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

consequences of viscous drag beneath a transform fault 1 a transform fault is modeled as a vertical cut through an elastic layer schizosphere of thickness h overlying a viscous substrate plastosphere we consider a steady transform motion accommodated in the schizosphere wholly by slip on the fault and in the plastosphere insofar as possible by viscous flow for the case where the viscosity in the plastosphere is strain rate dependent but independent of temperature the velocity solution in the plastosphere is v where v is the slip rate on the fault in the schizosphere and r and are the cylindrical coordinates with the origin at the bottom of the fault the viscous stress is singular at the bottom of the fault r 0 and exceeds the brittle frictional strength for r r0 equating the brittle strength to the viscous stress defines the brittle ductile boundary r0 in the plastosphere as a function of h and viscosity the additional condition that r0 must be small allows the viscosity to be estimated from h for small r the temperature independent solution is a valid approximation to the temperature dependent solution and the relation between viscosity and h should remain valid from the temperature independent model we estimate that self heating due to dissipation in the plastosphere for reasonable earth parameters is less than 20 c

past present and future of thermochronology in one form or another geochronologists have been practicing thermochronology 1 the use of radioisotopic dating to constrain thermal histories of rocks and minerals for over 40 years building from lessons learned over these four decades thermochronology continues to evolve due to technical developments increasingly sophisticated theoretical models and an expanding range of applications in geologic and planetary science most recently interest in earth surface processes and interactions between tectonics erosion and climate has drawn attention to techniques that can address the timing and rates of processes operating at temperatures below about 300 c the purpose of this rimg volume is to assess the current state of thermochronology as of circa 2005 which is coincidentally the 100th anniversary of the first radioisotopic date rutherford 1905 1906 excellent review papers and books on specific topics within this field have been published but no single volume has yet provided a comprehensive review of current practices basic theory and illustrative examples the motivation for this volume stems from these considerations knowing that in a fast developing field a book like this can quickly become dated we tried to include sufficient review of fundamentals and the literature to offer students and new users a useful introduction to thermochronology that may have some staying power in this chapter we first review the salient points of thermochronology s history before assessing our current capabilities and challenges and then taking the risk of suggesting where the field is headed we do not provide a comprehensive history of the method that does full justice to the work of the large and growing cohort of thermochronologists in this short space we instead opted to give our perspectives on where the intellectual and technological roots of the discipline lie which run deeper and go back farther than is sometimes appreciated

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

viscoelastic coupling model for the earthquake cycle driven from below in a linear system the earthquake cycle can be represented as the sum of a solution which reproduces the earthquake cycle itself viscoelastic coupling model and a solution that provides the driving force we consider two cases one in which the earthquake cycle is driven by stresses transmitted along the schizosphere and a second in which the cycle is driven from below by stresses transmitted along the upper mantle i e the schizosphere and upper mantle respectively act as stress guides in the lithosphere in both cases the driving stress is attributed to steady motion of the stress guide and the upper crust is assumed to be elastic the surface deformation that accumulates during the interseismic interval depends solely upon the earthquake cycle solution viscoelastic coupling model not upon the driving source solution thus geodetic observations of interseismic deformation are insensitive to the source of the driving forces in a linear system in particular the suggestion of bourne et al 1998 that the deformation that accumulates across a transform fault system in the interseismic interval is a replica of the deformation that accumulates in the upper mantle during the same interval does not appear to be correct for linear systems

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

timing of skarn gold deposition in the giant beiya polymetallic gold deposit southwest china constraints from in situ monazite sims u th pb geochronology abstract robust dating of hydrothermal deposits is critical to understand ore genesis which depends on judicious selection of mineralization related chronometers especially for complex polymetallic mineral systems the beiya deposit in southwest china is a world class polymetallic gold system 11 9 moz au at a grade of 2 52 g t and the main mineralization is considered as skarn type however available dating results for the gold mineralization give a wide range of ages which in some cases could be inaccurate due to the use of non matrix matched external isotope standards or an equivocal relationship between gold and the dated minerals in this contribution hydrothermal monazite coexisting with gold bearing ore minerals magnetite pyrite and chalcopyrite from high grade massive magnetite sulfide gold ores at beiya was dated in situ using secondary ion mass spectrometry sims the u th pb analyses of hydrothermal monazite yielded a 208pb 232th age of 36 0 0 5 ma 2 mswd 2 0 n 27 which is considered a robust age for the beiya skarn gold mineralization our study supports a genetic link between the skarn gold mineralization and the post collisional quartz monzonite magmatism at beiya based on a new zircon u pb age of 37 2 0 4 ma compared with the previously reported molybdenite re os and sphalerite rb sr isochron ages our monazite u th pb result suggests that the gold deposition was broadly coeval with the formation of molybdenite but probably prior to the local pb zn ag mineralization at beiya

postseismic relaxation following the 1992 m7 3 landers and 1999 m7 1 hector mine earthquakes southern california 1 postseismic relaxation measured postseismic deformation less the deformation that would have occurred at the preseismic rate has been monitored at the same 10 monuments over 6 years following both the 1992 landers and the 1999 hector mine earthquakes for both earthquakes the displacement components of the observed relaxation are well described by i if1 t where i and i are constants peculiar to each component at each monument t is the time after the earthquake and f1 t is a temporal function common to all components and all monuments for that earthquake the temporal function f1 t can be approximated by bt c loge 1 t where 38 7 15 2 days and 25 6 7 7 days for the landers and hector mine relaxations respectively because the estimated values of do not differ significantly the transient term loge 1 t in the temporal function may be the same for both earthquakes the asymptotic t relaxation rates ib are only a few mm a and do not appear to be significantly different following the two earthquakes the asymptotic deformation rates appear to be slightly greater than the preseismic deformation rates but the preseismic rates were not measured directly thus the deformations of the landers array measured over the first 5 6 years following the landers earthquake and over the first 6 4 years following the hector mine earthquake are generally consistent with a simple model in which the transient postearthquake relaxation depends upon time as loge 1 t with 28 5 days and the asymptotic postseismic speeds of the monuments exceed the preseismic speeds by at most only a few millimeters per annum

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

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

viscoelastic gravitational deformation by a rectangular thrust fault in a layered earth previous papers in this series have been concerned with developing the numerical techniques required for the evaluation of vertical displacements which are the result of thrust faulting in a layered elastic gravitational earth model this paper extends these methods to the calculation of fully time dependent vertical surface deformation from a rectangular dipping thrust fault in an elastic gravitational layer over a viscoelastic gravitational half space the elastic gravitational solutions are used together with the correspondence principle of linear viscoelasticity to give the solution in the laplace transform domain the technique used here to invert the displacements into the time domain is the prony series technique wherein the transformed solution is fit to the transformed representation of a truncated series of decaying exponentials purely viscoelastic results obtained are checked against results found previously using a different inverse transform method and agreement is excellent the major advantage in using the prony series technique is that deformations can be computed for arbitrary time intervals a series of results are obtained for a rectangular 30 dipping thrust fault in an elastic gravitational layer over viscoelastic gravitational half space time dependent displacements are calculated out to 50 half space relaxation times a or 100 maxwell times 2 m a significant effects due to gravity are shown to exist in the solutions as early as several a the difference between the purely viscoelastic solution and the viscoelastic gravitational solutions grows as time progresses typically the solutions with gravity reach an equilibrium value after 10 20 relaxation times when the purely viscoelastic solutions are still changing significantly additionally the length scaling which was apparent in the purely viscoelastic problem breaks down in the viscoelastic gravitational problem two independent length scales one of which changes with time are now seen to characterize the problem

postseismic and interseismic displacements near a strike slip fault a two dimensional theory for general linear viscoelastic rheologies 1 we present an analytic solution for the deformation near an infinite strike slip fault in an elastic layer overlying a linear viscoelastic half space the theory is valid for any linear viscoelastic rheology and any earthquake sequence this is a generalization of the work of j c savage and colleagues which only holds for models with a uniform shear modulus maxwell viscoelastic lower half space and periodic rupture recurrence we demonstrate the theory for models of an elastic layer over a maxwell standard linear solid burgers and triviscous half space for each of these models we calculate example postseismic displacements interseismic displacements in a periodic earthquake sequence and interseismic displacements for a nonperiodic earthquake sequence our solution is for a simple geometry however the model presents an elegant tool to explore the evolution of displacements for relatively complex rheologies and rupture recurrence histories

the origin of swash cusps on beaches abstract genetically there are two types of beach cusps those formed in the surfzone by the nearshore circulation system and those formed on the beachface by the swash and backwash the latter are here called swash cusps and a simple model relating the physical dimensions of swash cusps to the properties of the incident wave field and the mean beach slope is developed as in some previous models the cusp wavelength is controlled by the longshore wavelength of edge waves but the edge waves are now required only to provide small periodic perturbations on an originally uniform beach further cusp growth occurs because of the interactions between the incident waves and the perturbed topography the maximum cusp height apex to valley is hypothesized to be proportional to the significant vertical excursion of swash motions it follows from the above assumptions that the maximum possible cusp steepness cusp height cusp longshore wavelength is proportional to the mean on offshore beach slope this result agrees with field data and the value of the ratio of maximum cusp height to beach slope differs from that obtained theoretically by guza and bowen 1981 using a complicated non linear model with rather different physics the present model implies that edge waves although necessary for initiating the initial bedform perturbation need not persist for the development of mature cusp topography

tectonic evolution of the cenozoic olympic subduction complex washington state as deduced from fission track ages for detrital zircons

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

postearthquake relaxation and aftershock accumulation linearly related after the 2003 m 6 5 chengkung taiwan and the 2004 m 6 0 parkfield california earthquakes we treat both the number of earthquakes and the deformation following a mainshock as the superposition of a steady background accumulation and the postearthquake process the preseismic displacement and seismicity rates r u and r e are used as estimates of the background rates let t be the time after the mainshock u t u 0 the postseismic displacement less the background accumulation r u t and n t the observed cumulative number of postseismic earthquakes less the background accumulation r e t for the first 160 days duration limited by the occurrence of another nearby earthquake following the chengkung m 6 5 10 december 2003 eastern taiwan and the first 560 days following the parkfield m 6 0 28 september 2004 central california earthquakes u t u 0 is a linear function of n t the aftershock accumulation n t for both earthquakes is described by the modified omori law d n dt 1 t p with p 0 96 and 0 03 days although the chengkung earthquake involved sinistral reverse slip on a moderately dipping fault and the parkfield earthquake right lateral slip on a near vertical fault the earthquakes share an unusual feature both occurred on faults exhibiting interseismic fault creep at the surface the source of the observed postseismic deformation appears to be afterslip on the coseismic rupture the linear relation between u t u 0 and n t suggests that this afterslip also generates the aftershocks the linear relation between u t u 0 and n t obtains after neither the 1999 m 7 1 hector mine southern california nor the 1999 m 7 6 chi chi central taiwan earthquakes neither of which occurred on fault segments exhibiting fault creep

geodetic displacements and aftershocks following the 2001 mw 8 4 peru earthquake implications for the mechanics of the earthquake cycle along subduction zones we analyzed aftershocks and postseismic deformation recorded by the continuous gps station areq following the m w 8 4 23 june 2001 peru earthquake this station moved by 50 cm trenchward in a n235 e direction during the coseismic phase and continued to move in the same direction for an additional 15 cm over the next 2 years we compare observations with the prediction of a simple one dimensional 1 d system of springs sliders and dashpot loaded by a constant force meant to simulate stress transfer during the seismic cycle the model incorporates a seismogenic fault zone obeying rate weakening friction a zone of deep afterslip the brittle creep fault zone bcfz obeying rate strengthening friction and a zone of viscous flow at depth the ductile fault zone dfz this simple model captures the main features of the temporal evolution of seismicity and deformation our results imply that crustal strain associated with stress accumulation during the interseismic period is probably not stationary over most of the interseismic period the bcfz appears to control the early postseismic response afterslip and aftershocks although an immediate increase by a factor of about 1 77 of ductile shear rate is required placing constraints on the effective viscosity of the dfz following a large subduction earthquake displacement of inland sites is trenchward in the early phase of the seismic cycle and reverse to landward after a time t i for which an analytical expression is given this study adds support to the view that the decay rate of aftershocks may be controlled by reloading due to deep afterslip given the ratio of preseismic to postseismic viscous creep we deduce that frictional stresses along the subduction interface account for probably 70 of the force transmitted along the plate interface

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

postseismic relaxation and transient creep 1 postseismic deformation has been observed in the epicentral area following the 1992 landers m 7 3 1999 chi chi m 7 6 1999 hector mine m 7 1 2002 denali m 7 9 2003 san simeon m 6 5 and 2004 parkfield m 6 0 earthquakes the observations consist of repeated gps measurements of the position of one monument relative to another separation 100 km the early observations t 0 1 year are well fit by the function a c log t where t is the time after the earthquake and a and c are constants chosen to fit the data because a log t time dependence is characteristic of transient primary creep the early postseismic response may be governed by transient creep as benioff proposed in 1951 that inference is provisional as the stress conditions prevailing in postseismic relaxation are not identical to the constant stress condition in creep experiments the observed logarithmic time dependence includes no characteristic time that might aid in identifying the micromechanical cause

controls of shear zone rheology and tectonic loading on postseismic creep 1 postseismic deformation is well documented in geodetic data collected in the aftermath of large earthquakes in the postseismic time interval gps is most sensitive to creep in the lower crust or upper mantle activated by earthquake generated stress perturbations in these regions deformation may be localized on an aseismic frictional surface or on a ductile shear zone these two hypotheses imply specific rheologies and therefore time dependence of postseismic creep hence postseismic creep constitutes a potential probe into the rheology of aseismic regions of the lithosphere i present a simple shear zone model of postseismic creep in which the rheology of the creeping element can be varied in the absence of tectonic loading during the postseismic time interval the displacement history of the shear zone obeying a power law rheology with stress exponent n follows an analytical relaxation curve parameterized by 1 n for a frictional surface postseismic creep follows the same relaxation law in the limit 1 n 0 a rough estimate of the apparent stress exponent can be obtained from continuous gps records application to data collected after the 1994 sanriku earthquake yields 1 n 0 1 which is consistent with dislocation creep mechanisms however the records of two other subduction zone events the 2001 peru event and the 1997 kronotski earthquake and a continental strike slip earthquake the 1999 izmit earthquake require negative 1 n rather than characterizing the shear zone rheology these negative exponents indicate that reloading of the shear zone by tectonic forces is important numerical simulations of postseismic deformation with nonnegligible reloading produce curves that are well fit by the generalized relaxation law with 1 n 0 although the actual stress exponent of the rheology is positive while this prevents rheology from being tightly constrained by the studied gps records it indicates that reloading is important in the postseismic time interval in other words the stress perturbation induced by an earthquake is comparable to the stress supported by ductile shear zones in the interseismic period

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

postseismic relaxation driven by brittle creep a possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks application to the chi chi earthquake taiwan we evaluate the effect of coseismic stress changes on the fault slip at midcrustal depth assuming a velocity strengthening brittle creep rheology we show that this model can help reconcile the time evolution of afterslip as measured from geodesy with aftershocks decay we propose an analytical expression for slip of the brittle creeping fault zone bcfz that applies to any dynamic or static stress perturbation including shear stress and normal stress changes the model predicts an initial logarithmic increase of slip with time postseismic slip rate decays over a characteristic time t r a that does not depend on the amplitude of the stress perturbation and it asymptotically joins the long term creep imposed by interseismic stress buildup given that the seismicity rate might be considered proportional to the sliding velocity of the bcfz the model predicts a decay rate of aftershocks that follows omori s law with a mathematical formalism identical to that of dieterich 1994 although based on a different mechanical rationale our model also differs from dieterich s model in that it requires that aftershock sequences and deep afterslip as constrained from geodetic measurements should follow the same temporal evolution we test this for the 1999 chi chi earthquake m w 7 6 and find that both sets of data are consistent with a model of afterslip due to the response of the bcfz the inferred relaxation time t r 8 5 years requires a value for a log v being the coefficient of friction in the range between 1 3 10 3 and 10 2

postseismic relaxation associated with transient creep rheology 1 perfettini and avouac 2004 postulated that both the aftershock rate assumed proportional to the local stressing rate and the postseismic relaxation are driven by the loading imposed by postseismic slip on the brittle creep fault zone bcfz the downdip extension of the fault zone below the coseismic rupture i explore the consequences of that hypothesis for a long strike slip fault in the case where the bcfz rheology is compatible with ordinary transient creep creep strain proportional to loge 1 t 2 because the important relaxation occurs near the bottom of the coseismic rupture i calculate the postearthquake response with a model in which the bcfz is represented by a viscoelastic half space below the coseismic rupture i find that both the predicted postseismic relaxation and the cumulative number of aftershocks can be approximated by the same temporal dependence nmo t amo 1 1 t 1 p p 1 where t is the time after the earthquake and amo and p are the constants chosen to fit either data set notice that dnmo t dt amo 1 t p is the modified omori law used to describe the rate of aftershock occurrence thus the modified omori law can be understood as a consequence of the perfettini avouac hypothesis aftershocks driven by slip on the bcfz and a bcfz rheology compatible with ordinary transient creep moreover the temporal dependence nmo t has been shown to fit postseismic surface deformation following at least 9 earthquakes i also show that the conventional one dimensional spring block model of a bfcz with a rheology compatible with ordinary transient creep leads to the same temporal dependence nmo t

the 127 ma gold mineralization in the wulong deposit liaodong peninsula china constraints from molybdenite re os monazite u th pb and zircon u pb geochronology abstract the wulong deposit is a large tonnage deposit 80 t of au characterized by quartz vein style of gold mineralization in the liaodong peninsula china the auriferous quartz veins are mainly hosted by late jurassic gneissic two mica granite 165 157 ma and early cretaceous granodiorite 129 ma and are structurally controlled by nne and nw trending faults previous attempts to date the gold mineralization yielded ambiguous results 135 112 ma here we report the first in situ and direct age constraint for gold mineralization at wulong five molybdenite samples from mo bearing quartz pyrite veins yielded an isochron age of 127 6 2 3 ma in situ sims u th pb dating of hydrothermal monazite that coexists with gold bearing pyrite and quartz yielded a 208pb 232th age of 126 7 3 2 ma these robust ages together with new age data of the wulong host intrusion and post ore dike allow for a better interpretation of the ore genesis of the wulong deposit relative to a well constrained sequence of regional geological events zircon u pb dating of the wulong host intrusion gneissic two mica granite representing the oldest magmatic event at wulong gave a weighted mean age of 159 3 1 4 ma that is interpreted to be the magma emplacement age subsequent magmatic events are recorded by the early cretaceous dikes with zircon u pb ages between 127 and 113 ma a post ore diorite porphyry dike that crosscuts the early cretaceous dikes has a u pb zircon age of 121 5 1 5 ma all the lines of geochronology evidence suggest a distinct genetic link between the gold mineralization and the early cretaceous magmatism in the wulong orefield this episode of magmatism and mineralization corresponds to the lithospheric thinning within the northeastern north china craton which is triggered by the subduction of the paleo pacific plate

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

pb u and th diffusion in natural zircon zircon zrsio4 is one of the most widely used minerals for determining the age origin and thermal history of rocks by u th pb geochronology but the parameters describing the solid state volume diffusion rates of these elements in natural zircon which are themselves important for establishing the limits on the applicability of zircon for geochronological studies have remained poorly quantified1 this is because of the measurement difficulties associated with the low p p m concentrations and low diffusion rates of these elements in natural zircon and the chemical and physical heterogeneity present in most crystals here we present direct measurements of the uranium thorium and lead loss from a thermally treated gem quality natural zircon and show that lead diffuses much faster than uranium or thorium we find that the u th pb isotopic system in natural zircon will typically have a closure temperature greater than 900 c which explains why zircon is apparently such a robust geochrometer and is capable of remaining isotopically closed through extended periods of high grade metamorphism and partial melting of the host rock

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

the thermal significance of potassium feldspar k ar ages inferred from age spectrum results 40ar39ar age spectrum analyses of three microcline separates from the separation point batholith northwest nelson new zealand which cooled slowly 5 c ma 1 through the temperature zone of partial radiogenic 40ar accumulation are characterized by a linear age increase over the first 65 percent of gas release with the lowest ages 80 ma corresponding to the time that the samples cooled below about 100 c the last 35 percent of 39ar released from the microclines yields plateau ages 103 99 and 93 ma which reflect the different bulk mineral ages and correspond to cooling temperatures between about 130 to 160 c theoretical calculations confirm the likelihood of diffusion gradients in feldspars cooling at rates 5 c ma 1 diffusion parameters calculated from the 39ar release yield an activation energy e 28 8 1 9 kcal mol 1 and a frequency factor grain size parameter d0l2 5 6 3 9 14sec 1 this arrhenius relationship corresponds to a closure temperature of 132 13 c which is very similar to the independently estimated temperature from the observed diffusion compensation correlation this d0l2 implies an average diffusion half width of about 3 m similar to the half width of the perthite lamellae in the feldspars the range in microcline k ar ages from the separation point batholith is the result of relatively small temperature differences within the pluton during cooling comparison of the diffusion laws determined for microcline with those for anorthoclases and other homogeneous k feldspars e 40 to 52 kcal mol 1 reveals that ar diffusion is more highly temperature dependent in the disordered structural state than in the ordered structural state previously published u shaped age spectra are probably the result of the superimposition of excess 40ar upon diffusion profiles of the kind described here

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

coseismic and initial postseismic deformation from the 2004 parkfield california earthquake observed by global positioning system electronic distance meter creepmeters and borehole strainmeters global positioning system gps electronic distance meter creepmeter and strainmeter measurements spanning the m 6 0 parkfield california earthquake are examined using these data from 100 sec through 9 months following the mainshock the omori s law with rate inversely related to time 1 t p and p ranging between 0 7 and 1 3 characterizes the time dependent deformation during the postseismic period these results are consistent with creep models for elastic solids with an accurate function of postseismic response the coseismic displacements can be estimated from the high rate 1 min sampling gps and the coseismic displacements are approximately 75 of those estimated from the daily solutions consequently fault slip models using daily solutions overestimate coseismic slip in addition at 2 months and at 8 months following the mainshock postseismic displacements are modeled as slip on the san andreas fault with a lower bound on the moment exceeding that of the coseismic moment online material data description and supplementary figures tables and data used in models and time series analysis

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

thermochronology of economic mineral deposits dating the stages of mineralization at panasqueira portugal by high precision 40 39 ar age spectrum techniques on muscovite 40 ar 39 ar age spectrum dates for 13 muscovites have been used to reconstruct the thermal history thermochronology of the panasqueira portugal tin tungsten deposit a deposit spatially associated with a belt of hercynian plutons muscovite samples with an age difference as small as 2 2 m y 0 7 of the age are statistically distinct statistics are even better for comparison of multiple samples from separate events that is a difference of 0 9 m y 0 3 can be resolved in this approximately 300 m y old deposit the major tin and tungsten ore forming stages which are the oxide silicate stage the main sulfide stage and greisenization occurred between 296 3 or 0 8 1 sigma and 291 6 or 0 8 m y 1 sigma the first substage of the oxide silicate stage was a short lived thermal pulse at 296 3 or 0 6 m y the fluids responsible may have emanated from the known granite cupola the main sulfide stage was active at 294 5 or 0 9 m y as a slightly longer lived pulse with oldest evidence for this stage 295 8 or 0 6 m y coming from areas farthest away from the known cupola and youngest evidence 293 5 or 0 8 m y closest to the cupola a second substage of the oxide silicate stage occurred as a short lived thermal pulse at 292 9 or 0 7 m y synchronous with greisenization of the cupola and alteration of the silica cap at 292 1 or 0 4 m y the duration of activity of the oxide silicate stage the main sulfide stage greisenization and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4 2 or 0 5 m y 1 sigma minor argon loss from all dated muscovites occurred during later reheating probably during the longer lived pyrrhotite alteration stage a single center the known cupola had a prolonged role and was the source for main sulfide stage oxide silicate stage ii greisenization and alteration of the silica cap and possibly oxide silicate stage i and the pyrrhotite alteration stage however a separate source for these latter two stages cannot be ruled out this study is an example of a new and powerful application of 40 ar 39 ar age spectrum dating of muscovite because of the high precision demonstrated in this study it is now possible to establish time constraints necessary for solving some of the long standing problems in economic geology beyond this the unique geologic situation of panasqueira has allowed us to quantify the thermal characteristics of muscovite published fluid inclusion data have been used to estimate a muscovite argon closure temperature of approximately 325 degrees c during rapid cooling or short reheating and a temperature of approximately 270 degrees c during slow cooling or extended reheating argon loss patterns displayed by all dated muscovites resulted from reheating after original closure the mechanism for this argon loss appears to have been argon transport by volume diffusion thus 40 ar 39 ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age duration and number of episodes of mineralization

viscoelastic behavior of the crust around the longmenshan thrust belt inferred from post seismic deformation of the 2013 lushan earthquake china abstract seven continuous gps stations are located on the hanging wall of the longmenshan thrust belt and post seismic deformation data of the 2013 lushan earthquake have been recorded for nearly four years following the earthquake we transform the data from a global reference frame to the south china block reference frame and then the secular motion and post seismic deformation of the wenchuan earthquake are excluded using an exponential fit model based on our results the viscosities of the low velocity zone at a depth of 25 km and of the middle and lower crust around the longmenshan thrust belt are obtained as 2 75 10 17 p a s and 2 56 10 18 p a s respectively the post seismic rebound which was observed near the lushan epicenter may represent the occurrence of overslip during the earthquake the more complex structural style may have produced weaker fault activity along the southern segment of the longmenshan thrust belt than along its middle and northern segments

diffusion in zircon despite its low abundance in most rocks zircon is extraordinarily useful in interpreting crustal histories the importance of u th pb isotopic dating of zircon is well and long established davis et al this volume parrish et al this volume zircon also tends to incorporate trace elements useful as geochemical tracers such as the ree y and hf a number of characteristics of zircon encourage the preservation of internal isotopic and chemical variations often on extremely fine scale which provide valuable insight into thermal histories and past geochemical environments the relative insolubility of zircon in crustal melts and fluids as well as its general resistance to chemical and physical breakdown often result in the existence of several generations of geochemical information in a single zircon grain the fact that this information is so frequently retained as evidenced through backscattered electron or cathodoluminescence imaging that often reveal fine scale zoning down to the sub micron scale has long suggested that diffusion of most elements is quite sluggish in zircon in this chapter we present an overview of the findings to date from laboratory measurements of diffusion of cations and oxygen in zircon because of its importance as a geochronometer attempts have been made to measure diffusion especially of pb for over 30 years but only in the last decade or so have profiling techniques with adequate depth resolution been employed in these studies resulting in a plethora of new diffusion data these findings have important implications for isotopic dating interpretation of stable isotope ratios closure temperatures and formation and preservation of primary chemical composition and zoning in zircon efforts have been made for some time to quantify and characterize diffusion in zircon most notably of pb in deference to its significance in interpreting pb isotopic signatures and refining understanding of thermal histories as is evident from

postearthquake relaxation after the 2004 m6 parkfield california earthquake and rate and state friction 1 an unusually complete set of measurements including rapid rate gps over the first 10 days of postseismic deformation is available at 12 continuous gps stations located close to the epicenter of the 2004 m6 0 parkfield earthquake the principal component modes for the relaxation of the ensemble of those 12 gps stations were determined the first mode alone furnishes an adequate approximation to the data thus the relaxation at all stations can be represented by the product of a common temporal function and distinct amplitudes for each component north or east of relaxation at each station the distribution in space of the amplitudes indicates that the relaxation is dominantly strike slip the temporal function which spans times from about 5 min to 900 days postearthquake can be fit by a superposition of three creep terms each of the form l loge 1 t l with characteristic times l 4 06 0 11 and 0 0001 days it seems likely that what is actually involved is a broad spectrum of characteristic times the individual components of which arise from afterslip on different fault patches perfettini and avouac 2004 have shown that an individual creep term can be explained by the spring slider model with rate dependent no state variable friction the observed temporal function can also be explained using a single spring slider model i e single fault patch that includes rate and state dependent friction a single state variable and either of the two commonly used aging and slip state evolution laws in the latter fits the rate and state friction parameter b is negative

frictional afterslip following the 2005 nias simeulue earthquake sumatra continuously recording global positioning system stations near the 28 march 2005 rupture of the sunda megathrust moment magnitude m w 8 7 show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust with a major fraction of this slip in the up dip direction from the main rupture eleven months after the main shock afterslip continues at rates several times the average interseismic rate resulting in deformation equivalent to at least a m w 8 2 earthquake in general along strike variations in frictional behavior appear to persist over multiple earthquake cycles aftershocks cluster along the boundary between the region of coseismic slip and the up dip creeping zone we observe that the cumulative number of aftershocks increases linearly with postseismic displacements this finding suggests that the temporal evolution of aftershocks is governed by afterslip

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

improved calibration procedures and new standards for u pb and th pb dating of phanerozoic xenotime by ion microprobe abstract xenotime is a widely occurring mineral that is amenable to u pb and th pb dating but often is found as micrometre sized crystals that can only be dated by in situ microanalytical techniques determining accurate ages for phanerozoic samples and assessing concordance in older samples requires accurate determination of pb u and pb th however ion microprobe data for these ratios are affected by the highly variable trace element composition of xenotime we have identified calibration procedures including matrix corrections for the effects of the dominant trace elements u th and ree that provide an accuracy of 1 for pb u and

fundamentals of noble gas thermochronometry the ideal geochronometer would be a universally stable phase that quantitatively retains both parent and daughter isotopes though a few mineral systems such as zircon u pb dating come reasonably close to this ideal most minerals are incompletely retentive of daughter product nuclides under crustal conditions the mechanisms by which the daughter product can be lost from minerals include dissolution reprecipitation reactions e g salt obradovich et al 1982 recrystallization e g micas undergoing deformation chopin and maluski 1980 and diffusive loss e g 40ar degassing of k feldspar foland 1974 the latter mechanism is perhaps the most common source of discrepancy between a radiometric mineral date and the age of the rock from which it formed geochronologists have learned to turn this non ideal behavior to their advantage and we now understand that most mineral ages from exhumed crustal rocks act in effect as kinetic thermometers sensitive to geologically induced thermal effects such apparent ages are a measure of the temperature range over which daughter product ceased to be lost from a crystal with intracrystalline diffusion usually acting as the rate limiting process consider the case in which a mineral sample containing a radioactive parent element experiences a complex thermal evolution possibly involving heating as well as cooling within the sample daughter product is continually produced by radioactive decay and lost by diffusion at natural boundaries although random at the scale of an individual atom both diffusion and radioactive decay are highly predictable processes over longer and larger scales involving many particles coupled with the strong temperature dependence of diffusion the elegant mathematics of the production diffusion relationship make it possible to recover information about the thermal history experienced by such a sample simply by knowing the amount of daughter product remaining in the mineral following cooling or even better by knowing the distribution of daughter product within the

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

eocene volcanism above a depleted mantle slab window in southern alaska the caribou creek volcanic fi eld lies along the continent side edge of forearc basin rocks in south central alaska and consists of over 1000 m of shallow dipping basalt and andesite lavas with minor mafi c pyroclastic deposits dacite and rhyolite lavas along with shallow intrusions form dome complexes with associated pyroclastic deposits that overlie and crosscut the basalt and intermediate lavas the basalts are tholeiitic and strongly depleted in the light rare earth elements la yb 0 18 1 5 with concentrations of high fi eld strength elements e g zr hf ti y similar to mid ocean ridge basalt and with variable enrichment in fl uid mobile elements e g cs ba and pb intermediate and felsic rocks show enrichment in the rare earth elements and fl uid mobile elements plus rb and k but retain low la yb ratios 0 48 3 6 a few andesite and dacite samples are strongly depleted in the heavy rare earth elements and are geochemically similar to adakites e g sr y up to 52 ten 40 ar 39 ar ages for the caribou creek volcanic rocks range from 49 4 2 2 to 35 6 0 2 ma an adakite like tuff beneath the other volcanic rocks yields an age of 59 0 0 4 ma caribou creek basalts were derived from mid ocean ridge like depleted mantle that was emplaced beneath the southern margin of alaska through a slab window following spreading ridge subduction caribou creek volcanism was coeval with oblique subduction oroclinal bending and right lateral strike slip faulting in south central alaska all of which could have induced crustal extension to allow adiabatic melting of the depleted mantle reservoir to form basaltic magmas the basalts then evolved by fractional crystallization with moderate to high degrees of assimilation of jurassic arc basement rocks to form the intermediate and felsic magmas enrichment of the basaltic parent magmas in fl uid mobile elements occurred by contamination from the jurassic arc rocks and or by contamination with metasomatic mantle remnant from preceding subduction high heat fl ow through the slab window induced partial melting of garnet bearing mafi c parts of the jurassic arc basement to form the adakite like rocks the caribou creek volcanic rocks demonstrate that slab windows can directly infl uence magmatism inboard of accretionary prism and forearc basin settings given a suitable deformation regime e g crustal extension and that the infl uence of a slab window on continental margin magmatism can be long lived 20 m y

pb diffusion in zircon abstract chemical diffusion of ti under anhydrous conditions at 1 atm and under fluid present elevated pressure 1 1 1 2 gpa conditions has been measured in natural zircon the source of diffusant for 1 atm experiments was a zro2 tio2 zircon mixture with experiments run in crimped pt capsules diffusion experiments done in the presence of h2o co2 fluid were run in a piston cylinder apparatus using a source of ground tio2 zrsio4 and sio2 with oxalic acid added to produce h2o co2 vapor and partially melt the solid source material yielding an assemblage of rutile zircon melt vapor nuclear reaction analysis nra with the resonant nuclear reaction 48ti p 49v was used to measure diffusion profiles for both sets of experiments the following arrhenius parameters were obtained for ti diffusion normal to cover the temperature range 1350 1550 c at 1 atm d ti 3 33 10 2 exp 754 56 kj mol 1 r t m 2 s 1 ti diffusivities were found to be similar for experiments run under fluid present conditions a fit to all of the data yields the arrhenius relation d 1 34 102 exp 741 46 kj mol 1 rt m2 s 1 these data suggest that zircon should be extremely retentive of ti chemical signatures indicating that the recently developed ti in zircon crystallization geothermometer watson e b harrison t m 2005 zircon thermometer reveals minimum melting conditions on earliest earth science 308 841 844 will be quite robust in preserving temperatures of zircon crystallization titanium diffuses somewhat faster in zircon than larger tetravalent cations u th and hf but considerably more slowly than pb the ree and oxygen hence ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost

comparison of postseismic afterslip models with aftershock seismicity for three subduction zone earthquakes nias 2005 maule 2010 and tohoku 2011 we focus on the relation between seismic and total postseismic afterslip following the maule mw 8 8 earthquake on 2010 february 27 in central chile first we calculate the cumulative slip released by aftershock seismicity we do this by summing up the aftershock regions and slip estimated from scaling relations comparing the cumulative seismic slip with afterslip models we show that seismic slip of individual aftershocks exceeds locally the inverted afterslip model from geodetic constraints as the afterslip model implicitly contains the displacements from the aftershocks this reflects the tendency of afterslip models to smear out the actual slip pattern however it also suggests that locally slip for a number of the larger aftershocks exceeds the aseismic slip in spite of the fact that the total equivalent moment of the afterslip exceeds the cumulative moment of aftershocks by a large factor this effect seen weakly for the maule 2010 and also for the tohoku 2011 earthquake can be explained by taking into account the uncertainties of the seismicity and afterslip models in spite of uncertainties the hypocentral region of the nias 2005 earthquake is suggested to release a large fraction of moment almost purely seismically therefore these aftershocks are not driven solely by the afterslip but instead their slip areas have probably been stressed by interseismic loading and the mainshock rupture in a second step we divide the megathrust of the maule 2010 rupture into discrete cells and count the number of aftershocks that occur within 50 km of the centre of each cell as a function of time we then compare this number to a time dependent afterslip model by defining the afterslip to aftershock ratio asar for each cell as the slope of the best fitting line when the afterslip at time t is plotted against aftershock count although we find a linear relation between afterslip and aftershocks for most cells there is significant variability in asar in both the downdip and along strike directions of the megathrust we compare the spatial distribution of asar with the spatial distribution of seismic coupling coseismic slip and bouguer gravity anomaly and in each case we find no significant correlation

revisiting the baranof leech river hypothesis for early tertiary coastwise transport of the chugach prince william terrane abstract according to the baranof leech river hypothesis originally proposed in 1982 1 schists on southern baranof island in southeastern alaska were contiguous with the leech river schist on southern vancouver island until 40 ma and 2 both rock units were part of the 2200 km long chugach prince william terrane which was displaced northward about 1100 km after 40 ma isotopic data obtained since 1982 show that the syn magmatic metamorphism that produced the baranof and leech river schists occurred at 50 ma not at 40 ma large magnitude coastwise slip of the terrane is therefore post 50 ma igneous rocks in the baranof and leech river units are part of the sanak baranof magmatic belt of forearc magmatism which has been ascribed to the early tertiary subduction of an oceanic ridge the slab window also gave rise to early eocene near trench plutonic and volcanic rocks on north american basement in the north cascades of washington state and probably to coeval igneous rocks on the western coast of vancouver island these igneous suites in the forearc fix the location of the intersection of the ridge with the continental margin 50 myr ago at latitude ca 48 49 n present day coordinates paleomagnetic data obtained since 1982 imply that before 50 ma the parts of the chugach prince william terrane that were to become the baranof and leech river schists were south of 48 49 n from 61 to 50 ma the northward movement of the terrane relative to north america can be reconciled with the southward migration of forearc magmatism in the chugach prince william terrane if the ridge trench intersection was fixed at 48 n present day coordinates the border ranges fault system is the on land structure that most likely accommodated hundreds of kilometers of post early eocene displacement

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

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

matrix effects and calibration limitations in ion probe u pb and th pb dating of monazite abstract monazite can be used for u pb and th pb dating of a wide variety of rocks and geological processes particularly metamorphism in many instances ion microprobe analysis is the preferred method for dating monazite combining good analytical precision with m scale spatial resolution however ion microprobe dates can be compromised by matrix effects on the ionisation efficiencies of different secondary ionic species which can bias monazite pb tho n and pb uo n data by as much as 40 and 30 respectively for known monazite compositions these effects appear to be entirely attributable to the sputtering process in which case similar effects exist in data from all ion probes the effects on data ratios are modified sometimes exacerbated or reversed when data are subjected to the correlation based pb th and pb u calibrations that are now commonly used one dimensional calibrations of 206 pb 270 uo 2 and 208 pb 264 tho 2 are recommended corrections derived from data for a suite of reference materials with diverse compositions can reduce biases in 208 pb 232 th ages to 206 pb 238 u ages to 204 pb can be addressed without iterative data reduction

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

apparent argon diffusive loss 40ar 39ar age spectra in amphiboles detailed investigations have been made of two amphibole samples where 40ar 39ar age spectra have been interpreted to show argon diffusive loss both samples display complex compositional zoning that reflects partial major and minor element chemical re equilibration during later thermal events that is associated with the loss of radiogenic 40ar the apparent diffusive loss age spectra in these samples are an artefact of this chemical re equilibration process one sample additionally shows the effect of potassium gain and contamination with a potassium rich phase biotite the resulting ages in this sample are geologically meaningless and the apparent fit to a theoretical diffusive loss curve is coincidental this study shows that volume diffusive loss of argon appears to operate at slower rates than argon loss by chemical re equilibration in amphiboles

correlation of static stress changes and earthquake occurrence in the north aegean region a systematic analysis is made of static coulomb stress changes and earthquake occurrence in the area of the north aegean sea greece in order to assess the prospect of using static stress changes to construct a regional earthquake likelihood model the earthquake data set comprises all events of magnitude m 5 2 which have occurred since 1964 this is compared to the evolving stress field due to constant tectonic loading and perturbations due to coseismic slip associated with major earthquakes m 6 4 over the same period the stress was resolved for sixteen fault orientation classes covering the observed focal mechanisms of all earthquakes in the region analysis using error diagrams shows that earthquake occurrence is better correlated with the constant tectonic loading component of the stress field than with the total stress field changes since 1964 and that little if any information on earthquake occurrence is lost if only the maximum of the tectonic loading over the fault orientation classes is considered moreover the information on earthquake occurrence is actually increased by taking the maximum of the evolving stress field since 1964 and of its coseismic slip component over the fault orientation classes the maximum over fault orientation classes of linear combinations of the tectonic loading and the evolving stress field is insignificantly better correlated with earthquake occurrence than the maximum of the tectonic loading by itself a composite stress change variable is constructed from ordering of the maximum tectonic loading component and the maximum coseismic slip component in order to optimize the correlation with earthquake occurrence the results indicate that it would be difficult to construct a time varying earthquake likelihood model from the evolving stress field that is more informative than a time invariant model based on the constant tectonic loading

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

a field based estimate of the zircon fission track closure temperature abstract a field based estimate of the zircon fission track closure temperature is proposed from 13 zircon fission track cooling ages of the gold butte block se nevada using previously published and new thermochronological data the thermal history of the gold butte block is re evaluated resulting in a geothermal gradient estimate of 20 3 c km and a slow cooling rate of 0 55 0 02 c m y from the late jurassic to the early miocene before onset of rapid miocene cooling the rapidly cooled part of the gold butte block provides a slip rate of 10 5 km m y of the hanging wall that caused the miocene exhumation of this crustal section assuming these thermal conditions are correct the closure temperature of the zircon fission track system is determined at 205 18 c which is in good agreement with previous field based estimates because of the variation in zircon fission track annealing behavior with radiation damage field studies are a suitable way to calibrate the closure temperature of the zircon fission track system

excess40ar in metamorphic rocks from broken hill new south wales implications for40ar 39ar age spectra and the thermal history of the region 40ar 39ar age spectrum analyses of samples from broken hill new south wales indicate that the region has experienced a complex thermal history following high grade metamorphism 1660 ma ago the terrain cooled slowly 3 c ma 1 until about 1570 ma ago when the temperature fell below about 500 c following granitoid emplacement 1500 ma ago the region remained relatively cold until affected by a thermal pulse 520 40ma ago causing temperatures to rise to 350 c in some places during this event accumulated40ar was released from minerals causing a significant ar partial pressure to develop laboratory ar solubility data combined with the40ar 39ar age spectra gives a local estimate of this partial pressure of 10 4atm the region finally cooled below 100 c about 280 ma ago 40ar 39ar age spectrum analyses of hornblende plagioclase and clinopyroxene containing excess40ar are characterized by saddle shaped age spectra detailed analysis of plagioclase samples reveals a complex diffusion behaviour which is controlled by exsolution structures this effect in conjunction with the presumed different lattice occupancy of excess40ar with respect to radiogenic40ar appears to be responsible for the saddle shaped age spectra

geology and timing of ore formation in the willow creek gold district talkeetna mountains southern alaska the willow creek mining district was the third largest lode gold district in alaska in the 20 th century having produced 19 metric tons t of gold from vein deposits and another 2 t of gold from associated placer deposits the district is located in the southern talkeetna mountains north of the castle mountain strike slip fault system most gold occurs in widespread mineralized quartz veins hosted by granitic rocks of the willow creek pluton a geochronologic study of granitic rocks alteration minerals and adjacent metamorphic rocks was conducted in order to better understand the timing of magmatism thermochronologic evolution and age of gold mineralization in the district new u pb zircon dates from the talkeetna batholith including the willow creek pluton range from 72 1 to 71 3 ma the u pb dates are similar to reported u late cretaceous pb and k ar dates from elsewhere in the study area and tightly constrain the age of plutonic rocks that host the willow creek lode gold deposits granitic rocks that intrude the willow creek pluton along its northwestern margin yield u pb dates of 75 7 and 70 8 ma the 40 ar 39 ar thermochronologic data for the willow creek pluton and other granitoids reveal rapid postemplacement cooling through hornblende muscovite and biotite closure temperatures thermochronologic data from k feldspars document slower cooling rates through lower temperatures which may be related to slow uplift and exhumation during the paleocene eocene the data are compatible with a simple tectonothermal history following emplacement of the plutonic rocks with essentially no evidence of significant thermal disturbance of the rocks after about 64 ma uranium thorium lead dating of hydrothermal phosphate minerals monazite and xenotime and 40 ar 39 ar dates from hydrothermal sericite from wall rocks and veins indicate that the main stage of gold mineralization occurred at about 67 to 65 ma combining u th pb data from monazites from the independence talkeetna gold bullion and fern deposits gave an average of 65 4 2 3 ma hydrothermal xenotime from the independence vein also yields a statistically indistinguishable age of 64 5 2 3 ma these ages overlap 40 ar 39 ar dates of 67 to 66 ma obtained from hydrothermal sericite associated with formation of the gold bearing veins and the age of a muscovite from a weakly mineralized pegamatite that cuts the willow creek pluton in contrast to previous studies that suggested that at least some mineralization was eocene in age we found no compelling evidence for significant gold mineralization within the district at this time the 40 ar 39 ar and k ar dates from graphitic white micas from schist south of the hatcher pass fault zone yield ages of 61 to 50 ma that are probably related to uplift and cooling of these late cretaceous metasedimentary rocks the absence of evidence for postemplacement thermal events affecting the plutonic rocks of the willow creek district to the north indicates that the schists and granitoids do not share a similar tectonothermal history and that they have been juxtaposed by subsequent faulting along the hatcher pass fault zone

postseismic relaxation and aftershocks 1 perfettini et al 2005 suggested that the temporal dependence of surface displacements u t measured in the epicentral area following an earthquake is related to n t the cumulative number of aftershocks by the equation u t a bt cn t d 1 e t where a b c d and are constants chosen to fit the data and t is the postearthquake time n t appears in the expression for u t because both the aftershocks and a portion of u t are thought to be driven by the same source postseismic fault creep at subseismogenic depths on the downdip extension of the coseismic rupture we show that this equation with the actually observed n t fits the postseismic displacements recorded on several baselines following each of five earthquakes 1999 m7 6 chi chi taiwan 1999 m7 1 hector mine southern california 2002 m7 9 denali central alaska 2003 m6 5 san simeon central california and 2004 m6 0 parkfield central california earthquakes although there are plausible physical interpretations for each of the terms in the expression for u t the large number of adjustable constants a b c d and involved in fitting the rather simple postseismic displacements diminishes the significance of the fit because the observed n t is well fit by the modified omori s law fault creep at depth presumably exhibits the same temporal dependence that dependence could be explained if the rheology of the fault downdip from the coseismic rupture is consistent with ordinary transient creep montesi 2004 demonstrated that power law creep across a shear zone at depth would also produce that temporal signal

four zircon ages from one rock the history of a 3930 ma old granulite from mount sones enderby land antarctica ion microprobe u th pb analyses of zircons from a granulite grade orthogneiss from mount sones enderby land antarctica record the ages of four principal events in the history of the gneiss three of which already have been recognized through previous isotopic dating of other samples the structure of the zircons indicates at least four different stages of growth the several zircon ages were obtained by grouping the analyses according to the stage they represented in the observed stratigraphic succession of growth and thereby defining separate u pb discordance patterns for each stage the stratigraphically oldest zircon rare discrete cores is indistinguishable in age from the most common euhedrally zoned zircon both crystallized when the tonalitic precursor of the orthogneiss was emplaced into the crust 3927 10 ma ago making the orthogneiss currently the oldest known terrestrial rock the outer parts of most grains and some whole grains recrystallized at 2948 31 17 ma during or immediately after possibly 100 ma of high granulite grade metamorphism the recrystallized zircon was isotopically disturbed by tectonism associated with reactivation of the southern margin of the napier complex at 1000 ma in the intervening time at 2479 23 ma the cores and zoned zircon suffered a major isotopic disturbance involving movement of radiogenic pb which left most of the crystals with radiogenic pb deficiencies but produced local radiogenic pb excesses in others a new generation of zircon characterized by very high th u and low u grew at that time that event deformation and possibly a minor rise in temperature produced widespread perturbations of other isotopic systems throughout the napier complex

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

geochronology at the namew lake ni cu orebody flin flon area manitoba canada thermal history of a metamorphic terrane intermediate composition orthogneisses of the southward extension of the flin flon greenstone belt surround the ultramafic host rock of the namew lake ni cu deposit in northern manitoba the gneiss

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

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

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

geodetically inferred coseismic and postseismic slip due to the m 5 4 31 october 2007 alum rock earthquake on 31 october 2007 the m 5 4 alum rock earthquake occurred near the junction between the hayward and calaveras faults in the san francisco bay area producing coseismic and postseismic displacements recorded by 10 continuously operating global positioning system gps instruments the cumulative postseismic displacements over the four months following the earthquake are linearly related to the cumulative number of aftershocks and are comparable in magnitude to the coseismic displacements the postseismic signal suggests that in addition to afterslip at seismogenic depths localized right lateral reverse slip occurred on dipping shallow fault surfaces southwest of the calaveras the spatial distribution of slip inferred by inverting the gps data is compatible with a model in which moderate calaveras fault earthquakes rupture locked patches surrounded by areas of creep afterslip and microseismicity oppenheimer et al 1990 if this model and existing calaveras fault slip rate estimates are correct a slip deficit remains on the 2007 alum rock rupture patch that may be made up by aseismic slip or slip in larger earthquakes recent studies e g manaker et al 2005 suggest that at depth the hayward and central calaveras faults connect via a simple continuous surface illuminated by the mission seismic trend mst implying that a damaging earthquake rupture could involve both faults graymer et al 2008 if this geometry is correct the combined coseismic and postseismic slip we infer for the 2007 alum rock event predicts static coulomb stress increases of 0 6 bar on the mst surface and on the northern calaveras fault 5 km northwest of the alum rock hypocenter

orogenic gold common or evolving fluid and metal sources through time abstract orogenic gold deposits of all ages from paleoarchean to tertiary show consistency in chemical composition they are the products of aqueous carbonic fluids with typically 5 20 mol co 2 although unmixing during extreme pressure fluctuation can lead to entrapment of much more co 2 rich fluid inclusions in some cases ore fluids are typically characterized by significant concentrations of ch 4 and or n 2 common estimates of 0 01 0 36 mol h 2 s a near neutral ph of 5 5 and salinities of 3 7 wt nacl equiv with na k ca mg this fluid composition consistency favors an ore fluid produced from a single source area and rules out mixing of fluids from multiple sources as significant in orogenic gold formation nevertheless there are broad ranges in more robust fluid inclusion trapping temperatures and pressures between deposits that support a model where this specific fluid may deposit ore over a broad window of upper to middle crustal depths much of the reported isotopic and noble gas data is inconsistent between deposits leading to the common equivocal interpretations from studies that have attempted to define fluid and metal source areas for various orogenic gold provinces fluid stable isotope values are commonly characterized by the following ranges 1 18 o for precambrian ores of 6 to 11 and for phanerozoic ores of 7 to 13 2 d and 34 s values that are extremely variable 3 13 c values that range from 11 to 2 and 4 15 n of 10 to 24 for the neoarchean 6 5 to 12 for the paleoproterozoic and 1 5 to 10 for the phanerozoic secular variations in large scale earth processes appear to best explain some of the broad ranges in the o s and n data fluid rock interaction particularly in ore trap areas may cause important local shifts in the o s and c ratios the extreme variations in d mainly reflect measurements of hydrogen isotopes by bulk extraction of waters from numerous fluid inclusion generations many which are not related to ore formation radiogenic isotopes such as those of pb sr nd sm and os measured on hydrothermal minerals are even more difficult to interpret for defining metal source particularly as the low salinity ore fluids transport limited amounts of these elements and significant amounts of these may be locally added to the minerals during alteration reactions at the sites of gold deposition noble gas and halogen data are equally equivocal fluid exsolution from granitoids emplaced into the upper and middle crust metamorphism of the crust or fluids entering trans crustal fault zones from below the crust all remain as permissive scenarios associated with orogenic gold formation as the abundant geochemical data are equivocal however geological and geochronological data weigh heavily against a magmatic hydrothermal model in the upper to middle crust there is no universal temporal association between orogenic gold and magmatism and where there is an overlap in age there is no specific type of magmatism consistently associated with gold formation nor element zonation around any specific pluton a crustal metamorphic model for fluid and metal sources is very consistent with geological geochronological and geochemical data although metamorphism on a regional scale that releases these components into major fault zones can be associated with many processes along active continental margins these can include crustal thickening and radiogenic heating slab rollback and heating during crustal extension or subduction of a spreading ridge heating the base of an accretionary prism in rare examples where phanerozoic orogenic gold deposits are hosted in precambrian high grade metamorphic terranes fluids and metals must however enter a transcrustal fault system from a sub crustal source this could either be a devolatilized subducted relatively flat perhaps stalled slab and its overlying sediment or the corner of the fertilized mantle wedge that releases a fluid during a thermal event

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

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

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