near surface dynamical structure of the kuroshio extension 1 lagrangian data from 657 svp drifters cnes aviso archiving validation and interpretation of satellite oceanographic data time variable satellite altimeter sea level anomaly and levitus 98 hydrographic data are used to develop 0 25 spatial resolution maps of the mean and eddy circulations in the northwestern pacific during the 1990s drifter velocities at 15 m depth and 200 m temperature data clearly indicate in the kuroshio extension ke jet two prominent meanders that culminate in a 300 km northward deflection east of the shatsky rise at 160 e the interannual trends of aviso mesoscale variance are absent along the path of the meandering ke jet three anticyclonic recirculations can be identified south or southeast of the kuroshio the southernmost around daito island being a new discovery about 3 of the drifters with drogues attached crossed the kuroshio front the aviso currents are correlated at 0 8 with drifter geostrophic velocity the aviso geostrophic currents are adjusted in amplitude to the contemporaneous drifter observations and are further used to compute an unbiased mean geostrophic circulation and the quasi geostrophic reynolds stresses in the ke region the principal axes of the eddy reynolds stresses are oriented along the unbiased mean velocity vectors within the meandering ke jet the time mean horizontal momentum balance that includes both the mean and eddy momentum convergences is used to compute absolute sea level map and its uncertainty at 145 e the 2000 m depth absolute dynamic height referenced to the sea level reveals a heretofore unknown 70 dynamic cm drop from 25 to 42 n

simple climatic indices for the tropical atlantic ocean and some applications two indices related to the sea surface temperature sst variability in the tropical atlantic are proposed one index describes the sst averaged over the whole basin 30 n to 20 s 60 w to 15 e and the other illustrates a meridional dipole between the northern and southern hemispheres the computational method for obtaining these indices is intentionally kept simple the objective being to reproduce the signature of the main results previously provided from more complicated statistical analyses monthly time series for both indices are produced from 1964 up to the present time the whole basin index exhibits principally a sustained warming which has intensified since about 1975 and it has a significant periodicity close to that of the quasi biennial oscillation the dipole index exhibits a decadal scale variation and its building up seems to be related to other worldwide climatic changes as for instance el nino southern oscillation extreme episodes rainfall variabilities over the brazilian nordeste and african sahel

zonal jets in the equatorial atlantic ocean abstract we use position data from argo floats smoothed out over 400 km 200 km zonal ellipses and interpolated onto a 0 5 grid to investigate the zonal jet structure of the flow field at the sea surface and on three subsurface layers central waters cw 200 m antarctic intermediate waters aaiw 1000 m upper north atlantic deep waters unadw 1500 m in the equatorial atlantic ocean 15 s to 15 n the annual mean fields exhibit narrow zonal jets typically 4 5 wide at the sea surface and only 2 at the subsurface levels with directions alternating in latitude and maximum speeds about 0 5 m s 1 at the surface 0 1 m s 1 at cw and unadw and 0 03 m s 1 at aaiw the available data also allows us to explore the seasonal variability of these jets at the surface and aaiw levels the surface currents are dominated by an annual cycle between 4 n and 10 n and to a lesser degree by a semi annual contribution close to the equator this variability is an outcome of evolving zonal recirculations with the north equatorial countercurrent necc arising from the diversion of the northern branch of the south equatorial current nsec the diversion begins in the eastern atlantic and propagates west between april and august following the inter tropical convergence zone itcz the aaiw current field is largely affected by westward propagating anomalies most visible near 3 s 0 3 n and 7 n which give rise to current reversals annual averaging produces the illusion of more 5 instead of 3 and slower peak values about 0 03 m s 1 instead of 0 1 m s 1 jets than found on any month

relationship between the equatorial and meridional modes of climatic variability in the tropical atlantic the tropical atlantic ocean exhibits two primary modes of interannual climate variability an equatorial mode analogous to but weaker than the pacific el nino phenomenon and a meridional mode that does not have a pacific counterpart the equatorial mode is responsible for warm and cold sea surface temperature sst events mainly in the gulf of guinea and is identifiable by abnormal changes in the equatorial thermocline slope resulting from zonal wind anomalies in the western tropical atlantic the meridional mode is characterized by a north south interhemispheric gradient of sst anomalies here it is shown using observed surface and subsurface oceanic temperatures that the meridional mode is linked to the equatorial mode at both decadal and short interannual 1 2 years time scales both modes involve north south displacements of the itcz as in the annual response

equatorial undercurrent and north equatorial countercurrent at 38 w a new perspective from direct velocity data 1 the western equatorial undercurrent euc and north equatorial countercurrent necc are investigated at 38 w using contemporaneous subsurface adcp and high resolution near surface drifters satellite altimeter velocity measurements together with hydrographic ctdo2 data that were collected from 1998 to 2006 the observations reveal an euc with a strong semiannual pattern of intensification direct measurements also confirm the existence of a northern branch of the necc nnecc observed here for the first time in the western tropical atlantic the necc displays an annual cycle of northward migration on the basin driven by the sverdrup transport generated by the wind field in this cycle the nnecc is a semipersistent feature fed by waters from the northern hemisphere and the residual nnecc flow from the previous year

investigation of the north brazil current retroflection and north equatorial countercurrent variability 1 eight years of topex poseidon altimeter derived sea height anomaly and climatological hydrographic data are used to investigate the temporal and spatial variability of the north brazil current nbc retroflection and the north equatorial countercurrent necc the nbc retroflection exhibits a mean position of 6 6 n 2 0 with a strong annual signal and year to year variability the annual cycle of its location follows the meridional migration of the itcz and the strength of the wind stress curl over the equatorial atlantic a marked shift in the annual mean location of the nbc retroflection is observed in 1998 1999 that appears to be linked to an increase in wind stress curl during this period the mean latitude of the necc is estimated to be 6 0 n 1 3 with a semiannual cycle showing maximum northerly locations in february and august the baroclinic transport of the necc varies predominantly on an annual cycle with maximum transport of 12 sv occurring in november

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

transitional morphology in west deuteronilus mensae mars implications for modification of the lowland upland boundary abstract west deuteronilus mensae which lies along the lowland upland boundary of mars at 45 latitude 345 longitude exhibits both gradational l a rossbacher 1985 in models in geomorphology woldenberg ed pp 343 372 allen unwin boston and fretted terrain r p sharp 1973 j geophys res 78 4073 4083 boundary types to the west the boundary is gradational and to the east it is defined by fretted terrain the two types of boundaries do not merge with one another within the west deuteronilus mensae region however the gradational boundary materials appear to overlap the fretted terrain by about 500 km contacts between units associated with the gradational boundary and the fretted terrain boundary can both be recognized in the region of overlap the fretted terrain can be identified as much as 300 km north of the gradational boundary in this region lowland units associated with the gradational boundary embay canyons of the fretted terrain in a topographically conformal fashion changes in the fretted terrain across the gradational boundary from uplands to lowlands include a reduction of canyon wall slopes and depths such that the fretted terrain north of the gradational boundary appears mantled but not obscured there are at least two major classes of processes which might explain the lateral overlap 1 erosion of stratified upland terrain and 2 deposition of plains materials onto the sloping upland margin and fretted terrain erosion of stratified upland terrain does not adequately explain the plainward decrease in crater densities across the gradational boundary nor is it consistent with evidence that lowland plains material appears to onlap the sloping upland margin in several places of the possible plains emplacement mechanisms eolian deposition would not produce the sharp apparently topographically conformal gradational unit contacts volcanics plains emplacement would not preserve the complex geometry of the underlying fretted terrain sediment deposition in either a liquid or ice covered sea could produce the draped appearance of the fretted terrain outflow channels along the lowland upland boundary particularly those of the circum chryse and west elysium regions may have flooded the northern lowlands to depths of tens to hundreds of meters the gradational unit contacts may represent the shorelines of such a sea the scale of characteristic morphologies along these contacts may require an unfrozen condition of sufficient duration to allow lacustrine style wave erosion and redistribution of material along the contacts our limited understanding of the martian paleoclimate and h 2 o inventories allows the possibility of clement periods in the past and other geological evidence e g small valley networks and outflow channels strongly suggests an extensive role of liquid water

upper equatorial atlantic variability during 2002 and 2005 associated with equatorial kelvin waves on the basis of moored 35 degrees w 0 degrees and 23 degrees w 0 degrees and satellite observations we contrast the upper equatorial atlantic variability during 2002 with those during 2005 inspection of the interannual boreal summer cold tongue variability revealed a warm cold event in 2002 2005 with relaxed intensified winds in the west and the equatorial undercurrent euc embedded in a shallower deeper thermocline at 23 degrees w during both years 2002 and 2005 equatorial kelvin waves are present in moored observations as 20 degrees c isotherm depth anomalies and dynamic height anomalies basin wide sea surface height anomalies are used to derive an equatorial kelvin wave mode the time evolution of this mode represents the basis for a regression analysis to investigate related oceanic variability compared to the exceptionally strong wave activity in 2002 equatorial kelvin waves were generally weaker during 2005 the main effect of equatorial kelvin waves on zonal velocity anomalies at 23 degrees w 0 degrees is evident well below the euc core their direct influence on cold tongue sea surface temperature is small but they are found to affect the equatorial thermocline slope prior to the cold tongue onset in 2002 2005 the presence of equatorial kelvin waves is associated with a flattened steeper thermocline slope that is crucial for the shallowing deepening of the euc core at 23 degrees w and that might precondition the development of the warm cold event

wind driven currents in the tropical pacific abstract an analysis is made of the ensemble mean ageostrophic near surface circulation measured by 1503 lagrangian drifters drogued to 15 m depth in the tropical pacific between 1987 and 1994 it was found that the physical model of the wind driven currents in a weakly stratified upper layer in which the richardson number remains near unity accounts for 40 of the vector variance of the observations in such a model the amplitude of the current is proportional to u n f 1 2 and the depth scale of the wind driven layer is proportional to u n f 1 2 when the ageostrophic currents at 15 m depth are binned by the scaled ekman depth a net rotation of 0 87 radians was observed through the layer depth these measurements suggest that the vertical austausch coefficient of the upper ocean is proportional to u2 n ekman proposed such a model based on two reports of wind driven currents in 1905 at widely separated latitudes

coastal geomorphology of the martian northern plains the paper considers the question of the formation of the outflow channels and valley networks discovered on the martian northern plains during the mariner 9 mission parker and saunders 1987 and parker et al 1987 1989 data are used to describe key features common both in the lower reaches of the outflow channels and within and along the margins of the entire northern plains it is suggested that of the geological processes capable of producing similar morphologies on earth lacustrine or marine deposition and subsequent periglacial modification offer the simplest and most consistent explanation for the suit of features found on mars

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

equatorial currents transport changes for extreme warm and cold events in the atlantic ocean 1 in this work the equatorial atlantic ocean circulation dynamics for warm and cold composite events are analyzed warm and cold typical years were composited from the respective five warmest and the five coldest years of the available record equatorial currents velocity and transport are calculated during a typical warm event the circulation decreases in the upper ocean while during the typical cold event there is intensification the strengthening weakening of the circulation during cold warm events increases decreases the stress between the equatorial undercurrent euc and the south equatorial current sec associated with an increase decrease in entrainment of cold waters into the surface and their westward transport the euc showed striking differences between both composited events for the cold warm event the euc shows a greater reduced transport and core velocity and a deeper shallower structure

oxygen minimum zone in the north atlantic south and east of the cape verde islands the open ocean oxygen minimum zone omz south and east of the cape verde islands is studied from ctd hydrography adcp velocities argo float trajectories and historical data with a focus on the zonal supply and drainage paths the strongest oxygen minimum is located north of the north equatorial countercurrent necc at about 400 to 500 m depth just above the boundary between central water and antarctic intermediate water aaiw it is shown that the necc the north equatorial undercurrent at 4 to 6 n and a northern branch of the necc at 8 to 10 n are the sources for oxygen rich water supplied to the omz in summer and fall a weak eastward necc at 200 m depth also exists in winter and spring as derived from argo floats drifting at shallow levels historical oxygen data from 200 m depth confirm this seasonality showing high low oxygen content in summer and fall spring within the supply paths compared to the strong oxygen supply at 150 to 300 m depth the ventilation of the omz at 300 to 600 m depth is weaker westward drainage of oxygen poor water takes place north of the guinea dome i e north of 10 n most pronounced at 400 to 600 m depth in july 2006 the total eastward transport of both necc bands above 27 1 kg m 3 at 23 w was about 13 sv 1 sv 106 m3 s 1 about half of this water volume circulates within the guinea dome or recirculates westward north of the guinea dome

interaction between the atlantic meridional and nino modes 1 interaction between the tropical atlantic meridional and nino modes is investigated using observations and a quasi analytical linear equatorial wave model it is found that equatorial zonal wind stress anomalies associated with the boreal spring meridional mode generate eastward propagating equatorial kelvin waves in the central and eastern atlantic ocean where variability associated with the nino mode is strongest these same wind stress anomalies force westward propagating equatorial rossby waves that reflect at the western boundary into eastward propagating kelvin waves during boreal spring and summer the boundary generated kelvin waves are of the opposite sign to those directly forced by the winds earlier in the spring so they tend to damp the nino mode during boreal summer the interaction between the boreal spring meridional mode and the summer nino is therefore mediated by directly wind forced equatorial kelvin waves and the delayed negative feedback from western boundary reflections of wind forced rossby waves

the forced annual reversal of the atlantic north equatorial countercurrent abstract we analyze the variability of the thermal structure associated with the atlantic north equatorial countercurrent necc and its relation to the seasonally varying winds the analysis performed allows us to establish the period of time and the region where the necc reverses direction west of 25 w the depth of the thermocline in the southern side of the necc 4 to 7 n annually oscillates 180 out of phase to the oscillations on the northern side 7 to 10 n east of 25 w the thermocline rises and falls nearly in phase across the countercurrent if the flow can be uniquely presumed from the thermal structure the necc disappears during the boreal spring in the western basin the reversal of phase from north to south over one part of the ocean but no the other is shown to be mirrored in the annual variation of the curl of the stress induced at the surface by the winds in order to quantify this result the different terms of the vorticity equation are calculated from the data we conclude that t

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

an interannual study of the atlantic north equatorial countercurrent abstract beginning in 1983 the dynamic height difference at the sea surface defining the countercurrent trough at 38 w was continuously observed by inverted echo sounders at 3 n and 9 n for six years and ten months the amplitude of the average annual signal for that time period was 36 cm and the range of the interannual variability was 25 cm thus the annual signal dominates as expected but the interannual variability is of comparable magnitude two years 1983 and 1987 are noted as years of sharp increase in the interannual signal periods immediately following el nino events in the pacific from a derived relationship for geostrophic volume transport it is estimated that every year the north equatorial countercurrent attained a transport of 20 sv 106 m3 s 1 for at least one month while in the cited years it sustained this value for over half the year the output of an unbounded reduced gravity model forced by monthly averaged wind stress is compared to the observations the model can be t

147sm143nd 146sm142nd systematics of early archaean rocks and implications for crust mantle evolution combined high precision 147sm 143nd 146sm 142nd data have been obtained for two early archaean pre 3 8 ga samples a 4 0 0 2 ga meta komatiite and an approximately 3 9 ga orthogneiss from the northern labrador segment of the north atlantic craton the samples have t143nd values at 3 8 ga of 4 0 and 1 4 respectively however t142nd142nd for both samples is indistinguishable from the bulk earth value for the sample with t143nd 4 0 t142nd is 0 03 0 14 which suggests that it was derived from a source which differentiated from the primitive mantle at between 4 1 and 4 3 ga 14sm 143nd and 146sm 142nd data are also presented for a kyanite eclogite xenolith from a 350 ma kimberlite from yakutia siberia 142nd 144nd for this sample is also within error of the bulk earth value eclogite xenoliths such as those from kimberlite pipes are therefore unlikely to be residues of crystallization of a pre 4 4 ga magma ocean but instead may represent fragments of post 4 3 ga oceanic crust incorporated into the subcontinental lithospheric mantle the absence of widespread variations in 142nd144nd in early archaean rocks supports models in which the volume of the depleted mantle has grown through time continuous growth of the depleted mantle and continental crust at the expense of the primordial mantle at between 4 56 and 4 0 ga can generate variations in t143nd and account for the absence of detectable variations in 142nd144nd in most early archaean rocks

a possible link between off equatorial warm anomalies propagating along the necc path and the onset of the 1997 98 el nino n n by examining sea surface height ssh from the topex poseidon t p altimeter and upper ocean temperature current data from the ncep reanalysis product a well defined shallow pathway has been identified of subsurface temperature anomalies along the pacific north equatorial countercurrent necc a physical picture is developed to demonstrate how oceanic atmospheric anomalies leading to the 1997 98 el nino may be generated in the tropical pacific climate system prior to its onset a preconditioned oceanic state is set in the west during 1995 96 characterized by elevated sea level depressed thermocline and warm temperature anomalies in the western boundary along 6 10 degrees n with the seasonal intensification of the necc in the fall the warm anomalies propagated coherently eastward along the relatively shallow necc subsurface pathways centered about 100 m from the western boundary in mid 1996 to near the date line in late 1996 and early 1997 as the thermocline shoals eastward and upward along the necc the subsurface anomalies were exposed to the surface near the date line likely initiating warm sea surface temperature sst anomalies north of the equator in late 1996 due to the convergence of mean subsurface circulation onto the equator the equatorward flows helped move these initially subsurface produced sst anomalies southward onto the equator which would induce westerly wind anomalies

evidence for recent volcanism on mars from crater counts impact craters help characterize the age of a planetary surface because they accumulate with time they also provide useful constraints on the importance of surface erosion as such processes will preferentially remove the smaller craters earlier studies of martian crater populations revealed that erosion and dust deposition are important processes on mars they disagreed however on the age of the youngest volcanism these earlier studies were limited by image resolution to craters larger than a few hundred metres in diameter here we report an analysis using new images obtained by the mars global surveyor spacecraft of crater populations that extend the size distribution down to about 16 m our results indicate a wide range of surface ages with one region lava flows within the arsia mons caldera that we estimate to be no older than 40 100 million years we suggest that volcanism is a continuing process on mars

why were sea surface temperatures so different in the eastern equatorial atlantic in june 2005 and 2006 abstract a comparison of june 2005 and june 2006 sea surface temperatures in the eastern equatorial atlantic exhibits large variability in the properties of the equatorial cold tongue with far colder temperatures in 2005 than in 2006 this difference is found to result mainly from a time shift in the development of the cold tongue between the two years easterlies were observed to be stronger in the western tropical atlantic in april may 2005 than in april may 2006 and these winds favorably preconditioned oceanic subsurface conditions in the eastern atlantic however it is also shown that a stronger than usual intraseasonal intensification of the southeastern trades was responsible for the rapid and early intense cooling of the sea surface temperatures in mid may 2005 over a broad region extending from 20 w to the african coast and from 6 s to the equator this particular event underscores the ability of local intraseasonal wind stress variability in the gulf of guinea to initiate the cold tongue seaso

multiple westward propagating signals in south pacific sea level anomalies the characteristics of multiple westward propagating signals in the satellite observed south pacific sea level anomalies sla between 10 s and 50 s are analyzed using the two dimensional radon transform 2d rt we test the hypothesis that these signals are most likely to be the signature of the first few baroclinic rossby wave modes this involves a comparison of the estimated phase speeds of the 2d rt peaks against the first four baroclinic mode rossby wave speeds predicted from the extended theory the 2d rt analysis typically identified up to three propagating signals in the sla and very occasionally a fourth the first radon transform rt peak phase speeds corresponded very well with first baroclinic mode rossby wave phase speed estimates from linear theory between 15 s and 25 s and the extended theory phase speed estimates poleward of 25 s rt peak 2 speeds were less coherent but fell within the range of extended theory estimates of the first four baroclinic rossby wave modes consistent with large scale rossby wave dynamics the relationship between peaks 3 and 4 and the extended theory higher order baroclinic mode speed estimates varied markedly across the basin regional variability in the spectral characteristics of the peaks suggests that different dynamical regimes dominate north and south of 30 s in the south pacific basin the presence of secondary peaks in the middle to high latitudes suggests that higher order modes may play a role in these regions

a strong atlantic meridional mode event in 2009 the role of mixed layer dynamics in the first half of 2009 anomalous cooling of sea surface temperatures ssts in the equatorial north atlantic ena 28 128n triggered a strong atlantic meridional mode event during its peak in april may ssts in the ena were 18c colder than normal and ssts in the equatorial south atlantic 58s 08 were 0 58c warmer than normal associated with the sst gradient were anomalous northerly winds an anomalous southwardshiftoftheintertropicalconvergencezone andseverefloodingin northeastbrazil thisstudyuses in situ and satellite observations to examine the mechanisms responsible for the anomalous cooling in the enaduringborealwinterandspringof2009 itisfoundthatthecoolingwasinitiatedbystrongerthannormal trade winds during january and february 2009 associated with an anomalous strengthening of the subtropical north atlantic high pressure system between 68 and 128n unusually strong trade winds cooled the ocean through wind induced evaporation and deepened the mixed layer anomalously by 5 20 m closer to the equator surface equatorial winds responded to the anomalous interhemispheric sst gradient becoming northwesterly between the equator and 68n the anomalous winds drove upwelling of 0 5 1 m day 21 during march april a period when there is normally weak downwelling the associated vertical turbulent heat flux at the base of the mixed layer led to unusually cool ssts in the central basin further strengthening the anomalous interhemispheric sst gradient these results emphasize the importance of mixed layer dynamics in the evolution of the meridional mode event of 2009 and the potential for positive coupled feedbacks between wind induced upwelling and sst in the ena

interannual variability of the guinea dome and its possible link with the atlantic meridional mode using a high resolution ocean general circulation model forced by ncep ncar reanalysis data the interannual variability of the guinea dome is studied from a new viewpoint of its possible link with the atlantic meridional mode amm which is related to the meridional migration of the intertropical convergence zone itcz the dome develops off dakar seasonally from late spring to late fall owing to the wind induced ekman upwelling its seasonal evolution is associated with the northward migration of the itcz when the itcz is located anomalously northward southward from late spring to early summer as a result of the wind evaporation sea surface temperature sst positive feedback with positive negative sst anomaly over the northern hemisphere the dome becomes unusually strong weak in fall as a result of stronger weaker ekman upwelling this may contribute to the decay of the amm thus the coupled nature between the amm and the guinea dome could be important in understanding modeling and predicting the tropical atlantic variability

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

mars chronology assessing techniques for quantifying surficial processes abstract currently the absolute chronology of martian rocks deposits and events is based mainly on crater counting and remains highly imprecise with epoch boundary uncertainties in excess of 2 billion years answers to key questions concerning the comparative origin and evolution of mars and earth will not be forthcoming without a rigid martian chronology enabling the construction of a time scale comparable to earth s priorities for exploration include calibration of the cratering rate dating major volcanic and fluvial events and establishing chronology of the polar layered deposits if extinct and or extant life is discovered the chronology of the biosphere will be of paramount importance many radiometric and cosmogenic techniques applicable on earth and the moon will apply to mars after certain baselines e g composition of the atmosphere trace species chemical and physical characteristics of martian dust are established the high radiation regime may pose a problem for dosimetry based techniques e g luminescence the unique isotopic composition of nitrogen in the martian atmosphere may permit a mars specific chronometer for tracing the time evolution of the atmosphere and of lithic phases with trapped atmospheric gases other mars specific chronometers include measurement of gas fluxes and accumulation of platinum group elements pge in the regolith putting collected samples into geologic context is deemed essential as is using multiple techniques on multiple samples if in situ measurements are restricted to a single technique it must be shown to give consistent results on multiple samples but in all cases using two or more techniques e g on the same lander will reduce error while there is no question that returned samples will yield the best ages in situ techniques have the potential to be flown on multiple missions providing a larger data set and broader context in which to place the more accurate dates

direct measurements of upper ocean currents and water properties across the tropical pacific during the 1990s abstract meridional sections of upper ocean zonal currents potential temperature and salinity are estimated at ten longitudes from 143 e to 95 w using conductivity temperature depth and acoustic doppler current profiler data from 172 synoptic sections taken in the tropical pacific between 138 e and 86 w mostly in the 1990s data reduction is carried out in a potential isopycnal and mixed layer framework to preserve a sharp pycnocline a mixed layer water property extrema and velocity extrema mean zonal currents potential temperatures and salinities are produced at each longitude the seasonal cycles of these fields are also estimated as well as a simple el nino southern oscillation enso cycle zonal sections along the equator are also presented properties of the near equatorial zonal currents including transports temperatures and salinities are estimated separately from the synoptic sections the seasonal cycles of these quantities and their correlations with the southern oscillation index are investigated the work is distinguished from most existing literature in that direct estimates of zonal velocity are combined with contemporaneous temperature and salinity data allowing trans pacific estimates of near equatorial current transports and properties including those of the northern branch of the south equatorial current the new guinea coastal undercurrent and the equatorial undercurrent

interannual geostrophic current anomalies in the near equatorial western pacific abstract a network of island tide gauges is used to estimate interannual geostrophic current anomalies gcas in the western pacific from 1975 to 1997 the focus of this study is the zonal component of the current averaged between 160 e and 180 and 2 to 7 north and south of the equator in the mean flow regions associated with the north equatorial countercurrent necc and the south equatorial current sec respectively the tide gauge gca estimates agree closely with similarly derived currents from topex poseidon sea level anomalies the gcas in the western pacific relate to a basin scale adjustment associated with the el nino southern oscillation characterized here using empirical orthogonal functions of tide gauge and supporting sea surface temperature and heat storage data the dominant eof mode describes the mature phase of enso events and correlates 0 8 with the gca south of the equator the second mode describes transitions to and from enso events and correlates 0 9 with the gca north of th

local and equatorial forcing of seasonal variations of the north equatorial countercurrent in the atlantic ocean abstract the seasonal variation of the north equatorial countercurrent necc in the tropical atlantic ocean is investigated by using a linear one layer reduced gravity ocean model and by analyzing sea surface height ssh data from ocean topography experiment topex poseidon t p altimeters the t p data indicate that the seasonal variability of the necc geostrophic transport between 3 and 10 n is dominated by ssh changes in the southern flank of the current since the southern boundary of the necc is located partially within the equatorial waveguide the ssh variation there can be influenced considerably by the equatorial dynamics therefore it is hypothesized that the wind stress forcing along the equator is the leading driver for the seasonal cycle of the necc transport the wind stress curl in the necc region is an important but smaller contributor this hypothesis is tested by several sensitivity experiments that are designed to separate the two forcing mechanisms in the first sensitivity ru

interannual north equatorial countercurrent variability and its relation to tropical atlantic climate modes 1 a synthesis product of the surface geostrophic circulation is used to quantify the interannual variability of the wind driven north equatorial countercurrent necc the first mode of a complex empirical orthogonal function ceof decomposition of zonal geostrophic velocity in the necc region reveals pronounced latitudinal displacements in addition to variations in current strength while north south migrations of the necc are mainly captured by the real pattern the imaginary pattern accounts for variations in its strength associated with these spatial patterns is prevailing propagation toward the northwest that is most pronounced northward of the mean necc position 6 n there is evidence that the zonal propagation characteristics are consistent with long rossby waves forced in the northeastern tropical atlantic the relationship between interannual necc variations and the tropical atlantic climate modes is investigated through regression and composite analyses sea surface temperature and wind stress patterns resembling the meridional and zonal modes are found for the ceof regression composite analysis further shows consistent patterns for warm phases of the meridional mode and cold phases of the zonal mode the response of the necc to a positive meridional and negative zonal mode event may be viewed as a northward shift of its core and a current strengthening respectively these results support a link between the two dominant tropical atlantic climate modes and show that the relation between interannual necc variability and the meridional and zonal modes can primarily be regarded as a response to changes in the wind field

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

the response of the surface circulation of the arabian sea to monsoonal forcing abstracttwo decades of drifter and satellite data allow the authors to describe the seasonal evolution of the surface circulation of the arabian sea which reverses annually with the indian monsoon winds this study finds several features that advance current understanding most significantly northward flow appears along the length of the western boundary together with a weak anticyclone at 6 n a precursor to the great whirl as early as march or april one or two months before the southwest monsoon winds this circulation is driven by planetary waves which are initiated by wind curl forcing during the previous southwest monsoon leading the authors to speculate that there is an oceanic mechanism through which one monsoon may precondition the next second the authors find that the eastward south equatorial counter current secc is present year round fed by the northward east african coastal current eacc during the southwest monsoon the eacc overshoots the equator and splits feeding both northwa

propagation of a melting anomaly along the ultraslow southwest indian ridge between 46 e and 52 20 e interaction with the crozet hotspot summary regional axial depths mantle bouguer anomaly values geochemical proxies for the extent of partial melting and tomographic models along the southwest indian ridge swir all concur in indicating the presence of thicker crust and hotter mantle between the indomed and gallieni transform faults tfs 46 e and 52 20 e relative to the neighbouring ridge sections accreted seafloor between these tfs over the past 10 myr is also locally much shallower 1000 m and corresponds to thicker crust 1 7 km than previously accreted seafloor along the same ridge region two large outward facing topographic gradients mark the outer edges of two anomalously shallow off axis domains on the african and antarctic plates their vertical relief 2000 m locally and their geometry parallel to the present day axis along a 210 kmlong ridge section suggest an extremely sudden and large event dated between 8 magnetic anomaly c4n and 11 ma magnetic anomaly c5n asymmetric spreading and small ridge jumps occur at the onset of the formation of the anomalously shallow off axis domains leading to a re organization of the ridge segmentation we interpret these anomalously shallow off axis domains as the relicts of a volcanic plateau due to a sudden increase of the magma supply this event of enhanced magmatism started in the central part of the ridge section and then propagated along axis to the east and probably also to the west however it did not cross the gallieni and indomed tfs suggesting that large offsets can curtail or even block along axis melt flow we propose that this melting anomaly may be ascribed to a regionally higher mantle temperature provided by mantle outpouring from the crozet hotspot towards the swir

variability of the atlantic off equatorial eastward currents during 1993 2010 using a synthetic method 1 we have developed validated and applied a synthetic method to monitor the off equatorial eastward currents in the central tropical atlantic this method combines high density expendable bathythermograph xbt temperature data along the ax08 transect with altimetric sea level anomalies slas to estimate dynamic height fields from which the mean properties of the north equatorial countercurrent necc the north equatorial undercurrent neuc and the south equatorial undercurrent seuc and their variability can be estimated on seasonal to interannual timescales on seasonal to interannual timescales the synthetic method is well suited for reconstructions of the necc variability reproduces the variability of the neuc with considerable skill and less efficiently describes variations of the seuc which is located in a region of low sla variability a positive correlation is found between interannual variations of the necc transport and two indices based on an interhemispheric sea surface temperature sst gradient and southeasterly wind stress in the central tropical atlantic the neuc is correlated on interannual timescales with ssts and meridional wind stress in the gulf of guinea and zonal equatorial wind stress this study shows that both altimetry and xbt data can be effectively combined for near real time inference of the dynamic and thermodynamic properties of the tropical atlantic current system

evidence for recent climate change on mars from the identification of youthful near surface ground ice ground ice in the crust and soil may be one of the largest reservoirs of water on mars1 2 3 near surface ground ice is predicted to be stable at latitudes higher than 40 ref 4 where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed5 mid latitude soils have also been implicated as a water ice reservoir6 the capacity of which is predicted to vary on a 100 000 year timescale owing to orbitally driven variations in climate7 it is uncertain however whether near surface ground ice currently exists at these latitudes and how it is changing with time here we report observational evidence for a mid latitude reservoir of near surface water ice occupying the pore space of soils the thickness of the ice occupied soil reservoir 1 10 m and its distribution in the 30 to 60 latitude bands indicate a reservoir of 1 5 6 0 104 km3 equivalent to a global layer of water 10 40 cm thick we infer that the reservoir was created during the last phase of high orbital obliquity less than 100 000 years ago and is now being diminished

water masses and currents in the upper tropical northeast atlantic off northwest africa recent current measurements in the tropical eastern north atlantic reproduce the components of the large scale flow field however the observations as well as the 1 12 flame model computations indicate that a lot of eddy scale variability is superimposed on the mean flow field despite of the disturbance by variability the signature of the guinea dome is well present in november 2002 the guinea dome transport from direct observations was about 2 8 sv above 25 8 kg m3 and 4 sv between 25 8 and 27 1 kg m3 the oxygen minimum in the shadow zone comprises the central water and the antarctic intermediate water aaiw layers and is located between the equatorial current system and the north equatorial current the north equatorial counter and undercurrents at 3 to 6 n are major oxygen sources for the central water layer of the low oxygen regions in the northeastern tropical atlantic a second northern north equatorial countercurrent nnecc band exists at 8 to 10 n the nnecc carries oxygen rich water from the southern hemisphere eastward but with an admixture of water from the northern hemisphere a float at 200 m depth was spreading eastward in the north equatorial undercurrent neuc at 28 w it shifted northward into the nnecc and then was trapped in the guinea dome region for more than 3 years the model indicates the region 22 to 32 w as the area of exchange between the necc neuc and the nnecc bands in the aaiw layer the northern intermediate countercurrent acts as oxygen source for the oxygen minimum zone

influence of the meridional overturning circulation on tropical subtropical pathways abstract an ocean gcm is used for idealized studies of the atlantic circulation in a square basin the subtropical the tropical and the equatorial gyres are produced by forcing the model with a wind stress profile having only latitudinal dependence the goal is to understand the effect of the meridional overturning circulation moc on the atlantic intergyre exchanges the moc is imposed by prescribing an inflow all along the southern boundary and an outflow at the northern boundary the results indicate that the northward flow of the moc has a crucial effect on the subtropical tropical pathways in this idealized configuration the north atlantic wind field creates a basinwide potential vorticity barrier therefore the water subducted in the north atlantic has to flow to the western boundary before turning equatorward this is shown by the trajectories of floats injected in a band of northern latitudes the warm water return flow of the moc inhibits this pathway and reduces the inflow of north atlantic

low frequency meandering of the atlantic north equatorial countercurrent four 19 month time series of indirect measurements of dynamic height were obtained in the tropical atlantic along 28 w at 0 3 6 and 9 n with three inverted echo sounders and one current meter mooring the series were analyzed to study the time latitude variability of the north equatorial countercurrent necc the eastward flow associated with the necc was present at 28 w from 3 to 9 n during most of the observed period except in march april 1983 and april may 1984 periods that coincided with the onset of the wind at the equator the amplitude of the necc s annual cycle was maximum at 6 n and was larger in 1983 than in 1984 the analysis of the time latitude variability of differences in dynamic height shows a long period meridional shift of the necc the core of the current attains its northernmost location during august september in both years and its southernmost location during march april in 1983 and march in 1984 the location of the core is directly related to the position of the intertropical convergence zone from the time series of dynamic height obtained from the indirect measurements geostrophic velocities and transports were estimated and compared with direct observations of currents and values obtained from hydrographic casts