early winter in the northern stratosphere an account is given of the evolution and structure of the circulation in the stratosphere and upper troposphere of the northern hemisphere in the early winter of 1982 83 an early winter warming is described and it is shown to have some features in common with canadian warmings a tentative connection is made between the intensification in the troposphere of a trough ridge pattern associated with the east asian low and the establishment of the aleutian high as a persistent feature extending through the whole depth of the stratosphere processes leading to the formation of the so called surf zone are considered and aspects of zonalmean diagnostics are related to developments on synoptic maps

variations in mode of formation and temperature of oceanic deep waters over the past 125 000 years marked changes in the deep water temperature of the different oceanic basins during the past 125 kyr are revealed by a detailed comparison of the oxygen isotopic composition ofbenthicforaminiferafrom sediment cores taken from the norwegian sea and the pacific atlantic and southern oceans the last interglacial deep water temperatures were similar to the modern ones at the 5e 5d transition around 115 kyr bp the deep water temperatures dropped below approximately 0 c in the pacific and southern indian oceans in the atlantic ocean the deep water temperature dropped in 2 successive steps at 115 and 75ky bp the global ocean deep water temperatures were in the 0 to 1 c range for the whole of the last ice age isotope stages 4 2

methane derived authigenic carbonates on accretionary ridges miocene case studies in the northern apennines italy compared with modern submarine counterparts abstract we present new field data from three outcrops of miocene methane derived authigenic carbonates in the foredeep of the northern apennines that contain chemosynthetic fauna and record a long history 1 ma of shallow fluid seepage linked to seafloor anaerobic oxidation of methane the studied outcrops show similar features in terms of carbonate morphology facies spatial distribution and lateral and vertical contacts with the enclosing sediments methane derived carbonates occur in two structural positions 1 on the slope of the accretionary wedge in hemipelagites draping buried thrust related anticlines and 2 at the leading edge of the deformation front in the inner foredeep within fault related anticlines standing above the adjacent deep seafloor as intrabasinal ridges we compare fossil seeps with two extensively investigated modern analogues the hikurangi margin offshore new zealand and hydrate ridge on the cascadia margin offshore the u s a these analogues share a similar compressive structural setting and are marked by the presence of variably extensive and voluminous methane derived carbonate bodies and chemosynthetic fauna on the present day seafloor the comparison allows us to propose a model for the evolution of fluid seeps on thrust related ridges at the deformation front uplift and geometry of the anticlinal ridges are controlled by the growth of splay faults mostly blind connected to the basal detachment favoring the migration of fluids toward the incipient anticline fold development generates extensional stresses in the hinge zone of the anticline promoting the development of normal faults fluid migration pathways and seafloor seeps shift from the forelimb toward the crest of the ridge as the structures evolve in the slope setting far from the deformation front thrust faults and extensional faults in buried anticlines remain the main fluid migration pathways to sustain seepage at the seafloor after reaching a mature stage within the wedge the structure is less active and buried in the slope environment of the evolved prism

connections between the spring breakup of the southern hemisphere polar vortex stationary waves and air sea roughness a robust connection between the drag on surface layer winds and the stratospheric circulation is demonstrated in nasa s goddard earth observing system chemistry climate model geosccm specifically an updated parameterization of roughness at the air sea interface in which surface roughness is increased for moderate wind speeds 4 20ms 21 leads to a decrease in model biases in southern hemispheric ozone polar cap temperature stationary wave heat flux and springtime vortex breakup a dynamical mechanism is proposed whereby increased surface roughness leads to improved stationary waves increased surface roughnessleads to anomalouseddy momentumflux convergence primarily in the indian ocean sector where eddiesarestrongestclimatologically inseptemberandoctober thelocalizationoftheeddymomentumflux convergence anomaly in the indian ocean sector leads to a zonally asymmetric reduction in zonal wind and bygeostrophy toawavenumber 1stationarywavepattern thistroposphericstationarywavepatternleadsto enhanced upward wave activity entering the stratosphere the net effect is an improved southern hemisphere vortex the vortex breaks up earlier in spring i e the spring late breakup bias is partially ameliorated yet is no weaker in midwinter more than half of the stratospheric biases appear to be related to the surface wind speed biases as many other chemistry climate models use a similar scheme for their surface layer momentum exchange and have similar biases in the stratosphere the authors expect that results from geosccm may be relevant for other climate models

the last interglacial sea level change new evidence from the abrolhos islands west australia u series ages measured by thermal ionisation mass spectrometry tims are reported for a last interglacial li fossil coral core from the turtle bay houtman abrolhos islands western australia the core is 33 4 m long the top of which is approximately 5 m a p s l above present sea level from the232th concentrations and the reliability of the u series ages two sections in the core can be distinguished calculated u th ages in core section i 3 3 m a p s l to 11 m b p s l vary between 124 1 7 ka bp 3 3 m a p s l and 132 5 1 8 ka 4 m b p s l i e below present sea level and those of section ii 11 23 m b p s l between 140 3 and 214 5 ka bp respectively the ages of core section i are in almost perfect chronological order whereas for section ii no clear age depth relationship of the samples can be recognised further assessments based on the 234u t criteria reveal that none of the samples of core section ii give reliable ages whereas for core section i several samples can be considered to be moderately reliable within 2 ka the data of the turtle bay core complement and extend our previous work from the houtman abrolhos showing that the sea level reached a height of approximately 4 m b p s l at approximately 134 ka bp and a sea level highstand of at least 3 3 m a p s l at approximately 124 ka bp sea level dropped below its present position at approximately 116 ka bp although the new data are in general accord with the milankovitch theory of climate change a detailed comparison reveals considerable differences between the holocene and li sea level rise as monitored relative to the houtman abrolhos islands these observation apparently add further evidence to the growing set of data that the li sea level rise started earlier than recognised by specmap chronology a reconciliation of these contradictionary observations following the line of arguments presented by crowley 1994 are discussed with respect to the milankovitch theory

temporal and spatial evolution of a gas hydrate bearing accretionary ridge on the oregon continental margin a seismic reflection survey on the oregon continental margin conducted in 1989 indicates the widespread presence of gas hydrate beneath the middle and lower slope of this accretionary margin the seismic signature of gas hydrate a bottom simulating reflector bsr with negative polarity that locally cuts across stratigraphic horizons is especially well developed beneath hydrate ridge this anomalously shallow accretionary ridge was drilled during ocean drilling program leg 146 to study fluid venting in this paper we focus on the seismic data from the southern part of hydrate ridge where little evidence of active venting has previously been reported but where the seismic data indicate a complicated subsurface plumbing system apparent disruptions of the bsr beneath the western ridge flank suggest dissociation of gas hydrate in response to slumping a double bsr beneath the southern crest suggests hydrate destabilization in response to tectonic uplift and folding on the basis of these and other observations we propose a qualitative model for the evolution of a hydrate bearing ridge in an active accretionary complex in which gas hydrate initially stabilizes the sea floor permitting construction of large ridges that are then eaten away by slumps along their margins the north to south variation in sea floor venting and subsurface seismic structure along hydrate ridge may reflect different stages in the temporal evolution of one of these ridges

wave driven mean tropical upwelling in the lower stratosphere the mean meridional circulation induced by zonal momentum forcing is considered in the context of i a wave mean model in which the momentum forcing arises naturally from the explicit representation of the stratospheric wave response to lower boundary forcing and ii a zonally symmetric model in which the momentum forcing is prescribed externally wave forcing is confined to one hemisphere as a simple representation of the difference between the northern and southern hemispheres the main focus of the paper is on how the upwelling branch of the circulation in the tropics depends on nonlinearity model diffusion and the transient effects of the seasonal cycle significant tropical upwelling can occur in the steady state if the zonal momentum force extends into the subtropics provided the forcing is strong enough to redistribute angular momentum throughout the tropics the circulation in these strongly forced cases depends nonlinearly on the forcing amplitude if the forcing is weak so that the dynamics are approximately linear significant tropical upwelling can occur in the steady state if i the radiative equilibrium temperature is such that angular momentum contours tilt poleward and upward as at the winter solstice or ii the model diffusion is large in seasonally varying cases weak subtropical forcing can also induce a time average tropical upwelling through the interaction of the transient angular momentum distribution and the transient forcing when the forcing is strong the effect of the seasonal cycle leads to an increase in the tropical upwelling beyond that of the steady state response

fluid flow in accretionary prisms evidence for focused time variable discharge accretionary prisms are wedges of saturated sediment that are subject to intense deformation as a result of lithosphere convergence compressive stress and rapid burial of the accreted deposits result in sediment compaction and mineral dehydration these latter processes in conjunction with fermentation or thermal maturation of entrained organic matter yield hydrocarbon bearing pore fluids that are expelled from the prism regional fluxes of heat and a number of dissolved chemical species most notably carbon are controlled by the advective expulsion of the pore waters numerical modeling observation and monitoring of flow patterns and rates and recent in situ hydrogeological tests quantify the conditions that control rates of fluid flow dispersed intergranular flow 10 8 to 10 11 m s controlled by the vertical permeability of the prism 10 14 to 10 20 m is limited by low permeability lithologies and seems not to vary much from margin to margin focused flow 10 1 to 10 8 m s above the decollement is controlled by fault zones or sedimentary intrusions diapiric structures at low fluid pressures fault zone permeability may be similar to that of adjacent wall rock but as fluid pressure increases from hydrostatic 0 to near lithostatic levels 1 0 fault zones dilate and fracture permeability increases by 2 4 orders of magnitude 10 10 to 10 16 m similarly mud volcanoes and diapirs provide high permeability fluid conduits to the sediment water interface as a result faults and intrusions become primary flow paths and support surface vents at which syntectonic deposits carbonate and gas hydrates accumulate and chemosynthetic organisms cluster models of thermal and chemical anomalies and epigenetic deposits indicate that flow is temporally variable that conclusion has been quantified by extended 1 10 months seafloor and borehole experiments that measured temperature anomalies associated with flow events on the cascadia prism flow estimated velocity 3 10 5 m s 950 m yr confined to a thrust fault that cuts upward through the prism has brought thermogenic hydrocarbons from depths 1 5 km to the surface within the last 400 years

analysis of bubble plume distributions to evaluate methane hydrate decomposition on the continental slope cascadia margin sediments contain a rich reservoir of carbon derived both from terrestrial input and sea surface productivity a portion of this carbon exists as solid gas hydrate within sediment pore spaces which previous studies have shown to be a methane reservoir of substantial size on both the vancouver island and oregon portions of the cascadia margin multichannel seismic reflection profiles on the cascadia margin show the widespread presence of bottom simulating reflectors bsrs within the sediment column indicating the gas hydrate reservoir extends from the deformation front at 3000 m depth to the upper limit of gas hydrate stability near 500 m water depth in this study we compile an inventory of methane bubble plume sites on the cascadia margin identified in investigations carried out for a range of interdisciplinary goals that also include sites volunteered by commercial fishermen high plume density anomalies are associated with both the continental shelf 180 m and the depth of the upper limit of methane hydrate stability depth mhsd that occurs near 500 m in the ne pacific the observed anomalies on the cascadia slope may be due to the warming of seawater at intermediate depths suggesting that modern climate change has begun to destabilize the climate sensitive hydrate reservoir within the cascadia margin sediments reanalysis of similar plume images on the north american atlantic slope suggests a lack of correlation between observed plume depths and the mhsd for much of the latitudinal range

a study of the chemistry of pore fluids and authigenic carbonates in methane seep environments kodiak trench hydrate ridge monterey bay and eel river basin analyses of the chemical and isotopic composition of carbonates rocks recovered from methane seepage areas of the kodiak trench hydrate ridge monterey bay clam flats and the eel river basin coupled with the studies of the chemistry of the pore fluids have shown that these carbonates have grown within the sediment column geochemical profiles of pore fluids show that in deep water seeps kodiak trench 4450 m monterey bay 1000 m hydrate ridge 650 m 13c dic values are low isotopically light whereas in the eel river area 350 500 m 13c dic values are much higher isotopically heavier in all cases the 13c values indicate that processes of methane oxidation associated with sulfate reduction are dominant in the shallow sediments data on the isotopic composition of authigenic carbonates found at sites in kodiak trench eel river basin south and eel river basin north indicate a variable composition and origin in different geochemical environments some of the authigenic carbonates from the study sites show a trend in their 13c values similar to those of the pore fluids obtained in their vicinity suggesting formation at relatively shallow depths but others indicate formation at greater sediment depths the latter usually consist of high magnesium calcite or dolomite which from their high values of 13c up to 23 and 18o up to 7 5 suggest formation in the deeper horizons of the sediments in the zone of methanogenesis these observations are in agreement with observations by other workers at hydrate ridge in monterey bay and in the eel river basin

the seasonal cycle of planetary waves in the winter stratosphere a simple mechanistic model with time independent planetary wave forcing at the lower boundary is used to investigate the observed differences between the northern hemisphere nh and southern hemisphere sh stratospheric evolution considered here are differences in both the zonal mean and the zonal wavenumber 1 structure of the winter vortex throughout its seasonal evolution in particular for small and intermediate forcing values the model robustly produces the midwinter minimum in geopotential wavenumber 1 amplitudes observed in the sh lower and middle stratosphere this feature is considered from the different viewpoints of transitions between stable equilibria wave transmission properties of the mean flow and resonant type interactions with the lower boundary wave forcing to assess the extent to which these viewpoints previously studied in the context of models representing variation with height only are relevant to a more complicated model representing variation in both height and latitude results show that resonance with the lower boundary forcing in early and late winter leading to early and late winter wave maxima and hence to an associated midwinter minimum is the dominant mechanism in the model considered for large forcing amplitudes more typical of the nh two possible winter and late winter evolutions are found to exist for the same forcing amplitudes which of these is selected depends on the details of the forcing in early winter note that there is no constant value of wave forcing amplitude that produces both a sh like undisturbed winter evolution as well a strong final warming suggesting that time varying lower boundary wave forcing is necessary to simulate these aspects of the sh evolution

upper stratospheric circulations in the two hemispheres observed by satellites a global analysis is made of upper stratospheric circulations with the aid of nimbus 5 and tiros n satellite observations in order to make a comparison of characteristics between the northern hemisphere nh and the southern hemisphere sh it is shown that the reversal of north south gradient of the zonal mean temperature at the stratopause level is always observed in higher latitudes of the sh winter while the temperature gradient of the nh winter is variable because of the occurrence of sudden warmings consequently due to the thermal wind relation the polar night westerlies of the sh stratosphere are generally stronger than those of the nh stratosphere in association with this difference the activity of transient planetary waves of wavenumber 2 is striking in the sh in contrast to the predominance of steady waves in the nh finally the interrelation between the zonal mean field and planetary waves in the upper stratosphere is briefly discussed

constraints on the ocean oxygen isotopic enrichment between the last glacial maximum and the holocene paleoceanographic implications abstract we review the various methods which have been applied to estimate the change of seawater 18 o w between the last glacial maximum lgm and the holocene the most accurate constraints on these estimates are provided by the measurement of pore waters 18 o and by high resolution records of benthic foraminifer 18 o in the high latitude oceans of both hemispheres they show that the 18 o of seawater in the deep ocean during the lgm was 1 05 0 20 heavier than today with significant regional variations constraints resulting from ice sheet models are less accurate because both the volume and isotopic composition of each ice sheet are still poorly known the amplitude of the benthic 18 o change between the lgm and the holocene together with the 18 o and 13 c values of the benthic foraminifera genus cibicides during the lgm show that the southern ocean deep waters were extremely cold close to the freezing point during this time deep waters of the south atlantic and the pacific oceans were at least 1 3 c warmer than those of the southern ocean overall the glacial deep ocean below 2500 m was characterized by extremely cold temperatures everywhere lower than 0 c 18 o values of benthic foraminifer from the north atlantic are highly variable this variability suggests that deep atlantic waters were not homogeneous probably because they resulted from the sinking of different surface water masses at various locations during winter the deep waters in the north atlantic were at most 2 c warmer than in southern ocean alternatively they could have been nearer the freezing point with a 18 o value lighter than the mean ocean water brine formation during winter would preserve such light 18 o values of the northern north atlantic surface water

stable isotope patterns of coexisting pyrite and gypsum indicating variable methane flow at a seep site of the shenhu area south china sea aggregates of authigenic pyrite and gypsum were found at site hs373 in the shenhu seepage area south china sea most of the pyrite occurs as tubes consisting of framboids gypsum aggregates are mainly represented by rosettes and some of them grew over pyrite revealing that gypsum precipitation postdated pyrite formation at seeps extensive sulfate driven anaerobic oxidation of methane aom commonly leads to the accumulation of 34s enriched sulfide resulting in the formation of 32s depleted pyrite the sulfur isotopic composition of pyrite at site hs373 reveals a great variability of 75 5 in 34s values spanning from 37 6 to 37 9 v cdt with a distinct trend towards higher values with increasing depth this trend indicates an increase of the effect of sulfate driven aom with depth whereas pyrite at shallow depth apparently resulted mostly from organiclastic sulfate reduction to date reports on coexisting pyrite and gypsum in seep environments are limited and therefore the mechanism of gypsum formation is insufficiently understood this is the first time that the sulfur and oxygen stable isotope composition of gypsum has been analyzed to understand its formation at seeps the 34s values of gypsum vary from 24 5 to 0 9 revealing a similar trend with depth like pyrite the 18ogypsum values range from 5 3 to 12 3 v smow with a scattered trend to lower values with depth the combined evidence reveals that gypsum formation was linked to the establishment of more oxidizing conditions probably caused by waning seepage this led to the oxidation of pyrite and the associated increase in pore water sulfate and acidity which favored carbonate mineral dissolution providing the calcium ions required for gypsum formation the observed isotopic variability of gypsum suggests that oxidation occurred by different mechanisms at different depth whereby pyrite oxidation was dominated by aerobic processes at shallow depth involving dissolved molecular oxygen and by anaerobic processes at greater depth involving electron acceptors like ferric iron taken together the stable isotope compositions of pyrite and gypsum suggest that the redox conditions within the studied sediments were variable such variability was controlled by complex factors among which changes in seepage activity have been instrumental for the vertical displacement of the sulfate methane transition zone

last glacial emplacement of methane derived authigenic carbonates in the sea of japan constrained by diatom assemblage carbon 14 and carbonate content abstract we studied diatom assemblages and caco 3 contents of methane derived authigenic carbonates from the eastern margin of the sea of japan and assessed the formation time of these samples radioactive 14 c date was determined in selected samples to obtain the maximum age of the time the results of our study suggest mass formation of carbonate nodules in a glacial period within 40 ky consistent with a published u th dating result of carbonate nodules in the study area diatom assemblages and contents in the carbonate nodules abundance of 10 6 g dominance of neritic littoral species warm cold water species ratio lower than 25 differ from the near seafloor sediments in the study area which have characteristics of holocene sediments in the sea of japan and suggest cementation of glacial sediments laminated sediments in some nodule samples are glacial sediments because laminations are records of a low sea level period in the semi enclosed ocean similarity of diatom assemblages and contents in all carbonate samples is another evidence of glacial sediments in nodules glacial sediments with oceanic cold water species as low as holocene sediments restricts the sediment age to before 20 cal ky bp carbonate contents higher than 78 wt suggest the cementation of poorly compacted sediments near the seafloor and the date of carbonate cementation is therefore close to that of the cemented sediments most carbonate nodule samples in this study were formed in a glacial period and detection of 14 c restricts this period to within 40 ky

past methane release events and environmental conditions at the upper continental slope of the south china sea constraints by seep carbonates authigenic carbonates and seep biota are archives of seepage history and record paleo environmental conditions at seep sites we obtained the timing of past methane release events at the northeastern slope of the south china sea based on u th dating of seep carbonates and seep bivalve fragments from three sites located at 22 02 22 09 n 118 43 118 52 e water depths from 473 to 785 m also we were able to reconstruct the paleo bottom water temperatures by calculating the equilibrium temperature using the ages the corresponding past 18o of seawater 18osw and the 18o of the selected samples formed in contact with bottom seawater with negligible deep fluid influence a criterion consists of mineralogy redox sensitive trace elements and u th isotope systematics is proposed to identify whether the samples were formed from pore water or have been influenced by deep fluid our results show that all methane release events occurred between 11 5 0 2 and 144 5 12 7 ka when sea level was about 62 104 m lower than today enhanced methane release during low sea level stands seems to be modulated by reduced hydrostatic pressure increased incision of canyons and increased sediment loads the calculated past bottom water temperature at one site site 3 water depth 767 771 m during low sea level stands 11 5 and 65 ka ago ranges from 3 3 to 4 0 c i e 1 3 to 2 2 c colder than at present the reliability of 18o of seep carbonates and bivalve shells as a proxy for bottom water temperatures is critically assessed in light of 18o enriched fluids that might be emitted from gas hydrate and or clay dehydration our approach provides for the first time an independent estimate of past bottom water temperatures of the upper continental slope of the south china sea

oblique strike slip faulting of the central cascadia submarine forearc at least nine wnw trending left lateral strike slip faults have been mapped on the oregon washington continental margin using sidescan sonar seismic reflection and bathymetric data augmented by submersible observations the faults range in length from 33 to 115 km and cross much of the continental slope five faults offset both the juan de fuca plate and north american plates and cross the plate boundary with little or no offset by the frontal thrust left lateral separation of channels folds and holocene sediments indicate active slip during the holocene and late pleistocene offset of surficial features ranges from 120 to 900 m and displaced subsurface piercing points at the seaward ends of the faults indicate a minimum of 2 2 to 5 5 km of total slip near their western tips fault ages range from 300 ka to 650 ka yielding late pleistocene holocene slip rates of 5 5 2 to 8 5 2 mm yr the geometry and slip direction of these faults implies clockwise rotation of fault bounded blocks about vertical axes within the cascadia forearc structural relationships indicate that some of the faults probably originate in the juan de fuca plate and propagate into the overlying forearc the basement involved faults may originate as shears antithetic to a dextral shear couple within the slab as plate coupling forces are probably insufficient to rupture the oceanic lithosphere the set of sinistral faults is consistent with a model of regional deformation of the submarine forearc defined to include the deforming slab by right simple shear driven by oblique subduction of the juan de fuca plate

u th dating and post depositional alteration of a cold seep carbonate chimney from the campos basin offshore brazil abstract dating authigenic cold seep carbonates allows determining the timing of active seepage of hydrocarbon rich fluids at continental margins and ultimately the detection of the geological factors affecting it u th dating has been selected in this study the method having been successfully used before however incorporation of initial thorium in substantial amounts of detrital material due to the precipitation of carbonates within the seabed and post depositional alteration potentially pose a major problem violating the basic assumptions of the method here we report results from several samples from the campos basin off the coast of brazil they are unusual in their high 13 c values mean of 10 0 vpdb high detrital contents and being dominantly dolomite elevated 230 th 238 u activity ratios indicate that most of the carbonates lost uranium during diagenesis isochrones are obtained from the unaffected samples yielding an age of 140 4 3 1 ka vertical growth of the chimney must have been short and rapid since results from the top and bottom parts of the chimney concur within analytical uncertainties furthermore profiles of u th radioisotope specific activity 234 u and 232 th specific activity on two quarter slices of a carbonate chimney reveal the occurrence of three distinct diagenetic processes u loss u exchange with seawater and th gain

phase alignment of the tropical stratospheric qbo in the annual cycle abstract this paper investigates the occurrence of phase alignment of the tropical stratospheric quasi biennial oscillation qbo with the annual cycle first updating previous studies observational results are shown for ncep reanalysis data and singapore radiosondes both datasets show strong phase alignment of the qbo at 24 5 km phase alignment is investigated in a 3d mechanistic stratospheric model including explicit large scale planetary waves forced by a lower boundary geopotential anomaly and a simple equatorial wave parameterization the model simulates a qbo like oscillation with the period depending on the lower boundary momentum flux of the parameterized waves phase alignment is manifested in two different ways first simulated oscillations of both integer and noninteger year periods are shown to lock on to a certain phase of the annual cycle second when the magnitude of the lower boundary momentum flux is varied about a range implying oscillation period close to 2 yr the period of th

u th dating of cold seep carbonates an initial comparison authigenic carbonates from hydrocarbon seeps are unique archives of past seepage and associated environmental parameters in order to constrain the ages of a set of seep carbonates and the time involved in carbonate formation we applied uranium thorium u th dating to samples from the gulf of mexico the congo fan and the black sea the resulting u th ages indicate that environmental conditions must have been favorable for enhanced methane rich fluid seepage during the time intervals of 53 4 to 1 7 ka bp for the gulf of mexico and 45 5 to 3 0 ka bp for the congo fan the seep carbonates from the black sea formed at 1 6 to 1 1 ka bp our results suggest that enhanced fluid flow during these time intervals was closely related to 1 sea level variations associated with glacial interglacial cycles and 2 environmental alterations in the course of late quaternary climate change including variations in bottom water temperatures that affected the stability of gas hydrate reservoirs

on the seasonal cycle of stratospheric planetary waves quasi stationary planetary waves exhibit different seasonal behaviour in the two winter stratospheres whereas in a climatological sense wave amplitudes are large throughout northern winter in the southern hemisphere there is a climatological minimum in midwinter it is suggested here that the southern hemisphere behaviour is basically linear the midwinter minimum arising from the opacity of the strong westerlies of southern midwinter to stationary wave propagation on the other hand it is further suggested that in the northern hemisphere winter the westerlies are prevented from becoming so strong in a climatological sense by the action of the waves themselves on the mean state and that the penetration of large scale waves into the midwinter northern stratosphere thus depends on a nonlinear feedback process preliminary tests of this hypothesis are conducted using a highly truncated beta plane model of the stratospheric flow

uranium removal in oceanic sediments and the oceanic u balance pore water uranium data from the nw atlantic ocean cariaco trench black sea and san clemente basin are used to calculate fluxes across the sediment water interface all samples were collected in situ and show depletions in pore water u relative to the overlying water concentration the uptake rate of u derived from pore water gradients reflects the redox environment with lowest fluxes 10 g cm 2 ky in oxic su ic sediments of the nw atlantic dominated by no 3 reduction and higher fluxes 25 70 g cm 2 ky in the anoxic sulfate reducing sediments of the cariaco trench black sea and san clemente basin the anoxic fluxes compare well with previous estimates based on solid phase data calculations indicate that the areally integrated removal of u into su ic hemipelagic sediments is of greater magnitude than that into anoxic sulfate reducing sediments these fluxes are discussed in the context of the oceanic u balance the removal of u in all oceanic sediments is estimated to account for about 65 of the riverine input and this sink plus removal of u in altered oceanic crust balances the most probable value for riverine input

radiometric dating of submarine hydrocarbon seeps in the gulf of mexico massive abiotic carbonates and calcareous shells of the chemosynthetic mytilid bathymodiolus sp containing a detailed history of hydrocarbon seepage were investigated using radiocarbon and u series isotopes stable carbon isotopes and 87 sr 86 sr ratios were also determined in order to provide insights on the carbon source and the nature of the hydrocarbon rich fluids samples from five seepage sites on the northern gulf of mexico sea floor overlying subsurface salt diapirs and encompassing depths from 125 to 2000 m were selected as representative of the spectrum of active and extinct seeps examined from submersible dives in general paired 14 c and 230 th dates of carbonate buildups consisting of aragonite high mg calcite and dolomite mineralogies are highly discordant the cause of the discordance established on the basis of paired 14 c and 13 c values 14 c 898 to 992 13 c 9 5 to 53 3 for n 27 lies with the impairment of the radiocarbon dates resulting from dilution of the 14 c pool with fossil hydrocarbon derived carbon the validity of the ionium dates based on u rich 2 4 7 6 ppm samples is demonstrated by the concordance between 234 u 238 u and 230 th 234 u evolution in time and by the 234 u 238 u o activity ratios that are generally within the range of sea water value of 1 14 0 04 2 sigma some dolomite rich samples are exceptional because their 234 u 238 u o ratios are significantly higher 1 22 1 38 than sea water suggesting deposition from anoxic pore waters where the soluble u reached anomalous 234 u 238 u ratios the formation of the carbonates from sea water derived fluids rather than from formation fluids advecting from deep aquifers is supported by the 87 sr 86 sr composition of the samples mean 0 709145 19 10 6 n 14 that compares well with modern nonseep marine carbonates and the ambient gulf of mexico sea water 0 709171 8 10 6 calcareous shells the 13 c values of which indicate a carbon source in sea water 13 c 4 3 to 1 1 yield valid radiocarbon ages and show fair concordancy between their radiocarbon and ionium dates isotope migration attested by the observed u uptake in the fossil shells is likely to affect the accuracy of their ionium dates radiometric ages from extinct and senescent seep sites at upper bathyal depths indicate that hydrocarbon seepage occurred there during late pleistocene time 195 13 ka ages derived from nascent seep sites at mid bathyal and abyssal depths 12 3 0 0 ka indicate that currently vigorous seepage was initiated at the end of the last deglaciation these radiometric ages most likely reflect the time of sedimentary loading and associated salt diapirism that activated the fault conduits to the sea floor

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

the seasonal evolution of planetary waves in the southern hemisphere stratosphere and troposphere seasonality in planetary wave structure in the southern hemisphere stratosphere and troposphere 1000 1 mb is studied based on eight years 1979 1986 of daily geopotential data emphasis is placed on the distinctive seasonality in the stratosphere along with tracing the stratospheric fluctuations into the troposphere time filtering is used to separate stationary and transient components maximum geopotential height variance is observed in the middle to upper stratosphere in late winter spring with a distinct secondary smaller maximum in late fall early winter these maxima sandwich the strongest mid winter zonal winds this sequence occurs approximately one month earlier in the upper stratosphere two corresponding peaks are observed in stratospheric zonal mean wind and temperature fluctuations the two maxima in stratospheric wave variance are not in agreement with observed seasonal changes in quasi geostrophic refractive index of the zonal mean flow the stratospheric geopotential variance maxima result from nearly equal amounts of stationary and transient zonal wave 1 fluctuations with transient wave 2 also contributing during late winter stationary wave 1 shows intriguing seasonal evolution the early winter maximum is predominantly equivalent barotropic whereas that of late winter spring is highly baroclinic in the stratosphere stratospheric poleward fluxes of heat and momentum both exhibit pronounced maxima during september october these result primarily from the stationary wave 1 contributions and the transients assume a secondary role although not as pronounced as the stationary wave seasonality seasonal differences in transient wave behaviour are also documented including three dimensional propagation characteristics and wave mean flow interaction diagnostics

the roles of the hadley circulation and downward control in tropical upwelling abstract several idealized models of tropical upwelling are presented in order to clarify the roles of the nonlinear hadley circulation and extratropical wave driving in particular it is shown that the hadley circulation and wave driven circulation interact to determine the nature of tropical upwelling the authors explain several observed features such as maximum upwelling in the summer subtropics and the annual variation of the upwelling

oxygen isotope fractionation in marine aragonite of coralline sponges oxygen isotope values of the extant caribbean coralline sponge ceratoporella nicholsoni are compared with published temperatures and 18o of water calculated from salinities the measured values from aragonitic sponge skeletons have a mean offset of 1 0 0 1 from calculated calcite equilibrium values aragonite calcite 1 0010 this is in good agreement with published values from synthetic aragonite they further agree with published near equilibrium oxygen isotope values of temperate and cold water molluscs and foraminifera extrapolated to the temperature range of the coralline sponges these results and the mode of skeleton formation of ceratoporella nicholsoni suggest that these sponges precipitate aragonite close to isotopic equilibrium the temperature dependence of oxygen isotopic fractionation between the aragonite of ceratoporella nicholsoni and water is only roughly constrained by the available data due to the narrow temperature range of the caribbean reef sites however as the data suggest oxygen isotopic equilibrium we can calculate a well constrained temperature equation combining temperate and cold water equilibrium values from molluscs and foraminifera with our sponge data full size image 1 k and full size image 1 k

using chemical compositions of sediments to constrain methane seepage dynamics a case study from haima cold seeps of the south china sea abstract cold seeps frequently occur at the seafloor along continental margins the dominant biogeochemical processes at cold seeps are the combined anaerobic oxidation of methane and sulfate reduction which can significantly impact the global carbon and sulfur cycles the circulation of methane rich fluids at margins is highly variable in time and space and assessing past seepage activity requires the use of specific geochemical markers in this study we report multiple sedimentary proxy records for three piston gravity cores qdn 14a qdn 14b and qdn 31 from the haima seep of the south china sea scs by combining total organic carbon toc total inorganic carbon tic total nitrogen tn total sulfur ts acid insoluble carbon and sulfur isotope 13corganic carbon and 34sacid insoluble and 34s values of chromium reducibility sulfur 34scrs as well as carbon isotopes of tic 13ctic in sediments our aim was to provide constraints on methane seepage dynamics in this area we identified three sediment layers at about 260 300 cm 380 420 cm and 480 520 cm sediment depth characterized by particular anomalies of low 13ctic values and high ts content high ts and crs contents and high 34sacid insoluble and 34scrs values respectively on this basis we propose that these sediment horizons correspond to distinct methane release events preserved in the sediment record while the exact mechanisms accounting for the presence or absence of these particular geochemical signals in the sediment are not known we propose that they correspond to variations in methane flux and their duration through time overall our results suggest that sedimentary carbon and sulfur and their isotopes are useful tracers for better understanding of methane seepage dynamics over time

multi disciplinary investigation of fluid seepage on an unstable margin the case of the central nile deep sea fan we report on a multidisciplinary study of cold seeps explored in the central nile deep sea fan of the egyptian margin our approach combines in situ seafloor observation geophysics sedimentological data measurement of bottom water methane anomalies pore water and sediment geochemistry and 230 th u dating of authigenic carbonates two areas were investigated which correspond to different sedimentary provinces the lower slope at 2100 m water depth indicates deformation of sediments by gravitational processes exhibiting slope parallel elongated ridges and seafloor depressions in contrast the middle slope at not vert 1650 m water depth exhibits a series of debris flow deposits not remobilized by post depositional gravity processes significant differences exist between fluid escape structures from the two studied areas at the lower slope methane anomalies were detected in bottom waters above the depressions whereas the adjacent ridges show a frequent coverage of fractured carbonate pavements associated with chemosynthetic vent communities carbonate u th age dates 8 kyr bp pore water sulphate and solid phase sediment data suggest that seepage activity at those carbonate ridges has decreased over the recent past in contrast large 1 km2 carbonate paved areas were discovered in the middle slope with u th isotope evidence for ongoing carbonate precipitation during the late holocene since 5 kyr bp at least our results suggest that fluid venting is closely related to sediment deformation in the central nile margin it is proposed that slope instability leads to focused fluid flow in the lower slope and exposure of fossil carbonate ridges whereas pervasive diffuse flow prevails at the unfailed middle slope

formation of carbonate chimneys in the mediterranean sea linked to deep water oxygen depletion marine sediments at ocean margins vent substantial amounts of methane1 2 microbial oxidation of the methane released can trigger the precipitation of carbonate within sediments and support a broad diversity of seafloor ecosystems3 4 the factors controlling microbial activity and carbonate precipitation associated with the seepage of submarine fluid over geological time remain poorly constrained here we characterize the petrology and geochemistry of rocks sampled from metre size build ups of methane derived carbonate chimneys located at the amon mud volcano on the nile deep sea fan we find that these carbonates comprise porous structures composed of aggregated spherules of aragonite and closely resemble microbial carbonate reefs forming at present in the anoxic bottom waters of the black sea5 using u series dating we show that the amon carbonate build ups formed between 12 and 7 thousand years ago contemporaneous with the deposition of organic rich sediments in the eastern mediterranean the so called sapropel layer s1 we propose that the onset of deep water suboxic or anoxic conditions associated with sapropel formation resulted in the development of intense anaerobic microbial activity at the sea floor and thus the formation of carbonate chimneys

tectonic controls on greenhouse gas flux to the paleogene atmosphere from the gulf of alaska accretionary prism the late paleocene to early eocene ca 61 56 ma was a period of long term global warming perhaps the warmest in the cenozoic recent modeling suggests that methane loading of the atmosphere and related development ofpolar stratospheric clouds could have been an important forcing mechanism for this period of warm climate the gulf of alaska accretionary prism contained 6 x 10 6 km 3 of siliciclastic sediments deposited in trench and slope settings along alaska s maastrichtian and paleogene continental margin these sediments underwent complex deformation accretion and unusual high heat flow soon after deposition accretion processes thermally overmatured the sediments during a time that overlaps the 61 56 ma period of long term global warming assuming a modest average organic carbon content of 0 3 wt in these sediments an estimated 8 35 x 10 1 5 kg of methane were generated in the accretionary prism over an 5 m y period this methane was not effectively trapped and migration pathways to the atmosphere were developed through complexly deformed and emergent continental borderlands the gulf of alaska accretionary prism is a possible source of the atmospheric methane needed to force paleocene and early eocene global warming and an example of how tectonic processes can significantly recycle carbon from the geosphere

gas hydrate destabilization enhanced dewatering benthic material turnover and large methane plumes at the cascadia convergent margin mixed methane sulfide hydrates and carbonates are exposed as a pavement at the seafloor along the crest of one of the accretionary ridges of the cascadia convergent margin vent fields from which methane charged low salinity fluids containing sulfide ammonia 4he and isotopically light co2 escape are associated with these exposures they characterize a newly recognized mechanism of dewatering at convergent margins where freshening of pore waters from hydrate destabilization at depth and free gas drives fluids upward this process augments the convergence generated overpressure and leads to local dewatering rates that are much higher than at other margins in the absence of hydrate discharge of fluids stimulates benthic oxygen consumption which is orders of magnitude higher than is normally found at comparable ocean depths the enhanced turnover results from the oxidation of methane hydrogen sulfide and ammonia by vent biota the injection of hydrate methane from the ridge generates a plume hundreds of meters high and several kilometers wide a large fraction of the methane is oxidized within the water column and generates 13c anomalies of the dissolved inorganic carbon pool

constructing a stacked benthic δ18o record composite stacks were constructed by superimposing 6 to 13 benthic foraminiferal 1 8 o records covering the period 0 850 ka an initial timescale for each core was established using radioisotopic age control points and assuming constant sedimentation rates between these points the average of these records is our 13 core untuned stack next we matched the 41 kyr component of each record individually to variations in earth s obliquity four of the 13 records produced timescales that were inconsistent with one or more of the known radioisotopic ages the nine remaining cores were averaged to create a minimally tuned stack six of the minimally tuned cores were assembled into a tropical stack for each stack we estimated the uncertainty envelope from the standard deviation of the constituents spectral analysis of the three stacks indicates that benthic 1 8 o is dominated by a 100 kyr oscillation that has a narrow spectral peak the contribution of precession to the total variance is small when compared to prior results from planktic stacks

paleo cold seep activity in the southern south china sea evidence from the geochemical and geophysical records of sediments abstract over the past decade more than 30 cold seep sites have been reported along the continental slope of the south china sea scs these seep sites have all been located in the northern scs and no methane seepage has been discovered in the southern scs here we report on the analysis results of the geochemical and geophysical of the marine core sediments 58s collected from the southern continental slope of the scs we suggest that the sedimentary total sulfur ts total inorganic carbon tic 34scrs values of chromium reducible sulfur crs and carbonate 13ctic values of the bulk sediments coupled with the ratio of nrmaf60mt nrmaf80mt nrm can be used to trace the methane release events in a methane rich environment at least two methane release events were identified at depths of 5 5 6 2 m and 6 8 7 2 m moreover according to the characteristic of the ts toc and nrmaf60mt nrmaf80mt nrm ratio of sediments we suggest the methane flux has changed episodically this inference is supported by the occurrence of the strongly negative carbonate 13ctic values of bulk sediments and the positive 34scrs values which indicate the occurrence of anaerobic oxidation of methane aom and the location of a past or present sulfate methane transition zone smtz respectively ultimately these new data suggest that the combined geochemical and geophysical study of marine sediments provides a valuable tool with which to infer the temporal variations in methane seepage in a marine environment

fluid flow through carbonate platforms constraints from 234u 238u and cl in bahamas pore waters the geometry timing and rate of fluid flow through carbonate margins and platforms is not well constrained in this study we use u concentrations and isotope ratios measured on small volumes of pore water from bahamas slope sediment coupled with existing chlorinity data to place constraints on the fluid flow in this region and by implication other carbonate platforms these data also allow an assessment of the behaviour of u isotopes in an unusually well constrained water rock system we report pore water u concentrations which are controlled by dissolution of high u organic material at shallow depths in the sediment and by reduction of u to its insoluble 4c state at greater depths the dominant process influencing pore water 234 u 238 u is alpha recoil in holocene sediments the increase of pore water 234 u 238 u due to recoil provides an estimate of the horizontal flow rate of 11 cm year but with considerable uncertainty at depths in the sediment where conditions are reducing features in the u concentration and 234 u 238 u profiles are offset from one another which constrains the effective diffusivity for u in these sediments to be1 2 10 8 cm 2 s 1 at depths between the holocene and these reducing sediments pore water 234 u 238 u values are unusually low due to a recent increase in the dissolution rate of grain surfaces this suggests a strengthening of fluid flow probably due to the flooding of the banks at the last deglaciation and the re initiation of thermally driven venting of fluid on the bank top and accompanying recharge on the slopes interpretation of existing chlorinity data in the light of this change in flow rate constrain the recent horizontal flow rate to be 10 6 3 4 cm year estimates of flow rate from 234 u 238 u and cl are therefore in agreement and suggest flow rates close to those predicted by thermally driven models of fluid flow this agreement supports the idea that flow within the bahamas banks is mostly thermally driven and suggests that flow rates on the order of 10 cm year are typical for carbonate platforms where such flow occurs 1999 elsevier science b v all rights reserved

diagenetic mg calcite overgrowths on foraminiferal tests in the vicinity of methane seeps methane is a potent greenhouse gas and some episodes of past global warming appear to coincide with its massive release from seafloor sediments as suggested by carbon isotope records of foraminifera here we present structural geochemical and stable carbon isotope data from single foraminiferal calcite tests and authigenic mg calcite overgrowths in a sediment core recovered from an area of active methane seepage in western svalbard at ca 340 m water depth the foraminifera are from intervals in the core where conventional bulk foraminiferal 13c 13c values are as low as 11 3 mg ca analyses of the foraminiferal tests reveal that even tests for which there is no morphological evidence for secondary authigenic carbonate can contain mg rich interlayers with mg ca up to 220 mmol mol transmission electron microscopy tem of the contact point between the biogenic calcite and authigenic mg calcite layers shows that the two phases are structurally indistinguishable and they have the same crystallographic orientation secondary ion mass spectrometry sims analyses reveal that the mg rich layers are strongly depleted in 13c 13c 13c as low as 34 1 these very low 13c 13c values indicate that the authigenic mg calcite precipitated from pore waters containing methane derived dissolved inorganic carbon at the depth of the sulfate methane transition zone smtz as the depth of the smtz can be located several meters below the sediment seawater interface interpretation of low foraminiferal 13c 13c values in ancient sediments in terms of the history of methane seepage at the seafloor must be undertaken with care

new insights into geology and geochemistry of the kerch seep area in the black sea abstract high resolution 3d seismic data in combination with deep towed sidescan sonar data and porewater analysis give insights into the seafloor expression and the plumbing system of the actively gas emitting kerch seep area which is located in the northeastern black sea in around 900 m water depth i e well within the gas hydrate stability zone ghsz our analysis shows that the kerch seep consists of three closely spaced but individual seeps above a paleo channel levee system of the don kuban deep sea fan we show that mounded seep morphology results from sediment up doming due to gas overpressure each of the seeps hosts its own gas pocket underneath the domes which are fed with methane of predominantly microbial origin along narrow pipes through the ghsz methane transport occurs dominantly in the form of gas bubbles decoupled from fluid advection elevated sediment temperatures of up to 0 3 c above background values are most likely the result of gas hydrate formation within the uppermost 10 m of the sediment column compared to other seeps occurring within the ghsz in the black sea overall only scarce gas indications are present in geoacoustic and geophysical data transport reaction modeling suggests that the kerch seep is a young seep far from steady state and probably not more than 500 years old

interrelationship of fluid venting and structural evolution alvin observations from the frontal accretionary prism oregon seismic reflection and sea beam bathymetric data plus submarine geological measurements define a ramp anticline at the deformatoin front of the central oregon subduction zone at its northern termination the ramp anticline is deeply incised by a large 500 m deep submarine canyon and cut by a probable backthrust to the south along the strike of the fold a smaller submarine canyon shallowly erodes the anticline and backthrusting is not apparent in the submersible observations two alvin dives along a transect through the southern canyon show active fluid vents demarked by biological communities at the frontal thrust and at the breached crest of the anticline along a northern transect encompassing the large submarine canyon 10 alvin dives indicated no venting on the formal thrust limited venting in the canyon but numerous biological communities along a scarp interpreted as the surface trace of the backthrust these observations suggest a scenario of vent and structural geomorphic development consisting of 1 frontal thrust faulting and associated venting facilitated by high fluid pressure 2 erosion of the oversteepened seaward flank of the ramp anticline assisted by seepage forces and leading to fluid flow out of stratigraphically controlled conduits in the limbs of the overthrust deposits 3 lockingmore of the frontal thrust due to dewatering or a local decrease in wedge taper associated with development of the large canyon leading to failure along the backthrust and 4 redirection of fluid flow by the backthrust thus within le 0 3 m y deformation of the relatively permeable sediments of the oregon margin results in stratigraphically controlled flow being partially captured by faults less

planetary scale disturbances in the southern stratosphere during early winter abstract the early winter mid april to mid july circulation in the southern hemisphere stratosphere is studied emphasis is placed on the evolution of strong disturbances with structures dominated by the zonal wavenumber 1 component of the flow wave 1 the approach to this investigation is based on analysis of 12 years 1979 90 of observational data and comparative analyses of control and hypothesis testing simulations with a three dimensional primitive equation model of the stratosphere and mesosphere considerable interannual variability is found in both the intensity and timing of wave 1 amplification during early winter though usually quasi stationary there are six extended periods in the dataset when wave 1 travels steadily eastward and is of large amplitude two of these periods june 1980 and june 1985 are examined in detail the evolution of the circulation in these two cases resembles that during canadian warmings in the northern hemisphere in several ways first there is a large eastwar

a large drop in atmospheric 14c 12c and reduced melting in the younger dryas documented with 230th ages of corals paired carbon 14 14 c and thorium 230 230 th ages were determined on fossil corals from the huon peninsula papua new guinea the ages were used to calibrate part of the 14 c time scale and to estimate rates of sea level rise during the last deglaciation an abrupt offset between the 14 c and 230 th ages suggests that the atmospheric 14 c 12 c ratio dropped by 15 percent during the latter part of and after the younger dryas yd this prominent drop coincides with greatly reduced rates of sea level rise reduction of melting because of cooler conditions during the yd may have caused an increase in the rate of ocean ventilation which caused the atmospheric 14 c 12 c ratio to fall the record of sea level rise also shows that globally averaged rates of melting were relatively high at the beginning of the yd thus these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the mississippi to the st lawrence river triggered the yd event

methane hydrate and free gas on the blake ridge from vertical seismic profiling seismic velocities measured in three drill holes through a gas hydrate deposit on the blake ridge offshore south carolina indicate that substantial free gas exists to at least 250 meters beneath the bottom simulating reflection bsr both methane hydrate and free gas exist even where a clear bsr is absent the low reflectance or blanking above the bsr is caused by lithologic homogeneity of the sediments rather than by hydrate cementation the average methane hydrate saturation above the bsr is relatively low 5 to 7 percent of porosity which suggests that earlier global estimates of methane in hydrates may be too high by as much as a factor of 3

sublacustrine mud volcanoes and methane seeps caused by dissociation of gas hydrates in lake baikal four lake floor seeps have been studied in the gas hydrate area in lake baikal s south basin by using side scan sonar detailed bathymetry measurements of near bottom water properties heat flow measurements and selected seismic profiles in relation to results from geochemical pore water analysis the seeps at the lake floor are identified as methane seeps and occur in an area of high heat flow where the base of the gas hydrate layer shallows rapidly toward the vent sites from 400 m to 150 m below the lake floor at the site of the seep a vertical fluid conduit disrupts the sedimentary stratification from the base of the hydrate layer to the lake floor the seeps are interpreted to result from local destabilization of gas hydrate caused by a pulse of hydrothermal fluid flow along an active fault segment this is the first time that methane seeps and or mud volcanoes as sociated with gas hydrate destabilization have been observed in a sublacustrine setting the finding demonstrates the potential of tectonically controlled gas hydrate destabiliza tion to cause extreme pore fluid overpressure and short lived mud volcanism

structural controls on seepage of thermogenic and microbial methane since the last glacial maximum in the harstad basin southwest barents sea the harstad basin is a structural block on the continental shelf of sw barents sea where gas hydrates likely occurred below the grounded ice sheet during the last glaciation and it hosts active gas seepage at numerous seafloor sites we present an integrated study of fluid flow systems in the harstad basin by combining seismic profile interpretations and gas flare mapping data with the geochemical results obtained on seafloor seeping gas and methane derived carbonate crusts more than 190 acoustic gas flares were registered in water column many of them in association with pockmarks and carbonate crust fields however weak or absent seepage observed during remotely operated underwater vehicle transects across many pockmarks and crust fields suggests that seepage activity may have decreased since the last deglaciation in the western harstad basin seeps of microbial methane occur mainly above tertiary formations that are pinching out below the glacial sediments high amplitude seismic anomalies suggest the presence of gas pockets at the base of the glacial sediments and within tertiary deposits in contrast gas seeping in the eastern harstad basin originates from a biodegraded thermogenic source tentatively connected to the deeply faulted mesozoic rocks occurring below glacial sediments this spatial variability in fluid sources is also recorded in the carbon isotope data of seafloor carbonate crusts with 13 c values typically between 55 and 42 and 40 and 20 vpdb for carbonate crusts associated with microbial and thermogenic fluids respectively u th chronology combined with the stable isotope data suggests that this discrepancy in fluid sources over a distance of about 20 km has been stable since the last glaciation and highlights the significance of regional underlying geology in mediating fluid supply to the seafloor

modeling of hydraulically controlled exchange flow in the bosphorus strait abstract recent hydrographic observations obtained in the bosphorus strait illustrate several features of the flow that may be related with the internal hydraulics a two layer numerical model indicates that the two way exchange flow may indeed be subject to a series of internal hydraulic adjustments along the strait due to morphological features such as sills a contraction and abrupt expansion of the width of the strait the model identifies three distinct regions of the supercritical flow the lower layer flow of the marmara sea origin is directed to the north towards the black sea in a progressively thinning layer and is controlled by the sill located near the black sea entrance of the strait the upper layer water of the black sea origin flows in the opposite direction and is controlled upon reaching the constricted region located about 10 12 km away from the marmara end of the strait the upper layer flow is then matched to the subsequent subcritical conditions by undergoing an internal hydraulic ju

sr and nd isotopes of cold seep carbonates from the northern south china sea as proxies for fluid sources abstract in this study sr isotopes combined with nd isotopes of modern cold seep carbonates were studied to provide reliable proxies for sources and pathways of seep fluids we presented sr and nd isotopes together with stable carbon and oxygen isotope data of cold seep carbonates recovered from the northern continental slope of the south china sea scs based on the evidence for negligible detrital contamination and diagenetic alteration carbonate samples are considered dependable archives which record sr and nd isotope signals of the original pore waters from which carbonates have precipitated excellent correlation between 87sr 86sr ratios and 1 sr observed in carbonate samples indicates two end members with distinct sr isotopic signatures including modern seawater as a major source and a lesser contribution from methane rich seep fluid driven from a deep source besides these two end members release of nd from organic matter and fe mn oxyhydroxide is an additional contribution to pore water nd furthermore sr and nd isotopic compositions suggest water rock interactions between upward seep fluid and detrital component in sediments which resulted in the isotopic shift towards pronounced 143nd depleted and slightly 87sr enriched in the fluid phase this study provides insight into the knowledge for tracing seepage fluid circulation by sr nd isotope system at modern seep systems

fluid source and methane related diagenetic processes recorded in cold seep carbonates from the alvheim channel central north sea integrated petrography mineralogy geochronology and geochemistry of cold seep carbonate crusts and free gas from the alvheim channel elucidate diagenetic carbonate precipitation and related seepage histories in the central north sea free gas isotope characteristics coupled with carbonate 13c values as low as 66 vpdb indicate a predominantly microbial methane source with minor thermogenic contribution we estimate that 70 of the carbon sequestered into carbonate precipitates was derived from local oxidation of methane the early stage of crust growth is represented by microcrystalline aragonite and mg calcite 10 to 40 mol mgco3 cementing seafloor sediments consisting of clays quartz feldspar and minor detrital low mg calcite and dolomite typical association of aragonite cement with coarse grained detritus may reflect elevated fluid flow and flushing of fine particles prior to cementation close to the seafloor middle rare earth element enrichment in early generation microcrystalline cements containing framboidal pyrite indicates diagenetic precipitation within the zone of anaerobic methane oxidation contiguous to iron reduction the later generation diagenetic phase corresponds to less abundant radial fibrous and botryoidal aragonite which lines cavities developed within the crusts in contrast to early generation cements late generation cavity infills have rare earth elements and y patterns with small negative ce anomalies similar to seawater consistent with carbonate precipitation in a more open seawater dominated system aragonite u th ages indicate carbonate precipitation between 6 09 and 3 46 kyr bp in the northern part of the channel whereas in the southern part precipitation occurred between 1 94 and 0 81 kyr bp reflecting regional changes in fluid conduit position

complex flow patterns through hydrate ridge and their impact on seep biota our recent measurements of long term fluid flux rates and output fluid chemistry at seep sites on hydrate ridge cascadia suggest that the mechanisms driving fluid flow in gas hydrate bearing forearc settings may be significantly more complex than previously thought temporal changes in the polarity and magnitude of flow and in seep fluid chemistry were observed the nature of flow appears to generate a strong response in the chemosynthetic seep community ecology we document here 1 the frequency and range of temporal variability in flow rates 2 the relatively rapid changes in outflow composition 3 strong outflow of seawater like fluids 4 the association of calyptogena sp clams with oscillatory and inflow settings and 5 microbial mat communities associated with strong advection of altered fluids these results suggest that a reappraisal may be required of the nature of the hydrologic system and its effect on related processes such as benthic seep community ecology and biogeochemical cycles

drivers of focused fluid flow and methane seepage at south hydrate ridge offshore oregon usa methane seepage at south hydrate ridge offshore oregon united states one of the best studied examples of gas venting through gas hydrates is the seafloor expression of a vigorous fluid flow system at depth the seeps host chemosynthetic ecosystems and release significant amounts of carbon into the ocean with new three dimensional seismic data we image strata and structures beneath the ridge in unprecedented detail to determine the geological processes controlling the style of focused fluid flow numerical fluid flow simulations reveal the influence of free gas within a stratigraphic unit known as horizon a beneath the base of gas hydrate stability bghs free gas within horizon a increases the total mobility of the composite water gas fluid resulting in high fluid flux that accumulates at the intersection between horizon a and the bghs this intersection controls the development of fluid overpressure at the bghs and together with a well defined network of faults reveals the link between the gas hydrate system at depth and methane seepage at the surface

u th chronology and formation controls of methane derived authigenic carbonates from the hola trough seep area northern norway abstract we investigated methane derived authigenic carbonate mdac crusts and nodules from a cold seep site on the northern norwegian continental shelf in ca 220 m water depth to determine the timing and mode of their formation gas bubbling observed during remotely operated vehicle rov assisted sampling of mdac crusts revealed ongoing seep activity authigenic carbonates were present as crusts on the seafloor and as centimetre size carbonate cemented nodules at several intervals within an adjacent sediment core aragonite dominated mineralogy of the mdac crusts suggests formation close to the seafloor at higher rates of sulphate dependent anaerobic oxidation of methane aom in contrast dolomite cemented nodules are consistent with the formation at the sulphate methane transition zone deeper within the sediment at lower rates of aom the 13c carbonate values of bulk rock and of micro drilled aragonite samples vary between 22 2 and 34 6 vpdb we interpret the carbon in aragonite to be mainly derived from the anaerobic oxidation of thermogenic methane with a minor contribution from seawater dissolved inorganic carbon dic aom activity is supported by high concentrations of aom related biomarkers of archaea archaeol and 2 sn hydroxyarchaeol and sulphate reducing bacteria iso and anteiso c15 0 fatty acids in the crusts the dolomite nodules exhibit higher 13c carbonate values 12 vpdb suggesting a smaller amount of methane derived carbon presumably due to the contribution of dic migrating from depth and lower aom rates the latter is supported by orders of magnitude lower concentrations of archaeol and sn 2 hydroxyarchaeol in the sediment interval containing the largest dolomite nodules 18o values of pure aragonite samples and dolomite nodules indicate the precipitation of carbonate close to isotopic equilibrium with seawater and no influence of gas hydrate derived water u th dating of two mdac crusts shows that they formed between 1 61 0 02 and 4 39 1 63 ka bp and between 2 65 0 02 and 4 32 0 08 ka bp we infer both a spatial and temporal change in methane flux and related mdac formation at this seep site these changes might be caused by regional seismic events that can affect pore pressure or re activation of migration pathways thus facilitating fluid flow from deep sources towards the seabed

iron isotope constraints on diagenetic iron cycling in the taixinan seepage area south china sea abstract authigenic pyrite is a common mineral in seepage areas where it is mainly derived from sulfate driven anaerobic oxidation of methane so4 aom however reports on the iron isotopic composition of so4 aom generated pyrite are limited and the mechanisms controlling the fractionation of iron isotopes are insufficiently understood here we present new iron isotope data for pyrite and iron oxides from sediments of the taixinan seepage and gas hydrate bearing area sites hd109 and gmgs2 16 and revisit published data for pyrite from the shenhu area to unravel the impact of so4 aom on the iron isotope composition of pyrite the 56fe values relative to average igneous rock of pyrite were found to vary from 0 86 to 0 56 for site hd109 and from 1 57 to 0 25 for site gmgs2 16 in contrast the iron isotopic compositions of iron oxides from site gmgs2 16 reveal positive values throughout the core spanning from 0 52 to 0 74 in addition the extent of pyritization fepy fehr of the sediment was investigated revealing a variability between 0 01 and 0 29 for hd109 and between 0 00 and 0 36 for gmgs2 16 a previous study on the shenhu seepage area recognized an enrichment of 56fe in pyrite at paleo sulfate methane transition zones smtz which was regarded as a consequence of pronounced so4 aom however peaks in 56fepy values are not observed at paleo smtzs at sites hd109 and gmgs2 16 in this study the negative 56fepy values are likely to reflect the dominance of dissimilatory iron reduction dir during diagenesis in this area in addition for all samples of the taixinan and shenhu areas their 56fepy values and the extent of pyritization a clear positive correlation becomes apparent where both 56fepy values and fepy fehr ratios from the taixinan area are lower hence it can be inferred that the availability of sulfide is among the key factors that affect the iron isotopic composition of pyrite with respect to the taixinan area the low degree of pyritization was apparently insufficient to alter the iron isotopic composition of the iron sources i e iron oxides to a significant degree

u th systematics and ages of authigenic carbonates from hydrate ridge cascadia margin recorders of fluid flow variations uranium u concentrations and activity ratios 234u of authigenic carbonates are sensitive recorders of different fluid compositions at submarine seeps of hydrocarbon rich fluids cold seeps at hydrate ridge off the coast of oregon usa the low u concentrations mean 1 3 0 4 g g and high 234u values 165 317 of gas hydrate carbonates reflect the influence of sedimentary pore water indicating that these carbonates were formed under reducing conditions below or at the seafloor their 230th 234u ages span a time interval from 0 8 to 6 4 ka and cluster around 1 2 and 4 7 ka in contrast chemoherm carbonates precipitate from marine bottom water marked by relatively high u concentrations mean 5 2 0 8 g g and a mean 234u ratio of 166 3 their u isotopes reflect the 234u ratios of the bottom water being enriched in 234u relative to normal seawater simple mass balance calculations based on u concentrations and their corresponding 234u ratios reveal a contribution of about 11 of sedimentary pore water to the bottom water from the u pore water flux and the reconstructed u pore water concentration a mean flow rate of about 147 68 cm a can be estimated 230th 234u ages of chemoherm carbonates range from 7 3 to 267 6 ka 230th 234u ages of two chemoherms alvin and se knoll chemoherm correspond to time intervals of low sealevel stands in marine isotope stages mis 2 4 5 6 7 and 8 this observation indicates that fluid flow at cold seep sites sensitively reflects pressure changes of the hydraulic head in the sediments the 18o pdb ratios of the chemoherm carbonates support the hypothesis of precipitation during glacial times deviations of the chemoherm 18o values from the marine 18o record can be interpreted as to reflect temporally and spatially varying bottom water and or vent fluid temperatures during carbonate precipitation between 2 6 and 8 6 c

interannual variability of the stratospheric circulation in the southern hemisphere the variability from year to year of the seasonal evolution in the southern hemisphere stratosphere over a period of 10 years from 1980 to 1989 is investigated using the global geopotential height derived from the data from the stratospheric sounding unit on board the tiros noaa satellites as a measures of interannual variability the variance of the zonal mean geostrophic wind over the 10 years was calculated for each day although the major warming hardly occurs in the southern hemisphere stratosphere large variances can be observed during the winter and spring the maximum variances appear at low latitudes in late autumn move towards mid latitudes in midwinter and remain near 60 s in spring the seasonal movement of the zonal mean westerly jet in the southern hemisphere stratosphere can be classified into two categories in terms of the location of the maximum westerlies at the 1 mb level in midwinter namely hlj high latitude jet years with maximum westerlies around 50 s llj low latitude jet years with maximum westerlies around 40 s during the late winter the core of the westerly jet moves polewards earlier in hlj years in llj years in association with this earlier movement the growth of the amplitudes of planetary waves 1 and 2 during the period from winter to spring occurs earlier in hlj years than in llj years in autumn however the wave 1 amplitude only for llj years develops vigorously in the stratosphere and even the troposphere before the seasonal movement of the zonal mean westerly jet branches off into the two categories the appearances of hlj and llj years occur in groups of a few years this is quite different from the behaviour of the equatorial quasi biennial oscillation

cold seep driven carbonate deposits at the central american forearc contrasting evolution and timing in escarpment and mound settings continuous surface cores of cold seep carbonates were recovered offshore pacific nicaragua and costa rica from 800 to 1 500 m water depths meteor 66 3 in order to decipher their evolution and methane enriched fluid emanation in contrasting geological settings cores from the mounds iguana perezoso baula v and from the jaco scarp escarpment were used for a multi method approach for both settings aragonite was revealed as dominant authigenic carbonate phase in vein fillings and matrix cementation followed by mg calcite as second most abundant this common precipitation process of caco3 polymorphs could be ascribed as indirectly driven by chemical changes of the advecting pore water due to anaerobic oxidation of methane a more direct influence of seep related microbial activity on the authigenic mineral assemblage in both settings is probably reflected by the observed minor amounts of dolomite and a dolomite like camg carbonate mgco3 42 13c data of jaco scarp samples are significantly lower 43 to 56 pdb than for mound samples 22 to 36 pdb indicating differences in fluid composition and origin noteworthy 18o values of scarp samples correlate most closely with the ocean signature at their time of formation documenting the archive potential a high resolution case study of a mound core implies at least 40 changes in fluid supply within a time interval of approximately 14 ky as most striking difference the age data indicate a late stage downward progressing cementation front for all three mound cap structures approx 2 5 cm ky but a significantly faster upward carbonate buildup in the bulging sediments on top of the scarp environment approx 120 cm ky the latter data set leads to the hypothesis of chemoherm carbonate emplacement in accord with reported sedimentation rates until decompression of the advective fluid system probably caused by the jaco scarp landslide and dating this to approximately 13 000 years ago

glendonites from an early jurassic methane seep climate or methane indicators abstract an early jurassic late pliensbachian section margaritatus to spinatum ammonite zone northeast of cremlingen germany revealed three horizons with abundant glendonites calcite pseudomorphs after ikaite caco3 6h2o as well as authigenic carbonates these pseudomorphs have previously been used as indicators for organic and phosphate rich paleoenvironments with near freezing bottom water temperatures stable isotope measurements clearly show that the ikaite glendonite was precipitated at a methane seep location with methanotrophic sulfate reduction as the triggering geochemical process for ikaite formation at the sulfate methane interface the termination of methane seepage probably led to the disintegration of the primary mineral ikaite and successive pseudomorph formation reconstructed paleo bottom water temperatures ca 10 c from belemnites and ostracods indicate temperatures well above the previously observed range of ikaite stability near freezing raising the question if methane seeps are distinct geochemical sites promoting ikaite formation at higher temperatures