halocline structure in the canada basin of the arctic ocean 1 we examine the varieties and spatial distributions of pacific and eastern arctic origin halocline waters in the canada basin using 2002 2003 hydrographic data the halocline structure in the canada basin is different from the eastern arctic halocline because it includes fresher pacific winter waters that form a cold halostad which lies above the eastern arctic origin lower halocline waters the structure of the halostad in the canada basin however is not spatially uniform and depends on the pathway and history of the source water pacific winter water entering through the bering strait becomes salty due to sea ice formation and this in turn is dependent on the occurrence and distribution of polynyas in particular saline water from the eastern chukchi sea forms thick halostad and causes depression of the isohalines in the southern canada basin this depression influences thermohaline structure of the oceanic beaufort gyre

tectonic signatures in coseismic gravitational energy change summary we argue that the commonly ignored first order terms in displacement in the energetics of earthquakes may have tectonic significance chao et al 1995 demonstrated this point in the context of global energy budget but we demonstrate its significance in regional tectonics the two first order terms are elastic strain energy under hydrostatic stress and gravitational energy because the two terms cancel they are independently conserved and do not bear any significance to earthquake energy budget which is based on balancing of second order terms nevertheless balance of first order terms represent large quantities of energy transformation between one type of energy elastic strain energy and the other gravitational energy nature of this energy transformation can be examined by computing gravitational energy generated coseismically by earthquakes we evaluate this gravitational energy for the period from 1977 to 1998 by using the harvard moment tensor catalogue and discuss three aspects of the gravitational energy change which carry tectonic implications 1 regions of extensional tectonics show systematic gravitational energy loss and regions of compressional tectonics typically show energy gain for example regions of gravitational collapse in the crust of tibet and the andes are clearly identified in the maps 2 regions with complicated patterns are found in some subduction zones such as the western and the southern pacific they indicate the existence of short wavelength stress heterogeneities and temporal variations in the crustal gravitational energy the latter implies that the crust is going up and down over a time interval of one to a few years 3 energy gain loss patterns for depths between 400 and 1000 km imply strong resistance of the lower mantle to sinking slabs a notable exception is found near japan where energy loss is seen throughout this depth range suggesting a smoothly sinking slab in this region

lithospheric structure buoyancy and coupling across the southernmost ryukyu subduction zone an example of decreasing plate coupling abstract the okinawa trough is a backarc basin located behind the ryukyu arc trench system the southernmost part of the okinawa trough spot displays different tectonic features from the rest of the okinawa trough the spot area includes abundant seamounts with active hydrothermal venting and high heat flow values to understand better the rifting and magmatism context of the spot area we examine the lithospheric structure buoyancy and coupling across the southernmost ryukyu subduction zone the results show that beneath the spot area the continental crust and mantle lithosphere thickness of 25 30 and 120 km respectively are thick with little continental thinning the analysis of mantle lithosphere buoyancy across the southernmost ryukyu subduction zone shows strong plate coupling between the overriding and subducting plates however the two plates are actually decoupled as indicated by present day interface earthquakes this situation indicates that the southernmost ryukyu subduction zone displays a transitory case of a changing plate coupling from a strong to a weak plate coupling such a coupling decoupling transition is probably associated with the collision of the luzon arc with the asian continental margin additionally the curve of the mantle lithosphere buoyancy across the southernmost ryukyu subduction zone indicates that the submarine magmatism in the spot area is located within the volcanic arc area suggesting early arc magmatism in the spot area

is taiwan the result of arc continent or arc arc collision abstract conventionally it has been accepted that the formation of taiwan results from the collision of the luzon arc with the eurasian continental margin we suggest that taiwan results from the collision of the luzon arc with the former ryukyu subduction zone before the collision the latter extended a few hundred kilometres southwest of its present day termination in the early to middle miocene the subduction became inactive in its southwest portion and the manila trench migrated northeastward giving rise to the formation of the luzon arc the collision started in the late miocene by closing the oceanic domain located between the luzon arc and the former ryukyu arc because the luzon arc moved northwestward with respect to the former ne sw trending ryukyu arc the oblique collision first resulted in the indentation on the south ryukyu arc west of 123 5 e and the narrowing of the corresponding portion of the okinawa trough prior to the uplift of taiwan today the hsuehshan and backbone ranges represent the uplifted portion of the backarc basin and the longitudinal valley corresponds to the suture zone between the former ryukyu and the luzon arcs in this model we propose to link although they are not of the same age two truncated backarc basins the active okinawa trough to the northeast and the former active tainan backarc basin to the southwest the former backarc basin extended from southwest of taiwan to southern japan and could have been initiated near the paleo location of taiwan as early as the eocene oligocene the result of the collision is the truncation of the ancient backarc basin associated with the shortening deformation and uplift of the ancient outer arc and related backarc region which provides the fundamental mechanism of the taiwan mountain building this model is in agreement with a counterclockwise rotation of the portion of taiwan located west of the coastal range belonging to the luzon arc and a clockwise rotation of the south ryukyu arc earthquake focal mechanisms geodetic observations and the distribution of the petrologic and structural features are also consistent with the proposed arc arc collision model

melting and undercooled crystallisation of felsic xenoliths from minor intrusions jebilet massif morocco abstract granitic and gneissic xenoliths within microdiorite dykes from the palaeozoic jebilet massif morocco contain up to 40 of granophyric intergrowths that occur as films along quartz feldspar contacts and form an interconnected grain boundary network the composition of the feldspar megacrysts i e large embayed crystals surrounded by the granophyric intergrowths implies high temperature crystallisation t 900 c and the sievetexture or finger print texture indicates that these crystals underwent incipient melting moreover the microstructural position and bulk composition of the granophyre are similar to that of glass in partly molten felsic xenoliths from lavas or pyroclastics it is argued that the granophyre originated after partial melting of the xenoliths when incorporated into the dioritic magma crystallisation of that melt resulted in most cases in the formation of vermicular and or cuneiform granophyre which testifies to moderate degrees of undercooling a few occurrences of plumose granophyre i e very thin intergrowths that are close to quartz bearing spherulites indicate that some xenoliths crystallised at higher degrees of undercooling together with granophyric xenoliths a number of microgranular inclusions also occur these are characterized by phenocrysts of quartz and feldspar in a microgranular groundmass finger print texture in feldspar suggests that these inclusions like the granophyric xenoliths underwent ultra metamorphism and melting the microgranular groundmass is most probably indicative of crystallisation at lower degrees of undercooling but the relationships between the two types of xenoliths still remain to be explored in detail

tide modulated gas emissions and tremors off sw taiwan abstract the continental margin off sw taiwan is in an incipient stage of orogeny and contains numerous active mud diapirs and mud volcanoes gas emissions out of the seabed off sw taiwan are revealed by acoustic images from 38 khz echo sounders or sub bottom profilers however the mechanism for gas emissions is still poorly understood in this study we show that the gas emissions out of the seabed and the associated tremors off sw taiwan are strongly correlated with the ocean tides especially with the diurnal and semidiurnal constituents particularly for each tidal day the strong gas emissions expulsions and long duration tremors occur mainly during both the rising periods to the higher high tides and the falling periods to the lower low tides both the gas emissions and tremor activities are generally quiescent near the tidal datum on average the daily intensity of gas emissions and the magnitude of tremors are positively proportional to the daily tidal range a larger slope site implies a greater concentration of gas in the shallow sediments most of the individual tremors and long duration tremors observed off sw taiwan occur as results of the strong gas expulsions out of the gas bearing seabed the high frequency components of the induced tremors quickly decay and are followed by horizontal low frequency 7 hz harmonic oscillations of the seabed long duration tremors may enhance seafloor instability and increase the potential for submarine landslides

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

earthquake induced crustal gravitational potential energy change in the philippine area abstract the crustal gravitational potential energy change gpe caused by earthquakes in the philippine area from january 1976 to november 2011 was estimated in this study the active convergence between the philippine sea plate and the sundaland eurasian margin is reflected by the greatest gains in gpe along the philippine negros and cotabato trenches whereas the manila trench is covered by a gpe loss pattern although the philippine mobile belt pmb itself is actually affected by the ongoing collision and subduction processes almost the entire philippine fault zone is dominated by gpe loss revealing a slightly extensional environment along the fault the time evolution of the cumulated gpe for different segments along the philippine archipelago shows distinct patterns due to the numerous large underthrusting events that have occurred along the philippine trench the cumulated gpe is regularly increasing in its most southern segment however in the middle segments where the palawan block enters into collision with the pmb the increase in cumulated gpe is relatively small in the most northern segment where the north luzon is located a decrease of cumulated gpe demonstrates that the seismic characteristic of the manila trench is dissimilar from other subduction systems in the world we suggest that the collision of both the palawan block and the benham rise with the pmb promotes the rotation of the pmb and facilitates the northward escape of the northeastern luzon resulting in a decrease of cumulated gpe in the northern philippines

flow of winter transformed pacific water into the western arctic abstract the dynamics of the flow of dense water through barrow canyon is investigated using data from a hydrographic survey in summer 2002 the focus is on the winter transformed bering water the highest volumetric mode of winter water in the chukchi sea which drains northward through the canyon in spring and summer the transport of this water mass during the time of the survey was 0 2 0 3 sv as the layer flowed from the head of the canyon to the mouth it sank decelerated and stretched strong cyclonic relative vorticity was generated on the seaward side of the jet which compensated for the stretching this adjustment was incomplete however in that it did not extend across the entire current possibly because of internal mixing due to shear instabilities the resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation multiple eddies of winter transformed bering water were observed along the chukchi beaufort shelfbreak those to the west of barrow canyon were in the process of being spawned by the eastward flowing shelfbreak current emanating from herald canyon while the single eddy observed to the east originated from the barrow canyon outflow it is argued that such an eddy formation is a major source of the ubiquitous cold core anti cyclones observed historically throughout the canada basin implications for the ventilation of the upper halocline of the western arctic are discussed

on the origin of the chemical properties of the arctic ocean halocline profiles of chemical constituents in seawater above the alpha ridge in the central arctic ocean obtained during the canadian expedition to study the alpha ridge cesar support a model in which the halocline is maintained by dense saline water produced on the continental shelves within the arctic ocean by the formation of sea ice it is argued that nutrient regeneration on the continental shelves largely accounts for the nutrient maximum that has been observed in the upper halocline over a wide region of the arctic ocean and that while the bering sea and north altantic can be recognized as origins of halocline water water masses from these regions undergo sufficient changes in their chemical properties within the arctic ocean significant that they no longer retain their identity in the halocline

hydrographic conditions during the 2002 sbi process experiments abstract a review of the hydrographic data from the 2002 western arctic shelf basin interactions sbi process cruises permits the following conclusions 1 temperature salinity relationships were similar to canonical descriptions but at five stations in the outer shelf slope region warm high salinity atlantic layer water appeared to have risen displaced the lower halocline and mixed with shelf upper halocline water 2 primary production in the sbi study region was strongly influenced by the advection of dissolved inorganic nitrogen din entering via bering strait this import of din ammonium nitrate nitrite is modified by local processes but without the bering strait inflow biological productivity in the sbi region would be much lower 3 in comparison to the inflowing atlantic waters din urea phosphate and din urea silicate ratios in the pacific waters that dominated the upper 150 m of the water column were low they were also low relative to redfield uptake ratios for phytoplankton 4 microbial processes continue to destroy din in significant quantities as the pacific waters transit the sbi region 5 nitrate and ammonium were the principal contributors to din nitrite concentrations were always

back arc extension in the okinawa trough the okinawa trough lying to the east of china is a back arc basin formed by extension within continental lithosphere behind the ryukyu trench arc system middle to late miocene uplift associated with normal faulting of the initially adjacent ryukyu nonvolcanic arc and the taiwan sinzi folded belt corresponds to the first rifting phase the timing of rifting is supported by the presence of marine sediments of corresponding age drilled in the northern okinawa trough the rifting occurred after a major early miocene change in the motion of the philippine plate with respect to eurasia and ceased during the pliocene a second rifting phase started about 2 m y ago at the plio pleistocene boundary and has continued until the present time it has proceeded to a more advanced stage in the middle and southern okinawa trough than it has farther north detailed bathymetric sea beam seismic reflection and magnetics data collected during the pop 1 cruise of the r v jean charcot reveal the principal features of the extensional processes the back arc spreading phase started very recently in the southern and middle okinawa trough as exemplified by several en echelon and in some cases overlapping active central graben oriented n70 e n80 e some of these depressions are intruded by volcanic ridges of fresh back arc basalt with associated large magnetic anomalies transform faults between these en echelon active rifts are not obvious we suggest that the major part of the southern okinawa trough is underlain by a thinned continental crust and that except for the system of en echelon rifts of the southern okinawa trough the back arc basin oceanic domain is limited to a width of a few tens of kilometers or less in the axial portion of the trough the system of axial back arc volcanic ridges that occur in the rifts ends at the latitude of okinawa island whereas active volcanoes in the ryukyu arc occur only north of okinawa island we refer to this transition between active arc and back arc volcanism as the volcanic arc rift migration phenomenon vamp globally back arc volcanism propagated from the southern okinawa trough to the okinawa vamp area rifting continues to occur in the northern okinawa trough but is not yet accompanied by associated volcanism the okinawa vamp area is characterized by a series of parallel basaltic ridges oriented n75 e with associated linear magnetic anomalies characteristic of dyke intrusions we suggest that the formation of the back arc oceanic domain took place along the axial back arc extensional zone trending n75 e and that this zone presently ends at the southern extremity of the active volcanic chain the initial phase of formation of back arc basin oceanic crust is non steady state and is characterized by the lack of a developed fracture zone pattern the termination of the vamp area in the direction of the volcanic zone of the arc is consistent with the suggestion of molnar and atwater that the volcanic arc is a fundamental line of weakness which determines where initial back arc spreading occurs apparently back arc extension initially occurred within the continental lithosphere located westward of the ryukyu arc along its whole length but the subsequent back arc volcanism was initiated in the southernmost portion of the region and then moved northward this migration was accompanied by the shutting down of volcanic activity along the abandoned portions of the arc it is this transfer of volcanism that we call the vamp process thus arc and back arc basin volcanism seem to be associated in such a manner that spreading tends to migrate simultaneously with a cessation in volcanic activity along the arc this interplay of arc and back arc activity is probably linked to changes in the parameters of plate convergence since the plate motion in the phillippine sea is oblique to the trench at least in the southern part of the okinawa trough we suggest that the oblique resisting force applied to the edge of the overriding plate engenders the development of en echelon extensional features within and behind the arc the motion of the ryukyu platelet with respect to eurasia is consequently an extensional strike slip motion trending roughly parallel to the okinawa trough

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

coseismic changes of gravitational potential energy induced by global earthquakes based on spherical earth elastic dislocation theory we compute the coseismic gravitational potential energy eg change using the spherical earth elastic dislocation theory and either the fault model treated as a point source or the finite fault model the rate of the accumulative eg loss produced by historical earthquakes from 1976 to 2016 about 4 2000 events using the gcmt catalogue are estimated to be on the order of 2 1 1020 j a or 6 7 tw 1 tw 1012 watt amounting to 15 in the total terrestrial heat flow the energy loss is dominated by the thrust faulting especially the mega thrust earthquakes such as the 2004 sumatra earthquake mw 9 0 and the 2011 tohoku oki earthquake mw 9 1 it s notable that the very deep focus events the 1994 bolivia earthquake mw 8 2 and the 2013 okhotsk earthquake mw 8 3 produced significant overall coseismic eg gain according to our calculation the accumulative coseismic eg is mainly lost in the mantle of the earth and also lost in the core of the earth but with a relatively smaller magnitude by contrast the crust of the earth gains gravitational potential energy cumulatively because of the coseismic deformations we further investigate the tectonic signature in the coseismic crustal eg changes in some complex tectonic zone such as taiwan region and the northeastern margin of the tibetan plateau we found that the coseismic eg change is consistent with the regional tectonic character

physical and geochemical properties across the atlantic pacific water mass front in the southern canadian basin temperature salinity nutrients oxygen and halocarbon data collected in the arctic ocean reveal a frontal structure previously unrecognized in the hydrography of the canadian basin samples were collected on a 1300 km section extending from the beaufort sea in the canada basin to the east siberian sea in the makarov basin these data collected in 1993 aboard the ccgs henry larsen reveal a lateral boundary between water masses of atlantic and pacific origin the term water mass assembly is introduced to describe the basic arrangement or vertical stacking of water masses found in the arctic ocean recognizing that water mass components within each assembly may differ from basin to basin using historical data two primary water mass assemblies are defined each consisting of three layers an upper layer an atlantic layer and a deep layer these two assemblies are marked by important differences one assembly here defined as the western arctic wa assembly is characterized by an upper layer of relatively fresh high nutrient water of pacific origin below this by an atlantic layer with a core temperature generally below 0 5 c and finally by a deep layer of higher salinities and colder temperatures about 0 5 c than found in the overlying atlantic layer the second assembly here defined as eastern arctic ea assembly is characterized by the absence of pacific water in the upper layer below this by an atlantic layer core as warm as 2 to 3 c and by a colder about 0 9 c deep layer because the presence or absence of pacific origin water is a key characteristic distinguishing the two assemblies we will refer to the water mass boundary between the two assemblies as the atlantic pacific front earlier research indicated that water masses in the arctic ocean were separated by a front above the lomonosov ridge into the canadian and eurasian basins although all larsen 93 stations from the canada basin a1 d1 display classic wa assembly characteristics the makarov basin station e1 shows ea assembly characteristics in the upper and atlantic layers and a wa assembly deep layer this suggests a relocation in the position of the atlantic pacific boundary away from the lomonosov ridge further larsen 93 data show the transition region between the atlantic and deep layers is fresher in the makarov basin than corresponding water in either the canada or eurasian basins implying a source of cold low salinity water perhaps from the laptev and east siberian shelves the front separating these two assemblies lies above the mendeleyev ridge and is marked by large lateral gradients in all measured properties in particular the penetration of anthropogenic halocarbons is 2 to 3 times deeper in the makarov basin than in the canada basin implying enhanced rates of ventilation this suggests that direct exchange between the canadian and eurasian basins has occurred recently near the perimeter and that physical and chemical properties including contaminants may have been transported by boundary currents more quickly from one basin to the other

identification characterization and change of the near surface temperature maximum in the canada basin 1993 2008 1 sea ice in the canada basin of the arctic ocean has decreased significantly in recent years and this will likely change the properties of the surface waters a near surface temperature maximum nstm at typical depths of 25 35 m has been previously described however its formation mechanisms seasonal evolution and interannual variability have not been established based on summertime conductivity temperature and depth surveys and year round ice tethered profiler data from 2005 to 2008 we found that the nstm forms when sufficient solar radiation warms the upper ocean a seasonal halocline forms in summer once enough sea ice melt has accumulated to separate the surface mixed layer from the nstm the nstm becomes trapped below the summer halocline thereby storing heat from solar radiation this heat can be stored year round in the canada basin if the halocline is strong enough to persist through winter in addition energy from storm driven mixing can weaken the summer halocline and entrain the nstm thereby melting sea ice in winter throughout this cycle ekman pumping within the convergent beaufort gyre acts to deepen the nstm from 1993 through 2007 the nstm warmed and expanded northward and both the nstm and the summer halocline formed at successively shallower depths north of 75 n the temperature of the nstm increased from 2004 to 2007 by 0 13 c yr and the nstm and summer halocline shoaled by 2 1 m yr and 1 7 m yr respectively from 1997 to 2007 the formation and dynamics of the nstm are manifestations of both the ice albedo feedback effect and changes to the freshwater cycle in the canada basin

the age of the latest precambrian volcanism in southern israel northeastern sinai and southwestern jordan a re evaluation by regrouping late precambrian volcanic rocks originally dated by bielski in southern israel and northeastern sinai and by lenz et al in southwestern jordan to individual sites better rb sr isochron ages namely 535 15 ma to 523 9 ma are obtained for the alkaline rhyolitic association these are interpreted as the age of the volcanism which is typified by significant high initial 87sr 86sr ratios of 0 7099 0 0013 to 0 7132 0 0032 which were probably caused by contamination with crustal material the nearby rhyodacitic association yields an error chron date of 548 4 to 633 14 ma with a low initial ratio of 0 7035 0 0003 this estimated age points to an older volcanic eruption onlapping of the lower cambrian timna formation on the alkaline rhyolitic association rocks indicates 523 9 ma as the upper age limit for the lower cambrian section at the northern part of the arabian nubian massif

the chi chi earthquake sequence active out of sequence thrust faulting in taiwan we combined precise focal depths and fault plane solutions of more than 40 events from the 20 september 1999 chi chi earthquake sequence with a synthesis of subsurface geology to show that the dominant structure for generating earthquakes in central taiwan is a moderately dipping 20 to 30 thrust fault away from the deformation front a second subparallel seismic zone lies about 15 kilometers below the main thrust these seismic zones differ from previous models indicating that both the basal decollement and relic normal faults are aseismic

post collisional magmatism around northern taiwan and its relation with opening of the okinawa trough being part of an active mountain belt formed by oblique collision of the luzon arc with asia northern taiwan and the offshore islets are marked by a series of latest pliocene quaternary volcanoes whose eruptions have been conventionally ascribed to westward propagation of the ryukyu volcanic arc on the basis of new geochemical data along with supporting geologic and geophysical evidence we propose instead that this young volcanism resulted from post collisional lithospheric extension in the northern taiwan mountain belt and the mantle source regions involved in the melt generation have been significantly modified by the nearby ryukyu subduction related processes magmas thus produced through the northeast to the southwest in the northern taiwan volcanic zone ntvz vary from low k to calc alkaline and then shoshonitic compositions such a spatial geochemical variation characterized by southwestward increase in enrichments of potassium and incompatible trace elements runs subparallel to the southwestern part of the present day ryukyu trench the geochemical variation that can be explained by southwestward decrease in degrees of partial melting of the mantle sources is reconciled with a southwestward weakening extensional regime observed in the ntvz the post collisional extension in northern taiwan furthermore might have played a role in reactivation of the opening in the middle okinawa trough and gave way to its rapid southwestward propagation with associated development of the ryukyu subduction zone west of124oe this nascent subduction in turn resulted in abundant submarine volcanoes which delineate an embryo volcanic front along the southern margin of the trough therefore the southwestern okinawa trough is not a fore arc basin as had been previously alleged but represents an atypical back arc basin which developed broadly synchronously or prior to its arc trench system in this particular collision extension subduction tectonic environment 1999 elsevier science b v all rights reserved

east west differences in water mass nutrient and chlorophyll a distributions in the sea ice reduction region of the western arctic ocean 1 the r v mirai conducted hydrographic surveys in the western arctic ocean during summer 2004 across a front between cold arctic water and warm water from the pacific ocean where sea ice cover has been largely reduced in recent summers the hydrographic data indicate a new type of vertical temperature minimum water west of the front along isohaline surfaces with approximate salinity s of 32 which is fresher than the typical temperature minimum s 33 caused by spreading of pacific winter water pww mainly to the east of the front both of the temperature minimum waters are characterized by low potential vorticity with near freezing temperature suggesting that they are formed by winter convection with sea ice formation a difference between the waters results from a large contribution of sea ice meltwater to the fresh temperature minimum frtmin water of s 32 the distributions of the sea ice meltwater contribution and nitrogen deficit suggest that summer shelf water largely influenced by the sea ice melt in the chukchi sea is modified by winter convection on its way to the chukchi abyssal plain to form the frtmin water this water supplies nutrients through the water distribution to the west of the front at depths shallower than the nutrient maximum layer caused by the pww spreading the shallower nutrient supply by the frtmin water combined with light penetration without sea ice cover could produce a prominent chlorophyll a maximum layer west of the front

change of crustal potential energy by earthquakes an indicator for extensional and compressional tectonics earthquakes cause a potential energy change in earth s interior because they generate permanent vertical deformation in the gravitational field the cumulative change of this potential energy in the crust computed for the period between 1977 and 1998 shows systematic patterns in various tectonic provinces regions of extensional tectonics show systematic potential energy loss and regions of compressional tectonics typically show energy gain therefore we claim that the crustal potential energy change can serve as a good indicator of compressional and extentional tectonics

arctic cyclogenesis at the marginal ice zone a contributory mechanism for the temperature amplification 1 rapid sea ice retreat over the arctic ocean has a leading role in arctic amplification the sea ice extent dramatically recovers during every freezing season so despite the recent summer sea ice retreat there must be extraordinary heat exchange between the lower atmosphere and upper ocean however the underlying mechanisms for this remain uncertain here we show that autumn frontal cyclogenesis is a crucial event in the arctic air sea coupled system our shipboard doppler radar and intensive radiosonde observations at the marginal ice zone detected an explosive frontal cyclogenesis with coupling between upper and lower tropospheric vortices the thermal contrast between ocean and ice surfaces is likely favorable to cyclogenesis with an identical life cycle to that at mid latitudes this suggests a northward shift of meridional heat transport the 1 5 k temperature decrease in the upper ocean after the cold front has passed reveals that a large amount of heat is transported into the atmosphere this is an invaluable example of the fact that sea ice retreat contributes to polar amplification of surface air temperature increase

changes in temperature and tracer distributions within the arctic ocean results from the 1994 arctic ocean section abstract major changes in temperature and tracer properties within the arctic ocean are evident in a comparison of data obtained during the 1994 arctic ocean section to earlier measurements 1 anomalously warm and well ventilated waters are now found in the nansen amundsen and makarov basins with the largest temperature differences as much as 1 c in the core of the atlantic layer 200 400 m thus thermohaline transition appears to follow from two distinct mechanisms narrow order 100 km topographically steered cyclonic flows that rapidly carry new water around the perimeters of the basins and multiple intrusions 40 60 m thick which extend laterally into the basin interiors 2 altered nutrient distributions that within the halocline distinguish water masses of pacific and atlantic origins likewise point to a basin wide redistribution of properties 3 distributions of cfcs associated with inflows from adjacent shelf regions and from the atlantic demonstrate recent ventilation to depths exceeding 1800 m 4 concentrations of the pesticide hch in the surface and halocline layers are supersaturated with respect to present atmospheric concentrations and show that the ice capped arctic ocean is now a source to the global atmosphere of this contaminant 5 the radionuclide 129i is now widespread throughout the arctic ocean although the current level of 129i level poses no significant radiological threat its rapid arrival and wide distribution illustrate the speed and extent to which waterborne contaminants are dispersed within the arctic ocean on pathways along which other contaminants can travel from western european or russian sources

subsidence and conversion of the dead sea basin to an inland erosion base level in the early middle miocene as inferred from geomorphological analysis of its ancient western fluvial outlet abstract the first major subsidence of the dead sea pull apart basin dsb is evidenced by the thick hufeira member of the terrestrial hazeva formation the age of the hufeira member and the conversion of the dsb to an inland erosion base level are not well constrained for this purpose we studied the effect of the evolving basin on its ancient fluvial outlet to the arad be er sheva valley absv which served as a miocene corridor between the embryonic dsb region in the east and the mediterranean sea in the west we mapped and analyzed the morphostratigraphy of four series of rock cut erosion surfaces from top to bottom the barir kuseifa ar ara and shemen surfaces they are manifested in the east as fluvial erosion surfaces capped by conglomerates passing laterally westward to marine wave cut surfaces capped by a shallow marine limestone of the early middle miocene ziqlag formation the age of these surfaces is constrained to the early middle miocene langhian based on morphostratigraphy correlation with the ziqlag formation paleogeographic reconstruction of the two higher and older surfaces reveals transverse valleys which drained the dsb region and crossed the present route of the regional water divide these transverse valleys were presumably the western outlets to the mediterranean sea of the newly subsiding basin precambrian components in the assemblage of the clasts that cover the kuseifa surface were not found in the hufeira member and thus reflect an ongoing post hufeira exumation of the dsb drainage basin hence this early middle miocene surface postdates the hufeira member assigning an age of late early miocene to the first major subsidence of the dsb the two lower and younger surfaces represent local drainage systems confined to the absv this transition from regional to local drainage system marks the establishment of the present regional water divide and the conversion of the dsb to an inland erosion base level during the early middle miocene

how was taiwan created abstract since the beginning of formation of proto taiwan during late miocene 9 ma the subducting philippine ph sea plate moved continuously through time in the n307 direction at a 5 6 cm year velocity with respect to eurasia eu tearing the eurasian plate strain states within the eu crust are different on each side of the western ph sea plate boundary extensional in the okinawa trough and northeastern taiwan versus contractional for the rest of taiwan island the b feature corresponds to the boundary between the continental and oceanic parts of the subducting eurasian plate and lies in the prolongation of the ocean continent boundary of the northern south china sea strain rates in the philippines to northern taiwan accretionary prism are similar on each side of b contractional though with different strain directions perhaps in relation with the change of nature of the eu slab across b consequently in the process of taiwan mountain building the deformation style was probably not changing continuously from the manila to the ryukyu subduction zones the luzon intra oceanic arc only formed south of b above the subducting eurasian oceanic lithosphere north of b the luzon arc collided with eu simultaneously with the eastward subduction of a portion of eu continental lithosphere beneath the luzon arc in its northern portion the lower part of the luzon arc was subducting beneath eurasia while the upper part accreted against the ryukyu forearc among the consequences of such a simple geodynamic model i the notion of continuum from subduction to collision might be questioned ii traces of the miocene volcanic arc were never found in the southwestern ryukyu arc we suggest that the portion of eu continental lithosphere which has subducted beneath the coastal range might include the miocene ryukyu arc volcanoes formed west of 126 e longitude and which are missing today iii the 150 km wide oceanic domain located south of b between the luzon arc and the manila trench above the subducting oceanic eu plate south china sea was progressively incorporated into the eu plate north of b

stress tensor analysis in the taiwan area from focal mechanisms of earthquakes abstract we produce a map of the stress pattern in and around taiwan based on 200 earthquake focal mechanism solutions these solutions were determined by using data from taiwan telemetered seismographic network microearthquake surveys and wwssn the stresses are derived through a minimization of angles between the slip vector and the shear stress on each nodal plane considered as a fault employing appropriate weighting factors the whole set of focal mechanisms is divided into several groups mainly according to apparent clustering of the event locations the results show that the direction of maximum principal stress in taiwan area is nearly horizontal and se nw on average this is in good agreement with the direction of relative motion between the philippine sea plate and the eurasian plate in western taiwan the fan shaped distribution of the maximum principal stress is consistent with the direction of philippine sea eurasian plate convergence through a simple model of viscous material indented by a rigid wedge in the northeastern part of taiwan a nearly horizontal minimum principal stress oriented n s is found for shallow depths it occurs in a region of low seismic velocities probably related to the back arc activity of the okinawa trough down dip compressional and down dip extensional stresses have been identified in different depth ranges within the subducting slab of the philippine sea plate in the northern taiwan this may reflect the slab characteristics in this area a complex stress pattern prevails in the hualien area at the junction between the ryukyu subduction system and the taiwan collision zone

varieties of shallow temperature maximum waters in the western canadian basin of the arctic ocean the properties and spreading pathways of shallow temperature maximum waters stms in the western canadian basin are investigated using ctd and mooring data obtained in 1997 98 as part of the sheba surface heat budget of the arctic ocean drift experiment and available historical data three distinct varieties of stm are recognized on the basis of salinity range 1 surface mixed layer water smlw with s 32 psu these stms carry sufficient heat within the upper layers of the ocean to significantly affect the rates of ice cover and decay for example during the winter of 1997 98 anomalously warm stm 0 c originating from ecsw was observed to spread northwards along the northwind ridge and chukchi plateau where the maximum reduction of the ice covers was subsequently observed in late summer 1998 maslanik et al 1999 regional climate variability and ice cover in the western canadian basin are thus affected not only by anomalous atmospheric circulation patterns but also by the circulation of upper ocean water masses

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

earthquake induced gravitational potential energy change in the active taiwan orogenic belt summary the philippine sea plate is converging against the eurasian plate near taiwan at a velocity of 7 8 cm yr 1 this has caused the taiwan orogenesis and induced abundant earthquakes in this study we examine the corresponding change of gravitational potential energy gpe using 757 earthquakes from the earthquake catalogue of the broadband array in taiwan for seismology bats from 1995 july to 2003 december our results show that the variation of

the canada basin 1989 1995 upstream events and far field effects of the barents sea 1 the effects of upstream events on southern canada basin waters were examined using physical and geochemical data collected at one location between 1989 and 1995 these events included atlantic layer warming relocation of the atlantic pacific water mass boundary and increased ventilation of boundary current waters early signals of change in the canada basin first appeared in 1993 along the continental margin and by 1995 were evident in the basin interior and farther downstream differences in physical and geochemical properties nutrients oxygen 129i and cfcs were observed between 150 and 1600 m of the water column by 1995 the boundary between pacific and atlantic origin water was shallower and atlantic origin water occupied more of the canada basin water column atlantic origin lower halocline water was colder and more ventilated fram strait branch water was colder fresher and more ventilated and barents sea branch water was warmer fresher more ventilated and occupied a larger volume of the water column than in previous years water mass analysis showed that the composition of atlantic origin water in the canada basin in 1995 included 20 more water from the barents sea two related events upstream appear to be the source of this change an atmospheric regime shift in 1989 that increased cyclonic circulation a transition unprecedented within the latter half of the 20th century in magnitude geographic reach and apparent oceanographic impacts and a large volume of dense water flowed from the barents sea to the arctic ocean between 1988 and 1989 these two phenomena illustrate the close relationship between atmospheric and oceanic events whose combined influence was evident 6 years later and 5100 km downstream in the canada basin at depths 1000 m

recent changes in arctic sea ice melt onset freezeup and melt season length 1 in order to explore changes and trends in the timing of arctic sea ice melt onset and freezeup and therefore melt season length we developed a method that obtains this information directly from satellite passive microwave data creating a consistent data set from 1979 through present we furthermore distinguish between early melt the first day of the year when melt is detected and the first day of continuous melt a similar distinction is made for the freezeup using this method we analyze trends in melt onset and freezeup for 10 different arctic regions in all regions except for the sea of okhotsk which shows a very slight and statistically insignificant positive trend 0 4 d decade 1 trends in melt onset are negative i e toward earlier melt the trends range from 1 0 d decade 1 for the bering sea to 7 3 d decade 1 for the east greenland sea except for the sea of okhotsk all areas also show a trend toward later autumn freeze onset the chukchi beaufort seas and laptev east siberian seas observe the strongest trends with 7 d decade 1 for the entire arctic the melt season length has increased by about 20 days over the last 30 years largest trends of over 10 d decade 1 are seen for hudson bay the east greenland sea the laptev east siberian seas and the chukchi beaufort seas those trends are statistically significant at the 99 level

nutrient supply and biological response to wind induced mixing inertial motion internal waves and currents in the northern chukchi sea a fixed point observation station was set up in the northern chukchi sea during autumn 2013 and for about 2 weeks conductivity temperature depth ctd water samplings 6 h and microstructure turbulence measurements 2 to 3 times a day were performed this enabled us to estimate vertical nutrient fluxes and the impact of different types of turbulent mixing on biological activity there have been no such fixed point observations in this region where incoming low salinity water from the pacific ocean river water and sea ice meltwater promote a strong pycnocline halocline that stabilizes the water column previous studies have suggested that because of the strong pycnocline wind induced ocean mixing could not change the stratification to impact biological activity however the present study indicates that a combined effect of an uplifted pycnocline accompanied by wind induced inertial motion and turbulent mixing caused by intense gale force winds 10 m s 1 did result in increases in upward nutrient fluxes primary productivity and phytoplankton biomass particularly large phytoplankton such as diatoms convective mixing associated with internal waves around the pycnocline also increased the upward nutrient fluxes and might have an impact on biological activity there for diatom production at the fixed point observation station it was essential that silicate was supplied from a subsurface silicate maximum a new feature that we identified during autumn in the northern chukchi sea water mass distributions obtained from wide area observations suggest that the subsurface silicate maximum water was possibly derived from the ventilated halocline in the canada basin

the precambrian magmatic rocks of timna valley southern israel abstract in the timna valley in southern israel a small layered serpentinized chloritized gabbroic rock occupies the core of har timna and an alkali potassium syenite to granite composes most of the area intermediary rock types between the basic and acid rocks are common this magmatic sequence is in agreement with the latest model suggested for the last phase of precambrian activity in the arabo nubian massif mantle derived basaltic magma intruded the crust from a shallow layered magmatic chamber this magma was the heat source that caused a partial melting of the crust and the formation of a type alkali potassium rich granitic magma this acid magma was the source of the alkali rhyolitic dykes and the biqat hayareah volcanic rock types this whole process took place in a cyclic manner under a tensional tectonic regime creation or reactivation of deepseated faults caused a new pulse of intrusion of basic magma and a remelting of the crust serpentinization was the last phase hydrothermal activity at temperatures of less than 400 c this hydrothermal activity could have been caused by radioactive heating of the alkali granite after its final stage of crystallization or by recent dead sea rift hydrothermal waters

geochemistry geochronology and petrogenesis of a late precambrian 590 ma composite dike from the north eastern desert of egypt late precambrian 575 600 ma igneous activity in the north eastern desert of egypt produced large volumes of compositionally bimodal magmas a single composite dike was studied to further examine petrogenetic relationships between andesitic and rhyolitic melts the dike consists of 1 5 2 m of andesite on either side of a 5 6 m wide rhyolite core contact relations indicate that the andesite and rhyolite simultaneously existed as porphyritic liquids wholerock rb sr dating indicates an age of 591 ma but with considerable scatter andesite and rhyolite had similar initial87sr 86sr of 0 7032 2 indicating derivation from a low rb sr source either the upper mantle very young upper crust or depleted lower crust the composition of the andesites on either margin cannot be distinguished these are very similar to andesites of the dokhan volcanics of similar age correspondingly the rhyolite is compositionally similar to the epizonal pink granites this dike and others like it represent hypabyssal feeders for the extrusive and shallow intrusive members of the north eastern desert bimodal suite

the petrogenesis of a type magmas from the amram massif southern israel the 550 530ma alkaline magmatic suite of the amram massif southern israel was emplaced during the transition from an orogenic to an intra plate tectonic setting in the northeastern arabian nubian shield ans the suite ranges from 45 6t o 788 wt sio2 and consists of rhyolites alkali quartz syenites quartz syenites monzonites and co magmatic mafic to felsic alkaline dikes these rocks define a continuous chemical evolutionary trend and reveal a correlation between decreasing stratigraphic age and increasing silica content the felsic members of the suite display a type characteristics and are genetically linked through fractionation to the more mafic ones moderately positive initial end values a2 05 low initial 87 sr 86 sr values 07036 2 high mgo and fe2o3 concentrations 410 895 and 100 125 wt respectively and relatively flat rare earth element patterns la yb na 64 09 in the amram mafic dikes 456 495 wt sio2 suggest their derivation from the sub continental lithospheric mantle above the garnet stability zone the melts program was used to quantitatively model the chemical evolution of the suite extensive anhydrous fractionation 490 of plagioclase alkali feldspar clinopyroxene olivine and minor timagnetite and apatite from parental mafic magmas represented by the amram mafic dikes produced the rhyolitic compositions as well as the intermediate members of the suite this suggests the presence of a large unexposed body of cumulate rocks at depth as well as fusion of a large source region equivalent to an 5km layer in the lithospheric mantle regarded as a representative example for similar a type outcrops in this region this petrogenetic model further suggests that neoproterozoic early cambrian a type magmatism in the northeastern ans represents a significant post orogenic addition of mantlederived material to the juvenile crust this magmatic episode was of a similar magnitude to that of the cenozoic extensionrelated alkaline volcanism of the arabian plate

the east siberian sea as a transition zone between pacific derived waters and arctic shelf waters 1 in the present study we report hydrological t and s and hydrochemical data obtained during a russian trans arctic cruise in 2000 onboard the hydrographic vessel hv nikolay kolomeytsev and describe the top layer of the sediment a typical sample was taken from the upper 0 5 cm layer of bottom sediment and the distribution of the organic carbon 13corg and nitrogen 15norg isotope ratios using both historical water data and data from our cruise we divide the ess into two specific areas the western area influenced strongly by lena river input and the eastern area under direct influence of pacific derived water we also used the stable 13corg and 15norg isotopes to detect the sediment geochemical boundary or geochemical fz between pacific marine derived sediments and terrestrial derived sediments which can be considered to reflect the long term on a scale of 102 years position of the most westward extension of pacific water these are among the first reliable hydrological and geochemical data reported for the ess from the dmitry laptev strait to the long strait and they reveal novel insights about interaction between pacific water and local shelf water

okinawa trough backarc basin early tectonic and magmatic evolution the okinawa trough lying between japan and taiwan is a backarc basin formed by extension within the continental lithosphere behind the ryukyu trench arc system stress directions associated with the two last extensional phases in the southwestern okinawa trough have been deduced from a comparison with analog modeling the direction of extension is n 150 o for the pleistocene phase of extension 2 0 1 ma and n 170 o for the late pleistocene holocene phase of extension 0 1 0 ma the present day ryukyu volcanic arc a narrow continuous feature extending from japan to taiwan is located on the eastern side of the okinawa trough 80 100 km above the wadati benioff zone the minimum depth for emplacement of arc magmatism scarce present day backarc volcanism appears in the middle and southern okinawa trough within linear en echelon bathymetric depressions a n045 o oriented seamount volcanic chain cuts across obliquely the southwestern okinawa trough and lies in the direct line of extension of the gagua ridge a n s linear volcanic feature of the philippine sea plate associated with this extension of the gagua ridge a large reentrant located at the base of the ryukyu prism the uplift of part of the nanao forearc basin and the deformation of the sedimentary arc suggest that the voluminous cross backarc volcanism could be tied to the subduction of the gagua ridge located there at a depth of 80 100 km beneath the backarc basin a second area of anomalous volcanism has been identified in the middle okinawa trough in the ene extension of the daito ridge a wnw ese 400 km long volcanic feature of the philippine sea plate we suggest that the gagua and daito ridges initially induced stress at the base of the arc which is still brittle and cracks propagated through the overlying brittle lithosphere allowing magmas with arc affinities to erupt at the seafloor this excessive magmatism reaches the seafloor through conduits which preferentially follow in their shallowest portion the crustal normal faults of the backarc rifts the okinawa trough is consequently still in an early stage of evolving from arc type to backarc activity

waters of the makarov and canada basins abstract hydrographic measurements from the 1994 arctic ocean section show how the makarov and canada basins of the arctic ocean are related and demonstrate their oceanographic connections to the eurasian basin the inflow into the makarov basin consists largely of well ventilated water within a broad band of densities from a boundary flow over the siberian end of the lomonosov ridge the boundary flow contains a significant component of dense shelf water likely originating in the barents kara and laptev seas earlier ice camp data show that the canada basin is relatively more isolated from this ventilation source in the canada basin shelf sources influenced by bering sea water appear to add cold waters with high silicate concentrations to the halocline and deeper in 1994 the halocline silicate maximum over the central makarov basin was absent evidence of the recent displacement of the upper s 33 1 halocline water from the chukchi east siberian sea region by water from the eurasian basin much of the makarov basin water in and below the halocline is in fact from the eurasian basin with admixture of waters from the canada basin suggested by their higher silicate concentrations mid depth eddies may transport anomalous properties into the central arctic and create property gradients or fronts in mid depth and deep waters the complex topography of the mendeleyev ridge chukchi plateau region also may assist spreading of water from the boundary into the interior atlantic layer characteristics in 1994 differed from previous general depictions in particular the core temperatures at the chukchi mendeleyev boundary were at least 0 2 c warmer on average than indicated in earlier work the recent warming at intermediate depth has resulted from inflow of atlantic waters that have been cooled relatively little during their transit of the norwegian sea

incorporation of satellite derived thin ice data into a global ogcm simulation the presence of thin sea ice is indicative of active freezing conditions in the polar ocean we propose a simple yet effective method to incorporate information of thin ice category into coupled ocean sea ice model simulations in our approach the thin ice distribution restricts thick ice extent and constrains atmosphere ocean heat exchange through the sea ice our model simulation with the incorporation of satellite derived thin ice data for the arctic ocean showed much improved representation of sea ice and upper ocean fields including sea ice thickness in the canadian archipelago and the region north of greenland mixed layer depth over the central arctic and surface layer salinity over the open ocean enhanced sea ice production by the thin ice data constraint increased the total sea ice volume of the arctic ocean by 5 times 10 3 10 times 10 3 km3 subsequent sea ice melting was also enhanced leading to the greater amplitude of the seasonal cycle by approximately 2 times 10 3 km3 15 of the baseline value from the experiment without the thin ice data incorporation overall our results demonstrate that the incorporation of satellite derived information on thin sea ice has great potential for the improvement of coupled ocean sea ice simulations

spatial patterns of primary production on the shelf slope and basin of the western arctic in 2002 in the spring and summer of 2002 primary production in the chukchi sea was measured using 14 c uptake experiments our cruise track encompassed the shelf and continental slope area of the chukchi and beaufort seas progressing into deep water over the canada basin the study area experienced upwards of 90 ice cover during the spring with ice retreating into the basin during the summer production in the spring was light limited due to ice cover with average euphotic zone production rates of o0 3 g c m 2 d 1 values of 8 g c m 2 d 1 were observed in association with surface bloom conditions during the initial ice breakup considerable nutrient reduction in the surface waters took place between the spring and summer cruise and although not observed this was attributed to a spring bloom decreased ice cover and increased clarity of surface waters in the summer allowed greater light penetration the highest rates of production during the second cruise were found at 25 30 m coincident with the top of the nutricline daily euphotic zone productivity in the summer averaged 0 78 g c m 2 d 1 on the shelf and 0 32 g c m 2 d 1 on the edge of the canada basin these data provide an estimated annual production of 90 g c m 2 yr 1 in the study area

the volcanic massif of biq at hayareah sinai negev a case of potassium metasomatism on biq at hayareah an area 80 km 2 in size on the border between sinai egypt and the negev israel a sequence of late precambrian alkali rhyolites lavas tuffs and ignimbrites and their hypa byssal equivalents rhyolite porphyries are exposed these rocks form part of the alkaline katharina province representatives of which are found from the indian ocean to west africa about half the rocks of biq at hayareah have undergone a mainly metasomatic alteration not recognizable in hand specimens chemically the alteration is expressed by the almost total exchange of na by k and by the addition of about 3 silica and of a small amount of alumina the trace element composition remained almost unaffected mineralogically albite has been replaced by k feldspar and secondary quartz has crystallized while some primary quartz has been replaced by k feldspar it is concluded that the potash metasomatism is the result of an interaction between the originally partly glassy rhyolites and hyd

circulation of summer pacific halocline water in the arctic ocean 1 we present an analysis of arctic ocean hydrographic and sea ice observations from the 1990s with a focus on the circulation of water that originates in the north pacific ocean previous studies have shown the presence of two varieties of relatively warm summer halocline water in the vicinity of the chukchi sea i e the relatively fresh alaskan coastal water acw and the relatively saltier summer bering sea water sbsw here we extend these studies by tracing the circulation of these waters downstream into the arctic ocean we find that acw is generally most evident in the southern beaufort gyre while sbsw is strongest in the northern portion of the beaufort gyre and along the transpolar drift stream we find that this separation is most extreme during the early mid 1990s when the arctic oscillation was at historically high index values this leads us to speculate that the outflow to the north atlantic ocean through the canadian archipelago and fram strait may be similarly separated as arctic oscillation index values fell during the later 1990s acw and sbsw began to overlap in their regions of influence these changes are evident in the area north of ellesmere island where the influence of sbsw is highly correlated with a 3 year lag with the arctic oscillation index we also note the presence of winter bering sea water wbsw which underlies the summer varieties all together this brings the number of distinct pacific water types in our arctic ocean inventory to three acw sbsw and wbsw

the effects of k metasomatism in the bahia laura volcanic complex deseado massif argentina petrologic and metallogenic consequences abstract the deseado massif is a 60 000 km2 geological region located in southern argentinean patagonia the most important geological feature of this area is an extensive plateau characterized by complex and long lived middle to upper jurassic volcanism composed of intermediate to acid volcanic rocks of the bahia laura volcanic complex this voluminous volcanism originated in a widespread extensional environment that affected all of patagonia related to the opening of the atlantic ocean the volcanic rocks are genetically related to jurassic epithermal deposits consequently the region is an important gold and silver producer with four operational mines cerro vanguardia mina martha manantial espejo and san jose and more than 50 epithermal occurrences undergoing different levels of exploration potassic metasomatism identified in the bahia laura volcanic complex is difficult to recognize in hand specimen but is characterized by k2o na2o ratios higher than 2 5 and l o i values lower than 3 wt and affects only rocks with silica contents over 68 wt the metasomatism produced an intense geochemical change in the affected rocks with significant additions of k2o rb au sb w and a minor enrichment in cs cu as and probably ag and hg strongly depleted elements are mgo cao na2o p2o5 mno sr and u whereas feot tio2 l o i pb and zn are moderately depleted finally sio2 al2o3 mo and most trace elements and ree remained almost invariant during increasing metasomatism strong similarities in lithologies and geochemical signatures observed in k metasomatized areas around the world regardless of their geological settings and fluid origins suggest that volcanic glass probably played an important role as an ion exchanger during alteration due to the high mobility of elements that occurs during k metasomatism no classification or discrimination diagram based on major elements tio2 or rb are considered to be valid for the chemical characterization of volcanic rocks based on metasomatized samples the precious and base metals enrichment depletion pattern of k metasomatized rocks is identical to the geochemical signature observed in the upper parts of low sulfidation environments from the deseado massif this geochemical signature along with spatial relations observed between k metasomatized rocks and epithermal manifestations implies that hydrothermal fluids were responsible for the metasomatism observed in the bahia laura volcanic complex

crustal gravitational potential energy change and subduction earthquakes crustal gravitational potential energy gpe change induced by earthquakes is an important subject in geophysics and seismology for the past forty years the research on this subject stayed in the stage of qualitative estimate in recent few years the 3d dynamic faulting theory provided a quantitative solution of this subject the theory deduced a quantitative calculating formula for the crustal gpe change using the mathematic method of tensor analysis under the principal stresses system this formula contains only the vertical principal stress rupture area slip dip and rake it does not include the horizontal principal stresses it is just involved in simple mathematical operations and does not hold complicated surface or volume integrals moreover the hanging wall vertical moving up or down height has a very simple expression containing only slip dip and rake the above results are significant to investigate crustal gpe change commonly the vertical principal stress is related to the gravitational field substituting the relationship between the vertical principal stress and gravitational force into the above formula yields an alternative formula of crustal gpe change the alternative formula indicates that even with lack of in situ borehole measured stress data scientists can still quantitatively calculate crustal gpe change the 3d dynamic faulting theory can be used for research on continental fault earthquakes it also can be applied to investigate subduction earthquakes between oceanic and continental plates subduction earthquakes hold three types a crust only on the vertical up side of the rupture area b crust and seawater both on the vertical up side of the rupture area c crust only on the vertical up side of the partial rupture area and crust and seawater both on the vertical up side of the remaining rupture area for each type we provide its quantitative formula of the crustal gpe change we also establish a simplified model called crw model as follows for type b and type c subduction earthquakes if the seawater average depth on the vertical up side of the rupture area is less than a tenth of the hypocenter depth then take the approximation that the seawater above the continental plate is replaced by the upper crustal material of the continental plate the formula of quantitative calculating the crustal gpe change is also provided for this model finally for 16 september 2015 mw 8 3 illapel chile earthquake we apply crw model and obtain the following results the crustal gpe change is equal to 1 8 1019 j and the hanging wall vertical moving up height is 1 9 m with respect to the footwall we believe this paper might be the first report on the quantitative solution of the crustal gpe change for this subduction earthquake our results and related method will be helpful in research into the earthquakes in peru chile subduction zone and the andean orogeny in short this study expounds a new method for quantitative determining the crustal gpe change caused by subduction earthquakes which is different from other existing methods

use of ammonium and other nitrogen tracers to investigate the spreading of shelf waters in the western arctic halocline 1 the contribution of nutrient regeneration in summer to the nutrient maximum associated with bering sea winter water bsww is estimated from the ammonium data which was obtained in the outer shelf region of the chukchi sea for the first time by the r v mirai in 2002 the contribution rate reaches 20 30 which is larger than the rate studied earlier inside the chukchi shelf such bsww influenced by the regeneration spreads to the chukchi shelf slope up to the isobath of 3000 m however was not found in the canada basin the ammonium and a nitrogen deficit are also useful tracers to study the spreading of shelf waters that are less saline than bsww in the canada basin a small amount of ammonium 2 m was observed east of the northwind ridge this small amount of ammonium would be associated with the spreading of eastern chukchi summer water via the barrow canyon around the chukchi borderland a prominent nitrogen deficit layer was found it would be accompanied by western chukchi summer water via the hope valley herald valley channel the water flows into the chukchi abyssal plain and then spreads eastward to the west of the northwind ridge with the decrease of nitrogen deficit signal

impact of an unusually large warm core eddy on distributions of nutrients and phytoplankton in the southwestern canada basin during late summer early fall 2010 1 recent freshening of the arctic ocean due to melting of sea ice and enhanced ekman pumping has deepened the nutricline over the canada basin and reduced nutrient concentrations in the euphotic zone cold core eddies frequently transport nutrient rich shelf water to the canada basin but the eddies are much deeper than the euphotic zone because warm core eddies appear near the surface or at a depth range shallower than that of the cold core eddies they may play a crucial role in determining nutrient distributions in the euphotic zone and hence may affect primary production during late summer early fall 2010 we conducted detailed surveys of a warm core eddy which was unusually large 100 km in diameter we suggest that this warm core eddy which contained high ammonium shelf water could supply ammonium to the euphotic zone in the southwestern canada basin and may sustain 30 higher biomass of picophytoplankton 2 m than that in the surrounding water in the basin the role of warm core eddies in supplying nutrients to the euphotic zone and controlling phytoplankton distributions seems to be more important than previously because the recent deepening of the nutricline in the canada basin has decreased the nutrient supply to the euphotic zone

the najd fault system saudi arabia and egypt a late precambrian rift related transform system the najd fault system is a complex set of left lateral strike slip faults and ductile shear zones that strike nw se across the precambrian of arabia and egypt this system was developed during the interval 540 620 ma it is up to 400 km wide with an exposed length of 1100 km inferred buried extensions of the najd give it a total length of 2000 km it is the best exposed and may be the largest pre mesozoic zone of transcurrent faulting on earth previous models for the najd fault system suggest it formed as a result of a major late precambrian continent continent collision this model is not preferred here because 1 the lack of evidence for a pre late precambrian continent to the east of the najd fault system 2 the difference between the orientation of the najd fault system and that predicted by slip line theory 3 the younger age of najd movements compared with that of collisional sutures in the arabian shield and 4 lack of evidence for wide spread crustal uplift that would be expected to accompany collision a new model for the origin of the najd fault system accounts for each of these objections the najd fault system formed in response to a broad zone of nw se directed crustal extension that accompanied juvenile continental crustal formation in northernmost afro arabia this model also accounts for the following observations 1 strands of the najd parallel the direction of extension in the north eastern desert of egypt and sinai 2 the timing of the principal rifting movements ca 575 600 ma overlap with those of the najd ca 560 620 ma 3 in spite of observation 2 the najd fault system is not recognized in northernmost afro arabia instead the najd deformation becomes increasingly ductile and these zones are more commonly intruded by sheared and foliated granites as the principal zone of extension is approached the najd fault system thus represents a set of continental transforms developed in response to a major episode of late precambrian extensional continental crust formation in northernmost afro arabia

crustal gravitational energy change caused by earthquakes in the western united states and japan abstract we study the cumulative change of the coseismic crustal gravitational energy caused by earthquakes occurring in two regions with active tectonics the western usa during 1992 to 1999 and japan during january 1997 to august 2000 we use regional earthquake source mechanism catalogues available for these regions in order to increase spatial coverage and resolution the catalogues however contain very shallow earthquakes for which the conventional normal mode approach has difficulties in calculating the gravitational energy change under slow convergence in the mode summations to overcome this problem we employ a direct solution approach which allows to generate very accurate kernels for the integration of the coseismic gravitational energy change in the western usa the coast ranges and the transverse ranges show systematically positive gravitational energy changes while the margin of the basin and range shows negative changes in japan the northeastern part shows predominantly positive changes while the southwestern part shows negative to weak positive changes these systematic patterns well correspond to the regional tectonic regime gravitational energy gain for compressional tectonics and energy loss for extensional tectonics the total global cumulative crustal gravitational energy change caused by the earthquakes occurring in the western usa is 6 1 10 17 j and it is 2 7 10 17 j by the earthquakes in japan these energy changes are positive in both regions which indicates the predominance of the compressional stress state with respect to the earthquake occurrence

new gravity anomaly map of taiwan and its surrounding regions with some tectonic interpretations abstract in this study we compiled recently collected from 2005 to 2015 and previously reported published and open access gravity data including land shipborne and satellite derived data for taiwan and its surrounding regions based on the cross over error analysis all data were adjusted and new free air gravity anomalies were obtained shedding light on the tectonics of the region to obtain the bouguer gravity anomalies the densities of land terrain and marine sediments were assumed to be 2 53 and 1 80 g cm3 respectively the updated gravity dataset was gridded with a spacing of one arc minute several previously unnoticed gravity features are revealed by the new maps and can be used in a broad range of applications 1 an isolated gravity high is located between the shoushan and the kaoping canyon off southwest taiwan 2 along the luzon arc both free air and bouguer gravity anomaly maps reveal a significant gravity discontinuity feature at the latitude of 21 20 n 3 in the southwestern okinawa trough the ne sw trending cross back arc volcanic trail cbvt marks the low high gravity anomaly both free air and bouguer boundary

change of crustal gravitational potential energy in the taiwan orogen by the chi chi earthquake sequence abstract the active convergence between the northwest corner of the philippine sea plate and the southeast margin of the eurasian plate has given rise to the taiwan mountain building and produced numerous earthquakes among the earthquakes the 1999 chi chi earthquake is the largest one recorded in the century in this study we examine the crustal gravitational potential energy gpe change in the taiwan orogen caused by the chi chi earthquake sequence which was catalogued by the regional broadband seismometer array for a whole year as a result we find that the crust was going up and down randomly during the earthquake sequence but an overall cumulative gain of the crustal gpe 1 82 10 16 j was rapidly achieved in 1 month after the main shock the crustal gpe was nearly still afterwards and reached 1 90 10 16 j in 1 year spatially although the main surface faulting has occurred in western taiwan the crustal gpe gain is mainly distributed in central taiwan at the area where the existing crustal gpe is high and the existing lithospheric gpe is relatively low the crustal gpe loss by the chi chi earthquake sequence can also be observed and is generally distributed at both sides of the crustal gpe gain area the crustal gpe gain mainly found in central taiwan corroborates that the uplift of the taiwan orogen is principally taking place in central taiwan rather than in the more hazardous western taiwan

using the nutrient ratio no po as a tracer of continental shelf waters in the central arctic ocean historical nitrate phosphate and dissolved oxygen data from the central arctic ocean are examined with particular emphasis on the conservative parameters no 9 no sub 3 o sub 2 and po 135 po sub 4 o sub 2 the no po ratio is shown to increase with depth in the canada basin being approximately 0 78 in surface and upper halocline waters and approximately 1 0 in the atlantic layer and deep waters lower halocline water is marked by no and po minima and intermediate no po no po ratios from the arctic shelf seas are examined to determine possible source regions for the various water masses the no po ration of canada basin deep water implies an upper bound of approximately 11 shelf water contribution to this water mass a slight oxygen maximum core in the lower halocline water is identified at a salinity of s double bond 34 5 in the vicinity of the alpha ridge this core appears to be diminished by diapycnal mixing and does not extend into the beaufort gyre

a late proterozoic bimodal volcanic subvolcanic suite from wadi araba southwest jordan abstract geotectonic setting age relationships petrography and geochemistry of a pan african bimodal volcanic subvolcanic suite have been examined the volcanic phase terminated the pan african molasse evolution and spans the time interval 550 540 ma the volcanics forming a 70 km nne ssw trending belt are distributed predominantly as rhyolitic lava flows and subordinately as trachybasalts and trachyandesites the composition of the numerous dikes varies from basalt to trachyandesite and rhyolite the rhyolites are typified as alkali rhyolites and comendites geochemical criteria characterize a bimodal suite which is not of cogenetic origin the basalts are mantle derived fractionation controlled products whereas the alkali rhyolites and comendites were generated by partial melting of continental crustal rocks the investigated magmatic suite has been compared with equivalent suites from the arabian nubian shield

formation and evolution of the surface mixed layer and halocline of the arctic ocean fresh water from summer ice melt and the total freshwater content of the arctic ocean water column above the thermocline are estimated from vertical profiles of temperature and salinity observed on the i b oden 1991 cruise the seasonal ice melt ranges from 0 5 m to slightly above 1 m and is moderately uniform over the observation area regions of lower melting are seen over the morris jesup plateau the freshwater content is calculated relative to the salinity just above the thermocline north of the barents sea the freshwater content increases toward the interior of the arctic ocean showing that fresh water is advected from other regions into the observation area regions of different freshwater content are separated by fronts over the nansen gakkel ridge over the lomonosov ridge and in the western eurasian basin between waters derived from the eurasian and canadian basins denser water homogenized north of the barents sea is recognized by a temperature minimum layer the absence of the temperature minimum near the nansen gakkel ridge indicates that heat is transferred from the atlantic layer over a longer time than the shortest route would allow this observation can be explained if the layer circulates together with the atlantic layer i e toward the east and returns above the nansen gakkel ridge and along the amundsen basin north of the laptev sea this water formed north of the barents sea becomes covered by low salinity shelf water the increased freshwater content limits the winter convection so it no longer reaches the thermocline and an intermediate halocline is formed the halocline in the eurasian basin consists of water originating from winter convection in the arctic ocean north of the barents sea which then circulates around the basin such a formation mechanism also explains the observed distribution of low no water the strong density increase limits vertical exchange and the vertical diffusion coefficient in the halocline is small 1 10 6 m2 s 1 the increased temperature of the halocline shows that the heat lost upward by the atlantic layer mainly by double diffusive convection is trapped below the mixed layer

transition from oblique subduction to collision earthquakes in the southernmost ryukyu arc taiwan region tectonic characteristics of the region between taiwan and the southernmost ryukyu arc are inferred from a detailed analysis of local seismicity and source parameters of 62 recent earthquakes of 5 5 mb 6 6 five major seismogenic structures can be delineated the collision seismic zone csz the interface seismic zone isz the wadati benioff seismic zone wbsz the lateral compression seismic zone lcsz and the okinawa seismic zone osz in the csz located along the east coast of taiwan and offshore earthquake focal mechanisms show horizontal p axes distributed in two directions 287 10 and 333 16 possibly reflecting a strain partition associated with the relative plate convergence between the eurasia plate and the philippine sea plate the corresponding seismic strain tensor indicates a maximum compressive strain rate of 1 2 10 7 yr 1 along 293 and a comparable extension in vertical direction presumably resulted from plate collision in the region the geometry of the isz which is distorted significantly at its westernmost end can be approximated by a north dipping plane that is gradually pushed northward with increasing dip the seismogenic portion of the interface spans a short depth range from 10 km to 35 km a clear pattern of earthquake slip partition is observed the average slip vector residual is as large as 35 seismic strain patterns within the subducted philippine sea slab show predominantly downdip extension between 80 and 120 km and downdip compression at 270 km different from the pattern of strain segmentation observed for the rest of the ryukyu arc where the northern and southern portions are dominated by downdip extension and compression respectively owing to the large convergence obliquity the slab is descending at a rate significantly slower near taiwan than in the southern ryukyu thus we interpret the appearance of downdip extension within the subducted lithosphere as a combined result of oblique subduction and the slab s negative buoyancy a number of thrust or oblique strike slip earthquakes between isz and wbsz show a consistent pattern of lateral compression with p axes oriented roughly parallel to the local strike of the trench arc system they are probably due to the compressive strain originated from the collision and transmitted laterally within the lithosphere shallow normal faulting earthquakes show successive rotation of t axes from approximately n s in the okinawa trough to approximately e w in northeast taiwan possibly as a result of interaction between the extension from the opening of the okinawa trough and the compression from collision one normal event january 18 1991 mb 5 9 occurred in the central range with t axis roughly parallel to the structural trend of taiwan implying that the nature of the orogeny in taiwan has changed from thin skinned deformation to lithospheric collision involving the whole crust and uppermost mantle

shoaling of the nutricline with an increase in near freezing temperature water in the makarov basin 1 the water mass changes in the makarov basin and adjacent areas associated with the recent loss of arctic sea ice had not been studied in detail we combined data obtained from multiple cruises in these regions and used chemical tracers to investigate the spatial and temporal changes in water masses our data show that a previously present temperature maximum water has disappeared from the makarov basin and chukchi abyssal plain due to enhanced cooling and convection in the east siberian sea in addition a large volume of water has formed by cooling and convection and is flowing into the makarov basin producing a temperature minimum with relatively high nutrients and resulting in a shoaling of the nutricline this temperature minimum water likely originated from the eastern part of the east siberian sea where significant open water areas appeared after 2005 in the freeze up season the water mass boundary between this temperature minimum water and the pacific origin temperature minimum water shifted westward from the chukchi plateau in the early 2000s to the mendeleyev ridge in the late 2000s probably owing to a westward flow of the enhanced beaufort gyre associated with recent sea ice loss in the canada basin although the shoaling of the nutricline in the makarov basin could increase phytoplankton production such production could decrease in the southern makarov basin because a large amount of sea ice meltwater covers that region and might decrease the nutrient supply from the subsurface layer

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

beaufort gyre freshwater reservoir state and variability from observations 1 we investigate basin scale mechanisms regulating anomalies in freshwater content fwc in the beaufort gyre bg of the arctic ocean using historical observations and data collected in 2003 2007 specifically the mean annual cycle and interannual and decadal fwc variability are explored the major cause of the large fwc in the bg is the process of ekman pumping ep due to the arctic high anticyclonic circulation centered in the bg the mean seasonal cycle of liquid fwc is a result of interplay between the mechanical ep and thermal ice transformations factors and has two peaks one peak occurs around june july when the sea ice thickness reaches its minimum maximum ice melt the second maximum is observed in november january when wind curl is strongest maximum ep and the salt input from the growing ice has not yet reached its maximum interannual changes in fwc during 2003 2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a 1 in the center of ep influenced region decadal fwc variability in the period 1950 2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change the center of maximum fwc shifted to the southeast and appeared to contract in area relative to the pre 1990s climatology in spite of the areal reduction the spatially integrated fwc increased by over 1000 km 3 relative to climatology

formation and spreading of eurasian source oxygen rich halocline water into the canadian basin in the arctic ocean 1 we identify the source region and spreading pattern of cold oxygen rich water observed in the halocline of the northern canada basin using both joint western arctic climate studies 2002 2005 and other data this water originates in the winter mixed layer in the nansen basin and because of its convective origin can be traced by its cold oxygen rich properties together with a signature of low potential vorticity this water a component of the cold halocline complex spreads into the makarov basin across the lomonosov ridge between 82 n and 86 n enters the canada basin between the alpha and mendeleyev ridges and continues eastward into the beaufort gyre north of chukchi plateau