on the wave number spectrum of oceanic mesoscale variability observed by the seasat altimeter variations of sea surface height measured by the seasat altimeter in nearly repeat orbits during the last 24 days of the mission are used to compute the wave number spectrum of mesoscale variability in various parts of the oceans the instrument noise level 150 cm2 cycles km has limited the resulting oceanic spectrum to wavelengths longer than 100 km we found that the characteristics of the oceanic spectrum are dependent on the energy level of the mesoscale variability in the high energy areas close to major current systems most of the energy is contained at wavelengths longer than 250 km at wavelengths shorter than 250 km the spectrum basically follows a k 5 k is wave number dependence in the low energy areas remote from major current systems the spectrum follows a k 1 dependence at wave lengths from 100 to 1000 km based on the assumption of horizontal isotropy of mesoscale variability scalar wave number spectra of sea surface height and geostrophic kinetic energy are also presented dynamical implications of these spectra are discussed the effects of residual geoid and atmospheric water vapor on the computed oceanic spectra have been rigorously examined it was found that the general characteristics of the oceanic spectra were not significantly affected by them

soil metal pollution from former zn pb mining assessed by geochemical and magnetic investigations case study of the bou caid area tissemsilt algeria former zinc and lead mines that have been operating for half a century are located in the massif of bou caid tissemsilt algeria hazardous heavy metals emitted from the mines are abundant in the surrounding soil and cause strong metal pollution in the region this paper investigates the extent of lead and zinc mine activity derived pollution by characterizing both magnetic and geochemical properties of samples collected in the vicinity of the mines the results of the magnetic study show the coexistence of magnetic minerals such as magnetite hematite and goethite analyses on surface soils and weathered rocks suggest that hematite and goethite have ore related lithogenic origins magnetic susceptibility shows a positive correlation with lead content when present in low to medium concentrations 500 mg kg at higher lead concentrations there is no correlation with magnetic susceptibility the relationship between magnetic susceptibility and zinc content is not straightforward these observations are explained by the higher affinity of pb to iron oxides at lower pollution levels and their preferential bonding to carbonates when pb and zn contents are extremely high as demonstrated by iavazzo et al j geochem explor 113 56 67 2012 in a study of former zn pb mine in morocco based on the general features of the spatial maps of field measured magnetic susceptibility mass specific magnetic susceptibility pb and zn contents it is concluded that field magnetic measurements provide a good qualitative proxy of pollution spread out of the mining galleries while laboratory measurements afford a more detailed investigation of the links between iron oxides and the main heavy metals in the ore

from swallow floats to argo the development of neutrally buoyant floats neutrally buoyant floats have been a vital tool in the exploration of the global ocean circulation and now provide a central element of the in situ ocean observing system through the argo project the paper traces the development of neutrally buoyant floats from their origins in the mid 1950s to the present day and highlights areas of ocean science to which floats made significant contributions

potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

airborne expendable bathythermograph survey of the kuroshio extension and comparison with simultaneous altimeter measurements during the geosat exact repeat mission extensive airborne expendable bathythermograph axbt sections across the kuroshio extension during the geosat exact repeat mission erm were used to assess the ability of the geosat altimeter to monitor the locations of the kuroshio and its associated cold and warm core eddies the axbt sections in themselves provide detailed descriptions of the kuroshio extension to about 160 e these observations demonstrated that surface or near surface temperatures in this area may lead to incomplete and deceptive descriptions of the deeper thermal structure kuroshio eddy interactions in particular were not accurately portrayed by the near surface observations for this reason accurate mapping of the location of the kuroshio extension and of nearby eddies may not be practical from infrared ir imagery alone but requires augmentation from other measurement systems such as altimetry in the present analysis an estimate of the sea surface height was obtained from the altimeter ranges by time averaging sea surface heights in lieu of a geoid estimate sea surface height anomalies computed using the mean altimetric sea surface i e the geoid plus the temporal mean oceanographic signal can be significantly different from the actual oceanographic topography induced by mesoscale oceanographic features nevertheless it is shown that the positions of the kuroshio extension and of the stronger cold and warm core eddies associated with the kuroshio extension are easily located from these altimetric sea surface anomalies

status of the geopotential substantial progress has been made in modeling the geopotential field since the last reporting period anderle 1979a models of the gravity potential show improvement across the entire gravitational spectrum with resolution down to 1 haif wavelength major sources of data utilized for advancing our knowledge of the geopotential field consist of satellite laser ranging smith 1982 wilson 1979 linder 1981 which contributed to the long wavelength portion of the spectrum satellite altimetry geos 3 1979 seasat 1981 and improved surface gravity anomalies rapp 1981b both of which contributed to the intermediate and short wavelength features of the spectrum uniform global distribution of data in combination solutions is generally achieved by using altimeter data over the ocean and terrestrial gravity anomalies over land

quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation abstract a new method of analysing isothermal remanent magnetisation irm acquisition curves based on cumulative log gaussian analysis robertson and france phys earth planet inter 82 1994 223 234 is proposed it is based on the curve fitting of the irm acquisition curve versus the logarithm of the applied field with i the acquisition curve on a linear scale ii the acquisition curve expressed as a gradient and iii the acquisition curve on a probability scale even when a sample is not saturated its magnetic properties can be defined although with less certainty the number of magnetic components required for an optimal fit to a measured irm acquisition curve is evaluated statistically the method discriminates on the basis of different mineral coercivity therefore additional rock magnetic tests are still required to separate minerals with similar coercivities

comparison data for seasat altimetry in the western north atlantic the radar altimeter flown on seasat in 1978 collected approximately 1000 orbits of high quality data 5 8 cm precision in the western north atlantic these data have been combined with a detailed gravimetric geoid in an attempt to produce profiles of dynamic topography in order to provide a basis for evaluation of these profiles available oceanographic observations in the gulf stream sargasso sea region have been compiled into a series of biweekly maps the data include xbt s satellite infrared imagery and selected trajectories of surface drifters and subsurface sofar floats the maps document the known locations of the gulf stream cyclonic and anticyclonic rings and mid ocean eddies during the period july october 1978

a synthetic geoid validation of geosat mesoscale dynamic topography in the gulf stream region a validation study is carried out for the geosat altimeter in the gulf stream meander and ring region a synthetic geoid containing the medium scales of interest for mesoscale research is constructed by subtracting an independent estimate of the oceanographic mean dynamic topography from the altimetric sea surface the oceanographic mean dynamic topography which is concurrent with the altimetric mean is derived from a year of real time nowcasts and forecasts gulfcast based on assimilating a composite data set into a dynamical model using the synthetic geoid absolute dynamic topography from geosat and gulfcast for a year and 4 months in 1988 and 1989 compare very well in signal shape and feature locations sixteen cases of comparison of dynamic heights derived from axbts along geosat tracks in 1987 are made with geosat absolute topography the rms difference is less than 10 cm thus the comparison of these two independent data sets validates the altimeter and the synthetic geoid within the noise and error levels of the system

seasat altimeter determination of ocean current variability radar altimeters of great precision roughly equal10 cm such as the one that flew on the seasat satellite are capable of measuring the small oceanic height variations associated with geostrophic ocean currents an experiment was concluded in the kuroshio current east of japan verifying this capability air expendable bathythermographs axbt s were dropped to coincide with the seasat subtract during flights on september 25 and october 5 and 13 1978 changes in surface dynamic height between flights were inferred from the axbt data they agreed generally to within 10 cm of height changes observed in the altimeter data

magnetic mineral assemblages in soils and paleosols as the basis for paleoprecipitation proxies a review of magnetic methods and challenges abstract magnetic iron oxide minerals principally magnetite maghemite hematite and goethite are formed in well drained soils in response to a suite of physical chemical and biological factors despite a wide range of complexity in the pedogenic processes that lead to magnetic mineral formation dissolution and transformation there are well documented empirical relationships between various magnetic mineral assemblages in soils with environmental and climatic conditions recently there has been an increase in the number of quantitative magnetic paleoprecipitation proxies that have been developed and there is great potential for magnetic methods to be used in the geologic record to develop reconstructions of past climates magnetic paleoprecipitation proxies have been widely utilized in quaternary or younger loess paleosol systems however they have yet to be utilized in the pre quaternary fossil record future studies of magnetic mineralogy of soils and paleosols should aim to explore non loessic modern soils and pre quaternary paleosols with more focus on understanding the interaction between magnetic mineral assemblages and soil moisture applications of existing and novel magnetic paleoprecipitation proxies in the fossil record should prove to be a valuable resource for paleoclimatologists

the seasat altimeter data and its accuracy assessment the seasat satellite launched on june 27 1978 carried a radar altimeter designed to measure the altitude of the satellite above the ocean surface the surface wave height and the ocean surface backscatter coefficient from which wind speed can be inferred postlaunch engineering assessment indicated that the seasat altimeter met the performance specification for 10 cm precision noise in the altitude measurements however to determine the accuracy of this measurement as well as the accuracy of the wave height and wind speed measurements a significant calibration validation and model development effort was required this summary describes the instrument atmospheric and geophysical effects which influence the radar altimeter measurement accuracies and the attendant correction models adopted for the altimeter geophysical data record also summarized are the activities of the seasat altimeter precision orbit determination experiment team directed towards the validation and improvement of these models as well as the investigations required to assess the accuracy of the altimeter measurement and the computed satellite altitude ephemeris finally an accuracy assessment is made for the various altimeter measurement corrections which are included on the altimeter geophysical data record

seasat altimeter observations of dynamic topography in the gulf stream region individual seasat altimeter profiles in the western north atlantic have been differenced with the best available geoid model to remove the gravitational component the resulting sea surface height profiles compare remarkably well with independent oceanographic observations the gulf stream is clearly apparent in each profile as a 1 to 2 m step and known positions of cyclonic and anticyclonic rings correspond with depressions and elevations respectively with amplitudes as large as 95 cm some of the most important altimeter data for analyzing the dynamic ocean signal were gathered during the last month of the mission when the same ground track was repeated every 3 days these data allow detailed examination of time varying ocean phenomena since the gravitational component is time invariant one set of collinear passes clearly shows a cyclonic ring as it moves out from underneath the spacecraft s track an event which was simultaneously observed with the aid of a satellite tracked surface buoy another striking feature seen in the altimeter data set is the apparent variability exhibited by the gulf stream on time scales of a few days surface transport indicated by the sea surface height difference across the stream varied by nearly 30 and over the entire 3 month period much larger fluctuations were observed suggesting significant changes in total mass transport altimetry may provide an effective means of determining the time and space scales associated with these variations

on the accuracy of marine gravity measurements we have assessed the accuracy of lamont doherty geological observatory s global marine gravity data bank by examining the crossover errors coes at intersecting ship tracks more than 63 000 coes were found having a standard deviation of 22 43 mgal mgal 10 5 m s 2 we use the coes to find and remove linear drifts and dc shifts present in the data set this adjustment reduces the standard deviation to 13 96 mgal coes generally decrease with latitude which we attribute to uncertainties in the eotvos correction high coes occur in areas of high gravity gradients these two features point to poor navigation as the principal source of error in marine gravity surveys coes have generally been decreasing during the last two decades reflecting improvements in instrumentation and quality of navigation a comparison of the shipboard gravity data to seasat derived gravity revealed a 9 mgal bias in the terrestrial data which probably reflects uncertainties in choice of reference field the adjusted data set was used to generate a gravimetric geoid for the nw atlantic ocean by removing this geoid from the seasat sea surface heights a residual geoid was obtained a special feature of this map is an elongate ene trend that appears to correlate with the edge of the gulf stream

sea level variabilities in the gulf stream between cape hatteras and 50 w a geosat study sea level residuals relative to a 2 year mean sea level in the gulf stream downstream of cape hatteras between 80 w and 50 w longitude are studied using geosat altimetry between november 1986 and december 1988 spectral slopes computed at four nominal locations along the gulf stream 72 w 65 w 60 w and 55 w range between 1 5 and 0 9 significantly less steep than the 2 5 spectral slope found at bermuda because of increased short wavelength energy the spectra tend to become more white going eastward but this trend is not statistically significant energy at the annual cycle decreases eastward from around 40 of the total variance at 72 w to 20 of the total variance at 55 w maximum residual geostrophic sea surface velocities associated with the annual cycle were of the order of 70 cm s comparison between the gulf stream path from sea level residual maps and the north wall edge observed from noaa infrared ir imagery shows an rms difference of 49 km between 75 w and 60 w longitude but not all sea level maps show a clearly defined gulf stream using the ir estimates for gulf stream position sea level residuals were modeled as the meandering of a sea level front shaped as 0 5 m tanh x x0 50 km sin with the angle between the geosat track and the gulf stream edge and x0 is based on the observed ir north wall positions this showed that the annual signal in terms of the location and phase of its maxima is dominated by the meandering of the gulf stream

spatial variations of ocean wave directional spectra from the seasat synthetic aperture radar seasat synthetic aperture radar ocean wave spectra for a 900 km pass are analyzed and interpreted in the context of both their probable generation sources and their surface current and bathymetric modifiers systematic vector wavenumber variations of several times the standard error of determination 1 5 in magnitude and 0 9 in direction occur along the entire 900 km pass the large scale spatial variation of a 200 m swell system can be accurately accounted for as a result of dispersion from a distant storm the more local variations are qualitatively well correlated in position with known currents and bathymetry but show systematic biases that appear partly due to an environmentally dependent instrument transfer function in the regions of high current and highest sea state there is also substantial evidence that a large angular deviation in the center of the pass is the result of a mesoscale eddy just to the east

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

rock magnetic properties of multicomponent natural remanent magnetization in alluvial red beds ne spain summary an earlier study of the cyclic miocene red bed sequence of la gloria spain by krijgsman et al indicated complicated behaviour of the natural remanent magnetization nrm in parts of the section particularly close to reversal boundaries we resampled part of the section with high resolution and used extensive rock magnetic analyses to characterize the magnetic remanence carriers below a conspicuous hydromorphous layer the magnetic contributions of haematite and magnetite are approximately equal while in the brown layers on top of the hydromorphous layer the contribution of magnetite is drastically reduced this is probably related to a change in hydrological conditions the nrm is characterized by 1 a low temperature 200 360 c overprint of unknown age 2 a medium temperature 360 580 c component interpreted as the characteristic remanent magnetization chrm and 3 a high temperature haematite component 600 680 c carrying the same directions as the medium temperature component there is no perceivable delay in nrm acquisition between the medium and the high temperature components they are both regarded as primary the behaviour of the nrm seems to be similar in the cyclic lithologies the acquisition of nrm thus seems to be independent of lithology in the cyclic part of the section the higher sampling resolution yielded the detection of a new polarity zone which probably represents a geomagnetic feature according to rock magnetic properties however the more detailed magnetostratigraphy of the resampled part of the section indicates that the earlier correlation to the geomagnetic polarity timescale is no longer tenable therefore the la gloria section should no longer be used as a magnetostratigraphic dating tool of mammal biochronology

observations of eddy fields in the northwest atlantic and northwest pacific by seasat altimeter data sea level variability related to the eddy field activity can be calculated from repeating tracks of altimetric data such as the seasat 3 day repeat data september 13 to october 10 1978 if we consider the eddy field in geostrophic balance the geostrophic relation gives the surface eddy velocities also an estimation of the eddy kinetic energy can be deduced under the assumption of quasi isotropy of the velocity variability this approach is used in the northwest atlantic and northwest pacific through the processing of seasat data high variability of sea surface topography up to 20 cm and high eddy kinetic energy 800 1600 cm sup 2 s sup 2 are detected in the vicinity of the gulf stream and the kuroshio power spectra of the observed sea level fluctuations give wavelengths ranging from 100 to 900 km for time scales between 3 and 25 days maps of sea surface topography variability and eddy kinetic energy are presented and discussed

seasat derived ocean surface topography comparison with coincident kuroshio hydrographic data during the seasat repeat orbit period a ctd and deep 1800 m xbt hydrographic experiment was conducted across the kuroshio to obtain cotemporaneous surface topography measurements for comparison with the altimeter derived surface height measurements the results showed that the altimeter could detect and measure the change in sea surface topography caused by movement of the kuroshio and the cold rings that were found in the hydrographic data after compensation for the small differences in the time of the measurements the altimeter measured changes in the surface topography that matched those measured by the hydrographic sections with an average difference of 9 6 cm for the 41 comparison points

dynamic topography estimates using geosat data and a gravimetric geoid in the gulf stream region summary a gravimetric geoid undulation on a 3 x 3 grid has been calculated in the gulf stream region 30 5 i 45 278 5 i 5 318 these undulations were calculated using two 360 potential coefficient models land ship and altimeter derived gravity anomalies and bathymetric data least squares collocation and fast fourier transform procedures were used with various data selection and gridding procedures results from five different undulation computations are described with comparisons made with synthetic geoid undulations along geosut tracks in the region the standard deviation of the undulation differences was f14cm when a cubic polynomial was used to model long wavelength errors a point verification of the geoid undulation at the laser tracking station on bermuda was also made with a discrepancy ground truth minus model undulation of 40 cm within the predicted standard deviation the gravimetric geoid undulation was used to compute dynamic topography along geosat tracks for comparison with existing estimates based on hydrographic data in the gulf stream region the agreement between these two estimates is on the order of f15 cm although the discrepancies can reach 60 cm the larger differences are usually associated with a location on a track that passes near a seamount where the gravity data may be inadequate to represent the high frequency variations in the geoid undulations this effect will be represented in the undulation standard deviations that have been calculated using the least squares collocation procedure the average accuracy is fl6cm with the range from f14 to f48cm the dynamic height derived from the gravimetric undulations and altimeter data has been used to calculate characteristics of the gulf stream width velocity centre location height profile using an implied velocity model for the set the results are compared with previous estimates with generally good agreement however the maximum velocities and the jump function are approximately 30 per cent larger than previous studies that used an average of altimeter tracks to define the geoid undulation the dynamic topography was calculated for the entire region using a mean sea surface based on geos 3 seasat and geosat data the results are compared with two hydrographic estimates due to martel wunsch and letraon mercier the agreement is at the f25cm level with the best correlation coefficient reaching 0 72 with the martel wunsch model

uncertainties in the mean ocean dynamic topography before the launch of the gravity field and steady state ocean circulation explorer goce 1 in anticipation of the future observations of the gravity mission gravity field and steady state ocean circulation explorer goce the present day accuracy of mean dynamic topography mdt is estimated from both observations and models a comparison of five observational estimates illustrates that rms differences in mdt vary from 4 2 to 10 5 cm after low pass filtering the fields with a hamming window with wavenumber n 120 corresponding to an effective resolution of 167 km rms differences in observational mdt reduce to 2 4 8 3 cm for n 15 1334 km differences in data sources geoid model in situ data are mostly visible in the small scale oceanic features while differences in processing filtering inverse modeling techniques are reflected at larger scales a comparison of seven different numerical ocean models demonstrates that model estimates differ mostly in western boundary currents and in the antarctic circumpolar current rms differences between modeled and observed mdt are at best 8 8 cm for n 120 and reduce to 6 4 cm for n 15 for models with data assimilation a minimal rms difference of 6 6 cm n 120 to 3 4 cm n 15 is obtained with respect to the observational mdts the reduction of differences between mdts with increasing filtering scales is smaller than expected while it is expected that goce will improve mdt estimates at small spatial scales improvement of mean sea surface estimates from satellite altimetry may be needed to improve mdt estimates at larger scales

calibration of the cryosat 2 interferometer and measurement of across track ocean slope this paper describes the calibration of the cryosat 2 interferometer whose principal purpose is to accurately measure the height of the antarctic and greenland ice sheets a sequence of cryosat 2 data acquisitions over the tropical and midlatitude oceans were obtained between june and september 2010 from the siral a and redundant siral b radars operating in their sarin mode during a sequence of satellite rolls between 0 6 and 0 4 using the arrival angle of the echo relative to the interferometer baseline the attitude of the satellite determined by the star trackers and estimates of the ocean surface across track slope from the egm08 geoid we determined the errors in the interferometer estimate of surface slope as functions of the roll angle and ocean surface waveheight these were found to be in close agreement with the theoretical description the scale factor of the interferometric measurement of angle was determined to be 0 973 0 002 we estimate the accuracy of the across track slope measurement of the interferometer by applying this scale factor to the measured phase in applying this scale factor to the measurements the across track slope of the marine geoid was obtained with an accuracy of 26 rad at 10 km and 10 rad at 1000 km we conclude that the instrument performance considerably exceeds that needed for the accurate determination of height over the sloping surfaces of the continental ice sheets the results also demonstrate that cryosat 2 provides the first observations of the instantaneous vector gradient of the ocean surface and that the normal incidence interferometric configuration has a greater potential for the measurement of the ocean across track slope than has been previously recognized

a hafnium isotopic record of magmatic arcs and continental growth in the iapetus ocean the contrasting evolution of ganderia and the peri laurentian margin abstract we test the sensitivity of combined u pb hf isotopic analyses of detrital and magmatic zircon to document complex processes in accretionary orogens using ganderia from the canadian appalachian orogen as an example ganderia hosted a long lived magmatic arc that began at least by 650 ma and continued until 450 ma during which time it drifted northward from the amazonian margin its isotopic record suggests arc activity began earlier possibly at 750 ma proto ganderia within an oceanic domain the u pb hf zircon isotopic array suggests that ganderia formed on a sliver of paleoproterozoic mesoproterozoic basement tdmc 2 2 1 1 ga a transition towards more evolved hf isotopic compositions between 650 and 600 ma is interpreted to coincide with its accretion to the amazonian margin of gondwana consistent with other geological evidence accretion was followed by increasing amounts of juvenile crustal inputs between 550 and 500 ma which is interpreted to reflect subduction roll back and the onset of drift from the gondwanan margin trench retreat culminated in the separation of the ganderia arc and formation of the exclusively oceanic 510 450 ma penobscot popelogan victoria arcs on ganderia accretion of ganderia to the active notre dame subzone along the laurentian margin occurred in the late ordovician and is marked by the abrupt termination of ganderian arc magmatism the notre dame arc evolved along the laurentian margin between 515 and 425 ma and was built on paleoproterozoic archean t dm c 2 9 2 5 ga crust supra subduction zone magmatism occurred at 490 460 ma during the closure of the taconic seaway and was dominated by the recycling of laurentian crust with progressive mixing of evolved and juvenile arc magmas over time the preservation of very evolved notre dame arc zircon in ganderian overstep sequences confirms the arrival of the leading edge of ganderia to laurentia by 450 ma the hafnium isotopic method is proven here to be a powerful tool when used in conjunction with geological constraints and is able to identify the changing nature of magmatism during the evolution of complex accretionary systems

a study of the kuroshio s seasonal variabilities using an altimetric gravimetric geoid and topex poseidon altimeter data the first year of topex poseidon t p altimeter data were used to study the seasonal variabilities of the kuroshio current the intercomparison between the t p and gauge sea levels at selected tide gauge stations around taiwan shows that the two have a correlation of about 0 9 at the immediate vicinity of the deep ocean and both show an annual cycle with an amplitude of 15 cm a 3 3 geoid for the western pacific was constructed by least squares collocation using gravity anomalies and sea surface gradients derived from seasat geosat ers 1 and t p altimetry to account for the oceanographic signal in the altimeter data we derived a covariance function for the gradients of the sea surface topography sst based on a global averaging concept and a spherical harmonic expansion of the levitus sst to degree 50 the accuracy of the geoid ranges from 5 to 40 cm the sst values derived from the geoid and the data along t p s descending tracks were fitted to the hyperbolic functions in a two step procedure to find the kuroshio s seasonal axes and the parameters that describe its characteristics the mean variabilities in the kuroshio s path maximum velocity baroclinic transport and width are 22 km 19 cm 8 sv and 27 km respectively the averaged percentage variability of all quantities is 25 all the variabilities are relatively large near the northeast coast of taiwan and the starting point of the kuroshio extension the large scale circulations over the western pacific were obtained by median filtering the sst at the 1334 km spatial scale the pacific s subtropical gyre is clearly visible and it shows different features over the four seasons and its kinetic energy shows possible correlations with the determined parameters over the south china sea a warm ring with a radius of 300 400 km and a center at 15 n 113 e was detected in the spring and summer

dynamics of the slope water off new england and its influence on the gulf stream as inferred from satellite ir data abstract the movements of warm core rings and the gulf stream front were studied in the new england slope water region by using both satellite ir data and available in situ sea surface temperature data it is found that 1 the rotating speed of the rings exhibits a marked seasonal variation with the maximum speed occurring in the winter and the minimum in the late fall 2 the surface area of the rings increases monotonically with time and 3 the gulf stream front at the north wall migrates seasonally and attains its northernmost position in the late fall based on these findings we calculated the horizontal eddy viscosity for the rings as 4 10 8 cm 2 5 furthermore by comparing the seasonal variations of the rotational velocity of the rings and the total mass transport of the gulf stream we suggest that the seasonal variation of the slope water hydrography through local air sea interactions could play an important role in the dynamics of the gulf stream system

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

sm nd isotopic geochemistry of precambrian to paleozoic granitoid suites and the deep crustal structure of the southeast margin of the newfoundland appalachians in the eastern central mobile belt of the newfoundland appalachians late precambrian basement inliers have end from 3 to 2 but cambro ordovician metasedimentary rocks have initial end below 7

collinear track altimetry in the gulf of mexico from seasat measurements models and surface truth abstract from 17 september to 10 october 1978 seasat made collinear passes over the gulf of mexico altimeter data for eight three day repeat passes over the eastern gulf were examined using an arc segment fitting technique to determine the mesoscale temporal variability of the sea surface the pattern of sea height variability was then compared with sea height data generated by a numerical model of the gulf hurlburt and thompson 1980 from the simulation of a complete cycle of loop current intrusion and shedding of an anticyclonic eddy the model data was found to match that from the seasat altimeter when an anticyclonic eddy separated from the loop current and the loop began to repenetrate into the eastern gulf analysis of sparse ground truth data from ship of opportunity xbt s satellite infrared imagery of the loop current boundary and synthetic aperture radar sar imagery also from seasat tend to confirm the circulation patterns deduced from the altimeter data and the numerical model author

some new aspects for the modelling of isothermal remanent magnetization acquisition curves by cumulative log gaussian functions rock samples containing ferri magnetic minerals acquire an isothermal remanent magnetization irm after exposure to a direct magnetic field measuring irm b allows to produce irm acquisition curves which were modelled by cumulative log gaussian clg functions robertson and france 1994 to discriminate the different magnetic phases an approach of how to find the best model has been added to this method from the investigation of a magnetite sample it is inferred that with the method the remanence acquisition coercive force for each magnetic component in a sample can be deduced the method allows to detect minute concentrations of magnetically hard material in a predominant magnetically soft sample and vice versa it furthermore allows to extrapolate the irm behaviour of samples that do not reach saturation irm in the experiment the study of a natural hematite renders it possible that even well defined hematite may be contaminated by ferri magnetic impurities biasing the remanence acquisition coercive force of the sample towards lower values

a semianalytical model of the synthetic aperture interferometric radar altimeter mean echo and echo cross product and its statistical fluctuations this paper develops a model of the synthetic aperture interferometric satellite radar altimeter echo power and echo cross product the model uses the smallness of the satellite pitch and roll angles and the limited range of satellite altitude to provide a semianalytical echo model whose numerical dimensions are limited to two in the synthetic aperture case or three in the interferometric case at large roll angles making its application to extensive data practical by not implementing the synthetic beam formation it is demonstrated that the model recovers the conventional case of a pulse limited altimeter a theoretical description of the fluctuations in the multilooked interferometric cross product and the synthetic aperture and pulse limited powers is given by extending the model to describe correlations between individual looks in each case the model offers the potential to retrieve ocean surface parameters from synthetic aperture and pulse limited altimeter data simultaneously with obvious application to the new generation of altimeters onboard cryosat 2 sentinel 3 and sentinel 6 during the transition to operational synthetic aperture radar altimetry

recent progress in the application of satellite altimetry to observing the mesoscale variability and general circulation of the oceans recent progress in the application of satellite altimetry from seasat and geos 3 to the observation of the oceanic mesoscale variability and general circulation is reviewed the lack of accurate geoid models has been the major obstacle in the study of the general ocean circulation from altimetry the use of geoid independent methods that utilize the temporal differences in altimetric measurements taken at fixed locations however has made significant contributions to our knowledge of the mesoscale variability of the ocean the mesoscale energies of the sea surface height and geostrophic current have been mapped on a global basis their distributions in wave number space have also been analyzed because of many of the deficiencies of existing altimeter data short duration inadequate orbit poor accuracy etc most of these results describe only a small portion of the frequency wave number spectrum of the variability but they have nonetheless demonstrated the great value of an optimally designed altimetric mission in advancing our knowledge of the global mesoscale variability the current technology allows satellite altimetry to detect oceanic variability at periods from a few days to 3 5 years and wavelengths from 50 to 10 000 km determining the time averaged general ocean circulation from altimetry is more problematic because an accurate geoid is indispensable the currently available global geoid models have useful accuracies only at wavelengths greater than about 7000 km there have been several attempts at mapping the global ocean circulation at those scales using existing altimeter data and geoids when these results are compared with hydrographic surveys some qualitative agreement can be observed but the quantitative differences are mostly inconclusive because of the geoid and orbit errors it has been suggested however that an altimetric mission that is optimally designed with the current technology when complemented by a state of the art gravimetric mission to map the earth s gravity field is able to determine the ocean circulation quantitatively at scales from the ocean basin to about 200 km

absolute measurement by satellite altimetry of dynamic topography of the pacific ocean satellites are the only foreseeable possibility for obtaining observations of the ocean circulation on the basin and global scales required to understand it such observations are essential for an understanding of the role of the ocean in various important problems for example climate the 3 month seasat mission1 has demonstrated2 3 that altimetry is capable of providing global observations of oceanic variability we show here that the data from this short sub optimum mission are also adequate for a determination of the absolute sea surface topography of the ocean on large scales a much more difficult4 and even more valuable measurement an absolute determination of the subtropical gyre of the north pacific ocean has been obtained we believe this to be the first direct measurement showing the existence of such a feature that does not depend on conventional hydrography and a series of assumptions

mesoscale ocean eddy measurements by multibeam altimetry a multibeam microwave radar altimeter concept is numerically simulated to evaluate its capability to remotely sense mesoscale oceanographic features and eddies in particular the study tests the sensitivity of the sensor to variations of systematic and environmental parameters including sensor attitude angle sensor position and system errors a novel concept of computing eddy vorticity from the multibeam data is explored application of this concept to the detection of simulated ocean eddies in the presence of tracker noise gives excellent results the technique is shown to be simple and accurate the minimum size of the eddy detectable by the multibeam altimeter is presented for a given performance characteristic of the radar

frontal signals east of iceland from the geosat altimeter frontal sea surface height signals were identified in the iceland faeroe region for height differences from the three sets of geosat tracks july may 1987 these signals were verified with in situ measurements and then combined with them for an improved and synoptic estimate of frontal location the data assimilation context made the weak signals quantitatively useful real time analysis of geosat data contributed to a frontal nowcast and forecast scheme

zonal velocity structure and transport in the kuroshio extension abstract the meridional structure of the zonal flow in the kuroshio extension is investigated using a combination of data from hydrographic sections and moored current meter arrays we emphasize 165 e between 30 and 42 n where high quality and very stable current measurements at 150 and 4000 m extend over a two year period from october 1983 to october 1985 hydrographic ctd o2 sections were occupied during the initial deployment and a second time when the array of six moorings was reset in 1984 the deep currents were extremely reproducible from one year to the next and revealed a pattern of weak eastward flow at 4000 m under the axis of the kuroshio with strong westward flow on either flank when combined with the hydrographic data the total transport of the eastward flowing kuroshio extension was estimated to be 57 0 3 7 sv sv 106 m3 s 1 essentially the same as when referenced to the broom 57 0 2 0 sv south of 34 n the velocities were westward at all levels with a net transport of 8

paleomagnetism of fluorite veins in the devonian st lawrence granite newfoundland canada paleomagnetic results are reported from the devonian st lawrence granite and the fluorite veins within the granite or its related porphyry dikes paleomagnetic analysis of 359 specimens from 29 sites shows that there is no statistically significant difference at 95 confidence between the site mean characteristic remanent magnetization chrm directions carried by pyrrhotite and or magnetite of the granite and fluorite veins no post granite metamorphic event is known in the area thus these concordant directions indicate that the granite and fluorite veins are coeval and retain a primary remanence however the mean chrm direction of 25 vein and granite sites yields an early pennsylvanian paleopole of 316 ma on the north american apparent polar wander path at 35 5 n 129 2 e a95 3 4 that is younger than the 374 2 ma devonian u pb zircon age for the granite two intersecting vertical vein sets indicate that the st lawrence granite has not been tilted since emplacement of the fluorite veins t

new age data refine extent and duration of paleozoic and neoproterozoic plutonism at ganderia avalonia boundary newfoundland devonian and younger plutonic suites of the appalachian orogen in newfoundland form a curvilinear belt straddling the boundary between ganderia and avalonia and exhibit a general pattern of younging to the southeast however many individual plutonic suites within this belt remain undated or have ages that are poorly constrained this study reports u pb sensitive high resolution ion microprobe shrimp data from zircon and 40ar 39ar data from hornblende biotite and muscovite which collectively improve definition of post tectonic plutonic events in southeastern newfoundland but at the same time raise new questions for further study u pb zircon shrimp determinations provide valuable new geochronological information for the deadman s bay granite 390 4 ma the gander lake granite 378 4 ma the terra nova granite 384 4 ma the old woman stock 376 4 ma and the easternmost unit tolt phase of the composite ackley granite 372 4 ma the pass island granite long considered part of this

mid late ordovician magmatism and metamorphism along the gander margin in central newfoundland fieldwork coupled with u pb dating has clarified the relationships between the exploits and gander derived rocks in central newfoundland during the mid ordovician opening of the exploits back arc basin reinforcing correlation across the peri gondwanan segments of the appalachian caledonian orogen we have separated a new back arc related unit the red cross group from the arc related victoria lake supergroup this group includes 466 3 ma felsic volcanic rock interlayered with alkali basalt enriched mid ocean ridge basalt 457 6 ma gabbro llanvirn caradoc normal mid ocean ridge basalt island arc tholeite limestone black shale and melange locally the red cross group is in parautochthonous contact with low grade gander psammite this contact was overrun by the meelpaeg metamorphic nappe during the devonian the nappe contains gander metapsammite meelpaeg subzone and the coticule bearing howley waters complex exploits which hosts 467 3 ma felsic porphyry the gander and exploits metasediments in the nappe are stitched by arenig llanvirn granite 467 6 ma and 468 3 5 3 ma and caradoc intrusions 458 3 ma and 454 2 ma metamorphic monazite 462 1 ma and titanite 460 3 ma from the nearby mount cormack subzone gander indicate the coeval formation of a low pressure high temperature metamorphic dome the widespread presence of caradoc magmatism suggests that the width of the back arc basin remained relatively narrow

new insights into the appalachian orogen from geology and geochronology along the cape ray fault zone southwest newfoundland reverse oblique overthrusting of high grade port aux basques gneiss over the lower grade supracrustal windsor point group along the cape ray fault zone occurred during late silurian to early devonian time and is attributed to major oblique collision between gondwanan and laurentian continental blocks new u pb zircon 40 ar 39 ar and k ar data limit the timing of this orogenic event the megacrystic granitic phase of the cape ray igneous complex and the cape ray tonalite have been dated at 488 3 ma and 469 2 ma respectively a black rhyolite from the windsor point group yielded an ordovician age 453 5 4 ma a pretectonic gabbro sill within the windsor point group dated at 424 4 3 ma is cut by the windowglass hill granite dated at 424 2 ma synkinematic hornblende and biotite from the grand bay complex mylonites of the port aux basques gneiss have 40 ar 39 ar ages of 407 4 ma and 403 4 ma respectively which is indicative of a late silurian early devonian age for the amphibolite grade deformation these ages are compatible with a previously determined 415 ma monazite age interpreted as the time of peak metamorphism in the port aux basques gneiss and suggests rapid exhumation the east west flexure of the cape ray fault zone represents a tear fault accommodating differential shortening between the cape ray fault zone and the correlative fault system in central newfoundland mid devonian granites 386 3 384 2 ma intervene between the thrusting events and a younger sinistral transcurrent movement this deformation and magmatic history can be correlated throughout the northern appalachians along other major fault boundaries

interaction of the antarctic circumpolar current with bottom topography an investigation using satellite altimetry theoretical studies on the interaction of a zonal current with a zonal ridge an isolated bump and a meridional ridge compare favorably with hydrographic observations within the eastward flowing antarctic circumpolar current where it flows over similar topographic features however the existing hydrographic data are insufficient for examining the temporal stability and kinematic behavior of the resulting mesoscale structures in this study some of these transient features have been compared with patterns in sea surface variability derived from collinear satellite altimetric data when these features occurred near the crossing point of two satellite ground traces it was possible to characterize their length scales dynamic height relief and translational and surface geostrophic velocities

a comparison of ocean topography derived from the shuttle laser altimeter 01 and topex poseidon to assess the utility of laser altimetry for studies in dynamical oceanography the authors present a comparison of the shuttle laser altimeter sla 01 and the topex poseidon t p radar altimeter on global and regional scales they compare all spl sim 1 1 million sla 01 range measurements over the oceans to the csrmss95 gridded mean sea surface model and find the overall root mean square rms difference to be 2 33 m the misfit was improved significantly by removing the mean and trend from individual sla 01 profiles often resulting in rms differences less than 1 m they also show that in regions where sea surface height varies dramatically over relatively short horizontal scales such as across major subduction zones sla 01 as capable of resolving rapid changes in sea surface height finally they examine a number of coastal zones and illustrate sla 01 s ability to track continuously across the land sea interface even in regions of dramatic coastal topography the dominant sources of radial error in the sla 01 data are time interval unit tiu error spl plusmn 0 75 m and radial orbit error 1 m rms therefore limitations of the sla 01 data set are caused primarily by system constraints as opposed to instrumentation error their results indicate that future laser altimeters will provide valuable information regarding ocean topography in particular laser altimetry data can be used to supplement orbiting microwave ranging systems in coastal areas where such sensors are incapable of maintaining lock across the continent ocean transition

sampling strategies and model assimilation of altimetric data for ocean monitoring and prediction numerical forecasts using simulated altimeter data are generated in order to examine the assimilation of altimeter derived sea surface heights into numerical ocean circulation models a one layer reduced gravity primitive equation circulation model of the gulf of mexico is utilized the gulf of mexico is chosen because of its amenability to modeling and the ability of low vertical mode models to reproduce many of the observed dynamical features of gulf circulation the simulated data are obtained by flying a hypothetical altimeter over the model ocean and sampling the model sea surface in a manner similar to a real altimeter the data are used to examine spatial sampling requirements for accurate resolution of oceanic eddies and in forecast mode the assimilation of asynoptic altimeter data into numerical models results indicate that for a stationary circular eddy approximately two tracks either ascending or descending across the eddy are sufficient to ensure adequate spatial resolution an irregularly shaped eddy may require three or four tracks in addition the study reveals that if the track spacing is sufficient to resolve the height field of an eddy the along track geostrophic velocity component is determined with equivalent accuracy to that of the cross track component simulated gulf of mexico circulation forecasts suggest that the numerical model can effectively assimilate asynoptic altimeter measurements optimum sampling strategies for a single beam altimeter and intermittent updating of the nowcast forecast are examined

the gulf stream front a comparison between seasat altimeter observations and theory in a recent paper by cheney and marsh 1981 seasat altimeter data were used to derive quantitative information on sea surface height anomalies across the gulf stream in another recent paper by kao 1980 the dynamics of the gulf stream front was investigated and a similarity solution was obtained the model gives a universal shape of the sea surface height rise and the width of that anomaly across the gulf stream in this paper we present a quantitative comparison between the model and six gulf stream altimeter profiles representing a broad range of conditions the remarkable closeness of fit is mutually reinforcing to both the model and to the role of satellite altimetry in ocean dynamics comparisons of the data with the well known theories of stommel 1966 and charney 1955 are also made and implications of these comparisons are explored

ocean mesoscale variability from repeat tracks of geos 3 altimeter data the geos 3 satellite altimeter observed numerous sea surface profiles along nearly repeated tracks in the western north atlantic during its 3 5 year lifetime enabling observation of the variation of sea surface topography along these tracks analysis of 14 north going and 13 south going sets of repeated tracks has yielded the variability of the surface at a resolution of 1 from 25 to 41 n latitude and from 60 to 80 w longitude the observed rms variation of surface topography ranges from about 8 cm in the sargasso sea to a maximum of 48 cm in the gulf stream meander region in agreement with known mesoscale energetics of this region

magnetic fabrics in the holum granite vest agder southernmost norway implications for the late evolution of the sveconorwegian grenvillian orogen of sw scandinavia abstract the holum granite vest agder southernmost norway has been considered to be the oldest 980 ma undeformed post tectonic pluton of a late sveconorwegian granitoid series that form two belts in southern norway and sw sweden an integrated structural study of this granite pluton based on a survey of its anisotropy of low field magnetic susceptibility ams complemented by microstructural observations optical microscopy and rock magnetism investigations including measurements of partial anhysteretic remanent magnetization and its anisotropy paarm is presented here the magnetic susceptibility and the ams of the holum granite are carried by large magnetite grains coaxiality between the magnetite controlled ams fabric and the rock fabric is verified which allows the use of the former as a proxy for the latter microstructural evidence of a deformation continuum in the granite from magmatic to solid state and homogeneity and continuity of the ams fabrics across the pluton demonstrate that the holum granite is not post tectonic but that it was emplaced in a tectonic strain field a model of emplacement and deformation during the last sveconorwegian regional folding phase evidenced in the country rocks of the pluton is proposed

life history of a cyclonic ring detached from the kuroshio extension as seen by the geosat altimeter the sea surface dynamic topography ssdt sea surface height relative to the geoid is approximately estimated by combining the temporal fluctuation of ssdt determined from altimetry data with the climatological mean ssdt calculated from hydrographic data this approximated ssdt or composite ssdt is obtained in the area southeast of japan for the first year 1986 1987 of the geosat exact repeat mission variations in the kuroshio current system are well described by the composite ssdt in particular a complete life history of a cyclonic ring is observed for the first time in this region namely westward propagation of a southward meander of the kuroshio extension its pinching off to form a cyclonic ring the ring s westward movement its coalescence with the kuroshio and its eastward advection all available hydrographic data and cloud free satellite infrared images support the existence of this series of phenomena

the youngest paleozoic plutonism of the newfoundland appalachians u pb ages from the st lawrence and francois granites the posttectonic st lawrence and francois granites have long been regarded as the youngest paleozoic plutonic suites of the newfoundland appalachians their u pb ages of 374 2 and 378 2 ma respectively define a middle to late devonian magmatic event mid carboniferous magmatic and or rifting events suggested on the basis of earlier rb sr dating of the st lawrence granite are not supported by these new data both granites intrude major ductile and brittle structures that were active during the early paleozoic and they provide a younger age limit for major tectonic activity in the avalon zone and on the south coast of newfoundland the granites may correlate with plutons of closely similar age reported from the aspy and mira terranes of cape breton island nova scotia

preliminary estimates of gulf stream characteristics from topex data and a precise gravimetric geoid topex sea surface height data has been used with a gravimetric geoid to calculate sea surface topography across the gulf stream this topography was initially computed for nine tracks seven descending and two ascending on cycles 21 to 29 due to inaccurate geoid undulations on one track results for eight tracks are reported in the paper the sea surface topography estimates were used to calculate parameters that describe gulf stream characteristics from two models of the gulf stream one model was based on a gaussian representation of the velocity while the other was a hyperbolic representation of velocity or the sea surface topography the parameters of the gaussian velocity model fit were a width parameter a maximum velocity value and the location of the maximum velocity the parameters of the hyperbolic sea surface topography model were the width the height jump position and the sea surface topography at the center of the stream both models were used for the eight tracks and nine cycles studied comparisons were made between the width parameters the maximum velocities and the height jumps for one track d04 near 36 n 73 w the average width parameter was 69 15 km based on the gaussian velocity fitting and 75 14 km based on the hyperbolic sea surface topography fit with a 10 km smoothing function along the same track the average maximum velocity was 164 30 cm s using the velocity fit and 163 37 cm s with the hyperbolic sea surface topography fit some of the parameter estimates were found to be highly 0 9 correlated when the hyperbolic sea surface topography fit was carried out but such correlations were reduced for either the gaussian velocity fits or the hyperbolic velocity model fit a comparison of the parameters derived from 1 year of topex data showed good agreement with values derived by kelly 1991 using 2 5 years of geosat data near 38 n 66 w longitude width 78 22 km this paper 82 25 km kelly height jump 115 28 cm 123 19 cm maximum velocity 171 59 cm s 1 179 46 cm s 1 the accuracy of the geoid undulations used in the calculations was of the order of 16 cm with the accuracy of a geoid undulation difference equal to 15 cm over a 100 km line in areas with good terrestrial data coverage the north edge of the gulf stream was studied with topex data from cycles 1 to 37 the north edge was located at the position corresponding to the half width of the gulf stream north of the center of the stream along each track with all parameters estimated from the gaussian velocity fit procedure the location of the north edge along one track generally agreed with the location defined by national oceanic and atmospheric administration national ocean survey noaa nos maps based on advanced very high resolution radiometer avhrr data and with a north wall location provided by cornillon at 2 day intervals the results for this topex track showed the north edge at the highest 37 8 n latitude in october november 1992 falling to the lowest 36 9 n latitude in february march 1993 after which the stream moves north a second track 550 km to the east of the first track showed consistent agreement with the cornillon data for the edge location when such data were available in one case with the noaa data there was a 77 km discrepancy between the topex and noaa estimates of the north edge analysis of the sea surface topography suggested the noaa avhrr location may be inaccurate at this one location and time this paper demonstrates that our knowledge of geoid undulations and undulation differences in a portion of the gulf stream region is sufficiently accurate to determine characteristics of the jet when used with topex altimeter data the method used here has not been shown to be more accurate than methods that average altimeter data to form a reference surface used in analysis to obtain the gulf stream characteristics however the results in the paper show the geoid approach may be used in areas where lack of current meandering reduces the accuracy of the average surface procedure

measurements of dynamic topography during synop utilizing a geosat synthetic geoid dynamic topography estimates were obtained for the gulf stream region employing a previously derived synthetic geoid and geosat radar altimeter measurements ascending tracks passed through the central and eastern arrays of the synoptic ocean prediction experiment by utilizing the geoid estimate instead of the mean altimetric signal the axis position and velocity can be computed a time series of the dynamic height profiles crossing the gulf stream and a table of the positions of the axis of the stream along two tracks are given time series of the maximum velocity perpendicular to the ground track were computed for both arrays it was found that there was a seasonal cycle in this time series with a maximum in november

morin transition in hematite size dependence and thermal hysteresis 1 hematite is a frequently used mineral in paleomagnetic and environmental magnetic studies just below room temperature it undergoes a magnetic phase transition the morin transition whose nature is an important part of our basic understanding of hematite s magnetism and magnetic memory we have determined the temperature tm of the morin transition from saturation remanence warming curves to be 250 261 k for 0 5 6 mm hematite natural single crystals 257 260 k for 45 600 m sieved crystal fractions and 241 256 k for submicron synthetic hematites with grain sizes between 120 and 520 nm the variation must be due to differences in crystal morphology lattice strain and crystal defects common in both synthetic and natural crystals our results are compatible with published data for 100 nm to 10 mm hematites and show that tm is nearly size independent decreasing very gradually as particle size decreases over this broad range which includes both multidomain md and single domain sd structures however tm decreases sharply between 90 and 30 nm below 20 nm the transition disappears entirely as near surface spins deviate strongly from the antiferromagnetic easy axis our sd and md hematites exhibit a thermal hysteresis in the morin transition the values of tm in cooling and in heating are different for the same cooling warming rate tm is much greater for submicron hematites than for larger crystals we attribute the lag in the transition in both cooling and heating to crystal imperfections and resulting internal stresses and speculate that defects may serve to pin and stabilize surface spins preventing spin rotation in a region large enough to trigger the phase transition would inhibit destabilization of the weakly ferromagnetic phase in cooling and the antiferromagnetic phase in heating the wide distribution of particle sizes in our submicron samples may also play a role

southern ocean mean monthly waves and surface winds for winter 1978 by seasat radar altimeter data acquired by the seasat radar altimeter during the 3 month satellite lifetime are analyzed in a study of the sea state of the southern hemisphere oceans the lifetime of the seasat satellite july 7 to october 10 1978 corresponds to the antarctic winter mean monthly maps of wind speed significant wave height and swell have been generated from the altimeter measurements along the satellite tracks these maps delineate spatial and temporal differences of these parameters in the atlantic indian and pacific oceans several features of the southern ocean wind and wave fields agree with conventional descriptions for example the principle zonal wind regimes established by the southeast trades and westerlies are clearly evident in the monthly averages significant wave height and swell also exhibit minima near the doldrums at low latitudes with steady increases southward to the latitudes of the westerlies however superimposed on these general patterns is significant variability with horizontal scales as small as 1000 km the maps also document a gradual migration of the region of absolute maximum wind and wave from the atlantic eastward to the indian ocean and finally into the pacific

seasat altimeter height calibration the seasat altimeter has been calibrated for height bias using four overflight passes of bermuda that were supported by the bermuda laser the altimeter data was corrected for tides by using recorded tide gage data for propagation effects by using meteorological data taken around the time of each pass for acceleration lag and for sea state bias including both surface effects and instrumental effects altimeter data for each of the four passes was smoothed and extrapolated across the island interpolation between passes then produced an equivalent altimeter measurement to the geoid at the laser site so that the altimeter bias could be estimated without the use of a geoid model the estimated height bias was 0 0 0 07 m

altimetry ship gravimetry and the general circulation of the north atlantic gravity accelerations estimated from satellite altimetric mean sea surfaces seasat and geos 3 are compared to ship gravity measurements ship gravity are closer to an estimate based on least squares collocation orbit perturbations altimetry and terrestrial gravity than to an estimate based on fourier transforms orbit perturbations and altimetry only both altimetric estimates yield a smoothed picture of the geostrophic component of sea surface currents in the north atlantic when gravity acceleration data from only nine cruises are subtracted from the altimetric gravity

on determining the large scale ocean circulation from satellite altimetry to determine the surface geostrophic currents which are proportional to the slope of the dynamic topography from satellite altimetry one needs an accurate and independent estimate of the geoid currently these estimates are given in terms of spherical harmonics while the high degree terms short wavelengths are either uncertain or completely unknown the low degree terms long wavelengths are reasonably accurate furthermore in terms of spherical harmonics most of the dynamic topography s power is contained in the low degree terms if the dynamic topography is treated as the signal and the geoid uncertainty as the noise the signal to noise ratio is the highest for these low degree terms therefore a spherical harmonic expansion of the difference between the altimeter derived mean sea surface and the geoid estimate should reveal the large scale circulation of the ocean surface layer when one examines the low degree terms methods based on this principle are proposed and partially demonstrated over the pacific ocean using the mean sea surface derived from the seasat altimeter and the goddard earth model 9 earth gravity model the preliminary results show a well defined clockwise gyre in the north pacific and a much less well defined counterclockwise gyre in the south pacific when the dynamic topography so obtained is compared to wyrtki s 1975 dynamic topography derived from hydrographic data the agreement is within the limit of geoid uncertainties and satellite orbital errors to fully determine the three dimensional ocean circulation one still needs hydrography the three dimensional density distribution of the ocean a method is presented for the determination of the ocean circulation and the improvement of the geoid in the combined problem of geodesy hydrography and satellite altimetry

the branching of the gulf stream southeast of the grand banks during march april 1987 101 hydrographic stations were occupied on three sections spanning a triangle between the azores faial the southern tip of the grand banks of newfoundland and bermuda information on the near surface processes in the interior of the triangle were obtained from 32 satellite tracked buoys deployed during the cruise and a composite infrared image based on cloud free noaa 9 data during april 1987 the data were combined to analyze the eddy field and the branching of the gulf stream into the north atlantic current and the azores current calculations of mass transports through the legs of the triangle gave a total of 46 sv supplied by the gulf stream 31 sv of which left the area as the north atlantic current and westwind drift north of the azores the remaining 14 sv continued towards east southeast as the azores current and southern recirculation additional conductivity temperature depth stations from a cruise in april 1986 into the same area allowed also study of the large scale circulation within that triangle in deeper layers the azores current appears as a baroclinic stream which reaches down to approximately 1000 m intensive mixing was observed at the continental slope of newfoundland between water of the labrador current and the gulf stream mixed water owing to cabbeling and consecutive convective mixing this water penetrates down to 2000 m depth and creates horizontal density gradients to the surrounding gulf stream water which intensifies the north atlantic current this process is considered to be an important energy source for this current

the geoid edin2000 and mean sea surface topography around the british isles summary this paper describes a new rationale for computing a gravimetric geoid and reports that the resulting geoid model edin2000 is now good enough to resolve previously contradictory estimates for mean sea surface topography msst around great britain for at least 30 yr it has been known that msst derived from tide gauges levelling and oceanography were mutually inconsistent and differed by an order of magnitude when combined with an altimetric mean sea surface edin2000 is also able to map realistic msst over the northwest european shelf and identify and quantify mean currents flowing in the deep ocean parallel to the shelf edge when compared with 11 gps referenced tide gauges on the british mainland our estimate of msst has a standard deviation of only 0 03 m and its variation with latitude is not significantly different from zero for these sites long distance levelling errors are larger than geoid errors we identify a systematic jump by 0 24 0 05 m in the levelled transfer of ordnance datum newlyn affecting all sites in great britain to the north of latitude 53 n even after this correction the variability of levelling remains larger than that of the geoid and gps implying a more complex structure to the levelling error than a simple step away from coasts we find that the best way to validate marine gravity data is their ability to predict msst with low local variability when combined with altimetric mean sea level there is a large reduction in msst variability when marine gravity data are subjected to an anti aliased adjustment of the mismatch where ship tracks cross we also report two msst model comparisons from a shelf seas and a deep ocean model both of high resolution there is quantitative and qualitative agreement between our geoid derived msst and the model predictions indicating significant improvements compared with earlier geoid models we also show that with the improved accuracy of geoid based msst it will become necessary to validate models and observations at matching epochs