return of the coral reef hypothesis basin to shelf partitioning of caco3 and its effect on atmospheric co2 differences in the rate of coral reef carbonate deposition from the pleistocene to the holocene may account for the quaternary variation of atmospheric co sub 2 volumes of carbonate associated with holocene reefs require an average deposition rate of 2 0 times 10 sup 13 mol yr for the past 5 ka in light of combined riverine mid ocean ridge and ground water fluxes of calcium to the oceans of 2 3 times 10 sub 13 mol yr the current flux of calcium carbonate to pelagic sediments must be far below the pleistocene average of 1 2 times 10 sub 13 mol yr the authors suggest that sea level change shifts the locus of carbonate deposition from the deep sea to the shelves as the normal glacial interglacial pattern of deposition of quaternary global carbonates to assess the impact of these changes on atmospheric co sub 2 a simple numerical simulation of the global carbon cycle was developed atmospheric co sub 2 as well as calcite saturation depth and sediment responses to these carbonate deposition changes are examined atmospheric co sub 2 changes close to those observed in the vostok ice core approximately 80 ppm co sub 2 for the quaternary are observed as well as the approximate depth changes in percent carbonate of sediments measured in themore pacific ocean over the same time interval less

neritic and pelagic carbonate sedimentation in the marine environment ignorance is not bliss synthesis of available data allows us to define general patterns of late quaternary carbonate production and sedimentation in the global ocean during high stands of sea level the neritic and pelagic environments appear to sequester approximately similar amounts of carbonate whereas during low stands of sea level the decreased neritic zone produces and accumulates approximately an order of magnitude less carbonate assuming that global accumulation of deep sea carbonates remains more or less constant during glacially induced changes in sea level the ocean becomes depleted with respect to calcium carbonate during high stands and recharges during low stands before we can achieve a better understanding of the global carbonate system however we need a better understanding of key environments and processes a production and accumulation on continental shelves both as potential sinks accumulation and as sources export to the deep sea b a better measure of pelagic carbonate production and c late quaternary late pleistocene and holocene mass accumulation rates in the deep sea

neritic carbonate for six submerged coral reefs from northern australia implications for holocene global carbon dioxide abstract total contribution of six recently discovered submerged coral reefs in northern australia to holocene neritic caco3 and co2 is assessed to address a gap in global budgets caco3 production for the reef framework and inter reefal deposits is 0 26 0 28 mt holocene co2 production is 0 14 0 16 mt coral and coralline algae are the dominant sources of holocene caco3 although foraminifers and molluscs are the dominant constituents of inter reefal deposits the total amount of holocene neritic caco3 produced by the six submerged coral reefs is several orders of magnitude smaller than that calculated using accepted caco3 production values because of very low production a give up growth history and presumed significant dissolution and exports the contribution of submerged coral reefs to global holocene neritic caco3 is estimated to be 0 26 0 62 gt which yields 0 15 0 37 gt of co2 this amount of co2 is 0 02 0 05 of the 780 gt added to the atmosphere since 18 kyr bp contributions from australian submerged coral reefs are estimated to be 0 05 gt caco3 and 0 03 gt co2 for an emergent reef area of 47 9 103 km2 based on the growth history of the submerged coral reefs in the gulf of carpentaria maximum global holocene caco3 fluxes could have attained 0 3 gt yr 1 between 11 and 7 ka bp this additional caco3 would have culminated in a maximum caco3 production from all emergent and submerged coral reefs of 1 2 gt yr 1 and neritic caco3 production of 2 75 gt yr 1 the dilemma remains that the global area and caco3 mass of submerged coral reefs are currently unknown it is inevitable that many more submerged coral reefs will be found our findings imply that submerged coral reefs are a small but fundamental source of holocene neritic caco3 and co2

calibration of marine sediment core loggers for quantitative acoustic impedance studies abstract accurate density and p wave velocity measurements on marine sediment cores are needed for quantitative acoustic impedance studies an increasing number of international marine laboratories routinely measure p wave velocity and bulk density the product of which gives the acoustic impedance on marine sediment cores using automated core loggers mscls despite the progressive standardisation of mscls in recent years no standard calibration technique has been decided that will enable datasets from different marine laboratories to be validated and compared with confidence this problem is particularly acute for bulk density measurements because systematic mscl errors are typically much greater than 10 one solution is to use a calibration tube comprising a stepped aluminium insert inside a water filled core liner that mimics marine sediment porosities and velocities and that can be used during normal core logging the calibration tube enables a reliable gamma ray reference intensity to be measured and an apparent compton mass attenuation coefficient to be derived that is suitable for most marine sediments and that simplifies data processing the calibration tube results show that the mscl belonging to southampton oceanography centre soc used as part of the standard analysis procedure of the british ocean sediment core repository boscor gives measurement accuracies of better than 0 07 g cm 3 for bulk density and 0 3 for p wave velocity

controls on sonic velocity in carbonates compressional and shear wave velocities v p and v s of 210 minicores of carbonates from different areas and ages were measured under variable confining and pore fluid pressures the lithologies of the samples range from unconsolidated carbonate mud to completely lithified limestones the velocity measurements enable us to relate velocity variations in carbonates to factors such as mineralogy porosity pore types and density and to quantify the velocity effects of compaction and other diagenetic alterations

new evidence for drowned shelf edge reefs in the great barrier reef australia we present four new high resolution multibeam bathymetry datasets from the shelf edge of the northern great barrier reef gbr analysis of these data combined with chirp sub bottom profiles and existing submersible observation data provides a fresh insight into the detailed morphology and spatial distribution of submerged reefs and terraces at the shelf edge an extensive and persistent line of drowned shelf edge reefs exist on the gbr margin in about 40 to 70 m they appear as barrier reefs up to 200 m wide and comprising twin parallel ridges of rounded pinnacles subtle yet consistent terrace and step features lie between 78 and 114 m seaward of the shelf edge reefs in the southern study area submersible observations confirm that the drowned reefs now provide a favorable hard substrate for live soft corals and algae they form a consistent and extensive seabed habitat that extends for possibly 900 km along the gbr shelf edge the submerged reef and terraces features may reflect a complex history of growth and erosion during lower sea levels and are now capped by last deglaciation reef material

stratigraphic control of the geochemistry of holocene inner shelf facies great barrier reef received 15 august 1994 revision accepted 28 june 1995 abstract cleveland bay and halifax bay are adjacent embayments situated on the inner shelf region o 20 m of the central great barrier reef shelf off townsville northeast australia these bays contain holocene sediments up to 5 m in thickness deposited during the last stages of the post glacial sea level rise x ray diffraction and x ray fluorescence techniques were used to examine the mineralogy and geochemistry of the main holocene facies sampled in 40 vibrocores the sediments of southern halifax bay and cleveland bay consist mainly of quartz ca 50 alkali feldspars ca 20 clay minerals ca 20 consisting of mixed layer clays smectite kaolinite and illite and carbonate ca 10 including aragonite and calcite the holocene facies sequence comprises in order of increasing age modern bay shoreline and mangrove sediments the oxides of the major components sioz a o fe203 mgo cao k o na o p o in halifax bay show the predicted linear correlations with geochemically related minor elements pb rb sr y zr ga zn ni co mn cr ti sc v ba and can be used to discriminate holocene facies however in cleveland bay these elements are poorly correlated within each facies and provide very poor facies discrimination these findings probably result from the presence of sandy shoreline sediments up to 2 m in thickness in the holocene sequence of cleveland bay with the consequent development of a weak oxic zone and migration of elements between adjacent facies a similar oxic zone is poorly developed in halifax bay because the shoreline facies there is either thin or absent that the chemical signatures of holocene inner shelf facies are spatially variable and are strongly influenced by the stratigraphy has wide implications for geochemical studies of marine sediments

a new coral reef province in the gulf of carpentaria australia colonisation growth and submergence during the early holocene abstract multibeam sonar mapping drill cores and underwater video data have confirmed the existence of a previously unknown coral reef province in the gulf of carpentaria australia seven reefs comprised of coral limestone that support living corals have been mapped so far and as many as 50 other reefs may exist in the region u th ages show that reef growth commenced shortly after limestone pedestals were submerged by rising sea level around 10 5 kyr bp making them the oldest holocene reefs known in australia reef growth persisted for 2 0 kyr but it had ceased at most locations by 7 0 kyr bp measurements of reef growth rates 0 95 to 4 m kyr 1 indicate that the reefs were unable to keep pace with contemporaneous rapid sea level rise 10 m kyr 1 which is consistent with a give up reef growth history core samples from reef platforms demonstrate that pleistocene limestone is exposed at depths of 27 and 30 m below present mean sea level these depths represent regionally significant phases of reef growth during a prolonged sea level still stand we conclude that the reefs are therefore mostly relict features whose major phase of growth and development relates to an earlier pre holocene sea level still stand

cyclone pumping sediment partitioning and the development of the great barrier reef shelf system a review abstract the modern great barrier reef gbr is part of the world s largest and best known mixed terrigenous carbonate continental margin the gbr shelf contains three shore parallel sedimentary belts an inner shelf zone of terrigenous sedimentation at depths of 0 22 m a middle shelf zone of sediment starvation at depths of 22 40 m and an outer shelf reef tract with its inner edge at ca 40 m depth these zones are controlled by the dynamics of northward fair weather along shelf drift driven by southeasterly trade winds and by the regular passage of tropical cyclones cyclones cause wind driven north directed middle shelf flows in excess of 130 cm s which erode the seabed concentrate the sparse mobile sediment into sand ribbons and advect suspended load onto the outer part of the nearshore terrigenous sediment prism and into inter reef depocentres within the outer shelf reef tract cyclones largely control the input of new sediment into the gbr system via river flooding seabed erosion or reef breakage they also help to control the partitioning and dispersion of the three main shore parallel belts of sediment and hence stratigraphic accumulation acting as a sediment pump especially during interglacial highstands cyclones have exerted great control on the development of the modern gbr province and its sediments by maintaining a broad shelf parallel zone of episodically mobilised sediment and scoured seabed upon which coral reefs have been unable to form cyclones may also have partly controlled the timing of initiation of the first gbr at 0 6 mybp contrary to current models gbr storm beds are most likely to be preserved intact close to the shoreline and become coarser grained away from the shoreline for the central gbr highstand shedding only applies to carbonate sediment at the scale of local reefs system wide oceanographic controls cause high rates of carbonate sedimentation on the slope during both sea level rise and highstand concomitantly terrigenous sediment accumulates fastest on the slope during sea level rise and slowest during sea level lowstand and highstand

detection of widespread fluids in the tibetan crust by magnetotelluric studies magnetotelluric exploration has shown that the middle and lower crust is anomalously conductive across most of the north to south width of the tibetan plateau the integrated conductivity conductance of the tibetan crust ranges from 3000 to greater than 20 000 siemens in contrast stable continental regions typically exhibit conductances from 20 to 1000 siemens averaging 100 siemens such pervasively high conductance suggests that partial melt and or aqueous fluids are widespread within the tibetan crust in southern tibet the high conductivity layer is at a depth of 15 to 20 kilometers and is probably due to partial melt and aqueous fluids in the crust in northern tibet the conductive layer is at 30 to 40 kilometers and is due to partial melting zones of fluid may represent weaker areas that could accommodate deformation and lower crustal flow

seismicity of central tibet from project indepth iii seismic recordings as part of project international deep profiling of tibet and the himalaya iii a 400 km long densely spaced array of 57 broadband and short period seismic stations was deployed in central tibet from august 1998 through may 1999 although originally designed to image the lithosphere with teleseismic events the array also recorded numerous local and regional seismic events more than 900 local and regional events were detected on at least 10 stations during the 1 year deployment and we were able to locate 267 local earthquakes a substantial number of the events were found to cluster in or near large grabens and along known strike slip faults while other events show no obvious correlation with known structures in addition to spatial clustering at least one of the large clusters also exhibits temporal clustering that may be associated with magmatic or geothermal activity in the upper crust the average v p and v s are estimated to be 5 85 and 3 35 km sec for the upper crust and 7 0 and 3 9 km sec for the lower crust respectively the 50 focal mechanisms computed from this set of events are consistent with north south shortening and east west extension there are no clear indications of significant local perturbations in the regional stress field induced by the collision between india and eurasia the majority of the focal mechanisms indicate normal and strike slip faulting at least six of the newly computed focal mechanisms however indicate thrust faulting which is a phenomenon not well documented previously ninety nine percent of the local earthquakes have focal depths shallower than 25 km and the locations of the few deeper events are poorly constrained the shallow earthquake focal depths are consistent with high temperatures and proposed ductile or aseismic behavior in the middle to lower crust of central tibet figure 6 1 figure 6 a earthquake locations computed from this study shown on shaded topographic data triangles are indepth iii seismic stations circles are events and are scaled by magnitude graphic 2 a color version of this figure is available online at the ssa web site b earthquake locations shown with major geologic structures from taylor et al 2003 3 reproduced with permission m h taylor personal comm 2002 triangles are indepth iii seismic stations geologic structures are as in figure 2 4 1 pending yes 2 f1 embed inline graphic 1 gif 3 ref 46 4 f3

seismic stratigraphy and development of the shelf edge reefs of the great barrier reef australia extensive shelf edge reefs sers and terraces are common along the seaward margin of the great barrier reef gbr we aim to better understand the architecture of the sers deposited during a poorly constrained period the last glacial maximum lgm and early postglacial a dense array of topas seismic lines was interpreted at hydrographers passage in the southern central gbr following a seismic stratigraphic approach ground truthed against integrated ocean drilling program expedition 325 iodp exp 325 sediment core data we interpreted two prominent sub bottom reflectors an upper r1 and a lower r2 that separate three seismic units according to our borehole to seismic correlation in a representative location r1 corresponds to a downward increase of impedance which is also reflected in lithological and diagenetical changes r2 is poorly constrained but likely also represents a lithological contrast seismic velocities were also estimated in the same borehole location for inter reef deposits and reef framework together with the geomorphic interpretation we reconstructed velocity maps for the study area leading to the generation of a 3d geomorphic model of the antecedent topography or substrate and volumetric calculations geomorphic and thickness trends suggest a strong relationship between the antecedent topography and the morphology of the sers the distribution of seismic facies identified in the dataset coupled to geomorphic trends and published sea level curves allowed us to reconstruct the lgm to postglacial depositional history of these deposits our interpretation suggests significant regressive reefal accumulations formed on top of a marine flooding surface represented by reflector r2 during the sea level fall to the lgm r1 is the distal equivalent of an unconformity previously identified in the gbr inner and mid shelf widely affected by subaerial exposure on top of which a postglacial transgressive mainly reefal unit 1 was deposited two zones are distinguished 1 a distal zone below 80 mbsl with thick deposits displaying fringing reef morphologies influenced by the late lgm fall and subsequent early postglacial rise in sea level and by the updip availability of substrate and 2 a proximal zone above 80 mbsl of enhanced vertical growth with unfilled lagoons resulting from the lack of lateral substrate and the rapid sea level rise our seismic stratigraphic model of the development of the sers sediment volumetrics and 3d reconstruction of the antecedent topography provides a foundation for future forward modeling stratigraphic studies

implications of crustal property variations for models of tibetan plateau evolution shear coupled teleseismic p waves sampling the interior of the tibetan plateau provide evidence of systematic variations in crustal structure the crust thins by up to 20 km from south to north with a concomitant increase in poisson s ratio from normal values in the south to unusually high values in the north this suggests that the crust of the northern plateau is partially melted due to high temperatures these changes imply spatial and perhaps temporal variations in the way the elevation of the high plateau is created and maintained

late holocene sediment in nara inlet central great barrier reef platform australia sediment accumulation on the middle shelf of a tropical mixed clastic carbonate system nara inlet in the whitsunday islands is a natural depocenter for clastic and carbonate sediment on the middle shelf of the central great barrier reef gbr platform three sediment cores were collected from the inlet to understand sediment accumulation in this tropical mixed clastic carbonate system over time surface and subsurface sediment is comprised of two main components terrigenous clay and shallow marine carbonate similar to other regions on the middle shelf of the gbr platform the carbonate component 25 80 by weight and dominated by sr poor foraminifera tests and mollusc shells generally increases towards the surface radiocarbon ages derived from tests of benthic foraminifera indicate that the top 3 m of sediment accumulated within the last 3000 years but that the rate has slowed toward present day the change in clastic and carbonate abundance therefore indicates a system where both clastic and carbonate accumulation has decreased over time but where clastic accumulation has decreased faster reduced clastic accumulation may reflect progressive impedance of terrigenous input by a laterally growing fringing reef at the mouth of nara inlet likewise reduced carbonate accumulation may reflect preferential reef growth and carbonate deposition outside of the inlet even though clastic accumulation has decreased significantly over time the late holocene mass composition and distribution of clastic material in nara inlet implies a terrigenous source previously unrecognized in models for the evolution of the gbr platform large amounts of terrigenous sediment probably were stored around topographic highs on the middle shelf during lowstand and early transgression this clastic material was then removed over time mixed with autochthonous carbonate and deposited in embayments on the middle shelf the accumulation of sediment on the middle shelf of a tropical mixed clastic carbonate margin is not straightforward

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

submerged coral reefs in the gulf of carpentaria australia abstract we report the discovery of three submerged living patch coral reefs covering 80 km 2 in the southern gulf of carpentaria australia an area previously thought not to contain coral bioherms the patch reefs have their upper surfaces at a mean water depth of 28 6 0 5 m and were consequently not detected by satellites or aerial photographs the reefs were only recognised in our survey using multibeam swath sonar supplemented with seabed sampling and under water video their existence points to an earlier late quaternary phase of framework reef growth probably under cooler climate and lower sea level conditions than today submerged reefs with surfaces between 20 and 30 m water depth occur in other regions of the earth and existing bathymetry indicates they could be widespread in the gulf many tropical regions that today do not support patch or barrier reefs for reasons similar to the modern gulf may have done so in the past when environmental conditions were more suitable submerged reefs may provide an important refuge for corals during the next few decades when near surface reefs are threatened by widespread coral bleaching due to warmer global sea surface temperatures

nature of the upper crust beneath central tibet abstract a wide angle reflection refraction seismic line obtained through sino french joint research near the bangung nujiang suture in tibet 1 yielded crustal velocity estimates for both p and s waves avp vs ratio of 1 65 was derived fo waves propagating in the upper 50 c km near the surface a shallow low velocity zone is expected to form in a granitic upper crust for both p and s waves a two dimensional ray tracing study indicates that the observed first p and s waves 1 can be interpreted as diving waves above a low velocity zone where a positive gradient exists the low velocity zone commences at a depth of 10 km and extends possibly to 20 km or deeper

merged statistical analyses of historical monthly precipitation anomalies beginning 1900 abstract a monthly reconstruction of precipitation beginning in 1900 is presented the reconstruction resolves interannual and longer time scales and spatial scales larger than 5 over both land and oceans because of different land and ocean data availability the reconstruction combines two separate historical reconstructions one analyzes interannual variations directly by fitting gauge based anomalies to large scale spatial modes this direct reconstruction is used for land anomalies and interannual oceanic anomalies the other analyzes annual and longer variations indirectly from correlations with analyzed sea surface temperature and sea level pressure this indirect reconstruction is used for oceanic variations with time scales longer than interannual in addition a method of estimating reconstruction errors is also presented over land the reconstruction is a filtered representation of the gauge data with data gaps filled over oceans the reconstruction gives an estimate of the atmospheric respons

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

a three dimensional barotropic model of the response of the australian north west shelf to tropical cyclones abstract a three dimensional barotropic model using a coordinate or depth transformation and forced with tropical cyclone wind and atmospheric pressure fields has been applied to the continental shelf and slope regions of the australian north west shelf the atmospheric pressure field of the cyclone causes a nearly isostatic sea level response and weak currents in an unbounded ocean the wind field would produce currents that circulate around the center of the cyclone and eject water thus tending to reduce sea level the coastline forms a boundary for the ejected water resulting in a large sea level rise and strong currents between the cyclone path and the coastline the model provides a good description of the vertical current shear as observed at a number of moorings during two different cyclones sea level rises are accurately modeled and a reasonable description of observed current strengths is achieved however the predicted currents and sea level changes at offshore stations are sensitive to the

submerged reef systems on the central western continental shelf of india abstract echosounding and sidescan sonar data from the western continental shelf between vengurla and vijaydurg have revealed the presence of submerged reef systems oriented nearly parallel to the shoreline at water depths of 60 100 m dredge samples collected from the pinnacles show evidence of shallow reef building corals the reefs are in general up to 3 m high but at times have a low relief or are even buried in clay the n s extent of reefs was found to be of the order of about 8 km implying that the pinnacles observed on the echograms are part of a larger reef system now submerged it is inferred that the reefs began forming and continued advancing shoreward as a result of a rise in sea level the occurrence of reefs below the clay leads to the proposition that sudden climatic changes increased the runoff from the land causing the burial of the reefs after their formation during the mid late holocene

general bathymetry of the gulf of carpentaria and the quaternary physiography of lake carpentaria abstract a generalized bathymetric map of the gulf of carpentaria has been prepared from royal australian navy sounding data the results confirm earlier work of nix and kalma and indicate that a closed basin lake carpentaria below 53 m present water depth could have existed during quaternary low sea level stands an evaluation of previous and present work shallow seismic records of the canadian superior mining co australia and oil company fathometer profiles indicate the preservation of lake sediments at 65 m and 53 m water depth preserved shoreline feature at 19 m 29 m and 65 m as well as extensive underlying erosion and incision these findings are consistent with erosion and incision of gulf sediments during sea level lowering aeolian infilling and dune formation on the present arafura sill during the dry phase of maximum glaciation and subsequent lake carpentaria formation and lacustrine sediment deposition most probably during the sea level rise phase lake carpentaria clearly dominates the physiography and climatology of this land bridge during quaternary time

sea level controls on the post glacial development of the great barrier reef queensland abstract the central great barrier reef is situated on a 125 km wide continental shelf with a shallow shelf break at ca 70 m in consequence the earlier post glacial reef tract was confined to a narrow fringing belt along the present upper slope and outer shelf the reef province only started to assume its modern dimensions after ca 10 ky b p when sea level stabilised at depths around 28 m reef growth since 18 ky b p has been controlled by the episodic nature of the post glacial transgression being related to shorelines s8 to s1 developed at estimated eustatic depths and ages of 114 m 18 ky b p 88 m 17 ky b p 75 m 15 ky b p 56 m 12 ky b p 45 m 11 ky b p 39 m 10 ky b p 28 m 9 5 ky b p 23 m 9 ky b p 9 m 7 5 ky b p and 0 m 6 5 ky b p rates of sea level rise as high as 12 m ky 1 occurred between stillstands outpacing coral growth response and resulting in many mid outer shelf reefs being drowned in situ

precise temperature estimation in the tibetan crust from seismic detection of the α β quartz transition in the deep crust temperature which is among the key pa rameters controlling lithospheric dynamics is inferred by extrap olation from the surface using several assumptions that may fail in regions of active tectonics and fluid migration in the rare case that temperatures of 700 8c or higher are exceeded in the upper and middle continental crust composed of quartz rich felsic rocks the a b quartz transition abqt will occur generating a mea surable seismic signature and offering the possibility for precisely estimating temperature from the known abqt phase diagram here it is shown that all expected seismic features of the abqt are met by the boundary between the upper and middle crust be low the indepth iii profile in central tibet this finding implies that a temperature of 700 8c is achieved at a depth of 18 km under the southern qiangtang block which agrees with the depth to the top of a high electrical conductivity anomaly likely representing partially melted crust to the south in the northern lhasa block the abqt is at 32 km depth corresponding to a temperature of 800 8c it thus appears that this seismic boundary representing the abqt is the result of recent geologic processes rather than being a lithologic boundary

holocene sediments of wistari reef towards a global quantification of coral reef related neritic sedimentation in the holocene wistari reef within the southern great barrier reef is a shallow coral reef platform featuring a very clearly defined leeward accretionary wedge of carbonate sediments the total global area of shallowly submerged coral reef has been quantified as 255 000 km 2 the question then becomes what additional area of sediment of significant thickness is associated with the measured shallow reef areas t at wistari reef the leeward sedimentary wedge has an area and a thickness that are roughly equal to the holocene sediments that have accumulated on the platform several important observations can be made from these data firstly the area of significant neritic carbonate sedimentation 1 m ka associated with coral reefs is near 500000 km 2 secondly the production rate of neritic carbonates at wistari reef is almost 50 less than the accumulation rate needed to obtain the volume of holocene reef sediments observed this implies that both production and accumulation neritic carbonate must have been more than a factor of two higher in the early to mid holocene c 2001 elsevier science b v all rights reserved

cay sal bank bahamas a partially drowned carbonate platform abstract recent high resolution seismic reflection profiling sediment sampling scuba observations and landsat imagery show that cay sal bank csb has very limited reef development no active sand shoals few islands a thin to non existent sedimentary cover and a relatively deep margin 20 30 m and shelf lagoon system 10 20 m windward and leeward margins can be discerned but their general development is poor when compared to the shallower more active margins of little bahama bank lbb and great bahama bank gbb windward margins facing north and east along csb are generally deep rocky sediment barren terraces supporting limited low relief relict reefs leeward margins have small sand bodies maximum thickness 10 m covering reef structures at the bank edge indicating that offbank transport of sands has occurred however these marginal sand bodies are limited in areal extent suggesting that this transport system was not ubiquitous along the south and west facing margins seismic and grab sample data from the deep 200 500 m slopes seaward of the leeward margins show a thin discontinuous unit of periplatform sand containing halimeda molluscs and non skeletal components derived from shallow water the limited basinward extent no deeper than 300 m of this unit recognized by its reflection free seismic facies also indicates that sand production and transport off the bank were never prolific this is in stark contrast to new seismic data from the leeward margins of gbb which clearly show thick 20 m sand bodies covering high reefs 12 15 m along the outer margin and multiple reflection free units extending to great depths 600 m all along the adjacent slope the apparent immature development of normal bank top processes and facies and the absence of key modern depositional environments on csb may be related to the rate at which this platform was submerged due to its comparatively low elevation the initial holocene flooding occurred at approximately 8 10 ka when sea level rise was rapid 6 m ka 1 by comparison the higher lbb gbb were flooded later at a much slower rate 1 5 m ka 1 the relatively rapid flooding of csb provided little time for the shallow depositional environments to start up the continued rapid rate of sea level rise after drowning and offbank transport of sediment and the export of chilled waters formed during winter months prevented the resulting facies from catching up consequently csb appears to be partially drowned particularly when compared to the other healthier rimmed bahamian platforms drowned carbonate banks are very common in the ancient record and potentially provide excellent stratigraphic traps for hydrocarbons csb provides a modern example of a bank that may be in the very early stages of termination final drowning of carbonate platforms may occur as a result of frequent higher order sea level fluctuations superimposed on initial stage of a lower order sea level cycle

calibration and application of marine sedimentary physical properties using a multi sensor core logger abstract we examined geophysical data from a multi sensor core logger mscl a logging device providing continuous measurements of gamma ray attenuation p wave travel time and magnetic susceptibility on marine sediment cores in the first part we focused on the gamma ray system and compared two different calibration methods from the gamma ray attenuation we calculated densities and porosities by incorporating mass weighted attenuation coefficients the application of an iteration method reduces the error of the density and porosity estimates compared to grape data in addition we derived equations to calculate water content and dry bulk density from gamma ray attenuation measurements comparison with physical properties determined on discrete samples revealed a very good correlation of both data sets r 0 99 this correlation is valid for sediments from substantially different geological settings e g turbidites hemipelagic muds and opal rich sediments in the second part we applied our data to marine geological questions for sediments from the antarctic polar frontal zone there is indication that the content of biogenic opal can be assessed using a correlation of density and p wave velocity for sediments from the bengal fan the relationship between the mscl acoustic impedance the product of density and p wave velocity and the grain size distribution in discrete samples can be used to predict clay and sand silt ratios for sediment cores from the shelf and upper continental slope

tibetan satellite magnetic low evidence for widespread melt in the tibetan crust the tibetan plateau is associated with a pronounced satellite magnetic low forward modeling of this anomaly demonstrates that the crust underlying the tibetan plateau is weakly magnetic compared to the crust on either side and that the boundaries of the weakly magnetic region coincide closely with the topographic edges of the plateau himalaya kun lun because there are no obvious changes in the bulk magnetization of the crust associated with the principal terrane boundaries within the plateau banggong and yarlung zangbo sutures the low likely manifests hot crust beneath tibet forward modeling of the magnetic anomaly with simple assumptions suggests that the curie isotherm is likely to reside in the upper crust across the tibetan plateau 15 km depth implying that granite minimum melt temperature 600 650 c is also achieved in the upper crust across the plateau 16 18 km depth this inference is consistent with the shallow depth extent of earthquakes in tibet and with the recent suggestion that melt may be areally widespread within the tibetan crust

modes of multi decadal oceanic precipitation variations from a reconstruction and ar4 model output for the 20th century 1 monthly oceanic precipitation variations are available from satellite observations beginning 1979 and from models for earlier periods and both the observations and models indicate increasing global average precipitation with warming global temperatures recently the authors developed an indirect data based reconstruction of precipitation beginning 1900 which is used here to analyze near global average multi decadal oceanic variations through the 20th century we compare this new reconstruction to oceanic coupled model precipitation from ar4 models beginning 1900 and to gpcp precipitation beginning 1979 both the reconstruction and ar4 models indicate increasing precipitation over the 20th century the reconstruction increase is stronger than the ar4 increase largely due to a climate shift in the 1970s that is resolved by the reconstruction but absent in the ar4 ensemble the reconstruction climate shift has an enso like spatial pattern and in the reconstruction the shift is associated with an enso mode consistent with work done by others the influence of this mode indicates the need for coupled models to accurately simulate the tropical pacific in order to resolve that region s influence on multi decadal variations