the kaidun chondrite breccia petrology oxygen isotopes and trace element abundances abstract oxygen isotope and trace element data for 13 samples of the kaidun chondritic breccia reaffirm the complex polymict nature of this unique meteorite bulk kaidun samples most closely resemble cr chondrites but the matrix is ci like two separated clasts are cr like but have some properties that resemble cm two clasts are enstatite chondrites one el and one eh one clast is an aubrite like metal rich impact melt and one clast is a unique layered olivine bearing pyroxenite with the isotopic composition of an aubrite yet although each clast resembles a known meteorite group all deviate in some respect from the norms for those groups collectively kaidun has sampled materials not yet represented in the world meteorite collections and which greatly extend the definitions of known meteorite groups phyllosilicates in kaidun span a very wide range in composition and vary from clast to clast suggesting that the aqueous alteration experienced by the clasts predated assembly of the kaidun parent body

the pribilof islands temperature salinity and nitrate during summer 2004 abstract the pribilofs comprised of st paul and st george islands and two smaller islands are a highly productive area on the western edge of the eastern bering sea shelf proximity to both the slope and more shallow shelf waters and the confluence of multiple physical domains differentiates conditions in this region from those in other areas on this shelf this is a unique domain in the bering sea that we refer to as the pribilof domain hydrographic and biological data were collected during a 2004 summer research cruise in this region the study undertook testing the hypothesis that on shelf intrusion of slope waters supplies nutrients to this multi domain area thereby seasonally influencing new primary production and consequently the entire marine ecosystem the pribilof domain is characterized by enhanced mixing particularly the area between st paul and st george islands organized anti cyclonic flow around st paul island around st george island and around the island group strong tidal currents and is a location where nutrient rich water from the bottom layer of the middle shelf and deeper water from the slope are vertically mixed to sustain production throughout the summer

geochemistry of the ungrouped carbonaceous chondrite tagish lake the anomalous cm chondrite bells and comparison with ci and cm chondrites i have determined the composition via instrumental neutron activation analysis of a bulk pristine sample of the tagish lake carbonaceous chondrite fall along with bulk samples of the ci chondrite orgueil and of several cm chondrites tagish lake has a mean of refractory lithophile element cr ratios like those of cm chondrites and distinctly higher than the ci chondrite mean tagish lake exhibits abundances of the moderately volatile lithophile elements na and k that are slightly higher than those of mean cm chondrites refractory through moderately volatile siderophile element abundances in tagish lake are like those of cm chondrites tagish lake is distinct from cm chondrites in abundances of the most volatile elements mean ci normalized se co zn co and cs co for tagish lake are 0 68 0 01 0 71 0 07 and 0 76 0 02 while for all available cm chondrite determinations these ratios lie between 0 31 and 0 61 between 0 32 and 0 58 and between 0 39 and 0 74 respectively considering petrography and oxygen isotopic and elemental compositions tagish lake is an ungrouped member of the carbonaceous chondrite clan the overall abundance pattern is similar to those of cm chondrites indicating that tagish lake and cms experienced very similar nebular fractionations bells is a cm chondrite with unusual petrologic characteristics bells has a mean ci normalized refractory lithophile element cr ratio of 0 96 lower than for any other cm chondrite but shows ci normalized moderately volatile lithophile element cr ratios within the ranges of other cm chondrites except for na which is low iridium co ni and fe abundances are like those of cm chondrites but the moderately volatile siderophile elements au as and sb have abundances below the ranges for cm chondrites abundances of the moderately volatile elements se and zn of bells are within the cm ranges bells is best classified as an anomalous cm chondrite

origin of fayalitic olivine rims and lath shaped matrix olivine in the cv3 chondrite allende and its dark inclusions we have studied an allende dark inclusion by optical microscopy scanning electron microscopy electron microprobe analysis and transmission electron microscopy the inclusion consists of chondrules isolated olivines and matrix which as in the allende host is mainly composed of 5 20 m long lath shaped fayalitic grains with a narrow compositional range fa42 2 and nepheline olivine phenocrysts in chondrules and isolated olivine grains show various degrees of replacement by 5 10 m wide fayalitic rims fa39 2 and 100 1000 m wide translucent zones which consist of 5 20 m long lath shaped fayalitic grains fa41 1 intergrown with nepheline these fayalitic olivines like those in the matrix of the dark inclusion contain 10 20 nm sized inclusions of chromite hercynite and fe ni sulfides the fayalitic rims around remnant olivines are texturally and compositionally identical to those in allende host suggesting that they have similar origins chondrules are surrounded by opaque rims consisting of tiny lath shaped fayalitic olivines 1 3 m long intergrown with nepheline as in the allende host fayalitic olivine veins may crosscut altered chondrules fine grained chondrule rims and extend into the matrix indicating that alteration occurred after accretion we infer that fayalitic olivine rims and lath shaped fayalites in allende and its dark inclusions formed from phyllosilicate intermediate phases this explanation accounts for 1 the similarity of the replacement textures observed in the dark inclusion and allende host to aqueous alteration textures in cm chondrites 2 the anomalously high abundances of al and cr and the presence of tiny inclusions of spinels and sulfides in fayalitic olivines in allende and allende dark inclusions 3 abundant voids and defects in lath shaped fayalites in the allende dark inclusion which may be analogous to those in partly dehydrated phyllosilicates in metamorphosed cm ci chondrites we conclude that the matrix and chondrule rims in allende were largely converted to phyllosilicates and then completely dehydrated the allende dark inclusions experienced diverse degrees of aqueous hydrothermal alteration prior to complete dehydration the absence of low ca pyroxene in the dark inclusion and its significant replacement by fayalitic olivine in allende is consistent with the lower resistance of low ca pyroxene to aqueous alteration relative to forsteritic olivine hydro thermal processing of allende probably also accounts for the low abundance of planetary noble gases and interstellar grains and the formation of nepheline sodalite salite hedenbergite pyroxenes wollastonite kirschsteinite and andradite in chondrules and ca al rich inclusions

the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

oxygen isotope thermometry of brazilian potassic volcanic rocks of kamafugitic affinities abstract oxygen isotope analyses have been obtained for magnetite and diopside from mafic alkaline volcanic rocks of kamafugitic affinities from brazil these rocks are part of the alto do paranaiba and santo antonio volcanic provinces of cretaceous age based on the clinopyroxene magnetite pair the isotopic temperatures obtained for the rocks of the two provinces are mafitites 1140 920 c leucitites 920 830 c kalsilitites 820 c analcimites originally leucitites 1060 1050 c cumulate pyroxenites 750 690 c the mata da corda alto paranaiba province and santo antonio da barra range in 18 o coincides with typical values for mantle derived magmas

influences of sea ice on the eastern bering sea ncar cesm simulations and comparison with observations abstract we examine the influences of sea ice on the eastern bering sea ebs regional oceanography on seasonal and inter annual time scales using the national center for atmospheric research community earth system model ncar cesm simulations comparing the modeling results with satellite and in situ observations when possible while the modeled mean seasonal cycle of ice cover in the ebs middle shelf is generally within the uncertainty range of satellite observations in the northern domain north of 59 n the simulation reaches its annual maximum in april instead of in march as observed by satellite remote sensing modeled ice reduction in late spring in the region is also slower than observations despite this bias the simulation captures the observed seasonal transit of freshwater from the north to the south via ice advection en route the sea ice melts cooling and freshening the local water column on inter annual time scales modeling results suggest that extensive ice cover persisting into spring in the central ebs leads to cold anomalies in the bottom water especially on the middle and inner shelves of the southern domain the corresponding salinity anomalies are positive in the northern coastal domain and weak but negative in the southern middle shelf the associated 10 m ocean current anomalies are southward on the shelf and directed offshore in the slope region comparing years 1961 2005 versus years 2005 2050 the probability distribution function of ice cover on the ebs middle shelf shifts northward by 2 latitude

carbon isotopes and light element abundances in carbonaceous chondrites stepped combustions of whole rock samples of orgueil ci murchison cold bokkeveld and murray cm renazzo cr allende and mokoia c3v carbonaceous chondrites were carried out between 200 and 1200 c at each step co2 was collected for carbon isotope measurement and so2 and h2o yields were measured nitrogen was combined for several steps all samples released most of their carbon between 200 and 400 c due to combustion of the organic matter bulk carbon concentration and isotopic composition of each meteorite are therefore closely similar to those of this predominant reservoir between 400 and 700 c carbonates decomposed in all meteorites but the c3vs carbon isotopes in these carbonates matched previously published values in renazzo the carbonates have a 13c close to 42 pdb similar to those of cm meteorites above 700 c all meteorites but the c3vs show one or two occurrences of very13c rich carbon carbon concentration decreases from 350 to 30 ppb c as temperature increases between 700 and 885 c 13c reaches 240 4 in orgueil 73 9 in murchison 130 9 in cold bokkeveld and 125 5 in murray and then decreases between 950 and 1060 c 13c reaches 177 8 in renazzo 335 1 in cold bokkeveld and 384 6 in murchison finally murray yielded 3 ppm of carbon with a 13c of 1164 in the 1125 1210 c combustion step a qualitative inverse correlation among the c2 meteorites between the carbon concentration and 13c above 700 c suggests that these distinct heavy carbon releases could be actually due to a single heavy carbon component

oxygen isotope studies of carbonaceous chondrites abstract the carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula these isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions we present a comprehensive set of whole rock analyses of cv co ck cm cr ch and ci chondrites as well as selected components of some of these meteorites a simple model is developed which describes the isotopic behavior during parent body aqueous alteration processes the process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition

circulation on the central bering sea shelf july 2008 to july 2010 1 we examine the july 2008 to july 2010 circulation over the central bering sea shelf using measurements at eight instrumented moorings hindcast winds and numerical model results at sub tidal time scales the vertically integrated equations of motion show that the cross shelf balance is primarily geostrophic the along shelf balance is also mainly geostrophic but local accelerations wind stress and bottom friction account for 10 40 of the momentum balance depending on season and water depth the shelf exhibits highly variable flow with small water column average vector mean speeds 5 cm s 1 mean peak speeds in summer 3 6 cm s 1 10 30 cm s 1 are smaller than in winter and fall 6 12 cm s 1 30 70 cm s 1 low frequency flows 1 4 cpd are horizontally coherent over distances exceeding 200 km vertical coherence varies seasonally degrading with the onset of summer stratification because effects of heating and freezing are enhanced in shallow waters warm summers increase the cross shelf density gradient and thus enhance northward transport cold winters with increased ice production and brine rejection increase the now reversed cross shelf density gradient and enhance southward transport although the baroclinic velocity is large enough to influence seasonal transports wind forced ekman dynamics are primarily responsible for flow variations the system changes from strong northward flow with coastal convergence to strong southward flow with coastal divergence for northerly and easterly winds respectively under northerly and northwesterly winds nutrient rich waters flow toward the central shelf from the north and northwest replacing dilute coastal waters that are carried south and west

the oxygen isotope record in murchison and other carbonaceous chondrites the ranges of 18o and 17o in components of the murchison c2 chondrite exceed those in all other meteorites analyzed previous authors have proposed that c2 chondrites are the products of aqueous alteration of anhydrous silicates a model is presented to determine whether the isotopic variations can be understood in terms of such alteration processes the minimum number two of initial isotopic reservoirs is assumed two major stages of reservoir interaction are required one at high temperature to produce the16o mixing line observed for the anhydrous minerals and another at low temperature to produce the matrix minerals the isotopic compositions severely constrain the conditions of the low temperature process requiring temperatures 44 extension of the model to the data on c1 chondrites requires aqueous alteration in a warmer wetter environment

oxygen isotope ratios in authigenic magnetites from the belden formation colorado authigenic magnetites from the belden formation at bassam park colorado were analyzed for their 18o 16o composition using secondary ion mass spectrometry the 18o values of magnetite rimmed pyrite magpy grains averaged 8 5 versus vsmow small 25 50 m iron oxide grains had a range of 18o values from 9 7 to 5 5 consistent with a variably hematized magnetite population having a 18o value of around 9 for magnetite the 18o results suggest that the magnetite rims and grains formed in contact with a water having 18o of near 0 or less implying a meteoric or connate source rather than a highly evolved orogenic or basinal fluid this supports paleomagnetic results that suggest the formation of authigenic magnetites under mesozoic burial conditions at some belden formation localities rather than in response to orogenic fluid migration driven by early tertiary tectonic uplift the 18o results also support the observation that chemical remanent magnetizations related to authigenic magnetite formation cannot be universally applied to the dating of fluid migration events associated with orogenic deformation

compositions and taxonomy of 15 unusual carbonaceous chondrites abstract we used instrumental neutron activation analysis and petrography to determine bulk and phase compositions and textural characteristics of 15 carbonaceous chondrites of uncertain classification acfer 094 type 3 0 ungrouped cm related belgica 7904 mildly metamorphosed anomalous cm like chondrite possibly a member of a new grouplet that includes wisconsin range wis 91600 dhofar 225 and yamato 86720 dar al gani dag 055 and its paired specimen dag 056 anomalous reduced cv3 like dag 978 type 3 ungrouped dominion range 03238 anomalous magnetite rich co3 1 elephant moraine 90043 anomalous magnetite bearing co3 graves nunataks 98025 type 2 or type 3 ungrouped grosvenor mountains gro 95566 anomalous cm2 with a low degree of aqueous alteration hammadah al hamra hah 073 type 4 ungrouped possibly related to the coolidge loongana c l 001 grouplet lewis cliff lew 85311 anomalous cm2 with a low degree of aqueous alteration northwest africa 1152 anomalous cv3 pecora escarpment pca 91008 anomalous metamorphosed cm queen alexandra range 99038 type 2 ungrouped sahara 00182 type 3 ungrouped possibly related to hah 073 and or to c l 001 and wis 91600 mildly metamorphosed anomalous cm like chondrite possibly a member of a new grouplet that includes belgica 7904 dhofar 225 and y 86720 many of these meteorites show fractionated abundance patterns especially among the volatile elements impact volatilization and dehydration as well as elemental transport caused by terrestrial weathering are probably responsible for most of these compositional anomalies the metamorphosed cm chondrites comprise two distinct clusters on the basis of their 17o values approximately 4 for pca 91008 gro 95566 dag 978 and lew 85311 and approximately 0 for belgica 7904 and wis 91600 these six meteorites must have been derived from different asteroidal regions

oxygen isotopes in asteroidal materials measurement of the variation of the 17o 16o and 18o 16o ratios of extraterrestrial materials has proven to be a key tool in understanding the formation and evolution of the solar system this chapter attempts to collate the huge data set of oxygen isotopic measurements of asteroidal material as sampled by meteorites in order to understand some of the processes involved in the formation of these primitive bodies and how such events have affected the oxygen isotopic ratios ultimately offering a window back to the very origin of solar system and its primordialoxygen isotopic heterogeneity oxygen is generally a major element in the gas liquid and solid phases that have interacted throughout the evolution of the solar system its chemical properties ensuring that there is abundant opportunity for reactions and exchange the details of which can be recorded in the isotopic ratios of the products such processes can be crudely subdivided into the following six categories early solar nebular isotopic heterogeneity high temperature modifi cation of nebular components metamorphism and melting in asteroids aqueous alteration in asteroids mixing of components brecciation terrestrial weathering it is clear from the isotopic variation in the earliest formed nebular components such as refractory inclusions and chondrules that there was considerable oxygen isotopic heterogeneity in the early solar nebula spanning over 50 and perhaps much greater in both 17o and 18o the origin of this variation is discussed elsewhere in this volume however isotopic exchange between the 16o rich solids and 17o and 18o rich gas phase s resulted in a wide range of isotopic variation in these early formed components offering insight into the conditions of these processes and the evolution of the reservoirs with time and or space once accreted onto the early planetisemals much of the primitive nebular components experienced considerable modification the metamorphism and melting experienced by some of these bodies most probably the result of heating from the decay of short lived radionuclides e g 26al resulted in progressive homogenization within individual bodies of any original isotopic heterogeneity complete homogenization appears to have been achieved in the hed parent body indicating very high levels of melting and the development of a large magma ocean the carbonaceous and ordinary chondrite parent bodies experienced more modest heating sufficient to mobilize water ice that accreted along with the more refractory materials the subsequent reactions between the liquid and solid phases at low temperature imparted large isotopic fractionations which record some of the conditions of this alteration such as water rock ratio temperature and isotopic signature and thus potentially the origin of the water ice the evolution of the asteroidal bodies has been far from simple and an important use of oxygen isotope measurements has been in the identifi cation of the components present in some meteorites the result of breakup reassembly and mixing of different bodies during impact processing the final oxygen isotopic signatures imparted into meteorite samples are those associated with terrestrial weathering the isotopic compositions of the weathering products depend on location primarily latitude while the magnitude of the weathering is dependent on many factors with some meteorites e g highly reduced enstatite chondrites and the matrix rich co3s particularly susceptible to such effects

the oxygen isotopic composition of olivine and pyroxene from ci chondrites the ci chondrites are taken to represent average solar system material based on the similarity of their elemental compositions to that of the solar photosphere however their oxygen isotope geochemistry is dominated by secondary minerals that formed during aqueous alteration on the ci parent body precursors to this alteration namely olivine and pyroxene are extremely rare in ci chondrites precluding previous measurements of their oxygen isotopic composition we report ion microprobe analyses of oxygen isotopes in single olivine and pyroxene grains separated from ci chondrites orgueil and ivuna the ci chondrite olivine and pyroxene grains most likely represent liberated chondrule phenocrysts based on petrographic chemical and isotopic evidence consistent with crystallization from a melt the oxygen isotope data form an array that falls nearly along the carbonaceous chondrite 16o mixing line with 18o values ranging from 9 3 to 12 3 o and 17o from 11 3 o to 7 8 o consistent with nebular processes being the source of the oxygen isotopic compositions the degree of 16o enrichment in orgueil olivines is negatively correlated with feo content but the exact nature and timing of the process that introduced this variation remains unknown the pyroxene oxygen isotopic compositions are similar to those of olivines with 5 mol fayalite the oxygen isotopic analyses of the olivine and pyroxene in ci chondrites have been used to revise previous models for the isotopic evolution of ci materials our data require more complete gas solid equilibration in the nebula and constrain the initial aqueous fluids on the ci parent body to have lower 17o values than previously postulated the refined model indicates that the temperature of aqueous activity on the ci parent body was no higher than 50 c and the fluid rock ratio was significantly less than previously estimated even prior to alteration and formation of secondary minerals the ci chondrites were the most 16o depleted carbonaceous chondrites and thus the solids originally contained in the ci chondrites are the most equilibrated nebular materials represented in the carbonaceous chondrites the data suggest the oxygen isotopic composition of average solar system to be approximately equivalent to average terrestrial oxygen as recorded in the compositions of terrestrial and lunar basalts

the hydrology of carbonaceous chondrite parent bodies and the evolution of planet progenitors oxygen isotope ratio data from carbonaceous chondrites are explained if aqueous fluids flowed from high to low temperatures within the parent objects of these primitive meteorites recognition of ancient hydrological activity on primitive asteroid precursors affords a new class of constraints on the heat sources ages and sizes of planet precursors in the early solar system based on the geological evolution of planetesimals

mars as the parent body of the ci carbonaceous chondrites the hypothesis that the ci meteorites have an origin on southern mars is presented this hypothesis is based on the ci containing a martian pattern of oxygen isotopes and mineralogy indicative of deposition by liquid water as found in several martian meteorites other correlation s are discussed a model of the formation of ci meteorites as being late planetary accretion material that was concentrated as bottom sediment of lakes or seas in early mars history is proposed the model accounts for the similarity to solar composition of the cis because during the late accretion on mars the upper regolith would receive material that was martian in isotopic abundance but primordial in composition

on the bering sea ice edge front an oceanographic field program was carried out along the bering sea ice edge in winter 1982 83 to investigate the temperature salinity front associated with and paralleling the winter ice edge currents were measured using taut wire moorings that were in place over winter and an intensive ctd survey was carried out of the frontal structure in midwinter february march the midwinter front separated cold 0 c more saline 32 5 outer shelf water the front had northwestward baroclinic currents paralleling the front ice edge with near surface speeds of 5 6 cm s and an associated transport of about 0 3 106 m3 s these baroclinic currents were superimposed on a regional barotropic along isobath flow resulting in north westward midwinter upper layer flows with monthly mean speeds exceeding 10 cm s an upper layer flow component was directed beneath the ice and provided heat adequate to melt the ice and limit advance of the edge the resulting low salinity meltwater was mixed vertically to maintain the front by wind acting across a highly mobile hydrodynamically rough ice cover subtidal fluctuations were not significantly affected by the front or the ice cover and local winds accounted for less than one quarter of the observed current variability the remainder being probably due to regional variations in the barotropic flow

stratification in the northern bering sea in early summer of 2017 and 2018 abstract we investigated spatial and interannual variation in the physical environment in the northern bering sea focusing on stratification which is one factor affecting biological production in arctic subarctic regions in particular we analyzed in situ data obtained onboard the training ship oshoro maru in early summer in 2017 and 2018 we found that stratification in the areas just north of st lawrence island around 64 5 n and west of 168 5 w and south southwest of st lawrence island was significantly weaker in 2018 than in 2017 these results are consistent with the extremely low sea ice extent present in the winter of 2017 2018 which would have resulted in less freshwater being supplied to the surface layers and a warmer and less saline bottom water conversely stratification was as strong in 2018 as in 2017 in the area close to the alaska mainland including the bering strait area suggesting that the alaskan coastal water dominates stratification in this area in early summer moreover we found that the weakly stratified water column in the bering strait area stratified quickly shortly after the occurrence of strong northerly winds likely because of the ekman transport of warm and low salinity alaskan coastal water from the east

oxygen isotopes in magnetite and fayalite in cv chondrites kaba and mokoia we report in situ measurements of o isotopic compositions of magnetite and primary and secondary olivine in the highly unequilibrated oxidized cv chondrites kaba and mokoia in both meteorites the magnetite and the secondary olivine fayalite fa90 100 have o isotopic compositions near the terrestrial fractionation tf line the mean 17o 17o 0 52 18o value is about 1 in contrast the compositions of nearby primary chondrule low feo olivines fa1 2 are well below the tf line 17o values range from 3 to 9 krot et al 1998 summarized evidence indicating that the secondary phases in these chondrites formed by aqueous alteration in an asteroidal setting the compositions of magnetite and fayalite in kaba and mokoia imply that the o isotopic composition of the oxidant was near or somewhat above the tf line in mokoia the fayalite and magnetite differ in 18o by 20 whereas these same materials in kaba have virtually identical compositions the difference between mokoia magnetite and fayalite may indicate formation in isotopic equilibrium in a water rich environment at low temperatures 300 k in contrast the similar compositions of these phases in kaba may indicate formation of the fayalite by replacement of preexisting magnetite in dry environment with the o coming entirely from the precursor magnetite and silica the 17o of the oxidant incorporated into the cv parent body as phyllosilicates or h2o appears to have been much 7 8 lower than that in that incorporated into the ll parent body choi et al 1998 which suggests that the o isotopic composition of the nebular gas was spatially or temporally variable

factors influencing physical structure and lower trophic levels of the eastern bering sea shelf in 2005 sea ice tides and winds abstract in spring and fall 2005 cross and along shelf transects were sampled to evaluate the influence of physical forcing including sea ice tides and winds on the lower trophic levels of the bering sea ecosystem the hydrography nutrients chlorophyll and zooplankton abundance and species composition were all affected by the presence or absence of sea ice on a north south transect along the 70 m isobath in may shelf waters between 59 n and 62 n were cold and relatively fresh and benthic invertebrate larvae and chaetognaths were a significant fraction of the zooplankton community while to the south the water was warmer saltier and the zooplankton community was dominated by copepods the position of the transition between ice affected and ice free portions of the shelf was consistent among temperature salinity nutrients and oxygen this transition in the hydrographic variables persisted through the summer but it shifted 150 km northward as the season progressed while a transition also occurred in zooplankton species composition it was farther north than the physical chemical transition and did not persist through the summer mooring data demonstrated that the change in the position of the transition in physical and chemical properties was due to northward or eastward advection of water onto and across the shelf from south to north along the 70 m isobath tidal energy decreased resulting in a less sharply stratified water column on the northern portion of the middle shelf as opposed to a well defined two layered system in the southern portion this more gradual stratification in the north permitted a greater response to mixing from winds which were homogeneous from north to south thus the physical and biological structure at any one location over the middle shelf is dynamic over the course of a year and results from a combination of in situ processes and climate mediated regional forcing which is dominated in most years by sea ice

physical forcing and nutrient conditions associated with patterns of chl a and phytoplankton productivity in the southeastern bering sea during summer abstract measurements of nutrients primary 14 c productivity and new nitrate productivity collected in the southeastern bering sea in july and august 2004 together with measurements from july 1981 are used to characterize the regional production system during summer and to analyze the major physical and nutrient factors controlling biological patterns the patterns of surface productivity suggested by the two different summers were remarkably similar in the regions of data overlap and agree with recent compilations of summer conditions from remotely sensed data summer was characterized by low production in the middle and outer shelf associated with surface mixed layers that were stabilized by heat elevated productivity was restricted to regions associated with the surface expression of thermohaline fronts as well as to tidally mixed regions adjacent to and between the pribilof islands based on chl a and productivity measurements the biological impact of the shelf break front of the southeastern bering sea extends at least as far inshore as the pribilof islands the existence of elevated summer productivity associated with a recently identified shelf partition front between the pribilof domain and the middle shelf domain east of st paul island was confirmed and its thermohaline nature resulting from cumulative intrusions of slope derived water is described yearly estimates of new and primary productivity compiled for the various biophysical regimes range from 1800 mmol n m 2 yr 1 and 170 g c m 2 yr 1 at the shelf break front to less than 700 mmol n m 2 yr 1 and 100 g c m 2 yr 1 in oceanic and coastal waters we hypothesize that trace metals rather than macronutrients or grazing likely restrict the seaward extent of elevated production at the shelf break front iron may be supplied to the front by isopycnal mixing from deeper shelf waters that were in contact with sediments by extending elevated production throughout the summer the thermohaline and tidal fronts enhance the coupling of primary production to epipelagic food webs for the large populations of fish birds and mammals in the region changes in the intensity or location of these frontal systems may impact populations that forage in them from the nearby pribilof islands

accretionary dust mantles in cm chondrites evidence for solar nebula processes abstract the texture and modal composition of fourteen carbonaceous chondrites of the cm group were studied in detail to unravel the origin of their various components and the evolution of their parent body ies the analysis and mapping of complete thin sections by scanning electron and optical microscopy revealed textural units in most samples in which all coarse grained primordial chondritic components chondrules chondrule fragments refractory inclusions particles rich in hydrous silicates pcp and various mineral fragments are coated by fine grained serpentine and tochilinite rich dust the dust mantled particles have spheroidal shapes and form a special lithology in which they are densely aggregated and compacted without any interstitial clastic material the dust mantles termed accretionary dust mantles and their host lithology called primary accretionary rock are interpreted as products of accretion processes in the solar nebula an origin by processes on the parent body is excluded for textural and mineralogical reasons most cm chondrites are affected by secondary impact induced brecciation of variable intensity except for yamato 791198 which is composed entirely of a primary accretionary rock obviously unaltered by secondary parent body processes such as aqueous alteration or brecciation the cm chondrites y74662 haripura cold bokkeveld kivesvaara mighei pollen nogoya y793321 alh 83100 murray and murchison consist of clasts of primary accretionary rock embedded in a fine grained clastic matrix derived from primary rock material the volume percentage of the clastic matrix ranges from 5 y74662 to 76 murchison bells and essebi are brecciated and affected by aqueous alteration to an extent that fragments of primary rock are not preserved the evaluation of literature data indicates that solar wind implanted noble gases are absent in the primary accretionary rock component of cm chondrites they are only present in brecciated samples it must be concluded from the relation between the content of trapped solar wind and degree of brecciation that 1 the solar noble gases are residing exclusively in the clastic matrix and 2 some cm chondrites are regolith breccias and others are fragmental or monomict breccias both types were formed on the parent body although the latter were never exposed to the solar wind based on the results of textural chemical and mineralogical investigations we conclude that a major portion of the water bearing phases in cm chondrites were produced by the hydration of refractory phases prior to the formation of dust mantles and prior to the formation of the recent cm parent body this process requires special physicochemical conditions which allow the crystallization of oh bearing silicates e g higher density of the nebula gas or special precursor planetesimals of the cm chondrite parent body

a probabilistic assessment of the next geomagnetic reversal author s buffett b davis w abstract 2018 american geophysical union all rights reserved deterministic forecasts for the next geomagnetic reversal are not feasible due to large uncertainties in the present day state of the earth s core a more practical approach relies on probabilistic assessments using paleomagnetic observations to characterize the amplitude of fluctuations in the geomagnetic dipole we use paleomagnetic observations for the past 2 myr to construct a stochastic model for the axial dipole field and apply well established methods to evaluate the probability of the next geomagnetic reversal as a function of time for a present day axial dipole moment of 7 6 1022 a m2 the probability of the dipole entering a reversed state is less than 2 after 20 kyr this probability rises to 11 after 50 kyr an imminent geomagnetic reversal is not supported by paleomagnetic observations the current rate of decline in the dipole moment is unusual but within the natural variability predicted by the stochastic model

on the recent warming of the southeastern bering sea shelf abstract during the last decade the southeastern bering sea shelf has undergone a warming of 3 c that is closely associated with a marked decrease of sea ice over the area this shift in the physical environment of the shelf can be attributed to a combination of mechanisms including the presence over the eastern bering sea shelf of a relatively mild air mass during the winter especially from 2000 to 2005 a shorter ice season caused by a later fall transition and or an earlier spring transition increased flow through unimak pass during winter which introduces warm gulf of alaska water onto the southeastern shelf and the feedback mechanism whereby warmer ocean temperatures during the summer delay the southward advection of sea ice during winter while the relative importance of these four mechanisms is difficult to quantify it is evident that for sea ice to form cold arctic winds must cool the water column sea ice is then formed in the polynyas during periods of cold north winds and this ice is advected southward over the eastern shelf the other three mechanisms can modify ice formation and melt and hence its extent in combination these four mechanisms have served to temporally and spatially limit ice during the 5 year period 2001 2005 warming of the eastern bering sea shelf could have profound influences on the ecosystem of the bering sea from modification of the timing of the spring phytoplankton bloom to the northward advance of subarctic species and the northward retreat of arctic species

oxygen isotopic evolution of the solar nebula studies of the three oxygen isotopes in chondrite meteorites demonstrate that diverse o reservoirs characterized by their 17o values were present in the solar nebula the discovery that some chondritic materials have o isotopic compositions that cannot be explained by mass dependent fractionation of an initially well mixed reservoir has important implications for the history of the solar nebula on a plot of 17o versus 18o or 17o 16o versus 18o 16o terrestrial samples with the main exception of stratospheric ozone fall along a single line the terrestrial fractionation or tf line having a slope 0 52 an indication that the parental reservoir was homogenized a convenient measure of o isotopic heterogeneity is the deviation from the tf line 17o 17o 0 52 18o a popular model to explain the evolution of chondritic oxygen compositions during nebular and asteroidal aqueous alteration processes calls for the nebula to have formed from solids having 18o 40 and 17o 41 17o 20 and a gas having a composition roughly estimated to be 18o 30 and 17o 24 17o 9 this model encounters serious difficulties when examined in detail in particular it cannot readily account for the o isotopic compositions of both chondrules and refractory inclusions from individual chondrite groups or for the differences between groups particularly in the compositions of chondrules magnetite fe3o4 is a key phase for o isotope studies because during its formation by the oxidation of ferrous metal or fes all o comes from the oxidant probably h2o it appears that most and possibly nearly all magnetite formed during aqueous alteration processes that occurred in asteroids in all chondrite groups studied to date 17o of the magnetite is greater than or equal to that of the chondrule silicates if the h2o originated in the ambient local nebula then at the time of accretion the 17o of the nebular gas was generally higher than that of the solids an alternative view is that the heterogeneity in the o isotopic composition of chondrites indicates that the nebula formed from diverse batches of presolar materials the precise o isotopic composition of the mix varying during the accretion history of the nebula the large compositional gaps between groups suggest that agglomeration of nebular dust to form chondrites did not proceed at a constant rate but that periods with turbulence levels low enough to allow agglomeration were punctuated by periods of high turbulence during which the composition of the inner nebula sampled by chondrites changed appreciably

oxygen isotope systematics of chondrule phenocrysts from the co3 0 chondrite yamato 81020 evidence for two distinct oxygen isotope reservoirs high precision oxygen three isotope measurements of olivine and pyroxene were performed on 33 chondrules in the yamato 81020 co3 0 chondrite by secondary ion mass spectrometry in chondrules where oxygen isotopes were measured in both olivine and pyroxene the majority of grains have similar values indicating co magmatic crystallization however many chondrules contain relict grains with unique oxygen isotope ratios a striking feature of yamato 81020 chondrules is a bimodal distribution of oxygen isotope ratios as those with mg 97 phenocrysts range in 17o from 4 8 to 6 5 5 5 group and those with mg 96 36 phenocrysts have 17o values of 2 1 to 3 0 2 5 group a single mg 99 6 barred olivine chondrule has a 17o of 3 3 we discuss that 17o 5 5 chondrules are derivative of a reservoir with limited dust enrichment 100 solar system which yielded a relatively reduced chondrule forming environment in contrast the 17o 2 5 chondrules may have been influenced by 16o poor h2o ice that sublimed and then homogenized with precursor material the addition of h2o when combined with high dust enrichment 1000 solar system and greater bulk fe content could have induced an oxidized environment at high temperatures forming mg 96 36 chondrules among the 33 chondrules studied the al mg relative ages of 20 had been obtained previously comparing the oxygen isotope ratios and the 26al ages of these chondrules it is likely that the 5 5 and 2 5 oxygen isotope reservoirs existed contemporaneously this implies that the snow line was spatially fixed during chondrule formation and separated the co chondrite accretion region into two distinct volumes of precursors

the carbon and oxygen isotopic composition of meteoritic carbonates the 13c12c and 18o16o isotopic ratios of carbonates from carbonaceous and ordinary chondrites have been measured on co2 released by the action of h3po4 on whole rock samples carbonates from ci cm and cr carbonaceous chondrites exhibit a range in 18o of ca 15 20 5 to 35 1 relative to smow limited data from co2 water equilibration experiments suggest that meteoritic carbonates do not possess grossly anomalous 17o isotopic compositions therefore they are truly enriched in 13c with 13c between 23 7 and 80 7 relative to pdb large internal variations in 13c and 18o were found in individual meteorites and suggest that two or more isotopically distinct carbonates of different origin may be present the abundance 13c and 18o of carbonate in cm2 chondrites may be related to the extent of aqueous alteration of the meteorites carbonates in ci and cr chondrites have a median 13c ca 50 to 60 whereas 13c of cm meteorites lie in the range 40 to 50 although exceptions exist in both sets of samples cv3 and co3 carbonaceous chondrites and unequilibrated ordinary chondrites release small amounts of co2 on acid treatment which might be from carbonate dissolution but which is not enriched in 13c exhibiting 13c values ca 0 10 the exception to this is bishunpur with 13c ca 23 5 the difference in 13c of the ci cm and cr vs cv co and ordinary chondrite carbonates may be a result of the progressive enrichment in 13c of percolating fluids brought about by increasing solubilization of exotic 13c enriched grains

carbonates in cm chondrites complex formational histories and comparison to carbonates in ci chondrites cm chondrites are primitive solar system materials that have undergone high degrees of aqueous alteration resulting in the formation of secondary minerals including carbonates two different carbonate minerals calcite aragonite and dolomite together constitute 1 4 2 8 vol of cm chondrites in contrast ci chondrites contain four different carbonate minerals calcite aragonite dolomite breunnerite and siderite ci chondrites have abundant dolomite a mineral that seems to be absent in the most aqueously altered cm chondrites in this study carbonates in seven cm chondrites y 791198 lapaz icefield 04796 cold bokkeveld nogoya queen alexandra range 93005 allan hills 83100 and meteorite hills 01070 were studied petrographically and by electron microprobe the results indicate that carbonate formation in cm chondrites differs from that in ci chondrites and is more complex than previously recognized our studies of cm chondrites indicate that 1 carbonates formed on the parent asteroid in an aqueous environment that gradually changed in composition 2 at some stage ca and mg activities in the environment were high enough to form metastable dolomite and 3 dolomites disappeared in the most aqueously altered cm chondrites

magnetite morphologies in the essebi and haripura cm chondrites many of the unusual magnetite morphologies previously observed only in the ci chondrites have been seen in the cm chondrites essebi and haripura these include heavily textured spheroids which are possibly spherulites found both singly and in groups of up to a dozen and ranging in size from 4 to 10 m in diameter collections of microcrystals varying from 0 3 to 6 m in diameter spheres of 1 to 6 m in diameter layered nearly circular plates forming a spheroidal plaquette 7 5 m in diameter clusters of variable sized nodules 1 5 to 6 m with concave features framboidal magnetite and finally collections of less distinctive globules

3 d water properties and geostrophic circulation on the eastern bering sea shelf abstract the national oceanic and atmospheric administration s noaa alaska fisheries science center bottom trawl survey samples demersal fish at over 350 sites on the eastern bering sea continental shelf each summer on a 37 37 km 2 grid rugged conductivity temperature depth sensors ctds were added to the net hauls to obtain gridded data sets of temperature and salinity measurements for 2008 2010 results reveal the three dimensional thermohaline structure of the shelf including the cold pool and areas of fresher water around st matthew island and in bristol bay horizontal gradients are often strongest roughly along the 50 m and 100 m isobaths that traditionally separate the inner and outer shelf from the middle shelf centered along the 70 m isobath the summer mixed layer depth is less than 30 m over much of the region it reaches the bottom along the alaska peninsula in water depths greater than 70 m showing that the boundary of the well mixed inner shelf is not always at the 50 m isobath the greatest upper to lower layer density difference is found across the shelf north of 59 n the salinity difference is the main contributor to this density difference over most of the region in 2008 and 2010 but the temperature difference dominates in 2009 due to decreased ice melt and reduced freshening near st matthew island the geostrophic velocity relative to the bottom shows northwestward flow seaward of the 100 m isobath and northwestward transports integrated across the shelf of 0 10 0 25 10 6 m 3 s in 2008 and 2010 there was clockwise circulation in a region of less saline water around st matthew island in 2009 that fresher lens did not exist and flow was more concentrated along the 100 m isobath bringing saltier water across the shelf

an oxygen isotope study of wark lovering rims on type a cais in primitive carbonaceous chondrites calcium aluminium rich inclusions cais and the thin wark lovering wl rims of minerals surrounding them offer a record of the nature of changing conditions during the earliest stages of solar system formation considerable heterogeneity in the gas composition in the immediate vicinity of the proto sun had previously been inferred from oxygen isotopic variations in the wl rim of a cai from allende simon et al 2011 however high precision and high spatial resolution oxygen isotope measurements presented in this study show that wl rim and pristine core minerals of individual cais from meteorites that had experienced only low degrees of alteration or low grade metamorphism one from leoville reduced cv3 two in que 99177 cr3 0 and two in alha 77307 co3 0 are uniformly 16o rich this indicates that the previously observed variations are the result of secondary processes most likely on the asteroid parent body and that there were no temporal or spatial variations in oxygen isotopic composition during cai and wl rim formation such homogeneity across three groups of carbonaceous chondrites lends further support for a common origin for the cais in all chondrites 16o poor oxygen reservoirs such as those associated with chondrule formation were probably generated by uv photo dissociation involving self shielding mechanisms and must have occurred elsewhere in outer regions of the solar accretion disk

the isotopic composition of volatiles in the unique bench crater carbonaceous chondrite impactor found in the apollo 12 regolith abstract projectiles striking the moon have modified its crust and delivered volatile elements to its interior and surface direct evidence of impactor origins is recorded by the rare occurrence of sub cm sized meteorite fragments identified in apollo samples and lunar meteorites the bench crater meteorite is a millimetre sized carbonaceous chondrite collected in regolith on the rim of bench impact crater at the apollo 12 landing site transmission electron microscopy has previously shown that bench crater contains abundant hydrated silicates establishing the survivability of hydrated material impacting the lunar surface to provide further information on the volatile inventory of the bench crater meteorite we report here the isotope compositions of hydrogen nitrogen carbon and oxygen this is the first direct isotopic analysis of meteoritic material delivered to the lunar surface and provides context for volatile and organic element signatures in lunar regolith samples and the survivability of volatile material delivered to planetary surfaces during impact bombardment the bench crater meteorite is characterised by d values ranging between 36 40 and 200 40 and bulk average 13 c of 13 30 and 15 n of 40 36 all uncertainties at the 2 confidence level the oxygen isotope compositions measured in situ in matrix silicates and magnetite in bench crater are consistent with those measured in matrix and magnetite in ci and cm chondrite falls altogether these new h c n and o isotope data coupled to mineralogical and geochemical observations suggest that bench crater may have been derived from an asteroidal parent body not represented in the terrestrial meteorite collection this is a crucial outcome in the current context of sample return missions to carbonaceous asteroids and more broadly for investigating the flux of material delivered to the earth moon system through time

aqueous alteration and brecciation in bells an unusual saponite bearing cm chondrite the petrological and mineralogical characteristics of the unusual cm2 chondrite bells have been investigated in detail by scanning electron microscopy sem electron microprobe analysis epma and transmission electron microscopy tem bells is a highly brecciated chondrite which contains few intact chondrules a very low abundance of refractory inclusions and is notable in having an unusually high abundance of magnetite which is disseminated throughout the fine grained matrix fragmental olivines and pyroxenes are common and based on compositional data appear to have been derived from chondrules as a result of extensive brecciation the fine grained mineralogy of matrix in bells differs considerably from other cm chondrites and has closer affinities to matrix in ci chondrites the dominant phases are fine grained saponite interlayered with serpentine and phases such as tochilinite and cronstedtite which are typical of cm chondrite matrices are entirely absent pentlandite pyrrhotite magnetite anhydrite calcite and rare ti oxides also occur as accessory phases based on its oxygen and noble gas isotopic compositions zadnik 1985 rowe et al 1994 bells can be considered to be a cm2 chondrite although its bulk composition shows some departures from the typical range exhibited by this group however these variations in bulk chemistry are entirely consistent with the observed mineralogy of bells the unusual fine grained mineralogy of bells matrix can be reasonably attributed to the combined effects of aqueous alteration and advanced brecciation in a parent body environment extensive brecciation has assisted aqueous alteration by reducing chondrules and mineral grains into progressively smaller grains with high surface areas which are more susceptible to dissolution reactions involving aqueous fluids this has resulted in the preferential dissolution of fe rich chondrule olivines which are now completely absent in bells although present in other cm chondrites the formation of saponite in bells probably resulted from the dissolution of relatively silica rich phases such as pyroxene and olivine that were derived from chondrules the result of such dissolution reactions would be to increase the activity of silica in the fluid phase at least on a localized scale stabilizing saponite in preference to serpentine an increase in asio2 would also have destabilized preexisting cronstedtite which may have reacted to form magnetite and mg fe serpentine under conditions of constant o2

record of low temperature alteration in asteroids most chondritic materials experienced diverse styles of secondary alteration resulting in formation of hydrous and anhydrous oxygen bearing minerals silicates oxides and carbonates phyllosilicates magnetite calcite dolomite breunnerite ferrous olivine hedenbergite wollastonite grossular monticellite forsterite andradite nepheline sodalite brearley 2003 2005 and references therein petrographic mineralogic oxygen and short lived isotope systematics 26al 26mg 53mn 53cr 129i 129xe suggest that alteration occurred in the presence of aqueous solutions under variable physico chemical conditions temperature water rock ratio ph f o2 and fluid compositions in an asteroidal setting it started within 1 2 m y after formation of the cv cais was multistage and lasted up to 15 m y krot et al 2006 and references therein here we review bulk o isotopic compositions of chondritic materials o isotopic compositions of secondary minerals produced during asteroidal alteration and possible effects of fluid assisted thermal metamorphism on o isotopic exchange in primary high temperature minerals melilite and anorthite in the cv and co cais the implications of these data for understanding temperatures of alteration water rock ratios and oxygen isotopic composition of water that probably accreted into chondrite parent bodies in the form of ice are discussed the inferred or measured o isotopic composition of the meteoritic water is close to the terrestrial fractionation line 17o 2 it is very different from the inferred o isotopic compositions of the sun 17o 25 clayton 2002 yurimoto and kuramoto 2004 hashizume and chaussidon 2005 lyons and young 2005 suggesting significant evolution of o isotopic composition of the gaseous reservoir in the inner protoplanetary disk over its short 3 5 m y life time

comparison of warm and cold years on the southeastern bering sea shelf and some implications for the ecosystem the southeastern middle shelf of the bering sea has exhibited extreme variability in sea ice extent temperature and the distribution and abundance of species at multiple trophic levels over the past four decades from 1972 2000 there was high interannual variability of areal extent of sea ice during spring march april in 2000 this shifted to a 5 year 2001 2005 period of low ice extent during spring which transitioned to a 4 year 2007 2010 period of extensive sea ice high low areal extent of sea ice in spring was associated with cold warm water column temperatures for the following 6 7 months the ocean currents also differed between warm and cold years during cold years the monthly mean currents over the shelf were largely westward while in warm years the direction of currents was more variable with northward flow during december february and relatively weak flow during the remainder of the year the types and abundance of zooplankton differed sharply between warm and cold years this was especially true during the prolonged warm period 2001 2005 and cold period 2007 2010 and was less evident during the years of high interannual variability during the warm period there was a lack of large copepods and euphausiids over the shelf however their populations rebounded during cold period small crustacean zooplankton taxa did not appear to vary between and warm and cold years for both walleye pollock and pacific cod year class strength recruitment was low during the prolonged warm period but improved during the following cold period year class strength did not appear to vary as a function of warm and cold years during the period of high year to year variability also recruitment of arrowtooth flounder a predator of pollock and cod did not appear influenced by the warm or cold years finally the distribution and relative abundance of fin whales appeared to differ in warm and cold years with fewer whales on the southeastern middle shelf during warm years

low temperature aqueous alteration on the cr chondrite parent body implications from in situ oxygen isotope analyses the presence of hydrated minerals in chondrites indicates that water played an important role in the geologic evolution of the early solar system however the process of aqueous alteration is still poorly understood renazzo like carbonaceous cr chondrites are particularly well suited for the study of aqueous alteration samples range from being nearly anhydrous to fully altered essentially representing snapshots of the alteration process through time we studied oxygen isotopes in secondary minerals from six cr chondrites of varying hydration states to determine how aqueous fluid conditions including composition and temperature evolved on the parent body secondary minerals analyzed included calcite dolomite and magnetite the o isotope composition of calcites ranged from 18o 9 to 35 dolomites from 18o 23 to 27 and magnetites from 18o 18 to 5 calcite in less altered samples showed more evidence of fluid evolution compared to heavily altered samples likely reflecting lower water rock ratios most magnetite plotted on a single trend with the exception of grains from the extensively hydrated chondrite mil 090292 the mil 090292 magnetite diverges from this trend possibly indicating an anomalous origin for the meteorite if magnetite and calcite formed in equilibrium then the relative 18o fractionation between them can be used to extract the temperature of co precipitation isotopic fractionation in al rais carbonate magnetite assemblages revealed low precipitation temperatures 60 c assuming that the cr parent body experienced closed system alteration a similar exercise for parallel calcite and magnetite o isotope arrays yields global alteration temperatures of 55 to 88 c these secondary mineral arrays indicate that the o isotopic composition of the altering fluid evolved upon progressive alteration beginning near the al rais water composition of 17o 1 and 18o 10 and becoming increasingly 16o enriched toward a final fluid composition of 17o 1 2 and 18o 15

oxygen isotopic and chemical compositions of cosmic spherules collected from the antarctic ice sheet implications for their precursor materials abstract bulk chemical compositions and oxygen isotopic compositions were analyzed for 48 stony cosmic spherules melted micrometeorites collected from the antarctic ice sheet using electron and ion microprobes no clear correlation was found between their isotopic compositions and textures the oxygen isotopic compositions showed an extremely wide range from 28 to 93 in 18o and from 21 to 13 in 17o in 18o 17o space most samples 38 out of 48 plot close to the terrestrial fractionation line but 7 samples plot along the carbonaceous chondrite anhydrous mineral ccam line three samples plot well above the terrestrial fractionation line one of these has a 17o of 13 the largest value ever found in solar system materials one possible precursor for this spherule could be 16o poor planetary material that is still unknown as a meteorite the majority of the remaining spherules are thought to be related to carbonaceous chondrites

monthly and seasonal variability in the ocean ice atmosphere systems of the north pacific and the north atlantic four regional indices of sea ice variability and thirty years of monthly sea surface temperature sst and sea level pressure slp data are used to evaluate the large scale interactions within the ocean ice atmosphere systems of the north pacific and the north atlantic a direct association between positive negative sst anomalies and light heavy ice in the bering sea is indicated the sst ice coupling in the northern alaskan waters is also statistically significant the sst anomalies in both the north pacific and the north atlantic appear as persistent responses to atmospheric forcing the slp distributions over both oceans correlate significantly with the arctic slp distribution although the midlatitude atmospheric circulation shows no systematic tendency to lead or lag the arctic circulation sea ice fluctuations correlate most highly with the atmospheric forcing over antecedent periods of approximately 9 months in the northern alaskan waters 3 4 months in the bering sea and 5 7 months in the east greenland sea the strength of the 9 month mean onshore air flow component describes over 70 of the northern alaskan ice variance

fluid flow and chemical alteration in carbonaceous chondrite parent bodies abstract carbonaceous chondrites are a class of primitive meteorites that likely represent early solar system materials thus providing critical insights about planetary evolution however evidence shows that they have undergone considerable processing elucidating the complex formation history of aqueously altered chondrite groups has been a principal objective of cosmochemistry fulfilling this objective requires understanding the nature of the water rock interactions involved many current alteration models are generally founded upon an assumption of uniform alteration in a closed system in these models different chondrite groups must originate on separate parent bodies contrary to this common view we show that chondrite data are consistent with non uniform alteration in a convecting system so that multiple chondrite groups can form within a single body

shifts in the physical environment in the pacific arctic and implications for ecological timing and conditions abstract the northern bering sea and chukchi sea represent the gateway from the pacific to the arctic this contiguous marine system encompasses one of the largest continental shelves in the world and serves as the sole point of connection between the north pacific and arctic ocean this region has unique attributes and complex dynamics driven by the convergence of distinct water masses dynamic currents advection between pacific and arctic systems and important latitudinal gradients relevant to stratification and water mass structure water temperature and seasonal ice cover many processes and interactions in the region appear to be changing with important implications for both hydrography and ecology our analyses access remote and local data sources in us and russian waters to characterize oceanographic conditions and analyze the implications of dramatic shifts in recent years previously this region appeared resistant to trends apparent elsewhere in the greater arctic now the pacific arctic also appears to be in rapid transition the conditions observed in 2017 2019 are unprecedented we note important shifts in the phenology and magnitude of physical variables including sea ice extent concentration and duration as well as extreme reduction in the extent and intensity of the related bering sea cold pool we also note distinct regional dynamics in sea surface temperature in the bering chukchi system distinguishing western eastern and northern areas of the bering sea specifically our analyses distinguish the northern bering sea as an important transition zone between the pacific and arctic with higher frequency variability in sea surface temperature anomalies our results suggest that the strength and position of the aleutian low may be linked to warm and cold phases in the bering sea and has an important role in large scale circulation while cold winds out of the north are necessary to form ice in the northern bering sea strong winds may be associated with weak sea ice as wind action may break ice and enhance vertical mixing counteracting enhanced sea ice production from the advection of cold air research in this important region is complicated by international borders but may be enhanced through international collaboration this analysis represents an attempt to integrate data across russian and us waters to more fully represent system wide processes to contrast regional trends and to better understand physical interactions

stratification on the eastern bering sea shelf revisited abstract the timing and magnitude of stratification can have profound influences on the marine ecosystem on the eastern bering sea shelf in the absence of strong wind mixing stratification can be initiated by the melting of seasonal sea ice or by springtime warming of the surface temperature and salinity both influence the stratification of the eastern bering sea shelf with their relative importance varying spatially and temporally in the northern middle shelf domain north of 60 n salinity stratification is often as important as temperature stratification on the southern middle shelf while the influence of temperature on stratification dominates during summer the influence of salinity stratification plays a role in the interannual variability mooring 2 m2 56 9 n 164 1 w has been deployed at 70 m depth in the southern middle shelf domain since 1995 data from this mooring show that stratification typically begins to set up in may and to break down in september october but these dates can vary by 30 d while no trend is found in the timing of the spring setup the fall stratification breakdown exhibited a trend toward later breakdown 2 d later per year from 1996 to 2009 results suggest that it may be difficult to forecast stratification on the eastern bering sea shelf from climate models as simple indices of wind mixing or heat fluxes are not correlated with stratification contrary to intuition the strength of summer stratification is not correlated with depth averaged temperature warm years such as 2000 and 2001 can have low stratification and cold years such as 2007 can have very high stratification this decoupling of stratification and temperature has implications for forecasting the ecosystem in the face of climate change as we cannot assume that projections of a warmer climate simply imply higher stratification in the future

application of a data assimilative regional ocean modeling system for assessing california current system ocean conditions krill and juvenile rockfish interannual variability to be robust and informative marine ecosystem models and assessments require parameterized biophysical relationships that rely on realistic water column characteristics at appropriate spatial and temporal scales we examine how hydrographic properties off california from 1990 through 2010 during late winter and spring correspond to krill and juvenile rockfish sebastes spp abundances we evaluated coherence among temperature salinity depth of 26 0 potential density isopycnal and stratification strength at regionally and monthly time scales derived from shipboard and mooring observations and a data assimilative regional ocean model system reanalysis the reanalysis captures spatiotemporal physical variability of coastal ocean conditions in winter and spring months and elucidates mechanisms connecting the spatial and temporal upwelling and transport dynamics on observed krill and rockfish abundances in spring this provides evidence for a mechanistic connection between the phenology of upwelling in the california current system and seasonal development of the shelf ecosystem

an examination of the physical variability around the pribilof islands in 2004 the pribilof islands form a unique ecosystem an anti cyclonic oceanic flow exists around the islands nutrients are introduced into this circulation from two sources 1 the flow along the 100 m isobath with intrusions of nutrient rich water in pribilof canyon and 2 the westward transport and vertical mixing of middle shelf water which contains nutrient rich bottom water enhanced tidal mixing around the pribilofs introduces this deeper nutrient rich water into the euphotic zone and thus supports prolonged production around the islands further the middle shelf water that is advected into the region causes the upper 50 m of the water column around the islands to freshen throughout the summer this enhances the frontal structure and strengthens the baroclinic flow along the 100 m isobath the strengthening of the frontal structure can moderate ecosystem productivity by limiting the intrusion of slope water rich in nutrients and oceanic copepods

integrated assessment of the carbon budget in the southeastern bering sea abstract during the primary field program for the bering ecosystem study 2008 2010 independent seasonal estimates of net primary production npp net community production ncp vertical export production cexp and benthic carbon consumption bcc were used to construct a shelf wide carbon budget for the southeastern bering sea here we quantify the annual production utilization and transport of npp for the southeastern shelf region of the bering sea spatially partitioned into outer middle and coastal domains we observed that approximately 25 and 30 of npp on the shelf is exported horizontally from the middle and outer domains respectively this horizontal transport was the dominant mode of carbon export in the outer domain exceeding cexp by more than 30 g c m 2 yr 1 99 g c m 2 yr 1 compared to 67 g c m 2 yr 1 respectively in the middle domain cexp was more prominent than lateral transport 65 g c m 2 yr 1 and 46 g c m 2 yr 1 respectively and vertically exported carbon was more efficiently recycled in this domain than in the outer domain 53 and 32 of cexp respectively in the coastal domain lateral transport was a source of carbon to the bottom layer with estimated input of carbon exceeding npp by as much as 54 g c m 2 yr 1 while the source of this additional carbon is unknown one possible source is transport from the middle domain during wind events that induce coastal convergence overall the combined carbon reservoir attributed to burial and transport in the middle and outer domains is similar to a previous budget for this region 47 walsh and mcroy 1986 although some qualitative differences are apparent the data presented here indicate a more pelagic character in the outer domain relative to the middle domain and that the middle and coastal domain carbon budgets are balanced only when combined

spring and fall phytoplankton blooms in a productive subarctic ecosystem the eastern bering sea during 1995 2011 abstract the timing and magnitude of phytoplankton blooms in subarctic ecosystems often strongly influence the amount of energy that is transferred through subsequent trophic pathways in the eastern bering sea spring bloom timing has been linked to ice retreat timing and production of zooplankton and fish a large part of the eastern bering sea shelf 500 km wide is ice covered during winter and spring four oceanographic moorings have been deployed along the 70 m depth contour of the eastern bering sea shelf with the southern location occupied annually since 1995 the two northern locations since 2004 and the remaining location since 2001 chlorophyll a fluorescence data from the four moorings provide 37 realizations of a spring bloom and 33 realizations of a fall bloom we found that in the eastern bering sea if ice was present after mid march spring bloom timing was related to ice retreat timing p n 11 a fall bloom also commonly occurred usually in late september average day 274 se 4 2 n 33 and its timing was not significantly related to the timing of storms p 0 88 df 1 27 or fall water column overturn p 0 49 df 1 27 the magnitudes of the spring and fall blooms were correlated p 0 011 df 28 the interval between the spring and fall blooms varied between four to six months depending on year and location we present a hypothesis to explain how the large crustacean zooplankton taxa calanus spp likely respond to variation in the interval between blooms spring to fall and fall to spring

oxygen isotopes in separated components of ci and cm meteorites oxygen isotopic compositions have been determined for whole rock and separated components from the ci chondrites alais ivuna and orgueil and from the atypical cm chondrites bells and essebi the composition of ci matrix is in agreement with previous measurements and is systematically different from that of cm matrix probably due to warmer and wetter conditions of aqueous alteration for ci matrix although bells matrix is like that of other cm chondrites the matrix of essebi falls in the ci field essebi also contains abundant magnetite like cis and unlike other cms the isotopic compositions of magnetite in alais ivuna orgueil and essebi define a trend with 17o of 1 3 to 1 8 distinctly out of isotopic equilibrium with the phyllosilicates in each meteorite the magnetite serves as an isotopic tracer for the fluid which brought about aqueous alteration and oxidation and thus provides additional evidence for a gaseous reservoir in the solar nebula which was more 16o depleted than the earth

deuterium enrichments in chondritic macromolecular material implications for the origin and evolution of organics water and asteroids here we report the elemental and isotopic compositions of the insoluble organic material iom isolated from several previously unanalyzed meteorites as well as the reanalyses of h isotopic compositions of some previously measured samples alexander et al 2007 the iom in ordinary chondrites ocs has very large d enrichments that increase with increasing metamorphism and decreasing h c the most extreme d value measured being almost 12 000 we propose that such large isotopic fractionations could be produced in the oc parent bodies through the loss of isotopically very light h2 generated when fe was oxidized by water at low temperatures 200 c we suggest that similar isotopic fractionations were not generated in the iom of cv and co chondrites with similar metamorphic grades and iom h c ratios because proportionately less water was consumed during metamorphism and the remaining water buffered the h isotopic composition of the iom even a h was being lost from it hydrogen would also have been generated during the alteration of ci cm and cr carbonaceous chondrites the iom in these meteorites exhibit a considerable range in isotopic compositions but all are enriched in d as well as 15n relative to terrestrial values we explore whether these enrichments could also have been produced by the loss of h2 but conclude that the most isotopically anomalous iom compositions in meteorites from these groups are probably closest to their primordial values the less isotopically anomalous iom has probably been modified by parent body processes the response of iom to these processes was complex and varied presumably reflecting differences in conditions within and between parent bodies the d enrichments associated with h2 generation along with exchange between d rich iom and water in the parent bodies means that it is unlikely that any chondrites retain the primordial h isotopic composition of the water ice that they accreted the h isotopic compositions of the most water rich chondrites the cms and cis are probably the least modified and their compositions d 25 suggest that their water did not form at large radial distances from the sun where ice is predicted to be very d rich yet models to explain the o isotopic composition of inner solar system bodies require that large amounts of ice were transported from the outer to the inner solar system

variations in the o isotope composition of gas during the formation of chondrules from the cr chondrites to better understand the environment of chondrule formation and constrain the o isotope composition of the ambient gas in the renazzo like carbonaceous cr chondrite chondrule forming region we studied the mineralogy petrology and in situ o isotope compositions of olivine in 11 barred olivine bo chondrules and pyroxene and silica in three type i porphyritic chondrules from the cr chondrites gao guenie b graves nunataks gra 95229 pecora escarpment pca 91082 and shisr 033 bo chondrules experienced a higher degree of melting than porphyritic chondrules and therefore it has been hypothesized that they more accurately recorded the o isotope composition of the gas in chondrule forming regions we studied the o isotope composition of silica as it has been hypothesized to have formed via direct condensation from the gas bo chondrules constitute 4 of the total cr chondrule population by volume on a three isotope oxygen diagram 17o vs 18o olivine phenocrysts in type i and type ii bo chondrules plot along slope 1 line with the exception of a type ii bo chondrule that plots along slope 0 5 line olivine phenocrysts in type i and type ii bo chondrules have similar but more restricted ranges of 17o values 3 8 to 1 3 and 0 8 to 1 4 respectively than those in type i and type ii porphyritic chondrules 4 6 to 0 3 and 1 8 to 0 9 respectively the observation that olivine grains in type i bo chondrules have similar chemical and o isotope compositions to those of olivine in their porphyritic counterparts argues against the hypothesis that olivine grains in type i porphyritic chondrules are xenocrysts and represent relict fragments of early formed planetesimals the compositional and o isotope data suggest that bo chondrules experienced more extensive but incomplete exchange with the ambient gas than porphyritic chondrules we suggest that cr chondrules formed from relatively 16o enriched solids in the presence of relatively 16o depleted gaseous h2o the o isotope compositions of chondrule olivine likely result from differences in the o isotope composition of both the chondrule precursors and the ambient gas during chondrule formation the inferred o isotope composition of this gas 17o ranges from 3 to 3 is inconsistent with a high abundance of water from the outer solar system which has been predicted to be isotopically heavy

cetacean distribution and abundance in relation to oceanographic domains on the eastern bering sea shelf 1999 2004 abstract visual line transect surveys for cetaceans were conducted on the eastern bering sea shelf in association with pollock stock assessment surveys aboard the noaa ship miller freeman in june and july of 1999 2000 2002 and 2004 transect survey effort ranged from 1188 km in 1999 to 3761 km in 2002 fin whales balaenoptera physalus were the most common large whale in all years except 2004 when humpback whales megaptera novaeangliae were more abundant dall s porpoise phocoenoides dalli were the most common small cetacean in all years abundance estimates were calculated by year for each oceanographic domain coastal middle and outer slope the middle and outer slope domains were divided into two strata north and south because of variable survey effort the distribution and abundance of baleen whales changed between the earlier colder and later warmer survey years fin whales consistently occupied the outer shelf and secondarily the middle shelf and their abundance was an order of magnitude greater in cold compared to warm years humpback whales lived on the margin of the northern alaska peninsula eastern aleutian islands and bristol bay their preferred habitat is possibly associated with areas of high prey availability due to nutrient upwelling and aggregation mechanisms minke whales balaenoptera acutorostrata occur shoreward of fin whales in the outer and middle shelf and in coastal habitats along the alaska peninsula the highest abundance for this species was observed in a cold 1999 year no clear relationship emerged for odontocetes with regard to warm and cold years dall s porpoise occupied both outer and middle domains and harbor porpoise phocoena phocoena were more common in middle and coastal domains this study provided a unique broad scale assessment of cetacean distribution and abundance on the eastern bering sea shelf and a baseline for future comparisons

summer distributions of forage fish in the eastern bering sea abstract juvenile and small adult fish typically called forage fish are an important but poorly studied part of the eastern bering sea ebs ecosystem acoustic and trawl data from a non target survey were used to evaluate distributions of capelin mallotus villosus age 0 pacific cod gadus macrocephalus and age 0 walleye pollock theragra chalcogramma herein pollock in 2006 2010 within the surface zone 15 m to 35 m evaluated 2006 2010 capelin occurred throughout the ebs but primarily in the middle shelf capelin were also present in the midwater zone 35 m to 0 5 m off bottom in both 2009 and 2010 evaluated 2009 2010 and resulted in water column zone 15 m to 0 5 m off bottom distributions that differed from surface zone characterizations age 0 pacific cod occurred primarily in the surface zone of the middle and outer shelf regions in all years as midwater and surface zone age 0 pacific cod were often coincident water column zone distributions in 2009 2010 were similar to surface zone distributions age 0 pollock were found in the ebs surface zone in all years primarily in the middle and outer shelf regions high densities of age 0 pollock occurred in the midwater zone in 2006 2007 and 2009 2010 water column zone distributions of age 0 pollock were similar to surface zone distributions in 2006 2007 but differed in 2009 2010 due to low numbers of age 0 pollock in the surface zone and presence of high densities in the midwater zone of the outer shelf region while general patterns in capelin distribution in the surface zone were similar between the present and the previous studies the acoustic trawl characterization suggested that capelin densities were high in the middle shelf region as expected surface zone distributions of age 0 pacific cod and age 0 pollock were similar to previous characterizations observed high densities of midwater age 0 pollock have not been described by previous studies annual abundance indices based on bottom or surface trawl data alone will not be sufficient in all years data and conclusions from non target surveys may be constrained compared to dedicated survey efforts but can provide baseline distributions potential abundance indices and insight for planning future research

sea ice and water column structure on the eastern bering sea shelf abstract seasonal sea ice is a defining characteristic of the eastern bering sea shelf and plays a critical role in determining the vertical structure of temperature and salinity over this shelf ice movement relative to local winds ice composition and the impact of both arrival and retreat of ice on the water column at four mooring sites over the middle shelf are examined ice forms primarily in coastal regions and is advected over the southern and outer shelves ice drift from satellite data for two representative years 2003 and 2007 was 2 of local ncep wind speed and oriented 44 to the right of the winds r 2 0 25 measurements from 30 ice cores collected in 2006 2009 gave an average salinity of 5 62 0 88 and an average nitrate concentration of 0 99 0 83 m time series data collected at the biophysical moorings in the bering sea 1995 2012 were used to explore the evolution of the water column under ice at the northern mooring m8 the water column had mixed and cooled to 1 c prior to the arrival of ice little melt occurred after ice arrival at the other three moorings the ocean temperature was 2 4 c when ice arrived resulting in extensive melt melting ice freshened and cooled the upper water column resulting in stratification which persisted for 10 25 days wind induced water column mixing occurred more slowly under the ice than in ice free waters an estimated 1 4 m of ice melted with the first arrival of ice at the three southern moorings where the latent heat of fusion accounted for approximately half the observed cooling during ice retreat there appeared to be little ice melt around the southern two moorings but an estimated 0 8 m at m5 and m8 the extent of ice melt sets up the water column for the following summer

possible mechanism linking ocean conditions to low body weight and poor recruitment of age 0 walleye pollock gadus chalcogrammus in the southeast bering sea during 2007 abstract changes to physical and chemical oceanographic structure can lead to changes in phytoplankton biomass and growth which in turn lead to variability in the amount of energy available for transfer to higher trophic levels e g forage fish in general age 0 juvenile walleye pollock gadus chalcogrammus have been shown to have low fitness determined by energy density and size in warm years compared to average or cold years in the southeastern bering sea contrary to these findings the year 2007 was a cold year with low fitness of age 0 pollock compared to the transition year of 2006 transitioning from warm to cold conditions and cold years 2008 2011 in late summer early fall mid august through september significantly lower surface silicic acid concentrations coupled with low phytoplankton production and chlorophyll a chl a biomass were observed in 2007 among 2006 2012 p

fractionated sulfur isotopes in sulfides of the kaidun meteorite the kaidun meteorite contains carbonaceous chondrite cm1 clasts that have been highly altered by reactions with hydrothermal fluids pyrrhotite in these clasts occurs as unusual needles wrapped by sheaths of phyllosilicate and pentlandite forms veins that crosscut aggregates of phyllosilicate and garnet but not pyrrhotite the isotopic compositions of s 34scdt in individual sulfide grains measured by ion micro probe are fractionated compared to troilite in ordinary chondrites the s in kaidun sulfides is isotopically light as much as 4 2 for pyrrhotite and 5 7 0 for pentlandite unlike sulfides in other carbonaceous chondrites which are enriched in 34s the unusual s isotopic composition of these texturally unique sulfides supports the hypothesis that kaidun cm1 clasts were pervasively altered under extreme thermal conditions possibly by fluids that had lost isotopically heavy so2

effects of seasonal and interannual variability in along shelf and cross shelf transport on groundfish recruitment in the eastern bering sea the bering sea responds rapidly to atmospheric perturbations and over the past several decades has experienced extreme variability in both its physical and biological characteristics these changes can impact organisms that inhabit the region particularly marine fishes as normal current patterns to which reproductive habits are tuned can be disrupted which in turn may influence recruitment and population dynamics to understand the influence of ocean circulation on groundfish recruitment in the eastern bering sea we examined transport along and across the bering slope derived from 23 years 1982 2004 of simulations from a regional ocean modeling system roms ocean circulation model we expected that changes in the strength and position of the bering slope current bsc would affect recruitment in selected species pacific cod walleye pollock greenland halibut pacific halibut and arrowtooth flounder and that circulation features along and across the shelf edge would be strongly influenced by atmospheric forcing variability in along shelf transport at three transects along the path of the bsc cross shelf transport across the 100 and 200 m isobaths and transport through unimak pass were examined strong seasonal and interannual variations in flow were observed with transport typically highest during fall and winter months coinciding with timing of spawning activity in the five species significant correlations were found between transport bsc position and groundfish recruitment pacific cod in particular benefitted from decreased along shelf and on shelf flow while pacific halibut recruitment increased in relation to increased on shelf transport through southern canyons the results of this study improve our understanding of variability in circulation and associated effects on groundfish recruitment in the eastern bering sea

drivers of declining sea ice in the arctic winter a tale of two seas 1 while the summer perennial arctic sea ice has declined markedly in recent decades the maximum extent of the winter ice cover had decreased only slightly until the past few years when it also receded dramatically this investigation reveals that the timing of maximum extent varies greatly and the drivers of ice edge location differ strikingly between two of the areas where it varies most the bering and barents seas between 1979 and 2005 in the bering sea the ice edge is influenced mainly by anomalies in easterly winds associated with the aleutian low which was particularly strong during the 1980s the barents sea ice edge in contrast is driven primarily by two factors anomalies in sea surface temperature particularly close in time to the maximum extent and by southerly wind from the south anomalies integrated back to mid and early winter the hemispheric mean decline in winter ice extent is due in large part to increasing sea surface temperatures in the barents sea and adjoining waters which are consistent with increased concentrations of greenhouse gases

what processes contribute to the spring and fall bloom co variability on the eastern bering sea shelf abstract observations indicate that spring and fall phytoplankton blooms on the eastern bering sea ebs continental shelf tend to co vary on inter annual scales that is a year with a strong spring bloom also tends to have a strong fall bloom similar co variability of primary production is also seen in the multi year 1987 2007 integration of a coupled physical biological model moreover the modeled seasonal amplitudes of 10 meter chlorophyll a concentrations at the ebs middle shelf mooring locations computed using the canonical redfield ratio and a mean carbon to chlorophyll a ratio are generally consistent with the in situ mooring measurements the coupled physical biological model simulation is used to examine the relative contributions of wind mixing local nutrient recycling regeneration horizontal nutrient advection and water column stability to this co variability there is no significant correlation between the spring and fall surface wind mixing although wind mixing is an important mechanism for bringing nutrients in the lower water column to the surface layers it is not the mechanism tying the two seasons productivity together local regeneration recycling of the nutrients initially fueling spring production is an important mechanism for spring to fall nutrient accumulation in the bottom layers at the middle shelf horizontal advection does not appear to be the dominant factor for supplying nutrients to the middle shelf during the spring to fall period fall primary production in the model is strongly influenced by the lower water column stability stratification taken together these results highlight the importance of local recycling regeneration of nutrients assimilated by spring phytoplankton bloom in linking together the spring and fall primary productions on ebs middle shelf

sea ice impacts on spring bloom dynamics and net primary production in the eastern bering sea 1 in the eastern bering sea changes in sea ice have been implicated in recent major upper trophic level shifts however the underlying relationships between sea ice and primary producers have not been well tested here we combine data from multiple satellite platforms reanalysis model results and biophysical moorings to explore the dynamics of spring and summer primary production in relation to sea ice conditions in the northern bering sea sea ice consistently retreated in late spring leading to ice edge phytoplankton blooms in cold 0 1 c waters however in the southeastern bering sea sea ice retreat was far more irregular although this did not significantly alter bloom timing late retreat led to blooms at the ice edge while early retreat led to blooms in open waters that were warmer 5 4 c and 70 more productive early sea ice retreat also led to higher productivity in summer likely due to weaker thermal stratification overall annual net primary production during warm years of early sea ice retreat was enhanced by 40 50 compared to years with late sea ice retreat in the southeastern bering sea these findings suggest the potential for future sea ice loss to enhance overall carrying capacity of the southeastern bering sea ecosystem consistently warm blooms in the future may also channel more energy flow toward the pelagic rather than benthic environment to date however neither sea ice extent nor the timing of its retreat have undergone long term changes in the eastern bering sea

isotopic fractionation of iron potassium and oxygen in stony cosmic spherules implications for heating histories and sources abstract atmospheric heating alters the compositions and textures of micrometeorites to understand the changes and to test a proposed relationship between a micrometeorite s petrographic texture and its degree of heating we made elemental and multiple isotope analyses of stony cosmic spherules scs collected from the south pole water well specifically we analyzed the elemental compositions of 94 scs and the isotopic ratios of fe k and o on 43 12 and 8 of these scs respectively our results show that scs classified as strongly heated generally have lower concentrations of volatile and moderately volatile elements of the 43 spherules analyzed for fe isotopes only 5 have 57fe 5 in contrast enrichment of 41k is pervasive 41k 0 in all 12 spherules analyzed and large up to 183 the determination of k isotope abundances in scs may therefore be useful in deciphering thermal histories three of the eight scs analyzed for o isotopes are mass fractionated with 18o 30 we attribute two of these three 18o enrichments to evaporative losses of oxygen in the atmosphere and the third to the presence in the parent material of an exotic phase perhaps a sulfate or a carbonate the k isotope and o isotope data are broadly consistent with the proposed textural classification because most spherules were not heated enough to fractionate al mg or si we compared the measured mg al and si al ratios directly to those of conventional meteorites and their matrices 30 of the scs have compositions outside the range defined by the bulk and the matrix compositions of known meteorite groups but consistent with those of pyroxene and olivine rich materials and may be samples of chondrules the other 70 have mg al and si al ratios similar to those of ci cm co and cv chondrites natural variability of the mg al and si al ratios precludes the assignment of an individual scs to a particular class of c chondrite

characteristics and variability of the inner front of the southeastern bering sea the inner front of the southeastern bering sea shows marked spatial variability in frontal characteristics created by regional differences in forcing mechanisms differences in forcing mechanisms sea ice advance retreat and storm strength and timing and early spring water properties result in strong interannual variability in biological chemical and physical features near the front we have developed a simple model based on surface heat flux and water column mixing to explain the existence of cold belts cont shelf res 19 14 1999 1833 associated with such fronts hydrography fluorescence and nutrient observations show that pumping of nutrients into the euphotic zone occurs and this can prolong primary production at the inner front the effectiveness of this process depends on two factors the existence of a reservoir of nutrients in the lower layer on the middle shelf and the occurrence of sufficient wind and tidal energy to mix the water column

terrestrial alteration of carbonate in a suite of antarctic cm chondrites evidence from oxygen and carbon isotopes the oxygen 18o 17o and carbon 13c fmod14c the fraction of modern 14c isotopic compositions of carbonate were measured for a set of paired antarctic cm chondrites eet 96006 eet 96016 eet 96017 and eet 96019 while the oxygen isotopic compositions do not plot on the terrestrial fractionation line and indicate that a component of the carbonate minerals has an extraterrestrial origin they also do not fall on the array defined for carbonates by cm falls and are thus consistent with the presence of a terrestrial carbonate component the 13c and fmod14c measurements of carbonate suggest the presence of at least two carbon sources carbonate derived from atmospheric co2 that is inferred to have been produced as a result of silicate weathering reactions and carbonate derived from another carbon source that is either old or non atmospheric the relationships between oxygen and carbon isotope data provide additional constraints on the weathering process and allow the possibility that rock dominated weathering of the meteorite caused the oxygen isotopic composition of antarctic water added to the meteorite to evolve away from the terrestrial mass fractionation array leading to formation of low temperature terrestrial alteration products that do not lie on the terrestrial fractionation line

petrologic geochemical and experimental constraints on models of chondrule formation abstract the petrologic and geochemical properties of chondrules as well as results of experimental studies provide strong constraints on chondrule formation models nebular formation is indicated by the non mass fractionated oxygen isotopic compositions of bulk chondrules chondrule formation from a melt is required by the prototypical spheroidal shapes and the presence of euhedral phenocrysts and glassy mesostases incomplete melting is indicated by the abundance of porphyritic chondrules which experiments demonstrate require relict nuclei and coarse relict grains the length of time that chondrules were hot is constrained by their retention of relict grains and moderately volatile elements rapid cooling of chondrules after formation is supported by the presence of zoned phenocrysts isotopic anomalies and dynamic crystallization experiments it is clear from the presence of relict grains enveloping compound chondrules and igneous rims that many chondrules were heated again after cooling the heating mechanism responsible for chondrule formation seems to have operated at varying intensities over large regions of the inner solar nebula for at least the time it took ambient nebular temperatures to cool from above 900 to below 600 k the chondrule formation mechanism provided a repeatable source of energy capable of highly localized melting characteristic of flash heating the occurrence of ferroan microchondrules with low melting temperatures within some chondrule rims indicates that chondrule formation did not occur exclusively in high temperature regions near the sun as required in bipolar outflow models mechanisms for forming chondrules that are consistent with the constraints include various flash heating models nebular lightning magnetic reconnection flares gas dynamic shock waves and radiative heating

the oxygen isotope composition of chondrules and isolated forsterite and olivine grains from the tagish lake carbonaceous chondrite abstract the oxygen isotope compositions obtained by laser fluorination of hand picked separates of isolated forsterite isolated olivine and chondrules from the tagish lake carbonaceous chondrite describe a line 17o 0 95 18o 3 24 r2 0 99 similar to the trend known for chondrules from other carbonaceous chondrites the isolated forsterite grains fo99 6 99 8 18o 7 2 to 5 5 17o 9 6 to 8 2 are more 16o rich than the isolated olivine grains fo39 6 86 8 18o 3 1 to 5 1 17o 0 3 to 2 2 and have chemical and isotopic characteristics typical of refractory forsterite chondrules contain olivine fo97 2 99 8 with oxygen isotope compositions 18o 5 2 to 5 9 17o 8 1 to 1 2 that overlap those of isolated forsterite and isolated olivine an inverse relationship exists between the 17o values and fo contents of tagish lake isolated forsterite and chondrules the chondrules likely underwent greater exchange with 16o poor nebular gases than the forsterite the oxygen isotope compositions of the isolated olivine grains describe a trend with a steeper slope 1 1 0 1 r2 0 94 than the carbonaceous chondrite anhydrous mineral line ccamslope 0 95 the isolated olivine may have crystallized from an evolving melt that exchanged with 16o poor gases of somewhat different composition than those which affected the chondrules and isolated forsterite the primordial components of the tagish lake meteorite formed under conditions similar to other carbonaceous chondrite meteorite groups especially cms its alteration history has its closest affinities to ci carbonaceous chondrites

variability in bering sea ice cover as affected by a regime shift in the north pacific in the period 1947 1996 in the late 1970s a regime shift or step occurred in the climate of the north pacific causing among many other effects a 5 reduction in the ice cover in the eastern bering sea as well as shifts in the position of the aleutian low analyses of the aleutian low from monthly mean northern hemisphere sea level pressure for winters december march for 1947 1996 are presented and compared with monthly mean ice cover from the bering sea for 1952 1996 the southern oscillation index and the western pacific oscillation before the regime shift below normal ice cover in the bering sea was typically associated with el nino conditions which caused the aleutian low to move eastward of normal carrying warm pacific air over the bering sea conversely above normal ice cover was associated with la nina conditions which caused the aleutian low to move westward of normal allowing higher pressure to move over the bering sea since the regime shift during el ninos the aleutian low has been moving even farther east causing winds to blow from the east and north off alaska and resulting in above normal ice in the bering sea before the regime shift the occurrence of el nino and la nina conditions was about even since the regime shift el nino conditions are about 3 times more prevalent in recent work e g mantua et al 1997 minobe 1997 there is evidence that this regime shift is the latest in a series of climate shifts going back to at least the late 1800s and may be due to a 50 to 70 year oscillation in a north pacific atmospheric ocean coupled system

biogeochemical cycling in the bering sea over the onset of major northern hemisphere glaciation the bering sea is one of the most biologically productive regions in the marine system and plays a key role in regulating the flow of waters to the arctic ocean and into the subarctic north pacific ocean cores from iodp expedition 323 to the bering sea provide the first opportunity to obtain reconstructions from the region that extend back to the pliocene previous research at bowers ridge south bering sea has revealed stable levels of siliceous productivity over the onset of major northern hemisphere glaciation nhg c 2 85 2 73 ma however diatom silica isotope records of oxygen 18odiatom and silicon 30sidiatom presented here demonstrate that this interval was associated with a progressive increase in the supply of silicic acid to the region superimposed on shift to a more dynamic environment characterized by colder temperatures and increased sea ice this concluded at 2 58 ma with a sharp increase in diatom productivity further increases in photic zone nutrient availability and a permanent shift to colder sea surface conditions these transitions are suggested to reflect a gradually more intense nutrient leakage from the subarctic northwest pacific ocean with increases in productivity further aided by increased sea ice and wind driven mixing in the bering sea in suggesting a linkage in biogeochemical cycling between the south bering sea and subarctic northwest pacific ocean mainly via the kamchatka strait this work highlights the need to consider the inter connectivity of these two systems when future reconstructions are carried out in the region

oxygen isotopic ratios of primordial water in carbonaceous chondrites abstract in this work i estimate the 18 o and 17 o values of primordial water in cm chondrites to be 55 13 and 35 9 respectively based on whole rock o and h data also i found that the o and or h data of antarctic meteorites are biased which is attributed to terrestrial weathering this characteristic o isotopic ratio of water together with corresponding water abundances in cm chondrites are consistent with the origin of water as ice processed by photochemical reactions at the outer regions of the solar nebula where mass independent o isotopic fractionation and water destruction may have occurred another possible mechanism to produce the inferred o isotopic ratio of water would be o isotopic fractionation between water vapor and ice which likely occurred near the condensation front of h2o snow line in the solar nebula the inferred o isotopic ratio of water suggests that carbonate in cm chondrites formed at low temperatures of

mineralogy and oxygen isotope systematics of magnetite grains and a magnetite dolomite assemblage in hydrated fine grained antarctic micrometeorites

magnetite in ci chondrites on the basis of 939 measurements of the ci chondrites their magnetite contents have been determined to be alais 8 9 0 9 ivuna 11 1 0 3 orgueil 11 0 0 4 revelstoke 9 4 and tonk 8 5 standard statistical analysis of the data indicates the existence of two subgroups one comprised of ivuna and orgueil the other of alais revelstoke and tonk while we are not proposing a change in classification it is clear that distinctive differences exist between the two subgroups the precision of the method is 3 so that the standard deviations listed reflect the extent of actual variation in magnetite distribution the wide range from 6 to nearly 50 fe3o4 in previous estimates of the magnetite content of orgueil is due to experimental error not to a real heterogeneity

evidence of prolonged aragonite undersaturations in the bottom waters of the southern bering sea shelf from autonomous sensors abstract the southeastern shelf of the bering sea is a dynamic area that experiences seasonal variability in primary production and remineralization of organic matter both of which control the carbon biogeochemistry of the water column surface water partial pressure of carbon dioxide p co 2 is greatly reduced in summer by biological production which increases carbonate mineral saturation states in contrast the export of large quantities of organic matter from surface blooms drives an active remineralization loop that sharply increases p co 2 near the bottom lowering ph and suppressing new observations from moored biogeochemical sensors in 2011 showed that seasonal net community production lowers surface water p co 2 causing large gradients between the ocean and atmosphere that are sustained throughout the summer confirming that these waters likely remain supersaturated with respect to aragonite throughout the open water season on the other hand moored sensors deployed near the bottom showed that p co 2 levels exceed 500 atm by early june and remain at these high levels well into the autumn months indicating that the bottom waters are likely continuously undersaturated in aragonite for at least several months during each year only a small fraction of the increased p co 2 can currently be attributed to the intrusion of anthropogenic co 2 from the atmosphere while the majority is due to natural respiration processes the biological impacts along with the timing and duration of these undersaturation events could play a role in the development of larval and juvenile calcifiers in the region and will change as anthropogenic co 2 concentrations continue to rise