a numerical study on the influence of the mid atlantic ridge on nonlinear first mode baroclinic rossby waves generated by seasonal winds abstract a numerical model simulation investigates the influence of the mid atlantic ridge on nonlinear first mode baroclinic rossby waves generated by seasonal wind fluctuations the north atlantic is simulated by a square box two layer quasi geostrophic qg model the bottom topography is ridge like and compromises the qg approximation and the actual shape of the ridge sponge layers protect all boundaries except the eastern one from wave reflection and eliminate the build up of the western boundary current the model is forced by a purely fluctuating wind stress curl derived from the most significant eofs of the fgge winds a flat bottom and a ridge experiment are compared in both experiments the eastern boundary is an important source of annual period baroclinic rossby waves wave trains having a wavelength of about 1060 km and a westward phase speed around 3 4 cm s 1 propagate energy westward at 3 cm s 1 in the flat bottom experiment a source of directly wind forced baroclinic waves of annual per

frontogenesis subduction and cross front exchange at upper ocean fronts the subduction of water at upper ocean fronts driven by internal instabilities is investigated a simple analytic model which assumes conservation of potential density and potential vorticity is used to characterize the expected structure of subducted parcels as a function of the surface layer depth and the length scale of the parcel parcels subducted from a deep surface layer will be characterized by anomalously low potential vorticity and anticyclonic circulation while shallow surface layers result in subducted parcels with high potential vorticity and cyclonic circulation a nonlinear isopycnal primitive equation model is used to demonstrate how baroclinic instability and the resulting frontogenesis force the subduction of parcels below and across the front frontogenesis generates vertical velocities of 0 30 m d and ageostrophic cross front flows of 3 to 5 cm s the subduction is achieved by the deep ageostrophic flow which carries water from the surface layer below and across the front the subducted parcels quickly develop a circulation through balanced adjustment anticyclonic for deep surface layers and cyclonic for shallow surface layers the characteristics of parcels subducted in winter conditions closely resemble a class of eddies called submesoscale coherent vortices the horizontal and vertical scales of the vortices are determined by the frontogenetic mechanism and the depth of the surface layer the total permanent subduction rate is estimated to be 20 m yr for frontal subduction driven by frontogenesis although local and temporary subduction can be much larger the subducted anticyclonic vortices are often coupled to upper ocean cyclonic vortices thus forming a baroclinic dipole that propagates at approximately 3 5 cm s and is capable of transporting the anomalous water properties far from the region of formation similarities with observations in the north atlantic subtropical convergence zone and near the gulf stream are discussed

frontal surveys with a towed profiling conductivity temperature depth measurement package seasoar in april 1986 rv oceanus participated in the frontal air sea interaction experiment fasinex1 in the region 27 29 n 68 71 w the objective was to survey a pronounced oceanic front2 4 and its effect on the oceanic and atmospheric boundary layers although moorings have yet to be recovered and much of the data analysis is as yet only preliminary it is possible to report here the typical density structure of a front as derived from seasoar5 6 fig 1a observations which were analysed within a few hours of collection previously unreported detail is revealed including subducted pycnostads areas of weak vertical density gradient with anomalous temperature salinity signature splitting of the frontal jet and three dimensional structure not apparent in the surface temperature field

on the maintenance of the subtropical front and its associated countercurrent abstract in the north pacific and atlantic oceans the subtropical countercurrent is an eastward flow across the subtropical gyre at a latitude where a classical wind driven circulation theory would predict a westward flow it is in geostrophic balance with the subtropical front a zonal density front which runs across the ocean basin from previous numerical models it is argued that convergence of ekman transports can hardly be the primary reason for the existence of such a phenomenon and that thermodynamic effects play a crucial role to elucidate how them may be responsible for the frontal structure a very simple analytical model is constructed where the dynamics yield motions consisting of a nondivergent wind driven sverdrup current and a geostrophic thermal flow that is divergent on a beta plane the surface temperature is governed by a nonlinear hyperbolic equation for which the corresponding characteristics intersect separating the basin into two distinct regions limited by a temperature discon

linear instability of a mixed layer front the linear instabilities of a geostrophically balanced frontal jet are computed numerically in an effort to understand the origin of intense small scale cold core features observed in the north atlantic subtropical convergence zones during the frontal air sea interaction experiment fasinex a simple analytic continuously stratified basic state is used to represent the observed frontal structure the most unstable linear modes have e folding timescales of 2 3 days alongfront wavelengths near 70 km and significant asymmetry across the front the results provide indirect evidence that baroclinic instability of the frontal jet is a possible source of the cold core features observed during fasinex

late pleistocene granodiorite source for recycled zircon and phenocrysts in rhyodacite lava at crater lake oregon abstract rhyodacite tephra and three lavas erupted 27 ka interpreted to be early leaks from the climactic magma chamber of mount mazama contain ubiquitous resorbed crystals antecrysts that were recycled from young granodiorite and related plutonic rocks of the same magmatic system the shallow composite pluton is represented by blocks ejected in the 7 7 ka climactic eruption that formed crater lake caldera plagioclase crystals in both rhyodacite and granodiorites commonly have cores with crystallographically oriented fe oxide needles exsolved at subsolidus conditions at least 80 of plagioclase crystals in the rhyodacite are antecrysts derived from plutonic rocks other crystals in the rhyodacite notably zircon also were recycled sims 238 u 230 th dating indicates that zircons in 4 granodiorite blocks crystallized at various times between 20 ka and 300 ka with concentrations of analyses near 50 70 110 and 200 ka that correspond to periods of dacitic volcanism dated by k ar u th ages of zircon from a rhyodacite sample yield similar results no analyzed zircons from the granodiorite or rhyodacite are pre quaternary zircon minimum ages in blocks from different locations around the caldera reflect ages of nearby volcanic vents and may map the distribution of intrusions within a composite pluton survival of zircon in zircon undersaturated hydrous magma and of fe oxide needles in plagioclase suggests that little time elapsed from entrainment of antecrysts to the 27 ka eruption of the rhyodacite the 27 ka rhyodacite is an example of young silicic magma that preserved unstable antecrysts from a known source early during growth of a large high level magma chamber in contrast the voluminous 7 7 ka climactic rhyodacite pumice is virtually lacking in zircon indicating dissolution of any granodioritic debris in the intervening period mineralogical evidence of assimilation may be destroyed in hot vigorously growing silicic magma bodies such as ultimately produced the climactic eruption of mount mazama

forced ocean response during the frontal air sea interaction experiment a central hypothesis of the frontal air sea interaction experiment fasinex was that the strong gradients in the upper ocean associated with ocean fronts would spatially modulate the response of the ocean to local atmospheric forcing to test this hypothesis measurements of near surface meteorology and upper ocean variability were made for 5 months from an array of moorings and for one of those 5 months from two ships a number of fronts passed through the moored array and the moored meteorological and current meter data were used to examine the response of the upper ocean to atmospheric forcing at subinertial and near inertial frequencies at low frequencies an ekmanlike frictionally driven component in the mixed layer and a more deeply penetrating component thought to be forced by ekman pumping were found strong near inertial response was found in the mixed layer the near inertial motion showed considerable spatial variability in the seasonal thermocline here it was evident that the structure of the front influenced the downward propagating near inertial internal waves data were also obtained by profiling instruments deployed along cross frontal sections these data were used to examine the spatial and temporal variability of the internal waves microstructure and dissipation and the relation of that variability to oceanic fronts and atmospheric events the spectral densities of the components of the internal waves that rotated clockwise with increasing depth were higher in regions of negative relative vorticity than those predicted by garrett and munk munk 1981 and estimates of clockwise and total shear were highest in regions of negative relative vorticity in the strong shear of the ocean front significant anisotropy of the internal wave field was observed and kinetic energy dissipation levels relative to the rate of work by the wind were higher than previously reported

the three dimensional circulation near the eastern north pacific subtropical front abstract the purpose of our study is to describe and compute the large scale three dimensional circulation near the subtropical front in the eastern north pacific along 31 n this was accomplished through the use of four extensive hydrographic surveys historical wind stress data and also the movement of surface drifters our results indicate that in wintertime surface water sinks on the north side of the front and rises on its south side during the summer however the subtropical salty surface water overflows the frontal area to the north potential vorticity and heat are best conserved in a vertical flow pattern where the annual mean ekman convergence sinks to a depth of 300 m and water upwells throughout the main thermocline the computed horizontal flow below 700 m amounts to less than 0 6 cm s 1 both strength and direction depend greatly on the treatment of noise within the data set and also on the conservation statement that is specified in addition to geostrophic and hydrostatic dynamics a q

descriptive oceanography during the frontal air sea interaction experiment medium to large scale variability medium and large scale oceanographic variability in the sargasso sea is examined during the frontal air sea interaction experiment fasinex focusing primarily on processes that influence the formation of subtropical fronts from fall to spring the mean meridional gradient of meridional ekman transport in the subtropical convergence zone stcz enhances the meridional sea surface temperature ts gradients between 26 o and 32on in the presence of this enhanced mean gradient baroclinic eddies with zonal wavelengths of 800 km and periods of 200 days exert the dominant influence on the formation of subtropical fronts at medium and large scales these eddies generate westward propagating ts anomaly features with the same dominant wavelengths and periods they are confined between 26 o and 32on and have amplitudes that occasionally exceed ioc ts fronts tend to be found within bands 200 km wide that roughly follow the periphery of these anomaly features deformation in the horizontal eddy current field is primarily responsible for the existence of these frontal bands the migration of the strong front originally bracketed by the fasinex moored array was related to the westward propagation of the larger scale eddy anomaly frontal band pattern the moored array was located within a warm anomaly feature during most of the experiment which produced exceptionally warm conditions in the upper ocean these anomalies are confined between 26 o and 32on not only because the relatively large seasonal mean tsy there allows horizontal eddy currents to force strong anomalies but also because the baroclinic eddies with wavelengths of 800 km and periods of 200 days are confined to the stcz large meridional variability exists in many properties of the eddy field much of which can be traced to the influence of the sargasso sea mean current field on eddy variability

the mean circulation east of the bahamas as determined from a recent measurement program and historical xbt data abstract observational evidence from a two ship synoptic survey from one year long current measurements at four sites and from two independent long term expendable baththermograph xbt data sets is combined to describe the circulation east of the bahamas the results indicate that a weak antilles current actually exists at mid depths about 300 100 m with a northward transport along this boundary of about 4 106 m3 s 1 however both the dynamic height fields and water mass distributions suggest that this current does not represent return flow from the gyre wire sverdrup recirculation but instead is part of the northwestern gulf stream recirculation system west of about 50 w the near surface flow east of the bahamas is more complicated and consists of two isolated anticyclonic circulation cells along the boundary the most intense of these is centered just northeast of abaco island in the northern bahamas the southern weaker cell is centered at about 24 n 71 w in the area just north of puerto r

a planetary wave analysis using the acoustic and conventional arrays in the 1981 ocean tomography experiment abstract using the maximum likelihood estimation method quasi geostrophic wave solutions are fitted to the observations of the 1981 ocean acoustic tomography experiment the experiment occupied a 300 km square area centered at 26 n 70 w over a duration of approximately 80 days the dataset consists of acoustic travel time records moored temperature records and ctd profiles the acoustic data correspond to integral measurements of the temperature or sound speed filed the optimal fit to the data corresponds to three waves in the first baroclinic mode evolving under the presence of a westward mean flow with vertical shear the mean flow is found to be weak approximately 2 cm s 1 but changes the wave periods significantly by producing large doppler shifts the waves are found to be dynamically stable to the mean flow have weak nonlinear interactions with each other and do not form a resonant triad thus they constitute a fully linear solution evidence for the existence of the waves is strongly sup

ocean frontal variability in the frontal air sea interaction experiment oceanographic observations during the frontal air sea interaction experiment fasinex in the sargasso sea indicate that upper ocean fronts in the subtropical convergence are strongly surface intensified coherent flow structures which have a preferred orientation and translation speed fronts grow as they propagate in this region such that currents roughly double in strength in a time that they translate by twice their width while currents are dominated by geostrophic momentum balance the rossby number of these flows can reach a few tenths mixed layer water from the cold side of fronts appears to subduct under warm side near surface waters since isolated lenses of water with cold side temperature and salinity characteristics are found embedded in the seasonal thermocline on the warm side of fronts although plausible vertical speeds were observed no actual rates of subduction could be estimated typical frontal widths temperature contrasts horizontal currents vertical shears vertical currents and translation speeds of fronts in the region studied are 20 km 1 c 0 5 m s 1 0 005 s 1 0 0005 m s 1 and 0 2 m s 1 respectively

low δ18o rhyolites from yellowstone magmatic evolution based on analyses of zircons and individual phenocrysts the yellowstone plateau volcanic field is one of the largest centers exchange time to form zoned zircons is between a few hundred and a few thousand years which reflects the residence time of lowo of rhyolitic magmatism on earth major caldera forming eruptions are followed by unusual lowo rhyolites new oxygen isotope magmas after formation and before eruption petrologic and geochemical data from rhyolites belonging to the 2 0 my eruptive history of yellowstone are presented with emphasis on the genesis of lowo magmas erupted after the huckleberry ridge tuff 2 0 ma 2500 km and lava creek tuff 0 6 ma

towed thermistor chain observations of fronts in the subtropical north pacific a thermistor chain was towed 1400 km through the eastern north pacific subtropical frontal zone in january 1980 the observations resolve surface layer temperature features with horizontal wavelengths of 0 2 200 km and vertical scales of 10 70 m the dominant features which have horizontal wavelengths of 10 100 km amplitudes of 0 2 1 0 c and random orientation likely arise from baroclinic instability associated with them is a plateau below 0 1 cpkm in the horizontal temperature gradient spectrum strong temperature fronts o 1 2 c 3 10 km are observed near 33 n 31 n and 27 n temperature variability is partially density compensated by salinity with the fraction of compensation increasing northward there is evidence of vertical mixing during high winds temperature at 15 m depth is roughly normally distributed around the climatological surface mean with a standard deviation of approximately 0 5 c the standard deviation would correspond to an adiabatic meridional displacement of 80 100 km in the mean gradient horizontal temperature gradient at 15 m depth has maximum values in excess of 0 25 c 100 m and kurtosis near 80 in the band 0 10 1 cpkm the 15 m gradient spectrum is inversely proportional to wave number consistent with predictions from geostrophic turbulence theory while the spectrum at 70 m depth has additional variance that is consistent with garrett munk internal wave displacements

oxygen isotope evolution of volcanic rocks at the sturgeon lake volcanic complex ontario igneous zircons from the sturgeon lake volcanic complex host to several massive sulphide deposits in the superior province canada have an average 18o zircon of 5 4 0 3 vsmow n 9 rocks these zircons are from units differing in age by 18 million years in the 2 7 ga complex there is no detectable interaction of high 18o supracrustal lithologies in the magma quartz from volcanic units beneath the largest ore body the mattabi deposit has an average 18o of 9 3 0 6 quartz phenocrysts from the mattabi unit and overlying volcanics have elevated and heterogeneous 18o values averaging 13 8 0 9 and are not in magmatic equilibrium with zircons the 18o values of whole rock powders range from 5 6 to 14 3 and follow the trend observed in the 18o values of quartz healed microcracks are visible in cathodoluminescence images but are not obvious optically of quartz phenocrysts from units with high 18o values and disequilibrium quartz zircon suggesting that recrystallization facilitates

geosat and advanced very high resolution radiometer observations of oceanic planetary waves adjacent to the hawaiian islands geosat observations of the central north pacific ocean show westward propagating mesoscale features with length scales 500 km time scales 105 155 days and observed zonal phase speeds commensurate with those of nearly nondispersive baroclinic rossby waves advanced very high resolution radiometer derived sea surface temperatures observed during april 1988 showed a cusp shaped pattern north of the hawaiian islands congruent with concurrent geosat derived sea level height anomalies it is believed that the cusp shaped pattern is the surface manifestation of a baroclinic rossby wave the observed wavelength of the cusp shaped pattern was 560 km it had an observed meridional extent horizontal amplitude of 200 300 km and an inferred zonal propagation speed of 0 052 m s 1 the westward propagating sea level height structure was observed to amplify as it approached 150 w reaching amplitudes of 0 06 0 08 m in the vicinity of the cusp shaped feature these waves are believed to be locally forced by the topography either as the result of eastward flow over the submerged island ridge or as a result of baroclinic instability during periods of westward flow

variability and frontogenesis in the large scale oceanic frontal zones sea surface temperature sst from weekly global advanced very high resolution radiometer data for the period of 1982 1992 and estimates of the surface forcing due to wind stress and net heat flux are used to investigate a global monthly climatology of large scale oceanic frontal zones ofzs the variability of sst gradient in several frontal zones and the meridional frontogenesis in the north pacific subpolar frontal zones are identifiable in the sst gradient field throughout the whole year while subtropical frontal zones appear as seasonal phenomena in the northern hemisphere the magnitude and position of subtropical fronts were found to vary synchronously in both hemispheres with maximum intensity in november to march during this period subtropical fronts in the northern hemisphere become clearly identifiable separate features while in the southern hemisphere their southern boundaries tend to merge with the subpolar front in the northern hemisphere the northward shift of the subtropical frontal zones during late boreal spring results in a merger of the subpolar and subtropical zones by august in the southern hemisphere subtropical fronts separate from the subpolar front during this period and become clearly distinguishable though less intense singular spectrum analysis of the 11 year time series of sst gradient in several ofzs revealed a seasonal signal as well as interannual variations that in the equatorial zone are related to el nino events the amplitude of the annual cycle is comparable in the subtropical and subpolar north pacific but the subtropics leads the subpolar zone by about 4 months combined forcing due to wind stress and net surface heat flux was found to be sufficient to describe most of the observed frontogenesis variability in north pacific midlatitudes on seasonal timescales but not on shorter timescales in the subtropical zone the ekman convergence alone was not sufficient to provide the observed frontogenesis frontolysis on seasonal time scales in fact when the maximum frontogenesis associated with ekman convergence occurs in late spring early summer this is counteracted by the frontolytic effect of ekman pumping and the dominating frontolytic effect of surface heat forcing in summer ekman convergence is more important in the subpolar area where it is enhanced by the smaller frontogenetic effect of both ekman pumping and surface heat forcing surface forcing due to wind stress and heat flux considered in this study does not explain the high amplitude intraseasonal frontogenesis variations especially in the subpolar region

ion microprobe analysis of oxygen isotope ratios in quartz from skye granite healed micro cracks fluid flow and hydrothermal exchange quartz grains in hydrothermally altered granites from the isle of skye are highly heterogeneous and not equilibrated in oxygen isotope ratio at the 20 m scale ion microprobe analysis of one grain shows a gradient of 13 over 400 m and a greater range in 18o than all quartz previously analyzed on the isle of skye other crystals from the same outcrop are homogeneous digitized cathodoluminescence images reveal patterns of magmatic zoning and brittle fracturing not otherwise detectable the ion probe analysis correlates low 18o values on a micro scale to one set of healed cracks thus quartz exchanges oxygen isotopes primarily by solution and reprecipitation along fractures in contrast to more reactive feldspar that appears to exchange from the grain boundary inward macroscopic models of isotope exchange are not realistic for these rocks the flow of hydrothermal fluids was heterogeneous anisotropic and crack controlled

petrogenesis of metaluminous a type rhyolites from the st francois mountains missouri and the mesoproterozoic evolution of the southern laurentian margin abstract predominantly acid volcanic and intrusive rocks of the approximately 1 48 ga eastern granite rhyolite province are exposed only in the st francois mountains inlier missouri combined nd isotopic major and trace element analyses are presented for the predominantly acid volcanic rocks of the st francois mountains they are metaluminous to mildly peraluminous a type compositions with positive initial e nd values of 3 1 5 0 they are interpreted to be the result of crystal fractionation of partially melted calc alkaline igneous rocks formed at a recently active subduction zone the likelihood of a juvenile calc alkaline subduction generated protolith for the st francois mountains rhyolites leads to a hypothesis in which dacitic parental magmas resulted from partial melting in a continental back arc setting basaltic magmatism due to decompression melting of the mantle resulted from lithospheric extension and thinning and provided the heat source for melting in the middle or lower crust penecontemporaneous magmatism elsewhere in laurentia included subduction related calc alkaline rocks in the pinware terrane of labrador some felsic igneous rocks of uncertain plate tectonic setting within the grenville province also have 1 5 1 6 ga t dm ages these are interpreted as magmatic products of approximately 1 5 ga northward dipping subduction beneath much of the length of the southern margin of laurentia the eastern granite rhyolite province is consequently seen as an integral inboard expression of this subduction related igneous activity petrogenetic models involving a mantle plume or the development of a continental rift are not required to explain this granite rhyolite terrane and evidence against their involvement is discussed

variability of the climatic oceanic frontal zones and its connection with the large scale atmospheric forcing abstract global satellite sea surface temperature sst measurements and ncep ncar reanalysis wind data for the period of 1982 2009 have been used to study the seasonal and interannual variability of the main climatic oceanic frontal zones ofz subpolar subtropical and equatorial associated with the large scale atmospheric forcing the seasonal variability of the ofz is manifested in variations of their intensity magnitude of the meridional gradient of sst and latitudinal position of the cores defined as areas of maximum sst gradient the maximum intensity of the subpolar ofz is observed in summer of the corresponding hemisphere while subtropical ofz are intensified synchronously in both hemispheres during boreal winter subtropical ofz cores in both hemispheres shift synchronously to the south north during the winter summer of the northern hemisphere which is caused by the seasonal meridional migration of the areas of the maximum convergence of ekman transport all subpolar and subtropical ofz reveal a pronounced quasi decadal 7 10 years variability manifested in the variations of their intensity and latitudinal position of the zones cores strengthening of the sst gradient is accompanied by a displacement of the zones cores to the north in both hemispheres for subpolar ofz while subtropical ofz cores migrate to the poles in this situation positive correlations between the maximum magnitude of the meridional gradient of zonally averaged sst and meridional shear of zonal wind which is an estimate of the ekman convergence intensity were found for all subpolar and subtropical ofz variability of the latitudinal position of subpolar ofz cores is associated with the ekman advection variability due to zonal wind variations strengthening of zonal wind results in a shift of subpolar ofz cores to the south north in the northern southern hemispheres a period of the variability of the north pacific equatorial ofz is 4 5 years and is determined by the variability of the enso system during the el nino events the sharp decrease of the intensity of the equatorial ofz take place

empirical calibration of oxygen isotope fractionation in zircon new empirical calibrations for the fractionation of oxygen isotopes among zircon almandine rich garnet titanite and quartz are combined with experimental values for quartz grossular the resulting a coefficients k2 are zrc alm grs ttn qtz 2 64 2 71 3 03 3 66 zrc 0 07 0 39 1 02 alm 0 32 0 95 grs 0 63 full size table table options view in workspace download as csv for the relation 1000 ln y x ay x 106 t2 the fractionation of oxygen isotopes between zircon and coexisting minerals can provide otherwise unavailable evidence of magmatic processes including crystallization remelting and assimilation fractional crystallization

effects of horizontal advection on upper ocean mixing a case of frontogenesis abstract the wind stress on the ocean surface induces horizontal advection and vertical mixing two mechanisms which are capable of changing the surface water density advection and mixing can enhance or partially destroy the effects of each other frontogenesis due to convergent ekman transports forced by a wind stress field is one example a bulk model for the study of advection and mixing in such circumstances is constructed from a one dimensional model continuity of mass requires that water masses either downwell convergence or escape laterally confluence this distinction leads to a study of two extreme cases of frontogenesis each herein treated separately the model reduces to two coupled highly nonlinear prognostic equations for the mixed layer buoyancy and mixed layer depth scaling of the equations leads to the definition of a mixing parameter a nondimensional number which measures the relative importance of advection and mixing for large scale ocean frontogenesis this parameter is of th

the rapid heating defocused beam technique a co2 laser based method for highly precise and accurate determination of δ18o values of quartz abstract we describe a laser fluorination technique specifically for quartz that allows both high accuracy and high precision determination of oxygen isotope ratios regardless of grain size the rapid heating defocused beam technique rhd utilizes a defocused 32 w co 2 laser at full power which delivers 17 w 20 w mm 2 to the sample to quickly react quartz in contrast other recent laser fluorination studies use a tightly focused laser beam and slow heating i e sharp and kirschner 1995 fouillac and girard 1996 kirschner and sharp 1997 and find laser analysis of fine grained quartz to be inaccurate three quartz standards nbs 28 qz bra and qz cwru were analyzed using the rhd technique at the university of wisconsin to test for grain size effects rhd analyses show no correlation between grain size and 18 o values and are in excellent agreement with 18 o values obtained using conventional fluorination techniques additional analyses of the same quartz standards performed at university of wisconsin using slow heating and a focused beam yield 18 o values that are both less precise and significantly up to 0 8 lower than the accepted values attempts to use the rhd technique with a 20 w co 2 laser which delivers 8 w 10 w mm 2 to the sample at brgm were unsuccessful probably due to insufficient power density of the defocused beam we conclude that the rhd technique yields excellent accuracy and precision but that power densities of 15 20 w mm 2 may be necessary across a large part of the sample surface we recommend the use of lasers with at least 30 w of power

air sea fluxes and surface layer turbulence around a sea surface temperature front the observed effects of sharp changes in sea surface temperature sst on the air sea fluxes surface roughness and the turbulence structure in the surface layer and the marine atmospheric boundary layer are discussed in situ flux and turbulence observations were carried out from three aircraft and two ships within the fasinex framework three other aircraft used remote sensors to measure waves microwave backscatter and lidar signatures of cloud tops descriptions of the techniques intercomparison of aircraft and ship flux data and use of different methods for analyzing the fluxes from the aircraft data are described changing synoptic weather on three successive days yielded cases of wind direction both approximately parallel and perpendicular to a surface temperature front for the wind perpendicular to the front wind over both cold to warm and warm to cold surface temperatures occurred model results consistent with the observations suggest that an internal boundary layer forms at the sst

does the arc accretion model adequately explain the paleoproterozoic evolution of southern laurentia an expanded interpretation a common model for the paleoproterozoic crustal evolution of southern laurentia involves southerly accretion of successively younger island arcs from 1780 to 1650 ma this model may be oversimplified however for although andesite and basaltic andesite major components of modern island arcs occur they are relatively rare and large volumes of rocks are dominantly bimodal metavolcanic assemblages and related granitoids ophiolites occur but they are also rare and only one accretionary melange has been described inherited zircons and common pb and nd isotopic data indicate involvement of older crust in ca 1750 ma rocks of the mojave province of southeastern california and western arizona and the bimodal assemblages of central colorado these data suggest that the bimodal volcanic rocks were derived from pre existing continental crust likely of ca 1850 ma trans hudson penokean age during extension and partial melting associated with the development of transpressional crustal scale shear zones the occurrence of the 1840 1 ma elves chasm pluton in the grand canyon demonstrates that rocks of trans hudson penokean age are present in southwestern laurentia

generation of annual rossby waves in the north pacific by the wind stress curl abstract the rossby wave field generated by the annual cycle of the observed wind stress curl over the north pacific ocean 15 n 53 100 w 175 e has been obtained through numerical integration of the linearized reduced gravity vorticity equation in spherical coordinates the dominant source region of rossby waves is adjacent to the eastern boundary between 20 44 n more specifically this source is shown to be made up essentially of two distinct parts a southern region off california baja california which was first identified by white and saur and a northern region corresponding to a generation area first proposed by mysak in addition a second midocean generation region has been identified over the central north pacific from 35 to 45 n 150 to 160 w the behavior of the model is strongly affected by wave refraction due to the variation of phase velocity with latitude as described in schopf et al as waves emanate from the eastern boundary they are refracted such that the wavenumber vector init

overview of the frontal air sea interaction experiment fasinex a study of air sea interaction in a region of strong oceanic gradients from 1984 to 1986 the cooperative frontal air sea interaction experiment fasinex was conducted in the subtropical convergence zone southwest of bermuda the overall objective of the experiment was to study air sea interaction on 1 to 100 km horizontal scales in a region of the open ocean characterized by strong horizontal gradients in upper ocean and sea surface properties ocean fronts provided both large spatial gradients in sea surface temperature and strong jetlike flows in the upper ocean the motivation for and detailed objectives of fasinex are reviewed then the components of the field program are summarized finally selected results are presented in order to provide an overview of the outcome of fasinex

large scale sst variability in the western north atlantic subtropical convergence zone during fasinex part i description of sst and wind stress fields abstract we describe properties of large scale fluctuations in the wind field represented by two analyses fnoc and noaa atoll and in the sst field represented by maps derived from 5 day composite avhrr images within an 11 longitude by 10 latitude domain during fasinex january through june 1986 fnoc and atoll wind and wind stress time series were highly correlated with each other 0 8 over the entire domain and they were also highly correlated with time series measured at the fasinex site 0 89 at periods of 2 13 days clockwise energy exceeded anticlockwise energy by an order of magnitude while the energy was nearly partitioned equally at periods of 13 40 days mean atoll winds were everywhere more eastward than mean fnoc winds probably in part because the atoll fnoc analyses are intended to represent 850 mb 19 5 m winds the 850 mb winds are expected to be more eastward due to the thermal wind balance with the mean southward air temperature gradient the sst maps represented large s

ocean surface topography measured by the geosat radar altimeter during the frontal air sea interaction experiment an objective analysis oa technique was used to analyze geosat geodetic mission residual sea height anomalies rsha for the frontal air sea interaction experiment fasinex conducted in the western north atlantic preprocessing of the geosat data included removal of a mean sea surface and orbit error and corrections for tides wave height inverse barometer and ionospheric and dry tropospheric effects geosat data were not corrected for water vapor central to the analysis was the computation of a spatially anisotropic time dependent autocorrelation function directly from the geosat data results show a single autocorrelation function peak having a diameter of 270 km at 0 day time lag a 15 month time series of rsha topography was constructed at 10 day intervals forming a set of 47 oa maps these maps show a field of topographic features propagating to the west at 4 km d 1 the features exhibited spatial and temporal scales of 200 km and 50 days respectively the root mean square rms of the oa derived feature amplitudes fluctuated slowly between 0 05 and 0 09 m with a period of 200 days over the 15 month interval these fluctuations appeared to be related to the passage of large scale northeast southwest trending sea surface temperature sst anomaly features reported for fasinex which were surface manifestations of large scale first mode baroclinic rossby waves the rms amplitude of the oa derived features was maximal minimal during periods of negative positive sst anomaly when the depths of the mixed layer and main thermocline in the upper ocean shoaled deepened the fluctuations also appeared to be correlated with the structure of the field periods of decreased feature amplitudes corresponded to a closely packed structure while during times of increased amplitudes the field structure became zonal with regions of alternating sign during fasinex january june 1986 the field was characterized by the closely packed structure and decreasing feature amplitudes this corresponded to the period of positive sst anomaly and high upper ocean heat content reported for fasinex

large scale sst variability in the western north atlantic subtropical convergence zone during fasinex part ii upper ocean heat balance and frontogenesis abstract we analyzed the influence of wind deriven horizontal heat advection on the large scale o 1000 km wavelength variability of both the upper ocean mixed layer heat content and the subtropical frontal zone sfz within an 11 by 10 domain in the western north atlantic ocean during fasinex january through june 1986 by estimating heat advection due to both ekman transport and interior geostrophic sverdrup minus ekman transport from a slab mixed layer heat balance equation using satellite derived sea surface temperature ts and wind analysis maps it was found that these processes could not account for the observed variability in either beat content or the sfz the annual cycle of surface vertical heat flux had the dominant influence on the heat content even when the average heat balance was analyzed during a 4 month time interval when the net influence of the annual cycle was nearly zero mid january to mid may 1986 westward propagating ts spatial anomaly features with peak to peak scales

oxygen isotope evidence for magmatic variability and multiple alteration events in the proterozoic st francois mountains missouri abstract the st francois mountains contain at least two mesoproterozoic caldera complexes the butler hill and the taum sauk calderas each with diameters greater than 20 km igneous zircons from intrusive and extrusive units within the calderas have a range of 18o zircon from 5 8 to 8 2 v smow these zircons are similar to other proterozoic zircons from igneous rocks around the world and suggest a magma source from partial melting of older crust with variable mantle component there is no significant difference in the magmatic oxygen isotope ratios between the taum sauk and butler hill calderas values of 18o quartz zircon 2 1 2 4 indicating that most quartz from samples in the two calderas still preserves near magmatic oxygen isotope ratios the average 18o quartz from the two calderas is 8 6 2 6 in contrast felsic volcanic units within the taum sauk caldera exposed at johnson shut ins suggest interaction with water at low temperature resulting in 18o quartz as high as 16 7 quartz phenocrysts within a single sample from johnson shut ins range from 8 7 up to 16 7 the isotope heterogeneity coupled with evidence of healed microcracks in cathodoluminescence images suggests low temperature hydrothermal alteration affected the volcanics during or shortly after eruption after caldera collapse the hydrothermally altered rocks were partially re melted and incorporated into the magma chamber as evidenced by the slight increase in 18o zircon of the resurgent dome intrusions in contrast the butler hill caldera preserves evidence of high temperature hydrothermally altered country rock assimilated into the stono mountain granitic ring intrusion based on low 18o quartz values and visible zoning in cl the two calderas experienced different alteration histories suggesting the lack of any homogenizing regional fluid influx

on the geographical variability of the upper level mean and eddy fields in the north atlantic and north pacific abstract all available historical expendable bathythermograph data are used to compute means and standard deviations in temperature for the upper 500 m in the north atlantic and north pacific to take advantage of marked spatial differences in data coverage a variable grid scheme is employed both surface and subsurface annual mean temperature distributions agree well with published maps of these quantities climatological mean temperature salinity and salinity depth curves are used to infer salinities for the mean temperature profiles in order to compute 0 500 db inferred dynamic height and its standard deviation these mean curves are also used to compute eddy potential energy at 300 m the maps of mean annual inferred dynamic height agree well with traditional dynamic height maps and appear similar to the maps of mean temperature at 400 m the north atlantic eddy potential energy distribution is similar to an earlier calculation maps of the standard deviations in inferred dynamic height also represent

westward propagating sst anomaly features in the sargasso sea 1982 88 abstract sea surface temperature ts maps of the region from 59 5 to 75 5 w 22 5 to 33 5 n containing the western north atlantic subtropical convergence zone stcz were derived from avhrr 2 images the 7 year mean annual cycle was removed and the maps were filtered in space and time to represent anomaly variability with wavelengths 220 km and periods 50 days warm and cold anomaly features were observed cast of 71 w between 26 and 32 n that propagated westward at 3 4 km day 1 and that occasionally exceeded 1 c in amplitude they are generally strong and persistent from fall to spring and are only marginally detectable during summer during 1981 82 1982 83 and 1985 86 individual features could be followed through the entire fall spring interval during 1983 84 1986 87 and 1987 88 they could typically be followed for 2 4 months and during 1984 85 for only 1 2 months the features were anisotropic during all fall spring intervals except 1986 87 and they had characteristic wavelengths of 80

sea surface temperature anomalies planetary waves and air sea feedback in the middle latitudes the mechanisms that contribute to the generation and damping of large scale mid latitude sea surface temperature sst anomalies are discussed the sst anomalies reflect primarily the response of the upper ocean to the changes in air sea fluxes that are associated with daily weather fluctuations heat flux forcing is dominant in the lower middle latitudes while wind driven entrainment may be most effective in the high latitudes advection by anomalous ekman current is generally less important and ekman pumping is negligible the sst anomalies decay in part because of entrainment effects associated with mixed layer deepening and oceanic mixing and in part because of heat exchanges with the atmosphere the three approaches commonly used to model the evolution of sst anomalies are reviewed case studies based on monthly or seasonal anomaly maps of the large scale sst and atmospheric anomalies numerical simulations with one dimensional mixed layer models and stochastic forcing models we stress the similarities in the different approaches and discuss their main advantages and limitations the response of the atmosphere to mid latitude sst anomalies is considered first we discuss the poorly known relationship between sst anomalies and diabatic heating using a crude assumption for the air sea coupling we consider a two layer quasi geostrophic channel model and discuss the stationary wave response to sst anomaly forcing and the resulting air sea feedback it is found that the back interaction of the sst anomalies onto the atmosphere causes a weak sst anomaly damping at large scales and a strong one at small scales the air sea coupling should also act as an eastward propagator for the sst anomalies the response of more realistic linear wave models to prescribed diabatic heating is then reviewed and it is suggested that realistic mid latitude sst anomalies have a weak influence on the atmospheric circulation corresponding to changes in the geopotential height of 10 30 m at most this order of magnitude is consistent with the results of general circulation model experiments and with the limited climate predictability associated with mid latitude sst anomalies

evidence for wind driven current fluctuations in the western north atlantic two subsurface current meter moorings were deployed for 20 months along 70 w in a low energy portion of the western north atlantic the resulting data were compared with estimates of the wind stress curl in an attempt to seek a relationship between currents below the mixed layer and meteorological forcing at subinertial frequencies currents and temperature tend to be significantly coherent with the curl and are most coherent with the curl at remote locations usually more than 500 km away from the mooring and generally to the east coherences generally decrease with increasing frequency the current response is surface intensified a linear stratified model for stochastically wind forced rossby waves in a flat bottomed ocean is presented as an attempt to rationalize the results the effort was not entirely successful so that it appears that a more realistic model perhaps including bottom topography and mean currents will be needed to rationalize these observations fully

mixed layers and fronts in simple ocean circulation models abstract a three dimensional regime with a differentially heated mixed layer on top of an ideal fluid interior is considered in a situation which corresponds to the interior of the well known wind driven model by stommel 1948 although the transport field in this case is continuous and simple the same is not necessarily true for the density and velocity fields if the mixed layer is weakly coupled to the atmosphere a front is generated at the line of a maximum downwelling another front is expected at the line of a zero downwelling

low δ18o magma isle of skye scotland evidence from zircons abstract zircons in tertiary granitic rocks from the isle of skye scotland were resistant to measurable oxygen isotope exchange during intense hydrothermal activity in the subvolcanic environment five granite bodies from the western red hills complex were investigated four have 18o zrc 4 1 0 2 o vsmow while the fifth which intruded before major cauldron subsidence is 2 lower zircons from lewisian gneiss are visually and isotopically distinct indicating that zircons in the granite are not xenocrysts from the lewisian basement analysis of different magnetic and size fractions of zircon shows no significant correlation to 18o supporting the conclusion that these values represent the true magmatic compositions and that the western red hills granites intruded as low 18o magmas with a whole rock 18o 6 0 quartz separates from four granites are close to the calculated magmatic values in 18o but in the fifth values are 5 lower indicating variable exchange of quartz with low 18o heated meteoric waters these results might be explained by magmatic interaction with hydrothermally altered crust early in the evolution of the granites before crystallization of zircon followed by interaction with later hydrothermal fluids alternatively independent evidence for low 18o mafic magmatism in nw scotland suggests the presence of large quantities of low 18o subducted ocean crust in the subcontinental lithosphere that could contaminate or be the source of low 18o mantle derived melts

a study of the variability of ocean currents in the northwestern atlantic using satellite altimetry abstract altimeter data obtained from geos 3 during the three year period 1975 78 for a region of the western north atlantic which includes a portion of the gulf stream system and part of the open ocean area of the subtropical gyre are analyzed by a new technique which utilizes all the points along the satellite tracks the physical phenomenon studied are the time variable but almost geostrophic currents or mesoscale eddies so that geoid errors contaminate the scientific signal minimally and the dynamical interpretation is direct results presented include the spatial distribution of geostrophic eddy kinetic energy and examples of a synoptic map of the eddy field april 1977 and of a time series at a point these results are compared to and synthesized with a diverse and selected set of existing measurements and observations obtained in situ by a variety of instrumental techniques the agreement is generally good and the altimeter data analyzed provides new information on features in the map of mean e

soil processes and nutrient bioavailability in the rhizosphere of bolax gummifera in a subantarctic environment martial mountains ushuaia argentina abstract the aim of this study was to explore the effects of plants on the underlying substrate and the possible environmental implications of such effects in an extreme environment for this purpose we sampled the rhizosphere soil of bolax gummifera which is one of the most characteristic vascular plants in the martial mountains tierra del fuego argentina where plant cover is typically sparse superficial 0 5 cm rh5 and subsuperficial 5 15 cm rh15 samples of b gummifera rhizosphere and bulk soil were collected from a small homogeneous area and the following parameters were analyzed particle size ph total organic carbon toc total nitrogen tn total fe tfe fe and al associated with organic matter soluble in sodium pyrophosphate c pyro amorphous fe oxyhydroxides extracted with ammonium oxalate fe oxa crystalline fe oxyhydroxides extracted with sodium dithionite fe dit bioavailable plant nutrients soluble in mehlich 3 extractant and clay mineralogy several differences were found between rhizosphere soil rs and bulk soil the toc was 8 times higher and the tn and c pyro were 4 times higher in the rhizosphere than in the bulk soil mineralogical results suggest a slightly higher degree of chemical weathering mainly affecting biotite and amphibole minerals in the rs than in bulk soil consistent with significantly higher nutrient bioavailability in rs ca mg k co and fe on the other hand the higher concentrations of c and metals extracted with sodium pyrophosphate suggest the formation of more metal organic complexes in the rhizosphere than in the bulk soil this metal fraction is considered as readily mobilizable and available and can be leached from the soil to continental and coastal waters this effect will be enhanced in cold climates by expansion of plant cover due to the increased temperature expected under climate change