hydrographic conditions in the eastern pacific before during and after the 1982 83 el nino abstract between june 1981 and june 1984 a total of thirteen ctd sections were made across the equator along 85 w on some of these cruises additional sections were made along 5 s and 10 30 s between 85 w and the south american coast this sampling period covers the events that took place during the 1982 83 el nino these sections are used to describe the variability that took place before during and after this major event at the surface little evidence was found for a major southward flooding of warm low salinity water from north of the equator that has been observed during some previous el ninos major changes took place in the sub surface hydrographic structures the thermostad between 13 c and 16 c which is a prominent feature of the hydrography in this region disappeared early in 1983 and reappeared early in 1984 the vertical temperature gradient along the equator and along the coast which is usually quite variable with depth became much more uniform in early 1983 it regained its normal structure by early 1984 changes were not confined to the upper ocean but were evident over the whole depth interval sampled 1000m during november 1982 evidence was found for symmetric poleward spreading of the equatorial disturbance along the eastern boundary many of the changes that took place are consistent with linear models based on equatorial wave theory these observations presented a unique opportunity for observing the ocean response to a major interannual change in the wind forcing

painting a picture of gas hydrate distribution with thermal images 1 a study of cold thermal anomalies identified in continuous down core records of thermal structure acquired by an infrared ir camera during ocean drilling program odp leg 204 to southern hydrate ridge is combined with core based observations of structure and lithology to present new insights into the influence of lithology on hydrate distribution in an accretionary margin hydrate distribution is spatially associated with 0 5 cm thick laterally discontinuous sand horizons that compose 1 of the sedimentary section at all sites proximity to the fractured ridge crest determines the extent to which individual sand horizons host hydrate with 70 of the horizons hosting hydrate at the crest and only 29 in the basin this trend is consistent with focused up dip migration of fluids along permeable lithologic conduits and shows that lateral flow may be as important as vertical diffusion and fracture flow in determining gas hydrate distribution at hydrate ridge

distribution and height of methane bubble plumes on the cascadia margin characterized by acoustic imaging submersible investigations of the cascadia accretionary complex have identified localized venting of methane gas bubbles in association with gas hydrate occurrence acoustic profiles of these bubble plumes in the water column in the vicinity of hydrate ridge offshore oregon provide new constraints on the spatial distribution of these gas vents and the fate of the gas in the water column the gas vent sites remained active over the span of two years but varied dramatically on time scales of a few hours all plumes emanated from local topographic highs near the summit of ridge structures the acoustic images of the bubble plumes in the water column disappear at water depths between 500 to 460 m independent of the seafloor depth this coincides with the predicted depth of the gas hydrate stability boundary of 510 to 490 m suggesting that the presence of a hydrate skin on the bubble surface prevents them from rapid dissolution the upper limit of the acoustic bubble plumes at 460 m suggests that dissolution of the residual bubbles is relatively rapid above the hydrate stability zone

pore water anomalies of submarine gas hydrate zones as tool to assess hydrate abundance and distribution in the subsurface what have we learned in the past decade abstract the most significant new contributions to the study of natural gas hydrates in the past decade have come from findings of the ocean drilling program odp notably legs 112 141 146 and 164 and to a lesser extent legs 131 160 170 and 186 leg 164 in particular was dedicated to gas hydrate drilling in the blake ridge gas hydrate field in the west atlantic in an unprecedented multidisciplinary research effort paull et al 1996 proc ocean drill program initial rep 164 623 pp paull c k matsumoto r wallace p j dillon w p eds 2000a proc ocean drill program sci results 164 ocean drilling program college station tx 459 pp most important for the progress of hydrochemical studies related to gas hydrates has been the growing awareness of the significance of diffusion modulated advective processes shaping the chemical and isotopic pore water profiles in hydrate zones this started with qualitative evidence for advective flow from drilling the hydrate bearing peru and hydrate free barbados active margins continued with the nankai trough accretionary prism the japan trench slope and the cascadia and costa rica active margins and culminated in the quantitative advection diffusion model of egeberg and dickens chem geol 153 1999 53 for the passive margin setting of the blake ridge advective flow regimes are different at active and passive margins as there is a tendency for the flow at active margins to be focussed along landward dipping thrust planes and faults in the wedge of imbricated thrust sheets that finds expression in a step pattern of the pore water profiles for passive margins but also for some active margin sites advection is from sources below the drilled section either through subvertical faults passive margins or from the decollement zone active margins we have learned that the well known coupled pore water anomalies that are ascribed to hydrate dissociation downward chlorinity decrease combined with 18 o increase hesse and harrison 1981 earth planet sci lett 55 1981 453 need not occur together in the presence of hydrates because the isotope effect may be overprinted by the effects of other reactions such as volcanic ash alteration or by the advection of low 18 o fluids however if the anomalies show up hydrates are present almost invariably with the exception of advected low cl high 18 o waters coming to terms with the effects of advection and diffusion has allowed successful modeling of the simpler hydrate affected pore water profiles at passive margins instrumental for modeling are chlorine isotopes which provide an effective tool to assess advection rates the egeberg and dickens model allows estimation of hydrate concentration and distribution in the subsurface because it separates the effects of advection diffusion and hydrate dissociation but critically depends on samples taken under in situ pressure and temperature conditions modeling the more complex pore water profiles of active margins is a challenge for the future compared to geophysical methods to estimate hydrate concentration the geochemical method gives minimum amounts

synchronous seafloor spreading and subduction at the paleo convergent margin of semail and arabia the semail ophiolite is the largest and best exposed ophiolite having preserved intact record of a precollision system related to neotethyan ocean closure breaking with the alternative models of ophiolite exhumation and emplacement this paper builds on integrating the joined contribution of tectonic evolution of the continental margin in the premise of the ophiolite obduction connecting the along strike segmentation of the ophiolite recorded in the lithospheric flow structure and recent high precision dating results in a 3 d model of evolution of the ophiolite and its continental margin during jurassic cretaceous time among the relevant characteristics newly accounted 1 the contamination of the ophiolite by fluids and magmas of continental origin 2 the discrimination of different types of metamorphics associated to the ophiolite and conventionally classified metamorphic soles 3 the instability of the arabian margin during the late jurassic cretaceous times 4 the new precise ages relating to overlapping of spreading and detachment and 5 the inferred vergence of neotethyan closure during late mesozoic are stressed the complex stem revealed may relate to processes associated with spreading center subduction at ridge trench transform rtt triple junction as documented along a convergent margin the semail ophiolite emplacement on the arabia continental margin would result from a temporary arabian platform directed subduction zone that consumed the southern tethyan plate during late jurassic cretaceous time

observations of annual and el nino thermal and flow variations at 0 110 w and 0 95 w during 1980 1985 moored measurements of the surface wind and of the current and temperature fields within the uppermost 250 m were recorded from march 1980 to september 1985 at 0 110 w and from july 1981 to november 1983 at 0 95 w at these sites the annual mean thicknesses of the equatorial undercurrent euc and of the surface portion of the south equatorial current sec were about 200 m and 20 m respectively the annual mean euc core speed was 0 9 m s 1 annual cycles of temperature and zonal current at 110 w were most distinctive near the surface at nominal depths of 15 m and 47 5 m the average annual amplitudes were 1 5 c and 0 5 m s 1 at about 100 m the annual amplitudes were about 0 5 c and 0 10 m s 1 at 15 m the annual mean zonal current was 0 05 m s 1 which was not representative of the monthly mean zonal current in april the monthly mean direction was eastward and in october it was westward with speeds of about 0 5 m s 1 in both months warmer water occurred in april and colder water in october the direction of the zonal wind component was westward throughout the year and the annual amplitude of the zonal wind was only about 2 5 times larger than that of the zonal current the average amplitude of the annual cycle of the meridional current component was less than 0 05 m s 1 and not distinguishable from year to year monthly mean variations monthly mean anomalous or el nino currents at 110 w were defined as the difference between the observations and the annual cycle during the august december 1982 onset phase of el nino the strength of the normally westward flowing near surface sec was greatly reduced to near zero speed by an el nino eastward flowing zonal current of about 0 3 m s 1 the largest vertically averaged 15 250 m zonal current anomaly 0 5 m s 1 occurred in january and february 1983 and represented a substantial decrease in the eastward transport of the euc causing a disappearance of the undercurrent the duration of the euc disappearance was longer at 95 w than at 110 w a surface intensified eastward jet with a maximum daily speed of 1 75 m s 1 at 15 m occurred in may 1983 at 110 w but not at 95 w a massive redistribution of heat throughout the mixed layer and thermocline was associated with the 1982 1983 el nino beginning in august 1982 the thermocline at 110 w and 95 w sank 100 m reaching its maximum depth in december 1982 temperatures at 100 m and 150 m which normally were about 15 c and 14 c reached 27 5 c and 22 5 c the time rate of change of the 15 to 200 m heat content was 500 w m 2 during the august december 1982 warming phase and 460 w m 2 during the january february 1983 subsurface cooling phase the euc disappeared during the subsurface cooling phase a second less intensive mixed layer deepening occurred in may 1983 at 95 w but not at 110 w

off equatorial influence upon pacific equatorial dynamic height variability during the 1982 1983 el nino southern oscillation event anomalous sea level anomalous observed dynamic height 0 400 dbar and anomalous model dynamic height are compared at the locations of 13 island sea level stations in the tropical pacific for each 2 month interval of the 4 year period 1979 to 1982 sea level compares well with both observed dynamic height 0 400 dbar based on temperature depth observations made by volunteer observing ships and model dynamic height derived from a linear two layer wind driven model the cross correlation between sea level and either of the dynamic heights is generally greater than 0 75 the ratio of root mean square rms differences about the mean annual cycle of the sea level to rms differences of either of the dynamic heights is approximately unity starting in 1981 off equatorial rossby wave activity propagated toward the western boundary of the pacific basin this also occurred in model dynamic height both north and south of the equator yet neither sea level observations nor observed dynamic height has the spatial and temporal resolution to establish a connection between the off equatorial rossby wave activity and the equatorial kelvin wave activity in the western boundary region on the other hand the model dynamic height does have this capability therefore at the western boundary the model rossby wave activity is found to have excited coastally trapped kelvin munk wave activity which transmitted the anomalous sea level equatorward at the equator this model coastally trapped wave activity excited eastward propagating equatorial kelvin waves yielding a pair of anomalous peaks in dynamic height variability in the eastern equatorial pacific associated with the 1982 1983 el nino southern oscillation enso event the evolution of these two peaks in anomalous dynamic height associated with the 1982 1983 enso event is examined at eight locations in the tropical and equatorial pacific the major peak originated in the off equatorial south pacific and coincided with the wintertime 1982 1983 el nino event in the eastern equatorial pacific the secondary peak originated in the off equatorial north pacific and coincided with the anomalous peak which occurred in the eastern equatorial pacific the summer before the 1982 1983 enso event

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

a blast of gas in the latest paleocene simulating first order effects of massive dissociation of oceanic methane hydrate carbonate and organic matter deposited during the latest paleocene thermal maximum is characterized by a remarkable 2 5 excursion in delta 13c that occurred over approximately 10 4 yr and returned to near initial values in an exponential pattern over approximately 2 x 10 5 yr it has been hypothesized that this excursion signifies transfer of 1 4 to 2 8 x 10 18 g of ch4 from oceanic hydrates to the combined ocean atmosphere inorganic carbon reservoir a scenario with 1 12 x 10 18 g of ch4 is numerically simulated here within the framework of the present day global carbon cycle to test the plausibility of the hypothesis we find that 1 the delta 13c of the deep ocean shallow ocean and atmosphere decreases by 2 3 over 10 4 yr and returns to initial values in an exponential pattern over approximately 2 x 10 5 yr 2 the depth of the lysocline shoals by up to 400 m over 10 4 yr and this rise is most pronounced in one ocean region and 3 global surface temperature increases by approximately 2 degrees c over 10 4 yr and returns to initial values over approximately 2 x 10 6 yr the first effect is quantitatively consistent with the geologic record the latter two effects are qualitatively consistent with observations thus significant ch4 release from oceanic hydrates is a plausible explanation for observed carbon cycle perturbations during the thermal maximum this conclusion is of broad interest because the flux of ch4 invoked during the maximum is of similar magnitude to that released to the atmosphere from present day anthropogenic ch4 sources

earth s variable rotation recent improvements in geodetic data and practical meteorology have advanced research on fluctuations in the earth9s rotation theinterpretation of these fluctuations is inextricably linked with studies of the dynamics of the earth moon system and dynamical processes in the liquid metallic core of the earth where the geomagnetic field originates other parts of the earth9s interior and the hydrosphere and atmosphere fluctuations in the length of the day occurring on decadal time scales have implications for the topography of the core mantle boundary and the electrical magnetic and other properties of the core and lower mantle investigations of more rapid fluctuations bear on meteorological studies of interannual seasonal and intraseasonal variations in the general circulation of the atmosphere and the response of the oceans to such variations

geosat crossover analysis in the tropical pacific 2 verification analysis of altimetric sea level maps with expendable bathythermograph and island sea level data altimetric sea level map time series of the tropical pacific have been produced from the crossover differences generated in the first 17 months of the geosat mission to verify the validity of altimetric sea level so produced they are compared with the dynamic height field derived by expendable bathythermograph xbt and island sea level data overall the three fields show statistically significant correlation with each other at island sea level stations altimetric sea level in general has better correlation with island sea level than the xbt derived dynamic height complex empirical orthogonal function ceof analysis which is used to discern coherent structures from data contaminated by random errors has been conducted on the altimetric sea level and xbt derived dynamic height field the first ceof modes which each explain 70 of the variance of the respective field correlate significantly better with each other than the original fields the relatively short record is clearly dominated by the annual signal major features away from the equator are also observed to propagate to the west

high intensity gas seepage causes rafting of shallow gas hydrates in the southeastern black sea abstract submarine gas hydrates are a major global reservoir of the potent greenhouse gas methane since current assessments of worldwide hydrate bound carbon vary by one order of magnitude new technical efforts are required for improved and accurate hydrate quantifications here we present hydrate abundances determined for surface sediments at the high flux batumi seep area in the southeastern black sea at 840 m water depth using state of the art autoclave technology pressure sediment cores of up to 2 65 m in length were recovered with an autoclave piston corer backed by conventional gravity cores quantitative core degassing yielded volumetric gas bulk sediment ratios of up to 20 3 proving hydrate presence the cores represented late glacial to holocene hemipelagic sediments with the shallowest hydrates found at 90 cmbsf calculated methane concentrations in the different cores surpassed methane equilibrium concentrations in the two lowermost lithological black sea units sampled the results indicated hydrate fractions of 5 2 of pore volume in the sapropelic unit 2 and mean values of 21 pore volume in the lacustrine unit 3 we calculate that the studied area of 0 5 km2 currently contains about 11 3 kt of methane bound in shallow hydrates episodic detachment and rafting of such hydrates is suggested by a rugged seafloor topography along with variable thicknesses in lithologies we propose that sealing by hydrate precipitation in coarse grained deposits and gas accumulation beneath induces detachment of hydrate sediment chunks floating hydrates will rapidly transport methane into shallower waters and potentially to the sea atmosphere boundary in contrast persistent in situ dissociation of shallow hydrates appears unlikely in the near future as deep water warming by about 1 6 c and or decrease in hydrostatic pressure corresponding to a sea level drop of about 130 m would be required because hydrate detachment should be primarily controlled by internal factors in this area and in similar hydrated settings it serves as source of methane in shallow waters and the atmosphere which is mainly decoupled from external forcing

equatorial undercurrent disappears during 1982 1983 el nino the equatorial undercurrent at 159 w decayed during august 1982 partially reversed during september and rapidly reappeared in january 1983 the virtual disappearance is consistent with the basin wide adjustment of sea surface slope to the strong westerly winds in the western and central pacific that caused the 1982 1983 el nino event

increased continental margin slumping frequency during sea level lowstands above gas hydrate bearing sediments we present sup 14 c data on sediment samples from cores of the upper 7 m of the sediment column overlying a major continental rise gas hydrate field on the southern carolina rise and inner blake ridge offshore the southeastern united states the data show that glacial age sediments are underrepresented in the cores the observation is consistent with a previously predicted association between sea level lowstands and increased frequency of sea floor slumping on continental margins containing gas hydrates 26 refs 3 figs

hindcasts of sea level variations during the 1982 83 el nino abstract the sea level signature for the onset of the 1982 83 el nino is hindcasted using a linear wind driven model that consists of four vertical modes the hindcast solution is compared with sea level time series from 18 island and coastal stations throughout the tropical pacific the response of the first and second baroclinic modes when summed account for a significant portion of the phase and amplitude of the observed sea level the comparisons with observed sea level are best in the eastern tropical pacific along the equator and south american coast where the solutions are a function of integrals of the zonal wind field to the west the skill of the hindcast is notably less away from the equator

geophysical constraints on the surface distribution of authigenic carbonates across the hydrate ridge region cascadia margin on active tectonic margins methane rich pore fluids are expelled during the sediment compaction and dewatering that accompany accretionary wedge development once these fluids reach the shallow subsurface they become oxidized and precipitate cold seep authigenic carbonates faults or high porosity stratigraphic horizons can serve as conduits for fluid flow which can be derived from deep within the wedge and or if at seafloor depths greater than 300 m from the shallow source of methane and water contained in subsurface and surface gas hydrates the distribution of fluid expulsion sites can be mapped regionally using sidescan sonar systems which record the locations of surface and slightly buried authigenic carbonates due to their impedence contrast with the surrounding hemipelagic sediment hydrate ridge lies within the gas hydrate stability field offshore central oregon and during the last 15 years several studies have documented gas hydrate and cold seep carbonate occurrence in the region in 1999 we collected deep towed seamarc 30 sidescan sonar imagery across the hydrate ridge region to determine the spatial distribution of cold seep carbonates and their relationship to subsurface structure and the underlying gas hydrate system high backscatter on the imagery is divided into three categories i circular to blotchy with apparent surface roughness ii circular to blotchy with no apparent surface roughness and iii streaky to continuous with variable surface roughness we interpret the distribution of high backscatter as well as the locations of mud volcanoes and pockmarks to indicate variations in the intensity and activity of fluid flow across the hydrate ridge region seafloor observations and sampling verify the acoustic signals across the survey area and aid in this interpretation subsurface structural mapping and swath bathymetry suggest the fluid venting is focused at the crests of anticlinal structures like hydrate ridge and the uplifts along the daisy bank fault zone geochemical parameters link authigenic carbonates on hydrate ridge to the underlying gas hydrate system and suggest that some of the carbonates have formed in equilibrium with fluids derived directly from the destabilization of gas hydrate this suggests carbonates are formed not only from the methane in ascending fluids from depth but also from the shallow source of methane released during the dissociation of gas hydrate the decreased occurrence of high backscatter patches and the dramatic reduction in pockmark fields imaged on the eastern part of the survey suggest gas hydrate near its upper stability limit may be easily destabilized and thus responsible for these seafloor features high backscatter along the left lateral daisy bank fault suggests a long history of deep seated fluid venting probably unrelated to destabilized gas hydrate in the subsurface

the hawaii to tahiti shuttle experiment the shuttle experiment conducted between hawaii and tahiti from january 1979 to june 1980 was designed to observe the changing equatorial ocean structure and circulation to study the variations and interactions of the four major equatorial ocean currents and to develop a scientific basis for their monitoring by simple observations of thermal structure and sea level preliminary analyses of the results show that the equatorial thermal structure remains intact during a normal year and that only the positions and intensities of the currents are subject to change the water transport of the equatorial undercurrent varied from 25 x 106 cubic meters per second in january to 51 x 106 cubic meters per second in july but also exhibited strong short term pulsations the equatorial surface flow responded strongly to the winds at periods of 1 month and longer an array of drifter buoys in the equatoral countercurrent was subject to very little dispersion while traveling over 4500 kilometers in 4 months low frequency fluctuations in the north equatorial countercurrent can be monitored by means of the difference in sea level between fanning and majuro

trade wind fetch related variations in equatorial undercurrent depth speed and transport a dynamical model is developed to examine the dependence of equatorial undercurrent depth speed and volume transport on trade wind fetch the model ocean is linear continuously stratified vertically diffusive and formulated on the equatorial beta plane analytical solutions are derived in closed form for realistic choices of model parameters results indicate that the undercurrent would be significantly shallower and weaker in the atlantic than in the pacific because of the shorter atlantic trade wind fetch

variability in the eastern equatorial pacific ocean during 1986 1988 we examine variability in the eastern equatorial pacific during 1986 1988 using conductivity temperature depth data velocity and temperature data from equatorial moorings between 110 w and 140 w and wind data from a basin scale zonal array of islands and moorings between 110 w and 165 e the period studied coincides with the el nino southern oscillation enso event of 1986 1987 and a subsequent cold event in 1988 weak warm sea surface temperature anomalies first appeared in the eastern equatorial pacific in mid 1986 and increased to 1 c in september november 1986 in association with a 30 cm s 1 weakening of the south equatorial current and a 20 to 40 m depression of the thermocline these warm anomalies lasted until early 1988 after which a large scale shoaling of the thermocline led to sea surface temperatures more than 3 c colder than climatology year to year fluctuations in the eastern pacific were related primarily to zonal wind variations in the central and western pacific westerly wind stress anomalies of 0 02 0 05 n m 2 were observed between 140 w and 165 e from the latter half of 1986 until the end of 1987 these were replaced by easterly wind anomalies of similar magnitude between 157 w and 165 e in 1988 energetic intraseasonal fluctuations with periods of 2 3 months were also prominent in zonal current temperature and dynamic height time series these fluctuations propagate eastward at approximately first baroclinic mode kelvin wave phase speeds and are forced west of the date line by episodes of westerly winds extrema in several oceanic variables occurred in association with these waves though their precise dynamical link to the enso cycle is unclear from our data sea surface temperature and thermocline depth anomalies at 0 110 w were less pronounced during the 1986 87 enso than during the 1982 1983 enso the equatorial undercurrent though weaker than normal in early 1987 did not disappear as it did in early 1983

an interhemispheric tropical sea level seesaw due to el nino taimasa abstractduring strong el nino events sea level drops around some tropical western pacific islands by up to 20 30 cm such events referred to as taimasa in samoa expose shallow reefs thereby causing severe damage to associated coral ecosystems and contributing to the formation of microatolls during the termination of strong el nino events a southward movement of weak trade winds and the development of an anomalous anticyclone in the philippine sea are shown to force an interhemispheric sea level seesaw in the tropical pacific that enhances and prolongs extreme low sea levels in the southwestern pacific spectral features in addition to wind forced linear shallow water ocean model experiments identify a nonlinear interaction between el nino and the annual cycle as the main cause of these sea level anomalies

hindcast forecast of enso events based upon the redistribution of observed and model heat content in the western tropical pacific 1964 86 anomalous sea level anomalous observed dynamic height 0 400 db and anomalous model dynamic height are examined at the locations of 13 island sea level stations in the tropical pacific for each bimonth of the four year period 1979 to 1982 starting in 1981 the anomalous dynamic height data show off equatorial rossby waves propagated toward the w boundary of the pacific basin at the w boundary the model rossby wave activity was found to have excited coastally trapped kelvin munk waves which transmitted the anomalous dynamic height equatorward at the equator coastally trapped wave activity excited eastward propagating equatorial kelvin waves yielding a pair of anomalous peaks in dynamic height variability in the e equatorial pacific associated with the 1982 1983 enso event the evolution of the peaks in dynamic height associated with the rossby and kelvin wave activity reflects the redistribution of observed upper ocean heat content in the w tropical pacific providing a qualitative hindcast for the 1982 1983 enso event

the slope of sea level along the equator during the 1982 1983 el nino observed deviations of monthly mean sea level at seven island stations along the equator in the pacific have been superimposed on the mean dynamic topography to determine the variations of the east west slope of sea surface topography during the 1982 1983 el nino the normal east west slope is eliminated in january 1983 when the bulk of warm water flowing eastward has reached the coast of south america the sea surface remains essentially flat from january to june 1983 although zonal winds are very weak until april only the slope requires several months to be reestablished and in october and november sea level along the entire equator is 10 cm or more below normal indicating a net loss of warm water from the equatorial pacific