ionospheric effects during the total solar eclipse over southeast asia pacific on 9 march 2016 part 1 vertical movement of plasma layer and reduction in electron plasma density

a new mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of poc with ballast minerals abstract in simulation studies of the ocean s role in the global carbon cycle predicting the depth distribution for remineralization of particulate organic carbon poc is of particular importance following sarmiento et al global biogeochemical cycles 7 1993 417 most simulation models have the power law curve of martin et al deep sea research 34 1987 267 for this purpose the martin et al curve is an empirical fit to data most of which is from shallow floating sediment traps using such a fit implies that all the information necessary for prediction is contained in the carbon flux itself so that the organic carbon flux f oc z at any depth z can be predicted from the flux of organic carbon f oc z 0 at some near surface depth z 0 here we challenge this basic premise arguing that fluxes of ballast minerals silicate and carbonate biominerals and dust determine deep water poc fluxes so that a mechanism based model of poc flux must simultaneously predict fluxes of both poc and ballast minerals this assertion is based on the empirical observation that poc fluxes are tightly linked quantitatively to fluxes of ballast minerals in the deep ocean here we develop a model structure that incorporates this observation and fit this model to us jgofs eqpac data this model structure plus the preliminary parameter estimates we have obtained can be used to explore the implications of our model in studies of the ocean carbon cycle

controls on phosphorus concentration and accumulation in oceanic sediments understanding phosphorus p sedimentation in the ocean is important both for quantifying outputs in the marine phosphorus cycle and for determining the controls on phosphogenesis the authigenic formation of carbonate fluorapatite and phosphorite deposition large accumulations of p rich sediments on continental margins in this study i have compiled literature data on sedimentary p concentrations and sedimentation rates from continental margins phosphogenic continental margins and open ocean environments i have also calculated p accumulation rates the product of p concentration sediment density and sedimentation rate in these settings sedimentary p concentrations exhibit a similar range in a wide variety of oceanic environments and sedimentation rate conditions for example p concentrations in continental margin sediments range from 8 to 108 mol p g 1 with sedimentation rates from 80 to 8 000 m my 1 in open ocean sediments the p concentration range is similar 7 307 mol p g 1 even though sedimentation rates are generally about 100 times lower 2 50 m my 1 the exception to this are phosphogenic environments where p concentrations are exceptionally high 580 3 700 mol p g 1 while sedimentation rates are relatively low 20 310 m my 1 phosphorus accumulation rates appear to be controlled by sedimentation rate in ocean sediments although p concentrations generally exhibit similar ranges the large difference in sedimentation rates between various environments results in p accumulation rates that are several orders of magnitude higher in continental margins 90 8 000 mol p cm 2 kyr 1 compared to open ocean sediments 2 75 mol p cm 2 kyr 1 in the case of phosphogenic environments low sedimentation rates result in p accumulation rates 80 6 300 mol p cm 2 kyr 1 that are surprisingly similar to those of non phosphogenic continental margin sediments

does the arc accretion model adequately explain the paleoproterozoic evolution of southern laurentia an expanded interpretation comment and reply reply we were delighted to learn that karlstrom et al 2007 1 had written a comment on our recent article in geology one of our major purposes was to stir debate on the origin of the extensive paleoproterozoic crust of the southwestern united states this reply is intended not so much as a point by

ionospheric effects of the solar eclipse of march 9 1997 as deduced from gps data this paper presents data from first measurements of total electron content tec and its gradient during the solar eclipse of march 9 1997 obtained with the gps radio interferometer at irkutsk the interferometer consists of three receivers one turbo rogue snr 8000 and two ashtech z 12 located at the vertices of a triangle and spaced by about 3 5 km the measured tec variations are indicative of profound changes in the ion production process in the ionosphere attendant on the solar eclipse simultaneously in a large volume of space with a radius of at height 300 km at 300 km altitude the delay of a minimum value of tec with respect to the maximum phase of eclipse at 300 km altitude was about 10 min and the depression depth of tec growth varies from l 3 1016m 2 by analyzing the data on tec gradient variations one is led to conclude that the depression of tec growth during the eclipse is essentially independent of the longitude and of the latitude within the observation ranges 52 6 n and 104 11 e

proterozoic history and crustal evolution in southwestern colorado insight from u pb and sm nd data abstract new u pb age constraints and sm nd isotope data further establish the timing of magmatic and tectonic events from 1 8 to 1 4 ga in southwestern colorado and give insight into the interaction of crust and mantle systems during the assembly and evolution of orogenic belts along the southern margin of laurentia proterozoic orogenic events in the needle mountains led to crustal assembly thickening and tectonic reworking that was punctuated by periods of relative crustal stability pre 1 75 ga arc successions in southwestern colorado were produced and assembled into juvenile crust in an orogenic period that culminated in regional deformation and metamorphism that accompanied intrusion of synorogenic plutonic rocks from 1 73 to 1 71 ga emplacement of post orogenic plutonic rocks at 1 70 ga was followed by uplift and erosion and the deposition and deformation of siliciclastic sedimentary sequences paleoproterozoic crust underwent local melting and thermal metamorphism during invasion of felsic to mafic magmas at 1 43 ga that coincided with a pulse of intracratonic deformation invasion and melting of first cycle 1 8 1 7 ga crust at 1 71 and 1 43 ga involved heat and volatiles from mantle melts that were a catalyst for crustal melting and magmatic recycling sm nd isotopic signatures of 1 8 1 4 ga volcanic and plutonic rocks in southwestern colorado lend evidence to the emplacement of melts from depleted mantle and juvenile crust in the production continental crust with minor if any contamination by crust older than 1 8 ga the proterozoic magmatic record in southwestern colorado is consistent with continental growth by the addition of juvenile crust extracted from the mantle followed by periodic intracrustal growth during orogenic pulses in which mantle magmas underplate and melt the crust with consequent thickening

non recognition of continental tholeiites using the ti y zr diagram continental tholeiites cannot be identified using the ti y zr diagram two hundred and thirteen analyses from 16 localities representing 7 continental tholeiitic provinces all plot outside the within plate basalt field of this diagram

crystallinity and diagenesis of sedimentary apatites the crystallinity of sedimentary apatites was determined by fourier transform infrared spectroscopy ft ir using the splitting of a triply degenerate antisymmetric bending vibration of orthophosphate the crystallinity indices of recent marine apatites are low 3 0 3 6 while those of onland ancient apatites are high 4 5 7 8 indicating post depositional recrystallization the infrared spectra reveal that recrystallization is associated with a decrease in carbonate content substituting for po43 and an increase in fluoride order within the apatite structure the relationship between the crystallinity index and po43 18o suggests alteration of the primary isotopic composition by exchange reactions between po43 oxygens and surrounding waters the monterey samples have a large range of crystallinity index that reflects a set of complex and highly variable diagenetic conditions this demonstrates the use of ft ir criteria for differentiating between pristine and altered apatites and as a consequence for relating geochemical markers to formation or diagenetic environments it is suggested that only those samples that have low crystallinity indices c i 3 8 should be considered as pristine apatite spectra of fish remains indicate that differences in rare earth element ree patterns correspond to variations in crystallinity carbonate content and f order in the apatite lattice the fact that crystallinity is not correlated with geologic age suggests that environmental factors such as accumulation rate and pore water chemistry govern the recrystallization process in general sr content decreases and 18op exhibits high variability with increasing crystallinity

contrasting behavior of the f2 peak and the topside ionosphere in response to the 2 october 2013 geomagnetic storm in this study the ionospheric observations from ionosondes ground based gps receivers gravity recovery and climate experiment grace and metop a satellites and fabry perot interferometer over the asian australian sector have been used to investigate the responses of the f2 peak and the topside ionosphere to the 2 october 2013 geomagnetic storm particularly during the recovery phase the comparison between the multiple simultaneous observations revealed a contrasting behavior of the topside ionosphere and the f2 peak in east asia during the recovery phase the upward looking total electron content from low earth orbit leo satellites did not undergo such depletions as seen in the region near the f2 peak and they even showed increases furthermore the simulation results of the thermosphere ionosphere electrodynamics general circulation model are used to explore the possible mechanisms responsible for the observed features the model results and observations suggested that the contrasting behavior of the f2 peak and the topside ionosphere is mainly associated with the enhancement of the equatorward winds albeit the disturbed electric fields could play an important role in producing it

basinal and shelf sedimentation in relation to the archaean proterozoic boundary abstract in most countries the archaean proterozoic boundary has been designated as an unconformity between the oldest shelf type quartz arenites and a basement consisting of greenstone belts intruded by granitic rocks or high grade gneisses the quartz arenites have been characterized as shallow water shelf deposits and sediments in the greenstone belts as resedimented basinal wackes of volcanogenic origin radiometric ages for rocks of the canadian shield led to initial designation of the archaean proterozoic boundary as thus defined at about 2 5 ga subsequent age determinations have clearly established that a number of quartz arenites originally assigned to the proterozoic are 2 7 2 94 ga old e g witwatersrand and pongola supergroups of south africa to accommodate these old quartz arenites some have suggested that the arch aean proterozoic boundary should be regarded as diachronous embracing a span of time about equivalent to that of the phanerozoic however quartz arenites also are abundant in 3 2 3 5 ga old greenstone belts and high grade metamorphic terranes of south africa western australia and the u s a likewise large regions of basinal volcanogenic sediments occur in post 2 5 ga terranes this greatly expands the diachroneity of geological units that were initially regarded as either uniquely archaean or proterozoic we therefore recommend that chronometric and chronostratigraphic sense be retained for the archaean proterozoic boundary divested of the requirement for all quartz arenites to be proterozoic according to this analysis of the precambrian record shelf sediments have increased in abundance relative to basinal sediments through time but at different rates in different areas this change is attributable to progressive cratonization of shield areas a process that was strongly diachronous on a worldwide scale

an early proterozoic volcanic arc succession in southeastern wyoming the green mountain formation of early proterozoic age in the sierra madre range of southeastern wyoming comprises a bimodal mafic and felsic volcanic assemblage the rocks which are chiefly breccias agglomerates flows and volcaniclastic sediments represent both subaerial and submarine eruptions and in part were redeposited in fluvial and nearshore marine environments volcanic rocks are clearly calc alkaline in character and share a large number of geochemical features in common with continental margin arcs or evolved oceanic arc systems the low mg numbers and ni contents of the basalts require 30 40 olivine fractional crystallization and the high contents of the most incompatible elements high la sm n ratios and low zr nb ratios require an undepleted or enriched mantle source geochemical data are consistent with an origin for the felsic volcanics and associated encampment river granodiorite by shallow fractional crystallization of calc alkaline basalt in a tectonic setting similar to modern ar

short and long wavelength tids generated by the great american eclipse of 21 august 2017 on the 21 august 2017 the eclipse shadow drastically changed the state of the ionosphere over the united states this effect on the ionosphere is visible in the total electron content measured by global navigation satellite systems gnss the shadow moved with the supersonic speed of 1 000 m s over oregon to 650 m s over south carolina in order to exhaustively explore the ionospheric signature of the eclipse we use data of total electron content from 3 000 gnss stations seeing multiple global positioning system gps and global navigation satellite system glonass satellites to visualize the phenomena this tremendous dataset allows high resolution characterization of the frequency content and wavelengths using an omega k analysis based on 3 d fast fourier transform of the eclipse signature in the ionosphere in order to fully identify traveling ionospheric disturbances tids we confirm the generation of tids associated with the eclipse including tids interpreted as bow waves in previous studies additionally we reveal for the first time short 50 100 km and long 500 600 km wavelength tids with periods between 30 and 65 min the sources of the revealed short wavelength tids are co located with the regions of stronger gradient of the euv related to sunspots our work confirms and describes physical properties of the waves observable in the ionosphere during the great american eclipse

the impact of the january 15 2010 annular solar eclipse on the equatorial and low latitude ionospheric densities 1 the january 15 2010 solar annular eclipse crossed the magnetic equator in the middle of the day over india in a region instrumented with several magnetometers total electron content stations using gps data and an ionosonde located very near the center of the eclipse with the help of a one dimensional model appropriate for the region of interest we show that the ionosonde data was consistent with a lower f region plasma that was moving upwards with only modest velocities in the morning hours and moving resolutely downwards in the afternoon hours this motion agreed well with the local magnetometer data which revealed a weakened electrojet taking place in the morning hours while a full blown counter electrojet was present in the afternoon hours we show that the unusual solar eclipse induced electrodynamics resulted in a reduction in the total electron content depletion not just at the magnetic equator but also more markedly in the equatorial ionization anomaly eia zone a further 10 degrees to the north this latter point clearly shows that the eclipse led to a cut off in the supply of plasma provided through the equatorial fountain by altering a fundamental aspect of the equatorial electrodynamics

midlatitude ionospheric plasma temperature climatology and empirical model based on saint santin incoherent scatter radar data from 1966 to 1987 ionospheric plasma temperature variations have recently been studied based on incoherent scatter radar isr observations at a lower midlatitude site shigaraki in east asia otsuka et al 1998 and millstone hill a typical subauroral midlatitude site in north america zhang and holt 2004 the french saint santin isr with a geographic latitude slightly higher but an apex latitude 14 lower than millstone collected bistatic and quadristatic measurements for over two solar cycles beginning in september 1965 a database of these data containing observations between 1966 and 1987 has been used in this study in order to establish the midlatitude ionospheric climatology in particular that of the upper atmosphere thermal status as well as empirical models for space weather applications this paper presents in comparison with the millstone hill results variations of ion and electron temperatures ti and te with solar activity season time of the day and altitude the f2 region te at st santin is found to be lower than at millstone between march and july when the st santin electron density ne is relatively higher the midday te below 300 km increases with f10 7 as at millstone hill above 300 km it tends to decrease with f10 7 at st santin while it increases in summer at millstone hill ti between 250 and 350 km peaks midway between spring and summer we have also created st santin ionospheric models for ne te and ti using a bin fit technique similar to that used for the millstone hill models comparisons with corresponding iri predications indicate good agreement in ti at high solar activity and above the f2 peak te from the iri tends to be higher than both the st santin and millstone hill models

early proterozoic oceanic crust in the northern colorado front range implications for crustal growth and initiation of basement faults 1 early proterozoic oceanic crust exposed in a shear zone in the northern colorado front range provides insight into the tectonic evolution of the colorado province tectonically intermingled mylonitic amphibolite locally pillowed metagabbro clinopyroxenite metachert and melange are preserved within the buckhorn creek shear zone west of fort collins whole rock geochemical data support formation of the igneous protoliths in an oceanic environment major and trace element data overlap samples from modern oceanic ridges and are distinct from modern arc trends metagabbros and clinopyroxenites preserve a subhorizontal lineation defined by igneous pyroxenes core and mantle microstructures indicate initial deformation at temperatures 900 c secondary amphiboles define both subhorizontal and subvertical lineations kinematic analysis indicates that the rocks experienced e w strike slip deformation prior to and during amphibolite facies metamorphism followed by n s shortening 40ar 39ar data from secondary hornblende yield age steps as old as 1 9 ga based on the chemical data and kinematic evidence for strike slip deformation we propose that the buckhorn creek rocks originated at an oceanic ridge transform intersection the high t pyroxene fabrics formed during ocean floor deformation prior to 1 7 ga regional deformation of the colorado province the buckhorn creek fragment likely represents original oceanic basement for 1 8 1 7 ga arc magmatism and sedimentation that ultimately formed the colorado province continental crust reactivation of original oceanic fracture zones may be responsible for the network of regularly spaced northeast trending shear zones in colorado once formed subvertical transform faults are likely to survive the transition from oceanic to continental crust and persist as long lived crustal discontinuities

a proterozoic volcano plutonic terrane gunnison and salida areas colorado early proterozoic supracrustal rocks near gunnison and salida colorado include tholeiitic basalt dacite to rhyolite and intercalated sedimentary rocks these were intruded by essentially synchronous gabbroic sheets folded and intruded by major plutons ranging from quartz diorite to granite preservation of primary volcanic and sedimentary features is good to excellent sedimentary rocks in the gunnison area are mostly turbidite wackes whereas near salida they are mostly near source volcaniclastic rocks u pb age measurements on zircons indicate that the earliest bimodal volcanic rocks erupted between 1770 and 1760 m y ago and were intruded by granitic plutons between 1760 and 1750 m y ago renewed bimodal volcanism occurred between 1740 and 1730 m y ago and was followed by a period of deformation producing two fold sets before 1725 m y ago when the first of a series of younger plutons was emplaced the compositions and features of the sedimentary rocks and their association with volcanics are con

geochemistry nd and sr isotopes and u pb zircon ages of granitoid and metasedimentary xenoliths from the navajo volcanic field four corners area southwestern united states abstract proterozoic granitoid xenoliths from the navajo volcanic field nvf in the southwestern united states range in composition from tonalite diorite to granite with the latter greatly dominating there is no apparent relationship between chemical or isotopic composition and age geographic location or degree of alteration or deformation of the xenoliths two of the major ages of proterozoic plutonism recognized in the southwest 1 75 1 70 yavapai and 1 45 1 41 ga anorogenic are represented by the nvf xenoliths in some instances within a single diatreme we did not find any xenoliths in the 1 65 1 62 ma mazatzal range the xenoliths are dominantly i types and both nd and sr isotopes and trace element distributions indicate juvenile arc sources approximately 1 8 ga the granite magmas may have been produced by either vapor absent partial melting or fractional crystallization of a tonalite parent juvenile sources must have been available for melting in each of the three periods of magma production and hence some juvenile 1 8 ga crust in this region must have escaped melting in the first two episodes of magmatism and deformation metasedimentary xenoliths are chiefly biotite sillimanite schists garnet biotite schists and garnet paragneisses these three groups are strikingly similar in chemical and isotopic composition suggesting similar graywacke pelite protoliths the schists appear to be limited to the far northern part of the volcanic field consistent with a possible crustal boundary in the basement compositional and thermobarometric results suggest that the biotite schist xenoliths are not restites but that the paragneisses may be mixtures of melt and restite sedimentary protoliths may have been deposited in a forearc basin and later tectonically transported to the deep crust during one or more arc continent collisions in the late paleoproterozoic

a regional ionospheric tec mapping technique over china and adjacent areas on the basis of data assimilation in this paper a regional total electron content tec mapping technique over china and adjacent areas 70 degrees e 140 degrees e and 15 degrees n 55 degrees n is developed on the basis of a kalman filter data assimilation scheme driven by global navigation satellite systems gnss data from the crustal movement observation network of china and international gnss service the regional tec maps can be generated accordingly with the spatial and temporal resolution being 1 degrees x1 degrees and 5min respectively the accuracy and quality of the tec mapping technique have been validated through the comparison with gnss observations the international reference ionosphere model values the global ionosphere maps from center for orbit determination of europe and the massachusetts institute of technology automated processing of gps tec data from madrigal database the verification results indicate that great systematic improvements can be obtained when data are assimilated into the background model which demonstrates the effectiveness of this technique in providing accurate regional specification of the ionospheric tec over china and adjacent areas

ionospheric electron content within the equatorial f 2 layer anomaly belt this paper describes some new results on the day to day behavior of the location of the equatorial anomaly in the columnar electron content the measurements were made from a unique network of stations covering dip latitudes from 0 n to 25 n during the period in 1975 1976 near sunspot minimum when the ats 6 satellite was visible from india the latitudinal distribution of the total electron content on a particular day was found to depend only on the strength of the electrojet current as determined by the difference of the horizontal magnetic field at stations on the magnetic equator and another outside the equatorial electrojet rather than on the horizontal magnetic field measured only at the equatorial station during magnetically disturbed periods the presence or absence of the anomaly was also found to depend only upon the strength of the electrojet current the varying electrojet current that is the equatorial electric field is very effective in moving the ionization to the anomaly latitudes of 15 20 but the columnar electron content over the magnetic equator remains relatively constant

a study of tomographically reconstructed ionospheric images during a solar eclipse the low latitude ionospheric tomography network litn consists of a chain of six naval navigation satellite system nnss receiving stations established along 121 e longitude from a geographic latitude of 14 6 n to 31 n it is specifically designed to observe large scale ionospheric variations over the equatorial anomaly region by using tomographic imaging techniques recently the network litn was applied to observations of the october 24 1995 solar eclipse two dimensional images of ionospheric electron density during the eclipse period were reconstructed these images and the corresponding results from a nearby ionosonde were compared with those for a reference day it is shown that during the eclipse day the ionosphere experienced some large scale changes in particular four episodes of electron density enhancement or depression have been identified 1 the maximum enhancement occurred before the maximum phase of the solar eclipse at approximately 7 10 n geomagnetic latitude at the 275 300 km ionospheric height 2 the second enhancement appeared roughly 3 1 2 hours after the maximum obscuration at 15 22 n geomagnetic latitude and 300 325 km ionospheric height 3 the largest electron density depression occurred roughly 2 hours after the maximum obscuration at approximately 9 15 n geomagnetic latitude and on both the bottom and topside ionosphere 4 the second depression occurred about 4 hours after the maximum obscuration at approximately 5 5 n geomagnetic latitude and mainly on the topside ionosphere more detailed study suggests that the two enhancements have their origins in the ionospheric day to day variations the first depression is related to the combined photochemical and the equatorial fountain effects and the second depression may have its origin in geomagnetic coupling between conjugate ionospheres these observations are interpreted within the framework of ionospheric dynamics in the equatorial anomaly region

bow and stern waves triggered by the moon s shadow boat 1 it has been predicted that the moon s shadow the cooling region sweeping over the earth s atmosphere with a supersonic speed could trigger bow waves since 1970 the longest total solar eclipse within next hundred years occurring on 22 july 2009 sweeps over the eastern asia region during the noontime period an analysis of the hilbert huang transform hht is applied to study ionospheric tec total electron content derived from ground based gps receivers in taiwan and japan we not only find the feature of the predicted bow wave but also the stern wave on the equator side of the eclipse path as well as the stern wake right behind the moon s shadow boat the bow and stern waves are formed by acoustic gravity waves of periods about 3 and or 5 minutes traveling equatorward with a phase speed of about 100 m s in the ionosphere

day to day variability of the equatorial ionization anomaly and scintillations at dusk observed by guvi and modeling by sami3 1 the day to day variability in ionospheric irregularity generation giving rise to equatorial scintillation has remained an unresolved issue over many decades we take a fresh look at the problem utilizing the global imagery provided by the global ultraviolet imager guvi instrument on nasa s thermosphere ionosphere mesosphere energetics and dynamics satellite guvi has been acquiring images of 135 6 nm emission in the earth s ionosphere thermosphere system since 2001 these guvi disk images at dusk have been used to identify cases where the equatorial ionization anomaly eia crests lie near the magnetic equator over a relatively narrow longitude range so that the anomaly looks collapsed a 16 month period of guvi data collected during evening at solar maximum is used to study the morphology of these so called collapses since the eia collapse is shown to be linked to the suppression of equatorial plasma bubbles and scintillations in particular we look at the june solstice during which the atlantic and pacific show very different climatology and eia collapses are most frequent in the guvi data on the other hand eia collapses are a relatively rare occurrence during the equinox period when scintillations are most prevalent globally we obtained a few dramatic examples of day to day variability in eia behavior and scintillations over india the sami3 is also a model of the ionosphere sami3 model was used to investigate the conditions during the evening collapse of the anomaly in the indian longitude sector where measurements of total electron content tec and scintillations and estimates of the daytime vertical drifts and those at dusk were available results from sami3 show that the observed collapse of the anomaly at dusk can be simulated by a reversal of the upward vertical drift in midafternoon in agreement with the drift estimates from magnetometer observations such reversed vertical drifts at this time of the day are generally seen during counterelectrojet events introduction of neutral winds into sami3 better approximates the dusk behavior of tec at low latitude stations in india this study reveals that the longitudinally confined eia collapse may explain some of the differences in day to day variability of scintillations at different locations around the globe

refining the early history of the mojave yavapai boundary zone rifting versus arc accretion as mechanisms for paleoproterozoic crustal growth in southwestern laurentia abstractthree outstanding questions regarding paleoproterozoic crustal growth and assembly in southwestern laurentia are 1 the mechanisms of crustal growth back arc rifting and associated juvenile magmatism vs accretion of juvenile arcs 2 the nature and significance of pre yavapai orogeny 1 70 ga deformation and 3 how the isotopically mixed boundary zone between the mojave and yavapai paleoproterozoic crustal provinces formed supracrustal successions associated with the mojave yavapai boundary zone in northwestern arizona are dominated by 1730 ma bimodal metavolcanic sequences and compositionally siliciclastic metasedimentary rocks with minor ultramafic rocks chert and carbonate this lithologic assemblage requires juvenile mafic volcanism in a basin that also received abundant quartz rich i e continental detritus a pre d1 first deformational event back arc rift setting for northwestern arizona best explains the observed supracrustal assemblage plutonic rocks that intrude the s

gnss observations of ionospheric variations during the 21 august 2017 solar eclipse u s national science foundation grant nasa grant nasa lws funding support muri grant onr

sediment carbon nitrogen and phosphorus cycling in an anoxic fjord effingham inlet british columbia sediment geochemistry as well as benthic exchange of nutrients was investigated in effingham inlet a fjord located on the west coast of vancouver island in barkley sound the effect of bottom water oxygenation on sediment carbon nitrogen and phosphorus cycling was compared at sites overlain by oxic and anoxic bottom waters the sites separated by only 3 kilometers were similar in terms of key diagenetic parameters including mass accumulation rate and bulk sediment organic carbon content thus allowing a focus on diagenetic effects attributable to depositional oxygen availability benthic flux chamber incubations sulfate reduction rate measurements measurements of solid phase and pore water chemical profiles were compared for the sites these comparisons reveal that diagenetic processes in the site overlain by oxic waters act to retain more phosphorus in the sediment relative to the anoxic site differences in phosphorus benthic fluxes and burial between the two sites most likely result from differences in organic matter cycling under aerobic versus anaerobic conditions and are not strongly influenced by cycling of p associated with metal oxide phases

early proterozoic assembly of tectonostratigraphic terranes in southwestern north america a 500 km wide early proterozoic orogenic belt in arizona and adjacent areas is divided into lithotectonic blocks by northeast and north trending shear zones structural and u pb zircon studies suggest that these blocks may have experienced different tectonic histories prior to their juxtaposition by thrust and strike slip movements on shear zones a northwestern province here called the yavapai province is composed of at least five tectonic blocks and was assembled at about 1700 ma a southeastern province here called the mazatzal province is composed of at least three blocks and was assembled and juxtaposed with the northwestern province during the mazatzal orogeny between 1695 and 1630 ma the diversity of seemingly incompatible 1700 ma tectonic regimes now in close proximity to each other and the absence of systematic cross strike changes in age and character of deformation plutonism and metamorphism suggest a model whereby the orogenic belt developed and north america grew by assembly of d

early proterozoic bimodal volcanic rocks in central colorado u s a part ii geochemistry petrogenesis and tectonic setting abstract the early proterozoic supracrustal rocks of the salida area of central colorado consist of strongly bimodal sequences of volcanogenic rocks the mafic rocks basalts basaltic volcaniclastics and related gabbro sheets are distinctly tholeiitic display a strong iron enrichment trend and typically contain less than 50 sio 2 the felsites are rhyolites to dacites and contain more than 70 sio 2 major and trace element modeling show that the mafic rocks underwent two stages of crystal fractionation the first involving olivine and plagioclase the second involving plagioclase and clinopyroxene fractionation occurred within individual injections as they rose toward the surface rather than in a single magma chamber at depth field relations and major element data support the derivation of the felsic rocks from a magma generated by anatexis of sialic crust however the low sr and high heavy ree concentrations in these rocks are not compatible with a partial melting model and suggest that the felsic volcanic rocks could have been derived by extensive fractional crystallization of the mafic magma normalized trace element abundances and trace element ratios of the mafic rocks are most like continental flood basalts such as the columbia river basalts they also display some similarity to immature back arc basin tholeiites developed on continental crust such as those of the sarmiento complex the felsic rocks have strong chemical affinities to within plate rhyolites rather than calc alkaline rhyolites from orogenic areas the chemical data as well as the petrographic stratigraphic and regional field data all indicate that the early proterozoic supracrustal rocks of the salida area developed along a continental margin probably within an immature back arc basin underlain by sialic crust remnants of the arc system of similar age may lie to the south in northern new mexico and southwestern colorado

the influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern united states this paper reports systematic changes in mudrock composition through time on a single con tinental cmstal block the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton the major and trace element distributions reflect different aspects of the provenance of the mudrocks in this study major elements record sediment recycling processes as well as changing proportions of sedi mentary and first cycle source rocks with the exceptions of kzo which tends to increase and sioz and a o3 which show no trend most major oxides tend to decline in relative abundance in younger mud rocks patterns shown by the index of compositional variability fe03 kro naao cao mgo mno tiojialro and by k20 a1203 indicate that the major oxide trends are due to decreasing proportions of nonclay silicate minerals and a concomitant increase in the proportion of clay minerals probably due to decreasing input of first cycle detritus coupled with recycling of sedimentary material excursions from progressive trends marked by increases in mgo k20 and cao reflect episodes of large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift the chemistry of low solubility trace elements in contrast is not sensitive to recycling effects and reflects the composition of first cycle input incompatible elements are progressively enriched relative to compatible elements in younger mudrocks and values for chondrite normalised rare earth elements also increase in addition the eu anomaly becomes systematically more negative in younger samples these trends cmnot be explained by diagenetic or weathering processes and therefore indicate that the proportion of fnc tionated granitic first cycle detritus being added to the sedimentary system becomes greater with time these results confirm the importance of tectonic setting in controlling mudrock chemistry and also demonstrate that there is a dynamic relationship between the tectonic evolution of a continental block and the composition of its sedimentary mantle

influence of boundary scavenging and sediment focusing on 234th 228th and 210pb fluxes in the santa barbara basin abstract sediment trap samples were collected from the santa barbara basin to examine the flux of 234 th 228 th and 210 pb mean ratios of measured to predicted fluxes are 2 10 and 21 for 234 th 228 th and 210 pb respectively boundary scavenging may supply a portion of all three radionuclides however sediment focusing supplies additional 228 th and 210 pb but little 234 th sediment temporarily deposited on the shelf around the basin contains little excess 234 th due to its short half life 228 th and 210 pb fluxes to the sediments in the santa barbara basin are several times greater than predicted from their supply in the overlying water column these enhanced fluxes require lateral transport of 228 th and 210 pb to the basin through boundary scavenging and sediment focusing 234 th flux is poorly correlated with 228 th and 210 pb fluxes because individual radionuclide sources to the basin differ i e water column production boundary scavenging and or sediment focusing correlations between 228 th and 210 pb fluxes are high due to the strong influence of sediment focusing on both radionuclides there is a strong correlation between both the 228 th and 210 pb flux and total mass flux and lithogenic flux but a weak correlation with the other major sediment components e g organic carbon carbonate and biogenic opal in the santa barbara basin a large fraction of the total mass flux is lithogenic material 50 80 hence the strong correlation between 228 th and 210 pb fluxes and both total mass and lithogenic fluxes 234 th flux is poorly correlated with total mass and major sediment component fluxes

ionospheric bow waves and perturbations induced by the 21 august 2017 solar eclipse u s national science foundation grant ags 1242204 nasa grant nnx17ah71g nasa lws muri grant onr15 foa 0011 onr n00014 17 1 2186

gps tec response to the 22 july 2009 total solar eclipse in east asia 1 the longest total solar eclipse of this century occurred in east and south asia on 22 july 2009 the eclipse was accompanied with a medium magnetic storm whose main phase onset occurred 27 min after the passage of the moon s umbral shadow using tec data from 60 gps stations we construct differential tec maps to investigate the ionosphere response to the solar eclipse in central china in the range of 26 n 36 n 108 e 118 e i e the magnetic latitude 15 n 25 n during the eclipse s totality a shadow in the ionosphere shown as tec depletion area was formed 100 km south of the moon s umbral path with a maximum decrease of 5 tecu the tec depletion area moved eastward following the movement of the totality area with a time lag of 10 min enhancements of tec due to the storm are observed after the main phase onset the relative drop of tec due to the solar eclipse is evidently larger at lower latitudes than that at higher ones and around noontime than that in the morning by modeling work we find that the latitudinal dependence of the tec response may result from latitudinal variation of magnetic inclination which influences the diffusion of ionization among different layers besides the local time dependence of tec response is closely related to the local time variation of background atmosphere density which affects the electron loss efficiency in the ionosphere

study of the evening plasma drift vortex in the low latitude ionosphere using san marco electric field measurements san marco d electric field measurements have been averaged in terms of the equivalent plasma drifts for days near the 1988 autumn equinox the observed plasma drifts provide a satellite based composite in altitude and local time of the evening enhancements in the zonal and vertical drifts and the shear in the zonal drift the satellite data reveal details of the postsunset plasma drift vortex which have been studied in radar and chemical release experiments the averaged drift data show a proportional relationship between the prereversal enhancement of the vertical drift and the zonal derivative of the zonal drift this relationship suggests that the vertical drift enhancement is caused by a curl free response to the rapid increase of the zonal drift which in turn is tied to the f region zonal winds and the e region sunset the data also show a curl free drop off in altitude of the vertical plasma drift above and below the peak drift at 450 km altitude during the prereversal enhancement comparisons of the averaged data with results of coupled ionosphere electrodynamics models are used to examine the underlying causes of the evening plasma drifts the evening plasma drift vortex is shown to be a single drift structure with a single source the source of the evening drift vortex resides on the bottomside of the integrated f region just as originally supposed by rishbeth 1971 this dominant single source which is produced by the divergence of the wind driven current of the f region causes the evening enhancement of the eastward plasma drift the shear in the eastward drift and the prereversal enhancement of the vertical drift

on the height variation of the equatorial f region vertical plasma drifts we have used improved incoherent scatter radar measurements at the jicamarca radio observatory to study the height variation of the f region vertical plasma drift velocity driven by the zonal electric field during moderately quiet conditions preliminary results indicate a nearly linear change of the vertical drift velocity with altitude between 200 and 700 km but with considerable day to day variations in the value of the slope on the average the velocity gradients are positive in the late night and morning periods and negative during the afternoon and evening hours simultaneous vertical and zonal drift measurements confirm that the measured height variation of the vertical drift is consistent with the existence of a curl free electric field in the low latitude ionosphere the time dependence of the jicamarca vertical drifts extrapolated to higher altitudes closely resembles the diurnal variation of the drift component due to the zonal electric field observed at f region heights over arecibo

crustal evolution of southern laurentia during the paleoproterozoic insights from zircon hf isotopic studies of ca 1 75 ga rocks in central colorado lu hf depleted mantle model tdm ages obtained by analysis of zircons previously dated by u pb methods demonstrate that ca 1 75 ga bimodal paleoproterozoic rocks in the gunnison salida region of central colorado and by extension in much of the southwestern u s were formed by partial melting of preexisting crustal rocks the ages of which mostly ages greater than 2 0 ga indicate that range from 1 83 to 1 87 ga some calculated lu hf tdm even older crust was probably involved consistent with the limited presence of ca 2 5 ga xenocrystic zircons in some rocks these results suggest that rocks related to the trans hudson and penokean orogens are cryptically present much farther to the south than previously believed coupled with the bimodality of the volcanic suite in central colorado and indeed in much of the southwestern u s these results indicate that in contrast to current juvenile arc accretion models melting of older crust related to extensional tectonics played an important role in the genesis of many magmatic rocks between 1 6 and 1 8 ga

the prereversal enhancement of the zonal electric field in the equatorial ionosphere the electric fields in the ionospheric e and f regions near the magnetic equator often show a strong eastward enhancement shortly after sunset and before the eastward normally daytime field reverses to westward several theoretical models of the low latitude fields suggest that this enhancement is caused mainly or entirely by f region winds the f region dynamo but some authors have suggested that it could be produced solely by e region tidal winds we give here additional calculations and arguments in support of the f region source the enhancement of the eastward field for an eastward f region wind turns out to be a simple direct consequence of the fact that after sunset the ionospheric conductivity decreases far more rapidly in the e region than in the f region

nighttime ionospheric enhancements induced by the occurrence of an evening solar eclipse 1 the solar eclipse on 15 january 2010 traversed asia and completed its travel on the shandong peninsula in china at sunset two vertical incidence ionosondes at wuhan and beijing and the oblique incidence ionosonde network in north china were implemented to record the ionospheric response to the solar eclipse following the initial electron density decrease caused by the eclipse the ionosphere was characterized by a strong premidnight enhancement and a subsequent ionospheric decay and a 10 h later postmidnight enhancement neither geomagnetic disturbance occurred during the eclipse day nor did obvious nighttime peak appear for the 10 day mean of the f2 layer critical frequency fof2 the electron density profilogram of the beijing ionosonde indicates that the two enhancements were the result of the plasma flux downward from the top ionosphere possibly due to the steep decrease of the ionospheric electron density and plasma temperature during the solar eclipse the two dimensional differential fof2 maps present the regional variations of the nighttime electron density peaks and decay both the pre and postmidnight enhancements initially appeared in a belt almost in parallel with the eclipse track and then drifted southward the different magnitudes of greatest eclipse in the umbra and outside tend to account for the different occurrence times of the plasma flux the ionospheric decay following the premidnight enhancement is also considered as a consequence of the eclipse shade

age provenance and tectonic setting of paleoproterozoic quartzite successions in the southwestern united states new field studies combined with u pb zircon geochronology constrain the ages of deposition and sedimentary provenance of paleoproterozoic quartzite successions exposed in the southwestern united states orthoquartzites were deposited in short lived basins at two times ca 1 70 and 1 65 ga during crustal assembly of southern laurentia the more voluminous ca 1 70 ga successions occur in southern colorado northern new mexico and central arizona and are interpreted here to be time correlative though not necessarily deposited in the same basins detrital zircon from quartzites and metaconglomerates exposed in southern colorado and northern new mexico is characterized by a single population with a relatively narrow range of ages 1 80 1 70 ga and minimal archean input 5 of grains analyzed peak detrital zircon ages 1 76 1 70 ga vary slightly from location to location and mimic the age of underlying basement unimodal detrital populations suggest local sources and a first cycle origin of the orthoquartzites within a short time interval 1 70 1 68 ga during unroofing of local underlying basement the maximum age of quartzite exposed at blue ridge colorado is constrained by the 1705 1698 ma coarse grained granitoid basement on which quartzite was deposited unconformably the minimum age of ortega formation quartzite new mexico is constrained by ca 1680 1670 ma metamorphic monazite overgrowths these dates agree with direct ages on the lower mazatzal group arizona and suggest that orthoquartzite deposition occurred over a wide region during and soon after the ca 1 70 ga yavapai orogeny regional structural arguments and the thrust style of quartzite deformation suggest that the metasedimentary successions were deformed during the ca 1 66 1 60 ga mazatzal orogeny thus making them important time markers separating the yavapai and mazatzal orogenic events our model for syntectonic deposition involves extensional basin development followed by thrust closure possibly due to opening and closing of slab rollback basins related to outboard subduction the first cycle origin of orthoquartzites near the end of the arc collisions of the yavapai orogeny seems to contrast sharply with their extreme compositional maturity this can be explained in terms of protracted extreme diagenesis and or special environmental influences that enhanced chemical weathering but were unique to the transitional atmosphere and ocean chemistry of the proterozoic similarities among quartzites exposed throughout the southwestern united states and along the laurentian margin suggest that they represent a widespread regional and perhaps global episode of sedimentation involving a distinctive syntectonic setting and unique climatic conditions a combination that might make these units a signature lithology for paleoproterozoic time

does the arc accretion model adequately explain the paleoproterozoic evolution of southern laurentia an expanded interpretation a common model for the paleoproterozoic crustal evolution of southern laurentia involves southerly accretion of successively younger island arcs from 1780 to 1650 ma this model may be oversimplified however for although andesite and basaltic andesite major components of modern island arcs occur they are relatively rare and large volumes of rocks are dominantly bimodal metavolcanic assemblages and related granitoids ophiolites occur but they are also rare and only one accretionary melange has been described inherited zircons and common pb and nd isotopic data indicate involvement of older crust in ca 1750 ma rocks of the mojave province of southeastern california and western arizona and the bimodal assemblages of central colorado these data suggest that the bimodal volcanic rocks were derived from pre existing continental crust likely of ca 1850 ma trans hudson penokean age during extension and partial melting associated with the development of transpressional crustal scale shear zones the occurrence of the 1840 1 ma elves chasm pluton in the grand canyon demonstrates that rocks of trans hudson penokean age are present in southwestern laurentia

magnitude and composition of sinking particulate phosphorus fluxes in santa barbara basin california examined particulate p cycling in the santa barbara basin sbb off the coast of southern california using a 520 m deep moored sediment trap deployed from 1993 2006 and a sediment core collected in 2005 directly beneath the sediment trap at 590 m total particulate p tpp particulate inorganic p pip and particulate organic p pop were quantified using a 5 step sequential extraction method sedex that chemically separates pip into loosely bound oxide bound authigenic and detrital p phases pop fluxes while similar in magnitude to other coastal regions 22 10 mmol m 2 d 1 were a small component of the tpp pool 15 seasonal trends revealed significant increases in pop fluxes during upwelling due to increased biological production in surface waters by organisms that increased mineral ballast high particulate organic carbon poc to pop ratios 337 18 further indicated rapid and efficient remineralization of pop relative to poc as particles sank through the oxic water column however further reduction of pop ceased in the deeper anoxic waters loosely bound oxide bound and authigenic p dominated the tpp pool with pip fluxes substantially higher than those measured in other coastal settings strong correlations between oxide associated authigenic and detrital p fluxes with lithogenic material indicated a terrestrial source associated with riverine discharge furthermore more than 30 of the loosely bound and oxide bound p was remineralized prior to burial with the magnitude of dissolution far exceeding that of pop these results highlight the dynamic nature of the particulate p pool in coastal ecosystems and how changes in p source can alter the composition and lability of p that enters coastal waters

was magnetic storm the only driver of the long duration enhancements of daytime total electron content in the asian australian sector between 7 and 12 september 2017

the midlatitude f2 layer during solar eclipses observations and modeling national natural science foundation of china 40725014 40674090 40636032 national important basic research project 2006cb806306

geochemistry of the dubois greenstone succession an early proterozoic bimodal volcanic association in west central colorado abstract the dubois greenstone succession an early proterozoic supracrustal succession in west central colorado is composed of fine grained felsic volcaniclastic sediments ash flow tuffs and tholeiitic flows sills and dikes the volcanic rocks comprise a bimodal suite of tholeiite and rhyolite the tholeiites are divided into two groups group i exhibiting nearly flat ree patterns 20 30 chondrites and group ii with light ree enriched patterns 40 70 chondrites these groups can be produced by two stage melting of an undepleted or enriched garnet lherzolite source in which garnet remains in the residue of only the first melting stage which produces group ii magmas the felsic magmas can be produced by partial melting of a high grade gneiss in the lower crust in which zircon is entrained in the magma the dubois greenstone succession appears to have formed by felsic and mafic subaqueous eruptions in which some ash flows upon entering water underwent phreatomagmatic explosions giving rise to detritus which formed the volcaniclastic sediments although tectonic setting cannot be assigned to the succession with a high degree of confidence an immature back arc basin developed on sialic crust in consistent with most data

penetration of magnetospheric electric fields to the equator during a geomagnetic storm 1 penetration of the magnetospheric electric field to the equatorial ionosphere was examined for the geomagnetic storm on 6 november 2001 by analyzing the difference in magnitude of the geomagnetic storm recorded at the dayside geomagnetic equator yap 0 3 gml and low latitude okinawa 14 47 gml the penetrated electric field caused the dp2 currents at the equator i e eastward currents during the main phase of the storm while the overshielding currents i e westward currents dominated during the recovery phase it is shown that the ring current started to develop simultaneously with the onset of the equatorial dp2 within the temporal resolution of a few minutes these results imply prompt transmission of the dawn to dusk convection electric field to the inner magnetosphere as well as to the equatorial ionosphere it is found that the equatorial dp2 started to decrease one hour after the onset of the ring current development indicating shielding effects becoming effective at the equator during the latter half of the storm main phase the dp2 was then overwhelmed by the overshielding which resulted in the counter electrojet cej in the beginning of the storm recovery phase the image magnetometer chain data indicate that the westward auroral electrojet aej in the dawn sector was driven over midlatitude centered at 57 corrected geomagnetic latitude cgml during the main phase while the aej shifted rapidly poleward to the auroral latitude centered at 67 cgml in the beginning of the recovery phase the overshielding must be caused by the abrupt poleward shift of the rl facs as inferred from the poleward shift of the aej in addition to the decrease in their magnitude due to the decrease in magnitude of the southward imf the geomagnetic storm at the dayside geomagnetic equator was enhanced in amplitude with the ratio of 2 7 as compared with the geomagnetic storm at low latitude this amplification is a result of both effects of the dp2 currents and the cej associated with the main and recovery phases respectively it is suggested that the electric field associated with the dp2 currents contributed to the development of the ring current during the main phase while the overshielding electric field may contribute to cease developing the ring current during the recovery phase

ionospheric total electron content response to solar eclipses on october 24 1995 and march 9 1997 two solar eclipse events occur it is therefore of interest to investigate how the ionosphere responded to the eclipses five global positioning system gps ground based receivers are specifically designed to observe large scale ionospheric variations over the geomagnetic equatorial equatorial anomaly crest and midlatitude regions two dimensional images of ionospheric total electron content tec during the two eclipse periods are constructed the deviations in the tec images on eclipse days from those on reference days show that during the eclipse days the ionosphere experienced some large scale changes four features of the tec deviations pre ascension pa major depression md sunset ascension sa and secondary depression sd have been observed a detailed study shows that in geomagnetic low latitudes pas are possibly related to the locations of the equatorial anomaly crest the latitudinal location amplitude and occurrence time of mds suggest that the fountain effect is essential sas and sds occurring in geomagnetic equatorial and low latitudes and appearing respectively before around and after local sunset indicate that the prereversal enhancement plays an important role

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

ionospheric and geomagnetic response to the total solar eclipse on 1 august 2008 over northern hemisphere 1 the ionospheric and geomagnetic response to the total eclipse of the sun on 1 august 2008 over northern hemisphere has been examined using 14 gps three isr radar and three magnetometer ground based stations three different approaches were employed to examine the tec depletion occurrence at the gps stations determination of the tec depletion parameters during the solar eclipse with respect the quiet day tec variations comparison of the total tec tec during the solar eclipse period with respect to quiet day tec measurements for the same period of time and determination of the average daily tec obtained from eight gps stations and compares the values with the average quiet day tec at these stations the gps observations indicate obvious tec depression occurrence at all stations with the values was varying between 11 and 40 the observations show that tec depression at most gps stations started on the neck of the first contact of the eclipse followed by deeper negative deviation while the area of optical disk obscured getting larger periods of tec depletion were also observed before the first contact time of solar eclipse and after the fourth contact of solar eclipse due to earlier and later obscuration of the solar corona before and after the eclipse observation time the incoherent scatter radar observations at svalbard tromso and sondrestrom also show clear depletion occurrence in electron density electron temperature ion velocity and plasma cutoff frequency during the solar eclipse passage at these stations radar measurements show obvious difference in the ionospheric response between the e and f layers of ionosphere and between ion and electron temperature in the f layer the geomagnetic field response to the solar eclipse at cbb reso and nur stations was examined by using two different techniques first by comparing the daily variations of geomagnetic field during the eclipse period with the variations on the day before and day after the eclipse and second by determination the magnetic field with respect to the average quiet geomagnetic field the results show obvious decrease in the total field x and z components of geomagnetic field and obvious increase in the y component at both cbb and reso stations the depletion in x z and total field was in the range between 15 and 28 nt while the increase in the y component was 18 22 nt

feedbacks between oceanic redox states and marine productivity a model perspective focused on benthic phosphorus cycling a new model for the marine cycles of particulate organic carbon poc oxygen nitrate and phosphorus has been developed and applied to explore the controls and constraints on marine productivity and nutrient inventories the coupled benthic pelagic model uses a new approach for the simulation of the reactive phosphorus turnover preac corresponding to the sum of organic p authigenic p and adsorbed phosphate in marine sediments the simulated poc preac burial ratio in shelf slope and rise and deep sea sediments increases under strongly reducing conditions in agreement with field observation the model runs revealed that the spread of anoxia in bottom waters may enhance the productivity of the global ocean by one order of magnitude if sufficient nitrate is provided by n2 fixation thus anoxic bottom waters promote eutrophic conditions and vice versa additional model runs showed that the productivity and nutrient inventory of the glacial ocean were probably enhanced due to the falling sea level marine regression induced a narrowing of the depositional areas on the continental shelves and thereby an increase in the fraction of poc exported to the deep ocean the accelerated poc delivery in turn decreased the oxygen contents of the deep water and thus favored the release of phosphate from deep sea and rise sediments enhanced recycling of phosphate at the seafloor promoted further poc export in a positive feedback loop

phosphorus imbalance in the global ocean the phosphorus budget of the pre human modern ocean is constrained applying the most recent estimates of the natural riverine eolian and ice rafted input fluxes the phosphorus burial in marine sediments and the hydrothermal removal of dissolved phosphate from the deep ocean this review of current flux estimates indicates that the phosphorus budget of the ocean is unbalanced since the accumulation of phosphorus in marine sediments and altered oceanic crust exceeds the continental input of particulate and dissolved phosphorus the phosphorus mass balance is further tested considering the dissolved phosphate distribution in the deep water column the marine export production of particulate organic matter rain rates of phosphorus to the seafloor benthic dissolved phosphate fluxes and the organic carbon to phosphorus ratios in marine particles these independent data confirm that the phosphate and phosphorus budgets were not at steadystate in the pre human global ocean the ocean is losing dissolved phosphate at a rate of 11 6 x 1010 mol yr 1 corresponding to a decline in the phosphate inventory of 4 5 kyr 1 benthic data show that phosphate is preferentially retained in pelagic deep sea sediments where extended oxygen exposure times favor the degradation of particulate organic matter and the up take of phosphate in manganese and iron oxides and hydroxides enhanced c p regeneration ratios observed in the deep water column 400 m water depth probably reflect the preferential burial of phosphorus in pelagic sediments excess phosphate is released from continental margin sediments deposited in low oxygen environments the dissolved oxygen threshold value for the enhanced release of dissolved phosphate is 20 m benthic phosphate fluxes increase drastically when oxygen concentrations fall below this value

fertile granites of precambrian rare element pegmatite fields is geochemistry controlled by tectonic setting or source lithologies abstract a total of twenty fertile granites and their rare element pegmatite aureoles was examined to correlate their tectonic position relative to the preceding orogenic event with their geochemical signature namely li rb cs be ga sn nb ta y ree sc ti zr be th u f nyf the range of t time difference between metamorphism and or deformation and granite intrusion is 20 to 465 ma for the examined cases there is some tendency toward syn to late orogenic origin of lct s as opposed to post to anorogenic timing of nyf s but the correlation is poor compared to the previously accepted stereotype similarly both metaluminous and peraluminous fertile granites are about equally spread among syn late and anorogenic environments lct systems are largely associated with peraluminous granites whereas all metaluminous to peralkaline plutons bear the nyf signature tectonic control on geochemistry of granite pegmatite suites is poor and secondary to the fundamental influence of the source lithologies yielding granitic melts the lct type suites are derived from undepleted upper crustal lithologies suffering their first anatectic event which mobilizes the most volatile components into low temperature low percentage melts supracrustal sequences as well as ortho and para lithologies of their basement serve as protoliths with variable degrees of involvement the nyf type suites whose plutons have the geochemical signature of a granites may be derived by melting of depleted lower crustal sources residual after preceding anatectic events or possibly by melting of juvenile lithologies with short crustal residence differentiation from mantle derived magmas is highly improbable volatile extraction of nyf elements from the mantle and their pre enrichment in protoliths or melts seems to be required the few mixed systems with variable expressions of a nyf lct signature are derived basically as nyf suites but contaminated by the lct elements from undepleted upper crust via several possible mechanisms

u pb studies of zircon cores and overgrowths and monazite implications for age and petrogenesis of the northeastern idaho batholith u pb isotopic studies of zircons many containing xenocrystic cores with euhedral overgrowths and monazite from igneous rocks and metasedimentary inclusions of the northeastern idaho batholith yield linear arrays on concordia diagrams we interpret these as mixing lines between an old component cores and a young component overgrowths and zircons without cores the lower intercept of such arrays with concordia may yield the minimum age of the rocks if the overgrowths and zircons without cores are discordant or the crystallization age if they are concordant monazites yield apparently concordant ages either equal or less than the lower intercept zircon ages the samples studied yield lower intercept ages ranging from 73 5 pm 6 m y foliated quartz diorite to 46 5 pm 1 m y feldspar megacryst granite ages obtained are consistent with crosscutting relations observed in the field upper intercepts yield ages of 1700 to 2349 m y these are interpreted to indicate the mean age of xenocrystic zir

sheeting and dyking emplacement of the gunnison annular complex sw colorado abstract emplacement of the proterozoic gunnison annular complex colorado involved brittle failure and both subhorizontal sheeting and steeply dipping dyking the annular complex consists of a central diorite body 1730 ma surrounded by a ring of metamorphosed supracrustal rocks in turn ringed by tonalite and granodiorite 1721 ma the older central diorite was emplaced as sills parallel to bedding prior to regional deformation of the gunnison volcanic arc 1730 1710 m y ago this central body was deformed during regional shortening into an upright bowl with inward dipping walls the surrounding country rocks were folded and locally transposed against the central body forming an arcuate foliation conforming roughly to the shape of the body this foliation and bedding acted as mechanical planes of weakness which localized the syn deformational emplacement of the outer ring intrusions as multiple magma sheets parallel to steeply dipping bedding and foliation portions of the outer rings were also injected along concentric inward dipping shear fractures generated under high magma pressure a process similar to cone sheet emplacement in volcanic ring dyke complexes multiple mechanisms were therefore involved in the emplacement of this sheeted annular plutonic complex which otherwise superficially resembles a subvolcanic ring dyke complex

geochemistry and petrogenesis of early proterozoic amphibolites west central colorado u s a abstract early proterozoic supracrustal rocks exposed in west central colorado include amphibolites intimately associated with felsic volcanics and associated volcaniclastic sediments three successions are recognized the dubois succession 1770 1760 ma is comprised chiefly of amphibolites and felsic volcanics the amphibolites exhibit low concentrations of light ree and hfse and are broadly similar in composition to tholeiites from immature island arcs and in some respects to nmorb the cochetopa succession 1745 1730 ma includes large amounts of felsic volcanics and volcaniclastic sediments together with amphibolites that exhibit variable but slight incompatible element enrichment similar to basalts from evolved island arc systems and associated back arc basins the black canyon succession is coeval with the cochetopa succession and is comprised chiefly of volcaniclastic sediments with minor amphibolite these amphibolites exhibit significant incompatible element enrichment similar to basalts from continental margin arc systems geochemical modeling indicates that the amphibolites evolved by closed system fractional crystallization of depleted for the dubois succession to variably enriched parental basalts for the cochetopa and black canyon successions chiefly at shallow depths incompatible element distributions in the amphibolites indicate that mantle sources changed with time from relatively depleted 1770 1760 ma to variable but slightly enriched 1745 1730 ma a provisional model calls upon the dubois succession forming in an island arc system followed by collision with the archean wyoming province at 1750 ma the cochetopa succession was deposited in an intra arc basin developed within a new continental margin arc and the black canyon succession formed in a back arc basin associated with this arc