a subtropical oceanic ring of magnitude storm in the eastern north atlantic physical chemical and biological properties a subtropical oceanic ring of magnitude storm that budded from the azores current was studied in the eastern north atlantic ocean in april 1999 the cyclonic eddy called leticia was centred at 32 4 n 28 7 w and extended across more than 200 km in an east west direction leticia had been previously detected by means of topex poseidon altimetry data and further intensively investigated using expendable bathythermograph and conductivity temperature depth stations the altimeter surface signature of the eddy revealed a 20 cm sea level depression an upward displacement of the 16 c isotherm of 125 m was linked to the eddy centre and geostrophic transport of the amount of water swirling cyclonically was 7 sv the temperature nitrate and oxygen anomalies on the 0 26 5 isopycnal surface inside leticia were 0 4 c 1 mol l 1 and 0 3 ml l 1 respectively with respect to surrounding waters shallowing 50 m of the deep chlorophyll maximum 0 3 mg m 3 was observed at the eddy centre associated with vertical displacements of the isotherms 100 m within the photic layer vertical excursions of the isopycnals and the deep chlorophyll maximum of more than 30 m were observed over temporal scales of a few 3 6 h integrated nitrate concentration over the photic layer was 4 fold higher inside leticia than outside however primary production rates were only slightly higher eddy diffusive fluxes across the nitracline located 30 m below the deep chlorophyll maximum ranged from 0 02 to 0 10 mmol no3 m 2 d 1 and explained 25 of the nitrate required to sustain the estimated new production 0 24 0 48 mmol no3 m 2 d 1

the measurement of the synoptic scale wind over the ocean mesoscale and microscale features of the turbulent winds over the ocean are related to the synoptic xscale winds in terms of published spectral forms for the microscale a mesoscale valley and published values of u var u var v and z l as defined in the text and as obtained for moderate to gale force winds the frequencies involved correspond to periods longer than 1 hour and extend to the microscale which starts at a period near 2 min or so and continues to the kolmogorov inertial range nondimensional spectra that span both the mesoscale and the microscale are derived as a function of u f nz and z l where z is 10 m l is the monin obukhov stability length and is evaluated at 10 m for the same different values of z l produce a range of values of u which in turn result in variations of the eddy structure of the mesoscale and microscale spectra both conventional anemometer averages and remotely sensed winds contain a random component of the mesoscale wind in their values these components are differences and not errors when winds are compared and quantitative values for these differences are given ways to improve the measurement of the synoptic scale wind by transient ships data buoys and scatterometers on future spacecraft are described these ways are longer averaging times for ships and data buoys depending on the synoptic conditions and pooling spacecraft data to form superobservations design considerations for future remote sensing systems are given

a geosat altimeter wind speed algorithm and a method for altimeter wind speed algorithm development a geosat altimeter wind speed algorithm is derived by cross calibrating geosat and seasat altimeter estimates of the normalized radar cross section 0 and modifying an existing seasat altimeter wind speed model function to obtain a model function appropriate for geosat observations it is argued that the 0 distribution measured by an altimeter is relatively stable over a sufficiently large geographical region and a long enough time period systematic differences between 0 estimates from two altimeters can therefore be identified based on comparisons of their 0 histograms any such systematic differences can then be corrected using independent 0 estimates when this method is applied to the geosat and seasat altimeters a systematic difference between the two 0 histograms is shown to be consistent with differences between seasat altimeter and nadir seasat scatterometer estimates of 0 deduced independently by a previous study this supports the conclusions that 1 the 0 distribution is stable and 2 the seasat altimeter estimates of 0 were miscalibrated after modifying the existing seasat altimeter wind speed algorithm to account for this apparent 0 error the resulting geosat estimates of wind speed agree with high quality buoy observations to within an rms difference of less than 2 m s

southern ocean monthly wave fields for austral winters 1985 1988 by geosat radar altimeter four years of monthly averaged wave height fields for the austral winters 1985 1988 derived from the geosat altimeter data show a spatial variability of the scale of 500 1000 km that varies monthly and annually this variability is superimposed on the zonal patterns surrounding the antarctic continent and characteristic of the climatology derived from the u s navy 1992 marine climatic atlas of the world the location and the intensity of these large scale features which are not found in the climatological fields exhibit strong monthly and yearly variations a global underestimation of the climatological mean wave heights by more than 1 m is also found over large regions of the southern ocean the largest monthly averaged significant wave heights are above 5 m and are found during august of every year in the indian ocean south of 40 s the monthly wave fields show more variability in the atlantic and pacific oceans than in the indian ocean the seasat data from 1978 and the geosat data from 1985 and 1988 show an eastward rotation of the largest wave heights however this rotation is absent in 1986 and 1987 the former was a year of unusually low sea states and the latter was a year of unusually high sea states which suggests a link to the el nino southern oscillation event of 1986

glacial millennial scale fluctuations in central african precipitation recorded in terrigenous sediment supply and freshwater signals offshore cameroon abstract evidence of rapid climatic oscillations like those observed in the greenland ice cores and sediments from high latitudes of the northern atlantic have been recognized in the pulses of terrigenous material to continental margin sediments off cameroon fe ca ratios used as a parameter to quantify the relative proportions of terrigenous fluxes versus marine carbonate monitor the variability of the west african monsoon they reveal the history of abrupt changes in precipitation over western and central africa during the past 52 kyr these rapid changes are particularly pronounced during the last glacial period and occur at timescales of a few thousand years stable oxygen isotope 18o records of globigerinoides ruber pink show high negative values reflecting periods of high monsoon precipitation the fe ca pattern is very similar to the dansgaard oeschger cycles from the greenland ice cores the good correspondence between the warm interstadials of the dansgaard oeschger cycles from the gisp2 ice core records and the high pulses of fe ca sedimentation in our core suggest a strong teleconnection between the low latitude african climate and the high latitude northern hemisphere climate oscillations during the last glacial this climatic link is probably vested in the west african monsoonal fluctuation that alters tropical sea surface temperatures thermohaline circulations and in turn net export of heat from the south to the north atlantic coupled with the variability of the low latitude southeast trade winds

annual rainfall and nitrogen isotope correlation in macropod collagen application as a palaeoprecipitation indicator abstract collagen has been extracted and analysed for 15 n from modern kangaroos macropods macropus eugenii m antilopinus m fuliginosus m rufus m robustus in western australia and south australia comparison of nitrogen isotope ratios with annual rainfall for the respective areas produced a good negative correlation for macropods but not for other marsupials this may be related to metabolic adaptations in macropods to compete against water loss hence the correlation between 15 n and annual rainfall may be species specific nitrogen isotope analyses on collagenic material extracted from fossil macropods macropus spp have been determined from two late pleistocene deposits in south australia corroboration with spore pollen and sedimentological data confirm that 15 n of collagenic material can be used as a proxy for palaeoprecipitation levels in australia this has great potential for understanding palaeoclimatic changes especially drought periods in australia during the pleistocene

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

satellite altimeter measurements of surface wind recent analyses of wind speed measurements by the geosat altimeter showed that the radar cross section is affected by oceanographic factors particularly by the degree of sea development which are not directly accounted for in the geophysical model functions gmf in the present work two new gmfs which account for the effects of the actual degree of sea development are proposed along with the radar cross section these models use significant wave height information one particular version is recommended for applications in oceanographic and climate studies where wind speed or wind stress data have to be binned i e averaged over time and or space intervals the accuracy of this gmf overall bias of 0 1 m s and rms error of about 1 6 m s is higher than the accuracy of commonly employed gmfs while the wave age related trend is reduced to a geophysically insignificant level finally the wind speed histograms for the collocated data set are derived and compared with the ground truth data as well as with the histograms yielded by presently known gmfs it is also shown that the accuracy of altimeter measurements could be increased even further if some additional information on the wave field were available from independent sources e g the dominant wavelength from synthetic aperture radar images

validating a scatterometer wind algorithm for ers 1 sar the ocean surface wind field is observed from space operationally using scatterometry the european space agency s esas ers 1 satellite scatterometer routinely produces a wind product that is assimilated into forecast models scatterometry cannot give accurate wind estimates close to land however because the field of view of a spaceborne scatterometer is on the order of 50 km side lobe contamination due to the large contrast in backscatter between land and water compounds the problem synthetic aperture radar sar can provide wind speed and direction estimates on a finer scale so that high resolution wind fields can be constructed near shore an algorithm has been developed that uses the spectral expression of wind in sar imagery to estimate wind direction and calibrated backscatter to estimate wind strength three versions based on c band scatterometer algorithms are evaluated for accuracy in potential operational use algorithm estimates are compared with wind measurements from buoys in the gulf of alaska bering strait and off the pacific northwest coast by using a data set of 61 near coincident buoy and ers 1 sar observations representative figures for the accuracy of the algorithm are spl plusmn 2 m s for wind speed and spl plusmn 37 spl deg for wind direction at a 25 km spatial resolution

an estimate of the geosat altimeter wind speed algorithm at high wind speeds existing wind speed algorithms for satellite altimeters have been developed from data in the range 0 to 20 m s at higher wind speeds the available algorithms diverge alarmingly by comparing geosat altimeter values of the radar cross section with model predictions of the surface winds during satellite overpasses of tropical cyclones a wind speed algorithm valid for wind speeds between 20 and 40 m s is developed there is however considerable scatter in these data an error analysis shows that this observed scatter is consistent with the accuracy to which the tropical cyclone wind fields can be inferred an approximately linear dependence of the radar cross section on wind speed is however clearly evident within these data at the lower limit of its applicability u10 20 m s these data are consistent with the previously derived algorithms at its upper limit u10 40 m s mean squared slope values inferred from the radar cross section are consistent with the theoretical upper limit

antiquity of aridity in the chilean atacama desert the atacama desert of northern chile and southern peru has one of the longest histories of arid conditions known although most studies have focused on the hyper aridity prevalent since the miocene all terrestrial sediments in the region from the late triassic onwards also record evaporitic and thus arid climates supergene mineralization in the region did not develop under a more humid climate conducive to deep weathering but under arid conditions these processes may have been facilitated by hydrological changes during miocene uplift and drainage incision but were operational prior to the uplift similarly global cooling and changes to oceanic circulation in the post miocene period only accentuated existing conditions a whole regolith perspective is vital to understanding the history of aridity in the atacama desert and its relevance to arid zone morphogenesis regolith formation and supergene mineralization in particular the long history of aridity raises the possibility that supergene mineralisation under the appropriate conditions form in arid environments instead of requiring humid conditions

statistical problems of wind generated gravity waves arising in microwave remote sensing of surface winds the basic geometric features of a developed sea surface affecting the accuracy of wind speed measurements by satellite instruments are reviewed based on seasat scatterometer geosat altimeter and dmsp ssm i defense meteorological satellite program special sensor microwave imager observations collocated with buoy data error trends in the satellite winds are shown to be correlated with various measures of wave development these trends are explained by examining the rms wave slope of energy containing waves which directly or indirectly affects all microwave techniques statistics of temporal spatial rates of steep and breaking waves affecting the scatterometer and radiometer measurements are derived and compared with field observations

a significant wave height dependent function for topex poseidon wind speed retrieval the ocean surface roughness affects the radar cross section measured by altimeters the wind speed is responsible for this roughness and most of present algorithms use the radar cross section rcs to infer it a few authors monaldo and dobson 1989 glazman and greysukh 1993 emphasized the influence of the sea maturity on satellite measurements they found a marginal improvement in wind speed retrieval by including significant wave height in their algorithm in this paper several previously established algorithms relating altimeter radar cross section to ocean surface wind speed are first analyzed the shapes of the rcs versus wind speed curves are shown to depend mainly on the minimization methods used to generate the model functions an empirical wind speed algorithm is then derived from the two altimeters alt and ssalt on board topex poseidon t p satellite using a quality controlled data set in which north atlantic operational surface wind and wave analyses are collocated with altimeter alt measurements unlike usual algorithms this new function depends on both the radar cross section and the significant wave height the improvement in the t p wind speed estimate seems significant at the 99 9 level the accuracy of the derived function is evaluated using an independent collocated ssalt and numerical weather prediction models data set here again the improvement is significant but at the 90 level because of the smaller amount of data available the t p wind speed estimates are furthermore compared to collocated estimates from national oceanic and atmospheric administration data buoys the new algorithm retrieves wind speed from geosat measurements with an accuracy compatible with usual algorithms

diagnosing monthly mean boundary layer properties from reanalysis data using a bulk boundary layer model abstract the mixed layer approach to modeling the planetary boundary layer pbl is particularly well suited to inversion topped pbls such as the stratocumulus topped boundary layer found off the west coast of america in the subtropical pacific ocean at northern and southern latitudes however a strong temperature inversion near 850 hpa the trade wind inversion is not confined to the stratocumulus regimes but has been observed over most parts of the subtropical tropical pacific ocean in this paper the authors test the ability of a simple bulk boundary layer model bblm to diagnose entrainment velocity cumulus mass flux and surface latent heat flux from monthly mean reanalysis data the pbl depth is estimated from geoscience laser altimeter system data the model is based on the conservation equations for mass total water mixing ratio and moist static energy the bblm diagnoses entrainment velocities between 1 and 8 mm s 1 in the stratocumulus and trade wind regions with increasing rates towar

remote sensing of wind speed at sea surface level using hf skywave echoes from decametric waves using an hf skywave radar to study the decametric sea waves it appears that their amplitudes do not saturate as the wind speed increases a measurement method based on the kahma sea wave spectrum is proposed and radar estimations of the wind speed are compared with in situ measurements performed on board a ship the rms difference between the two measurements is 2 5m s and is probably mainly due to the spatial variability in the wind speed

on eddy scales in the eastern and northern north atlantic ocean as a function of latitude infrared satellite images and two ensembles of satellite tracked buoys have been used to analyze eddy scales in the central and eastern north atlantic between 35 n and 60 n both data sets yield eddy scales which decrease northward from the subtropical atlantic and can be closely related to the rossby radius of the first baroclinic mode

corrected spectra of wind speed and significant wave height in a recent paper monaldo 1988 i presented spatial spectra of wind speed and significant wave height swh variance the spectra were calculated from spatial variations of wind speed and swh as measured by the seasat and geosat radar altimeters it has recently come to my attention that these spectra were incorrectly calculated the shape of the corrected wind speed variance spectra no longer agree with theoretical predictions by thompson 1973 the expected differences between two altimeter wind speed or swh measurements separated a given distance apart were calculated in the time domain and not by inverse fourier transformation of the spectra the expected differences given by monaldo 1988 are therefore unaffected by the errors in the calculation of the swh and wind speed spectra

further development of an improved altimeter wind speed algorithm a previous altimeter wind speed retrieval algorithm was developed on the basis of wind speeds in the limited range from about 4 to 14 ms 1 in this paper we use a new approach which gives a wind speed model function applicable over the range 0 to 21 ms 1 the method is based on comparing 50 km along track averages of the altimeter normalized radar cross section measurements with neighboring off nadir scatterometer wind speed measurements the scatterometer winds are constructed from 100 km binned measurements of radar cross section and are located approximately 200 km from the satellite subtrack the new model function agrees very well with earlier versions up to wind speeds of 14 ms 1 but differs significantly at higher wind speeds we discuss the relevance of these results to the geosat altimeter launched in march 1985

barotropic and baroclinic tidal currents in the eastern basins of the north atlantic data from a large scale moored array in the iberian and canary basins are used to determine the energies of barotropic and baroclinic m2 and s2 tides an analysis of time varying dynamical modes is performed the results for barotropic modes confirm the global surface tide model results of schwiderski 1980 for this region the barotropic modes dominate in the deep basins but increased baroclinic contributions are usually found over rough topography at three locations near the continental slope in the southern canary basin the baroclinic modes dominate the barotropic mode results from an array of three moorings at the northern part of the cape verde rise show an inverse behavior of barotropic and baroclinic energies such that the baroclinic energy is steadily enhanced while the barotropic energy is reduced towards the continental margin the increase in baroclinic energy is consistent with a generation of internal tides close to the shelf by surface tidal forcing over topography further evidence for this process is provided by the 2 week periodicity of the first order baroclinic mode at the slope corresponding to the spring neap cycle of the barotropic tide

stable isotope chemistry population histories and late prehistoric subsistence change in the aleutian islands aleut population history has been a topic of debate since the earliest archaeological investigations in the region in this paper we use stable isotope chemistry to evaluate the hypothesis that two distinct groups of people paleo and neo aleut occupied the eastern aleutians after 1000 bp this study focuses on 80 sets of directly dated eastern aleutian burial assemblages from chaluka midden shiprock island and kagamil island we use a linear mixing model informed by isotopic analysis of two large aleut faunal assemblages to address temporal and spatial variation in human carbon and nitrogen stable isotope data from these sites the patterning we report addresses both aleut demographic and economic prehistory illustrating a transition in both at ca 1000 bp our results suggests that the chaluka diet dominated by paleo aleut inhumations differed in both trophic level and foraging location from the other two sites for much of the past 4000 years trends in our data also suggest that individuals from shiprock and kagamil burial caves primarily neo aleuts had enough access to higher trophic level foods to differentiate their bone chemistries from those buried in chaluka midden these trends in diet recently reported genetic differences as well as the introduction of novel mortuary practices at ca 1000 bp suggest that neo aleuts do represent a population new to the eastern aleutians

fingernails and diet stable isotope signatures of a marine hunting community from modern uummannaq north greenland c n ad s stable isotope compositions of fossil human bones are frequently used in palaeodiet studies but results from strictly marine communities are scarce modern hunting and fishing inuit greenlanders in the uummannaq district in north greenland are known to live from a diet high in local marine food seal whale halibut combined with basic foods bread cereals dairy products imported from denmark and thus provide an excellent test population here were report diet anamnesis data and stable isotope compositions of fingernails from 82 uummannaq district inuit individuals and a control group of 32 danes living in denmark the uummannaq fingernails are significantly enriched in 13c 15n 34s compared to the danish group t test 99 conf level calculated from isotope modelling the uummannaq inuit get on average 50 of their diet range 28 to 68 from marine food placed high in the trophic system reflecting high proportions of carnivorous marine mammals seal in the diet and the most 15n enriched individuals have trophic positions close to polar bears comparisons to other human hair and fingernail studies reveal the uummannaq inuit to be the most heavy isotope enriched modern community analysed so far the consistency of our data lead us to conclude that the fingernail isotope signatures are reliable measures of modern human diet composition and that fingernail isotope analyses can provide an easy quantitative supplement to other diet studies sulphur isotope analyses in special may provide unambiguous results in terrestrial to marine mixing systems

simultaneous observations of ocean surface winds and waves by geosat radar altimeter and airborne synthetic aperture radar during the 1988 norwegian continental shelf experiment quasi simultaneous measurements of the ocean surface by the canada centre for remote sensing ccrs convair 580 cv 580 synthetic aperture radar sar were acquired on march 20 1988 along an ascending pass of the geosat radar altimeter as part of the prelaunch ers 1 norwegian continental shelf experiment norcsex 88 over a region where the sar look direction is parallel to the wind vector a relationship between the ocean scattering cross sections measured by the geosat altimeter and the sar is obtained in the regions where the wind direction is changing an estimate of the wind direction is derived from the differences measured between the altimeter and the sar scattering cross sections wavelength and wave directions derived from the sar wave spectra are in good agreement with the sea truth data obtained with the wave directional buoys and with the altimeter derived swell estimates significant wave height measured by the geosat altimeter is compared with the buoy measurements and is used to assess the validity of the significant wave height deduced from the sar

the wave climate of the southern ocean abstractthe wave climate of the southern ocean is investigated using a combined dataset from 33 years of altimeter data in situ buoy measurements at five locations and numerical wave model hindca

oceanographic and geophysical applications of satellite altimetry since the last quadrennial report new satellite altimeter data have not been generally available nevertheless important progress has been made from analyses of geos 3 and seasat data the marine gravity field has been determined to an extraordinary resolution and accuracy and important solid earth geophysical interpretations made in the area of oceanography statistical estimates of the variability of dynamic topography have been published methods for incorporating altimeter data into numerical models have been developed and applied and tentative but interesting determinations of the mean circulation have been made in addition altimeter waveform analysis has made it possible to use altimeter data to determine elevations of major ice fields finally important new insights into the nature of satellite ephemeris error and its influence on altimetrically derived sea surface topography have been achieved

internal tides resulting from the passage of surface tides through an eddy field if a surface barotropic tide passes through a baroclinic eddy field the nonlinear terms produce among others internal waves having near tidal frequency but wavelength and vertical mode structure as given by the eddy field stationary eddy fields yield stationary internal tides whereas moving eddy fields yield modulated progressive internal tides these internal tidal currents have amplitudes in the range of observations 1 3 cm s 1

semidiurnal tides observed in the western equatorial pacific during the tropical ocean global atmosphere coupled ocean atmosphere response experiment the semidiurnal tide within a 100 km square region of the western equatorial pacific centered at 1 8 s 156 1 e is examined using shipboard survey and mooring data collected during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare baroclinic and barotropic tidal amplitudes and phases are estimated from the survey and mooring observations in the upper 300 m of the 1800 m deep ocean by specifying their horizontal and vertical structures the barotropic tide is assumed to have zero horizontal wavenumber over the domain while a component of the baroclinic tide that is phase locked to the barotropic tide is determined by a searching method using plane wave fits to the data the estimated barotropic tidal current is in good agreement with tide models derived from topex poseidon observations the plane wave analysis indicates a dominant mode one baroclinic wave propagating toward the northeast the second vertical mode can also be detected given the phase differences between the m2 and s2 constituents in the barotropic and baroclinic tides the source of the baroclinic tidal signal is determined to be about 320 km southwest of the observing region at a series of islands and shallow ridges the combined estimates of the barotropic and baroclinic tides typically account for only 40 60 of the observed semidiurnal band current variance in the mooring data indicating the high degree of temporal and spatial variability of the baroclinic tide in this region the results of this study suggest however that coherent barotropic and baroclinic tidal signals can be successfully distinguished in the deep ocean using shipboard survey data even when the data are limited to the upper 300 m

on using significant wave height and radar cross section to improve radar altimeter measurements of wind speed wind blowing across the ocean surface generates small centimeter scale roughness the radar cross section rcs measured by spaceborne nadir looking altimeters operating at about 13 5 ghz is responsive to this roughness present altimeter algorithms use rcs to infer wind speed we compare geosat altimeter estimates of wind speed and nearly coincident estimates from noaa data buoys to determine whether altimeter algorithms can be improved by using more of the information available from altimetry we find that a marginal improvement in wind speed retrievals can be obtained by including additional rcs information and significant wave height in the retrieval algorithm perhaps most important results also suggest that wind wave growth is suppressed in the presence of preexisting ocean swell

the effect of the degree of wave development on the sea state bias in radar altimetry measurement the effect of the degree of wave development on the sea state bias ssb in geosat altimeter height measurement is evaluated theoretical considerations suggest that the altimetric ssb is generally not a linear function of significant wave height but depends also on other factors of wave development of particular interest is its dependence on wave age defined as the ratio of the phase speed of the dominant ocean waves to ocean wind speed we estimate wave age rather crudely on the basis of the significant wave height h and wind speed measured by the altimeter under general conditions when the sea is not in equilibrium with the wind this estimate may not correspond to the wave age in a strict sense and hence is called pseudo wave age in this paper nevertheless the pseudo wave age is a rough indicator for the degree of wave development the general trend in the dependence of the ssb on pseudo wave age as found by analyzing 2 7 years worth of geosat data agrees well with the theoretical prediction for a given h the ssb decreases as the degree of the wave development measured by the pseudo wave age increases this empirical trend is modeled as ssb a m m h where and m are the pseudo wave age and its average value respectively a 0 013 0 005 and m 0 88 0 37 statistically this model performs slightly better than a standard model i e ssb h with being a constant in terms of the global rms error the improvement is by 1 6 cm however because the degree of wave development varies with the season and geographical location this small improvement could become important for more accurate altimetric missions in the future when the centimetric basin scale signals are the focus of the study

paleodiet in northern chile through the holocene extremely heavy δ15n values in dental calculus suggest a guano derived signature abstract dental calculus extracted from the teeth of 28 prehistoric human skeletons from coastal and valley archaeological sites in northern chile that date from the archaic period 2300 bc to the late intermediate period ad 1476 was analyzed for stable isotope 15 n 13 c compositions 15 n compositions were extremely heavy 17 8 to 33 1 but comparable to some studies using conventional human biomaterials hair nail muscle at other prehistoric sites in northern chile there was a negative correlation between 15 n and 13 c for coastal sites but a positive correlation for valley sites results for the valley sites point to a diet that was influenced by marine resources throughout all time periods the unusually heavy 15 n values for the coastal sites require a dietary component with a 15 n composition significantly heavier than that of marine resources the hyper aridity at the study area mean annual rainfall of 0 5 0 6 mm year is a likely contributing factor to the production of heavy 15 n values but is unlikely to account for the heaviest 15 n values 30 one possible explanation for the heaviest 15 n values is that dietary components were impacted by isotopically heavy guano which is abundant in the region guano may have been used as a fertilizer during crop cultivation at the onset of the formative period continuing through the historic period after spanish contact the indirect impact of guano from abundant bird habitats in the region may have influenced wild foodstuffs harvested throughout the pre agricultural period results provide support for the utility of dental calculus as a proxy for obtaining stable carbon and nitrogen isotope signatures for use in paleodietary studies

why western boundary currents in realistic oceans are inviscid a link between form stress and bottom pressure torques it is shown that wind stress curl is balanced by bottom pressure torque in a zonal integral over any strip wide enough to smooth out the effect of nonlinear terms typically about 3 of latitude the derivation is completely general as long as the zonal wind stress is balanced by form stress at each latitude as is known to be the case in the ocean this implies that viscous torques are not important in western boundary currents their place being taken by bottom pressure torques the prediction is confirmed in the context of a global eddy permitting numerical ocean model this link between form stress and bottom pressure torques makes it easier to consider southern ocean dynamics and subtropical gyre dynamics in the same conceptual framework with topographic interactions being important in both cases

effects of sea maturity on satellite altimeter measurements for equilibrium arid near equilibrium sea states the wave slope variance is a function of wind speed u and of the sea maturity the influence of both factors on the altimeter measurements of wind speed wave height and radar cross section 0 is studied experimentally the necessary theoretical background both on wave statistics and on the near nadir radar backscatter is outlined it is based on a recently proposed view that the effective fractal dimension for a surface patch corresponding to the equilibrium range of wave spectra increases as the wave field matures the experimental part is based on 1 year s worth of geosat altimeter observations colocated with in situ wind and wave measurements by 20 noaa buoys errors and biases in altimeter wind speed and wave height measurements are investigated a geophysically significant error trend correlated with the sea maturity i e with c0 u where c0 is the phase velocity of waves corresponding to the spectral peak and u is the mean wind speed well above the surface is found in wind speed measurements this trend is explained by examining the effect of the generalized wind fetch x gh1 32 u2 on the curves of the observed dependence 0 f u x we conclude in particular that unambiguous measurements of wind speed by altimeter in a wide range of sea states are impossible without accounting for the actual degree of wave development an approach to a more accurate retrieval of wind speeds is suggested as based on accounting for the actual degree of wave development which can be achieved through processing the total radar cross section simultaneously with the significant wave height information contained in altimeter waveforms the potential capability of a satellite altimeter to estimate wave age and similar measures of wind wave coupling is discussed this capability expands the use of satellite altimeters for air sea interaction studies

an assessment of geosat wave height and wind speed measurements an assessment is made of the significant wave height and wind speed measurements obtained by the geosat radar altimeter in comparison with buoy data it is found that geosat underestimated the significant wave height by 13 throughout the range of measurements an attempt to compare the wave measurements made by seasat and geosat reveals problems with both data sets for the geosat wind speed measurements it is found that the smoothed brown algorithm usually employed to convert backscattered power to wind speed does not give good results in comparison with buoy measurements a simple linear relationship between backscattered power and wind speed is derived which is in close agreement with the algorithm recently proposed by witter and chelton for wind speeds above 3 m s 1 the implications of these results for deriving wind and wave climatologies from altimeter data are discussed

seasonal and interannual changes in the north atlantic subpolar gyre from geosat and topex poseidon altimetry sea surface slopes from the altimetric satellites geosat and topex poseidon are used to calculate eddy kinetic energy of the north atlantic subpolar gyre 40 65 n 60 5 w using two years of data from each satellite december 1986 to december 1988 and october 1992 to september 1994 respectively interannual differences in the north atlantic current nac are revealed in regions of strong currents the eddies are driven by baroclinic instability of the mean flow are not seasonally varying and may therefore be used as a surrogate for the mean flow itself wind stress curl fields for the same periods show that the northward and southward shifts in the current branches across the mid atlantic ridge are related to interannual differences in the winter wind stress curl pattern when the zero in wind stress curl is well defined and wind stress is at a maximum outside the nac the eddies are driven primarily by wind stress indicated by a significant seasonality time series of eddy kinetic energy and wind stress are generated for the 4 years and the magnitude phase and significance of annual and semiannual signals are determined interannual changes in the timing of the maximum eddy kinetic energy are associated with that of the maximum wind stress with each being shifted by a month or two later or earlier throughout much of the northern north atlantic a significant annual signal in eddy kinetic energy is observed lagging the wind stress by on average 6 weeks a negligible lag is found in the region of the east greenland current and irminger sea whereas the greatest lag about 2 months is found in the labrador sea

estimation of wind friction velocity and direction at the ocean surface from physical models and space borne radar scatterometer measurements this paper presents a new technique for estimating the wind friction velocity at the ocean surface from c band radar scatterometer measurements this technique uses physical models of ocean surface waves and electromagnetic backscattering from a rough surface at intermediate angles of incidence to generate predictions of the normalized radar cross section nrcs or 0 of the ocean surface for a given wind friction velocity and observational geometry the ocean spectral model used in this technique has been developed specifically for this application it combines in situ wave measurements at low wave numbers with the phillips 1985 equilibrium spectral model this choice of ocean wave model is supported by a set of open ocean wave measurements summarized in this paper a suite of models derived from both in situ and remote measurements of the sea surface is used to characterize the directional spreading of ocean waves relative to the wind direction the resulting two dimensional ocean wave spectra are used with a composite surface model to predict radar backscattering from the ocean surface at c band these radar cross section predictions are combined with ers 1 scatterometer measurements in a cost function minimization scheme to yield estimates of the friction velocity vector at the ocean surface we present examples of this technique and compare friction velocity retrievals obtained via this scheme with buoy based measurements under a variety of wind and wave conditions on the basis of the analysis of a limited number of cases this technique yielded friction velocity estimates for which the magnitude was within 22 and the direction was within 25 given that scientific applications require magnitude estimates within 10 15 and directional estimates within 20 of in situ measurements these preliminary results suggest that this is a promising approach to wind retrieval

local climatology of wind and sea state by means of satellite radar altimeter measurements the wind speed and significant wave height swh climatology at a given location of the ocean is a matter of concern in marine technology for planning offshore structures or ship routing as well as in meteorology and oceanography the purpose of this paper is to present a feasibility study of a new approach to determine the local sea state and wind speed climatology using satellite borne radar altimeter the geosat data for the first two years cycles 1 to 43 of the exact repeat mission and the in situ data from the quarter platform qp of the frigg oil field 59 53 n 2 3 e in the north sea have been used for this study because of the satellite sampling scheme a given location of the ocean might never be overflown by the geosat radar altimeter thus altimetric measurements have to be considered for an area surrounding the location where the climatology is to be estimated thus the main question for the determination of the local climatology of wind and swh is this given the time and space sampling of geosat is it possible to estimate the statistical characteristics of a random process analysis of the geosat altimeter wind speed and swh data set over concentric zones surrounding qp frigg shows that up to 200 km the swh and wind speed data set belong to the same population and that the estimated probability laws are very stable comparison of the results of this analysis with the data set of in situ measurements available from qp frigg during the same period shows that the swh climatology computed from altimetric measurements in a zone of 100 km radius surrounding the platform is very close to the one computed from in situ data as compared to the in situ measurements the wind speed variability is not well represented by the altimetric measurements and the variance estimated from the altimetric data set is lower by more than 20 this can be attributed to poor signal dynamics with respect to the characteristic noise level in the altimeter wind measurements

first observations of the interaction of ocean swell with sea ice using satellite radar altimeter data the action of ocean waves and swell on sea ice in the marginal ice zone miz controls the size distribution of ice floes and thus affects ice dynamics and the thermodynamics of ice growth and decay an understanding of ice processes is important because of the influence of the sea ice cover on high latitude weather and global climate1 also long term changes in average sea ice extent could provide a sensitive indication of climatic change if the degree of shorter term variability were better understood2 previous observations of the propagation of swell within the ice pack have been limited in spatial and temporal extent3 6 here we present new results from the us seasat satellite which suggest that radar altimetry can provide a powerful means of global synoptic monitoring of the interaction between ocean and ice

the decay rate of ocean swell observed by altimeter abstractaltimeter data from transects across the southern ocean are analyzed to determine the decay of oceanic swell the resulting decay rate is shown to be proportional to wavenumber squared and swell amplitude cubed such a decay relationship is consistent with turbulent interaction with the background either in the air or water the present data cannot distinguish between these two cases the results are consistent with the limited previous studies and present a source term suitable for use in wave prediction models

global wind stress and sverdrup circulation from the seasat scatterometer abstract three months of vector wind observations from the seasat a satellite scatterometer sass are used to construct gridded fields of monthly average wind stress and wind stress curl over the global ocean these fields are examined to identify features either poorly resolved or not present in wind stress fields constructed from conventional data particular attention is focused on the spatial structures in the high southern latitudes and the tropical regions the sass wind stress fields are compared globally with the hellerman and rosenstein climatological monthly average surface wind stress fields and with monthly averages of wind stress computed from contemporaneous 1000 mb wind analyses produced by the national meterological center the potential for satellite scatterometry improving the present knowledge of the global wind stress field and making important contributions to ocean modeling is demonstrated by comparison of global maps of the sverdrup circulation computed from 3 month average sass an

alteration of 15n14n and 13c12c ratios of plant matter during the initial stages of diagenesis studies utilizing archaeological specimens from peru abstract the stable carbon and nitrogen isotope ratios of plants extracted from peruvian archaeological sites ranging in age from 400 to 4000 years b p have been measured the 13 c and 15 n values of prehistoric plants that were carbonized prior to deposition are similar to those of modern plants which have the same carbon dioxide fixation or nitrogen assimilation mechanisms in contrast the 15 n values of prehistoric plants that were not carbonized are generally 10 20 and as much as 35 more positive than those of their modern counterparts the 13 c and 15 n values of different parts of prehistoric uncarbonized plants differ by as much as 8 and 21 respectively whereas the same parts of modern plants have 13 c or 15 n values that lie within 2 of one another sem analysis etiminated the possibility that diagenetic alteration of the isotope ratios of the prehistoric uncarbonized plants was caused by the adsorption of particulate soil matter isotopic analysis of the organic residues that remained after the prehistoric uncarbonized plants were treated to remove fractions that might have been added in the depositional environment indicated that the alteration of the 13 c values resulted from the adsorption of humic and fulvic acids whereas the diagenetic shifts of the nitrogen isotope ratios were not caused by adsorption of 15 n enriched organic or inorganic forms of nitrogen from the soil our observations do not permit us to speculate on a mechanism that accounts for the 13 n enrichment of the prehistoric uncarbonized plant remains although the excellent state of preservation of these samples suggests that isotopic fractionation during microbial decomposition was not the cause the observation that the isotope ratios of the prehistoric carbonized plants are similar to those of their modern counterparts indicates that it will be possible to separate carbonized plants residues into three groups legumes non leguminous c 3 plants or c 4 and cam plants based on their 13 c and 15 n values this method should provide useful information to archaeologists working in environments in which carbonized plant remains often burned beyond morphological recognition are the only archaeobotanical remains which are recovered

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

retention of hunter gatherer economies among maritime foragers from caleta vitor northern chile during the late holocene evidence from stable carbon and nitrogen isotopic analysis of skeletal remains abstract on the basis of stable carbon and nitrogen isotope analysis of human remains this paper provides evidence for the retention of hunter gatherer economies among coastal inhabitants in northern chile during the late holocene at the same time that inland populations were adopting agricultural economies coastal diets from the caleta vitor region of the atacama desert were dominated by marine based foods predominantly from upper trophic levels the focus on reliable marine food resources is interpreted as a risk minimisation strategy in this marginal arid environment although these coastal hunter gatherers adopted other goods and traditions from agricultural populations their participation in this larger interregional exchange network did not affect their basic subsistence economies associated new radiocarbon dates from the site are also discussed skeletal remains and artefacts associated with the caleta vitor shell middens generally originate from sites with dates ranging from c 9000 476 bp however the human remains that are the subject of this research cover the time period c 4000 476 bp

validation of geosat altimeter derived wind speeds and significant wave heights using buoy data this paper presents a comparison of geosat radar altimeter derived wind speeds and significant wave heights with those measured by buoys in the national data buoy center ndbc network measurements from a subset of 43 buoys moored in coastal regions and deep ocean including the north pacific north atlantic and gulf of mexico were examined data from other buoys within the ndbc network were not included because of their proximity to land seven months of altimeter comparisons were obtained during the geosat geodetic mission for the periods may august and october december 1985 only geosat data within 150 km of buoy locations were accessed this resulted in 1166 wind speed and significant wave height pairs an error analysis was performed to better understand the differences between altimeter and buoy derived results and to establish consistency between the two sets of measurements the following error sources were identified and quantified in terms of their impact on wind speed and significant wave height uncertainties 1 inaccuracies due to buoy instrumentation 2 errors resulting from temporal and spatial separations 3 errors arising from averaging of the buoy data in time and averaging of altimeter data over its footprint and 4 altimeter instrumentation errors four algorithms relating altimeter radar cross section to ocean surface wind speed were investigated the brown algorithm brown et al 1981 and the smoothed form of the algorithm of brown et al goldhirsh and dobson 1985 were found to give the smallest rms errors these were 1 7 m s and less for a maximum altimeter track buoy separation of 50 km for most cases considered this uncertainty agreed with the error obtained from the error analysis significant wave heights measured by the altimeter were found to be in agreement with buoy derived values to within 0 5 m rms this value was also found to be in agreement with that derived from the error analysis the measurement goals for geosat were 1 8 m s rms for wind speeds from 1 m s to 18 m s and 0 5 m rms for significant wave height or 10 whichever is greater frain et al 1985 these goals were met for the range of wind speeds compared

growth of wind waves with fetch observed by the geosat altimeter in the japan sea under winter monsoon the wind speeds and the significant wave heights derived from the geosat altimeter are validated by comparing with the data obtained at japanese ocean data buoy stations a systematic error is found in the altimeter wind speeds at high winds an experimental equation is derived in order to correct this error for the present study by using the corrected wind speeds and the wave heights growth of wind waves with fetch in the japan sea under winter monsoon is investigated the altimeter derived nondimensional significant wave height and nondimensional fetch show good agreement with the empirical fetch graph formulas fetch variation of the wind speeds is also discussed in relation to the evolution of the turbulent boundary layer over wind waves by using the altimeter data