the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

the link between the north pacific climate variability and the north atlantic oscillation via downstream propagation of synoptic waves abstractthe north atlantic oscillation nao response to the northeast pacific climate variability is examined using the era 40 dataset the main objective is to validate a mechanism involving downstream wave propagation processes proposed in a recent idealized companion study a low frequency planetary scale ridge trough anomaly located in the eastern pacific north american sector induces more equatorward poleward propagation of synoptic scale wave packets on its downstream side which favors the occurrence of anticyclonic cyclonic wave breakings in the atlantic sector and the positive negative nao phase the mechanism first provides an interpretation of the canonical impact of the el nino southern oscillation on the nao in late winter the wintertime relationship between the pacific north american oscillation pna and the nao is also investigated for out of phase fluctuations between the pna and nao indices i e the most recurrent situation in late winter the eastern pacific pna ridge trou

zooplankton distributions and transport across the northeastern tidal front of georges bank tidal fronts are important sites of contact and mixing between zooplankton populations on and off georges bank in the northwest atlantic this study a component of the us globec program examined crossfrontal distributions of zooplankton especially the copepod calanus finmarchicus across the northeastern tidal front of georges bank relative to the tidal cycle frontal structure flow field and day night cycle a unique feature was a precisely executed sampling strategy designed to isolate spatial tidal and day night effects vertically stratified zooplankton sampling was done along tidally coordinated crossfrontal transects and during time series studies at specific locations zooplankton taxa differed in their spatial and vertical distributions relative to the front and the hydrographic structure of the water column there were significant associations between zooplankton assemblages and spatial location depth and water mass zooplankton distributions generally tracked water masses but usually showed crossbank abundance gradients consistent differences between day and night distributions were not apparent for most taxa meroplankton larvae of benthic animals were derived primarily from onbank populations the zooplankton community was advected with the tidal flow crossfrontal distributions characteristic of onbank and offbank flow regimes clearly differentiated tidal phases and interacted with the flow field and topography salinity a proxy for water mass and depth interacted in controlling vertical distributions as tidal forcing sloshed water masses up and down the bank slope some taxa followed isohalines through depth changes while other taxa maintained themselves within a relatively limited depth or salinity regime surface convergence and downwelling tidal upwelling of bottom water and mid depth tidal pumping influenced crossfrontal exchange

characterization of vertical mixing at a tidal front on georges bank studies of mixing were done at the northern flank of georges bank in the summer and autumn of 1988 two time series of the evolution and intensity of microstructure were examined over a tidal period in the context of tidal forcing and the evolution of the density and velocity field at the site from the ctd adcp and microstructure observations epsonde on georges bank several interesting features of the mixing processes were found high dissipation and diffusivity regions appear near the bottom of the bank turbulence near the bottom is highest in intensity and reaches farthest from the bottom at peak tidal flow and diminishes in intensity and vertical extent as the flow decreases the thickness of the bottom turbulent layer has its maximum value when the flow is strongest and the stratification is weakest characterization of the dissipation rate and turbulent diffusivities in respect to buoyancy frequency n current shear s richardson number ri and n2 was done dissipation and t showed little dependence on shear or n2 but decreased at larger ri t was found to be higher in regions of higher n2 and increased as n2 increased kt k and k were all highest near the bottom in excess of 10 2m2s 1 and decreased towards the surface there was little suggestion of a dependence of mixing efficiency on s2 ri or n2 but some indication that decreases with decreasing n2

synoptic systems interacting with the rocky mountain barrier observations and theories abstractusing a composite analysis for strong sea level pressure perturbations off the west coast of north america the evolution of large amplitude synoptic systems upstream of the rocky mountains is investigated for the winter season corresponding previous analyses are refined by avoiding multiple counting of events and extended by including potential vorticity vertical motion and deformation in the analysis cyclonic and anticyclonic anomalies behave similarly with weak local extrema forming in the lee of the mountain range southeast of the parent systems however neither the geopotential anomaly nor the associated potential vorticity anomaly cross the mountain range nevertheless these anomalies contribute to the sea level pressure anomaly in the lee for both positive and negative anomalies potential vorticity exhibits a bipolar structure with lobes over the reference point and over the cordillera respectively the relevance of several theories describing the interaction between synoptic syste

relationship between cyclone tracks anticyclone tracks and baroclinic waveguides abstract this study presents observational results concerning the structure and evolution of high frequency fluctuations with periods shorter than 6 days in the geopotential height field the results are based on a statistical analysis of 1000 500 and 250 mb height fields derived from twice daily nmc final analyses over the northern hemisphere for the 20 winters 1964 65 through 1983 84 the disturbances assume the form of waves elongated in the meridional direction with a mean wavelength of 4000 km a westward tilt with height and a mean eastward phase propagation of 12 1 5 m s 1 these results support an interpretation in terms of finite amplitude baroclinic waves whose structure and evolution varies with geographical location over the continents and especially along the eastern slopes of the rockies and the tibetan plateau the waves show marked departures in structure and evolution from those over the oceans in particular we find evidence of a systematic influence of the terrain in steering the

a new look at deformation as a diagnostic for large scale flow abstractdeformation plays a key role in atmospheric dynamics because it provides a dynamical measure of the interaction between different scales such as in frontogenesis a climatology of deformation constructed from interim ecmwf re analysis era interim data 1979 2013 reveals four main processes associated with deformation 1 frontogenesis at lower levels 2 movement and evolution of jet streams in the upper troposphere 3 orographic blocking and 4 rossby wave breaking the merits of deformation as an additional perspective are discussed for these processes on the basis of case studies and composite analyses in conjunction with analytic solutions this study shows that deformation can be used to unambiguously detect orographic blocking through the local strength of the flow diversion around orography moreover the deformation signature for orographic blocking observed in case studies and composites closely resembles the analytic solution for two dimensional flow around an obstacle the climatolo

multi reanalysis climatology of intermountain cyclones abstract the topography in and around the intermountain west strongly affects the genesis migration and lysis of extratropical cyclones here intermountain i e nevada or great basin cyclone ic activity and evolution are examined using the ecmwf re analysis interim era interim the north american regional reanalysis narr and the ncep ncar reanalysis from 1989 to 2008 the period during which all three are available the ics are defined and tracked objectively as 850 hpa geopotential height depressions of 40 m that persist for 12 h the monthly distribution of ic center and genesis frequency in all three reanalyses is bimodal with spring absolute and fall secondary maxima although the results are sensitive to differences in resolution topographic representation and reanalysis methodology both the era interim and narr produce frequent ic centers and genesis in the great basin cyclone region which extends from the southern high sierra to northwest utah and the canyonlands cyclone reg

the effects of water content on diffuse reflectance spectrophotometry studies of deep sea sediment cores abstract sediment cores recovered during odp drilling operations are commonly scanned using a minolta cm 2002 spectrophotometer to obtain spectral data core processing procedures aboard the joides resolution require that these spectral data be measured on wet cores however the effects of changing water content on the spectra of marine sediments is unknown we examined the effects of changing water content on visible light vis diffuse reflectance spectra for core samples composed of clay to foraminiferal ooze the spectra of dry powdered samples were measured then the samples were completely saturated 35 water content and spectra were measured at set time intervals as the samples progressively dried the fully saturated samples were appreciably darker than the initial dry samples the samples continued to darken during the initial phases of drying until the water content had decreased from 35 to 20 as the water content continued to decrease below 20 the samples became progressively lighter and attained spectral values similar to the fully saturated samples at water contents of 17 samples continued to lighten until they were totally dry however values never became as light as those of the dry samples prior to initial wetting changes in reflectance with decreasing water content are not uniform across the vis if the water content is greater than 5 the reflectance decrease relative to a dry sample is greater at the red end of the spectrum however at water contents of less than 5 the spectral curves of the wet and dry sediments are similar in shape but the wet sediments are still darker comparison of these data with data obtained from similar saturation experiments using a coarse grained beach sand suggest that the initial darkening of the saturated carbonate sediments apparently results from changing of the physical properties of the sediment decreasing the water content apparently rearranges the grains these studies suggest that maximum information will be obtained when spectral measurements are taken on samples that are allowed to dry as much as possible

the front on the northern flank of georges bank in spring 1 tidal and subtidal variability 1 during march april 1999 2 weeks of undulating ctd and shipboard acoustic doppler current profiler surveys revealed the variability of the intense internal tide on the northern edge of georges bank the nature of the internal tide was modulated by episodic surface intrusions of cool fresh scotian shelf water ssw stratifying the otherwise vertically well mixed outer bank the introduction of ssw created a system analogous to that in summer when the outer bank is thermally stratified and separated from well mixed regions by a tidal mixing front during ssw intrusions internal tidal behavior is characterized by tidal advection that is significantly faster than internal wave propagation speeds on the bank supercritical flow and slower than the lowest internal modes in deeper water to the north subcritical flow a large amplitude internal lee wave develops over the slope during off bank tidal flow this stalled energy is released to propagate on bank as a high frequency internal wave when the tide reverses it is suggested by analogy with the summer case that a portion of this energy is used by mixing at the on bank limit of ssw the presence of ssw thus modifies the internal tidal response enabling a mechanism that contributes to its assimilation with ambient bank water the off bank propagating internal tide is dominated by a mode 1 internal wave at the m2 frequency with cross bank velocities comparable to the barotropic tide

the structure and evolution of a simulated rocky mountain lee trough abstract this paper describes the life cycle of a lee trough associated with the passage of a baroclinic wave over the rocky mountains based on two overlapping simulations by the pennsylvania state university national center for atmospheric research mesoscale model the evolution of the lee trough may be summarized as follows a surface cyclone and lee trough developed and intensified as an upper level short wave trough approached and moved over the rockies near the low center the lee trough was found to be frontogenetical with the frontogenesis being forced by 1 confluent deformation associated with the wind fields of the developing cyclone and lee trough and 2 differential vertical motion along the eastern slopes of the rocky mountains and the adjacent sloping terrain of the high plains in turn the frontogenesis drove an ageostrophic circulation that sharpened the lee trough the lee trough represented a break in trajectory origin with trajectories ending ahead of the lee trough originating over

neogene changes in southern ocean sedimentation based on mass accumulation rates at four continental margins 1 high resolution mass accumulation rates mar were determined from lithologic logs based on downhole log and continuous core data for six sites at four continental margins around the southern ocean total mar was calculated at ocean drilling program odp site 1095 on the margin of the antarctic peninsula and odp site 1165 on the margin of prydz bay antarctica carbonate and noncarbonate terrigenous mar were calculated for odp sites 1123 and 1124 east of new zealand and sites 1168 and 1172 west and southeast of tasmania shifts in carbonate mar are seen around tasmania and new zealand at 23 and 14 ma suggesting changes in deep water circulation and surface carbonate productivity at these times carbonate mar dropped at sites 1124 and 1168 at 23 ma and increased at 14 ma at sites 1123 1168 and 1172 the overall character of total mar at antarctic sites 1095 and 1165 is a continual and relatively constant decrease in total mar during the neogene with periods of stepwise decrease one such decrease is seen at 14 ma at site 1165 coincident with increased carbonate mar in new zealand and tasmania sites 1123 1124 1168 and 1172 and likely related to mid miocene expansion of the east antarctic ice sheet another step drop in total mar is seen at 9 ma at site 1165 possibly reflecting diversion of sediment to a newly formed prydz channel fan

on the geographic and seasonal patterns of the near surface circulation on georges bank from real and simulated drifters abstract we examine the near surface circulation on georges bank by comparing data collected from satellite tracked drifters in the real ocean and data computed for simulated drifters in a virtual ocean the observed trajectory data set was obtained from drifters drogued at 10 m during the 1995 1997 us globec northwest atlantic georges bank field program the simulated drifter trajectories were computed based upon the seasonal circulation as predicted by the dartmouth circulation model using bimonthly climatological forcing the observed and simulated drifter patterns indicate well organized anticyclonic around bank flow on the northern flank northeast peak and southern flank throughout the year the key to recirculation around the bank is the seasonality of the northward flow in the great south channel winter months are characterized by little northward flow while there is significant northward flow in the great south channel in summer in late summer both observed and numerical drifters indicate a minimum recirculation time on georges bank of roughly 40 days the simulated drifter trajectories generally predict a seasonal climate consistent with the observed drifters though the effects of weather events on the observed drifters are not captured by the numerical simulations

long lived rossby wave trains as precursors to strong winter cyclones over europe the statistical connection between strong surface cyclones over europe and long lived upper tropospheric rossby wave trains is examined for the northern hemisphere winter season using 45 years of reanalysis data dates are selected for which the surface pressure anomaly over central europe is below a threshold yielding the 5 of lowest values composites of upper tropospheric meridional wind for these dates including a lead or lag in time display clear signs of a wave train the composite wave train lives for over two weeks and propagates eastward over more than 360 longitude the phase speed of individual lows and highs by contrast is close to zero and the same is true for the composite surface low there is a pronounced northward shift of the wave train as it propagates over the north american east coast although this composite wave train is statistically highly significant there is large scatter about the mean an index is defined that quantifies the similarity of the upper tropospheric meridional wind pattern for an arbitrary date with the composite wave train for a certain lead or lag given large positive values of the index there is an enhanced probability of a strong surface cyclone over central europe a few days later comparison with a previous study focusing on pacific cyclones shows noteworthy differences

differences in fine scale structure and composition of zooplankton between mixed and stratified regions of georges bank abstract transects were made with the video plankton recorder vpr in different water masses on the southern flank of georges bank in may 1992 ctd data chlorophyll fluorescence and attenuation were measured simultaneously images were recorded at a rate of 60 fields per second as the instrument was towed at 2 m s 1 4 knots tapes from high and low magnification cameras imaging volumes of 0 62 ml and 33 ml respectively were analyzed with respect to the distribution of copepods and other grazers as well as invertebrate predators this paper describes the differences in patterns of occurrence of important zooplankters in well mixed and stratified waters on the bank and in slope water south of these stations planktonic taxa were sampled over the same range of scales as the fluorescence and hydrography allowing direct visual comparisons of the spatial distributions of these variables late copepodites of calanus finmarchicus were strongly concentrated near the surface in the stratified area while a dense belt of limacina sp and oikopleura sp occurred below the pycnocline other fragile forms were also found to be dominant colonies of hydroid polyps were very abundant at the mixed station especially deeper in the water column indicating that they may have been transported up from the bottom colonies of the diatom chaetoceros socialis were abundant in the cold bottom water in the stratified region and also in the mixed area these colonies may have been in the process of sedimenting out of the water column as similarly sized and shaped marine snow was abundant in the same area in the slope water acantharia and trichodesmium were found in the chlorophyll maximum above the pycnocline other important genera encountered were pseudocalanus oithona centropages obelia pleurobrachia and sagitta taxa that occurred in all three areas were often differently distributed with respect to depth and physical parameters indicating that vernal stratification is an important structuring factor of plankton populations

the front on the northern flank of georges bank in spring 2 cross frontal fluxes and mixing buoyancy fluxes are downward and most intense reaching values of 5 10 7 w kg near the bottom at the edge of the bank and decrease both on and off bank horizontal crossbank buoyancy fluxes are partitioned into mean tidal pumping and nontidal eddy components and are computed as a function of cross isobath vertical position by averaging in the along isobath direction the tidal pumping component is dominant over most of the cross bank section with a peak value of 1 10 4 w kg directed off bank near the bank edge a diagnosed tidal vertical velocity field is used with mean buoyancy gradients to compute the along isopycnal skew flux the horizontal component of this skew flux has similar spatial structure and magnitude to that of the observed tidal pumping flux the divergent component of the skew flux at depths above the bottom boundary layer appears to be convergent north of the bank edge and divergent at the bank edge suggesting that tidally driven advective processes drive buoyant bank water downward and off bank at mid depth and force the upwelling of deep dense water near the bottom at the bank edge index terms 4528 oceanography physical fronts and jets 4568 oceanography physical turbulence diffusion and mixing processes 4560 oceanography physical surface waves and tides 1255 4544 oceanography physical internal and inertial waves keywords georges bank tidal mixing front globec internal tide skew eddy flux turbulent mixing

remote sensing for exploration an overview background material on measurement techniques and their physical basis as applied to rocks soils and vegetation new developments in high spectral resolution remote sensing for mineralogic and vegetation mapping modified journal abstract

imaging spectroscopy earth and planetary remote sensing with the usgs tetracorder and expert systems 1 imaging spectroscopy is a tool that can be used to spectrally identify and spatially map materials based on their specific chemical bonds spectroscopic analysis requires significantly more sophistication than has been employed in conventional broadband remote sensing analysis we describe a new system that is effective at material identification and mapping a set of algorithms within an expert system decision making framework that we call tetracorder the expertise in the system has been derived from scientific knowledge of spectral identification the expert system rules are implemented in a decision tree where multiple algorithms are applied to spectral analysis additional expert rules and algorithms can be applied based on initial results and more decisions are made until spectral analysis is complete because certain spectral features are indicative of specific chemical bonds in materials the system can accurately identify and map those materials in this paper we describe the framework of the decision making process used for spectral identification describe specific spectral feature analysis algorithms and give examples of what analyses and types of maps are possible with imaging spectroscopy data we also present the expert system rules that describe which diagnostic spectral features are used in the decision making process for a set of spectra of minerals and other common materials we demonstrate the applications of tetracorder to identify and map surface minerals to detect sources of acid rock drainage and to map vegetation species ice melting snow water and water pollution all with one set of expert system rules mineral mapping can aid in geologic mapping and fault detection and can provide a better understanding of weathering mineralization hydrothermal alteration and other geologic processes environmental site assessment such as mapping source areas of acid mine drainage has resulted in the acceleration of site cleanup saving millions of dollars and years in cleanup time imaging spectroscopy data and tetracorder analysis can be used to study both terrestrial and planetary science problems imaging spectroscopy can be used to probe planetary systems including their atmospheres oceans and land surfaces

the north atlantic oscillation response to large scale atmospheric anomalies in the northeastern pacific abstractingredients in the north pacific flow influencing rossby wave breakings in the north atlantic and the intraseasonal variations of the north atlantic oscillation nao are investigated using both reanalysis data and a three level quasigeostrophic model on the sphere first a long term run is shown to reproduce the observed relationship between the nature of the synoptic wave breaking and the phase of the nao furthermore a large scale low frequency ridge anomaly is identified in the northeastern pacific in the days prior to the maximum of the positive nao phase both in the reanalysis and in the model a large scale northeastern pacific trough anomaly is observed during the negative nao phase but does not systematically precede it then short term linear and nonlinear simulations are performed to understand how the large scale ridge anomaly can act as a precursor of the positive nao phase the numerical setup allows for analysis of the propagation of synoptic waves in the eastern pacific in the p

sediment mineralogy based on visible and near infrared reflectance spectroscopy visible and near infrared spectroscopy vnis can be used to measure reflectance spectra wavelength 350 2500 nm for sediment cores and samples a local ground truth cali bration of spectral features to mineral percentages is calculated by measuring reflectance spectra for a suite of samples of known mineralogy this approach has been tested on powders core plugs and split cores and we conclude that it works well on all three unless pore water is present initial vnis studies have concentrated on determination of relative proportions of carbonate opal smectite and illite in equatorial pacific sediments shipboard vnis based determination of these four components was demonstrated on ocean drilling program leg 199 rock colour is one of our oldest clues to com position and spectroscopy instruments now surpass the eye in providing quantitative compo sitional information the experimental technique is straightforward and non intrusive simply illu minate a rock surface record the spectrum of reflected light and extract any spectral responses that are sensitive to mineralogy reflectance spectroscopy can be used on powders core plugs and split cores and measurements take only seconds these advantages make the tech nique particularly attractive for depleted inter vals of core e g many basalts and for climate proxies requiring thousands of high resolution measurements

model study of the cross frontal water exchange on georges bank a three dimensional lagrangian experiment 1 characteristics of the cross frontal water exchange over georges bank are investigated through a sequence of numerical model experiments featuring realistic three dimensional 3 d bathmetry bi monthly averaged climatological stratification tidal forcing and mean and observed wind forcing the model used in this study is the ecom si version of the blumberg and mellor 1987 primitive equation model with mellor yamada 1982 level 2 5 turbulence closure the model domain includes georges bank and the gulf of maine and is forced at the open ocean boundary by the semidurnal m2 tide fluid particles were tracked in the 3 d time dependent eulerian flow field to examine the lagrangian flow field and passive tracer experiments were conducted to investigate the relative roles of advection and turbulent diffusion on cross frontal exchange two distinct paths for the on bank water movement were detected on georges bank one is over the northwestern flank of the bank where the bottom topography changes sharply in both along and cross bank directions and the other is near the bottom around the bank where the tidal mixing front is located over the northern flank the cross bank component of the lagrangian residual current is generally opposite in direction to that of the eulerian residual current resulting in an on bank cross frontal water transport near the bottom over the southern flank the near bottom water tends to converge toward the tidal mixing and shelf break fronts so that the near bottom flow over the shelf between these two fronts is divergent the response to wind forcing varied with ambient stratification and water depth in winter strong winds can drive a significant off bank water transport tending to wash out the bank in summer winds are generally too weak to alter the general pattern of tidal driven particle motion within the mixed region on the crest of the bank and the surrounding tidal mixing front some wind driven off bank transport occurs near the surface in the stratified region on the outer southern flank but this has little influence on water movement near the bottom passive tracer experiments reveal that the net cross frontal water flux near the bottom is caused primarily by advection and horizontal diffusion tidal induced vertical diffusion tends to make the tracer mix rapidly upward thus reducing the percent of the cross frontal flux due to advection our new model results are consistent with previous model studies of georges bank and agree in general with drifter and dye patches observed in the u s globec nw atlantic georges bank program

surface cyclones in the era 40 dataset 1958 2001 part i novel identification method and global climatology abstract a novel method is introduced to generate climatological frequency distributions of meteorological features from gridded datasets the method is used here to derive a climatology of extratropical cyclones from sea level pressure slp fields a simple and classical conception of cyclones is adopted where a cyclone is identified as the finite area that surrounds a local slp minimum and is enclosed by the outermost closed slp contour this cyclone identification procedure can be applied to individual time instants and climatologies of cyclone frequency fc are obtained by simple time averaging therefore unlike most other climatologies the method is not based on the application of a tracking algorithm and considers the size of cyclones in combination with a conventional cyclone center tracking algorithm that allows the determination of cyclone life times and the location of cyclogenesis and cyclolysis additional frequency fields can be obtained for special categories of cyclones that are gener

seasonal variability of sea surface temperature fronts on georges bank abstract sea surface temperature sst fronts extracted from archived 1985 1996 advanced very high resolution radiometer avhrr data are determined in the georges bank region resulting frontal locations clearly show the tidal mixing front on georges bank the probability of detecting an sst front at an individual pixel on georges bank is presented as a monthly climatology variations in the probability position and associated water depth of sst fronts in the georges bank region show the development of the tidal mixing front during the summer as well as the presence of a persistent front near the shelfbreak from the 12 yr time series of fronts 144 individual monthly frontal probability images are decomposed into the mean frontal position and empirical orthogonal functions eof using singular value decomposition svd spatial and temporal information from the first eof mode reveals the seasonal development of the tidal mixing front spatial patterns associated with the first mode also reveal the winter occurrence of fronts on the northeast peak area of georges bank which is most likely associated with scotian shelf water flow across the northeast channel the second mode also indicates the development of the hot spot often observed over georges bank during the late summer and early fall further evidence indicates that the mean position of detected sst fronts on southern georges bank changes approximately 10 km on bank from late spring to mid summer monthly mean positions are also compared to the distribution of simpson and hunter s 1974 tidal mixing parameter with resultant positions compared to historical stratification at those locations comparison of detected sst fronts to historical hydrographic data on georges bank points to the fronts being located in increasingly stratified water from may through august

quantification of glacial till chemical composition by reflectance spectroscopy abstract chemometric modelling of soil element concentrations from diffuse visible and near infrared vswir 350 2500 nm reflectance spectroscopic measurements holds potential for soil element analyses research has demonstrated it particularly for organic agricultural soils yet little is known about the vswir response of glacial tills soils with low organic matter content developed on unstratified glacial materials were studied at two geologically similar sites on the mafic metavolcanic rocks of the lapland greenstone belt in northern finland the till samples n 217 were composed primarily of quartz plagioclase and amphibole having less than 3 of clinochlore talc and illite vswir spectra of mineral powder

the impact of wave packets propagating across asia on pacific cyclone development abstract in this paper ecmwf 40 yr reanalysis data have been examined to study the influence of upper level wave packets propagating across asia into the pacific on surface cyclone development over the pacific previous studies have shown that in winter wave packets propagate across asia over two branches a northern branch over siberia and a southern branch along the subtropical jet across southern asia results presented here show that subsequent to the presence of wave packets on either branch the frequency of occurrence of deep cyclones defined as cyclones with central pressure below 960 hpa as well as explosively deepening cyclones those with a deepening rate of 1 bergeron or more are significantly enhanced this enhancement also clearly follows the wave packet eastward as it propagates across the pacific wave packets from the two branches are found to interfere with each other such that if wave packets of the appropriate configuration are present on both the northern and southern branch s

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

evaluating optical lightness as a proxy for carbonate content in marine sediment cores abstract optical lightness is increasingly being used as a proxy for the carbonate content of marine sediment we compared three measurements of optical lightness gray scale brightness and l to carbonate content to test the reliability of these measurements as carbonate content proxies in five piston cores from isotope stages 1 though 6 0 130 ka all measures of optical lightness are reasonable proxies of relative but not absolute changes in carbonate content in contrast in the upper sediments of odp hole 997a which are holocene to pliocene in age lightness values in only the top 10 m of the 180 m analyzed exhibit a strong correlation to carbonate content to better understand which factors control the optical lightness of sediments we analyzed samples in which carbonate content remained constant while the composition of three common clay minerals chlorite illite and kaolinite was varied kaolinite even at a concentration of 20 did not significantly change optical lightness however 20 illite reduced optical lightness by 30 and 20 chlorite reduced lightness by 20 we conclude that regional and temporal changes in the composition of the non carbonate sediment fraction may significantly alter the relationship between lightness and carbonate content we recommend that care must be taken when applying these measures to sediment sequences which span long time intervals or to sediment samples taken over a broad geographical areas

water sources for georges bank abstract the origins of georges bank source waters can be quantified by the oxygen isotope salinity tracer regionally water is tagged by freshwater of different h 2 18 o h 2 16 o ratios and these waters can subsequently be identified after mixing downstream this conservative lagrangian tracer of source waters is useful for tracking passive plankton and larvae that may be important to sustain the georges bank ecosystem the origin of georges bank freshwater sources is primarily in the gulf of st lawrence consisting of labrador shelf water which enters via the strait of belle isle and st lawrence river water these two mix with the underlying slope water in the gulf of st lawrence and along the scotian shelf at the northeast channel the input to the gulf of maine there is a single freshwater endmember consisting of 5 6 st lawrence river water and 94 6 labrador shelf water by volume these proportions remained constant for the years 1995 1997 the water on central georges bank consists of a mixture of water entering the northeast channel with gulf of maine river outflow there is considerable interannual variation in the maine river water proportion ranging from 3 3 in 1982 to 0 23 by volume in 1996 during 1995 1998 there was no correlation between georges bank salinity which decreased monotonically and the proportion of maine river water on the bank the interannual fluctuations of salinity on georges bank are driven by variations in upstream scotian shelf sources and its mixing onto the bank and not by changes in local river outflow

the modification of baroclinic waves by the rocky mountains abstract the author diagnoses two observed cases of rocky mountain lee cyclogenesis and perform several idealized simulations to understand the effect of the mountains on incident baroclinic waves several issues are examined 1 in what sense is the effect of the mountains cyclolytic and why 2 what is the effect of adding a mean surface wind 3 what sorts of behavior may result in differing mean flows and 4 what is a useful conceptual framework in which to view lee cyclogenesis the dynamical underpinning for analysis of observations and idealized simulations is the quasigeostrophic qg equations the author finds that the most important effect of the mountains is to alter the mean distribution of surface potential temperature and hence change the propagation characteristics of the incident baroclinic wave the presence of a mountain enhances the gradient of the qg approximation to surface potential temperature to the north of the peak and decreases it to the south thus the component of the b

chemical weathering and provenance evolution of holocene recent sediments from the western indus shelf northern arabian sea inferred from physical and mineralogical properties abstract we present a multi proxy mineral record based on x ray diffraction and diffuse reflectance spectrophotometry analysis for two cores from the western indus shelf in order to reconstruct changing weathering intensities sediment transport and provenance variations since 13 ka core indus 10 is located northwest of the indus canyon and exhibits fluctuations in smectite illite chlorite ratios that correlate with monsoon intensity higher smectite illite chlorite and lower illite crystallinity normally associated with stronger weathering peaked during the early mid holocene the period of maximum summer monsoon hematite goethite and magnetic susceptibility do not show clear co variation although they both increase at indus 10 after 10 ka as the monsoon weakened at indus 23 located on a clinoform just west of the canyon hematite goethite increased during a period of monsoon strengthening from 10 to 8 ka consistent with increased seasonality and or reworking of sediment deposited prior to or during the glacial maximum after 2 ka terrigenous sediment accumulation rates in both cores increased together with redness and hematite goethite which we attribute to widespread cultivation of the floodplain triggering reworking especially after 200 years ago over holocene timescales sediment composition and mineralogy in two localities on the high energy shelf were controlled by varying degrees of reworking as well as climatically modulated chemical weathering

statistical behavior of transient eddies near mountains and implications for theories of lee cyclogenesis abstract we examine the nature and spatial structure of meteorological high frequency variability in two selected areas one including the alps and the other the rocky mountains seven years of geopotential height data derived from ecmwf analysis set have been filtered in order to remove periods longer than 6 7 days statistical analysis performed on the filtered series include one point lag correlations and composites that reveal changes in the typical horizontal structure and path of traveling eddies as they move from the oceans to the adjacent mountainous regions the important modifying action of the orography is shown and lee cyclogenesis is interpreted as one aspect of such action cross correlation maps between upper and lower tropospheric levels reveal the effect that mountains also exert on the vertical structure of baroclinic eddies these statistical results are discussed and compared with those predicted by theories of cyclogenesis in the lee of the alps and the rocky mountains and by the

mineralogy of aeolian dust reaching the north pacific ocean 2 relationship of mineral assemblages to atmospheric transport patterns atmospheric dust particles actually comprise a small number of mineral assemblages we determined the composition of these assemblages and their geographic distribution by statistical analysis of mineralogy data air mass trajectory analysis was used to identify transport paths and possible source regions for these samples three types of trajectories are most common and each displays different proportions of four mineral assemblages the first indicates outflow of air from central asia and is associated with an illite rich mineralogy the second type comprises trajectories which include low altitude transport over the japanese islands for mixed mineralogies which contained a small amount of the illite rich end member the third type is made up of trajectories crossing the north american continent and is present exclusively in the eastern north pacific area there is a mixed mineralogy associated with these trajectories our results suggest that both source area mineralogy and transport pathway contribute to the compositional variability of the mineral aerosol at a given location the results presented here show that event specific meteorological data can be useful in understanding spatial patterns of eolian transport

interpretation of the effect of mountains on synoptic scale baroclinic waves abstract linear and nonlinear simulations of idealized baroclinic waves interacting with topography are examined in the context of quasigeostrophy the purpose is to provide a simple conceptual interpretation of the transients resulting from this interaction a perturbation expansion is employed with the small parameter being proportional to topographic slope to isolate fundamentally different topographic effects and show how they enter systematically at each order first and second order corrections appear to capture the essence of the topographic effect for all cases considered even for values of the small parameter as large as 0 5 and are qualitatively useful for a parameter value of unity results indicate the importance of surface rossby wave dynamics at first order near the mountain and downshear from the mountain a distance inversely proportional to the growth rate of the most unstable mode of the system the second order correction projects onto the initial baroclinic wave being primarily

near infrared spectral reflectance of mineral mixtures systematic combinations of pyroxenes olivine and iron oxides near infrared spectral reflectance data are presented for systematic variations in weight percent of two component mixtures of ferromagnesian and iron oxide minerals mixtures were chosen for application to the study of the dark materials on mars but the results are equally applicable to mafic and ultramafic assemblages elsewhere in the solar system olivine spectral features are greatly reduced in contrast by admixture of other phases but remain distinctive even for low olivine contents clinopyroxene and orthopyroxene mixtures show resolved pyroxene absorptions near 2 m the addition of limonite greatly modifies pyroxene and olivine reflectance but does not fully eliminate distinctive spectral characteristics using only spectral data in the 1 m region it is difficult to differentiate orthopyroxene and limonite goethite in a mixture additional spectral coverage or other evidence may be required for a unique interpretation all composite mineral absorptions observed in this study are either weaker than or intermediate in strength to the end member absorptions and have bandwidths greater than or equal to those for the end members in general spectral properties in an intimate mixture combine in a complex nonadditive manner with features demonstrating a regular but usually nonlinear variation as a function of end member phase proportions

diapycnal flow through the georges bank tidal front a dye tracer study a fluorescent dye tracer fluorescein injected into the bottom mixed layer at the seaward edge of the tidal front on georges bank has provided the first quantitative measurement of an on bank diapycnal lagrangian flow through the front from the warming of the dye patch 2 5 10 6 c s and 7 8 10 6 c s on the south flank and northeast peak respectively as it passed through the frontal temperature gradient we infer an on bank flow of 1 9 cm s on the south flank and 3 2 cm s on the northeast peak the heat flux required for this warming is predominantly due to vertical mixing within the tidal front these observations further demonstrate the utility of direct lagrangian measurements and provide quantitative estimates of the cross frontal exchange on georges bank the focus of the u s globec northwest atlantic georges bank phase iii program

development of sediment drifts approaching an active plate margin under the sw pacific deep western boundary current the abyssal pacific ocean is fed by a 1000 km wide deep western boundary current dwbc that flows northward along the continental margin east of new zealand between the passive margin of chatham rise and the subduction zone of kermadec trench a distance of 1200 km the dwbc has formed a suite of sediment drifts over a depth range of 2200 5700 m airgun and 3 5 khz profiles record a variety of drift types that reflect regional variations in bathymetry sediment supply and the tectonic volcanic framework on chatham rise the dwbc has deposited a sinuous linear body along the south flank 3000 m an extensive apronlike drift on the north flank 2200 4500 m and a ridgelike drift about the rise base 4500 5200 m the flow has also deposited a body of sediment over 400 km long within a moat at the base of the nearby louisville seamount chain further downcurrent the 250 km long rekohu drift 3600 4190 m has developed northward to 39 s south of this latitude drifts comprise mainly reworked pelagic hemipelagic material and sediment transported from distant southerly sources in contrast drifts north of 39 s have received a major injection of terrigenous sediment from hikurangi channel which runs 1400 km from new zealand eastward across the hikurangi plateau to disgorge on to the abyssal floor at the plateau edge en route turbidity current overspill from the channel has moved north under the influence of the shallow dwbc to contribute to a series of small ridge and patch drifts among the numerous seamounts on the plateau at 3500 4200 m off hikurangi channel mouth a large fan has accumulated the dwbc has extended the fan into a drift running over 250 km along the base of hikurangi plateau 5150 5770 m toward kermadec trench here drift sediment becomes increasingly disrupted by mass wasting associated with the active subduction in this area the seismic stratigraphy reveals the drifts to rest mainly on a widespread erosional surface that is interpreted to mark the inception of the dwbc in the region with the late oligocene opening of the australian antarctic seaway drift construction commenced during the miocene but was punctuated in the late miocene by another period of erosion that coincided with increased bottom water production in antarctica deposition resumed in plio pleistocene times when large quantities of sediment from the rapidly rising landmass of new zealand were injected into the boundary current the modern flow continues to affect drift deposition as manifest by an active boundary channel along the foot of hikurangi plateau and widespread scour zones and sediment wave fields

response of surface water masses and circulation to late quaternary climate change east of new zealand a series of cores from east of new zealand have been examined to determine the paleoceanographic history of the late quaternary in the sw pacific using planktonic foraminiferal data distinct shifts of species can be seen between glacial and interglacial times especially south of chatham rise east of south island foraminiferal fragmentation ratios and benthic planktonic foraminiferal ratios both show increased dissolution during glacials especially isotope stage 2 to the south of chatham rise the present day subtropical convergence appears to be tied to the chatham rise at 44 s but during glacial times this rise separated cold water to the south from much warmer water to the north with an associated strong thermal gradient across the rise we estimate that this gradient could have presented as much as an 8 c temperature change across 4 of latitude during the maximum of the last ice age there is only weak evidence of the younger dryas cool event but there is a clear climatic optimum between 8 and 6 4 ka with temperatures 1 2 c higher than the present day the marine changes compare well with vegetational changes on both south and north island

acoustical study of the spatial distribution of plankton on georges bank and the relationship between volume backscattering strength and the taxonomic composition of the plankton abstract high frequency 420 khz sound was used to study the volume backscattering from plankton and micronekton over georges bank as part of a study designed to determine the correlation length scales of plankton spatial patterns in relation to physical structure and to intercompare different kinds of sampling and remote sensing instrumentation two physically distinct areas were studied a well mixed area in a shallow portion of the bank and a stratified area on the deeper southern flank of the bank a submersible echo sounder with a down looking transducer was mounted in a towed v fin volume backscattering data were collected from near the sea surface to the bottom 40 80 m vertical and horizontal volume backscattering structure in the stratified region differed from that in the well mixed area in both mean and variance providing evidence that physical forcing of the pattern varied significantly between the two areas internal waves appeared to modulate the depth of dense mid depth volume scattering layers in the stratified sites in the mixed area there was little horizontal layering or coarse scale horizontal structure however fine scale vertical lineations were evident with horizontal length scales on the order of the depth of the water column one hypothesis to explain these vertical lineations in the well mixed areas involves the development of secondary vertical circulation cells associated with the tidal flows over a rough bottom although volume backscattering at the stratified sites was 4 7 times higher than at the mixed site there was no significant difference in mocness multiple opening closing net and environmental sensing system collected biovolumes between these locations the difference in volume backscattering was due to differences in both the acoustic scattering properties of zooplankton taxa and the taxonomic composition of the plankton between the sites correlations between taxon abundance and volume scattering were positive and significant only for pteropods and euphausiid larvae the abundances of copepods chaetognaths fish larvae and amphipods were not significantly correlated with volume scattering when taxon specific model predictions of acoustic backscattering cross section developed by stanton et al ices journal of marine science 51 1994 505 512 were used with field collected individual size and abundance data to predict measured volume backscattering data good agreement was found between observed and predicted volume backscattering strengths

new techniques in sediment core analysis an introduction marine sediment cores are the fundamental data source for information on seabed character depositional history and environmental change they provide raw data for a wide range of research including studies of global climate change palaeoceanography slope stability oil exploration pollution assessment and control and sea floor surveys for laying cables pipelines and siting of sea floor structures during the last three decades a varied suite of new technologies have been developed to analyse cores often non destructively to produce high quality closely spaced co located downcore measurements characterizing sediment physical properties geochemistry and composition in unprecedented detail distributions of a variety of palaeoenvironmentally significant proxies can now be logged at decadal and in some cases even annual or subannual scales allowing detailed insights into the history of climate and associated environmental change these advances have had a profound effect on many aspects of the earth sciences particularly palaeoceanography in this paper we review recent advances in analytical and logging technology and their application to the analysis of sediment cores developments in providing access to core data and associated datasets and data mining technology in order to integrate and interpret new and legacy datasets within the wider context of sea floor studies are also discussed despite the great advances in this field however challenges remain particularly in the development of standard measurement and calibration methodologies and in the development of data analysis methods new data visualization tools and techniques need to be developed to optimize the interpretation process and maximize scientific value amplified collaboration environments and tools are needed in order to capitalize on our analysis and interpretation capability of large multi parameter datasets sophisticated yet simple to use searchable internet databases with universal access and secure long term funding and data products resulting in user defined data mining query and display so far pioneered in the usa and australia provide robust models for efficient and effective core data stewardship

coastally trapped wind reversals along the united states west coast during the warm season part ii synoptic evolution abstract this paper describes the synoptic evolution associated with coastally trapped wind reversals along the west coast of the united states from april through september gridded national centers for environmental prediction formerly national meteorological center synoptic analyses are composited relative to the initiation of both weak and strong coastal southerlies at four coastal buoys offshore of oregon and california a similar composite synoptic evolution accompanies the transition from northerlies to southerlies at each site at 500 mb there is anomalous ridging over the eastern pacific while at 850 mb and the surface the east pacific high extends into southwestern canada and the pacific northwest the result is offshore flow and subsidence along the mountainous west coast that produces a strengthening and coastal extension of the trough normally resident over the interior of southern and central california this anomalous coastal troughing weakens the offshore gradient and establishes an alon

ultrahigh resolution total organic carbon analysis using fourier transform near infrarred reflectance spectroscopy ft nirs 1 fourier transform near infrared reflectance spectroscopy ft nirs is a cheap rapid and nondestructive method for analyzing organic sediment components here we examine the robustness of a within lake ft nirs calibration using a data set of almost 400 core samples from lake suigetsu japan as a means to rapidly reconstruct total organic carbon toc we evaluate the best spectra pretreatment examine different statistical approaches and provide recommendations for the optimum number of calibration samples required for accurate predictions results show that the most robust method is based on first order derivatives of all spectra modeled with partial least squares regression we construct a toc model training set using 247 samples and a validation test set using 135 samples for test set r2 0 951 rmse 0 280 to determine toc and illustrate the use of the model in an ultrahigh resolution e g 1 mm annual study of a long sediment core from a climatically sensitive archive

near surface horizontal convergence and dispersion near the tidal mixing front on northeastern georges bank abstract horizontal dispersion and convergence are evaluated from near surface drifter data collected during the summer and autumn of 1988 and summer of 1989 in the vicinity of the tidal mixing front on northeastern georges bank the effective horizontal diffusivity coefficient k e estimated from the relative motion of the drifters over the duration of the cluster tracking increases as the cluster length scale with a range from approximately 100 to 450 m 2 s 1 for length scales of approximately 5 to 58 km at length scales k e is near zero with many negative estimates indicative of convergence at length scales 20 km k e increases in magnitude and scatter above 30 km length scales k e is typically between 200 400 m 2 s 1 the dispersion as a function of length scale is compared to published estimates using apparent diffusivities which are adjusted for the finite size of the drifter cluster at release georges bank shows lower apparent diffusivities at length scales 20 km the latter are believed to be principally due to the large horizontal gradients in the seasonal flow field although other processes perhaps associated with the large tidal currents may also contribute at the shorter length scales the low dispersion is due to convergent processes examples of convergence at different locations and under different wind and stratification conditions are presented convergence near the tidal mixing front tends to occur under light wind conditions and was observed in both seasons and in both years during two intense southwestward windstorms drifters also converged in the bank s vertically well mixed zone apparently due to a combination of spatially varying ekman depth and topographic effects

lee cyclogenesis part i analytic studies abstract the growth of synoptic scale cyclones imbedded in a baroclinically unstable zonal flow over a long straight mountain range is investigated two different analytical models of the phenomenon are used the first model uses the linearized quasi geostrophic equations it allows a simple superposition of a steady state mountain forced solution and a transient eady wave there is no dynamic interaction between the two solutions but the time evolution of the combined solution reproduces many characteristics of a disturbance passing over the rocky mountains the semigeostrophic equations are used in the second model these equations allow a linear solution in transform space but the transformation of the solution to physical space is nonlinear this allows an interaction between the mountain forced and transient solutions the minimum pressure developed by the semigeostrophic system is the same as that of the quasi geostrophic system however the shape of the wave is distorted this effect is caused b

a novel sedimentological method based on ct scanning use for tomographic characterization of the galicia interior basin abstract non destructive techniques of core analysis especially of marine cores are being broadly employed for sedimentary paleoceanographic and paleoclimate research in particular computed tomography scanning ct scanning allows acquisition of 3d and 2d images according to desired planes and thus the identification of sedimentary structures large grains and their distributions as well as direct measurements of material densities the most significant contribution of this technique is the possibility of getting results before opening the core in this work ct scan data obtained for five cores from the galicia interior basin gib nw peninsula iberia are presented and discussed focussing on 1 methodology of the ct scan use 2 tomographic description of sedimentary facies identified in the gib 3 treatment of the numeric data obtained with ct scanning using specific software anidoc and 4 comparison of tomographic data with data obtained by conventional methodologies of core analysis the most singular feature of gib cores is the presence of ice rafted debris ird deposited during late pleistocene heinrich events he which can be easily recognized using the ct scan by the presence of high radio density grains immersed in a low radio density matrix comparison of ct scan data with analytical sedimentary data and he proxies performed on the cores validates the ct scanning method as a powerful tool to improve correlations identify well constrained events and make more accurate basin reconstructions without opening all the cores in an oceanographic study

a model of rocky mountain lee cyclogenesis abstract a quasi geostrophic model of cyclogenesis in the lee of the rocky mountains treats the cyclogenesis as a forecasting problem and uses an initial value approach the model consists of the interaction of a growing baroclinic wave with an infinitely long mountain ridge this transient interaction simulates many of the observed features of the phenomena including the formation of a lee trough concurrent with the poleward displacement of the incident low on the upstream side of the mountain and the development of a lee cyclone equatorward of the unperturbed storm track despite this development the low is weakened by its interaction with the orography these results are explained physically and compared with those using a normal mode approach to lee cyclogenesis

tidal front entrainment and retention of fish larvae on the southern flank of georges bank abstract from a grid of stations across the southern flank of georges bank in may 1997 larval haddock and cod were observed to be concentrated across the tidal front in a band 10 20 km wide several cross bank ctd and acoustic doppler current profiler adcp sections indicated a narrow 35 m cross isobath residual flow 0 6 1 2 cm s

the role of frontal currents in larval fish transport on georges bank abstract the hydrography and distributions of cod larvae on georges bank were surveyed during two research cruises in april and may 1993 in order to relate larval drift between cruises to the vernal intensification of the frontal component of the residual circulation we observed the transport of two patches of cod larvae one patch which had maximum larval cod densities of 45 larvae 100 m 3 in april appeared to have been advected south about 75 km between surveys while the other which had maximum larval cod densities of 20 larvae 100 m 3 in april appeared to have been advected north northeast about 25 km maximum larval densities in each patch sampled during the second cruise in may were 15 and 18 larvae 100 m 3 respectively and mean growth in total length for larvae in the two patches was approximately 5 5 mm and 4 5 mm respectively between the two cruises during the april cruise there was a large volume of anomalous cold fresh water of scotian shelf origin which occupied much of the eastern third of georges bank during may relatively cold fresh water appeared in a band from the northeast peak along the southern flank between georges bank water on the top of the bank and upper slope water offshore the distribution of cold fresh water suggests its participation in the general clockwise circulation around the bank the transport of cod larvae comprising the first patch appeared to become organized within and move along the frontal boundary established by the scotian shelf like water mass while larvae in the second patch which we assumed to have moved to the north may have been transported northward in an on bank flow of warmer and saltier upper slope water which may have originated from a gulf stream ring based upon observed transport of the first patch of larvae in relation to the frontal boundary we present a conceptual model of frontal mixing currents on georges bank where current velocities may reach 5 cm s 1 at the depth of the pycnocline we suggest that this frontal component of the residual circulation which is in addition to that resulting from tidal rectification may be important in the transport of fish larvae and that interannual variability in the degree of intrusion of extrinsic water masses may contribute to variable larval cod drift patterns to variable larval cod retention on the bank and ultimately to variable larval fish recruitment to the early juvenile stage

regional sediment recycling in the abyssal southwest pacific ocean an active plate boundary with a high sediment output three major submarine channels and the world9s largest deep western boundary current dwbc make up an extensive recycling system along the 4500 km continental margin east of new zealand seismic reflection sedimentary and oceanographic data demonstrate that detritus from the rising mountains of the new zealand plate boundary is transferred to the southwest pacific abyssal floor by turbidity currents flowing along solander 450 km long bounty 950 km and hikurangi 1400 km channels these conduits discharge directly into the dwbc which transports material north to form a series of sediment drifts the northernmost drift containing sediment from hikurangi channel and eroded drifts to the south is now subducting into kermadec trench geochemical data suggest that sediment is recycled through the mantle to re emerge in the arc volcanic rocks thus one cycle is completed and a new one begins

lee cyclogenesis part ii numerical studies abstract the effect of topography on the evolution of a disturbance in a baroclinically unstable mean flow is studied using a three dimensional primitive equation model a procedure is developed to compare control integrations with no topography with integrations that contain topography it is found that lee cyclogenesis is caused primarily by the superposition of a growing baroclinic wave with a steady orographically forced wave of the same scale some additional lee growth is found that may be orographically enhanced or it may be related to certain small problems in the experimental set up as the disturbances move over the ridge they are deflected to the north on the upwind side wore returning to their original latitudes on the lee side the numerical results in this paper are in general agreement with the authors previous analytic study

the onshore surge of marine air into the pacific northwest a coastal region of complex terrain abstract many coastal locations around the world experience rapid transitions from warm dry continental air to cool moist marine air these onshore pushes or surges of marine air can be accompanied by strong winds large temperature drops and a substantial increase in low clouds a detailed case study of a typical pacific northwest event as well as a composite of several events are presented it is shown that all major surges are initiated by synoptic scale changes and that the mesoscale topography of the region amplifies the synoptic signal annual monthly and diurnal climatologies are discussed this paper also discusses the origin of associated west coast phenomena such as heat troughs and narrow coastal pressure ridges

asian summer monsoon influence on chemical weathering and sediment provenance determined by clay mineral analysis from the indus submarine canyon clay minerals from the indus canyon and eastern clinoform since 12 ka are uniformly rich in smectite and illite similar to those from the holocene indus flood plains a systematic enrichment of smectite in the proximal delta compared to the canyon and eastern clinoform argues for preferential capture of smectite close to the river mouth since 12 ka there is a rapid shift to a more smectite rich assemblage in the canyon and eastern clinoform after 5 ka this change is probably caused by a change in sediment source with less direct flux from the himalaya and more erosion of older weathered smectite rich sediment from the indus river flood plains driven by incision of the indus and its tributaries into the floodplain as summer monsoon rains weakened this influx of smectite is consistent with lower kaolinite smectite values since 5 ka the onset of large scale agricultural activities since 5 ka especially starting with the harappan civilization may also have enhanced incision and erosion of floodplain sediments over the same time period this study reports for the first time how monsoon strength variations since 12 ka affected the clay mineral assemblages and sediment provenance in a major submarine canyon

determining the composition of late quaternary marine sediments from nuv vis and nir diffuse reflectance spectra abstract as the length of marine cores increases and sampling intervals decrease the need for rapid and inexpensive means of determining sediment composition has become apparent in this study we examine one potentially useful technique for assessing compositional changes in marine cores diffuse reflectance spectrophotometry we examined nearultraviolet visible and near infrared reflectance spectra from five data sets each data set consists of calibration samples and test samples the calibration samples spectra were related to a sediment component using multiple linear regression the resulting regression or calibration equations were then evaluated using the test samples calibration equations were written relating spectra to several sediment components including carbonate atlantic and east pacific rise odp site 847 organic carbon content atlantic and east pacific rise and opal content east pacific rise the correlation coefficients for the regression equations ranged from a high of 0 99 for carbonate and opal at odp site 847 to a low of 0 97 for atlantic carbonate indicating that spectral variations are highly correlated to sediment composition all of the equations include a substantial number of variables from shorter visible and longer near ultraviolet wavelengths suggesting that these wavelengths are especially important for devices designed specifically to scan marine cores although equations for estimating organic and carbonate content appear independent of other sediment components the opal equation is strongly dependent on carbonate content indicating that opal concentration is correlated to carbonate content tests of the calibration equations indicated that all our equations reasonably estimate the pattern of changes either down core or in surface sediments where our spectral estimates have difficulty is with absolute values frequently over or underestimating observed values by a substantial amount within these limitations diffuse reflectance spectrophotometry can be a useful tool for characterizing marine cores and as our understanding of the relationship between spectra and mineralogy improves so will estimates of absolute values