youngest volcanism about 1 million years ago at kahoolawe island hawaii abstract young volcanic deposits in kahoolawe island cutting up through the caldera filling lava colluvium and talus in the west wall of kanapou bay had long been stratigraphically considered the rejuvenated stage products new k ar ages combined with magnetic polarity data show that young volcanism was at about 0 98 1 04 ma and indicate no substantial quiescence between the filling of the caldera and the young volcanism this result and the tholeiitic characteristics of the young deposits suggest they are a component of late shield stage volcanism

role of orbital forcing in east asian monsoon climates during the last 350 kyr evidence from terrestrial and marine climate proxies from core rc14 99 proxy records of northeast asian precipitation marine pollen and northwest pacific sea surface temperatures marine fauna contain concentrations of variance frequency peaks coincident with those of orbital variations eccentricity obliquity and precession time series of these monitors of various components of the east asian monsoon system are coherent with changing solar insolation and climate boundary conditions ice volume snow cover albedo at 41 and 23 kyr frequencies winter sea surface temperature wsst maxima are in phase with global ice volume minima at all three milankovitch frequencies 100 41 and 23 kyr periods wsst maxima are also linearly related to summer insolation at 30 n lagging radiation maxima by 55 3 5 kyr across the precessional frequency band 23 kyr period our east asian monsoon rainfall indicator cryptomeria reaches highest values immediately following summer insolation maxima during periods of low ice volume interglacials across the eccentricity frequency band 100 kyr period cryptomeria maxima are in phase with ice volume minima at the higher frequency of orbital precession monsoon rainfall lags both summer radiation maxima 125 8 kyr and ice volume minima 60 3 8 kyr whereas much of the variation in northwest pacific wsst can be attributed to summer radiation forcing and changes in global climate mechanisms driving east asian monsoon precipitation are more complex involving other possibly internal factors

nb in hawaiian magmas constraints on source composition and evolution abstract published th and nb data for basalts from 11 volcanoes from the hawaiian islands and emperor seamount chain yield a nearly uniform concentration ratio of nb th 15 2 1 7 the basalts include tholeiites with nb concentrations ranging down to 4 ppm and alkali basalts with a maximum nb concentration of 127 ppm however nephelinites and melilitites from the honolulu volcanic series have much lower nb th ratios and are excluded from this analysis using the average th u ratio of 3 2 for the five volcanoes of the island of hawaii this corresponds to a nb u 48 6 5 3 which is indistinguishable from the mean value of a worldwide sample of oib and morb nb u 47 10 given by direct nb and u analyses in contrast the earth s primordial mantle had a nb th ratio of 8 6 and a nb u ratio of 30 these data demonstrate that none of the hawaiian volcanoes not even the isotopically most nearly primitive koolau series from oahu has refractory elements derived from an undifferentiated or primordial portion of the mantle an even less likely source is recycled continental crust which has a mean nb u ratio of 10 a consideration of the chromatographic theory of metasomatism and comparison with metasomatic rocks observed in the continental crust show that large scale metasomatism in the mantle which would be needed to account for the very large total volume of hawaiian emperor magmas is expected to produce a strongly zoned mantle yielding chemically highly heterogeneous magmas unless the metasomatic column has reached a steady state the expected heterogeneity is difficult to reconcile with observed chemical homogeneity of the main stage tholeiitic magmas the late stage alkali basalts and the nephelinites must be excluded from this consideration because their isotopic composition shows that they are derived from the depleted lithosphere or asthenosphere the consequence of a steady state metasomatic column would be that the tholeiitic melt itself represents the metasomatic fluid the model of recycled oceanic crust and lithosphere is consistent with the chemical and isotopic data the mantle that originally produced this oceanic crust was already depleted and rehomogenized as a result of prior separation of continental crust uniform source ratios of nb u and ba rb were established during this rehomogenization process the general enrichment of the hawaiian source and the chemical and isotopic heterogeneities found in the present day lavas were produced during the differentiation into oceanic crust and lithosphere secondary pb 1bpb model ages indicate that this crust was probably produced 1 ga ago

perspectives on basaltic magma crystallization and differentiation lava lake blocks erupted at mauna loa volcano summit hawaii explosive eruptions at mauna loa summit ejected coarse grained blocks free of lava coatings from moku aweoweo caldera most are gabbronorites and gabbros that have 0 26 vol olivine and 1 29 vol oikocrystic orthopyroxene some blocks are ferrogabbros and diorites with micrographic matrices and diorite veins 2 cm cross cut some gabbronorites and gabbros one block is an open textured dunite the mgo of the gabbronorites and gabbros ranges 7 21 wt those with mgo 10 wt have some incompatible element abundances zr y ree positive eu anomalies lower than those in mauna loa lavas of comparable mgo gabbros mgo 10 wt generally overlap lava compositions olivines range fo83 58 clinopyroxenes have mg s 83 62 and orthopyroxene mg s are 84 63 all evolved beyond the mineral mg s of mauna loa lavas plagioclase is an75 50 ferrogabbro and diorite blocks have 3 5 wt mgo tio2 3 2 5 4 k2o 0 8 1 3 la 16 27 ppm and a diorite vein is the most evolved sio2 59 k2o 1 5 la 38 ppm they have clinopyroxene mg s 67 46 and plagioclase an57 40 the open textured dunite has olivine fo83 5 seven isotope ratios are 87sr 86sr 0 70394 0 70374 and 143nd 144nd 0 51293 0 51286 and identify the suite as belonging to the mauna loa system gabbronorites and gabbros originated in solidification zones of moku aweoweo lava lakes where they acquired orthocumulate textures and incompatible element depletions these features suggest deeper and slower cooling lakes than the lava lake paradigm kilauea iki which is basalt and picrite clinopyroxene geobarometry suggests crystallization at 1 kbar p highly evolved mineral mg s 75 are largely explained by cumulus phases exposed to evolving intercumulus liquids causing compositional shifts ferrogabbro and diorite represent segregation veins from differentiated intercumulus liquids filter pressed into rigid zones of cooling lakes clinopyroxene geobarometry suggests 300 bar p open textured dunite represents olivine melt mush precursor to vertical olivine rich bodies as in kilauea iki its fo83 5 identifies the most primitive lake magma as 8 3 wt mgo mass balancing and melts show that such a magma could have yielded both ferrogabbro and diorite by 50 fractional crystallization but under different fo2 fmq 250 bar led to diorite and fmq 250 bar yielded ferrogabbro these segregation veins documented as similar to those of kilauea testify to appreciable volumes of rhyolitic liquid forming in oceanic environments namely sio2 rich veins are intrinsic to all shields that reached caldera stage to accommodate various sized cooling differentiating lava lakes

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

petrology of ultramafic and mafic xenoliths in picrite of kahoolawe island hawaii a picrite lava 22 wt mgo 35 vol ol along the western shore of the 1 3 1 4 ma kahoolawe tholeiitic shield hawaii contains small xenoliths of harzburgite lherzolite norite and wehrlite the various rock types have textures where either orthopyroxene clinopyroxene or plagioclase is in a poikilitic relationship with olivine the mg s of the olivine orthopyroxene and clinopyroxene in this xenolith suite range between 86 and 82 spinel mg s range from 60 to 49 and plagioclase is an75 80 a 87sr 86sr ratio for one ol norite xenolith is 0 70444 in comparison the host picrite has olivine phenocrysts with an average mg of 86 2 range 87 5 84 5 and a whole rock 87sr 86sr ratio of 0 70426 textural and isotopic information together with mineral compositions indicate that the xenoliths are related to kahoolawe tholeiitic magmatism but are not crystallization products of the magma represented by their host picrite rather the xenoliths are crystalline products of earlier primitive liquids feo mgo ranging 1 to 1 3 at 5 9 kbar in the cumulate environment of a magma reservoir or conduit system the presence of ultramafic xenoliths in picrite but not in typical kahoolawe tholeiitic lava 6 9 wt mgo is consistent with replenishment of reservoirs by dense mg rich magma emplaced beneath resident less dense tholeiitic magma mg rich magmas have proximity to reservoir cumulate zones and are therefore more likely than fractionated residual liquids to entrain fragments of cumulate rock

petrogenesis of alkaline basalts from socorro island mexico trace element evidence for contamination of ocean island basalt in the shallow ocean crust postcaldera mafic volcanism on socorro island mexico an island located in the eastern pacific ocean on a segment of a mid ocean ridge spreading center abandoned at 3 5 ma dominantly comprises alkalic basalt hawaiite and mugearite with subordinate mildly alkalic transitional basalt most major element data are consistent with differentiation of alkalic basalt to hawaiite and mugearite by up to 50 fractionation of plagioclase clinopyroxene olivine fe ti oxides high field strength element abundances are consistent with this interpretation and the narrow range in zr nb suggests that parental magmas formed by similar degrees of partial melting of a relatively homogeneous mantle source sr and nd isotopic ratios exhibit relatively narrow ranges 0 7031 0 7032 0 5128 0 5130 respectively despite this a subset of the alkalic basalts has negative ce anomalies and abundances of p2o5 ba y and some rare earth elements in excess of those predicted by fractional crystallization models these chemical features require open system processes the observed heterogeneities are perhaps best explained by assimilation of ocean crustal components by basalt in a shallow magma reservoir regional mantle heterogeneity is evident from elemental and isotopic data for mildly alkalic transitional basalt from socorro island mugearite from san benedicto island and submarine basalts from near socorro island evidence presented here indicates that compositional variations in ocean island basalts can be introduced by ocean crustal contamination and underscores the importance of considering this source of chemical heterogeneity in basalts before characterizing associated mantle

multidecadal variations in the early holocene outflow of red sea water into the arabian sea we present holocene stable oxygen isotope data from the deep arabian sea off somalia at a decadal time resolution as a proxy for the history of intermediate upper deep water these data show an overall 18o reduction by 0 5 between 10 and 6 5 kyr b p superimposed upon short term 18o variations at a decadal centennial timescale the amplitude of the decadal variations is 0 3 prior and up to 0 6 subsequent to 8 1 kyr b p we conclude from modeling experiments that the short term 18o variations between 10 and 6 5 kyr b p most likely document changes in the evaporation precipitation balance in the central red sea changes in water temperature and salinity cause the outflowing red sea water to settle roughly 800 m deeper than today

the role of tonalite and diorite in mauna kea volcano hawaii magmatism petrology of summit region leucocratic xenoliths anomaly and poikilitic texture indicate a cumulate origin leucocratic diorite 50 53 wt sio2 1 2 4 wt k2o xenoliths coexist with the tonalite these have intergranular andesine oligoclase 68 85 vol of an50 15 evolved clinopyroxene mg number

south asian monsoon climate change and radiocarbon in the arabian sea during early and middle holocene the 1 4 c ages of planktonic foraminifers globigerinoides sacculifer bracketing the younger dryas in a 1 8 o record of globigerinoides ruber from a laminated sediment core on the pakistani continental margin suggest thatsurface reservoir ages in the arabian sea were in excess of 1000 years during the deglaciation a least squares error fit of a detailed 1 4 c chronology to the atmospheric tree ring record gave variable early holocene reservoir ages between 780 and 1120 years well above the prebomb value of 640 years mid holocene reservoir ages are less well constrained but were probably closer to the prebomb value the method used to fit individual core sections to the tree ring record was designed to require only a rough a priori estimate of the time spans which in the core presented here were taken from each section s range of 1 4 c ages a significant 220 year quasi oscillation was present in the 1 8 o record during the early holocene but not thereafter this frequency and amplitude pattern resembles an early holocene 207 to 227 year oscillation previously observed in the atmospheric 1 4 c record which is generally interpreted as reflecting solar irradiance variability an early holocene climate event at 8150 8400 calendar years b p observed elsewhere within the asian east african monsoon system was again found in our record suggesting a reduction in precipitation over nw india and pakistan

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

geochemical evolution of kohala volcano hawaii kohala volcano the oldest of five shield volcanoes comprising the island of hawaii consists of a basalt shield dominated by tholeiitic basalt pololu volcanics overlain by alkalic lavas hawi volcanics in the upper pololu volcanics the lavas become more enriched in incompatible elements and there is a transition from tholeiitic to alkalic basalt in contrast the hawi volcanics consist of hawaiites mugearites and trachytes 87sr 86sr ratios of 14 pololu basalts and 5 hawi lavas range from 0 70366 to 0 70392 and 0 70350 to 0 70355 respectively this small but distinct difference in sr isotopic composition of different lava types especially the lower 87sr 86sr in the younger lavas with higher rb sr has been found at other hawaiian volcanoes our data do not confirm previous data indicating sr isotopic homogeneity among lavas from kohala volcano also some abundance trends such as mgo p2o5 are not consistent with a simple genetic relationship between pololu and hawi lavas we conclude that all kohala lavas were not produced by equilibrium partial melting of a compositionally homogeneous source

sea surface temperature and productivity records for the past 240 kyr in the arabian sea abstract deep sea sediments of two cores from the western ty93 929 p and the southeastern md900963 arabian sea were used to study the variations of the indian monsoon during previous climatic cycles core ty93 929 p was located between the sw monsoon driven upwelling centres off somalia and oman which are characterized by large seasonal sea surface temperature sst and particle flux changes by contrast core md900963 was situated near the maldives platform an equatorial ocean site with a rather small sst seasonality less than 2 c for both cores we have reconstructed sst variations by means of the unsaturation ratio of c37 alkenones which is compared with the 18o records established on planktonic foraminifera in general the sst records follow the 18o variations with an sst maximum during oxygen isotope stage 5 5 the last interglacial at about 120 130 kyr and a broad sst minimum during isotope stage 4 and 3 3 approximately 40 50 kyr the sst difference between the holocene and the last glacial maximum lgm is of the order of 2 c in both cores the ssts during isotope stage 6 are distinctly higher by 1 2 c than the cold sst minima during the last glacial cycle lgm and stage 3 to reconstruct qualitatively the past productivity variations for the two cores we used the concentrations and fluxes of alkenones and organic carbon together with a productivity index based on coccolith species florisphaera profunda relative abundance within each core there is a general agreement between the different palaeoproductivity proxies in the southeastern arabian sea core md900963 glacial stages correspond to relatively high productivity whereas warm interstadials coincide with low productivity all time series of productivity proxies are dominated by a cyclicity of about 21 23 kyr which corresponds to the insolation precessional cycle a hypothesis could be that the ne monsoon winds were stronger during the glacial stages which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone by contrast the records are more complicated in the upwelling region of the western arabian sea core ty93 929 p this is partly due to large changes in the sedimentation rates which were higher during specific periods isotope stages 6 5 4 5 2 3 and 2 unlike core md900963 no simple relationship emerges from the comparison between the 18o stratigraphy and productivity records the greater complexity observed for core ty93 929 p could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons the sw monsoon being enhanced during interglacial periods whereas the ne monsoon was increased during glacial intervals a similar line of reasoning also could help explain the sst records by the superimposition of variations of three components global atmospheric temperature and sw and ne monsoon dynamics

did kahoolawe volcano hawaii evolve to alkalic composition magmatism abstractuncertainty remains about whether kahoolawe the smallest of the main hawaiian islands evolved to alkalic magmatism to determine the compositional extent to which kahoolawe volcano evolved we examined eight new samples as candidates for hawaiite an unequivocally alkalic rock type petrography e g commonly aphyric and major and trace element and mineral compositions e g 49 5 wt sio2 at 6 wt na2o k2o an 50 60 document that four are hawaiites and two are mugearites the other two are basalts these six samples have compositions that overlap or are similar to those of known hawaiian hawaiites and mugearites some trace element differences e g the highest ni and lowest sr probably represent particular source characteristics for kahoolawe hawaiites mass balancing and melts modeling suggest that these kahoolawe lavas represent 58 65 residual liquids from alkalic basalt clinopyroxene dominated crystallization at pressures approaching that of the crust mantle boundary these mode

the effects of weathering on rare earth element y and ba abundances in tertiary basalts from southeastern australia tholeiitic basalts showing anomalously high ba y and rare earth element ree concentrations occur within the tertiary newer volcanic province of victoria and these geochemical characteristics are related to incipient alteration accompanying weathering ree and y released during weathering of basalts are retained either in secondary phosphate or clay minerals and in rocks showing very high ba concentrations the ba is present as baso4 leaching experiments suggest that glassy or fine grained rocks are more likely to release ree y and ba while more extensively altered rocks are likely to hold these elements probably because they substitute in or are adsorbed on clay minerals or because secondary baso4 and ree phosphates are resistant to acid leaching samples taken sequentially across a weathering profile in a tholeiitic basalt flow from fresh to intensively altered rock illustrate that in the very earliest stages of alteration extreme variations in the abundances of ba y and ree can occur this is reflected in the broad patterns of trace element behaviour manifested by an extensive analysed sample suite from the victorian newer volcanic province where there is no correlation between anomalous enrichments in ba y or ree and the level of incipient alteration ba anomalies are not necessarily accompanied by abnormal y and ree behaviour and this is probably because the mobility of each trace element is a function of a the ionic radius and charge of the ionic species it forms in solution b local groundwater parameters such as eh ph groundwater flux and concentrations in the groundwater of species such as so42 and c the secondary mineral assemblages developed in a particular situation sr isotopic compositions are not strongly affected by incipient weathering and do not show significant changes until alteration has progressed to the point where plagioclase begins to break down the study illustrates that relatively slight alteration at the earliest stages of weathering can produce drastic changes in the concentrations of ree y and ba and petrographic assessment of the freshness of samples is not precise enough to eliminate prior to analysis cases where these effects may be manifested where weathering has caused changes in abundance patterns these may be recognised by careful comparisons of appropriate elemental ratios e g ba rb throughout a particular analysed sample suite

high resolution temperature and evaporation changes during the late holocene in the northeastern arabian sea in order to reconstruct the monsoonal variability during the late holocene we investigated a complete annually laminated sediment record from the oxygen minimum zone omz off pakistan for oxygen isotopes of planktic foraminifera and alkenone derived sea surface temperatures sst significant sst changes of up to 3 c which cannot be explained by changes in the alkenone producing coccolithophorid species inferred from the gephyrocapsa oceanica emiliania huxleyi ratio suggest that sst changes are driven by changes in the monsoon strength our high decadal resolution data indicate that the late holocene in the northeastern arabian sea was not characterized by a stable uniform climate as inferred from the greenland ice cores but by variations in the dominance of the sw monsoon conditions with significant effects on temperatures highest sst fluctuations of up to 3 0 c and 2 5 c were observed for the time interval from 4600 to 3300 years b p and during the past 500 years the significant short term sst changes during the past 500 years might be related to climatic instabilities known from the northern latitudes little ice age and confirm global effects surface salinity values reconstructed from 18o records after correction for temperature related oxygen isotope fractionation suggest that in general the past 5000 years were characterized by higher than recent evaporation and more intense sw monsoon conditions however between 4600 and 3700 years b p evaporation dropped sw monsoon weakened and ne monsoon conditions were comparatively enhanced for the past 1500 years we infer strongly fluctuating monsoon conditions comparisons of reconstructed salinity records with ice accumulation data from published tibetan ice core and tibetan tree ring width data reveal that during the past 2000 years enhanced evaporation in the northeastern arabian sea correlates with periods of increased ice accumulation in tibet and vice versa this suggests a strong climatic relationship between both monsoon controlled areas

a 300 kyr record of upwelling off oman during the late quaternary evidence of the asian southwest monsoon in the northwest arabian sea upwelling occurs each summer driven by the strong sw monsoon winds upwelling results in high biological productivity and a distinctive assemblage of plankton species in the surface waters off oman that are preserved in the sediments along the oman continental margin creating a geologic record of monsoon driven upwelling sediments recovered from the oman continental margin during ocean drilling program leg 117 provide an opportunity to examine how upwelling has varied during the late quaternary spanning a longer interval than piston cores recovered prior to the odp cruise variations in foraminifer shell accumulation and in the relative abundance of globigerina bulloides indicate dominant cycles of variation at 1 100 kyr the dominant frequency of glacial interglacial variations and at 1 23 kyr the frequency of precessionally driven cycles in seasonal insolation the strongest monsoon winds indicated by increased upwelling occurred during interglacial times when perihelion was aligned with the summer solstice an orbital change that increased the insolation received during summer in the northern hemisphere during glacial times upwelling was reduced and although the precessional cycles were still present their amplitude was smaller at both frequencies the upwelling cycles are in phase with minimum ice volume evidence that glacial interglacial climate changes also include changes to the climate system that influence the low latitude monsoon we attribute the decrease in the monsoon winds observed during glacial times to changes in bare land albedo over asia and or to changes in the areal extent and seasonal cycle in asian snow cover that decrease the summer land sea temperature contrast other mechanisms may also be involved these new upwelling time series differ substantially from previous results however the previous work relied on cores located farther offshore where upwelling is less intense and other physical mechanisms become important our results support the observations derived from atmospheric general circulation models of the atmosphere that indicate that both glacial boundary conditions and the strength of summer insolation are important variables contributing to cycles in the monsoon winds during the late quaternary

cerium anomalies in lateritic profiles the ree geochemistry and mineralogy have been studied in four lateritic profiles one derived from a syenite akongo sw cameroon the others being developed on a gneissic basement and located along a soil toposequence goyoum e cameroon there is a fractionation between lree and hree in the lateritic samples during weathering the weathered residual products being enriched in lree from la to eu and depleted in hree from gd to lu sampled waters are enriched in hree in relation to the syenite host rock a positive ce anomaly has been found systematically at the top of the saprolite beneath a zone of iron oxide accumulation in the laterite up to 2000 ppm ce may be present in the akongo profile cerianite ceo2 is present as very fine coatings in non ferruginous clayey domains primary ree bearing accessory minerals are weathered at the bottom of the profile specifically allanite and apatite are transformed into florencite and rhabdophane but these phases have no ce anomaly all the data are interpreted as the result of the following processes 1 1 ree leaching in a reducing environment 2 2 oxidation of ce3 to ce4 in an oxidizing environment 3 3 deposition of cerium as cerianite whereas the other ree remain in solution

an extended kalman filter to assimilate satellite altimeter data into a nonlinear numerical model of the tropical pacific ocean method and validation a new implementation of the extended kalman filter scheme is developed for the purpose of assimilating observations into a high resolution nonlinear numerical model of the tropical pacific ocean it is characterized by two successive stages 1 approximation of the error covariance matrix by a singular low rank matrix which leads to making corrections only in those directions for which the error is not naturally attenuated by the system in this respect it is quite similar to the approach adopted by cane et al 1996 and 2 modification of these directions over time according to the model dynamics thus reflecting the evolutive nature of the filter the filter is initialized by a method based on the empirical orthogonal functions obtained from free runs of the model the reduction of the error covariance matrix avoids the overwhelming burden of computing the temporal evolution of the prediction error with all the degrees of freedom of the full state vector this assimilation scheme is implemented in the gent and cane 1989 primitive equation reduced gravity model this model has the advantage of using a coordinate in the vertical which allows a geographical refinement of the vertical resolution for thermocline gradients it is forced by the florida state university database winds and the chen et al 1994 hybrid scheme parameterization is assumed for the mixed layer the domain of application is the tropical pacific ocean basin between 120 e and 80 w longitude and 30 s and 30 n latitude the resolution is finest at the equator and steadily increases away from the equator in a first application validation twin experiments are conducted in which observations are assumed to be synthetic altimeter data sampled according to the topex poseidon mission features the method is shown to be efficient under various conditions and in particular to be capable of transferring information in the vertical from the surface only altimeter data to the deepest ocean layers and therefore of adequately constraining the thermal and the velocity profiles within the 300 or 400 m upper ocean in a second application real topex poseidon data are used and the results evaluated against independent in situ data namely tropical ocean global atmosphere toga tao mooring observations improvements in the model behavior are clear in terms of the time variability of the tropical ocean it therefore seems that the reduced state kalman filter with empirical orthogonal function eof initialization can be applied with success to such a primitive equation model of the pacific for the assimilation of altimeter data however at this stage the evolutivity of the filter seems to have a limited impact on the performances which was not the case for tests in the strongly nonlinear midlatitudes pham et al 1998a

synchronous holocene sea surface temperature and rainfall variations in the asian monsoon system abstract an increasing number of high resolution paleoclimate records show substantial natural variation during the holocene in order to improve climate projections on human lifetime the processes that potentially control teleconnections between different parts of the climate system need to be understood a highly suitable area to study these processes is the asian monsoon system as it is one of the most dynamic climate systems on earth and largely controls climate in asia and the indo w pacific realm here we present a holocene stable o isotope record from the summer dwelling planktic foraminifer g bulloides in core 905 off somalia initially dated by the radiocarbon method the record was tuned to atmospheric 14 c variations without violating the radiocarbon dates the o isotope variations in core 905 imply monsoon controlled holocene average summer sea surface temperature variations of up to 2 2 5 c within decades to centuries other proxy records from marine and continental settings representing key locations in the asian monsoon system were compared with the record of core 905 within the resolution of the individual age models holocene monsoonal records vary in concert for the arabian sea continental china and the south china sea and imply simultaneous warm wet and cool dry alternations in the asian monsoon within centuries to decades two potential scenarios are discussed to explain the coherent monsoonal records scenario one involves trade wind induced temperature variations in the w pacific warm pool as the driving force the second scenario advocates the controlling process to synchronous variations in trade wind strength simultaneously occurring over the pacific and indian ocean

bioturbational mixing depth and carbon flux at the seafloor radiocarbon dating series bulk sediment and organic carbon flux from various atlantic deep sea regions reveal that the thickness of the bioturbated zone increases by 2 cm if food supply increases by 1 gcm 2yr 1 r 0 8 bulk sediment accumulation rates do not influence the depth of bioturbational mixing under normal pelagic sedimentary conditions we believe that this relationship between nutrient supply and benthic mixing can be used for a quantitative and time variable unmixing procedure to improve high resolution stratigraphic correlations and paleoclimatic interpretations of deep sea records

the tholeiite to alkalic basalt transition at haleakala volcano maui hawaii previous studies of alkalic lavas erupted during the waning growth stages 0 9 ma to present of haleakala volcano identified systematic temporal changes in isotopic and incompatible element abundance ratios these geochemical trends reflect a mantle mixing process with a systematic change in the proportions of mixing components we studied lavas from a 250 m thick stratigraphic sequence in honomanu gulch that includes the oldest 1 1 ma subaerial basalts exposed at haleakaka the lower 200 m of section is intercalated tholeiitic and alkalic basalt with similar isotopic sr nd pb and incompatible element abundance ratios e g nb la la ce la sr hf sm ti eu these lava compositions are consistent with derivation of alkalic and tholeiitic basalt by partial melting of a compositionally homogeneous clinopyroxene rich garnet lherzolite source the intercalated tholeiitic and alkalic honomanu lavas may reflect a process which tapped melts generated in different portions of a rising plume and we infer that the tholeiitic lavas reflect a melting range of 10 to 15 while the intercalated alkalic lavas reflect a range of 6 5 to 8 melting however within the uppermost 50 m of section 87sr 86sr decreases from 0 70371 to 0 70328 as eruption age decreased from 0 97 ma to 0 78 ma we infer that as lava compositions changed from intercalated tholeiitic and alkalic lavas to only alkalic lavas at 0 93 ma the mixing proportions of source components changed with a morb related mantle component becoming increasingly important as eruption age decreased

melting in the hawaiian plume at 1 2 ma as recorded at maui nui the role of eclogite peridotite and source mixing 1 the volcanoes of maui nui west moloka i east moloka i lana i west maui haleakala and kaho olawe record hawaiian magmatism at 1 2 ma lavas from these volcanoes nearly span the compositional range erupted from all the hawaiian volcanoes over the past 5 myr and represent both the kea and ko olau compositional end members of hawaiian lavas many aspects of major and trace element and isotope compositions of hawaiian shield stage lavas are consistent with ancient recycled oceanic lithosphere in the plume sources of kea and ko olau type magmas lassiter and hauri 1998 blichert toft et al 1999 hypotheses that describe the compositional range of hawaiian lavas as originating from ancient oceanic lithosphere in the hawaiian plume implicitly or explicitly infer lithologic heterogeneity in the plume we present trace element models for the origin of these end members that explicitly address the petrologic complexities of melting eclogite derived from ancient oceanic lithosphere in the plume trace element la nb sm yb sm hf and sm nb major element and isotope compositions of lana i which erupts dominantly ko olau type lavas are consistent with the origin of these lavas in large degree 60 70 melts of ancient upper oceanic crust basalt sediment that mix with plume derived haleakala type melts trace element sm yb hf zr and hf nb and isotope compositions of west maui and east moloka i which erupt dominantly kea type magmas are consistent with an origin in ancient depleted oceanic lithosphere that has been refertilized with moderate degree melts 10 30 of associated crustal gabbro the physical mechanisms melt melt versus melt solid mixing through which the oceanic crustal components melt and mix within the plume lead to the generation of isotopically homogeneous kea type lavas and isotopically heterogeneous ko olau type lavas the volcanoes of maui nui record the exhaustion of the ko olau component and the initiation of the kea component as dominant compositional end members in the hawaiian plume

oxygen isotope salinity relationship in the northern indian ocean we analyze the surface 18o salinity relationships of the bay of bengal and the arabian sea in the northern indian ocean known for their contrasting hydrological conditions new measurements of these tracers show a very low 18o salinity slope associated with the strong dilution in the bay of bengal but a slope more typical of this latitude in the arabian sea although this region is marked by a complex monsoonal regime numerical modeling using a box model and a general circulation model is able to capture the 18o salinity slope and its geographical variation both models clearly show that the low 18o salinity slope is due to the evaporation minus precipitation balance with an important contribution of the continental runoff in the bay of bengal although the low value of these slopes 0 25 makes past salinity reconstructions uncertain insight into the last glacial maximum conditions shows a probable stability of these slopes and limited error on paleosalinity

geochemistry of flood basalts of the toranmal section northern deccan traps india implications for regional deccan stratigraphy unpublished data 1998 andthe southeastern deccan particularly the poladpur andambenali formations mitchell widdowson 1991 bilgrami 1999 for as much as 350 km from their south western type sections in addition lavas isotopically andchemicallyequivalenttothoseoftheambenaliformation fm arepresentinthenortheastern sectoroftheprovinceas far as 900 km from their southwesternmost counter parts mahoney 1988 deshmukh

isotopic constraints on the origin of hawaiian lavas from the maui volcanic complex hawaii strontium neodymium and lead isotopic data for samples from five volcanoes of the maui volcanic complex hawaii span nearly the total compositional range previously recognized for the hawaiian islands these data reveal a systematic compositional continuum for hawaiian tholeiites which is interpreted to result from partial melting of a variably mixed two component mantle plume source in contrast post shield building alkalic cap lavas define distinct compositional trends which appear to result from time and volume dependent binary mixing between hawaiian plume melts and a depleted mantle component

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

ages rare earth element enrichment and petrogenesis of tholeiitic and alkalic basalts from kahoolawe island hawaii kahoolawe island hawaii 18 11 km is a basaltic shield volcano with caldera filling lavas seven identified postshield vents and at least two occurrences of apparent rejuvenated stage eruptive we examined 42 samples that represent all stages of kahoolawe volcano stratigraphy for their petrography whole rock major and trace element contents mineral compositions and k ar ages the two oldest shield samples have an average age of 1 34 0 08 ma and four postshield samples 3 are alkalic average 1 15 0 03 ma ages of 1 08 and 0 99 ma for two additional tholeiitic samples probably are minimum ages whole rock major and trace element and mineral compositions of kahoolawe shield and caldera fill laves are generally similar to the lavas forming kilauea and mauna loa tholeiitic shields but in detail kahoolawe shield lavas have distinctive compositions an unusual aspect of many postshield ka hoolawe lavas is anomalously high ree and y abundances up to 200 ppm la and 175 ppm y and negative ce anomalies these enrichments reflect surficial processes where weathering and soil development promoted ree y transport at the weathering front major element abundances mgo 10 6 wt for shield and caldera fill basalts are consistent with fractionation of ol px pl in frequently replenished magma reservoirs in general tholeiitic basalts erupted from late vents are higher in sio2 than the shield lavas and temporal differences in parental magma compositions are the likely explanation alkalic basalts that erupted from vents are comparable in composition to those at other hawaiian volcanoes trace element abundance ratios indicate that alkalic basalts represent either relatively lower degrees of melting of the shield source or a distinct source apparent rejuvenated stage basalts i e emplaced after substantial kahoolawe erosion are tholeiitic unlike the rejuvenated stages at other hawaiian volcanoes alkalic kahoolawe like several other hawaiian volcanoes has intercalated tholeiitic and alkalic basalts in the postshield stage but it is the only volcano that appears to have produced tholeiitic rejuvenated stage lavas

hawaiian submarine manganese iron oxide crusts a dating tool black manganese iron oxide crusts form on most exposed rock on the ocean floor such crusts are well developed on the steep lava slopes of the hawaiian ridge and have been sampled during dredging and submersible dives the crusts also occur on fragments detached from bedrock by mass wasting on submerged coral reefs and on poorly lithified sedimentary rocks the thickness of the crusts was measured on samples collected since 1965 on the hawaiian ridge from 140 dive or dredge localities fifty nine 42 of the sites were collected in 2001 by remotely operated vehicles rovs the thinner crusts on many samples apparently result from post depositional breakage landsliding and intermittent burial of outcrops by sediment the maximum crust thickness was selected from each dredge or dive site to best represent crusts on the original rock surface at that site the measurements show an irregular progressive thickening of the crusts toward the northwest i e progressive thickening toward the older volcanic features with increasing distance from the hawaiian hotspot comparison of the maximum crust thickness with radiometric ages of related subaerial features supports previous studies that indicate a crust growth rate of about 2 5 mm m y the thickness information not only allows a comparison of the relative exposure ages of two or more features offshore from different volcanoes but also provides specific age estimates of volcanic and landslide deposits the data indicate that some of the landslide blocks within the south kona landslide are the oldest exposed rock on mauna loa kilauea or loihi volcanoes crusts on the floors of submarine canyons off kohala and east molokai volcanoes indicate that these canyons are no longer serving as channelways for down slope sediment laden currents mahukona volcano was approximately synchronous with hilo ridge both being younger than hana ridge the nuuanu landslide is considerably older than the wailau landslide the waianae landslide southwest of oahu has yielded samples with the greatest manganese iron oxide crusts 9 5 mm thick and therefore apparently represents the oldest submarine material yet found in the study area the submarine volcanic field 100 km southwest of oahu is apparently younger than the waianae landslide

hawaiian magma reservoir processes as inferred from the petrology of gabbro xenoliths in basalt kahoolawe island gabbro xenoliths in a tholeiitic lava of kahoolawe island hawaii a 1 3 1 4 ma shield volcano are 1 3 cm in size and comprised of plagioclase clinopyroxene and orthopyroxene gabbro textures while intergranular and in part subophitic are open due to 28 48 vol of vesicular basalt occupying xenolith space vesicles in and around the xenoliths are lined or filled with rhyolitic glass segregation vesicles the host is evolved tholeiite mgo 6 1 wt with phenocrysts microphenocrysts and glomerocrysts of olivine clinopyroxene orthopyroxene and plagioclase and megacrysts 1 cm of plagioclase the sr isotope ratio of one xenolith is 0 70489 the host basalt ratio is 0 70460 xenolith isotope composition grain resorption and clinopyroxene fs12 5 15wo38 35 5 orthopyroxene fs19 5 24wo4 1 and plagioclase an68 65or0 8 1 2 compositions suggest that these gabbros crystallized from kahoolawe tholeiitic magma of essentially the same composition as the host basalt but pre dating the magma represented by the host based on the absence of intergranular fe ti oxide phases from the pl cpx opx assemblages and the open vuggy textures we envision crystallization on a reservoir roof at temperatures 1100 c entrainment of gabbro assemblages and plagioclase megacrysts from a roof mush suspension zone occurred during convection associated with replenishment of the magma reservoir these open textured gabbro xenoliths are therefore not fragments of preexisting coarse grained bodies such as sills or segregation veins rhyolitic glass in vesicles represents a gas effervescence filtration process that forced fractionated residual liquids from the groundmass into voids associated with the xenoliths

sensitivity of the atlantic intertropical convergence zone to last glacial maximum boundary conditions 1 recent paleoproxy records suggest that the mean latitude of the atlantic intertropical convergence zone itcz varied synchronously with north atlantic climate over a range of timescales throughout the holocene and last glacial maximum we show that the present day meridional mode of atmosphere ocean variability in the tropical atlantic is a potentially useful model for understanding these paleoclimate changes the tropical atlantic in a coupled atmospheric general circulation and slab ocean model responds to last glacial maximum conditions with a southward displacement of the itcz this response arises primarily through the land ice sheet that forces increased north atlantic trades analogous to the forcing on the present day meridional mode changes to sea ice coverage and to ocean heat transport associated with a weakened atlantic thermohaline circulation also cause a meridional mode response though through different mechanisms our results highlight the potential for tropical atlantic paleoclimate to be driven from the high latitude influences in particular land ice on glacial interglacial timescales

a 5000 yr record of climate change in varved sediments from the oxygen minimum zone off pakistan northeastern arabian sea the upper holocene marine section from a kasten core taken from the oxygen minimum zone off karachi pakistan at water depth 700 m contains continuously laminated sediments with a sedimentation rate of 1 2 mm yr and a unique record of monsoonal climatic variability covering the past 5000 years our chronostratigraphy is based on varve counts verified by conventional and ams 14 c dating individual hemipelagic varve couplets are about 0 8 1 5 mm thick with light colored terrigenous laminae a deposited mainly during the winter monsoon alternating with dark colored laminae b rich in marine organic matter coccoliths and fish debris that reflect deposition during the high productivity season of the late summer monsoon august october precipitation and river runoff appear to control varve thickness and turbidite frequency we infer that precipitation decreased in the river watershed indicated by thinning varves after 3500 4000 yr b p this is about the time of increasing aridification in the near east and middle east as documented by decreasing nile river runoff data and lake level lowstands between turkey and northwestern india this precipitation pattern continued until today with precipitation minima about 2200 1900 yr b p 1000 yr b p and in the late middle ages 700 400 yr b p and precipitation maxima in the intervening periods as documented by spectral analysis the thickness of varve couplets responds to the average length of a 250 yr cycle a 125 yr cycle the gleissberg cycle of solar activity 95 yr and a 56 yr cycle of unknown origin higher frequency cycles are also present at 45 39 29 31 and 14 yr the sedimentary gray value also shows strong variability in the 55 yr band plus a 31 yr cycle because high frequency cyclicity in the enso band ca 3 5 and 5 yr is only weakly expressed our data do not support a straightforward interaction of the pacific enso with the monsoon driven climate system of the arabian sea

geochemistry of the 1984 mauna loa eruption implications for magma storage and supply the 1984 eruption of mauna loa volcano hawaii produced about 220 106 m3 of lava of remarkably homogeneous composition no significant compositional changes occurred during the 22 day eruption and along the 20 km vent system even though crystallinity increased substantially accompanying a decline in the eruption rate such homogeneity in lava composition is typical of many historic mauna loa eruptions the 1984 lava along with most other homogeneous mauna loa lavas is multiply saturated crystallizing olivine clinopyroxene and plagioclase bulk compositions are perched at the intersection of an olivine control trend with a trend for more differentiated lavas there is no evidence to indicate that the 1984 lava is a differentiate of the 1975 magma or that it results from mixing a new batch of magma with differentiated melt remaining in the magmatic plumbing system after the 1975 eruption it is proposed that these lavas are erupted directly from a small continuously replenished magma reservoir located about 3 4 km beneath the summit caldera successive eruptions therefore provide a sampling of magma chamber processes and small but discernible changes in lava composition reflect the competing processes of magma supply differentiation and eruption

geochemical variations in lavas from kahoolawe volcano hawaii evidence for open system evolution of plume derived magmas the kahoolawe shield volcano produced precaldera and caldera filling tholeiites and mildly alkalic post caldera lavas that petrographically and compositionally resemble such lavas from other hawaiian shield volcanoes however kahoolawe tholeiites display wide ranges in incompatible trace element ratios e g nb th 9 24 th ta 0 6 1 3 87sr 86sr 0 70379 0 70440 143nd 144nd 0 51273 0 51298 and 206pb 204pb 17 92 18 37 the isotopic variation exceeds that at any other hawaiian shield volcano and spans about half the range for all hawaiian tholeiites quasi cyclic temporal evolution of kahoolawe tholeiites is consistent with combined fractional crystallization and periodic recharge by primitive magmas ratios of highly incompatible trace elements and sr nd and pb isotopic ratios from coherent sub trends that reflect recurrent interactions between variably evolved magmas and two other mantle components whose compositions are constrained by intersections between these trends the most mgo rich kahoolawe tholeiites are partial melts of a high nb th 23 5 ascending plume possibly comprising ancient subducted oceanic lithosphere slightly evolved tholeiites experienced combined crystal fractionation and assimilation afc of material derived from a distinct reservoir nb th 9 of asthenospheric derivation the most evolved tholeiites display compositional shifts toward a third component having mid ocean ridge basalt like isotopic ratios but enriched oib like trace element ratios representing part of the lithospheric mantle or melts thereof periodic recurrence of all three magma variants suggests that eruptions may have tapped coeval reservoirs distributed over a large depth range kahoolawe provides new evidence concerning the nature of the hawaiian plume the distribution of compositional heterogeneities in the suboeanic mantle and the processes by which hawaiian tholeiites form and evolve

rare earth element behavior during groundwater seawater mixing along the kona coast of hawaii abstract groundwater and seawater samples were collected from nearshore wells and offshore along the kona coast of the big island of hawaii to investigate rare earth element ree behavior in local subterranean estuaries previous investigations showed that submarine groundwater discharge sgd is the predominant flux of terrestrial waters to the coastal ocean along the arid kona coast of hawaii groundwater and seawater samples were filtered through 0 45 m and 0 02 m pore size filters to evaluate the importance of colloidal and soluble i e truly dissolved ionic species and or low molecular weight lmw colloids fractions of the rees in the local subterranean estuaries mixing experiments using groundwater collected immediately down gradient from a wastewater treatment facility wwtf proximal to the kaloko hanokohau national historic park and more pristine groundwater from a well constructed in a lava tube at kiholo bay were conducted with local seawater to study the effect of solution composition i e ph salinity on the concentrations and fractionation behavior of the rees as groundwater mixes with seawater in kona coast subterranean estuaries the mixed waters were also filtered through 0 45 or 0 02 m filters to ascertain the behavior of colloidal and soluble fractions of the rees across the salinity gradient in each mixing experiment concentrations of the rees were statistically identical two tailed student t test 95 confidence between the sequentially filtered sample aliquots indicating that the rees occur as dissolved ionic species and or lmw colloids in kona coast groundwaters the mixing experiments revealed that the rees are released to solution from suspended particles or colloids when kona coast groundwater waters mix with local seawater the order of release that accompanies increasing ph and salinity follows light ree lree middle ree mree heavy ree hree release of rees in the mixing experiments is driven by decreases in the free metal ion activity in solution and the concomitant increase in the amount of each ree that occurs in solution as dicarbonato complexes i e ln co3 2 as ph increases across the salinity gradient input normalized ree patterns of kona coast groundwater and coastal seawater are nearly identical and relatively flat compared to north pacific seawater indicating that sgd is the chief source of these trace elements to the ocean along the kona coast additionally ree concentrations of the coastal seawater are between 10 and 50 times higher than previously reported open ocean seawater values from the north pacific further demonstrating the importance of sgd fluxes of rees to these coastal waters taken together these observations indicate that large scale removal of rees which characterizes the behavior of rees in the low salinity reaches of many surface estuaries is not a feature of the subterranean estuary along the kona coast a large positive gadolinium gd anomaly characterizes groundwater from the vicinity of the wwtf the positive gd anomaly can be traced to the coastal ocean providing further evidence of the impact of sgd on the coastal waters estimates of the sgd fluxes of the rees to the coastal ocean along the kona coast i e 1 3 2 6 mmol nd day 1 are similar to recent estimates of sgd fluxes of rees along florida s east coast and to rhode island sound all of which points to the importance of sgd as significant flux of rees to the coastal ocean

general characteristics of temperature variation in china during the last two millennia three alternate china wide temperature composites covering the last 2000 years were established by combining multiple paleoclimate proxy records obtained from ice cores tree rings lake sediments and historical documents five periods of temperature variation can be identified a warm stage in ad 0 240 a cold interval between ad 240 and 800 a return to warm conditions from ad 800 1400 including the medieval warm period between ad 800 1100 the cool little ice age period between 1400 1920 and the present warm stage since 1920 regional temperature variation is found during ad 800 1100 when warm conditions occurred in eastern china and in the northeastern tibetan plateau and in ad 1150 1380 when the southern tibetan plateau experienced a warm interval in contrast evidence for cool conditions during the lia is more consistent among the proxy records the temperature reconstructions for china and the northern hemisphere show good agreement over the past millennium

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

decadal centennial scale monsoon variations in the arabian sea during the early holocene 1 an essential prerequisite for the prediction of future climate change due to anthropogenic input is an understanding of the natural processes that control earth s climate on timescales comparable to human lifespan the early holocene period was chosen to study the natural climate variability in a warm interval when solar insolation was at its maximum the monsoonal system of the tropics is highly sensitive to seasonal variations in solar insolation and consequently marine sediments from the region are a potential monitor of past climate change here we show that during the early holocene period rapid 18o changes of the summer upwelling dwelling foraminifer g bulloides of up to 0 6 in core 905 from the arabian sea occurred on decadal centennial timescales this 18o change predominantly translates into summer temperature variations of roughly 2 3 c within the resolution of the ams14c dating the isotope changes occur in phase with precipitation induced 18o variations recorded in a stalagmite in the hoti cave in oman neff et al 2001 from this relationship we conclude that solar insolation affecting the monsoonal system not only induced the precipitation changes as recorded in oman in the sense of neff et al 2001 but also controlled temperature variations in the upwelled waters found off somalia the present study demonstrates that decadal scale climate records can be obtained from nonlaminated ocean sediment records and that coherent rapid high amplitude climate change is recorded in the arabian sea on a regional scale of 2000 km

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

hawaiian xenolith populations magma supply rates and development of magma chambers hawaiian volcanoes pass through a sequence of four eruptive stages characterized by distinct lava types magma supply rates and xenolith populations magma supply rates are low in the earliest and two latest alkalic stages and high in the tholeiitic second stage magma storage reservoirs develop at shallow and intermediate depths as the magma supply rate increases during the earliest stage magma in these reservoirs solidifies as the supply rate declines during the alkalic third stage these magma storage reservoirs function as hydraulic filters and remove dense xenoliths that the ascending magma has entrained during the earliest and latest stages no magma storage zone exists and mantle xenoliths of lherzolite are carried to the surface in primitive alkalic lava during the tholeiitic second stage magma storage reservoirs develop and persist both at the base of the ocean crust and 3 7 km below the caldera only xenoliths of shallow origin are carried to the surface by differentiated lava during the alkalic third stage magma in the shallow subcaldera reservoir solidifies and crustal xenoliths including oceanic crustal rocks are carried to the surface in lava that fractionates in an intermediate depth reservoir worldwide xenolith populations in tholeiitic and alkalic lava may reflect the presence or absence of subvolcanic magma storage reservoirs

prodigious submarine landslides on the hawaiian ridge the extensive area covered by major submarine mass wasting deposits on or near the hawaiian ridge has been delimited by systematic mapping of the hawaiian exclusive economic zone using the side looking sonar system gloria these surveys show that slumps and debris avalanche deposits are exposed over about 100 000 km2 of the ridge and adjacent seafloor from kauai to hawaii covering an area more than 5 times the land area of the islands some of the individual debris avalanches are more than 200 km long and about 5000 km3 in volume ranking them among the largest on earth the slope failures that produce these deposits begin early in the history of individual volcanoes when they are small submarine seamounts culminate near the end of subaerial shield building and apparently continue long after dormancy consequently landslide debris is an important element in the internal structure of the volcanoes the dynamic behavior of the volcanoes can be modulated by slope failure and the structural features of the landslides are related to elements of the volcanoes including rift zones and fault systems the landslides are of two general types slumps and debris avalanches the slumps are slow moving wide up to 110 km and thick about 10 km with transverse blocky ridges and steep toes the debris avalanches are fast moving long up to 230 km compared to width and thinner 0 05 2 km they commonly have a well defined amphitheater at their head and hummocky terrain in the lower part oceanic disturbance caused by rapid emplacement of debris avalanches may have produced high level wave deposits such as the 365 m elevation hulopoe gravel on lanai that are found on several islands most present day submarine canyons were originally carved subaerially in the upper parts of debris avalanches subaerial canyon cutting was apparently promoted by the recently steepened and stripped slopes of the landslide amphitheaters

evolution of alkalic lavas at haleakala volcano east maui hawaii the postshield and posterosional stages of haleakala volcano contain intercalated alkalic basalt and evolved alkalic lavas isotopic and incompatible element abundance ratios in the haleakala postshield basalts changed systematically with time providing evidence for significant temporal changes in the mantle components contributing to the magmatic sources specifically a depleted i e low87sr 86sr and high143nd 144nd mantle component is more abundant in younger lavas however as magma production rates decreased during the postshield and posterosional stages basaltic melts in magma reservoirs cooled and fractionated leading to evolved residual melts such as hawaiite because primary basalt compositions changed with time the evolved haleakala lavas formed from a range of parental compositions however basalts and evolved lavas of similar age and isotopic ratios sr and nd have major and trace element contents that are consistent with a crystal fractionation model although alkalic basalt and hawaiite are the dominant lavas of the postshield stages of both haleakala and mauna kea volcanoes there are important differences between their lavas for example compositional differences between the hawaiite suites at haleakala and mauna kea indicate that on average the evolved lavas at haleakala formed at lower pressures also at haleakala basalts are intercalated with hawaiites whereas at mauna kea basalts and hawaiites are separated by a sharp boundary these differences probably reflect a higher magma supply rate to the haleakala volcano

is el nino sporadic or cyclic abstract is el nino one phase of a continual self sustaining natural mode of the coupled ocean atmosphere that has la nina as the complementary phase or is el nino a temporary departure from normal conditions triggered by a random disturbance such as a burst of westerly winds a growing body of evidence stability analyses studies of the energetics simulations that reproduce the statistics of sea surface temperature variations in the eastern equatorial pacific indicates that reality corresponds to a compromise between these two possibilities the observed southern oscillation between el nino and la nina corresponds to a weakly damped mode that is sustained by random disturbances this means that the predictability of el nino is limited by the continual presence of noise so that forecasts should be probabilistic the southern oscillation is also subject to decadal modulations how it will be influenced by global warming is a matter of considerable uncertainty

ka ena volcano a precursor volcano of the island of o ahu hawai i ka ena and wai alu ridges form prominent submarine ridges nw of the island of o ahu hawai i we evaluate whether or not either one of these ridges represents a submarine extension of wai anae volcano on o ahu using new bottom observations geophysical surveys and geochemical data acquired on new samples from the region wai alu ridge has the morphology of a submarine rift zone but is too shallow for its distance from the o ahu shoreline ka ena ridge also is unusually shallow and is surmounted by two topographic shields ka ena and wai alu ridges have similar magmatic and volcanic evolutionary histories beginning ca 5 ma with a submarine shield phase of volcanism that produced high sio 2 low feo tholeiites with higher 208 pb 204 pb than in the adjacent wai anae volcano late shield volcanism included transitional and alkalic rock types with lower sio 2 and enrichment in incompatible elements especially p 2 o 5 nb zr ti and light rare earth elements the transition from shield to late shield stage occurred as the edifice was beginning to emerge from the sea geological observations and k ar ages indicate that ka ena emerged above sea level ca 3 5 ma reaching a maximum height of 4000 m above the abyssal ocean floor and 1000 m above sea level relatively weak gravity anomalies topographic lineaments and the orientation of dike complexes indicate a volcanic structure that is independent of wai anae volcano thus volcanic structure geochemistry and age all indicate a precursor volcano to the island of o ahu which we call ka ena volcano after emergence ka ena volcano tilted 2 to the south we estimate a total volume of 20 27 10 3 km 3 for ka ena volcano taking into account overlapping geometry of concurrently active volcanoes sample compositions from the ka ena landslide deposit are entirely consistent with derivation from ka ena whereas most samples from the wai anae slump are likely derived from wai anae volcano uniformly oriented dikes in the wai anae nw rift zone likely reflect buttressing by a preexisting ka ena volcano unusual isotopic compositions of some wai anae samples including unique hydrous silicic lavas probably reflect interaction with underlying ka ena crust a newly recognized lava flow field on the southern flank of ka ena ridge extends the previously known distribution of secondary volcanism in the kaua i channel putative submarine volcanic activity in the region in 1956 cannot have built a large edifice and is unlikely to have produced pumice that was found on o ahu shores this eruptive activity therefore remains unconfirmed

origin of differentiated lavas at kilauea volcano hawaii implications from the 1955 eruption kilauea s 1955 eruption was the first major eruption longer than 2 days on its east rift zone in 115 years it lasted 88 days during which 108 106 m3 of lava was erupted along a discontinuous 15 km long system of fissures a wide compositional range of lavas was erupted including the most differentiated lavas 5 0 wt mgo from a historic kilauea eruption lavas from the first half of the eruption are strongly differentiated 5 0 5 7 wt mgo later lavas are weakly to moderately differentiated 6 2 6 7 wt mgo previous studies using only major element compositions invoked either crystal fractionation macdonald and eaton 1964 or magma mixing wright and fiske 1971 as models to explain the wide compositional variation in the lavas to further evaluate these models detailed petrographic mineralogical and whole rock major and trace element xrf analyses were made of the 1955 lavas plagioclase and clinopyroxene in the early and late lavas show no petrographic evidence for magma mixing olivines from both the early and late lavas show minor resorption which is typical of tholeiitic lavas with low mgo contents core to rim microprobe analyses across olivine augite and plagioclase mineral grains give no evidence of disequilibrium features related to mixing instead plots of an ab vs distance from the core d and fo vs d 4 5 generated essentially linear trends indicative of simple crystal fractionation least squares mass balance calculations for major and trace element data using observed mineral compositions yield excellent results for crystal fractionation sum of residuals squared 0 01 for major elements and 5 for trace elements magma mixing produced less satisfactory results especially for cr furthermore trace element plots of zr vs sr cr and a12o3 generate curved trends indicative of crystal fractionation processes there is no evidence that mixing occurred in the 1955 lavas instead the data are best explained by crystal fractionation involving a reservoir that extends at least 15 km along kilauea s east rift zone a dike was intruded into the rift zone from the summit reservoir eight days after the eruption started instead of causing magma mixing the dike probably acted as a hydraulic plunger forcing more of the stored magma to be erupted