influence of sea ice on the thermohaline circulation in the arctic north atlantic ocean a fully prognostic coupled ocean ice model is used to study the sensitivity of the overturning cell of the arctic north atlantic system to sea ice forcing the strength of the thermohaline cell will be shown to depend on the amount of sea ice transported from the arctic to the greenland sea and further to the subpolar gyre the model produces a 2 3 sv increase of the meridional circulation cell at 25n at the simulation year 15 corresponding to a decrease of 800 km in the sea ice export from the arctic previous modeling studies suggest that interannual and decadal variability in sea ice export of this magnitude is realistic implying that sea ice induced variability in the overturning cell can reach 5 6 sv from peak to peak

climate information imprinted in oxygen isotopic composition of precipitation in europe abstract in this study we analyze the interannual variability of the oxygen isotopic composition of winter precipitation 18 o prec over europe and investigate its related climate information for this purpose we compare winter temperature precipitation and 18 o prec modeled by the atmospheric general circulation model echam5 wiso with different observational datasets over europe in general the model and data results are very similar for the present day climate and the modeled 18 o prec is matching the global network of isotopes in precipitation station data echam5 wiso only slightly underestimates the temperatures over europe mean difference 0 4 c the mean european precipitation amount is very similar 85 mm month however in central western europe the modeled precipitation is overestimated by up to 30 mm month we also evaluate the large scale circulation associated with the regional 18 o prec values by correlating the north atlantic oscillation nao index to modeled 18 o prec fields we show that the nao pattern is most pronouncedly imprinted in 18 o prec over central western europe consistent with observations we demonstrate for an example location near a stalagmite site in central germany how local isotope related climate variables are related to large scale european climate variability we find that in both the model results and the data present day winter variability of local 18 o prec is strongly related to atmospheric circulation remote sea level pressure fields and much less to the local and remote temperature or precipitation fields the simulated correlation pattern resembles the nao pattern but is tilted to the east due to the combined effect of temperature and precipitation

temperature extremes in the south of south america in relation to atlantic ocean surface temperature and southern hemisphere circulation 1 the objective of this research is to study the main variability modes of the frequency of extreme temperatures in the south of south america their relation to sea surface temperatures ssts and some indices of atmospheric circulation in the southern hemisphere observational data and reanalysis data were used for this purpose over the 1964 2003 period an initial analysis showed that between the months of march and june the frequency of warm events especially warm nights is highly associated with the sst in coastal zones a wavelet analysis showed that the main variability mode found at a seasonal scale was an 8 year wave signal present in spring that remains active until the 1990s it was noticeable in the analysis of cold nights atlantic ssts pacific ssts and the southern annular mode sam a cross wavelet analysis among them reflected this signal as a common variability mode with the positive phase of the sam congruent with the warmest conditions in the coastal zones of the atlantic ocean and lower cases with cold nights at the reference meteorological stations analyzed although longer series are desirable for low frequency variability analysis the results agree with previous studies that take into account an 8 year periodicity of the baroclinic waves at the southern hemisphere supporting the relevance of the 8 year signal

rheology and rupture of homogeneous silicate liquids at magmatic temperatures homogeneous silicate liquids have a newtonian rheology under conditions of modest stress but under relatively high stress or otherwise imposed high rates of deformation their viscosity may become non newtonian before the onset of rupture this behavior has been discussed semi empirically as well as in terms of the maxwell model liquid here it is shown that the configurational entropy theory for the occurrence of the glass transition can also explain this non newtonian rheology of silicate liquids ranging in composition from silica rich to silica poor the pressure and temperature dependence of the transition from newtonian to non newtonian flow is discussed qualitatively geological applications are indicated fragmentation of silicate liquids takes place when the glass transition is crossed and the liquid has become solid like experimental evidence indicates that the rupture strength is only slightly larger than the stress needed to cause the onset of non newtonian rheology

evolution of the relationship between near global and atlantic sst modes and the rainy season in west africa statistical analyses and sensitivity experiments monthly sea surface temperature anomalies ssta at near global scale 60 n 40 s and may to october rainfall amounts in west africa 16 n 5 n 16 w 16 e are first used to investigate the seasonal and interannual evolutions of their relationship it is shown that west african rainfall variability is associated with two types of oceanic changes 1 a large scale evolution involving the two largest ssta leading eigenmodes 16 of the total variance with stronger loadings in the equatorial and southern oceans related to the long term multiannual component of rainfall variability mainly expressed in the sudan sahel region and 2 a regional and seasonally coupled evolution of the meridional thermal gradient in the tropical atlantic due to the linear combination of the two largest ssta modes in the atlantic 11 with strong inverse loadings over the northern and southern tropics which is associated with the interannual and quasi decadal components of regional rainfall in west africa linear regression and discriminant analyses provide evidence that the main july september rainfall anomalies in sudan sahel can be detected with rather good skills using the leading april june or synchronous july september values of the four main oceanic modes in particular the driest conditions over sahel more marked since the beginning of the 1970s are specifically linked to the warm phases of the two global modes and to cold warm anomalies in the northern southern tropical atlantic idealized but realistic ssta patterns obtained from some basic linear combinations of the four main oceanic modes appear sufficient to generate quickly from mid july to the end of august significant west african rainfall anomalies in model experiments consistent with the statistical results the recent negative impact on west african rainfall exerted by the global oceanic forcing is primarily due to the generation of subsidence anomalies in the mid troposphere over west africa when an idealized north to south ssta gradient is added in the tropical atlantic strong north to south height gradients in the middle levels appear these limit the northward excursion of the rainbelt in west africa the sahelian area experiences drier conditions due to the additive effect subsidence anomalies latitudinal blocking while over the guinea regions wet conditions do not significantly increase since the subsidence anomalies and the blocking effect act here in opposite ways

role of conduit shear on ascent of the crystal rich magma feeding the 800 year b p plinian eruption of quilotoa volcano ecuador we have characterized pumice products belonging to the climactic phase of the 800 year b p quilotoa eruption bulk rock compositions petrography mineral and glass chemistry and textural investigations were performed on the three end member pumice types namely white gray and mingled pumices all the investigated pumice clasts are dacites characterized by the same bulk rock composition and mineralogical assemblage but glass compositions and bulk textures change according to different pumice types white pumice has higher crystallinity 48 wt abundant euhedral pheno microphenocrysts no groundmass microlites the most evolved glass compositions 74 78 wt sio2 and heterogeneous vesicle populations marked by deformed and highly coalesced vesicles with thin walls gray pumice exhibits lower crystallinity 29 36 wt abundant broken and or resorbed crystals ubiquitous groundmass phenocryst fragments and microlites the widest range of glass compositions 69 78 wt sio2 and quite homogeneous poorly deformed and coalesced vesicles with thicker walls mingled pumices are characterized by the alternation of bands or patches with white and gray pumice compositional and textural characteristics we attribute heterogeneities in glass compositions and crystal and vesicle textures to processes occurring within volcanic conduits as magma is ascending to the surface in particular the above observations and results are consistent with an origin of a gray magma by heating of the original white magma in a strongly sheared region of the conduit because of a mechanism of viscous dissipation and crystal grinding and resorption at the conduit walls the less viscous gray magma therefore would enable the onset and preservation of a high mass flux of the eruption otherwise difficult to explain for highly viscous crystal rich dacitic magmas

north atlantic climate and deep ocean flow speed changes during the last 230 years variations in the near bottom flow speed of iceland scotland overflow water isow are documented in a 230 year long deep sea sediment record from the eastern flank of reykjanes ridge in the subpolar north atlantic at sub decadal time scales for recent decades the isow palaeocurrent reconstructions show similarities with observational hydrographic data furthermore recent isow flow changes fall mostly within the range of its variability of the past 230 years the record also reveals a hitherto unrecognized coupling of deep flow speeds in the subpolar north atlantic with the north atlantic oscillation nao index with more less vigorous isow flow during negative positive phases of the nao our results suggest that the changes in isow vigor are largely controlled by the transport and characteristics of labrador sea water rather than variations in the overflow itself with implications for the meridional overturning of the atlantic ocean and climate

on multidecadal and quasi decadal north atlantic variability observed sea surface temperatures ssts in the north atlantic from 1958 through 2000 as well as data from an ocean model simulation driven with the atmospheric variability observed during the same period are examined using multichannel singular spectrum analysis the two leading oscillatory modes are associated with a multidecadal and a quasi decadal period the former is connected to a basinwide uniform sst pattern and changes in the deep north atlantic meridional overturning circulation the quasi decadal mode involves a tripolar sst anomaly pattern forced by atmospheric variability with a spatial structure resembling that of the north atlantic oscillation nao the upper ocean s dynamical response to this nao variability provides an instantaneous positive feedback to the sst pattern while a delayed negative feedback is due to shallow overturning circulation anomalies

mechanisms of decadal north atlantic climate variability and implications for the recent cold anomaly decadal sea surface temperature sst fluctuations in the north atlantic ocean influence climate over adjacent land areas and are a major source of skill in climate predictions however the mechanisms underlying decadal sst variability remain to be fully understood this study isolates the mechanisms driving north atlantic sst variability on decadal time scales using low frequency component analysis which identifies the spatial and temporal structure of low frequency variability based on observations large ensemble historical simulations and pre industrial control simulations we identify a decadal mode of atmosphere ocean variability in the north atlantic with a dominant time scale of 13 18 years large scale atmospheric circulation anomalies drive sst anomalies both through contemporaneous air sea heat fluxes and through delayed ocean circulation changes the latter involving both the meridional overturning circulation and the horizontal gyre circulation the decadal sst anomalies alter the atmospheric meridional temperature gradient leading to a reversal of the initial atmospheric circulation anomaly the time scale of variability is consistent with westward propagation of baroclinic rossby waves across the subtropical north atlantic the temporal development and spatial pattern of observed decadal sst variability are consistent with the recent observed cooling in the subpolar north atlantic this suggests that the recent cold anomaly in the subpolar north atlantic is in part a result of decadal sst variability

bathymetric distribution of fossil foraminifera within marine sediment cores from the eastern part of lutzow holm bay east antarctica and its paleoceanographic implications abstract faunal analysis of fossil foraminifera from marine gravity and piston cores collected by the japanese antarctic research expeditions 1981 and 1992 is used to estimate the impact of the latest quaternary paleoceanography on coastal environments of the eastern part of lutzow holm bay east antarctica accelerator mass spectrometry ams carbon 14 ages produced from sedimentary organic carbon were less than 16 ka non corrected detailed correlation among submarine cores and holocene elevated marine deposits exposed on the eastern shore of the embayment is difficult due to the indefinite reservoir correction value for marine organic matter and to upward increasing abnormal ages for some cores a local carbonate dissolution level can be delineated around the present depth of 300 400 m or shallower in the eastern part of lutzow holm bay during the holocene based on distributional trends of arenaceous calcareous benthic and planktonic foraminifera recognized within a depth less than 600 m downcore recovery of calcareous foraminifera containing bulimina aculeata from two cores obtained in a drowned glacial trough deeper than 600 m situated far beyond the dissolution depth of caco3 indicates the incursion of warm high nutrient and caco3 saturated circumpolar deep water cdw from the offshore area along the trough toward the southeastern coast of lutzow holm bay during the holocene the intrusion of cdw impacted on the marine environments of the southeastern coast thereby contributing to peripheral retreat of the ice sheet as well as increasing calcareous benthic foraminiferal productivity along the southeastern coast of lutzow holm bay

possible impacts of mega el nino southern oscillation and atlantic multidecadal oscillation on eurasian heatwave frequency variability identifying predictability sources of heatwave variations is a scientific challenge and of practical importance this study investigates the summertime heatwave frequency hwf over eurasia for 1950 2014 the eurasian hwf is dominated by two distinct modes the interdecadal id mode featured by an increasing pattern overall centred around eastern europe central asia and mongolia southwestern china and the interannual ia mode resembling a tripole anomaly pattern with three centres over western northern europe northeastern asia and east asia the id mode is found to be influenced by mega el nino southern oscillation mega enso and the atlantic multidecadal oscillation amo and the latter has far more effect whereas the ia mode is connected with mega enso further analysis suggests that mega enso variations can incite a gill type response spreading to eurasia while the amo changes cause eastward propagating rossby wave trains toward eurasia these two teleconnection patterns together contribute to the large scale circulation anomalies of the id mode and those related to the ia mode arise from the teleconnection pattern excited by mega enso a strong mega enso triggers subsidence with high pressure anomalies warms the surface and increases the hwf significantly over northeastern asia particularly likewise the warm amo induced circulation anomalies engender surface radiative heating and hwf growth in most of the eurasian continent except some localized siberian and asian regions the situation is opposite for a weak mega enso and amo those models from phase 5 of the coupled model intercomparison project cmip5 which realistically capture the features of the id mode can reproduce the amo like sea surface temperature anomalies sstas while signals resembling mega enso are found in those with favourable capability of simulating the ia mode on the contrary these relevant sstas linked to the respective modes vanish in the models with little skills thus mega enso and the amo might provide two critical predictability sources for heat waves over eurasia

simulated impacts of the south atlantic ocean dipole on summer precipitation at the guinea coast an intermediate complexity atmospheric general circulation model has been used to investigate the influence of the south atlantic ocean sao dipole saod on summer precipitation over the guinea coast of west africa two ensemble integrations in which idealized but realistic saod type sea surface temperature sst anomaly is prescribed only in the sao and then globally are performed and inter compared consistently above below the average precipitation is simulated over the guinea coast during the positive negative phase of the saod comparison of the two set of experiments reveal that in its active years the saod is a dominant mechanism that shapes the spatial character of summer precipitation at the guinea coast the global sst variability merely slightly moderate its effects during the saod cool sst anomaly in the extra tropical sao off the brazil uruguay argentina coast gives rise to suppressed convection and mass divergence in turn the subsidence tends to amplify the sub tropical arm of anomalous hadley type circulation and consequently large scale convection and mass flux convergence in the equatorial atlantic ocean gulf of guinea region bordering on the coastal fringes of west africa precipitation is therefore increased at the guinea coast

relations of the low level extratropical cyclones in the southeast pacific and south atlantic to the atlantic multidecadal oscillation abstractthe relations of the low level extratropical cyclones in the southeastern pacific and south atlantic with the sea surface temperature sst anomalies associated with the atlantic multidecad

multidecadal variability of the overturning circulation in presence of eddy turbulence at low resolution idealized ocean circulation models forced by prescribed differential surface heat fluxes show spontaneous multidecadal variability depending critically on eddy diffusivity coefficients the existence of this critical threshold in the range of observational estimates legitimates some doubt on the relevance of such intrinsic oscillations in the real ocean through a series of numerical simulations with increasing resolution up to eddy resolving ones 10 km and various diapycnal diffusivities this multidecadal variability proves a generic ubiquitous feature at least in model versions with a flat bottom the mean circulation largely changes in the process of refining the horizontal grid along with the associated implicit viscosity and diffusivity and the spatial structure of the variability is largely modified but there is no clear influence of the resolution on the main oscillation period the interdecadal variability appears even more robust to low vertical diffusivity and overturning when mesoscale eddies are resolved the mechanism previously proposed for these oscillations involving westward propagating baroclinically unstable rossby waves in the subpolar region and its feedback on the mean circulation appears unaffected by mesoscale turbulence and is simply displaced following the polar front

benthic foraminiferal assemblages from the eastern weddell sea between 68 and 73 s distribution ecology and fossilization potential surface sediment samples taken with a vented box corer from the eastern weddell sea on four profiles perpendicular to the continental margin have been investigated for their benthic foraminiferal content the live fauna was differentiated from empty tests comprising the foraminiferal death assemblage based on the dead assemblages potential fossil assemblages were calculated to facilitate the analogy with late neogene core material five distinct live assemblages inhabit the continental margin today six dead assemblages and five potential fossil assemblages respectively correspond to these biocoenoses a predominantly calcareous live fauna dominated by trifarina angulosa is correlated with strong bottom currents and sandy sediments at the shelf break and on the uppermost continental slope below this on the upper slope down to 2000 m water depth the predominantly calcareous bulimina aculeata assemblage coincides with the core of warm 0 c weddell deep water and with fine and more organic rich sediments these calcareous live assemblages completely change composition during early diagenesis because of calcite dissolution within the uppermost sediment which depends largely on the grain size distribution of the sediment and the fluxes of organic matter therefore a still calcareous t angulosa dominated fossil assemblage indicates the sandy substrates on the shelf break and the upper slope whereas the deeper slope with hemipelagic calm sedimentation and with high fluxes of organic matter is indicated by martinottiella nodulosa the characteristic arenaceous fossil remnant of the former predominantly calcareous live b aculeata fauna on a continental terrace between 2500 and 3500 m water depth cribrostomoides subglobosus dominates the live fauna but because of rapid disintegration of the empty tests of this agglutinated species a predominantly calcareous fauna characterized by oridorsalis umbonatus and epistominella exigua comprises the dead assemblage and the potential fossil assemblage respectively on the lower continental slope between the carbonate lysocline 3500 m and the carbonate compensation depth 4000 m tests of nuttallides umbonifer are the characteristic dead and potential fossil remnants of a former predominantly arenaceous live fauna which is associated with the lower part of the antarctic bottom water aabw this corroborates earlier investigations suggesting a relationship between the carbonate corrosiveness of water masses and the distribution of n umbonifer this is important for inferring paleo routes and estimates of paleo production rates of aabw during the neogene

biostratigraphic and paleoclimatic significance of a new pliocene foraminiferal fauna from the central arctic ocean abstract a pliocene benthic foraminiferal fauna containing a previously unknown species association was found in the basal section of a piston core collected from the crest of northwind ridge nwr in the central arctic ocean the fauna is dominated by epistominella exigua cassidulina reniforme eponides tumidulus cibicides scaldisiensis lagena spp cassidulina teretis eponides weddellensis bolivina arctica and patellina corrugata the presence of cibicides scaldisiensis in the assemblage and the occurrence of cibicides grossus higher in the core are indicative of an early pliocene age the morphologically distinctive species cibicidoides sp 795 of mcneil in press which occurs in the nwr core sample was previously known only from oligocene through miocene deposits in the beaufort mackenzie basin of arctic canada ehrenbergina sp a and cibicidoides aff c sp 795 also present in the core are new and endemic to the arctic late miocene and early pliocene these species and possibly others are survivors of the late miocene messinian sea level crisis which caused a significant faunal turnover in the arctic ocean the predominantly calcareous assemblage indicates deposition above the calcium carbonate compensation depth in an upper bathyal environment paleogeographic affinities for the bulk of the assemblage indicate probable connections between the arctic and the north atlantic oceans but the endemic species identify environmental differences or partial isolation of the western arctic ocean the species association suggests a cold but milder paleoclimate than that which existed during pleistocene glacial intervals

benthic foraminiferal assemblages from the eastern south atlantic polar front region between 35 and 57 s distribution ecology and fossilization potential abstract surface sediment samples taken with a multiple corer from the polar front region along two profiles in the eastern south atlantic sector between 35 and 57 s have been investigated for their benthic foraminiferal content live fauna was differentiated from the death assemblage based on the dead assemblages potential fossil assemblages dead fauna reduced by non resistant agglutinants were calculated for comparison with upper neogene core material the distribution of the potential fossil assemblages defined byq mode principal component analysis mirrors the recent hydrographic as well as the trophic situation in the eastern south atlantic ocean circulation and productivity two southern component bottom water faunas reflect the northward flow of antarctic bottom water aabw and lower circum polar deep water lcdw an assemblage dominated by the arenaceousmultifidella nodulosa below the calcite compensation depth ccd and anuttallides umbonifer dominated assemblage above the ccd in the region of highest bio silicious primary productivity south of the polar front and north of the winter sea ice limit these faunas are overprinted by a southern high productivity fauna dominated by infaunal species such aspullenia bulloides melonis pompilioides andm zaandamae north atlantic deep water nadw meets the circum polar deep water cdw at intermediate depth as reflected in the distribution of the northern component deep water fauna dominated byepistominella exigua the high productivity assemblage overprinting this fauna the northern high productivity fauna is dominated by the shallow endobenthicbulimina aculeata a strong bottom current fauna dominated byangulogerina angulosa characterizes areas between 400 and 900 m water depth with sandy sediment independent from water mass characteristics and food supply

distribution of arenaceous foraminifera in depth profiles of the southern ocean kerguelen plateau area abstract recent to subrecent benthonic arenaceous foraminifera from two areas of the southern ocean have been investigated with regard to their depth distribution and agglutination patterns strong differences exist between the arenaceous faunas from a diatomaceous sediments west of the kerguelen plateau and b glacial marine sediments from the slope of the antarctic continent major ecologic influences are seen in the effect of sedimentological factors especially the clay content of the sediment in the saturation level of calcium carbonate and in the nutrient condition of the biotope since these factors are a function of geographic position and related water masses the main differences of deep sea faunas are primarily induced by the overall situation of an oceanic area rather than by depth or oceanographic factors like temperature or salinity availability of colloidal iron compounds also seems to be a limiting factor for distinct arenaceous species

global patterns of decadal scale variability observed in sea surface temperature and lower tropospheric circulation fields the global patterns associated with decadal scale variability dsv are examined by a lag correlation technique based on local anomaly indices using the fields of measured sea surface temperature sst and 850 hpa geopotential height for the last 50 years the three dominant patterns are identified and the variability is examined the first spreads over the entire pacific which is concurrent with the decadal scale modulation of the el nino southern oscillation des variability the second is confined to the local midlatitude north pacific lnp variability and the third extends over the north atlantic with the decadal north atlantic oscillation nao dna variability the global sst pattern of des variability exhibits large scale equatorial symmetry in the pacific which is similar to that of the pacific decadal oscillation but is distinguished by the signals in the subtropical frontal zones these sst anomalies are accompanied by anomalous subtropical highs that appear prior to the anomalous depression around australia the lnp variability which is related with the arctic oscillation is characterized by the sst anomalies along the north pacific subarctic frontal zone moving eastward accompanied by the anomalous aleutian low this variability develops decays without with coherent variability in the tropics it shows the 6 year quadrature phase relationship with the des variability indicative of an interdecadal variability with a period of 24 years the dna variability is featured by the atmospheric nao and by the sst anomalies in four zonal bands that spread in the north atlantic from the tropics to high latitudes this variability is independent of either the des or lnp variability

non newtonian rheology of igneous melts at high stresses and strain rates experimental results for rhyolite andesite basalt and nephelinite the stress strain rate relationships of four silicate melt compositions high silica rhyolite andesite tholeiitic basalt and nephelinite have been studied using the fiber elongation method measurements were conducted in a stress range of 10 400 mpa and a strain rate range of 10 6 to 10 3 s 1 the stress strain rate relationships for all the melts exhibit newtonian behavior at low strain rates but non newtonian nonlinear stress strain rate behavior at higher strain rates with strain rate increasing faster than the applied stress the decrease in calculated shear viscosity with increasing strain rate precedes brittle failure of the fiber as the applied stress approaches the tensile strength of the melt the decrease in viscosity observed at the high strain rates of the present study ranges from 0 25 to 2 54 log10 pa s the shear relaxation times of these melts have been estimated from the low strain rate newtonian shear viscosity using the maxwell relationship s g non newtonian shear viscosity is observed at strain rates time 1 equivalent to time scales that lie 3 log10 units of time above the calculated relaxation time brittle failure of the fibers occurs 2 log10 units of time above the relaxation time this study illustrates that the occurrence of non newtonian viscous flow in geological melts can be predicted to within a log10 unit of strain rate high silica rhyolite melts involved in ash flow eruptions are expected to undergo a non newtonian phase of deformation immediately prior to brittle failure

on low frequency variability of the midlatitude ocean gyres the first two authors are thankful to the natural environment research council for the support of this work through the grant ne j006602 1 and the use of archer the uk national supercomputing service we express our gratitude to s burbidge and m harvey for their help with imperial college london cluster as well as to a thomas for his help with managing and maintaining the data storage the last two authors were supported by the spanish ministry of economy and competitiveness under grant tin2013 41049 p and this support is gratefully acknowledged we would also like to thank unknown referees for valuable comments and suggestions which helped us to improve the paper

interannual and decadal cycles in river flows of southeastern south america abstract the time series of annual streamflow of four rivers in southeastern and south central south america the negro paraguay parana and uruguay rivers for the period 1911 93 are analyzed application of the multitaper method shows that the following features are significant at the 95 level 1 a nonlinear trend 2 a near decadal component and 3 interannual peaks with enso timescales the trend and near decadal components are most marked in the two more central rivers the paraguay and parana with enso timescale variability most pronounced in the negro and uruguay rivers in the southeast composites of sst are made for each of the statistically significant oscillatory components of river flow by reconstructing each component using singular spectrum analysis these composites confirm the influence of enso on the streamflow variability of the negro and uruguay rivers with el nino associated with enhanced streamflow on the decadal timescale high river runoff is associated with anomalously coo

an equatorial extratropical dipole structure of the atlantic nino abstractequatorial atlantic variability is dominated by the atlantic nino peaking during the boreal summer studies have shown robust links of the atlantic nino to fluctuations of the st helena subtropical anticyclone and benguela nino events furthermore the occurrence of opposite sea surface temperature sst anomalies in the eastern equatorial and southwestern extratropical south atlantic ocean sao also peaking in boreal summer has recently been identified and termed the sao dipole saod however the extent to which and how the atlantic nino and saod are related remain unclear here an analysis of historical observations reveals the atlantic nino as a possible intrinsic equatorial arm of the saod specifically the observed sporadic equatorial warming characteristic of the atlantic nino 0 4 k is consistently linked to southwestern cooling 0 4 k of the atlantic ocean during the boreal summer heat budget calculations show that the saod is largely driven by the surface net heat flux anoma

state dependence of atmospheric response to extratropical north pacific sst anomalies by performing two sets of high resolution atmospheric general circulation model agcm experiments we find that the atmospheric response to a sea surface temperature sst anomaly in the extratropical north pacific is sensitive to decadal variations of the background sst on which the sst anomaly is superimposed the response in the first set of experiments in which the sst anomaly is superimposed on the observed daily sst of 1981 1990 strongly differs from the response in the second experiment in which the same sst anomaly is superimposed on the observed daily sst of 1991 2000 the atmospheric response over the north pacific during 1981 1990 is eddy mediated equivalent barotropic and concentrated in the east in contrast the atmospheric response during 1991 2000 is weaker and strongest in the west the results are discussed in terms of rossby wave dynamics with the proposed primary wave source switching from baroclinic eddy vorticity forcing over the eastern north pacific in 1981 1990 to mean flow divergence over the western north pacific in 1991 2000 the wave source changes are linked to the decadal reduction of daily sst variability over the eastern north pacific and strengthening of the oyashio extension front over the western north pacific thus both daily and frontal aspects of the background sst variability in determining the atmospheric response to extratropical north pacific sst anomalies are emphasized by our agcm experiments

comparison between instrumental observational and high resolution proxy sedimentary records of late holocene climatic change a discussion of possibilities abstract variability of the north atlantic region is a key factor in the workings of global climate changes related to orbital factors and to the thermohaline circulation thc occur on timescales ranging from 1000 to 100 000 years whereas subdecadal decadal and multidecadal trends are associated with changes in atmospheric circulation sea surface temperature sst and salinity long term changes are known only from proxies whereas shorter periodicities are identified in instrumental and other observational data between lies a range of less well known centennial periodicities too long to be recorded observationally and too short for all but the highest resolution proxy records such as tree rings atmospheric 14c and varved lake sediments numerous investigations of such periodicities involve comparisons between the proxy and the observational record however results depend on the length of the datasets being analysed the relative strength of the periodicities present whether data are stationary or non stationary the degree to which they have been smoothed in order to remove particular fluctuations and the methods of analysis employed ideally comparisons should be between datasets of equal length and of similar properties but these criteria are not always easy to fulfill a search for periodicities in a range of well known multidecadal datasets reveals that whilst some frequencies previously identified in the central england temperature cet record and in the koch sea ice index are statistically significant those found by several authors in the index of the north atlantic oscillation nao are not as the index approximates to white noise instead decadal periodicity of the nao described by several authors appears to be result of smoothing of the raw data periodicities of 6 1 33 9 and 213 years identified in a proxy record from laminated sediments from loch ness scotland appear respectively to be related to a subdecadal variations in sst and salinity in the north atlantic ocean b multidecadal interactions between the nao and the north atlantic thc and c a well known centennial solar periodicity

delayed brittle like fragmentation of vesicular magma analogue by decompression abstract a rapid decompression experiment using syrup containing gas bubbles was conducted in order to clarify the fragmentation of vesicular magma which is a key phenomenon in volcanic eruptions we focus on brittle like fragmentation which occurs with a longer time scale than brittle fragmentation the response of the bubbly syrup to the decompression for various viscosities and porosities was tested under various initial pressures pressure differences and decompression times the response observed by high speed photography was classified using the deborah number de dt which is defined as the ratio of the viscoelastic relaxation time of the syrup to the decompression time the maximum differential stress at the bubble surface max and a measure of instantaneous brittleness at the bubble surface c at the time when the differential stress at the surface reaches the critical fracture stress c in a number of the experimental runs in which both de dt and c indicated ductile response of the material brittle like fragmentation occurred when max substantially exceeded c for all of the runs in which brittle like fragmentation was observed the onset of fragmentation was delayed substantially from the relaxation time whereas the onset occurred within the characteristic time for viscous expansion of the bubbles in many cases of brittle like fragmentation fragmentation continued after the onset triggered by a single decompression event detailed analysis indicates that brittle like fragmentation started with a sudden release of the gas in the bubbly syrup through a surface crack which might lead to an increase in local brittleness magma fragmentation may be viewed as sequential brittle like fragmentation this view may provide an explanation for the observed time delay for the onset of an explosive eruption after a triggering decompression event

energetics of glass fragmentation experiments on synthetic and natural glasses 1 natural silicate glasses are an essential component of many volcanic rock types including coherent and pyroclastic rocks they span a wide range of compositions occur in diverse environments and form under a variety of pressure temperature conditions in subsurface volcanic environments e g conduits and feeders melts intersect the thermodynamically defined glass transition temperature to form glasses at elevated confining pressures and under differential stresses we present a series of room temperature experiments designed to explore the fundamental mechanical and fragmentation behavior of natural obsidian and synthetic glasses pyrex under confining pressures of 0 1 100 mpa in each experiment glass cores are driven to brittle failure under compressive triaxial stress analysis of the load displacement response curves is used to quantify the storage of energy in samples prior to failure the brittle release of elastic energy at failure and the residual energy stored in the post failure material we then establish a relationship between the energy density within the sample at failure and the grain size distributions d values of the experimental products the relationship between d values and energy density for compressive fragmentation is significantly different from relationships established by previous workers for decompressive fragmentation compressive fragmentation is found to have lower fragmentation efficiency than fragmentation through decompression i e a smaller change in d value with increasing energy density we further show that the stress storage capacity of natural glasses can be enhanced approaching synthetic glasses through heat treatment

fragmentation of a porous viscoelastic material implications to magma fragmentation fragmentation of vesicular magma by rapid decompression is one of the most likely triggers for explosive eruptions in this phenomenon the decompression rate and the viscoelastic nature of magma are considered to be key factors in order to obtain a clear idea on the effects of these two factors controlled fragmentation experiments have been conducted these experiments have three advantages first the specimen is made of a viscoelastic material with controlled porosity and geometry second the fragmentation process is directly monitored finally both the magnitude and rate of decompression are controlled brittle fragmentation and ductile expansion were both observed in the same porous material at different timescales the various mechanical responses of the specimen elastic flow and fragmentation were correlated with the pressure profile measured at the base of the specimen fragmentation was noted to occur when the decompression exceeded a critical value within a critical time two relevant timescales are discussed in terms of physical mechanisms of relaxation the first is the measured glass transition time the second is the estimated timescale for the onset of viscous bubble expansion the observed phenomena bear several similarities with natural magma fragmentation it is thus considered that the present results are a useful step toward constructing a model for magma fragmentation

frequency domain multimodel analysis of the response of atlantic meridional overturning circulation to surface forcing the dynamics of the atlantic meridional overturning circulation amoc vary considerably among different climate models for example some models show clear peaks in their power spectra while others do not to elucidate these model differences transfer functions are used to estimate the frequency domain relationship between surface forcing fields including sea surface temperature salinity and wind stress and the resulting amoc response these are estimated from the outputs of the coupled model intercomparison project phase 5 cmip5 and phase 3 cmip3 control runs for eightdifferent models with a specificfocus on geophysical fluid dynamics laboratory climate model version 2 1 gfdl cm2 1 and the community climate system model version 4 ccsm4 which exhibit rather different spectral behavior the transfer functionsshowvery littleagreement amongmodelsforany ofthe pairsofvariablesconsidered suggestingthe existence of systematic model errors and that considerable uncertainty in the simulation of amoc in current climate models remains however a robust feature of the frequency domain analysis is that models with spectral peaks in their amoc correspond to those in which amoc variability is more strongly excited by high latitude surface perturbations that have periods corresponding to the frequency of the spectral peaks this explains why different models exhibit such different amoc variability these differences would not be evident without using a method that explicitly computes the frequency dependence rather than a priori assuming a particular functional form finally transfer functions are used to evaluate two proposed physical mechanisms for model differences in amoc variability differences in labrador sea stratification and excitation by westward propagating subsurface rossby waves

ocean eddy dynamics in a coupled ocean atmosphere model the role of mesoscale oceanic eddies is analyzed in a quasigeostrophic coupled ocean atmosphere model operating at a large reynolds number the model dynamics are characterized by decadal variability that involves nonlinear adjustment of the ocean to coherent north south shifts of the atmosphere the oceanic eddy effects are diagnosed by the dynamical decomposition method adapted for nonstationary external forcing the main effects of the eddies are an enhancement of the oceanic eastward jet separating the subpolar and subtropical gyres and a weakening of the gyres the flow enhancing effect is due to nonlinear rectification driven by fluctuations of the eddy forcing this is a nonlocal process involving generation of the eddies by the flow instabilities in the western boundary current and the upstream part of the eastward jet the eddies are advected by the mean current to the east where they backscatter into the rectified enhancement of the eastward jet the gyre weakening effect which is due to the time mean buoyancy component of the eddy forcing is a result of the baroclinic instability of the westward return currents the diagnosed eddy forcing is parameterized in a non eddy resolving ocean model as a nonstationary random process in which the corresponding parameters are derived from the control coupled simulation the key parameter of the random process its variance is related to the large scale flow baroclinicity index it is shown that the coupled model with the non eddy resolving ocean component and the parameterized eddies correctly simulates climatology and low frequency variability of the control eddy resolving coupled solution

a thermal oscillation under a restorative forcing summary the authors report an interdecadal oscillation in a wind and thermally driven ocean general circulation model ogcm the oscillation is tantalizing in that it occursunder a relatively strong thermal damping 26 3 w m 2k examinations involving a two dimensional ogcm a simple thermal flip flop model and a three dimensional ogcm with and without the nonlinear effect of temperature in the state equation of sea water demonstrate that the oscillation is not driven by mechanisms such as the so called convective oscillator or the advective overshooting oscillator instead the oscillation is associated with the propagation of modelled long rossby waves with westward phase velocity it is found that the north south basin extent of the ogcm is an important factor a larger northsouth basin extent is conducive to the generation of thermal wind flows crucial for initiating the propagation of disturbances the geophysical relevance of these results is discussed

seismological analysis of conduit dynamics in fragmentation experiments we simulate gas burst and volcanic explosions under controlled laboratory conditions inducing fragmentation of volcanic rocks by rapid depressurization a series of experiments were performed in a shock tube apparatus at room temperature and a pressure range of 4 to 20 mpa using argon ar gas and particles or pumice samples of different porosities the instrumentation of this system with high precision piezoelectric sensors enabled us to capture elastic waves and to recognize their characteristic signatures by relating these signals to physical processes in the wave field we have been able to characterize the conduit mechanism and the source dynamics we compare and discuss conspicuous features of the waveforms and frequency spectra of these experimental signals with those of volcanic origin despite the fact that these signals are different in amplitude resulting from different scale conditions our observations indicate that the physical processes that occur during simulated explosions and those that occur during volcanic eruptions yield comparable signatures in their respective records the effects of the source receiver configuration and resonance also have significant implications all this suggests that the physical processes e g pressurization and depressurization of a system involve a system response that causes similar distinctive effects independent of the system size reflecting its intrinsic dynamics these similarities imply that powerful constraints on the source mechanisms of volcanic seismicity can emerge from seismic investigations of experimental simulations of volumetric sources such constraints may yield significant advances in the understanding of volcanic conduit dynamics and in the interpretation of seismic unrest at volcanic centers

the fragmentation threshold of pyroclastic rocks in response to rapid decompression porous magma may fragment explosively this occurs when the melt can no longer withstand forces exerted upon it due to the overpressure in included bubbles this occurs at a critical pressure difference between the bubbles and the surrounding magma in this study we have investigated this pressure threshold necessary for the fragmentation of magma here we present the first comprehensive high temperature experimental quantification of the fragmentation threshold of volcanic rocks varying widely in porosity permeability crystallinity and chemical composition we exposed samples to increasing pressure differentials in a high temperature shock tube apparatus until fragmentation was initiated experimentally we define the fragmentation threshold as the minimum pressure differential that leads to complete fragmentation of the pressurized porous rock sample our results show that the fragmentation threshold is strongly dependent on porosity high porosity samples fragment at lower pressure differentials than low porosity samples the fragmentation threshold is inversely proportional to the porosity of the other factors permeability likely affects the fragmentation threshold at high porosity values whereas chemical composition crystallinity and bubble size distribution appear to have minor effects the relationship for fragmentation threshold presented here can be used to predict the minimum pressure differential necessary for the initiation or cessation of the explosive fragmentation of porous magma

temporal evolution of the minoan eruption santorini greece as recorded by its plinian fall deposit and interlayered ash flow beds the plinian fall deposit of the minoan eruption santorini greece and its interlayered ash flow beds show textural componentry and chemical trends indicative of their temporal evolution and conditions that lead to the ash flow emplacement the deposits have been sampled in detail at a selected locality and the following features have been analyzed i maximum clast size ii grain size distribution iii componentry iv lithic types v pumice morphology vi pumice types and vii pumice crystal abundance stratigraphic variations of these features are assumed to record changes that occurred during the eruption including changes in eruptive plume height nature and relative efficiency of the magma fragmentation process conduit stability and magma flow in the conduit based upon the inferred temporal changes we propose the following eruption reconstruction the sustained plinian column activity reached its climax in terms of mass eruption rate and plume altitude soon after the beginning of the eruption and subsequently began to gradually subside as a result of eruption waning the conduit walls began to collapse causing an increase in the shear stress in the flowing vesicular magma and an increase in the efficiency of the magma fragmentation process eventually the conduit closed or became too narrow to support a high standing eruption column leading to ash flow eruption as a result of the collapse of what was left of the eruptive plume and or directly from emission of an overpressured jet subsequent conduit pressure increases led to conduit re opening and a plinian column with associated pumice fallout began anew the eruptive magma fragmentation process is proposed to have been of a brittle nature and linked to the shear stress generated by conduit wall friction fragmentation efficiency is recorded by grain size distributions and free crystal contents of the deposits

global scale modes of surface temperature variability on interannual to century timescales using 100 years of global temperature anomaly data we have performed a singular value decomposition of temperature variations in narrow frequency bands to isolate coherent spatio temporal modes of global climate variability statistical significance is determined from confidence limits obtained by monte carlo simulations secular variance is dominated by a globally coherent trend with nearly all grid points warming in phase at varying amplitude a smaller but significant share of the secular variance corresponds to a pattern dominated by warming and subsequent cooling in the high latitude north atlantic with a roughly centennial timescale spatial patterns associated with significant peaks in variance within a broad period range from 2 8 to 5 7 years exhibit characteristic el nino southern oscillation enso patterns a recent transition to a regime of higher enso frequency is suggested by our analysis an interdecadal mode in the 15 to 18 years period range appears to represent long term enso variability this mode has a sizeable projection onto global average temperature and accounts for much of the anomalous global warmth of the 1980s a quasi biennial mode centered near 2 2 years period and a mode centered at 7 to 8 years period both exhibit predominantly a north atlantic oscillation nao temperature pattern a potentially significant decadal mode centered on 11 to 12 years period also exhibits an nao temperature pattern and may be modulated by the century scale north atlantic variability

from rock to magma and back again the evolution of temperature and deformation mechanism in conduit margin zones abstract explosive silicic volcanism is driven by gas overpressure in systems that are inefficient at outgassing the zone at the margin of a volcanic conduit thought to play an important role in the outgassing of magma and therefore pore pressure changes and explosivity is the boundary through which heat is exchanged from the hot magma to the colder country rock using a simple heat transfer model we first show that the isotherm for the glass transition temperature whereat the glass within the groundmass transitions from a glass to an undercooled liquid moves into the country rock when the magma within the conduit can stay hot or into the conduit when the magma is quasi stagnant and cools on the centimetric scale over days to months we then explore the influence of a migrating viscous boundary on compactive deformation micromechanisms in the conduit margin zone using high pressure effective pressure of 40 mpa high temperature up to 800 c triaxial deformation experiments on porous andesite our experiments show that the micromechanism facilitating compaction in andesite is localised cataclastic pore collapse at all temperatures below the glass transition of the amorphous groundmass glass t g i e rock in this regime porosity is only reduced within the bands of crushed pores the porosity outside the bands remains unchanged further the strength of andesite is a positive function of temperature below the threshold t g due to thermal expansion driven microcrack closure the micromechanism driving compaction above t g i e magma is the distributed viscous flow of the melt phase in this regime porosity loss is distributed and is accommodated by the widespread flattening and closure of pores we find that viscous flow is much more efficient at reducing porosity than cataclastic pore collapse and that it requires stresses much lower than those required to form bands of crushed pores our study therefore highlights that temperature excursions can result in a change in deformation micromechanism that drastically alters the mechanical and hydraulic properties of the material within the conduit margin zone with possible implications for pore pressure augmentation and explosive behaviour

on the feasibility of magma fracture within volcanic conduits constraints from earthquake data and empirical modelling of magma viscosity 1 in the last decade several studies have indicated that magma within volcanic conduits can undergo repeated failure and healing thus providing a realistic source mechanism for the peculiar sequences of low frequency earthquakes that often announce eruptions although geological observations laboratory experiments and numerical modelling support such a hypothesis the links between geophysical observations and the proposed models remain qualitative this study focuses on providing constraints to the relationship between the occurrence of repeating earthquakes and magma fracture at andesite volcanoes empirical modelling of viscosity is incorporated into the fundamental physics of magma fracture in order to assess whether and where the conditions for brittle failure are met within volcanic conduits a case study from the 1995 ongoing eruption of soufriere hills volcano montserrat is presented the locations of earthquakes from a pre eruptive low frequency seismic swarm illuminate a relatively compact source volume at depths of 100 300 meters below sea level viscosity modelling confirms that the soufriere hills magma could rupture at those depths

decadal precipitation variability over europe and its relation with surface atmospheric circulation and sea surface temperature the relationships between decadal 5 year period observed winter precipitation pp variability over europe and atmospheric circulation and sea surface temperature sst during the period 1950 1995 are investigated more than 48 of the decadal precipitation variability is described by two modes a meridional dipolar pattern high pp over northern europe and low over southern europe the mediterranean and most of central europe explaining about 32 of the variance and an alternating pattern in latitude over europe high in central europe and low in far north western europe and the mediterranean explaining about 16 of the variance the first mode is strongly related to the north atlantic oscillation a canonical correlation analysis between regional precipitation and sea level pressure fields shows that a pp pattern similar to the first decadal pp mode is associated with a north westerly circulation anomaly pattern while a pp pattern similar to the second decadal pp mode is associated with a monopolar circulation anomaly pattern over most parts of europe the correlation map between the time series of expansion coefficients of the first pp mode and sea surface temperature emphasizes a global pattern which resembles the linear trend coefficients pattern of sst for the analysed period the second pp mode is associated with an sst anomaly pattern similar to that of the sst anomalies characterizing decadal el ni o southern oscillation sst pattern composite maps of global 500 mb geopotential height based on the time series of expansion coefficients of pp modes emphasize global patterns compatible with sst patterns after removing the linear trend from the data the first pp pattern remains almost unchanged but it emphasizes mainly regional connections the second spatial pattern of the second pp mode and its connections are not affected significantly by removing the trend

surface climate variations over the north atlantic ocean during winter 1900 1989 abstract the low frequency variability of the surface climate over the north atlantic during winter is described using 90 years of weather observations from the comprehensive ocean atmosphere data set results are based on empirical orthogonal function analysis of four components of the climate system sea surface temperature sst air temperature wind and sea level pressure an important mode of variability of the wintertime surface climate over the north atlantic during this century is characterized by a dipole pattern in ssts and surface air temperatures with anomalies of one sign cast of newfoundland and anomalies of the opposite polarity off the southeast coast of the united states wind fluctuations occur locally over the regions of large surface temperature anomalies with stronger than normal winds overlying cooler than normal ssts this mode exhibits variability on quasi decadal and biennial time scales the decadal fluctuations are irregular in length averaging 9 years before 1945 and 1

tectonic plate generation and two phase damage void growth versus grain size reduction 1 the generation of plate tectonics from mantle convection requires shear localization in order to yield narrow weak plate boundaries separating broad strong plates a plausible shear localizing mechanism involves damage e g distributed microcracking one theoretical model of which involves two phase mechanics two phase damage theory employs a nonequilibrium relation between interfacial surface energy pressure and viscous deformation thereby providing a description of void generation and microcracking and hence weakening failure and shear localization here we examine the application of this theory to the problem of generating plate like behavior from convective type divergent convergent poloidal motion through a source sink formulation we extend the previous damage theory to consider two possible damage effects 1 growth and nucleation of voids associated with dilation of the host matrix and 2 increasing fineness i e reducing coarseness of the mixture by for example grain size reduction void generating damage is found to be poor at plate generation because of the predominance of dilational motion that is adverse to the development of plate like flow fineness generating damage is found to be very efficient at generating plate like behavior if we assume that the matrix viscosity is a simple function of grain void size as is typical for diffusion creep the implied grain size reduction mechanism is different from that of dynamic recrystallization and appears to be more capable of generating the requisite shear localization for forming tectonic plates from mantle flow

repeated fracture and healing of silicic magma generate flow banding and earthquakes textures in an exceptionally preserved effusive rhyolite conduit at torfajokull iceland indicate that rising magma repeatedly fractured and healed at shallow levels in the conduit rfh process anastomosing tuffisite veins filled by fine grained juvenile clasts were generated by shear fracture of highly viscous magma in the glass transition interval welding of the particulate material during subsequent deformation led to thorough healing of veins allowing repeated fracture of the same body of magma we propose that the rfh process is a rechargeable trigger mechanism for hybrid seismicity and show that the time scale of the process and the fractures formed by it are consistent with the repeat time and magnitude of hybrid earthquakes during silicic eruptions the rfh process may also form the flow banding that is nearly ubiquitous in obsidian

rossby waves and eddies observed at a temperature mooring in northern south china sea abstractannual rossby waves in northern south china sea had previously been studied using altimetry and model data however how they connect to subsurface temperature fluctuations has not been examined this study analyzed a 22 month surface to 500 m temperature time series at 18 3 n 115 5 e together with satellite and other data to show the arrivals near z 300 m and deeper cool warm rossby waves after their generation near the luzon strait in winter summer temperature fluctuations with time scales of a few weeks and with maximum anomalies near z 100 m were also found embedded in the smooth rossby waves and caused by propagating eddies eddy fluctuations and propagation past the mooring were of two types southwestward from southwestern taiwan triggered by kuroshio intrusion that produced anticyclone cyclone pairs in late fall and winter and eddies propagating westward from luzon forced by annual anomalies of wind stress curl and kuroshio path in the luzon strait

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

remote and local forcing in the brazil malvinas region origins of the seasonal variability observed in current meter data from the malvinas falkland current are sought in the wind field on both a regional and circumpolar scale a singular value decomposition of the covariance of the fields makes it possible to distinguish between a local and a remote source of variability the local mode is the result of changes in the wind stress curl around 408s causing an annual modulation transverse to the mean path of the current and thus contributes little to the variability in transport it seems likely that the wind stress curl drives the annual excursions of the brazil malvinas front and forces the retroflection of the malvinas current the remote mode features increased transport trailing negative wind stress curl anomalies at drake passage with a lag of 20 30 days repeating this analysis with the winds on a circumpolar domain suggests that this might be the regional manifestation of a more global feature associating globally negative wind stress curl anomalies north of 608s with increased transport this analysis also shows that the malvinas current transport is anticorrelated with the zonal wind stress hence with the antarctic circumpolar current although initially counterintuitive this is confirmed through coherence analyses with bottom pressure measurements at the south of drake passage these results are further assessed using a 5 yr series of transport in the malvinas current derived from topex poseidon altimeter data which is compared with the circumpolar averages of both zonal wind stress and wind stress curl coherences are largest with the wind stress curl at latitudes north of drake passage up to the subtropics and also indicate that it is most influential in the pacific sector it is suggested that the antarctic circumpolar current and the malvinas current respond differently to the wind forcing and that these two modes cohabit at drake passage while the barotropic variations of the former have been shown to respond to the zonally averaged wind stress the fluctuations of the latter at timescales of 100 200 days are more sverdrupian that is sensitive to the wind stress curl lag 20 days explaining why they fluctuate with opposite phase superimposed on this intraseasonal variability at shorter periods 70 days results from baroclinic shelf waves trapped along the edge of the patagonian plateau these propagate from drake passage and may originate from equatorial kelvin waves in the pacific

pdo related wintertime atmospheric anomalies over the midlatitude north pacific local versus remote sst forcing abstractobserved wintertime atmospheric anomalies over the central north pacific associated with the pacific decadal oscillation pdo are characterized by a cold trough warm ridge structure tha

the influence of atlantic sea surface temperature anomalies on the north atlantic oscillation abstract the influence of atlantic sea surface temperature sst anomalies on the atmospheric circulation over the north atlantic sector during winter is investigated by performing experiments with an atmospheric general circulation model these consist of a 30 yr run with observed sst anomalies for the period 1961 90 confined geographically to the atlantic ocean and of a control run with climatological ssts prescribed globally a third 30 yr integration with observed ssts confined to the south atlantic is made to confirm present findings the simulated interannual variance of 500 hpa wintertime geopotential heights over the north atlantic attains much more realistic values when observed atlantic ssts are prescribed circulation patterns that resemble the positive phase of the north atlantic oscillation nao become more pronounced in terms of the leading eof of winter means and a cluster analysis of daily fields the variance of an interannual nao index increases by fivefold over its control value atl

brittleness of fracture in flowing magma 1 understanding the transition to brittle fracture of flowing magma is essential for estimating the explosiveness of a volcanic eruption in order to quantify brittleness of flowing magma a new parameter is introduced which is a function of the ratio of the rate of change of the strain energy due to elastic distortional deformation to the mechanical power due to total distortional deformation rate from the perspective of dependence of brittle fracture of magma on stress decompression rate strain rate and shear thinning effects are reviewed the experimental data of kameda et al 2008 for rapid decompression of simulants of bubbly magma have also been reexamined the results show that exhibits a strong transition that correlates well with the observed transition between ductile expansion to brittle fragmentation moreover is useful in considering the effects of shear thinning and steady creep conditions on brittle fracture statements in the literature that suggest that materials behave in a brittle manner at sufficiently high strain rate are correct however these statements do not precisely quantify the notion of high strain rate so they are easy to misinterpret when considering the effect of shear thinning although shear thinning tends to increase the absolute magnitude of the total strain rate it does not necessarily increase brittleness also in principle it is unlikely for brittle fracture to occur at steady creep cracking observed in steady creep experiments of magma lavallee et al 2007 2008 may be attributed to small fluctuations with sufficiently high frequencies to satisfy the conditions for brittle fracture

propagation of acoustic waves in a visco elastic two phase system influences of the liquid viscosity and the internal diffusion abstract the main purpose of the present paper is to present the mathematical expression for the frequency dependent effective acoustic properties of a liquid bubble mixture effects of the bubble resonance the heat and mass transfer between the liquid and bubbles and the viscoelasticity of the liquid are included in the expression several characteristic frequencies associated with these internal processes are represented by simple functions of the material and condition parameters using these expressions the acoustic properties of bubbly magmas are calculated and analyzed it is shown that the dispersion and attenuation of the pressure wave are particularly considerable in the frequency range lower than the characteristic frequency of the mass transfer and in the range near the characteristic frequency of the viscous response of the bubble radius in the frequency range bounded by these two frequencies the bubbly magma can be regarded as an elastic medium with the slow sound speed the significance of such acoustic properties on resonance of a body of bubbly magma is demonstrated in a simple one dimensional system

evidence for interannual and interdecadal climate variability in the south atlantic a singular value decomposition svd analysis is used to determine the coupled modes of variability of monthly sea surface temperature sst and sea level pressure slp data from the south atlantic region for the period 1953 1992 we find that the three leading svd modes respectively account for 63 20 and 6 of the total square covariance the first mode represents an approximately 15 year period oscillation in the strength of the subtropical anticyclone accompanied by fluctuations of a north south dipole structure in the sst it appears to be linked to the global scale interdecadal 15 year joint mode in sst and slp recently studied by mann and park the second mode is characterized by east west displacements of the anticyclone center in association with strong 6 to 7 year period fluctuations of sst off the coast of africa the third mode is characterized by north south displacements of the anticyclone and 4 year period fluctuations in the sst in a broad band across the central south atlantic this mode is strongly correlated with enso

rheological tests of polyurethane foam undergoing vesiculation deformation solidification as a magma analogue abstract in this study we examined the rheology of polyurethane foam puf as an analogue system of magma undergoing vesiculation deformation and solidification solid puf was formed by mixing two polymeric liquids followed by chemical reactions of foaming and curing the transient rheology during the processes was investigated using an instrument based on a stress controlled rheometer first the oscillatory rheology was measured applying small amplitude oscillations with cyclic frequency sweeps in the foaming stage the frequency dependence of the rheology depends on the dynamic capillary number in a similar way to the existing bubbly flow model in the curing stage the viscoelasticity of the liquid becomes dominant and the rheology of puf shows maxwell type viscoelasticity with relaxation time exponentially increasing with time when the reaction is rapid because of high temperature the viscoelasticity during curing is not scaled by the single relaxation time instead puf passes through a condition called gelation which is characterized by a power law relaxation spectrum next we examined the relationship between the dynamic viscosity measured by the small strain oscillation and the shear viscosity measured with a fixed shear rate at a large strain we found that puf obeys the cox merz rule which states that the two viscosities are equivalent when the shear rate and the angular frequency are equal specifically the shear viscosity tends to be smaller than the dynamic viscosity by a few tens of percent the difference was shown to be in the range expected for bubbly fluid in the foaming stage while it went beyond what can be explained by the bubbly fluid model when the viscoelasticity of the liquid becomes significant x ray computed tomography analyses revealed that samples in these cases contained large bubbles indicating bubble coalescence we infer that the difference is caused by bubble coalescence as well as non newtonian rheology during solidification including gelation all these processes might occur in actual magma during eruptions we show that the ranges of the capillary number comparing the deformation time and the bubble shape relaxation time and deborah number comparing the deformation time and the viscoelastic relaxation time in our experiments are comparable with their ranges expected for magma ascending in an eruptive conduit the characteristic time of viscosity increase of puf was also shown to be realizable for magma in natural volcanoes we conclude that puf is useful for simulating magma processes in eruptive conduits

wintertime variability in the euro atlantic region in observations and in ecmwf seasonal ensemble experiments an empirical orthogonal function eof decomposition of monthly mean analyses of 500 hpa height 1949 94 is used to describe the interannual variability of the large scale flow in the euro atlantic region during winter the first four eofs resemble low frequency variability patterns identified in previous studies such as the north atlantic oscillation and the eastern atlantic and eurasian teleconnection patterns the second eof and fourth eof eof4 are associated with the occurrence of el nino like sea surface temperature sst anomalies according to an observational analysis for eof4 correlations with sst anomalies in the west pacific are also important indications of an influence of tropical sst anomalies on the blocking like third eof emerging from the european centre for medium range weather forecasts ecmwf re analysis era data are not confirmed by a longer sst record a negligible correlation exists between the first eof and el nino indices during the era period although a link may be detected in earlier decades in the second part of the paper a 14 winter set of seasonal ensemble simulations performed with the ecmwf atmospheric model forced by observed sst is validated by comparing the projection of era data onto the four leading euro atlantic eofs with those of ensemble experiments and computing composite anomalies of analyses and model fields the performance of the model is uneven and depends on the large scale pattern considered model biases and flow dependent errors affect the simulations of some of the eofs in particular the model has strong problems reproducing the occurrence of european blocks the best correlation 69 between the time series of analysis and ensemble mean principal components is obtained for eof4 which seems to be forced by sst anomalies in the west pacific associated with el nino southern oscillation enso events the effects of this forcing are felt on the zonal wind structure over eurasia and are reasonably reproduced by the ecmwf model conversely the propagation into the atlantic region of planetary waves originating in the east pacific is poorly simulated thus degrading the model performance in predicting euro atlantic anomalies during some strong enso events

recent benthic foraminiferal associations and ecology of the scotia sea and argentine basin abstract we investigated 88 surface sediment samples taken with a multiple corer from the southwestern south atlantic ocean for their live rose bengal stained and dead benthic foraminiferal content using q mode principal component analysis six live and six dead associations are differentiated live and dead association distributions correspond fairly well differences are mainly caused by downslope transport and selective test destruction in addition four potential fossil associations are calculated from the dead data set after removal of non fossilizable species these potential fossil associations are expected to be useful for paleoceanographic reconstructions environments are described in detail for the live and potential fossil associations and for selected species along the upper argentine continental slope strong bottom currents control the occurrence of live dead and potential fossil angulogerina angulosa associations here particles of a high organic carbon flux rate remain suspended below this high energy environment live dead and potential fossil uvigerina peregrina dominated associations correlate with enhanced sediment organic carbon content and still high organic carbon flux rates the live a angulosa and u peregrina associations correlate with high standing crops furthermore live and dead epistominella exigua nuttallides umbonifer associations were separated dominance of a nuttallides umbonifer potential fossil association relates to coverage by antarctic bottom water aabw and lower circumpolar deep water lcdw above the calcite compensation depth ccd three associations of mainly agglutinated foraminifera occur in sediments bathed mainly by aabw or cdw a reophax difflugiformis association was found in mud rich and diatomaceous sediments below the ccd a psammosphaera fusca association occurs in coarse sediments poor in organic carbon while a cribrostomoides subglobosus ammobaculites agglutinans association covers a more variable environmental range with mud contents exceeding 30 one single eggerella bradyi martinottiella communis association poor in both species and individuals remains from the agglutinated associations below the ccd if only preservable species are considered for calculation

trends interdecadal and interannual oscillations in global sea surface temperatures this study aims at a global description of climatic phenomena that exhibit some regularity during the twentieth century multi channel singular spectrum analysis is used to extract long term trends and quasi regular oscillations of global sea surface temperature sst fields since 1901 regional analyses are also performed on the pacific northern and southern atlantic and indian ocean basins the strongest climatic signal is the irregular long term trend characterized by overall warming during 1910 1940 and since 1975 with cooling especially of the northern hemisphere between these two warming intervals substantial cooling prevailed in the north pacific between 1950 and 1980 and continues in the north atlantic today both cooling and warming are preceded by sst anomalies of the same sign in the subpolar north atlantic near decadal oscillations are present primarily over the north atlantic but also over the south atlantic and the indian ocean a 13 15 y oscillation exhibits a seesaw pattern between the gulf stream region and the north atlantic drift and affects also the tropical atlantic another 7 8 y oscillation involves the entire double gyre circulation of the north atlantic being mostly of one sign across the basin with a minor maximum of opposite sign in the subpolar gyre and the major maximum in the northwestern part of the subtropical gyre three distinct interannual signals are found with periods of about 60 65 45 and 24 30 months all three are strongest in the tropical eastern pacific the first two extend throughout the whole pacific and still exhibit some consistent albeit weak patterns in other ocean basins the latter is weaker overall and has no consistent signature outside the pacific the 60 month oscillation obtains primarily before the 1960s and the 45 month oscillation afterwards

south atlantic variability arising from air sea coupling local mechanisms and tropical subtropical interactions abstract interannual variability in the southern and equatorial atlantic is investigated using an atmospheric general circulation model agcm coupled to a slab ocean model som in the atlantic in order to isolate features of air sea interactions particular to this basin simulated covariability between sea surface temperatures ssts and atmosphere is very similar to the observed non enso related covariations in both spatial structures and time scales the leading simulated empirical coupled mode resembles the zonal mode in the tropical atlantic despite the lack of ocean dynamics and is associated with baroclinic atmospheric anomalies in the tropics and a rossby wave train extending to the extratropics suggesting an atmospheric response to tropical sst forcing the second non enso mode is the subtropical dipole in the sst with a mainly equivalent barotropic atmospheric anomaly centered on the subtropical high and associated with a midlatitude wave train consistent with atmospheric forcing of the sub

subtropical mode waters in the south atlantic ocean this systematic study of the subtropical mode waters in the south atlantic is based on hydrological data the basin wide south atlantic ventilation experiment oceanus and ajax sections and the world ocean circulation experiment woce sections in the brazil malvinas confluence region the woce expendable bathythermograph data set and the atmospheric forcing produced by the national centers for environmental prediction reanalysis the main ventilation window of the subtropical gyre lies in the southwest and corresponds to the southern part of the recirculation region and to the overshoot of the brazil current bc some ventilation occurs along the southern branch of the gyre through deep mixed layers in harsh winters and in the east through the rings shed by the agulhas current however the ventilation from the eastern border concerns a small volume of water with highly variable characteristics three main types of subtropical mode water are observed the lightest around the 26 2 density surface and the second and third around the 26 5 and 26 7 density surfaces respectively the 26 2 subtropical mode water stmw1 corresponds to potential temperatures between 16 and 18 c and salinities between 35 9 and 36 2 the stmw1 thickness does not exceed 150 m the volume of the 26 5 mode water stmw2 is larger it is produced through the formation of deep mixed layers reaching 300 m or more in the active ventilation window over the bc overshoot its potential temperature ranges between 14 and 16 c and its salinity ranges between 35 5 and 35 9 its thickness can be above 300 m the last component observed around the 26 7 density surface stmw3 has a potential temperature between 12 and 14 c and a salinity of about 35 2 to 35 5 it is formed on the eastern flank of the bc overshoot and during harsh winters in the center of the southern branch of the gyre within the main ventilation window the stmws exhibit quite a significant variability in characteristics and volume there is a large interannual variability in the atmospheric forcing over the bc recirculation and bc extension and the observed variations of the subtropical mode waters are qualitatively correlated to the atmospheric forcing variations

the southern ocean as a source region for tropical atlantic variability abstract a coupled model of intermediate complexity is used to examine the effect of the southern ocean on tropical atlantic variability model experiments with positive surface temperature freshwater and wind forcings in the southern ocean show an increased advection of polar water into the atlantic basin resulting in anomalously cold freshwater in the eastern atlantic ocean at 25 s with time these anomalies spread northward and away from the coast into the tropical thermocline the magnitude of the response increases linearly with the strength of the forcing the results of these experiments show that southeastern atlantic ocean temperature and salinity are particularly sensitive to changes in the southern ocean these findings suggest that this link could be the oceanic branch of a mode of variability linking the southern and tropical atlantic oceans a possible mechanism for the as yet unexplained decadal mode of tropical atlantic variability

pulse like crack like and supershear earthquake ruptures with shear strain localization 1 we incorporate shear strain localization into spontaneous elastodynamic rupture simulations using a shear transformation zone stz friction law in the stz model plastic strain in the granular fault gouge occurs in local regions called stzs the number density of stzs is governed by an effective disorder temperature and regions with elevated effective temperature have an increased strain rate stz theory resolves the dynamic evolution of the effective temperature across the width of the fault zone shear bands spontaneously form in the model due to feedbacks amplifying heterogeneities in the initial effective temperature in dynamic earthquake simulations strain localization is a mechanism for dynamic fault weakening a shear band dynamically forms reduces the sliding stress and decreases the frictional energy dissipation on the fault we investigate the effect of the dynamic weakening due to localization in generating pulse like crack like and supershear rupture our results illustrate that the additional weakening and reduction of on fault energy dissipation due to localization have a significant impact on the initial shear stress required for supershear or pulse like rupture to propagate on a fault

bubble deformation in magma under transient flow conditions abstract we investigate the transient behavior of bubble deformation in magma previous studies have used the relationships between capillary number and equilibrium shape for a single bubble under either steady simple shear or steady pure shear to estimate strain rates in pyroclasts and to calculate bubble shapes in a conduit flow we developed a deformation model for a bubble by adjusting the empirical functions used in an existing model for a droplet to fit experimental data for bubble deformation the modified model was used to calculate transient large deformations of a single bubble in arbitrary shear flows in this paper we demonstrate the significance of the modified model through two different applications firstly using this model we are able to simulate the entire history of the evolution of bubble shapes in a time dependent flow using the computational code conflow in this simulation we further include the effect of gas expansion on the bubble shape from this simulation we show that bubble deformation in conduit flow is controlled by the history of both capillary number and strain secondly by using this model to analyze bubble shapes observed in natural magma samples we are able to better estimate the strain rates and deformation durations we apply this model to certain transient features in the relationship between bubble shape and radius in the published data of obsidian clasts from newberry volcano and estimate a deformation duration of 2 7 4 0 min

atlantic thermohaline circulation in a coupled general circulation model unforced variations versus forced changes a 1200 yr unforced control run and future climate change simulations using the parallel climate model pcm a coupled atmosphere ocean land sea ice global model with no flux adjustments and relatively high resolution 2 8 for the atmosphere and 2 3 for the oceans are analyzed for changes in atlantic ocean circulations for the forced simulations historical greenhouse gas and sulfate forcing of the twentieth century and projected forcing for the next two centuries are used the atlantic thermohaline circulation thc shows large multidecadal 15 40 yr variations with mean peak amplitudes of 1 5 3 0 sv 1 sv 10 6 m 3 s 1 and a sharp peak of power around a 24 yr period in the control run associated with the thc oscillations there are large variations in north atlantic ocean heat transport sea surface temperature sst and salinity sss sea ice fraction and net surface water and energy fluxes which all lag the variations in thc strength by 2 3 yr however the net effect of the sst and sss variations on upper ocean density in the midlatitude north atlantic leads the thc variations by about 6 yr which results in the 24 yr period the simulated sst and sea ice spatial patterns associated with the thc oscillations resemble those in observed sst and sea ice concentrations that are associated with the north atlantic oscillation nao the results suggest a dominant role of the advective mechanism and strong coupling between the thc and the nao whose index also shows a sharp peak around the 24 yr time scale in the control run in the forced simulations the thc weakens by 12 in the twenty first century and continues to weaken by an additional 10 in the twenty second century if co2 keeps rising but the thc stabilizes if co2 levels off the thc weakening results from stabilizing temperature increases that are larger in the upper and northern atlantic ocean than in the deep and southern parts of the basin in both the control and forced simulations as the thc gains loses strength and depth the separated gulf stream gs moves southward northward while the subpolar gyre centered at the labrador sea contracts from expands to the east with the north atlantic current nac being shifted westward eastward these horizontal circulation changes which are dynamically linked to the thc changes induce large temperature and salinity variations around the gs and nac paths

oscillatory climate modes in the eastern mediterranean and their synchronization with the north atlantic oscillation abstract oscillatory climatic modes over the north atlantic ethiopian plateau and eastern mediterranean were examined in instrumental and proxy records from these regions aside from the well known north atlantic oscillation nao index and the nile river water level records the authors study for the first time an instrumental rainfall record from jerusalem and a tree ring record from the golan heights the teleconnections between the regions were studied in terms of synchronization of chaotic oscillators standard methods for studying synchronization among such oscillators are modified by combining them with advanced spectral methods including singular spectrum analysis the resulting cross spectral analysis quantifies the strength of the coupling together with the degree of synchronization a prominent oscillatory mode with a 7 8 yr period is present in all the climatic indices studied here and is completely synchronized with the north atlantic oscillation an energy analysis of the synchronization

upper ocean singular vectors of the north atlantic climate with implications for linear predictability and variability the limits of predictability of the meridional overturning circulation moc and upper ocean temperatures due to errors in ocean initial conditions and model parametrizations are investigated in an idealized configuration of an ocean general circulation model gcm singular vectors optimal perturbations are calculated using the gcm its tangent linear and adjoint models to determine an upper bound on the predictability of north atlantic climate the maximum growth time scales of moc and upper ocean temperature anomalies excited by the singular vectors are 18 5 and 13 years respectively and in part explained by the westward propagation of upper ocean anomalies against the mean flow as a result of the linear interference of non orthogonal eigenmodes of the non normal dynamics the ocean dynamics are found to actively participate in the significant growth of the anomalies an initial density perturbation of merely 0 02 kg m 3 is found to lead to a 1 7 sv moc anomaly after 18 5 years in addition northern hemisphere upper ocean temperature perturbations can be amplified by a factor of 2 after 13 years the growth of upper ocean temperature and moc anomalies is slower and weaker when excited by the upper ocean singular vectors than when the deep ocean is perturbed this leads to the conclusion that predictability experiments perturbing only the atmospheric initial state may overestimate the predictability time interestingly optimal moc and upper ocean temperature excitations are only weakly correlated thus limiting the utility of sst observations to infer moc variability the excitation of anomalies in this model might have a crucial impact on the variability and predictability of atlantic climate the limit of predictability of the moc is found to be different from that of the upper ocean heat content emphasizing that errors in ocean initial conditions will affect various measures differently and such uncertainties should be carefully considered in decadal prediction experiments copyright c

south atlantic response to el nino southern oscillation induced climate variability in an ocean general circulation model 1 the response of the south atlantic ocean to el nino southern oscillation enso is investigated by means of an ocean general circulation model orca2 forced with national centers for environmental prediction ncep reanalyses for the 1948 1999 period seasonal enso composites suggest that the enso induced wind anomalies play a major role in driving upper ocean temperatures by altering the net surface heat fluxes the meridional ekman heat transport and ekman pumping model diagnostics indicate that the ekman heat transport changes are in better agreement with the upper ocean temperature anomalies during the first half of the enso event whereas in the latter half the surface heat flux anomalies agree better in general the atmospheric forcing tends to lead to a coherent ocean response with a time lag of about one season subsurface temperatures evolve more slowly in response to enso forcing than the upper ocean they receive time filtered enso signals from mainly ekman pumping suction and variations in thermocline depth that result in the poleward and equatorward margins of the subtropical gyre exhibiting temperature anomalies of the same sign but opposite to those in the central regions of the gyre

interannual variations in the southern hemisphere winter circumpolar vortex relationships with the semiannual oscillation abstract several studies of southern hemisphere circulation report changes in the late 1970s and 1980s through the mid and high latitudes that are associated with a weakening in the semiannual oscillation sao of sea level pressure and geopotential height this weakening is thought to reflect changes in the amplitude of zonal wavenumber 3 a deepening of the subantarctic trough intensification of subtropical ridging and an increase in the strength of the westerlies these conclusions suggest an equatorial expansion of the circumpolar vortex in high latitudes and a poleward contraction of the vortex in the midlatitudes the goal of this study is to examine the size and spatial variation of the southern hemisphere circumpolar vortex in winter for evidence of such change the size of the 500 hpa vortex was calculated for the mid and high latitudes in 5 longitude sectors from both the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis dataset 1

plio quaternary sedimentation on the wilkes land continental rise preliminary results abstract the wilkes land continental rise is characterised by mounds and channels with approximately a north south elongation perpendicular to the margin proximal mound relief is up to 1000 m decreasing to about 300 m in the central part during the geophysical and geological survey conducted on in february march 2000 by the joint italian and australian wega project onboard r v tangaroa 11 piston cores were collected along two transects crossing the channel mound system all cores were logged for physical magnetic susceptibility and density and acoustic properties p wave velocity split cores were x rayed and samples were analysed for clay mineral assemblages chemical and micropaleontological diatoms foraminifera and nannofossils content glacial and interglacial intervals have been recognised in the sediment cores the interglacial facies consists of massive mud distinguished by a bioturbated massive mud occasionally with fine grained ice rafted debris ird and b structureless massive mud with abundant fine to coarse grained ird containing well preserved open ocean diatoms the glacial facies is represented by laminated mud with planar and or cross laminations with occasional isolated dropstones and rare poorly preserved sea ice diatoms the sharp boundary characterizing the limit between massive to laminated facies is interpreted to indicate a fast glacial onset in contrast the smooth passage presents from laminated to massive sediments indicates a gradual glacial waning recent down slope gravity flows have been identified in a turbidite a normally graded coarse grained sand recovered in the thalweg of jussie canyon and probably also in the massive debris facies from the steep side of mound a the massive debris is characterised by structureless and unsorted gravel and pebbles within a muddy matrix clay mineral assemblages and grain lithologies indicate a hinterland wilkes basin and continental shelf provenance for the terrigenous fraction

interdecadal variations in north atlantic sea surface temperature and associated atmospheric conditions abstract evidence is presented for a distinct pattern of ocean atmosphere relationship associated with interdecadal variability in the north atlantic region using a century of surface marine observations it is shown that middle and high latitude sea surface temperature sst display a long term fluctuation with negative anomalies before 1920 and during the 1970s and 1980s positive sst conditions prevailed from about 1930 to 1960 the pattern of interdecadal sst variability is constructed by subtracting the average field during 15 cold years from that during a similar interval of warm years the early century warming and the more recent cooling display a similar spatial pattern in both cases the pattern is basin scale and largely of one polarity with maxima in the vicinity of iceland in the labrador sea and northeast of bermuda the corresponding differences in surface atmospheric conditions are determined by averaging and subtracting in the same manner fields of sea level pressure slp and surf

influence of the south atlantic ocean dipole on west african summer precipitation abstract this paper demonstrates a causal link between the air sea phenomenon referred to as the south atlantic ocean sao dipole saod and the interannual variability of precipitation over west africa during the boreal summer monsoon rainy season in which most of the annual rainfall is recorded using an array of observational datasets analyses show that positive precipitation anomalies exceeding 40 mm month 1 over most locations at the guinea coast are associated with the positive phase of the saod which is characterized by warm sea surface temperature anomalies sstas in the northeastern part of the sao or the northeast pole nep that is the atlantic nino sector and cool ssta in the southwestern part southwest pole swp off the argentina uruguay brazil coast on the other hand interannual variability in the sahel is closely connected to the west african summer monsoon and the atlantic nino the results of this study reveal that the well known influence of the atlantic nino on guinea coast pre

atmosphere ocean coupled variability in the south atlantic abstract the climate variability of the south atlantic region is determined from 40 yr 1953 92 of comprehensive ocean atmosphere data set monthly sea surface temperature sst and sea level pressure slp data using the empirical orthogonal function eof and the singular value decomposition svd analysis methods the eof method is applied to each field separately whereas the svd method is applied to both fields simultaneously the significance of the atmosphere ocean interaction is revealed by a strong resemblance between individual eof and coupled svd modes of sst and slp the three leading modes of coupled variability on interannual and interdecadal timescales are discussed in some detail the first coupled mode which accounts for 63 of the total square covariance represents a 14 16 yr period oscillation in the strength of the subtropical anticyclone accompanied by fluctuations of a north south dipole structure in the sst the atmosphere ocean coupling is strongest during the southern summe

low frequency variability in the midlatitude atmosphere induced by an oceanic thermal front abstract this study examines the flow induced in a highly idealized atmospheric model by an east west oriented oceanic thermal front the model has a linear marine boundary layer coupled to a quasigeostrophic equivalent barotropic free atmosphere the vertical velocity at the top of the boundary layer drives the flow in the free atmosphere and produces an eastward jet parallel to the oceanic front s isotherms a large gyre develops on either side of this jet cyclonic to the north and anticyclonic to the south of it as the jet intensifies during spinup from rest it becomes unstable the most unstable wave has a length of about 500 km it evolves into a meander and eddies detach from the eastern edge of each gyre the dependence of the atmospheric dynamics on the strength t of the oceanic front is studied the gulf stream and kuroshio fronts correspond roughly in the scaling used here to t 7 c for weak fronts t 4 c the circulation is steady and exhibits two large antisymmetric gyres sepa

an interdecadal climate cycle in the south atlantic and its links to other ocean basins a singular value decomposition analysis and a combined complex empirical orthogonal function analysis are performed on 80 years of monthly sea surface temperature sst and sea level pressure slp data from the south atlantic region the analyses reveal the existence of interdecadal fluctuations in the coupled atmosphere ocean system with a period of around 20 years the sst anomalies are observed to propagate anticyclonically around the south atlantic basin following the subtropical gyre circulation at the same time a westward propagation of slp anomalies across the basin generates changes in the atmospheric circulation that appear to reinforce such sst anomalies through anomalous exchanges of heat it is thus proposed that the dominant physical processes involved in this interdecadal cycle include the horizontal advection of heat by the ocean currents and changes in the atmosphere ocean heat fluxes through local air sea interactions the global sst and slp patterns that accompany the different phases of the south atlantic cycle are also presented they show similarities with other well known interdecadal signals observed by several investigators in other ocean basins e g the low frequency part of the north atlantic oscillation this suggests that the south atlantic signal described in this study may be a regional aspect of global interdecadal variability

viscous heating in rhyolite an in situ experimental determination viscous heating during magmatic flow may play a major role in eruption dynamics in order to document viscous heating during deformation of magma we have conducted a series of rheological experiments where viscous heating is directly monitored via thermocouples in high viscosity magmas we observe experimentally the strain rate dependence of viscous heating viscous heating becomes rheologically significant in the highly viscous lavas investigated at strain rates above ca 10 3 s 1 a simple analysis shows that the temperature increase generated through viscous heating during deformation of melts with viscosities ranging from 108 to 1012 pa s can account for their apparent non newtonian rheology in these experiments this thermal correction transforms apparent non newtonian strain rate dependent rheology of magma to a newtonian behavior over the range of conditions accessed in this work in this manner this study provides an experimental basis for separating the relative roles of structural relaxation and viscous heating in the generation of apparent non newtonian rheology at high strain rates here viscous heating dominates and the observation of the structural onset of non newtonian behavior is precluded by a viscous heating induced lowering of the newtonian viscosity the interplay of viscous heating and structural relaxation in melts in nature is discussed briefly

transport of the north atlantic deep western boundary current about 39 n 70 w 2004 2008 abstract begun in spring 2004 a sustained measurement program line w is returning high resolution observations of the north atlantic s deep western boundary current dwbc southeast of new england the study focuses on the cold limb of the atlantic meridional overturning circulation near the boundary between the subpolar and subtropical gyres the field study consists of a 6 element continental slope spanning moored array on a line underlying an altimeter satellite ground track and periodic reoccupations of a full depth hydrographic section along the line extending from the continental shelf towards bermuda here data from the first 4 years of the array may 10 2004 april 9 2008 are analyzed along with 9 realizations of the section the array a mix of moored profiler and discrete fixed depth instrument moorings returned temperature salinity and horizontal velocity data with various temporal and depth resolutions after averaging to filter inertial tidal and other high frequency motions the combined moored data set was binned to the lowest common temporal resolution of 5 days the nominal burst sample interval of the moored profilers and interpolated to 2 dbar vertical resolution temperature salinity dissolved oxygen tracer chemical concentrations and direct velocity data were acquired on the hydrographic cruises the present work focuses on the 4 year mean and time varying meridional transport in 4 layers bounded by neutral density surfaces upper and classical labrador sea waters iceland scotland overflow waters and denmark strait overflow waters the 5 d 4 layer summed meridional transport estimates range between 3 5 and 79 9 sv with a record mean average transport of 25 1 sv and standard deviation of 12 5 sv bias adjustment to account for the finite width of the moored array increases the 4 layer mean transport estimate to 28 7 sv at time scales longer than about 1 month the variations in equatorward dwbc transport appear correlated with meridional position of the gulf stream north wall with stronger transport observed when the stream is displaced south

strain induced outgassing of three phase magmas during simple shear a major factor determining the explosivity of silicic eruptions is the removal of volatiles from magma through permeability controlled outgassing we studied the microstructural development of permeability during deformation of highly viscous magma by performing simple shear experiments on bubble 0 12 0 36 volume fraction and crystal bearing 0 0 42 volume fraction silicate melts experiments were performed under torsion at high temperature and pressure 723 873 k and 150 200 mpa in a paterson deformation apparatus at bulk shear strains between 0 and 10 the experimental setup allows for gas escape if bubble connectivity is reached on the sample periphery three dimensional imaging and analysis of deformed bubbles was performed using x ray tomography the development of localized deformation in all samples enhanced by crystal content leads to brittle fracture at bulk strains 2 and sample wide fracturing in samples deformed to strains 5 a decrease in both bubble fraction and dissolved volatile content with increasing strain along with strain hardening rheological behavior suggests significant shear induced outgassing through the fracture networks applicable to shallow conduit degassing in magmas containing crystal fractions of 0 0 42 this study contributes to our understanding of highly viscous magma outgassing and processes governing the effusive explosive transition

dominant modes of variability in the south atlantic a study with a hierarchy of ocean atmosphere models using an atmosphere model of intermediate complexity and a hierarchy of ocean models the dominant modes of interannual and decadal variability in the south atlantic ocean are studied the atmosphere simplified parameterizations primitive equation dynamics speedy model has t30l7 resolution the physical package consists of a set of simplified physical parameterization schemes based on the same principles adopted in the schemes of state of the art agcms it is at least an order of magnitude faster whereas the quality of the simulated climate compares well with those models the hierarchy of ocean models consists of simple mixed layer models with an increasing number of physical processes involved such as ekman transport wind induced mixing and wind driven barotropic transport finally the atmosphere model is coupled to a regional version of the miami isopycnal coordinate ocean model micom covering the south atlantic with a horizontal resolution of 1 and 16 vertical layers the coupled modes of mean sea level pressure and sea surface temperature simulated by speedy micom strongly resemble the modes as analyzed from the ncep ncar reanalysis indicating that this model configuration possesses the required physical mechanisms for generating these modes of variability using the ocean model hierarchy the authors were able to show that turbulent heat fluxes ekman transport and wind induced mixing contribute to the generation of the dominant modes of coupled sst variability the different roles of these terms in generating these modes are analyzed variations in the wind driven barotropic transport mainly seem to affect the sst variability in the brazil malvinas confluence zone the spectra of the mixed layer models appeared to be too red in comparison with the fully coupled speedy micom model due to the too strong coupling between sst and surface air temperatures sats resulting from the inability to advect and subduct sst anomalies by the mixed layer models in speedy micom anomalies in the southeastern corner of the south atlantic are subducted and advected toward the north brazilian coast on a time scale of about 6 yr

multiscale variabilities in global sea surface temperatures and their relationships with tropospheric climate patterns el nino southern oscillation enso is a global phenomenon with significant phase propagation within and between basins this is captured and described in the first mode of a complex empirical orthogonal function ceof analysis of sea surface temperature anomaly ssta from the midnineteenth century through 1991 the global enso from the ssta data plus a linear trend everywhere are subsequently removed in order to consider other global modes of variability uncontaminated by the intra and interbasin effects of enso an ordinary eof analysis of the ssta residuals reveals three non enso modes of low frequency variability that are related to slow oceanic and climate signals described in the literature the first two modes have decadal to multidecadal timescales with high loadings in the pacific they bear some spatial similarities to the enso pattern but are broader more intense at high latitudes and differ in the time domain a ceof analysis confirms that they are not merely the phase related components of a single mode and that all three modes are without significant phase propagation the third mode is a multidecadal signal with maximal realization in the extratropical north atlantic southeast of greenland it is consistent with studies that have documented connections between north atlantic ssta and the tropospheric north atlantic oscillation nao all three ssta modes have midtropospheric associations related to previously classified northern hemisphere teleconnection patterns the relationships between ssta modes and tropospheric patterns are consistent with the ocean atmosphere interactions discussed in previous studies to explain low frequency climate oscillations in the north pacific and north atlantic sectors the first three leading modes of non enso ssta are most related to the tropospheric patterns of the pacific north american the north pacific and the arctic oscillations ao respectively the 500 hpa pattern associated with the third ssta mode also bears similarities to the nao in its atlantic sector this north atlantic mode has a region of high positive ssta loadings in the gulf of alaska which appear to be connected to the north atlantic ssta by a tropospheric bridge effect in the ao

non newtonian rheological law for highly crystalline dome lavas volcanic eruption models are hampered by the lack of multiphase magmatic flow laws most rheological models estimate the viscosity of multiphase lavas via the einstein roscoe equation but this simplification cannot be used for high crystallinity and it does not consider the non newtonian strain rate dependence of viscosity we carried out parallel plate experiments on natural samples to simulate multiphase lava deformation under various stresses and strain rates multiphase lavas exhibit an important component of shear thinning and appear to invalidate the adequacy of einstein roscoe based formulations for highly crystalline lava rheology the remarkable singular dependence of viscosity on strain rate yields a novel universal rheology law at eruptive temperatures t i e log 0 993 8974 t 0 543 log our work reveals the importance of considering microcracking and viscous dissipation at very high strain rate 10 3 s 1 explaining the occurrence of seismic swarms along the conduit margins and consequently supporting plug like magma ascent models

freshwater forcing control on early holocene south american monsoon abstract climate anomalies due to lake agassiz outbursts and hudson bay ice dome melting are commonly considered triggers of north american atmospheric cooling however in the southern hemisphere these freshwater fluxes are mostly associated with increased precipitation and a possible intensification of the south american monsoon system sams here we tested how the sams responded to early holocene meltwater events based on both proxy data and simulations we find that sea surface temperatures ssts and precipitation indicate a freshwater driven strengthening of the sams due to a weakening of the south atlantic subtropical dipole simulated sams strengthening accounts for up to 50 of the variance in early holocene precipitation in south america in turn changes in the south atlantic subtropical dipole accounts for up to 31 of the variance in south atlantic ssts additionally we propose that the stronger sams in the early holocene might have been due to a freshwater driven weakening of the southeasterly trade winds slower trade winds weaken the zonal and meridional surface water transport concentrating warm waters in the northeastern south atlantic

volcanic dilemma flow or blow volcanic eruptions can be either slow outpourings of lava or explosive ejections of fragmented rock in his perspective dingwell discusses the physical and chemical properties of magma that lead to these two styles of eruption new experiments and computer simulations are pointing to the involvement of solidlike behavior of liquid magma when it makes a transition to a glass

oscillations in land surface hydrological cycle abstract hydrological cycle is the perpetual movement of water throughout the various component of the global earth s system focusing on the land surface component of this cycle the determination of the succession of dry and humid periods is of high importance with respect to water resources management but also with respect to global geochemical cycles this knowledge requires a specified estimation of recent fluctuations of the land surface cycle at continental and global scales our approach leans towards a new estimation of freshwater discharge to oceans from 1875 to 1994 as recently proposed by labat et al labat d godderis y probst jl guyot jl 2004 evidence for global runoff increase related to climate warming advances in water resources 631 642 wavelet analyses of the annual freshwater discharge time series reveal an intermittent multiannual variability 4 to 8 y 14 to 16 y and 20 to 25 y fluctuations and a persistent multidecadal 30 to 40 y variability continent by continent reasonable relationships between land water cycle oscillations and climate forcing such as enso nao or sea surface temperature are proposed even though if such relationships or correlations remain very complex the high intermittency of interannual oscillations and the existence of persistent multidecadal fluctuations make prediction difficult for medium term variability of droughts and high flows but lead to a more optimistic diagnostic for long term fluctuations prediction