mangrove forest evolution in a sediment rich estuarine system opportunists or agents of geomorphic change the majority of the world s mangrove forests occur on mostly mineral sediments of fluvial origin two perspectives exist on the biogeomorphic development of these forests i e that mangroves are opportunistic with forest development primarily driven by physical processes or alternatively that biophysical feedbacks strongly influence sedimentation and resulting geomorphology on the firth of thames coast new zealand we evaluate these two possible scenarios for sediment accumulation and forest development using high resolution sedimentary records and a detailed chronology of mangrove forest avicennia marina development since the 1950s cores were collected along a shore normal transect of known elevation relative to mean sea level msl activities for lead 210 pb 210 caesium 137 cs 137 and beryllium 7 be 7 and sediment properties were analysed with pb 210 sediment accumulation rates sars compensated for deep subsidence similar to 8 mm yr 1 used as a proxy for elevation gain at least four phases of forest development since the 1950s are recognized an old growth forest developed by the late 1970s with more recent seaward forest expansion thereafter excess 210pb profiles from the old growth forest exhibit relatively low sars near the top 7 12 mm yr 1 and bottom 10 22 mm yr 1 of cores separated by an interval of higher sars 33 100 mm yr 1 a general trend of increasing sar over time characterizes the recent forest biogeomorphic evolution of the system is more complex than simple mudflat accretion progradation and mangrove forest expansion surface elevation gain in the old growth forest displays an asymptotic trajectory with a secondary depocentre developing on the seaward mudflat from the mid 1970s two to ten fold increases in 210pb sars are unambiguously large and occurred years to decades before seedling recruitment demonstrating that mangroves do not measurably enhance sedimentation over annual to decadal timescales this suggests that mangrove forest development is largely dependent on physical processes with forests occupying mudflats once they reach a suitable elevation in the intertidal copyright c 2015 john wiley sons ltd

mechanisms limiting the northward extent of the northern summer monsoons over north america asia and africa abstract mechanisms determining the poleward extent of summer monsoon convergence zones for north america asia and africa are examined in an intermediate atmospheric model coupled with a simple land model and a mixed layer ocean observations show that thermodynamical factors associated with the net heat flux into the atmospheric column provide favorable conditions for the monsoon convergence zone to extend farther poleward than actually occurs to understand the discrepancy a series of experiments are designed to test the importance of mechanisms previously examined in the south american case by the authors namely soil moisture ventilation and the interactive rodwell hoskins mechanism the latter refers to the interaction between baroclinic rossby wave dynamics and convective heating in north america experiments suggest that ventilation by both temperature and moisture advection is a leading effect the interactive rodwell hoskins mechanism tends to favor east coast rainfall and west coast dryne

relationships between heavy metals distribution and organic matter cycling in mangrove sediments conception bay new caledonia mangroves of new caledonia act as a buffer between a lagoon of more than 20 000 km2 and the island which suffers intense processes of erosion resulting from urbanization and natural resources exploitation this preliminary study aims at determining how heavy metals are distributed in mangrove sediments and pore waters in relationship with their organic content to reach our goal a series of 50 cm deep cores were collected in the mangrove of conception bay the various coring sites are representative of live forests avicennia marina rhizophora stylosa dead forest and intertidal unvegetated area the ranges of concentrations in sediments were the following mol g 1 cu 0 08 to 0 51 co 0 01 to 0 38 ni 0 03 to 3 55 cr 0 36 to 3 11 zn 0 68 to 2 36 mn 1 13 to 5 0 and fe 22 64 to 721 69 heavy metals distribution within sediments and pore water appear to result from diagenetic processes linked to om decomposition beneath the dead avicennia forest and in the unvegetated sediments the higher the organic content the higher the metal concentration in the solid phase beneath living mangrove stands despite a higher organic content as well as higher sulphur content heavy metals concentrations were not higher than those measured in the other sampling sites beneath these forests redox conditions were mainly controlled by the length of waterlogging and the activity of root system we suggest that because of the specificity of the avicennia root system and its position in the intertidal zone heavy metals are more bioavailable and potentially more mobile than beneath rhizophora stand

topographically controlled fronts in the ocean and their biological influence headlands islands and reefs generate complex three dimensional secondary flows that result in physical and biological fronts mixing and diffusion processes near these reefs and headlands are quite different from these processes in the open sea and classical advection diffusion models that were developed for the open sea are not valid near shore topographically generated fronts affect the distribution of sediments and they aggregate waterborne eggs larvae and plankton this aggregation influences the distribution and density of benthic assemblages and of pelagic secondary and tertiary predators

environmental geochemistry of core sediments from serthalaikkadu creek east coast of india the serthalaikkadu creek in muthupet mangroves region is the only e w trending coastal strip in the se coast of india and it also acts as a barrier to natural disasters natural anthropogenic signals and accumulation of elements were studied by collecting sediments from two cores textural parameters were studied in detail and carbonates caco3 organic carbon oc major si al fe na k ca mg p and trace elements mn cr cu ni co pb zn were determined textural parameters caco3 oc and al normalized pattern of elements indicate depositional events in core samples that can be directly related to natural events during the last decade the calculated enrichment anthropogenic factors and comparison of data indicate that the observed trace metals especially pb co are enriched mainly due to the anthropogenic activities in the land as well as in the coastal zone palk strait

reduced atlantic storminess during last glacial maximum evidence from a coupled climate model the last glacial maximum lgm 21 000 yr before present was the time of maximum land ice extent during the last ice age a recent simulation of the lgm climate by a state of the art fully coupled global climate model is shown to exhibit strong steady atmospheric jets and weak transient eddy activity in the atlantic sector compared to today s climate in contrast previous work based on uncoupled atmospheric model simulations has shown that the lgm jets and eddy activity in the atlantic sector are similar to those observed today with the main difference being a northeastward extension of their maxima the coupled model simulation is shown to agree more with paleoclimate proxy records and thus is taken as the more reliable representation of lgm climate the existence of this altered atmospheric circulation state during lgm in the model has implications for understanding the stability of glacial climates for the possibility of multiple atmospheric circulation regimes and for the interpretation of paleoclimate proxy records

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

orographic effects of the tibetan plateau on the east asian summer monsoon an energetic perspective this paper investigates the dynamical processes through which the tibetan plateau tp influences the east asian summer monsoon easm within the framework of the moist static energy mse budget using both observations and atmospheric general circulation model agcm simulations the focus is on the most prominent feature of the easm the so called meiyu baiu mb which is characterized by a well defined southwest northeast elongated quasi stationary rainfall band spanning from eastern china to japan and into the northwestern pacific ocean between mid june and mid july observational analyses of the mse budget of the mb front indicate that horizontal advection of moist enthalpy and primarily of dry enthalpy sustains the front in a region of otherwise negative net energy input into the atmospheric column a decomposition of the horizontal dry enthalpy advection into mean transient and stationary eddy fluxes identifies the longitudinal thermal gradient due to zonal asymmetries and the meridional stationary eddy velocity as the most influential factors determining the pattern of horizontal moist enthalpy advection numerical simulations in which the tp is either retained or removed show that the tp influences the stationary enthalpy flux and hence the mb front primarily by changing the meridional stationary eddy velocity with reinforced southerly wind over the mb region and northerly wind to its north changes in the longitudinal thermal gradient are mainly confined to the near downstream of the tp with the resulting changes in zonal warm air advection having a lesser impact on the rainfall in the extended mb region

influence of glacial ice sheets on the atlantic meridional overturning circulation through surface wind change coupled modeling studies have recently shown that the existence of the glacial ice sheets intensifies the atlantic meridional overturning circulation amoc however most models show a strong amoc in their simulations of the last glacial maximum lgm which is biased compared to reconstructions that indicate both a weaker and stronger amoc during the lgm therefore a detailed investigation of the mechanism behind this intensification of the amoc is important for a better understanding of the glacial climate and the lgm amoc here various numerical simulations are conducted to focus on the effect of wind changes due to glacial ice sheets on the amoc and the crucial region where the wind modifies the amoc first from atmospheric general circulation model experiments the effect of glacial ice sheets on the surface wind is evaluated second from ocean general circulation model experiments the influence of the wind stress change on the amoc is evaluated by applying wind stress anomalies regionally or at different magnitudes as a boundary condition these experiments demonstrate that glacial ice sheets intensify the amoc through an increase in the wind stress at the north atlantic mid latitudes which is induced by the north american ice sheet this intensification of the amoc is caused by the increased oceanic horizontal and vertical transport of salt while the change in sea ice transport has an opposite though minor effect experiments further show that the eurasian ice sheet intensifies the amoc by directly affecting the deep water formation in the norwegian sea

the mechanisms that determine the response of the northern hemisphere s stationary waves to north american ice sheets abstractstationary waves describe the persistent meanders in the west east flow of the extratropical atmosphere here changes in stationary waves caused by ice sheets over north america are examin

maintenance of northern summer stationary waves in a gcm abstract the maintenance of northern summer stationary waves is studied with data from a 15 year integration of the general circulation model gcm experiment performed at the geophysical fluid dynamics laboratory the model has relatively high resolution rhomboidal 30 wavenumbers 9 vertical levels and simulates the summertime stationary waves reasonably well a steady linear baroclinic model is used to understand the various forcing mechanisms for the northern summer stationary waves the linear model response to global diabatic heating is found to play a dominant role in maintaining the summertime stationary waves in the gcm especially in the subtropics this response to diabatic heating shows a baroclinic structure in the vertical with a node at about 0 5 on the other hand stationary nonlinear interaction terms are found to be largely responsible for the extratropical equivalent barotropic stationary wave features it is hypothesized that this nonlinear interaction is a result of the therm

rain driven by receding ice sheets as a cause of past climate change 1 the younger dryas cold period which interrupted the transition from the last ice age to modern conditions in greenland is one of the most dramatic incidents of abrupt climate change reconstructed from paleoclimate proxy records changes in the atlantic ocean overturning circulation in response to freshwater fluxes from melting ice are frequently invoked to explain this and other past climate changes here we propose an alternative mechanism in which the receding glacial ice sheets cause the atmospheric circulation to enter a regime with greater net precipitation in the north atlantic region this leads to a significant reduction in ocean overturning circulation causing an increase in sea ice extent and hence colder temperatures positive feedbacks associated with sea ice amplify the cooling we support the proposed mechanism with the results of a state of the art global climate model our results suggest that the atmospheric precipitation response to receding glacial ice sheets could have contributed to the younger dryas cooling as well as to other past climate changes involving the ocean overturning circulation

tropical pacific response to continental ice sheet topography the last glacial maximum was marked by maximum land ice extent and lowest greenhouse gases concentration during the last ice age we explore the impact of glacial continental ice sheet topography on the large scale tropical ocean atmosphere climate in particular the tropical pacific in an intermediate complexity coupled model increasing the thickness of continental ice sheets causes a southward displaced pacific intertropical convergence zone itcz and a strengthening weakening of northern southern hemisphere winter hadley cell the equatorial zonal sea surface temperature gradient weakened with an increased continental ice sheets thickness the reduction being caused by cooling in the western equatorial pacific and warming in the eastern equatorial pacific the evolution of the tropical climate with changing ice thickness has distinct quasi linear and nonlinear parts while the linear part is a direct response to the ice topographic changes the nonlinear part was a result of the tropical thermocline adjustment our analysis of a fully coupled transient deglacial simulation strongly indicates the dominant role of ice sheet topography in determining the deglacial evolution of the simulated pacific climate the thickness of continental ice sheet separate from ice albedo effect has significant impact on the tropical ocean atmosphere climate in particular with the meridional displacement in the pacific itcz the altered circulation states seen in the model may aid understanding of the relationship between tropical and high latitude climate records in glacial interglacial cycles

review of methods to measure short time scale sediment accumulation this review paper aims at providing a list of methods available to measure sediment accumulation in underwater or intertidal environments over short term periods in the order of hours to months at the most both in situ and under laboratory conditions methods are classified based on two criteria a whether they measure sediment accumulation or sediment elevation change and b whether they allow continuous or discontinuous measurements the main characteristics of each method are outlined along with its vertical resolution its accuracy its temporal resolution its spatial coverage capacity and an indication of its relative cost typical examples of applications are also provided the purpose of this review is to be a starting point for readers who need an overview of existing techniques that measure short term sediment accumulation in order to guide and facilitate for instance the selection of an appropriate technique for a given application with set requirements

role of seasonal transitions and westerly jets in east asian paleoclimate abstract the summer rainfall climate of east asia underwent large and abrupt changes during past climates in response to precessional forcing glacial interglacial cycles as well as abrupt changes to the north atlantic during the last glacial however current interpretations of said changes are typically formulated in terms of modulation of summer monsoon intensity and do not account for the known complexity in the seasonal evolution of east asian rainfall which exhibits sharp transition from the spring regime to the meiyu and then again from the meiyu to the summer regime we explore the interpretation that east asian rainfall climate undergoes a modulation of its seasonality during said paleoclimate changes following previous suggestions we focus on role of the westerly jet over asia namely that its latitude relative to tibet is critical in determining the stepwise transitions in east asian rainfall seasons in support of this linkage we show from observational data that the interannual co variation of june july august rainfall and upper tropospheric zonal winds show properties consistent with an altered timing of the transition to the meiyu summer and with more northward shifted westerlies for earlier transitions we similarly suggest that east asian paleoclimate changes resulted from an altered timing in the northward evolution of the jet and hence the seasonal transitions in particular the transition of the jet from south of the plateau to the north that determines the seasonal transition from spring rains to the meiyu in an extreme scenario which we speculate the climate system tended towards during stadial cold phases of d o stadials and periods of low northern hemisphere summer insolation the jet does not jump north of the plateau essentially keeping east asia in prolonged spring conditions we argue that this hypothesis provides a viable explanation for a key paleoproxy signature of d o stadials over east asia namely the heavier mean 18o of precipitation as recorded in speleothem records the southward jet position prevents the low level monsoonal flow which is isotopically light from penetrating into the interior of east asia as such precipitation there will be heavier consistent with speleothem records this hypothesis can also explain other key evidences of east asian paleoclimate changes in particular the occurrence of dusty conditions during north atlantic stadials and the southward migration of the holocene optimal rainfall

linear weakening of the amoc in response to receding glacial ice sheets in ccsm3 the transient response of the atlantic meridional overturning circulation amoc to a deglacial ice sheet retreat is studied using the community climate system model version 3 ccsm3 with a focus on orographic effects rather than meltwater discharge it is found that the amoc weakens significantly 41 in response to the deglacial ice sheet retreat the amoc weakening follows the decrease of the northern hemisphere ice sheet volume linearly with no evidence of abrupt thresholds a wind driven mechanism is proposed to explain the weakening of the amoc lowering the northern hemisphere ice sheets induces a northward shift of the westerlies which causes a rapid eastward sea ice transport and expanded sea ice cover over the subpolar north atlantic this expanded sea ice insulates the ocean from heat loss and leads to suppressed deep convection and a weakened amoc a sea ice ocean positive feedback could be further established between the amoc decrease and sea ice expansion

fluxes and exchange of suspended sediment in tidal inlets draining a degraded mangrove forest in kenya abstract this study focuses on sediment exchange in the degraded mwache mangrove forest wetland located in southern kenya it involved measurement of total and particulate organic suspended sediment concentrations tssc and posc tidal water elevation and current velocities results showed that in the heavily degraded backwater zone mangrove forest the ebb and flood tide total sediment fluxes were of same order of magnitude however flood tide sediment fluxes were slightly higher than the ebb ones in the moderately degraded frontwater zone mangrove forest the flood tide sediment fluxes were more than 50 higher than the ebb tide fluxes the peak net sedimentation in the highly degraded backwater zone was 4 g m 2 tide 1 but that in the moderately degraded frontwater zone was 63 g m 2 tide 1 in the frontwater zone of the mangrove forest the peak instantaneous ebb tide sediment flux was 3206 kg tide 1 equivalent to 35 6 g m 2 tide 1 and the flood one 8574 kg tide 1 95 g m 2 tide 1 the peak instantaneous flood and ebb tide particulate organic sediment pos fluxes in the frontwater zone mangrove forest were 1316 kg tide 1 15 g m 2 tide 1 and 587 kg tide 1 6 5 g m 2 tide 1 respectively the peak ebb and flood tide sediment fluxes in the backwater mangrove forest were 3206 kg tide 1 36 g m 2 tide 1 and 3305 kg tide 1 36 7 g m 2 tide 1 respectively in case of pos fluxes in the backwater zone mangrove forest the peak flood period pos flux was 969 kg tide 1 10 7 g m 2 tide 1 while the ebb period one was 484 kg tide 1 5 4 g m 2 tide 1 in both highly degraded backwater and moderately degraded frontwater zone of the mangrove forest there is net import of sediments however the net import is relatively lower in the backwater zone forest where the trapping efficiency is 27 in the moderately degraded frontwater zone of the mangrove forest the sediment trapping efficiency is 65 the net sediment import occurs mainly in periods of high river discharge in both neap and spring tides but occurs only in spring tides during dry season the net accretion rates in the backwater and frontwater zone mangrove forests are 0 25 and 3 5 cm year 1 respectively

the partitioning of transitional metals fe mn ni cr in mangrove sediments downstream of a ferralitized ultramafic watershed new caledonia abstract in new caledonia one third of the island is composed of ultramafic rocks and lateritic soils enriched in fe ni and cr open cast mining occurs all around the island and processes of erosion and sedimentation which occur naturally along the coastline are strongly amplified by mining activities due to their position at the interface between land and sea mangroves receive extensive amounts of particles emanating from rivers through estuaries the purpose of this study is to understand the distribution and partitioning of some transitional metals fe mn ni cr in sediments and pore waters in a mangrove swamp which is situated downstream of a catchment characterized by lateritic soils that were exploited a century ago quantitative analyses on bulk and after selective extraction were carried out on cores collected along a transect within the intertidal zone i e beneath a rhizophora stylosa stand an avicennia marina stand and within a salt flat mean metal concentrations were mol g 1 fe 1997 ni 44 2 cr 31 9 mn 8 8 thus ni cr and fe concentrations in this study are substantially higher than mangrove world average in addition ni concentrations are 10 to 100 times higher than in other new caledonian mangrove developing downstream of a catchment not composed of ultramafic rocks the studied mangrove is characterized by gradients of water and organic contents with depth and along the intertidal zone which induced different redox conditions and thus different metals partitioning transitional metals are deposited in the mangrove mainly as oxides and or oxy hydroxides that are subsequently dissolved by bacteria for the decomposition of organic matter and which leads to a strong increase of metals in the dissolved phase then dissolved metals were precipitated with organic and sulfide compounds to conclude organic diagenesis in mangrove sediments leads to the transfer of transitional metals from oxide form to organic and sulfide forms

morphology hydrography and sediment dynamics in a mangrove estuary the konkoure estuary guinea the konkoure estuary in the republic of guinea is a poorly understood atypical mangrove system sediment dynamics in tropical estuaries are controlled by a combination of processes including river discharge morphology salinity erosion and deposition processes the settling of mud physico chemical processes and mangrove swamps here we present a consistent set of data aimed at characterising the estuary and thus increasing our understanding of tropical systems as well as studying the impact of human intervention in the region water elevations current measurements salinity suspended sediment concentrations bathymetry and sediment cover are presented following a 3 year survey of the konkoure estuary here we provide conclusive evidence that the lower konkoure is a shallow funnel shaped mesotidal mangrove fringed tide dominated estuary well mixed during low river discharge the estuary becomes stratified during high river flows and spring tides whereas a salt wedge appears during neap tides the konkoure estuary has been described as hypersynchronous and has three terminal outlets two of which are landward directed attesting to a tidal pumping effect while the third one is seaward directed and is controlled by the mangrove the suspended matter is transported by the tidal effect within the middle estuary and is therefore trapped in the turbidity maximum zone tmz the location of the tmz is river controlled and is correlated with residual currents but not with salinity front a dam constructed 130 km upstream impacts on the hydrodynamics and reduces the salinity intrusion by about 25 it causes an increased low river discharge whereas its efficiency over high river flows is unclear

late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments the modern indian ocean summer monsoon is driven by differential heating between the asian continent and the indian ocean to the south this differential heating produces a strong pressure gradient which drives southwest monsoon winds during june july and august satellite and meteorological observations aerosol measurements sediment trap studies and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest arabian sea analyses of lithogenic grain size and mass accumulation rate mar records from the owen ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr visual inspection shows that the mar record is positively correlated with global ice volume as indicated by the marine 18o record in contrast the grain size record varies at a much higher frequency showing little correlation to either the mar or the 18o records spectral analyses confirm these relationships indicating that the lithogenic grain size and mar records are coherent only over the precession band whereby the grain size leads the mar by 124 8 kyr we conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and mar with independent eolian records we use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic mar as a paleoclimatic indicator of source area aridity these interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength globigerina bulloides upwelling record and aridity a loess record from central china such comparisons indicate high coherence and zero phase relationships our work supports the findings of previous studies which have documented the link between monsoon strength and the earth s axial precession cycles both the lithogenic mar and the grain size records have high coherency with precessional insolation maximum lithogenic mar source area aridity is in phase with 18o global ice volume and leads maximum precessional insolation by 88 6 kyr we attribute this lead to the influence of glacial conditions on the aridity and therefore the deflation potential of the source areas maximum lithogenic grain size summer monsoon wind strength lags maximum precession by 148 9 kyr we attribute this lag both to the influence of global and or local ice volume and to the availability of latent heat from the southern hemisphere indian ocean the two of which combine to determine the strength of the indian ocean monsoon

currents and sediment transport in mangrove forests abstract a field study of the tidal currents cohesive sediment dynamics and transport of organic carbon in a highly vegetated mangrove swamp was carried out at middle creek cairns australia the interaction of tidal currents and the vegetation generated jets eddies and zones of stagnant waters which were numerically modelled a high value of the manning friction coefficient n 0 1 was derived by the dense vegetation about 80 of the suspended sediment brought in from coastal waters at spring flood tide was trapped in the mangroves corresponding to about 10 12 kg of sediment m 1creek length spring tide resulting in a rise of the substrate by about 0 1 cm year 1 the selective trapping of clay was caused by flocculation of the finer particles in the mangroves there was an indication of a slight inwelling of organic carbon creek water was readily differentiated from mangrove water by large differences in the molecular weight distribution of the dissolved organic carbon

holocene and modern sediment storage in the subtropical macrotidal fitzroy river estuary southeast queensland australia the fitzroy river estuary is a macrotidal tide dominated estuary located in the dry tropics of central queensland and represents the major source of terrestrial sediment to the southern great barrier reef gbr lagoon the estuary currently receives most of its sediment during large episodic floods that are typically associated with cyclones mean annual sediment budgets for such systems are difficult to estimate due to the sporadic nature of flood discharge events which are highly seasonal and vary greatly in magnitude between years we have estimated the quantity and long term rate of accumulation of catchment derived sediment in the estuarine floodplain using the holocene stratigraphic sequence determined from a series of sediment cores dated with radiocarbon and optically stimulated luminescence osl methods approximately 13 760 million tonnes mt of fluvial sediment has accumulated in the fitzroy estuary during the past 8000 years which equates to an average of 1720 kt yr 1 sediment has accumulated in the fitzroy estuary during the past 8000 years which equates to an average of 1720 kt yr 1 over the past 100 years sediment accumulation has been focused around mangrove and tidal creek environments which cover an area of 13 0 km 2 cores from the tidal creeks dated using cs c 137 pb 210 and osl provide sedimentation rates of approximately 15 mm yr 1 for the past 45 120 years or sediment mass accumulation of 1700 kt yr 1 which includes a component that is reworked into the estuary by tidal currents combined with the small amount of sediment that accumulates on the floodplain during floods similar to 1 mm yr 1 640 kt yr 1 we estimate that approximately 2350 kt yr 1 of sediment is trapped in the modem lower floodplain and estuary this estimate of sediment storage suggests that greater than 50 of the modem mean annual sediment discharge of the fitzroy river 4162 kt yr 1 may be retained in the lower floodplain and estuary these results provide useful insights into the spatial pattern of sedimentation long term rates of accumulation and estimates of sediment trapping in a tropical macrotidal sedimentary system crown copyright c 2007 published by elsevier b v all rights reserved

what is the timing of orbital scale monsoon changes abstract a major but little noted divergence of opinion has developed among climate scientists over the orbital scale periodicity and phasing of tropical monsoon variations kutzbach 1981 monsoon climate of the early holocene climate experiment with earth s orbital parameters for 9000 years ago science 214 59 61 proposed that monsoons are driven by northern summer insolation at the precession period but clemens and prell 1990 late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments paleoceanography 5 109 145 2003 a 350 000 year summer monsoon multi proxy stack from the owen ridge northern arabian sea marine geology 201 35 51 inferred a more complicated response tied to latent heat transfer from the southern hemisphere because tropical monsoons affect climate over a vast area resolving this divergence is an important task for the climate community the purpose of this note is to highlight definitive evidence from high resolution dating of speleothem calcite that provides unambiguous support for the kutzbach hypothesis

evaluating deep subsidence in a rapidly accreting mangrove forest using gps monitoring of surface elevation benchmarks and sedimentary records abstract ultimately the fate of mangrove forests depends on substrate elevation gains keeping pace with relative sea level rise rslr some of the world s largest mangrove forests occur on tectonically active margins river deltas and sedimentary basins where sea level trends are largely controlled by vertical land motion i e subsidence so that rslr can be markedly higher than sea level rise induced by climate warming the rod surface elevation table marker horizon rset mh method has been applied globally to evaluate coastal wetland resilience to slr by quantifying net rates of elevation change relative to a benchmark a limitation of the rset method is that the stability of the benchmark i e vertical trend is unknown and rslr in wetlands is typically inferred from regional tide gauge records in the present study we evaluate rslr in a rapidly subsiding avicenna marina mangrove forest with a large terrigenous sediment supply firth of thames new zealand using independent and complimentary methods 1 campaign gps surveys of the stability of three rset benchmarks driven 18 m into unconsolidated sediment a tide gauge some 10 km distant and a reference station located on basement rock 2007 2016 that are tied to a network of satellite based geodetic sites and 2 137cs validated 210pb sediment accumulation rates sar measured in cores as a proxy for rslr the similarity of deep subsidence rates at the rset benchmarks located several hundred metres apart 7 7 0 5 to 9 4 0 5 mm yr 1 provides confidence in these results these subsidence rates are two to five fold higher than recorded at the nearby tide gauge 3 6 0 7 mm yr 1 and reference station 1 6 0 5 mm yr 1 weighted average 210pb sar of 9 9 mm and 9 3 mm yr 1 yield similar estimates of deep subsidence i e 8 4 and 6 9 mm yr 1 slr adjusted for vertical land motion indicating that this geological process is the major driver of the long term sea level trend in the mangrove forest our findings suggest that regional tide gauge records may not provide reliable estimates of rslr for all coastal wetlands due to local subsidence associated with natural processes and human activities subsidence rates and rslr within coastal wetlands can be evaluated using campaign gps surveys of rset benchmarks and independently from longer term sedimentary records finally evaluations of the resilience of coastal wetlands to rising sea levels over the coming decades must be based on measurements of rslr from these systems themselves

abrupt glacial climate shifts controlled by ice sheet changes the volume of the northern hemisphere ice sheet controlled abrupt millennial scale climate changes during the last glacial dansgaard oeschger events are millennial scale warm periods interrupting cold glacial climates although they are perhaps the most prominent example of abrupt change observed in the ice core record of the past 800 000 years their underlying physical controls remain debated xu zhang and colleagues now use a fully coupled climate model to show that dansgaard oeschger events tend to occur when ice sheets are at an intermediate height a condition in which small perturbations to the coupled atmosphere ocean sea ice system can lead to rapid nonlinear feedbacks and abrupt changes in climate during glacial periods of the late pleistocene an abundance of proxy data demonstrates the existence of large and repeated millennial scale warming episodes known as dansgaard oeschger do events1 this ubiquitous feature of rapid glacial climate change can be extended back as far as 800 000 years before present bp in the ice core record2 and has drawn broad attention within the science and policy making communities alike3 many studies have been dedicated to investigating the underlying causes of these changes but no coherent mechanism has yet been identified3 4 5 6 7 8 9 10 11 12 13 14 15 here we show by using a comprehensive fully coupled model16 that gradual changes in the height of the northern hemisphere ice sheets nhiss can alter the coupled atmosphere ocean system and cause rapid glacial climate shifts closely resembling do events the simulated global climate responses including abrupt warming in the north atlantic a northward shift of the tropical rainbelts and southern hemisphere cooling related to the bipolar seesaw are generally consistent with empirical evidence1 3 17 as a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets minor changes in the height of the nhiss and the amount of atmospheric co2 can trigger the rapid climate transitions via a local positive atmosphere ocean sea ice feedback in the north atlantic our results although based on a single model thus provide a coherent concept for understanding the recorded millennial scale variability and abrupt climate changes in the coupled atmosphere ocean system as well as their linkages to the volume of the intermediate ice sheets during glacials

wet season fine sediment dynamics on the inner shelf of the great barrier reef fine sediment dynamics were recorded in february 2007 in coastal waters of the great barrier reef during a moderate flood of the tully river an estuarine circulation prevailed on the inner continental shelf with a surface seaward velocity peaking at 0 1 m s 1 and a near bottom landward flow peaking at 0 05 m s 1 much of the riverine mud originating from eroded soils was exported onto a 10 km wide coastal strip during the rising stage of the river flood in the first flush in coastal waters suspended sediment concentration peaked at 0 2 kg m 3 near the surface and 0 4 kg m 3 at 10 m depth during calm weather and 0 5 kg m 3 near the surface and 2 kg m 3 at 10 m depth during strong winds when bottom sediment was resuspended diurnal irradiance at 4 m depth was almost zero for 10 days the sedimentation rate averaged 254 33 g m 2 d 1 over the 28 day study period and concentrations of dissolved and particulate nutrients originating from the river were high the observed low irradiance would have prevented coral photosynthesis while the sedimentation rate would have been lethal to some juvenile corals the mud may ultimately be minnowed out over long periods however flushing of the mud occurs at time scales much longer than the flood event and the mud is likely to affect coral physiology for significant periods after the flood has subsided the data show the need to better control erosion on farmed land for the conservation of coral reefs on the inner shelf of the great barrier reef

microfacies characteristics of a tropical mangrove fringed shoreline cleveland bay queensland australia sedimentary and taphonomic controls on mangrove facies development mangrove ecosystems strongly influence the sedimentology and geomorphology of contemporary intertidal environments and are known to have occupied similar ecological niches at least as far back as the early cenozoic given this it is remarkable how few records of mangrove occurrence have been reported in the geologic record here a microfacies approach is adopted to examine the characteristics of a contemporary mangrove colonized intertidal succession along an active prograding shoreline in north queensland australia and compared with a proximal mid late holocene preserved intertidal succession this enables a comparison of microfacies development and preservation potential in like for like depositional environments over short temporal and spatial scales in the contemporary intertidal system active shoreline progradation has produced a highly gradational shallowing upward succession mid to low intertidal substrates characterized by an abundant and diverse bioclast especially molluscan fauna and a rich calcareous foraminiferal assemblage are overlain by organic rich upper intertidal mangrove facies characterized by abundant organic material especially wood and bark fragments and a distinct fauna of agglutinated foraminifera the major sedimentary effects of mangrove progradation are to introduce substantial amounts of organic matter into the substrate effectively overprinting the mudflat facies to mix and re texture due to root network development and infaunal bioturbation the sediment substrate and to modify the depth ranges over which infaunal molluscs and foraminifera occur variations in the relative abundance of constituents permit however the clear delineation of mangrove and intertidal mudflat facies whilst an essentially similar facies succession is identifiable in the sub recent many of the diagnostic facies constituents are either not preserved or are present in far lower abundances than in the modern in particular the inferred mangrove units contain far less organic material most wood and root material is absent are essentially devoid of bioclastic material and contain a depauperate agglutinated foraminiferal fauna the primary drivers of this are 1 loss of calcareous foraminifera and bioclasts due to carbonate dissolution 2 loss of agglutinated foraminifera due primarily to biological fiddler crab test degradation and mineralization of their organic binding agents and 3 aerobic and anaerobic degradation of organic material consequently actual criteria for identifying the presence of a former mangrove in this succession are limited such poor preservation even within sub recent mangrove deposits suggest that the longer term preservation potential of key diagnostic criteria is likely to be extremely poor within similar terrigenoclastic dominated organically enriched successions thus whilst mangroves significantly modify and re texture intertidal substrates use may often need to be made of sparsely preserved faunal or floral remains or traces interpreted in the context of the broader intertidal depositional succession to infer the presence of mangrove colonized substrates in the rock record

mangroves and shoreline erosion in the mekong river delta viet nam the question of the rampant erosion of the shorelines rimming the mekong river delta has assumed increasing importance over the last few years among issues pertinent to this question is how it is related to mangroves using high resolution satellite images we compared the width of the mangrove belt fringing the shoreline in 2012 to shoreline change advance retreat between 2003 and 2012 for 3687 cross shore transects spaced 100 m apart and thus covering nearly 370 km of delta shoreline bearing mangroves the results show no significant relationships we infer from this that once erosion sets in following sustained deficient mud supply to the coast the rate of shoreline change is independent of the width of the mangrove belt numerous studies have shown that 1 mangroves promote coastal accretion where fine grained sediment supply is adequate 2 a large and healthy belt of fringing mangroves can efficiently protect a shoreline by inducing more efficient dissipation of wave energy than a narrower fringe and 3 mangrove removal contributes to the aggravation of ongoing shoreline erosion we fully concur but draw attention to the fact that mangroves cannot accomplish their land building and coastal protection roles under conditions of a failing sediment supply and prevailing erosion ignoring these overarching conditions implies that high expectations from mangroves in protecting and or stabilizing the mekong delta shoreline and eroding shorelines elsewhere will meet with disappointment among these false expectations are 1 a large and healthy mangrove fringe is sufficient to stabilize the eroding shoreline 2 a reduction in the width of a large mangrove fringe to the benefit of other activities such as shrimp farming is not deleterious to the shoreline position and 3 the effects of human induced reductions in sediment supply to the coast can be offset by a large belt of fringing mangroves

temporal changes in physical chemical and biological sediment parameters in a tropical estuary after mangrove deforestation abstract dated sediment cores taken near the head and mouth of a tropical estuary nha phu binh cang in south central viet nam were analyzed for changes over time in physical chemical and biological proxies potentially influenced by removal of the mangrove forest lining the estuary a time series of satellite images was obtained which showed that the depletion of the mangrove forest at the head of the estuary was relatively recent most of the area was converted into aquaculture ponds mainly in the late 1990 s the sediment record showed a clear increase in sedimentation rate at the head of the estuary at the time of mangrove deforestation and a change in diatom assemblages in the core from the mouth of the estuary indicating an increase in the water column turbidity of the entire estuary at the time of the mangrove deforestation the proportion of fine grained sediment and the 13 c signal both increased with distance from the head of the estuary while the carbon content decreased the nitrogen content and the 15 n signal were more or less constant throughout the estuary the proportion of fine grained material and the chemical proxies were more or less stable over time in the core from the mouth while they varied synchronously over time in the core from the head of the estuary the sediment proxies combined show that mangrove deforestation had large effects on the estuary with regard to both the physical and chemical environment with implications for the biological functioning

the relative importance of landward directed tidal sediment transport versus freshwater flood events in the normanby river estuary cape york peninsula australia variation in freshwater discharge into the tropical estuaries of northern australia is extreme between wet and dry seasons and the resultant effect upon sedimentary processes in relation to the geomorphological evolution of the coastal plain is largely undocumented observations of tidal height currents and suspended sediment concentrations were taken over a 3 week period in july 1994 dry season in the mesotidal normanby river estuary northeastern australia the estuary and adjacent inner shelf were surveyed using a 3 5 khz seismic system and an echo sounder and sampled with a total of 175 grab samples and 17 vibrocores sediment sampling occurred in july 1994 december 1994 and march 1996 the latter following the 1995 96 wet season flood tidal currents dominate the estuary at spring tides with peak velocities of 0 85 m s 1 recorded at the mouth measured tidally driven sediment transport is landward at the mid estuary site and extrapolation gives estimates of 15 000 30 000 tonnes of bedload and ca 50 000 tonnes of suspended load moved landward per year the surficial sediments in the main estuarine channel are inferred to be holocene and are 1 delta front sediments which extend to at least 6 km seawards of the mouth 2 lower estuarine silts located at 2 11 km landwards of the mouth and 3 channel dune sands 13 to 50 km i e nearly to the tidal limit all dunes surveyed on the river bed during the dry season showed a strong asymmetry with lee faces consistently facing landward whether surveyed at high or low water indicating landward bedload sediment transport in the dry season an underlying hard regional surface is exposed at 11 13 km landward of the estuary mouth in the absence of direct measurements we have estimated sediment transport during wet season freshwater flood events a major freshwater flood event may transport only 6000 32 000 tonnes of bedload seawards and modern wet season events appear incapable of supplying sand in significant quantities to the inner shelf we infer that for the late holocene the frequency magnitude and duration of wet season events has been insufficient to reverse the landward bedload transport driven by tidal currents in the dry season

structure of the earth oceanic crust and uppermost mantle the past four years have witnessed the introduction of a variety of new instruments and methods for the study of the seismic structure of the oceanic crust and lithosphere the application of these and existing tools has led to the discovery of a number of new phenomena and to a fuller understanding of the genesis and evolution of the oceanic ithosphere borehole seismic instrumentation has become more widely employed ocean bottom seismographs while generally decreasing in number have become significantly more reliable and useful and multichannel seismic systems have been employed in innovative experiments ranging from studies of fracture zones to the regular detection of magma chambers beneath rise axes the techniques available for the analysis of seismic data have become more sophisticated waveforms collected in seismic experiments can now be used directly in constructing and evaluating seismic velocity models and travel time data are regularly inverted directly for structure trial and error modeling has become increasingly unimportant marine seismologists are becoming increasingly involved in understanding the coupling between the ocean and the underlying oceanic lithosphere this has led to a more complete understanding of seafloor noise processes and the partitioning of energy between acoustic and elastic waves

abrupt intensification of enso forced by deglacial ice sheet retreat in ccsm3 the influence of ice sheet retreat on the el nino southern oscillation enso variability is studied using a transient simulation in ncar ccsm3 forced only by variations in continental ice sheets during the last deglaciation the most striking feature is an abrupt strengthening of enso by 25 at 14 thousand years before present ka bp in response to a significant retreat an equivalent 25 m sea level rise of the laurentide ice sheet lis this abrupt intensification of enso is caused mainly by a sudden weakening of the equatorial annual cycle through the nonlinear mechanism of frequency entrainment rather than an increase in the coupled ocean atmosphere instability the weakened annual cycle corresponds to a reduced north south cross equatorial annual mean sst contrast in the eastern pacific this reduced interhemispheric sst gradient significant cooling north of the equator is forced predominantly by an anomalous easterly from an abrupt polarward shift of the jet stream in the northern hemisphere which extends to the northeastern tropical pacific ocean surface and is reinforced by the wind evaporation sst feedback then propagates equatorward it could also be contributed by a fast sea ice expansion and a consequent cooling in the north pacific and north atlantic that is induced by the retreat of the lis

hydrodynamic and geomorphological controls on suspended sediment transport in mangrove creek systems a case study cocoa creek townsville australia in tide dominated sedimentary systems close relationships exist between tidal hydrodynamics sediment transport and geomorphology tropical coastlines contain many tide dominated mangrove creeks yet few studies to date have examined the detail of such relationships for these environments time series observations of tidal height currents and suspended sediment concentrations were taken between 1992 and 1996 in cocoa creek a mangrove creek system near townsville ne australia the creek and surrounding mangrove swamps and salt flats were surveyed with an echo sounder and total survey station respectively for within channel tides the flood tide is always the fastest at up to 0 5 m s 1 in contrast for overbank tides i e tidal height 1 5 m australian height datum ahd ebb currents are fastest in july december and january but flood currents are fastest in august and september at up to 1 m s 1 in both cases the tidal asymmetry of overbank tides in cocoa creek is controlled by the interaction between offshore tidal forcing and the intertidal storage effect of the mangrove swamps and salt flats with the result being that during certain periods of the year there tends to be a predominance of either faster flood or ebb velocities on overbank tides significant tidal suspended sediment transport in the channel is only initiated at overbank height on overbank tides measured net suspended sediment fluxes in the channel are mostly seaward directed up to 180 t per tidal cycle however the net flux measured over a neap spring period may be either landwards or seawards up to 465 and 60 t respectively furthermore on the larger overbank tides where the maximum tidal height 1 85 m ahd net sediment fluxes may be reduced because of a limited supply of available material thus hydrodynamic and sediment sampling durations of up to a month may not be representative of long term trends given that our large dataset has not identified a clear long term net transport direction within the creek system we conclude tentatively that the geomorphology of cocoa creek may be near a long term equilibrium

ice age terminations 230th dated oxygen isotope records of stalagmites from sanbao cave china characterize asian monsoon am precipitation through the ends of the third and fourthmost recent ice ages as a result am records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments establishing the timing and sequence of major events in all four cases observations are consistent with a classic northern hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets meltwater and icebergs entering the north atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon causing increases in atmospheric co2 and antarctic temperatures that drive the termination in the southern hemisphere increasing co2 and summer insolation drive recession of northern ice sheets with probable positive feedbacks between sea level and co2

impact of ice sheet induced north atlantic oscillation on east asian summer monsoon during an interglacial 500 000 years ago marine isotope stage mis 13 an interglacial about 500 000 years ago is unique due to an exceptionally strong east asia summer monsoon easm occurring in a relatively cool climate with low greenhouse gas concentrations ghg this paper attempts to find one of the possible mechanisms for this seeming paradox simulations with an earth system model loveclim show that the presence of ice sheets over north america and eurasia during mis 13 induces a positive phase of the winter north atlantic oscillation nao like feature the ocean having a longer memory than the atmosphere the oceanic anomalies associated with nao persists until summer the signals of summer nao are transmitted to east asia to reinforce the monsoon there through the stationary waves excited at the asian jet entrance the geopotential height shows clearly a mid latitude wave train with positive anomalies over the eastern mediterranean caspian sea and the okhotsk sea and a negative anomaly over lake baikal this reinforces the effect of the high latitude wave train induced independently by the eurasian ice sheet topography as shown in previous study these features reinforce the meiyu front and enhance the precipitation over east asia the results obtained from loveclim are further confirmed by an atmospheric general circulation model arpege

sedimentation in an estuarine mangrove system abstract sediment dynamics were studied in a mangrove system in the ba lat estuary of the red river vietnam the study area was situated on a riverbank which consisted of a bare mudflat containing a vegetation gradient from pioneering mangroves to 5 to 7 year old mangroves measurements were conducted in the dry season february march 2000 and in the wet season july august 2000 actual sedimentation rates were measured using sediment traps and the elevation of the area was surveyed in both periods two undisturbed sediment cores were taken in the densely vegetated area for 210pb dating analysis and showed long term sedimentation rates of 0 22 g cm 2 yr 1 and 0 36 g cm 2 yr 1 sedimentation rates recorded by the sediment traps in the vegetated area were 2 94 g cm 2 yr 1 in the dry season and 3 46 g cm 2 yr 1 in the wet season in both seasons the sedimentation rates on the bare mudflat were five to ten times higher than in the densely vegetated area however the elevation of the mudflat was slightly lower in the wet season than in the dry season this implies that erosion must have taken place between march and july this study demonstrates that the bare mud bank of an estuary is highly dynamic until mangroves cover it sediment delivery to the vegetated zones is low but the protective effect of vegetation against erosion by waves and currents is strong this results in small but steady actual sedimentation rates under mangroves and therefore sustained long term accretion the study further identifies the need for similar measurements to be made in different seasons covering the effects of periodic storm events

bioavailable trace metals in micro tidal thambraparani estuary gulf of mannar se coast of india abstract thirty surface sediment samples from two different seasons pre monsoon prm post monsoon pom were analyzed for texture carbonates organic matter om and leachable trace metals ltms fe mn cr cu ni pb zn cd from the micro tidal estuary of thambraparani river located in gulf of mannar se coast of india finer fractions mud 3 87 and om 2 6 8 0 dominate the region and the concentration pattern of ltms indicate that mostly all the metals are concentrated in the pom season than prm correlation analysis indicates that ltms are also bound with the om mud and are bound with fe mn oxides pb concentration 14 103 g g 1 exceeds the sediment quality guideline value indicating its anthropogenic origin low flow condition exists in the estuarine region due to the control over fresh water inflow in the upstream side and the higher concentration of metals avg g g 1 cr 10 cu 11 zn 28 is due to the precipitation from estuarine water to the sediments and is also bioavailable to the marine biota in the region

northern hemisphere forcing of southern hemisphere climate during the last deglaciation changes in ocean circulation are the most plausible explanation for the early southern hemisphere deglacial warming and its lead over northern hemisphere temperature milankovitch theory which was developed to explain the relationship between earth s movement and the climate holds that glacial cycles are ultimately controlled by variations in northern hemisphere summer insolation exposure to the sun s rays spectral analyses of palaeoclimate records support this theory but a mechanistic test has been elusive other lines of evidence also show that climate changes in the southern hemisphere may have led those in the northern hemisphere casting doubt on the main theory here feng he and colleagues use a coupled ocean atmosphere model to show that the last deglaciation was indeed triggered by northern hemisphere insolation changes amplified by albedo co2 and ocean circulation changes according to the milankovitch theory changes in summer insolation in the high latitude northern hemisphere caused glacial cycles through their impact on ice sheet mass balance1 statistical analyses of long climate records supported this theory but they also posed a substantial challenge by showing that changes in southern hemisphere climate were in phase with or led those in the north2 although an orbitally forced northern hemisphere signal may have been transmitted to the southern hemisphere3 insolation forcing can also directly influence local southern hemisphere climate potentially intensified by sea ice feedback4 5 6 suggesting that the hemispheres may have responded independently to different aspects of orbital forcing signal processing of climate records cannot distinguish between these conditions however because the proposed insolation forcings share essentially identical variability7 here we use transient simulations with a coupled atmosphere ocean general circulation model to identify the impacts of forcing from changes in orbits atmospheric co2 concentration ice sheets and the atlantic meridional overturning circulation amoc on hemispheric temperatures during the first half of the last deglaciation 22 14 3 kyr bp although based on a single model our transient simulation with only orbital changes supports the milankovitch theory in showing that the last deglaciation was initiated by rising insolation during spring and summer in the mid latitude to high latitude northern hemisphere and by terrestrial snow albedo feedback the simulation with all forcings best reproduces the timing and magnitude of surface temperature evolution in the southern hemisphere in deglacial proxy records8 9 amoc changes associated with an orbitally induced retreat of northern hemisphere ice sheets10 is the most plausible explanation for the early southern hemisphere deglacial warming and its lead over northern hemisphere temperature the ensuing rise in atmospheric co2 concentration provided the critical feedback on global deglaciation9 11

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

differential sediment trapping abilities of mangrove and saltmarsh vegetation in a subtropical estuary abstract saltmarsh and mangrove are common coastal wetland types and their ability to enhance deposition has been investigated extensively but rarely compared directly this study carried out in situ observations to compare the sediment transport processes between a bare mudflat a mangrove stand and a saltmarsh stand within a subtropical estuary turbidity variations over the latter portion of a spring tide were recorded alongside measurements of flow data to estimate sediment trapping by hydraulic forces under similar hydroperiods in addition vegetation was transplanted to compare the direct sediment trapping by high standings and short seedlings the suspended sediment concentration ssc time series showed an overall reduction between the bare mudflat and the vegetated flats suspended sediment flux estimates revealed that a considerable amount of sediment was trapped by the saltmarsh and the mangrove edges the flux estimates find that the saltmarsh edge is more efficient than the mangrove edge in trapping sediments transported normal to the edge the sediment trapping mechanisms were considered based on two approaches the hydrodynamic related sediment settling and direct trapping by vegetation the calculation of deposition tendency showed that the presence of vegetation altered the flow direction and the tidal asymmetry of the deposition process resulting in a higher deposition tendency during the flood phase to enhance sediment settling in addition to sediment settling vegetation surfaces were found to trap sediments directly in combination with rinsing by precipitation these trapped sediments accumulated on the bed and contributed to the deposition against the background of similar inundation periods the saltmarsh grass showed a greater sediment trapping ability than the mangrove trees in terms of both the hydraulic sediment trapping and the direct trapping by vegetation surface

balancing aggradation and progradation on a vegetated delta the importance of fluctuating discharge in depositional systems vegetation is an important component of constructional landscapes as plants enhance deposition and provide organic sediment that can increase aggradation rates to combat land loss we conducted two sets of laboratory experiments using alfalfa medicago sativa to determine the effects of plants on channel organization and large scale delta dynamics in the first set we found that rapid vegetation colonization enhanced deposition but inhibited channelization via increased form drag that reduced the shear stress available for sediment entrainment and transport a second set of experiments used discharge fluctuations between flood and base flow or interflood interfloods were critical for reworking the topset via channel incision and lateral migration to create channel relief and prevent rapid plant colonization these low flow periods also greatly reduced the topset slope in the absence of vegetation by removing topset sediment and delivering it to the shoreline floods decreased relief by filling channels with sediment resulting in periods of rapid progradation and enhanced aggradation over the topset surface which was amplified by vegetation the combination of discharge fluctuations and vegetation thus provided a balance of vertical aggradation and lateral progradation we conclude that plants can inhibit channelization in depositional systems and that discharge fluctuations encourage channel network organization to naturally balance against aggradation thus variations in discharge are an important aspect of understanding the ecomorphodynamics of aggrading surfaces and modeling vegetated deltaic systems and the combined influences of plants and discharge variations can act to balance vertical and lateral delta growth

seismic observations from an ocean subbottom seismometer in the northwest pacific basin one of the primary objectives in placing seismic systems in deep ocean boreholes is the detection of teleseismic earthquakes and nuclear events if the oceanic basement is substantially quieter than the ocean floor and island sites then the added data could yield information of considerable value in nuclear test detection this paper presents and evaluates data relevant to this problem the smallest teleseismic 30 earthquake observed on the hawaii institute of geophysics ocean subbottom seismometer oss had a body wave magnitude of 5 4 only one nuclear explosion mb 5 6 was clearly observed with additional filtering and processing nuclear explosions as small as mb 5 1 can be marginally observed oss records many regional earthquakes of the northwest circum pacific area which are not listed in the neis catalog teleseismic p wave arrivals for several events contain frequencies as high as 8 hz above the background noise no teleseismic short period s waves were seen although high frequency s waves from regional events were abundant this dichotomy in the observability of s waves at oss suggests that the lithosphere of the northwest pacific has a high q but that the underlying asthenosphere is more highly attenuative

the use of computational fluid dynamics in predicting the tidal flushing of animal burrows numerical hydrodynamic modelling has been used extensively over the last few decades to simulate flow in the ocean bays and estuaries however modelling of much smaller scale phenomena is less common in this work a commercially available computational fluid dynamics package fidap normally used for industrial applications was used to simulate tidally induced flow in multi opening animal burrows u shaped burrows of varying complexities were modelled to determine the effect of different surface characteristics and burrow geometries on surface water velocities burrow velocities and burrow flushing times the turbulent 2d model showed the slope of the surface water was proportional to the square of both the surface and burrow velocities the effect of placing a root in the surface flow was to reduce the surface water velocity however the burrow flow depended upon the root position for the root location either upstream or downstream of the burrow the burrow velocity was reduced by 50 with the root located between the burrow openings the burrow velocity increased by 200 due to the increase in pressure difference across the burrow openings a buttress root placed in the flow immediately downstream of the upstream burrow caused the burrow flushing rate to increase significantly with increasing buttress height flushing times for burrows of varying depth were determined computationally by use of a tracer for the burrow water for a burrow of depth 1 2 m the flushing times were 5 and 28 min for root location between the burrow openings and downstream of the burrow respectively animal burrows often consist of multiply connected loops a second burrow was added to the primary burrow and flushing times were found to be 15 and 38 min respectively a burrow system of four connected burrows was modelled which had corresponding flushing times up to 24 and 47 min respectively the calculated times are consistent with the hypothesis that a significant flushing of animal burrows occurs within a single tidal event this preliminary investigation indicates that cfd models may be very useful in studying small scale hydrodynamic phenomena such as flow in animal burrows

intertidal substrate modification as a result of mangrove planting impacts of introduced mangrove species on sediment microfacies characteristics a programme of mangrove planting has been undertaken around the island of rodrigues sw indian ocean since the mid 1980 s involving the introduction of the species rhizophora mucronata we examined three coastal embayment sites baie diamant anse goeland and anse pansia in which planting has been undertaken over different time periods within the past 20 years planting has met with variable success in the different sites probably due to variations in fluvial and groundwater influence at two sites baie diamant first planted in 1990 and anse pansia first planted in 1995 ecological data indicates that the mangroves are becoming well established and sedimentary evidence suggests that relatively rapid modification of intertidal substrates has occurred this is evident in the form of significant increases in sediment organic matter content especially fibrous organic matter and an increase in the accumulation of sediment fines inside the mangroves a strong correlation exists between the magnitude and depth of substrate modification and mangrove forest density especially root and sapling density at the third site anse goeland first planted in 2001 mangrove establishment has not been successful many of the seedlings have died and no secondary colonisation has occurred sediment substrates show no deviation from background levels in terms of organic content or weight fines content and we find no evidence for mangrove planting influencing sediment substrates despite evidence for the development of a distinctive mangrove facies at baie diamant and anse pansia there is however no evidence as yet for a marked change in substrate geochemistry such as would be demonstrated by evidence of active bioclast dissolution a common process in many natural mature mangrove substrates we infer this to be a function of the present relative immaturity of the still developing mangrove substrates but may also be a function of the apparent paucity of burrowing crabs which play an important role in nutrient cycling and sediment geochemistry thus whilst the mangroves in some of the study sites are reaching a stage where they are producing distinctive sedimentary facies the systems appear to be in a state of progressive sedimentary and diagenetic modification as the floral and infaunal components of the mangroves continue to develop

dynamic effect of last glacial maximum ice sheet topography on the east asian summer monsoon the effect of ice sheet topography on the east asian summer monsoon easm during the last glacial maximum is studied using ccsm3 in a hierarchy of model configurations it is found that receding ice sheets result in a weakened easm with the reduced ice sheet thickness playing a major role the lower ice sheet topography weakens the easm through shifting the position of the midlatitude jet and through altering northern hemisphere stationary waves in the jet shifting mechanism the lowering of ice sheets shifts the westerly jet northward and decreases the westerly jet over the subtropics in summer which reduces the advection of dry enthalpy and in turn precipitation over the easm region in the stationary wave mechanism the lowering of ice sheets induces an anomalous stationary wave train along the westerly waveguide that propagates into the easm region generating an equivalent barotropic low response this leads to reduced lower tropospheric southerlies which in turn reduces the dry enthalpy advection into east asia and hence the easm precipitation less

spectra of nuclear explosions earthquakes and noise from wake island bottom hydrophones spectral characteristics of p phases from 4 shallow focus earthquakes and 8 underground explosions and of 52 samples of ocean bottom background noise are examined by using tape recordings of ocean bottom hydrophones near wake island from july 1979 through march 1981 significant differences are found between spectra of large shallow focus earthquakes and explosions 5 7 6 hz observed in the teleseismic p phases indicate high q values for the deep mantle ambient noise levels on the ocean bottom near wake are comparable to levels at the quietest continental sites for frequencies between 3 and 15 hz also high levels of coherence at least as high as 0 85 have been observedmore for p phases recorded on sensors with 40 km separation less

azimuth energy q and temperature variations on p wave amplitudes in the united states mean relative p wave 1 s amplitude characteristics are determined for standardized seismic stations in the united states data are compiled from three azimuths to the north explosions in russia to the northwest earthquakes along the asian pacific arc and to the south southeast earthquakes in south america characteristic receiver amplitudes are found to be azimuthally dependent high amplitude areas occur in the central united states and lowest amplitudes occur along the rocky mountain front range and the rio grande rift zone amplification effects of low velocity sediments are significant in the central united states azimuthal amplitude variations in the eastern united states are consistent with an anomalous attenuating or defocusing body in the lower mantle beneath colombia south america nonazimuthal amplitude studies are tied to the azimuthal data set to increase station amplitude coverage the regional and local stability of amplitudes is analyzed amplitudes are stable with an average variation of a factor of about 1 3 around the regional mean for seismic stations situated on hard bedrock the squared amplitude variations are related to energy variations in the p wave fronts acknowledging the likely importance of elastic focusing defocusing and scattering effects at individual stations variations of anelastic attenuation are derived that are consistent with the observed energy amplitude variations assuming that the variations of anelastic attenuation occur in the upper 400 km of the earth high amplitude stations may be unattenuated low amplitude stations are consistent with q 110 and a mean amplitude implies q 220 240 the range of variation of q is mapped into temperature variations assuming a thermally activated q mechanism and an olivine activation energy for the upper mantle the apparent q variations are consistent with temperature variations of 135 287 c between high and low amplitude seismic station sites geophysical and physiographic correlations with the p wave amplitude variations are discussed accounting for the motion of the north american plate low p wave amplitudes along the rocky mountain front may be related to the uplift of the colorado plateau low amplitudes extending from northern texas to new england lie along the approximate boundary of the continental craton

holocene pollen records from caution bay southern mainland papua new guinea this study presents new palynological data from caution bay south central papua new guinea png it explores holocene mangrove transitional events along a tide dominated shoreline and expands reconstructive detail for the wider southern png lowlands coinciding with recent regional archaeological research this study also holds implications for interpretations of the holocene settlement of caution bay and long term people landscape interactions data demonstrate a late holocene mangrove to mudflat transition with vegetation patterns largely a function of low sediment loading sedimentary redistributions and salinisation upon sea level decline c 2000 cal yr bp these trends appear unique to caution bay highlighting a variety of holocene shoreline vegetation changes along the png south coast each dependent on geomorphologic setting and hydrological fluxes further work is required to elucidate vegetation change inland of the coastal zone greater understanding of burning patterns and an archaeological collaboration are required to determine more concisely dryland plant spatial and temporal variability

a numerical model study on the behaviour of asian summer monsoon and amoc due to orographic forcing of tibetan plateau simulations using the echam5 mpi om coupled atmosphere ocean model both with and without the tibetan plateau are performed in order to study the large scale effects of orographic forcing on the behaviour of the asian summer monsoon system our analysis emphasises the significant impact of plateau forcing on the atmosphere ocean interactions it is argued that in addition to the orographic forcing of the tibetan plateau on the climate of asia such as sensible heat pumping and thermal insulation other significant direct processes exist which link the asian summer monsoon to the sea surface temperatures in the north atlantic ocean the removal of the tibetan plateau modifies the wind driven ocean circulations over the north atlantic which leads to a decrease in the surface heat advection over the north atlantic ocean and a decrease in the atlantic meridional overturning circulation this in turn affects via teleconnections both the monsoon rainfall and the position of the intertropical convergence zone

mangrove bank sedimentation in a mesotidal environment with large sediment supply gulf of papua the most extensive mangrove forests on earth are associated with major river systems the indo pacific region has numerous large rivers that discharge onto broad continental shelves and mangroves occur widely along these coastlines in the gulf of papua gop alone there are 3350 km2 of mangrove forests the majority of which 2900 km2 are associated with the fly kikori and purari river deltas this study examines data from 28 vibracores to describe preserved sedimentary strata and to determine rates of sediment accumulation in this dynamic coastal environment the observations suggest a common stratigraphy is contained in prograding mangrove banks of the mesotidal western gop and that it is similar to mud dominated and physically stratified stratigraphy recorded by other intertidal areas with and without mangroves experiencing large tidal range 2 m and sediment supply e g ganges brahmaputra and yangtze river deltas grain size sedimentary structure radionuclide and remotely sensed data are analyzed and four stratigraphic facies are identified 1 supratidal to high tidal muds 2 mid tidal sandy muds 3 low tidal sand and mud and 4 subtidal channel sands supratidal and high tidal sediments of gop mangrove forests are typically muddy but can have high sand contents 30 in areas exposed regularly to ocean waves these muds can be homogenous but commonly have physical structures laminations and bedding probably reflecting high rates of sediment accumulation relative to bioturbation mangrove muds may have low water contents due to infrequent inundation and because of their cohesive nature and abundant roots can form steep intertidal banks and erosional scarps mid tidal and low tidal sediments are thinly laminated 2 mm laminations likely deposited from fluid mud transport channel sediments have thin and thick mud and sand laminations but are identified by thick 5 cm sand beds a conceptual model of mangrove bank progradation is created using sedimentological and radionuclide data maximum sediment accumulation rates were determined using steady state 210pb profiles and greatest mean rates are found in mid tidal areas 4 4 cm year 3 9 g cm2 year slower accumulation occurs in high tidal and low tidal areas 1 8 and 1 5 cm year respectively 1 2 and 1 0 g cm2 year respectively remotely sensed data indicate that areas of erosion and accretion co exist in the kikori purari region very large 210pb accumulation rates were measured in areas of significant accretion supporting the validity of the calculated rates in areas of rapid accretion cores can have non steady state or event related 210pb profiles reflecting episodic sedimentation or complex radionuclide scavenging dynamics most cores from the fly river delta are of this type sediment trapping in western gop mangroves is estimated to account for 2 14 of the total gop sediment load

a 350 000 year summer monsoon multi proxy stack from the owen ridge northern arabian sea five summer monsoon proxies from the northern arabian sea are combined using stacking and principal components analysis pca to create two very similar multi proxy records of summer monsoon variability the five individual proxies all respond to monsoon variability but are largely independent in terms of the processes that complicate their interpretation as summer monsoon indicators e g preservation dissolution diagenesis sediment reworking as such stacking and pca average out non monsoon variance yielding a more pure monsoon signal these stacked and pca records hereafter summer monsoon stack and summer monsoon factor allow evaluation of relative monsoon strength through time as well as the relative concentration of variance within orbital bands these two parameters are less reliable when estimated from individual proxy records in fact the summer monsoon factor smf accounts for only 33 of the total variance in the five records suggesting that relative amplitude variations in each individual proxy time series are influenced by non monsoon processes the summer monsoon stack sms and smf are spectrally very similar dominated by variance in the 41 k y obliquity and 23 k y precession bands there is very little variance at the 100 k y eccentricity band associated with large scale changes in global ice volume indeed equally strong monsoons occur in both glacial and interglacial intervals within the 23 k y precession cycle monsoon maxima fall at 121 relative to precession minima june 21 perihelion maximum northern hemisphere nh summer insolation this phase falls midway between 18o minima 78 and december 21 perihelion 180 indicating that two mechanisms exert equal influence in determining the timing of strong summer monsoons within the precession band 1 sensible heating of the asian plateau which is maximized at times of ice volume minima 78 and 2 latent heat export from the southern subtropical indian ocean which is maximized at times of december 21 perihelion 180 the seasonal cycle at december 21 perihelion is characterized by warm southern hemisphere sh summers followed by cold sh winters a combination that preconditions the ocean to export latent heat during the boreal summer monsoon season summer monsoon winds transport this latent heat into asia where it is released during precipitation enhancing the asian monsoon low within the 41 k y obliquity cycle monsoon maxima are in phase with obliquity maxima this indicates that two mechanisms quite similar to those in the precession band influence the timing of strong summer monsoons in the obliquity band 1 sensible heating of the asian plateau but with no ice volume delay and 2 latent heat export from the southern subtropical indian ocean which is maximized at times of obliquity maxima again the seasonal cycle at obliquity maximum is characterized by warm sh summers followed by cold sh winters ideal for maximizing latent heat export during the boreal summer monsoon

sensitivity of the atlantic intertropical convergence zone to last glacial maximum boundary conditions 1 recent paleoproxy records suggest that the mean latitude of the atlantic intertropical convergence zone itcz varied synchronously with north atlantic climate over a range of timescales throughout the holocene and last glacial maximum we show that the present day meridional mode of atmosphere ocean variability in the tropical atlantic is a potentially useful model for understanding these paleoclimate changes the tropical atlantic in a coupled atmospheric general circulation and slab ocean model responds to last glacial maximum conditions with a southward displacement of the itcz this response arises primarily through the land ice sheet that forces increased north atlantic trades analogous to the forcing on the present day meridional mode changes to sea ice coverage and to ocean heat transport associated with a weakened atlantic thermohaline circulation also cause a meridional mode response though through different mechanisms our results highlight the potential for tropical atlantic paleoclimate to be driven from the high latitude influences in particular land ice on glacial interglacial timescales

sulfur diagenesis under rapid accumulation of organic rich sediments in a marine mangrove from guadeloupe french west indies the biogeochemistry of sulfur and carbon during early diagenetic processes within organic rich marine mangrove sediments was studied in the manche a eau lagoon guadeloupe west indies these sediments are characterized by a total organic carbon content toc mostly above 11 wt 13ctoc below 25 vpdb and c nmolar ratios exceeding 15 rates of mangrove derived organic carbon accumulation vary between 200 and 400 goc m 2 yr 1 with highest rates at the shore of the lagoon on the lagoon border where colorless filamentous sulfur oxidizing bacteria colonize the sediments active sulfate reduction within the upper 20 cm with a net removal rate of 0 5 mol cm 3 d 1 is assumed to be essentially driven by organic carbon oxidation this is expressed by relatively low apparent sulfur isotope fractionation 34enet 33 and a gentle 18o 34ssulfate apparent slope of 0 36 0 03 2s further inside the lagoon in the absence of sulfur oxidizing bacteria higher apparent sulfur isotope fractionation and a steeper 18o 34ssulfate slope 0 67 0 20 suggest an overall lower sulfate removal rate that may be coupled to minor sulfur disproportionation spatial and vertical variation in sulfur cycling reflected by oxygen and sulfur isotopic characteristics seem to be mainly controlled by unsteady to relatively steady organic matter deposition and its reactivity in all sediments 34s values of pyrite are positively correlated with the toc ts ratio and negatively correlated with 13ctoc suggesting a primary control of the quantity and quality of organic matter on the pyrite isotope records despite potential iron limiting conditions for the most active sites our results provide insights into the role of organic carbon input on sulfur cycling stimulating sulfate reduction and in turn the presence of sulfur oxidizing microbial mats resulting in an intense cycling of both carbon and sulfur in these marine mangrove sediments

spectral characteristics of high frequency pn sn phases in the western pacific pn and sn phases from 25 selected earthquakes recorded since july of 1979 on ocean bottom hydrophones near wake island are used to complement and extend prior investigations of high frequency pn sn spectra in the western pacific at a distance of about 18 sup 0 approx 2000 km frequencies for pn and sn are as high as 30 and 35 hz respectively at a distance of about 30 sup 0 approx 3300 km as high as 15 and 20 hz respectively pn phases lose their high frequency energy more rapidly than sn phases do yet pn wavetrains are much longer than sn wavetrains pn wavetrains of longer duration more energy and higher frequencies are found for travel paths primarily in the northwestern pacific basin than for travel paths across the transition zone from the shallow ontong java plateau to the deep northwestern pacific basin sn phases are extremely weak or absent for travel paths crossing this transition zone from the shallower ontong java plateau to the deeper northwestern pacific basin whereas sn phases are well recorded for travel paths crossing the transition zone in the opposite direction although normal mantle refracted p phases are well recorded beyond about 21 sup 0 approx 2300 km available data indicatemore that detectable normal mantle refracted p phases may not exist at distances from about 17 sup 0 to 21 sup 0 less

decadal scale morphological evolution of a muddy open coast analysis of the long term morphological evolution of a muddy open coast sediment transport suggests a growth of mudbanks migrating along the coast cross shore exchange of sediment is equally significant as longshore transport mudbank and shoreline erosion accretion trends are reversed

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

sequential mineral transformation from kaolinite to fe illite in two brazilian mangrove soils abstract mangrove soils have peculiar chemical and physical conditions generated by the variable water salinity cyclic tidal changes and intense biological activity that produce complex clay suites in this study the crystal chemical characteristics of clay minerals from two mangrove soils were investigated in detail to further our understanding of the processes taking place the two brazilian mangroves are from zones of contrasting climatic type and continental sediment character 1 tropical wet climate area receiving highly weathered sediments braganca para state and 2 mild semiarid climate area supplied with a mixture of highly and moderately weathered sediments acarau ceara state the investigation of the 2 0 2 m and 4 ions abundant in the interstitial water superior fe rich illite contents in acarau mangrove compared to braganca mangrove are explained by high inputs of 2 1 clays from sediment source areas inland the above clay mineral reactions shed light on the role of clays and the interaction between minerals and biotic components in mangrove soils in addition these reactions may influence the cycle of major elements in coastal ecosystem surrounding mangroves

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

differential rates of vertical accretion and elevation change among aerial root types in micronesian mangrove forests abstract root systems in mangrove swamps have captured the attention of scientists for decades among the postulated roles of root structures include a contribution to the geomorphological stability of mangrove soils through sediment trapping and binding in this study we used feldspar marker horizons and sediment pins to investigate the influence of three different functional root types prop roots in rhizophora spp root knees in bruguiera gymnorrhiza and pneumatophores in sonneratia alba on vertical accretion and elevation change in three mangrove forests in the federated states of micronesia prop roots facilitated vertical accretion 11 0 mm year 1 more than pneumatophores or bare soil controls mean 8 3 mm year 1 sediment elevation on the other hand increased at an average rate of only 1 3 mm year 1 across all root types with rate differences by root type ranging from 0 2 to 3 4 mm year 1 being detected within river basins this investigation demonstrates that prop roots can assist in the settling of suspended sediments from estuarine waters yet prop root structures are not as successful as pneumatophores in maintaining sediment elevation over 2 5 years as root densities increase over time an increase in turbulence induced erosion and in shallow subsidence as organic peat layers form is expected in micronesian mangrove forests

non hydrostatic modeling of drag inertia and porous effects in wave propagation over dense vegetation fields a new wave vegetation model is implemented in an open source code swash simulating waves till shore the governing equations are the nonlinear shallow water equations including non hydrostatic pressure besides the commonly considered drag force induced by vertical vegetation cylinders drag force induced by horizontal vegetation cylinders in complex mangrove root systems as well as porosity and inertia effects are included in the vegetation model providing a logical supplement to the existing models the vegetation model is tested against lab measurements and existing models good model performance is found in simulating wave height distribution and maximum water level in vegetation fields the relevance of including the additional effects is demonstrated by illustrative model runs we show that the difference between vertical and horizontal vegetation cylinders in wave dissipation is larger when exposed to shorter waves because in these wave conditions the vertical component of orbital velocity is more prominent both porosity and inertia effects are more pronounced with higher vegetation density porosity effects can cause wave reflection and lead to reduced wave height in and behind vegetation fields while inertia force leads to negative energy dissipation that reduces the wave damping capacity of vegetation overall the inclusion of both effects leads to greater wave reduction compared to common modeling practice that ignores these effects but the maximum water level is increased due to porosity with good model performance and extended functions the new vegetation model in swash code is a solid advancement toward refined simulation of wave propagation over vegetation fields

tidal scale flow routing and sedimentation in mangrove forests combining field data and numerical modelling tidal scale biophysical interactions establish particular flow routing and sedimentation patterns in coastal mangroves sluggish water flows through the mangrove vegetation and enhanced sediment deposition are essential to maintain these valuable ecosystems thereby enabling their contribution to coastal protection and stabilization spatially explicit field observations of tidal scale flow routing and sediment deposition were obtained in an elevated mangrove stand dissected by tidal creeks located in the trang river estuary at the thai andaman coast an accurate and efficient depth averaged process based numerical model of this field site was developed in delft3d to study the contributions of various biogeophysical mangrove settings to the observed tidal dynamics and to study the impacts of changes of these environmental conditions the creeks are found to form the major pathway for the tidal inflow during the lower tides while the sheltered interior of the forest is an effective sediment sink during the higher tides a numerical sensitivity analysis of the initial response or adaptive capacity of the studied mangrove system to instantaneous environmental changes reveals the stable state of the study site deposition rates are largely imposed by the topography and relative elevation while they are rather independent of the vegetation density deeper inundations of the mangroves favor sheet flows through the forest and spatially averaged deposition rates decrease particularly when this coincides with decreasing vegetation densities moreover the sediment trapping efficiency is found to reduce significantly with diminishing sediment inputs and with mangrove area losses these results clearly indicate the sensitivity of mangroves ecosystem engineering ability in terms of sedimentation to climate change and anthropogenic threats

efficient three dimensional reconstruction of aquatic vegetation geometry estimating morphological parameters influencing hydrodynamic drag abstract aquatic vegetation can shelter coastlines from energetic waves and tidal currents sometimes enabling accretion of fine sediments simulation of flow and sediment transport within submerged canopies requires quantification of vegetation geometry however field surveys used to determine vegetation geometry can be limited by the time required to obtain conventional caliper and ruler measurements building on recent progress in photogrammetry and computer vision we present a method for reconstructing three dimensional canopy geometry the method was used to survey a dense canopy of aerial mangrove roots called pneumatophores in vietnam s mekong river delta photogrammetric estimation of geometry required 1 taking numerous photographs at low tide from multiple viewpoints around 1 m2 quadrats 2 computing relative camera locations and orientations by triangulation of key features present in multiple images and reconstructing a dense 3d point cloud and 3 extracting pneumatophore locations and diameters from the point cloud data step 3 was accomplished by a new sector slice algorithm yielding geometric parameters every 5 mm along a vertical profile photogrammetric analysis was compared with manual caliper measurements in all 5 quadrats considered agreement was found between manual and photogrammetric estimates of stem number and of number mean diameter which is a key parameter appearing in hydrodynamic models in two quadrats pneumatophores were encrusted with numerous barnacles generating a complex geometry not resolved by hand measurements in remaining cases moderate agreement between manual and photogrammetric estimates of stem diameter and solid volume fraction was found by substantially reducing measurement time in the field while capturing in greater detail the 3d structure photogrammetry has potential to improve input to hydrodynamic models particularly for simulations of flow through large scale heterogenous canopies

the influence of continental ice sheets on the climate of an ice age the climate influence of the land ice that existed 18 000 years before present 18k b p is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean simulated climates are obtained from two versions of the model one with the land ice distribution of the present and the other with that of 18k b p in the northern hemisphere the tropospheric flow field is strongly influenced by the laurentide ice sheet and features a split flow straddling the ice sheet with a strong jet stream forming the southern branch the northern branch of the flow brings very cold air over the north atlantic ocean where thick sea ice is maintained the distribution of sea surface temperature sst difference between the two experiments in the northern hemisphere resembles the difference between the sst at 18k b p and at present as estimated by the climap project 1981 the 18k b p ice sheets have very little influence upon atmospheric temperature and sst in the southern hemisphere this is because the interhemispheric heat transport hardly changes as the loss of heat energy due to the reflection of solar radiation by continental ice sheets in the northern hemisphere is almost completely counterbalanced by the in situ reduction of upward terrestrial radiation hydrologic changes in the model climate are also found with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in north america and eurasia these findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum

large scale dynamics of the meiyu baiu rainband environmental forcing by the westerly jet abstract meiyu baiu is the major rainy season from central china to japan brought by a zonally elongated rainband from june to mid july large scale characteristics and environmental forcing of this important phenomenon are investigated based on a reanalysis dataset the meiyu baiu rainband is accompanied by a trough of sea level pressure horizontal shears and sharp moisture gradients near the surface a westerly jet tilted northward with height and large northeastward moisture transport from the south the analysis here reveals the westerly jet as an important culprit for meiyu baiu along the rainband mean ascending motion corresponds well with a band of warm horizontal temperature advection in the midtroposphere throughout summer this adiabatic induction of upward motion originates from the advection of warm air by the westerlies from the eastern flank of the tibetan plateau the ascending motion both induces convection and is enhanced by the resultant condensational heating the westerly jet anch

geochemical variations of core sediments of pichavaram lagoon southeast coast of tamil nadu india a provenance and paleoenvironmental study the present study aims to identify the natural and anthropogenic imprints left by the accumulation of elements and to determine identify the current level of enrichment of major oxides in the pichavaram mangrove sediments pichavaram mangrove is a dynamic intertidal environment lying in between the vellar and coleroon estuaries in the cauvery delta along the east coast of india in the present study results of texture studies reveal highly variable depositional environment in upper and lower portion of core 1 and middle portion of core 2 in both the cores decrease in grain size is observed in the upper portion which may suggest that the sediments in the upper portion were deposited at low energy condition mn al mg al ca al ti al p al and k al ratios are found to be low in the both the core samples ti elemental ratio is lower in both core samples indicating that ti concentrations in marine sediments are the best indicators of lithogenous material flux to the marine environment the concentration of various elements in the core can be summarized as si al fe mn mg ca ti p k the pia values of core 1 indicate that the sediments were derived from predominant weathering up to 40 cm and the remaining sediments derived from unweathered matrices plagioclase index of alteration pia values of most of the downcore samples of core 2 are found to be more than 40 suggesting the predominance of weathering activity low pia values are observed at the depth of 54 70 cm indicating the moderately weathered nature of the sediments in the study area positive correlation between fe and mg and their negative relationship with silica indicates the presence of ferromagnesian debris in top of the sediments major oxide geochemistry indicates a heterogeneous and moderately weathered to unweathered source for the sediments of the present study area

trapping of fine sediment in a semi enclosed bay palau micronesia airai bay palau is a small 3 km2 semi enclosed mangrove fringed meso tidal coral lagoon on the southeast coast of palau it drains a small catchment area 26 km2 of highly erodible soils in an area with high annual rainfall 3 7 m river floods are short lived and the sediment load is very large with suspended fine sediment concentration exceeding 1500 mg l 1 the resulting river plume is about 2 m thick the brackish water residence time is about 7 days during this period the plume remains a distinct surface feature even after river runoff has ceased about 98 of the riverine fine sediment settles in airai bay of which about 15 30 is deposited in the mangroves during river floods this mud remains trapped in airai bay because the bay is protected from ocean swells and the tidal currents and locally generated wind waves are too small to resuspend the mud in quantity the mud is smothering coral reefs creating a phase shift from coral to fleshy algae dominance and is even changing habitats by creating mud banks the persistence of airai bay marine resources may not be possible without improved soil erosion control in the river catchment

mean and turbulent velocity fields near rigid and flexible plants and the implications for deposition 1 the transport of fine sediment and organic matter plays an important role in the nutrient dynamics of shallow aquatic systems and the fate of these particles is closely linked to vegetation we describe the mean and turbulent flow near circular patches of synthetic vegetation and examine how the spatial distribution of flow is connected to the spatial distribution of suspended sediment deposition patches of rigid emergent and flexible submerged vegetation were considered with two different stem densities for the rigid emergent vegetation flow adjustment was primarily two dimensional with flow deflected in the horizontal plane horizontal shear layers produced a von karman vortex street flow through the patch shifted the vortex street downstream resulting in a region directly downstream of the patch in which both the mean and turbulent velocities were diminished net deposition was enhanced within this region in contrast for the flexible submerged vegetation flow adjustment was three dimensional with shear layers formed in the vertical and horizontal planes because of strong vertical circulation turbulent kinetic energy was elevated directly downstream of the patch consistent with this deposition was not enhanced at any point in the wake this comparison suggests that morphological feedbacks differ between submerged and emergent vegetation further enhanced deposition occurred only in regions where both turbulent and mean velocities were reduced relative to the open channel reduced deposition indicating enhanced resuspension occurred in regions of high turbulence kinetic energy regardless of local mean velocity these observations highlight the importance of turbulence in controlling deposition

patterns of tidal flooding within a mangrove forest coombabah lake southeast queensland australia tidal flooding and surface drainage patterns have often been used to describe mangrove species zonation however in mangrove forests exhibiting little topography ambiguous species distributions and or few species such approaches are ineffective we identified four physiognomic mangrove forest types riverine fringing overwash and basin at coombabah lake a tidal lake in southeast queensland australia and investigated tidal flooding patterns using synoptic surveys of tidal observations at the local standard port combined with local water depth observation subsequently three sub types of the basin forest type were identified 1 deep basin forest with mature trees 50 cm standing water and 3 tides per year 2 medium depth basin forest with intermediate tree development 15 30 cm standing water and 20 40 tides per year and 3 shallow basin forest with relatively recent mangrove establishment 5 15 cm standing water and 80 tides per year these three basin sub types were found to flood at different tide heights with the shallow basin flooding for tides above mean high water springs and the deep basin flooding only for tide heights approaching the highest astronomical tide we propose that these basin types represent a succession in mangrove forest development that corresponds with increasing water depth and tree maturation over time the succession not only represents increasing age but also change in basin substrate composition this is manifest as increasing pneumatophore density and an increasing area of basin surface occupied by contiguous pneumatophore cover as a result it seems that mangrove development is able to modify tidal flooding into the basin by increasingly impeding water movement

response of a comprehensive climate model to a broad range of external forcings relevance for deep ocean ventilation and the development of late cenozoic ice ages over the past few million years the earth descended from the relatively warm and stable climate of the pliocene into the increasingly dramatic ice age cycles of the pleistocene the influences of orbital forcing and atmospheric co2 on land based ice sheets have long been considered as the key drivers of the ice ages but less attention has been paid to their direct influences on the circulation of the deep ocean here we provide a broad view on the influences of co2 orbital forcing and ice sheet size according to a comprehensive earth system model by integrating the model to equilibrium under 40 different combinations of the three external forcings we find that the volume contribution of antarctic aabw vs north atlantic nadw waters to the deep ocean varies widely among the simulations and can be predicted from the difference between the surface densities at aabw and nadw deep water formation sites minima of both the aabw nadw density difference and the aabw volume occur near interglacial co2 270 400 ppm at low co2 abundant formation and northward export of sea ice in the southern ocean contributes to very salty and dense antarctic waters that dominate the global deep ocean furthermore when the earth is cold low obliquity i e a reduced tilt of earth s rotational axis enhances the antarctic water volume by expanding sea ice further at high co2 aabw dominance is favoured due to relatively warm subpolar north atlantic waters with more dependence on precession meanwhile a large laurentide ice sheet steers atmospheric circulation as to strengthen the atlantic meridional overturning circulation but cools the southern ocean remotely enhancing antarctic sea ice export and leading to very salty and expanded aabw together these results suggest that a sweet spot of low co2 low obliquity and relatively small ice sheets would have poised the amoc for interruption promoting dansgaard oeschger type abrupt change the deep ocean temperature and salinity simulated under the most representative glacial state agree very well with reconstructions from the last glacial maximum lgm which lends confidence in the ability of the model to estimate large scale changes in water mass geometry the model also simulates a circulation driven increase of preformed radiocarbon reservoir age which could explain most of the reconstructed lgm preindustrial ocean radiocarbon change however the radiocarbon content of the simulated glacial ocean is still higher than reconstructed for the lgm and the model does not reproduce reconstructed lgm deep ocean oxygen depletions these ventilation related disagreements probably reflect unresolved physical aspects of ventilation and ecosystem processes but also raise the possibility that the lgm ocean circulation was not in equilibrium finally the simulations display an increased sensitivity of both surface air temperature and aabw volume to orbital forcing under low co2 we suggest that this enhanced orbital sensitivity contributed to the development of the ice age cycles by amplifying the responses of climate and the carbon cycle to orbital forcing following a gradual downward trend of co2

morphologic and transport properties of natural organic floc 1 the morphology entrainment and settling of suspended aggregates floc significantly impact fluxes of organic carbon nutrients and contaminants in aquatic environments however transport properties of highly organic floc remain poorly understood in this study detrital floc was collected in the florida everglades from two sites with different abundances of periphyton for use in a settling column and in racetrack flume entrainment experiments although everglades flocs are similar to other organic aggregates in terms of morphology and settling rates they tend to be larger and more porous than typical mineral flocs because of biostabilization processes and relatively low prevailing shear stresses typical of wetlands flume experiments documented that everglades floc was entrained at a low bed shear stress of 1 0 x 10 2 pa which is considerably smaller than the typical entrainment threshold of mineral floc because of similarities between everglades floc and other organic floc populations floc transport characteristics in the everglades typify the behavior of floc in other organic rich shallow water environments highly organic floc is more mobile than less organic floc but because bed shear stresses in wetlands are commonly near the entrainment threshold wetland floc dynamics are often transport limited rather than supply limited organic floc transport in these environments is therefore governed by the balance between entrainment and settling fluxes which has implications for ecosystem metabolism materials cycling and even landscape evolution

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

the evolution time scale of macro tidal estuaries examples from the pacific rim the evolution of shallow macro tidal estuaries is a process that has been taking place since the last glaciation it is site specific and dependent on tides wave climate and relative fluvial dominance it is suggested that because of the increased efficiency of the tidal pumping effect with decreasing water depth these estuaries are geomorphologically unstable and may evolve much faster in the future than in the past as a result of human disturbances in the catchment principally the damming of rivers and increasing erosion from poor land use practices these estuaries may become further destabilised by a sea level rise

a comparison between a downhole seismometer and a seismometer on the ocean floor abstract we have compared the signal and noise characteristics recorded by a downhole seismometer and a nearby within 200 m ocean bottom seismometer in the deep ocean 5 5 km absolute noise levels and signal to noise ratios from the two instruments are remarkably similar we attribute this unexpected similarity to the shallow emplacement depth of the downhole instrument 194 m subbottom and the soft sediment into which it was clamped

sticky waters in the great barrier reef the great barrier reef is a mosaic of regions of high and low reef density current meter observations upstream from a region of high reef density revealed that the tidal and low frequency currents were steered away from the region during spring tides but not during neap tides a mathematical model suggests that this effect was due to both tidal friction and to the dissipation of energy by eddies behind reefs at spring tides for a high reef density region this results in a longer residence time at spring tides than at neap tides conversely this effect also diminishes connectivity between regions of high and low reef density at spring tides this process may affect the recruitment and dispersion of fish and other larvae in the great barrier reef it may also invalidate the use of satellite altimetry and tidal harmonic analysis for currents in the great barrier reef

estuarine flocs their size settling velocity and density the size and settling velocity of flocs of suspended sediments from the chesapeake bay were measured in laboratory experiments and in the field the curves between floc diameter and settling velocity showed a non stoke s relationship that was best described by the following settling velocity cm s 1 73 floc diameter cm 0 78 furthermore the relationship between floc diameter and settling velocity indicated that the floe density decreased as the floes increased in size in addition to changing density a cylinder shape was found to be the best shape factor