late precambrian u pb ages for the brookville gneiss southern new brunswick tonalitic orthogneiss from the brookville gneiss in southern new brunswick has an igneous protolith age of 605 pm 3 ma based on u pb dating of zircon metamorphic titanite from the same sample gives a minimum age of 564 pm 6 ma for upper amphibolite facies metamorphism of the unit based on u pb analyses of single detrital zircons a maximum sedimentary protolith age of about 641 ma is suggested for associated paragneiss these ages indicate that the igneous protolith of the orthogneiss was at most 35 ma younger than the sedimentary rocks it intruded and that the brookville gneiss is younger than the green head group to which it was previously considered basement both orthogneiss and paragneiss in the brookville gneiss contain proterozoic and archean detrital zircon grains suggesting an old heterogeneous continental source we conclude that the brookville gneiss does not represent the basement to the avalon terrane

air sea interactions during an arctic storm 1 the impacts of increased open water in the beaufort sea were investigated for a summer arctic storm in 2008 using a coupled atmosphere ice ocean model the storm originated in northern siberia and slowly moved into the beaufort sea along the ice edge in late july the maximum wind associated with the storm occurred when it was located over the open water near the beaufort sea coast after it had moved over the chukchi and beaufort seas the coupled model system is shown to simulate the storm track intensity maximum wind speed and the ice cover well the model simulations suggest that the lack of ice cover in the beaufort sea during the 2008 storm results in increased local surface wind and surface air temperature compared to enhanced ice cover extents such as occurred in past decades in addition due to this increase of open water the surface latent and sensible heat fluxes into the atmosphere are significantly increased however there were no significant impacts on the storm track the expanded open water and the loss of the sea ice results in increases in the surface air temperature by as much as 8 c although the atmospheric warming mostly occurs in the boundary layer there is increased atmospheric boundary turbulence and downward kinetic energy transport that reach to mid levels of the troposphere and beyond these changes result in enhanced surface winds by as much as 4 m s during the 2008 storm compared to higher ice concentration conditions typical of past decades the dominant sea surface temperature response to the storm occurs over open water storm generated mixing in the upper ocean results in sea surface cooling of up to 2 c along the southern beaufort sea coastal waters the ekman divergence associated with the storm caused a decrease in the fresh water content in the central beaufort sea by about 11 cm

crustal structure and surface zonation of the canadian appalachians implications of deep seismic reflection data in 1986 1181 km of marine seismic reflection data was collected to 18 20 s of two way traveltime in the gulf of st lawrence area the seismic profiles sample all major surface tectono stratigraphic zones of the canadian appalachians they complement the 1984 deep reflection survey northeast of newfoundland together the seismic profiles reveal the regional three dimensional geometry of the orogen three lower crustal blocks are distinguished on the seismic data they are referred to as the grenville central and avalon blocks from west to east the grenville block is wedge shaped in section and its subsurface edge follows the form of the appalachian structural front the grenville block abuts the central block at mid crustal to mantle depths the avalon block meets the central block at a steep junction that penetrates the entire crust consistent differences in the seismic character of the moho help identify boundaries of the deep crustal blocks the moho signature varies from uniform over extended di

directional properties of van s ses and ulf mt signals at ioannina greece abstract in order to examine the validity of the earthquake prediction technique developed in greece by van varotsos alexopoulos and nomicos and elucidate the underlying physical processes we performed a magnetotelluric mt recording of the ulf band 3 200 s in the vicinity of van s sensitive station ioannina ioa by comparing mt electric field of ionospheric or magnetospheric origin electric field of lightning origin and van s seismic electric signals ses the following facts were revealed 1 the mt electric field always varies in the ene wsw direction indicating existence of significant electrical conductivity contrast near the site 2 the lightning electric field orientation is somewhat more scattered but still holds the same preferred direction as that of the mt electric field the scatter is larger for larger lightning field probably due to closer location of lightning stroke to the station and or due to no linear saturation of the recording signals 3 the ses electric field orientation is even more scattered than that of the lightning origin these observations suggest that the sources of the ses are in the neighborhood of the station it is still unclear how the ses associated with distant earthquakes are emitted from the sources near the ioa station

the summer cyclone maximum over the central arctic ocean abstract a fascinating feature of the northern high latitude circulation is a prominent summer maximum in cyclone activity over the arctic ocean centered near the north pole in the long term mean this pattern is associated with the influx of lows generated over the eurasian continent and cyclogenesis over the arctic ocean itself its seasonal onset is linked to the following an eastward shift in the urals trough migration of the 500 hpa vortex core to near the pole and development of a separate region of high latitude baroclinicity the latter two features are consistent with differential atmospheric heating between the arctic ocean and snow free land variability in the strength of the cyclone pattern can be broadly linked to the phase of the summer northern annular mode when the cyclone pattern is well developed the 500 hpa vortex is especially strong and symmetric about the pole with negative sea level pressure slp anomalies over the pole and positive anomalies over middle latitudes net prec

tectonic implications of 40ar 39ar hornblende ages from late proterozoic cambrian plutons in the avalon composite terrane nova scotia canada the avalon composite terrane in nova scotia mainly represents a late proterozoic rifted cratonic magmatic arc complex the geo chemistry of the volcanic rocks indicates that most of southeastern cape breton island is underlain by a volcanic arc whereas the antigonish and cobequid highlands expose intra arc rift sequences in cape breton island late proterozoic rocks are both volcanic and plutonic south of the macintosh brook fault transecting the boisdale hills whereas they are mainly plutonic rocks north of the fault these igneous units are unconformably overlain by subaerial to shallow marine cambrian ordovician sedimentary sequences containing an atlantic fauna that are interbedded with early to middle cambrian within plate continental rift volcanic rocks 4o ar 39 ar plateau ages recorded by hornblende from plutons spatially associated with these volcanic rocks correspond to three groupings 1 ca 600 635 ma in cape breton island south of the macintosh brook fault 2 ca 525 555 ma in cape breton island north of the macintosh brook fault boisdale hills north mountain and creignish hills 3 ca 600 625 ma in the antigonish and cobequid highlands based upon the low metamorphic grade of the late proterozoic and early paleozoic rocks and the low pressures recorded in contact aureoles and plutons it is inferred that these plutons were emplaced at relatively shallow crustal levels and therefore the 40 ar 39 ar plateau ages probably closely date their emplacement interpretation of the age data suggests that plutonism in nova scotia associated with the rifted magmatic arc lasted from ca 635 600 ma igneous activity continued between ca 555 525 ma and may have been related to the cambrian within plate rift volcanism

an ice ocean coupled model an ice model an ocean model and a method of coupling the models are described the ice model is a synthesis with variations and extensions of previous modeling ideas ice thickness concentration velocity and internal energy are prognostic variables the ice thermodynamics are represented by temperatures at the snow surface ice surface the interior and the bottom surface melting and freezing rates are calculated at the ice atmosphere ice ocean and atmosphere ocean interfaces a prescribed portion of summer meltwater can be stored on the surface and refrozen in the fall the ocean model includes a second moment turbulence closure submodel and enables one to solve for oceanic heat flux the interfacial stress and subsurface properties in this paper the model is applied to one dimensional simulations but the equations are cited in a form for implementation by two and three dimensional models in a companion paper kantha and mellor this issue the model is used for two dimensional vertical plane simulations in the bering sea several one dimensional sensitivity studies are performed in the case where the ice model is decoupled from the ocean here the oceanic heat flux and sea surface temperature are prescribed constants the studies reveal the role and sensitivity of surface trapped meltwater ice concentration and ice divergence with the coupled ice ocean model the seasonally varying oceanic heat flux and mixed layer properties are determined by the model some comparisons with observations in the central arctic ocean are possible the role of the molecular sublayer immediately adjacent to the ice is examined frazi ice production is related to the large disparity in the molecular diffusivities for temperature and salinity the mixed layer model contains empirical constants which are known from turbulence data the molecular sublayer parameterization requires one empirical parameter b which is uncertain but from this study is assuredly greater than zero the value implicit in previous models the ice model requires the empirical parameters ci f and ci u to quantitatively account for freezing or melting processes in open leads their values are also uncertain but we present reasoning and sensitivity studies to suggest specific values finally an empirical parameter g is introduced it is the ratio of the value of the ice thickness used to represent average ice volume in the dynamic and thermodynamic equations to the value of the thickness needed in the heat conduction equation estimates of g are made from observed thickness distribution functions sensitivity studies show it to be an important parameter

freshwater content variability in the arctic ocean 1 arctic ocean model simulations have revealed that the arctic ocean has a basin wide oscillation with cyclonic and anticyclonic circulation anomalies arctic ocean oscillation aoo that has a prominent decadal variability proshutinsky and johnson 1997 this study explores how the simulated aoo affects the arctic ocean stratification and its relationship to the sea ice cover variations the simulation uses the princeton ocean model coupled to sea ice hakkinen and mellor 1992 hakkinen 1999 the surface forcing is based on national centers for environmental prediction national center for atmospheric research reanalysis and its climatology of which the latter is used to force the model spin up phase our focus is to investigate the competition between ocean dynamics and ice formation melt on the arctic basin wide freshwater balance we find that changes in the atlantic water inflow can explain almost all of the simulated freshwater anomalies in the main arctic basin the atlantic water inflow anomalies are an essential part of aoo which is the wind driven barotropic response to the arctic oscillation ao the baroclinic response to ao such as ekman pumping in the beaufort gyre and ice melt freeze anomalies in response to ao are less significant considering the whole arctic freshwater balance

storm driven mixing and potential impact on the arctic ocean 1 observations of the ocean atmosphere and ice made by ice ocean environmental buoys indicate that mixing events reaching the depth of the halocline have occurred in various regions in the arctic ocean our analysis suggests that these mixing events were mechanically forced by intense storms moving across the buoy sites in this study we analyzed these mixing events in the context of storm developments that occurred in the beaufort sea and in the general area just north of fram strait two areas with quite different hydrographic structures the beaufort sea is strongly influenced by inflow of pacific water through bering strait while the area north of fram strait is directly affected by the inflow of warm and salty north atlantic water our analyses of the basin wide evolution of the surface pressure and geostrophic wind fields indicate that the characteristics of the storms could be very different the buoy observed mixing occurred only in the spring and winter seasons when the stratification was relatively weak this indicates the importance of stratification although the mixing itself was mechanically driven we also analyze the distribution of storms both the long term climatology and the patterns for each year in the past 2 decades the frequency of storms is also shown to be correlated but not strongly to arctic oscillation indices this study indicates that the formation of new ice that leads to brine rejection is unlikely the mechanism that results in the type of mixing that could overturn the halocline on the other hand synoptic scale storms can force mixing deep enough to the halocline and thermocline layer despite a very stable stratification associated with the arctic halocline the warm subsurface thermocline water is not always insulated from the mixed layer

geochemistry of late proterozoic basaltic rocks from southeastern cape breton island nova scotia late proterozoic volcanic rocks of the fourchu group from the avalon zone in southeastern cape breton island nova scotia are composed predominantly of mafic and felsic types with subordinate inte

electric field polarization around ioannina van station greece inferred from a resistivity mapping abstract in the summer of 1997 we made a bipole dipole mapping survey around ioannina station of van varotsos alexopoulos and nomicos where detection of the pre seismic electric signal ses has been repeatedly reported since we had found the characteristic directional properties of the electric field in the previous study the present study was aimed to examine it by investigating the shallow electric structure around the station the apparent resistivity tensor was derived from two sets of measured voltages at each receiver position from a rough sketch of the resistivity tensor distribution we found that the electric field was enhanced along the direction parallel to the trend of the basin at receivers located in the conductive basin and perpendicular to it at receivers in the resistive mountainside conductance distribution models with thin plates were constructed by using the measured voltages the results showed that the van station is located on the resistive portion near the contact between the conductive and the resistive part furthermore we simulated the apparent resistivity tensor near the van station on the inferred conductance distribution model although the directional property similar to those of magnetotelluric mt and lightning electric field was not reproduced there we found that the electric field polarization is affected by heterogeneous structure not only around receivers but also around the source

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

dating transcurrent terrane accretion an example from the meguma and avalon composite terranes in the northern appalachians the polygenetic minas geofracture separates the meguma and avalon composite terranes of the maritime appalachians dynamically recrystallized muscovite and biotite occur within d3 shear zones which developed during dextral movement along the geofracture these record 40ar 39ar plateau ages between circa 360 and 370 ma comparable plateau ages are recorded by micas within undeformed portions of granitic plutons and their low pressure contact metamorphic aureoles these are similar to u pb ages previously reported for igneous monazite therefore indicating relatively rapid postmagmatic cooling at shallow crustal levels the d3 fabrics were superimposed on earlier s1 structures which formed during initial amalgamation of the meguma and avalon composite terranes whole rock slate phyllite samples collected outside high temperature portions of the plutonic contact aureoles yield 40ar 39ar plateau ages which correspond to groupings of circa 400 395 ma 390 385 ma and 380 375 ma these are interpreted to date diachronous formation of the s1 fabrics and concomitant low grade regional metamorphism in the circa 25 ma between initial amalgamation and granitic plutonism it is inferred that there was a slow rise of isotherms through the crust as a result of overthrust tectonic thickening this led to crustal melting and the production of widespread granitic magmas which were emplaced immediately prior to d3 dextral shearing

the effect of a storm on the 1992 summer sea ice cover of the beaufort chukchi and east siberian seas for the summer beaufort chukchi and east siberian seas a variety of active and passive microwave satellite data are used to determine the response of the ice edge and interior to a storm specifically the study concentrates on a low pressure system that passed over the region between august 14 and 20 1992 with peak geostrophic winds of about 18 m s 1 through the use of the ers 1 imaging radar and the special sensor microwave imager the ice response is examined at two locations at the ice edge for a nearly stationary location in the chukchi sea and in the ice interior along three swaths in the beaufort chukchi and east siberian seas the ice edge observations show that the storm fractures the large floes into small floes some of which are advected into the adjacent warm water the ice interior observations show that the storm caused an increase in the open water amount and a shift in the floe size distribution toward smaller floes in the ice interior application of the cumulative number distribution n d where n is the number of floes per unit area that are no smaller than some floe diameter d shows that for d 1 km n behaves like d where lies in the range 1 8 2 9 our analysis also shows that this slope is not affected by the storm and is slightly larger near the ice edge

influence of sea ice on ocean water vapor isotopes and greenland ice core records a warming climate results in sea ice loss and impacts to the arctic water cycle the water isotope parameter deuterium excess a moisture source proxy can serve as a tracer to help understand hydrological changes due to sea ice loss however unlocking the sea ice change signal of isotopes from ice cores requires understanding how sea ice changes impact deuterium excess which is unknown here we present the first isotope data linking a gradient of sea ice extents to oceanic water vapor deuterium excess values initial loss of sea ice extent leads to lower deuterium excess moisture sources and then values progressively increase with further ice loss our new process based interpretation suggests that past rapid 1 3 years greenland ice core changes in deuterium excess during warming might not be the result of abrupt atmospheric circulation shifts but rather gradual loss of sea ice extent at northern latitude moisture sources

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

what drove the dramatic retreat of arctic sea ice during summer 2007 1 a model study has been conducted of the unprecedented retreat of arctic sea ice in the summer of 2007 it is found that preconditioning anomalous winds and ice albedo feedback are mainly responsible for the retreat arctic sea ice in 2007 was preconditioned to radical changes after years of shrinking and thinning in a warm climate during summer 2007 atmospheric changes strengthened the transpolar drift of sea ice causing more ice to move out of the pacific sector and the central arctic ocean where the reduction in ice thickness due to ice advection is up to 1 5 m more than usual some of the ice exited fram strait and some piled up in part of the canada basin and along the coast of northern greenland leaving behind an unusually large area of thin ice and open water thin ice and open water allow more surface solar heating because of a much reduced surface albedo leading to amplified ice melting the arctic ocean lost additional 10 of its total ice mass in which 70 is due directly to the amplified melting and 30 to the unusual ice advection causing the unprecedented ice retreat arctic sea ice has entered a state of being particularly vulnerable to anomalous atmospheric forcing

dynamics of the mackenzie river plume on the inner beaufort shelf during an open water period in summer abstract the oceanographic conditions of the mackenzie river plume in the arctic ocean were examined during a 12 day period in august 2007 field observations in the river channel and the delta region 2 6 m depth ship based observations on the shelf and satellite observations of sea surface temperatures indicate that movements of plume density fronts cause changes in water temperatures of over 10 c over a few days we used a 1d model to compare the strength of stratification versus surface wind stress and a 3d numerical model to simulate the plume motions under forcing from the river flows local wind and water level variations from tides and wind driven surge the results indicate that the coastal region is stratified with a 2 m thick surface plume even in water depths of 3 4 m resulting in strong vertical variation of horizontal currents moderate easterly winds of 5 10 m s are sufficient to induce offshore transport of the surface plume and onshore transport of the deeper shelf water leading to large fluctuations in temperature and salinity in the coastal region this study examined a period of offshore transport and mean water level set down and indicates the rapid response of the plume to wind over the shallow delta

modeling the seasonal variation of sea ice in the labrador sea with a coupled multicategory ice model and the princeton ocean model we use a multicategory sea ice model coupled to the princeton ocean model which is driven by monthly climatological atmospheric forcing to study the seasonal variation of ice cover in the labrador sea initial ocean conditions are derived from a gridded objectively analyzed temperature salinity data set that provides improved resolution of gradients in the vicinity of the shelf break the model produces a realistic seasonal variation of sea ice there is ice growth over the inner shelf and ice melt over the outer shelf and slope over the inner shelf advection and diffusion decrease the ice mass over the outer shelf advection and diffusion increase the ice mass which maintains the location of the ice edge near the offshore ice edge the melt rate exceed s1mp er month and the heat to melt ice together with the heat lost to the atmosphere exceeds 500 wm 22 the heat lost at the ocean surface is compensated for by advection of heat from an offshore convective region the dominant heat source for the spring retreat of ice in the south is shortwave radiation over the open water fraction marginal ice zones are regions of dynamic interaction be tween atmosphere ice and ocean in the labrador marginal ice zone the ice edge is located near the labrador current and its associated shelf break front wintertime convection in the western labrador sea is thought to form labrador intermedi ate water clarke and gascard 1983 since the ice edge bor ders the convective region it is important to clarify the pro cesses that limit the ice extent and to examine the heat and salt fluxes in the vicinity of the ice edge in this study we investigate the seasonal evolution of sea ice over the labrador shelf with a coupled ice ocean model our objective is to assess the capability of the model in simulating the evolution of the ice cover and to identify model deficien cies we examine the processes that limit the ice extent labrador sea ice has been the subject of a number of studies with numerical models most recently ikeda et al 1996 cou pled a two category ice model hibler 1979 with the geo physical fluid dynamics laboratory gfdl ocean model bryan 1969 cox 1984 there was overall agreement with the seasonal cycle as well as with interannual variations the re sults showed that shoreward advection of relatively warm off shore water is an important source of heat to melt ice how ever the model ice decayed too rapidly partly because the two category ice model underestimates ice concentration there are a number of differences between the present model and the model of ikeda et al 1996 we have imple mented a multicategory ice model and used the sigma coordi nate princeton ocean model blumberg and mellor 1987 mel lor 1996 with its embedded turbulence closure submodel we use a climatology from the national centers for environmen tal prediction ncep national center for atmospheric re

the geochemistry and petrology of the late precambrian georgeville group a volcanic arc rift succession in the avalon terrane of nova scotia

sensitivity of the telluric monitoring array in parkfield california to changes of resistivity parkfield is the site of characteristic earthquakes which repeat every 22 plus minus 5 years so that the next one is due between 1983 and 1993 the authors have installed a telluric monitoring array to detect possible changes of resistivity prior to the next characteristic earthquake however the array detects only changes in the telluric response and an independent estimate of the geoelectrical structure is needed in order to locate the perturbed regions and to determine the magnitude of the change in resistivity they have developed a three dimensional electrical model for parkfield based on 12 shallow 1 500 m schlumberger soundings and 31 deep soundings using their array the model is complex but shows that rock adjacent to and southwest of the san andreas fault is conductive less than 10 ohm m to depths of at least 10 km the authors infer that these low resistivities are due to brecciation from intense shearing along the fault they have also used this geoelectric structure to predict the sensitivity of their telluric array to changes in resistivity along the fault changes in resistivity beneath the array at depths from 1 5 to 6km produce the largest effects at the surface 1 change formore a perturbation of 1 at depth changes of resistivity from depths of 6 12 km yielded lower sensitivities but are still detectable because the top of the seismogenic zone in parkfield is at 5 km the array should be sensitive to changes of resistivity prior to the next earthquake less

tectono stratigraphic terranes in cape breton island nova scotia implications for the configuration of the northern appalachian orogen cape breton island is divided into four terranes on the basis of contrasts in pre carboniferous geology the blair river complex in the north is an exposure of north american grenvillian basement analogous to the humber zone basement in newfoundland ordovician to devonian metavolcanic metasedimentary gneissic and granitic rocks of the aspy terrane are correlative with parts of the gander terrane of newfoundland and new brunswick the bras d9or terrane characterized by low pressure gneisses a carbonate clastic platform sequence and late precambrian early cambrian plutons may be correlative with units previously included in the gander terrane in southern newfoundland and the avalon terrane in southern new brunswick the mira terrane in southeastern cape breton island including late precambrian to early cambrian volcanic and sedimentary sequences and fossiliferous cambrian ordovician units is clearly part of the avalon terrane therefore with the exception of the dunnage terrane which is not represented in cape breton island the terranes of newfoundland continue through cape breton island they are offset to the northwest to the mainland part of the appalachian orogen in new brunswick

comment and reply on tectono stratigraphic terranes in cape breton island nova scotia implications for the configuration of the northern appalachian orogen

late proterozoic tectonic model for the avalon terrane in maritime canada the avalon terrane in maritime canada extends from cape breton island through northern nova scotia antigonish and cobequid highlands to southern new brunswick the terrane contains abundant late proterozoic volcanic rocks 570 680 m y old the geochemistry of the volcanic rocks of southern cape breton island and southern new brunswick indicates that they were erupted in a volcanic arc environment in both regions the mafic rocks display a remarkably similar compositional zonation which resembles the across arc variations observed in modern volcanic arcs the progressive compositional changes that include a transition from island arc tholeiites along the southeastern coasts to calc alkaline rocks inland to the northwest are probably due to a northwest dipping subduction zone with a trench located to the southeast in the antigonish and cobequid highlands continental tholeiites and calc alkaline volcanic rocks are interbedded and overlain by turbidites that have probably been deposited in a back arc or intra arc environment the superimposed positive gravity and magnetic anomalies that may be traced discontinuously from the grand banks through nova scotia collector anomaly and along the northern side of the gulf of maine to near boston probably represent late proterozoic ophiolitic remnants preserved by incomplete suturing along a late proterozoic plate boundary northeast trending segments are inferred to mark subduction zones and the e w portions could correspond to transform faults thus the present geographical distribution of the late proterozoic volcanic rocks is explained by a tectonic model involving a single subduction zone offset by two late proterozoic transform faults located approximately along the minas fault and the scatarie ridge

the upper hadrynian jeffers group cobequid highlands avalon zone of nova scotia a back arc volcanic complex the upper hadrynian jeffers group of the cobequid highlands avalon zone of northern nova scotia consists of volcanic rocks of the gilbert hills formation interfingering deeper water argillite of the humming brook formation and overlying turbidite lithic arkose and siltstone of the cranberry lake formation the jeffers group has a spatially inhomogeneous flat lying cleavage associated with thrust faults of late hadrynian age that were in part reactivated during carboniferous strike slip motion on the cobequid fault the basal rocks of the gilbert hills formation consist of felsic pyroclastics and minor mafic and felsic flows of the lakelands facies locally passing up into sandstone and marble overlain by the humming brook formation thrust over this sequence is the harrington river facies of the gilbert hills formation comprising flows ranging in composition from subalkalic basalt to rhyodacite and pyroclastic rocks two groups of igneous rocks are distinguished geochemically high ti basalts of the lakelands facies and associated hypabyssal intrusions have tholeiitic character enrichment in ba rb and k flat light ree spectra little or no depletion in nb and ta and high feo t and ti they are associated with voluminous felsic rocks the harrington river facies has a calc alkaline differentiation series from basalt to rhyodacite but with more enrichment in feo t p nb and zr than is found in typical calc alkaline rocks these two groups are also represented in hypabyssal rocks the jeffers group rocks are compared geochemically with other predominantly continental back arc basins in the aegean sea and bransfield strait all three basins show the presence of a rock phase derived from partial melting of mantle only slightly modified by subduction processes the lakelands facies tholeiites of the jeffers group they all also contain a more differentiated series showing more subduction related chemical characteristics the harrington river facies of the jeffers group geochemical differences between these rocks and typical calc alkali series are related to the lesser role of hydrous fluids in the back arc basins as a result titanomagnetite and amphibole are not important fractionating phases and nb and ta are not significantly depleted

geochemistry of late proterozoic basaltic rocks from southeastern new brunswick canada late proterozoic volcanic rocks of the coldbrook group 630 600 ma from the avalon zone of the appalachians in southeastern new brunswick canada are predominantly bimodal and occur in three belts fault blocks eastern central and western the basaltic rocks were emplaced in a convergent plate margin setting and range from incompatible element depleted island arc tholeiites in the eastern belt to calc alkalic types of the western belt the distinct compositional zonation of the basaltic rocks resembles the across arc variation observed in recent volcanic arc systems the trends include an increase of the lile and hfse abundances and the zr sio2 th sio2 la yb th nb th hf and zr y ratios from the eastern belt in the southeast through the central belt to the western belt in the northwest the zonation of the coldbrook group is attributed to a northwest dipping subduction zone during late proterozoic time it is suggested that some of the late proterozoic basins in the avalon zone of the northern appalachians reached a stage of oceanization

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

changes in ocean temperature in the barents sea in the twenty first century abstractpossible modifications to ocean temperature in the barents sea induced by climate change are explored the simulations were performed with a coupled ice ocean model ciom driven by the surface fields from the canadian regional climate model crcm simulations ciom can capture the observed water volume inflow through the barents sea opening the ciom simulation and observations suggest an increase in the atlantic water volume inflow and heat transport into the barents sea in recent decades resulting from enhanced storm activity while seasonal variations of sea ice and sea surface temperature in ciom simulations are comparable with observations ciom results underestimate the sea surface temperature but overestimate ice cover in the barents sea consistent with an underestimated heat transport through the barents sea opening under the sres a1b scenario the loss of sea ice significantly increases the surface solar radiation and the ocean surface heat loss through turbulent heat fluxes and longwa

u pb age constraints on the stratigraphy and tectonic history of the avalon terrane new brunswick canada six new u pb ages for avalonian plutonic and volcanic rocks from the eastern caledonia highlands southern new brunswick indicate that magmatic activity occurred between 625 600 ma ago with another probably separate major episode at ca 550 ma this gap in igneous activity is consistent with differences in the metamorphic and deformational character of rocks from the two episodes the 625 600 ma activity was calc alkalic and probably occurred in an andean type magmatic arc it correlates with most volcanism and plutonism in the type avalon terrane of newfoundland the ca 550 ma activity formed bimodal volcanic rocks and high level plutons probably in an extensional setting u pb ages of xenocrystic zircons from avalonian igneous rocks indicate both archean and proterozoic components at depth in avalonian basement an observation consistent with pb isotopic signatures which suggest an old radiogenic crustal source the african craton for the magmatic products

petrology of upper ordovician lower silurian rocks of the antigonish highlands nova scotia upper ordovician to lower silurian rocks in the antigonish highlands consist of interlayered basalts rhyodacites arkoses and conglomerates overlain by a thick sequence of marine clastic rocks and minor rhyolites the stratigraphy documents a marine transgression the volcanic rocks were deposited in a within plate continental extensional environment the basalts display alkalic and tholeiitic affinities and the rhyodacites were formed by anatexis of the crust the origin of the younger rhyolites is not clear they are compositionally distinct from the rhyodacites but may be related to them as late stage differentiates at present it is not possible to evaluate whether the tectonic setting and magmatic affinities are regionally or locally controlled the geological history is very similar to that of lower silurian rocks immediately north of the antigonish highlands at arisaig in the simplest sense this indicates these areas may have been juxtaposed prior to the late ordovician and limits cumulative

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

offshore continuation of meguma terrane southwestern nova scotia eight short drill cores have been examined from the continental shelf southwest of nova scotia four cores recovered granitoid rocks of two types ilmenite bearing granitoid rocks petrographically and geochemically resemble granodiorites of the south mountain batholith and granites of the seal island pluton magnetite bearing granitoid rocks are also peraluminous but have no exact analogues onshore in nova scotia two cores recovered metamorphic rocks in a small area 50 km south of seal island one consits of chlorite muscovite quartz schist geochemically similar to rocks of the halifax formation the second sampled epidote chlorite quartz schist similar to metavolcanic rocks of the white rock formation one further core sampled quartzite and another sampled a metavolcanic rock possibly erratic the regional extent of these lithotypes can be inferred from gravity and aeromagnetic data regional gravity data suggest the presence of a large granite body off southwestern nova scotia in this area magneti

dramatic interannual changes of perennial arctic sea ice linked to abnormal summer storm activity 1 the perennial september arctic sea ice cover exhibits large interannual variability with changes of over a million square kilometers from one year to the next here we explore the role of changes in arctic cyclone activity and related factors in driving these pronounced year to year changes in perennial sea ice cover strong relationships are revealed between the september sea ice changes and the number of cyclones in the preceding late spring and early summer in particular fewer cyclones over the central arctic ocean during the months of may june and july appear to favor a low sea ice area at the end of the melt season years with large losses of sea ice are characterized by abnormal cyclone distributions and tracks they lack the normal maximum in cyclone activity over the central arctic ocean and cyclones that track from eurasia into the central arctic are largely absent fewer storms are associated with above average mean sea level pressure strengthened anticyclonic winds an intensification of the transpolar drift stream and reduced cloud cover all of which favor ice melt it is also shown that a strengthening of the central arctic cyclone maximum helps preserve the ice cover although the association is weaker than that between low cyclone activity and reduced sea ice the results suggest that changes in cyclone occurrence during late spring and early summer have preconditioning effects on the sea ice cover and exert a strong influence on the amount of sea ice that survives the melt season

arctic sea ice retreat in 2007 follows thinning trend the minimum of arctic sea ice extent in the summer of 2007 was unprecedented in the historical record a coupled ice ocean model is used to determine the state of the ice and ocean over the past 29 yr to investigate the causes of this ice extent minimum within a historical perspective it is found that even though the 2007 ice extent was strongly anomalous the loss in total ice mass was not rather the 2007 ice mass loss is largely consistent with a steady decrease in ice thickness that began in 1987 since then the simulated mean september ice thickness within the arctic ocean has declined from 3 7 to 2 6 m at a rate of 0 57 m decade 1 both the area coverage of thin ice at the beginning of the melt season and the total volume of ice lost in the summer have been steadily increasing the combined impact of these two trends caused a large reduction in the september mean ice concentration in the arctic ocean this created conditions during the summer of 2007 that allowed persistent winds to push the remaining ice from the pacific side to the atlantic side of the basin and more than usual into the greenland sea this exposed large areas of open water resulting in the record ice extent anomaly

grenvillian basement in the northern cape breton highlands nova scotia the northernmost cape breton highlands are underlain by the blair river complex a distinctive assemblage of basement rocks including felsic and mafic gneisses foliated gabbroic to granitic rocks

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

the arctic frontal zone as seen in the ncep ncar reanalysis abstract calculations of a thermal front parameter using ncep ncar reanalysis data over the period 1979 98 reveal a relative maximum in frontal frequencies during summer along northern eurasia from about 60 to 70 n best expressed over the eastern half of the continent a similar relative maximum is found over alaska which is present year round although best expressed in summer these high latitude features can be clearly distinguished from the polar frontal zone in the midlatitudes of the pacific basin and collectively resemble the summertime arctic frontal zone discussed in several early studies while some separation between high and midlatitude frontal activity is observed in all seasons the summer season is distinguished by the development of an attendant mean baroclinic zone aligned roughly along the arctic ocean coastline and associated wind maxima in the upper troposphere the regions of maximum summer frontal frequency correspond to preferred areas of cyclogenesis and to where the summertime

identification and analysis of electromagnetic signals in greece the case of the kozani earthquake van prediction an electric station was installed in july 1993 4 5 km away from the van station of ioannina and recorded in the following two years a number of anomalous signals including those of april 18 and 19 1995 interpreted by the van group as seismic electric signals precursors to the may 13 kozani earthquake west macedonia a magnetic station was also installed and clearly recorded the magnetic components of the same events the amplitude shape characteristic pattern and duration magnetic characteristics and polarisation of the anomalous signals suggest that they are generated by artificial industrial sources

the response of the sea ice edge to atmospheric and oceanic jet formation abstractthe sea ice edge presents a region of many feedback processes between the atmosphere ocean and sea ice maslowski et al here the authors focus on the impact of on ice atmospheric and oceanic flows at the sea ice edge mesoscale jet formation due to the coriolis effect is well understood over sharp changes in surface roughness such as coastlines hunt et al this sharp change in surface roughness is experienced by the atmosphere and ocean encountering a compacted sea ice edge this paper presents a study of a dynamic sea ice edge responding to prescribed atmospheric and oceanic jet formation an idealized analytical model of sea ice drift is developed and compared to a sea ice climate model the los alamos sea ice model cice run on an idealized domain the response of the cice model to jet formation is tested at various resolutions it is found that the formation of atmospheric jets at the sea ice edge increases the wind speed parallel to the sea ice edge and results in the formation of a

u s geological survey deep seismic reflection profile across the gulf of maine deep seismic reflection and magnetic data suggest that the gulf of maine is underlain by four crustal blocks of differing reflection and magnetic character two of these blocks the gulf of maine fault zone and adjacent central plutonic zone can be correlated with avalonian rocks in southern new england and new brunswick the boundary between them the fundy fault projects onshore near the ponkapoag fault in southeastern massachusetts in a region where no major crustal boundary has yet been identified a third block called the southern plutonic zone is interpreted as avalonian although the reflection and magnetic data are ambiguous the fourth block along the rifted continental margin is correlated with meguma rocks of nova scotia the late paleozoic variscan front crosses the gulf of maine within the gulf of maine fault zone and indicates significant compressional movement rather than strike slip the moho surface throughout the region is essentially flat and may have been produced by mesozoic crustal extension associated modification of the lower crust was minimal in the northern gulf and may have been moderate in the central and southern gulf the franklin rift basin formed by reactivation of the inferred avalon meguma boundary beneath georges bank as a low angle detachment

northeastern extension and crustal expression of terranes from cape breton island nova scotia based on geophysical data the narrowest section of the appalachian orogen in atlantic canada from grenville age basement in the west to the avalon terrane in the east is preserved in cape breton island where components of four terranes display distinctive stratigraphic igneous metamorphic aeromagnetic and gravity characteristics the blair river complex of northwestern cape breton island is a fragment of grenvillian rocks that is similar to units in western newfoundland the aspy terrane is characterized by mid paleozoic granitic rocks and high pressure paragneisses and appears to continue across the cabot strait as the gander terrane of the hermitage flexure in newfoundland the bras d or terrane is composed of hadrynian to early cambrian low pressure metasedimentary units and dioritic to granitic plutonic rocks as indicated by aeromagnetic anomalies this terrane continues across the laurentian channel to the south coast of newfoundland where it may be terminated by the hermitage fault the avalon terrane of southeaster