temporal spatial distribution of thin moist layers in the midtroposphere over the tropical eastern pacific abstract the temporal spatial distribution of thin moist layers in the midtroposphere over the tropical eastern pacific is studied by data analyses of radiosonde soundings and downscaling numerical experiments with a regional model radiosonde soundings at san cristobal galapagos show frequent existence of thin moist layers between 2 and 10 km in altitude with a local minimum at 7 8 km the downscaling experiments with global objective analyses are completed for 2005 06 september and december of 1999 2004 and march of 2000 04 the vertical distribution of thin moist layers has three local maxima at 5 10 and 16 km where bimodality of the frequency distribution of water vapor is evident between 4 and 7 km an annual variation is dominant in the occurrence ratio of thin moist layers which tend to appear in nonconvective regions in boreal winter the layers appear to the north of the intertropical convergence zone itcz whereas in boreal summer the layers appear in the equator side of the itcz i

observations of variability on synoptic timescales in the east pacific itcz abstract data obtained in the eastern pacific intertropical convergence zone itcz during the tropical eastern pacific process study tepps show a 3 6 day variability the noaa ship ronald h brown collected surface meteorological observations c band doppler radar volumes atmospheric soundings and rainfall data while on station at 7 8 n 125 w from 8 23 august 1997 the 3 6 day variability was a prominent timescale in the meridional wind and humidity data the maxima of the surface to 700 mb meridional wind anomalies were 5 12 m s 1 maxima of the moisture anomalies at the same levels were 1 3 g kg 1 in phase with the low level southerlies while upper level moisture lagged the southerlies by less than a day the radar indicated a close connection between precipitation in the vicinity of the ship and the meridional wind with the precipitation occurring when the surface southerlies were strongest the meridional and zonal wind components had a maximum of 850 450 mb wind shear during the southerly e

the annual cycle in equatorial convection and sea surface temperature abstract the coupled atmosphere ocean system in the equatorial eastern pacific and atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes the contrasts are so strong that they dominate the annual march of zonally averaged outgoing longwave radiation for the equatorial belt the march equinox corresponds to the warm season when the equatorial cold tongues in the eastern pacific and atlantic are absent with the onset of summer monsoon convection over colombia central america and west africa in may june northward surface winds strengthen over the eastern pacific and atlantic the equatorial cold tongues reappear and the marine convection shifts from the equatorial belt to the intertropical convergence zones itczs along 8 n as the northern summer program the itczs remain strong and shift northward to new 10 n while sea surface temperature sst continues to drop over the cold tongues and the southern tropics perhaps in response to the

multiyear satellite observations of the atmospheric response to atlantic tropical instability waves 1 high resolution satellite measurements from the tropical rainfall measuring mission trmm quick scatterometer quikscat and special sensor microwave imager ssm i are used to study the variability of sea surface temperature sst surface wind velocity water vapor cloud liquid water and precipitation associated with westward moving tropical instability waves tiws in the atlantic ocean from 1998 to 2005 coherent ocean atmosphere patterns are shown during these 8 years southeasterly trades strengthen and water vapor increases over warm sst anomalies associated with tiws the opposite is true over cold tiw sst anomalies the cloud liquid water and rain response to the ssts follows a similar pattern appearing generally downstream of sst anomalies in the central tropical atlantic the atmospheric response to the tiw sst anomalies extends north of the tiw active region suggesting a remote response to the tiws the atmospheric response to the atlantic tiws also exhibits interannual variations in 1999 owing to the southward movement of the atlantic intertropical convergence zone itcz the rainfall response to the tiw sst anomalies is much larger than in other years when the atlantic itcz moves south it is more susceptible to tiw influence

reconstruction of the mid holocene paleoclimate of the ecuadorian andean paramo at tres lagunas ecuador previous paleoclimate studies have suggested a warm dry event during the mid holocene in paramo vegetation of the tropical andes of south america however the timing of the mid holocene warm dry event in tres lagunas ecuador remains uncertain since a previously reported bog core record characterized the warm dry event during a hiatus in sediment deposition in order to understand the timing of the warm dry event in tres lagunas in relation to regional records a lake sediment core was collected subsamples from the core were analyzed for radiocarbon dates pollen magnetic susceptibility and charcoal to reconstruct the depositional vegetational and fire history of the area a near constant sedimentation rate in the lake core indicated that the lake did not dry in contrast to the adjacent previously reported bog core increases in lower elevation pollen types suggest

the tropical precipitation response to andes topography and ocean heat fluxes in an aquaplanet model this aquaplanet modeling study using the geophysical fluid dynamics laboratory atmospheric model version 2 1 gfdl am2 1 examines how ocean energy transport and topography influence the location of tropical precipitation addingrealistic andes topographyregionally displaces tropical rainfallfromthe equator into the northern hemisphere even when the wind evaporation feedback is disabled the relative importance of the andes compared to the asymmetric hemispheric heating of the atmosphere by ocean transport is examined by including idealized and realistic zonally averaged surface heat fluxes also known as q fluxes in the slab ocean a hemispherically asymmetric q flux displaces the tropical rainfall toward the hemisphere receiving the greatest heating by the ocean the zonal mean displacement of rainfall is greater in simulations with a realistic q flux than with a realistic andes topography simulations that add both a q flux and topography displace rainfallfarthertothenorthintheregion1208tothewestoftheandesthaninsimulationsthatonlyhaveaqflux cloud and clear sky radiative feedbacks in the tropics and subtropics of this model both act to amplify the energy flux and the precipitation response to a given hemispheric asymmetry in oceanic forcing

horizontal and vertical structure of easterly waves in the pacific itcz abstract outgoing longwave radiation olr and low level wind fields in the atlantic and pacific intertropical convergence zone itcz are dominated by variability on synoptic time scales primarily associated with easterly waves during boreal summer and fall this study uses spectral filtering of observed olr data to capture the convective variability coupled to pacific easterly waves filtered olr is then used as an independent variable to isolate easterly wave structure in wind temperature and humidity fields from open ocean buoys radiosondes and gridded reanalysis products the analysis shows that while some pacific easterly waves originate in the atlantic most of the waves appear to form and strengthen within the pacific pacific easterly waves have wavelengths of 4200 5900 km westward phase speeds of 11 3 13 6 m s 1 and maximum meridional wind anomalies at about 600 hpa a warm moist boundary layer is observed ahead of the waves with moisture lofted quickly through the troposphere by deep co

influences of continental monsoons and air sea coupling on the climate of the equatorial pacific abstract an air sea land coupled model of intermediate complexity was used to reveal the important roles of air sea coupling and adjacent continental monsoons i e american monsoons and asian australian monsoons on the annual cycle and mean state of the equatorial pacific excluding the effects of adjacent continental monsoons the simulated mean sst in the western pacific displays a warm bias the sst seasonal cycle exhibits an erroneous dominant annual component in the western pacific and insufficient strength and a 2 month phase delay in the equatorial eastern pacific the air sea coupling alone cannot sustain the full strength of the annual marches of the itcz cold tongue complex this is because the diabatic heating associated with the itcz rainfall generates both a southerly and a westerly component to its equatorward side while the southerly cools the cold tongue establishing a positive feedback to enhance the itcz and the equatorial westerly favors cold tongue warming inducing a negative fe

air sea heat exchange along the northern sea surface temperature front in the eastern tropical pacific abstract the atmospheric response to the oceanic forcing in the eastern pacific along the northern equatorial sea surface temperature sst front is investigated in terms of sensible and latent heat flux during the 6 month period from 28 july 1999 to 27 january 2000 and the 7 month period from 28 june 2000 to 27 january 2001 of particular interest is the atmospheric boundary layer abl response to oceanic tropical instability waves tiws that distort the sst front during may january in normal years in previous studies time series of surface heat fluxes clearly show the influence of tiws but the relationship to spatial patterns of sst and wind speed has been inferred only from sparse in situ data in this study satellite observations are used as a basis for compositing in situ data from moorings to compensate for the lack of a spatially dense mooring array the variability in the position of the sst front caused by westward propagating tiws enables fixed mooring locations to measure the abl response

millennial scale variations in hydrography and biogeochemistry in the eastern equatorial pacific over the last 100 kyr abstract in this study we use records of nitrogen isotope ratios 15n uk 37 temperature estimates organic carbon and opal percentages from high resolution sediment cores located in the eastern equatorial pacific eep to explore the mechanisms linking millennial scale changes in low latitude sea surface temperature water column denitrification and surface productivity to the timing of northern or southern polar climate during the last 100 000 yr our results support a hypothesis that the southern hemisphere and its connection to the low latitudes via shallow subsurface ocean circulation has a primary influence on the biogeochemistry of the eep in addition our results suggest that during the last glacial stage denitrification rates fluctuated on millennial timescales in response to water column ventilation rather than upstream oxidant demand in intermediate depth waters however due to the poor age constraints available for marine isotopic stage mis 3 the eep sedimentary data presented here could support two conflicting mechanisms one driven by enhanced intermediate overturning circulation in the southern ocean during heinrich events antarctic warm events implying that subsurface flow rates control thermocline ventilation and a second one consistent with more sluggish intermediate circulation during antarctic warm events and giving a central role to the temperature control on oxygen solubility in southern ocean surface waters

equatorial atlantic variability and its relation to mean state biases in cmip5 coupled general circulation model gcm simulations participating in the coupled model intercomparison project phase 5 cmip5 are analyzed with respect to their performance in the equatorial atlantic in terms of the mean state 29 out of 33 models examined continue to suffer from serious biases including an annual mean zonal equatorial sst gradient whose sign is opposite to observations westerly surface wind biases in boreal spring play an important role in the reversed sst gradient by deepening the thermocline in the eastern equatorial atlantic and thus reducing upwelling efficiency and sst cooling in the following months both magnitude and seasonal evolution of the biases are very similar to what was found previously for cmip3 models indicating that improvements have only been modest the weaker than observed equatorial easterlies are also simulated by atmospheric gcms forced with observed sst they are related to both continental convection and the latitudinal position of the intertropical convergence zone itcz particularly the latter has a strong influence on equatorial zonal winds in both the seasonal cycle and interannual variability the dependence of equatorial easterlies on itcz latitude shows a marked asymmetry from the equator to 15 n the equatorial easterlies intensify approximately linearly with itcz latitude when the itcz is south of the equator on the other hand the equatorial easterlies are uniformly weak despite serious mean state biases several models are able to capture some aspects of the equatorial mode of interannual sst variability including amplitude pattern phase locking to boreal summer and duration of events the latitudinal position of the boreal spring itcz through its influence on equatorial surface winds appears to play an important role in initiating warm events

bacterially mediated authigenesis of clays in phosphate stromatolites authigenic clays in close textural relation to carbonate fluorapatite within finely laminated phosphate stromatolites of upper jurassic age have been studied using scanning electron microscopy sem transmission electron microscopy tem and analytical electron microscopy aem stromatolite laminae consist of hexagonal prisms of francolite sizes ranging between 0 1 and 1 m that are surrounded by poorly crystalline smectite and amorphous fe si al oxyhydroxides microanalyses show that smectite is fe rich with highly variable composition particularly regarding fe and si contents smectite has significant beidellitic montmorillonitic and non tronitic substitutions although the lack of fringe contrast in some areas adjacent to the smectite packets with 1 0 1 3 nm spacing is due to differences in orientation of layers textural and analytical data clearly indicate the presence of fe si al amorphous phases intimately intergrown with smectite the occurrence of poorly crystalline smectite and associated amorphous phases within microbially precipitated stromatolite laminae both as envelopes around and as pore fillings between extremely small calcium phosphate crystals demonstrates authigenic smectite growth from a precursor fe si al amorphous material this material is formed in close association with a phosphate rich precursor the textural and structural relations the preservation of chemical precursors of glauconite such as nontronitic montmorillonite and the presence of fe si al amorphous mineral phases imply crystallization of the observed crystalline phases from synsedimentary bacterially precipitated amorphous precursors during early diagenesis in postoxic environments carbonate fluorapatite was the first phase to crystallize from the primary gel smectite and associated amorphous fe si al oxyhydroxides were the residual material of the crystallization process the slow rate of transformation at low temperatures from fe si al rich gels to smectite explains the textural relations between the poorly crystalline phases and the phosphate crystals as well as the preservation of amorphous substances in relation to clays authigenic smectite represents the first step in glauconitization

formation and variability of a northerly itcz in a hybrid coupled agcm continental forcing and oceanic atmospheric feedback abstract despite the equatorial symmetry of the annual mean insolation the intertropical convergence zone itcz and the collocated band of high sea surface temperature sst assume perennial northern latitudes over the eastern pacific and atlantic an atmospheric general circulation model is coupled with an intermediate ocean model to study continental forcing and oceanic atmospheric interaction that act to break the equatorial symmetry the model reaches a statistically symmetric mean state under perfectly symmetric conditions with the continental coasts running along meridians when a bulge of landmass is added to the eastern continent north of the equator it initiates a coupled ocean atmosphere wave front that propagates westward across the ocean basin cooling the ocean surface and suppressing deep convection on and south of the equator as a result the itcz shifts into the northern hemisphere in contrast to this basinwide response little latitudinal asymmetry develops in the coupled model when

variability of the atlantic meridional mode during the atlantic hurricane season abstract an observational and modeling study is conducted to investigate the structure of the atlantic meridional mode amm during the atlantic hurricane season and the relationship between amm related sst anomalies and environmental conditions that influence seasonal tropical cyclone activity the observational analysis shows that during the atlantic hurricane season the amm exhibits a similar sst and low level wind structure as during boreal spring when the amm is most active observed amm sst variations are accompanied by air temperature and moisture anomalies that are limited to the boundary layer and an anomalous baroclinic circulation structure in the northern subtropical atlantic with an anomalous lower level cyclonic circulation residing under an anomalous upper level anticyclone during a warm phase this baroclinic structure contributes to a reduction in vertical wind shear over the tropical atlantic that is dominated by changes in the upper level flow two sets of model experiments were cond

mg rich clay mineral formation associated with marine shallow water hydrothermal activity in an arc volcanic caldera setting abstract shallow water hydrothermal activity represented by venting of hydrothermal fluid around 200 c occurs in the wakamiko submarine crater at 200 m water depth in kagoshima bay southwest japan the crater is the center of large eruptions that formed a volcanic caldera which is semi submerged at present the crater is covered with thick volcanic sediments of felsic composition we studied the distribution and chemical composition of hydrothermal clay minerals that are abundant in the sediment collected by piston coring we also conducted chemical analysis of pore fluids squeezed from the sediment to understand hydrothermal interactions that resulted in formation of these clay minerals the pc 2 core 340 cm in length collected in the vicinity of a high temperature fluid venting site was characterized by abundant mg saponite that is limited to a layer between 270 and 300 centimeters below the seafloor cmbsf and montmorillonite throughout the core below 55 cmbsf vertical profiles of pore fluid chemistry suggest that saponite formation is related to the interface between the seawater and the hydrothermal component in the sediment layer formation temperatures of the montmorillonite were estimated to be 118 163 c based on oxygen isotope thermometry formation of the montmorillonite is attributed to hydrothermal interaction between seawater dominant pore fluid and volcanic glass the formation temperature of the saponite was estimated to be 164 c based on oxygen isotope thermometry formation of the saponite is attributed to hydrothermal interaction between seawater dominant pore fluid and the montmorillonite which had been formed at a prior stage the pc 1 core 240 cm in length collected from a relatively low temperature fluid shimmering site was characterized by the occurrence of kerolite in the lower section 210 240 cmbsf vertical profiles of pore fluid chemistry suggest that the kerolite formation occurred at the interface between seawater and the hydrothermal component of the sediment layer formation temperature of the kerolite was estimated to be about 211 c based on oxygen isotope thermometry formation of the kerolite is attributed to precipitation from a fluid that was a mixture of a hydrothermal component and seawater this study revealed the occurrence of mg rich clay minerals saponite and kerolite beneath a submarine hydrothermal field that developed within sediment of felsic composition during hydrothermal interactions that formed these clay minerals seawater penetrated into the sediment and was an important mg source formation of mg rich clay minerals saponite and kerolite are controlled by pore fluid chemistry which varies from a seawater dominant to hydrothermal dominant component exclusive formation of mg rich clay minerals at different sites could be explained by different water rock ratios of the hydrothermal interaction saponite formation at low water rock ratio and kerolite precipitation at high water rock ratio occurrence of mg rich clay minerals provides clues to the hydrological structure in sediment covered hydrothermal systems in an arc volcanic caldera setting

influence of the annual cycle of sea surface temperature on the monsoon onset 1 differing from the traditional focus on land sea thermal contrasts this paper examines the influence of the annual cycle of sea surface temperature sst on the monsoon onset it is found that sst is a major driver of tropical circulations in the atmospheric boundary layer in the trade wind regions the annual cycle of sst involves a shift in the warmest sst axis wssta between two local maxima on either sides of the equator or slight movement of wssta north of the equator consequently wssta has little effect on the regional meridional sst gradient and wind direction however in the monsoon regions the annual cycle of sst is characterized by an abrupt northward jump of wssta resulting in a marked change in regional meridional sst gradient and consequent onset of winds the onset of the southwesterlies lags behind the abrupt northward jump of wssta as an example the climatological onset of the monsoon in the bay of bengal bob shows that the abrupt northward jump of wssta is caused by an increase in sst in the bob leading to the monsoon onset after about 2 pentads sst shows a maximum before the monsoon onset contributing to destabilization of the atmosphere a strong meridional sst gradient occurs between bob and south of the equator after the abrupt northward jump of wssta associated with cross equatorial flow in the eastern indian ocean case studies indicate that an abrupt northward jump in wssta from the equator to north of 10 n is a good omen for the monsoon onset citation jiang x and j li 2011 influence of the annual cycle of sea surface temperature on the monsoon onset j geophys res 116 d10105 doi 10 1029 2010jd015236

short time scale correlation between slow slip and tremor in cascadia 1 we use borehole strain and seismic data to show that slow slip and tremor in central cascadia are correlated on a range of time scales shorter than 1 day the recorded strain rate is our proxy for the slow slip moment rate and the seismic amplitude is our proxy for the tremor amplitude we find that on average the strain rate is higher when the seismic amplitude is larger this correlation persists on time scales between 15 min and 16 h and it can be seen in each of the five slow slip events between 2007 and 2011 our results imply that the slow slip moment rate varies by a large amount even at these short time scales for instance we observe a factor of 2 variation on time scales shorter than 4 h this apparently aperiodic variation is larger than the previously observed variation in moment rate resulting from tidal forcing it is a lower bound on the actual moment rate variation as we detect only changes in slow slip that are correlated with tremor amplitude

effect of bacillus subtilis on granite weathering a laboratory experiment abstract we performed a comparative experiment to investigate 1 how the ubiquitous soil bacterium bacillus subtilis weathers granite and 2 which granite forming minerals weather more rapidly via biological processes batch system experiments granite specimen in a 500 ml solution including nacl glucose yeast extract and bacteria b subtilis at 27 c were carried out for 30 days granite surfaces were observed by sem before and after the experiment b subtilis had a strong influence on granite weathering by forming pits there were 2 4 times as many pits and micropores were 2 3 times wider in granite exposed to b subtilis when compared with bacteria free samples b subtilis appear to preferentially select an optimum place to adhere to the mineral and dissolve essential elements from the mineral to live plagioclase was more vulnerable to bacterial weathering than biotite among the granite composing minerals

hydrothermal interaction between basaltic glass deionized water and seawater abstract this paper presents the results of a series of experiments on the interactions of a basaltic glass with deionized water and natural seawater at 200 c and autogenous pressure in a closed system investigations showed the different mineralogical and geochemical behavior of the basaltic glass in the two solutions the initial stage of interaction with deionized water was characterized by hydration and rapid hydrolysis of the basaltic glass variations in ion concentration showed a parabolic trend from the first hours of interaction indicating selective dissolution of the glass phillipsite mg smectite and analcime were the alteration products according to ph values reached in the solution our data also suggest that only the first reaction stages are affected by grain size and that this controls the times of appearance of the secondary phases experiments on seawater fall into the category of rock dominated but acid ph and quite high mg content persisted throughout this behavior may be correlated to the alteration layer that covers the granules reducing exchanges between glass and seawater and changing our system into the seawater dominated type the continuous acid ph throughout the experiments favoured 6 coordination of al ions in aqueous solution and prevented the crystallization of zeolitic phases mg smectite and anhydrite were the only alteration products in this set of experiments grain size played a minor role in the alteration process since it did not control the time of appearance of secondary phases

local and remote atmospheric response to tropical instability waves a global view from space a la nina took place in the equatorial pacific in 1999 and strong tropical instability waves tiws developed causing large meanders of a sea surface temperature sst front between the equator and 3 n high resolution satellite measurements are used to describe the variability of sst surface wind velocity column integrated water vapor cloud liquid water and precipitation associated with these strong tiws in 1999 coherent ocean atmosphere patterns emerge in both the pacific and atlantic revealing rich regional characteristics in the far eastern pacific southeasterly trades strengthen weaken over positive negative sst anomalies apparently due to enhanced reduced mixing with high speed winds aloft in the central pacific we find evidence that sst induced sea level pressure changes also contribute substantially to wind fluctuations similar sst wind covariability also exists in the southern hemisphere along 2 s but the wind variability induced by unit sst anomaly is much larger than that north of the equator in the central pacific where the equatorial front is broad the northern sst pattern has a large meridional scale and reaches as far north as 6 n further to the north in the intertropical convergence zone itcz where local sst anomalies are small significant variability is found in clouds and precipitation which is further correlated with surface wind convergence in the atlantic tiw signals in sst are strongly trapped near the equator but they induce significant remote response in the itcz which takes a more southern position than its pacific counterpart and thus more susceptible to tiw influence

forcing of anomalous sea surface temperature evolution in the tropical atlantic during pacific warm events the seasonal evolution of anomalous interhemispheric sea surface temperature sst gradients in the tropical atlantic from january to april is studied by composites of the 10 warmest warm and 10 coldest cold januaries during 1948 1993 in the equatorial pacific using comprehensive ocean atmosphere data set ship observations in the warm as compared with the cold years an anomalous weakening of the northward sst gradient develops mainly due to anomalous warming in the tropical north atlantic this stems from the combination of three forcings all related to the weakened north atlantic trade winds during pacific warm events most important are the reduced latent heat flux in much of the tropical north atlantic and anomalous downwelling equatorward of 20 n with a further contribution from increased net radiation resulting from the reduced cloudiness due to the diminished convergence in the downstream portion of the north atlantic trades in response to the development of warm anomalies in the tropical north atlantic during january march the cross equatorial northward winds accelerate to april and this leads south of the equator not only to ekman downwelling enhanced divergence reduced cloudiness and increased net radiation but also to enhanced wind speed and evaporation the result is a modest anomalous warming in the western tropical south atlantic increased air temperature over the entire basin presumably due to atmospheric advection from the pacific has little effect on the atlantic sst pattern the anomalous interhemispheric sst gradient controlled primarily by the warm anomaly in the north atlantic has a pivotal role to play in steering the late boreal winter atmospheric circulation in the tropical atlantic sector and thus regional climate anomalies

influence of south america orography on summertime precipitation in southeastern south america impacts of the main south american orographic structures the andes the brazilian plateau and the guiana shield on the regional climate and associated global teleconnection are investigated through numerical experiments in which some of these features are suppressed simulations are performed with a two way nesting system coupling interactively the regional and global versions of the lmdz4 atmospheric general circulation model at regional scale the simulations confirm previous studies showing that both the andes and the brazilian plateau exert a control on the position and strength of the south atlantic convergence zone sacz mainly through their impact on the low level jet and the coastal branch of the subtropical anticyclones the northern topography of south america appears to be crucial to determine the leading mode of rainfall variability in eastern south america which manifests itself as a dipole like pattern between southeastern south america and the sacz region the suppression of south america orography also shows global scale effects corresponding to an adjustment of the global circulation system changes in atmospheric circulation and precipitation are found in remote areas on the globe being the consequences of various teleconnection mechanisms when the brazilian plateau and the andes are suppressed there is a decrease of precipitation in the sacz region associated with a weakening of the large scale ascendance changes are described in terms of anomalies in the walker circulation meridional displacements of the mid latitude jet stream southern annular mode anomalies and modifications of rossby wave train teleconnection processes

influences of atlantic climate change on the tropical pacific via the central american isthmus recent global coupled model experiments suggest that the atmospheric bridge across central america is a key conduit for atlantic climate change to affect the tropical pacific a high resolution regional ocean atmosphere model roam of the eastern tropical pacific is used to investigate key processes of this conduit by examining the response to a sea surface temperature sst cooling over the north atlantic the atlantic cooling increases sea level pressure driving northeasterly wind anomalies across the isthmus of panama year round while the atmospheric response is most pronounced during boreal summer fall when the tropical north atlantic is warm and conducive to deep convection the pacific sst response is strongest in winter spring when the climatological northeast trade winds prevail across the isthmus during winter the northeasterly cross isthmus winds intensify in response to the atlantic cooling reducing the sst in the gulf of panama by cold and dry advection from the atlantic and by enhancing surface turbulent heat flux and mixing this gulf of panama cooling reaches the equator and is amplified by the bjerknes feedback during boreal spring the equatorial anomalies of sst and zonal winds dissipate quickly in early summer as the seasonal development of the cold tongue increases the stratification of the atmospheric boundary layer and shields the surface from the atlantic influence that propagates into the pacific as tropospheric rossby waves the climatological winds over the far eastern pacific warm pool turn southwesterly in summer fall superimposed on which the anomalous northesterlies induce a weak sst warming there the roam results are compared with global model water hosing runs to shed light on intermodel consistency and differences in response to the shutdown of the atlantic meridional overturning circulation implications for interpreting paleoclimate changes such as heinrich events are discussed the results presented here also aid in understanding phenomena in the present climate such as the central american midsummer drought and atlantic multidecadal oscillation

dynamics of the itcz boundary layer abstractthis paper presents high resolution numerical solutions of a nonlinear zonally symmetric slab model of the intertropical convergence zone itcz boundary layer the boundary layer zonal and meridional flows are forced by a specified pressure field which can also be interpreted as a specified geostrophically balanced zonal wind field ug y one narrow on equatorial peak in boundary layer pumping is produced when the forcing is easterly geostrophic flow along the equator and two narrow peaks in boundary layer pumping are produced on opposite sides of the equator a double itcz when the forcing is westerly geostrophic flow along the equator in the case when easterlies are surrounding a westerly wind burst once again a double itcz is produced but the itczs have significantly more intense boundary layer pumping than the case of only westerly geostrophic flow a comparison of the numerical solutions to those of classical ekman theory suggests that the meridional advection term y plays a vita

mechanisms of abrupt climate change of the last glacial period 1 more than a decade ago ice core records from greenland revealed that the last glacial period was characterized by abrupt climate changes that recurred on millennial time scales since their discovery there has been a large effort to determine whether these climate events were a global phenomenon or were just confined to the north atlantic region and also to reveal the mechanisms that were responsible for them in this paper we review the available paleoclimate observations of abrupt change during the last glacial period in order to place constraints on possible mechanisms three different mechanisms are then reviewed ocean thermohaline circulation sea ice feedbacks and tropical processes each mechanism is tested for its ability to explain the key features of the observations particularly with regard to the abruptness millennial recurrence and geographical extent of the observed changes it is found that each of these mechanisms has explanatory strengths and weaknesses and key areas in which progress could be made in improving the understanding of their long term behavior both from observational and modeling approaches are suggested finally it is proposed that a complete understanding of the mechanisms of abrupt change requires inclusion of processes at both low and high latitudes as well as the potential for feedbacks between them some suggestions for experimental approaches to test for such feedbacks with coupled climate models are given

monsoons itczs and the concept of the global monsoon earth s tropical and subtropical rainbands such as intertropical convergence zones itczs and monsoons are complex systems governed by both large scale constraints on the atmospheric general circulation and regional interactions with continents and orography and coupled to the ocean monsoons have historically been considered as regional large scale sea breeze circulations driven by land sea contrast more recently a perspective has emerged of a global monsoon a global scale solstitial mode that dominates the annual variation of tropical and subtropical precipitation this results from the seasonal variation of the global tropical atmospheric overturning and migration of the associated convergence zone regional subsystems are embedded in this global monsoon localized by surface boundary conditions parallel with this much theoretical progress has been made on the fundamental dynamics of the seasonal hadley cells and convergence zones via the use of hierarchical modeling approaches including aquaplanets here we review the theoretical progress made and explore the extent to which these advances can help synthesize theory with observations to better understand differing characteristics of regional monsoons and their responses to certain forcings after summarizing the dynamical and energetic balances that distinguish an itcz from a monsoon we show that this theoretical framework provides strong support for the migrating convergence zone picture and allows constraints on the circulation to be identified via the momentum and energy budgets limitations of current theories are discussed including the need for a better understanding of the influence of zonal asymmetries and transients on the large scale tropical circulation

shallow meridional circulation in the tropical eastern pacific abstract based on four independent datasets this study presents observational evidence of a shallow meridional circulation cell in the eastern tropical pacific in this shallow meridional circulation cell the northerly cross equatorial return flow from the itcz into the southern hemisphere is found immediately above the atmospheric boundary layer in contrast to the classic concept of the hadley type deep meridional circulation whose northerly return flow resides in the upper troposphere the strength and depth of this shallow meridional circulation undergo a distinct annual cycle possible causes and climatic implications of this shallow meridional circulation are discussed

the obduction of equatorial 13 c water in the pacific identified by a simulated passive tracer the obduction of equatorial 13 degrees c water in the pacific is investigated using a simulated passive tracer of the consortium for estimating the circulation and climate of the ocean ecco the result shows that the 13 degrees c water initialized in the region 8 degrees n 8 degrees s 130 degrees 90 degrees w enters the surface mixed layer in the eastern tropical pacific mainly through upwelling near the equator in the costa rica dome and along the coast of peru approximately two thirds of this obduction occurs within 10 years after the 13 degrees c water being initialized with the upper portion of the water mass reaching the surface mixed layer in only about a month the obduction of the 13 degrees c water helps to maintain a cool sea surface temperature year round equivalent to a surface heat flux of about 6 0 w m 2 averaged over the eastern tropical pacific 15 degrees s 15 degrees n 130 degrees w eastern boundary for the period of integration 1993 2006 during el nino years when the thermocline deepens as a consequence of the easterly wind weakening the obduction of the 13 degrees c water is suppressed and the reduced vertical entrainment generates a warming anomaly of up to 10 w m 2 in the eastern tropical pacific and in particular along the coast of peru providing explanations for the warming of sea surface temperature that cannot be accounted for by local winds alone the situation is reversed during la nina years

glacial interglacial dynamics of the eastern equatorial pacific cold tongue intertropical convergence zone system reconstructed from oxygen isotope records record mean late holocene lh last glacial maximum lgm d 18 o amplitudes ranging between 1 0 and 1 3 we estimate that mean sea surface temperatures sst in this region during the lgm were on average 1 5 0 5 c lower than the lh larger d 18 o amplitudes are observed in sites north of the equator indicating a spatial pattern of reduced meridional sst gradient across the equator during the lgm this result is supported by comparison of mg ca sst reconstructions from two sites straddling the equator we interpret the reduction of this gradient during the lgm as evidence for a less intense cold tongue intertropical convergence zone itcz frontal system a more southerly position of the itcz and weaker southeast equatorial trades in the eep indexterms 1620 global change climate dynamics 3309 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 3344 meteorology and atmospheric dynamics paleoclimatology 4231 oceanography general equatorial oceanography 4267 oceanography general paleoceanography keywords cold tongue itcz oxygen isotopes tropical pacific

the effect of the galapagos islands on the equatorial pacific cold tongue abstract a reduced gravity ocean general circulation model of the tropical pacific ocean is used to determine potential improvements to the simulated equatorial pacific cold tongue region through choices in horizontal resolution and coastline geometry in particular for the galapagos islands four simulations are performed with identical climatological forcing results are compared between model grids with and without the galapagos islands with coarse and fine resolutions it is found that properly including the galapagos islands results in the obstruction of the equatorial undercurrent euc which leads to improvements in the simulated spatial structure of the cold tongue including a basinwide warming of up to 2 c in the east central pacific the obstruction of the euc is directly related to the improvements east of the galapagos islands and for the basinwide reduction of the tropical cold bias through an equatorial dynamical adjustment the pattern of sst warming resulting from the inclusion of the

a new heuristic lagrangian marine boundary layer cloud model abstract a new heuristic model of stratocumulus cloudiness in the inversion capped marine boundary layer is developed and tested the essential ingredient is a new method for predicting the statistical distribution of temperature and specific humidity at the inversion base under partially decoupled conditions along steady state marine boundary layer mbl trajectories mbl decoupling is parameterized as an increasing function of the height difference between the inversion base and lifting condensation level lcl of the mixed layer air required inputs are sea surface temperature sst free air above inversion temperature and humidity subsidence velocity and mean boundary layer wind speed upstream boundary conditions must also be specified but have little influence at sufficient downstream distances 2000 km the model is applied to the cold advection regime of the northeastern subtropical pacific and to both warm and cold advection regimes of the eastern equatorial pacific ocean the model is con

on the role of microbes in the alteration of submarine basaltic glass a tem study abstract the alteration of submarine basaltic glass that has been attributed to microbial activity was investigated via transmission electron microscopy in order to document glass alteration and to understand the chemical reactions that bacteria could utilize the features that were examined occur within fresh glass at the alteration front and consist of 0 1 2 3 m patches or tubes of phyllosilicates rimmed by 0 1 0 3 m wide zones of altered glass the altered glass has lost significant mg fe ca and na slight amounts of al and mn and exhibits an order of magnitude increase of k this incongruent dissolution occurred at neutral to acid ph and temperatures 100 fracture volumes which may be important for the supply of nutrients for microbial activity

metal sorption and mineral precipitation by bacteria in two amazonian river systems rio solimoes and rio negro brazil the surfaces of epiphytic and episammic bacteria from the solute rich waters of the rio solimoes brazil interacted with available cations in solution and provided major sites for iron deposition once bound to the bacteria the iron served as nucleation sites for the formation and growth of fine grained authigenic mineral phases because of progressive mineralization the precipitates exhibited a wide range of morphologies from amorphous gel like to crystalline structures complete encrustation of some bacterial cells was observed the most abundant mineral phase associated with the bacteria was a complex fe al silicate with a variable composition energy dispersive x ray spectroscopy suggested that the gel like structures were similar in composition to a chamositic clay whereas the crystalline phases were increasingly kaolinitic bacteria collected from the solute deficient waters of the rio negro remained conspicuously unmineralized suggesting that metal sorption and biomineralization largely reflect the availability of dissolved metals in the water column in a solute rich river system the fate of the metal loaded bacteria has profound implications for the transfer of metals from the hydrosphere to the sediment through diagenesis the bound metals may either be recycled to the overlying water column or become immobilized as stable mineral phases if the latter occurs microorganisms will have played an important role in metal deposition low temperature clay formation and invariably mudstone diagenesis this implies that in the geologic record microorganisms may have been instrumental in the genesis of many sedimentary rocks of fluvial origin

on the atmospheric boundary layer over the equatorial front abstract this paper presents surface meteorological data and boundary layer profiles from a single meridional transect across the equator along 125 w collected during the pan american climate study mooring cruise in september of 1998 these observations are unique because they occurred at the start of a cold event in the eastern tropical pacific when the sst gradients along the equatorial front were near their climatological maximum in addition to the anomalous cold conditions encountered near the equator an added benefit of this limited study is the relatively high station resolution across the front the meridional minimum in sst and center of the cold tongue was 20 9 c and occurred at 0 4 n an equatorial front was located to the north where sst increased linearly to 25 5 c at 2 0 n the atmospheric boundary layer abl was stable over the cold tongue an unstable abl developed over the warm side of the front in less than 55 km the unstable abl was found at two more stations over the warm side of

wind stress variations and interannual sea surface temperature anomalies in the eastern equatorial pacific abstract vertical advection of temperature is the primary mechanism by which el nino southern oscillation enso time scale sea surface temperature sst anomalies are generated in the eastern equatorial pacific variations in vertical advection are mediated primarily by remote wind forced thermocline displacements which control the temperature of water upwelled to the surface however during some enso events large wind stress variations occur in the eastern pacific that in principle should affect local upwelling rates the depth of the thermocline and sst in this study the impact of these wind stress variations on the eastern equatorial pacific is addressed using multiple linear regression analysis and a linear equatorial wave model the regression analysis indicates that a zonal wind stress anomaly of 0 01 n m 2 leads to approximately a 1 c sst anomaly over the nino 3 region 5 n 5 s 90 150 w due to changes in local upwelling rates wind stress variations of this magnitude occurred in the easte

links between annual variations of peruvian stratocumulus clouds and of sst in the eastern equatorial pacific abstract the hypothesis that peruvian stratocumulus play an important role on both the annual mean and annual variations of sea surface temperature sst in the eastern equatorial pacific is examined the problem is addressed by performing sensitivity experiments using the university of california los angeles coupled atmosphere ocean gcm with different idealized temporal variations of stratocumulus in a region along the coast of peru the results obtained are consistent with the notion that peruvian stratocumulus are a key component of the interhemispherically asymmetric features that characterize the annual mean climate of the eastern equatorial pacific including the cold ssts off peru and the absence of a southern itcz the principal new finding of this study is that the annual variations i e deviations from the annual mean of peruvian stratocumulus are linked to the differences between the amplitude duration and westward propagation of the warm and cold phases of the equatorial cold tongue in

a cloudsat cloud object partitioning technique and assessment and integration of deep convective anvil sensitivities to sea surface temperature a cloud object partitioning algorithm is developed to provide a widely useful database of deep convective clouds it takes contiguous cloudsat cloudy regions and identifies various length scales of clouds from a tropical oceanic subset of data the methodology identifies a level above which anvil characteristics become important by analyzing the cloud object shape below this level in what is termed the pedestal region convective cores are identified based on reflectivity maxima identifying these regions allows for the assessment of length scales of the anvil and pedestal of deep convective clouds cloud objects are also appended with certain environmental quantities from european centre for medium range weather forecasts simple geospatial and temporal assessments show that the cloud object technique agrees with standard observations of local frequency of deep convective cloudiness deep convective clouds over tropical oceans play important roles in earth s climate system the newly developed data set is used to evaluate the response of tropical deep convective clouds to sea surface temperature sst several previously proposed responses are examined the fixed anvil temperature hypothesis the iris hypothesis and the thermostat hypothesis when the data are analyzed per cloud object increasing sst is found to be associated with increased anvil thickness decreased anvil width and cooler cloud top temperatures implications for the corresponding hypotheses are discussed a new response suggesting that the base temperature of deep convective anvils remains approximately constant with increasing ssts is introduced these cloud dependencies on sst are integrated to form a more comprehensive theory for deep convective anvil responses to sst

some overlooked features of tropical atlantic climate leading to a new nino like phenomenon abstract the atlantic nino an equatorial zonal mode akin to the pacific el nino southern oscillation enso is phase locked to boreal summer when the equatorial easterly winds intensify and the thermocline shoals in the gulf of guinea a suite of satellite and in situ observations reveals a new mode of tropical atlantic variability that displays many characteristics of the zonal mode but instead peaks in november december nd this new mode is found to be statistically independent from both the atlantic nino in the preceding summer and the pacific enso the origin of this nd zonal mode lies in an overlooked aspect of the seasonal cycle in the equatorial atlantic in november the equatorial easterly winds intensify for the second time increasing upwelling and lifting the thermocline in the gulf of guinea an analysis of high resolution climatological data shows that these dynamical changes induce a noticeable sst cooling in the central equatorial atlantic the shoaling thermocline and increased upwelli

saline lake diagenesis as revealed by coupled mineralogy and geochemistry of multiple ultrafine clay phases pliocene olduvai gorge tanzania mineralogical and geochemical analyses of ultrafine 0 1 m extracts of pliocene clays from olduvai gorge reveal the complexities of clay diagenesis in saline alkaline paleo waters multiple authigenic phases are routinely present these may be distinguished and quantified by decomposition of xrd 060 peaks coupled with geochemical microprobe hrtem aem and crystallographic ir investigation by assigning geochemistry based on xrd results we identify three principal phases by octahedral composition dioctahedral al rich dioctahedral relatively fe rich and mg rich with a trioctahedral component average octahedral formulae are al 1 30 fe 0 57 mg 0 13 al rich al 0 56 fe 0 80 mg 0 62 fe rich and al 0 09 fe 0 23 mg 2 09 mg rich per half formula unit ir analyses support these octahedral structures the mg rich phase either has coexisting dioctahedral and trioctahedral domains within individual sheets or a homogeneous octahedral sheet of intermediate composition this is to our knowledge the first report of an intermediate octahedral occupancy in a 2 1 phyllosilicate hrtem observations indicate both solid state octahedral and illitization reactions and dissolution precipitation layer charge and interlayer cations suggest that during illitization layer charge increase was due to interaction with na rich brines but later k uptake may have been with either saline or fresher fluids with higher k na ratios all three phases occur throughout the basin relative proportions and octahedral compositions vary total mg content of bulk 0 1 m clay fractions a paleochemical indicator in this and other basins is the product of both the relative abundance and the mg content of the mg rich phase in addition to shedding light on the crystal chemistry of authigenic 2 1 phyllosilicates these results demonstrate the paleolimnologic importance of discriminating the presence of multiple authigenic clay phases in lacustrine deposits

formation of fine grained metal and silicate precipitates on a bacterial surface bacillus subtilis abstract the ability of the gram positive bacterium b subtilis to bind and nucleate precipitates from silicate anions has been studied over 24 weeks in the presence of fe and a1 at concentrations close to those levels in soils and at slightly acid 5 5 and basic 8 0 ph in all cases formation of silicate crystallites quasi crystalline precipitates on the bacterial surfaces was observed bacterially mediated minerals were more diverse in composition and morphology less crystalline smaller and sometimes more abundant than those that were abiotically formed fe pretreatment of the bacterial cells enhanced the binding of silicate at ph 8 0 walls which were not pretreated with fe bound silicate more favourably at acid values when heavy metals pb cd zn cr ni cu were added to the mixture at ph 4 5 silicate retention was greatly favoured giving greater retention of either si or metals than was seen in abiotic controls experiments with only heavy metals showed a high affinity of the bacterial walls for the metals even at low temperatures 4 c it is postulated that a cationic bridging mechanism is involved in the binding of silicate anions by bacterial cell walls

the influence of amazon rainfall on the atlantic itcz through convectively coupled kelvin waves abstract using outgoing longwave radiation olr and tropical rainfall measuring mission trmm daily rain rate data systematic changes in intensity and location of the atlantic intertropical convergence zone itcz were detected along the equator during boreal spring it is found that the changes in convection over the tropical atlantic may be induced by deep convection in equatorial south america lagged regression analyses demonstrate that the anomalies of convection developed over the land propagate eastward across the atlantic and then into africa the eastward propagating disturbances appear to be convectively coupled kelvin waves with a period of 6 7 5 days and a phase speed of around 15 m s 1 these waves modulate the intensity and location of the convection in the tropical atlantic and result in a zonal variation of the atlantic itcz on synoptic time scales the convectively coupled kelvin wave has substantial signals in both the lower and upper troposphere both a reanalysis dataset and the qui

microbial and inorganic control on the composition of clay from volcanic glass alteration experiments biological activity plays a substantial role in the geochemistry of the earth s surface particularly interesting are effects on clay formation because clays are abundant and have high surface to volume ratio resulting in clays making up a large fraction of the overall mineral fluid interface and having an effective control of mineral reactions thus biological control on clay composition would affect element budget globally and the mineralogy of subsequent diagenetic processes biological acceleration of clay production would result in enhanced clay control of mineral reactions and faster organic c sequestration by adsorption on clay minerals with implications for the c and related cycles we investigated the combined effect of microbial activity and water chemistry on the composition of neoformed clay by reacting volcanic glass with natural waters covering a large composition range fresh water from a lake and a spring seawater and hypersaline water the microbes bacteria fungi and algae were totally or partially identified using molecular and microscopy techniques the solid alteration products were analyzed using cryo sem to investigate the mineral microbe interface and tem aem to study the composition of the neoformed clay the solution chemistry was also investigated we found that clay composition was controlled mainly by glass chemistry rather than biological activity through a mechanism of in situ transformation the resulting clay was al rich dioctahedral composition in one case inorganic experiment freshwater lake the specific inorganic conditions of ph and mg and si concentration promoted formation of mg rich trioctahedral clay microbes however did influence clay composition by confining glass grains in biofilms where water chemistry is significantly different from the bulk solution alteration in such conditions generated significant amounts of trioctahedral mg rich clay in the hypersaline water experiment whereas it favored production of dioctahedral al rich clay in the freshwater lake experiment it is thus demonstrated that biofilms can exert an effective control on clay mineralogy

microbial proliferation coinciding with volcanism during the permian triassic transition new direct evidence from volcanic ashes south china abstract coupling with major biotic extinction both widespread microbially mediated deposits and ash beds characterize the permian triassic boundary ptb successions worldwide thus active volcanism through the ptb interval has been proposed to account for contemporary microbial bloom direct evidence however has long been scarce here we present several lines of evidence for microbial proliferation in the ptb ashes from south china petrographic analysis reveals annular granular and tubular bioalteration textures that formed during microbial dissolution of glass and subsequent precipitation annular textures appear as fresh glass shards connected with bands in different thicknesses showing rough and sharp interfaces and are bordered with fibrous textures granular textures are composed of clusters of near spherical bodies ranging in size from 0 05 to 2 m tubular textures occur as straight curved or spiral tunnels excavating into fresh glass their distinctive morphologies microbe analogous sizes and log normal size distributions all indicate a biogenic origin element mapping along alteration fronts shows enrichment of organic carbon and depletion in metabolically significant elements providing further support for their biogenicity besides textural relationships low n k and high c contents as well as pronounced microstructure density variations between different ash beds in same section all suggest that the bioalteration textures are syngenetic with volcanic glass relevant to microfossils rather than recent microbes we interpret the fossilized organic remains e g small coccoid like spheroids rods filaments and thin films as extracellular polymeric substances eps probably produced by microorganisms which might have served as templates for nucleation and played a crucial role in bio mineralization process the diversity of microstructure sizes shapes and organic remains may reflect a complex community of microbes in the ptb ashes we infer that microbial proliferation may contribute to negative c isotope excursions in the ptb ashes microbial blooms in ash beds directly triggered by large scale volcanism may reveal that extreme environmental stresses prevailed during the ptb crisis

microbial alteration of 0 30 ma seafloor and sub seafloor basaltic glasses from the australian antarctic discordance scanning electron microscopic observations of alteration rims in basaltic glasses dredged from 0 2 5 ma seafloor and drilled from 18 28 ma ocean crust ocean drilling program odp leg 187 in the australian antarctic discordance aad document the presence of endolithic microbes in altered basalt glass in very young aad lavas 10 m thick alteration rims are developed along intersecting fractures and cracks and the altered glass contains numerous spherical rod and star shaped partially fossilised microbial cells similar to those from the arctic ridges 1 2 in 2 5 ma basalt glasses altered rims are up to 250 m thick and zeolite phillipsite is present within many fractures spherical cells occur in porous outer zones of alteration rims and on zeolite crystal surfaces within fractures indicating that microbial activity persists in the region for at least 2 5 ma mn rich microbial cell encrustations associated with zeolite suggest that mn is used in an energy yielding metabolic process combined with recent results from the arctic ridges the results from this study demonstrate that endolithic microbial growth is a persistent feature of mid ocean spreading ridges in glasses from odp cores 1 mm thick alteration rims are developed along the widest fractures lined with mn fe oxyhydroxides and or clay and filled by zeolite and calcite most common however are 10 200 m thick rims developed along zeolite filled more narrow fractures and cracks zeolite filled fractures with only minor to no alteration indicate several episodes of fracturing followed by relatively fast sealing there is no age progression in alteration thickness along fractures or other characteristics suggesting that alteration is essentially completed between 2 5 and 18 ma a comparison of alteration in the 2 5 ma glass with that in the odp samples indicates that a significant proportion of the glass alteration in the drilled samples developed prior to burial although one type of diffuse highly irregular front that is only observed in the odp samples most likely developed after burial these diffuse alteration fronts are caused by dissolution and alteration of the glass into minute globules 0 05 0 2 m in diameter with no associated microbial morphologies fossilised mn rich cells do occur within zeolite filled fractures possibly indicating that microbial activity continued in the fractures for as long as circulation continued the apparent non biological origin of diffuse irregular alteration fronts in buried aad glasses indicates that these textural features are not reliable as diagnostic criteria for the existence of a deep biosphere in the volcanic ocean crust

geomicrobiology its significance for geology abstract some microorganisms including various kinds of bacteria fungi algae and protozoa serve as geochemical agents in the uppermost lithosphere and in the hydrosphere some promote rock weathering by mobilizing mineral constituents with inorganic or organic acids or ligands that they excrete others promote rock weathering by redox attack of mineral constituents such as fe and mn still others cause active or passive mineral formation by precipitation and subsequent nucleation of crystal formation on or in the cell or in the bulk phase they play a role in some phases of fossil fuel formation and accumulation they modulate the terrestrial and marine cycles of c n s and p and some other elements and they influence the composition of the atmosphere in respect to o 2 co 2 and ch 4 some discriminate between stable isotopes of h c o n and s

weathering and alteration of volcanic ashes in various depositional settings during the permian triassic transition in south china mineralogical elemental and isotopic approaches to better understand the alteration of volcanic ash in different depositional environments we measured the clay mineralogy major and trace element geochemistry and sr and nd isotopic composition of altered ashes in two permian triassic boundary ptb successions in southern china the pengda and xinmin sections in guizhou province represent different depositional settings allowing us to investigate the role of the early burial environment on authigenic clay formation the ptb ash beds in both sections consist predominantly of mixed layer illite smectite clays altered ashes in the relatively shallow pengda section contain predominantly r2 and r3 i s clays with 70 to 85 illite layers whereas their stratigraphic equivalents in the deeper xinmin section contain only r3 i s clays which are of two types with 88 and 99 illite layers respectively the two studied ash beds can be stratigraphically correlated between the pengda and xinmin sections and show similar 143nd 144nd ratios 0 511991 for pd 1 and 0 511983 for xm 1 0 512073 for pd 2 and 0 512074 for xm 2 ree distributions and immobile element cross plots are consistent in suggesting that the altered ashes may have originated via felsic volcanism altered ashes in the deep sea xinmin section have notably high 87sr 86sr ratios 0 764209 and 0 795921 relative to those from equivalent horizons in shallower environments 0 728455 and 0 749953 this difference in 87sr 86sr ratios is likely attributable to different degrees of chemical weathering elemental ratios such as sio2 al2o3 k2o al2o3 y sr and zr sr all support more intensive chemical leaching in deep water environments the altered ashes at xinmin contain substantially more k2o than those at pengda suggesting greater incorporation of k into clay minerals due to lower ph during early diagenesis clay mineral assemblages and stacking structures of i s clays in the altered ashes are consistent with a general sequence of smectite illitization during diagenesis and burial metamorphism in both sections

observations of coupling between surface wind stress and sea surface temperature in the eastern tropical pacific satellite measurements of surface wind stress from the quikscat scatterometer and sea surface temperature sst from the tropical rainfall measuring mission microwave imager are analyzed for the three month period 21 july 20 october 1999 to investigate ocean atmosphere coupling in the eastern tropical pacific oceanic tropical instability waves tiws with periods of 20 40 days and wavelengths of 1000 2000 km perturb the sst fronts that bracket both sides of the equatorial cold tongue which is centered near 1 8s to the east of 1308w these perturbations are characterized by cusp shaped features that propagate systematically westward on both sides of the equator the space time structures of these sst perturbations are reproduced with remarkable detail in the surface wind stress field the wind stress divergence is shown to be linearly related to the downwind component of the sst gradient with a response on the south side of the cold tongue that is about twice that on the north side the wind stress curl is linearly related to the crosswind component of the sst gradient with a response that is approximately half that of the wind stress divergence response to the downwind sst gradient the perturbed sst and wind stress fields propagate synchronously westward with the tiws this close coupling between sst and wind stress supports the wallace et al hypothesis that surface winds vary in response to sst modification of atmospheric boundary layer stability

polar climate instability and climate teleconnections from the arctic to the midlatitudes and tropics abstract it is generally accepted that the ocean thermohaline circulation plays a key role in polar climate stability and rapid climate change recently reported analyses of the impact of anomalous freshwater outflows from the north american continent onto either the north atlantic or arctic oceans demonstrate that in either case a clear reduction in the atlantic meridional overturning circulation accompanied by an increase in sea ice extent is predicted the results also reconcile proxy inferred younger dryas greenland temperature variations the aim of the present work is to provide a detailed investigation of the pathways along which the signal associated with overturning circulation anomalies propagates into both the midlatitudes and the tropics and the effect such teleconnections have on the tropical ocean atmosphere system the authors consider both the impact of substantial slowing of the overturning circulation due to freshwater forcing of the north atlantic as well as its recovery after the a