the role of caco3 compensation in the glacial to interglacial atmospheric co2 change the only viable explanations put forth to date for the glacial to interglacial change in atmospheric co2 content suggested from measurements of the co2 content of gas extracted from ice cores involve changes in the ocean s nutrient cycles any nutrient change capable of creating the 80 atm changes in atmosphere co2 pressure suggested by the ice core results also creates significant change in the deep ocean s co3 content evidence from deep sea sediments suggests that these co3 changes are compensated on the time scale of a few thousand years by reductions or increases in amount of caco3 accumulating in deep sea sediments this compensation process has two important consequences first it significantly increases the magnitude of the co2 change per unit of nutrient forcing second it causes a delay in the response of the atmospheric co2 change while the first of these consequences is a boon to those seeking to explain the co2 change the second may prove to be a curse the ice core co2 record shows no evidence of a significant lag between the co2 response and the polar warming in any case it is important that we improve our knowledge of the magnitude and timing of the caco3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes

palaeoproterozoic crustal accretion and collision in the southern capricorn orogen the glenburgh orogeny abstract the capricorn orogen in central western australia records the palaeoproterozoic collision of the archaean pilbara and yilgarn cratons until recently only one orogenic event was thought to be the cause of this collision the 1830 1780 ma capricorn orogeny however recent work has uncovered an older event the glenburgh orogeny that occurred between 2000 and 1960 ma the glenburgh orogeny reflects the collision of a late archaean to palaeoproterozoic microcontinent the glenburgh terrane with the archaean yilgarn craton and is therefore tectonically distinct as well as significantly older than the widespread 1900 1800 ma tectonothermal events recorded in northern australia the glenburgh terrane preserves a different history from either the yilgarn or pilbara cratons granitic gneiss protoliths dated at ca 2550 ma were intruded by widespread granite magmatism dated at 2005 1970 ma accompanied by high grade metamorphism and deformation throughout the terrane at ca 1960 ma silicic granite of the bertibubba supersuite intruded the northern margin of the yilgarn craton along the errabiddy shear zone a crustal scale shear zone that today marks the contact of the glenburgh terrane and yilgarn craton at ca 1950 ma silicic dykes intruded the southernmost part of the glenburgh terrane marking the end of the glenburgh orogeny east of the glenburgh terrane the glenburgh orogeny resulted in the cessation of mafic volcanism in the bryah basin and the basin s eventual closure siliciclastic carbonate and chemical sedimentary rocks were deposited in the padbury basin that formed a retro arc foreland basin on top of the bryah basin and probably records the later stages of the glenburgh orogeny collision

assembling and reactivating the proterozoic capricorn orogen lithotectonic elements orogenies and significance abstract the capricorn orogen was initiated during palaeoproterozoic suturing events that brought together the archaean yilgarn and pilbara cratons to form the west australian craton the orogen comprises palaeoproterozoic plutonic and medium to high grade metamorphic rocks of the gascoyne complex a series of palaeoproterozoic volcano sedimentary and sedimentary basins including the ashburton blair yerrida bryah padbury and earaheedy basins and the deformed margins of the pilbara and yilgarn cratons major pulses of deformation and metamorphism took place during the ca 2200 ma ophthalmian orogeny the 2000 1960 ma glenburgh orogeny the 1830 1780 ma capricorn orogeny and a more localized unnamed event at the end of the palaeoproterozoic 1670 1620 ma the orogen has been the site of repeated intracratonic reactivation with renewed basin formation magmatism and orogeny during the mesoproterozoic and the neoproterozoic the exhumed palaeoproterozoic components of the orogen are unconformably overlain by the intracratonic mesoproterozoic edmund and collier basins bangemall supergroup which have been deformed during the neoproterozoic edmundian orogeny the ophthalmian and glenburgh orogenies affected the northern and southern margins of the orogen respectively the former resulted in the development of a foreland basin along the pilbara craton margin whereas the latter is associated with accretion of an allochthonous element the glenburgh terrane of the gascoyne complex to the northwestern margin of the yilgarn craton effects of the capricorn orogeny extended across the entire orogen and provide a younger limit for amalgamation of the yilgarn and pilbara cratons a number of basins developed along both the northern and southern margin of the orogen during this event and were filled with sediment eroded from the yilgarn craton the gascoyne complex and a presently unexposed early palaeoproterozoic terrane the capricorn orogeny corresponds with a major phase of continental collision both in australia and world wide which appears to mark a major phase of supercontinent assembly mineralization within the orogen includes a wide variety of deposit types that can be related to collisional settings including the world class iron orebodies of the hamersley basin

precambrian tectonic evolution of part of gondwana southwestern australia southwestern australia has a long dynamic precambrian history of crustal fragmentation and aggregation by continental collision and accretion this interpretation contrasts with the widely held belief that most of australia was part of a proterozoic supercontinent in which all tectonic magmatic and metamorphic activity was intracontinental the pilbara and yilgarn cratons are two quite different fragments of archean continental crust that collided to form the capricorn orogen between 2000 and 1600 ma the albany fraser orogen formed along the southern margin of the yilgarn craton during another major continental collision at 1300 to 1100 ma rifting removed the northeastern part of these combined cratons and orogens between 1100 and 700 ma subsequent continental collision along this rifted margin formed the paterson orogen at 700 to 600 ma therefore the assembly of this considerable part of gondwana may not have been completed until about 600 ma

introduction to the illinois deep hole project commonwealth edison recently drilled 3 engineering test holes in n w illinois the 3 holes uph 1 2 and 3 were 0 6 1 6 and 1 6 km deep respectively and the latter 2 penetrated nearly one kilometer of precambrian granitic basement in 1980 continuous core from all 3 holes and access to uph 3 were made available for scientific investigations through the illinois deep hole project the principal study of these holes was an integrated investigation of surface and in hole experiments plus detailed petrologic geochemical and physical property studies of the core samples 50 references

sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization in two contrasting regions of the ocean the equatorial pacific and the southern ocean the 15n of core top sediments were strongly related to no3 in surface waters with distance from the equator in the equatorial pacific 15n increased from 7 to 16 as no3 decreased from 8 m to 0 1 m going from 60 to 30 s in the se indian ocean core top 15n increased from 5 to 11 as surface no3 decreased from 25 m to 0 1 m these results are strong evidence that sedimentary 15n in these regions is recording the increasing isotopic enrichment of near surface no3 with its depletion by phytoplankton in the case of the equatorial pacific 15n values for sinking particles collected at 150 m matched well the core top sediment values demonstrating little diagenetic alteration of the near surface generated isotopic signal these equatorial pacific data sets have variations with near surface no3 consistent with rayleigh fractionation kinetics for a fractionation factor u of 2 5 this value is substantially lower than previously found for temperate or polar regions perhaps as a result of differences in phytoplankton species assemblage or growth condition in the southern ocean south of the polar front comparison of 15n values for opal rich sediments south and sinking particles indicates an apparent 5 diagenetic enrichment relative to the surface generated signal that requires further investigation this exception aside our observations show that the surface water relationship of increasing 15n with increasing no3 depletion is generally transmitted to and preserved in the sediments an important requirement for further development and application of this important paleoceanographic tool

calcitic foraminiferal data confirmed by cadmium in aragonitic hoeglundina application to the last glacial maximum in the northern indian ocean a core top study of cadmium uptake into the shells of the aragonitic benthic foraminifera hoeglundina elegans demonstrates that the hoeglundina cd ca partition coefficient is close to 1 0 throughout the ocean cd uptake by hoeglundina is far less depth dependent than that of calcitic benthic foraminifera furthermore manganese carbonate does not precipitate on these aragonitic shells allowing for the recovery of cd estimates in some samples where calcitic species are spoiled by contaminating overgrowths because cd incorporation into hoeglundina shows little depth dependence a comparison of calcitic and hoeglundina cd data can be used to verify the assumption that the depth dependence observed for calcitic benthic foraminifera is time invariant this comparison has been undertaken in downcore and last glacial maximum lgm samples from the northern indian ocean aragonitic and calcitic foraminiferal estimates for cd in the lgm ocean are in excellent agreement this result indicates upper ocean estimates of lgm cd are reliable despite a factor of two variation in cd uptake by calcitic species over this depth range cd and 13c data indicate that the uppermost waters of the lgm arabian sea were strongly nutrient depleted relative to today but that the deepest waters of the northern bay of bengal had nutrient concentrations at least as high as or higher than modern levels a strong vertical gradient of increasing nutrients with increasing depth existed in both basins during the lgm a west to east gradient of increasing nutrient concentrations also is evident at all depths in the bay of bengal there is evidence for an enhanced gradient of nutrients increasing from south to north the lgm deep arabian sea and intermediate depth bay of bengal were nutrient depleted compared to the modern ocean however cd and 13c data indicate that nutrient depletion in the northern indian ocean did not exceed that of the deep eastern tropical pacific except during the latest part of oxygen isotope stage 2 and according to cd data only the early stages of deglaciation during oxygen isotope stage 3 and early stage 2 cd in the northern indian ocean and cd in the eastern tropical pacific were indistinguishable although both regions have lower cd at these times compared to the holocene

high resolution holocene climate record from maxwell bay south shetland islands antarctica the highest resolution holocene sediment core from the antarctic peninsula to date was collected during the first shaldril cruise nbp0502 drilling yielded a 108 2 m long core 87 recovery site nbp0502 1b from maxwell bay south shetland islands this high resolution sediment record comes from a region that is currently experiencing dramatic climate change and associated glacial retreat such records can help to constrain the nature of past climate change and causal mechanisms and to provide a context for evaluating current climate change and its impacts the base of the drill site sampled till and or proximal glacimarine sediments resting directly on bedrock glacimarine suspension deposits composed of dark greenish gray silty mud with variable diatom abundance and scattered very fine sand laminations make up the majority of the sedimentary section detailed sedimentological and geochemical analyses including magnetic susceptibility total organic carbon toc content carbon and nitrogen isotopic composition pebble content and biogenic silica content allow subdivision of the glacimarine section into nine units and seismic facies analyses resulted in the identification of six distinct seismic units we used 29 radiocarbon ages to construct an age model and calculate sedimentation rates that vary by two orders of magnitude from 0 7 mm a to 30 mm a radiocarbon ages from glacimarine sediments just above the till date back to between 14 1 and 14 8 ka thus ice was grounded in the fjord during the last glacial maximum and eroded older sediments from the fjord following initial retreat of grounded ice from maxwell bay the fjord was covered by a permanent floating ice canopy probably an ice tongue the highest sedimentation rate corresponds to an interval that contains abundant sand laminations and gravelly mud intervals and likely represents a melt out phase or period of rapid glacial retreat from 10 1 ka to 8 2 ka there is no evidence for an early holocene climatic reversal as recorded farther south at the palmer deep drill site minimum sea ice cover and warm water conditions occurred between 8 2 and 5 9 ka from 5 9 to 2 6 ka there was a gradual cooling and more extensive sea ice cover in the bay after 2 6 ka the climate varied slightly causing only subtle variation in glacier grounding lines there is no compelling evidence for a little ice age readvance in maxwell bay the current warming and associated glacial response in the northern antarctic peninsula appears to be unprecedented in its synchroneity and widespread impact

late quaternary paleochemistry of high latitude surface waters recent studies have stressed the role of high latitude nutrient levels and productivity in controlling the carbon isotopic composition of the deep sea and the co2 content of the atmosphere we undertook a study of the chemical composition of the polar planktonic foraminifer neogloboquadrina pachyderma s sinistral coiling from 30 late holocene samples and 49 down core records from the high latitude north and south atlantic oceans to evaluate the history of sea surface chemical change from glacial to interglacial time stable isotopic analysis of coretop samples from the atlantic pacific and southern oceans shows no significant correlation between the 13c of n pachyderma and either 13c or po4 in seawater conversely cd ca ratios in planktonic foraminifera are consistent with the po4 content of surface waters the level of maximum glaciation 18 000 yr b p identified by climap and 18o was chosen for mapping isopleths of 18o on n pachyderma s in the north atlantic reveal a pattern largely influenced by sea surface temperature s s t and generally support the s s t reconstruction of climap differences between the two suggest significantly lower salinity in north atlantic surface waters at high latitudes than in lower latitudes down core 13c records of n pachyderma confirm that low 13c values occurred in the northeast atlantic during the latest glacial maximum labeyrie and duplessy 1985 however a map of 13c for the 18 000 yr b p level for a much larger region in the north atlantic shows that minimum n pachyderma 13c occurred in temperate waters n pachyderma 13c decreased toward the southwest reaching a minimum of 1 at 37 n despite the variability seen in 13c records of n pachyderma none of our cores show significant temporal variability in cd ca from the combined cd ca and 13c data we can see no evidence for an upwelling gyre in the eastern north atlantic during the latest glacial maximum nor evidence that the southern and northern oceans had significantly different levels of preformed nutrients than today

climatically linked carbon isotope variation during the past 430 000 years in southern ocean sediments we use the isotopic composition of carbon from organic matter enclosed within diatom frustules as a proxy for paleoproductivity and paleo dissolved carbon dioxide concentrations in ocean surface waters a southern ocean record from south of the antarctic polar front and spanning 430 000 years of carbon isotopic variation in diatomaceous organic matter is presented for the first time the most refractory diatomaceous organic matter fraction was extracted and analyzed to avoid problems associated with diagenesis the results clearly indicate cyclic changes in organic carbon isotopic ratios with 13c depleted values associated with all of the last five glacial periods reflecting changes in surface water properties and primary productivity changes in dissolved carbon dioxide concentrations are the most probable cause of these cycles but the possible effect of seawater ph changes cannot be excluded

large scale crustal structure of the northwestern yilgarn craton western australia evidence from nd isotopic data and zircon geochronology u pb zircon geochronology and nd isotope geochemistry have been used in the northwestern yilgarn craton region of western australia to map gneiss units of different ages and to provide a model for late archean crustal evolution despite the inherent difficulties of minimal exposure and variations in the appearance of units brought about by heterogeneous strain the 3300 3730 ma gneisses and intercalated metasedimentary units crop out in a 100 km wide tract bounded on both sides by areas containing 2920 3000 ma gneisses between 2750 and 2620 ma several generations of granitoids were emplaced throughout the region regardless of whether the granitoids intruded the 3300 3730 ma or 2920 3000 ma gneisses modeling of their initial nd isotopic compositions shows that they were most likely formed by partial melting of predominantly 2920 3000 ma gneisses only a minor input from early archean sources is indicated for granitoids cutting the 3300 3730 ma gneisses and intercalated metasediments some of the granitoids that intrude the 3300 3730 ma gneisses contain 2920 ma inherited zircons supporting the nd evidence that their source is dominated by 2920 3000 ma gneisses the 3300 3730 ma gneisses are interpreted as belonging to an allochthonous terrain emplaced over a younger terrain comprising the 2920 3000 ma gneisses subsequently partial melting concentrated in the underlying 2920 3000 ma terrain gave rise to the late archean granitoids

zirconology of the meeberrie gneiss yilgarn craton western australia an early archaean migmatite abstract the meeberrie gneiss a major component of the early archaean narryer gneiss complex of western australia is a polyphase migmatite comprising monzogranites together with minor tonalitic and trondhjemitic components ranging in age from 3730 to 3300 ma with important resolvable age components at 3670 3620 and 3600 ma ion probe u pb studies of zircons from numerous localities show that almost all hand specimens of the gneiss consist of multiple generations of magmatically crystallized zircons even down to the scale of individual centimetre sized bands the earliest age components generally are not found in inherited cores but rather in separate zircon grains usually indistinguishable from the younger grains in terms of morphology internal structure and trace element composition only in rare low strain zones are original cross cutting relationships between individual magmatic components and pegmatite segregations preserved for the remainder late archaean deformation has blended units and erased pre existing structures however deformation state appears to have little bearing on the zircon isotopic systematics geochemical data for such rocks are thus composite as are nd isotopic compositions which nonetheless show that the younger generations of material in the gneisses are produced predominantly by reworking of older crust

sampling of brine in cores of precambrian granite from northern illinois the composition of groundwater in deep seated rocks is of great interest both geochemically and in connection with the disposal of radioactive waste however sampling of deep seated groundwater is expensive and often difficult we describe here a simple technique for the elution of pore fluid groundwater from cores of igneous rocks and we describe brine eluted from a core of precambrian granite from northern illinois drill hole uph 3 the brine is predominantly nacl and cacl2 with a ca na mole ratio of about 0 05 to 0 1 from analysis of soluble chloride in a crushed sample the chloride concentration in the pore water is estimated as 2 3 m the brine is similar to brine in the illinois basin and it was probably derived from the overlying sediments

on the late pleistocene ocean geochemistry and circulation a box model of the atmosphere and ocean was developed to investigate how geochemical distributions extant during the late pleistocene may have come about the model simulates the regional distribution of calcium carbonate dissolution as well as the chemical oceanography and atmospheric co2 13c and radiocarbon if the downward biological flux of particulate carbon increases by a factor of 2 to 3 in the antarctic and if this increase is combined with a relative increase of the atlantic sector antarctic bottom water aabw versus north atlantic deep water nadw source ratio from 1 3 to about 2 1 then the model predicts several changes that seem to be recorded in the sedimentary record as follows 1 a global redistribution of nutrients and 12c from the intermediate to deep water takes place with the atlantic intermediate water phosphate decreasing 0 6 mole kg 1 and the 13c increasing 0 3 to 0 5 2 the dissolved oxygen level of the deep sea is reduced from an average of about 180 to 70 mole kg 1 but the intermediate water oxygen declines only a small amount 3 the decrease in intermediate water nutrient concentration results in lower average organic carbon and calcium carbonate production in the warm surface ocean 4 the atmospheric co2 decreases by 90 to 110 ppm 5 initially a global increase in calcium carbonate dissolution occurs which is followed by a relaxation toward better preservation than exists for the present ocean in the model in this paper the reduction of nadw by itself does not produce these effects rather the nutrient decrease that does occur is found mostly in north pacific intermediate water and the model atmospheric co2 decrease is only 10 to 30 ppm it is observed that 92 of the atmospheric co2 change takes place according to a 200 year time constant in the model this corresponds to the response time of the upper ocean and atmosphere to a change in the stationary state atmospheric pco2 thus according to this model the time lag between the nutrient based cause and the atmospheric co2 response is not expected to be particularly large

the isotopic composition of diatom bound nitrogen in southern ocean sediments treatment of diatom microfossils from southern ocean sediments with hot perchloric acid leaves a diatom bound n fraction which is 0 4 lower in 15n than the bulk sediment typically 3 lower in recent antarctic diatom ooze results from southern ocean surface sediments indicate that early diagenetic changes in bulk sediment n content and 15n are not reflected in diatom bound n suggesting that diatom bound n is physically protected from early diagenesis by the microfossil matrix a meridional transect of multicores from the indian sector of the southern ocean shows a northward increase in the 15n of diatom bound n suggesting that diatom bound 15n like bulk sedimentary 15n varies with nitrate utilization in the overlying surface waters the 15n of diatom bound n is 3 4 higher in glacial age antarctic sediments than in holocene sediments supporting the hypothesis previously based on bulk sediment 15n that nitrate utilization in the surface antarctic was higher during the last ice age while there are important uncertainties the inferred range of utilization changes could potentially explain the entire 80 ppm amplitude of observed glacial interglacial variations in atmospheric co2

provenance of the earaheedy basin implications for assembly of the western australian craton abstract the palaeoproterozoic earaheedy basin in western australia lies at the southern end of the capricorn orogen the earaheedy group the sole lithostratigraphic unit comprising the basin fill is a 5 km thick succession of shallow marine siliciclastic and carbonate sedimentary rocks it consists from oldest to youngest of the yelma frere windidda chiall wongawol kulele and mulgarra formations u pb age data for 312 detrital zircon grains from seven siliciclastic samples from the yelma formation the wandiwarra and princess ranges members of the chiall formation and the mulgarra sandstone reveal the presence of both archaean 3 4 2 5 ga and palaeoproterozoic 2 4 1 8 ga detritus zircon grains of archaean age are dominantly in the range 2 7 2 6 ga similar to those of the yilgarn craton which unconformably underlies the southern margin of the earaheedy basin age peaks in the range 2 3 2 2 2 0 and 1 8 ga characterise the palaeoproterozoic detritus the two younger ages overlap with those of the adjoining gascoyne complex of the capricorn orogen to the west of the basin source components with ages in the range 2 3 2 2 ga are extremely rare in western australia undeformed granite in the mullingarra complex within the pinjarra orogen to the west of the darling fault yielded an age of around 2 2 ga in addition rare rims on detrital zircon grains from gneisses within basement of the glenburgh terrane of the gascoyne complex as well as a few detrital grains in metamorphosed quartz arenites of the terrane have yielded ages of around 2 4 2 2 ga suggesting early palaeoproterozoic activity in this region detrital grains as young as 1800 ma combined with deposition of the unconformably underlying strata in the yerrida basin at c 1840 ma and deformation of the earaheedy group at around 1750 ma provide a relatively tight constraint on the depositional age of the earaheedy group

the calcite lysocline as a constraint on glacial interglacial low latitude production changes we investigate the response of the calcite lysocline to changes in the export production of the low latitude surface ocean the combined equatorial tropical and subtropical regions we employ different caco3 throughput schemes in a time dependent ocean carbon cycle model to separate the caco3 production lysocline balance from the other components of the model response and to estimate the effect of dissolution driven by organic matter decomposition in surface sediments with this model we carry out three experiments based on previous hypotheses for the cause of glacial interglacial atmospheric co2 variations 1 a simple increase in low latitude production 2 a decrease in its caco3 organic carbon rain ratio and 3 an increase in the depth of organic carbon regeneration none of these changes when taken alone can lower atmospheric co2 to glacial levels without violating observations of the glacial lysocline depth if a low latitude production increase were accompanied by a decrease in the caco3 organic carbon rain ratio then these simultaneous changes could lower atmospheric co2 to observed glacial levels without causing a significant change in the ocean average depth of the lysocline however even with these simultaneous changes the required increase in production is 50 or more of the modern rate of production

characterisation of pore water in crystalline rocks abstract the mass of pore water present in the rock matrix of a crystalline rock mass is significant and its influence on fracture groundwater and future deep repositories needs to be understood yet the rock matrix has a hydraulic transmissivity generally well below 10 10 m 2 s 1 inhibiting sampling of pore water by conventional sampling techniques various innovative techniques for the chemical and isotopic characterisation of pore water in crystalline rocks are applied and evaluated direct sampling of pore water was facilitated by collecting seepage water in a specially designed borehole located at a depth of 420 m in the aspo underground research laboratory aspo hrl sweden over a period of 7 5 a during the entire time span seepage waters collected from different sampling sections showed constant but individual chemical and isotopic compositions compositional differences compared to nearby fracture groundwaters indicate that the collected waters originated from the low permeability rock mass without mutual influence via more conductive microfractures within the metre scale they are interpreted as representing pore water in a transient state of diffusive interaction with different types of old palaeowaters which have periodically characterised the fracture network at the aspo hrl over geological times thousands to hundreds of thousands of years pore water compositions derived by indirect methods out diffusion and diffusive isotope equilibration experiments from originally saturated drillcore samples collected at the laxemar and forsmark sites sweden can be interpreted within a wider palaeohydrogeological framework the chemical and isotope compositions of the pore water show distinct trends related to rock type and with depth becoming more saline at greater depth at both sites concentration gradients established between pore water and fracture groundwater commonly coincide with higher fracture frequency and transmissivity in the host rocks differences developed in the attainment of near steady state conditions between pore water and fracture water from laxemar and forsmark support a different hydrogeological and therefore hydrogeochemical evolution at least during holocene times the observed compositional differences between pore water and fracture groundwater support diffusion dominated solute transport in the low permeable rock masses which is consistent with measured and experimentally derived hydraulic properties from the present investigations it can be concluded that in such rock masses the diffusion accessible porosity extends over significant distances of at least metres to tens of metres

determination of δ18o of seawater in the deep ocean during the last glacial maximum we present a method for determining the 18o of seawater in the deep ocean during the last glacial maximum from the measured 18o values of deep sea pore fluids using data from deep sea drilling project dsdp site 576 in the western pacific this method yields a glacial to interglacial change in 18osw of 1 0 0 25 this value for 18osw is the first direct measurement of deep ocean 18o for the last glacial maximum and avoids the problems of spatial and temporal variability of the 18o of surface water implicit in previous determinations more precise higher resolution pore fluid measurements are required to improve this determination

an isotopic study of biogeochemical relationships between carbonates and organic carbon in the greenhorn formation carbon isotopic compositions of total carbonate inoceramid carbonate micritic carbonate secondary cements total organic carbon and geoporphyrins have been measured in 76 different beds within a 17 m interval of a core through the greenhorn formation an interbedded limestone and calcareous shale unit of cretaceous age cenomanian turonian from the western interior seaway of north america results are considered in terms of variations in the processes of primary production which led to the biosynthesis of the molecular precursors of the geoporphyrins and in secondary processes those mediating the transformation of primary organic material into sedimentary total organic carbon it is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the toc isotopic record and that in these sediments toc is enriched in 13c relative to its primary precursor by 0 6 to 2 8 this enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy variations in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate this correlation is attributed to effects of environmental changes on the marine foodweb these may have included increased atmospheric oxygen associated with the cenomanian turonian oceanic anoxic event the isotopic fractionation associated with fixation of carbon by primary producers is observed to have varied by 1 5 during the interval of deposition it is suggested that this change is due to a variation in the makeup of the community of primary producers and or to a decrease in the atmospheric abundance of co2 during the oceanic anoxic event

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

the cause of the glacial to interglacial atmospheric co2 change a polar alkalinity hypothesis in an attempt to create a scenario for the cause of the glacial to interglacial co2 change recorded in air trapped in polar ice we call on an increase in the alkalinity of polar surface waters in this way we circumvent a major deficiency of the polar nutrient scenarios of sarmiento and toggweiler 1984 siegenthaler and wenk 1984 and knox and mcelroy 1984 namely our scenario does not require a drop in the nutrient content of polar surface waters in conformity with the demonstration by boyle 1988a b that the cadmium content of planktonic foraminifera from polar regions did not decrease from late glacial to holocene time the rise in alkalinity required by our model is a natural consequence of the demise during glacial time of north atlantic deep water as a major force in ocean circulation and of the nutrient maximum deepening of boyle 1988b rather than being original our hypothesis builds on the concept basic to the polar nutrient hypotheses namely that the co2 partial pressure in polar waters controls that for both the atmosphere and warm surface ocean it also requires the alkalinity increase in surface waters produced by boyle s nutrient deepening

early permian sediment provenance and paleogeographic reconstructions in southeastern gondwana using detrital zircon geochronology northern perth basin western australia abstract the perth basin western australia forms part of a north trending belt of intracratonic rift basins that initiated in southeastern gondwana in the late paleozoic existing provenance studies have highlighted the dominance of proterozoic zircons derived from southerly terranes such as the albany fraser orogen leeuwin complex and more distant provinces in east antarctica with limited input from the adjacent archean western australian craton new u pb geochronology data were acquired using a sensitive high resolution ion microprobe shrimp ii on detrital zircons from lower permian formations exposed in the northeastern perth basin in contrast to previous studies archean zircons showing fine oscillatory zoning dominate the age spectra with up to 90 grains ranging between 3 0 and 2 6 ga indicating that granitic parent rocks of the adjacent craton were a major sediment source during the early permian a minor paleoproterozoic age population from the gascoyne complex of the capricorn orogen was likely transported southward and dispersed in the basin by a combination of longshore drift and tidal currents meso and neoproterozoic detritus became prominent only from the middle artinskian and may relate to the establishment of large northward flowing river systems draining the albany fraser province the prydz leeuwin belt and or the wilkes land in east antarctica this study shows that integrating depositional processes and stratigraphic evolution of sedimentary formations with provenance analysis can enhance reconstruction of dispersal pathways to and within basins

glacial to interglacial changes in surface nitrate utilization in the indian sector of the southern ocean as recorded by sediment δ15n we present a new approach for paleoceanographic reconstruction of surface nutrient utilization in the southern ocean it has been observed in the contemporary ocean that due to preferential uptake of 14no3 during photosynthesis the 15n of planktonic organic matter increases with increasing nitrate depletion in surface waters our results demonstrate that the 15n signal produced in surface waters is reflected in the underlying surface sediments core top 15n is inversely correlated with surface nitrate concentration along a transect across the subtropical convergence and the polar front in the southeast indian ocean these results are consistent with a four box model showing that the nitrogen isotopic composition of sinking organic matter depends on percent nitrate utilization in the euphotic zone by comparing the 15n of surface sediments with that measured in the glacial sections of several cores we infer changes in the intensity and latitudinal distribution of nitrate uptake in this region during the last glacial maximum these preliminary results argue against increased biological uptake of nutrients in southern polar waters as a major mechanism for glacial lowering of atmospheric co2 they also suggest that subantarctic waters in the se indian sector became more nutrient depleted as they migrated northward increased nitrate depletion might have also occurred slightly south of the glacial polar front we use a six box model to explore the possible impact of this observation on atmospheric co2

seismic structure of the crust and uppermost mantle of the capricorn and paterson orogens and adjacent cratons western australia from passive seismic transects abstract the seismic structure of the proterozoic capricorn and paterson orogens and adjacent archaean yilgarn and pilbara cratons western australia is determined using a passive seismic approach we use recordings of distant earthquakes made along two transects of 3 component broadband stations the stations were deployed for approximately 1 year mid 2006 2007 during which time 70 earthquakes were recorded at each station with a suitable signal to noise ratio for receiver function analysis and hence the s wavespeed profiles of the crust and uppermost mantle beneath each recording station are determined we investigate the deep crustal constraints on terrane boundary locations the patterns of seismic discontinuities in the crust and the variations in the depth and character of the moho this broad scale information regarding the present day crustal architecture and hence the crustal evolution of western australia complements previous surface geological and other geophysical studies western australia is an exceptionally large well preserved region of ancient crust and hence this work also adds to the body of knowledge regarding proterozoic orogenic processes in general the new passive seismic work shows a region of double crust or upper mantle discontinuities beneath the glenburgh terrane adjacent to the northwest yilgarn craton the upper crust of the orogens is always layered whereas the cratons have a simple upper crust both the capricorn and paterson orogens are characterised by deeper moho discontinuities with a lesser wavespeed contrast than the very sharp discontinuity observed beneath the adjacent pilbara and yilgarn cratons this is consistent with the weaker orogenic crust of the capricorn and paterson orogens accommodating most of the horizontal deformation during assembly and reworking of the west australian craton while the pilbara and yilgarn cratons acted as rigid crustal blocks

reconstructing the ocean carbon system variation during the last 150 000 years according to the antarctic nutrient hypothesis in this study the vostok ice core co2 record and the 13c difference between the deep atlantic and pacific a p are used in combination with model simulations to analyze the history of the ocean carbon pump and the sources of atlantic deep water during the last 150 kyr it is assumed that the mechanism by which the glacial atmospheric co2 decreased is an increase in the ratio of antarctic net carbon production to upwelling in that region results from a wide range of circulations and antarctic net carbon productions input into a 14 box ocean atmosphere model show that similar distributions of phosphate 13c atmospheric co2 content and surface versus deep radiocarbon age are produced once the following parameters are fixed 1 the ratio of net carbon production to upwelling in the antarctic region 2 the ratio of northern component water to antarctic bottom water input into the atlantic and 3 the total upwelling into the low latitude surface waters therefore rather arbitrary circulations and antarctic net production values can be used to map model simulated geochemical properties as a function of these parameters decrease in atmospheric co2 and atlantic to pacific 13c difference are calculated from the model for constant low latitude upwelling and these are mapped as a function of the ratios 1 and 2 above the isolines of these two geochemical properties tend to be orthogonal and one can position any pco2 a p pair on an overlay of the two maps this is done for coeval ice core co2 and marine sedimentary 13c data for the last 150 kyr one finds that the history of the antarctic carbon pump efficiency varies with the same pattern as that of the atmospheric co2 the fraction of northern component water entering the atlantic tends to vary with the same shape function as the global marine 18o curve

the role of vertical chemical fractionation in controlling late quaternary atmospheric carbon dioxide the 30 decrease in atmospheric carbon dioxide during glacial maxima must be driven by some change in the chemical circulation of the ocean here a new model for late quaternary co2 variability is presented which resolves some problems occurring in previous models including the timing of carbon dioxide response and changes in the oxygen content of the deep ocean the primary driving factor in this model is a rearrangement of chemical distributions in the ocean whereby labile nutrients and metabolic co2 are concentrated in deep waters rather than in intermediate waters as observed in the modern ocean this new bottom heavy chemical structure does not affect atmospheric carbon dioxide directly instead co2 induced acidity lowers the deep ocean carbonate ion concentration and temporarily increases carbonate dissolution rates oceanic alkalinity then rises until the deep ocean carbonate ion is restored to its steady state value the resulting increase in oceanic alkalinity draws co2 out of the atmosphere into the ocean alkalinity and atmospheric co2 lag several thousand years behind the change in oceanic chemical structure this delayed response is determined by the limited rate of continental weathering and deep ocean carbonate dissolution relative to the oceanic alkalinity inventory it is proposed that characteristic deglacial and preglacial states of the ocean are leading factors driving glacial interglacial climate changes this concept reinterprets the carbon isotope contrast between surface water and deep waters 13c p b as due to a shift of light metabolic carbon from intermediate waters into deep waters the process is illustrated here by a simple equilibrium five box ocean model the observed intermediate depth nutrient depletion is not sufficient in itself to determine which of several possible mechanisms are operating and some mechanisms are not as effective in changing atmospheric co2 as others the largest response is seen from deepening the regeneration cycle of organic carbon the least response is seen from converting north atlantic deep water into intermediate water

a new paleoproterozoic tectonic history of the eastern capricorn orogen western australia revealed by u pb zircon dating of micro tuffs abstract the earaheedy basin is one of several paleoproterozoic siliciclastic basins in the eastern part of the capricorn orogen in western australia in the absence of an adequate chronostratigraphic framework multiple conflicting models have been proposed for the tectonic history of the basin we present in situ shrimp u pb zircon dates of 1971 11 ma 1954 5 ma and 1949 10 ma from three thin tuff horizons micro tuffs in the yelma formation at the base of the basin succession these micro tuffs are only slightly younger than the 1990 6 ma imbin porphyry which has been interpreted as a basement inlier our new dates combined with field mapping suggest that the imbin porphyry is a volcanic subvolcanic complex within the basin micro tuffs in the yelma formation are more than 50 m y older than c 1890 ma micro tuffs within the overlying frere formation deposition of the yelma formation was coeval with continent continent collision farther west in the orogen marked by the 2005 1950 ma glenburgh orogeny and the formation is possibly correlative with peripheral foreland deposits of the padbury group the frere formation was deposited in shallow marine conditions within an intracratonic basin about 60 m y after the glenburgh orogeny the frere formation is unconformably or disconformably overlain by the miningarra group the youngest unit of which is the mulgarra sandstone this sandstone was deposited after c 1865 ma and derived either from exposed frere formation or from a now buried source within the capricorn orogen that was uplifted by inception of the 1820 1770 ma capricorn orogeny therefore the earaheedy basin comprises at least three distinct unconformity bound successions deposited in contrasting tectonic settings

inclusions of sedimentary brines in post variscan mineralizations in the federal republic of germany a study by neutron activation analysis abstract the post variscan vein mineralizations in the federal republic of germany are characterized by highly saline fluid inclusions t e t mice 26 to 20 c t h 1 ca 22 000 60 000 mg kg 1 cl 85 000 200 000 mg kg 1 and br 550 2 600 mg kg 1 composition and salinity of the inclusion solutions are similar to brines in deep sedimentary basins it is assumed that formation waters of the na ca cl type migrated out of permo triassic sediment troughs into culmination zones of the variscan orogen where they were heated and caused mineralizations through cooling and mixing with sulfate bicarbonate waters when reascending

reconnaissance dating of events recorded in the southern part of the capricorn orogen abstract zircon geochronology confirms the errabiddy shear zone as a major structural boundary separating two distinct geological terranes within the southern part of the palaeoproterozoic capricorn orogen of western australia rocks on the south side of the errabiddy shear zone represent parts of the archaean yilgarn craton that were variably reworked during the c 2 0 ga glenburgh and c 1 8 ga capricorn orogenies rocks on the north side represent an exotic terrane the glenburgh terrane comprising c 2500 ma and possibly older gneisses which evidently record tectonothermal activity c 2390 ma and which together with quartzitic metasedimentary units deposited after c 2270 ma collided with the yilgarn craton during the glenburgh orogeny regional deformation high grade metamorphism and voluminous felsic plutonism occurred throughout the complex in association with both the glenburgh and capricorn orogenies

the northern margin of the capricorn orogen western australia an example of an early proterozoic collision zone abstract the early proterozoic 2200 1600 ma capricorn orogen is a major zone of deformation metamorphism and granite emplacement between the archaean yilgarn and pilbara cratons of northwest australia capricorn orogen structures are recognized along the southern margin of the pilbara craton deforming the archaean granite greenstone terrain of the sylvania inlier together with rocks of the hamersley ashburton and blair basins in the sylvania inlier deformation is characterized by large scale shear zones interpreted as nne directed thrusts in the hamersley basin orogenic deformation forms the ophthalmia fold belt and can be divided into two groups of structures in the southwest large scale dome and basin folds pre ashburton basin are present in the southeast folds and faults are part of a younger syn ashburton basin n directed foreland fold and thrust belt directly linked to deformation in the sylvania inlier the deformed ashburton basin and adjacent parts of the hamersley basin form the ashburton fold belt two periods of deformation are recognized early recumbent folding d1a post ashburton basin pre blair basin and later dextral wrench faulting and associated folding d2a syn or post blair basin capricorn orogen structures are interpreted as the result of an oblique continent continent collision between the pilbara and yilgarn cratons along the southern pilbara margin collision first occurred in the southeast and migrated northwest with the ashburton basin evolving as a foreland basin late stage dextral wrench faulting was the result of westward extrusion of material caught between the opposing craton margins

bacterial proteolytic activity in sediments of the subantarctic indian ocean sector abstract organic material entering the oceanic benthic zone can be permanently buried or recycled to co2 in the sediment therefore it is important to know the carbon flux across the sediment water interface to determine the initial and rate limiting step in carbon oxidation a bacterial enzymatic activity bacterial density and ectoproteolytic activity determined using a fluorogenic substrate analog l leucine 7 amino 4 methyl coumarin leu mca were investigated in the water column and in sediments during the antares 1 jgofs cruise in the indian sector of the southern ocean a strong decrease in ectoproteolytic activity was observed with increasing water depth peak activity in surface water was three orders of magnitude less than in surface sediment analysis of experimental data revealed for most sediment bacterial communities the existence of a biphasic mechanism with different velocities for organic matter degradation and different affinities of enzymatic systems for substrates to explain this we hypothesize a strategy of bacterial communities that use the episodic supplies of organic matter reaching the sediment microbial ectoproteolytic activities were highest in surface sediment horizons and decreased progressively with depth as benthic microbial activities reflect the quantity and quality of organic matter reaching the sea floor high potential ectoproteolytic activities pea measured in the sediment of the polar front zone could indicate a direct and rapid coupling of relatively high surface productivity and deep ocean water by sinking particle fluxes lower values of pea were found in sediment in the northern study area where lateral processes associated with ocean circulation antarctic circumpolar current have an important influence on settling particles the lowest sediment pea values were measured at 52 s a region in which low primary production provides a poor supply of organic matter for the sea floor

geochemistry of late 1 1 ga fluid inclusions in rocks of the kapuskasing archean crustal section three outcrops well constrained by geochronological and structural studies and representing a traverse running from tonalite dominated outcrops in the eastern wawa gneiss terrane to high grade granulites of the kapuskasing structural zone were mapped and sampled in detail in order to study the trapped fluids all fluid inclusions in quartz are secondary and consist mostly of co2 dominated type ii and saline aqueous type iiia fluids usually occurring on separate healed fractures but also coexisting on some fractures healed fractures in quartz contain fluid inclusions but are associated with carbonate sericite alteration where they pass into adjacent mineral grains homogeneous h2o co2 salt fluid inclusions type ia in carbonate rich veins of probable keweenawan 1 1 ga age were trapped at 400 550 c and ambient pressures of 1 5 2 kbar 1 kbar 100 mpa as these fluids cooled on penetration into cool 200 c country rocks along fractures they underwent open system h2o co2 phase separation f

the nature of proterozoic reworking of early archaean gneisses mukalo creek area southern gascoyne province western australia abstract the gascoyne province a key segment of the early proterozoic capricorn orogen which separates the archaean pilbara and yilgarn cratons of western australia may be divided into northern central and southern zones the southern zone comprises predominantly archaean granulite facies quartzo feldspathic gneisses and passes southwards into the western gneiss terrain of the yilgarn block this area was part of the lower crust of a stabilized continental landmass at the end of the archaean development of the capricorn orogen 2 ga ago resulted in discontinuous deformation of the northern part of this landmass deformation was concentrated in ductile shear zones leaving blocks of relatively undeformed gneiss between them the shear zones trend between ene wsw and ese wnw and dip to the south at 50 60 strong down dip stretching lineations and asymmetric feldspar porphyroclasts indicate that the shear zones are reverse faults however metamorphic assemblages in early proterozoic dolerite dykes which post date the shear zones show that the area was still in the lower crust following the earliest proterozoic deformation isothermal uplift of the southern gascoyne province northern yilgarn block by 10 km or more occurred 1 7 1 5 ga ago and was accompanied by granitoid intrusion deformation within e w trending shear zones continued after uplift and was accompanied by patchy greenschist facies retrogression of both static and dynamic style on the local scale the effects of early proterozoic deformation on the early archaean gneisses are generally confined to shear zones and their immediate surroundings they comprise 1 realignment of gneissic trends from n s to e w 2 development of quartz ribbon mylonites by elongation of quartz grains into lenses and ribbons and reduction of feldspar grainsize by crystal plastic processes 3 growth of porphyroblastic and corona garnet in felsic and mafic gneisses the later proterozoic deformation occurred at lower temperatures and resulted in 1 further realignment of gneissic trends from northerly to easterly 2 reduction of quartz grainsize by crystal plastic processes and reduction of feldspar grainsize largely by brittle fracture 3 greenschist facies retrogression that the earliest deformation in the southern gascoyne province resulted in crustal shortening and was followed by significant uplift and granitoid intrusion indicates that proterozoic reworking of this area resulted from regional n s compression this favours development of the capricorn orogen in a collision zone between the pilbara and yilgarn cratons rather than in an ensialic mobile zone

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

identifying the lithospheric structure of a precambrian orogen using magnetotellurics the capricorn orogen western australia abstract a 300 km long magnetotelluric mt survey was carried out across the capricorn orogen in western australia the capricorn orogen includes reworked crust of the archaean yilgarn and pilbara cratons and the allochthonous latest archaean to palaeoproterozoic glenburgh terrane in the southern gascoyne complex and the palaeoproterozoic northern gascoyne complex the survey aimed to increase our understanding of the juxtaposition of these crustal elements by obtaining information about their electrical structure with depth phase tensor analysis of the data showed that 2d mt inversion could only be carried out for stations in the centre of the profile crossing the gascoyne complex the resulting model showed that there is no electrical distinction between the glenburgh terrane and the northern gascoyne complex suggesting that the glenburgh terrane may form basement to the whole of the gascoyne complex 3d forward modelling was carried out for the entire survey line incorporating the basement blocks as well as the surrounding ocean and sedimentary basins station data are most closely reproduced by a model in which the margin between the glenburgh terrane and the yilgarn craton the errabiddy shear zone dips south with crust of the glenburgh terrane wedged beneath the northern yilgarn craton forward modelling results also suggest that the main boundary between the gascoyne complex and the pilbara craton to the north is a steeply dipping structure beneath the edmund and collier basins that may correlate with the talga fault

evidence for a bathyal front at 2000 m depth in the glacial pacific based on a depth transect on ontong java plateau data on oxygen and carbon isotope compositions of the benthic foraminifer planulina wullerstorfi from 18 cores 17 box cores and one piston core from ontong java plateau provide proxy depth profiles for temperature water mass and nutrient content for the late holocene the last transition and the last glacial the 18o profile during glacial time shows an increased gradient at a depth near 2000 m the corresponding 13c data suggest that a bathyal nutricline existed close to the same depth level the 13c values provide limits on the global change in carbon content of the glacial ocean which may be estimated as distinctly less than 1 atmospheric carbon mass 1 acm 700 gtc the greater co2 content of glacial deep waters which is reflected in the more negative 13c values may be at least in part due to a more sluggish renewal of abyssal deep waters if so the water of the deep pacific was up to 400 years older than now in turn ventilation in the upper waters above 2000 m may have been more vigorous than today

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

oceanographic conditions associated with high abundances of the radiolarian cycladophora davisiana abstract the cosmopolitan radiolarian cycladophora davisiana usually comprises less than 5 of the radiolarian fauna in holocene sediments in recent sediments from the sea of okhotsk however this species frequently represents more than 20 of the radiolarian assemblage at times during the late pleistocene abundances of this species in excess of 40 are recorded in marine sediments from high latitude oceans 40 of both hemispheres the sea of okhotsk apparently represents a modern analogue of climatic and oceanographic conditions that existed throughout large portions of high latitude oceans at times during the late pleistocene the near surface water structure of the sea of okhotsk is characterized by a low salinity surface layer with a strong temperature minimum near its base the low surface salinities are responsible for maintaining near freezing subsurface temperatures as well as establishing relatively stable temperatures and salinities at depths below the temperature minimum this water structure is produced at least in part by intense freezing of sea ice in winter with subsequent summer melting the physical characteristics of the upper water column affect the abundance and activity of shallow dwelling flora and fauna while providing a stable subsurface environment for deeper dwelling fauna

glacial interglacial changes in sediment rain rate in the sw indian sector of subantarctic waters as recorded by 230th 231pa u and δ15n high resolution records of opal carbonate and terrigenous fluxes have been obtained from a high sedimentation rate core md84 527 43 50 s 51 19 e 3269 m by normalization to 230th this method estimates paleofluxes to the seafloor on a point by point basis and distinguishes changes in sediment accumulation due to variations in vertical rain rates from those due to changes in syndepositional sediment redistribution by bottom currents we also measured sediment 15n to evaluate the changes in nitrate utilization in the overlying surface waters associated with paleoflux variations our results show that opal accumulation rates on the seafloor during the holocene and stage 3 based on 14c dating were respectively tenfold and fivefold higher than the vertical rain rates at this particular location changes in opal accumulation on the seafloor appear to be mainly controlled by sediment redistribution by bottom currents rather than variations in opal fluxes from the overlying water column correction for syndepositional sediment redistribution and the improved time resolution that can be achieved by normalization to 230th disclose important variations in opal rain rates we found relatively high but variable opal paleoflux during stage 3 with two maxima centered at 36 and 30 kyr b p low opal paleoflux during stage 2 and deglaciation and a pronounced maximum during the early holocene we interpret this record as reflecting variations in opal production rates associated with climate induced latitudinal migration of the southern ocean frontal system sediments deposited during periods of high opal paleoflux also have high authigenic u concentrations suggesting more reducing conditions in the sediment and high pa 231 th 230 ratios suggesting increased scavenging from the water column sediment 15n is circa 1 5 per mil higher during isotopic stage 2 and deglaciation the low opal rain rates recorded during that period appear to have been associated with increased nitrate depletion this suggests that opal paleofluxes do not simply reflect latitudinal migration of the frontal system but also changes in the structure of the upper water column increased stratification during isotopic stage 2 and deglaciation could have been produced by a meltwater lid leading to lower nitrate supply rates to surface waters

low temperature phanerozoic history of the northern yilgarn craton western australia abstract the phanerozoic cooling history of the western australian shield has been investigated using apatite fission track aft thermochronology aft ages from the northern part of the archaean yilgarn craton western australia primarily range between 200 and 280 ma with mean confined horizontal track lengths varying between 11 5 and 14 3 m time temperature modelling of the aft data together with geological information suggest the onset of a regional cooling episode in the late carboniferous early permian which continued into late jurassic early cretaceous time present day heat flow measurements on the western australian shield fall in the range of 40 50 mw m 2 if the present day geothermal gradient of 18 2 c km 1 is representative of average phanerozoic gradients then this implies a minimum of 50 c of late palaeozoic to mesozoic cooling assuming that cooling resulted from denudation the data suggest the removal of at least 3 km of rock section from the northern yilgarn craton over this interval the perth basin located west of the yilgarn craton contains up to 15 km of mostly permian to lower cretaceous clastic sediment however published u pb data of detrital zircons from permian and lower triassic basin strata show relatively few or no grains of archaean age this suggests that the recorded cooling can probably be attributed to the removal of a sedimentary cover rather than by denudation of material from the underlying craton itself the onset of cooling is linked to tectonism related to either the waning stages of the alice springs orogeny or to the early stages of gondwana breakup

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

variability in the deep and intermediate water circulation of the atlantic ocean during the past 25 000 years northern hemisphere modulation of the southern ocean the relative flux of north atlantic deep water nadw out of the atlantic can be monitored in the southern ocean where high 13c nadw mixes rapidly with low 13c recirculated pacific water before forming antarctic bottom water aabw by using 13c measured in benthic foraminifera as a water mass tracer it is shown that the southern ocean was dominated by pacific water with little nadw contribution during the last glaciation these tracer results document the direct physical connection between insolation controlled northern hemisphere oscillations and changes in the chemical and physical properties of southern ocean water the 13c records from the deep tropical atlantic document the transition from an atlantic dominated by southern ocean water during the last glaciation to an atlantic dominated by nadw during the holocene with more southern ocean water in the deep atlantic during the last glaciation the boundary between nadw and southern ocean water was north of its modern position allowing more southern ocean water to enter the eastern atlantic through the romanche fracture zone carbon isotope records from the caribbean and mediterranean seas suggest that the influence of mediterranean overflow water mow extended to the caribbean during the last glaciation and therefore was a volumetrically much more important water mass in the intermediate depth atlantic than it is today

the narryer gneiss complex of the yilgarn block western australia a segment of archaean lower crust uplifted during proterozoic orogeny the narryer gneiss complex of the yilgarn block is a key segment of the western australian precambrian shield it is a regional granulite facies terrain comprised of predominantly quartzo feldspathic gneisses derived from granitic intrusions c 3 6 3 4 ga old granulite facies metamorphism occurred c 3 3 ga ago and conditions of 750 850 c and 7 10 kbar are estimated for the mukalo creek area mca near errabiddy in the north the p t path of the mca has been derived from metamorphic assemblages in younger rocks that intruded the gneisses during at least three subsequent events and this path is supported by reaction coronas in the older gneisses there is no evidence for uplift immediately following peak metamorphism of the mca and a period of isobaric cooling is inferred from the pressures recorded in younger rocks pressures and temperatures estimated from metadolerites which intruded the older gneisses during granite greenstone tectonism at about 2 6 ga and during early proterozoic thrusting show that the errabiddy area remained in the lower crust although it was probably reheated during the younger events isothermal uplift to upper crustal levels occurred at c 1 6 ga ago and was followed by further deformation and patchy retrogression of high grade assemblages the effects of younger deformation cooling and reheating can be discerned in the older gneisses but as there has been no pervasive deformation or rehydration the minerals and microstructures formed during early archaean granulite facies metamorphism for the most part are retained the mca remained in the lower crust for about 1700 ma following peak metamorphism and some event unrelated to the original metamorphism was required to exhume it uplift occurred during development of the capricorn orogen when some 30 35 km were added to the crust beneath the errabiddy area the recognition of early proterozoic thrusting plus crustal thickening suggests that the capricorn orogen is a belt of regional compression which resulted from convergence of the yilgarn and pilbara cratons

a 20 000 year record of ocean circulation and climate change from the santa barbara basin much of the evidence for climate driven fluctuations in ocean circulation during the past 20 000 years has come from studies of the north atlantic region1 6 the extent to which such interactions have occurred in other ocean basins and any associated teleconnec tions between basins is poorly understood here we present high resolution palaeoclimate and palaeoceanographic records from a 20 000 year sedimentary sequence from the santa barbara basin on the eastern margin of the north pacific ocean the sequence shows oscillations of the benthic environment between low oxygen conditions laminated sediments during periods of warm climate and higher oxygen conditions non laminated bioturbated sediments during cool intervals age differences between coexisting benthic and planktonic foraminifers indicate climate related changes in the age and source and hence oxygen content of basin bottom waters relatively young bottom waters are associated with the cooler intervals and are considered to reflect high proportions of intermediate waters derived from proximal sources conversely older bottom waters are associated with the warmer intervals and were derived from more distal sources these climate driven variations in ocean circulation appear to be synchronous with the main ocean climate fluctuations in the north atlantic region1 6 suggesting that a tight coupling mechanism operates between the two basins

southern ocean winter mixed layer austral winter 1986 observations from the polarstern along the greenwich meridian from the ice edge to the antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation incorporation of weddell deep water wdw into the winter mixed layer responsible for this undersaturation also introduces heat and salinity into the surface layer which strongly influences the mixed layer sea air exchanges and sea ice formation processes the total wdw transfer into the mixed layer averages 45 myr 1 implying a residence time for the surface water of 2 5 years the associated winter heat flux is 41 w m 2 which limits ice thickness to about 0 55 m agreeing quite well with observations the air temperatures during the cruise are just sufficient to remove the wdw heat input in the presence of observed ice thickness and concentration this suggests that the sea ice cover and wdw heat input into the mixed layer are in approximate balance by midwinter the annual heat flux from wdw to the surface layer and hence into the atmosphere is estimated as 16 w m 2 extrapolation of the greenwich meridian wdw entrainment value to the full circumpolar 60 70 s belt yields total up welling of 24 106 m3 s 1 similar extrapolation of the heat flux value gives a circumpolar total of 2 8 1014 w as a consequence of circulation topography interaction the maud rise water column stands out as an anomaly relative to the surrounding region with a significantly more saline and dense mixed layer below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m this uplifting is believed to be a response of the upstream flow encountering the rise increased upstream flow would be expected to increase maud rise upwelling and the dependent salinity density of the mixed layer slight increases in the mixed layer density could trigger a convective mode and generation of a polynya it is hypothesized that spin up of the weddell gyre s barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over maud rise

formation waters from cambrian age strata illinois basin usa constraints on their origin and evolution abstract recently brine samples from the cambrian age mount simon formation the deepest most inaccessible sedimentary rock formation of the illinois basin and the overlying ironton galesville formation were collected as part of a major research effort evaluating the feasibility of sequestration of carbon dioxide in deep geologic formations halide and halide cation ratios especially cl br and na br ratios from groundwater samples collected during this investigation suggest that the brines of the cambrian age strata formed by the evaporation of seawater well beyond the point of halite precipitation the cl br and na br ratios the presence of mississippi valley type mvt ore mineralization in close proximity to the illinois basin and the tectonic history of the region and the illinois basin suggest that components of ore forming brines and perhaps crystalline basement brine are likely still present within the mount simon formation halide and cation halide ratio plots show that these brines have mixed with and have been diluted by subaerially evaporated seawater seawater and dilute groundwater movement of brines out of the mount simon formation and or exchange with brines of other formations is constrained by the overlying siltstone and shale rich eau claire formation a low permeability layer the most plausible interpretation of the halide and halide cation ratio data is that the brines of the cambrian age strata were introduced to the illinois basin from outside of the basin perhaps when the illinois basin was connected to the arkoma oklahoma and arkansas and black warrior basins alabama and mississippi via the reelfoot rift during cambrian and early ordovician time in addition the presence of some percentage of high nacl low cl br brines from the crystalline basement is suggested given the geochemical relationships of the halide and cation halide ratios and the tectonic history of the illinois basin finally halide and cation halide ratios determined by this investigation and regional geochemical evidence and hydrogeologic modeling by others suggest that the brines of these strata probably were affected by regional hydrothermal activity during permian time that was responsible for the mvt ore deposits of the midwestern u s thus the brines of the deepest strata of the illinois basin constitute a different more complex type of fluid than those found elsewhere in the basin halide and halide cation ratios suggest that these deep brines are dominated by residual evaporitic brine possibly originating as ore forming brines with dilution by seawater and dilute groundwater other components may include subaerially evaporated seawater and crystalline basement brines

microbial respiration and diffusive oxygen uptake of deep sea sediments in the southern ocean antares i cruise abstract benthic microbial respiration and diffusive oxygen uptake were measured and used to calculate rates of aerobic mineralisation of organic matter and concomitant co2 production at the sediment water interface in the abyssal region of the crozet basin this study was part of the antares i cruise on the r v marion dufresne in the permanent open ocean zone of the southern ocean on a south to north transect from 52 to 42 s in the indian ocean at all stations oxygen penetrated much deeper than 10 cm aerobic respiration was maximal in the top 1 cm 10 96 nmol cm 3 day 1 was always detectable down to 5 cm depth and at some stations even to 10 cm depth total depth integrated oxygen consumption corresponded to within 25 of the diffusive oxygen uptake across the sediment water interface the shape of the profile indicated that a diffusive downward flow of oxygen occurred below 10 cm depth thymidine incorporation experiments suggested that bacteria present at depths of between 15 cm and 1 m in the sediment were in a dormant state or growing extremely slowly however rapid dna synthesis started within 4 h after thymidine was added indicating a deep bacterial biosphere in southern ocean sediments it is proposed that the diffusive downward flux of oxygen below 10 cm depth sustains aerobic bacterial metabolism and survival at greater depths along the transect the total depth integrated oxygen uptake peaked at 48 s close to the polar front and at the subantarctic and subtropical convergence frontal zone nevertheless in general the differences were not very pronounced the average value of depth integrated microbial o2 consumption was 0 61 mmol m 2 day 1 which is equivalent to a carbon mineralisation rate of 2 3 g c m 2 year 1 these observations together with relatively high electron transport system ets values 6 6 l o2 g 1 h 1 and bacterial numbers 4 109 g 1 dry weight in the top centimeter imply that this region is less oligotrophic than previously assumed

antares i a biogeochemical study of the indian sector of the southern ocean abstract the first expedition of the antares program the french contribution to southern jgofs investigated the biology and the chemistry of the benthic environment and the water column in a region located between 60 s 72 e and 39 s 55 e in this special issue we present a detailed description of the transports of water masses across the polar front zone which are corroborated by chemical and microbial tracer studies a description of the sediment water interface bridging biological chemical and microbial studies and new insights into the diagenesis of biogenic silica

the role of radiogenic heat in prolonged intraplate reworking the capricorn orogen explained links between intraplate crustal deformation and the thermal regime of the lithosphere have been investigated using numerical models but these conceptual models must be tested using well constrained natural systems the proterozoic capricorn orogen of western australia is ideally suited for such a study after arc accretion it records a protracted history of intracrustal differentiation and over one billion years of subsequent tectonic reworking the early addition of juvenile arc material initially reduced the heat production of the crust whereas subsequent recycling of the deep crust ultimately produced radiogenic granites in the shallow crust using whole rock and magmatic zircon compositions we show that the shallow crust of the capricorn orogen has been progressively enriched in heat producing elements with time the high heat production is mainly controlled by thorium concentrated in lree enriched phosphates that grew during the late stages of crystallization of crustally derived granites using a numerical model we investigate the thermal effects of this evolved crustal stratification and compare them with quantitative data on the pressure temperature time evolution of a non magmatic mesoproterozoic reworking event the results provide new information concerning the process by which the thermal conditions necessary for the reworking of orogenic crust are generated and sustained for prolonged timescales 110 ma furthermore we demonstrate that perturbations to the radiogenic crust lead to warmer geotherms and consequent lithospheric weakening which has a fundamental control on intraplate reworking of long lived orogens

evolution of the southern ocean winter mixed layer and sea ice open ocean deepwater formation and ventilation an analytical model has been developed to describe the nature of the winter ocean sea ice interaction in the southern ocean to determine the principal processes responsible for maintaining stability in this marginally stable region and to predict the response to changes in the external forcing and initial conditions the model accurately describes the sparse winter observations and the general temporal evolution of the ice mixed layer depth and salinity for the period following the elimination of the seasonal pycnocline by rapid fall ice growth a scale analysis and sensitivity study reveal the system parameter dependence this indicates that the magnitude of entrainment is proportional to fst h0 s where fs is the external salt flux h0 the depth of the winter mixed layer and s the salinity gradient through the pycnocline thermodynamic ice growth reflects predominantly the competition between the oceanic diffusive heat gain across the base of the mixed layer and the loss to the atmosphere through the ice and leads a strong thermal gradient across the pycnocline leads to a significant diffusive flux which balances most of the heat lost to the atmosphere this limits the amount of ice growth possible and plays the principal role in maintaining the system stability since the ice growth is required for destabilization through haline rejection during the growth process the system is also sensitive to the large ratio of heat to salt in the pycnocline this introduces a negative feedback where increasing ice growth induces entrainment by the associated salt flux which in turn drives an entrainment heat flux which compensates for heat lost to the atmosphere this moderates the ability to grow ice and drive further entrainment the absolute strength of the salinity gradient on the other hand dictates the effectiveness which a same magnitude external salt flux will have in driving entrainment the effectiveness with which changes in these parameters as well as several other external parameters can influence the southern ocean stability is explicitly evaluated through the sensitivity study and analysis

surface area control of organic carbon accumulation in continental shelf sediments the relationship between organic carbon oc and grain size found in most continental shelf sediments is here reinterpreted in terms of the surface area of the sediments cores from many north american shelf environments show downcore decreases in oc to similar refractory background concentrations if expressed relative to the surface area of the sediments this consistent concentration is 0 86 mg oc m 2 which is equivalent in concentration to a monolayer of organic matter coating all mineral surfaces a more global collection of sediment water interface samples show that this relationship is even more extensive with exceptions occurring in areas of very high riverine sediment input organic pollution or low oxygen water columns density separations indicate that organic matter is largely adsorbed to mineral grains the microtopography of surfaces was examined with n2 sorption and most surface area was found to be inside pores of 10 nm width these data lead to a hypothesis that organic matter is protected by its location inside pores too small to allow functioning of the hydrolytic enzymes necessary for organic matter decay such protection would likely work in concert with other protection mechanisms such as humification this consistent surface area correlation with oc concentration may explain control of spatial and temporal variations in oc burial rates by sedimentation rates the pore protection hypothesis provides a causal mechanism for this observed control

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