isotope dating of waters at fram iii measurements of tritium helium 3 together with salinity yield 11 years as arctic basin residence time of the halocline waters in the arctic outflow in the fram strait radiocarbon and tritium data on the deeper waters point at some penetration of surface waters down to 1500 m during the last 20 years even at 2500 m the 14c activity is within 1 80 years of modern pre bomb values

vertical profile of artificial radionuclide concentrations in the central arctic ocean abstract the artificial radionuclides 90 sr 137 cs 238 pu 239 240 pu and 241 am have been measured in eight water samples collected in 1979 at intervals from surface to bottom through the ice at the lorex satellite camp ss near the north pole differences in the concentrations and ratios of these nuclides compared with values measured over time in the various water masses that flow into the arctic ocean can be used as semi independent checks on rates of flow to the lorex stations and on residence times in the arctic ocean an unexpected finding was that water labelled with low level liquid waste from the windscale plant on the irish sea is a major component of the 1500 m lorex sample and has reached there in no more than eight to ten years even from this one station in the polar ocean estimation of the inventories of the various radionuclides is good enough to emphasize the importance of horizontal advection of the various supply terms to the arctic

the biogeochemistry of aluminum in the pacific ocean abstract vertical distributions and horizontal surface transects of dissolved and particulate al at several locations in the pacific ocean are presented here concentrations of dissolved al in the pacific range from 0 3 to 5 nmol kg in the surface waters from 0 1 to 1 nmol kg in mid depths and from 0 5 to 2 nmol kg in the deep waters from these data and published data from other regions it is evident that al has a unique oceanic chemistry relative to that of other metals external sources and rapid particle scavenging throughout the water column are the major controls on dissolved al distributions in the oceans vertical profiles generally exhibit a surface maximum a mid depth minimum and increasing concentrations toward the sediment water interface this suggests two sources of dissolved al one to the surface waters and one to the deep waters concentrations of dissolved al in surface waters are lowest within the eutrophic low salinity california current 0 3 1 nmol kg and increase westwardly into the subtropical gyre of the north pacific 5 nmol kg values in the south pacific gyre are fivefold lower these horizontal trends indicate that the primary source of dissolved al to the surface waters of the central pacific is from eolian input dissolved al supplied by rivers to the eastern north pacific appears to be rapidly scavenged in estuaries and or the highly productive coastal region the source of dissolved al to the deep waters is not known but could be due to a flux out of the sediments or a remineralization process suspended particulate al concentrations increase with depth at all stations and decrease with distance from the ocean boundary surface values range from 1 5 nmol kg near shore to 0 3 nmol kg in the central gyres of the pacific deep water concentrations range from 22 nmol kg near shore to 4 nmol kg in the north pacific central gyre and decrease to 1 3 nmol kg in the south pacific central gyre observed distributions indicate that suspended particulate al varies with the intensity of bottom sediment resuspension and the horizontal mixing of the resulting nepheloid layer out from ocean boundary regions particle residence times estimated are consistent with other reported values

variability in deep exchange between the eurasian and greenland basins evidence from tritium and helium 3 observations of decay corrected tritium in the deep eurasian basin and northern fram strait since 1979 indicate a significant decrease in 1993 whereas a box model predicts a steady decline with time the model simulates the greenland sea and eurasian basin deep water observations reasonably closely up to the early 1990s when it is retuned to simulate the 1993 decrease in the deep eurasian basin water tritium the deep exchange between the greenland sea and eurasian basin occurs over a shorter time scale this is likely in response to the reduced deep water formation in the greenland sea in the early 1980s modeled tritium in the deep eurasian basin shows the same trends as in the greenland sea and deep norwegian sea but with time lags of 8 2 y and 17 2 y respectively these lags are in close agreement with values indicated by tritium helium3 dating

critical levels and mixing layers induced by convectively generated gravity waves during cepex we study data from the central equatorial pacific experiment in particular the soundings providing temperature pressure wind and ozone profiles and we link them to the large scale conditions deduced from the analyses of the european centre for medium range weather forecasts to the west of the date line the mean wind shows a strong shear at the tropopause between the easterlies of the upper troposphere and the westerlies of the lower stratosphere these are conditions propitious to the formation of critical levels for quasi stationary gravity waves generated by deep convection the measured wind profiles show the main characteristics of the encounter of a wave with its critical level and in the ozone and potential temperature profiles the existence of a conspicuous mixing layer in the vicinity of this critical level our interpretation that the mixing layer is a consequence of the critical level is supported by numerical simulations with a nonlinear time dependent two dimensional model the occurrence of a mixing layer in the tropopause structure seems to be characteristic of large scale equatorial convective areas during westerly phases of the quasi biennial oscillation

mechanisms controlling the distribution of helium and neon in the arctic seas the case of the knipovich ridge abstract helium concentration and isotopic ratio in the ocean are influenced by four sources the mantle atmosphere crust and tritium decay in addition the concentration of dissolved gases can be altered by air injection and ice related mechanisms such as brine rejection sea ice melting and glacial melting especially in the high latitude seas the knipovich ridge a northern continuation of the mid atlantic ridge 74 79 n 6 8 e is potentially affected by all the sources and mechanisms mentioned above this suggests that the ridge should be a good place to investigate these mechanisms during the knipovich 2000 expedition water samples were collected for helium and neon analysis along the axis of the ridge although mn and ch 4 results suggest the existence of hydrothermal activity in the ridge we could not detect a significant increase of helium isotopic ratio 3 he 4 he at corresponding water depths instead the bottom waters in the northern section of the ridge were supersaturated by up to 40 for 4 he the helium isotopic ratio of 1 3 10 6 indicates the dominance of atmospheric helium using he and ne saturation anomalies we further explored the mechanisms affecting the distribution of helium and neon in the ridge around 5 supersaturation of he and ne at most deep waters is explained by air injection and brine rejection however the large excess in the northern ridge was attributed to the input of 2 5 glacial meltwater possibly originating from the glacier covered islands svalbard

feldspar influenced rock rheologies progressive fracture subsequent cataclasis and syntectonic alteration of feldspar to phyllosilicates transformed a massive granite into a quartz mica phyllonite during early tertiary deformation in a 20 30 m wide shear zone in southeastern arizona the ductile deformation proceeded at temperatures and pressures approximating middle to upper crustal levels most of the deformation was taken up by the feldspar and its alteration products quartz deformed by both brittle fracture and crystal plastic mechanisms these results show that under certain temperature pressure strain rate conditions feldspars are weaker than quartz the observed deformation mechanisms indicate that the brittle to ductile transition in fault zones is not simply a function of the onset of temperature activated plastic deformation in quartz nor of the frictional behavior of rocks as inferred in the familiar strength vs depth curves it is more likely that the transition is complex and depends on a variety of parameters one such factor delineated in this study is the fracture and fracture facilitated syntectonic alteration of feldspar under hydrated conditions

dissolved gas dynamics in perennially ice covered lake fryxell antarctica we use the concentrations of noble gases he ne and ar helium isotopes and tritium to characterize the mechanisms and rates of ventilation for lake fryxell antarctica as well as the physical processes controlling dissolved gases the upper oxic zone is ventilated on timescales of several decades the anoxic bottom waters are weakly ventilated with a turnover time of 3 800 years in the upper euphotic zone helium and neon are greatly undersaturated with respect to solubility equilibrium with the atmosphere whereas argon is greatly supersaturated owing to equilibrium partitioning of the gases between ice water and air inclusions in the ice in the bottom waters the inert dissolved gas concentrations may be remnants of a near desiccation event that occurred 2 000 years b p consistent with current paleoclimatic theories

water rock interactions in fault gouge measurements were made of the amounts of d 18o and h2o in fault gouge collected over a depth of 400 m in the san andreas fault of california the amounts and isotopic compositions of the pore fluids also analyzed suggest that formation waters from adjacent franciscan rocks have migrated into the gouge and mixed with local meteoric water thus the gouge is an open system permeable to fluid flow this permeability has important implications concerning heat flow along the fault zone

reply to comment on oxygen budget of a perennially ice covered antarctic lake top top et al 1983 1985 has found that in laboratory grown ice and in arctic ice floes 50 of the gas is retained in the ice upon freezing as top points out in his comment bari and hallett 1974 whom we cite in wharton et al 1986 actually discussed how and when the ice rejected dissolved gas gets back into the ice we did not misquote this reference careful examination of the bari and hallett paper will reveal that in their experiments bubbles cease abruptly at freezing rates below about 3 pm sl the freezing rate of the ice in the antarctic lakes is estimated to be 30 cm yrl which corresponds to 0 009 pm s l well below the limit of bubble formation the rate of freezing is an important variable in the exclusion of gas when water freezes hence we do not expect a significant amount of gas to be retained in the antarctic lake ice this is consistent with observations of the ice cover the results from laboratory experiments and arctic floes reported by top are not relevant since much higher freezing rates occur in these relatively thin ice environments indeed the thick stable perennial ice cover of an antarctic lake is unique in nature therefore it is not too surprising that arctic experience led top to an incorrect conclusion in conclusion we feel that our original assumption of 100 exclusion is indeed representative of the conditions in the antarctic lake top s other comments are based on his incorrect estimate of the gas retention and hence do not apply

dissolved al in sediments and waters of the east china sea implications for authigenic mineral formation abstract numerous previous studies indicate that several different authigenic aluminosilicates form in the oceans in this study we show using dissolved al distributions in sediments and waters from the nearshore regions of the east china sea that the process of aluminosilicate formation probably begins rapidly upon contact of detrital clays with seawater statistical analyses of dissolved al si h relations in surface sediments indicate that the minerals forming in east china sea sediments low in dissolved fe are dioctahedral chlorites with an average composition ex 0 91 mg 0 77 al 5 0 si 2 7 o 10 oh 8 where ex exchangeable 1 cation this composition is also consistent with dissolved al and si measurements as a function of salinity in turbid overlying waters results suggest a dissolution reprecipitation mechanism for clay mineral reconstitution this mechanism can help to explain why different authigenic clays are found in different areas of the oceans in the east china sea the total amount of authigenic clays present must constitute a very minor fraction of the bottom sediments thus the formation of these minerals has a relatively small impact upon dissolved si distributions clay mineral reconstitution in nearshore regions may provide a mechanism for buffering sediments and overlying waters with respect to ph as the composition of minerals formed should be a direct function of the h activity in the surrounding environment

the distribution of aluminium in the greenland sea and its relationship to ventilation processes during two cruises to the greenland sea in 1988 and 1989 a total of 690 on board aluminium al determinations were performed on samples collected from profiles located along four transects in the greenland sea as part of the greenland sea project al concentrations range from extremely low values 0 4 nm in the polar waters of the east greenland current draining the arctic ocean to 17 9 nm in the newly formed norwegian sea deep water nsdw at the periphery of the greenland gyre the al content in the component water masses serves to constrain the make up of these water masses from the various mixing products of the region the enrichment of al in the nsdw both at its site of formation within the greenland sea up to 17 9 nm and in the lofoten basin of the norwegian sea up to 40 3 nm leads to the conclusion that there must be an additional external source of al to these water masses the apparent inability of water column or sedimentary diagenetic processes to provide this enrichment and the observation of enriched al values associated with a high salinity shelf brine leads us to the conclusion that these brines may be responsible for the observed enrichments the high concentration of al in the greenland sea deep water compared with the water masses that produce it suggests that al may be acting as an inverse tracer of the processes that ventilate this basin by convective overturn i e the al concentration which increases with time as a result of continuous brine or other external inputs is reduced during convective events it is also argued that this flushing of elevated al water during convective events may have a similar counterpart in the iceland sea and that this mechanism could go some way toward solving the al deficit that exists between the enriched north atlantic deep water and its depleted precursor water masses observed in the intermediate waters of the greenland and iceland seas

the evolution of the dehydration in the antarctic stratospheric vortex in 1994 an intensive program of balloon borne frost point measurements was performed at mcmurdo antarctica during this program a total of 19 frost point soundings was obtained between february 7 and october 5 which cover a wide range of undisturbed through strongly dehydrated situations together with several soundings from south pole station between 1990 and 1994 they give a comprehensive picture of the general development of the dehydration in the antarctic stratospheric vortex the period of dehydration typically starts around the middle of june and a rapid formation of large particles leads to a fast dehydration of the vortex the evaporation of falling particles leads to rehydration layers which have significantly higher water vapor concentrations than the undisturbed stratosphere through the formation of these rehydration layers in the early stages of the dehydration we can estimate a particle fall speed of km d and thus a mean particle size of 4 m ice saturation was observed over mcmurdo in only two cases and only well after the onset of the dehydration from the inspection of synoptic maps it then follows that a small cold region inside the vortex seems to be sufficient to dehydrate the entire vortex above 20 km the dehydration is completed by the end of july from the descent of the upper dehydration edge we can estimate a mean descent rate inside the vortex of 1 5 km month in mcmurdo we observed occasional penetration of the vortex edge in cases where the vortex edge was close to mcmurdo however these cases seem to have little effect on the bulk of the vortex a sounding from november 3 1990 at south pole shows that the dehydration may persist into november and indicates that there is no significant transport into the vortex throughout winter and early spring

dissolved aluminium in the tamar estuary southwest england abstract distributions of dissolved al in the tamar estuary have been recorded through spring neap tidal cycles in winter and summer dissolved al is a highly reactive constituent in this estuary undergoing net removal in the very low salinity region and net input to the mid estuary the extent of both the depletion and the augmentation varied systematically with tidal energy input indicating that tidal sediment disturbance was the principal controlling agency these field data supported by the results of laboratory simulations show that the removal is regulated by sorption onto resuspended sediment particles which dominates kinetically over authigenic aluminosilicate formation removal of dissolved al by flocculation of riverborne colloids is not significant the mid estuarine input is consistent with dissolution of authigenic aluminosilicate following net remobilization of estuarine sediment the internal cycling of al in the estuary generated by these processes alters both the time course and the soluble particulate balance of the riverine discharge of al to the adjacent coastal water

hydrologic and geochemical properties of the san andreas fault at the stone canyon well the stone canyon well penetrates 600 m of highly fractured and severely altered quartz diorite intimately associated with the creeping segment of the san andreas fault of central california geophysical logs reveal a complex hydrology dominated by major fractures fluid pressure in some fractures is sufficient to prevent invasion of the formation by heavy drilling mud implying pore pressures at least 10 higher than hydrostatic ones at least three chemically distinct waters are encountered including a chloride brine clearly segregated from the shallow potable groundwater chemical alteration of the quartz diorite persists throughout the well far below the depth where the water rock reactions responsible for the ubiquitous chlorite and mixed layer clays can be considered weathering whole rock 18o analyses indicate significant interaction of the rocks with a low 18o fluid within some of the fractured and altered zones whereas a deeper sample shows18o enrichment high pore pressures encountered in stone canyon may be due to tectonic compression measurements of temporal variations in the pore pressure at the well may provide a means of predicting earthquakes along this segment of the san andreas fault

magnetotelluric imaging of the creeping segment of the san andreas fault near hollister 1 fluids may play a significant role in the earthquake rupture process since fluids can dramatically change the electrical resistivity of crustal rocks electromagnetic exploration methods can image in situ fault zone fluids magnetotelluric mt data has been collected on segments of the san andreas fault saf in central california exhibiting a range of seismic behavior from locked to creeping this paper describes mt data from the creeping segment of the saf near hollister california inversion models image a zone of enhanced conductivity beneath the surface trace of the saf that has similar geometry and greater depth extent than the fault zone conductor at parkfield comparison with geologic and seismic tomographic studies show this zone is bounded by the san andreas and calaveras faults and coincident with a zone of low seismic p wave velocities combined with previous mt studies this indicates a correlation between seismicity and the presence of fault zone fluids

the distribution of dissolved and total dissolvable aluminum in the beaufort sea and canada basin region of the arctic ocean 1 vertical profiles of the concentrations of dissolved al d al and total dissolvable al t al are reported from a transect extending from the continental shelf of the beaufort sea into the canada basin in the arctic ocean sampling was performed in late summer and early autumn 2007 a year of historically extensive sea ice melt vertical profiles of d al displayed surface maxima 1 3 nmol kg 1 subsurface minima 300 m depth suggest that al is likely lost through particle scavenging in the interior of the canada basin concentrations of t al show that particulate al 0 2 m is the dominant form of al in the water column except at greater depths at the most offshore stations lateral transport of d al and t al off the shelf likely results from the offshore progression of cyclonic eddies spawned inshore oscillating upwelling and downwelling favorable winds and brine rejection during sea ice formation that can drive currents sufficiently energetic to resuspend shelf sediments

aluminium in the northwest atlantic abstract a series of profiles between woods hole and bermuda has been measured on board ship for al the extrema in the upper waters can be explained by the accumulation of aeolian inputs in the thin summer mixed layer the depletion of the underlying winter water by scavenging during the spring bloom and the enrichment of the subtropical mode 18 c water by aeolian accumulation during winter and local convection before the spring bloom the pronounced minimum at mid depth is associated with the antarctic intermediate water and the underlying labrador sea med water complex presumably the aaiw and the med water are depleted by the ageing effect on this short residence time element during their transit to the area the lsw is formed from surface waters containing a large component of arctic waters extremely depleted in al advected south in the east greenland current the linear increase to the bottom is caused by mixing of enriched lower north atlantic deep water with the depleted bottom water and lsw cores the enrichment in the deep water appears to be produced by the entrainment of high al waters from the north european shelf by the gyre in the norwegian greenland sea and its injection into the denmark straits overflow waters in a manner recently described for the radiocaesium releases from the windscale reprocessing plant on the irish sea an additional contribution probably comes from the shelf north of iceland

geochemical profiles in the central arctic ocean their relation to freezing and shallow circulation temperature salinity nutrient tritium and oxygen isotope data collected during the lomonosov ridge experiment along a drift track between the makarov and fram basins over the lomonosov ridge are presented the relationship of these quantities to the processes that maintain the halocline in particular to the production of more saline waters by addition of brines formed during the freezing of seawater is described the results support the idea that the wide continental shelves of the arctic ocean play an important role in maintaining the halocline productivity and to the chemical and physical effects of freezing sea water a comparison of this ocean with its low productivity at least during winter with other oceanic regions should help to elucidate some of the effects of biological activity on marine chemistry for example trace metal cycling and speciation aagaard et al 1981 discussed the way in which the cold waters of the halocline which lie immediately below the surface mixed layer and extend to the top of the warm atlantic layer could be produced on the wide continental margins surrounding the arctic ocean the processes in volve freezing with release of highly saline brines having a temperature close to the freezing point of surface sea water this water flows over the shelves and into the central basin sinking then to the appropriate density surface the distribu tions of various chemical parameters will be affected in predictable ways by these processes as a part of the lomonosov ridge experiment lorex which ran from late march until the end of may 1979 a program was undertaken aimed at describing more accurate ly the hydrography of the central arctic ocean and studying the geochemistry of selected trace elements in this unusual environment to this end water samples were collected from a drifting ice station lorex satellite camp 1 for the measurement of salinity silicate phosphate 5 80 trace metals moore 1981 1983 carbon 14 tritium helium 3 caesium 137 caesium 134 strontium 90 plutonium ameri cium h d livingston et al manuscript in preparation 1983 alkalinity and ph ice cores were collected to investi gate the possibility of deducing the extent of temporal changes in the tritium content of the surface waters

oceanographic distributions of zinc cadmium copper and aluminium in waters of the central arctic vertical profiles are presented of dissolved cadmium zinc copper and aluminium at the lorex 79 site in the central arctic ocean cd zn and cu show unusually high surface concentrations of 0 3 3 and 5 nmoll 1 respectively these levels are related to contributions from surface run off and from the underlying nutrient rich bering sea winter water al has lower surface concentrations than observed elsewhere and shows no correlation with the nutrients the importance of aeolian supply is questioned and the results point to a major role for inorganic removal of al at least in the arctic ocean

the distribution of nutrients in the southeastern beaufort sea implications for water circulation and primary production hydrographic data collected above the shelf and slope in the southeastern beaufort sea show marked contrast in surface properties of nutrients temperature salinity and oxygen between august 1974 a year when ice remained close to shore and august 1975 a year with much open water the near surface properties are dominated by river inputs biological activity and the ice regime below the winter mixed zone 40 50 m properties are similar to those observed elsewhere in the arctic ocean bering sea water is detected at 50 60 m as a very weak signal in temperature nutrients and oxygen upwelling in both years was observed at the eastern side of mackenzie canyon this upwelling likely results from the interaction of coastal circulation with topography estimates of new productivity based on nutrient budgets are low 20 g c m 2 yr 1 compared to temperate coastal waters but fall in the range expected for the arctic in 1974 the heavy ice year turbid water and ice cover appear to have reduced new production by about 30 calculations show that this production over the shelf could potentially supply a significant portion of the nutrients found in the upper halocline over a wide region of the arctic ocean by regeneration at the shelf bottom and transport off the shelf in brine drainage

ventilation rates of the waters in the nansen basin of the arctic ocean derived from a multitracer approach tritium sup 3 he sup 14 c and helium neon data from a station located in the central nansen basin of the arctic ocean are reported and discussed it is demonstrated that sup 3 he is a valuable tracer for studies of the upper water column and together with tritium sup 3 he provides a rough time scale of the ventilation of these waters the apparent tritium sup 3 he age is about 7 years in the surface water and about 14 years in the lower part of the halocline water of atlantic origin defined by a temperature maximum shows tritium sup 3 he ages between 7 and 9 years this variation of ages indicates that the circulation of the individual water layers of the upper water column is largely decoupled and occurs on different time scales tritium sup 3 he ages observed in the arctic intermediate water suggest a ventilation on a time scale of 15 to 20 years depth 1 000 m the mean age of the eurasian basin bottom water is estimated on the basis of sup 14 c data to approximately 200 to 250 years there is no indication of noble gas fractionation due to sea ice formation below the surface layer from analysis of the sup 3 he backgroundmore it appears that there is a small primordial sup 3 he component in eurasian basin bottom water less

new evidence for the stratospheric dehydration mechanism in the equatorial pacific water vapor profile measurements obtained in the western and central pacific during the central equatorial pacific experiment cepex show a strong connection between the water vapor content near the tropopause and areas of deep convection we show that air ascending within deep convective towers can be dried to mixing ratios below 1 part per million by volume ppmv which is much lower than the average mixing ratio observed in the stratosphere a sharp increase of water vapor mixing ratio above the tropopause is an indication of the evaporation of ice particles at the top of deep convective cells a mixed layer of up to around 1 km thickness above the tropopause in the regions of deep convection is indicated by the vertical profiles of ozone water vapor and potential temperature furthermore a local maximum was observed at 20 km which is an indication for the seasonal cycle of the tropopause temperature

component separation of oceanic helium a new procedure to quantify the components of oceanic helium terrigenic 3he and 4he released from the ocean floor and tritiugenic 3he from tritium decay is described terrigenic he and nonatmospheric 3he i e terrigenic and tritiugenic combined are obtained in terms of measured concentrations of the he isotopes and also of neon ne which improves the separation considerably assuming terrigenic he to vanish in the mixed layer for the subsequent separation of terrigenic and tritiugenic 3he additional information is required and 3he due to natural tritium represents a complication the procedure is applied to data from a hydrographic section in the south atlantic 19 s 1991 and one in the eastern mediterranean 1987 the 1 data precisions and a systematic error accounting for uncertainties in mixed layer he are approximately 0 3 sections of the new representations of oceanic he and 3he and comparisons to the nearest classical quantities i e 3he he are presented in the south atlantic the 3he distribution reflects the hydrographic structure east of 20 w the average 3he 4he ratio of terrigenic he below 800 m is 4 5 0 8 times the atmospheric ratio which implies a substantial contribution of crustal he in the upper waters tritiugenic 3he 0 5 tritium units 20 is separated from terrigenic 3he in the eastern mediterranean tritiugenic 3he is quantified throughout the water column in the presence of substantial levels of terrigenic he the release rate of terrigenic he from the sea floor is found to be 3 1 1 2 1010 atoms m 2 s 1 similar to the rate for continental crust with a mantle he contribution of 5 1 2 only recommendations for future work are to reduce the mentioned systematic error and the uncertainty margins of the he and ne solubilities and of 3he due to natural tritium

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

the effect of deep tropical convection on the tropical tropopause layer 1 there is evidence that most detrainment from tropical convection occurs below 14 km about 2 km below the tropopause on the other hand it is also generally accepted that convection does occasionally reach the altitude of the tropopause the question is whether the relatively infrequent penetrations above 14 km are sufficient to influence the composition of the atmosphere above 14 km using o3 and co data as tracers of convective activity i quantify the height distribution of mass detraining from convection near the tropopause using data obtained in february 1996 the calculation suggests significant detrainment is occurring as high as 380 k potential temperature 17 km with as much as 60 of the mass crossing the 380 k surface detraining above 370 k 15 km these findings contrast with the previously published suggestion that convective transport of mass does not significantly influence the composition of the atmosphere above 14 km

the potential source of dissolved aluminum from resuspended sediments to the north atlantic deep water abstract laboratory and field studies were conducted to investigate the significance of resuspended sediments as a source of dissolved al to the deep northwest atlantic sediment resuspension experiments demonstrate the effect on dissolved al concentration initially 11 nm of adding natural suspended sediments ca 0 1 10 mg l to seawater the concentration of dissolved al increased by the resuspension of sediments for example addition of 0 15 mg l sediments caused dissolved al to increase by 10 nm distributions of dissolved and leachable particulate al off the tail of the grand banks near the highenergy western boundary current show elevated levels in the near bottom waters we suggest that resuspended sediments associated with nepheloid layers along the western boundary of the north atlantic are a source of dissolved al strong western boundary currents provide the energy to resuspend and maintain intense nepheloid layers of sediments continued resuspension and deposition of sediments within the nepheloid layer promotes the release of al from sediments to the overlying water the al rich terrigenous sediments that predominate along the deep boundary of the denmark strait labrador sea newfoundland and off nova scotia constitute a potentially significant source of dissolved al release of al from resuspended sediments associated with nepheloid layers at a more northern location e g denmark strait may contribute to the near linear increase in dissolved al with depth observed in the deep northwest atlantic

rheology and deformation mechanisms of an isotropic mica schist we have investigated the transitional semibrittle deformation of a mica schist 75 biotite by shortening cylinders cored at 0 45 and 90 to foliation to varying strains at confining pressures pc to 500 mpa constant strain rates e from 1 5 10 7 to 1 6 10 4 s 1 and temperatures t from 25 to 400 c deformation is concentrated within one or more throughgoing millimeter wide shear zones at all conditions these localize at low strains e 2 through the nucleation and coalescence of dense sets of intragranular microkink bands mkbs despite distinct differences in the relative number of mica grains oriented favorably for slip and kinking in different loading directions the differential stresses required for shear zone development vary little with fabric orientation biotite schist undergoes a transition from strain softening to steady strength mechanical response at confining pressures in the range 75 to 150 mpa the pressure sensitivity of strength characterized by the slope of the mohr envelope decreases from 0 5 at pc 100 mpa to 0 1 at pressures greater than 200 mpa reflecting the increasing contribution of glide and kinking in biotite at higher pressures however dilatancy associated with microcracking and void formation along mkb boundaries persists to at least 500 mpa within the pressure insensitive regime 200 pc 500 mpa temperature and strain rate dependencies of strength determined in stepping tests reveal a strong history dependence to flow that cannot strictly be described by a steady state constitutive law samples deformed in steps from low to high temperatures or fast to slow strain rates consistently exhibit stronger temperature and strain rate sensitivities than those deformed along t decreasing or e increasing paths path dependent effects may reflect differences in the degree to which inherited dislocation substructures are utilized or overprinted during later deformation increments by assuming an exponential relationship between differential stress d and strain rate e of the form e c exp d exp q rt we fit the data with two end member flow laws with a single activation energy q 89 kj mol and exponential constants ss 0 15 0 01 mpa 1 and ws 0 55 0 04 mpa 1 that account for the different responses observed along stepping paths that are strongly sensitive or weakly sensitive to t and e respectively application of the results to crustal deformation suggests that mica rich aggregates are weaker than other common rock types throughout a broad midcrustal depth range supporting the inference that retrograde reaction to phyllosilicates may be important in localizing crustal deformations within large faults and shear zones

a study of the depth of weathering and its relationship to the mechanical properties of near surface rocks in the mojave desert weathered granite extends 70 m deep at hi vista in the arid central mojave desert of southern california the low strength of this granite is due to the alteration of biotite and chlorite montmorillonite deep weathering probably occurs in most granites although we cannot rule out some anomalous mechanisms at hi vista geophysical instruments set in these slightly altered rocks are limited by the unstable behavior of the rocks thus tectonic signals from instruments placed in shallow boreholes give vague results geophysical measurements of these weathered rocks resemble measurements of granitic rocks near major faults the rheology of the rocks in which instruments are placed limits the useful sensitivity of the instruments

hafnium isotopes in arctic ocean water the first isotopic compositions of dissolved hafnium in seawater from across the arctic ocean are reported most samples from the four sub basins of the arctic ocean have values within error of an average of ehf 0 8 combined hf nd isotope compositions do not fall on the well established positive correlation for mantle and crustal rocks instead arctic waters have hf that is more radiogenic than that typically found in rocks with similar nd isotope compositions a feature previously found in ferromanganese crusts and waters from the pacific ocean arctic seawater samples generally fall on the lower part of the ferromanganese crust array reflecting influences of inputs from arctic rivers and interactions of shelf waters with underlying sediments arctic rivers have much higher hf concentrations 7 30 pm than arctic seawater 0 36 4 2 pm water from the mackenzie river has the least radiogenic hf with ehf 7 1 1 7 and plots furthest away from the ferromanganese crust array while waters from the ob yenisey and lena rivers have values that are indistinguishable from most arctic waters in the amundsen makarov and canada basins hf concentrations are highest at the surface and lowest in the deeper waters reflecting the influences of riverine inputs and of waters that have flowed over the extensive siberian continental shelves and have nd and hf characteristics that reflect water sediment interactions this is in contrast to the relatively low near surface hf concentrations reported for locations elsewhere the pacific water layer in the canada basin exhibits the highest value of ehf 6 8 1 8 reflecting the hf isotopic composition of waters entering the arctic from the pacific ocean mixing relationships indicate that a substantial fraction of the hf in the mackenzie river is lost during estuarine mixing the behaviour of hf from other rivers is less constrained

in situ fluid pressure measurements for earthquake prediction an example from a deep well at hi vista california short term earthquake prediction requires sensitive instruments for measuring the small anomalous changes in stress and strain that precede earthquakes instruments installed at or near the surface have proven too noisy for measuring anomalies of the size expected to occur and it is now recognized that even to have the possibility of a reliable earthquake prediction system will require instruments installed in drill holes at depths sufficient to reduce the background noise to a level below that of the expected premonitory signals we are conducting experiments to determine the maximum signal to noise improvement that can be obtained in drill holes in a 592 m well in the mojave desert near hi vista california we measured water level changes with amplitudes greater than 10 cm induced by earth tides by removing the effects of barometric pressure and the stress related to earth tides we have achieved a sensitivity to volumetric strain rates of 10 9 to 10 10 per day further improvement may be possible and it appears that a successful earthquake prediction capability may be achieved with an array of instruments installed in drill holes at depths of about 1 km assuming that the premonitory strain signals are in fact present

cadmium isotope fractionation in seawater a signature of biological activity investigations of cadmium isotope variations in the oceans may provide new insights into the factors that control the marine distribution and cycling of this element here we present the results of cd isotope and concentration analyses for 22 seawater samples from the atlantic southern pacific and arctic oceans the results reveal for the first time large and well resolved cd isotope fractionations in the marine environment the majority of the seawater samples display an inverse relationship between dissolved cd contents and isotope compositions which range from e114 110cd 3 0 5 for cd rich waters 0 8 1 0 nmol kg to e114 110cd 38 6 for surface water with a cd concentration of only 0 003 nmol kg all e114 110cd data are reported relative to the jmc cd munster standard this suggests that the cd isotope variations reflect kinetic isotope effects that are generated during closed system uptake of dissolved seawater cd by phytoplankton a few samples do not follow this trend as they exhibit extremely low cd contents 0 008 nmol kg and nearly un fractionated cd isotope compositions such complexities which are not revealed by concentration data alone require that the cd distribution at the respective sites was affected by additional processes such as water mass mixing atmospheric inputs of cd and or adsorption uniform isotope compositions of e114 110cd 3 3 0 5 1 s d were determined for seawater from 900 m depth despite of cd concentrations that display the expected increase along the global deep water pathway from the atlantic 0 3 nmol kg to the pacific ocean 0 9 nmol kg this indicates that the biomass which is remineralized in the deeper ocean is also characterized by a very constant cd isotope composition this observation is in accord with the interpretation that the cd distribution in surface waters is primarily governed by rayleigh fractionation during near quantitative uptake of dissolved seawater cd

vertical profiles of ccl3f f 11 and ccl2f2 f 12 in the central arctic ocean basin the anthropogenic chlorofluoro methanes ccl3f f 11 and ccl2f2 f 12 have been measured to depths of 1800 m in the canada basin of the arctic ocean approximate position 85 50 n 108 50 w the measurements were made as part of the canadian expedition to study the alpha ridge cesar during april 1983 surface layer concentrations beneath the ice were 4 79 10 12 mol kg f 11 and 2 11 10 12 mol kg f 12 both profiles exhibit a rapid concentration decrease with depth through the halocline and very low but detectable concentrations at depths of 350 900 m in the atlantic layer in the arctic ocean deep water 900 1800 m concentrations are at or below our practical detection limit of 0 01 10 12 mol kg the profiles have been interpreted using two extreme case lateral ventilation models in order to place bounds on the water column ventilation rates the ventilation age of the upper portion of the halocline 60 150 m increases with depth from 4 to 14 years the core of the atlantic layer at this location appears to have been isolated from the surface for at least 30 years

transport of water through the tropical tropopause total water was measured in the high troposphere and low stratosphere over panama during ten aircraft flights the results show that convective storms provide the means of transporting water into the stratosphere from a consideration of the anvil heights over different areas of the tropical zone it follows that a negative gradient of water vapor mixing ratio with altitude must exist over most of the lower stratosphere

anomalous neon helium ratios in the arctic ocean measurements of dissolved helium and neon were made on seawater samples collected at the lomonosov ridge experiment site lorex 1979 and at the fram iii drifting ice station 1981 in the arctic ocean the most striking feature of the results is the high values of ne he in the shallow depths compared to previous results in other oceans ice formation and refreezing of meltwater appear to be the mechanisms which could explain the observed ne he anomaly

first data on trace metal level and behaviour in two major arctic river estuarine systems ob and yenisey and in the adjacent kara sea russia dissolved and colloidal trace element concentrations cd cu fe ni and pb were determined in the ob and yenisey river estuary systems and in the adjacent kara sea in september 1993 the data show a natural low concentration level of dissolved 0 4 m trace metals cd cu fe ni and pb in the two rivers and in the kara sea as compared to world unpolluted rivers and the central arctic ocean suggesting that the region studied is pristine with respect to trace metals the pathway of trace metals transported from rivers to the ocean seems to be complicated and largely influenced by biogeochemical processes taking place in the estuarine mixing zone colloidal material 104 daltons 0 4 m in addition to its significant contribution to the so called dissolved fraction has been shown to play a fundamental role in determining the behaviour of both conservative and non conservative trace metals during estuarine mixing hence colloids may control to a large extent the fate of dissolved trace metals as well as their net input from the rivers to the kara sea

mixing layer formation near the tropopause due to gravity wave critical level interactions in a cloud resolving model abstract a plausible mechanism for the formation of mixing layers in the lower stratosphere above regions of tropical convection is demonstrated numerically using high resolution two dimensional 2d anelastic nonlinear cloud resolving simulations one noteworthy point is that the mixing layer simulated in this study is free of anvil clouds and well above the cloud anvil top located in the upper troposphere hence the present mechanism is complementary to the well known process by which overshooting cloud turrets causes mixing within stratospheric anvil clouds the paper is organized as a case study verifying the proposed mechanism using atmospheric soundings obtained during the central equatorial pacific experiment cepex when several such mixing layers devoid of anvil clouds had been observed the basic dynamical ingredient of the present mechanism is quasi stationary gravity wave critical level interactions occurring in association with a reversal of stratospheric westerlies to easterlies b