continuous h2o co2 222rn and temperature measurements on merapi volcano indonesia abstract a set of analytical instruments consisting of a gas chromatograph for water and carbon dioxide an alpha scintillation counter to measure radon and a temperature sensor was especially designed and constructed to monitor volcanic gases and was successfully operated over weeks in the high temperature fumaroles at the summit of merapi volcano indonesia the analytical unit runs automatically and is remote controlled through a radio link over a period of several weeks concentrations of h 2 o and co 2 were measured every 35 min and rn activity was monitored at about 90 min intervals the fumarole temperatures were continuously recorded every minute from july 2000 to the end of january 2001 the composition and temperature of the gas emitted at merapi volcano show significant variations due to a regular stronger degassing of the magma concentrations of co 2 increase periodically while h 2 o concentrations decrease on the other hand rn activity rises with increasing atmospheric pressure and higher water concentrations after intensive rainfall infiltration of cold meteoric water into the volcanic edifice possibly causes an increase in the concentration of water vapour and a decrease in the temperature of the gases in the fumarole several seismic events recorded at merapi correlate with gas temperature

broadband seismic experiment at merapi volcano java indonesia very long period pulses embedded in multiphase earthquakes abstract multiphase mp and low frequency lf earthquakes with spectral peak amplitudes at 3 4 and 1 hz respectively are two common types of shallow volcanic earthquakes previously recognized at merapi volcano their mechanisms are poorly understood but mps have been temporally associated with lava dome growth we conducted a seismic experiment in january february 1998 using four broadband seismographs to investigate the nature of seismic activity associated with dome growth during our experiment merapi experienced mild dome growth with low level seismic activity we compare our data to that recorded on a local short period sp network with the following preliminary results mp and lf events as recorded and classified on the short period network instruments were recognized on the broadband network frequency spectrograms revealed similar patterns in the near summit region at widely separated broadband stations higher frequency spectra than previously recognized were identified for both mp and lf events and were strongly attenuated as a function of radial distance from the source thus the spectral characteristics of these events as recorded on far field stations are not fully indicative of the source processes in particular many events classified as lf type appear to have much high frequency energy near the source this aspect of these so called lf earthquakes and their association with very long period vlp pulses suggests that many events identified in the far field as lf events are in actuality a variety of the mp event and involve similar source processes broadband records indicated that simple large amplitude vlp pulses were embedded in mp and lf wavetrains from event to event these pulses were similar in their waveforms and had periods of 4 s vlp events embedded in lf and mp earthquakes were located using particle motions the epicenters were clustered in a central region of the dome complex and preliminary source depths were within about 100 m of the dome surface suggesting a source region deep within the dome or the uppermost conduit a similar source location was established by study of mp high frequency onsets our broadband data suggests that we have recorded both elastic seismic waves and a simple embedded pulse that is interpreted to represent a surface tilt at the seismometer site the inferred tilt indicates an inflation and subsequent deflation possibly caused by a gas pressure pulse or episodic shallow magma transport with stick slip movement of the conduit wall

volcanic eruption velocities measured with a micro radar a novel technique to quantitatively assess volcanic eruption dynamics is presented we report on measurements of volcanic eruption velocities with a modified micro radar doppler anemometer on stromboli volcano italy the mean vertical eruption velocity recorded during a four day period in late 1996 was around 10 m s which is somewhat on the small side for strombolian eruptions however the activity of stromboli volcano during this period was very weak explaining the relatively small velocities the technique used is much better in resolution than older techniques based on static photos and allows a continuous monitoring of the volcanic activity in addition to the velocity information recorded by the doppler spectrum it also contains information on the density of the ejected material and the size distribution of the particles in the volcanic jet

opening of the fram strait gateway a review of plate tectonic constraints abstract we have revised the regional crustal structure oceanic age distribution and conjugate margin segmentation in and around the lena trough the oceanic part of the fram strait between the norwegian greenland sea and the eurasia basin arctic ocean the lena trough started to open after eurasia greenland relative plate motions changed from right lateral shear to oblique divergence at chron 13 times 33 3 ma earliest oligocene a new bouguer gravity map supported by existing seismic data and aeromagnetic profiles has been applied to interpret the continent ocean transition and the influence of eocene shear structures on the timing of breakup and initial seafloor spreading assuming that the onset of deep water exchange depended on the formation of a narrow oceanic corridor the gateway formed during early miocene times 20 15 ma however if the initial lena trough was blocked by terrigenous sediments or was insufficiently subsided to allow for deep water circulation the gateway probably formed with the first well developed magnetic seafloor spreading anomaly around chron 5 times 9 8 ma late miocene paleoceanographic changes at odp site 909 northern hovgard ridge are consistent with both hypotheses of gateway formation we cannot rule out that a minor gateway formed across stretched continental crust prior to the onset of seafloor spreading in the lena trough the gravity seismic and magnetic observations question the prevailing hypotheses on the yermak plateau and the morris jesup rise as eocene oceanic plateaus and the hovgard ridge as a microcontinent

the mediterranean sea a miniature ocean for climatic and environmental studies and a key for the climatic functioning of the north atlantic the mediterranean sea provides a case study not only for dense water formation and climatic functioning at a basin scale but also as a body of water evolving in response to the effects of environmental changes through marine circulation marine signatures of changes may be used to provide estimates of the evolution of the external driving forces of climate and environment that is to say to provide a coupling between marine sciences and climatic and socio economic studies different examples may be given i nutrients and trace metal changes in the western mediterranean permit quantification of external changes at a basin scale ii sapropels organic rich layers sedimented in anoxic conditions provide records for the last 2 million years of interactions between marine circulation climate and biology iii temperature and salinity changes that have taken place since the 1960s in response to changes in heat and water budgets across the sea surface sapropel studies and ongoing changes in temperature and salinity also require that the mediterranean functioning be considered in relation to global climate and to the atlantic ocean as well as taking into account the changing role of salty mediterranean waters in the atlantic ocean these factors highlight a dual role for the mediterranean sea which acts as a miniature ocean for physical chemical or climatic and environmental studies and also as a key factor in understanding global ocean circulation in which past changes have taken place

gravitational symmetric and baroclinic instability of the ocean mixed layer abstract a hierarchy of hydrodynamical instabilities controlling the transfer of buoyancy through the oceanic mixed layer is reviewed if a resting ocean of horizontally uniform stratification is subject to spatially uniform buoyancy loss at the sea surface then gravitational instability ensues in which buoyancy is drawn from depth by upright convection but if spatial inhomogeneities in the ambient stratification or the forcing are present as always exist in nature then horizontal density gradients will be induced and within a rotation period horizontal currents in thermal wind balance with those gradients will be set up within the mixed layer there are two important consequences on the convective process upright convection will become modified by the presence of the thermal wind shear fluid parcels are exchanged not along vertical paths but rather along slanting paths in symmetric instability theoretical considerations suggest that this slantwise convection sets the potential vorticity of th

avtis a novel millimetre wave ground based instrument for volcano remote sensing during may and june 2004 we tested a novel millimetre wave ground based dual mode radar and radiometer on soufriere hills volcano montserrat avtis all weather volcano topography imaging sensor has an active radar mode designed to image the distance to lava domes on volcanoes whose summits are commonly obscured by persistent cloud such as soufriere hills volcano the passive radiometer mode can be employed to measure the surface temperature of the imaged topography in its current form avtis can be deployed by two people and takes 50 min to acquire a 20 5 scene at 0 1 increments during the fieldwork period the lava dome was not growing and only the radar mode was used the data recorded indicate that the maximum distance imaged was about 3800 m combining datasets acquired from different viewpoints can potentially provide a full 3d topographic model the accuracy and completeness of this reconstruction are reduced by two factors firstly relatively small grazing angles of the ground based line of sight rendered incised valleys invisible secondly methods currently used to orient the instrument limit the accuracy of the resulting topographic information nevertheless valuable information on new topographic surfaces was obtained in an area north of the lava dome where a valley has been infilled by deposits and in the amphitheatre created by the giant collapse event of july 2003

a mechanism governing the estuarine circulation in deep strongly stratified fjords the estuarine circulation in deep strongly stratified fjords is discussed it is argued that a two layer description of the stratification in the fjord is correct in very wide fjords wide compared to the width of the mouth and possibly also in narrow fjords with high runoff and or weak mixing a theory for the thickness and the salinity of the brackish layer in a wide fjord was earlier developed by the present author and published in swedish 1975 and it is presented here among other findings in that theory we may mention that the thickness of the brackish layer is primarily determined by the internal hydraulic control for high specific runoff runoff unit horizontal surface area of the fjord and weak mixing in the other extreme with low specific runoff and strong mixing the thickness of the brackish layer is found to be proportional to the monin obukhov length the circulation in not very wide fjords is also discussed it is found that recirculation in the brackish layer may be expected whereby a two layer description of the flow field breaks down at least locally a critical rayleigh number that seems to control the recirculation of brackish water within the fjord is found a theory for the density difference between the mouth and the head in the brackish layer in the fjord is developed from the critical rayleigh number condition it is found that this density difference normally is proportional to the density difference between the brackish water at the mouth and the underlying sea water provided that the river runoff is not too heavy and or the mixing is not too weak this prediction is confirmed by extensive measurements from the nordfjord

a conceptual model for block and ash flow basal avalanche transport and deposition based on deposit architecture of 1998 and 1994 merapi flows the 1998 block and ash flow baf deposits on the western flanks of merapi were described both immediately following emplacement and after one and two wet seasons of erosion this afforded a unique combination of data on deposit morphology and internal structure from proximal to distal reaches the deposits of the basal avalanches from individual baf events were classified into three major and two minor facies in channelised reaches primarily resulting from effects of channel confinement and slope termination reaches were classified into three facies related to preevent topography the deposit facies architecture was interpreted to understand particle transport and deposition within the framework of granular flow systematics the transport model we propose for these basal avalanches involves unsteady flow conditions generated by pulses of collapse as the source and or by development of kinetic waves during the granular flow the coarsest clasts along with low density material migrated to the wave pulse fronts within these flows whereas in bulk flow grain dispersive pressures and kinetic sieving result in coarsest clasts being buoyed to the flow top with this tendency being greatest on higher slopes greater kinetic energy and with greater flow confinement maximising particle collisions deposition begins as the flow reaches near its full extent an initial pulse or flow wave freezes rapidly from its base upward and its rear forward as it looses kinetic energy and dispersive pressure such that an upper higher energy part of the flow is still able to move downstream over the frozen base later waves or pulses then accrete progressively horizontally upslope banking up onto or overtopping earlier deposited sediment hence the overall flow freezes from its front to its tail at termination reaches in unconfined areas the overflowing upper part of flow gradually deposits from its base upward resulting in a slightly tapering sheet formed deposit marked by a front made up of wood fragments and large boulders on sudden slope breaks in termination areas piling up of sediment occurs in flat reaches producing whaleback type forms as the flows rapidly lost competence one implication of this model is that each kinetic wave or flow pulse crest developed within the basal avalanche represents a portion of greater flow depth or stage height hence development of these crests control the ability of parts of the basal avalanche to escape from confined channels and generate unexpected hazards

automatic hypocenter determination of volcano induced seismic transients based on wavefield coherence an application to the 1998 eruption of mt merapi indonesia in order to monitor the seismic activity of mt merapi indonesia over a long period of time we installed a permanent array of both broadband and short period seismometers during the summer of 1997 considering the requirements of an automatic classification and localization system for seismic monitoring and surveillance at active volcanoes we split this network into three small aperture arrays distributed around the volcano we introduce here a newly developed method to determine the hypocenters in an automatic non linear manner using the coherence of seismic waves observed at the different arrays to test this method we analyze a swarm of vt b events recorded by the network the first step in this algorithm is based on a modified smoothed coherence transform in the second step we perform a semblance analysis applied to the 3d problem evaluating the quality of the estimated relative onset times after more than one year of dormancy mt merapi renewed its activity at the end of june 1998 this gave us the opportunity to analyze all stages of dome growth collapse and new intrusion of magma using the associated seismicity in a post processing sense this also allowed us to calibrate and test our newly developed automatic monitoring system using the more pronounced waveforms of vt b events by detecting and classifying different event types automatically we are able to localize a large number of vt b events which occurred just before the initial eruption we are also able to resolve some properties of the wavefield at mt merapi which are essential for further interpretations finally the results show that the source region of the vt b type seismicity just before the 1998 eruption is closely related to the region of subsequent high volcanic activity and therefore may represent a promising tool to forecast future eruptions

a model for the exchange of water and salt between the baltic and the skagerrak abstract a model for the exchange of salt and water between the baltic and the sea the skagerrak is presented because of strong inter basin interactions in the baltic entrance area the model must include the kattegat and the belt sea these are modeled by horizontally homogeneous two layer sub models the most prominent dynamical properties of the sub models are wind driven entrainment flows and rotational baroclinic hydraulic controls the model is driven by a meteorologically forced barotropic transport qh calculated from the freshwater supply to the baltic qf and the sea level fluctuations in the kattegat and turbulent entrainment flows coupled to the wind speed w and in the belt sea also to the barotropic transport the most important bathymetric features of the basins are included the model equations are integrated numerically for a test period of 1 years the stratification in the kattegat as well as in the belt sea is quite well predicted it is found that approximately one half of

introduction to special section on cenozoic paleoceanography of the central arctic ocean 1 in late summer 2004 the integrated ocean drilling program iodp conducted one of the most transformational missions in the almost 40 year history of scientific ocean drilling the arctic coring expedition acex backman et al 2006 moran et al 2006a this technically challenging expedition moran et al 2006b to the lomonosov ridge near 88 n recovered the first long term cenozoic sediment record from the arctic ocean extending previous records from 1 5 ma to an unprecedented 56 ma glimpses of the breadth of this transformation were seen during the acex cruise when the massulae from freshwater ferns azolla were found in 49 ma old sediments brinkhuis et al 2006 and the presence of apectodinium augustum confirmed that the paleocene eocene thermal maximum petm 55 ma was unexpectedly recovered sluijs et al 2006 2 soon after the expedition when the cores were opened and analyzed ice rafted debris was found in surprisingly old 46 ma sediments moran et al 2006a these middle eocene sediments are characterized also by their high organic carbon content stein et al 2006 the exciting early results attracted other investigators that expanded the scientific investigating team to more than 40 people analyses were extended to include studies that revealed surprisingly high arctic ocean surface water temperatures sluijs et al 2006 and an amplified hydrological system pagani et al 2006 during the petm initial analyses revealed an extensive hiatus encompassing about 26 million years that occurred below a short interval showing starkly alternating black and white layers that is now dubbed the zebra interval thus the time interval from the late early miocene 18 ma to the middle middle eocene 44 ma is missing although the hiatus is a lost window in time for the arctic paleoclimate record it spawned other studies that integrated the regional tectonic history with acex results revealing a major oceanographic reorganization at 17 5 ma ventilation of the arctic ocean to the north atlantic through the fram strait jakobsson et al 2007 in terms of ventilation and water mass history neogene neodymium isotope data reveal that arctic intermediate waters originate from brine formation on eurasian shelf areas between 15 and 2 ma and during glacial periods throughout pleistocene times haley et al 2008a they conclude that this mode of arctic circulation differs markedly from today s situation showing relatively high contributions of north atlantic intermediate water and minor input from brine formation 3 in this special section the transformation continues results from the large acex scientific family include a robust age model detailed analyses of the middle eocene that document a unique brackish water environment sea ice and iceberg history reconstructions as well as the provenance of ice rafted debris from the eocene to present evolution of depositional environments times of isolation and connection to the global ocean geochemical analyses of the organic carbon rich sediments and unique applications of high resolution proxies and cyclostratigraphy highlights from this special section are presented here

salinity of the eocene arctic ocean from oxygen isotope analysis of fish bone carbonate stable isotope analysis was performed on the structural carbonate of fish bone apatite from early and early middle eocene samples 55 to 45 ma recently recovered from the lomonosov ridge by integrated ocean drilling program expedition 302 the arctic coring expedition the 18o values of the eocene samples ranged from 6 84 to 2 96 vienna peedee belemnite with a mean value of 4 89 compared to 2 77 for a miocene sample in the overlying section an average salinity of 21 to 25 was calculated for the eocene arctic compared to 35 for the miocene with lower salinities during the paleocene eocene thermal maximum the azolla event at 48 7 ma and a third previously unidentified event at 47 6 ma at the azolla event where the organic carbon content of the sediment reaches a maximum a positive 13c excursion was observed indicating unusually high productivity in the surface waters

glacial holocene salinity changes in the mediterranean sea hydrographic and depositional effects oxygen isotope changes as recorded by pleistocene foraminifera from open ocean sediments are primarily a function of changes in the isotopic composition of the global seawater reservoir caused by ice volume changes with a secondary temperature component1 oxygen isotope records from marginal basins such as the gulf of mexico2 the mediterranean sea3 5 and the red sea6 also exhibit the global signal but are far more complicated owing to the strong overprint of local climate conditions in particular glacial interglacial changes in continental aridity and river runoff produce significant salinity changes in these semi enclosed basins using available oxygen isotope records we estimate that glacial 18 000 yr bp salinities in the eastern and western mediterranean sea were 2 7 and 1 2 higher respectively than at present these elevated glacial salinities played an important part in preconditioning the eastern mediterranean for the eventual accumulation of organic carbon rich sediments sapropels at the end of deglaciation

weather radar observations of the hekla 2000 eruption cloud iceland the hekla eruption cloud on 26 27 february 2000 was the first volcanic cloud to be continuously and completely monitored advecting above iceland using the c band weather radar near the keflavik international airport real time radar observations of the onset advection and waning of the eruption cloud were studied using time series of ppi plan position indicator radar images including vmi normal echotop and cappi level 2 displays the reflectivity of the entire volcanic cloud ranges from 0 to 60 dbz the eruption column above the vent is essentially characterised by vmi normal and cappi level 2 values 30 dbz due to the dominant influence of lapilli and ash tephra on the overall reflected signal the cloud generated by the column was advected downwind to the north northeast it is characterised by values between 0 and 30 dbz and the persistence of these reflections likely result from continuing water condensation and freezing on ash particles echotop radar images of the eruption onset document a rapid ascent of the plume head with a mean velocity of 30 to 50 m s 1 before it reached an altitude of 11 12 km the evolution of the reflected cloud was studied from the area change in pixels of its highly reflected portions 30 dbz and tied to recorded volcanic tremor amplitudes the synchronous initial variation of both radar and seismic signals documents the abrupt increase in tephra emission and magma discharge rate from 18 20 to 19 00 utc on 26 february from 19 00 the 45 dbz and 30 45 dbz portions of the reflected cloud decrease and disappear at about 7 and 10 5 h respectively after the eruption began indicating the end of the decaying explosive phase the advection and extent of the reflected eruption cloud were compared with eyewitness accounts of tephra fall onset and the measured mass of tephra deposited on the ground during the first 12 h differences in the deposit map and volcanic cloud radar map are due to the fact that the greater part of the deposit originates by fallout off the column margins and from the base of the cloud followed by advection of falling particle in lower level winds

instrumental lahar monitoring at merapi volcano central java indonesia abstract more than 50 volcanic debris flows or lahars were generated around mt merapi during the first rainy season following the nuees ardentes of 22 november 1994 the rainfalls that triggered the lahars were analyzed using such instruments as weather radar and telemetered rain gauges lahar dynamics were also monitored using new non contact detection instrumentation installed on the slopes of the volcano these devices include real time seismic amplitude measurement rsam seismic spectral amplitude measurement ssam and acoustic flow monitoring afm systems calibration of the various systems was accomplished by field measurements of flow velocities and discharge contemporaneously with instrumental monitoring the 1994 1995 lahars were relatively short events their duration in the boyong river commonly ranging between 30 min and 1 h 30 min the great majority 90 of the lahars was recognized at kaliurang village between 13 00 and 17 30 h due to the predominance of afternoon rainfalls the observed mean velocity of lahar fronts ranged between 1 1 and 3 4 m s whereas the peak velocity of the flows varied from 11 to 15 m s under the gardu pandang viewpoint location at kaliurang to 8 10 m s at a section 500 m downstream from this site river slopes vary from 28 to 22 m km at the two sites peak discharges recorded in various events ranged from 33 to 360 m3 s with the maximum value of peak discharge 360 m3 s on 20 may 1995 to improve the lahar warning system along boyong river some instrumental thresholds were proposed large and potentially hazardous lahars may be detected by rsam units exceeding 400 ssam units exceeding 80 on the highest frequency band or afm values greater than 1500 mv on the low gain broad band setting

volcanic ash cloud retrieval by ground based microwave weather radar the potential of ground based microwave weather radar systems for volcanic ash cloud detection and quantitative retrieval is evaluated the relationship between radar reflectivity factor ash concentration and fall rate is statistically derived for various eruption regimes and ash sizes by applying a radar reflectivity microphysical model to quantitatively evaluate the ash detectability by weather radars a sensitivity analysis is carried out by simulating synthetic ash clouds and varying ash concentration and size as a function of the range radar specifications are taken from typical radar systems at s c and x band a prototype algorithm for volcanic ash radar retrieval varr is discussed starting from measured single polarization reflectivity the statistical inversion technique to retrieve ash concentration and fall rate is based on two cascade steps namely 1 classification of eruption regime and volcanic ash category and 2 estimation of ash concentration and fall rate expected accuracy of the varr algorithm estimates is evaluated using a synthetic data set an application of the varr technique is finally shown taking into consideration the eruption of the grinodotacutemsvoumltn volcano in iceland on november 2004 volume scan data from a doppler c band radar which is located at 260 km from the volcano vent are processed by means of the varr algorithm examples of the achievable varr products are presented and discussed

the thermohaline circulation of the arctic ocean and the greenland sea the thermohaline circulation of the arctic ocean and the greenland sea is conditioned by the harsh high latitude climate and by bathymetry warm atlantic water loses its heat and also becomes less saline by added river run off in the arctic ocean this leads to rapid cooling of the surface water and to ice formation brine released by freezing increases the density of the surface layer but the ice cover also insulates the ocean and reduces heat loss this limits density increase and in the central arctic ocean a low salinity surface layer and a permanent ice cover are maintained only over the shallow shelves where the entire water column is cooled to freezing can dense water form and accumulate to eventually sink down the continental slope into the deep ocean the part of the atlantic water which enters the arctic ocean is thus separated into a low density surface layer and a denser deep circulation these two loops exit through fram strait the waters are partly rehomogenized in the greenland sea the main current is confined to the greenland continental slope but polar surface water and ice are injected into the central gyre and create a low density lid allowing for ice formation in winter this leads to a density increase sufficient to trigger convection upwelling and subsequent ice melt the convection maintains the weak stratification of the gyre and also reinforces the deep circulation loop as the transformed waters return to the north atlantic the low salinity upper water of the east greenland current enters the labrador sea and influences the formation of labrador sea deep water the dense loop passes through denmark strait and the faroe shetland channel and sinks to contribute to the north atlantic deep water changes in the forcing conditions might alter the relative strength of the two loops this could affect the oceanic thermohaline circulation on a global scale

radar doppler velocimetry of volcanic eruptions theoretical considerations and quantitative documentation of changes in eruptive behaviour at stromboli volcano italy summary the use of radar doppler velocimetry for the observation of volcanic activity is new we used this method to continuously observe the activity of one vent of stromboli volcano italy from the end of 2000 april until early may during this period we recorded 702 eruptions 132 of which occurred before a strong rain storm passed over the island on april 29 in order to interpret the recorded doppler data we developed a program that simulates different strombolian eruption scenarios for which we then calculate the theoretical doppler spectra comparing our theoretical data with the observed data we are able to show that most of the eruptions are nearly vertical although we did observe only one component of the eruption vector with our doppler radar one of the most interesting features of the data set is a significant change in eruptive behaviour that correlates with the occurrence of the rain storm we find that on average the eruption duration increased by a factor of 2 eruptive velocities were much higher and indirect evidence indicates that the average particle diameter of the erupted material decreased this change may have several causes but the coincidence with the rain storm may be evidence of magma water interaction and feedback on the volcanic activity if the fluid source rain changing the eruptive style is at the surface and in near surface layers then the main control on final eruption dynamics at stromboli volcano must also be in rather shallow regions

on the asymmetry between cyclonic and anticyclonic flow in basins with sloping boundaries the authors present results from laboratory experiments and numerical simulations of the barotropic circulation in a basin with sloping boundaries forced by a surface stress focus is placed on flows with large scale rossby numbers that are significantly smaller than unity the results of the laboratory experiments and simulations show that cyclonic circulation follows the isobaths the flow pattern being independent of the strength of the forcing for anticyclonic circulation the flow pattern changes with forcing strength it is similar to the cyclonic topographically steered pattern for weak forcing and it develops strong cross slope flows for strong forcing linear dynamics are symmetric between cyclonic and anticyclonic circulations and give a good description of the cyclonic and weakly forced anticyclonic circulations the analysis of the nonlinear dynamics shows that topographically steered cyclonic flows are all stable and steady energy minimum solutions to the inviscid nonlinear equations this implies that the nonlinear terms advection of relative vorticity are always small for the topographically steered cyclonic flow for anticyclonic flow the situation is very different it is possible that no anticyclonic topographically steered flow is ever a solution to the steady inviscid equations and if such a steady anticyclonic flow does exist it is likely to be unstable since it must correspond to a saddle point in energy rather than to a minimum or a maximum the nonlinear terms are important when the rossby number is larger than the ekman number which is the case for the anticyclonic experiments with strongest forcing for these experiments the advection of relative vorticity prevents the flow from following topography creating locations with strong relative vorticity and cross slope flow the development of cross slope flow can be understood from the conservation of potential vorticity in basins with irregular topography the separation of anticyclonic flow from steep topography shown in the laboratory experiments and the theoretical analysis herein are in agreement with features like the gulf stream separation from the continental slope at cape hatteras north carolina

early oligocene initiation of north atlantic deep water formation dating the onset of deep water flow between the arctic and north atlantic oceans is critical for modelling climate change in the northern hemisphere1 2 and for explaining changes in global ocean circulation throughout the cenozoic era3 from about 65 million years ago to the present in the early cenozoic era exchange between these two ocean basins was inhibited by the greenland scotland ridge3 4 but a gateway through the faeroe shetland basin has been hypothesized3 5 previous estimates of the date marking the onset of deep water circulation through this basin on the basis of circumstantial evidence from neighbouring basins have been contradictory5 6 7 8 9 ranging from about 35 to 15 million years ago here we describe the newly discovered southeast faeroes drift which extends for 120 km parallel to the basin axis the onset of deposition in this drift has been dated to the early oligocene epoch 35 million years ago from a petroleum exploration borehole we show that the drift was deposited under a southerly flow regime and conclude that the initiation of deep water circulation from the norwegian sea into the north atlantic ocean took place much earlier than is currently assumed in most numerical models of ancient ocean circulation

first testing of a volcano doppler radar voldorad at mount etna italy a medium power 1 kw doppler radar of limited weight 110 kg and working in the uhf band has been developed for active remote sensing of volcanic eruptions named voldorad this radar is designed to monitor eruptive activities of variable magnitude at medium distance range 0 5 5 km in any weather condition and fills the gap between low and high power radar or sodar systems previously tested on volcanoes voldorad was operated for the first time during an eruption of mt etna on october 11 12 1998 doppler spectra recorded at 1 km distance from the vent reveal powerful echoes during the eruption paroxysm lava fountains which gradually decreased along with declining activity an average vertical velocity of 80 87 m s 1 is inferred for the eruptive jets

anoxia and high primary production in the paleogene central arctic ocean first detailed records from lomonosov ridge 1 except for a few discontinuous fragments of the late cretaceous early cenozoic climate history and depositional environment the paleoenvironmental evolution of the pre neogene central arctic ocean was virtually unknown prior to the iodp expedition 302 arctic ocean coring expedition acex drilling campaign on lomonosov ridge in 2004 here we present detailed organic carbon oc records from the entire ca 200 m thick paleogene oc rich section of the acex drill sites these records indicate euxinic black sea type conditions favorable for the preservation of labile aquatic marine algae type oc occur throughout the upper part of the early eocene and the middle eocene explained by salinity stratification due to freshwater discharge the superimposed short term milankovitch type variability in amount and composition of oc is related to changes in primary production and terrigenous input prominent early eocene events of algae type oc preservation coincide with global 13c events such as the petm and elmo events the elmo 13c event has been identified in the arctic ocean for the first time

improved os isotope stratigraphy of the arctic ocean 1 the history of the arctic ocean remained poorly known until the 2004 iodp coring of lomonosov ridge sediments early studies of the recovered sequence demonstrated the existence of an eocene lake stage prior to the transition to marine conditions the marine stage onset was inferred to be 17 5 million years ma ago thus implying a nearly 26 ma gap between the lacustrine and marine episodes and an unusual tectonic history for lomonosov ridge in order to explain this gap more recently rhenium osmium re os isotope measurements of the transition from the lacustrine to marine sediments suggested a much earlier inception of marine conditions and the absence of any significant gap between both episodes here an improved osmium isotope stratigraphy and re os data concur to assign a late eocene age 36 ma to the marine invasion consistent with a relative change in sea level on top of lomonosov ridge either from tectonic origin or from another cause

crumbling of dacite dome lava and generation of pyroclastic flows at unzen volcano recent modelling of volcanic eruptions has shown that the efficiency of subsurface degassing of magmas determines whether magma erupts explosively or effuses quietly1 2 slow uprise of magma is often accompanied by effective degassing leading to the extrusion of lava flows and domes although lava dome extrusion is one of the less explosive modes of eruption it is often accompanied by explosive pyroclastic activities3 5 the 1991 eruption of unzen volcano provided an opportunity to observe at close range several types of small scale pyroclastic flow glowing avalanches originating from lava domes most of the pyroclastic flows are of merapi type caused by blocks falling from a collapsing dome others are of pelean type originating in an explosion from the side of a dome the lavas apparently show variable degrees of self explosivity we suggest that variable degrees of degassing of the magma produced a wide range of excess pore pressures in the extruded lava domes resulting in both merapi type and pelean type pyroclastic flows from the domes

an idealized model of the world ocean part i the global scale water masses abstract a primitive equation three dimensional numerical model of the ocean employing idealized versions of the real topography and surface boundary conditions is used to study the water mass structure of the world ocean in particular the response of the model to three fundamental changes in boundary conditions is investigated in an attempt to identify the mechanisms in the model which are responsible for the establishment of the largest scale features of the global water mass structure with the drake passage closed thermohaline driving alone and a fresh north atlantic surface salinity specified only the coarsest aspects of the observed t and s structure are reproduced and the entire world ocean below the thermocline is dominated by water formed at the southern boundary the salinity configuration in particular lacks much of its observed structure in this case when the drake passage is opened the resulting circumpolar flow serves to isolate the extreme southern ocean this allows waters of no

generation of block and ash flows during the 1990 1995 eruption of unzen volcano japan processes generating block and ash flows by gravitational dome collapse merapi type pyroclastic flow were observed in detail during the 1990 1995 eruption of unzen volcano japan two different types were identified by analysis of video records and observations during helicopter flights most of the block and ash flows erupted during the 1991 1993 exogenous dome growth stage initially involved crack propagation due to cooling and flowage of the dome lava lobes the mass around the crack became unstable locally decreasing in tensile strength finally a slab separated from the lobe front fragmented progressively from the base to the top within a few seconds and became a block and ash flow rock falls immediately followed in response to local instability of the lobe front clasts in these rock falls fragmented and merged with the preceding flow in contrast block and ash flows during the endogenous dome growth stage in 1994 were generated due to local bulge of the dome unstable lava blocks collapsed and subsequently fragmented to produce block and ash flows

historical eruptions of merapi volcano central java indonesia 1768 1998 abstract information on merapi eruptive activity is scattered and much is remotely located a concise and well documented summary of this activity has been long needed to assist researchers and hazard mitigation efforts and the aim of this paper is to synthesize information from the mid 1700s to the present a descriptive chronology is given with an abbreviated chronology in a table that summarizes events by year assigns preliminary volcanic explosivity index vei ratings and hartmann classifications and provides key references the history of volcano monitoring is also outlined the study reveals that a major difference in eruption style exists between the twentieth and nineteenth centuries although the periodicity between larger events seems about the same during the twentieth century activity has comprised mainly the effusive growth of viscous lava domes and lava tongues with occasional gravitational collapses of parts of oversteepened domes to produce the nuees ardentes commonly defined as merapi type in the 1800s however explosive eruptions of relatively large size occurred to vei 4 and some associated fountain collapse nuees ardentes were larger and farther reaching than any produced in the twentieth century these events may also be regarded as typical eruptions for merapi the nineteenth century activity is consistent with the long term pattern of one relatively large event every one or two centuries based on the long term eruptive record deduced by others from volcanic stratigraphy it is uncertain whether or not a recurrence time model continues to apply to merapi but if so merapi could soon be due for another large event and its occurrence with only modest or inadequately appreciated precursors could lead to a disaster unprecedented in merapi s history because the area around the volcano is now much more densely populated

evolution of atlantic thermohaline circulation early oligocene onset of deep water production in the north atlantic the flow of deep water masses is a key component of heat transport in the modern climate system yet the role of deep ocean heat transport during periods of extreme warmth is poorly understood the present mode of meridional overturning circulation is characterized by deep water formation in both the north atlantic and the southern ocean however a different mode of meridional overturning circulation operated during the extreme greenhouse warmth of the early cenozoic during which time the southern ocean was the dominant region of deep water formation the combination of general global cooling and tectonic evolution of the atlantic basins over the past 55 m y ultimately led to the development of a mode of overturning circulation characterized by both southern ocean and north atlantic deep water sources the change in deep water circulation mode may in turn have affected global climate however unraveling the causes and consequences of this transition requires a better understanding of the timing of the transition new nd isotope data from the southeastern atlantic ocean indicate that the initial transition to a bipolar mode of deep water circulation occurred in the early oligocene ca 33 ma the likely cause of significant deep water production in the north atlantic was tectonic deepening of the sill separating the greenland norwegian sea from the north atlantic

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

liquid freshwater transport and polar surface water characteristics in the east greenland current during the ao 02 oden expedition dynamical features of the east greenland current egc are synthesized from a survey conducted by the swedish icebreaker oden during the international arctic ocean 02 expedition ao 02 in may 2002 with emphasis on the liquid freshwater transport and polar surface water the data include hydrography and lowered acoustic doppler current profiler ladcp velocities in eight transects along the egc from the fram strait in the north to the denmark strait in the south the survey reveals a strong confinement of the low salinity polar water in the egc to the continental slope shelf a feature of relevance for the stability of the thermohaline circulation in the arctic mediterranean the southward transport of liquid freshwater in the egc was found to vary considerably between the sections ranging between 0 01 and 0 1 sverdrup computations based on geostrophic as well as ladcp velocities give a section averaged southward freshwater transport of 0 06 sverdrup in the egc during may 2002 furthermore oden data suggest that the liquid freshwater transport was as large north of the fram strait as it was south of the denmark strait

the age of water and ventilation timescales in a global ocean model abstract the age of water in the world ocean is studied using a passive age tracer introduced into a global ocean model additional information is derived from a transient dye tracer that tracks the time dependent spreading of surface waters into the model ocean interior of particular interest is the nature of ocean ventilation over the 10 100 yr timescale as well as the simulated age of deep and bottom water masses in the upper model levels young water is found to correspond with regions of convergence and downwelling in the surface ekman layer upwelling and convection are both shown to age the upper ocean by entraining older waters into the surface mixed layer in the deep model levels water age varies greatly between oceans with young water found in convectively active regions in the north atlantic and in the ross and weddell seas and old water found in the deep north pacific the oldest water mass mixture located at 2228 m depth in the western pacific ocean is dated at 1494 years made

catastrophic flood of the mediterranean after the messinian salinity crisis around 5 6 million years ago the mediterranean sea became disconnected from the world s oceans and during the period that followed known as the messinian salinity crisis sea levels fell dramatically as the waters evaporated the water returned about 5 3 million years ago but the details about this the largest known flood in earth s history remain sketchy a study making use of boreholes seismic data and numerical modelling suggests that it was a catastrophic event though it started as a trickle that may have lasted several thousand years as much as 90 of the incoming water was transferred in less than two years such an abrupt flood may have involved peak rates of sea level rise of more than 10 metres a day 5 33 million years ago in an event known as the zanclean flood atlantic waters refilled a mostly desiccated mediterranean sea which had become disconnected from the world s oceans however the nature abruptness and evolution of this flood remain poorly constrained using borehole and seismic data and a model study it is now suggested that 90 per cent of the water was transferred in a short period of a few months to two years with peak rates of sea level rise in the mediterranean possibly reaching more than 10 metres per day the mediterranean sea became disconnected from the world s oceans and mostly desiccated by evaporation about 5 6 million years ago during the messinian salinity crisis1 2 3 the atlantic waters found a way through the present gibraltar strait and rapidly refilled the mediterranean 5 33 million years ago in an event known as the zanclean flood4 the nature abruptness and evolution of this flood remain poorly constrained4 5 6 borehole and seismic data show incisions over 250 m deep on both sides of the gibraltar strait that have previously been attributed to fluvial erosion during the desiccation4 7 here we show the continuity of this 200 km long channel across the strait and explain its morphology as the result of erosion by the flooding waters adopting an incision model validated in mountain rivers this model in turn allows us to estimate the duration of the flood although the available data are limited our findings suggest that the feedback between water flow and incision in the early stages of flooding imply discharges of about 108 m3 s 1 three orders of magnitude larger than the present amazon river and incision rates above 0 4 m per day although the flood started at low water discharges that may have lasted for up to several thousand years our results suggest that 90 per cent of the water was transferred in a short period ranging from a few months to two years this extremely abrupt flood may have involved peak rates of sea level rise in the mediterranean of more than ten metres per day

boundary currents and watermass transformation in marginal seas the properties of watermass transformation and the thermohaline circulation in marginal seas with topography and subject to a spatially uniform net surface cooling are discussed the net heat loss within the marginal sea is ultimately balanced by lateral advection from the open ocean in a narrow boundary current that flows cyclonically around the basin heat loss in the interior is offset by lateral eddy fluxes originating in the boundary current the objectives of this study are to understand better what controls the density of waters formed within the marginal sea the temperature of the outflowing waters the amount of downwelling and the mechanisms of heat transport within the marginal sea the approach combines heat budgets with linear stability theory for a baroclinic flow over a sloping bottom to provide simple theoretical estimates of each of these quantities in terms of the basic parameters of the system the theory compares well to a series of eddy resolving primitive equation model calculations the downwelling is concentrated within the boundary current in both a diffusive boundary layer near topography and an eddy driven region on the offshore edge of the boundary current for most high latitude regions the horizontal gyre is expected to transport more heat than does the overturning gyre

estimating particle sizes concentrations and total mass of ash in volcanic clouds using weather radar observations of the march 19 1982 ash eruption of mount st helens made by the national weather service nws portland oregon on 5 cm radar were used to estimate the volume of the ash cloud 2000 500 km3 the concentration of ash 0 2 0 6 g m 3 and the total mass of ash erupted 3 10 1011 g the position of the cloud was also tracked by radar particle sizes in the ash cloud were estimated from settling velocities suggested by decreases in maximum ash cloud height with time as it moved away from the volcano the march 19 1982 ash blanket was sampled and mapped ash fallout times and accumulation rates were reconstructed from ground observations grain size distributions for various samples were used to obtain particle concentration 0 2 g m 3 total ashfall mass 1 3 1011 g and radar reflectivity factor 4 5 mm6 m 3 for the ash cloud our preferred estimate for total ashfall mass 4 1011 g is that obtained from the product of the ash cloud volume determined by radar 2000 500 km3 and the particle concentration inferred from ashfall data 0 2 g m 3 previously published ashfall data for the may 18 1980 mount st helens eruption has been studied using our ashfall inversion technique to estimate 6 hour mean particle concentration 3 g m 3 the size distribution total ashfall mass 5 1014 g and radar reflectivity factors 7 60 mm6 m 3 for the ash cloud a somewhat higher value 9 g m 3 for particle concentration was estimated from radar observations harris et al 1981 for an ash cloud formed during the peak eruption rate at mount st helens the two independent estimates are consistent given the many uncertainties of the problem the reflectivity factors for very dense ash clouds 3 9 g m 3 are several orders of magnitude smaller than for severe weather considered routinely detectable by airborne weather radar and dangerous for aviation because volcanic ash clouds with particle concentrations of at least 0 2 g m 3 are produced in extremely small eruptions in terms of total ashfall mass of duration less than 1 minute volcanic ash clouds must be considered an extremely serious hazard to in flight aircraft regardless of eruption magnitude these factors should be considered in hazard evaluations for known volcanoes located near air routes radar observations and calculations can provide scientists monitoring eruptive activity with significant information for estimating duration of eruption particle concentrations in ash clouds total mass of solid material erupted magma eruption rate potential ashfall mass ashfall locations and accumulation rates and duration and amounts of ashfall detailed analysis of ashfall data and nws radar observations of ash clouds from mount st helens demonstrate that weather radar can yield such timely information during and following volcanic eruptions

installation of a doppler radar monitoring system at merapi volcano indonesia merapi volcano indonesia is one of the most active dome building volcanoes worldwide instabilities at the growing dome cause rockfalls and hot block and ash flows which can reach run out distances of several kilometers therefore merapi has been monitored extensively for many years however direct visual observation of the dome is often impossible due to cloud coverage of the summit in october 2001 a first prototype doppler radar system was installed to overcome this shortcoming the system is able to penetrate clouds and observe material movements at the dome giving valuable information about dynamic processes in the dome area the system also allows detection of rainfall in several distance intervals for precise positioning of the beam the system was equipped with an electromechanical mounting in 2003 a charge coupled device ccd camera attached to the radar mirror documents the radar beam position and provides visual observation of the dome recorded data camera images and status information are telemetered to the merapi volcano observatory where they can be processed and interpreted status information is also sent via short message service via a global system for mobile communications gsm modem by processing the doppler radar data we are able to discriminate between three different types of instability events sliding dome material dome material gravitationally breaking off the dome and explosive outbursts of dome material due to expansion of volcanic gas in order to independently verify our observations we compared rockfall events detected by the radar system to seismic recordings and found a good correlation

lahars at merapi volcano central java an overview abstract merapi volcano in central java is one of the most active volcanoes in the world at least 23 of the 61 reported eruptions since the mid 1500s have produced source deposits for lahars the combined lahar deposits cover about 286 km 2 on the flanks and the surrounding piedmonts of the volcano at merapi lahars are commonly rain triggered by rainfalls having an average intensity of about 40 mm in 2 h most occur during the rainy season from november to april and have average velocities of 5 7 m s at 1000 m in elevation a wide range of facies may be generated from a single flow which may transform downvalley from debris flow to hyperconcentrated streamflow because of the high frequency and magnitude of the lahar events lahar related hazards are high below about 450 600 m elevation in each of the 13 rivers which drain the volcano hazard zone maps for lahar were produced by pardyanto et al volcanic hazard map merapi volcano central java 1 100 000 geol surv of indonesia bandung ii 4 1978 and the japanese indonesian cooperation agency master plan for land conservation and volcanic debris control in the area of mt merapi jakarta 1980 but these maps are of a very small scale to meet modern zoning requirements more recently a few large scale maps 1 10 000 and 1 2000 scale and risk assessments have been completed for a few critical river systems

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 early miocene onset of a ventilated circulation regime in the arctic ocean deep water formation in the northern north atlantic ocean and the arctic ocean is a key driver of the global thermohaline circulation and hence also of global climate1 deciphering the history of the circulation regime in the arctic ocean has long been prevented by the lack of data from cores of cenozoic sediments from the arctic s deep sea floor similarly the timing of the opening of a connection between the northern north atlantic and the arctic ocean permitting deep water exchange has been poorly constrained this situation changed when the first drill cores were recovered from the central arctic ocean2 here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ventilated conditions in the arctic ocean occurred during the later part of early miocene times we attribute this pronounced change in ventilation regime to the opening of the fram strait a palaeo geographic and palaeo bathymetric reconstruction of the arctic ocean together with a physical oceanographic analysis of the evolving strait and sill conditions in the fram strait suggests that the arctic ocean went from an oxygen poor lake stage to a transitional estuarine sea phase with variable ventilation and finally to the fully ventilated ocean phase 17 5 myr ago the timing of this palaeo oceanographic change coincides with the onset of the middle miocene climatic optimum3 although it remains unclear if there is a causal relationship between these two events

palynology paleoclimatology and correlation of middle miocene beds from porcupine river locality 90 1 alaska abstract beds in the upper ramparts canyon of the porcupine river alaska 67 20 n 141 20 w yielded a flora rich in pollen of hardwood genera now found in the temperate climates of north america and asia the beds are overlain or enclosed by two basalt flows which were dated to 15 2 0 1 ma by the 40 ar 39 ar method fixing the period of the greatest abundance of warm loving genera to the early part of the middle miocene the assemblage is the most northern middle miocene flora known in alaska organic bed 1 underlies the basalt and is older than 15 2 ma but is of early to middle miocene age the pollen assemblage from organic bed 1 is dominated by conifer pollen from the pine and redwood cypress yew families with rare occurrences of temperate hardwoods organic bed 2 is a forest floor containing redwood trees in life position engulfed by the lowest basalt flow a pine log has growth rings up to 1 cm thick organic beds 3 and 4 comprise lacustrine sediment and peat between the two basalt flows their palynoflora contain conifers and hardwood genera of which about 40 have modern temperate climatic affinities hickory katsura walnut sweet gum wingnut basswood and elm pollen are consistently present and beech and oak alone make up about 20 of the pollen assemblage a warm high latitude climate is indicated for all of the organic beds but organic bed 3 was deposited under a time of peak warmth climate data derived by comparison with modern east asian vegetation suggest that at the time of deposition of organic bed 3 the mean annual temperature mat was ca 9 c the warm month mean temperature wmmt was 20 c and the cold month mean temperature cmmt was ca 2 c in contrast the modern mat for the region is 8 6 c wmmt is 12 6 c and cmmt is 28 c organic beds 3 and 4 correlate to rocks of the middle miocene late seldovian stage of cook inlet and also probably correlate to and more precisely date the lower third of the suntrana formation in the alaska range beds at unalaklect part of the upper mackenzie bay sequence in the beaufort mackenzie basin and the mary sachs gravel of banks island this suggests that forests with significant percentages of temperate deciduous angiosperms existed between latitudes 60 and 72 n during the early middle miocene

ventilation of the miocene arctic ocean an idealized model study a model study of an idealized early miocene arctic ocean has been undertaken the work is motivated by the first drill core retrieved from the lomonosov ridge in the central arctic ocean which sug

lagrangian decomposition of the deacon cell the meridional overturning cells in the southern ocean are decomposed by lagrangian tracing using velocity and density fields simulated with an ocean general circulation model particular emphasis is given to the deacon cell the flow is divided into four major components 1 water circling around antarctica in the antarctic circumpolar current acc 2 water leaving the acc toward the north into the three world oceans 3 water coming from the north and joining the acc mainly consisting of north atlantic deep water nadw and 4 interocean exchange between the three world oceans without circling around antarctica the deacon cell has an amplitude of 20 sv of which 6 sv can be explained by the the east west tilt of the acc 5 sv by the east west tilt of the subtropical gyre and the remaining 9 sv by the differences of the slope and depth of the southward transport of nadw and its return flow as less dense water the diabatic or cross isopycnal deacon cell is only 2 sv

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

in situ observation of dome instabilities at merapi volcano indonesia a new tool for volcanic hazard mitigation understanding the mechanism and repetition frequency of dome instability events at high risk dome building volcanoes located near densely populated areas is one crucial piece of information when dealing with volcanic hazard mitigation although some visual in situ observations of such processes have been made at unzen volcano and on montserrat continuous monitoring of dome activity has been severely hampered by weather conditions such as cloud coverage using a newly designed microwave doppler system we are able to continuously monitor in situ processes at active dome systems with our instrument we can determine the velocity of material breaking off an active dome as well as the approximate amount of material passing through the radar beam allowing us to continuously identify different types of dome instabilities a data set collected during a highly active period at the end of oct early nov 2001 at merapi volcano indicates two different instability types a purely gravitational instabilities and b gravitational instabilities that are followed immediately by an explosion such information continuously collected allows tight constrains on the activity status of dome building volcanoes and is an important information for hazard mitigation the number of instabilities detected by the radar during the observational period is larger than the number of rockfall events detected by the seismic network operated at merapi during that time

magnetic monitoring at merapi volcano indonesia abstract merapi volcano located 30 km north of the heavily populated city of yogjakarta java is one of the most active of the 129 volcanoes in indonesia about every 2 years a new phase of activity is observed depending on the past activity the unrest gives rise either to an endogenous dome which partly collapses in the southwest direction or to pyroclastic flows which travel as far as 15 km the 1990 1997 period has involved a plume emission on 30 august 1990 an extrusion on 20 january 1992 and a pyroclastic eruption on 22 november 1994 the intensity of the earth magnetic field has been measured simultaneously and digitally recorded at four stations since 1990 two overhauser magnetometers with resolution of 0 01 nt have been installed in the summit area to strengthen the volcano monitoring outstanding magnetic changes appear to correlate with volcanic activity three types of volcanomagnetic signals can be identified long term trends up to 15 nt with period 10 years medium term cyclic variations at most 3 nt in amplitude and with 1 2 years period and small events reaching 1 5 nt lasting a few months and associated with any remarkable volcanic activity merapi volcano began a new cycle of activity in 1995 leading to a dome growth in july 1996 and accompanied by 27 nuees ardentes in august the comparison between magnetic data seismicity and surface phenomena suggests that some long term trends of decade periods could be of thermomagnetic origin while mid term volcanomagnetic variations associated with the cycles of merapi activity could be of piezomagnetic origin short term variations of a few weeks duration less than 1 5 nt are well correlated with the 1995 1996 seismic activity

choking the mediterranean to dehydration the messinian salinity crisis strait uplift due to isostasy played a pivotal role in the development and maintenance of a desiccated mediterranean basin during the late miocene messinian salinity crisis new three dimensional flexure models for the western mediterranean suggest that most of the giant evaporite body was deposited before sea level lowering any mechanism that subsequently caused a mediterranean sea level lowering by a few hundred meters during several thousand years sufficed to cause isostatic uplift and closure of the gateways thus choking the mediterranean to desiccation due to this isostatic feedback multiple desiccation and reflooding phases driven by milankovitch cycles are unlikely when the atlantic connection had been lost and sea level had dropped a sizeable regional uplift of the strait of gibraltar developed that presented a formidable obstacle to reflooding rollback and steepening of the gibraltar slab may have played a key role at the end of the miocene by dynamically lowering the sill region thus reinstating the oceanic connection

circulation and exchange in choked marginal seas a theory for the exchange between a rotating buoyancy forced marginal sea and an ocean is developed and tested numerically cooling over the marginal sea leads to sinking and sets up a two layer exchange flow with a warm surface layer entering from the ocean and a cool layer exiting at depth the connecting strait is sufficiently narrow and shallow to cause the exchange flow to be hydraulically controlled the incoming surface layer forms a baroclinically unstable boundary current that circles the marginal sea in a cyclonic sense and feeds heat to the interior by way of eddies consistent with the overall heat and volume balances for the marginal sea there is a continuous family of hydraulically controlled states with critical flow at the most constricted section of the strait included in this family is a limiting maximal exchange solution with two sections of hydraulic control in the strait and with fixed layer depths at the most constricted section the state of exchange for a given forcing is predicted using a theory that assumes energy conservation over a certain path connecting the strait to the marginal sea or in some cases the ocean depending on the configuration of the exchange long wave information may be blocked from entering the strait from the marginal sea from the open ocean or both the scenario that holds determines what is predicted and what needs to be input numerical tests of the prediction for the temperature difference and the state of exchange are carried out for straits with a pure contraction in width and for a constant width strait with a topographic sill the comparison is reasonable in most cases though the numerical model is not able to reproduce cases of multiple states predicted by the theory for certain forcing values the analytical model is an alternative to the price and yang and siddall et al models of a marginal sea outflow

an overview of the seismicity of merapi volcano java indonesia 1983 1994 abstract from 1982 to 1995 merapi volcano java indonesia experienced two main eruptive cycles from 1984 to 1986 and from 1992 to 1994 each cycle had a duration slightly larger than 2 years four major eruptive events occurred in 1984 1986 1992 and 1994 these eruptions were monitored by a telemetered seismic network we present an overview of the seismicity observed between 1983 and 1995 from seismological observations several types of characteristic events are recognised volcanotectonic earthquakes are standard microearthquakes either shallow an aseismic zone is situated between two seismic zones at a depth between 1 5 and 2 5 km below the summit we postulate that it is a small shallow magma reservoir where magma injected from below can be stored temporarily we try to relate seismic observations during both eruptive cycles to the initial injection of deep magma to the superficial magma system the first eruption in each case seems to involve magma enriched in gas that extrudes the content of the conduit and explodes the old dome a regular outflow of magma follows the initial explosion and gradually a dome is building up then it stops and a period of repose is observed later a second episode of dome growth occurs the height of the dome reaches a maximum corresponding to a state of lithostatic equilibrium the time delay of more than 2 years between the beginning and the end of a cycle may result from crystallisation in a volatile rich magma and from the building up of pressure in the superficial magma pocket some important events like the collapse of the dome on 22 november 1994 are not preceded by any seismic precursor when it reaches a large volume the dome is not stable and is likely to collapse by gravity for instance after the sudden influx of matter or gas or after a heavy rain on merapi tremors are observed but do not always precede a dangerous event

structure of magma reservoirs beneath merapi and surrounding volcanic centers of central java modeled from ambient noise tomography we present a three dimensional model of the distribution of s wave velocity in the upper crust to a depth of 20 km beneath central java based on the analysis of seismic ambient noise data recorded by more than 100 seismic stations in 2004 associated with the meramex project to invert the rayleigh wave dispersion curves to construct 2d group velocity maps and 3d distributions of s wave velocity we have used a new tomographic algorithm based on iterative linearized inversion we have performed a series of synthetic tests that demonstrate significantly higher resolution in the upper crust with this model compared to the local earthquake travel time tomography let model previously applied for the same station network beneath the southern flank of merapi we identify a large low velocity anomaly that can be split into two layers the upper layer reflects the 1 km thick sedimentary cover of volcanoclastic deposits the deeper anomaly at depths of 4 8 km may represent a magma reservoir with partially molten rock that feeds several volcanoes in central java beneath the merapi summit we observe another low velocity anomaly as deep as 8 km that may be associated with the active magma reservoir that feeds the eruptive activity of merapi in the southern portion of the study area in the lower crust we identify a low velocity anomaly that may represent the top of the pathways of volatiles and melts ascending from the slab that was previously inferred from the let model results we observe that this anomaly is clearly separate from the felsic magma reservoirs in the upper crust this article is protected by copyright all rights reserved

automatic classification of dome instabilities based on doppler radar measurements at merapi volcano indonesia part i summary in this paper we analyse a 3 yr long time series of activity at merapi volcano indonesia which was recorded using a doppler radar system between november 2001 and july 2004 about 57 000 events associated with dome instabilities have been recorded by the radar system because of the huge amount of data an automatic classification system has been developed which identifies different types of instabilities at the lava dome i e sliding material gravitational break offs and explosive outbursts as well as rainfall comparing the record of detected instabilities to rockfall measurements deduced from the seismic network of the volcanological technology research center vtrc we are able to demonstrate the high potential of doppler radar measurements for monitoring of dome activity when aligned to the most active area at the dome the radar detects significantly more events than the seismic system in combination with seismic measurements the doppler radar allows for identifying changes in the location of the most active area at the dome this is particularly helpful since the dome of merapi is covered by clouds about 50 per cent of the time additionally the radar data can help to distinguish between rockfalls and multiphase events in the seismic measurements the different types of instabilities have been analysed for their occurrence frequency in terms of size volume and mean velocity significant temporal changes in the relative occurrence frequencies or the characteristic properties of the different types of instabilities have not been observed however during the period of fastest activity decrease explosive instability events with a gravitational precursor decreased faster than events starting explosively because the radar system is able to observe rainfall the data has been analysed for a link between rain and dome activity throughout the observation period no such link could be found however this might be due to the fact that the activity has been almost continuously decreasing

doppler radar sounding of volcanic eruption dynamics at mount etna besides their common use in atmospheric studies doppler radars are promising tools for the active remote sensing of volcanic eruptions but were little applied to this field we present the observations made with a mid power uhf doppler radar voldorad during a 7 h strombolian eruption at the se crater of mount etna on 11 12 october 1998 main characteristics of radar echoes are retrieved from analysis of doppler spectra recorded in the two range gates on either side of the jet axis from the geometry of the sounding the contribution of uprising and falling ejecta to each doppler spectrum can be discriminated the temporal evolution of total power backscattered by uprising targets is quite similar to the temporal evolution of the volcanic tremor and closely reproduces the overall evolution of the eruption before during and after its paroxysm moreover during the sharp decrease of eruptive activity following the paroxysm detailed analysis of video from camera recording radar and seismic measurements reveals that radar and video signals start to decrease simultaneously approximately 2 5 min after the tremor decline this delay is interpreted as the ascent time through a magma conduit of large gas slugs from a shallow source roughly estimated at about 500 m beneath the se crater detailed analysis of eruptive processes has been also made with voldorad operating in a high sampling rate mode signature of individual outburst is clearly identified on the half part of doppler spectra corresponding to rising ejecta temporal variations of the backscattered power exhibit quasi periodic undulations whereas the maximum velocity measured on each spectrum displays a sharp peak at the onset of each outburst followed by a slow decay with time periodicity of power variations between 3 8 and 5 5 s is in agreement with the occurrence of explosions visually observed at the se vent maximum vertical velocities of over 160 m s 1 were measured during the paraoxysmal stage and the renewed activity finally by using a simplified model simulating the radar echoes characteristics we show that when voldorad is operating in high sampling rate mode the power and maximum velocity variations are directly related to the difference in size and velocity of particles crossing the antenna beam

self potential and ground temperature at merapi volcano prior to its crisis in the rainy season of 2000 2001 abstract rainwater infiltration into the active lava dome of merapi volcano central java has often been suggested as a triggering mechanism for partial dome collapse and subsequent eruptive behavior however the phenomenon has not been systematically investigated we use a multi parametric approach to study the interaction of the hydrologic and magmatic system near the lava dome prior to its crisis in early 2001 we describe the hardware concept for a continuous monitoring system for self potentials u sp and ground temperature t installed in august 2000 at the solfatara woro only 150 m from the active lava dome relating the data from this station to measurements of rainfall air pressure solfatara temperature and seismicity several effects can be distinguished a a long term correlation is observed between electrode temperature difference and sp with estimated coupling coefficients of 2 1 0 5 mv c b after individual rainfall events u t signatures show a typical pattern of positive charge accumulation at the hot electrodes near the fumarolic vents c an exceptional anti correlation between u and t is observed in january 2001 during a period of rapid dome growth prior to the collapse and eruptive crisis d wavelet analysis of sp reveals the sporadic occurrence of periodic fluctuations with a clear 12 h s2 component because of their amplitude of up to 100 mv km and their periodicity s2 but not 24 h or lunar 12 h 25 min these fluctuations are unlikely to be caused by natural magnetic field variation or by earth tides instead they do seem correlated but not in phase with atmospheric pressure changes we discuss effects a d in the framework of source mechanisms related to water lava interactions

influence of brine formation on arctic ocean circulation over the past 15 million years the early oceanographic history of the arctic ocean is important in regulating and responding to climatic changes however constraints on its oceanographic history preceding the quaternary the past 1 8 myr have become available only recently because of the difficulties associated with obtaining continuous sediment records in such a hostile setting here we use the neodymium isotope compositions of two sediment cores recovered near the north pole to reconstruct over the past approx15 myr the sources contributing to arctic intermediate water a water mass found today at depths of 200 to 1 500 m we interpret high neodymium ratios for the period between 15 and 2 myr ago and for the glacial periods thereafter as indicative of weathering input from the siberian putoranan basalts into the arctic ocean arctic intermediate water was then derived from brine formation in the eurasian shelf regions with only a limited contribution of intermediate water from the north atlantic in contrast the modern circulation pattern with relatively high contributions of north atlantic intermediate water and negligible input from brine formation exhibits low neodymium isotope ratios and is typical for the interglacial periods of the past 2 myr we suggest that changes in climatic conditions and the tectonic setting were responsible for switches between these two modes

continuous monitoring of volcanic eruption dynamics a review of various techniques and new results from a frequency modulated radar doppler system in situ measurement of volcanic eruption velocities is one of the great challenges left in geophysical volcanology in this paper we report on a new radar doppler technique for monitoring volcanic eruption velocities in comparison with techniques employed previously e g photographic methods or acoustic doppler measurements this method allows continuous recordings of volcanic eruptions even during poor visibility also radar doppler instruments are usually light weight and energy efficient which makes them superior to other doppler techniques based on laser light or sound the proposed new technique was successfully tested at stromboli volcano in late 1996 during a period of low activity the recorded data allow a clear distinction between particles rising from the vent and particles falling back towards the vent the mean eruption velocity was approximately 10 m s most of the eruptions recorded by radar were correlated to seismic recordings the correlation between the magnitude of the volcanic shocks and the eruption force index defined in the paper may provide new insights into magma transport in the conduit

the role of eddy transfer in setting the stratification and transport of a circumpolar current abstract high resolution numerical experiments of a circumpolar current are diagnosed to study how lateral and vertical transfer of buoyancy by geostrophic eddies balances advection by a meridional circulation driven by surface wind stresses and buoyancy fluxes a theory is developed in the framework of the residual circulation to relate the vertical and horizontal stratification set up to the transfer properties of eddies and the patterns of imposed wind and buoyancy forcing simple expressions are found for the depth of penetration stratification baroclinic transport and residual circulation of the current finally the ideas are applied to the antarctic circumpolar current acc and yield predictions for how its properties depend on wind and buoyancy forcing