explosive volcanism during the holocene in the upper limay river basin the effects of ashfalls on human societies northern patagonia argentina abstract in order to understand human response to holocene ashfall events tephra layers found in archaeological sites along the upper limay river basin northern patagonia argentina were bracketed with radiocarbon dates and correlated with tephra from a lacustrine sediment core and from outcrops and the archaeological evidence was analyzed a dark tephra associated with seismic activity was identified in the el trebol rockshelter filling interstices between fallen blocks together with remains of human activity and bones of extinct fauna marking a seismo volcanic event occurring between 11 758 and 12 866 cal yr bp this same seismic event affected the cuyin manzano site where the roof collapse made the site uninhabitable for a time a white tephra present in epullan grande epullan chica and traful i caves is correlated with nahuel huapi tephra nht equivalent to laya s rio blanco and rio pereyra members rio pireco formation nht is considered to have been derived from the same eruptive event with dates ranging between ca 1950 2500 cal yr bp a dark tephra from ortega s cave and several tephra from puerto tranquilo i rockshelter ranging between 521 and 2069 cal yr bp show how the mobile hunters gatherers of northern patagonia were able to cope with the changing circumstances

effect of organic carbon flux and dissolved oxygen on the benthic foraminiferal oxygen index bfoi variations in oceanic primary productivity flux of organic carbon to the sediments and dissolved oxygen levels in the water column are thought to be important in the control of benthic foraminiferal test size wall thickness morphology and species composition of assemblages by many foraminiferal paleontologists aspects of these processes should be reflected by the benthic foraminiferal oxygen index bfoi based on these foraminiferal characteristics however analyses indicate that the bfoi correlates most strongly with dissolved oxygen levels in overlying water r2 0 81 weakly with oceanic primary productivity r2 0 55 and weakly with organic carbon flux to the sediments r2 0 51 although both dissolved oxygen and organic carbon flux are main controlling factors for benthic foraminiferal assemblages the bfoi is a useful indicator extracted from benthic foraminiferal assemblages for estimating the condition of dissolved oxygen in cretaceous and cenozoic oceans

analysis and modeling of atmospheric gravity waves observed in radarsat sar images four case studies of radarsat synthetic aperture radar sar observations of atmospheric gravity waves are presented to demonstrate sar s capability to measure associated near surface wind field variations a brief review of the main characteristics and scales of atmospheric gravity waves agws first establishes their importance in atmospheric dynamics the shape and scale of the wave patterns observed in successive sar images are compared with those calculated from agw models there is agreement between the small scale wind variations across wave patterns in sar images and the larger scale wind field that plays a role in the generation of the observed waves

species duration and evolution benthic foraminifera on the atlantic continental margin of north america average species durations were estimated for 131 commonly occurring modern species the duration of species occurring at depths of less than 200 meters is 16 million years while for those at greater than 200 meters and at all depths it is 25 to 26 million years species less than 200 meters distributed from florida to newfoundland and from florida to cape hatteras have about the same durations 18 to 20 million years the duration for species restricted to north of cape hatteras is only 7 million years the data suggest that evolutionary rates are greater in shallower than in deeper depths and greatest in the shallower northern area

an atmospheric solitary gust observed with a doppler radar a tall tower and a surface network abstract doppler radar and a 444 m tall instrumented tower provide a detailed view of the kinematic and thermodynamic structure of a solitary gust a study of the data fields and comparison with theoretical and laboratory work leads to the conclusion that the gust is an internal solitary wave of permanent form launched by a thunderstorm outflow onto an inversion layer formed by the passage of an earlier storm comparisons with results from fluid experiments and numerical models are made and the similarities are striking both observations show turbulent breakdown at the rear of the wave the ease with which solitary waves can be generated in experiments gives reason to believe that these nonlinear waves might be of considerable interest in the context of geophysical fluid dynamics

observational analysis of a gust front to bore to solitary wave transition within an evolving nocturnal boundary layer abstract the evolution of a gust front to bore to solitary wave transition and comprehensive information on the evolving nocturnal boundary layer nbl associated with this change are described with analysis of radar and profiler measurements the observations were obtained on 21 june 2002 in the oklahoma panhandle during the international h2o project the evolution of this system from a strong bore initiated by a vigorous gust front to a solitary wave was observed over a 4 h period with doppler radar and surface measurements detailed information on the mature bore structure was obtained by a cluster of profiling instruments including two boundary layer wind profilers a lidar ceilometer and a microwave profiling radiometer a strong bore was initiated by an extensive gust front that perturbed an incipient nbl whose development prior to sunset was enhanced by shading from the parent mesoscale convective system at the time of bore formation the nbl was about 300 m deep and exhibited a surface t

middle miocene isotope stratigraphy and paleoceanographic evolution of the northwest and southwest australian margins wombat plateau and great australian bight abstract the benthic stable isotope record from odp site 761 wombat plateau nw australia 2179 3 m water depth documents complete recovery of the middle miocene 13c excursion corresponding to the climatic optimum and subsequent expansion of the east antarctic ice sheet the six main 13c maxima of the monterey excursion between 16 4 and 13 6 ma and the characteristic stepped increase in 18o between 14 5 and 13 9 ma are clearly identified the sedimentary record of the shallower odp sites 1126 and 1134 great australian bight gab sw australia 783 8 and 701 m water depth respectively is truncated by several unconformities however a composite benthic stable isotope curve for these sites provides a first middle miocene bathyal record for southwest australia the 18o and 13c curves for sites 1126 and 1134 indicate a cooler better ventilated water mass at 700 m water depth in the great australian bight since approximately 16 ma this cooler and younger water mass probably originated from a close southern source cooling of the bottom water at 16 ma started much earlier than at other sites of equivalent paleodepths in the central and western parts of the indian ocean at site 761 the 18o curve shows an excellent match with the global sea level curve between 11 5 and 15 1 ma and thus closely reflects changes in global ice volume prior to 15 1 ma the mismatch between the 18o curve and the sea level curve indicates that 18o fluctuations are mainly due to changes in bottom water temperature

mid holocene climatic variability reconstruction from pollen records 32 52 s argentina abstract this study reviews 42 published pollen records to gain a better understanding of holocene climate variability especially of the past displacement and location of the arid semiarid region asr between 32 and 52 s in argentina at present the asr is delimited approximately between the 500 mm isohyet in the pampa region and the 300 mm isohyet in the andean sector south of 37 s represented by arid and semiarid climate types where precipitation can be as low as 200 mm mid holocene climatic variability affected the regional vegetation patterns and the borders of the asr paleoenvironmental reconstruction is based on comparison of fossil pollen records from different depositional environments maps of distribution patterns of plant formations are reconstructed at 2000 500 year intervals from 8000 to 4000 14 c years bp vegetation changes are mainly explained by changes in the position and the seasonal amplitude of latitudinal shifts of the pacific and atlantic anticyclones and of the westerlies from 8000 to 4000 bp the eastern limit of the asr was displaced eastward the western limit reached the maximum eastward displacement in the southern extreme of patagonia at 6000 years bp at this time at the center of asr shrub steppes and the monte developed suggesting maximum dry conditions and the establishment of the arid diagonal north of 42 s while the present day espinal dry pampa ecotone became established at 4000 years bp paleodata suggest a transitional stage towards the present situation of the asr

travelling waves and bores in the lower atmosphere the morning glory and related phenomena abstract observations of solitary wave and travelling bore like disturbances in the lower atmosphere are reviewed together with relevant theoretical laboratory and numerical studies concerning the structure propagation and genesis of such disturbances primary emphasis is given to a discussion of the morning glory phenomenon in northern australia the example par excellence of these types of disturbance and the best documented observationally to date observations of related phenomena elsewhere are reviewed briefly while such occurrences appear to be less frequent in any single location than in the southern gulf of carpentaria region of northern australia reported occurrences are widespread and there is mounting evidence that such disturbances are more common than is generally supposed the evidence suggests that whenever a suitable wave guide exists for the propagation of disturbances the latter can be generated as the natural response of quite general forcing mechanisms examples being the collision of two sea breezes from opposite directions on a peninsula the interaction between a thunderstorm outflow and a sea breeze front or simply the transformation of a thunderstorm or squall line outflow as it moves into a low level stable layer because of the large vertical displacements they produce the larger amplitude disturbances typically with surface pressure jumps of 1 mb or more must be considered as potential triggers for deep convection if the atmosphere is sufficiently conditionally unstable and the large low altitude wind shears associated with them present a serious hazard to low flying aircraft

equatorial pacific deep sea benthic foraminifera faunal changes before the middle miocene polar cooling data on the composition of benthic foraminiferal faunas at deep sea drilling project site 575 in the eastern equatorial pacific ocean were combined with benthic and planktonic carbon and oxygen isotope records and caco 3 data changes in the composition of the benthic foraminiferal faunas at site 575 predated the middle miocene period of growth of the antarctic ice cap and cooling of the deep ocean waters by about 2 m y and thus were not caused by this cooling as has been proposed the benthic faunal changes may have been caused by increased variability in corrosivity of the bottom waters possibly resulting from enhanced productivity in the surface waters

steppe expansion in patagonia abstract westward expansion of the patagonian steppe and retrocession of andean forests due to increasing aridity over the past one or two millennia has been a persistent theme in the ecological and paleoecological literature for at least half a century new evidence from pollen profiles tree ring analysis vegetation structure and photographic and documentary historical sources does not show the expansion of the steppe instead over the past century trees have invaded the steppe as a consequence mainly of human induced changes in the fire regime and trees have regenerated in forest areas that were heavily burnt at the onset of european colonization

last glacial maximum environments in northwestern patagonia revealed by fossil small mammals abstract comparisons of historical and modern assemblages of mammals can yield important insights into patterns and processes of environmental change here we present the first analyses of small mammal assemblages present in northern patagonia during the last glacial maximum lgm using remains obtained from owl pellets excavated from an archeological cave site arroyo corral i levels vii v carbon dates of 22 400 21 530 cal yr bp we generate estimates of the minimum number of individuals for all species detected these estimates in turn are used to determine relative species abundances comparisons of these data with similar analyses of small mammal remains obtained from a second archeological site acoii levels iv v carbon dates of 10 010 9220 cal yr bp as well as from modern owl pellets reveal pronounced changes in relative species abundance since the lgm in particular euneomys chinchilloides and ctenomys sociabilis the predominant species during the lgm declined markedly suggesting a change from open bare habitat punctuated by patches of wet meadows and shrubs to the more densely vegetated mosaic of ecotone habitats found in this region today these data provide important new insights into the environmental changes that have occurred in northern patagonia over the last 20 000 years

turbulent mixing processes in atmospheric bores and solitary waves deduced from profiling systems and numerical simulation abstract families of solitary waves solitons associated with two atmospheric bores on the same day were observed by an unprecedented number of ground based and airborne profiling systems during the international h2o project ihop in addition a very high resolution numerical weather prediction model initialized with real data was used with success to simulate one of the bores and the evolving soliton the predicted wave amplitude phase speed wavelength and structure compared well to these extraordinarily detailed observations the observations suggest that during the active phase when turbulent mixing was active which was prior to bore collapse the bores and waves vigorously mixed dry air from above a nocturnal boundary layer down to the surface refractivity computed from near surface radar observations showed pronounced decreases due to sudden drying during the passage of the bores in this phase but refractivity increases appeared during the period of bore collapse during both phases the

observation of a nonlinear wave disturbance in the marine atmosphere by the synthetic aperture radar aboard the ers 1 satellite a nonlinear wave disturbance in the marine atmosphere associated with an atmospheric cold front has been identified on a spaceborne radar image of the north sea by its imprint on the sea surface this nonlinear wave disturbance is either a solitary wave disturbance or an undular bore propagating in the lower marine atmosphere the radar image showing sea surface manifestations of this atmospheric wave disturbance was acquired over the north sea by the synthetic aperture radar sar aboard the first european remote sensing satellite ers 1 on march 8 1992 atmospheric waves become visible on radar images of the sea surface because they are associated with a varying wind field at the sea surface which modulates the sea surface roughness and thus the backscattered radar power the identification of the wave pattern visible on the ers 1 sar image as a sea surface manifestation of an atmospheric nonlinear wave disturbance has been possible because this disturbance was also captured by meteorological sensors mounted on an 80 m high meteorological mast located on the island of heligoland geophysical parameters characterizing the atmospheric wave disturbance are derived from the ers 1 sar image and from the in situ meteorological data the wave period in the reference frame moving with the average wind is 9 5 min the average wavelength is 2300 m and the propagation velocity is 4 5 4 9 m s 1 estimates of the amplitude of the wind speed fluctuations in the wave propagation direction derived from the meteorological measurements at heligoland and from the gray level variations in the sar image yield values between 1 3 and 3 0 m s 1 the experimental data are interpreted in terms of theories of atmospheric nonlinear gravity waves

climatic controls of holocene fire patterns in southern south america holocene fire climate vegetation linkages are mostly understood at individual sites by comparing charcoal and pollen records with other paleoenvironmental proxy and model simulations this scale of reconstruction often obscures detection of large scale patterns in past fire activity that are related to changes in regional climate and vegetation a network of 31 charcoal records from southern south america was examined to assess fire history along a transect from subtropic to subantarctic biomes the charcoal data indicate that fire activity was greater than present at ca 12 000 cal yr bp and increased further and was widespread at 9500 cal yr bp fire activity decreased and became more spatially variable by 6000 cal yr bp and this trend continued to present atmospheric circulation anomalies during recent high fire years show a southward shift in westerlies and paleoclimate model simulations and data syntheses suggest that such conditions may have prevailed for millennia in the early holocene when the pole to equator temperature gradients were weaker and annual temperatures were higher than present in response to orbital time scale insolation changes

cenozoic record of elongate cylindrical deep sea benthic foraminifera in the north atlantic and equatorial pacific oceans abstract in the late pliocene middle pleistocene a group of 95 species of elongate cylindrical deep sea lower bathyal abyssal benthic foraminifera became extinct this extinction group ext gp belonging to three families all the stilostomellidae and pleurostomellidae some of the nodosariidae was a major component 20 70 of deep sea foraminiferal assemblages in the middle cenozoic and subsequently declined in abundance and species richness before finally disappearing almost completely during the mid pleistocene climatic transition mpt so what caused these declines and extinction in this study 127 ext gp species are identified from eight cenozoic bathyal and abyssal sequences in the north atlantic and equatorial pacific oceans most species are long ranging with 80 originating in the eocene or earlier the greatest abundance and diversity of the ext gp was in the warm oceanic conditions of the middle eocene early oligocene the group was subjected to significant changes in the composition of the faunal dominants and slightly enhanced species turnover during and soon after the rapid eocene oligocene cooling event declines in the relative abundance and flux of the ext gp together with enhanced species loss occurred during middle late miocene cooling particularly at abyssal sites the overall number of ext gp species present began declining earlier at mid abyssal depths in middle miocene than at upper abyssal in late pliocene early pleistocene and then lower bathyal depths in mpt by far the most significant ext gp declines in abundance and species loss occurred during the more severe glacial stages of the late pliocene middle pleistocene clearly the decline and extinction of this group of deep sea foraminifera was related to the function of their specialized apertures and the stepwise cooling of global climate and deep water we infer that the apertural modifications may be related to the method of food collection or processing and that the extinctions may have resulted from the decline or loss of their specific phytoplankton or prokaryote food source that was more directly impacted than the foraminifera by the cooling temperatures

global deep sea extinctions during the pleistocene ice ages comment and reply hayward 2001 1 drew attention to the little known pleistocene extinctions of deep sea elongate benthic foraminifera and showed that the loss of diversity was far greater than previously reported he concluded that these extinctions of elongate benthic taxa occurred during pleistocene glacial

small mammal remains from cueva huenul 1 northern patagonia argentina taphonomy and paleoenvironments since the late pleistocene abstract small mammal samples from the archaeological sequence of cueva huenul 1 ch1 36 56 45 s 69 47 32 w neuquen province argentina are described and taphonomic and paleoenvironmental conditions assessed this site is located near the steppe monte ecotone in the northernmost patagonia small mammal remains nisp 1426 mne 1409 mni 87 were recovered from late pleistocene 13 800 11 800 14 c bp early holocene 9500 14 c bp and late holocene layers 1400 14 c bp taphonomic analysis indicates that the ch1 assemblage is an archaeofaunistic owl pellet accumulation it has a good post depositional preservation since it was rapidly incorporated in the sedimentary matrix although it previously experienced trampling action from latest pleistocene to late holocene the assemblages are mainly composed by the sigmodontines eligmodontia spp and phyllotis xanthopygus and the caviomorphs microcavia australis and ctenomys sp suggesting in overall terms a marked ecological stability chl is one of the few sites where the pleistocene holocene transition is represented by faunal evidence the latest pleistocene sample spanning 13 800 and 11 800 14 c bp indicate scrub steppe with substantial open ground and rocky exposition one early holocene sample 9500 14 c bp suggests a more heterogeneous environment as evidenced by the first occurrence of akodon iniscatus and euneomys chinchilloides in this context ch1 assemblages do not reflect the small mammal community reworking that putatively accompanied the pleistocene holocene transition

simulated density currents in idealized stratified environments abstract the effects of three distinct stratifications on density current dynamics are investigated using a nonhydrostatic numerical model i a stably stratified layer underneath a deep neutrally stratified flow representing a nocturnal boundary layer over land ii a neutrally stratified layer underlying a deep stably stratified flow representing a daytime boundary layer and iii a continuously stratified atmosphere in the first case a weak or intermediate stratification decreases the height of density currents and increases the propagation speed the same result holds in strongly stratified situations as long as the generated disturbances in the neighborhood of the head do not propagate away classical density currents occur in weak stratification multiheaded density currents in intermediate stratification and multiheaded density currents with solitary wave like or borelike disturbances propagating ahead of the current in strong stratification in the second case the upper layer stratificati

some simple simulations of thunderstorm outflows three idealized simulations of thunderstorm outflows are presented each outflow is a response to an instantaneous low level cooling the vertical structures of the coolings differ as do the environments in which the outflows form and consequently the dynamics of the outflows differ one outflow is a gravity current another is a gravity wave and the third comprises both a gravity current and a gravity wave the horizontal transport of mass is important for the advance of the gravity current outflow but not for the gravity wave outflow and it is suggested that this is the defining dynamical distinction between the two outflows the simulations are compared to observations and it is suggested that some outflows previously characterized as gravity currents may better fit the gravity wave or gravity current wave archetypes it is also noted that the gravity wave component of an outflow may be generated directly by low level cooling in addition to the commonly suggested mechanism of the interaction of a gravity current with a stable layer

variations in deep sea benthic foraminifera at odp hole 756b southeastern indian ocean evidence for changes in deep ocean circulation abstract seventy three core samples of 10 cc volume were analysed from ocean drilling program odp site 756 hole b with an average interval of 236 kyr per sample factor and cluster analyses of 37 high ranking species of benthic foraminifera enabled us to identify four clusters representing four biofacies biofacies sl om is characterised by stilostomella lepidula orthomorphina modesta robulus gibbus bulimina miolaevis and cibicides cf lucidus this biofacies dominates the latest oligocene to early miocene interval 24 21 ma and 18 75 16 5 ma indicating low to intermediate dissolved oxygen organic carbon rich environment warm and sluggish deep waters during 21 18 75 ma the biofacies gp nu globocassidulina pacifica nuttallides umbonifera trifarina angulosa quinqueloculina weaveri robulus gibbus and pullenia bulloides dominates the benthic assemblage at hole 756b this biofacies also has a short lived presence at 16 5 ma this was an interval of intense circulation of cold and corrosive deep water similar to antarctic intermediate water aaiw and intermediate to high flux of organic matter to hole 756b the antarctic circumpolar current acc initiated during this time from 16 5 to 10 6 ma the benthic assemblage at hole 756b is dominated by biofacies ub gs characteristic species uvigerina buzasi globocassidulina subglobosa laticarina pauperata indicating intermediate to high food supply and cold deep water this interval coincides with the middle miocene positive oxygen isotope shift and permanent build up of antarctic ice sheets the late miocene interval 10 6 6 5 is characterised by biofacies ec bs dominant species ehrenbergina carinata bolivina spathulata osangularia culter and pullenia osloensis indicating low oxygen condition with high food supply in the study area this corresponds to an interval of global biogenic bloom

mid pleistocene extinction of deep sea foraminifera in the north atlantic gateway odp sites 980 and 982 abstract the pulsed decline and eventual extinction of 51 species of elongate cylindrical deep sea benthic foraminifera stilostomellidae pleurostomellidae and some nodosariidae occurred at intermediate water depths 1145 2168 m sites 980 and 982 in the northern north atlantic during the mid pleistocene transition mpt 1 2 0 6 ma in the early pleistocene prior to their disappearance these species comprised up to 20 of the total abundance of the benthic foraminiferal assemblage at 2168 m but up to only 2 at 1145 m the mpt extinction of 51 species represents 20 of the total benthic foraminiferal diversity at bathyal depths in the north atlantic excluding the myriad of small unilocular forms the extinction rate during the mpt was approximately 10 species per 0 1 myr being one or two orders of magnitude greater than normal background turnover rates of deep sea benthic foraminifera comparison of the precise timings of declines and disappearances highest occurrences of each species shows that they were often diachronous between the two depths the last of these species to disappear in the north atlantic was pleurostomella alternans at 0 679 and 0 694 ma in sites 980 and 982 respectively which is in good agreement with the previously documented global stilostomella extinction datum within the period 0 7 0 58 ma comparison with similar studies in intermediate depth waters in the southwest pacific gateway indicates that 61 of the extinct species were common to both regions and that although the pattern of pulsed decline was similar the precise order and timing of the extinction of individual species were mostly different on opposite sides of the world previous studies have indicated that this extinct group of elongate cylindrical foraminifera lived infaunally and had their greatest abundances in poorly ventilated lower oxygen environments this is supported by our study where there is a strong positive correlation r 0 8 between the flux of the extinction group and low oxygen high organic input species such as uvigerina bulimina and bolivina during the mpt suggesting a close relationship with lower oxygen levels and high food supply to the sea floor the absolute abundance flux and number of the extinction group of species show a progressive withdrawal pattern with major decreases occurring in cold periods with high 13c values this might be related to increasing chemical ventilation of glacial intermediate water

deep sea faunal provinces and their inferred environments in the indian ocean based on distribution of recent benthic foraminifera abstract multivariate analysis was performed on percentages of 46 species of unstained deep sea benthic foraminifera from 131 core top to near core top samples 322 5013 m from across the indian ocean faunal data are combined with geosecs geochemical data to investigate any relationship between benthic foraminifera assemblages and species and deep sea properties in general benthic foraminifera show a good correlation to surface productivity organic carbon flux to the sea floor deep sea oxygenation and to a lesser extent to bottom temperature without correlation with the water depths the foraminiferal census data combined with geochemical data has enabled the division of the indian ocean into two faunal provinces province a occupies the northwestern indian ocean arabian sea region where surface primary production has a major maximum during the summer monsoon season and a secondary maximum during winter monsoon season that leads to high organic flux to the seafloor making the deep sea one of the most oxygen deficient regions in the world ocean with a pronounced oxygen minimum zone omz this province is dominated by benthic foraminifera characteristic of low oxygen and high organic food flux including uvigerina peregrina robulus nicobarensis bolivinita pseudopunctata bolivinita sp bulimina aculeata bulimina alazanensis ehrenbergina carinata and cassidulina carinata province b covers southern southeastern and eastern parts of the indian ocean and is dominated by nuttallides umbonifera epistominella exigua globocassidulina subglobosa uvigerina proboscidea cibicides wuellerstorfi cassidulina laevigata pullenia bulloides pullenia osloensis pyrgo murrhina oridorsalis umbonatus gyroidinoides gyroidina soldanii and gyroidinoides cf gemma suggesting well oxygenated cold deep water with low oligotrophic and pulsed food supply

neogene and quaternary paleoceanographic changes in the southern south china sea site 1143 the benthic foraminiferal record deep sea benthic foraminiferal assemblages from ocean drilling program odp site 1143 located in the southern south china sea scs were investigated to evaluate the relationship between faunal composition patterns and paleoceatiographic changes during the last 6 million years late miocene to holocene we used multivariate statistics correspondence analysis to analyze carbon flux related changes in assemblage composition of benthic foraminifers additional proxies for carbon flux and deep water ventilation include delta 13 c records of epifaunal cibicidoides wuellerstoifi and infaunal uvgefina peregrina var dirupta and melonis pompilioides benthic foraminiferal accumulation rates bfarss diversity indices and relative abundances of indicator species we observe three significant benthic faunal changes in the southern south china sea during the last 6 million years strong fluctuations in bfar and relative abundance of productivity indicator species between glacial and inter glacial stages after the mid pleistocene revolution mpr at approximately 0 9 ma indicating stronger seasonal carbon flux fluctuations are accompanied by the extinction of such species as stilostomella spp increases in carbon flux indicator species are coupled with an overall deer ease in benthic foraminifer diversity around 3 0 ma in the late pliocene this may indicate increasing carbon flux in a period of productivity maximum caused by enhanced offshore upwelling from intensified winter monsoon wind strength c 2004 elsevier b v all rights reserved

an observational study of atmospheric bore formation from colliding density currents abstract observations from east central florida during the convection and precipitation electrification cape experiment are used to investigate the factors that influence atmospheric bore formation from colliding density currents ten cases involving the collision of a gust front with a sea breeze front are analyzed with doppler radar and sounding and surface mesonet data the gust fronts in these collisions were generally deeper denser and faster propagating than their sea breeze front counterparts seven of the 10 cases produced dual boundaries that moved away from each other in a relative sense after the collision post collision boundaries moving in the same direction and oriented similarly to the pre collision gust front occurred in all 10 cases they transported mass in the manner of a density current in six cases while the others behaved more like bores or bore density current hybrids as they were characterized by little or no mass transport similarity of gust front and sea breeze front prop

evidence of very large amplitude solitary waves in the atmosphere atmospheric solitary waves are gravity waves that retain their integrity over long periods because of a near balance between nonlinearity and dispersion they have been observed on various scales in many regions of the world1 3 but we present here detailed measurements of solitary waves with amplitudes comparable to the scale height of the lower troposphere two such waves were generated downstream of intense mid tropospheric pressure troughs over the central united states they propagated over 1 000km several times their wavelength with no appreciable change in structure within a waveguide formed by surface inversion and a middle tropospheric critical level fluctuations in surface pressure associated with the two waves exceeded 6 mbar and 10 mbar the waves caused banded patterns of precipitation and significantly influenced other meteorological phenomena the restoration of balance between pressure driven air flow and the coriolis force geostrophic adjustment seems to have a prominent role in the formation of these solitary waves

evolution of the sedimentary system beneath the deep pacific inflow off eastern new zealand results from ocean drilling program sites 1121 1124 show the eastern new zealand oceanic sedimentary system enzoss evolved in response to 1 the inception of the circum antarctic circulation 2 orbital and non orbital regulation of the global thermohaline flow and 3 development of the new zealand plate boundary enzoss began in the early oligocene following opening of the tasmanian gateway and inception of the ancestral antarctic circumpolar current acc and sw pacific deep western boundary current dwbc widespread erosion marked by the marshall paraconformity was followed by extensive drift formation in the late oligocene early miocene alternating nannofossil chalk and nannofossil rich mud deposited in response to 41 kyr orbital regulation of the abyssal circulation with the mudstones representing times of increased inflow of corrosive southern source waters drift deposition at the deepest sites was interrupted by bouts of erosion coincident with mi1 5 isotopic events signifying expansions of the east antarctic ice sheet and enhanced bottom water formation by late miocene times the basic enzoss was established south of bounty trough the energetic acc instigated an erosional low depositional regime to the north where the dwbc prevailed orbitally regulated drift deposition continued increased convergence at the new zealand plate boundary enhanced the terrigenous supply but little of this sediment reached the deep enzoss as the three main sediment conduits solander bounty and hikurangi channels had not fully developed the plio pleistocene heralded a change from a carbonate to terrigenous dominant supply caused by interception of the dwbc by the three channels 1 6 ma for bounty and hikurangi time of solander interception unknown the solander and bounty fans and hikurangi fan drift systems formed and drifts downstream of those systems received terrigenous detritus supply increased with accelerating uplift along the plate boundary but delivery to the dwbc was regulated by eustatic fluctuations of sea level times of maximum supply to all three channels was during glacial lowstands whereas the supply either ceased bounty solander or reduced hikurangi in highstands in glacial times sediment was entrained by a dwbc invigorated by an increased input of antarctic bottom water the acc also accelerated under strengthened glacial winds thus glacials were times of optimum sediment supply to enzoss depocentres where depositional rates were 2 3 times more than interglacial rates

benthic foraminiferal extinctions linked to late pliocene pleistocene deep sea circulation changes in the northern indian ocean odp sites 722 and 758 during the late pliocene middle pleistocene 63 species of elongate bathyal upper abyssal benthic foraminifera extinction group stilostomellidae pleurostomellidae some nodosariidae declined in abundance and finally disappeared in the northern indian ocean odp sites 722 758 as part of the global extinction of at least 88 related species at this time the detailed record of withdrawal of these species differs by depth and geography in the indian ocean in northwest indian ocean site 722 2045 m the extinction group of 54 species comprised 2 15 of the benthic foraminiferal fauna in the earliest pleistocene but declined dramatically during the onset of the mid pleistocene transition mpt at 1 2 1 1 ma with all but three species disappearing by the end of the mpt 0 6 ma in northeast indian ocean site 758 2925 m the extinction group of 44 species comprised 1 5 of the benthic foraminiferal fauna at 3 3 2 6 ma but declined in abundance and diversity in three steps at 2 5 1 7 and 1 2 ma with all but one species disappearing by the end of the mpt at both sites there are strong positive correlations between the accumulation rate of the extinction group and proxies indicating low oxygen conditions with a high organic carbon input in both sites there was a pulsed decline in extinction group abundance and species richness especially in glacial periods with some partial recoveries in interglacials we infer that the glacial declines at the deeper site 758 were a result of increased production of colder well ventilated antarctic bottom water aabw particularly in the late pliocene and during the mpt the extinction group at shallower water depths site 722 were not impacted by the deeper water mass changes until the onset of the mpt when cold well ventilated glacial north atlantic intermediate water gnaiw production increased and may have spread into the indian ocean increased chemical ventilation at various water depths since late pliocene particularly in glacial periods possibly in association with decreased or more fluctuating organic carbon flux might be responsible for the pulsed global decline and extinction of this rather specialised group of benthic foraminifera d 2005 elsevier b v all rights reserved

benthic foraminiferal proxy evidence for the neogene palaeoceanographic history of the southwest pacific east of new zealand abstract canonical correspondence analysis indicates that the distribution of neogene benthic foraminiferal faunas 63 m in seven dsdp and odp sites 500 4500 m water depth east of new zealand 38 51 s 170 e 170 w is most strongly influenced by depth water mass stratification and secondly by age palaeoceanographic changes influencing faunal composition and biotic evolution stratigraphic faunal changes are interpretted in terms of the pulsed sequential development of southern and later northern polar glaciation and consequent cooling of bottom waters increased vertical and lateral stratification of ocean water masses and increased overall and seasonal surface water productivity oligocene initiation of the antarctic circumpolar current and deep western boundary current dwbc flowing northwards past new zealand resulted in extensive hiatuses throughout the southwest pacific some extending through into the miocene planktic foraminiferal fragmentation index values indicate that carbonate dissolution was significant at abyssal depths throughout most of the neogene peaking at upper abyssal depths in the late miocene 11 7 ma with the lysocline progressively deepened thereafter miocene abyssal faunas are dominated by globocassidulina subglobosa and oridorsalis umbonatus with increasing epistominella exigua after 16 ma at upper abyssal depths peak abundances of epistominella umbonifera indicate increased input of cold southern component water to the dwbc at 7 6 ma faunal association changes imply establishment of the modern oxygen minimum zone upper circumpolar deep water in the latest miocene significant latitudinal differences between the benthic foraminiferal faunas at lower bathyal depths indicate the existence of an oceanic front along the chatham rise location of present subtropical front since the early late miocene at least with more pulsed productivity higher e exigua along the south side modern antarctic intermediate water faunal associations were established north of the chatham rise at 10 9 ma and south of it at 3 1 5 ma middle upper bathyal faunas on the campbell plateau are dominated by reticulate bolivinids during the early and middle miocene indicative of sustained productivity above relatively sluggish suboxic bottom waters faunal changes and hiatuses indicate increased current vigour over the campbell plateau from the latest miocene on surface water productivity food supply appears to have increased in three steps at times of enhanced global cooling marked by substantially increased relative abundance of 1 abditodentrix pseudothalmanni alabaminella weddellensis cassidulina norvangi 16 15 ma increased pulsed productivity 2 bulimina marginata f aculeata nonionella auris trifarina angulosa uvigerina peregrina 3 1 5 ma increased overall productivity and 3 cassidulina carinata 1 0 5 ma increased overall productivity three intervals of deep sea benthic foraminiferal taxonomic turnover are recognised 16 15 11 5 10 2 0 5 ma corresponding to intervals of enhanced global cooling and possible productivity changes the late pliocene middle pleistocene extinction associated with increasing northern hemisphere glaciation culminating in the middle pleistocene climatic transition was more significant in the study area than the earlier neogene turnovers

cenozoic oceanographic evolution of the sw pacific gateway introduction the region from the southern tip of the campbell plateau to the northern hikurangi plateau spans 21 of latitude equivalent to the distance between southern florida and newfoundland in the north atlantic from new zealand eastwards along the chatham rise to the louisville seamounts is 22 of longitude about 2000 km this region equivalent in area to a major part of the north american basin of the north atlantic now contains 11 stratigraphically useful drill holes seven more than the four of the dsdp sites 277 278 279 and 594 the latest holes ocean drilling program sites 1119 1125 were drilled on odp leg 181 the rst visit of the drilling ship joides resolution to the region in august october 1998 under arduous southern winter conditions fig 1

influence of gravity waves on fog structure revealed by a millimeter wave scanning doppler radar 1 multiscale band structure in fog influenced by gravity waves and kelvin helmholtz instability khi is studied based on observations with a millimeter wave scanning doppler radar on 1 august 2000 in kushiro district hokkaido prefecture japan band structure in fog having radar reflectivity 20 dbz and a scale of 1 5 km was observed around 50 m altitude the band structure was also observed in doppler velocity the band structure in both radar reflectivity and doppler velocity propagated northwestward with a speed of 4 17 m s 1 from linear gravity wave theory it is estimated that the observed gravity waves had a horizontal wavelength of 1 5 km and period of 6 min the updraft induced by gravity waves is estimated to be 7 8 cm s 1 the increase in liquid water content lwc caused by the updraft is 0 035 g m 1 and the increase of radar reflectivity is 2 dbz within the band structure induced by the gravity waves horizontal scale 1 5 km roll structure with a smaller horizontal scale 300 600 m was also observed in radar reflectivity a previous study has shown that this smaller scale roll structure is caused by shear induced khi this study shows that both gravity waves and khi modulated the structure of fog and resulted in the existence of multiscale 1 5 km and 300 600 m scale fog structure

evolution and vertical structure of an undular bore observed on 20 june 2015 during pecan abstractthis study documents the evolution of an impressive largely undular bore triggered by an mcs generated density current on 20 june 2015 observed as part of the plains elevated convection at night pecan experiment the university of wyoming king air with profiling nadir and zenith viewing lidars sampled the south bound bore from the time the first bore wave emerged from the nocturnal convective cold pool and where updrafts over 10 m s 1 and turbulence in the wave s wake were encountered through the early dissipative stage in which the leading wave began to lose amplitude and speed through most of the bore s life cycle its second wave had a higher or equal amplitude relative to the leading wave striking roll clouds formed in wave crests and wave energy was detected to about 5 km agl the upstream environment indicates a negative scorer parameter region due to flow reversal at midlevels providing a wave trapping mechanism the observed bore strength of 2 4 2 9 and speed of 15 16 m s 1 agree

extinction of deep sea foraminifera as a result of pliocene pleistocene deep sea circulation changes in the south china sea odp sites 1143 and 1146 during the late pliocene middle pleistocene 56 species and 15 genera of elongate cylindrical benthic foraminifera disappeared from the deep sea in the south china sea odp sites 1143 and 1146 as part of the last global extinction in the deep sea this extinction group ext gp exhibited a pulsed decline in abundance and species richness mostly during glacials and often associated with periods of expansion of polar ice that resulted front increased cooling of the earth s climate since similar to 2 5 ma particularly during the mid pleistocene climate transition mpt 1 2 0 6 ma we infer that the ext gp decline in abundance and disappearance was a result of the increased glacial cooling and consequent increased ventilation of the deep sea water masses the detailed record of withdrawal of the ext gp differs between the two sites with far more disappearances occurring prior to the mpt in the deeper site 1143 2772m than in the shallower site 1146 2092 in the late pliocene and early pleistocene declines in deeper parts of the south china sea site 1143 may have resulted from enhanced glacial production of deep southern sourced water passing over the sill into the basin from the north west pacific during the mpt however the ext gp declines and disappearances were of similar timing and magnitude in both sites implying that both were influenced by the same deep water mass during glacials at this time this could have been north pacific deep water which many workers infer was formed in the northern pacific during the last glacial and may have begun forming during mpt glacials in association with the progressively enhanced cooling of the northern hemisphere c 2006 elsevier ltd all rights reserved

the life cycle of a mesoscale gravity wave as observed by a network of doppler wind profilers abstract for the first time an analysis has been made of the evolving vertical structure of a long lived mesoscale gravity wave that exerted a strong influence upon the precipitation distribution across a large area this paper describes this gravity wave system on 14 february 1992 which was observed using a combination of a surface mesonetwork digital satellite and radar imagery and several doppler wind profilers the resulting vertical structures are compared to the predictions of linear stability theory since the signature of the gravity waves in the profiler vertical beam data was often complicated by the presence of precipitation a kinematic method was developed for estimating the vertical air motions during these periods the resultant time height fields show vertical and horizontal winds that are consistent with a gravity wave conceptual model the microbarograph traces and the cloud and precipitation patterns in the early stages of development a strong vertically erect wave of depression

review of wave turbulence interactions in the stable atmospheric boundary layer flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods understanding turbulence intermittency and wave turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans the stable atmospheric boundary layer sabl commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces or even daytime over snow and ice surfaces and when warm air is advected over cold surfaces intermittent turbulence intensification in the sabl impacts human activities and weather variability yet it cannot be generated in state of the art numerical forecast models this failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow in which wave turbulence interaction is a potential mechanism for turbulence intermittency a workshop on wave turbulence interactions in the sabl addressed the current understanding and challenges of wave turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory observations and numerical parameterization there have been a number of reviews on waves and a few on turbulence in stably stratified flows but not much on wave turbulence interactions this review focuses on the nocturnal sabl however the discussions here on intermittent turbulence and wave turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general

late early oligocene deep sea benthic foraminifera and their faunal response to paleoceanographic changes in the eastern equatorial pacific abstract we documented new data on the late early oligocene benthic foraminifera and sediment geochemistry in the eastern equatorial pacific ocean eep from integrated ocean drilling program exp 320 site u1334 paleo water depth 3650 to 3850 m with some published data on those from ocean drilling program leg 199 sites 1218 3850 to 4000 m and 1219 4270 to 4370 m in order to understand the response of abyssal benthic foraminifera to paleoceanographic conditions during the interval 32 28 ma the relative abundances of nuttallides umbonifer were distinctly different between sites 1218 and 1219 during 31 0 to 29 9 ma although other major taxa e g globocassidulina subglobosa cibicidoides spp and oridorsalis umbonatus showed no marked changes the characteristics e g shannon wiener h of the benthic foraminiferal fauna are affected by the abundance of a few dominant species rather than by the change in the number of species in the eep based on multi dimensional scaling mds two mds axes were recognized mds axis 1 characteristic taxa n umbonifer and cibicidoides sp a and mds axis 2 characteristic taxa g subglobosa and bolivina huneri the tendency of both mds axes 1 and 2 showed a distinct depth gradient among the three sites after 28 6 ma whereas the tendency was different from 31 0 to 28 6 ma especially at site 1218 increased abundance of n umbonifer in the eep after 29 ma was similar to that in the atlantic ocean after the expanded distribution of this species to shallower depths was finished the faunal change at 28 6 ma might be related to the change of deep water circulation possibly with the influences of the southern component water scw and or northern component water in the south atlantic ocean in contrast the faunal change at 31 0 ma might be related to the formation of the scw and or meridional overturning circulation in the southern ocean in particular mds axis 1 exhibited the opposite tendency between sites 1218 and 1219 around the oi 2 event whereas the depth gradient was clearly observed among the sites around the oi 2 event the opposite tendency of mds axis 1 around the oi 2 event might be explained by the varying influences of the scw on different depths of the eep especially in terms of carbonate undersaturation the influence of the scw on benthic foraminifera in the eep was different among the depths of the three sites in the oi 2 event however the depth gradient of the scw influence was gradually intensified in the oi 2 event and the 28 6 28 0 ma interval

pacific caco3 preservation and δ18o since 4 ma paleoceanic and paleoclimatic implications the pliocene pleistocene history of caco3 preservation in the central equatorial pacific is reconstructed from a suite of deep sea cores and is compared to fluctuations in global ice volume inferred from 18o records the results are highlighted by 1 a strong covariation between caco3 preservation and ice volume over 104 to 106 year time scales 2 a long term increase in ice volume and caco3 preservation since 3 9 ma demonstrated by a deepening of the lysocline and the carbonate critical depth 3 a dramatic shift to greater caco3 preservation at 2 9 ma 4 distinctive ice volume growth and caco3 preservation events at 2 4 ma which are associated with the significant intensification of northern hemisphere glaciation 5 a mid pleistocene transition to 100 kyr cyclicity in both caco3 preservation and ice volume and 6 a 600 kyr brunhes dissolution cycle superimposed on the late pleistocene glacial interglacial 100 kyr cycles caco3 preservation primarily reflects the carbonate chemistry of abyssal waters and is controlled by long term 106 year and short term 104 to 105 year biogeochemical cycling and by distinct paleoclimatic events we attribute the long term increase in caco3 preservation primarily to a fractionation of caco3 deposition from continental shelf to ocean basin and secondarily to a gradual rise in the riverine and glaciofluvial flux of ca on shorter time scales the fluctuations in caco3 preservation slightly lag ice volume fluctuations and are attributed to climatically induced changes in the circulation and chemistry of pacific deep water

a new source of water in seismogenic subduction zones 1 seismogenic plate boundary faults at accretionary margins e g the nankai margin southwest japan may occur where the uppermost part of subducting oceanic crust composed of basaltic rocks is in contact with the overriding plate of a lithified accretionary prism the plate boundary faults in ancient accretionary complexes typically record high velocity slip under fluid rich conditions although previous studies have emphasized the mechanical significance of fluids in terms of dynamic slip weakening the source of fluid in seismogenic subduction zones remains poorly constrained in this work we focus on the hydrous smectite in the uppermost oceanic crust an alteration product of intact basalt before arrival at the trench axis a comparison between 1 new mineralogical data on basalt drillcore recovered by integrated ocean drilling program iodp expedition 322 at site c0012 a reference site for subduction input to the nankai trough and 2 mineralogical data on basalt within ancient oceanic crust embedded in a fossil accretionary complex of the shimanto belt southwest japan suggests that progressive smectite chlorite conversion would liberate bound fluids at a rate of 0 34 to 0 65 10 14 s 1 along the plate interface this rate of fluid production appears to be more than an order of magnitude greater than that from other possible sources including from overlying sediments via smectite illite conversion and the expulsion of pore fluids and may facilitate seismic slip along plate boundary faults

paleoceanographic changes during the past 1 9 myr at dsdp site 238 central indian ocean basin benthic foraminiferal proxies abstract deep sea benthic foraminifera have been quantitatively analyzed in samples 125 m size fraction from ocean drilling program odp site 238 to understand paleoceanographic changes in the central indian basin over the past 1 9 myr factor and cluster analyses of the 25 highest ranked species made it possible to identify five biofacies characterizing distinct deep sea environmental settings the environmental interpretation of each biofacies is based on the ecology of recent deep sea benthic foraminifera the benthic faunal record indicates fluctuating deep sea conditions in environmental parameters including oxygenation surface productivity and organic food supply these changes appear to be linked to indian summer monsoon variability the main climatic feature of the indian ocean region the benthic assemblages show a major shift at 0 7 to 0 6 ma marked by major turnovers in the relative abundances of species coinciding with an increased amplitude of glacial cycles these cycles appear to have influenced low latitude monsoonal climate as well as deep sea conditions in the central indian ocean basin

last global extinction in the deep sea during the mid pleistocene climate transition 1 twenty percent 19 genera 95 species of cosmopolitan deep sea 500 4000 m benthic foraminiferal species became extinct during the late pliocene middle pleistocene 3 0 12 ma with the peak of extinctions 76 species occurring during the mid pleistocene climate transition mpt 1 2 0 55 ma one whole family stilostomellidae 30 species was wiped out and a second pleurostomellidae 29 species was decimated with just one species possibly surviving through to the present our studies at 21 deep sea core sites show widespread pulsed declines in abundance and diversity of the extinction group species during more extreme glacials with partial interglacial recoveries these declines started in the late pliocene in southern sourced deep water masses antarctic bottom water circumpolar deep water and extending into intermediate waters antarctic intermediate water north atlantic deep water in the mpt with the youngest declines in sites farthest downstream from high latitude source areas for intermediate waters we infer that the unusual apertural types that were targeted by this extinction period were adaptations for a specific kind of food source and that it was probably the demise of this microbial food that resulted in the foraminiferal extinctions we hypothesize that it may have been increased cold and oxygenation of the southern sourced deep water masses that impacted on this deep water microbial food source during major late pliocene and early pleistocene glacials when antarctic ice was substantially expanded the food source in intermediate water was not impacted until major glacials in the mpt when there were significant expansion of polar sea ice in both hemispheres and major changes in the source areas temperature and oxygenation of global intermediate waters

the behavior of squall lines in horizontally heterogeneous coastal environments abstractinland squall lines respond to the stable marine atmospheric boundary layer mabl as they move toward a coastline and offshore as a storm s cold pool collides with the marine layer characteristics of both determine the resulting convective forcing mechanism over the stable layer and storm characteristics idealized numerical experiments exploring a parameter space of mabl characteristics show that the postcollision forcing mechanism is determined by the buoyancy of the cold pool relative to the mabl when the outflow is less buoyant storms are forced by a cold pool within the marine environment when the buoyancies are equivalent a hybrid cold pool internal gravity wave develops after the collision the collision between a cold pool and less buoyant mabl initiates internal waves along the stable layer regardless of mabl depth these waves are inefficient at lifting air into the storm and ascent from the trailing cold pool is needed to support deep convection storm intensity decreases with

the cold front of 15 april 1994 over the central united states part i observations abstract detailed observations of the interactions of a cold front and a dryline over the central united states that led to dramatic undulations in the boundary layer including an undular bore are investigated using high resolution water vapor mixing ratio profiles measured by raman lidars the lidar derived water vapor mixing ratio profiles revealed the complex interaction between a dryline and a cold frontal system an elevated well mixed and deep midtropospheric layer as well as a sharp transition between 5 and 6 km altitude to a drier region aloft was observed the moisture oscillations due to the undular bore and the mixing of the prefrontal air mass with the cold air at the frontal surface are all well depicted the enhanced precipitable water vapor and roll clouds the undulations associated with the bore the strong vertical circulation and mixing that led to the increase in the depth of the low level moist layer and the subsequent lifting of this moist layer by the cold frontal surface

global deep sea extinctions during the pleistocene ice ages the dark near freezing environment of the deep oceans is regarded as one of the most stable habitats on earth and this stability is generally reflected in the slow turnover rates extinctions and appearances of the organisms that live there by far the best fossil record of deep sea organisms is provided by the shells of benthic foraminifera protista a little known global extinction of deep sea benthic foraminifera occurred during the pleistocene ice ages in the southwest pacific it caused the disappearance of at least two families 15 genera and 48 species 15 25 of the fauna of dominantly uniserial elongate foraminifera with distinctive apertural modifications these forms progressively died back and became extinct during glacial periods in the late pliocene to middle pleistocene ca 2 5 0 6 ma most extinctions occurred between 1 0 and 0 6 ma at the time of the middle pleistocene climatic revolution this first high resolution study of this extinction event indicates that it was far more significant for deep sea diversity loss than previously reported 10 species the middle pleistocene extinction was the most dramatic last phase of a worldwide decline in the abundance of these elongate forms a phase that began during cooling near the eocene oligocene boundary and continued during the middle miocene clearly these taxa declined when the world cooled but the reason is yet to be resolved

analytical studies of low level internal gravity waves over the kanto plain associated with a stationary front abstract an observational analysis of the low level internal gravity waves over the kanto plain in japan on 17 october 1998 was performed the data from the doppler radar for airport weather draw as well as aircraft communications addressing and reporting system acars data of wind and temperature provided unique observations with high spatial and temporal resolutions and were used to analyze detailed wave structures and environmental conditions especially the wave trapping mechanism according to the data analysis the horizontal wavelength was approximately 7 km the ground relative phase speed of the waves was approximately 1 m s 1 and the direction of propagation was toward 50 ne the profiles from acars revealed that the scorer parameter decreased rapidly with height above 1500 m agl and became less than the horizontal wavenumber near 2600 m agl these results indicate that the atmosphere acts as a duct and the waves were trapped vertically and reflected downward the observed horizontal wa

paleoenvironmental changes at the northern limit of the subantarctic nothofagus forest lat 37 s argentina paleoenvironmental changes dating back to before 10 000 yr b p at the northernmost occurrences of nothofagus forests in argentina at about latitude 37 s permit the reconstruction of past changes in the intensity of the winter rains related to the southern westerlies that appear to determine the forest boundary the paleoenvironmental interpretation is based on changes in the proportions of different nothofagus species and changes in the ratio betwen forest and steppe taxa the relatively most diverse and dense nothofagus forest developed only during the last 4500 yr prior to human impact during the last 300 yr before the middle holocene climatic conditions must have been different from the modern ones with less overall precipitation judging from the overall lower amount of tree pollen and the reduction to primarily nothfagus pumilio an interval dated to older than 10 000 yr b p is characterized by co occurrence of prumnopitys andina nothofagus pumilio and shrub steppe taxa prumnopitys andina is known today only from scattered upper montane forest sites in chile between 36 and 43 s lat and its ecological requirements are essentially unknown the taxa combination however suggests that late glacial climate must have been drier and probably cooler than today this implies that the winter rains and consequently the seasonal shift of the westerly circulation was reduced during the late pleistocene and did not reach modern levels before 8500 yr b p

postglacial vegetation climate and fire history along the east side of the andes lat 41 42 5 s argentina abstract the history of the low elevation forest and forest steppe ecotone on the east side of the andes is revealed in pollen and charcoal records obtained from mid latitude lakes prior to 15 000 cal yr bp the vegetation was characterized by steppe vegetation with isolated stands of nothofagus the climate was generally dry and the sparse vegetation apparently lacked sufficient fuels to burn extensively after 15 000 cal yr bp a mixture of nothofagus forest and shrubland steppe developed fire activity increased between 13 250 and 11 400 cal yr bp contemporaneous with a regionally defined cold dry period huelmo mascardi cold reversal the early holocene period was characterized by an open nothofagus forest shrubland mosaic and fire frequency was high in dry sites and low in wet sites the data suggest a sharp decrease in moisture eastward from the andes a shift to a surface fire regime occurred at 7500 cal yr bp at the wet site and at 4400 cal yr bp at the dry site preceding the expansion of austrocedrus by 1000 1500 yr the spread of austrocedrus is explained by a shift towards a cooler and wetter climate in the middle and late holocene the change to a surface fire regime is consistent with increased interannual climate variability and the onset or strengthening of enso the present day mixed forest dominated by nothofagus and austrocedrus was established in the last few millennia

microfossil assemblages on tuscaloosa seamount and their constraints on the age of the nuʻuanu landslide north of oahu hi abstract the nu uanu submarine landslide north of the island of oahu is the largest of many debris avalanches along the flanks of the hawaiian islands several attempts have been made to date the nu uanu landslide and to assess its relationship to the shield building stage of ko olau volcano as an indication of hazards that might be anticipated during the evolution of oceanic volcanoes previous age determinations based on magnetostratigraphy and the temporal distribution of turbidites have yielded a range of possible ages we describe a distinctive fine grained silty mudstone representing mantling sediment on the largest landslide block within the debris field tuscaloosa seamount this mudstone contains foraminifera and nannofossil assemblages that yield a micropaleontological age and paleoenvironmental determination for the interval immediately following landslide emplacement the microfossils constrain the mantling sediment to have been deposited between 2 5 and 3 3 ma in offshore mid to lower bathyal 1500 3000 m water depth consistent with a position on the upper flanks of tuscaloosa seamount these findings indicate that landsliding occurred prior to or near the end of shield building at ko olau volcano 2 9 ma and may have precipitated dramatic changes in volcano growth and deformation behavior as well as changes in basalt geochemistry

an observational and modeling study of an atmospheric internal bore during name 2004 abstract observations from the 2004 north american monsoon experiment name have been used to identify an atmospheric internal bore that occurred over the gulf of california goc on 31 july 2004 this bore disturbance was identified at bahia kino along the northwest coast of mexico during the late evening of 31 july it was hypothesized to have originated from the interaction of a gravity current from a large mesoscale convective system mcs which formed along the western slopes of the sierra madre occidental during the afternoon and a surface stable layer that developed from a sea breeze circulation it is suggested that the bore s energy was trapped at low levels by an elevated stable layer the vertical structure and undular nature of the bore was initially identified from 915 mhz wind profiler data at bahia kino results show a series of waves along the bore s leading edge and turbulent mixing of air from above the stable layer to the surface on the downstream face of the leading undulation the

cenozoic deep sea benthic foraminifers tracers for changes in oceanic productivity from late middle eocene through earliest oligocene high latitude regions cooled and by the end of the period continental ice sheets existed in antarctica diversity of planktonic microorganisms declined and modern groups of terrestrial vertebrates originated coeval faunal changes in deep sea benthic foraminifers have been related to cooling of deep waters and increased oxygenation cooling however occurred globally whereas species richness declined at high latitudes and not in the tropics the late eocene and younger lower diversity high latitude faunas typically contain common epistominella exigua and alabaminella weddellensis opportunistic phytodetritus exploiting species that indicate a seasonally fluctuating input of organic matter to the sea floor we speculate that the species richness gradient and increase in abundance of phytodetritus exploiting species resulted largely from the onset of a more unpredictable and seasonally fluctuating food supply especially at high latitudes

radiometer and profiler analysis of the effects of a bore and a solitary wave on the stability of the nocturnal boundary layer abstract this study uses data from a microwave profiling radiometer mpr along with 915 mhz wind profiler doppler radar and surface data to quantify the kinematic and thermodynamic effects of two wave features an undular bore and a soliton on the nocturnal boundary layer nbl at high temporal resolution both wave features passed directly over the mpr and the wind profiler allowing for detailed analyses the effects of the wave features on the convective environment are examined and convective initiation ci associated with the wave features is discussed the undular bore was illustrated well in doppler velocity data and profiler measurements indicated that it produced four wavelengths of upward and downward motion mpr derived time height sections of potential temperature and mixing ratio showed an increase in the depth of the stable boundary layer along with a decrease in stability partially associated with mixing of the nbl the soliton produced a temporary decrease in the depth of the nbl

the mid pleistocene climate transition a deep sea carbon isotopic perspective five 13c records from the deep ocean extending back to 1 3 ma were examined in order to constrain changes in mean ocean carbon isotope composition and thermohaline circulation over the 41 to 100 ka climate transition these data show that significant perturbations in mean ocean carbon chemistry were associated with the mid pleistocene climate transition notable features of the last 1 3 myr are 1 a pronounced 0 3 decrease in mean ocean 13c between 0 9 and 1 0 myr followed by a return to pre 1 0 ma values by 400 ka b p which we propose was due to the onetime addition of isotopically depleted terrestrial carbon to the ocean possibly associated with an increase in global aridity and decrease in the size of the biosphere across the 41 to 100 ka transition 2 no change in the atlantic pacific a p 13c gradient over the last 1 3 myr suggesting no change in mean ocean nutrient content accompanied the addition of light carbon and 3 stronger vertical nutrient fractionation in the north atlantic in the middle pleistocene between sites 607 and 552 suggesting weaker north atlantic deep water formation at this time relative to the early and late pleistocene we also find evidence for a more pronounced deep recirculation gyre in the western north atlantic basin in the early brunhes as evidenced by aging of deep northern basin water site 607 relative to deep water in the equatorial atlantic site 664

benthic foraminifera and the late quaternary last 150 ka paleoceanographic and sedimentary history of the bounty trough east of new zealand abstract the bounty trough east of new zealand lies along the southeastern edge of the present day subtropical front stf and is a major conduit via the bounty channel for terrigenous sediment supply from the uplifted southern alps to the abyssal bounty fan census data on 65 benthic foraminiferal faunas 63 m from upper bathyal odp 1119 lower bathyal dsdp 594 and abyssal odp 1122 sequences test and refine existing models for the paleoceanographic and sedimentary history of the trough through the last 150 ka marine isotope stages mis 6 1 cluster analysis allows recognition of six species groups whose distribution patterns coincide with bathymetry the climate cycles and displaced turbidite beds detrended canonical correspondence analysis and comparisons with modern faunal patterns suggest that the groups are most strongly influenced by food supply organic carbon flux and to a lesser extent by bottom water oxygen and factors relating to sediment type major faunal changes at upper bathyal depths 1119 probably resulted from cycles of counter intuitive seaward landward migrations of the southland front sf north south sector of the stf benthic foraminiferal changes suggest that lower nutrient cool subantarctic surface water saw was overhead in warm intervals and higher nutrient bearing warm neritic subtropical surface water stw was overhead in cold intervals at lower bathyal depths 594 foraminiferal changes indicate increased glacial productivity and lowered bottom oxygen attributed to increased upwelling and inflow of cold nutrient rich antarctic intermediate water aaiw and shallowing of the oxygen minimum zone upper circum polar deep water cpdw the observed cyclical benthic foraminiferal changes are not a result of associations migrating up and down the slope as glacial faunas dominated by globocassidulina canalisuturata and eilohedra levicula at upper and lower bathyal depths respectively are markedly different from those currently living in the bounty trough on the abyssal bounty fan 1122 faunal changes correlate most strongly with grain size and are attributed to varying amounts of mixing of displaced and in situ faunas most of the displaced foraminifera in turbiditic sand beds are sourced from mid outer shelf depths at the head of the bounty channel turbidity currents were more prevalent during but not restricted to glacial intervals

glacial interglacial variations in quaternary production of marine organic matter at dsdp site 594 chatham rise southeastern new zealand margin abstract caco3 and total organic carbon concentrations organic matter c n and carbon isotope ratios and sediment accumulation rates in late quaternary sediments from dsdp site 594 provide information about glacial interglacial variations in the delivery of organic matter to the chatham rise offshore of southeastern new zealand low c n ratios and nearly constant organic 13c values of 23 indicate that marine production dominates organic matter supply in both glacial and interglacial times during oxygen isotope stages 1 through 6 0 140 ka and 17 through 19 660 790 ka increased organic carbon mass accumulation rates in isotope stages 2 4 6 and 18 record enhanced marine productivity during glacial maxima excursions of organic 13c values to ca 29 in portions of isotope stage 2 suggest that the local concentration of dissolved co2 was occasionally elevated during the last glacial maximum probably as a result of short periods of lowered sea surface temperature dilution of carbonates by clastic continental sediment generally increases at this location during glacial maxima but enhanced delivery of land derived organic matter does not accompany the increased accumulation of clastic sediments

initiation of northern hemisphere glaciation and strengthening of the northeast indian monsoon ocean drilling program site 758 eastern equatorial indian ocean the indian monsoon system as recorded by ocean floor biota benthic foraminifera at ocean drilling program site 758 in the eastern equatorial indian ocean has varied dramatically over the past 5 5 m y long after the onset of the monsoons at 10 8 ma benthic foraminifera that thrive with high productivity year round were common before the formation of northern hemisphere continental ice sheets ca 3 1 2 5 ma indicating that the summer southwest monsoon had high intensity and long seasonal duration ca 2 8 ma benthic faunas became dominated by taxa that flourish with a seasonally strongly fluctuating food supply indicating that the northeast winter monsoon during which primary productivity is relatively low increased in duration and strength to form a system similar to that of today the change occurred coeval with the initiation of the northern hemisphere glaciation documenting a close link between the development of the indian monsoon and northern hemisphere glaciation

a nonclassical cold front observed during cops 91 frontal structure and the process of severe storm initiation abstract this case study addresses the issue of gravity current and bore development at surface cold fronts and the role of these phenomena in the generation of severe frontal convection the event investigated occurred on 27 april 1991 during the cooperative oklahoma profiler studies 1991 field project the development of a bore from a gravity current like structure along a cold front the subsequent propagation of the bore ahead of the front on a low level inversion and the process of severe thunderstorm development along the front are revealed by a dense network of remote sensing and other special observations evidence for the gravity current and bore is strengthened by comparisons made between the synthesized observations and theory the bore developed after a nocturnal inversion which acted as a waveguide had become established the bore and gravity current were both evident as fine lines in the radar reflectivity displays a microscale envelope of enhanced water vapor with an embedded roll cl

impact of the middle miocene climate transition on elongate cylindrical foraminifera in the subtropical pacific fifty eight species of elongate cylindrical benthic foraminifera here referred to as the extinction group belonging to genera that became extinct during the mid pleistocene climate transition mpt were documented similar to 50 kyr resolution through the early middle miocene 15 13 ma in two sites on opposite sides of the subtropical pacific ocean odp sites 1146 south china sea odp site 1237 southeast pacific the study was undertaken to investigate the response of the extinction group ext gp to the major cooling during the middle miocene climate transition mct to look for clues that might explain the causes of the extinction during the glacials of the mid pleistocene climate transition ext gp faunal differences between the two sites attributed to regional and bathymetric differences in food supply to the seafloor are greater than those that occurred through the 2 myr time span at either site the middle miocene climate transition was not an interval of enhanced species turnover or a decline in ext gp abundance in contrast to the major extinctions that occurred during the mid pleistocene climate transition distinct changes in the composition of the ext gp faunas did occur through this time more pronounced in site 1237 at both sites the pre middle miocene climate transition faunas were transformed into their post middle miocene climate transition composition during the period of major cooling 14 0 13 7 ma during this transition interval the faunal composition swung back and forth between the two end member faunas these faunal changes are attributed to changes in productivity decrease in south china sea increase in southeast pacific brought about by major changes in global climate and continental aridity c 2010 elsevier b v all rights reserved

radar and profiler analysis of colliding boundaries a case study abstract the kinematics of a head on collision between two gust fronts followed by a secondary collision between a third gust front and a bore generated by the initial collision are described using analyses of weather surveillance radar 1988 doppler wsr 88d and mobile integrated profiling system mips data each gust front involved in the initial collision exhibited a nearly north south orientation and an east west movement the eastward moving boundary was 2 c colder and moved 7 m s 1 faster than the westward moving boundary two dimensional wind retrievals reveal contrasting flows within each gravity current one exhibited a typical gravity current flow structure while the other assumed the form of a gravity wave current hybrid with multiple vortices atop the outflow one of the after collision boundaries exhibited multiple radar finelines resembling a solitary wave shortly after the collision about 1 h after the initial collision a vigorous gust front intersected the eastward moving bore severa

the source and fate of massive carbon input during the latest paleocene thermal maximum lithologic faunal seismic and isotopic evidence from the blake nose subtropical western north atlantic links a massive release of biogenic methane 55 5 million years ago to a warming of deep ocean and high latitude surface waters a large perturbation in the combined ocean atmosphere carbon cycle the largest of the past 90 million years a mass extinction event in benthic faunas and a radiation of mammalian orders the deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming massive carbon input to the global exogenic carbon cycle pelagic carbonate dissolution a decrease in dissolved oxygen and a benthic foraminiferal extinction event these events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the blake nose as a site of methane release

near synchroneity of new zealand alpine glaciations and northern hemisphere continental glaciations during the past 750 kyr the brunhes magnetochron 0 730 kyr at deep sea drilling project site 594 off eastern south island new zealand comprises up to 100 m of alternating units of pelagic and hemipelagic ooze formed during interglacial and glacial periods respectively the youngest hemipelagic interval corresponds to glacial isotope stage 2 and can be correlated with extensive glacial and glacio fluvial deposits of the late last glaciation 27 13 kyr bp on south island inferring the same genetic link for the other hemipelagic sediment units down core we show here that as many as 12 major episodes of expanded alpine glaciation have occurred on south island in the past 730 kyr each of these glacial episodes coincided with a period of significant 18o enrichment 2 in the core resulting from changes in ocean isotope composition associated with major growth phases of the northern hemisphere ice sheets the inferred history of alpine glaciations on this remote south pacific island appears to be closely phase locked 3 kyr to world wide climate changes

the transition from density driven to wave dominated isolated flows an isolated fluid mass travelling horizontally in a stratified layer is a phenomenon described alternatively as a detached gravity current head or a strongly nonlinear solitary wave a key feature of this flow is the transport of mass laboratory experiments examine the transition in time from a regime in which the flow is density driven to one in which it is wave dominated a simple means of creating this transitional regime an isolated flow that exhibits both density and wave effects is achieved by dropping a thermal into a linearly stratified layer this transitional regime is called an isolated propagating flow parameters for which the transitional regime occurs are identified particle tracking studies reveal the vertical flow structure there is an upper zone that is wave dynamical and a lower zone in which transport of mass occurs the transported mass slowly leaks out until the phenomenon resembles a weakly nonlinear solitary wave the experiments mimic a thunderstorm microburst impacting a temperature inversion which has aviation safety implications in the ocean cracks in the ice cap polar leads cause similar flows impacting the thermocline

human subsistence and environmental stability during the last 2200 years in epullan chica cave northwestern patagonia argentina a perspective from the zooarchaeological record abstract the faunal content from epullan chica archaeological site ech thereafter a small cave located in northwestern patagonia argentina was studied from taphonomic and paleoenvironmental points of view this cave is placed in the ecotone between monte desert and the patagonian steppe in the middle limay river basin was occupied since the end of the late holocene zooarchaeological evidence retrieved from ech is diverse including fresh water mollusk shells diplodon chilensis eggshell and bone fragments of rheidae bones and teeth of large lama guanicoe medium e g chaetophractus villosus conepatus chinga and micro sized several species of sigmodontine and caviomorph rodents mammals most of the recorded taxa were the result of human exploitation however owl pellets preserved in the sediments and other taphonomic signatures clearly indicate that avian predators are responsible for part of the micromammal record micromammal abundances during the last 2 2 ka bp are suggestive of a relative environmental stability around ech at least until the beginning of the last century in this sense late holocene landscapes were dominated by open steppe areas and large rocky outcrops with minor changes in humidity and temperature during this period

holocene stability and recent dramatic changes in micromammalian communities of northwestern patagonia abstract micromammalian fossil sequences of two classical archaeological sites cueva traful i cti and cueva epullan grande ll both in the province of neuquen northwestern patagonia argentina were studied these sequences cover the entire holocene with assemblages mainly composed by rodent and marsupial remains accumulated by owls both sites are located near the ecotone fringes of the major vegetation units currently present in patagonia forest patagonian steppe cti and patagonian steppe monte desert ll comparisons between fossil and recent owl pellet samples in a regional approach indicated that micromammal communities remained stable over the major part of the last 10 ka with some minor expansion of desert adapted taxa to the west since the middle holocene and a dramatic change in the assemblages during the last 100 150 years two alternative but not contradictory explanations can be presented to interpret the stable period first climate environmental changes were not of sufficient magnitude to produce a clear reorganization of micromammal communities forest did not invade cti surroundings and monte did not reach around ll second the basic structure of northwestern patagonian steppe micromammal communities was resilient to minor or moderate climate environmental changes the strong shift depicted in the studied sequences in very recent times 100 150 years can be linked to human impact on the regional environment this change involves a deep restructuration of small mammal communities ranging from virtual extirpations of some species to dramatic increments of opportunistic taxa a century of sheep overgrazing coupled with the introduction of exotic shrubs was the main factor driving the configuration of present small mammal assemblages in northwestern patagonia

diversity in deep sea benthic macrofauna the importance of local ecology the larger scale history and the antarctic abstract high diversity in macrobenthos in the deep sea still lacks satisfactory explanation even if this richness may not be exceptional compared to that in coastal soft sediments explanations have assumed a highly ecologically interactive saturated local community with co existence controlled by either niche heterogeneity or spatio temporal heterogeneity embodying disturbance all have failed to provide convincing support local regional scale biodiversity relationships support the idea of local richness in macrobenthos being predominantly dependent on the larger rather local scale local scale ecological interactions seem unlikely to have overriding importance in co existence of species in the deep sea even for relatively abundant core species with wide distributions variety in observed larger scale pattern and the strong inter regional pattern particularly in the poorly known southern hemisphere seem to have a pluralistic causation these include regional scale barriers and extinctions e g arctic and ongoing adaptive zone re colonisation e g mediterranean along with other historical constraints on speciation and migration of species caused by changes in ocean and ocean basin geometry at the global scale lack of knowledge of the antarctic deep sea for example blocks coherent understanding of latitudinal species diversity gradients we need to reconcile emerging understanding of large scale historical variability in the deep sea environment with massive extinctions among microfossil indicators as recently as the pliocene to results from cladistic studies indicating ancient lineages such as asellote isopods that have evolved entirely within the deep sea the degree to which the great age diversity and high degree of endemism in antarctic shelf benthos might have enriched biodiversity in the adjacent deep seas basins remains unclear basin confluence with the atlantic indian and pacific oceans may have encouraged northwards dispersion of species from and into the deep antarctic basins so that any regional identity is superficial interpretation of the antarctic deep sea as a diversity pump for global deep sea biodiversity may simply reflect re colonisation via basin confluence of northern hemisphere areas impoverished by the consequences of rapid environmental change during the quaternary