nucleosynthetic osmium isotope anomalies in acid leachates of the murchison meteorite abstract we present osmium isotopic results obtained by sequential leaching of the murchison meteorite which reveal the existence of very large internal anomalies of nucleosynthetic origin e 184 os from 108 to 460 e 186 os from 14 1 to 12 6 e 188 os from 2 6 to 1 6 e 190 os from 1 7 to 1 1 despite these large variations the isotopic composition of the total leachable osmium weighted average of the leachates is close to that of bulk chondrites this is consistent with efficient large scale mixing of os isotopic anomalies in the protosolar nebula the os isotopic anomalies are correlated and can be explained by the variable contributions of components derived from the s r and p processes of nucleosynthesis surprisingly much of the s process rich osmium is released by relatively mild leaching suggesting the existence of an easily leachable s process rich presolar phase or alternatively of a chemically resistant r process rich phase taken together with previous evidence for a highly insoluble s process rich carrier such as sic these results argue for the presence of several presolar phases with anomalous nucleosynthetic compositions in the murchison meteorite the s process composition of os released by mild leaching diverges slightly from that released by aggressive digestion techniques perhaps suggesting that the presolar phases attacked by these differing procedures condensed in different stellar environments the correlation between e 190 os and e 188 os can be used to constrain the s process 190 os 188 os ratio to be 1 275 0 043 such a ratio can be reproduced in a nuclear reaction network for a macs value for 190 os of 200 22 mbarn at 30 kev more generally these results can help refine predictions of the s process in the os mass region which can be used in turn to constrain the amount of cosmoradiogenic 187 os in the solar system and hence the age of the galaxy we also present evidence for extensive internal variation of 184 os abundances in the murchison meteorite a steep anti correlation is observed between e 184 os and e 188 os since 184 os is formed uniquely by the p process this anti correlation cannot be explained by variable addition or subtraction of s process os to average solar system material instead this suggests that p process rich presolar grains e g supernova condensates may be present in meteorites in sufficient quantities to influence the os isotopic compositions of the leachates nevertheless 184 os is a low abundance isotope and we cannot exclude the possibility that the measured anomalies for this isotope reflect unappreciated analytical artifacts

a major circulation anomaly in the western bering sea the alaskan stream ceased to flow northward into the western bering sea starting in summer 1990 this unexpected lack of inflow caused by a southward shift in the path of the alaskan stream persisted through at least fall 1991 if the anomalous flow continues substantial changes in the physical environment will occur possibly leading to impacts on the rich fisheries stocks in the region

heat and fresh water transport by eddies into the gulf of alaska abstract anticyclonic mesoscale eddies form in winter along the continental margin of canada and southeast alaska between the latitudes of 51n and 60n and drift westward into the gulf of alaska carrying warmer fresher water away from the continental margin detailed measurements of temperature and salinity between 1995 and 2001 were examined to determine the amount of heat and fresh water transported seaward by several eddies that formed west of the queen charlotte islands eddies formed in a typical winter carry about 30 10 18 j of heat into the gulf which is about 35 to 60 of the heat transported northward each winter along the continental margin toward this region the observed range of eddy heat transport is 10 19 to 10 20 j largest observed eddy heat transport coincided with increased northward heat flow along the continental margin during the el nino winter of 1997 1998 fresh water volume was determined by evaluating the amount of fresh water required to reduce the salinity from a reference level to that observed in eddies this volume varied from 0 to 70 km 3 and was largest during the 1997 1998 el nino winter eddies formed in a typical winter transport 50 km 3 of fresh water seaward which is about 15 of the estimated fresh water input to the continental margin in winter between the columbia river and 54n attributed to local runoff plus direct rainfall and flow in major rivers

the shedding of an anticyclonic eddy from the alaskan stream as observed by the geosat altimeter the evolution of a meander into an anticyclonic eddy which separates from the alaskan stream in the vicinity of the central aleutian islands is observed in two years of sea surface height anomalies computed from geosat exact repeat mission altimeter data the trajectory of the center of mass is estimated using a modified perpendicular bisector method eddy separation is inferred to occur where the trajectory makes a distinct turn to the southwest the observed region of meander growth and eddy separation agrees with that predicted by theory the evolution of meander eddy height and radius is estimated from least squares fits of the data to an axially symmetric gaussian profile the heights and radii are used to calculate the strength vorticity and energetics of the meander eddy ekman dynamics are assumed to govern the eddy decay spin down times based on vorticity are much longer than those based on energetics this is consistent with an eddy s ability to maintain its integrity as it decays representative height diameter and velocity scales of the eddy are characteristic of rings spawned by other current systems assuming a ring structure for this eddy the estimated ring volume represents a 21 transport anomaly referenced to the mean annual transport into the bering sea

multi year meanders and eddies in the alaskan stream as observed by topex poseidon altimeter the birth life and decay of long lived anticyclonic eddies or meanders in the alaskan stream are observed from topex poseidon t p satellite their surface height anomalies approach 72 cm average diameter is about 160km and they live for 1 to 3 years propagating along the stream with mean speed of 2 5 km d 1 of the six observed the last three were formed after the first t p observations in september 1992 of these two evolved from eddies near alaskan panhandle in winter drifting across the northern gulf of alaska before entering the alaskan stream while another formed in the stream west of shelikof strait

mineralogy of tagish lake an ungrouped type 2 carbonaceous chondrite in this paper we describe the recovery handling and preliminary mineralogical investigation of the tagish lake meteorite tagish lake is a type 2 carbonaceous chondrite which bears similarities to ci1 and cm chondrite groups but is distinct from both abundant phyllosilicates as well as chondrules however sparse and common olivine grains in the matrix preclude any other classification the bulk density of tagish lake 1 67 g cc which is far lower than ci or cm chondrites 2 2 2 3 and 2 6 2 9 g cc respectively or any other meteorite for that matter we have identified two lithologies a dominant carbonate poor lithology and a less abundant carbonate rich lithology the meteorite is a breccia at all scales we have noted similarities between tagish lake and some clasts within the enigmatic meteorite kaidun possibly there are genetic relationships here worth exploring in the paper we describe a clast of cm1 material within tagish lake which is very similar to a major lithology in kaidun

dynamical analysis of a satellite observed anticyclonic eddy in the northern bering sea the characteristics and evolution of a satellite observed anticyclonic eddy in the northern bering sea during march and april 1999 are investigated using a three dimensional princeton ocean model pom the anticyclonic like current pattern and asymmetric feature of the eddy were clearly seen in the synthetic aperture radar sar sea surface temperature and ocean color images in april 1999 the results from model simulation reveal the three dimensional structure of the anticyclonic eddy its movement and dissipation energy analysis indicates that the barotropic instability bti is the main energy source for the growth of the anticyclonic eddy the momentum analysis further reveals that the larger magnitude of the barotropic pressure gradient in the meridional direction causes the asymmetry of the anticyclonic eddy in the zonal and meridional directions while the different magnitudes of the meridional baroclinic pressure gradient are responsible for the different intensity of currents between the northern and southern parts of the anticyclonic eddy

tracing subarctic pacific water masses with benthic foraminiferal stable isotopes during the lgm and late pleistocene abstract as the largest ocean basin the pacific helps to set the global climate state since its circulation affects mean ocean properties air sea partitioning of carbon dioxide and the distribution of global oceanic poleward heat transport there is evidence that during the last glacial maximum lgm the subarctic pacific contained a better ventilated relatively fresh intermediate water mass above 2000 m that may have formed locally the source and spatial extent of this water mass is not known nor do we know how formation of this water mass varied during pleistocene glaciations with different orbital and ice sheet boundary conditions here we present a 0 5 my multi species benthic stable isotope record from site u1345 1008 m on the northern bering slope and a 1 0 my record from u1339 1868 m from the umnak plateau in the southeastern basin we find that the relatively well ventilated low 18o intermediate water reaches 1000 m in the bering sea during mis2 but that the hydrographic divide between this water mass and poorly ventilated deep water was shallower than 1000 m for earlier glaciations we also compare bering sea piston core and iodp expedition 323 uvigerina data from the holocene and lgm with the modern hydrography and to previously published profiles from the okhotsk sea and emperor seamounts we find that the carbon and oxygen stable isotope signatures of well ventilated water in the bering and okhotsk seas are distinct suggesting that there may have been intermediate water formation in both basins during the lgm

a quasi geostrophic circulation model of the northeast pacific part i a preliminary numerical experiment abstract a limited area quasi geostrophic numerical model with mesoscale resolution is developed to study the circulation in the northeast ne pacific ocean the model domain extends from the british columbia alaska coast out to 170 w and down to 45 n and incorporates the coastline geometry and bottom topography of the region a long term integration was conducted using a steady climatological wind stress curl field to drive the circulation several statistical properties of the solution are determined and compared with observations a cyclonic circulation develops in the model basin with a meandering alaska current feeding at the head of the gulf of alaska into an intense boundary current corresponding to the alaskan stream the head of the gulf is a region where anticyclonic closed streamline features are occasionally generated with characteristics resembling those of the sitka eddy in the downstream region the boundary current separates and is subject to lateral meandering due to topographic wave

molybdenum isotope anomalies in meteorites constraints on solar nebula evolution and origin of the earth the early evolution of the solar nebula involved substantial transport of mass resulting in mixing and homogenization of isotopically diverse materials that were contributed to the solar system from multiple stellar nucleosynthetic sources the efficiency of this mixing as well as its timescale can be quantified by determining nucleosynthetic isotope variations among meteorites and terrestrial planets here we present mo isotopic data for a wide range of samples including ca al rich inclusions chondrites and differentiated meteorites as well as martian and terrestrial samples most meteorites are depleted in s process mo relative to the earth and only the iab iiicd irons angrites and martian meteorites have terrestrial mo isotopic compositions in contrast most ca al rich inclusions are enriched in r process mo but one inclusion is characterized by a large s process deficit molybdenum isotopic anomalies in the bulk meteorites correlate with those in ru exactly as predicted from nucleosynthetic theory but no obvious correlation is apparent between mo and ni anomalies therefore s process mo and ru seem to be hosted in the same carrier which must be distinct from the carrier responsible for isotopic anomalies in the fe group elements ni cr ti furthermore the isotopic heterogeneity in mo and other elements contrasts with the isotopic homogeneity for hf and os indicating that different s process carriers once existed in the early solar nebula and that only some of these were heterogeneously distributed the mo isotopic anomalies of meteorites and their components decrease over time and with increasing size of the parent bodies providing evidence for a progressive homogenization of the solar nebula however the carbonaceous chondrites exhibit larger mo anomalies than expected for their age indicating that they received a greater portion of material from the outer solar system where homogenization was slow than other meteorite parent bodies and terrestrial planets compared to the meteorites earth is enriched in s process mo and must have accreted from material distinct from the meteorites combined mo and o isotopic data show that the composition of the earth cannot be reconstructed by any known combination of meteorites implying that meteorites may be inappropriate proxies for the isotopic composition of the bulk earth this is exemplified by the covariation of 92mo and 142nd anomalies in chondrites showing that the 142nd deficit of chondrites compared to the accessible earth may not unequivocally be interpreted as a signature of an early differentiation of the earth however further high precision isotopic data are needed to evaluate the role of chondrites in defining the isotopic composition of the earth

effects of mesoscale eddies on the flow of the alaskan stream 1 using a high resolution pan arctic ice ocean model forced with realistic atmospheric data we examine the mean transport and temporal and spatial variability within the alaskan stream model results are analyzed and compared with observations including satellite altimetry and ctd measurements the mean net transport of the alaskan stream is found to be between 34 and 44 sv intensifying downstream mesoscale eddies are found to periodically move along the path of the alaskan stream and alter the mean position of the typically westward flowing current however the strength of the current is not reduced as an anticyclonic eddy passes a point along the path instead there appears to be an offshore or southward shift in the current velocity core stationary measurement instruments may not be able to detect this shift in position over the slope if their southernmost location does not coincide with the current shift due to an eddy this may result in recording of a weakened or sometimes reversed flow finally we examine and demonstrate that modeled eddies within the alaskan stream have dominant effect on northward transport and variability through the eastern and central aleutian island passes

recent observations of variability in the path and vertical structure of the alaskan stream abstract current records were recently obtained from two sites on the continental slope southwest of kodiak island at the inshore site 10 month record flow mainly resembled the weak shelf break flow typical of the gulf of alaska except for two periods each of 3 months duration the offshore site 31 mouth record was in the path of the alaskan stream during the alaskan stream segments flow characteristics low eddy energy high vertical coherence and high stability were similar to those in the stream at other locations when the stream was absent from the offshore site it made a seaward excursion of 50 km as evidences by satellite tracked drifters the cause of this migration is unclear during a period of 6 months a subsurface velocity maximum was measured at 165 m flow near 1000 m was very weak for almost two years geostrophic flow estimates however suggest this is a rare situation

the role of the alaskan stream in modulating the bering sea climate 1 a numerical ocean circulation model with realistic topography but with an idealized forcing that includes only lateral transports is used to study the role of the alaskan stream as in modulating the bering sea bs variability sensitivity experiments each one with a different strength of the as transport reveal a nonlinear bs response an increase of as transport from 10 to 25 sv causes warming 0 25 c mean 0 5 c maximum and sea level rise in the bs shelf due to increased transports of warmer pacific waters through the eastern passages of the aleutian islands but an increase of as transport from 25 to 40 sv had an opposite impact on the bs shelf with a slight cooling 0 1 c mean 0 5 c maximum as the as transport increases flows through passages farther downstream in the western aleutian islands are affected and the variability in the entire bs is reduced transport variations of 0 1sv in the bering strait are found to be correlated with mesoscale variations of the as and associated transport variations in the aleutian islands passages these results have important implications for understanding the observed variations in the bering strait and potential future climate variations in the arctic ocean

eddies in the eastern gulf of alaska from topex poseidon altimetry eddy activity in the gulf of alaska goa is evidenced to fluctuate with the el nino southern oscillation enso cycle altimetry from topex poseidon is used to study eddy formation along a single descending track in the far eastern goa from late 1992 through late 1998 the track is sampled between 45 n and 60 n where it is roughly parallel to the eastern boundary the geoid and mean currents are removed from the data through extraction of the temporal mean at each point the resulting anomalies are passed through a matched filter designed to detect gaussian signals embedded in noise the filter is optimized to detect eddies with amplitude 10 cm and diameters roughly 50 350 km both anticyclonic and cyclonic structures are examined the distribution of eddies in space is similar for both anticyclonic and cyclonic eddies with most occurring between 50 n and the northern limits of the goa few eddies of either sign were found south of 50 n anticyclonic eddies are stronger and have a broader distribution of amplitudes typically 5 30 cm compared to cyclonic features which are more symmetrically distributed over 5 15 cm the detection of weak 15 cm eddies is sensitive to the filter threshold but detection of larger amplitude eddies is robust the average amplitude of anticyclonic eddies increases following the 1993 1994 1995 and 1998 el nino events eddy amplitude appears to vary with enso strength the strongest eddies detected form in early 1998 these results support previous numerical studies of eddy development in the eastern goa

iron transport by mesoscale haida eddies in the gulf of alaska abstract a two year study of the iron distributions in anticyclonic mesoscale haida eddies of the eastern north pacific ocean has shown that such eddies are a major source of iron to the high nitrate low chlorophyll hnlc waters of the central gulf of alaska basin these eddies which are typically about 100 km in diameter form off the west coast of canada in winter and then track roughly westward into the open ocean therefore they carry large quantities of iron rich coastal waters into iron limited waters of the oligotrophic gyre when the eddies had first formed their dissolved iron concentrations were nearly two orders of magnitude higher than is typically observed at station papa 50 n 145 w 3 n m versus less than 0 05 n m and the total iron in the eddies surface waters 10 40 m was more than 13 n m higher than open ocean waters of the alaska gyre 14 n m versus 0 5 n m while the overall iron content of the eddies decreased rapidly during the first year after they formed the eddy we were able to track the longest still contained 1 5 2 times more iron than the surrounding waters 16 months after its formation therefore although iron concentrations in the surface mixed layers of the eddies drop to levels observed outside very rapidly within 4 months upward transport along isopycnals and upwelling due to eddy decay as well as vertical advective and diffusive transports typical of north pacific waters probably provide steady fluxes of iron into the euphotic zone from the still iron rich eddy core waters throughout the lifetime of the eddy

recent shifts in the state of the north pacific 1 the winters of 1999 2002 for the north pacific were characterizedbyspatialpatternsinsealevelpressureanomaly slpa and sea surface temperature anomaly ssta with little resemblance to those of the leading pattern of north pacific climate variability the pacific decadal oscillation pdo in essence the southeastern northern portion of the north pacific was subject to atmospheric forcing characteristic of that before after the major regime shift of 1976 77 recent major changes in the ecosystems off the west coast of the united states and continued conditions similar to those of the early 1990s in the gulf of alaska bering sea and sea of okhotsk are consistent with these slpa and ssta patterns our result illustrates that a single indicator such as the pdo is incomplete in characterizing north pacific climate index terms 1635 global change oceans 4203 1610 global change atmosphere 0315 0325 4215 oceanography general climate and interannual variability 3309 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 citation bond n a j e overland m spillane and p stabeno recent shifts in the state of the north pacific geophys res lett 30 23 2183 doi 10 1029 2003gl018597 2003

evidence for homogeneous distribution of osmium in the protosolar nebula separate s r and possibly p process enriched and depleted components have been shown to host os in low metamorphic grade chondrites although no measureable os isotopic anomalies have yet been discovered for bulk chondrites here iron meteorites from groups iab iiab iiiab iva and ivb as well as the main group pallasites are examined many of these meteorites show well resolved anomalies in e190os e189os and e186osi the anomalies however differ from those observed in chemically extracted components from chondrites and are interpreted to reflect long term exposure of the meteorites to cosmic rays rather than nucleosynthetic effects a neutron capture model is presented that can well account for observed isotopic variations in 190os and 189os the same model predicts greater enrichment in 186osi than is observed for at least one iron suggesting as yet unaccounted for effects or failings of the model despite the variable anomalies resulting from cosmic ray exposure each of the major meteorite groups examined contains at one member with normal os isotopic compositions that are unresolved from chondritic compositions this indicates that some domains within these meteorites were little affected by cosmic rays these domains are excellent candidates for application of the 182hf 182w system for dating metal silicate segregation on their parent bodies the normal os also implies that os was homogeneously distributed throughout the protosolar nebula on the scale of planetesimal accretion within the current level of analytical resolution the homogeneity in os contrasts with isotopic heterogeneity present for other siderophile elements including mo ru and w the contrast in the scale of anomalies may reflect a late stage injection of s and p process rich material into the coalescing nebula alternately nebular thermal processing and destruction of some presolar host phases of mo ru and w may also be responsible

aleutian basin of the bering sea thermohaline oxygen nutrient and current structure in july 1993 an overview is given of the surface to bottom thermohaline oxygen nutrient and baroclinic flow structures in the aleutian basin of the bering sea and the adjacent north pacific based on high resolution field measurements in july 1993 a basic four layer vertical structure is observed in the upper 1500 m the 30 m top layer is warm low in salinity and nutrients and high in oxygen beneath it a 100 to 150 m thick temperature minimum layer is found believed to be a remnant of winter convection this is followed by a 300 m thick warm layer in which the main halocline oxycline and nutricline are located below it lies a layer of minimum oxygens and maximum nitrates and phosphates centered at a depth of 900 m in the bering sea but rising to 400 m south of the aleutians this basic structure is disrupted in the vicinity of amchitka pass due to strong tidal mixing the deep and abyssal waters of the aleutian basin differ substantially from those at comparable depth in the adjacent pacific by being warmer 0 1 c less saline 0 01 less dense 0 01 kg m3 poorer in oxygen 50 mol kg and richer in silicates 80 mol kg nitrates 1 0 mol kg and phosphates 0 3 mol kg the highest silicate concentrations 240 mol kg occur at the foot of the bering shelf unusual hydrographic conditions exist in an isolated tidal mixing basin in amchitka pass where the bottom mixed layer is 600 m thick 0 7 c warmer 0 14 less saline and 21 mol kg less oxygenated than at comparable depths outside baroclinic currents indicate strong deep jetlike flows on both sides of the aleutian ridge weak shallow eddies in the middle of the aleutian basin and somehat enhanced flows near the bering shelf edge the alaska stream in july 1993 was 100 km wide had a double core with a top speed of 0 54 m s and had a westward volume transport of 38 sv with 14 sv below 1000 dbar the north aleutian current had a speed of 0 2 m s and an eastward transport of 10 sv with 4 sv below 1000 dbar off the bering slope both eastward and westward flows were observed with volume transports near 7 sv

deep currents in the central subarctic pacific ocean abstract sections of closely spaced ctd stations along longs 165 w 175 w and 175 e in combination with 14 month current records from the central longitude define two deep nearly zonal currants with speed increasing upward in the subarctic pacific one flows eastward above the aleutian rise and aleutian trench and appears to be a concentration of geostrophic flow forced by the bottom topography the other flows westward along the aleutian island arc and is the northern boundary current predicted by deep circulation theory both currents reach to the sea surface the boundary current being simply the deep part of the alaskan stream the current records were too few to permit better than rough estimates of volume transports but to the extent that they could be combined with thermal wind calculations they suggest at 175 w 1 a transport of 28 106 m3 s 1 for the alaskan stream of whch 5 106 m3 s 1 was found below 1500 m and 2 a transport of around 20 1o6 m3 s 1 for the eastward jet of wh

correlated study of initial sr 87 sr 86 and al mg isotopic systematics and petrologic properties in a suite of refractory inclusions from the allende meteorite we have studied a suite of six coarse grained ca al rich inclusions cais from the allende meteorite applying in concert detailed petrographic and chemical characterization ion probe mass spectrometric analyses of the al mg isotopic system to determine the abundance and distribution of 26a1 and thermal emission mass spectrometric analyses of the rb sr system to determine initial 87sr86sr ratios the simplest inclusion is a type bl usnm 3529 z that shows evidence of minor alteration and recrystallization since solidification from a melt droplet e g some of the coarse grained anorthite in the inclusion especially near the inclusion rim apparently formed by recrystallization or melting of fine grained secondary anorthite that had replaced melilite four other type bs contain evidence of more widespread recrystallization in addition to evidence of local replacement of melilite by coarse anorthite e g melilite zoning is complex and not igneous in origin and in one inclusion usnm 3529 21 melilite and pyroxene crystals enclose relicts of an earlier generation of the same phases the sixth inclusion usnm 3898 is a type a whose properties appear to be largely metamorphic in origin all six inclusions show variations in mg isotopic compositions indicating that they incorporated 26a1 in 3529 z the relative abundance of 26a1 26al27al 4 0 0 1 10 5 is close to the canonical value 26al27al 5 10 5 for cais but both anorthite and melilite show minor departures from a strict isochron relationship between mg and al in particular the coarse anorthite near the inclusion rim has initial 26al27al ratios of 1 2 10 5 implying formation at least 1 5 million years after the first generation anorthite the other four type bs exhibit larger disturbances of the al mg system that can be understood in terms of local recrystallization and isotopic exchange primarily between anorthite and melilite only 3898 is consistent with a strict al mg isochron relationship but this cai lacks primary anorthite and the small range of al mg among the phases analyzed may preclude resolution of any small isotopic disturbances the rb sr isotopic system also typically indicates some level of disturbance some of which must have been relatively recent nevertheless phases characterized by very low rb sr permit precise identification of initial 87sr86sr our al mg and sr data are largely consistent with a simple chronological interpretation of both systems i e the 26al results suggest that all the initial 87sr86sr ratios should have the same value and with one exception our initial 87sr86sr ratios are consistent with a single value this value is somewhat higher than the primitive value all reported by gray et al 1973 however also with one exception the very low rb sr cai data reported by gray et al 1973 are consistent with the same value the exception is the same inclusion in both studies our analysis of usnm 3898 yields an initial 87sr86srhigher than that of the other cais while gray et al 1973 obtained an initial 87sr86srlower than that of the other cais for the same inclusion labeled as d7 on which all is based neither result can be readily explained as a chronological aberration since 3898 has nearly canonical 26al27al the present data are the first which establish a firm association between primitive 26al27al and primitive 87sr86sr by analysis of both isotopic systems in the same inclusions the comparison of both isotopic systems interpreted as simple nebular chronometers does not reveal any chronological inconsistencies that demand resolution in terms of a grossly heterogeneous distribution of 26al

evidence from the rb sr system for 4 4 ga alteration of chondrules in the allende cv3 parent body the timing and processes of alteration in the cv parent body are investigated by the analysis of sr isotopes major and trace elements and petrographic type and distribution of the secondary minerals nepheline and sodalite in 22 chondrules from the allende cv3 chondrite the sr isotopic compositions of the chondrules are scattered around the 4 0 ga reference line on the 87sr 86sr evolution diagram indicating that the chondrules have been affected by late thermal alteration event s in the parent body the degree of alteration determined for individual chondrules based on the distribution of nepheline and sodalite is unrelated to the disturbance of the rb sr system suggesting that the alteration process that produced nepheline and sodalite is different from the thermal process that disturbed the rb sr system of the chondrules considering the geochemical behavior of rb and sr the main host phase of sr in chondrules is likely to be mesostasis which could be most susceptible to late thermal alteration as there is a poor connection between the alteration degree determined from abundances of nepheline and sodalite and the disturbance of rb sr isotopic system we consider the mesostasis to provide a constraint on the late parent body alteration process from this point of view 23 mesostasis rich chondrules including those from literature data were selected the selected chondrules are closely correlated on the 87sr 86sr evolution diagram with an inferred age of 4 36 0 08 ga this correlation would represent an age of the final major sr isotopic redistribution of the chondrules in the parent body

osmium isotope anomalies in chondrites results for acid residues and related leachates abstract we have investigated os isotope anomalies in acid residues enriched in insoluble organic matter iom extracted from ten primitive chondrites acid leachates and residues of these fractions as well as acid leachates of bulk chondrites osmium isotopic compositions of bulk carbonaceous ordinary and enstatite chondrites are also reported consistent with prior results bulk chondrites have homogeneous os isotope compositions for s r and p process nuclides that are indistinguishable from terrestrial at the current level of resolution in contrast nearly all the iom rich residues are enriched in s process os evidently due to the preferential incorporation of s process enriched presolar grains most likely presolar sic presolar silicate grains that formed in red giant branch rgb or asymptotic giant branch agb stars are also likely hosts of additional s process os in chondrites consistent with one prior study os released by weak acid leaching of bulk chondrites is slightly to strongly enriched in r process nuclides of which the carrier may be fine grained presolar silicates formed in supernovae or unidentified solar phases collectively the different chemically concentrated components in these meteorites are variably enriched in s r and possibly p process os of which the individual carriers must have been produced in multiple stellar environments the lack of evidence for os isotopic heterogeneity among bulk chondrites contrasts with evidence for isotopic heterogeneities for various other elements at approximately the same levels of resolution e g cr mo ru ba sm and nd one possible explanation for this is that the heterogeneities for some elements in bulk materials reflect selective removal of some types of presolar grains as a result of nebular processes and that because of the strong chemical differences between os and the other elements the os was not significantly affected another possible explanation is that late stage injection of isotopically distinct materials into the nebula led to heterogeneous distribution of some elements osmium may not have been affected because of a lack of isotopic contrast with the pre injection well mixed nebula

nucleosynthetic strontium isotope anomalies in carbonaceous chondrites abstract precise sr isotopic compositions in samples from sequential acid leaching experiments have been determined for three carbonaceous chondrites allende murchison and tagish lake together with those in the bulk aliquots of these meteorites the chondritic acid leachates and residues were characterized by sr isotope anomalies with variable 84sr values 106 relative deviation from a standard material ranging from 120 to 4700 ppm documenting multiple nucleosynthetic sources within a single meteorite in addition the 84sr patterns across leaching samples for individual chondrites differed from one another the highest 84sr values were observed for leaching step 3 hcl h2o 75 c for allende and murchison likely because of the incorporation of calcium and aluminum rich inclusions cais in contrast extremely low 84sr values were observed in the later fractions steps 6 and 7 for murchison and tagish lake suggesting the existence of s process enriched presolar sic grains derived from agb stars a 84sr 54cr diagram was prepared with the cais and bulk aliquots of carbonaceous chondrites and other meteorites noncarbonaceous that were plotted separately however they still formed a global positive correlation cais presented the highest 84sr and 54cr values whereas carbonaceous chondrites and noncarbonaceous meteorites had intermediate and the lowest 84sr and 54cr values respectively the positive trend was interpreted as resulting from global thermal processing in which sublimation of high 84sr and 54cr carriers generated the excess 84sr and 54cr signatures in cais while noncarbonaceous planetesimals accreted from materials that underwent significant thermal processing and thus had relatively low 84sr and 54cr values apart from the global trend the carbonaceous chondrites and noncarbonaceous meteorites both exhibited intrinsic variations that highlight an isotopic dichotomy similar to that observed in other isotope combinations e g 54cr 50ti 54cr 17o a plausible scenario for creation of the intrinsic variations involves local thermal processing e g flash heating for chondrule formation caused by additional selective destruction of presolar grains differently than that caused by global thermal processing the existence of such a global positive trend and local variations for two meteorite groups suggests a complicated dynamic history for the dust grains with respect to thermal processing material transportation and mixing in the protoplanetary disk prior to planetesimal formation

ocean circulation and exchanges through the northern bering sea 1979 2001 model results abstract we have developed and run a model with sufficiently high resolution 9 km and 45 levels and a large enough spatial domain to allow for realistic representation of flow through the narrow and shallow straits in the northern bering sea this is potentially important for quantification of long term mean and time dependent ocean circulation and water mass and property exchanges between the pacific and arctic oceans over a 23 year interval 1979 2001 mean transport through bering strait is estimated to be 0 65 sv comparison of our model results with published observations indicates that ocean circulation is not only variable at seasonal to interdecadal scales but it is also responsive to short term atmospheric forcing one of such events occurred during the winter of 2000 2001 with reversed oceanic flow in some areas and much reduced sea ice cover analyses of eddy kinetic energy fields identify some high biological productivity regions of the chirikov basin coincident with persistent high energy up to 2700 cm 2 s 2 in the surface layer and up to 2600 cm 2 s 2 at mid depth throughout the annual cycle model output in the bering strait region is validated against several time series of moored observations of water mass properties comparison with shipboard observations of near bottom salinity from late winter through autumn indicates that the model reasonably represents the major water mass properties in the region the modeled vertical water column structure in the northern bering sea allows increased understanding of the mechanisms of water transformation and transport northward through bering strait into the chukchi and beaufort seas we conclude that the long term model results for the northern bering sea provide important insights into the ocean circulation and fluxes and they are a useful frame of reference for limited observations that are short term and or cover only a small geographic region

satellite and hydrographic observations of eddy induced shelf slope exchange in the northwestern gulf of alaska 1 satellite and hydrographic observations of oceanographic conditions in the northwestern gulf of alaska indicate that anticyclonic eddies propagating adjacent to the continental shelf alter the structure of the shelf break front and in doing so influence the shelf slope exchange of biota and water mass properties eddies typically form in the northern gulf of alaska during fall and winter and propagate southwestward within an 200 km wide corridor along and above the continental slope eddy activity within this corridor diminishes in the downstream direction the trajectories of faster propagating 4 km day eddies tend to lie closer to the shelf break than do the trajectories of slower propagating 1 5 km day eddies the interaction between azimuthal eddy currents and the shelf break frontal jet 1 establishes an upwelling zone associated with the leading flank of the eddy that strengthens cross slope gradients 2 weakens cross slope gradients and promotes shelf slope exchange where the eddy is adjacent to the shelf and 3 reestablishes a weak upwelling zone associated with the trailing flank of the eddy

non nucleosynthetic heterogeneity in non radiogenic stable hf isotopes implications for early solar system chronology abstract nucleosynthetic heterogeneity and secondary neutron capture reactions may have important implications for 176 lu 176 hf chronology and modelling of early planetary evolution so far the relevance of these phenomena for the lu hf system has not been explored we therefore have analyzed the non radiogenic stable hf isotope composition 177 hf 178 hf 179 hf and 180 hf of meteorites meteorite components and terrestrial rock samples to identify nucleosynthetic or neutron capture induced variations all analyzed chondrites have uniform 178 hf 177 hf and 180 hf 177 hf values that cannot be resolved from the average terrestrial composition thus there is no evidence for nucleosynthetic heterogeneity in chondrites or earth and these data support the use of a chondritic reference value for the hf isotope composition of the bulk silicate earth this homogeneity contrasts with nucleosynthetic heterogeneities found in lighter elements and provides evidence for a separate synthesis of light and heavy r process nuclei various mesosiderite samples and one lunar meteorite display coupled 178 hf 177 hf and 180 hf 177 hf anomalies that are associated with neutron capture induced deviations in 149 sm 154 sm and 150 sm 154 sm however the analyzed chondrites and an aubrite show only sm isotope anomalies and these are the result of neutron capture the hf isotope anomalies require substantial capture of epithermal neutrons whereas sm anomalies result primarily from thermal neutron capture the non radiogenic stable isotope composition of hf is thus a suitable monitor for epithermal neutron capture reactions the data reveal distinct neutron energy spectra mesosiderites are characterized by high epithermal to thermal neutron fluence ratios whereas the remaining samples show low epithermal to thermal ratios secondary neutron capture may significantly increase the measured 176 hf 177 hf in whole rock meteorite samples without causing a resolvable shift in 176 lu 177 hf thus it could potentially induce scatter in lu hf whole rock isochrons and produce spurious initial 176 hf 177 hf values however the slopes of internal i e mineral isochrons cannot be increased significantly by secondary neutron capture this process therefore cannot account for the unrealistically old 176 lu 176 hf ages e g 4 75 ga of some meteorites

the influence of an alaskan stream eddy on flow through amchitka pass flow into the bering sea through amchitka pass in the central aleutian islands is shown to respond to the presence of a large meander eddy in the alaskan stream south of the pass maximum flow into the aleutian basin of the bering sea occurs when the eddy center lies nearest to the axis of amchitka pass a conceptual model of low frequency circulation variability within the bering sea based upon results of empirical orthogonal function analyses of sea surface height anomalies measured by the geosat radar altimeter is presented

nickel isotope heterogeneity in the early solar system article i nfo ni of bulk iron and chondritic meteorites carbonaceous chondrites have variable positive e 62 ni 0 05 to 0 25 whereas ordinary chondrites have negative e 62 ni 0 04 to 0 09 the ni isotope compositions of iron meteorites overlap with those of chondrites and define an array with negative slope in the e 60 ni versus e 62 ni diagram the ni isotope compositions of the volatile depleted group ivb irons are similar to those of the refractory co cv carbonaceous chondrites whereas the other common magmatic iron groups have ni isotope compositions similar to ordinary chondrites only enstatite chondrites have identical ni isotope compositions to earth and so appear to represent the most appropriate terrestrial building material differences in e 62 ni reflect distinct nucleosynthetic components in precursor solids that have been variably mixed but some of the e 60 ni variability could reflect a radiogenic component from the decay of 60 fe comparison of the e 60 ni of iron and chondritic meteorites with the same e 62 ni allows us to place upper limits on the 60 fe 56 fe of planetesimals during core segregation we estimate that carbonaceous