island wakes and headland eddies a comparison between remotely sensed data and laboratory experiments island wakes and headland eddies in coastal waters are identified from spaceborne and airborne remotely sensed imagery in the visible wavelengths the imagery were obtained for the bristol and english channels united kingdom which are characterized by high tidal currents and levels of turbidity suspended matter in the surface waters is used as a passive tracer for the flow features scaling parameters e g the reynolds ekman and rossby numbers obtained from the depth averaged equation of motion are presented based upon information on oceanographic conditions at the times of the overpasses the parameters are compared then with data obtained from laboratory model investigations presented by other experimenters in the published literature the remotely sensed data demonstrate that in coastal waters with nonuniform obstacles and bathymetry for a given ekman number the flow regimes occur at a lower rossby number than might be expected from laboratory experiments in the absence of a method for the accurate determination of the horizontal eddy viscosity hence the reynolds number it is concluded that an island wake parameter wolanski et al 1984a should be adopted to describe such features in coastal waters

dynamics of hypersaline coastal waters in the great barrier reef the coastal waters of the great barrier reef gbr are hypersaline salinity 37 during the dry season as a result of evaporation greatly exceeding rainfall of shallow waters and of the presence of numerous bays along the coast preventing rapid flushing these hypersaline waters are not flushed out by salinity driven baroclinic currents because these waters are vertically well mixed instead these waters are transported by a longshore residual current and thus form a coastal boundary layer of hypersaline waters as a result the hypersalinity distribution is 2 d with both cross shelf and longshore gradients of salinity the cross shelf gradients are largely controlled by turbulent diffusion while the longshore gradients are controlled by the residual currents that transport hypersaline waters longshore south ward in the central and southern regions of the gbr because every bay supplies hypersaline waters the width of the coastal hypersaline layer increases southwards steady state is reached in about 100 days which is the typical duration of the dry season the dynamics of the gbr hypersaline coastal boundary layer thus differ from the classical inverse hypersaline systems e g in saloum river estuary laguna san ignacio mission bay tomales bay san diego bay hervey bay shark bay coorong coast lagoon spencer gulf gulf of california and many others where the salinity gradient is mainly 1 d with a dominant along channel salinity gradient

hydrodynamic control of the supply of reworked terrigenous sediment to coral reefs in the bay of banten nw java indonesia abstract the bay of banten is an example of a shallow water reef environment adjacent to an eroding delta system where corals survive in turbid conditions this study investigated the hydrodynamic controls over residual fluxes of terrigenous sediment in the bay observations of wind waves currents and suspended sediment concentrations in 1998 and 1999 revealed contrasting dynamic turbidity conditions influenced by tides monsoon driven flows and locally generated waves the most sediment rich suspensions originate from the shallow coastal margin of an inactive delta where waves resuspend sediment and small creeks discharge freshwater and sediment because of coupling between monsoonal wind throughflow in the bay and wave height when wave induced resuspension peaks seasonally during the northwest monsoon an eastward throughflow prevents the nearshore reefs in the bay from being directly exposed to turbid water masses generated in the eroding delta in inshore waters tidal asymmetry and the spatial variation of current amplitudes cause residual sediment transport largely depending on the availability of erodible sediment in the center of the bay where there is a patch reef complex the tidal and subtidal currents are weak and therefore here there is a zone where sediment accumulates

the gulf of carpentaria heated torres strait and the northern great barrier reef during the 2016 mass coral bleaching event the 2015 16 enso event increased the temperature of waters surrounding northeast australia to above 30 c with large patches of water reaching 32 c for over two months which led to severe bleaching of corals of the northern great barrier reef ngbr this study provides evidence gained from remote sensing data oceanographic data and oceanographic modeling that three factors caused this excessive heating namely 1 the shutdown of the north queensland coastal current which would otherwise have flushed and cooled the northern coral sea and the ngbr through tidal mixing 2 the advection of warm 30 c water from the gulf of carpentaria eastward through torres strait and then southward over the ngbr continental shelf and 3 presumably local solar heating the eastward flux of this warm water through torres strait was driven by a mean sea level difference on either side of the strait that in turn was controlled by the wind which also generated the southward advection of this warm water onto the ngbr shelf on the ngbr shelf the residence time of this warm water was longer inshore than offshore and this may explain the observed cross shelf gradient of coral bleaching intensity the fate of the great barrier reef is thus controlled by the oceanography of surrounding seas

tides on the northern great barrier reef continental shelf sea level and current data are used to show that at least for the dominant semidiurnal tides the northern great barrier reef is permeable to tides the longshore gradients of the phase and amplitude of the tide at the shelf break are very small and the tidal currents are controlled by the shelf bathymetry the bulk friction coefficient may be enhanced by the secondary circulation around coral reefs

weathering by wetting and drying some experimental results a series of experiments on sandstone and dolerite was undertaken in an attempt to better understand the wetting and drying weathering process as rock samples are frequently subjected to wet dry cycles within the simulation of other weathering mechanisms e g freeze thaw three common methods of moisture application were used and the influences of these evaluated it was found that the method of moisture application could affect the nature of the weathering products resulting from wetting and drying it was also observed that there were changes in the internal properties of the rock e g porosity microporosity and that these could influence the synergistic operation of other weathering processes although not all of the observations could be explained it is apparent that wetting and drying has both a direct and an indirect effect on the weathering of rock that has not been taken into account in simulations greater cognizance needs to be given to the role of this process both in the field and in laboratory simulations

the estuarine chemistry of rare earth elements comparison of the amazon fly sepik and the gulf of papua systems abstract a comparison of the amazon fly gulf of papua and sepik river systems has shown that there are two distinct processes operating on dissolved rare earth elements ree in estuaries large scale salt induced coagulation in the low salinity region and small to extensive release in the mid to high salinity region fractionation of the ree occurs during both removal and release the order of removal follows lree mree hree and the order of release follows hree mree lree where l m and h refer to light middle and heavy ree respectively hence estuarine reactions can modify the relative abundance of dissolved ree reaching the oceans operating in tandem the removal and release lead to the preferential removal of the lree and the preferential release of hree during estuarine mixing this combination in turn results in an effective river water flux river flux after modifications by estuarine chemistry which is evolved toward the ree composition of seawater which has a heavy ree enriched composition when normalized against the ree composition of rivers or the earth s continental crust the increase of dissolved ree in the mid to high salinity waters of the amazon and fly estuaries suggests a sediment and or suspended sediment source the lack of ree increases in the sepik river estuary strengthens this explanation as the mixing zone of this estuary is located over a deep shelf where there is little physical contact between bottom sediment and estuarine waters in marked contrast the amazon and fly estuaries are dominated by the active resuspension and deposition of bottom sediments the resupply of ree accompanied by fractionation may result from ree carbonate complexation during the reaction of seawater with suspended particles and or bottom sediment estuarine and shelf sediments may be important sources of dissolved nd to the oceans thereby helping to maintain the inter ocean differences in the nd isotopic composition of seawater by reducing the residence time of nd in the oceans

potential transport pathways of terrigenous material in the gulf of papua t this work discusses potential transport pathways of plume water may infrequently enter the torres straits terrigenous material in the gulf of papua gop new because of sub tidal water elevation differences between guinea using lagrangian tracers as proxies for clay the gop and the arafura sea modeling studies have been minerals and finer particles the tracers are transported by used in conjunction with measurement programs to elucicurrents from the east asia seas implementation of the date dispersal mechanisms for noncohesive sediments in the navy coastal ocean model the results suggest that clay gop wolanski el al 1984 1995 hemer et al 2004 minerals input from rivers along the northwest coast of the 4 this study complements earlier work by examining gop accumulate on the inner shelf with high concentrations the dispersal of dissolved and fine grained suspended ternear the mouth of the fly and purari rivers finer particles rigenous material within the gop for a year long interval which are also representative of dissolved metals are using a combination of hydrodynamic and lagrangian transported eastward along the gop coast into the solomon tracer modeling furthermore because of the large model sea as well as into the torres strait to the west the results domain used in this study we are able to study the impact of also suggest that some finer particles are entrained by eddies large scale flows on transport patterns without imposing within the northern coral sea these results are in artificial boundary conditions the use of tracers to examine qualitative agreement with observations from the region complex multidisciplinary problems in oceanography has citation keen t r d s ko r l slingerland s riedlinger led to understanding the behavior of both suspended and and p flynn 2006 potential transport pathways of terrigenous dissolved constituents in a range of ocean environments material in the gulf of papua geophys res lett 33 l04608 nakano and povinec 2003 mcmanus and prandle 1997

bedform facies in western torres strait and the influence of hydrodynamics coastal geometry and sediment supply on their distribution abstract this study uses outputs from hydrodynamic and bedload transport models combined with satellite imagery aerial photography and bathymetric data to understand the distributions and mechanisms maintaining six spatially extensive bedform facies in western torres strait changes in bedform morphology occur along north south variations in coastal geometry and east west variations in hydrodynamic regime numerous islands create an environment that favours the formation of banner banks in the south while other sandbank morphologies occur on an extensive and comparatively flat basement to the north the western side of torres strait experiences net bedload transport that is directed to the west throughout the year and favours the formation of bedforms that prefer unidirectional bedload transport regimes i e barchan shaped sandbanks and sand ribbons the eastern side of the strait experiences seasonal changes in the direction of net bedload transport and maintains s and v shaped sandbanks sediment availability also influences the bedform facies western torres strait experiences net westward bedload transport through the strait however sandbanks indicating high sediment availability are found in the central shallow and high current velocity areas while sand ribbons indicating low sediment availability are a distal facies on the western side of the strait this sequence of bedforms indicates that sediments are preferentially trapped within the central portion of the strait and not transported further west into the gulf of carpentaria

geochemical mass balance for lithium boron and strontium in the gulf of papua papua new guinea project tropics a mass balance has been calculated for the elements li b and sr in the gulf of papua from sampling undertaken during 1993 to 1999 parameters measured included fly kikori and purari river inputs of dissolved and particulate phases removal flux to sediment traps at the base of the continental shelf slope and century scale accumulation rates in shelf and slope sediments derived from excess 210pb profiles in sediment cores about 91 of river input li was in particulate form and there was conservative behavior of dissolved li in the salinity gradient of the estuaries li accumulation rate in inner shelf sediments was slightly less than river inputs suggesting that more than 90 of li river inputs were trapped in rapid aluminosilicate mud accumulation zones of the inner shelf 50 m depth li removal rate to sediment traps at the base of the slope at 1000 m water depth was an order of magnitude smaller than the inner shelf sedimentation export of li to deep water coral sea was estimated to be 1 2 108 mol yr 1 and this amount is equivalent to the riverine dissolved li annual supply rate about 66 of river input of b was in the particulate phase and low dissolved b concentrations in freshwater were conservatively mixed with higher concentrations of b in seawater across the salinity gradient removal of b to inner shelf sediments was about 83 of the total river input indicating a small export of b 1 2 108 mol yr 1 to the coral sea about half of the dissolved b input from rivers is sorbed to particles and trapped in inner shelf sediments only 24 of river input of sr was in particulate form and low freshwater concentrations of dissolved sr were conservatively mixed with higher concentrations of sr in seawater across the salinity gradient only 20 of total river inputs of sr were buried in shelf sediments and there was a large export 7 3 108 mol yr 1 of sr off the shelf to the coral sea a sediment core from a rapidly accumulating mud deposition zone of the inner shelf shows twofold sympathetic variations in li b and sr ca supply rates over 200 to 1000 yr time intervals

tidal jets nutrient upwelling and their influence on the productivity of the alga halimeda in the ribbon reefs great barrier reef abstract a field experiment was carried out to study water circulation and benthic biological productivity near a passage through the ribbon reefs in the northern great barrier reef of australia the currents through the passage were phase locked with the tide during rising tides strong currents through the passage generated localized upwelling on the upper continental slope enriching the depleted surface waters in nutrients particularly nitrate and phosphate simultaneously on the shelf side of the passage a tidal jet vortex pair system developed which separated from the ribbon reefs so that the coral reefs themselves received little of the upwelled water this was propagated as a bottom trapped layer towards the meadows of the calcareous alga halimeda situated several kilometres inshore of the reefs halimeda can accumulate nutrients particularly nitrate from the relatively low concentrations available from the upwelling events the quantity of nitrogen upwelled was more than sufficient to supply the total nitrogen requirements of the halimeda vegetation a tidal jet also formed offshore from the reef passage during falling tides and the coral covered offshore side of the ribbon reefs may be sustained by the subsequent vertical turbulent entrainment into the jet of deep nutrient rich water immediately offshore from the reef passages these processes require a continuous barrier reef with only narrow passages several kilometers apart numerical models successfully reproduce the observations of jet driven upwelling and of the dynamics of the tidal jet vortex pair system the model predictions are very sensitive to the details of the bathymetry of reef passages as such data are presently unavailable it is not yet possible to use these models to calculate the jet driven nutrient upwelling for the whole great barrier reef

modeling of bathymetry locked residual eddies in well mixed tidal channels with arbitrary depth variations abstract the concept of the in out type exchange flow in estuaries only applies to situations with significant freshwater discharge and or elongated channels with relatively simple variations in depth and coastline along the channel in waterways with complex bottom topography the in out type exchange flows may be replaced by residual eddies that are locked to bathymetry this paper develops an analytic model for such tidally induced residual eddies the model allows arbitrary depth variations in both along and across channel directions the model produces residual eddies locked to bathymetry features similar to observations in wassaw sound using a ship mounted adcp analysis indicates that for problems in a short channel with standing wave characteristics the residual circulation is significantly influenced by advection the frictional effect however is dominant and the wave propagation effect cannot be uniformly neglected i e it sometimes can still compete or reinforce the effect of advection

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

u th pb systematics and ages of himalayan leucogranites south tibet abstract the age and origin of five leucogranites from the high and tethys himalaya and two country rock gneisses were investigated by u pb dating of zircon fractions and single grains and fractions of monazite additionally th u concentrations in whole rock powders and isotopic compositions of pb in leached k feldspars were determined monazites yield ages of 16 8 0 6 m y for the nialam migmatite granite 15 1 0 5 m y for the lhagoi kangri granite 14 3 0 6 m y for a granite from mt everest and 9 8 0 7 m y and 9 2 0 9 m y for two varieties of the maja granite these data together with monazite ages of 21 9 0 2 and 24 0 0 4 m y determined earlier on the makalu granite 1 substantiate a period of intracontinental granite emplacements from 24 to 9 m y ago i e from uppermost oligocene to late miocene times such a period of plutonic activity is consistent with the view that all these granites result from intracrustal melting following the collision of india with eurasia furthermore the individual ages together with structural relationships between granites and country rocks suggest that granite formation and tectono metamorphism occurred as alternating and strongly related processes with a periodicity of 7 to 9 m y inherited lead components present in all granite zircons point to large proportions of precambrian material in the magma source regions up to 2200 m y old th u systematics between monazite and country rocks indicate that u has been leached from most of the granites after crystallisation of monazite zircon dating of the kangmar granite gneiss which occurs in a window through the tethys himalayan sediments shows that this pluton transformed to a gneiss during the alpine orogeny crystallised in lowermost palaeozoic times 562 4 m y ago

biological indicators of sedimentary dynamics in the central gulf of papua seasonal and decadal perspectives 1 benthic and pelagic communities in the central gulf of papua a major deltaic clinoform located on the south coast of papua new guinea reflect the spatial and seasonal patterns in physical sedimentation conditions and the availability of food resources across this system the distribution of terrigenous and marine organic substrates the transport of riverine derived sediment and seafloor dynamics are largely controlled by two seasons and wind patterns the relatively quiescent nw monsoon and more energetic se trades the physically disturbed inner topset deposits 20 m are dominated at all times by bacterial biomass and have depressed numbers of macrofauna with evidence of periodic recolonization recorded in sedimentary structures the inner topset region also shows strong seasonality in the production and availability of labile organic matter and in bacterial activity as measured by the concentrations of photopigments and microbial biomass in the upper 2 cm of surface sediments and in the water column the comparatively quiescent nw monsoon period is associated with net delivery of reactive substrates as labile organic matter to the bottom and net growth of the benthic microbial community whereas the transition period between the nw monsoonal winds nw monsoon and se trade winds se trades and the se trades are periods of reactive substrate depletion in bottom deposits and decreased benthic bacterial and macroinfaunal biomass in contrast to the inner topset the less physically disturbed outer topset and foreset show relatively enhanced but still low abundances of large macrobenthos and possible evidence of variation related to food supply the greatest observed seasonal variation in macrofauna occurs in the umuda valley off the fly river an apparent mobile sediment conduit

the transhimalaya gangdese plutonism in the ladakh region a upb and rbsr study abstract the age and origin of the transhimalaya gangdese plutonic belt in the ladakh area has been studied by high resolution u pb analyses of accessory minerals zircon and monazite allanite and rb sr measurements on whole rock samples the ages determined of 101 2m y for a granodiorite and of 60 7 0 4m y for a granite substantiate that the transhimalaya plutonism was active at least in mid cretaceous albian and earliest tertiary palaeocene times a rb sr isochron of 73 4 2 4m y might be fortuitous because the rb sr systematics shows important heterogeneities on the whole rock scale the inherited radiogenic lead in zircon demonstrates that anatexis of continental crust was involved in magma genesis the thus recycled continental material was heterogeneous with respect to its primary ages and or metamorphic history the approximate minimum ages of the continental sources range from 350 to 590 m y the 101 2m y old transhimalaya granodiorite which intrudes a series of mainly basaltic island arc rocks dras series shows that this island arc was attached to the continental margin at that time this is consistent with the hypothesis that the ladakh tethys closed through two subduction regimes 1 an early cretaceous subduction which formed the dras island arc and 2 a late cretaceous to palaeocene subduction at the continental margin which caused the emplacement of the transhimalaya plutonic belt

sources and sinks of unradiogenic osmium runoff from papua new guinea the fly and sepik are two of the largest rivers draining the island of new guinea and among the world s large rivers in discharge and sediment yield sediment from the upper fly river and its delta have low 187os 188os of 0 511 0 560 and sediments from the upper and lower sepik river have even lower ratios of 0 294 0 418 filtered waters 1 2 burial of os of both seawater and riverine derivation occurs in conjunction with organic carbon burial in the gulf of papua there is a negative correlation between the os isotopic composition of the bulk sediment and the fraction of organic matter of terrestrial origin based on c isotopes the systematic relationship between c and os isotopic compositions in these samples indicates that organic matter is the major host of os in tropical estuarine sediments the os corg of gulf of papua surface sediments is intermediate between that of other modern and ancient sediments approximately 1011 mol yr of corg and 20 57 mol yr of os are buried in the inner shelf 50 m depth of the gulf of papua over an area of only 21 000 km2 corresponding to 1 3 of the global marine os burial flux in 0 006 of the total sea surface area these results suggest that a large proportion of the global burial flux of os may take place in conjunction with the deposition of low corg sediments lowering of the os isotopic composition of ambient seawater due to a large flux of unradiogenic riverine os may be indicated by the os isotopic composition of water from the coral sea 187os 188os 0 844 and marine sediments within the gulf of papua the island of new guinea is estimated to provide 4 5 of the global riverine os flux given the very large particulate and dissolved flux to the oceans from rivers in the wet tropics the effect of the weathering of young arc related crust in the sw pacific is an important source of unradiogenic os to modern seawater

u th pb systematics in hydrothermally altered granites from the granite mountains wyoming abstract u th pb systematics were investigated in 15 samples representing two types of deuterically altered archean granite albitized and silicified epidotized granite from the granite mountains wyoming the loss of k feldspar during both types of deuteric alteration was accompanied by an extreme reduction of pb content from roughly 40 ppm to less than 12 ppm in the most altered samples nine of the 15 samples yield anomalously young whole rock pb pb and th pb ages compared to concordia ages for zircons and to whole rock pb pb and th pb ages for samples of unaltered granite the young ages are interpreted to be the result of radiogenic pb loss during a middle proterozoic metamorphism that disturbed several isotopic systems in the unaltered granite the loss of radiogenic pb from the whole rock systems of the deuterically altered granites is most likely due to the absence of microcline in many granitic rocks potassium feldspar tends to act as a receptor for pb that has been mobilized and this effect may account for the closed system behavior of pb in whole rock samples of the unaltered granite it may also account for the apparent gain of radiogenic pb during the proterozoic by one sample which was collected at the edge of an alteration zone the deuterically altered granites may have also lost u during the proterozoic but except for two samples the dominant u loss occurred relatively recently probably during tertiary uplift and erosion the low common pb contents and rather high u and th contents of the hydrothermally altered granites might seem to indicate that these rocks are well suited for geochronologic studies in the u th pb system because such rocks should have a high percentage of radiogenic pb unfortunately open system behavior in response to post crystallization metamorphism shows that apparent ages for these types of rocks must be interpreted with caution

early diagenetic remineralization of sedimentary organic c in the gulf of papua deltaic complex papua new guinea net loss of terrestrial c and diagenetic fractionation of c isotopes oceania supplies 40 of the global riverine flux of organic carbon approximately half of which is injected onto broad continental shelves and processed in shallow deltaic systems the gulf of papua on the south coast of the large island of new guinea is one such deltaic clinoform complex it receives 4 mt yr 1 particulate terrestrial organic carbon with initial particle corg loading 0 7 mg m 2 corg loading is reduced to 0 3 mg m 2 in the topset upper foreset zones of the delta despite additional inputs of mangrove and planktonic detritus and high net sediment accumulation rates of 1 4 cm yr 1 carbon isotopic analyses 13c 14c of co2 and corg demonstrate rapid 100 yr remineralization of both terrestrial 13c 28 6 and marine corg 13c 20 5 ranging in average age from modern bomb 14c 60 to 1000 yr 14c 140 efficient and rapid remineralization in the topset upper foreset zone is promoted by frequent physical reworking bioturbation exposure and reoxidation of deposits the seafloor in these regions particularly 20 m apparently functions as a periodically mixed suboxic batch reactor dominated by microbial biomass although terrestrial sources can be the primary metabolic substrates at inshore sites relatively young marine corg often preferentially dominates pore water co2 relative to bulk corg in the upper foreset thus a small quantity of young rapidly recycled marine organic material is often superimposed on a generally older less reactive terrestrial background whereas the pore water co2 reflects both rapidly cycled marine and terrestrial sources terrestrial material dominates the slower overall net loss of corg from particles in the topset upper foreset zone i e recycled marine corg leaves little residue preferential utilization of corg subpools and diagenetic fractionation of c isotopes supports the reactive continuum model as a conceptual basis for net decomposition kinetics early diagenetic fractionation of c isotopes relative to the bulk sedimentary corg composition can produce changes in 14c activity independent of radioactive decay in the gulf of papua topset upper foreset 14c of pore water co2 averaged 300 greater than corg sediment between 1 3 m depth in deposits diagenetic fractionation and decomposition aging of sedimentary corg compromises simple application of 14c for determination of sediment accumulation rates in diagenetically reactive deposits

osmium isotope geochemistry of a tropical estuary abstract fundamental aspects of the estuarine geochemistry of os were investigated by analysis of the os isotope composition and concentration variations in filtered water samples from a salinity transect taken in the estuary of the tropical fly river of new guinea 187os 188os of the waters in the salinity transect increase with salinity from 0 6165 in the river endmember 0 1 salinity to a maximum of 0 913 in the most saline water 33 these values are distinctly lower than the 187os 188os of 1 06 reported for open ocean waters from the indian and pacific oceans sharma et al 1997 levasseur et al 1998 woodhouse et al 1999 the os concentrations in the waters range from a minimum of 4 59 pg os g in the river to a maximum of 5 66 pg os kg at 12 salinity these concentrations are all significantly lower than the open ocean range of 6 6 to 10 86 pg os kg levasseur et al 1998 woodhouse et al 1999 the isotopic results indicate that the rivers draining the new guinea landmass provide unradiogenic dissolved os to the oceans and led to a lowering of the 187os 188os of the local seawater the os concentration salinity relationship indicates that the mixing process is not conservative and that removal of os from the dissolved state has taken place the proportion of os lost from solution increases with salinity resulting in removal of a large proportion of seawater os in the estuary high concentrations of os in marine sediments within the gulf of papua were previously interpreted to be due to incorporation of seawater derived os into organic matter martin et al 2000 earth planet sci lett 183 261 274 and are the likely complement to the processes observed in the dissolved state enhanced removal of seawater os in estuaries could help to resolve the differences in estimates of os residence time made on the basis of oceanic deposits versus those based on measured river water concentrations

rb sr geochronology of granites and gneisses from the mount everest region nepal himalaya nineteen samples of granites orthogneisses and paragneisses from the high himalaya basement nappe s of the mount everest region have been dated by the rb sr method the post metamorphic tourmaline leucogranites of the upper imja drangka nuptse lhotse glacier have high initial sr87 sr86 characteristic of an anatectic origin from crustal material a whole rock isochron age of 52 m y early eocene has been obtained for the samples from the granite body of lhotse glacier apparently sr isotopic homogenization was not reached throughout the much larger nuptse granite

flow around islands in rupert bay an investigation of the bottom friction effect aerial photographs of transverse shear flows around islands in rupert bay a shallow and turbid estuary in northern quebec were studied for the effect of bottom friction the island wake depends on the stability of the transverse shear layers developed along the two sides of the island two basic patterns of wake flows were observed a vortex street wake was formed when transverse shear was large as in flows around small islands on the other hand for small transverse shear as in flows around large islands the shear layers were stabilized by bottom friction and in that case a clear water wake of low turbulence and low sediment concentration was observed laboratory demonstration of the bottom friction influence on the turbulent wake in shallow water was made using a shallow water table a similarity solution was obtained for the wake flow in the far field region and numerical calculations were made of the recirculating flow in the wake bubble a wake stability parameter was introduced for wake classification and for correlation of field and laboratory data in rupert bay vortex street wakes were observed in nine out of 27 events when the wake stability parameter was less than a critical value this result is consistent with the laboratory and numerical simulations

shallow water flow around model conical islands of small side slope part ii submerged experiments have been conducted to study the unsteady wakes of submerged conical islands the islands used in the tests have side slopes ranging from 8 0 to 33 1 experiments in a shallow water channel with a steady subcritical free stream showed vortex shedding to occur in the wake when the water depth above the island apex was relatively small flow separation from positions near the island apex was found to be important in producing this unsteady wake as the water depth was increased the shedding was observed to become less vigorous and eventually stop all islands tested produced similar results with the angle of the island side slope exerting relatively little influence on the process the results of wind tunnel visualization studies which used a rigid top plate to produce the effect of fluid depth support the results from the water channel pictures of the surface flow patterns produced on the islands by the wind action are presented two dimensional 2d and three dimensional 3d shallow wate

the tibetan side of the india eurasia collision results are reported from the 1980 joint french chinese field expedition in tibet the area covered was from the high himalaya in the south to the region of nagqu 250 km north of yangbajain ophiolites in the zangbo valley represent remnants of the crust of an ocean basin which lay adjacent to the gangdise granodiorite belt in the late mesozoic the ophiolites were thrust to the south onto the cretaceous melange and triassic flysch but the age of this event is unclear in the tertiary sediments of the indian margin and the xigaze basin were folded with steeply dipping cleavage which indicates some north south shortening of the crust however the tertiary volcanic sequence on the lhasa block and further north shows comparatively little folding and thrusting in the quaternary deformation of tibet was characterized by east west extension

sensitivity analysis of the physical dynamics of the fly river plume in torres strait abstract the intrusion in the torres strait of the fly river plume polluted by mine tailings is an international water issue to investigate the physical mechanisms involved in the intrusion process numerical simulations were conducted to assess the relative influence of the bathymetry and the external forcing namely the tides the mean sea level slope across the strait river runoff and wind forcing the wind data from horn island the only long term wind station in the torres strait is shown to be unreliable due to orographic effects mean sea level data from altimetry compare well with those from tide gauges in these shallow reef studded waters the wind has a dominant effect on the mean sea level at seasonal and inter annual periods the resulting mean sea level difference across the strait fluctuated seasonally and strongly influenced the intrusion of the fly river plume in the torres strait the 3d finite volume mohid model reproduced the observation that the river plume starts by being stratified in the gulf of papua where it originates and it mixes vertically when it enters the torres strait the mohid and the slim models were applied with different resolution to the torres strait and responded similarly to the external forcings the predicted and observed fly river plume intrusion in the eastern torres strait agreed well with each other including the formation of patches due to flow reversals however the two models predicted a widely different fly river plume in its far field in the western torres strait the differences were attributed to the different bathymetry in the australian and british us bathymetry data for these poorly charted waters which demonstrated the importance of the details of the bathymetry in controlling the extent of plume intrusion

late pleistocene and holocene sedimentation organic carbon delivery and paleoclimatic inferences on the continental slope of the northern pandora trough gulf of papua 1 we investigated sediment and organic carbon accumulation rates in two jumbo piston cores mv 54 mv 51 retrieved from the midslope of the northeastern pandora trough in the gulf of papua papua new guinea our data provide a first assessment of mass fluxes over the past 33 000 14c years b p and variations in organic carbon sources core sediments were analyzed using a suite of physical properties organic geochemistry and micropaleontological measurements mv 54 and mv 51 show two periods of rapid sediment accumulation the first interval is from 15 000 to 20 400 cal years b p mv 51 1 09 m ka 1 and 81 2 g cm 2 ka 1 and the second occurs at 32 000 14c years b p 2 70 m ka 1 and 244 g cm 2 ka 1 extremely high accumulation rates 3 96 m ka 1 428 g cm 2 ka 1 characterize 15 800 17 700 cal years b p in mv 54 and likely correspond to early transgression when rivers delivered sediments much closer to the shelf edge a benthic foraminiferal assemblage in mv 51 from 18 400 to 20 400 cal years b p indicates a seasonally variable flux of organic carbon possibly resulting from enhanced contrast between monsoon seasons the oldest sediments 32 000 14c years b p contain toc fluxes 200 g cm2 ka 1 with 50 of it derived from c3 vascular plant matter magnetic susceptibility values are 2 to 3 times higher and benthic foraminiferal accumulation rates are 6 times higher during this interval than at any younger time indicating a greater influence of detrital minerals and labile organic carbon the ms data suggest more direct dispersal pathways from central and eastern png rivers to the core site

upb geochronology of gangdese transhimalaya plutonism in the lhasa xigaze region tibet abstract a series of different plutons from the lhasa xigaze segment of the gangdese transhimalaya belt has been studied by high resolution u pb analyses of zircon using zircon fractions of 5 100 grains each selected upon specific grain characteristics for two diorites located east of xigaze dazhuka the zircons yield concordant ages of 93 4 1 0 and 94 2 1 0 m y respectively also concordant ages of 41 1 0 4 and 41 7 0 4 m y have been obtained for two granodiorites collected southwest of lhasa qushui the precision on the ages of two granites from the xigaze and lhasa area is limited by two factors the presence of inherited radiogenic lead and the occurrence of subsequent lead loss however some concordant zircons detected in both granites define approximate ages of about 67 and 53 m y respectively the inherited lead components show that melting of precambrian material was involved in magma genesis the u pb ages substantiate a magmatic activity lasting from mid cretceous cenomanian to eocene lutetian time such a period of plutonism at the southern margin of eurasia as well as the occurrence of magma generation from continental crust suggest that the gangdese range results from the subduction of tethys oceanic lithosphere indian plate underneath eurasia eurasian plate if this model is true the collision of india with eurasia along the lhasa xigaze sector postdates the emplacement of the 41 m y old gangdese granodiorites i e the collision occurred after lutetian time

himalayan metamorphism and deformations in the north himalayan belt southern tibet china abstract the kangmar massif which has been attributed to the north himalayan belt of two mica granites in southern tibet china is shown to be an orthogneiss in the core of a dome which displays an intermediate high pressure type metamorphism himalayan in age 40 to 20 ma and above the main central sheet this metamorphism took place during high shear strain deformation and it is not recorded to the west where north himalayan plutons have developed contact metamorphism

building the holocene clinothem in the gulf of papua an ocean circulation study received 31 august 2006 revised 21 august 2007 accepted 15 november 2007 published 28 march 2008 1 this paper investigates the role that tidal and wind driven flows and buoyant river plumes play in the development of the holocene clinothem in the gulf of papua time series data from bottom tripods and a mooring were obtained at four locations near the mouth of the fly river during portions of 2003 and 2004 flows in the gulf of papua during calendar year 2003 were hindcast every 3 h using the navy coastal ocean model ncom with boundary conditions from the navy atmospheric prediction system the east asian seas implementation of ncom and the otis tidal inversion system results show that tidal flows on the modern clinoform are strong and are landward and seaward directed peak spring tidal velocities can provide the shear stresses necessary to keep sediment up to sand size in motion as the wind driven and baroclinic currents distribute it from the river mouths across and along the shelf in two circulation states during the monsoon season the clinoform topset is swept by a seaward surface flow and landward bottom flow reflecting river plumes and coastal upwelling seaward this structure evolves into a sw directed surface current over the clinothem foreset with accompanying landward directed near bed currents that trend obliquely up the foreset to the wsw over much of the clinothem during the trade wind season the inner and outer topset are swept by ne directed contour parallel surface currents underneath which lie obliquely landward near bed currents these modeled flows and complex gyres in shallow water coupled with wave and current supported gravity flows or river floods can explain the form internal clinoform shapes and mineralogy of the modern gulf of papua clinothem

anatomy and growth of a holocene clinothem in the gulf of papua 1 high resolution seismic profiles and sedimentological data from grab samples and long cores provide an unprecedented picture of the structure sedimentology and late quaternary development of two gulf of papua gop clinothems one probably stage 3 and 4 in age and one holocene in age the older was partially eroded during stage 2 and partially covered by the younger clinothem during stage 1 the younger clinothem consists of three stratigraphic units separated by two surfaces of erosion bypass or correlative surfaces of lap the surfaces were formed by changes in accommodation and sediment supply the underlying physiography of the older clinothem also appears to play an important role in governing the shape of the younger clinothem in the northern gulf oblique clinoforms of the younger clinothem suggest that the rate of sediment supply from the northern rivers outstripped the formation of new accommodation whereas in the south sigmoidal clinoforms indicate that accommodation increased faster than sediment supply the origin of the new accommodation remains uncertain because of limited age constraints on the basis of sediment thickness stratal geometry and acoustic character off shelf transport appears to be the dominant sediment transport direction with preferential accumulation on the promontories and bypass in the valleys presently observed and computed modern flows and complex gyres in shallow water coupled with wave and current supported gravity flows or river floods can explain the form internal clinoform shapes and mineralogy of the younger gulf of papua clinothem

early diagenetic cycling incineration and burial of sedimentary organic carbon in the central gulf of papua papua new guinea 1 the clinoform complex of the gulf of papua represents a major deltaic system in oceania two seasons largely control seafloor dynamics and sedimentary c cycling the relatively quiescent nw monsoon and the se trades characterized by remobilization and reoxidation of topset deposits surface sediments 20 cm are reactive with co2 production fluxes 35 42 mmol m 2 d 1 at mangrove channel and topset sites during the monsoon and 10 20 mmol m 2 d 1 on the foreset bottomset 40 m fluxes decrease by a factor of 0 3 on the topset during the transition period and trades the 13 14c isotopic compositions of pore water co2 reveal diagenetic fractionation with dominant utilization of young 14c 1 4 31 1 terrestrial c substrates inshore channels topset 13c 29 to 25 and a progressive increase of young marine c sources seaward outer topset foreset bottomset 13c 22 2 to 19 5 remineralization patterns of terrestrial and marine corg demonstrate cross shelf exchange multiple tracers show that a suboxic mobile mud layer 10 60 cm thick usually 10 30 cm characterizes the central gulf topset and umuda valley off the fly river and unconformably overlies methanic deposits releasing old co2 14c 159 to 229 residual terrestrial corg delivered to the bioturbated foreset continues to be remineralized slowly generating co2 having net 14c 270 within sediments deposited 100 200 years ago the reactivity of corg below 0 5 m in the foreset is 10 20 times lower than expected based on accumulation rates reflecting loss of 50 of sedimentary corg on the topset which functions as a suboxic incinerator

geochemical investigations of the origin of the manaslu leucogranite himalaya nepal the himalayan orogeny is characterized by an intraplate subduction zone the thrusting of the tibetan slab over the foreland is probably responsible for the origin of the manaslu type leucogranites this geochemical study tries to examine the crustal origin of the granite to verify whether the paragneisses of the tibetan slab are the most probable parent material and to determine the subsequent petrogenetic processes the rb sr systematics suggest that 1 1 the scatter of data points in the 87sr86srvs 87rb86sr diagram may be due to the heterogeneity of the initial 87sr86sr ratios 2 2 the initial isotopic ratios are very high 0 730 0 760 and are in agreement with those of the gneisses of the tibetan slab at the time of the melting pb isotopic ratios are homogeneous they are also consistent with a crustal prehistory the ree and th contents are unexpectedly low in comparison with the much higher contents of the parent material monazite left in the residue of melting or more probably extracted in an early stage of the magmatic history may explain the observed ree and th abundances alternatively field observations show that the emplacement of the granite has been accompanied by a very strong hydrothermal activity in consequence the low ree and th contents of the granite could also be due to the loss by solution during prolonged fluid circulation throughout the granitic melt and the sr and pb isotope distribution to the effect of late to post magmatic fluids the isotopic character of which was determined by the underlying tibetan slab

river plumes coral reefs and mixing in the gulf of papua and the northern great barrier reef abstract the mean annual freshwater discharge in the gulf of papua principally from the fly kikori and purari rivers is estimated to be 13000 m 3 s 1 water from these rivers forms a low salinity surface layer in the gulf where it has a residence time of about two months and flows generally eastward a small fraction of this water intrudes through bligh entrance on the great barrier reef continental shelf horizontal patchiness and mixing of these intruding waters with shelf waters are considerably enhanced by secondary circulation wakes around coral reefs the wakes shapes visible in enhanced landsat imagery are similar to those around cylinders and plates in laboratory experiments at low reynolds numbers topographically enhanced mixing may explain why the cross shelf gradients of temperature and of the structure of fish communities are smaller in the northern region than in the central region of the great barrier reef

wind driven circulation on the northern great barrier reef continental shelf in summer abstract observations of wind atmospheric pressure sea levels and current are presented for the northern 9 14 s great barrier reef continental shelf for november 1981 to may 1982 strong low frequency non tidal oceanic fluctuations were observed resulting in alternating northward and southward transport and a weak mean circulation and are the result of long arrested topographic waves driven by a quasi steady longshore wind stress and damped by turbulent bottom friction the coefficient of friction for low frequency currents is found to be proportional to the tidal velocities the coefficient is also found to be much larger than that in the central 15 19 s region of the great barrier reef continental shelf and this difference is attributed to the greatly enhanced energy dissipation by secondary circulation around coral reefs in the reef studded northern region sough of cape york 10 5 s the primary effect of the cross shelf wind is to complement the geostrophic set up due to the longshore current intense tidal currents in the vicinity of cape york combined with a dissipative western boundary in torres strait appear to prevent long wave propagation north of cape york where a steady state analytical model is used to show that both cross and longshore wind components generate the reversing currents observed through bligh entrance

importance of biologically mediated removal of fine sediments from the fly river plume papua new guinea abstract a freshwater plume from the fly river papua new guinea stretched to the south west over a distance of more than 150 km from the estuary towards torres strait the highly turbid freshwater was mixed with the relatively clear water of the gulf of papua producing a sharp boundary around 23 salinity sediment concentrations were typically more than 50 mg l 1 inside the turbid water mass and were rapidly reduced to a few milligrams per litre in the area where salinity was still as low as 26 the area had relatively high levels of phytoplankton 1 g chl l 1 resulting in rapid depletion of nitrate and phosphate biological as well as physico chemical flocculation processes seemed responsible for the rapid removal of sediments from the plume settling particles collected near the estuary consisted largely of fine sediments bound loosely by flocculant organic matter and contained very few plankton and their remains further away from the estuary however settling particles were dominated by colonies of phytoplankton fecal pellets and macroscopic aggregates of apparently biological origin fine sediments were found firmly attached to or embedded in these settling particles the area of high biological activities in the plume probably functions as a barrier limiting a further offshore transport of sediments

island wakes in shallow coastal waters rattray island northeast australia is 1 5 km long 300 m wide and lies in well mixed water approximately 25 m deep its long axis is inclined at about 60 into the direction of the dominant semidiurnal tidal current the length of the wake in the lee of the island as documented by aerial photographs and satellite imagery appears to equal that of the wake behind a flat plate in a two dimensional flow at a reynolds number of about 10 however current metering drogues measurements and temperature mapping indicate internal wake velocities much greater than would be consistent with such a simple low reynolds number model further estimates of the turbulent eddy coefficient suggest an effective reynolds number more in the vicinity of 103 to reconcile these observational differences and to explain the observed upwelling in the core of the wake an ekman pumping model is proposed it is postulated that the ekman benthic boundary layer driven by rotation in the wake allows the vertical vorticity introduced into the water at the tip of the island at the point of separation to be negated by the vorticity of opposite sign introduced at the bottom further it is shown that a large fraction of the kinetic energy of the upstream flow facing the island is used to drive the wake eddies leading to the conclusions that the trapping of water in the lee of islands greatly increases head losses on continental shelves with numerous islands coral reefs and rock outcrops

lhasa block and bordering sutures a continuation of a 500 km moho traverse through tibet a north south wide angle fan profile through the yarlung zangbo suture across the lhasa block and through the bangong nujiang suture shows several significant and sharp changes in crustal thickness both sutures appear as vertical 20 km steps in the moho and may have been the loci for eastward strike slip motion of the tibetan lithosphere