flow of abyssal water into wake island passage properties and transports from hydrographic surveys 1 water mass characteristics and volume transports of abyssal water flowing northward into wake island passage in the north pacific ocean were examined by carrying out high quality hydrographic surveys in may 2003 october 2004 and december 2005 along with mooring observations from may 2003 to december 2005 close linear relationships between potential temperature and salinity dissolved oxygen and silicate were seen below 1 1 c 4000 m the relationships above 1 1 c were scattered and were separated into relatively salty oxygen rich silicate poor water to the south and water with the opposite properties to the north the results suggested that there was a boundary between water masses at 1 1 c in the deep passage in addition to the three hydrographic sections two hydrographic sections previously surveyed in the deep passage in 1975 and 1999 were reexamined for transport estimates geostrophic calculations relative to the 1 1 c surface indicated northward transports of the abyssal water from 0 5 to 2 2 sv 1 sv 106 m3 s 1 below this surface when 1 year mean estimated velocities at 1 1 c surface were used for reference mean transport from the five estimates increased from 1 4 to about 4 sv the temperature of abyssal water colder than 1 1 c was found to have increased by an average of 0 012 c between 1975 and 2005 this warming is greater than double the standard deviation from the temporal mean temperature profile obtained from mooring observations

nonisostatic response of sea level to atmospheric pressure in the eastern mediterranean abstract we analyze 5 months of sea level data from katakolon greece in terms of local atmospheric pressure and the two components of geostrophic wind the response to pressure is isostatic at low and high frequencies but significantly nonisostatic for intermediate frequencies centered on about 0 01 cycles per hour the response is consistent with a simple theory in which the fluctuating barotropic flow through the straits of gibraltar and sicily is geostrophically controlled at low frequency the local geostrophic wind contributes very little to the sea level variance the response coefficients while not well determined are qualitatively as expected and quantitatively correspond to a very narrow near shore region of shallow water

the flux and mixing rates of antarctic bottom water within the north atlantic calculation was made of the northward flow of antarctic bottom water into the western north atlantic basin through a passageway approximately 300 km wide between the ceara rise and the mid atlantic ridge at about 4 n two moorings carrying four current meters each were placed in the region where currents were expected to be the greatest and were left for 360 days the current was not steady but exhibited large surges with approximately a 60 day time scale whose cause is unknown current meters in the fastest flowing region all exhibited a net northward flow it is estimated that approximately 0 8 106 m3 s 1 of water colder than 1 9 c potential temperature flowed on the average into the north atlantic with this number possibly being too small by 0 3 106 m3 s 1 or too big by 0 1 106 m3 s 1 depending upon estimates of the width of the region which the current meters sample however these numbers differ from geostrophic estimates of 1 98 106 m3 s 1 the disagreement coming almost entirely from the fact that the geostrophic estimates give a sizeable flux of water colder than 1 2 c while the current meters do not based upon the two different flux rates residence times and mixing coefficients are calculated for antarctic bottom water for each 0 1 c potential temperature interval from 1 0 c to 1 9 c finally some comments on the dynamics of the northward flow are made

single borehole and cross borehole resistivity anomalies of thin ellipsoids and spheroids hole to hole resistivity measurement is a useful method of detecting deeply buried fractures and ore deposits in the subsurface with drilling costs continually rising there is a growing need for developing methods of borehole geophysics such as this in this study we present theoretical results relating to detection of thin oblate spheroids and ellipsoids with arbitrary attitude if we assume that individual fractures within a fracture zone are connected to each other and are of finite lateral and vertical extent then we can model the fracture zone as a thin conductive oblate ellipsoid or spheroid with arbitrary orientation of the major axis detection of such deeply buried fracture zones is the object of this study here the effects of the surface of the earth are neglected and the body is assumed to be enclosed within an infinite homogeneous mass the surface of the body is divided into a series of subsurfaces and a numerical solution of the fredholm integral equation is applied once a solution fo

eastward flow through the mid atlantic ridge at 11 n and its influence on the abyss of the eastern basin abstract the dilute antarctic bottom water of the north atlantic eastern trough is supplied from the western trough through fractures in the mid atlantic ridge in particular the influence on eastern trough property distributions of flow through the romanche and vema fracture zones near the equator and 11 n respectively has been noted previously here new observations are reported that document the abyssal circulation of the northeastern atlantic basins gambia abyssal plain south canary basin and north canary basin in particular the dominance of vema influence the absence of romanche influence and the existence of a system of deep western boundary currents and estimated transport deep isopycnals slope steeply across the vema s eastern end near 39 w corresponding to a geostrophic transport through the vema of 2 1 to 2 3 106 m3s 1 colder than 2 0 c this is half or more of the estimated bottom water that flows north across the equator into the subtropical western north atlantic this transp

deep water flow in the mariana and caroline basins two major water masses dominate the deep layers in the mariana and caroline basins the lower circumpolar water lcpw arriving from the southern ocean along the slopes north of the marshall islands and the north pacific deep water npdw reaching the region from the northeastern pacific ocean hydrographic and moored observations and multibeam echosounding were performed in the east mariana and the east caroline basins to detail watermass distributions and flow paths in the area the lcpw enters the east mariana basin from the east at about 13 n however in the southern part of the basin a part of this water mass arrives in a southward western boundary flow along the izu ogasawara mariana ridge both hydrographic observations and moored current measurements lead to the conclusion that this water not only continues westward to the west mariana basin as suggested before but also provides bottom water to the east caroline basin the critical throughflow regions were identified by multibeam echosounding at the yap mariana junction between the east and west mariana basins and at the caroline ridge between the east mariana and east caroline basins the throughflow is steady between the east and west mariana basins whereas more variability is found at the caroline ridge at both locations throughflow fluctuations are correlated with watermass property variations suggesting layer thickness changes the total transport to the two neighboring basins is only about 1 sverdrup 1sv 106 m3 s 1 but has considerable impact on the watermass structure in these basins estimates are given for the diapycnal mixing that is required to balance the inflow into the east caroline basin farther above in the water column the high silica tongue of npdw extends from the east to the far southwestern corner of the east mariana basin with transports being mostly southward across the basin

woce section p1w in the sea of okhotsk 1 oceanographic data description we describe the results of a world ocean circulation experiment woce survey line p1w from the open pacific ocean through the bussol strait and across the sea of okhotsk observations are presented of distributions of temperature and salinity dissolved oxygen and nutrients and some derived quantities discussion centers on the distribution of the sea of okhotsk component of the north pacific intermediate water mass and its properties the sea of okhotsk has been suggested as the only location where deep convection may occur within the north pacific or its marginal seas our analysis suggests that the surface 26 85 has recently been ventilated and arguments might be made to suggest that ventilation has occurred to 27 05 this is discussed here but detailed evidence is covered in a companion paper analyzing cfc observations the okhotsk component of the north pacific intermediate water extends to substantially greater depths and densities and so some other process is needed to create the denser water mass

flow through discovery gap abstract a narrow gap discovery gap in the east azores fracture zone at 37 n in the eastern atlantic provides a channel for the exchange of bottom water between the madeira and iberian abyssal basins a detailed survey defines its length 150 km width 10 50 km depth of sills near 4800 m and sediment thickness 0 500 m year long measurements of deep flow are made from six moorings and ten current meters mean flows are about 5 cm s 1 these data are supplemented by 10 days of float tracking near 4700 m and numerous density profiles within and around the gap a persistent southwest northeast flow of dense water is found in discovery gap and the flux of water colder than a potential temperature of 2 05 c is measured to be 0 21 04 106 m3 s 1 this discharge spreads over an area of about 1011 m2 beyond the gap exit where it is warmed both by geothermal heating and by mixing with overlying water an estimate of 1 5 to 4 cm2 s 1 is derived for the diapycnal diffusivity similar to values dete

cold outflow from the faroe bank channel abstract the exchange of water between the norwegian sea and the north atlantic around the faroe islands was investigated in 1987 and 1988 combining ctd data with shipborne acoustic doppler current profiler adcp measurements tests were devised to assess the accuracy of the adcp measurements and the results are described it is found that estimating a reference velocity for geostrophic measurements is limited by the presence of tides of order 10 cm s 1 in the outflow of cold water from the faroe bank channel which reaches speeds of nearly 1 m s 1 the error is acceptably small but strong time dependent components are revealed the discharge of cold water is traced 75 km beyond the sill of this channel and changes in potential temperature salinity and potential vorticity on an isopycnal surface are attributed to intense mixing an effective diffusivity near 100 cm2 s 1 is derived and k h instability demonstrated as a plausible source of the turbulent energy six current meter moorings were deployed from

on sensitivity of surface to borehole resistivity measurements to the attitude and the depth to center of a three dimensional spheroid borehole to surface and surface to borehole resistivity measurements are versatile but not totally tested methods for detecting anomalies in the vicinity of a borehole the former method has been discussed by several authors alfano 1962 merkel 1971 merkel and alexander 1971 barnett 1972 snyder and merkel 1973 snyder 1976 daniels 1977 1978 and 1983 but the latter has not received much attention morrison 1971 and daniels 1977 are among the few who have addressed the problem each method has its own advantages surface to borehole resistivity measurements are made by placing a current source on the surface and measuring the apparent resistivity in a borehole in which the measuring electrodes are closer to the body than in the borehole to surface case pilot studies presented here suggest that the surface to borehole method can provide indicators of the attitude and the depth to the center of a body this paper illustrates a simple method for qualitatively determining the attitude and t

eruption of the nevado del ruiz volcano colombia on 13 november 1985 gas flux and fluid geochemistry the 13 november 1985 eruption of nevado del ruiz volcano in colombia released a small volume of pyroclastic material and a disproportionately large volume of volcanic gas before the eruption summit fumarole gases became less water rich and the sulfur chlorine ratio increased remote measurements of sulfur dioxide flux after the eruption indicated active degassing at levels associated with eruptive or inter eruptive stages of other volcanoes thermal water analyses revealed increases in magnesium calcium and potassium and an increase in the magnesium chlorine ratio suggesting that these elements may have been leached from new magma ash leachate data showed sulfate and chloride concentrations and ratios that would be expected for the late stages ofa major plinian eruption water from the lahar contained high concentrations of sulfate and had a sulfur chlorine ratio of 4 67 suggesting that water ejected from the crater lake and turbulent mixing of pyroclasts and glacial ice triggered the lahar microprobe analyses of pumice from this eruption and the most recent previous event showed similar mixed andesites the uniform composition of the pumices and the unusually high ratio of gas to magma suggest that although a new batch of magma triggered this eruption the pumice that erupted may actually be old large volumes of new magma and glacial ice make the volcano dangerous and should stimulate development of an integrated long term monitoring program to include tolima volcano 25 kilometers to the south

three dimensional model results for an electrical hole to surface method application to the interpretation of a field survey an important objective of borehole geophysics is to maximize information about inhomogeneities in the vicinity of existing boreholes three dimensional models parallelepipedic inhomogeneities in a homogeneous half space are used here to characterize the responses of an electrical hole to surface method elecent electrode enterree where conductive or resistive inhomogeneities orebodies occur in the vicinity of a borehole two types of surface measurements are carried out simultaneously at each station electrical potential v as in mise a la masse and associated electrical field e these two measured parameters give rise to three other parameters two apparent resistivities one for each v and e case and another parameter quantifying the orientation of the e field the influence of various geometrical and electrical parameters such as the horizontal and vertical distances between the current source the stations and the inhomogeneity and the size and resistivity of the inhomogeneity on the five

nevado del ruiz volcano colombia an example of the state of the art of volcanology four years after the tragic november 13 1985 eruption

laboratory simulation of exchange through fram strait laboratory experiments and theory were conducted to observe the flow patterns and transport in both buoyancy driven and wind driven rotating fluids in lock exchange experiments water with one density flows into a second basin after a sliding gate is removed water of a second density flows back into the first basin the size and location of the currents for various values of density difference rotation rate and assorted sidewall geometries was recorded volume flux of the fluid was also measured and compared with a theory for lock exchange flow of a rotating fluid in a separate group of experiments with a passive upper layer easterly winds like those in the arctic ocean drive the upper level water into the arctic ocean and therefore oppose the buoyant exchange westerly winds would drive the water out of the arctic ocean this indicates that the exchange between the arctic ocean and the greenland norwegian sea is likely to be driven by buoyancy rather than by driven by wind crude estimates of the volumetric and fresh water exchange rate from the lock exchange formulas are compared with observed ocean fluxes and approximate agreement is found

structure of the deep spillway in the western part of the romanche fracture zone structure of the deep spillway was studied on the basis of conductivity temperature depth lowered acoustic doppler current profiler and mooring measurements in 2011 2014 in the romanche fracture zone 22 27 22 32 w the spillway exists quasi permanently in the regime of hydraulic control overflow and consists of two flows in the layer 1 20 c deeper than 4 150 m the first flow enters the fracture from the south through a gap in the southern wall the second flow is directed to the east along the narrow valley of the fracture the sill depths of these passages are 4 570 and 4 430 m respectively the depths over the surrounding ridges are shallower than 4 100 m both flows descend to the local depression of the fracture with 5 000 m depth bottom potential temperatures over both sills were 0 51 c and the measured velocities were 20 40 cm s when the flows descend down the slope they accelerate in supercritical regime maximal measured velocities were up to 65 cm s analysis of the 189 day time series of velocities on the mooring deployed in the flow descending from the gap showed a very high level of fluctuation energy 10 times greater than the energy of the barotropic tide at this point the only energy source of these fluctuations is the available potential energy of the deep thermocline in the west atlantic transforming to the kinetic energy of the deep spillway the total transport of the bottom water below 1 2 c based on the lowered acoustic doppler current profiler measurements is estimated at 0 29 0 35 sv which agrees with the predicted values

transequatorial flow of antarctic bottom water in the western atlantic ocean abyssal geostrophy at the equator abstract in its general northward flow along the western trough of the atlantic antarctic bottom water aabw must pass over several sills separating the various abyssal basins at the equator the western trough is deformed by major east west offsets of the mid atlantic ridge and the continental margin of brazil forming a newly zonal abyssal channel about 250 km wide centered at the equator and extending approximately 1000 km along its axis in which the aabw is confined thus the general northward flow of aabw is topographically constrained to be westward as it crosses the equator a hydrographic section across this channel at 37 w shows the aabw isopycnals to be bowl shaped within and beneath the level of the channel walls the equatorial geostrophic relation permits us to compute a zonal velocity from the well defined parabolic distribution of dynamic height relative to a reference level at the transition between aarw and the overlying deep water here 4 3 106 m3 s 1 is estimated for the wes

hydraulic control of sill flow with bottom friction abstract the hydraulics of strait and sill flow with friction is examined using a reduced gravity model it is shown that friction moves the critical or control point from the sill to a location downstream if the strait has constant width the control point lies where the bottom slope is the negative of the drag coefficient cd if cd exceeds the bottom slope everywhere the flow cannot be controlled in the classical sense that energy and flow force are minimized friction also decreases the minimum obstacle height required to establish hydraulically controlled flow in the classical laboratory towing experiment also friction greatly encourages the establishment of stationary hydraulic jumps in the lee of the sill and under certain conditions gives rise to stationary jumps on the upstream face of the obstacle some consequences of these results for deep ocean overflows are given using the iceland faroe overflow as an example

major holocene block and ash fan at the western slope of ice capped pico de orizaba volcano mexico implications for future hazards abstract a major block and ash fan extends more than 14 km westward from the summit of pico de orizaba volcano in the eastern part of the trans mexican volcanic belt radiocarbon dating of charcoal within the fan deposits yielded holocene ages that range between 4040 80 and 4660 100 y b p stratigraphical sedimentological geochemical and scanning electron microscope studies indicate that this fan originated within a relatively short time span by multiple volcanic explosions at the summit crater this activity produced a series of pyroclastic flows mainly block and ash flows and lahars which were channelized by a glacial cirque and connecting u shaped valleys as they descended toward the base of the volcano a recurrence of a similar eruption today would pose severe hazards to the population of more than 50 000 people who live in a potentially dangerous zone a detailed reconstruction of the sequence of events that led to the formation of the block and ash fan is presented to help mitigate the risk special attention is given to the effects of an ice cap and the role of pre existing glacial morphology on the distribution of products from such an eruption

on the sources of north atlantic deep water abstract because the volumetric census of deep and bottom water in the north atlantic ocean consists of three isolated linear ridges along which heat and salt flow through the main volumetric mode and point of intersection it is possible to deduce the expected ratio of heat flux and ratio of salt fluxes measured in the denmark strait overflow off greenland and in the antarctic bottom water near the equator the weakly stratified layers of upper north atlantic deep water fall on the nearly linear ridge at temperatures above that of the mode there is an incompatibility between observed ratio and deduced ratio it is predicted that a remeasurement of the flux of antarctic bottom water near the equator will show that the previous determination of 4 n is unrepresentatively low

topographic control of oceanic flows in deep passages and straits saddle points between neighboring deep ocean basins are the sites of unidirectional flow from one basin to the next depending on the source of bottom water flow in these sites appears to be topographically controlled so the interface between the bottom water and the water above adjusts itself to permit bottom water flow from the basin that contains a source of bottom water into the next examples in the atlantic include flow in the romanche fracture zone the vema channel the ceara abyssal plain the anegada jungfern passage and the discovery gap but there are many more theoretical predictions of volume flux using a method that requires only conductivity temperature depth data archives and detailed knowledge of bathymetry near the saddle point are compared with volume flux estimates using current meters and or geostrophic estimates for seven cases the ratio of prediction to volume flux estimate ranges from 1 0 to 2 7 some ocean straits that separate adjacent seas are also found to critically control bidirectional flows between basins theory of the influence of rotation on such critical flows is reviewed predictions of volume flux in eight cases are compared with ocean estimates of volume flux from traditional methods

a new method for geoelectrical investigations underwater1 a new electrical method is proposed for determining the apparent resistivity of multi earth layers located underwater the method is based on direct current geoelectric sounding principles a layered earth model is used to simulate the stratigraphic target the measurement array is of pole pole type it is located underwater and is orientated vertically this particular electrode configuration is very useful when conventional electrical methods cannot be used especially if the water depth becomes very important the calculated apparent resistivity shows a substantial quality increase in the measured signal caused by the underwater targets from which little or no response is measured using conventional surface electrode methods in practice however different factors such as water stratification underwater streams or meteorological conditions complicate the interpretation of the field results a case study is presented where field surveys carried out on lake geneva were interpreted using the calculated apparent resistivity master curves

the pristine shape of olympus mons on mars and the subaqueous origin of its aureole deposits abstract the tallest volcano in the solar system olympus mons on mars is bordered by at least ten enormous sub circular hummocky deposits forming a welded halo termed the aureole the aureole units or simply aureoles which are the deposits of landslides from olympus mons have dramatically transformed the pristine size and shape of the volcanic edifice topographic data are used to determine the amount of collapsed material and so reconstruct the original outline of olympus mons before the landslides took place under the assumption that the edifice did not start failing until it had reached this maximum size due to post aureole deposition on the eastern and southern flanks and to the uncertainty of the slippage level on the northern side the reconstruction is sufficiently precise along the western and north western olympus mons flank it is more uncertain for the northern flank while it is not feasible around the rest of the volcano it appears that the radius along the western and north western olympus mons before the collapse of the aureole landslides was approximately 200 km longer or more the results show that the volume of the aureoles even if enormous is insufficient to fill the ideal conical edifice which would be obtained prolonging the olympus mons flanks with present slope angles thus an overhang remains in the pre aureole reconstructed olympus mons which would also explain the onset of instability that led to the aureole collapse further a drape deposit blanketing the southern acheron fossae ridge just at the front of the western w aureole landslide deposit and a fan channel system carved on the same w aureole are investigated and it is suggested that these morphologies have been emplaced in subaqueous setting while the drape may indicate a landslide thrust water splash akin to a tsunami deposit caused by the fast travelling w aureole landslide the fan channel system is similar to certain morphologies in the terrestrial oceans a numerical model of the collapse of the western aureole unit in water shows final runouts on both acheron ridge and amazonis planitia compatible with observations provided that the friction angle is extremely small of the order of a tenth of degree simulations indicate that the w aureole could have reached acheron fossae ridge with velocities in excess of 100 m s which would explain the several tens of km long distance reached by the landslide thrust tsunami deposit in short morphological and numerical lines of evidence would indicate a subaqueous origin for the largest w aureole landslide

on the flow through broad gaps with application to the windward passage abstract the flow through broad passage connecting oceans and marginal seas is examined by a simplified two layer analytical model attention is focused on the flow resulting from the difference between the upper layer depth in the two basis which imposes a pressure gradient along the passage the land masses separating the ocean from the adjacent marginal sea are represented by two portions of an infinitely long wall extending from the free surface to the bottom of the ocean the passage whose width is larger than the deformation radius is represented by a gap separating the two portions of the wall the model is frictionless hydrostatic and nondiffusive but the movements within the gap are not constrained to be quasi geostrophic in the sense that the local rossby number is not necessarily small and the interface displacements are of the same order as the upper layer depth steady solutions for the upstream and downstream fields are obtained analytically using the momentum equation in an integrated fo

on the deep water flow through the faroe bank channel a substantial part of the norwegian sea deep water outflow into the north atlantic takes place via the faroe bank channel the deepest passage through the greenland scotland ridge in order to estimate this flux of cold low saline bottom water a field survey comprising hydrographie observations as well as current measurements was carried out in the channel during may 1983 transport calculations were undertaken for a total of four sets of observations and yielded values ranging from 1 5 to 1 9 sverdrup the outflow is most likely subjected to hydraulic control and consequently a simple model has been formulated in order to determine the maximum discharge through a rotating channel of parabolic cross section this geometry is well adapted to the topography of the faroe bank channel and the theoretically predicted magnitude of the transport was found to be in good agreement with the observations

three dimensional mise a la masse modeling applied to mapping fracture zones a numerical scheme applying the method of volume integral equations has been developed for borehole to borehole and borehole to surface modeling of the apparent resistivity response of a thin conductive body in a half space the inhomogeneity simulates a fracture zone in a geothermal system the algorithm is applicable for the direct current case when the buried electrode is either inside mise a la masse or outside near miss the body in implementing the scheme the integral equation is transformed into a matrix equation as a result of discretizing the inhomogeneity into rectangular cells all physical properties are assumed constant within each cell the rectangular cells are used through out execution of the algorithm the computed surface and subsurface apparent resistivity responses are examined for bodies of similar shape and size but with different orientations 1 vertical 2 horizontal 3 dipping at 60 degrees and 4 dipping at 30 degrees the four bodies produce apparent resistivity cr

oceanic boundary conditions for jakobshavn glacier part i variability and renewal of ilulissat icefjord waters 2001 14 jakobshavnglacier west greenland has respondedtotemperaturechangesinilulissaticefjord intowhich it terminates thisstudycollectedhydrographicobservationsinsideilulissaticefjordandfromadjacentdiskobay between2001and2014 thewarmestdeepdiskobaywaterswereblockedbytheentrancesillanddidnotreach jakobshavn glacier in the fjord basin the summer mean temperature was 2 88c from 2009 to 2013 excluding 2010 whenitwas 18c cooler despitethisvariability summerpotential densities in the basinwereinthe narrow range of 27 20 su 27 31kgm 23 and basin water properties matched those of disko bay in this layer each summer this relation has likely held since at least 1980 basin waters from 2009 and 2011 13 were therefore similar tothosein1998 99 whenjakobshavn glacier began toretreat whilebasin watersin2010wereascoolas in the 1980s the 2010 basin temperature anomaly was advected into disko bay not produced by local atmospheric variability this anomaly also shows that ilulissat icefjord basin waters were renewed annually or faster time series fragments inside the fjord did not capture the 2010 anomaly but show that the basin temperatures varied little subannually outside of summer fjord velocity profiles from summer 2013 implied a basin renewal time scale of about 1 month in model simulations of the fjord circulation subglacial discharge from jakobshavn glacier could drive renewal of the fjord basin over a single summer while baroclinic forcing from outside the fjord could not because of the sill at the mouth

finding eruptive mechanisms through pyroclasts from the current eruption 1984 present at nevado del ruiz volcanic complex colombia abstract the dominant fragmentation mechanisms in the magma involved in a volcanic eruption can be understood from the compositional and textural analysis of the fragments emitted as pyroclasts individual pyroclasts can be juvenile accessory and accidental and detailed analyses of their relative proportions as well as the juvenile clast features can shed light into the fragmentation processes involved in the eruption despite the multiple hundreds eruptive pulses since the nevado del ruiz re activation in 1984 following a quiescence of nearly 100 years such analyses have not been carried out for the ash emissions preceding the recently emplaced plug here four deposits related to the recent emissions were analysed from their pyroclasts the samples correspond to eruptive pulses from the years 1985 1986 1988 and 2012 their characterisation allowed proposing differences between likely juvenile fragments i e representative of involved magma and accessory fragments i e pre existing co magmatic the results indicate that alteration can be used as a criterion to distinguish them although this could not account for syn eruptive hydrothermal alteration of juvenile glass or for the preservation of accessory glass emplaced in glacial conditions this criterion could serve as a foundation to direct fresh glass fragment analyses following this criterion the fresh glass fragments which are assumed to be juvenile fragments are highly vesicular they exhibit spongy and fibrous textures that are related to the predominant vesicle shape their predominance suggests a magmatic fragmentation mechanism while blocky shaped poorly vesicular cracked glass shards suggest a phreato magmatic origin specifically november of 1985 and january of 1986 glassy ashes are primarily highly vesicular suggesting magmatic explosive events by contrast samples from the march of 1988 and may of 2012 events are primarily characterised by low fresh glass content they also exhibit quenched surfaces indicating that the magma water interaction acted as an important factor for triggering the eruptive pulses real time componentry petrography and glass characterisation in fine ash could significantly complement traditional geophysical monitoring and importantly improve the hazard assessments on the civil aviation during the ongoing nevado del ruiz activity

turbulent mixing and hydraulic control of abyssal water in the samoan passage 1 we report the first direct turbulence observations in the samoan passage sp a 40 km wide notch in the south pacific bathymetry through which flows most of the water supplying the north pacific abyssal circulation the observed turbulence is 1000 to 10 000 times typical abyssal levels strong enough to completely mix away the densest water entering the passage confirming inferences from previous coarser temperature and salinity sections accompanying towed measurements of velocity and temperature with horizontal resolution of about 250 m indicate the dominant processes responsible for the turbulence specifically the flow accelerates substantially at the primary sill within the passage reaching speeds as great as 0 55 m s 1 a strong hydraulic response is seen with layers first rising to clear the sill and then plunging hundreds of meters downward turbulence results from high shear at the interface above the densest fluid as it descends and from hydraulic jumps that form downstream of the sill in addition to the primary sill other locations along the multiple interconnected channels through the samoan passage also have an effect on the mixing of the dense water in fact quite different hydraulic responses and turbulence levels are observed at seafloor features separated laterally by a few kilometers suggesting that abyssal mixing depends sensitively on bathymetric details on small scales

northward abyssal transport through the samoan passage and adjacent regions a conductivity temperature depth hydrographic survey in january february 1994 and a 17 month deployment of current meter moorings from september 1992 to march 1994 were carried out to determine the volume transport water mass characteristics and diathermal fluxes of northward flowing abyssal waters in the samoan passage and adjacent regions of the south pacific ocean geostrophic calculations relative to 1 2 c potential temperature indicated northward transport of 7 8 sv in the samoan passage 1 1 sv through a gap in robbie ridge and 2 8 sv along the eastern flank of the manihiki plateau all of the total of 11 7 sv of northward geostrophic transport was in waters colder than 1 1 c the northward transport distribution was bimodal in temperature with a cold mode of 3 6 sv in the range 0 65 0 70 c occurring entirely in the samoan passage and a warm mode of 3 0 sv in the range of 0 80 0 85 c occurring mainly along the manihiki plateau within the samoan passage 7 1 sv of the northward transport was below 4000 m where the geostrophic calculation was confirmed by an equal estimate of transport from current meters during the simultaneous 3 day period the 17 month mean transport from the moored array was 6 0 sv 0 5 by using the observed temporally varying flow within the samoan passage together with the hydrographic snapshot across the region an estimate of the total mean northward transport of 10 6 sv 1 7 was obtained estimates of the flow across near bottom potential temperature surfaces indicate extraordinarily high rates of mixing with heating of the abyssal layer up to 20 w m 2 corresponding to diffusivities up to 10 1 m2 s 1

direct velocity measurements in the samoan passage an array of six current meter moorings was deployed in the samoan passage 10 s 170 w from september 1992 to february 1994 with the goal of determining the northward abyssal transport the 17 month mean transport beneath 4000 m was 6 0 sv 106 m3 s 1 the time series were low passed at a period of 100 hours to remove near inertial and tidal variability and the resulting transport had a standard deviation of 1 5 sv a minimum of 1 1 sv and a maximum of 10 7 sv the dominant low frequency variability in transport and area averaged temperature was at a period of 30 days where the temperature led the transport as would be expected if the heat balance were advective the temporal and spatial variability suggested that the mean transport is known to within a 1 standard deviation error of 0 5 sv the along passage flow was intensified to the west and toward the bottom as might be expected in a rotating geostrophic system three pathways through the sill region were identified on the basis of bathymetry and current direction the flow was strongly controlled by topography as indicated by the flow s orientation and directional steadiness the 30 day variability in transport might be described as a resonance of the northward abyssal flow

sea level variability due to meteorological forcing in the northeast gulf of st lawrence in an attempt to understand the causes of low frequency flow through the strait of belle isle we relate sea level data from four stations in the northeast gulf of st lawrence to meteorological forcing our main tool is a multiple regression at each frequency of sea level on local atmospheric pressure and two orthogonal large scale pressure gradients which represent geostrophic winds the results show an inverted barometer response to atmospheric pressure and a frequency dependent response to wind which can be tentatively interpreted in terms of coastal setup due to wind driven longshore currents or barotropic setup of semi enclosed regions such as the northeast gulf or the whole gulf a simple model for barotropic flow through the strait is developed in order to provide an estimate from data at the western end of the strait of sea level changes on the labrador shelf

the rotating hydraulics of the open channel flow between two basins the theory of rotating open channel flow between two basins is presented and experimentally verified for three cases the first case considered is the submerged weir flow i e the height of the channel floor is below the free surface height of the fluid in the lower basin flow for this case is found to depend on the fluid level in the downstream basin when the fluid level there is high and is independent of the fluid level downstream as soon as the level falls below a critical height at that point the flow in the channel becomes critical controlled the dependence of the flow on upstream potential vorticity and on rotation rate is also examined it is shown that transport of the flow decreases whenever rotation rate or upstream potential vorticity is increased the second case studied is controlled flow through a channel of irregular cross section the truncated channel transport of this flow is shown to increase at some moderate rotations if the channel floor has a cross channel slope similar to that of the surface of the current otherwise the transport always decreases with rotation rate the final case is concerned with supercritical separation of the current downstream of the control section i e the current separates from the left wall of the channel looking downstream visual evidence and measurements of formation of such a boundary current are obtained comparisons between the theory and the experiment for the three cases are generally reasonable except when flow separates in the control section the theory is found inapplicable to such separation

synoptic sections of the denmark strait overflow we report on a rapid high resolution survey of the denmark strait overflow dso as it crosses the sill the first such program to incorporate full water column velocity profiles in addition to conventional hydrographic measurements seven transects with expendable profilers over the course of one week are used to estimate volume transport as a function of density our observations reveal the presence of a strongly barotropic flow associated with the nearly vertical front dividing the arctic and atlantic waters the seven section mean transport of water denser than 27 8 is 2 7 0 6sv while the mean transport of water colder than 2 0 c is 3 8 0 8 sv although this is larger than the 2 9 sv of 2 c water measured by a 1973 current meter array we find that a sampling of our sections equivalent to the extent of that array also measures 2 9sv of cold water both the structure and magnitude of the measured flow are reproduced well by a high resolution numerical model of buoyancy driven exchange with realistic topography

effects of geologic noise on cross borehole electrical surveys using a finite element algorithm which allows for subsurface current and potential electrodes in dc resistivity we have analyzed the detection of a thin 2 d conductive inhomogeneity in the presence of several sources of geologic noise the pole pole array with the current electrode fixed in one borehole and the potential electrode movable in adjacent boreholes is the main array of concern the sources of noise are surface topography buried topography random geologic noise quasi random geologic noise nontarget inhomogeneities layering and a vertical contact for several positions of a downhole source electrode normalized apparent resistivities have been computed these resistivities have been contoured in section view as appropriate to cross borehole investigations for the models studied here surface topography buried topography random and quasi random geologic noise do not obscure the anomaly due to the thin conductive inhomogeneity in a vertically or horizontally layered earth the anomal

pacific abyssal transport and mixing through the samoan passage versus around the manihiki plateau abstractthe main source feeding the abyssal circulation of the north pacific is the deep northward flow of 5 6 sverdrups sv 1 sv 106 m3 s 1 through the samoan passage a recent field campaign

the intrusion of a density current along the coast of a rotating fluid when light rotating fluid spreads over heavier fluid in the vicinity of a vertical wall coast a boundary jet of width forms the leading edge or nose of which propagates with speed along the coast a certain fraction 8 of the boundary transport is not carried by the nose but is deflected backwards detrained and left behind the propagating nose theoretical and experimental results for and are given for a quasi equilibrium constant regime over longer time intervals the laboratory observations suggest that the nose slows down and stagnates whereupon the trailing flow separates from the coast and an intermittent boundary current forms these processes may be relevant to the mixing of oceanic coastal currents and the maintenance of the mean current

the flow of antarctic bottom water into the brazil basin the total transport of antarctic bottom water across the rio grande rise including the western boundary the vema channel and the hunter channel is estimated from hydrographic measurements across these pathways the contribution of the vema channel is greatest at 3 9 106 m3 s 1 which is very close to earlier estimates the western boundary current contribution is 2 0 106 m3 s 1 and that of the hunter channel 0 7 106 m3 s 1 the lower values outside the vema channel are offset by the important source of mass they form to the lower density classes of bottom water about 40 of the flow is concentrated in the highest density class representing the source of weddell sea deep water to the brazil basin the flow structure is characterized by horizontal and vertical recirculation

geostrophic control of fluctuating barotropic flow through straits abstract a simple model in which the cross strait sea surface slope is geostrophically balanced and the along strait slope is balanced by acceleration and friction is shown to be supported by the results of buchwald and miles for fluctuating flow through a gap between two semi infinite oceans for a narrow gap compared with the rossby radius and the scale of the motion in the far field the transport through it is exactly the same as that predicted by the model provided that the gap is regarded as having an elective length as determined in this paper the importance of the models is that they demonstrate that at low frequency the flow may be geostrophically controlled and the transport limited to a value much less than that which would arise in a nonrotating system the neglect of nonlinear advective terms in the models is justified by a comparison or the bernoulli set down in the strait with the driving head and the mean water depth the formula for the flux through a strait may be applied in stu

bottom water observations in the vema fracture zone the vema fracture zone trough at 11 n between 41 and 45 e is open to the west at the 5000 m level but is silled at the 4650 m level on the east where it intersects the axis of the mid atlantic ridge the trough is filled with antarctic bottom water aabw with a potential temperature of 1 32 c and salinity of 34 82 ppt the bottom water is thermally well mixed in a nearly homogeneous layer about 700 m thick the great thickness of this bottom layer as compared with the bottom water structure of the western atlantic basin may result from enhanced mixing induced by topographic constriction at the west end of the fracture zone trough a benthic thermocline with potential temperature gradients of about 1 2 mdeg m 1 is associated with an abrupt increase in turbidity with depth at about 1200 m above bottom a transitional layer of more moderate temperature gradients about 0 4 mdeg m 1 lies between the benthic thermocline above and the aabw below the aabw layer whose depth averaged suspended paniculate concentrations range from 8 to 19 g l 1 is consistently higher in turbidity than the overlying waters at the eastern end of the trough 140 m below sill depth very low northeastward current velocities with maximums of 3 cm s 1 were recorded for an 11 day period

flow properties in rotating stratified hydraulics abstract this paper discusses three distinct features of rotating stratified hydraulics using a reduced gravity configuration first a new upstream condition is derived corresponding to a wide almost motionless basin and this is applied to flow across a rectangular sill and compared with the case of a zero potential vorticity upstream condition for this geometry it is shown that unidirectional flow permits more water to pass through the sill than bidirectional flow second the general problem is considered of flow from any upstream configuration that passes through sills that vary slowly in depth cross sill and so are effectively many deformation radii wide only two flow configurations permit any realistic amount of flux across the sill either the fluid occupies a narrow region within the sill with a small flux or the fluid occupies a wide region with sluggish geostrophic flow except for at boundary layers at each side in the latter case hydraulic control is not likely to occur the zero

antarctic bottom water flux in the equatorial western atlantic a moored array at the equator in the western basin of the atlantic provides a 604 day time series of abyssal currents and temperatures spanning the full breadth of the antarctic bottom water aabw flowing from the brazil basin to the guiana basin mean aabw transport is estimated to be 2 0 sv sv 106 m3 s21 comprising organized westward flow of 2 24 sv and return flow of 0 24 sv the low frequency variability is dominated by a quasi annual transport cycle of amplitude 0 9 sv and a 120 day period of amplitude 0 6 sv maximum transports occur in september october while minimum transports occur in february march allowing for this quasiannual cycle and extrapolating the 604 day record to a full two years adds about 7 to the estimated mean aabw transport the array also provides limited sampling in the overlying lower north atlantic deep water lnadw where a southern boundary intensified flow of lnadw gives the strongest recorded mean speed through the array 9 9 cm s21 into the brazil basin the lnadw records also have a quasi annual cycle with strong lnadw flow episodes occurring in april may time series of temperature indicate that the lnadw aabw transition layer rises and falls in synchrony with the quasi annual aabw transport cycle uplifted transition layer during strong aabw transport periods an observed overall warming trend appears to be accompanied by a decline in aabw transport

anomalously shallow palaeomagnetic inclinations and the question of the age of the canarian archipelago summary extensive geological geophysical and geochronological data available from the canary islands establish conclusively that formation of the oldest subaerial volcanic structure of the islands began during the miocene a mid cretaceous age for these volcanic formations has been postulated in previous works on the basis of palaeomagnetic determinations the results obtained in the present palaeomagnetic study of lanzarote include analysis of the record of variations of magnetic inclination in boreholes that penetrate the whole of the oldest volcanic series they show that the excessive age previously assigned to these formations is due to the utilization of volcanic units with abnormally low 15 magnetic inclinations lgis in lanzarote lavas exhibiting lgis appear interbedded in a volcanic series that overall shows a typical miocene inclination 45 the units stratigraphically beneath and above the lgi horizons give in fact directions consistent with the middle upper miocene field direction d 359 i 45 with k 29 a95 6 7 and a palaeopole of 87 n 178 e thereby confirming the miocene age of the oldest subaerial volcanics of lanzarote short excursions of the geomagnetic field seem likely to be the explanation for these lgis since other factors such as tectonic tilting post eruptive modification of the primary remanence or errors in sample orientation can be disregarded the detection in the canary archipelago of volcanic units with abnormally low magnetic inclinations seems to be related to the relatively continuous record of the geomagnetic field in rapidly growing volcanic edifices as seems to be indicated by the presence of a few usually one or two short polarity events in volcanic suites of several hundred metres thickness

the flux of overflow water through the charlie gibbs fracture zone we report the results of a set of measurements made within the charlie gibbs fracture zone in 1988 1989 the principal data sources are year long current meter records 16 in number and 23 conductivity temperature depth stations the aim was to determine the flux of overflow water passing westward out of the iceland basin in the eastern north atlantic within the fracture zone overflow water is defined either as having salinity greater than 34 94 at the present time or more generally as having a potential density 0 27 8 kg m3 in 1988 1989 the core salinity had a value equal to that reported in 1981 and 1983 but was fresher by about 0 02 than was found in 1964 the flux was estimated twice per day and was found to fluctuate strongly with energy spread in a broad band of periods ranging from 10 to 400 days no annual signal could be detected the mean value was 2 4 0 5 sv less than all previous estimates based on hydrography alone it is suggested that hydrography may systematically overestimate transport because diffusion is neglected flux estimates from current meter arrays are rarely used in initializing numerical ocean models consequently measurements like those reported here are an independent and important means for assessing the performance of such models at the deepest levels water enters the two transform valleys of the fracture zone from the west in the northern valley the flow is periodically flushed out by energetic bursts of overflow water a critical value of an inverse froude number is shown to define the flushing threshold

observations of the flow of abyssal water through the samoa passage abstract during the fall of 1994 a conductivity temperature depth hydrographic survey was carried out as part of the world ocean circulation experiment one time survey line p15n the survey included standard water properties required by woce line p15n extended southward from the aleutian islands along 165 w into the vicinity of the samoa passage the line was adjusted to follow the axis of the passage and time was found to complete a cross section survey across the passage this paper will present geostrophic computations of flow velocities through the gap including transport estimates and will present longitudinal plots of properties the longitudinal plots show evidence of hydraulic control at the sill in the samoa passage a best estimate of northward transport of water colder than 1 2 c potential temperature is determined to be 8 4 sv

2 d and 3 d resistivity image reconstruction using crosshole data theoretical changes in the distribution of electrical potential near subsurface resistivity anomalies have been studied using two resistivity models the results suggest that the greatest response from such anomalies can be observed with buried electrodes and that the resistivity model of a volume between boreholes can be accurately reconstructed by using crosshole data the distributive properties of crosshole electrical potential data obtained by the pole pole array method have also been examined using the calculated partial derivative of the observed apparent resistivity with respect to a small cell within a given volume the results show that for optimum two dimensional 2 d and three dimensional 3 d target imaging in line data and crossline data should be combined and an area outside the zone of exploration should be included in the analysis in this paper the 2 d and 3 d resistivity images presented are reconstructed from crosshole data by the combination of two inversion algorithms the first algorithm uses the alpha center method for forward modeling and reconstructs a resistivity model by a nonlinear least squares inversion alpha centers ex press a continuously varying resistivity model and the distribution of the electrical potential from the model can be calculated quickly an initial general model is determined by the resistivity backprojection technique rbpt prior to the first inversion step the second process uses finite elements and a linear inversion algorithm to improve the resolution of the resistivity model created by the first step simple 2 d and 3 d numerical models are discussed to illustrate the inversion method used in processing data from several field studies are also presented to demonstrate the capabilities of using crosshole resistivity exploration techniques the numerical experiments show that by using the combined reconstruction algorithm thin conductive layers can be imaged with good resolution for 2 d and 3 d cases the integration of finite element computations is shown to improve the image obtained by the alpha center inversion process for 3 d applications the first field test uses horizontal galleries to evaluate complex 2 d features of a zinc mine the second field test illustrates the use of three boreholes at a dam site to investigate base rock features and define the distribution of an altered zone in three dimensions

bathymetry constrains ocean heat supply to greenland s largest glacier tongue mass loss from the greenland ice sheet has increased over the past two decades currently accounting for 25 of global sea level rise this is due to increased surface melt driven by atmospheric warming and the retreat and acceleration of marine terminating glaciers forced by oceanic heat transport we use ship based profiles bathymetric data and moored time series from 2016 to 2017 of temperature salinity and water velocity collected in front of the floating tongue of the 79 north glacier in northeast greenland these observations indicate that a year round bottom intensified inflow of warm atlantic water through a narrow channel is constrained by a sill the associated heat transport leads to a mean melt rate of 10 4 3 1 m yr 1 on the bottom of the floating glacier tongue the interface height between warm atlantic water and colder overlying water above the sill controls the ocean heat transport s temporal variability historical hydrographic data show that the interface height has risen over the past two decades implying an increase in the basal melt rate additional temperature profiles at the neighbouring zachariae isstrom suggest that ocean heat transport here is similarly controlled by a near glacier sill we conclude that near glacier sill controlled ocean heat transport plays a crucial role for glacier stability ocean heat transport underneath the floating tongue of 79 north glacier greenland is controlled by a sill in the inflow channel according to ship based and mooring data as well as bathymetric data

the overflows across the ninetyeast ridge abstract water deeper than say 3800 m in the central indian basin comes from the west australian basin across deep saddles on the ninetyeast ridge near lats 5 s 10 s and 28 s the woce hydrographic program in the indian ocean 1994 1996 provided opportunities for more detailed measurements of water properties in these overflows than any made earlier with zero velocity surfaces inferred from contrasts in oxygen and silicic acid concentrations and from distributions of specific volume anomaly geostrophic estimates of these overflow rates are respectively 1 0 1 1 and 0 1 10 6 m 3 s 1 westward these constructions also imply strong zonal flows of mid depth water between 2000 db and the zero velocity surfaces through the passages 2 2 and 6 7 10 6 m 3 s 1 westward at lats 5 s and 10 s respectively and 1 8 10 6 m 3 s 1 eastward at lat 28 s as in the southward flow through denmark strait density stratification explains the splitting of westward currents at 5 s and 10 s into mid depth and deep flows as they pass over their saddles but not why such vertically extended flows should exist in the first place the cause of opposed eastward flow at 28 s is less certain but might be related to the particular geometry of the west australian basin

intense mixing of antarctic bottom water in the equatorial atlantic ocean the spreading of antarctic bottom water the densest global scale water mass is highly constrained by ocean floor topography in the atlantic ocean the mid atlantic ridge confines this water mass mainly to the western basins the bottom waters in the eastern basins being renewed by flows through gaps in the ridge1 one such gap is the romanche fracture zone a large offset of the ridge which straddles the equator it has been observed2 that sills within this fracture zone block the passage of waters colder than 0 9 c warmer less dense waters passing over the sills appear to cascade downslope where they are modified by mixing here we present direct measurements which quantify these processes the flow is vertically sheared and exhibits remarkably intense turbulence comparable to that seen at the ocean surface in the presence of winds of l0ms 1 this turbulence mixes the densest waters passing through the fracture zone with the warmer overlying waters so that the coldest waters exiting this region have been warmed by 0 6 c during transit topographic obstructions and turbulent mixing together thus determine the properties of the flows renewing the deepest waters of the atlantic ocean s eastern basins

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic

physical characterization of rock masses using borehole methods a convenient view of geophysical phenomena is based on the categorization of techniques according to the governing partial differential equation the laplace diffusion or wave equation each category is examined nonmathematically in the context of those borehole methods used to investigate large volumes of a rock mass away from the borehole in which the instrumentation is deployed the published literature reflects the variety of applications some of which occur more frequently than others our discussion of the physics focuses on electric potential electromagnetic induction and seismic methods respectively as representatives of each category choice of a single technique for characterization of rock masses involves a compromise which depends upon the geophysical problem and the type of information desired the complementary nature of the information means however that integrated studies using two or more types of methods may be worthwhile