palaeomagnetic study of llandovery lower silurian red beds in north west england high unblocking temperature magnetization components carried by haematite have been isolated from 12 sites of llandovery lower silurian red mudstones from nw england the principal deformation phase in this area is acadian mid devonian however some faults with related folds were also active during the later variscan orogeny the site mean magnetization directions pass a regional fold test at the 95 per cent confidence level implying that the magnetization components pre date acadian folding the overall mean direction declination 43 4d inclination 24 1d 95 12 4d gives a pole position at 13 6ds 313 9de and a palaeolatitude of 12ds the low palaeolatitude implies closure of the iapetus ocean between eastern avalonia and laurentia by late llandovery time and is consistent with a recently published palaeolatitude 13ds for the wenlock mid silurian of southern britain comparison of these values with the published palaeolatitude from nw england of 43ds for caradoc late ordovician time implies very rapid at least 15 cm yr 1 northward drift of eastern avalonia during late ordovician early silurian time the new pole position from the llandovery red beds lies close to late silurian and early devonian poles from scotland and wales but is significantly different from a group of mid silurian poles comprising data from scottish intrusions and from swedish sediments this discrepancy may be due to late silurian early devonian pre acadian remagnetization of our sampling sites or local clockwise rotation of the sampling sites during acadian and or variscan deformation however the positive fold test presence of reversals and local deformation history tend to mitigate against these possibilities the more likely interpretation is that although baltica scotland were one continental block from the mid silurian scandian orogeny eastern avalonia did not become part of this block until latest silurian

joint sun glitter and radar imagery of surface slicks a method is proposed to retrieve and interpret fine spatial variations of the sea surface roughness in sun glitter imagery observed sun glitter brightness anomalies are converted using a transfer function determined from the smoothed shape of sun glitter brightness the method is applied to modis and meris sun glitter imagery of natural oil seeps and the catastrophic deepwater horizon oil spill in the gulf of mexico the short scale roughness variations in the presence of mineral oils slicks are consistently extracted and compared to variations associated with the biogenic slicks in doing so the wind speed dependency on the roughness anomalies is also considered a comparison to normalized radar cross section nrcs anomalies taken from the corresponding high resolution asar images is performed and similarities as well as differences are investigated the results document significant benefit from the synergetic use of sun glitter and radar imagery for detection and monitoring of surface slicks

evolution of ocean slicks under a rising wind 1 airborne synthetic aperture radar and high resolution infrared imagery are used to examine the evolution of natural ocean slicks during a period of freshening wind initially the slicks are of the order of 50 m in width and have radar and thermal contrasts of the order of 10 db and several 0 1 c while there can be over time a transient reorganization of surface film material by internal waves the slicks are observed to disperse and are no longer detectible after 5 h the dispersion occurs through the action of langmuir circulation which results in along wind streaks or windrows as well as other effects prominent streaks occur preferentially along a slick s upwind side the downwind side resembling more of a leading edge at least early on over time the leading edge develops a corrugated shape and gaps begin to develop within the slicks the formation of gaps is compared with a conceptual model by dysthe 2006 for the tearing of a surface film in the region of positive surface straining eventually the slicks break into elongated patches that co exist with windrows which is consistent with the effects of advective dispersion

the lower middle ordovician palaeofield of scandinavia southern sweden revisited abstract we present a palaeomagnetic pole for the arenig llanvirn swedish orthoceras limestones based on a new analysis of some earlier reported palaeomagnetic data this new pole 18 n and 046 e differs from the original estimate of 30 n and 46 e the revised pole probably represents the most reliable ordovician pole from baltica although some uncertainties remain concerning the relative importance of diagenetic depositional controls on remanence acquisition based on the new pole from the swedish orthoceras limestone and recent palaeomagnetic results from the northern scandinavian caledonides it is now evident that baltica lay within southerly latitudes of between 30 and 60 s in cambro ordovician times subsequent anticlockwise rotation relative to eastern avalonia southern britain may indicate dextral shear across the tornquist suture prior to mid late ordovician amalgamation of eastern avalonia and baltica

paleomagnetism of middle miocene volcanic rocks in the mojave sonora desert region of western arizona and southeastern california paleomagnetic directions have been obtained from 190 early to middle miocene 12 20 ma mafic volcanic flows in 16 mountain ranges in the mojave sonora desert region of western arizona and southeastern california these flows generally postdate early miocene tectonic deformation accommodated by low angle normal faults but predate high angle normal faulting in the region after detailed demagnetization experiments 179 flows yielded characteristic directions interpreted as original thermal remanent magnetizations trm because of the episodic nature of basaltic volcanism in this region the 179 flows yielded only 65 time distinct virtual geomagnetic poles vgps the angular dispersion of the 65 vgps is consistent with the angular dispersion expected for a data set that has adequately averaged geomagnetic secular variation the paleomagnetic pole calculated from the 65 cooling unit vgps is located at 85 5 n 108 9 within a 4 4 circle of 95 confidence this pole is statistically indistinguishable at 95 confidence from reference poles calculated from rocks of similar age in stable north america and from a paleomagnetic pole calculated from rocks of similar age in baja california the coincidence of paleomagnetic poles from the mojave sonora desert region with reference poles from the stable continental interior indicates that 1 significant vertical axis net tectonic rotations have not accompanied post middle miocene high angle normal faulting in this region 2 there has been no detectable post middle miocene latitudinal transport of the region and 3 long term nondipole components of the middle miocene geomagnetic field probably were no larger than those of the recent 0 5 ma geomagnetic field in contrast paleomagnetic data indicate vertical axis rotations of similar age rocks in the transverse ranges the eastern transverse ranges and the mojave block we speculate that a major structural discontinuity in the vicinity of the southeastward projection of the death valley fault zone separates western areas affected by vertical axis rotations from eastern areas that have not experienced such rotations

further paleomagnetic results from the builth wells ordovician inlier wales a characteristic magnetization has been isolated from 18 sites in middle ordovician igneous and sedimentary rocks from the builth inlier wales two conglomerate tests demonstrate that the characteristic magnetization in two of the volcanic units was acquired early perhaps during initial emplacement six sites from the northern and central parts of the inlier give a mean direction of d 153 8 i 69 8 k 45 8 95 10 that passes a regional fold test however 12 sites from the southern end of the inlier in and near the llanelwedd quarry yield a significantly different direction after correction for local tilt d 176 4 i 44 5 k 42 4 95 6 7 the llanelwedd quarry data are anomalous with respect to both results from the northern parts of the inlier and those obtained from approximately coeval rocks from the shelve inlier we have searched for an explanation for the discrepancy between the magnetization directions of the two areas and have now ruled out some possibilities including superimposed magnetization components at one of the two areas the llanelwedd quarry lies within a wedge of dominantly andesitic volcanic rocks that appear only locally and which are overlain by two unconformities that are also not present elsewhere in the inlier one possible explanation for the anomalous nature of the llanelwedd quarry magnetization is that the strata were not horizontal at the time of magnetization either due to early volcano tectonic tilting or primary dips on the flanks of a volcano another possibility is that the llanelwedd quarry rocks were extruded rapidly enough that the geocentric coaxial dipole field hypothesis cannot be applied results from cenozoic volcanic rocks from the western united states suggest that even highly anomalous fields can be preserved virtually unchanged over a number of separate flow events we currently regard this to be the most viable explanation for the anomalous nature of the llanelwedd quarry magnetization we conclude that the data from the 6 northern sites represent the best estimate of the middle ordovician axial dipole field for the inlier

sunglint images of current gradients at high resolution critical angle and directional observing strategy abstract high resolution satellite images of the ocean surface in and around the sunglint often provide unique observations of sub mesoscale upper ocean surface processes local anomalies of wind waves currents or surfactants appear on the images as local anomalies of brightness a quantitative interpretation of those brightness anomalies must relate them to slope properties of the wave field which are to the lowest order described by the mean square slope mss the prevailing paradigm for such interpretation is that of the critical zenith angle it states that for sub critical zenith view angle brightness and mss anomalies have opposite signs and this defines the so called inversion region this prevailing paradigm implicitly builds on the assumption that the mss decomposition between upwind and crosswind components is conserved the mss anomalies are then isotropic and can be reduced to a scalar i e one dimensional quantity in such a case one single sunglint image would be sufficient to retrieve the mss anomaly this isotropic case likely applies for surface wave changes induced by varying wind speed or by surfactants yet satellite and airborne observations at multiple view angles recently revealed anisotropic mss anomalies e g with mss increase in the upwind direction and decrease in the crosswind direction this anisotropic behavior likely characterizes wave modulations by anisotropic surface current gradients this paper details the expected properties of such anisotropic mss modulations it is shown that 1 the classical concept of critical angle does not systematically hold neither for frontal current shear nor for internal wave divergence 2 at least two sunglint images at different zenith and azimuth angles are needed to retrieve the mss anomalies and a single observation is not sufficient 3 a satellite with radiometers looking at multiple zenith angles is capable of providing a geometry favorable to retrieve mss anomalies an illustration is discussed with internal waves observed by the multi angle imaging spectroradiometer misr where the upwind and crosswind components of the retrieved mss anomalies are anisotropic those results provide guidelines to interpret available observations and to help refine strategy for future satellite missions

direct measurements of ocean surface velocity from space interpretation and validation the median doppler shift of radar echoes is analyzed in measurements by envisat s advanced synthetic aperture radar asar over the ocean this doppler centroid differs from a predicted signal based on the predicted motion of the satellite and earth this anomaly converted to a surface doppler velocity u d appears to be of geophysical origin two wide swath images over the gulf stream around cape hatteras suggest that u d contains high resolution information on surface currents while on a global scale u d is found to vary with the wind speed in the range direction a simple quantitative forward model is proposed based on a practical two scale decomposition of the surface geometry and kinematics the model represents the effect of the wind through the wave spectrum and gives u d u 10 u c with u 10 and u c as the 10 m wind speed and quasi eulerian current in the line of sight of the radar projected on the sea surface respectively and as a coefficient function of the wind speed wave development and radar geometry it is found that for an incidence angle of 23 0 3 for moderate winds and fully developed seas this model is validated with a global data set of asar wave mode observations with colocated model winds acquired over the global ocean during the years 2003 and 2004 the doppler signal therefore provides the signed parameter u d that can be used to reduce the wind direction ambiguity in the inversion of high resolution wind fields from sar imagery a qualitative validation of current effects is shown for the english channel where tidal currents dominate thus it should be possible to combine this previously ignored geophysical doppler signal with traditional information on sea surface roughness in order to provide very high resolution wind and current fields

brunhes chron excursion polarity episode recorded during the late pleistocene albuquerque volcanoes new mexico usa summary all basaltic lava flows of the albuquerque volcanoes lat 35 2 n long 253 2 e albuquerque belen basin new mexico record a short excursion polarity episode k ar isotopic age determinations weighted average 155 f 47 ka and evaluation of soil profiles on flow surfaces suggest the late pleistocene circa between 250 and 80 ka as the time of extrusion results from 63 sites in a minimum of eight flows yield a mean direction of d 101 lo z 36 lo ag5 1 2 a 0 7 a 1 2 k 2219 n 8 flows and a corresponding virtual geomagnetic pole position vgp of 354 1 e 20 2 s dp 0 8 dm 1 4 a 0 5 1 4 and vgp angular standard deviation asd 1 8 the unusual magnetization in flows of the albuquerque volcanoes is carried by fine grained single domain sd and or pseudo single domain psd low ti magnetite and is apparently not a function of complex sub solidus alteration of magnetic phases underlying baked soils contain a relatively low coercivity magnetization with directions comprising two groups one is roughly antipodal to the lava remanence the other intermediate between the lava remanence and present field direction because all flows yield statistically indistinguishable directions a field directional path clearly cannot be defined at the precision level of our age determinations the albuquerque feature may correlate with other short polarity episodes or excursions of late pleistocene age e g blake or jamaica though characteristically limited in directional morphology well dated polarity episodes i e sub chrons and excursions recorded in volcanic rocks may provide information on the frequency of significant dynamo instabilities

theory of radar imaging of internal waves radar images taken over ocean areas in particular those obtained by the synthetic aperture radar sar onboard the american seasat satellite in 19781 2 sometimes show features that seem to be surface manifestations of oceanic internal waves3 11 here i present a theory explaining the large radar signatures of internal waves in which the imaging is attributed to variations in the short scale surface roughness induced by current variations associated with internal waves

seasonal thermal fronts on the northern south china sea shelf satellite measurements and three repeated field surveys seasonal thermal fronts associated with wind driven coastal downwelling upwelling in the northern south china sea are investigated using satellite measurements and three repeated fine resolution mapping surveys in winter spring and summer the results show that vigorous thermal fronts develop over the broad shelf with variable widths and intensities in different seasons which tend to be approximately aligned with the 20 100 m isobaths driven by the prevailing winter summer monsoon the band shaped fronts were observed with a magnitude exceeding 0 1 degrees c km in the subsurface and accompanied by energetic coastal downwelling upwelling due to shoreward offshore ekman transport the downward upward tilting of seasonal thermoclines across the shelf exceeds 20 m significantly contributing to the development of thermal fronts over the shelf in addition the diagnostic analysis of potential vorticity pv suggests that the summer frontal activities induced by the coastal upwelling are more stable to convection and symmetric instabilities in comparison to the winter fronts associated with downwelling favorable monsoon forcing this is primarily due to their essential differences in the upper ocean stratification and horizontal buoyancy gradients arising from wind forcing at the same time the coastal currents are substantially regulated by the seasonal winds an expected lag correlation between the velocity from mooring measurements and alongshore wind stress is detected near the frontal region these results indicate that seasonal wind forcing plays an important role in the frontal activities and coastal water transport over the shelf

palaeogeographic significance of mid silurian palaeomagnetic results from southern britain major revision of the apparent polar wander path for eastern avalonia summary wenlock c 430 ma lavas from the east mendips inlier southern briain are characterized by either single component magnetizations type 1 or a more complex system of three magnetization components type 2 during stepwise thermal demagnetization the type of demagnetization behaviour is related to changes in magnetic petrology within the lava pile the lower and intermediate unblocking temperature components of type 2 represent magnetic overprints of tertiary recent and hercynian mid carboniferous origin respectively the primary nature of the high unblocking temperature magnetization component types 1 and 2 dec 095 c inc 24 ag5 8 8 is demonstrated by positive agglomerate tests conversely an overlying upper old red sandstone sequence did not provide primary magnetizations the magnetic signature is governed by syn tectonic hercynian remagnetizations the primary silurian data demonstrate that the east mendips inlier experienced considerable clockwise rotation probably of the order of 80 prior to partial remagnetization during hercynian deformation and folding the silurian palaeopole vgp 13 n 271 e dp dm 5 9 cannot therefore be used for apparent polar wander path construction nevertheless the palaeolatitude estimate 13 f 5s suggests that southern britain eastern avalonia was at comparable mid silurian latitudes to baltica and northern britain 10 20 s both the iapetus ocean and tornquist sea therefore which separated southern britain from laurentia and baltica respectively in ordovician times were closed by wenlock time as ordovician and silurian palaeomagnetic data from baltica and eastern avalonia now record a comparable northwards translation from high southerly to near equatorial latitudes during this time we postulate pre wenlock collision of these blocks to form balonia baltica eastern avalonia a new apparent polar wander path for eastern avalonia constructed on the basis of this palaeogeographic model is presented

paleomagnetism of the pennington mountain terrane a near laurentian back arc basin in the maine appalachians paleomagnetic studies of volcanic terranes in the appalachians provide quantitative data on the ordovician paleogeography of the iapetus ocean new paleomagnetic results from submarine volcanics of the middle to late ordovician winterville formation of maine further constrain the evolution of iapetus ten sites yield a tilt corrected direction of d i 327 21 95 9 3 k 27 9 the corresponding paleomagnetic pole calculated for the average site location 46 8 n 291 3 e is located at 26 n 148 e d p 5 d m 10 a 95 7 7 a silurian conglomerate frenchville formation test is inconclusive due to a strong present day field overprint which obscures any primary remanence the presence of a positive tilt test however supports the conclusion that the characteristic magnetization of the winterville formation is a prefolding primary magnetization an ordovician paleolatitude of 111 5 for the pennington mountain terrane of northern maine is indistinguishable from that of the laurentian margin 15 20 during the middle to late ordovician the paleolatitude of the pennington mountain terrane is also similar to but slightly more equatorial than that of the previously studied bluffer pond formation of the nearby munsungun terrane 18 9 we conclude that the ordovician pennington mountain and munsungun volcanic terranes of maine were formed and acquired their characteristic magnetization near the laurentian margin the paleolatitudes of these terranes are also similar to that obtained from the stacyville volcanics of the more outboard lunksoos terrane 20 8 but they contrast strongly with the ordovician miramichi terrane of northern new brunswick that yielded a paleolatitude of 51 21 16 these results from maine support the presence of one or more backarc basins adjacent to the laurentian margin during the middle to late ordovician

estuarine plume a case study by satellite sar observations and in situ measurements estuary plumes on the western louisiana continental shelf in the gulf of mexico outside of constricted channels of the sabine and calcasieu lakes were observed on two radarsat 1 synthetic aperture radar sar images the in situ data showed a change in salinity of 2 3 psus across the front on the northwest edge of the plume corresponding to locations of vertical salinity variation of 5 5 7 5 psu velocity magnitude outside of the inlet reached more than 2 3 ms mathrm 1 seaward and a brackish lens in the upper 4 5 m of the water column the spread of which contributed to the development of a plume the volume of brackish water within the plume was estimated an order of magnitude larger than the volume output from the calcasieu river within an entire ebb tidal period this implies that the plume was formed during multiple tidal cycles and it sustained during the flood tides because only weak diurnal tides exist both satellite and in situ observations showed an interesting western intensification of the plume an analysis to the momentum vorticity equations suggests that the western intensification is due to the asymmetry of the vorticity divergence relationship under the coriolis force this can also be enhanced by an ambient coastal current that strengthens the convergence at the front estuary plumes are shown as bright and dark features in two sar images results from a radar model simulation and in situ water temperature data showed that the sar observed plume features were dominated by the water temperature differences

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

on radar imaging of current features 2 mesoscale eddy and current front detection 1 the surface signatures of meandering fronts and eddies have been regularly observed and documented in synthetic aperture radar sar images wave current interactions the suppression of short wind waves by natural film and the varying wind field resulting from atmospheric boundary layer changes across an oceanic temperature front all contribute to the radar image manifestation of such mesoscale features the corresponding imaging mechanisms are quantitatively explored using a new radar imaging model kudryavtsev et al 2005 that solves the energy balance equation where wind forcing viscous and wave breaking dissipation wave wave interactions and generation of short waves by breaking waves are taken into account high quality and synoptic in situ observations of the surface conditions should ideally be used in this model however such data are rarely available instead the fields of temperature and ocean current are herein derived from two distinct numerical ocean models sar image expressions of current fronts and eddies are then simulated based on these fields the comparison of simulated images with european remote sensing ers sar and envisat advanced sar asar images is favorable we consequently believe that the new radar imaging model provides promising capabilities for advancing the quantitative interpretation of current features manifested in sar images

surface roughness imaging of currents shows divergence and strain in the wind direction images of sea surface roughness for example obtained by synthetic aperture radars sar or by radiometers viewing areas in and around the sun glitter at times provide clear observations of meso and submesoscale oceanic features interacting with the surface wind waves particular deformation properties of surface currents are responsible for those manifestations ignoring other sources of surface roughness variations the authors limit their discussion to the mean square slope mss variability this study confirms that vortical currents and currents with shear in the wind direction shall not be expressed in surface roughness images only divergent currents or currents with no divergence but strained in the wind direction can exhibit surfaceroughnesssignatures morespecifically nondivergentcurrentsmightbetracedwitha458sensitivityto the wind direction a simple method is proposed in order to interpret high resolution roughness images where roughness variations are proportional to u x 1 a y y a linear combination of the along wind and crosswind current gradients the polarization parameter a depends upon the sensor look direction and the directional properties of the surface waves selected by the sensor the use of multiple look directions or possible acquisitions with different wind directions shall thus help to retrieve surface currents from surface roughness observations

paleomagnetic results from volcanic rocks of the shelve inlier wales evidence for a wide late ordovician iapetus ocean in britain abstract in order to shed light on the early paleozoic paleogeography of iapetus bordering continents samples for paleomagnetic study were collected from middle ordovician llanvirn volcanic rocks of the shelve inlier welsh borderland the folding within the inlier is constrained to late ordovician ashgill time thus offering a fold test with tight age brackets after stepwise thermal demagnetization a pre folding characteristic magnetization component was isolated from 95 specimens the mean of 11 site mean directions for the characteristic magnetization gives d i 116 4 67 9 k 89 4 95 4 9 and the paleomagnetic pole lies at 26 6 n 36 1 e p 6 9 m 8 2 the fold test is positive at the 99 confidence level indicating that the magnetization was acquired during the middle or late ordovician we infer from geological considerations that this magnetization is not a primary thermoremanence but was acquired during late ordovician time as a result of a thermochemical disturbance of that age our results indicate that southern britain was near 51 south latitude during the later ordovician since middle to late ordovician paleolatitudes for gondwana and laurentia are well determined our result can be used to test various scenarios for the closure of iapetus we conclude that 1 the iapetus ocean in britain still had a latitudinal width of some 30 at this time thus rendering a postulated ordovician closure unlikely 2 southern britain avalon and hercynian europe all occupied high latitudes during the later ordovician consistent with a paleoposition near the northern margin of gondwana and 3 the acadian orogeny in britain and north america could have been the result of the collision of gondwana and laurentia during early devonian time

volcanic hazards in the region of the armenian nuclear power plant abstract we address volcanic hazards in the region of the armenian nuclear power plant and discuss the assessment of these hazards conducted in the framework of the international atomic energy agency iaea programs in 1994 1995 an important problem of volcanic hazard assessment is posed by assumptions that the apparent absence of recent volcanic activity in armenia means that future eruptions in the vicinity of the site are impossible we present new historical archaeological and field data as well as records of the volcanic activity based on radiocarbon fission track k ar and plateau age determinations this new evidence attests to volcanism in armenia and adjacent areas during holocene and historical time volcanic activity is demonstrated for tskhouk karckar porak vaiyots sar smbatassar gegham ridge and ararat volcanoes volcanic eruptions occurred on ararat at distances of 27 and 52 km from the plant site in 2500 2400 bc and in 1840 ad respectively new information permits a re assessment of the volcanic hazards at a level higher than in the 1994 1995 studies

measurements of sea surface currents in the baltic sea region using spaceborne along track insar the main challenging problems in ocean current retrieval from along track interferometric ati synthetic aperture radar sar are phase calibration and wave bias removal in this paper a method based on differential insar dinsar technique for correcting the phase offset and its variation is proposed the wave bias removal is assessed using two different doppler models and two different wind sources in addition to the wind provided by an atmospheric model the wind speed used for wave correction in this work is extracted from the calibrated sar backscatter this demonstrates that current retrieval from ati sar can be completed independently of atmospheric models the retrieved currents from four tandem x tdx acquisitions over the oresund channel in the baltic sea are compared to a regional ocean circulation model it is shown that by applying the proposed phase correction and wave bias removal a good agreement in spatial variation and current direction is achieved the residual bias between the ocean model and the current retrievals varies between 0 013 and 0 3 m s depending on the doppler model and wind source used for wave correction this paper shows that using sar as a source of wind speed reduces the bias and root mean squared error rmse of the retrieved currents by 20 and 15 respectively finally the sensitivity of the sea current retrieval to doppler model and wind errors are discussed

kinematics of strike slip faulting builth inlier mid wales abstract strike slip faulting in the builth ordovician inlier is demonstrated by large scale maps of the llanelwedd quarries near builth wells and by fault plane and slickenline data in the main quarry steep nnw striking strike slip faults dominate the structure together with significant strike slip displacement on the w dipping bedding surfaces and bedding parallel faults a zone of steep n striking extensional dip slip faults links two of the strike slip strands and there is a weaker e striking set of strike slip faults when the four fault sets are rotated so that the regional bedding is horizontal three become vertical and one horizontal probably their attitude during active life in late ordovician to early silurian time they formed a linked fault system capable of accommodating three dimensional bulk strain the fault flats have the same kinematic role in a strike slip system as lateral ramps or transfer faults in dip slip systems in the nearby gelli cadwgan quarry strike slip faults are again dominant but strike e or ese this heterogeneity of fault pattern in the southern builth inlier resolves into more homogeneous domains with areas of 0 1 to 0 5 km 2 separated by e to ne striking dextral strike slip faults domainal structure an important general feature of strike slip tectonics may be present on a variety of scales

early devonian pre acadian magnetization directions in lower old red sandstone of south wales uk summary two components of magnetization have been resolved from the lower old red sandstone of south wales all 39 sampled sites lie north of the variscan front and all but three are largely unaffected by variscan folding thirteen sites yield a high unblocking temperature magnetization component which pre dates acadian mid devonian folding the site mean direction for this component dec 232 2 inc 31 9 95 8 5 yields a pole position lat 7 3 s long 306 7 e which can be assigned an early devonian age a lower unblocking temperature component is present at 38 of the sampled sites this component post dates both the acadian and variscan folding has reversed polarity and a mean direction dec 193 8 inc 7 2 95 2 6 which corresponds to a pole position lat 40 4 s long 338 0 e consistent with a latest carboniferous or early permian age the early devonian pole position confirms the existence of a siluro devonian inflexion in the apparent polar wander path apwp for southern britain which coincides with an inflexion in the apwp for scotland britain north of the iapetus suture indicating the closure of the iapetus ocean by siluro devonian time the early devonian palaeolatitude 17 s 5 is consistent with an early devonian configuration in which gondwana laurentia baltica and avalonia were part of a single supercontinent

historical volcanoes of armenia and adjacent areas what is revisited abstract the validity of some data in karakhanian et al karakhanian a djrbashian r trifonov v philip h arakelian s avagian a 2002 holocene historical volcanism and active faults as natural risk factor for armenia and adjacent countries journal of volcanology and geothermal research 113 1 319 344 karakhanian a jrbashyan r trifonov v philip h arakelian s avagyan a baghdassaryan h davtian v ghoukassyan yu 2003 volcanic hazards in the region of the armenian nuclear power plant journal of volcanology and geothermal research 126 1 2 31 62 that are revisited by r haroutiunian is considered a conclusion is made that the revisions suggested by haroutiunian concern unessential parts of the content of work by karakhanian et al karakhanian a djrbashian r trifonov v philip h arakelian s avagian a 2002 holocene historical volcanism and active faults as natural risk factor for armenia and adjacent countries journal of volcanology and geothermal research 113 1 319 344 karakhanian a jrbashyan r trifonov v philip h arakelian s avagyan a baghdassaryan h davtian v ghoukassyan yu 2003 volcanic hazards in the region of the armenian nuclear power plant journal of volcanology and geothermal research 126 1 2 31 62 this article presents new evidence and re proves the earlier conclusions that are disputed or revised by r haroutiunian

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

is the southern uplands of scotland really an accretionary prism we argue that there is little which demands the accretionary prism model for the widespread silurian rocks of the southern uplands of scotland and ireland with new data from ireland we reinterpret these rocks as the turbidite fill of a successor basin that formed after the subduction of iapetus oceanic crust finally stopped at the end of the ordovician the structure of the basin is a sinistral transcurrent imbricate stack the result of oblique terminal collision of cadomia with laurasia at the end of the silurian

paleomagnetism of the ordovician bluffer pond formation paleogeographic implications for the munsungun terrane of northern maine the munsungun area of northern maine is an early paleozoic terrane within the central mobile belt cmb of the northern appalachians the bluffer pond formation of the munsungun terrane is composed primarily of pillow basalt and gabbro with minor intercalated sediments and has a maximum thickness of 1230 m this unit is of early late ordovician caradocian age based on paleontological data and folding most likely occurred during the devonian acadian orogeny this region has been metamorphosed to subgreenschist facies samples for paleomagnetic study have been obtained from 15 sites of pillow basalt and seven sites of gabbro within the bluffer pond formation natural remanent magnetization nrm directions are similar to the expected present day field direction and are interpreted to be strongly affected by a viscous overprint detailed stepwise thermal demagnetization fails to adequately resolve a partial overprint direction with intermediate blocking temperature but stable endpoints combined with great circles do isolate a characteristic high temperature component carried by magnetite as indicated by unblocking temperatures and rock magnetic experiments after tilt correction the formation mean calculated from pillow basalt sites only is d 339 i 33 k 12 95 14 n 11 with a corresponding paleopole of 23 n 133 e p 9 m 16 calculated for an average site location of 46 5 n 291 e when both pillow basalt and gabbro sites are used to calculate a tilt corrected formation mean the result is d 339 i 28 k 12 95 12 n 14 and this characteristic component passes a tectonic tilt test the calculated paleopole 26 n 134 e p 7 m 13 from pillows and gabbros falls near but not on the ordovician apparent polar wander path segment for north america and yields a paleolatitude 18 9 s similar to that of the lunksoos terrane which is located farther to the southeast within the cmb of maine the laurentian margin at this time was located at paleolatitudes of 15 20 s the paleogeographic implication of this result is that the munsungun terrane was located near the laurentian margin within the iapetus ocean and this near continent location is consistent with a marginal or back arc basin tectonic environment for the extrusion of the bluffer pond volcanics

new palaeomagnetic constraints on the position of central bohemia during early ordovician times summary apparently conflicting data within the palaeomagnetic database suggest that bohemia was at much shallower palaeolatitudes than the armorican and iberian massifs in ordovician times in order to resolve this controversy a palaeomagnetic study of arenig and llanvirn volcanic and sedimentary rocks from the barrandfan basin central bohemia has been carried out this basin comprises a sequence of unmetamorphosed lower palaeozoic rocks the main folding of which occurred in late devonian to early carboniferous times the samples collected l sites 153 samples were subjected to stepwise thermal and alternating field treatment eleven sites yielded reliable magnetic directions with analysis of the results using standard principal component and great circle analyses up to three directions of magnetiza tion can be identified in these rocks the first termed a is generally removed below 200 c although in some cases it persists up to 450 oc in the volcanic rocks it is approximately parallel to the present day earth s magnetic field in the study area dec inc 360 67 and is thus thought to be of recent origin the second direction identified termed b is isolated at intermediate blocking temperatures 150 350 c and yields an overall in situ mean direction of 195 8 k 22 3 a 95 13 1 seven sites these directions fail the fold test of mcfadden 1990 and correspond to a palaeopole position of 34 s 356 e this coincides with the late carboniferous sector of the european apparent polar wander path and thus the b direction is interpreted as being a secondary overprint of this age the highest blocking temperature direction termed c is identified at temperatures between 350 and 450 600 c it passes the fold test resulting in an overall mean direction of 312 83 k 21 9 a 95 14 6 six sites after bedding correction this direction is interpreted as being representative of the early ordovician palaeomagnetic field direction in the bohemian massif and yields a palaeopole position of 58 n 355 e this translates into palaeolatitudes of 76 s for bohemia thus demonstrating that the bohemian massif was at similar peri polar latitudes to the rest of armorica during early mid ordovician times and formed part of the northern margin of gondwana

a palaeomagnetic study of the builth wells llandrindod wells ordovician inlier wales palaeogeographic and structural implications summary discrepancies exist in the southern british ordovician palaeomagnetic data set with individual studies indicating either high southerly or temperate southerly palaeolatitudes although previous palaeomagnetic investigations from the builth inlier have delineated a three component remanence structure doubts have been raised concerning i the magnetization age of the supposed primary component p ii the structural setting of the sampling area llanelwedd quarry within a zone of strike slip deformation and iii whether detailed step wise demagnetization has fully separated the various magnetization components in addressing these problems we present new palaeomagnetic results as follows i a positive palaeomagnetic conglomerate test establishing a pre late llanvirn age for component p ii an enlarged geographic sampling embracing several tectonic domains indicating that relative rotations linked to strike slip tectonism are minor within the builth sampling area and iii evidence that component p is uncontaminated by overprints at some sites suggesting the resulting palaeolatitude of 35 s to be representative for the builth inlier we also present evidence for local syn volcanic deformation within llanvirn volcanics and for intrusion related deformation of llanvirn shales when the revised llanvirn pole from the inlier 3 s 4 e is combined with other data from southern britain in a statistical spline analysis a mean palaeolatitude of 44 5 s is calculated for builth in llanvirn times a palaeoreconstruction for 468 474 ma c mid llanvirn is presented utilizing this analysis

some examples of detection of oceanic mesoscale eddies by the seasat synthetic aperture radar this note presents images of three dynamically different regions in the ocean to demonstrate the variety of mesoscale variabilities detected by the seasat synthetic aperture radar sar south of the grand banks of newfoundland a cold eddy is observed to form as the result of the southward intrusion of labrador sea water perhaps having led to the birth of a gulf stream extension ring off the northern coast of california features resulting from the offshore intrusions of cold upwelling water are observed two topographically generated eddies are detected near misteriosa bank on the cayman ridge in the northwestern caribbean comparisons are made with concurrent noaa 5 infrared images whenever the eddies have thermal signatures

intense deformation field at oceanic front inferred from directional sea surface roughness observations fine scale current gradients at the ocean surface can be observed by sea surface roughness more specifically directional surface roughness anomalies are related to the different horizontal current gradient components this paper reports results from a dedicated experiment during the laser lagrangian submesoscale experiment drifter deployment a very sharp front 50 m wide is detected simultaneously in drifter trajectories sea surface temperature and sea surface roughness a new observational method is applied using sun glitter reflections during multiple airplane passes to reconstruct the multi angle roughness anomaly this multi angle anomaly is consistent with wave current interactions over a front including both cross front convergence and along front shear with cyclonic vorticity qualitatively results agree with drifters and x band radar observations quantitatively the sharpness of roughness anomaly suggests intense current gradients 0 3 m s 1 over the 50 m wide front this work opens new perspectives for monitoring intense oceanic fronts using drones or satellite constellations

near laurentian paleogeography of the lawrence head volcanics of central newfoundland northern appalachians abstract paleomagnetic analyses were completed on two volcanic units of the exploits group in newfoundland s central mobile belt which are part of an ordovician arc back arc system the tea arm volcanics display scattered and unstable characteristic directions that cannot be interpreted however stable end points in six sites supported by great circle analysis of seven sites in the mid arenigian to llanvirnian lawrence head volcanics yield a tilt and strike corrected characteristic direction of d 56 i 23 95 19 k 14 n 6 the magnetization is carried by magnetite and passes a tilt test the corresponding paleolatitude of 12 10 is interpreted as southerly and is similar to the paleolatitude of 11 4 for arc volcanics of the nearby moreton s harbour group however this near laurentian paleolatitude is distinctly different from the paleolatitude of 31 8 reported for the robert s arm cottrell s cove chanceport summerford volcanic terrane the low paleolatitude of the lawrence head volcanics supports the location of a major ordovician subduction system near the laurentian margin of iapetus whereas the present day juxtaposition of latitudinally distinct elements in the area represents a complex accretionary history involving early silurian or older thrusting and younger strike slip faulting of several iapetan island arc terranes to laurentia

estimating slip rates and recurrence intervals for strong earthquakes along an intracontinental fault example of the pambak sevan sunik fault armenia north of the arabian plate active tectonics is characterised by both n s compression and e w extension associated with strike slip faults the pambak sevan sunik fault pssf zone in armenia is one of the major active structures of the region the fault is comprised of four main segments and it displays morphological evidence for dextral movement during the holocene however no large earthquake m 7 has occurred in the northern or central parts of the fault during the last 2000 years we undertook a geomorphological and paleoseismological investigation along the pambak sevan sunik fault with the aim of estimating the long term slip rate and recurrence interval of strong earthquakes trenches were excavated at three sites detailed studies of trench cross sections and dating radiocarbon and ceramics show three faulting events that occurred in the vanadzor artanih segment fioletovo and semionovka areas whereas a single event took place in the artanish sunik segment khonarhasar area in both areas we estimated the average slip rate using i the offset of rivers along the vanadzor artanish segment 2 24 0 96 mm year over an interval of 120 300 ka and ii the offset of volcanic cones along the artanish sunik segment 0 53 0 04 mm year over an interval of 1 4 ma these results suggest that a greater slip rate characterises the vanadzor artanish segment fioletovo site from the artanish sunik khonarhasar site segment division of the pambak sevan sunik fault zone into two main branches east of the artanish peninsula sevan lake could explain the difference in slip rate in addition to its segmented seismic behaviour the pambak sevan sunik fault is a well documented example of a fault that generates strong earthquakes with long recurrence time intervals about 3000 4000 years d 2001 elsevier science b v all rights reserved

mapping the agulhas current from space an assessment of asar surface current velocities 1 over 2 years of surface current information collected in the agulhas current region and derived from the doppler centroid anomalies of envisat s advanced synthetic aperture radar asar are examined the sources of errors and potential use of asar surface current velocities for oceanographic research are assessed asar surface current velocities are compared to surface drifter data and merged altimetry observations maps of sea surface temperature are used to establish the asar s capacity to capture the synoptic circulation discrepancies between observed and predicted asar velocities result predominantly from inadequate wind corrections combined with radar incidence angles below 30 occasionally observed wind induced outliers cause a bias in the estimated asar velocities but do not affect the ability of the asar to systematically image regions of strong surface current flow and shear time averaged maps of asar derived surface current velocity seem able to accurately capture the position as well as the intensity of the agulhas current the ability of the asar to pick up the smaller features of the circulation along the shelf break also shows that variability along the agulhas bank is of the same order of magnitude as that observed in the agulhas retroflection asar surface current velocities offer a very good complement to altimetry in regions where the mean dynamic topography is poorly resolved the quasi synoptic nature of asar acquisitions combined with the relatively high resolution of asar surface current velocities also make it attractive for studies of submesoscale processes and western boundary current dynamics

palaeomagnetic data from the borrowdale volcanic group volcano tectonics and late ordovician palaeolatitudes nineteen palaeomagnetic sampling sites from the borrowdale volcanic group between borrowdale and langdale english lake district yield high unblocking temperature magnetization components which postdate the structural tilt and therefore postdate the formation of the broad block faulted syncline which characterizes this part of the central lake district the mean magnetization direction before tilt correction dec 347 2 inc 61 9 95 6 9 corresponds to a palaeolatitude of 43 s 5 7 the magnetization is associated with pervasive late ordovician hydrothermal alteration and is certainly pre devonian based on comparison with available palaeomagnetic data from southern britain this implies that the block faulted synclinal structure of the borrowdale langdale region is pre acadian in age consistent with recent interpretations of late ordovician volcano tectonics based on mapping and volcanological studies

late neoproterozoic to early palaeozoic palaeogeography of avalonia some palaeomagnetic constraints from nuneaton central england palaeomagnetic studies have been carried out on neoproterozoic cambrian and ordovician rocks in the nuneaton inlier england 52 5 n 1 5 w three magnetic components were recognized which provide a consistent structural and magnetic history of the inlier neoproterozoic volcaniclastic and intrusive rocks acquired a characteristic remanent magnetization chrm dated at 603 ma late ordovician rocks are represented by lamprophyre and diorite intrusions and their chrms were probably imprinted during their emplacement at about 442 ma the lower cambrian sedimentary sequence of the hartshill sandstone formation which unconformably overlies the neoproterozoic rocks and hosts the ordovician intrusions does not preserve a primary magnetization but shows the imprints of the late ordovician 442 ma remagnetization as well as a probable end carboniferous remagnetization palaeolatitudes calculated for the late neoproterozoic rocks and ordovician intrusions are in good agreement with other palaeolatitudes calculated for avalonia during those times both the late neoproterozoic and late ordovician rocks additionally show chrms with declination anomalies indicating a large tectonic rotation of the nuneaton area possibly during one of the caledonian phases of deformation affecting southern britain

the occurrence and origin of late paleozoic remagnetization in the sedimentary rocks of north america although it has been known for 25 years that some paleozoic sedimentary rock units in europe and north america were remagnetized during pennsylvanian or permian time it is only very recently that the complex and widespread nature of the late paleozoic remagnetization phenomenon has been generally acknowledged it is now recognized that many paleozoic paleomagnetic poles for north america that were once considered reliable are in fact the result of remagnetization and as a consequence the paleomagnetic data base for the paleozoic is undergoing rapid and drastic revision the causes of late paleozoic remagnetization in north america are currently the focus of much interest and active research the remagnetization can reside in either hematite or magnetite and different remagnetization mechanisms have been important in different settings chemical remagnetization processes some related to specific diagenetic events are dominant in hematite bearing sandstones and carbonates in magnetite bearing carbonates both chemical and thermoviscous remagnetization processes appear to have been important but it is difficult to determine which process is the dominant one in some settings some of the observed remagnetizations can be linked to the migration of chemically active and perhaps hot fluids during the mountain building events that affected much of the continent during the late paleozoic paleomagnetic studies promise to be important in assessing the role of orogeny in driving fluid migrations within sedimentary basins and in constraining the age of the migrations and the nature of the fluids

holocene historical volcanism and active faults as natural risk factors for armenia and adjacent countries abstract examples of holocene historical volcanism in the territory of armenia and adjacent areas of eastern anatolia and western iran are discussed holocene historical activity is proved for the volcanoes of tskhouk karckar porak vaiyots sar smbatassar and ararat based on the analysis of remote sensing data field work and historical and archeological information it is demonstrated that there was a considerable number of cases of volcanic activity in armenia and adjacent regions of turkey syria and iran during the historical period the holocene volcanic centers are situated within pull apart basin structures and controlled by active faults situated in an area prone to many types of natural hazards armenia and adjacent countries face high natural risk the evidence presented shows that volcanic hazard also contributes to the natural risk for these countries

storm effects on siliciclastic and carbonate shelf sediments in the medial silurian succession of pennsylvania abstract upper llandoverian through wenlockian strata in the pennsylvania part of the northern appalachian basin formed on a gentle epeiric ramp that extended from marginal tidal flats through coarser grained mid shelf shoals to a muddy basin center over approximately 10 million years the composition of the accumulating sediment evolved from siliciclastic to carbonate while the ramp maintained a relatively similar configuration and position below sea level and while storm generated processes continued as the major producers of sediment characteristics in both siliciclastic and carbonate parts of the succession sedimentary structures and their sequences are generally similar with only a small number of dissimilar features resulting from the differences in composition small scale coarsening and shallowing upward sequences are present in both mid shelf bar and basin transition deposits although specific sequence characteristics are different in siliciclastic and carbonate parts such sequences record cyclic fluctuations of relative sea level while the composition of the sediment evolved over this extended period the gentle ramp gradient was maintained largely by the processes generated by storms such processes were more effective because of the fluctuations of relative sea level

a plate tectonic scenario for the iapetus and rheic oceans abstract the tectonics dynamics and biogeographic landscape of the early paleozoic were dominated by the opening and expansion of one large ocean the rheic and the diminution to terminal closure of another iapetus an understanding of the evolution of these oceans is thus central to an understanding of the early paleozoic but their chronicle also presents a rich temporal profile of the wilson cycle illustrating continental scale rifting microcontinent formation ocean basin development arc accretion and continent continent collision nevertheless contemporary paleogeographic models of the iapetus and rheic oceans remain mostly schematic or spatiotemporally disjointed which limits their utility and hinders their testing moreover many of the important kinematic and dynamic aspects of the evolution of these oceans are impossible to unambiguously resolve from a conceptual perspective and the existing models unsurprisingly present a host of contradictory scenarios with the specific aim to resolve some of the uncertainties in the evolution of this early paleozoic domain and a broader aim to instigate the application of quantitative kinematic models to the early paleozoic i present a new plate tectonic model for the iapetus and rheic oceans the model has realistic tectonic plates which include oceanic lithosphere that are defined by explicit and rigorously managed plate boundaries the nature and kinematics of which are derived from geological evidence and plate tectonic principles accompanying the presentation and discussion of the plate model an extensive review of the underlying geological and paleogeographic data is also presented

geomorphological effects of the 1840 ahora gorge catastrophe on mount ararat eastern turkey abstract ahora gorge is a 400 m deep canyon located along the north eastern flank of mt ararat turkey a compound volcanic complex covered by an ice cap in the past several diarists and scientific authors reported a calamitous event on july 2 1840 when a landslide triggered by a volcanic eruption and or an earthquake obliterated several villages located at the foot of the volcano the reasons and effects of this ahora gorge catastrophe agc event have been obscure and ambiguous to reappraise the 1840 catastrophe and the geomorphic evolution of the ahora gorge we used high resolution satellite images remote sensing thermal data supplemented by observations collected during two field surveys according to our interpretation an earthquake in 1840 triggered an abrupt volcanic eruption which caused the consequent rapid melting of glacial ice and mountain snow this event produced significant mud and ice flow along the ahora gorge that inundated the villages downslope the flooding which we interpret as a lahar deposited a wide alluvial fan at the foot of the volcano today an elongated landform present within the ahora gorge has alternately been interpreted as a landslide deposit our multi data integrated analysis and ground based observations demonstrate that this feature is an unmapped glacier the shape of the landform coupled with aster thermal satellite data and ground based observations reveal that a debris covered glacier dcg formed soon after the catastrophic lahar our discovery of the ahora gorge glacier in context of a reappraisal of the ahora gorge catastrophe demonstrates the contribution of glaciers in shaping the landscape near ice capped volcanoes moreover our data underscore the importance of being more aware of the potential future geo hazards posed by mount ararat particularly where glaciers are still present along several valleys and seismically induced lahar events might occur

faunal evidence for oceanic separations in the palaeozoic of britain the faunal criteria for the recognition of the relative separation of old continents are 1 the contrast between shallow not deep water faunas off opposite shorelines 2 the recognition of deeper water facies surrounding the edges of continents and 3 the recognition of the disposition of ancient climatic belts these criteria are defined and used to assess the relative position of the various parts of what is now britain in the palaeozoic the iapetus ocean is well characterized by faunal differences from the cambrian until the lower ordovician but from caradoc times onwards these differences dwindle until by the latest silurian only the distribution of the ostracods separates the two sides of the ocean on faunal grounds in the early ordovician s british faunas are comparable with those from bohemia france and elsewhere to the s indicating connection with gondwanaland and these faunas differ from those in the baltic area a distribution which we attribute to a true ocean tornquist9s sea between n and s europe tornquist9s sea probably closed in the upper ordovician and from ashgill times onwards the s british and baltic faunas remained similar during the middle and late silurian there is evidence of increasing faunal distinction between britain the baltic area and north america on the one hand and southern europe and gondwanaland on the other indicating an opening rheic ocean which appears to have persisted until late carboniferous times

sar observing large scale nonlinear internal waves in the white sea abstract the compiled archive of synthetic aperture radar sar images acquired by the advanced sar asar onboard the envisat satellite over the white sea during the extended summer periods may september between 2007 and 2011 provides the first detailed analysis of 2 d patterns of internal waves iws in the white sea unambiguously the primary region of iw activity is the southwestern sw gorlo strait gs iw packets emerging from this area are regularly observed to reach crest lengths up to 200 km and also to propagate a few hundred kilometers from their origin model results confirm that large scale iws can be generated every tidal cycle and are able to cross the entire sea as suggested the source of these packets is governed by the intense dynamics of the frontal zone in the tidal cycle over local complex bottom as further revealed these large scale iws cascade into intense large amplitude short iw packets on the shoaling white sea shelf significantly impacting vertical turbulent exchange and the overall hydrology

radar imaging of intense nonlinear ekman divergence in general given an oceanic thermal front there is a strong positive correlation between sea surface temperature sst gradients and surface winds and the marine atmospheric boundary layer mabl is unstable over the warm side of the oceanic thermal front the gulf stream is a notable example of an oceanic thermal front and its warm side is often detected as enhanced backscatter in synthetic aperture radar sar images however in some anomalous sar images low backscatter is sometimes observed on the warm side of the front which seems inconsistent therefore we propose a mechanism to interpret the generation of the low backscatter based on interactions between ocean surface wind waves and intense nonlinear ekman divergence this mechanism is verified by showing that patterns in an observed anomalous sar image are in good agreement with those in the simulated radar signature in addition this methodology and analysis demonstrate that sar is potentially important for detecting and diagnosing small scale air sea interactions and upper ocean dynamics with strong vertical transports induced by submesoscale processes

summer upwelling and thermal fronts in the northwestern south china sea observational analysis of two mesoscale mapping surveys persistent coastal upwelling and upwelling induced thermal fronts in the northwestern south china sea are investigated using satellite measurements two intensive mesoscale mapping surveys and three bottom mounted adcps the results indicate that pronounced surface cooling and upwelling related fronts with a width of 20 50 km occur around hainan island and persist through the summer upwelling season driven by the prevailing southwesterly monsoon the subsurface cooling band is approximate to 6 degrees c colder than the water offshore of the east coast where the thermal gradients are generally more than 0 1 degrees c km the cold and nutrient rich coastal water is identified to be derived primarily from the deep water of the outer shelf at the same time the spatial structure of the upwelling and thermal front as well as the upwelling related coastal currents is significantly regulated by wind forcing a prominent lagged correlation between the moored temperature records and alongshore wind stress is detected in the east coast the correlation coefficient is 0 8 with the temperature lagging behind wind stress by 2 2 days indicating that the cooling band off the east coast is dominated mostly by the alongshore southwesterly monsoon during the upwelling season

a new silurian palaeolatitude for eastern avalonia and evidence for crustal rotations in the avalonian margin of southwestern ireland summary palaeomagnetic data are presented from mid silurian homerian upper wenlock 425 ma sediments from the dingle peninsula sw ireland which forms part of thenorthern margin of the palaeozoic microcontinent of avalonia three remanencecomponents were recognized after removal of a low temperature component l oriented parallel to the present earth eld at the sampling area two higher stabilitycomponents were isolated an intermediate unblocking temperature component i with mean in situ d 196 9 i 11 0 a95 10 8 with a corresponding palaeopole at330 0 e 30 6 s dp 5 6 dm 11 0 and a high unblocking temperature component h with mean tilt corrected d 218 6 i 22 1 a95 7 9 with a correspondingpalaeopole at 309 5 e 18 3 s dp 4 4 dm 8 4 a primary wenlock age is indicatedfor the h component by a positive intraformational conglomerate test whereas the i component is thought to be a secondary mid carboniferous partial remagnetization these data con rm that the sector of the iapetus ocean between avalonia andlaurentia was essentially closed within the limits of palaeomagnetic resolution by thewenlock there is still however a discrepancy between the declinations recorded bysimilar aged sequences to the north and south of the iapetus suture these point toeither an approximately 30 clockwise rotation of the entire avalonian microcontinentrelative to laurentia during closure or local vertical axis rotations of the samplingsites in southern britain

superimposed recent permo carboniferous and ordovician palaeomagnetic remanence in the builth volcanic series wales the builth volcanic series of llanvirnian age in llanelwedd quarries mid wales carries three components of natural remanent magnetisation component p regarded as primary is a thermochemical remanence directed at d 181 7 i 54 5 95 4 4 relative to bedding component s is a secondary component with in situ d 178 7 i 6 7 95 5 4 and is believed to be a low temperature chemical remanence crm of permo carboniferous age component r is directed close to the present geomagnetic field and is believed to be a recent viscous remanence vrm the results are of interest for three reasons first they are an unusually good example of multi component nrm analysis the three components being so clearly discriminated by thermal demagnetisation because they have almost completely separate blocking temperature ranges second they provide evidence of a permo carboniferous event possibly a mild thermal or hydrothermal pulse promoting crm acquisition some 40 km north of the hercynian orogenic front third they illustrate very clearly the importance of detailed demagnetisation this work revises the pole position for these rocks by 10 and removes an obstacle to the palaeomagnetic recognition of the 1000 km wide iapetus ocean cutting britain in ordovician time

mesoscale variability in the alboran sea synthetic aperture radar imaging of frontal eddies in autumn 1992 the entire alboran sea western mediterranean was sampled by the spanish r v garcia del cid the incoming jet of atlantic water its associated meandering front and the two big anticyclonic gyres were described from conductivity temperature depth ctd and acoustic doppler current profiler adcp data smaller scale eddies were also observed additionally 36 ers 1 synthetic aperture radar sar scenes were obtained from mid september to mid october the sar images capture these features when wind conditions are suitable the current shear is mainly depicted as narrow lines of low backscatter because of the damping of waves by natural surface films these lines delineate the northern border of both gyres and the beginning of the alongslope algerian current at the eastern limit of the alboran sea adcp observations confirm that lines on sar imagery follow the direction of the surface currents the two gyres present high backscatter values in their center while their frontal boundaries appear modulated by the variation of the marine atmospheric boundary layer stratification due to the surface thermal front sar has observed small spiral eddies that were not evidenced by the almost contemporaneous but too coarse ctd in situ sampling good spatial correspondence between radar detected and in situ measured structures occurs when comparing sar images to the surface dynamic topography rather than strictly surface water characteristics

eddies in the western arctic ocean from spaceborne sar observations over open ocean and marginal ice zones the western arctic ocean is a host to major ocean circulation systems many of which generate eddies that can transport water masses and corresponding tracers over long distances from their formation sites however comprehensive observations of critical eddy characteristics are currently not available and are limited to spatially and temporally sparse in situ observations here we use high resolution spaceborne synthetic aperture radar measurements to detect eddies from their surface imprints in ice free sea surface roughness and in sea ice patterns throughout marginal ice zones we provide the first estimate of eddy characteristics extending over the seasonally ice free and marginal ice zone regions of the western arctic ocean including their locations diameters and monthly distribution using available synthetic aperture radar data we identified over 4 000 open ocean eddies as well as over 3 500 eddies in marginal ice zones from june to october in 2007 2011 and 2016 eddies range in size between 0 5 and 100 km and are frequently found over the shelf and near continental slopes but also present in the deep canada basin and over the chukchi plateau we find that cyclonic eddies are twice more frequent compared to anticyclonic eddies at the surface distinct from the dominating anticyclonic eddies observed at depth by in situ moorings and ice tethered profilers our study supports the notion that eddies are ubiquitous in the western arctic ocean even in the presence of sea ice and emphasizes the need for improved ocean observations and modeling at eddy scales

volcanological evolution and caldera forming eruptions of mt nemrut eastern turkey abstract mt nemrut volcano situated at the west of lake van is one of the historically active volcanoes of the eastern anatolia it has an 8 5 7 km diameter summit caldera volcanic activity of mt nemrut started 1 ma ago the most recent eruptions were in 1441 1597 and 1692 a d among the eastern anatolian volcanoes mt nemrut is the most hazardous volcano for its vicinity present day volcanic activity is represented by intra caldera hydrothermal and fumarolic output and low level volcano seismic events geological evolution and chronostratigraphy of the volcano is subdivided in three stages pre caldera syn caldera and post caldera stages pre caldera products are dominated by felsic lava flows and domes trachytic nemrut and kantasi pyroclastics represent the caldera forming activity of which sequences are composed of fallout units and ignimbrite flows both nemrut and kantasi ignimbrite units are low aspect ratio ignimbrites they are generally densely welded and present columnar jointed outcrops locally extent of nemrut ignimbrite volume 32 6 km 3 is greater than the kantasi ignimbrite volume 3 8 km 3 post caldera activity of the volcano is marked by peralkaline rhyolitic comendite intra caldera lava flows and explosive hydrovolcanic activities historical activity of the volcano is represented by bimodal basaltic rhyolitic effusive activity along nemrut rift zone

les bassins d avant pays de la chaine hercynienne au carbonifere inferieur the evolution of marine sedimentary basins deformed by the hercynian orogeny was studied in germany france iberia northwest africa and north america in the lower carboniferous these basins opened along strike slip faults and were filled with turbidites and shelf deposits until the main compressive phase at the end of visean and the namurian the infilling was interrupted with frequent volcanic episodes and gravity induced movements according to sedimentary vergence these basins were set into two festoons on both sides of an elongated and emergent swell structured during the devonian and corresponding to the internal zones of the orogen these basins were filled during a general tectonic compression phase they correspond to the foreland basins of the hercynian belt

reply to comment of a trench and t h torsvik on paleomagnetic results from volcanic rocks of the shelve inlier wales evidence for a wide late ordovician iapetus ocean in britain

is the welsh borderland fault system a terrane boundary the welsh borderland fault system forms one of the most prominent tectonic lines in southern britain and along with the menai straits and malverns fault systems is a candidate for a terrane boundry a review of stratigraphic linkage across the system reveals significant contrasts in pre ashgill sequences these contrasts occur particularly across its north west edge the pontesford and tywi lineaments rather than across the church stretton lineament the ashgill event produced strike slip dominated structure and an unconformity that expands from the welsh basin towards the platform an important linkage sequence was produced by the subsequent late ashgill to llandovery marine transgression across the fault system silurian facies changes are marked but gradational and no more than expected across a basin margin from stable to thinned crust devonian acadian sinistral transpression and later phanerozoic movements reactivated the fault system but did not engineer major terrane amalgamation across it this reactivation has obscured the early history of the fault system the remaining evidence admits though does not prove major ashgill or earlier transcurrent movements broader considerations suggest that the welsh borderland fault system originated either as a cambro ordovician extensional system on the south eastern margin of the welsh basin or during late precambrian early cambrian transcurrent movements occurring within avalonia inboard from the menai strait line

direct ocean surface velocity measurements from space improved quantitative interpretation of envisat asar observations previous analysis of advanced synthetic aperture radar asar signals collected by esa s envisat has demonstrated a very valuable source of high resolution information namely the line of sight velocity of the moving ocean surface this velocity is estimated from a doppler frequency shift consistently extracted within the asar scenes the doppler shift results from the combined action of near surface wind on shorter waves longer wave motion wave breaking and surface current both kinematic and dynamic properties of the moving ocean surface roughness can therefore be derived from the asar observations the observations are compared to simulations using a radar imaging model extended to include a doppler shift module the results are promising comparisons to coincident altimetry data suggest that regular account of this combined information would advance the use of sar in quantitative studies of ocean currents

discordant silurian paleolatitudes for central newfoundland new paleomagnetic evidence from the springdale group ancient remanences are retained by the early silurian 429 6 5 ma mafic volcamcs of the sprmgdale caldera five sites and the overlying red beds seven sites dual polarity magnetizations are obtained by thermal demagnehzation of samples from the red beds whereas single polarity d rectlons are observed m the volcamcs high unblockmg temperatures indicate hematite as the remanence carrier m both the volcamcs and sedxments these h gh temperature characteristic remanences are easily solated and pass both the tilt and conglomerate tests they are likely to be of primary silurian age characteristic dechnatlons are predominantly northerly and northeasterly and md cate s gmficant structural rotahons on a local scale when the results of the red beds and the voleamcs are combined they show characteristic mchnatlons that are shallower than those of the correlative botwood group ca 36 vs 43 but not nearly as shallow as those reported from the king george iv lake area 0 5 mean mchnatlons obtained from the sprmgdale red beds are however slgmficantly shallower than those of the sprmgdale volcanlcs the same difference can be seen m other previous silurmn paleomagnehc studies of central newfoundland we infer that an mcllnat on error affects the red bed magnetizations of the sprmgdale group botwood group wigwam formation and rocks of the king george iv lake area therefore the results from sdurlan red beds should not be used to determine paleolahtudes for central newfoundland the mean paleolatltude of the sprlngdale group volcamcs is 30 the mean paleolatltudes for both the sprlngdale volcanlcs and botwood volcamcs lawrenceton formation are md stmgmshable w thm paleomagnetlc error hm ts from the predicted paleolatltude of newfoundland on the northeast trendi ng north american margin thus no detectable post silurian displacement ts shown by the volcamcs of the sprmgdale group with respect to cratomc north america

airborne synthetic aperture radar observations of spiral eddy slick patterns in the southern california bight 1 repeat sampling on hourly time scales using an airborne synthetic aperture radar sar is used to investigate the occurrence and evolving characteristics of spiral shaped slick patterns commonly presumed to be indicators of submesoscale ocean eddies in the area around santa catalina island california 33 4 n 118 4 w simultaneous sar imagery and boat survey data are examined over two 5 h long periods spaced 3 days apart in april 2003 the sar imagery reveals several spiral like patterns roughly 5 km in diameter occurring downstream of the western end of catalina we believe that the most likely formation mechanism for these patterns is current wake instability related to the flow of the southern california countercurrent along the north shore of catalina in one case there is an observed cold core eddy and vortex sheet attached to the tip of the island similar to island wake simulations done by dong and mcwilliams 2007 in another case the sar imagery shows a series of slick patterns that at least initially resemble spiral eddies but the data show no clear evidence of actual ocean eddies being present either at depth or through a rotating surface expression a speculation is that such features signify island wake eddies that are relatively weak and dissipate quickly an unexpected finding was how quickly a spiral slick pattern could deteriorate suggesting a time scale for the surface feature of the order of only several hours an implication of this result is that care is needed when interpreting a single satellite sar imagery for evidence of active submesoscale eddies recommendations are made for future field studies

retrieval of sea surface range velocities from envisat asar doppler centroid measurements the processing steps and error corrections needed to retrieve estimates of sea surface range doppler velocities from envisat advanced synthetic aperture radar wide swath medium resolution image products are presented retrieval accuracies based on examination of the corrected doppler shift measurements are assessed the root mean square errors of the doppler shift after bias corrections are found to be 4 7 and 3 9 hz in vv and hh polarizations respectively at 35 incidence angle this corresponds to horizontal doppler velocities of 23 and 19 cm s

palaeomagnetism of late ordovician igneous intrusions from the northern welsh borderlands implications to motion of eastern avalonia and regional rotations the palaeomagnetism of a late ordovician dolerite suite widely distributed in the northern welsh borderlands has been investigated to evaluate i regional rotations associated with later deformations and ii lower palaeozoic latitudes of eastern avalonia only local effects of acadian and variscan overprinting are observed in this region and most bodies appear to preserve a primary cooling related magnetization magnetic properties in the breidden dolerite are related to primary igneous differentiation and a dual polarity characteristic remanence d i 333 1 71 6 6 sites 95 10 4 predates late ordovician folding dolerites elsewhere in the breidden hills inlier record the same reversal of remanence and the combined mean d i 314 3 72 8 is rotated clockwise from the mean remanence d i 291 5 59 5 21 sites 95 6 0 in a similar dolerite suite within the adjoining shelve inlier which is also of dual polarity and predates late ordovician folding the difference in magnetic declinations is similar to the rotation of late ordovician fold axes and fracture systems between the two inliers and is probably the resultant effect of local rotation possibly about a constraining bend in the severn valley fault system the moel y golfa andesite of caradocian soudleyan age has a remanence d i 294 3 50 4 13 samples 95 2 8 which study of an adjoining volcanic conglomerate shows to be of primary cooling related origin the equivalent palaeolatitude is 31 s in early caradocian times a similar estimate is derived from a probable diagenetic overprint in the contemporaneous castle hill conglomerate at montgomery the mynydd bryn andesite in the berwyn inlier of probable similar origin and age to moel y golfa has a magnetization of opposite polarity but similar inclination d i 239 1 47 4 14 samples 86 5 5 declination differences between these volcanic outcrops are a possible signature of later block rotations between the lower palaeozoic inliers and identify the importance of terrane definition in analysis of lower palaeozoic palaeomagnetic results from the caledonides a dolerite sheet complex at hendre in the berwyn hills has a younger remanence d i 182 3 3 0 20 samples 95 7 8 probably of mid carboniferous age the collective upper ordovician results define a rapid movement of the avalonian plate probably spanning no more than 10 ma from 30 s in early caradocian times to 57 s prior to folding of the dolerites in late caradocian to early ashgill times this motion into higher southerly palaeolatitudes marks a reversal of the motion of avalonia into more shallow southerly palaeolatitudes between arenig and llanvirn times and shows that ordovician closure of the iapetus ocean was more complex than recognized hitherto

coastal ocean fronts and eddies imaged with ers 1 synthetic aperture radar ers 1 c band synthetic aperture radar sar data were collected during the norwegian continental shelf experiment norcsex both in november 1991 during the ers 1 commissioning phase and at different seasons in 1992 and 1993 characteristic sar image expressions are observed in relation to perturbation of the surface current short wave interaction across the norwegian coastal current front for winds less than 10 12 rn s 1 in situ measurements document the existence of alternating zones of convergence and divergence coexisting with a strong near surface current shear of nearly 4f where f is the coriolis parameter across a distance of a few kilometers under calm to moderate winds i e 4 7 rn s 1 characteristic expressions of upper ocean circulation features also include the manifestation of eddies through the presence of surface film which damps the bragg waves comparison of a near coincident national oceanic and atmospheric administration advanced very high resolution radiometer image and an ers 1 sar image supports the interpretation that surface current fronts are imaged by sar in combination with an sar image simulation model the relative quantitative importance of shear convergence and divergence along the front is examined although the model formulation is simple and the absolute magnitude of the perturbations is uncertain the study shows that the sar images can sometimes be used to interpret frontal dynamics including growth and decay of meanders

an improved composite surface model for the radar backscattering cross section of the ocean surface 2 model response to surface roughness variations and the radar imaging of underwater bottom topography in the companion paper we have presented an improved composite surface model for the calculation of normalized radar backscattering cross sections nrcs of the ocean surface the proposed model accounts for the impact of the full two dimensional ocean wave spectrum on the radar backscatter and was shown to reproduce measured absolute nrcs values for a variety of radar configurations and wind speeds satisfactorily after some reasonable tuning of the input ocean wave spectrum this paper focuses on the modulation of the nrcs in the presence of spatially varying surface currents first the sensitivity of the nrcs to intensity variations of different ocean wave spectral components is investigated then the hydrodynamic modulation of the wave spectrum over underwater bottom topography in tidal waters is computed in different ways and the resulting radar signatures are discussed the composite surface model yields comparable radar signatures at high 10 ghz x band and low 1 ghz l band radar frequencies which is in much better agreement with experimental results than the predictions of a first order bragg scattering model on the other hand measured variations of the nrcs at high radar frequencies appear to be still underestimated in some cases which may be due to shortcomings of our description of the wave current interaction by conventional weak hydrodynamic interaction theory possible improvements of the theory are discussed and requirements for future experiments are formulated

palaeozoic palaeomagnetic studies in the welsh basin recent advances in the last two years new palaeomagnetic data fro m wale s have resulted i n radical revision of the ordovician palaeogeography of eastern avalonia part of the southern margin of the iapetus ocean combined with palaeozoic palaeomagnetic data from laurentia and gondwana these data suggest that eastern avalonia was a peri gondwanide high latitude continental fragment during at least part of ordovician time with a palaeolatitude of about 62 s and 51 s in arenig and llanvirn time respectively this implies a latitudinal width of the early ordovician iapetus ocean between eastern avalonia and laurentia of at least 30 geological evidence for the proximity of eastern avalonia and laurentia suggests that the intervening iapetus ocean closed during silurian time from late llandovery to early ludlow recent palaeolatitude data from the iapetus bordering continents are consistent wit h closure b y middle to late silurian time new pre acadian early devonian palaeomagnetic data from the old red sandstone places the welsh basin at about 17 s consistent with a palaeogeography in which laurentia baltica avalonia armorica and possibly gondwana wer e part o f a singl e supercontinent pervasiv e lat e carboniferous early permia n remagnetization affect s the welsh basin the remagnetization i s probably associated with fluids emanating from th e variscan thrust front w e do not observe remagnetization associate d with acadian orogen y and the remagnetizations which have been studied in more detail in north america appear to be a unique feature of the variscan hercynian alleghenian orogeny

paleozoic paleogeography of north america gondwana and intervening displaced terranes comparisons of paleomagnetism with paleoclimatology and biogeographical patterns new paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the silurian and devonian in this paper the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data the data from the three fields of paleomagnetism paleoclimatology and biogeography are generally in excellent agreement and an internally consistent paleogeographic evolutionary picture of the interactions between north america gondwana and intervening displaced terranes is emerging during the interval of the ordovician silurian and devonian north america stayed in equatorial paleoposition while rotating counter clockwise the northwest african part of gondwana was in high southerly latitudes during the late ordovician and was fringed by peri gondwanide terranes such as southern europe armorica and avalonian basement blocks now found in eastern newfoundland nova scotia the boston basin the appalachian piedmont and northern florida subsequently gondwana and the peri gondwanide terranes displayed rapid drift with respect to the pole this drift translates into the following pattern of movement for northwest africa during the latest ordovician early silurian this area moved rapidly northward from polar to subtropical latitudes followed by equally rapid southward motion from subtropical to intermediate about 50 s paleolatitudes during the late silurian middle devonian it is likely that significant east to west motion accompanied the latter shift in paleolatitudes with the caledonian acadian orogeny the result of silurian to early devonian convergence and collision between gondwana and north america this collision sandwiched several of the intervening displaced terranes between gondwana and north america subsequent to this collision gondwana was separated in the late devonian by a medium width ocean from north america and the avalonian and southern european blocks which were left behind adjacent to north america this new ocean closed during the carboniferous and the resulting convergence and collision were the cause of the hercynian alleghanian orogenic belt problems remaining for future research besides the further gathering of reliable paleopoles involve the uncertain pre devonian position of the southern british isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid late ordovician silurian apparent polar wander for gondwana

imaging mesoscale upper ocean dynamics using synthetic aperture radar and optical data a synergetic approach for quantitative analysis of high resolution ocean synthetic aperture radar sar and imaging spectrometer data including the infrared ir channels is suggested this approach first clearly demonstrates that sea surface roughness anomalies derived from sun glitter imagery compare very well to sar roughness anomalies as further revealed using these fine resolution similar to 1 km observations the derived roughness anomaly fields are spatially correlated with sharp gradients of the sea surface temperature sst field to quantitatively interpret sar and optical in visible and ir ranges images equations are derived to relate the surface roughness signatures to the upper ocean flow characteristics as developed a direct link between surface observations and divergence of the sea surface current field is anticipated from these satellite observations intense cross frontal dynamics and vertical motions are then found to occur near sharp horizontal gradients of the sst field as a plausible mechanism it is suggested that interactions of the wind driven upper layer with the quasi geostrophic current field via ekman advective and mixing mechanisms result in the generation of secondary ageostrophic circulation producing convergence and divergence of the surface currents the proposed synergetic approach combining sst sun glitter brightness and radar backscatter anomalies possibly augmented by other satellite data e g altimetry scatterometry ocean color can thus provide consistent and quantitative determination of the location and intensity of the surface current convergence divergence upwelling downwelling this in turn establishes an important step toward advances in the quantitative interpretation of the upper ocean dynamics from their two dimensional satellite surface expressions