on the relationship between southern ocean overturning and acc transport the eddy field in the southern ocean offsets the impact of strengthening winds on the meridional overturning circulation and antarctic circumpolar current acc transport there is widespread belief that the sensitivities of the overturning and acc transport are dynamically linked with limitation of the acc transport response implying limitation of the overturning response here an idealized numerical model is employed to investigate the response of the large scale circulation in the southern ocean to wind stress perturbations at eddy permitting to eddy resolving scales significant differences are observed between the sensitivities and the resolution dependence of the overturning and acc transport indicating that they are controlled by distinct dynamical mechanisms the modeled overturning is significantly more sensitive to change than the acc transport with the possible implication that the southern ocean overturning may increase in response to future wind stress changes without measurable changes in the acc transport it is hypothesized that the dynamical distinction between the zonal and meridional transport sensitivities is derived from the depth dependence of the extent of cancellation between the ekman and eddy induced transports

residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

origin of trace gases in submarine hydrothermal vents of the kolbeinsey ridge north iceland two hydrothermal fields of the kolbeinsey ridge area north of iceland show vent gas characteristics which can be related to the subsurface conditions helium isotopes r r air 9 8 10 9 indicate a mantle derived origin and can be considered as a mixture of more helium and a deep mantle plume helium component the carbon isotope composition of co2 ranges between 2 4 and 7 8 parts per thousand the less negative delta 13 c co2 values were found at grimsey the data from grimsey are very similar to those previously published and regarded as being characteristic for the icelandic magmatic source however small amounts of biogenic co2 and or subsurface calcite precipitation are responsible for the lighter isotope values of co2 from kolbeinsey ch4 he 3 ratios which are higher than in morb indicate an additional sedimentary methane source for kolbeinsey and grimsey hydrothermal gases the presence of higher hydrocarbons up to butane together with the carbon isotope values of methane delta 13 c 26 1 to 39 8 parts per thousand suggest a probably high mature organic source within thick sediments of the tjornes fracture zone and smaller depressions on the west side of the kolbeinsey ridge crest geochemical characteristics of hydrocarbons present in kr hydrothermal fluids are however typical for a mixed thermogenic and high temperature hydrothermal e g epr type origin moreover it is likely that secondary processes such as bacterial oxidation and thermal cracking determined the geochemical characteristics of the gases c 1999 elsevier science b v all rights reserved

chemical and isotopic investigations into the origin of clay minerals from the galapagos hydrothermal mounds field abstract a dark green authigenic nontronite is the major component of the galapagos hydrothermal mounds field sediments oxygen isotopic compositions of the chemically purified in situ mounds temperatures of up to 15 c assuming an authigenic origin the fe rich montmorillonite that dominates in the noncarbonate clay fraction of the surrounding pelagic ooze has isotopic formation temperatures of 27 to 39 c compared with measured in situ temperatures of ca 3 5 to 6 5 c the higher isotopic formation temperatures calculated for the hydrothermal nontronite suggest either complex patterns of fluid circulation and nontronite precipitation presently within the mounds or a higher thermal history associated with rapid and episodic periods of deposition during the holocene pleistocene the apparent high isotopic temperature of the fe rich montmorillonite may reflect 1 formation under hydrothermal conditions at spreading centers with subsequent dispersal by bottom currents 2 a detrital origin of the mineral or 3 a mixture of authigenic fe montmorillonite and detrital al montmorillonite in this region

the role of mesoscale eddies in the rectification of the southern ocean response to climate change abstract simulations from a fine resolution global coupled model the geophysical fluid dynamics laboratory climate model version 2 4 cm2 4 are presented and the results are compared with a coarse version of the same coupled model cm2 1 under idealized climate change scenarios a particular focus is given to the dynamical response of the southern ocean and the role played by the eddies parameterized or permitted in setting the residual circulation and meridional density structure compared to the case in which eddies are parameterized and consistent with recent observational and idealized modeling studies the eddy permitting integrations of cm2 4 show that eddy activity is greatly energized with increasing mechanical and buoyancy forcings buffering the ocean to atmospheric changes and the magnitude of the residual oceanic circulation response is thus greatly reduced although compensation is far from being perfect changes in poleward eddy fluxes partially compensate for the enhanced equatorward

composition and origin of sediments on the mid oceanic kolbeinsey ridge north of iceland in order to characterize the sediments of the south kolbeinsey ridge and to determine the influence of morpho and hydrodynamic conditions in this area a comprehensive sedimentological investigation was combined with detailed geochemical analyses lithological composition and grain size are mainly controlled by the input from two different sources the submarine active mid ocean ridge and iceland coarse grained volcanic material dominates in the ridge area whereas fine grained detritus from iceland characterizes the adjacent basin further the distribution of these sediments is largely influenced by hydrodynamic conditions and redeposition processes strong bottom water currents indicated by the benthic foraminifer species cibicides lobatulus prevent extensive deposition of fine grained material on the top of the ridge the ridge slope is characterized by redeposited sediments of various grain sizes bulk sediment chemical analyses show element distribution patterns that are strongly correlated with the ratio of volcanic vs detritic particle composition this ratio reflects particle input and distribution processes two element associations are notable elements coupled with 1 ridge derived volcanic particles and 2 the detrital 2 m fraction which reflects weathered material from iceland

on the transport and angular momentum balance of channel models of the antarctic circumpolar current abstract angular momentum balances are discussed both in general as well as in the context of simple channel models of the antarctic circumpolar current acc particular emphasis is placed on the close relationship between the angular momentum balance and the meridional circulation it is found that topographic form drag is established very early in the integration whereas interfacial form drag can take much longer to develop restrictions on the geostrophic portion of the meridional circulation imposed by zonally reconnecting potential vorticity contours in the upper ocean allow derivation of an estimate for the steady state transport the estimate assumes there to be little or no circumpolar flow at great depth an assumption that stems from the belief that the band of zonally reconnecting geostrophic contours in the southern ocean does not extend to the ocean floor the predicted transport is proportional to the strength of the stratification and compares favorably with numerical results in the lite

the effects of mesoscale eddies on the main subtropical thermocline abstract the effects of mesoscale eddies on the main subtropical thermocline are explored using a simply configured wind and buoyancy driven primitive equation numerical model in conjunction with transformed eulerian mean diagnostics and simple scaling ideas and closure schemes if eddies are suppressed by a modest but nonnegligible horizontal diffusion and vertical diffusion is kept realistically small the model thermocline exhibits a familiar two regime structure with an upper advectively dominated ventilated thermocline and a lower advective diffusive internal thermocline and together these compose the main thermocline if the horizontal resolution is sufficiently high and the horizontal diffusivity is sufficiently low then a vigorous mesoscale eddy field emerges in the mixed layer and upper mode water regions the divergent eddy fluxes are manifestly across isopycnals and so have a diabatic effect beneath the mixed layer the mean structure of the upper i e ventilated thermocline is still

the origin of hydrothermal chlorite and anhydrite rich sediments in the middle okinawa trough east china sea abstract during the integrated ocean drilling program iodp expedition 331 five sites were drilled into the iheya north knoll hydrothermal system in the okinawa trough ot a back arc basin characterized by thick terrigenous sediment following up on the previous study by shao et al 2015 we present new mineralogical geochemical and sr nd isotope data to investigate the origin of the hydrothermal sediments and characterize the hydrothermal system the substrate at the iheya north knoll is dominated by pumiceous sediment and other volcanoclastic materials interbedded with hemipelagic terrigenous and biogenous sediments impermeable layers separate the hydrothermal sediments into distinct units with depth that are characterized by various assemblages of alteration materials including polymetallic sulfides sulfates chlorite and kaolinite rich sediments the rare earth elements rees and nd isotope data suggest that the chlorite rich and kaolinite rich layers primarily resulted from the alteration of pumiceous materials in different chemical and physical conditions kaolinite rich sediment likely reflects low ph and low mg concentration fluids while chlorite rich sediment formed from fluids with high ph and increased mg contents likely at higher temperatures the sr isotopic compositions of subsurface anhydrite reflect high seawater hydrothermal fluid ratios in the mid ot hydrothermal area compared with chlorite rich sediments from other sediment covered or felsic hosted hydrothermal systems the chlorite rich sediments in the mid ot are characterized by lower concentrations of al and fe but much higher y zr hf th and rees indicative of the distinct nature of the precursor rocks in this region

seismic hazard in hawaii high rate of large earthquakes and probabilistic ground motion maps the seismic hazard and earthquake occurrence rates in hawaii are locally as high as that near the most hazardous faults elsewhere in the united states we have generated maps of peak ground acceleration pga and spectral acceleration sa at 0 2 0 3 and 1 0 sec 5 critical damping at 2 and 10 exceedance probabilities in 50 years the highest hazard is on the south side of hawaii island as indicated by the m i 7 0 m s 7 2 and m i 7 9 earthquakes which occurred there since 1868 probabilistic values of horizontal pga 2 in 50 years on hawaii s south coast exceed 1 75 g because some large earthquake aftershock zones and the geometry of flank blocks slipping on subhorizontal decollement faults are known we use a combination of spatially uniform sources in active flank blocks and smoothed seismicity in other areas to model seismicity rates of earthquakes are derived from magnitude distributions of the modern 1959 1997 catalog of the hawaiian volcano observatory s seismic network supplemented by the historic 1868 1959 catalog modern magnitudes are m l measured on a wood anderson seismograph or m s historic magnitudes may add m l measured on a milne shaw or bosch omori seismograph or m i derived from calibrated areas of mm intensities active flank areas which by far account for the highest hazard are characterized by distributions with b slopes of about 1 0 below m 5 0 and about 0 6 above m 5 0 the kinked distribution means that large earthquake rates would be grossly underestimated by extrapolating small earthquake rates and that longer catalogs are essential for estimating or verifying the rates of large earthquakes flank earthquakes thus follow a semicharacteristic model which is a combination of background seismicity and an excess number of large earthquakes flank earthquakes are geometrically confined to rupture zones on the volcano flanks by barriers such as rift zones and the seaward edge of the volcano which may be expressed by a magnitude distribution similar to that including characteristic earthquakes the island chain northwest of hawaii island is seismically and volcanically much less active we model its seismic hazard with a combination of a linearly decaying ramp fit to the cataloged seismicity and spatially smoothed seismicity with a smoothing half width of 10 km we use a combination of up to four attenuation relations for each map because for either pga or sa there is no single relation that represents ground motion for all distance and magnitude ranges great slumps and landslides visible on the ocean floor correspond to catastrophes with effective energy magnitudes m e above 8 0 a crude estimate of their frequency suggests that the probabilistic earthquake hazard is at least an order of magnitude higher for flank earthquakes than that from submarine slumps

eddy saturation of equilibrated circumpolar currents abstractthis study uses a sector configuration of an ocean general circulation model to examine the sensitivity of circumpolar transport and meridional overturning to changes in southern ocean wind stress and global diapycnal mixing at eddy permitting and finer resolution the sensitivity of circumpolar transport to forcing magnitude is drastically reduced at sufficiently high resolution there is little or no sensitivity of circumpolar transport to wind stress even in the limit of no wind in contrast the meridional overturning circulation continues to vary with southern ocean wind stress but with reduced sensitivity in the limit of high wind stress both the circumpolar transport and meridional overturning continue to vary with diapycnal diffusivity at all model resolutions the circumpolar transport becomes less sensitive to changes in diapycnal diffusivity at higher resolution although sensitivity always remains in contrast the overturning circulation is more sensitive to change in diapycnal

response to increasing southern hemisphere winds in ccsm4 abstractresults from two perturbation experiments using the community climate system model version 4 where the southern hemisphere zonal wind stress is increased are described it is shown that the ocean response is in accord with experiments using much higher resolution ocean models that do not use an eddy parameterization the key to obtaining an appropriate response in the coarse resolution climate model is to specify a variable coefficient in the gent and mcwilliams eddy parameterization rather than a constant value this result contrasts with several recent papers that have suggested that coarse resolution climate models cannot obtain an appropriate response

what sets the strength of the middepth stratification and overturning circulation in eddying ocean models abstract the processes maintaining stratification in the oceanic middepth between approximately 1000 and 3000 m are explored using an eddy resolving general circulation model composed of a two hemisphere semienclosed basin with a zonal reentrant channel in the southernmost eighth of the domain the middepth region lies below the wind driven main thermocline but above the diffusively driven abyssal ocean here it is argued that middepth stratification is determined primarily in the model s antarctic circumpolar current competition between mean and eddy overturning in the channel leads to steeper isotherms and thus deeper stratification throughout the basin than would exist without the channel isotherms that outcrop only in the channel are nearly horizontal in the semienclosed portion of the domain whereas isotherms that also outcrop in the northern hemisphere deviate from horizontal and are accompanied by geostrophically balanced meridional transport a northern source of deep water water with temp

numerical modeling of the global semidiurnal tide in the present day and in the last glacial maximum 1 a hydrodynamic model incorporating a self consistent treatment of ocean self attraction and loading sal and a physically based parameterization of internal tide it drag is used to assess how accurately barotropic tides can be modeled without benefit of data and to explore tidal energetics in the last glacial maximum lgm m2 solutions computed at high resolution with present day bathymetry agree with estimates of elevations from satellite altimetry within 5 cm rms in the open ocean this accuracy and agreement with atlimetric estimates of energy dissipation are achieved only when sal and it drag are included in the model solutions are sensitive to perturbations to bathymetry and inaccuracies in available global databases probably account for much of the remaining error in modeled elevations the 100 m drop in sea level during the lgm results in significant changes in modeled m2 tides with some amplitudes in the north atlantic increasing by factors of 2 or more dissipation is also significantly changed by the drop in sea level if it drag estimated for the modern ocean is assumed dissipation increases by about 50 globally and almost triples in the deep ocean however it drag depends on ocean stratification which is poorly known for the lgm tests with modified it drag suggest that the tendency to a global increase in dissipation is a robust result but details are sensitive to stratification significant uncertainties about paleotides thus remain even in this comparatively simple case where bathymetry is well constrained

late pleistocene eolian sediments related to pyroclastic eruptions of mauna kea volcano hawaii abstract loess and dune sands that mantle volcanic rocks on the northwest flank of mauna kea volcano consist predominantly of fine grained pyroclasts of the alkalic laupahoehoe volcanics produced by explosive eruptions the loess is divided into lower and upper units separated by a well developed paleosol while older and younger dune sands are separated by loess four interstratified tephra marker horizons aid in regional stratigraphic correlation radiocarbon ages of charcoal fragments within the loess u series ages of rhizoliths in the dune sand and k ar ages and relative stratigraphic positions of lava flows provide a stratigraphic and temporal framework the lower loess overlies lava flows less than 103 000 10 000 k ar yr old and 14 c dates from the paleosol developed at its top average ca 48 000 yr loess separating the dune sand units ranges from ca 38 000 to 25 000 14 c yr old the youngest ages from the upper loess are 17 000 18 000 14 c yr b p dips of sand dune foreset strata isopachs on the upper loess and reconstructed isopachs representing cumulative thickness of tephra associated with late pleistocene pyroclastic eruptions suggest that vents upslope upwind from the sand dunes were the primary source of the eolian sediments average paleowind directions during the eruptive interval ca 50 000 15 000 yr b p inferred from cinder cone asymmetry distribution of tephra units orientation of dune foreset strata and the regional pattern of loess isopachs suggest that mauna kea has remained within the trade wind belt since before the last glaciation

where do winds drive the antarctic circumpolar current the strength of the antarctic circumpolar current acc is believed to depend on the westerly wind stress blowing over the southern ocean although the exact relationship between winds and circumpolar transport is yet to be determined here we show based on theoretical arguments and a hierarchy of numerical modeling experiments that the global pycnocline depth and the baroclinic acc transport are set by an integral measure of the wind stress over the path of the acc taking into account its northward deflection our results assume that the mesoscale eddy diffusivity is independent of the mean flow while the relationship between wind stress and acc transport will be more complicated in an eddy saturated regime our conclusion that the acc is driven by winds over the circumpolar streamlines is likely to be robust

relation of landslides triggered by the kiholo bay earthquake to modeled ground motion abstract the 2006 kiholo bay hawaii earthquake triggered high concentrations of rock falls and slides in the steep canyons of the kohala mountains along the north coast of hawaii within these mountains and canyons a complex distribution of landslides was triggered by the earthquake shaking in parts of the area landslides were preferentially located on east facing slopes whereas in other parts of the canyons no systematic pattern prevailed with respect to slope aspect or vertical position on the slopes the geology within the canyons is homogeneous so we hypothesize that the variable landslide distribution is the result of localized variation in ground shaking therefore we used a state of the art high resolution ground motion simulation model to see if it could reproduce the landslide distribution patterns we used a 3d finite element analysis to model earthquake shaking using a 10 m digital elevation model and slip on a finite fault model constructed from teleseismic records of the mainshock ground velocity time histories were calculated up to a frequency of 5 hz dynamic shear strain also was calculated and compared with the landslide distribution results were mixed for the velocity simulations with some areas showing correlation of landslide locations with peak modeled ground motions but many other areas showing no such correlation results were much improved for the comparison with dynamic shear strain this suggests that 1 rock falls and slides are possibly triggered by higher frequency ground motions velocities than those in our simulations 2 the ground motion velocity model needs more refinement or 3 dynamic shear strain may be a more fundamental measurement of the decoupling process of slope materials during seismic shaking

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

hydrothermally precipitated mixed layer illite smectite in recent massive sulfide deposits from the sea floor mixed layer illite smectite i s in recent massive sulfide deposits from a seamount near the east pacific rise has been studied by x ray powder diffraction xrd and scanning and transmission electron microscopy sem tem the i s fills pore space between quartz and sulfides and xrd and tem analyses indicate that the i s contains 25 45 smectite with r1 type ordering isisis microprobe and analytical electron microscope analyses indicate a rectorite like composition k being the dominant interlayer cation the occurrence of the i s within a hydrothermally precipitated sulfide deposit the pore filling texture and the internal structure of the i s are all consistent with direct precipitation from hydrothermal solutions direct precipitation of i s from solution has two important implications first some sericite in ancient volcanogenic massive sulfide deposits may have similarly originated as hydrothermal precipitates rather than as alteration products with implications for mobility and transport of al second direct precipitation of r1 ordered i s from fluid implies that during diagenetic evolution of smectite to illite the sequence of smectite random i s ordered i s illite may not be followed

analysis of the attenuation of strong ground motion on the island of hawaii abstract we develop a horizontal peak ground acceleration pga predictive equation for the island of hawaii by applying the joyner and boore 1993 1994 two stage regression method to a data set that consists of 51 pga from 22 events magnitudes vary from 4 0 to 7 2 and event depths vary from 4 to 14 km the resulting equation is log 10 p g a 0 518 0 387 m 6 log 10 r 0 00256 r 0 335 s where pga is measured in units of g m is magnitude r d 2 11 29 2 1 2 and s is 0 for lava sites and 1 at ash sites the distance parameter d is the closest distance from the recording site to the surface projection of the fault rupture area and varies from 0 to 88 km for the hawaii pga data set we find that the attenuation of high frequency strong ground motion is significantly greater than a previous relationship used for the island of hawaii the ash site coefficient s which represents accelerometer sites with shear wave velocities that vary from 60 to 200 m sec is generally larger than the soil site coefficients in other attenuation relationships

first observations of high temperature submarine hydrothermal vents and massive anhydrite deposits off the north coast of iceland high temperature 250 c hydrothermal vents and massive anhydrite deposits have been found in a shallow water sediment filled graben near 66 36 n in the tjornes fracture zone north of iceland the site is located about 30 km offshore near the small island of grimsey the main vent field occurs at a depth of 400 m and consists of about 20 large diameter up to 10 m mounds and 1 3 m chimneys and spires of anhydrite and talc a north south alignment of the mounds over a 1 km strike length of the valley floor suggests that their distribution is controlled by a buried fault widespread shimmering water and extensive white patches of anhydrite in the sediment between the mounds indicates that the entire 1 km2 area occupied by the vents is thermally active a 2 man research submersible jago was used to map the area and to sample vent waters gases and chimneys actively boiling hydrothermal vents occur on most of the mounds and extensive two phase venting indicates that the field is underlain by a large boiling zone 200 300 m the presence of boiling fluids in shallow aquifers beneath the deposits was confirmed by sediment coring the highest temperature pore fluids were encountered in talc and anhydrite rich sedimentary layers that occur up to 7 m below the mounds baked muds underlie the talc and anhydrite layers and pyrite is common in stockwork like fractures and veins in the hydrothermally altered sediments however massive sulfides pyrite marcasite crusts were found in only one relict mound subseafloor boiling has likely affected the metal carrying capacity of the hydrothermal fluids and deposition of sulfides may be occurring at greater depth although the mounds and chimneys at grimsey resemble other deposits at sedimented ridges e g middle valley escanaba trough guaymas basin the shallow water setting and extensive boiling of the hydrothermal fluids represent a distinctive new type of seafloor hydrothermal system

nontronite from a low temperature hydrothermal system on the juan de fuca ridge abstract a deposit of fe rich al poor hydrothermal nontronite was recovered from the juan de fuca ridge analyses show the deposit to be mineralogically and chemically similar to nontronite described at other oceanic localities the deposit is located near the tip of a propagating segment of the juan de fuca ridge rare earth elements and sr isotopes indicate that the nontronite precipitated from seawater a formation temperature of 57 c is suggested by oxygen isotopic composition the low temperature nontronite deposits apparently form from newly established hydrothermal systems associated with the propagating rift segment more mature hydrothermal systems that deposit sulfide on the seafloor may develop from these low temperature systems

mineralogy and geochemistry of clay samples from active hydrothermal vents off the north coast of iceland active hydrothermal vent sites were sampled during 1997 in a series of submersible dives at the active grimsey ghf and kolbeinsey khf hydrothermal fields off the north coast of iceland this study focuses on secondary clay minerals which were formed in two different settings the ghf is characterized by the presence of clay minerals precipitated within active chimneys by contrast the khf is characterized by the presence of secondary clay minerals which are the products of hydrothermal alteration of lava fragments based on xrd electron microprobe and icp ms analyses the dominant clay mineral in both hydrothermal fields is saponite mg rich smectite chlorite and chlorite smectite mixed layer minerals also occur at the khf the mg rich nature of saponite from the ghf chimneys suggests intense mg metasomatism in the mixing zone where hydrothermal fluids interact with seawater at temperatures of 250 c saponite formation resulted in the additional uptake of cu zn and pb enrichment in ba is evident in the almost pure saponite from the khf based on oxygen isotope data the saponite formation at the khf occurred at 148 c which is close to the maximum measured fluid temperature of 131 c in this field

interdecadal variability of the southern ocean the intrinsic variability of the antarctic circumpolar current is investigated using an idealized wind driven model the model uses three quasigeostrophic layers with steady wind stress forcing and no diabatic effects despite the idealized nature of the model the simulations display a robust mode of low frequency variability in the flow it is demonstrated that this variability is dependent upon the explicit simulation of the dynamics of mesoscale eddies as such the variability is sensitive to stratification horizontal viscosity bottom stress and topography the energetic balance of the variability is diagnosed and a driving mechanism is proposed that involves positive feedback between the generation of eddies through baroclinic instability and the dynamics of the mean circulation

tidal mixing and the meridional overturning circulation from the last glacial maximum 1 using a global tidal model it is shown that the supply of tidal energy to the deep ocean was larger during the last glacial maximum lgm 18 000 22 000 years bp the results were used to modify the rate of vertical mixing in a coupled ocean atmosphere model set up for the present and lgm oceans the increased levels of mechanical energy during the lgm were countered by a fresher upper north atlantic which led to a reduced circulation and deep water formation in spite of a trebling of the implicit mixing energy this identifies the significance of accurately representing vertical mixing in climate models to estimate the recovery time scales and timings of rapid catastrophic paleoceanographic events from the estimated levels of implicit energy in the vertical mixing scheme an amendment to diffusivity based mixing schemes is suggested

lunar degree 2 potential love number determination from satellite tracking data 1 the lunar potential love number k2 has been determined using available satellite tracking data coming from the lunar orbiters i v the apollo 15 and 16 subsatellites clementine and lunar prospector some smart 1 spacecraft tracking data are also included a previous determination using spacecraft data reported k2 0 026 0 003 ten times the formal error whereas lunar laser ranging results report lower values around k2 0 0210 0 0025 the best estimate obtained here results in k2 0 0213 0 0075 ten times the formal error as well closer in agreement with the lunar laser ranging values

seafloor hydrothermal clay alteration at jade in the back arc okinawa trough mineralogy geochemistry and isotope characteristics seafloor hydrothermal activity at jade has resulted in extensive alteration of the host epiclastic sediments and pumiceous tuffs forming mica kaolins kaolinite and halloysite mg rich chlorite talc montmorillonite and a mixed layer mineral of dioctahedral chlorite and montmorillonite chl mont clay mineral assemblages show a vertical variation which reflects variable amounts of cold seawater incorporated into hot hydrothermal fluids in subsurface sediments and tuff however mixing alone cannot explain the occurrence of abundant kaolin minerals at jade the formation of kaolin minerals requires much more acidic fluid than expected from simple mixing of hydrothermal fluids and cold seawater low ph values are likely attained by oxidation of h2s either dissolved in the hydrothermal fluid or released from the fluid during decompression the fluid reaching the seafloor is discharged into cold seawater which caused precipitation of sulfides close to vents and native sulfur and barite at the margins of the vent areas halloysite barite and anhydrite show sr isotope compositions similar to marine sr indicating the derivation of marine sr directly from seawater or by the dissolution of calcareous nannoplanktons the isotopic compositions of kaolinite 18o 7 4 d 23 chl mont 18o 7 0 d 32 and mica 18o 5 4 to 9 9 d 30 to 26 suggest fluids of a heated seawater origin the o isotopic data yielded formation temperatures of 170 c for kaolinite 61 to 110 c for halloysite and 145 to 238 c for mica barite 34s values 21 0 to 22 5 are very similar to the marine sulfate value confirming that the barite formation took place due to mixing of ba bearing hydrothermal fluids and sulfate rich seawater native sulfur shows a large variation in 34s in one hand specimen probably because of rapid disequilibrium precipitation of s during fluid exhalation on the seafloor sulfur in hydrothermal fluids is usually consumed to form metal sulfides therefore abundant native sulfur at jade suggests high h2s metals ratios of the hydrothermal fluids the alteration assemblages and isotopic data of hydrothermal minerals from jade are very similar to those of kuroko type barite deposits of middle miocene age which formed from fluids of high s metals ratios at less than 200 c at jade there is only one black smoker actively discharging high temperature 320 c fluid but there are many fossil sulfide chimneys and mounds in the area the mineralogy and high au and cu in these precipitates suggest highly metalliferous hydrothermal activity in the past these activities likely resulted in discharge of hydrothermal plumes and fall outs of sulfides and sulfates on the seafloor these fall outs were incorporated in sediments far from the vent areas they are now recorded as high metal contents in sediments with no petrographic and mineralogical evidence of in situ hydrothermal activity some are high as 8 100 ppm for cu 12 500 ppm for zn 1 000 ppm for as 100 ppm for ag and 21 000 ppm for pb detrital grains of montmorillonite in such sediments are coated with fe oxyhydroxides during the suspension in seawater before settling on the seafloor the depths of such metal anomalies in sediments suggest high levels of metalliferous hydrothermal activities from 1 800 to 300 ybp

reconciling theories of a mechanically driven meridional overturning circulation with thermohaline forcing and multiple equilibria it has recently been suggested that the structure and strength of the meridional overturning circulation in the global ocean is governed by the input of mechanical energy to the system by winds and tides however it is not clear how this suggestion relates to the existence of multiple equilibria of the meridional overturning circulation which depends on thermohaline feedbacks and is more consistent with a buoyancy driven view of the circulation both theories have been illustrated by box models in the past stommel in tellus 13 224 230 1961 gnanadesikan in science 283 2077 2079 1999 here we incorporate these two theories into a single box model in an attempt to reconcile the roles of mechanical and buoyancy forcing in driving the meridional overturning circulation the box model has two equilibrium solutions one with sinking at high northern latitudes as in the present day atlantic and one without the circulation is mechanically driven but the northern sinking can be thought of as a release valve which acts as a sink of potential energy when the surface water at high northern latitudes is dense enough to convect while the source of energy comes from mechanical forcing the presence or otherwise of multiple equilibria is therefore determined by thermohaline feedbacks in some areas of parameter space an oscillation between the model s two circulation regimes occurs reminiscent of a bipolar seesaw

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

widespread intense turbulent mixing in the southern ocean observations of internal wave velocity fluctuations show that enhanced turbulent mixing over rough topography in the southern ocean is remarkably intense and widespread mixing rates exceeding background values by a factor of 10 to 1000 are common above complex bathymetry over a distance of 2000 to 3000 kilometers at depths greater than 500 to 1000 meters this suggests that turbulent mixing in the southern ocean may contribute crucially to driving the upward transport of water closing the ocean s meridional overturning circulation and thus needs to be represented in numerical simulations of the global ocean circulation and the spreading of biogeochemical tracers

last glacial maximum and holocene climate in ccsm3 abstract the climate sensitivity of the community climate system model version 3 ccsm3 is studied for two past climate forcings the last glacial maximum lgm and the mid holocene the lgm approximately 21 000 yr ago is a glacial period with large changes in the greenhouse gases sea level and ice sheets the mid holocene approximately 6000 yr ago occurred during the current interglacial with primary changes in the seasonal solar irradiance the lgm ccsm3 simulation has a global cooling of 4 5 c compared to preindustrial pi conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at lgm tropical sea surface temperature sst cools by 1 7 c and tropical land temperature cools by 2 6 c on average simulations with the ccsm3 slab ocean model suggest that about half of the global cooling is explained by the reduced lgm concentration of atmospheric co2 50 of present day concentrations there is an increase in the antarctic circumpolar current an

origin of fluids and anhydrite precipitation in the sediment hosted grimsey hydrothermal field north of iceland the sediment hosted grimsey hydrothermal field is situated in the tjornes fracture zone tfz which represents the transition from northern iceland to the southern kolbeinsey ridge the tfz is characterized by a ridge jump of 75 km causing widespread extension of the oceanic crust in this area hydrothermal activity occurs in the grimsey field in a 300 m 1000 m large area at a water depth of 400 m active and inactive anhydrite chimneys up to 3 meters high and hydrothermal anhydrite mounds are typical for this field clear metal depleted up to 250 c hydrothermal fluids are venting from the active chimneys anhydrite samples collected from the grimsey field average 21 6 wt ca 1475 ppm sr and 3 47 wt mg the average molar sr ca ratio is 3 3 10 3 sulfur isotopes of anhydrite have typical seawater values of 22 0 7 34s indicating a seawater source for so42 strontium isotopic ratios average 0 70662 0 00033 suggesting the precipitation of anhydrite from a hydrothermal fluid seawater mixture the endmember of the venting hydrothermal fluids calculated on a mg zero basis contains 59 8 mol kg sr 13 2 mmol kg ca and a 87sr 86sr ratio of 0 70634 the average sr ca partition coefficient between the hydrothermal fluids and anhydrite of about 0 67 implies precipitation from a non evolved fluid a model for fluid evolution in the grimsey hydrothermal field suggests mixing of upwelling hydrothermal fluids with shallowly circulating seawater before and during mixing seawater is heated to 200 250 c which causes anhydrite precipitation and probably the formation of an anhydrite rich zone beneath the seafloor

the role of mesoscale eddies in the remote oceanic response to altered southern hemisphere winds abstract it has been suggested that a strengthening of the southern hemisphere winds would induce a more vigorous overturning through an increased northward ekman flux bringing more light waters into the oceanic basins and enhancing the upwelling of north atlantic deep water in the southern ocean thereby increasing ocean ventilation simulations from a coarse and a fine resolution version of a coupled model subject to idealized wind stress changes in the southern ocean are presented in the fine resolution eddy permitting model changes in poleward eddy fluxes largely compensate for the enhanced equatorward ekman transport in the southern ocean as a consequence northward transport of light waters pycnocline depth northern hemisphere overturning and southern ocean upwelling anomalies are much reduced compared with simulations in the coarse resolution model with parameterized eddies these results suggest a relatively weak sensitivity of present day global ocean overturning circulation to the proj

hydrothermal clay mineral formation of east pacific rise and bauer basin sediments samples of surface metalliferous sediment recovered from the crest of the east pacific rise at 6 s and 10 s latitudes and from the adjacent bauer basin are characterized by an authigenically formed fe rich montmorillonite that dominates the non carbonate mineralogy of the clay fraction 2 m oxygen isotopic formation temperatures indicate that the fe montmorillonites are created by low temperature hydrothermal processes 30 50 c in the 10 s region of the east pacific rise and bauer basin possibly as a result of cooling and oxidation of unstable high temperature 380 30 c sulfide assemblages or as a result of the percolation of hydrothermally altered seawater solutions through underlying basalt and sediments the widespread sedimentation of the clay mineral is suggested to be caused by colloidal transport possibly as a result of erosion of hydrothermal mounds by bottom currents hydrothermal fe montmorillonite nontronite formation may act as a direct and significant oceanic sink for si and fe released by the high temperature hydrothermal alteration of basalt at ocean spreading centers

location of potential energy sources and the export of dense water from the atlantic ocean the export of dense water from the atlantic and into the indo pacific oceans and heat transport in the opposite direction is traditionally attributed to the fact that dense water forms in the atlantic but not the pacific evidence from two models presented here suggests this is an incomplete explanation it is found that dense water export from the atlantic depends on a poten tial energy pe sink associated with dense water downwelling in the at lantic that is not balanced by a pe source within the atlantic therefore increasing the atlantic pe source reduces dense atlantic water export tide models suggest that the atlantic pe source may have been much higher at the last glacial maximum this could have significantly reduced dense wa ter export from the atlantic ocean even if atlantic overturning was stronger than it is today

experimental study of the hydrothermal formation of kaolinite kaolinite was hydrothermally precipitated starting from amorphous aluminosilicates with si al ratio from 1 8 to 0 76 at temperatures of 150 175 200 225 and 250 c at time periods varying from 6 h to 60 days the solutions were analysed for ph si al and k and their saturation state was calculated by using the computer program solmineq 88 the solids were studied by surface area xrd and dta tg analyses kaolinite was the only crystalline phase found in the products of the runs and its formation and crystallinity depended on time temperature and si al ratio of the starting material the kaolinite yield increased as starting material was aged for longer times products synthesized at higher temperature contain more kaolinite which was more crystalline than in the experiments carried out at lower temperature the gel with si al 0 99 produced the most disordered kaolinite and better crystallinity was obtained from products richest in al or si the process of kaolinite formation was the result of two stages during the first one aggregates of domains having a kaolinite like structure were formed the second stage corresponded to the formation of hexagonally outlined platy crystals the formation rates indicated that the first stage was approximately one order of magnitude faster than the second stage with average activation energies of 82 5 kj mol 1 and 71 5 kj mol 1 respectively si al ratio of the starting material exerted only a slight influence on the activation energies the precipitation rates obtained for the second stage were consistent with literature data and may be considered precipitation rates of kaolinite in hydrothermal environments

wind driven flow over topography in a zonal β plane channel a quasi geostrophic model of the antarctic circumpolar current abstract the paper gives a detailed account of the dynamical balance of a wind driven zonally unbounded flow over topography the problem is investigated with a quasi geostrophic plane channel with two layers and eddy resolution the channel has a width of 1500 km and a zonal periodicity of 4000 km apart from the dimensions the model structure is similar to the one used by mcwilliams et al the experiments with this model address the problem of the relative role of transient and standing eddies as well as bottom friction and topographic form stress in the balance of a current driven by a steady surface windstress the response of the system is investigated for different values of the friction parameter and various locations of topographic obstacles in the bottom layer of the channel the principal momentum balance emerging from these experiments supports the concept of munk and palmen for the dynamics of the antarctic circumpolar current which proposes that the momentum input by windstress is transfe

global abyssal mixing inferred from lowered adcp shear and ctd strain profiles abstract internal wave wave interaction theories and observations support a parameterization for the turbulent dissipation rate e and eddy diffusivity k that depends on internal wave shear vz2 and strain z2 variances its latest incarnation is applied to about 3500 lowered adcp ctd profiles from the indian pacific north atlantic and southern oceans inferred diffusivities k are functions of latitude and depth ranging from 0 03 10 4 m2 s 1 within 2 of the equator to 0 4 0 5 10 4 m2 s 1 at 50 70 diffusivities k also increase with depth in tropical and subtropical waters diffusivities below 4500 m depth exhibit a peak of 0 7 10 4 m2 s 1 between 20 and 30 latitudes where semidiurnal parametric subharmonic instability is expected to be active turbulence is highly heterogeneous though the bulk of the vertically integrated dissipation e is contributed from the main pycnocline hotspots in e show some correlation with small scale bottom roughness and near bottom flow at sites where st

simulated changes in the extratropical southern hemisphere winds and currents 1 the results from 12 global climate models show a remarkably consistent strengthening and poleward shifting of the zonal wind stress through the 20th and 21st centuries at extratropical southern hemisphere latitudes changes in the zonal circulation of the ocean in the region are broadly consistent with the changes in zonal wind stress in particular the climate models simulate a strengthening and a poleward shift of the antarctic circumpolar current the strengthening of the zonal wind stress also results in intensifying northward ekman transport across the antarctic circumpolar current which in the unblocked latitudes of drake passage implies increasing southward geostrophic transport in the ocean below about 2000 m zonal wind stress changes such as these may be expected to enhance the mesoscale eddy activity in the southern ocean

isopycnal averaging and the residual mean circulation abstract the zonally averaged circulation in the atmosphere or ocean can be misleading if the averaging is performed at constant height in the ocean there is apparently anomalously large diapycnal motion forming the so called deacon cell the atmospheric equivalents are the ferrel cells there are two zonal averaging techniques commonly used to avoid these spurious cells one involves averaging at constant density and this technique has been used in both fluids the other technique which has so far been applied only in the atmosphere involves taking into account perturbation correlation terms to form the residual mean circulation using a taylor series expansion we show that these apparently dissimilar techniques are formally equivalent at leading order in perturbation amplitude the equivalence is demonstrated using output from the fram southern ocean numerical model

basin and channel contributions to a model antarctic circumpolar current the idea that basinlike dynamics may play a major role in determining the antarctic circumpolar current acc transport is revisited a simple analytic model is developed to describe the relationship between the wind stress and transport at very low wind stress a nonzero minimum is predicted this is followed by two distinct dynamical regimes for stronger forcing 1 a stommel regime in which transport increases linearly with forcing strength and 2 a saturation regime in which the transport levels off the baroclinic structure of the sverdrup flux into the drake passage latitude band is central to the analytic model and the geometry of characteristics or geostrophic contours is key to predicting the transition between the two regimes a robustness analysis is performed using an eddy permitting quasigeostrophic model in idealized geometries many simulations were carried out in large domains across a range of forcing strengths the simulations agree qualitatively with the analytic model with two main discrepancies being related to zonal jet structures and to a western boundary inertial recirculation eddy fluxes associated with zonal jets modify the baroclinic structure and lower the saturation transport value inertial effects increase the transport although this effect is mainly limited to smaller domains

occurrence of kaolinite and mixed layer kaolinite smectite in hydrothermal sediments of grimsey graben tjornes fracture zone north of iceland the sediments at a site situated among high temperature vents in the grimsey graben tjornes fracture zone north of iceland exhibit features of strong hydrothermal alteration 1 almost total dissolution of the volcaniclastic material composing the background sediment 2 sulfate and sulfide precipitation 3 kaolinitisation smectite precipitated in the shallowest sediment is gradually replaced downward by mixed layer kaolinite smectite and pure well crystallised kaolinite the kaolinite smectite is interstratified with up to 10 swelling smectitic layers according to the oxygen isotope composition kaolinite smectite mixed layer mineral most likely formed at temperatures near 160 degrees c the vertical sequence kaolinite kaolinite smectite smectite as well as the distinct zonation across the kaolinitic veins almost pure kaolinite in the central zone and kaolinite smectite along the rim suggest hydrothermal transformation of initially formed smectite kaolinite smectite kaolinite most probably this conversion occurred in an evolving from alkaline to slightly acidic hydrothermal environment c 2004 elsevier b v all rights reserved

hydrothermal alteration of a 1 km section through the upper oceanic crust deep sea drilling project hole 504b mineralogy chemistry and evolution of seawater basalt interactions deep sea drilling project hole 504b penetrates 1076 m into oceanic layer 2 and is the first hole to pass through the transition from pillow basalts altered at low temperatures into hydrothermally metamorphosed sheeted dikes alteration of the crust at site 504 occurred in four stages related to the movement of the crust away from the spreading axis 1 dikes reacted with seawater 200 300 c in the upwelling zone of an axial convection cell at the spreading axis resulting in the formation of greenschist facies parageneses in veins and host rocks mixing of the upwelling hydrothermal fluids with seawater circulating in the overlying more permeable pillow section occurred in the upper part of the lithologic transition zone causing a steep temperature gradient at the base of the pillow section secondary minerals formed in the lower pillow section from the resultant reducing mixed fluids at temperatures of around 100 c at the same time the initial effects of seafloor weathering began in the upper 320 m of the pillow section at low temperatures 50 c and under conditions of open circulation of oxidizing seawater 2 following refracturing of the dikes a second stage of axial upwelling occurred hydrothermal fluids 200 380 c were probably similar to those presently sampled from spreading ridges on the seafloor mixing of these fluids with seawater in the lithologic transition zone caused deposition of quartz epidote and sulfides in veins and formation of a sulfide rich stockworklike zone within this transition zone alteration of the pillow section proceeded under the prior conditions with the effects of seafloor weathering extending progressively downward into the crust 3 seawater recharge penetrated to depths of at least 1075 5 m subbasement and deposited anhydrite locally in veins 4 off axis alteration of the dikes was characterized by formation of zeolites calcite and prehnite in veins and host rocks from more highly evolved and lower temperature 100 250 c fluids alteration in the upper pillow section evolved from seafloor weathering conditions to more reducing and rock dominated as cracks in the basalt were sealed with secondary minerals and the basement was covered with a layer of sediment zeolites and calcite were the last phases to form throughout the pillow section sealing of the crust to convective cooling also allowed conductive reheating of the crust from below calculations of seawater crustal chemical fluxes from whole rock data are complicated by the low recovery and heterogeneity of alteration effects but indicate that basalt seawater interactions are a sink for seawater mg and k and a source for si and ca

the deacon cell and the other meridional cells of the southern ocean abstract the meridional circulation cells of the southern ocean are investigated using the results from a fine resolution primitive equation model zonal integration along depth levels shows the classical series of meridional cells but integration along density layers shows a number of differences including the virtual disappearance of the deacon cell to investigate the differences the meridional transport is calculated as a function of both density and depth the results show that the deacon cell is associated with systematic changes in the depth of density surfaces between the western boundary current region off south america and the return flow in the interior of the ocean water flowing on each density surface produces a meridional cell with a vertical excursion of a few hundred meters thew cells combine without water crossing density surfaces to produce a single integrated deacon cell extending from the surface to below 2000 m the results also show that at each latitude water on each of the

the response of southern ocean eddies to increased midlatitude westerlies a non eddy resolving model study 1 the midlatitude westerlies of the southern hemisphere have intensified since the 1970s non eddy resolving general circulation models respond to such wind intensification with steeper isopycnals a faster antarctic circumpolar current acc and a stronger atlantic meridional overturning circulation amoc however hydrographic observations show little change in the slope of the southern ocean isopycnals over the past 40 years this insensitivity seems to result from a compensating mechanism whereby an initial increase in the slope of the isopycnals causes eddy activity to intensify and forces the isopycnal slopes down climate models do not yet resolve ocean eddies and the eddy parameterizations included in them do not capture well the compensation mechanism mentioned above we present simulations with a non eddy resolving model incorporating an eddy parameterization in which eddy compensation is greatly enhanced by the use of a non constant spatially varying thickness diffusivity the sensitivity of the simulated acc and amoc to increased southern hemisphere westerlies is greatly reduced compared to simulations using constant and uniform diffusivities

remote forcing of the antarctic circumpolar current by diapycnal mixing 1 we show that diapycnal mixing can drive a significant antarctic circumpolar current acc volume transport even when the mixing is located remotely in northern hemisphere ocean basins in the case of remote forcing the globally averaged diapycnal mixing coefficient is the important parameter this result is anticipated from theoretical arguments and demonstrated in a global ocean circulation model the impact of enhanced diapycnal mixing on the acc during glacial periods is discussed

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode 1 we present the first direct evidence that interannual changes in ocean transport through drake passage are forced by variability in the southern annular mode sam this evidence is derived from two decades 1980s and 1990s of subsurface pressure measurements from the tide gauge at faraday station western antarctic peninsula combined with the output of an ocean general circulation model in recent decades the sam has moved toward a higher index state stronger circumpolar winds this trend is not simply monotonic but is the product of a long term change in the seasonality of the sam whilst we cannot address directly the effect of the long term trend on circumpolar transport bottom pressure data from drake passage during the 1990s demonstrate that ocean transport showed the same changes in seasonality as did the sam this offers a mechanism for atmospheric climate change to influence directly the largescale ocean circulation indexterms 4207 oceanography general arctic and antarctic oceanography 4215 oceanography general climate and interannual variability 3309 4532 oceanography physical general circulation 1635 global change oceans 4203 4556 oceanography physical sea level variations citation meredith m p p l woodworth c w hughes and v stepanov 2004 changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode geophys res lett 31 l21305 doi 10 1029 2004gl021169

influence of wind stress wind stress curl and bottom friction on the transport of a model antarctic circumpolar current abstracteddy permitting simulations of a wind driven quasigeostrophic model in an idealized southern ocean setting are used to attempt to describe what sets the wind driven circumpolar transport of the antarctic circumpolar current acc for weak forcing the transport is well described as a linear sum of channel and basin components the authors main focus is on stronger forcing in this regime an eddy driven recirculation appears in the abyssal layer and all time mean circumpolar streamlines are found to stem from a sverdrup like interior the sverdrup flux into drake passage latitudes can then be thought of as the sum of one part that feeds the circumpolar current and another that is associated with the recirculation the relative fractions of this partitioning depend on the bottom drag the midchannel wind stress and the wind stress curl increasing the strength of the bottom drag reduces the recirculation and increases circumpolar transport increasing a zero curl eastward wind stress reduces th

a theory of the interhemispheric meridional overturning circulation and associated stratification abstracta quantitative theoretical model of the meridional overturning circulation and associated deep stratification in an interhemispheric single basin ocean with a circumpolar channel is presented the theory includes the effects of wind eddies and diapycnal mixing and predicts the deep stratification and overturning streamfunction in terms of the surface forcing and other parameters of the problem it relies on a matching among three regions the circumpolar channel at high southern latitudes a region of isopycnal outcrop at high northern latitudes and the ocean basin between the theory describes both the middepth and abyssal cells of a circulation representing north atlantic deep water and antarctic bottom water it suggests that although the strength of the middepth overturning cell is primarily set by the wind stress in the circumpolar channel middepth stratification results from a balance between the wind driven upwelling in the channel and deep water formation at high northern latitudes d

ground motion prediction equations for hawaii from a referenced empirical approach ground motion prediction equations gmpes for hawaii are developed using the referenced empirical approach the technique is based on the use of residual analysis that models discrepancies between ground motion observations for hawaii and a reference gmpe in this case the gmpe of boore and atkinson 2008 for shallow crustal earthquakes in active tectonic regions the referenced empirical approach provides gmpes for hawaii that are in agreement with regional ground motion observations while being constrained to follow the overall scaling behavior of ground motion that is observed in better instrumented regions gmpes are developed for both shallow depth 20 km and deep 35 to 40 km earthquakes in hawaii

do we require adiabatic dissipation schemes in eddy resolving ocean models abstract use of horizontal diffusion of temperature and salinity in numerical ocean models causes spurious diapycnal transfers the veronis effect leading to erosion of the thermocline and reduced poleward heat transports the authors derive a relation between these diapycnal transfers and the dissipation of vorticity gradients an increase in model resolution does not significantly reduce the diapycnal transfers since vorticity gradients cascade to smaller scales and must ultimately be dissipated to maintain numerical stability this is confirmed in an idealized primitive equation ocean model at a variety of resolutions between 1 and 1 8 thus the authors conclude that adiabatic dissipation schemes are required even in eddy resolving ocean models the authors propose and implement a new biharmonic form of the gent and mcwilliams scheme which adiabatically dissipates at the grid scale while preserving larger scale features

hydrothermal alumina rich clays and boehmite on the gorda ridge abstract hydrothermal alteration of basalt on the northern gorda ridge produced an alteration crust up to 1mm thick that can be divided into two layers based on mineralogy an inner layer next to the basalt surface is an al rich interlayered smectite chlorite similar to high temperature al rich clays recovered from the east pacific rise 21 n with minor quartz zeolite phillipsite and relict plagioclase an exterior layer of boehmite alo oh and minor anatase results from severe leaching of the underlying clays the alteration crust is progressively enriched in al ti v and cr from interior to exterior by residual weathering the presence of boehmite and absence of a silica rich phase in the exterior of the crust indicates the hydrothermal fluids were silica undersaturated or silica was maintained in solution by extremely acidic fluids this constitutes the first reporting of boehmite as a major alteration mineral in a mid ocean ridge hydrothermal environment

interhemispheric influence of surface buoyancy conditions on a circumpolar current 1 this study shows that the surface buoyancy conditions in the northern hemisphere may influence the stratification and transport of the antarctic circumpolar current acc we use a course resolution ocean general circulation model ogcm in an idealized single basin configuration with a circumpolar channel a decrease in the magnitude of the surface temperature meridional gradient in the northern hemisphere reduces production of the deep water affecting the interhemispheric meridional overturning circulation moc and deepening the thermocline in both hemispheres the induced change of stratification in the southern hemisphere circumpolar region increases the zonal volume transport of circumpolar current because of an increase in the local meridional density gradient and the associated thermal wind shear which is the dominant baroclinic component of the total volume transport the result is robust to variations in the background vertical mixing and the parameterization scheme for mesoscale eddies

determining paleoceanographic circulations with emphasis on the last glacial maximum the inference from radiocarbon and other data that the north atlantic ocean circulation during the last glacial maximum was reduced is examined because glacial periods are thought to be windier than non glacial ones a reduced circulation is difficult to rationalize a first step is to note that the circulation of mass is unlikely to correspond simply to the circulation of heat or freshwater salt by merely permitting an enhanced input of southern hemisphere water into the north atlantic one can accommodate significantly increased radiocarbon ages such an input is equally interpretable as owing to an increased mass circulation rather than a decreased one inferred estimates from paleo shear estimates in the florida current are re interpreted as producing an indeterminate net flow there determination of the paleocirculation rates is not simpler than the problem in the modern ocean it is fully three dimensional and requires an adequate data base to determine the mass flux rates

sensitivity of the southern ocean overturning circulation to surface buoyancy forcing 1 the sensitivity of the southern ocean overturning to altered surface buoyancy forcing is investigated in a series of eddy permitting idealised simulations the modelled response indicates that heat and freshwater fluxes in the southern hemisphere mid latitudes may play a significant role in setting the strength of the overturning circulation enhanced buoyancy fluxes act to increase the meridional overturning up to a limit approaching the wind driven ekman transport the sensitivity of the overturning to surface buoyancy forcing is strongly dependent on the relative locations of the wind stress profile buoyancy forcing and upwelling region the numerical simulations provide support for the hypothesis that changes in upwelling during deglaciations may have been driven by changes in heat and freshwater fluxes instead of or in addition to changes in wind stress

shear wave velocity characterization of the usgs hawaiian strong motion network on the island of hawaii and development of an nehrp site class map abstract to assess the level and nature of ground shaking in hawaii for the purposes of earthquake hazard mitigation and seismic design empirical ground motion prediction models are desired to develop such empirical relationships knowledge of the subsurface site conditions beneath strong motion stations is critical thus as a first step to develop ground motion prediction models for hawaii spectral analysis of surface waves sasw profiling was performed at the 22 free field u s geological survey usgs strong motion sites on the big island to obtain shear wave velocity v s data nineteen of these stations recorded the 2006 kiholo bay moment magnitude m 6 7 earthquake and 17 stations recorded the triggered m 6 0 mahukona earthquake v s profiling was performed to reach depths of more than 100 ft most of the usgs stations are situated on sites underlain by basalt based on surficial geologic maps however the sites have varying degrees of weathering and soil development the remaining strong motion stations are located on alluvium or volcanic ash v s 30 average v s in the top 30 m values for the stations on basalt ranged from 906 to 1908 ft s national earthquake hazards reduction program nehrp site classes c and d because most sites were covered with soil of variable thickness based on these data an nehrp site class map was developed for the big island these new v s data will be a significant input into an update of the usgs statewide hazard maps and to the operation of shakemap on the island of hawaii

circumpolar response of southern ocean eddy activity to a change in the southern annular mode 1 analysis of satellite altimeter data reveals anomalously high eddy kinetic energy eke in the antarctic circumpolar current acc during the period 2000 2002 around 2 3 years earlier 1998 the circumpolar eastward wind stress as quantified by the southern annular mode sam showed a significant positive peak and we have shown previously that the acc peaked around 1998 in response an eddy resolving ocean model is used to investigate the delay between wind forcing and the eddy response and demonstrates that the lag is due to the time taken to influence the deep circulation of the acc winds over the southern ocean have shown a strong climatic increase over the past few decades if this increase in winds is also reflected as an increase in eddy activity as our analysis suggests it might then the increased poleward heat flux may have played a significant role in the observed warming of the southern ocean citation meredith m p and a m hogg 2006 circumpolar response of southern ocean eddy activity to a change in the southern annular mode geophys res lett 33 l16608 doi 10 1029 2006gl026499

high latitude salinity effects and interhemispheric thermohaline circulations a general circulation model for the ocean is used to investigate the interaction between the global scale thermohaline circulation and the salinity distribution it is shown that an equatorially asymmetric circulation can be maintained even under equatorially symmetric basin geometry and surface forcing multiple equilibrium solutions are obtained for the same forcing by perturbing the high latitude salinity field in an otherwise equatorially symmetric initial condition the timescale of the transition from the symmetric circulation to an asymmetric circulation depends critically on the sign of the initial salinity perturbation

the effects of mesoscale eddies on the stratification and transport of an ocean with a circumpolar channel abstract the effects of eddies in a primitive equation ocean model configured in a single hemisphere domain with circumpolar channels at their poleward ends are investigated in particular two regimes for the mass balance in the channel are investigated with small overlying winds the channel stratification is largely set by diffusion operating in the gyre portion of the domain the depth scale varies with a fractional power of the diffusivity but has little dependence on the wind stress as the winds are increased the depth becomes increasingly controlled by a tendency toward small residual circulation in this limit a scaling theory is derived for the stratification in the channel that predicts the overall depth of the thermocline as a power of the wind stress and that allows the eddy length scale to differ from the channel length scale the predicted depth depends on the details of the closure chosen for the eddy buoyancy flux but in general it varies as some fractional power of the wind stress a

isopycnal averaging at constant height part i the formulation and a case study simple eulerian averaging of velocities density and tracers at constant position is the most natural way of averaging however eulerian averaging gives incorrect watermass distributions and properties as well as spurious diabatic circulations such as the deacon cell instead of averaging at constant height averaging along isopycnals removes such fictitious mixing and diabatic circulations such isopycnal averaging is normally performed at constant latitude that is averaging along isopynals as they heave up and down as a result height information is lost and the sea surface becomes much warmer or lighter than with simple eulerian averaging in fact averaging can be performed along arbitrarily aligned surfaces this study considers a particular case in which isopycnal averaging is performed at constant height thus this new isopycnal averaging follows isopycnals as they meander horizontally at constant z height information is now retained at the cost of losing latitudinal information the advantage of this averaging is that it avoids the problem of giving a surface that is too warm associated with this new isopycnal averaging a vertical transport streamfunction in r z space can be defined in analogy to the conventional meridional overturning streamfunction in y r space here in part i this constant height isopycnal averaging is explained and illustrated in an idealized zonal channel model in part ii the relationship between the two different isopycnal averagings and the eulerian mean eddy flux divergence is explored

simulated impact of altered southern hemisphere winds on the atlantic meridional overturning circulation 1 previous work has suggested that the strength and latitudinal position of the southern hemisphere sh mid latitude westerly winds has an important impact on climate and the atlantic meridional overturning circulation amoc we probe this hypothesis by conducting ensembles of experiments using the gfdl cm2 1 coupled ocean atmosphere model with altered sh wind stress we find consistent with previous work that enhanced reduced and poleward equatorward displaced sh westerly winds lead to an amoc intensification weakening while the amoc takes more than a century to respond fully to the altered sh winds initial effects in the north atlantic can occur within a few decades the amoc changes generate sst and surface air temperature responses in the north atlantic and adjacent continental regions in the southern hemisphere the atmosphere responds to the altered ocean circulation with a further strengthening and poleward movement of the sh winds thereby constituting a modest positive feedback

geochemistry of hydrothermal deposits from loihi submarine volcano hawaii abstract dredging across the northeast rim of the summit crater of loihi seamount recovered several morphologically similar but chemically and mineralogically distinct hydrothermal deposits encrusting the surface of fresh pillow lava talus the multicolored deposits suggest a precipitation sequence that may be controlled by an oxidation reduction gradient in which smectite ranging in composition from fe montmorillonite to nontronite has precipitated along with iron oxide under slightly reducing conditions this deposition was apparently followed by amorphous iron oxide and silica precipitation possibly under more oxic conditions oxygen isotope geothermometry indicates formation temperatures in the range of 31 57 c for the loihi smectites trace element enrichments appear to be positively correlated with the isotopic formation temperature of the smectite suggesting either increased trace element solubility within the higher temperature vent fluids or increased smectite and iron oxide scavenging with increased precipitation rates the trace element abundances further suggest the presence of polymetallic sulfides that either are directly associated with the smectites as amorphous phases or occur beneath these deposits in the volcanic pile of the seamount

isopycnal averaging at constant height part ii relating to the residual streamfunction in eulerian space in part i the vertical transport streamfunction was defined as resulting from isopycnic averaging at constant height in the same way that the meridional streamfunction results from averaging at constant latitude part ii here discusses the relationship between these two isopycnic streamfunctions and the eulerian residual streamfunction that arises from the transformed eulerian mean tem it is known that the meridional isopycnic streamfunction can be approximated by a taylor expansion to give an eulerian residual streamfunction involving the horizontal eddy flux this taylor expansion approximation works well in the interior removing the spurious mixing associated with the simple eulerian averaged streamfunction however it fails near the surface where isopycnals outcrop to the surface it can be shown in a similar way that the vertical isopycnic streamfunction can formally be approximated by a residual streamfunction involving the vertical eddy flux however if horizontal isopycnal displacements are large this approximation fails even in the ocean interior inspired by the two different residual streamfunctions a more general form of tem formulation is explored it is shown that the different tem residual streamfunctions arise from decomposing the eddy flux into a component along isopycnals which leads to advective flow and a remaining diffusive component which is oriented either vertically or horizontally in theory the diffusive flux can be oriented in any direction although in practice the orientation should be such that neither the advective flow nor the diffusive flux cross any boundary surface sidewalls and bottom however it is not clear how to merge the continuously changing orientation in a physically meaningful way a variety of approaches are discussed

hydrothermal oxide and nontronite deposits on seamounts in the eastern pacific deposits of fe oxide mud nontronite and fe mn crusts were sampled from the summits of two seamounts in the eastern pacific where low temperature 0 15 c hydrothermal fluids are issuing the deposits consist of x ray amorphous fe oxyhydroxide and are rich in fe 43 wt contain minor si and p 4 and 3 5 respectively and have very low mn 0 01 and other trace element contents other deposits where no current hydrothermal activity was observed consist of mud and crusts composed of amorphous material and poorly crystalline hematite goethite and smectite these deposits have slightly higher mn up to 2 and other trace element contents the mineralogical and chemical differences between the active and inactive deposits and crusts are interpreted to be due to recrystallization and contamination with detrital biogenic hydrogenous and possibly hydrothermal sulfide material nontronite deposits capped by fe mn oxides were sampled from one of the seamounts these deposits have compositions similar to other seafloor nontronite deposits and formed at low temperatures 30 c during mixing of low temperature hydrothermal fluids with seawater the oxide deposits consist almost entirely of long delicate filaments remarkably similar in morphology to genera of fe oxidizing bacteria such bacteria were probably important in catalyzing the oxidation and precipitation of iron from hydrothermal fluids on the seamounts the occurrence of nearly identical filament rich oxide deposits on two widely separated seamounts suggests that this type of deposit may be common on seamounts but previously unrecognized