pacific interdecadal variability in this century s sea surface temperatures analysis of this century s sea surface temperatures over the pacific ocean reveals an interdecadal oscillation with a period of 15 20 years our results show that the well known 1976 77 climate regime shift is not unique but represents one of several phase transitions associated with this interdecadal oscillation also found around 1924 25 1941 42 and 1957 58 the oscillation s striking north south symmetry across the equator implies strong interactions between tropics and extratropics a mode with a period of approximately 70 years and an apparently different spatial pattern is also identified tentatively but has to be evaluated further using longer time series

an 15 000 year record of el nino driven alluviation in southwestern ecuador debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the pacific ocean in ecuador these storm induced events were dated by radiocarbon and the age of laminae that are less than 200 years old matches the historic record of el nino events from about 15 000 to about 7000 calendar years before the present the periodicity of clastic deposition is greater than or equal to 15 years thereafter there is a progressive increase in frequency to periodicities of 2 to 8 5 years this is the modern el nino periodicity which was established about 5000 calendar years before the present this may reflect the onset of a steeper zonal sea surface temperature gradient which was driven by enhanced trade winds

mesoscale physical and bio optical structure of the antarctic polar front near 170 w during austral spring as part of the u s joint global ocean flux study southern ocean program high resolution surveys of the antarctic polar front near 170 w were conducted during october november 1997 with a towed undulating system equipped with conductivity temperature depth and bio optical sensors transects along 170 w and two successive mapping surveys revealed zonal bands with sharp meridional gradients in east west velocity the polar front pf was characterized by a sea surface temperature drop from 1 6 to 1 6 c between 60 35 and 61 10 s with eastward velocities of 0 4 0 5 m s 1 in the core of the pf jet deep mixed layers 200 m were found within and north of the pf but mixed layers shoaled to 100 125 m south of the pf to the edge of loose ice at 62 3 s highest mixed layer chlorophyll concentrations 0 35 mg m 3 in late october along 170 w were to the south of the pf and associated with cold fresh water a large meander of the pf was observed with an alongfront wavelength of 175 km a cross front peak to peak amplitude of 100 km and an eastward phase propagation of 0 05 0 08 m s 1 all of which are consistent with its formation via hydrodynamic instability of the pf jet highest phytoplankton biomass was located just poleward of the center of the pf jet a high chlorophyll up to 1 1 mg m 3 50 by 50 km region was found downstream of the cyclonic bend associated with the meander a survey 7 5 days later revealed growth of this high biomass region so that chlorophyll was in excess of 0 8 mg m 3 over an 80 km cross front by at least 80 km alongfront region high biomass was observed to grow in place with respect to the meander rather than being displaced far downstream as would be expected from advection this pattern is consistent with meander driven upwelling of nutrients and or trace metals which in turn stimulates phytoplankton growth detailed cross sections of the pf reveal narrow 10 20 km wide bands or filaments of phytoplankton biomass that have temperature salinity properties distinct from surrounding water and are coherent for at least 120 km alongfront

detection of small scale heterogeneities at the inner core boundary 2018 elsevier b v the hemispherical pattern of seismic velocities in the uppermost inner core has been described at the global scale in many studies in this paper we investigate shorter scale heterogeneities in the vicinity of the inner core boundary icb using differential travel time and amplitude measurements between the pair of core phases pkp df and pkikp seismic events occurring close to sumatra and recorded at usarray stations in the distance range 132 142 are used to investigate the velocity and attenuation structure at the icb and in the uppermost 100 km of the inner core beneath eastern russia in this distance range pkp df and pkikp are difficult to separate due to their proximity in travel time we present a new method based on the envelope of the seismic signal to identify them following which we measure differential travel time residuals and amplitude ratios by comparison with synthetics computed using the direct solution method which allows us to take into account the correct phase shift of the pkikp we found that in our region of study the compressional velocity is slower in the uppermost inner core than the ak135 model however the sampled region is located in the eastern hemisphere generally considered as faster and more attenuating than the ak135 model this suggests significant regional departures from the simple hemispherical pattern reported in the literature we also deduce from the amplitude ratios that the attenuation is stronger than the global average at the top of the inner core in this region as expected from its location in the eastern hemisphere our results confirm the presence of a low attenuation zone at the top of the inner core followed by a highly attenuating layer centered around 35 km depth in the inner core as found in the eastern hemisphere in previous studies this zone is however thinner 15 km and more attenuating q reaching values less than 50

enso variability and teleconnections during glacial climates abstract understanding the origin of sub milankovitch and millennial scale abrupt climate change still poses a major challenge an important role of communicating the orbital scale forcing into abrupt climate change on millennial and centennial timescales has been hypothesized for the tropics in earlier studies based on the assumption of stationary teleconnections this paper presents a modelling study for the last glacial maximum and marine isotope stage 3 using the comprehensive climate model ccsm3 glacial boundary conditions and freshwater hosing at high latitudes of the north atlantic are imposed to mimic a heinrich stadial and dansgaard oeschger stadials and interstadials it is shown that glacial enso variability is strongly enhanced by a substantial slowdown of the atlantic meridional overturning circulation the simulations also suggest that glacial boundary conditions induce major modifications to enso teleconnections and that the blueprint of modern enso teleconnections should only be applied with caution to glacial climate periods

the evolution of el nino past and future abstract we review forecasts of the future of el nino and the southern oscillation enso a coupled instability of the ocean atmosphere system in the tropical pacific with global impacts enso in the modern world is briefly described and the physics of the enso cycle is discussed particular attention is given to the bjerknes feedback the instability mechanism which figures prominently in enso past and future our knowledge of enso in the paleoclimate record has expanded rapidly within the last 5 yr the enso cycle is present in all relevant records going back 130 kyr it was systematically weaker during the early and middle holocene and model studies indicate that this results from reduced amplification in the late summer and early fall a consequence of the altered mean climate in response to boreal summer perihelion data from corals shows substantial decadal and longer variations in the strength of the enso cycle within the past 1000 yr it is suggested that this may be due to solar and volcanic variations in solar insolation amplified by the bjerknes feedback there is some evidence that this feedback has operated in the 20th century and some model results indicate that it will hold sway in the greenhouse future but it is very far from conclusive the comprehensive general circulation models used for future climate projections leave us with an indeterminate picture of enso s future some predict more enso activity some less with the highly uncertain consensus forecast indicating little change

dynamics and thermodynamics of a warming event in a coupled tropical atmosphere ocean model abstract a simple coupled ocean atmosphere model similar to that of zebiak and cane is used to examine the dynamic and thermodynamic processes associated with el nino southern oscillation enso the model is run for 300 years the interannual variability which results is regular with a period of either 3 or 4 years quantized by the annual cycle the amplitude 1 5 m s 1 wind and 2 c sst anomalies period and structure of the interannual variability compare well with observations the model warm event is initiated in the spring prior to the event peak and is well described as an instability of the coupled system during instability growth the sea surface temperature sst anomaly is primarily generated by vertical upwelling processes the sst anomaly can be approximately described by the expression t t kth t where t is the sst anomaly t time h the upper layer thickness pycnocline perturbation and an effective damping time which includes heat loss to the atmosphere kt parameterizes

why do we have el nino quantifying a diabatic and nonlinear perspective using observations el nino due to its global impact on weather patterns ecosystems agriculture and public health has become as commonly known to the public as the recent global warming but why we have el nino is not yet as well answered as it may have been assumed linear theories have been successful in explaining the transition from the warm phase to the cold phase of the eastern tropical pacific that results from the rise and fall of el nino but failed to explain the asymmetry between the two phases a nonlinear theory for el nino has suggested that there exist two equilibrium states for the tropical pacific one is zonally symmetric or nearly so with the warm pool extending all the way to the eastern pacific and the other is strongly zonally asymmetric with the warm pool confined to the western half of the tropical pacific under this hypothesis enso results from the fact that under the current radiative heating both states are unstable resulting in the apparent wandering behavior in between these two states as seen in the observations to test this hypothesis the authors have obtained the best approximations for the two equilibrium states empirically using updated ocean assimilation data and quantified the stability of these two empirically obtained equilibrium states using two stability analysis methods the results suggest that the two states are unstable offering support for the nonlinear view of why we have el nino

seismic velocity and attenuation structures in the top 400 km of the earth s inner core along equatorial paths 1 we study seismic velocity and attenuation structures in the top 400 km of the earth s inner core based on modeling of differential traveltimes amplitude ratios and waveforms of the pkikp pkikp phases observed at the epicentral distance range of 120 141 and the pkpbc pkikp phases observed at the distance range of 146 160 along equatorial paths our data are selected from the seismograms recorded in the global seismographic network from 1990 to 2001 and many regional seismic networks the observed pkikp pkikp and pkpbc pkikp phases exhibit distinctive east west hemispheric patterns 1 at the distance ranges of 131 141 and 146 151 pkikp phases arrive about 0 3 s earlier than the theoretical arrivals based on the preliminary reference earth model prem for the pkikp phases sampling the eastern hemisphere 40 e 180 e of the inner core and about 0 4 s later for those sampling the western hemisphere 180 w 40 e at the distance range of 151 160 pkikp phases arrive about 0 7 s earlier than the predicted arrivals based on prem for those sampling the eastern hemisphere and about 0 1 s later for those sampling the western hemisphere 2 amplitude ratios of the pkikp pkikp phases at the distance range of 131 141 and of the pkikp pkpbc phases at the distance range of 146 151 are in general smaller for the pkikp phases sampling the eastern hemisphere than for those sampling the western hemisphere at distances greater than 151 the pkikp pkpbc amplitude ratios become indistinguishable for the two hemispheres these observations can be best explained by two different types of seismic velocity and attenuation models along equatorial paths one for each hemisphere in the top 400 km of the inner core for the eastern hemisphere the velocity structure has a velocity increase of 0 748 km s across the inner core boundary icb a small velocity gradient of 0 0042 km s 100 km in the top 235 km followed by a steeper velocity gradient of 0 1 km s 100 km extending from 235 km to 375 km and a velocity gradient of 0 01 km s 100 km in the deeper portion of the inner core the attenuation structure has an average q value of 300 in the top 300 km and an average q value of 600 in the deeper portion of the inner core for the western hemisphere the velocity structure has a velocity increase of 0 645 km s across the icb and a velocity gradient of 0 049 km s 100 km in the top 375 km the attenuation structure has an average q value of 600 in the top 375 km of the inner core our results suggest that the inner core hemispheric variations in velocity extend deeper than 375 km below the icb and the top 235 km of the inner core in the eastern hemisphere is anomalous compared to the rest of the inner core in having a small velocity gradient high velocity and high attenuation

silicon dynamics within an intense open ocean diatom bloom in the pacific sector of the southern ocean abstract an intense diatom bloom developed within a strong meridional silicic acid gradient across the antarctic polar front at 61 s 170 w following stratification of the water column in late october early november 1997 the region of high diatom biomass and the silicic acid gradient propogated southward across the seasonal ice zone through time with the maximum diatom biomass tracking the center of the silicic acid gradient high diatom biomass and high rates of silica production persisted within the silicic acid gradient until the end of january 1998 ca 70 d driving the gradient over 500 km to the south of its original position at the polar front the bloom consumed 30 to 40 m si oh 4 in the euphotic zone between about 60 and 66 s leaving near surface concentrations our observations indicate that high diatom biomass and high silica production rates previously observed in the marginal seas around antarctica also occur in the deep ocean near the polar front the bloom we observed propagated across the latitudinal band overlying the sedimentary opal belt which encircles most of antarctica implying a role for such blooms in the formation of those sediments comparison of our surface silica production rates with new estimates of opal accumulation rates in the abyssal sediments of the southern ocean which have been corrected for sediment focusing indicate a burial efficiency of 4 6 for biogenic silica that efficiency is considerably lower than previous estimates for the southern ocean

a seasonal progression of si limitation in the pacific sector of the southern ocean we conducted kinetic experiments using the radioisotope 32si to assess si limitation in the pacific sector of the southern ocean between 53 and 71 s from early december 1997 through mid march 1998 a diatom bloom developed near the edge of the pack ice in late november or early december and then propagated southward depleting silicic acid in surface waters from 45 to 5 m and occasionally to 1 m in an area that extended from 61 to 65 s we performed kinetic experiments of two kinds 26 multiple concentration experiments in which the specific rate of silicic acid uptake v was measured as a function of the extracellular silicic acid concentration si oh 4 and 61 two concentration experiments in which v was measured only at the ambient concentration si oh 4 a and one concentration 30 70 m above ambient the rate of si uptake was almost always limited by si oh 4 a in the si depleted waters within the bloom and to its north in those waters v increased with si oh 4 in accordance with the michaelis menten saturation function and si oh 4 a often limited v to 40 of its potential maximum vmax si limiting conditions followed the bloom southward during spring and summer and extended 500 km south of the antarctic polar front apf by late january seventeen of the 87 kinetic experiments showed no si limitation all but three of those non limiting sites were in si rich waters south of the apf however there was occasional relatively weak limitation of si uptake even south of the apf at si oh 4 a 40 m this unexpected result was caused by very low affinity for si uptake high ks in the michaelis menten function seventy percent of all measured ks values 49 of 70 were between 0 7 and 10 m a range only about twice that reported from elsewhere but the remaining 21 ks values ranged from 10 7 to 61 m eleven of these were 20 m which is extraordinarily high in comparison with most values from other oceans there was no clear tendency for ks to change with latitude or with si oh 4 a but there was an apparent seasonal progression in which both the highest ks values and the variability in ks increased with time the initial slopes of the kinetic curves vmax ks a measure of the ability to exploit low concentrations for the southern ocean diatom assemblages were very low compared to other regions of the ocean in the southern ocean data 52 of 73 initial slopes 71 are 2 mm h 1 while only one of 37 initial slopes 3 from other systems is that low the lowest slopes were observed south of the apf which may be a consequence of the high silicic acid concentrations that prevail in that region the ability to compete for silicic acid at low concentrations appears not to impart a significant competitive advantage in the si rich system south of the apf

interannual variability in a tropical atmosphere ocean model influence of the basic state ocean geometry and nonlinearity abstract the behavior of a tropical coupled atmosphere ocean model is analyzed for a range of different background states and ocean geometries the model is essentially that of cane and zebiak for the tropical pacific except only temporally constant background states are considered here for realistic background states and ocean geometry the model solutions feature oscillations of period of 3 5 yr by comparing the full model solution with a linearized version of the model it is shown that the basic mechanism of the oscillation is contained within linear theory a simple linear analog model is derived that describes the nature of the interannual variability in the coupled tropical atmosphere ocean system the analog model highlights the properties that produce coupled atmosphere ocean instability in the eastern ocean basin and the equatorial wave dynamics in the western ocean basin that are responsible for a delayed negative feedback into this instability growth the growth rate of the local instabil

enso like and enso induced tropical pacific decadal variability in cgcms abstractoutputs from coupled general circulation models cgcms are used in examining tropical pacific decadal variability tpdv and their relationships with el nino southern oscillation enso herein tpdv is classified as either enso induced tpdv eit or enso like tpdv elt based on their correlations with a decadal modulation index of enso amplitude and spatial pattern eit is identified by the leading eof mode of the low pass filtered equatorial subsurface temperature anomalies and is highly correlated with the decadal enso modulation index this mode is characterized by an east west dipole structure along the equator elt is usually defined by the first eof mode of subsurface temperature of which the spatial structure is similar to enso generally this mode is insignificantly correlated with the decadal modulation of enso eit closely interacts with the residuals induced by enso asymmetries both of which show similar spatial structures on the other hand elt is controlled by slowly varying oc

pkp travel times at near antipodal distances implications for inner core anisotropy and lowermost mantle structure abstract previous studies from pkp ab df differential travel times at large distances suggest that the central part of the inner core is very anisotropic these differential times however can be affected greatly by strong heterogeneity in the lowermost mantle here we examine a unique data set of pkp travel times from global digital and analog stations at near antipodal distances where the effects of both inner core anisotropy and mantle heterogeneity are the greatest our results show that the ab df residuals for the polar paths are consistently larger than those of the equatorial paths by over 3 4 standard deviations we also measured df and ab absolute times and found that the df residuals are negatively correlated with the ab df residuals while the ab residuals have a much weaker correlation with the ab df residuals we compare several mantle models with the data our results suggest that the mantle structure can explain part of the residuals of the equatorials paths but cannot explain the polar path anomalies these results strongly suggest that most of the ab df anomalies for the polar paths are likely from the inner core anisotropy and not from mantle heterogeneity assuming a uniform cylindrical anisotropy model the average inner core anisotropy amplitude is about 2 5 on the other hand equatorial paths from events in the west pacific and recorded at south america show a steep azimuthal change in ab df times about 4 s over a 60 azimuthal range the sharp change is well predicted by existing p and s tomographic models the azimuthal change occurs as the ab paths sweep across the great slow anomaly in the central pacific the high correlation between the p and s velocities suggests that the central pacific slow anomaly may be of thermal origin

melting induced stratification above the earth s inner core due to convective translation several observed properties of earth s solid inner core and liquid outer core remain enigmatic including an east west seismic asymmetry and the presence of a roughly 250 kilometre thick layer of reduced seismic velocity at the base of the outer core alboussiere et al now suggest a model that can produce both of these features based on experiment and numerical modelling they propose that simultaneous crystallization and melting at opposite sides of earth s inner core surface can result in a translational mode of thermal convection within the inner core which also introduces an asymmetry between hemispheres these authors show that simultaneous crystallization and melting at the surface of the earth s inner core can result in a translational mode of thermal convection within the inner core producing the observed stratified layer of reduced seismic velocity at the base of the outer core the dynamical model they propose also introduces an asymmetry between hemispheres that may explain the enigmatic east west asymmetry in seismic properties of the inner core in addition to its global north south anisotropy1 there are two other enigmatic seismological observations related to the earth s inner core asymmetry between its eastern and western hemispheres2 3 4 5 6 and the presence of a layer of reduced seismic velocity at the base of the outer core6 7 8 9 10 11 12 this 250 km thick layer has been interpreted as a stably stratified region of reduced composition in light elements13 here we show that this layer can be generated by simultaneous crystallization and melting at the surface of the inner core and that a translational mode of thermal convection in the inner core can produce enough melting and crystallization on each hemisphere respectively for the dense layer to develop the dynamical model we propose introduces a clear asymmetry between a melting and a crystallizing hemisphere which forms a basis for also explaining the east west asymmetry the present translation rate is found to be typically 100 million years for the inner core to be entirely renewed which is one to two orders of magnitude faster than the growth rate of the inner core s radius the resulting strong asymmetry of buoyancy flux caused by light elements is anticipated to have an impact on the dynamics of the outer core and on the geodynamo

regional variation of inner core anisotropy from seismic normal mode observations earth s solid inner core is surrounded by a convecting liquid outer core creating the geodynamo driving the planet s magnetic field seismic studies using compressional body waves suggest hemispherical variation in the anisotropic structure of the inner core but are poorly constrained because of limited earthquake and receiver distribution here using normal mode splitting function measurements from large earthquakes based on extended cross coupling theory we observe both regional variations and eastern versus western hemispherical anisotropy in the inner core the similarity of this pattern with earth s magnetic field suggests freezing in of crystal alignment during solidification or texturing by maxwell stress as origins of the anisotropy these observations limit the amount of inner core super rotation but would be consistent with oscillation

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

location and dynamics of the antarctic polar front from satellite sea surface temperature data the location of the antarctic polar front pf was mapped over a 7 year period 1987 1993 within images of satellite derived sea surface temperature the mean path of the pf is strongly steered by the topographic features of the southern ocean the topography places vorticity constraints on the dynamics of the pf that strongly affect spatial and temporal variability over the deep ocean basins the surface expression of the pf is weakened and the pf meanders over a wide latitudinal range near large topographic features width and temperature change across the front increase and large scale meandering is inhibited elevated mesoscale variability is seen within and downstream of these areas and may be the result of baroclinic instabilities initiated where the pf encounters large topographic features the strong correlations between topography and pf dynamics can be understood in the context of the planetary potential vorticity ppv or f h field mean ppv at the pf varies by more than a factor of 2 along its circumpolar path however at the mesoscale the pf remains within a relatively narrow range of ppv values around the local mean away from large topographic features the pf returns to a preferred ppv value of 25 10 9 m 1 s 1 despite large latitudinal shifts the mean paths of the surface and subsurface expressions of the pf are closely coupled over much of the southern ocean

tropical pacific ocean thermocline depth reconstructions for the last glacial maximum we evaluate the relationship between ten surface ocean 0 300 m hydrographic parameters and the spatial distribution of factor analyzed core top planktonic foraminiferal abundances in the tropical pacific ocean 24 n 24 s for core tops 3800 m the spatial distribution of the first three faunal factor loadings 88 of the variance are most highly correlated to subsurface variability mixed layer depth thermocline depth and resistant species percent rsp however rsp is not related to dissolution but is related to thermocline depth factor i mixed layer species g glutinata g ruber and factor iii g ruber can be distinguished from each other by low abundances of g glutinata in factor iii both assemblages spatially comprise the deep mixed layer region of the western tropical and equatorial pacific ocean but are associated with distinct water mass properties a combination of factor i and iii loadings shows a higher correlation to thermocline depth r 0 70 factor ii loadings dominated by thermocline dwelling species n dutertrei are most significantly correlated with the thermocline depth r 0 73 most factors show only marginally significant correlation to sea surface temperatures ssts indicating that sst is not the primary forcing factor on the planktonic foraminiferal species distributions in the tropical pacific a new transfer function was calculated to predict tropical pacific thermocline depth from planktonic foraminifera abundances using the imbrie kipp method ikm standard deviation of residuals 22 m 1 an additional 5 m error is attributed to low species counts in the core top database the modern analog technique mat was also used to predict thermocline depth standard deviation of residuals 21 m while last glacial maximum lgm thermocline depth changes by ikm and mat were generally within error estimated changes were geographically uniform suggesting an oceanographic response to climate forcing we estimate that the thermocline depth of the lgm was shallower than present by 20 m south of 8 s possibly due to a shift in the south pacific anticyclone to the northeast both the ikm and mat estimate a steeper east west thermocline slope along the equator suggesting that zonal wind stress walker circulation was intensified during the lgm collectively the thermocline estimates for the lgm suggest an equatorward compression of the climate zones in both hemispheres

impact of mountains on tropical circulation in two earth system models abstracttwo state of the art earth system models esms were used in an idealized experiment to explore the role of mountains in shaping earth s climate system similar to previous studies removing mountains from both esms results in the winds becoming more zonal and weaker indian and asian monsoon circulations however there are also broad changes to the walker circulation and el nino southern oscillation enso without orography convection moves across the entire equatorial indo pacific basin on interannual time scales enso has a stronger amplitude lower frequency and increased regularity a wider equatorial wind zone and changes to equatorial wind stress curl result in a colder cold tongue and a steeper equatorial thermocline across the pacific basin during la nina years anomalies associated with enso warm events are larger without mountains and have greater impact on the mean tropical climate than when mountains are present without mountains the centennial mean pacific walker circulation wea

depth extent of hemispherical inner core from pkp df and pkp cdiff for equatorial paths abstract differential travel times and amplitude ratios of pkp df and pkp cdiff partly including pkp bc for equatorial paths at epicentral distances from 150 to 160 are examined to discuss the radial structure of the uppermost 500 km of the inner core by using seismograms with a predominant frequency of approximately 0 5 hz 649 measurements are successfully collected including 295 and 354 readings for the eastern and western hemispheres respectively forward modeling with the reflectivity method suggests that the best fit velocity structures in the eastern and western hemispheres are 0 5 faster and 0 9 slower respectively than an average structure at the inner core boundary icb and that the velocity perturbations become linearly closer to the average with depth finally coinciding with the average at 400 km and 250 km below the icb respectively if ak135 is adopted for the structure above the icb in the eastern hemisphere the q values in the uppermost 250 km of the inner core and that in the range from 300 to 450 km below the icb are approximately 180 and 1000 respectively in contrast the q value in the western hemisphere is almost constant at approximately 300 400 in the uppermost 450 km of the inner core

investigating the role of the tibetan plateau in enso variability abstractthe role of the tibetan plateau tp in el nino southern oscillation enso variability is investigated using coupled model experiments with different topography setups removing the tp res

ocean atmosphere interaction and the tropical climatology part i the dangers of flux correction abstract this sequence of papers examines the role of dynamical feedbacks between the ocean and the atmosphere in determining features of the tropical climatology a stripped down intermediate coupled ocean atmosphere model is used to provide a prototype problem for the pacific basin here the authors contrast the fully coupled case with the case where flux correction is used to construct the climatology in the fully coupled case the climatology is determined largely by feedback mechanisms within the ocean basin winds driven by gradients of sea surface temperature sst within the basin interact with the ocean circulation to maintain sst gradients for all realistic cases these lead to a unique steady solution for the tropical climatology in the flux corrected case the artificially constructed climatology becomes unstable at sufficiently large coupling leading to multiple steady states as found in a number of coupled models using continuation methods we show that there is a topological change i

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

regionally heterogeneous uppermost inner core observed with hi net array studies of velocity structure in the earth s inner core and its volumetric variations illuminate our understanding of inner core dynamics and composition here we use an extensive number of seismograms recorded by the hi net array to construct complete empirical curves of pkpbc pkpdf differential traveltimes the nature of these curves implies that significant variations in traveltimes are accumulated during the passage of pkpdf waves through the uppermost inner core and rules out outer core structure effects uniform cylindrical anisotropy of a plausible strength in the uppermost inner core can also be ruled out as a cause of the observed traveltime variations because the range of sampled ray angles is too narrow the configuration and strength of inhomogeneities from a recent tomographic model of the lowermost mantle cannot account for the observed traveltime variations therefore we infer that either variations of p wave isotropic velocity on the scale of about hundred km and less are present in the uppermost inner core or the material may be organized in distinctive anisotropic domains and both of these features may be superimposed on long wavelength hemispherical structure if the former holds true the absolute magnitude of required p wave velocity perturbations from referent values is 0 60 0 10 in the quasi eastern and 1 55 0 15 in the quasi western hemisphere 0 85 0 05 and 1 10 0 10 respectively with the lowermost mantle correction the existence of these variations is a plausible physical outcome given that vigorous compositional convection in the outer core and variations in heat exchange across the inner core boundary may control the process of solidification

robust enso across a wide range of climates abstractel nino southern oscillation enso is a pronounced mode of climate variability that originates in the tropical pacific and affects weather patterns worldwide growing evidence suggests that despite extensive changes in tropical climate enso was active over vast geological epochs stretching millions of years from the late cretaceous to the holocene in particular enso persisted during the pliocene when a dramatic reduction occurred in the mean east west temperature gradient in the equatorial pacific the mechanisms for sustained enso in such climates are poorly understood here a comprehensive climate model is used to simulate enso for a broad range of tropical pacific mean climates characterized by different climatological sst gradients it is found that the simulated enso remains surprisingly robust when the east west gradient is reduced from 6 to 1 c the amplitude of enso decreases only by 30 40 its dominant period remains close to 3 4 yr and the spectral peak stays above red noise t

seismic velocity structure in the earth s outer core 1 we constrain seismic velocity structure in the earth s outer core by analyzing differential travel times waveforms and amplitude ratios of several pairs of core phases we use differential travel times and waveforms of pkpbc pkikp at 144 148 pkikp pkikp at 120 141 pkikp pkpbdiff at the pkp caustics distance range 141 145 and differential travel times and amplitude ratios of pkpab pkpbc at 146 159 to avoid the influence of the inner core anisotropy in velocity we only use the pkikp pkikp and the pkpbc pkikp observations whose pkikp phases sample the inner core along the equatorial paths paths with their ray angles being larger than 35 from the earth s rotation axis these observations show the following characteristics 1 both the observed pkpbc pkikp and pkikp pkikp differential travel times show a distinct east west hemispheric pattern pkikp phases arrive about 0 7 s earlier for those sampling the eastern hemisphere 40 e 180 e than those sampling the western hemisphere 180 w 40 e 2 the observed differential pkikp pkpbdiff travel time residuals also exhibit a hemispheric difference pkikp pkpbdiff differential travel times are about 0 9 s larger for those sampling the western hemisphere than those sampling the eastern hemisphere and 3 both the observed pkpab pkpbc differential travel times and pkpbc pkpab amplitude ratios show scatter overall these observations can be best explained by two one dimensional p velocity models one for each hemisphere at the bottom of the outer core the seismic data sampling the eastern hemisphere can be explained by prem at the bottom of the outer core while those sampling the western hemisphere can be explained by a lower velocity gradient at the bottom of the outer core which has reduced velocities relative to prem linearly increasing from 0 at 200 km above the inner core boundary icb to 0 35 at the icb different velocity gradients at the bottom of the outer core indicate that there may exist a compositional difference and or a large scale temperature difference there and that inner core formation processes may be different between the two hemispheres different inner core formation processes may produce different geometric inclusions of melt in the top of the inner core and thus may provide an explanation to the hemispheric variation of seismic velocity and attenuation in the top of the inner core the seismic data also suggest that the variation of seismic velocity in the tangential cylinder of the outer core if it exists is less than 0 1 we use a compressional wave tomographic model to study the travel time delays caused by the seismic heterogeneities in the mantle the tomographic model is unable to explain the scatter of the travel time data suggesting the existence of unknown strong small scale seismic heterogeneities in the mantle

absolute or convective instability in the equatorial pacific and implications for enso the el nino southern oscillation enso is driven by ocean atmosphere inter actions in the equatorial pacific and this variability is often attributed to coupled modes that are evidenced by the temporal stability analysis of anomaly models here the further diagnostic of absolute convective instability is considered which assesses whether small perturbations localized in space and time e g random wind disturbances lead to instabilities that develop in place or propagate away from the perturbed region it is shown that boundary conditions play a secondary role for this approach and that the development of large scale wave packets in the equato rial pacific basin is possible as in the case of an infinite domain as an illustration two simple coupled models are diagnosed that rely either on thermocline processes or zonal advective processes the model with thermocline processes is absolutely unstable and therefore develops intrinsic oscillations while the model with zonal advective processes is convectively unstable and therefore acts as a noise amplifier the identification of the two instability regimes may characterize different enso formation mechanisms as a response to random wind disturbances for the abso lutely unstable regime a standing enso like oscillation can develop in the equato rial pacific without involving boundary reflections while for the convectively unsta ble regime boundary reflections are essential copyright c

independent estimate of velocity structure of earth s lowermost outer core beneath the northeast pacific from pkikp pkpbc differential traveltime and dispersion in pkpbc the presence of a low velocity layer at the base of earth s outer core has been proposed however the seismic profile of the basal layer indeed has been poorly constrained in previous seismic studies the model parameters of the layer are substantially nonunique and there are tradeoffs between the seismic velocity of the layer and the properties of the mantle and inner core a more tightly constrained profile of the layer helps further examine the composition and dynamics of the layer in this study we obtained the p wave velocity profile of the basal layer beneath the northeast pacific based on two new seismic observations by analyzing seismograms of the hi net in japan the new observations are particularly sensitive to the layer structure and are relatively insensitive to the structure of the other parts of the earth 1 the frequency dispersion in p waves that graze or are diffracted at the inner core boundary pkpbc and pkpc diff and 2 differential traveltimes between the p waves reflected from the inner core boundary pkikp and those that turn above the boundary pkpbc the resulting velocity model of the lowermost outer core called f layer velocity model for the western hemisphere fvw has p wave velocities that lie between those of ak135 and the preliminary reference earth model prem and a velocity gradient that is slightly gentler than that of prem models with a uniform p wave velocity value within the layer are not supported by the observations for the region investigated which appears not to support the presence of a thick basal layer that is fe rich and dense there

the structure of the base of the outer core inferred from seismic waves diffracted around the inner core 1 we systematically searched for seismograms of waves diffracted around the inner core pkpcdiff from all the temporary seismic arrays with data currently available at the iris dmc as well as some permanent regional seismic arrays including f net in japan and grf in germany to assemble the largest high quality pkpcdiff database ever created pkpcdiff waves preferentially sample the base of the outer core and so contain important clues about earth structure in this region we measured pkpdf pkpcdiff differential traveltimes and pkpcdiff pkpdf amplitude ratios in the distance range of 154 160 and modeled the observations using grid searches and full wave theory synthetic seismograms the optimum model found by fitting the differential traveltimes has relatively low velocity at the base of the outer core as in ak135 which is consistent with many previous traveltime studies however the optimum model found by fitting the amplitude ratios pkpcdiff pkpdf does not exhibit this feature and instead is closer to prem the discrepancy may be explained by two likely causes one is that small scale topography or roughness on the icb tends to scatter energy away from pkpcdiff waves by generating trailing coda waves the other is that there exists a thin layer with relatively low q at the base of the outer core this might be expected if there are suspended solid particles at the base of the outer core as proposed decades ago both mechanisms could generate smaller pkpcdiff amplitudes without significantly affecting pkpcdiff traveltimes

geoarchaeological evidence from peru for a 5000 years b p onset of el nino for the tropical west coast of south america where el nino southern oscillation enso is most pronounced archaeological and associated paleontological deposits in northern peru revealed a major climate change at about 5000 years before the present yr b p the data implied the presence of stable warm tropical water as far south as 10 s during the early mid holocene about 8000 to 5000 yr b p these data suggest that enso did not occur for some millennia preceding 5000 yr b p when global and regional climate was warmer than today

seismic structure near the inner core boundary in the south polar region 1 it is crucial to obtain good spatial coverage of seismic data points for better understanding the earth s core but the core beneath the polar regions remains largely unexplored we analyzed differential traveltimes and amplitude ratios of core phases whose raypaths run beneath antarctica for determining the vp and qp structure near the inner core boundary in the south polar region the model we obtained south polar region model spr is described relative to the preliminary reference earth model prem as follows a 0 05 km s lower vp value at the top of the inner core a 1 5 times steeper vp gradient in the upper 300 km of the inner core a smaller qp 300 in the upper 300 km of the inner core and a 0 04 km s lower vp at the bottom of the outer core the vp values of spr in the lowermost outer core lie between those of prem and ak135 being closer to those of ak135 the lowermost outer core vp inside the tangent cylinder is thus close to the global average in the upper inner core spr has lower vp than ak135 and prem the spr vp profile is close to that of previous models for the western hemisphere although most of our data sample the eastern hemisphere of the inner core our results indicate that the inner core does not have a simple hemispherical variation as usually supposed our data support an eyeball shaped high vp anomaly with compressional velocity higher than in 1 d reference earth models concentrated to a smaller region beneath eastern asia

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

silica production in the monterey california upwelling system silica cycling was examined during a major upwelling event in monterey bay california strong upwcllingfavorable winds blew for 6 d with speeds up to 15 m s just prior to the study a survey of the region near the end of the wind event showed newly upwelled water at the north end of the bay with silicic acid concentrations up to 29 8 pm silicic acid concentrations decreased to a minimum of 15 i along the upwelling plume biogenic silica concentrations in the upwelling plume were generally between 2 and 5 pmol si liter i specific rates of biogenic silica production were co 2 d l in the freshly upwelled waters ald increased to 1 0 d l downplume kinetic experiments indicated that silicic acid concentrations throughout the upwelling plume supported maximal rates of silica production silica production rates were 1 pmol si liter tl i at the upwelling source increasing to 7 pmol liter d i downplume the upwelling event was followed by several days of calm winds creating ideal conditions for a phytoplankton bloom integrated biogenic silica concentrations between the surface and the 0 1 light depth during the calm period ranged from 56 to 566 mmol si m2 w th 8 of 11 stations exhibiting concentrations 100 mmol si mp2 specific production rates of biogenic silica wl re generally 1 d i with production rates between 10 and 30 pmol si liter i d i integrated silica production rate averaged 205 mmol si m d l range 13 1 140 mmol m 2 d l which is four times greater than the average rate observed for other coastal upwelling systems the maximum value observed i 140 mmol m 2 d l is nearly four times greater than levels ever observed before in the sea the high silica production rates seemed to result from an inefficient silicate pump on average 72 of the biogenic silica produced in the upwelling plume was retained in the surface waters resulting in biogenic silica concentrations of 6 7 13 7 pmol si liter i at stations where integrated production rates were 200 mmol si rn d l ambient silicic acid concentrations in thcsc same waters were generally 8 pm kinetic studies showed that these silicic acid concentrations supported nearly maximal rates of sil ca production substrate limitation of silica production became readily detectable at 5 pm si oh by that time 80 to 90 of the silicic acid and 90 of the nitrate in the upwellcd waters had been consumed indicating that substrate limitation of silica production played only a minor role in controlling the magnitude of both net si ica production and new production by diatoms

uppermost inner core heterogeneity from differential travel times of pkikp vs pkp bdiff and pkp cdiff phases we evaluate the average p wave velocity perturbations of the earth s uppermost inner core ic by analyzing two pairs of core phases pkikp pkp bdiff 456 observations in the distance range of 138 5 142 and pkikp pkp cdiff 1215 observations at 155 162 the former is most sensitive to inner core velocities in the depth range of 350 590 km and the latter from 0 to 100 km below the inner core boundary the differential travel time residuals exhibit the roughly east west hemispheric pattern especially beneath the pacific ocean here the separation between the two quasi hemispheres is near the 150 w meridian from pkp bdiff observations but possibly rotated toward a nw se orientation from pkp cdiff alternately a velocity heterogeneity could be present here in agreement with the previously reported pkikp vs pkpbc observations assuming the conventional definition for the ic quasi hemispheres i e the qeh between 0 and 180 e and the qwh between 0 and 180 w the quasi eastern hemisphere exhibits perturbations of 1 17 0 04 from pkikp pkp bdiff and 0 19 0 01 from pkikp pkp cdiff the corresponding perturbations in the quasi western hemisphere are of 0 06 0 06 and 0 19 0 02 respectively an anomalous ic zone beneath the indian ocean is not conspicuous in our pkikp pkp cdiff observations beneath the north atlantic the separation between the ic quasi hemispheres appears to be located between 60 w and 30 w from the pkp bdiff observations but it remains unresolved from the pkp cdiff data due to scarce observations here

simulation of el nino southern oscillation like variability in a global aogcm and its response to co2 increase abstract a 75 year integration of a coupled atmosphere ocean model is examined for tropical interannual variability the atmospheric model has interactive cloud and a seasonal cycle the fluxes of heat and salinity into the ocean component of the model are flux corrected the model has tropical variability that is qualitatively similar to that of the observed el nino southern oscillation enso the maximum amplitude of the model nino3 signal is approximately half that observed and the modeled enso timescale is greater than that observed in the first 50 years of the integration the model has eight warm events each event is one of two types one characterized by a standing sst anomaly in the central and eastern pacific and the other by a westward propagating sea surface temperature anomaly the majority of the model warm events are of the first type the first type of event is triggered by the eastward propagation of kelvin waves across the pacific and the second by westward propagation of warm temperat

abrupt shift in subsurface temperatures in the tropical pacific associated with changes in el nino radiocarbon 14c content of surface waters inferred from a coral record from the galapagos islands increased abruptly during the upwelling season july through september after the el nino event of 1976 sea surface temperatures ssts associated with the upwelling season also shifted after 1976 the synchroneity of the shift in both 14c and sst implies that the vertical thermal structure of the eastern tropical pacific changed in 1976 this change may be responsible for the increase in frequency and intensity of el nino events since 1976

dissolved fe in the upper waters of the pacific sector of the southern ocean the concentration of dissolved fe was determined in upper ocean waters along 170 degreesw between 53 and 72 degreess during four cruises between october 1997 and march 1998 as part of the us jgofs southern ocean antarctic polar frontal zone cruises fe concentrations were extremely variable in both space and time as a result of advection of meso scale eddys through the region observed values ranged from a maximum of 0 34 nm at 64 degreess in november next to the retreating ice edge to 0 075 nm in march at 71 degreess in the northern ross sea gyre in general the highest average mixed layer fe concentrations and the largest seasonal changes were observed in the two frontal zones at similar to 60 degreess and similar to 64 degreess formation of deep mixed layers during winter and the entrainment of sub surface waters enriched in fe is the primary source of this element to surface waters in this region of the southern ocean additionally upwelling of circumpolar deep water in the circumpolar current along its northern boundary at the polar front and its southern boundary at the southern antarctic circumpolar current front is an important mechanism supplying fe to surface waters in these areas throughout the summer comparison of integrated fe concentrations and th derived poc export and n drawdown all suggest that the maximum changes in these properties are comparable to those that would be predicted by fe availability fe concentrations determined by shipboard flow injection analysis measures et al mar chem 50 1995 3 were significantly higher than those found in replicate samples determined by shored based flameless atomic absorption spectrophotometry after preconcentration by chelation solvent extraction johnson et al mar chem 57 1997 137 the concentration differences which appear to be restricted to the upper 200 300 m do not appear to arise from different sampling or handling processes but instead are believed to result from the different sensitivity of the methods to organic fractions of fe in seawater c 2001 elsevier science ltd all rights reserved

iron and silicic acid concentrations regulate si uptake north and south of the polar frontal zone in the pacific sector of the southern ocean abstract we investigated the relative roles of fe and silicic acid availabilities in regulating si uptake rates across the polar frontal zone in the pacific sector of the southern ocean 59 68 s 170 w during the us jgofs antarctic environment southern ocean process study aesops meridional gradients in silicic acid concentration si oh 4 of about 0 25 0 56 m km 1 were observed in this area during austral spring and summer 1997 1998 with si oh 4 ranging from 32 si oh 4 and 15 no 3 uptake rates biogenic silica concentrations and si oh 4 no3 uptake ratios fe addition had little or no effect on si uptake rates in enrichments conducted in the low si waters north of the si gradient however fe addition increased si uptake rates 3 5 times over controls in enrichments conducted in the high si waters south of the gradient in both spring and summer fe addition decreased si oh 4 no3 uptake ratios by 2 5 times largely due to stimulation of no3 uptake rates zn addition had no effect on si oh 4 and no3 uptake rates short term 24 h si additions had varying effects on si uptake rates depending on season and location in spring additions of 40 m si to water from bottle enrichments conducted north of the si gradient in situ si oh 4 15 m did not increase si uptake rates initially but did increase uptake rates after 8 days in the summer enrichment north of the si gradient in situ si oh 4 5 m 50 m si additions doubled in situ si uptake rates in the initial water collected for the enrichment and increased si uptake rates as much as 16 fold during the experiment south of the si gradient where in situ si oh 4 was 40 m in both spring and summer si addition had no effect on in situ si uptake rates in the initial enrichment water nor on any si uptake rates measured during the experiment our results indicate that both fe and si availabilities regulate si uptake rates and silica production in the southern ocean along 170 w fe limitation appears to restrict si uptake rates south of the si gradient and plays a role in preventing si depletion south of the acc where ambient si oh 4 never fell below 40 m during 1997 1998 our experiments in the seasonal ice zone at 62 suggest that si uptake in this area switched from being fe limited in the spring when in situ si oh 4 was 40 m to si limited in the summer when si oh 4 was

productivity of the glacial ocean discussion of the iron hypothesis an increase in the productivity of the glacial age southern ocean has been postulated to explain the decrease in pc0 of the atmosphere observed in ice cores a plausible mechanism has been proposed elsewhere that productivity is limited by the availability of fe in this region and that the greater supply of eolian dust during glacial time removed this limit recently published evidence from cores from the southern ocean suggests that in fact there was no change in productivity in the assumed manner glacial age productivity was indeed greatly increased in the equatorial pacific and in the eastern boundary upwelling systems the cause presumably was the mechanical action of glacial age winds rather than a greater supply of fe however a role of increased supply of micronutrients from the continents in the increase of equatorial productivity during glacial time cannot be excluded such enhancement from increased supply of dust would have the interesting corollary of more efficient export transfer to depth possibly contributing to nutrient depletion in glacial age deep intermediate waters there is some indication as well of a general decrease in nutrient content in the tropical thermocline in the western pacific during the last several million years a depletion that may have been fostered by increasing supply of dust from emerging asian highlands alternative explanations are available the case for fe as a major modifier of productivity and biogenic sedimentation on geological time scales cannot be made in the absence of criteria diagnostic for fe supply as opposed to stirring and upwelling

phytoplankton biomass and photosynthetic competency in the summertime mertz glacier region of east antarctica abstract vertical profiles of water temperature salinity beam transmission density pressure wind speed wind direction phytoplankton biomass chlorophyll a chl a plus phaeophytin a and photosynthetic competency by fast repetition rate fluorometry are presented for the mertz glacier region east antarctica for a 3 week period during the austral summer 2000 2001 injection of low salinity water from the melting of the ice pack formed a shallow ca 25 m mixed layer offshore two distinct deep mixing features were observed associated to varying degrees with high chlorophyll levels and high photosynthetic competency along the adelie land coast a deep mixing layer 1400 m with chl a concentrations of 386 mg m 2 and elevated fv fm 0 5 was observed at the eastern end of the study area along a seaward extension of fast ice a bloom of phaeocystis antarctica bloom formed within a shallow 24 m mixed layer with surface chl a concentrations of ca 8 mg m 3 and elevated fv fm 0 5 this feature also had high surface salinity 34 and was contiguous with a deep mixing feature 236 m frrf parameters fv fm and psii were strongly suppressed in surface waters

hemispherical structure in inner core velocity anisotropy 1 we investigate the hemispherical pattern in inner core velocity anisotropy using a new and independent high quality data set of pkpbc pkpdf and pkpab pkpdf body wave observations our data show no evidence for a tilted anisotropy axis with respect to the earth s rotation axis and is significantly better fit by a model with 4 4 anisotropy in the western hemisphere and only 1 0 in the eastern hemisphere than by a model of uniform anisotropy we carry out variance minimization and find the boundaries between the hemispheres at lines of constant longitude at 14 e and 151 w variance minimization enables us to extract the imprint of hemispherical structure from all of the data and not just polar paths resulting in boundaries which are nearly 30 from the results of previous studies the high quality of the data allows us to provide robust evidence that the isotropic velocity in the eastern hemisphere is 0 2 lower than in the western hemisphere in the top 660 km of the inner core our data set also suggests an increase in inner core anisotropy in the eastern hemisphere from 1 to around 6 at depths deeper than 660 km indicating that the hemispherical pattern in anisotropy may disappear at greater depths the presence of hemispherical structure rules out mechanisms for creating anisotropy which are unable to sustain longitudinal variations in the inner core furthermore steady inner core superrotation of the order of 0 1 year would eradicate the hemispherical differences though inner core oscillation would still be permissible

intricate heterogeneous structures of the top 300 km of the earth s inner core inferred from global array data i regional 1d attenuation and velocity profiles abstract we apply a waveform inversion method based on simulated annealing to complex core phase data observed by globally deployed seismic arrays and present regional variation of depth profiles of attenuation and velocity for the top half of the inner core whereas measured attenuation parameters exhibit consistent trends for data sampling the eastern hemisphere of the inner core for the western hemisphere there is a remarkable difference between data sampling the inner core beneath africa w1 and beneath north america w2 obtained attenuation profiles suggest that intricate heterogeneities appear to be confined in the top 300 km the profile for the eastern hemisphere has a high attenuation zone in the top 150 km that gradually diminishes with depth conversely for the western hemisphere the profile for w1 shows constant low attenuation and that for w2 represents a gradual increase from the inner core boundary to a peak at around 200 km depth velocity profiles obtained from differential traveltimes between pkp df and pkp cd bc phases for the eastern and western hemispheres are respectively about 0 8 faster and 0 6 slower than the reference model at the top of the inner core and the difference nearly disappears at about 200 km depth our result suggests the presence of intricate quasi hemispherical structures in the top 200 300 km of the inner core

a stability analysis of tropical ocean atmosphere interactions bridging measurements and theory for el nino abstract interactions between the tropical oceans and atmosphere permit a spectrum of natural modes of oscillation whose properties period intensity spatial structure and direction of propagation depend on the background climatic state i e the mean state this mean state can be described by parameters that include the following the time averaged intensity of the pacific trade winds the mean depth h of the thermocline and the temperature difference across the thermocline t a stability analysis by means of a simple coupled ocean atmosphere model indicates two distinct families of unstable modes one has long periods of several years involves sea surface temperature variations determined by vertical movements of the thermocline that are part of the adjustment of the ocean basin to the fluctuating winds requires a relatively deep thermocline and corresponds to the delayed oscillator the other family requires a shallow thermocline has short periods of a year or two has sea surface tempe

reduced enso variability at the lgm revealed by an isotope enabled earth system model studying the el nino southern oscillation enso in the past can help us better understand its dynamics and improve its future projections however both paleoclimate reconstructions and model simulations of enso strength at the last glacial maximum lgm 21 ka bp have led to contradicting results here we perform model simulations using the recently developed water isotope enabled community earth system model icesm for the first time model simulated oxygen isotopes are directly compared with those from enso reconstructions using the individual foraminifera analysis ifa we find that the lgm enso is most likely weaker comparing with the preindustrial the icesm suggests that total variance of the ifa records may only reflect changes in the annual cycle instead of enso variability as previously assumed furthermore the interpretation of subsurface ifa records can be substantially complicated by the habitat depth of thermocline dwelling foraminifera and their vertical migration with a temporally varying thermocline

particle fluxes to the interior of the southern ocean in the western pacific sector along 170 w abstract an array of five bottom tethered moorings with 19 parflux time series sediment trap at three depths 1 and 2 km below the surface and 0 7 km above the sea floor was deployed in the western pacific sector of the southern ocean along 170 w the five stations were selected to sample settling particles in the main hydrological zones of the southern ocean the sampling period spanned 425 days november 28 1996 january 23 1998 and was divided into 13 or 21 synchronized time intervals a total of 174 sequential samples were recovered and analyzed to estimate fluxes of total mass tmf organic carbon carbonate biogenic silica and lithogenic particles the fluxes of biogenic material were higher than anticipated challenging the notion that the southern ocean is a low productivity region organic carbon fluxes at 1 km depth within the polar frontal zone and the antarctic zone were relatively uniform 1 7 2 3 g m 2 yr 1 and about twice the estimated ocean wide average ca 1 g m 2 yr 1 carbonate fluxes were also high and uniform between the subantarctic front and ca 64 s 11 13 g m 2 yr 1 a large fraction of the carbonate flux in the antarctic zone was due to the presence of pteropod shells coccoliths were found only to the north of the polar front and calcium carbonate became the dominant phase in the subantarctic zone in contrast carbonate particles were nearly absent near 64 s latitudinal variations in biogenic silica fluxes were substantial the large opal flux 57 g m 2 yr 1 measured in the antarctic zone suggests that opal productivity in this region has been previously underestimated and helps to explain the high sedimentary opal accumulation often found south of the polar front unlike biogenic material fluxes of lithogenic particles were among the lowest measured in the open ocean 0 12 0 05 g m 2 yr 1 reflecting a very low dust input

phytoplankton pigment distribution in relation to silicic acid iron and the physical structure across the antarctic polar front 170 w during austral summer in order to study the factors controlling the phytoplankton distribution across the antarctic polar frontal region pfr surface pigment samples were collected during austral summer january february 1998 near 170 w both the polar front pf and the southern antarctic circumpolar current front saccf were regions of enhanced accumulation of phytoplankton pigments the mesoscale survey across the pf revealed two distinct phytoplankton assemblages on either side of the front the phytoplankton community was dominated by diatoms south of the pf and by nanoflagellates primarily by prymnesiophytes to the north surprisingly chlorophyll a concentrations did not correlate with mixed layer depths however an increase of the dominance of diatoms over prymnesiophytes was observed with decreasing mixed layer depths despite this relationship we conclude that the average light availability in the mixed layer was not an important factor influencing the shift in phytoplankton composition across the pf although no correlation was found between the surface distribution of the major phytoplankton taxa and dissolved iron or silicic acid concentrations the location of the strongest vertical gradient in silicic acid and iron concentration coincides with the maximum abundance of diatoms we conclude that the difference in taxonomic composition is a result of increased silicic acid and iron flux to the upper mixed layer as a result of the increased vertical gradient of these key nutrients south of the front

historical changes in el nino and la nina characteristics in an ocean reanalysis 1 the variation of el nino southern oscillation enso events from the mid nineteenth century until the beginning of the twenty first century is explored using an ocean reanalysis a comparison of the reanalysis with three sea surface temperature reconstructions shows that the timing of events is similar in all four products however there are important differences in the strength and location of events the difference between the reconstructions is sometimes larger than the difference between the reanalysis and a given reconstruction these differences are larger in the first half of the record a period for which there are relatively sparse observations the reanalysis is used to explore decadal variability and trends in the frequency duration and propagation direction of enso events there is considerable decadal variability of these enso characteristics with the time between events ranging from several months to ten years and the duration of enso varying from 5 to 27 months as has been previously shown for the strength and location of enso there is little overall trend in the characteristics having a three dimensional representation of the ocean from the reanalysis allows exploration of subsurface changes during enso an analysis of subsurface anomalies shows that during enso events the subsurface anomalies are highly correlated with the strength of surface anomalies over the 140 year period overall there is no evidence that there are changes in the strength frequency duration location or direction of propagation of el nino and la nina anomalies caused by global warming during the period from 1871 to 2008

relationship of d structure with the velocity variations near the inner core boundary 1 variations in regional differential times between pkikp i and pkikp i have been attributed to hemispheric p velocity variations of about 1 in the upper 100 km of the inner core referred to as hic the top of the inner core appears relatively fast beneath asia where d is also fast an alternative interpretation could be the lateral variation in p velocity at the lowermost outer core hoc producing the same differential times to resolve this issue we introduce the diffracted pkp phase near the b caustic bdiff in the range of 139 145 epicenter distances and the corresponding differential times between bdiff and pkikp and pkikp as observed on broadband arrays due to the long wavelength nature of bdiff we scaled the s wave tomography model with k values k dlnvs dlnvp to obtain large scale p wave velocity structure in the lower mantle as proposed by earlier studies waveform synthetics of bdiff constructed with small k s predict complex waveforms not commonly observed confirming the validity of large scaling factor k with p velocity in lower mantle constrained at large scale the extra travel time constraint imposed by bdiff helps to resolve the hoc hic issue our preliminary results suggest k 2 for the lowermost mantle and support hic hypothesis an important implication is that there appears to be a relationship of d velocity structures with the structures near the inner core boundary via core dynamics

ocean atmosphere interaction and the tropical climatology part ii why the pacific cold tongue is in the east abstract the influence of coupled process on the climatology of the tropical pacific is studied in a model for the interaction of equatorial sst the associated component of the walker circulation and upper ocean dynamics in this part the authors show how different physical mechanisms affect the spatial pattern of the pacific warm pool and cold tongue in this coupled climatology when model parameters give a suitable balance between effects of upwelling and thermocline depth on sea surface temperature and for suitable atmospheric parameters a good prototype for the observed cold tongue configuration is produced this is largely determined by coupled ocean atmosphere processes within the basin presence of an easterly wind s component produced by factors external to the pacific basin can be important in setting up a cooling tendency but this is magnified and modified by a chain of nonlinear feedbacks between trade winds and ocean dynamics affecting the sst gradient within the basin these feedbacks d

seismic structures in the earth s inner core below southeastern asia documenting seismic heterogeneities in the earth s inner core ic is important in terms of getting an insight into its history and dynamics a valuable means for studying properties and spatial structure of such heterogeneities is provided by measurements of body waves refracted in the vicinity of the inner core boundary icb here we investigate eastern hemisphere of the solid core by means of pkpbc pkpdf differential travel times that sample depths from 140 to 360 km below its boundary we study 292 polar and 133 equatorial residuals measured over the traces that probe roughly the same volume of the ic in both planes equatorial residuals show slight spatial variations in the sampled ic volume mostly below the level of 0 5 whereas polar residuals are up to three times as big direction dependent and can exhibit higher local variations the measurements reveal fast changes in seismic velocity within a restricted volume of the ic we interpret the observations in terms of anisotropy and check against several anisotropy models few of which have been found capable of fitting the residuals scatter we particularly quantify the model where a dipping discontinuity separates fully isotropic roof of the ic from its anisotropic body whereas the depth of isotropy anisotropy transition increases in southeast direction from 190 km below southeastern asia off the coast of china to 350 km beneath australia another acceptable model cast in terms of localized anisotropic heterogeneities is valid if 33 largest polar measurements over the rays sampling a small volume below southeastern asia and the rest of polar data are treated separately this model envisages almost isotropic eastern hemisphere of the ic at least down to the depth of 360 km below the icb and constrains the anisotropic volume only to the ranges of north latitudes from 18 to 23 east longitudes from 125 to 135 and depths exceeding 170 km the anisotropy strength in either model is about 2 further effective pursuit of the models presents challenges in terms of resolution and coverage and basically requires a significant dataset extension

hemispherical variations in seismic velocity at the top of the earth s inner core knowledge of the seismic velocity structure at the top of the earth s inner core is important for deciphering the physical processes responsible for inner core growth1 2 3 previous global seismic studies4 5 6 7 8 9 have focused on structures found 100 km or deeper within the inner core with results for the uppermost 100 km available for only isolated regions10 11 12 here we present constraints on seismic velocity variations just beneath the inner core boundary determined from the difference in travel time between waves reflected at the inner core boundary and those transmitted through the inner core we found that these travel time residuals observed on both global seismograph stations and several regional seismic networks are systematically larger by about 0 8 s for waves that sample the eastern hemisphere of the inner core 40 e to 180 e compared to those that sample the western hemisphere 180 w to 40 e these residuals show no correlation with the angle at which the waves traverse the inner core this indicates that seismic anisotropy is not strong in this region and that the isotropic seismic velocity of the eastern hemisphere is about 0 8 higher than that of the western hemisphere

ocean response to wind variations warm water volume and simple models of enso in the low frequency approximation abstract physical processes that control enso are relatively fast for instance it takes only several months for a kelvin wave to cross the pacific basin tk 2 months while rossby waves travel the same distance in about half a year compared to such short time scales the typical periodicity of el nino is much longer t 2 7 yr thus enso is fundamentally a low frequency phenomenon in the context of these faster processes here the author takes advantage of this fact and uses the smallness of the ratio ek tk t to expand solutions of the ocean shallow water equations into power series the actual parameter of expansion also includes the oceanic damping rate using such an expansion referred to here as the low frequency approximation the author relates thermocline depth anomalies to temperature variations in the eastern equatorial pacific via an explicit integral operator this allows a simplified formulation of enso dynamics based on an integro differential equation within this formulation

heterogeneity and anisotropy of earth s inner core seismic observations provide strong evidence that earth s inner core is anisotropic with larger velocity in the polar than in the equatorial direction the top 60 80 km of the inner core is isotropic evidence for an innermost inner core is less compelling the anisotropy is most likely due to alignment of hcp hexagonal close packed iron crystals aligned either during solidification or by deformation afterward the existence of hemispherical variations used to be controversial but there is now strong evidence from both seismic body wave and normal mode observations showing stronger anisotropy less attenuation and a lower isotropic velocity in the western hemisphere two mechanisms have been proposed to explain the hemispherical pattern either a inner core translation wherein one hemisphere is melting and the other is solidifying or b thermochemical convection in the outer core leading to different solidification conditions at the inner core boundary neither is yet able to explain all se