on the relationship between southern ocean overturning and acc transport the eddy field in the southern ocean offsets the impact of strengthening winds on the meridional overturning circulation and antarctic circumpolar current acc transport there is widespread belief that the sensitivities of the overturning and acc transport are dynamically linked with limitation of the acc transport response implying limitation of the overturning response here an idealized numerical model is employed to investigate the response of the large scale circulation in the southern ocean to wind stress perturbations at eddy permitting to eddy resolving scales significant differences are observed between the sensitivities and the resolution dependence of the overturning and acc transport indicating that they are controlled by distinct dynamical mechanisms the modeled overturning is significantly more sensitive to change than the acc transport with the possible implication that the southern ocean overturning may increase in response to future wind stress changes without measurable changes in the acc transport it is hypothesized that the dynamical distinction between the zonal and meridional transport sensitivities is derived from the depth dependence of the extent of cancellation between the ekman and eddy induced transports

contribution of enhanced antarctic bottom water formation to antarctic warm events and millennial scale atmospheric co2 increase abstract during marine isotope stage 3 the atlantic meridional overturning circulation amoc weakened significantly on a millennial time scale leading to greenland stadials ice core records reveal that each greenland stadial is associated with a warming over antarctica so called antarctic isotope maximum aim and that atmospheric co 2 increases with antarctic temperature during the long greenland stadials here we perform transient simulations spanning the period 50 34 ka b p with two earth system models loveclim and the uvic escm to understand the possible link between changes in the amoc changes in high latitude southern hemispheric climate and evolution of atmospheric co 2 we find that oceanic carbon releases due to the amoc resumption during stadial interstadial transitions lead to an atmospheric co 2 increase however the atmospheric co 2 increases observed during the first parts of aim12 47 6 ka b p and aim8 39 8 ka b p occur during periods of weak amoc hs5 and hs4 respectively and could instead be explained by enhanced antarctic bottom water transport enhanced antarctic bottom water formation is shown to effectively ventilate the deep pacific carbon and lead to co 2 outgassing into the atmosphere in addition changes in the amoc alone are not sufficient to explain the largest antarctic isotope maxima namely aim12 and aim8 stronger formation of antarctic bottom water during aim12 and aim8 would enhance the southern high latitude warming and lead to a better agreement with high southern latitude paleoproxy records the robustness of this southern warming response is tested using an eddy permitting coupled ocean sea ice model we show that stronger antarctic bottom water formation contributes to southern ocean surface warming by increasing the southern ocean meridional heat transport

feldspathic clasts in yamato 86032 remnants of the lunar crust with implications for its formation and impact history abstract low concentrations of th and fe in the yamato y 86032 bulk meteorite support earlier suggestions that y 86032 comes from a region of the moon far distant from the procellarum kreep terrain pkt probably from the lunar farside 39 ar 40 ar rb sr sm nd and sm isotopic studies characterize the chronology of y 86032 and its precursors in the mega regolith one of the rock types present in a light gray breccia lithology is an anorthosite characterized by plagioclase with an 93 i e more sodic than lunar fans but with very low 87 rb 86 sr and 87 sr 86 sr similar to those of fans fan stands for ferroan anorthosite this an93 anorthosite has nd isotopic systematics similar to those of nearside norites a fan like an97 anorthosite is present in a second light colored feldspathic breccia clast and has a more negative e nd value consistent with residence in a lree enriched environment as would be provided by an early plagioclase flotation crust on the lunar magma ocean lmo this result contrasts with generally positive values of e nd for apollo 16 fans suggesting the possibility of assymetric development of the lmo other possible explanations for the dichotomy in e nd values are advanced in the text the y 86032 protolith formed at least 4 43 0 03 ga ago as determined from a sm nd isochron for mineral fragments from the breccia clast composed predominantly of an93 anorthosite and a second clast of more varied composition we interpret the mineral fragments as being predominatly from a cogenetic rock suite an 39 ar 40 ar age of 4 36 4 41 0 035 ga for a third clast composed predominantly of an97 anorthosite supports an old age for the protolith initial 143 nd 144 nd in that clast was 0 64 0 13 e units below 143 nd 144 nd in reservoirs having chondritic sm nd ratios consistent with prior fractionation of mafic cumulates from the lmo a maximum in the 39 ar 40 ar age spectrum of 4 23 0 03 ga for a second sample of the same feldspathic breccia clast probably reflects some diffusive 40 ar loss lack of solar wind and lunar atmosphere implanted ar in the light gray breccia clast allows determination of an 39 ar 40 ar age of 4 10 0 02 ga which is interpreted as the time of initial brecciation of this litholgy after correction for implanted lunar atmosphere 40 ar impact melt and dark regolith clasts give ar ages of 3 8 0 1 ga implying melt formation and final breccia assembly 3 8 ga ago some breccia lithologies were exposed to thermal neutron fluences of 2 10 15 n cm 2 only about 1 of the fluence experienced by some other lunar highlands meteorites other lithologies experienced neutron fluences of 1 10 15 n cm 2 thus y 86032 spent most of the time following final brecciation deeply buried in the megaregolith the neutron fluence data are consistent with cosmogenic 38 ar cos cosmic ray exposure ages of 10 ma variations among differing lithologies in the amount of several regolith exposure indicators including cosmogenic noble gas abundances neutron capture induced variations in sm isotopic abundances and ir contents are consistent with a period of early 3 8 ga ago lunar regolith exposure subsequent deep burial at 5 m depth and ejection from the moon 7 10 ma ago

chronology and petrogenesis of a 1 8 g lunar granitic clast 14321 1062 abstract a study was undertaken to determine the chronology of a pristine granite clast 1062 from apollo 14 breccia 14321 using rb sr sm nd and 39ar 40ar methods the genesis of the granite as constrained by the isotopic results and trace element characteristics is discussed chronology the rb sr internal isochron is slightly disturbed and yields an age of 4 09 0 11 ae 87 rb 0 0139 ae 1 and an imprecise initial i sr 0 702 008 if two data are excluded the age becomes 4 13 0 03 ae and i sr 0 698 003 the whole rock and mineral separates are extremely radiogenic they yield model ages which are relatively well defined the average model age is 4 12 0 03 ae relative to babi 0 69898 the sm nd internal isochron is also slightly disturbed and gives an age of 4 11 0 20 ae 147 sm 0 00654 ae 1 the 39ar 40ar average age of the non magnetic fraction of the sample yields a slightly younger age of 3 88 0 03 ae k ar constants from steiger and a 1977 the concordancy of rb sr and sm nd internal isochrons with the rb sr model age strongly suggests that the granitic clast formed at 4 1 ae ago in the shallow crust and was later excavated and brecciated about 3 88 ae ago petrogenesis isotopic and trace element data of the lunar granite show large k la and rb sr fractionations small sm nd fractionation and the distinct v shaped ree distribution pattern at the time of crystallization a two stage model involving crystal fractionation followed by silicate liquid immiscibility sli is proposed for lunar granite genesis we propose that the granite can be the immiscible acidic liquid produced by sli from a residual liquid which underwent fractionation of ca 3 of phases with ree distribution coefficients similar to those of phosphate minerals from a highly evolved parental magma with ree contents about twice those of the 15405 85 quartz monzodiorite qmd the extreme scarcity of lunar granitic samples and their young formation ages suggest that they are probably not directly crystallized from the differentiation of the primordial magma ocean our isotopic results and trace elements data from other workers suggest that granites qmd and probably mggabbronorites may be genetically related and may have formed in a plutonic environment similar to gabbro granophyre associations in terrestrial layered intrusions such as the skaergaard intrusions

a petrogenetic model for the origin and compositional variation of the martian basaltic meteorites the major element trace element and isotopic compositional ranges of the martian basaltic meteorite source regions have been modeled assuming that planetary differentiation resulted from crystallization of a magma ocean the models are based on low to high pressure phase relationships estimated from experimental runs and estimates of the composition of silicate mars from the literature these models attempt to constrain the mechanisms by which the martian meteorites obtained their superchondritic cao al2o3 ratios and their source regions obtained their parent daughter 87 rb 86 sr 147 sm 144 nd and 176 lu 177 hf ratios calculated from the initial sr nd and hf isotopic compositions of the meteorites high pressure experiments suggest that majoritic garnet is the liquidus phase for mars relevant compositions at or above 12 gpa early crystallization of this phase from a martian magma ocean yields a liquid characterized by an elevated cao al2o3 ratio and a high mg olivine pyroxene garnet dominated cumulates that crystallize subsequently will also be characterized by superchondritic cao al2o3 ratios melting of these cumulates yields liquids with major element compositions that are similar to calculated parental melts of the martian meteorites furthermore crystallization models demonstrate that some of these cumulates have parent daughter ratios that are similar to those calculated for the most incompatible element depleted source region i e that of the meteorite queen alexandra que 94201 the incompatible element abundances of the most depleted que 94201 like source region have also been calculated and provide an estimate of the composition of depleted martian mantle the incompatible element pattern of depleted martian mantle calculated here is very similar to the pattern estimated for depleted earth s mantle melting the depleted martian mantle composition reproduces the abundances of many incompatible elements in the parental melt of que 94201 e g ba th k p hf zr and heavy rare earth elements fairly well but does not reproduce the abundances of rb u ta and light rare earth elements the source regions for meteorites such as shergotty are successfully modeled as mixtures of depleted martian mantle and a late stage liquid trapped in the magma ocean cumulate pile melting of this hybrid source yields liquids with major element abundances and incompatible element patterns that are very similar to the shergotty bulk rock

separating the influence of projected changes in air temperature and wind on patterns of sea level change and ocean heat content we present ocean model sensitivity experiments aimed at separating the influence of the projected changes in the thermal near surface air temperature and wind near surface winds forcing on the patterns of sea level and ocean heat content in the north atlantic the distribution of sea level change is more due to the thermal forcing whereas it is more due to the wind forcing in the north pacific in the southern ocean the thermal and wind forcing have a comparable influence in the ocean adjacent to antarctica the thermal forcing leads to an inflow of warmer waters on the continental shelves which is somewhat attenuated by the wind forcing the structure of the vertically integrated heat uptake is set by different processes at low and high latitudes at low latitudes it is dominated by the heat transport convergence whereas at high latitudes it represents a small residual of changes in the surface flux and advection of heat the structure of the horizontally integrated heat content tendency is set by the increase of downward heat flux by the mean circulation and comparable decrease of upward heat flux by the subgrid scale processes the upward eddy heat flux decreases and increases by almost the same magnitude in response to respectively the thermal and wind forcing regionally the surface heat loss and deep convection weaken in the labrador sea but intensify in the greenland sea in the region of sea ice retreat the enhanced heat flux anomaly in the subpolar atlantic is mainly caused by the thermal forcing

the lunar regolith chemistry mineralogy and petrology the lunar regolith a several meter thick layer of unconsolidated debris forms the interface between the moon and its space environment the regolith forms from lithic sources by the destructional processes of comminution and the constructional processes of agglutinate formation in this manner a steady state soil can develop and will remain in a type of dynamic equilibrium until the system is disturbed by burial or mixing with new soil mixing takes place mainly on a local scale vertically through meters and horizontally over several kilometers lateral transport is a relatively inefficient process and therefore most of the lunar soil components were derived locally there is no evidence for preferential transport of the finer soil fractions relative to the coarser fractions the truly exotic derived at distances of tens of kilometers component is generally in low abundance 1 therefore remotely sensed data should provide a reasonably accurate picture of bedrock geology the chemical composition of the regolith varies with grain size the 10 m fraction is chemically fractionated from the bulk soil in most cases the 10 m fraction is enriched in al2o3 cao na2o k2o light rare earth elements and th and depleted in mgo feo mno and sc these systematics are largely a result of simple comminution with feldspar and friable mesostasis from local source rocks concentrating in the finest fraction there is evidence that agglutinate glass forms preferentially by fusion of the finest soil fractions therefore agglutinate glass like the 10 m soil fraction appears to be fractionated from bulk soil compositions highland soils are distinct from mare soils both chemically and petrologically soil samples collected near mare highland contacts are mixtures of the two lithologies mineral chemical systematics of monomineralic fragments in the lunar soil provide important clues to soil provenance they can in some cases sort out the highland mare contributions and in special cases can even further pinpoint a lithic source in theory lunar regolith cores can serve as solar probes recording the sun s activity over billions of years in practice this has generally not been the case the formation and evolution of most cores is still poorly understood for most we have not established how they formed for example how many depositional and erosional events were involved what the time span involved in the accretion of the sampled soil column was and how long that soil column has remained in situ without this information it is difficult if not impossible to read the sun s record more interdisciplinary studies on cores must be carried out before they can be used as solar probes

sims u pb study of zircon from apollo 14 and 17 breccias implications for the evolution of lunar kreep abstract we report the results of a sims u pb study of 112 zircons from breccia samples from the apollo 14 and 17 landing sites zircon occurs in the breccia matrices as rounded irregular shaped broken and rarely euhedral grains and as constituent minerals in a variety of lithic clasts ranging in composition from ultra mafic and mafic rocks to highly evolved granophyres crystallisation of zircon in magmatic rocks is governed by the zirconium saturation in the melt as a consequence the presence of zircon in mafic rocks on the moon implies enrichment of their parent melts in the kreep component our sims results show that the ages of zircons from mafic to ultramafic clasts range from ca 4 35 ga to ca 4 00 ga demonstrating multiple generations of kreepy mafic and ultramafic magmas over this time period individual zircon clasts in breccia matrices have a similar age range to zircons in igneous clasts and all represent zircons that have been incorporated into the breccia from older parents the age distributions of zircons from breccias from both the apollo 14 and apollo 17 landing sites are essentially identical in the range 4 35 4 20 ga however whereas apollo 14 zircons additionally show ages from 4 20 to 3 90 ga no zircons from apollo 17 samples have primary ages less than ca 4 20 ga also in contrast to previous suggestions that the magmatism in the lunar crust is continuous our results show that the zircon age distribution is uneven with distinct peaks of magmatic activity at ca 4 35 ga ca 4 20 ga in apollo 14 and 17 and a possible third peak in zircons from apollo 14 at ca 4 00 ga to explain the differences in the zircon age distributions between the apollo 14 and 17 landing sites we propose that episodes of kreep magmatism were generated from a primary reservoir and that this reservoir contracted over time towards the centre of procellarum kreep terrane we attribute the peaks in kreep magmatism to impact induced emplacement of kreep magma from a primary mantle source or to a progressive thermal build up in the mantle source until the temperature exceeds the threshold for generation of kreep magma which is transported into the crust by an unspecified possibly plume like process

the role of vertical eddy flux in southern ocean heat uptake 1 the role of changing vertical eddy heat flux on southern ocean heat uptake is investigated in an idealized eddy permitting ocean model enhanced air sea heat flux drives deep reaching southern warming due to a reduction in the isopycnal meridional temperature gradient and therefore decreased upward eddy heat flux this mechanism is qualitatively similar in models with either permitted or parameterized eddies due to its dependence on the isopycnal temperature gradient rather than the dynamical response of the eddy field in contrast increased wind stress drives mid depth southern ocean cooling through an enhancement of the eddy field and resultant eddy heat divergence the transient cooling extends over multiple decades while the mean flow adjusts to balance the faster eddy response this wind driven cooling mechanism has not been captured by coarse resolution models with fixed eddy parameterizations and is a possible candidate for the recent cooling observed in the southern ocean

crustal structure of a nonvolcanic rifted margin east of newfoundland a detailed seismic refraction study was undertaken of the rifted continental margin southeast of the grand banks of newfoundland along a preexisting deep multichannel seismic reflection profile the primary objectives were to determine the topography of moho across the margin to detect any evidence for crustal underplating and to determine the position of the continent ocean boundary data were obtained from nine ocean bottom seismometers deployed along the profile with an array of six 1000 inch3 air guns as the source two additional refraction lines were shot parallel to structure over the continental slope the resultant velocity model is well constrained and consistent with the observed gravity the crust thins abruptly beneath the continental slope to a major structural transition identified as the continent ocean boundary there is no significant magmatic underplating of the thinned continental crust seaward of the transition the seismic velocity structure is characterized by a 50 km wide zone of intermediate velocity 7 2 7 6 km s beyond this is a thin 3 5 km crust with low velocity 4 5 5 km s and high gradient over mantle with a velocity of 7 7 km s increasing to 8 0 km s the zone of intermediate velocity is interpreted to be highly serpentinized mantle material beneath a very thin crust suggesting little or no magmatic activity during and immediately after rifting this interpretation is consistent with results from adjacent and conjugate margins

southern ocean eddy phenomenology mesoscale eddies are ubiquitous features in the southern ocean yet their phenomenology is not well quantified to tackle this task we use satellite observations of sea level anomalies and sea surface temperature sst as well as in situ temperature and salinity measurements from profiling floats over the period 1997 2010 we identified over a million mesoscale eddy instances and were able to track about 105 of them over 1 month or more the antarctic circumpolar current acc the boundary current systems and the regions where they interact are hot spots of eddy presence representing also the birth places and graveyards of most eddies these hot spots contrast strongly to areas shallower than about 2000 m where mesoscale eddies are essentially absent likely due to topographical steering anticyclones tend to dominate the southern subtropical gyres and cyclones the northern flank of the acc major causes of regional polarity dominance are larger formation numbers and lifespans with a contribution of differential propagation pathways of long lived eddies areas of dominance of one polarity are generally congruent with the same polarity being longer lived bigger of larger amplitude and more intense eddies extend down to at least 2000 m in the acc eddies show near surface temperature and salinity maxima whereas eddies in the subtropical areas generally have deeper anomaly maxima presumably inherited from their origin in the boundary currents the temperature and salinity signatures of the average eddy suggest that their tracer anomalies are a result of both trapping in the eddy core and stirring

a combined sm nd rb sr and u pb isotopic study of mg suite norite 78238 further evidence for early differentiation of the moon abstract lunar mg suite norite 78238 was dated using the sm nd rb sr and u pb isotopic systems in order to constrain the age of lunar magma ocean solidification and the beginning of mg suite magmatism as well as to provide a direct comparison between the three isotopic systems the sm nd isotopic system yields a crystallization age for 78238 of 4334 37 ma and an initial e nd 143 value of 0 27 0 74 the age initial e nd 143 t i systematics of a variety of kreep rich samples including 78238 and other mg suite rocks kreep basalts and olivine cumulate nwa 773 suggest that lunar differentiation was completed by 4492 61 ma assuming a chondritic uniform reservoir bulk composition for the moon the rb sr isotopic systematics of 78238 were disturbed by post crystallization processes nevertheless selected data points yield two rb sr isochrons one is concordant with the sm nd crystallization age 4366 53 ma the other is 4003 95 ma and is concordant with an ar ar age for 78236 the 207pb 206pb age of 4333 59 ma is concordant with the sm nd age the u pb isotopic systematics of 78238 yield linear arrays equivalent to younger ages than the pb pb system and may reflect fractionation of u and pb during sample handling despite the disturbed nature of the u pb systems a time averaged 238u 204pb value of the source can be estimated at 27 30 from the pb pb isotopic systematics because kreep rich samples are likely to be derived from source regions with the highest u pb ratios the relatively low value calculated for the 78238 source suggests the bulk moon does not have an exceedingly high value

thin crust at the western iberia ocean continent transition and ophiolites western iberia is bounded by a nonvolcanic rifted continental margin made up of three apparently independent segments the age of breakup decreases from south to north seismic refraction and reflection profiles and magnetic and gravity data from each segment show a consistent pattern of geophysical observations across the ocean continent transition oct zone which is a few tens of kilometers wide we emphasize here the discovery of thin 2 4 km oceanic crust underlain by 7 6 km s 1 material within the oct the available evidence favors the suggestion that the 7 6 km s 1 layer is serpentinized peridotite and that the thin oceanic crust is primarily the result of a poor magma supply for a few million years immediately after continental breakup this thin crust may be the source of some ophiolites which exhibit thin crustal sections and continental margin affinities

the isotopic record of lunar volcanism abstract the timing and extent of lunar volcanism was determined primarily by the internal thermal evolution of the moon a late heavy bombardment produced most of the observable lunar basins easily recognized stratigraphic markers and also may have influenced lunar volcanism most of the nearside basins seem to have been produced 3 8 4 0 ga ago during a period often referred to as the lunar cataclysm the pre cataclysm period was characterized by formation of the lunar crust plutonic rocks within the crust and pre mare volcanism isotopic analysis of breccia clasts pre dating the cataclysm has yielded an outline of this period the isotopic record of post cataclysm mare volcanism is clear but incomplete because samples from the youngest mare areas are lacking specifically the isotopic data show that some lunar anorthosites formed 4 45 ga ago consistent with early formation of an anorthositic lunar crust some mg suite norites troctolites and dunites also formed approximately contemporaneously with the oldest anorthosites but others are up to 200 300 ma younger more evolved rocks granites and quartz monzodiorites also formed between 4 4 and 4 0 ga ago the earliest known pre mare volcanism at 4 25 ga ago included aluminous mare like basalts and an olivine gabbronorite similar to apollo 12 basalts kreep basalt volcanism began at least 4 1 ga ago approximately contemporaneously with that of the ancient mare like basalts and continued during the cataclysm recorded instances of high ti mare basalt volcanism began during or immediately after the cataclysm low ti mare basalt volcanism is the most recent for which samples are available the isotopic data record an early primary lunar differentiation during which mare basalt sources formed probably by crystallization of cumulus minerals from a lunar magma ocean the isotopic record of post cataclysm basalts indicates a heterogeneous lunar mantle and can be explained by partial melting of cumulate sources but more complex petrogenesis also has been suggested more complex petrogenetic processes including assimilation and assimilation fractional crystallization afc seem to be required for pre mare volcanics the isotopic data contain a hint that petrogenesis of the oldest pre mare volcanics may be linked to formation of the so called procellarum basin possibly the oldest and largest lunar basin such a basin would provide a geologic context for the pre mare volcanics and its formation may have been a defining moment in lunar history

comments about the age of the canada basin abstract the canada basin appears to have formed over a 60 ma interval during the cretaceous period the opening process can be divided into two parts continental breakup widespread in hauterivian through aptian time about 113 131 ma ago along what was about to become the polar margin of north america and seafloor formation active during the extended cretaceous interval of normal geomagnetic polarity to marine magnetic anomaly 33 time about 118 79 ma ago presently available age controls indicate that all parts of the north american polar margin could have formed at about the same time two styles of margin formation are evident from brock to axel heiberg island there appears to be an extended 70 ma stratigraphic hiatus and northeastward from ellef ringnes island extensive tholeiitic igneous activity associated with continental breakup from banks island to northeastern alaska the breakup interval is abbreviated 20 30 ma and few igneous rocks are observed a progressive difference may be indicated in the amount and or rate of crustal stretching during margin formation with relatively less slower stretching having occurred along the segment southwest of brock island and relatively more faster stretching having taken place along the segment to the northeast

subdivision of the mg suite noritic rocks into mg gabbronorites and mg norites mg suite noritic rocks can be divided into two groups the mg gabbronorites and the mg norites the rocks of these groups differ in ratios of high ca pyroxene to total pyroxene compositions of pyroxene and plagioclase assemblages of ti nb and zr bearing minerals compositions of chrome spinel bulk rock ti sm and sc sm and measured ages the two groups probably crystallized from different types of parent magmas two hypotheses are offered for the differences in composition of the parent magmas one hypothesis ascribes the differences to compositional heterogeneity of the mantle source areas the other hypothesis ascribes the differences to variations in extent of partial melting of the mantle source regions and variations in extent of assimilation of the anorthosite and the highly differentiated residual liquid that were produced during the primordial lunar differentiation

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

ages of pristine noritic clasts from lunar breccias 15445 and 15455 abstract rb sr and sm nd isotopic studies were undertaken of two apollo 15 breccias 15445 and 15455 collected near spur crater on the apennine front seven pristine lithic clasts including four norites one anorthositic norite one troctolitic anorthosite and one spinel troctolite as well as a matrix sample of 15445 were analysed in addition a k ar age determination was also made for a plagioclase separate from a different anorthositic norite clast sm nd isotopic data of a pristine mg norite sample 15445 17 from the large white clast b of breccia 15445 yielded a precise internal isochron age of 4 46 0 07 ga for 147 sm 0 00654 ga 1 and an initial 143 nd 144 nd of 0 506058 0 000078 normalized to 148 nd 144 nd 0 24308 corresponding to an initial nd of 0 71 however sm nd isotopic results of another mg norite sample 15445 247 chipped from the same clast b about 1 cm away from 15445 17 yielded a significantly younger isochron age of 4 28 0 03 ga and a higher initial 143 nd 144 nd of 0 506246 0 000037 corresponding to an initial nd of 0 35 the sm nd data indicate that clast b is heterogeneous and contains at least two similar lithologies the rb sr isotopic systems were severely disturbed for both norites no useful isochron ages were observed the sm nd age and nd data for a 15 mg norites 15445 17 and 15445 247 a 17 mgnorite 78236 and two mg gabbronorites 73255 27 45 and 67667 are clearly resolved from each other four distinct parental magmas are required for derivation of these two major groups of mg suite noritic rocks the rb sr isotopic system of an anorthositic norite clast 15455 228 was slightly disturbed and isotopic data defined an isochron age of 4 59 0 13 ga for 87 rb 0 0139 ga 1 or 4 55 0 13 ga for 87 rb 0 01402 ga 1 the corresponding initial 87 sr 86 sr for the rock is 0 69899 0 00006 and is in satisfactory agreement with the luni value of nyquist et al 1974 the sm nd system is more disturbed than the rb sr system for this rock a tie line between whole rock samples and a pyroxene separate gives a sm nd age of 4 53 0 29 ga which is in nominal agreement with the rb sr isochron age the 39ar40ar age of a plagioclase separate of the rock has a weighted average value of 3 83 ga suggesting that the age was reset by the imbrium impact event probably the sm nd and rb sr systems of the clast were also partly reset by this event our age results indicate that some mg suite rocks are as old as ferroan anorthosite suite rocks furthermore age data of three major crustal rocks a mg suite a ferroan anorthosite suite and an evolved suite show that they all have variable ages these observations are difficult to explain by the magma ocean hypothesis alone petrogenetic processes such as production of mg suite rocks by serial magmatism walker 1983 of ferroan anorthosite suite rocks by multiple diapiric intrusions longhi and ashwal 1985 and evolved suite rocks by continuous magmatism meyer et al 1988 1989 probably all played a role these processes seem to be able to accommodate the wide ranges of ages and different origins observed for lunar crustal rocks

role of mesoscale eddies in cross frontal transport of heat and biogeochemical tracers in the southern ocean abstractthis study examines the role of processes transporting tracers across the polar front pf in the depth interval between the surface and major topographic sills which this study refers to as the pf core a preindustrial control simulation of an eddying climate model coupled to a biogeochemical model gfdl climate model version 2 6 cm2 6 simplified version of the biogeochemistry with light iron nutrients and gas minibling 0 1 ocean model is used to investigate the transport of heat carbon oxygen and phosphate across the pf core with a particular focus on the role of mesoscale eddies the authors find that the total transport across the pf core results from a ubiquitous ekman transport that drives the upwelled tracers to the north and a localized opposing eddy transport that induces tracer leakages to the south at major topographic obstacles in the ekman layer the southward eddy transport only partially compensates the northward ekman transport while below the ekman layer the sout

60025 relict of primitive lunar crust abstract new isotopic analyses are presented for 3 plagioclase rich fractions and one mafic fraction from ferroan anorthosite 60025 the observed206pb 204pb ratios vary between 52 5 and 60 5 all much higher than the ratio for terrestrial contamination in a207pb 206pb 204pb 206pb correlation diagram the plagioclase data define a model pb pb age of 4 520 0 007 ae using meteoritic primordial lead for the non radiogenic component in the concordia diagram the plagioclase data yield intersections at 4 503 0 007 and 0 28 ae the meaning of the lower intercept is obscure the earlier 60025 analysis of tera and wasserburg 1 with an observed206pb 204pb of 23 0 agrees closely with the new plagioclase data in the isotope correlation and concordia diagrams since the apparent age does not correlate with the206pb 204pb ratios and u contents of the samples it does not appear to be controlled by terrestrial lead contamination the time averaged values for the plagioclase leads are exceptionally low 16 55 and agree within factors of 2 with the observed values in the samples these are much lower than the values observed for mafic rocks or their sources showing that the anorthosite lead has never been associated for a substantial length of time with any high source in this way the 60025 data differ substantially from u pb data for two other lunar anorthosites 15415 and 60015 the results suggest that the averaged model pb ages of 4 51 0 01 ae closely approximate the crystallization age for the plagioclase fraction of the anorthosite and that it dates back to an early phase in lunar history one sample from the mafic fraction of 60025 yields a younger model pb age of 4 42 ae the age may have been lowered by post crystallization disturbances or perhaps this fraction is not coeval with the plagioclase fraction

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

rb sr and sm nd chronology of an apollo 17 kreep basalt sm nd and rb sr mineral isochrons were determined for an apollo 17 kreep pigeonite basalt clast 543 from breccia 72275 collected from boulder 1 station 2 in the valley of taurus littrow sm nd analyses of the basalt yield a precise mineral isochron age of 4 08 0 07 ga for 147sm 0 00654 ga 1 the rb sr mineral isochron age of 4 13 0 08 ga for 87rb 0 0139 ga 1 is concordant with the sm nd age however the rb sr isotopic system has been slightly disturbed probably by the serenitatis impact event 3 95 ga ago the sm nd age is interpreted as the crystallization age of this apollo 17 kreep basalt ages and initial 87sr 86sr and end values for this basalt and apollo 14 and 15 kreep basalts suggest that these two types of kreep basalts could be produced from sources having similar rb sr and sm nd ratios these new age data suggest that kreep basaltic volcanism started 200 ma earlier than the 3 85 ga age generally accepted from studies of apollo 15 pristine kreep basalts apollo 17 kreep basalts probably pre date the serenitatis impact strongly indicating that not all kreep basaltic volcanism was necessarily related to basin forming impacts the younger apollo 15 and 14 kreep basalts probably are related to the imbrium impact however the ages and end values for kreep basalts granites troctolites and norites from a variety of lunar sites form a linear array corresponding to source s with sm nd lower by 15 than the chondritic value slightly enriched in lree suggesting that these rocks could be genetically related formation of a common sm nd isotopic growth curve by these data is most easily explained by an early moon wide differentiation accompanying the formation and subsequent solidification of a global magma ocean

vertical heat flux in the ocean estimates from observations and from a coupled general circulation model the net heat uptake by the ocean in a changing climate involves small imbalances between the advective and diffusive processes that transport heat vertically generally it is necessary to rely on global climate models to study these processes in detail in the present study it is shown that a key component of the vertical heat flux namely that associated with the large scale mean vertical circulation can be diagnosed over extra tropical regions from global observational data sets this component is estimated based on the vertical velocity obtained from the geostrophic vorticity balance combined with estimates of absolute geostrophic flow results are compared with the output of a non eddy resolving coupled atmosphere ocean general circulation model reasonable agreement is found in the latitudinal distribution of the vertical heat flux as well as in the area integrated flux below about 250 m depth the correspondence with the coupled model deteriorates sharply at depths shallower than 250 m due to the omission of equatorial regions from the calculation the vertical heat flux due to the mean circulation is found to be dominated globally by the downward contribution from the southern hemisphere in particular the southern ocean this is driven by the ekman vertical velocity which induces an upward transport of seawater that is cold relative to the horizontal average at a given depth the results indicate that the dominant characteristics of the vertical transport of heat due to the mean circulation can be inferred from simple linear vorticity dynamics over much of the ocean

evidence of a southward eddy corridor in the south west indian ocean mesoscale eddies and meanders have been shown to be one of the dominant sources of flow variability in the world s ocean one example of an isolated eddy hotspot is the south west indian ridge swir several investigations have shown that the swir and the corresponding planetary potential vorticity field f h exert a strong influence on the location and dynamics of the antarctic circumpolar current acc resulting in substantial fragmentation of the jets downstream of the ridge the easterly extension of this eddy corridor appears to be restricted to the deep channel separating the conrad rise from the del cano and crozet plateau however while the fate of eddies formed at the swir has been widely investigated and the frontal character of this eastward extension is well known the zone of diminishing variability that extends southwards to approximately 60 s remains poorly sampled using a combination of argo aviso and ncep ncar datasets the character of this eddy corridor as a conduit for warm core eddies to move across the acc into the antarctic zone is investigated in this study we track a single warm core eddy as it moves southwards from an original position of 31 e 50 20 s to where it dissipates 10 months later in the enderby basin at 56 20 s an argo float entrained within the eddy confirms that its water masses are consistent with water found within the antarctic polar frontal zone north of the apf latent and sensible heat fluxes are on average 8w m2 and 10w m2 greater over the eddy than directly east of this feature it is estimated that the eddy lost an average of 5w m2 of latent heat and 5w m2 of sensible heat over a 1 year period an amount capable of melting approximately 0 92m of sea ice in addition using an eddy tracking algorithm a total of 28 eddies are identified propagating southwards 25 of which are anti cyclonic in rotation based on the new argo float data combined with aviso and ncep ncar datasets these results suggest that the southward passage of warm core eddies act as vehicles transporting heat salt and biota southwards across the acc and into the eastern boundary of the weddell gyre

frontal movements and property fluxes contributions to heat and freshwater trends in the southern ocean we examine the synoptic variability of temperature and salinity in the southern ocean using a static gravest empirical mode gem mapping based on historical hydrography and a time evolving projection of the gem created using satellite altimetry satgem the gem and satgem projections allow the separation of observed trends into a component due to a shift of the circumpolar fronts adiabatic using the satgem and a component due to changes in water masses diabatic expressed as a temporal trend in residual between historical hydrography and the static gem the mean southward movement of the antarctic circumpolar current acc fronts drives an adiabatic warming of 1 196 0 090 w m 2 distributed over most of the acc and at all depths this is strongest where the meridional temperature gradient is largest such as in the upper 1000 dbar of the subantarctic front saf there is a weak adiabatic freshening of 6 57 0 18 mm yr 1 m 2 concentrated mainly below the antarctic intermediate water and south of the saf residuals between historical hydrography and the static gem field driven by diabatic changes in the water mass structure have temporal trends in temperature and salinity when these trends are integrated over the whole acc there is a net cooling of 0 628 0 129 w m 2 and strong freshening of 30 27 0 70 mm yr 1 m 2 by combining the diabatic and adiabatic components and integrating over the acc the net increase in heat and freshwater in the region is 0 570 0 099 w m 2 and 36 91 0 72 mm yr 1 m 2 respectively the sum of the adiabatic and diabatic changes are consistent with previous trends inferred from observations

sediment thickness in the southern canada basin abstract multichannel seismic reflection data are used in conjunction with deep crustal seismic refraction data to estimate the thickness of sediments in the southern canada basin of the arctic ocean north of alaska the sediments are interpreted to be of hauterivian mid early cretaceous to holocene age comparison of the seismic reflection character of seismic reflections in the study area with that in other basins indicates that a base of sediment top of oceanic layer 2 reflection is not present above the depth at which the water bottom multiple obscures all deeper arrivals which is in conflict with the conclusions drawn from aeromagnetic refraction and other reflection studies seismic velocity structure determined from the reflection data indicates that the reflections above the multiple are from sedimentary strata in the absence of seismic reflection evidence for the top of layer 2 above the multiple we estimate total sediment thickness by using the layer 3 refractions and subtracting an average assumed layer 2 thickness from the top of layer 3 assuming that an average thickness of oceanic layer 2 1 4 km overlies layer 3 in the southern canada basin sediment thickness in the study area is estimated to range between 6 5 km where water depth is 3 8 km to greater than 11 km where the water depth is 2 km this is nearly double that of any previous estimates and should have a significant effect on calculations such as the age of canada basin regional heat flow and long term sedimentation rates

impact of mesoscale eddy transfer on heat uptake in an eddy parameterizing ocean model abstractusing a set of experiments with an eddy parameterizing ocean model it is found that the strength of the atlantic meridional overturning circulation amoc intensifies with the decrease of

a mechanism of mixed layer formation in the indo western pacific southern ocean preconditioning by an eddy driven jet scale overturning circulation abstractthe formation of a narrow band of the deep winter mixed layer hereinafter mixed layer wedge in the indo western pacific southern ocean is examined using an eddy resolving parallel ocean program pop model simulation the mixed layer wedge starts to deepen in june centered at 47 5 s with a meridional scale of only 2 latitude its center is located 1 north of the model s subantarctic front saf the argo based observed mixed layer is similarly narrow and occurs adjacent to the observed saf in the small sector of 130 142 e where the saf is persistent and the mixed layer is deepest the formation of the narrow mixed layer wedge coincides with destratification underneath the mixed layer this destratification can be attributed primarily to the downwelling branch of a jet scale overturning circulation jsoc the jsoc which was reported in an earlier study by the authors is driven by eddy momentum flux convergence and is therefore thermally indirect its descending branch occurs on the

circumpolar response of southern ocean eddy activity to a change in the southern annular mode 1 analysis of satellite altimeter data reveals anomalously high eddy kinetic energy eke in the antarctic circumpolar current acc during the period 2000 2002 around 2 3 years earlier 1998 the circumpolar eastward wind stress as quantified by the southern annular mode sam showed a significant positive peak and we have shown previously that the acc peaked around 1998 in response an eddy resolving ocean model is used to investigate the delay between wind forcing and the eddy response and demonstrates that the lag is due to the time taken to influence the deep circulation of the acc winds over the southern ocean have shown a strong climatic increase over the past few decades if this increase in winds is also reflected as an increase in eddy activity as our analysis suggests it might then the increased poleward heat flux may have played a significant role in the observed warming of the southern ocean citation meredith m p and a m hogg 2006 circumpolar response of southern ocean eddy activity to a change in the southern annular mode geophys res lett 33 l16608 doi 10 1029 2006gl026499

vertical heat transport in eddying ocean models 1 the effect of mesoscale eddies on the vertical heat transport of the ocean is examined using two eddy resolving numerical models the global heat transport by the mean flow and diffusion are both downwards and are balanced by an upward eddy heat flux mean and eddy advective heat fluxes dominate the subpolar regions while diffusive flux is important primarily in the subtropics in the subtropical abyss the mean advective heat flux is balanced by a combination of eddy and diffusive fluxes and the classical munk type advective diffusive heat balance must be modified the munk and wunsch 1998 expression for the vertical turbulent diffusivity over estimates the diffusivity by as much as a factor of four near the base of the main thermocline this implies that the mixing required to close the meridional overturning circulation determined by munk and wunsch 1998 may be an over estimate due to the neglect of mesoscale eddies

the continent ocean crustal transition across the southwest greenland margin this paper examines the complete crustal transition across the nonvolcanic southwest greenland continental margin of the labrador sea using wide angle and coincident vertical incidence seismic profiles six ocean bottom seismometers and a sonobuoy record p and s wave first and multiple arrivals from the crust and upper mantle which are analyzed by two dimensional dynamic ray tracing and one dimensional reflectivity modeling the resulting seismic velocity model requires that the preexisting 30 km thick continental crust is thinned abruptly to 3 km across the continental slope primarily by removal of the lower crust farther seaward the crust thickens to 6 km primarily through the addition of a high velocity 7 0 7 6 km s layer in the lower crust this lower crustal layer is 4 5 km thick extends for a horizontal distance of 80 km and is interpreted as partially serpentinized upper mantle it is overlain by a low velocity 4 0 5 0 km s upper layer which is interpreted as highly fractured upper continental crust our model suggests that seafloor spreading did not start until chrons 27 28 13 ma younger than previously suggested this interpretation is supported by two dimensional modeling of gravity and magnetic data along the refraction line our results are consistent with a simple shear mechanism for the initial rifting with the sw greenland margin as the upper plate however a full characterization of the rifting mechanism must await comparison with a seismic model for the conjugate margin east of labrador

observations of anomalous oceanic crust in the canada basin arctic ocean abstract we present a seismic reflection frofile and coincident refraction data in deep water north of the northwind ridge in the canada basin the reflection profile shows a package of bright events which are locally nonparallel and discontinuous about 2 5 s below the seafloor these bright reflectors are of interest because previous reflection profiles in the canada basin have not penetrated the coherent flat lying events which are typical of bedded sedimentary rocks these prominent reflections are recorded on the refraction profile as wide angle reflections and the locally nonparallel and discontinuous event as a refraction on the refraction profile the nonparallel and discontinuous event exhibits lower frequencies and has an associated refraction with a velocity of 4 5 km s and a high gradient this event is interpreted as representing the top of oceanic layer 2 which is observed for the first time in the canada basin three kilometres beneath layer 2 a velocity of 7 2 7 5 km s is measured this layer could represent either a high velocity layer 3 or serpentinized mantle based on comparison with the eastern grand banks and the west iberian and labrador sea margins the interpretation of serpentinized mantle is preferred

the energetics of a collapsing meridional overturning circulation a well studied example of natural climate variability is the impact of large freshwater input to the polar oceans simulating glacial melt release or an amplification of the hydrological cycle such forcing can reduce or entirely eliminate the formation of deep water in the polar latitudes and thereby weaken the atlantic meridional overturning circulation moc this study uses a series of idealized eddy permitting numerical simulations to analyze the energetic constraints on the atlantic ocean s response to anomalous freshwater forcing inthismodel thechangesinmocarenotcorrelatedwiththeglobalinputofmechanicalenergy both kinetic energy and available potential energy ape increase with northern freshwater forcing while the moc decreases however a regional analysis of ape density supports the notion that local maxima in ape density control the response of the moc to freshwater forcing perturbations a coupling between ape input and changes in local density anomalies accounts for the difference in time scales between the recovery and collapse of the moc

a process based analysis of ocean heat uptake in an aogcm with an eddy permitting ocean component about 90 of the anthropogenic increase in heat stored in the climate system is found in the oceans therefore it is relevant to understand the details of ocean heat uptake here we present a detailed process based analysis of ocean heat uptake ohu processes in higem1 2 an atmosphere ocean general circulation model with an eddy permitting ocean component of 1 3 resolution similarly to various other models higem1 2 shows that the global heat budget is dominated by a downward advection of heat compensated by upward isopycnal diffusion only in the upper tropical ocean do we find the classical balance between downward diapycnal diffusion and upward advection of heat the upward isopycnal diffusion of heat is located mostly in the southern ocean which thus dominates the global heat budget we compare the responses to a 4xco2 forcing and an enhancement of the windstress forcing in the southern ocean this highlights the importance of regional processes for the global ocean heat uptake these are mainly surface fluxes and convection in the high latitudes and advection in the southern ocean mid latitudes changes in diffusion are less important in line with the cmip5 models higem1 2 shows a band of strong ohu in the mid latitude southern ocean in the 4xco2 run which is mostly advective by contrast in the high latitude southern ocean regions it is the suppression of convection that leads to ohu in the enhanced windstress run convection is strengthened at high southern latitudes leading to heat loss while the magnitude of the ohu in the southern mid latitudes is very similar to the 4xco2 results remarkably there is only very small global ohu in the enhanced windstress run the wind stress forcing just leads to a redistribution of heat we relate the ocean changes at high southern latitudes to the effect of climate change on the antarctic circumpolar current acc it weakens in the 4xco2 run and strengthens in the wind stress run the weakening is due to a narrowing of the acc caused by an expansion of the weddell gyre and a flattening of the isopycnals which are explained by a combination of the wind stress forcing and increased precipitation

sm nd systematics of chondrites we have studied the 147sm 143nd and 146sm 142nd isotopic systems in phosphate fractions and chondrules from six ordinary chondrites and one carbonaceous chondrite previously dated with pb pb method 147sm 144nd ratios vary between 0 182 and 0 191 in phosphates and between 0 179 and 0 243 in chondrules the 147sm 143nd isochron regression through all 34 phosphate and chondrule analyses yields a date of 4588 100 ma and is in good agreement with more precise pb pb dates of the same chondrites the initial 143nd 144nd is 0 50665 0 00014 the same analyses define a 146sm 142nd isochron with a slope corresponding to 146sm 144sm 0 0075 0 0027 initial 142nd 144nd 1 14160 0 00011 corresponds to e142nd 2 62 0 93 compilation of the published chondritic whole rock sm nd analyses yields the median 147sm 144nd 0 1964 0 0003 0 0007 which is our preferred chondritic uniform reservoir chur value using this value and its error limits we find the present day chur 143nd 144nd 0 512637 0 000009 0 000021 from the chondritic sm nd isochron that includes all available data for whole rocks chondrules and phosphates this value is identical within error with the currently accepted number an estimate of the bulk earth 147sm 144nd 0 1941 0 0059 is obtained from intercept of chondritic 146sm 142nd isochron with the terrestrial value of 142nd 144nd this estimate is independent of measured sm nd ratios in chondrites the same approach was applied to published 146sm 142nd internal isochrons for differentiated meteorites and yielded similar although less precise values our data are completely consistent with the currently accepted chur parameters and substantiate their use as terrestrial reference values

formation ages and evolution of shergotty and its parent planet from u th pb systematics the isotopic composition of lead was determined in different phases from shergotty zagami and eeta 79001 using phases with low 238 u 204 pb the initial leads of these meteorites could be well defined and are distinct from each other and have high 204 pb 206 pb from 0 0652 to 0 0739 these leads evolved in different reservoirs over most of solar system history in a low 238 u 204 pb 5 environment it follows that the parent planet of the shergottites has a high 204 pb concentration relative to u and must also be high in other volatiles if the parent planet of the shergottites is mars then this planet must be volatile rich compared to the earth by a factor of 1 8 this implies that mars lost its original atmosphere and that the present atmosphere was derived from a previously outgassed martian upper mantle the u th pb isotopic relationships involving phases with high 238 u 204 pb are quite regular and give ages for three shergottites which indicate an event of u th pb fractionation at 200 m y the initial leads at that time were highly evolved relative to the primordial lead the absence of substantial additions of radiogenic lead above the initial lead in high u phases precludes an older age for the u th pb fractionation however details of the data arrays are complex the young age is in general agreement with some of the ages obtained by other methods but precise concordance between the different methods is not established it is suggested that the shock event that produced maskelynite may possibly be associated with the late stage breakup at 2 5 m y and not necessarily related to the 180 m y record the major event of chronometer resetting is taken to be 180 m y this event does not appear to be an endogenic igneous event but an almost complete equilibration during a major impact on more ancient igneous rocks which were contained in the target problems of the polymetamorphic history of meteorites appear as complicated as those of polymetamorphic terrestrial terranes