40 ar 39 ar ages from subsurface crystalline basement of the wiggins uplift and southwesternmost appalachian piedmont implications for late paleozoic terrane accretion during assembly of pangea

transoceanic wave propagation links iceberg calving margins of antarctica with storms in tropics and northern hemisphere 1 we deployed seismometers on the ross ice shelf and on various icebergs adrift in the ross sea including b15a a large 100 km by 30 km fragment of b15 which calved from the ross ice shelf in march 2000 the data reveal that the dominant energy of these floating ice masses is in the 0 01 to 0 1 hz band and is associated with sea swell generated in the tropical and extra tropical pacific ocean in one example a strong storm in the gulf of alaska on 21 october 2005 approximately 13 500 km from the ross sea generated swell that arrived at b15a immediately prior to and during its break up off cape adare on 27 october 2005 if sea swell influences iceberg calving and break up a teleconnection exists between the antarctic ice sheet mass balance and weather systems worldwide

seismic observations of sea swell on the floating ross ice shelf antarctica 1 a seismometer operating on the floating ross ice shelf near its seaward ice front nascent iceberg for 340 days out of 730 days during the 2004 2005 and 2006 antarctic field seasons recorded the arrival of 93 distantly sourced ocean swell events displaying frequency dispersion characteristic of surface gravity waves propagating on deep water comparison of swell event dispersion with the noaa wave watch iii nww3 ocean wave model analysis reveals that 83 of these events were linked to specific storms located in the pacific southern and indian oceans nearly all major storms in the nww3 analysis of the pacific ocean were linked to signals observed at the nascent site during the period of seismometer operation swell induced motion of the ross ice shelf is found to increase by several orders of magnitude over the time period that sea ice surrounding antarctica decreases from its maximum extent october to its minimum extent february the amplitude of vertical vibration of the ice shelf in the frequency band between 0 025 and 0 14 hz varies between tens of micrometers to millimeters as sea ice decays to its minimum seasonal extent this suggests that climate influence on sea ice extent may indirectly modulate swell energy incident on the calving margins of the antarctic ice sheet the largest swell signals observed on the ross ice shelf come from storms in the tropical pacific and gulf of alaska these remote events emphasize how the iceberg calving margin of antarctica is connected to environmental conditions well beyond antarctica

interannual modulation of east african early short rains by the winter arctic oscillation in the present study we analyzed the interannual linkage between the boreal winter arctic oscillation ao and east african early short rains when the indian ocean dipole and el nino southern oscillation variance are excluded by linear regression the boreal winter ao index is significantly correlated with the october east african precipitation over the domain of 5 n 5 s and 35 45 e for the period 1979 2014 r 0 46 the upper ocean heat content likely acts as a medium that links the ao and east african precipitation significant subsurface warming and positive upper ocean heat content anomalies occur over the western indian ocean during the autumn following positive ao winters which enriches the atmospheric moisture intensifies convection and enhances precipitation oceanic dynamics play a key role in causing this subsurface warming winter ao related atmospheric circulation creates anomalous wind stress which forces a downwelling oceanic rossby wave between 60 75 e and 5 10 s where the thermocline significantly deepens this rossby wave propagates westward and accompanies significant subsurface warming along the thermocline the rossby wave arrives at the western indian ocean in the late summer significantly warming the region to the west of 55 e at a depth of 60 100 m this warming remains significant through october correspondingly the upper ocean heat content significantly increases by approximately 2 3 108 j m 2 in the region west of 60 e between 5 and 10 s the role of these oceanic dynamics in linking the winter ao and anomalous subsurface warming was tested by numerical experiments with an oceanic general circulation model the experiments were performed with the forcing of ao related wind stress anomalies over the indian ocean in the winter the oceanic rossby wave generated in the central indian ocean during boreal winter the consequent subsurface warming and the anomalous upper ocean heat content in october over the western indian ocean were all adequately reproduced the winter ao can serve as a precursor of east african short rain anomalies

atmospheric hydrospheric mechanisms of climate anomalies in the western equatorial indian ocean atmosphere ocean mechanisms of rainfall anomalies at the coast of eastern africa are studied using long term ship observations in the indian ocean surface current measurements subsurface casts upper air analyses by the european centre for medium range weather forecasts rain gauge series in eastern africa and india and an index of the southern oscillation so the high so phase being defined by anomalously high low pressure at tahiti darwin the causalities of precipitation anomalies at the coast of eastern africa differ for the two rainy seasons centered on april may and october november and only the latter is strongly related to the so in the high so phase april may pressure is low over the entire indian ocean domain whereas in october november pressure is high in the west and low in the east concomitantly surface waters are anomalously cold in the west and strong westerlies sweep the equatorial zone of the indian ocean eastern african rainfall anomalies are related to the so through a combination of cooperative mechanisms that function most effectively in the boreal autumn rainy season of eastern africa 1 equatorial westerly winds are conducive to lower tropospheric divergence over equatorial east africa and in the high so phase these are accelerated especially in october november owing to the anomalous eastward pressure gradient 2 the equatorial westerly winds drive the eastward equatorial jet in the upper hydrosphere which entails cold water upwelling in the western extremity of the basin where sea surface temperature further hydrostatically affects the zonal pressure gradient and thus feeds back into the equatorial westerly winds 3 in addition cold water anomalies in the western indian ocean most pronounced in october november during the high so phase also suppress convection 4 in the high so phase the indian summer monsoon tends to be strong leaving behind an anomalously cold western indian ocean which in turn feeds into mechanisms 1 to 3 the eastward equatorial jet thus has a role to play in feedback mechanisms contributing to the anomalies of the boreal autumn rains at the coast of eastern africa

dynamical mechanisms for asymmetric ssta patterns associated with some indian ocean dipoles indian ocean dipole iod can be divided into two types according to their sst anomaly ssta patterns the symmetric iods and the asymmetric iods dynamical mechanisms for the two types of iods are investigated using an ocean general circulation model and the numerical experiments indicate that the setup time of the equatorial easterly wind anomalies eewa associated with iods is crucially important for the symmetrical characteristics of the ssta patterns early setup of the eewa in spring can induce intense cooling in the east pole but weak warming in the west pole making the two poles asymmetric the intense cooling in the east pole is linked to the seasonal variations of thermocline depth horizontal sst gradient and unusually long duration of the eewa and the weak warming in the west pole is due to unusually cold zonal advection resulted from zonal sst gradient change the numerical experiments demonstrate that the strength of the eewa also plays an important role in the symmetrical characteristics of iods the ssta in the two poles both intensify as the eewa strength increases only when the eewa speed is below a critical value above the critical value the warming in the west pole starts to decrease while the cooling in the east pole still keeps increasing leading to an asymmetric ssta pattern the mechanism behind this phenomenon is similar to the one in the situation when eewa sets up earlier

abnormal upwelling and chlorophyll a concentration off south vietnam in summer 2007 the present study investigates a strong upwelling and concurrent phytoplankton bloom off the south vietnam coast in august 2007 analysis of the alongshore wind offshore ekman transport wind stress curl and other parameters indicates the southwesterly summer monsoon plays an important role in this peculiar case the change of monsoonal wind involves variations of atmospheric circulation on multiple time scales on the interannual time scale a positive indian ocean dipole iod in 2007 accompanying with a la nina event acts to enhance the southwesterly monsoon over the south china sea scs the enhanced southwesterly wind is regarded as a major factor in promoting the upwelling and the phytoplankton bloom off the south vietnam coast on the intraseasonal time scale variations of the sea surface temperature sst and sea surface wind at 30 60 day periods reveal that the sst cooling develops with the evolution of the southwesterly wind anomalies with nearly one week delay implying the great significance of the madden julian oscillation mjo moreover a tropical storm formed in the western scs in early august reinforces the westerly wind and sst cooling among multiple factors on different time scales the mjo event is considered as the major cause since it induces the maximum velocity 4 m s of the southwesterly wind anomalies as a result the high chlorophyll a concentration 0 56 mg m 3 and low sst center 27 degrees c develops in the region off the south vietnam coast and advects to the central scs riding on the northern rim of the southern anticyclonic gyre

diagnosing the 2005 drought in equatorial east africa abstract equatorial east africa suffered severe drought during its 2005 short rains centered on october november the circulation mechanisms of such precipitation anomalies are examined using long term upper air and surface datasets and based on diagnostic findings from earlier empirical investigations the steep eastward pressure gradient is conducive to fast westerlies over the central equatorial indian ocean surface manifestation of a powerful zonal circulation cell with subsidence over east africa and ascending motion over indonesia with fast westerlies rainfall in east africa is deficient and they tend to be accompanied by anomalously cold waters in the northwestern and warm anomalies in the southeastern extremity of the equatorial indian ocean basin without any seesaw between these domains in october november 2005 pressure in the west was anomalously high entailing a steep eastward pressure gradient along the equator conducive to fast westerlies and further symptomatic of the zonal ci

an investigation of interannual rainfall variability in africa abstract interannual variations in african rainfall are examined using rotated principal component analysis pca applied to anomalies from the annual mean as well as seasonal anomalies the rotated pca loading patterns suggest several preferred continental scale rainfall anomaly patterns the dominant features of year to year variations in african rainfall appear to be the high spatial coherence of rainfall anomalies over large portions of the continent in addition several dipole regions that is adjacent regions which tend to experience rainfall anomalies of opposite sign are found and discussed one dipole region the sub saharan region appears to have a relationship with a characteristic atlantic sea surface temperature anomaly pattern during boreal summer during austral summer the tendency for a large scale dipole pattern in southeast africa is apparent as is an association of this pattern with the warm and cold phases of the el nin southern oscillation enso phenomenon normalized rainfal

carbon and oxygen isotopic composition of a guam coral and their relationships to environmental variables in the western pacific we examine the high resolution 32 samples year carbon and oxygen isotopic composition 13ccoral and 18ocoral in a coral core porites lobata from double reef guam over the years 1980 2000 the 13ccoral shows clear seasonal variations with mean seasonal amplitude of 1 89 which roughly corresponds with seasonal variations in solar radiation the seasonal amplitude of 18ocoral variations are small 0 23 0 57 but they are significantly correlated with sea surface temperature sst and salinity sss the 18ocoral and sst are more strongly correlated during el nino southern oscillation enso warm phases r 0 81 p 28 c and lower values of 18osw at guam these differences in oceanic parameters result from movements of the western pacific warm pool wpwp during the different phases of enso anomalies in 18osw inferred from the 18ocoral and instrumental sst are consistent with sss anomalies for the years 1980 2000 these 18osw anomalies may reflect changes in sss and evaporation precipitation due to movements of the wpwp this detailed analysis of a coral from guam suggests that it may contain an excellent archive of past enso events

late quaternary productivity changes in the equatorial indian ocean odp hole 716a abstract the equatorial indian ocean is swept by the indian ocean equatorial westerlies iew which intensify in monsoon transitions during april may and october november driving eastward equatorial current eec to the upper ocean the eec brings significant changes in the surface productivity in the equatorial region influencing the life style of the surface and deep sea fauna this study is aimed at understanding 300 kyr record 450 150 kyrs ago of productivity changes linked to variations in iew eec in the equatorial indian ocean using high resolution microfaunal record from integrated ocean drilling program iodp hole 716a maldives ridge in total 451 core samples of 10 cm 3 volume from the 300 kyr long sequence ranging 450 150 kyrs ago were analyzed at every 1 cm interval to generate census data of the benthic foraminiferal fauna factor and cluster analyses using percentages of 53 highest ranked benthic foraminiferal species were run that enabled us to identify five biofacies indicating the varied nature of deep sea environments during the late quaternary the results show a major shift roughly 300 kyr ago across marine isotope stages 9 and 8 mis 9 8 recorded in this study as mid brunhes transition at hole 716a the present study also combines published planktic foraminiferal fauna and pteropod records from hole 716a to understand if the surface to shallow and intermediate water paleoenvironments were coupled with deep water changes during the late quaternary in the maldivian archipelago biofacies robulus nicobarensis trifarina reussi rn tr uvigerina porrecta reussella simplex upo rs and cymbaloporetta squammosa bolivinita sp cs bsp dominate before the mid brunhes transition and document high organic flux with relatively low oxygen paleoenvironment similar to the planktic foraminifer globigerina bulloides population while benthic foraminiferal biofacies hoeglundina elegans miliolinella subrotunda he ms and uvigerina peregrina quinqueloculina seminulum upe qs record high seasonality in food supply with well oxygenated deep water following the mid brunhes climatic transition 300 kyr ago at hole 716a these changes are also recorded in the population of planktic foraminiferal species globigerinoides ruber and neogloboquadrina dutertrei as well as pteropods organic carbon flux linked to changes in the iew eec strength appears to be the most plausible factor controlling faunal assemblages and hence paleoproductivity dynamics in the maldivian region our results suggest that the strength of the iew is inversely related with the indian ocean dipole iod the iod strengthened across mis 9 8 during which time the iew weakened leading to major changes at hole 716a

insolation cycles as a major control of equatorial indian ocean primary production analysis of a continuous sedimentary record taken in the maldives indicates that strong primary production fluctuations 70 to 390 grams of carbon per square meter per year have occurred in the equatorial indian ocean during the past 910 000 years the record of primary production is coherent and in phase with the february equatorial insolation whereas it shows diverse phase behavior with 18o depending on the orbital frequency eccentricity obliquity or precession examined these observations imply a direct control of productivity in the equatorial oceanic system by insolation in the equatorial indian ocean productivity is driven by the wind intensity of westerlies which is related to the southern oscillation therefore it is suggested that a precession forcing on the southern oscillation is responsible for the observed paleoproductivity dynamics

tsunami and infragravity waves impacting antarctic ice shelves the responses of the ross ice shelf ris to the september 16 2015 8 3 mw chilean earthquake tsunami 75 s period and to oceanic infragravity ig waves 50 300 s period were recorded by a broadband seismic array deployed on the ris from november 2014 to november 2016 here we show that tsunami and ig generated signals within the ris propagate at gravity wave speeds 70 m s as water ice coupled flexural gravity waves ig band signals show measureable attenuation away from the shelf front the response of the ris to chilean tsunami arrivals is compared with modeled tsunami forcing to assess ice shelf flexural gravity wave excitation by very long period vlp 300 s gravity waves displacements across the ris are affected by gravity wave incident direction bathymetry under and north of the shelf and water layer and ice shelf thicknesses horizontal displacements are typically about 10 times larger than vertical displacements producing dynamical extensional motions that may facilitate expansion of existing fractures vlp excitation is continuously observed throughout the year with horizontal displacements highest during the austral winter with amplitudes exceeding 20 cm because vlp flexural gravity waves exhibit no discernable attenuation this energy must propagate to the grounding zone both ig and vlp band flexural gravity waves excite mechanical perturbations of the ris that likely promote tabular iceberg calving consequently affecting ice shelf evolution understanding these ocean excited mechanical interactions is important to determine their effect on ice shelf stability to reduce uncertainty in the magnitude and rate of global sea level rise

the seasonal development of an sst anomaly in the indian ocean and its relationship to enso abstract the seasonal development of the sea surface temperature sst anomaly in the indian ocean is investigated in relation to el nino southern oscillation enso using noaa optimally interpolated sst and ncep reanalysis data the result shows that the onset season of el nino affects the seasonal development of surface wind anomalies over the equatorial eastern indian ocean eeio these surface wind anomalies in turn determine whether the sst anomaly in the eeio evolves into the eastern pole of the dipole pattern in years when the dipole pattern develops surface zonal wind anomalies over the eeio switch from westerly to easterly in spring as la nina switches to el nino the seasonal zonal wind over the eeio also switches from westerly to easterly in spring and the anomalous wind strengthens seasonal wind from winter to summer stronger winds and resultant thermal forcings produce the negative sst anomaly in the eeio in winter and its amplitude increases in summer the sst anomaly becomes the ea

resonance vibrations of the ross ice shelf and observations of persistent atmospheric waves recently reported lidar observations have revealed a persistent wave activity in the antarctic middle and upper atmosphere that has no counterpart in observations at mid and low latitude locations the unusual wave activity suggests a geographically specific source of atmospheric waves with periods of 3 10 hours here we investigate theoretically the hypothesis that the unusual atmospheric wave activity in antarctica is generated by the fundamental and low order modes of vibrations of the ross ice shelf ris simple models are developed to describe basic physical properties of resonant vibrations of large ice shelves and their coupling to the atmosphere dispersion relation of the long surface waves which propagate in the floating ice sheet and are responsible for its low order resonances is found to be similar to the dispersion relation of infragravity waves in the ice free ocean the phase speed of the surface waves and the resonant frequencies determine the periods and wave vectors of atmospheric waves that are generated by the ris resonant oscillations the altitude dependent vertical wavelengths and the periods of the acoustic gravity waves in the atmosphere are shown to be sensitive to the physical parameters of the ris which can be difficult to measure by other means predicted properties of the atmospheric waves prove to be in a remarkable agreement with the key features of the observed persistent wave activity

stable isotopes in east african precipitation record indian ocean zonal mode observational stable isotope data and model simulations show that the 18 o composition of precipitation in east africa is closely related to the coupled ocean atmosphere system over the indian ocean during the rainy seasons 18 o is a very sensitive recorder of the indian ocean zonal mode iozm the link between 18 o and the iozm is established through adjustments in the large scale overturning circulation over the indian ocean and associated changes in convective activity and precipitation over east africa the iozm is recorded as significant departures in 18 o not only over east africa but as a dipole mode with opposite sign to the east and west of the indian ocean

mayotte coral reveals hydrological changes in the western indian ocean between 1881 and 1994 we reconstruct the hydrologic history of the tropical western indian ocean by calculating the 18oseawater from coupled coral sr ca and 18o measurements in a massive porites coral from mayotte comoros between 1881 and 1994 we found that the precipitation evaporation balance varies naturally on time scales of 5 6 years and 18 25 years high low ssts are associated with positive negative 18oseawater implying that atmospheric variability is linked with remote climate modes in the indian ocean and the tropical extratropical pacific ocean warm el nino southern oscillation events are associated with a negative freshwater balance at mayotte this case study demonstrates that a much denser network of 18oseawater reconstructions is crucial for understanding the spatial patterns of hydrological conditions

potential predictability of the sea surface temperature forced equatorial east african short rains interannual variability in the 20th century in this article the predictability of the 20th century sea surface temperature sst forced east african short rains variability is analyzed using observational data and ensembles of long atmospheric general circulation model agcm simulations to our knowledge such an analysis for the whole 20th century using a series of agcm ensemble simulations is carried out here for the first time the physical mechanisms that govern the influence of sst on east african short rains in the model are also investigated it is found that there is substantial skill in reproducing the east african short rains variability given that the ssts are known consistent with previous recent studies it is found that the indian ocean and in particular the western pole of the indian ocean dipole iod play a dominant role for the prediction skill whereas ssts outside the indian ocean play a minor role the physical mechanism for the influence of the western indian ocean on east african rainfall in the model is consistent with previous findings and consists of a gill type response to a warm cold anomaly that induces a westerly easterly low level flow anomaly over equatorial africa and leads to moisture flux convergence divergence over east africa on the other hand a positive el nino southern oscillation enso anomaly leads to a spatially non coherent reducing effect over parts of east africa but the relationship is not strong enough to provide any predictive skill in our model the east african short rains prediction skill is also analyzed within a model derived potential predictability framework and it is shown that the actual prediction skill is broadly consistent with the model potential prediction skill low frequency variations of the prediction skill are mostly related to ssts outside the indian ocean region and are likely due to an increased interference of enso with the indian ocean influence on east african short rains after the mid 1970s climate shift

circulation mechanisms of kenya rainfall anomalies abstract expanding earlier studies on the boreal spring and autumn rainy seasons in equatorial east africa pending challenges on the mechanisms of rainfall variability are investigated eastward pressure gradient and slack south indian ocean trade winds allow surface equatorial westerlies in spring and autumn complementing that upper tropospheric easterlies are required for the development of a zonal vertical circulation cell along the indian ocean equator because of the summer warming and high stand of upper tropospheric topography over south asia strong upper tropospheric easterlies over the tropical northern and equatorial indian ocean persist from summer into autumn thus allowing the development of a zonal vertical circulation cell by contrast the winter cooling entails low stand of upper tropospheric topography in the north thus hindering easterlies over the equator consequently an equatorial zonal circulation cell does not develop in boreal spring the equatorial zonal circulation cell

termination of indian ocean dipole events in a coupled general circulation model abstract using 200 yr of coupled general circulation model cgcm results causes for the termination of indian ocean dipole iod events are investigated the cgcm used here is the scale interaction experiment frontier research center for global change sintex f1 model which consists of a version of the european community hamburg echam4 6 atmospheric model and a version of the ocean parallelise opa8 2 ocean general circulation model this model reproduces reasonably well the present day climatology and interannual signals of the indian and pacific oceans the main characteristics of the intraseasonal disturbances isds oscillations are also fairly well captured by this model however the eastward propagation of isds in the model is relatively fast in the indian ocean and stationary in the pacific compared to observations a sudden reversal of equatorial zonal winds is observed as a result of significant intraseasonal disturbances in the equatorial indian ocean in november december of iod events

tidal bending and strand cracks at the kamb ice stream grounding line west antarctica an extensive set of shore parallel fractures are observed at the grounding line of kamb ice stream kis in west antarctica seismicity measured in the grounding zone is as elsewhere around antarctica tidally forced and moreover strand cracks propagate nearly exclusively on the falling tide measured surface deflection and a model of fracture propagation are used to conclude that bending on the falling tide favors propagation while bending on the rising tide suppresses propagation without the perturbation due to tidal bending strand cracks would be rare and appear farther downstream than observed we speculate that the very large number of cracks observed at kis is due to the stagnant to floating transition at that grounding line which allows cyclic bending of the same ice and relatively large stretching rates

role of indian ocean warming in the development of philippine sea anticyclone during enso 1 the anomalous low level anticyclone near the philippines and suppressed convection over the western pacific associated with the mature warm phase of el nino southern oscillation enso have been suggested as important elements in the interaction between enso and the east asian monsoon we examined the causes of these anomalies in the circulation and convection using a newly developed linear baroclinic model that includes interactive moist processes of the cumulus convection and surface heat fluxes a conventional version of the linear model forced by prescribed heating indicates that the diabatic cooling due to suppressed convection over the maritime continent generates the philippine sea anticyclone from a series of the moist linear model experiments we found that the modest warming of the indian ocean in addition to the strong warming in the central eastern pacific and weak cooling in the western pacific is significant to suppress the convection over the maritime continent observed data also show a coincidence of the development between the philippine sea anticyclone indian ocean warming and the ascending motion over the indian ocean supporting the model results the above results indicate that the atmosphere ocean system in the indian ocean may be one of important factors to improve predictability of the east asian climate during enso

breakup of the larsen b ice shelf triggered by chain reaction drainage of supraglacial lakes this research is supported by the u s national science foundation under grant geop ant 0944248 awarded to d r m and grants ant 0838811 and arc 0934534 awarded to o v s

african hydroclimatic variability during the last 2000 years abstract the african continent is characterised by a wide range of hydroclimate regimes ranging from humid equatorial west africa to the arid deserts in the northern and southern subtropics the livelihoods of much of its population are also vulnerable to future climate change mainly through variability in rainfall affecting water resource availability a growing number of data sources indicate that such hydroclimatic variability is an intrinsic component of africa s natural environment this paper co authored by members of the pages africa 2k working group presents an extensive assessment and discussion of proxy historical and instrumental evidence for hydroclimatic variability across the african continent spanning the last two millennia while the african palaeoenvironmental record is characterised by spatially disjunctive datasets with often less than optimal temporal resolution and chronological control the available evidence allows the assessment of prominent spatial patterns of palaeomoisture variability through time in this study we focus sequentially on data for six major time windows the first millennium ce the medieval climate anomaly 900 1250 ce the little ice age 1250 1750 ce the end of the lia 1750 1850 ce the early modern period 1850 1950 and the period of recent warming 1950 onwards this results in a continent wide synthesis of regional moisture balance trends through history allowing consideration of possible driving mechanisms and suggestions for future research

zonal circulations over the equatorial indian ocean abstract the ncep ncar 1958 97 upper air dataset and surface observations have been analyzed for evidence of zonal vertical circulations along the indian ocean equator and their role in climatic variability the long term mean upper tropospheric circulation is dominated in boreal winter by divergent outflow from the southern indian ocean northwestward into southern asia and in summer from southern asia southwestward into the southern hemisphere in boreal autumn only divergent easterlies blow from indonesia along the equator into an upper tropospheric convergence band over east africa and only then a closed zonal vertical circulation cell materializes along the indian ocean equator between the centers of ascending motion over indonesia and of subsidence over equatorial east africa and featuring westerlies in the lower layers the boreal autumn zonal vertical circulation varies interannually a regime of intense circulation features accelerated equatorial surface westerlies enhanced subsidence and d

sea surface temperature productivity and hydrological changes in the northern indian ocean maldives during the interval 575 175 ka mis 14 to 7 abstract the south asian monsoon sam drives seasonal changes in the atmospheric and ocean circulation of the tropical indian ocean affecting precipitation on land and oceanic primary productivity this work examined sediments from the international ocean discover program iodp site u1467 iodp expedition 359 located in the maldives inner sea northern indian ocean at a water depth of 487 m the maldives inner sea is a perfect location to study past changes in tropical climate and ocean circulation related to monsoon dynamics in the equatorial indian ocean this study focuses on the 575 175 ka interval from marine isotope stage mis 14 to 7 an important period for human evolution and dispersal to eurasia we reconstructed sea surface temperature sst based on alkenone unsaturation index u 37 k hydrological changes based on terrestrial input of n alkanes and past surface ocean productivity based on total c37 alkenones concentration the u 37 k sst record shows a difference of about 1 5 c between glacial and interglacial periods clearly showing all stages and substages from mis 14 to 7 and revealing a connection between ice sheets extension and sst at the equatorial region the n alkanes concentration and average chain length index indicate vegetation changes at the indian peninsula with drier conditions generally associated with glacial periods precipitation increases abruptly at the end of terminations lasting for a variable time interval in each interglacial period except for mis 13 however other mechanisms superimposed to the glacial interglacial forcing such as the indian ocean dipole iod mode have been invoked to explain shorter scale variability in precipitation over india the total alkenone concentration record indicates that primary productivity at site u1467 is strongly associated with orbital changes probably related to the summer inter tropical insolation gradient sitig 23n 23s on june 21st high primary productivity occurred during intervals of low sitig which resulted in strong inter monsoon april may and october november indian ocean equatorial westerlies iew and reduced precipitation in the equatorial region this mechanism may also be related to the iod which affects the strength of the iew

empirical predictability study of october december east african rainfall relationships between september atmospheric dynamics over the global tropics and the east africa short rains over the domain 4 s 4 n 30 39 e were investigated to define a seasonal rainfall forecasting scheme from total and partial correlation analyses over the period 1968 97 three major and useful signals appear in september precursor components of the october december east west circulation cell appear over the equatorial indian ocean eio they were discovered through various indices of sea surface temperature sst zonal wind vertical velocity and moist static energy computed over the western central and eastern parts of the eio principal component analyses were applied to these indices to form two synthetic indices which discriminate ocean atmosphere variability in the eastern and western parts of the basin the indian monsoon dynamics control the ssts off the somalia coast which are known to play an important role in the variability of the short rains ridge trough systems develop off south africa which when persistent enough drive sst anomalies in the eastern tropical and equatorial atlantic these in turn are associated with anomalies in the middle levels over an equatorial band ranging from the guinea gulf to the western indian ocean the three september signals used as predictors in a multiple linear regression model explain 64 of the rainfall variance a comparable efficiency is also achieved with a linear discriminant analysis model copyright 2002 royal meteorological society

low frequency 0 045 hz swell from the southern ocean unusual low frequency one dimensional energy spectra of surface gravity waves from measurements with a buoy in deep water 167 m near cape town south africa are discussed here classical treatment of the time series of spectra showed that the wave source was 2 800 nautical miles distant and probably in the southern ocean examination of south african weather bureau surface pressure analyses of the south atlantic depict an intense slow moving cyclone with geostrophic wind velocities 50 knots at the same time and place as the origin of the waves the wave spectra are highly unusual in that they reveal quasi regular swell at very low frequencies with spectral energy densities an order of magnitude larger than those normally present at these frequencies the wave event and its associated meteorological conditions are also discussed

subtropical sst dipole events in the southern indian ocean sea surface temperature sst anomalies in the subtropical southern indian ocean show interannual dipole events that are seasonally phase locked to the austral summer a positive phase of the event is characterized by cold sst anomalies in the eastern part i e off australia and warm sst anomalies in the southwestern part south of madagascar such an event is found to produce above normal rainfall over many regions in south central africa the cooling of sst in the eastern part is mainly caused by the enhanced evaporation this is associated with stronger winds along the eastern edge of the subtropical high which is strengthened and shifted slightly to the south during the event on the other hand relative decrease in the seasonal latent heat loss due to reduced evaporation dominates the warming in the southwestern part evolution of such subtropical dipole events shows quite a contrast to that of the tropical dipole events discovered recently in the indian ocean

indian ocean response to anomalous conditions in 2006 1 the equatorial indian ocean eio exhibited anomalous conditions characteristic of an indian ocean dipole iod during 2006 the eastern eio had cold sea surface temperature anomalies ssta lower sea level shallow thermocline and higher chlorophyll than normal the anomalies in the east restricted to the south of the equator were highest off sumatra the western pole of the iod was marked by warm ssta and deeper thermocline with maxima on either side of the equator an ocean general circulation model of the indian ocean forced by quikscat winds reproduces the iod of 2006 remarkably well the switch over to cooling in the east and warming in the west happened during may and july respectively in the east airsea heat flux initiated cold ssta in the model which were sustained later by oceanic processes in the west surface heat fluxes and horizontal advection caused warm ssta and contribution by the latter decreased after august citation vinayachandran p n j kurian and c p neema 2007 indian ocean response to anomalous conditions in 2006 geophys res lett 34 l15602 doi 10 1029 2007gl030194

abrupt rainfall transitions over the greater horn of africa observations and regional model simulations 1 we examine the yearly occurrence of a monsoon jump of approximately 20 latitude during the boreal spring and summer rainy seasons over the greater horn of africa gha this jump is in contrast with a simple model of a smoothly varying itcz over the region the rainfall jump is observed annually during april and may in three precipitation data sets and in regional climate model simulations using the psu ncar mesoscale model mm5 the mm5 simulations show the rainfall jump to be roughly coincident with abrupt circulation changes that occur as the somali jet develops during april may and june in particular the cross equatorial meridional branch of the somali jet forms along the east african coast in april bringing moisture and rainfall northward to the southern slopes of the ethiopian plateau this meridional branch forms well before the northern zonal branch of the jet which diverts moisture eastward from southern ethiopia and feeds the indian monsoon these results establish a framework for understanding the precipitation cycle over the gha and provide a foundation for improving subseasonal forecasts over drought prone regions of eastern africa

mississippian fossils from southern appalachian metamorphic rocks and their implications for late paleozoic tectonic evolution fossils of periastron reticulatum unger emended beck recovered from the erin slate of the talladega slate belt of alabama establish that these rocks have a mississippian kinderhookian tournaisian age the talladega slate belt the southwestern extension of the western blue ridge belt was interpreted to have been affected by regional dynamothermal metamorphism and coeval deformation as a result of the acadian orogeny this fossil find indicates that metamorphism and deformation of the talladega belt occurred after the early carboniferous alleghanian requiring a reevaluation of tectonic interpretations of the southernmost appalachians

mechanisms for anomalous warming in the western indian ocean during dipole mode events 1 during a typical indian ocean dipole mode iod event the weakening and reversal of winds in the central equatorial indian ocean lead to the development of unusually warm sea surface temperatures ssts in the western indian ocean here we report an analysis of model results and observations for the 1990 1999 period showing the anomalous warming that occurred during 1997 1998 and 1994 1995 iod events in the western indian ocean it was primarily the result of the internal oceanic processes within the arabian sea rather than a direct response to external forcing from the eastern indian ocean as previously suggested we compare the evolution of subsurface temperatures in the arabian sea just prior to 1996 1997 representative of a normal year and during the iod event 1997 1998 to infer the physical processes responsible for the anomalous warming during the iod events in a normal year such as 1996 the existence of a unique open ocean upwelling feature the arabian sea dome asd raises the thermocline in the southern arabian sea a result of the positive wind stress curl of the winter monsoon during an iod year 1997 with the collapse of the monsoon wind system in the arabian sea the cold tongue the strip of cool water indicative of asd that normally occupies the southern arabian sea fails to develop as a result the thermocline remains deep which in turn enhances the heat content of the upper ocean leading to warm ssts volume integrated heat budget terms in the asd region illustrate the role of horizontal and vertical advection in the upper ocean warming an implication is that ssts remain higher than 28 c in the southern arabian sea thereby supporting large scale deep convection in the atmosphere during the winter monsoon a band of deep convective cloud forms directly over the warm asd region during the iod events which bring greater than average rainfall over the southern arabian sea and east africa whereas convection is suppressed over the cold asd region during the normal years resulting in less than average rainfall

the mechanism of growth of the low frequency east asia pacific teleconnection and the triggering role of tropical intraseasonal oscillation the east asia pacific eap pattern is a well known meridional teleconnection over east asia during boreal summer in this study the mechanism for growth of the eap on intraseasonal timescale is investigated through a vorticity budget it is found that the beta effect and high frequency transient eddies have primary contributions to the growth of the low frequency eap the former leads to a westward shift of disturbances associated with the low frequency eap and the latter favors an amplification of disturbances respectively the interaction between low frequency disturbances and zonal flow has a damping effect by dragging disturbances eastward the impact of boreal summer intraseasonal oscillation bsiso on the triggering of the low frequency eap is also examined in this study based on observational analysis and a linear model experiment it is shown that an elongated anomalous convection band located in the vicinity of philippines associated with the dominant mode of bsiso has a significant impact on the initiation of low frequency eap via rossby wave propagation whereas anomalous convection located over the north indian ocean has a limited impact based on the results of present study the low frequency eap could be a self sustained mode and the bsiso plays a substantial role in triggering the low frequency eap

ambient seismic hydroacoustic and flexural gravity wave noise on a tabular iceberg cross correlation of ambient seismic noise between four seismographs on tabular iceberg c16 ross sea antarctica reveals both the source and the propagation characteristics of signals associated with icebergs we find that noise correlation functions computed from station data are asymmetric about zero time lag and this indicates that noise observed on the iceberg originates primarily from a compact localized source associated with iceberg collisions between c16 and a neighboring iceberg b15a we additionally find two and possibly more distinct phases of noise propagation we believe that flexural gravity wave propagation dominates the low frequency noise 10 s period and that hydroacoustic wave propagation in the water column between the ice and seabed appears to dominate high frequency noise 10 hz faster seismic propagation dominates the intermediate band 2 6 hz however we do not have sufficient data to characterize the wave mechanisms more precisely e g by identifying distinct longitudinal and shear body waves and or surface waves secular changes in the amplitude and timing of ambient noise correlations e g a diurnal cycle and an apparent shift in the noise correlation of fast seismic modes between two periods of the deployment allow us to speculate that ambient noise correlation analysis may be helpful in understanding the sources and environmental controls on iceberg generated ocean noise as well as geometric properties such as water column thickness of subglacial lakes

interannual displacements of convection and surface circulation over the equatorial indian ocean the interannual variability of surface observations in the equatorial indian ocean is investigated from 23 years of ship reports 1954 1976 in october and november during certain years the monthly analyses show strong wind anomalies in the eastern and central equatorial indian ocean simultaneously cloud cover anomalies of opposite signs are observed in the eastern indian ocean and in the central indian ocean a linear analysis of heat induced circulation suggests that the surface wind anomalies are forced by anomalies of rainfall this circulation is probably dissipative with time scales in the range two to five days the reasons for the maintenance of anomalous circulations are not well known it is noted that during most el nino events in the pacific ocean anomalies are observed in the indian ocean however there are other years with the same anomalous pattern 1961 for example during the years with anomalously little cloudiness in the eastern indian ocean sea surface temperatures lower than normal are found in the eastern indian ocean this suggests that coupled air sea dynamics must be taken into account to understand the interannual variability

abrupt termination of the 1997 98 el nino in response to a madden julian oscillation the role of the madden julian oscillation a global atmospheric wave in the tropics that is associated with convective activity and propagates eastwards with a period of about 30 60 days refs 1 2 in triggering el nino events has been discussed before3 4 5 6 7 8 but its possible connection with a termination of el nino has yet to be investigated despite the difficulty in explaining the timing of el nino terminations by the basic wind induced oceanic wave processes9 10 for the extreme 1997 98 event the mechanism of both onset and termination have been investigated3 but the reason for the abruptness of the termination has yet to be resolved here we present global data of precipitation sea surface temperatures and wind speeds that show a precipitation system associated with an exceptionally strong madden julian oscillation travelling around the equator in may 1998 the propagation of this atmospheric system was associated with an abrupt intensification of the easterly trade winds over the eastern equatorial pacific ocean combined with the already shallow equatorial thermocline in the central and eastern pacific ocean at that time3 these strong winds provided the triggering mechanism for the observed accelerated ending of the 1997 98 el nino event

planktonic foraminifera stable isotopes and water column structure disentangling ecological signals differential carbon and oxygen stable isotope 13c and 18o fractionation between planktonic foraminifera test calcite and sea water related to ecology and life stage confound the potential for reconstructing palaeo water column temperature and carbon gradients multi species analysis and strict selection of test sizes are useful methods for identifying these fractionation processes also known as vital effects in fossil taxa however there are a limited number of species with adequate size controlled data sets needed for ground truthing the approach in the modern here we report 13c and 18o measurements made on twelve species of modern planktonic foraminifera across a range of fourteen tightly constrained size windows from a tropical indian ocean core top sample this data set includes more test size windows per species especially from the smallest identifiable test size classes and a wider range of species than previously attempted we use the size controlled 18o calcite trajectories to infer depth habitats and calculate species specific calcification temperatures the temperatures are then used to constrain species specific calcification depths along the modern vertical temperature profile in the western tropical indian ocean by overlaying the per species 13c calcite trajectories on local water column 13cdic profiles we estimate if and when i e at which test sizes the planktonic foraminifera species investigated approach ambient 13cdic values the profiling shows significant size controlled 13c deviation from seawater values in all species at some life growth stage which we attribute to i metabolic fractionation in tests 300 m of mixed layer photosymbiotic taxa for most species there is a size window where these effects appear to be at a minimum and or in balance exceptions are globigerinita glutinata a small 200 m surface living species globigerina bulloides which is highly opportunistic and deep living globorotalia tumida and globorotaloides hexagonus the latter two species being affected by various unexplained 13c vital effects use of our refined guidelines for test size selection should improve the potential for making realistic reconstructions of water column 13cdic in a modern tropical stratified setting and potentially in the distant geological past when there are no living analogues present

tidal flexure at ice shelf margins hinge zones accommodate the differential tidal movement between floating ice shelves which move with the sea tide and grounded ice sheets which do not observations on rutford ice stream and ronne ice shelf antarctica using the kinematic method of global positioning system have yielded the first continuous tidal displacement profiles from an ice sheet hinge zone the form of these tidal displacement profiles indicates that the flexure can be fit to an elastic beam model using a parameter space optimization technique the model matches the observed tidal deflection profile to within 5 cm which is similar to the observational uncertainty the same model and parameter fitting technique is then successfully applied to various other published and unpublished tidal displacement data from doake ice rumples bach ice shelf and ekstrom ice shelf antarctica and jakobshavns glacier greenland i conclude that the elastic beam model with a single value of the elastic modulus 0 88 0 35 gpa adequately describes almost all the data and so can usefully be applied elsewhere earlier studies of tidal dissipation in ice shelf hinge zones based on a viscous or transient creep rheology showed that perhaps 30 of global tidal energy dissipation could be occurring in ice shelf hinge zones this study suggests however that an elastic rheology may be equally appropriate in which case this estimation of the tidal energy dissipation is excessively high

reconstructing east african rainfall and indian ocean sea surface temperatures over the last centuries using data assimilation the relationship between the east african rainfall and indian ocean sea surface temperatures ssts is well established the potential interest of this covariance to improve reconstructions of both variables over the last centuries is examined here this is achieved through an off line method of data assimilation based on a particle filter using hydroclimate related records at four east african sites lake naivasha lake challa lake malawi and lake masoko and ssts related records at six oceanic sites spread over the indian ocean to constrain the last millennium ensemble of simulations performed by cesm1 skillful reconstructions of the indian ssts and east african rainfall can be obtained based on the assimilation of only one of these variables when assimilating pseudo proxy data deduced from the model cesm1 the skill of these reconstructions increases with the number of particles selected in the particle filter although the improvement becomes modest beyond 99 particles when considering a more realistic framework the skill of the reconstructions is strongly deteriorated because of the model biases and the uncertainties of the real proxy based reconstructions however it is still possible to obtain a skillful reconstruction of ssts over most of the indian ocean only based on the assimilation of the six sst related proxy records selected as far as a local calibration is applied at all individual sites this underlines once more the critical role of an adequate integration of the signal inferred from proxy records into the climate models for reconstructions based on data assimilation

interdecadal changes of 30 yr sst normals during 1871 2000 abstract sst predictions are usually issued in terms of anomalies and standardized anomalies relative to a 30 yr normal climatological mean cm and standard deviation sd the world meteorological organization wmo suggests updating the 30 yr normal every 10 yr in complying with the wmo s suggestion a new 30 yr normal for the 1971 2000 base period is constructed to put the new 30 yr normal in historical perspective all the 30 yr normals since 1871 are investigated starting from the beginning of each decade 1871 1900 1881 1910 1971 2000 using the extended reconstructed sea surface temperature ersst on a 2 grid for 1854 2000 and the hadley centre sea ice and sst dataset hadisst on a 1 grid for 1870 1999 eleven 30 yr normals are calculated and the interdecadal changes of seasonal cm seasonal sd and seasonal persistence p are discussed the interdecadal changes of seasonal cm are prominent 0 3 0 6 in the tropical indian ocean the midlatitude north pacific the midlatitude no

two distinct modes of tropical indian ocean precipitation in boreal winter and their impacts on equatorial western pacific abstractthe observational analysis reveals two distinct precipitation modes the zonal dipole dp mode and the monopole mp mode in the tropical indian ocean tio during the el nino mature winter even though sea surface temperature anomalies sstas have a similar basinwide warming pattern referred to as the indian ocean basin mode iobm the formation of the two precipitation modes depends on the distinct evolutions of the ssta in the tropical pacific and indian ocean both of the precipitation modes are preceded by an indian ocean dipole iod the iod associated with the dp mode developed in late summer and was triggered by pacific el nino through a sumatra philippine pattern the iod associated with the mp mode developed in early summer when the pacific sstas were still normal the different iod onset time leads to salient differences in subsequent evolution including the transfer of a dipole sst pattern to a basinwide pattern as a result in the boreal winter the zonal ssta gradient assoc

a model of viscoelastic ice shelf flexure we develop a formal thin plate treatment of the viscoelastic flexure of floating ice shelves as an initial step in treating various problems relevant to ice shelf response to sudden changes of surface loads and applied bending moments e g draining supraglacial lakes iceberg calving surface and basal crevassing our analysis is based on the assumption that total deformation is the sum of elastic and viscous or power law creep deformations i e akin to a maxwell model of viscoelasticity having a spring and dashpot in series the treatment follows the assumptions of well known thin plate approximation but is presented in a manner familiar to glaciologists and with glen s flow law we present an analysis of the viscoelastic evolution of an ice shelf subject to a filling and draining supraglacial lake this demonstration is motivated by the proposition that flexure in response to the filling drainage of meltwater features on the larsen b ice shelf antarctica contributed to the fragmentation process that accompanied its collapse in 2002

application of the ncar regional climate model to eastern africa 2 simulation of interannual variability of short rains we have applied the ncar regcm2 to the simulation of the interannual variability of precipitation over eastern africa for the short rains season by performing a set of experiments for the years 1982 to 1993 the model reproduced the observed interannual variability of precipitation in most of the years the results show that remote factors play a dominant role in determining the precipitation anomalies interannual variability of precipitation over tanzania is closely related to el nino events in their mature phase and sea surface temperature sst anomalies over the indian and atlantic oceans the southward shift of the arabian high results in a southward shift of the zonal component of the intertropical convergence zone itcz which is responsible for early onset of the rainy season e g 1982 and 1986 the enhanced st helena high and weaker mascarene high lead to the eastward shift of the meridional branch of the itcz for the wet years model simulations confirmed a strong positive correlation between precipitation anomalies over lake victoria and the warm el nino southern oscillation events by which enhanced moist westerly flow from the atlantic ocean and the mainly easterly flow from the indian ocean converge over lake victoria during wet years the interannual variability of precipitation over lake victoria and the western kenya highlands wkh are strongly coupled positive precipitation anomalies over the wkh region are usually associated with weaker arabian high and mascarene high which weaken the large scale divergence over the wkh region and favor the development of convection the interannual variability of precipitation over eastern kenya highlands ekh is not directly related to the el nino events but the association with a warm sst anomaly pattern over the western indian ocean is evident during wet years an el nino signal is however evident for wet years over the turkana channel warm sst anomalies over the northern indian ocean contribute enhanced water vapor transport over the region

the role of burial diagenesis in hydrocarbon destruction and h2s accumulation upper jurassic smackover formation black creek field mississippi organic inorganic interactions during burial of the smackover formation at black creek field mississippi have resulted in nearly complete destruction of hydrocarbons the formation has been buried to a depth of 6 km has experienced temperatures of over 200 degrees c and presently contains 78 h 2 s 20 co 2 and 2 ch 4 three distinct stages of burial diagenesis correspond to three phases of organic matter maturation pre oil window diagenesis was dominated by precipitation of prebitumen calcite cement diagenesis in the oil window was characterized by precipitation of saddle dolomite and anhydrite in water filled layers and by formation of solid bitumen in the oil column diagenesis in the gas window was dominated by thermochemical sulfate reduction tsr resulting in hydrocarbon destruction anhydrite dissolution large amounts of h 2 s co 2 and s generation and postbitumen calcite cementation during tsr anhydrite reacted with h 2 s to produce s which in turn reacted with ch 4 to generate more h 2 s in a self reinforcing cycle the lack of metal cations to stabilize h 2 s as metal sulfides availability of sufficient sulfate to generate h 2 s and a closed system to prevent h 2 s from escaping resulted in the continuation of the tsr cycle until nearly all hydrocarbons were consumed in mississippi concentration of h 2 s is nearly zero in smackover hydrocarbon reservoirs that have experienced temperatures of 120 degrees c for more than 50 m y suggesting that tsr is not a kinetic time dependent process high h 2 s concentrations initiate at temperatures above 140 degrees c and increase with temperature indicating that tsr is a thermodynamic phenomenon reported high h 2 s concentrations at low temperatures 80 120 degrees c from other locations may be explained by the following processes 1 migration of h 2 s into these reservoirs 2 high geothermal gradients or local thermal perturbations in the past 3 a biochemical origin for the h 2 s or 4 exposure of these reservoirs to temperatures greater than 150 degrees c and a rapid uplift in black creek field burial cementation and pressure solution resulted in total destruction of porosity and permeability in limestone reservoirs but not in dolomite reservoirs which still possess up to 20 porosity and 100 md permeability secondary porosity was not created as a result of hydrocarbon migration abundant co 2 derived during hydrocarbon destruction resulted in calcite cementation rather than carbonate dissolution late secondary porosity development in carbonates may be related to acids generated by metal sulfide precipitation

generation and termination of indian ocean dipole events in 2003 2006 and 2007 evolution of indian ocean dipole iod events in 2003 2006 and 2007 is investigated using observational and re analysis data products efforts are made to understand various processes involved in three phases of iod events activation maturation and termination three different triggers are found to activate the iod events in preceding months leading to the iod evolution the thermocline in southeastern indian ocean shoals by reflection of near equatorial upwelling rossby waves at the east african coast into anomalous upwelling equatorial kelvin waves strengthening weakening of northern southern portion of itcz in march april and may june of iod years leads to strengthening of alongshore winds along sumatra java coasts with the combined shallow thermocline and increased latent heat flux due to enhanced wind speeds the sst in the southeastern indian ocean cools in following months on intraseasonal time scales convection suppressing phase of madden julian oscillation mjo propagates from west to east in may june of iod year and easterlies associated with this phase of mjo causes further shoaling of thermocline in southeastern indian ocean through anomalous upwelling kelvin wave all these three mechanisms appear to be involved in initiating iod event in 2006 on the other hand except the strengthening weakening of itcz all other mechanisms are involved in activation of 2003 iod event activation of 2007 iod event was due to propagation of convection suppressing mjo in may june and strengthening of mean winds along sumatra java coast from march to june through changes in convection the iod events matured into full fledged events in the following months after activation by surface heat fluxes vertical and horizontal advection of cool waters supported by local along shore upwelling favorable winds and remote equatorial easterly wind anomalies through excitation of upwelling kelvin waves propagating mjo signals in the tropical indian ocean brings significant changes in evolution of iod events on mjo time scales termination of 2003 and 2007 iod events is achieved by strong convection enhancing mjos propagating from west to east in the tropical indian ocean which deepen the thermocline in the southeastern equatorial indian ocean iod event in 2006 was terminated by seasonal reversal of monsoon winds along sumatra java coasts which stops the local coastal upwelling

antarctic ice shelf calving triggered by the honshu japan earthquake and tsunami march 2011 we use european space agency envisat data to present the first observational evidence that a northern hemisphere tsunami triggered antarctic ice shelf calving more than 13 000 km away the honshu tsunami of 11 march 2011 traversed the pacific ocean in 46 years this event further illustrates the growing evidence of ocean wave impact on antarctic calving and emphasizes the teleconnection between the antarctic ice sheet and events as far away as the northern hemisphere

mid brunhes strengthening of the indian ocean dipole caused increased equatorial east african and decreased australasian rainfall 1 the tropical indian ocean is an important component of the largest warm pool marked by changes in sea surface temperatures and depths of thermocline and mixed layer in its western and eastern extremities leading to the development of a dipole mode the indian ocean dipole iod a narrow band of westerlies 7 n to 7 s sweep the equatorial indian ocean during the april may and october november transitions between the summer and winter monsoon seasons these indian ocean equatorial westerlies iew are closely related to the iod intensifying the upper ocean eastward equatorial current also known as wyrtki jets the strength of the iod iew determines the moisture content in east africa a major decrease in the strength of the iew strengthening or positive mode of the iod during the mid brunhes epoch 300 250 kyr bp coincides with a wetter equatorial east africa a drier australasia and a stronger indian summer monsoon indicating that the iod iew play a significant role in driving climate change in east africa australasia and south asia

a diagnostic study of the indian ocean dipole mode in el nino and non el nino years abstract the indian ocean dipole mode iodm is examined by comparing the characteristics of oceanic and atmospheric circulations heat budgets and possible mechanisms of iodm between el nino and non el nino years forty year ecmwf re analysis era 40 data reynolds sst data and ocean assimilation data from the modular ocean model are used to form composites of the iodm that occur during el nino 1972 1982 and 1997 and non el nino 1961 1967 and 1994 years in el nino years two off equatorial anticyclonic circulations develop associated with the increased pressure over the eastern indian ocean the anticyclonic circulation over the northern hemisphere enhances the easterly component of the winds in the northwestern indian ocean this enhanced easterly component increases the mixed layer temperature by inducing an anomalous westward ocean current that advects the warm mean mixed layer from the central to the western indian ocean meanwhile the anticyclonic circulation over the southeastern ind

a recipe for simulating the interannual variability of the asian summer monsoon and its relation with enso this study investigates how accurately the interannual variability over the indian ocean basin and the relationship between the indian summer monsoon and the el nino southern oscillation enso can be simulated by different modelling strategies with a hierarchy of models from an atmospherical general circulation model agcm forced by observed sst to a coupled model with the ocean component limited to the tropical pacific and indian oceans the role of heat fluxes and of interactive coupling is analyzed whenever sea surface temperature anomalies in the indian basin are created by the coupled model the inverse relationship between the enso index and the indian summer monsoon rainfall is recovered and it is preserved if the atmospherical model is forced by the ssts created by the coupled model if the ocean model domain is limited to the indian ocean changes in the walker circulation over the pacific during el nino years induce a decrease of rainfall over the indian subcontinent however the observed correlation between enso and the indian ocean zonal mode iozm is not properly modelled and the two indices are not significantly correlated independently on season whenever the ocean domain extends to the pacific and enso can impact both the atmospheric circulation and the ocean subsurface in the equatorial eastern indian ocean modelled precipitation patterns associated both to enso and to the iozm closely resemble the observations

mechanisms of climate anomalies in the equatorial indian ocean 1 building on earlier work on the interannual variability of the boreal autumn equatorial westerlies ueq over the indian ocean and concomitant rainfall anomalies at the coast of east africa and in indonesia the inherent circulation mechanisms are here explored further from long term surface and upper air data fast ueq and deficient east african rainfall come with positive sea level pressure p and negative sea surface temperature t departures in a domain w at the northwestern extremity and opposite departures in a domain e at the southeastern extremity of the equatorial indian ocean however there is no seesaw between w and e in either p or t and no indication of local forcing of t on p the large scale pressure field in particular the zonal pressure gradient along the equator and the south indian ocean pressure and southern tradewinds control the evolution of ueq fast ueq steepens the zonal temperature gradient thus tightening the inverse relationships between the zonal gradients of pressure and temperature the rainfall anomalies associated with the interannual variability of ueq surface manifestation of a zonal circulation cell along the indian ocean equator are favored by the kinematic and thermodynamic conditions in w and e thus with fast ueq the domain w features departure lower tropospheric divergence and subsidence and favored by the cold t and subsidence reduced precipitable water all conducive to deficient precipitation by contrast e has departure lower tropospheric convergence and ascending motion and favored by the warm t and ascending motion enhanced precipitable water in conjunction conducive to abundant rainfall the interannual variability of the boreal autumn equatorial westerlies dominated as it is by the large scale pressure field is crucial in the climate dynamics of the equatorial indian ocean region this leads to the question what controls the pressure pattern over the indian ocean basin

assessing the impact of diagenesis on foraminiferal geochemistry from a low latitude shallow water drift deposit abstract due to their large heat and moisture storage capabilities the tropics are fundamental in modulating both regional and global climate furthermore their thermal response during past extreme warming periods such as super interglacials is not fully resolved in this regard we present high resolution analytical foraminiferal geochemical 18 o and mg ca records for the last 1800 kyr from the shallow 487 m inner sea drift deposits of the maldives archipelago in the equatorial indian ocean considering the diagenetic susceptibility of these proxies in carbonate rich environments we assess the integrity of a suite of commonly used planktonic and benthic foraminifera geochemical datasets globigerinoides ruber white globigerinita glutinata with bulla pulleniatina obliquiloculata with cortex and cibicides mabahethi and their use for future paleoceanographic reconstructions using a combination of spot secondary ion mass spectrometer electron probe micro analyzer and scanning electron microscope image data it is evident that authigenic overgrowths are present on both the external and internal test shell surfaces yet the degree down core as well as the associated bias is shown to be variable across the investigated species and proxies given the elevated authigenic overgrowth mg ca 12 22 mmol mol and 18 o values closer to the benthic isotopic compositions the whole test planktonic g ruber w geochemical records are notably impacted beyond 627 4 ka 24 7 mcd yet considering the setting i e bottom water location for overgrowth formation the benthic foraminifera 18 o record is markedly less impacted with only minor diagenetic bias beyond 790 0 ka 28 7 mcd even though only the top of the g ruber w and c mabahethi records whole test data would be suitable for paleo reconstructions of absolute values i e sea surface temperature salinity seawater 18 o the long term cycles while dampened appear to be preserved furthermore planktonic species with thicker tests i e p obliquiloculata w c might be better suited in comparison to thinner test counter parts i e g glutinata w b g ruber w for traditional whole test geochemical studies in shallow carbonate rich environments a thicker test equates to a smaller overall bias from the authigenic overgrowth overall if the diagenetic impact is constrained as done in this study these types of diagenetically altered geochemical records can still significantly contribute to studies relating to past tropical seawater temperatures latitudinal scale ocean current shifts and south asian monsoon dynamics

the last 1 million years of the extinct genus discoaster plio pleistocene environment and productivity at site u1476 mozambique channel abstract a detailed paleoenvironment reconstruction from the mozambique channel western indian ocean based on the calcareous nannoplankton assemblages was conducted for the interval between 2 85 and 1 85 myr this study covers the period during which the successive extinction of the last five species of discoasters occurred new productivity data obtained from the abundances of the discoaster species discoaster brouweri d triradiatus d pentaradiatus d surculus and d tamalis and other indicative calcareous nannoplankton taxa showed abundance variations which were at paced with the 100 41 and 23 kyr astronomical periodicities a shift in the productivity and water column stratification proxies occurred at 2 4 ma after the onset of the northern hemisphere glaciation here we propose that the variability recorded at international ocean discovery program site u1476 reflects the interplay between forcing associated with warm tropical pacific and cold southern ocean influences the former is shown by consistent occurrence of warm water taxa calcidiscus leptoporus oolithotus spp rhabdosphaera clavigera syracosphaera spp umbellosphaera spp typical of indonesian throughflow surface waters on the other hand the occurrence of coccolithus pelagicus indicates the influence of cold nutrient rich sub antarctic surface waters a more mixed water column initiated at 2 4 ma and a consequent productivity increase led to the gradual reduction of the discoaster species until their extinction at 1 91 ma this period was characterized by the low values of the florisphaera profunda index and high abundances of upper photic zone flora indicative of nutrient rich surface water conditions high productivity at the location during this period could have also been amplified by localized upwelling events driven by the mozambique channel eddies

olr perspective on the indian ocean dipole with application to east african precipitation inter annual variability of precipitation over eastern africa somalia ethiopia and kenya is impacted by the indian ocean dipole iod which has its maximum amplitude during autumn during northern spring sea surface temperature sst in the tropical indian ocean is nearly always sufficiently high to sustain convection but it exhibits no clear pattern of variability thus precipitation variability over eastern africa during spring is not connected to any indian ocean inter annual mode sustained by sst anomalies yet seasonal variability in atmospheric convection might sustain interannual modes during spring independent from sst we construct an index for the iod based on outgoing longwave radiation anomaly olra instead of sst anomaly during northern spring analysis of this index shows that inter annual precipitation over eastern africa is correlated with inter annual variability similar to the iod as measured by olr the largest part of that relationship originates from western indian ocean with smaller contributions from the eastern indian ocean results indicate that atmospheric convection over the tropical indian ocean couples the atmospheric circulation over the eastern and western indian basin irrespective of sst anomalies results from constructed analog analysis show that positive sst anomaly during northern winter caused by persistence of subsidence and cloud radiation sst negative feedback over the south eastern indian ocean from the previous positive iod is associated with formation of negative iod later during the following autumn

importance of the indian ocean for simulating rainfall anomalies over eastern and southern africa the relative contributions of the indian ocean and pacific ocean sea surface temperatures ssts to the rainfall variability over eastern central and southern africa during the austral spring summer are examined the variability of african rainfall is statistically related to both oceans but the variability in the two oceans is also related to separate the effects of the indian and pacific oceans a suite of numerical model simulations is presented goga the atmosphere is forced by observed ssts globally ioga the atmosphere is forced by observed ssts only in the indian ocean basin and poga the atmosphere is forced by observed ssts only in the tropical pacific basin while the sst variability of the tropical pacific exerts some influence over the african region it is the atmospheric response to the indian ocean variability that is essential for simulating the correct rainfall response over eastern central and southern africa analyses of the dynamical response s seen in the numerical experiments and in the observations indicate that the pacific and indian oceans have a competing influence over the indian ocean african region this competition is related to the influence of the two oceans on the walker circulation and the consequences of that variability on low level fluxes of moisture over central and southern africa finally given the high correlation found between sst variability in the indian and pacific oceans with the pacific leading by 3 months we speculate on an approach to long lead dynamical climate prediction over central east and southern africa

contrasting accreted terranes in the southern appalachian orogen basement beneath the atlantic and gulf coastal plains and west african orogens abstract a variety of lithostratigraphic units may be outlined within the pre mesozoic crystalline basement of the atlantic and gulf coastal plains these include 1 a group of metamorphic rocks of variable grade together with deformed and retrogressed granite in southwestern alabama and southeastern mississippi wiggins uplift hornblende and biotite within higher grade units record 40ar 39ar post metamorphic cooling ages of 310 300 ma 2 a suite of contrasting igneous rocks granite basalt and agglomerate and serpentinite which occurs along the brunswick altamaha magnetic anomaly in southwestern alabama and 3 an extensive apparently coherent tectonic element the suwannee terrane comprised of undeformed granite in which biotite records 40ar 39ar post magmatic cooling ages of 530 525 ma low grade felsic metavolcanic rocks a suite of high grade metamorphic lithologies st lucie metamorphic complex in which hornblende yields 40ar 39ar post metamorphic cooling ages of 515 510 ma and a succession of lower ordovician middle devonian sedimentary rocks characterized by gondwanan fauna the west african orogens mauritanides bassarides and rokelides record a locally complex polyphase tectonothermal evolution the earliest event corresponded to westward rifting of a continental fragment from the west african craton at 700 ma this led to development of a rift facies lithotectonic succession which included sedimentary units and intracontinental igneous sequences rifting was limited and a western ensialic arc began to develop by 680 ma the associated convergence culminated in an episode of folding and metamorphism at 650 ma pan african i orogenesis following widespread deposition of late paleozoic glacial and flyschoid sediments a second tectonothermal event occurred between 550 and 500 ma pan african ii orogenesis the west african orogens were marked by general tectonic quiescence throughout most of the early and middle paleozoic late paleozoic 300 ma collision of gondwana and laurentia resulted in eastward translation of previously tectonized mauritanide units over their foreland and emplacement at highest structural levels of previously imbricated nappes which include sequences with uncertain palinspastic origins the late paleozoic hercynian transport was largely intracontinental and only westernmost portions of the exposed mauritanides record an associated penetrative tectonothermal overprint characteristics of pre mesozoic basement units which comprise the suwannee terrane in the florida subsurface suggest they represent extensions of the bassaride rokelide orogen there is no apparent record of paleozoic tectonothermal activity in the suwannee terrane this contrasts markedly with penetrative late paleozoic reworking of basement units in the wiggins uplift this suggests that a major dextral transcurrent fault was active during the late paleozoic and that proximal basement units were directly involved in collisional aspects of pangea assembly the various basement units of the coastal plain are not correlative with any of the non laurentian terranes exposed in the southern appalachian orogen e g carolina terrane of the eastern piedmont which accreted in the ordovician devonian to exterior positions along the eastern margin of the north american craton these exotic appalachian terranes were transported into their present structural positions during late paleozoic collision of gondwana and laurentia they are separated from gondwanan elements of the suwannee terrane by a suture approximately marked by the brunswick altamaha magnetic anomaly

a mechanism for the formation of large icebergs the calving of floating glaciers to form icebergs is a major form of ice loss from the antarctic ice sheet disintegration of massive unconfined seaward extending ice shelves or glacier tongues gives rise to the largest type of iceberg some of which have horizontal dimensions exceeding 100 km several ice tongues are known to exhibit a quasi cyclic pattern of calving and subsequent regrowth a mechanism that would seem to explain this type of calving behavior is based on the vibrational characteristics of the system of a buoyant ice plate floating in shallow water ocean wave energy responsible for the motion is intercepted by the glacier either directly from open ocean or after transmission through and subsequent filtering by sea ice the glacier also acts as a wave filter with filtering characteristics depending on the ice thickness when a dominant frequency occurring in the incident wave spectrum coincides with one of the natural frequencies of the glacier then a resonant motion will occur for relatively high modes of oscillation low level but sustained cyclic bending stresses may lead to crack propagation and subsequent fatigue failure in the ice the contribution of other mechanisms which induce tensile stresses in the ice are considered to be very important in an overall view of the calving problem and some of these mechanisms are discussed in relation to the vibration mechanism it is possible to view the proposed vibration mechanism as a trigger which raises the resultant stresses in the ice to the point where fracture will occur

interaction between the enso and the asian monsoon in a coral record of tropical climate the oxygen isotopic composition of a banded coral from the western equatorial indian ocean provides a 150 year long history of the relation between the el nino southern oscillation enso phenomenon and the asian monsoon interannual cycles in the coral time series were found to correlate with pacific coral and instrumental climate records suggesting a consistent linkage across ocean basins despite the changing frequency and amplitude of the enso however decadal variability that is characteristic of the monsoon system also dominates the coral record which implies important interactions between tropical and midlatitude climate variability one prominent manifestation of this interaction is the strong amplitude modulation of the quasi biennial cycle

lithospheric sources of north florida usa tholeiites and implications for the origin of the suwannee terrane abstract sr nd and pb isotopic data for mesozoic tholeiites from six drillholes in northern florida suwannee terrane indicate derivation of the magmas from a source that was slightly incompatible element enriched with respect to bulk earth probably continental lithospheric mantle variably contaminated by more enriched crust initial isotopic compositions of the florida tholeiites show a considerable range 87 sr 86 sr 0 7059 to 0 7097 end 4 6 to 0 1 206 pb 204 pb 18 30 to 18 65 207 pb 204 pb 15 57 to 15 66 and 208 pb 204 pb 38 22 to 38 35 these compositions are distinctly different from those of mesozoic alkali basalts from the subsurface of southwestern florida heatherington a l mueller p a 1991 geochemical evidence for triassic rifting in southwestern florida tectonophysics 188 291 302 it is suggested that the north florida tholeiites were derived from within the continental lithosphere in contrast with mesozoic volcanic rocks from southwestern florida which have been previously suggested to be related to a mantle plume sm nd isotope systematics suggest derivation of the tholeiites from a 1 ga source a similar age to that proposed by pegram pegram w j 1990 development of continental lithospheric mantle as reflected in the chemistry of the mesozoic appalachian tholeiites usa earth and planetary science letters 97 316 331 for the source of tholeiitic basalts within the carolina terrane this supports proterozoic tectonic models which suggest that both the suwannee and carolina terranes had affinities with south american portions of gondwana containing 1 ga crust specifically the sunsas rondonian province nance murphy 1996 mueller p a kozuch m heatherington a l wooden j l offield t w koeppen r p klein t l nutman a p 1996 evidence for mesoproterozoic basement in the carolina terrane and speculations on its origin in nance r d thompson m d eds avalonian and related peri gondwanan terranes of the circum north atlantic gsa special paper 304 pp 207 218

impact of atmospheric intraseasonal oscillations on the indian ocean dipole during the 1990s abstract effects of atmospheric intraseasonal oscillations isos on the indian ocean zonal dipole mode iozdm are investigated by analyzing available observations and a suite of solutions to an ocean general circulation model namely the hybrid coordinate ocean model hycom data and model solutions for the period 1991 2000 are analyzed a period that includes two strong iozdm events during 1994 and 1997 and a weak one in 1991 both the data analysis and model results suggest that atmospheric isos play a significant role in causing irregularity of the two strong iozdm events and the premature termination of the weak one of particular interest is a basinwide wind driven oceanic resonance with a period near 90 days involving the propagation of equatorial kelvin and first meridional mode rossby waves across the basin before the onset of the strong 1997 dipole wind variability had significant power near 90 days and the resonance was strongly excited associated with the resonance was a deepened t

dynamics of the surface wind field over the equatorial indian ocean the annual cycle and interannual variability of the equatorial westerlies over the indian ocean are examined in the context of the equations of motion using long term surface ship observations eastward pressure gradient along the equator may accelerate equatorial westerlies but the process is more intricate the south indian ocean trade winds can recurve in the southern hemisphere only with an eastward pressure gradient this is counteracted by the coriolis acceleration directed at right angles to the left of the motion with weak trades and strong eastward pressure gradient the flow can recurve at relatively high southern latitudes thus allowing a broad equatorial zone in which westerlies can develop in the annual cycle the southern indian ocean high and trade winds are closest to the equator and strongest in austral winter when however the eastward pressure gradient in the equatorial zone is also steepest accordingly the latitude of flow recurvature in the southern trade winds stays farthest away from the equator in boreal spring and autumn consequently the equatorial westerlies peak in these short transition seasons the boreal autumn equatorial westerlies are the surface manifestation of a powerful zonal circulation cell along the indian ocean equator the interannual variability of boreal autumn is characterized by weak westerlies accompanying a slack zonal pressure gradient and strong southern trade winds with recurvature near the equator such an ensemble of circulation departures is characteristic of abundant rainfall in east africa and deficient precipitation in indonesia copyright 2004 royal meteorological society

a triggering mechanism for the indian ocean dipoles independent of enso abstractalthough the indian ocean dipole iod and enso are significantly correlated there are indeed some iods independent of enso in this research the characteristics of independent iod are investigated and a new triggering mechanism is proposed based on case study and statistical analysis results show that the independent iods peak in an earlier season and have a weaker intensity compared with the iods associated with enso the wind anomaly associated with the independent iod is very unique and shows a monsoonlike pattern in addition to the equatorial easterly wind anomaly eewa common to all iods the evolution of the eewa associated with the independent iod is well captured by the second eof mode of the equatorial zonal wind interannual variability suggesting that the independent iod is an important climate mode inherent to the tropical indian ocean the eewa associated with the independent iod is tightly linked to indian summer monsoon activities in spring and the convection anomalies associ

relative role of dynamic and thermodynamic processes in the development of the indian ocean dipole an ogcm diagnosis 1 the relative role of oceanic dynamics and surface heat fluxes in the initiation and development of the indian ocean dipole was investigated by analyzing results from an oceanic general circulation model the model was forced by observed surface wind stress and heat flux fields for 1958 1997 the results show that it was capable of reproducing observed dipole events over the tropical indian ocean the diagnosis of the mixed layer heat budget indicates that the sst anomaly ssta in the east pole is primarily induced by anomalous surface latent heat flux and vertical temperature advection whereas in the west pole it is mainly caused by meridional and vertical temperature advection anomalies in both regions shortwave radiation anomalies tend to damp the ssta the ocean rossby waves are essential in linking the anomalous wind and sst off sumatra and subsurface temperature variations in southwest indian ocean

extremes of the indian summer monsoon rainfall enso and equatorial indian ocean oscillation it is well known that anomalies of the indian summer monsoon rainfall ismr are linked to el nino and southern oscillation enso we show that large anomalies of the ismr are also linked to the equatorial indian ocean oscillation equinoo between states with enhancement suppression of atmospheric convection over the western part of the equatorial indian ocean with suppression enhancement over the eastern part and associated changes in the anomaly of the zonal wind along the equator equinoo is the atmospheric component of the coupled indian ocean dipole mode there is a strong relation between the large anomalies of ismr and a composite index which is a linear combination of the indices for enso and equinoo with all seasons with large deficits excess characterized by small large values of the index however the variation of ismr within one standard deviation is more complex and does not appear to be related to the composite index

abrupt termination of indian ocean dipole events in response to intraseasonal disturbances 1 we have investigated the role of atmospheric intraseasonal disturbances on termination of the indian ocean dipole iod using multiple datasets we observed significant 30 60 day atmospheric disturbances associated with equatorial westerly zonal winds prior to termination of all iod events except for the 1982 and 1997 events the westerlies excite anomalous downwelling kelvin waves that terminate the basin wide coupled processes by warming the eastern indian ocean the 1982 and 1997 iod events coincide with the strongest el nino events during those years the intraseasonal disturbances are weak

organic petrology of the aptian age section in the downdip mississippi interior salt basin mississippi usa observations and preliminary implications for thermal maturation history abstract this study identifies a thermal maturity anomaly within the downdip mississippi interior salt basin misb of southern mississippi usa through examination of bitumen reflectance data from aptian age strata sligo formation pine island shale james limestone and rodessa formation u s geological survey usgs reconnaissance investigations conducted in 2011 2012 examined aptian age thermal maturity trends across the onshore northern gulf of mexico region and indicated that the section in the downdip misb is approaching the wet gas condensate window ro 1 2 a focused study in 2012 2013 used 6 whole core one sidewall core and 49 high graded cutting samples depth range of 13 000 16 500 ft 3962 4 5029 2 m below surface collected from 15 downdip misb wells for mineralogy fluid inclusion organic geochemistry and organic petrographic analysis based on native solid bitumen reflectance ro generally 0 8 interpreted to be post oil indigenous bitumens matured in situ ro values increase regionally across the misb from the southeast to the northwest thermal maturity in the eastern half of the basin ro range 1 0 to 1 25 appears to be related to present day burial depth and shows a gradual increase with respect to depth to the west thermal maturity continues to increase even as the aptian section shallows structurally on the adams county high ro range 1 4 to 1 8 after evaluating the possible thermal agents responsible for increasing maturity at shallower depths i e igneous activity proximity to salt variations in regional heat flux and uplift we tentatively propose that either greater paleoheat flow or deeper burial coupled with uplift in the western part of the misb could be responsible for the thermal maturity anomaly further research and additional data are needed to determine the cause s of the thermal anomaly

enhanced multidecadal climate variability in the seventeenth century from coral isotope records in the western indian ocean 1 the slowly growing coral diploastreaheliopora affords a novel opportunity to obtain multicentury records of paleoclimate including details of the interannual rhythms associated with the el nino southern oscillation enso system we examine climate variability in an enso teleconnected region using new oxygen isotope records from d heliopora spanning most of the twentieth 1896 1998 and seventeenth 1622 1722 centuries from the mafia archipelago tanzania the modern record demonstrates coherency with relevant instrumental and proxy time series documents twentieth century warming and displays significant power at enso periodicities the seventeenth century record lacks any trend exhibits interannual variance comparable to the modern record and displays a pronounced interdecadal signal not evident in the twentieth century that correlates with other tropical and hemispheric climate records we find no clear evidence of solar irradiance influence on interannual variability in the western indian ocean during these intervals although the mean sea surface temperature appears to vary inversely with insolation

behavior of flexural gravity waves on ice shelves application to the ross ice shelf ocean waves continuously impact floating ice shelves and affect their stress regime low frequency long period 75 400 s ocean waves are able to reach ice shelf cavities from distant sources and excite flexural gravity waves that represent coupled motion in the water of the cavity and the ice covering above analytic treatment of simplified geometric configuration and three dimensional numerical simulations of these flexural gravity waves applied to the ross ice shelf show that propagation and ice shelf flexural stresses are strongly controlled by the geometry of the system bathymetry of the ice shelf cavity and ice shelf cavity thickness the derived dispersion relationships group and phase velocities of these waves can be used to infer poorly constrained characteristics of ice shelves from field observations the results of numerical simulations show that the flexural gravity waves propagate as beams the orientation of these beams is determined by the direction of the open ocean waves incident on the ice shelf front the higher frequency ocean waves cause larger flexural stresses while lower frequency waves can propagate farther away from the ice shelf front and cause flexural stresses in the vicinity of the grounding line

vibrations of mertz glacier ice tongue east antarctica at the time of its calving in february 2010 mertz glacier east antarctica was characterized by a 145 km long 35 km wide floating tongue in this paper we use gps data from the collaborative research into antarctic calving and iceberg evolution crac ice 2007 08 and 2009 10 field seasons to investigate the dynamics of mertz glacier two months of data were collected at the end of the 2007 08 field season from two kinematic gps stations situated on each side of the main rift of the glacier tongue and from rock stations located around the ice tongue during 2008 09 using precise point positioning with integer ambiguity fixing we observe that the two gps stations recorded vibrations of the ice tongue with several dominant periods we compare these results with a simple elastic model of the ice tongue and find that the natural vibration frequencies are similar to those observed this information provides a better understanding of their possible effects on rift propagation and hence on the glacier calving processes

orbital scale variation of primary productivity in the central equatorial indian ocean maldives during the early pliocene abstract we investigate the response of the central equatorial indian ocean odp site 716 maldives upwelling system to orbital forcing between 3 64 and 4 19 ma this time interval in the early pliocene was characterized by global average temperatures considerably warmer than present and reduced zonal and meridional sea surface temperature gradients across the major oceans chlorin a degradation product of chlorophyll and a potential indicator of primary productivity was previously shown to record orbital scale variations at this site to confirm that chlorin records primary productivity and to understand the mechanism controlling the orbital variations we compare changes in the planktic foraminiferal assemblages with the chlorin content of the sediment cross wavelet analysis demonstrates the in phase relationship between the abundance of thermocline species and chlorin content indicating that upwelling and a shallower thermocline drive the productivity changes the aragonite content in periplatform carbonates is known to reflect variations in sea level and or climate with high values generally indicating sea level highstands the aragonite content in the studied interval shows precession and eccentricity astronomical cycles whereas the primary productivity proxies show only precessional cycles the negative correlation between aragonite content and the relative abundance of thermocline species on the precessional band implies that the primary productivity increased during sea level lowstands this phase coupling is consistent with quaternary productivity records from the central indian ocean that were proposed to be controlled by orbital induced variations of the el nino southern oscillation enso we therefore propose that a similar mechanism was active in the early pliocene despite major changes in the global boundary conditions

elastic response of floating glacier ice to impact of long period ocean waves 1 disintegration of ice shelves along the antarctic peninsula over the past two decades has clearly demonstrated their high sensitivity to recent changes in the local thermal regime of the atmosphere and ocean and has given rise to the question of whether mechanical coupling with waves in the ocean may provide the triggering mechanism that starts collapse events motivated by these events this study considers a more general question how ocean waves affect the stress regime of floating ice and in particular how ocean waves can influence the creation of fractures and its fatiguing that may lead to breakup and collapse a new treatment of ice shelf ocean wave interaction in which the typical thin plate approximation is relaxed is presented here and exact analytic solutions describing ice shelf stresses induced by long 60 s period ocean waves in various idealized ice ocean geometries are derived the numerical calculations demonstrate that the amplitudes of the wave induced stresses are sufficiently large to initiate top to bottom crevasse penetration through the depth of the ice shelf the cyclic nature of the wave induced stresses contributes to ice fatigue and damage that is also a precursor to ice shelf disintegration although primarily theoretical the results of the present analysis suggest that ocean waves could be a potential trigger of ice shelf collapse as well as less dramatic but equally important episodic calving

argo profiles a rare occurrence of three consecutive positive indian ocean dipole events 2006 2008 1 during 2006 2008 the indian ocean io experienced a rare realization of three consecutive positive io dipoles piods including an unusual occurrence with a la nina in 2007 common to all three piods is an early excitation of equatorial easterly anomalies argo profiles reveal that for the 2008 and 2006 piods the wind anomalies are generated by the following process upwelling rossby waves propagating into the western io and their subsequent reflection as equatorial upwelling kelvin waves enhance the seasonal upwelling changing sea surface temperature sst gradients for the 2007 piod coastal upwelling kelvin waves off the sumatra java coast associated with the 2006 piod el nino radiate into the io as upwelling rossby waves they curve sharply equatorward to arrive at the central equatorial io inducing easterly anomalies upwelling kelvin waves and the unusual piod our results suggest that real time argo observations when assimilated into predictive systems will enhance iod forecasting skills

structure and evolution of the central gulf of mexico continental margin and coastal plain southeast united states as in many continental margins mesozoic rifting in the gulf of mexico trended subparallel to older tectonic structures created by opening and closure of a prior ocean basin unlike the situation in most other margins however extension in the gulf of mexico did not involve widespread reactivation of these older tectonic features this difference may be related to the unusual facts that 1 the antecedent passive continental margin was a transform rather than a rift margin and 2 the prior orogeny did not substantially thicken the crust in order to characterize the interaction between mesozoic rifting and prior tectonic events two geophysical transects were constructed across the central gulf of mexico coastal plain and continental shelf the transects show that the early paleozoic passive continental margin buried beneath the late paleozoic ouachita orogen was little affected by compressional tectonism or mesozoic extension during opening of the gulf of mexico the thickness of the crust on this ancient margin decreases from 35 km to 10 km over a distance of only 50 km consistent with previous interpretations that this was a transform margin the ouachita fold and thrust belt is shown to be a thin skinned doubly vergent orogen that formed above a well preserved southward dipping subduction system relict cambrian oceanic crust may exist beneath the southern part of the orogen but its presence is not required by the data the thin crust and shallow mantle in the ouachita suture created a zone of relatively high strength that acted as a barrier to mesozoic extension which is restricted to regions south of the orogen extension was initially distributed over a broad area that included the mississippi interior salt basin and regions south of the wiggins arch extension became progressively more focused south of the wiggins arch with time culminating in the onset of seafloor spreading beneath the modern continental rise mesozoic extension factors are 1 4 1 9 beneath the mississippi interior salt basin 2 9 immediately south of the wiggins arch and 4 adjacent to the oldest oceanic crust in the central gulf of mexico

potential relation between equatorial sea surface temperatures and historic water level variability for lake turkana kenya summary water level in lake turkana kenya in the past ca 150 years is controlled primarily from the biannual passage of the east and west african monsoon with rainfall volume related partially to sea surface temperatures ssts in the western indian and east atlantic oceans empirical orthogonal function analyses show significant correlation between eastern atlantic or western indian ssts and lake level anomalies with the first mode accounting for 66 and 55 of the variability the primary geographic loadings are consistent with a gulf of guinea moisture source and positive indian ocean dipole iod state the second mode explains 10 of variability and reflects the westward extension of an indian ocean cool pool potentially indicative of a normal to a negative iod state there is significant spatial correlation between basin rainfall anomalies associated with eastern atlantic ssts and a low in the continental divide between the kenyan and the ethiopian highlands which is a passage for moisture from the congo basin linear regression analysis with bootstrap sampling and monte carlo simulations define numeric relations between western indian and eastern atlantic ssts and lake level change for ad 1992 2013 the monthly and yearly lake level reconstructions based on this numeric analysis capture the decadal scale variability and the 15 m drop in water level in the early 20th century meter scale variability in lake level since ca ad 1930 is associated with precipitation sourced from the western indian ocean with iod variability whereas the 15 m drop in water level in the early 20th century may reflect a profound decrease in moisture from atlantic congo basin source these numerical solutions are poised to reconstruct water level variations in the past ca 300 years for lake turkana with new proxy records of ssts from the western indian ocean and the gulf of guinea

an investigation into the forces that drive ice shelf rift propagation on the amery ice shelf east antarctica for three field seasons 2002 03 2004 05 2005 06 we have deployed a network of gps receivers and seismometers around the tip of a propagating rift on the amery ice shelf east antarctica during these campaigns we detected seven bursts of episodic rift propagation to determine whether these rift propagation events were triggered by short term environmental forcings we analyzed simultaneous ancillary data such as wind speeds tidal amplitudes and sea ice fraction a proxy variable for ocean swell we find that none of these environmental forcings separately or together correlated with rift propagation this apparent insensitivity of ice shelf rift propagation to short term environ mental forcings leads us to suggest that the rifting process is primarily driven by the internal glaciological stress our hypothesis is supported by order of magnitude calculations that the glaciological stress is the dominant term in the force balance however our calculations also indicate that as the ice shelf thins or the rift system matures and iceberg detachment becomes imminent short term stresses due to winds and ocean swell may become more important

improved prediction of the indian ocean dipole mode by use of subsurface ocean observations abstractthe numerical seasonal prediction system using the scale interaction experiment frontier version 1 sintex f ocean atmosphere coupled model has so far demonstrated a good performance for prediction of the indian ocean dipole mode iod despite the fact that the system adopts a relatively simple initialization scheme based on nudging only the sea surface temperature sst however it is to be expected that the system is not sufficient to capture in detail the subsurface oceanic precondition therefore the authors have introduced a new three dimensional variational ocean data assimilation 3dvar method that takes three dimensional observed ocean temperature and salinity into account since the new system has successfully improved iod predictions the present study is showing that the ocean observational efforts in the tropical indian ocean are decisive for improvement of the iod predictions and may have a large impact on important socioeconomic activities particularly in the indian ocean rim co

two flavors of the indian ocean dipole the indian ocean dipole iod is known as a climate mode in the tropical indian ocean accompanied by negative positive sea surface temperature sst anomalies over the eastern western pole during its positive phase however the western pole of the iod is not always covered totally by positive sst anomalies for this reason the iod is further classified into two types in this study based on sst anomalies in the western pole the first type hereafter canonical iod is associated with negative positive sst anomalies in the eastern central to western tropical indian ocean the second type hereafter iod modoki on the other hand is associated with negative sst anomalies in the eastern and western tropical indian ocean and positive sst anomalies in the central tropical indian ocean based on composite analyses it is found that easterly wind anomalies cover the whole equatorial indian ocean in the canonical iod and as a result positive rainfall anomalies are observed over east africa also due to the basin wide easterly wind anomalies the canonical iod is accompanied by strong sea surface height ssh anomalies in contrast zonal wind anomalies converge in the central tropical indian ocean in the iod modoki and no significant precipitation anomalies are found over east africa also only weak ssh anomalies are seen because equatorial downwelling anomalies induced by westerly wind anomalies in the west are counteracted by equatorial upwelling anomalies caused by easterly wind anomalies in the east