the chronology and structure of the western new caledonian barrier reef tracts abstract the mainland of new caledonia grande terre is surrounded by one of the largest continuous barrier reef system in the world in order to study the development history and internal structure of this system drilling operations have been carried out at two sites amedee and kendec islets located on the barrier reef tract extending from the south west 33 to the north west of new caledonia the extracted cores are 128 50 and 148 75 m in length respectively lithological and paleoecological descriptions combined with uranium thorium dating magnetostratigraphy and nannofossil based biostratigraphy allowed a reef evolutionary scheme to be drawn as a result of the interplay between margin subsidence and sea level changes 11 reef units formed successively during interglacial episodes at high sea levels in both sites depending on the subsidence rate of the western shelf margin major building in new caledonia appears to have started during the mis 11 400 000 yr from shallow water carbonate platform deposits older than 780 000 yr comparing development patterns between the new caledonian barrier reef and the australian great barrier reef clearly indicates that both global climate and regional tectonic history have been the major controls on reef initiation and growth along both sides of the coral sea climatic conditions are likely to have not been optimal before the late quaternary probably resulting in luxuriant reef expansion only during the last 400 000 yr

ages of subsurface stratigraphic intervals in the quaternary of enewetak atoll marshall islands abstract drill cores of enewetak atoll marshall islands reveal six stratigraphic intervals numbered in downward sequence which represent vertical coral growth during quaternary interglaciations radiocarbon dates indicate that the holocene sea transgressed the emergent reef platform by about 8000 yr b p the reef grew rapidly upward about 5 to 10 mm yr until about 6500 yr b p afterward vertical growth slowed to about 0 5 mm yr then lateral development became dominant during the last several thousand years the second interval is dated at 131 000 3000 yr b p by uranium series this unit correlates with oxygen isotope substage 5e and with terrace viia of huon peninsula new guinea and of main reef 2 terrace at atauro island the third interval is not dated because corals were recrystallized and it is tentatively correlated with either oxygen isotope stages 7 or 9 the age of the fourth interval is estimated at 454 000 100 000 yr b p from measured 234 u 238 u activity ratios this unit is correlated with either oxygen isotope stage 9 11 or 13

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

global sea level rise published values for the long term global mean sea level rise determined from tide gauge records exhibit considerable scatter from about 1 mm to 3 mm yr this disparity is not attributable to instrument error long term trends computed at adjacent sites often agree to within a few tenths of a millimeter per year instead the differing estimates of global sea level rise appear to be in large part due to authors using data from gauges located at convergent tectonic plate boundaries where changes of land elevation give fictitious sea level trends in addition virtually all gauges undergo subsidence or uplift due to postglacial rebound pgr from the last deglaciation at a rate comparable to or greater than the secular rise of sea level modeling pgr by the ice 3g model of tushingham and peltier 1991 and avoiding tide gauge records in areas of converging tectonic plates produces a highly consistent set of long sea level records the value for mean sea level rise obtained from a global set of 21 such stations in nine oceanic regions with an average record length of 76 years during the period 1880 1980 is 1 8 mm yr 0 1 this result provides confidence that carefully selected long tide gauge records measure the same underlying trend of sea level and that many old tide gauge records are of very high quality

holocene turn on and evolution of the southern great barrier reef revisiting reef cores from the capricorn bunker group abstract extensive drilling of the great barrier reef gbr in the 70s and 80s illuminated the main factors controlling reef growth during the holocene however questions remain about 1 the precise nature and timing of reef turn on or initiation 2 whether consistent spatio temporal patterns occur in the bio sedimentologic response of the reef to holocene sea level rise then stability and 3 how these factors are expressed in the context of the different evolutionary states juvenile mature senile reefs combining 21 new c 14 ams and 146 existing re calibrated radiocarbon and u th ages we investigated the detailed spatial and temporal variations in sedimentary facies and coralgal assemblages in fifteen cores across four reefs wreck fairfax one tree and fitzroy from the southern gbr our newly defined facies and assemblages record distinct chronostratigraphic patterns in the cores displaying both lateral zonation across the different reefs and shallowing upwards sequences characterised by a transition from deep porites faviids to shallow acropora isopora coral types the revised reef accretion curves show a significant lag period ranging from 0 7 2 ka between flooding of the antecedent pleistocene substrate and holocene reef turn on this lag period and dominance of more environmentally tolerant early colonizers e g domal porites and faviids suggests initial conditions that were unfavourable for coral growth we contend that higher input of fine siliciclastic material from regional terrigenous sources exposure to hydrodynamic forces and colonisation in deeper waters are the main factors influencing initially reduced growth and development all four reefs record a time lag and we argue that the size and shape of the antecedent platform is most important in determining the duration between flooding and recolonisation of the holocene reef finally our study of capricorn bunker group holocene reefs suggests that the size and shape of the antecedent substrate has a greater impact on reef evolution and final evolutionary state mature vs senile than substrate depth alone

seismic and stratigraphic evidence for reef expansion and onset of aridity on the northwest shelf of australia during the pleistocene abstract modern reef the great barrier reef and ryukyu reef distribution in the indo pacific region is strongly controlled by warm currents east australian and kuroshio currents that radiate from the indo pacific warm pool the modern distribution of reefs south of 15 s on the western australian shelf is related to the presence of the warm leeuwin current however the age of the reefs south of 15 s and hence their temporal relationship to the leeuwin current has been largely unknown seismic and subsurface stratigraphic data show that reef growth and expansion on the northwest shelf of australia began in the middle pleistocene 0 5 ma the oldest ooids in the region are approximately synchronous with reef growth we suggest a two stage process for the spread of reefs to higher latitudes on the western australian coast first an increase in leeuwin current activity at approximately 1 ma brought warm waters and a tropical biota to the region and second increased aridity after 0 6 ma led to a decline in clastic input and increased alkalinity triggering ooid formation and reef expansion to higher latitudes associated with the switch to higher amplitude glacio eustatic cycles at the end of the middle pleistocene transition the timing and mechanisms for reef expansion south along the western australian coast has implications for the origin of the eastern australian middle pleistocene great barrier reef the new caledonia barrier reef and japanese ryukyu reef systems

depositional environments beneath the shelf edge slopes of the great barrier reef inferred from foraminiferal assemblages iodp expedition 325 abstract to understand sea level changes since the last glacial maximum lgm and their effects on coral reef systems the shelf edge slopes of the great barrier reef gbr were cored during the integrated ocean drilling program iodp expedition 325 recovered unconsolidated sediments beneath the submerged shelf edge reefs contain abundant foraminiferal tests which record changes in depositional environments and paleo water depths a total of 177 sediment samples were collected from 17 holes along three transects located within two geographical areas noggins pass and hydrographers passage and were analyzed to determine stratigraphic changes in foraminiferal assemblages 2 0 5 mm size fraction results show that four foraminiferal assemblages a b c and d are delineated by multivariate analyses q mode cluster analysis and non metric multidimensional scaling nmds and these assemblages correspond to a back reef to reef margin zone 0 10 m deep assemblage a an upper photic zone 10 30 m deep associated with hard substrates assemblage b an intermediate to lower photic zone 30 90 m deep characterized by soft substrates assemblage c and a lower photic zone 90 130 m deep only found in modern shelf slopes assemblage d gradual shifts in these four foraminiferal assemblages superimposed on a two dimensional nmds ordination mainly reflect water depth gradients and the relative dominance of two substrate types hard and soft substrates pre lgm older than marine isotope stage 3 mis3 sediments along transects at hydrographers passage were deposited at intermediate to lower photic zones in contrast relatively shallow water sequences found in mis3 deposits at noggins pass likely owe their origin to either turbidite and or land slide processes the lack of assemblage d in mis3 deposits from all transects could be related to lowering temperature and or increasing terrestrial influences i e more light attenuation shallowing upward sequences found in lgm mis 2 deposits at hydrographers passage are likely related to stepwise sea level falls to the full extent of the lgm these foraminifer based paleoenvironmental interpretations suggest that the gbr shelf edge slopes have changed their depositional environments continuously in response to sea level fluctuations during the last glacial cycle

late quaternary sea surface temperatures in the western coral sea implications for the growth of the australian great barrier reef recent chronostratigraphic evidence suggests that the central australian great barrier reef formed within the past 780 k y periplatform sediments of the same age recovered from the western coral sea record a progressive decrease in the 18o of planktonic foraminifera to the present several investigators have proposed that this trend represents an appreciable late pleistocene warming 4 c of ocean surface temperatures which they posit catalyzed the growth of the great barrier reef contrary to this hypothesis we demonstrate using alkenone paleothermometry batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document u 37 k prime end document on sediments from ocean drilling program odp site 820 that sea surface temperatures ssts in the western coral sea changed by 1 5 c or less during the past 800 k y if the central great barrier reef rose in the late quaternary it was therefore not due to a warming of ssts we explore whether a major moisture balance change and or diagenetic alteration of calcareous microfossils can explain the higher 18o values observed at depth in the planktonic 18o record at odp site 820 our results suggest that diagenesis provides a large isotopic overprint

pacific north america plate motions new results from very long baseline interferometry expansion and densification of the very long baseline interferometry vlbi network by the nasa crustal dynamics project continues to clarify details of pacific north america motions in this paper i construct for the first time rigid plate tectonic models based purely on space geodetic data construction of vlbi plate models has the advantages of averaging the bias and errors of individual site velocities making failures in the rigid plate assumption easy to document and allowing the consistency of specified plate models to be quantified against the vlbi data set as a whole vlbi based rigid plate models vm2 and vm3 obtained by fitting vector velocities of 10 sites in the stable interiors of the north america and pacific plates reveal a misfit of vlbi observations and rm2 minster and jordan 1978 predictions significant at the 99 confidence level nuvel l demets et al 1990 reproduces the velocities of these 10 sites far better than rm2 and offers a fit to the data which is statistically indistinguishable from vm2 and vm3 by including velocities of 16 additional stations in the deforming plate margin vm2 and vms can resolve all four terms vpn total pacific north america motion vsa san andreas slip ve w path integrated deformation east and west of the san andreas in the vector equation characterizing pacific north america plate boundary deformation vpn vsa ve vw for several points along the san andreas without reference to a global plate model geological or local geodetic measurements or restrictions on distributed shear in most cases instantaneous vlbi determined rates agree with geologically based estimates mapped to point c 36 0 n 120 6 w in central california vm2 gives vpn c 46 8 1 4 mm yr n36 2 w vsa c 38 6 1 3 mm yr n36 2 w and ve c 8 2 1 3 mm yr n34 7 w vlbi substantially eliminates vw c the component of the san andreas discrepancy west of c although a few millimeters per year of right lateral strike slip on offshore faults can not be rejected at point d 34 1 n 117 0 w in southern california vm2 returns vsa d 25 0 1 1 mm yr n52 3 w ve d 8 8 1 1 mm yr n25 8 w and vw d 13 3 1 6 mm yr n21 5 w vw d is accommodated west of the san andreas to the channel islands the azimuth of san andreas slip suggests that the transverse ranges north of los angeles are absorbing 8 1 mm yr of compression perpendicular to the trend of the fault

interplate coupling in northeast japan deduced from inversion analysis of gps data abstract the spatial distribution of the strength of interplate coupling between the subducting pacific plate and the overlying continental plate in northeast japan was investigated through an inversion analysis of gps data employing akaike s bayesian information criterion the gps data used for the inversion analysis are rates of baseline length changes and vertical displacement rates of crustal movements during the period from april 6 1996 to march 20 1998 which were obtained at 161 continuous gps observation stations operated by the geographical survey institute of japan the result shows the average drag rates of the overriding plate on the model source regions off the tohoku and hokkaido districts are 6 7 cm yr and 6 8 cm yr respectively which are 0 85 and 0 87 as interplate coupling ratio these values are much higher than those in previous studies the average directions of drag rates are oriented n73 w 15 and n78 w 13 on the model source regions off the tohoku and hokkaido districts respectively these directions agree well with the direction of coseismic slip of the foot wall side n75 w of the 1978 miyagiken oki earthquake m 7 4 but differ slightly from the direction estimated from the plate motion model n65 w seno et al j geophys res 101 1996 11305 11315 we also found afterslip of 5 5 cm yr associated with the 1994 sanriku haruka oki earthquake m 7 5 off aomori prefecture interestingly enough large afterslip occurred on the plate boundary even when more than a year had passed after the sanriku haruka oki earthquake the amount of drag rate becomes dramatically small at depths greater than about 50 km on the model source regions indicating weak interplate coupling there

pleistocene reef development in the southwest ryukyu islands japan abstract calcareous nannofossil and sedimentological studies of the pleistocene ryukyu group based on 13 cores and surface outcrops on irabu jima and shimoji jima the ryukyu islands southwestern japan suggest that these sediments were deposited at 1 5 0 3 ma and unconformably overlie the pliocene shimajiri group the ryukyu group consists mainly of reef complex deposits which accumulated in a wide range of depositional environments from shallow reef flat to deep insular shelf carbonate lithofacies representing 10 depositional environments were delineated by comparison with the present day marine sediments and biota around the ryukyus five coral assemblages were defined by species composition and the morphology of fossil forms within the coral limestone each indicating a particular environment the ryukyu group in the study area is composed of 13 lithologic units a complete succession of units commences with coral limestone lst or tst grading upward into rhodolith and larger foraminiferal limestones tst overlain by coral limestone hst episodic subaerial exposure and subordinate karstification commonly occurred after deposition the study area subsided during the deposition of units 1 12 and then was uplifted during deposition of unit 13 reef development may have been dominated by obliquity or precessional cycles sixth and seventh order cycles respectively for the first 0 5 million years 1 5 1 ma after which it may have responded to fifth order eccentricity cycles

measurements of strain at plate boundaries using space based geodetic techniques we have used the space based geodetic techniques of satellite laser ranging slr and very long baseline interferometry vlbi to study strain along subduction and transform plate boundaries and have interpreted the results using a simple elastic dislocation model six stations located behind island arcs were analyzed as representative of subduction zones while 13 sites located on either side of the san andreas fault were used for the transcurrent zones the length deformation scale was then calculated for both tectonic margins by fitting the relative strain to an exponentially decreasing function of distance from the plate boundary results show that space based data for the transcurrent boundary along the san andreas fault help to define better the deformation length scale in the area while fitting nicely the elastic half space earth model for subduction type boundaries the analysis indicates that there is no single scale length which uniquely describes the deformation this is mainly due to the difference in subduction characteristics for the different areas and the use of an elastic stress model then helps us understand some of these differences

the somalia plate and the east african rift system present day kinematics summary the motion of the somalia plate relative to the nubia africa arabia and antarctica platcs is re evaluated using a new inversion method based on a monte carlo technique and a least absolute value misfit criterion a subset of the nuvel 1 data set with additional data along the levant fault and in the red sea is used the results confirm that the motion of arabia with respect to africa is significantly different from the motion relative to somalia it is further shown that the data along the sw indian ridge are compatible with a pole of relative motion between africa and somalia located close to the hypothetical diffuse triple junction between the ridge and thc east african rift the resulting africa somalia motion is then compatible with the geological structures and seismological data along the east african rift system assuming a separate somalia plate thus solves kinematic and geological problems around the afar triple junction and along the east african rift

a new model of holocene reef initiation and growth in response to sea level rise on the southern great barrier reef the fossil record provides valuable data for improving our understanding of both past and future reef resilience and vulnerability to environmental change the spatial and temporal pattern of the initiation of the holocene great barrier reef presents a case study of reef response to rapid sea level rise past studies have been limited by the lack of well dated and closely spaced reef core transects and have not closely examined the composition of the reef building communities through time this study presents 80 new high precision u sbnd th and 5 radiocarbon ages from twelve new cores located along three transects across different geomorphic and hydrodynamic settings of one tree reef southern great barrier reef to document three distinct stages of holocene reef development in unprecedented detail temporal constraints on changing paleoecological assemblages of coral coralline algae and associated biota revealed three distinct phases of reef development consisting of 1 a fast shallow and clear water reef initiation from 8 2 until 8 ka 2 a shift to slower deeper and more turbid water reef growth from 8 to 7 ka and 3 a return to shallow and rapid branching coral growth in clear water conditions as the reef catches up to sea level a minimum lag prior to reef initiation of 700 years was identified which differs in length depending on reef environment and pleistocene substrate height in this new model reef growth initiated on the topographically lower leeward margin and patch reef prior to the start of windward margin development contrary to the traditional reef growth model while there was a shift to conditions less favorable for reef growth at 8 ka this did not prevent the slow accretion of more sediment tolerant coral communities the majority of the reef reached sea level by 6 ka this new conceptual model of holocene reef growth provides new constraints on changes in paleoenvironment that controlled reef community composition and growth trajectories through sea level rise following inundation

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

reef response to sea level and environmental changes during the last deglaciation integrated ocean drilling program expedition 310 tahiti sea level the last deglaciation is characterized by a rapid sea level rise and coeval abrupt environmental changes the barbados coral reef record suggests that this period has been punctuated by two brief intervals of accelerated melting meltwater pulses mwp occurring at 14 08 13 61 ka and 11 4 11 1 ka calendar years before present that are superimposed on a smooth and continuous rise of sea level although their timing magnitude and even existence have been debated those catastrophic sea level rises are thought to have induced distinct reef drowning events the reef response to sea level and environmental changes during the last deglacial sea level rise at tahiti is reconstructed based on a chronological sedimentological and paleobiological study of cores drilled through the relict reef features on the modern forereef slopes during the integrated ocean drilling program expedition 310 complemented by results on previous cores drilled through the papeete reef reefs accreted continuously between 16 and 10 ka mostly through aggradational processes at growth rates averaging 10 mm yr 1 no cessation of reef growth even temporary has been evidenced during this period at tahiti changes in the composition of coralgal assemblages coincide with abrupt variations in reef growth rates and characterize the response of the upward growing reef pile to nonmonotonous sea level rise and coeval environmental changes the sea level jump during mwp 1a 16 2 m of magnitude in 350 yr induced the retrogradation of shallow water coral assemblages gradual deepening and incipient reef drowning the tahiti reef record does not support the occurrence of an abrupt reef drowning event coinciding with a sea level pulse of 15 m and implies an apparent rise of 40 mm yr 1 during the time interval corresponding to mwp 1b at barbados

coral reef records of quaternary changes in climate and sea level abstract although coral reefs have long been regarded as documenting climate change largely through its effects on sea level the temporal continuity and sensitivity to disturbance of their records appears to fall short of those provided by ice cores deep sea sediments and similar proxies the reasons for this anomaly relate principally to shifts in the loci of deposition the temporal windows in which accretion has been able to occur in a given place reflecting sea level at a particular height relative to the present datum are severely constrained where it has been possible coral growth and reef accretion have been and are sensitive to the signals provided by the environment in the form of changes in water depth temperature salinity nutrient supply turbidity and ph acidity concomitant with changes in sea level itself changes in these environmental parameters are directly or indirectly controlled by climate however because the responses of corals to stimuli are commonly site specific and the nature of the changes evoked so disparate it is likely that only major sea level cycles will provide evidence of a consistent global response in what has been a segmented record

microearthquakes and faulting in the southern okinawa trough abstract southern okinawa trough represents an early stage of back arc rifting and is characterized by normal faulting and microearthquakes earthquake distribution and deep structure of fault was investigated to clarify active rifting in the southern okinawa trough where two parallel grabens are located a network of ocean bottom seismometers obss that displayed the hypocenters of 105 earthquakes were observed for a period of 4 days in southern graben sg most of the microearthquakes occurred in a cluster about 7 km wide which on a cross section striking n45 e dips 48 to the southwest relocated hypocenters which are recorded by a local seismic network show scattered distribution around the southern graben there are no remarkable surface faults in the southern graben on the other hand the recalculation of hypocenter locations of 1996 earthquakes swarm recorded by a local seismic network suggests that the swarm is associated with normal faulting on the southern side of northern graben ng thus the undeveloped southern graben is located to the south of the developed northern graben southward migration of rifting which may be caused by migration of volcanism could thus be occurring in the southern okinawa trough the extension rate computed for the southern okinawa trough from the fault model of the northern graben is 4 6 cm year which is 59 102 of the extension rate gps measurements this result indicates that the majority of extensional deformation is concentrated within the center of the northern graben in the okinawa trough

the amurian plate motion and current plate kinematics in eastern asia we use global positioning system gps velocity data to model eastern asian plate kinematics out of 15 stations in korea russia china and japan studied here three sites considered to be on the stable interior of the hypothetical amurian plate showed eastward velocities as fast as 9 10 mm yr with respect to the eurasian plate they were stationary relative to each other to within 1 mm yr and these velocity vectors together with those of a few additional sites were used to accurately determine the instantaneous angular velocity euler vector of the amurian plate the predicted movement between the amurian and the north american plates is consistent with slip vectors along the eastern margin of the japan sea and sakhalin which reduces the necessity to postulate the existence of the okhotsk plate the euler vector of the amurian plate predicts left lateral movement along its boundary with the south china block consistent with neotectonic estimates of the displacement at the qinling fault possibly the southern boundary of the amurian plate the amurian plate offers a platform for models of interseismic strain buildup in southwest japan by the philippine sea plate subduction at the nankai trough slip vectors along the baikal rift the boundary between the amurian and the eurasian plates are largely inconsistent with the gps based euler vector suggesting an intrinsic difficulty in using earthquake slip vectors in continental rift zones for such studies

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

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

holocene reef growth in the tropical southwestern atlantic evidence for sea level and climate instability the holocene epoch offers a potential analogue for understanding future sea level variability as both sst s and global mean sea levels gmsl were at times higher than observed today however gmsl can differ significantly from relative sea level rsl even at far field sites remote from margins of former ice sheets much of this spatial variability has been shown to be consistent with the predictions of glacial isostatic adjustment gia models whilst it is generally accepted that rsl at far field sites reached its maximum during the mid holocene there have been many interpretations of sea level fall following the highstand from 6 ka here we present a rsl history from several tectonically stable far field sites in eastern brazil derived from 17 microatoll and 45 fossil reef flat ages our results show evidence for two periods of rsl instability during the holocene which differ from gia predictions including a hiatus in reef growth 3 7 2 5 ka these results are broadly synchronous with several other locations in the southern hemisphere suggesting global rather than regional climatic forcing mechanisms are responsible variations in sst and southern hemisphere ice sheet dynamics are proposed as possible controlling mechanisms for the observed rsl oscillations beginning at 3 7 ka and 2 ka respectively we suggest that these global processes combined with increased precipitation and higher sediment flux from several regional climatic forces created inhospitable conditions for reef growth contributing to the observed hiatus and reduced reef flat accretion during the late holocene 2 ka to present

postglacial sediment deposition along a mixed carbonate siliciclastic margin new constraints from the drowned shelf edge reefs of the great barrier reef australia a seismic stratigraphy analysis was conducted at two sites hydrographers and noggin passages separated by about 540 km on the shelf edge of the central great barrier reef gbr australia we used recently available seismic and bathymetry data and a new synthesis of downhole logs and lithological petrophysical and radiometric data from cores recovered by the integrated ocean drilling program expedition 325 great barrier reef environmental changes we compared the stratigraphy of both sites identifying a full depositional sequence with deposits from at least 28 ka bp to 7 ka bp bounded by two marine flooding surfaces within this sequence each systems tract is represented by unique depositional features characteristic of the shelf edge systems despite the broad environmental and geomorphic similarities between the two sites differences in postglacial reef development were remarkable these contrasts can be explained as a result of 1 local antecedent substrate variations and 2 the interplay of shelf physiography with late quaternary sea level fluctuations which favoured changes in biological production and sediment flux as the palaeo shoreline evolved from linear to complex during intermediate sea levels during these intermediate sea levels the northern estuarine coast and its steep substrate at shelf edge locations contrasted strongly with the protected palaeo lagoons and the extensive gentle marginal terraces found at the southern central gbr this setting enhanced the regional differences in sediment transport and reef development through the last transgression the conceptual model presented here provides a broader depositional framework and improves the understanding of the main processes controlling the spatial and temporal depositional patterns on the shelf edge of mixed siliciclastic carbonate margins

trench parallel stretching and folding of forearc basins and lateral migration of the accretionary wedge in the southern ryukyus a case of strain partition caused by oblique convergence detailed seafloor mapping in the area east of taiwan revealed trench parallel stretching and folding of the ryukyu forearc and lateral motion of the accretionary wedge under oblique convergence east of 122 40 e a steep accretionary wedge is elongated in an e w direction a major transcurrent right lateral strike slip fault accommodates the strain partitioning caused by an oblique convergence of 40 a spectacular out of sequence thrust may be related to the subduction of a structural high lying in the axis of the n s trending gagua ridge this asperity is likely responsible for the uplift of the accretionary wedge and forearc basement and may have augmented strain partitioning by increasing the coupling between the two plates west of 122 40 e the low taper accretionary wedge is sheared in a direction subparallel to the convergence vector with respect to the ryukyu arc the bayonet shape of the southern ryukyu arc slope partly results from the recent re opening of the southern okinawa trough at a rate of about 2 to 4 cm yr right lateral shearing of the sedimentary forearc with respect to the nonlinear ryukyu backstop generates trench parallel extension in the forearc sediment sequence at dilational jogs and trench parallel folding at compressive jogs the hoping basin lies above a diffuse trench trench fault ttf or tff unstable triple junction moving toward the south along a n s transform zone which accommodates the southward drift of the ryukyu arc with respect to eurasia

secular and earthquake related vertical crustal movements in japan as deduced from tidal records 1951 1981 abstract monthly tidal records for the last 31 years from about 100 tidal stations are used to delineate vertical crustal movements in japan a new computer aided processing system was created for this purpose its principle is differential use of tidal records in a region so that the oceanographic disturbances of common causes may be eliminated from the sea level data this method enables us to observe nearly absolute vertical land movement at tidal stations with a precision of a few centimeters the japanese islands are divided into nine regions taking oceanographic conditions into account general discussion on recent vertical movements has yielded several notable features and trends as follows 1 1 rapid and stationary subsidence in the northeastern part of japan presumably of tectonic origin 2 2 a complex pattern of uplift and subsidence in the southwestern part of japan which seems to reflect subduction of the philippine sea plate against the honshu block 3 3 relatively stable land on the japan sea side of honshu movements related to the earthquakes during the period 1951 1981 are also discussed although few of the cases show clear cut premonitory movements if abnormal movements in a coastal area appeared with an amplitude exceeding 2 or 3 cm we could detect them by the present system

mid holocene coral community data as baselines for understanding contemporary reef ecological states land use changes and associated deteriorations in water quality are cited as major drivers of marine ecosystem change and can modify community abundance and diversity on coral reefs this study uses palaeoecological data derived from a mid holocene age coral reef in the wet tropics region of australia s great barrier reef to develop a record of coral community composition and diversity from a period that significantly pre dates european settlement in the region major changes in catchment sediment and nutrient yields since european settlement have been documented and thus the data presented provides a baseline against which to compare contemporary ecological datasets natural variations in coral assemblage composition as preserved in core records clearly occurred in this mid holocene reef and were associated with the reef shallowing to sea level as it accreted vertically comparisons between modern and mid holocene coral community data from equivalent water depths did not reveal marked shifts in coral community composition and diversity suggesting the long term persistence of a resilient coral assemblage over these time periods

earthquake strain rates and instantaneous relative motions within central and eastern asia summary we use the spatial distribution of moment tensors of earthquakes in this century to estimate the velocity field in asia within a eurasian reference frame in a least squares inversion strain rates on the surface of the earth are matched with continuous spline functions in order to recover the velocity gradient tensor associated with the seismic moment release in asia earthquakes account for 40 60 per cent of the expected motion of india relative to eurasia with the missing component of strain rate equivalent to about 20 mm yr 1 of n s shortening between siberia and india in this solution south china rotates counterclockwise and moves eastwards relative to siberia using rigid plate constraints we next investigate the characteristics of the complete horizontal strain field in asia that accommodates plate motions our strain rate solutions are analogous to the response of a newtonian thin viscous sheet in which the rate of work done by the straining medium in accommodating the velocity boundary conditions is a minimum in these solutions the euler pole for india relative to eurasia is constrained nuvel 1a demets et al 1994 but in the process of fitting the vlbi velocity at shanghai china ward 1994 heki et al 1995 the euler pole for south china is determined in the inversion a solution that both fits the velocity at shanghai china and yields a strain rate field consistent with the earthquake mechanisms is one where the south china block has a motion relative to siberia described by the pole at 51 n 131 e 0 3 deg myr 1 comparison of the complete strain field that accommodates plate motion with the seismic strains indicates that earthquake moment release rates in this century within mongolia are about a factor of 4 larger than the long term rate within gansu ningxia the earthquake moment rates have been about a factor of 2 higher than the long term rate the strike slip faulting within mongolia gansu ningxia western sichuan and yunnan is possibly a direct result of velocity boundary conditions imposed on the south china block by forces unrelated to continental collision of india and eurasia such as forces associated with subduction along the margins of south eastern asia verification of this requires a better understanding of the role of pre existing zones of weakness within the asian continental lithosphere

deglacial mesophotic reef demise on the great barrier reef abstract submerged reefs are important recorders of palaeo environments and sea level change and provide a substrate for modern mesophotic deep water light dependent coral communities mesophotic reefs are rarely if ever described from the fossil record and nothing is known of their long term record on great barrier reef gbr sedimentological and palaeo ecological analyses coupled with 67 14c ams and u th radiometric dates from dredged coral algae and bryozoan specimens recovered from depths of 45 to 130 m reveal two distinct generations of fossil mesophotic coral community development on the submerged shelf edge reefs of the gbr they occurred from 13 to 10 ka and 8 ka to present we identified eleven sedimentary facies representing both autochthonous in situ and allochthonous detrital genesis and their palaeo environmental settings have been interpreted based on their sedimentological characteristics biological assemblages and the distribution of similar modern biota within the dredges facies on the shelf edge represent deep sedimentary environments primarily forereef slope and open platform settings in palaeo water depths of 45 95 m two coral algal assemblages and one non coral encruster assemblage were identified 1 massive and tabular corals including porites montipora and faviids associated with lithophylloids and minor mastophoroids 2 platy and encrusting corals including porites montipora and pachyseris associated with melobesioids and sporolithon and 3 melobesiods and sporolithon with acervulinids foraminifera and bryozoans based on their modern occurrence on the gbr and coral sea and modern specimens collected in dredges these are interpreted as representing palaeo water depths of 100 m respectively the first mesophotic generation developed at modern depths of 85 130 m from 13 to 10 2 ka and exhibit a deepening succession of 100 m palaeo water depth through time the second generation developed at depths of 45 70 m on the shelf edge from 7 8 ka to present and exhibit stable environmental conditions through time the apparent hiatus that interrupted the mesophotic coral communities coincided with the timing of modern reef initiation on the gbr as well as a wide spread flux of siliciclastic sediments from the shelf to the basin for the first time we have observed the response of mesophotic reef communities to millennial scale environmental perturbations within the context of global sea level rise and environmental changes

origin of the southern okinawa trough volcanism from detailed seismic tomography 1 magmatism associated with subducting plate edges or slab tears has been suggested in the southern okinawa trough the cross back arc volcanic trail which consists of a cluster of about 70 seamounts is located above a ryukyu slab tear lying along the 123 3 e meridian in november 2003 more than 3300 earthquakes recorded in this area by 15 ocean bottom seismometers and surrounding land stations during a period of 12 days were used to determine the three dimensional vp and vs velocity structures and vp vs ratios a mantle inflow characterized by low vp and vs and high vp vs passing through the slab tear is imaged the fluid and or melt component is rising obliquely from the slab tear in the directions of the cross back arc volcanic trail the northern slope of the southern okinawa trough and to north of iriomote island the asthenospheric intake is also imaged by an inclined chip like high vp vs and low vp and vs body dipping northerly which might be linked to the slab retreat west of the slab tear most of the earthquakes are located around low vp and vs and high vp vs bodies which suggests that the seismicity is related to magmatic and or fluid activities east of it earthquakes are concentrated in an area characterized by high vp and vs velocities and low vp vs suggesting that the magma chamber is absent beneath the axial part of the trough and that normal faulting is the main factor controlling the seismicity

holocene sea level record from corals reliability of paleodepth indicators at ishigaki island ryukyu islands japan abstract holocene sea level change provides direct evidence of the melting of ice sheets however our understanding of the timing and course of such change is limited by a lack of information regarding environmental condition of corals for example holocene sea level curves are compiled based on water depths estimated from the occurrence of a small number of coral species as species identification is difficult work the error associated with this method of estimating sea level exceeds 2 5 m in addition there generally occurs a difference in the living water depth of corals between high energy reefs and low to moderate energy reefs this difference in living water depth also results in an error in reconstructed sea level curves in the present study we analyzed drill core and recorded the vertical distribution of corals at the high energy ibaruma reef and low to moderate energy fukido reef ishigaki island ryukyu islands japan analyses of corymbose acropora a digitifera massive goniastrea g retiformis massive pocillopora p verrucosa massive platygyra p ryukyuensis and other corals enables the accurate reconstruction of a sea level curve because these species are distributed in a narrow range with a weighted mean m w error of between 0 5 and 2 5 m these observation data from ibaruma and fukido reefs can be used to reconstruct holocene sea level curves based on drill core data from ibaruma reef however the two reefs yield contrasting sea level curves the curve reconstructed based on data from fukido reef is several meters deeper than that reconstructed based on data from ibaruma reef this discrepancy reflects the different energy levels of the two reefs high energy at ibaruma reef and low to moderate energy at fukido reef therefore the accurate reconstruction of a holocene sea level curve requires the identification of species from drill core and observations of the vertical distribution of species at the present day reef at a location close to the drilling site the holocene sea level curve reconstructed based on drill core data from ibaruma reef reveals a rapid sea level rise of approximately 7 5 m kyr 1 between 8000 and 6000 cal years bp the rate of sea level rise decreased from 7 5 to 3 5 m kyr 1 between 6000 and 5000 cal years bp a mid holocene highstand occurred at around 5000 cal years bp at a level of approximately 3 2 5 m above the present mean sea level the increase in ocean volume corresponding to this sea level rise indicates that melting of the antarctic ice sheet continued beyond 6000 cal years bp as most of the northern hemisphere ice sheets had melted by 6000 cal years bp resulting in sea levels similar to those of the present day

crustal velocities from geodetic very long baseline interferometry we have used very long baseline interferometry observations from the international radio interferometric surveying and crustal dynamics project programs taken over a time span of 5 8 years through august 1990 to derive relative velocities of 16 sites on the north american eurasian pacific and african plates the data reduction scheme simultaneously estimates earth orientation parameters and nutation for each session local atmosphere and clock correction terms source positions and initial site positions as well as the site velocities no a priori geophysical crustal model whatsoever is imposed to obtain the velocities instead we introduce a minimal set of geometric constraints to obtain the solution two alternative constraint formulations are considered they are shown to be equivalent in that they yield equivalent velocity sets with allowance for translation and rotation these are 1 setting the secular motion of the pole and mean length of day to fixed values and 2 fixing the net rotation of the sites the resulting velocities have formal standard errors typically 0 2 cm yr and most velocities are significantly different from zero they agree closely to within 0 5 cm yr with velocities predicted by the minster jordan and nuvel 1 plate motion models after allowing for the arbitrary rotation and translation between the systems the velocity of kashima japan is much more consistent with the north american plate than the eurasian plate where current plate model boundaries place it we suggest another possibility kashima does lie on the eurasia plate but its motion is so modified by interaction with the nearby pacific plate as to result in the observed velocity sites near the active plate boundary in california also show motions intermediate between those of the adjoining plates

evolution of ocean temperature and ice volume through the mid pleistocene climate transition earth s climate underwent a fundamental change between 1250 and 700 thousand years ago the mid pleistocene transition mpt when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing over this time an increase occurred in the amplitude of change of deep ocean foraminiferal oxygen isotopic ratios traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep ocean temperature we have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios our results suggest that the mpt was initiated by an abrupt increase in antarctic ice volume 900 thousand years ago we see no evidence of a pattern of gradual cooling but near freezing temperatures occur at every glacial maximum

discussion on displacement analysis detection of crustal deformation in using geodetic networks to detect crustal motion there is always a question about what to use as a reference if the stations in a subset of the network can be shown to remain fixed relative to one another then this subset can be used as a reference for determining the motion of the remaining stations in the network we derive such a solution for the displacement of a geodetic network referred to as a stationary station solution the advantage of this technique over other solutions to the same problem is that it neither depends on a single station nor makes assumptions about the movement of all the stations of the network application of the technique to a geodetic network near hollister california indicates that stations between the faults are stationary although for the block between the calaveras and san andreas faults the stations are only marginally stationary relative to one another the technique is then extended to give the total block motion between the faults

coral reef response to quaternary sea level and environmental changes state of the science there is considerable uncertainty about future sea level projections due to the current poor understanding of the vulnerability and sensitivity of ice sheets to global warming fossil coral reefs represent a unique archive of sea level and associated environmental changes that extend far beyond instrumental records here recent advances in this field are summarized focusing on periods of earth history typified by rapid sea level rise and short term climate excursions sea level and reef response records from the last deglaciation and periods characterized by higher sea level stands and short term and low magnitude sea level oscillations such as the mid to late holocene and the last interglacial are synthesised special emphasis is given to understanding how coral reefs have responded to these changes in terms of reef development architecture and composition finally seven major challenges and future research directions are identified

the great barrier reef the chronological record from a new borehole abstract a new borehole 210 mbsf meters below sea floor deep drilled in ribbon reef 5 on the great barrier reef off cooktown ne australia reveals a shallowing upwards succession the younger part of which is punctuated by a series of erosion surfaces nine depositional units have been defined by lithological changes and are numbered sequentially from the base of the hole upwards aminostratigraphy magnetostratigraphy radiocarbon dating uranium series dating and modeling together with strontium ratios have been applied in an attempt to establish a chronology of accumulation carbonate deposition began about 770 ka ago in a relatively deep water slope environment and is represented by a series of debris flows lithoclasts within these rocks indicate that older limestones already existed in the area subsequent accretion involved the downslope accumulation of grainstones and wackestones sometimes cross laminated characterized by intervals with abundant rhodoliths and scattered probably reworked corals four units at the base of the hole reflect deposition that probably began during isotope stage 16 and continued through stage 15 from about 770 to about 564 ka unit 5 probably extended to stage 11 about 400 ka and unit 6 to stage 9 330 ka typical reefal associations of corals and calcareous algae were established in this area only above depths of about 100 m in the borehole units 5 4 the succession is apparently unbroken to an erosion surface at 36 mbsf indicating subaerial emergence the lack of evidence of emergence below this surface reflects progressive accretion or progradation or both two younger erosion surfaces define further periods of lowered sea level unit 7 is attributed to deposition during isotope stage 7 but erosion during stage 8 resulted in the preservation of only 8 m of unit 7 limestones unit 8 is correlated with stage 5 125 ka and unit 9 is interpreted as holocene post 7 700 ka the limited thicknesses of units 7 8 and 9 are considered to reflect erosion the progressive shallowing brought the depositional surface within the zone exposed during lowstands and there is no sedimentological evidence that aggradation was restricted by a lack of accommodation

the initiation of the southern central great barrier reef new multiproxy data from pleistocene distal sediments from the marion plateau ne australia abstract significant synchronous shifts in the chemistry mineralogy grain sizes and color of the sediments at 6 m below sea floor mbsf at odp site 1195 on the marion plateau ne australia are interpreted to reflect a major regional paleoceanographic change the initiation of the southern province of the great barrier reef gbr the onset of this massive carbonate production centre nearby resulted primarily in increased deposition of carbonate rich sediments of neritic origin both sedimentation rate and terrigenous input record a coincident decline attributed to inshore trapping of materials behind the reefs our best estimate places the development of reef framework in the southern part of the gbr between 560 and 670 kyr b p based on an age model combining magnetostratigraphic and biostratigraphic data the proposed estimation agrees with previous studies reporting an age between 500 and 930 kyr b p constraining more tightly their results however it does not support research placing the birth of the gbr in marine isotope stage mis 11 400 kyr nor the theory of a worldwide modern barrier reef development at that time

revisiting the quaternary development history of the western new caledonian shelf system from ramp to barrier reef abstract the present paper is based on the study of a new core tenia 3 151 20 m long and revisitation of previous core data from the western new caledonian barrier reef based on variations in lithology and stable isotope signatures and the occurrence of unconformity surfaces the tenia 3 sequence is subdivided into ten units regarded as deposited during interglacial high sea levels five detrital and two framework facies are delineated using their biological and textural attributes including coral growth forms and assemblages these facies are interpreted as representative of outer to inner carbonate shelf ramp to barrier reef environments variations in the facies within each stratigraphic unit occur mainly as vertical transitions from lower energy and probably deeper to higher energy probably shallower settings the succession of depositional events is reconstructed using all available age criteria including lithostratigraphy magnetostratigraphy uranium series dating and nannofossil biostratigraphy shallow water coral communities appear to have been developed as soon as carbonate deposition started at around 1 2 million years ma but the initiation of typical coral reef tracts is likely to have occurred not prior to 0 40 million years during marine isotope stage mis 11 carbonate deposition previous to mis 11 is considered to have operated along an open shelf margin i e a ramp or non rimmed platform based on the re examination of the core dataset previously acquired from the new caledonian reefs the coral communities dominated by massive forms mainly poritids are assumed to have remained stable in composition over the past 1 4 ma similarly as indicated by a preliminary study of pollen assemblages in the core the composition of terrestrial flora dominated by podocarpaceae and araucariaceae has not apparently suffered significant change over the past 1 ma and reflects climate conditions cooler and drier than today mean subsidence rates are derived tentatively over the past 1 ma from the stratigraphic position at present reached by the top of depositional units mean rates of 0 08 mm yr 1 for the western new caledonian margin are consistent with past sea level estimates the quaternary depositional history of the new caledonian shelf margin appears to have been controlled by both the amplitude of sea level changes and by differing vertical tectonic movements comparison between the depositional shelf histories from western new caledonia north eastern australia southern belize and the ryukyu islands supports the assumption that coral populations over the early and mid pleistocene developed as non reefal communities along ramp systems not forming continuous outer shelf reef rims at a global scale quaternary reef rimmed platforms are likely to have initiated after the mid pleistocene climate transition from marine isotope stage 11 at about 0 4 ma

significance of shallow core transects for reef models and sea level curves heron reef great barrier reef a sequence of shallow reef cores from heron reef great barrier reef provides new insights into holocene reef growth models isochron analysis of a leeward core transect suggests that the north western end of heron reef reached current sea level by ca 6 5 kyr bp and then prograded leeward at a rate of ca 19 6 m kyr between 5 1 kyr and 4 1 kyr bp pre 1950 to the present reef margin a single short core on the opposing margin of the reef is consistent with greater and more recent progradation there further to the east one windward core reached modern sea level by ca 6 3 kyr bp suggesting near keep up behaviour at that location but the opposing leeward margin behind the lagoon reached sea level much more recently hence heron reef exhibited significantly different reef growth behaviour on different parts of the same margin mean reef accretion rates calculated from within 20 m of one another in the leeward core transect varied between ca 2 9 m and 4 7 m kyr depending on relative position in the prograding wedge these cores serve as a warning regarding the use of isolated cores to inform reef growth rates because apparent aggradation at any given location on a reef varies depending on its location relative to a prograding margin only transects of closely spaced cores can document reef behaviour adequately so as to inform reef growth models and sea level curves the cores also emphasize potential problems in u series dates for corals within a shallow ca 1 5 m zone beneath the reef flat apparent age inversions restricted to that active diagenetic zone may reflect remobilization and concentration of th in irregularly distributed microbialites or biofilms that were missed during sample vetting importantly the th containing contaminant causes ages to appear too old rather than too young as would be expected from younger cement

motion of the philippine sea plate consistent with the nuvel 1a model summary we determine euler vectors for 12 plates including the philippine sea plate ph relative to the fixed pacific plate pa by inverting the earthquake slip vectors along the boundaries of the philippine sea plate gps observed velocities and 1122 data from the nuvel 1 and the nuvel 1a global plate motion model respectively this analysis thus also yields euler vectors for the philippine sea plate relative to adjacent plates our results are consistent with observed data and can satisfy the geological and geophysical constraints along the caroline cr ph and pa cr boundaries the results also give insight into internal deformation of the philippine sea plate the area enclosed by the ryukyu trench nankai trough izu bonin trench and gps stations s102 s063 and okino torishima moves uniformly as a rigid plate but the areas near the philippine trench mariana trough and yap palau trench have obvious deformation

response of the great barrier reef to sea level and environmental changes over the past 30 000 years previous drilling through submerged fossil coral reefs has greatly improved our understanding of the general pattern of sea level change since the last glacial maximum however how reefs responded to these changes remains uncertain here we document the evolution of the great barrier reef gbr the world s largest reef system to major abrupt environmental changes over the past 30 thousand years based on comprehensive sedimentological biological and geochronological records from fossil reef cores we show that reefs migrated seaward as sea level fell to its lowest level during the most recent glaciation 20 5 20 7 thousand years ago ka then landward as the shelf flooded and ocean temperatures increased during the subsequent deglacial period 20 10 ka growth was interrupted by five reef death events caused by subaerial exposure or sea level rise outpacing reef growth around 10 ka the reef drowned as the sea level continued to rise flooding more of the shelf and causing a higher sediment flux the gbr s capacity for rapid lateral migration at rates of 0 2 1 5 m yr 1 and the ability to recruit locally suggest that as an ecosystem the gbr has been more resilient to past sea level and temperature fluctuations than previously thought but it has been highly sensitive to increased sediment input over centennial millennial timescales

a comparison of vlbi data with the ice 3g glacial rebound model crustal motion predicted by the ice 3g glacial rebound model exhibits a pattern of tangential horizontal divergence away from the centres of uplift which in north america and europe are located around hudson bay and the gulf of bothnia tangential velocities reach peak magnitudes of 1 2 mm yr and must be included when predicting very long baseline interferometry vlbi baseline length change rates due to post glacial rebound out of 18 observed vlbi baselines examined 3 are situated such that their predicted length rates are around their 2 uncertainties or greater it is encouraging that 2 of these baselines exhibit predicted length rates within 2 of the observed rates

large river offsets and plio quaternary dextral slip rate on the red river fault yunnan china using multispectral spot images and 1 100 000 topographic data we present an improved map of the active red river fault zone between midu yunnan china and hanoi vietnam the fault zone is composed of parallel strands one of which the yuanjiang fault was previously undetected there also appears to be a component of extension all along the fault zone such extension increases toward the se from yunnan to the south china sea coast and the vector describing the motion of south china relative to indochina points within the n45 135 e quadrant we attempt to assess the plio quaternary dextral slip rate on the red river fault rrf by restoring large river offsets and searching for the largest plausible one across much of yunnan the fault is perpendicular to local catchments that drain into the red river from precise mapping of the river courses on spot satellite images and on 1 100 000 topographic maps numerous multiple offsets along the fault can be detected and reconstructed the lack of correlation between the apparent offsets and the lengths of the rivers upstream from the fault suggests either that the drainage system was in large part established prior to the onset of dextral slip along the fault or that frequent captures have occurred we thus try to find the best fit between series of river channels upstream and downstream from the fault by progressively restoring the dextral displacement in increments of 500 m up to an offset of 50 km for each increment we measure the misfits root mean squares rms between the upstream and downstream channels the best fit and smallest rms are obtained for an offset of 25 0 5 km that we interpret to represent the clearest large right lateral displacement recorded in the geomorphology along the active red river fault since dextral motion is likely to have started around 5 myr the most probable average plio quaternary slip rate on the fault is of order of 5 mm yr we attribute the apparent lack of seismic activity on a large stretch of the fault to millennial recurrence times between great earthquakes our study shows that relatively small drainage systems can keep a good record of fairly large cumulative fault offsets

new constraints on the origin of the australian great barrier reef results from an international project of deep coring two new boreholes provide the first direct evidence of the age of the australian great barrier reef an inner shelf sequence total depth 86 m basal age 210 40 ka comprises a dominantly siliciclastic unit thickness 52 86 m overlain by four carbonate units total thickness 0 34 m a shelf edge and slope sequence total depth 210 m reveals three major sections 1 a lower section of resedimented flows deposited on a lower slope 2 a mid section including intervals of corals rhodoliths and calcarenites with low angle graded laminae and 3 an upper section of four shelf margin coral reef units separated by karst surfaces bearing paleosols sr isotope and magnetostratigraphic data indicate that the central great barrier reef is relatively young post bruhnes matuyama boundary time and our best estimate for the onset of reef growth on the outer barrier system is ca 600 280 ka this date suggests that reef initiation may have been related to the onset of full eccentricity dominated glacio eustatic sea level oscillation as inferred from large amplitude saw tooth 100 k y 18o cycles after marine isotope stage 17 rather than to some regional environmental parameter a major question raised by our study is whether reef margins globally display a similar growth history the possibility of a global reef initiation event has important implications for basin to shelf partitioning of caco3 atmospheric carbon dioxide levels and global temperature change during quaternary time

no net rotation model of current plate velocities incorporating plate motion model nuvel 1 we present nnr nuvel1 a model of plate velocities relative to the unique reference frame defined by requiring no net rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model nuvel 1 demets et al 1990 differences between nnr nuvel1 and no net rotation plate motion model am0 2 minster and jordan 1978 are as large as 15 mm yr in nnr nuvel1 the pacific plate rotates in a right handed sense relative to the no net rotation reference frame at 0 67 m y about 63 s 107 e this rotation nearly parallels but is 32 slower than the pacific hotspot euler vector of hs2 nuvel1 which is a global model of plate hotspot velocities constrained to consistency with nuvel 1 gripp and gordon 1990 at hawaii the pacific plate moves relative to the no net rotation reference frame at 70 mm yr which is 25 mm yr slower than the pacific plate moves relative to the hotspots differences between nnr nuvel1 and hs2 nuvel1 are described completely by a right handed rotation of 0 33 m y about 49 s 65 e the 99 confidence ellipsoids for plate hotspot motion in model hs2 nuvel1 exclude the corresponding euler vectors from model nnr nuvell thus the no net rotation reference frame differs significantly from the hotspot reference frame if the difference between reference frames is caused by motion of the hotspots relative to a mean mantle reference frame then hotspots beneath the pacific plate move with coherent motion towards the east southeast alternatively the difference between reference frames may show that the uniform drag no net torque reference frame which is kinematically equivalent to the no net rotation reference frame is based on a dynamically incorrect premise possible exceptions to the assumption of uniform drag include a net torque on the lithosphere due to attached subducting slabs and greater resistance to plate motion beneath continents than beneath oceans

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

1200 year paleoecological record of coral community development from the terrigenous inner shelf of the great barrier reef increased terrestrial sediment and nutrient yields are regarded as significant threats to coral reef health within the central great barrier reef lagoon where water quality has reportedly declined since european settlement since ca a d 1850 inner shelf reef conditions have purportedly deteriorated however the link between reef decline and water quality change remains controversial primarily because of a lack of pre european period ecological baseline data against which to assess contemporary ecological states here we present a high resolution record of reef accretion and coral community composition from a turbid zone nearshore reef on the inner shelf of the great barrier reef the record is based on six radiocarbon date constrained cores and extends back to ca 1200 calibrated yr b p results demonstrate not only the potential for coral communities to initiate and persist in settings dominated by fine grained terrigenous sediment accumulation but also that a temporally persistent but low diversity suite of corals has dominated the reef building community at this site for at least the past millennium furthermore the coral assemblages exhibit no evidence of community shifts attributable to post european water quality changes while extrapolation of these findings to other turbid zone reefs must remain tentative the study raises important questions about the resilience of inner shelf reefs that are under terrestrial sediment influence and subject to elevated turbidity conditions and demonstrates the potential to develop detailed millennial time scale coral community records from holocene reef systems

mass balance loss of mount baker washington glaciers 1990 2010 mount baker north cascades wa has a current glacierized area of 38 6 km2 from 1984 to 2010 the north cascade glacier climate project has monitored the annual mass balance ba accumulation area ratio aar terminus behaviour and longitudinal profiles of mount baker glaciers the ba on rainbow easton and sholes glaciers from 1990 to 2010 averaged 0 52 m w e a 1 m a 1 terminus observations on nine principal mount baker glaciers 1984 2009 indicate retreat ranging from 240 to 520 m with a mean of 370 m or 14 m a 1 aar observations on rainbow sholes and easton glaciers for 1990 2010 indicate a mean aar of 0 55 and a steady state aar of 0 65 a comparison of ba and aar on these three glaciers yields a relationship that is used in combination with aar observations made on all mount baker glaciers during 7 years to assess mount baker glacier mass balance utilizing the aar ba relationship for the three glaciers yields a mean ba of 0 55 m a 1 for the 1990 2010 period 0 03 m a 1 higher than the measured mean ba the mean ba based on the aar ba relationship for the entire mountain from 1990 to 2010 is 0 57 m a 1 the product of the mean observed mass balance gradient determined from 11 000 surface mass balance measurements and glacier area in each 100 m elevation band on mount baker yields a ba of 0 50 m a 1 from 1990 2010 for the entire mountain the median altitude of the three index glaciers is lower than that of all mount baker glaciers adjusting the balance gradient for this difference yields a mean ba of 0 77 m a 1 from 1990 to 2010 all but one estimate converge on a loss of 0 5 m a 1 for mount baker from 1990 to 2010 this equates to an 11 m loss in glacier thickness 12 20 of the entire 1990 volume of glaciers on mount baker copyright 2012 john wiley sons ltd

coral community changes in the great barrier reef in response to major environmental changes over glacial interglacial timescales abstract the ribbon reef 5 borehole offers a unique record of reef growth spanning the entire history of the northern great barrier reef gbr previous studies have reported the main stratigraphical lithological and chronological patterns as well as basic descriptions of the coralgal assemblages but no detailed coral community analysis was undertaken we present a quantitative analysis of the nature and distribution of pleistocene coral communities and apply several statistical tools to define recurrent coral associations and compare the eight reef building cycles recognized throughout the evolution of the gbr the start of significant reef building occurs at 137 m based on a major change in coral community structure and the inception of the reef cycles cy1 8 this revision along with available stratigraphical and chronological data suggests that barrier reef initiation may have occurred prior to mis 11 earlier than previous reports the coral assemblages at 137 m reflect the transition from lower mesophotic 60 100 m to upper mesophotic 30 60 m settings while the eight reef cycles above are characterized by three recurrent shallow water reef coral associations porites montipora faviids po mo fa pocilloporids poc and acropora isopora acro iso typically these cycles begin with the po mo fa association and end with the acro iso association reflecting shallowing and a catch up growth mode however the first two cycles are characterized by a transitional phase dominated by the poc association the dominance of pocilloporids during the early stages of the gbr s history and the long term shift to an acropora isopora dominated community may reflect an increase in competitive pressure of acroporids over pocilloporids our findings are consistent with the view that reef coral community structure is predictable over 100 kyr time scale however variations within reef cycles highlight the importance of environmental changes operating at millennial time scales further studies are needed to better refine the reef chronology and clarify the influence of environmental variables i e sea surface temperature turbidity on reef coral community structure

crustal thickening versus lateral expulsion in the indian asian continental collision since the beginning of the continental collision between india and asia there has been about 2500 km of convergence and the northward movement of india has been accommodated by major internal deformation of the asian lithosphere the crustal thickening in and around the tibetan plateau is clearly a direct consequence of this collision but there is considerable debate as to whether a large fraction of the indentation has been accommodated by eastward motion of the lithospheric blocks of southeastern asia and southern china numerical experiments described here test this hypothesis for a range of indentation geometries and rheological models of the lithosphere we employ a thin viscous sheet model of the lithosphere with a depth averaged nonlinear viscous rheology described by a stress strain rate exponent n and including gravitational buoyancy forces scaled by the dimensionless argand number ar the eastern boundary for the collision region is described as a lithostatic boundary the precollision normal stress is determined by static balance and that constant stress is applied throughout the collision the experiments show that during collision the eastern boundary is smoothly displaced to the east at a rate about 1 4 of the indentation rate with only minor variation due to geometry or rheology crustal thickening rates in the region of the plateau are reduced by between 10 and 25 of the corresponding rates determined for similar experiments with a rigid eastern boundary to generalize from the results of these experiments the total north south shortening strain produced by the collision is partitioned between crustal thickening and eastward displacement in the ratio of at least 3 1 and more probably 4 1

continuous gps array and present day crustal deformation of japan a gps array with about 1 000 permanent stations is under operation in japan the gps array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the japanese islands based on daily coordinate data of the gps stations strain rate distribution is estimated most regions with a large strain rate are related to plate boundaries and active volcanoes in addition the niigata kobe tectonic zone nktz is recognized as a region of large strain rate along the japan sea coast and in the northern chubu and kinki districts this newly found tectonic zone may be related to a hypothetical boundary between the eurasian or amurian and the okhotsk or north america plates precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations

a 300 000 yr coral reef record of sea level changes mururoa atoll tuamotu archipelago french polynesia abstract the accurate dating of fossil coral reefs is of prime importance in determining the timing of deglaciation events and thus understanding the mechanisms driving glacial interglacial cycles so far the most useful coral reef records of past sea level changes are those related to the last deglaciation and the last interglacial period u th ages for older isotopic stages are more limited due to the scarcity of datable material reflecting diagenetic alteration most data are from emergent parts of reefs and reef terraces in active subduction zones where relative sea level records may be biased by variations in rates of tectonic uplift new constraints on sea level changes over the past 300 000 yr are based on high precision u series age measurements of successive reef units on mururoa these have been cored in four continuous 300 m long drill holes with seaward inclinations of 30 to 45 on the northeastern rim of the atoll past sea level positions have been calculated from the radiometric ages of corals by correcting the present depth of subsurface horizons both for thermal subsidence and for depositional palaeodepth the location of this atoll at a considerable distance from former ice sheets far field minimises the influence of glacio isostatic rebound prominent units formed during four periods of relative sea level highstands including the holocene and stages 5 125 ka 7 212 ka and 9 332 ka these are primarily composed of coralgal frameworks that grew in very shallow water three periods of relative low stand correspond to stages 2 17 23 ka 4 60 ka and 8 270 ka during which small reefs developed in association with large bioclastic accumulations good agreement with the timing of sea level changes based on oxygen isotope measurements in deep sea cores is noted for most of the dated reef units we report here the first accurate coral record of the last glacial maximum in the pacific 135 143 m below the present sea surface suggesting that sea level may have been lower than expected during this period

horizontal and vertical crustal movements from three dimensional very long baseline interferometry kinematic reference frame implication for the reversal timescale revision three dimensional kinematic reference frame of geodetic very long baseline interferometry vlbi stations tied to a geologic plate motion model was established using the glb907 solution by first selecting globally distributed stable plate interior stations and then applying a small translation and a rotation for the entire network in a three dimensional space so that the differences in the horizontal velocities between the vlbi observations and the model predictions are minimized since the vlbi network is global we only assume that the horizontal movements of technically stable stations obey a plate motion model we need not introduce any unwarranted constraints to the vertical velocities of specific stations to realize the frame a suggestive correlation was found between the estimated vertical velocities of north american stations and those predicted by a postglacial rebound model the revision of the magnetic polarity timescale mpts causes a uniform increase or decrease of the predicted velocities which could be detected as the small difference between the measured and the predicted relative plate velocities direct estimation of the correction suggests that the vlbi data fit best to the model when the nuvel1 model is corrected by 3 4 1 2 which differs significantly from the 4 5 deduced from the astronomical mpts calibration this was further confirmed by estimating the rotation rates for individual plate pairs

active deformation in eastern indonesia and the philippines from gps and seismicity data in this study we combine global positioning system gps velocities with information on the style of regional seismicity to obtain a self consistent model velocity and strain rate field for the entire eastern indonesia and philippines region in the process of interpolating 93 previously published gps velocities the style and direction of the seismic strain rate field inferred from earthquakes with m0 1 1020 n m from the harvard centroid moment tensor catalog are used as constraints on the style and direction of model strain rates within the plate boundary zones the style and direction of the seismic strain rate field are found to be self similar for earthquakes up to m0 1 1020 n m equivalent to mw 7 3 our inversion result shows the following the java trench which lacks any significant historic seismicity delineates the australian plate au sunda block sunda plate boundary west of the island of sumba east of sumba convergence is distributed over the back arc and banda sea and there is no subduction at the timor trough suggesting that the northern boundary of the au plate runs north of this part of the banda arc through the banda sea in new guinea most motion is taken up as strike slip deformation in the northern part of the island delineating the pacific plate pa au boundary however some trench normal convergence is occurring at the new guinea trench evidence that the strain is partitioned in order to accommodate oblique pa au motion pa au motion is consistent with nuvel 1a direction but 8 mm yr 1 slower than the nuvel 1a estimate for pa au motion the sulawesi trench and molucca sea delineate zones of high strain rates consistent with high levels of active seismicity the sulawesi trench may take up some of the au sunda motion philippine sea plate motion is in a direction slightly northward of the nuvel ia estimate and is partitioned in some strike slip strain rates along the philippine fault and relatively larger trench normal convergence along the philippine trench and on the philippine mainland in the southern philippines and along the manila trench in the northern philippine islands the high level of strain rate along the manila trench is not released by any significant historic seismic activity for the entire eastern indonesia philippines region seismicity since 1963 has taken up 40 of the total moment rate inferred from our model

comparison of terrestrial reference frame velocities determined from slr and vlbi the most recent site velocity solutions from the vlbi analysis group at the goddard space flight center and the slr analysis group at the university of texas center for space research are compared the results indicate that the horizontal velocities agree after removing a velocity transformation of a few millimeters per year to the 2 3 millimeter per year level in an rms sense the velocities of the best observed sites agree to nearly 1 mm yr in each horizontal component in addition when only sites with adjusted velocities are compared the agreement of epoch site positions is improved over previous studies to the subcentimeter level in the horizontal components the sites in the western united states agree at the few millimeter level

scleractinian assemblages under sediment input their characteristics and relation to the nutrient input concept abstract in the geological record scleractinian dominated turbid water bioconstructions that accumulated under substantial terrigenous input along with shallow neritic marls rich in well preserved corals are common these occurrences indicate that beyond some threshold the ecologic and taphonomic effects of sedimentation prevail over the effects of nutrification field data and experiments on recent corals show that some taxa cope well with terrigenous turbidity and sedimentation and acclimate to increased heterotrophy colonial corals resilient to sediment input commonly are massive to platy forms of high skeletal plasticity and with large polypars to effectively reject sediment or are branched species providing a very small sedimentation area cleaned by feeble currents or small polyped massive taxa that tolerate intermittent veneering by sediment these corals may comprise siltation assemblages of recent turbid water reefs and level bottoms in siliciclastic environments conversely excess input of even low amounts of dissolved inorganic nutrients into clear waters adversely affects many coral species fossil turbid water bioconstructions twb were situated in inner shelf to shore zone settings or near storm wave base on shelves or ramps did not stack into reef complexes mostly show a cluster to segment fabric are scarce in or devoid of frame pores with marine cement and lacked a high carbonate slope relative to fossil clear water buildups preserved in pure limestone successions fossil twb contain moderately diverse coral assemblages with an increased proportion of sediment resistant forms aside from coral behaviour that is elusive in fossils the sediment resistance of corals was mainly determined by colony shape and polypar size but small polyped sediment tolerant corals became common since the early cretaceous late jurassic to cretaceous turbid water coral assemblages are dominated by plocoid or thamnasterioid forms corresponding cainozoic assemblages consist mainly of cerioid and plocoid taxa in fossil twb bioerosion and encrustation are similar or higher than in contemporaneous clear water buildups under higher sediment input accumulation of discrete twb was quenched and level bottoms of both corals and soft substrate biota formed in the resulting coral marls depending on turbidity sedimentation and substrate stability the coral fauna consists largely of both solitary corals and mainly sediment resistant pseudocolonial colonial forms or is dominated by solitary corals many corals show growth anomalies resulting from partial mortality due to episodic rapid sedimentation and unstable substrate in coral marl environments because of terrigenous input nutrient levels probably were elevated yet macroboring and encrustation are very scarce beyond some threshold of terrigenous sediment input and accumulation the ecologic and taphonomic effects of sedimentation and unstable substrate prevail over the effects of nutrient enrichment during the meso cainozoic evolution of scleractinians increasing photoautotrophy and progressive invasion of oligotrophic environments is in contrast to a late cretaceous to cainozoic increase in the relative number of reefs in marginal marine siliciclastic settings this trend may be explained by second order sea level fall and shrinking of epicontinental carbonate seas and isolated platforms driving corals to more narrow attached shelves and by a wider total trophic range in which distinct coral assemblages can thrive as a result of coral evolution and diversification

reef coralgal assemblages as recorders of paleobathymetry and sea level changes in the indo pacific province the coralgal framework within the outer reef margin of many indo pacific reefs exhibits three main shallow water communities the environmental significance of which can be inferred by comparison with their modern counterparts a community dominated by tabular acropora gr hyacinthus cytherea with branching pocillopora damicornis p eydouxi montipora digitata occasional domal faviids and mm thick crusts of the coralline algae lithophyllum and mesophyllum mainly typical of the 6 15 m paleodepth range a community including robust branching acropora gr danai robusta a humilis a digitifera and subordinate favia stelligera echinopora gemmacea associated to vermetid gastropods and thick coralline crusts of hydrolithon cf onkodes and neogoniolithon cf fosliei flourishing in depths less than 6 m in medium to high water energy settings a community composed of domal porites cf lutea and p cf lobata with occasional acropora gr danai robusta and cm thick crusts of coralline algae in sheltered habitats in depths less than 10 m these biological assemblages allow us to determine relationships between reef growth and paleobathymetry and consequently to reconstruct regional relative sea level curves high water energy reefal assemblages provide stronger evidence for reconstructing sea level curves than low energy buildups because they have generally been controlled by a keep up growth mode subsiding reef sites seem to be more reliable indicators of sea level variations because they usually present expanded reef sequences

the great barrier reef a 700 000 year diagenetic history a deep borehole through ribbon reef 5 in the great barrier reef off north eastern australia has identified a variety of cements including epitaxial radial prismatic and spherular aragonite together with blocky prismatic and fibrous calcite these cements are discontinuously arranged within the sequence that consists predominantly of grainstones but locally includes clotted muddy and filamentous textures that may be of microbial origin calcite cements vary in morphology with groups of crystals that include acute scalenohedral rhombohedral and flattened concordant terminations these show varying densities of inclusions that locally define growth zones and in some terminations divide in the manner of split crystals to form fibrous fringes morphological changes in calcite are inferred to reflect changes in water chemistry and crystal growth rates at the time of growth allied to their relationship to the palaeo water table and linked in turn to changes in sea level neomorphism and dissolution are widespread and variations in the severity of both imply response to the degree of undersaturation of pore waters that at times were probably balanced within very narrow limits a total of 10 depositional units are identified those units at the base of the borehole reflect deposition and diagenesis within a marine environment the influence of meteoric waters indicated by stable isotopes is first apparent at the top of unit 1 and in unit 2 184 to 155 m below sea floor petrographic evidence of vadose conditions appears at the tops of unit 3 131 to 99 m below sea floor units 4 to 8 all deposited under marine conditions provide isotopic evidence of meteoric or mixing zone waters and petrographic indicators of vadose conditions typically at the top of the units evidence indicates that in unit 5 the water table was mobile and units 6a 6b 7 and 8 all characterized by ultraviolet fluorescent cements are capped by sub aerial erosion surfaces unit 9 the holocene reflects the recent re establishment of marine conditions the extent of alteration of the entire sequence reflects the substantial and pervasive influence of meteoric waters this effect is interpreted as a result of a greater rainfall and river flow from the mainland during early and late stages of interstadial periods the study reflects progress in the ability to recognize the diagenetic signal generated by sea level change however whereas the isotopic results reflect the changing relationships between vadose and phreatic zones in groundwater systems beneath successive emergent surfaces their correspondence with petrographic features is expressed only weakly and commonly lacks the systematic sequential overprinting implied by the distribution of cathodoluminescent zones of cements in many ancient limestones

holocene key coral species in the northwest pacific indicators of reef formation and reef ecosystem responses to global climate change and anthropogenic stresses in the near future abstract the geological record of key coral species that contribute to reef formation and maintenance of reef ecosystems is important for understanding the ecosystem response to global scale climate change and anthropogenic stresses in the near future future responses can be predicted from accumulated data on holocene reef species identified in drillcore and from data on raised reef terraces the present study analyzes a dataset based on 27 drillcores raised reef terraces and 134 radiocarbon and u th ages from reefs of the northwest pacific with the aim of examining the role of key coral species in reef growth and maintenance for reef ecosystem during holocene sea level change the results indicate a latitudinal change in key coral species arborescent acropora acropora intermedia and acropora muricata was the dominant reef builder at reef crests in the tropics whereas porites porites australiensis porites lutea and porites lobata was the dominant contributor to reef growth in the subtropics between 10 000 and 7000 cal years bp when the rate of sea level rise was 10 m ka acropora digitifera acropora hyacinthus acropora robusta a abrotanoides isopora palifera favia stelligera and goniastrea retiformis from the corymbose and tabular acropora facies were the main key coral species at reef crests between 7000 and 5000 cal years bp when the rate of sea level rise was 5 m ka and during the following period of stable sea level massive porites p australiensis p lutea and p lobata contributed to reef growth in shallow lagoons during the period of stable sea level key coral species from the corymbose and tabular acropora facies have the potential to build reefs and maintain ecosystems in the near future under a global sea level rise of 2 6 m ka as do key coral species from the arborescent acropora facies and massive porites facies which show vigorous growth and are tolerant to relatively deep water low energy environments however these species are likely to experience severe mortality in upcoming decades due to natural and anthropogenic stresses consequently this damage will lead to a collapse in reef formation and the maintenance of reef ecosystems in the near future this study emphasizes the need for research into the conservation of key coral species

on the surface circulation in the western coral sea and residence times in the great barrier reef surface velocity observations from satellite tracked drifters made between 1987 and 2008 were used to resolve the surface circulation of the western coral sea west of 158 e and the great barrier reef gbr the mean surface current map depicts well the major circulation patterns of the region such as the position of the north vanuatu and north caledonia jets nvj and ncj and the western boundary currents the north queensland current nqc and the east australian current eac are well defined flowing at speeds greater than 50 cm s 1 to the north south of 15 s and 19 s respectively the nqc eac is mainly formed by the nvj ncj flows respectively the presence of the queensland plateau greatly affects the westward flow causing a zone of weak and highly variable currents that extends from 15 s to 18 s between the queensland plateau and the gbr shelf of the 235 drifters that crossed the western coral sea 75 entered the gbr analysis of the drifter trajectories inside the gbr reveals the presence of a northwestward circulation at speeds of 22 cm s 1 north of 18 s and 0 5 cm s 1 south of 18 s drifter travel times used to evaluate the water residence times within the gbr indicate residence times of a few weeks for most of the lagoon

coral reefs and sea level change abstract coral reefs provide significant evidence for former sea level positions because of their geological preservation and suitability for dating interpretation of this evidence presumes an understanding of reef geomorphology modern reef organism distributions and environmental factors influencing them fossil reef terraces formed during the last interglacial marine oxygen isotope mis substage 5e 128 116 ka are prevalent on many tropical shorelines and there has been ongoing debate as to the height reached by sea level during that highstand observations from numerous last interglacial sites suggest that sea level was at least 3 m above present sea level implying less extensive icesheets than at present an elevation of 6 m has commonly been adopted when correcting tectonically active sites for uplift recent compilations suggest elevations up to 8 9 m but incorporate few observations from reefs where the last interglacial is found below sea level oscillation of sea level during mis 5e has been interpreted from several sites with recent studies inferring rapid rise of several metres at the end of the interglacial these interpretations are at the limits to the precision with which corals can currently be dated and their palaeo water depths inferred it is not surprising that constraining last interglacial sea level changes within uncertainties of less than 1 2 m remains controversial considering sea level variations recognised between reef sites in the holocene and observed geographical variation in isostatic or flexural adjustments fossil coral reefs on uplifting margins also provide clear evidence for mis substages 5c and 5a and those on huon peninsula indicate fluctuations related to heinrich events mis 3 interpretations show considerable variability between sites with still greater uncertainties about sea level timing and elevation during previous interglacials future study of extensive sequences of fossil reefs preserved on rapidly subsiding margins could address these uncertainties submerged reefs have already yielded important information about sea level rise during the last deglaciation coring around barbados and tahiti as well as on the huon peninsula has produced a broadly consistent picture of ice melt reflecting eustatic change since the last glacial maximum these studies have shown the sensitivity of reefs to rapid sea level rise associated with meltwater pulses with some reefs drowning while others back stepped integrated ocean drilling program iodp expeditions to tahiti and recently the great barrier reef extended these records but details of timing nature and impact of deglacial meltwater pulses remain elusive studies of holocene reefs have indicated different growth strategies some kept up with sea level while others caught up when sea level decelerated holocene sea level appears to have experienced a gradual rise up to present across the caribbean providing accommodation space for reefs to accrete vertically whereas in the indo pacific sea level has been near its present level since 7 ka with many reef flats emergent following a slight fall of sea level caused by ocean siphoning microatolls on reef flats provide perhaps the clearest evidence of past sea level position but in their absence novel biological or other sea level indicators are required to better constrain palaeo water depths there is an urgent need for further research from additional key reef locations not only to decipher processes driving past sea level change and its geographical variability but also to better understand how coral reefs will respond in the context of future sea level rise

large scale tectonic plate motions measured with the doris space geodesy system we have analysed approximately 3 years of doppler tracking measurements of the doris system on the spot2 and topex poseidon satellites absolute velocities of 19 stations of the doris network have been computed through a dynamic orbit computation method these stations are located on 9 major tectonic plates for 14 stations relative velocities across 28 plate boundaries involving 8 different plates agree quite well with the nuvel 1 geological estimates with a correlation coefficient of 0 982 and a slope of 1 00 0 02 this study provides the first space geodesy derived motion of the african plate which is based on data taken at 4 stations computed rotation vectors for the relative motions between the eurasian pacific and african plates show a good agreement with nuvel 1 vectors for the remaining sites which are typically located close to plate boundaries measured motions depart significantly from the ones predicted by nuvel 1 the site of fairbanks alaska appears to move anomalously compared to earlier vlbi results

origin of the palau and yap trench arc systems summary this paper attempts to account for several unique morphological and geological characteristics of the palau and yap trench arc systems in the northwestern pacific ocean using a new hydrodynamic model postulated herein the model is a simple mathematical treatment of a stationary viscous flow pattern in the asthenosphere that causes an appreciable amount of mechanical resistance against a vertically subducted rigid slab moving horizontally together with the flat plate a couple of thrusting forces comprising uplifting pressure generated in the frontal edge of the overriding lid and a new type of tectonic erosion along the surface of the vertical slab seem to reasonably explain apparently contradictory features of the palau and yap trench arcs long term gps measurements show that the palau and yap trench arcs are moving over the viscous asthenosphere toward the nww with velocities as great as 10 cm yr 1 stresses along the trench arcs predicted by the model would be sufficiently large to maintain their present morphology 1 water depths greater than 8000 m in spite of the extremely small plate convergence rates and relatively young ages of subducted plate 2 v shaped cross section of the axial bottom of these trenches implying little cover of slumped deposits in spite of very steep landward slopes 3 serpentinized peridotites gabbros basalts and limestones are exposed on the landward slope with neither sediment cover nor ferromanganese hydro oxide coatings 4 abnormally close proximity of the palau and yap islands to the trench axis 5 predominant distribution of barrier reefs in their western periphery apparently opposite to the easterly to northeasterly prevailing wind

coral variation in two deep drill cores significance for the pleistocene development of the great barrier reef abstract variations in lithology and coral assemblages in drill cores from outer and inner shelf reefs are used to characterize the pleistocene development of the great barrier reef based on petrographic isotopic and seismic characteristics the outer shelf core from ribbon reef 5 is divided into three sections 1 a main reef section from 0 to 96 m is composed of six reef units 2 a rhodolith section from 96 to 158 m is interbedded with two thin reef units and 3 a basal section from 158 to 210 m is composed of non reefal skeletal grainstones and packstones two distinct coral assemblages identified in this core represent a shallow high energy community and lower energy community these two assemblages are repeated throughout the main reef section with some units recording transitions between assemblages and others composed of only a single assemblage these coral assemblage data also correlate with transitions recorded by coralline algae using similar criteria the inner shelf core from boulder reef is divided into two sections 1 an upper carbonate dominated section from 0 to 34 m is comprised of four reef units and 2 an underlying mud section from 34 to 86 m is composed of siliciclastics and two thin coral bearing units the four reef units in the upper section are dominated by a single coral assemblage representing a community typical of low energy turbid environments taken together these data indicate that 1 reef growth on the inner shelf initiated later than on the outer shelf 2 true reef turn on in outer shelf areas as represented by the main reef section in ribbon reef 5 was preceded by a transitional period of intermittent reef development and 3 the repeated occurrence of similar coral assemblages in both drill cores indicates that the great barrier reef has been able to re establish itself repeatedly producing reefs of similar composition over the last 500 ky despite major environmental fluctuations in sea level and perhaps temperature