average seasonal variation of the atlantic equatorial currents from historical ship drifts abstract surface currents in the tropical atlantic were studied using historical ship drift data these are the only available data capable of resolving the long term seasonal fluctuations of currents over a broad geographical region the north equatorial countercurrent was found to extend as a continuous eastward flowing current across the atlantic in the band 5 8 n from july to december the maximum average eastward velocity was 30 cm s 1 during july september east of 20 w the countercurrent continued throughout the year west of 20 w and from january to june the countercurrent disappeared and westward currents were observed average westward velocity reached 20 cm 1 in april and may centered near 40 w the annual cycle in surface velocity 20 cm s 1 amplitude agrees closely with that of geostrophic velocity inferred from variations in thermocline depth across the counter current jets centered near 2 n and 4 s separated by a minimum near 1 s the northern jet has a large 14 cm s 1 semiannual v

high frequency oscillations and their correlation with the wind forcing during the first sequal year two arrays of inverted echo sounders one along the equator and the other across the north equatorial countercurrent are analysed together with a wind record from st peter and st paul rocks the dominant high frequency feature along the equator is an energetic oscillation with a period of 5 8 days that shows strong coherence with the meridional component of the wind the sounder at 3 n 28 w on the other hand shows a high degree of coherence with the zonal component of the wind at a period of 4 5 days comparison of these measurements in 1983 with measurements made in 1979 suggest considerable non stationarity

anoxia controlled by relative sea level changes an example from the mississippian barnett shale formation abstract a continuous core drilled in the barnett shale formation fort worth basin texas united states a remarkable example of paleozoic organic rich sediments deposited in a narrow inland seaway was analysed by means of sedimentological geochemical and biostratigraphic data as the influence of sea level fluctuations on benthic anoxia in ancient seas is still poorly understood our work aims to shed light on the control exerted by relative sea level variations on the paleoceanographic processes that drove fine grained sediment deposition organic matter dispersal and preservation during the sedimentation of the barnett shale formation using spectral gamma ray log a large second order sequence modulated by a total of thirteen third order sequences was inferred third order relative sea level cycles modulated the level of restriction of the basin through time alternating pulses of bottom water oxygenation and relatively more efficient watermass circulation with times of sluggish bottom water and stagnation which controlled the facies stacking pattern and organic matter preservation in particular relatively increased stagnation occurred during lowstand phases while relatively reduced restriction was principally associated with transgressive and highstand systems tracts with more efficient bottom current circulation on a larger scale second order eustatic cycles played a crucial role in determining the paleoceanographic and depositional processes responsible for anoxia during the early phase of sea level rise the pre existing topography was flooded establishing the conditions for a shallow strongly restricted anoxic basin during the second order regression the basin experienced increased isolation with bottom water stagnation and deep water renewal of 6000 years anoxia terminated abruptly corresponding to the eustatic sea level rise associated with the beginning of a new second order sequence therefore the barnett shale formation represents a significant example of the complex interplay between sea level controlled basin physiography and local paleoceanographic conditions

near equatorial eddies in the north atlantic surveys of the large scale near equatorial eddies 400km across off the northeast coast of south america with expendable bathythermographs from ships of opportunity and aircraft indicate that a large eddy 6n 11n to the north and a southern eddy like feature 2n 6n probably are a permanent part of the circulation both features were observed during the periods of seasonal extremes march and september although during the latter period the structure of the eddies had enlarged and deepened indicating a pronounced seasonal variability

palaeoclimate change recorded in upper cretaceous albian cenomanian kazhdumi formation borehole spectral gamma ray logs south pars gas field persian gulf abstract th u and th k data from spectral gamma ray logs obtained from outcrop successions have been used as a rapid and inexpensive proxy for determining possible episodes of humid arid palaeoclimate change such outcrop based measurements have never been tested using spectral gamma ray data obtained from wireline logs in subsurface boreholes th k and th u ratios have traditionally been used to decipher sequence stratigraphic patterns at outcrop and in borehole the possible influence of palaeoclimate on such ratio changes has yet to be proven especially from borehole data in this work we compare borehole derived th k and to a lesser extent th u to palaeoenvironmental changes inferred from palynology and deduce that both sea level and changing hinterland weathering regimes caused discrete fluctuations observed in the spectral gamma ray logs this is the first time such subsurface information has been used in this way interpretation of wireline logs in terms of palaeoclimate as well as sea level may now be considered and the use of such logs in palaeoclimate reconstruction is strengthened

role of clastic sedimentology in the exploration and production of oil and gas in the north sea summary the nature and quality of clastic reservoir rocks is the result of a complex interplay of tectonic setting provenance depositional environment and diagenesis in particular it is now well established that the reconstruction of depositional environments in clastic successions provides the optimum framework for describing and predicting reservoir development and reservoir quality distribution on both regional exploration and field production scales this review in the context of the 21st anniversary of the british sedimentological research group bsrg expands the above mentioned theme in relation to the development of depositional models of each of the major oil and or gas bearing clastic reservoirs in the u k sector of the north sea which has been the subject of a surge in geological interest following the first gas discoveries approximately 21 years ago each major reservoir interval is used to illustrate specific themes with emphasis placed on how the application of depositional models has contributed to a better understanding of the exploration for and the production from the following reservoirs i permian aeolian and fluvial sands rotliegendes sandstones southern north sea ii jurassic fluvial deltaic and marginal marine sands lower jurassic statfjord formation and middle jurassic brent group northern north sea iii jurassic shallow marine and deeper marine mass flow sands and conglomerates upper jurassic fulmar piper type sands and brae magnus type deposits central and northern north sea and iv tertiary deep marine turbidite fan deposits palaeocene and eocene sands central and northern north sea

episodic river flooding events revealed by palynological assemblages in jurassic deposits of the brent group north sea spore and pollen sporomorph assemblages from middle jurassic marine deposits of the brent group in the northern north sea are investigated to assess temporal and spatial variations in vegetation and depositional processes four wells were sampled for palynology from the penguins cluster and the don north east fields through the rannoch formation shoreface succession hyperpycnite deposits occur throughout but are concentrated within the lower part of the section these are expressed by sand prone beds displaying waxing and waning current motifs normally graded muddy beds and structureless mudstones hyperpycnal hypopycnal deposits resulting from episodic river flooding represent important sedimentary features as they may be preserved below fair weather wave base in more offshore settings and potentially be the only record of the former presence of a nearby river mouth the hyperpycnites typically contain abundant botryoccocus spp amorphous organic matter aom and hinterland sporomorph taxa with relatively few marine components compared to associated marine shoreface facies variations in palynofacies assemblages and botryococcus spp abundances indicate frequent river mouth avulsion ordination of samples using non metric multidimensional scaling nmds indicates that shoreface samples of the sampled wells are relatively distinct but hyperpycnite samples are highly similar regardless of their sampled well this suggests that depositional processes and spore pollen sources i e catchment zones were similar among hyperpycnite events across different wells abundant bisaccate pollen botryococcus spp and aom within interpreted hyperpycnites suggest sediment mixing along the fluvial drainage path during flooding events the terrestrial signature of hyperpycnite sporomorph assemblages demonstrates that underflows remained coherent as they descended the shoreface profile with little turbulent mixing with ambient marine waters sporomorph assemblages display few large changes through time suggesting vegetation on the adjacent coastal plain was relatively static through the studied interval

surface equatorial current system along 23 w july 1982 january 1984 oceanographic observations were made during the first seven cruises of the focal program along 23 w from july 1982 to january 1984 using both direct current measurements and the dynamical method the equatorial current system is described the seasonal variations of the north equatorial countercurrent and south equatorial current are related to the wind field a weak eastward surface current near 2 3 s seems to be a permanent feature during the period of observation

instability waves observed on the equator in the atlantic ocean during 1983 a packet of surface confined westward propagating waves apparently generated by barotropic instability of the surface currents was observed in the equatorial atlantic during 1983 initial wavenumber analyses and energetics calculations are presented local working by the horizontal reynolds stress was large enough and at the correct time to account for the wave packet s existence the amplitude of the waves was comparable to the mean currents implying that the waves are of primary importance in the momentum balance of the seasonally varying equatorial surface currents

isopycnal and diapycnal circulation of the upper equatorial atlantic ocean in 1983 1984 isopycnal circulation and diapycnal processes in the equatorial atlantic ocean are investigated using eight cruises from november 1982 to july 1984 an eastward decrease of the transport of the equatorial undercurrent is observed averaging 18 2 106 m3 s 1 at 35 w to 10 2 106 m3 s 1 at 4 w there is also a meridional convergence at the undercurrent level and a larger meridional divergence in the surface layer of 15 106 m3 s 1 between 35 w and 4 w in the eastern equatorial atlantic the undercurrent core density as well as the salinity above the undercurrent experience a large seasonal cycle during the season where the eastern atlantic thermocline is closest to the surface and surface waters are coldest the current peaks in denser waters and subsurface salinity maximum are weaker an analysis of the salinity on isopycnal surfaces indicates that there is significant diapycnal mixing in the upper thermocline in the eastern atlantic the upper thermocline vertical heat diffusivity coefficient scaled over 1 of latitude varies between 3 cm2 s 1 during the upwelling season and nearly 0 early in the year this seasonal mixing is an important element of undercurrent dynamics the turbulent heat flux at the base of the surface layer averages 50 w m 2 between 1 5 n and 1 5 s the surface layer heat budget implies an average oceanic gain of 60 w m 2 between 1 5 n and 1 5 s which could result from exchanges with the atmosphere the heat flux and fresh water seasonal cycles needed to close the budgets are not realistic however the eastern equatorial atlantic thermocline seasonal upwelling is associated with a large inflow into the surface layer over the two years this flow averaging 11 12 106 m3 s 1 originates from the upper thermocline and diapycnal transports near the core of the undercurrent or below are found to be small below the core of the undercurrent we also find that mixing is not intense for instance at 26 5 in the upper part of the thermostad vertical heat diffusivity is only 0 6 cm2 s 1 assuming that mixing takes place over 1 of latitude the uncertainties on these budgets are however large and assumptions on the dynamics that were used could not be checked

winds at st peter and st paul rocks during the first sequal year wind observations were obtained during the first nine months of the sequal field program from a station maintained at st peter and st paul spp rocks winds are very steady from may to november and very unsteady during april when the intertropical convergence zone itcz crosses the site wind stress components are computed and comparison with 1979 data shows that the onset of the winds occurred one month earlier in 1983 but is of similar amplitude the spectral analysis of the wind shows a significant increase in the variance for periods between 3 5 days and 10 15 days

meanders observed in surface currents and hydrography during an equatorial atlantic transect data collected during an equatorial atlantic transect in june 1983 aboard the rv marion dufresne indicate the presence of energetic meanders of the surface south equatorial current with a zonal wavelength of 1000 km and an amplitude of 0 50 cm sec 1 organized structures appear in the surface salinity and temperature fields as well with amplitudes of 0 1 and 0 1 c respectively these disturbances are similar to those that have been previously observed in the atlantic and pacific and based on contemporaneous mooring data are the manifestation of an unstable wave propagating westward with a period of 25 days

zonal pressure gradient velocity and transport in the atlantic equatorial undercurrent from focal cruises july 1982 february 1984 the zonal pressure gradient zpg along the atlantic equator and the equatorial undercurrent euc transport are discussed for four cruises representative of each season a very clear sea surface slope reversal occurred in the eastern area during autumn as far west as 14 w an early onset of the equatorial thermocline rising was evident during spring 1983 an eastward equatorial surface jet clearly distinct from the euc was observed at 35 w and 29 w the greatest zpg but the lowest euc transport were observed during summer 1983 a nearly total absence of the zpg and a large surfacing of the euc as far as 10 w characterized the 1984 winter

drifting buoy trajectories in the atlantic north equatorial countercurrent during 1983 during 1983 21 freely drifting buoys measured trajectories in the vicinity of the atlantic north equatorial countercurrent these provide a visualization of the flow field and the first direct measure of the seasonal variation of the velocity during a single year from february to may the buoys moved gradually westward from june to december the buoys moved swiftly eastward with maximum speeds of 90 cm sec 1 located in the western atlantic the seasonal variation in current was similar to that measured by historical ship drifts except that the onset of the countercurrent in 1983 was about a month earlier than usual of the buoys that drifted eastward in the countercurrent three went into the north equatorial current two into the south equatorial current and seven into the guinea current

magnetostratigraphy of the middle jurassic brent group in the oseberg oil field northern north sea abstract magnetopolarity stratigraphy of the brent group and the uppermost part of the dunlin group has been established in two well cores from the oseberg field well 30 6 7 and well 30 9 2 northern north sea palaeomagnetic analysis of thermal demagnetization results defines a series of normal and reverse magnetozones in both wells remanent coercivity analysis of these middle jurassic clastic sediments indicates a magnetomineralogy independent of grain size interpreted to be of diagenetic origin thus suggesting that the magnetization is of early post depositional origin integration with the existing palynostratigraphic framework results in the establishment of several isochronous horizons especially in the ness formation which suggests lateral continuity of magnetostratigraphic datum planes between the two wells at the oseberg field although the exact dating of the magnetozones is not established the combined application of magnetopolarity and biostratigraphy provides a stratigraphic framework of improved resolution for these rock formations

observing the seasonal variability in the tropical atlantic from altimetry the tropical atlantic circulation is dominated by a strong wind driven seasonal cycle which is here described by means of the sea level heights measured by geos 3 and seasat altimeters seasat worked for just 3 months and geos 3 yielded an inhomogeneous space time coverage during its 3 5 years of operation to remedy this coverage shortfall all geos 3 and seasat data were merged together on a monthly basis without regard to year thereby ignoring the weak interannual perturbations of the tropical atlantic in this way a complete time series was produced for 1 year along each profile altirnetric heights were referenced to a global mean sea surface and then filtered to remove high and low frequency noise the residual heights were objectively analyzed to produce monthly maps of sea level anomaly between 10 s and 20 n these maps show a large annual signal in the western side of the basin between the equator and 10 n where the north equatorial countercurrent and south equatorial current are predominant the signal has an amplitude of 8 cm from a minimum in april may to a maximum in october november in the east the signal is weaker and depicts a semiannual cycle these results have been compared to similar maps obtained from historical hydrographic data merle and arnault 1985 the two sets of maps are in good agreement especially north of the equator where the largest seasonal variability occurs the major difference comes from underestimation of the altimetric signal amplitude due to the strong filtering and uneven distribution of the data

seasonal cycle of velocity in the atlantic north equatorial countercurrent as measured by surface drifters current meters and ship drifts this report describes the general circulation and seasonal variation of currents in the equatorial atlantic concentrating on the north equatorial countercurrent necc using data collected as part of the seasonal response of the equatorial atlantic and programme francais ocean et climat dans l atlantique equatorial experiments plus historical ship drifts during 1983 1985 the lagrangian circulation was studied by launching and tracking 30 freely drifting drogued buoys in the north equatorial countercurrent and 23 in the south equatorial current sec in addition continuously recording current meters were moored for 20 months at depths from 20 to 300 m near the center of the necc at 6 n 28 w these measurements are the longest series ever obtained in this current and provide information about its seasonal and interannual variations and zonal meridional and vertical structure the seasonal cycle of the necc is very regular from year to year each year the necc starts up in may june it flows eastward across the atlantic with surface speeds of up to 143 cm s in the west extending down to 350 m at 28 w and flowing into both the guinea current and north equatorial current it disappears or reverses from about january june west of 18 w some near surface water of the necc is inferred to downwell and flow equatorward toward the equatorial undercurrent the sec flows into the north brazil current which during spring continues up the coast into the caribbean during fall however the whole north brazil current retroflects or turns back on itself between 45 and 50 w forming the western necc the retroflection establishes a meander pattern in the necc that slowly propagates westward during fall at a speed of 4 cm s the meanders have a displacement of about 300 km in latitude a wavelength of 900 km and meridional velocity fluctuations of up to 100 cm s the swift currents and time dependent meanders in the western necc cause a high eddy kinetic energy 2400 cm2 s2 equivalent to that of the energetic part of the gulf stream

temperature variations in the equatorial atlantic as revealed by drifting buoys from may through september 1983 surface buoys deployed as a component of the focal experiment programme francais ocean et climat dans l atlantique equatorial drifted in the cold waters of the south equatorial current in the equatorial atlantic ocean the surface temperature sst is analysed along the buoy tracks in late may the strong temperature drop near 4 w and 3 s is associated with vertical mixing as cold patches appear near the equator horizontal advection is important in june and july as the cold water tongue expands southwards and westwards it is also important later in the western atlantic south of the equator where the cooling by advection is balanced primarily by heating from the atmosphere

on the origins of the north brazil current the analysis of the hydrographic data obtained during the nordeste iii neiii survey by the r v almirante saldanha brazilian navy between may 4 and july 12 1986 is reported in this work distributions of geostrophic speeds and transports relative to 1000 m reveal the north brazil current nbc and other major features of the tropical atlantic circulation west of 30 30 w between 4 s and 10 30 s the well developed nbc appears in all analyzed crossisobath sections bordering the brazilian continental slope between 10 s and 5 s transporting an average of 21 sv the velocity core of the nbc is found to be centered at about 100 200 m instead of at the surface as previously thought the central branch of the south equatorial current csec enters the study region at about 5 s 6 s and separates into two portions the northern portion of the csec transports about 15 sv northwestward and north of 5 s it coalesces with the nbc to form a 300 km wide current that transports more than 36 sv equatorward the southern branch of the csec transports 14 sv southwestward until about 9 30 s where it makes a cyclonic turn to the north and merges with northward flow from the southernmost branch of south equatorial current ssec the high salinity signature of waters from the ssec appears in the nbc indicating that it is formed to the south of the study area by contrast historical ship drift and lagrangian drifter observations suggest that the nbc and the brazil current are formed at the bifurcation of the csec this apparent contradiction is explained by the surface ekman drift which obscures the geostrophic flow patterns

near surface current and temperature variability observed in the equatorial atlantic from drifting buoys we examine data from 23 surface drifters which were deployed between june 1983 and july 1984 at 4 w 1 5 4 s the drifters were equipped with a window shade drogue centered at 15 m depth and in most cases a 117 m long thermistor chain drift data indicate a westward south equatorial current with typical speeds of about 20 cm s 1 south of the equator maximum westward flow of 30 40 cm s 1 occurred in june through september of 1983 and 1984 consistent with climatology near zero westward flow which was significantly weaker than was expected from climatology by about 20 cm s 1 occurred from february to april 1984 this probably represents real interannual variability and may be related to the fact that the equatorial atlantic was warmer than usual in the spring and summer of 1984 energetic variations on time scales of o 1 month and less and space scales of o 100 km and less are ubiquitous in the drift and temperature data kinetic energy levels associated with these variations south of the equator are typically 100 cm2 s 2 with slightly higher values in boreal summer energy levels north of the equator are about 500 cm2 s 2 on the basis of data available only during the boreal summer and fall the sources of this energy include inertia gravity waves instabilities of the general circulation and other phenomena for which there is no simple explanation

palynofacies classification of submarine fan depositional environments outcrop examples from the marnoso arenacea formation italy abstract basin floor fans contain some of the largest deep water hydrocarbon accumulations discovered however they also demonstrate extremely complex stratigraphic architecture understanding of which is crucial for maximum recovery here we develop a new method based upon palynofacies analysis for the distinction of the different depositional environments that are commonly associated with basin floor fans previous studies and our sedimentological analysis allow good confidence in the discrimination of the different depositional environments of the outcropping marnoso arenacea formation fan system one hundred and thirty five samples were collected from mudstones in conjunction with sedimentary logging of 871 m of outcrops six lithofacies associations are described and interpreted to represent lobe axis lobe fringe fan fringe contained interlobe basin plain and starved high depositional sub environments palynofacies of these elements demonstrate turbidites to be rich in terrestrial organic matter with sixteen categories of matter recognised the abundances and proportions of particles varies between sub environments with lobe axis deposits containing the largest densest particles with a transition to ever smaller and lighter particles moving toward the basin plain fuzzy c means statistical analysis was used to explore this trend distribution of organic matter is not random but is dominated by hydrodynamic sorting and sequential fall out of particles as turbidity currents passed across the basin this allows a palynofacies classification scheme to be constructed to assist the identification of depositional environments of submarine fans which may be combined with subsurface data to assist reservoir characterisation

long waves in the equatorial atlantic ocean during 1983 long waves appeared at a zonally oriented sea surface temperature sst front in the eastern equatorial atlantic during june and july of 1983 the low frequency westward moving long waves 1000 km 24 days are monitored in the noaa 7 satellite infrared images as meridional displacements of the front the long waves observed in the atlantic are similar to the waves previously seen in the eastern equatorial pacific with several exceptions the atlantic long waves have a shorter duration nearly three wave cycles at 15 w and the wave amplitude is limited eastward of longitude 10 w the atlantic equatorial front appears to have a minimum north south displacement between longitudes 5 w and 10 w while westward of 10 w the displacements exceed 400 km several buoys were launched south of the equator at longitude 4 w by the programme francais ocean climat en atlantique equatorial group on june 21 1983 for the first 3 weeks three of the buoys moved westward parallel to the equatorial sst front and measured relatively constant temperatures at 2 m during mid july changes were observed in the buoy temperatures the buoy trajectories and the long wave pattern a comparison of the buoy temperatures at a depth of 2 m and atmospherically corrected satellite estimates of sst show a residual dependence of the satellite data on the zenith angle even when the angle is limited to 45 in general the satellite sst measurements reproduce the trends observed in the buoy measurements but small bias differences occur between buoys and between day and nighttime sst comparisons equatorial cross sections by ship and satellite over a 7 day interval in june 1983 also show that sst trends are comparable in both sets of data

a model for the distribution of trace elements between calcite and dolomite abstract a crystal growth model is proposed which allows ions of a trace element to enter the ca and mg sites of dolomite in proportion to the size of the ions relative to that of ca and mg ions and which assigns equal portions of the trace element to the ca site of dolomite and the ca site of associated calcite the model produces calcite dolomite distribution coefficients of 0 79 for mn and 0 43 for fe which may be compared with 0 85 and 0 28 as observed in marble and a distribution coefficient of 2 0 for sr and ba which may be compared with observed values of 2 3 for sr and 1 8 for ba

seasonal variations of the subsurface thermal structure in the gulf of guinea abstract the subsurface thermal structure in the gulf of guinea is analyzed using the historical hydrographic data file of particular interest is the rapid vertical displacement of the thermal structure from the warm march may season to the cold july august season this displacement field is trapped at the equator with vertical and meridional scales appropriate to a second or third mode baroclinic kelvin wave it has a maximum amplitude between 4 w and 10 w with a node near 2 e south of 4 s no seasonal displacement of the thermocline underlies the seasonal variation in the sea surface temperature along the eastern boundary north of the equator to 3 e the displacement field vanishes thus the coastal upwelling associated with a vertical displacement tightly bound to the northern coast from 2 e to 10 w appears detached from the equatorial regime

the origin and recognition of laterally continuous carbonate cemented horizons in the upper lias sands of southern england abstract the upper lias sands of southern england contain numerous laterally extensive carbonate cemented horizons petrographical analyses of samples from outcrop sections and the marchwood no 1 borehole indicate that these horizons result from preferential cementation of bioclast rich clay poor sediments by comparison with interbedded clay rich bioclast poor sediments the alternation of the two sediment types is attributed to the effects of respectively fairweather and storm processes on a submerged marine shoal petrographical and ichnological data indicate an early distinction of the strongly and weakly cemented horizons the widespread extent of the cemented horizons as indicated by outcrop studies on the dorset coast is considered to be a direct consequence of episodic storm activity on the low relief shoal sedimentological palynological and petrophysical criteria are presented to assist in recognition of similar extensive cements in subsurface reservoir horizons that do not outcrop

observations of eastward currents in the tropical south atlantic ocean 1978 1980 data from four cruises to the tropical south atlantic ocean are used to describe the current distribution at 25 w and 27 5 28 w two distinct eastward flowing countercurrents separated by a branch of the westward flowing south equatorial current sec were observed during all the cruises the south equatorial undercurrent located between 3 s and 5 s has a subsurface velocity core with maximum speeds of about 0 4 m s geostrophic volume transports of the seuc from the surface to 1000 m range from 5 to 23 sv surface flow above the core of the seuc can be to the east or west the south equatorial countercurrent secc is located typically between 7 s and 9 s although weaker than the seuc with transports ranging from 3 to 7 sv the secc also has a subsurface velocity core maximum speeds of 0 1 m s are observed at about 275 m surface flow above the core of the secc is typically to the east upper layer waters of the secc are saltier and warmer than waters within similar density layers to the north

tropical instability wave kinematics observations from the tropical instability wave experiment the kinematics of planetary waves originating from instability of the nearsurface equatorial currents are reported on using velocity measurements from an array of acoustic doppler current profilers deployed in the equatorial pacific during the tropical instability wave experiment a distinctive wave season was observed from august to december 1990 with wave energy confined primarily above the core of the equatorial undercurrent particle motions in the horizontal plane are described by eccentric ellipses oriented toward the north but tilting into the cyclonic shear of the south equatorial current the tilt is maximum near the surface just north of the equator and decreases to the south and with depth the distribution of wave variance is narrowband in both frequency and zonal wavenumber with central period zonal wavelength and westward directed phase propagation estimated to be 500 hours 1060 km and 59 cm s 1 respectively neither the meridional nor the vertical wavenumber component is statistically different from zero these results generally agree with previous findings on tropical instability waves from the atlantic and pacific oceans and in the undersampled arena of geophysical measurements they provide an example where statistical inference is supported by an ensemble of independent measurements

horizontal reynolds stresses in the central equatorial pacific seven 13 month long current records from the north pacific experiment hawaii to tahiti shuttle experiment during 1979 1980 were analyzed to investigate eddy energetics of the upper ocean within 75 km of the equator profiling current meter data from the experiment were also used in an attempt to relate the eddy motions to the mean zonal flow the current fluctuations are highly anisotropic with zonal current dominating after removal of a linear trend plus annual and semiannual harmonics the residual high frequency current fluctuations are much more nearly isotropic the high frequency eddy kinetic energy decreases by a factor of 2 over the upper 250 m and at 100 m has a relative minimum on the equator the seasonal time scale eddy kinetic energy shows a much more dramatic decrease below the thermocline with the exception of tidal peaks the spectra of zonal current are red while meridional current spectra show a flattening at the lowest resolvable frequencies meridional current was non stationary with an energetic packet of 10 to 15 day period oscillations occurring in early 1980 the off diagonal component of the reynolds stress tensor u calculated from the high frequency residuals is everywhere positive decreasing from north to south and with depth the implied cross equatorial flux of zonal momentum is at odds with eddy viscosity parameterizations which relate u to the mean meridional shear of the zonal current the observed distribution of reynolds stresses might be explained by radiation of energy from an instability of the portion of the south equatorial current north of the equator in all cases the high frequency u time series are significantly skewed toward positive values and show no evidence of periodicity indicating that the process es responsible is are intermittent and broadband this is consistent with the instability mechanism

the silurian climatic transition recorded in the epicontinental baltica sea abstract the transition from the middle to late ordovician cold climate to the silurian greenhouse phase was marked by major climatic and oceanographic changes the vast epereic sea that during the early paleozoic extended over the baltic plate for hundreds of kilometres recorded the dynamic processes that characterized this important climatic evolution this shallow epicontinental sea experienced phases of hypoxic conditions for millions of years during the silurian favouring the sedimentation of organic rich deposits a continuous core drilled in the silurian fine grained succession of the baltic basin was studied integrating sedimentological palynological and geochemical data the succession deposited in a restricted environment in low energy settings recorded three long term variations in bottom water redox conditions our data highlight a direct control of long term climatic changes on oceanic redox cycles phases of cool and dry climate with reduced runoff alternated with periods of warmer and humid conditions with higher runoff and fluvial discharge during warmer and more humid climatic phases the presence of a stable pycnocline hampered deep water renewal efficiency and together with increased nutrients led by enhanced weathering and runoff favoured the onset of anoxic bottom water conditions cooler and drier intervals favoured instead a weaker and less stable pycnocline that coupled with more oligotrophic conditions drove the formation of oxic bottom waters the variation through time in water salinity and temperature influenced both the type of organic matter in the surface waters as well as its preservation along the water column in fact the extended residence time at the stable pycnocline during the anoxic phases led to the degradation of the organic matter and limited its accumulation at the sediment water interface the waning of the latest ordovician cooling to the silurian greenhouse climate was characterized by the progressive alternation of cool phases and warmer periods the effect of this dynamic climatic instability on the redox state of the baltica epicontinental sea protracted over millions of years up to the middle silurian

eddy kinetic energy in the north atlantic from surface drifters one hundred ten satellite tracked freely drifting buoys measured velocities and trajectories of the near surface currents in the north atlantic mean velocity values and the velocity variance about the mean were calculated for different regions a horizontal map of eddy kinetic energy was prepared on a 2 2 grid between latitudes 20 and 55 n maximum eddy energy 3000 cm2 s 2 coincides with the high speed gulf stream jet where it begins large amplitude meanders near 37 n 67 w a tongue of high eddy energy coincides with the stream s path eastward and around the grand banks into the newfoundland basin where values of 1000 cm2 s 2 are found a weaker tongue extends eastward across the mid atlantic ridge near 45 n a second weak extension reaches southeastward from the stream and crosses the mid atlantic ridge between 30 and 35 n north and south of the stream eddy energy diminishes rapidly reaching an e folding at 300 km from the axis values of 200 cm2 s 2 were observed in the mid gyre region and 100 cm2 s 2 in the eastern north atlantic and north equatorial current although the gross distribution of eddy energy is similar to that determined from ship drift measurements there are significant differences eddy energy from drifters amounts to about twice the value measured by ship drift in the gulf stream and one half the ship drift values in the mid gyre it is suggested that these differences are due to the horizontal averaging of mesoscale motion and the errors in navigation both of which are problems with the ship drift technique

observations of near surface currents and temperature in the central and western tropical atlantic ocean eleven satellite tracked drifting buoys were deployed in the central south atlantic ocean during two austral summer and two austral winter cruises between 7 s and 11 s and 23 w and 31 w during austral winter net buoy drift was to the west surface geostrophic flow was to the east between 7 s and 9 s it is proposed that strong southeast trade winds can induce directly driven surface flows to the west that are more intense than the eastward geostrophic flows associated with the south equatorial countercurrent secc a sustained period of eastward drift within the secc was observed during austral summer when the trades are weaker the trajectories indicate surface waters north of 8 s have a mean northward meridional component and those south of 8 s a southward component the buoys which drifted north became entrained into the north brazilian coastal current nbcc and those that drifted south into the brazil current one buoy left the nbcc at about 5 n to drift northeastward in the north equatorial countercurrent necc this trajectory and historical ship drift reports suggest that the necc may extend only to 35 w to 40 w during boreal winter temperature data obtained as the buoys drifted westward and northward suggest that increases in upper layer heat content can be attributed to heat fluxes through the sea surface