synoptic eddy feedbacks and circulation regime analysis abstract a method to incorporate synoptic eddies into the diagnosis of circulation regimes using cluster analysis is illustrated using boreal winter reanalyses of the national centers of environmental prediction hereafter observations over the pacific north american region the motivation is to include the configuration of the high frequency periods less than 10 days transients as well as the low frequency periods greater than 10 days flow explicitly into the definition of the regimes principle component analysis is applied to the low frequency 200 hpa height field and also to the low frequency envelope modulations of the rms of high frequency meridional velocity at 200 hpa a maximum covariance analysis of the height and envelope fields carried out using the appropriate principal components defines three modes as explaining most of the covariance this defines the minimum dimensionality of the space in which to apply k means cluster analysis to the covariance coefficients clusters found usin

stratospheric influences on the mjo induced rossby wave train effects on intraseasonal climate abstractthe tropical madden julian oscillation mjo excites a northward propagating rossby wave train that largely determines the extratropical surface weather consequences of the mjo previous wo

the mjo cycle forcing of the north atlantic circulation intervention experiments with the community earth system model abstracta three dimensional evolution of madden julian oscillation mjo diabatic heating for october march from satellite data is constructed the heating propagates eastward for three cycles modulated by the likelihood for a given mjo phase to occur on a given calendar day this heating is added to the temperature tendencies of each member of an ensemble of 48 1 october 31 march simulations with the community earth system model the leading two most predictable modes of the planetary wave vertically integrated total added plus model generated heating capture 81 of the ensemble mean variance and form an eastward propagating oscillation with very high signal to noise ratio the two most predictable modes of the extratropical northern hemisphere 200 hpa height form an oscillation as do those of the 300 hpa height tendency due to synoptic vorticity flux convergence the 200 hpa rossby wave source and the envelope transient kinetic energy the north atlantic oscillation nao occurs 15 25 days after

migration of widespread long lived volcanism across the galapagos volcanic province evidence for a broad hotspot melting anomaly abstract the well studied galapagos archipelago is a small part of the much larger galapagos volcanic province gvp consisting of the cocos carnegie coiba and malpelo aseismic ridges and related seamount provinces although these aseismic ridges and seamounts dominate the morphology of the region little is known about their origin due to a lack of direct age and geochemical information in order to establish how well the gvp fits with the predictions of the standard fixed hotspot and mantle plume hypotheses we conducted a first reconnaissance dredge grab sampling of submerged regions of the gvp we present here 40ar 39ar ages for many of these new basement samples and evaluate their implications for the various models put forward to explain the origin of the gvp correlating new and published sample site ages with distance from the western side of the galapagos islands show that volcanism has not progressed in narrow time progressive lines of seamounts and ridges as predicted by the conventional fixed hotspot and mantle plume hypothesis rather volcanism apparently migrated time progressively across the gvp in broad regions of long lived and possibly concurrent volcanism we propose that the most viable explanation for these observations is that the gvp is the product of cocos and nazca plate motions across a broad hotspot melt anomaly the complex spreading history of the cocos nazca spreading centre likely controlled the relative distribution of gvp volcanism between the cocos and nazca plates while creating lithosphere of variable age thickness across the region while the notion of a broad galapagos hotspot melting anomaly linked to a complex regional tectonic history requires significant testing it nevertheless highlights the need to test alternative mantle upwelling shapes and sizes compared to the widely accepted notion of a narrow continuous long lived galapagos mantle plume conduit defined by the size and location of a galapagos island

comparative geochemistry of apollo 16 surface soils and samples from cores 64002 and 60002 through 60007 new data are presented for the concentrations of 23 to 27 elements in nine apollo 16 surface soil samples two subsplits each of 12 splits of core 60002 7 and one subsplit each of 10 splits of drive tube 64002 the surface soils are generally similar to other surface soils collected at their respective stations all ten 64002 samples are similar to each other and to the station 4 surface soils and distinctly different from soils at other stations high iron concentrations previously reported for these same subsplits of 60002 7 result primarily from meteoritic metal one sample from each core is contaminated by stainless steel the recently proposed ferroan anorthositic norites are required to explain the soil compositions a yet uncharacterized component with high concentrations of na sr and eu is also needed

constraints on age and construction process of the foundation chain submarine volcanoes from magnetic modeling abstract the interaction between the foundation hotspot and the pacific antarctic ridge south pacific is one of the two known cases where a ridge is approaching a hotspot this ridge hotspot relative movement results in a change in the morphology of the volcanoes along the chain as the age of the lithosphere at the time of edifice formation progressively diminishes four hundred kilometers west of the pacific antarctic ridge axis volcanism is distributed along two sub parallel lines of volcanoes separated by distances diminishing from 100 km at the west to 50 km near the axis of the ridge the magnetic anomalies mapped on this part of the chain show a pattern clearly dominated by the magnetic signature of the seamounts the anomalies were forward modeled using a remanent magnetization of normal or reversed polarity within the volcano topography the resulting pattern of normal and reversed magnetization is consistent with the intervals of the geomagnetic polarity time scale for the last 5 ma the age of the oldest studied volcano these magnetic anomalies therefore represent an independent means of dating the volcanic edifices the ages deduced from the modeling are consistent with the hypothesis of volcanoes built by a hotspot on the fast moving pacific plate and are in good agreement with the published radiometric dates although these dates tend to correspond to the late constructional stages of the edifices the differences between magnetic and radiometric ages suggest that the average time span to build a volcano of the foundation chain is about 1 million years in agreement with other intraplate edifices the difference between the magnetic ages of the seamounts and of the underlying crust both deduced from the magnetic anomaly analysis show that the ridge has approached the hotspot at a rate of 40 km ma

petrologic comparisons of cayley and descartes on the basis of apollo 16 soils from stations 4 and 11 petrologic aspects of the cayley and descartes formations are reviewed in the light of new data on apollo 16 soils specific comparison of the modal abundances of lithic fragments in drive tube sample 64001 2 from the slopes of stone mountain station 4 and in soil 67941 from the north ray crater rim station 11 shows that melt rocks especially poikilitic rocks are more abundant at station 4 than at station 11 the reverse is true for fragmental breccias such lithologic differences suggest that stations 4 and 11 do not belong to the same geologic formation metamorphosed breccias are pervasive in both the formations and may represent a local component that has been reworked and diluted as fresh materials were added lithologic compositions inferred from the study of soil samples are different from lithologic compositions inferred from the study of rake samples or breccia clasts this difference may be related to a mixing of material of different grain size distributions the petrology of soils at the apollo 16 site may not accurately reflect original material associated with either the descartes or the cayley formation because of extensive mixing with local material

origin of the lunar highlands mg suite an integrated petrology geochemistry chronology and remote sensing perspective the mg suite represents an enigmatic episode of lunar highlands magmatism that presumably represents the first stage of crustal building following primordial differentiation this review examines the mineralogy geochemistry petrology chronology and the planetary scale distribution of this suite of highlands plutonic rocks presents models for their origin examines petrogenetic relationships to other highlands rocks and explores the link between this style of magmatism and early stages of lunar differentiation of the models considered for the origin of the parent magmas for the mg suite the data best fit a process in which hot solidus temperature at 2 gpa 1600 to 1800 c and less dense 3100 kg m3 early lunar magma ocean cumulates rise to the base of the crust during cumulate pile overturn some decompressional melting would occur but placing a hot cumulate horizon adjacent to the plagioclase rich primordial crust and kreep rich lithologies at temperatures of 1300 c would result in the hybridization of these divergent primordial lithologies producing mg suite parent magmas as urkreep primeval kreep is not the petrologic driver of this style of magmatism outside of the procellarum kreep terrane pkt mg suite magmas are not required to have a kreep signature evaluation of the chronology of this episode of highlands evolution indicates that mg suite magmatism was initiated soon after primordial differentiation 10 m y alternatively the thermal event associated with the mantle overturn may have disrupted the chronometers utilized to date the primordial crust petrogenetic relationships between the mg suite and other highlands suites e g alkali suite and magnesian anorthositic granulites are consistent with both fractional crystallization processes and melting of distinctly different hybrid sources

the support mechanism of the young foundation seamounts inferred from bathymetry and gravity summary the youngest volcanoes of the foundation volcanic chain were built on a plate less than 5 myr near the pacific antarctic ridge par axis the progressive approach of the spreading ridge to the hotspot during the last 10 myr resulted in the building of the edifices upon a progressively younger plate estimates of the effective elastic thickness te using two independent methods show that the elastic thickness of the plate diminishes towards the spreading ridge from 5 3 km to 2 0 km the spatial variation of te correlates with a significant change in both the morphology and the volume of the volcanoes suggesting an important control of the elastic thickness on the volcanic processes the reduction in te also explains conveniently the reduction in the distance between the north and the south systems the double volcanic line that characterizes the young part of the foundation chain in the direction of young loading ages the south system formed at the top of a flexural bulge created by the emplacement of the north system the main volcanic line the low te estimate for the south system and the shape of the bouguer anomalies confirm this model the effective elastic thicknesses obtained in this study are well matched by isotherms between 200 c and 300 c and support the hypothesis of a weak plate three mechanisms possibly acted to lower the plate rigidity re heating of a normal plate by the hotspot north system local fracturing south system and the creation of a thin lithosphere at the par axis by the coupling of a hotspot and the ridge related melting zones near ridge volcanoes

plume ridge interaction revisited evidence for melt mixing from he ne and ar isotope and abundance systematics abstract submarine volcanic glass he ne and ar data from the pacific antarctic rise at its intersection with the foundation seamount chain have been obtained to further elucidate one of the main outstanding problems in plume ridge interaction studies the physical state in which mantle flow and mixing occur in those settings mixing of plume mantle and mid ocean ridge basalt source material may either be in the form of two solids of solid melt or of two melt phases only the positive correlation of 4 he 40 ar with 206 pb 204 pb as well as the negative correlation of 4 he 40 ar with 40 ar and 4 he concentrations combined with a lack of correlation between 4 he 40 ar and ridge depth or mgo concentration indicate that the enriched mantle plume material has been extensively degassed prior to mixing with the mid ocean ridge source material degassing of the plume source and mid ocean ridge source material prior to mixing is also suggested by the he versus pb isotope systematics however the occurrence of degassing processes requires the existence of melts implying that mixing between the plume and the mid ocean ridge material occurs in the physical form of melts

nonlinear 40ar 39ar age systematics along the gilbert ridge and tokelau seamount trail and the timing of the hawaii emperor bend over the last three decades the first order correlation in morphology and orientation of seamount trails has been called upon to support the concept of a fixed pacific hot spot frame of reference and to explain the hawaii emperor bend heb by a dramatic change in pacific plate motion in this paper however we present 40ar 39ar ages for the gilbert ridge and tokelau seamounts pacific that show similar changes or bends in their orientation but at different geological times up to 20 myr earlier than the heb changes in pacific plate motion alone cannot explain these observations because these asynchronous bends should have been reflected in the morphology of each of these seamount trails together with the lack of linear age progressions and inconsistent apparent local plate velocities of 131 and 87 mm yr we rule out a fixed hot spot origin for the gilbert ridge and tokelau seamount trails instead we invoke secondary or alternate processes to explain the complex age systematics and morphologies in these seamount trails we propose here that the heb type bends in these seamount trails were likely formed by short term jerk like plate extensions in the studied southwestern region of the pacific plate reactivating a preconditioned lithosphere that can be characterized by a complex structure and precursory magmatic impingements the remarkable differences observed in these colinear seamount trails fundamentally question the existence of heb type bends in the formation of pacific volcanic lineaments they also show us that applying geometric and morphologic observations alone is insufficient in constraining past plate motions nevertheless the need and search for alternate volcano tectonic mechanisms offer opportunities to better understand intraplate volcanism in general

the influence of the madden julian oscillation on northern hemisphere winter blocking abstractthe persistent and quasi stationary nature of atmospheric blocking is associated with long lasting extreme weather conditions that influence much of the northern hemisphere during boreal winter the madden julian oscillation mjo has been previously shown to influence important factors for blocking including rossby wave breaking and the north atlantic oscillation nao however the extent to which the mjo influences blocking across the northern hemisphere is not yet fully understood utilizing a two dimensional blocking index composites of north pacific north atlantic and european blocking are generated relative to mjo phase in the west and central pacific all mjo phases demonstrate significant changes in blocking particularly at high latitudes a significant decrease in east pacific and atlantic blocking occurs following phase 3 of the mjo characterized by enhanced convection over the tropical east indian ocean and suppressed convection in the west pacific the opposite signed mjo heatin

en echelon volcanic elongate ridges connecting intraplate foundation chain volcanism to the pacific antarctic spreading center abstract the development of volcanic elongate ridges vers could be controlled in many cases by complex processes related to interaction between mantle plumes and spreading centers we report here measured ages for the foundation chain se pacific showing that volcanism along morphologically distinct vers can develop occasionally as rapidly formed continuous lines of coeval volcanism extending from a region of intraplate volcanism to the pacific antarctic spreading center but a significantly more dominant trend is for coeval yet structurally disconnected segments of foundation chain vers to develop in a series of en echelon ne sw elongate zones of coeval hotspot volcanism these elongate zones developed at intervals of approximately 1 myr while maintaining a basically steady state orientation and size as the pacific antarctic spreading center migrated continually closer to the foundation plume hotspot we infer from this new information that foundation chain ver development was controlled by an interplay between short lived local factors e g location of nearest spreading center segment lithospheric stress and long lived attributes of the foundation plume hotspot e g size orientation periodicity

non hotspot formation of volcanic chains control of tectonic and flexural stresses on magma transport the south pacific in the vicinity of both the superswell and the east pacific rise is repleat with volcanic chains that unlike the emperor hawaiian chain defy the hypothesis of formation via the relative motion of plates and hotspots we propose two nearly identical models for the origin of near axis and superswell chains assuming that both regions are underlain by significant quantities of more or less uniformly distributed partial melt given an initial volcanic load or a local anomaly in the melt source region volcanic chains form by magmatic hydrofracture at local tensile maxima of flexural and membrane stresses fracture wall erosion by magma flow provides a feedback which results in discrete edifices within the chains the model predicts island chains aligned with a deviatorically tensile tectonic stress near the ridge the elastic lithosphere is thin and observations and theoretical considerations indicate a strong deviatorically tensile stress field perpendicular to the ridge axis under such conditions the model results in parallel lines of volcanoes perpendicular to the spreading ridge later interstitial volcanism within the individual chains reduces the average spacing and results in nearly continuous ridges on the thicker lithosphere of the superswell membrane stresses are negligible and the model produces chains of much more widely spaced volcanoes a more isotropic stress field may result in broader chain like patterns of volcanoes in both cases the chains represent self propagating disturbances the resulting age progressions are thus independent of plate velocity but depend only on the dynamics of volcano formation and evolution

rock 67015 a feldspathic fragmental breccia with kreep rich melt clasts breccia 67015 one of the feldspathic fragmental breccias ffbs from the rim of north ray crater contains a wider range of clast lithologies than has been described previously in ffb s our petrologic and inaa studies have revealed two components of major petrologic and geologic significance one of these is a dark vesicular kreep rich melt rock of vha very high alumina basalt composition which occurs in clasts up to 6 cm long melt rocks of this type are common at the apollo 16 site but in previous years had not been discovered as prominent constituents of the feldspathic fragmental breccias their apparent absence led to hypotheses no longer valid that the kreepy melt rocks were younger than the anorthositic breccia matrices and that the two lithologies might represent imbrian and nectaris ejecta respectively the second lithology we discovered is a large clast of medium grained ferroan anorthositic norite with a composition that falls among the most magnesian members of the ferroan anorthosite suite of pristine cumulate rocks this material constitutes a previously missing member of certain mixing models designed to account for the north ray crater melt rocks and bulk breccias

intraplate versus ridge volcanism on the pacific antarctic ridge near 37 s 111 w exploration of the foundation volcanic chain 33 s 131 w 37 s 111 w revealed the existence of different magmatic provinces with relation to their geological settings 1 the pacific antarctic ridge par is made up of several en echelon segments where both glassy midocean ridge basalts morbs with low incompatible elements k2o 150 ppm and ce 48 ppm at about 306 1300 km from the par axis 4 the old pacific seamounts built on a crust older than 23 m y located west of longitude 124 w 1300 km from the par axis consist of t and emorb on the par axis extensive crystal fractionation 65 produced the silicic lavas on the basis of pacific plate reconstruction using a half spreading rate of about 50 mm yr and integrating the observed compositional changes with respect to the structural settings it is inferred that the last volcanic events giving rise to the fs took place at about 110 km from the par axis about 5 m y ago the oblique ridges built between 5 m y and 23 m y with morb volcanics comparable to those of the the oblique ridge par provinces could also have been formed by an interaction between the foundation seamount dredge site 28 hotspot magmatism and that of an ancient accreting ridge magmatism precursor of the par

multiple weather regimes over the north atlantic analysis of precursors and successors abstract the algorithm developed by vautard and legras is applied to a series of 37 winter of 700 mb geopotential height observations in order to identify quasi stationary patterns occurring over the extratropical north atlantic area weather regimes are obtained as solutions of a act of nine nonlinear statistical equations giving the balance of the large scale average tendency four regime patterns are found the first one exhibits the typical european blocking dipole the second one is an enhanced zonal flow the third one consists of a positive anomaly over greenland and the last one is characterized by a ridge over the eastern atlantic ocean the role played by the transient small scales in the maintenance of thew four regimes is discussed next the backward and forward memory times of the different weather regimes are established evidence is brought that the atmosphere keeps its memory of regime occurrences into the medium range 10 20 days backward memory times are shorter 5 10 days showin

lunar granulites and their precursor anorthositic norites of the early lunar crust lunar granulites are breccias with metamorphic textures they are not pristine having been contaminated with meteoritic siderophiles nonetheless they constitute an abundant class of highlands rocks that are important because they are ancient and kreep free they may represent our best samples of the early lunar crust the granulites can be divided into ferroan and magnesian groups and each group can be subdivided on the basis of mineral composition and ree concentrations textural and compositional data show that some of the granulites especially 67215 and 67415 may be derived from distinct anorthositic norite precursors while some other granulites 79215 78155 are clearly polymict even the polymict granulites probably had anorthositic norites as their dominant precursors and not anorthosites norites or troctolites the granulites have compositions similar to those of the two lunar meteorites one of which yamato 791197 is ferroan the other alha81005 magnesian these meteorites are soil breccias from an unknown location distant from the apollo landing sites and contain anorthositic norites as abundant clasts compositions of granulites and lunar meteorites more closely resemble the average composition of lunar highlands as determined by remote sensing than do those of any other returned lunar samples the predominance of plutonic anorthositic norite precursors in material having the composition typical of highlands suggests that plutonic anorthositic norites were more abundant in the early lunar crust than is implied by their scarcity among pristine rocks from apollo missions

circulation factors determining the propagation speed of the madden julian oscillation abstractthe eastward propagating madden julian oscillation mjo events exhibit various speeds ranging from 1 to 9 m s 1 but what controls the propagation speed remains elusive this study attempt

the foundation seamounts tectonic setting of a newly discovered seamount chain in the south pacific abstract large areas of the south pacific remain unsurveyed because they are so remote a major volcanic chain the foundation seamounts lies between 33 s and 39 s and between 111 w and 125 w poorly defined on conventional bathymetric charts it becomes very apparent when combining an analysis of conventional geophysical data with the satellite altimeter data the length of the seamount chain is 1350 km and the volcanoes are clustered within a 180 km wide band trending approximately n70w which is the direction of absolute motion of the pacific plate over a fixed reference system some of these volcanoes are so shallow that they may have emerged above the sea surface at an earlier time no dates are known for the seamounts surrounding the foundation seamounts chain the tectonic setting is that of the pacific plate at the time when the strike of the spreading ridge changed from a northwesterly direction to the present northeasterly one this episode of spreading reorganization involved the existence of a short lived microplate west of the pacific antarctic ridge a captured segment of nazca plate accounts for the large discrepancies in the magnetic anomalies offsets along the agassiz fracture zone large propagators like the adventure and kurchatov troughs are described the newly discovered western segment of the chile fracture zone is the pacific plate match of the chile fracture zone on the nazca plate

ridge hotspot interaction the pacific antarctic ridge and the foundation seamounts the study of different magmatic provinces between the resolution fracture zone 33 s 131 w and the pacific antarctic ridge par axis 37 s 111 w suggests that similar processes of interaction between hotspot and spreading axial magmatism occurred 20 25 ma and 0 5 ma ago there is evidence of this process from the changes in composition observed in the lavas erupted near 400 300 km between the present day par axis 37 s 111 w and the eastern tip of the foundation seamount fs hotspot near 36 20 s 114 w where the last alkali enriched volcanics k ti 0 30 zr y 6 and ce yb n 4 have erupted this transitional province between the par and the fs consists of volcanic cones built on several volcanic ridges 20 ma also built on volcanic ridges are identified west 1200 km from the par axis of a failed rift propagator frp forming the eastern boundary of the ancient selkirk microplate some of these seamounts made of alkali basalts were built during the initiation of the fs hotspot 20 23 ma ago the interaction and the influence thermal of mantle plume magmatism with the ancient spreading ridge of the farallon pacific plates was responsible for the eruptions of the t morbs and andesitic lavas this situation is comparable to that presently observed on the par axis where silicic lavas are also erupted in association with t morbs

effective elastic thickness of the lithosphere along the easter seamount chain bathymetry and gravity data collected during legs 5 6 and 7 of the 1993 gloria expedition and the recently released 2 min altimetry derived global gravity grid are used to determine the effective elastic thickness of the lithosphere along the easter seamount chain esc forward modeling admittance and coherence methods yield consistent restfits with the exception of the eastern and western ends of the esc the effective elastic thickness along the chain is 1 4 km the thin elastic thickness for the majority of the esc seamounts is compatible with a young seafloor age at the time of loading derived from new radiometric ages of the seamounts along the chain and a magnetic isochron age interpretation of the nazca plate seafloor age the elastic thickness southeast of the nazca fracture zone is 6 km apparently because of the seafloor age discontinuity across the fracture zone the elastic thickness near the san felix island at the eastern end of the esc is even greater 11 km which is compatible with the estimated seafloor age at the time of loading a slight increase in the effective elastic thickness of the far western part of the esc suggests dynamic compensation or less thermal weakening of lithosphere above a plume channel versus directly above the plume center these findings combined with published geochemistry support a hotspot origin for the esc complicated by large scale plate boundary reorganizations and channeling of plume material to the east pacific rise

circulation response to fast and slow mjo episodes abstractfast and slow madden julian oscillation mjo episodes have been identified from 850 and 200 hpa zonal wind and outgoing longwave radiation olr for 32 winters 16 october 17 march 1980 81 2011 12 for 26 fast cases the olr took no more than 10 days to propagate from phase 3 convection over the indian ocean to phase 6 convection over the western pacific for 8 slow cases the propagation took at least 20 days fast episode composite anomalies of 500 hpa height z500 show a developing rossby wave in the mid pacific with downstream propagation through mjo phases 2 4 changes in the frequency of occurrence of the nao weather regime are modest this rossby wave is forced by anomalous cooling over the maritime continent during phases 2 and 3 seen in phase independent wave activity flux the upper level anticyclonic response to phase 3 heating is a secondary source of wave activity the z500 slow episode composite response to mjo phases 1 and 2 is an enhanced aleutian low followed by a north a

propagating versus nonpropagating madden julian oscillation events abstractbasinwide convective anomalies over the indian ocean io associated with the madden julian oscillation mjo sometimes propagate eastward and reach the west pacific wp but sometimes do not long term observations and reanalysis products are used to investigate the difference between the propagating and nonpropagating mjo events io convection onset events associated with the mjo are grouped into three categories based on the strengths of the simultaneous dry anomalies over the eastern maritime continent and wp the io convection anomaly preferentially makes eastward propagation and reaches the wp when the dry anomaly is stronger analysis of the column integrated moist static energy mse budget shows that horizontal advection moistens the atmosphere to the east of the positive mse anomaly associated with the active convection over the io and is of sufficient magnitude to explain the eastward propagation of the positive mse anomaly interpretation is complicated however by lack of closure in

bathymetric prediction from dense satellite altimetry and sparse shipboard bathymetry the southern oceans south of 30 s are densely covered with satellite derived gravity data track spacing 2 4 km and sparsely covered with shipboard depth soundings hundreds of kilometers between tracks in some areas flexural isostatic compensation theory suggests that bathymetry and downward continued gravity data may show linear correlation in a band of wave lengths 15 160 km if sediment cover is thin and seafloor relief is moderate at shorter wave lengths the gravity field is insensitive to seafloor topography because of upward continuation from the seafloor to the sea surface at longer wavelengths isostatic compensation cancels out most of the gravity field due to the seafloor topography we combine this theory with wiener optimization theory and empirical evidence for gravity noise to signal ratios to design low pass and band pass filters to use in predicting bathymetry from gravity the prediction combines long wavelengths 160 km from low pass filtered soundings with an intermediate wavelength solution obtained from multiplying downward continued band pass filtered 15 160 km gravity data by a scaling factor s s is empirically determined from the correlation between gravity data and existing soundings in the 15 160 km band by robust regression and varies at long wave lengths we find that areas with less than 200 m of sediment cover show correlation between gravity and bathymetry significant at the 99 level and s may be related to the density of seafloor materials in these areas the prediction has a horizontal resolution limit of 5 10 km in position and is within 100 m of actual soundings at 50 of grid points and within 240 m at 80 of these in areas of very rugged topography the prediction underestimates the peak amplitudes of seafloor features images of the prediction reveal many tectonic features not seen on any existing bathymetrie charts because the prediction relies on the gravity field at wavelengths 160 km it is insensitive to errors in the navigation of sounding lines but also cannot completely reproduce them therefore it may be used to locate tectonic features but should not be used to assess hazards to navigation the prediction is available from the national geophysical data center in both digital and printed form

the global atmospheric circulation response to tropical diabatic heating associated with the madden julian oscillation during northern winter abstractthe detailed dynamical mechanisms of the upper tropospheric circulation response to the madden julian oscillation mjo convection are examined by integrating a primitive equation model a series of initial value calculations with the climatological boreal winter background flow forced by the mjo like thermal forcing successfully capture the key aspects of the observed circulation response to the mjo convection this suggests that a large fraction of mjo related circulation anomalies are direct responses to tropical heating in both the tropics and extratropics and can be largely explained by linear dynamics it is found that mjo like dipole heatings not only intensify tropical upper tropospheric anomalies but also weaken them at certain regions because of the interaction between equatorial kelvin and rossby waves the rossby wave train primarily excited by horizontal divergence of upper level perturbation flow propagates northeastward and then heads back to the equator in this way rossby wave act

impact of enso on the atmospheric variability over the north atlantic in late winter role of transient eddies abstractthe dynamical mechanism for the late winter teleconnection between el nino southern oscillation enso and the north atlantic oscillation nao is examined using the output from a 2000 yr integration of a coupled general circulation model gcm the coupled model captures many salient features of the observed behavior of both enso and nao as well as their impact on the surface climate in late winter both the observational and model data indicate more occurrences of negative phase of nao in late winter during el nino events and positive nao in la nina episodes the potential role of high frequency transient eddies in the above teleconnection is diagnosed during el nino winters the intensified transient disturbances along the equatorward shifted north pacific storm track extend their influences farther downstream the eddy induced negative height tendencies are found to be more coherent and stronger over north atlantic than that over north pacific these negative height tendencies over the north

pulsing of a focused mantle plume evidence from the distribution of foundation chain hotspot volcanism 1 using the rare case of a hotspot chain crossing a fossil microplate we reveal fundamental mantle plume characteristics by comparing hotspot volcanism in a sequence of contrasting tectonic settings key new 40ar 39ar ages show that the foundation mantle plume pulses hot masses from depth with an apparent periodicity of one myr synchronous magmatism over large distances indicates that masses associated with individual pulses are focused initially into similarly sized zones under the pacific plate since the plume spreading on impact with the lithosphere influences a very wide area apparently unconnected hotspot volcanism can be produced simultaneously across wide swaths often crosscutting seamount chains our model might explain in part much of the midplate volcanism scattered across the pacific seafloor indicating the episodic addition of significantly greater masses of plume material into the upper mantle than suggested by the narrowness of major seamount chains

the modulation of the subtropical and extratropical atmosphere in the pacific basin in response to the madden julian oscillation abstract the 40 yr ecmwf re analysis era 40 data are combined with a number of novel climatologies to conduct a comprehensive examination of the response of the subtropical and extratropical atmosphere over the pacific basin to an evolving madden julian oscillation mjo event the adopted approach constitutes a symbiosis of a climatological analysis during the northern hemisphere winter from 1979 to 2002 and a case study analysis of a distinct mjo event that occurred in january february 1993 the former is designed to obtain the general characteristics observed during a composite mjo life cycle while the latter is used to provide insight into the instantaneous mechanisms responsible for the observed composite evolution a primary component of the study involves the diagnosis of anomalous wave breaking activity in response to mjo forcing in the form of tropical convection and or upper level divergence wave breaking events are separated by their characteristic life cycles lc1 anticyclonic and lc2 c

the global response to tropical heating in the madden julian oscillation during the northern winter a life cycle of the madden julian oscillation mjo was constructed based on 21 years of outgoing long wave radiation data regression maps of ncep ncar reanalysis data for the northern winter show statistically significant upper tropospheric equatorial wave patterns linked to the tropical convection anomalies and extratropical wave patterns over the north pacific north america the atlantic the southern ocean and south america to assess the cause of the circulation anomalies a global primitive equation model was initialized with the observed three dimensional 3d winter climatological mean flow and forced with a time dependent heat source derived from the observed mjo anomalies a model mjo cycle was constructed from the global response to the heating and both the tropical and extratropical circulation anomalies generally matched the observations well the equatorial wave patterns are established in a few days while it takes approximately two weeks for the extratropical patterns to appear the model response is robust and insensitive to realistic changes in damping and basic state the model tropical anomalies are consistent with a forced equatorial rossby kelvin wave response to the tropical mjo heating although it is shifted westward by approximately 20 longitude relative to observations this may be due to a lack of damping processes cumulus friction in the regions of convective heating once this shift is accounted for the extratropical response is consistent with theories of rossby wave forcing and dispersion on the climatological flow and the pattern correlation between the observed and modelled extratropical flow is up to 0 85 the observed tropical and extratropical wave patterns account for a significant fraction of the intraseasonal circulation variance and this reproducibility as a response to tropical mjo convection has implications for global medium range weather prediction copyright 2004 royal meteorological society

migration rate of volcanism along the foundation chain se pacific abstract volcanism has migrated along the nw se trending foundation chain se pacific at a rate of 91 2 mm y for the past 21 million years my the foundation chain is at least 1900 km long and was erupted mostly in the interior of the pacific plate the linear migration of intraplate often geochemically enriched volcanism along the foundation chain can be explained by the theory of tectonic plate drift over a narrow stationary plume of hot mantle material upwelling from depth the present hotspot or at least its eastern extent generated by this foundation plume is now located on or close to the pacific antarctic spreading axis local spreading microplate boundaries have migrated systematically towards the foundation plume for at least the past 21 my a process that was however interrupted by the creation of the selkirk microplate the foundation chain has erupted therefore onto ocean crust ranging in age from 17 ma to 0 ma with distances between the foundation plume and local spreading microplate boundaries varying from 900 km to 0 km such interplay between the foundation plume and local seafloor spreading and microplate boundaries probably in combination with changing stresses in the lithosphere apparently induced major changes in the fabric and composition of the foundation chain e g the switch from individual seamounts to elongated en echelon ridges at 5 ma it can also explain why ages for a few foundation seamounts located at the edges of the selkirk microplate do not lie along the overall linear trend of migrating volcanism the linear velocity of the pacific plate over the foundation plume calculated on the basis of the migration rate of volcanism along the foundation chain is predicted by a number of rotation poles for the motion of the pacific plate in a fixed hotspot reference frame the fact that the measured migration rates of volcanism along the foundation and hawaiian chains are predicted by these rotation poles 1 confirms that the distribution of foundation chain ages records the absolute motion of the pacific plate and 2 supports the fundamental assumption of stationary mantle plumes in the case of hawaii versus foundation for at least the past 21 my the foundation chain was created by a weak plume primarily as relatively small probably rapidly erupted 1 my individual seamounts or seamount clusters at a rate of approximately one every my linear migration rates of volcanism are most likely defined unequivocally along such types of hotspot chain on the basis of age distance data it should also be easier to identify and characterize volcanism created as a result of plume interactions with local spreading microplate boundaries rotation poles for pacific plate drift show that the initial stages of volcanism along the southern austral chain 34 ma could have been created by the foundation plume suggesting that the path of pacific plate drift over the stationary foundation plume could be at least 3000 km long

the pacific antarctic ridge foundation hotspot interaction a case study of a ridge approaching a hotspot the foundation hotspot pacific antarctic ridge par system is the best documented case of a fast spreading ridge approaching a hotspot and interacting with it the morphology crustal structure inferred from gravity anomalies and the chemical composition of the lavas of the axial area of the par show evidence of the influence of the hotspot that is presently located roughly 35 km west of the spreading ridge axis along axis variation in the mantle bouguer anomaly is about 28 mgal corresponding to a crustal thickening of 1 5 km where the hotspot is nearer to the par anomalous ridge elevation is 650 m and the along axis width of the chemical anomaly is 200 km a comparison of these axial parameters with those derived for other ridge hotspot systems suggests that the amount of plume material reaching the ridge axis is smaller for the foundation par system this implies a weaker connection between the plume and the ridge cumulative effects of a fast spreading rate and of a fast ridge hotspot relative motion can be responsible for this weak plume ridge flow the flow from the hotspot may be less efficiently channelled towards the ridge axis when a fast ridge is rapidly moving towards a hotspot

geochemical studies of feldspathic fragmental breccias and the nature of north ray crater ejecta major and trace element analyses of clasts and matrix from feldspathic fragmental breccias show that these breccias are not all alike but vary widely in their bulk compositions and clast assemblages these studies together with analyses of other north ray crater large rocks reveal the major components to be anorthosites ferroan anorthositic norites magnesian granulites feldspathic melt rocks and vha impact melts the ferroan anorthositic norites are important lunar crustal rocks identified here for the first time the kreepy vha melts are found to be much more important in north ray crater ejecta than was previously assumed sodic ferrogabbro is an important minor component the compositional characteristics of bulk breccias and feldspathic melt rocks are modeled quantitatively as mixtures of two to five components anorthosites ferroan anorthositic norites magnesian granulites sodic ferrogabbros and vha melt rocks breccia 67455 is unique in consisting wholly of ferroan kreep free components

upper mantle heterogeneities and dynamics the width of geochemical and residual elevation anomalies along the mid ocean ridge system decrease as both the distance between migrating ridge segments and related hotspots and the local geochemical dispersion in the anomalies increase these observations provide further evidence that flows of mantle plumes in the upper mantle are deflected by migrating ridge sinks once they override hotspots

an observed connection between the north atlantic oscillation and the madden julian oscillation abstract based on the bivariate madden julian oscillation mjo index defined by wheeler and hendon and 25 yr 1979 2004 of pentad data the association between the north atlantic oscillation nao and the mjo on the intraseasonal time scale during the northern hemisphere winter season is analyzed time lagged composites and probability analysis of the nao index for different phases of the mjo reveal a statistically significant two way connection between the nao and the tropical convection of the mjo a significant increase of the nao amplitude happens about 5 15 days after the mjo related convection anomaly reaches the tropical indian ocean and western pacific region the development of the nao is associated with a rossby wave train in the upstream pacific and north american region in the atlantic and african sector there is an extratropical influence on the tropical intraseasonal variability certain phases of the mjo are preceded by the occurrence of strong naos a significant change of upper zonal

tracking of tropical intraseasonal convective anomalies 1 seasonality of the tropical intraseasonal oscillations a tracking algorithm based upon a multiple object tracking method is developed to identify track and classify tropical intraseasonal oscillations tiso on the basis of their direction of propagation daily national oceanic and atmospheric administration outgoing longwave radiation anomalies from 1979 2017 are lanczos band pass filtered for the intraseasonal time scale 20 100 days and spatially averaged with nine neighboring points to get spatially smoothed anomalies over large spatial scales 105 km2 tiso events are tracked by using a two stage kalman filter predictor corrector method two dominant components of the tiso eastward propagating and northward propagating are classified and it is found that tiso remains active throughout the year eastward propagating tiso events occur from november to april with a phase speed of 4 m s and northward propagating tiso events occur from may to october with a phase speed of 2 5 m s in both the indian and pacific ocean basins composites of the mean background states wind sea surface temperature sst and moisture reveal that the co occurrence of warm sst and mean westerly zonal wind plays an important role in the direction of propagation and the geographical location of tiso events in mean state sensitivity experiments with sp cam4 we have found that the seasonality of tiso in terms of the geographical location of occurrences and direction of propagation is primarily associated with the annual march of the maximum sst and low level zonal wind which tends to follow the sst

topographic influence on the mjo in the maritime continent abstract this study demonstrates that during the passage of the mjo through the maritime continent in the boreal winter the corresponding deep convection and near surface wind anomalies tend to skirt around mountainous islands flow bifurcation around elongated mountainous islands such as new guinea is clearly seen topographic blocking generates distinctive vorticity and convergence distributions in this specific domain mountain wave like structures are also observed throughout the maritime continent with a clear spatial relationship with the high terrains in sumatra sulawesi and new guinea the existence of topography seems to create extra lifting and sinking within the large scale circulation and thus the convective system exhibits quasi stationary features near the major topography during the mjo passage through the maritime continent it is suggested that resolving the detailed topographic effects may play a key role in simulating realistic characteristics of the mjo in the maritime continent

geochemistry of lunar crustal rocks from breccia 67016 and the composition of the moon global differentiation of the moon has produced a plagioclase rich crust overlying an ultramafic mantle we have conducted a major and trace element study of anorthositic clasts from an apollo 16 breccia to investigate the geochemical features of these highlands lithologies and their role in lunar crustal evolution samples analyzed for this study have aluminous alkali poor compositions and varied feo and mgo contents al2o3 25 35 na2o 0 3 1 k2o 1 ferroan noritic and 1 magnesian troctolitic respectively these mafic enriched varieties have considerably higher lithophile element concentrations at levels similar to that of the bulk lunar crust the ferroan noritic clasts may represent a fundamental type of igneous rock in the lunar crust which has not been widely recognized liyb ratios of highlands and mare rocks demonstrate the complementary nature of the lunar crust and mantle which is best explained by a global differentiation event such as crystallization of a magma ocean the most primitive mantle derived lunar material for which data are available the apollo 15 green glass has liyb virtually identical to those of the mafic enriched anorthosites providing an estimate of the magma ocean composition the moon and the earth have liyb ratios that are similar to each other but the absolute abundances of both li and yb appear to be higher in the moon the liyb ratios of the earth and moon are distinct from those of ci and ordinary chondrites and the eucrite parent body but are similar to those of cv co and el chondrites precluding a unique match between the composition of the earth and moon

geochronology of galapagos seamounts lavas from seamounts of the central galapagos platform and the carnegie ridge increase in age with distance from the western edge of the platform consistent with a hotspot model for the generation of these features the areal distribution of seamount ages suggests that the pattern of dispersed volcanism seen on the present islands also prevailed between 5 and 6 ma age distance relationships are consistent with a decrease in the velocity of the nazca plate relative to the galapagos hotspot during the past 9 m y most likely at 5 ma when there was a change in pacific hotspot motion alternatively the plate velocity remained constant and volcanism at a single seamount endured up to 7 m y lavas from seamounts along the wolf darwin lineament to the northwest of the galapagos platform are young 1 ma with the youngest measured ages closest to the platform

testing the sensitivity of the extratropical response to the location amplitude and propagation speed of tropical convection abstractthe dynamical core of a dry global model is used to investigate the role of central pacific versus warm pool tropical convection on the extratropical response over the north pacific and north america a series of model runs is performed in which the amplitude of the warm pool wp and central pacific cp heating anomalies associated with the mjo and el nino southern oscillation enso is systematically varied in addition model calculations based on each of the eight mjo phases are performed first using stationary heating and then with heating corresponding to a 48 day mjo cycle and to a 32 day mjo cycle in all model runs the extratropical response to tropical convection occurs within 7 10 days of the convective heating the response is very sensitive to the relative amplitude of the heating anomalies for example when heating anomalies in the wp and cp have similar amplitude but opposite sign the amplitude of the extratropical response is much weaker than is typical for the mjo and enso f

geomorphology and structural segmentation of the crest of the southern pacific antarctic east pacific rise geomorphology of the boundary between pacific and antarctic plates was mapped with a sea beam multibeam echosounder and a seamarc ii bathymetric side scan sonar from the southern end of juan fernandez microplate at 35 s to heezen transform at 56 s there are six spreading center systems separated by two large left stepping nontransform offsets at 36 5 s and 41 5 s two right stepping transform fault systems and a left stepping hybrid structure with equally long strike slip and nontransform offsets axial rift zones spreading axes are generally within 1 of normal to the relative motion predicted by current plate rotation models most axial rift zones crop out along the crests of typical east pacific rise epr axial ridges which commonly have flat rather than humped long profiles about 2 of this fast spreading 84 100 mm yr rise crest has an axial rift valley instead of an axial ridge the longest rift valley segment is midway between menard and vacquier transforms near 51 s where an anomalously deep rise crest may mark a zone of below average mantle upwelling nontransform offsets structurally similar to those on the tropical epr but mostly formed by differential asymmetric spreading subdivide the four longest spreading center systems on the northern transform free two thirds of the rise net rift propagation at migrating offsets has been into the faster pacific plate this causes right steps to migrate north left steps to migrate south and crust to be transferred to the east flank this pattern has prevailed for several million years judging from the oblique fracture zones pseudofaults mapped on the rise flanks with older marine data and geosat altimetry on this rise crest the difference in stress on two plates with very different velocities may control the direction of offset migration

lithospheric structure and compensation mechanisms of the galapagos archipelago volcanic islands of the galapagos archipelago are the most recent subaerial expression of the galapagos hotspot these islands and numerous seamounts are constructed mainly upon a broad volcanic platform that overlies very young 10 m y oceanic lithosphere just south of the active galapagos spreading center the 91 w fracture zone crosses the platform and creates an estimated 5 m y age discontinuity in the lithosphere major tectonic features of the galapagos include an unusually broad distribution of volcanic centers pronounced structural trends such as the nw se wolf darwin lineament wdl and a steep escarpment along the western and southern margins of the archipelago we use shipboard gravity and bathymetry data along with geosat geoid data to explain the tectonic and structural evolution of the galapagos region we model the gravity anomalies using a variety of compensation models including airy isostasy continuous elastic flexure of the lithosphere and an elastic plate with embedded weaknesses and we infer significant lithospheric strength variations across the archipelago the outboard parts of the southern and western escarpment are flexurally supported with an effective elastic thickness of 12 km this area includes the large shield volcanoes of fenandina and isabela islands where the lithosphere regionally supports these volcanic loads the central platform is weaker with an elastic thickness of 6 km or less and close to airy isostasy the greatest depths to the moho are located beneath eastern isabela island and the central platform thinner lithosphere in this region may account for the broad distribution of volcanoes the extended period of eruption of the central volcanoes and their reduced size the transition from strong to weak lithosphere along the southern escarpment appears to be abrupt within the resolution of our models and can be best represented by a free end or faultlike discontinuity also modeling the wdl as a lithospheric fault increases the match to the observed gravity anomalies the primary feature is the weak central platform whose existence is a logical convergence of several factors the 91 w transform age offset the possible increase in age of the lithosphere along the southern part of the platform due to ridge jumping and the formation of the central platform at a spreading ridge

the foundation seamount chain a first survey and sampling the foundation seamounts form a 1400 km long chain on the pacific plate from 32 s 127 w to the pacific antarctic spreading axis at 38 s 111 w previously only known from sparse single beam echosoundings and satellite altimetry we present here the first multibeam bathymetric survey and geological sampling results we confirm that the submarine topography correlates with the altimetry and that the chain is volcanic rather than tectonic or microcontinental in origin the chain can be divided up morphologically and geochemically into three section 1 west of 125 w large flat topped volcanoes composed of incompatible element depleted lavas 1 of a near ridge origin with little or no plume influence 2 between 125 and 115 w true intraplate volcanoes with incompatible element enrichment 1 9 generated over the foundation plume 3 east of 115 w e w trending volcanic ridges with compositions 2 0 0 3 suggestive of interaction between the plume and the pacific antarctic spreading axis on the spreading axis moderate incompatible element enrichments 0 8 cf 0 3 outside the foundation area also suggest plume influence it appears that the activity of the foundation plume in the last few million years has 1 significantly waned and 2 become wholly channeled towards the spreading axis the foundation plume may be in the process of dying

observations of ridge hotspot interactions in the southern ocean the evolution of ridge hotspot systems is not well understood in this investigation satellite derived marine gravity data are used in conjunction with underway bathymetric and magnetic anomaly profiles to investigate the nature of ridge hotspot interaction at four sparsely explored systems in the southern ocean these systems illustrate three different stages of ridge hotspot interaction in which a migrating spreading center approaches a hotspot pacific antarctic louisville passes over or is captured by the hotspot mid atlantic shona discovery and ultimately migrates away from the hotspot southeast indian kerguelen all of these systems show some evidence of discrete ridge jumps in the direction of the hotspot as the spreading center attempts to relocate toward the hotspot by asymmetric spreading interestingly these ridge jumps show no evidence of propagating offsets as have been seen on many other ridge hotspot systems a simple model predicts that typical plume excess temperatures can weaken the lithosphere sufficiently to promote asymmetric spreading and possibly allow a discrete ridge jump the presence of previously uncharted obliquely oriented aseismic ridges and gravity lineations between the ridge and the hotspot supports the notion of asthenospheric flux from the plume to the spreading center both before and after the time when the hotspot is ridge centered the azimuths of the aseismic ridges cannot be explained by plate kinematics alone they consistently extend from the ends toward the centers of the adjacent spreading segments suggesting some interaction between plume derived asthenospheric flux and local lithospheric structure the features discussed here also indicate that the transfer of asthenospheric material from the plume to the spreading center is influenced by the local plate boundary configuration and interaction with transform offsets