asymmetric crustal growth on the moon indicated by primitive farside highland materials the origin of the dichotomy between the lunar nearside and farside is unclear analysis of spectral reflectance data from the kaguya lunar orbiter indicates a systematic difference in the degree of differentiation in the oldest lunar crustal terrains linking the lunar dichotomy to crystallization of the magma ocean

on the petrogenesis of lunar troctolites new insights into cumulate mantle overturn mantle exposures in impact basins abstract we investigate lunar troctolite petrogenesis with a series of forward models we simulate the cumulate mantle overturn hypothesis by modeling the adiabatic ascent and decompression melting of primary mantle cumulates produced during differentiation of a lunar magma ocean lmo combined equilibrium and fractional crystallization of candidate liquids generated by the melting model can reproduce the predominant constituents of the lunar magnesian suite mg suite troctolites and norites contrary to previous hypotheses model results are consistent with previous studies challenging the proposed and long standing genetic relationship between mg suite and gabbronorites our mg suite petrogenetic model validates a direct temporal and chemical link between mg suite melt production and pressure release melting of primary lmo cumulates if so mg suite crystallization ages 4345 15 ma can be used to constrain the onset and duration of melting associated with mantle overturn based on our model results we propose an alternative mantle overturn hypothesis whereby upwelling olivine dominated cumulates experience decompression melting to produce the mg suite primary melt 1 9 melt at 2 1 gpa but that this melt was extracted from depth akin to lunar picritic glass magmas low degree partial melts at depths corresponding to 1 3 2 5 gpa thus our revised mantle overturn hypothesis reconciles mg suite petrogenesis without the expanse of an olivine dominated upper mantle as suggested by the current paradigms but contradicted by orbital data this hypothesis supports the presence of a low ca pyroxene dominated upper mantle consistent with mantle stratigraphy constrained by experimental and numerical simulations of lmo differentiation and proposed mantle exposures within impact basins

sm nd age of lherzolite 67667 implications for the processes involved in lunar crustal formation abstract pristine samples from the lunar highlands potentially offer important information bearing on the nature of early crustal development on all the terrestrial planets one apparently unique sample of this group of lunar crustal rocks the feldspathic lherzolite 67667 was studied utilizing the sm nd radiometric system in an attempt to define its age and the implications of that age for the evolution of the lunar highlands data for 67667 precisely define an isochron corresponding to an age of 4 18 0 07 ae the observed lack of disturbance of the sm nd system of this sample may suggest that this time marks its crystallization at shallow depth in the lunar crust however the possibility that this age as well as those of other highland rocks indicate the time of their impact induced excavation from regions deep enough in the lunar crust to allow subsolidus isotopic equilibrium to be produced or maintained between their constituent minerals is also considered taken together bulk rock sm nd data for four high mg rocks including 67667 indicate that the chemical characteristics of all their source materials were established 4 33 0 08 ae ago and were intimately associated with the parent materials of kreep this finding provides more support for the concept of a large scale differentiation episode early in lunar history the possible roles of the crystallization of a global magma ocean endogenous igneous activity and of planetesimal impact in producing the observed geochemical and chronological aspects of lunar highland rocks are discussed

internal tides and vertical mixing over the kerguelen plateau within the context of the natural iron fertilization study keops time series measurements of ctd and ladcp profiles at a site 50 6 s 72 e 528 m coinciding with an annual phytoplankton bloom over the kerguelen plateau were made during the january february 2005 keops cruise an important activity of highly nonlinear semidiurnal internal tides having peak to peak isopycnal displacements of up to 80 m is identified these internal tides appear to be a principal agent for promoting elevated vertical mixing indispensable for upward transfer of iron within the seasonal thermocline we estimate local vertical eddy diffusivities of the order of 4 10 4 m2 s 1 using a thorpe scale analysis although this estimate is higher by an order of magnitude than the canonical value o 0 1 10 4 m2 s 1 in the open ocean away from boundaries it is consistent with nonlinear internal wave wave interaction theories as verified by independent diffusivity estimates using the vertical wavenumber spectral methods for shear and strain it is also suggested that the general ocean circulation may play an important role in preconditioning the bloom in that the relatively sluggish circulation over the shallow plateau compared to the much more dynamic neighbouring deep ocean may foster the bloom s observed annual recurrence over the plateau

surface lithofacies biofacies and diatom diversity patterns as models for delineation of climatic change in the southeast atlantic ocean abstract distribution of diatom species in surface sediments of the southeast atlantic ocean is regulated by present day oceanographic and hydrodynamic processes five assemblages vectors defined by factor vector analysis reflect different environments and conditions assemblage a is a high diversity flora associated with the nutrient rich relatively cold waters south of the polar front in the diatom ooze belt occurrence of this flora on maud rise and vicinity may reflect periodic occurrence of a polynya in that area assemblage b is a reworked assemblage that dominates the southern portion of the study area productivity there is low reflecting sea ice cover during most of the year the area north of the polar front is dominated by assemblage c whose characteristic species reflect the relatively warm subantarctic surface water winnowing and frustule breakage have altered assemblage d found in three isolated samples by removing relatively delicate forms leaving lag deposits of more robust species assemblage e is a low diversity stress flora reflecting unstable unpredictable environments along the polar front antarctic slope and the northern boundary of winter sea ice these sites are characterized by the sinking of cold water downcore analysis of cores lying adjacent to the polar front and the diatom ooze pelagic clay boundary show evidence for past climatic variation the low trophic level occupied by diatoms and the subsequent sensitivity of these organisms to abiotic environmental parameters such as light quality make relative diatom abundance a useful tool for monitoring fluctuations of winter sea ice and the temperature changes responsible for these fluctuations the position of the polar front has migrated at least three times within the last 0 015 m y b p within the last 0 3 m y b p warm maxima have occurred at approximately 0 0 0 015 0 125 and 0 3 m y b p

a new approach to cosmogenic corrections in 40 ar 39 ar chronometry implications for the ages of martian meteorites abstract anomalously old 40ar 39ar ages are commonly obtained from shergottites and are generally attributed to uncertainties regarding the isotopic composition of the trapped component and or the presence of excess 40ar old ages can also be obtained if inaccurate corrections for cosmogenic 36ar are applied current methods for making the cosmogenic correction require simplifying assumptions regarding the spatial homogeneity of target elements for cosmogenic production and the distribution of cosmogenic nuclides relative to trapped and reactor derived ar isotopes to mitigate uncertainties arising from these assumptions a new cosmogenic correction approach utilizing the exposure age determined on an un irradiated aliquot and step wise production rate estimates that account for spatial variations in ca and k is described data obtained from nwa 4468 and an unofficial pairing of nwa 2975 which yield anomalously old ages when corrected for cosmogenic 36ar using conventional techniques are used to illustrate the efficacy of this new approach for these samples anomalous age determinations are rectified solely by the improved cosmogenic correction technique described herein ages of 188 17 and 184 17 ma are obtained for nwa 4468 and nwa 2975 respectively both of which are indistinguishable from ages obtained by other radioisotopic systems for other shergottites that have multiple trapped components have experienced diffusive loss of ar or contain excess ar more accurate cosmogenic corrections may aid in the interpretation of anomalous ages the trapped 40ar 36ar ratios inferred from inverse isochron diagrams obtained from nwa 4468 and nwa 2975 are significantly lower than the martian atmospheric value and may represent upper mantle or crustal components

time and duration of lunar highlands crust formation abstract all radiometric systems indicate that crust mantle differentiation on the moon is dominated by events which occurred very early in lunar history however due to remaining uncertainties in model parameters and assumptions in the calculation of model ages it is not yet possible to resolve the precise times of occurrence of these events nor the duration of the formation of the highlands crust the strongest time constraints are offered by direct radiometric ages of samples formed during this earliest period two possible candidates for this material norites 78236 and 73255 27 45 were examined utilizing the sm nd radiometric system sm nd systematics of 78236 show post crystallization disturbance but indicate that this norite crystallized in the lunar crust about 4 34 ae ago data for 73255 27 45 define an isochron and yield a crystallization age of 4 23 0 05 ae the initial nd isotopic composition of both norites is within uncertainty of a chondritic reference reservoir at the time of their respective crystallizations the implications for lunar crustal formation persisting over a time span of close to 350 m y are discussed

a young solidification age for the lunar magma ocean abstract the time at which the lunar magma ocean solidified can be determined from the lu hf isotope systematics of lunar rocks derived from magma sources that formed during crystallization of the lunar magma ocean the final magma ocean crystallization product termed urkreep is enriched in incompatible elements including k ree and p we have determined the initial hf isotopic compositions of four samples two kreep basalts and two mg suite norites the incompatible trace element compositions of these samples are controlled by an urkreep component and therefore the initial hf isotopic compositions of these samples represent the hf isotopic evolution of urkreep in order to correct the effects of neutron irradiation on the hf isotopic compositions of these samples we have developed a model that uses the stable hf and sm isotopic compositions measured on an irradiated sample to determine and correct for the thermal and epithermal neutron fluence that has modified the hf isotopic composition of the sample we use our corrected results to calculate a 176 lu 176 hf urkreep model age of 4353 37 ma and the 176 lu 177 hf of urkreep to be 0 0153 0 0033 the lu hf model age is concordant with the re calculated sm nd urkreep model age of 4389 45 ma and we take the average of these ages 4368 29 ma to represent the time at which urkreep formed this age is concordant with the age of the most reliably dated ferroan noritic anorthosite as well as 142 nd model ages for the formation or re equilibration of mare basalt sources taken together these ages indicate that the moon experienced a widespread large scale magmatic event around 4370 ma most plausibly attributed to solidification of the lunar magma ocean

nepheloid and suspended particulate matter in south eastern lake michigan a persistent benthic nepheloid layer with high total suspended matter tsm and high total particulate surface area was observed in south eastern lake michigan the layer thickens from a few metres near the shelf slope boundary to greater than 10 m at the base of the slope when compared to the hypolimnion tsm increases by a factor of 2 20 at 1 m above the bottom the greatest increase detected at the slope basin boundary sediment trap profiles within the nepheloid layer show that the particulate flux increases exponentially from about 10 m above the bottom to 1 m above the bottom suggesting that a large fraction of the collected material came from resuspension a nepheloid layer is created during the formation of the thermal bar and maintained during the stratified period apparently through the action of weak but persistent currents this layer is supplemented by lakeward transport of fine particles resuspended near the shelf slope boundary due to impingement of the thermocline on the bottom or during higher energy events

response of the benthic nepheloid layer to near inertial internal waves in southern lake michigan 1 time series measurements of water transparency water temperature and current velocity were made at a station located in 58 m of water in southern lake michigan during the summer of 1995 currents generated by near inertial internal waves are correlated with variations in the thickness and in the vertical distribution of suspended sediment in the benthic nepheloid layer although a direct causal link between internal wave action and changes in the nepheloid layer could not be established the data suggest that local resuspension by shoaling internal waves maintains the layer during the stratified period the origin and maintenance of the benthic nepheloid layer is most likely the result of local resuspension due to a combination of internal wave action and longer term processes

probing natural iron fertilization near the kerguelen southern ocean using natural phytoplankton assemblages and diatom cultures abstract natural phytoplankton assemblages collected in surface waters above the kerguelen plateau or in the open ocean and single species cultures of southern ocean diatoms were used to address the existence and effects of natural iron fertilization near the kerguelen islands southern ocean the phytoplankton was transferred during so called translocation experiments into water collected at the surface over the plateau open ocean surface water or water collected close to the sediment of the plateau these watertypes differed in iron iron rich deep water and iron poor surface water and silicic acid concentration silicic acid rich plateau deep and open ocean surface water silicic acid poor plateau surface water as a general trend in the natural phytoplankton assemblages cell numbers chlorophyll autofluorescence photosynthetic efficiency of photosystem ii chlorophyll a and phytoplankton carbon concentrations increased especially after translocation into plateau deep water this response was most pronounced in terms of increase in carbon assimilation in the larger sized phytoplankton 8 m in cell diameter mainly diatoms effects of translocation on bacteria and viruses followed those of the phytoplankton experiments with single species cultures of large diatoms fragilariopsis kerguelensis thalassiosira sp chaetoceros dichaeta which have high iron requirements confirmed the observations made for the natural phytoplankton assemblages assuming a continuous flux of deep water to the surface over the kerguelen plateau the translocation experiments provide evidence that this water contains the growth stimulating factor most likely iron responsible for the formation of a phytoplankton bloom as is observed over the kerguelen plateau

a new view of lunar ferroan anorthosites postmagma ocean petrogenesis 1 new melting experiments in the range of 0 1 mpa to 4 7 gpa provide the basis for calculations of polybaric crystallization which show that both a 300 km deep magma ocean mo enriched in refractory elements and a 600 km deep magma ocean with refractory element concentrations similar to the earth s upper mantle produce sufficient amounts of differentiated residual liquid capable of crystallizing the troctolitic noritic mineral assemblages that are prevalent in lunar ferroan anorthosites lfa however the both oceans become saturated with augite after 20 30 crystallization of the plagioclase saturated residuum and thereafter are no longer capable of producing noritic assemblages a second set of melting experiments reveals the existence of a previously unrecognized equilibrium augite liquid pigeonite plagioclase and a thermal minimum on the pigeonite plagioclase liquidus surface at 0 6 gpa these equilibria will produce melts of mafic cumulates with lower wo content than those from which the cumulates originally formed in a postmagma ocean environment of overturning mafic cumulates melt thus formed and entrained in a buoyant segregation of plagioclase would then form diapiric masses that would crystallize troctolitic noritic assemblages after intruding upward diapiric intrusions could also provide the local deformational environment needed to produce the apparently high 95 plagioclase modes of the lfa an unstable density profile in the cumulate pile following crystallization of most of the mo should provide the impetus for overturn and the heat for partially remelting mafic cumulates

origin of the lunar highlands mg suite an integrated petrology geochemistry chronology and remote sensing perspective the mg suite represents an enigmatic episode of lunar highlands magmatism that presumably represents the first stage of crustal building following primordial differentiation this review examines the mineralogy geochemistry petrology chronology and the planetary scale distribution of this suite of highlands plutonic rocks presents models for their origin examines petrogenetic relationships to other highlands rocks and explores the link between this style of magmatism and early stages of lunar differentiation of the models considered for the origin of the parent magmas for the mg suite the data best fit a process in which hot solidus temperature at 2 gpa 1600 to 1800 c and less dense 3100 kg m3 early lunar magma ocean cumulates rise to the base of the crust during cumulate pile overturn some decompressional melting would occur but placing a hot cumulate horizon adjacent to the plagioclase rich primordial crust and kreep rich lithologies at temperatures of 1300 c would result in the hybridization of these divergent primordial lithologies producing mg suite parent magmas as urkreep primeval kreep is not the petrologic driver of this style of magmatism outside of the procellarum kreep terrane pkt mg suite magmas are not required to have a kreep signature evaluation of the chronology of this episode of highlands evolution indicates that mg suite magmatism was initiated soon after primordial differentiation 10 m y alternatively the thermal event associated with the mantle overturn may have disrupted the chronometers utilized to date the primordial crust petrogenetic relationships between the mg suite and other highlands suites e g alkali suite and magnesian anorthositic granulites are consistent with both fractional crystallization processes and melting of distinctly different hybrid sources

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

surficial deep sea sediments across the polar frontal system southern ocean indian sector particulate carbon content and microphyte signatures abstract two main subjects are addressed in this study concerning a complex sub antarctic hydrological system during the antares i md75 cruise southern ocean indian sector 1 the 13 c org signature in waters fluffs and sediments and their relationships with anthropogenic effects and 2 the degree of preservation of the deep sea phytodetritus a north to south gradient was observed for the deep sea microphytes signatures with the higher concentrations in the higher latitude chaetoceros spores dominant species chaetoceros cf neglectus were abundant in the fluffy layers from the permanent open ocean zone pooz and associated with the highest chl a concentration the diatom spores were absent in the northern part of that transect the coccolith repartition and preservation also showed a latitudinal gradient the presence of coccoliths more or less intact below the lysocline may result from different sedimentation rates along this gradient undisturbed and thick fluffs in the pooz and southern polar frontal zone stations were enriched with coccoliths and chaetoceros resting spores even at 4700 m and the revival experiments demonstrated their recent origin via a possible in mass or in pulse sedimentation a latitudinal gradient clearly appeared for 13 c org poc and chloropigments with a relationship between 13 c org and chl a direct positive for the phytoplankton and indirect negative for the fluffs and sediments these observed gradients are in part attributed to the latitudinal effects and to the physical characteristic of the water bodies differences between plankton and sediment 13 c org signatures are attributed to an anthropogenic influence however diagenetic processes leading to slight 13 c org enrichment in sediments cannot be absolutely rejected at this stage a stronger deep northward advection to the north of the polar front may also in part explain these north to south bio geochemical deep sea gradients

radium isotopes to investigate the water mass pathways on the kerguelen plateau southern ocean abstract natural iron fertilization promotes the phytoplankton bloom that takes place on the kerguelen plateau in the indian sector of the southern ocean we measured 228 ra t 1 2 5 75 yr and 226 ra t 1 2 1602 yr in waters above the kerguelen plateau in order to provide information on the water mass pathways which in turn could help elucidate the mechanisms controlling iron fertilization in that area 228 ra activities are extremely low in this region being in most cases 18 g kg station a3 520 m depth located on the plateau in the middle of the bloom area also displays such low values but with higher 228 ra activities and higher 228 ra 226 ra ratios in the upper 150 m such a pattern suggests the presence of a water mass that recently interacted with sediments and therefore has been advected onto the kerguelen plateau elevated 228 ra activities were found in shallow waters in the vicinity of heard island south of the kerguelen plateau contact of the water masses with the shallow lithogenic sediments likely explains these high 228 ra activities when combined with physical observations these results suggest that the water mass advected onto the plateau originates from the south of the kerguelen plateau this northward advection might represent a supply of dissolved and or particulate fe for the observed phytoplankton bloom using the 228 ra profile obtained at station a3 we could estimate the vertical eddy diffusivity k z on the kerguelen plateau our k z estimate 1 5 10 4 1 3 10 4 m 2 s compares well with that reported by park et al 2008a internal tides and vertical mixing over the kerguelen plateau deep sea research ii doi 10 1016 j dsr2 2007 12 027 based on ctd ladcp data by combining this k z estimate with the gradient of dissolved fe observed at a3 blain s sarthou g laan p 2008 distribution of dissolved iron during the natural iron fertilization experiment keops kerguelen plateau southern ocean deep sea research ii doi 10 1016 j dsr2 2007 12 028 we calculate a vertical fe flux of 1 0 14 3 nmol m 2 d

chronological evidence that the moon is either young or did not have a global magma ocean a new age determination for a moon rock collected close to the site of the apollo 16 lander has yielded a surprisingly young age of around 4 360 million years this age would require either that the moon solidified some 200 million years after the formation of the solar system significantly later than is assumed by most lunar formation models or that the long held theory that the moon once had a primordial global magma ocean is flawed in the latter case much of the lunar crust could have been produced by non magma ocean processes such as serial magmatism chemical evolution of planetary bodies ranging from asteroids to the large rocky planets is thought to begin with differentiation through solidification of magma oceans many hundreds of kilometres in depth1 2 3 the earth s moon is the archetypical example of this type of differentiation evidence for a lunar magma ocean is derived largely from the widespread distribution compositional and mineralogical characteristics and ancient ages inferred for the ferroan anorthosite fan suite of lunar crustal rocks the fans are considered to be primary lunar flotation cumulate crust that crystallized in the latter stages of magma ocean solidification according to this theory fans represent the oldest lunar crustal rock type2 3 4 attempts to date this rock suite have yielded ambiguous results however because individual isochron measurements are typically incompatible with the geochemical make up of the samples and have not been confirmed by additional isotopic systems5 6 7 8 9 by making improvements to the standard isotopic techniques we report here the age of crystallization of fan 60025 using the 207pb 206pb 147sm 143nd and 146sm 142nd isotopic systems to be 4 360 3 million years this extraordinarily young age requires that either the moon solidified significantly later than most previous estimates or the long held assumption that fans are flotation cumulates of a primordial magma ocean is incorrect if the latter is correct then much of the lunar crust may have been produced by non magma ocean processes such as serial magmatism10

impact of iron on silicon utilization by diatoms in the southern ocean a case study of si n cycle decoupling in a naturally iron enriched area abstract biogenic silica stocks and fluxes were investigated in austral summer over the naturally iron fertilized kerguelen plateau and in nearby high nutrient low chlorophyll hnlc off plateau surface waters the kerguelen plateau hosted a large diatom bloom with high levels of biogenic silica bsi but relatively low silicic acid si oh 4 uptake rates 1100 600 mmol m 2 and 8 4 mmol m 2 d 1 respectively diatoms of the naturally iron enriched area presented high affinities for silicic acid allowing them in combination with a beneficial nutrient vertical supply to grow in low silicic acid waters

potential and limitations of marine and ice core sea ice proxies an example from the indian ocean sector diatom assemblages in marine cores and sea salt deposition fluxes in ice cores have been used as sea ice proxies in the southern hemisphere here a marine and an ice core proxy record for the indian ocean covering the last two glacial cycles are compared in order to illustrate their potential and limitations the marine core was extracted in a location completely ice free under present day conditions and therefore was unable to record changes to the recent sea ice extent similarly no sea ice was recorded at that location during the previous interglacial period during the last glacial period however the site was seasonally covered by sea ice and the diatom assemblages allowed an estimation of average seasonal sea ice presence the ice core data originated from the east antarctic plateau the marine sodium present in the ice core was used as a proxy of the sea ice coverage and on average a larger sea ice surface led to an increased sea salt aerosol flux seen e g at the last glacial inception however the response of the sea salt flux to increasing sea ice extent diminished during peak glacial conditions when only minimal variability was recorded in the ice core record a first order approximation is used to take this non linear response of the ice core sea ice proxy into account based on the ice core proxy record sea ice extent was reduced considerably during the warm episodes of the previous two interglacial periods compared to modern sea ice extent in particular during the peak warmth of the last interglacial the ice core proxy also showed a very strong precessional variability pronounced spectral peak at 23 ka period over the past 240 ka the advantage of combining the two proxy records lies in the complementary nature of their response while the ice core proxy showed limited sensitivity during full glacial conditions the marine proxy recorded the seasonal sea ice coverage once the sea ice retreated south of the location of the marine core the ice core proxy responded to changes in sea ice extent a composite of marine and ice core records may thus provide a data basis for a more detailed reconstruction of sea ice around antarctica over the last few glacial interglacial cycles

impact of lateral transport on organic proxies in the southern ocean lateral transport of fine grained organic carbon particles can complicate the interpretation of paleoclimate records based on organic proxies here we investigated the effect of lateral transport on newly developed temperature and soil organic matter proxies tex86 and bit index respectively in core md88 769 recovered from the south east indian ridge our results show that tex86 and bit records in comparison to diatom and foraminifera records were representative for more local climate changes while alkenones and n alkanes originated from distant areas by oceanic and atmospheric transport respectively this suggests that tex86 and bit paleoclimate records are primarily influenced by local conditions and less subjected to long distance lateral transport than other organic proxies in the southern ocean

distribution of dissolved iron during the natural iron fertilization experiment keops kerguelen plateau southern ocean abstract the southern ocean is the largest high nutrient low chlorophyll hnlc region of the world ocean it is now well recognized that the low biological productivity in this region is mainly due to the limitation of phytoplankton growth by iron however in the core of the southern ocean a massive bloom occurs annually above the kerguelen plateau in the context of keops kerguelen plateau and ocean compared study we investigated the three dimensional distribution of dissolved iron dfe concentrations southeast of the island we show that in surface waters dfe was low and not significantly different above and outside the plateau 0 090 0 034 and 0 073 0 014 nm respectively by contrast below 150 m major differences in vertical profiles of dfe were observed the deep waters above the plateau were clearly enriched with dfe concentrations up to 0 6 nm near the seafloor the regeneration from sinking biogenic material and the input from the sediments are very likely the major processes delivering dfe to the deep water the deep iron rich reservoir existing above the plateau was responsible for the natural iron fertilization of the surface water by two different mechanisms i winter mixing provided 5 times more dfe to the surface waters above the plateau than outside and ii enhanced vertical gradients of dfe and elevated vertical diffusivity resulted in an 8 fold higher diapycnal diffusive flux the natural iron fertilization presented major differences from artificial iron fertilization experiments carried out in the southern ocean the amount of dfe required to stimulate the biological activity is much less and the mode of addition is clearly different the quantification of the excess of dfe supplied in the naturally fertilized area leads to the conclusion that the natural iron fertilization is 10 150 times more efficient to export carbon below 200 m than in artificial fertilization experiments the bloom above the kerguelen plateau was contingent to iron fertilization but it was also sustained by continuous input of major nutrients thus the natural fertilization described here mimics quite well glacial period scenarios where iron fertilization of the southern ocean might have occurred from below

sedimentary processes in the great lakes sediments in the great lakes are subject to four general categories of processes input transport deposition and postdepositional alteration sedimentary input is from coastal erosion 64 riverine input 26 atmospheric transport 3 and several lesser sources 7 once in the lake sediments are transported to their place of deposition along the bottom and or in suspension depending upon grain size and density the rate of deposition in the great lakes is variable and ranges from zero in some areas to over 6000 g m sup 2 yr sup 1 in the eastern basin of lake erie after deposition sediments undergo bioturbation dissolution of carbonate and opal remobilization of many metals followed by reprecipitation within the surficial oxidized layer and degradation of organic compounds

diatom distribution in southern ocean surface sediments atlantic sector implications for paleoenvironmental reconstructions abstract a study of 230 surface sediment samples collected in the atlantic sector of the southern ocean between the southernmost weddell sea and the subtropical zone documents the modern distribution of diatoms revealing patterns of paleoenvironmental significance estimations of diatom valves per gram dry sediment display numbers of 50 200 106 in the zone of high opal burial located between the mean position of the winter sea ice edge and the polar front and maximum values of greater than 200 106 in the near shore sedimentary basins off the antarctic peninsula lowest diatom concentrations and assemblages strongly affected by dissolution were encountered in the weddell basin despite alteration of the diatom assemblages prior to their incorporation into the sediment record the biogeographic distribution and the abundance pattern of most of the 35 studied diatom species shows a close relationship with the surface hydrography water temperature these relationships can be used to estimate past surface water temperatures based on statistical treatments of the assemblages or on simple relations of species occurrences in the geological record another close link occurs between the distribution of sea ice and sea ice related diatoms

the biogeography of major diatom taxa in southern ocean sediments 2 open ocean related species diatoms from 228 southern ocean core top sediment samples were examined to determine the geographic distributions of 32 major diatom species taxa preserved in the sediments of three zonally distinct regions sea ice open ocean and the tropical subtropical in the first of three papers 14 species taxa occurring in the region where sea ice covers the ocean surface on an annual basis are geographically documented comparisons are drawn between the diatom abundances on the sea floor sea ice parameters annual duration and concentration in february and september and february sea surface temperature such parameters are commonly used in reconstructing past oceanographic conditions in the sea ice and open ocean zones analysis of the geographic patterns and sea surface parameter correlations reveals species specific distributions regulated primarily by sea ice coverage and sea surface temperature which support the use of diatom remains for the estimation of these past seasurface environmental parameters comparison with reliable accounts of the 14 species from the sediments or plankton also provides the first glimpses into species specific ecology and habitat linkages d 2005 elsevier b v all rights reserved

cross frontal exchange of antarctic intermediate water and antarctic bottom water in the crozet basin abstract the hydrographic survey made across the antarctic circumpolar current acc in the southwestern crozet basin during the april may 1993 antares 1 cruise revealed unprecedented strong cross frontal injections of newly formed antarctic intermediate water aaiw into the subtropical zone north of the acc the acc in this area is mostly associated with the subantarctic front saf and subtropical front stf which are tightly merged into one structure bordered to the north with the eastward extension of the agulhas return current the oxygen and salinity extrema of the newly injected aaiw at a depth of 1200 m well north of the stf reach as high as 6 17 ml l 1 and 34 15 these values coincide almost exactly with those in the aaiw source found at a depth of 500 m just south of the saf but surpass considerably oxygen by 1 35 ml l 1 and salinity by 0 23 psu those values corresponding to the old aaiw at the nearby subtropical stations such spectacular cross frontal injections of new aaiw were not continuous in space and time but were found to be rather local intermittent and impulsive this was closely correlated with the highly perturbed meandering frontal zone due to the frequent passages of strong atmospheric depressions during the cruise there is also clear evidence of the northward penetration of antarctic bottom water aabw through the crozet kerguelen gap and its northward flow along the deep western boundary of the crozet basin supporting previous observations moreover our observations indicate more precisely the bottom water pathway which is concentrated against the continental rise west of 56 e following roughly the 4000 m isobath it is concluded that the crozet basin frontal zone acts as a barrier only for the upper layer water masses and that it is dynamically transparent for the cross frontal exchange of intermediate and deeper layer water masses of potential density anomalies greater than 27 1 including aaiw and aabw

a review of lunar chronology revealing a preponderance of 4 34 4 37 ga ages in this study data obtained from sm nd and rb sr isotopic measurements of lunar highlands samples are renormalized to common standard values and then used to define ages with a common isochron regression algorithm the reliability of these ages is evaluated using five criteria that include whether 1 the ages are defined by multiple isotopic systems 2 the data demonstrate limited scatter outside uncertainty 3 initial isotopic compositions are consistent with the petrogenesis of the samples 4 the ages are defined by an isotopic system that is resistant to disturbance by impact metamorphism and 5 the rare earth element abundances determined by isotope dilution of bulk of mineral fractions match those measured by in situ analyses from this analysis it is apparent that the oldest highlands rock ages are some of the least reliable and that there is little support for crustal ages older than 4 40 ga a model age for ur kreep formation calculated using the most reliable mg suite sm nd isotopic systematics in conjunction with sm nd analyses of kreep basalts is 4389 45 ma this age is a good match to the lu hf model age of 4353 37 ma determined using a subset of this sample suite the average modelmore age of 4353 25 ma determined on mare basalts with the 146sm 142nd isotopic system with a peak in pb pb ages observed in lunar zircons of 4340 20 ma and the oldest terrestrial zircon age of 4374 6 ma the preponderance of ages between 4 34 and 4 37 ga reflect either primordial solidification of a lunar magma ocean or a widespread secondary magmatic event on the lunar nearside the first scenario is not consistent with the oldest ages reported for lunar zircons whereas the second scenario does not account for concordance between ages of crustal rocks and mantle reservoirs less

geochronology and petrogenesis of apollo 14 very high potassium mare basalts rb sr k ar and sm nd isotopic studies were undertaken for two apollo 14 very high potassium vhk mare basaltic clasts from breccias 14305 and 14168 the samples are distinctly more radiogenic than other lunar mare basalts rb sr data for the whole rock and mineral separates determine internal isochrons corresponding to essentially identical ages of 3 83 0 08 b y and 3 82 0 12 b y for samples 14305 and 14168 respectively for 87rb 0 0139 b y 1 their corresponding initial 87sr 86sr ratios are indistinguishable and are 0 6995 0 0005 and 0 6997 0 0004 respectively the 39ar 40ar age spectra for the two samples are very similar and give identical plateau ages of 3 85 0 02 b y for 14305 and 3 85 0 05 b y for 14168 the identical rb sr and k ar isotopic results for the two rocks indicate that they could be derived from the same flow the sm nd isotopic data of whole rock and mineral separates for the two vhk basalts define an internal isochron age of 3 94 0 16 b y for 147sm 0 00654 b y 1 and an initial 143nd 144nd of 0 50673 21 the averaged model age relative to the chondritic initial 143nd 144nd of 0 505893 for the basalts is 4 56 0 04 b y the concordance of rb sr k ar and sm nd ages strongly suggests that vhk basalts crystallized from a melt 3 85 b y ago the rb sr and sm nd isotopic data indicate that vhk basalts show very large rb sr fractionation but no significant sm nd fractionation at the time of crystallization the source material for these basalts had a rb sr ratio similar to those of apollo 14 high a1 mare basalts and a nearly chondritic sm nd ratio extreme enrichments of rb sr and k la during the formation of vhk basalts can be adequately explained by an assimilation model that involves basalt granite interaction k rb rich components of granitic wall rocks in highland crust were selectively introduced into ascending hot high a1 mare basaltic magma upon contact a similar crustal assimilation process has been frequently observed in terrestrial mantle derived magma that ascended through the continental crust

146sm 142nd formation interval for the lunar mantle now extinct 146sm t1 2 103ma was present in the early solar system and lunar basalts might be expected to have inherited small anomalies in 142nd abundances from mantle sources with variable sm nd ratios established during the early global differentiation of the moon 142nd 144nd ratios were measured for several lunar basalts and values of nd142 deviations from terrestrial 142nd 144nd in parts in 104 calculated for them the nd142 values show very small variations attributable to 146sm decay neutron capture near the lunar surface also modified both the samarium and neodymium isotopic compositions of the basalt samples the calculated neutron fluences range from 0 to 7 8 1016 n cm2 both thermal and epithermal neutron fluences were calculated from the sm isotopic compositions of the basalts and used to correct the nd142 values for neutron capture by neodymium well resolved radiogenic enrichments nd142 and 0 17 0 08 2 respectively were measured for lunar meteorite asuka 881757 and apollo 17 basalt 74255 respectively for which the neutron fluences were nil basalts 70135 and 75075 which were exposed to small measureable neutron fluences of 2 5 1015 and 7 7 1015 n cm2 respectively have neutron corrected nd142 values of 0 25 0 15 and 0 29 0 11 respectively the average value of radiogenic nd142 for the three high ti basalts from apollo 17 is 0 22 0 06 neutron capture effects were greater for the other basalts but can be corrected using the measured neutron fluences derived from the samarium isotopic data the neutron corrected nd142 for apollo 12 ilmenite basalt 12056 consistent with its derivation from a highly depleted mantle source also three low ti basalts from apollo 12 and apollo 15 12038 15076 15555 have neutron corrected nd142 which are not resolved from zero and average 0 04 0 06 a fourth low ti basalt 12039 has neutron corrected nd142 but is subject to the largest neutron correction of 0 32 e units kreep basalt 14078 was exposed to only a small neutron fluence of 6 4 1015 n cm2 and has a small deficit of 142nd corresponding to nd142 the average neutron corrected nd142 of three kreep basalts is 0 05 0 04 the nd142 values of the basalts correlate with 147sm 144nd values for their source regions as calculated from their ages and initial nd142 values 147sm 143nd and 146sm 142nd systematics were combined in a three stage model yielding an isochron equation for the lunar mantle formation interval which was calculated to be 238 40 56 ma 2 sm nd ratios for the source regions also are derived from the model and compare favorably with values from conventional geochemical models of mare basalt petrogenesis if the moon were formed by impact of a large mars sized planetesimal with the earth the impact was early enough that the lunar mantle cooled to neodymium isotopic closure by 4 32 ga ago the bulk lunar moon142 evaluated from the mantle isochron at 147sm 144nd chur 0 1967 is 0 01 0 03 2 consistent with derivation of lunar and terrestrial neodymium from a common reservoir

identifying impact events within the lunar cataclysm from 40ar 39ar ages and compositions of apollo 16 impact melt rocks abstract lunar impact melt breccias provide a unique record of the timing and frequency of collisional events during the early history of the inner solar system prior to the development of a significant rock record on earth the predominance of ages clustering between 3 8 and 4 0 ga was a major unexpected discovery obtained from geochronological studies of lunar impact melts and is the basis of the concept that a cataclysmic bombardment of large planetesimals struck the earth and moon and possibly the entire inner solar system about 3 85 0 10 billion years ago as a test of the cataclysm hypothesis we measured high resolution 20 50 steps 40 ar 39 ar age spectra on 25 samples of apollo 16 impact melt breccias using a continuous laser heating system on sub milligram fragments twenty one of these 25 breccias produced multi step plateaus that we interpret as crystallization ages with 20 of these ages falling in the range 3 75 3 96 ga we propose that at least four different melt producing impact events can be distinguished based on the ages bulk compositions and petrographic characteristics of apollo 16 melt breccias the recognition of multiple impact events within the apollo 16 melt breccia suite shows that numerous impact events occurred on the lunar surface within a relatively narrow time interval providing additional evidence of a heavy bombardment of the moon during the early archean

chronologic implications for slow cooling of troctolite 76535 and temporal relationships between the mg suite and the ferroan anorthosite suite abstract ages have been obtained using the 87 rb 87 sr 147 sm 143 nd and 146 sm 142 nd isotopic systems for one of the most slowly cooled lunar rocks apollo 17 mg suite troctolite 76535 the 147 sm 143 nd 146 sm 142 nd and rb sr ages derived from plagioclase olivine and pyroxene mineral isochrons yield concordant ages of 4307 11 ma 4299 29 35 ma and 4279 52 ma respectively these ages are slightly younger than the age determined on ferroan anorthosite suite fas rock 60025 and are therefore consistent with the traditional magma ocean model of lunar differentiation in which the mg suite is intruded into the anorthositic crust however the sm nd ages record when the rock passed below the closing temperature of the sm nd system in this rock at 825 c whereas the rb sr age likely records the closure temperature of 650 c a cooling rate of 3 9 c ma is determined using the ages reported here and in the literature and calculated closure temperatures for the ar ar pb pb rb sr and sm nd systems this cooling rate is in good agreement with cooling rates estimated from petrographic observations slow cooling can lower apparent sm nd crystallization ages by up to 80 ma in the slowest cooled rocks like 76535 and likely accounts for some of the variation of ages reported for lunar crustal rocks nevertheless slow cooling cannot account for the overlap in fas and mg suite rock ages instead this overlap appears to reflect the concordance of mg suite and fas magmatism in the lunar crust as indicated by ages calculated for the solidus temperature of 76535 and 60025 of 4384 24 ma and 4383 17 respectively not only are the solidus ages of 76535 and 60025 nearly concordant but the sm nd isotopic systematics suggest they are derived from reservoirs that were minimally differentiated prior to 4 38 ga although the sr isotopic composition of 60025 indicates its source was minimally differentiated the sr isotopic composition of 76535 indicates it underwent fractionation just prior to solidification of the 76535 these observations are consistent with both a magma ocean or a serial magmatism model of lunar differentiation in either model differentiation of lunar source regions must occur near the solidification age of thee samples perhaps the best estimate for the formation age of lunar source regions is the rb sr model age of the 76535 source region age of 4401 32 ma this is in good agreement with sm nd model ages for the formation of ur kreep and suggests that differentiation of a least part of the moon could not have occurred prior to 4 43 ga

constraints on the formation age and evolution of the moon from 142 nd 143 nd systematics of apollo 12 basalts the moon likely formed as a result of a giant impact between proto earth and another large body the timing of this event and the subsequent lunar differentiation timescales are actively debated new high precision nd isotope data of apollo mare basalts are used to evaluate the low ti high ti and kreep mantle source reservoirs within the context of lunar formation and evolution the resulting models are assessed using both reported 146sm half lives 68 and 103 myr the linear relationship defined by 142nd 143nd systematics does not represent multi component mixing and is interpreted as an isochron recording a mantle closure age for the sm nd system in the moon using a chondritic source model with present day 142nd of 7 3 the mare basalt mantle source reservoirs closed at 4 45 09 10 ga t1 2sm146 68 myr or 4 39 14 16 ga t1 2sm146 103 myr in a superchondritic 2 stage evolution model with present day nd142 of 0 mantle source closure ages are constrained to 4 41 08 10 t1 2sm146 68 myr or 4 34 14 15 ga t1 2sm146 103 myr the lunar mantle source reservoir closure ages 4 5 ga may be reconciled by 3 potential scenarios first the moon formed later than currently favored models indicate such that the lunar mantle closure age is near or at the time of lunar formation second the moon formed ca 4 55 to 4 47 ga and small amounts of residual melts were sustained within a crystallizing lunar magma ocean lmo for up to ca 200 myr from tidal heating or asymmetric lmo evolution third the lmo crystallized rapidly after early moon formation thus the sm nd mantle closure age represents a later resetting of isotope systematics this may have resulted from a global wide remelting event while current earth moon formation constraints cannot exclusively advocate or dismiss any of these models the fact that u pb ages and hf isotopes for jack hills zircons from australia are best explained by an earth that re equilibrated at 4 4 ga or earlier following the moon forming impact does not favor a later forming moon if magma oceans crystallize in a few million years as currently advocated then a global resetting possibly by a large impact at 4 40 to 4 34 ga such as that which formed the south pole aitken basin best explains the late mantle closure age for the coupled sm nd isotope systematics presented here

an ancient sm nd age for a ferroan noritic anorthosite clast from lunar breccia 67016 strontium and neodymium systematics have been examined in a clast of ferroan noritic anorthosite from apollo 16 breccia 67016 two splits 328 and 326 of the same clast give different sm nd results split 328 gives a well defined internal isochron age of 4 562 0 068 ga and an initial 143nd 144nd ratio of 0 50673 10 corresponding to nd 0 1 0 2 2 optimized error relative to the murchinson carbonaceous chondrite the pyroxene separate from split 326 lies on the same isochron in contrast the plagioclase and whole rock from split 326 fall below this line indicating a small scale disturbance of the sm nd system this may reflect either an isotopic exchange between the plagioclase and a low sm nd mineral or a loss of radiogenic 143nd from the plagioclase possibly during the period of major impacts at 3 9 ga the preservation of an extremely old age for the noritic ferroan anorthosite 67016 328 suggests a rapid cooling of this rock at an early stage in the evolution of the lunar magma ocean this old age is also consistent with giant impact models for the formation of the moon but implies a relatively early event pre 4 50 ga and therefore rapid accretion and differentiation of the terrestrial planets

a valid margules formulation for an asymmetric ternary solution revision of the olivine ilmenite thermometer with applications abstract the olivine ilmenite thermometer of andersen and lindsley 1979 was based on an incorrect formulation for the excess free energy of an asymmetric ternary solution a valid formulation is derived and used to revise the parameters of the olivine ilmenite thermometer for olivine and ilmenite that have equilibrated above 700 c temperature can be calculated from t c 273 12549 p 0 03x fa 0 01099 x gk x il 0 062 10496 x fa 5767 x gk x il x hem 38602 141550x il 47183x gk 5 67 r ln k d 6 52x fa 3 09 x gk x il x hem 16 49 109 46 x il 36 49x gk with k d x il x fo x gk x fa the revised model gives wil gkg 5767 3 09t 0 011p and gexch 7301 8 9t 0 047p t in k p in bars applications include apollo 17 breccias and kimberlites

lunar magma transport phenomena abstract an understanding of the most significant events during the first ga or so of lunar history global differentiation associated with a lunar magma ocean lmo and the later generation of about 107 km3 of mare basalts depends profoundly on magma transport dynamics lmo evolution is dominated by the characteristics of hard turbulent convection of a fluid undergoing phase change quench protocrust formed at the ocean surface in early times is repeatedly disrupted by bolide impact ocean body tides and associated crustal foundering during this epoch the ocean temperature is set by the balance between convective heat brought to the surface and brown body radiation from the surface at later times the convective flow is organized into a number of regimes from top to bottom these include conductive crustal lid a viscous sublayer an inertial core a lower viscous sublayer and a mushy cumulate region crystal settling and flotation is restricted to the viscous sublayer regions dilatancy pumping may prevent the efficient expulsion of intercumulus melt during cumulate formation typical velocities within the inertial region are of order 10 m s because late stage ti rich cumulates are dense relative to the earlier mg rich cumulates hyper to sub solidus convection tends to mix lmo crystallization products numerical simulations that account simultaneously for compositional and thermal buoyancy effects indicate a characteristic mixing time 200 ma statistical measures of mixing variance and spatial correlation length quantify the details of mixing the darcy percolative and vein drain models of melt extraction are briefly discussed because compaction lengths are small 102 m the rate of melt extraction is governed by the balance between melt buoyancy and darcy friction differential melt matrix velocities are of order 10 km ma for nominal values appropriate for mare basalt melt extraction from a heterogeneous mixed lmo source transport of magma through the lunar lithosphere via a connected crack network seems highly probable for the range of inferred discharge rates applicable for lunar mare volcanism lmv 103 to 107 m3 s typical fracture widths and ascent speeds are 10 1 to 50 m and 10 1 to 10 m s respectively a simple model is proposed to evaluate the extent of fractionation as magma traverses cold lunar lithosphere if apollo green glasses are primitive and have not undergone significant fractionation en route to the surface then mean ascent rates of 10 m s and cracks of widths 40 m are indicated lunar tephra and vesiculated basalts suggest that a volatile component plays a role in eruption dynamics the predominant vapor species appear to be co co2 and cos near the lunar surface the vapor fraction expands enormously and vapor internal energy is converted to mixture kinetic energy with the concomitant high speed ejection of vapor and pyroclasts to form lunar fire fountain deposits such as the apollo 17 orange and black glasses and apollo 15 green glass

contribution of resuspended sedimentary particles to dissolved iron and manganese in the ocean an experimental study abstract a number of trace metals play essential roles in marine ecosystem structure and biological productivity until recently it has been argued that phytoplankton access primarily dissolved iron while particulate iron was considered a refractory material with little use biologically and limited interaction with the dissolved pool in order to assess the transfer mechanisms between sediment sourced particulate trace metals and the dissolved pool we conducted a 14 month incubation that reacted resuspended sediments with natural seawater both originating from the kerguelen area keops cruises southern ocean in the dark and at concentrations replicating natural conditions three types of sediments were investigated named biosi biosi ca and basalt mostly composed of i biogenic silica bsio2 ii bsio2 and calcite and iii basaltic fragments respectively the release of dissolved silicon dsi iron dfe and manganese dmn was monitored regularly throughout the incubation as well as living bacteria density and fe organic ligands depending on the origin and composition of the sediment unique dfe and dmn fluxes were observed including a strong decoupling between dfe and dmn the basaltic sediment released up to 1 09 0 04 nmol l 1 of dfe and 0 28 0 09 nmol l 1 of dmn while the biogenic sediments released a higher 3 91 0 04 nmol l 1 and 8 03 0 42 nmol l 1 of dfe and dmn respectively several factors influencing the release and removal of dfe and dmn were discernable at the temporal sampling resolution of the incubation including the structural composition of the sediment bacterial abundance and the formation of manganese oxides the regular sampling over short timescales and the extended sampling over one year proved to be critical to constrain the processes and exchanges that govern the contribution of the particulate to the dissolved pools overall this incubation provides a strong basis for reassessing the role of resuspended sedimentary particles in the marine biogeochemical cycles of fe and mn indeed we show that biogenic silica calcite rich and basaltic particles can contribute substantial dissolved fe and mn to the overlying water column in the future the global extent of this previously overlooked external metal source should be quantified through further process studies and biogeochemical models this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

timing of mantle overturn during magma ocean solidification abstract solidification of magma oceans mos formed early in the evolution of planetary bodies sets the initial condition for their evolution on much longer time scales ideal fractional crystallization would generate an unstable chemical stratification that subsequently overturns to form a stably stratified mantle the simplest model of overturn assumes that cumulates remain immobile until the end of mo solidification however overturning of cumulates and thermal convection during solidification may act to reduce this stratification and introduce chemical heterogeneity on scales smaller than the mo thickness we explore overturning of cumulates before the end of mo crystallization and the possible consequences for mantle structure and composition in this model increasingly dense iron rich layers crystallized from the overlying residual liquid mo are deposited on a thickening cumulate layer overturn during solidification occurs if the dimensionless parameter r c measuring the ratio of the mo time of crystallization m o to the timescale associated with compositional overturn o v g h exceeds a threshold value if overturn did not occur until after solidification this implies that the viscosity of the solidified mantle must have been sufficiently high possibly requiring efficient melt extraction from the cumulate for a given rate of solidification for the lunar mo possible implications for the generation of the mg suites and mare basalt are suggested

application of modern analog technique to marine antarctic diatoms reconstruction of maximum sea ice extent at the last glacial maximum modern analog technique mat applied to antarctic diatoms is a new approach for quantitative sea ice paleoreconstructions in the southern ocean in a first step we show that mat is a better approach than the imbrie and kipp method to reconstruct the modern sea ice pattern we then use this approach to reconstruct sea ice presence in number of months per year during the last glacial maximum lgm at this time sea ice presence was greater than today leading to a shorter diatom growing season the maximum sea ice extent inferred from quantitative values of sea ice presence was located 5 8 north of its actual position leading to double the surface of modern winter sea ice this greater sea ice extent may have played a significant role on atmospheric and surface oceanic circulations and therefore on southern mid latitude and high latitude climates it may also have reduced the amount of heat moisture and co2 from the ocean to the atmosphere thus participating in the lowering of atmospheric co2 during the lgm

the formation and evolution of the moon s crust inferred from the sm nd isotopic systematics of highlands rocks abstract ages determined for magnesian and ferroan anorthosite crustal rock suites overlap suggesting they formed contemporaneously about 4 3 4 5 ga a notable exception is the sm nd age previously determined on mg suite gabbronorite 67667 which is at least 100 ma younger than the youngest ferroan anorthosite new chronologic measurements of 67667 presented here yield concordant sm nd and rb sr mineral isochron ages of 4349 31 ma and 4368 67 ma suggesting the sample is older than previous estimates furthermore a whole rock sm nd isochron of mg suite rocks from the apollo 14 15 16 and 17 landing sites yields an age of 4348 25 ma indicating that mg suite magmatism was widespread and roughly contemporaneous on the lunar nearside analysis of sm nd internal isochron ages confirms that mg suite magmatism was restricted to a period between about 4 33 and 4 35 ga at the apollo 14 15 16 and 17 landing sites and was synchronous with magmatism at the apollo 16 site associated with the ferroan anorthosite suite between 4 35 and 4 37 ga magnesian and ferroan anorthosite suite rocks with ages younger than 4 33 ga appear to have experienced slow cooling in the deep lunar interior so that the ages record when the samples cooled below the closure temperature of the sm nd isotopic system and not the time they crystallized the ages determined for mg suite and ferroan anorthosite suite rocks are concordant with the age determined for the formation of urkreep of 4350 34 ma using the sm nd isotopic systematics of 67667 and measurements completed on norite 78238 troctolite 76535 kreep basalt 15386 and gabbronorite nwa 773 crystallization ages of mg suite and fas are also concordant with the average of 146sm 142nd ages previously determined for the formation of the mare basalt source region of 4333 30 ma the similarity of ages for mg suite magmatism ferroan anorthosite suite magmatism urkreep formation and formation of the mare basalt source regions implies the processes that produced these rocks were petrogenetically linked it also implies that both early stage and late stage lunar magma ocean cumulates formed over a relatively short duration of

isotopic evidence for a young lunar magma ocean abstract mare basalt sources and ferroan anorthosite suite cumulates define a linear array on a 146sm 144nd versus 142nd 144nd isochron plot demonstrating these materials were derived from a common reservoir at 4336 31 32 ma the minimum proportion of the moon that was in isotopic equilibrium at this time is estimated to be 1 3 of its entire volume based on the geographic extent from which the analyzed samples were collected and the calculated depths from which the samples were derived scenarios in which large portions of the moon were molten to depths of many hundreds of kilometers are required to produce the observed sm nd isotopic equilibrium between the mantle and crustal rocks at 4 34 ga this is a consequence of the fact that limited heating of a solid moon above the blocking temperature of the sm nd isotopic system is insufficient to diffusively homogenize radiogenic nd throughout the mantle and crust there are three scenarios that might account for global scale isotopic equilibrium on the moon relatively late in solar system history including 1 sm nd re equilibration of a solid moon resulting from widespread melting in response to mantle overturn or a very large impact 2 early accretion of the moon followed by delayed cooling due to the presence of an additional heat source that kept a large portion of the moon molten until 4 34 ga or 3 late accretion of the moon followed by rapid cooling of the magma ocean late in solar system history neither density driven overturn of the mantle nor a large impact are likely to homogenize the mantle and crust to the extent required by the sm nd isochron likewise secondary heating mechanisms such as tidal heating or radioactive decay are not efficient enough to keep the moon molten to the depth of the mare basalt source regions for many tens to hundreds of millions of years instead the age of equilibrium between such a compositionally diverse set of rocks produced on a global scale likely records the time of primordial solidification of the moon from a magma ocean this scenario accounts for both the petrogenetic characteristics of lunar rock suites as well as their sm nd isotopic systematics it is supported by the preponderance of 4 35 ga ages obtained for other hypothetical magma ocean crystallization products such as ferroan anorthosite suite rocks and k ree and p enriched cumulates that are thought to represent flotation cumulates of the magma ocean and the last vestiges of magma ocean solidification respectively

extensive phytoplankton blooms in the atlantic sector of the glacial southern ocean 1 the sources and sinks of atmospheric carbon dioxide over glacial interglacial cycles are under debate variation in productivity of the antarctic circumpolar current acc could potentially play a significant role but current interpretations of sedimentary geochemical proxies suggest that glacial productivity was not higher than today we present areal and down core distribution patterns of previously overlooked diatom resting spores that indicate the occurrence of extensive phytoplankton blooms across the entire atlantic sector of the acc particularly in the seasonal ice zone siz linked to higher iron input during the last glacial sea ice acts as an effective transporter of iron and enhances its bioavailability the dominance of the deep living radiolarian cyladophora davisiana in glacial siz sediments indicates that organic carbon export to mesopelagic depths was at least tenfold higher than today

sinking particle properties from polyacrylamide gels during the kerguelen ocean and plateau compared study keops zooplankton control of carbon export in an area of persistent natural iron inputs in the southern ocean the kerguelen ocean and plateau compared study keops examined the origin of elevated phytoplankton biomass in naturally iron fertilized waters over the kerguelen plateau during midsummer january february 2005 we report sinking particle characteristics determined from image analysis of thousands of individual particles collected in viscous polyacrylamide gels placed in free drifting sediment traps at two sites a high phytoplankton biomass site over the central plateau a3 and a moderate biomass site at its periphery c5 the particles were divided into three types 1 oval fecal pellets 2 cylindrical fecal pellets and 3 aggregates the aggregates were most abundant and mainly consisted of agglomerations of the cylindrical fecal pellets conversion of the pellet and aggregate volumes to carbon contents suggests export fluxes of 50 60 mg c m22 d21 at 100 m depth in reasonable agreement with independent estimates from carbon and 234th measurements our observation that the majority of the particle flux was processed through the heterotrophic foodweb contrasts with the results of artificial iron fertilization experiments and with models for export from productive diatomdominated waters that emphasize direct export of phytoplankton detritus the keops results may offer more appropriate scaling for the response of ecosystem structure and carbon export to persistent iron fertilization in the southern ocean

diatoms preserved in surface sediments of the northeastern kerguelen plateau abstract an island mass effect was observed from the sedimentary distribution of diatoms on the northeastern kerguelen plateau five new samples placed in context to species distributions previously reported from the permanently open ocean zone pooz revealed a plateau community dominated by three species taxa fragilariopsis kerguelensis thalassionema nitzschioides f nitzschioides and chaetoceros hyalochaete resting spores intermediate abundances of thalassiosira antarctica were unique to the plateau sediment signature as were increased abundances of eucampia antarctica v antarctica the off plateau sediment sample contained typical pooz sediment distributions dominated by f kerguelensis thalassiosira lentiginosa and thalassiothrix antarctica the role of deposition from the surface waters to the sediments was investigated by comparison to the diatom thanatocoenose observed in surface waters these results suggest that the use of sediment abundances of c hyalochaete resting spores and f kerguelensis to determine past productivity events such as wind sourced iron enrichment of the southern ocean at the last glacial maximum is not straightforward the elevated abundance of t nitzschioides f nitzschioides on the plateau did not indicate an iron deplete regime but the converse for the evaluation of paleo productivity hypotheses for the open southern ocean we suggest caution in the use of subantarctic and kerguelen plateau sediment signatures and emphasize that there is a need to also study antarctic coastal and especially sea ice melt water stimulated blooms

the age of ferroan anorthosite 60025 oldest crust on a young moon abstract sm nd isotopic data for mineral separates from the ferroan anorthosite 60025 define a precise isochron of 4 44 0 02ga age this age is roughly 110 m y younger than the formation of the first large solid objects in the solar nebula as recorded by the radiometric ages of the differentiated meteorites in the magma ocean model for early lunar differentiation ferroan anorthosites are the first crustal rocks to form on the moon if the moon is as old as the oldest meteorites the relatively young age determined for 60025 implies either that the magma ocean did not form synchronously with lunar formation or that the magma ocean required over 100 m y before reaching the stage of ferroan anorthosite crystallization alternatively we propose that the accumulated body of radiogenic isotope data for lunar rocks permit the moon to be as young as 4 44 4 51 ga if so isotopic evidence for chemical differentiation on the earth at about this same time suggests that the formation of the moon is reflected in the chemical evolution of the earth this in turn is consistent with the idea that the materials that now make up the moon were derived from the earth perhaps ejected by collision between the earth and another very large planetesimal during the final stages of accumulation of the terrestrial planets terrestrial origin models for the moon lessen the requirement that the earth and moon each have near chondritic relative abundances of the refractory elements and could require that certain chemical and isotopic characteristics of both bodies be considered in the framework of the chemical mass balance of the combined earth moon system

geochronology of an apollo 16 clast provides evidence for a basin forming impact 4 3 billion years ago we examined lithic breccias from the apollo sample collection in order to identify ferroan anorthosite samples suitable for geochronology and better define the age relationships between rocks of the lunar highlands clast 3a is a previously unstudied noritic anorthosite from apollo 16 lithic breccia 60016 with textural evidence of slow subsolidus recrystallization we estimate a cooling rate of 10 c myr and calculate a pyroxene solvus temperature of 1 100 1 000 c pyroxene exsolution lamellae 1 3 m indicate that the last stage of cooling was rapid at 0 2 c year typical of rates observed in thick ejecta blankets we calculate concordant ages from the 147sm 143nd 146sm 142nd rb sr and ar ar isotopic systems of 4 302 28 4 296 39 53 4 275 38 and 4 311 31 ma respectively with a weighted average of 4 304 12 ma the closure temperature of the sm nd system is 855 14 c whereas the closure temperature of the ar ar system is 275 25 c cooling from 855 to 275 c at 10 c myr should result in an age difference between the two isotopic systems of 60 myr the concordant sm nd rb sr and ar ar ages imply that they record the time the rock was excavated by a large impact from the midcrust the ages clearly predate various late accretion scenarios in which an uptick in impacts at 3 8 ga is preceded by a period of relative quiescence between 4 4 and 4 1 ga and instead are consistent with decreasing accretion rates following the formation of the moon

diatom assemblages from coastal settings of west antarctica abstract diatom assemblages from 33 core tops collected along a 2500 km transect of the northern antarctic peninsula and pine island bay areas were examined for their use as paleoenvironmental proxies environmental affinities of assemblages were interpreted within a broad geographical context and a wide range of ecological conditions four major assemblages were identified three pelagic assemblages related to different sea ice duration sst and other conditions affecting primary production and one benthic and epiphytic dominated assemblage typical of near shore shallow water habitats chaetoceros resting spores are an important component of diatom assemblages their high concentrations may reflect increased primary production and are associated with low total assemblage diversities the lowest diversities are observed at sites with increased resting spore percentages along the nw coast of the antarctic peninsula sedimentation rates strongly influence total diatom concentrations by contrast relative abundances of chaetoceros resting spores remain mostly unaffected by terrigenous flux and may serve as a reliable proxy for primary production this broad sampling of antarctic coastal environments fills a gap in our knowledge of phytoplankton communities in polar regions and helps establish the framework for reconstructing paleoenvironments from the paleorecord

late pliocene sea ice expansion and its influence on diatom species turnover in the southern ocean abstract fossil diatom records from the southern ocean are needed to clarify the detailed conditions under warmer than present global climate in the piacenzian stage 3 60 2 588 ma and to provide direct evidence of simultaneity between changes in environmental conditions and diatom species turnovers in this study fossil diatom records between 3 5 and 2 8 ma were investigated at two sites located along a latitudinal gradient within the indian sector of the southern ocean offshore from prydz bay and south east of the kerguelen plateau paleoceanographic changes were assessed from assemblage changes of extant diatom indicators fluctuations of their relative percentages were compared with those of extinct diatom species the diatom assemblage between 3 5 and 3 1 ma consisted of open ocean species which indicate warmer than present sst notable increases in sea ice associated species were identified at 3 3 ma and 3 1 ma at both sites our results suggest sea ice existence during short intervals of 3 3 ma and 3 1 2 8 ma at the studied area at both sites relative abundances of species which have first occurrences during the piacenzian increased at 3 2 3 1 ma conversely those of species which have last occurrences during the piacenzian decreased at the same period these diatom records show a correlation with cooling at 3 1 ma suggested from extant indicators and compositional changes in fossil diatoms from the southern ocean this comparison can provide insights into the environmental effects on diatom evolutionary acceleration which can help identify ecologies of extinct species

distribution of chaetoceros resting spores in modern peri antarctic sediments abstract one hundred and sixty five surface sediment samples from the southern ocean were examined for distribution and relative abundance of chaetoceros resting spores the contribution of resting spores to the total diatom assemblage ranges from 0 in the subantarctic zone to 95 in the antarctic peninsula sector on the basis of both absolute and relative abundances four biogeographic zones are distinguished 1 the antarctic peninsula sector 2 the embayment systems ross sea and weddell sea 3 the continental shelf zone water depth 2000 m chaetoceros resting spores abundance reaches up to 900 10 6 valves g of dry sediment in the gerlache strait southwest of the antarctic peninsula the hydrology of this region is characterized by an intense stratification of the water column due to sea ice meltwater inputs continental glacial runoffs and thermal warming of the surface water layer the availability of nutrients the lack of vertical mixing in those surface waters having low salinity 2 4 c is thought to be the main pre condition for development of large chaetoceros species blooms we propose that increased relative abundances of chaetoceros resting spores in fossil diatom assemblages from the southern ocean can therefore be used as tracers of water column stratification due to glacial melt water

the timing of lunar solidification and mantle overturn recorded in ferroan anorthosite 62237 abstract ferroan anorthosite suite fas rocks are widely interpreted to represent primordial lunar crust despite their importance in pinpointing the timing of lunar crust formation robust chronological investigations for this rock type are scarce here we report the ar ar rb sr and sm nd isotopic systematics for the fas troctolitic anorthosite 62237 the ar ar isotopic system has been reset by a thermal event at 3710 48 ma and the rb sr isotopic systematics has been disturbed such that a rb sr isochron age cannot be determined however an internal isochron for the sm nd isotopic system has yielded an age of 4350 73 ma mswd 2 0 with an initial 143 ndchur of 0 53 0 26 the mineral and whole rock fractions of 62237 plot on the same internal isochron as fas sample 60025 the combined datasets define an age of 4372 35 ma mswd 4 0 with an initial 143 ndchur of 0 17 0 22 literature sm nd data for fas and mg suite whole rocks also plot on the 60025 62237 isochron the coherence of data from both fas and mg suite rocks examined thus far suggests that both rock suites formed contemporaneously from identical or nearly identical sources in addition the concordance of fas and mg suite ages suggests that primordial crust solidification either involved both magmatic suites or that mg suite magmatism was contemporaneous with fas magmatism within resolution of the sm nd chronometer the ages for fas and mg suite also coincide with the formation ages of the mare basalt source regions and urkreep ferroan anorthosite suite rocks and urkreep are thought to represent primordial lmo solidification products whereas mg suite and the mare basalt source regions are argued to represent mixtures of various lmo crystallization products that were formed during density driven overturn of the lmo the concordance of ages implies that the 4372 35 ma sm nd isochron records the age of mantle overturn and that overturn occurred during or shortly after solidification of the lmo

large scale circulation over and around the northern kerguelen plateau abstract the kerguelen plateau is known to constitute a major barrier to the eastward flowing antarctic circumpolar current however there is limited knowledge on the regional circulation due to sparse observations especially in the northern kerguelen plateau between the fawn trough and the kerguelen islands as part of the physical component of the multidisciplinary keops cruise systematic ctd measurements along three sw ne oriented sections were made on the latter plateau cutting through the annual phytoplankton bloom across the eastern flank of the plateau into deep water major hydrographic features and geostrophic velocities perpendicular to the sections were first documented from these in situ observations in order to interpret the results within the general circulation context and to trace the upstream pathways of the observed water masses we established a synthetic picture of the large scale circulation over and around the entire northern kerguelen plateau using the combination of new data from keops with historical hydrographic data together with all available information on mid depth and near surface velocities derived from autonomous floats surface drifting buoys and satellite altimetry this synthesis shows that the time mean geostrophic flow over the shallow platform is sluggish of the order of 3 5 cm s 1 with a general anticyclonic circulation roughly following the local bathymetry this weak flow is bordered to the east by relatively strong up to 18 cm s 1 northwestward flow along the eastern flank of the northern kerguelen plateau due to a northward bifurcation of cold antarctic waters of eastern enderby basin origin carried by the powerful fawn trough current we have shown the utmost importance of the general circulation for the spatial distribution of primary productivity in that the sluggish circulation over the complex shallow topography of the northern kerguelen plateau may precondition the recurrence of annual blooms in contrast to neighboring strong advective regimes without blooming in deep water

the lunar magma ocean reconciling the solidification process with lunar petrology and geochronology abstract the moon is thought to have originated with a magma ocean that produced a plagioclase flotation crust as solidification proceeded ages of anorthositic crust range over at least 200 million years the model for solidification presented here integrates chemical and physical constraints of lunar magma ocean solidification to determine 1 the final thickness of flotation crust generated by a fractionally solidifying magma ocean 2 the timescale of crystallization before plagioclase is a stable phase 3 the timescale of solidification after the formation of the plagioclase flotation crust and 4 the post overturn lunar mantle composition and structure we find that magma oceans of as much as 1000 km depth are consistent with creating an anorthositic crust 40 to 50 km in thickness solidification of the magma ocean prior to formation of the flotation crust may occur on the order of 1000 years and complete solidification would require additional ten to tens of millions of years reconciling these short model timescales with radiometric dates of crustal samples requires either a very late forming moon combined with finding older crustal ages to be incorrect or calling on tidal heating of the crust by the early earth to prolong solidification gravitationally driven overturn of cumulates during tidal heating provides a mechanism for creating the compositions and ages of the lunar mg suite of crustal rocks further we find that upon crystallization the moon likely began with an azimuthally heterogeneous gravitationally stable mantle after magma ocean cumulate overturn this result may help explain the experimentally determined origin of picritic glasses at similar depths but from different source materials

chronology geochemistry and petrology of a ferroan noritic anorthosite clast from descartes breccia 67215 clues to the age origin structure and impact history of the lunar crust the petrology major and trace element geochemistry and nd ar sr isotopic compositions of a ferroan noritic anorthosite clast from lunar breccia 67215 have been studied in order to improve our understanding of the composition age structure and impact history of the lunar crust the clast designated 67215c has an unusually well preserved igneous texture mineral compositions are consistent with classification of 67215c as a member of the ferroan anorthositic suite of lunar highlands rocks but the texture and mineralogy show that it cooled more rapidly and at shallower depths than did more typical ferroan anorthosites fans incompatible trace element concentrations are enriched in 67215c relative to typical fans but diagnostic signatures such as ti sm sc sm plagiophile element ratios and the lack of zr hf and nb ta fractionation show that this cannot be due to the addition of kreep alternatively 67215c may contain a greater fraction of trapped liquid than is commonly present in lunar fans 147sm 143nd isotopic compositions of mineral separates from 67215c define an isochron age of 4 40 0 11 gyr with a near chondritic initial 143nd of 0 85 0 53 the 40ar 39ar composition of plagioclase from this clast records a post crystallization thermal event at 3 93 0 08 gyr with the greatest contribution to the uncertainty in this age deriving from a poorly constrained correction for lunar atmosphere 40ar rb sr isotopic compositions are disturbed probably by the same event recorded by the ar isotopic compositions trace element compositions of fans are consistent with crystallization from a moderately evolved magma ocean and do not support a highly depleted source composition such as that implied by the positive initial 143nd of the ferroan noritic anorthosite 62236 alternatively the nd isotopic systematics of lunar fans may have been subject to variable degrees of modification by impact metamorphism with the plagioclase fraction being more strongly affected than the mafic phases 147sm 143nd isotopic compositions of mafic fractions from the 4 ferroan noritic anorthosites for which isotopic data exist 60025 62236 67016c 67215c define an age of 4 46 0 04 gyr which may provide a robust estimate for the crystallization age of lunar ferroan anorthosites

dissolved rare earth elements tracing lithogenic inputs over the kerguelen plateau southern ocean abstract dissolved rare earth elements rees were measured in the water masses upstream from and over the kerguelen plateau indian sector of the southern ocean upstream from the plateau the ree profiles were consistent with published data from the southern and indian oceans over the plateau a one box model yields a lithogenic nd flux from the dissolution of lithogenic material of 89 20 t nd y 1 and a corresponding dissolved iron input larger than 100 000 t fe y 1 however despite evidence of this significant lithogenic input dissolved fe is strongly depleted in the upper layers contrasting with the enriched ree concentrations this contrast stresses the different behaviours of ree and iron in the surface waters and the fact that strong fertilization does not imply dissolved fe replete waters

lunar feldspathic meteorites constraints on the geology of the lunar highlands and the origin of the lunar crust abstract the composition of the lunar crust provides clues about the processes that formed it and hence contains information on the origin and evolution of the moon current understanding of lunar evolution is built on the lunar magma ocean hypothesis that early in its history the moon was wholly or mostly molten this hypothesis is based on analyses of apollo samples of ferroan anorthosites 90 plagioclase molar mg mg fe mg 75 and the assumption that they are globally distributed however new results from lunar meteorites which are random samples of the moon s surface and remote sensing data show that ferroan anorthosites are not globally distributed and that the apollo highland samples used as a basis for the model are influenced by ejecta from the imbrium basin in this study we evaluate anorthosites from all currently available adequately described lunar highland meteorites representing a more widespread sampling of the lunar highlands than apollo samples alone and find that 80 of them are significantly more magnesian than apollo ferroan anorthosites interestingly luna mission anorthosites collected outside the continuous imbrium ejecta are also highly magnesian if the lunar highland crust consists dominantly of magnesian anorthosites as suggested by their abundance in samples sourced outside imbrium ejecta a reevaluation of the lunar magma ocean model is a sensible step forward in the endeavor to understand lunar evolution our results demonstrate that lunar anorthosites are more similar in their chemical trends and mineral abundance to terrestrial massif anorthosites than to anorthosites predicted in a lunar magma ocean this analysis does not invalidate the idea of a lunar magma ocean which seems a necessity under the giant impact hypothesis for the origin of the moon however it does indicate that most rocks now seen at the moon s surface are not primary products of a magma ocean alone but are products of more complex crustal processes

a chemical model for generating the sources of mare basalts combined equilibrium and fractional crystallization of the lunar magmasphere abstract it is generally considered that mare basalts were generated by the melting of a cumulate mantle formed in an early moon wide magma ocean or magmasphere however the nature and chemistry of this cumulate mantle and the logistics of its origin have remained elusive extensive studies of terrestrial layered mafic intrusions over the past sixty years have emphasized the imperfection of fractional crystallization and attendant crystal crystal and crystal liquid separation in a convecting magma chamber crystal liquid and crystal crystal separations were similarly inefficient during evolution of the lunar magma ocean lmo allowing for the trapping of interstitial liquid and entrainment of a small proportion of less dense plagioclase into the denser mafic cumulate mush indeed petrography of lunar highlands samples demonstrates this for anorthosites with 1 10 olivine the residual liquid after 80 90 crystallization was very evolved in fact kreepy and even in small proportions 1 5 would have a noticeable effect on the trace element chemistry of melts generated from these cumulates this trapped residual liquid would elevate total ree abundances in the cumulate pile while synchronously deepening the already negative eu anomaly essentially this trapped liquid will make the cumulate more fertile for melting to generate both kreep basalt and mare basalt magmas plagioclase entrained in the mafic cumulate pile adds an essential al component to the high ti basalt source and will moderate the requisite negative eu anomaly in the cumulate early in the evolution of the lunar mantle when the lmo still was largely liquid it is likely that vigorous convection was an important factor in crystallization such convection would allow crystals to remain suspended and in equilibrium with the lmo liquid for relatively long periods of time this extended period of equilibrium crystallization would then have been followed by fractional crystallization once plagioclase became a liquidus phase and began to float to form the lunar highlands crust previous authors have proposed a three component model for the evolution of high ti mare basalt source regions this model includes kreep early olivine rich high mg cumulates and late ilmeniterich low mg cumulates in various proportions however we propose a model for high ti basalt parent magmas which is in accord with studies of terrestrial layered intrusions this model for the high ti source includes trapped instantaneous residual liquid tirl 1 3 and entrainment of a small 2 5 proportion of plagioclase into the late stage cumulate pile in order to account for both the observed al compositions and trace element characteristics of high ti mare basalts melting of this relatively shallow ilmenite and clinopyroxene bearing late stage cumulate can generate high ti mare basalt magmas furthermore we are in agreement with other workers that only through a process of nonmodal melting will the high ti values for the parent magmas be realized large scale convective overturn of the cumulate pile and mixing of kreep with early and late stage cumulates is not required however localized overturn of the upper tenth of the cumulate pile is likely and in fact required to achieve an appropriate major element balance for the high ti mare basalt source region

isotopic studies of ferroan anorthosite 62236 a young lunar crustal rock from a light rare earth element depleted source isotopic analyses of mineral fractions and whole rocks from the ferroan anorthosite 62236 yield a sm nd isochron with an age of 4 29 0 06 ga and an initial end143 value of 3 1 0 9 we have also measured end142 anomalies of 0 25 on two fractions of 62236 these values are higher than the value of 0 1 predicted if 62236 was derived from a chondritic source at 4 29 ga but are consistent with the positive initial end143 value the sm nd isotopic composition of 62236 has been modified by the capture of thermal neutrons such that the 147sm 144nd 143nd 144nd and 142nd 144nd ratios measured on the mineral fractions and whole rocks must be corrected the corrections do not significantly alter the sm nd isotopic results determined on 62236 despite the fact that the ar ar and rb sr isotopic systematics of 62236 have been reset by impact metamorphism at 3 93 0 04 ga the sm nd systematics appear to have been unaffected the sm nd isotopic systematics of 62236 provide several constrains on models of lunar crustal differentiation provided they have not been reset since crystallization first the relatively young age of 62236 as well as the old ages determined on several crustal plutonic rocks of the mg suite require multiple sources of magmas on the moon very early in its history second positive end143 values determined on all analyzed ferroan anorthosites suggest that they were derived from sources depleted in light rare earth elements and third models based on initial end143 and present day end142 values suggest that the source of 62236 was depleted in light rare earth elements at 4 46 ga in order to reconcile these observations with the lunar magma ocean model 1 the magma ocean must have existed for a very short period of time and may have had a sub chondritic nd sm ratio and 2 the youngest ferroan anorthosites such as 62236 cannot be cumulates from the magma ocean but must form by other processes

stratigraphy of the lunar highland crust depths of burial of lunar samples from cooling rate studies current models of lunar crustal stratigraphy are based primarily on models of impact cratering coupled with what is known about the distribution of rock types in the ejecta blankets associated with the large multiring basins these models postulate an upper crust rich in the ferroan anorthosite component underlain by a more mafic noritic lower crust spudis 1993 we attempted to test these models by determining the depth at which various lunar plutonic rocks formed despite intense brecciation and shock many lunar highland samples retain vestiges of a prior magmatic history for example pyroxene samples preserve a record of their thermal history in such phenomena as cation ordering and exsolution textures by computer simulation of the growth of exsolution lamellae in augite and pigeonite we deduced cooling rates and from these estimated a depth of burial on the basis of a simple model for the thermal evolution of the lunar crust despite the fairly large uncertainties in the calculations it is clear that the ferroan anorthosite samples we studied formed at a depth between 10 and 20 km whereas some members of highland magnesian and alkali suites formed as cumulates in magma chambers intruded into the uppermost layers of the crust as yet there is no evidence to indicate that crystalline rocks from the lower half of the lunar crust are present in the samples returned by the apollo missions most samples derived from the lower crust appear to be impact melts oflow k fra mauro noritic composition

composition and distribution of suspended sediments in lake michigan during summer stratification a quantitative description of the composition and distribution of suspended sediments is a necessary prerequisite to the determination of the transport and fate of those particles and of the chemical substances associated with them this report is the first to make such a description for materials in the great lakes suspended sediment samples were collected from lake michigan during august from several depths at six locations between grand haven michigan and milwaukee wisconsin concentrations of total suspended material range from 1 05 2 40 mg l diatoms comprise nearly all of the biogenic fraction and approximately 60 of the total quartz plus feldspar 25 is usually more abundant than carbonate minerals 13 and clays are a minor component abundances of all constituents were higher near the shore where shoreline input provides both nutrients and minerals suspended materials were concentrated at the base of the thermocline and in a bottom nepheloid layer of resuspended sediment mineral ratios in the nepheloid layer were similar to those in the surface centimeter of bottom sediment but diatom abundance decreased markedly below the sediment water interface the residence time of suspended inorganic materials in lake michigan is about 1 8 yrs ample time for suspended sediment grains to be distributed throughout the lake

microfossil and stable isotope evidence for changes in late holocene palaeoproductivity and palaeoceanographic conditions in the prydz bay region of antarctica microfaunal and microfloral data from two gravity cores and stable isotope results from one of these cores taken on fram bank near prydz bay antarctica indicate changes in sea ice patterns and oceanographic conditions which may have been linked to regional and global climate changes that occurred over the past 8000 yr modern diatom assemblages indicative of ice free conditions 1 2 months of the year and dominated by nitzschia species became prevalent some time around 2000 2700 yr b p the occurrence of chaetoceros spp diatom spore dominated assemblages and increased abundances of benthic and planktonic foraminifera ostracods and diatoms coupled with carbon and oxygen isotope changes around 2700 3400 yr b p strongly suggests that this area of the shelf experienced conditions conducive to increased productivity during this time period based on diatom assemblage associations recognized in modern environments the upper water column of fram bank shelf waters was probably stratified during that time due to the presence of low salinity melt water and a very shallow mixed layer protected from storms with sea ice cover for less than 10 months per year the close correspondence of 13c and 18o values from n pachyderma r2 0 74 throughout one core suggests that whatever oceanographic conditions influenced 18o also influenced 13c changes in prydz bay microfossil abundances and isotopes may result from alterations in circulation patterns upwelling conditions or sea ice patterns which significantly affected benthic and planktonic productivity in the area the environmental conditions indicated by older sediments in the cores are less clear but an ice tongue may have been in place 3200 3800 yr b p and minor fluctuations in productivity are indicated around 6000 and 7000 7500 yr b p the lower 100 cm of both cores may not represent in situ deposition but if the corrected ams dates reflect the actual age of the sediments analyzed microfossil and isotope data indicate that productivity and oceanographic conditions were very variable around 8500 8600 yr b p the chronology adopted herein must be regarded as tentative until further study of the area has been undertaken

microphyte pigments and resting spores at the water sediment interface in the subantarctic deep sea indian sector of the southern ocean during the antares i cruise april may 1993 in the indian sector of the southern ocean deep sea sediments were collected using a multiple gravity corer in the polar frontal zone pfz and frontal zone between crozet and kerguelen islands and in the permanently open ocean zone pooz south west of kerguelen and heard islands microphyte biomass indicators chl a b c and related phaeopigments measured by spectrofluorometry tests on natural fluorescence and detection of encysted diatoms observed by scanning electron microscopy sem were carried out on both sediment and overlying fluff whenever present evaluation of the phytoplankton biomass in the overlying surface water masses also was performed at each sampling station the phytoplankton biomass was on the whole very low and decreased from north to south 0 25 0 10 g 1 1 chl a with a maximum on the frontal zone whereas the sediment water interface of the southern sampling stations pooz was pigment enriched a consistent bioclastic fluffy layer was only present in the pooz stations up to 13 g 1 1 chl a 157 g 1 1 phaeo a biodeposition of this type was very thin or absent north of the pf polar front illustrating stronger advection in the northern part of the study area hydrodynamic studies of the crozet basin and the presence of benthic pennate coastal diatoms at the sediment interface of these northern stations further suggest increased advective activity in the north surficial sediments first 5 mm also were enriched with pigments in the pooz up to 0 15 g g 1 dw chl a 3 5 g g 1 dw phaeo a whereas in the pfz the chl a concentrations were insignificant pigment gradients in the sediments particularly well marked in the pooz indicate the absence of a secondary intense reworking such as bioturbation or resuspension nevertheless also in the pooz an unusual and well preserved megafaunal faecal cast was sampled and analysed sediments at southern stations 50 55 s 56 75 e 3600 4700 m depth were the most enriched with encysted microphytic cells mainly diatoms belonging to the genus chaetoceros this was related primarily to the presence of a fluffy layer composed mainly of well preserved detritic frustules of various diatom genera including robust nitzschia and thalassiosira as well as chains of delicate chaetoceros corethron and rhizosolenia well preserved coccoliths and silicoflagellates also were noticeable in the fluffs revival tests cultures on f2 medium initiated with samples from the water sediment interface were positive for the southern stations leading to low diversity diatom assemblages dominated by the genera chaetoceros and nitzschia

timescale of overturn in a magma ocean cumulate abstract the formation and differentiation of planetary bodies are thought to involve magma oceans stages we study the case of a planetary mantle crystallizing upwards from a global magma ocean in this scenario it is often considered that the magma ocean crystallizes more rapidly than the time required for convection to develop in the solid cumulate this assumption is appealing since the temperature and composition profiles resulting from the crystallization of the magma ocean can be used as an initial condition for convection in the solid part we test here this assumption with a linear stability analysis of the density profile in the solid cumulate as crystallization proceeds the interface between the magma ocean and the solid is a phase change interface convecting matter arriving near the interface can therefore cross this boundary via melting or freezing we use a semi permeable condition at the boundary between the magma ocean and the solid to account for that phenomenon the timescale with which convection develops in the solid is found to be several orders of magnitude smaller than the time needed to crystallize the magma ocean as soon as a few hundreds kilometers of cumulate are formed on a mars to earth size planet the phase change boundary condition is found to decrease this timescale by several orders of magnitude for a moon size object the possibility of melting and freezing at the top of the cumulate allows the overturn to happen before complete crystallization the convective patterns are also affected by melting and freezing at the boundary the linearly most unstable mode is a degree 1 translation mode instead of the approximately aspect ratio one convection rolls found with classical non penetrative boundary conditions the first overturn of the crystallizing cumulate on mars and the moon could therefore be at the origin of their observed degree 1 features