evolution of the large scale temperature field in the greenland sea during 1988 89 from tomographic measurements the greenland sea ocean acoustic tomography experiment was conducted during 1988 89 as one component of the international greenland sea project to study deep water formation and the response of the gyre to variations in wind stress and ice cover six acoustic transceivers moored in an array 200 km across transmitted to one another at four hour intervals near the end of february 1989 a sub surface temperature maximum at several hundred meters depth disappeared over a surprisingly large area of the central greenland sea while the water column was modified to about 1000 m depth over much of the gyre the surface remained colder than the deeper water contrary to what might be expected from simple models of convective renewal

a two phase approach to the simulation of the combined isotope salinity signal of marine ice a modified boundary layer box diffusion model is used to simulate the production of the combined oxygen isotope salinity signal of a body of marine ice the final signal is considered to be the result of fractionation and segregation processes occurring first upon the formation of frazil crystals in suspension and second during their accumulation and consolidation due to the advancement of a freezing front the model results are compared to oxygen isotope and salinity values in a 45 m marine ice core from the nansen ice shelf antarctica parameters more suitable to the modeling of marine ice as opposed to sea ice are introduced and conclusions are drawn on the origin of the impurity characteristics of marine ice including the still unresolved question of its anomalously low salinity

temporal analysis of water masses and sea ice formation rate west of the antarctic peninsula in 2008 estimated from southern elephant seals srdl ctd data abstract as an alternative method to collect oceanographic data in the polar oceans especially during winter when traditional methods are very difficult to be used sea mammals can be tagged with satellite relay data loggers with ctd capabilities srdl ctd using data from nine southern elephant seals ses mirounga leonina tagged during a field campaign of the meop br project the brazilian counterpart to the marine mammal exploration of the oceans pole to pole this work presents a temporal analysis of the water masses and the sea ice formation rate at the western part of the antarctic peninsula ap during 2008 we found that the seasonal and local processes controlling the surface and intermediate layers of the ocean produced differences in the water mass composition and the sea ice formation rates in our study region sea ice formation rates ranged from less than 1 cm day in deep sea waters off the northern part of the ap to 14 cm day at the vicinity of ice shelves such as the abbot and wilkins ice shelves further south in the ap maximum sea ice formation rates as expected occurred during autumn to winter after the successive collapse events of the wilkins ice shelf wis in 2008 the sea ice formation rate endured significant reductions even when sea ice concentrations were high in the region these reductions observed by ses in the vicinity of wis can be associated with freshwater input derived from shelf collapses the presence of the circumpolar deep water cdw over the continental shelf west of the ap affected the sea ice formation rate by both contributing to the observed low sea ice coverage and to the acceleration of the ice shelf melting another process that demonstrated influence on the formation of sea ice was the advection of more saline waters in the oceanic layer considered here for the application of salt balance equation this advection resulted in unrealistic sea ice formation rates in regions where there was no sea ice cover the data and results presented here can be used to feed and to validate climate ocean atmosphere coupled models the data can be combined with other more traditional meteorological and oceanographic data in order to provide a better understanding of both oceanic and ocean atmosphere coupled processes yet not very well known in our study region

study of the impact of ice formation in leads upon the sea ice pack mass balance using a new frazil and grease ice parameterization abstractleads are cracks in sea ice that often form because of deformation during winter months leads expose the ocean to the cold atmosphere resulting in supercooling and the formation of frazil ice crystals within the mixed layer here the authors investigate the role of frazil ice formation in leads on the mass balance of the sea ice pack through the incorporation of a new module into the los alamos sea ice model cice the frazil ice module considers an initial cooling of leads followed by a steady state formation of uniformly distributed single size frazil ice crystals that precipitate to the ocean surface as grease ice the grease ice is pushed against one of the lead edges by wind and water drag that the authors represent through a variable collection thickness for new sea ice simulations of the sea ice cover in the arctic and antarctic are performed and compared to a model that treats leads the same as the open ocean the processes of ice formation in the new module slow down the refreezing o

mapping of sea ice production in the arctic coastal polynyas 1 high ice production in coastal polynyas over the continental shelves in the arctic ocean is responsible for the formation of cold saline water which contributes to the maintenance of the arctic ocean halocline the accurate detection of coastal polynyas including an estimate of thin ice thickness is essential for the estimation of sea ice production this paper presents an algorithm that estimates thin ice thickness using special sensor microwave imager ssm i data in the arctic ocean detection and estimation of sea ice thicknesses of 0 15 m are based on the ssm i 85 and 37 ghz polarization ratios pr85 and pr37 through a comparison with sea ice thicknesses estimated from the advanced very high resolution radiometer avhrr data in the three different arctic coastal polynyas thus for the entire arctic ocean the algorithm can be used for the detection of coastal polynyas and for the estimation of sea ice production through combination with heat flux calculation this study provides the first circumpolar mapping of sea ice production in coastal polynyas over the entire arctic ocean high ice production is confined to the major arctic coastal polynyas with the highest ice production rate being in the north water polynya this study also presents the interannual variability of sea ice production in the 10 major coastal polynyas from 1992 to 2007 in general interannual variability in sea ice production has good correlation with polynya extent rather than surface air temperature the mapping also provides surface heat and salt flux conditions in the ice covered region which have not been well understood to date

contributions of the siberian shelf polynyas to the arctic ocean intermediate and deep water the role of the open water regions or polynyas in the winter ice pack over the siberian continental shelves in the production of arctic ocean intermediate and deep water is examined through use of a combination of passive microwave satellite data coastal weather station data and oceanographic data the satellite data allow us to derive a time series of the open water areas of selected polynyas for the 1978 1982 winters the polynyas which occur north of svalbard around franz josef land along the west coast and north end of novaya zemlya and to the east of severnaya zemlya and the taymyr peninsula are the primary oceanographic contributors the open water time series for these polynyas are used in combination with coastal weather station data to estimate the heat loss from each polynya for the region north of svalbard which is historically known as whalers bay the study shows that the heat loss is sufficient to provide the observed cooling of the west spitsbergen current for the other polynyas the heat loss is used to compute the ice production rates and the oceanic salt flux we then use the historic oceanographic salinities with the salt fluxes to estimate the contribution of each polynya to the arctic ocean water masses if we assume that the salt contributes only to the arctic intermediate water our results show that the shelves are capable of producing about 20 60 of this water alternatively if the salt contributes only to the deep water of the eurasian basin then without consideration of the mixing of the bottom water with the greenland and norwegian sea water the contribution from the shelves yields a renewal time of about 100 years our results imply that there is insufficient water produced in the shelf polynyas to perform all of the roles that have been historically assigned to it

pattern recognition applied to seismic signals of the llaima volcano chile an analysis of the events features abstract this paper proposes a computer based classifier to automatically identify four seismic event classes of the llaima volcano one of the most active volcanoes in the southern andes situated in the araucania region of chile a combination of features that provided good recognition performance in our previous papers concerning the llaima and villarica located 100 km south of llaima volcanoes is utilized in order to train the classifiers these features are extracted from the amplitude frequency and phase of the seismic signals unlike the previous works where fixed length windows were used to obtain the seismic signals this paper employs signals of variable lengths that span the entire seismic event the classifiers are implemented using support vector machines a confidence analysis is also included to improve reliability of the classification results indicate that the features used for recognition of the events of villarica volcano also provide good recognition results for the llaima volcano yielding classification exactitude of over 80

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

carbon isotope compositions of fluid inclusions in charnockites from southern india models for the formation of crustal granulites which include the metamorphism of anhydrous lithologies1 2 the extraction of hygroscopic granite melts3 4 and fluxing by co25 7 constrain the thermal and geochemical evolution of the lower crust and its interaction with mantle derived volatiles here we present abundances and carbon isotope compositions of co2 in fluid inclusions in quartz and garnet from gneiss granulite pairs from the incipient char nockite quarries of southern india determined by a stepped combustion thermal decrepitation carbon extraction technique which quantifies problematic sample contamination and allows precise lithological control the results show that the co2 in incipient charnockite is more abundant and isotopically heavier than the co2 in associated gneiss providing evidence for the influx of co2 rich fluids during their formation the inferred carbon isotope compositions of these fluids are consistent with a mantle source and at ponmudi the isotopic composition of coexisting graphite and co2 implies fluid rock volume ratios in excess of 0 15

numerical study of winter water formation in the chukchi sea roles and impacts of coastal polynyas winter water formation is examined in the chukchi sea for the winters of 1992 2006 using a primitive equation ocean model forced by ncep wind and surface salinity flux derived from ssm i thin ice thickness estimates the model is also forced by an external inflow of 0 8 sv through the bering strait the model successfully reproduces the oceanic circulation on the chukchi shelf thus providing numerous insights into behaviors of salt enriched water produced on the shelf the experiments show that under northeasterly winds northward throughflow across barrow canyon is reduced this results in salinity buildup under freezing conditions and ultimately in greater enhancement of salinity of the waters carried into the arctic basin the flow and salinity enhancement of the flow through herald canyon is less extreme but more steady than through barrow canyon together with moored salinity in the bering strait the model results estimate the actual salinity to be 32 9 0 8 psu and 32 7 0 3 psu respectively for waters moving through the barrow and herald canyons both estimates are less than 33 1 psu that is typically observed for the cold halostad layer in the canada basin suggesting the importance of diapycnal mixing with saltier atlantic origin water

supercooled water in an arctic polynya observations and modeling in situ field measurements of an active polynya in storfjorden svalbard during april 2006 are presented a surface heat flux estimated to be 400 w m 2 produced frazil ice that was advected away from the fast ice edge during the end of a polynya event driven by cold winds from the northeast conductivity temperature and depth casts from the fast ice edge of the polynya were calibrated by accompanying water samples and reveal a supercooling event that lasted for 3 days in a 5 m deep water column surface salinity reached 35 9 psu from brine release during ice growth the maximum supercooling measured was 0 037 0 005 c below the in situ freezing point near the surface and 0 016 0 005 c at the bottom the mean supercooling gradient was 0 020 0 005 c between the surface and the bottom these measurements are consistent with results from a one dimensional frazil ice model confirming that such supercooling levels can be expected frazil ice concentrations in the water were modeled to be lower than 0 02 g l 1 due to advection in the surface layer seven frazil grease ice samples taken from a place where advection was blocked along the fast ice edge showed a mean salinity of 26 2 psu indicating 25 frazil ice and 75 sea water in the grease ice the water column salinity decreased during the measurement period due to less saline water replacing newly formed brine enriched shelf water flowing down to deeper parts of storfjorden the supercooling ceased when the wind direction turned to the east with higher air temperatures and warmer and less saline water being pushed into storfjorden by the northward ekman transport these are the first in situ observations from an active arctic polynya with concurrent sampling of hydrography and frazil ice and the supercooling is the maximum observed in recent years with modern and accurate instrumentation

sea ice thickness distribution in fram strait hm nuclear submarine sovereign has obtained the first synoptic measurements of the ice thickness distribution in fram strait the main outflow from the arctic ocean the ice nearest the ice edge is of quite different character from ice in the interior of the strait with a greater proportion of first year ice and less pressure ridging an estimate of the ice flux through fram strait can be made from the distribution of mean ice drafts

observations of frazil ice formation and upward sediment transport in the sea of okhotsk a possible mechanism of iron supply to sea ice in the sea of okhotsk sediment incorporation transport and release by sea ice potentially plays important roles in the bio related material such as iron cycle and ecosystem the backscatter strength data of bottom mounted acoustic doppler current profilers have suggested signals of frazil ice down to 30 m depth and signals of upward sediment transport throughout the water column simultaneously in the region northeast of sakhalin with a water depth of 100 m such events occurred under turbulent conditions with strong winds of 10 20 m s 1 during such events newly formed ice was present near the observational sites shown by satellite microwave imagery sediment dispersion from the bottom occurred in association with strong currents of 1 0 1 5 m s 1 during these events the mixed layer reaches near the bottom due to wind induced stirring inferred from the high frequency component of vertical velocity thus the winter time turbulent mixing brings re suspended sediment up to near the ocean surface this study provides the first observational evidence of a series of processes on the incorporation of sedimentary materials into sea ice sedimentary particles are dispersed by the strong bottom current subsequently brought up to near the surface by winter time mixing and finally incorporated into sea ice through underwater interaction with frazil ice and or flooding of sea ice floes this wintertime incorporation of bottom sediment into sea ice is a possible mechanism of iron supply to sea ice which melts in spring and releases bio reactive iron into the ocean

influence of co2 on melting of model granulite facies assemblages a model for the genesis of charnockites it is shown that partial melting studies at crustal pressures in sio2 rich portions of the system kalsio4 mg2sio2 h2o co2 can be used in modeling the anatectic origin of charnockites the univariant reaction phlogopite sanidine quartz vapor enstatite liquid yields an sio2 rich melt granite analog at 3 kbar the vapor composition at the solidus is buffered to high h2o contents by virtue of the coexistence of phlogopite with its breakdown products with higher pressures 8 and 15 kbar the fluid phase is buffered to higher co2 contents and the melt composition becomes enriched in k2o and mgo charnockite analog melting relations are controlled through the expansion of the quartz liquidus field relative to the enstatite and sanidine fields with increasing pressure it is noted that partial melts generated at the base of the crust in the presence of co2 rich fluid will be of an alkaline nature and will crystallize enstatite at lower pressures co2 saturated melting of similar sio2 rich bulk compositions phlogopite absent through the reaction enstatite sanidine quartz co2 liquid occurs at temperatures above 1000 c to about 15 kbar

polynya impacts on water properties in a northeast greenland fjord abstract polynyas are an important yet poorly understood phenomena of high latitude oceans a storm event during late december 2013 with down fjord winds of up to 25 m s forced the collapse of the landfast ice over the young sound ys fjord outlet in northeast greenland this storm created a coastal polynya that was further maintained by several consecutive wind events until early march 2014 during the polynya period three landfast ice tethered oceanographic moorings recorded an enhanced surface layer 0 40 m transport towards the mouth of ys and a layer below 40 140 m flowing into the fjord and supplying the interior with cool and saline water from the polynya subsequent ctd transects in may 2014 reveal that this lower layer contained polynya originated cool saline and oxygen enriched water with oxygen concentrations significantly exceeding values from the previous summer salt balance bulk estimates show that the polynya generated a sufficient amount of brine to ventilate the fjord interior

research on snow and ice this review unlike its predecessor martinelli et al 1979 is an intentionally selective survey of recent advances in selected areas of snow and ice research i have chosen to concentrate on studies relating to large scale aspects of the cryosphere and to consider their wider significance for other disciplines results obtained by new measurement techniques and the application of remote sensing methods are also stressed at the same time the broad lines of advance in glaciological research as represented in books conference themes and major field or laboratory programs are noted and a detailed bibliography is appended

continuous hidden markov models application to automatic earthquake detection and classification at las canadas caldera tenerife abstract a possible interaction of volcano tectonic earthquakes with the continuous seismic noise recorded in the volcanic island of tenerife was recently suggested also recently the zone close to las canadas caldera shows unusual high number of near

observations of ice thickness and frazil ice in the st lawrence island polynya from satellite imagery upward looking sonar and salinity temperature moorings 1 for the 1999 winter this paper examines the behavior of the bering sea st lawrence island polynya using a combination of advanced very high resolution radiometer avhrr radarsat synthetic aperture radar sar meteorological data over winter moored upward looking sonars uls and seabird salinity temperature sensors we define a thermal ice thickness from the avhrr retrieval of ice surface temperature combined with meteorological observations and a heat flux model south of the island we compare the uls and thermal thicknesses for congelation and frazil ice when the satellites observe congelation ice over the ulss the uls and thermal ice thicknesses generally agree when sar observes langmuir plumes over the ulss which indicate frazil ice formation the ulss show scatterers at 5 20 m depths in the water column and the seawater temperatures are either within 0 01 c of freezing or are slightly supercooled this suggests that during frazil events crystals either nucleate at depth or are transported to depth by the langmuir circulation the combination of the sar imagery and uls observations also allow measurement of the pack ice advection velocity the polynya width and the downwind frazil accumulation thickness giving widths of 10 to 30 km and thicknesses of 0 1 0 2 m substitution of these observed values with the heat flux into the pease polynya model yields polynya widths that approximately agree with the observed

beaufort chukchi seas summer and fall ice margin data from seasat conditions with similarities to the labrador sea the margin of the sea ice pack of the beaufort and chukchi seas is examined using the microwave data from seasat taken during the summer to early fall july 4 through october 8 1978 and the observations are compared to the analogous observations taken in limex 87 the sensors used are synthetic aperture radar sar the seasat a scatterometer system and the scanning multichannel microwave radiometer

identification of new events in apollo 16 lunar seismic data by hidden markov model based event detection and classification detection and identification of interesting events in single station seismic data with little prior knowledge and under tight time constraints is a typical scenario in planetary seismology the apollo lunar seismic data with the only confirmed events recorded on any extraterrestrial body yet provide a valuable test case here we present the application of a stochastic event detector and classifier to the data of station apollo 16 based on a single waveform example for each event class and some hours of background noise the system is trained to recognize deep moonquakes impacts and shallow moonquakes and performs reliably over three years of data the algorithm s demonstrated ability to detect rare events and flag previously undefined signal classes as new event types is of particular interest in the analysis of the first seismic recordings from a completely new environment we are able to classify more than 50 of previously unclassified lunar events and additionally find over 200 new events not listed in the current lunar event catalog these events include deep moonquakes as well as impacts and could be used to update studies on temporal variations in event rate or deep moonquakes stacks used in phase picking for localization no unambiguous new shallow moonquake was detected but application to data of the other apollo stations has the potential for additional new discoveries 40 years after the data were recorded besides the classification system could be useful for future seismometer missions to other planets e g the insight mission to mars

the influence of the physical properties of ice on reflectivity a model for the plane wave reflection coefficient from a layered elastic solid bounded on either side by a fluid half space is developed and applied to study environmental factors affecting the reflectivity of smooth arctic ice experimental measurements of the internal friction in ice and snow are reviewed and applied to compute realistic attenuation profiles an examination of the effect of ice layers conforming with measured temperature profiles in floe ice shows that the use of average values for sound speed and attenuation is an acceptable approximation for modeling purposes a study of the reflectivity due to the absorption of shear and compressional waves demonstrates that shear wave attenuation is the most important loss mechanism from 20 to 60 incidence the effect of an additional snow layer is to produce more attenuation without shifting the pattern of reflection nulls major results are presented for a frequency of 2 khz data comparisons are performed from 0 5 3 khz that show a limited qual

a model for the influence of wind and oceanic currents on the size of a steady state latent heat coastal polynya abstract this paper presents a model for determining the size and shape of a steady state latent heat coastal polynya in terms of the following free parameters 1 the frazil ice production rate f 2 the wind stress 3 the surface ocean velocity field u 4 the offshore consolidated thin ice transport t 5 the coastline shape and 6 the intersection of the polynya ice edge with the coastline all of which must be prescribed frazil ice trajectories are determined via the free drift ice momentum balance analytical solutions for the polynya shape are derived for a straight coastline in the special case when u t and are uniform in the alongshore direction and the rotation of the earth is neglected when the latter constraint is relaxed an expression for the asymptotic uniform polynya width is obtained an expression for the alongshore adjustment length scale of the polynya associated with alongshore variations in the coastline shape u t and is derived with rotation of the earth incl

possible interaction between tectonic events and seismic noise at las canadas volcanic caldera tenerife spain continuous seismic noise is recorded in the volcanic island of tenerife canary islands spain the origin of this noise strongly augmented by anthropogenic contamination is still under debate in this paper we discuss the relationship between this noise and the occurrence of local tectonic events in the same area in particular transitions are sought in the time evolution of dynamic parameters computed on the seismic noise and examples are shown where abrupt transitions may be associated with the occurrence of tectonic events these transitions provide further evidence of the existence of a natural origin for at least part of the seismic noise which is strongly contaminated if not dominated by anthropogenic sources

dense water formation in the laptev sea flaw lead 1 two primitive equation based models are used to estimate the formation of total volumes either of arctic cold halocline water chw intermediate water imw or deep water dw through freeze related salt rejection in the siberian laptev sea flaw lead system model a assumes that the rejected salt remixes with surface mixed water smw beyond the leads until salinities allow for contribution to the midlayers of either the chw the imw or the dw model b simulates direct salt rejection to the upper layer of the cold halocline and after remixing here further contribution to the midlayers of chw imw or dw averaging both model estimates laptev leads contribute either 0 161 sv of chw 0 075 sv of imw or 0 065 sv of dw which represents as much as 23 16 or 30 of arctic wide lead derived dense water contribution to the appropriate layer respectively northwestern laptev leads produce the greatest amount of dense water these lead sections show very short buoyancy equilibrium timescales 6 to 13 days and local dense water production may potentially be amplified by lateral brine injection into the cold halocline through bottom eddies central southern and southeastern leads generally produce little salt due to low surface water salinities as definite separation mechanisms and proportion distributions of rejected lead brines into chw iwm and dw are still unidentified in nature a combination of lead salt rejection and remixing model a and direct downward expulsion of brine packages model b is assumed to steer laptev lead dense water production

sea ice topography of the arctic ocean in the region 70 degrees w to 25 degrees e in october 1976 a cooperative experiment was made to survey the sea ice topography in the european sector of the arctic ocean h m submarine sovereign acquired 4000 km of ice draft data by using an upward looking sonar while a canadian forces aircraft flew along the submarine s track and acquired 2200 km of ice elevation data by using a laser profilometer the two types of profile were processed in corresponding 100 km section lengths and the following statistical analyses and comparisons were made i probability density functions o f ice draft and elevation each distribution shows a peak for young ice and for undeformed multi year ice at large ice thicknesses the distributions take the analytical form of a negative exponential the mean drafts enable two distinct geographical ice regimes to be identified there is an offshore zone of very heavy pressure ridging extending up to 400 km from the coasts of ellesmere island and of north greenland with mean ice draft in the range 5 0 to 7 5 m while out in the central arctic ocean the mean ice draft is lower 3 9 5 1 m and the characteristics of the ice cover remain homogeneous over a length scale of 1000 km the transition between the two regimes is abrupt taking place in less than 25 km data from the same part of the central arctic taken in march 1971 showed a mean ice draft 0 3 m lower while data from the central beaufort sea showed a mean draft more than 0 8 m lower ii level ice distributions ice with a local gradient of less than 1 in 40 was defined as level ice and used as an indicator of the quantity and thickness distribution of undeformed i e thermodynamically grown ice in the arctic ocean the distribution has a mode at 3 0 3 1 m draft and level ice percentages are in the range 30 40 bottom side and 70 80 top side in the offshore zone and 45 55 bottom and 85 95 top in the central arctic thus about half of the arctic ice cover consists of deformed ice iii pressure ridge spacings the spacings of ridge keels fit a negative exponential distribution characteristic of randomness except at close spacings where there is a deficit of keels explained as a geometrical effect and at very large spacings where there is an excess due to the contribution of polynyas the distribution of sail spacings exhibits these two effects but also differs from a random distribution at moderate sail separations iv ridge elevations and drafts keel drafts fit a law of form p h d oc exp ah 2 d h except for an excess of keels at drafts beyond 20 m there is a positive correlation between mean keel draft and keel frequency there are 3 5 4 5 keels per kilometre with draft exceeding 9 m in the offshore zone and 2 3 in the central arctic sail elevations fit a law of form p h d h x exp a h d h with a positive correlation between mean sail elevation and sail frequency the sail elevation and ice elevation distributions can be related by assuming that all thick ice is contained in pressure ridges of triangular cross section v keel sail comparison for the 21 corresponding 100 km sections there are positive correlations between mean sail height and mean keel draft and between keel frequency and sail frequency from these it is possible to convert a sail distribution computed from a laser profile into a keel distribution enabling sea ice bulk characteristics to be derived from airborne surveys alone vi leads and polynyas a lead was defined as a continuous sequence of depth points greater than 5 m long and not exceeding 1 m draft the number density n d of leads per kilometre of width d m fits the power law n d 15 d 2 exceptionally wide leads were concentrated in the offshore zone and in the marginal ice zone close to the open water of the greenland sea

a real time microearthquakes detector based on voice activity detection and endpoint detection an approach to cotopaxi volcano abstract the ring of fire represents a constant threat in the case of possible eruptions due to its 160 active volcanoes consequently several studies have determined that an increase of tectonic and long period events could indicate the beginning of a volcanic eruptive process in this context it is crucial to improve microearthquake detection by using real time automatic recognition systems for this purpose this work aims to improve microearthquake detection based on voice activity detection vad and endpoint detection furthermore we propose the use of signal segmentation considering the signal to noise ratio and adapting vad techniques for microearthquake detection the results tested in real time have demonstrated the reliability of our detector by obtaining 97 89 precision 97 10 accuracy and a value of 0 015 of balanced error rate ber we considered a dataset for real time testing of 744 h of continuous data from cotopaxi volcano in ecuador in these tests the mda detector is 8 89 more precise than the classical sta lta detector

interaction of stokes edge waves with near shore ice formation l interaction des ondes de stokes cotieres avec la formation de la glace pres des rivages est envisagee sous deux aspects on etudie d une part l influence d une suspension de fragments de glace sur les classiques ondes de stokes cotieres et d autre part la possibilite que les bancs de glace et plus tard les monticules de glace ou volcans puissent tirer leur origine des ondes cotieres ces resultats montrent que l effet d un champ de glaces tres fragmentees a une influence negligeable sur l equation de la dispersion de stokes pour les longueurs d ondes generalement observees mais que la presence d onde de stokes cotieres stationnaires peut conduire a l apparition de bancs de glace lorsque la mer gele pres de la cote

a review of ocean acoustic tomography 1987 1990 the techniques and instruments used in acoustic tomography of the oceans are surveyed and results are summarized sections are devoted to theoretical studies and numerical simulations mesoscale mapping vertical slice tomography flow imaging and nonlinear bias series of tomographic experiments analyses to identify global changes and outstanding problems the forward and inverse problems and ocean physics typical data are presented in tables and graphs and a comprehensive bibliography is provided 72 refs

frazil formation in water of different salinities and supercoolings les experiences de formation de frazil ont ete realisees dans des eaux de mer naturelles et artificielles on trouve que la vitesse de production du frazil est tres sensible a la surfusion initiale

the las canadas caldera tenerife canary islands an overlapping collapse caldera generated by magma chamber migration abstract the las canadas caldera is one of the most important geological structures of tenerife stratigraphic structural volcanological petrological geochronological and geophysical data suggest that the las canadas caldera resulted from multiple vertical collapse episodes that occurred during the construction of the las canadas edifice upper group three long term 200 ka cycles of phonolitic explosive activity each culminating with a caldera collapse have been identified in the upper group during the construction of the upper group the focus of felsic volcanism migrated from west to east using the results of field observations experimental analogue models and numerical studies we propose that the formation of the overlapping las canadas collapse caldera is related to the migration of the associated magma chamber our model implies that each collapse of this overlapping caldera partly or completely destroyed the feeding magma chamber this destruction led to changes in the local stress field that favoured the formation of a new chamber at one side of the previous one resulting in magma chamber migration the proposed model accounts for the formation of the las canadas caldera in particular it explains the geometrical relationships stratigraphy and chronology of the caldera wall deposits comparison with other overlapping collapse calderas suggests that our model may apply to other overlapping calderas

the ice thickness distribution across the atlantic sector of the antarctic ocean in midwinter during the first leg of the winter weddell sea project antarktis v 2 cruise of f s polarstern the entire width of the antarctic sea ice zone was traversed in the vicinity of 0 longitude in the period july 18 to september 10 1986 ice thicknesses were measured by direct drilling and by helicopter profiling using an exstar 100 mhz impulse radar system in addition aerial photography of the ice cover was done from 100 to 2000 m altitude using a 70 mm aerial camera mounted in the helicopter the results of the point measurements drilling are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area averaged ice thickness distributions it was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes this formed out of a 250 km wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice preferred thicknesses of undeformed floes were 40 60 cm of ice covered with 5 15 cm of snow the individual pancakes attained almost all of this thickness before consolidation subsequent congelation growth was slow estimated at 0 4 cm d 1 the floes contained much small scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation but pressure ridging was modest except in the far south a few very thick 8 11 m multiyear floes were observed embedded in the pack at latitudes beyond 66 s

marginal ice zone thickness and extent due to wave radiation stress abstractocean surface wave radiation stress represents the flux of momentum due to the waves when waves are dissipated or reflected by sea ice that momentum is absorbed or reflected resulting in

post metamorphic co2 rich fluid inclusions in granulites in granulite facies samples from the adirondack mountains ny estimates of peak metamorphic co2 fugacities based on mineral equilibria are not consistent with estimates based on data for high density co2 rich fluid inclusions of the 21 adirondack samples investigated for this study all contain co2 rich inclusions inclusions occur in quartz apatite and garnet they range in size from 3 to 50 m and are without visible h2o in a few of the inclusions freezing point determinations and preliminary laser raman spectroscopy show the presence of small amounts 3 of other fluids n2 and h2s co2 liquid vapor homogenization temperatures are between 46 and 31 c corresponding to densities between 1 14 and 0 5 gm cc some of these densities are consistent with peak metamorphic entrapment 1 06 to 1 1 gm cc

initial processing of volcanic seismic signals using hidden markov models nevado del huila colombia abstract volcanic eruptions are commonly preceded by seismic signals that carry important information about the underlying physical processes driving the eruptive activity the manual classification of this seismicity is often difficult during seismic crises and timely responses in volcanic surveillance depend upon on how fast this work is performed automatic classification programs are an excellent alternative because they can classify seismic signals in near real time although these programs have been successfully tested for many volcanoes they have not yet been applied to the monitoring of volcanic crises we automated the initial processing of the seismic activity recorded at nevado del huila volcano in colombia using hidden markov models the technique consists of classifying seismic signals extracting the main characteristics of each classified signal and deriving important physical parameters that are important in volcanic surveillance continuous seismic data from 2007 to 2012 were used to develop this project a total of 2142 events were selected to train the program the best characteristic model obtained during the training had an accuracy of 91 25 and a similar pattern in volcanic behavior to that from manual classification was modeled the encouraging results demonstrate that automatic classification programs are a powerful tool that can be used in surveillance and monitoring of active volcanoes as they provide timely information for the proper management of volcanic crises and subsequent hazards mitigation

the use of sar to measure ocean wave dispersion in frazil pancake icefields abstract icefields composed of frazil and pancake ice play important roles in both polar regions in winter during the early to midwinter period pancake ice is a major component of the antarctic sea ice cover while in the arctic the odden ice tongue in the greenland sea associated with deep convection is composed mainly of pancake ice the retrieval of sea ice thickness by remote sensing is in general a very difficult task in this paper the change in dispersion of ocean waves as they penetrate into pancake ice is considered so as to gain insight into its possible relationship with thickness spectral analysis of subscenes from ers 2 second european remote sensing satellite synthetic aperture radar sar images yields the wavelength and direction of the principal spectral component both outside and inside the ice cover there is a decrease of wavelength at the ice edge as well as refraction toward the normal and a loss of amplitude the analysis is complex because the true wave spectrum must be re

discriminating seismic events of the llaima volcano chile based on spectrogram cross correlations abstract the surveillance of active volcanoes around the world has become a critical security issue for many countries requiring a continuous monitoring of seismic signals by analyzing such signals we intend to understand volcanic activities e g explosions eruptions and depressurization and take decisions to reduce the effects and damages to the economy and society of nearby regions active volcanoes constantly produce signals which may then be characterized as data streams making impractical the presence of specialists to monitor and label every activity to overcome this drawback we present a new and straightforward approach to discriminate volcano seismic signals using spectrogram cross correlations spcc in conjunction with the k nearest neighbors algorithm a supervised machine learning strategy experiments were performed on signals collected from the llaima volcano chile and results confirmed the ability of our approach to discriminate events with a sensitivity over 95 for three out of the five classes considered

the underside of arctic sea ice imaged by sidescan sonar despite extensive submarine operations in the arctic little is yet known about the three dimensional morphology of the ice underside several studies have been done using upward looking sonar1 7 which yields a linear profile of ice draft from which the distributions of features such as pressure ridges and leads may be derived such a profile gives no information about the spatial morphology or appearance of the ice bottom surface in contrast the upper ice surface has been well documented from airborne and satellite borne sensors such as synthetic aperture radar passive microwave infrared and visual imaging here i report the first extensive set of imagery of the underside of sea ice in the arctic ocean sidescan sonar images show a distinct difference between the appearance of first year ice and of multi year ice first year ice has a smooth bottom except for a network of cracks while multi year ice is covered with an array of blisters or bulges the clear discrimination between ice types enables sidescan sonar to be used as a means of validating airborne passive microwave data

spectro temporal features applied to the automatic classification of volcanic seismic events abstract feature extraction and selection are very relevant processes in the design of automatic classifiers in the context of volcanic seismic signal classification most of the features presented in the literature have been extracted separately from a single domain such as time or frequency however spectrograms which combine time and frequency information are widely used by experts during the classification of manual seismic events this paper proposes to evaluate the performance of classifiers trained with features extracted from the spectro temporal domain individually or combined with other conventional features the parameters were extracted from the spectrogram based on a curve which combines the high energy components and the frequency bandwidth information through the duration of the event the tests were performed at the llaima volcano and seismic events were classified into four classes long period tremor volcano tectonic and tectonic using a database of signals recorded between the years 2009 and 2017 the main achievements of this study were the reduction of more than 70 of the error and false positive rates and also a reduction of approximately 30 of the number of features compared with a baseline established in previous studies thus the inclusion of spectro temporal information was considered relevant to complement the conventional features and to support classification

structural changes of volcanic tremor at stromboli volcano abstract the occurrence of a tectonic event sufficiently close to a volcano and or sufficiently energetic can trigger a change in its eruptive activity examples include ambrym vanuatu teide spain tungurahua ecuador and villarrica chile of course the possibility that an earthquake can even trigger a new eruption has serious implications in terms of hazard however no serious attempt has been carried out so far to formalize the identification of these structural changes with a statistical approach in this work a statistical approach is applied to identify structural changes in volcanic tremor recorded at stromboli from april to july 2006 we considered different fluctuation type tests using the open source package strucchange written in r language zeileis a leisch f hornik k kleiber c 2002 strucchange an r package for testing for structural change in linear regression models j stat softw 7 2 1 38 stromboli is a particularly interesting case study whilst previous work falsaperla s alparone s spampinato s 2003 seismic features of the june 1999 tectonic swarms in the stromboli volcano region italy j volcanol geotherm res 125 1 2 121 136 had suggested that tectonic events have no influence on volcanic activity most recent results carniel r tarraga m 2006 can tectonic events change volcanic tremor at stromboli geophys res lett 33 l20321 doi 10 1029 2006gl027690 suggest otherwise the aim of this work is to confirm by use of a statistical method the presence of changes in the recorded tremor related to the occurrence of volcano tectonic events on stromboli as pointed out by carniel and tarraga carniel r tarraga m 2006 can tectonic events change volcanic tremor at stromboli geophys res lett 33 l20321 doi 10 1029 2006gl027690 we found that there was at least one variation in the time series associated to every earthquake even in the cases for which previous analyses could not recognize any variation carniel r tarraga m 2006 can tectonic events change volcanic tremor at stromboli geophys res lett 33 l20321 doi 10 1029 2006gl027690

a coupled dynamic thermodynamic model of an ice ocean system in the marginal ice zone wind driven ice ocean processes in the marginal ice zone are studied when thermodynamics is included into a coupled ice ocean model the ocean is considered to be a two layer ocean where a fresh and cold freezing mixed layer is lying above the stagnant warm and saline lower layer the essential part of the thermodynamics is the entrainment between the mixed layer and the lower layer which is parameterized using the frictional velocity at the ocean surface a kraus turner type parameterization it is shown that upwelling at the ice edge which is generated by the difference in the air ice and air water surface stresses will give rise to a strong entrainment by bringing the pycnocline nearer to the surface furthermore the entrainment is negligible outside the areas affected by the ice edge upwelling when cooling at the top is included the heat and salt exchange are further enhanced in the upwelling areas because the entrainment depends inversely on the density difference between the layers new ice formation occurs in the area which is not affected by ice edge upwelling that is no entrainment of the warm lower layer fluid so the mixed layer temperature stays at the freezing point the ice growth will give rise to a large salt flux to the upper layer but the subsequent salinity change is not as large as that due to the entrainment of the lower layer fluid the mixed layer in the areas affected by the ice edge upwelling is only slightly less saline than the lower layer it is suggested that these high salinity mixed layer regions with a scale of a few rossby radii of deformation 10 km will overturn due to cooling possibly as a plume and may this contribute to the formation of deep water

southern ocean frontal structure and sea ice formation rates revealed by elephant seals polar regions are particularly sensitive to climate change with the potential for significant feedbacks between ocean circulation sea ice and the ocean carbon cycle however the difficulty in obtaining in situ data means that our ability to detect and interpret change is very limited especially in the southern ocean where the ocean beneath the sea ice remains almost entirely unobserved and the rate of sea ice formation is poorly known here we show that southern elephant seals mirounga leonina equipped with oceanographic sensors can measure ocean structure and water mass changes in regions and seasons rarely observed with traditional oceanographic platforms in particular seals provided a 30 fold increase in hydrographic profiles from the sea ice zone allowing the major fronts to be mapped south of 60 s and sea ice formation rates to be inferred from changes in upper ocean salinity sea ice production rates peaked in early winter april may during the rapid northward expansion of the pack ice and declined by a factor of 2 to 3 between may and august in agreement with a three dimensional coupled ocean sea ice model by measuring the high latitude ocean during winter elephant seals fill a blind spot in our sampling coverage enabling the establishment of a truly global ocean observing system

seismic attenuation at rabaul volcano papua new guinea abstract the attenuation structure around rabaul volcano new britain papua new guinea is studied using broadband records from a pair of sites inside and outside of the rabaul caldera complex using regional earthquakes estimates of attenuation for p and s waves between 0 5 and 5 hz indicate that near surface rocks within the caldera complex are significantly more attenuative than outside the caldera the average strength of this anomaly is defined in terms of t s 0 2 s over and above the region outside the caldera t s is the time integral of the inverse quality factor of attenuation in this case along the path of a shear wave this attenuation anomaly appears to be strongest at depth and to the south of the kaivuna site in the northern part of the caldera complex the ratio of attenuation estimates for p and s waves is t s t p 2 7 indicating that intrinsic attenuation contributes significantly to the process of attenuation no frequency dependence of the quality factor is resolved within this frequency band path averaged lithospheric attenuation is estimated from s p spectral ratios at both stations yielding quality factors on average q 180 but possibly significantly lower around and below the volcano shear waves are observed along paths passing underneath the central southern caldera at depths greater than about 5 km although they are strongly attenuated this indicates that they have not passed through a large extensively molten body

the role of langmuir circulation in suspension freezing in november 2004 we used an acoustic doppler velocimeter adv to measure the three components of velocity in langmuir circulation lc cells when frazil was forming in a lake lc circulation was indicated by windrows of slush ice on the water surface we also collected samples of lake water ice interstitial water and ice to determine their sediment concentrations the adv record showed rotating currents in the cross wind vertical plane indicative of lc downward directed velocities were large enough to entrain frazil into the water column for 27 of the 97 min observation time at the adv location sediment concentrations in the ice and interstitial water samples were greater than concentrations in water column samples collected in upwelling zones of lc cells we conclude that suspension freezing was forming particle laden ice as frazil trapped below lc convergence zones grew in downwelled supercooled water the rotating roll vortices of langmuir circulation play an important role in forming sediment laden ice

mapping of sea ice production for antarctic coastal polynyas 1 active sea ice production in antarctic coastal polynyas causes dense water formation finally leading to antarctic bottom water aabw formation this study gives the first mapping of sea ice production in the antarctic ocean based on heat flux calculation with ice thickness data derived from satellite data the highest ice production occurs in the ross ice shelf polynya region the ice production there decreased by 30 from the 1990s to the 2000s which can be one candidate for causing the recent freshening of aabw the cape darnley polynya in east antarctica is found to be the second highest production area suggesting a possible aabw formation area according to our estimation around 10 of southern ocean sea ice is produced in the major antarctic coastal polynyas the mapping provides surface heat and salt flux conditions in the ice covered region which have not been well understood

aircraft and satellite passive microwave observations of the bering sea ice cover during mizex west passive microwave measurements of the bering sea ice cover were made with the nasa cv 990 airborne laboratory and with the nimbus 7 scanning multichannel microwave radiometer smmr during february 1983 as part of the bering sea marginal zone experiment mizex west microwave data obtained with the cv 990 include radiances from both imaging and dual polarized fixed beam radiometers spanning a range of frequencies from 10 to 183 ghz the imagery at 19 and 92 ghz provide a description of the marginal ice zone delineating regions of open water ice compactness and ice edge structure comparison of these images with ice concentration maps derived from the smmr data shows that the maps provide an accurate description of the ice edge and interior pack polynyas analysis of the fixed beam data shows that spectral differences increase with a decrease in ice thickness and the polarization at both 18 and 37 ghz distinguishes among new young and first year sea ice types finally these results are shown to agree with surface based radiometric measurements

travel time changes in a tomography array caused by a sea ice cover abstract in september 1988 an acoustic tomography array was deployed in the greenland sea in the region 74 76 n 1 e 5 w we have modelled travel time changes which may be produced in this array by the presence or growth of a sea ice cover three types of icefield are considered a typical east greenland marginal ice zone miz thickness distribution using as input data a sonar profile from a british submarine a field of discrete floes without pressure ridging and a pancake frazils mix growing on the open sea firstly we calculated travel time changes caused by an ice sheet uniform thickness the travel time decreases with increasing ice thickness by 2 10 ms for 3 m thickness at a frequency of 250 hz and a range of 200 km but the magnitude depends on grazing angle and strongly on compressional and shear velocities in ice with some values for velocity the relationship is no longer monotonic in a real icefield we surmised that the modal ice thickness is responsible for the coherent reflected ray which is detected secondly we calculated the progressive travel time decrease resulting from the increase in mixed layer salinity caused by salt rejection from a growing ice cover we conclude that this is negligible for miz type ice covers but is detectable for rapidly growing pancake fields and in the case of shallow rays may reach 3 5 ms per day finally we calculated the scattering loss associated with ice bottom roughness in miz type icefields finding that for steep rays it is about 15 db on average at 200 km range so that signal to noise ratios in such arrays need to be raised to ensure adequate timing precision if this is achieved we conclude that acoustic tomography can be used as a means of monitoring modal ice thickness in the greenland sea

statistical properties of arctic sea ice morphology derived from sidescan sonar images abstract using a transparent overlay technique the authors have classified a 140km long stretch of sidescan sonar imagery of the arctic sea ice underside 700m swath width into regions occupied by unique ice types the categories used were multi year ice first year ice pressure ridge apparently open dark lead apparently refrozen bright lead and randomly deformed ice the technique was validated by comparing these classifications with data obtained simultaneously using a narrow beam upward looking sonar the pattern of ice types thus observed was tested statistically for associations between adjacent regions the distribution of lead widths spacings and orientations and the distribution of ridge spacings and orientations significantly non random sequences of ice types were observed lead orientations and spacings were clustered and were set to preferred values and ridge spacings fitted a negative exponential distribution the extent of uniformly deformed ice with no apparent linearity was much greater on the underside of the ice than has ever been observed on the upper surface

simulating pancake and frazil ice growth in the weddell sea a process model from freezing to consolidation 1 processes controlling the formation and transformation of frazil to pancake ice are examined using data from an array of drifting buoys deployed at the advancing ice edge in the weddell sea a simple thermodynamic model is coupled to the buoy dynamics and to an ice redistribution model to determine the influence of deformation thermodynamics and mechanical scavenging incorporating frazil crystals from the surrounding slick into the pancakes on the partitioning of ice volume between frazil and pancakes ice production was examined from the time the buoys were deployed until the frazil pancake cover consolidated into the more familiar pack ice the model reproduced the expected ice cover thickness at consolidation 60 cm rafting was the dominant contribution to thickening in the region owing to large scale compression of the initial area by northerly winds from passing low pressure weather systems which are rather typical in the region high resolution positional forcing from the buoys 20 min intervals doubled the contribution of mechanical scavenging to final pancake thickness compared to the coarser 2 h result owing to the larger path length that the pancakes traverse through the frazil slick and produced a significantly larger volume of ice in the pancake phase the ice cover generated at consolidation was approximately twice as thick as would have formed by the more familiar congelation ice growth under the same forcing reinforcing the importance of correctly parameterizing the early stages of ice formation in the antarctic the study highlighted uncertainties in the effect of the frazil pancake cover on ocean atmosphere heat exchange both in terms of the area contributing to ice production and the effect on turbulent exchange coefficients further work placing the empirical parameters into a more constrained physical framework and introducing wave properties is suggested

the seismic noise at las canadas volcanic caldera tenerife spain persistence characterization and possible relationship with regional tectonic events abstract the origin of the continuous seismic noise recorded during the last few years in the volcanic island of tenerife canary islands spain is under debate due to the important implications in terms of hazard the seismic noise is strongly affected by anthropogenic contamination but previous work has shown that nevertheless a significant fraction of this noise has a natural origin an origin that appears to be related to the generation of local tectonic events within or close to the island in this paper the variogram tool is used to characterize the so called persistence of the seismic noise this analysis can quantify how much memory the seismic noise has of its recent past this has important implications in terms of how informative the recorded noise can be about its future evolution and this in turn puts important constraints on how likely it is for the seismic noise to be the source of potential precursors highlighting variations in the volcanic activity that is supposed to generate part of this seismic noise in particular the memory characterization can help to distinguish the naturally generated seismic noise from the anthropogenic contamination although only a few clear examples have been observed until now the possibility that this memory can be affected by the occurrence of local tectonic events is also discussed

a field and laboratory study of wave damping by grease ice in a field and laboratory study we discuss the formation growth and wave absorption properties of grease ice our field observations show that grease ice formation occurs under cold windy conditions in both leads and polynyas in leads grease ice forms in the open water then is herded to the down wind edge of the lead in polynyas a langmuir circulation herds the grease ice into long plumes parallel to the wind in the laboratory we grow grease ice in a wave tank and measure its wave absorption properties for single frequency two dimensional waves on a large scale we find that the thickness of the grease ice which increases away from the paddle is determined by a balance between the wave momentum flux and the free surface tilt on a small scale our photographs show that the crystals which make up the grease ice consist of discs measuring about 1 mm in diameter and 1 10 m thick which at low rates of shear sinter together into larger clumps yielding a viscosity increase to measure this non linear viscosity we study the decay of wave amplitude between two critical distances measured inwards from the leading edge the first occurs when the depth of grease ice exceeds k 1 where k is the wave number the second further distance is a line of transition from liquid to solid behavior which we call the dead zone between these two distances the wave amplitude decays with a linear slope which increases as a 0 k 2 where a0 is the wave amplitude in open water concurrent measurements of ice concentration show that it increases from values of 18 22 at the leading edge to a local maximum of 32 44 at the dead zone while the values at the dead zone increase non linearly with a0k finally comparison of the observed to that calculated from a yield stress viscosity model shows if the yield stress coefficient is proportional to the incident wave momentum flux the model predicts the observed

metamorphism of reduced granulites in low co 2 vapour free environment pervasive flooding of co2 has been proposed as the cause of granulite facies metamorphism that is capable of producing many distinctive characteristics of the deep continental crust reduced water activity orthopyroxene bearing assemblages depletion of large ion lithophile lil elements and dehydration1 6 the calculations presented here of c o h fluid composition for conditions of granulite facies metamorphism show that oxygen fugacity f o2 estimates from many terranes are sufficiently low that the addition of co2 rich fluid causes graphite to precipitate for values of pressure p and temperature t common to granulites and with f o2 slightly below the quartz fayalite magnetite buffer qfm the addition of co2 sufficient to grow 10 vol orthopyroxene requires the precipitation of 1 5 vol graphite as 0 1 vol graphite is readily recognizable but is not reported in most low f o2 granulites these rocks have not been flooded by co2 and low f h2o is probably due to extraction of a magma or recrystallization of an already dry rock7 8 granulite terranes may thus result from a combination of these three processes and the dominance of any one cannot now be demonstrated on a regional basis

antarctic sea ice mapping using the avhrr abstract a sea ice mapping scheme based on advanced very high resolution radiometer avhrr data from the national oceanic and atmospheric administration noaa polar orbiting satellites has been developed and applied to daylight images taken between november 1989 to january 1990 and november 1990 to january 1991 over the weddell and the ross seas after masking the continent and ice shelves sea ice is discriminated from clouds and open sea using thresholds applied to the multidimensional space formed by avhrr channel 2 3 and 4 radiances sea ice concentrations in cloud free regions are then computed using the tie point method results based on the analysis of more than 70 images show that the proposed scheme is capable of properly discriminating between sea ice open sea and clouds under most conditions thus allowing high resolution sea ice maps to be produced during the austral summer season

lagrangian modelling of frazil ice in the ocean a new modelling framework using lagrangian particle tracking has been developed to assess dynamic and thermodynamic effects of underwater frazil ice this frazil ice model treats a lagrangian particle as a bulk cluster of many frazil crystals and calculates the thermodynamic growth of each particle and the corresponding budget of latent heat and fresh water the effective density and viscosity of sea water depend on the mass fraction of underwater frazil ice and hence affect ocean convection an idealized experiment using our model successfully reproduces the formation of underwater frazil ice and its transition to grease ice at the surface because underwater frazil ice does not reduce the atmosphere ocean heat exchange surface heat flux and net sea ice production in the experiment with frazil ice are relatively high compared with the experiment where surface cooling directly leads to columnar growth of a solid ice cover which effectively insulates the heat flux these results suggest that large scale sea ice models which do not take account of the effects of frazil ice might underestimate atmosphere ocean heat exchange particularly at times of active new ice formation

stratigraphy structure and geochronology of the las canadas caldera tenerife canary islands after a long period of subaerial fissure fed extrusions of basaltic magmas 12 to 3 ma volcanic activity was then concentrated in the central part of tenerife phonolitic magma chambers formed and a central volcanic complex was constructed the las canadas edifice the formation of a large depression the las canadas caldera truncated the top of the edifice the active twin strato cones teide pico viejo are sited in this depression the history of the las canadas caldera and edifice are established from stratigraphy geochronology k ar dates and volcanological studies two different groups are recognized separated by a major unconformity the lower group is dated at 2 to 3 ma and includes the products of several volcanic centres which together represent several cycles the upper group ranges from 1 56 to 0 17 ma and includes three different formations representing three long term 100 to 300 ka volcanic cycles the periods of dormancy between each formation were of 120 to 250 ka duration the las canadas caldera is a multicyclic caldera which formed over the period 1 18 0 17 ma each cycle of activity represented by a formation culminated in caldera collapse which affected different sectors of the las canadas edifice geological observation and geochronology support an origin by collapse into a magma chamber the minimum volume of pyroclastic ejecta is substantially greater than the present caldera depression volume 45 km3 but approaches the inferred volume of the original caldera depression 140 km3 after the formation of the caldera sector collapses could also occur at the northern flank of the volcano causing the disappearance of the northern side of the caldera wall

ambrym vanuatu july august 2000 spectral and dynamical transitions on the hours to days timescale abstract ambrym is a large basaltic volcano with a 12 km wide 1900 year old caldera located in the vanuatu archipelago formerly known as new hebrides two cones are currently active in the caldera marum and benbow each with several active vents that hosted visible lava lakes until 1999 on 26 november 1999 an earthquake m w 7 5 located near the northern part of the island caused important changes to the vent morphology during july 2000 we installed a short period seismic station on the eastern rim of benbow crater in the western side of the caldera the station acquired continuous data for about 1 month during this period volcanic tremor was permanently recorded together with discrete events in this paper first results from these data are discussed focusing attention on the existence of significant transitions in the long term volcano dynamics studied both with spectrally derived dominant and average frequencies and more properly dynamical embedding dimensions and delay time parameters during the observation period on 9 august 2000 another significant earthquake was recorded m b 6 3 about 65 km north of the volcano the influence of this and other regional tectonic events on the volcano dynamics are discussed

circulation dense water formation and outflow on the northeast chukchi shelf we investigated circulation and water mass modification processes in the chukchi sea using 1 temperature salinity and velocity data collected between september 1991 and september 1992 from moorings in bering strait and the northeast shelf and 2 meteorological data and ice concentrations derived from special sensor microwave imager ssm i imagery in october 1991 and from february to august 1992 the mean monthly circulation was steady and northward from november to january strong northeast winds diverted the low salinity bering inflow onto the western shelf and weakened and reversed flow over the northeast shelf the winds also opened extensive polynyas wherein cold hypersaline salinity 34 waters formed the fall winter circulation enhanced dense water formation by diverting low salinity waters away from and prolonging the residence time of water within the polynyas alongshore convergence of the coastal flow swept some of the cold hypersaline water offshore across isobaths but the coastal current carried most of it into the arctic ocean through barrow canyon the dense outflow mixed little during its descent through the upper canyon where bottom friction and rotation but not entrainment were important in the plume momentum balance if the outflow is not diluted by mixing in the lower canyon where theory suggests this will occur then the densest shelf waters can ventilate layers deeper than the halocline salt rejection estimates using ssm i data and surface heat budget calculations agree within a factor of 2 with independent estimates from the mooring hence remote sensing techniques can monitor winter salt rejection rates in the chukchi sea

entrainment and export of laptev sea ice sediments siberian arctic sea ice sediments sis sediments rafted by ice and shelf surface deposits from the siberian laptev sea were analyzed to study turbulent entrainment processes this study focused on the silt and clay fractions on average representing 63 4 and 30 4 total 93 7 of the bulk sis respectively generally the sis contains 50 more silt than the shelf deposits while the clay percentages in both sample groups are similar sand sized particles are less abundant in sis than in bottom sediment although sis is clearly enriched in silt no evidence was found for preferential ice entrainment of any silt subfraction coarse medium fine statistical tests of sis and shelf silt parameters and the similar clay mineral compositions of both sample groups provide evidence for entrainment of laptev bottom deposits into newly forming ice the entrainment is related to the mechanism known as suspension freezing accordingly coarser clasts sand and plant debris may be lifted upward by buoyant anchor ice while coarse silt particles are supposed to be transported to the surface by rising frazil aggregates additionally turbulent interaction of convergent langmuir circulation and near surface frazil ice streaks is proposed to support ice entrainment of the finest particles 6 4 phi 12 m entrainment and export of sis from the laptev sea were assessed for ten individual flaw leads extended narrow polynyas separating fast and drifting ice using particle concentrations in ice samples and new ice formation rates the results show that roughly 20 mt of sis can be annually exported from the laptev sea by lead ice only thus formation and export of sediment laden lead ice may play a major geological role in siberian arctic shelf erosion and coastal retreat

ice production and brine formation in storfjorden svalbard brines which appear as salty and cold bottom water layers on arctic shelves form by salt rejection during sea ice formation high ice production occurs in latent heat polynyas such as the one that appears in storfjorden under northerly winds using ers 2 synthetic aperture radar imagery we observed the ice cover in storfjorden over the winter 1997 1998 revealing an area of over 6000 km 2 of the open water and thin ice that are characteristic of a polynya changes in the polynya extent correlated well with a simple wind driven polynya size algorithm furthermore using a frazil ice formation algorithm and the hypothesis of ice accumulation at the lee side of the polynya we distinguished between open water thin ice and fast pack ice the average polynya width during the 6 winter months was about 30 km with a maximum of 130 km in march thus storfjorden was composed of 5 6 fast and pack ice and 1 6 polynya open water occupied about half of the polynya the other half was composed of brash ice and thin ice involved in ridging and rafting a total ice volume of 40 km 3 was produced in storfjorden between november 15 1997 and may 15 1998 about 57 of it was formed in the open water area 9 in the thin ice area and 34 in the fast pack ice area this ice production released more than 1 gt gigaton of salt able to increase the salinity of the storfjorden waters by 1 4 practical salinity units psu assuming that brine enriched waters are 0 3 psu more saline than the parent waters the above salt release is able to ventilate storfjorden 4 5 times during the course of the productive season

pattern recognition applied to seismic signals of llaima volcano chile an evaluation of station dependent classifiers abstract automatic pattern recognition applied to seismic signals from volcanoes may assist seismic monitoring by reducing the workload of analysts allowing them to focus on more challenging activities such as producing reports implementing models and understanding volcanic behaviour in a previous work we proposed a structure for automatic classification of seismic events in llaima volcano one of the most active volcanoes in the southern andes located in the araucania region of chile a database of events taken from three monitoring stations on the volcano was used to create a classification structure independent of which station provided the signal the database included three types of volcanic events tremor long period and volcano tectonic and a contrast group which contains other types of seismic signals in the present work we maintain the same classification scheme but we consider separately the stations information in order to assess whether the complementary information provided by different stations improves the performance of the classifier in recognising seismic patterns this paper proposes two strategies for combining the information from the stations i combining the features extracted from the signals from each station and ii combining the classifiers of each station in the first case the features extracted from the signals from each station are combined forming the input for a single classification structure in the second a decision stage combines the results of the classifiers for each station to give a unique output the results confirm that the station dependent strategies that combine the features and the classifiers from several stations improves the classification performance and that the combination of the features provides the best performance the results show an average improvement of 9 in the classification accuracy when compared with the station independent method

gold graphite association in granulite terrains implications for ore genesis abstract the gold occurrences of sri lanka are closely associated with the graphite deposits and are genetically related the quartz graphite margins of the vein graphite are shown to be metal accumulating the movement of co 2 rich fluids formation of graphite and the concentration of au are closely related whereas the co 2 rich fluids may well be the carbon carriers in the formation of graphite the original source of co 2 is still debated hydrothermal solutions when in contact with the graphite tend to activate the carbon thereby producing sites for the enrichment of gold the genetic link between the graphite veins and gold deposition has useful implications in the investigation of ore genesis in high grade metamorphic terrains and the exploration for gold

can tectonic events change volcanic tremor at stromboli 1 besides the well known strombolian activity stromboli shows the presence of a continuous volcanic tremor tectonic events in the area are rare and no evidence of a local tectonic event changing the characteristics of the tremor was previously known in april and may 2006 a swarm of tectonic events was recorded located very close to the island of stromboli possibly within the same volcanic edifice in this paper we analyse the time evolution of several dynamical parameters computed on the volcanic tremor and show examples where abrupt transitions can be associated to the occurrence of such local tectonic events this suggests that these events may be related to the volcanic activity i e be proper volcano tectonic events