide with averages of delta o 17 of bulk analyses of h l and ll chondrites this study demonstrates that in situ oxygen isotope data measured by sims are accurate and precise if carefully standardized and can be used to classify individual extraterrestrial chromite grains found in sediments c 2009 elsevier ltd all rights reserved less

direct observations of the ekman balance at 10 n in the pacific abstract the wind driven transport and velocity structure are estimated from direct current measurements and geostrophic shears along a transpacific section at 10 n the total velocity field is dominated by the north equatorial current and its eddies while the shear features near inertial oscillations and a wind driven current spiral the section averaged cross track ageostrophic shear can be approximated as a slab layer 30 40 m thick with a velocity of 0 05 m s 1 overlying a sheared layer in which the velocity goes to zero below 80 m the resulting zonally integrated ageostrophic mass transport is 62 10 109 kg s 1 northward similar to the estimate of 52 10 109 kg s 1 predicted by the ekman balance using winds measured from the ship climatological winds yield similar transport the zonally averaged velocity relative to the top of the thermocline forms a clockwise spiral decaying with depth as has been found at higher latitudes this mean wind driven spiral results from the diurnal cycling o

observations of the velocity response to wind forcing in the upper ocean the response of the horizontal velocity field to forcing by the local wind was observed in the upper 150 m of the ocean by profiling with vector measuring current meters from the research platform flip as it drifted off the coast of california in january 1977 in the mixed layer approximately 50 m deep motion at frequencies lower than 0 1 cph was coherent with the wind stress rotary cross spectral analysis showed that the shear in the surface layer was related to the local wind stress and that the structure of the response at low frequencies was similar to but did not agree completely with the predictions of simple linear eddy viscosity models

the ordovician chondrite from brunflo central sweden i general description and primary minerals abstract the brunflo chondrite was found in the rodbrottet quarry near brunflo central sweden lat 63 5 n long 14 53 e the meteorite ca 11 cm 9 5 cm occurs in a polished slab of middle ordovician limestone which based on its content of conodonts belongs to the aserian segerstad limestone the meteorite fell in the iapetus ocean close to its eastern coast line the original minerals except chromite are replaced by secondary minerals mainly calcite remarkably even minute details of textures and structures are preserved in some areas the various types of chondrules and their frequencies could therefore be studied they are similar to present falls of ordinary chondrites of petrologic types 3 and 4 chromite occurs as up to ca 0 1 mm large grains microprobe analyses of 59 grains show that except for zn the composition is fairly constant and similar to h4 h5 chromites the zn content varies from 0 2 to 6 8 wt zno mean ca 0 6 wt two analyses show that also chrome spinel is present tentatively brunflo is classified as h4 h5

ordinary chondritic micrometeorites from the indian ocean extraterrestrial particulate materials on the earth can originate in the form of collisional debris from the asteroid belt cometary material or as meteoroid ablation spherules signatures that link them to their parent bodies become obliterated if the frictional heating is severe during atmospheric entry we investigated 481 micrometeorites isolated from 300 kg of deepsea sediment out of which 15 spherules appear to have retained signatures of their provenance based on their textures bulk chemical compositions and relict grain compositions seven out of these 15 spherules contain chromite grains whose compositions help in distinguishing sub groups within the ordinary chondrite sources there are seven other spherules which comprise either entirely of dusty olivines or contain dusty olivines as relict grains two of these spherules appear to be chondrules from an unequilibrated ordinary chondrite in addition a pop porphyritic olivine pyroxene chondrule like spherule is also recovered the bulk chemical composition of all the spherules in combination with trace elements the chromite composition and presence of dusty olivines suggest an ordinary chondritic source these micrometeorites have undergone minimal frictional heating during their passage through the atmosphere and have retained these features these micrometeorites therefore also imply there is a significant contribution from ordinary chondritic sources to the micrometeorite flux on the earth

extraterrestrial chromite in the resurge deposits of the early late ordovician lockne crater central sweden the distribution of extraterrestrial chromite grains 63 mu m has been studied in the resurge deposit of the early late ordovician 458 ma lockne impact structure in central sweden a 1 kg sample of resurge sediment from the rim of the crater is extremely rich in extraterrestrial chromite in total the sample contains 125 chromium spinel grains kg 1 most grains being chromite due to post depositional alterations the origin of several of the grains is dubious although it is clear that the major part of the chromites is of extraterrestrial origin 75 grains kg 1 most likely derived from the impactor the alterations are primarily due to the hydrothermal system induced by the impactor with zinc enrichment in the chromites as the most common characteristic the element chemistry of the least altered chromite grains indicates that the impactor was an ordinary l chondrite this concurs with a suggested increase in the flux of l chondritic asteroids to earth following the disruption of the l chondrite parent body at ca 470 ma more than 170 impact craters are known from around the earth but only few of the impactors have been identified mainly due to the low survival rate of projectile material further studies of impact craters will reveal if survival of extraterrestrial chromite is unique for the lockne structure c 2006 elsevier b v all rights reserved less

wind driven motions in the northeast pacific as measured by lagrangian drifters abstract analysis is presented of the time dependent motion of 47 surface drifters in the northeast pacific during fall 1987 and 16 drifters in fall and winter 1989 90 the drifters were designed at 15 m depth and were designed to have wind produced slips less than 2 cm s 1 for wind speeds up to 20 m s 1 the coherence of velocity and local wind is presented for motions with periods between 1 day and 40 days for periods between 5 and 20 days drogue motion at 15 m depth is found to be highly coherent with local wind with an average phase of 70 to the right of the rotating wind vector these results differ from analyses of fgge type drifters as reported by mcnally et al and niiler in the same area a model of wind produced slip as a function of drifter design is used to provide a possible explanation of the differences a linear regression which accounts for 20 40 of the current variance gives water motion al 0 5 of wind speed and 68 to the right of the wind vector assuming an ekman type balance

turbulence intensity measurements in a wind driven mixed layer neutrally buoyant high drag floats were used to measure vertical velocity in the upper ocean mixed layer during a period of rapid mixed layer deepening resulting from a storm salinity and temperature profiles air sea fluxes and surface wave spectra were also measured the location georgia strait british columbia is coastal with strong horizontal variability and may not be representative of the open ocean the floats moved freely within the deepening mixed layer the envelope of their motion corresponded closely to the extent of the mixed layer the maximum vertical velocity was 0 12 m s21 the rms vertical velocity was about 0 02 m s21 2 the mean square vertical velocity excluding surface waves was 1 5 3 0 clearly higher than the upper bound 2 u of found in solid wall turbulent boundary layers the authors speculate that these anomalously high vertical 2 u velocities were due to langmuir circulations generated by surface waves these cannot occur in solid wall boundary layers

the origin of the brunflo fossil meteorite and extraterrestrial chromite in mid ordovician limestone from the garde quarry jamtland central sweden the brunflo fossil meteorite was found in the 1950s in mid ordovician marine limestone in the garde quarry in jamtland it originates from strata that are about 5 million years younger than similar limestone that more recently has yielded 50 fossil meteorites in the thorsberg quarry at kinnekulle 600 km to the south based primarily on the low tio2 content about 1 8 wt of its relict chromite the brunflo meteorite had been tentatively classified as an h chondrite the meteorite hence appears to be an anomaly in relation to the kinnekulle meteorites in which chromite composition chondrule mean diameter and oxygen isotopic composition all indicate an l chondritic origin reflecting an enhanced flux of meteorites to earth following the disruption of the l chondrite parent body 470 ma new chondrule size measurements for the brunflo meteorite indicate that it too is an l chondrite related to the same parent body breakup chromite maximum diameters and well defined chondrule structures further show that brunflo belongs to the l4 or l5 type chromites in recently fallen l4 chondrites commonly have low tio2 contents similar to the brunflo chromites adding support for brunflo being an l4 chondrite the limestone in the circle quarry is relatively rich about 0 45 grain kg 1 in sediment dispersed extraterrestrial chromite grains 63 mu m with chemical composition similar to those in l chondrites and the limestone 1 3 grains kg 1 at kinnekulle suggesting that the enhanced flux of l chondrites prevailed although somewhat diminished at the time when the brunflo meteorite fell less

mineralogy of meteorite groups approximately 275 mineral species have been identified in meteorites reflecting diverse redox environments and in some cases unusual nebular formation conditions anhydrous ordinary carbonaceous and r chondrites contain major olivine pyroxene and plagioclase major opaque phases include metallic fe ni troilite and chromite primitive achondrites are mineralogically similar the highly reduced enstatite chondrites and achondrites contain major enstatite plagioclase free silica and kamacite as well as nitrides a silicide and ca mg mn na cr k and ti rich sulfides aqueously altered carbonaceous chondrites contain major amounts of hydrous phyllosilicates complex organic compounds magnetite various sulfates and sulfides and carbonates in addition to kamacite and taenite iron meteorites contain carbides elemental c nitrides phosphates phosphides chromite and sulfides silicate inclusions in iab iiicd and iie iron meteorites consist of mafic silicates plagioclase and various sulfides oxides and phosphates eucrites howardites and diogenites have basaltic to orthopyroxenitic compositions and consist of major pyroxene and calcic plagioclase and several accessory oxides ureilites are made up mainly of calcic chromian olivine and low ca clinopyroxene embedded in a carbonaceous matrix accessory phases include the c polymorphs graphite diamond lonsdaleite and chaoite as well as metallic fe ni troilite and halides angrites are achondrites rich in fassaitic pyroxene i e al ti diopside minor olivine with included magnesian kirschsteinite is also present martian meteorites comprise basalts lherzolites a dunite and an orthopyroxenite major phases include various pyroxenes and olivine minor to accessory phases include various sulfides magnetite chromite and ca phosphates lunar meteorites comprise mare basalts with major augite and calcic plagioclase and anorthositic breccias with major calcic plagioclase several meteoritic phases were formed by shock metamorphism martensite 2 fe ni has a distorted body centered cubic structure and formed by a shear transformation from taenite during shock reheating and rapid cooling the c polymorphs diamond lonsdaleite and chaoite formed by shock from graphite suessite formed in the north haig ureilite by reduction of fe and si possibly from olivine via reaction with carbonaceous matrix material ringwoodite the spinel form of mg fe 2sio4 and majorite a polymorph of mg fe sio3 with the garnet structure formed inside shock veins in highly shocked ordinary chondrites secondary minerals in meteorite finds that formed during terrestrial weathering include oxides and hydroxides formed directly from metallic fe ni by oxidation phosphates formed by the alteration of schreibersite and sulfates formed by alteration of troilite

from the mid ordovician into the late silurian changes in the micrometeorite flux after the l chondrite parent breakup we present the first reconstruction of the micrometeorite flux to earth in the silurian period we searched 321 kg of condensed marine limestone from the late silurian cellon section southern austria for refractory chrome spinel grains from micrometeorites that fell on the ancient sea floor a total of 155 extraterrestrial spinel grains 10 grains 63 m and 145 in the 32 63 m fraction were recovered for comparison we searched 102 kg of similar limestone from the mid ordovician komstad formation in southern sweden this limestone formed within 1 ma after the breakup of the l chondrite parent body lcpb in the asteroid belt in the sample we found 444 extraterrestrial spinel grains in the 63 m fraction and estimate a content of at least 7000 such grains in the 32 63 m fraction our results show that in the late silurian 40 ma after the lcpb the flux of ordinary equilibrated chondrites has decreased by two orders of magnitude almost down to background levels among the ordinary chondrites the dominance of l chondritic micrometeorites has waned off significantly from 99 in the post lcpb mid ordovician to 60 in the late silurian with 30 h and 10 ll chondritic grains in the late silurian primitive achondrite abundances are similar to today s value contrasting to the much higher abundances observed in pre lcpb mid ordovician sediments

the three dimensional steady circulation in a homogenous ocean induced by a stationary hurricane based on the classical ekman layer theory a simple analytical solution of the steady flow induced by a stationary hurricane in a homogenous ocean is discussed the model consists of flow converging in an inward spiral in the deeper layer and diverging in the upper layer the simple analytical model indicates that both the upwelling flux and the horizontal transport increase linearly with increasing radius of maximum winds furthermore they both have a parabolic relationship with the maximum wind speed the coriolis parameter also affects the upwelling flux the response to a hurricane is stronger at low latitudes than that at middle latitudes numerical solutions based on a regional version of an ocean general circulation model are similar to the primary results obtained through the analytical solution thus the simplifications made in formulating the analytical solution are reasonable although the analytical solution in this paper is sought for a rather idealized ocean it can help to make results from the more complicated numerical model understandable these conceptual models provide a theoretical limit structure of the oceanic response to a moving hurricane over a stratified ocean

the fusion crusts of stony meteorites implications for the atmospheric reprocessing of extraterrestrial materials fusion crusts develop on all meteorites during their passage through the atmosphere but have been little studied we have characterized the textures and compositions of the fusion crusts of 73 stony meteorites to identify the nature of meteorite ablation spheres mas and constrain the processes operating during the entry heating most chondrite fusion crusts are porphyritic and are dominated by olivine glass and accessory magnetite whereas those of the achondrites are mainly glassy chondrite fusion crusts contain sulphide droplets with high ni contents 55 wt the partially melted substrate of ordinary chondrites underlying the outer melted crusts are dominated by silicate glass and composite metal sulphide and cr bearing fe oxide droplets that form as coexisting immiscible liquids enstatite chondrite substrates contain cr and mn bearing sulphides the substrates of the carbonaceous chondrites comprise a sulphide enriched layer of matrix the compositions of melted crusts are similar to those of the bulk meteorite however differences from whole rock suggest that three main processes control their chemical evolution 1 the loss and reaction of immiscible fe rich liquids 2 mixing between substrate partial melts and bulk melts of the melted crust and 3 the loss of volatile components by evaporation and degassing data from fusion crusts suggest that mas produced at low altitude have compositions within the range of those of silicate dominated cosmic spherules that are formed by the melting dust particles meteorite ablation spheres produced at high altitude probably have compositions very different from bulk meteorite and will resemble cosmic spherules derived from coarse grained precursors

a search for h chondritic chromite grains in sediments that formed immediately after the breakup of the l chondrite parent body 470 ma ago abstract a large abundance of l chondritic material mainly in the form of fossil meteorites and chromite grains from micrometeorites has been found in mid ordovician 470 ma old sediments globally the material has been determined to be ejecta from the l chondrite parent body breakup event a major collision in the asteroid belt 470 ma ago in this study we search the same sediments for h chondritic chromite grains in order to improve our understanding of the extraterrestrial flux to earth after the asteroid breakup event we have used sims in conjunction with quantitative sem eds to determine the three oxygen isotopic and elemental compositions respectively of a total of 120 randomly selected sediment dispersed extraterrestrial chromite grains mainly representing micrometeorites from 470 ma old post breakup limestone from the thorsberg quarry in sweden and the lynna river site in russia we show that 99 or more of the grains are l chondritic whereas the h chondritic fraction is 1 or less the l h chondrite ratio after the breakup thus was 99 compared to 1 1 in today s meteoritic flux this represents independent evidence in agreement with previous estimates based on sediment dispersed extraterrestrial chromite grain abundances and sedimentation rates of a two orders of magnitude higher post breakup flux of l chondritic material in the micrometeorite fraction finally we confirm the usefulness of three oxygen isotopic sims analyses of individual extraterrestrial chromite grains for classification of equilibrated ordinary chondrites the h and l chondritic chromites differ both in their three oxygen isotopic and elemental compositions but there is some overlap between the groups in chromite tio 2 is the oxide most resistant to diagenesis and the combined application of tio 2 and oxygen three isotope analysis can resolve uncertainties arising from the compositional overlaps

large spinel grains in a cm chondrite acfer 331 implications for reconstructions of ancient meteorite fluxes by dissolving 30400kg of marine limestone in hcl and hf acid our group has previously recovered common relict chromite grains approximately 63250m from ordinary chondritic micrometeorites that fell on ancient sea floors up to 500myr old here we evaluate if cm group carbonaceous chondritic material which makes up an important fraction of the micrometeorite flux today contains analogous grains that can be searched for in acid residues we dissolved 8g of cm2 meteorite acfer 331 in hf which yielded a characteristic assemblage of both transparent mg al and opaque cr spinels 28m we find on average 4 6 and 130 mg al spinel grains per gram in the 63250 and 2863m size fractions respectively these grains are mostly pink or colorless and often characterized by heterogeneous cr content black opaque cr spinel grains are absent from the 63m fraction but in the 2863m fraction we find approximately 65 such grains per gram meteorite the individual grains have a characteristic composition with heterogeneous major element compositions e g 44 461 7wt cr2o3 but narrow ranges for maximum tio2 0 61 6wt and v2o3 0 51 0wt concentrations the content of spinel grains in the 2863m fraction of cm meteorites appears comparable at the order of magnitude level with the content of 63m sized chromite grains in fossil l chondrites from ordovician limestone our approach of recovering meteoritic spinel from sediment may thus be extended to include cm meteorites but the smaller size fraction of the acid residues should be searched less

sediment dispersed extraterrestrial chromite traces a major asteroid disruption event abundant extraterrestrial chromite grains from decomposed meteorites occur in middle ordovician 480 million years ago marine limestone over an area of 250 000 square kilometers in southern sweden the chromite anomaly gives support for an increase of two orders of magnitude in the influx of meteorites to earth during the mid ordovician as previously indicated by fossil meteorites extraterrestrial chromite grains in mid ordovician limestone can be used to constrain in detail the temporal variations in flux of extraterrestrial matter after one of the largest asteroid disruption events in the asteroid belt in late solar system history

extraterrestrial chromite distribution across the mid ordovician puxi river section central china evidence for a global major spike in flux of l chondritic matter previous studies of mid ordovician limestone in sweden have shown that over a stratigraphic interval representing a few million years there is a two orders of magnitude enrichment in fossil l chondritic meteorites empty set 1 21 cm and sediment dispersed extraterrestrial chromite ec grains 63 mu m this has been interpreted as a dramatic increase in the flux of l chondritic matter to earth following the breakup of the l chondrite parent body which based on ar ar gas retention ages 470 6 ma of recently fallen meteorites occurred at about this time here we show that the general trend in the distribution of sediment dispersed ec grains can be reproduced in the puxi river section in central china a total of 288 kg of limestone was searched for chrome spinels in samples spanning the lower 8 m of the section representing the paroistodus originalis and lenodus antivariabilis conodont zones a total of 110 kg of limestone yielded only one ec grain similarly to the swedish sections ec grains begin to be common in the overlying l variabilis zone and remain common throughout the upper 9 m of the section representing the l variabilis yangtzeplacognathus crassus and l pseudoplanus zones in this part of the section 178 kg of limestone yielded 290 ec grains with an average chemical composition very similar to chromite from recent l chondrites in most of the beds over this interval one finds 1 4 ec grains per kilogram rock a clear two orders of magnitude enrichment relative to the lower part of the section small bed by bed variations in the ec content over the upper interval most likely reflect small variations in sedimentation rates the puxi river section contains only very rare terrestrial chrome spinel grains which can be distinguished already by their rounded abraded appearance compared to the angular pristine extraterrestrial spinels in the mid ordovician based on paleoplate reconstructions the puxi river site was positioned at mid latitudes on the southern hemisphere a couple of thousand kilometers east of the swedish sites the prominent enrichment of ec grains over the same stratigraphic interval in china and sweden is supporting evidence for a dramatic increase in the flux of l chondritic matter to earth shortly after the disruption of the l chondrite parent body in the asteroid belt c 2010 elsevier inc all rights reserved less

a simple analytical model of the diurnal ekman layer abstractthe effects of time varying turbulent viscosity on horizontal currents in the ocean surface boundary layer are considered using a simple theoretical model that can be solved analytically this model reproduces major aspects of the near surface ocean diurnal cycle in velocity and shear while retaining direct parallels to the steady state ekman solution the parameter dependence of the solution is explored and quantitative measures of the low frequency rectification of velocity and shear are derived results demonstrate that time variability in eddy viscosity leads to significant changes to the time averaged velocity and shear fields with important implications for the interpretation of observations and modeling of the near surface ocean these findings mirror those of more complete numerical modeling studies suggesting that some of the rectification mechanisms active in those studies may be independent of the details of the boundary layer turbulence

noble gases in fossil micrometeorites and meteorites from 470 myr old sediments from southern sweden and new evidence for the l chondrite parent body breakup event we present noble gas analyses of sediment dispersed extraterrestrial chromite grains recovered from similar to 470 myr old sediments from two quarries hallekis and thorsberg and of relict chromites in a coeval fossil meteorite from the gullhogen quarry all located ill southern sweden both the sediment dispersed grains and the meteorite gullhogen 001 were generated in the l chondrite parent body breakup about 470 myr ago which was also the event responsible for the abundant fossil meteorites previously found in the thorsberg quarry trapped solar noble gases in the sediment dispersed chromite grains have partly been retained during similar to 470 myr of terrestrial residence and despite harsh chemical treatment in the laboratory this shows that chromite is highly retentive for solar noble gases the solar noble gases imply that a sizeable fraction of the sediment dispersed chromite grains are micrometeorites or fragments thereof rather than remnants of larger meteorites the grains in the oldest sediment beds were rapidly delivered to earth likely by direct injection into all orbital resonance in the inner asteroid belt whereas grains in younger sediments arrived by orbital decay due to poynting robertson p r drag the fossil meteorite gullhogen 001 has a low cosmic ray exposure age of similar to 0 9 myr based on new he and ne production rates in chromite determined experimentally this age is comparable to the ages of the fossil meteorites from thorsberg providing additional evidence for very rapid transfer times of material after the l chondrite parent body breakup

late eocene 3he and ir anomalies associated with ordinary chondritic spinels during the late eocene there was an enigmatic enhancement in the flux of extraterrestrial material to earth evidence comes from sedimentary 3he records indicating an increased flux of interplanetary dust during ca 2 myr as well as two very large impact structures popigai 100 km diameter and chesapeake bay 40 85 km that formed within 10 20 kyr at the peak of the 3he delivery the massignano section in italy has one of the best sedimentary records of these events including a well defined 3he record an ir rich ejecta bed related to the popigai impact event and two smaller ir anomalies recently we showed that the popigai ejecta is associated with a significant enrichment of chromite grains 63 m with an h chondritic elemental composition 17 grains in 100 kg of rock most likely these grains are unmelted fragments from the impactor slightly higher up ca 20 cm in the section where a small ir anomaly possibly related to the chesapeake bay impact has been measured we found a weak enrichment in l chondritic grains 8 grains in 208 kg of rock here we report an extended data set increasing the total amount of sediment dissolved in acid and searched for extraterrestrial chromite grains from 658 to 1168 kg in altogether 760 kg of background sediment from 17 levels over 14 m of strata outside the interval corresponding to the popigai and chesapeake bay impacts we only found 2 extraterrestrial chromite grains both grains have l chondritic compositions and were found in a 100 kg sample from the ca 10 25 m level in the section where the second of the smaller ir anomalies has been reported a correlation appears to exist between ir 3he and chromite from ordinary chondrites we also report oxygen three isotope measurements of the extraterrestrial chromite grains associated with the popigai ejecta and confirm an h chondritic composition the new results strengthen our scenario that the upper eocene 3he and ir enrichments originate from the asteroid belt rather than the oort cloud as originally proposed when the 3he anomaly was discovered the generally low background concentrations of extraterrestrial chromite through the section speak against any major single asteroid breakup event such as in the mid ordovician after the break up of the l chondrite parent body instead the data reconcile with a small possibly a factor of 2 3 increase in the flux of extraterrestrial material to earth but of both h and l chondritic composition we also report the composition of all the 2310 terrestrial chrome spinel grains recovered and show that their chemical composition indicates a dominantly regional ophiolitic source four anomalous chrome spinel grains with high ti and v concentrations were found in the popigai ejecta these grains originate from siberian traps basalts in the popigai crater at the time of impact less

a rain of ordinary chondritic meteorites in the early ordovician forty fossil meteorites with a total original mass of v7 7 kg have been recovered in the first systematic search for fossil meteorites pursued in an active quarry in lower ordovician 480 ma marine limestone in southern sweden the meteorites represent at least 12 different falls over a seafloor area of v6000 m 2 during 91 75 myr making the quarry one of the most meteorite dense areas known in the world geochemical analyses of relict chromite grains indicate that all or most of the meteorites are ordinary chondrites and probably l chondrites mechanisms for meteorite delivery from the asteroid belt to earth were the same 480 ma as today however the flux was one to two orders of magnitude higher most likely reflecting the disruption of the l chondrite parent body at about that time this is a major event in late solar system history which may also have led to an enhanced flux of asteroids to earth during v30 myr fl 2001 elsevier science b v all rights reserved

petrographic classification of middle ordovician fossil meteorites from sweden the maximum diameter of chromite fecr2o4 grains within l chondrites reflects the petrographic type of the sample on the basis of our measurements of nine recent l chondrites l3 chromite d mac 34 50 mu m l4 87 150 mu m l5 76 158 mu m and l6 253 638 mu m this variation reflects the crystallization of the chromite grains during parent body thermal metamorphism we use this calibration to classify six fossil meteorites from the middle ordovician in sweden as type 3 or 4 to 6 the high flux of l chondrites at 470 ma contained a range of petrographic types and may have had a higher proportion of lower petrographic type meteorites than are found in recent l chondrite falls the fossil meteorites have in places preserved recognizable chondrule textures including porphyritic olivine barred olivine and radiating pyroxene a large relict clast and fusion crust have also been tentatively identified in one fossil meteorite apart from chromite all of the original meteorite minerals have been replaced by carbonate and sheet silicate and sulfate during diagenesis within the limestone host the preservation of chondrule definition has allowed us to measure the mean diameters of relict chondrules the range 0 4 0 6 mm is consistent with measurements made in the same way on recent l chondrites less

stratified ekman layers under fair weather conditions the time averaged wind driven current forms a spiral in which the current vector decays and turns clockwise with increasing depth these spirals resemble classical ekman spirals they differ in that their rotation depth scale exceeds the e folding depth of the speed by a factor of 2 to 4 and they are compressed in the downwind direction a related property is that the time averaged stress is evidently not parallel to the time averaged vertical shear we develop the hypothesis that the flat spiral structure may be a consequence of the temporal variability of stratification within the upper 10 20 m of the water column this variability is associated primarily with the diurnal cycle and can be treated by a time dependent diffusion model or a mixed layer model the latter can be simplified to yield a closed solution that gives an explicit account of stratified spirals and reasonable hindcasts of midlatitude cases at middle and higher latitudes the wind driven transport is found to be trapped mainly within the upper part of the ekman layer the diurnal warm layer at tropical latitudes the effects of diurnal cycling are in some ways less important and ekman layer currents are likely to be significant to much greater depths in that event the lower part of the ekman layer is likely to be affected by stratification variability that may be nonlocal

on the slippage of deep drogued drifters deep drogued drifters are in use to measure the near surface geostrophic currents an attempt is made to study the slippage of these drifters due to wind and ekman currents the results are based on a data set from the unstratified north sea obtained in winter 1991 1992 where the currents were decomposed into ekman currents and barotropic currents the influence of these ekman currents on the drift performance of drifters drogued below the mixed layer in the barotropic current is determined by using quadratic drag laws in 90 of all cases 1540 data points the combined effect of wind drag and ekman currents on buoy and 100 m tether produces a slippage of less than 2 cm s drifters drogued within the mixed layer show less slippage due to the reduced drag on the tether but they are primarily designed to measure the actual near surface currents which are strongly dependent on the wind conditions it is concluded that deep drogued drifters are a reliable device to study weakly baroclinic geostrophic currents

detecting and characterizing ekman currents in the southern ocean abstractthis study presents a unique array of velocity profiles from electromagnetic autonomous profiling explorer em apex profiling floats in the antarctic circumpolar current acc north of kerguelen the authors use these profiles to examine the nature of ekman spirals formed by the action of the wind on the ocean s surface in light of ekman s classical linear theory and more recent enhancements vertical decay scales of the ekman spirals were estimated independently from current amplitude and rotation assuming a vertically uniform geostrophic current decay scales from the ekman current heading were twice as large as those from the current speed decay indicating a compressed spiral consistent with prior observations and violating the classical theory however if geostrophic shear is accurately removed the observed ekman spiral is as predicted by classical theory and decay scales estimated from amplitude decay and rotation converge toward a common value no statistically robust relationship is

relict silicate inclusions in extraterrestrial chromite and their use in the classification of fossil chondritic material abstract chromite is the only common meteoritic mineral surviving long term exposure on earth however the present study of relict chromite from numerous ordovician 470 ma fossil meteorites and micrometeorites from sweden reveals that when encapsulated in chromite other minerals can survive for hundreds of millions of years maintaining their primary composition the most common minerals identified in the form of small analyses of recent meteorites holding both inclusions in chromite and corresponding matrix minerals show that for olivine and pyroxene inclusions sub solidus re equilibration between inclusion and host chromite during entrapment has led to an increase in chromium in the former in the case of olivine the re equilibration has also affected the fayalite fa content lowering it with an average of 14 in inclusions for ca poor pyroxene the ferrosilite fs content is more or less identical in inclusions and matrix by these studies an analogue to the commonly applied classification system for ordinary chondritic matrix based on fa in olivine and fs in ca poor pyroxene can be established also for inclusions in chromite all olivine and ca poor pyroxene inclusions 1 5 m in chromite from the ordovician fossil chondritic material plot within the l chondrite field which is in accordance with previous classifications the concordance in classification together with the fact that inclusions are relatively common makes them an accurate and useful tool in the classification of extraterrestrial material that lacks matrix silicates such as fossil meteorites and sediment dispersed chromite grains originating primarily from decomposed micrometeorites but also from larger impacts

a fossil winonaite like meteorite in ordovician limestone a piece of the impactor that broke up the l chondrite parent body about a quarter of all meteorites falling on earth today originate from the breakup of the l chondrite parent body similar to 470 ma ago the largest documented breakup in the asteroid belt in the past similar to 3 ga a window into the flux of meteorites to earth shortly after this event comes from the recovery of about 100 fossil l chondrites 1 21 cm in diameter in a quarry of mid ordovician limestone in southern sweden here we report on the first non l chondritic meteorite from the quarry an 8 cm large winonaite related meteorite of a type not known among present day meteorite falls and finds the noble gas data for relict spinels recovered from the meteorite show that it may be a remnant of the body that hit and broke up the l chondrite parent body creating one of the major asteroid families in the asteroid belt after two decades of systematic recovery of fossil meteorites and relict extraterrestrial spinel grains from marine limestone it appears that the meteorite flux to earth in the mid ordovician was very different from that of today c 2014 the authors published by elsevier b v less

drift and mixing under the ocean surface revisited stratified conditions and model data comparisons 1 a one dimensional model of the ocean near surface currents is presented it includes the enhanced near surface mixing due to the waves the wave induced stokes drift the stokes coriolis sc effect and the stratification near surface current shears from this model are compared with the shears of the quasi eulerian currents measured using a wave following platform during the shelf mixed layer experiment smile it is shown that the downwind current shears observed during smile are well modeled however the observed crosswind shears are in poor agreement with the model the stokes coriolis sc term could qualitatively explain this misfit but it is one order of magnitude too weak the ekman stokes spiral of the model is compared with the spiral observed during the long time series of measurements long term upper ocean study 3 the effects of stratification are taken into account the mean velocity profiles of the model closely agree with observations however there is no evidence of the sc effect on the shape of the observed current profile the observed profile is found to be a consequence of the current rectification due to the time varying stratification the sc effect calculated from a numerical wave hindcast is weak but should have been observed in fact it is estimated that the wave induced bias in the current measurements is larger than the sc effect finally it is shown that the variation of surface drift with wave age which was estimated to be small in unstratified conditions is important in the presence of shallow mixed layers

biotic dynamics and carbonate microfacies of the conspicuous darriwilian middle ordovician taljsten interval south central sweden enclosed in the darriwilian middle ordovician part of the reddish orthoceratite limestone of baltoscandia is a conspicuous c 1 5 m thick unit colloquially known as the taljsten interval it has a wide geographical distribution in the baltoscandian paleocontinent but is particularly well exposed in south central sweden the unit is characterized by its deviant gray color and beds with a mass occurrence of cystoid echinoderms moreover the recent discovery of an anomalous abundance of extraterrestrial chromite grains and micrometeorites in the taljsten and immediately adjacent strata bear witness of a time of deposition correlating to an increased influx of extraterrestrial matter to earth in this study we analyze the faunal dynamics based primarily on microfossils and carbonate microfacies across this intriguing interval generally known as a macrolithologically monotonous succession the taljsten proved more heterogeneous than previously believed in terms of fossil content and preservation as well as mineral content and composition the general texture is wackestone packstone but local heterogeneities are frequent a microfaunal reorganization occurred with a transition from a trilobite and brachiopod dominated community to one dominated by echinoderms which is mirrored also macroscopically by the cystoids the latter pelmatozoans seem to have flourished and might even have aided in the formation of the numerous hardgrounds the increase in echinoderms is linked to a volkhovian increase in echinoderms in eastern baltica in the immediate post taljsten strata there is no distinct change back to the pre taljsten biota conodont and ostracod faunal diversity data reveal peak values in the taljsten compared to the enclosing strata suggesting that the paleoenvironment was more suitable for higher diversity faunas of these metazoan groups all data collectively support a regression in the beginning of the taljsten likely followed by transgression in its upper part c 2012 elsevier b v all rights reserved less

determining the impactor of the ordovician lockne crater oxygen and neon isotopes in chromite versus sedimentary pge signatures abundant chromite grains with l chondritic composition in the resurge deposits of the lockne impact crater 458 myr old dia similar to 10 km in sweden have been inferred to represent relict fragments of an impactor from the break up of the l chondrite parent body at 470 ma this view has been challenged based on it cr and platinum group element pge patterns of the same resurge deposits and a reinterpretation of the origin of the chromite grains an impactor of the non magmatic iron meteorite type was proposed instead here we show that single grain oxygen and noble gas isotope analyses of the chromite grains from the resurge deposits further support an origin from an l chondritic asteroid we also present pge analyses and ir cr ratios for fossil l chondritic meteorites found in mid ordovician marine limestone in sweden the l chondritic origin has been confirmed by several independent methods including major element and oxygen isotopic analyses of chromite although the meteorites show the same order of magnitude pge and cr concentrations as recent l chondrites the elements have been redistributed to the extent that it is problematic to establish the original meteorite type from these proxies different pge data processing approaches can lead to highly variable results as also shown here for the lockne resurge deposits we conclude that the lockne crater was formed by an l chondritic impactor and that considerable care must be taken when inferring projectile type from pges in sedimentary ejecta deposits c 2011 elsevier b v all rights reserved less

observations of seasonal variation in the ekman layer abstract the seasonal variation in the ekman layer is examined using observations from the long term upper ocean study lotus including surface meteorology current and temperature the near surface current is found to be coherent with the wind at low frequencies periods greater than one day using a wind relative averaging method the authors find the observed near surface volume transport to be consistent with ekman transport the mean current profile has a spiral shape that is flat compared to the classic ekman spiral in that it rotates less with depth than does the ekman spiral the mean current e folds over 12 m in the summer and 25 m in the winter with a decay in amplitude that implies eddy viscosities of 60 10 4 and 250 10 4 m2 s 1 respectively diurnal cycling is the dominant mode of variability in the summer and it determines the vertical structure of the spiral in the winter diurnal cycling is almost nonexistent due to greatly reduced solar insolation and stronger winds a persisten

the micrometeorite flux to earth during the earliest paleogene reconstructed in the bottaccione section umbrian apennines italy based on sediment dispersed extraterrestrial spinel grains in the bottaccione limestone section in italy we reconstructed the micrometeorite flux to earth during the early paleocene from a total of 843 kg of limestone 86 extraterrestrial spinel grains 12 grains 63 m and 74 in the 32 63 m fraction have been recovered our results indicate that the micrometeorite flux was not elevated during the early paleocene ordinary chondrites dominated over achondritic meteorites similar to the recent flux but h chondrites dominated over l and ll chondrites 69 22 and 9 respectively this h chondrite dominance is similar to that recorded within an enigmatic 3he anomaly 70 27 and 3 in the turonian but different from just before this 3he anomaly and in the early cretaceous where ratios are similar to the recent flux 45 45 and 10 the k ar isotopic ages of recently fallen h chondrites indicate a small impact event on the h chondrite parent body 50 to 100 ma ago we tentatively suggest that this event is recorded by the turonian 3he anomaly resulting in an h chondrite dominance up to the paleocene our sample spanning the 20 cm above the cretaceous paleogene k pg boundary did not yield any spinel grains related to the k pg boundary impactor less

wind waves and fronts frictional effects in a generalized ekman model abstractocean currents in the surface boundary layer are sensitive to a variety of parameters not included in classic ekman theory including the vertical structure of eddy viscosity finite boundary layer depth baroclinic pressure gradients and surface waves these parameters can modify the horizontal and vertical flow in the near surface ocean making them of first order significance to a wide range of phenomena of broad practical and scientific import in this work an approximate green s function solution is found for a model of the frictional ocean surface boundary layer termed the generalized ekman or turbulent thermal wind balance the solution admits consideration of general more physically realistic forms of parameters than previously possible offering improved physical insight into the underlying dynamics closed form solutions are given for the wind driven flow in the presence of coriolis stokes shear a result of the surface wave field and thermal wind shear arising from a baroclinic

late wisconsinan pre valley heads glaciation in the western mohawk valley central new york and its regional implications the history of late wisconsinan pre valley heads glaciation about 18 15 5 ka implies that major glaciological controls as well as overall climatic warming influenced the pattern of deglaciation in the western mohawk valley the middleville formation in the west canada valley contains the most complete record of pre valley heads ice recession in central new york the lithostratigraphic succession was determined through detailed mapping and logging of measured sections provenance study of diamicton units and the analysis of declination of detrital remanent magnetization drm in laminated lacustrine silt and clay the initial recession of southwest flowing ice from the adirondacks and at least two glacial re advances of the mohawk lobe are recorded in these units glacial lake newport impounded in the west canada valley during ice recession attained levels that required ice damming by coalescent ontario and mohawk lobes and a subglacial outlet across the mohawk valley to the susquehanna drainage basin initial ice recession in the mohawk valley was mostly by calving of active valley lobes in deep water up to 350 m embayments and not by regional stagnation and simple downwasting a shift of ice flow from the adirondacks to ice flow from the mohawk lobe marks the development of low land lobes during pre valley heads time before the complete uncovering of the adirondacks the later dominance of the ontario lobe in valley heads time may have been the result of 1 a reduced supply of ice to the mohawk lobe from a diminished adirondack ice dome 2 changing ice flow conditions in quebec associated with an eastern st lawrence ice stream and calving bay and 3 nonsynchronous surging of the mohawk and ontario lobes as these lobes became fronted by deep lacustrine waters at different times

impact of mesoscale eddies on kuroshio intrusion variability northeast of taiwan abundant mesoscale eddies propagate to the east of taiwan and affect the kuroshio current and its onshore intrusion northeast of taiwan but the dynamical process of how eddy activities modulate the kuroshio intrusion is still unclear in this study in situ ocean velocity observations drifter trajectories tide gauge measurements satellite sea surface height data and assimilative hybrid coordinate ocean model hycom reanalysis outputs were used to analyze a cyclonic eddy induced large kuroshio onshore intrusion during late autumn 2008 along with nine anticyclonic eddy events and seven cyclonic eddy events extracted from long term hycom reanalysis outputs the variability of the eddy induced intrusion were quantified the impacts of the cyclonic eddy and the anticyclonic eddy were opposite under the impact of cyclonic anticyclonic eddy the total onshore intrusion between 122 e and 124 e across the 200 m isobaths was decreased increased by 15 7 7 3 while the onshore intrusion west of 122 6 e and the northeastward current on the outer shelf was increased decreased by 30 6 4 7 and 31 10 1 respectively the arrival of cyclonic anticyclonic eddy brought positive negative potential vorticity pv flux and modulated the local ocean vertical stratification which weakened enhanced the cross slope pv gradient and the shelf slope constraint on the upper layer current therefore favored inhibited the kuroshio onshore intrusion this article is protected by copyright all rights reserved

a russian record of a middle ordovician meteorite shower extraterrestrial chromite at lynna river st petersburg region numerous fossil meteorites and high concentrations of sediment dispersed extraterrestrial chromite ec grains with ordinary chondritic composition have previously been documented from 467 1 6 ma middle ordovician darriwilian strata these finds probably reflect a temporarily enhanced influx of l chondritic matter following the disruption of the l chondrite parent body in the asteroid belt 470 6 ma in this study a volkhovian kundan limestone marl succession at lynna river northwestern russia has been searched for ec grains 63 mu m eight samples forming two separate sample sets were collected five samples from strata around the asaphus expansusa raniceps trilobite zone boundary in the lower middle kundan yielded a total of 496 ec grains in 65 5 kg of rock average 7 6 ec grains kg 1 but up to 10 2 grains kg 1 these are extremely high concentrations three orders of magnitude higher than background levels in similar condensed sediment from other periods ec grains are typically about 50 times more abundant than terrestrial chrome spinel in the samples and about as common as terrestrial ilmenite three stratigraphically lower lying samples close to the a lepidurusa expansus trilobite zone boundary at the volkhov kunda boundary yielded only two ec grains in 38 2 kg of rock 0 05 grains kg 1 the lack of commonly occurring ec grains in the lower interval probably reflects that these strata formed before the disruption of the l chondrite parent body the great similarity in ec chemical composition between this and other comparable studies indicates that all or most ec grains in these russian mid ordovician strata share a common sourcethe l chondrite parent body less

large eddy simulation of the ekman transport in a stratified coastal sea a case study of the persian gulf abstract ekman transport is a key factor in the coastal upwelling regimes in the northern coastal region of the persian gulf in this paper the ocean module of parallelized large eddy simulation model palm was utilized so as to investigate the ekman layer and estimate the water mass transport in the persian gulf for the first time in order to take into account the effect of the topography on the ekman transport three experiments with the same initial and boundary conditions and different topographies were carried out the results indicated that in the vicinity of the shoreline and in shallow waters turbulent kinetic energy tke is 10 times stronger than in the offshore area it was concluded that in the presence of the shoreline the vertical velocity increases and in the onshore area the upwelling speed is 3 4 times larger than in the offshore area it was revealed that the ekman transport reached a steady state at the end of the simulation and reached a constant value of about 250 kg ms

factors controlling compositions of cosmic spinels application to atmospheric entry conditions of meteoritic materials abstract during their deceleration through the earth s atmosphere meteoritic materials i e interplanetary dust particles micrometeorites and meteorites experience thermal shocks which may alter their pristine mineralogy texture or chemical characteristics among these changes one of the most ubiquitous is the formation of spinels resulting from partial melting and subsequent crystallization of the meteoritic material these cosmic spinels differ from terrestrial spinels by their high ni and fe3 contents and show large variations in composition in order to better understand the factors controlling their chemistry pulse heating experiments simulating atmospheric entry of extraterrestrial objects were carried out using orgueil samples as proxies of meteoritic material covering a large range of experimental conditions temperature 500 c we also show that due to their fast crystallization kinetics cosmic spinels can record through their composition i e al2o3 contents and feo fe2o3 ratio the diverse conditions of the atmosphere crossed by the extraterrestrial object during its fall towards the earth s surface chemistry of cosmic spinels is thus a powerful tool for constraining the entry conditions in the earth s atmosphere of any extraterrestrial object including altitude of deceleration entry angle and incident velocity these in turn may provide valuable information on the origin of the extraterrestrial material

a 3 d study of mineral inclusions in chromite from ordinary chondrites using synchrotron radiation x ray tomographic microscopy method and applications abstract a method is described for imaging in 3 d the interiors of meteoritic chromite grains and their inclusions using synchrotron radiation x ray tomographic microscopy in ordinary chondrites chromite is the only common mineral that survives long term weathering on earth information about the silicate matrix of the original meteorite however can be derived from mineral inclusions preserved in the protecting chromite the inclusions are crucial in the classification of fossil meteorites as well as sediment dispersed chromite grains from decomposed meteorites and larger impacts as these are used for characterizing the past influx of material to earth but have previously been difficult to locate the method is non destructive and time efficient for locating inclusions the method allowed quantitative and morphological studies of both host chromite grains and inclusions in three dimensions the study of 385 chromite grains from eight chondrites h4 6 l4 6 ll4 ll6 reveals that inclusions are abundant and equally common in all samples almost two thirds of all chromite grains contain inclusions regardless of group and type the study also shows that the size of the inclusions and the host chromite grains as well as the number of inclusions within the host chromite grains vary with petrographic type thus the petrographic type of the host of a suite of chromite grains can be determined based solely on inclusion content the study also revealed that the amount of fractures in the host chromite can be correlated to previously assigned shock stages for the various chondrites the study has thus shown that the features and inclusions of fossil chromite grains can give similar information about a former host meteorite as do studies of an unweathered whole meteorite meaning that this technique is essential in the studies of ancient meteorite flux to earth

extraterrestrial chromite in middle ordovician marine limestone at kinnekulle southern sweden traces of a major asteroid breakup event the distribution of sediment dispersed extraterrestrial chromite grains and other cr rich spinels 63 mu m has been studied in middle ordovician orthoceratite limestone from two quarries at kinnekulle southern sweden in the thorsberg quarry all similar to 3 2 m thick sequence of beds previously shown to be rich in fossil meteorites is also rich in sediment dispersed extraterrestrial chromite grains typically 1 3 grains are found per kilogram of limestone in the nearby hallekis quarry the same beds show similarly high concentrations of extraterrestrial chromite grains but in samples representing the 9 m downward continuation of the section exposed at this site only 5 such grains were found in a total of 379 kg of limestone the extraterrestrial equilibrated ordinary chondritic chromite grains call be readily distinguished by a homogeneous and characteristic major element chemistry including 2 0 3 5 wt tio2 and stable v2o3 concentrations close to 0 7 wt terrestrial cr rich spinels have a wide compositional range and co exist with extraterrestrial chromite in some beds these grains may be derived for example from mafic dykes exposed and weathered at the sea floor considering lithologic and stratigraphic aspects variations in sedimentation rate cannot explain the dramatic increase in extraterrestrial chromite seen in the upper part of the composite section studied instead the difference may be primarily related to all increase in the ancient flux or extraterrestrial matter to earth in connection with the disruption of the l chondrite parent body in the asteroid belt at about this time the coexistence in some beds of high concentrations of chondritic chromite and terrestrial cr rich spinels however indicates that redistribution of heavy minerals on the sea floor related to changes in sea level and sea floor erosion and currents must also be considered less

multiproxy record of holocene paleoenvironmental change tierra del fuego argentina abstract we interpret holocene environmental conditions in a subantarctic high andean valley from palynological and diatom analysis peat stratigraphy and local geomorphology the multiproxy data from las cotorras mire 54 41 13 s 68 02 51 w 420 m a s l indicate the development of a soligenous mire as a result of a fine grained tephra layer deposition over the mineral soils sometime prior to 8000 cal yr bp the paleoecological conditions in the mire after 8000 cal yr bp show a rapid succession from a limnic to a telmatic stage as the mire is colonized by sedges cyperaceae and herbaceous communities the upland vegetation changed from cushion and shrub heaths to an expansion of nothofagus forest at high altitudes after 6500 cal yr bp the peat is interbedded with clastic sediment that originates from mass wasting events or floods these depositional changes affected the mire ecosystem water table level and nutrient status oligotrophic and or eutrophic conditions maxima in total pollen influx at about 2800 1100 and 700 cal yr bp coincide with heightened mineral flux and these changes are related to precipitation and slope processes the major vegetational change registered in the pollen record is the decline of nothofagus pollen after 1000 cal yr bp which reaches a minimum between ca 680 and 300 cal yr bp this minimum was likely caused by cool wet conditions that coincided with the little ice age lia in the southern hemisphere our results indicate the sensitivity of subantarctic nothofagus forest and mire ecosystems to changes during the holocene

variational estimation of the wind stress drag coefficient and the oceanic eddy viscosity profile abstract a variational optimal control technique is used to assimilate both meteorological and oceanographic observations into an oceanic ekman layer model an identical twin experiment is discussed first in which the observations are created by the dynamic model the field measurements from the lotus 3 long term upper ocean study 3 buoy are then analysed by fitting the model results to the data the unknown boundary condition the wind stress drag coefficient and the unknown vertical eddy viscosity distribution are deduced simultaneously from the data and an optimal estimate of the current field is obtained though the model is simple the results show that the variational assimilation technique is capable of extracting from the available observations a reasonable wind stress drag coefficient and vertical eddy viscosity distribution