productivity collapses in the arabian sea during glacial cold phases 1 productivity in the arabian sea is one of the highest in the world it is controlled by seasonally reversing monsoonal wind driven upwelling of nutrient rich deeper waters which fuel phytoplankton growth the detailed history of upwelling induced productivity in the eastern arabian sea is unknown here we present paleoproductivity records from a composite sediment core at the millennial scale during the last 80 kyr b p these records are based on relative abundance counts of planktonic foraminifera and organic carbon contents which are shown to mainly vary in concert the eastern arabian sea upwelling induced productivity was higher in the glacial period than in the holocene but it fell repeatedly on millennial timescales these productivity declines occurred during cold events in the north atlantic region with the most pronounced changes prevailing during the heinrich events hence seasonal monsoon winds that drive upwelling induced productivity in the east were weak when the north atlantic was cold these weak winds resulted in stratification of the water column comparable to today s arabian sea stratification in the intermonsoonal period combining the new eastern with published western arabian sea results shows that the entire biological factory was severely diminished during the north atlantic heinrich events and the seasonal productivity change in the arabian sea monsoon system was reduced with year round low productivity

oxygen isotopic composition of multiple species of planktonic foraminifera recorders of the modern photic zone temperature gradient abundances of 12 species of planktonic foraminifera collected in two plankton tows from the east tropical atlantic are compared to the chlorophyll content and the temperature of the sea water from which they were collected as expected from previous work in the tropics all dominant tropical species occur in greatest abundance within the photic zone many species occur in greatest abundances in the seasonal thermocline in association with the maximum chlorophyll concentration while a few algal symbiont bearing species occur in greatest abundance in the mixed layer the 18o measurements of planktonic foraminifera shells from core top sediment samples confirm the vertical stratification within the photic zone that is suggested by the relationship between hydrography and abundances found in the plankton tows and found in the statistical study by ravelo et al 1990 comparison between the measured 18o values of planktonic foraminifera with the predicted 18o profiles of the overlying water column at three core locations indicate that species abundances in the sediment record the seasonally integrated conditions of the photic zone and suggests that the abundance of a species in the sediment depends on whether the preferred ecological conditions of that species may be found within the photic zone of the overlying water column sometime during the year species which calcify below the photic zone have only trace relative abundances finally it appears that the total range of 18o values of the dominant species approximates the predicted annual 18o of calcite range in the upper 80 m of the water column

multiple monsoon controlled breakdown of oxygen minimum conditions during the past 30 000 years documented in laminated sediments off pakistan abstract late holocene laminated sediments from a core transect centred in the oxygen minimum zone omz impinging at the continental slope off pakistan indicate stable oxygen minimum conditions for the past 7000 calendar years high sw monsoon controlled biological productivity and enhanced organic matter preservation during this period is reflected in high contents of total organic carbon toc and redox sensitive elements ni v as well as by a low diversity high abundance benthic foraminiferal buliminacea association and high abundance of the planktonic species globigerina bulloides indicative of upwelling conditions surface water productivity was strongest during sw monsoon maxima stable omz conditions reflected by laminated sediments were found also during warm interstadial events preboreal bolling allerod and dansgaard oeschger events as well as during peak glacial times 17 22 5 ka all ages in calendar years sediment mass accumulation rates were at a maximum during the preboreal and younger dryas periods due to strong riverine input and mobilisation of fine grained sediment coinciding with rapid deglacial sea level rise whereas eolian input generally decreased from glacial to interglacial times in contrast the occurrence of bioturbated intervals from 7 to 10 5 ka early holocene in the younger dryas 11 7 13 ka from 15 to 17 ka heinrich event 1 and from 22 5 to 25 ka heinrich event 2 suggests completely different conditions of oxygen rich bottom waters extremely low mass and organic carbon accumulation rates a high diversity benthic fauna all indicating lowered surface water productivity during these intervals the omz was very poorly developed or absent and a sharp fall of the aragonite compensation depth favoured the preservation of pteropods the abundance of lithogenic proxies suggests aridity and wind transport by northwesterly or northeasterly winds during these periods coinciding with the north atlantic heinrich events and dust peaks in the tibetan loess records the correlation of the monsoon driven omz variability in the arabian sea with the rapid climatic fluctuations in the high northern latitudes suggests a close coupling between the climates of the high and low latitudes at a global scale

evolution of productivity and monsoonal dynamics in the eastern arabian sea during the past 68ka using dinoflagellate cyst records for the first time here we report the dinoflagellate cyst assemblage response to the monsoon variability over the last 68 ka from the eastern arabian sea eas based on the cyst assemblage five dinoflagellate cyst zones were established corresponding to four marine isotopic stages mis 1 4 an increased abundance of autotrophic gonyaulacoid species especially spiniferites during glacials mis 2 and 4 and late mis 3 41 67 to 25 3 ka reflects high productivity driven by strong winter convection during the northeast monsoon in contrast their decreased abundance during mis 1 and early mis 3 58 6 to 42 87 ka reveals decrease in productivity due to strong stratification caused by intense monsoon precipitation induced runoff from the western ghats and reduced light penetration driven by cloud cover the variation in heterotrophic protoperidinium species abundance could be related to variation in the oxygen minimum zone omz intensity with better preservation during intense omz in mis 3 and the late holocene 3 ka onwards therefore it is proposed here that the abundance of protoperidinium can be used as an index of omz in the eas

primary production in the arabian sea during the last 135 000 years abstract variations in primary productivity pp have been reconstructed in eutrophic mesotrophic and oligotrophic parts of the arabian sea over the past 135 000 years applying principal component analysis and transfer function to planktic foraminiferal assemblages temporal variation in paleoproductivity is most pronounced in the mesotrophic northern nast site and oligotrophic eastern east site arabian sea and comparatively weak in the western eutrophic geob 3011 1 site in the upwelling area off oman higher pp during interglacials 250 320 g c m 2 year 1 than during cold stages 210 270 g c m 2 year 1 at geob 3011 1 could have been caused by a strengthened upwelling during intensified summer monsoons and increased wind velocities at nast during interglacials pp is estimated to exceed 250 g c m 2 year 1 and during glacials to be as low as 140 180 g c m 2 year 1 these fluctuations may result from a 1 varying impact of filaments that are associated to the oman coastal upwelling and 2 from open ocean upwelling associated to the findlater jet at east highest productivity of about 380 g c m 2 year 1 is documented for the transition from isotope stage 5 to 4 we suggest that during isotope stages 2 4 5 2 the transition 5 4 and the end of stage 6 deep mixing of surface waters was caused by moderate to strong winter monsoons and induced an injection of nutrients into the euphotic layer leading to enhanced primary production the deepening of the mixed layer during these intervals is confirmed by an increased concentration of deep dwelling planktic foraminiferal species a high productivity event in stage 3 displayed by estimated pp values and by planktic foraminifera and radiolaria flux and accumulation rate likely resulted from a combination of intensified sw monsoons with moderate to strong ne monsoons differential response of globigerina bulloides globigerinita glutinata and mixed layer species to the availability of food is suited to subdivide productivity regimes on a temporal and spatial scale

abrupt climate induced changes in carbonate burial in the arabian sea causes and consequences we present high resolution records of aragonite contents and pteropods abundance in two sediment cores sk 17 and md 76 131 within the oxygen minimum zone omz of the eastern arabian sea we show large increases in aragonite contents during glacial and particularly during stadials heinrich events using aragonite content pteropods abundance organic carbon percentage and abundance of fertile species of planktonic foraminifer we demonstrate that aragonite contents in the eastern arabian sea primarily reflects preservation linked to the deepening of aragonite compensation depth acd in the arabian sea we show that these aragonite preservation events correspond with time equivalents of henrich events when arabian sea experienced large declines in monsoon driven productivity and greater penetration of antarctica intermediate water aaiw into the arabian sea thus pteropod preservation in the arabian sea appears to be the result of rapid climate change through atmospheric and oceanic teleconnections we suggest that the role of aragonite carbonate production and burial in margins and the resultant co2 climate feedback to rapid climate changes remains poorly constrained

a numerical study of circulation in a coastal reef lagoon system 1 a coupled wave circulation numerical model was used to simulate the distribution of wave energy as well as the circulation induced by wave breaking wind and tidal forcing within a coral reef system in kaneohe bay oahu hawaii modeled wave current and wave setup fields were compared with field measurements collected on the forereef reef flat and reef channels and in the lagoon over a 4 week period the predicted wave height transformation across the reef lagoon system was in good agreement with field observations using single parameter spatially uniform values to describe both wave breaking and frictional dissipation the spatial distribution of the resulting wave setup field drove a persistent wave driven flow across the reef flat that returned to the ocean through two deeper channels in the reef both the magnitude and direction of these currents were well described using a spatially uniform hydraulic roughness length scale notably the model lends support to field observations that setup within the coastally bounded lagoon was a substantial fraction of the maximum setup on the reef 60 80 which generated relatively weak cross reef wave driven flows 10 20 cm s 1 compared with reefs having mostly unbounded lagoons e g many atolls and barrier reefs numerical experiments conducted using lagrangian particle tracking revealed that residence times within kaneohe bay are extremely heterogeneous typically ranging from 1 month within its sheltered southern lagoon

paleoproductivity in the equatorial indian ocean for the last 260 000 yr a transfer function based on planktonic foraminifera a principal component analysis pca of planktonic foraminifera in surface sediment of the northern equatorial indian ocean defines two major assemblages the first one dominated by globigerinoides sacculifer g ruber globigerinella aequilateralis and globoquadrina conglomerata characterizes non upwelling areas the second dominated by globigerina bulloides g falconensis and globigerinita glutinata characterizes upwelling areas the distribution of planktonic foraminiferal species in the area is mainly related to primary production pp the pca applied to core md 900963 samples defines an alternation of the two assemblages through time a non upwelling one similar to that present in the core tops and an upwelling assemblage which contains in addition neogloboquadrina dutertrei globorotalia menardii and g crassaformis equatorial indian ocean core top samples are introduced as additional rows in the pca calculated on core md 900963 samples and a transfer function is constructed correlating factorial coordinates of core tops within the range of changes occurring in core md 900963 with estimated pp values applied to the last 260 000 yr the transfer function indicates that the precession is the major orbital forcing on equatorial productivity changes and that annual pp increases by about 85 from interglacial to glacial interstadials these results are in agreement with an independent productivity index based on coccoliths direct impact of insolation on equatorial productivity could be explained by the link between southern oscillation and intensity of zonal winds which seem to lead the productivity of surface waters at the location of core md 900963

a 3d approach to study the interaction between hydraulic and natural fracture a real 3d model is developed to study the interaction between hydraulic fracture and natural fracture the hydraulic fracture propagation behavior and fracture geometry under impact of natural fracture are studied through a series of numerical results different horizontal stress anisotropies intersection angles friction coefficients as well as hydraulic parameters the final results demonstrate the key role of horizontal stress anisotropy on the interaction between hydraulic fracture and natural fracture under a higher intersection angle it is difficult for hydraulic fracture to cross the natural fracture with low horizontal stress anisotropy in addition the natural fracture at a lower intersection angle has a higher probability to capture the hydraulic fracture normally the natural fracture is more likely to be activated in the top branch at a low intersection angle as the lower branch is located in the induced stress shadow of hydraulic fracture by contrast two different branches especially two symmetrical braches at the intersection of 90 are activated on the other hand a higher friction coefficient slows down the propagation in natural fracture even prevents the activation of natural fracture besides increased injection rate as well as fluid viscosity will promote the fracture propagation under the same conditions to lead to a longer and wider fracture

atmospheric forcing intensifies the effects of regional ocean warming on reef scale temperature anomalies during a coral bleaching event 1 we investigate how local atmospheric conditions and hydrodynamic forcing contributed to local variations in water temperature within a fringing coral reef lagoon system during the peak of a marine heat wave in 2010 2011 that caused mass coral bleaching across western australia a three dimensional circulation model regional ocean modeling system roms with a built in air sea heat flux exchange module coupled ocean atmosphere experiment coare was coupled with a spectral wave model simulating waves nearshore swan to resolve the surface heat exchange and wave driven reef circulation in coral bay ningaloo reef using realistic oceanic and atmospheric forcing the model predictions were in good agreement with measured time series of water temperature at various locations in the coral reef system during the bleaching event through a series of sensitivity analyses we found that the difference in temperature between the reef and surrounding offshore waters dt was predominantly a function of both the daily mean net heat flux qnet and residence time whereas diurnal variations in reef water temperature were dependent on the diurnal fluctuation in the net heat flux we found that reef temperatures were substantially higher than offshore in the inner lagoon under normal weather conditions and over the entire reef domain under more extreme weather conditions 0 7 c 1 5 c although these temperature elevations were still less than that caused by the regional ocean warming 2 c 3 c the arrival of peak seasonal temperatures in the summer of 2010 2011 when net atmospheric heat fluxes were positive and abnormally high caused substantially higher thermal stresses than would have otherwise occurred if offshore temperatures had reached their normal seasonal maxima in autumn when net atmospheric heat fluxes were negative or cooling therefore the degree heating weeks calculated based on offshore temperature substantially underestimated the thermal stresses experienced by the reef in the period leading up to the observed bleaching

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

planktonic foraminifera of the northern indian ocean distribution and preservation in surface sediments in the northern indian ocean planktonic foraminiferal tests accumulate in a wide variety of surface water environments and depositional settings this variability enables us to isolate the effects that surface water ecology and differential dissolution have on the distribution of planktonic foraminifera from 251 geographically widespread surface sediment samples foraminiferal abundance varies from 0 to 104 whole foraminifera in the greater than 150 m fraction per gram dry sediment values 10 characterize the three deep basins of the equatorial indian ocean and the western bay of bengal foraminiferal tests are most abundant on carbonate covered ninety east and carlsberg ridges absolute abundance patterns are mainly controlled by non ecological processes variations in dissolution resistant species rsp with water depth reveal that the foraminiferal lysocline fl varies regionally the fl is deepest 3 800 m in the equatorial region rises abruptly to 3 300 m in the arabian sea and varies from 2 600 m to near 2 000 m moving northward in the bay of bengal deep samples with anomalously low rsp 30 suggest redeposition systematic geographic and depth related variation is observed for the 17 most abundant foraminiferal species dissolution resistant species g menardii g tumida g dutertrei p obliquiloculata generally exhibit a rapid and continuous increase in relative abundance at and below the fl susceptible species g ruber g bulloides g glutinata for example exhibit a rapid and continuous decrease in relative abundance at and below the fl moderately susceptible species g conglobatus g aequilateralis g conglomerata for example rapidly increase in abundance at the fl and systematically decrease with depth below the fl principal components analysis pca of faunal data from minimally dissolved 30 rsp samples reveals important ecologically related species intercorrelations the major biogeographic gradient is the negative covarying relationship between ag bulloides g glutinata species pair and a grouping ofg sacculifer g conglobatus g aequilateralis andg ruber pca of all samples demonstrates how differential dissolution alters this and other species relationships species groupings that incorporateg ruber g menardii andg dutertrei are particularly affected by dissolution comparison of average faunal data from minimally dissolved samples in the northern indian ocean with similar samples from other tropical regions suggests varying environmental factors produce distinct faunas within the tropical ocean for example g bulloides g falconensis andg hexagona are significantly more abundant in northern indian ocean surface sediments while such species asg ruber g sacculifer g dutertrei andp obliquiloculata dominate in other tropical regions

the combined influence of hydrodynamic forcing and calcification on the spatial distribution of alkalinity in a coral reef system 1 we investigated the influence of hydrodynamic forcing waves tides alongshore currents and winds and net calcification by coral reef organisms on the spatial distribution of total alkalinity ta in a fringing reef system through a combination of field measurements and numerical modeling a field experiment was conducted over 10 days in coral bay ningaloo reef western australia during which we measured wave heights currents and tides as well as the spatial distribution of ta across the fore reef reef crest and lagoon we used observed changes in ta on the adjacent reef flat along with synoptic measurements of cross reef transport to estimate in situ rates of net calcification gcv using a control volume approach based on the gcv estimated we simulated light driven diurnal variations in benthic net calcification within a three dimensional ocean circulation model roms regional ocean modeling system by coupling roms with a spectral wave model simulating waves nearshore we were able to simulate currents within coral bay reef lagoon system that were in good agreement with the field observations and demonstrate that circulation with the system was wave dominated both the field measurements and numerical model output confirmed that both residence time r and ta varied primarily with offshore wave heights and location within the bay however variations in ta were also affected by the nonlinear interaction between rates of net calcification that varied as a function of diurnally changing light and water residence time that varied as a function of offshore wave heights

monsoonal dynamics and evolution of the primary productivity in the eastern arabian sea over the past 30 ka abstract this study presents a high resolution primary productivity record for the last 30 ka in the eastern arabian sea eas based on the coccolithophore assemblage at sk 17 core in the continental slope off goa india coccolithophores were proposed as indicators of primary productivity and nutricline position and the results were used to reconstruct the monsoonal dynamics which is a main factor controlling productivity changes in the eas both seasons in the indian monsoon winter and summer monsoon exert a strong control over the primary productivity in the arabian sea an increased productivity was recorded during the late glacial period in the eas contrasting with records obtained in the western and northern arabian sea this enhanced productivity was related to strengthened winter monsoon winds planktonic foraminifera data suggested a weakened winter mixing during the last deglaciation which would reduce productivity in the area however our coccolithophore data reveal a high primary productivity during the deglaciation provably maintained by the nutrient supply from the continental runoff due to the presence of enhanced summer monsoon regarding the holocene surface waters were highly stratified since 10 5 ka our data were compared with ice cores isotopic records from high latitudes of both hemispheres allowing us to observe a good correlation between the stratification of the eas and the climate variability over high latitude regions in the northern hemisphere however there has been some inconsistency between our coccolithophore data and planktonic foraminiferal records particularly during the short time intervals corresponding to the heinrich cold events described in the north atlanctic region

assessing the drivers of spatial variation in thermal forcing across a nearshore reef system and implications for coral bleaching we examined the seasonal and spatial variability in the temperatures of nearshore reef waters over 19 months across coral bay at ningaloo reef western australia local deviations in the mean daily temperature of nearshore reef waters from offshore values dt were a linear function of the combined effect of net atmospheric heating qnet and offshore wave height and period hs ffiffiffiffiffi tp p whereas intra annual variation in local heat exchange was driven mainly by seasonal changes in shortwave radiation intra annual variation in local cooling was driven mostly by changes in relative humidity r2 5 0 60 and wind speed r2 5 0 31 that exhibited no apparent seasonality we demonstrate good agreement between nearshore reef temperatures modeled from offshore sea surface temperatures offshore wave forcing and local atmospheric heat fluxes with observed temperatures using a simple linear model r2 5 0 31 0 69 root mean square error 5 0 4 0 9uc using these modeled nearshore reef temperature records we show that thermal stresses across the reef reached between 16uc weeks and 22uc weeks in the summer of 2011 when a mass coral bleaching event was reported and between 12uc weeks and 13uc weeks in the following summer of 2012 when no mass bleaching was reported after compensating for differences between observed and modeled thermal stresses we found that maximum thermal stresses across the reef likely reached as high as 18 34uc weeks in the summer of 2011 the approach used here could thus improve our ability to predict spatial variation in thermal stress and bleaching across other wavedriven nearshore reef systems

sea surface temperature and productivity records for the past 240 kyr in the arabian sea abstract deep sea sediments of two cores from the western ty93 929 p and the southeastern md900963 arabian sea were used to study the variations of the indian monsoon during previous climatic cycles core ty93 929 p was located between the sw monsoon driven upwelling centres off somalia and oman which are characterized by large seasonal sea surface temperature sst and particle flux changes by contrast core md900963 was situated near the maldives platform an equatorial ocean site with a rather small sst seasonality less than 2 c for both cores we have reconstructed sst variations by means of the unsaturation ratio of c37 alkenones which is compared with the 18o records established on planktonic foraminifera in general the sst records follow the 18o variations with an sst maximum during oxygen isotope stage 5 5 the last interglacial at about 120 130 kyr and a broad sst minimum during isotope stage 4 and 3 3 approximately 40 50 kyr the sst difference between the holocene and the last glacial maximum lgm is of the order of 2 c in both cores the ssts during isotope stage 6 are distinctly higher by 1 2 c than the cold sst minima during the last glacial cycle lgm and stage 3 to reconstruct qualitatively the past productivity variations for the two cores we used the concentrations and fluxes of alkenones and organic carbon together with a productivity index based on coccolith species florisphaera profunda relative abundance within each core there is a general agreement between the different palaeoproductivity proxies in the southeastern arabian sea core md900963 glacial stages correspond to relatively high productivity whereas warm interstadials coincide with low productivity all time series of productivity proxies are dominated by a cyclicity of about 21 23 kyr which corresponds to the insolation precessional cycle a hypothesis could be that the ne monsoon winds were stronger during the glacial stages which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone by contrast the records are more complicated in the upwelling region of the western arabian sea core ty93 929 p this is partly due to large changes in the sedimentation rates which were higher during specific periods isotope stages 6 5 4 5 2 3 and 2 unlike core md900963 no simple relationship emerges from the comparison between the 18o stratigraphy and productivity records the greater complexity observed for core ty93 929 p could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons the sw monsoon being enhanced during interglacial periods whereas the ne monsoon was increased during glacial intervals a similar line of reasoning also could help explain the sst records by the superimposition of variations of three components global atmospheric temperature and sw and ne monsoon dynamics

creation of residual flows in a partially stratified estuary the creation of residual flows in estuaries is examined using acoustic doppler current profiler data sets from northern san francisco bay the data sets are analyzed using principal component analysis to examine the temporal variability of the flows which create the residual circulation it is seen that in this periodically and partially stratified estuary the residual flows are created through a series of pulses with strong variability at the 24 hour timescale through the interaction of shear stratification and mixing this interaction is captured through the use of a dimensionless number the horizontal richardson number rix which is developed to examine the local balance between the stratifying and destratifying forces at the tidal timescale it is seen that rix is a valuable parameter in predicting the onset of the residual creating events with a threshold value of 3 on ebb tides this critical value is argued to be a threshold above which the stratification and shear flow create a feedback effect each further intensifying the other this feedback results in a highly variable exchange flow which creates the estuarine residual in intermittent pulses rather than as a steady flow although typically attributed to baroclinic forcing an argument is made that these pulses of residual creating exchange flow could be created by barotropic forcing in the presence of variable stratification which is asymmetric between flood and ebb tides this result poses a great challenge for turbulence modeling as the timing and magnitude of stratification and shear must be correctly simulated on the tidal timescale in order to reproduce the effects seen in the data sets presented

two dimensional modelling of wave dynamics and wave forces on fringing coral reefs abstract two dimensional numerical modelling of swell wave dynamics on idealized fringing reefs is performed using swan covering a wide range of bathymetries climate forcing conditions and water depths over the reefs the results illustrate the impact of reef geometry and bathymetry coral species and sea level rise on key hydrodynamic parameters on the reef and on forces on corals the modelling demonstrates that one dimensional models underestimate the wave action on the reef flat wide short reefs and narrow long reefs have similar wave heights at the centre of the reef flat for a given reef length the wave height first decreases with increasing reef width then increases to a local maximum when reef width is approximately equal to the reef length and then decreases for further increases in width this pattern is a result of combined dissipation and refraction processes which combine to lead to different zones of cross reef wave transformation provided that a reef retains its hydrodynamic functions in breaking and refracting the waves sea level rise enhances the wave heights and wave orbital velocities on the reef flat if vertical coral growth does not keep pace with sea level rise loss of the hydrodynamic functions of the reef may occur on deeper reefs and result in a reduction of near bed velocities with sea level rise hydrodynamic forces on corals vary by coral species and slr changes the magnitude of the forces on different species in different ways which may lead to less favourable conditions for certain coral species for long period swell the intermediate size corals are drag dominated and behave similarly to branching corals whereas for short period swell their behavior is similar to that of the inertia dominated massive corals for intermediate corals different responses to slr may therefore be expected for different overall regional wave climates over time this process may contribute to changes in the structural complexity of reefs the influence of sea level rise on the forces on corals on the reef flat is different under swell and cyclonic wind conditions since wind influences wave period in the latter case

temporal variability in the northern arabian sea oxygen minimum zone omz during the last 225 000 years the northern arabian sea is one of the few regions in the open ocean where thermocline water is severely depleted in oxygen the intensity of this oxygen minimum zone omz has been reconstructed over the past 225 000 years using proxies for surface water productivity water column denitrification winter mixing and the aragonite compensation depth acd changes in omz intensity occurred on orbital and suborbital timescales lowest o2 levels correlate with productivity maxima and shallow winter mixing precession related productivity maxima lag early summer insolation maxima by 6 kyr which we attribute to a prolonged summer monsoon season related to higher insolation at the end of the summer periods with a weakened or even non existent omz are characterized by low productivity conditions and deep winter mixing attributed to strong and cold winter monsoonal winds the timing of deep winter mixing events corresponds with that of periods of climatic cooling in the north atlantic region

morphological characterisation of reef types in torres strait and an assessment of their carbonate production coral reefs represent major accumulations of calcium carbonate caco3 the particularly labyrinthine network of reefs in torres strait north of the great barrier reef gbr has been examined in order to estimate their gross caco3 productivity the approach involved a two step procedure first characterising and classifying the morphology of reefs based on a classification scheme widely employed on the gbr and then estimating gross caco3 productivity rates across the region using a regional census based approach this was undertaken by independently verifying published rates of coral reef community gross production for use in torres strait based on site specific ecological and morphological data a total of 606 reef platforms were mapped and classified using classification trees despite the complexity of the maze of reefs in torres strait there are broad morphological similarities with reefs in the gbr the spatial distribution and dimensions of reef types across both regions are underpinned by similar geological processes sea level history in the holocene and exposure to the same wind wave energetic regime resulting in comparable geomorphic zonation however the presence of strong tidal currents flowing through torres strait and the relatively shallow and narrow dimensions of the shelf exert a control on local morphology and spatial distribution of the reef platforms a total amount of 8 7million tonnes of caco3 per year at an average rate of 3 7kg caco3m 2yr 1 g were estimated for the studied area extrapolated production rates based on detailed and regional census based approaches for geomorphic zones across torres strait were comparable to those reported elsewhere particularly values for the gbr based on alkalinity reduction methods however differences in mapping methodologies and the impact of reduced calcification due to global trends in coral reef ecological decline and changing oceanic physical conditions warrant further research the novel method proposed in this study to characterise the geomorphology of reef types based on classification trees provides an objective and repeatable data driven approach that combined with regional census based approaches has the potential to be adapted and transferred to different coral reef regions depicting a more accurate picture of interactions between reef ecology and geomorphology

spectral wave dissipation over a barrier reef 1 a 2 week field experiment was conducted to measure surface wave dissipation on a barrier reef at kaneohe bay oahu hawaii wave heights and velocities were measured at several locations on the fore reef and the reef flat which were used to estimate rates of dissipation by wave breaking and bottom friction dissipation on the reef flat was found to be dominated by friction at rates that are significantly larger than those typically observed at sandy beach sites this is attributed to the rough surface generated by the reef organisms which makes the reef highly efficient at dissipating energy by bottom friction results were compared to a spectral wave friction model which showed that the variation in frictional dissipation among the different frequency components could be described using a single hydraulic roughness length scale surveys of the bottom roughness conducted on the reef flat showed that this hydraulic roughness length was comparable to the physical roughness measured at this site on the fore reef dissipation was due to the combined effect of frictional dissipation and wave breaking however in this region the magnitude of dissipation by bottom friction was comparable to wave breaking despite the existence of a well defined surf zone there under typical wave conditions the bulk of the total wave energy incident on kaneohe bay is dissipated by bottom friction not wave breaking as is often assumed for sandy beach sites and other coral reefs

thermally driven exchanges between a coral reef and the adjoining ocean abstract in this paper hydrographic observations made over a fringing coral reef at the northern end of the gulf of aqaba near eilat israel are discussed these data show exchange flows driven by the onshore offshore temperature gradients that develop because shallow regions near shore experience larger temperature changes than do deeper regions offshore when subjected to the same rate of heating or cooling under heating conditions the resulting vertically sheared exchange flow is offshore at the surface and onshore at depth whereas when cooling dominates the pattern is reversed for summer conditions heating and cooling are both important and a diurnally reversing exchange flow is observed during winter conditions heating occupies a relatively small fraction of the day and only the cooling flow is observed when scaled by v the observed profiles of the cross shore during cooling velocity collapse onto a single curve the value of v depends on the convective velocity scale uf and the bottom s

tide effects on wave attenuation and wave set up on a caribbean coral reef abstract the effects of tides on wave attenuation and wave set up were investigated at great pond bay a caribbean reef located in st croix u s virgin islands measurements of wave pressure fluctuations were made at three stations across the reef profile total wave set up was measured between the forereef and the reef crest or backreef lagoon wave spectra indicate significant filtering of energy at the peak frequencies as waves traveled across the reef the energy dissipation calculations imply an average energy reduction of 62 between the forereef and reef crest mean energy reduction between the forereef and lagoon was 90 energy dissipation between the forereef and reef crest increased 15 between high and low tide and 6 between forereef and lagoon tidal reduction of water depth at the reef crest intensified wave breaking and this condition increased energy dissipation measurements of wave set up ranged from 0 8 to 1 5 cm calculations of wave set up using tait s 1972 model showed good agreement with observations

spatial and temporal variations in wave characteristics across a reef platform warraber island torres strait australia a field experiment was conducted at warraber island torres strait australia to investigate spatial and temporal variations in wave characteristics and energy across a mesotidal coral reef platform measurements of water depth were obtained using five pressure sensors deployed across a 2 7 km section of reef flat from july 3 5 2001 the reef surface was uneven and consisted of an outer reef flat a central reef flat depression an inner reef ramp a palaeo reef surface and the shoreline water levels decreased landward across the platform with tide ranges at the shoreline being almost 50 lower than at the outer reef flat rising and falling tides were characterised by a bimodal energy distribution with both short period 0 3 s and wind 3 8 s waves present higher water levels were dominated by wind waves the highest waves occurred at high tides associated with nocturnal tidal cycles with hs decreasing from 0 5 to 0 2 m from the outer reef flat to the shoreline wave energy at swell 8 20 s and infragravity 20 s frequencies was negligible across the reef platform although there was evidence of wave groups at higher water levels reef geometry and changes in water level determine the magnitude of wave energy on the reef platform up to 85 95 of incident wave energy is attenuated by the central reef flat depression at high and low tide respectively and strong linear relationships exist between hs and h at all locations both wave height and wave type are strongly depth dependent critical reef rim depths required to produce hs of a given size vary spatially across the reef rim due to variations in reef topography a distinct depth related threshold exists at which short period and wind wave dominance reverses over a 14 day spring neap tidal cycle the time of occurrence of wave action diminishes across the reef platform to the shoreline larger waves hs 0 2 m occur for only 9 of time at the outer reef flat and for less than 0 5 over the remaining reef platform this implies that on mesotidal reef platforms sediment entrainment and transport are severely constrained under normal wave energy conditions and significant change is likely restricted to extreme events

nearshore circulation in a tropical fringing reef system 1 the role of waves tide and wind on the circulation of a fringing reef system was investigated using data collected during a 6 week field experiment in a section of ningaloo reef off western australia the high correlation observed between current velocities and wave height throughout the system revealed the dominant role wave breaking plays in driving the overall reef lagoon circulation whereas the modulation of the currents at tidal frequencies suggested that the wave driven currents responded to tidal variations in the mean water level over the reef the influence of the various forcing mechanisms on the current field was investigated for both high and low frequency bands wave breaking was found to be the dominant forcing mechanism for the low frequency subtidal currents with the subtidal flow pattern consisting of a cross reef flow over the reef alongshore flow in the lagoon and water exiting back to the ocean through the main channel the tides controlled the high frequency current variability via two mechanisms one associated with the ebb flood cycle of the tides and the second associated with tidal modulations of the wave driven currents wind forcing and buoyancy effects were both found to be negligible in driving the circulation and flushing of the system during the observation period flushing time scale estimates varied from as low as 2 h to more than a day for the wide range of observed incident wave heights the results suggest that the circulation of ningaloo reef will be strongly influenced by even a small mean sea level rise

boundary layer turbulence and flow structure over a fringing coral reef measurements of velocity and rates of turbulence were made across a fringing coral reef in the gulf of aqaba red sea to determine the effect that the rough topography has on boundary layer mixing and flow dynamics observations were made at two fore reef sites and a nearby sandy slope the friction velocity u and drag coefficient cd were determined directly from turbulent reynolds stresses measured using acoustic doppler velocimeters values of cd for the coral substrates ranged from 0 009 to 0 015 three to five times greater than over the sandy bottom site the turbulence dissipation rate e was determined by fitting spectra of vertical velocity to the theoretical 5 3 law expected for the inertial subrange of turbulence there was a local balance between production and dissipation of turbulent kinetic energy signifying that we could estimate u from either the mean velocity profile turbulence or dissipation rate of turbulent kinetic energy estimates from all three measures agreed well with mean u uo ranging from 0 10 6 0 03 to 0 12 6 0 03 indicating that existing turbulent boundary layer flow theory can be applied to flows over the rough topography of coral reefs the bottom topography by enhancing both reef scale and local drag and mixing levels allows reef biota to more effectively exchange dissolved and particulate matter with oceanic waters

salinity variability in the arabian sea argo floats deployed in the arabian sea provided an opportunity to look at the temporal variability of the core depth of arabian sea high salinity water mass ashsw at three locations in the north central and southern arabian sea these three locations show distinctly different variability patterns at the northern location we see a prominent semi annual cycle whereas at the central location an annual cycle dominates comparison with topex jason sea level data shows that this difference can be attributed to the influence of rossby waves at the central location in the southern arabian sea the variability in core depth is also dominated by an annual mode but there are 2 high frequency components near the madden julian oscillation frequencies thus the salinity distribution in the arabian sea apparently is influenced by both remote forcing and ocean atmospheric coupling

transient tidal circulation and momentum balances at a shallow inlet an analysis of transient momentum balances is carried out to elucidate circulation dynamics and exchange mechanisms at shallow barotropic tidal inlets circulation is computed using a depth integrated fully nonlinear time stepping finite element model with variably spaced grids having horizontal resolution down to 50 m velocity and elevation fields from the model are used to directly evaluate the contribution of each term in the momentum equations to the overall momentum balance a transformation of the x y momentum terms into an s n coordinate system is used to simplify the interpretation of the dynamics and provide vivid illustrations of the forces and resulting accelerations in the flow the analysis is conducted for an idealized inlet and contrasted with a highly detailed model of beaufort inlet north carolina results show that momentum balances in the immediate vicinity of these inlets vary significantly in time and space and oscillate between two dynamical states near maximum ebb or flood the alongstream momentum balances are dominated by advective acceleration pressure gradient and bottom friction cross stream balances are dominated by centrifugal acceleration and pressure gradients near slack balances more closely follow linear wave dynamics with local accelerations balancing pressure gradients and to a lesser degree coriolis comparisons between the idealized inlet and beaufort inlet show broad similarities in these momentum balances however natural inlet geometry and bottom topography as well as the tidal transmission characteristics of the sounds behind beaufort inlet produce strong asymmetries moreover momentum balances are highly localized often with subkilometer length scales the dynamics are used to explain the physical mechanisms for inlet exchange in particular the results indicate that the cross stream dynamics generate a wall along the length of an inlet during the stronger phases of the tide the wall is established by opposing cross inlet pressure gradients and centrifugal forces and it poses a significant barrier to cross inlet exchange during the stronger phases of the tide but is absent near slack

a 23000 year old record of paleoclimatic and environmental changes from the eastern arabian sea abstract climate of the eastern arabian sea is highly influenced by both global climate and indian monsoon we produced multi proxy records of benthic foraminiferal biofacies and stable isotope ratio 13c and 18o planktic foraminifera and total organic carbon wt content of sediments from core sk291 gc11 in the upper continental shelf off mangalore off eastern arabian sea eas to decipher paleoenvironmental and paleoclimatic changes during the past 23 000 years the monsoon was weak during the last glacial maximum 23 000 18 000 calibrated years before present cal yr bp when sea level was lower globigerinoides ruber populations fluctuate from 30 to 60 in the studied interval with a maximum during 6000 5000 cal yr bp and a minimum during 19 000 17 000 cal yr bp the 18o values of benthic foraminifer ammonia gaimardii suggest pronounced cooling phases during 23 000 18 000 cal yr bp and a short term cooling at 6000 cal yr bp several intervals of high organic productivity and low oxygen conditions were identified based on benthic foraminiferal biofacies during 23 247 682 cal yr bp wind induced surface mixing was intense during 3200 530 cal yr bp as evidenced by high globigerina bulloides abundances the core was affected by moderate chemical weathering and solar variability appears to have been an important forcing factor in shaping climate of the region

field observations of wave driven water level gradients across a coral reef flat 1 field measurements of still water surface elevations were obtained across a narrow leeward reef flat on lady elliot island great barrier reef australia in june 2003 stilling wells were deployed from the reef crest landward to the island beach and waves and mean water levels were monitored over both rising and falling tides during low to moderate wave energy conditions wave setup of up to 13 8 cm above still water level occurred in the presence of incident waves of 0 4 m yielding maximum water surface slopes greater than 6 results show that the magnitude of wave setup varies both temporally and spatially across the reef with changing water depth setup is dominant on the reef edge at low tide evolving into a dual setup system at both the reef edge and shoreline at midtide and finally a dominant shoreline setup at high tide on lady elliot island the dual setup system is considered to result from spatial differences in transformation and breaking of swell and wind waves at midtide stages the presence of a dual setup system across a reef flat has not been previously identified in field or modeling studies and has potentially significant implications for reefal current development sediment transport and the stability of reef island shorelines

morphological constraints to wave driven circulation in coastal reef lagoon systems a numerical study 1 the response of the wave driven circulation within coastally bounded reef lagoon systems to varying lagoon and channel morphology was investigated using a two dimensional coupled wave circulation numerical model numerical experiments were conducted using a series of coastal reefs that incorporated a wide range of different lagoon depths and channel widths with the morphology of both the reef forereef and reef flat and incident wave forcing held constant the wave driven circulation was found to increase substantially as dimensionless reef morphology parameters characterizing the relative lagoon depth and channel width were each independently increased analysis of the wave setup fields revealed that this increased flow was due to an enhancement of the cross reef water level gradient resulting from a sharp reduction in the lagoon setup as the frictional resistance on the lagoon channel return flow was diminished this follows similar trends observed in existing field and laboratory studies of wave driven reef flows analysis of flushing time scales computed for each reef lagoon geometry predicted the existence of optimal dimensionless lagoon depths and channel widths for a reef system to establish maximal coastal flushing overall the circulation and flushing of coastal reef lagoon systems was found to be largely controlled by the particular morphology of the lagoon and channel region rather than solely by the morphology of the forereef and reef flat that has been the primary focus of analytical models developed to predict wave setup and circulation on reefs

variations in tropical convection as an amplifier of global climate change at the millennial scale the global expression of millennial scale climatic change during the glacial period and the persistence of this signal in holocene records point to atmospheric teleconnections as the mechanism propagating rapid climate variations we suggest rearrangements in the tropical convection system globally affected the concentration and location of atmospheric water vapour and modulated terrestrial and marine emissions of ch4 and n2o providing a tropical mechanism of amplifying and perpetuating millennial scale climate changes a multi proxy reconstruction reflecting various aspects of the intensity of the arabian sea summer monsoon shows strong millennial scale variability over the past 90 kyr in which low intensity is associated with a southern shift of the intertropical convergence zone itcz and an eastward shift in the equatorial convergence zone the monsoon reconstruction which is based on new data from a somali margin sediment core is supported by previously reported tropical paleoclimatic records and suggests that global scale millennial climatic variability is in part driven by modulations in the tropical hydrological cycle and tropical emissions of the greenhouse gases ch4 and n2o

oxygen minimum zones in the eastern tropical atlantic and pacific oceans within the eastern tropical oceans of the atlantic and pacific basin vast oxygen minimum zones omz exist in the depth range between 100 and 900 m minimum oxygen values are reached at 300 500 m depth which in the eastern pacific become suboxic dissolved oxygen content 4 5 mol kg 1 with dissolved oxygen concentration of less than 1 mol kg 1 the omz of the eastern atlantic is not suboxic and has relatively high oxygen minimum values of about 17 mol kg 1 in the south atlantic and more than 40 mol kg 1 in the north atlantic about 20 40 of the north pacific volume is occupied by an omz when using 45 mol kg 1 or 90 mol kg 1 respectively as an upper bound for omz oxygen concentration for ocean densities lighter than 27 2 kg m 3 the relative volumes reduce to less than half for the south pacific 7 and 13 respectively the abundance of omzs are considerably smaller 1 and 7 for the south atlantic and only 0 and 5 for the north atlantic thermal domes characterized by upward displacements of isotherms located in the northeastern pacific and atlantic and in the southeastern atlantic are co located with the centres of the omzs they seem not to be directly involved in the generation of the omzs omzs are a consequence of a combination of weak ocean ventilation which supplies oxygen and respiration which consumes oxygen oxygen consumption can be approximated by the apparent oxygen utilization aou however aou scaled with an appropriate consumption rate aour gives a time the oxygen age here we derive oxygen ages using climatological aou data and an empirical estimate of aour averaging oxygen ages for main thermocline isopycnals of the atlantic and pacific ocean exhibit an exponential increase with density without an obvious signature of the omzs oxygen supply originates from a surface outcrop area and can also be approximated by the turn over time the ratio of ocean volume to ventilating flux the turn over time corresponds well to the average oxygen ages for the well ventilated waters however in the density ranges of the suboxic omzs the turn over time substantially increases this indicates that reduced ventilation in the outcrop is directly related to the existence of suboxic omzs but they are not obviously related to enhanced consumption indicated by the oxygen ages the turn over time suggests that the lower thermocline of the north atlantic would be suboxic but at present this is compensated by the import of water from the well ventilated south atlantic the turn over time approach itself is independent of details of ocean transport pathways instead the geographical location of the omz is to first order determined by i the patterns of upwelling either through ekman or equatorial divergence ii the regions of general sluggish horizontal transport at the eastern boundaries and iii to a lesser extent to regions with high productivity as indicated through ocean colour data

wave driven flow over shallow reefs long term 1 month observations of waves and currents over a natural reef are presented which show a strong correlation between offshore rms incident wave height and cross reef currents at subtidal frequencies the energy spectrum of the cross reef currents shows a significant peak at twice the semidiurnal tidal frequency while the spectrum of sea surface elevation over the reef flat shows no corresponding peak furthermore experimental results reported by gourlay 1993 show setup over the reef occurs in the absence of a beach and the cross reef transport decreases with an increase in the sea surface slope across the reef flat due to an increase in setup at the top of the reef face analytic solutions for flow forced by wave breaking over an idealized reef explain the above features of cross reef flows in the absence of a beach through the surf zone on the reef face the cross reef gradient in the radiation stress due to wave breaking is partitioned between balancing an offshore pressure gradient associated with setup over the reef and forcing a mean flow across the reef over the reef flat where the depth is constant there is no forcing due to wave breaking and the flow is driven by a pressure gradient which results from the setup through the surf zone the magnitude of the setup through the surf zone is such that the transport across the reef flat matches the transport through the surf zone which is forced by the gradient in the radiation stress solutions are presented for general reef geometry defined by the reef width and slope of the seaward reef face and incident wave forcing defined by the depth at the breakpoint and the depth of water over the reef as the depth over the reef goes to zero the solutions converge to the plane beach solutions described by longuet higgins and stewart 1964 wave setup is maximized and the cross reef transport is zero in other cases the relative magnitudes of the setup and the cross reef transport depend on the geometry of the reef and the incident wave forcing

wave breaking hydrodynamics within coral reef systems and the effect of changing relative sea level this paper considers the hydrodynamics of wave driven flow across a coral reef and the resultant flushing of its lagoon current depth coefficients are introduced that describe the fractional change of across reef and lagoonal current with change in the relative local sea level i e the depth of water over the reef flat the coefficients are derived from an analytical hydrodynamic model and compared with data from two reefs the first is ningaloo reef in northwest australia which is a typical barrier reef with a narrow coastal lagoon and the second is kaneohe bay in oahu hawaii where the reef is both unusually deep and wide the current depth coefficients are shown to be sensitive to the form of the frictional law on the reef flat and can be deduced from measurements of the astronomical tidal currents in the lagoon both quadratic and linear friction laws are considered for the reef flat and good agreement obtained with a linear law based on the high frequency motion due to surface gravity waves

wave generated flow on coral reefs an analysis for two dimensional horizontal reef tops with steep faces waves breaking on the seaward rim of a coral reef generate a flow of water from the exposed side of the reef to the sheltered side and or to either channels through the reef rim or lower sections of the latter this wave generated flow is driven by the water surface gradient resulting from the wave set up created by the breaking waves this paper reviews previous approaches to modelling wave generated flows across coral reefs and discusses the influence of reef morphology and roughness upon these flows laboratory measurements upon a two dimensional horizontal reef platform with a steep reef face provide the basis for extending a previous theoretical analysis for wave set up on a reef in the absence of a flow gourlay m r 1996b wave set up on coral reefs 2 set up on reefs with various profiles coastal engineering 28 1755 to include the interaction between a unidirectional flow and the wave set up the laboratory model results are then used to demonstrate that there are two basic reef top flow regimes reef top control and reef rim control using open channel flow theory analytical relationships are derived for the reef top current velocity in terms of the offreef wave conditions the reef top water depth and the physical characteristics of the reef top topography the wave set up and wave generated flow relationships are found to predict experimental values with reasonable accuracy in most cases the analytical relationships are used to investigate wave generated flows into a boat harbour channel on heron reef in the southern great barrier reef c 2005 elsevier b v all rights reserved

mass transfer limitation of nutrient uptake by a wave dominated reef flat community maximum rates of phosphate nitrate and ammonium uptake by a reef flat community were estimated from rates of frictional dissipation that were calculated from the attenuation of waves propagating over the kaneohe bay barrier reef flat time averaged flow speeds across the entire study area ranged from 0 08 to 0 22 m s 21 observed decreases in wave energy fluxes and near bottom orbital velocities gave a mean estimate for the bottom friction coefficient cf of 0 22 6 0 03 friction coefficients were used to estimate nutrient mass transfer coefficients of 5 9md 21 for phosphate and 9 16 m d 21 for ammonium and nitrate wave heights offshore of kaneohe bay were also used to estimate an annual phosphate mass transfer coefficient of 8 6 2md that was determined from measured changes in phosphate concentrations across the reef flat we conclude that rates of phosphate uptake by the kaneohe bay barrier reef flat community are occurring near the limits of mass transfer net primary production is a major pathway by which mass and energy flow into coral reef ecosystems the uptake of dissolved nutrients is often the rate limiting step for net pri mary production in marine ecosystems thus a knowledge of the kinetics of nutrient uptake by coral reef communities is necessary for assessing how nutrient loading rates change in response to natural or anthropogenic increases in nutrient concentrations bilger and atkinson 1992 proposed that nutrient uptake by shallow reef communities was limited by mass transfer the physical transfer of nutrients across con centration boundary layers covering the surfaces of reef au totrophs these authors used mass transfer correlations for rough surfaces taken from the engineering literature to cor relate maximum rates of nutrient uptake with the frictional characteristics of experimental reef communities subse quent studies demonstrated the ability of such mass transfer correlations to predict nutrient uptake kinetics for experi mental reef communities within closed recirculating flumes atkinson and bilger 1992 bilger and atkinson 1995 thomas and atkinson 1997 and a large experimental me socosm atkinson et al 2001 the results of these studies made it clear that shallow water reef communities are ca pable of taking up nutrients from the water column at rates that are limited by mass transfer however it had not yet been demonstrated whether in situ rates of nutrient uptake

the greenland ice sheet project 2 depth age scale methods and results the greenland ice sheet project 2 gisp2 depth age scale is presented based on a multiparameter continuous count approach to a depth of 2800 m using a systematic combination of parameters that have never been used to this extent before the ice at 2800 m is dated at 110 000 years b p with an estimated error ranging from 1 to 10 in the top 2500 m of the core and averaging 20 between 2500 and 2800 m parameters used to date the core include visual stratigraphy oxygen isotopic ratios of the ice electrical conductivity measurements laser light scattering from dust volcanic signals and major ion chemistry gisp2 ages for major climatic events agree with independent ages based on varve chronologies calibrated radiocarbon dates and other techniques within the combined uncertainties good agreement also is obtained with greenland ice core project ice core dates and with the specmap marine timescale after correlation through the 18 o of o 2 although the core is deformed below 2800 m and the continuity of the record is unclear we attempted to date this section of the core on the basis of the laser light scattering of dust in the ice

coupled sea surface temperature seawater δ18o reconstructions in the arabian sea at the millennial scale for the last 35 ka two sediment cores from the western 905 10 46 9 n 51 56 4 e water depth 1586 m and eastern sk17 15 15 n 72 58 e water depth 840 m arabian sea were used to study past sea surface temperatures sst and seawater 18o 18ow variations for the past 35 ka we used coupled mg ca 18o calcite variability in two planktonic foraminiferal species globigerinoides ruber which thrives throughout the year and globigerina bulloides which occurs mainly when surface waters contain high nutrients during upwelling or convective mixing ssts in both areas based on mg ca in g ruber were 3 to 4 c lower during the last glacial maximum lgm 21 ka than today and the holocene period the sst records based on g bulloides also indicate general cooling down to 18 c in both areas ssts in the western arabian sea based on g bulloides were always lower than those based on g ruber indicating the presence of strong seasonal temperature contrast during the holocene and lgm we interpret the consistent presence of this seasonal temperature contrast to reflect a combination of seasonal summer upwelling sw monsoon and winter convective mixing ne monsoon in the western arabian sea in the eastern arabian sea g bulloides based ssts were slightly lower about 1 c than g ruber based ssts during the holocene indicating the almost absence of a seasonal temperature gradient similar to today however a large seasonal temperature contrast occurred during the lgm which favors the assumption that strong ne monsoon winds forced winter upwelling or convective mixing offshore goa sst and 18ow reconstructions reveal evidence of millennial scale cycles particularly in the eastern arabian sea here the stadial periods northern hemisphere cold periods such as younger dryas and heinrich events are marked by increasing ssts and salty sea surface conditions relative to those during the interstadial periods indeed the 18ow record shows evidence of low saline surface waters during interstadial periods indicating increased freshwater runoff from the western ghats as a consequence of enhanced sw monsoon intensity

paleoproductivity changes in the upwelling system of socotra somali basin nw indian ocean during the last 72 000years evidence from biological signatures abstract high resolution analyses of foraminiferal and radiolarian assemblages were performed on core md 85682 10 53 5n 52 23 e 3092 m depth 7 23 m length located close to the socotra island beneath the 10 n gyre of the upwelling area of the somali basin nw indian ocean in order to reconstruct the paleoproductivity changes during the last 72 kyr correspondence and cluster analyses of combined planktonic foraminiferal and radiolarian quantitative data show that the distribution pattern of the microfauna is partly controlled by temperature and hydrographic structures and their interrelations on water mass fertility the continuous occurrence of high abundances of foraminiferal species well known in fertile areas such as globigerinita glutinata globigerina bulloides and globigerina falconensis as well as radiolarian species characteristic of upwelling systems testifies to a sustained activity of the upwelling during the last 72 kyr downcore evolution of these biological proxies suggests an increase in paleoproductivity during isotope stages 1 and 3 which reflects a stronger upwelling activity during these periods these observations are in agreement with the results previously obtained by geochemical markers such as biogenic barium phosphorus organic matter and also trace elements related to the organic matter and indicators of redox conditions vanadium samples from isotope stage 2 record a more complex biological and geochemical signature resulting from increased terrigenous input comparison between the biological signatures obtained both under the socotra 10 n and somali 5 n upwelling areas indicates higher productivity throughout the last 72 kyr record of the socotra upwelling system in both areas a similar evolution of biological proxies indicative of high fertility is observed during isotope stages 1 and 3 however minor differences in the biological and geochemical signatures are related to local conditions prevailing beneath the two gyres

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

rapid switch in monsoon wind induced surface hydrographic conditions of the eastern arabian sea during the last deglaciation abstract surface water hydrography in the arabian sea is primarily governed by the asian monsoon wind system changes in the composition of fossil planktic foraminiferal assemblages and sea surface temperatures sst in sediment core sk17 retrieved from offshore of central india are used to decipher past changes in sea surface hydrographic conditions linked mainly to the winter monsoon winds the planktic foraminiferal assemblage and the sst records indicate a rapid switch in sea surface hydrographic conditions around 17 5 ka bp marking the end of last glacial period the data show that intensified winter winds during 17 5 23 5 ka bp resulted in nutrient injection into surface waters and eutrophic conditions mainly through deep vertical mixing and or moderate upwelling and reduction in winter wind intensity caused stratification characterized by the high tropical sst since 17 5 ka bp the timing of the rapid switch in seawater conditions caused by a drop in strength of winter monsoon winds is coeval with the cold climate excursion in the northern hemisphere heinrich event 1 suggesting that the two areas are climatically linked

paleohydrographic changes in the somali basin 5 n upwelling and equatorial areas during the last 160 kyr based on correspondence analysis of foraminiferal and radiolarian assemblages this study documents the biological signatures impressed upon the sedimentary record underlying both the 5 n upwelling system of the somali current and the equatorial area of the somali basin out of the upwelling influence the evolution of these two distinct hydrographic systems is compared for the last 160 kyr correspondence and cluster analyses are performed on combined radiolarian and planktonic foraminiferal quantitative data in order to study the changes of the planktonic assemblages through time and space the upwelling radiolarian index uri is used as a productivity proxy the water temperature and hydrographic structure of the upper water masses appear to be the major factors controlling the distribution patterns of the fauna the relative abundances of three groups of foraminifera cold water form dextral n pachyderma mixed layer dwellers g trilobus g ruber g sacculifer g conglobatus and g glutinata and thermocline dwellers g menardii g tumida n dutertrei g crassaformis and p obliquiloculata follow distinct evolutionary patterns at the two sites during the last 160 kyr at the equatorial site core md 85668 downcore fluctuations in the relative abundances of the three groups are closely related to the glacial interglacial cyclicity and provide some insights into the interpretation of hydrographic changes the dominance of the mixed layer foraminifera at the transition intervals between isotope stages 6 5 and 2 1 combined with weak uri values is thought to reflect the reorganization of the oceanographic circulation these short term events with a duration of 5000 year could be related to the rapid inflow of oxygen depleted water through the indonesian straits as a result of sea level rise during deglaciation underneath the 5 n gyre core md 85674 the response to global climatic changes is overprinted by the regional effect of the somalian upwelling which has been persistent over the last 160 kyr

episodic circulation and exchange in a wave driven coral reef and lagoon system we examined the role of wave driven circulation relative to wind and buoyancy forcing in a coral reef lagoon system circulation measurements in paopao bay moorea french polynesia during austral summer show the importance of waves in driving flows over the reef crest through the lagoon and out the reef pass tides were comparatively weak due to proximity to amphidromic points and exhibited an unusual spring neap cycle where the major lunar tide modulated the major solar tide and the overall tidal phase stayed approximately constant wind had only a secondary effect compared to surface waves a simple fluid mass balance indicated rapid flushing of the shallow back reef and export through the reef pass and a reef capture zone width of 2 3 km the reef pass circulation dynamics exhibited two layer baroclinic exchange flow when waves were small which was suppressed during large wave events the unusually weak tidal forcing provided an opportunity to more closely investigate wave driven circulation dynamics as expected theoretically there was a wave driven setup of the free surface across the shallow lagoon which drove a highly frictional flow evident by a large drag coefficient cp 0 1 diverging from extant theory the observed setup varied strongly with significant wave height and period overall the circulation and exchange between this coral reef system and the adjacent open ocean were largely determined by episodic remote forcing events and differed significantly from periodic tidal exchange mechanisms

a high resolution record of late quaternary upwelling along the oman margin arabian sea based on planktonic foraminifera planktonic foraminiferal abundances fluxes test sizes and coiling properties are influenced in various ways by the southwest monsoon winds and associated upwelling in the western arabian sea to determine the short term changes in the southwest monsoon we have carried out a high resolution time series analysis of three upwelling indices total flux of planktonic foraminiferal tests and flux and relative abundance of the planktonic foraminiferal species globigerina bulloides from ocean drilling program odp site 723a oman margin western arabian sea spanning the last 19 kyr in addition we have determined the relationships between upwelling intensity and the relative abundance fluxes and shell concentrations of various planktonic foraminiferal species upwelling indices suggest that from 19 to 16 ka 22 to 18 2 cal kyr b p the sw monsoon was relatively strong compared to the period 15 8 to 12 5 ka 17 8 to 13 8 cal kyr b p the intensification of the sw monsoon took place at 12 ka 13 1 cal kyr b p and reached a peak between 10 and 5 ka 10 6 and 4 8 cal kyr b p the high resolution data further demonstrate that the sw monsoon has started weakening from 5 ka 4 8 cal kyr b p and the weakest phase was in place at 3 5 ka 3 cal kyr b p which coincides with evidence of an arid climate in western tibet fluxes and shell concentrations of many of the planktonic foraminiferal species increased between 12 and 5 ka in response to the intensification of the sw monsoon winds after the last glacial period globigerina bulloides shows a fivefold to tenfold increase in flux during this period of intense upwelling the other species whose fluxes are influenced by this upwelling change are in order from strongest to weakest response globigerinita glutinata globigerinoides ruber neogloboquadrina dutertrei globigerinella aequilateralis globigerina falconensis and globigerinoides sacculifer the relative abundances of g bulloides and g ruber increased during intense upwelling whereas the relative abundances of g glutinata n dutertrei g falconensis and g sacculifer did not increase during this period which might be due to differences in the productivity of various species in relation to upwelling change therefore the fluxes and shell concentrations provide better and more reliable information about the changes in the monsoon system in the arabian sea than relative abundance data

seasonal circulation and temperature variability near the north west cape of australia 1 the circulation and temperature variability on the inner shelf near the north west cape of australia off ningaloo reef was investigated using field data obtained from two moorings deployed from 2004 to 2009 the results revealed that alongshore currents on the inner shelf were on average only weakly influenced by the offshore poleward southward leeuwin current flow i e monthly averaged alongshore current velocities were 0 1 m s 1 or less the presence of a consistent summer time wind driven equatorward northward counter flow on the inner shelf referred to in the literature as the ningaloo current was not observed instead the shelf waters were strongly influenced year round by episodic subtidal current fluctuations time scale 1 2 weeks that were driven by local wind forcing analysis of the current profiles showed that periods of strong equatorward winds were able to overcome the dominant poleward pressure gradient in the region leading to upwelling on the inner shelf contrary to prior belief these events were not limited to summer periods the forcing provided by these periodic wind events and the associated alongshore flows can explain much of the observed temperature variability with timescales 1 month that influences ningaloo reef

numerical investigation of hydraulic fracture network propagation in naturally fractured shale formations abstract hydraulic fracture network hfn propagation in naturally fractured shale formations is investigated numerically using a 3d complex fracturing model based on the discrete element method to account for the plastic deformation behavior of shales the drucker prager plasticity model is incorporated into the fracturing model parametric studies are then conducted for different young s moduli horizontal differential stresses natural fracture nf properties injection rates and number and spacing of perforation clusters numerical results show that horizontal differential stress primarily determines the generation of a complex hfn the plastic deformation of shale can reduce the stimulated reservoir volume this is more obvious with young s modulus of less than 20 gpa in addition a higher injection rate could largely increase the fracture complexity index fci moreover increasing perforation cluster numbers per fracturing stage is beneficial for increasing the fci but it also increases the potential merging of neighboring fractures which may lead to non uniform development of hfn in far wellbore regions to achieve uniform development of hfn within a fracturing stage the distribution of nfs should be fully considered the results presented here may provide improved understanding of hfn generation and are favorable for optimizing fracturing treatment designs for shale formations

wave spectral energy variability in the northeast pacific 1 the dominant characteristics of wave energy variability in the eastern north pacific are described from noaa national data buoy center ndbc buoy data collected from 1981 to 2003 ten buoys at distributed locations were selected for comparison based on record duration and data continuity long period lp t 12 s intermediate period 6 t 12 s and short period t 6 s wave spectral energy components are considered separately empirical orthogonal function eof analyses of monthly wave energy anomalies reveal that all three wave energy components exhibit similar patterns of spatial variability the dominant mode represents coherent heightened or diminished wave energy along the west coast from alaska to southern california as indicated by composites of the 700 hpa height field the second eof mode reveals a distinct el nino southern oscillation enso associated spatial distribution of wave energy which occurs when the north pacific storm track is extended unusually far south or has receded to the north monthly means and principal components pcs of wave energy levels indicate that the 1997 1998 el nino winter had the highest basin wide wave energy within this record substantially higher than the 1982 1983 el nino an increasing trend in the dominant pc of lp wave energy suggests that storminess has increased in the northeast pacific since 1980 this trend is emphasized at central eastern north pacific locations patterns of storminess variability are consistent with increasing activity in the central north pacific as well as the tendency for more extreme waves in the south during el nino episodes and in the north during la nina

observations of spatial flow patterns at the coral colony scale on a shallow reef flat 1 although small scale spatial flow variability can affect both larger scale circulation patterns and biological processes on coral reefs there are few direct measurements of spatial flow patterns across horizontal scales 1 had similar spatial patterns to wakes while higher frequency variations 0 05 0 1 hz kc 1 had no observable spatial structure on the reef flat both drag and inertial forces exerted by coral colonies could have significant effects on flow but within different frequency ranges drag dominates for low frequency flow variations and inertial forces dominate for higher frequency variations including the wave band our scaling analyses suggest that spatial flow patterns at colony and patch scales could have important implications for both physical and biological processes at larger reef scales through their effects on forces exerted on the flow turbulent mixing and dispersion

precession phasing offset between indian summer monsoon and arabian sea productivity linked to changes in atlantic overturning circulation results from transient climate modeling experiments indicate an in phase relationship between insolation forcing and indian summer monsoonal precipitation this is in contrast to high resolution radioisotopically dated speleothem oxygen isotope 18o records of china which showed that east asian monsoon maxima lag northern hemisphere peak summer insolation by 2 700 years while an approximately 8 000 year time lag was derived from late pleistocene records of arabian sea sediments here we evaluate the precession phase of the arabian sea signal by comparing a new high resolution productivity and oxygen minimum zone omz intensity record from the arabian sea over the past 450 000 years with the results of a transient climate modeling experiment that includes glacial bound ice volume variations the well established tuning technique between radioisotopically dated north atlantic cold events and the occurrence of deep dwelling planktonic foraminifera in the arabian sea for the last glacial cycle was used to extend the arabian sea chronology independent of orbital tuning cross spectral analysis over the last 224 000 years reveals that arabian sea productivity maxima lag precession minima by 6 900 200 years i e in close agreement with previous reconstructions also our climate modeling simulations are in accord with previous studies indicating an in phase relationship between precession minima and maximum summer monsoon intensity we argue that the summer monsoon is most likely not the main driver of changes in arabian sea biological productivity and omz intensity at the precession frequency band but that changes in the intensity of the atlantic meridional overturning circulation amoc have played the prominent role in controlling the nutrient delivery into the euphotic layer of the northern indian ocean and hence the amount of primary productivity and intensity of the oxygen minimum zone in the arabian sea such a mechanism explains the large precession related time lag between minimum precession and maximum productivity and omz conditions in the arabian sea since intensified amoc occurred during precession maxima

prediction and analysis of the stimulated reservoir volume for shale gas reservoirs based on rock failure mechanism the ultra low permeability shale gas reservoir has a lot of well developed natural fractures it has been proven that hydraulic fracture growth pattern is usually a complex network fracture rather than conventional single planar fractures by micro seismic monitoring which can be explained as the shear and tensile failure of natural fractures or creation of new cracks due to the increase in reservoir pore pressure caused by fluid injection during the process of hydraulic fracturing in order to simulate the network fracture growth a mathematical model was established based on full tensor permeability continuum method and fluid mass conservation equation firstly the governing equation of fluid diffusivity based on permeability tensor was solved to obtain the reservoir pressure distribution then mohr coulomb shear failure criterion and tensile failure criterion were used to decide whether the rock failed or not in any block on the basis of the calculated reservoir pressure the grid block permeability was modified according to the change of fracture aperture once any type of rock failure criterion was met within a grid block finally the stimulated reservoir volume srv zone was represented by an enhancement permeability zone after calibrating the numerical solution of the model with the field micro seismic information a sensitivity study was performed to analyze the effects of some factors including initial reservoir pressure injection fluid volume natural fracture azimuth angle and horizontal stress difference on the srv shape size bandwidth and length the results show that the srv size increases with the increasing initial pore reservoir and injection fluid volume but decreases with the increase in the horizontal principal stress difference and natural fracture azimuth angle the srv shape is always similar for different initial pore reservoir and injection fluid volume the srv is observed to become shorter in length and wider in bandwidth with the decrease in natural fracture azimuth angle and horizontal principal stress difference

the island scale internal wave climate of moorea french polynesia 1 analysis of five year records of temperatures and currents collected at moorea reveal strong internal wave activity at predominantly semi diurnal frequencies impacting reef slopes at depths 30 m around the entire island temperature changes of 1 5 c to 3 c are accompanied by surges of upward and onshore flow and vertical shear in onshore currents superimposed on annual temperature changes of approximately 3 c internal wave activity is high from oct may and markedly lower from jun sep the offshore pycnocline is broadly distributed with continuous stratification to at least 500 m depth and a subsurface fluorescence maximum above the strong nutricline at approximately 200 m minimum buoyancy periods range from 4 8 to 6 min with the maximum density gradient occurring at 50 to 60 m depth in summer and deepening to approximately 150 to 200 m in winter the bottom slope angle around all of moorea is super critical relative to the vertical stratification angle suggesting that energy propagating into shallow water is only a portion of total incident internal wave energy vertical gradient richardson numbers indicate dominance by density stability relative to current shear with relatively limited diapycnal mixing coherence and lagged cross correlation of semi diurnal temperature variation indicate complex patterns of inter site arrival of internal waves and no clear coherence or lagged correlation relationships among island sides semi diurnal and high frequency internal wave packets likely arrive on moorea from a combination of local and distant sources and may have important impacts for nutrient and particle fluxes in deep reef environments

sea surface temperatures and the history of monsoon upwelling in the northwest arabian sea during the last 500 000 years abstract arabian sea sediments record changes in the upwelling system off arabia which is driven by the monsoon circulation system over the nw indian ocean in accordance with climate models and differing from other large upwelling areas of the tropical ocean a 500 000 yr record of productivity at odp site 723 shows consistently stronger upwelling during interglaciations than during glaciations sea surface temperatures ssts reconstructed from the alkenone unsaturation index uk 37 are high up to 27 c during interglaciations and low 22 24 c during glaciations indicating a glacial interglacial temperature change of 3 c in spite of the dampening effect of enhanced or weakened upwelling the increased productivity is attributed to stronger monsoon winds during interglacial times relative to glacial times whereas the difference in ssts must be unrelated to upwelling and to the summer monsoon intensity the winter ne monsoon was more effective in cooling the arabian sea during glaciations then it is now

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

numerical modeling of an estuary a comprehensive skill assessment i numerical simulations of the hudson river estuary using a terrain following three dimensional model regional ocean modeling system roms are compared with an extensive set of time series and spatially resolved measurements over a 43 day period with large variations in tidal forcing and river discharge the model is particularly effective at reproducing the observed temporal variations in both the salinity and current structure including tidal spring neap and river discharge induced variability large observed variations in stratification between neap and spring tides are captured qualitatively and quantitatively by the model the observed structure and variations of the longitudinal salinity gradient are also well reproduced the most notable discrepancy between the model and the data is in the vertical salinity structure while the surface to bottom salinity difference is well reproduced the stratification in the model tends to extend all the way to the water surface whereas the observations indicate a distinct pycnocline and a surface mixed layer because the southern boundary condition is located near the mouth the estuary the salinity within the domain is particularly sensitive to the specification of salinity at the boundary a boundary condition for the horizontal salinity gradient based on the local value of salinity is developed to incorporate physical processes beyond the open boundary not resolved by the model model results are sensitive to the specification of the bottom roughness length and vertical stability functions insofar as they influence the intensity of vertical mixing the results only varied slightly between different turbulence closure methods of k e k and k kl

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

microfossil evidence for changing salinity patterns in the bay of bengal over the last 20 000 years the monsson climate characterizing the northern indian ocean produces salinity gradients that are large compared with those in other open ocean areas these gradients are substantially independent of thermal and other ecologically important gradients this situation makes it possible not only to isolate the effect of salinity on sea bed distribution patterns of planktonic foraminifera but also to investigate past salinity changes along a north south transect of piston cores in the bay of bengal analysis of 152 surface sediment samples reveals that at least three factors other than salinity are important in controlling foraminiferal distribution sea bed dissolution surface productivity and surface temperature of these dissolution is the most important therefore in order to reconstruct past salinity patterns in the bay of bengal faunal indices need to be developed that isolate the effect of salinity we have developed two independent approaches the first uses ternary diagrams of the three dominant dissolution resistant species globoquadrina dutertrei globorotalia menardii pulleniatina obliquiloculata high values of g dutertrei are associated with low surface salinities the second approach uses dissolution buffered salinity transfer functions based on the total foraminiferal fauna in the 152 surface samples from the northern indian ocean applied to downcore samples these methods show the same basic historical pattern of salinity variation which is in turn consistent with independent inferences based on preliminary oxygen isotope data duplessy 1980 historical changes in the bay of bengal salinity are reconstructed along a north south transect of seven cores at 90 e the stratigraphy of the transect is controlled by oxygen isotope profiles that are similar to the generalized patterns observed in other areas over the past 20 000 yr salinity gradients are reconstructed for three time intervals 1 the last glacial maximum lgm 2 the mid termination mt and 3 the holocene during the lgm interval salinity was highger in the bay of bengal particularly in the north thus reducing the north south salinity gradient during the mt the middle of the transition from glacial to interglacial global climatic regimes northern bay of bengal surface salinity was considerably reduced while salinity to the south was generally similar to today thus the salinity gradient between 10 n and 15 n was considerably steeper than today in contrast the holocene gradient was approximately the same as the modern gradient with absolute values along the transect being slightly but uniformly higher these changes in the pattern of salinity are explained in terms of changes in the local patterns of precipitation and river run off during the lgm the salinity pattern probably results from decreased precipitation and decreased run off by the ganges brahmaputra river system during the mt decreased salinity in the northern bay of bengal is caused by increased precipitation and run off rather than by the influx of glacial meltwater the steeper mt salinity gradient in the central bay of bengal suggests increased eastward advection of equatorial surface waters by a southwest monsoon current somewhat more vigorous than today these patterns can be correlated with faunal evidence from the western arabian sea that suggest decreased upwelling during the lgm and increased upwelling during the mt this coupling of events may be associated with changes in the pattern or intensity of circulation during the southwest monsoon decreased intensity at the lgm 18 000 b p and increased intensity at the mt 10 500 to 12 500 b p