the interrelation of glaciotectonic and glaciodepositional processes within the glacial environment abstract in recent years it has been recognised that ice sediment coupling occurred beneath the quaternary ice sheets that advanced over the soft sediments of lowland areas this paper looks in detail at the effects of this coupling on the sediments which results in glaciotectonic deformation and also discusses the interaction of deformation and deposition within the subglacial environment two types of glaciotectonic deformation are discussed that are produced by the active movement of ice 1 proglacial tectonics at the margin which include compressive fold styles such as listric thrusts and faults and open folding 2 subglacial tectonics formed beneath the glacier which include fold styles resulting from simple shear and represent a soft rock purely dynamic shear zone styles of deformation associated with stagnant ice are also investigated we argue that glaciotectonic deformation is a common phenomenon and an integral part of geological record from continental ice sheets it is suggested that zones of deformation within the sediment are related to similar zones of strain in the ice sheet and complex deformation sequences are produced by the superimposition of these differing styles upon one another as the ice sheet advances and retreats it is also argued that subglacial deposition and deformation are related and that on soft beds underformed till is rare whilst deformed till is very common

three dimensional deformation measured in an alaskan glacier measurements of movement along 28 boreholes reveal the three dimensional flow field in a 6 million cubic meter reach of worthington glacier a temperate valley glacier located in alaska sliding at the bed accounted for 60 to 70 percent of the glacier s surface motion strain rates in the ice were low from the surface to a depth of about 120 meters but then increased rapidly toward the bed ice deformation was not affected by temporal changes in the sliding rate the three dimensional pattern of motion indicates that plane strain which is often assumed by models is a poor approximation of this viscous flow

a multi step model for the origin of e3 enstatite chondrites it appears that the mineralogy and chemical properties of type 3 enstatite chondrites could have been established by fractionation processes removal of a refractory component and depletion of water in the solar nebula and by equilibration with nebular gas at low to intermediate temperatures approximately 700 950 k we describe a model for the origin of type 3 enstatite chondrites that for the first time can simultaneously account for the mineral abundances bulk chemistry and phase compositions of these chondrites by the operation of plausible processes in the solar nebula this model which assumes a representative nebular gas pressure of 10 5 bar entails three steps 1 initial removal of 56 of the equilibrium condensed phases in a system of solar composition at 1270 k 2 an average loss of 80 85 water vapor in the remaining gas and 3 two different closure temperatures for the condensed phases the first step involves a refractory element fractionation and is needed to account for the overall major element composition of enstatite chondrites assuming an initial system with a solar composition the second step water vapor depletion is needed to stabilize si bearing metal oldhamite and niningerite which are characteristic minerals of the enstatite chondrites variations in closure temperatures are suggested by the way in which the bulk chemistry and mineral assemblages of predicted condensates change with temperature and how these parameters correlate with the observations of enstatite chondrites in general most phases in type 3 enstatite chondrites appear to have ceased equilibrating with nebular gas at approximately 900 950 k except for fe metal which continued to partially react with nebular gas to temperatures as low as 700 k

role of narrow mountains in large scale organization of asian monsoon convection abstract the asian summer monsoon is organized into distinct convection centers but the mechanism for this organization is not well understood analysis of new satellite observations reveals that narrow mountain ranges are an important organizing agent anchoring monsoon convection centers on the windward side the bay of bengal convection in particular features the heaviest precipitation on its eastern coast because of orographic lifting as the southwest monsoon impinges on the coastal mountains of myanmar also known as burma this is in contrast to the widely held view that this convection is centered over the open ocean as implied by coarse resolution datasets a view that would require an entirely different explanation for its formation narrow in width and modest in height 1 km these mountains are hardly mentioned in conceptual depictions of the large scale monsoon and poorly represented in global climate models the numerical simulations of this study show that orographic rainbands are not a

wind generated eddy characteristics in the lee of the island of hawaii 1 weekly satellite sea surface height ssh anomaly data are used to clarify the mesoscale eddy characteristics in the lee of the island of hawaii the largest island in the hawaiian island chain the lee eddy variability can be separated into two geographical regions in the immediate lee southwest of hawaii region e eddy signals have a predominant 60 day period and a short life span whereas in the region along 19 n west of 160 w region w the eddy variability is dominated by 100 day signals and extends over a broad region by applying a linear ekman pumping model forced by the weekly quikscat wind data we find that the observed 60 day eddy signals originate in the southwest corner of hawaii and are induced by the local 60 day wind stress curl variability associated with the blocking of the trade wind by the island of hawaii the relationship between the wind forcing and the observed ssh signals demonstrates the role of the ocean as an integrator that responds more effectively to the low frequency synoptic atmospheric forcing 60 days than to the higher frequency forcing 30 days since the large amplitude 60 day ssh anomalies take 1 2 weeks to fully develop it is possible that real time observed wind stress data can be used for the prediction of these anomalies in contrast to the wind induced 60 day eddy signals in the lee of the island of hawaii the 100 day eddy signals in region w are likely generated by the instability of the sheared north equatorial current and hawaii lee countercurrent

mineral chemistry and the origin of enstatite in unequilibrated enstatite chondrites abstract a comprehensive study of the petrography cathodoluminescence cl rare earth element ree abundances and magnesium and silicon isotopic compositions of enstatite the major mineral in unequilibrated enstatite chondrites uecs is reported for comparison observations were also made in equilibrated enstatite chondrites eecs and aubrites in uecs there are no ree patterns or abundances that uniquely characterize the cl color and intensity grain size or occurrence of enstatite red enstatite is dominant in uecs and blue enstatite in eecs three ree patterns represent the diversity observed in uec enstatite many grains are depleted in one or more of the three most volatile rees under reducing conditions i e yb eu and sm all ree patterns are compatible with the fractional crystallization during chondrule formation of melts whose precursors either had flat ree patterns or were depleted in the most volatile rees no evidence was found to suggest that enstatite grains require nebular condensation or multiple reservoirs as suggested by others magnesium and silicon isotopic ratios are normal therefore excluding the role of evaporation in separating the rees this fractionation was most likely accomplished during condensation of the chondrule precursors our data combined with synthetic experiments support the idea that coexisting red and blue cl enstatites formed by crystallization from a single melt most of the red enstatite was converted to blue by diffusion and recrystallization to form the more equilibrated e chondrites it is not clear why enstatite is depleted in the most volatile rees while oldhamite a highly refractory mineral which is the major carrier of ree in e chondrites commonly has enrichments of these elements

styles of subglacial glaciotectonic deformation within the context of the anglian ice sheet a substantial proportion of the glacial sediments of east anglia england are chaotic and highly deformed this has been attributed to a direct glaciotectonic deformation or b slumping of glaciomarine sediments we show that interpretation a leads to a classification of subglacial glaciotectonic deposits into sites of constructional deformation where little or no erosion of the preglacial deposits has occurred and styles of deformation are preserved moving up in the sequence and excavational deformation where substantial erosion of preglacial sediments has occurred and deformational styles are superimposed on each other by using glaciological and geotechnical theory we show that the expression of these deformational styles in east anglia is a natural response to the stress fields imposed by the ice sheet and that in consequence their spatial relationships are explicable the depth of deformation is related to the geotechnical properties of till and substrate the stress and effective stress fields and found to be consistent with observations

oxygen isotope studies of carbonaceous chondrites abstract the carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula these isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions we present a comprehensive set of whole rock analyses of cv co ck cm cr ch and ci chondrites as well as selected components of some of these meteorites a simple model is developed which describes the isotopic behavior during parent body aqueous alteration processes the process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition

the wake of st vincent abstract the island of st vincent and the other windward islands in the southeastern caribbean were chosen as a field site for the study of weak mountain wakes by the authors definition a weak wake forms when the potential vorticity generated by a mountain is not strong enough to advect itself into eddies rather it is simply advected downstream by the ambient flow goes 8 and landsat sunglint images unambiguously revealed that the mountainous windward islands have remarkably long straight wakes the length of st vincent s wake exceeds 300 km although its width is only 20 km near the islands the wake structures reflect the details of the island topography these wakes do not exhibit any obvious diurnal effect boat surveys in the lee of st vincent confirmed the existence of features seen in the images the sharp wake boundary the small valley induced jet embedded in the near wake and the absence of any reverse flow aircraft surveys gave evidence of descent over the island and showed that the

the effect of grain texture on the occurrence of microstructural properties in subglacial till in this paper we examine whether till grain size affects the range and occurrence of micromorphological features associated with subglacial shear our till samples were collected from two glaciers in iceland and varied in texture from a coarse sandy clast rich till fjallsjokull to a fine grained silty sandy till vestari hagafellsjokull we found a wide range of deformational microstructures that included skelsepic plasmic fabric intraclasts of pre existing eroded bedrock basalt and weathered clay and mini shear zones between clasts we classified our micromorphological data into three classes rotational intermediate and linear in addition to these observations we performed extensive microfabric analysis at different scales on all of our samples we found that the coarse grained till contained a greater number and variety of microstructures than the fine grained till in addition the fine grained till showed a distinct lack of rotational structures that we attribute to the lack of significantly sized clasts in the matrix we argue that the varied texture of the coarse grained till provides a greater degree of perturbation within the shearing layer and so more distinct microstructures form in a more fine grained till shearing is more homogeneous since there are less perturbations in the matrix and this leads to a more singular kind of microstructure our observations suggest that subglacial shear occurs within a multi layered patchwork of different grain sizes competence and pore water pressures it is these factors that are so crucial in determining the occurrence and type of microstructural evidence we see in subglacial tills

oxygen isotopes in asteroidal materials measurement of the variation of the 17o 16o and 18o 16o ratios of extraterrestrial materials has proven to be a key tool in understanding the formation and evolution of the solar system this chapter attempts to collate the huge data set of oxygen isotopic measurements of asteroidal material as sampled by meteorites in order to understand some of the processes involved in the formation of these primitive bodies and how such events have affected the oxygen isotopic ratios ultimately offering a window back to the very origin of solar system and its primordialoxygen isotopic heterogeneity oxygen is generally a major element in the gas liquid and solid phases that have interacted throughout the evolution of the solar system its chemical properties ensuring that there is abundant opportunity for reactions and exchange the details of which can be recorded in the isotopic ratios of the products such processes can be crudely subdivided into the following six categories early solar nebular isotopic heterogeneity high temperature modifi cation of nebular components metamorphism and melting in asteroids aqueous alteration in asteroids mixing of components brecciation terrestrial weathering it is clear from the isotopic variation in the earliest formed nebular components such as refractory inclusions and chondrules that there was considerable oxygen isotopic heterogeneity in the early solar nebula spanning over 50 and perhaps much greater in both 17o and 18o the origin of this variation is discussed elsewhere in this volume however isotopic exchange between the 16o rich solids and 17o and 18o rich gas phase s resulted in a wide range of isotopic variation in these early formed components offering insight into the conditions of these processes and the evolution of the reservoirs with time and or space once accreted onto the early planetisemals much of the primitive nebular components experienced considerable modification the metamorphism and melting experienced by some of these bodies most probably the result of heating from the decay of short lived radionuclides e g 26al resulted in progressive homogenization within individual bodies of any original isotopic heterogeneity complete homogenization appears to have been achieved in the hed parent body indicating very high levels of melting and the development of a large magma ocean the carbonaceous and ordinary chondrite parent bodies experienced more modest heating sufficient to mobilize water ice that accreted along with the more refractory materials the subsequent reactions between the liquid and solid phases at low temperature imparted large isotopic fractionations which record some of the conditions of this alteration such as water rock ratio temperature and isotopic signature and thus potentially the origin of the water ice the evolution of the asteroidal bodies has been far from simple and an important use of oxygen isotope measurements has been in the identifi cation of the components present in some meteorites the result of breakup reassembly and mixing of different bodies during impact processing the final oxygen isotopic signatures imparted into meteorite samples are those associated with terrestrial weathering the isotopic compositions of the weathering products depend on location primarily latitude while the magnitude of the weathering is dependent on many factors with some meteorites e g highly reduced enstatite chondrites and the matrix rich co3s particularly susceptible to such effects

ring shear studies of till deformation coulomb plastic behavior and distributed strain in glacier beds a ring shear device was used to study the factors that control the ultimate steady strength of till at high shear strains tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26 3 and 18 6 for tills containing 4 and 30 clay sized particles respectively other tests at steady normal stresses and variable shear strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate this weakening may be due to small increases in till porosity these results provide no evidence of viscous behavior and suggest that a coulomb plastic idealization is reasonable for till deformation however viscous behavior has often been suggested on the basis of distributed shear strain observed in subglacial till we hypothesize that deformation may become distributed in till that is deformed cyclically in response to fluctuations in basal water pressure during a deformation event transient dilation ofdiscrete shear zones should cause a reduction in internal pore water pressure that should strengthen these zones relative to the surrounding till a process called dilatant hardening consequent changes in shear zone position when integrated over time may yield the observed distributed strain

discrete element modeling of subglacial sediment deformation 1 the discrete element method dem is used in this study to explore the highly nonlinear dynamics of a granular bed when exposed to stress conditions comparable to those at the bed of warm based glaciers complementary to analog experiments the numerical approach allows a detailed analysis of the material dynamics and the shear zone development during progressive shear strain the geometry of the heterogeneous stress network is visible in the form of force carrying grain bridges and adjacent volumetrically dominant inactive zones we demonstrate how the shear zone thickness and dilation depend on the level of normal overburden stress and we show how high normal stress can mobilize material to great depths the particle rotational axes tend to align with progressive shear strain with rotations both along and reverse to the shear direction the results from successive laboratory ring shear experiments on simple granular materials are compared to results from similar numerical experiments the simulated dem material and all tested laboratory materials deform by an elastoplastic rheology under the applied effective normal stress these results demonstrate that the dem is a viable alternative to continuum models for small scale analysis of sediment deformation it can be used to simulate the macromechanical behavior of simple granular sediments and it provides an opportunity to study how microstructures in subglacial sediments are formed during progressive shear strain

the classification and complex thermal history of the enstatite chondrites we have carried out instrumental neutron activation analyses of 11 enstatite chondrites and electron microprobe analyses of 17 enstatite chondrites most of which were previously little described we report here the third known eh5 chondrite lew 88180 and an unusual el6 chondrite lew 87119 new data on four el3 chondrites alh 85119 eet 90299 pca 91020 and mac 88136 which is paired with mac 88180 and mac 88184 the second el5 chondrite til 91714 and an unusual metal rich and sulfide poor el3 chondrite lew 87223 the often discussed differences in mineral composition displayed by the eh and el chondrites are not as marked after the inclusion of the new samples in the database and the two classes apparently experienced a similar range of equilibration temperatures however texturally the el chondrites appear to have experienced much higher levels of metamorphic alteration than eh chondrites of similar equilibration temperatures most of the petrologic type criteria are not applicable to enstatite chondrites and unlike the ordinary chondrites texture and mineralogy reflect different aspects of the meteorite history we therefore propose that the existing petrologic type scheme not be used for enstatite chondrites we suggest that while textural type reflects peak metamorphic temperatures the mineralogical type reflects equilibration during postmetamorphic probably regolith processes unlike the ordinary chondrites and eh chondrites el chondrites experienced an extensive low temperature metamorphic episode there are now a large number of enstatite meteorite breccias and impact melts and apparently surface processes were important in determining the present nature of the enstatite chondrites

the influence of the hawaiian archipelago upon the wind driven subtropical gyre in the western north pacific in the middle of the subtropical gyre in the western north pacific is the subtropical counter current comprised of at least three narrow bands of eastward geostrophic mean flow near 20 n 24 n and 26 n each extending from the sea surface through the main pycrocline the origin of these narrow bands of eastward mean flow has not previously been explained in this study these bands are shown in the mean to extend zonally from the philippine sea i e 140 e to the vicinity of the hawaiian archipelago i e 160 w east of there they cannot be found therefore a hypothesis is presented wherein the hawaiian archipelago extending from 19 n to 26 n near 165 w is seen to act as an effective barrier modifying the response of the western subtropical north pacific to wind driven effects in the eastern subtropical north pacific and in so doing giving rise to these bands of eastward mean flow in the middle of the western subtropical gyre a test of this hypothesis utilizes a sverdrup 1947 model driven by the annual long term mean wind stress curl constructed on a 2 latitude longitude grid from synoptic 6 hourly surface wind observations for the 13 year period 1968 1980 two model simulations are conducted one in the absence of the hawaiian archipelago and one in the presence of it in the absence of the archipelago none of the bands of eastward mean flow are simulated in the presence of the archipelago the narrow bands of eastward mean flow at 20 n 26 n and 24 n are simulated although the latter band is very weak these narrow bands of eastward flow are shown to occur in response to the deflection northward of the wind driven geostrophic streamlines in the central subtropical north pacific by the hawaiian archipelago

pore water controlled grain fracturing as an indicator for subglacial shearing in tills genetic classification of glacial deposits still proves to be highly controversial in many cases it remains unclear whether a particular sediment has been sub glacially deformed in the present paper it is suggested that micromorphological research is helpful where current techniques fail to lead to unambiguous interpretations it is argued that the occurrence of fractured grains in glacial sediments is indicative of subglacial shearing and that such grains may be used as diagnostic evidence of glaciotectonism deformational mechanisms associated with the fracturing process are outlined and explained using a series of thin sections from wijnjewoude the netherlands

deep atmospheric response to the north pacific oceanic subtropical front in spring abstract the north pacific subtropical front stf is a zone of high sea surface temperature sst gradients located around 25 n in the western basin and is most pronounced in spring the stf s atmospheric effects are investigated using satellite observations and an atmospheric reanalysis during april may along the stf surface wind stress curl turns weakly cyclonic in the general background of anticyclonic curls atmospheric column integrated water vapor displays a pronounced meridional maximum along this surface trough suggesting a deep vertical structure cyclonic wind curls occur intermittently at intervals of a few days along the stf in subsynoptic low pressure systems accompanying larger synoptic highs in the main storm track to the north in the subsynoptic surface lows convective rain takes place with deep upward motion moistening the entire troposphere the lows are enhanced by condensational heating leading to the formation of weak cyclonic wind curls the lows display vertical structure ch

on the formation dynamics of the north equatorial undercurrent abstractbased on a physics oriented modeling study we investigate the underlying forcing processes of the north equatorial undercurrent neuc made up of large scale 90 and mesoscale 10 c

a ring shear device for the study of till deformation tests on tills with contrasting clay contents abstract deformation of subglacial sediment may have had a profound influence on the geomorphic effects and dynamics of pleistocene ice sheets but data that bear on the rheology of such sediment are few and contradictory a means of studying systematically the mechanical properties of glacial tills is provided by a ring shear device that shears a large annular specimen to high strains at variable rates special features of the device allow continuous observation of the distribution of shear strain measurement of local stresses normal to the direction of shear and isolation of wall effects thus far a linear viscous putty and two tills with different clay contents 4 and 32 by weight have been tested the experiments with till indicate as expected that the presence of dispersed clay minerals reduces markedly both the residual strength and hydraulic diffusivity of till clay also reduces spatial variations in normal stress associated with grain bridges the walls bounding the specimen support only 9 17 of the total resistance to shearing strain was localized in both tills but not in the linear viscous putty strain localization in the tills indicates that their theology departs significantly from linear and bingham viscous models

the meteoritical bulletin no 82 1998 july abstract meteoritical bulletin no 82 lists information for 974 new meteorites including 521 finds from antarctica 401 finds from the sahara 21 finds from the nullarbor region of australia and 7 falls ban rong du burnwell fermo jalanash juancheng monahans 1998 and silao many rare types of meteorites are reported counting pairing groups as one these include one cr chondrite two ck chondrites two co chondrites four cv chondrites one ch chondrite or bencubbin like six c2 unclassified chondrites two eh chondrites two el chondrites three r chondrites thirty unequilibrated ordinary chondrites one un grouped chondrite three eucrites six howardites one diogenite eleven ureilites nine iron meteorites one mesosiderite two brachinites one lodranite one winonaite and two lunar meteorites dar al gani 400 and eet 96008 all italicized abbreviations refer to addresses tabulated at the end of this document

ubiquitous high feo silicates in enstatite chondrites our electron microprobe studies of four type 3 enstatite chondrites show that olivines and low ca pyroxenes with more than 3 wt feo are more abundant than previously recognized 4 8 of clear pyroxene grains and a higher proportion of dusty pyroxenes have fs 5 20 from scanning electron microscope and electron probe surveys of these four eh3 chondrites we discovered 542 objects that contain silicates very largely pyroxene with 3 wt feo 18 chondrules 381 rimmed or unrimmed grains and 143 mineral aggregates with fs 5 27 pyroxene or fa 3 14 olivine aggregates and grains may have been derived from chondrules by comminution rims of enstatite with fs 0 3 on many grains formed by reduction or growth in the nebula or parent body in two eh4 5 chondrites we identified 89 feo rich objects that are all enstatite grains with fs 1 10 having feo poor enstatite rims which grew during planetary metamorphism two of the 18 feo rich chondrules in eh3 chondrites have textures and mineral compositions that are consistent with crystallization of feo rich melts in others these textures are modified by nebula or planetary reduction along cracks and grain edges that formed low feo silicates and metallic fe ni however several feo rich chondrules contain crystals of both high and low feo silicates that appear to have igneous origins but could not have formed by closed system crystallization of chondrule melts these probably reflect either reduction of chondrule melts by the nebula during crystallization or collisions of partly molten chondrules having very different feo concentrations an origin involving partial melting of chondrule precursor grains seems less plausible

oxygen isotopes of chondritic components we review the oxygen isotopic compositions of chondrite components refractory inclusions chondrules and matrix and their inter and intra crystalline oxygen isotopic distributions primary oxygen isotopic compositions acquired before planetesimal accretion are easily disturbed by parent body processes such as aqueous alternation and thermal metamorphism primary or original oxygen isotopic compositions of refractory inclusions ca al rich inclusions and amoeboid olivine aggregates distribute along a slope 1 line on the three oxygen isotope diagram over the range of 60 17 o 18 o 16 o rich and 17 o 18 o rich during refractory inclusion formation on the other hand primary minerals of most chondrules have small isotopic variations and are enriched in 17 o and 18 o relative to refractory inclusions suggesting that chondrule formation occurred in 17 o 18 o rich nebular gas however rare 16 o rich chondrules have been found suggesting some overlap in the timing of formation of chondrules and refractory inclusions in the solar nebula oxygen isotopic compositions of matrix grains distribute along the slope 1 line over the same range as refractory inclusions and chondrules the similarity in oxygen isotopic distributions suggests that matrix was originally a mechanical mixture of nebular dusts co generated with chondrules and refractory inclusions presolar grains with oxygen isotopic compositions that are clearly distinct from those of solar nebular materials are a trace component of chondrite matrices based on these oxygen isotopic characteristics more than 99 5 of the solid materials in the nebula formed locally in the solar nebula and the remainder formed in interstellar space the astrophysical setting of chondrite component formation in the early solar system is also discussed refractory inclusions and 16 o rich matrix dusts formed around the inner edge of the solar nebula on the other hand most chondrules and 17 o 18 o rich matrix dusts seem to have formed elsewhere in the solar nebula efficient large scale radial mixing of the solar nebular materials may have been an essential process in the formation of chondritic planetesimals

interdecadal thermocline variability in the north pacific for 1958 97 a gcm simulation an ocean general circulation model is forced with the ncep reanalysis wind stress for 1958 97 to understand mechanisms of ocean subsurface variability with relatively high horizontal 1 83 18 and vertical 41 levels resolutions the model produces mode waters on a range of density surfaces in the western central and eastern north pacific in qualitative agreement with observations these mode waters appear as a thermostad or a region of weak stratification in the upper thermocline as they flow southward from their formation regions in the kuroshio and its extension in the model subsurface temperature variability in the central subtropical gyre reaches a maximum within the thermostad in contrast to what might be expected from the linear baroclinic rossby wave theory this variance maximum is associated with the longitudinal shift in the path of mode waters in particular deepened mixed layer and accelerated eastward currents in the kuroshio extension by wind changes in the mid 1970s act cooperatively to move the central mode waters toward the east causing large subsurface temperature anomalies besides the local maximum in the central north pacific subtropical gyre two additional maxima of the subsurface anomaly are identified in the northwestern and southern parts of the gyre respectively among these subsurface anomaly centers the one in the northwestern north pacific has a strong effect on the model sea surface temperature suggesting that the kuroshio and its extension are a key region to decadal interdecadal ocean atmosphere interaction finally possible effects of atmospheric thermal forcing are discussed

ventilated thermocline strongly affected by a deep mixed layer a theory for subtropical countercurrent abstract the mixed layer thickness generally increases in the northward direction but its change seems to occur rather sharply in a narrow transition zone referred to as a mixed layer front here the author investigates the effects of the mixed layer front on the ventilated thermocline structure especially focusing on the generation mechanism of the subtropical countercurrent if the mixed layer front is not parallel to the surface density contour the fluid with minimum isopycnal potential vorticity is formed around the intersection of the mixed layer front and outcrop line if the mixed layer front slants northeastward and surface density is zonally uniform as seen in a numerical experiment carried out by kubokawa and inui in which the subtropical countercurrent was reproduced the minimum potential vorticity on a high density isopycnal occurs in the east while that in a low density isopycnal occurs in the west in the present study analytic solutions for a simple three layer model are presented f

far reaching effects of the hawaiian islands on the pacific ocean atmosphere system using satellite data we detected a wind wake trailing westward behind the hawaiian islands for 3000 kilometers a length many times greater than observed anywhere else on earth this wind wake drives an eastward ocean current that draws warm water from the asian coast 8000 kilometers away leaving marked changes in surface and subsurface ocean temperature standing in the path of the steady trade winds hawaii triggers an air sea interaction that provides the feedback to sustain the influence of these small islands over a long stretch of the pacific ocean

surface winds divergence and vorticity in stratocumulus regions using quikscat and reanalysis winds 1 high spatial resolution quikscat data are used to examine surface winds divergence and vorticity over oceanic regions during the boreal summer these analyses are compared to those from earlier observational studies as well as ecmwf and ncep reanalysis products quikscat analyses generally confirm the results from early studies and the reanalyses but add important details to our view of the surface circulation in atlantic and east pacific regions

feo rich silicates in the sahara 97159 eh3 enstatite chondrite mineralogy oxygen isotopic compositions and origin we report the mineralogy and oxygen isotopic compositions of feo rich silicates in the sahara 97159 eh3 chondrite this component is referred to as feo rich because it contains substantially more feo than the characteristic feo poor silicates in the highly reduced enstatite meteorites these feo rich silicates are mostly low ca pyroxene fs535 and their compositions suggest an origin under more oxidizing conditions like those for the ordinary chondrites however the mafic silicates in ordinary and carbonaceous chondrites are dominantly olivine and the feo rich silicates in the e chondrites are less commonly olivine the oxygen isotopic compositions of the feo rich silicates are indistinguishable from those of feo poor silicates in sahara 97159 these observations suggest that both the feo rich silicates and the feo poor silicates in eh chondrites formed from the same oxygen reservoir where redox conditions varied widely

till fabric associated with deformable beds this paper investigates the development of till fabric associated with glaciers overlying deformable beds first the till fabrics from both modern and ancient soft bed and hard bed subglacial environments are investigated and then soft bedded sites with specific strain histories are examined the results indicate that lodgement tills had a strong fabric whilst there is a wide range of much weaker fabric strengths associated with soft bed tills it is suggested from a theoretical study of soft bed till deposition that longitudinal and vertical processes in the subglacial deforming layer are important in fabric development field sites were chosen to isolate these two factors and fabrics investigated in areas of known relative shear strain and known relative thickness of the deforming layer the results indicate that 1 for a fixed deforming layer fabric strength does increase with increasing deformation except at very high strains where the development of a transverse fabric can lead to a reduction in the overall fabric strain and 2 lodgement tills and soft bed tills associated with a thin deforming layer have a high fabric strength whilst soft bed tills associated with a thick deforming layer have a low fabric strength where the deforming layer is thin clasts are oriented parallel with the glacier direction either by lodging against a hard bed or ploughing against a soft bed however where the deforming layer is thicker and shear strains are high melt out processes encourage a parallel fabric but the increased shear strain and changes in the deforming layer thickness cause the clasts to develop both a parallel and transverse fabric these processes combine to reduce the overall fabric strength till fabric studies are a further sedimentological technique to separate the depositional processes associated with a homogeneous till

influence of the glacier bed lithology on the formation of a subglacial till sequence ring shear experiments as a tool for the classification of subglacial tills abstract a glaciogenic sediment sequence deposited by a local glacier in the rhine catchment area near sargans eastern swiss alps was investigated in order to examine the shear behaviour of two different tills in addition to ring shear experiments examination of clast lithology clay mineralogy and physical properties of all samples were determined sem analyses of artificially produced deformation patterns in the till samples show only a very thin shear zones of 2 3 m thickness despite long shear distances of up to 145 mm a clear relationship between local bedrock and the formation of a thin basal layer of heavily deformed till can be demonstrated this locally derived till layer exhibits distinctly different shearing properties compared to the massive overlying till unit that is composed of more distantly transported lithic material from the upper catchment area of the glacier the difference in the angle of internal friction between the two tills is 10 at residual shear strength although the clay mineralogy of both tills is similar it can further be demonstrated that after the deposition of a 10 15 cm thin till layer directly on bedrock the flow dynamics of the glacier tongue may have changed due to differences in glacier bed debris lithology differences in the shear behaviour of the sediments allied to microscopic analyses point to an important environmental change from a deformation till to an overlying non deformed till

till beneath ice stream b 3 till deformation evidence and implications most of the velocity of ice stream b near the upstream b camp upb west antarctica appears to arise from deformation of a seismically detected subglacial till layer that averages 6 m thick available evidence indicates that the entire thickness of this till layer is deforming and is eroding subjacent bedrock into flutes parallel to ice flow and hundreds of meters across the resulting till flux beneath upb is equivalent to an average erosion rate of about 0 4 mm yr 1 in the catchment area and suggests that till deltas tens of kilometers long have been deposited at the grounding line during the holocene such deltas should be characterized by partial ice till decoupling across a water film and by a small ice air surface slope they may have been discovered by recent geophysical work

oxygen isotope studies of ordinary chondrites several stages in the evolution of ordinary chondritic meteorites are recorded in the oxygen isotopic composition of the meteorites and their separable components chondrules fragments clasts and matrix the whole rock isotopic compositions reflect the iron group of the meteorite h l or ll isotopic uniformity of h3 to h6 and l3 to l6 are consistent with closed system metamorphism within each parent body ll3 chondrites differ slightly from ll4 to ll6 implying a small degree of opensystem aqueous alteration and carbon reduction on the scale of individual chondrules the meteorites are isotopically heterogeneous allowing recognition of the solar nebular processes of chondrule formation chondrules for all classes of ordinary chondrites are derived from a common population which was separate from the population of chondrules in carbonaceous or enstatite chondrites chondrules define an isotopic mixing line dominated by exchange between 16o rich and 16o poor reservoirs the oxygen isotopic compositions of chondrites serve as fingerprints for identification of genetic association with other meteorite types achondrites and iron and for recognition of source materials in meteoritic breccias

approaches to the study of glacier bed deformation investigation of glacier bed conditions and subglacial processes is an obligatory requirement for the modelling and understanding of contemporary glacier behaviour past glacier behaviour glacier response to both spatial and temporal variations in bed material and glacier response to external forcing factors such as climate change the recognition of the importance of coupling between the glacier and its bed resulted in a paradigm shift in the subject and drew attention to the critical importance of subglacial deformation as opposed to simply subglacial deposition and sliding a number of methods have been adopted to measure glacier bed deformation ranging from direct observation and instrumentation the interpretation of macroscale and microscale sedimentary structures to the interpretation of glacier bedforms and glacier bed modelling this paper is concerned to describe the methods used by the two authors and co workers and attention is given to field methods the type and arrangement of sedimentary structures thin section micromorphology and microfabric and clast microfabric and glacier bedform morphology as evidence of subglacial deformation sedimentary structures macro and mesoscale are used to identify constructional deformation where deformational units are preserved one on top of another due to the formation of a thin deforming layer by low basal stresses and excavational deformation in which the deformational style is superimposed on pre existing styles due to increasing thicknesses of glacier deformation caused by increasing basal shear stresses thin section micromorphology has been used to define a range of glacial processes of which subglacial deformation is just one but has drawn attention to critical criteria such as discrete microscale shears orientated matrix kink structures and fractured grains as well as deformed intraclasts that can be used to recognise deformational processes more recently individual aggregates taking the form of rounded pebbles within till matrix have been shown to reflect rotational processes during glacial deformation and provide an additional mechanism to discrete shear within subglacial deformation and an explanation for the transport paths of subglacial materials finally measurements of sediment flow directions using clast macrofabric characteristics coupled with measurement of quantities of sediment transfered and detailed palaeoglacial properties have been used to determine the rates and scales of subglacial deformation associated with the formation of small scale glacier bedforms

the source of 90 day oscillations at wake island energetic 90 day oscillations of sea level have been intermittently observed at wake island in the western tropical pacific during the past 2 decades the oscillations tend to occur about 1 5 years after el nino southern oscillation events to have amplitudes of 10 15 cm and to persist for about 1 year sea surface heights from the geosat altimeter are used to establish that these signals take the form of rossby waves and have an energy source near the big island of hawaii which lies 40 of longitude to the east sea level and upper layer currents from an eddy resolving numerical model are examined and suggest that the energy source is eddies generated off the big island of hawaii these eddies appear to be associated with westward currents that intermittently impinge on the island several alternate hypotheses are also discussed and rejected

ocean response to wind sheltering in the southern california bight 1 a particularly warm surface oceanic wake persisted during the period 6 16 june 1999 in the south eastern part of santa catalina island in the southern california bight from satellite images regional atmospheric model results and hydrographic measurements around catalina island a strong correlation appears between observed sea surface temperature wind stress and surface stratification it is suggested that the warm island wake was probably due to lower turbulent mixing rates associated with wind sheltering effect we argue that the sheltering effect may also account for a portion of the relatively warm sea surface temperature characteristic of the whole bight opposing previous arguments that temperature evolution of the surface ocean in this region is primarily driven by lateral advective fluxes

evidence against pervasively deformed bed material beneath rapidly moving lobes of the southern laurentide ice sheet abstract during the wisconsin glaciation the ice lobes of the southern part of the laurentide ice sheet moved rapidly as the result of elevated subglacial water pressure the rapid movement was probably not accompanied by wide spread pervasive deformation of unfrozen material under the ice the till stratigraphy of much of this area is well known and it is clear that the stratigraphic sequence is generally intact therefore such deformation if it occurred would have been restricted to the till sheet that was currently being deposited however this seems unlikely as well because the till of the region commonly contains lenses and clasts of unlithified bedded sand that should have been destroyed by pervasive shearing if unfrozen deformed till layers were widely present they must have been confined to the thin upper parts of till sheets

formation of niningerite by silicate sulfidation in eh3 enstatite chondrites unequilibrated eh chondrites contain silica bearing chondrules with abundant niningerite mg fe mn s and troilite fes distinguishing them from the silica bearing chondrules in ordinary and carbonaceous chondrites the conventional explanation for the origin of niningerite and oldhamite cas is that they are condensates from c rich nebular gas however models of condensation from a solar gas with an elevated c o ratio predict mineralogy that is inconsistent with petrographic observations we report petrographic and chemical evidence from 45 silica bearing chondrules from the eh3 chondrites sahara 97072 and alan hills 84170 for formation of niningerite and oldhamite by sulfidation of ferromagnesian silicates the results indicate extensive thermal processing of the chondrules including melting before during and after sulfidation bulk compositions of chondrules exhibiting varied degrees of sulfidation suggest that depletion of mg and enrichment of fe mn and na accompany the reactions sulfidation of feo bearing silicates which formed at oxidizing conditions at least iw 3 can occur with exposure to a h poor c and s rich gaseous reservoir 6 8 fo2 log units below the iw buffer at temperatures high enough for partial melting of silicates physicochemical analysis of mineral reactions inferred from sulfidized chondrules suggests a melted metal sulfide assemblage in a h poor environment is capable of generating sufficient s vapor to drive sulfidation the reaction of silicates with the s gas will result in progressive extraction of fe ca and mg into sulfides with the stoichiometric amounts of silica either reacting with olivine to form enstatite or when olivine is exhausted precipitating as free silica the sulfidation environment drastically increases mg volatility resulting in evaporative loss until saturation in the ambient gas is reached the newly formed mg rich niningerite will tend to reach equilibrium composition by losing mg and gaining fe plus mn from the ambient gas consistent with the observed chemical fractionation in the sulfidized chondrules therefore sulfidation of ferromagnesian silicates can also explain the low bulk mg si ratios of the enstatite chondrites if the sulfidizing gas was lost before accretion of the enstatite chondrite parent body

extreme sea level events at hawaii influence of mesoscale eddies 1 the highest daily mean sea levels recorded at the honolulu harbor tide gauge occurred during september 2003 examination of tide gauge satellite altimeter and hydrographic measurements in the region indicate that the extreme event was largely due to an anticyclonic eddy with offshore amplitude of about 15 cm and a diameter of 300 km the eddy propagated from approximately 3 000 km to the east over a one to two year period although eddies of this size are not uncommon at hawaii the september 2003 sea level was extreme because the eddy coincided with high periods in both the seasonal and decadal cycles and because sea level at honolulu has been rising at 1 5 cm decade for the past century this long term trend has increased the impact of short term events on coastal sea level prediction of such events requires real time altimeter data and improved modeling near hawaii

petrology and oxygen isotope compositions of chondrules in e3 chondrites chondrules in e3 chondrites differ from those in other chondrite groups many contain near pure endmember enstatite fs 1 some contain si bearing feni metal cr bearing troilite and in some cases mg mn and ca sulfides olivine and more feo rich pyroxene grains are present but much less common than in ordinary or carbonaceous chondrite chondrules in some cases the feo rich grains contain dusty inclusions of metal the oxygen three isotope ratios 18o 17o of olivine and pyroxene in chondrules from e3 chondrites which are measured using a multi collection sims show a wide range of values most enstatite data plots on the terrestrial fractionation tf line near whole rock values and some plot near the ordinary chondrite region on the 3 isotope diagram pyroxene with higher feo contents 2 10 wt feo generally plots on the tf line similar to enstatite suggesting it formed locally in the ec enstatite chondrite region and that oxidation reduction conditions varied within the e3 chondrite chondrule forming region olivine shows a wide range of correlated 18o and 17o values and data from two olivine bearing chondrules form a slope 1 mixing line which is approximately parallel to but distinct from the ccam carbonaceous chondrite anhydrous mixing line we refer to this as the ecm enstatite chondrite mixing line but it also may coincide with a line defined by chondrules from acfer 094 referred to as the pcm primitive chondrite mineral line ushikubo et al 2011 the range of o isotope compositions and mixing behavior in e3 chondrules is similar to that in o and c chondrite groups indicating similar chondrule forming processes solid gas mixing and possibly similar 16o rich precursors solids however e3 chondrules formed in a distinct oxygen reservoir internal oxygen isotope heterogeneity was found among minerals from some of the chondrules in e3 chondrites suggesting incomplete melting of the chondrules survival of minerals from previous generations of chondrules and chondrule recycling olivine possibly a relict grain in one chondrule has an r chondrite like oxygen isotope composition and may indicate limited mixing of materials from other reservoirs calcium aluminum rich inclusions cais in e3 chondrites have petrologic characteristics and oxygen isotope ratios similar to those in other chondrite groups however chondrules from e3 chondrites differ markedly from those in other chondrite groups from this we conclude that chondrule formation was a local event but cais may have all formed in one distinct place and time and were later redistributed to the various chondrule forming and parent body accretion regions this also implies that transport mechanisms were less active at the time of and following chondrule formation

high porosity of basal till at burroughs glacier southeastern alaska debris rich basal ice at burroughs glacier southeastern alaska has 60 vol to 70 vol debris recently deposited basal till exceeds 60 vol sediment with 30 to almost 40 porosity where basal ice is very rich in debris basal till is deposited through melt out with only slight compaction of the debris porosity this high in till is commonly associated with subglacially deforming and dilated sediment however the recently deposited basal melt out till at burroughs glacier has not been deformed after deposition but has porosity values similar to tills elsewhere interpreted to be subglacially deforming and dilated in an unfrozen state high porosity can occur in basal melt out till deposited directly by basal melt out

circumventing rain related errors in scatterometer wind observations satellite scatterometer observations of surface winds over the global oceans are critical for climate research and applications like weather forecasting however rain related errors remain an important limitation largely precluding satellite study of winds in rainy areas here we utilize a novel technique to compute divergence and curl from satellite observations of surface winds and surface wind stress in rainy areas this technique circumvents rain related errors by computing line integrals around rainy patches using valid wind vector observations that border the rainy patches the area averaged divergence and wind stress curl inside each rainy patch are recovered via the divergence and curl theorems we process the 10 year quikscat dataset and show that the line integral method brings the quikscat winds into better agreement with an atmospheric reanalysis largely removing both the divergence bias and anticyclonic curl bias in rainy areas noted in previous studies the corrected quikscat wind stress curl reduces the north pacific midlatitude sverdrup transport by 20 30 we test several methods of computing divergence and curl on winds from an atmospheric model simulation and show that the line integral method has the smallest errors we anticipate that scatterometer winds processed with the line integral method will improve ocean model simulations and help illuminate the coupling between atmospheric convection and circulation

the oxygen isotopic record in enstatite meteorites oxygen isotopic compositions were determined for a suite of enstatite chondrites and aubrites in agreement with previous work clayton et al 1984 most samples have o isotopic compositions close to the terrestrial fractionation line tfl and there appear to be no significant differences in o isotopic compositions between individual eh and el chondrites and aubrites five enstatite meteorites have o isotopic compositions that are significantly different from the other samples and 0 2 away from the tfl two of these have petrographic evidence of brecciation and interaction between other meteorite types for the other three similar scenarios are suggested there appears to be a systematic increase in 18o from enstatite chondrites both eh and el of petrologic type 3 to those of type 6 there is also good evidence that the eh meteorites do not fall along a mass fractionation line but along a line slope 0 66 at the present time detailed understanding of the origin of these o isotopic systematics remain elusive but clearly point to a complex accretion history parent body evolution or both

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

zonal jets in the pacific ocean 1 the spatial and temporal properties of zonally coherent jet like structures found in high resolution ocean models is examined we focus on the pacific ocean we find the properties of the jets are not very sensitive to the model configuration distinct differences are found in the persistence and vertical structure of the jets poleward of 30 n and s compared with those in the tropics we make a quantitative comparison between the meridional scale of the jets and the rhines scale we find a local scaling applies in that the horizontal variation of the meridional scale of the jets is consistent with horizontal variations in the rhines scale

the 3d microscopic signature of strain within glacial sediments revealed using x ray computed microtomography abstract x ray computed microtomography ct a non destructive analytical technique was used to create volumetric three dimensional 3d models representing the internal composition and structure of undisturbed pro and subglacial soft sediment sample plugs for the purposes of identifying and analysing kinematic indicators the technique is introduced and a methodology is presented addressing specific issues relating to the investigation of unlithified polymineralic sediments six samples were selected based on their proximity to type brittle and ductile deformation structures or because of their perceived suitability for successful application of the technique analysis of a proglacial ideal specimen permitted the 3d geometry of a suite of micro faults and folds to be investigated and the strain history of the sample reconstructed the poor contrast achieved in scanning a diamicton of glaciomarine origin is attributable to overconsolidation under normal loading the sediment demonstrated to have undergone subsequent subglacial deformation another overconsolidated diamicton contains an extensive small scale the subglacial sample evidence indicates that complex polyphase brittle ductile deformation histories are common in such diamictic soft sediments and that the local micro scale environment composition structure shear forces and effective pressure controls rheology the sediment void ratio is a key indicator of strain three of the samples are tentatively placed at different points on the strain cycle for subglacially deforming soft sediment based on their void ratio characteristics and distribution it has been demonstrated that ct offers significant potential for elucidating glacial soft sediment kinematics the ability of the technique to both test a variety of hypotheses pertaining to mechanisms operating within the subglacial environment and evaluate efforts to replicate those processes under controlled laboratory conditions is therefore discussed along with solutions to the problems encountered within this project ct also permits the seamless linking of analytical techniques applied at the hand specimen mm micromorphological m mm scanning electron microscopy and x ray diffraction fluorescence nm m scales and the archiving duplication and dissemination of sample volumetric 3d data

clastic matrix in eh3 chondrites patches of clastic matrix 15 to 730 m in size constitute 4 9 vol of eh3 yamato y 691 and 11 7 vol of eh3 allan hills alh 81189 individual patches in y 691 consist of 1 25 vol relatively coarse opaque grain fragments and polycrystalline assemblages of kamacite schreibersite perryite troilite some grains with daubreelite exsolution lamellae niningerite oldhamite and caswellsilverite 2 30 vol relatively coarse silicate grains including enstatite albitic plagioclase silica and diopside and 3 an inferred fine nebular component 45 vol comprised of submicrometer size grains clastic matrix patches in alh 81189 contain relatively coarse grains of opaques 20 vol kamacite schreibersite perryite and troilite and silicates 30 vol enstatite silica and forsterite as well as an inferred fine nebular component 50 vol the o isotopic composition of clastic matrix in y 691 is indistinguishable from that of olivine and pyroxene grains in adjacent chondrules both sets of objects lie on the terrestrial mass fractionation line on the standard three isotope graph some patches of fine grained matrix in y 691 have distinguishable bulk concentrations of na and k inferred to be inherited from the solar nebula some patches in alh 81189 differ in their bulk concentrations of ca cr mn and ni the average compositions of matrix material in y 691 and alh 81189 are similar but not identical matrix in alh 81189 is much richer in mn 0 23 0 05 versus 0 07 0 02 wt and appreciably richer in ni 0 36 0 10 versus 0 18 0 05 wt than matrix in y 691 each of the two whole rocks exhibits a petrofabric probably produced by shock processes on their parent asteroid

theory of glacial erosion transport and deposition as a consequence of subglacial sediment deformation a theory of erosion transport and deposition of unlithified sediments by glaciers is presented it predicts the large scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle together with the resultant intensity of large scale lincations drumlins which will be incised in the landscape the theory also predicts the dispersal patterns of subglacial lithologies together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till it predicts major erosional discontinuities within tills and the formation of boulder pavements it suggests that the dominant proportion of the lowland tills produced by pleistocene mid latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine grained the theory is based on an analysis of glacier dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition

a global oceanic data assimilation system abstract a global oceanic four dimensional data assimilation system has been developed for use in initializing coupled ocean atmosphere general circulation models and many other applications the data assimilation system uses a high resolution global ocean model to extrapolate the information forward in time the data inserted into the model currently consists only of conventional sea surface temperature observations and vertical temperature profiles the data are inserted continuously into the model by updating the model s temperature solution every timestep this update is created using a statistical interpolation routine applied to all data in a 30 day window centered on the present timestep large scale features in the sea surface temperature analyses are consistent with those from independent analyses subsurface fields created from the assimilation are much more realistic than those produced without the insertion of data furthermore information contained in the assimilation field is shown to be re

aerial observations of hawaii s wake abstract under the influence of the east northeasterly trade winds the island of hawaii generates a wake that extends about 200 km to the west southwest during the harp project in july and august 1990 five wake surveys were carried out by the ncar electra the patterns of wind and aerosol concentration revealed by these flights suggest that hawaii s wake consists of two large quasi steady counterrotating eddies the southern clockwise rotating eddy carries a heavy aerosol load due to input from the k volcano at the eastern end of the wake the eddies are potentially warmer and more humid than the surrounding trade wind air several other features are discussed sharp shear lines near the northern and southern tips of the island dry and warm air bands along the shear lines a small embedded wake behind the kohala peninsula wake centerline clouds hydraulic jumps to the north and south of the island a descending inversion connected with accelerating trade winds and evidence for side to side wake mo

on the formation of subtropical countercurrent to the west of the hawaiian islands 1 analysis of recent ocean model assimilation results suggest that the eastward countercurrent in the northern subtropical pacific may be divided into two branches one in the northwestern pacific 19 n 27 n to the west of 170 e and the other to the west of the hawaii islands to the west of the 158 w along 19 n 20 n two mechanisms contribute to the formation of the eastward countercurrent to the west of hawaii first the hawaiian islands blocks the easterly trade winds and generates a dipole of wind stress vorticity with positive wind curl to the north of the islands 20 n 23 n and with negative curl to the south 16 n 19 n this dipole of wind stress vorticity acts to create an eastward current jet to the west of the hawaii island through the sverdrup relation second the islands can directly block the westward north equator current nec to generate an eastward current to the west of the islands we use a numerical model to test these mechanisms for the generation of the eastward countercurrent to the west of the hawaii islands the results show that while the dipole of the wind stress vorticity is helpful in the forming of the eastward countercurrent and as the nec impinges upon the islands the westward traveling vortex streets formed in the ocean plays a key role in intensifying the eastward current to the west of the hawaiian islands

interactions among the winter monsoon ocean eddy and ocean thermal front in the south china sea 1 sea surface temperature sst in boreal winter shows a robust feature of ocean front west of luzon island where a cyclonic ocean eddy is associated with the winter northeast monsoon our analyses further show that cold warm water is located in the northwest southeast part of the luzon eddy due to ocean advection forming the west luzon front the results suggest a novel mechanism of the positive feedback among the winter monsoon ocean eddy and ocean front over the south china sea a strong positive wind stress curl associated with the winter monsoon and mountainous islands produces the luzon eddy with eddy heat advection the luzon eddy is accompanied by negative positive sst anomalies in the northwest southwest part of the eddy inducing the west luzon thermal front the sst anomalies can further force an anomalous wind pattern that converges onto the positive sst anomalies and diverges from the negative sst anomalies the anomalous wind distribution in turn enhances the positive wind stress curl west of luzon island

soft lodgement till deposition and syndepositional deformation anielinek the polish lowlands the paper presents a case study of sediment termed soft lodgement till a product of subglacial deposition by active ice described previously on the basis of macro evidence from poland and canada but not yet studied in detail in one particular site the till at anielinek about 7 m thick was examined by macroscopic observation thin section description and qualitative and quantitative scanning electron microscopy sem analyses it shows a macroscopic massive structure and overlies a flat top of glaciolacustrine sediments these sediments form upward intrusions within the till owing to the existence of reversed density gradients among the deposits and the upper parts of the intrusions are tilted in consistent directions within the successive parts of the till moreover sem images also record uniformly oriented microintrusions within this diamictic material the occurrence of these macro and microstructures within the successive parts of the till point to an almost continuous process of intrusion du

interannual variability of the north pacific subtropical countercurrent and its associated mesoscale eddy field interannual changes in the mesoscale eddy field along the subtropical countercurrent stcc band of 188 258n in the western north pacific ocean are investigated with 16 yr of satellite altimeter data enhanced eddy activities were observed in 1996 98 and 2003 08 whereas the eddy activities were below average in 1993 95 and 1999 2002 analysis of repeat hydrographic data along 1378e reveals that the vertical shear between the surface eastward flowing stcc and the subsurface westward flowing north equatorial current nec was larger in the eddy rich years than in the eddy weak years by adopting a 2 layer reduced gravity model it is shown that the increased eddy kinetic energy level in 1996 98 and 2003 08 is because of enhanced baroclinic instability resulting from the larger vertical shear in the stcc nec s background flow the cause for the stcc nec s interannually varying vertical shear can be sought in the forcing by surface ekman

summer upwelling in the south china sea and its role in regional climate variations seasonal and interannual variations of summer upwelling off the south vietnam coast and the offshore spread of cold water are investigated using a suite of new satellite measurements in summer as the southwesterly winds impinge on annam cordillera a north south running mountain range on the east coast of indochina a strong wind jet occurs at its southern tip offshore east of saigon resulting in strong wind curls that are important for ocean upwelling off the coast in july and august an anticyclonic ocean eddy develops to the southeast advecting the cold coastal water offshore into the open south china sea scs the center of this cold filament is located consistently north of the wind speed maximum indicating that open ocean upwelling helps to cool the ocean surface corroborating evidence for the cold filament is found in ocean color observations that reveal a collocated tongue of high chlorophyll concentration the development of this cold filament disrupts the summer warming of the scs and causes a pronounced semiannual cycle in sst moreover the cold filament is an important player in interannual variability in the summer scs in 1998 the cold filament and mid summer cooling never took place giving rise to a strong basin wide surface warming interannual sst variance has a local maximum over the climatological cold filament and is much greater than the variance over the adjacent indian and western pacific oceans a cold filament index is constructed which displays significant lagged correlation with sst in the eastern equatorial pacific and indian oceans indicative of a teleconnection from el nino

microscopic evidence of subglacial deformation abstract subglacial deformation is by now a well established process however recognition of this process in pleistocene tills is not always clear studies of thin sections of pleistocene tills show that there are a variety of microscopic features caused by deformation this paper gives a review of microscopic evidence for subglacial deformation and starts with a case where deformation could be established macroscopically then traces the microscopic features through planar and rotational movements which are described and separated accordingly attention is also given to features caused by crushing of grains and sediment dewatering these studies indicate that almost all basal tills show evidence of subglacial deformation rather than sedimentary derivation this implies that if we want to understand subglacial processes such tills should be described in tectonic rather than sedimentary terminology

covariations of sea surface temperature and wind over the kuroshio and its extension evidence for ocean to atmosphere feedback abstract satellite microwave measurements are analyzed revealing robust covariability in sea surface temperature sst and wind speed over the kuroshio extension ke east of japan ocean hydrodynamic instabilities cause the ke to meander and result in large sst variations increased reduced wind speeds are found to be associated with warm cold sst anomalies this positive sst wind correlation in ke is confirmed by in situ buoy measurements and is consistent with a vertical shear adjustment mechanism namely an increase in sst reduces the static stability of the near surface atmosphere intensifying the vertical turbulence mixing and bringing fast moving air from aloft to the sea surface south of japan the kuroshio is known to vary between nearshore and offshore paths these paths are very persistent and can last for months to years as the kuroshio shifts its path coherent wind changes are detected from satellite data in particular winds are high south of tokyo when the kuroshio takes the near

glider observations of a mesoscale oceanic island wake abstractin this study a 2 yr time series of velocity profiles to 1000 m from meridional glider surveys is used to characterize the wake in the lee of a large island in the western tropical north p

evidence for relict grains in chondrules of qingzhen an e3 type enstatite chondrite abstract petrographic and chemical studies of the qingzhen chondrite strongly suggest that it is the most highly unequilibrated type 3 enstatite chondrite recognized so far qingzhen contains abundant well defined chondrules some of which were incompletely molten during the chondrule formation process the relict olivine grains within these chondrules contain dusty inclusions of almost pure metallic fe which appear to be the in situ reduction product of the fayalitic component of the olivine the reduction process presumably took place at the time of chondrule formation and the chondrule precursor material must have been more oxidized than average enstatite chondrite material we believe that this oxidized material may have formed at the enstatite chondrite formation location in the solar nebula provided fluctuations in the degree of oxidation of the nebular gas existed at such locations reheating of this material under more reducing conditions would lead to the observed reduction of the olivine igneous olivines within chondrules always contain detectable amounts of cao while relict olivines are essentially cao free this seems to suggest that the relict olivines did not originate during a previous igneous process of chondrule formation and might represent condensation products from the early solar nebula

atmospheric manifestation of tropical instability wave observed by quikscat and tropical rain measuring mission observations from two new spaceborne microwave instruments in 1999 clearly reveal the atmospheric manifestation of tropical instability waves north of the pacific equatorial cold tongue a unique zonal temporal band pass filter enables the isolation of the propagating signals and the determination of their phase differences the phase differences between the propagation of wind and sea surface temperature sst signals observed from space and the vertical wind profiles measured from a research ship are consistent with the hypothesis that the coupling between wind and sst is caused by buoyancy instability and mixing which reduces the wind shear in the atmospheric boundary layer the coupling causes higher evaporative cooling over the warm phase and infers a negative thermal feedback

unusually abundant refractory inclusions from sahara 97159 eh3 a comparative study with other groups of chondrites abstract sixty eight refractory inclusions and fragments were found in two polished thin sections of the sahara 97159 eh3 chondrite indicative of the highest abundance of refractory inclusions 22 cm 2 or 0 06 vol in enstatite chondrites studied to date all of the inclusions are intensely altered mainly producing feldspathoids and albite cao depletion and minor ti rich compounds such as ti sulfides the alteration assemblages and feo poor spinel suggest that the reactions took place under reducing and sio 2 rich conditions this is consistent with the redox state of the host enstatite chondrite the presence of ti sulfides and low feo alteration phases distinguishes alteration of e chondrite refractory inclusions from that of carbonaceous and ordinary chondrites most of the inclusions are referred to as type a like 35 and spinel rich 26 respectively assuming melilite has been altered these inclusions could be analogues of individual concentrically zoned objects of fluffy melilite spinel rich type a and spinel pyroxene rich inclusions from carbonaceous chondrites such as the ningqiang cv anomalous and y 81020 co3 chondrites two inclusions consist mainly of ca pyroxene fine grained alteration products feldspathoids and albite and spinel they are probably altered fragments of ca pyroxene plagioclase rich type c inclusions assuming all plagioclase has been altered to produce the fine grained groundmass five other inclusions are hibonite and or corundum bearing similar to those reported in carbonaceous chondrites abundance ratios of various types of the inclusions from sahara 97159 are similar to those from ningqiang and y 81020 most of the observations including mineral assemblages mineral chemistry texture bulk compositions o isotopic compositions and ree patterns of the sahara inclusions suggest a common reservoir of refractory inclusions in enstatite ordinary and carbonaceous chondrites the apparent differences such as absence of melilite and anorthite rare wark lovering rim and small size can be explained by intense alteration due to large change of postformation environment of these inclusions size sorting and collision during transfer hence these differences are not inconsistent with the common reservoir model refractory inclusions in non carbonaceous chondrites may put additional constraints on origins of refractory inclusions and provide hints for a spatial relationship of their host meteorites

subtropical countercurrent in an idealized ocean gcm abstract in the north pacific there is a shallow eastward current called the subtropical countercurrent which flows across the central subtropical gyre the present article studies the generation mechanism of the subtropical countercurrent reproduced in an ocean general circulation model gcm with a simple geometry driven by surface wind stress and surface buoyancy forcing in the ocean gcm the deep mixed layer occurs in the northern part of subtropical gyre and shoals abruptly in the central subtropical gyre the mixed layer front the narrow transition zone of the mixed layer depth slants from the western central subtropical gyre to the northeast and the low potential vorticity fluid is formed at the intersection of the mixed layer front and the outcrop line since the surface density is almost zonally uniform and the mixed layer front slants northeastward the minimum potential vorticity fluids on denser isopycnals are formed in the northeastern region while those on lighter isopycnals are form

deformation till in the great lakes region implications for rapid flow along the south central margin of the laurentide ice sheet structural and lithologic data indicate that while deposited under actively moving ice considerable portions of three muddy calcareous subglacial tills in the great lakes region probably experienced some component of ductile deformation viscous till flow and ductile shear are invoked to explain a combination of features such as recumbent isoclinal folds unlithified sediment clasts mixed ostracode shells reversed stone lee ends girdle and transverse fabrics irregular stone pavements fine striae following stone curves and inconsistent stone striae and a axes deforming fine textured subglacial till is considered as a subhorizontal shear zone rheologically layered with associated structures in descending order ductile e g isoclinal folds brittle ductile e g fissility and brittle e g till wedges rheology would be controlled mainly by till pore water content matrix texture and stone content spatial and temporal superposition of rheologies and subglacial processes probably occur

linear wind forced beta plumes with application to the hawaiian lee countercurrent abstracttwo numerical ocean models are used to study the baroclinic response to forcing by localized wind stress curl i e a wind forced plume which is a circulation cell developing to the west of the source region and composed of a set of zonal jets with implications for the hawaiian lee countercurrent hlcc an idealized primitive equation model regional ocean modeling system roms and a global eddy resolving general circulation model ocean general circulation model for the earth simulator ofes in addition theoretical ideas inferred from a linear continuously stratified model are used to interpret results in roms vertical mixing preferentially damps higher order vertical modes the damping thickens the plume to the west of the forcing region weakening the near surface zonal jets and generating deeper zonal currents the zonal damping scale increases monotonically with the meridional forcing scale indicating a dominant role of vertical viscosity over diffusion a consequence of the