intraseasonal interactions between the tropics and extratropics in the southern hemisphere abstract the mechanics of the interaction between tropical beating estimated from outgoing longwave radiation olr and southern hemisphere sh subtropical and extratropical circulations on intraseasonal time scales are discussed base points are selected from teleconnectivity and teleconnection maps between olr and zonal wind heights and meridional component of the divergent wind then composites are formed for pentads with olr anomalies at the base point greater in magnitude than one standard deviation enhanced convection over indonesia is found to be associated with increases of both the southward component of the meridional divergent wind and of the westerly zonal wind to the south of the heating region during the sh summer the increased westerly wind gradients resulting to a certain extent from strengthened northerly flow together with increased values of the southward component of the divergent wind lead to an enhancement of the rossby wave source in the vorticity equation in the vicinit

intraseasonal modulation of south american summer precipitation intraseasonal variation of convection over south america is examined using singular spectrum analysis ssa the dipole convection pattern with centers of action over the sacz and the subtropical plains is modulated by modes of different timescales both oscillatory modes with periods of 36 40 days mode 40 and 22 28 days mode 22 influence convection over the sacz with the faster mode mode 22 leading the variability over the subtropical plains mode 40 is related to the madden julian oscillation outgoing longwave radiation anomalies olra propagate eastward from the western pacific to the central pacific with a period of 40 48 days the 200 hpa streamfunction composites show a wavenumber 1 structure in the tropics and a wave train propagating downstream from the convective area in the tropical pacific the development of the dipole pattern is also contributed by mode 22 which features the meridional propagation of olra over south america from midlatitudes to the tropics the streamfunction composites for mode 22 show a wave train extending from the central pacific eastward to about 608s and curving toward the northeast over south america when the sacz is enhanced these two modes become meridionally aligned locally such episodes are characterized by a wave train propagating northeastward from southern south america toward the tropics composites based on the ssa decomposition indicate that the dominant periods of variability 22 and 40 days cancel out over the pacific region and reinforce each other over the sacz for times close to onset of the enhanced sacz episodes

re os geochronology and isotope systematics and organic and sulfur geochemistry of the middle late paleocene waipawa formation new zealand insights into early paleogene seawater os isotope composition abstract in the middle late paleocene a marine organic rich sedimentary unit waipawa formation fm in which the organic matter was derived mainly from terrestrial plants was deposited in many of new zealand s sedimentary basins the unique organofacies of this formation has not been identified in any other time interval within the geological history of the southwest pacific indicating that unusual climatic and oceanographic conditions likely prevailed during this time it has therefore attracted wide scientific interest due to its significance for regional and global reconstruction of the early paleogene transitional climate as well as potential for oil and gas production scarcity of age diagnostic fossils presence of unconformities and lack of volcanic interbeds have however hindered precise dating and correlations of all the known occurrences of the formation here rhenium osmium re os geochronology has yielded the first radiometric age for the formation 57 5 3 5 ma which is consistent with available biostratigraphic age determinations 59 4 58 7 ma further a comparison of re os bulk pyrolysis sulfur and palynofacies data for the waipawa fm with those of more typical marine sediments such as the underlying whangai fm supports the interpretation that the chelating precursors or fundamental binding sites responsible for uptake of re and os are present in all types of organic matter and that these elements have a greater affinity for organic chelating sites than for sulfides the results also indicate that sedimentation rate may not play a dominant role in enhanced uptake of re and os by organic rich sedimentary rocks the initial 187os 188os values for the waipawa 0 28 and whangai 0 36 formations are broadly similar to those reported for coeval pelagic sediments from the central pacific ocean further constraining the low resolution marine 187os 188os record of the paleocene we present a compilation of 187os 188os values from organic rich sedimentary rocks spanning the period between 70 and 50 ma which shows that seawater os gradually became less radiogenic from the latest cretaceous reaching a minimum value in the earliest late paleocene 59 ma during the deposition of waipawa fm and then increased through the later paleocene and into the early eocene the composite os isotope record broadly correlates with global temperature 18o and tex86 and carbon isotope 13c records from the middle paleocene to early eocene which is inferred to reflect climate modulated changes in continental weathering patterns

a geochemical clock in earliest paleogene pelagic carbonates based on the impact induced os isotope excursion at the cretaceous paleogene boundary 1 an impact induced osmium os isotope excursion provides a unique means of assessing the completeness of marine cretaceous paleogene k pg boundary sections and surmounting challenges associated with constraining the time scale of the earth system recovery from this extreme perturbation a model of the recovery of seawater187os 188os following the impact event allows independent estimates of the time elapsed since the impact which can be directly compared to time estimates derived from biostratigraphy magnetostratigraphy and cyclostratigraphy this approach is tested using data from three deep ocean sites cored by the ocean drilling program odp data from odp 1262b south atlantic and odp 690c southern ocean display the expected 187os 188os minimum very close to the biostratigraphically defined k pg boundary and yield os based accumulation rate estimates similar to those obtained from magnetostratigraphy and orbital tuning in contrast the187os 188os minimum in odp 1209c western pacific occurs 9 cm below the k pg boundary low os concentrations throughout the boundary interval and an implausibly rapid recovery to higher pre impact187os 188os ratios provide strong evidence for a previously unrecognized gap in the k pg interval of site 1209 results presented here provide strong empirical evidence that os isotope data are uniquely valuable in assessing the completeness and accumulation rates of earliest paleogene sediments from the deep sea they are of broad interest because they have implications for astronomical tuning of the geologic time scale and illustrate that whole ocean geochemical perturbations can provide an alternative to biostratigraphy for correlation and timekeeping during abrupt biotic events

influence of the madden julian oscillation on precipitation and surface air temperature in south america the regional influence of the madden julian oscillation mjo on south america is described maps of probability of weekly averaged rainfall exceeding the upper tercile were computed for all seasons and related statistically with the phase of the mjo as characterized by the wheeler hendon real time multivariate mjo rmm index and with the olr mjo index the accompanying surface air temperature and circulation anomalies were also calculated the influence of the mjo on regional scales along with their marked seasonal variations was documented during december february when the south american monsoon system is active chances of enhanced rainfall are observed in southeastern south america sesa region mainly during rmm phases 3 and 4 accompanied by cold anomalies in the extratropics while enhanced rainfall in the south atlantic convergence zone sacz region is observed in phases 8 and 1 the sesa sacz signal is characterized by upper level convergence divergence over tropical south america and a cyclonic anticyclonic anomaly near the southern tip of the continent impacts during march may are similar but attenuated in the extratropics conversely in june november reduced rainfall and cold anomalies are observed near the coast of the sacz region during phases 4 and 5 favored by upper level convergence over tropical south america and an anticyclonic anomaly over southern south america in september november enhanced rainfall and upper level divergence are observed in the sacz region during phases 7 and 8 these signals are generated primarily through the propagation of rossby wave energy generated in the region of anomalous heating associated with the mjo

the emplacement of the late miocene monte capanne intrusion elba island central italy constraints from magnetic fabric analyses anisotropy of magnetic susceptibility ams analysis has been carried out in the thermometamorphic aureole surrounding the late miocene monte capanne pluton elba island central italy the identification and separation of the main carriers of the magnetic susceptibility by low temperature and high field ams measurements demonstrate that a correct knowledge of the magnetic fabric is needed in order to use ams for tectonic interpretations magnetic fabric data combined with structural data from the aureole and their comparison with data from the pluton itself were used to constraint the mode of pluton emplacement results document an intimate linkage between the magmatic flow pattern and the syn metamorphic fabrics acquired during pluton emplacement in the host rocks the magnetic structural fabric in the aureole rocks is dominated by flattening deformation and no systematic relationship with any regional tectonic feature is observed these results suggest that local processes induced by magma ascent in the upper crust might have played a primary role in space generation for pluton emplacement in the tuscan magmatic province suggesting a revaluation of the modes of pluton emplacement during the post orogenic evolution of the northern apennine system as a whole

the seawater osmium isotope record of south china sea implications on its history and evolution abstract the south china sea is the largest marginal basin in the world and is located in the confluence of three major tectonic plates pacific philippine sea indo australia eurasia its tectonic history and evolution throughout the cenozoic has been the subject of much discussion with regards to its mechanism timing and relationship to neighboring geological features we conducted the first re os isotope study of the south china sea cores recovered from ocean drilling odp ocean drilling program and iodp international ocean discovery program and from philippine oil exploration wells in order to investigate whether or not the basin s tectonic evolution will be reflected in the seawater os isotope record these cores represent the northern and southern conjugate margins of the south china sea and should have complementary records of the tectonic events in the basin we found three important negative anomalies in the south china sea s seawater os isotope record at 35 33 ma 26 23 ma and 13 6 ma which are temporally related to tectono magmatic events at the northern margin the record starts with the lowest 187os 188os i values of 0 37 and 0 32 for the oldest samples which then progresses to more radiogenic values for younger sediments the trend is consistent with the start of seafloor spreading at 33 ma that saw the peak in the flux of mantle derived material which later slowed down until the second peak between 26 and 23 ma however these unradiogenic values also mark the eocene oligocene transition and more likely implies south china sea connectivity to global ocean circulation since pre oligocene in both margins slight to marked decrease in 187os 188os i values deviate from the global trend and coincides with the ridge jump at 23 ma in the southern conjugate margin 187os 188os i show a general decreasing tendency opposite that of the northern margin and the global trend starting from mid to late miocene 13 6 ma mass balance modeling suggests that the two younger negative excursions may be accounted for by mantle and hydrothermal os inputs of 372 mol my at 23 ma and post 13 ma we suggest that the post 13 ma protracted decrease in 187os 188os i values for the southern margin reflects localized input of mantle derived lithogenic os from the luzon arc combined with post spreading magmatic intrusions and possibly gradual changes in paleoceanographic condition at the southern east sub basin

the record of sea water 187os 186os variation through the cenozoic the variation of sea water 187os 186os during the cenozoic has been determined by analyzing the hydrogenous os released by acidic hydrogen peroxide leaching of layers in an abyssal north pacific pelagic clay core overall sea water 187os 186os has increased from 3 2 at 58 ma to the present day value of 8 6 this pattern is similar to the well known 87sr 86sr evolution of sea water the increase in the proportion of continental os 187os 186os 10 could be due to enhanced weathering rates of black shales associated with the uplift of the himalayas other elements associated with black shale weathering such as u and p should show effects in the sedimentary record

search for the proverbial mantle osmium sources to the oceans hydrothermal alteration of mid ocean ridge basalt abstract we present os and sr isotopes and mg os and sr concentrations for ridge crest high temperature and diffuse hydrothermal fluids plume fluids and ridge flank warm spring fluids from the juan de fuca ridge the data are used to evaluate the extent to which 1 the high and low temperature hydrothermal alteration of mid ocean ridge basalts morbs provides os to the deep oceans and 2 hydrothermal contributions of non radiogenic os and sr to the oceans are coupled the os and sr isotopic ratios of the high temperature fluids 265 353 c are dominated by basalts 187 os 188 os 0 2 87 sr 86 sr 0 704 but the concentrations of these elements are buffered approximately at their seawater values the 187 os 188 os of the hydrothermal plume fluids collected 1 m above the orifice of hulk vent is close to the seawater value 1 05 the low temperature diffuse fluids 10 40 c associated with ridge crest high temperature hydrothermal systems on average have os 31 fmol kg 1 187 os 188 os 0 9 and sr 86 mol kg 1 87 sr 86 sr 0 709 they appear to result from mixing of a high temperature fluid and a seawater component the ridge flank warm spring fluids 10 62 c on average yield os 22 fmol kg 1 187 os 188 os 0 8 and sr 115 mol kg 1 87 sr 86 sr 0 708 the data are consistent with isotopic exchange of os and sr between basalt and circulating seawater during low temperature hydrothermal alteration the average sr concentration in these fluids appears to be similar to seawater and consistent with previous studies in comparison the average os concentration is less than seawater by more than a factor of two if these data are representative they indicate that low temperature alteration of morb does not provide adequate non radiogenic os and that another source of mantle os to the oceans must be investigated at present the magnitude of non radiogenic sr contribution via low temperature seawater alteration is not well constrained if non radiogenic sr to the oceans is predominantly from the alteration of morb our data suggest that there must be a different source of non radiogenic os and that the os and sr isotope systems in the oceans are decoupled

u pb and re os geochronology of the aptian albian and cenomanian turonian stage boundaries implications for timescale calibration osmium isotope seawater composition and re os systematics in organic rich sediments abstract presented is the first absolute age for the basal albian from the schwicheldt ton member gault formation vohrum germany a 206 pb 238 u age of 113 1 0 3 ma is determined for chemically abraded zircon from a tuff horizon 65 cm above the aptian albian boundary the new u pb age although within uncertainty of the gts 2008 determination 112 1 ma is nominally older the younger gts 2008 basal albian age is obtained from cyclostratigraphy using an 40 ar 39 ar age from the base cenomanian the nominal difference between the gts 2008 age and new basal albian age is consistent with the documented ca 0 65 bias between u pb and 40 ar 39 ar geochronology the new 206 pb 238 u age calls into question a recently published age for the basal albian 106 9 0 4 ma determined from k ar glauconite analysis as well as the k ar age for the gl o international standard rhenium osmium isotope analysis of the basal albian grey clay of the schwicheldt ton member gault formation and basal turonian grey shale of the schwarz weisse wechselfolge hesseltal formation recording oceanic anoxic event 2 yields low and similar 187 re 188 os values 49 167 that are positively correlated with 187 os 188 os values for both sections imprecise re os ages 6 9 2 that overlap the stratigraphic boundary ages are determined aptian albian 108 9 6 2 ma cenomanian turonian 91 5 8 6 ma although the re os data suggest that organic rich sediments other than black shales are potentially amenable for re os geochronology the large uncertainties contrast with that from previous re os organic rich sediment studies the latter show sample sets with a significant spread in 187 re 188 os ratios several hundred units the imprecise re os geochronology presented here relates to the limited spread in the 187 re 188 os values the redox conditions of deposition are suggested to control the 187 re 188 os ratio of an organic rich sediment however trace element and re os data for samples from nw germany and previous re os geochronology studies show no direct relationship between 187 re 188 os values and the redox condition of the water column these results suggest that the fractionation of re and os in organic rich sediments is not controlled by water column redox conditions instead re os fractionation in organic rich sediments may be controlled by sedimentation rate recharge of re and os to the water column and or post deposition mobility of re and os within the sediment the initial os isotope composition of an organic rich sediment is inferred to reflect the seawater composition at the time of deposition for the cenomanian turonian boundary grey shale a seawater os composition of 0 33 0 02 is determined this os isotope composition contrasts with that of the stratotype section at pueblo colorado 0 15 and for those obtained from furlo italy and odp site 1260b 0 5 this data may suggest that the cenomanian turonian ocean was not homogeneous with respect to os suggesting either alternate oceanic circulation or basin dynamics

os isotope chemostratigraphy applied to organic rich marine sediments from the eocene oligocene transition on the west african margin odp site 959 1 the known temporal relationship between the benthic foraminiferal 18o record and the marine os isotope record is used to reinterpret the absolute chronology and paleoceanographic context of an episode of organic carbon burial on the west african margin ocean drilling program odp site 959 although organic rich sediments require significant corrections for in situ decay of 187re to 187os these results demonstrate the utility of the marine os isotope record for chemostratigraphic correlation of organic rich sediments that are devoid of age diagnostic microfossils with pelagic carbonate sequences revision of the odp site 959 chronology shifts the age assignment of an interval of biosiliceous organic rich sediment deposition from the oligocene to the late eocene and earliest oligocene likely culminating with the first major glaciation of the oligocene oi1 we speculate that enhanced organic carbon burial over much of the west african margin may have contributed to drawdown of atmospheric carbon dioxide before and during the oi1 event and suggest that os isotope chemostratigraphy provides a valuable tool for further exploring this possibility

evidence for a modulation of the intraseasonal summer temperature in eastern patagonia by the madden julian oscillation we describe the relationship between the intraseasonal component of surface air temperature sat variability in eastern patagonia and the madden julian oscillation mjo during austral summer based on 50 years of daily instrumental records the twentieth century reanalysis and a century long mjo index reconstruction our results show that the summer sat variability in patagonia is highly driven by the intraseasonal activity 80 especially by that associated with the mjo the active mjo phases modulate the spatial mean intraseasonal temperature signal in eastern patagonia with 1 5 c of amplitude in most of the region the warmest coldest conditions are found during active phase 8 4 these opposite states of the temperature perturbations are related to almost inverse midlevel circulation anomalies over southern south america and the southwest atlantic which are part of a large scale rossby like wave train of alternating circulation anomalies extended along the south pacific the corresponding outgoing longwave radiation anomalies suggest that these structures may be triggered by anomalous convection in the tropics furthermore we show that intraseasonal heat waves in southeastern patagonia tend to occur during active mjo phase 8 these events are also induced by a wave train pattern over the south pacific associated with other intraseasonal variability sources hence as shown in a case study circulation anomalies over the south pacific triggered in general by tropical convection variability and in particular by the mjo activity may constructively interact with circulation patterns resulting from the extratropical dynamics eventually leading to intraseasonal heat waves in southeastern patagonia

chemostratigraphic evidence of deccan volcanism from the marine osmium isotope record continental flood basalt cfb volcanism is hypothesized to have played a causative role in global climate change and mass extinctions uncertainties associated with radiometric dating preclude a clear chronological assessment of the environmental consequences of cfb volcanism our results document a 25 decline in the marine 187 os 188 os record that predates the cretaceous tertiary boundary ktb and coincides with late maastrichtian warming we argue that this decline provides a chemostratigraphic marker of deccan volcanism and thus constitutes compelling evidence that the main environmental consequence of deccan volcanism was a transient global warming event of 3 to 5 c that is fully resolved from the ktb mass extinction

osmium isotopes in hydrothermal fluids from the juan de fuca ridge we present os data for axial high temperature and off axial low temperature hydrothermal solutions from the juan de fuca ridge the high temperature h s bearing axial fluids have unradiogenic os isotopes pointing to a nearly complete domination of osmium isotopes from the basalts during hydrothermal circulation the ridge axis fluids typically do not show large enrichment in osmium concentration over seawater although one high temperature fluid has an os concentration enhanced by a factor of 4 above seawater it appears that the os concentration of high temperature hydrothermal fluids is typically buffered at roughly the seawater concentration we suggest that subseafloor precipitation of pyrite from the high temperature hydrothermal fluids controls the osmium transportation the axial hydrothermal activity does not supply significant amounts of unradiogenic osmium to the deep oceans in contrast a low temperature off axis fluid is enriched in non radiogenic osmium over seawater by a factor of 9 showing much less precipitation of osmium at low temperature because a large fraction of the cooling of oceanic lithosphere occurs on ridge flanks os from low temperature ridge flank hydrothermal circulation may be a significant contributor to the balance of os in the oceans a detailed balance between os contributions from dissolution of cosmic dust and hydrothermal fluids is still not possible the low temperature hydrothermal sample gives os os 0 110 0 001 this extremely unradiogenic osmium can only come from a source that underwent depletion of re over 2 6 ga ago assuming no contamination during sample collection this result suggests that the convecting upper mantle contains ancient depleted material that imparted unradiogenic osmium to intruding basaltic melts

re os geochronology of arctic black shales to evaluate the anisian ladinian boundary and global faunal correlations abstract boreal and tethyan faunas differ throughout the triassic limiting the use of biostratigraphy for global correlation rhenium osmium re os dating of organic rich black shales calibrated with existing biostratigraphy provides a new means to establish correlations of global fauna using absolute time here we present re os radiometric ages for middle triassic organic rich shales from two biostratigraphically defined sections at svalbard and the svalis dome in the barents sea mature black shales from svalbard inferred to be middle to late anisian define a 241 2 2 2 ma isochron with an initial 187 os 188 os ratio of 0 831 0 025 the highest seawater os isotope ratio yet recorded between the cambrian and lower jurassic svalis dome shales in the uppermost anisian yield a 239 3 2 7 ma age and initial 187 os 188 os ratio of 0 679 0 020 the higher initial 187 os 188 os ratio for svalbard shales most likely reflects global seawater at the time of deposition whereas the lower initial 187 os 188 os ratio for the svalis dome may represent seawater with limited communication to the open ocean as suggested by the ratio of trace metal abundances and total organic carbon contents these age data indicate a maximum age of 239 3 2 7 ma for the anisian ladinian boundary in the arctic boreal realm this age agrees with the proposed boundary in the tethyan realm 240 to 243 ma and thus confirms the correlations between boreal and tethys based on biostratigraphy and magnetostratigraphy our study affirms that re os geochronology of black shale is a reliable method for obtaining depositional ages and establishing biostratigraphic correlations between paleogeographically separated regions

high resolution dating of deep sea clays using sr isotopes in fossil fish teeth abstract strontium isotopic compostitions of ichthyoliths microscopic fish remains in deep sea clays recovered from the north pacific ocean odp holes 885a 886b and 886c are used to provide stratigraphic age control within these otherwise undatable sediments age control within the deep sea clays is crucial for determining changes in sedimentation rates and for calculating fluxes of chemical and mineral components to the sediments the sr isotopic ages are in excellent agreement with independent age datums from above diatom ooze below basalt basement and within cretaceous tertiary boundary the clay deposit the 87 sr 86 sr ratios of fish teeth from the top of the pelagic clay unit 0 708989 indicate an late miocene age 5 8 ma as do radiolarian and diatom biostratigraphic ages in the overlying diatom ooze the 87 sr 86 sr ratio 0 707887 is consistent with a cretaceous tertiary boundary age as identified by anomalously high iridium shocked quartz and sperules in hole 886c the 87 sr 86 sr ratios of pretreated fish teeth from the base of the clay unit are similar to late cretaceous seawater 0 707779 0 707519 consistent with radiometric ages from the underlying basalt of 81 ma calculation of sedimentation rates based on sr isotopic ages from hole 886c indicate an average sedimentation rate of 17 7 m myr in unit ii diatom ooze 0 55 m myr in unit iiia pelagic clay and 0 68 m myr in unit iiib distal hydrothermal precipitates the sr isotopic ages indicate a period of greatly reduced sedimentation or possible hiatus between about 35 and 65 ma eocene paleocene with a linear sedimentation rate of only 0 04 m myr the calculated sedimentation rates are generally inversely proportional to cobalt accumulation rates and ichthyolith abundances however discrepancies between sr isotope ages and cobalt accumulation ages of 10 15 myr are evident particularly in the middle of the clay unit iiia oligocene paleocene

influence of the intraseasonal variability on heat waves in subtropical south america the influence of the intraseasonal variability on heat wave development over subtropical south america during austral summer is analyzed the role of the south atlantic convergence zone sacz on this development is documented results show that intraseasonal variability can explain on average at least 32 of summer temperature variance moreover 73 of the heat waves in subtropical south america develop in association with an active sacz the analysis of pentad maps shows that warm conditions in the region under study develop in association with the strengthening of an anticyclonic anomaly which is discernible over the subtropical regions at least 15 days before temperature peak occurrence that circulation anomaly is embedded in a large scale rossby wave train extending along the south pacific ocean that is linked to convection anomalies at the equatorial western and central pacific ocean in addition the development of the anticyclonic circulation over subtropical south america appears to be strengthened by the subsidence conditions promoted by the active sacz which result in temperature rise in the subtropical region under relatively dry conditions on the other hand during the last 2 days of evolution sacz activity weakens and the progressive temperature rise in the region is dominated by warmer and moister air being anomalously advected from the north results confirm the important role that sacz activity on intraseasonal time scales has in inducing persistent circulation anomalies at the subtropical regions that can result in the development of persistent heat waves and very extreme daily temperature

the osmium isotopic composition change of cenozoic sea water as inferred from a deep sea core corrected for meteoritic contributions a detailed study was made of the oceanic 187os 186os variation through the cenozoic by using a hydrogen peroxide leaching procedure on a pelagic clay core from the north pacific long lines 44 gpc3 a 6 h2o2 solution was used the range of 187os 186os obtained by this procedure was between 2 and 8 2 a milder leach 0 15 h2o2 in three out of four samples yielded a slightly higher 187os 186os value than the stronger leach implying that the stronger leach released some meteoritic os with 187os 186os of 1 using published 3he concentrations in gpc3 and cosmic dust 3he and os fluxes to deep sea sediments the extraterrestrial os concentration was estimated for each core segment and subtracted to yield corrected values of 187os 186os the results based on the milder leaching protocol and the 3he correction protocol yield similar values the corrected ocean water 187os 186os pattern for the past 25 million years is similar to that obtained by other workers and is compatible with other results for the entire cenozoic the variation with time in gpc3 uniquely provides a statigraphic signature for the paleogene

tracking drainage basin evolution continental tectonics and climate change implications from osmium isotopes of lacustrine systems abstract organic matter in the lacustrine eocene green river formation in two cores separated by 16 km in the uinta basin record similar centimeter scale initial 187os 188os denoted as osi stratigraphic profiles this demonstrates that the os isotopic composition of lacustrine organic matter is spatially homogeneous and in this case documents variation on the time scale of thousands of years the osi stratigraphy developed here indicates temporal change in the os isotopic composition of lake water which is regulated by the os isotopic composition of inflowing chemical weathering products from the surrounding drainage basin although observed osi variability is just above the level of analytical uncertainty it can be modeled with less than a 6 change in water input from radiogenic to nonradiogenic sources this highlights the sensitivity of this isotopic tracer changes in os isotope composition may reflect changes in relative discharge of rivers with different os isotope composition changes in the footprint of the drainage area to include or exclude different rock types or unroofing thus this study suggests that os isotope stratigraphy in lacustrine settings can be used to link basin stratigraphy to changes in the drainage basin which are driven by climatic tectonic and geomorphic processes the similarity in os isotope stratigraphy between the two cores documented here highlights its utility for detailed chronostratigraphic correlation within and between lacustrine basins a conservative sedimentation rate suggests that osi in these lacustrine deposits changed at a rate of 0 01 per kiloyear two orders of magnitude faster than has been reported in marine organic rich sedimentary rocks ravizza 2007 furthermore linear regression of 187re 188os and 187os 188os ratios of all samples yields a model 3 depositional age determination of 48 3 2 8 ma 2 mswd 8 2 which statistically indistinguishable from a weighted mean laser fusion 40ar 39ar sanidine age of 49 58 0 32 ma smith and carroll 2015 of a temporally adjacent volcanic ash

mapping the relationship between northern hemisphere winter surface air temperature and the madden julian oscillation abstracta regression based modeling approach is described for mapping the dependence of atmospheric state variables such as surface air temperature sat on the madden julian oscillation mjo for the special case of a linear model the dependence can be described by two maps corresponding to the amplitude and lag of the mean atmospheric response with respect to the mjo in this sense the method leads to a more parsimonious description than traditional compositing which usually results in eight maps one for each mjo phase another advantage of the amplitude and phase maps is that they clearly identify propagating signals and also regions where the response is strongly amplified or attenuated a straightforward extension of the linear model is proposed to allow the amplitude and phase of the response to vary with the amplitude of the mjo or indices that define the background state of the atmosphere ocean system application of the approach to global sat for boreal winter clearly shows the propagation of

a comparative study of accumulation rates derived by he and th isotope analysis of marine sediments abstract we present a detailed down core analysis of helium isotope ratios and concentrations for bulk sediments from the central equatorial pacific that span the last two glacial interglacial cycles measured 3 he 4 he ratios range from 1 0 10 5 to 2 1 10 4 or 7 4 to 149 times the atmospheric ratio the 3he from interplanetary dust particles idps constitutes virtually all of the 3he measured within the sediment because carbonate accumulation rates are high in the equatorial pacific the measured 3he concentrations are lower than have been measured elsewhere and range from 4 7 10 13 to 3 0 10 12 cm3stp g 1 if the cosmic dust 3he flux is constant with time sediment mass accumulation rates can be determined from the 3he concentration in sediments the excess 230th technique is an entirely independent method for calculating sediment mass accumulation rates because its source is in situ decay of 234u in seawater to first order initial excess 230th activities correlate with 3he concentrations within this core based on the 230th results we estimate the 3he flux to the earth s surface as 9 6 2 0 10 16 cm3stp cm 2 a 1 if this flux has remained constant over extended periods of time it can be used to determine sediment accumulation rates beyond the 230th range 300 000 yr

reconstructing the marine 187os 188os record and the particulate flux of meteoritic osmium during the late cretaceous abstract paired analyses of os isotope composition and concentration of bulk sediment and leachable os in a metalliferous pelagic clay sequence from the north pacific odp site 886c are used to reconstruct the marine os isotope record and the particulate meteoritic os flux between 65 5 and 78 ma measured 187os 188os of bulk sediments ranges from approximately 0 64 to 0 32 and those of leach analyses are very similar to bulk analyses hydrogenous os dominates the sedimentary os inventory throughout most of the studied interval as a result the measured 187os 188os of leachable os approximates that of contemporaneous seawater the odp 886c record shows rising 187os 188os in the deepest portion of the core with a local maximum of 0 66 close to 74 ma the 67 72 ma portion of the record is characterized by nearly constant 187os 188os ratios close to 0 6 the structure of the marine os isotope record from odp 886c differs markedly from the seawater 87sr 86sr curve which rises monotonically throughout the time interval studied here calculated particulate meteoritic os fluxes are between 0 5 and 2 pg cm 2 kyr 1 throughout most of the studied interval two discrete intervals of the core one of which is within cretaceous tertiary boundary ktb interval are characterized by higher fluxes of meteoritic os excluding these two intervals the average background flux of particulate meteoritic os is roughly half of that estimated from analyses of cenozoic marine sediments these are the first os isotope data to provide evidence of resolvable temporal variations in the background flux of particulate meteoritic material to the earth

extraterrestrial 3 he as a tracer of marine sediment transport and accumulation the deposition rate of deep sea sediments and their focused redeposition by deep sea currents can be evaluated from analyses of sedimentary 230th with a temporal resolution limited only by bioturbation6 7 10 11 230th is produced uniformly throughout the ocean by radioactive decay of dissolved 234u and is removed sufficiently fast by sorption onto sinking particles to act as a constant flux tracer of sedimentation rates but the half life of 230th 75 kyr limits its use for this purpose to the past 200 250 kyr here we explore the use of extraterrestrial 3he from interplanetary dust particles1 4 idps as a constant flux proxy that is free from this limitation a comparison of 3he with 230th in two cores from the equatorial pacific ocean indicates that the variability in the mean flux of idps over the past 200 kyr is less than 75 but in contrast to this relatively constant rate of supply of 3he to the deep sea the local burial rates of 3he and 230th have varied by a factor of five over the past 450 and 200 kyr respect ively we interpret this variability as reflecting sediment focusing with a temporal pattern that suggests regular cycles of climate driven reorganization of near bottom currents in the deep pacific ocean

strontium isotopic variations in jurassic and cretaceous seawater a high resolution seawater strontium isotope curve has been generated through the analysis of well dated and well preserved belemnites and oysters from the middle and upper jurassic and the lower cretaceous of great britain analysis of fe and mn concentrations in these fossils has yielded criteria for eliminating samples that are diagenetically altered the strontium isotope curve remains relatively flat through the aalenian and early bajocian rapidly descends through the late bajocian and bathonian and reaches a minimum in the callovian and oxfordian it then begins a rapid increase in the kimmeridgian and portlandian that continues through much of the early cretaceous the curve levels off in the barremian suddenly dips downwards in the aptian and recovers gradually through the albian the strontium isotopic variations are sufficiently large and the data are presented with sufficient stratigraphic detail to allow precise correlation to the classic ammonite zones and lithologic sections of great britain using the techniques of strontium isotope stratigraphy model results indicate that much of the variation in seawater 87sr86sr between 120 and 40 ma can be explained by changing the intensity of mid ocean ridge hydrothermal fluxes proportionally to estimated mid ocean ridge crustal generation rates it is also possible that the variations during the rest of the mesozoic and the permian are primarily reflections of changing hydrothermal inputs the model results have several important implications first they provide an example in which the variations in the strontium isotope curve are not necessarily driven by changes in fluvial inputs second they suggest that from at least the aptian through the eocene variations in continental weathering were minimal this heightens the importance of the rapid rise in seawater 87sr86sr beginning 40 ma as a significant transition to an extended period of increasing fluvial 87sr fluxes continuing to the present finally the results suggest that several documented short term excursions towards lower 87sr86sr in the latest triassic pliensbachian toarcian callovian oxfordian aptian albian and cenomanian turonian are interpretable as pulses of seafloor hydrothermal activity if so the strontium isotope record offers a means of constraining the timing duration and magnitude of known or proposed hydrothermal events in the geological record

subseasonal variations of rainfall in south america in the vicinity of the low level jet east of the andes and comparison to those in the south atlantic convergence zone abstract regional and large scale circulation anomalies associated with variations in rainfall downstream of the south american low level jet are identified and compared to those in the south atlantic convergence zone sacz composites of precipitation associated with strong jets reveal an approximate doubling of the quantities one would expect from climatology with an evolution of the rainfall pattern from south to north the occurrence of extreme precipitation events follows a similar pattern meridional cross sections of composite wind reveal a distinct low level jet near 20 s and a baroclinic development farther south that appears to force the jet geopotential height temperature and large scale wind composites suggest that this developing disturbance is tied to a wave train that originates in the midlatitude pacific and turns equatorward as it crosses the andes mountains similar composites based on sacz rainfall reveal similar features but of opposite sign suggesting that the phase of the wave

mjo initiation in the real time multivariate mjo index abstractmadden julian oscillation mjo initiation in the real time multivariate mjo rmm index is explored through an analysis of observed case studies and composite events specific examples illustrate that both the dates of mjo initiation and the existence of the mjo itself can vary substantially among several well known mjo indices depending on whether the focus is on convection or circulation composites of primary mjo initiation events in which the rmm index rapidly increases in amplitude from a non mjo state to an mjo state are presented and are supplemented by two case studies from the 1985 86 winter season results illustrate that for primary mjo initiation events in the indian ocean rmm phase 1 slowly eastward propagating 850 hpa 200 hpa easterly westerly anomalies over the indian ocean precede the amplification of the rmm index by at least 10 days while suppressed convection over the western pacific ocean precedes the amplification by 5 days these local eastern hemispheric prede

deposition of osmium and other platinum group elements beneath the ultramafic hosted rainbow hydrothermal plume osmium and other platinum group elements pges have been measured in sediments accumulating directly under the rainbow hydrothermal plume at 36 deg n on the mid atlantic ridge 187os 188os and pge concentrations in the sediments of four cores taken 2 25 km from the active vent site reveal evidence of both radiogenic os scavenged from seawater and importantly unradiogenic os released by hydrothermal venting the majority of analyses n 16 yield 187os 188os ratios that fall in a narrow range 0 99 1 06 close to that of modern seawater in these samples os concentrations correlate linearly with hydrothermal v enrichments which are also derived from seawater scavenging a smaller subset of samples characterized by unusually high concentrations of ni and cr derived from ultramafic rock fragments exhibit distinctly lower 187os 188os ratios their ir content is also higher and their pge ratios are more similar to mantle material than the pge patterns of the larger set of samples dominated by seawater scavenged os although the two most proximal cores lack evidence for any similar ultramafic detritus in their surficial sediments 187os 188os ratios in these samples are also lower than that of ambient seawater suggesting they are likely to have been influenced by unradiogenic os from vent fluid incorporated into the plume samples from the most distal core by contrast exhibit 187os 188os ratios indistinguishable from that of seawater compared with background ne atlantic sediments os is enriched four fold in the seawater dominated samples while pd pt and ir are twice the background value burial fluxes of os scavenged by hydrothermal fe in these sediments are 200 400 pg cm 2 kyr 1 up to twice that found on the epr and several times the background bg of 50 pg cm 2 kyr 1 for pt burial fluxes are 1800 3000 pg cm 2 kyr 1 bg ca 1000 pg cm 2 kyr 1 and for pd 2700 4600 pg cm 2 kyr 1 bg ca 800 pg cm 2 kyr 1

the marine osmium isotope record over the past decade the marine osmium isotope record has been developed into a new tracer in palaeoceanographic research several analytical developments particularly in the past few years have significantly increased our ability to study the behaviour of osmium in the surficial environment the 187os 188os and osmium concentration of seawater river water rain and hydrothermal vent fluids have been measured directly recently the behaviour of osmium in estuaries critical for estimating the marine residence time of osmium has been studied our knowledge of the surficial osmium cycle has thus significantly improved in addition reconstructions of past variations in the marine 187os 188os recently have been extended back into the mesozoic this review attempts to summarize our current understanding of the marine osmium system present and past the 187os 188os of seawater during the cenozoic to first order mimics the marine 87sr 86sr record it is therefore tempting to interpret both records as reflecting increased input of radiogenic osmium and strontium resulting from enhanced continental weathering regulated by climatic tectonic processes however the marine osmium isotope system differs fundamentally from the marine strontium isotope system this review emphasizes three important differences first large impacts are capable of resetting the 187os 188os to unradiogenic values without significantly affecting the marine strontium system second organic rich sediments are characterized by high 187re 188os resulting 187os 188os ingrowth trajectories are similar to the average slope of the cenozoic 187os 188os seawater record trends towards more radiogenic 187os 188os seawater therefore can be caused by weathering of organic rich sediments at a constant rate third the marine residence time of osmium is sufficiently short to capture short periodic glacial interglacial fluctuations that are inaccessible to the buffered marine strontium isotope system this offers the opportunity to discriminate between high frequency climatic and low frequency tectonic forcing

accretion of extraterrestrial matter during the last 80 million years and its effect on the marine osmium isotope record the flux of particulate extraterrestrial et matter to the deep sea has been calculated using a four component mixing model based on osmium concentrations and isotope ratios in slowly accumulating pelagic sediments from the pacific ocean nineteen published bulk leach osmium isotope data pairs that cover the last 80 million years have been used for the calculation the calculated annual particulate flux averaged over several 100 ka by slow accumulation and bioturbation ranges from 18 000 to 67 000 tons with a mean value of 37 000 13 000 tons the data indicate no significant variability in the flux with time except at the k t boundary and are thus compatible with results based on ir accumulation in deep sea sediments the inferred constancy of the et matter flux is in contrast to recent results based on the et 3he flux that integrates only a small size fraction of the entire et matter flux 3he data indicate variability by a factor of 6 over the past 70 ma and a fivefold increase in the et flux between 3 ma and 1 ma that is not seen in the bulk et matter flux based on osmium isotope data the apparent constancy of the cosmic matter flux over the past 80 ma stands in marked contrast to the dynamic nature of the marine osmium isotope record and indicates that dissolution of cosmic matter does not drive changes in this record except at the k t boundary a comparison between osmium isotope and ir data from two pelagic sediment cores from the pacific dsdp site 596 and ll44 gpc3 indicates that the seawater soluble fraction of et os cannot exceed 36 kg a and most likely is significantly smaller the maximum value of 36 kg a can account for approximately one half of the seawater soluble et matter flux necessary to balance the radiogenic continental runoff of os without any additional unradiogenic source simple mass balance calculations indicate that an additional unradiogenic source of os to the oceans most likely alteration of oceanic crust is required to balance the present day seawater osmium isotopic composition this source is probably more important in balancing radiogenic continental runoff than is dissolution of cosmic matter in seawater

cenozoic variations in the flux of interplanetary dust recorded by 3he in a deep sea sediment helium 3 concentrations and 3he 4he ratios in modern pelagic sediments are known to be far in excess of terrestrial values as a result of micrometeorite fallout here i report that extraterrestrial helium is easily detected in a pelagic clay core dating back more than 70 myr the remarkable preservation of the extraterrestrial signature arises from high retention of 3he within interplanetary dust particles coupled with loss of radiogenic 4he from terrestrial mineral grains the core provides a continuous record of the fallout of extraterrestrial helium for the cenozoic era this record suggests that there have been significant variations in the influx of interplanetary dust through time probably related to asteroidal breakup events or the passage of comets through the inner solar system the results also show 3he to be a far more sensitive tracer of the interplanetary dust flux than is iridium

the south atlantic convergence zone intensity form persistence and relationships with intraseasonal to interannual activity and extreme rainfall abstract the characteristics of intensity geographical location and persistence of the south atlantic convergence zone sacz during the austral summer are investigated intensity and spatial features of the sacz are identified by performing a factor analysis of structural properties of outgoing longwave radiation olr data the first two leading factors explain 65 of the total variance of structural properties and characterize the sacz according to intensity and location oceanic versus continental an index is constructed based on the magnitude of the factor scores to identify intense weak and oceanic continental sacz the intense sacz category is associated with negative olr anomalies over a large area of tropical south america extending from the western amazon to the atlantic ocean the weak sacz category is observed with positive olr anomalies over tropical south america and negative olr anomalies over southeastern south america oceanic and continental aspects of the sacz are related to a

evidence for weathering and volcanism during the petm from arctic ocean and peri tethys osmium isotope records sudden global warming during the paleocene eocene thermal maximum petm 55 9 ma occurred because of the rapid release of several thousand gigatonnes of isotopically light carbon into the oceans and atmosphere however the cause of this release is not well understood some studies have linked carbon injection to volcanic activity associated with the north atlantic igneous province naip while others have emphasised carbon cycle feedbacks associated with orbital forcing this study presents the osmium isotope compositions of mudrocks that were deposited during the petm at four locations one from the arctic ocean and three from the peri tethys the os isotope records all exhibit a shift of similar magnitude towards relatively radiogenic values across the petm this observation confirms that there was a transient global increase in the flux of radiogenic os from the weathering of continental rocks in response to elevated temperatures at that time the tectonic effects of naip volcanic emplacement near the onset of the petm is recorded by anomalously radiogenic os isotope compositions of petm age arctic ocean samples which indicate an interval of hydrographic restriction that can be linked tectonic uplift due to hotspot volcanism in the north atlantic seaway the peri tethys data also document a transient higher flux of unradiogenic osmium into the ocean near the beginning of the petm most likely from the weathering of young mafic rocks associated with the naip these observations support the hypothesis that volcanism played a major role in triggering the cascade of environmental changes during the petm and highlight the influence of paleogeography on the os isotope characteristics of marine water masses

accretion rate of extraterrestrial particles determined from osmium isotope systematics of pacific pelagic clay and manganese nodules abstract pelagic clay and mn nodules from domes sites in the north pacific and a varved glacial lake deposit from connecticut were analysed for os concentration and isotopic composition by isotope dilution secondary ion mass spectrometry after treatment by nis fusion or oxalic acid leaching bulk pelagic clay from domes site c has 187 os 186 os 6 5 and os 0 14 ng g oxalic acid leaches of this same sediment and of mn nodules from domes sites a and c have more radiogenic 187 os 186 os ratios which average 8 3 bulk glacial lake hitchcock sediment has 187 os 186 os 12 5 and os 0 06 ng g the total os flux to north pacific pelagic clay is 7 to 10 ng os cm2 106 y lake hitchcock sediment provides an integrated value for the local crustal 187 os 186 os ratio the oxalic acid leaches are assumed to attack hydrogenous phases selectively a simple model in which the only sources of os to the ocean are continental crust with the isotopic composition of lake hitchcock 187 os 186 os 12 5 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of osmium to the sediment of 4 9 ngos cm2 106 y of which 20 is hydrogenous a model in which the sources of os to the ocean are continental crust with an 187os 186os ratio of 30 from the model of palmer and turekian 1986 oceanic mantle or crust with 187 os 186 os 1 04 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of os to the sediment of 5 7 ngos cm2 106 y of which none is hydrogenous these extraterrestrial os fluxes correspond to maximum c 1 chondrite accretion rates of between 4 9 104 and 5 6 104 tonnes y

extra terrestrial influx rates of cosmogenic isotopes and platinum group elements realizable geochemical effects we present estimates of realizable influx of selected cosmogenic isotopes 3he 10be 26al and 14c and platinum group elements ir os and re on the earth via influx of meteoroids we define realizable as the particulate fraction of mass influx which is included in standard geochemical analyses of terrestrial sediments this is the surviving mass fraction of size 0 5 1 cm which gets mixed with terrestrial samples and is analyzed in normal terrestrial assays of sediments larger surviving meteoroid fragments of the order of cm to m or larger obviously belong to the non realizable flux category since i their distribution in terrestrial samples would be very patchy resulting in a highly variable density matrix and ii they would also generally except in wide diameter cores be excluded from sediment cores we estimate the realizable influx of meteoritic particles based on a recent model describing production of smaller size fragments arising during the atmospheric entry of meteoroids implicit in this work is the assumption that the secondary fragments are not subject to much heating and therefore most of the initial 3he and noble gases would be preserved in the secondary fragments since after break up they are not subjected to much heating under this assumption production of small size fragments in the ablation process constitutes a safe landing mechanism for parts of the meteoroid in this paper we show that the meteoritic ablation fragmentation process produces a significant flux of 3he platinum group metals and cosmogenic 26al in fact measurements of these isotopes in ocean sediments should allow a reasonable estimate of temporal variations in the flux of meteoroids of 50 cm to 5 m radii which produce most of the secondary fragments in the size range 1 cm we would like to state here that as pointed out in our previous work stratospheric collections would be biased towards collection of the primary incident extra terrestrial particles whereas terrestrial accumulations representing large area time accumulations as in the case of ocean sediments would efficiently sample the fragmented particles

platinum group elements pge and rhenium in marine sediments across the cretaceous tertiary boundary constraints on re pge transport in the marine environment the nature of re platinum group element pge pt pd ir os ru transport in the marine environment was investigated by means of marine sediments at and across the cretaceous tertiary boundary ktb at two hemipelagic sites in europe and two pelagic sites in the north and south pacific a traverse across the ktb in the south pacific pelagic clay core found elevated levels of re pt ir os and ru each of which is approximately symmetrically distributed over a distance of 1 8 m across the ktb the re pge abundance patterns are fractionated from chondritic relative abundances ru pt pd and re contents are slightly subchondritic relative to ir and os is depleted by 95 relative to chondritic ir proportions a similar depletion in os 90 was found in a sample of the pelagic ktb in the north pacific but it is enriched in ru pt pd and re relative to ir the two hemipelagic ktb clays have near chondritic abundance patterns the 1 8 m wide re pge peak in the pelagic south pacific section cannot be reconciled with the fallout of a single impactor indicating that postdepositional redistribution has occurred the elemental profiles appear to fit diffusion profiles although bioturbation could have also played a role if diffusion had occurred over 65 ma the effective diffusivities are 10 13 cm 2 s much smaller than that of soluble cations in pore waters 10 6 cm 2 s the coupling of re and the pges during redistribution indicates that postdepositional processes did not significantly fractionate their relative abundances if redistribution was caused by diffusion then the effective diffusivities are the same fractionation of os from ir during the ktb interval must therefore have occurred during aqueous transport in the marine environment distinctly subchondritic os ir ratios throughout the cenozoic in the south pacific core further suggest that fractionation of os from ir in the marine environment is a general process throughout geologic time because most of the inputs of os and ir into the ocean have os ir ratios 1 mass balance calculations show that os and re burial fluxes in pelagic sediments account for only a small fraction of the riverine os 10 and re 0 1 inputs into the oceans in contrast burial of ir in pelagic sediments is similar to the riverine ir input indicating that pelagic sediments are a much larger repository for ir than for os and re if all of the missing os and re is assumed to reside in anoxic sediments in oceanic margins the calculated burial fluxes in anoxic sediments are similar to observed burial fluxes however putting all of the missing os and re into estuarine sediments would require high concentrations to balance the riverine input and would also fail to explain the depletion of os at pelagic ktb sites where at most 25 of the k t impactor s os could have passed through estuaries if os is preferentially sequestered in anoxic marine environments it follows that the os ir ratio of pelagic sediments should be sensitive to changes in the rates of anoxic sediment deposition there is thus a clear fractionation of os and re from ir in precipitation out of sea water in pelagic sections accordingly it is inferred here that re and os are removed from sea water in anoxic marine depositional regimes

influence of the madden julian oscillation on east african rainfall i intraseasonal variability and regional dependency the influence of the madden julian oscillation mjo on rainfall amounts over equatorial east africa kenya and northern tanzania is analysed for the period 1979 95 at the intraseasonal pentad time scale the two rainy seasons march to may and october to december are considered intraseasonal wet events in east africa are embedded in large scale zonal circulation anomaly patterns along the equator showing distinct eastward propagation it is further found that these wet events display a clear phasing with respect to the mjo cycle this phasing is expressed as out of phase variations between the highland and the coastal areas such a pattern is suggested to reflect different rain causing mechanisms mjo phases leading to wet spells in the western highland region are those associated with the development of large scale convection in the africa indian ocean region these events are unambiguously related to deep convection fuelled by low level westerly moisture advection mjo phases leading to wet spells in the eastern coastal region are often those associated with overall suppressed deep convection in the africa indian ocean region however these phases induce moisture advection from indian ocean the possible role of stratiform rainfall or relatively shallow convection in the coastal wet spells observed in this phase is discussed the contrasting rainfall conditions found in the two regions for the two opposite mjo phases are strongly correlated with the pressure gradient between the indian and atlantic oceans copyright 2006 royal meteorological society

the osmium riverine flux and the oceanic mass balance of osmium the osmium concentration os and isotopic composition were determined in a set of 17 of the largest rivers of the world os varies between 4 6 and 52 1 pg kg and the 187os 188os ratio varies between 0 64 and 2 94 measurement of rainwater samples shows that there is no input of oceanic os to the continent through rain assuming a negligible anthropogenic os input in the dissolved load the natural average river water has an os concentration of 7 9 pg kg and a mean 187os 188os ratio of 1 54 the total riverine flux of os to the ocean is estimated to be 295 kg yr the dissolved os flux from island arcs and oceanic islands represents less than 5 of the total riverine flux and is not further considered the continental os flux to the ocean is then represented by the riverine flux as dissolved os from eolian dust and glacial sediments is negligible assuming steady state it is possible to estimate a maximum unradiogenic flux to the ocean of 126 kg yr cosmic dust or mantle derived and an oceanic residence time between 2 5 104 and 5 4 104 with a mean of 3 5 104 year the estimation of the flux of dissolved cosmic particles shows that their contribution to the seawater os would be 14 of the contribution of the unradiogenic component which means that the mantle derived flux should contribute a major part the first results on water from high temperature axial hydrothermal systems indicate that their input is probably negligible which would necessitate that dominant contribution from the low temperature alteration of the oceanic crust and or of the ultramafic exposures contributes dominantly to the input of unradiogenic os to the seawater we show that it would be necessary to leach 1 3 of the os contained in the volume of ultramafic exposures accessible to seawater to account for all of the unradiogenic component contribution another simpler but less likely possibility is that the dissolved cosmic dust represents the only source of dissolved unradiogenic os to the ocean in which case the riverine input represents 94 of the total dissolved flux to the ocean instead of 70 the modern global dissolved os flux to the ocean would then have a 187os 188os ratio of 1 44 instead of 1 06 and the system would be far from steady state

interpreting low frequency modes of southern hemisphere atmospheric variability as the rotational response to divergent forcing abstract the principal modes of southern hemisphere low frequency variability have recently been calculated using a 39 yr record of 300 hpa streamfunction fields from the ncep ncar reanalysis dataset the authors attempt to interpret these modes as the rotational response to some divergent forcing for a range of mean states the linearized barotropic vorticity equation bve is used to solve for the divergent wind that would generate or at least be consistent with the observed vorticity modes several of these low frequency modes can be generated by forcing the bve with fairly simple divergent wind fields that could easily be interpreted as resulting from anomalous tropical convection in particular this is found to be true for streamfunction anomalies with el nino southern oscillation enso high latitude mode south pacific wave and madden julian oscillation structure the authors speculate that it may be possible to relate these calculated divergent wind fields to recently observed olr fields and h

the influence of extraterrestrial material on the late eocene marine os isotope record abstract a reconstruction of seawater 187os 188os ratios during the late eocene 36 34 ma based upon bulk sediment analyses from the sub antarctic southern atlantic ocean ocean drilling program odp site 1090 eastern equatorial pacific ocean odp sites 1218 and 1219 and the uplifted land based tethyan section massignano italy confirms that the previously reported abrupt shift to lower 187os 188os is a unique global feature of the marine os isotope record that occurs in magnetochron c16n 1n this feature is interpreted to represent the change in seawater 187os 188os caused by the popigai impact event higher in the massignano section two other iridium anomalies previously proposed to represent additional impact events do not show a comparable excursion to low 187os 188os suggesting that these horizons do not record multiple large impacts comparison of records from three different ocean basins indicates that seawater 187os 188os begins to decline in advance of the popigai impact event at massignano this decline coincides with a previously reported episode of elevated 3he flux suggesting that increased influx of interplanetary dust particles idps contributed to the pre impact shift in 187os 188os and not to the longer term latest eocene 187os 188os decline that occurred 1 million year after the popigai impact event

a 35 myr record of helium in pelagic limestones from italy implications for interplanetary dust accretion from the early maastrichtian to the middle eocene we have determined the helium concentration and isotopic composition of a suite of early maastrichtian through middle eocene pelagic limestones in the italian apennines the results provide a 35 myr record of the implied flux of extraterrestrial 3he which is a proxy for the accretion rate of interplanetary dust particles idps our measurements show that the 3he flux was fairly constant in the maastrichtian except for possible minor increases factor of two or less from 70 5 ma to 68 ma and at 66 ma which probably reflect transient increases in the accretion rate of asteroidal and or cometary idps we find no evidence for an increase in idp accretion at or immediately before the k t boundary implying that the k t impact was not associated with enhanced solar system dustiness this observation precludes the possibility that the k t impactor was a member of a major comet shower and is more consistent with impact of a lone comet or asteroid our data suggest a 2 to 4 fold increase in idp accretion between 57 and 54 ma followed by a factor of three decrease over an 4 myr period in the early to middle eocene the duration and magnitude of this variability is inconsistent with previous observations attributed to a shower of long period comets and is more likely the result of collisions in the asteroid belt and or kuiper belt in the entire 35 myr record we find no evidence for major enhancements of the idp accretion rate of the type expected from comet showers our results in combination with earlier 3he measurements do not support models that predict recurrent comet showers with periods of 38 myrs if there is a periodicity in the cratering record that is caused by periodic modulation of the oort cloud it is not evident in the apennine sediment data along with the 3he measurements we also obtained 4he concentrations which record temporal changes in the flux or composition of terrigenous matter the most significant change in 4he occurs in the last 4 myrs of the cretaceous over which the concentration of 4he in the detrital component rises by 300 this rise tracks a strong increase in the seawater 87 sr 86 sr ratio suggesting a globally significant change in the composition of continental detritus delivered to the oceans possibly arising from increased continental weathering

os isotope insights into major environmental changes of the arctic ocean during the cenozoic 1 recent studies of lomonosov ridge sediments provided evidence for an eocene lacustrine stage in the arctic basin and concluded at its merging into global oceanic circulation some 17 5 ma ago with a 26 ma gap in between here re os data are used to document these events high os concentrations in the lacustrine unit and overlying transitional layer point to low sedimentary o2 conditions highly radiogenic os isotope values mark this layer suggesting massive input of old continental material above os concentrations decrease to typical oxic sediment values whereas 187os 188os ratios follow the trend observed in other oceans however re os isochrons from layers assigned to the upper and lower limit of the 26 ma gap yield identical ages suggesting a short transitional event marking the opening of fram strait and a ca 38 ma for the inception of marine conditions if confirmed this new chronology would modify views about the tectonic evolution of lomonosov ridge

on relationships between nonrecurving western north pacific tropical cyclones the madden julian oscillation and the east asian subtropical jet abstracta 200 hpa zonal momentum budget is performed to examine the role that western north pacific tropical cyclones tcs play in helping to organize intraseasonal extratropical circulation anoma

the accretion rate of extraterrestrial 3he based on oceanic 230th flux and the relation to os isotope variation over the past 200 000 years in an indian ocean core abstract in the eastern equatorial indian ocean the flux of extraterrestrial 3 he a proxy of interplanetary dust particles idps has been relatively constant over the past 200 ka the flux is equal to 1 1 0 4 10 12 cm 3 stp cm 2 ka 1 a value obtained using the xs 230 th profiling method variations in mass accumulation rates mars derived assuming a constant extraterrestrial 3 he flux have a 40 ka periodicity similar to that observed in the 18 o derived mars this frequency is similar to that of the earth s obliquity measured 187 os 188 os ratios are less radiogenic than present day seawater 0 49 0 98 reflecting the mixing of os derived from extraterrestrial terrigenous and hydrogenous sources when coupled with he data measured on the same samples os isotope data yield important information about the terrigenous component supplied to the eastern equatorial indian ocean the amount of os in the sample derived from the extraterrestrial component can be deduced with the help of the helium systematics once corrected for the extraterrestrial component of os os isotope signatures in conjunction with the 4 he concentrations suggest a supply of terrigenous material from indonesian ultramafic and himalayan crustal sources that clearly varies through time

ichthyolith strontium isotope stratigraphy of a neogene red clay sequence calibrating eolian dust accumulation rates in the central north pacific abstract cenozoic pelagic red clays of predominantly eolian and hydrogenous origin blanket much of the central north pacific ocean basin the eolian component is a key indicator of past paleoclimatic conditions thus cenozoic atmospheric circulation can potentially be reconstructed through provenance studies of pacific red clays provided there are precise age controls methods commonly employed in the past to date red clay cores have included cobalt accumulation rates ichthyolith biostratigraphy magnetostratigraphy and ichthyolith strontium isotope stratigraphy the first two dating methods yield ages with large uncertainties while magnetostratigraphy is only relevant to cores with accumulation rates in excess of 1 mm kyr ichthyolith strontium isotope stratigraphy has shown promise as a chronological tool in marine studies but has been only sparingly employed in the dating of marine red clay sequences in this study we present a complete age depth profile for a large diameter piston core from the central north pacific ocean ew9709 pc 01 32 5 n 141 2 w consisting of 11 m of primarily wind deposited dust to generate this age depth profile strontium isotopic compositions were determined on fish teeth ichthyoliths previously cleaned of contaminants using a newly modified reductive cleaning procedure ages were determined by reference to the recently refined sr isotope curve for neogene seawater comparison with nearby giant piston core ll44 gpc3 reinforces the accuracy of our methods the data for ew9709 pc 01 indicate a fairly constant sediment accumulation rate of 0 45 mm kyr over most of the 24 myr time period represented by this core

hot acidic late permian seas stifle life in record time abstract the end of permian time 252 251 ma hosts the largest mass extinction in earth history yet events heralding this global catastrophe remain intensely disputed we present a chemostratigraphic marker the 187re 188os ratio which soars to unprecedented levels approaching the permo triassic boundary these ratios are tied to profound trace element changes and a precise re os time record at 252 ma preserved in black shales from east greenland and the mid norwegian shelf within a 36 meter shale section an 80 fold increase in re concentrations two fold for os signals seawater conditions that became increasingly inhospitable to life unwavering initial 187os 188os ratios of 0 6 preclude mafic volcanism and meteorite impact as the direct cause of late permian anoxia we argue that extraordinarily high 187re 188os ratios are the hallmark of simultaneously rising ocean temperature and acidity leading to loss of oxygen and the stifling of life in latest permian time

intraseasonal variability in south america during the cold season intraseasonal is variability in south america is analyzed during the cold season using 10 90 day bandpass filtered olr anomalies folr is variability explains a large percentage of variance with maximum values over paraguay northeastern argentina and southern brazil the leading pattern of folr as isolated from an eof analysis cold season is pattern csis is characterized by a monopole centered over southeastern south america sesa with a northwest southeast orientation csis induces a large modulation on daily precipitation anomalies especially on both wet spells and daily precipitation extremes which are favored during positive wet csis phases large scale olr anomalies over the tropical indian and west pacific oceans associated with csis exhibit eastward propagation along tropical latitudes in addition circulation anomalies in the southern hemisphere reveal the presence of an anticyclonic anomaly over antarctica with opposite sign anomalies in middle latitudes 10 days before csis is maximum as well as evidence of rossby wave like patterns positive precipitation anomalies in sesa are favored during wet csis phases by the intensification of a cyclonic anomaly located further south which is discernible over the southeastern pacific for at least 14 days before csis peaks the cyclonic anomaly evolution is accompanied by the intensification of an upstream anticyclonic anomaly which remains quasi stationary near the antarctica peninsula before the csis peak we speculate that the stationary behavior of the anticyclonic center is favored by a hemispheric circulation anomaly pattern resembling that associated with a negative southern annular mode phase and a wavenumber 3 4 pattern at middle latitudes

tracking the hirnantian glaciation using os isotopes article i nfo article history here we present initial 187 os 188 os osi values integrated with 13 corg for the first paleozoic section the ordovician silurian boundary gssp at dob s linn scotland our 187 os 188 os data tracks major changes in climate that occurred during the late ordovician hirnantian glaciation which coincides with the second largest known mass extinction during the complanatus and early anceps biozones osi values increase from 0 28 1 08 this provides evidence for a period of increased silicate weathering of radiogenic continental crust likely from the caledonian orogen this increase in weathering was likely the driving mechanism for the drawdown in atmospheric co2 and global cooling that resulted in the onset of the hirnantian glaciation a decrease to less radiogenic osi occurs at the base hirnantian extraordinarius biozone and coincides with the trend to more positive 13 corg values that mark the onset of the hirnantian glaciation the trend in osi during this interval is ascribed to hirnantian ice cover and reduced chemical weathering rates cutting the supply of radiogenic material to the iapetus ocean the reduction in silicate weathering enabled atmospheric co2 to return back to greenhouse levels causing rapid deglaciation during the mid persculptus biozone this period is marked by an abrupt increase in osi values from 0 6 to 1 08 over 19 cm of stratigraphy and coincides with the deglacial limb of the 13 corg profile we interpret the osi data to reflect the leaching of exposed

the pacific south american modes and tropical convection during the southern hemisphere winter abstract atmospheric circulation features and convection patterns associated with two leading low frequency modes in the southern hemisphere sh are examined in multiyear global reanalyses produced by ncep ncar and nasa dao the two leading modes referred to as the pacific south american psa modes are represented by the first two eof patterns the two patterns are in quadrature with each other and are dominated by wavenumber 3 in midlatitudes with large amplitudes in the pacific south american sector in the pacific anomalies in the subtropics and in the midlatitudes are opposite in phase taken together the two psa modes represent the intraseasonal oscillation in the sh with periods of roughly 40 days the evolution of the psa modes shows a coherent eastward propagation a composite analysis was conducted to study the evolution of tropical convection and the corresponding circulation changes associated with the psa modes outgoing longwave radiation olr anomaly composites during the mature phase

evaluation of osmium isotopes and iridium as paleoflux tracers in pelagic carbonates new osmium os isotope and platinum group element pge concentration data are used in conjunction with published 3 he and th isotope data to determine the relative proportions of lithogenic extraterrestrial and hydrogenous iridium ir in a pacific pelagic carbonate sequence from the ocean drilling program odp site 806 on the ontong java plateau ojp these calculations demonstrate that lithogenic and extraterrestrial contributions to sedimentary ir budget are minor while hydrogenous ir accounts for roughly 85 of the total ir application of analogous partitioning calculations to previously reported data from a north pacific red clay sequence ll44gpc3 yields very similar results total ir burial fluxes at site 806 and ll44 gpc3 are also similar 45 and 30 pg cm 2 kyr 1 respectively average ir 3 he and ir xs 230 thinitial ratios calculated from the entire site 806 data set are similar to those reported earlier for pacific sites in general down core profiles of ir 3 he and xs 230 thinitial are not well correlated with one another however all three data sets show similar variance and yield sediment mass accumulation rate estimates that agree within a factor of two while these results indicate that ir concentration has potential as a point paleoflux tracer in pelagic carbonates ir based paleoflux estimates are likely subject to uncertainties that are similar to those associated with co based paleoflux estimates consequently local calibration of ir flux in space and time will be required to fully assess the potential of ir as a point paleoflux tracer measured 187 os 188 os of the ojp sediments are systematically lower than the inferred 187 os 188 os of contemporaneous seawater and a clear glacial interglacial 187 os 188 os variation is lacking mixing calculations suggest os contributions from lithogenic sources are insufficient to explain the observed 187 os 188 os variations the difference between the 187 os 188 os of bulk sediment and that of seawater is interpreted in terms of subtle contributions of unradiogenic os carried by particulate extraterrestrial material down core variations of 187 os 188 os with pt ir and os ir also point to contributions from extraterrestrial particles mixing calculations for each set of several triplicate analyses suggest that the unradiogenic os end member cannot be characterized by primary extraterrestrial particles of chondritic composition it is noteworthy that in efforts aimed at determining the effect of extraterrestrial contributions 187 os 188 os of pelagic carbonates has greater potential compared to abundances of pge an attempt has been made for the first time to estimate sediment mass accumulation rates based on amount of extraterrestrial os in the ojp samples and previously reported extraterrestrial os flux throughout most of the ojp record os isotope based paleoflux estimates are within a factor of two of those derived using other constant flux tracers meaningful flux estimates cannot be made during glacial maxima because the ojp sediments do not record the low 187 os 188 os reported previously we speculate that this discrepancy may be related to focusing of extraterrestrial particles at the ojp as has been suggested to explain down core 3 he variations

a high resolution marine 187os 188os record for the late maastrichtian distinguishing the chemical fingerprints of deccan volcanism and the kp impact event abstract a composite late maastrichtian 65 5 to 68 5 ma marine osmium os isotope record based on samples from the southern ocean odp site 690 the tropical pacific ocean dsdp site 577 the south atlantic dsdp site 525 and the paleo tethys ocean demonstrates that subaerially exposed pelagic carbonates can record seawater os isotope variations with a fidelity comparable to sediments recovered from the seafloor new results provide robust evidence of a 20 decline in seawater 187os 188os over a period of about 200 kyr early in magnetochron c29r well below the cretaceous paleogene boundary kpb confirming previously reported low resolution data from the south atlantic ocean new results also confirm a second more rapid decline in 187os 188os associated with the kpb that is accompanied by a significant increase in os concentrations complementary platinum pt and iridium ir concentration data indicate that the length scale of diagenetic remobilization of platinum group elements from the kpb is less than 1 m and does not obscure the pre kpb decline in 187os 188os increases in bulk sediment ir concentrations and decreases in bulk carbonate content that coincide with the os isotope shift suggest that carbonate burial flux may have been lower during the initial decline in 187os 188os we speculate that diminished carbonate burial rate may have been the result of ocean acidification caused by deccan volcanism

impact of mjo on the intraseasonal variation of summer monsoon rainfall over india the summer monsoon rainfall over india exhibits strong intraseasonal variability earlier studies have identified madden julian oscillation mjo as one of the most influencing factors of the intraseasonal variability of the monsoon rainfall in this study using india meteorological department imd high resolution daily gridded rainfall data and wheeler hendon mjo indices the intra seasonal variation of daily rainfall distribution over india associated with various phases of eastward propagating mjo life cycle was examined to understand the mechanism linking the mjo to the intraseasonal variability during mjo phases of 1 and 2 formation of mjo associated positive convective anomaly over the equatorial indian ocean activated the oceanic tropical convergence zone otcz and the resultant changes in the monsoon circulation caused break monsoon type rainfall distribution associated with this negative convective anomalies over monsoon trough zone region extended eastwards to date line indicating weaker than normal northern hemisphere inter tropical convergence zone itcz the positive convective anomalies over otcz and negative convective anomalies over itcz formed a dipole like pattern subsequently as the mjo propagated eastwards to west equatorial pacific through the maritime continent a gradual northward shift of the otcz was observed and negative convective anomalies started appearing over equatorial indian ocean during phase 4 while the eastwards propagating mjo linked positive convective anomalies activated the eastern part of the itcz the northward propagating otcz merged with monsoon trough western part of the itcz and induced positive convective anomalies over the region during phases 5 and 6 the dipole pattern in convective anomalies was reversed compared to that during phases 1 and 2 this resulted active monsoon type rainfall distribution over india during the subsequent phases 7 and 8 the convective and lower tropospheric anomaly patterns were very similar to that during phase 1 and 2 except for above normal convective anomalies over equatorial indian ocean a general decrease in the rainfall was also observed over most parts of the country the associated dry conditions extended up to northwest pacific thus the impact of the mjo on the monsoon was not limited to the indian region the impact was rather felt over larger spatial scale extending up to pacific this study also revealed that the onset of break and active events over india and the duration of these events are strongly related to the phase and strength of the mjo the break events were relatively better associated with the strong mjo phases than the active events about 83 of the break events were found to be set in during the phases 7 8 1 and 2 of mjo with maximum during phase 1 40 on the other hand about 70 of the active events were set in during the mjo phases of 3 to 6 with maximum during phase 4 21 the results of this study indicate an opportunity for using the real time information and skillful prediction of mjo phases for the prediction of break and active conditions which are very crucial for agriculture decisions

the marine187os 186os record of the past 80 million years we report new187os 186os data and re and os concentrations in metalliferous sediments from the pacific to construct a composite os isotope seawater evolution curve over the past 80 m y analyses of four samples of upper cretaceous age yield187os 186os values of between 3 and 6 5 and187re 186os values below 55 mass balance calculations indicate that the pronounced minimum of about 2 in the os isotope ratio of seawater at the k t boundary probably reflects the enormous input of cosmogenic material into the oceans by the k t impactor s following a rapid recovery to187os 186os of 3 5 at 63 ma data for the early and middle part of the cenozoic show an increase in187os 186os to about 6 at 15 ma variations in the isotopic composition of leachable os from slowly accumulating metalliferous sediments show large fluctuations over short time spans in contrast analyses of rapidly accumulating metalliferous carbonates do not exhibit the large oscillations observed in the pelagic clay leach data these results together with sediment leaching experiments indicate that dissolution of non hydrogenous os can occur during the hydrogen peroxide leach and demonstrate that os data from pelagic clay leachates do not always reflect the os isotopic composition of seawater new data for the late cenozoic further substantiate the rapid increase in the187os 186os of seawater during the past 15 ma we interpret the correlation between the marine sr and os isotope records during this time period as evidence that weathering within the drainage basin of the ganges brahmaputra river system is responsible for driving seawater sr and os toward more radiogenic isotopic compositions the positive correlation between87sr 86sr and u concentration the covariation of u and re concentrations and the high dissolved re u and sr concentrations found in the ganges brahmaputra river waters supports this interpretation accelerating uplift of many orogens worldwide over the past 15 ma especially during the last 5 ma could have contributed to the rapid increase in187os 186os from 6 to 8 5 over the past 15 ma prior to 15 ma the marine sr and os record are not tightly coupled the heterogeneous distribution of different lithologies within eroding terrains may play an important role in decoupling the supplies of radiogenic os and sr to the oceans and account for the periods of decoupling of the marine sr and os isotope records

a complete os excursion across a terrestrial cretaceous paleogene boundary at the west bijou site colorado with evidence for recent open system behavior abstract the few previously reported values of 187os 188os ratios from non marine k pg boundary sections are distinctly higher than the range of 187os 188os ratios measured in chondrites and the range of ratios predicted by models of physical mixing between chondrites and upper crust here re os data from the west bijou continental k pg boundary site located within the denver basin are used to better constrain the os isotopic composition of fallout from the chicxulub ejecta plume for the first time full vertical profiles of 187os 188os ratios and re and os concentrations across a continental k pg boundary section are reported within this section of lignite the lowest measured 187os 188os ratio 0 182 coincides with the k pg boundary interval as previously determined by palynology and the distribution of shocked quartz in a nearby outcrop however sediments with elevated os concentrations and measured 187os 188os below 0 23 extend over a 30 cm interval from 5 cm above the clay rich boundary interval 5 cm thick to 25 cm below maximum ir and os concentrations occur 3 cm and 10 cm below the k pg boundary respectively demonstrating greater diagenetic mobility of os relative to ir low 187os 188os above the k pg boundary suggests that accumulation of impact derived os at this site persisted after the impact event perhaps due to redistribution of impact debris in the surrounding area importantly calculated initial 187os 188os ratios throughout most of the section are impossibly low and require open system behavior likely in the form of re addition within the last 10 million years within the boundary interval re concentrations are among the lowest measured at bowring pit and calculated initial 187os 188os ratios are very similar to those previously reported from the western interior of the united states k pg boundary material 0 14 suggesting super chondritic 187os 188os is characteristic of the chicxulub ejecta plume beyond implications for our understanding of os as an impact tracer this study emphasizes the dramatic effect diagenesis can have on the re os system in organic rich environments especially through post depositional addition of re

the nature of a heat wave in eastern argentina occurring during salljex this note describes the physical processes associated with the occurrence of a heat wave over central argentina during the austral summer of 2002 03 during which the south american low level jet experiment salljex was carried out the salljex heat wave that lasted between 25 january and 2 february 2003 was punctuated by extreme conditions during its last 3 days with the highest temperature recorded over the last 35 yr at several stations of the region it was found that not only the activity of synoptic scale waves but also the intraseasonal oscillation variability had a strong impact on the temperature evolution during this summer during the weeks previous to the heat wave development an intensified south atlantic convergence zone sacz dominated the atmospheric conditions over tropical south america temperatures started to increase in the subtropics due to the subsidence and diabatic warming associated with the sacz as depicted by salljex upper air observations an extratropical anticyclone that evolved along southern south america further intensified subsidence conditions by the end of january the warming processes associated with sacz activity weakened while horizontal temperature advection began to dominate over central argentina due to the intensification of the south american low level jet this mechanism led to temperature extremes by 2 february with temperature anomalies at least two standard deviations larger than the climatological mean values intense solar heating favored by strong subsidence was responsible for the heat wave until 31 january after which horizontal temperature advection was the primary process associated with the temperature peak

summer precipitation variability over south america on long and short intraseasonal timescales a dipole pattern in convection between the south atlantic convergence zone and the subtropical plains of southeastern south america characterizes summer intraseasonal variability over the region the dipole pattern presents two main bands of temporal variability with periods between 10 and 30 days and 30 and 90 days each influenced by different large scale dynamical forcings the dipole activity on the 30 90 day band is related to an eastward traveling wavenumber 1 structure in both olr and circulation anomalies in the tropics similar to that associated with the madden julian oscillation the dipole is also related to a teleconnection pattern extended along the south pacific between australia and south america conversely the dipole activity on the 10 30 day band does not seem to be associated with tropical convection anomalies the corresponding circulation anomalies exhibit in the extratropics the structure of rossby like wave trains although their sources are not completely clear

impact of the madden julian oscillation on summer rainfall in southeast china abstract the impact of the madden julian oscillation mjo on summer rainfall in southeast china is investigated using the real time multivariate mjo rmm index and the observational rainfall data a marked transition of rainfall patterns from being enhanced to being suppressed is found in southeast china east of 105 e and south of 35 n on intraseasonal time scales as the mjo convective center moves from the indian ocean to the western pacific ocean the maximum positive and negative anomalies of regional mean rainfall are in excess of 10 relative to the climatological regional mean such different rainfall regimes are associated with the corresponding changes in physical fields such as the western pacific subtropical high wpsh moisture and vertical motions when the mjo is mainly over the indian ocean the wpsh shifts farther westward and the moisture and upward motions in southeast china are increased in contrast when the mjo enters the western pacific the wpsh retreats eastward and the moi