coupled ice ocean dynamics in the marginal ice zones upwelling downwelling and eddy generation this study is aimed at modeling mesoscale processes such as upwelling downwelling and ice edge eddies in the marginal ice zones a two dimensional coupled ice ocean model is used for the study the ice model is coupled to the reduced gravity ocean model through interfacial stresses the parameters of the ocean model were chosen so that the dynamics would be nonlinear the model was tested by studying the dynamics of upwelling winds parallel to the ice edge with the ice on the right produce upwelling because the air ice momentum flux is much greater than air ocean momentum flux thus the ekman transport is greater under the ice than in the open water the stability of the upwelling and downwelling jets is discussed the downwelling jet is found to be far more unstable than the upwelling jet because the upwelling jet is stabilized by the divergence a constant wind field exerted on a varying ice cover will generate vorticity leading to enhanced upwelling downwelling regions i e wind forced vortices steepening and strengthening of vortices are provided by the nonlinear terms when forcing is time varying the advection terms will also redistribute the vorticity the wind reversals will separate the vortices from the ice edge so that the upwelling enhancements are pushed to the open ocean and the downwelling enhancements are pushed underneath the ice

detection of miocene saucer shaped sills offshore senegal via integrated interpretation of seismic magnetic and gravity data the atlantic margin offshore senegal has been explored by seismic reflection and grav mag surveys high amplitude laterally transgressive seismic reflectors are found to coincide with gravimetric and magnetic highs once seismic data are integrated with potential fields modelling these reflectors can be safely interpreted as saucer shaped igneous sills up to some hundreds of metres thick some km wide the occurrence of hydrothermal vent complexes and forced folds in the stratigraphic sequence above the sills constrain the intrusion age to the miocene field observations and in situ magnetic susceptibility measurements of oligocene miocene and quaternary igneous rocks emplaced in coastal senegal support this interpretation

the annual cycle in equatorial convection and sea surface temperature abstract the coupled atmosphere ocean system in the equatorial eastern pacific and atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes the contrasts are so strong that they dominate the annual march of zonally averaged outgoing longwave radiation for the equatorial belt the march equinox corresponds to the warm season when the equatorial cold tongues in the eastern pacific and atlantic are absent with the onset of summer monsoon convection over colombia central america and west africa in may june northward surface winds strengthen over the eastern pacific and atlantic the equatorial cold tongues reappear and the marine convection shifts from the equatorial belt to the intertropical convergence zones itczs along 8 n as the northern summer program the itczs remain strong and shift northward to new 10 n while sea surface temperature sst continues to drop over the cold tongues and the southern tropics perhaps in response to the

the accretion of oceanic crust by episodic sill intrusion seismic refraction data from mature oceanic regions show remarkable consistency in crustal thickness between sites yet the characteristics of different spreading centers show great variation this leads to the paradox that the similarity in mature oceanic crust suggests that the igneous processes in crustal accretion are the same across a range of spreading rates but that the differences in the spreading centers themselves imply the opposite we have developed a simple two dimensional model for crustal accretion at oceanic spreading centers by the episodic addition of sills at a high level within the crust as implied by recent geophysical studies of spreading centers using our model we have calculated velocity and temperature fields in the crust including the effects of hydrothermal cooling we show that oscillations in the temperature field due to episodicities of 200 20000 years have an effect localized to the region within 50 500 m of the intrusion by assuming that all latent heat and excess specific heat introduced by the injection of sills is convected away by hydrothermal circulation we estimate that the maximum heat transfer associated with hydrothermal cooling in the upper crust is of the order of 10 times greater than the conductive flux we have calculated seismic velocities associated with the model temperature field in the crust and we show that these are consistent with results from both seismic refraction and reflection experiments the model may be applied to both fast and slow spreading ridges and it accounts for the apparent increases in both the mean crustal temperature and the frequency of presence of melt with increasing spreading rate hence resolving the paradox we also show that the implications of this model are consistent with geological observations of layering in ophiolites

discovery of a magma chamber and faults beneath a mid atlantic ridge hydrothermal field crust at slow spreading ridges is formed by a combination of magmatic and tectonic processes with magmatic accretion possibly involving short lived crustal magma chambers the reflections of seismic waves from crustal magma chambers have been observed beneath intermediate and fast spreading centres but it has been difficult to image such magma chambers beneath slow spreading centres owing to rough seafloor topography and associated seafloor scattering in the absence of any images of magma chambers or of subsurface near axis faults it has been difficult to characterize the interplay of magmatic and tectonic processes in crustal accretion and hydrothermal circulation at slow spreading ridges here we report the presence of a crustal magma chamber beneath the slow spreading lucky strike segment of the mid atlantic ridge the reflection from the top of the magma chamber centred beneath the lucky strike volcano and hydrothermal field is approximately 3 km beneath the sea floor 3 4 km wide and extends up to 7 km along axis we suggest that this magma chamber provides the heat for the active hydrothermal vent field above it we also observe axial valley bounding faults that seem to penetrate down to the magma chamber depth as well as a set of inward dipping faults cutting through the volcanic edifice suggesting continuous interactions between tectonic and magmatic processes

large heat and fluid fluxes driven through mid plate outcrops on ocean crust geophysical data for the cocos plate sea floor suggest that basement outcrops along mid ocean ridge flanks can discharge very large quantities of heat and fluid this is indicative of high crustal permeability at the regional scale

fabric analysis using the intercept method abstract the intercept method is a convenient yet powerful method for the numerical analysis of fabrics for geological applications it can be used when a set of objects e g pores grains or aggregates of a specific mineral lineaments etc with unique characteristics can be identified in an image the intercept method analyses boundaries of objects as a population of lines how intercepts are definined is therefore important in order to establish the significance of the intercept counts when the method is applied to digital images the subdivision of the information into square pixels must also be considered we apply a linear filter which minimizes the effects of grid anisotropy on the counting of intercepts analysis of the resulting rose of intercept counts by a fourier series considerably facilitates the interpretation of the data a rose of directions can readily be derived for the phase boundaries if a population of objects can be assumed to have started with an originally isotropic orientation and to have been deformed passively the fourier components of the rose of intercepts also give the sectional strain the fourier components also permit an objective test of the validity of describing a fabric as resulting from a homogeneous strain on an initially isotropic section two computer programs for the counting and analysis of intercepts on digital images are presented and applied in four examples which illustrate the usefulness of the intercept method for magmatic fabric measurement strain analysis and lineament analysis we also illustrate the importance of fourier series decomposition of rose of intercept counts for fabric interpretations intercept results are also shown to be compatible with those derived by other methods eigenvector surfor inertia tensor autocorrelation methods

abrupt seasonal variation of the itcz and the hadley circulation 1 using global precipitation climatology project gpcp daily data we show that the seasonal migration of the global zonal mean intertropical convergence zone itcz is not smooth but jumps from the winter hemisphere to the summer hemisphere the abrupt migration is within 10 days detailed analyses reveal that the phenomenon of the abrupt seasonal migration of the itcz mainly exists over particular tropical domains such as indian ocean western and central pacific and south america which gives the rise of the jump of the global zonal mean itcz because the itcz constitutes the ascending branch of the hadley circulation we also examine whether there exists such an abrupt seasonal change in the hadley circulation it is found that the intensity of the hadley cells evolves smoothly with time however the horizontal scales of the hadley cells demonstrate abrupt seasonal changes corresponding to the abrupt seasonal migration of the global itcz the winter cell extends rapidly across the equator while the summer cell rapidly narrows this suggests that the solsticial cell is the dominant component of the hadley circulation and that the equinoctial symmetric pattern is ephemeral

preferred orientation and anisotropy of seismic and magnetic properties in gabbronorites from the bushveld layered intrusion abstract the preferred orientation of plagioclase and pyroxene in gabbronorites from the bushveld layered igneous intrusion south africa was investigated using electron backscatter diffraction in two localities 200 km apart belfast and rustenburg strong preferred orientation was observed with the principal fabric features aligned in the subhorizontal foliation plane defined by 010 planes of plagioclase and 100 planes of pyroxene the pattern appears to result from the orientation of tabular crystals during the dynamic intrusion events that formed the layered structure primary magmatic oxides are also influenced by the preferred orientation of plagioclase generating an oblate magnetic susceptibility fabric parallel to the foliation plane plagioclase preferred orientation gives rise to other directionally dependent geophysical properties including a large seismic anisotropy with p waves traveling 4 8 faster in the vertical than in the horizontal direction

determination of fabric and strain ellipsoids from measured sectional ellipses implementation and applications abstract geologists examine fabrics to constrain models of formation or of deformation of rocks and it is often convenient to summarise the results by a fabric ellipsoid as fabric data are commonly collected on planar sections through the rock estimating a fabric ellipsoid from sectional ellipses often with arbitrary orientations is an important task an algebraic method to calculate such an ellipsoid presented in an earlier paper has been implemented with the program ellipsoid it is used here on examples that illustrate questions and issues that arise when collecting selecting and processing sectional fabric data and when assessing the results the quality of fit of the ellipsoid to the data is assessed in all cases examples include a case in which the average sizes of markers on individual sections can be used in the determination of the ellipsoid and other cases in which such sizes are not useful a case in which sectional ellipses are not obtained from closed markers and a case in which data scatter and insufficient coverage of section orientations lead to a hyperboloid instead of an ellipsoid

the sonju lake layered intrusion northeast minnesota internal structure and emplacement history inferred from magnetic fabrics abstract the sonju lake intrusion sli in northeastern minnesota is a layered mafic complex of keweenawan age 1096 1 0 8 ma related to the midcontinent rift the cumulate paragenesis of the intrusion is recognized as broadly similar to the skaergaard intrusion a classic example of closed system differentiation of a tholeiitic mafic magma the sli represents nearly closed system differentiation through bottom up fractional crystallization geochemical studies have identified the presence of a stratabound 50 100 m thick zone anomalously enriched in au pge similar to the pge reefs of the skaergaard intrusion this pge enriched zone is hosted within oxide gabbro cumulates about two third of the way up from the base of the intrusion we present a petrofabric study using the anisotropy of magnetic susceptibility ams to investigate the emplacement and flow patterns within the sonju lake intrusion petrographic and electron microprobe studies combined with ams and hysteresis measurements indicate the primary source of the magnetic signal is pseudo single domain psd magnetite or titanomagnetite low field ams was measured at 32 sites within the sonju lake intrusion which provided information about primary igneous fabrics the magnetic fabrics in the layered series of the sonju lake intrusion are consistent with sub horizontal to inclined emplacement of the intrusion and show evidence that the cumulate layers were deposited in a dynamic environment well aligned magnetic lineations consistently plunging shallowly toward the southwest indicate the source of the magma is a vertical sill like feeder presumably located beneath the finland granite the finland granite acted as a density trap for the sonju lake magmas forcing lateral flow of magma to the northeast the strongly oblate magnetic shape fabrics indicate the shallowly dipping planar fabrics were enhanced by compaction of the crystal mush

submesoscale sea ice ocean interactions in marginal ice zones signatures of ocean eddies fronts and filaments are commonly observed within marginal ice zones mizs from satellite images of sea ice concentration and in situ observations via ice tethered profilers or underice gliders however localized and intermittent sea ice heating and advection by ocean eddies are currently not accounted for in climate models and may contribute to their biases and errors in sea ice forecasts here we explore mechanical sea ice interactions with underlying submesoscale ocean turbulence we demonstrate that the release of potential energy stored in meltwater fronts can lead to energetic submesoscale motions along mizs with spatial scales o 10 km and rossby numbers o 1 in low wind conditions cyclonic eddies and filaments efficiently trap the sea ice and advect it over warmer surface ocean waters where it can effectively melt the horizontal eddy diffusivity of sea ice mass and heat across the miz can reach o 200 m 2 s 1 submesoscale ocean variability also induces large vertical velocities order 10 m d 1 that can bring relatively warm subsurface waters into the mixed layer the ocean sea ice heat fluxes are localized over cyclonic eddies and filaments reaching about 100 w m 2 we speculate that these submesoscale driven intermittent fluxes of heat and sea ice can contribute to the seasonal evolution of mizs with the continuing global warming and sea ice thickness reduction in the arctic ocean submesoscale sea ice ocean processes are expected to become increasingly prominent

remote sensing of the fram strait marginal ice zone sequential remote sensing images of the fram strait marginal ice zone played a key role in elucidating the complex interactions of the atmosphere ocean and sea ice analysis of a subset of these images covering a 1 week period provided quantitative data on the mesoscale ice morphology including ice edge positions ice concentrations floe size distribution and ice kinematics the analysis showed that under light to moderate wind conditions the morphology of the marginal ice zone reflects the underlying ocean circulation high resolution radar observations showed the location and size of ocean eddies near the ice edge ice kinematics from sequential radar images revealed an ocean eddy beneath the interior pack ice that was verified by in situ oceanographic measurements

the east greenland polar front in autumn closely spaced salinity and temperature measurements in the region of the east greenland polar front from 75 n to 79 n in october november 1981 are presented the return atlantic current rac having a core of relatively warm and saline atlantic intermediate water aiw t 0 5 to 3 0 c s 34 9 to 35 0 was found everywhere along a steep front separating it from the colder fresher polar water a narrow frontal jet was found to have velocities greater than 0 80 m s where the station density was great enough to resolve its concentrated character notable fine structure was present especially in the warm aiw just east of the front a cold saline water forming a knee in the temperature salinity correlation was present in the upper margins of the rac the knee is formed primarily by warm aiw or atlantic water flowing under the upper layers of water flowing from the arctic ocean calculations are presented to show that an initially isothermal underflow could be modified to a thick thermocline by double diffusion calculations of the rate of cooling of fine structure elements by double diffusion indicate that the fine structure would have a limited lifetime about 12 days if its waters were not continually replenished

spring distributions of density nutrients and phytoplankton biomass in the ice edge zone of the weddell scotia sea we collected data on temperature salinity nutrient concentrations nitrate nitrite phosphate and silicic acid and phytoplankton biomass chlorophyll a particulate carbon nitrogen and biogenic silica in the upper 150 m in the marginal ice zone of the eastern scotia sea and northwestern weddell sea during november and early december of 1983 a distinct hydrographic front separating drake passage water from weddell and scotia sea surface waters was located at approximately 59 s and was the site of a consistent maximum in phytoplankton biomass in addition there was a pronounced phytoplankton biomass maximum associated with a surface salinity minimum near the northern limit of pack ice in the waters of the weddell scotia confluence that characterized the western portion of the study area in the eastern half of the study area characterized by largely unmodified weddell sea surface water the phytoplankton biomass near the ice edge was 2 5 times lower than that in the weddell scotia confluence but was increasing with time the water column structure nutrient fields and phytoplankton biomass distribution all suggest that the high phytoplankton biomass in the ice edge zone of the weddell scotia confluence and the lower but temporally increasing biomass near the ice edge in unmodified weddell sea water reflect ice edge phytoplankton blooms in different stages of their seasonal development a bloom had become well established in the waters of the weddell scotia confluence by mid november but the ice free vertically stable near surface water column necessary for enhanced phytoplankton growth had apparently not been present long enough for high biomass levels to develop within the weddell sea proper

mesoscale eddies in the fram strait marginal ice zone during the 1983 and 1984 marginal ice zone experiments during the summer marginal ice zone experiment in fram strait in 1983 and 1984 fourteen mesoscale eddies in both deep and shallow water were studied between 78 o and 81on sampling combined satellite and aircraft remote sensing observations conductivity temperature depth observations drift of surface and subsurface floats and current meter measurements typical scales of these eddies were 20 40 km rotation was mainly cyclonic with a maximum speed in several cases subsurface of up to 40 cm s observations further suggest that the eddy lifetime was at least 20 to 30 days five generation sources are suggested for these eddies several of the eddies were topographically trapped while others primarily formed by combined baroclinic and barotropic instability moved as much as 10 15 km d with the mean current the vorticity balance in the nontrapped eddies is dominated by the stretching of isopycnals accompanied by a change in the radial shear in the most completely observed eddy south of 79on the available potential energy exceeded the kinetic energy by a factor of 2 quantitative estimates suggest that the abundance of these eddies enhances the ice edge melt up to 1 2 km d

the interrelationship between magmatic and ore forming hydrothermal processes in the oman ophiolite the semail ophiolite of oman contains numerous gossans minor sulfide showings and ferromanganoan deposits as well as several massive sulfide deposits the largest of which 8 x 10 6 metric tons is the deposit of lasail detailed field mapping of the lavas and shallow intrusions around this deposit in conjunction with petrographic studies of their metamorphic assemblages enables the ore forming hydrothermal activity to be related to the location and evolution of an underlying magma chamber it can be demonstrated that the deposit formed in the short time interval between the eruption of a lava unit the geotimes unit at a marginal ocean basin spreading axis and the eruption of a second lava unit the lasail unit at an off axis or arc seamount moreover it was the seamount not the spreading axis magma chamber which drove the ore forming hydrothermal convection providing both a near surface heat source and by virtue of its intrusive pressure a localized fracture system on its flanks subsequent eruptions from this same magma chamber then provided a protective capping for the deposit the orientations and distributions of andesitic cone sheets show that the magma chamber lay some 1 5 km from the deposit itself and was in fact a magma cupola developed on the flanks of a much larger magma chamber similar though less detailed studies of other deposits in oman indicate that only very small mound deposits lie within the spreading axis lavas themselves the majority of deposits lie at the boundary between the spreading axis and seamount lavas and another group of deposits is related to the magma chambers that fed a third submarine lava unit the alley unit also associated with the construction of the seamounts these results may provide useful constraints for future mineral exploration programs in the oman and perhaps also in other ophiolite complexes and on the ocean floor

oceanography of the eastern bering sea ice edge zone in spring1 the ice edge region of the southeast bering sea was studied in terms of the hydrographic regime phytoplankton biomass and primary productivity during the springs of 1975 through 1977 the results showed that a phytoplankton bloom occurs at the ice edge just as the spring ice decay period begins and that this accounts for a significant proportion of the annual carbon input over the shallow shelf the bloom is intensified in time and space by the influence of the ice edge on the physical structure of the water column specifically melting ice seems to increase the stability of the water column near and under the ice by lowering the salinity frontal structure in salinity and temperature are apparent at the ice edge and are attributed to the melting ice but also at times to wind driven ekman type upwelling these data are also related to recent short term ca months year climatic fluctuations that seem to control the seasonal position of the ice edge zone relative to the shelf break in cold years the ice edge comes southward to the shelf break and overlies the more nutrientrich alaska stream bering sea source water in warm years the ice edge zone does not reach this nutrient rich water this may be important to the biology of the ice edge ecosystem the edge zones of seasonal sea ice are biologically productive serving as focal points for the congregation of large numbers of marine birds and mammals and thus represent ecologically critical habitats in subpolar regions the presence of a cold and solid boundary influences the biological regime in several ways including effects on the physical and chemical regimes in the adjacent seawater at least three structural features of the water column often associated with high oceanic primary production can occur in such an area simultaneously water column stability frontal structures and under certain conditions ice edge upwelling we show here that there is enhanced primary production due to water column stability and frontal structure at the edge of the seasonal sea ice in spring our data also suggest that ice edge upwelling occurs we show further that the intense

spatial and year to year patterns in new and primary productivity in sea ice melt regions of the eastern bering sea abstract four years of data on for new nitrate regenerated ammonium and primary carbon productivity 2007 through 2010 confirm the elevated productivity associated with the marginal ice zone miz of the eastern bering sea ebs in spring the greatest levels of productivity were associated with ice melt regions along the western edge of the ice pack population seeding and the shallowing of the mixed layer depth near the ice edge were less important in the development of elevated miz productivity than was the amount of ice melt entering surface water suggesting that ice contributed substances stimulating phytoplankton growth based on ice melt as an index of bloom development primary productivity continued to increase after new productivity peaked at the miz environments with optimal growth conditions new productivity averaged 18 6 mmol n m 2 d 1 with a ratio of 0 61 and primary productivity averaged 492 mmol c m 2 d 1 although these features were consistently recorded in late april early may they varied with the dynamics of ice cover whose retreat was later in 2008 relative to 2007 and 2009 the intense but localized miz blooms appear to be under sampled in ocean color imagery under ice productivity was generally low ave no3 0 45 mmol n m 2 d 1 ave primary prod 4 16 mmol c m 2 d 1 although larger values were measured under the western edge of the ice pack and in the st lawrence polynya region the advection of ice and water may contribute to the large values under the western ice edge and the highly transparent new ice may play a role in the polynya new and primary productivity rates of under ice samples were significantly inhibited when exposed to ice free irradiance levels in situ productivity could be estimated to 35 from rates measured on deck by adjusting for the impact of ice on submarine light the carbon to nitrate uptake ratio was closely related to specific carbon production in the in situ incubations

ice edge eddies in the fram strait marginal ice zone five prominent ice edge eddies in fram strait on the scale of 30 to 40 kilometers were observed over deep water within 77 n to 79 n and 5 w to 3 e the use of remote sensing a satellite tracked buoy and in situ oceanographic measurements showed the presence of eddies with orbital speeds of 30 to 40 centimeters per second and lifetimes of at least 20 days ice ablation measurements made within one of these ice ocean eddies indicated that melting which proceeded at rates of 20 to 40 centimeters per day is an important process in determining the ice edge position these studies give new insight on the formation propagation and dissipation of ice edge eddies

abrupt seasonal migration of the itcz into the summer hemisphere abstract although the maximum of solar radiation at the top of the atmosphere moves gradually from one hemisphere to the other as part of the seasonal cycle the intertropical convergence zone itcz moves abruptly into the summer hemisphere an axisymmetric circulation model is developed to study this rapid transition the model consists of an upper and lower layer of the hadley circulation hc with the surface layer attached to a slab ocean and the lower layer connected to the upper layer by a constant lapse rate the model is forced by solar heating and the itcz is prescribed to coincide with the warmest sea surface temperature sst the collocation of tropical rainfall with warm sst allows the model itcz migration to be understood in terms of the relative influence of solar heating and atmospheric dynamics upon ocean temperature atmospheric dynamics allow the itcz to move off the equator by flattening the meridional temperature gradient that would exist in radiative convective equilibrium for th

time dependent nonlinear hadley circulation the time dependent hadley circulation is studied numerically in a nonlinear nearly inviscid axially symmetric primitive equation model with the heating varying periodically on an annual cycle the annual average of the hadley circulation strength in this model with time dependent heating is about a factor of 2 stronger than the steady state response to the annual mean heating and is closer to the observed strength in the real atmosphere this is caused by the fact that heating centered off equator tends to produce stronger meridional circulation in the winter hemisphere than in the case when the heating maximum is located at the equator as pointed out previously by lindzen and hou however unlike the steady state solutions there is no abrupt change as the heating center is moved off the equator the temperature response in this time dependent model is simple to understand in the tropical region where there is a variable but persistent hadley circulation the temperature is homogenized latitudinally in the highlatitude region where there is no meridional circulation in the absence of the eddies the temperature response goes through an annual cycle with a phase lag relative to the phase of the heating this response is as predicted by the simple time dependent temperature equation in the absence of meridional circulation

drilling to gabbro in intact ocean crust sampling an intact sequence of oceanic crust through lavas dikes and gabbros is necessary to advance the understanding of the formation and evolution of crust formed at mid ocean ridges but it has been an elusive goal of scientific ocean drilling for decades recent drilling in the eastern pacific ocean in hole 1256d reached gabbro within seismic layer 2 1157 meters into crust formed at a superfast spreading rate the gabbros are the crystallized melt lenses that formed beneath a mid ocean ridge the depth at which gabbro was reached confirms predictions extrapolated from seismic experiments at modern mid ocean ridges melt lenses occur at shallower depths at faster spreading rates the gabbros intrude metamorphosed sheeted dikes and have compositions similar to the overlying lavas precluding formation of the cumulate lower oceanic crust from melt lenses so far penetrated by hole 1256d

relation of material exchange between sea ice and water to a coupled ice ocean ecosystem at the hokkaido coastal region of the okhotsk sea 1 in this paper the material exchange between the sea ice and the water just below the ice and its relation to the lower trophic ice system are examined using field observations in the hokkaido coastal region of the okhotsk sea and a coupled ice ocean ecosystem model which in detail formulates the material exchange between the ice and the water the accuracy of the model is confirmed by a comparison of the results of the numerical computation with the observations the estimation of the transport of the organic carbon and nutrients based on the computation demonstrates that the physical coupling effect between the ice and water plays a prominent role in supplying the nutrients from the water to the ice ecosystem and in efficiently releasing the organic matter produced by the primary producer in the ice ice algae as a result this study quantitatively clarifies that the physical coupling effect tidal mixing and biological activity in the ice drive the material cycle in the ice and water under the ice

a satellite derived climatology of the itcz abstract this paper presents fundamental climatological characteristics of the intertropical convergence zone itcz in a simple concise manner using the highly reflective cloud hrc dataset this satellite derived dataset uses both visible and infrared observations to measure the frequency of occurrence of large scale convective systems over the global tropics at a 1 spatial resolution these dataset characteristics make the hrc particularly well suited for climatological analysis of the itcz because the dataset is based on estimates of organized deep convective cloud systems rather than observations of clouds as a whole and it provides the spatial resolution needed to identify thew large wale convective structures furthermore the dataset covers a time period extending nearly two decades which provides for a fairly robust climatology and the opportunity to examine seasonal and interannual variability of both the convection and the latitude of the itcz

textural character of gabbroic rocks from pito deep a record of magmatic processes and the genesis of the upper plutonic crust at fast spreading mid ocean ridges

deformation of granitoids at low metamorphic grade i reactions and grain size reduction abstract deformation and chemical reaction in granitoids at greenschist facies conditions were investigated in samples from three shear zones two from the alps corvatsch granodiorite and aiguilles rouges granite switzerland and one from eastern australia wyangala granite when examined by light and electron microscopy all show similar features of deformation that progressed from coarse parent rock through to fine grained mylonite quartz deformed plastically while both k feldspar and plagioclase fractured and recrystallized in conjunction with chemical change which had as its end point an assemblage albite quartz white mica caal silicates k feldspar and calcic plagioclase depending on fluid chemistry from the parent rock were unstable at low metamorphic grades in the presence of aqueous fluid since ca bearing plagioclase was not stable in these environments myrmekite did not replace k feldspar in any of the rocks examined recrystallization of feldspar which should perhaps be termed neocrystallization was initiated predominantly at clast margins or along microfractures that are marked by fluid inclusions and twin offsets in old feldspar grains particularly in plagioclases dislocations exist in wall like structures that are commonly associated with voids suggesting origins in microfractures these dislocations had severely limited mobility and subgrain rotation does not appear to have contributed to recrystallization we conclude that recrystallization mainly occurred via a classical nucleation mechanism with minor contributions from twin boundary migration we argue that the 450 550 c lower limit for recrystallization of feldspar referenced throughout the literature is not applicable to the rock systems under investigation and should be discarded as a universal limit microfracturing microboudinage and reaction are seen as the prerequisites for mylonite formation from coarse grained granitic rocks at low metamorphic grades see part ii of this paper neocrystallization fluid access and nucleation appear to have accompanied or immediately followed the first deformation increments and were primarily responsible for continued grain size reduction transgranular fracture was comparatively important only at the onset of deformation since the formation of shear zones in granitoids commonly takes place under conditions of low metamorphic grade in the presence of aqueous fluids in the earth s crust breakdown reactions and nucleation recrystallization in feldspars may be important influences upon localization of deformation in granitoids

magmatic accretion and thermal convection at the sheeted dike complex gabbro boundary in superfast spreading crust odp hole 1256d abstract the magmatic processes responsible for accretion of new oceanic plutonic crust at fast spreading centers remain unclear expedition 312 at ocean drilling program hole 1256d on the eastern flank of the east pacific rise barely drilled through the uppermost gabbros but offers unparalleled opportunities to constrain deep magmatic processes and the mode of construction of the gabbroic layer gabbro 1 and gabbro 2 respectively 52 and 24 m thick were intruded in an altered and baked sheeted dike complex both gabbros lack a macroscopic fabric and were until now considered isotropic here we use digital 3 d fabric analysis of plagioclase phenocrysts in 33 non azimuthally oriented samples in contrast with previous observations the two gabbros display a distinct and consistent shape preferred orientation both gabbros exhibit magmatic equilibrated microstructures with minor submagmatic microstructures the calculated rayleigh numbers range between 10 15 and 10 18 proving that the gabbroic magma was initially undergoing turbulent magmatic flow magmatic foliations dip moderately with a mean of 48 in gabbro 1 and 61 in gabbro 2 magmatic lineations plunge in gabbro 1 between 1 and 44 mean 28 while in gabbro 2 plunges range from 6 to 69 mean 41 these inclined magmatic structures combined with the inclined magmatic contacts between the gabbros and their host rock show that these two gabbro bodies instead of being horizontal sills more likely are inclined intrusions that cut obliquely through the sheeted dike complex seismic reflection data around hole 1256d shows inclined reflectors similar to those produced by gabbroic saucer shaped intrusions in passive margins on the basis of the inclined fabrics inclined contacts and the regional seismic data we propose that the uppermost gabbroic intrusions at fast spreading centers form with a saucer shape this new shape of intrusion never reported before in the oceanic environment may constitute a significant component of oceanic accretion

distribution of planktic foraminifera at the ice margin in the arctic fram strait planktic foraminifera were collected in net tows 63 m along two east west transects at 78 and 80 n in the fram strait northern nordic seas at five concurrent depth intervals in the upper 200 m of the water column in the ice free zone absolute abundances in the upper 200 m of the water column up to 500 individuals m3 were obtained along the ice margin the absolute abundances reached up to 1250 ind m3 while in the ice covered areas not more than 50 ind m3 have been found surprisingly these strong variations in abundance are not accompanied by significant changes in faunal assemblages between the ice free and the ice covered regions neogloboquadrina pachyderma is the dominant species in most samples making up to 60 of the total faunal assemblage globigerina quinqueloba contributes 38 and all other species combined make up only 2 of the total fauna both absolute and relative abundances of the collected foraminifera are strongly dependent on the mesh size used using smaller mesh sizes provides a wider species spectrum which is of special interest for paleoceanographic reconstructions in the nordic seas where fossil assemblages 150 m often consist of only one species the specific hydrographic conditions in the fram strait with warm atlantic waters underlying cold polar surface waters result in a rather atypical depth distribution of the planktic foraminifera all species seem to prefer the temperate atlantic waters between 50 m and 200 m thus the species composition as well as geochemical tracers do not reflect the surface ocean conditions which again has potentially interesting implications for paleoceanographic reconstructions

saucer shaped sill with lobate morphology revealed by 3d seismic data implications for resolving a shallow level sill emplacement mechanism we use 3d seismic data to describe the 3d geometry of a large igneous intrusion the solsikke compound sill and address a number of issues related to sill emplacement the solsikke compound sill formed by amalgamation of a number of sills and exhibits a complex internal morphology dominated by saucer shaped depressions and linear discontinuities one of the saucer shaped sub elements of the compound sill the solsikke lobate sill has a previously unrecognized morphology it has a basal feeder and consists of a bifurcating network of interlinked lobe shaped sill segments we propose two models for the development of this intrusive style based on analogues from igneous systems and hydrofracturing experiments the lobate pattern indicates that the solsikke lobate sill was fed at its deepest point and adopted its geometry through outwards and upwards propagation the feeder location is coincident with a fault intersection suggesting that magma transport from the underlying source exploited the zone surrounding the intersection

magma flow inferred from ams fabrics in a layered mafic sill insizwa south africa the insizwa sill is a 25 km diameter 1000 m thick layered mafic intrusion part of the karoo igneous province in south africa the peridotitic and gabbronoritic rocks are undeformed and mineral fabrics demonstrably result from magma flow a horizontal centimeter scale model layering is visible in numerous outcrops plagioclase crystals are both tabular and elongated their preferred orientation parallel to the layering forms a foliation and a nw se lineation respectively interpreted as the magma flow plane and flow direction throughout the 78 stations of this study 699 specimens magnetic susceptibilities km range from 750 to 10 000 10 6 si the magnetic anisotropy pj ranges from 1 03 to 1 08 magnetic ellipsoids are both prolate and oblate average tjc0 anisotropy of magnetic susceptibility ams fabrics are dominated by multidomain to pseudo single domain magnetite high field magnetic experiments indicate that the paramagnetic contribution from the mafic silicates is less than 50 for low susceptibility rock types the anisotropy results from magnetite grain shape solely as shown by no significant increase in pj with increasing km the magnetic lineation 305j 0 5j is consistent throughout the sill at various scales and coincides with the mineral lineation in average in contrast the magnetic foliation 125j ne 10j is generally perpendicular to the mineral foliation and to the layering several explanations for this odd configuration are discussed the variations of magnetic parameters across the layering and field observations point to a multiple injection the magnetic lineation is consistent with the presence of a single feeder dike situated to the se of the sill d 2002 elsevier science b v all rights reserved

dykes cups saucers and sills analogue experiments on magma intrusion into brittle rocks magma is transported in the crust by blade like intrusions such as dykes sills saucers and also collects in thicker laccoliths lopoliths and plutons recently the importance and great number o

early cenozoic saucer shaped sills of the faroe islands an example of intrusive styles in basaltic lava piles abstract the early cenozoic igneous activity of the north atlantic igneous province that generated widespread sill complexes in sedimentary basins at the nw european margins also generated various intrusive systems in the contemporaneous basaltic lava pile of the faroe islands the faroe island basalt group comprises seven formations with a total thickness of about 6 5 km of which four major formations are built up of tholeiitic lava flows each being several hundred metres thick and three thinner formations are mostly built up of volcaniclastic lithologies each being a few metres to a few tens of metres thick the largest sills are exposed as partly saucer shaped bodies in the three uppermost formations where inner gently dipping basal sill sections gradually give way to more steeply inclined discordant outer rims that commonly cut several hundred metres into overlying lava flows numerous subvertical and moderately inclined dykes ranging in thickness from c 0 5 to c 4 0 m intersect the areas affected by sill intrusion but only inclined dykes or sheets have been positively identified as sill feeders locally controlled rotations of least principal stress axes 3 during initial sill intrusion or propagation may have been an important contributing factor in determining the overall geometry of the investigated intrusions

seismic structure of 15 ma oceanic crust formed at an ultrafast spreading east pacific rise evidence for kilometer scale fracturing from dipping reflectors 1 a grid of seismic reflection data from 15 ma cocos plate offers an unprecedented view of the structure of mature oceanic crust formed at an ultrafast spreading 200 mm yr full rate east pacific rise epr the data contain an unexpected quantity of bright reflectors throughout the crust generally 5 km in length significant reflection dip angles 10 30 are seen only on the isochron profiles and several reflectors have a confirmed isochron dip orientation certain upper crustal reflectors ucrs appear to form a single network with isochron dip the most prominent example apparent reflection coefficient 0 2 projects toward a 70 m disruption in the igneous seafloor and waveform analysis demonstrates that the reflector is likely the product of a low velocity zone on the order of tens of meters thick our observations suggest that the isochron dipping ucrs represent small slip kilometer scale faults fractures and none are primarily related to the seismic 2 3 boundary or to the sheeted dike gabbro transition lower crustal reflectors lcrs have no preferred orientation or regular pattern on the 30 km scale of this survey certain lcrs may be similar to the ucrs in origin while others may originate from near axis ductile flow lithologic banding off axis magmatism or some combination thereof overall reflectors in this area are abundant and complex consistent with previous off axis studies but at odds with observations of young crust 5 ma near the epr this dichotomy may be resolved by a delay in reflector formation through some combination of postaccretionary tectonics magmatism and hydrothermal alteration

gabbros from iodp site 1256 equatorial pacific insight into axial magma chamber processes at fast spreading ocean ridges the odp iodp multileg campaign at odp site 1256 cocos plate eastern equatorial pacific provides the first continuous in situ sampling of fast spreading ocean crust from the extrusive lavas through the sheeted dikes and down into the uppermost gabbros this paper focuses on a detailed petrographic and microanalytical investigation of the gabbro section drilled during iodp expedition 312 the marked patchy and spotty features that can be observed in many hole 1256d gabbros is mostly due to a close association of two different lithological domains in variable amounts 1 subophitic domains and 2 a granular matrix major and trace element mineral compositions geothermometry and petrological modeling suggest that subophitic and granular domains follow one single magma evolution trend formed by in situ fractionation the subophitic domains correspond to the relative primitive high temperature end member compositionally similar to the basalts and dikes from the extrusive unit upsection while the granular domains fit with a magma evolution by crystal fractionation to lower temperatures up to a degree of crystallization of 80 our results support the following scenario for the fossilization of the axial melt lens at odp site 1256 relatively primitive morb melts under near liquidus conditions fill the melt lens and feed the upper extrusive crust near the melt lens sheeted dike boundary at lower temperatures crystallization starts with first plagioclase before clinopyroxene in a mushy zone forming the subophitic domains at decreasing temperatures the subophitic domains continue to crystallize finally forming a well connected framework evolved residual melt is finally trapped within the subophitic network crystallizing at near solidus conditions to the granular matrix another important textural feature in hole 1256d gabbros is the presence of microgranular domains which are interpreted as relics of stoped assimilated sheeted dikes transformed to granoblastic dikes by contact metamorphism all these different domains can be observed in close association often at the thin section scale demonstrating the extremely complex petrological record of combined crystallization assimilation processes ongoing in the axial melt lens very similar gabbros with a marked spotty patchy appearance and bearing the same close association of lithological domains as observed at site 1256 are known in the so called varitextured gabbro unit from the oman ophiolite located at the same structural level between cumulate gabbros and granoblastic dikes the close petrological similarity of the gabbro dike transition between both iodp hole 1256d and the oman ophiolite suggests that in situ fractionation and dike assimilation contamination are major magmatic processes controlling the dynamics and fossilization of the axial melt lens at fast spreading oceanic ridges

cooling of the lower oceanic crust thermal models of mid ocean ridges that balance the influx of heat from magmatic sources with the removal of heat by conduction and hydrothermal circulation allow quantification of cooling of young oceanic crust these models reproduce key observations relating to crustal accretion and hydrothermal cooling at fast spreading ridges the rate of cooling is constrained both by the bathymetry of ridge axes and by olivine compositions from ophiolite gabbros successful models involve extensive hydrothermal cooling of the lower crust within 20 km of the ridge with 50 70 kw of hydrothermal cooling for every 1 m of ridge axis at crustal ages of 0 1 0 4 ma these timates can be used to refine global models of geochemical and thermal fluxes close to spreading ridges

anatomy of an active submarine volcano most of the magma erupted at mid ocean ridges is stored in a mid crustal melt lens that lies at the boundary between sheeted dikes and gabbros nevertheless images of the magma pathways linking this melt lens to the overlying eruption site have remained elusive here we have used seismic methods to image the thickest magma reservoir observed beneath any spreading center to date which is principally attributed to the juxtaposition of the juan de fuca ridge with the cobb hotspot northwestern usa our results reveal a complex melt body which is 14 km long 3 km wide and up to 1 km thick beneath the summit caldera the estimated volume of the reservoir is 18 30 km3 more than two orders of magnitude greater than the erupted magma volumes of either the a d 1998 or 2011 eruption our images show a network of sub horizontal to shallow dipping 30 features that we interpret as pathways facilitating melt transport from the magma reservoir to the eruption sites

petrography of the dike gabbro transition at iodp site 1256 equatorial pacific the evolution of the granoblastic dikes 1 the ocean drilling program odp integrated ocean drilling program iodp three leg campaign at site 1256 leg 206 expeditions 309 and 312 provides the first continuous in situ sampling of fast spread ocean crust from the extrusive lavas through the sheeted dikes and down into the uppermost gabbros cocos plate east pacific rise eastern equatorial pacific the lowest 60 m of the dikes above the gabbros were transformed to granoblastic dikes through a metamorphic overprint characterized by two pyroxene domains formed under granulite facies conditions equilibrium temperatures estimated by the two pyroxene thermometer range between 930 c and 1050 c implying that conditions within the granoblastic zone were appropriate for hydrous anatexis with the potential to generate partial melts of trondhjemitic composition the downhole evolution of the granoblastic overprint is expressed by systematic changes in texture phase composition and calculated equilibrium temperature consistent with thermal metamorphism by a deeper heat source thermal modeling implies a long lasting heat source located beneath the granoblastic dikes providing thermal energy over several thousands of years the most likely such source is a steady state high level axial magma chamber amc located at the base of the sheeted dike section we interpret the interval of granoblastic dikes as part of a dynamic conductive boundary overlying the amc

a fossil melt lens in the oman ophiolite implications for magma chamber processes at fast spreading ridges from seismic evidence we know that a small body of magma is present at mid crustal levels beneath most fast spreading ridges and that this small sill or melt lens overlies a much broader area of hot but largely solid material a crystal mush that constitutes the lower ocean crust beyond this however we have little direct knowledge of the physical and chemical processes that operate in and below the melt lens nor the role the melt lens plays in the storage and aggregation of mid ocean ridge basalts morb we here offer constraints on the processes of melt transport modification and residence beneath fast spreading ridges from a coupled structural and geochemical study through the crustal section of the oman ophiolite concentrating on the uppermost plutonic rocks and transition into sheeted dykes we find that almost the entire oman plutonic suite the layered gabbro and most of the high level gabbro is dominated by cumulate rocks containing very low proportions of trapped interstitial melt the exception to this is the very uppermost part of the section within 150 metres of the base of the sheeted dyke complex at which level the gabbros instead display a marked heterogeneity of structure texture and composition and plutonic rocks of generally basaltic composition occur for the first time associated pegmatitic ferrogabbros formed by in situ fractionation of these liquids this horizon passes up into a more homogeneous microgabbroic facies also of basaltic composition within which isolated asymmetric doleritic chilled margins are found and thence into doleritic sheeted dykes we argue that the thin heterogeneous gabbro horizon is a fossilised melt lens containing pooled liquids of net basaltic composition mg of 65 expelled from the crystal mush beneath existing models have suggested that steep fabrics observed in homogeneous gabbros beneath this horizon formed by subsidence of originally horizontal cumulus layers formed at the base of the melt lens but this is not supported by the field relationships instead we propose that the fabrics record the buoyant ascent of magma through the mush pile probably in part by porous flow and reflect crystallisation essentially in situ without significant vertical transport of the mush low residual melt porosities in the sub melt lens region imply efficient extraction of interstitial liquid and at least episodically high permeabilities in the upper part of the lower crust

the josephine ophiolite northwestern california the 157 m y old josephine ophiolite is a complete ophiolite consisting of the following units harzburgite tectonite cumulate ultramafics cumulate gabbro interlayered with cumulate ultramafics cumulate gabbro high level gabbro and diorite a 1 5 km thick sheeted dike complex and 0 4 km of pillow lava and breccia the ophiolite is conformably overlain by the galice formation consisting of a thin siliceous pelagic sequence overlain by a thick sequence of turbidites having both volcanic arc and continental margin sources the ophiolite and overlying galice formation were intruded by numerous 150 to 151 m y old calc alkaline dikes and sills followed shortly by deformation and regional metamorphism under conditions of prehnite pumpellyite to lower greenschist facies the josephine peridotite makes up the base of the ophiolite and covers 800 km2 it is an alpine type peridotite that represents upper mantle material and the residue of partial melting ultramafic rocks overlying the josephine peridotite are olivine spinel clinopyroxene cumulates that grade upward into clinopyroxene and orthopyroxene olivine plagioclase cumulates and finally to clinopyroxene plagioclase cumulates high level gabbros and diorites are characterized by highly variable textures complex intrusive relationships strongly zoned plagioclase and abundant mafic dikes plagiogranites occur at this level as dikes small intrusions and screens between mafic dikes but they are rare the sheeted dike complex consists of mafic dikes averaging 0 6 m in thickness chilled margins are locally well preserved and many of the dikes have been split and intruded by younger dikes resulting in half and marginless dikes the dike complex is composed of 100 sheeted dikes near the center but contains gabbro screens near the base and pillow lava and breccia screens in its upper parts the dikes are inclined at 40 to bedding after correcting for folding and are inferred to have been rotated shortly after formation the extrusive sequence consists predominantly of pillow lavas but contains abundant pillow breccias and some massive lavas some of the breccias formed as talus deposits whereas others are graded and matrix supported indicating transport and redeposition possibly in an area of rugged submarine topography the dikes and lavas have geochemical affinities to island arc tholeiites but are in some aspects transitional to mid ocean ridge basalts the dikes and lavas are cogenetic with the underlying plutonic sequence as indicated by similarity in crystallization sequence contradictory intrusive relationships between sheeted dikes and high level plutonic rocks and lack of diabase dikes in the lowermost cumulates and harzburgite the upper portions of the ophiolite were hydrothermally metamorphosed at the spreading center resulting in downward changes in mineralogy texture and 18o in addition metalliferous sediments and massive sulfides that occur overlying and within the pillow lavas probably were formed by precipitation from thermal springs a geothermal gradient of 250 350 c km is inferred from mineral assemblages on the basis primarily of its regional setting the ophiolite is inferred to have formed in a back arc basin in particular it is within a thrust sheet sandwiched between a coeval magmatic arc complex and a slightly older arc complex remnant arc this interpretation is consistent with abundant volcanic arc detritus in graywackes overlying the ophiolite the island arc magmatic affinities of the lavas and dikes may be the result of formation of the ophiolite during the earliest stages of back arc spreading

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

a coupled ice ocean model of upwelling in the marginal ice zone a dynamical coupled ice ocean numerical model for the marginal ice zone miz is suggested and used to study upwelling dynamics in the miz the nonlinear sea ice model has a variable ice concentration and includes internal ice stress the model is forced by stresses on the air ocean and air ice surfaces the main coupling between the ice and the ocean is in the form of an interfacial stress on the ice ocean interface the ocean model is a linear reduced gravity model the wind stress exerted by the atmosphere on the ocean is proportional to the fraction of open water while the interfacial stress ice ocean is proportional to the concentration of ice a new mechanism for ice edge upwelling is suggested based on a geostrophic equilibrium solution for the sea ice medium the upwelling reported in previous models invoking a stationary ice cover is shown to be replaced by a weak downwelling due to the ice motion most of the upwelling dynamics can be understood by analysis of the divergence of the across ice edge upper ocean transport on the basis of numerical model an analytical model is suggested that reproduces most of the upwelling dynamics of the more complex numerical model

a numerical study of mesoscale ocean eddy interaction with a marginal ice zone observations made during the marginal ice zone experiment mizex program indicated the presence of mesoscale eddies in a marginal ice edge ocean front in the east greenland current the eddies range in scale from 5 to 80 km physical mechanisms including barotropic and baroclinic instability may be responsible for their presence although the evolution of isolated eddies at low latitudes has been the focus of many studies the effect of ice cover on eddy evolution and vice versa has had less attention here an examination of the interaction of isolated mesoscale ocean eddies with a marginal ice zone is presented results are obtained with a two layer nonlinear primitive equation ocean model and a coupled free drift ice model in the absence of winds the ice equilibrates rapidly to the ocean eddy velocity resulting in radial ice motion the ocean sea surface slope is found to provide an important force in the ice momentum balance in no wind simulations with along ice edge 10 m s winds the ice responds largely to the wind and to a lesser extent to the ocean eddy under ice the ocean eddy can be rapidly eroded by wind driven ice motion cyclones anticyclones are rapidly destroyed by along ice edge winds with ice on the left right

submagmatic microfractures in granites microstructures in hercynian granite plutons of the pyrenees indicate fracturing of plagioclase crystals in the presence of melt this is represented mainly by quartz and or feldspar that fills fractures electron microprobe analyses demonstrate that in compositional agreement with the rims of the zoned plagioclase the feldspar infillings are more sodic with decreasing melt fraction fracturing resulted from concentration of stress at contacts between grains while the granite was submagmatic i e when the melt was below the critical fraction for magmatic flow material compositionally far from eutectic is petrologically the best candictate to develop submagmatic fractures because during cooling the volume fraction of melt remains low for a large temperature range a strong tendency for microfractures to be oblique to flow foliation may constitute a new criterion for shear sense in magmas

effects of el nino southern oscillation and north pacific weather patterns on interannual variability in the subarctic bering sea extraordinary interannual variability in ice cover air and sea surface temperatures sst and surface winds in the eastern bering sea have been observed over recent years to investigate the causes of this interannual variability long term 20 30 years time series of air ocean and ice parameters from the bering sea were cross correlated with the southern oscillation index soi an index of el nino southern oscillation enso events in the tropical southern hemisphere as well as with an index of pacific north american pna events in the north pacific five to thirty percent of the interannual variability linear regression with various smoothing in the bering sea data sets with the exception of surface winds is explained by the soi when the bering sea data lags the soi for comparison 29 52 of the variability in the sst off south america can be explained by the soi the signs of the correlations all suggest that warming in the bering sea follows negative anomalies in the soi that is enso events positive anomalies in the soi which tend to precede el nino events were found to precede cooling in the bering sea significant correlation persists for 18 20 months higher order polynomial regressions between the soi and bering sea data can explain up to 40 of the bering sea variability the mechanism for the connection between enso events and bering sea interannual variability appears to be of atmospheric nature and is associated with the winter position and intensity of the aleutian low the aleutian low is intensified and eastward of normal in association with el nino i e warm events but is weaker and westward of normal during cool events it is the regional winds associated with the variable position of the aleutian low that cause the regional warming and cooling events this seesaw in the aleutian low is also used to explain the out of phase ice conditions between the bering sea and the sea of okhotsk pna events are also associated with an intensified aleutian low as well as 700 mbar ridging over northwestern north america causing southerly flow over alaska however while correlation between enso events and pna was significant the correlation between the bering sea and pna was marginal except for surface winds here surface winds from the north were significantly correlated with the pna this apparent inconsistency as well as the lack of correlation of surface winds with the soi is explained by the lack of preferred site of the aleutian low during enso events this lack of preferred site helps explain why the major el nino event of 1982 1983 had little apparent effect on the bering sea

response of idealized hadley circulations to seasonally varying heating 1 the response of hadley circulations to displacements of the latitude of maximum heating is investigated in idealized axisymmetric and eddy permitting models consistent with an earlier study and with theory for the nearly inviscid limit lindzen and hou 1988 the strength of the hadley circulation is sensitive to displacements of heating the winter cell strengthens and summer cell weakens when the maximum heating is displaced off the equator however in conflict with the nearly inviscid limit but consistent with observations of earth s atmosphere the strength of an annually averaged hadley circulation is comparable to the hadley circulation driven by an annually averaged heating the disagreement between these results and the nearly inviscid limit is ascribed to vertical diffusion of momentum and dry static energy in the axisymmetric model and to baroclinic eddy fluxes in the eddy permitting model nonlinear amplification of the annually averaged hadley circulation is only seen near the upper boundary in simulations with a rigid lid near the tropopause suggesting that the amplification is an artifact of the upper boundary condition

atmospheric boundary layer structure and drag coefficients over sea ice this paper estimates the air sea drag coefficient for first year ice from recent aircraft measurements and reconciles the range of observed drag coefficients 103cd 1 2 3 7 referenced to 10 m for all sea ice types based on ice roughness and seasonal meteorology for the purpose of sea ice modeling it is necessary to define an effective drag coefficient which relates regional stress to regional wind because sea ice is heterogeneous on scales less than 20 km regional stress is influenced by the distribution of surface roughness the buoyancy flux from quasi periodic leads and external atmospheric conditions principally the inversion height 103cd is 1 3 1 5 for smooth ice but is much greater for nonflat surfaces for wind speeds greater than 5 m s and air temperatures below freezing the effective 103cd is 2 5 3 0 for nearly continuous pack ice such as first year ice in seasonal ice zones and central arctic basin the range of values of 103cd is 3 0 3 7 for unstable boundary layers typical of off ice winds in the marginal ice zone miz or even greater if the ice has been broken by a recent storm cd values at the lower end of these ranges are associated with low inversion heights these coefficients are confirmed by 103cd of 2 9 2 5 and 3 1 for first year sea ice calculated from gust probe data collected by the noaa p 3 aircraft interior to the inner miz in the bering sea during the marginal ice zone experiment mizex west in february 1983 and 103cd of 2 6 for the arctic calculated from arctic ice dynamics joint experiment aidjex aircraft data for february 1976 the effective drag coefficient with the presence of even a small concentration of sea ice is greater than the oceanic value as shown by a 103cd of 2 2 calculated from noaa p 3 gust probe data over a 40 km track of 0 4 ice concentration in the outer miz of the greenland sea in june 1984 during mizex 84 the relation of surface wind and stress to the geostrophic wind for shallow inversion heights typical of high latitudes is reviewed with a turbulent closure atmospheric boundary layer model the winter arctic is typified by low inversions 100 m low geostrophic drag coefficients and large geostrophic surface wind turning angles with low functional dependence on surface roughness seasonal ice zones are typified by a more modest influence of the inversion on boundary layer characteristics

preferred latitudes of the intertropical convergence zone abstract the latitude preference of the intertropical convergence zone itcz is examined on the basis of observations theory and a modeling analysis observations show that convection is enhanced at latitudes of about 4 to 10 relative to the equator even in regions where the sea surface temperature sst is maximum on the equator both linear shallow water theory and a moist primitive equation model suggest a new explanation for the off equatorial latitude preference of the itcz that requires neither the existence of zonally propagating disturbances nor an off equatorial maximum in sst the shallow water theory indicates that a finite width zonally oriented midtropospheric heat source i e an itcz produces the greatest local low level convergence when placed a finite distance away from the equator this result suggests that an itcz is most likely to be supported via low level convergence of moist energy when located at these preferred latitudes away from the equator for a plausible range of

saucer shaped intrusions occurrences emplacement and implications abstract magmatic intrusions and fluidized injected sands represent the two main types of sheet intrusions in the earth s crust in this paper we show that both intrusion types often display a saucer like geometry as revealed by 3d seismic imaging and field observations saucer shaped intrusions are fairly common in sedimentary basins as for example offshore in the norwegian and north sea basins and onshore in the karoo basin of south africa the formation of the saucer geometry is controlled by the low viscosity of the injected fluid and by the interaction between a growing shallow hydraulic fracture and overburden deformations statistics gathered from observations and modelling show a linear relationship between the depth of emplacement and the size of the saucer shaped intrusions we anticipate future cross disciplinary studies aiming to discover other occurrences of saucer shaped intrusions and to identify the physical processes controlling the development of this fundamental geometry

effects of the legacy of axial cooling on partitioning of hydrothermal heat extraction from oceanic lithosphere the predicted and observed heat flux across the seafloor these methods have assumed a dynamic steady state thermal system we show that this assumption is not warranted and leads to an incorrect partitioning of hydrothermal circulation between ridge axes and flanks to more accurately estimate hydrothermal heat loss on ridge axes and flanks we consider the spatial and temporal extent and vigor of axial hydrothermal circulation in calculating hydrothermal heat extraction axial fluid circulation perturbs the thermal state of oceanic lithosphere for 5 ma after that circulation ceases reducing the hydrothermal heat extraction on ridge flanks we find 30 of hydrothermal heat extracted on axis 10 extractednearaxis fromendofaxialhydrothermalcirculationto1ma and 60 extracted from lithosphere 1 ma

a numerical model of mesoscale physical biological interactions in the fram strait marginal ice zone a numerical model of marginal ice zones is presented which includes ice atmosphere ocean interactions and couples biological processes to the physical dynamics of the ice edge we have used initial conditions from the fram strait in spring when stratification is increasing nutrient concentrations are high and solar radiation is increasing conditions which are found prior to an ice edge phytoplankton bloom we present three sets of experiments 1 a standard case and variations resulting from different initial conditions with oceanic and ice melt stratification but no winds or eddies 2 one with wind forcing and ice cover but no eddies and 3 cases with cyclonic and anticyclonic eddies under ice cover in general stratification within the upper layers accelerates the growth and accumulation of phytoplankton when the stratification is due to ice melt only the bloom is horizontally constrained between the ice and the ice edge frontal structure maximum primary productivity occurs 7 to 10 days after the introduction of stratification and chlorophyll reaches a maximum approximately 3 days later the bloom s biomass is eventually limited by nutrients wind driven ice edge upwelling alone was ineffective in stimulating phytoplankton growth however any wind induced horizontal movement of ice either uncovers nutrient rich water or advects nutrients into open water which stimulates phytoplankton growth when a cyclonic eddy rotates under the ice a surface divergence results causing the ice to open in the center while upwelling at the eddy core injects nutrients into the euphotic zone anticyclonic eddies induce downwelling at the eddy s core and upwelling and surface divergence at the outer edges with the increased irradiance and high nutrient concentrations phytoplankton biomass within the eddy increases rapidly

impact of a warm anomaly on export fluxes of biogenic matter in the eastern fram strait as part of the hausgarten long term observatory sediment trap deployments were carried out before during and after the anomalously warm atlantic water inflow observed from 2005 to 2007 in the eastern fram strait downward export of particulate organic carbon poc zooplankton fecal pellet carbon fpc and biogenic particulate silica bpsi were measured from august 2002 to june 2003 and from july 2004 to july 2008 to indirectly assess the impact of the warm anomaly on phytoplankton and zooplankton communities in the region lower and less frequent bpsi fluxes were observed during most of the warm anomaly period reflecting a shift in phytoplankton community composition towards dominance of small sized phytoplankton under warmer conditions lower fpc fluxes observed concurrently with the lower bpsi fluxes may indicate a decrease in fecal pellet production due to changing feeding conditions in addition the export of smaller fecal pellets in fall 2005 and spring 2006 suggests a dominance of smaller zooplankton during the warm anomaly nonetheless bpsi and fpc export always increased in the presence of ice cover in the area above the sediment trap even during the warm anomaly period suggesting that sea ice is a key factor influencing the frequency of export events in the eastern fram strait the scarcity of ice over the sampling area in 2005 and 2006 may partly be due to the warm anomaly although solar radiation and ice drift due to wind stress also govern ice cover extent in the region overall the warm anomaly resulted in a shift in the composition of the export fluxes when associated with an absence of ice cover in the eastern fram strait